g.Al23 A\^3 mtI}eCttpoflrttigork College of ^ijpsictanst anb ^urgeong ILibrarp Digitized by the Internet Archive in 2010 with funding from Columbia University Libraries http://www.archive.org/details/morrisshumananaOOmorr MORRIS'S TEEATISE ON ANATOMY FIFTH EDITION CONTRIBUTORS TO FIFTH EDITION CHARLES R. BARDEEN, University of Wisconsin. ELIOT R CLARK, Johns Hopkins University. IRVING HARDESTY, Tulane Uni- versity of Louisiana. C. M. JACKSON, University of Min- nesota. F. W. JONES, London School of Medi- cine for Women. ABRAM T. KERR, Cornell University. J. PLAYFAIR McMURRICH, Uni- versity of Toronto. JOHN MORLEY, Manchester Univer- sity. H. D. SENIOR, University and Belle- vue Hospital Medical College., N. Y. R. J. TERRY, Washington University, St. Louis. PETER THOMPSON, University of Birriiingham. DAVID WATERSTON, King's Col- lege, London. For arrangement of subjects and authors see page v. THIS WORK IS ALSO PUBLISHED IN FIVE PARTS AS FOLLOWS: PART I. Morphogenesis. Osteology. Articulations. Index. $L50. PART II. Muscles. Blood-Vascular System. Lymphatic System. Index. $2.50. PART III. Nervous System. Special Sense Organs. Index. $2.00. PART IV. Digestive System. Respiratory System. Skin, Mammary and Duct- less Glands. Urogenital System. Index. $L50. PART V. Clinical and Topographical Anatomy. Index. $1.50. MOEEIS'S HUMAN ANATOMY A COMPLETE SYSTEMATIC TREATISE BY ENGLISH AND AMERICAN AUTHORS EDITED BY • C. M. JACKSON, M. S., M. D. PROFESSOR AND DIRECTOR OF THE DEPARTMENT OF ANATOMY UNIVERSITT OF MINNESOTA ELEVEN HUNDRED AND EIGHTY TWO ILLUSTRATIONS THREE HUNDRED AND FIFTY EIGHT PRINTED IN COLOURS FIFTH EDITION, REVISED AND LARGELY REWRITTEN PHILADELPHIA P. BLAKISTON'S SON & CO, 1012 WALNUT STREET Copyright, 1914, by P. Blakiston's Son & Co. hi 4 . YORK- PA AREANGEMENT OF SUBJECTS AND AUTHORS The names of the more recent of those who wrote or revised articles for previous editions have been retained in the following list in order that due credit should be given them for the work done and for their share in the great success which Morris's "Anatomy" has achieved. MORPHOGENESIS. Revised and largely rewritten for the fifth edition by C. M. Jackson, M.S., M.D., Professor of Anatomy in the University of Minne- sota. Originally written by J. Playfair McMurrich, A.M., Ph.D., Professor of Anatomy, University of Toronto. OSTEOLOGY. Revised for the third, fourth and fifth editions by Peter Thompson, M.D., Professor of Anatomy, University of Birmingham; Member of Anatomical Society of Great Britain. This article was originally written by Sir John Bland Sutton, F.R.C.S. ARTICULATIONS. Revised for the fifth edition by Frederic Wood Jones, D.Sc, M.B., B.S. (Lond.), M.R.C.S., L.R.C.P., Head of the Department of Anatomy and Lecturer in the London School of Medicine for Women. Originally written by Su- Henry Morris, A.M., M.B. MUSCLES. Rewritten and revised for the fourth and fifth editions by Charles R. Bardeen, A.B., M.D., Professor of Anatomy in the University of Wisconsin; Member Association of American Anatomists; Member of Editorial Board of "American Journal of Anatomy." BLOOD-VASCULAR SYSTEM. Revised and in part rewritten by Harold D. Senior, M.B., F.R.C.S., Professor of Anatomy, University and Bellevue Hos- pital Medical College. The section on Blood-vessels was formerly revised by Florence R. Sabin, B.S., M.D., Associate Professor of Anatomy, Johns Hopkins University. LYMPHATIC SYSTEM. Revised and partly rewritten for the fifth edition by Eliot R. Clark, A.B., M.D., Associate in Anatomy, Johns Hopkins Uni- versity. Revised for previous edition by Florence R. Sabin, B.S., M.D. NERVOUS SYSTEM. Revised and largely rewritten for the fourth and fifth editions by Irving Hardesty, A.B., Ph.D., Professor of Anatomy, Tulane University, Louisiana; Member Association of American Anatomists. SPECIAL SENSE ORGANS. Revised for the fifth edition by David Waterston, M.A., M.D., F.R.C.S., Professor of Anatomy in the University of London. In the earlier edition, the Ear, Nose, Tongue were revised by Abram T. Kerr, B.S., M.D. DIGESTIVE SYSTEM. Revised and largely rewritten for the fifth edition by C. M. Jackson, M.S., M.D., Professor of Anatomy, LTniversity of Minnesota. Revised for the fourth edition by G. Carl Huber, M.D. vi ARRANGEMENT OF SUBJECTS AND AUTHORS RESPIRATORY SYSTEM. Revised for the fourth and fifth editions by R. J. Terry, A.B., M.D., Professor of Anatomy, Washington University, St. Louis; Member Association of American Anatomists. UROGENITAL SYSTEM. Revised for the fourth and fifth editions by J. Playfair McMurrich, A.M., Ph.D., Professor of Anatomy, University of Toronto; Member Association of American Anatomists. THE SKIN AND MAMMARY GLAND; THE DUCTLESS GLANDS. By Abram T. Kerr, B.S., M.D., Professor of Anatomy, Cornell University; Member Association of American Anatomists, etc. The article on the Ductless Glands was originally written by G. Carl Huber, M.D. CLINICAL AND TOPOGRAPHICAL ANATOMY. By John Morley, Ch.M., F.R.C.S., Honorary Surgeon, Ancoats Hospital, Manchester, and Lecturer in Clinical Anatomy, Manchester University. Originally written by W. H. A. Jacobson, F.R.C.S. EDITOR'S PREFACE TO THE FIFTH EDITION One criticism upon most of the current text-books of human anatomy is that they are too extensive for the beginner. Much precious time is wasted by him in floundering through a mass of details which obscure the fundamental facts. And yet it is important to have these details conveniently accessible for both present and future reference. To meet this difficulty, the attempt is made in this edition to discriminate systematically in the use of sizes of type. The larger type is used for the more fundamental facts, which should be mastered first, and the smaller type for details. While it has been found difficult to apply this principle uni- formly through the various sections, it is hoped that the plan, even though but imperfectly realized, will prove useful to the beginner. In the illustrations of the bones, as heretofore, the origins of muscles are in- dicated by red lines, the insertions by blue lines, and the attachments of ligaments by dotted black lines. While the authors of the present edition are for the most part the same as in the previous edition, a few changes have been made as noted under the preceding section, "Arrangement of Subjects and Authors." Owing to the retirement of the distinguished originator and former editor of this work. Sir Henry Morris, and of Professor McMurrich as co-editor, the responsibility for the general supervision of the fifth revision has fallen to the present editor. Each author is alone responsible for the subject-matter of the article following his name. Care has been exercised on the part of the editor, however, to make the whole uniform, complete and systematic. As to nomenclature, the Anglicised form of the BNA has been continued, excepting those cases where the Latin form is adopted into English (e. g., most of the muscles), and rare cases where the BNA term seems undesirable. As a rule, the Anglicised form where first used is followed by the BNA Latin term in brackets, except where the two are practically identical. For convenience of refer- ence, some of the commoner synonyms of the old nomenclature are also added in parenthesis. The previous edition of Morris's Anatomy was the first general text-book of anatomy in English to adopt the BNA. During the past few years the merit of this system of nomenclature has become so widely recognized that it is now very generally accepted among the English-speaking nations. Lack of space forbids the enumeration here of the many advantages of this system, not the least of which is the reduction of some 30,000 anatomical terms (including synonyms) to 5000. The comparatively few defects of the BNA will doubtless be remedied by revision (preferably through the International Anatomical Congress). For a full discussion of the BNA system, with complete Hst of the Latin terms and English equivalents, the reader is referred to the excellent work on the BNA by Professor L. F. Barker, of Johns Hopkins University. In addition to the bibliographical references scattered throughout the text, a brief list is given at the close of each section. These brief lists of carefully selected references are intended merely as a guide to put the student "on track" of the original literature. viii EDITOR'S PREFACE TO THE FIFTH EDITION In addition to a thorough revision of the various sections, there has also been a rearrangement of a part of the subject matter in the present edition. The Teeth have been transferred from the section on Osteology to the Digestive System. The Tongue and Nose are transferred to the Digestive System and Respiratory System, respectively, excepting those portions forming the organs of Taste and Smell, which have been retained in the section on Special Sense Organs. The Pelvic Outlet has been discontinued as a separate section, the subject matter being divided between Musculature and Clinical and Topographical Anatomy. The Ductless Glands have been included in the section with the Skin and Mam- mary Glands. Due credit has been given throughout the book wherever illustrations have been taken, or modified, from other works. Special acknowledgment should be made of our indebtedness to the works of Toldt, Rauber-Kopsch, Poirier and Charpy, Henle and Spalteholz. The number of figures in the present edition has been increased about one hundred and sixty and in addition many of the older figures have been improved or replaced. For the generosity of the publishers in this connection, and for the hearty cooperation of the contributors in the revision of the various sections, the editor desires to express his deep indebtedness. Valuable assistance has been rendered by Mr. Walter E. Camp in the reading of proof and preparation of the index. C. M. Jackson. Minneapolis. CONTENTS Introduction. By C. M. Jackson, M.S., M.D. SECTION I MORPHOGENESIS By C. M. Jackson, M.S., M.D. Segmentation of the Ovum 9 Embryonic Disc and Derivatives 10 Metamerism 15 ' Branchiomerism 16 Viscera and Limbs 18 Prenatal Growth 22 Variability 25 References 25 SECTION II OSTEOLOGY By Peter Thompson, M.D. The Skeleton 27 I. The Axial Skeleton 29 A. The Vertebral Column 29 The Cervical Vertebrae 31 The Thoracic Vertebrae 36 The Lumbar Vertebrae 37 The Sacrum 39 The Coccygeal Vertebrae 42 The Vertebral Column as a Whole 43 B. Bones of the Skull 51 The Occipital 51 The Parietal 57 The Frontal 59 The Sphenoid 62 The Sphenoidal Conchae 67 The Epipteric and Wormian Bones 68 The Temporal Bone 68 The Tympanum 77 The Osseous Labyrinth 80 The Ethmoid 81 The Inferior Nasal Concha. . . 84 The Lacrimal Bone 85 The Vomer 85 The Nasal Bones 86 The Maxilla or Upper Jaw ... 87 The Palate Bone 91 The Zygomatic or Malar Bone 93 The Mandible or Lower Jaw. . 95 The Hyoid Bone 99 The Skull as a Whole 100 The Orbits 109 The Nasal Fossa 110 The Interior of the Skull 112 The Morphology of the Skull . 117 The Skull at Birth 120 C. The Thorax 126 The Ribs 126 The Sternum 132 The Thorax as a Whole 138 The Appendicular Skeleton 139 A, Bones of the Upper Extremity. 139 The Clavicle 139 The Scapula 141 The Humerus 146 The Radius 152 The Ulna 165 The Carpus 159 The Metacarpals 164 The Phalanges 167 B. Bones of the Lower Extremity . . 169 The Coxal Bone 169 The Pelvis 175 The Femur or Thigh Bone... 178 The Patella 184 The Tibia 185 The Fibula 189 The Tarsus 191 The Metatarsus 200 The Phalanges 203 The Bones of the Foot 205 Homology of the Bones of the Extremities 206 References 209 CONTENTS SECTION III THE ARTICULATIONS By F. W. Jones, D. Sc, M. B., M. R. C. S., L. R. C. P. Constituents of an Articulation 211 Classifioation of Articulations 212 Development and Morphology 213 Movements of Joints 214 Articulations of the Skull 215 Mandibular Articulation 215 Ligaments and Joints between the Skull and Vertebral Column 218 Articulations of Atlas with Occiput. . 218 Articulations between Atlas and Epis- tropheus 220 Ligaments uniting the Occiput and Epistropheus 223 Articulations of the Trunk 224 1. The Articulations of the Verte- bral Column 225 a. The Bodies of the Verte- brffi 225 6. The Articular Processes . . 228 c. The Lamina 229 d. The Spinous Processes . . . 229 e. The Transverse Processes 231 2. Sacro-vertebral Articulations. 232 3. Articulations of the Pelvis. . . . 234 4. Articulations of the Ribs with the Vertebrfe 241 5. Articulations at the Front of the Thorax 244 Movements of the Thorax 247 The Articulations of the Upper Ex- tremity 248 PAGE 1. Sterno-costo-olavicular Articu- lation 248 2. Scapulo-clavioular Union .... 250 3. Shoulder-joint 253 4. Elbow-joint 258 5. Union of Radius with Ulna. . 261 6. Radio-carpal Articulation. . . . 265 7. Carpal Joints 268 8. Carpo-metacarpal Joints 272 9. Intermetacarpal Articulations. 273 10. Metacarpo-phalangeal Joints. 274 11. Interphalangeal Articulations. 276 The Articulations of the Lower Limb . . . 276 1. Hip-joint 276 2. Knee-joint 284 3. Tibio-fibular Union 295 4. Ankle-joint 297 5. Tarsal Joints 301 a. The Talo-calcaneal Union.. 301 b. Articulations of Anterior Part of Tarsus 303 c. Medio-tarsal or Trans- verse Tarsal Joints 305 6. Tarso-metatarsal Articulations 307 7. Intermetatarsal Articulations. 309 8. Metatarso-phalangeal Articu- lations 310 9. Interphalangeal Joints 310 References 311 SECTION IV THE MUSCULATURE By C. R. Bardeen, A.B., M.D. General Remarks on Muscles 313 Muscle Fasciae 313 Gross Structure 314 Finer Structure of Muscles 315 Tendons 317 Synovial Bursse 318 Synovial Sheaths 318 Nerves and Vessels 318 Nomenclature 319 Variation 320 Physiology 320 I. Musculature of the Head and Neck and Shoulder Girdle 323 Physiological and Morphological. . 323 1. Facialis Musculature 329 2. Cranio-mandibular Muscula- ture 338 3. Supra-hyoid Musculature.... 343 4. Muscles of the Tongue 345 5. Superficial Shoulder Girdle Musculature 347 6. Infrahyoid Muscles 350 7. Scalene Musculature 353 8. Prevertebral Musculature .... 355 9. Anterior and Lateral Inter- transverse Muscles 356 10. Deep Musculature of the Shoulder Girdle 356 II. Musculature of the Upper Limb. . 360 A. Musculature of the Shoulder. . 363 B. Pectoral Muscles and Axillary Fascia 370 C. Musculature of the Arm 374 1. Dorsal or Extensor Group. . 377 2. Ventral or Flexor Group .... 379 D. Musculature of the Forearm and Hand 383 1. Dorsal-Radial Division 387 a. Superficial Layer 387 6. Deep Layer 392 2. Ulno-Volar Division 395 a. First Layer 395 6. Second Layer 399 c. Third Layer 401 d. Fourth Layer 402 3. Musculature of the Hand... 403 III. Spinal Musculature 410 A. Superficial Lateral Dorsal Sj's- tem 414 B. Deep Lateral Dorsal Muscles. 417 C. Superficial Medial Dorsal Sys- tem 417 CONTENTS PAGE D. Deep Medial Dorsal System . . 417 E. Suboccipital Muscles 419 IV. Thoracic-abdominal Musculature. 422 A. Ventral Division 430 B. Lateral Division 431 1. Serratus Group 431 j 2. External Oblique Group.... 432 3. Internal Oblique Group 433 4. Transverse Group 434 C. Lumbar Muscle 436 D. Diaphragm 436 V. Musculature of the Pelvic Outlet. 439 A. Muscles of the Pelvic Dia- '• phragm, Coccyx and Anus. . 448 B. Muscles of the Urogenital Diaphragm 449 ' C. External Genital Muscles 450 , VI. Musculature of the Lower Limb . . 452 A. Musculature of the Hip 454 i 1. Ilio-femoral Musculature. . . 454 i a. Anterior Group 455 i b. Posterior Group 457 2. Ischio-pubo-femoral Muscu- lature of the Hip 463 B. Musculature of the Thigh 464 1. Anterior Group 468 2. Medial (Adductor) Group. . 471 3. Posterior (Hamstring) Group 474 C. Musculature of the Leg 477 1. Muscles of the Front of the Leg 480 2. Lateral Musculature of the Leg 483 3. Musculature of the Back of the Leg 484 D. Muscles of the Foot 491 1. Muscle of the Dorsum of the Foot 492 2. Muscles of the Sole 493 Muscles Grouped According to Function 500 References 506 SECTION V BLOOD-VASCULAR SYSTEM By Harold D. Senior, M.B., M.D. A. The Heart and Pericardium 508 1. The Heart 508 Exterior of the Heart 509 Atrial Portion 511 Atrio- Ventricular Valves 515 Ventricular Portion 516 Semilunar Valves 517 Architecture of the Heart 518 Vessels and Nerves 519 2. The Pericardium 522 3. Surface Relations 523 4. Morphogenesis 523 B. The Arteries and Veins 527 1. Pulmonary Arteries and Veins. . . 528 2. The Systemic Arteries 529 The Aorta 529 Innominate Artery 532 Branches 532 Common Carotid Arteries 533 E.xternal Carotid Artery 536 Branches 536 Internal Carotid Artery 549 Branches 552 Subclavian Artery 556 Branches 658 Axillary Ai-tery 569 Branches 570 Brachial Artery 573 Branches 575 Ulnar Artery 576 Branches 577 Superficial Volar Arch 582 Branches 582 Radial Artery 582 Branches 583 Deep Volar Arch 586 Branches 586 Descending or Thoracic Aorta. . 586 Visceral Branches 588 Parietal Branches 588 Abdominal Aorta 590 Parietal Branches 592 Visceral Branches 593 Terminal Branches 603 Middle Sacral Artery 603 Common Iliac Arteries 603 Hypogastric Artery 605- Parietal Branches 606 Visceral Branches 609 External Iliac Artery 614 Branches 614 Femoral Artery 616 Branches 618 PopUteal Artery 621 Branches 622 Posterior Tibial Artery 624 Branches 626 Lateral Plantar Artery 627 Branches 628 Medial Plantar Artery 629 Branches 629 Anterior Tibial Artery 629 Branches 630 Dorsahs Pedis Artery 632 Branches 632 Morphogenesis and Variations of the Arteries 633 a. Arteries of the Head and Trunk 6.33 6. Arteries of the Extremities 639 The Systemic Veins 640 Veins Emptying into the Vena Cava Superior 641 Veins of the Head and Neck 642 Superficial Veins of the Head and Neck 643 Deep Veins of the Head and Neck 648 Veins of the Thorax 662 Superficial Veins of the Thorax. 662 Deep Veins of the Thorax 662 Veins of the Upper Extremity. . . 667 Superficial Veins of Upper Ex- tremity 667 Deep Vems of Upper Extremity 670 Veins Emptying into the Vena Cava Inferior 672 Portal Vein and its Tributaries. 675 Common lUao Veins 679 Hypogastric Vein 679 CONTENTS PAG£ External Iliae Vein 683 Superficial Veins of Abdominal Wall 683 Veins of the Lower Extremity. . . 683 Superficial Veins of Lower Ex- tremity 684 Deep Veins of Lower Extremity 686 Morphogenesis and Variations of the Veins 690 PAGE a. Vena Cava Superior and Tributaries 690 b. Vena Cava Inferior and Tributaries 693 c. Portal System 694 The Foetal Circulation 695 References 696 SECTION VI THE LYMPHATIC SYSTEM By Eliot R. Claek, A.B., M.D. I . General Anatomy of the Lymphatic System 697 1. Lymphatic Capillaries 697 2. Lymphatic Vessels 702 3. Lymphoid Organs 704 4. Development of the Lym- phatic System 706 II. Special Anatomy of the Lymphatic System 709 A. Lymphatics of the Head and Neck 709 1. Superficial Nodes of Head and Neck 709 2. Lymphatic Vessels of the Face 712 3. Deep Lymphatic Nodes of the Head and Neck 714 4. Deep Lymphatic Vessels of the Head and Neck 714 B. Lymphatics of the Upper Ex- tremity 719 1. Lymphatic Nodes of the Up- per Extremity 719 2. Lymphatic Vessels of the Up- per Extremity 721 C. Lymphatics of the Thorax 723 1. Superficial Lymphatic Vessels of the Thorax 723 2. Lymphatic Nodes of the Thorax 724 3. Deep Lymphatics of the Tho- rax 725 Thoracic Duct 726 Right Collecting Ducts 728 Deep Lymphatic Vessels 728 D. Lymphatics of Abdomen and Pelvis 730 1. Lymphatic Nodes of the Ab- domen and Pelvis 730 2. Lymphatic Vessels of the Ab- dominal WaUs 733 3. Visceral Lymphatic Vessels of the Abdomen and Pelvis . . . 733 Lymphatics of Alimentary Tract 733 Lymphatics of Excretory Or- gans 737 Lymphatics of Reproductive Organs 742 E. Lymphatics of the Lower Ex- tremity 746 1. Lymphatic Nodes of the Lower Extremity 746 2. Lymphatic Vessels of the Lower Extremity 748 References 750 SECTION VII THE NERVOUS SYSTEM 5y Irving Hardestt, A.B., Ph.D. General Considerations 751 Central Nervous System 770 I. Spinal Cord 771 External Morphology 771 Internal Structure 775 II. Brain or Encephalon 792 General Topography 793 Rhombencephalon 799 1. Medulla Oblongata 799 2. Pons VaroUi 804 3. Cerebellum 804 Cerebrum 833 1. Mesencephalon (Mid-brain). 833 2. Prosencephalon (Fore-brain) 843 A. Diencephalon(Inter-brain) 843 B. Telencephalon (End-brain) 847 III. General Summary of Principal Conduction Paths of Nervous System 895 IV. Meninges 908 The Peripheral Nervous System 924 I. Cranial Nerves 927 Olfactory Nerves 929 Optic Nerves 930 Oculo-motor Nerves 931 Trochlear Nerves 933 Abducens Nerves 934 Trigeminal Nerves 934 Masticator Nerves 942 Facial Nerves 943 Glosso-palatine Nerves 946 Vestibular Nerves 949 Cochlear Nerves 950 Glosso-pharyngeal Nerves 951 Hypoglossal Nerves 952 Vagus Nerves 954 Spinal Accessory Nerves 958 Gangliated Cephalic Plexus 959 II. Spinal Nerves 964 A. Posterior Primary Divisions. . . 970 CONTENTS xiu 1. Cervical Nerves 971 2. Thoracic Nerves 971 3. Lumbar Nerves 973 4. Sacral Nerves 973 B. Anterior Primary Divisions .... 973 1. Cervical Nerves 974 Cervical Plexus 974 Brachial Plexus 980 2. Thoracic Nerves 994 3. Lumbar Nerves 996 Lumbo-sacral Plexus 996 Lumbar Plexus 998 Lumbo-sacral Trunk 1005 4. Sacral Nerves 1006 Sacral Plexus 1006 Pudendal Plexus 1016 Coccygeal Plexus. . 1018 III. Distribution of the Cutaneous Branches 1018 Cutaneous Areas of Scalp 1018 Cutaneous Areas of Face 1018 PAGE Cutaneous Areas of Neck 1019 Cutaneous Areas of Trunk 1020 Cutaneous Areas of Limbs 1020 The Sympathetic System 1026 Sympathetic Trunks 1032 Cephalic and Cervical Portions of the Sympathetic Trunk 1033 1. Superior Cervical Ganglion 1035 2. Middle Cervical GangUon 1036 3. Inferior Cervical Ganghon 1036 Thoracic Portion of Sympathetic Trunk 1037 Lumbar Portion of Sympathetic Trunk 1039 Sacral Portion of Sympathetic Trunk. 1040 Great Prevertebral Plexuses 1040 1. Cardiac Plexus 1041 2. CcEliac Plexus 1043 3. Hypogastric Plexus 1045 References 1047 SECTION VIII SPECIAL SENSE ORGANS By David Waterston, M.A., M.D., F.R.C.S. General Considerations 1049 I. Olfactory Organ 1049 II. Organ of Taste 1051 III. The Eye 1051 General Surface View 1052 Examination of Eyeball 1055 Cavity of Orbit 1066 General Arrangement 1066 Optic Nerve 1073 Blood-vessels and Nerves of Orbit 1074 Eyelids 1076 Lacrimal Apparatus 1079 Development of the Eye 1080 The Ear 1082 External Ear 1082 Middle Ear 1086 Internal Ear 1092 Development of the Ear 1096 References 1098 SECTION IX THE DIGESTIVE SYSTEM By. C. M. Jackson, M.S., M.D. The Mouth 1100 The Lips and Cheeks 1102 The Palate 1104 The Tongue 1106 The Salivary Glands 1113 The Teeth 1117 The Pharynx 1128 The (Esophagus 1138 The Abdomen 1142 The Peritoneum 1145 The Stomach 1151 The Small Intestine 1161 The Duodenum 1161 The Jejunum and Ileum 1165 The Large Intestine 1170 The Liver 1180 The Bile Passages 1186 The Pancreas 1192 References 1197 SECTION X THE RESPIRATORY SYSTEM By R. J. Terry, A.B., M.D. The Nose 1200 The Larynx 1209 Cartilages of Larynx. . 1209 Joints and Membranes of Larynx. . . 1213 Muscles of Larynx 1218 Cavity of Larynx and Mucosa 1220 The Trachea and Bronchi 1225 The Lungs 1228 The Thoracic Cavitv, 1235 The Pleura; .' 1236 Mediastinal Septum 1239 References 1240 CONTENTS SECTION XI UROGENITAL SYSTEM By J. Playpair McMubeich, A.M., Ph.D. PAGE The Urinary Apparatus 1241 The Kidneys 1241 The Ureters 1247 The Urinary Bladder 1249 The Male Reproductive Organs 1253 The Testes and Their Appendages. . . 1254 The Scrotum 1254 The Testes and Epididymis 1255 The Ductus Deferentes and Seminal Vesicles 1257 The Spermatic Cord 1259 The Penis 1260 The Male Urethra 1262 PAGE The Prostate 1264 The Bulbo-urethral Glands 1265 The Female Reproductive Organs 1265 The Ovaries 1268 The Tuba; Uterinas 1269 The Uterus 1271 The Vagina 1274 Female External Genitalia and Ure- thra 1276 Development of the Reproductive Or- gans 1278 References 1280 SECTION XII THE SKIN, MAMMARY AND DUCTLESS GLANDS By Abeam T. Kerr, B.S., M.D. The Skin 1281 Appendages of the Skin 1290 Hairs 1290 Nails 1293 Cutaneous Glands 1296 Mammary Glands 1299 The Ductless Glands 1306 The Spleen 1306 The Thyreoid Gland 1312 Parathyreoid Glands 1318 Thymus 1319 Suprarenal Glands 1323 Glomus Caroticum 1327 Aortic Paraganglia 1329 Glomus Coccygeum 1329 References 1329 SECTION XIII CLINICAL AND TOPOGRAPHICAL ANATOMY By John Morley, Ch.M., F.R.C.S. The Head 1331 The Cranium 1333 The Bony Sinuses 1335 Cranio-cerebral Topography 1338 The Hypophysis Cerebri 1342 The Face 1342 The Orbit and Eye 1346 The Mouth 1349 The Nose 1352 The Neck 1354 The Thorax 1363 The Abdomen 1370 The Pelvis 1382 Male Pelvis 1382 Female Pelvis 1391 Hernia 1394 Inguinal Hernia 1394 Femoral Hernia 1398 Umbilical Hernia 1402 The Back 1403 The Upper Extremity 1409 The Shoulder and Arm 1409 The Elbow 1417 The Forearm 1419 The Wrist and Hand 1424 The Lower Extremity 1434 The Hip and Thigh 1434 The Knee 1444 Popliteal Space 1451 The Leg 1453 The Ankle 1459 The Foot 1464 Arches of the Foot 1468 Index 1471 INTRODUCTION By C. M. JACKSON, M.S., M.D. PROFESSOR OP ANATOMY, TJNrVEHSITT OP MINNESOTA. ANATOMY, as the term is usually employed, denotes the study of the /-\ structure of the human body. Properly, however, it has a much wider -^-*- significance, including within its scope not man alone, but all animal forms, and, indeed, plant forms as well; so that, when its application is limited to man, it should be qualified by the adjective human. Human Anatomy, then, is the study of the structure of the human body, and stands in contrast to, or rather in correlation with. Human Physiology, which treats of the functions of the human body, the two sciences, Anatomy and Physiology, including the complete study of man's organization and functional activities. In the early history of the sciences these terms sufficed for all practical needs, but as knowledge grew, specialization of necessity resulted and new terms were from time to time introduced to designate special lines of anatomical inquiry. With the improvement of the microscope a new field of anatomy was opened up and the science of Histology came into existence, assuming control over that portion of Anatomy which dealt with the minuter details of structure. So, too, the study of the development of the various organs gradually assumed the dignity of a more or less independent study known as Embryology, and the study of the structural changes due to disease was included in the science of Pathology; so that the term Anatomy is sometimes limited to the study of the macroscopic structure of normal adult organisms. It is clear, however, that the lines of separation between Anatomy, Histology, Embryology, and Pathology are entirely arbitrary. Microscopic anatomy necessarily grades ofi' into macroscopic anatomy; the development of an organism is a progressive process and the later embryonic or foetal stages shade gradually into the adult; and structural anomalies lead insensibly from the normal to the pathological domains. Furthermore it is found that in its individual develop- ment the organism passes through stages corresponding to those of its ancestry in evolution; in other words, Ontogeny repeats Phylogeny. A comprehensive study of Anatomy must therefore include more or less of the other sciences, and since an appreciation of the significance of structural details can only be obtained by combining the studies of Anatomy, including Histology and Embryology, and since, further, much light may be thrown on the significance of embryological stages by comparative studies, Anatomy, Embryology, and Comparative Anatomy form a triumvirate of sciences by which the structure of an organism, the signi- ficance of that structure, and the laws which determine it are elucidated. For this combination it is convenient to have a single term, and that which is used is Morphology, a word meaning literally the science of form. In morphological comparisons, the term liomology denotes similarity of structure, due to a common origin in the evolution of organs or parts; while analogy denotes merely physiological correspondence in function. Thus the arm of man and the wing of a bird are homologous, but not analogous, structures; on the other hand, the wing of a bird and the wing of an insect are analgous, but not homologous. Serial homology refers to oorresp ending parts in successive segments of the body. Nomenclature. — Formerly there was much confusion in the anatomical nomenclature, due to the multiphcity of names and the lack of uniformity in using them. Various names were applied to the same organs and great diversity of usage prevailed, not only between various countries, but also even among authors of the same country. Recently, however, a great improvement has been made by the general adoption of an international sj^stem of anatomical nomen- 2 INTRODUCTION clature. This system was first adopted by the German Anatomical Society at a meeting in Basel, in 1895, and is hence called the Basel Nomina Anatomica, or briefly, the BNA. The BNA provides each term in Latin form, which is es- pecially desirable for international usage. Each nation, however, is expected to translate the terms into its own language, wherever it is deemed preferable for everyday usage. Thus in the present work the Anglicised form of the BNA is generally used. Where not identical, however, the Latin form is added once for each term in a place convenient for reference, and is designated by enclosure in brackets [ ]. Where necessary the older terms have also been added as synonyms. The Commission by whom the BNA was prepared included eminent anatomists represent- ing various European nations. The work of the Commission was very thorough and careful, and extended through a period of six years. Among the guiding principles in the difficult task of selecting the most suitable terms were the following: (1) Each part should have one name only. (2) The names should be as short and simple as possible. (3) Related structures should have similar names. (4) Adjectives should be in opposing pairs. A few exceptions were found necessary, however. On account of its obvious merits, the BNA system has been generally adopted throughout the civilised world, and the results are very satisfactory. Comparatively few new terms have been thereby introduced, over 4000 of the 4500 names in the BNA corresponding almost exactly to older terms already in use by the Enghsh-speaking nations. Certain minor defects in the system have been criticised; but these are outweighed by the advantages of this uniform system. Abbreviations. — Certain frequently used words in the BNA are abbreviated as follows: a., arteria (plural, aa., arterise); b., bursa; g., ganglion; gl., glandula; lig., ligamentum (plural, ligg., ligamenta); m., musculus (plural, mm., muscuU); n., nervus (plural, nn., nervi); oss., ossis (or ossium); proc, processus; r., ramus (plural, rr., rami); v., vena (plural, vv., venae). Terms of position and direction. — The exact meaning of certain fundamental terms used in anatomical description must be clearly understood and kept in mind. In defining these terms, it is supposed that the human body is in an upright position, with arms at the sides and palms to the front. The three fundamental planes of the body are the sagittal, the transverse and the frontal. The vertical plane through the longitudinal axis of the trunk, dividing the body into right and left halves, is the median or mid-sagittal plane; and any plane parallel to this is a sagittal plane. Any vertical plane at right angles to a sagittal plane, and dividing the body into front and rear portions is a frontal (or coronal) plane. A plane across the body at right angles to sagittal and coronal planes is a transverse or horizontal plane. Terms pertaining to the front of the body are anterior or ventral; to the rear, 'posterior or dorsal] upper is designated as superior or cranial] and lower as inferior or caudal. The term medial means nearer the mid-sagittal plane, and lateral, further from that plane. These terms should be carefully distinguished from internal (inner) and external (outer), which were formerly synonymous with them. Internal, as now used (BNA), means deeper, i. e., nearer the central axis of the body or part; while external refers to structures more superficial in position. Proximal, in describing a limb, refers to position nearer the trunk; while distal refers to a more peripheral position. 'Adverbial forms are also employed, e. g., anteriorly or ventrally (forward, before); poster- iorly or dorsally (backward, behind); superiorly or cranially (upward, above); and inferiorly or caudally (downward, below). It should also be noted that the terms ventral, dorsal, cranial and caudal are independent of the body posture, and therefore apply equally weU to corresponding surfaces of vertebrates in general with horizontal body axis. On this account these terms are preferable, and wiU doubt- less ultimately supplant the terms anterior, posterior, superior and inferior. The discrimination in the use of several similar terms of the BNA should also receive atten- tion. Thus medianus (median) refers to the median plane. Medialis (medial) means nearer the median plane and is opposed to lateral, as above stated. Medius (middle) is used to desig- nate a position between anterior and posterior, or between internal and external. Between medialis and lateralis, however, the term intermedius is used. Finally, transversalis means trans- verse to the body axis; transversus, transverse to an organ or part; and iransversarius, pertaining to some other structure which is transverse. Parts of the body. — The primary divisions of the human body (fig. 1) are the head, neck, trunk and extremities. The head [caput] includes cranium and face [facies]. The neck [coUum] connects head and trunk. The trunk [truncus] includes thorax, abdomen, and pelvis. The upper extremity [extremitas superior] includes arm [brachium], forearm [antibrachium], and hand [man us]. The INTRODUCTION lower extremity [extremitas inferior] includes thigh [femur], leg [crus], and foot [pes]. Each of the parts mentioned has further subdivisions, as indicated in fig. 1. The cranium includes : crown [vertex] ; hack of the head [occiput] ; frontal region [sinciput], including forehead [frons]; temples [tempora]; ears [aures], including auricles [auriculfe]. Pig. 1. — Parts op the Human Body. A, Posterior view. B, Anterior view. ERTEXl EYE [OCULUS] ^EAR [AURIS] NOSE [NASUS] MOUTH [OS] The face includes the regions of the eye [oculus], nose [nasus], and mouth [os], the subdivisions of which will be given later under the appropriate sections. The thorax includes: hreast [pectus]; mammary gland [mamma]; and thoracic cavity [cavum thoracis]. The hack [dorsum] includes the vertebral column [columna vertebralis]. The abdomen includes: navel [umbilicus] ; ^awfc [latus]; groin [inguen]; loin [lumbus]; and the abdominal cavity [cavum abdominis]. The pelvis includes: "pelvic cavity [cavum pelvis]; genital organs [organa genitalia], 4 INTRODUCTION buttocks [nates], separated by a cleft [crena ani] at the anus. The hip [coxa] connects the pelvis with the lower extremity. In the lower extremity, the thigh is joined to the leg by the knee [genu]. The foot includes: heel [calx]; sole [planta]; instep [tarsus]; metatarsus; and five toes [digiti I-V], including the great toe [hallux] and little toe [digitus minimus]. The upper extremity is joined to the thorax by the shoulder. The arm is joined to the forearm at the elboiv [cubitus]. The hand includes: wrist [carpus]; Fig. 2. — Section of the Epidehmi.s of a Finger, prom a Human Embryo of 10.2 cm. metacarpus, with palm [vola or palma] and back [dorsum manus]. The five fingers [digiti I-V] include: thumb [pollex], index finger [index]; middle finger [digitus medius]; ring finger [digitus annularis] and little finger [digitus minimus]. Organ-systems. — Each of the various parts of the body above outlined is composed of various organs, and the groups of related organs make up organ- systems. The various organ-systems are treated as special branches of descriptive anatomy. The study of the bones is called osteology; of the ligaments and joints, Fig. 3. — Diagram op a Typical Cell. (Szymonowicz.) 'Granules Nuclear membrane ^ Nuclear fluid' Interfibrillar substanc "Fibrillar substance -~^ — Microsome syndesmology for arthrology); of the vessels, angiology; of the muscles, myology; of the nervous system, neurology; and of the viscera, splanchnology. Further subdivi- sions are also made. The viscera, for example, include the digestive tract, respiratory tract, urogenital tract, etc. Tissues and cells. — The body, as above stated, has various parts, each of which may be subdivided into its component systems and organs. A further analysis reveals a continued series of structm'al units of gradually decreasing complexity. Thus each organ is found to con- sist of a number of tissues (epithehal, connective, muscular or nervous). Finally, each tissue is composed of a group of similar units called cells (figs. 2, 3) which are the ultimate structural units INTRODUCTION 5 of the body. The body may therefore be regarded as composed of myriads of cell units, organ- ized into units of gradually increasing complexity, very much as a social community is composed of individuals organized into trades, municipalities, etc. Most of the individual tissues can be recognized by their gross appearance. In fact, the principal tissues were first demonstrated by Bichat through skilful dissection, maceration, etc., and without the aid of the microscope. The cellular structure of the tissues was later discovered by Schwann in 1839. Each cell (fig. 3) is composed of a material called ■protoplasm, a viscid substance variable in appearance and exceedingly complex in chemical composition. It readily breaks down into sim- pler chemical compounds, whereby energy (chiefly in the form of heat and mechanical energy) is liberated. It has also the power of absorbing nutritive material to build up and replace what was lost. Its decomposition results from stimuli of various kinds, and hence it is said to be irritable. The mechanical energy which it liberates is manifested by its contractihty, especially in the muscle cells. It excretes the waste products produced by its decomposition. Each cell has the power, under favourable conditions, of reproducing itself by division. Protoplasm pre- sents, in short, all the forms of activity manifested by the body as a whole; and, indeed, the ac- tivities of the body are the sum of the activities of its constituent cells. In the protoplasm of each cell is a specially differentiated portion, the nucleus (fig. 3). The nucleus plays an important part in regulating the activities of the cytoplasm, the general proto- plasm of the cell body. The nucleus differs from the cytoplasm both structurally and chem- ically, and contains a very important substance, chromat^in, which during cell division is aggre- gated into a definite number of masses called chromosomes. The cytoplasm of actively growing cells also contains the archoplasm and centrosome, structures of importance in the process of cell division. Further details concerning the cells and tissues may be found in the text-books of cytology and histology. In earher days Human Anatomy was almost entirely a descriptive science, but little atten- tion being paid to the significance of structure, except in so far as it could be correlated with physiological phenomena as they were at the time understood. In recent years attention has been largely paid to the morphology of the human body and much valuable information as to the meaning of the structure and relations of the various organs has resulted. Since the form and structure of the body are the final result of a series of complicated developmental changes, the science of Embryology has greatly contributed to our present knowledge of human Mor- phology; and, accordingly, a brief sketch of some of the more important phases of morphogenesis will form a fitting introduction to the study of the adult. References. — General: For looking up the literature upon any anatomical topic, the best guide is the " Jahresbericht ueber die Fortschritte der Anatomie und Entwicldungsgeschichte," which contains classified titles and brief abstracts of the more important papers in gross anatomy, histology and embryology. Other useful aids are the "Zentralblatt fuer normale Anatomie," the "Index Medicus" and the catalogue of the Surgeon Genera 's Library of the War Dep't. (Washington, D. C). The latter two contain titles only, but cover the whole field of medicine. The "Concilium Bibliographicum" also provides a conveni- ent card-index system of references for the biological sciences, including Anatomy. For nomenclature: His, Archiv f. Anat., 1895 (BNA system); Barker, Ana- tomical Nomenclature. Cells and tissues: Wilson, The Cell; Hertwig, Zelle und Gewebe (also English transl.) ; Sehaefer, Microscopic Anatomy (in Quain's Anatomy, 11th ed.) ; Heidenhain, Plasma und Zelle. SECTION 1 MOEPHOGENESIS Revised for the Fifth Edition By C. M. JACKSON, M.S., M.D. PROFESSOR OF ANATOMY IN THE tJNIVERaiTY OF MIN CHANGE is a fundamental characteristic of all living things. The human body during its life cycle accordingly passes through various phases of form and structure. In the earliest embryonic phases of development the changes are very rapid, decreasing in rapidity during the later foetal stages, but continuing at a diminishing rate throughout infancy, childhood and youth up to the adult. Following the acme of maturity, changes continue which lead gradually to senescence and final death of the body. This cycle of change in the body depends upon similar changes in its various component organs, each having its own characteristic hfe cycle. In a few of the organs this cycle is very short, as in some of the organs of the embryo (e. g., mesonephros). Other organs persist only during childhood (e. g., thymus); while the majority continue, with varying degrees of change, throughout postnatal life. The final death of the body is due to the breakdown of some of the essential organs. A further analysis reveals the fact that the characteristic life cycles of the organs depend ultimately upon similar changes in their constituent tissues and cells. Every ceU has a definite life cycle, an early period characterised by rapid and vigourous changes, later periods of differen- tiation and maturity, followed by stages of degeneration and death. This cycle of cell changes has been designated by Minot as cytomorphosis. Growth. — Associated with the process of cell differentiation (cytomorphosis), and even more important as a factor in the morphogenesis of the body, is the process of growth. The developmental changes in form and structure of the body are due largely to the unequal growth of its various parts. Growth, like other changes in the body and its parts, depends ultimately upon the characteristics of the constituent cells. Fig. 4. — The Ovum op a New-bohn Child, with Follicle Cells. (After Mertens.) Nucleus The cell changes during growth may be grouped under two heads. The first, or growth proper, involves merely the enlargement (hypertrophy) of the individual cells and intercellular products. The second includes the muUiplication (hyperplasia) of the cells, which is accom- plished by mitotic division. Cell division is necessary in ceU growth, for otherwise the cell would soon reach a size where its surface (for nutritive, respiratory and excretory purposes) would be inadequate for its mass. In general, however, cell division is most active in the earher embryonic periods, during which the cells remain small. Later, cell division diminishes or ceases, and growth is due chiefly to enlargement of the cells already present. It is also during the later period, when the cells have ceased rapid division, that the process of cell differentiation and tissue formation is most marked. The principle of the ratio of surface to mass often apphes to the growing organs as well as to the individual cells. To maintain the necessary ratio, the surface area is increased by the for- mation, through localised unequal growth, of projections (e. g., villi or folds) or invaginations (e. g., glands) from surfaces. Innumerable modifications of this principle occur throughout the process of morphogenesis. 7 8 MORPHOGENESIS Fig. 5. — Ovum fkom Ovaey of a Woman Thibtt Years of Age. cr, corona radiata. n, nucleus, y, yolk, p, clear protoplasmic zone, ps, perivitelline space, zp, zona pellucida. (McMurrich's Embryology, from Nagel.) zp % ;>s vJ ^ ~ii^\ Fig. 6. — Stages of Segmentation in the Ovum of the Mouse, x, polar body. (McMurrich's Embryology, from Sobotta.) SEGMENTATION OF THE OVUM 9 While the present work deals primarily with the adult human organism in the stage of maturity, reference is made also to its changes according to age. Although these changes for the various systems of organs are described under the ap- propriate sections, it is desirable to consider first some of the more fundamental features pertaining to the body as a whole. This apphes particularly to the earlier embryonic period, which includes the more general phases of morpho- genesis. No attempt will be made to describe fully the process of development, the details of which are to be found in text-books of embryology. Segmentation of the ovum. — The human body, like all living organisms, arises from a single cell, the egg-cell or ovum. An early stage in the development of the ovum is shown in fig. 4, and a later stage, approaching maturity, in fig. 5. The mature human ovum is about 0.2 mm. in diameter. In the uterine (Tallopian) tube, the fertilised ovum undergoes segmentation, the various stages of which are represented in figs. 6 and 7. Fig. 7. — Diagram of Section through a mammalian ovum at the Morula Stage. Fig. 8. — Diagram of Section of A Mammalian Ovum Showing the Inner Cell Mass. fi 0~ ^ ., J'\ ^ ^ i — A^; \;^-:^ ('**-• -t^ While the processes of maturation, fertilisation and segmentation have not as yet been ob- served in the human ovum, the evidence of comparative anatomy makes it very prolDable that in all essential respects these processes are like those found in other mammals. As a result of the successive divisions of the ovum in segmentation, a spherical mass of cells, the morula (fig. 7) is formed. In this mass, an excentric cavity forms (fig. 8) whereby the mass is transformed into a hollow vesicle. The wall of this vesicle is probably formed throughout the greater part of its extent by a single layer of cejls; but at one point of the circumference there is a group of cells termed the inner cell mass (fig. 8). Probably about this time the ovum enters the uterine cavity, and through the activity of the outer layer of ceUs {trophoblasi) becomes embedded in the uterine mucosa. Formation of the embryonic disc and germ layers. — -In the earliest human embryos which have been described, development has already proceeded beyond Fig. 9. — Diagram Showing the Relations of the Germ Layers in an Early EimRYO. Ac, amniotic cavity, lined by ectoderm. D, yolk-sac, lined by endoderm (En). Me, Me', mesoderm, C, extra,-embryonic calom. B, chorion. T, trophoblast. (McMurrich.) the stage represented by fig. 8, and has reached that of fig. 9. Within the inner cell mass, two cavities have appeared. The more superficial fac) is the amniotic 10 MORPHOGENESIS ■cavity; the deeper (D) is the cavity of the yolk-sac; while between them is a plate of cells forming the embryonic disc. The embryonic disc (figs. 9 and 10) contains three layers of cells, — the fundamental germ layers, — ectoderm (Ec), endoderm (En), &n.A mesoderm. The germ layers of the embryonic disc are of prime importance in the development of the body. From the ectoderm, which hes next to the amniotic cavity and represents the upper (later outer) germ layer, are derived the epidermis and the entire nervous system. From the ■endoderm, which hes next to the yolk-sac, and represents the lower (later inner) germ layer, is derived the epithehal lining of the digestive mucosa and its derivatives. From the mesoderm, or middle germ layer, is differentiated the remainder of the body, including the skeletal and sup- porting tissues, vascular system, muscle and most of the urogenital organs. The germ layers also extend beyond the embryonic disc, as shown in figs. 9 and 10. The yolk-sac is made up of a lining of endoderm and an outer layer of mesoderm. The amnion, which Fig. 10. — Diagram op Section of a Mammalian Ovum showing the Embryonic Disc, Amniotic Cavity and the Germ Layers. Endoderm later becomes separated from the chorion, is composed of mesoderm lined by endoderm. The outer cell layers form the chorion, which likewise shows two layers, the outermost of which (trophoblast) is ectoderm, the inner, mesoderm. In fig. 10 the chorion is beginning to send out root-like projections (villi) which invade the uterine mucosa. It is thus noteworthy that of the cells']derived from the ovum relatively only a few — those of the embryonic disc — enter directly into the formation of the body. The yolk-sac, a rudimentary organ of phylogenetic significance, is later chiefly absorbed, although the proximal portion may enter slightly into the formation of the intestinal wall. The amnion is a protective membrane, while the chorion forms the foetal part of the placenta. Development of the embryonic disc. — When first formed, the surface of the embryonic disc shows no trace of differentiation. A slightly later but still comparatively early stage in its development is shown in fig. 11. It is here Fig. 11.- — Model Showing the Embryonic Disc from an Embryo 1.17 mm. In Length. Viewed from above and laterally, the roof of the amniotic cavity having been removed, n, primitive pit (neurenteric canal), pg, primitive groove, mg, neural groove, b, body-stalk. (McMurrich. from Frassi.) viewed from above, the amnion having been removed. The disc is an elliptical plate, whose long axis represents the mid-line of the embryo. Near the center is a small rounded depression, the primitive pit. Extending backward (toward the tail end of the embryo) from this is a dark line, the 'primitive streak, corresponding to a groove, the primitive groove. Extending forward from the primitive pit is an indistinct wide shallow groove, the neural groove. At an earlier stage, the primitive streak extends further forward, possibly to the anterior end of the embryonic disc (Spee). The primitive streak and groove probably con-espond to the TOPOGRAPHY OF THE EMBRYONIC DISC 11 fused lips of a primitive blastopore. They represent a centre of proliferation from which the mesoderm is budded off from the ectoderm and spreads out to form the middle germ layer of the embryonic disc. At the anterior end of the primitive streak this proliferation extends forward as a plate of cells, the so-called 'head process.' The axial portion of this process is the anlage of the rtoto- chord, the embryonic skeletal axis. It contains a canal, which opens into the primitive pit. The notochordal anlage soon fuses with the underlyiag endoderm, and its canal forms the transient neurenteric canal. In the mid-line anterior to the primitive streak there appears the shallow neural groove (fig. 11), corresponding to a thickened plate of ectodermic cells, the neural plate. The neural groove is slightly forked at its posterior extremity, in the region of the primiiive node (Hensen's node), which forms the dorsal lip of the primitive pit. As development proceeds, the neural plate extends posteriorly, and the primitive pit is accordingly shifted backward, the correspond- ing part of the primitive groove being converted into 'head process.' The primitive streak thus becomes progressively shortened (cf. figs. 11 and 13). Fig. 12. — Topogkapht of the Embryonic Disc. Diagram op Relations at the Length OF ABOUT 1 MM. ng, neural groove, pn, primitive node, pp, primitive pit. U, upper limb. L, lower limb. Topography of the embryonic disc. — Although only slight signs of differentia- tion are visible in the embryonic disc at the stage shown in fig. 11, it is already possible to map out more or less definite areas corresponding to all the various regions of the future body, as shown in fig. 12. Beginning anteriorly, the head region is relatively enormous in size, occupying at this time the entire portion in front of the primitive pit and forming about half of the entire disc. The cervical, thoracic, lumbar and sacro-coccygeal regions appear successively smaller, ap- proaching the posterior end ('tail bud') of the primitive streak. It is also a striking fact that the future dorsal region of the body wall, corresponding to the central portion of the disc, along each side of the mid-line, is now larger than the ventro-lateral regions, which occupy a relatively narrow area around the periphery of the disc. 12 MORPHOGENESIS The topography of the germinal areas in the embryonic disc shown in fig. 12 is based partly upon a study of the succeeding stages of development, and partly upon the results of experi- ments upon the germinal disc in lower forms, especially in the chick (Assheton, Peebles, Kopsch). Law of developmental direction. — In the relative size of the various embryonic areas is foreshadowed what may be termed the law of direction in development. In general it is found that development (including growth and differentiation) in Fig. 13. — Human Embryo 1.54 mm. long. Viewed from above, the roof of the amniotic cavity having been removed. (Minot, after Graf Spee.) Neurenteric canal Primitive groove Body-stalk Chorion with villi the long axis of the body appears first in the head region and progresses toward the tail region. Similarly in the transverse plane development begins in the mid-dorsal region and progresses latero-ventrally (in the limbs, proximo-distally). These principles are of great importance in morphogenesis. Fig. 14. — Diagrams Showing the Constriction of the Embryo prom the Yolk-sac. A and C, longitudinal sections; B and D, corresponding cross-sections. (McMurrich.) The law of developmental direction is also probably of phylogenetic significance. The cranio-caudal direction of development is in accordance with the theory that the head is the most primitive portion of the body, and hence precocious in development. The trunk is perhaps a secondary acquisition, hence arising as an extension of the primitive head region. DERIVATION OF BODY TUBE FROM EMBRYONIC DISC 13 The dorso-ventral direction of development, together with the plate-hke form of the embry- onic disc, has a different phylogenetio significance. Both are probably inherited from an ances- tral type with a yolk-laden ovum. In such an ovum, with the meroblastic type of segmentatien, the flattened embryonic disc gradually spreads from the dorsal surface in a ventral direction around the underlying yolk-mass. Derivation of body tube from embryonic disc. — ^The primary result of the precocious growth in the dorsal region of the embryonic disc is the conversion of the disc into the body tube, curved ventrally in its long axis (fig. 14). Fig. 15. — ■Portion op Cross Section of the Embryo shown in Fig. 13. ch, notochord. ct, somatic mesoderm, df, splanchnic mesoderm, g, junction of extra-embryonic somatic and splanchnic mesoderm, ek, ectoderm, en, endoderm. me, embryonic mesoderm. /, neural groove, p, beginning of embryonic coelom (pericardial cavity). (Minot, after Graf Spee.) As a result of the more rapid expansion of the germ layers (especially the ectoderm) near the mid-line, the dorsal surface of the embryonic disc in general becomes convex, with a depres- sion laterally (where growth is less rapid) forming a groove at the line of attachment of the am- nion (figs. 11,12, 13, 14 B). The unequal growth in the germ layers is clearly evident in the cross section shown in fig. 15. By a continuation of this process, the margins of the embryonic disc become still further depressed and finally folded in ventrally so as to transform the disc into a tube (fig. 14 D). Similarly, by a more rapid expansion of the dorsal layer of the disc in the lon- gitudinal axis, the head and tail ends of the disc are folded and tucked in ventrally, and the primitive body tube is thus correspondingly curved in its long axis (figs. 14 A, 14 C). Fig. 16. — Model op Human Embryo 1.8 mm. Long. Viewed from above, the roof of the amniotic cavity having veen removed. Near the caudal end of the neural groove, the primitive pit (opening of neurenteric canal) is visible. The primitive somites are appearing in the occip- ital region, the fourth corresponding to the boundary between head and neck. (McMurrich, from Keibel and Elze.) The embryonic disc is thus converted into a tube composed of an outer layer of ectoderm, a middle layer of mesoderm and an inner layer of endoderm. The yolk-sac now presents an expanded yolk-vesicle fined by endoderm which is still continuous through the constricted yolk- stalk with the endoderm lining the primitive enteric cavity (fig. 14 C). The enteric cavity (or archenteron) has a bhnd tubular prolongation (fore gut) into the head region, and another (hind gut) into the tail region. From the latter a slender diverticulum, the allantois, extends into the body stalk (later the umbiUcal cord). The allantois is an organ of phylogenetic importance, with which the urinary bladder is later connected. Formation of the neural tube. — The principle of unequal growth applies to the formation not only of the body as a whole, but also of its constituent parts. Thus the anlage of the nervous system arises from the ectoderm as a wide groove 14 MORPHOGENESIS whose edges (neural ridges) by local growth are folded upward so as to meet in the mid-line where they fuse, thus transforming the groove into the neural tube (fi*gs. 11, 12, 13, 15, 16, 17, 18). The closure begins, not at the anterior end (as might be expected from the general law of cranio-oaudal development), but in the cervical region, extending forward into the brain region, and backward along the spinal cord. Thus the extreme ends (anterior and posterior neuropores) are the last to close. The precocious and energetic growth of the neural anlage is largely responsible for the ven- tral flexure of the embryonic body axis, especially in the head region, where the flexures of the brain are very conspicuous (figs. 22, 26). With the closure of the neural tube dorsally and of the aUmentary canal ventraUy the human embryo assumes the typical vertebrate form. The cyhndrioal body wall now encloses two tubes (neural and enteric) with the longitudinal axis (notochord) between them (figs. 18, 24). After the embryonic disc has been transformed into a tube, the body of the human embryo in cross section appears not circular but elongated dorso-ventrally. This is the typical form for vertebrates with horizontal body axis. In later foetal stages, the body becomes more rounded in cross section, and finally, with the assumption of the erect posture in postnatal life, becomes decidedly flattened dorso-ventrally (figs. 20, 21). Fia. 17. — A HoMAN Embryo 2.5 mm. in Length. (After Kollmann.) Mesodermic somite Medullary canal Development of the mesoderm. — The mesodermic layer on each side of the notochord in the embryonic disc develops in two divisions. The medial (or dorsal) divisions form a series of hollow segments, the somites (figs. 16, 17, 18). The lateral (later ventral) divisions each spht into an upper (outer) or somatic layer and a lower (inner) or visceral layer. When the embryonic disc becomes folded, the corresponding somatic and visceral layers unite ventrally and enclose between them the common cmlom or primitive body cavity (fig. 18). (As previously noted, the mesoderm arises chiefly from the lateral portions of the 'head process.' A comparatively early stage before the appearance of the somites is shown m cross section in fig. 15. The somites appear first in the occipital region, and rapidly differentiate successively in the cranio-oaudal direction (figs. 16, 17, 22). In embryos 7 or 8 mm. in length, about 40 somites may be distinguished, 3 to 5 occipital, 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 5 or 6 coccygeal (in the rudimentary tail region). The cmlom or body cavity is unsegmented. Two.primitive pericardial cavities appear sepa- DEVELOPMENT OF THE SOMITES 15- rate at first, but soon fuse and unite with the general coelom. Later the general ccelom becomes secondarily divided into the permanent pericardial, pleural and peritoneal cavities. The outer layer of the lateral mesodermic division forms the somatic or parietal layer of the peritoneum, etc. The inner layer forms the visceral or splanchnic layer, and develops not only the serous membrane, but also the muscular and connective tissue of the walls of the alimentarj' canal and its derivatives. Development of the somites. Metamerism. — The appearance of the somites marks the beginning of nietdmerism, the arrangement of the body in successive Fig. 18. — Diagram of a Cross Section op a Human Embryo. Spinal cord Mesodermic somite Intermediate cell i ^'",,. Ventral mesoderm, visceral layer /^^'SlLl^V entral mesoderm, somatic layer segments or metameres. Each somite develops a primitive muscle segment, myotome, and a skeletal segment, sclerotome (figs. 18, 19). Moreover, the cor- responding nerves and .blood-vessels likewise assume a metameric arrangement. This metamerism persists (more or less modified) in the adult neck and trunk. The differentiation of the somites is illustrated by figs. 18 and 19. The medial wall of each somite forms the sclerotome. Its cells migrate to form the corresponding vertebra, rib, etc., as Fig. 19. — Diagrams Illustrating the History of the Mesoderm. M, myotome, dM, dorsal portion of myotome. vM, ventral portion of myotome. SC, sclerotome, gr, genital ridge. PFd, Wolffian duct. iSm, somatic layer of mesoderm, bto, visceral layer of mesoderm. mr, membrana reuniens. I, intestine. A'', neural tube. (MoMurrich.) well as the mesenchyme forming the various connective tissues in this region. The remainder of the somite forms the myotome, from which the voluntary musculature of the trunk, the neck and (in part) the head is derived. The dorsal portions of the myotomes develop the muscle in the dorsal region of the trunk, while the ventral portions extend ventralward to form the muscula- ture of the latero-ventral body walls (figs. 19, 20, 21, 23). At the junction of the dorsal and ventral divisions of the mesoblast is a group ofJceUs called the intermediate cell mass. This mass becomes segmented (corresponding to the somites) and 16 MORPHOGENESIS each segment, or nephrotome, gives rise to a portion of tlie mesonephros, the provisional kidney. Other cells of the mass become mesenchyme, which is converted into blood-vessels, connective tissue, etc. As development proceeds, the metamerism of the muscles and arteries becomes more or less obscured, but that of the vertebrfe and nerves is fully retained even in the adult. In the case of the muscle plates, from which all the voluntary musculature of the trunk is derived, great modi- fications occur. Extensive fusion of successive plates occurs, the intervening connective tissue disappearing more or less completely; associated with this fusion there is longitudinal and tan- gential splitting of the somites to form individual muscles; and portions of some of the plates may wander far from their original position. But notwithstanding these complicated changes, in- dications of the primary metameric arrangement of the muscle plates are abundant, and even in the most e.xtreme cases of modification the developmental history of a muscle can be determined by means of its nerve supply. For the fibres derived from each plate will usually retain, up matter what changes of independence or position they may undergo, the innervation by their originally corresponding segmental nerve; so that the occurence in the lumbar region of the body of muscle-fibres (the diaphragm) supplied by nerve-fibres from a cervical nerve is evidence that the muscle-fibres have been derived from a cervical mesodermic somite and have subsequently migrated to the position they finally occupy. As regards the arteries, they arise primarily from a longitudinal stem, the aorta, in a strictly segmental manner, each metamere having distributed to it two pairs of arteries and a single median one (fig. 20). One pair of arteries supplies the body wall, and these retain very distinctly their original metameric arrangement; the other pair passes to the paired viscera, such as the lungs, kidneys, ovaries (or testes), so many of the pairs disappearing, however, that their meta- meric arrangement is not very evident in the adult. The unpaired vessels supply the digestive tract and its unpaired appendages, such as the liver and pancreas, and undergo great modifica- tions, those of the lower thoracic and lumbar regions becoming reduced by fusion and degenera- tion to three main trunks. Fig. 20. — Diagram of a Transvehsb Section through the Abdominal Region. DORSAL MUSCLES , =99aiv DORSAL MUSCLES .\ HYPOSK.ELETAL MUSCLE VERTEBR.o, X_/ — PERITONEUM \ PARIETAL LAYER X. Branchiomerism. — Throughout the trunk and neck regions, then, a funda- mental metameric plan underlies and determines the arrangement of many parts. In the head there is also evident a primary arrangement of the parts in succession; but this arrangement appears to be somewhat different from that of the trunk in that it involves the ventral instead of the dorsal mesoderm and is associated with the occurrence of branchial arches rather than with true mesodermic somites. It is consequently termed branchiomerism. Not but that there are also indications of metamerism in the head, the muscles of the orbit, and the majority of the extrinsic muscles of the tongue, together with the nerves supplying these muscles, being apparently metameric structures, but the metamerism of this region of the body is largely overshadowed by the branchiomerism. If an embryo of about the fifth week of development (fig. 22) be examined, there will be observed on the surface of the body in the pharyngeal region three or four linear depressions, DEVELOPMENT OF THE SOMITES 17 and sections will show that similar and corresponding grooves also occur upon the inner surface of the pharyngeal wall. These are the branchial grooves, and since they are four in number (with a rudimentary fifth) in the human embryo, they mark off five branchial (or visceral) arches, the first of which hes between the oral depression and the first branchial groove, while the fifth is situated behind the fourth groove. These branchial arches are so named because they repre- sent the arches which (excepting the first) support the gills (branchise) in the lower vertebrates, the grooves representing the branchial slits, even although they do not become perforated in the human embryo. Each branchiomere consists of an axial skeletal structure, of muscles which act on this skel- eton, of a nerve which supphes the muscles and the neighbouring integument and mucous mem- brane, and of an artery which carries blood to all these structures. The arches, however, do npt in the human embryo retain their original branchial function, but undergo extensive modi- fications, becoming adapted to various functions and showing less in the adult of their originally simple arrangement than do the metameres. Nevertheless no matter what modifications the musculature of any arch may undergo, it will retain its original innervation and, to a large extent, its relations to the skeletal elements of its arch; and even the arteries in their distribu- tion show clear indications of being arranged in correspondence to the various arches. Fig. 21. — Diagram of a Transverse Section through the Thoracic Region. (The pleura is represented in blue and the pericardium in red.) With respect to the fate of the various structures pertaining to each branchial arch, their general arrangement in the adult body may be stated in the following table: — Arch Relations of the Branchial Arches in the Adult Skeleton Muscles First arch Mandible, malleus and ' incus. Second arch Hyoid (lesser cornu), I styloid process and stapes. Third arch ! Hyoid (greater cornu), . Masticatory, mylohoid and di- gastric (ant.), tensor tympani. Stylohyoid, digastric (post.), muscles of expression, stape- dius. Pharyngeal Nerve Trigeminus. Facialis. Glossopharyn- geus. Fourth and fifth Thyreoid cartilage ; Pharyngeal and laryngeal 1 Vagus. arches. ! , » Branchial grooves. — Of the external branchial grooves, the first (lying between mandibular and hyoid arches) becomes deepened to form the external auditory meatus, the margins becom- ing elevated to form the auricle (fig. 26). The region corresponding to the second, third and fourth external grooves becomes depressed, forming the sinus cervicalis, which soon closes up and disappears. The internal branchial grooves or pouches communicate with the pharjTigeal cavity and are 18 MORPHOGENESIS lined with endoderm. The first internal groove becomes transformed into the auditory (Eu- stachian) lube, tympanic cavity, etc. The second internal groove persists in part as the fossa of the palatine tonsil. The third and fourth grooves are probably represented in part by the vallecula and recessus piriformis, detached portions of their lining endoderm giving rise to the thymus, parathyreoid glands, etc. The rudimentary fifth groove is said to give rise to the ultimobranchial body, a structure of uncertain significance (fig. 27). Development of the face, — -The facial region is at first relatively small. It includes the sense organs (eye, ear, nose) and mouth region. Some of the more important developmental features may be briefly mentioned. In an embryo of the sixth week (fig. 28) the wide mouth aperture is seen to be bounded below (posteriorly) by the lower (mandibular) portion of the Fig. 22. — Htjman Embryo of 4.2 mm., Showing Three Branchial Grooves. (After His.) tory vesicle Branchial grooves Mesodermic somite first arch, laterally^by the upper (maxillary) process of the first arch. Above it is bounded by a median plate, the nasal process, which on either side forms a protuberance, the globular process. Lateral to the globular process is a rounded depression, the nasal pit. The maxillary process extends forward and fuses with the globular process to form the upper jaw region (failure to unite resulting in the malformation known as 'hare-lip'). The nose is at first broad, due to the width of the nasal process, which later becomes the nasal septum (fig. 29). The nasal pits deepen and later acquire openings into the primitive mouth cavity. The viscera. — The structures so far considered belong, for the most part, to the body wall; it remains to consider the general plan of arrangement of the viscera. It has been pointed out that the body may be regarded as a cylinder enclosing two tubes, one of which constitutes the central nervous system and the THE VISCERA 19 other the digestive tract. The latter may be regarded as being primarily a straight tube traversing lengthwise the body cavity enclosed by the body wall (figs. 18, 20). The layers of both the visceral and somatic plates which im- FiG. 23. — Sagittal Section Showing the Primitive Pericardial and Ccelomic Com- munication, Septum Transversum, Liver, etc., in a Human Embryo op 3 mm. (After KoUmann, from a model by His.) Truncus aortse _ Mesocardium posterius Pericardial cavity . Anterior wall of pericardium Septum transversum and floor of pericardium Venous trunk of the heart Mesocardium laterale Ductus Cuvieri v. umbilicalis v. omphalo-mesenterica Ccelomic communication Peritoneal cavity mediately enclose the body cavity become transformed into a characteristic pleuro-peritoneal membrane. Near the mid-dorsal line, a vertical double plate of peritoneum extends ventrally connecting the somatic (parietal) and visceral layers of peritoneum, and constituting what is termed the mesentery (fig. 20). Fig. 24. — Diagram Illustrating the Recession of the JDiaphragm (Septum Trans- versum) IN the Human Embryo. On the right are indicated the vertebral levels; on the left, the position of the septum transversum in a series of embryos from 2 mm. (XII) to 24 mm. (VI) in length, pp, pleuro-peritoneal cavity. (Mall.) 'MtJuJ^ _ As development proceeds the digestive tract grows in length more rapidly than the cavity which contains it, and so gradually becomes thrown into numerous coils in the abdominal region, these changes leading to numerous modifications of the original arrangement of the mes- entery. These will be described later on in the section on the digestive system. Several out- growths also arise from the primitive digestive tract, to form important organs, such as the lungs, 20 MORPHOGENESIS the liver, the pancreas and the urinary bladder; and, with the exception of the bladder, each of^these becomes completely invested by primitive peritoneum. In the case of the liver this original condition is practically retained, but the investment of the pancreas later becomes a partial one on account of the modifications which ensue in the mesentery. The bladder has only a portion of its surface in contact with the peritoneum, but the investment of the lungs remains complete, each lung, indeed, appropriating to itself the entire visceral layer' of its half of the thorax, with the exception of a small ventral portion which forms the investment of the heart. Furthermore, the cavities which surround each of the three organs named, the two lungs and the heart, become completely separated from one another; and since each investment con- sists of a visceral and a parietal layer, each of the organs is enclosed within a double-waUed sac, which in the case of each lung forms its pleura, while that of the heart is known as the pericardium. The spaces which occur within the thorax between the pleurte of the two sides are known as the mediastina, which include the heart, oesophagus, etc. (fig 21). Tn addition to the viscera mentioned there are some organs, such as the spleen and genito- urinary organs, which are developments of the mesoderm, the spleen arising in the mesentery which passes to the stomach and the genito-urinary organs primarily from the intermediate cell mass. The morphogeny of these structures and also of the vascular system, nervous system, and sense organs will be considered later in connection with their structure. Fig. 25. — Diagram op a Cross Section of the Embetonic Body and Limb. (McMurrich, after Kollman.) Dorsal (posterior) division of spinal nerre Ventral (anterior) division of spinal nerve Dorsal limb mus- culature Peritoneal cavity - Recession of the diaphragm and heart. — In the early stages of development the heart is situated far forward, in what will eventually be the pharyngeal region (figs. 12, 17). Just behind (caudal to) the heart, between it and the yolk- sac, is a plate of connective tissue, the septum transversum, which serves for the passage of large veins from the body wall to the heart (figs. 17, 23). This septum together with certain accessory structures eventually gives rise to the diaphragm, which becomes a complete partition separating the thoracic and abdominal por- tions of the body cavity. The diaphragm and heart are therefore originally situated far above (cranial to) their final position and recede in the course of development, producing an elongation of the vessels and nerves associated with them and forcing downward such organs as the stomach and liver (fig. 24). The chief factor in this displacement is probably the ventral head flexion and the precocious growth and expansion of the organs in the head region. The effects of this recession are especially noticeable in the nerves, these passing to the various organs concerned arising from a much higher level than that occupied by the organs. The nerve to the diaphragm, for instance, comes from the fourth cervical segment, those passing to the cardiac and pulmonary plexuses from the cervical region, and those to the plexus in relation with the stomach, liver and adjacent organs from the thoracic region. The blood-vessels, however, may shift their origins from the main trunks by successive anastomotic roots, so that in general they keep pace with the viscera in the migration caudalward. The limbs. — Each limb at its first appearance (fig. 22) is a flat, plate-like outgrowth from the side of the body, and consists of an axial mass (blastema) of mesodermic tissue from which the limb skeleton will develop, and, surrounding this, a layer, also of mesodermic tissue, from which the muscles and blood-vessels will arise. It is as yet uncertain whether the muscle blastema is derived from the myotomes (as in lower vertebrates) or whether it develops from the mesenchyme. THE LIMBS 21 Fig. 26. -Lateral View of a Human Embryo 18 mm. Long, Showing the Development op THE Extremities. M, mandibular arch. Fig. 27. — Diagram to Show the Derivatives op the Branchial Clefts. le, lie, Ille, IVe, Ve, external branchial grooves, li, Hi, llli, IVi, Yi, internal branchial grooves. Tons., palatine tonsil. Ep III, Ep IV, epithelial bodies. Ub, ultimobranchial body. Th.^ 'thyreoid D.th. gl., ductus thyreoglossus. (Modified rom Keibel and Mall.) Ub. ^_^ Thymus 22 MORPHOGENESIS As the muscles become differentiated, nerves grow to ttiem from a definite number of spinal segments (fig. 25). At first each limb plate is so placed that one of its surfaces looks dorsally and the other ven- trally, and one border (that corresponding to the thumb or great toe) is anterior (i. e., cranial) and the other posterior (caudal). Later, however, each limb becomes bent caudally through about ninety degrees, so that the limbs whose long axes were at first at right angles to the long axis of the body come to he parallel to that axis. In addition there occurs a rotation of each fore-limb in such a manner that the thumb turns latero-dorsally, while in the lower Umb the direction of the movement is exactly the opposite, the great toe turning ventro-medially. As a result there is an apparent reversal of the surfaces in the two limbs, the flexor muscles of the arm reaching on the surface which is directed anteriorly, while in the lower limb the corre- sponding muscles occupy the posterior surface. The dorsum of the foot and the great toe side correspond respectively to the back and thumb side of the hand, the tibia corresponds to the radius and the fibula to the ulna. The limb anlage soon becomes divided into three primary segments. The distal segment (hand or foot) is a flattened rounded disc, in which the digits soon appear (fig. 26). The proximal portion forms the forearm or leg and the arm or thigh. In general, the extremities follow the law of cranio-caudal and dorso-ventral (proximo-distal) development. Fig. 28A. — Face of Human Embryo of ABOUT 8 MM. (His.) "^Tasal fossa Lateral nasal process ^lobular process Maxillary process Mandibular process Fig. 28B. — Face of Human Embryo AT Stage Slightly Later than 28A. (After Kallius.) Nasal fossa Lateral nasal process Globular process Maxillary process Prenatal Growth in Length and Weight Age in lunar Crown-rump or sitting height Crown-heel or standing height Weight at end of month, grams Ratio of increase to weight at be- months (Mall), cm. (Mall), cm. ginning of month 0 (diameter of ovum = 0.2 mm.) (Ovum = 0.000004 g.) I 0.25 0.25 0.004 999.0 II 2.5 3.0 2.0 499.0 III 6.8 9.8 24.0 11.0 IV 12.1 18.0 120.0 4.0 V 16.7 25.0 330.0 1.75 VI 21.0 31.5 600.0 0.82 VII 24.5 37.1 1000.0 0.67 VIII 28.4 42.5 1600.0 O.BO IX 31.6 47.0 2400.0 0.50 *x 33.6 50.0 3200.0 0.33 Prenatal growth. — The prenatal growth of the human body in length and weight is indi- cated in the preceding table. According to Hasse, the age of the foetus may be estimated from its total length as follows. Before the fifth month, the square of the age in (lunar) months gives the length in centimetres. After this, the age in months multiphed by five gives the length. This gives approximate results, except for the first month. While the growth in absolute weight increases from month to month, it is important to note that the real (relative) growth rate rapidly diminishes. The ovum increases in weight during the first month about 1000 times, or 100,000 per cent, (not including the extra-embryonic structures). This rate diminishes rapidly, however, so that the increase during the last foetal month is only about 33 per cent. The continuation of growth in length and weight during the postnatal period is shown in the following chart (fig. 30). The following chart is based upon data from Camerer (1-5 yrs.). Porter (6-17 yrs.), and Roberts (18-20 yrs.), showing the average postnatal growth in height and weight by sexes. The average height at birth is about 50 cm. (20 inches) ; weight, about 3200 g. (7 pounds). The male is slightly heavier and taller than the female, except during the acceleration at the period * 270 days (Mall). PRENATAL GROWTH 23 Fig. 29. — Face op a Human Embryo after Completion of the Upper Jaw. (McMurrich from His.) Fig. 30. — Chart Showing Average Postnatal Growth in Height and Weight. ^ ^ -X- ^' Heig tit in Cen timet ers • ;^ Male F< male ,.-«*' ^ J'*^ ^ ^ / ■"^ <^ ^' / .... y^' **** A ^j -'' V ^ >{^ /' J /' ,'' / , f ,''^ y / _y ^ «> / ^ ^ i^' \ k^eig-} it ii iKik igrai IS <<' 'i^' r Male Fe nale g-". the constituent parts of the vertebrae in each region of the column. The body (centrum) of the vertebra is that part which immediately surrounds the noto- chord. This part is present in all the vertebrae of man, but the centrum of the atlas is disso- ciated from its arch, and ankylosed to the body of the epistropheus. The reasons for regard- FiG. 64. — Morphology of the Tkansverse and Articular Processes. Cervical vertebra Transverse process Costo-transverse foramen Transverse process Costo-transverse foramen Neuro-central suture Rib .Transverse process Lumbar rib Sacral vertebra Netiro-central suture Costal process ing the dens as the body of the atlas are these: In the embryo the notochord passes through it on its way to the base of the cranium. Between the dens and the body of the axis there is a swelling of the notochord in the early embryo as in other intervertebral regions. This swell- ing is later indicated by a small intervertebral disc hidden in the bone, but persistent even in old age. Moreover, the dens ossifies from primary centres, and in chelonians it remains as a separate ossicle throughout life; in Ornithorhynchus it remains distinct for a long time, and it has been found separate even in an adult man. Lastly, in man and many mammals, an epi- BONES OF THE SKULL 51 physial plate develops between it and the body of the axis. The anterior arch of the atlas represents a cartilaginous hypochordal bar, which is present in the early stages of development of the vertebrae, but disappears in all but the atlas in the ossification of the body. The arches and spinous processes are easily recognised throughout the various parts of the column in which complete vertebrae are present. The articular processes or zygapophyses are of no morphological value, and do not require consideration here. •The transverse processes offer more difficulty. They occur in the simplest form in the tho- racic series. Here they articulate with the tubercles of the ribs, whence the term tubercular processes or diapophyses has been given them (the place of articulation of the head of the rib with the vertebra is the capitular process or parapophysis), and the transverse process and the neck of the rib enclose an arterial foramen named the costo-transverse foramen. In the cer- vical region the costal element (pleur apophysis) and the transverse process are fused together, and the conjoint proce.ss thus formed is pierced by the costo-transverse foramen. The com- pound nature of the process is indicated by the fact that the anterior or costal processes in the lower cervical vertebrte arise from additional centres and occasionally retain their independence as cervical ribs, and in Sauropsida (birds and reptiles) these processes are represented by free ribs. In the lumbar region, the compound nature of the transverse process is further marked. The true transverse process is greatly suppressed, and its extremity is indicated by the accessory tubercle. Anterior to this in the adult vertebrae a group of holes represents the costo-transverse foramen, and the portion in front of this is the costal element. Occasionally it persists as an independent ossicle, the lumbar rib. In the sacral series the costal elements are coalesced in the first three vertebrae to form the greater portion of the lateral portion for articulation with the ilium, the costo-transverse fora- mina being completely obscured. In rare instances the first sacral vertebra will articulate with the ilium on one side, but remain free on the other, and under such conditions the free process exactly resembles the elongated transverse process of a lumbar vertebra. The first three sacral vertebrae which develop costal processes for articulation with the ilium are termed true sacral vertebrae, while the fourth and fifth are termed pseudo-sacral. A glance at fig. 64 will show the homology of the various parts of a vertebra from the cervical, thoracic, lumbar, and sacral regions. B. BONES OF THE SKULL The skull is the expanded upper portion of the axial skeleton and is supported on the summit of the vertebral column. It consists of the cranium, a strong bony case enclosing the brain and made up of eight bones — viz., occipital, tvs^o parietal, frontal, two temporal, sphenoid, ethmoid; and the bones of the face, surrounding the mouth and nose, and forming with the cranium the orbital cavity for the reception of the eye. The bones of the face are fourteen in number — viz., two maxillae, two zygomatic {malar), two nasal, two lacrimal, two palate, two inferior conchoe {turbinates), the mandible, and the vomer. All the bones enumerated above, with the exception of the mandible, are united by suture and are therefore immovable. The proportion between the facial and cranial parts of the skull varies at different periods of life, being in the adult about one (facial) to two (cranial), and in' the new-born infant about one to eight. A group of movable bones, comprising the hyoid, suspended from the basilar surface of the cranium, and three small bones, the incus, malleus, and stapes, situated in the middle ear or tympanic cavity, is also included in the enumeration of the bones of the skull. According to the BNA nomenclature, the term cranium is used in a wider sense as synony- mous with skull, and is subdivided into cranium cerebrate (cranium in the narrower sense) and cranium viscerate (facial skeleton). In the BNA, seven bones above listed with the facial, — two inferior conchae, two lacrimal, two nasal and the vomer — are classed with the cranium cerebrate. THE OCCIPITAL The occipital bone [os occipitale] (fig. 65) is situated at the posterior and inferior part of the cranium. In general form it is flattened and trapezoid in shape, curved upon itself so that one surface is convex and directed backward and somewhat downward, while the other is concave and looks in the opposite direction. It is pierced in its lower and front part by a large aperture, the foramen magnum, by which the vertebral canal communicates with the cavity of the cranium. The occipital bone is divisible into four parts, basilar, squamous, and two condylar, so arranged around the foramen magnum that the basilar part lies in front, the condylar parts on either side, and the squamous part above and behind. 52 THE SKELETON Speaking generally, this division corresponds to the four separate parts of which the bone consists at the time of birth (fig. 69), known as the basi-occipital, supra-occipital, and ex- occipital. In early life these parts fuse together, the lines of junction of the supra-occipital and ex-occipitals extending lateralward from the posterior margin of the foramen magnum, and those of the ex-occipitals and basi-occipital passing through the condyles near their anterior extremities. It must be noted, however, that the upper portion of the squamous part represents an additional bone, the interparietal. The squamous part [squama occipitalis] (supra-occipital and interparietal) presents on its convex posterior surface, and midway between the superior angle and the posterior margin of the foramen magnum, a prominent tubercle known as the external occipital protuberance, from which a vertical ridge — the external occipital crest — runs downward and forward as far as the foramen. The pro- tuberance and crest give attachment to the ligamentum nuchse. Fig. 65. — The Occipital. (External view.) External occipital protuberance Trapezius Semispinalis capitis Area covered by scalp Rectus capitis anterior Longus capitis 'Attachment of superior constrictor of pharynx to pharyngeal tubercle Arching lateralward on each side from the external occipital protuberance toward the lateral angle of the bone is a semicircular ridge, the superior nuchal line [linea nuchce superior], which divides the surface into two parts — an upper [planum occipitale] and a lower [planum nuchale]. Above this line, a second less distinctly marked ridge — the highest nuchal line [linea nuchse suprema] — is usually seen. It is the most curved of the three lines on this surface and gives attachment to the epicranial aproneuosis and to a few fibres of the occipitalis muscle. Between the superior and highest curved lines is a narrow crescentic area in which the bone is smoother and denser than the rest of the surface, whilst the part of the bone above the hnea suprema is convex and covered by the scalp. The lower part of the surface is ver.y uneven and subdivided into an upper and a lower area by the inferior nuchal line, which runs laterally from the middle of the crest to the jugular process. THE OCCIPITAL BONE 53 The curved lines and the areas thus mapped out between and below them give attachment to several muscles. To the superior nuchal line are attached, medially the trapezius, and laterally the occipitalis and sterno-cleido-mastoid; the area between the superior and inferior curved lines receives the semispinalis capitis (complexus) medially, and splenius capitis and ohliquus capitis superior laterally; the inferior nuchal line and the area below it afford insertion to the rectus capitis posterior minor and major. The anterior or cerebral surface is deeply concave and marked by two grooved ridges which cross one another and divide the surface into four fossse of which the two upper, triangular in form, lodge the occipital lobes of the cerebrum, and the two lower, more quadrilateral in outline, the lobes of the cerebellum. The vertical ridge extends from the superior angle to the foramen magnum and the transverse ridge from one lateral angle to the other, the point of intersection being indicated by the internal occipital protuberance [eminentia cruciata]. The Fig. 66. — -Occipital Bone, Cerebral Stjefacb. Superior angle Cerebral fossa Groove for transverse sinus Lateral angle Cerebellar fossa Groove for transverse smus Jugular process For petrosal i upper part of the vertical ridge is grooved [sulcus sagittalis] for the superior sagittal {longitudinal) sinus and gives attachment, by its margins, to the falx cerebri; the lower part is sharp and known as the internal occipital crest, and affords attachment to the falx cerebelli. Approaching the foramen magnum the ridge divides, and the two parts become lost upon its margin. The angle of divergence sometimes presents a shallow fossa for the extremity of the vermis of the cerebellum, and is called the vermiform fossa. The two parts of the transverse ridge are deeply grooved [sulcus transversus] for the transverse {lateral) sinuses, and the margins of the groove give attachment to the tentorium cerebelli. To one side of the internal occipital protuberance is a wide space, where the vertical groove is continued into one of the lateral grooves (more frequently the right), and this is termed the torcular Herophili; it is sometimes exactly in the middle line. The squamous portion has three angles and four borders. The superior angle forming the summit of the bone is received into the space formed by the union of the two parietals. The lateral angles are ver}' obtuse and correspond in situatio n with the lateral ends of the transverse ridges. Above the lateral angle on each side the margin is deeply serrated, forming the lambdoid or superior border which extends to the superior angle and articulates with the posterior border of the parietal in the lambdoid suture. The mastoid or inferior border extends 54 THE SKELETON from the lateral angle to the jugular process and articulates with the mastoid portion of the temporal. The condylar or lateral portions [partes laterales] (ex-occipitals) form the lateral boundaries of the foramen magnum and bear the condyles on their in- ferior surfaces. The condyles are two convex oval processes of bone with smooth articular surfaces, covered with cartilage in the recent state, for the superior articular processes of the atlas. They converge in front, and are somewhat everted. Their margins give attachment to the capsular ligaments of the occipito-atlantal joints and on the medial side of each is a prominent tubercle for the alar (lateral odontoid) ligament. The anterior extremities of the condyles extend beyond the ex-occipitals on the basi-occipital portion of the bone. The hypoglossal (anterior condyloid) foramen or canal [canalis hypoglossi] perforates the bone at the base of the condyle, and is directed from the interior of the cranium, just above the foramen magnum, forward and laterally; it transmits the hypoglossal nerve and a twig of the ascending pharyngeal artery. The foramen is sometimes double, being divided by a delicate spicule of bone. Above the canal is a smooth convexity known as the tuberculum jugulare sometimes marked by an oblique groove for the ninth, tenth and eleventh cranial nerves. Posterior to each condyle is a pit, the Fig. 67. — Cerebral Surface of the Occipital, Showing an Occasional Disposition of THE Channels. Vermiforin fossa Condylar foramen Hypoglossal foramen. condylar fossa, which receives the hinder edge of the superior articular process of the atlas when the head is extended. The floor of the depression is occasionally perforated by the condylar (posterior condyloid) canal or foramen [canalis condyloideus], which transmits a vein from the transverse sinus. Projecting laterally opposite the condyle is a quadi'ilateral portion of bone known as the jugular process, the extremity of which is rough for articulation with the jugular facet on the petrous portion of the temporal bone. Up to twenty-five years the bones are united here by means of cartilage; about this age ossification of the cartilage takes place, and the jugular process thus becomes fused with the petrosal. Its anterior border is deeply notched to form the posterior boundary of the jugular foramen, and the notch is directly continuous with a groove on the upper surface which lodges the termination of the transverse sinus. In or near the groove is seen the inner opening of the condylar foramen. The lower surface of the process gives attachment to the rectus capitis lateralis and the oblique occipito-atlantal ligament. Occa- sionally the mastoid air cells extend into this process and rarely a process of bone, representing the paramastoid process of many mammals, projects downward from its under aspect and may be so long as to join or articulate with the transverse process of the atlas. The basilar portion (basi-occipital) is a quadrilateral plate of bone projecting forward and upward in front of the foramen magnum. Its superior surface presents a deep groove — the basilar groove [chvus]; it supports the medulla oblongata and gives attachment to the tectorial membrane (occipito-axial ligament). The lower surface presents in the middle line a small elevation known as the pharyngeal tubercle for the attachment of the fibrous raphe of the pharynx, and immediately in front of the tubercle there is frequently a shallow THE OCCIPITAL BONE 55 fossa — the scaphoid fossa — which originally received the primitive anterior extremity of the foregut. On each side of the middle line are impressions for the insertions of the longus capitis (rectus capitis anterior major) and rectus capitis anterior (minor), the impression for the latter being Fig. 68. — The Foramen Magnum at the Sixth Year. Condylar foramen Ex-occipital portion of the condyle, J Hypoglossal foramen. Basi-occipital portion' I of the condyle i Basi-occipitaj nearer to the condyle, and near the foramen magnum this surface gives attachment to the anterior occipito-atlantal ligament. Anteriorly the basilar process articulates by synchondrosis with the body of the sphenoid up to twenty years of age, after which there is complete bony union. Posteriorly it presents a smooth rounded border forming the anterior boundary of the foramen magnum. It gives attachment to the apical odontoid ligament, and above this Fig. 69. — The Occipital at Birth. (Anterior view.) Interparietal portion (develops in' membrane) The interparietal and supra-occipital portions form the squamous portion of the adult Supra-occipital portion (develops in cartilage) to the ascending portion of the crucial ligament. In the occipital bone at the sixth year the lateral extremities of this border are enlarged to form the basilar portion of the condyles. The lateral borders are rough below for articulation with the petrous portion of the temporal bones, but above, on either side of the basilar groove, is a half-groove, which, with a similar half -groove on the petrous portion of the temporal bone, lodges the inferior petrosal sinus. 56 THE SKELETON The foramen magnum is oval in shape, with its long axis in a sagittal direc- tion. It transmits the medulla oblongata and its membranes, the accessory nerves (spinal portions) , the vertebral arteries, the anterior and posterior spinal Fia. 70. — The Occipital with a Separate Interparietal. arteries, and the tectorial membrane (occipito-axial ligament). It is widest behind, where it transmits the medulla, and is narrower in front, where it is encroached upon by the condyles. Fig. 71. — Skull showing a Pre-inteeparietal Bone (P.I.)- Occasionally a facet is present on the anterior margin, forming a third occipital condyle for articulation with the dens. Between the condyles and behind the margin of the foramen mag- num the posterior occipito-atlantal ligament obtains attachment. Blood-supply. — The occipital bone receives its blood-supply from the occipital, posterior auricular, middle meningeal, vertebral and the ascending pharyngeal arteries. Articulations. — The occipital bone is connected by suture with the two parietals, the two temporals, and the sphenoid; the condyles articulate with the atlas, and exceptionally the occip- ital articulates with the dens of the epistropheus by means of the third occipital condyle. THE PARIETAL BONE 57 Ossification. — The occipital bone develops in four pieces. The squamous portion is ossi- fied from four centres, arranged in two pairs, which appear about the eighth week. The upper pair are deposited m membrane, and this part of the squamous portion represents the interparietal bone of many animals. The lower oair, deposited in cartilage, form the true supra-ocoipital element, and the four parts quickly coalesce near the situation of the future occipital protuberance. For many weeks two deep lateral fissures separate the interparietal and supraoccipital portions, and a membranous space extending from the centre of the squamous portion to the foramen magnum partially separates the lateral portions of the supra-occipital. This space is occupied later by a spicule of bone, and is of interest as being the opening through which the form of hernia of the brain and its rneninges, known as occipital meningocele or en- cephalocele, occurs. The basi-occipital and the two ex-occipitals are ossified each from a single nucleus which appears in cartilage from the eighth to the tenth week. At birth the Ijone consists of four parts united by strips of cartilage, and in the squamous portion fissures running in from the upper and lateral angles are still noticeable. The osseous union of the squamous and ex-occipital is completed in the fifth year, and that of the ex- occipitals with the basi-occipital before the seventh year. Up to the twentieth year the basi- occipital is united to the body of the sphenoid by an intervening piece of cartilage, but about that date ossific union begins and is completed in the course of two or three years. Occasionally the interparietal portion remains separate throughout Ufe (fig. 70), forming what has been termed the inca hone, or it may be represented by numerous detached ossicles or Wormian bones. In some cases a large Wormian bone, named the pre-interparietal, is found, partly replacing the interparietal bone (fig. 71). A pre-interparietal bone is found in some mammals, and it has occasionally been observed in the human foetal skull. In fig. 71 the bone is seen in an adult human skull — a distinctly rare condition. I THE PARIETAL The two parietal bones (figs. 72, 73), interposed between the frontal before and the occipital behind, form a large portion of the roof and sides of the cranium. Each parietal bone [os parietale] is quadrilateral in form, convex externally, concave internally, and each presents for examination two surfaces, four borders, and four angles. The parietal surface is smooth and is crossed, just below the middle, by two curved lines known as the temporal lines. The superior line gives attachment to the temporal fascia; the lower, frequently the better marked, limits the origin of the temporal muscle; whilst the narrow part of the surface enclosed between them is smooth and more poHshed than the rest. Immediately above the ridges is the most convex part of the bone, termed the parietal eminence [tuber parietale], best marked in young bones, and indicating the point where ossification com- menced. Of the two divisions on the parietal surface marked off by the temporal lines, the upper is covered by the scalp, and the lower, somewhat striated, ait'ords attachment to the temporal muscle. Close to the upper border and near to the occipital angle is a small opening — the parietal foramen — which transmits a vein to the superior sagittal {longitudinal) sinus. The cerebral surface is marked with depressions corresponding to the cerebral convolutions and by numerous deep furrows, running upward and backward from the sphenoidal angle and the lower border, for the middle meningeal vessels (sinus and artery). A shallow depression running close to the superior border forms, with the one of the opposite side, a channel for the superior sagittal sinus, at the side of which are small irregular pits for the Pacchionian bodies; the pits are usually present in adult skulls, but are best marked in those of old persons. The margins of the groove for the superior sagittal sinus give attachment to the falx cerebri. Borders. — The sagittal or superior border, the longest and thickest, is deeply serrated to articulate with the opposite parietal, with which it forms the sagittal suture. The frontal or anterior border articulates with the frontal to form the coronal suture. It is deeply serrated and bevelled, so that it is overlapped by the frontal above, but overlaps the edge of that bone below. The occipital or posterior border articulates with the occipital to form the lambdoid suture, and resembles the superior and anterior in being markedly serrated. The squamosal or inferior border is divided into three portions : — the anterior, thin and bevelled, is overlapped by the tip of the great wing of the sphenoid; the middle portion, arched and also bevelled, is overlapped by the squamous part of the tempora,l; and the posterior portion, thick and serrated, articulates with the mastoid portion of the temporal bone. Angles. — The frontal or anterior superior, almost a right angle, occupies that part of the bone which at birth is membranous and forms part of the anterior 58 THE SKELETON fontanelle. The sphenoidal or anterior inferior angle is thin and prolonged downward to articulate with the tip of the great wing of the sphenoid. Its inner surface is marked by a deep groove, sometimes converted into a canal for a short Fig. 72. — The Left Parietal. (Outer surface.) Sagittal border Parietal foramen Portion covered by Superior temporal line Inferior temporal line For temporal muscle, and forms part of the temporal fossa Sphenoidal angle' Fig. 73. — The Left Parietal. (Inner surface.) Parietal foramen Groove for superior sagittal sinus Depressions for Pacchionian bodies Groove for transverse Grooves for middle meningeal artery distance, for the middle meningeal vessels (chiefly for the sinus). The occipital or posterior superior angle is obtuse and occupies that part which during foetal life enters into formation of the posterior fontanelle. The mastoid or posterior THE FRONTAL BONE 59 inferior angle is thick and articulates with the mastoid portion of the temporal bone. Its inner surface presents a shallow groove which lodges a part of the transverse (lateral) sinus. Blood-supply. — The parietal bone receives its blood-supply from the middle meningeal, occipital, and supra-orbital arteries. Articulations. — The parietal articulates with the occipital, frontal, sphenoid, temporal, its fellow of the opposite side, and the epipterio bone when present. Occasionally the temporal and epipteric bones exclude the parietal from articulation with the great wing of the sphenoid. Ossification. — The parietal ossifies from a single nucleus which appears in the outer layer of the membranous wall of the skull about the seventh week. The ossification radiates in such a way as to leave a cleft at the upper part of the bone in front of the occipital angle, the Fig. 74. — Unusual Form op Pabietal Exhibiting a Horizontal Suture Separating the Bone into Two Pif.ces, Upper and Lower. ^f^^^^^^^sy^m cleft of the two side forming a lozenge-shaped space across the sagittal suture known as the sag- ittal fontanelle. This is usually closed about the fifth month of intra-uterine life, but traces may sometimes be recognised at the time of birth, and the parietal foramina are to be regarded as remains of the cleft. According to Dr. A. W. W. Lea, a well-developed sagittal fontanelle is present in 4 . 4 per cent, of infants at birth. In such cases it closes within the first two months of life, but at times it may remain open for at least eight months after birth and possibly longer. Rarely the parietal bone is composed of two pieces (fig. 74), one above the other, and separated by an antero-posterior suture (sub-sagittal suture), more or less parallel with the sagittal suture. In such cases the parietal is ossified from two centres of ossification. THE FRONTAL The frontal bone [os frontale] closes the cranium in front and is situated above the skeleton of the face. It consists of two portions — a frontal {vertical) portion [squama frontalis], forming the convexity of the forehead, and an orbital {hori- zontal) portion, which enters into formation of the roof of each orbit. Frontal {vertical) portion. — The frontal surface is smooth and convex, and usually presents in the middle line above the root of the nose some traces of the suture which in young subjects traverses the bone from the upper to the lower part. This suture, known as the frontal or metopic suture, indicates the line of junction of the two lateral halves of which the bone consists at the time of birth; in the adult the suture is usually obliterated except at its lowest part. On each side is a rounded elevation, the frontal eminence [tuber frontale], very prominent in young bones, below which is a shallow groove, the sulcus transversus, separat- ing the frontal eminence from the superciliary arch. The latter forms an arched pi^ojection above the margin of the orbit and corresponds to an air-cavity within the bone known as the frontal sinus; it gives attachment to the orbicularis oculi and the corrugator muscles. The ridges of the two sides converge toward the ' 60 THE SKELETON median line, but are separated by a smooth surface called the glabella (nasal eminence). Below the arch the bone presents a sharp curved margin, the supra- orbital border, forming the upper boundary of the circumference of the orbit and separating the frontal from the orbital portion of the bone. At the junction of its medial and intermediate third is a notch, sometimes converted into a foramen, and known as the supra-orbital notch or foramen ; it transmits the supra-orbital nerve, artery, and vein, and at the bottom of the notch is a small opening for a vein of the diploe which terminates in the supra-orbital. Sometimes, a second less marked notch is present, medial to the supra-orbital, and known as the frontal notch; it transmits one of the divisions of the supra-orbital nerve. The extremities of the supra-orbital border are directed downward and form the medial and zygomatic (lateral angular) processes. The prominent zygomatic proc- ess articulates with the zygomatic bone and receives superiorly two well-marked lines which converge somewhat as they curve downward and forward across the bone. These are the superior and inferior temporal lines, continuous with the Fig. 75. — The Frontal. (Anterior view.) 'Temporal line Supra-orbital notch Zygomatic process temporal lines on the parietal bone, the upper giving attachment to the temporal fascia and the lower to the temporal muscle. Behind the lines is a slight con- cavity which forms part of the fioor of the temporal fossa and gives origin to the temporal muscle. The medial angular processes articulate with the lacrimals and form the lateral limits of the nasal notch, bounded in front by a rough, semilunar surface which articulates with the upper ends of the nasal bones and the frontal (nasal) processes of the maxillae. In the concavity of the notch hes the nasal portion of the frontal, which projects somewhat beneath the nasal bones and the nasal processes of the maxillfe. It is divisible into three parts: — a median frontal (nasal) spine, which descends in the nasal septum between the crest of the nasal bones in front and the vertical plate of the ethmoid behind, and, on the posterior aspect of the process, two alee, one on either side of the median ridge from which the frontal (nasal) spine is continued. Each ala forms a small grooved surface which enters into the formation of the roof of the nasal fossa. The cerebral surface presents in the middle line a vertical groove — the sagittal sulcus — which descends from the middle of the upper margin and lodges the superior sagittal (longitudinal) sinus. Below, the groove is succeeded by the frontal crest, which terminates near the lower margin at a small notch, converted into a foramen by articulation with the ethmoid. THE FRONTAL BONE 61 The foramen is called the foramen caecum, and is generally closed below, but sometimes transmits a vein from the nasal fossje to the superior sagittal (longitudinal) sinus. The frontal crest serves for the attachment of the anterior part of the falx cerebri. On each side of the middle line the bone is deeply concave, presentino: depressions for the cerebral convolutions and numerous small furrows which, running medially from the lateral margin, lodge branches of the middle meningeal vessels. At the upper part of the surface, on either side of the frontal sulcus, are some depressions for Pacchionian bodies. The horizontal portion consists of two somewhat triangular plates of bone called the orbital plates, which, separated from one another by the ethmoidal Fig. 76. — The Frontal Bone. (Inferior view.) Frontal spine Articulation with nasal bone Articulation with max- illa ^y Carotid canal Non-ossified area of tbe tympanic plate around which it is developed as a cartilaginous capsule. This is known as the periotic capsule or petrosal element, and its base abuts on the outer aspect of the 70 THE SKELETON cranium, where it forms a large part of the so-called mastoid portion of the temporal bone. Besides containing the internal ear, it bears on its cranial side a foramen for the seventh and eighth cranial nerves (internal auditory meatus), and on its outer side two openings — the fenestra vestibuli and fenestra cochleae (fig. 91). The squamosal is a superadded element and is formed as a membrane bone in the lateral wall of the cranium. It is especially developed in man in consequence of the large size of the brain, and forms the squamous division of the adult bone, and by a triangular shaped process which is prolonged behind the aperture of the ear it also contributes to the formation of the mastoid portion. It is obvious, therefore, that the mastoid is not an independent element, but belongs in part to the petrous, and in part to the squamous. The tympanic portion, also superadded, is a ring of bone developed in connection with the external auditory meatus, and eventually forms a plate constituting part of the bony wall of this passage. These three parts are easily separable at birth, but eventually become firmly united to form a single bone which affords little trace of its complex origin. Lastly a process of bone, developed in the second visceral arch, coalesces with the under surface of the temporal bone and forms the styloid process. Fig. 92. — The Left Temporal Bone. (Outer view.) Zygomatic process Tympanic plati Stylo-pharyngeus Stylo-hyoid Stylo-glossus Styloid process Mastoid process The squamous portion [squama temporalis] is flat, scale-like, thin, and trans- lucent. It is attached almost at right angles to the petrous portion, forms part of the side wall of the skull and is limited above by an uneven border which describes about two-thirds of a circle. The outer surface is smooth, slightly convex near the middle, and forms part of the temporal fossa. Above the external auditory meatus it presents a nearly vertical groove for the middle temporal artery. Connected with its lower part is a narrow projecting bar of bone known as the zygomatic process. At its base the process is broad, directed lateralljr, and flattened from above downward. It soon, however, becomes twisted on itself and runs forward, almost parallel with the squamous portion. This part is much narrower and compressed laterally so as to present medial and lateral surfaces with upper and lower margins. The lateral surface is sub- cutaneous; the medial looks toward the temporal fossa and gives origin to the masseter muscle. The lower border is concave and rough for fibres of the same muscle, whilst the upper border, thin and prolonged further forward than the lower, receives the temporal fascia. The extremity of the process is serrated for articulation with the zygomatic bone. At its base the zygomatic process presents three roots — anterior, middle, and posterior. THE TEMPORAL BONE 71 The anterior, continuous with the lower border, is short, broad, convex, and directed medially' to terminate in the articular tubercle, which is covered with cartilage in the recent state, for articulation with the condyle of the lower jaw. The middle root, sometimes very prominent, forms the post-glenoid process. It separates the articular portion of the man- dibular fossa from the external auditory meatus and is situated immediately in front of the petro-tympanic (Glaserian) fissure. The posterior root, prolonged from the upper border, is strongly marked and extends backward as a ridge above the external auditory meatus. It is called the temporal ridge (supra-mastoid crest), and marks the arbitrary line of division be- tween the squamous and mastoid portions of the adult bone. It forms part of the posterior boundary of the temporal fossa, from which, as well as from the ridge, fibres of the temporal muscle arise. Where the anterior root joins the zygomatic process is a slight tubercle — the preglenoid tubercle — for the attachment of the temporo-mandibular ligament, and between the anterior and middle roots is a deep oval depression, forming the part of the mandibular fossa for the condyle of the lower jaw. The mandibular fossa is a considerable hollow, bounded in front by the articular tubercle and behind by the tympanic plate which separates it from the external auditory meatus. It is divided into two parts by a narrow slit — the petro-tympanic (Glaserian) fissure. The anterior part [facies articularis], which belongs to the squamous portion, is articular, and, like the articular tubercle, is coated with cartilage. The posterior Fig. 93. — The Left Temporal Bone. (Seen from the inner side and above.) Squaipous portion Meningeal groove { Zygomatic process Eminentia arcuata Sigmoid groove Mastoid foramen Masseter Hiatus canalis facialis Internal auditory meatus Aquasductus vestibuli Fossa subarcuata Mastoid process Aquaeductus cochleaE Stylo-pharyngeus Styloid process part, formed by the tympanic plate, is non-articular and lodges a lobe of the parotid gland. Immediately in front of the articular tubercle is a small triangular surface which enters into the formation of the roof of the zygomatic fossa. The inner or cerebral surface of the squamous portion is marked by furrows for the con- volutions of the brain and grooves for the middle meningeal vessels. At the upper part of the surface the inner table is deficient and the outer table is prolonged some distance upward, forming a thin scale, with the bevelled surface looking inward to overlap the corresponding edge of the parietal. Anteriorly the border is thicker, serrated, and slightly bevelled on the outer side for articulation with the posterior border of the great wing of the sphenoid. Pos- teriorly it joins the rough serrated margin of the mastoid portion to form the parietal notch. The line separating the squamous from the petrous portion is indicated at the lower part of the inner surface by a narrow cleft, the internal petro-squamous suture, the appearance of which varies in different bones according to the degree of persistence of the original line of division. The mastoid portion [pars mastoidea] is rough and convex. It is bounded above by the temporal ridge and the parieto-mastoid suture; in front, by the external auditory meatus and the tympano-mastoid fissure; and behind, by the suture between the mastoid and occipital. As already pointed out, it is formed by the squamous portion in front and by the base of the petrosal behind, the line of junction of the two component parts being indicated on the outer surface by the external petro-squamous suture (squamo-mastoid). The appearance of the suture varies, being in some bones scarcely distinguishable, in others, a series 72 THE SKELETON of irregular depressions, whilst occasionally it is present as a well-marked fissure (fig. 92) directed obliquely downward and forward. The mastoid portion is prolonged downward behind the external acoustic meatus into a nipple-shaped projection, the mastoid process, the tip of which points forward as well as down- ward. The process is marked, on its medial surface, by a deep groove, the mastoid notch (digastric fossa), for the origin of the digastric muscle, and again medially by the occipital groove for the occipital artery. The outer surface is perforated by numerous foramina, one, of large size, being usually situated near the posterior border and called the mastoid foramen. It transmits a vein to the transverse (lateral) sinus and the mastoid branch of the occipital artery. The mastoid portion gives attachment externally to the auricularis posterior (retrahens aurem) and occipitalis, and, along with the mastoid process, to the sterno-mastoid, splenius capitis, and longissimus capitis {trachelo-mastoid) . Projecting from the postero-superior margin of the external auditory meatus there is frequently a small tubercle — the supra-meatal spine — behind which the surface is depressed to form the mastoid (supra-meatal) fossa. The inner surface of the mastoid portion presents a deep curved sigmoid groove, in which is lodged a part of the transverse sinus ; the mastoid foramen is seen opening into the groove. The interior of the mastoid portion, in the adult, is usually occupied by cavities lined by mucous membrane and known as the mastoid air-cells (fig. 97). These open into a small chamber — the mastoid antrum — which communicates with the upper part of the tympanic cavity. The mastoid cells are arranged in three groups: (1) antero-superior, (2) middle, and (3) apical. The [apical cells, situated at the apex of the mastoid process, are small and usually contain marrow. Borders. — -The superior border is broad and rough for articulation with the hinder part of the inferior border of the parietal bone. The posterior border, very uneven and serrated, articulates with the inferior border of the occipital bone, extending from the lateral angle to the jugular process. The petrous portion [pars petrosa; pyramis] is a pyramid of very dense bone presenting for examination a base, an apex, three (or four) surfaces, and three (or four) borders or angles. Two sides of the pyramid look into the cranial cavity, the posterior into the posterior cranial fossa, and the anterior into the middle cranial fossa. The inferior surface appears on the under surface of the cranium . The medial and posterior walls of the tympanic cavity in the temporal bone are sometimes described as a fourth side of the pyramid. The base forms a part of the lateral surface of the cranium; the apex is placed medially. The posterior surface of the pyramid is triangular in form, bounded above by the superior angle and below by the posterior angle Near the middle is an obliquely directed foramen [porus acusticus internus] leading into a short canal — ■ the internal auditory meatus — at the bottom of which is a plate of bone, pierced by numerous foramina, and known as the lamina cribrosa. The canal transmits the facial and auditory nerves, the pars intermedia, and the internal auditory artery. The bottom of the internal auditory meatus can be most advantageously studied in a temporal bone at about the time of birth, when the canal is shallow and the openings relatively wide. The fundus of the meatus is divided by a transverse ridge of bone, the transverse crest, into a superior and inferior fossa. Of these, the superior is the smaller, and presents anteriorly the beginning of the facial canal (aqueduct of Fallopius), which transmits the seventh nerve. The rest of the surface above the crest is dotted with small foramina (the superior vestibular area) which transmit nerve-twigs to the recessus elliptious (fovea hemielliptica) and the ampuUae of the superior and lateral semicircular canals (vestibular division of the auditory nerve). Below the crest there are two depressions and an opening. Of these, an anterior curled tract (the spiral cribriform tract) with a central foramen (foramen oentrale cochleare) marks the base of the cochlea; the central foramen indicates the orifice of the canal of the modiolus, and the smaller foramina transmit the cochlear twigs of the auditory nerve. The posterior opening (foramen singulare) is for the nerve to the ampulla of the posterior semicircular canal. The middle depression (inferior vestibular area) is dotted with minute foramina for the nerve-twigs to the saccule, which is lodged in the recessus sphsericus (fovea hemisphaeri- ca). The inferior fossa is subdivided by a low vertical crest. The fossa in front of the crest is the fossula cochlearis, and the recess behind it is the fossula vestibularis. Behind and lateral to the meatus is a narrow fissure, the aquseductus vestibuli, covered by a scale of bone. In the fissure lies the ductus endolymphaticus, a small arteriole and venule, and a process of connective tissue which unites the dura mater to the sheath of the internal ear. Occasionally a bristle can be passed through it into the vestibule. Near the upper margin, and opposite a point about midway between the meatus and the aqueduct of the vesti- THE TEMPORAL BONE 73 bule, is an irregular opening, the fossa subarcuata, the remains of the floccular fossa, a con- spicuous depression in the foetal bone. In the adult the depression usually lodges a process of dura mater and transmits a small vein, though in some bones it is almost obhterated. .The anterior surface of the pyramid, sloping downward and forward, forms the back part of the floor of the middle fossa of the cranium. Upon the anterior surface of the pyramid will be found the following points of interest, proceeding from the apex toward the base of the pyramid: — (1) a shallow trigeminal im- pression for the semilunar (Gasserian) ganglion of the trigeminal nerve; (2) two small grooves running backward and laterally toward two small foramina overhung by a thin osseous lip, the larger and medial of which, known as the hiatus canalis facialis, transmits the great superfi- cial petrosal nerve and the petrosal branch of the middle meningeal artery, whilst the smaller and lateral foramen is for the small superficial petrosal nerve; (3) behind and lateral to these is an eminence — the eminentia arcuata — best seen in young bones, corresponding to the su- perior semicircular canal in the interior; (4) still more laterally is a thin transulcent plate of bone, roofing in the tympanic cavity, and named the tegmen tympani. Fig. 94. — The Foramina in the Fundtts of the Left Internal Auditory Meatus op a Child at Birth (y). (Diagrammatic.) Superior fossa Superior cribriform area Foramen singulare Entrance to the facial canal - Transverse crest Middle cribriform area \j,'^ j^^^g\ Orifice of the canal of the modiolus Spiral cribriform tract The inferior or basilar surface of the pyramid is very irregular. At the apex it is rough, quadrilateral, and gives attachment to the tensor tympani, levator veil palatini, and the pharyngeal aponeurosis. Behind this are seen the large circular orifice of the carotid canal for the transmission of the carotid artery and a plexus of sympathetic nerves, and on the same level, near the posterior border, a small three-sided depression, the canaliculus cochleae, which transmits a small vein from the cochlea to the internal jugular. Behind these two openings is the large elliptical jugular fossa which forms the anterior and lateral part of the bony wall of the jugular foramen, in which is contained a dilatation on the commencement of the internal jugular vein; on the lateral wall of the jugular fossa is a minute foramen, the mastoid canaliculus, for the entrance of the auricular branch of the vagus (Arnold's nerve) into the interior of the bone. Between the inferior aperture of the carotid canal and the jugular fossa is the sharp carotid ridge, on which is a small depression, the fossula petrosa, and at the bottom of this a minute opening, the tympanic canaliculus, for the tympanic branch of the glosso-pharyngeal or Jacobson's nerve, and the small tympanic branch from the ascending pharyngeal artery. Behind the fossa is the rough jugular surface for articulation with the jugular process of the occipital bone, on the lateral side of which is the prominent cylindrical spur known as the styloid process with the stylo-mastoid foramen at its base. The facial nerve, and sometimes the auricular branch of the vagus, leave the skull, and the stylo-mas- toid artery enters it by this foramen. Running backward from the foramen are the mastoid and occipital grooves already described. The tympanic surface of the pyramid, forming the medial and posterior walls [paries labyrinthica] of the tympanic cavity, is shown by removing the tympanic plate (fig. 91). It presents near the base an excavation, known as the tympanic or mastoid antrum, covered by the triangular part of the squamous below and behind the temporal line. The opening of the antrum into the tympanic cavity is situated immediately above the fenestra vestibuli, an oval- shaped opening which receives the base of the stapes; below the fenestra vestibuli is a convex projection or promontory, marked by grooves for the tympanic plexus of nerves and containing the commencement of the first turn of the cochlea. In the lower and posterior part of the promontory is the fenestra cochlesB, closed in the recent state by the secondary membrane of the tj^mpanum. Running downward and forward from the front of the fenestra vestibuli is a thin curved plate of bone [septum canalis musculotubarii], separating two grooves converted 74 THE SKELETON into canals by the overlying tympanic plate. The lower is the groove for the Eustachian tube [semicanalis tubse audi tivse], the communicating passage between the tympanum and the pharynx ; the upper is the semicanalis m. tensoris tympani, and the lateral apertures of both canals are visible in the retiring angle, b-etween the petrous and squamous portions of the bone. The apex of the pyramid is truncated and presents the medial opening of the carotid canal. The latter commences on the inferior surface, and, after ascending for a short distance, turns forward and medially, tunnelling the bone as far as the apex, and finally opens into the upper part of the foramen lacerum formed between the temporal and sphenoid bones. One or two minute openings in the wall of the carotid canal, known as the carotico -tympanic canaliculi, transmit communicating twigs between the carotid and tympanic plexuses. The upper part of the apex is joined by cartilage to the posterior petrosal process of the sphenoid. The base is the part of the pyramid which appears laterally at the side of the cranium and takes part in the formation of the mastoid portion. It is described with that chvision of the bone. Fig. 95. — The Left Temporal Bone. (Inferior view.) Carotid canal- Tensor tympani Levator veil palatini' Carotid canal Tympanic canaliculus Canalicul Mastoid canaliculus Jugular fossa Jugular surface Zygomatic process Masseter Articular tubercle Mandibular fossa ■Petro-tympanic fissure Tympanic plate Styloid process Stylo-pharyngeus Tympano-mastoid fissure Stylo-mastoid foramen Mastoid process Digastric Occipital groove Angles. — The superior angle (border) of the pyramid is the longest and separates the pos- terior from the anterior surface. It is grooved for the superior petrosal sinus, gives attachment to the tentorium cerebelli, and presents near the apex a semilunar notch upon which the fifth cranial nerve lies. Near its medial end there is often a small projection for the attachment of the petro-sphenoid.al ligament, which arches over the inferior petrosal sinus and the sixth nerve. The posterior angle separates the posterior from the inferior surface, and when ar- ticulated with the occipital, forms the groove for the inferior petrosal sinus, and completes the jugular foramen formed by the temporal in front and on the lateral side, and by the occipital behind and on the medial side. The jugular foramen is divisible into three compartments: an anterior for the inferior petrosal sinus, a middle for the glossopharyngeal, vagus and accessory cranial nerves, and a posterior for the internal jugular vein and some meningeal branches from the occipital and ascending pharyngeal arteries. The anterior angle is the shortest and consists of two parts, one joined to the squamous in the petro-squamous suture and a small free part internally which articulates with the sphenoid. A fourth or inferior border may be distinguished, which runs along the line of junction with the tympanic plate and is continued on to the rough area below the apex. THE TEMPORAL BONE 75 The tympanic portion [pars tympanica] is quadrilateral in form, hollowed out above and behind, and nearly flat, or somewhat concave, in front and below. It forms the whole of the anterior and inferior walls, and part of the posterior wall, of the external auditory meatus, and is separated behind from the mastoid process by the tympano-mastoid (auricular) fissure through which the auricular branch of the vagus in some cases leaves the bone. In front it is separated by the petro-tympanic fissure from the squamous portion. Through the petro-tympanio fissure the tympanic branch of the internal maxillary artery and the so- called laxator tympani pass. The processus graoihs of the malleus is lodged within it, and a narrow subdivision at its inner end, known as the canal of Huguier, transmits the chorda tympani nerve. The tympanic part presents for examination two surfaces and four borders. The antero-inferior surface, directed downward and forward, lodges part of the parotid gland. Near the middle it is usually very thin, and sometimes presents a small foramen (the foramen of Huschke), which represents a non-ossified portion of the plate. The postero- superior surface looks into the external auditory meatus and tympanic cavity, and at its medial end is a narrow groove, the sulcus tympanicus, deficient above, which receives the membrana tympani. The lateral border is rough and everted, forming the external auditory process for the attachment of the cartilage of the pinna; the superior border enters into the formation of the petro-tympanic fissure; the inferior border is uneven and prolonged into the vaginal process [vagina processus styloideil which surrounds the lateral aspect of the base of the styloid process and gives attachment to the front part of the fascial sheath of the carotid vessels; the medial border, short and irregular, lies immediately below and to the lateral side of the opening of the Eustachian tube, and becomes continuous with the rough quadrilateral area on the inferior aspect of the apex. The external auditory meatus is formed partly by the tympanic and partly by the squamous portion. It is an elliptical bony tube leading into the tym- panum, the extrance of which is bounded throughout the greater part of its circumference by the external auditory process of the tympanic plate. Above, the entrance is limited by the temporal ridge or posterior root of the zygomatic process. The styloid process is a slender, cylindrical spur of bone fused with the inferior aspect of the temporal immediately in front of the stylo-mastoid foramen. It consists of two parts, basal (tympano-hyal), which in the adult lies under cover of the tympanic plate, and a projecting portion (stylo-hyal) , which varies in length from five to fifty millimetres. When short, it is hidden by the vaginal process, but, on the other hand, it may reach to the hyoid bone. The projecting portion gives attachment to three muscles and two ligaments. The slylo-pharyngeus arises near the base from the medial and slightly from the posterior aspect; the slylo-hyoid from the posterior and lateral aspect near the middle; and the slylo- glossus from the front near the tip. The tip is continuoiis with the stylo-hyoid ligament, which runs down to the lesser cornu of the hyoid bone. A band of fibrous tissue — the stylo-mandibular ligament — passes from the process below the origin of the stylo-glossus to the angle of the lower jaw. Blood-supply. — The arteries supplying the temporal bone are derived from various sources. The chief are: — Stylo-mastoid from posterior auricular: it enters the stylo-mastoid foramen. Anterior tympanic from internal maxillary: it passes through the petro-tympanic fissure. Superficial petrosal from middle meningeal: transmitted by the hiatus canalis facialis. Carotieo-tympanic from internal carotid whilst in the carotid canal. Internal auditory from the basilar: it enters the internal auditory meatus, and is distributed to the cochlea and vestibule. Other less important twigs are furnished by the middle meningeal, the meningeal branches of the occipital, and by the ascending pharyngeal artery. The squamous portion is supplied, on its internal surface, by the middle meningeal, and externally by the branches of the deep temporal from the internal maxillary. Articulations. — The temporal bone articulates with the occipital, parietal, sphenoid, zygomatic, and, by a movable joint, with the mandible. Occasionally the squamous portion presents a process which articulates with the frontal. A fronto -squamosal suture is common in the skulls of the lower races of men, and is normal in the skulls of the chimpanzee, gorilla, and gibbon. Ossification. — Of the three parts which constitute the temporal bone at birth, the squa- mosal and tympanic develop in membrane and the petrosal in cartilage. The squamosal is formed from one centre, which appears as early as the eighth week, and ossification extends into the zygomatic process, which grows concurrently with the squamosal. At first the tym- panic border is nearly straight, but soon assumes its characteristic horseshoe shape. At birth the post-glenoid tubercle is conspicuous, and at the hinder end of the squamosal there is a pro- cess which comes into relation with the mastoid antrum The centre for the tympanic ele- ment appears about the twelfth week. At birth it forms an incomplete ring, open above, and slightly ankylosed to the lower border of the squamosal. The anterior extremity terminates 76 THE SKELETON in a small irregular process, and the medial aspect presents, in the lower half of its circumfer- ence, a groove for the reception of the tympanic membrane. Up to the middle of the fifth month the periotio capsule is cartilaginous; it then ossifies so rapidly that by the end of the sixth month its chief portion is converted into porous bone. The ossifio material is deposited in four centres, or groups of centres, named according to their relation to the ear-capsule in its embryonic position. The nuclei are deposited in the following order; — 1. The opisthotic appears at the end of the fifth month. The osseous material is seen first on the promontory, and it quickly surrounds the fenestra cochleae from above downward, and forms the floor of the vestibule, the lower part of the fenestra vestibuli, and the internal au- ditory meatus; it also invests the cochlea. Subsequently a plate of bone arises from it to sur- round the internal carotid artery and form the floor of the tympanum. 2. The prootic nucleus is deposited behind the internal auditory meatus near the medial limb of the superior semicircular canal. It covers in a part of the cochlea, the vestibule, and the internal auditory meatus, completes the fenestra vestibuli, and invests the superior semi- circular canal. 3. The pterotic nucleus ossifies the tegmen tympani and covers in the lateral semicircular canal; the ossific matter is first deposited over the lateral limb of this canal. 4. The epiotic, often double, is the last to appear, and is first seen at the most posterior part of the posterior semicircular canal. At birth the bone is of loose and open texture, thus offering a striking contrast to the dense and ivory-like petrosal of the adult. It also differs from the adult bone in several other par- ticulars. The floccular fossa is widely open and conspicuous. VoltoUni has pointed out that a small canal leads from the floor of the floccular fossa and opens posteriorly on the mastoid surface of the bone; it may open in the mastoid antrum. The hiatus canalis facialis is unclosed Fig. 96. — -Temporal Bone at the Sixth Year. External auditory meatus Non-ossified area of the tympanic plate Petro-tympamc fissure Wormian bone in parietal notch and the tympanum is filled with gelatinous connective tissue. The mastoid process is not developed, and the jugular fossa is a shallow depression. After birth the parts grow rapidly. The tympanum becomes permeated with air, the var- ious elements fuse, and the tympanic annulus grows rapidly and forms the tympanic plate. Development of the tympanic plate takes place by an outgrowth of bone from the lateral aspect of the tympanic annulus. This outgro\vth takes place most rapidly from the tubercles or spines at its upper extremities, and in consequence of the slow growth of the lower segment a deep notch is formed; gradually the tubercles coalesce, lateral to the notch, so as to enclose a foramen which persists until puberty, and sometimes even in the adult. In most skuUs a cleft capable of receiving the nail remains between the tympanic element and the mastoid process; this is the tympano-mastoid fissure. The anterior portion of the tympanic plate forms with the inferior border of the squamosal a cleft known as the petro-tympanic fissure, which is sub- sequently encroached upon by the growth of the petrosal. As the tympanic plate increases in size it joins the lateral wall of the carotid canal and presents a prominent lower edge, known as the vaginal process (sheath of the styloid). The mastoid process becomes distinct about the first year, coincident with the obliteration of the petro-squamous suture, and increases in thickness by deposit from the periosteum. According to most writers, the process becomes pneumatic about the time of puberty, but it has been shown by Young and Milligan that the mastoid air-cells develop at a much earlier period than is usually supposed. These writers have described specimens in which the air-cells were present, as small pit-like diverticula from the mastoid antrum, in a nine months' foetus and in an infant one year old. In old skulls the air-cells may extend into the jugular process of the occipital bone. At birth the mastoid antrum is relatively large and bounded laterally by a thin plate of bone belonging to the squamosal (post-auditory process). As the mastoid increases in thick- ness the antrum comes to lie at a greater depth from the surface and becomes relatively smaller. THE TYMPANUM 77 The styloid process is ossified in cartilage from two centres, one of which appears at the base in the tympano-hyal before birth. This soon joins with the temporal bone, and in the second year a centre appears for the stylo-hyal, which, however, remains very small until pu- berty. In the adult it usually becomes firmly united with the tympano-hyal, but it may remain permanently separate. THE TYMPANUM The tympanum (middle ear) includes a cavity [cavum tympani] of irregular form in the temporal bone, situated over the jugular fossa, between the petrous portion medially and the tympanic and squamous portions laterally. When fully developed, it is completely surrounded by bone except where it communicates with the external auditory meatus, and presents for examination six walls — lateral, medial, posterior, anterior, superior (roof), and inferior (floor). The lateral and medial wails are flat, but the remainder are curved, so that they run into adjoining surfaces, without their limits being sharply indicated. The roof or tegmen tympani [paries tegmentalis] is a translucent plate of bone, forming part of the superior surface of the petrous portion and separating the tympanum from the middle fossa of the skull. The floor [paries jugularis] is the plate of bone which forms the roof of the jugular fossa. The medial wall [paries labyrinthica] is formed by the tympanic surface of the petrous portion. In the angle between it and the roof is a horizontal ridge which extends backward as far as the posterior wall and then turns downward in the angle between the medial and posterior walls. This is the facial (Fallopian) canal, and is occupied by the facial nerve. The other features of this surface — viz., the fenestra vestibuli, the fenestra cochleae, and the promontory — have previously been described with the anterior surface of the petrous portion of the temporal bone. The posterior wall [paries mastoidea] of the tympanum is also formed by the anterior surface of the petrous portion. At the superior and lateral angle of this wall an opening Fig. 97. — The Medial Wall of the Tympanum. Carotid canal Tensor tympani Groove for Eustacliian. tube Levator veli palatini' Canal for small deep. petrosal nerve Stylo pharyngeus Stylo-hyoxd Stylo gl( Lateral semicircular canal Mastoid antrum Facial canal Canal for chorda tympani Stylo-mastoid foramen leads into the mastoid antrum. Immediately below this opening there is a small hoUow cone, the pyramidal eminence, the cavity of which is continuous with the descending limb of the facial canal. The cavity is occupied by the stapedius and the tendon of the muscle emerges at the apex. One or more bony spicules often connect the apex of the pyramid with the promontory. The roof and floor converge toward the anterior extremity of the tympanum, which is, in consequence, very low; it is occupied by two semicanals, the lower for the Eustachian tube, the upper for the tensor tympani muscle. These channels are sometimes described together as the canalis musculo-tubarius. In carefully prepared bones the upper semicanal is a small hori- zontal hollow cone (anterior pyramid), 12 mm. in length; the apex is just in front of the fenestra vestibuli, and is perforated to permit the passage of the tendon of the muscle. As a rule, the thin walls of the canal are damaged, and represented merely by a thin ridge of bone. The posterior portion of this ridge projects into the tympanum, and is known as the processus cochleariformis. The thin septum between the semicanal for the tensor tympani and the tube is pierced by a minute opening which transmits the small deep petrosal nerve. The lateral wall [paries membranaeea] is occupied mainly by the external auditor}' meatus. This opening is closed in the recent state by the tympanic membrane. The rim of bone to which the membrane is attached is incomplete above, and the defect is known as the tympanic notch (notch of Rivinus). Anterior to this notch, in the angle between the squamous portion and the tympanic plate, is the petro-tympanic (Glaserian) fissure, and the small passage which transmits the chorda tympani nerve, known as the canal of Huguier. Up to this point the description of the middle ear conforms to that in general usage. But Young and Milligan have laid stress on the fact that the middle ear is really a cleft, named by them the "middle-ear cleft," which intervenes between the periotic capsule, on the one hand, and the squamo-zygomatic and tympanic elements of the temporal bone on the other. This cleft, as development proceeds, gives rise to three cavities: — -(1) the mastoid antrum; (2) 78 THE SKELETON tympanum; and (3) the Eustachian tube. They point out that "the cleft is primarily con- tinuous, and however much it may be altered in shape and modified in parts to form these three cavities, that continuity is never lost." It will be clear that the mastoid antrum, according to this view, is not an outgrowth from the tympanum, but is simply the lateral end of the middle- ear cleft. The tympanic cavity may be divided into three parts. The part below the level of the superior margin of the external auditory meatus is the tympanum proper ; the portion above this level is the epitympanic recess or attic ; it receives the head of the malleus, the body of the incus, and leads posteriorly into the recess known as the mastoid antrum. The third part is the downward extension known as the hypotympanic recess. The tympanic or mastoid antrum. — The air-cells which in the adult are found in the interior of the mastoid portion of the temporal bone open into a small cavity termed the mastoid antrum. This is an air-chamber, communicating with the attic of the tympanum, and separated from the middle cranial fossa by the posterior portion of the tegmen tympani. The floor is formed by the mastoid portion of the petrosal, and the lateral wall by the squamosal, below the temporal ridge. In children the outer wall is exceedingly thin, but in the adult it ia of considerable thickness. The lateral semicircular canal projects into the antrum on its Fig. 98." -Temporal Bone at Birth Dissected prom above and behind to show the Semi- circular Canals and the Mastoid Antrum. (Enlarged \.) Opening into tympanura Superior semicircular canal Mastoid antrum 'Lateral semicircular canal Posterior semicircular canal medial wall, and is very conspicuous in the foetus. Immediately below and in front of the canal is the facial nerve, contained in the facial canal. The mastoid antrum has somewhat the form of the bulb of a retort (Thane and Godlee) compressed laterally, and opening by its narrowed neck into the attic or epitympanic recess. Its dimensions vary at different periods of hfe. It is well developed at birth, attains its maxi- mum size about the third year, and diminishes somewhat up to adult life. In the adult the plate of bone which forms the lateral wall of the antrum is 12 to 18 mm. (| to J in.) in thickness, whereas at bu-th it is about 1.8 mm. (j^ in.) or less. The deposition of bone laterally occurs, therefore, at average rate of nearly 1 mm. a year in thickness. In the adult the antrum ia about 12 mm. (i in.) from front to back, 9 mm. (f in.) from above downward, and 4.5 mm. (j^V in.) from side to side. A canal occasionally leads from the mastoid antrum through the petrous bone to open in the recess which indicates the position of the fioecular fossa; it is termed the petro-mastoid canal. (Gruber.) The facial (Fallopian) canal. — This canal begins at the anterior angle of the superior fossa of the internal auditory meatus, and passes forward and laterally above the vestibular portion of the internal ear for a distance of 1.5-2.0 mm. At the lateral end of this portion of its course it becomes dilated to accommodate the geniculate ganglion, and then turns abruptly back- ward and runs in a horizontal ridge on the medial wall of the tympanurn, lying in the angle between it and the tegmen tympani, immediately above the fenestra vestibuli, and extending as far backward as the entrance to the mastoid antrum. Here it comes into contact with the inferior aspect of the projection formed by the lateral semicircular canal, and then turns verti- cally downward, running in the angle between the medial and posterior walls of the tympanum to terminate at the stylo-mastoid foramen. The canal is traversed by the facial nerve. Numerous openings exist in the walls of this passage. At its abrupt bend, or genu, the greater and smaller superficial petrosal nerves escape from, and a branch from the middle meningeal artery enters, the canal, and in the vertical part of its course the cavity of the pyramid opens into it. There is also a small orifice by which the auricular branch of the vagus joins the facial, and near its termination the iter chordae posterius for the chorda tympani nerve leads from it into the tympanum. THE SMALL BONES OF THE TYMPANUM 79 The small bones of the tympanum. — These bones, the malleus, incus and stapes, are contained in the upper part of the tympanic cavity. Together they form a jointed column of bone connecting the membrana tympani with the fenestra vestibuli. The malleus. — This is the most external of the iiuditory ossicles, and hes in relation with the tympanic membrane. Its upper portion, or head, is lodged in the epitympanic recess. It is of rounded shape, and presents posteriorly an elliptical depression for articulation with the incus. Below the head is a constricted portion or neck, from which three processes diverge. The largest is the handle or manubrium, which is slightly twisted and flattened. It forms an obtuse angle with the head of the bone, and lies between the membrana tympani and the mucous membrane covering its inner surface. The tensor tympani tendon is inserted into the manubrium near its junction with the neck on the medial side. Fig. 99. — The Bones of the Ear. (Modified from Henle.) Fossa for incus Posterior crus ■Head of malle Lateral process Anterior process Articular surface for malleus Lenticular process The anterior process (processus gracilis or Folii) is a long, slender, dehoate spiculum of bone (rarely seen of full length except in the fcetus), projecting nearly at right angles to the anterior aspect of the neck, and extending obliquely downward. It lies in the petro-tympanic fissure, and in the adult usually becomes converted into connective tissue, except a small basal stump. The lateral process is a conical projection from the lateral aspect of the base of the manu- brium. Its apex is connected to the upper part of the tympanic membrane, and its base receives the lateral ligament of the malleus. The malleus also gives attachment to a superior hgament and an anterior ligament, the latter of which was formerly described as the laxator tymipani muscle. The incus. — This bone is situated between the malleus externally and the stapes internaUy. It presents for examination a body and two processes. The body is deeply excavated anteriorly for the reception of the head of the malleus. The short process projects backward, and is connected by means of ligamentous fibres to the posterior wall of the tympanum, near the entrance to the mastoid antrum. The long process is slender, and directed downward and in- ward, and lies parallel with the manubrium of the maUeus. On the medial aspect of the distal extremity of this process is the lenticular process (orbicular tubercle), separate in early life, but 80 THE SKELETON subsequently joined to the process by a narrow neck. Its free surface articulates with the head of the stapes. The stapes is the innermost ossicle. It has a head directed horizontally outward, capped at its outer extremity by a disc resembling the head of the radius. The cup-shaped depression receives the lenticular process of the incus. The base occupies the fenestra vestibuli, and like this opening, the inferior border is straight, and the superior curved. The base is connected with the head by means of two crura, and a narrow piece of bone called the neck. Of the two crura, the anterior is the shorter and straighter. The crura with the base form a stirrup-shaped arch, of which the irmer margin presents a groove for the reception of the membrane stretched across the hollow of the stapes. In the early embryo this hollow is traversed by the stapedial artery. The neck is very short, and receives on its posterior border the tendon of the stapedius muscle. Development. — The tympanic cavity represents the upper extremity of the first endodermal branchial groove, which becomes converted into a blind pouch, the communication of which with the pharyngeal cavity is the tuba auditiva (Eustachian tube). The thin membrane which separates the endodermal from the ectodermal groove becomes the tympanic membrane, and it is from the upper extremities of the axial skeletons of the first and second branchial arches, which bound the groove anteriorly and posteriorly, that the auditory ossicles are formed, the malleus and incus belonging to the first arch and the stapes to the second (Reichert). The ossicles consequently lie originally in the walls of the cavity, but they are surrounded by a loose spongy tissue, which, on the entrance of air into the cavity, becomes compressed, allowing the cavity to enfold the ossicles. These therefore are enclosed within an epithelium which is con- tinuous medially with that lining the posterior tympanic wall, and laterally with that lining the internal surface of the tympanic membrane. The mastoid cells are outgrowths of the cavity into the adjacent bone, and are therefore lined with an epithelium continuous with that of the cavity. THE OSSEOUS LABYRINTH The osseous labyrinth [labyrinthus osseus] (fig. 100) is a complex cavity hollowed out of the petrous portion of the temporal bone and containing the membranous labyrinth, the essential part of the organ of hearing. It is in- completely divided into three parts, named the vestibule, the semicircular canals, and the cochlea. Fig. 100. — The Left Osseous L.\byrinth. (After Henle. From a cast.) Superior semicircular caaal Lateral semicircular canal Posterior semicircular canal Fenestra cochleae Fenestra vestibul: The vestibule. — This is an oval chamber situated between the base of the internal auditory meatus and the medial wall of the tympanum, with which it communicates by way of the fenestra vestibuh. Anteriorly, the vestibule leads into the cochlea, and posteriorly it receives the extremities of the semicircular canals. It measures about 3 mm. transversely, and is some- what longer antero-posteriorly. Its medial wall presents at the anterior part a circular depression, the spherical recess (fovea. hemispherica), which is perforated for the passage of nerve-twigs. This recess is sepa- rated by a vertical ridge (the crista vestibuli) from the vestibular orifice of the aquseductus Fig. 101. — The Cochlea in S.agittal Section. (After Henle.) Internal auditory meritus The spiral canal vestibuli, which passes obhquely backward to open on the posterior surface of the petrosal. The roof contains an oval depression — the elliptical recess (fovea hemielUptioa). The semicircular canals are three in number. Arranged in different planes, each forms about two-thirds of a circle. One extremity of each canal is dilated to form an ampulla. _ The superior canal lies transversely to the long axis of the petrosal, and is nearly vertical; i THE ETHMOID 81 its highest limb makes a projection on the superior surface of the bone. The ampulla is at the lateral end; the medial end opens into the vestibule conjointly with the superior limb of the posterior canal. The posterior canal is nearly vertical and lies in a plane nearly parallel to the posterior sur- face of the petrosal. It is the longest of the three; its upper extremity joins the medial hmb of the superior canal, and opens in common with it into the vestibule. The lower is the ampul- lated end. The lateral canal is placed horizontally and arches laterally; its lateral limb forms a prominence in the mastoid antrum. This canal is the shortest; its ampulla is at the lateral end near the fenestra vestibuli. The cochlea. — This is a cone-shaped cavity lying with its base upon the internal auditory meatus, and the apex directed forward and laterally. It measures about five millimetres in length, and the diameter of its base is about the same. The centre of this cavity is occupied by a column of bone — the modiolus — around which a canal is wound in a spiral manner, making about two and a half turns. This is the spiral canal of the cochlea; its first turn is the largest and forms a bulging, the promontory, on the medial wall of the tympanum. Projecting into the canal throughout its entire length there is a horizontal, shelf-like lamella, the lamina spiralis, which terminates at the apex of the cochlea in a hook-like process, the hamulus. The free edge of the lamina spiralis gives attachment to the membranous cochlea, a canal having in section the form of a triangle whose base is attached to the lateral wall of the spiral canal. By this the spiral canal is divided into a portion above the lamina spiralis, termed the scaia vestibuli, which communicates at its lower end with the osseous vestibule, and a portion below, termed the scala tympani, which abuts at its lower end upon the fenestra cochlea. The two scalae communicate at the apex of the cochlea by the helicotrema. Near the commencement of the scala tympani, and close to the fenestra rotunda, is the cochlear orifice of the canaliculus cochlese (ductus perilymphaticus). In the adult this opens below, near the middle of the pos- terior border of the petrous bone, and transmits a small vein from the cochlea to the jugular fossa. Measurements of the principal parts connected with the auditory organs: — Internal auditory meatus Length of anterior wall, 13-14 mm. Length of posterior waU, 6.7 mm. External auditory meatus 14^16 mm. (Gruber.) Tympanum Length, 13 mm. Height in centre of cavity, 15 mm. Width opposite the membrana tympani, 2 mm. Width opposite the tubal orifice, 3-4 mm. (Von Troltsch.) The capsule of the osseous labyrinth is in length 22 mm. (Schwalbe.) Superior semicircular canal measures along its convexity 20 mm. The posterior semicircular canal measures along its convexity 22 mm. The lateral semicircular canal measures along its convexity 15 mm. The canal is in diameter 1.5 mm. (Huschke.) The ampulla of the canal, 2.5 mm. Development. — The membranous internal ear arises in the embryo as a depression of the ectoderm of the surface of the head opposite the fifth neuromere of the hind-brain and later becomes a sac-like cavity, the otocyst, which separates from its original ectodermal connec- tions and sinks deeply into the subjacent mesoderm, a part of which becomes incorporated with it. The rest of the mesodermal tissue which surrounds the otocyst becomes later the petrous portion of the temporal bone, the perilymph and the internal periosteal layer; the osseous labyrinth is therefore merely the portions of the petrous which enclose the cavity occupied by the membranous internal ear. THE ETHMOID The ethmoid [os ethmoidale] is a bone of delicate texture, situated at the an- terior part of the base of the cranium (figs. 102, 103, 104). Projecting downward from between the orbital plates of the frontal, it enters into the formation of the orbital and nasal fossae. It is cubical in form, and its extreme lightness and delicacy are due to an arrangement of very thin plates of bone surrounding irregular spaces known as air-cells. The ethmoid consists of four parts: the hori- zontal or cribriform plate, the ethmoidal labyrinth on each side, and a perpen- dicular plate. The cribriform plate [lamina cribrosa] forms part of the anterior cranial fossa, and is received into the ethmoidal notch of the frontal bone. It presents on its upper surface, in the median line, the intra-cranial portion of the perpendicular plate, known as the crista galli, a thick, vertical, triangular process with the high- est point in front, and a sloping border behind which gives attachment to the f alx cerebri. The anterior border is short and in its lower part broadens out to form two alar processes which articulate with the frontal bone and complete the foramen caecum. The ci'ista galli is continuous behind with a median ridge, and on each side of the middle line is a groove which lodges the olfactory bulb. 82 THE SKELETON The cribriform plate is pierced, on each side, by numerous foramina, arranged in two or three rows, which transmit the filaments of the olfactory nerves descending from the bulb. Those in the middle of the groove are few and are simple perforations, through which pass the nerves to the roof of the nose; the medial and lateral series are more numerous and constitute the upper ends of small canals, which subdivide as they course downward to the upper parts of the septum and the lateral wall of the nasal fossa. At the front part of the cribriform plate is a narrow longitudinal sht, on each side of the crista gaUi, which transmits the anterior eth- moidal (nasal) branch of the ophthalmic division of the fifth nerve. The posterior border articulates with the ethmoidal spine of the sphenoid. Fig. 102. — Section through the Nasal Fossa to show the Mesethmoid (Lamina Perpendiculaeis). Crest of sphenoid -palatine nerve: Crest of maxilla The perpendicular plate (mesethmoid) [lamina perpendicularis is directly continuous with the crista galli on the under aspect of the cribriform plate, so that the two plates cross each other at right angles. The larger part of the perpendicular plate is below the point of intersection and forms the upper third of the septum of the nose. It is quadrangular in form with unequal sides. Fig. 103. — The Ethmoid. (Lateral view.) -Crista galli Anterior ethmoidal groove — - Uncinate process Inferior nasal concha Jt'osterior ethmoidal groove ' -|- Lamina papyracea Sphenoidal concha Middle nasal concha The anterior border articulates with the spine of the frontal and the crest of the nasal bones. The inferior border articulates in front with the septal cartilage of the nose and behind with the anterior margin of the vomer. The posterior margin is very thin and articulates with the crest of the sphenoid. This plate, which is generally deflected a little to one side, presents above a number of grooves and minute canals which lead from the inner set of foramina in the cribri- form plate and transmit the olfactory nerves to the septum. The labyrinth (lateral mass) is oblong in shape and suspended from the under aspect of the lateral part of the cribriform plate. It consists of two scroll-like THE ETHMOID 83 pieces of bone, the superior and middle nasal conchse (turbinate bones), and encloses numerous irregularly shaped spaces, known as the ethmoidal cells. These are arranged in three sets — anterior, middle, and posterior ethmoidal cells — and, in the recent state, are lined with prolongations of the nasal mucous membrane. Laterally the labyrinth presents a thin, smooth, quadrilateral plate of bone — the lamina papyracea (os planum) — which closes in the middle and posterior ethmoidal cells and forms a large part of the medial wall of the orbit. By its anterior border it articulates with the lacrimal, and by its posterior border with the sphenoid; the inferior border articulates with the medial margin of the orbital plate of the maxilla and the orbital process of the palate bone, whilst the superior border articulates with the horizontal plate of the frontal. Two notches in the superior border lead into grooves running horizontally across the lateral mass to the cribriform plate, which complete, with the frontal bone, the ethmoidal canals. The anterior canal transmits the anterior ethmoidal ves- sels and (nasal) nerve; the posterior transmits the posterior ethmoidal vessels and nerve. Fig. 104. — Section THRonGH the Nasal Fossa to show the Labyrinth of .the Ethmoid. It shows also the lateral wall of the left nasal fossa. Superior nasal concha Probe in sphenoidal foran Sphenoidal sinus Sella turcica { Superior meatus Spheno-palatine foramen Uncinate process of ethmoid Medial pterygoid plate Palate bone Probe in posterior palatine canal Agger nasi Lacrimal bone Lower end of bristle in middle meatus Middle meatus Inferior nasal concha Probe at lower end of naso-lacrimal canal where it opens into inferior meatus Incisive canal At the lower part of the lateral surface is a deep groove, which belongs to the middle meatus of the nose, and is bounded below by the thick curved margin of the inferior nasal concha. Anteriorly the middle meatus receives the in- fundibulum, a sinuous passage which descends from the frontal sinus through the anterior part of the labyrinth. The anterior ethmoidal cells open into the lower part of the infundibulum, and in this way communicate with the nose, whereas the middle ethmoidal cells open directly into the middle or horizontal part of the meatus. In front of the lamina papyracea are seen a few broken cells, which extend under, and are completed by, the lacrimal bone and the frontal process of the maxilla; from this part of the labyrinth an irregular lamina, known as the uncinate process, projects downward and backward. The uncinate process articulates with the ethmoidal process of the inferior nasal concha and forms a small part of the medial wall of the maxillary sinus. Medially the labyrinth takes part in the formation of the lateral wall of the nasal fossa, and presents the superior and middle nasal conchae (turbinate processes), continuous anteriorly, but separated behind by a space directed for- ward from the posterior margin. This channel is the superior meatus of the nose and communicates with the posterior ethmoidal cells. The conchse are covered 84 THE SKELETON in the recent state with mucous membrane and present numerous foramina for blood-vessels and, above, grooves for twigs of the olfactory nerves. Each concha has an attached upper border and a free, slightly convoluted, lower border, and in the case of the middle concha, the lower margin has already been noticed on the outer aspect, where it overhangs the middle meatus of the nose. The posterior extremity of the labyrinth articulates with the anterior surface of the body of the sphenoid and is commonly united with the sphenoidal concha. A rounded prominence on the lateral wall of the middle meatus is known as the bulla ethmoidalis. Antero-inferior to the bulla is a large semilunar depression [hiatus semilunaris] which corresponds to the lower aperture of the infundibulum. Man}' of the ethmoidal cells are imperfect and are completed by adjacent bones. Those along the superior edge of the lateral mass are the fronto-ethmoidal; those at the anterior border, usually two in number, are known as lacrimo-ethmoidal. Those along the lower edge of the lamina papyraoea are the maxillo-ethmoidal; and posteriorly, are the spheno- ethmoidal, completed by the sphenoidal concha, and a palate -ethmoidal cell. The anterior extremity presents one or two incomplete cells closed by the nasal process of the maxilla. Blood-supply. — The ethmoid receives its blood-supply from the anterior and posterior ethmoidal arteries and from the spheno-palatine branch of the internal maxillary. Articulations. — With the frontal, sphenoid, two palate bones, two nasals, vomer, two inferior nasal conchae, two sphenoidal oonohse, two maxills, and two lacrimal bones. The posterior surface of each labyrinth is in relation with the sphenoid on each side of the crest and rostrum, and helps to close in the sphenoidal sinus. Ossification. — The ethmoid has three centres of ossification. Of these, a nucleus appears in the fourth month of intra-uterine hfe in each labyrinth, first in the lamina papyraoea and afterward extending into the middle concha. At birth each lateral portion is represented by two scroll-like bones, very delicate and covered with irregular depressions, which give it a worm- eaten appearance. Six months after birth a nucleus appears in the ethmo-vomerine cartilage lor the vertical plate which gradually extends into the crista galU, and the cribriform plate is formed by ossification extending laterally from this centre, and medially from the labyrinth. The three parts coalesce to form one piece in the fifth or sixth year. The ethmoid.al cells make their appearance about the third year, and gradually invade the labyrinths. In many places there is so much absorption of bone that the cells perforate the ethmoid in situations where it is overlapped by other bones. Along the lower border, near its articulation with the maxilla, the absorption leads to the partial detachment of a narrow strip known as the uncinate process. Sometimes a second but smaller hook-like process is formed, above and anterior to this, so fragile that it is difficult to preserve it in disarticulated bones. The relations of the uncinate process are best studied by removing the lateral wall of the maxillary sinus. THE INFERIOR NASAL CONCHA The inferior nasal concha (inferior turbinate) (fig. 105) is a slender, scroll-Hke lamina, attached by its upper margin to the lateral wall of the nasal fossa, and hanging into the cavity in such a way as to separate the middle from the inferior Fig. 105. — The Inferior Concha, Adult Sphenoidal Turbinate, and Lacrimal Bones. The crest of lacrimal Tensor tarsi The orbital surface Lacrimal groove Hamular process, Conchal process The lacrimal process The ethmoidal process The maxillary process Middle nasal concha meatus of the nose. It may be regarded as a dismemberment of the ethmoidal labyrinth, with which it is closely related. It presents for examination two surfaces, two borders, and two extremities. The lateral surface is concave, looks toward the lateral wall of the nasal fossa, THE LACRIMAL 85 and is overhung by the maxillary process. The medial surface is convex, pitted with depressions, and grooved for vessels, which, for the most part, run longi- tudinally. The superior or attached border articulates in front with the conchal crest of the maxilla, then ascends to form the lacrimal process, which articulates with the lacrimal bone and forms part of the wall of the lacrimal canal. Behind this, it is turned downward to form the maxillary process, already mentioned, which overhangs the orifice of the maxillary sinus and serves to fix the bone firmly to the lateral wall of the nasal fossa. The projection behind the maxillary process is the ethmoidal process, joined in the articulated skull with the uncinate process of the ethmoid across the opening of the maxillary sinus. Posteriorly the upper border articulates with the conchal crest of the palate. The inferior border is free, rounded, and somewhat thickened. The anterior extremity is blunt and flattened, and broader than the posterior extremity, which is elongated, narrow, and pointed. Articulations. — With the maxilla, lacrimal, palate, and ethmoid. Ossification. — The inferior nasal conotia is ossified in cartilage from a single nucleus which appears in the fifth month of intra-uterine life. At birth it is a relatively large bone and filla up the lower part of the nasal fossa. THE LACRIMAL The lacrimal bone [os lacrimale] (fig. 105) is extremely thin and delicate, quadrilateral in shape, and situated at the anterior part of the medial wall of the orbit. It is the smallest of the facial bones. The orbital surface is divided by a vertical ridge, the posterior lacrimal crest, into two unequal portions. The anterior, smaller portion is deeply grooved to form the lacrimal groove, which lodges the lacrimal sac and forms the com- mencement of the canal for the naso-lacrimal duct. The portion behind the ridge is smooth, and forms part of the medial wall of the orbit. The ridge gives origin to the orbicularis oculi (pars lacrimalis) muscle and ends below in a hook-like process, the lacrimal hamulus, which curves forward to articulate with the lacrimal tubercle of the maxilla and completes the superior orifice of the naso-lacrimal canal. The medial surface is in relation with the two anterior cells of the ethmoid (lacrimo-ethmoidal), forms part of the infundibulum, and inferiorly looks into the middle meatus of the nose. The superior border is short, and articulates with the medial angular process of the frontal. The inferior border posterior to the crest joins the medial edge of the orbital plate of the maxilla. The narrow piece, anterior to the ridge, is prolonged downward as the descending process to join the lacrimal process of the inferior nasal concha. The anterior border articulates with the posterior border of the frontal process of the maxilla and the posterior border with the lamina papyracea of the ethmoid. The vessels of the lacrimal bone are derived from the infra-orbital, dorsal nasal branch of the ophthalmic, and anterior ethmoidal arteries. Articulations. — The lacrimal articulates with the ethmoid, maxilla, frontal, and inferior nasal concha. Ossification. — This bone arises in the membrane overlying the cartilage of the fronto-nasal plate, and in its mode of ossification is very variable. As a rule, it is formed from a single nucleus which appears in the third or fourth month of intra-uterine life. Not infrequently, the hamulus is a separate element, and occasionally the bone is divided by a horizontal cleft, a pro- cess of the lamina papyracea projecting between the two halves to join the frontal process of the maxilla. More rarely the bone is represented by a group of detached ossicles resembling Wormian bones. The hamular process is regarded as representing the remains of the facial part of the lacrimal seen in lower animals. THE VOMER The vomer (fig. 106) (ploughshare bone) is an unpaired flat bone, which lies in the median plane and forms the lower part of the nasal septum. It is thin and irregularly quadrilateral in form, and is usually bent somewhat to one side, though the deflection rarely involves the posterior margin. Each lateral surface is covered in the recent state by the mucous membrane of the nasal cavity, and is traversed by a narrow but well-marked groove, which lodges the naso-palatine nerve from the spheno-palatine ganglion. i 86 THE SKELETON The superior border, by far the thickest part of the bone, is expanded laterally into two alse. The groove between them receives the rostrum of the sphenoid, and the margin of each ala comes into contact with the sphenoidal process of the palate and the vaginal process of the medial pterygoid plate. The inferior border is uneven and lies in the groove formed by the crests of the maxillary and palate bones of the two sides. The anterior border slopes downward and forward and is grooved below for the septal cartilage of the nose; above it is united with the perpendicular plate of the ethmoid. The posterior border, smooth, rounded, and covered by mucus membrane, separates the posterior nares. The anterior and inferior borders meet at the anterior extremity of the bone which forms a short vertical ridge behind the incisor crest of the maxillae. From near the anterior extremity, a small projection passes downward between the incisive foramina. Fig. 106.— The Vomer. (Side view.) Anterior border -palatine nerve Groove for septal cartilage — ^^^f\^ Inferior border Blood-supply. — The arterial supply of the vomer is derived from the anterior and posterior ethmoidal and the spheno-palatine arteries. Branches are also derived from the posterior palatine through the foramen incisivum. Ossification. — The vomer is ossified from two centres which appear about the eighth week in the membrane investing the ethmo-vomerine cartilage. The two lamellae unite below during the third month and form a shallow bony trough in which the cartilage lies. In the process of growth the lamells extend upward and forward and gradually fuse to form a rectangular plate of bone, the cartilage enclosed between them undergoing absorption at the same time. The alae on the superior margin and the groove in front are evidence of the original bilaminar condition. THE NASAL The nasal (figs. 107 and 108) are two small oblong bones situated at the upper part of the face and forming the bridge of the nose. Each bone is thicker and narrower above, thinner and broader below, and presents for examination two surfaces and four borders. Fig. 107. — The Left Nasal Bone, Facial Surface. Superior borde Medial border Lateral border- Inferior border' Fig. 108. — The Left Nasal Bone, Nasal Surface. Medial border The facial surface is concave from above downward, convex from side to side, and near the centre is perforated by a small foramen, which transmits a small tributary to the facial vein. The posterior or nasal surface, covered in the recent state by mucous membrane, is concave laterally, and traversed by a longitudinal groove [sulcus ethmoidalis] for the anterior ethmoidal branch of the ophthalmic division of the fifth nerve. The short superior border is thick and serrated for articulation with the medial part of the nasal notch of the frontal. The inferior border is thin, and serves for the attachment of the lateral nasal cartilage. It is notched for the external nasal branch of the anterior ethmoidal nerve. The nasal bones of the two sides are united by their medial borders, forming the inter- nasal suture. The contiguous borders are prolonged backward to form a crest which rests on the frontal spine and the anterior border of the perpendicular plate of the ethmoid. The lateral border articulates with the frontal process of the maxilla. THE MAXILLA 87 Blood-supply. — Arteries are supplied to this bone by the nasal branch of the ophthalmic, the frontal, the angular, and the anterior ethmoidal arteries. Articulations. — With the frontal, maxilla, ethmoid, and its fellow of the opposite side. Ossification. — Each nasal bone is developed from a single centre which appears about the eighth week in the membrane overlying the fronto-nasal cartilage. The cartilage, which is continuous with the ethmoid cartilage above and the lateral cartilage of the nose below, sub- sequently undergoes absorption as a result of the pressure caused by the expanding bone. A.t birth the nasal bones are nearly as wide as they are long, whereas in the adult the length is three times greater than the width. THE MAXILLA The maxilla or upper jaw-bone (figs. 109, 110, 111) is one of the largest and most important of the bones of the face. It supports the maxillary teeth and takes part in the formation of the orbit, the hard palate, and the nasal fossa. It is divisible into a body and four processes, of which two — the frontal and zygomatic — belong to the upper part, and the palatine and alveolar to the lower part of the bone. The body is somewhat pyramidal in shape and hollowed by a large cavity known as the sinus maxillaris (antrum of Highmore) , lined by mucous membrane in the recent state, and opening at the base of the pyramid into the nasal cavity, the zygomatic process forming the apex. The anterior (or facial) surface looks forward and outward and is marked at its lower part by a series of eminences which indicate the positions of the fangs of the teeth. The eminence produced by the fang of the canine tooth is very prominent and separates two fossa. That on the medial side is the incisive fossa, and gives origin to the alar and transverse portions of the nasalis, and just above the socket of the lateral incisor tooth, to a slip of the orbicularis oris; on the lateral side is the canine fossa, from which the caninus {levator anguli oris) arises. Above the canine fossa, and close to the margin of the orbit, is the infra-orbital foramen, through which the terminal branches of the infra-orbital nerve and vessels emerge, and from the ridge im- mediately above the foramen the quadratus labii superioris takes origin. The medial margin of the anterior surface is deeply concave, forming the nasal notch, and is prolonged below into the anterior nasal spine. A ridge of bone extending upward from the socket of the first molar tooth separates the anterior from the infratemporal (zygomatic) surface. This latter surface is convex and presents near the middle the orifices of the posterior alveolar canals, transmitting the posterior alveolar vessels and nerves. The posterior inferior angle, known as the tuberosity [tuber maxillare], is rough and is most prominent after eruption of the wisdom tooth. It gives attachment to a few fibres of the internal pterygoid muscle and articulates with the tuberosity of the palate. The orbital surface [planum orbitale] is smooth, irregularly triangular, and forms the greater part of the floor of the orbit. Anteriorly, it is rounded and reaches the orbital circumference for a short distance at the root of^the nasal process; lateraUy is the rough surface for the zygomatic bone. The posterior border, smooth and rounded, forms the inferior boundary of the inferior orbital fissure. The medial border is nearly straight and presents behind the frontal process, a smooth rounded angle forming part of the circumference of the orbital orifice of the naso-lacrimal canal, and a notch which receives the lacrimal bone. The rest of the medial border is rough for articulation with the lamina papyracea of the ethmoid and orbital process of the palate bone. The orbital surface is traversed by the infra-orbital groove, which, com- mencing at the posterior border, deepens as it passes forward and finally becomes closed in to form the infra-orbital canal. It transmits the second division of the fifth nerve and the infra-orbital vessels and terminates on the anterior surface immediately below the margin of the orbit. From the infra-orbital, other canals — the anterior and middle alveolar — run downward in the wall of the antrum and transmit the anterior and middle alveolar vessels and nerves. Lateral to the commencement of the lacrimal canal is a shallow depression for the origin of the inferior oblique. The nasal surface takes part in the formation of the lateral wall of the nasal fossa. It presents a large irregular aperture which leads into the antrum and, immediately in front of this, the lacrimal groove, directed downward, backward, and laterally into the inferior meatus of the nose. The groove is converted ( THE SKELETON into a canal by the lacrimal and inferior nasal concha and transmits the naso- lacrimal duct. In front of the groove is a smooth surface crossed obhquely by a ridge, the concbal crest, for articulation with the inferior nasal concha. The surface below the crest is smooth, concave, and belongs to the inferior meatus; the surface above the crest extends on to the lower part of the frontal process and forms the wall of the atrium of the middle meatus. Behind the open- ing of the antrum the surface is rough for articulation with the vertical plate of the palate bone, and crossing it obliquely is a smooth groove converted by the ipalate into the pterygo- palatine canal for the passage of the (descending) palatine nerves and the descending palatine artery. Fig. 109. — The Left Maxilla. (Outer view.) Infra-orbital foramen- Nasal notch. Canine fossa' al spine Canin eminence Border of inferior orbital fissure For sphenoid Zygomatic surface Zygomatic process Posterior alveolar canals W , It /J -Tuberosity The frontal process, somewhat triangular in shape, rises vertically from the angle of the maxilla. Its lateral surface is continuous with the anterior surface of the body, and gives attachment to the orbicularis oculi, the medial palpebral ligament and the quadratus labii superioris {caput angular e). The medial sur- face forms part of the lateral boundary of the nasal fossa and is crossed obliquely by a low ridge, known as the agger nasi, limiting the atrium of the middle meatus. The hinder part of this surface rests on the anterior extremity of the labyrinth of the eth- moid and completes the maxillo-ethmoidal cells. The superior border articulates with the frontal; the anterior border articulates with the nasal bone; the posterior border is thick and vertically grooved, in continuation with the lacrimal groove, and lodges the lacrimal sac. The medial margin of the groove articulates with the lacrimal bone, and the junction of its lateral margin with the orbital surface is indicated by the lacrimal tubercle. Fig. 110. — The Left Maxilla. (Inner view.) 'Frontal process Posterior palatine groove Palatine process The zygomatic process, rough and triangular, forms the summit of the prominent ridge of bone separating the anterior and infratemporal surfaces. It articulates above with the zygomatic, and from its inferior angle a few fibres of the masseter take origin. The anterior and posterior surfaces are continuous with the anterior and infratemporal surfaces of the body. The palatine process projects horizontally from the medial surface and, with the corresponding process of the opposite side, forms about three-fourths of the hard palate. The superior surface is smooth, concave from side to side, and THE MAXILLA 89 constitutes the larger part of the floor of the nasal fossa. The inferior surface is vaulted, rough, and perforated with foramina for nutrient vessels. Near its lateral margin is a longitudinal groove for the transmission of the vessels and nerves which issue at the posterior palatine canal and course along the lower aspect of the palate. When the bones of the two sides are placed in apposition, a large orifice may be seen in the middle line immediately behind the incisor teeth. This is the incisive foramen, at the bottom of whjch are four foramina. Two are small and arranged one behind the other exactly in the meso-palatine suture. These are the foramina of Scarpa and transmit the naso-palatine nerves, the left Fig. 111. — Section op Maxilla to show the Floor op the Maxillary Antrum. (Reduced J.) ( passing through the anterior and the right through the posterior aperture. The lateral and larger orifices are the foramina of Stenson, representing the lower apertures of two passages by which the nose communicates with the mouth ; they transmit some terminal branches of the descending palatine artery to the nasal fossae, and lodge recesses of the nasal mucous membrane and remnants of Jacobson's organs. Fig. 112. — Maxilla and Zygomatic Bone, to show Muscular Attachments. Inferior oblique (Poirier.) Quadrate muscle, zygomatic head Orbicularis oculi Quadrate muscle, angular head Dilator narisposterii Nasalis (alar portion) Running laterally from the incisive foramen to the space between the second incisor and canine tooth, an indistinct suture may sometimes be seen, indicating the hne of junction of the maxillary and pre-maxillary portions of the bone. The premaxilla or incisive bone is the part which bears the incisor teeth and in some animals exists tliroughout life as an independent element. The posterior border of the palate process is rough and serrated for articulation with 90 THE SKELETON the horizontal plate of the palate bone which completes the hard palate. The medial border joins with its fellow to form the nasal crest upon wliich the vomer is received. The more elevated anterior portion of this border is known as the incisor crest, and is continued forward into the anterior nasal spine. The septal cartilage of the nose rests on its summit and the anterior extremity of the vomer lies immediately behind it. At the side of the incisor crest is seen the upper aperture of the canal leading from the nose to the mouth (Stenson's canal), which in its course downward becomes a groove by a deficiency of its medial wall. Thus when the two bones are articulated a canal is formed (incisive) with the lower ends of two canals opening into it. The alevolar process is crescentic in shape, spongy in texture, and presents cavities [alveoli dentales] in which the upper teeth are lodged. When complete there are eight tooth-cavities (alveoli), with wide mouths, gradually narrowing as they pass into the substance of the bone, and forming exact impressions of the corresponding fangs of the teeth. The pit for the canine tooth is the deepest; those for the molars are the widest, and present subdivisions. Along the lateral aspect of the alveolar process the buccinator arises as far forward as the first molar tooth. The maxillary sinus or antrtma of Highmore, as the air-chamber occupying the body of the bone is called, is somewhat pyramidal in shape, the base being represented by the nasal or medial surface, and the apex corresponding to the zygomatic process. In addition it has four walls: the superior is formed by the orbital plate, and the inferior by the alveolar ridge. The anterior wall corre- sponds to the anterior surface of the maxilla, and the posterior is formed by the infratemporal surface. The medial boundary or base presents a very irregular Fig. 113. — The Maxilla at Birth. Premaxillary portion Inferior view orifice at its posterior part; this is partially filled in by the vertical plate of the palate bone, the uncinate process of the ethmoid, the maxillary process of the inferior nasal concha, and a small portion of the lacr'mal bone. Even when these bones are in their relative positions, the orifice is very irregular in shape, and requires the mucous membrane to form the definite rounded aperture (or apertures, for they are often multiple) known as the opening of the sinus through which the cavity communicates with the middle meatus of the nose. The cavity of the sinus varies considerably in size and shape. In the young, it is small and the walls are thick: as life advances it enlarges at the expense of its walls, and in old age they are often extremely thin, so that occasionally the cavity extends even into the substance of the zygomatic bone. The floor of the sinus is usually very uneven, due to prominences corre- sponding to the roots of the molar teeth. In most oases the bone separating the teeth from the sinus is very thin, and in some cases the roots project into it. The teeth which come into closest relationship with the sinus are the first and second molars, but the sockets of any of the teeth lodged in the maxilla may, under diseased conditions, communicate with it. As a rule, the cavity of the sinus is single, but occasionally specimens are seen in which it is divided by bony septa into chambers, and it is not uncommon to find recesses separated by bony processes. The roof of the sinus presents near its anterior aspect what appears to be a thick rib of bone; this is hollow and corresponds to the infra-orbital canal. The most satisfactory method of studying the relation of the bones closing in the base of the antrum is to cut away the lateral wall of the cavity (see fig. 128). Blood-supply. — The maxilla is a very vascular bone and its arteries are numerous and large. They are derived from the infra-orbital, alveolar, descending palatine, spheno-pala- tine, ethmoidal, frontal, nasal, and facial vessels. Articulations. — With the frontal, nasal, lacrimal, ethmoid, palate, vomer, zygomatic, inferior nasal concha and its fellow of the opposite side. Occasionally it articulates with the great wing, and the pterygoid process, of the sphenoid. THE PALATE BONE 91 Ossification. — The maxilla is developed from several centres which are deposited in mem- brane during the second month of intrauterine life. Several pieces are formed which speedily fuse, so that at birth, with the exception of the incisor fissure separating the maxilla from the premaxiUa, there is no trace of the composite character of the bone. The centres of ossification comprise — (1) the malar, which gives rise to the portion of bone outside the infra-orbital canal; (2) the maxillary, from which the greater part of the body and the frontal process are developed; (3) the palatine, forming the hinder three-fourths of the palatal process and adjoining part of the nasal wall; (-1) the premaxiilary, giving rise to the independent premaxiUary bone (os incisivum), which lodges the incisor teeth and completes the anterior fourth of the hard palate. In the early stages of growth the premaxiUa may consist of two pieces arising from two centres of ossification which AJbrecht has named as follows: — the endognathion, or medial division for Fig. 114. — Maxilla at the end op the First Dentition in both op which the Sutures BETWEEN Maxilla and Premaxilla, and between the two Parts op the Prbmaxilla, ARE seen. £ndo-mesognathic suture Meso-exognatliic suture { the central incisor, and the mesognathion, or lateral division for the lateral incisor; the rest of the maxilla is named the exognathion; (5) the prepalatine, corresponding to the infra-vomerine centre of Rambaud and Renault, forms a portion of bone interposed between the premaxiUary in front and the palatine process behind. It gives rise to a part of the nasal surface and com- pletes the medial waU of the incisive canal. At birth the sinus is narrow from side to side and does not extend laterally to any appre- ciable extent between the orbit and the alveoli of the teeth. During the early years of life it graduaUy enlarges, but does not attain its fuU growth untU after the period of the second dentition. THE PALATE The palate bone [os palatinum] (figs. 115, 116) forms the posterior part of the hard palate, the medial wall of the nasal fossa between the maxilla and the medial pterygoid plate, and, by its orbital process, the hinder part of the floor of the orbit. It is somewhat L-shaped and presents for examination a horizontal part and a perpendicular part; at their point of junction is the pyramidal process, and surmounting the top of the vertical plate are the orbital and sphenoidal processes, separated by the spheno-palatine notch. The horizontal part resembles the palatine process ofthe maxilla, but is much shorter. The superior surface is smooth, concave from side to side, and forms the back part of the floor of the nasal fossa; the inferior surface completes the hard palate behind and presents near its prosterior border a transverse ridge which gives attachment to the tensor veli 'palatini muscle. The anterior border is rough for articulation with the palatine process of the maxiUa; the posterior is free, curved, and sharp, giving attachment to the soft palate. MediaUy it is thick and broad for articulation with its fellow of the opposite side, forming a continuation of the crest of the palatal processes of the maxiUae and supporting the vomer. The posterior extremity of the crest is the posterior nasal spine, from which the azygos uvulce arises. LateraUy, at its junction with the perpendicular part, it is grooved by the lower end of the pterygo-palatine canal. The perpendicular part is longer and thinner than the horizontal plate. The lateral surface is in relation with the maxilla and is divided into two parts by 92 THE SKELETON a vertical groove which forms with the maxilla the pterygo -palatine canal for the transmission of the anterior palatine nerve and the descending palatine artery. The part of the surface in front of the groove articulates with the nasal surface of the maxilla and overlaps the orifice of the antrum by the maxillary process, a variable projection on the anterior border. Behind the groove the surface is rough for articulation with the maxilla below and the medial pterygoid plate above. Fig. 115. — Palate Bone (Left). (Medial view.) Sphenoidal process. -palatine notcli (when complete in the palate bone, it is due to ankylosis with sphenoidal concha) Orbital process (ethmoidal surfaced Superior meatus ■Ethmoidal crest Middle meatus Conchal crest Inferior meatus The medial or nasal surface presents two nearly horizontal ridges separating three shallow depressions. Of the depressions, the lower forms part of the inferior meatus of the nose, and the limiting ridge or conchal (inferior turbinate) crest articulates with the inferior nasal concha. Above this is the depression forming part of the middle meatus, and the ridge or ethmoidal (superior turbinate) crest, constituting its upper boundary, articulates with the middle nasal concha. Fig. 116. — Palate Bone. (Posterior view.) Orbital surface Zygomatic surface Spheno-palatine foramen (usually a notch) Groove for external pterygoid- Groove for pterygoid fo Groove for internal pterygoid Tuberosity- Orbital process Sphenoidal process The upper groove is narrower and deeper than the other two and forms a large part of the superior meatus of the nose. The anterior border of the vertical plate is thin and bears the maxillary process, a tongue-like piece of bone, which e.xtends over the opening of the maxillary sinus from behind. This border is continuous above with the orbital process. The posterior border is rough and articulates with the anterior border of the medial pterygoid plate. It is continuous superiorly with the sphenoidal process. The pyramidal process or tuberosity fits into the notch between the lower extremities of the pterygoid plates and presents posteriorly three grooves. The middle, smooth and concave, completes the pterygoid fossa, and gives origin to a few fibres of the internal -pterygoid; the medial and lateral grooves are rough for articulation with the anterior border of the correspond- ing pterygoid plate. Inferiorly, close to its junction with the horizontal plate, are the openings of the greater palatine and smaller palatine canals, of which the latter are the smaller and less constant; they transmit the palatine nerves. Medially the pyramidal process gives origin to a few fibres of the superior constrictor of the pharynx, and laterally a small part appears in the zygomatic fossa between the tuberosity of the maxilla and the pterj'goid process of the sphenoid. The sphenoidal process, the smaller of the two processes surmounting the vertical part, curves upward and medially and presents three surfaces and two borders. The superior sur- face is in contact with the body of the sphenoid, and the top of the medial pterygoid plate, where it completes the pharyngeal canal. The medial or inferior surface forms part of the lateral THE ZYGOMATIC BONE 93 wall and roof of the nasal fossa, and at its medial end tounhes the ala of the vomer. The lateral surface looks forward and laterally into the pterygo-palatine (spheno-maxillary) fossa. Of the two border3,the posterior is thin and articulates with the medial pterygoid plate; the anterior border forms the posterior boundary of the spheno-palatine foramen. The orbital process is somewhat pyramidal in shape, and presents for examination five surfaces, three of which — the posterior, anterior, and medial — are articular and the rest non- articular. The posterior or sphenoidal surface is small and joins the anterior surface of the body of the sphenoid; the medial or ethmoidal articulates with the labyrinth of the ethmoid; and the anterior or maxillary, which is continuous with the lateral surface of the perpendicular part, is joined with the maxilla. Of the two non-articular surfaces, the superior or orbital, directed upward and laterally, is slightly concave, and forms the posterior angle of the floor of the orbit; the lateral or zygomatic, smooth and directed lateral, looks into the pterygo- palatine (spheno-maxillary) and zygomatic fossse, and forms the anterior boundary of the spheno-palatine foramen. The process is usually hollow and the cavity completes one of the posterior ethmoidal cells or communicates with the sphenoidal sinus. Fig. 117. — Maxilla and Palate Bones showing how the Inpha-okbital Groove Runs Outwakd almost at Right Angles phom the Neighbourhood op the Spheno- palatine Foramen on the Back of the Maxilla and the Orbital Process op the Palate. Posterior View. (E. Fawcett.) .Infra-orbital groove Between the orbital and sphenoidal processes is the spheno-palatine notch, converted by the body of the sphenoid, into a complete foramen. It leads from the pterygo-palatine fossa into the back part of the nasal cavity close to its roof, and transmits the medial branches from the spheno-palatine ganglion and the spheno-palatine vessels. Blood-supply. — The palate bone receives branches from the descending palatine and the spheno-palatine arteries. Articulations. — With the sphenoid, maxilla, vomer, inferior nasal concha, ethmoid, and its fellow of the opposite side. Ossification. — The palate is ossified in membrane from a single centre which appears about the eighth week at the angle between the horizontal and perpendicular parts. At birth the two parts are nearly equal in length, but as the nasal fossae increase in vertical depth, the perpendicular part is lengthened until it becomes about twice as long as the horizontal part. THE ZYGOMATIC The zygomatic [os zygomaticum] or malar bone (fig. 118) forms the promi- nence known as the cheek and joins the zygomatic process of the temporal with the maxilla. It is quadrangular in form with the angles directed vertically and horizontally. The malar (or external) surface is convex and presents one or two small orifices for the transmission of the zygomatico-facial nerves and vessels. It is largely covered by the orbicularis oculi and near the middle is slightly ele- vated to form the malar tuberosity, which gives origin to the zygomaticus and zygomatic head of quadrate muscle of upper lip. The temporal (or internal) surface is concave and looks into the temporal and infratemporal fossae; it is excluded from the orbit by a prominent curved plate 94 THE SKELETON of bone, the orbital process, which forms the anterior boundary of the temporal fossa. The upper part gives origin to a few fibres of the temporal muscle, while at the lower part is a large rough area for articulation with the zygomatic process of the maxilla. The orbital process is placed at right angles to the remaining part of the bone and forms the anterior portion of the lateral wall of the orbit. On the orbital Fig. 118. — The Left Ztgoma.tic Bone. A, the malar surface. B, the temporal and orbital surfaces. Frontal process Frontal process Orbital border Malar canal Processus marginalis Temporal — Temporal border Temporal border Zygomatic process Infra- orbital process Intraorbital head ^'^ of quadrate muscle X-^ Maxillary border Zygomatic head of quadrate muscle Zygomaticus Masseter Malar tubercle Malar tubercle surface of the process are seen the foramina of two zygomatico -orbital canals, which transmit the zygomatico-facial and zygomatico-temporal branches of the zygomatic branch of the fifth, together with two small arteries from the lacri- mal. In some cases, however, the canal is single at its commencement on the orbital plate and bifurcates as it traverses the bone. The rough free edge of the Fig. 119. — Skull showing the Right Malar Bone DrviDED into Two Parts by a Hori- zontal Suture. (From a specimen in the Museum of University College, London.) process articulates above with the zygomatic border of the great wing of the sphenoid, and below with the maxilla. When the orbital process is large, it excludes the great wing of the sphenoid from articulation with the maxilla, and the border then presents near the middle a short, non-serrated portion THE MANDIBLE 95 which closes the anterior extremity of the inferior orbital (spheno-maxillary) fissure. All the four angles of the zygomatic bone have distinguishing featm-es. The superior, forming the fronto-sphenoidal process, is the most prominent, and is serrated for articulation with the zygomatic process of the frontal; the anterior or infra-orbital process, sharp and pointed, articulates with the maxilla and occasionally forms the superior boundary of the infra- orbital foramen; the posterior or temporal process is blunt and serrated rnainly on its medial aspect for articulation with the zygomatic process of the temporal; the inferior angle, blunt and rounded, is known as the malar tubercle. Of the four borders, the orbital is the longest and extends from the fronto-sphenoidal to the infra-orbital process. It is thick, rounded, and forms more than one-third of the circumference of the orbit; the temporal border, extending from the fronto-sphenoidal to the temporal process, is sinuously curved and gives attachment to the temporal fascia. Near the frontal .angle is usually seen a sHght elevation, the processus marginalis, to which a strong shp of the fascia is attached; the masseteric border, thick and rough, completes the lower edge of the zygomatic arch and gives origin to the anterior fibres of the masseler; the maxillary border, rough and eon- cave, is connected by suture with the maxilla, and near the margin of the orbit gives origin to the infra-orbital head of the guadratus Inbii svperioris. Blood-supply. — The arteries of the zygomatic are derived from the ^infra-orbital, lacrimal, transverse facial, and deep temporal arteries. Articulations. — With the maxilla, frontal, temporal, and sphenoid. Ossification. — The zygomatic is ossified in membrane from three centres which appear in the eighth week of intra-uterine life. The three pieces, which have received the names of ■pre- violar, poslmalar, and hypnmalar, unite .about the fifth month. Occasionally the primary nuclei fail to coalesce, and the bone is then represented in the adult by two or three portions sepa- rated by sutures. In those cases in which the premalar and postmalar unite and the hypo- malar remains distinct, the suture is horizontal; if the independent portion is the premalar, then the suture is vertical. The bipartite zygomatic has been observed in skulls obtained from at least a dozen different races of mankind, but because of the greater frequency in which it occurs in the crania of the Japanese (seven per cent.), the name of o.« Japonicum has been given to it. THE MANDIBLE The mandible [mandibula] or lower jaw-bone (figs. 120, 121) is the largest and strongest bone of the face. It supports the mandibular teeth, and by means of a pair of condyles, moves on the skull at the mandibular fossse of the temporal bones. It consists of a horizontal portion — the body- — strongly curved, so as to somewhat resemble in shape a horseshoe, from the ends of which two branches or rami ascend almost at right angles. The body is marked in the middle line in front by a faint groove which in- dicates the symphysis or place of union of the two originally separate halves of the bone. This ends below in the elevation of the chin known as the mental protuberance, the lowest part of which is slightly depressed in the centre and raised on each side to form the mental tubercle. Each half of the mandible presents two surfaces and two borders. On the lateral surface, at the side of the symphysis, and below the incisor teeth, is a shallow depression, the incisor fossa, from which the vientalis and the incisivus labii inferioris muscle arise; and more laterally, opposite the second bicuspid tooth, and midway between the upper and lower margins, is the mental foramen, which transmits the mental nerve and vessels. Below the foramen is the oblique line, extending backward and upward from the mental tubercle to the anterior border of the rairius; it divides the body into an upper or alveolar part and a lower or basilar part, and affords attachment to the quadratus labii inferioris and the triangularis oris. The medial surface presents at the back of the symphysis four small pro- jections, called the mental spine (genial tubercles). These are usually arranged in two pairs, one above the other; the upper comprising a pair of prominent spines, gives origin to the genio-glossi, and the lower, represented in some bones by a median ridge or only a slight roughness, gives origin to the genio-hyoid muscles. At the side of the symphysis near the inferior margin is an oval depression, the digastric fossa, for the insertion of the digastric muscle. Commencing below the mental spine, and extending upward and backward to the ramus, is the mylo-hyoid line, which becomes more prominent as it approaches ,the alveolar border; it gives attachment along its whole length to the mylo-hyoid muscle, at its posterior fifth to the superior constrictor of the pharynx, and at the pos- terior extremity to the pterygo-mandibular raphe. Above this line at the side of the symphysis is a smooth depression [fovea sublingualis] for the sublingual gland, and below it, farther back, is another for the submaxillary gland. 96 THE SKELETON The alveolar part or superior border is hollowed out into eight sockets or alveoli. These are conical in shape and form an exact counterpart of the roots- of the teeth which they contain. From the lateral aspect of the alveolar process, as far forward as the first molar tooth, the buccinator muscle takes origin. The base or inferior border is thick and rounded. In the anterior part of its extent it gives attachment to the platysma, and near its junction with the ramus is a groove for the external maxillary artery which here turns upward into the face. The ramus is thinner than the body and quadrilateral in shape. The lateral surface is flat, gives insertion to the masseter, and at the lower part is marked by several oblique ridges for the attachment of tendinous bundles in the substance of the muscle. The medial surface presents near the middle the mandibular (inferior dental) foramen, leading into the mandibular (inferior dental) canal which traverses the bone and terminates at the mental foramen on the lateral surface of the body. From the canal, which in its posterior two-thirds is nearer to the medial, and in its anterior third nearer to the lateral, surface of the mandible, Fig. 120.^The Mandible. (Lateral view.) Coronoid Temporal process Mandibular notch External pterygoid Plat\ sma Triangularis' oris Groove for external maxillary artery External oblique line a series of small channels pass upward to the sockets of the posterior teeth and transmit branches of the inferior alveolar (dental) vessels and nerve; in front of the mental foramen a continuation of the canal extends forward and conveys the vessels and nerves to the canine and incisor teeth. The mandibular foramen is bounded medially by a sharp margin forming the lingula (mandibular spine), which gives attachment to the spheno-mandibular ligament. The posterior margin of the. lingula is notched. This notch forms the commencement of a groove, the mylo-hyoid groove [sulcus mylohyoideus], which runs obliquely downward and forward and lodges the mylo-hyoid nerve and artery, and, in the embryo, Meckel's cartilage. Behind the spine is a rough area for the insertion of the internal pterygoid muscle. The posterior border of the ramus is thick and rounded, and in meeting the inferior border of the ramus forms the angle of the jaw, which is rough, obtuse, usually everted, and about 122° in the adult; the angle gives attachment to the stylo-mandibular ligament. The inferior border is thick, rounded, and continu- ous with the base. The anterior border is continuous with the oblique line, whilst the upper border presents two processes separated by a deep concavity, the mandibular (sigmoid) notch. Of the processes, the anterior is the coronoid; the posterior, the condylar. THE MANDIBLE 97 The condylar process consists of the condyle [capitulum mandibulse] and the narrowed portion by which it is supported, the neck. The condyle is oval in shape, with its long axis transverse to the upper border of the ramus, but oblique with regard to the median axis of the sicull, so that the lateral extremity, which presents the condylar tubercle for the temporo-mandibular ligament of the temporo-mandibular articulation, is a little more forward than the medial ex- tremity. The convex surface of the condyle is covered with cartilage in the recent Fig. 121. — The Mandible. (Medial view.) Lin^ula Mandibular foramen Spheno-mandib- ular ligament Superior constnctor Mylo-hyoid groove Internal pterygoid Stylo-mandibular ligament ^ > " tii { — Groove for sub- lingual gland Genio-glossus Genio-hyoid Digastric Mylo-hyoid Groove for submaxillary gland Mylo-hyoid line state, and rests in the mandibular fossa; the neck is flattened from before back- ward, and presents, in front, a depression [fovea pterygoidea] for the insertion of the external pterygoid muscle. The coronoid process, flattened and triangular, is continued upward from the anterior part of the ramus. The lateral surface is smooth and gives insertion to the temporal and masseter muscles; the medial surface is marked by a ridge which descends from the tip and becomes continuous with the posterior part of the mylo-hyoid line. On the medial surface, as well as on the tip of the coronoid Fig 122 — Mandiblb showing Relations op Meckel's Cartilage in Human Fcetus op 8 CM. Cbown-Rump Length. (After KoUmann, Handatlas der Entwickelungsgeschichte.) Groove for teeth Meckel's cartilage AnniUus tym- panicus process, the temporal muscle is inserted. The mandibular notch, the deep semi- lunar excavation separating the coronoid from the condylar process, is crossed by the masseteric nerve and vessels. Blood-supply. — Compared with other bones, the superficial parts of the mandible are not so freely supplied with blood. The chief artery is the inferior alveolar which runs in the man- dibular canal, and hence, as the bone is exposed to injury and sometimes actually laid bare in its alveolar portion, it often necroses, especially if the artery is involved at the same time. 7 98 THE SKELETON Ossification. — The mandible is mainly formed by ossification in the fibrous tissue investing the cartilage of the first branchial arch or Meckel's cartilage, although a small portion of the cartilage itself is directly converted into bone. It is now generally admitted that the lower jaw is developed in membrane as a single skel- etal element. The centre of ossification appears in the outer aspect of Meckel's cartilage and gives rise to the bony plate known as the dentary. This plate extends forward right up to the middle line in front, and from it a shelf grows upward for the support of the tooth germs. Fig. 123. — The Mandible at Birth. Meckel's cartilage lies below and medial to the dentary plate, and the inferior alveolar nerve passes forward between the two structures. Meckel's cartilage itself takes some small part in the formation of the lower jaw. Ossification from the primary nucleus invades the cartilage at a point opposite the interval between the first and second tooth germs, and the resulting bone contributes to the formation of the alveolar margin opposite these two teeth. Behind this point the cartilage atrophies except in so far as it helps to form the spheno-mandibular ligament and the malleus and incus. Behind the symphysis the anterior extremity of the cartilage does not enter into the formation of the jaw, but it usually persists throughout foetal Fig. 124. — The Skull op a Woman Eighty-three Years Old, to show the Changes in THE Mandible and Maxilla life as one or two small, rounded, cartilaginous masses. Occasionally they become ossified and give rise to accessory ossicles in this situation. The lamella of bone situated on the medial side of Meckel's cartilage, corresponding to the distinct splenial element in some animals, arises in man as an extension from the dentary element. In connection with the condylar and coronoid processes, cartilaginous masses are developed. These do not, however, indicate separate elements, but are adaptations to the growth of the lower jaw. 'They are ossified by an extension from the surrounding membrane bone. THE HYOID BONE The process of ossification of the lower jaw commences very early, between the sixth and eighth week, and proceeds rapidly, so that by the fourth month the various parts are formed. Age-changes. — At birth the mandible is represented by two nearly horizontal troughs of bone, lodging unerilpted teeth, and joined at the symphysis by fibrous tissue. The body is mainly alveolar, the basal part being but little developed; the condyle and the upper edge of the symphysis are nearly on a level; the mental foramen is nearer the lower than the upper margin, and the angle is about 175°. The inferior alveolar nerve lies in a shallow groove between the spleuial and dentary plates. During the first year osseous union of the two halves takes place from below upward, but is not complete until the second year. After the first dentition, the ramus forms with the body of the mandible an angle of about 140°, and the mental foramen is situated midway between the upper and lower borders of the bone opposite the second milk-molar. In the adult, the angle formed by the ramus and body is nearer to a right angle, and the mental foramen is oppo- site the second bicuspid, so that its relative position remains unaltered after the first dentition. In old age, after the fall of the teeth, the alveolar margin is absorbed, the angle formed by the ramus and body is again increased, and the mental foramen approaches the alveolar margin. In a young and vigorous adult the mandible is, with the exception of the petrous portion of the temporal, the densest bone in the skeleton; in old age it becomes exceedingly porous, and often so soft that it may easily be broken. ( THE HYOID BONE The hyoid bone [os hyoideum] or os linguae (fig. 125), situated in the anterior part of the neck between the chin and the thyreoid cartilage, supports the tongue and gives attachment to numerous muscles. It is suspended from the lower extremities of the styloid processes of the temporal bones by two slender bands known as the stylo-hyoid ligaments, and is divisible into a body and two pairs of processes, the greater and lesser cornua. The body, constituting the central portion of the bone, is transversely placed and quadrilateral in form. It is compressed from before backward and lies obliquely so that the anterior surface looks upward and forward and the posterior surface in the opposite direction. The anterior surface is convex and divided by a horizontal ridge into a superior and an inferior portion. Frequently it also presents a vertical ridge crossing the former at right angles, and just above the point of intersection is the glosso-hyal Fig. 125. — The Hyoid Bone. A, Male, B, Female (Natural Size) process, the vestige of a well-developed process in this situation in the hyoid bone of some of the lower animals (reptiles and the horse). In this way four spaces or depressions for muscular attachments are marked off, two on either side of the middle line. The posterior surface is deeply concave and separated from the epiglottis by the thyreo-hyoid membrane, and by some loose areolar tissue. The membrane passes upward from the thyreoid cartilage to be attached to the superior border, and interposed between it and the concavit.y on the back of the body is a small synovial bursa. The inferior border, thicker than the upper, gives insertion to muscles. The lateral borders are partly in relation with the greater cornua, \vith which they are connected, up to middle life, by synchondrosis, but after this period, usually by bone. 100 THE SKELETON The greater cornua projects upward and backward from the sides of the body. They are flattened from above downward, thicker near their origin, and terminate posteriorly in a rounded tubercle to which the thyreo-hyoid ligament is attached. The lesser cornua are small conical processes projecting upward and back- ward opposite the lines of junction between the body and the greater cornua, and by their apices give attachment to the stylo-hyoid ligaments; they are connected to the body by fibrous tissue. Professor Parsons has shown that a joint with a synovial cavity is common between the smaller and geater cornua. The lesser cornua are sometimes partly or even completely cartilaginous in the adult. Fig. 126. — Hyoid Bone Enlarged to show Muscular Attachments. (After F. G. Parsons.) Greater cornu' Attachment to digastric tendon Hyo-glossus The muscles attached to each half of the hyoid bone may be enumerated as follows: — Body Genio-hyoid, genio-glossus, mylo-hyoid, sterno-hyoid, omo-hyoid, stylo- hyoid, thyreo-hyoid and hyo-glossus. Greater cornu Thyreo-hyoid, middle constrictor, hyo-glossus, and digastric. Lesser cornu Chondro-glossus, and middle constrictor. Ossification. — In the early months of intra-uterine life the hyoid bone is composed of hyahne cartilage and is directly continuous with the styloid processes of the temporal bones. Ossification takes place from six centres, of which two appear in the central piece of cartilage, one on either side of the middle line, either just before or just after birth; soon after their appearance, however, they coalesce to form the body of the bone (basi-hyal). The centre for each of the greater cornua (thyreo-hyals) appears just about the time of birth, and for each of the lesser cornua (oerato-hyals) some years after birth, even as late as puberty. (F. G. Parsons.) The greater cornua and the body unite in middle life; the lesser cornua rarely anky- lose with the body and only in advanced age. Professor Parsons has shown, however, that the lesser cornua more frequently unite with the greater cornua. THE SKULL AS A WHOLE The skull, formed by the union of the cranial and facial bones already de- scribed, may now be considered as a whole. Taking a general view, it is spheroidal in shape, smooth above, compressed from side to side, flattened and uneven below, and divisible into six regions : a superior region or vertex, a posterior or occipital region, an anterior or frontal region, an inferior region or base, and two lateral regions. (1) The Superior Region Viewed from above {norma verticalis) the skull presents an oval outline with the broader end behind, and includes the frontal, parietals, and the interparietal portion of the occipital. In a skull of average width the zygomatic arches are visible, but in very broad skulls they are obscured. THE SKULL AS A WHOLE 101 The sutures of the vertex are : — The metopic, which is, in most skulls, merely a median fissure in the frontal bone just above the glabella; occasionally it involves the whole length of the bone. It is due to the persistence of the fissure normally separating the two halves of the bone in the infant. The sagittal is situated between the two parietals, and extends from the bregma to the lambda. The coronal lies between the frontal and parietals, and extends from pterion to pterion. The lambdoid is formed by the parietals and interparietal portion of the occipital. It extends from asterion to asterion. The occipital suture is only present when the interparietal exists as a separate element (figs. 70 and 71). The more important points are: — The bregma, which indicates the situation of the frontal (gi-eater) fontanelle, and marks the confluence of the coronal, the sagittal, and, when present, the metopic sutures. The lambda, where the sagittal enters the lambdoid suture; it marks the situation of the occipital (lesser) fontanelle. The obelion, a little anterior to the lambda, is usually indicated by a median or two lateral foramina. (2) The Posterior Region Viewed from behind {norma occipitalis) the skull is somewhat pentagonal in form. Of the five angles, the superior or median is situated in the line of the sagittal suture; the two upper lateral angles coincide with the parietal eminences and the two lower with the mastoid processes of the temporal bones. Of the sides, four are somewhat rounded, and one, forming the basal line, running between the mastoid processes, is flattened. The centre is occupied by the lambda, and radiating from this point are three sutures, the sagittal, and the two parts of the lambdoid. Each half of the lambdoid suture bifurcates at the mastoid portion of the temporal bone, the two divisions constituting the parieto-mastoid and occipito-mastoid sutures; the point of bifurcation is known as the asterion. In the lower part of the view is seen the external occipital protuberance (inion), the occipital crest, and the thi-ee pairs of nuchal lines, which give it a rough and uneven appearance. The occipital point is the point of the occiput furthest from the glabella in the median plane. It is situated above the external occipital protuberance. (3) The Lateral Region The lateral region (norma lateralis) (fig. 127) is somewhat triangular in shape, being bounded above by a line extending from the zygomatic process of the frontal, along the temporal line to the lateral extremity of the superior nuchal line of the occipital bone; this forms the base of the triangle. The two sides are represented by lines drawn from the extremities of the base to the angle of the jaw. It is divisible into two portions, one in front, the other behind, the emi- nentia articularis [tuberculum articulare]. The posterior portion presents, in a horizontal line from behind forward, the mastoid portion of the temporal, with its process and foramen, the external auditory meatus, the centre of which is known as the atiricular point, the mandibular fossa, and the condyle of the mandible. In the anterior portion are three fossaj, (a) temporal, (b) infratemporal, (c) pterygo-palatine (spheno-maxillary), and two fissures, the inferior orbital (spheno- maxillary) and pterygo-palatine. (a) The temporal fossa, somewhat semilunar in shape, is bounded above and behind by the temporal line, in front by the frontal, zygomatic, and great wing of sphenoid, and laterally by the zygomatic arch, by which it is separated superficially from the infratemporal fossa; more deeply the infratemporal ridge separates the two fossae. The fossa is formed by parts of five bones, the zygomatic, temporal, parietal, frontal, great wing of sphenoid, and is traversed by six sutures, coronal, spheno-zygomatic, sphcno- sc(uamosal, spheno-parietal, squamosal, and spheno-frontal. The point where the temporal ridge is crossed by the coronal suture is the stephanion, and the region where the frontal, sphenoid, temporal, and parietal meet is the pterion. The latter is frequently occupied in the adult by the epipteric bone. The temporal fossa is concave in front, convex behind, filled by the temporal muscle, and roofed in by a strong glistening aponeurosis, the temporal fascia, which serves to bind down the muscle. (b) The infratemporal fossa (zygomatic fossa), irregular in shape, is situated below and to the medial side of the zj'goma, covered in part by the ramus of the mandible. It is bounded in front by the lower part of the medial surface of the zygomatic, and by the infratemporal surface of the maxilla, on which are seen the orifices of the posterior superior alveolar canals; behind by the posterior border of the lateral pterygoid plate, the spine of the sphenoid, and the articular tubercle; above by the infratemporal ridge, a small part of the squamous portion of 102 THE SKELETON the temporal, the great wing of the sphenoid perforated by the foramen ovale and foramen spinosum; helow by the alveolar border of the maxilla; laterally by the ramus of the mandible and the zygoma formed by zygomatic and temporal; medially by the lateral pterygoid plate, a line from which to the spine of the sphenoid separates the infratemporal fossa from the base of the skull. It contains the lower part of the temporal muscle and the coronoid process of the mandible, the external and internal pterygoids, the internal maxillary vessels, and the mandibular division of the fifth nerve with numerous branches. At its upper and medial part are seen the inferior orbital and pterygo-palatine fissures. The inferior orbital (or spheno-maxillary) fissure is horizontal in position, and lies between the maxQla and the great wing of the sphenoid; laterally it is usually completed by the zygo- matic, though in some cases the sphenoid joins the maxilla, and in this way excludes the zygo- matic bone from the fissure; medially it is terminated by the infratemporal surface of the orbital process of the palate bone. Through this fissure the orbit communicates with the pterygo- palatine (spheno-maxillary), infratemporal, and temporal fossae. It transmits the infra- orbital nerve and vessels, the zygomatic nerve, ascending branches from the spheno-palatine ganglion to the orbit, and a communicating vein from the ophthalmic to the pterygoid plexus. Fig. 127.^The Skull. (Norma lateralis.) The pterygo-palatine (pterygo-maxillary) fissure forms a right angle with the inferior orbital fissure and is situated between the maxilla and the anterior border of the pterygoid process of the sphenoid. At its lower angle, where the two lips of the fissure approximate, the lateral pterj'goid plate occasionally articulates with the maxilla, but they are usually separated by' a thin portion of the pyramidal process of the palate. The pterygo-palatine fissure, which serves to connect the infratemporal fossa with the pterygo-palatine fossa, is bounded medially by the perpendicular part of the palate; it transmits branches of the internal maxillary artery, and the corresponding veins, to and from the pterygo-palatine fossa. (c) The pterygo-palatine (spheno-maxillary) fossa is a small space, of the form of an inverted pyramid, situated at the angle of junction of the inferior orbital (spheno-maxil- lary) with the pterygo-palatine (pterygo-maxillary) fissure, below the apex of the orbit. It is bounded infroid by the infratemporal surface of the maxilla; behind, by the base of the pterygoid process and the lower part of the anterior surface of the great wing of the sphenoid; medially by the perpendicular part of the palate with its orbital and sphenoidal processes; above by the lower surface of the body of the sphenoid. Three fissures terminate in it — viz., the superior orbital, pterygo-palatine, and inferior orbital; through the superior orbital fissuje it communi- cates with the cranium, through the pterygo-palatine fissure with the infratemporal fossa, through the inferior orbital fissure with the orbit, and throagh the spheno-palatine foramen on the medial wall it communicates with the upper and back part of the nasal fossa. In- THE SKULL AS A WHOLE 103 eluding the spheno-palatine foramen sL\ foramina open into the fossa. Of these, three are on the posterior wall: enumerated from without inward, and from above downward, they are the foramen rotundum, the pterygoid (Vidian) canal, and the pharyngeal (pterygo-palatine) canal. The apex of the pyramid leads below into the pterygo-palatine canal and the accessory palatine canals which branch from it; and anteriorly is the orifice of the infra-orbital canal. The fossa contains the spheno-palatine ganglion, the maxillary nerve, and the terminal part of the internal maxillary artery, and the various foramina and canals in relation with the fossa serve for the transmission of the numerous branches which these vessels and nerves give off. Fig. 128. — A Section of the Skull, showing the Medial Wall of the Orbit, the Medial Wall of the Antrum, and the Pterygo-palatine Fossa. Frontal sinus Frontal process of maxilla ~7 Lacrimal -— Lacrimal canal Orifice of antrum Inferior nasal concha Palate bone Anterior nasal spine Anterior ethmoid canal Posterior ethmoid canal Spheno-palatine foramen Pterygoid canal, leading into the pterygo-palatine fossa Sphenoid Lateral pterygoid plate (4) Inferior Region or External Base of Skull The external base of the skull {norma basilaris) (figs. 130, 131) extends from the incisor teeth to the occipital protuberance, and is bounded on each side by the alveolar arch, the zygomatic, the zygoma, the temporal, and the superior nuchal line of the occipital bone. It is very uneven and, excluding the lower jaw, divisible into three portions: (a) anterior, (b) middle or subcranial, and (c) posterior or suboccipital. Fig. 129. — Hard Palate of a Child Five Years Old. Palate bonet^ L^f'Cc ^ Palate process of maxilla Greater palatine foramen Lesser palatine foramen (a) The anterior division consists of the hard palate, the alveolar arch, and the choanse (posterior nares). When the skull is inverted, the hard palate stands at a higher level than the rest, and is bounded anteriorly and laterally by the alveolar ridges containing the teeth. The bones appearing in the intermediate space are the premaxillary and palatine portions of the maxillse and the horizontal parts of the palate bones. 104 THE SKELETON Fig 130 — The Skull (Norma basilaris.) Tensor veli palatini Azygos uvulee Superior constrictor Internal pterygoid Tensor veli palatini Tensor tympani Levator veli palatini Longus capitis Superior constrictor Rectus capitis anterior Anterior longitudinal ligament of spine Vertical part of crucial ligament Alar ligament Articular capsule Posterior occipito-atlantal membrane Superior oblique Rectus capitis posterior major Rectus capitis posterior minor f- - Ligamentum nuchse Trapezius THE SKULL AS A WHOLE 105 Fig. 131. — The Skull. (Norma basilaris.) Scarpa^s foramen Stenson's foramen Scarpa's foramen : fossa Palatine groove Posterior palatine foramen Spine of the palate bone Hamular process VO\ER Sphenoidal process of palate bone Foramen lacerum Pharyngeal tubercle Carotid canal Tubercle for alar ligament Condylar foramen' External occipital crest External occipital protuberance 106 THE SKELETON They are rough for the attachment of the muco-periosteum, and near the posterior margin is the ridge for the fibrous expansion of the tensor veli 'palatini. The fol- lowing points are readily recognised (fig. 129) : — The meso-palatine suture commences at the alveolar point, traverses the incisive fossa, and terminates at the posterior nasal spine. The transverse palatine suture, between the palate bones and palatine processes of the maxiUae. In young skulls the incisive sutures, and behind the incisor teeth four small openings known aS the gubemacular canals (see figs. 114 and 129). The incisive fossa containing the termination of four canals: two small orifices, foramina of Fig. 1.32. — The Skull. (Norma facialis.) Quadratus lahii superions (zygomatic head) Orbicularis oculi Quadratus labii superioris (ancular head) Quadratus labii superiosis (infraorbital head) Nasalis (transverse portion) Nasalis (alar portion) Orbicularis oris Scarpa, situated one behind the other in the meso-palatine suture; and two larger openings, the foramina of Stenson. The foramina of Scarpa transmit the naso-palatine nerves, and those of Stenson are in relation (embryonic) with the organs of Jacobson. At the posterior angles of the hard palate are the greater palatine foramina, through which the descending palatine vessels and the anterior palatine nerves emerge on to the palate; a thin lip of bone separates them from the lesser palatine foramen in the tuberosity of the palate bone on each side, for the posterior palatine nerve. The hamular process of the medial pterygoid plate is the most posterior limit of the hard palate. At the posterior extremity of each alveolar ridge is the tuberosity of the maxilla, and between it and the palate bone is a foramen (variable in size and sometimes absent), the middle palatine foramen, for the middle palatine nerve. This foramen is often included under the lesser pala- tine foramina (BNA). THE SKULL AS A WHOLE 107 Behind the hard palate are the choanae (posterior nares), separated from each other by the vomer. Each is bounded laterally by the medial pterygoid plate; below by the horizontal plate of the palate bone; above by the under surface of the body of the sphenoid, with the ala of the vomer and a portion of the sphenoidal process of the palate bone. Lateral to the choanae there is on each side a vertical fossa lying between the pterygoid plates. It extends upward to the under surface of the great wings of the sphenoid; it is com- pleted anteriorly by the coalescence of the pterygoid plates and below by the pyramidal process of the palate bone. It contains the following points of interest: — An elongated furrow, the scaphoid fossa, for the tensor veli palatini muscle and the carti- lage of the Eustachian tube. The general cavity of the pterygoid fossa which lodges the tensor veli palatini and internal pterygoid muscles. Fig. 133. — ^The Skuli,. (Norma facialis.) Ophryoa Superciliary arch Glabella Nasion Nasal (piriform) apertxire Subnasal point Canine fossa Canine eminence Alveolar point ( Frequently there is a notch in the lateral pterygoid plate close beside the foramen ovale. The posterior termination of the pterygoid (Vidian) canal. If a line be drawn across the base of the skull from one preglenoid tubercle to the other, it will fall immediately behind the lateral pterygoid plate and bisect the foramen spinosum on each side. A second transverse line, drawn across the opisthion or posterior margin of the foramen magnum, will fall behind the mastoid processes. The space between these arbitrary lines may be called the subcranial region; that behind the second hne, the suboccipital region. (b) The subcranial region is separated from the infratemporal fossa by a line drawn from the posterior margin of the lateral pterygoid plate to the spine of the 108 THE SKELETON sphenoid. It is formed by the inferior surface of the basilar process of the occipital and the body of the sphenoid, the petrous portion of the temporal bone, a small piece of the squamosal portion, the posterior part of the great wing of the sphenoid, and the condylar portions of the occipital bone. It presents the following points for examination (Figs. 95, 131): — The pharyngeal tubercle. The foramen magnum and the occipital condyles. The most anterior point of the foramen is termed the basion, and the most posterior point the opisthion. On each side will be seen: — The hypoglossal foramen for the hypoglossal nerve and a men- ingeal branch of the ascending pharyngeal artery. The condylar fossa with the condylar foramen (this foramen is not constant). The under aspect of the jugular process, from which the rectus capitis lateralis takes origin. The foramen lacerum and the orifice of the pterygoid (Vidian) canal. The canalis musculo -tubarius for the tensor tympani muscle and Eustachian tube. The carotid canal. The quadrilateral area for the origin of the levator veli palatini and tensor tympani muscles. The canaliculus cochleae, or ductus perilymphaticus. The jugular foramen and fossa for the glosso-pharyngeal, vagus, and spinal accessory nerves, the internal jugular vein, and a meningeal branch of the ascending pharyngeal artery. The tympanic canaliculus for Jacobson's nerve (tympanic branch of glossopharyngeal). The spine of the sphenoid; this is sometimes fifteen miUimetres in length. The mandibular fossa with the petro-tympanic fissure. This lodges the anterior process of the malleus, the tympanic twig of the internal maxillary artery. A small passage beside it, the canal of Huguier, conducts the chorda tympani nerve from the tympanum. The external auditory meatus. The auricular or tympano-mastoid fissure. The tympanic plate and vaginal process. The styloid process. The stylo -mastoid foramen for the stylo-mastoid artery and the exit of the facial nerve and, in some cases, the auricular branch of the vagus. The mastoid process with the digastric and occipital grooves. (c) The suboccipital region is largely formed by the tabular portion of the occipital bone with its ridges and areas for muscular attachment. Laterally a small part of the mastoid portion of the temporal is seen, pierced by a small foramen, of variable size, the mastoid foramen, which transmits a vein from the transverse (lateral) sinus and a meningeal branch of the occipital artery. (5) The Anterior Region The anterior region {norma facialis) (figs. 132, 133) comprises the anterior end of the cranium or forehead, and the skeleton of the face; also the cavities known as the orbits, formed by the junction of the two parts of this region, and the nasal fossae, situated on either side of the septum of the nose. The upper part or forehead, narrowest between the temporal crests about half an inch above the zygomatic processes of the frontal, presents at this level the two transverse sulci ; above are the frontal eminences, below the superciliary arches, and still lower the supra-orbital margins, interrupted near their medial ends by the supra-orbital notches. Below the forehead are the openings of the orbits, bounded laterally by the zygomatic bones constituting the prominences of the cheeks, and between them the bridge of the nose, formed by the nasal bones and the frontal processes of the maxillae. Below the nasal bones is the apertura piriformis or anterior nasal aperture, leading into the nasal fossse. The teeth form a conspicuous feature in this view of the skull, the outline of which is completed below by the mandible. The bones entering into formation of the norma facialis are: — the frontal, nasals, lacrimals, orbital surfaces of the small and the great wings, and a portion of the body of the sphenoid, the laminas papjrraceoB of the ethmoids, the orbital processes of the palate bones, the zygomatics, maxillse, inferior nasal conchae, and the mandible. The sutures are numerous, and for the most part unimportant: — The transverse sutiu-e (fig. 133) extends from one zygomatic process of the frontal to the other. The upper part of the suture is formed by the frontal bone; below are the zygomatic, great and small wings of the sphenoid, lamina papyracea, lacrimal, maxillary, and nasal bones. A portion of this complex suture, lying between the sphenoidal and frontal bones, appears in the anterior cranial fossa. Other fissures are the internasal, naso-maxillary, inter-maxillary and zygomatioo-maxillary. The small sutures seen in the orbit are described with that cavity. The foramina are: — the supra-orbital, infra-orbital, optic, zygomatico-facial, and mental; the naso-lacrimal canal; the ethmoidal canals; and the inferior and superior orbital fissures. THE ORBITS 109 The following points may also be noticed: — The glabella, a smooth space between the converging superciliary arches. The ophryon, the most anterior point of the metopic suture. The nasion, the middle of the naso-frontal sutui'e. The subnasal point, the middle of the inferior border of the pyriform aperture at the base of the nasal spine. The alveolar point, the centre of the anterior margin of the upper alveolar arch. THE ORBITS The orbits [orbitse] (fig. 134) are two cavities of pyramidal shape, with their bases directed forward and laterally and their apices backward and medially; their medial walls are nearly parallel, but their lateral walls diverge so as to be nearly at right angles to each other. Each cavity forms a socket for the eyeball and the muscles, nerves, and vessels associated with it. Seven bones enter into formation of its walls, viz., the frontal, zygomatic, sphenoid, ethmoid, lacrimal, palate, and maxilla; but as three of these — the frontal, sphenoid, and ethmoid — are single median bones which form parts of each cavity, there are only eleven bones represented in the two orbits. Each orbit presents for examination four walls, a circumference or base, and an apex. The superior wall or roof, vaulted and smooth, is formed mainly by the orbital plate of the frontal and is completed posteriorly by the small wing of the sphenoid. At the lateral angle it presents the lacrimal fossa for the lacrimal gland, and at the medial angle a depression or a spine for the puOey of the superior oblique muscle. Fig. 134. — The Medial Wall of the Orbit. Frontal process of maxilla / V T.arrimfll- /— Lacrimal canal Orifice of antrum Inferior nasal concha Palate b( Anterior nasal spine Anterior ethmoid canal Posterior ethmoid canal Optic foramen Lamina papyracea of ethmoid \ r^Spheno-palatine foramen ?^— ^Pterygoid canal, leading into the ^^^ pterygo -palatine fossa Sphenoid External pterygoid plate The inferior wall or floor is directed upward and laterally and is not so large as the roof. It is formed by the orbital plate of the maxilla, the orbital process of the zygomatic, and the orbital process of the palate bone. At its medial angle it presents the naso-laorimal canal, and near this, a depression for the origin of the inferior oblique muscle. It is marked near the middle by a furrow for the infra-orbital artery and the second division of the fifth nerve, terminating anteriorly in the infra-orbital canal, through which the nerve and artery emerge on the face. Near the commencement of the canal a narrow passage, the anterior alveolar canal, runs for- ward and downward in the anterior wall of the antrum, transmitting nerves and vessels to the incisor and canine teeth. The lateral wall, directed forward and medially, is formed by the orbital surface of the great wing of the sphenoid, and the zygomatic. Between it and the roof, near the apex, is the superior orbital (sphenoidal) fissure, by means of which the third, fourth, ophthalmic division of the fifth, and sixth nerves enter the orbit from the cranial cavity; it also transmits some filaments from the cavernous plexus of the sympathetic, the orbital branch of the middle men- ingeal artery, recurrent branches of the lacrimal artery, and an ophthalmic vein. The lower margin of the fissure presents near the middle a small tubercle, from which the inferior head of the lateral rectus muscle arises. Between the lateral wall and the floor, near the apex, is the inferior orbital (spheno-maxiUary) fissure, tlu-ough which the second division of the fifth and the infra-orbital vessels pass from the pterygo-palatine fossa to enter the infra-orbital groove. At the anterior margin of the fissure the sphenoid occasionally articulates with the maxilla, but no THE SKELETON the two are usually separated by the orbital plate of the zygomatic, and on the latter are seen the orifices of the zygomatico-temporal and zygomatico-facial canals, which traverse the zygomatic bone. The commencement of the zygomatico-temporal canal is sometimes seen in the spheno-zygomatic sutm-e connecting the sphenoid and zygomatic bones. The medial wall, narrow and nearly vertical, is formed from before backward by the frontal process of the maxilla, the lacrimal, the lamina papyracea of the ethmoid, and the body of the sphenoid. At the junction of the medial wall with the roof, and in the suture between the ethmoid and frontal, are seen the orifices of the anterior and posterior ethmoidal canals, the anterior, transmitting the anterior ethmoidal vessels and nerve; and the posterior, the posterior vessels and nerve. Anteriorly is the lacrimal groove for the lacrimal sac, and behind this the lacrimal crest, from which the tensor tarsi arises. The medial wall, which is the smallest of the four, is traversed by three vertical sutures: — one between the frontal process of the maxilla and the lacrimal, a second between lacrimal and lamina papyracea, and a third between the lamina papyracea and the sphenoid. Occasionally the sphenoidal concha appears in the orbit between the ethmoid and the body of the sphenoid. The apex of each orbit corresponds to the optic foramen, a circular orifice which transmits the optic nerve and ophthalmic artery. The base or circumference is quadrilateral in form and is bounded by the frontal bone above, the frontal process of the maxilla and the medial angular process of the frontal on the medial side, the zygomatic bone and the zygomatic process of the frontal on the lateral side, and by the zygomatic and the body of the maxilla below. The following points may also be noted: — The suture between the zygomatic process of the frontal bone and the zygomatic; the supra-orbital notch (sometimes a complete foramen); the sutiu'e between the frontal bone and the frontal process of the maxilla; and in the lower segment, the zygomatico-maxillary suture. The orbit communicates with the cranial cavity by the optic foramen and superior orbital fissure; with the nasal fossa, by means of the naso-lacrimal canal; with the zygomatic and ptery go-palatine fossae, by the inferior orbital fissure. In addition to these large openings, the orbit has five other foramina — the infra-orbital, zygomatico-orbital, and the anterior and posterior ethmoidal canals — opening into it or leading from it. The following muscles arise within the orbit : — the four recti, the -tuperior oblique, and levator palpebrce superioris, near the apex; the inferior oblique on the floor of the orbit lateral to the naso-lacrimal canal; and the tensor tarsi from the lacrimal crest. The margins of the inferior orbital fissure give attachment to the orhitalis muscle. THE NASAL FOSS^ The nasal fossae (figs. 135, 136) are two irregular cavities situated on each side of a median vertical septum. They open in front by the piriform aperture and communicate behind with the pharynx by the choanse. They are somewhat . Fig. 135. — Section through the Nasal Fossa to show the Septum. Left Half, with Septum looking toward Right Nasal Fossa. Crest of sphenoid—^ ';4 Groove for naso-palatine nerve Crest of maxilla oblong in transverse section, and extend vertically from the anterior part of the base of the cranium above to the superior surface of the hard palate below. Their transverse extent is very limited, especially in the upper part. Each fossa presents for examination a roof, floor, medial and lateral walls, and communicates with the sinuses of the frontal, sphenoid, maxilla, and ethmoid bones. THE NASAL FOSSAE 111 The roof is horizontal in the middle, but sloped downward in front and behind. The anterior slope is formed by the posterior surface of the nasal bone and the nasal process of the frontal; the horizontal portion corresponds to the cribriform plate of the ethmoid and the sphe- noidal concha; the posterior slope is formed by the inferior surface of the body of the sphenoid, the ala of the vomer, and a small portion of the sphenoidal process of the palate. The sphe- noidal sinus opens at the upper and back part of the roof into the spheno-ethmoidal recess, above the superior meatus. The floor is concave from side to side, and in the transverse diameter wider than the roof. It is formed mainly by the palatine process of the maxilla and completed posteriorly by the hori- zontal part of the palate bone. Near its anterior extremity, close to the septum, is the incisive canal. The septum or medial waO is formed by the perpendicular plate of the ethmoid, the vomer, the rostrum of the sphenoid, the crest of the nasal bones, the frontal spine, and the rnedian crest formed by the apposition of the palatine processes of the maxilte and the horizontal parts of the palate bones. The anterior border has a triangular outline limited above by the perpendicular plate of the ethmoid and below by the vomer, and in the recent state the defi- ciency is filled up by the septal cartilage of the nose. The posterior border is formed by the Fig. 136.- -Section throctgh the Nasal Fossa to show the Lateral Wall with THE Meatuses. Superior nasal concha Probe in sphenoidal foramen Sphenoidal sinus Sella turcica Superior meatus Spheno-palatine Uncinate process of ethmoid Internal pterygoid plate Palate bone Probe in posterior palatine canal Probe in naso- lachrymal canal Frontal sinus Agger nasi ?r — Lachrymal bone ■*■ Lower end of bristle in middle meatus Middle meatus r nasal concha Probe at lower end of naso-lachrymal canal where it opens into inferior meatus Incisive canal pharyngeal edge of the vomer, which separates the two choanaj. The septum, which is usually deflected from the middle line to one side or the other, is occasionally perforated, and in some cases a strip of cartilage, continuous with the triangular cartilage, extends backward between the vomer and perpendicular plate of the ethmoid (posterior or sphenoidal process). The lateral wall is the most extensive and the most comphcated on account of the forma- tion of the meatuses of the nose. It is formed by the frontal process and the medial surface of the maxilla, the lacrimal, the superior and inferior conchse of the ethmoid, the inferior nasal concha, the vertical part of the palate bone, and the medial surface of the medial pterygoid plate. The three conchae, which project medially, overhang the three recesses known as the meatuses of the nose. The superior meatus, the shortest of the three, is situated between the superior and middle nasal conch®, and into it open the orifice of the posterior ethmoidal cells and the spheno-palatine foramen. The middle meatus lies between the middle and inferior conchse. At its fore part it communicates with the frontal sinus by means of the infundibulum, and near the middle with the maxillary sinus (antrum); the communication with the sinus is very irregular and sometimes represented by more than one opening (fig. 136). Two sets of ethmoidal cells — the middle and anterior — also open into the middle meatus, the anterior in common with the infundibulum, the middle on an elevation known as the bulla ethmoidalis. The inferior meatus, longer than either of the preceding, is situated between the inferior nasal concha and the floor of the fossa, and presents, near the anterior part, the lower orifice of the canal for the naso-lacrimal duct. 112 THE SKELETON The nasal fossae open on the face by means of the apertura piriformis, a heart-shaped or piriform opening whose long axis is vertical and whose broad end is below. The orifice is bounded above by the lower borders of the nasal bones, laterally by the maxillae, inferiorly by the premaxillary portions of the maxiUae, and in the recent state the orifice is divided by the septal cartilage. Below, where the lateral margins slope inward to meet in the middle line, is the anterior nasal spine. The choanae (posterior nares) are bounded superiorly by the alae of the vomer, the sphe- noidal processes of the palate, and the inferior surface of the body of the sphenoid; laterally by the lateral pterygoid plates; and inferiorly by the posterior edge of the horizontal plates of the palate bones. They are separated from each other by the posterior border of the vomer. The nasal fossae communicate with all the more important fossae and the air-sinuses of the skull. By means of the foramina in the roof they are in connection with the cranial cavity; Fig. 137. — The Choan^. Veiwed from behind. Pharyngeal canals Pterygoid canal Foramen ovale Scaphoid fossa Pterygoid fossa Lateral pterygoid plate Tuberosity of palate bone Medial pterygoid plate Hamular process by the infundibulum each fossa is in communication with the frontal and anterior ethmoidal cells; the posterior ethmoidal cells open into the superior meatuses and the sphenoidal sinuses into the recesses above; the spheno-palatine foramina connect them with the pterygo-palatine fossae, and by means of an irregular orifice in each lateral wall they communicate with the max- illary sinuses. The canals for the naso-lacrimal ducts connect them with the orbits,Jand the incisive canals with the oral cavity. THE INTERIOR OF THE SKULL In order to study the interior of the skull it is necessary to make sections in three directions — sagittal, coronal, and horizontal. This enables the student to examine the various points with facility, and displays the great proportion the brain cavity bears to the rest of the skull. The sagittal section (fig. 138) should be made slightly to one side of the median line, in order to preserve the nasal septum. The black line (fig. 138) drawn from the basion (anterior margin of the foramen magnum) to the gonion (the anterior extremity of the sphenoid) represents the basi-cranial axis ; whilst the line drawn from the gonion to the subnasal point lies in the basi-facial axis. These two axes form an angle termed the cranio -facial, which is useful in making comparative measurements of crania. A line prolonged vertically upward from the basion will strike the bregma. This is the basi-bregmatic axis, and gives the greatest height of the cranial cavity. A line drawn from the ophryon to the occipital point indicates the greatest length of the cranium. Near its middle, the cranial cavity is encroached upon by the petrous portion of the temporal bone on each side; the walls are channelled vertically by narrow grooves for the middle and small meningeal vessels, and toward the base and at the vertex are broader furrows for the venous sinuses. The coronal section is most instructive when made in the basi-bregmatic axis. The section will pass through the petrous poition on each side in such a way as to traverse the external auditory passage and expose the tympanum and vestibule, and will also partially traverse the internal auditory meatus. Such THE INTERIOR OF THE SKULL 113 a section will divide the parietal bones slightly posterior to the parietal eminences, and a line drawn transversely across the section at the mid-point will give the greatest transverse measurement of the cranial cavity. A skull divided in this way facilitates the examination of the parts about the choanse (posterior nares) . The horizontal section (figs. 139, 140) of the skull should be made through a line extending from the ophiyon to the occipital point, passing laterally a few millimetres above the pterion on each side. It is of great advantage to study the various parts on the floor of the cranial cavity in a second skull in which the dura mater and its various processes have not been removed. The floor [basis cranii interna] of the cranial cavity presents three irregular depressions termed the anterior, middle, and posterior fossse (figs. 139 and 140). The Anterior Cranial Fossa. — The floor of this fossa is on a higher level than the rest of the cranial floor. It is formed by the horizontal plate of the frontal bone, the cribriform plate of the ethmoid, and the lesser wings of the Fig. 138. — The Skull in Sagittal Section. Bregma Ophryon sphenoid, which meet and exclude the body of the sphenoid from the anterior fossa. The free margins of the lesser wings and the anterior margin of the optic groove mark the limits of this fossa posteriorly. The central portion is depressed on each side of the crista galli, presents the numerous apertures of the cribriform plate, and takes part in the formation of the roof of the nasal fossse; laterally, the floor of the anterior cranial fossa is convex; it forms the roof of the orbits, and is marked by irregular furrows. It supports the frontal lobes of the cerebrum. The sutures traversing the floor of the fossa are the fronto-ethmoidal, forming three sides of a rectangle, that portion of the transverse facial suture which tra- verses the roof of the orbit, and the ethmo-sphenoidal suture, the centre of which corresponds to the gonion. The other points of interest in the fossa are:^ A groove for the superior sagittal sinus. The foramen caecum which frequently transmits a small vein to the nasal cavity. The crista galli. • The ethmoidal fissure for the anterior ethmoida,l branch of the fifth nerve. The cranial orifice of the anterior ethmoidal canal, transmitting the anterior ethmoidal branch of the fifth nerve, and a meningeal branch of the anterior ethmoidal artery. The cranial orifice of the posterior ethmoidal canal, transmitting a meningeal branch of the posterior ethmoidal artery. The ethmoidal spine of the sphenoid. Furrows for meningeal vessels. 114 THE SKELETON Fig. 139. — The Skull in Horizontal Section. Ethmoidal fissure for anterior eth- Ethmoidal foramina for olfactory nerve Ethmoid Optic foramen (for optic nerve) Foramen ovale (third divis trigeminus Notch for abducens nerve Interior auditory meatus (facial and auditory nerves) Jugular foramen (glosso-^ haryngeal vagus and accessary nerves) Hypoglossal foramen (hypoglossal nervo THE INTERIOR OF THE SKULL 115 Fig. 140. — The Skull in Horizontal Section. Frontal bo Ridge for falx cerebri Crista galli Anterior fossa Cribriform plate Lesser wing of sphenoid The limbus Optic groove- Pituitary fossa- Dorsum sellae. Petro-sphenoidal proces Internal occipital crest Internal occipital protuberance Foramen magnum 116 THE SKELETON The Middle Cranial Fossa, situated on a lower level than the anterior, consists of a central and two lateral portions. In front it is limited by the posterior borders of the lesser wings of the sphenoid and the anterior margin of the optic groove, behind by the dorsum sellse and the upper angle of the petrous portion of both temporal bones. Laterally it is bounded on each side by the squamous portion of the temporal, the great wing of the sphenoid, and the parietal bone, whilst the floor is formed by the body and great wings of the sphenoid and the anterior surface of the petrous portion of the temporals. It contains the follow- ing sutures: — spheno-parietal, petro-sphenoidal, squamo-sphenoidal, squamous, and a part of the transverse suture. The central portion of the fossa presents from before backward : The optic groove, above and behind which is the optic chiasma. The optic foramen on each side, transmitting the optic nerve and ophthalmic artery. The tuberculum sellae, indicating the hne of junction of pre- and post-sphenoid elements. The anterior clinoid processes. The fossa hypophyseos or sella turcica, with the middle clinoid processes, and grooves for the internal carotid arteries. The dorsum sellse, with the posterior clinoid processes, and notches for the sixth pair of cranial nerves. The central portion is in direct relation with the parts of the brain within the circle of Willis. The lateral portions are of considerable depth and marked by numerous elevations and depressions corresponding to the convolutions of the temporal lobes of the brain, and by grooves for the branches of the middle and small meningeal vessels. The following foramina are seen on each side: — The superior orbital (sphenoidal) fissure, leading into the orbit and transmitting the third, fom-th, three branches of the ophthalmic division of the fifth and sixth cranial nerves, some filaments from the cavernous plexus of the sympathetic, an ophthalmic vein, the orbital branch of the middle meningeal, and a recurrent branch of the lacrimal artery. The foramen rotundum, for the passage of the second division of the fifth nerve into the pterygo-palatine fossa. The foramen ovale, which transmits the third division of the fifth nerve with its motor root (mandibular nerve), the small meningeal artery, and the small superficial petrosal nerve. The foramen Vesalii (not always present) for a small vein. The foramen spinosum, for the middle meningeal artery and its venae comitantes; also the N. spinosus. The foramen lacerum is the irregular aperture between the body and great wing of the sphenoid, and the apex of the petrous portion of the temporal. In the recent state it is closed below by a layer of fibro-cartilage which is perforated by the Vidian nerve, a meningeal branch of the ascending pharynge.False ribs 138 THE SKELETON at twenty-five they form a single piece, but exhibit, even in advanced hfe, traces of their original separation. A sternal foramen is usually the result of non-union across the middle line or a defect of ossification. The metasternum is always imperfectly ossified, and does not join with the mesosternum till after middle life. The presternum and mesosternum rarely fuse. The dates given above for the various nuclei, and for the union of the various segments, are merely approximate, hence the sternum affords very uncertain data as to age. Abnormalities of the Sternum. — The mode of development of the sternum as described above is of importance in connection with some deviations to which it is occasionally subject. In rare instances the two lateral halves fail to unite, giving rise to the anomaly of a completely cleft sternum. The union of the two halves may occur in the region of the manubrium and fail below, whilst in other cases the upper and lower parts have fused but remain separate in the middle. The clefts are in many instances so small as not to be of any moment, and are not even recognised until the skeleton is prepared. In a few individuals, however, they have been so extensive as to allow the pulsation of the heart to be perceptible to the hand, and even to the eye, through the skin covering the defect in the bone. A common variation in the sternum is asymmetry of the costal cartilages. Instead of cor- responding, the cartilages may articulate with the sternum in an alternating manner. The cause of this asymmetry is not known. THE THORAX AS A WHOLE The bony thorax (fig. 166) is somewhat conical in shape, deeper behind than in front and compressed antero-posteriorly, so that in the adult it measures less in the sagittal than in the transverse axis. The posterior wall, formed by the thoracic vertebrae and the ribs as far Fig. 167.- -The Thorax. (Posterior view.) The scapulae are drawn from an X-ray photograph of a man 33 years old. outward as their angles, is convex from above downward, and the backward curve of the ribs produces on each side of the vertebrae a deep furrow, the costo-vertebral groove, in which the sacro-spinalis (erector spinoe) muscle and its subdivisions are lodged. The anterior wall is formed by the sternum and costal cartilages. It is slightly convex and inchned forward in its lower part, forming an angle of about 20° with the vertical plane. The lateral walls are formed by the ribs from the angles to the costal cartilages. The top of the thorax presents an elUp- tical aperture, the superior thoracic aperture, which measures on an average 12.5 centimetres (5 THE CLAVICLE 139 inches) transversely and 6.2 centimetres (2J inches) in its sagittal axis. It is bounded by the first thoracic vertebra behind, the upper margin of the manubrium sterni in front, and the first rib on each side. As the upper margin of the manubrium sterni is oftenest on a level with the disc between the second and third thoracic vertebrae, it follows that the plane of the open- ing is directed obliquely upward and forward. The angle of the sternum {angulus Ludovici) is usually opposite the body of the fifth thoracic vertebra and the xiphi-sternal junction corre- sponds to the disc between the ninth and tenth thoracic vertebrae. The lower aperture of the thorax is very irregular, and is formed by the twelfth thoracic vertebra behind, the twelfth ribs laterally, and in front by two curved lines, ascending one on either side from the last rib, along the costal margin to the lower border of the gladiolus. The two borders form the costal arch, which in the median line below the sternum forms the infrasternal angle. From this angle the xiphoid process projects downward. The intervals between the ribs are the intercostal spaces, and are eleven in number on each side. The ratio of the sagittal and the transverse diameter of the thorax forms the thoracic index, which is higher in the female and in children, in whom the thorax is more rounded. In the embryo, the index is very much higher, the sagittal diameter being greater than the transverse. In the early embryo, the index is nearly 200; at birth it is about 90. In the adults it_ varies from 70 to 75, averaging 2 or 3 per cent, lower in the male than in the female. It is also lower in the negro than in the white race. (Rodes, Zeitschr. f. Morph. u. Anthrop., Bd. 9.) //. THE APPENDICULAR SKELETON A. BONES OF THE UPPER EXTREMITY The bones of the upper extremity may be arranged in four groups correspond- ing to the division of the limb into four segments. In the shoulder are the clavicle and the scapula, which together constitute the pectoral or shoulder girdle; in the arm is the humerus; in the forearm are the radius and ulna; and in the hand the carpus, the metacarpus, and the phalanges. THE CLAVICLE The clavicle [clavicula] or collar bone (figs. 168, 169) is situated immediately above the first rib and extends from the upper border of the manubrium sterni, laterally and backward to the acromion process of the scapula. It connects the upper limb with the trunk, and is so arranged that whilst the medial end rests on the sterniun and first costal cartilage, the lateral end is associated with the scapula in all its movements, supporting it firmly in its various positions and preventing it from falling inward on the thorax. The clavicle is a long bone, and when viewed from the front presents a double curvature, so that it somewhat resembles in shape the italic letter /. The medial curve, convex forward, extends over two-thirds of the length of the bone; the lateral, concave forward, is smaller and confined to the lateral part. For descrip- tive purposes the clavicle may be divided into a medial prismatic portion, a lateral flattened portion, and two extremities. Prismatic portion. — The medial two-thirds of the bone, extending from the sternal extremity to a point opposite the coracoid process of the scapula, has the form of a triangular prism. This portion, however, is subject to considerable variations of form, being more cylindrical in ill-developed specimens and be- coming almost quadrangular when associated with great muscular development. In a typical specimen it is marked by three borders separating three surfaces. Of these, the anterior surface is convex and divided near the sternal end by a prominent ridge into two parts, a lower, giving origin to the clavicular portion of the pectoralis major; an upper, for the clavicular portion of the sterno-cleido- mastoid. Near the middle of the shaft the ridge disappears, the surface is smooth, and is covered by the platysma myoides. Occasionally this surface is pierced by a small canal, transmitting a cutaneous nerve from the cervical plexus. The posterior surface is concave, forming an arch over the brachial plexus and the subclavian artery, broadest medially and smooth in its whole extent. It gives origin near the sternal extremity to a part of the sterno-hyoid and occasion- ally to a few fibres of the sterno-thyreoid. Somewhere near the middle of this surface is a small foramen, directed laterally, for the chief nutrient artery of the bone, derived from the transverse scapular (suprascapular) artery. Sometimes the 140 THE SKELETON foramen is situated on the inferior surface of the bone, in the subclavian groove. On the inferior surface near the sternal end is a rough area, the costal tuberosity, about three-quarters of an inch in length, for the attachment of the costo- clavicular ligament, by which the clavicle is fixed to the first rib. More laterally is a longitudinal groove for the subclavius, bordered by two lips, to which the sheath of the muscle is attached. To the posterior of the two lips the layer of deep cer- vical fascia which binds down the posterior belly of the omo-hyoid to the clavicle is also attached. Of the three borders, the superior separates the anterior and posterior surfaces. Be- ginning at the sternal end, it is well-marked, becomes rounded and indistinct in the middle, whilst laterally it is continuous with the posterior border of the outer third. The posterior border separates the inferior and posterior surfaces and forms the posterior lip of the subclavian Fig. 168. — The Left Clavicle. Anterior (Superior surface.) Pectoralis major Epiphysial line groove. It begins at the costal tuberosity and can be traced laterally as far as the coracoid tubercle, an eminence on the under aspect of the bone near the junction of prismatic and flat- tened portions. The anterior border is continuous with the anterior border of the flattened portion and separates the anterior and inferior surfaces. Medially, it forms the lower boundary of the elliptical area for the origin of the pecloralis major, and approaches the posterior border. Near the middle of the bone it coincides with the anterior lip of the subclavian groove. Flattened portion. — The lateral third of the bone, extending from a point opposite the coracoid process of the scapula to the acromial extremity, is flat- Oblique line for Articular trapezoid capsule ligament Fig. 169. — The Left Clavicle. Posterior Coracoid tubercle for conoid ligament Subclavius (Inferior surface.) Costo -clavicular ligament and sterno- hyoid Sterno-thyreoid (occasional) Facet for first •costal cartilage sternal facet Acromial facet tened from above downward and presents two surfaces and two borders. The superior surface is rough and looks directly upward and gives attachment to the trapezius behind and the deltoid in front; between the two areas the surface is subcutaneous. On the inferior surface, near the posterior border, is a rough elevation, the coracoid (conoid) tubercle ; it overhangs the coracoid process and gives attachment to the conoid ligament. From the coracoid tubercle, a promi- nent ridge, the trapezoid or oblique line, runs laterally and forward to near the lateral end of the bone. To it the trapezoid ligament is attached. The conoid and trapezoid ligaments are the two parts of the coraco-clavicular liga- ment which binds the clavicle down to the coracoid process. The anterior border is sharp, gives origin to the deltoid muscle, and frequently presents near the junction of the flattened and prismatic portions a projection known as the deltoid tubercle. The posterior border is thick and rounded, and receives the insertion of the upper fibres of the trapezius. THE SCAPULA 141 Extremities. — The sternal extremity of the clavicle presents a triangular articular surface, directed medially, downward, and a little forward, slightly concave from before backward and convex from above downward, which articu- lates with a facet on the upper border of the manubrium sterni through an interposed interarticular fibro-cartilage. Of the three angles, one is above and two below. The postero-inferior angle is prolonged backward, and so renders this surface considerably larger than that with which it articulates; the superior angle receives the attachment of the upper part of the fibro-cartilage. The lower part of the surface is continuous with a facet on the under aspect of the bone, medial to the costal tuberosity, for the first costal cartilage. The circumference of the extremity is rough, and gives attachment to the interclavicular ligament above and the anterior and posterior sterno-clavicular ligaments in front and behind. The acromial extremity presents a smooth, oval, articular facet, flattened or convex, directed shghtly downward for the acromion; its border is rough, for the attachment of the capsule of the acromio-clavicular joint. Structure. — The clavicle consists e.\ternally of a compact layer of bone, much thicker in the middle and thinning out gradually toward the two extremities. There is no true medullary Fig. 170. — The Sternal Ends op Two Clavicles with Epiphyses. A, right clavicle from below and behind. B, left clavicle from below and behind. (From Royal College of Surgeons Museum.) Sternal epiphyses cavity, for the interior is occupied from end to end by cancellous tissue, the amount in the vari- ous parts of the bone being in inverse proportion to the thickness of the outer compact shell Ossification. — From observations made by F. P. Mall, D. C. L. Fitzwilliams, and E. Faw- cett it seems almost certain that there are two centres of ossification of the shaft of the clavicle, at the juncture of the middle and lateral thirds. They appear very early, about the fifth week of embryonic life, and rapidly fuse. The ossific process extends medially and laterally along the shaft toward the medial and lateral extremities, respectively. About the eighteenth year a secondary centre appears at the sternal end and forms a small epiphysis which joins the shaft about the twenty-fifth year. THE SCAPULA The scapula (figs. 171, 172) is a large flat bone, triangular in shape, situated on the dorsal aspect of the thorax, between the levels of the second and seventh ribs. Attached to the trunk by means of the clavicle and various muscles it articulates with the lateral end of the clavicle at the acromio-clavicular joint, and with the humerus at the shoulder-joint. The greater part of the bone con- sists of a triangular plate known as the body, from which two processes are prolonged: one anterior in position, is the coracoid; the other, posterior in posi- tion, is the spine, which is continued laterally into the acromion. The body presents for examination two surfaces, three borders, and three angles. The costal (anterior) surface, or venter, looks considerably medialward, is deeply concave, forming the subscapular fossa, and marked by several oblique lines which commence at the posterior border and pass obliquely upward and laterally; these lines or ridges divide the surface into several shallow grooves, from which the suhscapularis takes origin, whilst the ridges give attachment to the tendinous intersections of that muscle. The lateral third of the surface is smooth and overlapped by the subscapularis, whilst medially are two small flat areas in front of the upper and lower angles respectively, but excluded from the subscapular fossa by. fairly definite lines and joined by a ridge which runs close to the vertebral border. The ridge and its terminal areas serve for the insertion of the serratus anterior {magnus). The dorsal (posterior) surface is generally convex and divided by a prominent plate of bone — the spine — into two unequal parts. The hollow above the spine is the supraspinous fossa and lodges the supraspinatus muscle. The part below 142 THE SKELETON the spine is the infraspinous fossa; it is three times as large as the supraspinous fossa, is alternately concave and convex, and gives origin to the infraspinatus. The muscle is attached to its medial three-fourths and covers the lateral fourth, without taking origin from it. The infraspinous fossa does not extend as far as tlie axillary border, but is limited laterally by a ridge — the oblique hne— Which runs from the glenoid cavity — the large articular surface for the head of the humerus — downward and backward to join the posterior border a short dis- tance above the inferior angle. Tliis line, which gives attachment to a stout aponeurosis, cuts ofi an elongated surface, narrow above for the origin of the teres minor, and crossed near its middle by a groove for the circumflex (dorsal) artery of the scapula; below, the surface is broader for the origin of the teres major and occasionally a few fibres of the latissimus dorsi. The two areas are separated by a line which gives attachment to an aponeurotic septum situated between the two teres muscles. Fig. 171. — The Left Scapula. (Dorsal surface.) Coraco-acromial ligament Omo-hyoid and the superior transverse ligament Superior angle Rhomboideus major Teres ma jo The supra- and infraspinous fossa communicate through the great scapular notch at the lateral border of the spine, and through the notch the suprascapular nerve and transverse scapular artery are transmitted from one fossa to the other. Borders. — The three borders of the scapula are named superior, vertebral, and axillary. The superior is short and thin and extends from the upper angle to the coracoid process. Laterally it presents a deep depression, the scapular notch, to the extremities of which the superior transverse ligament is attached. Not infrequently the notch is replaced by a scapular foramen, and it is interesting to note that a bony foramen occurs normally in some animals, notably the great ant-eater (Myrmeco- phaga jubata). The notch or foramen transmits the suprascapular nerve, whilst the transverse scapular artery usually passes over the ligament. From the adjacent margins of the notch and from the ligament the posterior belly of the omo-hyoid takes origin. THE SCAPULA 143 The vertebral border (sometimes called the base) is the longest, and extends from the upper or medial to the lower angle of the bone. It is divisible into three parts, to each of which a muscle is attached: an upper portion, extending from the medial (superior) angle to the spine, for the insertion of the levator scapulae; a middle portion, opposite the smooth triangular area at the commencement of the spine, for the rhomhoideus minor; and the lowest and longest portion, extending below this as far as the inferior angle, for the rhomhoideus major, the attachment of which takes place through the medium of a fibrous arch. The axillary border is the thickest, and extends from the lower margin of the glenoid cavity to the inferior angle of the bone. Near its junction with the glenoid cavity there is a rough surface, about 2.5 cm. (1 in.) in length the in- fraglenoid tubercle, from which the long head of the triceps arises, and below Fig. 172. — The Left Scapula. (Ventral surface.) Trapezoid ligament Pectoralis minor Scapular notch Conoid lig Serratus anten Coraco-acromial ligament Biceps and coraco- brachialis Clavicular facet Glenoid fossa Articular capsule Triceps (middle or long head) the tubercle is the groove for the circumflex (dorsal) artery of the scapula. The upper two-thirds of the border is deeply grooved on the ventral aspect and gives origin to a considerable part of the subscapidaris. Angles. — The three angles are named medial, inferior, and lateral. The medial (or superior) angle, forming the highest part of the body, is thin, smooth, and either rounded or approximating a right angle. It is formed by the junction of the superior and vertebral borders and gives insertion to a few fibres of the levator scapula. The inferior angle, constituting the lowest part of the body, is thick, rounded, and rough. It is formed by the junction of axillary and vertebral borders, gives origin to the teres major, and is crossed liorizontally by the upper part of the lalissimus dorsi, the latter occasionally receiving from it a small slip of fleshy fibres. The lateral angle forms the expanded portion of the bone known as the head, bearing the glenoid cavity, and supported by a somewhat constricted neck. The 144 THE SKELETON glenoid cavity is a wide, shallow, pyriform, articular surface for the head of the humerus, directed forward and laterally, with the apex above and the broad end below. Its margin is raised, and affords attachment to the glenoid ligament, which deepens its concavity. The margin is not, however, of equal prominence throughout, being somewhat defective where it is overarched by the acromion, notched anteriorly, and emphasised above to form a small eminence, the supra- glenoid tubercle, for the attachment of the long head of the biceps. The circumference and adjoining part of the neck give attachment to the articular capsule of the shoulder-joint, and the anterior border to the three accessory ligaments of the capsule, known as the superior, middle, and inferior gleno-humeral folds. The superior fold (Flood's ligament) is attached above the notch near the upper end; of the two remaining folds, which together constitute Schlemm's ligament, the middle is attached immediately above the notch and the inferior below the notch. In the recent state the glenoid fossa is covered with hyaline cartilage. The neck is more prominent behind than before and below than above, where it supports the coracoid process. It is not separated by any definite boundary from the body. Processes. — The spine is a strong, triangular plate of bone attached obliquely to the dorsum of the scapula and directed backward and upward. Its apex is situated at the vertebral border; the base, corresponding to the middle of the neck, is free, concave, and gives attachment to the inferior transverse ligament, which arches over the transverse scapular (suprascapular) vessels and suprascapular nerve. Of the two borders, one is joined to the body, whilst the other is free, forming a prominent subcutaneous crest. The latter commences at the vertebral border, in a smooth triangular area, over which the tendon of the trapezius glides, usually without the intervention of a bursa, as it passes to its insertion into a small tubercle on the crest beyond. Further laterally, this border is rough, and presents two lips — a superior for the insertion of the trapezius and an inferior for the origin of the deltoid. Laterally the crest is continued into the acromion. The spine has two sm-faces, the superior, which also looks medialward and forward, is concave, contributes to the formation of the supraspinous fossa, and gives origin to the supraspinatus muscle; the inferior surface, also slightly concave, is directed lateralward and backward, forms part of the infraspinous fossa, and affords origin to the infraspinatus muscle. On both surfaces are one or more prominent vascular foramina. The acromion, a process overhanging the glenoid cavity, springs from the angle formed by the junction of the crest with the base of the spine. Somewhat crescentic in shape, it forms the summit of the shoulder and is compressed from above downward so as to present for examination two surfaces, two borders, and two extremities. The posterior part sometimes terminates laterally in a prominent acromial angle (meta- cromion) and the process then assumes a more or less triangular form. Of the two extremities, the posterior is continuous with the spine, whilst the anterior forms the free tip. The upper surface, directed upward, backward, and slightly lateralward, is rough and convex, and affords origin at its lateral part to a portion of the deltoid; the remaining part of this surface is sub- cutaneous. The lower surface, directed downward, forward, and slightly medialward, is con- cave and smooth. The medial border, continuous with the upper lip of the crest, presents, from behind forward, an area for the insertion of the trapezius; a small, oval, concave articular facet for the lateral end of the clavicle, the edges of which are rough for the acromio-clavioular ligaments; and, beyond this, the anterior extremity or tip, to which is attached the apex of the coraco-acromial ligament. The lateral border, continuous with the inferior lip. of the crest, is thick, convex, and presents three or four tubercles with intervening depressions; from the tubercles the tendinous septa in the acromial part of the deltoid arise, and from the depressions, some fleshy fibres of the same muscle. Projecting upward from the neck of the scapula is the coracoid process, bent finger-like,' pointing forward and laterally. It consists of two parts, ascending and horizontal, arranged at almost a right angle to each other. The ascending part arises by a wide root, extends upward and medially for a short distance, and is compressed from before backward; it is continuous above with the horizontal part and below with the neck of the scapula; the lateral border lies above the glenoid cavity and gives attachment to the coraco-humeral ligament; the medial border, which forms the lateral boundary of the scapular notch, gives attachment to the conoid ligament above and the transverse liga- ment below. Its anterior and posterior surfaces are in relation with the subscapularis and supraspinatus respectively. The horizontal part of the process runs forward and lateralward; it is compressed from above downward so as to present two borders, two surfaces, and a free extremity. The medial border gives insertion along its anterior half to the pectoralis minor and nearer the base to the oosto-coracoid membrane; the lateral border is rough for the coraco- acromial and coraco-humeral ligaments ;_the upper surface is irregular and gives insertion in THE SCAPULA 145 front to the ■pectoralis minor, and behind to the trapezoid ligament; the inferior surface is smooth and directed toward the glenoid cavity, which it overhangs; the free extremity or apex gives origin to the conjoined coraco-brachialis and short head of the biceps. The greater part of the body of the scapula and the central parts of the spinous process are thin and transparent. The coracoid and acromion processes, the crest of the spine and in- ferior angle, the head, neck, and axillary border, are thick and opaque. The young bone consists of two layers of compact tissue with an intervening cancellous layer, but in the transparent parts of the adult bone the middle layer has disappeared. The vascular foramina on the costal surface transmit twigs from the subscapular and transverse scapular (suprascapular) arteries; those in the infraspinous fossa, twigs from the circumflex (dorsal) and transverse scapular (suprascapular) arteries, the latter also giving off vessels which enter the foramina in the supra- spinous fossa. The acromion is supplied by branches from the thoraco-acromial (acromio- thoracic) artery. The line of attachment of the spinous process to the dorsum of the scapula is known as the morphological axis, and the obtuse angle in the subscapular fossa opposite the spine as the Fig. 173. — Ossification op the Scapula. The right Scapula at the twelfth year, showing the subcoracoid element (a little larger than half the natural size, i. e. ^). Acromial cartilage Subcoracoid element The Scapula at the third year, showing the caracoid element. (Anterior view.) Tee Scapula at birth. (Anterior view.) A B subscapular angle. From the axis three plates of bone radiate as from a centre, the prescapula forward, the mesoscapula laterally, and the postscapula backward, being named in accordance with the long axis of the body in the horizontal position. In the human subject the postscapula is greatly developed, and this is associated with the freedom and versatility of movement possessed by the upper limb. Ossification. — The scapula is ossified from nine centres. Of these, two (for the body of the scapula and the coracoid) may be considered as primary, and the remainder as secondary. The centre for the body appears in a plate of cartilage near the neck of the scapula about the eighth week of intra-uterine life, and quickly forms a triangular plate of bone, from which the spine appears as a slight ridge about the middle of the third month. At birth the glenoid fossa and part of the scapular neck, the acromion and coracoid processes, the vertebral border and inferior angle, are cartilaginous. During the first year a nucleus appears for the coracoid, and at the tenth year a second centre appears for the base of the coracoid and the upper part of the glenoid cavity (subcoracoid, fig. 173). During the fifteenth year the coracoid unites with the scapula, and about this time the other secondary centres appear. Two nuclei are deposited in the acromial cartilage, and fuse to form the acromion, which joins the spine at the twentieth year. The union of spine and acromion may be fibrous, hence the latter is sometimes found separate in macerated specimens. The cartilage along the vertebral border ossifies from two centres, one in the middle, and another at the inferior angle. A thin lamina is added along the upper surface of the coracoid process and 146 THE SKELETON occasionally another at the margin of the glenoid cavity. These epiphyses join by the twenty- fifth year. The occurrence of a special primary centre for the coracoid process is of morphological im- portance in that the process is the representative of what in the lower vertebrates is a distinct coracoid hone. This primarily takes part in the formation of the glenoid cavity and extends medially to articulate with the sternum. In man and all the higher mammals only the lateral portion of the bone persists. THE HUMERUS The^humerus (figs. 174, 175, 176) is the longest and largest bone of the upper limb, and extends from the shoulder above, where it articulates with the scapula. Fig. 174. — The Left Humerxts. (Anterior view.) Subscapularis- Latissimus dorsi- Teres major -Intertubercular groove Pectoralis major Coraco-brachialis - -Brachio-radialis ' carpi radialis longus iiKl Pronator teres- Fexor carpi radialis . Palmaris longus Flexor digitorum sublimis Flexor carpi ulnaris I Extensor carpi radialis brevis J Extensor digitorum communis F Extensor digiti quinti proprius Extensor carpi ulnaris Supinator to the elbow [cubitus] below, where it articulates with the two bones of the fore- arm [anti-brachium]. It is divisible into a shaft and two extremities; the upper extremity includes the head [caput], neck [collum], and two tuberosities — great and small; the lower extremity includes the articular surface ^\dth the surmounting fossae in front and behind, and the two epicondyles. THE HUMERUS 147 Upper extremity. — The head forms a nearly hemispherical articular surface, cartilage-clad in the recent state and directed upward, medially, and backward toward the glenoid cavity. Below the head the bone is rough and somewhat constricted, constituting the anatomical neck, best marked superiorly, where it forms a groove separating the articular surface from the two tuberosities. The circumference of the neck gives attachment to the capsule of the shoulder-joint and the gleno-humeral folds, the upper of which is received into a depression near the top of the intertubercular (bicipital) groove. The lowest part of the capsule Fig. 175. — The Left HuMERtrs. (Posterior view.) Articular capsule Infraspinatus Triceps (lateral head)- Groove for radial nerve- Triceps (medial bead)- Articular capsule 1 fossa- Lateral epicondyle Anconeus and radial collateral ligament -Medial epicondyle descends upon the humerus some distance from the articular margin. Laterally and in front of the head are the two tuberosities, separated by a deep furrow. The greater tuberosity [tuberculum majus], lateral in position and reaching higher than the lesser tuberosity [tuberculum minus}, is marked by three facets for the insertion of muscles: an upper one for the supraspinatus, a middle for the in- 148 THE SKELETON fraspinatiis, and a lower for the teres minor. The lesser tuberosity is situated in front of the head and is the more prominent of the two ; it receives the insertion of the subscapularis. The furrow between the tuberosities lodges the long tendon of the biceps and forms the commencement of the intertubercular (bicipital) groove, which extends downward along the shaft of the humerus. Between the tuberosities the transverse humeral ligament converts the upper end of the groove into a canal. In addition to the long tendon of the biceps and its tube of synovial Fig. 176. — The Left Humerus with a Suphacondyloid Process and some Irregular Muscle Attachments. (Anterior view.) Lesser tuberosity_ Subscapula Capsular ligament- brevis (Rotator_ - Greater tuberosity -Transverse humeral ligament -Fourth head of biceps Intertubercular groove- Coraco-brachialis- -Rough surface for deltoid Third head of biceps- . The lateral condylar ridge Pronator teres- Medial epicondyle Ulnar collateral ligament ~ Trochlea - -Radial fossa ^"I'i- Lateral epicondyle ip- Capitulum membrane, the groove transmits a branch of the anterior circumflex artery. Immediately below the two tuberosities the bone becomes contracted and forms the surgical neck. The shaft or body [corpus humeri] is somewhat cylindrical above, flattened and prismatic below. Three borders and three surfaces may be recognised. Borders. — The anterior border commences above at the greater tuberosity, and its upper part, forming the crest of this tuberosity [crista tuberculi majoris], THE HUMERUS 149 receives the pectoralis major. In the middle of the shaft it is rough and prominent and gives insertion to fibres of the deltoid; below it is smooth and rounded, giviiig origin to fibres of the brachialis, and finally it passes along lateral to the coronoid fossa to become continuous with the ridge separating the capitulum and trochlea. It separates the antero-medial from the antero-lateral surface. The lateral margin extends from the lower and posterior part of the greater tuberosity to the lateral epicondyle. Smooth and indistinct above, it gives attachment to the teres minor and the lateral head of the triceps; it is interrupted in the middle by the groove for the radial nerve (musculo-spiral groove), but the lower third becomes prominent and curved laterally to form the lateral supracondylar ridge, which affords origin in front to the brachio-radialis and the extensor carpi radialis longus; behind to the medial head of the triceps, and between these muscles in front and behind to the lateral intermuscular septum. It separates the antero-lateral from the posterior surface. The medial border commences at the lesser tuberosity, forming its crest which receives the insertion of the teres major, and continuing downward to the medial epicondyle. Near the middle of the shaft it forms a ridge for the insertion of the coraco-brachialis and presents a foramen for the nutrient artery, directed downward toward the elbow-joint. Below it forms a distinct medial supracondylar ridge, curved medially, which gives origin to the brachialis in front, the medial head of the triceps behind, and the medial intermuscular septum in the interval between the muscles. This border separates the antero-medial from the posterior surface. Fig. 177. — A Diagram showing Prbssuee and Tension Curves in the Head OF THE Humerus. (After Wagstaffe.) Surfaces. — The antero-lateral surface is smooth above, rough in the middle, forming a large impression for the insertion of the deltoid, below which is the termination of the groove for the radial nerve. The lower part of the surface gives origin to the lateral part of the brachialis. The antero-medial surface is narrow above, where it forms the floor of the intertubercular (bicipital) groove, and receives the insertion of the latissimus dor si. Near the junction of the upper and middle thirds of the bone the groove, gradually becoming shallower, widens out and, with the exception of a rough impression near the middle of the shaft for the coraco-brachialis, the remaining part of the antero-medial surface is flat and smooth, and gives origin to the brachialis. Occasionally, a prominent spine of bone, the supracondylar process, projects downward from the medial border about 5 cm. (2 in.) above the medial epicondyle, to which it is joined by a band of fibrous tissue. Through' the ring thus formed, which corresponds to the supracon- dylar foraman in many of the lower animals, the median nerve and brachial artery are trans- mitted, though in some cases it is occupied by the nerve alone. The process gives origin to the pronator teres, and may afford insertion to a persistent lower part of the coraco-brachialis. The posterior surface is obliquely divided by a broad shallow groove, which runs in a spiral direction from behind downward and forward and transmits the radial (musculo-spiral) nerve and the profunda artery. The lateral part of the surface above the groove gives attachment to the lateral head, and the part below the groove, to the medial head of the triceps. The lower extremity of the humerus is flattened from before backward, and terminates below in a sloping articular surface, subdivided by a low ridge into the 150 THE SKELETON trochlea and the capitulum. The trochlea is the pulley-hke surface which extends over the end of the bone for articulation with the semilunar notch (great sigmoid cavity) of the ulna. It is constricted in the centre and expanded laterally to form two prominent edges, the medial of which is thicker, descends lower, and forms a marked projection; the lateral edge is narrow and corresponds to the interval between the ulna and radius. Above the trochlea are two fossae : on the anterior surface is the coronoid fossa, an oval pit which receives the coronoid process of Fig. 178.- -ossification of the humerus ; the figure also shows the relations of the Epiphysial and Capsular Lines nites with the shaft at the twentieth year. The upper epiphysis is formed by the union of the nucleus- for the head, greater tuberosity, and that for the lesser tuberosity. These form a common epiphysis before uniting with the shaft Capsular line^ Shaft begins to ossify in the eighth week of intra-uterine life 1 r#^ Capsular line Nucleus for the medial epicondyle i appears at fifth, fuses at ***" ' eighteenth year Nucleus for trochlea appears at the - tenth year Nucleus for lateral epicondyle ap- pears at fourteenth year _ Nucleus for capitulum appears in the third year The centres for the radial epicondyle, trochlea, and capitulum unite to- gether and form an epiphysis which fuses with the shaft at the seven- teenth year the ulna when the forearm is flexed; on the posterior aspect is the olecranon fossa, a deep hollow for the reception of the anterior extremity of the olecranon in exten- sion of the forearm. These fossae are usually separated by a thin, translucent plate of bone, sometimes merely by fibrous tissue, so that in macerated specimens a perforation, the supratrochlear foramen, exists. The capitulum, or radial head, is much smaller than the trochlea, somewhat globular in shape, and limited to the anterior and inferior surfaces of the extremity. It articulates with the con- THE HUMERUS 151 cavity on the summit of the radius. The radial fossa is a slight depression on the front of the bone, immediately above the capitulum, which receives the anterior edge of the head of the radius in complete flexion of the forearm, whilst between the capitulum and the trochlea is a shallow groove occupied by the medial margin of the head of the radius. In the recent state the inferior articular surface is covered with cartilage, the fossae are lined by synovial membrane, and their margins give attachment to the capsule of the elbow-joint. Projecting on either side from the lower end of the humerus are the two epicondyles. The medial one is large and by far the more prominent of the two, rough in front and below, smooth behind, where there is a shallow groove for the ulnar nerve. The rough area serves for origin of the pronator teres above, the common tendon of origin of the flexor carpi radialis, palmaris longus, flexor digitorum sublimis and flexor carpi ulnaris in the middle, and the ulnar collateral ligament below. The lateral epicondyle is flat and irregular. Above, it gives attachment to a common tendon of origin of the extensor carpi radialis brevis, extensor digitorum communis, extensor quinti digiti proprius, extensor carpi ulnaris, and supinator; to a depression near the outer margin of the capitulum, the radial collateral ligament is attached, and from an area below and behind, the anconeus takes origin. Architecture. — The interior of the shaft of the humerus is hollowed out by a large medullary canal, whereas the extremities are composed of cancellated tissue invested by a thin compact layer. The arrangement of the cancellous tissue at the upper end of the humerus is shown in fig. 177. The lamellae converge to the axis of the bone and form a series of superimposed arches which reach upward as far as the epiphysial line. In the epiphyses the spongy tissue forms a fine network, the lamellae resulting from "pressure" being directed at right angles to the articular surface of the head and to the great tuberosity. Blood-supply. — The foramina which cluster round the circumference of the head and tuber- osities transmit branches from the transverse scapular (suprascapular) and anterior and pos- terior circumflex arteries. At the top of the intertubercular groove is a large nutrient foramen Fig. 179. — The Head of the Humebus at the Sixth Year. (In section.) The centre for the head appears during the first year; it is some- times present at birth The centre for the greater tuberosity appears in the third year for a branch of the anterior circumflex artery which supplies^the head. The nutrient artery of the shaft is derived from the brachial, and in many cases, an additional branch, derived from the profunda artery, enters the foramen in the groove for the radial nerve (musculo-spiral groove) . The lower extremity is nourished by branches derived from the profunda (superior profunda) , the superior and inferior ulnar collateral (inferior profunda and anastomotic), and the recurrent branches of the radial, ulnar, and interosseous arteries. Ossification. — The humerus is ossified from one primary centre (diaphysial) and six second- ary centres (epiphysial). The centre for the shaft appears about the eighth week of intra- uterine life and grows very rapidly. At birth only the two extremities are cartilaginous, and these ossify in the following manner: Single centres appear for the head in the first year, for the greater tuberosity in the third year, and for the lesser tuberosity in the fifth year, though sometimes the latter ossifies by an extension from the greater tuberosity. These three nuclei coalesce at six years to form a single epiphysis, which joins the shaft about the twentieth year. The inferior extremity ossifies from four centres: one for the capitulum appears in the third year, a second for the medial epicondyle in the fifth year, a third for the trochlea in the tenth year, and a fourth for the lateral epicondyle in the fourteenth year. The nuclei for the capitu- lum, trochlea, and lateral epicondyle coalesce to form a single epiphysis which joins the shaft in the seventeenth year. The nucleus of the medial epicondyle joins the shaft independently at the age of eighteen years. A study of the upper end of the humeral shaft before its union with the epiphysis is of interest in relation to what is known as the neck of the humerus. The term neck is appUed to three parts of this bone. The anatomical neck is the constriction to which the articular capsule is mainly attached, and its position is accurately indicated by the groove which Ues internal to the tuberosities. The upper extremity of the humeral shaft, before its union with the epiphysis , terminates in a low three-sided pyramid, the surfaces of which are separated from one another by ridges. The medial of these three surfaces underlies the head of the bone, and the two lateral surfaces underhe the tuberosities. The part supporting the head constitutes the morpho- logical neck of the humerus, whilst the surgical neck is the indefinite area below the tuberosities where the bone is liable to fracture. 152 THE SKELETON THE RADIUS The radius (figs. 180-185) is the lateral and shorter of the two bones of the forearm. Above, it articulates with the humerus; below, with the carpus; and on the medial side with the ulna. It presents for examination a shaft and two extremities. The upper extremity, smaller than the lower, includes the head, neck, and tuberosity. The head [capitulum], covered with cartilage in the recent state, i& a circular disc forming the expanded, articular end of the bone. Superiorly it presents the capitular depression [fovea capituli] for the reception of the capitulum Fig. 180. — The Left Ulna and Radius. (Antero-medial view.) Articular capsule" ^^*- %;^ Ulnar collateral ligament^ Tubercle for the flexor digitorum sublimis — Ulnar collateral ligament — Brachialis — Pronator teres (lesser head) — Flexor pollicis longus (accessory head) — Interosseous membrane. Flexor digitorU|BU profundu "'Semilunar notch ^Head of radius "Neck of radius "Lower Umit of annular ligament -Oblique ligament - Tuberosity "Oblique ligament -Supinator Flexor sublimis digitorum ObUque line Radius ■ Pronator teres Flexor pollicis longus Pronator quadratus . Anterior radio-ulnar ligament- Ulnar collateral ligament' Pronator quadratus Interarticular fibro-cartilage Brachio-radialis Radial collateral ligament Anterior radio-carpal ligament of the humerus; its circumference [circumferentia articularis], deeper on the medial aspect, articulates with the radial notch (lesser sigmoid cavity) of the ulna, and is narrow elsewhere for the annular ligament by which it is embraced. Below the head is a short cylindrical portion of bone, somewhat constricted, and known as the neck. The upper part is surrounded by the hgament which embraces the head, and below this it gives insertion antero-laterally to the supinator. Below the neck, at the antero-medial aspect of the bone, is an oval eminence, the radial tuberosity, divisible into two parts: a rough posterior portion for the insertion of THE RADIUS 153 the tendon of the biceps, and a smooth anterior surface in relation with a bursa which is situated between the tendon and the tuberosity. The body [corpus radii] or shaft is somewhat prismatic in form, gradually in- creasing in size from the upper to the lower end, and slightly curved so as to be concave toward the ulna. Three borders and three surfaces may be recognised. Of the borders, the medial or interosseous crest [crista interossea] is best marked. Commencing at the posterior edge of the tuberosity, its first part is round and in- distinct, and receives the attachment of the oblique cord of the radius; it is con- FiG. 181. — The Left Ulna and Radius. (Postero-lateral view.) Triceps -yjy^^^ Articular capsule ^^mMi Olecranon Subcutaneous surface Lower limit of annular ligament " Abductor pollicis longus- Extensor pollicis brevis- -Abductor pollicis longus An aponeurosis is attached to this border from which the flexor and extensor carpi ulnaris, and flexor digitorum profundus arise - Extensor polHcis longus Ulna -Extensor indicis proprius Grooves for abductor longus and ex- tensor pollicis hrevis For extensor carpi radialis longus^ and brevis ~~ Extensor pollicis longus- -Ettensor quinti digiti proprius -iiixtensor carpi ulnaris ^Ulnar collateral ligament Extensor digitorum communis and Posterior Posterior radio-ulnar ligament extensor indicis proprius radio-carpal ligament tinned as a sharp ridge which divides near the lower extremity to become continu- ous with the anterior and posterior margins^of the ulnar notch (sigmoid cavity). The prominent ridge and the posterior of the two lower lines give attachment to the interosseous membrane, whilst the triangular surface above the ulnar notch receives a part of the pronator quadratus. The interosseous crest separates the volar from the dorsal surface. The volar border [margo volaris] runs from the tuberosity obliquely downward to the lateral side of the bone and then descends vertically to the anterior border of the styloid process. The upper third, consti- 154 THE SKELETON tuting the oblique line of the radius, gives origin to the radial head of the flexor digitorum suhlimis, limits the insertion of the supinator above, and the origin of the flexor pollicis longus below. The volar border separates the volar from the lateral surface. The dorsal border extends from the back of the tuberosity to the prominent middle tubercle on the posterior aspect of the lower extremity. Separating the lateral from the dorsal surface, it is well marked in the middle third, but becomes indistinct above and below. Surfaces. — The volar (or anterior) surface is narrow and concave above; broad, flat, and smooth below. The upper two-thirds is occupied chiefly by the flexor pollicis longus and a little less than the lower third by the pronator quadratus. Near Fig. 182. — Articulae Facets on the Lower End op Left Radius and Ulna. Posterior For naviculi For Iunat( styloid process of ulna Head of ulna : it articulates with the interarticular fibro-cartilage of the wrist-joint the junction of the upper and middle thirds of the volar surface is the nutrient fora- men, directed upward toward the proximal end of the bone. It transmits a branch of the volar interosseous artery. The lateral surface is rounded above and affords insertion to the supinator; marked near the middle by a rough, low, vertical ridge for the pronator teres; smooth below, where the tendons of the exten- sor carpi radialis longus and brevis lie upon it, and where it is crossed by the abductor pollicis longus and extensor pollicis brevis. The dorsal (or posterior) surface, smooth and rounded above, is covered by the supinator; grooved longi- tudinally in the middle third for the abductor pollicis longus and the extensor pollicis Fig. 183. — Dorsal View op the Lower End op the Radius and Ulna. Insertion of brachio -radialis Abductor pollicis longus and ext. pollicis brevis i Extensor carpi radialis longus | and brevis r Tubercle for posterior annular- — p-j ligament fcii^ Extensor pollicis longus \\j styloid process Ext. digitorum communis and extensor indicis proprius Extensor quinti digiti proprius lies in the groove between the radius and ulna Extensor carpi ulnaris Styloid process brevis; the lower third is broad, rounded, and covered by tendons. The line which forms the upper limit of the impression for the abductor pollicis longus is known as the posterior oblique line. The lower extremity of the radius is quadrilateral; its carpal surface [facies articularis carpea] is articular and divided by a ridge into a medial quadrilateral portion, concave for articulation with the lunate bone; and a lateral triangular portion, extending onto the styloid process for articulation with the navicular (scaphoid) bone. The medial surface, also articular, presents the ulnar notch (sigmoid cavity) for the reception of the rounded margin of the head of the ulna. To the border separating the ulnar and carpal articular surfaces the base of the THE ULNA 155 articular disc is attached, and to the anterior and posterior borders, the anterior and posterior radio-ulnar ligaments respectively. The anterior surface is raised into a prominent area for the anterior ligament of the wrist-joint. The lateral surface is represented by the styloid process, a blunt pyramidal eminence, to the base of which the hrachio-radialis is inserted, whilst the tip serves for the attach- ment of the radial (external) collateral ligament of the wrist. Its lateral surface is marked by two shallow furrows for the tendons of the abductor pollicis longus and extensor pollicis brevis. The posterior surface is convex, and marked by three prominent ridges separating three furrows. The posterior annular ligament is attached to these ridges, thus forming with the bone a series of tunnels for the passage of tendons. The most lateral is broad, shallow, and frequently subdivided by a low ridge. The lateral subdivision is for the extensor carpi radialis longus, the medial for the extensor carpi radialis brevis The middle groove is narrow and deep for the tendon of the extensor pollicis longus. The most medial is shallow and transmits the extensor indicts proprius, the extensor digitorum communis, the dorsal branch of the interosseous artery, and the dorsal interosseous nerve. When the radius and ulna are articulated, an additional groove is formed for the tendon of the extensor quinti digiti proprius. Ossification. — The radius is ossified from a centre which appears in the middle of the shaft in the eighth week of intra-uterine hfe and from two epiphysial centres which appear after birth. The nucleus for the lower end appears in the second year, and that for the upper end, which forms simply the disc-shaped head, in the fifth year. The head unites with the shaft at the seventeenth year, whilst the inferior epiphysis and the shaft join about the twentieth year. THE ULNA The ulna (figs. 180, 181, 189) is a long, prismatic bone, thicker above than below, on the medial side of the forearm and parallel with the radius, which it Fig. 184. — Upper End of Left Ulna. (Lateral view.) Olecranon- Semilunar notch Coronoid process Annular ligament Flexor digitorum profundu Radial notch Oblique ligament iPilI) HI S Supinator Interosseous membn exceeds in length by the extent of the olecranon process. It articulates at the upper end with the humerus, at the lower end indirectly \vith the carpus, and on the lateral side with the radius. It is divisible into a shaft and two extremities. The upper extremity is of irregular shape and forms the thickest and strongest part of the bone. The superior articular surface is concave from above dowTiward, convex from side to side, and transversely constricted near the middle. It belongs 156 THE SKELETON partly to the olecranon, the thick upward projection from the shaft, and partly to the coronoid process, whicli projects horizontally forward from the front of the ulna. This semilunar excavation forms the semilunar notch (greater sigmoid cavity) and articulates with the trochlear surface of the humerus. The olecranon is the large curved eminence forming the highest part of the bone. The superior surface of the olecranon, uneven and somewhat quadrilateral in shape, receives behind, where there is a rough impression, the insertion of the triceps, and along the anterior margin the articular capsule of the elbow-joint. The posterior surface, smooth and triangular in outline, is separated from the skin by a bursa. The anterior surface, covered with cartilage in the recent state, is dii'ected downward and forward, and its margins give attachment to the articular capsule of the elbow-joint. This surface, as already noticed, forms the upper and back part of the semilunar notch. On the medial surface of the olecranon is a tubercle for the origin of the ulnar head of the flexor carpi ulnaris, and in front of this a fasciculus of the ulnar collateral ligament of the elbow-joint is attached to the bone; the lateral surface is rough, concave, and gives insertion to a part of the anconeus. The extremity of the olecranon lies during extension of the elbow in the olecranon fossa of the humerus. Fig. 185. — Ossification of the Radius and Ulna; the Figure also shows the Relations OP THE Epiphysial and Capsular Lines. Appears at the fifth year ; fuses at the seventeenth year Appears at the second year; fuses at the twentieth year The coronoid process, forming the lower and anterior part of the semilunar notch, has a superior articular surface continuous with the anterior surface of the olecranon, and, like it, covered with cartilage. The inferior aspect is rough and concave, and gives insertion to the brachialis. It is continuous with the volar surface of the shaft, and near the junction of the two is a rough eminence, named the tuberosity of the ulna, which receives the attachment of the obhque cord of the radius and the insertion of the brachialis. The medial side presents above a smooth tubercle for the origin of the ulnar portion of the flexor digitorum suhlimis, and a ridge below for the lesser head of the pronator teres and the rounded accessory bundle of the flexor pollicis longus, whilst immediately behind the subhmis tubercle there is a triangular depressed surface for the upper fibres of the flexor digitorum profundus. THE ULNA 157 On the lateral surface is the radial notch (lesser sigmoid cavity), an oblong articular surface which articulates with the circumference of the head of the radius, the anterior and posterior margins of which afford attachment to the annular ligament and the radial collateral ligament of the elbow-joint. In flexion of the elbow the tip of the process is received into the coronoid fossa of the humerus. The body [corpus ulnae] or shaft throughout the greater part of its extent is three-sided, but tapers toward the lower extremity, where it becomes smooth and rounded. It has three borders and three surfaces. Of the three borders, the lateral, the interosseous crest, is best marked. In the middle three-fifths of the shaft it is sharp and prominent, but becomes indistinct below; above it is contin- ued by two lines which pass to the anterior and posterior extremities of the radial notch and enclose a depressed triangular area (bicipital hollow), the fore part of which lodges the tuberosity of the radius and the insertion of the biceps tendon during pronation of the hand, while from the posterior part the supinator takes origin. The interosseous crest separates the volar from the dorsal surface and gives attachment by the lower four-fifths of its extent to the interosseous mem- brane. The volar border is directly continuous with the medial edge of the rough surface for the brachialis and terminates inferiorly in front of the styloid process. Fig. 186. — Upper End of Ulna Showing Two Epiphyses. (E. Faweett.) " Beak centre Scale on summit of olecranon t^^WMwk 1 Semilunar notch Throughout the greater part of its extent it is smooth and rounded, and affords origin to the flexor digitorum profundus and the pronator quadratus. It separates the volar from the medial surface. The dorsal border commences above at the apex of the triangular subcutaneous area on the back of the olecranon, and takes a sinuous course to the back part of the styloid process. The upper three-fourths gives attachment to an aponeurosis common to three muscles, viz., the flexor and extensor carpi ulnaris and the. flexor digitorum profundus. This Isorder separates the medial from the dorsal surface. Surfaces. — The volar (or anterior) surface is grooved in the upper three- fourths of its extent for the origin of the flexor digitorum profundus, narrow and convex below, for the origin of the pronator quadratus. The upper limit of the area for the latter muscle is sometimes indicated by an oblique line — the pronator ridge. Near the junction of the upper and middle thirds of the anterior surface is the nutrient foramen, directed upward toward the proximal end of the bone. It transmits a branch of the volar interosseous artery. The medial surface, smooth and rounded, gives attachment, on the upper two-thirds, to the flexor digitorwn profundus, whereas the lower third is subcutaneous. The dorsal (or posterior) surface, directed laterally as well as backward, presents at its upper part the oblique line of the ulna running from the posterior extremity of the radial notch to the dorsal border. 158 THE SKELETON The oblique line gives attachment to a few fibres of the supinator and marks off the posterior surface into two unequal parts. That above the hne, much the smaDer of the two, receives the insertion of the anconeus. The more extensive part below is subdivided by a vertical ridge into a medial portion, smooth, and covered by the extensor carpi ulnaris, and a lateral portion which gives origin to three muscles, viz., the abductor pollicis longus, the extensor pollicis longus and the extensor indicis proprius, from above downward. The lower extremity of the uhia is of small size and consists of two parts, the head and the styloid process, separated from each other on the inferior surface by a groove into which the apex of the articular disc is inserted. That part of the head adjacent to the groove is semilunar in shape and plays upon the articular disc which thus excludes the ulna from the radio-carpal or wrist-joint. The margin of the head is also semilunar, and is received into the ulnar notch of the radius. The styloid process projects from the medial and back part of the bone, and appears as a continuation of the dorsal border. To its rounded summit the ulnar collateral ligament of the wrist-joint is attached, and its dorsal surface is grooved for the passage of the tendon of the extensor carpi ulnaris. Immediately above the articular margin of the head the anterior and posterior radio-ulnar ligaments are attached in front and behind. Fig. 187. — The Left Radius and Ulna in Pronation. (Anterior view.) Ossification. — The ulna is ossified from three centres. The primary nucleus appears near the middle of the shaft in the eighth week of intra-uterine life. At birth the inferior extremity and the greater portion of the olecranon are cartilaginous. The "nucleus for the lower end ap- pears during the fourth year and the epiphysis joins with the shaft from the eighteenth to the twentieth year. The greater part of the olecranon is ossified from the shaft, but an epiphysis is subsequently formed from a nucleus which appears in the tenth year. The epiphysis varies in size, and may be either scale-like and form a thin plate on the sum- mit, or involve the upper fourth of the olecranon and the corresponding articular surface. In the latter case the epiphysis is probably composed of two parts fused together: (1) The scale on the summit of the olecranon process, and (2) the beak centre which enters into the formation of the upper end of the semilunar notch (see fig. 186). The epiphysis unites to the shaft in the sixteenth or seventeenth year. THE CARPUS 159 THE CARPUS The carpus (figs. 188, 189) consists of eight bones, arranged in two rows, four bones in each row. Enumerated from the radial to the ulnar side, the bones of the proximal row are named navicular (scaphoid), lunate (semilunar), triquetral (cuneiform), and pisiform; those of the distal row, greater multangular (trape- zium), lesser multangular (trapezoid), capitate (os magnum), and hamate (unciform) . When the bones of the carpus are articulated, they form a mass somewhat quad- rangular in outline, wider below than above, and with the long diameter trans- verse. The dorsal surface is convex and the volar surface concave from side to side. The concavity is increased by four prominences, which project forward, one Fig. 188. — Bones of the Left Hand. (Dorsal surface.) Lunate Extensor carpi radialis longus Extensor carpi, radialis brevis Extensor digitorum communis Extensor digitorum communis Third, ungual, or terminal phalanx from each extremity of each row. On the radial side are the tuberosity of the navicular and the ridge of the greater multangular; on the ulnar side, the pisiform and the hook of the hamate. Stretched transversely between these prominences, in the recent state, is the transverse carpal ligament forming a canal for the passage of the flexor tendons and the median nerve into the palm of the hand. The proxi- mal border of the carpus is convex and articulates with the distal end of the radius and the articular disc. The pisiform, however, takes no share in this ar- ticulation, being attached to the volar surface of the triquetral. The distal border forms an undulating articular surface for the bases of the metacarpal bones. The 160 THE SKELETON line of articulation between the two rows of the carpus is concavo-convex from side to side, the lateral part of the navicular being received into the concavity formed by the greater multangular, lesser multangular, and capitate, and the capitate and hamate into that formed by the navicular, lunate, and triquetral bones. Fig. 189. — -Bones of the Left Hand. (Volar surface.) Adductor poUicis obliquus Abductor polUcis brevis Flexor carpi ulnaris Abductor digiti quinti Flexor brevis and opponens digiti quinti Flexor carpi ulnaris Adductor pollicis transversus Opponens digiti quinti Opponens and flexor brevis pollicis Occasional insertion into greater multangular Abductor pollicis longus carpi radialis ep head of flexor pollicis brevis (ist volar interosseus) Opponens pollicis iexor brevis and abductor poUicis Abductor pollicis and ist volar interosseus Abductor and flexor brevis digiti quinti The individual carpal bones have several points of resemblance. Each bone (excepting the pisiform) has six surfaces, of which the anterior or volar and poste- rior or dorsal are rough for the attachment of ligaments, the volar surface being the broader in the proximal row, the dorsal surface in the distal row. The supe- rior and inferior surfaces are articular, the former being generally convex and the latter concave. The lateral surfaces, when in contact with adjacent bones, are also articular, but otherwise rough for the attachment of ligaments. Further, the whole of the carpus is cartilaginous at birth and each bone is ossified from a single centre. The Navicular The navicular [os naviculare] or scaphoid (fig. 190) is the largest bone of the proximal row, and so disposed that its long axis runs obhquely downward and lateralward. The superior surface is convex and somewhat triangular in shape for articulation with the • lateral facet on the distal end of the radius. The inferior surface, smooth and convex, is divided THE CARPUS 161 into two parts by a ridge running from before backward. The lateral part articulates with the greater multangular, the medial with the lesser multangular. The volar surface, rough and con- cave above, is elevated below into a prominent tubercle for the attachment of the transverse carpal ligament and the abductor pollicis brevis. The dorsal surface is narrow, being reduced Fig. 190. — The Left Naviculae For lunate For ligament For greater multangular For lesser multangular- to a groove running the whole length of the bone; it is rough and serves for the attachment of the dorsal radio-carpal ligament. The medial surface is occupied by two articular facets, of which the upper is crescentio in shape for the lunate bone, whilst the lower is deeply concave for the reception of the head of the capitate. The lateral surface is narrow and rough for the attachment of the radial collateral ligament of the wTist-joint. Articulations. — With the radius above, greater and lesser multangular below, lunate and capitate medially. The Lunate The lunate [os luuatum] or semilunar (fig. 191), placed in the middle of the proximal row of the carpus, is markedly crescentic in outline. The superior surface is smooth and oonve.x and articulates with the medial of the two facets on the distal end of the radius. The inferior surface presents a deep concavity divided into two parts by a line running from before backward. Of these, the lateral and larger articulates with the capitate; the medial and smaller with the hamate. The volar surface is large and convex, Fig. 191. — The Left Lunate. For triquetral- the dorsal surface narrow and flat, and both are rough for the attachment of ligaments. The medial surface is marked by a smooth quadrilateral facet for the base of the triquetral. The lateral surface forms a narrow crescentic articular surface for the lunate. Articulations. — With the radius above, capitate and hamate below, navicular laterally and triquetral medially. The Triquetral The triquetral [os triquetrum] or cuneiform (fig. 192) is pyramidal in shape and placed obliquely, so that its base looks upward and laterallj^ and the apex downward and medially. Fig. 192. — The Left Triquetral. For lunate " For pisiform For hamate The superior surface presents laterally near the base a small, convex articular facet which plays upon the articular disc interposed between it and the distal end of the ulna, and medially a rough non-articular portion for ligaments. The inferior surface forms a large, triangular undulating facet for articulation with the hamate. The volar surface can be readily recognised by the conspicuous oval facet near the apex for the pisiform bone. The dorsal surface is rough for the attachment of ligaments. The medial and lateral surfaces are represented by the base and the apex of the pyramid. The base is marked by a flat quadrilateral facet for the lunate. The apex forms the lowest part of the bone and is roughened for the attachment of the ulnar collateral ligament of the WTist. Articulations. — With the pisiform in front, lunate laterally, hamate below, articular disc above. 162 THE SKELETON The Pisiform The pisiform [os pisiform e] (fig. 193), the smallest of the carpal bones, is in many of its characters a complete contrast to the rest of the series. It deviates from the general type in its shape, size, position, use, and development. Forming a rounded bony nodule with the long axis directed vertically, it is situated on a plane in front of the oth^r bones of the carpus. Fig. 193. — The Left Pisiform. For triquetral- On the dorsal surface is a single articular facet for the triquetral which reaches to the upper end of the bone, but leaves a free non-articular portion below. The volar surface, rough and rounded, gives attachment to the transverse carpal ligament, the flexor carpi ulnaris, the ab- ductor quinti digiti, the piso-metacarpal and the piso-hamate ligaments. The median and lateral surfaces are also rough and the lateral presents a shallow groove for the ulnar artery. It is usually considered that the pisiform is a sesamoid bone developed in the tendon of the ^ea;or carpi ulnaris, though by some writers it is regarded as part of a rudimentary digit. The Greater Multangular The greater multangular [os multangulum ma jus] or trapezium (fig. 194), situated between the navicular and first metacarpal, is oblong in form with the lower angle prolonged downward and medially. Fig. 194. — The Left Greater Multangular. -The ridge For navicular For lesser multangular For second metacarpal ■Groove for flexor carpi radialis 'For first metacarpal The superior surface is concave and directed upward and medially for articulation with the lateral of the two facets on the distal surface of the navicular, and on the inferior surface is a saddle-shaped facet for the base of the first metacarpal. The volar surface presents a prominent ridge with a deep groove on its medial side which transmits the tendon of the^exor carpi radialis. The ridge gives attachment to the transverse carpal ligament, the abductor pollicis brevis, the opponens pollicis, and occasionally a tendinous slip of insertion of the abductor pollicis longus. The dorsal and lateral surfaces are rough for ligaments. The medial surface is divided into two parts by a horizontal ridge. The upper and larger portion is concave and articulates with the lesser multangular; the lower — a small flat facet on the projecting lower angle — articulates with the base of the second metarcarpal. Articulations. — With the navicular above, first metacarpal below, the lesser multangular and second metacarpal on the medial side. The Lesser Multangular The lesser multangular [os multangulum minus] or trapezoid (fig. 195), the smallest of the bones in the distal row, is somewhat wedge-shaped, with the broader end dorsally and the narrow end ventrally. Fig. 195. — The Left Lesser Multangular. Volar surface. For greater multangular For second metacarpal The superior surface is marked by a small, quadrilateral, concave facet, for the media of the two facets on the lower surface of the navicular. The inferior surface is convex from side to side and concave from before backward, forming a saddle-shaped articular surface for the base of the second metacarpal. Of the volar and dorsal surfaces, the former is narrow and rough. THE CARPUS 163 the latter broad and rounded, constituting the widest sui-face of the bone, and both are rough for the attachment of ligaments. The lateral surface slopes downward and medially and is convex for articulation with the corresponding sm-face of the greater multangular. On the medial surface in front is a smooth flat facet for the capitate; elsewhere it is rough for ligaments. Articulations. — With the navicular above, second metacarpal below, greater multangular laterally, and the capitate medially. The Capitate The capitate [os capitatum] or os magnum (fig. 196) is the largest bone of the carpus. Situated in the centre of the wrist, the upper expanded portion, globular in shape and known as the head, is received into the concavity formed above by the navicular and lunate. The cubical portion below forms the body, whilst the intermediate constricted part is distinguished as the neck. For lunati For navicular' Fig. 196. — The Left Capitate. tacarpal Of the six surfaces, the superior is smooth and convex, elongated from before backward for articulation with the concavity of the lunate bone. The inferior surface is divided into three unequal parts by two ridges. The middle portion, much the larger, articulates with the base of the third metacarpal; the lateral, narrow and concave, looks lateral as well as downward to articulate with the second metacarpal, whilst the medial portion is a small facet, placed on the projecting angle of the bone dorsally, for the fom'th metacarpal bone. The volar surface is convex and rough, giving origin to fibres of the oblique adductor pollicis; the dorsal surface is broad and deeply concave. Thelateral surface presents, from above downward: — (1) a smooth convex sm-face, forming the outer aspect of the head, with the superior surface of which it is continuous, for articulation with the navicular; (2) a groove representing the neck, indented for hgaments; (3) a small facet, flat and smooth, for articulation with the lesser multangular. Behind this facet is a rough area for attachment of an interosseous ligament. The medial surface has extending along its whole hinder margin an oblong articular surface for the hamate; the lower part of this smooth area sometimes forms a detached facet. The volar part of the surface is rough for an interosseous ligament. Articulations. — With the lunate and navicular above, second, third, and fourth meta- carpals below, lesser multangular laterally, and hamate medially. The Hamate The hamate [os hamatum] or unciform (fig. 197) is a large wedge-shaped bone, bearing a hook-like process, situated between the capitate and triquetral, with the base directed downward and resting on the two medial metacarpals. Fig. 197. — The Left Hamate. Hamulus— Fifth metacarpal- Fourth metacarpal- The apex of the wedge forms the narrow superior surface, directed upward and laterally for articulation with the lunate. The inferior surface or base is divided bj' a ridge into two (juadrilateral facets for the fourth and fifth metacarpal bones. The volar svu-face is triangular in outline and presents at its lower part a prominent hamulus (unciform process), a hook-like eminence, projecting forward and curved toward the carpal canal. It is flattened from side to side so as to present two surfaces, two borders, and a free extremity. To the latter the trans- verse carpal ligament and the flexor carpi ulnaris (by means of the piso-hamate ligament) are attached, whilst the medial surface affords origin to the flexor brcvis and the opponens digili quinli. The lateral surface is concave and in relation to the flexor tendons. The dorsal surface is triangular and rough for ligaments. The lateral surface has extending along its upper and 164 THE SKELETON hinder edges a long flat surface, wider above than below, for articulation with the capitate. In front of this articular facet the surface is rough for the attachment of an interosseous liga- ment. The medial surface is oblong and undulating, i. e., concavo-conve.x from base to apex, for articulation with the triquetral. Articulations. — With the triquetral, lunate, capitate, and the fourth and fifth metacarpal bones. Ossification of the Carpal Bones Capitate first year Hamate second year Triquetral third year Lunate fourth year Greater multangular fifth year Navicular sixth }rear Lesser multangular eighth year Pisiform twelfth year Additional carpal elements are occasionally met with. The os centrale occurs normally in the carpus of many mammals, and in the human fcetus of two months it is present as a small carti- laginous nodule which soon becomes fused with the cartilage of the navicular. Failure of fusion, with subsequent ossification of the nodule, leads to the formation of an os centrale in the human carpus which is then found on the dorsal aspect, between the navicular, capitate, and lesser multangular. In most individuals, however, it coalesces with the navicular or under- goes suppression. An additional centre of ossification, leading to the formation of an accessory carpal element, occasionally appears in connection with the greater multangular and the hamate. An accessory element {os Vesalianum) also occurs occasionally in the angle between the hamate and the fifth metacarpal, and others occur between the second and third metacarpals and the lesser multan- gular and capitate. THE METACARPALS The metacarpus (figs. 188, 189) consists of a series of five cylindrical bones [ossa metacarpalia], well described as 'long bones in miniature.' Articulated with the carpus above, they descend, slightly diverging from each other, to sup- port the fingers, and are numbered from the lateral to the medial side. With the exception of the first, which in some respects resembles a phalanx, they con- form to a general type. A typical metacarpal bone presents for examination a shaft and two extrem- ities. The body or shaft is prismatic and curved so as to be slightly convex toward the back of the hand. Of the three surfaces, two are lateral in position, Fig. 198. — The First (Left) Metacarpal. separated in the middle part of the shaft by a prominent palmar ridge, and con- cave for the attachment of interosseous muscles. The third or dorsal surface presents for examination a large, smooth, triangular area with the base below and apex above, covered in the recent state by the extensor tendons of the fingers, and two sloping areas, near the carpal extremity, also for interosseous muscles. The triangular area is bounded by two hnes, which commence below in two dorsal tubercles, and, passing upward, converge to form a median ridge situated be- tween the sloping areas on either side. A little above or below the middle of the shaft, and near the volar border, is the medullary foramen, entering the bone obliquely upward. The base or carpal extremity, broader behind than in front, is quadrilateral, and both palmar and dorsal surfaces are rough tor hgaments; it articulates above with the carpus and on each side with the adjacent metacarpal bones. The head [capitulum] or digital extremity presents a large rounded ar- ticular surface, extending further on the palmar than on the dorsal aspect, for THE METACARPALS 165 articulation with the base of the first phalanx. The volar surface is grooved for the flexor tendons and raised on each side into an articular eminence. On each side of the head is a prominent tubercle, and immediately in front of this a well- marked fossa, to both of which the collateral hgament of the metacarpo-phalangeal joint is attached. Fig. 199. — The Second (Left) Metacarpal. For greater multangular I h For third metacarpal ■For capitate The second is the longest of all the metacarpal bones, and the third, fourth, and fifth successively decrease in length. The several metacarpals possess dis- tinctive characters by which they are readily identified. The first metacarpal (fig. 198) is the shortest and widest of the series. Diverging from the carpus more widely than any of the others the palmar surface is directed medially and marked Fig. 200. — The Third (Left) Metacarp.^.l. For second metacarpal For fourth metacarpal Styloid process bj' a ridge placed nearer to the medial border. The lateral portion of the surface slopes gently to the lateral border and gives attachment to the opponens poUicis; the medial portion, the smaller of the two, slopes more abruptly to the medial border, is in relation to the deep head of the flexor pollicis brevis, and presents the nutrient foramen, directed downward toward the head of the bone and transmitting a branch of the arteria princeps poUicis. The dorsal surface, wide and flattened, is in relation to the tendons of the extensor poUicis longus and brevis. 166 THE SKELETON The base presents a saddle-shaped articular surface for the greater multangular, prolonged in front into a thin process. There are no lateral facets, but laterally a small tubercle receives the insertion of the abductor pollicis longus. Medially is a rough area from which fibres of the inner head of the flexor pollicis brevis take origin. The margin of the articular surface gives attachment to the articular capsule of the carpo-metacarpal joint. The inferior extremity or head is rounded and articular, for the base of the first phalanx; the greatest diameter is from side to side and the surface is less convex than the corresponding surface of the other metacarpal bones. On the volar surface it presents two articular eminences corresponding to the two sesamoid bones of the thumb. Of the two margins, the medial gives origin to the lateral head of the first dorsal interosseous, the lateral receives fibres of insertion of the opponens pollicis. Fig. 201. — The Fouhth (Left) Metacarpal. For third metacarpal For capitate For fifth metacarpal The second metacarpal (fig. 199). — The distinctive features of the four remaining meta- carpals are almost exclusively confined to the carpal extremities. The second is easily recog- nised by its deeply cleft base. The terminal surface presents three articular facets, arranged as follows, from lateral to medial border : — (1) a small oval facet for the greater multangular; (2) a hollow for the lesser multangular; and (3) an elongated ridge for the capitate. The dorsal surface is rough for the insertions of the extensor carpi radialis longus and a part of the extensor carpi radialis brevis; the palmar surface receives the insertion of the flexor carpi radialis and gives origin to a few fibres of the oblique adductor pollicis. The lateral aspect of the extremity is rough and non-articular; the medial surface bears a bilobed facet for the third metacarpal. Fig. 202. — The Fifth (Left) Metacarpal. Fourth metacarpal' The shaft of the second metacarpal gives attachment to three interosseous muscles, and the nutrient foramen, directed upward on the ulnar side, transmits a branch of the second volar metacarpal artery. The third metacarpal (fig. 200) is distinguished by the prominent styloid process projecting upward from the lateral and posterior angle of the base. Immediately below it, on the dorsal surface, is a rough impression for the extensor carpi radialis brevis. The carpal surface is concave behind and convex in front, and articulates with the middle of the three facets on the inferior surface of the capitate. On the lateral side is a bilobed articular facet for the second metacarpal, and on the medial side two small oval facets for the fourth metacarpal. The volar a.spect of the base is rough and gives attachment to fibres of the oblique adductor pollicis and THE PHALANGES 167 sometimes a slip of insertion of the flexor carpi radialis. The shaft of the third metacarpal serves for the origin of the transverse adductor pollicis and two interosseous muscles. The nutrient foramen is directed upward on the radial side and transmits a branch of the second volar metacarpal artery. The fourth metacarpal (fig. 201) has a small base. The carpal surface presents two facets: a medial, large and flat, for articulation with the hamate, and a small facet, at the lateral and posterior angle, for the capitate. On the lateral side are two small oval facets for the correspond- ing surfaces on the third metacarpal and a single concave facet on the medial side for the fifth metacarpal. The shaft of the fourth metacarpal gives attachment to three interosseous muscles, and the nutrient foramen, directed upward on the radial side, transmits a branch of the third volar metacarpal artery. The fifth metacarpal (fig. 202) is distinguished by a semilunar facet on the lateral side of the base for the fourth metacarpal, and a rounded tubercle on the medial side for the extensor carpi ulnaris, in place of the usual medial facet. The carpal surface is saddle-shaped for the hamate; the palmar surface is rough for ligaments including the piso-metacarpal prolongation from the flexor carpi ulnaris. The dorsal surface of the shaft presents an oblique line separating a lateral concave portion for the fourth dorsal interosseous muscle from a smooth medial por- tion covered by the extensor tendons of the little finger. The palmar surface gives attachment laterally to the third palmar interosseous muscle and medially to the opponens digili quinti. The nutrient foramen is directed upward on the radial side and transmits a branch of the fourth volar metacarpal artery. THE PHALANGES The phalanges (fig. 203) are the bones of the fingers, and number in all fourteen. Each finger consists of three phalanges distinguished as first or proximal, second Fig. 203. — The Phalanges op the Third Digit op the Hand. (Dorsal view.) [The arrows indicate the direction of the nutrient canals.] Third terminal or ungual phalanx Second phalanx or middle, and third or distal. In the thumb, the second phalanx is wanting. Arranged in horizontal rows, the phalanges of each row resemble one another and differ from those of the other two rows. In all the phalanges the nutrient canal is directed downward, toward the distal extremity. First phalanx, — The shaft of a phalanx from the first row is flat on the palmar surface, smooth and rounded on the dorsal surface, i. e., semi-cyUndrical in shape. The borders of the palmar surface are rough for the attachment of the sheaths of the flexor tendons. The base or metacarpal extremity presents a single concave articular surface, oval in shape, for the 168 THE SKELETON convex head of the metacarpal bone. The distal extremity forms a pulley-like surface, grooved in the centre and elevated at each side to form two miniature condyles, for articulation with the base of a second phalanx. Second phalanx. — The second phalanges are four in number and are shorter than those of the first row, which they closely resemble in form. They are distinguished, however, by the articular surface on the proximal extremity, which presents two shallow depressions, separated by a ridge and corresponding to the two condyles of the first phalanx. The distal end for the base of the third phalanx is trochlear or pulley-like, but smaller than that of the first phalanx. The palmar surface of the shaft presents on each side an impressionSfor the tendon of the flexor digitorum sublimis, and the dorsal aspect of the base is marked by a projection for the insertion of the extensor digitorum communis. Third phalanx. — A third phalanx is readily recognised by its small size. The proximal end is identical in shape with that of a second phalanx, and bears a depression in front for the tendon of the flexor digitorum profundus. The free, flattened and expanded distal extremity presents on its palmar surface a rough semilunar elevation for the support of the pulp of the finger. The somewhat horseshoe-shaped free extremity is known as the ungual tuberosity [tuberositas unguicularis], and the bone is accordingly referred to as the ungual phalanx. Ossification of. the Metacarpus and Phalanges Each of the metacarpal bones and phalanges is ossified from a primary centre for the greater part of the bone, and from one epiphysial centre. The primary nucleus appears from the eighth to the tenth week of intra-uterine life. In four metacarpal bones the epiphysis is distal, whilst Fig. 204. — Ossification of the Metacarpals and Phalanges. Appears in th Consolidates i year Epiphysis for base- Metacarpal of thum^ Epiphysis for head 1 Appear in the third, and con- J soiidate in the twentieth year Appear between the third and fifth year. Consolidate in the eighteenth year in the first metacarpal bone, and in all the phalanges, it is proximal. The epiphysial nuclei appear from the third to the fifth year and are united to their respective shafts about the twen- tieth year. In many cases the first metacarpal has two epiphyses, one for the base in the third year and an additional one for the head in the seventh year, but the latter is never so large as in the other metacarpal bones. The third metacarpal occasionally has an additional nucleus for the prominent styloid process which may remain distinct and form a styloid bone, and traces of a proximal epiphysis have been observed in the second metacarpal bone. In many of the Cetacea (whales, dolphins, and porpoises) and in the seal, epiphyses are found at both ends of the metacarpal bones and phalanges (Flower). The ossification of a terminal phalanx is peculiar. Like the other phalanges, it has a pri- mary nucleus and a secondary nucleus for an epiphysis. But whereas in other phalanges the primary centre appears in the middle of the shaft, in the case of the distal phalanges the earthy matter is deposited in the free extremity. Sesamoid Bones The sesamoid bones are small and rounded and occur imbedded in certain tendons where they exert a considerable amount of pressure on subjacent bony structures. In the hand five sesamoid bones are of almost constant occurrence, namely, two over the metacarpo-phalangeal joint of the thumb in the tendons of the flexor pollicis brevis, one over the interphalangeal joint of the thumb, and one over the metacarpo-phalangeal joints of the second and fifth fingers. THE COXAL BONE 169 Occasionally sesamoids occur over the metacarpo-phalangeal joint of the third and fourth digits, and an additional one may occur over that of the fifth. Very rarely a sesamoid is developed in the tendon of the biceps over the tuberosity of the radius. B. THE BONES OF THE LOWER EXTREMITY The bones of the lower extremity may be arranged in four groups correspond- ing to the division of the limb into the hip, thigh, leg, and foot. In the hip is the coxal or hip-bone, which constitutes the pelvic girdle [cingulum extremitatis inferioris], and contributes to the formation of the pelvis; in the thigh is the femur; in the leg, the tibia and fibula, and in the foot the tarsus, metatarsus, and phalanges. Associated with the lower end of the femur is a large sesamoid bone, the patella or knee-cap. THE COXAL BONE The coxal (innominate) bone or hip-bone [os coxse] (figs. 205, 206) is a large, irregularly shaped bone articulated behind 'with the sacrum, and in front with its fellow of the opposite side, the two bones forming the anterior and side walls of the pelvis. The coxal bone consists of three parts, named ilium, ischium, and pubis, which, though separate in early life, are firmly united in the adult. The three parts meet together and form the acetabulum (or cotyloid fossa), a large, cup-like socket situated near the middle of the lateral surface of the bone for articulation with the head of the femur. The ilium [os ilium] is the upper expanded portion of the bone, and by its inferior extremity forms the upper two-fifths of the acetabulum. It presents for examination three borders and two surfaces. Borders. — When viewed from above, the thick crest [crista iliaca] or superior border is curved somewhat like the letter /, being concave medially in front and concave laterally behind. Its anterior extremity forms the anterior superior iliac spine, which gives attachment to the inguinal (Poupart's) ligament and the sartorius; the posterior extremity forms the posterior superior iliac spine and affords attachment to the sacro-tuberous (great sacro-sciatic) ligament, the pos- terior sacro-iliac ligament, and the multifidus. The crest is narrow in the middle, thick at its extremities, and may be divided into an inner lip, an outer lip, and an intermediate line. About two and a half inches from the anterior superior spine is a prominent tubercle on its external lip. The external lip of the crest gives attachment in front to the tensor fascia latw; along its whole length, to the fascia lata; along its anterior half to the external oblique; and behind this, for about an inch, to the latissimus dorsi. The anterior two-thirds of the intermediate line gives origin to the internal oblique. The internal lip gives origin, by its anterior two-thirds, to the iransversus; behind this is a small area for the quadratus lumborum, and the remainder is occupied by the sacro-spinalis (erector spince). The internal lip, in the anterior two-thirds, also serves for the attachment of the iliac fascia. The anterior border of the ilium extends from the anterior superior iliac spine to the margin of the acetabulum. Below the spine is a prominent notch from which fibres of the sartorius arise, and this is succeeded by the anterior inferior iliac spine, smaller and less prominent than the superior, to which the straight head of the rectus and the ilio-femoral ligament are attached. On the medial side of the anterior inferior spine is a broad, shallow groove for the ilio-psoas as it passes from the abdomen into the thigh, limited below by the ilio-pectineal eminence, which indicates the point of union of the ilium and pubis. The posterior border of the ilium presents the posterior superior iliac spine, and below this, a shallow notch terminating in the posterior inferior iliac spine which corresponds to the posterior extremity of the auricular surface and gives attachment to a portion of the sacro-tuberous (great sacro-sciatic) hgament. Below the spine the posterior border of the ilium forms the upper limit of the greater sciatic notch. Surfaces. — The external surface or dorsum is concave behind, convex in front, limited above by the thick superior border or crest, and traversed by three gluteal lines. 170 THE SKELETON The posterior gluteal line commences at the crest about two inches from the posterior superior iliac spine and curves downward to the upper margin of the greater sciatic notch. The space included between this ridge and the crest affords origin at its upper part to the gluteus maximus, and at its lower part, to a few fibres of the piriformis, while the intermediate portion is smooth and free from muscular attachment. The anterior gluteal line begins at the crest, one inch behind its anterior superior iliac spine, and curves across the dorsum to terminate near the lower end of the superior line, at the upper margin of the greater sciatic notch. The surface of bone between this line and the crest is for the origin of the gluteus medius. The inferior gluteal line commences at the notch immediately below the anterior Fig. 205." Insertion of external oblique Internal oblique Tensor fasicEe latee Sartorius -The Left Coxal or Hip-bone. (Lateral view.) Posterior limit of external oblique Latissimus dorsi Crest of ilium Posterior superior iliac spine •informis Posterior inferior iliac spine Greater sciatic (ilio-sci- atic) notch Pectineus Rectus abd Pyramidali Adducto longu Adducto brevi Descending ramus of pubis Gracilis Ramus of ischium Obturator externus superior iliac spine and terminates posteriorly at the front part of the greater sciatic notch- The space between the anterior and inferior gluteal lines, with the exception of a small area adjacent to the anterior end of the spine for the tensor fasciw latce, gives origin to the gluteus minimus. Between the inferior gluteal line and the margin of the acetabulum the surface affords attachment to the capsule of the hip-joint, and on a rough area (sometimes a depression) toward its anterior part, to the reflected tendon of the rectus femoris. The internal surface presents in front a smooth concave portion termed the iliac fossa, which lodges the iliacus muscle. The fossa is limited below by linea arcuata, the iliac portion of the terminal (iho-pectineal) line. This is a rounded border separating the fossa from a portion of the internal surface below the line, which gives attachment to the obturator internus and enters into the formation of the minor (true) pelvis. Behind the iliac fossa the bone is uneven and presents THE COXAL BONE 171 an auricular surface, covered with cartilage in the recent state, for articulation with the lateral aspect of the upper portion of the sacrum; above the auricular surface are some depressions for the posterior sacro-iliac ligaments and a rough area reaching as high as the crest, from which parts of the sacro-spinalis {erector spince) and vmltifidus take origin. The rough surface above the auricular facet is known as the tuberosity of the ilium. The ischium [os ischii] consists of a body, a tuberosity, and a ramus. The body, which has somewhat the form of a triangular pyramid, enters superiorly into Fig. 206. — The Left Coxal or Hip-bone. (Medial aspect.) Quadratus lumborum Transversus muscle and iliac fasica Auricular surface Ant. inf. spine of ilium Symphysial surface Levator ani Junction of pubis Cms penis and Sphincter Arcuate and ischium Ischio- urethra ligament cavernosas membranacese the formation of the acetabulum, to which it contributes a little more than two- fifths, and forms the chief part of the non-articular portion or floor. The inner surface forms part of the minor (true) pelvis and gives origin to the obturator in - ternus. It is continuous with the ilium a little below the terminal (ilio-pectineal) line, and with the pubis in front, the line of junction with the latter being fre- quently indicated in the adult bone by a rough line extending from the ilio-pec- tineal eminence to the margin of the obturator foramen. The outer surface in eludes the portion of the acetabulum formed by the ischium. The posterior sur- face is broad and bounded laterally by the margin of the acetabulum and behind 172 THE SKELETON by the posterior border. The capsule of the hip-j oint is attached to the lateral part and the -pirijorniis, the great sciatic and posterior cutaneous nerves, the inferior gluteal (sciatic) artery, and the nerve to the quadratus femoris lie on the surface as they leave the pelvis. Inferiorly this surface is limited by the obturator groove, which receives the posterior fleshy border of the obturator externus when the thigh is flexed. Of the three borders, the external, forming the prominent rim of the acetabulum, separates the posterior from the external surface and gives attach- ment to the glenoid lip. The inner border is sharp and forms the lateral boundary of the obturator foramen. The posterior border is continuous with the posterior border of the ilium, with which it joins to complete the margin of the great sciatic notch [incisura ischiadica major]. The notch is converted into a foramen by the sacro-spinous (small sacro-sciatic) ligament, and transmits the piriformis muscle, the gluteal vessels, the superior and inferior gluteal nerves, the sciatic and posterior cutaneous nerves, the internal pudic vessels and nerve, and the nerves to the obturator internus and quadratus femoris. Below the notch is the prominent ischial spine, which gives attachment internally to the coccygeus and levator ani, externally to the gemellus superior, and at the tip to the sacro- spinous ligament. Below the spine is the small sciatic notch [incisura ischiadica minor], covered in the recent state with cartilage, and converted into a foramen by the sacro-tuberous (great sacro-sciatic) ligament. It transmits the tendon of the obturator internus, its nerve of supply, and the internal pudic vessels and nerve. The rami form the flattened part of the ischium which runs first downward, then upward, forward and medially from the tuberosity toward the inferior ramus of the pubis, with which it is continuous. The rami together form an L- shaped structure with an upper vertical ramus [ramus superior] and a lower horizontal ramus [ramus inferior]. The outer surface of the rami gives origin to the adductor magyius and obturator externus; the inner surface, forming part of the anterior wall of the pelvis, receives the crus penis (or clitoridis) and the ischio- cavernosus, and gives origin to a part of the obturator internus. Of the two borders, the upper is thin and sharp, and forms part of the boundary of the obturator foramen; the lower is rough and corresponds to the inferior ramus. It is some- what everted and gives attachment to the fascia of Colles, and the transversus perinei. To a ridge immediately above the impression for the cms penis (or clitoridis) and the ischio-cavernosus , the urogenital trigone (triangular ligament) is attached. The posterior and inferior aspect of the superior ramus is an ex- panded area forming the tuberosity [tuber ischiadicum]. The tuberosity is that portion of the ischium which supports the body in the sitting posture. It forms a rough, thick eminence continuous with the inferior border of the infeiior ramus, and is marked by an oblique line separating two impressions, an upper and lateral for the semimembranosus, and a lower and medial for the common tendon of the biceps and semitendi- nosus, while the lower part is markedly uneven and gives origin to the adductor magnus. The upper border gives origin to the inferior gemellus; the inner border, sharp and. prominent, re- ceives the sacro-tuberous (great sacro-sciatic) ligament, while the surface of the tuberosity immediately in front is in relation with the internal pudic vessels and nerve. The outer border gives origin to the quadratus femoris. The pubis [os pubis] consists of a body and two rami — superior and inferior. The body is somewhat quadrilateral in shape and presents for examination two surfaces and three borders. The anterior surface looks downward, forward and slightly outward, and gives origin to the adductor longus, the adductor brevis, the obturator externus, and the gracilis. The posterior surface is smooth, looks into the pelvis, and affords origin to the levator ani, the obturator internus, and the pubo- prostatic ligaments. The upper border or crest of the body is rough and presents laterally a prominent bony point, known as the tubercle [tuberculum pubicum] or spine, for the attachment of the inguinal (Poupart's) ligament. The upper border extends from the pubic tubercle medialward to the upper end of the symphysis, with which it forms the angle of the pubis. The upper border is a short horizontal ridge, which gives attachment to the rectus abdominis and pyram- idalis. The medial border is oval in shape, rough, and articular, forming with the bone of the opposite side the symphysis pubis [facies symphyseos]. The lateral border is sharp and forms part of the boundary of the obturator foramen. The inferior ramus, like the inferior ramus of the ischium, with which it is continuous, is thin and flattened. To its anterior surface are attached the THE COXAL BONE 173 adductor hrevis, adductor magnus, and obturator externus. The posterior surface is smooth and gives attachment to the crus penis or clitoridis, the sphincter urethrce (urogenitalis) , the obturator internus, and the urogenital trigone (triangular liga- ment). The lateral border forms part of the circumference of the obturator foramen, and the medial border forms part of the pubic arch and gives attach- ment to the gracilis. The superior ramus extends from the body of the pubis to the ilium, forming by its lateral extremity the anterior one-fifth of the articular surface of the acetab- ulum. It is prismatic in shape and increases in size as it passes laterally. Above it presents a sharp ridge, the pecten or pubic portion of the terminal (ilio-pectineal) line continuous with the iliac portion at the ilio-pectineal eminence, and affording Fig. 207. — An Immature Coxal (Innominate) Bone, showing a Cotyloid Bone. Tha cotyloid bone attachment to the conjoined tendon [falx aponeurotica inguinalis], the lacunar (Gimbernat's) hgament, the reflected inguinal ligament (fascia triangularis), and the pubic portion of the fascia lata; the ihac portion of the terminal (ilio- pectineal) line gives attachment to the psoas minor, the iliac fascia, and the pelvic fascia. Immediately in front of the pubic portion of the line is the pectineal surface; it gives origin at its posterior part to the pectineus, and is limited below by the obturator crest, which extends from the pubic tubercle to the acetabular notch. The inferior surface of the ascending ramus forms the upper boundary of the obturator foramen and presents a deep groove [sulcus obturatorius] for the passage of the obturator vessels and nerve. The posterior surface is smooth, forms part of the anterior wall of the pelvic cavity, and gives attachment to a few fibres of the obturator internus. According to the BNA, the body [corpus ossis pubis] is the portion corresponding to the acetabulum. The remainder of the bone is described as consisting of the ramus superior and the ramus inferior, which meet at the symphysis. Thus the divisions according to the BNA are different from those in the description above given. The acetabulum is a circular depression in which the head of the femur is lodged and consists of an articular and a non-articular portion. The articular portion is circumferential and semilunar in shape [facies lunata], with the defi- ciency in the lower segment. One-fifth of the acetabulum is formed bj^ the pubis, two-fifths by the ischium, and the remaining two-fifths are formed by the ilium. In rare instances the pubis may be excluded by a fourth element, the cotyloid bone. The non-articular portion [fossa acetabuli] is formed mainly by the ischium, and is continuous below with the margin of the obturator foramen. The articular portion presents a lateral rim to which the glenoid lip is attached, and a medial margin to which the synovial membrane which excludes 174 THE SKELETON the ligamentum teres from the synovial cavity is connected. The opposite extremities of the articular lunate surface which limit the acetabular notch are united by the transverse ligament, and through the acetabular foramen thus formed a nerve and vessels enter the joint. The obturator (thyreoid) foramen is sHuated between the ischium and pubis. Its margins are thin, and serve for the attachment of the obturator membrane. At the upper and posterior angle it is deeply grooved for the passage of the obtu- rator vessels and nerve. Fig. 208. — The Pelvis of a Fcetus at Birth, to show the Three Portions of the CoxAL Bones. The nucleus for the pubis appears bout the end of the fourth month 3 nucleus for the ischium appears Q the third month Blood-supply. — The chief vascular foramina of the coxal bone are found where the bone is thickest. On the inner surface, the ilium receives twigs from the ilio-lumbar, deep circumflex iliac, and obturator arteries, by foramina near the crest, in the iliac fossa, and below the terminal line near the greater sciatic notch. On the outer surface the chief foramina are found below the inferior gluteal line and the nutrient vessels are derived from the gluteal arteries. The ischium receives nutrient vessels from the obturator, internal and external circumflex arteries, and the largest foramina are situated between the acetabulum and the ischial tuberosity. The pubis is supplied by twigs from the obturator, internal and external circumflex arteries, and from the pubic branches of the common femoral artery. Fig. 209. — Coxal or Hip-bone, showing Secondary Centres. Appears at fifteen. Unites at twenty- Appears at fifteen. Unites at twenty. Appears at fifteen. Fuses at twenty Fuses at twenty Ossification. — The cartilaginous representative of the hip-bone consists of three distinct portions, an iliac, an ischiatic, and a pubic portion; the iliac and ischiatio portions first unite and later the pubic portion, so that eventually there is found a single cartilaginous mass. Early in the second month a centre of ossification appears above the acetabulum for the ilium. A little later a second nucleus appears below the cavity for the ischium, and this is followed in the fourth month by a deposit in the pubic portion of the cartilage. At birth, the three nuclei THE PELVIS 175 are of considerable size, but are surrounded by relatively wide tracts of cartilage; ossification has, however, extended into the margin of the acetabulum. In the eighth j^ear the rami of the pubis and ischium become united by bone, and in the tweKth year the triradiate cartilage which separates the three segments of the bone in the acetabulum begins to ossify from several centres. Of these, one is more constant than the others and is known as the acetabular nucleus. The triangular piece of bone to which it gives rise is regarded as the representative of the cotyloid or acetabular bone, constantly present in a few mammals. It is situated at the medial part of the acetabulum and is of such a size as to exclude entirely the pubis from the cavity. With this bone, however, it eventually fuses, and afterward becomes joined with the ilium and Fig. 210. — Coxal or Hip-bone (Inner Surface) at the Eighth Year. ischium, so that by the eighteenth or twentieth year the several parts of the acetabulum have become united. In the fifteenth year other centres appear in the cartilage of the crest of the ilium, the anterior inferior iliac spine, the tuberosity of the ischium, and the pubic pecten. The epiphyses fuse with the main bone about the twentieth year. The fibrous tissue connected with the tubercle of the pubis represents the epipubio bones of marsupials. THE PELVIS The pelvis (figs. 211, 212, 213, 214) is composed of four bones: the two coxal or hip-bones, the sacrum, and the coccyx. The hip-bones form the lateral and anterior boundaries, meeting each other in front to form the pubic symphysis [symphysis ossium pubis]; posteriorly they are separated by the sacrum. The interior of the pelvis is divided into the major and minor pelvic cavity. The major (or false) pelvis is that part of the cavity which lies above the ter- minal (ihopectineal) lines and between the iliac fossse. This part belongs really to the abdomen, and is in relation with the hypogastric and iliac regions. The minor (or true) pelvis is situated below the terminal (ilio-pectineal) lines. The upper circumference, known as the superior aperture (inlet or brim) of the pelvis, is bounded anteriorly by the tubercle and pecten of the pubis on each side, posteriorly by the anterior margin of the base of the sacrum, and laterally by the terminal lines. The inlet in normal pelves is heart-shaped, being obtusely pointed in front; posteriorly it is encroached upon by the promontory of the sacrum. It has three principal diameters; of these, the antero-posterior, called the conjugate diameter [conjugata], is measured from the sacro-vertebral angle to the symphj^sis. The transverse diameter represents the greatest width of the pelvic cavity. The oblique diameter is measured from the sacro-iliac synchondrosis of one side to the ilio-pectineal eminence of the other. The cavity of the minor (true) pelvis is bounded in front by the pubes, behind bjr the sacrum and coccj^x, and laterally by a smooth wall of bone formed in part by the ilium and in part by the ischium. The cavity is shallow in front, where it is formed by the pubes, and is deepest posteriorly. 176 THE SKELETON The inferior aperture, or outlet, of the minor pelvis is verj' irregular, and en- croached upon by three bony pi'ocesses: the posterior process is the coccyx, and the two lateral processes are the ischial tuberosities. They separate three notches. The anterior notch is the pubic arch, and is bounded on each side by the conjoined rami of the pubes and ischium. Each of the two remaining gaps, bounded by the Fig. 211.— The Male Pelvis. ischium anteriorly, the sacrum and coccjrx posteriorly, and the ilium above, cor- responds to the greater and lesser sciatic notches. These are converted into foramina bj^ the sacro-tuberous (great sacro-sciatic) and sacro-spinous (small sacro-sciatic) ligaments. The position of the pelvis. — In the erect position of the skeleton the plane of the pelvic inlet forms an angle with the horizontal plane, which varies in indi%dduals from 50° to 60°. 212. — The Female Pelvis. The base of the sacrum in an average pelvis lies nearly ten centimetres (four inches) above the upper margin of the symphysis pubis. The axis of the pelvis.— This is an imaginary curved line drawn through the minor pelvis at right angles to the planes of the inlet, cavity, "and outlet through then central points. As the posterior wall, formed by sacrum and coccyx, is nearly five inches long and concave, and the anterior waU at the symphysis pubis one one and a half to two inches long, it follows that the axis must be cm-ved. THE PELVIS 177 The average measurements of the diameters of the minor pehas in the three planes are given below: — Inlet... Cavit}' . Outlet . Conjugate or axtero-posterior. a inches (10.6 cm.) 4i " (11.8 cm.) 3f " (9.0 cm.) Oblique. o inches (12.5 cm.) 5i " (13.0 cm.) 4i " (11.2 cm.) Thaxsverse. 5t inches (13.0 cm.) 4J " (11.8 cm.) 4i " (10.6 cm.) Fig. 213. — M.^le Pewis. (Lateral view.) Fig. 214. — Female PEL-\as. (Lateral view.) There is, however, a difference between the sexes, the diameters of the male pelvis in general averaging slighth- less, and those of the female sUghtly greater than the figures above given. Differences according to sex. — There is a marked difference in the size and form of the male and female pelvis, the pecularities of the latter being necessary to qualify it for its func- tions in partm-ition. The various points of divergence may be tabulated as follows: — M.\.LE. Bones heavier and rougher. Ilia less vertical. Iliac fossEB deeper. Major pehds relatively wider. Minor pelvis deeper. " " narrower. Superior aperture move heart-shaped. Symphysis deeper. Tuberosities of ischia inflexed. Pubic angle narrow and pointed. Margins of ischio-pubic rami more everted. Obturator foramen oval. Sacrum narrower and more curved. Capacity of minor pelvis less. Female. Bones more slender. Ilia more vertical. Iliac fossae shallower. Major pelvis relatively narro'srer. Minor pelvis shallower. " " wider. Superior aperture more oval. Symphj'sis shallower. Tuberosities of ischia everted. Pubic arch wider and more rounded. Margins of ischio-pubic rami less everted. Obturator foramen triangular. Sacrum wider and less curved. Capacity of minor pelvis greater. The sexual characters of the pelvis as shown by A. Thomson are manifest as early as the fourth month of fcetal life. Quite recently attention has been drawn by D. Derry to some special points in which the OS coxaj differ in the two sexes, and two figures are shown here in which one of these points is clearly brought out. It will be seen that the great sciatic notch is larger in the female, and that the sacrum projects less forward at its apex. Moreover the facies auricularis is smaller whilst below and in front of this surface, the sulcus preauricularis, a depression for the attach- ment of the ligamenta sacroiliaca anteriora, is usualh- more pronounced. In comparison with the pelves of lower animals, which, speaking generally, are elongated and narrow, the human pelvis is characterised by its breadth, shallowness, and great capacity. Differences are also to be recognised in the form of the pelvis in the various races of mankind, the most important being the relation of the antero-posterior to the transverse diameter, measured at the inlet. This is expressed bj' the pelmc index = —^^-^r. transverse diameter In the average European male the index is about 80; in the lower races of mankind, 90 to 95. Pelves with an index below 90 are platypellic, from 90 to 95 are mesatipellic, and above 95 dolichopellic. (Sir WiUiam Turner.) 178 THE SKELETON THE FEMUR The femur or thigh bone (figs. 215, 216) is the largest and longest bone in the skeleton, and transmits the entire weight of the trunk from the hip to the tibia. In the erect posture it inclines from above downward and medially, approaching at the lower extremity its fellow of the opposite side, but separated from it above by the width of the true pelvis. It presents for examination a superior extremity, including the head, neck, and two trochanters, an inferior extremity, expanded laterally into two condyles, and a shaft. The upper extremity is surmounted by a smooth, globular portion called the head, forming more than half a sphere, directed upward and medially for articu- lation with the acetabulum. With the exception of a small rough depression, the fovea, for the ligamentum teres, a little below and behind the centre of the head, . its surface is covered with cartilage in the recent state. The head is connected with the shaft by the neck, a stout rectangular column of bone which forms with the shaft, in the adult, an angle of about 125*. Its anterior surface is in the same plane with the front aspect of the shaft, but is marked off from it by a ridge to which the capsule of the hip-joint is attached. The ridge, which commences at the great trochanter in a small prominence, or tubercle, extends obliquely down- ward, and winding to the back of the femur, passes by the lesser trochanter and becomes continuous with the medial lip of the linea aspera, on the posterior aspect of the shaft. This ridge forms the intertrochanteric line or spiral line of the femur. The intertrochanteric line receives the bands of the ilio-femoral thickening of the capsule of the hip-joint. The posterior surface of the neck is smooth and concave and its medial two-thirds is enclosed in the capsule of the hip-joint. The superior border of the neck, perforated by large nutrient foramina, is short and thick, and runs downward to the great trochanter. The inferior border, longer and narrower than the superior, curves downward to terminate at the lesser trochanter. The trochanters are the prominences which afford attachment to the rotator muscles of the thigh; they are two in number — great and lesser. The great trochanter is a thick, quadrilateral process surmounting the junction of the neck with the shaft, and presents for examination two surfaces and four borders. The lateral surface is broad, rough, and continuous with the lateral surface of the shaft. It is marked by a diagonal ridge running from the postero- superior to the antero-inferior angle, which receives the insertion of the gluteus medius. The ridge divides the surface into two triangular areas : an upper, cov- ered by the gluteus medius, and occasionally separated from it by a bursa, and a lower, covered by a bursa to permit the free gliding of the tendon of the gluteus maximus. Of the medial surface the lower and anterior portion is joined with the rest of the bone; the upper and posterior portion is free, concave, and presents a deep depression, the trochanteric or digital fossa, which receives the tendon of the obturator externus. The fore part of the surface is marked by an impression for the insertion of the obturator internus and two gemelli. Of the four borders, the superior, thick and free, presents near the centre an oval mark for the insertion of the -piriformis; the anterior border, broad and irregular, receives the gluteus minimus; the posterior border, thick and rounded, is continuous with the intertrochanteric crest, the prominent ridge uniting the two trochanters behind. Above the middle of this line is an elevation, termed the tubercle of the quadratus, for the attachment of the upper part of the quadralus femoris. The inferior border corresponds with the line of junction of the base of the trochanter with the shaft; it is marked by a prominent ridge for the origin of the upper part of the vastus lateralis. The lesser trochanter is a conical eminence projecting medially from the poste- rior and mecUal aspect of the bone, where the neck is continuous with the shaft. Its summit is rough and gives attachment to the tendon of the ilio-psoas. The fibres of the iliacus extend beyond the trochanter and are inserted into the surface of the shaft immediately below. The body or shaft of the femur is almost cylindrical, but is slightly flattened in front and strengthened behind by a projecting longitudinal ridge, the linea aspera, for the origin and insertion of muscles. The linea aspera extends along the middle third of the shaft and presents a medial lip and a lateral lip separated by a narrow interval. When followed into the upper third of the shaft, the three parts diverge. The lateral lip becomes continuous with the gluteal tuberosity and ends at the base of the great trochanter. The ridge affords insertion to the gluteus maximus, THE FEMUR 179 Fig. 215. — The Left Femur. (Anterior view.) Greater trochanter Superior cervical tubercl Adductor tubercl Adductor magnu; Capsular line — ^ Piriformis Obturator internus and gemelli Gluteus minimus Vastus lateralis Fibular collateral ligament Popliteus Literal condyle 180 THE SKELETON Fro. 216. — The Left Femur. (Posterior view.) Obturator externus . Fovea for ligamentum teres Gluteus medius -^'^ Quadratus femoris Capsule -Intertrochanteric crest Vastus lateralis - Gluteal tuberosity Gluteus maximus |r~ -Psoas -Lesser trochante -Iliacus -Pectineus -Adductor brevis Adductor magnus Lateral lip of the Hnea aspera Biceps Vastus laterahs - Vastus intermedn Intervening space of the linea aspera "Adductor longus Vastus medialis "Medial lip of the linea aspera . Nutrient foramen - For femoral artery Plantaris _ Gastrocnemius- Anterior crucial ligament- Intercondylar fossa- l« pCapsule -Tibial collateral ligament Lateral condyle Posterior crucial ligament ' Medial condyle THE FEMUR 181 and when very prominent is termed the third trochanter. The medial Hp curves medialward below the lesser trochanter, where it becomes continuous with the intertrochanteric line; the intervening portion bifurcates and is continued upward as two lines, one of which ends at the small trochanter, and receives some fibres of the iliacus, whilst the other is the linea pectinea and marks the insertion of the pectineus muscle. Toward the lower third of the shaft the medial and lateral lips of the linea aspera again diverge, and are prolonged to the condyles by the medial and lateral supra-condylar lines, enclosing between them a triangular surface of bone, the popliteal surface [planum popliteum] of the femur, which forms the upper part of the floor of the popliteal space. The lateral line is the more prominent and ter- minates below in the lateral epicondyle. The medial one is interrupted above, where the femoral vessels are in relation with the bone, better marked below, where it terminates in the adductor tubercle, a small sharp projection at the sum- mit of the medial epicondyle, which affords attachment to the tendon of the ad- ductor magnus. Fig. 217. — A Diagram to show the Pressure and Tension Curves of the Femur. (After Wagstaffe.) Near the centre of the linea aspera is the foramen for the medullary artery, directed upward toward the head of the bone. From the medial lip of the linea aspera and the lower part of the int-ertrochanteric line arises the vastus medialis (internus), and from the lateral lip and the side of the gluteal ridge arises the vastus lateralis (externus). The adductor magnus is inserted into the medial lip of the linea aspera, from the medial side of the gluteal tuberosity above, and the medial supra- condylar line below. Between the adductor magnus and vastus medialis (internus) four muscles are attached: the pectineus and iliacus above, then the adductor brevis, and lowest of all, the adductor longus. Above, in the interval between the adductor magnus and the vastus lateralis (externus), the gluteus maximus is inserted; in the interval lower down is the short head of the biceps, taking origin from the lower two-thirds of the lateral] lip of the linea aspera and the upper two-thirds of the lateral supra-condylar line. On the popliteal surface of the bone, just above the condyles, are two rough areas from which fibres of the two heads of the gastrocnemius take origin. Above the area for the lateral head of the gastrocnemius is a slight roughness for the plantaris. For purposes of description it is convenient to regard the shaft of the femur as presenting anterior, medial, and lateral surfaces, although definite borders separat- ing the surfaces from one another do not exist. All three surfaces are smooth and the anterior is not separated from the lateral by ridges of any kind. In the middle third of the shaft the medial and lateral surfaces approach one another behind, being separated by the linea aspera. 182 THE SKELETON The shaft is overlapped on its medial side by the vastus medialis (internus) , and on its lateral side by tlie vastus lateralis (externus). The upper three-fourths of the anterior and lateral surfaces afford origin to the vastus intermedius (crureus), and the lower fourth of the anterior surface, to the articularis genu (sub-crureus) . The medial surface is free from muscular attachment. Fig. 218. — Transverse Section op Shaft of Femtjr to show the Medttllary Cavity. Fig. 219. — Section of Upper End of Femur to show the Calcar Femorale. Lateral lip Linea aspera Medial Up . Nutrient canal Lateral surface Medial surf ace Anterior surface Fig. 220. — The Femur at Birth. The lower extremity presents two cartilage-covered eminences or condyles, separated behind by the intercondyloid fossa. The lateral condyle is wider than its fellow and more prominent anteriorly; the medial condyle is narrower, more prominent, and longer, to compensate for the obliquity of the shaft. When the femur is in the natural position, the inferior surfaces of the condyles are on the THE FEMUR 183 same plane, and almost parallel, for articulation with the upper surfaces on the head of the tibia. The two condyles are continuous in front, forming a smooth trochlear surface [facies patellaris] for articulation with the patella. This surface presents a median vertical groove and two convexities, the lateral of which is wider, more prominent, and prolonged farther upward. The patellar surface is faintly marked off from the tibial articular surfaces by two irregular grooves, best seen while the lower end is still coated with cartilage. The lateral groove commences on the medial margin of the lateral condyle near the front of the intercondylar fossa, and extends obliquely forward to the lateral margin of the bone. The general direction of the medial groove is from front to back, turning medially in front and extending backward as a faint ridge which marks off from the Fig. 221. — The Left Femur at the Twentieth Year. (Posterior view ,) The figure shows the relations of the epiphysial and capsular lines. Appears in the firsts and fuses in the nineteenth year the f ourth, and unites the e ighteenth year Appears in the fourteenth, and unite in the seventeenth year Appears early in the ninth month of, intra-uterine life, and unites at the twentieth year rest of the medial condyle a narrow semilunar facet for articulation with the medial perpendicular facet of the patella in extreme flexion. The grooves receive the semilunar menisci in the extended position of the joint. The tibial surfaces are almost parallel except in front, where the medial turns laterally to become continuous with the patellar surface. The opposed surfaces of the two condyles form the boundaries of the inter- condylar fossa and give attachment to the crucial ligaments which are lodged within it. The posterior crucial ligament is attached to the fore part of the lateral surface of the medial condyle and the anterior crucial ligament to the back part of the medial surface of the lateral condyle. The two remaining surfaces of the condyles are broad and convex, and each presents an epicondyle (tuberosity) for the attachment of lateral ligaments. The medial epicondyle, the larger of the two, is surmounted by the adductor tubercle, behind which is an impression for 184 THE SKELETON the medial head of the gastrocnemius on the upper aspect of the condyle; below and behind the lateral epicondyle is a deep groove which receives the tendon of the popliteus muscle when the knee is flexed, and its anterior end terminates in a pit from which the tendon takes origin. Above the lateral epicondyle is a rough impression for the lateral head of the gastrocnemius. The interior of the shaft of the femur is hollowed out by a large medullary canal, and the extremities are composed of cancellated tissue invested by a thin compact la3'er. The arrange- ment of the cancelli in the upper end of the bone forms a good illustration of the effect produced by the mechanical conditions to which bones are subject. In the upper end of the bone the cancellous tissue is arranged in divergent curves. One system springs from the lower part of the neck and upper end of the shaft medially and spreads into the great trochanter ('pressure lamellae'). A second system springs from the lateral part of the shaft and arches upward into the neck and head ('tension lamelte'), crossing the former almost at right angles. A second set of pressure lamellae springs from the lower thick wall of the neck, and extends into the upper part of the head to end perpendicularly in the articular surface mainly along the lines of greatest pressure. A nearly vertical plate of compact tissue (calcar femorale) projects into the neck of the bone from the inferior cervical tubercle toward the great trochanter. This is placed in the line through which the weight of the body falls, and adds to the stability of the neck of the bone; it is said to be liable to absorption in old age. In the lower end of the bone the vertical and horizontal fibres are so disposed as to form a rectangular meshwork. Blood-supply. — The head and neck of the femur receive branches from the inferior gluteal, obturator, and circumflex arteries, and the trochanters from the circumflex arteries. The nutrient vessel of the shaft is derived from either the second or third perforating artery, or there may be two nutrient vessels arising usually from the first and third perforating. The vessels of the inferior extremity arise from the articular branches of the popliteal and the anastomotic branch of the femoral (supremagenu). Ossification. — The femur is ossified from one primary centre for the shaft and from four epiphysial centres. The shaft begins to ossify in the seventh week of intra-uterine life. Early in the ninth month a nucleus appears for the lower extremity. During the first year the nucleus for the head of the bone is visible, and in the fourth year that for the trochanter major. The centre for the lesser trochanter appears about the thirteenth or fourteenth year. The lesser trochanter joins the shaft at the seventeenth, the great trochanter at the eighteenth, the head about the nineteenth, and the lower extremity at the twentieth year. The neck of the femur is an apophysis, or outgrowth from the shaft. The line of fusion of the condylar epiphysis with the shaft passes through the adductor tubercle. The morphological relation of the patellar facet to the tibial portions of the condyles is worthy of notice. In a few mammals, such as the ox, this facet remains separated from the condyles by a furrow of rough bone, The angle which the neck of the femur forms with the shaft at birth measures, on an average, 160°. In the adult it varies from 110° to 140°; hence the angle decreases greatly during the period of growth. When once growth is completed, the angle, as a rule, remains fixed. (Humphry.) THE PATELLA The patella (fig. 222) or knee-pan, situated in front of the knee-joint, is a sesa- moid bone, triangular in shape, developed in the tendon of the quadriceps femoris. Its anterior surface, marked by numerous longitudinal striae, is slightly convex, and Fig. 222.- Anterior surface -The Left Patella. perforated by small openings which transmit nutrient vessels to the interior of the bone. It is covered in the recent state by a few fibres prolonged from the com- mon tendon of insertion (supra-patellar tendon) of the quadriceps femoris, into the ligamentum patellae (infra-patellar tendon), and is separated from the skin by one THE TIBIA 185 or more bursse. The posterior surface is largely articular, covered with cartilage in the recent state, and divided by a slightly marked vertical ridge, corresponding to the groove on the trochlear surface of the femur, into a lateral larger portion for the lateral condyle, and a medial smaller portion for the medial condyle. Close to the medial edge a faint vertical ridge sometimes marks off a narrow articu- lar facet, for the lateral margin of the medial condyle of the femur in extreme flexion of the leg. Below the articular surface is a rough, non-articular depression, giving attachment to the ligamentum patellae, and separated by a mass of fat from the head of the tibia. The base or superior border is broad, sloped from behind downward and for- ward, and affords attachment, except near the posterior margin, to the common Fig. 223. — The Superior Border or Base of the Left Patella. Anterior surface tendon of the quadriceps. The borders, thinner than the base, converge to the apex below, and receive parts of the two vasti muscles. The apex forms a blunt point directed downward, and gives attachment to the ligamentum patellae, by which the patella is attached to the tibia. Structurally the patella consists of dense cancellous tissue covered by a thin compact layer, and it receives nutrient vessels from the articular branch of the suprema genu (anastomotic), the anterior tibial recurrent, and the inferior articular branches of the popliteal. Ossification. — The cartilaginous deposit in the tendon of the quadriceps muscle takes place in the fourth month of intra-uterine life. Ossification begins from a single centre during the third year, and is completed about the age of puberty. THE TIBIA The tibia (figs. 224, 225) or shin-bone is situated at the front and medial side of the leg and nearly parallel with the fibula. Excepting the femur, it is the largest bone in the skeleton, and alone transmits the weight of the trunk to the foot. It articulates above with the femur, below \vith the tarsus, and laterally with the fibula. It is divisible into two extremities and a shaft. The upper extremity (or head) consists of two lateral eminences, or condyles. Their superior articular surfaces receive the condyles of the femur, the articular parts being separated by a non-articular interval, to which ligaments are attached. The medial articular surface is oval in shape and concave for the medial condyle of the femur. The lateral articular surface is smaller, somewhat circular in shape, and presents an almost plane surface for the lateral condyle. The peripheral portion of each articular surface is overlaid by a fibro-cartilaginous meniscus of semilunar shape, connected with the margins of the condyles by bands of fibrous tissue termed coronary ligaments. Each semilunar meniscus is attached firmly to the rough interval separating the articular surfaces. This interval is broad and depressed in front, the anterior intercondyloid fossa, where it affords attach- ment to the anterior extremities of the medial and lateral menisci and the anterior crucial ligament; elevated in the middle to form the intercondyloid eminence or spine of the tibia, a prominent eminence, presenting at its summit two compressed intercondyloid tubercles, on to which the condylar articular surfaces are prolonged ; the posterior aspect of the base of the eminence affords attachment to the posterior extremities of the lateral and medial semilunar menisci, and limits a deejj notch, inclined toward the medial condyle, known as the posterior intercondyloid fossa or popliteal notch. It separates the condyles on the posterior aspect of the head and gives attachment to the posterior crucial ligament, and part of the posterior ligament of the knee-joint. Anteriorly, the two condyles are confluent, and form a somewhat flattened surface of triangular outline, the apex of which forms the tuberosity of the tibia. The tuberosity is divisible into two parts. The upper 186 THE SKELETON. part, rounded and smooth, receives the attachment of the ligamentum patellse. The lower part is rough, and into its lateral edges prolongations of the ligamentum patella are inserted. A prominent bursa intervenes between the ligament and the anterior aspect of the upper extremity of the bone. Fig. 224. — -The Left Tibia and Fibitla. (Anterior view.) Intercondyloid eminence Medial meniscus Coronary ligament Anterior crucial ligament- Medial condyle Tibial collateral ligament Ligamentum patellge Gracilis Sartorius border of crest of the tibi Medial surface of tibia, Interosseous membrane- Anterior ligament of ankle-joint Deltoid ligament- Medial malleolus- Lateral meniscus Capsule Lateral condyle Biceps and the anterior tibio-fibular ligament Fibular collateral ligament Extensor digitorum longus Peroneus longus Peroneus brevis Extensor digitorum longus Peroneal surfa.ce of fibula Extensor surface of fibula Extensor hallucis longus Peroneus tertius Subcutaneous portion Anterior tibio-fibular ligament Lateral malleolus Anterior talo-fibular ligament The medial condyle is less prominent though more extensive than the lateral, and near the posterior part of its circumference is a deep horizontal groove for the attachment of the central portion of the semimembranosus tendon. The margins of this groove, and the surface THE TIBIA 187 of bone below, give attachment to the tibial (internal) lateral ligament of the knee. On the under aspect of the lateral condyle is a rounded articular facet for the head of the fibula, flat and nearly circular in outline, directed downward, backward, and laterally. The circumfer- ence of the facet is rough and gives attachment to the ligaments of the superior tibio-fibular joint, while above and in front of the facet, at the junction of the anterior and lateral surfaces Fig. 225. — The Left Tibia and Fibula. (Posterior view.) Posterior intercondyloid notch Lateral meniscus ^^__^ ~f^ 1 iV^-= ^ Medial meniscus Capsule 3(f*^*«io«.» ^* '*!>uui»--i^'ir^ Capsule Posterior crucial ligament V^g,; • ■■ vyf^in. kT vJ j^pgx ^ \' ^.L-w ^ J£Buff'*'w**>Kk*^ 'Semimembranosus Posterior tibio-fibular ligament' Flexor hallucis longus- Flexor surface of fibula Nutrient foramen' Peroneus brevis Posterior tibio-fibular ligament' Groove for flexor hallucis longus- Posterior talo-fibular ligament Calcaneo-fibular ligament Nutrient foramen flexor digitorum longus Groove for tibialis posterior and flexor digitorum longus Deltoid ligament Posterior ligament of ankle-joint of the condyle, is a ridge for the ilio-tibial band. A slip from the tendon of the biceps and parts of the extensor longus digitorum and peroneus longus muscles are attached to the head below the ilio-tibial band. 188 THE SKELETON The shaft or body [corpus] of the tibia, thick and prismatic above, becomes thinner as it descends for about two-thirds of its length, and then gradually ex- pands toward its lower extremity. It presents for examination three borders and three surfaces. The anterior border is very prominent and known as the anterior crest of the tibia. It commences above on the lateral edge of the tuberosity and terminates below at the anterior margin of the medial malleolus. It runs a some- what sinuous course, and gives attachment to the deep fascia of the leg. The medial border extends from the back of the medial condyle to the posterior margin of the medial malleolus, and affords attachment above, for about three inches, to Fig. 226. — The Tibia and Fibula at the Sixteenth Yeae. The figure shows the relations of the epiphysial and capsular lines. apsule .Appears at birth; unites at twenty- one : but union is sometimes delayed to twenty-five Appears at the fourth year; unites at twenty -four Capsule Appears at the twenty cond year; unites at the tibial (internal) lateral ligament of the knee-joint and in the middle third, to the soleus. The interosseous crest or lateral border, thin and prominent, gives attachment to the interosseous membrane. It commences in front of the fibular facet, on the upper extremity, and toward its termination bifurcates to enclose a triangular area for the attachment of the interosseous ligament uniting the lower ends of the tibia and fibula. The medial surface is bounded by the medial margin and the anterior crest; it is broad above, where it receives the insertions of the sartorius, gracilis, and semi- tendinosus; convex and subcutaneous in the remainder of its extent. The lateral surface lies between the crest of the tibia and the interosseous crest. The upper two-thirds presents a hollow for the origin of the tibialis anterior; the rest of the THE FIBULA 189 surface is convex and covered by the extensor tendons and the anterior tibial vessels. The posterior surface is limited by the interosseous crest and the medial border. The upper part is crossed obliquely by a rough popliteal line, extending from the fibular facet on the lateral condyle to the medial border, a little above the middle of the bone. The popliteal line gives origin to the soleus and attachment to the popliteal fascia, while the triangular surface above is occupied by the popliieus muscle. Descending along the posterior surface from near the middle of the popliteal line is a vertical ridge, well marked at its commencement, but gradually becoming indistinct below. The portion of the surface between the ridge and the medial border gives origin to the flexor digilorum longus; the lateral and narrower part, between the ridge and the interosseous border, to fibres of the tibialis posterior. The lower third of the posterior surface is covered by flexor tendons and the posterior tibial vessels. Immediately below the popliteal line and near the interosseous border is the large medullary foramen directed obliquely downward. The lower extremity, much smaller than the upper, is quadrilateral in shape and presents a strong process called the medial malleolus, projecting downward from its medial side. The anterior surface of the lower extremity is smooth and rounded above, where it is covered by the extensor tendons, rough and depressed below for the attachment of the anterior ligament of the ankle-joint. It some- times bears a facet for articulation with the neck of the talus (astragalus) . (A. Thomson.) The posterior surface is rough and is marked by two grooves. The medial and deeper of the two encroaches on the malleolus, and receives the tendons of the tibialis posterior and flexor digitorum longus; the lateral, very shallow and sometimes indistinct, is for the tendon of the flexor hallucis longus. The lateral sur- face is triangular and hollowed for the reception of the lower end of the fibula and rough for the interosseous ligament which unites the two bones, except near the lower border, where there is usually a narrow surface, elongated from before back- ward, covered with cartilage in the recent state for articulation with the fibula. The lines in front of and behind the triangular surface afford attachment to the anterior and posterior ligaments of the inferior tibio-fibular articulation. The medial surface, prolonged downward on the medial malleolus, is rough, convex, and subcutaneous. The lateral surface of this process is smooth and articulates with the facet on the medial side of the talus (astragalus). Its lower border is notched, and from the notch, as well as from the tip and anterior border, the fibres of the deltoid Hgament of the ankle-joint descend. The inferior or terminal surface, by which the tibia articulates with the talus, is of quadrilateral form, concave from before backward, wider in front than behind, and laterally than medially where it is continuous with the lateral surface of the malleolus. The occasional facet on the anterior siu'face of the lower extremity of the tibia is a pressure facet, produced by extreme flexion of the ankle joint. It is therefore sometimes designated as the squatting facet." (See fig. 333.) Blood-supply. — The tibia is a very vascular bone. The nutrient artery of the shaft is furnished by the posterior tibial, and is the largest of its kind in the body. The head of the bone receives numerous branches from the inferior articular arteries of the popliteal and the recurrent branches of the anterior and posterior tibial. The lower extremity receives twigs from the posterior and anterior tibial, the peroneal, and the medial malleolar arteries. Ossification. — The tibia is ossified from one principal centre for the shaft, which appears in the eighth week of intra-uterine life, and two epiphyses, the centres for which appear in the cartilaginous head of the bone toward the end of the ninth month, and in the lower extremity during the second year. The latter unites with the shaft at eighteen, but the union of the head with the shaft does not take place until the twenty-first year, and it may even be delayed until twenty-five. The upper part of the tubercle of the tibia is ossified from the upper epiphysis, and the lower part from the diaphysis. THE FIBULA The fibula (figs. 224, 225) is situated on the lateral side of the leg and, in proportion to its length is the most slender of all the long bones. It is placed nearly parallel to the tibia with which it is connected above and below. In man it is a rudimentary bone and bears none of the weight of the trunk, but is retained on account of the muscles to which it gives origin and its participation in the formation of the ankle-joint. Like other long bones, it is divisible into a shaft and two extremities. The head [capitulum fibulae], or upper extremity, is a rounded prominence. Its upper surface presents laterally a rough eminence for the attachment of the 190 THE SKELETON biceps tendon and the fibular (long external) collateral ligament of the knee-joint, medially it presents a round or oval facet [fades articularis capituli], directed upward, forward, and medially, for articulation with the lateral condyle (tuber- osity) of the tibia. The margin of the facet gives attachment to the articular capsule of the superior tibio-fibular articulation. Posteriorly, the head rises into a pointed apex (styloid process), which affords attachment to the short lateral ligament of the knee-joint, and on the lateral side, to part of the biceps tendon. The posterior aspect of the head gives attachment to the soleus, the lateral aspect, extend- ing also in front of the eminence for the biceps, to the peroneus longus; from the anterior aspect fibres of the extensor digiiorum longus arise, whilst the medial side lies adjacent to tlie tibia. The shaft [corpus fibulse], in its upper three-fourths, is quadrangular, possessing four borders and four surfaces, whereas its lower fourth is flattened from side to side, so as to be somewhat triangular. The borders and surfaces vary exceed- ingly so that their description is difficult. The anterior crest (or antero-lateral border) commences in front of the head and terminates below by dividing to enclose a subcutaneous surface, triangular in shape, immediately above the Fig. 227. — The Upper End of the Left Flbtjla to show Musculae and Ligamentous Attachments X 2. (G. J. Jenkins.) Fibular collateral ligament Biceps ^ V^^^^^^^- 9 JBt — Capsule of superior tibio- ^ ' fibular joint Styloid process Posterior superior tibio- fibular ligament lateral malleolus. It gives attachment to a septum separating the extensor muscles in front from the peronei muscles on the lateral aspect. The interosseous crest (or antero-medial border), so named from giving attachment to the interos- seous membrane, also commences in front of the head, close to the anterior crest, and terminates below by dividing to enclose a rough triangular area immediately above the facet for the talus {astragalus) ; this area gives attachment to the inferior interosseous ligament, and may present at its lower end a narrow facet for articula- tion with the tibia. The medial crest (or postero-medial border), sometimes described as the oblique line of the fibula, commences at the medial side of the head and terminates below by joining the interosseous crest, in the lower fourth of the shaft. It gives attachment to an aponeurosis separating the tibialis posterior from the soleus and flexor hallucis longus. The lateral crest (or postero- lateral border) runs from the back of the head to the medial border of the peroneal groove on the back of the lower extremity; it gives attachment to the fascia sepa- rating the peronei from the flexor muscles. The anterior or extensor surface is the interval between the interosseous and anterior crests. In the upper third it is extremely narrow, but broadens out below, where it is slightly grooved longitudinally. It affords origin to three muscles : laterally, in the upper two-thirds, to the extensor digitorum longus, and, in the lower third, to the peroneals tertius; medially, in the middle third, also to the extensor hallucis longus. The medial surface, situated between the interosseous and medial crests, is narrow above and below, and broadest in the middle. It is grooved and sometimes crossed obliquely by a prominent ridge, the secondary oblique line of the fibula; the surface gives origin to the tibialis posterior, and the ridge to a tendinous septum in the substance of the muscle. The posterior surface THE TARSUS 191 is the interval between the medial and lateral crests, and is somewhat twisted so as to look backward above and medially below. It serves, in its upper third, for the origin of the soleus, and in its lower two-thirds for the flexor hallucis longus. Near the middle of the surface is the medullary foramen, directed downward toward the ankle. The lateral surface, situated between the anterior and lateral crests, is also somewhat twisted, looking laterally above and backward below, where it is continuous with the groove on the back of the lateral malleolus. The surface is often deeply grooved and is occupied by the peroneus longus in the upper two-thirds and by the peroneus brevis in the lower two-thirds. The lateral malleolus or lower extremity is pyramidal in form, somewhat flattened from side to side, and joined by its base to the shaft. It is longer, more prominent, and descends lower than the medial malleolus. Its lateral surface is convex, subcutaneous, and continuous with the triangular subcutaneous surface on the shaft, immediately above. The medial surface is divided into an anterior and upper area [facies articularis malleoli], triangular in outline and convex from above downward for articulation with the lateral side of the talus (astragalus), and a lower and posterior excavated area, the digital fossa, in which are attached the transverse iriferior tibio-fibular ligament and the posterior talo-fibular (posterior fasciculus of the external lateral) ligament of the ankle. The anterior border is rough and gives attachment to the anterior talo-fibular (anterior fasciculus of the external lateral) ligament of the ankle, and the anterior inferior tibio-fibular liga- ment. The posterior border is grooved for the peronei tendons, and near its upper part gives attachment to the posterior inferior tibio-fibular ligament. The apex or summit of the process affords attachment to the calcaneo-fibular (middle fasciculus of the external lateral) ligament of the ankle. Blood-supply. — The shaft of the fibula receives its nutrient artery from the peroneal branch of the posterior tibial. The head is nourished by branches from the inferior lateral articular branch of the popliteal artery, and the lateral malleolus is supplied mainly by the peroneal, and its perforating and malleolar branches. Ossification. — The shaft of the fibula commences to ossify in the eighth week of intra- uterine life. A nucleus appears for the lower extremity in the second year, and one in the upper extremity during the fourth or fifth year. The lower extremity fuses with the shaft about twenty, but the upper extremity remains separate until the twenty-second year or even later. It is interesting, in connection with the times of appearance of the two epiphyses of the fibula, to note that the ossification of the lower epiphysis is contrary to the general rule — viz., that the epiphysis toward which the nutrient artery is directed is the last to undergo ossification. This is perhaps explained by the rudimentary nature of the upper extremit}'. In birds the head of the bone is large and enters into the formation of the knee-joint; and in human embryos, during the second month, the fibula is quite close up to the femur. The human fibula is characterised by the length of its malleolus, for in no other vertebrate does this process descend so far below the level of the tibial malleolus. On the other hand, in the majority of mammals the tibial descends to a lower level than the fibular malleolus. In the human embryo of the third month, the lateral is equal in length to the medial malleolus. At the fifth month the lateral malleolus exceeds the medial by 1.5 mm.; at birth, the lateral malleolus is still longer; and by the second year it assumes its adult proportion. THE TARSUS The tarsal bones [ossa tarsi] (figs. 228, 229) are grouped in two rows: — a proximal row, consisting of the talus and calcaneus, and a distal row, consisting of four bones which, enumerated from tibial side, are the first, second, and third cuneiform bones and the cuboid. Interposed between the two I'ows on the tibial side of the foot is a single bone, the navicular ; on the fibular side the proximal and distal rows come into contact. Compared with the carpus, the tarsal bones present fewer common characters, and greater diversity of size and form, in consequence of the modifications for sup- porting the weight of the trunk. On each, however, six surfaces can generally be recognised, articular when in contact with neighbouring bones, elsewhere sub- cutaneous or rough for the attachment of ligaments. As regards ossification, they correspond in the main with that of the bones of the carpus. Each tarsal bone is ossified from a single centre, but the calcaneus has, in addition, an epiphysis for a large part of its posterior extremity, and the talus, an occasional centre for the os trigonum. 192 THE SKELETON The Talus The talus (or astragalus) (figs. 230, 231) is, next to the calcaneus, the largest of the bones of the tarsus. Above it supports the tibia, below it rests on the cal- caneus, at the sides it articulates with the two malleoli, and in front it is received into the navicular. For descriptive purposes, it may be divided into a head, neck, and body. Fig. 228. — The Left Foot. (Superior surface.) Tendo Achill Extensor digitorum brevis Peroneus brevis Peroneus tertius Metatarsus |\ [I First phalanx Second phalam l.h Third phalanx Extensor digitorum longus The body is somewhat quadrilateral in shape. The upper surface presents a broad, smooth surface for the tibia, slightly concave from side to side, convex from before backward, and wider in front than behind. "The diminution in width posteriorly is associated with an obliquity of the lateral margin, which is directed medially as well as backward and downward. The inferior surface is occupied by a transversely disposed oblong facet [taoies articularis calcanea THE TARSUS 193 posterior], deeply concave from side to side, which articulates with a corresponding surface on the calcaneus. Of the malleolar sm-faces, the lateral is almost entirely occupied by a large triangular facet, broad above, where it is continuous with the superior surface, concave from above downward, for articulation with the lateral malleolus; on the medial malleolar surface is a pyriform facet continuous with the superior surface, broad in front and narrow behind, which articulates with the medial malleolus. Below this facet the medial surface is rough for the attachment of the deep fibres of the deltoid (internal lateral) ligament of the ankle. The Fig. 229. — The Left Foot. (Plantar surface.) Abductor digiti quinti Abductor ossis metatarsi quiati Quadratus plantae (lateral head) Flexor hallucis brevis Abductor ossis metatarsi quinti Flexor brevis digiti quinti Adductor hallucis Third plantar interosseous Second plantar interosseous First plantar interosseou Flexor brevis digiti quinti Abductor digiti quinti Third plantar interosseous Second plantarinterosseous' First plantar interosseouE. Flexor digitorum brevis. Flexor digitorum longus Abductor hallucis Flexor digitorumi brevis Quadratus plantce (medial head) Tibiahs posterior Tibialis anterior Peroneus longus Abductor hallucis Flexor hallucis brevis (medial) portion) Flexor hallucis brevis (lateral) portion) Adductor hallucis Transversus pedis Flexor hallucis longus superior surface and the two malleolar surfaces together constitute the trochlea. The poste- rior Surface is of small extent and marked by a groove which lodges the tendon of the flexor hallucis longus. Bounding the groove on either side are two tubercles, of which the lateral [processus posterior tali] is usually the more prominent, for attachment of the posterior talo-fibular ligament of the ankle-joint; the medial tubercle gives attachment to the medial talo-calcaneal ligament. Continuous, with the anterior aspect of the body is the neck, a con- 194 THE SKELETON strioted part of the bone supporting the head. Above it is rough, and perforated by numerous vascular foramina. Below, it presents a deep groove [sulcus tali], directed from behind forward and lateralward. When the talus is articulated with the calcaneus, this furrow is converted into a canal [sinus tarsi] in which is lodged the interosseous talo-calcaneal ligament. The head is the rounded anterior end of the bone, and its large articular surface is divisible into three parts: in front, a smooth, oval convex area, directed downward and forward for the navicular bone; below, an elongated facet, convex from front to back, for articulation with the sustentacu- lum taJi of the calcaneus; and between these, is a small facet which rests on the calcaneo- FiG. 230. — The Left Talus. (Plantar view.) Groove for the flexor hallucis longus For calcaneus ■For the sustentaculum tall For the calcaneo-navicular (or the spring) ligament For navicular navicular ligament, separated from it by the synovial membrane of the talo-calcaneo-navicular joint. Articulations. — The talus articulates with four bones and two ligaments. Above and medially with the tibia, below with the calcajieus, in front with the navicular, laterally with the fibula. The head articulates with the calcaneo-navicular ligament and the lateral border of the superior surface, at its posterior part, with the transverse ligament of the inferior tibio- fibular joint. The talus is a very vascular bone and is nourished by the dorsalis pedis artery and its tarsal branch. It gives attachment to no muscles. Fig. 231. — A Talus with the Os Trigonum. Os trigonum Ossification. — The talus is ossified from one, occasionallj* from two, nuclei. The principal centre for this bone appears in the middle of the cartilaginous talus at the seventh month of intra-uterine life. The additional centre is deposited in the posterior portion of the bone, and forms the lateral posterior tubercle which may remain separate from the rest of the bone and form the os trigonum. At birth, the talus presents some important peculiarities in the disposi- tion of the articular facet on the tibial side of its body, and in the obliquity of its neck. If, in the adult talus, a line be drawn through the middle of the superior trochlear surface parallel with its medial border, and a second line be drawn along the lateral side of the neck of the bone so as to intersect the first, the angle formed by these two lines will express the obliquity of the neck of the bone. This in the adult varies greatly, but the average may be taken as 10°. In the THE TARSUS 195 foetus at birth the angle averages 35°, whilst in a young orang it measures 45°. In the normal adult talus the articular surface on the tibial side is limited to the body of the bone. In the foetal talus it extends for some distane on to the neck, and sometimes reaches almost as far forward as the navicular facet on the head of the bone. This disposition of the medial malleolar facet is a characteristic feature of the talus in the chimpanzee and the orang. It is related to the inverted position of the foot which is found in the human foetus almost up to the period of birth, and is of interest to the surgeon in connection with some varieties of club-foot. (Shattock and Parker.) The Calcaneus The calcaneus (or os calcis) (figs. 232, 233) is the largest and strongest bone of the foot. It is of an elongated form, flattened from side to side, and expanded at its posterior extremity, which projects downward and backward to form the heel. It presents six surfaces, superior, inferior lateral, medial, anterior and posterior. The superior surface presents in the middle a large, oval, convex, articular facet for the under aspect of the body of the talus. In front of the facet the bone is marked by a deep Fig. 232. — The Left Calcaneus. (Dorsal view.) Media] process Calcaneal groove' Peroneal tubercle Facet for talus depression, the floor of which is rough for the attachment of ligaments, especially the talo- calcaneal, and the origin of the extensor digitorum hrevis muscle; when the calcaneus and talus are articulated, this portion of the bone forms the floor of a cavity called the sinus tarsi. Medi- ally, the upper surface of the bone presents a well-marked process, the sustentaculum tali, furnished with an elongated concave facet, occasionally divided into two, for articulation with the under aspect of the head of the talus. The posterior part of the upper surface is non- articular, convex from side to side, and in relation with a mass of fat placed in front of the tendo Aohillis. The inferior surface is narrow, rough, uneven, and ends posteriorly in two processes: the medial is the larger and broader, the lateral is narrower but prominent. The medial process affords origin to the abductor hallucis, the flexor digitorum brevis, and the abductor digiti quinti; the last muscle also arises from the lateral process and from the ridge of bone between. The rough surface in front of the tubercles gives attachment to the long plantar ligament (calcaneo- cuboid) and the lateral head of the quadratus plantoe. Near its anterior end this surface forms a rounded eminence, the anterior tubercle, from which (as well as from the shallow groove in front) the plantar (short) calcaneo-cuboid ligament arises. (According to the BNA nomen- clature, the medial and lateral processes belong to the tuber calcanei or the posterior extremity of the bone.) The lateral surface is broad, flat, and slightly convex. It represents near the middle a small eminence for the calcaneo-fibular ligament of the ankle-joint. Below and in front of this is a well-marked tubercle — the trochlear process [processus trochlearis] (or peroneal tubercle), separating two grooves, the upper for the peroneus brevis and the lower for the peroneiis longus. The medial surface is deeply concave, the hollow being increased by the prominent medial process behind and the overhanging sustentaculum tali in front. The latter forms a promi- nence of bone projecting horizontally, concave and articular above, grooved below for the tendon of the flexor hallucis longus, and giving attachment to a slip of the tendon of the tibialis posterior, the inferior calcaneo-navicular ligament, and some fibres of the deltoid ligament of the ankle-joint. The hollow below the process receives the plantar vessels and nerves and its lower part gives attachment to the medial head of the quadratus planice. 196 THE SKELETON The anterior surface is somewhat quadrilateral in outline with rounded angles, and presents a saddle-shaped articular surface for the cuboid. The posterior surface is oval in shape, rough, and convex. It is divided into three parts: — an upper, smooth and separated by a bursa from the tendo Aohillis; a middle part giving attachment to the tendo Achillis and the plantaris, and a lower part in relation to the skin and fat of the heel. The expanded posterior extremity of the bone is known as the tuber calcanei. Articulations. — The calcaneus articulates with two bones, the talus above and the cuboid in front. Blood-supply. — The calcaneus is nourished by numerous branches from the posterior tibial and the medial and lateral malleolar arteries. They enter the bone chiefly on the inferior and medial surfaces. Fig. 233. — The Calcaneus at the Fifteenth Year, showing the Epiphysis. Appears at the tenth, and unites at the sixteenth year Ossification. — The primary nucleus appears in the sixth month of intra-uterine life. The epiphysis, for its posterior extremity, begins to be ossified in the tenth year and is united to the body of the bone by the sixteenth year. It may extend over the whole of the posterior surface, as shown in fig. 233, or over the lower two-thirds only, leaving a part above in relation to the bursa beneath the tendo Achillis, which is formed from the primary nucleus. The medial and lateral processes are formed by the epiphysis. The Naviculae The navicular [os naviculare pedis] (figs. 234, 235) is oval in shape, flattened from before backward, and situated between the talus behind and the three cuneiform bones in front. It is characterised by a large oval, concave, articular Fig. 234. — The Left Navicular. (Anterior view.) For first cuneiform' Medial border Tuberosity ■For second cuneiform Lateral border ■For third cuneiform facet on the posterior surface, which receives the head of the talus; a broad, rough, rounded eminence on the medial surface, named the tuberosity of the navicular, the lower part of which projects downward and gives insertion to the tendon of Fig. 235. — The Left Navicular, showing a Facet for the Cuboid. For first cuneif' For second cuneiform ■For third cuneiform For cuboid the tibialis posterior; and an oblong-shaped anterior surface, convex and chvided by two vertical ridges into three facets which articulate with the three cuneiform bones. The superior (dorsal) surface is rough, convex, and slopes downward to THE TARSUS 197 the tuberosity; the inferior (plantar) surface is irregular and rough for the attach- ment of the inferior cAlcaneo-navicular ligament, and the lateral surface is rough and sometimes presents a small articular surface for the cuboid. Articulations. — With the talus behind, with the three cuneiform bones in front, and occasionally with the cuboid on its lateral aspect. Ossification. — The nucleus for the navicular appears in the course of the fourth year. The tuberosity of the navicular, into which the tibialis posterior acquires its main insertion, occasion- ally develops separately, and sometimes remains distinct from the rest of the bone. The Cuneiform Bones Of the three cuneiform bones, the first is the largest, the second is the smallest, and the third intermediate in size. They are wedge-shaped bones placed between the navicular and the first, second and third metatarsal bones. Posteriorly, the ends of the bones lie in the same transverse line, but in front, the first and third project farther forward than the second, and form the sides of a deep recess into which the base of the second metatarsal bone is received. Fig. 236. — The Left First Cuneiform. (Medial surface.) For first metatarsal The first cuneiform [os cuneiforme primum] (figs. 236, 237) is distinguished by its large size and by the fact that when articulated, the base of the wedge is directed downward and the apex upward. The posterior surface is concave and pyritorm for articulation with the medial facet on the anterior surface of the navicular. The anterior surface forms a reniform articular facet for the base of the first metatarsal. The medial surface is rough, and presents an oblique groove for the tendon of the tibialis anterior; this groove is limited inferiorly by an oval facet into which a portion of the tendon is inserted. The lateral surface is concave and presents along its superior and posterior borders a reversed L-shaped facet for articulation with the second cuneiform, and, at its anterior extremity, with the second metatarsal. Anteriorly it is rough for ligaments. The inferior surface is rough for the insertion of the peroneus longus, tibialis anterior, and (usually) the tibialis posterior. The superior surface is the narrow part of the wedge and is directed upward. FiQ 237. — The Left First Cuneiform. (Lateral aspect.) For second metatarsal For second cuneiform Articulations. — With the navicular behind, second cuneiform and second metatarsal on its lateral side, and first metatarsal in front. Ossification. — From a single nucleus which appears in the course of the third year. The second cuneiform [os cuneiforme secundum] (figs. 238, 239) is placed with the broad extremity upward and the narrow end downward, and is readily recognised by its nearly square base. The posterior surface, triangular and concave, articulates with the middle facet on the anterior surface of tlie navicular. The anterior surface, also triangular, but narrower than the posterior surface, articulates with the base of the second metatarsal. The medial surface has a reversed L-shaped facet running along its superior and posterior margins for articulation with the corresponding facet on the first cuneiform, and is rough elsewhere for the 198 THE SKELETON attachment of ligaments. On the lateial surface near its posterior border is a vertical facet, sometimes bilobed, for the third cuneiform, and occasionally a second facet at the anterior inferior angle. The superior surface forms the square-cut base of the wedge and is rough for the attachment of ligaments. The inferior surface is sharp and rough for ligaments and a slip of the tendon of the tibialis posterior. Fig. 238. — The Left Second Cuneiform. (Medial sm-face.) For first cuneiform For second metatarsal Articulations. — With the navicular behind, second metatarsal in front, third cuneiform on the lateral side, and first cuneiform on the medial side. Ossification. — From a single nucleus which appears in the fourth year. The third cuneiform bone (figs. 240, 241) also placed with the broad end directed upward and the narrow end downward, is distinguished by the oblong shape of its base. Like the Fig. 239. — The Left Second Cuneiform. (Lateral surface.) -For third cuneiform For navicular jional facet for third cuneiform second cuneiform, the posterior surface presents a triangular facet for the navicular; and the anterior surface a triangular facet, longer and narrower, for the third metatarsal. The medial surface has a large facet extending along the posterior border for the second cuneiform, and along the anterior border a narrow irregular facet for the lateral side of the base of the second metatarsal. Occasionally, a small facet is present near the anterior inferior angle for the second Fig. 240. — The Left Third Cuneiform (Medial surface.) For second cuneiform - For navicular Foi second metatarsal. The circular facet near the inferior angle is for the second cuneiform cuneiform. The lateral surface has a large distinctive facet near its posterior superior angle for the cuboid, and at the anterior superior angle there is usually a small facet for the medial side of the base of the fourth metatarsal. The superior surface, oblong in shape, is rough for ligaments, and the inferior, forming a rounded margin, receives a slip of the tibialis posterior and gives origin to a few fibres of the^e:!;or hallucis brevis. Fig. 241. — The Left Third Cuneiform. (Lateral surface.) T^ z ..t- 1. 4. , i T. =^ ^1 i^-rt-t-i — For cuboid For fourth metatarsal i v,.^ -«i i , >• i For third metatarsal Articulations. — With the navicular behind, third metartarsal in front, cuboid and fourth metatarsal on the lateral side, .second cuneiform and second metatarsal on the me'dial side. Ossification. — A single nucleus appears in the course of the first year. THE TARSUS 199 The Cxiboid The cuboid (figs. 242, 243, 244), irregularly cubical in shape, is placed on the lateral aspect of the foot, forming a continuous line with the calcaneus and the fourth and fifth metatarsals. Its posterior surface is somewhat quadrangular with rounded angles and presents a saddle- shaped articular surface for the calcaneus. Its lower and medial angle is somew-hat prolonged backward beneath the sustentaculum tali (calcaneal process of the cuboid), an arrangement to oppose the upward or outward movement of the bone. This process occasionally terminates Fig. 242. — The Left Cdboid. (Medial view.) For third cuneiform j|^iq5\-J — J'''', 'A — For fourth metatarsal For calcaneus Groove for tendon of the per longus "■ ■- - in a rounded facet which plays on the head of the talus lateral to the facet for the calcaneo navicular ligament. The anterior surface is smaller and divided by a vertical ridge into two articular facets, a lateral for the base of the fifth, and a medial for the base of the fourth meta- tarsal. The superior surface is rough, non-articular, and directed obliquely upward. The inferior surface presents a prSminent ridge for the attachment of the long plantar (calcaneo- cuboid) ligament, in front of which is a deep groove — the peroneal groove — running obliquely forward and medially and lodging the tendon of the peroneiis longus. The ridge terminates laterally in an eminence, the tuberosity of the cuboid, on which there is usually a facet for a sesamoid bone of the tendon contained in the groove. The part of the surface behind the ridge is rough for the attachment of the plantar (short) calcaneo-cuboid ligament, a slip of the tibialis posterior, and a few fibres of the flexor hallucis hrevis. Fig. 243.- -The Left Cuboid. (Medial view.) For third cuneiform For calcaneus -fSpTM For navicular (occasional) "z/^vA .^^v-^'Il Groove for tendon of the peroneus_ longus ^^^^ The medial surface presents, near its middle and upper part, an oval facet for articulation with the third cuneiform bone (fig. 242); behind this, a second facet for the navicular is fre- quently seen (fig. 243). Generally the two facets are confluent and then form an elliptical surface (fig. 244). The remainder of this surface is rough for the attachment of strong inter- osseous ligaments. The lateral surface, the smallest and narrowest of all the surfaces, presents a deep notch which leads into the peroneal groove. Articulations. — With the calcaneus behind, fourth and fifth metatarsals in front, third cuneiform and frequently the navicular on the medial side; occasionally also the talus. Fig. 244. — The Left CtTBOiD. (Medial view.) For third cuneiform For navicular Ossification. — The cuboid is ossified from a single nucleus which appears about the time of birth. Accessory tarsal elements. — As in the carpus, a number of additional elements may occur in the tarsus. The most frequent of these is the os trigonum, which has already been noticed. Ne.\t in frequency is an additional first cuneiform, resulting from the ossification of the plantar half of that bone independently of the dorsal half, so that the bone is represented by a plantar and a dorsal first cuneiform. Other additional elements may occasionally occur at the upper posterior angle of the sustentaculum tali; at the anterior superior angle of the cal- caneus, between that bone and the navicular; in the angle between the first cuneiform and the first and second metatarsals; and in the fibular angle between the fifth metatarsal and the cuboid (os Vesalianum). 200 THE SKELETON The fibular portion of the navicular is sometimes united to the cuboid and quite separate from the rest of the navicular, the cuboid in such eases articulating with the talus. This con- dition suggests the recognition of the fibular portion of the navicular as a distinct accessory tarsal element, the cuboides secundarium, though it has not yet been observed as an inde- pendent bone in the human foot. THE METATARSUS The metatarsus [ossa metatarsalia] consists of a series of five somewhat cylindrical bones. Articulated with the tarsus behind, they extend forward, nearly parallel with each other, to their anterior extremities, which articulate with the toes, and are numbered according to their position from great toe to small toe. Like the corresponding bones in the hand, each presents for examination a three-sided shaft, a proximal extremity termed the base, and a distal extremity or head. The shaft tapers gradually from the base to the head, and is slightly curved longitudinally so as to be convex on the dorsal and concave on the plantar aspect. A typical metatarsal bone. — The shaft [corpus] is compressed laterally and presents for examination three borders and three surfaces. The two borders, dis- tinguished as medial and lateral, are sharp and commence behind, one on each side of the dorsal aspect of the tarsal extremity, and, gradually approaching in the middle of the shaft, separate at the anterior end to terminate in the corresponding Fig. 245. — The First (Left) Metatarsal. For peroneus longus Facet for second meta- tarsal (occasional) tubercles. The inferior border is thick and rounded and extends from the under aspect of the tarsal extremity to near the anterior end of the bone, where it bi- furcates, the two divisions terminating in the articular eminences on the plantar aspect of the head. Of the three surfaces, the dorsal is narrow in the middle and wider at either end. It is directed upward and is in relation -with the extensor tendons. The medial and lateral surfaces, more extensive than the dorsal, corresponding with the interosseous spaces, are separated above, but meet to- gether at the inferior border; they afford origin to the interosseous muscles. The base is wedge-shaped, articulating by its terminal surface with the tarsus, and on each side with the adjacent metatarsal bones. The dorsal and plantar surfaces are rough for the attachment of ligaments. The head presents a semicircular articular surface for the base of the first jjhalanx, and on each side a depression, surmounted by a tubercle, for the attachment of the lateral ligaments of the metatarso-phalangeal joint. The inferior surface of the head is grooved for the passage of the flexor tendons and is bounded by two eminences continuous with the terminal articular surface. The several metatarsals possess distinctive characters by which they can be readily recognised. THE METATARSUS 201 The first metatarsal (fig. 245) is the most modified of all the metatarsal bones, and deviates widely from the general description given above. It is the shortest, the thickest, the strongest, and most massive of the series. The base presents a large reniform, slightly concave facet for the first cuneiform and projects downward into the sole to form the tuberosity, a rough eminence into which the peroneus longus and a slip of the tibialis anterior are inserted. A little Fig. 246. — The Second (Left) Metatarsal. Medial side An occasional facet for the first metatarsal / First cuneiform — Facets for third metatarsal Facets for third cuneiform above the tuberosity, on its lateral side, there is occasionally a shallow, but easily recognised facet, for articulation with the base of the second metatarsal. The head is marked on the plan- tar surface by two deep grooves, separated by a ridge, in which the two sesamoid bones of the flexor hallucis brevis glide. The shaft is markedly prismatic. The dorsal surface is smooth, broad, and convex, directed obliquely upward; the plantar surface is concave longitudinally Fig. 247 — The Third (Left) Metatarsal. Facets for second metatarsal Facets for second metatarsal Facet for fourth metatarsal and covered by the flexor hallucis longus and brevis, whilst the lateral surface is triangular in outline, almost vertical, and in relation with the first dorsal interosseous and adductor hallucis obliquus. A few fibres of the medial head of the fii'st dorsal interosseous occasionally arise from the hinder part of the surface adjoining the base, or from the border separating the lateral from the dorsal surface. Somewhere near the middle of the shaft, and on its fibular side, is the nutrient foramen, directed toward the head of the bone. 202 THE SKELETON The second metatarsal (fig. 246) is the longest of the series. Its base is prolonged back- ward to occupy the space between the first and third cuneiform, and accordingly it is marlced by facets for articulation with each of these bones. The tarsal surface is triangular in outline, with the base above and apex below, and articulates with the second cuneiform bone. On the tibial side of the base, near the upper angle, is a small facet for the first cuneiform, and occa- FiG. 248. — The Fourth (Left) Metatarsal. Facet for third metatarsal Facet for third metatarsal Facet for third cuneiform - Facet for fifth metatarsal sionally another for the first metatarsal a little lower down. The fibular side of the base pre- sents an upper and a lower facet, separated by a non-articular depression, and each facet is divided by a vertical ridge into two, thus making four in all. The two posterior facets articu- late with the third cuneiform and the two anterior with the third metatarsal. The base gives attachment to a slip of the tibialis posterior and the adductor hallucis obliquus, whilst from the Fig. 249. — The Fjfth (Left) Metatarsal. Tibial Medial side Fourth metatarsal Fibular lateral side shaft the first and second dorsal interosseous muscles take origin. The nutrient foramen is situated on the fibular side of the shaft near the middle and is directed toward the base of the bone. The third metatarsal (fig. 247), a little shorter than the second, articulates by the tri- angular surface of its base with the third cuneiform. On the medial side are two small facets, one below the other, for the second metatarsal, and on the lateral side, a single large facet for the fourth metatarsal. The base gives attachment to a slip of the tibialis posterior and the adductor hallucis obliquus, and from the shaft three interosseous muscles take origin. The nutrient foramen is situated on the tibial side of the shaft and is directed toward the base. THE PHALANGES 203 The fourth metatarsal (fig. 248), smaller in size than the preceding, is distinguished by the quadrilateral facet on the base, for the cuboid. The medial side presents a large facet •divided by a ridge into an anterior portion for articulation with the third metatarsal and a, posterior portion for the third cuneiform. Occasionally the cuneiform part of the facet is wanting. On the lateral side of the base is a single facet for articulation with the fifth metatarsal. The fifth metatarsal (fig. 249), is shorter than the fourth, but longer than the first. It is recognised by the large nipple-shaped process, known as the tuberosity, which projects on the lateral side of the base. It constitutes the hindmost part of the bone and gives insertion to the -peroneus brevis on the dorsal aspect, and flexor brevis digili quinli and the occasional ■abduclor ossis metatarsi quinli on the plantar aspect. The fifth metatarsal articulates behind by an obliquely directed triangular facet with the cuboid, and on the medial side with the fourth metatarsal. The plantar aspect of the base is marked by a shallow groove which lodges the tendon of the abductor digili quinli, and the dorsal surface, continuous with the superior surface of the shaft, receives the insertion of the peroneus terlius. The head is small and turned somewhat laterally in consequence of the curvature of the shaft in the same direction. The shaft differs from that of any of the other metatarsals in being compressed from above downward, instead of from side to side, so as to present superior, inferior, and medial surfaces. It gives origin to the lateral head of the fourth dorsal interosseous and the third plantar interosseous muscles. The nutrient foramen is situated on its tibial side and is directed toward the base. Ossification. — Each metatarsal ossifies from two centres. The primary nucleus for the shaft appears in the eighth week of embryonic life in the middle of the cartilaginous metatarsal. At birth, each extremity is represented by cartilage, and that at the proximal end is ossified by extension from the primary nucleus', except in the case of the first metatarsal. For this, a nucleus appears in the third year. The distal ends of the four lateral metatarsals are ossified by secondary nuclei which make their appearance about the third year. Very frequently an epiphysis is found at the distal end of the first metatarsal as well as at its base. The shafts and epiphyses consolidate at the twen- tieth year. The sesamoids belonging to the flexor hallucis brevis begin to ossify about the fifth year. THE PHALANGES The phalanges (fig. 250) are the bones of the toes, and number in all fourteen. Except the great toe, each consists of three phalanges, distinguished as first (proximal), second and third (distal) ; in the great toe the second phalanx is absent. Fig. 250. — The Phalanges of the Middle Toe. 5?1 There is thus a similarity as regards number and general arrangement with the phalanges of the fingers. With the exception of the phalanges of the great toe, which are larger than those of the thumb, the bones of the toes are smaller and more rudimentary than the corresponding bones of the fingers. In all the pha- langes, the nutrient foramen is directed toward the distal extremity. The phalanges of the first row are constricted in the middle and expanded at either ex- tremity. The shafts are narrow and laterally compressed, rounded on the dorsal and concave 204 THE SKELETON on the plantar aspects. The base of each presents a single oval concave facet for the convex head of the corresponding metatarsal, whilst the head forms a pulley-like surface [trochlea phalangis], grooved in the centre and elevated on each side for the second phalanx. The phalanges of the second row are stunted, insignificant bones. Their shafts, besides being much shorter, are flatter than those of the first row. The bases have two depressions, separated by a vertical ridge, and the heads present trochlear surfaces for the ungual phalanges. The third, or ungual phalanges are easily recognised. The bases articulate with the second phalanges; the shafts are expanded, forming the ungual tuberosities which support the nails, and their plantar surfaces are rough where they come into relation with the pulp of the digits. The muscles attached to the various phalanges may be tabulated thus: — The first phalanx of the hallux gives insertion to the flexor haUucis brevis; abductor halluois; adductor hallucis transversus and obliquus; extensor digitorum brevis. The first phalanx of second toe : The first and second dorsal interosseous. The first phalanx of third toe : Thii'd dorsal interosseous; first plantar interosseous. The first phalanx of fourth toe : Second plantar interosseous; fourth dorsal interosseous. The first phalanx of fifth toe: Third plantar interosseous; flexor digiti quinti brevis; and abductor digiti quinti. The terminal phalanx of hallux: Flexor hallucis longus; extensor hallucis longus. Fig. 251. — A Longitudinal Section of the Bones of the Lower Limb at Birth. The centre for the lower extremity of the femur appears early in the ninth month The centre for the upper end of the tibia appears about a week before The centre for the navicular appears in the fourth year For the first cuneiform appears in the third year First phalanx of hallux Second phalanx of hallux The second phalanges of the remaining toes : Dorsal expansion of the extensor tendons, including extensor digitorum longus, extensor digitorum brevis (except in the case of the fifth toe), and expansions from the interossei and lumbricales. The third phalanges : Flexor digitorum longus; dorsal expansion of the extensor tendon with the associated muscles. Ossification, — Like the corresponding bones of the fingers, the phalanges of the toes ossify from a primary and a secondary nucleus. In each, the centre for the shaft appears during the eighth or ninth week of embryonic life. The secondai-y centre forms a scale-like epiphysis for the proximal end between the fourth and eighth years, and union takes place in the eighteenth or nineteenth year — i. e., earlier than the corresponding epiphj'ses in the fingers. The primary centres for the third phalanges appear at the distal extremities of the bones. Sesamoid Bones In the foot a pah- of sesamoid bones is constant over the metatarso-phalangeal joint of the great toe in the tendons of the flexor hallucis brevis. One sometimes occurs over the inter- phalangeal joint of the same toe and over the metatarso-phalangeal joints of the second and fifth and rarely of the third and fourth toes. BONES OF THE FOOT AS A WHOLE 205 A sesamoid also occurs in the tendon of the peroneus longus, where it glides over the groove in the cuboid; another may be found, especially in later life, in the tendon of the tibialis anterior over the first cuneiform bone, and another in the tendon of the tibialis posterior over the medial surface of the head of the talus. Further a sesamoid, the fabella, sometimes occurs in the lateral head of the gastrocnemius, and another may be found in the tendon of the ilio-psoas over the pubis. BONES OF THE FOOT AS A WHOLE Although the foot is constructed on the same general plan as the hand, there is a marked difference in its architecture to qualify it for the different functions which it is called upon to perform. When in the erect posture, the foot forms a firm basis of support for the rest of the body, and the bones are arranged in an elliptical arch, supported on two pillars, a posterior or calcaneal pillar and an Fig. 252. — The Secondary Ossific Centres op the Foot. The centre for the epiphysis for calcaneus appears at the tenth year consolidates at the sixteenth year The centre for the epiphysis for the metatarsal of the hallux appears at the third year; consolidates at the twentieth year The centres for the base of the ter- minal phalanges appear at sixth year, and consolidate at the eight- eenth year The'centres for the heads of the metatarsals appear'atlthelthird year, and consoUdate at the twentieth year anterior or metatarsal pillar. It is convenient, however, to regard the anterior part of the arch as consisting of two segments, corresponding to the medial and lateral borders of the foot respectively. The medial segment is made up of the three metatarsal bones, the three cuneiform, the navicular, and talus; the lateral segment is made up of the fourth and fifth metatarsal bones, the cuboid, and the calcaneus, and both segments are supported behind on a common calcaneal pillar. The division corresponds to a difference in function of the two longitudinal arches. Both are intimately concerned in ordinarj- locomotion. In addition, the medial, characterised by its great curvature and remarkable elasticitj^, sustains the more violent concussions in jumping and similar actions, whereas the lateral, less curved, more rigid, and less elastic arch forms, with the pillars in front and behind, a firm basis of support in the upright posture. Both arches are completed and maintained by strong ligaments and tendons. The weakest part is the joint between the talus and navicular bone, and special 206 THE SKELETON provision is accordingly made, by the addition of a strong calcaneo-navicular liga- ment, for the support of the head of the talus. This ligament is in turn supported by its union with the deltoid ligament of the ankle, and by the tendon of the tibialis posterior which passes beneath it to its insertion. Besides being arched longitudinally, the foot presents a transverse arch formed by the metatarsal bones in front and the distal row of the tarsus behind. It is produced by the marked elevation of the central portion of the medial longitudinal arch above the ground, whereas the lateral longitudinal arch is much less raised, and at its anterior end becomes almost horizontal. Both the longitudinal and transverse arches serve the double purpose of increasing the strength and elasticity of the foot and of providing a hollow in which the muscles, nerves, and vessels of the sole may lie protected from pressure. Homology of the Bones of the Limbs That there is a general correspondence in the plan of construction of the two extremities is apparent to a superficial observer, and this becomes more marked when a detailed examination of the individual bones, their forms and relations, their embryonic and adult peculiarities, is systematically carried out. In each limb there are four segments, the shoulder girdle corre- sponding to the pelvic girdle, the arm to the thigh, the forearm to the leg, and the hand to the foot. These parts have been variously modified, in adaptation to the different functions of the two limbs, particularly as regards the deviations or changes from what is regarded as their primi- FiG. 253.- Subscapular fo -Diagrammatic Representation op the Bones op the Two Limbs, to SHOW Homologous Parts. (Modified from Flower.) Iniiaspinous fossa Great trochanti ^^' '^V. tive position, and as a knowledge of these changes is essential to a clear understanding of the homologous bones, it will be advantageous to refer briefly to the relations of the limbs in the earliest stages of development. The limbs first appear as flattened, bud-like outgrowths from the sides of the trunk. Each presents a dorsal or extensor surface, and a ventral or flexor surface, as well as two borders, an anterior, or cephalic, directed toward the head end of the embryo, and a posterior or caudal, du-ected toward the tail end. In reference to the axis of the limb itself, the borders have been called pre-axial and post-axial, respectively. When, somewhat later, the various divisions of the limb make their appearance, it is seen that the gi-eater tuberosity, the lateral epicondyle, the radius, and the thumb he on the pre-axial border of the anterior extremity, and the small trochanter, the medial condyle, the tibia, and the great toe on the pre-axial border of the posterior extremity. Further on the post-axial border of the anterior extremity are seen the lesser tuberosity, the medial epicondyle, the ulna, and little finger, whilst on the corresponding border of the posterior limb are the great trochanter, the lateral condyle, the fibula, and the little toe. The parts now enumerated on the corresponding borders of the two limbs must therefore be regarded as serially homologous (fig. 253). HOMOLOGY OF THE BONES OF THE LIMBS 207 It is necessary to trace next the further changes which take place in the segments of the limbs up to the time when they assume their permanent positions. They may be arranged in stages as follows: — (1) Each segment of the limb is bent upon the one above it. The humerus and femur remain unchanged. The forearm segment, however, is bent so that the ventral surface looks medially and the dorsal surface laterally. Moreover, the joints between these segments — i. e., elbow and knee — form marked projections. The terminal segments (hand and foot) are bent in the opposite direction to the middle one, so that the primitive position is retained, and the ends of the digits directed laterally. It will be noticed that in this series of changes the relations of the pre-axial and post-axial borders of the limbs remain as before. (2) This stage consists in a rotation of the whole limb from the proximal end, though in an exactly opposite direction in each case. The anterior extremity is rotated backward so that the humerus lies parallel with the trunk; the elbow is directed toward the caudal end, the pre-axial (radial) border becomes lateral, and the post-axial border medial. The ends of the digits point backward. The posterior extremity undergoes a rotation forward to the same extent, so that the femur is also nearly parallel with the trunk; the knee is directed toward the head end, the pre-axial (tibial) border becomes medial, and the post-axial border lateral. The tibia and fibula are parallel, the ends of the digits are directed forward, the gi-eat toe is on the pre-axial and the Uttle toe on the post-axial border of the Umb, and in this position the posterior extremity remains, the changes being finally completed by the extension of the Hmb at the hip-joint as the body attains its full development. (3) This stage affects the anterior extremity alone and consists in a rotation of the radius, carrying the hand round the ulna so that the digits are brought round from the back to the front of the limb, and in many animals the maOus is thus placed permanently in the prone position. But in man, in whom the capacity for pronation and supination is highly developed, the hand can assume either position at will. In his case the final change is the extension which takes place at the shoulder-joint with the assumption of the upright posture, the limb dropping loosely at the side of the body, and being endowed with the greatest freedom of movement. Homological comparison of — I. The shoulder and pelvic girdles. — Primarily the lateral half of each girdle consists of a curved bar or rod of cartilage placed at right angles to the longitudinal axis of the trunk and divisible into a dorsal segment, and a ventral segment, the point of division corresponding to the place of articulation with the limb-stalk — i. e., the glenoid and acetabular cavities. In the fore-limb the dorsal segment is the scapula, and the ventral segment the coracoid, whilst in the hind-hmb the dorsal segment is the iUum and the ventral segment the ischium and pubis. The dorsal segments of the two girdles — i. e., scapula and ihum — are accordingly regarded as homologous bones, the chief difference being that whereas the scapula is free from articulation with the vertebral column, the ilium is firmly jointed to the rib elements (lateral mass) of the sacrum. But the correspondence is not quite so clear with regard to the ventral segments. In the primitive condition the coracoid articulates with the side of the sternum, an arrangement which persists throughout hfe in certain animals, such as reptiles and Ornithorhynchus. But in aU the higher mammals it undergoes reduction, withdrawing from the side of the sternum, and eventually forming a more or less rudimentary process attached to the scapula. In the more generahsed form of shoulder girdle the ventral bar is double, consisting of coracoid and pre- coracoid elements, the latter being situated in front and almost parallel with the coracoid. The pre-coracoid in mammals is largely replaced by the development over it of the clavicle, a dermal or membranous splint-bone which eventually invades the underlying cartilage. Parts, however, remain distinct and form the sternal epiphysis of the clavicle, the inter-articular cartilage between it and the sternum, the supra-sternal bones, and the inconstant inter-articular cartilage in the acromio-clavicular joint. It has already been noticed that in the hip girdle the ventral segment also consists of two elements, the pubis and ischium. Both take part in the formation of the acetabular cavity, and the pubis meets in the ventral median line the corresponding segment of the opposite side. It is generally agreed that the coracoid and ischium are homologous structures. The pubic portion of the ventral segment appears to correspond most closely with the pre-coracoid element of reptiles, so that there is no true homologue of the clavicle in the pelvis. If, however, the clavicle corresponds to the reptilian pre-coracoid, as believed by many anatomists, it then be- comes the representative of the pubis, From a consideration of the condition in oranio-cleido-dysostosis, Mr. FitzwiUiams has put forward the following views regarding the homology of the shoulder girdle: — Coracoid bar is represented by (a) medial two-thu'ds of clavicle; (b) coraco-clavicular ligaments; and (c) sub-coracoid centre of coracoid process. The clavicula, a membranous bone, is represented by the lateral third of adult clavicle. The pre-coracoid bar is represented by: — (a) the coracoid process (less the sub-coracoid centre) ; and (b) the costo-coracoid ligament. The epi-coracoid is represented by the meniscus of the sterno-clavicular joint. Moreover, it is possible to establish a comparison between the individual parts of the ilium and scapula. A reference to fig. 253 shows that both the scapula and ilium may be resolved into three-sided prismatic rods, each of which has thi-ee surfaces and three borders. In the primitive position of the limb one surface — the internal — is turned toward the vertebral column, the remaining surfaces are external, and named -pre-axial and post-axial, corresponding to the borders of the limb. The borders separating the internal from the external surfaces are antero-internal (terminating in the acromion or pubis) and postero-internal (terminating in the coracoid or ischium). The two external surfaces are separated by a ridge, terminating below at the upper margin of the glenoid cavity or acetabulum (glenoid and cotyloid borders). The primitive arrangement is lost by the marked growth of the borders of the rods leading to the formation of fossae and by the rotation of each rod, the scapula laterally and the ihum medially, in association with the rotation which takes place in the free part of the limb, so that 208 THE SKELETON the inner surface of the one comes to correspond with the outer surface of the other. It results that the primitive vertebral surface of the scapula is now the pre-scapular or supraspinous fossa, and the corresponding surface in the ilium is the sacral, which, on account of its close con- nection with the vertebral column, undergoes but little change in position. Further, the primi- tive pre-axial surfaces are the infraspinous fossa and the iliac fossa, which accordingly are to be regarded as homologous, as well as the two post-axial surfaces, the subscapular fossa and the dorsum ilii. The correspondence between the various parts of the scapula and ilium is shown in the appended table (after Flower). I. Surfaces • II. Borders: ScAPUIiA Supraspinous fossa. Infraspinous fossa. Subscapular fossa. Axillary or glenoid. Spine. Superior or coracoid. Base. Primitive Arrangement Vertebral. Pre-axial. Post-axial. External. Antero-internal. Postero-internal. Dorsal extremity. Ilium Sacral surface. Iliac fossa. Gluteal surface. Cotyloid or anterior border. Terminal line. Posterior border. Crest of ilium. II. Bones of the arm and thigh, forearm, and leg. — It has already been pointed out in describing the deviation of the limbs from the primitive position that the humerus corresponds to the femur, the radius to the tibia, and the ulna to the fibula; also that in consequence of the rotation backward of the fore-limb, and forward of the hind-limb, the lateral side of the humerus corresponds with the medial aide of the femur, the radial border of the forearm to the tibial border of the leg, and the ulnar (border of the forearm) to the fibular border of the leg. The corresponding parts are tabulated below: — Fore-Limb Humerus Greater tuberosity Lesser tuberosity Lateral epicondyle and capitulum Medial epicondyle and trochlea Radius Ulna Not represented Hind-Limb Femur Lesser Trochanter Great Trochanter Medial Condyle Lateral Condyle Tibia Fibula Patella III. Bones of the hand and foot. — It is obvious that the carpus and tarsus, the meta- carpus and metatarsus, and the various digits, commencing at the thumb, in the hand, and at the great toe, in the foot, are serially homologous. Fig. 254. — Dorsal Surface of the Right Manus of a Water-tortoise, Chelydra serpentina. ("After Gegenhaur.l In order to trace the correspondence between the various elements of the carpus and tarsus it is convenient to refer in the first place to the primitive type of hand and foot as found in the water-tortoise and the lizard (fig. 254). In each segment nine elements may be recognised, arranged in a proximal row of three, named respectively radiate or tibiale, intermedium, and ulnare, or flbulare, a distal row of five carpalia, or tarsalia, numbered from one to five, commenc- ing at the pre-axial border, and between the two rows an os cenlrale. In man the carpus is derived from the typical form in the following manner: The radiale forms the navicular, intermedium the lunate, and the ulnare, the triquetral; carpale I forms the greater multangular, oarpale II the lesser multangular, carpale III the capitate, whilst car- paha IV and V coalesce to form the hamate. The os centrale is present in the human carpus at an early stage, but in the second month it joins the navicular. It is occasionally separate — a normal arrangement in most of the primates. HOMOLOGY OF THE BONES OF THE LIMBS 209 In the tarsus, the tibiale and intermedium coalesce to form the talus, and the fibulare becomes the calcaneus. It is interesting to note that although in the human subject there are three bones in the first row of the carpus and two in the first row of the tarsus, in carnivores the navicular and lunate are united to form a naviculo-lunate bone — the homologue of the talus. In the human tarsus the intermedium occasionally remains distinct as the os trigonum. Tarsale I forms the first cuneiform, tarsale 11 the second cuneiform, tarsale III the third cuneiform, and tarsale IV and V are joined to form the cuboid. The os centrale forms the navicular. In addition to the carpal and tarsal elements enumerated above, brief mention must now be made of the sesamoid bones of the two segments, which are regarded by many anatomists as vestiges of suppressed digits. In the hand are the ulnar and radial sesamoids, the ulnar being represented by the pisiform and the radial probably by the tuberosity of the navicular. (In the mole and other aUied species with fossorial habits, the radial sesamoid is greatly de- veloped to form a sickle-shaped bone which has received the name of os falciforme.) The corresponding structures in the foot are the tibial and fibular sesamoids, the tibial being most nearly represented by the tuberosity of the navicular and the fibular by the tuber of the calcaneus. Table Showing the HoMOLOGOtis Bones op the Carpus and Tarsus. in Quain's Anatomy.) [After G. D. Thane Carpus Priaiitive Names Tarsus > Calcaneus I Talus > Navicular First cuneiform Second cuneiform Third cuneiform } Cuboid References. — ^For the development of the skeleton, consult the bibliography in Bardeen's article in Keibel and Mall's ' Human Embryology,' Vol. 1. For further references concerning the adult structure and morphology of the skeleton, the sections on osteology in the larger works on human anatomy by Quain, von Bardeleben, Rauber-Kopsch. Poirier-Charpy, etc., should be consulted. Refer- ences to the most recent literature may be found in Schwalbe's Jahresbericht, the Index Medicus, and in the various anatomical journals. Triquetral Ulnare Fibulare Pisiform Ulnar sesamoid Fibular sesamoid Lunate Intermedium Intermedium ■ Radiale Tibiale Navicular Radial sesamoid Tibial sesamoid Centrale Centrale Greater multangular Carpale I Tarsale I Lesser multangular II II Capitate " III " III Hamate r " IV ( " V " IV V I SECTION III THE ARTICULATIONS Revised for the Fifth Edition By FREDERIC WOOD JONES, D.Sc, M.B., B.S.(Lond.), M.R.C.S.,L.R.C.P. HEAD OF THE DEPARTMENT OF ANATOMY AND LECTURER IN THE LONDON SCHOOL OP MEDICINE FOR WOMEN. THE CONSTITUENTS OF AN ARTICULATION THE section devoted to the Articulations or Joints deals with the union of the various and dissimilar parts of the human skeleton. The followiing struc- tures enter into the formation of joints. Bones constitute the basis of most joints. The long bones articulate by their ends, the flat by their edges, and the short at various parts on their surfaces. The articular ends are usually expanded, and are composed of cancellous tissue, sur- rounded by a dense and strong shell of compact tissue. This shell has no Haversian canals (the vessels of the cancellous tissue turn back and do not perforate it), or large lacunae, and no canaliculi, and is thus well adapted to bear pressure. This "osteoid" layer may represent in part calcified cartilage rather than true bone. The cartilage which covers the articular ends of the bones is called articular, and is of the hyaline variety. It is firmly implanted on the bone by one surface, while the other is smooth, polished, and free, thus reducing friction to a minimum, while its slight elasticity tends to break jars. It ends abruptly at the edge of the articulation, and is thickest over the areas of greatest pressure. Another form of cartilage, the white fibrous, is also found in joints: — (i) As inlerarlicular cartilage in diarthrodial joints — viz., in the knee, mandibular, sterno-clavicular, radio-carpal, and occasionally in the acromio-clavicular joint. It is interposed between the ends of the bones, partially or completely dividing the synovial cavity into two. It serves to adjust dissimilar bony surfaces, adding to the security of, while it increases the extent of motion at, the joint; it also acts as a buffer to break shocks. (ii) As circumferential or marginal iibro-cartilages, which serve to deepen the sockets for the reception of the heads of bones — e. g., the glenoid ligaments of the shoulder and hip. Another form of marginal plate is seen in the accessory volar ligaments of the fingers and toes, which deepen the articulations of the phalanges and add to their security. (iii) As connecting fibro-cartilage. The more pliant and elastic is the more cellular form, and is found in the intervertebral discs; while the less yielding and more fibrous form is seen in the sacro-iliac and pubic articulations, where there is little or no movement. The ligaments which bind the bones together are strong bands of white fibrous tissue, forming a more or less perfect capsule [capsula articularis], round the articu- lation. They are pliant but inextensile, varying in shape, strength, and thick- ness according to the kind of articulation into which they enter. They are closely connected with the periosteum of the bones they unite. In some cases — as the ligamenta flava which unite parts not in contact — they are formed of j'ellow elastic tissue. The synovial membrane [stratum synoviale] lines the interior of the fibrous ligaments, thus excluding them, as well as the cushions or pads of fatty tissue situate within and the tendons which perforate the fibrous capsule, from the articular cavity. It is a thin, delicate membrane, frequently forming folds and fringes which project into the cavity of the joint; or, as in the knee, stretches across the cavity, forming a so-called synovial ligament. In these folds are often found pads of fatty tissue, which fill up interstices, and form soft cushions between the contiguous bones. The amount of fat that is normally present within a joint varies greatly. It is an old observation that although there is always fat in the hip- 211 I 212 THE ARTICULATIONS and knee-joints, there is usually none within the shoulder-joint. Sometimes these fringes become villous and pedunculated, and cause pain on movement of the joints. They contain fibro-fatty tissue, with an isolated cartilage cell or two. The synovial membrane is well supplied with blood, especially near the margins of the articular cartilages and in the fringes. It secretes a thick, glairy fluid like white of egg, called synovia, which lubricates the joint. Another variety of synovial membrane is seen in the bursas, which are interposed between various moving surfaces. In some instances bursas in the neighbourhood of a joint may communicate with the synovial cavity of that joint. CLASSIFICATION OF ARTICULATIONS Joints may be classified: — (a) From an anatomical point of view, with regard to the substances and the arrangement of the substances by which the constituent parts are united. (6) From a physiological standpoint, with regard to the greater or smaller mobility at the seat of union, (c) From a physical standpoint, either the shapes of the portions in contact being mainly considered or the axes round which movement can occur. Or again (d) a combination of the preceding methods may be adopted, and this is the plan most generally followed. None of the classi- fications hitherto used is quite satisfactory, but perhaps, on the whole, that suggested by Prof. Alex. Macalister is the least open to objection, and therefore with slight modification it is utilised here. There are three chief groups of joints: — 1. Synarthroses. In joints of this class the bones are united by fibrous tissue. 2. Synchondroses. Or joints in which the uniting substance intervening be- tween the bones is cartilage. 3. Diarthroses. The constituent parts of joints of this class are (a) two or more bones each covered by articular hyaline cartilage ; (6) a fibrous capsule uniting the bones, and (c) a synovial membrane which lines the fibrous capsule and covers any part of bone enclosed in the capsule and not covered with articular cartilage. An interarticular plate of cartilage may or may not be present. Synarthroses. — (a) Sutures or immovable joints, in which the' fibrous tissue between the bones is too small in amount to allow movement. (1) Harmonic. The edges of the bones are comparatively smooth and are in even apposition, e. g., vertical plate of palate and maxilla. (2) Squamous. The margin of one bone overlaps the other, e. g., temporal and parietal. (3) Serrate. The opposed edges interlock by processes tapering to a point. (4) Dentate. The opposed edges are dovetailed, e. g., occipital and parietal. (5) Limbous. The opposed edges alternately overlap, e. g., parietal and frontal. (6) Schindylesis. A ridge or flattened process is received into a corresponding socket, e. g., rostrum of sphenoid and vomer. (7) Gotnphosis. A peg-like process is lodged in a corresponding socket, e. g., the fangs of the teeth. (6) Syndesmoses. Movable joints in which the fibrous tissue between bones or carti- lages is sufficiently lax to allow movement between the connected parts, e. g., thyreo-hyoid membrane. Interosseous membranes of forearm and leg. 2. Synchondroses. — In all synchondroses a certain amount of movement is possible, and they are often called amphiarthroses. (1) True synchondroses. The cartilage connecting the bones is the remains of the bar in which the bones were ossified, e. g., occipito-sphenoidal joint. (2) False synchondroses. The plate of cartilage intervening between and connecting the bones is fibro-cartilage and is not part of the cartilage in which the bones were ossified, but is developed separately, e. g., intervertebral joint and pubic sym- physis. The articular end of each bone may be covered with hyaUne cartilage and there may be a more or less well-marked cavity in the intervening plate of fibro-cartilage. 3. Diarthroses. — In diarthrodial joints the surfaces in contact may be equal and similar or unequal and dissimilar. In the former case the joints are homomorphic; in the latter, heteromorphic. (A) HomomorTphic. (a) Plane or arlhrodial. Flat surfaces, admitting gliding movement, e. g., intercarpal and acromio-clavicular joints. (6) Ephippial. Saddle-shaped surfaces placed at right angles to each other, ad- mitting free movement in all directions, e. g., metacarpo-phalangeal joint of thumb. DEVELOPMENT OF JOINTS 213 (B) Heteromorphic. (a) Enarlhrodial. Ball-and-socket, allowing the most free movement, e. g., hip- and shoulder-joints. (6) Condylarlhroses. The convex surface is ellipsoidal, and fits into a corresponding concavity, e. g., wrist and metacarpo-phalangeal joints, (c) Ginglymi. One surface consists of two conjoined condyles or of a segment of a cone or cylinder, and the opposite surface has a reciprocal contour. In these joints movement is only permitted round one axis, which may be transverse; e. g., elbow, ankle; or it may be vertical, in which case the joint is trochoid; e. g., odontoid process of axis with atlas, radius with ulna. Such a classification should be considered as being purely academic and the student must always remember that it is not enough to discuss a joint by assigning it to a particular class in any scheme; for he must be familiar with the actual conditions present in every joint. No classification, however perfect, must be taken as final, and each joint should be studied as a separate thing altogether apart from any general systematic arrangement. DEVELOPMENT AND MORPHOLOGY OF JOINTS The arrangement of the various parts which constitute an articulation is best appreciated by a study of the development of the various types of joints. In this way it is easy to recog- nise a primitive condition typical of each class; but it must be remembered that various modi- fications take place during growth, that these modifications vary in the individual joints, and produce adult departures from the primitive arrangement which are peculiar to each joint and which must be studied separately. In the case of bones ossifying in membrane the articulation will be a suture, the ossifications from neighbouring centres extending until they practically come into contact. Fig. 255. — Development of Joints A. Stage in which primary embryonic tissue separates the developing cartilages. B. Primary embryonic tissue transformed into cartilage (synchondrosis), or fibrous connec- tive tissue (syndesmosis). C. Degeneration of embryonic tissue with production of a joint cavity (diarthrosis). tWith cartOage bones the articulation may be either a syndesmosis, a synchondrosis, or a diarthrosis. The embryonic tissue in which the cartilage is to develop is at first continuous; centres of chondrification, corresponding in number to the bony elements which are destined to be formed, appearing in it. As the chondrifications approach each other a small portion of the primary embryonic tissue persists between them (fig. 255), and it is the subsequent fate of this intermediate tissue that determines the nature of the articulation. (1) When the ossification of the cartilage occurs to form the articulating bones, the inter- mediate tissue may undergo transformation into cartilage (fig. 255), a synchondrosis being thus produced. (2) Or the intermediate tissue may be converted into fibrous connective-tissue I 214 THE ARTICULATIONS (fig. 255), the result being a syndesmosis. (3) Or, finally, the central portion of the inter- mediate tissue may degenerate, so that an articular cavity is produced, the peripheral portions being converted into connective tissue, forming a sleeve-like capsule surrounding the cavity, continuous at either extremity with the periosteum of the articulating bones (fig. 255). This is the articular capsule, and the connective-tissue cells arranging themselves in a layer upon its inner surface give rise to a synovial membrane. As the result of these processes a diarthrosis is produced, and from its mode of formation it is clear that the cavity of such an articulation is completely closed. In a typical diarthrosis there is therefore a ligamentous capsule which entirely encloses the joint cavity, which is continuous with the periosteum of the bones entering into the articulation but which is not attached to nor reflected onto the cartilaginous ends of the bones which consti- tute the articulating surfaces. Such a capsule constitutes the primitive bond between the articu- lating bones and furnishes a complete lubricating bag in which these smooth cartilaginous ends gKde over one another. This primitive capsule, however, becomes modified in most adult joints, (1) by unequal development of various parts of the capsule; and (2) by the more or less complete incorporation of other structures which are developmentaUy separate from the capsule. Under the first heading come specially thickened bands which may be so distinctly marked off from the rest of the capsule as to be named as separate hgaments (e. g., the temporo-mandibular ligament of the mandibular joint). Again certain thickened bands of capsule may, with alteration of joint contour, take up anatomical positions which are apparently separated from the rest of the capsule; advanced examples of this process are, in all probability, seen in the ligamentum teres of the hip-joint and the crucial ligaments of the knee. Under the second heading comes a series of ligaments derived from a gi'eat variety of soirrces; the most common origin being from the divorced or rearranged tendons of the muscles around the joint. Muscles arising from, or inserted into, bones in the immediate vicinity of a joint tend to become metamorphosed into tendon near their attachments, and a comprehensive study of myology in low vertebrate forms indicates that there is associated with this tissue-change a tendency for the muscle to alter its point of attachment; hence a muscle originally inserted below a joint may eventually come to have its insertion above the joint. In the same way, a muscle arising above a joint may, as a result of altered environment, shift its origin to some point below the joint. To this change of position the term migration of muscles has been applied. In many instances a portion of the muscle equivalent to the distance between the original and the acquired attachment persists as a fibrous band and fulfils the function of a Ugament. This is well seen in the knee-joint, where the tibial collateral ligament is derived from the adductor magnus, this muscle having shifted its insertion from the tibia to the femur. In the same way the fibular collateral ligament represents the tendon of the peroneus longus, which has migrated from the femur to the head of the fibula. Among other ligaments derived in a similar way from muscles may be mentioned the sacra- tuberous ligament. This was originally the tendon of origin of the biceps femoris. (H. Morris, Med. Times and Gazette, 1877, p. 361.) The sacro-spinous is derived from the fibrous retro- gression of portions of the coccygeus. The sacro-coccygeal ligaments represent the muscles which lift, depress, and wag the tail in those mammals furnished with such an appendage; indeed, these ligaments are occasionally replaced by muscle-tissue. The coraco-humeral ligament is derived from the original tendon of insertion of the pectorahs minor, and not unfrequently the muscle is inserted into the lesser tuberosity of the humerus, the ligament being then replaced by the tendon of the muscle. The coraco-clavicular, rhomboid, and gleno-humeral ligaments are probably derived from modifications of the subclavius muscle. Other anatomical structures besides muscles may, when degenerated or functionally altered, form the basis of ligaments in connection with joints. The spheno-mandibular ligament is the fibrous remnant of the cartilaginous mandibular bar. The pulpy substance in the centre of each interoertebral disc is derived from the notochord; the apical ligament passing from the tip of the dens to the anterior margin of the foramen magnum is a remnant of the sheath of the notochord, and indicates its position as it passed from the vertebral column into the base of the cranium. The transverse ligament of the atlas (as pointed out by Professor Cleland) is a persistent and functional form of the posterior conjugal ligament uniting the rib-heads in seals and many other mammals, whilst the interosseous ligament of the head of a rib in man is the feeble representative of this structure in the thoracic region of the spine. The ligamentum conjugate costarum was described by Mayer in 1834 (Mtiller's Archiv fiir Anatomie). According to Luschka's account of this ligament it would seem as though the posterior superior fibres of the capsule of the costo-central joint represented it in man, rather than the interosseous ligament. THE MOVEMENTS OF JOINTS The movements which may take place at a joint are either gliding, angular, rotatory, or circumductorJ^ The gliding motion is the simplest, and is common to aU diarthrodial joints; it consists of a simple sliding of the apposed surfaces of the bones upon one another, without angular or rotatory motion. It is the only kind of motion permitted in the carpal and tarsal joints, and in those between the articular processes of the vertebne. The angular motion is more elaborate, and increases or diminishes the angle between difi'er- ent parts. There are four varieties, viz., flexion and extension, which bend or straighten the various joints, and take place in a forward and backward direction (in a perfect hinge-joint this is the only motion permitted) ; and adduction and abduction, which, except in the case of the fin- gers.and toes, signifies an approach to, or deviation from, the median plane of the body. In the ARTICULATIONS OF THE SKULL 215 case of the hand, the line to or from which adduction and abduction are made is drawn through the middle finger, while in the foot it is through the second toe. Rotation is the revolution of a bone about its own axis without much change of position. It is only seen in enarthrodial and trochoidal joints. The knee also permits of slight rotation in certain positions, which is a distinctive feature of this articulation. Circumduction is the movement compounded of the four angular movements in quick succession, by which the moving bone describes a cone, the proximal end of the bone forming the apex, while the distal end describes the base of the cone. It is seen in the hip and shoulder, as well as in the carpo-metacarpal joint of the thumb, which thus approximates to the ball-and- socket joint. In some situations where a variety of motion is required, strength, security, and celerity are obtained by the combination of two or more joints, each allowing a different class of action, as in the case of the wrist, the ankle, and the head with the spine. Many of the long muscles, which pass over two or more joints, act on all, so tending to co-ordinate their movements and enabhng them to be produced with the least expenditure of power. Muscles also act as elastic ligaments to the joints; and when acting as such, are diiJusers and combiners, not producers of movement; the short muscles producing movement, the long diffusing it, and thus allowing the short muscles to act on more than one joint. Muscles are so disposed at their attachments near the joints as never to strain the Uga- ments by tending to pull the bones apart, but, on the contrary, they add to the security of the joint by bracing the bones firmly together during their action. The articulations may be divided for convenience of description into those: 1 . of the Skull; 2. of the Trunk; 3. of the Upper Limb; and 4. of the Lower Limb. THE ARTICULATIONS OF THE SKULL The movable articulations of the skull comprise (1) the mandibular; and (2) those between the skull and the vertebral column, namely (a) between the occiput and atlas ; (6) between the atlas and epistropheus (axis) ; and (c) the ligaments which connect the occiput and epistropheus. The union of the atlas and epistropheus is described in this section because, (1) there is often a direct communication between the synovial cavity of the trans- verse epistrophic and the occipito-atlantal joints; (2) the rotatory movements of the head take place around the dens (odontoid process) ; and (3) important liga- ments from the dens pass over the atlas to the occiput. (1) THE MANDIBULAR ARTICULATION Class. — Diarthrosis. Subdivision. — Condylarthrosis. The parts entering into the formation of this joint (figs. 256, 257) are: — the anterior portion of the mandibular fossa and glenoid ridge (eminentia articularis) of the temporal bone above, and the condyle of the lower jaw below. Both are covered with articular cartilage, which extends over the front of the glenoid ridge to facilitate the play of the interarticular cartilage. The ligaments which unite the bones are: 1. Articular capsule. 3. Spheno-mandibular. 2. Articular disc. 4. Stylo-mandibular. The articular capsule is often described as consisting of four portions, anterior, posterior, lateral and medial, which are, however, continuous with one another around the articulation. 1. The anterior portion consists of a few stray fibres connected with the anterior margin of the articular disc, and attached below to the anterior edge of the condyle, and above to the front of the articular eminence. Some fibres of insertion of the external pterygoid pass between them to be inserted into the margin of the articular disc. 2. The posterior portion is attached above, just in front of the petro-tympanic {Glaserian) fissure, and is inserted into the back of the jaw just below its neck. 3. The lateral portion or temporo-mandibular (external lateral) ligament (fig. 256) is the strongest part of the capsule. It is broader above, where it is attached to the lower edge of the zygoma in nearly its whole length, as well as to the tubercle at thu point where the two roots of the zygoma meet. It is inoUned downward and backward, to be inserted into the condyle and neck of the mandible laterally. Its fibres diminish in obliquity and strength from before backward, those coming from the tubercle being short and nearly vertical. 4. The medial portion (or short internal lateral ligament) (fig. 257) consists of well-defined fibres, having a broad attachment, above to the lateral side of the spine of the sphenoid and medial edge of the mandibular fossa; and below, a narrow insertion to the medial side of the neck 216 THE ARTICULATIONS of the condyle. Fatty and cellular tissue separate it from the spheno-mandibular ligament which is medial to it. The articular disc (fig. 258) is an oval plate of fibro-cartilage interposed between and adapted to the two articular surfaces. It is thinner at the centre than at the circumference, and is thicker behind, where it covers the thin bone at the bottom of the mandibular fossa which separates it from the dura mater, than in front, where it covers the articular eminence. Fig. 256. — Lateral View op the Mandebtjlar Joint. I Temporo mandibular ligament mandibular ligament Fig. 257. — Medial View of the Mandibijlar Joint. Stylo-hyoid, ligament Its inferior surface is concave and fits on to the condyle of the lower jaw; while its superior surface is concavo-convex from before backward, and is in contact with the articular surface of the temporal bone. It divides the joint into two separate synovial cavities, but is occasion- ally perforated in the centre, and thus allows them to communicate. It is connected with the articular capsule at its circumference, and has some fibres of the exiernallpterygoid muscle inserted into its anterior margin. There are usually two synovial membranes (fig. 258), the superior being the larger and looser, passing down from the margin of the articular surface above, to the upper surface of the articular disc below; the lower and smaller one passes THE MANDIBULAR JOINT 217 from the articular disc above to the condyle of the jaw below, extending somewhat further down behind than in front. When the disc is perforated, the two sacs communicate. The spheno-mandibular ligament (long internal lateral) (fig. 257) is a thm, loose band, situated some little distance from the joint. It is attached above to the spine of the sphenoid and contiguous part of the temporal bone, and is inserted into the lingula of the lower jaw. It covers the upper end of the mylo-hyoid groove, and is here pierced by the mylo-hyoid nerve. Its origin is a little medial to, and immediately behind, the origin of the medial por- tion of the capsule. It is separated from the joint and ramus of the jaw by the external ■ptery- goid muscle, the internal maxillary artery and vein, the inferior alveolar {dental) nerve and artery, the auriculo-temporal nerve, and the middle meningeal artery. It is really the fibrous remnant of a part of the mandibular (Meckelian) bar. The stylo -mandibular ligament (stylo-maxillary) (figs. 256 and 257) is a process of the deep cervical fascia extending from near the tip of the styloid proc- ess to the angle and posterior border of the ramus of the jaw, between the masseter and internal ■pterygoid muscles. It separates the parotid from the submaxillary gland, and gives origin to some fibres of the st^ylo-glossus muscle. Fig. 258. — Sagittal Section through the Condyle op Jaw to show the Two Synqviai. Sacs and the Articular Disc. Articular disc -l^j^ftr •rr _^ r Section through condyle^ — -> — i-4- Posterior portion of -ji/lTiN u capsule \»4T^^ Spheno-mandibular hgament Stylo-mandibular hgament The arterial supply of the mandibular joint is derived from the'temporal, middle meningeal and ascending pharyngeal arteries, and from the latter by its branches to the Eustachian tube. The nerves are derived from the masseteric and auriculo-temporal. Movements. — The chief movement of this joint is of (i) a ginglymoid or hinge character, accompanied by a slight gliding action, as in opening or shutting the mouth. In the opening movement the condyle turns like a hinge on the articular disc, while at the same time the ar- ticular disc, together with the condyle, glides forward so as to rise upon the eminentia articularis, reaching as far as the anterior edge of the eminence, which is coated with articular cartilage to receive it; but the condyle never reaches quite so far as the summit of the eminence. Should the condyle, however, by excessive movement (as in a convulsive yawn), glide over the summit, it slips into the zygomatic fossa, the mandible is dislocated, and the posterior portion of the capsule is torn. In the shutting movement the condyle revolves back again, and the articular disc glides back, carrying the condyle with it. This combination of the hinge and gUding motions gives a tearing as well as a cutting action to the incisor teeth, without any extra muscu- lar exertion. There is (ii) a horizontal gliding action in an antero-posterior direction, by which the lower teeth are thrust forward and drawn back again: this takes place almost entirely in the upper compartment, because of the closer connection of the articular disc with the condyle than with the squamosal bone, and also because of the insertion of the external pterygoid into both bone and cartilage. In these two sets of movements the joints of both sides are simultaneously and similarly engaged. The third form of movement is called (iii) the oblique rotatory, and is that by which the grinding and chewing actions are performed. It consists in a rotation of the cond3'le about I 218 THE ARTICULATIONS the vertical axis of its neck in the lower compartment, while the cartilage glides obUquely for- ward and inward on one side, and backward and inward on the other, upon the articular surface of the squamosal bones, each side acting alternately. If the symphysis be simply moved from the centre to one side and back again, and not from side to side as in grinding, the condyle of that side moves round the vertical axis of its neck, and the opposite condyle and cartilage ghde forward and inward upon the mandibular fossa. But in the ordinary grinding movement, one condyle advances and the other recedes, and then the first recedes while the other advances, slight rotation taking place in each joint meanwhile. Relations. — The chief relations are: Behind, and overlapping the lateral side, the parotid gland. Laterally, the superficial temporal artery. Medially, the internal maxillary artery and auriculo-temporal nerve. In front, the nerve to the masseter muscle. Muscles acting on the joint. — Elevators of the mandible. — temporals, masseters, int. pterygoids. Depressors. — -Mylo-hyoids, digastrics, genio-hyoid, muscles connecting the hyoid bone to lower points. Ext. pterygoids. The weight of the jaw. Protractors. — Ext. pterygoids, superficial layer of masseters, anterior fibres of temporals. Retractors. — Posterior fibres of temporals, slightly by the int. pterygoids and deep layer of the masseters. (2) THE LIGAMENTS AND JOINTS BETWEEN THE SKULL AND VERTEBRAL COLUMN, AND BETWEEN THE ATLAS AND EPISTROPHEUS (a) The Articulation of the Atlas with the Occiput Class. — Diarthrosis. Subdivision. — Double Condylarthrosis. This articulation [articulatio atlanto-occipitalis] consists of a pair of joints symmetrically situated on either side of the middle line. The parts entering into their formation are the cup-shaped superior articular processes of the atlas and the condyles of the occipital bone. They are united by the following ligaments : — 1. Anterior atlanto-occipital. 3. Two articular capsules. 2. Posterior atlanto-occipital. 4. Two anterior oblique. The anterior atlanto-occipital ligament [membrana atlanto-occipitalis anterior] (fig. 259) is less than an inch (about 2 cm.) wide, and is composed of densely woven fibres, most of which radiate slightly lateralward as they ascend from the front surface and upper margin of the anterior arch of the atlas to the anterior border of the foramen magnum; it is continuous at the sides with the articular capsules, the fibres of which overlap its edges, and take an opposite direction medially and upward. The central fibres ascend vertically from the anterior tubercle of the atlas to the pharyn- geal tubercle on the occipital bone; they are thicker than the lateral fibres, and are continuous below with the superficial part of the anterior atlanto-epistrophic ligarnent, and through it with the anterior longitudinal ligament of the vertebral column. It is in relation, in front, with the recti capitis anteriores; and behind, with the apical dental or suspensory ligament. The posterior atlanto-occipital ligament (fig. 260) is broader, more mem- branous, and not so strong as the anterior. It extends from the posterior surface and upper border of the posterior arch of the atlas to the posterior margin of the foramen magnum from condyle to condyle; being incomplete on either side for the passage of the vertebral artery into, and suboccipital nerve out of, the canal. It is somewhat thickened in the middle line by fibres, which pass from the posterior tubercle of the atlas to the lower end of the occipital crest. It is not tightly stretched between the bones, nor does it limit their movements; it corre- sponds with the position of the ligamenta flava, but has no elastic tissue in its composition. It is in relation in front with the dura mater, which is firmly attached to it; and behind with the recti capitis posteriores minores, and enters into the floor of the suboccipital triangle. Its lateral margins, which do not reach the occipital bone but terminate on the posterior end of the superior articular processes of the atlas, form the so-called oblique ligaments of the atlas. The lateral margins of these ligaments are free and they form the posterior boundaries of the apertures through which the vertebral arteries enter and the suboccipital nerves leave the vertebral canal. The atlanto-occipital articular capsules (figs. 259 and 260) are very distinct and strongly marked, except on the medial side, where they are thin and formed only of short membranous fibres. They are lax, and do not add much to the security of the joint. ARTICULATION OF ATLAS WITH OCCIPUT 219 In front, the capsule descends upon the atlas, to be attached, some distance below the articular margin, to the front surface of the lateral mass and to the base of the transverse proc- ess ; these fibres take an obUque course upward and medialward, overlapping the anterior atlan to- occipital. At the sides and behind, the capsule is attached above to the margins of the occipital condyles; below, it skirts the medial edge of the foramen for the vertebral artery, and behind is attached to the prominent tubercle overhanging the groove for that vessel; these latter fibres are strengthened by a band running obliqviely upward and medialward to the posterior margin of the foramen magnum. The anterior oblique or lateral occipito-atlantal ligament is an accessory band which strengthens the capsule laterally (fig. 259). It is an oblique, thick band of fibres, sometimes quite separate and distinct from the rest, passing upward and medialward from the upper surface of the transverse process beyond the costo-transverse foramen to the jugular process of the occipital bone. The synovial membrane of these joints occasionally communicates with the synovial sac between the dens (odontoid process) and the transverse ligament. The arterial supply is derived from twigs of the vertebral, and occasionally from twigs from the meningeal branches of the ascending pharyngeal. Fig. 259. — Anteriok View of the Upper End of the Vertebral Column. Continuation of tiie anterior longitudinal ligament of Atlanto- V ,/^ '^' A ' ' ' /K H_ '^ 'he vertebral occipital" ^~\ ^ /y^^a 1%"'K ^ I column articular ^j; \ i ' 222 THE ARTICULATIONS an anterior between the dens and the arch of the atlas, and a posterior between the dens and the transverse hgament. The transverse ligament (figs. 260, 261, and 263) is one of the most important structures in the body, for on its integrity and that of the alar ligaments our lives largely depend. It is a thick and very strong band, as dense and closely woven as fibro-cartilage, about a quarter of an inch (6 mm.) deep at the sides, and somewhat more in the middle line. Attached at each end to a tubercle on the inner side of the lateral mass of the atlas, it crosses the ring of this bone in a curved manner, so as to have the concavity forward; thus dividing the ring into a smaller anterior portion for the dens and a larger posterior part for the spinal cord and its membranes, and the spinal accessory nerves. It is flattened from before backward, being smooth in front, and covered by synovial mem- brane to allow it to glide freely over the posterior facet of the dens. Where it is attached to the atlas it is smooth and well rounded off to provide an easy floor of communication between the transverso-dental and occipito-atlantal joints. To its posterior surface is added, in the middle line, a strong fasciculus of vertical fibres, passing upward from the root of the dens to the basilar border of the foramen magnum on its cranial aspect. Some of these fibres are derived from the transverse ligament. These vertical fibres give the transverse liga- ment a cruciform appearance; hence the name, the crucial ligament (figs. 260 and 263) applied to the whole. The atlanto-dental articular capsule (fig. 261) is a tough, loose membrane, completely surrounding the apposed articular surfaces of the atlas and dens. At the dens it blends above with the front of the alar and central occipito-odontoid liga- ments, and arises also along the sides of the articular facet as far as the neck of the dens; the fibres are thick, and blend with the capsules of the lateral joint. At the atlas they are attached to the non-articular part of the anterior arch in front of the tubercles for the transverse liga- ment, blending, above and below the borders of the bone, with the anterior atlanto-occipital and atlanto-epistrophic ligaments, as well as with the medial portion of the articular capsules. It holds the dens to the anterior arch of the atlas after aU the other ligaments have been divided. The synovial membranes (figs. 260 and 261) are two in number: — one for the joint between the dens and atlas; and another (transverso-dental) for that between the transverse ligament and the dens. This last often communicates with the atlanto-occipital articulations; it is closed in by membranous tissue between the borders of the transverse ligament and the margin of the facet on the dens, and is separated from the front sac by the atlanto-dental articular capsule. The arterial supply is from the vertebral artery, aiid the nerve-supply from the loop between the first and second cervical nerves. Movements. — The chief and characteristic movement at these joints is the rotation, in a nearly horizontal plane, of the collar formed by the atlas and transverse ligament, round the dens as a pivot, which is extensive enough to allow of an all-round view without twisting the trunk. Partly on account of its ligamentous attachments, and partly on account of the shape of the articular siirfaces, the cranium must be carried with the atlas in these movements. The rotation is checked by the ligaments passing from the dens to the occiput (alar ligarnents), and also by the atlanto-epistrophic. Owing to the fact that the facets of both atlas and epistropheus, which enter into the formation of the lateral atlanto-epistrophic articulations, are convex from before backward, and have the articular cartilage thicker in the centre than at the circumfer- ence, the motion is not quite horizontal but slightly curvilinear. In the erect position, with the face looking directly forward, the most convex portions of the articular surfaces are alone in contact, there being a considerable interval between the edges; dm-ing rotation, therefore, the prominent portions of the condyles of the atlas descend upon those of the epistropheus, dimin- ishing the space between the bones, slackening the ligaments, and thus increasing the amount of rotation, without sacrificing the security of the joint in the central position. Besides rotation, forward and backward movements and some lateral flexion are permitted between the atlas and epistropheus, even to a greater extent than in most of the other vertebral joints. The muscles acting upon the atlanto-epistrophic joints. — The muscles capable of producing rotation at the atlanto-epistrophic joints are those which take origin from near the mesial plane either in front or behind and which are attached above either to the atlas or the skull, lateral to the atlanto-epistrophic joints. When the muscles which lie at the back of the joint on one side act they will turn the head to the same side and will be aided by the muscles in front on the opposite side. If the muscles in front and behind on the same side act simultaneously, they will pull down the head to that side and will be aided by muscles which pass more or less vertically from the transverse process of the atlas to points below. LIGAMENTS OF OCCIPUT AND EPISTROPHEUS 223 (c) The Ligaments uniting the Occiput and Epistropheus The following ligaments unite bones not in contact, and are to be seen from the interior of the canal after removing the posterior arches of the epistropheus and atlas and posterior ring of the foramen magnum : — 1. The tectorial membrane. 2. The crucial ligament. 3. Two alar (or check) ligaments. 4. The apical dental ligament. The tectorial membrane (occipito-cervical hgament) (figs. 261, 262, and 263) consists of a very strong band of fibres, connected below to the upper part of the body of the third vertebra and lower part of the body of the epistropheus as far as the root of the dens. It is narrow below, but widens out as it ascends, to be fastened to the basilar groove of the occiput. Laterally, it is connected with the accessory fibres of the atlanto-epistrophic capsule. It is really only the upward prolongation of the deep stratum of the posterior longitudinal ligament, the superficial fibres of which run on to the occipital bone without touching the epistropheus, thus giving rise to two strata. It is in relation in front with the crucial ligament. Fig. 262. — The Superficial Layer of the Posteeioe Longitudinal Vertebral Liga- ment HAS BEEN Removed to show its Deep oh Short Fibres. These Deep Fibres FORM the Tectorial Membrane. Viewed from behind. $/ Membrana tectoria, i. e.^ the deep stratum of the posterior longitudinal vertebral hgament Transverse process of atlas The crucial ligament has been already described (see p. 222). The alar (or check) ligaments (figs. 260 and 263) are two strong rounded cords, which extend from the sides of the apex of the dens, transversely lateral- ward to the medial edge of the anterior portion of the occipital condyles. They are to be seen immediately above the upper border of the transverse ligament, which they cross obliquely owing to its forward curve at its attachments to the atlas. Some of their fibres occasionally run across the middle line from one alar ligament to the other. At the dens they are connected with the atlan to-dental capsule, and at the condyles they strengthen the atlanto-occipital articular capsule. The apical dental or suspensory ligament (figs. 260 and 263) consists of a slender band of fibres ascending from the summit of the dens to the lower surface of the occipital bone, close to the foramen magnum. It is best seen from the front, after removing the anterior atlanto-occipital ligament, or from behind by drawing aside the crucial ligament. 224 THE ARTICULATIONS The apical ligament is tightened by extension and relaxed by flexion or nodding; the alar ligaments not only limit the rotatory movements of the head and atlas upon the epistropheus, but by binding the occiput to the pivot, round which rotation occurs, they steady the head and prevent its undue lateral inclination upon the vertebral column. (See Transverse Ligament, p. 222.) By experiments, it has been proved that the head, when placed so that the orbits look a little upward, is poised upon the occipital condyles in a line drawn a little in front of their middle; the amount of elevation varies slightly in different cases, but the balance is always to be obtained in the human body — it is one of the characteristics of the human figm'e. It serves to maintain the head erect without undue muscular effort, or a strong ligamentum nuchse and prominent dorsal spines such as are seen in the lower animals. Disturb this balance, and let the muscles cease to act, the head will either drop forward or backward according as the centre of gravity is in front or behind the balance line. The ligaments which pass over the dens to the occiput are not quite tight when the head is erect, and only become so when the head is flexed; if this were not so, no flexion would be allowed; thus, muscular action, and not liga- mentous tension, is employed to steady the head in the erect position. It is through the com- bination of the joints of the atlas and epistrophaus, and occiput and epistropheus (consisting of two paii-s of joints placed symmetrically on either side of the median line, while through the median line there passes a pivot, also with a pair of joints), that the head enjoys such freedom and celerity of action, remarkable strength, and almost absolute security against violence, which could only be obtained by a ball-and socket joint; but the ordinary ball-and-socket joints are too prone to dislocations by even moderate twists to be reliable enough when the life of the individual depends on the perfection of the articulation: hence the importance of this combination of joints. > Fig. 263. — Coronal Section of the Vertebral Column and the Occipital Bone TO SHOW Ligaments. (The tectorial membrane (1), though shown as a distinct stratum, is really the deeper part of the posterior longitudmal ligament (2) The upper ends have been reflected upward the lower downward Viewed from behind.) Vertical portion of crucial ligament Apical dental ligament Accessory ^ band of atlanto epistropbic capsules Atlanto -epistrophic joint Tectorial membrane Posterior longitudinal ligament THE ARTICULATIONS OF THE TRUNK These may be divided into the following sets: — 1. Those of the vertebral column. Joints and ligaments connecting: (a) The bodies. {h) The articular processes. (c) The laminae. 2. Vertebral column with the pelvis. 3. Pelvis. (d) The spinous processes. (e) The transverse processes. (o) Sacro-iliac (b) Sacro-coccygeal. (c) Intercoccygeal. (d) Symphysis pubis. 'ARTICULATIONS OF VERTEBRAL COLUMN 225 4. Ribs with the vertebral column. 5. The articulations at the front of the thorax. (a) Costal cartilages with the sternum. (6) Costal cartilages with the ribs. (c) Sternal. (d) Certain costal cartilages with each other. 1. THE ARTICULATIONS OF THE VERTEBRAL COLUMN There are two distinct sets of articulations in the vertebral column : — (a) Those between the bodies and intervertebral discs which form synchon- droses and which are amphiarthrodial as regards movement. (6) Those between the articular processes which form arthrodial joints. The ligaments which unite the various parts may also be divided into two sets, viz. — immediate, or those that bind together parts which are in contact; and intermediate, or those that bind together parts which are not in contact. Immediate. (a) Those between the bodies and discs. (6) Those between the articular processes. Intermediate. (c) Those between the laminae. (d) Those between the spinous processes. (e) Those between the transverse processes. Fig. 264. — Horizontal Section through an Intervektebbal Fibro-cartilage and THE Corresponding Ribs. Fibrous ring of intervertebral fibro-cartilage Tubercular ligament (a) The Aeticxtlations of the Bodies of the Vertebra Class. — False Synchondrosis. The ligaments which unite the bodies of the vertebrae are : — Intervertebral fibro-cartilages. Short lateral ligaments. Anterior longitudinal. Posterior longitudinal. The intervertebral fibro-cartilages (figs. 260 and 264) are tough, but elastic and compressible discs of composite structure, which serve as the chief bond of union between the vertebrae. They are twenty-three in number, and are inter- posed between the bodies of all the vertebrae from the epistropheus to the sacrum (figs. 260 and 271). Similar discs are found between the segments of the sacrum and coccyx in the younger stages of life, but they undergo ossification at their surfaces and often throughout their whole extent. 226 THE ARTICULATIONS Each disc is composed of two portions — a circumferential laminar, and a central pulpy portion; the former tightly surrounds and braces in the latter, and forms somewhat more than half the disc. The fibrous ring [annulus fibrosus] or laminar portion consists of alternating layers of fibrous tissue and fibro-oartilage; the component fibres of these layers are firmly con- nected with two vertebriE, those of one passing obliquely down and to the right, those of the next down and to the left, malving an X -shaped arrangement of the alterriate layers. A few of the superficial lamellie project beyond the edges of the bodies, their fibres being connected with the edges of the anterior and lateral surfaces; and some do not completely siu-round the rest, but terminate at the intervertebral foramina, so that on horizontal section the circum- ferential portion is seen to be thinner posteriorly. The more" central lamellae are incomplete, less firm, and not so distinct as the rest; and as they near the pulp they gradually assume its characters, becoming more fibro-cartilaginous and less fibrous, and have cartilage cells in their structure. The pulpy nucleus [nucleus pulposus] or central portion is situated somewhat behind the centre of the disc, forming a baU of very elastic and tightly compressed material, which bulges freely when the confining pressure of the laminar portion is removed by either horizontal or vertical section. Thus, it has a constant tendency to spring out of its confinement in the direction of least resistance, and constitutes a pivot round which the bodies of the vertebrae can twist, tilt, or incline. It is yellowish in colour, and is composed of fine white and elastic Fig. 265. — The Anterior Longitudinal Ligament, the Radiate, the Interarticular, AND THE Anterior Costo-transverse Ligaments. The interarticular ligament The anterior costo- transverse ligaments The radiate ligament fibres amidst which are ordinary connective-tissue cells, and pecuhar cells of various sizes which contain one or more nuclei. Together with the most central laminee, it is separated from im- mediate contact with the bone by a thin plate of articular cartilage. The central pulp of the intervertebral substance is the persistent part of the notochord. The intervertebral substances vary in shape with the bodies of the vertebrae they unite, and are widest and thickest in the lumbar region. In the cervical and lumbar regions they are thicker in front than behind, and cause, the convexity forward of the cervical, and increase that of the lumbar; the curve in the thoracic region, almost entirely due to the shape of the bodies, is, however, somewhat increased by the discs. Without the discs the column loses a quarter of its length, and assumes a curve with the concavity forward, most marked a little below the mid-thoracic region. Such is the curve of old age, which is due to the shrinking and drying up of the intervertebral substances. The disc between the epistropheus and third cervical is the thinnest of all (fig. 260) ; that between the fifth lumbar and sacrum is the thickest, and is much thicker in front than behind (fig. 271). The intervertebral discs are in relation, in front with the anterior longitudinal ligament; behind, with the posterior longitudinal ligament; laterally, with the short lateral; and in the thoracic region, with the interarticular and radiate ligaments. In the cervical region lateral diarthrodial joints are placed one on each side of the inter- vertebral discs. They are of small extent and are confined to the intervals between the promi- nent lateral lips of the upper surface of the body below and the bevelled lateral edges of the lower surface of the body above. Situated in front of the issuing spinal nerves and between those parts of the bodies formed from the neural arches, they are homologous with the joints between the atlas and epistropheus, and between the atlas and occipital bone. VERTEBRAL LIGAMENTS 227 The anterior longitudinal ligament (figs. 259 and 265) commences as a narrow band attached to the inferior surface of the occipital bone in the median line, just in front of the atlanto-occipital Ugament, of which it forms the thickened central portion. Attached firmly to the tubercle of the atlas, it passes down as the central portion of the atlanto-epistrophic ligament, in the mid-line, to the front of the body of the epistropheus. It now begins to widen out as it descends, until it is nearly two inches (5 cm.) wide in the lumbar region. Below, it is fixed to the upper segment of the sacrum, becoming lost in periosteum about the middle of that bone; but is again distinguishable in front of the sacro-coccygeal joint, as the anterior sacro-coccygeal ligament. Its structure is bright, pearly-white, and gUstening. Its lateral borders are separated from the lateral bands by clefts through which blood-vessels pass; they are frequently indistinct and are best marked in the thoracic region. It is thickest in the thoracic region, and thicker in the lumbar than the cervical. It is firmly connected with the bodies of the vertebra, and is composed of longitudinal fibres, of which the superficial extend over several, while the deeper pass over only two or three vertebrae. It is connected with the tendinous expansion of the pre- vertebral muscles in the cervical, and the crura of the diaphragm are closely attached to it in the lumbar region. Fig. 266. — Posterior Longitudinal Ligament. (Thoracic region.) (Pedicles cut through, and posterior arches of vertebrae removed.) The posterior longitudinal ligament (figs. 263, 266, 267, and 274) extends from the occipital bone to the coccyx. It is wider above than below, and com- mences by a broad attachment to the cranial surface of the basi-occipital. In the cervical region it is of nearly uniform width, and extends completely across the bodies of the vertebrae, upon which it rests quite flat. It does, however, extend slightly further laterally on each side opposite the intervertebral discs. In the thoracic and lumbar regions it is distinctly dentated, being broader over the inter- vertebral substances and the edges of the bones than over the middle of the bodies, where it is a narrow band stretched over the bones without resting on them, the anterior internal vertebral venous plexus being interposed. The narrow median portion consists of longitudinal fibres, some of which are super- ficial and pass over several vertebrae; and others are deeper, and extend only from one vertebra to the next but one below. The dentated or broader portions (fig. 267) are formed by oblique fibres which, springing from the bodies near the intervertebral foramina, take a curved course downward and back- 228 THE ARTICULATIONS ward over an intervertebral fibro-cartilage, and reach the narrow portion of the ligament on the centre of the vertebra next below; they then diverge to pass over another intervertebral dies to end on the body of the vertebra beyond, near the intervertebral notch. They thus pass over two discs and three vertebrae. Deeper still are other fibres thickening these expansions of the longitudinal hgament, and extending from one bone to the next. The last well-marked expansion is situated between the first two segments of the sacrum: 'below this, the ligament becomes a deUcate central band with rudimentary expansions, being more pronounced again over the sacro-coccygeal joint, and losing itself in the ligamentous tissue at the back of the coccyx. The dura mater is tightly attached to it at the margin of the foramen magnum and behind the bodies of the upper cervical vertebrae, but is separated from it in the rest of its extent by loose cellular tissue which becomes condensed in the sacral region to form the sacro-dural ligament. The filum terminale becomes blended with it at the lower part of the sacrum and back of the coccyx. Fig. 267. — Postbbior Longitudinal Ligament. (Lumbar region.) Median band Expanded lateral portion The lateral (or short) vertebral ligaments (fig. 265) consist of numerous short fibres situated between the anterior and posterior longitudinal ligaments, and passing from one vertebra over the intervertebral disc, to which it is firmly adherent, to the next vertebra below. The more superficial fibres are more or less vertical, but the deeper decussate and have a crucial arrangement. They are connected with the deep surface of the anterior longitudinal ligament, and so tie it to the edges of the bodies of the vertebrae and to the intervertebral discs. They blend behind with the expansions of the posterior longitudinal ligament, and so complete the casing round each amphiarthrodial joint. In the thoracic region, they overlie the radiate ligament, and in the lumbar they radiate toward the transverse processes. In the cervical region they are less well marked. (b) The Ligaments Connecting the Articular Processes Class. — Diarthrosis. Subdivision. — Arthrodia. The articular capsules (fig. 259) which unite these processes are composed partly of yellow elastic tissue and partly of white fibrous tissue. In the cervical region only the medial side of the capsule is formed by the ligamenta flava, which in the thoracic and lumbar regions, however, extend anteriorly to the margins of the intervertebral foramina. The part formed of white fibrous tissue consists of short, well-marked fibres, which in the cervical region pass obhquely downward and forward over the joint, between the articular proc- VERTEBRAL LIGAMENTS 229 esses and the posterior roots of the transverse processes of two contiguous vertebra. In the thoracic region the fibres are shorter, and vertical in direction, and are attached to the bases of the transverse processes; in the lumbar, they are obhquely transverse. The articular capsules in the cervical region are the most lax, those in the lumbar region are rather tighter, and those in the thoracic region are the tightest. There is one s3movial membrane to each capsule. (c) The Ligaments uniting the Lamina The ligamenta flava (fig. 268) are thick plates of closely woven yellow elastic tissue, interposed between the laminae of two adjacent vertebrae. The first con- nects the epistropheus with the third cervical, and the last the fifth lumbar with Fig. 268.- Canal. -Ligamenta Flava in the Lumbar Region, seen from within the Vertebral Portion of ligamentu flavum removed to show the articular cavity Ligamentum flavum the sacrum. Each ligament extends from the medial and posterior edge of the intervertebral foramen on one side to a corresponding point on the other ; above, it is attached close to the inner margin of the inferior articular process and to a well-marked ridge on the inner surface of the laminae as far as the root of the spine; below, it is fixed close to the inner margin of the superior articular process and to the dorsal aspect of the upper edge of the laminae. Thus each ligamentum flavum, besides filling up the interlaminar space, enters into the formation of two articular capsules; they do so to a greater extent in the thoracic and lumbar regions than in the cervical, where the articular processes are placed wider apart. When seen from the front after removing the bodies of the vertebrae, they are concave from side to side, but convex from above downward; they make a more decided transverse curve than the arches between which they are placed. This concavity is more marked in the thoracic, and still more in the lumbar region than in the cervical; in the lumbar region the hgamenta flava extend a short distance between the roots of the spinous process, blending with the interspinous ligament, and making a median sulcus when seen from the front; there is, however, no separation between the two parts. In the cervical region, where the spines are bifid, there is a median fissure in the yellow tissue which is filled up by fibro-areolar tissue. The ligaments are thickest and strongest in the lumbar region; narrow but strong in the thoracic; thinner, broader, and more membranous in the cervical region. (d) The Ligaments connecting the Spinous Processes These include supraspinous ligament, interspinous ligaments, and the liga- mentum nuchae. 230 THE ARTICULATIONS The supraspinous ligament (fig. 270) extends without interruption as a well-marked band of longitudinal fibres along the tips of the spines of the vertebrae fromthat of the seventh cervical downward till it ends on the median sacral crest. Fig. 269. — Side View op Ligamentum Nuch^. Ligamentum auchs First iuterspinalis muscle' Fig. 270. —The Interspinous and Supraspinous Ligaments in the Lumbar Region. -The interspinous ligament jttJ — The supraspinous ligament Its more superiioial fibres are much longer than the deep. The deeper fibres pass over adjacent spines only, while the superficial overlie several. It is connected laterally with the aponeurotic structures of the back; indeed, in the lumbar region, where it is well marked, it VERTEBRAL LIGAMENTS 231 appears to result from the interweaving of the tendinous fibres of the several muscles which are attached to the tips of the spinous processes. In the dorsal region it is a round slender cord which is put on the stretch in flexion and relaxed in extension of the back. The ligamentum nuchse, or the posterior cervical ligament (fig. 269), is the continuation in the neck of the supraspinous ligament, from which, however, it differs considerably. It is a slender vertical septum of an elongated triangular form, extending from the seventh cervical vertebra to the external protuberance and the crest of the occipital bone. Its anterior border is firmly attached to the tips of the spines of all the cervical vertebrte, including the posterior tubercle of the atlas, as well as to the occiput. Its posterior border gives origin to the trapezii, with the tendinous fibres of which muscle it blends. Its lateral, tri- angular surfaces afford numerous points of attachment for the posterior muscles of the head and neck. In man it is rudimentary, and consists of elastic and white fibrous tissues. As seen in the horse, elephant, ox, and other pronograde mammals, it is a great and important elastic ligament, which even reaches along the thoracic part of the spinal column. In these animals it serves to support the head and neck, which otherwise from their own weight would hang down. Its rudimentary state in man is the direct consequence of his erect position. The interspinous ligaments (fig. 270) are thin membranous structures which extend between the spines, and are connected with the ligamenta flava in front, and the supraspinous ligament behind. The fibres pass obliquely from the root of one spine to the tip of the next; they thus decus- sate. They are best marked in the lumbar region, and are replaced by the well-developed inierspinales muscles in the cervical region. (e) The Ligaments connecting the Transverse Processes The intertransverse ligaments are but poorly developed. In the thoracic region they form small rounded bundles, and in the lumbar they are flat membranous bands, unimportant as bonds of union. They consist of fibres passing between the apices of the transverse processes. In the cervical region they are replaced by the inter- transversarii muscles. The arterial supply for the column comes from twigs of the vertebral, ascending pharyn- geal, ascending cervical, superior and aortic intercostals, lumbar, iUo-lumbar, and lateral sacral. The nerve-supply comes from the spinal nerves of each region. Movements. — The vertebral column is so formed of a number of bones and intervertebral discs as to serve many purposes. It is the axis of the skeleton; upon it the skull is supported; and with it the cavities of the trunk and the limbs are connected, As a fixed column it is capable of bearing great weight, and, through the elastic intervertebral substances, of resisting and breaking the transmission of shocks. Moreover, it is flexible. Now, the range of movements of the column as a whole is very considerable; but the movements between any two vertebrae are slight, so that motions of the spine may take place without any change in the shape of the column, and without any marked disturbance in the relative positions of the vertebrae. It is about the pulpy part of the intervertebral discs, which form a central elastic pivot or ball, upon which the middle of the vertebras rest, that these movements take place. The amount of motion is everywhere limited by the common vertebral Ugaments, but it depends partly upon the width of the bodies of the vertebrae, and partly upon the depth of the discs, so that in the loins, where the bodies are large and wide, and the discs very thick, free motion is permitted; in the cervical region, though the discs are thinner, yet, as the bodies are smaller, almost equally free motion is allowed. As the ball-Uke pulpy part of the intervertebral disc is the centre of movement of each vertebra, it is obvious that the motion would be of a rolUng character in any direction but for the articular processes, wtiich serve also to give steadi- ness to the column and to assist in bearing the superincumbent weight. Were it not for these processes, the column, instead of being steady, endowed with the capacity of movement by muscular agency, would be tottering, requiring muscles to steady it. The influence of the articular processes in limiting the direction of incUnation will appear from a study of the movements in the three regions of the spine. In the neck all movements are permitted and are free, except between the second and third cervical vertebrje, where they are slight, owing to the shallow intervertebral disc and the great prolongation of the anterior hp of the inferior surface of the body of the epistropheus, which checks forward flexion considerably. On the whole, however, extension and lateral inclination are more free and extensive in this than in any other region of the column, whilst flexion is more limited than in the lumbar region. Rotatory movements are also free, but take place, on ac- count of the position and inclination of the articular facets, not, as in the thoracic region, round a vertical axis, but round an oblique axis, the articular process of one side gliding upward and forward and that of the opposite side downward and backward. In the thoracic region, especially near its middle, antero-posterior flexion and extension are very slight; and, as the concavity of the curve here is forward, the flat and nearly vertical surfaces of the articular processes prevent anything like sliding in a curvilinear manner of the 232 THE ARTICULATIONS one set of processes over the sharp upper edges of the other, which would be necessary for forward flexion. A fair amount of lateral inclination would be permitted but for the impedi- ment offered by the ribs; while the position and direction of the articular processes allows rota- tion round a vertical axis which passes through the centres of the bodies of the vertebrae. This rotation is not very great, and is freer in the upper than in the lower part of the thoracic region. In the lumbar region, extension and flexion are very free, especially between the third and fourth and fourth and fifth vertebrae, where the lumbar curve is sharpest; lateral inclination is also very free between these same vertebrae. It has been stated that the shape and position of the articular processes of the lumbar and the lower two or three dorsal are such as to prevent any rotation in these regions; but, owing to the fact that the inferior articular processes are not tightly embraced by the superior, so that the two sets of articular processes are not in contact on both sides of the bodies at the same time, there is always some space in which horizontal motion can occur round an axis drawn through the central part of the bodies and interverte- bral discs, but it is very slight. Thus, the motions are most free in those regions of the column which have a convex curve forward, due to the shape of the intervertebral discs, where there are no bony waOs surrounding solid viscera, where the spinal canal is largest and its contents are less firmly attached, and where the pedicles and articular processes are more nearly on a transverse level with the posterior surface of the bodies of the vertebrae. Nor must the uses of the ligamenta flava be forgotten: these useful structures — (1) com- plete the roofing-in of the vertebral canal, and yet at the same time permit an ever-changing variation in the width of the interlaminar spaces in flexion and extension; (2) they also restore the articulating surfaces to their normal position with regard to each other after movements of the column; (3) and by forming the medial portion of each articular capsule, they take the place of muscle in preventing it from being nipped between the articular surfaces during movement. Muscles which take part in the movements of the vertebral column. — Flexors : When acting with their fellows of the opposite side. Rectus abdominis, infra-hyoid muscles (slightly) sterno-mastoid, external oblique, internal obHque, intercostals, scalenus anterior, psoas major and minor, longus colli, longus capitis (rectus capitis anterior major). Extensors : When acting with their fellows of the opposite side. Sacro-spinalis, quadratus lumborum, semispinalis, multifidus, rotatores, interspinales, serrati posteriores, the splenius, and with the scapula fixed the levator scapulae and the upper fibres of the trapezius. Muscles which help to incline the column to their own side. — Sacro-spinaUs, quadratus lumborum, semispinalis, multifidus, the intercostals helping to fix the ribs, the external and internal oblique muscles, levatores costarum, serrati posteriores, the scalenes, splenius cervicis, longus coUi (oblique part), rotatores, intertransversales, psoas, and with the scapula fixed the levator scapulae and the upper and lower fibres of the trapezius. Muscles which rotate the column and turn the body to their own side. — Splenius cervicis, internal oblique (the ribs being fixed), serratus posterior inferior, and with the scapula fixed the lower fibres of the trapezius. Muscles which rotate the column and turn the body to the opposite side. — Multifidus, semispinalis, external oblique, the lower oblique fibres of the longus colli, and with the scapula and humerus fixed the latissimus dorsi and trapezius. 2. THE SACRO-VERTEBRAL ARTICULATIONS (a) Class. — False Synchondrosis. (b) Class. — Diarthrosis. Subdivision. — Arihrodia. As in the intervertebral articulations, so in the union of the first portion of the sacrum with the last lumbar vertebra, there are two sets of joints — viz. (a) a synchondrosis, between the bodies and intervertebral disc; and (6) a pair of arthrodial joints, between the articular processes. The union is effected by the following ligaments, which are common to the vertebral column: — (i) anterior, and (ii) posterior longitudinal; (iii) lateral or short vertebral; (iv) capsular; (v) ligamenta flava; (vi) supraspinous and (vii) interspinous ligaments. Two special accessory ligaments on either side, viz., the sacro-lumbar and the ilio- lumbar, connect the pelvis with the fourth and fifth lumbar vertebrae. The sacro-lumbar ligament (fig. 271) is strong, and triangular in shape. Its apex is above and medial, being attached to the whole of the lower border and front surface of the transverse process of the fifth liunbar vertebra, as well as to the pedicle and body. It is intimately blended with the ilio-lumbar ligament. Below, it has a wide, fan-shaped attachment, extending from the edge of the ilio- lumbar ligament forward to the brim of the true pelvis; blending with the perios- teum on the base of the sacrum and in the iliac fossa, and with the superior sacro- iliac ligament. By its sharp medial border it Umits laterally the foramen for the last lumbar nerve. It is pierced by two large foramina, which transmit arteries to the saoro-iliac synchondrosis. This ligament is in series with the intertransverse ligaments of the spinal column. It is sometimes described as a part of the ilio-lumbar ligament. SACRO-VERTEBRAL ARTICULATIONS 233 The ilio-lumbar ligament (fig. 271) is a strong, dense, triangular ligament connecting the fourth and fifth lumbar vertebrae with the iliac crest. It springs from the front surface of the transverse process of the fifth lumbar vertebra as far as the body, by a strong fasciculus from the posterior surface of the process near the tip, and also from the front surface and lower edge of the transverse process and pedicle of the fourth lumbar vertebra, as far medialward as the body. Between these two lumbar vertebrae it is inseparable from the intertransverse hgament. At its origin from the transverse process of the fifth lumbar vertebra it is closely inter- woven with the sacro-lumbar ligament, and some of its iibres spread downward on to the body of the fifth vertebra, while others ascend to the disc above. At the pelvis it is attached to the inner lip of the crest of the ilium for about two inches (5 cm.) . The highest fibres at the column form the upper edge of the ligament at the pelvis, those which come from the posterior portion of the transverse process of the fifth lumbar vertebra forming the lower, while the fibres from the front of the same process pass nearly horizontally lateralward. Near the column the surfaces Fig. 271. — Anterior View of the Ligaments between Vertebra and Pelvis. anterior primary branch of fourth Foramen for last lumbar nerve Intervertebral disc between last lum- bar and first sacral vertebrae The ilio-lumbar ligament The sacro-luml ligament Superior sacro- ligament Anterior sacro- ligament Sacro-tuberous ligament Sacro-spinous ligament look directly backward and forward, but at the ilium the ligament gets somewhat twisted, so that the posterior surface looks a little upward, and the anterior looks a Mttle downward. The anterior surface forms part of the posterior boundary of the major (false) pelvis, and over- lies the upper part of the posterior sacro-iliao ligament; the posterior surface forms part of the floor of the spinal groove, and gives origin to the mullifidus muscle. Of the borders, the upper is oblique, has the anterior lamella of the lumbar fascia attached to it, and gives origin to the quadralus lumborum; the lower is horizontal, and is adjacent to the upper edge of the sacro- lumbar ligament; while the medial is crescentic, and forms the lateral boundary of a foramen through which the fourth lumbar nerve passes. The arterial supply is very free, and comes from the last lumbar, ilio-lumbar, and lateral sacral. The nerve-supply is from the sympathetic, as well as from twigs from the fourth and fifth lumbar nerves. Movements. — The angle formed by the sacrum with the spinal column is called the sacro- vertebral angle. The pelvic inclination does not depend entirely upon this angle, but in great part upon the obUquity of the co.xal (innominate) bones to the sacrum, so that in males in whom the average pelvic obliquity is a Uttle greater, the average sacro-vertebral angle is considerably less than in females. The sacro-vertebral angle in the male shows that there is a greater and more sudden change in direction at the sacro-vertebral union than in the female. A part of this change in direction is due to the greater thickness in the anterior part of the intervertebral fibro-cartilage between the last lumbar vertebra and the sacrum. Owing to the greater thickness of the intervertebral 234 THE ARTICULATIONS disc here than elsewhere, the movements permitted at this joint are very free, being freer than those between any two lumbar vertebrEe. As the diameter of the two contiguous bones is less in the sagittal than in the frontal plane, the forward and backward motions are much freer than those from side to side. The backward and forward motions take place every time the sitting is exchanged for the standing position, and the standing for the sitting posture; in rising, the back is extended on the sacrum at the sacro-lumbar union; in sitting down it is flexed. The articular processes provide for the ghding movement incidental to the extension, flexion, and lateral movements; they also allow some horizontal movement, necessary for the rotation of the vertebral column on the pelvis, or pelvis on the column. The inferior articular processes of the fifth differ considerably from the inferior processes in the rest of the lumbar vertebrae, and in direction they resemble somewhat those of the cervical vertebrae; while the su- perior articular processes of the sacrum differ in a similar degree from the superior processes of the lumbar vertebrae. This difference allows for the freer rotation which occurs at this joint. The sacro-vertebral angle averages 117° in the male, and 130° in the female; while the pelvic incKnation averages 155° in the male, and 150° in the female. As already stated, the movements at the sacro-vertebral joint are the same as those in other parts of the spinal column, but more extensive, and the muscles which produce the movements are those mentioned in the preceding groups which cross the plane of the articulation. 3. THE ARTICULATIONS OF THE PELVIS This group may again be subdivided into — - (a) The sacro-iliac. (6) The sacro-coccygeal. (c) The intercoccygeal. (d) The symphysis pubis. (a) The Sacro-iliac Articulation and Sacro-sciatic Ligaments Class. — Diarthrosis. Subdivision. — Arthrodia. It is now generally admitted that the sacro-iliac joint is a diarthrosis, the articular surface of each bone being covered with a layer of cartilage, whilst the cavity of the joint is a narrow cleft and the capsule is extremely thick posteriorly. The cartilage on the sacrum is much thicker than that on the ilium and the cartilages are sometimes bound together here and there by fibrous strands. The different character of the joint in the two sexes should be noted. Briefly, the female joint has strong ligamentous bonds with but little bony apposition, while the male joint gains its strength by virtue of extensive areas of bony contact and a slighter development of ligaments. This difference is, of course, a physiological one; for some laxity of the joint is demanded during pregnancy and labour. The bones which enter into the joint are the sacrum and ilium, and they are bound together by the following ligaments: — Anterior sacro-iliac. Superior sacro-iliac. Posterior sacro-iliac. Inferior sacro-iliac. Interosseous. The anterior sacro-iliac ligament (figs. 271 and 272) consists of well-marked glistening fibres which pass above into the superior, and below into the inferior, ligaments. It extends from the first three bones of the sacrum to the ilium between the brim of the pelvis minor and the great sciatic notch, blending with the periosteum of the sacrum and ilium as it passes away from the united edges of the bones. The superior sacro-iliac ligament (figs. 271 and 272) extends across the upper margins of the joint, from the ala of the sacrum to the iliac fossa, being well marked along the brim of the pelvis, where it is thickened by some closely packed fibres. Behind, it is far stronger, especially beneath the transverse process of the fifth lumbar vertebra. This ligament is connected with the strong sacro- lumbar ligament, which spreads lateralward and forward over the joint to reach the iliac fossa and terminal line. By some authors it is described as a part of the ilio-lumbar ligament. The posterior sacro-iliac ligament is extremely strong and consists essentially of two sets of fibres, deep and superficial. The deep fibres (short posterior sacro- iliac ligament) pass downward and medialward from the rough area of the PELVIC ARTICULATIONS 235 ilium behind the auricular surface to the back of the lateral mass of the sacrum, both lateral to and between the upper foramina and to the upper sacral articular process, and the area between it and the first sacral foramen. The deepest fibres of this group constitute the so-called interosseous ligament. The more superficial fibres (long posterior sacro-iliac ligament) are oblique or vertical, and pass from the posterior superior iliac spine to the second, third, and fourth tubercles on the back of the sacrum, a more or less well-defined band which goes to the third and fourth sacral tubercles being called sometimes the oblique saero-iliac band and sometimes the long straight band. The inferior sacro-iliac ligament (fig. 272) is covered behind by the upper end of the sacro-tuberous ligament; it consists of strong fibres extending from the lateral border of the sacrum below the articular facet to the posterior iliac spines; some of the fibres are attached to the deep surface of the ilium and join the interosseous ligament. Fig. 272. — Median Sagittal Section op the Pelvis, Showing Ligaments. Anterior sacro-iliac liga- ment Inferior sacro-iliac liga- ment Sacro-spinous ligament Sacro-tuberous ligament i The interosseous ligament is the strongest of all, and consists of fibres of different lengths passing in various directions between the two bones. Imme- diately above the interspinous notch of the ilium the fibres of this ligament are very strong, and form an open network, in the interstices of which is a quantity of fat in which the articular vessels ramify. Tlie ear-shaped cartilaginous plate, which unites the bones firmly, is accu- rately applied to the auricular surfaces of the sacrum and ilium. It is about one-twelfth of an inch (2 mm.) thick in the centre, but becomes thinner toward the edges. Though closely adherent to the bones, it tears away from one entirely, or from both partially, on the application of violence, sometimes breaking irregu- larly so that the greater portion remains connected with one bone, leaving the other bone rough and bare. It is usually one mass, and is only occasionally formed of two plates with a synovial cavity between them. Because of the occasional presence of a more or less extensive synovial ca^dty within the fibro-cartilage, and also of a synovial lining to the Ugaments passing in front and behind the articulation, the term 'diarthro-amphiarthrosis' has been given to this joint, and also to the sympliysis pubis. Testut mentions certain folds of sjiiovial membrane filling up gaps which here and there occur at the margin of the fibro-cartilage but they are not usually seen. The sacro-tuberous (great sciatic) ligament (figs. 271, 272, and 273) is at- tached above to the posterior extremity of the crest of the ilium and the lateral aspect of the posterior iliac spines. From this attachment some of its fibres 236 THE ARTICULATIONS pass downwai'd and backward to be attached to the lateral borders and posterior surfaces of the lower three sacral vertebrae and upper two segments of the coccyx; while others, after passing for a certain distance backward, curve forward and downward to the ischium, forming the anterior free margin of the ligament where it limits posteriorly the sciatic foramina. These fibres are joined by others which arise from the posterior surfaces of the lower three sacral vertebrse and upper pieces of the coccyx. At the ischium it is fixed to the medial border of the tuberosity, and sends a thin sharp process upward along the ramus of the ischium which is called the falciform process (fig. 273), and is a prolongation of the posterior edge of the ligament. A great many fibres pass on directly into the tendon of the biceps muscle, so that traction on this muscle braces up the whole ligament, and the coccyx is thus made to move on the sacrum. The ligament may not unfairly be described as a tendinous expansion of the muscle, whereby its action is extended and a more advantageous leverage given. It is broad and flat at its attached ends, but narrower and thicker in the centre, looking like two triangular expansions- Fig. 273. — Sacro-tuberous and Sacro-spinous Ligaments. (Posterior view.) Falciform process of sacro-tuberous ligament joined by a flat band, the larger triangle being at the ilium, and the smaller at the ischium^ The fibres of the ligament are twisted upon its axis at the narrow part, so that some of the- superior fibres pass to the lower border. The posterior surface gives origin to the gluteus maximus muscle, and on it ramify the loop; from the posterior branches of the sacral nerves; its anterior surface is closely connected at its origin ,with the sacro-spinous ligament, and some fibres of the piriformis muscle arise from its below the obturator internus passes out of the pelvis under its cover, and the internal pudic vessels and nerve pass in. At the ilium, its posterior edge is continuous with the vertebra, aponeurosis; while to the anterior edge is attached the thick fascia covering the gluteus mediusl The obturator fascia is attached to its falciform edge. It is pierced by the coccygeal branches of the inferior gluteal {sciatic) artery and the inferior clunial {perforating cutaneous) nerve from the second and third sacral. The sacro-spinous (small sciatic) ligament (figs. 271, 272, and 273) is tri- angular and thin, springing by a broad base from the lateral border of the sacrum and coccyx, from the front of the sacrum both above and below the level of the fourth sacral foramen, and from the coccyx nearly as far as its tip. By its apex it is attached to the front surface and the borders of the ischial spine as far out- ward as its base. Its fibres decussate so that the lower ones at the coccyx be- come the highest at the ischial spine; muscular fibres are often seen intermingled with the ligamentous. The sacro-spinous ligament is situated in front of the sacro-tuberous Hgament, with which it is closely connected at the sacrum, and separates the greater from the lesser sciatic foramen. SACRO-COCCYGEAL ARTICULATION 237 Its front surface gives attachment to the coccygeus muscle, which overlies it. Behind, it is connected with, and hidden by, the sacro-tuberous ligament, so that only the lateral inch or less (2 cm.) and a small part of its attachment to the coccyx can be seen; the internal pudic nerve also passes over the posterior surface. The arterial supply of the sacro-Uiac joint comes from the superior gluteal, ilio-lumbar, and lateral sacral. The nerve-supply is from the superior gluteal, sacral plexus, and external twigs of the posterior divisions of the first and second sacral nerves. Movements. — Recent investigations have shown that in spite of the interlocking of the articular surfaces and the strong ligaments connecting the bones together a slight amount of movement, both a gUding and rotatory, does occur at the sacro-iliac joint. The gliding move- ment is both up and down, and forward and backward, and the latter is associated with a slight rotation round a transverse axis which passes through the upper tubercles on the back of the sacrum. The movement is but small in extent, nevertheless as the base of the sacrum moves Fig. 274. — Ligaments connecting Sacrum and Coccyx posteriorly. Superficial part of the supraspinous ligament, turned Deep part of the su- praspinous ligament turned up Lateral sacro-coccygeaL ligament The deep posterior sacro- cocygeal ligament, or the lower end of the poste- rior longitudinal liga- ment The superficial posterior sacro-coccygeal 1 i g a - ment connecting the cornus of the sacrum and coccyx, cut and turned down downward and forward the conjugate (antero-posterior) diameter of the pelvic inlet is diminished and at the same time, as the coccyx moves up and back, the conjugate diameter of the outlet is increased. This rotatory movement is limited principally by the sacro-sciatic (sacro- tuberous and sacro-spinous) Ugaments which prevent any extensive upward and backward movement of the coccyx and lower part of the sacrum. Downward displacement of the sacrum when the body is in the sitting posture is prevented not only by the surrounding hgaments, but also by the wedge-like character of the sacrum, which is broader above than below. Downward and forward displacement of the sacrum in the erect posture is prevented by the ligaments and more particularly by the posterior sacro- iliac bands, while backward displacement would be hindered by the breadth of the anterior as contrasted with the posterior part of the sacrum as well as by the anterior ligaments. Relations. — The sacro-ihac joint is in relation above with psoas and iUaous. In front it is in relation at its upper part with the hypogastric vessels and obturator nerve, and at its lower part with the piriformis muscle. (b) The Sacro-coccygeal Articulation Class. — False Synchondrosis. The last piece of the sacrum and first piece of the coccyx enter into this union [symphysis sacrococcygea] and are bound together by the following ligaments : — Anterior sacro-coccygeal. Deep posterior sacro-coccygeal. Superficial posterior sacro-coccygeal. Lateral sacro-coccygeal. Intervertebral substance. 238 THE ARTICULATIONS The intervertebral fibro -cartilage is a small oval disc, three-quarters of an inch (about 2 cm.) wide, and a little less from before backward, closely con- nected with the surrounding ligaments. It resembles the other discs in struc- ture, but is softer and more jelly-like, though the laminse of the fibrous portion are well marked. The anterior sacro-coccygeal ligament is a prolongation of the glistening fibrous structure on the front of the sacrima. It is really the lower extremity of the anterior longitudinal ligament, which is thicker over this joint than over the central part of either of the bones. The posterior sacro-coccygeal ligament (fig. 274) is divided into two layers of which one (the deep) is a direct continuation of the posterior longitudinal ligament of the column, consisting of a narrow band of closely packed fibres, which become blended at the lower border of the first segment of the coccyx with the filum terminate and deep posterior ligament. The superficial layer of the posterior sacro-coccygeal ligament (or supra- cornual ligament), (fig. 274) is the prolongation of the supraspinous which be- comes inseparably blended with the aponeurosis of the sacro-spinalis (erector spince) opposite the laminse of the third sacral vertebra, and is thus prolonged downward upon the back of the coccyx, passing over and roofing in the lower end of the spinal canal where the laminge are deficient. The median fibres (the supraspinous ligament) extend over the back of the coccyx to its tip, blending with the deep fibres of the posterior sacro-coccygeal ligament and filum terminale; the deeper fibres run across from the stunted laminae on one side to the next below on the oppo- site side, and from the sacral cornua on one side to the coccygeal on the opposite, some passing between the two cornua of the same side, and bridging the aperture through which the fifth sacral nerve passes. Its posterior surface gives origin to the gluteus inaximus muscle. The lateral sacro-coccygeal or intertransverse ligament (fig. 274) is merely a quantity of fibrous tissue which passes from the transverse process of the coccyx to the lateral edge of the sacrum below its angle. It is connected with the saerosciatic ligaments at their attachments, and the fifth sacral nerve escapes behind it. It is perforated by twigs from the lateral sacral artery and the coccygeal nerve. The arterial supply of the sacro-coccygeal joint is from the lateral sacral and middle sacral arteries. The nerves come from the fourth and fifth sacral and coccygeal nerves. The movements permitted at this joint are of a simple forward and backward, or hinge- like character. In the act of defecation, the bone is pushed back by the faecal mass, and, in parturition, by the foetus; but this backward movement is controlled by the upward and forward puU of the levator ani and Qoccygeus. The external sphincter also tends to puU the coccyx forward. (c) Intercoccygeal Joints The several segments of the coccyx are held together by the anterior and posterior longitudinal ligaments, which completely cover the bony nodules on their anterior and posterior aspects. Laterally, the sacro-sciatic ligaments, being attached to nearly the whole length of the coccyx, serve to connect them. Between the first and second pieces of the coccyx there is a very perfect amphiar- throdial joint, with a well-marked intervertebral substance. Movements. — But Uttle movement occurs as a rule at the sacro-coccygeal and inter- coccygeal joints, but when the head of the child is passing through the pelyic outlet at birth, the tip of the coccyx is displaced backward, it may be to the extent of one inch. (d) The Symphysis Pubis Class. — False Synchondrosis. The bones entering into this joint are the pubic portions of the hip-bones. This joint is shorter and broader in the female than in the male. The ligaments, which completely surround the articulation, are : — Superior. Anterior. Arcuate. Posterior. Interpubic cartilage. The superior ligament (figs. 275 and 276) is a well-marked stratum of yellowish fibres which extends lateralward along the crest of the pubis on each side, blending in the middle line with the interosseous cartilage. SYMPHYSIS PUBIS 23& It is continuous in front with the deep traverse fibres of the anterior ligament, and be- hind with the posterior ligament. It gives origin to the rectus abdominis tendon. The posterior ligament (fig. 277) is slight, and, excepting above and below, consists of little more than thickened periosteum. Near the uipper part is a band of strong fibres, reaching the whole width of the pubic bones, and continuous with the thickened periosteal fibres along the terminal line. Below, many of the upper and superficial fibres of the arcuate ligament ascend over the back of the joint, and interlace across the median line with fibres from the opposite side nearly as high as the middle of the symphysis. Fig. 275. — Anteeiob View of the Symphysis Pubis (Male), showing the Decussation OF THE Fibres of the Anterior Ligament. Superior pubic ligament X Arcuate ligament The anterior ligament (figs. 275 and 276) is thick and strong, and is closely connected with the fascial covering of the muscles arising from the body of the pubis. It consists of several strata of thick, decussating fibres of different de- grees of obliquity, the superficial being the most oblique, and extending lowest over the joint. The most superficial descending fibres extend from the upper border of the pubis, cross others from the opposite side about the middle of the symphysis, and are attached to the ramus of the opposite bone. The most superficial ascending fibres come from the arcuate ligament, Fig. 276. — Anterior View of the Symphysis Pubis (Female), showing greater Width between the Bones. Superior pubic ligament Arcuate ligament arch upward,"and decussate with other fibres across the middle line, and are lost on the oppo- site side beneath the descending set. There is another deeper set of descending fibres which arise below the angle, but do not descend so far as the superficial; and a deeper set of ascending, which decussate, and reach higher than the superficial set, and are connected with the arcuate ligament. Some few transverse fibres pass from side to side, especially above and below^the points of decussation. The arcuate (inferior or subpubic) ligament (figs. 275, 276, and 277) is a thick, arch-like band of closety packed fibres which fills up the angle between the pubic rami, and forms a smooth, rounded summit to the pubic arch. On section, it is yellowish in colour and three-eighths of an inch (1 cm.) thick in the middle line; it is inseparably connected with the interpubic cartilage. 240 THE ARTICULATIONS Both on the front and back aspects of the joint it gives off decussating fibres, which, by their interlacement over the anterior and posterior ligaments of the symphysis, add very materi- ally to its security. In fact, the ligament may be said to split superiorly into two layers, one passing over the front, and the other over the back, of the articulation. The interpubic fibro -cartilage varies in thickness in different subjects, but is thicker in the female than in the male. It is thicker in front than behind, and projects beyond the edges of the bones, especially posteriorly (see fig. 277), blending intimately with the ligaments at its margins. It is sometimes uninter- ruptedly woven throughout, but at others has an elongated narrow fissure, partially dividing the cartilage into two plates, with a little fluid in the interspace Fig. 277. — Posterior View of the Symphysis Pubis, showing the Decussation op the Fibres prom the Arcuate Ligament. Arcuate ligament (fig. 278). This is situated toward the upper and posterior aspects, but does not usually reach either; it generally extends about half the length of the cartilage. When this cavity is large, especially if it reaches or approaches very near to the circumfer- ence of the cartilage (which, however, it very rarely does), it is thought by some anatomists that it more nearly resembles a diarthrodial than an amphiarthrodial joint, and it is then classed with the sacro-Uiac joint under similar conditions, as 'diarthroamphiarthrosis.' The interos- seous cartilage is intimately adherent to the layer of hyaline qartUage which covers the medial surface of each pubic bone; the osseous surface is ridged to give a firmer attachment; and, on forcing the bones apart, it does not frequently spht into two plates, but is torn from the bone on one side or the other. Fig. 278. — Section of Symphysis to show the Synovial Cavity. The arterial supply of the interpubic joint is from twigs of the internal pudic, pubic branches of the obturator and epigastric, and ascending branches of the internal circumflex and super- ficial external pudic. The nerve-supply has not been satisfactorily made out, but it probably comes, m part, from the internal pudic and in part from the ilio-hypogastric and Uio-inguinal. The movements amount only to a slight yielding of the cartilage; neithermuscular force nor extrinsic forces produce any appreciable movement in the ordinary condition. Occasion- ally, as the result of child-bearing, the joint becomes unnaturally loose, and then waMng and standing are painfully unsteady. It is known that, during pregnancy and parturition, the COSTO-VERTEBRAL ARTICULATIONS 241 symphyseal cartilage becomes softer and more vascular, so as to permit the temporary enlarge- ment of the pelvis; but it must be remembered that the fibres of the obhque muscles decussate and thus, during labour, while they force the head of the fcetus down, they strengthen the joint by bracing the bones more tightly together. Relations. — The interpubic joint is in relation above with the Unea alba. Behind with the prostate and the anterior border of the bladder. In front with the suspensory ligament of the penis or chtoris and below with the dorsal vein of the penis or clitoris and the upper border of the urogenital trigone (triangular ligament). 4. THE COSTO-VERTEBRAL ARTICULATIONS These consist of two sets, viz. : — ■ (a) The capitular (costo-central) : i. e., the articulation of the head of the rib with the vertebrae. (6) The costo-transverse, or the articulation of the tubercle (of each of the first ten ribs) with the transverse process of the lower of the two vertebree, with which the head of the rib articulates: i.e., the one bearing its own number, as the first rib with the first thoracic vertebra, the second rib with the second thoracic vertebra, and so on. Fig. 279. — -The Capsular Ligaments op the Costo-vertebral Joints. Capsular ligament of capitular joint (a) The Capitular (Costo-central) Articulation Class. — Diarthrosis. Subdivision. — Condylarthrosis. It is a very perfect joint, into the formation of which the head of the rib and two vertebrae, with the intervertebral disc between them, enter. In the case of the first, tenth, eleventh, and twelfth ribs, it is formed by the head of the rib articulating with a single vertebra. The ligaments are : — Articular capsule. Interarticular. Radiate. The articular capsule (fig. 279) consists of short, strong, woolly fibres, com- pletely surrounding the joint, which are attached to the bones and intervertebral substances, a little beyond their articular margins. At its upper part it reaches through the intervertebral foramen toward the back of the bodies of the vertebrae, being strengthened here by fibres which at intervals connect the anterior with the posterior longitudinal ligaments. The lower fibres extend downward nearly to the demi-faoet (costal pit) of the rib below; behind, it is continuous with the neck ligament, and in front is overlaid by the radiate. The interarticular ligament (fig. 280) consists of short, strong fibres, closely interwoven with the outermost ring of the intervertebral disc, and attached to the transverse ridge separating the articular facets on the head of the rib. It completely divides the articulations into two parts, but does not brace the rib tightly to the spine, being loose enough to allow a moderate amount of rotation 242 THE ARTICULATIONS on its own axis. There is no interarticular ligament in the costo-vertebral joints of the first, tenth, eleventh, and twelfth ribs. The radiate (or stellate) ligament, a thickening of the anterior part of the capsule (figs. 280 and 281), is the most striking of all, and consists of bright, pearly-white fibres attached to the anterior surface, and upper and lower borders of the neck of the rib, a little way beyond the articular facet; from this they radiate upward, forward, and downward, so as to form a continuous layer of distinct and sharply defined fibres. The middle fibres run straight forward to be attached to the intervertebral disc; the upper ascend to the lower half of the lateral surface of the vertebra above, and the lower descend to the upper half of the vertebra below. The radiate ligament is overlapped on the vertebral bodies by the lateral (short) vertebral ligaments. In the case of the first, tenth, eleventh, and twelfth ribs, each of which articulates with one vertebra, the ligament is not quite so distinctly radiate, but even in these the ascending fibres reach the vertebra above that with which the rib articulates. Fig. 280. — Showing the Anterior Longitudinal Ligament, and the Connection op the Ribs with the Vertebra. The interarticular ligament The costo-transverse ligaments ^ — The radiate ligament The synovial membranes (fig. 281) consist of two closed sacs which do not communicate: one above, and the other below, the interarticular ligament. In the case of the first, tenth, eleventh, and twelfth articulations, there is but one synovial membrane, as these joints have no interarticular ligament. The arterial supply is from the intercostal arteries, the twigs piercing the radiate and capsular ligaments. The nerve -supply comes from the anterior primary branches of the intercostal nerves. These joints approach most nearly in their movements to the condylarthroses. The movements are ginglymoid in character, consisting of a slight degree of elevation and depression around an obliquely horizontal axis corresponding with the interarticular ligament; there is also a slight amount of forward and backward gliding; and a slight degree of screwing or rotatory movement is also possible . There is a considerable difference in the degree of mobility of the different ribs, for while the first rib is almost immobile except in a very deep inspiration, the mobility of the others increases from the second to the last; the two floating ribs being the most mobile of all. The head of the rib is the most fixed point of the costal arch, and upon it the whole arch rotates; the interarticular ligament allows only a very limited amount of flexion and extension (i. e., elevation and depression), and of gliding. Gliding is checked by the radiate ligament. In inspiration, the rib is elevated, and glides forward in its socket, too great elevation being checked not only by the ligaments, but also by the overhanging upper edge of the cavity itself. In expiration, the rib is depressed, and glides backward in its cavity. COSTO-TRANSVERSE ARTICULATIONS 243 (6) The Costo-transvehse Articulation Class. — Diarthrosis. Subdivision. — Arthrodia. This joint is formed by the tubercle of the rib articulating with the anterior part of the tip of the transverse process. The eleventh and twelfth ribs are devoid of these joints, for the tubercles of these ribs are absent, and the transverse processes of the eleventh and twelfth thoracic vertebrae are rudimentary. The ligaments of the union are :- Articular capsule. Neck ligament. Tubercular ligament. Costo-transverse ligaments. The articular capsule (figs. 279 and 281) forms a thin, loose, fibrous envelope to the synovial membrane. Its fibres are attached to the bones just beyond the articular margins, and are thickest below, where they are not strengthened by any other structure. It is connected medially with the neck ligament, above with the costo-transverse, and laterally with the tubercular (posterior costo- transverse) ligaments. The eleventh and twelfth ribs are unprovided with costo- transverse capsules. Fig. 281. — Horizontal Section through the Inteevertebeal Disc and Ribs. Fibrous ring of intervertebral fibro-cartilage Radiate ligament i Costo-transverse synovial sac Tubercular ligament The neck ligament [lig. colli costae] (middle costo-transverse, or interosseous ligament) (fig. 281), consists of short fibres passing between the back of the neck of the rib and front of the transverse process, with which the tubercle articulates. It extends from the capsule of the capitular joint to that of the costo-transverse. It is best seen on horizontal section through the bones. In the eleventh and twelfth ribs this ligament is rudimentary. The tubercular ligament (posterior costo-transverse) (fig. 281) is a short but thick, strong, and broad ligament, which extends laterally and upward from the extremity of the transverse process to the non-articular surface of the tubercle of the corresponding rib. The eleventh and twelfth ribs have no posterior ligament. The (superior) costo-transverse ligament (fig. 280) is a strong, broad band of fibres which ascends laterally from the crest on the upper border of the neck of the rib, to the lower border of the transverse process above. A few scattered posterior fibres pass upward and medially from the neck to the transverse process. The costo-transverse ligament is subdivided into a stronger anterior portion (anterior costo-transverse ligament) best seen from the front (fig. 280) , and a weaker posterior portion (posterior costo-transverse ligament). Its medial border bounds the foramen through which the posterior branches of the inter- costal vessels and nerves pass. To the lateral border is attached the thin aponeu- I 244 THE ARTICULATIONS rosis covering the external intercostals. Its anterior surface is in relation with the intercostal vessels and nerve; the posterior with the longissimus dor si. The first rib has no (superior) costo-transverse ligament. The synovial membrane (fig. 281) is a single sac. The arterial and nerve supplies come from the posterior branches of the intercostal arteries and nerves. The movements which take place at these joints are limited to a gliding of the tubercle of the rib upon the transverse process. The exact position of the facet on the transverse process varies slightly from above downward, being placed higher on the processes of the lower vertebrae. The plane of movement in most of the costo-transverse joints is inclined upward and backward in inspiration, and downward and forward in expiration. The point round which these move- ments occur is the head of the rib, so that the tubercle of the rib gUdes upon the transverse process in the circumference of a circle, the centre of which is at the capitular joint. 5. THE ARTICULATIONS AT THE FRONT OF THE THORAX These may be divided into four sets, viz.: — ■ (a) The intersternal joints, or the union of the several parts of the sternum with one another. (6) The costo -chondral joints, or the union of the ribs with their costal cartilages. (c) The chondro-stemal joints, or the junction of the costal cartilages with the sternum. (d) The interchondral joints, or the union of five costal cartilages (sixth, seventh, eighth, ninth, and tenth) with one another. (a) The Intersternal Joints The sternum being composed, in the adult, of three distinct pieces — the manubrium, body, and the xiphoid process — has two articulations, viz., the superior, which unites the manubrium with the body (gladiolus), and the inferior, which unites the body with the xiphoid. 1. The Superior Intersternal Articulation Class. — False Synchondrosis. The lower border of the manubrium and the upper border of the body of the sternum present oval-shaped, fiat surfaces, with their long axes transverse, and covered with a thin layer of hyaline cartilage. An interosseous fibro-cartilage is interposed between the bony surfaces: it corresponds exactly in shape and intimately adheres to them. At each lateral border this fibro-cartilage enters into the formation of the second chondro-sternal articulation (fig. 282). In consistence it varies, being in some oases uniform throughout, in others softer in the centre than at the circumference, and in others again an oval-shaped synovial cavity is found toward its anterior part. When such a cavity exists in the fibro-cartilage this joint has a remote resemblance to the diarthroses, and is classed, with the sacro-iliac joint and the symphy- sis pubis under similar conditions, as 'diarthro-amphiarthrosis.' The periosteum passes uninterruptedly over the joint from one segment of the sternum to the other, forming a kind of capsular ligament [membrana sterni]. This capsule is strength- ened, especially on its pos'erior aspect, by longitudinal ligamentous fibres as well as by the radiating and decussating fibres of the chondro-sternal ligaments. In some instances the fibro-cartilage is replaced by short bundles of fibrous tissue which unite the cartilage-coated articular bony sm'faces. 2. The Inferior Intersternal Articulation Class. — False Synchondrosis. The gladiolus is joined to the xiphoid cartilage by a thick investing mem- brane, by anterior and posterior longitudinal fibres, and by radiating fibres of the sixth and seventh chondro-sternal ligaments. The costo-xiphoid ligament also connects the xiphoid with the anterior surface of the sixth and seventh costal cartilages, and thus indirectly with the gladiolus; and some fine fibro-areolar tissue also connects the xiphoid with the back of the seventh costal cartilage. STERNO-COSTAL ARTICULATIONS 245 The junction of the xiphoid with the sternum is on a level somewhat posterior to the junc- tion of the seventh costal cartilage with the sternum. The union is a synchondrosis, each bone being covered by hyahne cartilage which is connected with the intervening fibro-cartilage plate. (b) The Costo-chondral Joints Class. — Synarthrosis. The extremity of the costal cartilage is received into a cup-shaped depression at the end of the rib, which is somewhat larger than the cartilage. The two are joined together by the continuity of the investing membranes, the periosteum of the rib being continuous with the perichondrium of the cartilage. (c) The Steeno-costal Articulations Class. — Diarthrosis. Subdivision — Ginglymus. These articulations are between the lateral borders of the sternum and the ends of the costal cartilages. The union of the first rib with the sternum is synchondrodial, and therefore forms an exception to the others. From the second to the seventh inclusive, the articulations have the following ligaments, which together form a complete capsule: — Radiate (anterior) sterno-costal. Superior sterno-costal. Posterior sterno-costal. Inferior sterno-costal. The radiate (anterior) sterno-costal ligament (fig. 282) is a triangular band composed of strong fibres which cover the medial half-inch of the front of the costal cartilage, and radiate upward and downward upon the front of the sternum. Some of the fibres decussate across the middle line with fibres of the opposite ligament. At its upper and lower borders it is in contact with the superior and inferior ligaments respectively. The posterior sterno-costal ligament consists of little more than a thickening of the fibrous envelopes of the bone and cartilage, the joint being completed behind by a continuity of perichondrium with periostemn. The superior and inferior ligaments are strong, well-marked bands, which pass from the upper and lower borders respectively of the costal cartilage to the lateral edges of the sternum. The sixth and seventh cartilages are so close that the superior ligament of the seventh is blended ^^^th the inferior of the sixth rib. Deeper than the fibres of these ligaments are short fibres passing from the margins of the sternal facets to the edges of the facets on the cartilages; they are most distinct in the front and lower part of the joint, and may encroach so much upon the synovial cavity as to reduce it to a very small size, or almost obliterate it. This occurs mostly in the case of the sixth and seventh joints, especially the latter. The interarticular ligament (fig. 282) is by no means constant, but is usually present in the second joint on one, if not on both sides of the same subject. It consists of a strong transverse bundle of fibres passing from the ridge on the facet on the cartilage to the fibrous substance between the manubrium and body; sometimes the upper part of the synovial cavity is partially or entirely obliterated by short, fine, ligamentous fibres. The costo-xiphoid ligament (fig. 282) is a strong flat band of fibres passing obliquely upward and laterally from the front surface of the xiphoid cartilage to the anterior surface of the sternal end of the seventh costal cartilage, and most frequently to that of the sixth also. Synovial membranes. — -The union of the first cartilage with the sternum being synchondro- dial, it has no synovial membrane; the second has usually two, separated by the interarticular Ugament. The rest usually have one synovial membrane, which may occasionally be subdivided into two (fig. 2S2). The arterial supply is derived from perforating branches of the internal mammary; and the nerves come from the anterior branches of the interoostals. Movements. — -Excepting the first, the chondro-sternal joints are ginglymoid, but the motion of which they are capable is verj' limited. It consists of a hinge-like action in two direc- tions: first, there is a slight amount of elevation and depression which takes place round a transverse axis, and, secondly, there is some forward and backward movement round an ob- liquely vertical axis. In inspiration the cartilage is elevated, the lowest part of its articular facet is pressed into the sternal socket, and the sternum is thrust forward so that the upper i 246 THE ARTICULATIONS aad front edges of the articular surfaces separate a little; in expiration the reverse movement takes place. Thus the two extremities of the costal arches move in their respective sockets in opposite directions. This difference results necessarily from the fact that the costal arch moves upon the verte- bral column, and, having been elevated, it in its turn raises the sternum by pushing at upward and forward. The costo-.xiphoid ligament tends to prevent the xiphoid cartilage from being drawn back- ward by the action of the diaphragm. Fig. 282. — The Articulation at the Front of the Thorax. (Left side, showing ligaments, right side, the synovial cavities.) For clavicle and first rib The plate of fibre- - -,^.3 cartilage betW' ^^" ' '^ manubriuDi i body ^^Radiate sterno- costal ligameat (d) The Interchondral Articulations Class. — Diarthrosis. Subdivision. — Arthrodia. A little in front of the point where the costal cartilages bend upward toward the median line the sixth is united with the seventh, the seventh with the eighth, the eighth with the ninth, and the ninth with the tenth. At this point each of the cartilages from the sixth to the ninth inclusive is deeper than elsewhere, owing to the projection downward from its lower edge of a broad blunt process, which comes into contact with the cartilage next below. Each of the apposed surfaces is smooth. MOVEMENTS OF THE THORAX 247 and they are connected at their margins by ligamentous tissue, which forms a complete capsule for the articulation, and is hned by a synovial membrane (fig. 282). The largest of these cavi- ties is between the seventh and eighth; those between the eighth and ninth, and ninth and tenth, are smaller, and are not free to play upon each other in the whole of their extent, being held together by ligamentous tissue at theii' anterior margins. Sometimes this fibrous tissue com- pletely obliterates the synovial cavity. The arteries are derived from the musoulo-phrenio, and the nerves from the intercostals. Movements. — -By means of the costal cartilages and interchondral joints, strength with elasticity is given to the wall of the trunk at a part where the cartilages are the only firm struc- tures in its composition; while a slight gliding movement is permitted between the costal carti- lages themselves, which takes place round an axis corresponding to the long axis of the cartilages. By this means, the outward projection of the lower part of the thoracic wall is increased by deep inspiration. MOVEMENTS OF THE THORAX AS A WHOLE Before describing these movements as a 248 THE ARTICULATIONS muscles also come into play: The pectoralis minor, the muscles which extend the head and the cervical part of the vertebral column, the sterno-mastoid and the supra- and infra-hyoid mus- cles, the lower fibres of the pectoralis major, some of the lower fibres of the serratus anterior, and, when the clavicle is fixed, the subclavius. Expiration is produced by the elasticity of the lungs and the weight of the thorax, aided by the elastic reaction and contraction of the external and internal oblique muscles, the recti and pyramidales, the transversus abdominis, and the levatores ani and coccygei. In forcible expiration all muscles which depress the ribs and reduce the dimensions of the abdomen are thrown into action. The internal interoostals probably tend to contract the thorax, excepting, the parts between the costal cartilages, which tend to expand the thorax. THE ARTICULATIONS OF THE UPPER EXTREMITY The articulations of the upper extremity are the following: — 1. The stemo-costo -clavicular. 2. The scapulo-clavicular union. 3. The shoulder-joint. 4. The elbow-joint. 5. The radio-ulnar union. 6. The radio-carpal or wrist-joint. 7. The carpal joints. 8. The carpo-metacarpal joints. 9. The intermetacarpal joints. 10. The metacarpo-phalangeal joints. 11. The interphalangeal joints. 1. THE STERNO-COSTO-CLAVICULAR ARTICULATION Class. — Diarthrosis. Subdivision. — Condylarthrosis. At this joint the large medial end of the clavicle is united to the superior angle of the manubrium sterni, the first costal cartilage also assisting to support the clavicle. It is the only joint between the upper extremity and the trunk, and takes part in all the movements of the upper limb. Looking at the bones, one would say that they were in no waj^ adapted to articulate with one another, and yet they assist in constructing a joint of security, strength, and importance. The bones are nowhere in actual contact, being completely separated by an articular disc. The interval between the joints of the two sides varies from one inch to an inch and a half (2.5-4 cm.). The ligaments of this joint are: — (1) Articular capsule. (3) Articular disc. (2) Interclavicular. (4) Costo-clavicular. The articular capsule (fig. 284) consists of fibres, having varying directions and being of various strength and thickness, which completely surround the articulation, and are firmly connected with the edges of the interarticular fibro- cartilage. The fibres at the back of the joint, sometimes styled the posterior stemo-clavicular liga- ment, are stronger than those in front or below, and consist of two sets: a superficial, passing upward and laterally from the manubrium sterni, to the projecting posterior edge of the end of the clavicle, a few being prolonged onward upon the posterior surface of the bone. A deeper set of fibres, especiallj^ thick and numerous below the clavicle, connect the interarticular car- tilage with the clavicle and with the sternum, but do not extend from one bone to the other. The fibres in front, the anterior sterno -clavicular ligament, are well marked, but more lax and less tough than the posterior, and are overlaid by the tendinous sternal origin of the sterno- mastoid, the fibres of which run parallel to those of the ligament. They extend obliquely up- ward and laterally from the margin of the sternal facet to the anterior surface of the clavicle some little distance from the articular margin. The fibres which cover in the joint below are short, woolly, and consist more of fibro-areolar tissue than true fibrous tissue; they extend from the upper border of the first costal cartilage to the lower border of the clavicle just lateral to the articular margin, and fill up the gap between it and the costo-clavicular ligament. The superior portion consists of short tough fibres passing from the sternum to the articular disc; and of others welding the fibro-cartilage to the upper edge of the clavicle, onlj' a few of them passing from the clavicle direct to the sternum. The interclavicular ligament (fig. 284) is a strong, concave band, materially strengthening the superior portion of the capsule. It is nearly a quarter of an STERNO-COSTO CLAVICULAR JOINT 249 inch (6 mm.) deep with the concavity upward, its upper border tapering to a narrow, almost sharp edge. It is connected with the posterior superior angle of the sternal extremity of each clavicle, and with the fibres which weld the inter- articular cartilage to the clavicle; and then passes across from clavicle to clavicle along the posterior aspect of the upper border of the manubrium sterni. The lowest fibres are attached to the sternum, and join the posterior fibres of the capsule of each joint. In the middle line, between the ligament and the sternum, there is an aperture for the passage of a small artery and vein. In addition to the interclavicular ligament Mr. Carwardine ("Journal of Anatomy and Physiology," vol. 7, new series, p. 232) has described a special band of the upper portion of the sterno-clavioular capsule which he proposes to name the 'suprasternal hgament.' It descends from the upper border of the sternal end of the clavicle to the upper border of the sternum, and is of special importance as it encloses the suprasternal bones, when these rudiments are present. The costo -clavicular or rhomboid ligament (fig. 284) is a strong dense band, composed of fine fibres massed together into a membranous structure. It extends from the upper (medial) border of the first costal cartilage (and rib), Fig. 284.^Posteeior View op the Stbrno-costo-claviculak Joint. upward, backward, and distinctly laterally to the costal tuberosity on the under surface of the medial extremity of the clavicle, to which it is attached just lateral to the lower part of the capsule. Frequently some of the lateral fibres pass up- ward and medially behind the rest, and give the appearance of decussating. It is from half to three-quarters of an inch (1.5-2 cm.) broad. The articular disc (fig. 285) is a flattened disc of nearly the same size and outline as the medial articular end of the clavicle, which it fairly accurately fits. It is attached above to the upper border of the posterior edge of the clavicle ; and below to the cartilage of the first rib at its union with the sternum, where it assists in forming the socket for the clavicle. At its circumference it is connected with the articular capsule, and this connection is very strong behind, and still stronger above, where it is blended with the interclavicular ligament. It is usually thinnest below, where it is connected with the costal cartilage. It varies in thickness in different parts, sometimes being thinner in the centre than at the circumference sometimes the reverse, and is occasionally perforated in the centre. It divides the joint into two compartments. There are two synovial membranes (fig. 285) ; a lateral one, which is reflected from the clavicle and capsule over the lateral aspect of the disc and is looser than the medial one; the medial is reflected from the sternum over the medial side of the articular disc, costal cartilage, and capsule. Occasionally a communi- cation takes place between them. The arterial supply is derived from branches — (1) from the internal mammary; (2) from the superior thoracic branch of the axillary; (3) twigs of a muscular branch often arising from the subclavian artery pass over the interclavicular notch; (4) twigs of the transverse scapular (suprascapular) artery. The nerve-supply is derived from the nerve to the subclavius and sternal descending branch of the cervical plexus. 250 THE ARTICULATIONS Relations. — In front of the joint is the sternal head of the sterno-mastoid. Behind it are the sterno-hyoid and sterno-thyreoid muscles. Still further back, on the right side, are the innominate and internal mammary arteries, and, on the left side, the left common carotid, the left subclavian, and the internal mammary arteries. Above and behind, between the sterno- mastoid and s terno-hyoid muscles, the anterior jugular vein passes back and laterally toward the posterior triangle. The movements permitted at this joint are various though limited, owing to the capsular ligament being moderately tense in every position of the clavicle. Motion takes place in nearly every direction — viz., upward, downward, forward, backward, and in a circumductory manner. The upward and downward motions occur between the clavicle and the articular disc; during elevation of the arm the upper edge of the clavicle with its attached articular disc is pressed into the sternal socket, and the lower edge gUdes away from the disc; during depression of the limb, the lower edge of the clavicle presses on to the disc, while the rest of the articular surface of the clavicle inclines laterally, bringing with it to a slight degree the upper edge of the articular disc. These movements occur on an antero-posterior axis drawn through the outer compartment of the joint. The forward and backward motions take place between the articular disc and sternum, the clavicle with the disc gUding backward upon the sternum when the shoulder is brought forward, and forward when the shoulder is forced backward; these movements odcur round an axis drawn nearly vertically through the sternal socket. FiQ. 285. — Anterior View of Stbrno-costo-clavicular Joint, with Section SHOWING Cavities opened on the Right Side. Interclavicular ligament Joint between ster- num and second cos- tal cartilage The articular disc serves materially to bind the bones together, and to prevent the media and upward displacements of the clavicle. It also forms an elastic lauffer which tends to break shocks. The capsule, by being moderately tight, tends to limit movements in all directions, while the interclavicular ligament is a safeguard against upward displacement during depression of the arm. Tlie costo-clavicular ligament prevents dislocation upward during elevation of the arm, and resists displacements backward. Muscles which move the clavicle at the sterno-clavicular joint. — Elevators. — Trapezius, clavicular part of sterno-mastoid, levator scapulae, omo-hyoid, rhomboids. Depressors. — Subclavius, pectoraUs minor, lower fibres of trapezius and serratus anterior (magnus). Depression is aided by the weight of the upper extremity. Protractors. — PectoraUs major and minor. Serratus anterior (magnus). -Latissimus dorsi, trapezius. 2. THE SCAPULO-CLAVICULAR UNION The scapula is connected with the clavicle by a synovial joint with its liga- ments at the acromio-clavicular articulation; and also by a set of ligaments pass- ing between the coracoid process and the clavicle. So that we have to consider — (a) The acromio-clavicular articulation. lb) The cor aco -clavicular ligaments. (c) The proper scapular ligaments are also best described in this section — viz., the coraco-acromial and transverse. COROCO-CLAVICULAR UNION 251 (a) The Acromio-claviculae Joint Class. — Diarthrosis. Subdivision. — Arthrodia. The acromio-clavicular joint is surrounded by an articular capsule and fre- quently contains an articular disc. The articular capsule (figs. 287 and 290) completely surrounds the articular margins, and is composed of strong, coarse fibres arranged in parallel fasciculi, of fairly uniform thickness, which are attached to the borders as well as the surfaces of the bones. It is somewhat lax in all positions of the joint, so that the clavicle is not tightly braced to the acromion. The fibres extend three-quarters of an inch (2 cm.) along the clavicle posteriorly, but only a quarter of an inch (6 mm.) anteriorly. Superiorly, they are attached to an oblique line joining these two points, while inferiorly they reach to the ridge for the trapezoid liga- ment with which they blend. At the acromion they extend half way across the upper and lower surfaces, but at the anterior and posterior limits of the joint they are attached close to the articular facet. The anterior fibres become blended with the insertion of the eoraco-acromial ligament. The fibres are strengthened above by the aponeuroses of the trapezius and deltoid muscles; and all run from the acromion to the clavicle medially and backward. The articular disc is occasionally present, but is usually imperfect, only oc- cupying the upper part of the joint; it may completely divide the joint into two cavities, or be perforated in the centre. It is usually thicker at the edge than in the centre, and some of the fibres of the articular capsule are blended with its edges. The synovial membrane lining the joint is occasionally either partially or entirely divided into two by the articular disc. Relations. — Superiorly skin and fascia and the tendinous intersection between the deltoid and the trapezius. Inferiorly, the eoraco-acromial ligament and supraspinatus. Anteriorly, part of the origin of the deltoid. Posteriorly, part of the insertion of the trapezius. Movements. — A certain amount of gliding movement occurs at this joint, but the most important movement is a rotation of the scapula whereby the glenoid cavity is turned forward and upward, or downward. As these movements occur the inferior angle of the scapula moves forward as the glenoid cavity turns upward and the superior angle recedes. The forward movement of the inferior angle is produced mainly by the inferior fibres of the serratus anterior (magnus), aided by the inferior fibres of the trapezius, and it is by this movement that the arm is raised above the level of the shoulder forward. The reverse movement is produced mainly by the rhomboideus major aided by the latissimus dorsi. (6) The Coraco-clavicular Union The coraco-clavicular ligament (figs. 286, 287, and 290) consists of two parts, the conoid and the trapezoid ligaments. The conoid ligament is the medial and posterior portion, and passes upward and laterally from the coracoid process to the clavicle. It is a very strong and coarsely fasciculated band of triangular shape, the apex being fixed to the medial and posterior edge of the root of the coracoid process just in front of the scapular notch, some fibres joining the transverse ligament. Its base is at the clavicle, where it widens out, to be attached to the posterior edge of the inferior surface, as well as to the cora- coid tubercle. It is easily separated from the trapezoid, without being absolutely distinct. A small bursa often exists between it and the coracoid process; medially, some of the fibres of the subclavius muscle are often attached to it. The trapezoid ligament is the anterior and lateral portion of the coraco- clavicular ligament. It is a strong, flat, quadrilateral plane of closely woven fibres, the surfaces of which look upward and medially toward the clavicle, and downward and laterally over the upper surface of the coracoid process. At the coracoid it is attached for about an inch (2.5 cm.) to a rough ridge which runs forward from the angle, along the anterior border of the process. At the clavicle it is attached to the oblique ridge which runs laterally and forward from the coracoid tubercle, reaching as far as, and blending with the inferior part of the acromio-clavicular ligament. Its anterior edge is free, and overlies the eoraco-acromial Ugament; the posterior edge is shorter than the anterior, and is in contact with the posterior and lateral portion of the conoid hgament. The arterial supply is derived from the transverse scapular (suprascapular), acromial branches of the thoraco-acromial, and the anterior circumflex. The nerve-supply is derived from the suprascapular and axillary (circumflex) nerves. 252 THE ARTICULATIONS Movements. — In the movements of the shoulder girdle, the scapula moves upon the lateral end of the clavicle, and the clavicle, in turn, carried by the uniting Ugaments, moves upon the sternum; so that the entire scapula moves in the arc of a circle whose centre is at the sterno- clavicular joint, and whose radius is the clavicle. The scapula, in moving upon the clavicle, also moves upon the thorax forward and backward, upward and downward, and also in a rota^ tory direction upon an axis drawn at right angles to the centre of the bone. Throughout these movements the inferior angle and base of the scapula are kept in contact with the ribs by the Fig. 286.— Anterior View op Shoulder, showing also Coraco-clavicular and cohaco-acromial ligaments. Conoid ligament Superior transverse scapular ligament t Coraco-acromial ligament > Short head of biceps 'Subscapular tendon Capsule of shoulde Long tendon of biceps latissimus dorsi, which straps down the former, and the rhomboids and serratus anterior {magnus), which brace down the latter. The glenoid cavity could not have preserved its obUquely forward direction had there been no acromio-clavicular joint, but would have shifted round a vertical axis, and thus the shoulder would have pointed medialward when the scapula was advanced, and lateralward when it was drawn backward. By means of the acromio-clavicular joint, the scapula can be forcibly advanced upon the thorax, the glenoid cavity all the time keeping its face duly forward. Thus the muscles of the shoulder and forearm can be with advantage combined, as, for example, in giving a direct blow. The acromio-clavicular joint also permits the lower angle of the scapula to be retained in contact with the chest wall during the rising and faUing of the shoulder, the scapula turning in a hinge-like manner round the horizontal axis of the joint. There are no actions in which the scapula moves on a fixed clavicle, or the clavicle ona fixed scapula; the two bones, bound together by their connecting ligament, must move in unison. (c) The Phoper Scapular Ligaments There are three proper ligaments of the scapula, which pass portions of the bone, viz. — Coraco-acromial. Superior transverse. Inferior transverse. The coraco-acromial ligament (figs. 286 and 290) is a flat, triangular band with a broad base, attached to the lateral border of the coracoid process, and a blunt apex which is fixed to the tip of the acromion. It is made up of two broad marginal bands, and a smaller and thinner intervening portion. The anterior band, which arises from the anterior portion of the coracoid process, is the stronger, and some of its marginal fibres can often be traced into the short head of the biceps, which can then make tense this edge of the ligament. The pos- terior band, coming from the posterior part of the coracoid process, is also strong. between different THE SHOULDER-JOINT 253 The intermediate part, of variable extent, is thin and membranous, containing but few ligamentous fibres; it is often incomplete near the coracoid process, leaving a small gap (fig. 286). The superior surface of the ligament looks upward and a little forward, and is covered by the deltoid muscle; the inferior looks downward and a little backward, and is separated from the capsule of the shoulder-joint by a bursa and the tendons of the supraspinatus and sub- scapularis muscles. At the coracoid process it overlies the coraco-humeral ligament. It is barely one-third of an inch (8 mm.) above the capsule of the shoulder, and in the undissected state there is scarcely a quarter of an inch (6 mm.) interval. The anterior band projects over the centre of the head of the humerus, and is continued into a tough fascia under the deltoid; the posterior band is continuous with the fascia over the supraspinatus muscle. It binds the Fig. 287. — Posterior View of the Shoulder-joint, showing also the Acromio-ola- vicuLAR Joint and the Special Ligaments or the Scapula. Superior transverse ligament Conoid ligament Acromio-clavicular ligament Tendon of infra spinatus and teres minor Inferior transverse ligament Capsule of shoulder two processes firmly together, and so strengthens each; it holds the deltoid off the capsule of the shoulder, and protects the joint from slight injuries directed downward and backward against it. The superior transverse (coracoid, or suprascapular) ligament (figs. 286, 287, and 288) is a small triangular band of fibrous tissue, the surfaces of which look forward and backward; and its edges, which are thin and sharp, are turned upward and downward. It continues the superior border of the scapula, bridging over the scapular notch. It is broader medially, where it springs from the upper border of the scapula on its dorsal surface; and narrow laterally, where it is attached to the base of the coracoid process; some of its fibres are inserted under the edge of the trapezoid ligament, and others pass upward with the conoid to reach the clavicle. The transverse scapular {suprascapular) artery passes over it, and the suprascapular nerve beneath it. Medially, some fibres of the omo-hyoid muscle arise from it. The inferior transverse (spino-glenoid) ligament (fig. 287) reaches from the lateral border of the spine of the scapula to the margin of the glenoid cavity, and so forms a foramen under which the transverse scapular (suprascapular) vessels and suprascapular nerve gain the infraspinous fossa. It is usually a weak membranous structure with but few ligamentous fibres. 3. THE SHOULDER-JOINT Class. — Diarthrosis. Subdivision. — Enarthrodia. The shoulder [articulatio humeri] is one of the most perfect and most movable 254 THE ARTICULATIONS of joints, the large upper end of the humerus playing upon the shallow glenoid cavity. Like the hip, it is a ball-and-socket joint. It is retained in position much less by ligaments than by muscles, and, owing to the looseness of its cap- sule, as well as to all the other conditions of its construction and position, it is exceedingly liable to be displaced; on the other hand, it is sheltered from violence by the two projecting processes — the acromion and coracoid. The ligaments of the shoulder-joint are: — - Articular capsule. Gleno-humeral. Coraco-humeral. Glenoid: The articular capsule (figs. 286, 287, and 288) is a loose sac, insufficient in itself to maintain the bones in contact. It consists of fairly distinct but not coarse fibres, closely woven together, and directed, some straight, others ob- liquely, between the two bones, a few circular ones being interwoven amongst them. At the scapula, it is fixed on the dorsal aspect to the prominent rough Fig. 288. — Vertical Section through the Shoulder-joint to show the Gleno-humeral Ligament. (The joint is opened from behind.) Supraspinatus muscle Subacromial bursa Tendon of biceps with gleno-humeral liga- Articular capsule Superior trans- verse ligament Glenoid ligament (lip) Articular capsule surface around the margin of the glenoid cavity, reaching as far as the neck of the bone. Superiorly, it is attached to the root of the coracoid process; an- teriorly, to the ventral surface, at a variable distance from the articular margin, often reaching half an inch (12 mm.) upon the neck of the bone, and thus allow- ing the formation of a pouch; it may not, however, extend for more than a quarter of an inch (6 mm.) beyond the articular margin; inferiorly, it blends with the origin of the long head of the triceps. At the humerus, the superior half is fixed to the anatomical neck, sending a prolongation downward between the two tuberosities which attenuates as it descends, and covers the transverse hmneral ligament. The lower half of the capsule descends upon the hmnerus further from the articular margin, some of the deeper fibres being reflected upward so as to be attached close to the articular edge, thus forming a kind of fibrous in- vestment for the neck of the humerus. This ligament is more uniform in thickness than that of the hip. Gleno-humeral bands of the capsule (figs. 288 and 289) . — There are three accessory bands, known as the superior, middle and inferior gleno-humeral bands, which project toward the interior of the joint from the fore part of the capsule and are consequently best seen when the joint is opened from behind. The middle band reaches from the anterior margin of the glenoid cavity along the lower border of the subscapularis tendon to the lower border of the lesser tuberosity, and the inferior band from the inferior part of the glenoid cavity to the inferior part of the neck of the humerus. THE SHOULDER-JOINT 255 The superior band, known also as the gleno -humeral ligament, runs from the edge of the glenoid cavity at the root of the coracoid process, just medial to the origin of the long tendon of the biceps, and, passing laterally and downward at an acute angle to the tendon, for which it forms a slight groove or sulcus, is fixed to a depression, the fovea capitis humeri, above the lesser tuberosity of the humerus. It is a thin, ribbon-hke band, of which the superior surface is attached to the capsule, while the inferior is free and turned toward the joint. In the foetus it is often, and in the adult occasionally, quite free from the capsule, and may be as thick as the long tendon of the biceps (fig. 289). The tendons of the supra- and infraspinatus, teres minor, and subscapularis muscles strengthen and support the capsule, especially near their points of insertion, and can be with difficulty dissected off from it. The long head of the triceps supports and strengthens the capsule below. The capsule also receives an upward sUp from the pectoralis major. The supraspinatus often sends a shp into the capsule from its upper edge (fig. 288). The coraco-humeral ligament (fig. 290) is a strong broad band, which is attached above to the lateral edge of the root and horizontal limb of the coracoid process nearly as far as the tip. From this origin it is directed backward along the line of the biceps tendon to blend with the capsule, and is inserted into the greater tuberosity of the humerus. Seen from the back, it looks like an uninterrupted continuation of the capsule, while from the front it looks like a fan-shaped prolongation from it overlying the rest of the ligament. At its origin there is sometimes a bursa between it and the capsule. The glenoid ligament or lip [labrum glenoidale] (figs. 288 and 292) is a narrow rim of dense fibro-cartilage, which surrounds the edge of the glenoid socket and deepens it. It is about a quarter of an inch (6 mm.) wide above and below, but less at its sides. Its peripheral edge is inseparably welded, near the bone, with Fig. 289. — Fcbtal Shoulder-joint, showing the Glbno-humeeal Ligament, and also the Short Head op the Biceps, being continuous wtith the Coraco-acromial Ligament. Short tendon of biceps running -Long tendon of biceps nto'anterior ba'nd'of coraco- | " iiiBS//^''\i\\\\)/ H/'^ — Gleno-humeral ligament acromial Ugament I , |,«!#^^ ILlUW^Iil^ Capsule of shoulder, turned back the articular capsule. Its structure is almost entirely fibrous, with but few cartilage cells intermixed. At the upper part of the fossa the biceps tendon is prolonged into the glenoid ligament, the tendon usually dividing and sending fibres right and left into the ligament, which may wind round nearly the whole circumference of the socket. It may, however, send fibres into one side only, usually into the lateral. The articular cartilage covering the glenoid fossa is thicker at the circumfer- ence than in the centre, thus tending to deepen the cavity. It is usually thickest at the lower part of the fossa; over the head of the humerus the cartilage is thickest at and below the centre. The synovial membrane lines the glenoid ligament, and is then refiected over the capsule as far as its attachment to the humerus, from which it ascends as far as the edge of the articular cartilage. The tendon of the biceps receives a long tubular sheath, which is continuous with the synovial membrane, both at its attached extremity and at the bicipital groove, but is free in the rest of its extent. The synovial cavity almost always communicates with the bursa under the subscapularis, and sometimes with one under the infraspinatus muscle. It also sends a pouch-like prolongation beneath the coracoid process when the fibrous capsule is attached wide of the margin of the glenoid fossa. A few fringes are seen near the edge of the glenoid cavity, and there is often one which runs down the medial edge of the biceps tendon, extending slightly below it and making a slight groove for the tendon to lie in. 256 THE ARTICULATIONS The transverse humeral Ugament (fig. 290) is so closely connected with the capsule of the shoulder that, although it is a proper hgament of the humerus, it may well be described here. It is a strong band of fibrous tissue, which extends Fig. 290. — Lateral View of the Shoulder-joint, showing the Coraco-humbral and Transverse Humeral Ligaments. Capsule of the acromio-cla- vicular joint Coraco-acromial ligament Coraco-humeral ligament -Transverse humeral ligament Tendon of biceps Fig. 291. — The Upper Extremity or the Humerus, Anterior View, to Show the Rela- tion OF THE Articular Capsule of the Shoulder-joint (in red) to the Epiphysial Line. between the two tuberosities, roofing in the intertubercular (bicipital) groove. It is covered by a thin expansion of the capsule. It is limited to the portion of the bone above the line of the epiphysis. THE SHOULDER-JOINT 257 Relations. — -The following muscles are in contact with the capsule of the shoulder-joint. In front, the subscapularis; above, the supraspinatus; above and behind, the infraspinatus; behind, the teres minor; below, the long head of the triceps and the teres major. In the interval between the subscapularis and the supraspinatus the subacromial bursa is close to the capsule and occasionally its cavity communicates with the cavity of the joint. The axillary (circumflex) nerve and posterior circumfle.x artery pass beneath the capsule in the intei'val between the long head of the triceps, the humerus, and the teres major. When the arm is abducted, the long head of the triceps and the teres major are drawn into closer rela- , tion with the capsule and help to prevent dislocation of the humerus. The axillary vessels, the great nerves of the axilla, the short head of the biceps, and the coraco-brachialis are separated from the joint by the subscapularis, whilst the deltoid forms a kind of cap, which extends from the front to the back over the more immediate relations. The arterial supply is derived from the transverse scapular (suprascapular), anterior and posterior circumflex, subscapular, circumflex scapular (dorsalis scapulae), and a branch from the second portion of the axiUary artery. The nerve-supply is derived from the suprascapular, by branches in both fossse; and from the axillary (circumflex) and subscapular nerves. The movements of the shoulder-joint consist of flexion, extension, adduction, abduction, rotation and circumduction. Flexion is the swinging forward, extension the swinging backward, of the humerus; abduc- tion is the raising of the arm from, and adduction depression of the arm to, the side. In flexion and extension the head of the humerus moves upon the centre of the glenoid fossa round an Fig. 292. — Biceps Tendon, Bifukcating and Blending on each Side with the Glenoid Ligament. Tendon of biceps- Tendon of biceps blended with glenoid, ligament oblique line corresponding to the axis of the head and neck of the humerus, flexion being more free than extension, and in extreme flexion the scapula follows the head of the humerus, so as to keep the articular surfaces in apposition. In extension the scapula moves much less, if at all. In abduction and adduction the scapula is fixed, and the humerus roUs up and down upon the glenoid fossa; during abduction the head descends until it projects beyond the lower edge of the glenoid cavity, and the greater tuberosity impinges against the arch of the acromion; during adduction, the head of the humerus ascends in its socket, the arm at length reaches the side, and the capsule is completely relaxed. In circumduction, the humerus, by passing quickly through these movements, describes a cone, whose apex is at the shoulder-joint, and the base at the distal extremity of the bone or hmb. Rotation takes place round a vertical axis drawn through the extremities of the humerus from the centre of the head to the inner condyle; in rotation forward (that is, medialward) the head of the bone rolls back in the socket as the great tuberosity and shaft are turned forward; in rotation backward (that is, lateral ward) the head of the bone glides forward, and the tuber- osity and shaft of the humerus are turned backward, i. e., lateralward. Great freedom of movement is permitted at the shoulder, and this is increased by the mobility of the scapula. Restraint is scarcely exercised at all upon the movements of the shoulder by the ligaments, but chiefly by the muscles of the joint. In abduction, the lower part of the capsule is somewhat, and in extreme abduction con- siderably, tightened; and in rotation medialward and lateralward, the upper part of the capsule is made tense, as is also, in the latter movement, the coraco-humeral ligament. The movements of abduction and extension have a most decided and definite resistance offered to them other than by muscles and ligaments, for the greater tuberosity of the humerus, by striking against the acromion process and coraco-acromial ligament, stops short any further advance of the bone in these directions, and thus abduction ceases altogether as soon as the arm 258 THE ARTICULATIONS is raised to a right angle with the trunk, and extension shortly after the humerus passes the Hne of the trunk. Further elevation of the arm beyond the right angle, in the abducted or extended position, is effected by the rotation of the scapula round its own axis by the action of the trapezius and serratus anterior muscles upon the sterno-clavioular and acromio-clavicular joints respectively. The acromion and coracoid process, together with the coraco-acromial ligament, form an arch, which is separated by a bursa and the tendon of the supraspinatus from the capsule of the shoulder. Beneath this arch the movements of the joint take place, and against it the head and tuberosities are pressed when the weight of the trunk is supported by the arms; the greater tuberosity and the upper part of the shaft impinge upon it when abduction and extension are carried to their fullest extent. No description of the shoulder-joint would be complete without a short notice of the peculiar relation which the biceps tendon bears to the joint. It passes over the head of the humerus a little to the medial side of its summit, and lies free within the capsule, surrounded only by a tubular process of synovial membrane. It is fiat, with the surfaces looking upward and down- ward, until it reaches the intertubercular (bicipital) groove, when it assumes a rounded form. It strengthens the articulation along the same course as the coraco-humeral hgament, and tends to prevent the head of the humerus from being pulled upward too'.forcibly against the inferior surface of the acromion. It also serves the purpose of a ligament by steadying the head of the humerus in various movements of the arm and forearm, and to this end is let into a groove at the upper end of the bone, from which it cannot escape on account of the abutting tuberosities and the strong transverse humeral ligament which binds it down. Further, it acts Uke the four shoulder muscles which pass over the capsule, to keep the head of the humerus against the glen- oid socket; and, moreover, it resists the tendency of the pecloralis major and latissimus dorsi muscles, in certain actions when the arm is away from the side of the body, to pull the head of the humerus below the lower edge of the cavity. Muscles which act upon the shoulder-joint.- — Flexors or protractors. — Deltoid (anterior fibres), peotoralis major (clavicular fibres), coraco-brachiahs, biceps (short head),Eubscapularis (upper fibres). Extensors or retractors. — ^Latissimus dorsi, deltoid (posterior fibres), teres major, teres minor, infraspinatus (lower fibres). [Abductors. — Deltoid, supraspinatus, biceps (longhead). Adductors. — Pectorahs major, latissimus dorsi, subscapularis, infraspinatus, teres major, teres minor, coraco-brachiahs, biceps (short head), triceps (lower head). Medial rotators. — Pectoralis major, latissimus dorsi, teres major, subscapularis, deltoid (anterior fibres). Lateral rotators. — Deltoid (posterior fibres), infraspinatus, teres minor. Circumductors. — The above groups acting consecutively. 4. THE ELBOW-JOINT Class. — Diarthrosis. Subdivision. — Ginglymus. The elbow [articulatio cubiti] is a complete hinge, and, unlike the knee, depends for its security and strength upon the configuration of its bones rather than on the number, strength, or arrangement of its ligaments. The bones composing it are the lower end of the humerus above, and the upper ends of the radius and ulna below; the articular surface of the humerus being received partly within the semilunar notch (great sigmoid cavity) of the ulna, and partly upon the cup-shaped area (fovea) of the radial head. The ligaments form one large and capacious capsule [capsula articularis], which, by blending with the annular ligament, and then passing on to be attached to the neck of the radius, embraces the elbow and the superior radio-ulnar joints, uniting them into one. Laterally, it is considerably strengthened by superadded fibres arising from the epicondyles of the humerus and inseparably connected with the capsule. For convenience of description it will be spoken of as consisting of four portions:- — Anterior. Medial. Posterior. Lateral. The anterior portion (fig. 293) is attached to the front of the humerus above the articular surface and coronoid fossa, in an inverted V-shaped manner, to two very faintly marked ridges which start from the front of the medial and lateral epicondyles, and meet a variable distance above the coronoid fossa. Below, it is fixed, just beyond the articular margin, to the front of the coronoid process and it is intimately blended with the front of the annular ligament, a few fibres passing on to the neck of the radius. It varies in strength and thickness, being sometimes so thin as barely to cover the syriovial membrane; at others, thick and strong, and formed of coarse decussating fibres, the majority of which descend from the medial side laterally to the radius. THE ELBOW-JOINT 259 The posterior portion (fig. 294), thin and membranous, is attached superiorly to the humerus, in much the same inverted V-shaped way as the anterior; ascend- ing from the medial epicondyle, along the medial side of the olecranon fossa nearly to the top; then, crossing the bottom of the fossa, it descends on the lateral side, skirting the lateral margin of the trochlear surface, and turns laterally along the posterior edge of the capitulum. Inferiorly, it is attached to a slight groove Fig. 293. — Medial View of the Elbow-joint. Anterior ligament Ulnar collateral- ligament Annular ligament — Tendon ot biceps Oblique ligament Upper edge of in- terosseous mem- brane along the superior and lateral surfaces of the olecranon, and the rough surface of the ulna just beyond the radial notch, and to the annular ligament, a few fibres passing on to the neck of the radius. It is composed of decussating fibres, most of which pass vertically or obliquely downward, a few taking a transverse course at the summit of the olecranon fossa where the ligament is usually thinnest. Fig. 294. — Lateral View of the Elbow-joint. Annular ligament ■Radial collateral ligment ■Posterior ligament The medial portion, the ubiar collateral ligament (fig. 293), is thicker, stronger, and denser than either the anterior or posterior portions. It is triangular in form, its apex being attached to the anterior and under aspect of the medial epicondyle, and to the condyloid edge of the groove between the trochlea and the condyle. The fibres radiate downward from this attachment, the anterior passing forward to be fixed to the rough overhanging medial edge of the coronoid 260 THE ARTICULATIONS process ; the middle descend less obliquely to a ridge running between the coronoid and olecranon processes, while the posterior pass obliquely backward to the medial edge of the olecranon just beyond the articular margin. Fig. 295. — Lower Extremity of the Humerus, to show the Relation of the Articu- lar Capsule of the Elbow-joint (in red) to the Epiphysial Lines. Fig. 296. — The Upper Extremity of the Ulna, to show the Relation of the Articu- lar Capsule of the Elbow-joint (in red) to the Epiphysial Lines. An oblique band (the oblique ligament of Sir Astley Cooper) connects the margin of the olecranon process with the margin of the coronoid process. It lies superficial to the posterior fibres of the ulnar collateral ligament. The anterior fibres are the thickest, strongest, and most pronounced. RADIO-ULNAB JOINTS 26L The lateral portion, the radial collateral ligament (fig. 294), is attached above to the lower part of the lateral epicondyle, and from this the fibres radiate to their attachment into the lateral side of the annular ligament, a few fibres being prolonged to reach the neck of the radius. The anterior fibres reach further forward than the posterior do behind. It is strong and well-marked, but less so than the medial portion. The synovial membrane lines the whole of the capsule, and extends into the superior radio-ulnar joint, lining the annular ligament. Outside the synovial membrane, but inside the capsule, are often seen some pads of fatty tissue; one is situated on the medial side at the base of the olecranon, another is seen on the lateral side projecting into the cavity between the radius and ulna; this latter, with a fold of synovial membrane opposite the front of the lateral hp of the trochlea, suggests the division of the joint into two parts — one medially for the ulna, and another laterally for the radius. There are also pads of fatty tissue at the bottom of the olecranon and coronoid fossas, and at the tip of the olecranon process. The arterial supply is derived from each of the vessels forming the free anastomosis around the elbow, and there is also a special branch to the front and lateral side of the joint, from the brachial artery, and the arterial branch to the brachialis also feeds the front of the joint. The nerve-supply comes chiefly from the musculo-cutaneous; the ulnar, median, and radial (musculo-spiral) also give fUaments to the joint. Relations. — In front of the joint, and in immediate relation with the capsule, are the brachiahs, the superficial and deep branches of the radial (musculo-spiral) nerve, the radial re- current artery, and the brachio-radiahs. The brachial artery, the median nerve, and the pro- nator teres are separated from the capsule by the brachiahs. Directly behind the capsule are the triceps, the anconeus, and the posterior interosseous recurrent artery. On the medial side are the ulnar nerve, the superior ulnar collateral (posterior ulnar recurrent) artery, and the upper parts of the flexor carpi ulnaris and flexor digitorum subhmis. On the lateral side lie the extensor carpi radiahs longus and the upper part of the common tendon of origin of the superficial extensors of the wrist and fingers. The movements permitted at the elbow are those of a true hinge joint, viz., flexion and extension. These movements are oblique, so that the forearm is inclined medially in flexion, and laterally in extension ; they are limited by the contact respectively of the coronoid and ole- cranon processes of the ulna with their corresponding fossae on the humerus, and their extent is determined by the relative proportion between the length of the processes and depth of the fossae which receive them, rather than by the tension of the ligaments, or the bulk of the soft parts over them. The anterior and posterior portions of the capsule, together with the corres- ponding portions of the collateral ligament, are not put on the stretch during flexion and exten- sion; but, although they may assist in checking the velocity, and thus prevent undue force of impact, they do not control or determine the extent of these movements. The limit of exten- sion is reached when the ulna is nearly in a straight line with the humerus; and the limit of flexion when the ulna describes an angle of from 30° to 40° with the humerus. The obliquity of these movements is due to the lateral inclination of the upper and back part of the trochlear surface, and the greater prominence of the medial lip of the trochlea below; thus the plane of motion is directed from behind forward and medially, and carries the hand toward the middle third of the clavicle. The obliquity of the joint, the twist of the shaft of the humerus, and the backward direction of its head, all tend to bring the hand toward the mid- line of the body, under the immediate observation of the eye, whether for defence, employment, or nourishment. This is in striking contrast to the lower limb, where the direction of the foot diverges from the median axis of the trunk, thus preventing awkwardness in locomotion. In flexion and e.xtension, the cup-like depression of the radial head glides upon the capitulum, and the medial margin of the radial head travels in the groove between the capitulum and the trochlea. This allows the radius to rotate upon the humerus while following the ulna in all its movements. In full extension and supination, the head of the radius is barely in contact with the inferior surface of the capitulum, and projects so much backward that its posterior margin can be felt as a prominence at the back of the elbow. In full flexion the anterior edge of the radial head is received into, and checked against, the depression above the capitulum ; while in mid-flexion the cup-like depression is fairly received upon the capitulum, and in this position, the radius being more completely steadied by the humerus than in any other, pro- nation and supination take place most perfectly. Muscles which act upon the elbow-joint. — Flexors. — Brachialis, biceps, brachio-radialis, pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum sublimis, flexor carpi ulnaris. Extensors. — Triceps, anconeus, and the muscles which spring from the lateral epico ndyle 5. THE UNION OF THE RADIUS WITH THE ULNA The radius is firmly united to the ulna by two joints, and an intermediate fibrous union, viz. : — • (a) The superior radio-ulnar — whereat the head of the radius rotates within the radial notch and annular ligament. (b) The union of the shafts — the mid radio-ulnar union. (c) The inferior radio-ulnar — whereat the lower end of the radius rolls round the head of the ulna. 262 THE ARTICULATIONS . (a) The Superior Radio-ulnar Joint Class. — Diarthrosis. Subdivision. — Trochoides. The bones which enter into this joint (which is often included with the elbow- joint) are, the ulna by its radial notch and the radius by the smooth vertical border or rim on its head. There is but one ligament special to the joint, viz.: — Annular. The annular ligament consists of bands of strong fibres, somewhat thicker than the capsule of the elbow-joint, which encircle the head of the radius, re- taining it against the side of the ulna. The bulk of these fibres forms about three- fourths of a circle, and they are attached to the anterior and posterior margins of the radial notch; some few are continued round below the radial notch, and form a complete ligamentous circle. The ligament is inseparably connected along its upper edge and lateral (i. e., its non- articular) surface with the anterior, posterior, and lateral portions of the capsule of the elbow, a few of the fibres of these portions, especially of the lateral, descending to be attached to the necli of the radius. The lower part of the articulation is covered in anteriorly, posteriorly, and laterally by a thin independent membranous layer, which passes from the lower edge of the annular ligament to the neck of the radius, strengthened on the lateral side by those fibres passing down from the capsule. They are loose enough to allow the bone to rotate upon its Fig. 297. — Annular Ligament. (The head of the radius removed to show the membranous connection of this ligament with the radius.) Capsule of elbow-joint CusMon of fatty tissue Membranous tissue joining the an- nular ligament to the neck of the radius Radius Annular ligament own axis (fig. 297). Medially and below the cavity is closed in by a loose membrane, the liga- mentum quadratum, which passes from the lower border of the radial notch to the neck of the radius. The synovial membrane is the same as that of the elbow-joint, and, after lining the annular ligament, passes on to the neck of the radius, and thence up to the lower margin of the articular cartilage. The arterial and nerve -supply are the same as those to the lateral part of the elbow-joint. Relations. — Behind lies the anconeus and in front the lateral border of the brachiaUs. (b) The Mid Radio-ulnar Union Class. — Synarthrosis. Subdivision. — Syndesmosis. There are two interosseous ligaments which pass betweeen the shafts of the bones and unite them firmly together, viz. : — Oblique cord. Interosseous membrane. The oblique cord [chorda obliqua] (figs. 293 and 298) is a fairly strong, narrow band, which passes from the lower end of the rough lateral border of the coronoid RADIO-ULNAR JOINTS 263 process, downward and laterally to be attached to the posterior edge of the lower end of the tuberosity of the radius and the vertical ridge running from it to the medial border of the bone. Some of its fibres blend with the fibres of insertion of the biceps tendon; behind, it is in close contact with the supinator; below, a thin membrane passes off from it to the upper edge of the interosseous membrane; the posterior interosseous vessels pass in the space between it and the interosseous membrane; occasionally a slip is continued into the annular ligament of the superior radio-ulnar articulation (see fig. 298). The interosseous membrane (fig. 293) is attached to the ulna at the lowest part of the ridge in front of the depression for the supinator, and along the whole length of the interosseous border as far as the inferior radio-ulnar articulation, approaching the front of the bone in the lower part of its attachment. To the radius it is attached along the interosseous border, from an inch (2.5 cm.) below the tuberosity to the ulnar notch for the lower end of the ulna. It is strongest and broadest in the centre, where the fibres are dense and closely packed ; it is also well marked beneath the pronator quadratus, and thickens considerably at the lower end, forming a strong band of union between the two bones. Its fibres pass chiefly downward and medially, from the radius to the ulna, though some take the opposite direction; at the lower end some are transverse. On the posterior surface are one or two bands, which pass downward and laterally from the ulna to the radius, and frequently there is a strong bundle as large as the Fig. 298. — Upper Portions of Left Ulna and Radius, to show an Occasional Slip prom THE Oblique Cohd to the Lower Part op the Annular Ligament. This condition is present in the spider monkey (Ateles), which has no external thumb but only rudimentary bones of one. (From a dissection by Mr. W. Pearson, Royal CoUege of Surgeons, England.) Annular ligament Occasional slip from oblique cord to annular ligament Oblique cord oblique cord; this, which may be called the inferior oblique ligament (fig. 303), stretches from the ulna, an inch and a half above its lower extremity, downward and laterally to the ridge above and behind the ulnar notch of the radius. At its attachment to the bones, the interosseous membrane blends with the periosteum. Its upper border is connected with the oblique cord by a thin membrane, which is pierced by the posterior interosseous vessels; and the lower border, which stretches across between the two bones just above the inferior radio-ulnar articulation, assists in completing the capsule of that joint. Its anterior surface is iii relation with the flexor digitorum profundus and flexor pollids longus in the upper three-quarters, the lower fourth being in relation with the pronator quadratus. The anterior interosseous vessels and nerve descend along the middle of the membrane, the artery being bound down to it. About an inch from the lower end it is pierced by the anterior interosseous artery. The posterior surface is in relation with the supinator, abductor pollids longus (extensor ossis metacarpi pollids), extensor pollids longus and brevis, and the extensor indids proprius; at its lower part, also with the posterior branch of the anterior interosseous artery, and the deep branch of the radial nerve (posterior interosseous). (c) The Inferior Radio-xjlnar Joint Class. — Diarthrosis. Subdivision. — Trochoides. This is, in one respect, the reverse of the superior; for the radius, instead of presenting a circular head to rotate upon the facet on the ulna, presents a concave facet which rolls round the ulna. The articulation may be said to consist of two 264 THE ARTICULATIONS parts at right angles to each other; one between the radius and ulna, and the other between the ulna and the articular disc (triangular fibro-cartilage) . Anterior radio-ulnar. The ligaments are: Articular disc. Posterior radio-ulnar. The articular disc (triangular fibro-cartilage) (figs. 303 and 304) assists the radius in forming an arch under which is received the first row of carpal bones. Its base is attached to the margin of the radius, separating the ulnar notch from the articular surface for the carpus, while its apex is fixed to the fossa at the base of the styloid process of the ulna. It gradually and uniformly diminishes in width from base to apex, becoming rounded where it is fixed to the ulna; it is joined by fibres of the ulnar collateral ligament of the wrist. The articular disc is about three-eighths of an inch (1 cm.) wide, and the same from base to apex; thicker at the circumference than in the centre; smooth and concave above to adapt Fig. 299. — ^Lower Extremities op the Radius and Ulna to Show the Relation op THE Articulab Capsule OP THE Wrist Joint (In red) to the Epiphysial Lines. Note the upward extension of the membrana saccLformis. itself to the ulna, and smooth and slightly concave below to fit over the triquetral bone. Its anterior and posterior borders are united to the anterior and posterior radio-ulnar and radio- carpal ligaments. It is the most important structure in the inferior radio-carpal articulation, as it is a very firm bond of union between the lower ends of the bones, and serves to hmit their movements upon one another more than any other structure in either the upper or lower radio- ulnar joints. Its structure is fibrous at the circumference, while in the centre there is a prepon- derance of cells. It differs from all other fibro-cartilages in entering into two distinct articula- tions; and separates entirely the synovial membrane of the radio-ulnar joint from that of the wrist. The lower end of the interosseous membrane extends between the ulna and radius immediately above their points of contact. Transverse fibres between the two bones form a sort of arch above the concave articular facet of the radius, and, joining the anterior and posterior radio-ulnar ligaments, complete the articular capsule of the inferior radio-ulnar joint. The ligaments represent merely thickenings of the capsule. The anterior radio-ulnar ligament (fig. 300) is attached by one end to the anterior edge of the ulnar notch of the radius, and by the other to the rough bone above the articular surface of the ulna as far mediaDy as the notch, as well as into the anterior margin of the trianguar cartOage from base to apex. The posterior radio-ulnar ligament (fig. 301) is similarly attached to the posterior margin of the ulnar notch at one end, and at the other to the rough bone above the articular surface of the extremity of the ulna as far medially as the groove for the extensor carpi ulnaris, with the sheath of which it is connected, as well as into the whole length of the posterior margin of the articular disc. Both the radio-ulnar ligaments consist of thin, almost scattered, fibres. THE WRIST-JOINT 265 The synovial membrane, sometimes called the membrana sacciformis, is large and loose in proportion to the size of the joint. It is not onty interposed between the radial and ulnar articular surfaces, but lines the terminal articular surface of the ulna and the upper surface of the articular disc. The arterial supply is derived from the volar interosseous artery and branches of the volar carpal rate. The nerve-supply comes from the volar interosseous of the median, and the deep branch of the radial (posterior interosseous). Relations. — Behind hes the tendon of the extensor digiti quinti proprius and in front the flexor digitorum profundus. The movements of the radius. — The upper end of the radius rotates upon an axis drawn through its own head and neck within the coUar formed b}' the radial notch and the annular ligament, while the lower end, retained in position by the articular disc, rolls round the head of the ulna. This rotation is called pronation, when the radius from a position nearly parallel to the ulna turns medialward so as to lie obliquely across it; and supination, when the radius turns back again, so as to uncross and lie nearly parallel with the ulna. In these move- ments the radius carries with it the hand, which rotates on an axis passing along the ulnar side of the hand; thus, the hand when pronated hes with its dorsum upward, as in playing the piano, whUe when supinated, the palm lies upward — the attitude of a beggar asking alms. Ward thus expresses the relations of the two extremities of the radius in pronation and supina- tion: 'The head of the radius is so disposed in relation to the sigmoid cavitj' (ulnar notch) at the lower end that the axis of the former if prolonged falls upon the centre of the circle of which the latter is a segment;' the axis thus passes through the lower end of the ulna at a point at which the articular disc is attached, and if prolonged further, passes through the ring finger. Thus the radius describes, in rotating, a blunt-pointed cone whose apex is the centre of the radial head, and whose base is at the wrist; partial rotation of the bone being unaccompanied by anj' hinge-like or antero-posterior motion of its head, and pronation and supination occurring with- out disturbance to the parallelism of the bones at the superior radio-ulnar joint. Associated with this rotation in the ordinary way, there is some rotation of the humero-ulnar shaft, which causes lateral shifting of the hand from side to side; thus, with pronation there is some abduc- tion, and with supination some adduction combined, so that the hand can keep on the same superficies in both pronation and supination. The power of supination in man is much greater than pronation, owing to the immense power and leverage obtained by the cm-ve of the radius, and bj' the attachment of the biceps tendon to the back of the tuberosity. For this reason all our screw-driving and boring tools are made to be used bj- supination movements. In the undissected state, the amount of rotation it is possible to obtain is about 135°, so that neither the palm nor the fore part of the lower end of the radius can be turned completely in opposite directions; j-et in the hving subject this amount can be greatly increased by rotation of the humero-ulnar shaft at the shoulder-joint. Pronation is checked in the living subject by (a) the posterior inferior radio-ulnar ligament, which is strengthened by the connection of the sheath of the extensor tendons with it; (b) the lowermost fibres of the interosseous membrane; (c) the back part of the ulnar collateral and adjacent fibres of the posterior hgament of the wrist, and (d) the meeting of the soft parts on the front of the forearm. Supination is checked mainly (a) by the medial ulnar collateral ligaments of the wrist, but partly also by (b) the oblique cord; (c) the anterior inferior radio-ulnar hgament, and (d) the lowest fibres of the interosseous membrane. The interosseous membrane serves, from the direction of its fibres downward and medially from the radius to the ulna, to transmit the weight of the body from the ulna to the radius in the extended position of the elbow, as in pushing forward with the arms extended, or in support- ing one's own weight on the hands, the ulna being in intimate contact with the humerus, but not at all with the carpus; whOe the area of contact of the radius with the humerus is small, and that of the radius with the carpus large. Hence the weight transmitted bj' the ulna is communicated to the radius by the tightening of the interosseous membrane. Conversely, in falls upon the hand with the arm extended, the interosseous membrane acts as a sUng to break the violence of the shock, and prevents the whole force of the impact from expending itself directly upon the capitulum. Muscles which act upon the radio-ulnar joints.— Pronators. — Pronator teres, pronator quadratus, flexor carpi radiahs, palmaris longus. Supinators. — Biceps, supinator, extensor poUicis longus. The brachio-radialis is chiefly a flexor of the elbow-joint, but it takes part in the initiation of the movement of supination when the hand is fully pronated and of pronation when the hand is fully supinated. 6. THE RADIO-CARP.\L OR WRIST-JOINT Class. — Diarthrosis. Subdivision. — Condylarthrosis. The wrist-joint is formed by the imion of the radius and articular disc above, articulating -^vith the navicular, lunate, and triquetral bones below; the ulna being excluded by the intervention of the articular disc. The radius and disc together present a smooth surface, slightly concave both from before backward, and from side to side, whilst the three bones of the carpus present a smooth, 266 THE ARTICULATIONS convex surface, made uniformly even by the interosseous ligaments which bind them together. The capsule of the wrist-joint has been usually described as four separate liga- ments, and it will be convenient for the sake of a complete description to follow this method; but it must be understood that these four portions are continuous around the joint, extending from styloid process to styloid process on both its aspects. The four portions are : — Volar radio-carpal. Dorsal radio-carpal. Ulnar collateral. Radial collateral. The volar (or anterior) radio-carpal (fig. 300) is a thick strong ligament, at- tached superiorly to the radius immediately above the anterior margin of the terminal articular facet, to the curved ridge at the root of the styloid process of the radius, and to the anterior margin of the articular disc, blending with some fibres of the capsule of the inferior radio-ulnar joint. It passes downward and in a medial direction to be attached to both rows of carpal bones, especially the second, and to the volar intercarpal ligament. Fig. 300.- — Anterior View op Wrist. Ulnar radio-ulnar ligament Ulnar collateral liga- ment of wrist Flexor carpi ulnaris Volar radio-carpal ligament Tendon of flexor carpi radialis Capsular ligament of first carpo-metacarpal joint The strongest and most oblique fibres arise from the root of the styloid process of the radius, and pass obhquely over the navicular, with which only a few fibres are connected, to be inserted into the lunate, capitate, and triquetral bones. Another set, less oblique, passes from the margin of the facet for the lUnate to be attached to the adjacent parts of the capitate, hamate, and tri- quetral bones. Between the two sets of fibres, small vessels pass into the joint. The dorsal (or posterior) radio-carpal ligament (fig. 301) is attached above to the dorsal edge of the lower end of the radius, the back of the styloid process, and the posterior margin of the fibro-cartilage. It passes downward and in a medial direction to be connected with the first row of the carpal bones, chiefly with the lunate and triquetral, and the dorsal intercarpal ligament. This ligament is thin and membranous. It is strengthened by (i) strong fibres passing from the back of the articular disc where they are blended with the posterior inferior radio-ulnar ligament, and, from the edge of the radius just behind the ulnar notch, to the triquetral bone; (ii) from the ridge and groove for the extensor pollicis longus to the back of the lunate and triquetral bones; and (iii) from the groove for the radial e.xtensors to the back of the navicular and lunate. It is in relation with, and strengthened by, the extensor tendons which pass over it. The ulnar collateral ligament (fig. 301) is fan-shaped, with its apex above, at the styloid process of the ulna, to which it is attached on all sides, blending with THE WRIST-JOINT 267 the apex of the articular disc. Some of the fibres pass forward and laterally to the base of the pisiform bone and to the medial part of the upper border of the transverse carpal ligament, where it is attached to the pisiform bone; they form a thick, rounded fasciculus on the front of the wrist. Other fibres descend vertically to the medial side of the triquetral bone, and others again laterally to the dorsal surface of the triquetral. The tendon of the extensor carpi ulnaris is posterior to, and passes over, part of the fibres of the ligament. The radial collateral ligament (fig. 300) consists of fibres which radiate from the fore part and tip of the styloid process of the radius. Some pass downward and medially, in front, to the navicular and adjacent edge of the capitate; some downward, a little forward and medially, to the tubercle of the navicular and ridge of the greater multangular; and others downward and laterally to the rough dorsal surface of the navicular. The fibres of this ligament are not so long and strong, nor do they radiate so much as those of the ulnar collateral ligament. It is in relation with the radial artery, and the abductor pollicis longus {extensor ossis metacarpi pollicis) and extensor pollicis brevis, the artery separating the tendons from the ligament. Fig. 301. — Posterior View op Whist. Dorsal radio-carpal ligament Posterior radio-ulnar ligament Ulnar collateral ligament of wrist The synovial membrane is extensive, but does not usually communicate with the synovial membrane of the inferior radio-ulnar joint, being shut out by the articular disc. It is also excluded, in almost every instance, from that of the carpal joints by the interosseous ligaments between the first row of carpal bones. The styloid process of the radius is cartilage-covered medially, and forms part of the articular cavity, while that of the ulna does not. The arterial supply is derived from the anterior and posterior carpal rami, the dorsal division of the volar interosseous, and from twigs direct from the radial and ulnar arteries. The nerve -supply is derived from the ulnar and median in front, and the deep branch of the radial (posterior interosseous) behind. Relations. — In front of the radio-carpal joint are the tendons of the flexor muscles of the wrist and fingers, the synovial sheaths associated with thern, the radial and ulnar arteries, and the median and ulnar nerves. Behind the joint are the majority of the tendons of the extensor muscles of the wrist and fingers, with their synovial sheaths, the terminal part of the anterior and posterior interosseous arteries, and the deep branch of the radial nerve (posterior interosseous). On the radial side lie the tendons of the abductor pollicis longus {extensor ossis metacarpi pollicis) and the extensor pollicis brevis. On the ulnar side the joint is subcutaneous and it is crossed by the dorsal cutaneous branch of the ulnar nerve. Movements. — The wrist is a condyloid joint, the carpus forming the condyle. It allows of movements upon a transverse axis, i. e., flexion and extension; and around an antero-pos- terior axis, i. e., abduction and adduction; together with a combination of these in quick succes- 268 THE ARTICULATIONS sion — oiroumduction. Lacking only rotation on a vertical axis, it thus possesses most of the movements of a ball-and-socket joint, without the weakness and liability to dislocation which are peculiar to these joints. This deficiency of rotation is compensated for by the movements of the radius at the radio-ulnar joints, viz., supination and pronation. Its strength depends chiefly upon the number of tendons which pass over it, and the close connection which exists between the fibrous tissue of their sheaths and the capsule of the wrist; also upon the proximity of the medio-carpal and carpo-metacarpal joints, which permits shocks and jars to be shared and distributed between them; another source of strength is the absence of any long bone on the distal side of the joint. In flexion and extension the carpus rolls backward and forward, respec- tively, beneath the arch formed by the radius and articular disc; flexion being limited by the dorsal ligament and dorsal portions of the collateral; extension by the volar, and volar portions of the collateral ligaments. In adduction and abduction the carpal bones ghde from the ulnar to the radial side and from the radial to the ulnar side, respectively. Abduction is more limited than adduction, and is checked by the ulnar collateral hgament and by contact of the styloid process of the radius with the greater multangular; adduction is checked by the radial collateral ligament alone. One reason for adduction being more free than abduction is that the ulna does Fig. 302. — Front of Wrist with Transverse Carpal Ligament. ulnar collateral ligament of wrist with slip to annu- lar ligament Pisiform- Transverse carpal ligament' Volar radio-carpal ligament not reach so low down as the radius, and the yielding articular disc allows of greater movement upward of the ulnar end of the carpus. In circumduction the hand moves so as to describe a cone, the apex of which is at the wrist. These movements are made more easy and extensive by the slight gliding of the carpal bones upon one another, and the comparatively free motion at the medio-carpal joint. The oblique direction of the fibres of the collateral hgaments pre- vents any rotation at the radio-carpal joint, while it permits considerable freedom of abduction and adduction. Muscles which act upon the radio-carpal joint. — Flexors. — The flexors of the carpus and the long flexors of the fingers and the thumb, and the pahnaris longus. Extensors. — The exten- sors of the carpus and fingers. Abductors. — Extensor carpi radialis longus, the abductor pol- licis longus (extensor ossis metacarpi poUicis. Adductors. — Flexor carpi ulnaris, extensor carpi ulnaris. 7. THE CARPAL JOINTS The joints of the carpus may be subdivided into — • (a) The joints of the first row. (6) The joints of the second row. (c) The medio-carpal, or junction of the two rows with each other. THE CARPAL JOINTS 269 (a) The Joints of the First Row of Carpal Bones Class. — Diarthrosis. Subdivision. — Arthrodia. The bones of the first row, the pisiform excepted, are united by two sets of ligaments and two interosseous fibro-cartilages. Dorsal. Volar. Interosseous. The two dorsal intercarpal ligaments extend transversely between the bones, and connect the navicular with the lunate, and the lunate with the triquetral. Their posterior siu-faces are in contact with the posterior ligament of the -nTist. The two volar intercarpal ligaments extend nearly transversely between the bones connect- ing the navicular with the lunate, and the lunate with the triquetral. They are Wronger than the dorsal ligaments, and are placed beneath the anterior ligament of the wrist. The two interosseous intercarpal ligaments (fig. 304) are interposed between the navicular and lunate, and the lunate and triquetral bones, reaching from the dorsal to the volar surfaces. Fig. 303. — Posterior View op the Wrist, with Capsule cut to show Articular Surfaces, 'll^^ — ^J Lower end of interosseous ligament Inferior oblique ligament Articular disc Band of posterior ligament of wrist i^ujH .,,,,, n^ .. V >,i|i left to keep bones in situ Transverse dorsal ligament v*w».«™/ ^ / Tendon flexor carpi ulnaris and being connected with the dorsal and volar ligaments. They are narrow fibro-cartilages which extend between small portions only of the osseous surfaces. They help to form the convex carpal surface of the radio-carpal joint, and are somewhat wedge-shaped, their bases being toward the wrist, and their thin edges between the adjacent articular surfaces of the bones. The synovial membrane is a prolongation from that of the medio-oarpal joint. The arterial and nerve-supplies are the same as for the medio-carpal joint. The Joint of the Pisiform Bone with the Triquetral This is an arthrodial joint which has a loose fibrous capsule attached to both the pisiform and triquetral bones just beyond the margins of their articular surfaces. It is lined by a separate synovial membrane. Two strong rounded or flattened bands pass downward from the pisiform, one to the process of the hamate [Ug. pisohamatum], and the other [Ug. pisometacarpeum] to the bases of the third to fifth metacarpals; these are regarded as prolongations of the tendon of the flexor carpi ulnaris, and the pisiform bone may be looked upon in the light of a sesamoid bone developed in that tendon. (b) The Joints of the Second Row of Carpal Bones Class. — Diarthrosis. Subdivision. — Arthrodia. The four bones of this row are united by three dorsal, three palmar, and three interosseous ligaments. 270 THE ARTICULATIONS The three dorsal ligaments (fig. 303) extend transversely and connect the greater with the lesser multangular, the lesser multangular with the capitate, and the capitate with the hamate. The three volar ligaments are stronger than the dorsal, and are deeply placed beneath the mass of flexor tendons; they extend transversely between the bones in a similar manner to the dorsal ligaments. Three interosseous ligaments connect the bones of the lower row of the carpus together. Two are connected with the capitate, one uniting it with the hamate (fig. 304) and the other binding it to the lesser multangular. The third Mgament joins the greater and lesser multangular. The synovial membrane is a prolongation of that lining the medio-carpal joint. The arterial and nerve -supplies are the same as for the medio-carpal joint. (c) The Medio-carpal Joint, or the Union op the Two Rows of the Carpus WITH EACH other (I) Class. — Diarthrosis. Subdivision. — Arthrodia. (II) Class.- — Diarthrosis. Subdivision. — Condylarthrosis. The inferior surfaces of the bones of the first row are adapted to the superior articular surfaces of the bones of the second row. The line of this articulation is concavo-convex from side to side, and is sometimes described as having the course of a Roman S placed horizontally, co , a resemblance by no means strained, (i) The lateral part of the first row consists of the navicular alone; it is convex, and bears the greater and lesser multangulars. (ii) Then follows a transversely elongated socket formed by the medial part of the navicular, the lunate, and triquetral, into which are received — (a) the head of the capitate, which articulates with the navicular and lunate; (6) the upper and lateral angle of the hamate, which articulates with the navicular; and (c) the upper convex portion of the medial surface of the hamate, which articulates with the lateral and concave portion of the inferior surface of the triquetral, (iii) The medial part of the inferior sur- face of the triquetral bone is convex, and turned a little backward to fit into the lower portion of the medial surface of the hamate, which is a little concave and turned forward to receive it. The central part, which forms a socket for the capi- tate and hamate, has somewhat the character of a condyloid joint, the capitate and hamate being the condyle, to fit into the cavity formed by the navicular, lunate, and triquetral; the other portions are typically arthrodial. The liga- ments are: — (1) radiate or anterior medio-carpal; (2) posterior medio-carpal; (3) transverse dorsal. The radiate, anterior or volar medio-carpal is a ligament of considerable strength, consisting mostly of fibres which radiate from the capitate to the navicular, lunate, and triquetral; some few fibres connect the greater and lesser multangular with the navicular, and others pass between the hamate and triquetral. It is covered over and thickened by fibrous tissue derived from the sheaths of the flexor tendons and the fibres of origin of the small muscles of the thumb and httle finger. The posterior or dorsal medio-carpal ligament, consists of fibres passing obliquely from the bones of the first row to those of the second. It is stronger on the ulnar side than on the radial, but is not so strong as the volar ligament. The transverse dorsal ligament (fig. 303) is an additional band, well marked and often of considerable strength, which passes across the head of the capitate from the navicular to the triquetral bone; besides binding down the head of the capitate, it serves to fix the upper and lat- eral angle of the hamate in the socket formed by the first row. The dorsal ligaments, like the volar, are strengthened by a quantity of fibrous tissue belong- ing to the sheaths of the extensor tendons, and by an extension of some of the fibres of the capsule of the wrist. There are no proper collateral medio-carpal hgaments; they are but prolongations of the collateral ligaments of the wrist. The synovial membrane (fig. 304) of the carpus is common to all the joints of the carpus, and extends to the bases of the four medial metacarpal bones. Thus, besides hning the inter- or medio-carpal joint, it sends two processes upward between the three bones of the first row, and thi'ee downward between the contiguous surfaces of the lesser and greater multangular, the lesser multangular and capitate, and capitate and hamate. From these latter, prolongations extend to the four medial carpo-metacarpal joints and the three intermetacarpal joints. The arterial supply is derived from — (a) the volar and dorsal carpal rami of the radial and ulnar arteries; (b) the carpal branch of the volar interosseous; (c) the recurrent branches from the deep palmar arch. The terminal twigs of the volar and dorsal interosseous arteries supply the joint on its dorsal aspect. The nerve -supply comes from the ulnar on the ulnar side, the median on the radial side, and the deep branch of the radial (posterior interosseous) behind. Relations. — The relations of this joint are practically the same as those of the radio-carpal joint, except that the flexor carpi ulnaris does not cross the front, the ulnar artery is separated THE CARPAL JOINTS 271 from it by the transverse carpal ligament, and the radial artery passes across its lateral border instead of in front. The movements of the carpal articulations between bones of the same row are very hmited and consist only of slight gliding upon one another; but, slight as they are, they give elasticity to the carpus to break the jars and shocks which result from blows or falls upon the hand. The movements of one row of bones upon the other at the medio-carpal joint are more extensive, especially in the direction of flexion and extension, so that the hand enjoys a greater range of these movements than is permitted at the wrist-joint alone. At the wrist, extension is more free than flexion; but this is balanced by the greater freedom of flexion than of extension at the medio-carpal joint, and by flexion at the carpo-metacarpal joint, so that on the whole- the range of flexion of the hand is greater than that of extension. Fig. 304. — Synovial Membranes of Wri&t Hand, and Fingers. Synovial sac of the wrist-joint Synovial sac of the carpus Synovial sac, occasionally separate, for the fourth and fifth metacarpal bones .Synovial sac of the carpo-meta- carpal joint of the thumb Collateral ligaments of the metacarpo- pha angeal and interphalangeal A slight amount of side to side motion accompanied by a limited degree of rotation also takes place; this rotation consists in the head of the capitate and the superior and lateral angle of the hamate bone rotating in the socket formed by the three bones of the upper row, and in^a gliding forward and backward of the greater and lesser multangular upon the navicular. In addition to the ligaments, the undulating outUne and the variety of shapes of the apposed facets render this joint very secure. Bearing in mind the mobility of this medio-carpal joint and of the carpo-metacarpal, we see at once the reason for the radial and ulnar flexors and extensors of the carpus being prolonged down to their insertion into the base of the metacarpus, for they produce the combined effect of motion at each of the three transverse articulations: — (1) at the wrist; (2) at the medio-carpal; (3) at the carpo-metacarpal joints. Muscles which act upon the mid-carpal joint. — The muscles which act upon this joint are the same as those which act upon the radio-carpal joint, except the flexor carpi ulnaris, which is inserted into the pisiform bone. 272 THE ARTICULATIONS 8. THE CARPO-METACARPAL JOINTS These may be divided into two sets, namely: — (a) The carpo-metacarpal joints of the four medial fingers. (6) The carpo-metacarpal joints of the thumb. The inferior surfaces of the bones of the second row of the carpus present a composite surface for the four medial metacarpal bones ; the greater multangular presents in addition a distinct and separate saddle-shaped surface for the base of the metacarpal bone of the thumb. (a) The Four Medial Carpo-metacarpal Joints Class. — Diarthrosis. Subdivision. — Arthrodia. These joints exist between the greater and lesser multangular, capitate, and hamate bones above, and the four medial metacarpal bones below. The liga- ments which unite them are, dorsal, volar, and interosseous. The dorsal ligaments (fig. 303). — Three dorsal ligaments pass to the second metacarpal bone: one from each of the carpal bones with which it articulates, viz., the greater and lesser multangular, and capitate. Two dorsal bands pass from the capitate to the third metacarpal bone. Two dorsal bands pass to the fourth bone: viz., one from the hamate, and another from the capitate; the latter is sometimes wanting. The fifth bone has only one band passing to it from the hamate. The volar ligaments (fig. 300). — One strong band passes from the second metacarpal bone to the greater multangular medial to the ridge for the transverse carpal ligament; it is covered by the sheath of the flexor carpi radialis. Three bands pass from the third metacarpal: one laterally to the greater multangular, a middle one upward to the capitate, and a third medially over the fourth to reach the fifth meta- carpal and the hamate bones. One ligament connects the fourth bone to the hamate. One ligament connects the fifth bone to the hamate, the fibres extending medially, and con- necting the dorsal and volar ligaments. The ligament to the fifth bone is strengthened in front by the prolonged fibres of the flexor carpi ulnaris and the strong medial sUp of the ligament of the third metacarpal bone; and posteriorly, by the tendon of the extensor carpi ulnaris. The interosseous ligament (fig. 304) is Hmited to one part of the articulation, and consists of short fibres connecting the contiguous angles of the hamate and capitate with the third and fourth metacarpal bones toward their volar aspect. There is, however, a thick strong ligament connecting the edge of the greater multangular with the lateral border of the base of the second metacarpal bone; it helps to separate the carpo-metacarpal joint of the thumb from the common carpo-metacarpal joint, and to close in the radial side of the latter joint. The synovial membrane is a continuation of the medio-carpal joint; occasionally there is a separate membrane between the hamate and fourth and fifth metacarpal bones (fig. 304) ; while that between the fourth and capitate is lined by the synovial sac of the common joint. The arteries to the four medial carpo-metacarpal joints are as follows: — (1) For the index finger: twigs are supphed by the trunk of the radial on the dorsal and volar aspects, and by the dorsal and volar metacarpal branches. (2) For the middle finger: the first dorsal metacarpal by the branch which passes upward to join the dorsal carpal arch, and a branch from the deep volar arch which joins the volar carpal arch. (3) For the ring finger: the deep volar arch and recurrent twigs from the second dorsal metacarpal in the same manner as for the middle finger. (4) For the little finger: the ulnar and its deep branch; also twigs from the second dorsal metacarpal. The nerves are supplied to these joints by the deep volar branch of the ulnar, the deep branch of the radial (posterior interosseous), and the median. Relations. — In front of the four medial carpo-metacarpal joints are the flexors of the fingers with their synovial sheath. The flexor carpi radialis crossing in front of the lateral part of the joint and the fibres of the oblique adductor poUicis which spring from the capitate and lesser multangular are also anterior relations. Behind the joints are the extensors of the wrist and fingers with their synovial sheaths and the dorsal metacarpal arteries. At the lateral border of the joints between the index and lesser multangular hes the radial artery. The movements permitted at these joints, though slight, serve to increase those of the medio-carpal and wrist-joints. The joint between the fifth metacarpal and the hamate bones approaches somewhat in shape and mobihty the first carpo-metacarpal joint; it has a greater range of flexion and extension, but its side to side movement is nearly as limited as that of the three other metacarpal bones; the process of the hamate bone hrnits its flexion. Motion toward the ulnar side is checked by the strong palmar band which unites the base of the fifth meta- carpal to the base of the third, and the strong transverse ligament at the head of the bones. The mobility of the second, third, and fourth metacarpal bones is very limited, and consists almost entirely of a slight gliding upon the carpal bones, i. e., flexion and extension; that of the third and fourth bones is extremely slight, as there is no long flexor attached to either; but, INTERMETACARPAL JOINTS 273 owing to the close connection of the bases of the metacarpal bones, the radial and ulnar flexors and extensors of the carpus act on all by their pull on the particular bone into which they are inserted. Abduction, or movement toward the radial side, is prevented by the impaction of the second bone against the greater multangular; a little adduction is permitted, and is favoured by the slope given to the hamate and fifth metacarpal bones. There is also a slight gliding between the fourth and fifth bones, when the concavity they present toward the palm is deepened to form the 'cup of Diogenes.' Muscles which act upon the four medial carpo-metacarpal joints are the flexors and ex- tensors of the wrist and fingers, except the flexor carpi ulnaris. (6) The Carpo-metacarpal Joint of the Thumb Class. — Diarthrosis. Subdivision. — Saddle-shaped Arthrodia. The bones entering into this joint are the base of the first metacarpal and the greater multangular. The first metacarpal bone diverges from the other four, contrasting very strongly with the position of the great toe. It is due to this divergence that the thumb is able to be opposed to each and all the fingers. The ligament which unites the bones is the Articular capsule. The articular capsule (figs. 300 and 301) consists of fibres which pass from the margin of the articular facet on the greater multangular, to the margin of the articular facet at the base of the first metacarpal bone. The fibres are stronger on the dorsal than on the palmar aspect. They are not tense enough to hold the bones in close contact, so that while they restrict they do not prevent motion in any direction. The medial fibres are stronger than the lateral. The synovial membrane is lax, and distinct from the other synovial membranes of the carpus. The arteries of the carpo-metacarpal joint of the thumb are derived from the trunk of the radial, the first volar metacarpal, and the dorsahs pollicis. The nerves are supplied by the branches of the median to the thumb. Relations. — Behind are the long and short extensor tendons of the thumb, and behind and laterally the tendon of the abductor pollicis longus (extensor ossis metacarpi pollicis). The tendon of the flexor pollicis longus is in front and fibres of the flexor pollicis brevis and op- ponens pollicis muscles are also anterior relations. To the medial side is the radial artery as it passes forward into the palm of the hand. The movements of this joint are regulated by the shape of the articular surfaces, rather than by the ligaments, and consist of flexion, extension, abduction, adduction, and circum- duction, but not rotation. In flexion and extension the metacarpal bone slides to and fro upon the multangular; in abduction and adduction it slides from side to side or, more correctly, re- volves upon the antero-posterior axis of the joint. The power of opposing the thumb to any of the fingers is due to the forward and medial obliquity of its flexion movement, which is by far its most extensive motion. Abduction is very free, while adduction is limited on account of the proximity of the second metacarpal bone. The movement of the greater multangular upon the rest of the carpus somewhat increases the range of all the movements of the thumb. Muscles which act upon the carpo-metacarpal joint of the thumb. — Flexors. — Flexor pollicis brevis, flexor pollicis longus, opponens pollicis. Extensors. — Extensores pollicis brevis and longus and abductor pollicis longus. Ahduclors. — Abductores pollicis longus and brevis. Adductors. — The transverse and oblique adductor pollicis, opponens, fii'st dorsal interosseous. Muscles "producing opposition. — Opponens, flexor brevis, oblique adductor. 9. THE INTERMETACARPAL ARTICULATIONS Class. — Diarthrosis. ■ Subdivision. — Arthrodia. The metacarpal of the thumb is not connected with any other metacarpal bone. The second, third, fourth, and fifth metacarpal bones are in actual contact at their bases, and are held firmly together by the following ligaments (in addition to the articular capsule) : — Dorsal. Volar. Interosseous hgaments. The dorsal ligaments (fig. 302) are layers of variable thickness of strong, short fibres, which pass transversely from bone to bone, filUng up the m-egularities on the dorsal surfaces. The volar ligaments are transverse layers of hgamentous tissue passing from bone to bone; they cannot be well differentiated from the other ligaments and fibrous tissue covering the bones. The interosseous ligaments (fig. 304) pass between the apposed surfaces of the bones, and are attached to the distal sides of the articular facets, so as to close in the synovial cavities on 274 THE ARTICULATIONS this aspect; where there are two articular facets, the fibres extend upward between them nearly as far as their carpal facets. That between the fourth and fifth is the weakest. The synovial membrane is prolonged downward from the common carpal sac. The arteries to the intermetacarpal joints are twigs from the volar and dorsal metacarpal arteries; the twigs pass upward between the interosseous muscles. The nerves are derived from the ulnar and the deep branch of radial (posterior interosseous). The Union of the Heads of the Metacarpal Bones The distal extremities of these bones are connected together on their palmar aspects by what is called the transverse ligament [lig. capitulorum]. This consists of three short bands of fibrous tissue, which unite the second and third, third and fourth, and the fourth and fifth bones. They are rather more than 6 mm. (J in.) deep, and rather less in width, and limit the distance to which the metacarpal bones can be separated. They are continuous above with the fascia covering the interosseous muscles; below, they are connected with the subcutaneous tissue of the web of the hand. They are on a level with the front surface of the bones, and are blended on either side with the edges of the glenoid hgament in front, with the lateral Ligaments Fig. 305. — Anterior and Posterior Views of Ligaments of the Fingers. Transverse ligament between the heads ■ of the metacarpal ! bones _ Accessory volar ligament -Collateral ligament Areolar tissue . capsule Collateral ligament - noid ligament -Collateral ligament -Flexor tendon Areolar tissue capsule Collateral ligament — ^ Extensor tendon -Flexor tendon of the metacarpo-phalangeal joint, and also with the sheaths of the tendons. In front, a lum- brical muscle passes with the digital arteries and nerves; while behind, the interossei muscles pass to their insertions. 10. THE METACARPO-PHALANGEAL JOINTS (a) The Metacarpo-phalangeal Joints of the Four Medial Fingers Class.- — Diarthrosis. Subdivision. — Condylarihrosis. In these joints the cup-shaped extremity of the base of the first phalanx fits on to the rounded head of the metacarpal bone, and is united by the following ligaments (in addition to the articular capsule) : — Collateral. Volar accessory. The volar accessory (or glenoid) ligament (fig. 305) is a fibro-cartilaginous plate which seems more intended to increase the depth of the phalangeal articular facet in front, than to unite the two bones. It is much more firmly attached to the margin of the phalanx than to the metacarpal bone, being only loosely connected with the palmar surface of the latter by some loose areolar tissue which covers in the synovial membrane, here prolonged some little distance upon the surface of the bone. At the sides, it is connected with the collateral ligaments and the METACARPO-PHALANGEAL JOINTS 275 transverse metacarpal ligament. It corresponds to the sesamoid bones of the thumb; a sesa- moid bone sometimes exists at the medial border of the joint of the little finger. The collateral ligaments (304 and 305) are strong and firmly connect the bones with one another; each is attached above to the corresponding tubercle, and to a depression in front of the tubercle, of the metacarpal bone. From this point the fibres spread widely as they de- scend on either side of the base of the phalanx; the anterior fibres are connected with the glenoid ligament; the posterior blend with the tendinous expansion at the back of the joint. The joint is covered in posteriorly by the expansion of the extensor tendon, and some loose areolar tissue passing from its under surface to the bones (fig. 305). The synovial membrane is loose and capacious, and invests the inner surface of the liga- ments which connect the bones. The arteries come from the digital or volar metacarpal vessels of the deep arch. The nerves are derived from the digital branches, or from twigs of the branches of the ulnar to the interosseous muscles. Relations. — I. The metacarpo-phalangeal joints of the middle three digits. In front, the tendons of the flexor profundus and flexor subhmis digitorum. On the radial side, a lum- brical, an interosseous muscle, and digital nerves and vessels; on the ulnar side, an interosseous muscle and digital vessels and nerves. Behind, the common extensor tendon and in the case of the index digit the tendon of the extensor indicis. II. The metacarpo-phalangeal joint of the little finger. In front, the flexor quinti digiti brevis and the tendons of the flexor profundus and subhmis digitorum muscle which go to this digit. Behind, the extensor digiti quinti to a slip of the extensor digitorum communis sometimes. On the radial side, a lumbrical, the third palmar interosseous muscle, digital ves- sels and nerves. On the ulnar side, digital vessels and nerves. The movements permitted at these joints are flexion, extension, abduction, adduction, and circumduction. Flexion is the most free of all and may be continued until the phak nx is at a right angle with the metacarpal bone. It is on this account that the articular surface of the head of the bone is prolonged so much further on the palmar aspect, and that the synovial membrane is here so loose and ample. Extension is the most limited of the movements, and can only be carried to a little beyond the straight line. Abduction and adduction are fairlj' free, but not so free as flexion. Flexion is associated with adduction, and extension with abduction. This may be proved by opening the hand, when the fingers involuntarily separate as they extend, while in closing the fist they come together again. The free abduction, adduction, and circumduction which are permitted at these joints are due to the fact that the long axes of the articular facets are at right angles to one another. Muscles acting on the middle three digits. — Flexors. — Flexor digitorum profundus, flexor digitorum sublimis. Extensors. — Extensor digitorum communis and on the index digit the extensor indicis. Abductors. — Dorsal interossei. Adductors. — Volar interossei. Muscles acting on the metacarpo-phalangeal joint of the little finger. — Flexors. — Flexor quinti digiti brevis, flexor digitorum sublimis, flexor digitorum profundus. Extensors. — Exten- sor digitorum communis, extensor quinti digiti. Abductor. — Abductor quinti digiti. Adductor. — Third volar interosseous. (6) The Metacarpo-phalangeal Joint of the Thumb Class. — Diarthrosis. Subdivision. — Condylarthrosis. The head of the metacarpal bone of the thumb differs considerably from the corresponding ends of the metacarpal bones of the fingers. It is less convex, wider from side to side, the palmar edge of the articular surface is raised and irregular, and here on either side of the median line are the two facets for the sesamoid bones. The base of the first phalanx of the thumb, too, is more like the base of the second phalanx of one of the other fingers. The ligaments are : — Collateral. Dorsal. Articular capsule. The collateral ligaments are short, strong bands of fibres, which radiate from depressions on either side of the head of the metacarpal bone to the base of the first phalan.x and sesamoid bones. As they descend they pass a little forward, so that the gi'eater number are inserted in" front of the centre of motion. The dorsal ligament consists of scattered fibres which pass across the joint from one col- lateral Ugament to the other, completing the articular capsule and protecting the synovial sac. The sesamoid bones are two in number, situated on either side of the middle fine, and con- nected together by strong transverse fibres which form the floor of the groove for the long flexor tendon; they are connected with the base of the phalanx and head of the metacarpal bone by strong fibres. Anteriorly they give attachment to the short muscles of the thumb, and pos- teriorly are smooth for the purpose of gliding over the facets. The collateral ligaments are partly inserted into their sides. The arteries and nerves come from the digital branches of the thumb. Relations. — Of the metacarpo-phalangeal joint of the thumb: In front and externally abductor poUicis brevis and superficial head of flexor poUicis brevis. In front and medially oblique and transverse adductors and deep head of flexor poUicis brevis. Directly in front flexor pollicis longus and terminal branches of first volar metacarpal artery. Behind, extensor pollicis brevis and longus tendons. On either side, the dorsal digital vessels and the digital nerves. 276 THE ARTICULATIONS The movements are chiefly flexion and extension, very little side to side movement being permitted, and that only when the joint is slightly bent. Thus this joint more nearly approaches the simple hinge character than the corresponding articulations of the fingers. The thumb gets its freedom of motion at the carpo-metacarpal joint; the fingers get theirs at the meta- carpo-phalangeal, but they are not endowed with so much freedom as the thumb enjoys. Muscles which act upon the metacarpo-phalangeal joint of the thumb. — Flexors. — Flexor poUicis brevis, flexor pollicis longus. Extensors. — Extensor poUicis brevis, extensor pollicis longus. 11. THE INTERPHALANGEAL ARTICULATIONS Class. — Diarthrosis. Subdivision. — Ginglymus . The ligaments which unite the phalanges of the thumb and of the fingers are (in addition to the articular capsule) : — Accessory volar. Collateral. The accessory volar (or glenoid) ligament (fig. 305), sometimes called the sesamoid body, is very firmly connected with the base of the distal bone, and loosely, by means of fibro-areolar tissue, with the head of the proximal one. It blends with the collateral ligaments at the sides, and over it pass the flexor tendons. Occasionally a sesamoid bone is developed in the cartilage of the interphalangeal joint of the thumb. The collateral ligaments (figs. 304 and 305) are strong bands which are attached to the rough depressions on the sides of the upper phalanx, and to the projecting margins of the lower phalanx of each joint. They are tense in every position, and entirely prevent any side to side motion; they are connected posteriorly with the expansion of the extensor tendon. Dorsally (fig. 305) the joint is covered in by the deep surface of the extensor tendon, and a little fibro-areolar tissue extends from the tendon, and thickens the posterior portion of the synovial sac, completing the articular capsule. The synovial membrane is loose and ample, and extends upward a little way along the shaft of the pro.ximal bone. The arteries and nerves come from their respective digital branches. The relations of the interphalangeal joints are the flexor and extensor tendons and the digital vessels and nerves. The movements are limited to flexion and extension. Flexion is more free, and can be continued till one bone is at a right angle to the other, and is most free at the junction of the first and second bones; the second phalanx can be flexed on the first through 110° to 115° when the latter is not flexed. The greater freedom of flexion is due to the greater extent of the articu- lar surface in front of the heads of the proximal bones, and to the direction of the flbres of the collateral hgaments, which pass a little forward to their insertion into the distal bone. The muscles which act upon the interphalangeal joints are the extensors and flexors of the digits. THE ARTICULATIONS OF THE LOWER LIMB The articulations of the lower limb are the following : — 1. The hip-joint. 2. The knee-joint. 3. The tibio-fibular union. 4. The ankle-joint. 5. The tarsal joints. 6. The tarso -metatarsal joints. 7. The intermetatarsal joints. 8. The metatarso-phalangeal joints. 9. The interphalangeal joints. 1. THE HIP-JOINT Class. — Diarthrosis. Subdivision. — Enarthrodia. The hip is the most typical example of a ball-and-socket joint in the body, the round liead of the femur being received into the cup-shaped cavity of the acetab- ulum. Both articular surfaces are coated with cartilage, that covering the head of the femur being thicker above where it has to bear the weight of the body, and thinning out to a mere edge below; the pit for the ligamentum teres is the only part uncoated, but the cartilage is somewhat heaped up around its margin. Covering the acetabulum, the cartilage is horseshoe-shaped, and thicker above than below, being deficient over the depression at the bottom of the acetabulum, THE HIP-JOINT 277 where a mass of fatty tissue — the so-called synovial or Haversian gland — is lodged. The ligaments of the joint are: — Articular capsule. Ligamentum teres. Transverse. . Glenoid lip. The articular capsule is one of the strongest ligaments in the body. It is large and somewhat loose, so that in every position of the body some portion of it is relaxed. At the pelvis it is attached, superiorly, to the base of the anterior inferior iliac spine; curving backward, it becomes blended with the deep surface of the reflected tendon of the rectus Jemoris; posteriorly, it is attached a few millimetres from the acetabular rim ; and below, to the upper edge of the groove between the acetabulum and tuberosity of the ischium. Thus it reaches the Fig. 306. — Anterior View of the Articitlar Capsule op the Hip-joint. ■Tendon of rectus pulled up Tendino-trochanteric band passing between rectus and vastus lateralis Placed on the weak spot of capsule, which is some- times perforated to allow the bursa under psoas to communicate with joint Ilio-f emoral ligament ■Pubo-capsular ligament transverse ligament, being firmly blended with its outer surface, and frequently sends fibres beyond the notch to blend with the obturator membrane. Anteriorly it is attached to the pubis near the obturator notch, to the ilio-pectineal eminence and thence backward to the base of the inferior iliac spine. A thin strong stratum is given off from its superficial aspect behind; this extends beneath the gluteus minimus and small rotators, to be attached above to the dorsum of the ihum higher than the reflected tendon of the rectus, and posteriorly to the ilium and ischium nearly as far as the sciatic notch. As this expansion passes over the long tendon of the rectus, the tendon may be described as being in part contained within the substance of the capsule. At the femur, the capsule is fixed to the anterior portion of the upper border of the great trochanter and to the cervical tubercle. Thence it runs down, the intertrochanteric line as far as the medial border of the femur, where it is on a level with the lower part of the lesser trochanter. It then runs upward and backward along an oblique line about 1.6 cm. (f in.) in front of the lesser trochanter, and con- tinues its ascent along the back of the neck nearly parallel to the intertrochanteric crest, and from 12 to 16 mm. (| to f in.) above it; finally, it passes along the medial side of the trochanteric fossa to reach the anterior superior angle of the great trochanter. 278 THE ARTICULATIONS On laying open the capsule, some of the deeper fibres are seen reflected upward along the neck of the femur, to be attached much nearer the head: these are the retinacula. One corre- sponds to the upper, and another to the lower, part of the intertrochanteric line; a third is seen at the upper and back part of the neck. They form flat bands,which lie on the femoral neck. Superadded to the capsule, and considerably strengthening it, are three auxil- iary bands, whose fibres are intimately blended with, and in fact form part of, the capsule, viz., the ilio-femoral, ischio-capsular, and pubo-capsular ligaments. The ilio-femoral ligament (fig. 306) is the longest, widest, and strongest of the bands. It is of triangular shape, with the apex attached above to a curved line on the iUum immediately below and behind the anterior inferior spine, and its base below to the anterior edge of the greater trochanter and to the spiral line as far as the medial border of the shaft. The highest or most lateral fibres are coarse, almost straight, and shorter than the rest; the most medial fibres are also thick and strong, but obhque. This varying obliquity of the fibres, and their accumula- tion at the borders, explain why this band has been described as the Y-shaped ligament; but it Fig. 307. — Upper Extremity of the Femur (Anterior View), to snow the Relation OP THE Articular Capsule op the Hip-joint (in red) to the Epiphysial Lines. should be noted that the Y is inverted. About the centre of its base, near the femoral attach- ment, is an aperture transmitting an articular twig from the ascending branch of the external circumflex artery. The ischio-capsular ligament (fig. 308) is formed of very strong fibres attached all along the upper border of the groove for the external obturator, and to the ischial margin of the ace- tabulum above the groove. The highest of these incline a little upward as they pass laterally to be fixed to the greater trochanter in front of the insertion of the piriformis tendon, while the other fibres curve more and more upward as they pass laterally to their insertion at the inner side of the trochanteric fossa, blending with the insertion of the external rotator tendons. When the joint is in flexion, these fibres pass in nearly straight lines to their femoral attachment, and spread out uniformly over the head of the femur; but in extension they wind over the back of the femur in a zonular manner [zona orbicularis], embracing the posterior aspect of the neck of the femur. The pubo-capsular (pectineo-femoral) band (fig. 306) is a distinct but narrow set of fibres which are individually less marked than the fibres of the other two bands; they are fixed above to the obturator crest and to the anterior border of the iUo-pectineal eminence, reaching as far down as the pubic end of the acetabular notch. Below, they reach the neck of the femur, and are fixed above and behind the lowermost fibres of the iho-femoral band, with which they blend. THE HIP'JOINT 279 In thickness and strength the capsule varies greatly; thus, if two lines be drawn, one from the anterior inferior spine to the medial border of the femur near the lesser trochanter, and the other from the anterior part of the groove for the Fig. 308. — Posterior View of the Articular Capsule of the Hip-joint. The reflected tendon of the rectus and the triangular ilio- trochanteric ' band Ischio-capsular ligament This is placed on the weak portion of the capsule Fig. 309. — Section through the Hip-joint, showing the Glenoid Lip, Ligamentum Teres, and Retinacula. Ligamentum teres. The upper line is placed on the fem- oral, the lower on the ischial, attach- ment Articular capsule Reflected fibres of capsule (retin- acula) Reflected fibres of capsule external obturator to the trochanteric fossa, all the ligament between these lines on the lateral and upper aspects of the joint is very thick and strong, while that below and to the medial side, except at the narrow pubo-capsular ligament, is 280 THE ARTICULATIONS thin and weak, so that the head of the bone can be seen through it. The capsule is thickest in the course of the iho-femoral ligament, toward the lateral part of which it measures over 6 mm. (J in.). Between the ilio-femoral and ischio-cap- sular ligaments the capsule is very strong, and with it here, near the acetabulum, is incorporated the reflected tendon of the rectus, and here also a triangular band of fibres runs downward and forward to be attached by a narrow insertion to the ridge on the front border of the greater trochanter near the gluteus minimus (the ilio-trochanteric band) (fig. 308). The capsule is strengthened also at this point by a strong band from the under surface of the gluteus minimus, and by the tendino-trochanteric band which passes down from the reflected tendon of the rectus to the vastus lateralis (externus) (fig. 306). This is closely blended with the capsule near the lateral edge of the ilio-femoral Ugament. The thinnest part of the capsule is between the pubo-capsular and ilio-femoral ligaments; this is sometimes perforated, allowing the bursa under the psoas to communicate with the joint. The capsule is also very thin at its attachment to the back of the femoral neck, and again opposite the acetabular notch. Pig. 310.- -Hip-joint after Dividing the Aeticulab Capsule and Disarticulating the Femur. Articular capsule, cut Glenoid lip Articular capsule Ligamentum teres Articular capsule The ligamentum teres (figs. 309 and 310) is an interarticular flat band which extends from the acetabular fossa to the head of the femur, and is usually about 3.7 cm. (1| in.) long. It has two bony attachments, one on either side of the acetabular notch immediately below the articular cartilage, while intermediate fibres spring from the lower surface of the transverse ligament. The ischial portion is the stronger, and has several of its fibres arising outside the cavity, below and in connection with the origin of the transverse ligament, where it is also continuous with the capsule and periosteum of the ischium. At the femur it is fixed to the front part of the depression on the head, and to the cartilage round the margin of the depression. It is covered by a prolongation of synovial membrane, which also covers the cushion of fat in the recess of the acetabulum; the portion of the membrane reflected over the fatty tissue does not cling closely to the round hgament, but forms a triangular fold, the apex of which is at the femur. The transverse ligament (fig. 311) passes across the acetabular notch and converts it into a foramen; it supports part of the glenoid fibro-cartilage, and is connected with the ligamentum teres and the capsule. It is composed of decus- sating fibres, which arise from the margin of the acetabulum on either side of the notch, those coming from the pubis being more superficial, and passing to form THE HIP-JOINT 281 the deep part of the ligament at the ischium, while those superficial at the ischium are deep at the pubis. It thus completes the rim of the acetabulum. The glenoid lip (cotyloid fibro-cartilage) (figs. 309 and 310) is a yellowish- white structure, which deepens the acetabulum by surmounting its margin. It Fig. 311.- -PoETiONS OP Ischium and Pubis, showing the Acetabular Notch and the LiGAMENTUM TeBES ATTACHED OUTSIDE THE ACETABULUM. Transverse ligament ^>^^^ Transverse ligament Ligamentum teres at- tached to ischium out- side the acetabulum varies in strength and thickness, but is stronger at its iliac and ischial portions than elsewhere. Its base is broad and fixed to the bony rim as well as to the articular cartilage of the acetabulum on the inner, and the periosteum on the outer, side of it, and blends inseparably with the transverse ligament which supports it over the acetabular notch. Fig. 312. — The Uppek Extremity op the Femur (Posterior View), to show the Rela- tion OP the Articular Capsule op the Hip-joint (in red) to the Epiphysial Lines. Its free margin is thin; on section it is somewhat lunated, having its outer surface convex and its articular face concave and very smooth in adaptation to the head of the bone, which it tightly embraces a little beyond its greatest circumference. It somewhat contracts the aper- ture of the acetabulum, and retains the head of the femur within its grasp after division of the muscles and capsular hgament. It is covered on both aspects by synovial membrane. 282 THE ARTICULATIONS The synovial membrane lines the capsule and both surfaces of the glenoid lip, and passes over the border of the acetabulum to reach and cover the fatty cushion it contains. The part covering the fatty cushion is unusually thick, and is attached round the edges of the rough bony surface on which the cushion rests. The membrane is loosely reflected off this on to the ligamentum teres, along which it is prolonged to the head of the femur; thus the fibres of the round liga- ment are shut out from the joint cavity. From the capsule the synovial mem- brane is also reflected below on to the neck of the femur, whence it passes over the retinacula to the margin of the articular cartilage. A fold of synovial mem- brane on the under aspect of the neck often conveys to the head of the femur a branch of an artery — generally a branch of the medial circumflex. The arterial supply comes from — (a) the transverse branches of the medial and lateral circumflex arteries; (6) the lateral branch of the obturator sends a branch through the acetabular notch beneath the transverse ligament, which ramifies in the fat at the bottom of the ace- tabulum, and travels down the round ligament to the head of the femur; (c) the inferior branch of the deep division of the superior gluteal; and (d) the inferior gluteal (sciatic) arteries. The branch from the obturator to the ligamentum teres is sometimes very large when the branch from the medial circumflex does not also supply the hgament. The superior and inferior gluteal send several branches through the innominate attachment Fig. 313. — ^Ligamentum Teres, lax in Flexion. of the articular capsule: these anastomose freely beneath the capsule around the outer aspect of the acetabulum, and supply some branches to enter the bone, and others which enter the substance of the glenoid lip. There is quite an arterial crescent upon the posterior and postero- superior portions of the acetabulum; but no vessels are to be seen on the inner aspect of the glenoid lip. The nerve-supply comes from — (a) femoral (anterior crural), (6) anterior division of the obtm-ator, (c) the accessory obturator, and (d) the sacral plexus, by a twig from the nerve to the quadratus femoris, or from the upper part of the great sciatic, or from the lower part of the sacral plexus. Relations. — In front and in contact with the capsule are the psoas bursa, the tendinous part of the psoas magnus, and the Uiacus. StiU more anteriorly and not in contact are the femoral artery, the femoral (anterior crural) nerve, the rectus femoris, the sartorius, and the tensor fasciae latse. Above and in close relation with the capsule are the piriformis, the obturator internus and the gemelli, and the reflected head of the rectus femoris, whilst more superficially lie the gluteus minimus and medius. Behind and in close relation with the capsule are the obturator externus, the gemeUi and obturator internus, and the piriformis. More superficially he the quadratus femoris, the sciatic nerves, and the gluteus maximus. Below the obturator externus, the pectineus, and the medial circumflex artery are in close relation with the capsule. The movements. — The hip-joint, like the shoulder, is a ball-and-socket joint, but with a much more complete socket and a corresponding limitation of movement. Each variety of movement is permitted, viz., flexion, extension, abduction, adduction, circumduction, and rota- tion; and any two or more of these movements not being antagonistic can be combined, i. e., flexion or extension associated with abduction or adduction can be combined with rotation in or out. THE HIP-JOINT 283 It results from the obliquity of tne neck of the femur that the movements of the head in the acetabulum are always more or less of a rotatory character. This is more especially the case during flexion and extension, and two results follow from it. First, the bearing surfaces of the femur and acetabulum preserve their apposition to each other, so that the amount of articular surface of the head in the acetabulum does not sensibly diminish pari passu with the transit of the joint from the extended to the flexed position, as would necessarily be the case if the move- ment of the femoral head, like that of the thigh itself, was simply angular, instead of rotatory and angular. Secondly, as rotation of the head can continue until the ligaments are tight with- out being checked by contact of the neck of the thigh bone with the rim of the acetabulum, flexion of the thigh so far as the joint is concerned is practically unlimited. Flexion is the most important, most frequent, and most extensive movement, and in the dissected limb, before the ligaments are disturbed, can be carried to 160°, and is then checked by the lower fibres of the ischio-capsular ligament. In the living subject simple flexion can continue until checked by the contact of the soft parts at the groin, if the knee be bent; if the knee be straight, flexion of the hip is checked in most persons by the hamstring muscles at nearly a right angle. This is very evident on trying to touch the ground with the fingers without bending the knees, the chief strain being felt at the popliteal space. This is due to the shortness of the] hamstrings. Extension is limited by the ilio-femoral ligament. Fig. 314. — ^Ligamentum Teres, vekt lax in Complete Extension. Abduction and lateral rotation can be performed freely in every position of flexion and extension — abduction being limited by the pubo-capsular hgament; lateral rotation by the ilio-femoral Ugament, especially its medial portion, during extension; but by the lateral portion, as well as by the ligamentum teres, during flexion. Adduction is very limited in the extended thigh on account of the contact with the opposite limb. In the slightly flexed position adduction is more free than in extension, and is then limited by the lateral fibres of the ilio-femoral band and the superior portion of the capsule. In flexion the range is still greater, and limited by the ischio-capsular hgament, the hgamentum teres being also rendered nearly tight. Medial rotation in the extended position is limited by the lower fibres of the ilio-femoral ligament; and in flexion by the ischio-capsular ligament and the portion of the capsule between it and the ilio-femoral band. The ilio-femoral band also prevents the tendency of the trunk to roU backward on the thigh bones in the erect posture, and so does away with the necessity for muscular power for this pur- pose; it is put on stretch in the stand-at-ease position. The ligamentum teres is of little use in resisting violence or in imparting strength to the joint. It assists in checking lateral rotation, and adduction during flexion. A ligament can only be of use when it is tight, and it was found by trephining the bottom of the acetabulum, removing the fat, and threading a piece of whipcord round the ligament, that the ligament was slack in simple flexion, and very loose in complete extension, but that its most slack condition was in abduction. It is tightest in flexion combined with adduction and lateral rotation and almost as tight in flexion with lateral rotation alone, and in flexion with adduction alone (flgs. 313-315). Muscles which act upon the hip-joint. — Flexors. — The psoas and iliacus, the rectus femoris, the pectineus, the adductors, the sartorius, the tensor fasciae latse, and the gluteus medius. 284 THE ARTICULATIONS Fig. 315. — Ligamentum Teres, drawn Tight in I'lexion Combined with Lateral Rotation and Adduction. Extensors. — The gluteus maximus, the posterior fibres of the glutei medius and miQimus, the biceps, the semitendinosus, the semimembranosus, and the ischial fibres of the adductor magnus; also (slightly) the piriformis, obturator internusand gemelli. Abductors. — Gluteus maximus (upper fibres), tensor fasciae latae, gluteus medius, gluteus minimus, and, when the joint is flexed, the pii-iformis, obturator internus, the gemelli, and the sartorius also become abductors. Adductors. — Adduotores magnus, longus, brevis, and minimus, semitendinosus, biceps^ the gracilis, the peotineus, the quadratus femoris, and the lower fibres of the gluteus maxunus. Medial rotators. — Psoas (slightly), adductor magnus, semimembranosus, the anterior fibres of the gluteus medius and minimus, and the tensor fascise latae. Lateral rotators. — Gluteus maximus, posterior fibres of gluteus medius and minimus, the adductors, obturator extemus, quadratus femoris, obturator internus, the gemelli, and the piriformis when the joint is extended. 2. THE KNEE-JOINT Class. — Diarthrosis. Subdivision. — Ginglymus. The knee is the largest joint in the body. It is rightly described as a gingly- moid joint, but there is also an arthrodial element; for, in addition to flexion and extension, there is a sliding backward and forward of the tibia upon the femoral condyles, as well as slight rotation round a vertical axis. It is one of the most superficial, and, as far as adaptation of the bony surfaces goes, one of the weakest joints, for in no position are the bones in more than partial contact. Its strength lies in the number, size, and arrangement of the ligaments, and the powerful muscles and fascial expansions which pass over the articulation and enable it to withstand the leverage of the two longest bones in the bodj\ It may be said'to consist of two articulations with a common synovial membrane — the patello- femoral and the tibio-femoral, the latter being double. It is composed of the condyles and trochlear surface of the femur, the condyles of the tibia, and the patella, united by the following ligaments, which may be divided into an external and internal set: — External (1) Fibrous expansion of the extensors. (2) Articular capsule. (3) Oblique popliteal ligament. (4) Fibular collateral. (5) Tibial collateral. (6) Ligamentum patellae Internal (1) Anterior crucial. (2) Posterior crucial. (3) Medial meniscus. (4) Lateral meniscus. (5) Coronary. (6) Transverse. THE KNEE-JOINT 285 External Ligaments Superficial to the fibrous expansion of the quadriceps extensor tendons the fascia lata of the thigh covers the front and sides of the knee-joint. The deep fascia of the thigh, as it descends to its attachment to the tuberosity and oblique lines of the tibia, not only overhes but blends with the fibrous expansion of the extensor tendons. The oblique lines of the tibia curve upward and backward from the tuberosity on each side to the postero-lateral part of the condyles. The process of fascia attached to the lateral ridge of the tibia and to the head of the fibula descends from the tensor fascise latas and is very thick and strong. It is firmly blended with the tendinous fibres of the vastus laterahs. The fascia lata, on the medial side of the patella, besides being attached to the medial oblique ridge of the tibia, sends some longitudinal fibres lower down to become blended with the fibrous expansion of the sartorius. The fascia is much thinner on the medial side of the patella than on the lateral, and blends much less with the tendon of the vastus niedialis than the lateral part of the fascia does with the vastus lateralis. A thin layer of the fascia lata in the form of transverse or aroi- form fibres passes over the front of the joint. These fibres are speciaUy well marked over the ligamentum patellae, and blend here with the central portion of the quadriceps extensor fibres. Fig. 316. — The Lower Extremity of the Femur (Posterior View), to show the Rela- tion OP the Articular Capsule of the Knee-joint (in red) to the Epiphysial Line. The fibrous expansion of the extensor tendons consists — (1) of a central portion, densely thick and strong, 3.7 cm. (1| in.) broad, which is inserted into the anterior two-thirds of the upper border of the patella, many of its superficial fibres passing over the subcutaneous surface of the bone into the ligamentum patellfe; (2) of two side portions thinner, but strong. The side portions are inserted into the patella along its upper border on either side of the central portion and also into its medial and lateral borders, nearer the anterior than the posterior surface, as low down as the attachment of the ligamentum patellar; passing thence along the sides of the ligamentum patelte to the tibia, they are attached to the obhque lines which extend from the tuberosity to the medial and lateral condyles, and reach as far as the tibial and fibular collateral ligaments. On the lateral side, the fibres blend with the ilio-tibial band of the fascia lata, and on the medial they extend below the oblique line to blend with the periosteum of the shaft. Thus there is a large hood spread over the whole of the front of the joint, investing the patella, and reaching from the sides of the ligamentum pateUse to the collateral ligaments, at- tached below to the tibia, and separated everywhere from the synovial membrane by a layer ■of fatty tissue. The ligamentum patellae (fig. 320) is the continuation in line of the central portion of the conjoined tendon, some fibres of which are prolonged over the front 286 THE ARTICULATIONS of the patella into the ligament. It is an extremely strong, flat band, attached above to the lower border of the patella; below, it is fixed to the lower part of the tuberosity and upper part of the crest of the tibia, somewhat obliquely, being prolonged downward further on the lateral side, so that this border is fully 2.5 cm. (1 in.) longer than the medial, which measures 6.7 cm. {2\ in.) in length. Behind, it is in contact with a mass of fat which separates it from the synovial membrane, and a small bursa intervenes between it and the head of the tibia. In front, a large bursa separates it from the subcutaneous tissue, and at the sides it is continuous with the fibrous expansion of the extensors. The tibial (internal) collateral ligament (fig. 317) is a strong, flat band, which extends from the depression on the tubercle on the medial side of the medial Fig. 317. — Posterior View op the Knee-joint. Plantaris Lateral head of gastrocnemius Fibular collateral ligament anterior portion Posterior part of fibular collateral ligament Tendon of popliteus Tendon of biceps Superior posterior tibio- fibular ligament Tendon of adductor magaus Medial head of gastrocnemius Tendon of semimembra- nosus with its slip to thicken the oblique pop- liteal ligament Tibial collateral ligament epicondyle of the femur, to the medial border and medial surface of the shaft of the tibia, 3.7 cm. (1| in.) below the condyle. It is 8.7 cm. (3| in.) long, well defined anteriorly, where it blends with the expansion of the conjoined extensor tendons; but not so well defined posteriorly, where it merges into the oblique popliteal ligament. Some of the lower fibres blend with the descending portion of the semimembranosus tendon. Its deep surface is firmly adherent to the edge of the medial meniscus and coronary ligament, while part of the semimembranosus tendon and inferior medial articular vessels and nerve pass between it and the bone. Superficially, a bursa separates it from the tendons of the gracilis and semitendinosus muscles and from the aponeurosis of the sartorius muscle. The fibular (external) collateral ligament (fig. 317) consists of two portions: the anterior, which is the longer and better marked, is a strong, rounded cord, about 5 cm. (2 in.) long, attached above to the tubercle on the lateral side of the lateral epicondyle of the femur, just below and in front of the origin of the lateral head of the gastrocnemius, whilst the tendon of the popliteus arises from the groove below and in front of it. Below, it is fixed to the middle of the lateral surface of the head of the fibula, 1.25 cm. (J) in. or more anterior to the apex. Superficially is the tendon of the biceps, which sphts to embrace its lower extremity; while beneath it pass the popliteus tendon in its sheath, and the inferior lateral articular vessels and nerve. THE KNEE-JOINT 287 Some fibres of the peroneus longus occasionally arise from the lower end of the ligament. The posterior portion is 8 mm. (\ in.) behind the anterior. It is broader and less defined; fixed below to the apex of the fibula, it inclines upward and somewhat backward, and ties down the popliteus against the lateral condyle of the tibia, blending beneath the lateral head of the gastrocnemius with the oblique popliteal ligament of the knee, of which it is really a portion. The oblique popliteal ligament or ligamentum Winslowii (fig. 317) is a broad dense structure of interlacing fibres, with large orifices for vessels and nerves. It is attached above to the femur close to the articular margins of the condyles, stretching across the upper margin of the intercondyloid fossa, to which it is connected by fibro-fatty tissue; it thus reaches across from the tibial to the fibular collateral ligaments. Below, it is fixed to the border of the lateral condyle of the tibia, to the bone just below the posterior intercondyloid notch, and to the shaft of the tibia below the medial condyle, blending with the descending slip of the semimembranosus and tibial collateral ligament. Superficially, an oblique fasciculus from the semimembranosus runs across the centre, passing upward and laterally from near the back part of the medial condyle of the tibia to the lateral Fig. 318. — The Lower Extremity op the Femur (Anterior View) to show the Rela- tion OP THE Articular Capsule op the Knee-joint (in red) to the Epiphysial Line. epicondyle of the femur, where it joins the lateral head of the gastrocnemius, a sesamoid plate being sometimes developed at the point of junction. This slip greatly strengthens the oblique pophteal ligament, of which, if not the chief constituent, it is at least a very important part. Its deep surface is closely connected with the semilunar menisci (especially the medial) and coronary ligaments, and in the interval between the cartilages with the posterior crucial ligament and fibro-fatty tissue within the joint. Superficially it forms part of the floor of the popHteal space. A special band, the arcuate ligament, is sometimes found extending from the lateral epicondyle to the oblique ligament. The articular capsule (fig. 319) is thin but strong, covering the synovial membrane, and looking like a loose sac. It is attached to the femur near the articular margin on the medial side, but further away on the lateral; it passes beneath the fibular collateral ligament to join the sheath of the popliteus. Medi- ally it joins the tibial collateral ligament. Below, it is fixed to the upper as well as the medial and lateral borders of the patella and the anterior border of the head of the tibia. It is strengthened superficially between the femur and patella by an expansion from the articularis genu {suh-crureus) and is separated from 288 THE ARTICULATIONS the fibrous expansion of the extensor tendon by a layer of fatty tissue. The synovial membrane lines its deep surface, and holds it against the borders of the semilunar menisci; it is also attached to the coronary ligaments. Internal Ligaments The anterior crucial ligament (figs. 319 and 320) is strong and cord-like. It is attached to the medial half of the fossa in front of the intercondyloid eminence of the tibia, and to the lateral border of the medial articular facet as far back as the medial intercondyloid tubercle. It passes upward, backward, and laterally to the back part of the medial surface of the lateral condyle of the femur. To Fig. 319. — Anterior View of the Internal Ligaments op the Knee-joint. Aperture leading into the bursa beneath the quadri ' ceps extensor Attachment of articular, capsule to femur Posterior crucial ligament Medial meniscus Transverse ligament Coronary ligament Anterior crucial ligament' Lateral Coronary ligament the tibia, it is fixed behind the anterior extremity of the medial semilunar menis- cus. Behind and to the lateral side it has the anterior extremity of the lateral meniscus, a few fibres of which blend with the lateral edge of the ligament. Its anterior fibres at the tibial end are strongest and longest; being fixed highest on the femur; while the posterior, springing from the intercondyloid eminence, are shorter and more oblique. Near the spine, a slip is sometimes given off to the posterior crucial hgament. The posterior crucial ligament (fig. 319, 320, and 322) is stronger and less oblique than the anterior. It is fixed below to the greater portion of the fossa behind the intercondyloid eminence of the tibia, especially the lateral and pos- terior portion, and then medially along the posterior intercondyloid fossa; being joined by fibres which arise between the intercondyloid tubercles, it ascends to the anterior part of the lateral surface of the medial condyle of the femur, having a wide crescentic attachment 1.5 cm. (f in.) in extent just above the articular surface. Behind, it is connected at the tibia directly with the posterior Ugament, and a little higher up by means of a quantity of interposed areolar tissue. In front it rests upon the posterior THE KNEE-JOINT 289 horn of the medial semilunar meniscus, and receives a large slip from the lateral meniscus, which ascends along it, either in front or behind, to the femur; higher up in front it is connected with the anterior crucial hgament. Until they rise above the intercondyloid eminence of the tibia the two crucial ligaments are closely bound together, so that no interspace exists between their tibial attachments and the point of decussation; the only space between them is therefore a v-shaped one correspond- ing to the upper half of their x-shaped arrangement, and this is a mere chink in the undissected state, and can be seen from the front only, owing to the fatty tissue beneath the synovial mem- brane which sm-rounds their femoral attachment. The interarticular menisci or semilunar fibro-cartilages (figs. 319 and 320) are two crescentic discs resting upon tlie circumferential portions of the articular facets of the tibia, and moving with the tibia upon the femur. They some- what deepen the tibial articular surfaces, and are dense and compact in structure, becoming looser and more fibrous near their extremities, where they are firmly fixed in front of and behind the intercondyloid eminence of the tibia. The circumferential border of each is convex, thick, and somewhat loosely attached to the borders of the condyles of the tibia by the coronary ligaments and the re- flexion of the synovial membrane. The inner border is concave, thin, and free. Half an inch (1.3 cm.) broad at the widest part, they taper somewhat toward their Fig. 320. — Strtjctuhes lying on the Head op the Tibia. (Right knee.) Ligamentum pateUee yiTTTiTT nt J'ili] Transverse ligament Lateral meniscus Anterior crucial ligament Medial meniscus — W- \ Posterior crucial ligament Tendon of biceps Fibulai* collateral ligament extremities, and cover rather less than two-thirds of the articular facets of the tibia. Their upper surfaces are slightly concave, and fit on to the femoral condyles, while the lower are flat and rest on the head of the tibia; both surfaces are smooth and covered by synovial membrane. The lateral meniscus (fig. 320) is nearly circular in form and less firmly fixed than the medial, and consequently slides more freely upon the tibia. Its anterior cornu is attached to a narrow depression along the lateral articular facet, just in front of the lateral intercondyloid tubercle of the tibia, close to, and on the lateral side of, the anterior crucial hgament; a small slip from the cornu is often fixed to the tibia in front of the crucial ligament. The posterior cornu is firmly attached to the tibia behind the lateral intercondyloid tubercle, blending with the posterior crucial ligament, and giving off a well-marked fasciculus, which runs up along the anterior border of the ligament to be attached to the femur (ligament of Wrisberg). It also sends a narrow slip into the back part of the anterior crucial ligament. Its outer border is grooved toward its posterior part by the popliteus tendon, which is held to it by fibrous tissue and synovial membrane, and separates it from the fibular collateral hgament. From its anterior border is given off the transverse hgament. The medial meniscus (fig. 320) is a segment of a larger circle than the lateral, and has an outline more oval than cuxular. Its anterior cornu is wide, and has a broad and oblique attach- ment to the anterior margin of the head of the tibia. It reaches from the margin of the condyle toward the middle of the fossa in front of the intercondyloid eminence, being altogether in front of the anterior crucial ligament. The posterior cornu is firmly fixed by a broad insertion in an antero-posterior line along the medial side of the posterior intercondyloid fossa, from the medial tubercle to the posterior margin of the head of the tibia. Its convex border is connected with the tibial collateral ligament and the seviimeinhrmiosus tendon. The transverse ligament (figs. 319 and 320) is a rounded, slender, short cord, which extends from the convex border of the lateral meniscus to the concave border or anterior cornu of the medial, near which it is sometimes attached to the bone. It is an accessory band of the lateral meniscus, and is situated beneath the synovial membrane. 290 THE ARTICULATIONS The coronary ligaments (fig. 319) connect the margins of the semilunar discs with the head of the tibia. The lateral is much more lax than the medial, permitting the lateral disc to change its position more freely than the medial. They are not in reality separate structures, but consist of fibres of the several surrounding ligaments of the knee-joint which become attached to the margins of the discs as they pass over them. The synovial membrane (fig. 324) of the knee forms the largest synovial sac in the body. Bulging upward from the patella, it follows the capsule of the joint into a large cul-de-sac beneath the tendon of the extensor muscles on the front of the femur. It reaches some distance beyond the articular surface of the bone, and communicates very frequently with a large bursa interposed between the tendon and the femur above the line of attachment of the articular capsule. After investing the circumference of the lower end of the femur, it is reflected upon the Fig. 321. — The Uppee Extremity of the Tibia (Anterior View), to show the Rela- tion OP THE Articular Capsule op the Knee-joint (in red) to the Epiphysial Line. fibrous envelope of the joint formed by the capsular, posterior, and collateral ligaments. The synovial membrane covers a great portion of the crucial ligaments, but leaves uncovered the back of the posterior crucial where the latter is connected with the posterior hgament, and the lower part of both crucial ligaments where they are united. Thus the hgaments are com- pletely shut out of the synovial cavity. Along the fibrous envelope the synovial membrane is conducted down to the semilunar menisci, over both surfaces of which it passes, and is reflected off the under surface on to the coronary ligaments, and thence down to the head of the tibia, around the circumference of which it extends a short way. It dips down between the external meniscus and the head of the tibia as low as the superior tibio-fibular ligament, reaching inward nearly as far as the intercondyloid notch, and forming a bursa for the play of the popliteal tendon. At the back of the joint two pouches are prolonged beneath the muscles, one on each side between the condyle of the femur and the origin of the gastrocnemius. Large processes of syno- vial membrane also project into the joint, and being occupied by fat serve as padding to fill up spaces. The chief of these processes, the patellar synovial fold (ligamentum mucosum) (figs. 322 and 324), springs from the infrapatellar fatty mass. This so-called ligament is the central portion of the large process of synovial membrane, of which the alar folds form the free margins. It extends from the fatty mass, below the patella, backward and upward to the intercondyloid notch of the femur, where it is attached in front of the anterior crucial, and lateral to the poste- rior crucial ligament. Near the femur it is thin and transparent, consisting of a double fold of synovial membrane, but near the patella it contains some fatty tissue. Its anterior or upper edge ia free, and fully 2.6 cm. (an inch) long; the posterior or lower edge is half the length, and is attached to the crucial ligaments above, but is free below. THE KNEE-JOINT 291 Passing backward from the capsule on each side of the patella is a prominent crescentic fold formed by reduplications of the synovial membrane — these are the alar folds (fig. 3?2). Their free margins are concave and thin, and are lost below in the patellar fold. There is a slight fossa above and another below each Ligament. Fig. 322.— Anterior View of the Knee-joint, showing the Stnoviai, Ligaments. (Anterior portion of capsule with the extensor tendon thrown downward.) Posterior crucial ligament Synovial pouch under tendon quadriceps femoris Fig. 323. — The Upper Extremity op the Tibia (Posterior View), to show the Relation OF THE Articular Capsule op the Knee-joint (in red) to the Epiphysial Line. The arterial supply is derived from the art. genu suprema (anastomotica) ; the superior ajid inferior medial and lateral articular; the medial articular; the descending branch of the lateral circumflex; the anterior recurrent branch from the anterior tibial; and the posterior tibial recurrent. 292 THE ARTICULATIONS The nerve-supply comes from the great sciatic, femoral, and obturator sources. The great sciatic pves off the tibial and common peroneal; the tibial sends tAvo, sometimes three bi'anches — one with the medial articular artery; one with the inferior medial, and sometimes one with the superior medial articular artery; the common peroneal gives a branch which accom- panies the superior, and another which accompanies the inferior articular artery, and a recurrent branch which follows the course of the anterior recm-rent branch of the anterior tibial artery. The femoral sends an articular branch from the nerve to the vastus lateralis; a second from the nerve to the vastus mediaiis; and sometimes a third from that to the vastus intermedins. Thus there are three articular twigs to the knee derived from the muscular branches of the femoral. The obturator by its deep division sends a branch through the adductor magnus on to the pop- liteal artery, which enters the joint posteriorly. Fig. 324. — Sagittal Section of the Knee-joint. (The bones are somewhat drawn apart.) Fatty tissue Opening in synovial mem- brane behind crucial ligament leading into inner half of joint Synovial membrane re- flectedoff crucialligaments Cut end of anterior crucial ligament Posterior crucial ligament Oblique popliteal ligament Muscular fibres of quadriceps femoris (,. Extension of synovial sac of knee I \\\ upon femur \V.\\ .Tendon of quadriceps femoris, 'H\ l\^ forming fibrous capsule of joint Patella Pre-patellar bursa Condyle of femur ^medial) Patellar synovial fold Fatty tissue between ligamentum patellas and synovial sac Bursa beneath ligamentum patellas Relations. — Anteriorly and at the sides the knee-joint is merely covered and protectedlby skin, fascia, and the tendinous expansions of the quadriceps extensor muscle. Laterally and posteriorly it is crossed by the biceps tendon. Medially and posteriorly lie the sartorius and the tendons of the gracilis and seinitendinosus muscles. Posteriorly it is in relation with the popliteal vessels and nerves, the semimembranosus, the two heads of the gastrocnemius, and the plantaris. The tendon of the popliteus pierces the capsule behind and medial to the biceps tendon. The movements which occur at the knee-joint are flexion and extension, with some slight amount of rotation in the bent position. These movements are not so simple as the correspond- ing ones at the elbow, for the knee is not a simple hinge joint. The movements of rotation instead of occurring between tibia and fibula, as between radius and ulna, are movements of the tibia with the fibula upon the condyles of the femur. The knee differs from a true hinge joint, like the elbow or ankle, in the following par- ticulars:— 1. The points of contact of the femur with the tibia are constantly changing. Thus, in THE KNEE-JOINT 293 the flexed position, the posterior part of the articular surface of the tibia is in contact with the rounded bacli part of the femoral condyles; in the semiflexed position the middle parts of the tibial facets Articulate with the anterior rounded part of the condyles; while in the fully extended position the anterior and middle parts of the tibial facets are in contact with the anterior flat- tened portion of the condyles. So with the patella: in extreme flexion the medial articular facet rests on the lateral part of the medial condyle of the femur; in flexion the upper pair of facets rests on the lower part of the trochlear surface of the femur; in mid-flexion the middle pan- rests on the middle of the trochlear surface; while in extension the lower pair of facets on the patella rests on the upper portion of the trochlear surface of the femur. Fig. 325. — The Collateral Ligaments op the Knee in Flexion and Extension. This difference may be described as the shifting of the points of contact of the articular surface. 2. It differs from a true hinge in that, in passing from a state of extension to one of flexion, the tibia does not revolve round a single transverse axis drawn through the lower end of the femur, as the ulna does round the lower end of the humerus. The articular surface of the tibia slides forward in e.xtension and backward in flexion; thus the axis round which the tibia revolves upon the femur is a shifting one, as is seen by reference to fig. 325, B, C, D. 3. Another point of difference is that extension is accompanied by lateral rotation, and flexion by medial rotation. This rotation occurs round a vertical axis drawn through the middle of the lateral condyle of the femur and the lateral condyle of the tibia, and is most marked at the termination of extension and at the commencement of flexion. This rotation of the leg at the knee is a true rotation about a vertical axis, and thus differs from the obliquity of the flexion 294 THE ARTICULATIONS and extension movements at the elbow wMcIi is due to the oblique direction of the articular surfaices of the bones. 4. The antero-posterior spiral curve of the femoral condyles is such that the anterior part is an arc of a greater circle than the posterior; hence certain ligaments which are tightened during Fig. 326. — Section op Knee, showing Crucial Ligaments in Extension. Anterior crucial ligament Intercondyloid eminence of tibia Transverse ligament Slip from lateral meniscus to femur (ligament of Wrisberg) Posterior crucial ligament Latetal meniscus Coronary ligament Anterior tibio-fibular ligament extension are relaxed during flexion, and thereby a considerable amount of rotatory movement is- permitted in the flexed position. The axis of this rotation is vertical, and passes through the medial intercondyloid tubercle of the tibia, so that the lateral condyle moves in the arc of a larger circle than does the medial, and is therefore required to move more freely and easily; Fig. 327. — Crucial Ligaments in Flexion. Posterior crucial Anterior crucial Medial meniscus Transverse ligament Slip from lateral cartilage to femur Lateral meniscus Coronary ligament Anterior tibio-fibular ligament hence the shape of the lateral articular facet and the loose connection of the lateral meniscus which is adapted to it. In extension, all the ligaments are on the stretch with the exception of the ligamentum patellae and front of the capsule. Extension is checked by both the crucial ligaments and the cSlateral ligaments (figs. 325, A, B, and 326). THE KNEE-JOINT 295 In flexion the ligamentum patellae and anterior portion of the capsule are on the stretch; so also is the posterior crucial in extreme flexion, though it is not quite tight in the semiflexed state of the joint. All the other ligaments are relaxed (fig. 325, C, D), although the relaxation of the anterior crucial ligament is slight in extreme flexion (fig. 327). Flexion is only checked during hfe by the contact of the soft parts, i. e., the calf with the back of the thigh. Rotation medially is checked by the anterior crucial ligament; the collateral ligaments being loose. Rotation laterally is checked by the collateral Ugaments; the crucial hgaments have no controlling effect on it, as they are untwisted by it. Sliding movements are checked by the crucial and collateral ligaments — sliding forward especially by the anterior, and sliding backward by the posterior crucial. Muscles which act upon the knee-joint. — Flexors. — Biceps, semimembranosus, semiten- dinosus, sartorius, gastrocnemius, plantaris, and pophteus. Extensor. — Quadriceps extensor. Medial Bolators. — Sartorius, gracilis, semitendinosus, semimembranosus, popliteus. Lateral Rotator. — Biceps. 3. THE TIBIO-FIBULAR UNION The fibula is connected with the tibia throughout its length by an interosseous membrane, and at the upper and lower extremities by means of two joints. Very little movement is permitted between the two bones. (a) The superior tibio-fibular joint. (6) The middle tibio-fibular union. (c) The inferior tibio-fibular joint. (a) The Superior Tibio-fibular Joint Class. — Diarthrosis. Subdivision. — Arthrodia. The superior tibio-fibular joint is about 6 mm. (J in.) below, and quite distinct from, the knee at its upper and anterior part; but at its posterior and superior aspect, where the border of the lateral condyle of the tibia is bevelled by the pop- liteus muscle, the joint is in the closest proximity to the bursa beneath the tendon of that muscle, and is only separated from the knee-joint by a thin septum of areolar tissue. There is often a communication between the synovial cavities of the two joints. The ligaments uniting the bones are: — Articular capsule. Anterior tibio-fibular. Posterior tibio-fibular. The articular capsule is a well-marked fibro-areolar structure; it is attached close round the articular margins of the tibia and fibula. In front it is shut off completely from the knee-joint by the capsule of the knee and the coronary liga- ment; but behind, it is often very thin, and may communicate with the bursa under the pophteus tendon. The anterior tibio-fibular (capitular) ligament (fig. 326) consists of a few fibres which pass upward and medially from the fibula to the tibia. It lies beneath the anterior portion of the tendon of the biceps. The posterior tibio-fibular (capitular) ligament (fig. 317) consists of a few fibres which pass upward and medially between the adjacent bones, from the head of the fibula to the lateral condyle of the tibia. The superior interosseous ligament consists of a mass of dense yellow fibroareolar tissue, binding the opposed surfaces of the bones together for 2 cm. (f in.) below the articular facets. It is continuous with the interosseous membrane along the tibia. The biceps tendon is divided by the fibular collateral ligament of the knee; of the two divisions the anterior is by far the stronger, and is inserted into the lateral condyle of the tibia as well as to the front of the head of the fibula, and thus the muscle, acting on both bones, tends to brace them more tightly together; indeed, it holds the bones strongly together after all other connections have been severed. The synovial membrane which lines the joint sometimes communicates with the knee-joint through the bursa beneath the popliteus tendon. The arterial supply is from the inferior lateral articular and recurrent tibial arteries. The nerve-supply is from the inferior lateral articular, and also from the recurrent branch of the common peroneal. Relations. — In front, the upper ends of the tibialis anterior, the extensor digitorum longus, and the peroneus longus. Behind, the tendon of the popliteus overlapped by the lateral head of the gastrocnemius. Laterally, the biceps tendon and the common peroneal nerve. Below and medially, the anterior tibial vessels. The movements are but slight, and consist merely of a gliding of the two bones upon each other. The joint is so constructed that the fibula gives some support to the tibia in transmitting 296 THE ARTICULATIONS the weight to the foot. The articular facet of the tibia overhangs, and is received upon the articular facet of the head of the fibula in an oblique plane. This joint allows of slight yielding of the lateral malleolus during flexion and extension of the ankle-joint, the whole fibula gUding slightly upward in flexion, and downward in extension, of the anlde. (6) The Middle Tibio-fibular Union Class. — Synarthrosis. Subdivision. — Syndesmosis. The interosseous membrane is attached along the lateral border of the tibia and the interosseous border of the fibula. It is deficient above for about 2.5 cm. (1 in.) or more, measured from the under aspect of the superior joint. Its upper border is concave, and over it pass the anterior tibial vessels. The membrane consists of a thin aponeurotic and translucent lamina, formed of oblique fine fibres, some of which run from the tibia to the fibula, and some from the fibula to the tibia, but all are inchned downward. They are best marked at their attachment to the bones, and gradually grow denser and thicker as they approach the inferior interosseous ligament. The Fig. 328. — Lower Ends op Left Tebia and Fibula, showing the Ligaments. The synovial fold between these bones has been removed to show the transverse ligament forming part of the capsule of the joint, and the deeper fibres of the anterior lateral malleolar hgament which come into contact with the talus. (From a dissection by Mr. W. Pearson, of the Royal College of Surgeons' Museum.) Deltoid ligament Anterior lateral malle- _ / olar ligament Lateral ligament Transverse ligament Posterior lateral malle- olar ligament chief use of the membrane is to afford a surface for the origin of muscles. It is continuous below with the inferior interosseous ligament. In front of the interosseous membrane lie the tibialis anterior, the extensor digitorum longus, the extensor hallucis longus, and the anterior tibial vessels and nerves. Behind it is in relation with the tibialis posterior, the flexor hallucis longus, and the peroneal artery. (c) The Inferior Tibio-fibular Articulation Class. — Diarihrosis. Subdivision. — Arthrodia. This junction is formed by the lower ends of the tibia and fibula. The rough triangular surface on each of these bones formed by the bifurcation of their interosseous lines is closely and firmly united by the inferior interosseous liga- ment. The fibula is in actual contact with the tibia by an articular facet, which is small in size, crescentic in shape, and continuous with the articular facet of the malleolus. The ligaments which unite the bones are: — • 1. Anterior lateral malleolar ligament. 2. Posterior lateral malleolar ligament. 3. Transverse ligament. 4. Inferior interosseous ligament. The anterior lateral malleolar ligament (anterior inferior tibio-fibular liga- ment) (figs. 328 and 334) is a strong triangular band about 2 cm. (f in.) wide, and is attached to the lower extremity of the tibia at its anterior and lateral angle, close to the margin of the facet for the talus and passes downward and THE ANKLE-JOINT 297 laterally to the anterior border and contiguous surface of the lower end of the fibula, some fibres passing along the edge nearly as far as the origin of the anterior talo-fibular ligament. The fibres increase in length from above downward. In front it is in relation with the peroneus tertius and deep fascia of the leg, and gives origin to fibres of the anterior Kgament of the ankle-joint. Behind, it Lies in contact with the interosseous Ugament, and comes into con- tact with the articxilar surface of the talus (see figs. 328 and 329). The posterior lateral malleolar ligament (figs. 328 and 334) is very similar to the anterior, extending from the posterior and lateral angle of the lower end of the tibia downward and laterally to the lowest 1.5 cm. (| in.) of the border separating the medial from the posterior surface of the shaft of the fibula, and to the upper part of the posterior border of the lateral malleolus. It is in relation in front with the interosseous ligament; below, it touches the transverse ligament. The inferior interosseous ligament is a dense mass of short, felt-like fibres, passing trans- versely between and firmly uniting the opposed rough triangular surfaces at the lower ends of the Fig. 329. — Right Ankle-joint, showing the Ligaments. (From dissection by Mr. W. Pearson, of the Royal College of Surgeons' Museum.) Superficial fibres of anterior lateral malleolar ligament Deep fibres of anterior lateral. malleolar Ugament Anterior talo-fibular ligament — Posterior talo-fibular ligament — Calcaneo-fibular ligament — Deltoid ligament tibia and fibula, except for 1 cm. (f in.) at the extremity, where there is a synovial cavity. It extends from the anterior to the posterior lateral malleolar hgaments, reaching upward 4 cm. (l-J- in.) in front, but only half this height behind. The transverse ligament (fig. 331) is a strong rounded band, attached to nearly the whole length of the inferior border of the posterior svu-face of the tibia, just above the articular facet for the talus. It then inclines a little forward and downward, to be attached to the medial surface of the lateral malleolus, just above the fossa, and into the upper part of the fossa itself. The synovial membrane is continuous with that of the ankle-joint; it projects upward between the bones beyond their articular facets as high as the inferior interosseous ligament. The nerve-supply is the same as that of the ankle-joint; the arterial supply is from the peroneal and the anterior peroneal, and sometimes from the anterior tibial, or its lateral malleolar branch. Relations. — In front of the inferior tibio-fibular joint are the anterior peroneal artery and the tendon of the peroneus tertius, and behind it are the posterior peroneal artery and the pad of fat which Ues La front of the tendo Achillis. The movement permitted at this joint is a mere gliding, chiefly in an upward and downward direction, of the fibula on the tibia. The bones are firmly braced together and yet form a slightly yielding arch, thus allowing a slight side to side expansion during extreme flexion, when the broad part of the talus is brought under the arch, by the upward gliding of the fibula on the tibia. To this end the direction of the fibres of the lateral malleolar ligaments is downward from tibia to fibula. This mechanical arrangement secures perfect contact of the articular surfaces of the ankle-joint in all positions of the foot. 4. THE ANKLE-JOINT Class. — Diarthrosis. Subdivision. — Ginglymus. The ankle [articulatio talo-cruralis] is a perfect ginglymus or hinge joint. The bones which enter into its formation are: the lower extremity and medial malleolus of the tibia, and the lateral malleolus of the fibula, above; and the upper 298 THE ARTICULATIONS and lateral articular surfaces of the talus (astragalus) below, (supplementing the articular capsule) uniting the bones are: — The ligaments Anterior. Posterior. Deltoid. Lateral ligament. The anterior ligament (fig. 334) is a thin, membranous structure, which completes the capsule in front of the joint. It is attached above to the anterior border of the medial malleolus, to a crest of bone just above the transverse groove at the lower end of the tibia, to the anterior lateral malleolar ligament, and to the anterior border of the lateral malleolus. Below, it is attached to the rough upper surface of the neck of the talus (astragalus). Medially it is thicker, and is fixed to the talus close to the facet for the medial malleolus, being continuous with the deltoid ligament, and passing forward to blend with the talo-navicular ligament. Laterally it is attached to the talus, just below and in front of the angle between the superior and lateral facets, close to their edges, and joins the anterior talo- fibular ligament. It is in relation, in front with the tibialis anterior muscle, the anterior tibial vessels and nerve, the extensor tendons 0/ the toes, and the peroneus tertius; and behind with a mass of fat and syno- vial membrane. Fig. 330. — Medial View of the Ankle and the Tarsus, showing the Groove for the Tendon of the Tibialis Posterior. Plantar calcaneo-cuboid ligament Long plantar ligament The posterior ligament (fig. 331) is a very thin and disconnected membranous structure, connected above with the lateral malleolus, medial to the peroneal groove; to the posterior margin of the lower end of the tibia lateral to the groove for the tibialis posterior; and to the posterior lateral malleolar ligament. Below, it is attached to the posterior surface of the talus from the deltoid to the lateral ligaments. The passage of the flexor hallucis longus tendon over the back of the joint serves the purpose of a much stronger posterior ligament. The deltoid ligament (fig. 330) is attached superiorly to the medial malleolus along its lower border, and to its anterior surface superficial to the anterior liga- ment; some very strong fibres are fixed to the notch in the lower border of the malleolus, and, getting attachment below to the rough depression on the medial side of the talus, form a deep portion to the ligament. The ligament radiates; the posterior fibres are short, and incline a little backward to be fixed to the rough medial surface of the talus, close to the superior articular facet, and into the THE ANKLE-JOINT 299 tubercle to the medial side of the flexor hallucis longus groove. The fibres next in front are numerous and form a thick and strong mass, filling up the rough depression on the medial surface of the talus, whilst some pass over the talo- calcaneal joint to the upper and medial border of the sustentaculum tali. The fibres which are connected above with the anterior surface of the malleolus pass downward and somewhat forward to be attached to the navicular and to the margin of the calcaneo-navicular ligament. The lateral ligament (figs. 329 and 334) consists of three distinct slips (fas- ciculi). The anterior talc -fibular ligament (anterior fasciculus), is ribbon-like and passes from the anterior border of the lateral malleolus near the tip to the rough surface of the talus in front of the lateral facet, and overhanging the sinus pedis. The calcaneo -fibular ligament (middle fasciculus) , is a strong roundish bundle, which extends downward and somewhat backward from the anterior border of the lateral malleolus close to the attachment of the anterior fasciculus, and from the lateral surface of the malleolus, just in front of the apex, to a tuber- cle on the middle of the lateral surface of the calcaneum. The posterior talo- FiG. 331. — Ligaments seen from the Back of the Ankle-joint. Posterior ligament of ankle-joim Posterior part of the deltoid ligament Transverse ligament of inferior tibio-fibular joint Posterior talo-fibular ligament Calcaneo-fibular ligament fibular ligament (posterior fasciculus), is almost horizontal; it is a strong, thick band attached at one end to the posterior border of the malleolus, and slightly to the fossa on the medial surface; and at the other end to the talus, behind the articular facet for the fibula, as well as to a tubercle on the lateral side of the groove for the flexor hallucis longus. The middle fasciculus is covered by the tendons of the peronei longus and brevis; and in extension, the posterior fasciculus is received into the pit on the medial surface of the lateral malleolus. The synovial membrane is very extensive. Besides lining the ligaments of the ankle, it extends upward between the tibia and fibula, forming a short cul- de-sac as far as the interosseous ligament. Upon the anterior and posterior liga- ments it is very loose, and extends beyond the limits of the articulation. It is said to contain more synovia than any other joint. The nerve -supply is from the saphenous, posterior tibial, and the lateral division of the anterior tibial. 300 THE ARTICULATIONS The arterial supply comes from the anterior tibial, the anterior peroneal, the lateral malleolar, the posterior tibial, and posterior peroneal. Relations. — In front and in contact with the anterior hgament, from medial to lateral aspects, are the tendons of the tibiahs anterior, the tendon of the extensor haUucis longus, the anterior tibial vessels, the anterior tibial nerve, the tendons of the extensor digitorum longus, and the tendon of the peroneus tertius. To the medial side of the tibiahs anterior and to the lateral side of the peroneus tertius the joint is subcutaneous anteriorly. Behind and laterally are the tendons of the peroneus longus and brevis. Behind and medially, from medial to lateral side, are the tendon of the tibialis posterior, the tendon of the flexor digitorum longus, the posterior tibial vessels, the posterior tibial nerve, and the tendon of the flexor hallucis longus. Directly behind is a pad of fat which intervenes between the tendo Achillis and the joint. Below and on the lateral side, crossing the middle fasciculus of the lateral ligament, are the tendons of the peroneus longus and brevis. Below and on the medial side, crossing the deltoid ligament, are the tendons of the tibialis posterior and the flexor digitorum longus. Movements. — This being a true hinge joint, flexion and extension are the only movements of which it is capable, there being no side to side motion, except in extreme extension, when the narrowest part of the talus is thrust forward into the widest part of the tibio-fibular arch. Fig. 332. — Tne Lower Extremity op the Tibia (Anterior view), to Show the Relation OP the Articular Capsule op the Ankle-joint (in red) to the Epiphysial Line. In flexion the talus is tightly embraced by the malleoli, and side to side movement is impossible. Flexion of the ankle-joint is hmited by: — (i) nearly the whole of the fibres of the deltoid ligament, none but the most anterior being relaxed; (ii) the posterior and middle portions of the lateral liga- ment, especially the posterior; (iii) the posterior ligament of the ankle. It is also hmited by the neck of the talus abutting on the edge of the tibia. In most European ankle-joints the anterior edge of the lower end of the tibia is kept from actual contact with the neck of the talus in positions of extreme flexion by the intervention of a pad of fat situated beneath the anterior extension of the anterior hgament. In races which adopt a squatting posture, however, an actual articulation may be developed between these two bony surfaces, a facet being present both upon the anterior margin of the tibia and upon the neck of the talus. These facets are known as "squatting facets" (fig. 333, A) and are of common occurrence in ancient bones and in the bones of modern oriental people. Extension of the ankle-joint is limited by: — (i) the anterior fibres of the deltoid ligament; (ii) the anterior and middle portions of the lateral hgament; (ui) the medial and stronger fibres of the anterior hgament. It is also limited by the posterior portion of the talus meeting with the tibia. Thus the middle portion of the lateral ligament is always on the stretch, owing to its obliquely backward direction, whereby it hmits flexion; and its attachment to the fibula in front of the malleolar apex, whereby it prevents over-extension as soon as the foot begins to twist THE TARSAL JOINTS 301 medialward. .This medial twisting, or adduction of the foot, is partly due to the greater pos- terior length of the medial border of the superior articular surface of the talus, and to the less proportionate height posteriorly of the lateral border of that surface, but chiefly to the side to side movement in the talo-calcaneal joints. Fle.xion and extension take place round a transverse axis drawn through the body of the talus. The movement is not in a direct antero-posterior plane, but on a plane inclined forward and laterally from the middle of the astragalus to the intermetatarsal joint of the second and third toes. Muscles which act on the ankle-joint. — Flexors. — Tibialis anterior, extensor hallucis longus, extensor digitorum longus, peroneus tertius. Extensors. — Tibialis posterior, flexor digitorum longus, flexor hallucis longus, peroneus longus, peroneus brevis, soleus, gastrocnemius, plantaris. Fig. 333. — Anterior Aspect of the Lower Extremity op the Tibia. In A, the articular surface is prolonged upward in front, forming a "squatting facet" which articulates with a corresponding facet on the neck of the talus. In B (the usual condition) the articular surface is confined to the lower aspect of the bone. 5. THE TARSAL JOINTS These may be divided into the following sub-groups : — (a) The talo-calcaneal union. (b) The articulations of the anterior portion of the tarsus. (c) The medio-tarsal joint. (a) The Talo-calcaneal Union There are two joints which enter into this union — viz., an anterior and a posterior. (i) The Posterior Talo-calcaneal Joint Class. — Diarthrosis. Subdivision. — Arthrodia. '. The calcaneus articulates with the talus by two joints, the anterior and posterior: the former communicates with the medio-tarsal; the posterior is separate and complete in itself. At the latter joint the two bones are united by an articular capsule with the following ligaments: — Interosseous. Posterior talo-calcaneal. Lateral talo-calcaneal. Medial talo-calcaneal. The interosseous ligament (figs. 334 and 335) is a strong band connecting the apposed surfaces of the calcaneus and talus along their oblique grooves. It is composed of several vertical laminae of fibres, with some fatty tissue in between. 302 THE ARTICULATIONS It is better marked, deeper, and broader laterally. Strong laminse extend from the rough inferior and lateral sm-faces of the neck of the talus to the rough superior surface of the calcaneus anteriorly, forming the posterior boundary of the anterior talo-caloaneal joint; these have been described as the anterior (interosseous) ligament. The posterior lamina extend from the roof of the sinus pedis to the calcaneus immediately in front of the lateral facet, thus forming the anterior part of the capsule of the posterior joint. The lateral talo-calcaneal ligament (fig. 334) extends from the groove just below and in front of the lateral articular facet of the talus, to the calcaneus some little distance from the articu- lar margin. Its fibres are nearly parallel with those of the calcaneo-fibular ligament of the ankle, which passes over it and adds to its strength. It fiUs up the interval between the calcaneo- fibular and anterior talo-fibular ligaments, a considerable bundle of its fibres blending with the anterior border of the calcaneo-fibular. The posterior talo-calcaneal ligament passes from the lateral tubercle of the talus and lower edge of the groove for the flexor haUucis longus to the calcaneus, a variable distance from the articular margin. The medial talo-calcaneal ligament includes two portions. The first is a narrow band of well-marked fibres passing obliquely downward and forward from the medial tubercle of the talus, just behind the medial end of the sinus tarsi, to the calcaneus behind the sustentaculum tali, thus completing the floor of the groove for the flexor hallucis longus tendon. The second portion, which is often considered a separate ligament, is described below with the anterior talo-calcaneal joint. The synovial sac is distinct from any other. The nerve-supply is from the posterior tibial or one of its plantar branches. The arteries are, a branch from the posterior tibial, which enters at the medial end of the sinus pedis; and twigs from the tarsal, lateral malleolar, and the peroneal, which enter at the lateral end of the sinus. (ii) The Anterior Talo-calcaneal Joint Class. — Diarthrosis. Subdivision. — Arthrodia. This joint is formed by the anterior facet on the upper surface of the calcaneus and the facets on the lower surface of the neck and head of the talus; it is bounded on the sides and behind by ligaments, and communicates anteriorly with the talo-navicular joint. The ligaments are: — Interosseous. Medial talo-calcaneal. Lateral calcaneo-navicular. The interosseous ligament by its anterior laminae limits this joint posteriorly. It has been already described. The medial talo-calcaneal ligament (second portion; see above) consists of short fibres at- tached above to the medial surface of the neck of the talus, and below to the upper edge of the free border of the sustentaculum tali, blending posteriorly with the medial extremityof the inter- osseous ligament, and anteriorly with the upper border of the plantar calcaneo-navicular liga- ment. It is strengthened by the deltoid ligament, the anterior fibres of which are also attached to the plantar calcaneo-navicular ligament. The lateral calcaneo-navicular (figs. 334 and 335) limits this, as well as the talo-navicular joint, on the lateral side. It is a strong, well-marked band, extending from thorough upper sur- face of the calcaneus, lateral to the anterior facet, to a slight groove on the lateral surface of the navicular near the posterior margin. It blends below with the plantar calcaneo-navicular, and above with the talo-navicular ligament. Its fibres run obliquely forward and medially. The deltoid ligament and middle fasciculus of the lateral ligament of the ankle-joint also add to the security of these two joints, and assist in limiting movements between the bones by pass- ing over the talus to the calcaneus. The synovial membrane is the same as that of the talo-navicular joint. The arteries and nerves are derived from the same sources as those of the medio-tarsal joints. The movements of which these two joints are capable are adduction and abduction, with some amount of rotation. Adduction, or inclination of the sole medialward, is combined with some medial rotation of the toes, and some lateral rotation of the heel; while abduction, or in- clination of the foot lateralward, is associated with turning of the toes laterally and the heel medially. Thus the variety and the range of movements of the foot on the leg, which at the ankle are almost limited to flexion and extension, are increased. The cuboid moves with the calca- neus, while the navicular revolves on the head of the talus. In walking, the heel is first placed on the ground; the foot is slightly adducted; but as the body swings forward, first the latei-al then the medial toes touch the ground, the talus presses against the navicular and sinks upon the plantar calcaneo-navicular ligament; the foot then becomes slightly abducted. When the foot is firmly placed on the ground, the weight is trans- mitted to it obliquely downward and medially, so that if the ligaments between the calcaneus and talus did not check abduction, medial displacement of the talus from the tibio-fibular arch would only be prevented by the tendons passing round the medial ankle (especially the tibialis posterior). If the ligaments be too weak to limit abduction, the weight of the body increases it, and forces the medial malleolus and talus downward and medially, giving rise to flat foot. The advantages of the obhquity and pecuUar arrangement of the posterior talo- calcaneal articulation are seen in walking: — (i) for the posterior facet of the calcaneus receives THE TARSAL JOINTS 303 the whole weight of the body when the heel is first placed on the ground; (ii) by the upward pressure of this facet against the talus it transfers the weight to the ball of the toes as the heel is raised, the posterior edge of the sustentaculum tali and the anterior and lateral part of the upper surface of the calcaneus preventing the talus from being displaced too far forward by the superincumbent weight; and (iii) the calcaneus serves to suspend the talus when, with the heel raised by muscular action, the other foot is being swung forward. Fig 334 — ^Lateral View of the Ligaments op the Foot and Ankle. Posterior lateral malleolar ligament Anterior lateral malleolar bgament Anterior (mterosseous) talo- calcaneal ligament Lateral calcaneo navic ular ligament Posterior talo-fibular ligament JJorsal cuboideo navicular \ ligament I Medial calcaneo-cuboid Dorsal Lateral Calcaneo-fibular ligament calcaneo- talo- cuboid calcaneal ligament (b) The Articulations of the Anterior Part of the Tarsus These include (i) the cuboideo-navicular; (ii) cuneo-navicular; (iii) inter- cuneiform; and (iv) cuneo-cuboid joints. (i) The Cuboideo-navicular Union Class. — Diarthrosis. Subdivision. — A rthrodia . The joint cavity is only occasionally present and this joint is often included in the transverse tarsal. The ligaments which unite the cuboid and navicular are: — Dorsal. Plantar. Interosseous. The dorsal cuboideo-navicular ligament (fig. 334) runs forward and laterally from the lateral end of the dorsal surface of the navicular to the middle third of the medial border of the cuboid on its dorsal aspect, passing over the posterior lateral angle of the third cuneiform bone. It is wider laterally. The plantar cuboideo-navicular ligament is a well-marked strong band, which runs forward and laterally, from the plantar surface of the navicular to the depression on the medial siurface of the cuboid, and slightly into the plantar surface just below it. The interosseous cuboideo-navicular ligament is a strong band which passes between the apposed surfaces of these bones from the dorsal to the plantar ligaments. Some of its posterior fibres reach the plantar surface of the foot behind the cuboideo-navicular ligament, and radiate laterally and backward over the medial border of the cuboid to blend with the anterior ex- tremity of the plantar calcaneo-cuboid ligament. 304 THE ARTICULATIONS (ii) The Cuneo-navicular Articulation Class. — Diarthrosis. Subdivision. — Arthrodia. The ligaments uniting tlie navicular with the three cuneiform bones are : — Dorsal. Plantar. Medial. The dorsal cuneo-navicular ligament is very strong, and stretches as a continuous structure on the dorsal surface of the navicular, between the tubercle of the navicular on the medial side, and the dorsal cuboideo-navicular ligament laterally, passing forward and a little laterally to the dorsal surfaces of the three cuneiform bones. The medial cuneo-navicular ligament is a very strong thick band which connects the tuber- cle of the navicular with the medial surface of the first cuneiform bone. It is continuous with the dorsal and plantar ligaments. Its lower border touches the tendon of the tibialis posterior. The plantar cuneo-navicular ligament forms, like the dorsal, a continuous structure ex- tending between the plantar surfaces of the bones. Its fibres pass forward and laterally. It is in relation below with the tendon of the tibialis posterior. It must be noticed that the expanded tendon of insertion of the tibialis posterior, and the ligaments uniting the navicular with the cuboid and cuneiform bones, pass forward and later- aUy, while the peroneus longus tendon and the ligaments uniting the first and second rows of bones, except the medial half of the dorsal talo-navicular ligaments, pass forward and medially. This arrangement is admirably adapted to preserve the arches of the foot, and especially the transverse arch. Had these tendons and ligaments run directly forward, all the strain on the transverse arch would have fallen on the interosseous ligaments, but as it is, the arch is braced up by the above-mentioned structures. (iii) The Intercuneiform and (iv) The Cuneo-cuboid A^'ticulations Class. — Diarthrosis. Subdivision — Arthrodia. The uniting ligaments of these bones are divided into three sets : — Dorsal. Plantar. Interosseous. The dorsal ligaments are three in number, two, the dorsal intercuneiform, connecting the three cuneiform bones, and a thhd, the dorsal cuneo-cuboid, uniting the third cuneiform with the cuboid. They pass between the contiguous margins of the bones, and are blended behind with the dorsal ligaments of the cuboideo-navicular and cuneo-navicular joints. The plantar ligaments are two in number: a very strong one, the plantar intercuneiform, passes laterally and forward from the lateral side of the base of the first cuneiform to the apex of the second cuneiform, winding somewhat to its lateral side. The second, the plantar cuneo- cuboid, connects the apex of the third cuneiform with the anterior half of the medial surface of the cuboid along its plantar border, joining with the plantar cuboideo-navicular hgament behind. The interosseous ligaments are three in number. They are strong and deep masses of ligamentous tissue which connect the second cuneiform with the first and third cuneiform bones, and the third cuneiform with the cuboid; occupying all the non-articular portions of the apposed surfaces of the bones. The ligaments extend the whole vertical depth between the second cunei- form and the third, and the third cuneiform and the cuboid, and blend with the dorsal and plantar ligaments; they are situated in front of the articular facets, and completely shut off the synovial cavity behind from that in front. The hgament between the first and second cunei- form bones occupies the inferior and anterior two-thirds of the apposed surfaces, and does not generally extend high enough to separate the synovial cavity of the anterior tarsal joint from that of the second and third metatarsal and cuneiform bones. If it does extend to the dorsal sur- face, it divides the facets completely from one another, making a seventh synovial sac in the foot. The synovial cavity will be described later on. The arterial supply is from the metatarsal and plantar arteries. The nerves are derived from the deep peroneal and medial and lateral plantar. The movement permitted in these joints is very limited, and exists only for the purpose of adding to the general pliancy and elasticity of the tarsus without allowing any sensible alteration in the position of the dilferent parts of the foot, as the medio-tarsal and talo-cal- caneal joints do. It is simply a gUding motion, and either deepens or widens the transverse arch. The third cuneiform being wedged in between the others is less movable, and so forms a pivot upon which the rest can move. The movement is more produced by the weight of the body than by direct muscular action; and of the muscles attached to this part of the tarsus, all deepen the arch save the tibiahs anterior, which pulls the first cuneiform up, and so tends to widen it. THE TARSAL JOINTS 305 (c) The Tbansverse Tarsal Joints The articulations of the anterior and posterior portions of the tarsus, although in the same transverse line, consist of two separate joints, viz., (i) a medial, the talo-navicular, which communicates with the anterior talo-calcaneal articulation; and (ii) a lateral, the calcaneo-cuboid, which is complete in itself. The move- ments of the anterior upon the posterior portions of the foot take place at these joints simultaneously. It will be most convenient to deal with the joints sepa- rately as regards the ligaments; while the arteries, nerves, and movements will be considered together. (i) The Talo-navicular Articulation Class. — Diarthrosis. Subdivision. — Enarthrodia. This is the only ball-and-socket joint in the tarsus. It communicates with the anterior talo-calcaneal articulation, and two of the ligaments which close it in do not touch the talus, but pass from the calcaneus to the navicular. The uniting ligaments include, in addition to the articular capsule, the following: — Lateral calcaneo-navicular. Plantar calcaneo-navicular Talo-navicular. The lateral calcaneo-navicular has been already described (p. 302). The plantar calcaneo-navicular ligament (figs. 335 and 336) is an exceedingly dense, thick plate of fibro-elastio tissue. It extends from the sustentaculum tali and the under surface of the calcaneus in front of a ridge curving laterally to the anterior tubercle of that bone, to the Fig. 335. — View of the Foot from above, with the Talus removed to show the Plantar AND Lateral Calcaneo-navicular Ligamenti? Dorsal cuboideo-navicular ligament Dorsal calcaneo-cuboid ligament' Medial calcaneo-cuboid ligament* Lateral calcaneo-navicular ligament' Plantar calcaneo-navicular ligament Tendon of tibialis posterior Cut edge of interosseous ligament' whole width of the inferior surface of the navicular, and also to the medial surface of the navicular behind the tubercle. Medially it is blended with the anterior portion of the deltoid ligament of the ankle, and laterally with the lower border of the lateral calcaneo-navicular hgament. It is thickest along the medial border. Its upper surface loses the well-marked fibrous appear- ance which the ligament has in the sole, and becomes smooth and faceted. In contact with the under surface of the ligament the tendon of the libialis posterior passes, giving consider- able support to the head of the talus by assisting the power and protecting the spring of the ligament. The fibres of the ligament run forward and mediaUy. On account of its elasticity it is sometimes termed the spring ligament. 306 THE ARTICULATIONS The talo -navicular ligament is a broad, thin, but well-marked layer of fibres which passes from the dorsal and lateral surfaces of the neck of the talus to the whole length of the dorsal surface of the navicular. Many of the fibres converge to their insertion on the navicular. The fibres low down on the lateral side blend a little way from their origin with the upper edge of the lateral calcaneo-navicular ligament, and then pass forward and medially to the navicular; those next above pass obliquely and with a distinct twist over the upper and lateral side of the head of the talus to the centre of the dorsum of the navicular, overlapping fibres from the medial side of the talus as well as some from the anterior ligament of the ankle-joint. Synovial membrane. — The talo-navicular is lined by the same synovial membrane as the anterior talo-calcaneal joint. (ii) The Calcaneo-cuboid Articulation - Class. — Diarthrosis. Subdivision. — Saddle-shaped Arthrodia. The ligaments which are supplementary to the articular capsule and unite the bones forming the outer part of the medio-tarsal joint are: — Medial calcaneo-cuboid. Long plantar. Dorsal calcaneo-cuboid. Plantar calcaneo-cuboid. The medial calcaneo-cuboid ligament (fig. 335) is a strong band of fibres attached to the calcaneus along the medial jiiirt ol' the non-articular ridge above the articular facet for the cuboid, and also to the upper part of tlie medial surface close to the articular margin, and passes forward to be attached to the depression on the medial surface of the cuboid, and also to the rough angle Fig. 336. — Ligaments op the Sole of the Left Foot. Long plantar ligament Tendon of peroneuslongus Groove for flexor hallucis longus Plantar calcaneo-navicular ligament _U ^Plantar calcaneo-cuboid (short plantar) ligament ' "A — Tubercle of navicular "".if Medial cuneiform Insertion of peroneus longus between the medial and inferior surfaces. At the calcaneus this ligament is closely connected with the lateral calcaneo-navicular Mgament. Toward the sole it is connected with the plantar calcaneo-cuboid ligament, and superiorly with the dorsal calcaneo-cuboid. The dorsal calcaneo-cuboid (fig. 335) is attached to the dorsal surfaces of the two bones, extending low down laterally to blend with the lateral part of the plantar calcaneo-cuboid ligament. Over the medial half, or more, the ligament stretches some distance beyond the mar- gins of the articular surfaces, reaching well forward upon the cuboid to be attached about midway between its anterior and posterior borders; but toward the lateral side, the ligament is much shorter, and is attached to the cuboid behind its tubercle. TARSO-METATARSAL JOINTS 307 The long plantar ligament (fig. 336) is a strong, dense band of fibres which is attached pos- teriorly to the whole of the inferior surface of the calcaneus between the posterior tubercles and the rounded eminence (the anterior tubercle) at the anterior end of the bone. Most of its fibres pass directly forward, and are fixed to the lateral two-thirds or more of the oblique ridge behind the peroneal groove on the cuboid, while some pass further forward and medially, expanding into a broad layer, and are inserted into the bases of the second, thu-d, fourth, and medial half of the fifth metatarsal bones. This anterior expanded portion completes the canal for the peroneus hiugiiK tvndnn, and from its under surface arise the oblique adductor hallucis and the flexor quinii iliijili lircris muscles. The plantar calcaneo-cuboid (short plantar) (fig. 336) is attached to the rounded eminence (anterior tubercle) at the anterior end of the under surface of the calcaneus, and to the bone in front of it, and then takes an oblique course forward and medially, and is attached to the whole of the depressed inferior surface of the cuboid behind the oblique ridge, except its lateral angle. It is strongest near its lateral edge, and is formed by dense strong fibres. The synovial membrane is distinct from that of any other tarsal joint. The arterial supply of the medio-tarsal joints is from the anterior tibial, from the tarsal and metatarsal branches of the dorsalis pedis, and from the plantar arteries. The nerve-supply of the medio-tarsal joints is from the lateral division of the deep peroneal, and occasionally from the superficial peroneal or lateral plantar. Relations. — On the dorsal aspect of the mid-tarsal joint lie the tendons of the tibialis anterior, extensor hallucis longus, extensor digitorum longus, and peroneus tertius, the muscular part of the extensor digitorum brevis, the dorsalis pedis artery, and the anterior tibial nerve. On its plantar aspect are the tendons of the flexor digitorum longus and hallucis longus, quadratus plantse (accessorius), and the medial and lateral plantar vessels and nerves. It is crossed later- ally by the tendons of the peroneus longus and brevis and medially by the tendon of the tibialis posterior. The movements which take place at the medio-tarsal joints are mainly flexion and extension, with superadded side-to-side and rotatory movements. Flexion at these joints is simultaneous with extension of the ankle, and vice versa. Flexion and extension do not take place upon a transverse, but round an oblique, axis which passes from the medial to the lateral side, and some- what backward and downward through the talus and calcaneus. Combined with flexion and extension is also some rotatory motion round an antero-posterior axis which turns the medial or lateral border of the foot upward. There is also a fail' amount of side-to-side motion whereby the foot can be inclined medially (i. e., adducted) or laterally (i. e., abducted). These movements of the medio-tarsal joint occur in conjunction with those of the ankle' a,nd talo-calcaneal joints. Rotation at the talo-calcaneal joint is, however, round a vertical axis in a horizontal plane, and so turns the toes medially or laterally; whereas at the medio- tarsal union the axis is antero-posterior and the medial or lateral edge of the foot is turned up- ward. Gliding at the talo-calcaneal joint elevates or depresses the edge of the foot, while at the medio-tarsal it adducts or abducts the toes without altering the relative position of the cal- caneus to the talus. Thus flexion at the medio-tarsal joint is associated with adduction and medial rotation of the foot, occurring simultaneously with extension of the ankle; and extension at the medio- tarsal joint is associated with abduction and lateral rotation, occurring simultaneously with flexion of the ankle. Flexion and medial rotation are far more free than extension and lateral rotation, which latter movements are arrested by the ligaments of the sole as soon as the foot is brought into the position in which it rests on the ground. Although the talo-navicular is a baU-and-socket joint, yet, owing to the union of the navicular with the cuboid, its movements are limited by the shape of the calcaneo-cuboid joint; this latter being concavo-convex from above downward, prevents rotation round a vertical axis, and also any side-to-side motion except in a direction obliquely downward and mediaUy, and upward and laterally. This is also the direction of freest movement at the talo-navicular joint. Movement is also limited by the ligamentous union of the calcaneus with the navicular. The twisting movement of the foot, such as turning it upon its medial or lateral edge, and the increase or diminution of the arch, take place at the tarsal joints, especially the medio-tarsal and talo- calcaneal articulations. Here too those changes occur which, owing to paralysis of some mus- cles or contraction of others, result in talipes equino-varus, or valgus. Muscles which act on the mid-tarsal joint. — Medial rotators. — Tibialis anterior and posterior acting simultaneously; they are aided by the flexor digitorum longus and flexor hallucis longus. Lateral rotators. — The peronei longus, brevis, and tertius, acting simultaneously. They are aided by the extensor digitorum longus. 6. THE TARSO-METATARSAL ARTICULATIONS There may be said to be three articulations between the tarsus and metatarsus, viz. : — (a) The medial, bet'ween the first cuneiform and first metatarsal bones. (6) The intermediate, between the three cuneiform and second and third metatarsal bones. (c) The lateral, or cubo-metatarsal, between the cuboid and fourth and fifth metatarsal bones. 308 THE ARTICULATIONS (a) The Medial Taeso-metatarsal Joint Class. — Diarthrosis. Subdivision. — Arthrodia. A complete articular capsule unites the first metatarsal with the first cunei- form, the fibres of which are very thick on the inferior and medial aspects; those on the lateral side pass from behind forward in the interval between the interos- seous ligaments which connect the two bones forming this joint with the second metatarsal. The ligament on the plantar aspect is by far the strongest, and blends at the cuneiform bone with the cuneo-navicular ligament. (6) The Intermediate Taeso-metatarsal Joint Class. — Diarthrosis. Subdivision. — Arthrodia. Into this union there enter the three cuneiform and second and third meta- tarsal bones, which are bound together by the following ligaments (supplementary to the articular capsule) : dorsal, plantar, interosseous. The dorsal ligaments. — 1. Some short fibres cross obliquely from the lateral edge of the first cuneiform bone to the medial border of the base of the second metatarsal bone; they take the place of a dorsal metatarsal hgament, which is wanting between the first and second meta- tarsal bones. 2. Between the second cuneiform and the base of the second metatarsal bone some fibres run directly forward. 3. The third cuneiform is connected with (1) the lateral corner of the second metatarsal bone by a narrow band passing obliquely medially; (2) with the third metatarsal by fibres passing directly forward; and (3) with the fourth metatarsal by a short band passing obUquely laterally to the medial edge of its base. The plantar ligaments. — A strong hgament unites the first cuneiform and the bases of the second and third metatarsal bones. The tibialis posterior is inserted into these bones close beside it. Other slender ligaments connect the second cuneiform with the second, and the third cuneiform with the third metatarsal bones. The interosseous ligaments. — (1) A strong broad interosseous hgament extends between the lateral surface of the first cuneiform and the medial surface of the base of the second meta- tarsal bone. It is attached to both bones below and in front of the articular facets, and sepa- rates the intermediate [from the medial tarso-metatarsal joint. (2) A second band is attached behind to a fossa on the anterior and lateral edge of the third cuneiform and to the interosseous ligament between it and the cuboid, and passes horizontally forward to be attached to the whole depth of the fourth metatarsal bone behind its medial facet, and to the opposed surfaces of the third and fourth below the articular facets upon their sides. It separates the middle tarso- metatarsal, and intermetatarsal between the third and fourth bones, from the oubo-metatarsal joint. It is more firmly connected with the third bone than with the fourth. (3) A slender ligament composed only of a few fibres often passes from a small tubercle on the medial and an- terior edge of the third cuneiform to a groove on the lateral edge of the second metatarsal bone between the two facets upon then- sides. The synovial membrane is prolonged forward from that of the naviculari-cuneiform and inter-cuneiform articulations. The arteries for the tarso-metatarsal joints are derived: — (1) for the medial, from the dor- saUs pedis and medial plantar; (2) for the rest, twigs from the arcuate and deep plantar arch. The nerve-supply comes from the deep peroneal and plantar nerves. The movements permitted at these joints are flexion and extension of the metatarsus on the tarsus; and at the medial and lateral divisions, slight adduction and abduction. In the lateral, the side-to-side motion is freer than in the medial joint, and freest between the fifth metatarsal bone and the cuboid. In the medial joint, flexion is combined with sUght abduction and extension with abduction. There is also a little gliding, which aflows the transverse arch to be increased or diminished in depth; the medial and lateral two bones sliding downward, and the two middle a little upward, when the arch is increased; and vice versa when the arch is flattened. (c) The Lateral or Cubo-metatarsal Joint Class. — Diarthrosis. Subdivision. — Arthrodia. The bones comprising this joint are the fourth and fifth metatarsal and the anterior surface of the cuboid, firmly connected on all sides by the articular cap- sule, strengthened by the following ligaments: — Dorsal. Plantar. Interosseous. The plantar cubo-metatarsal ligament is a broad, well-marked ligament, which extends from the cuboid behind to the bases of the fourth and fifth metatarsal bones in front. It is INTERMETATARSAL JOINTS 309 continuous along the groove at the base of the fifth metatarsal bone with the dorsal ligament, and as it passes round the lateral border of the foot it is somewhat thickened, and may be de- scribed as the lateral cubo-metatarsal ligament. On its medial side it joins the interosseous ligaments, thus completing the capsule below. It is not a thick structure, and to see it the long plantar ligament, the peroneus longus, and lateral slip of the tibialis posterior must be removed; the attachment of these structures to the fourth and fifth metatarsal bones considerably assists to unite them with the tarsus. The dorsal cubo-metatarsal ligament is composed of fibres which pass obliquely outward and forward from the cuboid to the bases of the fourth and fifth metatarsal bones. They com- plete the capsule above, and are continuous laterally with the lateral cubo-metatarsal hgament. The interosseous ligament shuts off the cubo-metatarsal from the middle tarso-metatarsal joint. It is attached to the third cuneiform behind, and to the whole depth of the fourth meta- tarsal behind its medial facet, and to the apposed surfaces of the third and fourth bones below their articular facets. It is continuous below with the plantar ligament. The synovial membrane is separate from the other synovial sacs of the tarsus, and is con- tinued between the fourth and fifth metatarsal bones. Relations. — The line of the tarso-metatarsal joints is crossed dorsally by the tendons of the long and short extensor muscles of the toes and the tendon of the peroneus tertius. On the plantar aspect it is in relation with the obUque adductor of the great toe, the short flexor of the great toe, the lateral plantar artery, and the tendon of the peroneus longus. Its medial end is subcutaneous except that it is crossed, near the plantar surface, by a slip of the tendon of the tibialis anterior, and its lateral end is crossed by the tendon of the peroneus brevis. Fig. 337. — Section to show the Synovial Cavities op the Foot. 7. THE INTERMETATARSAL ARTICULATIONS Class. — Diarthrosis. Sub division. — A rthrodia . The bases of the metatarsal bones are firmly held in position by dorsal, plantar, and interosseous ligaments, supplementing the articular capsules. The first occasionally articulates by means of a distinct facet with the second metatarsal (figs. 245 and 246). The dorsal ligaments are broad, membranous bands passing between the four lateral toes on their dorsal aspect; but in place of one between the first and second metatarsal bones, a ligament extends from the first cuneiform to the base of the second metatarsal bone. The plantar ligaments are strong, thick, well-marked ligaments which connect the bones on their plantar aspect. The interosseous ligaments are three in number, very strong, and are situated at the points of union of the shaft with the bases of the bones, and fill up the sulci on their sides. They limit the synovial cavities in front of the synovial facets. The common synovial membrane of the tarsus extends between .the second and third, and third and fourth bones; that of the cubo-metatarsal joint extending between the fourth and fifth. The arterial and nerve-supply is the same as for the tarso-metatarsal joints. The movements consist merely of gliding, so as to allow the raising or widening of the transverse arch. Considerable flexibihty and elasticity are thus given to the anterior part of the foot, enabling it to become moulded to the irregularities of the ground. The Union of the Heads of the Metatarsal Bones The heads of the metatarsal bones are connected on their plantar aspect by the transverse ligament [Ligg. capitulorum transversa], consisting of four bands 310 THE ARTICULATIONS . of fibres passing transversely from bone to bone, blending witli the fibro-cartilagi- nous or sesamoid plates of the metatarso-phalangeal joints, and the sheaths of the flexor tendons where they are connected witli the fibro-cartilages. It differs from the corresponding ligament in the hand by having a band from the first to the second metatarsal bone. 8. THE METATARSO-PHALANGEAL ARTICULATIONS (0) The Metatarso-phalangeal Joints op the Four Lateral Toes Class. — Diarthrosis. Subdivision. — Condylarthrosis. These joints are formed by the concave proximal ends of the first phalanges articulating with the rounded heads of the metatarsal bones, and united by articular capsules strengthened by the following ligaments: — Collateral. Dorsal. Plantar accessory. The two collateral ligaments are strong bands passing from a ridge on each side of the head of the metatarsal bone to the sides of the proximal end of the first phalanx, and also to the sides of the sesamoid plate which unites the two bones on their plantar surfaces. On the dorsal aspect they are united liy the dorsal ligament. The dorsal ligament consists of loose fine fibres of areolo-fibrous tissue, extending between the collateral ligaments, thus completing a capsule. It is connected by fine fibres to the \inder surface of the extensor tendons, which pass over and considerably strengthen this portion of the capsule. The plantar accessory ligament or sesamoid plate helps to deepen the shallow facet of the phalanx for the head of the metatarsal bone, and corresponds to the accessory volar ligament of the fingers. It is firmly connected to the collateral Ugaments and the transverse ligament, and is grooved inferiorly where the flexor tendons pass over it. It serves to prevent dorsal disloca- tion of the phalanx. The second metatarso-phalangeal joint is 6 mm. (J in.) in front of both the first and third metatarso-phalangeal joints. The third metatarso-phalangeal joint is 6 mm. (J in.) in front of the foui-th, and the fourth 9 mm. (I in.) in front of the fifth. The head of the fifth metatarsal is in line with the neck of the fourth. Thus the lateral side of the longitudinal arch of the foot is shorter than the medial, it is also distinctly shallower. (b) The Metatarso-phalangeal Joint of the Great Toe The metatarso-phalangeal joint of the great toe differs from the rest in the folloTftdng particulars : — (1) The bones are on a larger scale, and the articular surfaces are more extensive. (2) There are two grooves on the plantar surface of the metatarsal bone, one on each side of the median hne, for the sesamoid bones. (3) The sesamoid bones replace the accessory plantar ligament (sesamoid plate). They are two small hemispherical bones developed in the tendons of the flexor hallucis brevis, convex below, but flat above where they play in grooves on the head of the metatarsal bone; they are united by a strong transverse hgamentous band, which is smooth below and forms part of the channel along which the long flexor tendon plays. They are firmly united to the base of the phalanx by strong short fibres, but to the metatarsal bone they are joined by somewhat looser fibres. At the sides they are connected with the collateral ligaments and the sheath of the flexor tendon. They provide shifting leverage for the flexor hallucis brevis as well as for the flexor hallucis longus. The arteries come from the digital and metatarsal branches ; and the nerves from the cuta- neous digital, or from small twigs of the nerves to the interossei muscles. The movements permitted are: flexion, extension, abduction, adduction, and circumduction. Flexion is more free than extension, and is limited by the extensor tendons and dorsal liga- ments; extension is limited by the flexor tendons, the plantar fibres of the collateral ligaments, and the sesamoid plates. The side-to-side motion is possible from the shape of the bony surfaces, but is very limited, being most marked in the great toe. It is limited by the collateral ligaments and sesamoid plates. 9. THE INTERPHALANGEAL JOINTS Class. — Diarthrosis. Subdivision. — Ginglymus. The articulations between the first and second and second and third phalanges of the toes are similar to those of the fingers, with this important difference, that INTERPHALANGEAL JOINTS 311 the bones are smaller and the joints, especially between the second and third phalanges, are often ankylosed. The ligaments which unite them include, in addition to the articular capsule : — Collateral. Dorsal. Accessory plantar. The two collateral ligaments are well marked, and pass on each side of the joints from a little rough depression on the head of the proximal, to a rough border on the side of the base of the distal phalanx of the joint. The dorsal ligament is thin and membranous, and extends across the joint from one col- lateral ligament to the other beneath the extensor tendon, with the deep surface of which it is connected and by which it is strengthened. The accessory plantar ligament covers in the joint on the plantar surface. It is a fibro- cartilaginous plate, connected at the sides with the collateral hgaments, and with the bones by short ligamentous fibres; the plantar surface is smooth, and grooved for the flexor tendons. The arteries and nerves are derived from the corresponding digital branches. The only movements permitted at these joints are flexion and extension. At the interphalangeal joint of the great toe there is very frequently a small sesamoid bone which plays on the plantar surface of the first phalanx, in the same way as the sesamoid bones of the metatarso-phalangeal joint play upon the plantar surface of the head of the metatarsal bone. Relations of the muscles acting on the metatarso-phalangeal and interphalangeal joints of the foot. — If the student will refer to the accounts given of the relations of the corresponding joints in the hand and of the actions of the muscles upon those joints, and if he contrasts and compares the muscles of the hand with those of the foot, he will readily be able to construct tables of the relations of the metatarso-phalangeal and interphalangeal joints of the foot, and tables of the muscles acting upon the joints. References. — A complete bibliography for the joints is given in the "Hand- buch der Anatomie und Mechanik der Gelenke," by Professor Rudolf Tick (in von Bardeleben's Handbuch der Anatomie). References are also given in the larger works on human anatomy by Quain, Rauber-Kopsch, Poirier-Charpy, etc. References to the most recent literature may be found in Schwalbe's Jahres- bericht, the Index Medicus and the various anatomical journals. SECTION IV THE MUSCULATURE Revised fob the Fifth Edition By C. R. BARDEEN, A.B., M.D. PROFESSOR OF ANATOMY IN THE UNIVERSITT OF WISCON SIN MUSCLES, the movements of which are under the control of the will, almost completely envelope the skeletal framework of the body; close in the oral, abdominal, and pelvic cavities; separate the thoracic from the abdominal cavity; surround the pharynx and the upper portion of the cesophagus; and are found connected with the eye, ear, larynx, and other organs. They constitute about two-fifths to three-sevenths of the weight of the body. In this section an account is given of the gross anatomy of the musculature attached to the skeleton and the skin, with the exception of certain of the muscles which are more conveniently treated in connection with the organs to which they are appended. Thus, the muscles of the eye, the ear, the pharynx, the larynx, and the intrinsic muscles of the tongue are described in the sections devoted to those structures. Relations to the skin. — Beneath the skin is a sheet of connective tissue, the tela subcutanea. In this, in some regions of the body (the head, neck, and palm), thin, flat, subcutaneous muscles are embedded. Superficial muscles of this kind constitute a panniculus carnosus, much more extensive in the lower mammals than in man. The tela subcutanea is separated from the more deeply seated muscu- latiu-e by areolar tissue, which, in most places, is loose in texture over the muscles. In some regions, as over the upper part of the back, the tela subcutanea is firmly united to the underlying musculature and is less freely movable. In the tela sub- cutanea more or less fat is usually embedded. This constitutes the panniculus adiposus, which varies greatly in thickness in different parts of the body. As a rule, it is much more developed over muscles than over those regions where bone and joints lie beneath the skin. From the tela subcutanea of the eyelids, penis, and scrotum fat is absent. The deeper layer of the tela subcutanea is more or less free from fat, and in it run the main trunks of the cutaneous nerves and vessels. In some regions, as over the lower part of the abdomen, one or more fibrous mem- branes are differentiated in this deeper layer. To the tela subcutanea the term superficial fascia has been commonly applied, but since this leads to a confusion with the superficial fascia; which immediately invest the muscles, it seems better to restrict the term fascia to the membranes connected with the muscular system, and to use the term tela subcutanea for the layer of connective tissue which underlies the skin and is continuous over the whole surface of the body. In several places where the skin overlies bony prominences well-marked synovial bursse, or sacs (bursae mucosae), are developed in the tela subcutanea. Since the skin and the subcutaneous tissue must be removed in order to study the muscles of various regions, the tela subcutanea and subcutaneous bm-sse may be conveniently described in connection with the muscles, and brief references will, therefore, be made to them in connection with the musculature of various regions. Muscle fasciae. — The musculature of the body, with the exception of some of the subcutaneous muscles, is ensheathed by fibrous tissue, which, in certain regions forms distinct membranes, while in other regions it is delicate and not clearly to be distinguished from the superficial connective tissue of the muscles, the perimy- 313 I 314 THE MUSCULATURE sium externum. The membranes, or muscle fasciae, are united to various parts of the skeleton, eitlaer directly or by means of intermuscular septa, and, where strong, keep the underlying musculature in place. In some regions they are united to the muscles; in others they are separated from the underlying musculature by loose areolar tissue, which allows free movement between the surface of the mus- cles and the overlying fascia. The best example of a strong fascia of this nature is that which envelopes the extensor muscles of the thigh. Where the fasciee are well developed, the main bundles of constituent fibres take a course directly or obliquely transverse to the direction of the underlying muscles. They may be composed of several successive layers of fibrous tissue, the fibres of one layer tak- ing a different direction from those of the next layer. The function of the fascicS is the mechanical one of restraining or modifying muscle action. The direction of the main component fibre-bundles indicates the direction of the greatest stress to which the fascia? are subjected. Indirectly the fasciae promote the circulation of the blood and lymph in places where the vessels lie between the contracting muscles and the overlying fascia. Intermuscular septa. — Muscle fasciae enclose not only the external layer of the musculature of the body, but also the various groups of more deeply seated muscles. In addition, between the individual muscles, and between the different layers and groups of muscles, there intervenes a greater or less amount of connective tissue, sometimes loose in texture, sometimes dense in structure. In these intermuscular septa run the chief nerves and blood-vessels of the region in which the musculature lies. Gross structure of the muscles. — The muscles are composed of bundles of red- dish fibres surrounded by a greater or less extent of white and glistening connective tissue. They are attached by prolongations of this tissue in the form of tendons or aponeuroses usually to the bony skeleton, but also in places to cartilages, as in the thorax and larynx; to the skin, as in the face; to mucous membranes, as in the tongue and cheeks; to the tendons of other muscles, as in the case of the lumbrical muscles; to muscle fasciae, as in the case of the oblique and transverse muscles of the abdomen; and to other structures, as, for instance, to the eyeball. The fleshy portion of the muscle is called the belly. The belly is usually attached at one extremity to a portion of the skeleton or to some other structure which serves as a support for its action on the structures to which its other ex- tremity is attached. The attachment to the more fixed part is called the origin of the muscle; the attachment to the structure chiefly acted on is called the insertion. Thus the origin of the biceps muscle, the chief flexor of the forearm at the elbow, is from the scapula; the insertion is into the radius and into the fascia of the fore- arm. The part of the muscle attached to the origin is called the head of the mus- cle. The part attached to the insertion is sometimes called the tail, but this term is much less frequently used than the former. The muscles vary greatly in size and form. Thus the stapedius muscle of the middle ear is a slender little structure, only a few millimetres long, while the glu- teus maximus muscle of the hip is a large, rhomboid structure often several centi- metres thick and with a surface area of over 500 square centimetres. The length of a muscle from origin to insertion may be much less than the width of the muscle, as in the intercostal muscles; or much greater than the width, as in most of the long muscles of the limbs. The thickness of a muscle is usually less than the width — so much so in some instances that the muscle is described as flat, sheet-like, or ribbon-like; while in other instances the belly is cylindrical. In flat muscles the general outline is usually quadrilateral or triangular. In triangular muscles in most instances one angle of the triangle marks the insertion of the muscle, while the opposite side marks the origin. In cylindrical muscles the belly usually has a somewhat fusiform shape, and grows smaller both toward the origin and the in- sertion of the muscle. Some muscles are divided by tendons transverse to the long axis of the muscle. When one such tendon exists, the muscle is called digastric (fig. 348) ; when sev- eral, polygastric, e. g., rectus abdominis (fig. 388). Two muscle masses with separate origins may have a common insertion. Such muscles are usually designated bicipital muscles (biceps muscles of the arm and thigh). Other muscles have three heads (the triceps muscle of the arm) or four (the quadriceps muscle of the thigh). In the latter case special names are given FINER STRUCTURE OF MUSCLES 315 to the four parts or muscles which constitute the quadriceps as a whole. In ad- dition to these comparatively simple compound muscles there are others in which the various component fasciculi and the tendons of origin and insertion are numer- ous and complexly interrelated. The intrinsic muscles of the back offer good illustrations of muscles of this nature. In addition to muscles with distinct regions of origin and insertion, there are a few voluntary muscles which surround hollow viscera or their orifices and have a circular or tube-like form (sphincter muscles, voluntary muscles of the oesophagus, ■etc.). Number of muscles. — A logical constancy does not appear always to have been followed in the commonly accepted division of the musculature into muscles indi- vidually designated. Most of the muscles are symmetrically placed in pairs, one on each side of the body. Authors not only vary in the extent to which they carry the subdivisions of the musculature on each side of the body into individual muscles, but also in describing muscles placed near the median line either as single muscles with bilateral halves or as paired muscles. In addition some muscles are not constantly present, and there are differences of opinion as to which of these less constant muscles should be classed with the normal musculature. The BNA recognises 347 paired and two unpaired skeletal muscles, and 47 paired and two unpaired muscles belonging to the visceral system and organs of special sense. Of the skeletal muscles the head has 25 paired and one unpaired; the neck 16 paired; the back 112 paired; the thorax 52 paired, one unpaired; the abdomen and pelvis 8 paired; the upper extremity, 52 paired; the lower extremity, 62 paired (Eisler). Finer structure of muscles. — While no attempt can be made here to describe in detail the finer microscopic features of muscle structure, some of the more general features of muscle architecture may be briefly mentioned. The contractile cells of voluntary muscle are long, slender, multinucleated 'fibres,' the pro- toplasm of which exhibits both cross and longitudinal striation. The longitudinal striation is due to the presence of fibrils situated in the sarcoplasma. The cross striation is due to alter- nate segments of singly and doubly refracting substance in these fibrils. The length of these fibres in the human body varies from a few millimetres to sixteen centimetres or more, and the thickness from ten to eighty microns. Each muscle-fibre is surrounded by an especially differ- entiated sheath, the sarcolemma. Outside of this is a layer of delicate connective tissue, the perimysium internum or endomysium, the fibres of which are in part inserted into the sarco- lemma. This connective tissue, which is especially developed at the ends of the fibres, serves to .attach them either directly to the structures on which the muscle acts or to the skeletal frame- work of the muscle. In the simplest mammalian muscles the muscle-fibres take a parallel course from tendon to tendon, and are not definitely bound into secondary groups. An example may be seen in fig. 338, a, which represents two segments of the rectus abdominis muscle of a mouse. More often, however, the individual fibres do not run the entu-e distance from tendon to tendon, but instead . they interdigitate, and the interdigitating fibres are bound up into secondary and tertiary anastomosing fibre-bundles by connective tissue, in which there is usually a considerable amount of elastic tissue. Fig. 338, b, represents diagrammatically this interdigitation of fibre-bundles as seen in the abdominal musculature of one of the larger mammals. In most of the flat muscles of the body the fibre-bundles either take a nearly parallel course from tendon to tendon or they converge from the tendon of origin toward the tendon of insertion (see fig. 338, c-e). The gi-eater the distance from tendon to tendon, the more marked is the interdigitation of the constituent fibre-bundles. In elongated muscles the tendons of origin and insertion may either arise near the extremities of the muscle or may extend for a considerable distance on the surface or within the substance of the muscle. In the former case the belly of the muscle is composed of bundles of interdigitating fibres which take a course parallel with the long axis of the muscle. This is shown diagi'ammatic- ally in fig. 338, f. An example may be seen in the sartorius muscle of the thigh (fig. 411). When the tendons extend far on the surface or within the substance of the muscle, the con- stituent fibre-bundles take a course oblique to the long axis of the muscle. When they take a course from a tendon of origin on one side toward a tendon of insertion on the other, the muscle is called unipenniform (see fig. 338, g, and the extensor digitorum longus, fig. 415). In other instances the fibre-bundles converge from two sides toward a central tendon. Such a muscle is called bipenniform (see fig. 338, h, and the flexor hallucis longus, fig. 416). When there are several tendons in the muscle between which the fibre-bundles run obliquely, the muscle is called multipenniform. In fusiform muscles the tendons usually either embrace the ex- tremity of the muscle like a hollow cone, or they extend far on the surface or within the sub- stance of the muscle. In such muscles the fibre-bundles take a curved course from one tendon to the other. The bundles which arise highest on one tendon are inserted highest on the other, and the fibre-bundles of lowest origin have the lowest insertion. This structm-e is diagram- matically shown in fig. 338, i. A good example may be found in the rectus femoris muscle (fig. 411). Many other arrangements of the fibre-bundles are found, and the arrangements here shown may be variously combined. In most muscles the architecture is decidedly complex. In the 316 THE MUSCULATURE more complex muscles dense connective-tissue septa, or intramuscular fasciae, serve to separate different regions of the muscle from one another. In general there are groups of muscle fibre- bundles surrounded by a greater amount of connective tissue, or perimysium internum, than that surrounding the individual fibre-bundles, and the latter are surrounded by a denser connective Fig. 338. — Diagrammatic Outlines to Illustrate Various Types op Muscle Archi- tecture AND THE Relations of the Main Nerve Branches to the Fibre-bundles op THE Muscle. a. Two segments of the rectus abdominis muscle of a small mammal, b. Portion of sheet-like muscle with two nerve-branches and intramuscular nerve plexus, c. Typical quadrilateral muscle with nerve passing across the muscle about midway between the tendons, d and e. Two triangular muscles with different types of innervation, f. Long ribbon-like muscle with interdigitating fibre-bundles, g. Unipenniforra muscle, h. Bipenniform muscle, i. Typical fusiform muscle. The main intramuscular nerve-branches are distributed to the fibre-bundles about midway between their origins and insertions, n. nerve. > V tissue than that surrounding the component muscle-fibres. The muscles are surrounded exter- nally by a more or less dense sheet of connective tissue called the perimysium externum, or epimysium, which is continuous with the connective tissue within the muscle, the perimysium internum. In the following pages 'muscle fibre-bundle' is used to denote small groups of muscle-fibres, 'fasciculus' to denote large, more or less isolated, groups of fibre-bundles. Embryonic development of muscles. — The voluntary muscles are of mesodermal origin. The muscles of the trunk arise chiefly from the myotomes, those of the head and limbs chiefly from the mesenchyme in these regions. New muscle fibres are formed mainly before birth. After birth, growth of muscles depends on growth of individual muscle fibres. TENDONS 317 Tendons. — Muscles vary not only in general form and in the relations of the constituent fibre-bundles to the intrinsic skeletal framework, but also in the mode of attachment to the parts on which they act. In many instances the fibre-bun- dles impinge, perpendicularly or obliquely, directly upon a bone or cartilage. The tendinous tissue arising from the fibre-bundles of the muscle here is attached to the periosteum or perichondrium or to the bone directly. A broad attachment is thus offered the muscle. Instances of this mode of attachment may be seen in the attachment of the intercostal muscles and of many of the muscles attached to the shoulder and hip girdles. In the case of most thin, flat muscles the muscle is continued at one or both extremities into thin, tendinous sheets called aponeuroses, composed of connective tissue. Well-marked instances may be seen in the transverse muscle of the abdo- men (fig. 390), and the trapezius and latissimus dorsi muscles of the back (fig. 355) . The extent of development of these aponeuroses is generally inversely proportional to the development of the muscle — the more extensively developed the muscle is in a given individual, the less extensive the aponeurotic sheet.* Most muscles are continue,d at one or both extremities into dense, tendinous bands which may be comparatively short and thick, like the tendon of Achilles (fig. 413) , or very long and narrow, like the tendon of the palmaris longus (fig. 370) . In this latter case the tendon represents in part the remnants of musculattu-e more highly developed in the lower vertebrates. In most instances, however, the tendons are structures specifically differentiated for definite functions and are composed of bundles of parallel connective-tissue fibrils held together by an inter- lacing fibrous-tissue framework. The tendons usually contain a relatively small amount of elastic tissue. The tendons are attached to the skeleton early in embryonic development. As the bones enlarge the tendons become in part incorporated in the substance of the bone and ossified. In some tendons sesamoid bones are developed in the neighbourhood of joints over which the tendons pass. Examples of these are the patella at the knee-joint (fig. 412) and the sesamoid bones of the thumb and great toe. Where muscles or tendons closely envelope a joint, there is usually formed a close union between the connective tissue of the capsule of the joint and that of the muscle or the tendon. Special bands may develop in the direction of the pull of the muscle (lig. popliteum obhquum). Where tendons run for some distance across or beneath a fascia, they are usually either bound to the fascia by a special investment, as near the wrist and knee (fig. 366 and fig. 414), or are fused with the fascia, as in the case of the ilio- tibial band. Fibrous tracts in the fascia may indicate stress under muscle con- traction (the lacertus fibrosus of the fascia of the forearm) . Often in broad aponeurotic attachments of muscles there is formed in the ten- don near the attachment a fibrous archway [arcus tendineus] for the passage of blood-vessels, nerves, muscles, or tendons. The tendinous arch is either fastened at both ends to the bone, or at one end it is connected with'a joint capsule or other membrane. The dorsal attachment of the diaphragm (fig. 391) and that of the adductor magnus to the femur (fig. 409) offer good examples of tendon arches. In digastric and polygastric muscles the transverse tendons which separate the bellies are often composed of narrow, incomplete bands of fibrous tissue. Such a transverse band is called an inscriptio tendinea (see Rectus Abdominis Muscle, fig. 388). Tendon sheaths. — The tendons are held in place by sheaths composed of dense connective tissue. These sheaths vary in different regions. In the most com- plete form they confine tendons in osseous grooves which they convert into osteo- fibrous canals on the flexor surface of the digits. The sheath is here called a vagina fibrosa tendinis. It is strengthened by tendinous bands (vaginal liga- ments). In other regions special dense bands or ligaments, retinacula tendinum, confine a series of tendons in place, as at the ankle (fig. 417), or fasciae may be modified for this purpose, as at the back of the wrist (fig. 366) . A tendinous loop, * The terms fascia and aponeurosis are often loosely and interchangeably used. It seems best to make a distinction by restricting the term fascia to membranous sheets of investment, and aponeurosis to broad tendons. The latter may, however, be inserted into and form a part of the former. > 318 THE MUSCULATURE annulus fibrosus, may hold a tendon in place, as, for instance, the trochlea of the tendon of the superior oblique muscle of the eye. Synovial bursas [bursae mucosae]. — Where there is freedom of action between muscles and tendons and the surrounding parts, there intervenes a loose connective tissue. In regions where the pressure is great or considerable friction would re- sult were these conditions retained, there are developed special cavities with smooth surfaces and containing fluid. Most of these bursas are developed from the intervening connective tissue at a period in embryonic life preceding muscular activity, but special bursas may later be developed as the result of unusual pressure or muscular activity after birth. An instance of a bursa lying in a region of fric- tion may be seen in the bur?a intervening between the tendinous posterior surface of the ilio-psoas muscle and the ilio-femoral ligament. As an instance of a bursa lying in a region of intermittent pressure may be cited that between the tendon of Achilles and the calcaneus. Most synovial burste intervene between a tendon and a bone, a tendon and a ligament, or between two tendons (subtendinous bursse mucosae). Others lie be- tween two muscles, a muscle and some skeletal part, or between a muscle and a tendon (submuscular bursae mucosae) ; or below a fascia (subfascial bursae mu- cosas). Subcutaneous bm-sse have been referred to in connection with the tela subcutanea (see p. 313). Most bursas are developed near joints. The bursae may so expand during active life that they come to communicate with other bursae or with a neighbouring joint cavity. Synovial sheaths [vaginae mucosae tendinum]. — Synovial sheaths are developed about tendons where the latter are confined in osteo-fibrous canals, as in the fingers. The wall of the canal and the enclosed tendon, or tendons, are each covered by a smooth membrane which at the extremities of the canal is reflected from the wall to the tendon. Between the membrane covering the tendon and that lining the canal is a sjaiovial cavity. An interesting feature of these tendon- sheaths is the presence of mesotendons, delicate bands of vascular connective tissue which run in places from the osseous groove to the tendon and carrj^ blood- vessels and nerves. Trochlese. — Where a tendon passes at an angle about a bone, the tissue in the groove in which the tendon runs frequently is composed of hj'aUne cartilage instead of bone. An example may be seen in the trochlear process of the calcaneus. Nerves. — To each muscle of the body a nerve containing motor and sensory fibres is distributed. A few muscles receive two or more nerves. Sherrington has estimated that in the muscle-nerves of the cat two-fifths of the fibres are sensory and thi-ee-fifths motor. The muscles of the liead and in part those of the neck are supplied by branches of the cranial nerves. The intrinsic muscles of the neck, back, thorax, and abdo- men are supplied by branches which arise fairljr directty from the spinal nerves. The muscles of the limbs are supplied by branches from nerve-trunks which arise from plexuses formed by the spinal nerves in the regions near which the limbs are attached. The main nerve-trunks lie beneath the superficial muscles. They usually run in the intermuscular septa which separate the deeper groups of muscles from one another and from the superficial muscles. The nerve-branches which enter a given muscle usually pass in where the larger intramuscular septa approach the surface of the muscle, and then ramify tlu-ough the perimysium internum, the smaller branches being distributed in the finer layers of connective tissue which surround and separate the primary muscle fibre-bundles, to the constituent muscle- fibres of which terminal branches are given. Special sensory end organs are distributed chiefly in the large intramuscular septa, in the tendons and in the muscles near the tendons. Simple sensory endings are found on the muscle fibres. The size of a nerve supplying a muscle is not proportional to the size of the latter, but rather to the comple.xity of movements in which the muscle plays a part. Muscles receive then- nerve supply early in development. During later development the muscle may wander a considerable distance from its place of origin and carry its nerve with it. The diaphragm, innervated by cervical nerves, is a good example. The distribution of the motor nerves varies according to the architectm-e of the muscle, but in general it appears that the nerves are so distributed as to carry the main branches of distri- bution most directly to the middle of the constituent fibre-bundles. This is seen most clearly in muscles with comparatively short fibre-bundles, where the individual muscle-fibres run nearly or quite the entire distance from tendon to tendon (fig. 338 a, c, d, e, g, h, and i). When the distance is long, a marked plexiform arrangement is found (fig'. 338, b andf). To each muscle NOMENCLATURE 319 fibre there is distributed a terminal nerve-fibre which passes through the sarcolemma and ends in a motor end organ (muscle plate) . Occasionally there are two such nerve-fibres to one muscle- fibre. Vessels. — The muscles are richly supplied with blood. In many instances the larger blood-vessels accompany the larger nerve-trunks as they enter the muscle, and their primary branches are distributed in the larger intramuscular septa. Often, however, the main blood-vessels approach a muscle from a direction dif- ferent from that taken by the nerves. Each muscle has, however, its own blood supply. There is little anastomosis between the blood-vessels of a muscle and those of a neighbouring structure, but the anastomosis between the vessels within the muscle is exceedingly rich. Veins, as a rule, accompany all but the smallest arteries within the muscle. The veins are richly supplied with valves, so that muscle contraction promotes the flow of blood through the muscle. Rich cap- illary plexuses sm-round the muscle-fibres. The capillaries are of unusually small diameter. During contraction, the blood is forced from the muscles; during expansion it rushes in through dilated arteries which furnish five or six times as much blood to muscles during exercise as that supplied to them during rest. The connective-tissue sheaths, the larger intramuscular septa, and the tendons of muscles are richly supplied vnih. lymphatics. There are no lymphatics within the muscle bundles or in small muscles. Nomenclature. — The names of the various muscles and their classification are less satisfactory than is desirable. The muscular system was first carefully studied in the human body, and names based sometimes upon the shape, structure, size, or position, at other times upon the supposed function or other associated facts, were applied to the muscles found in various regions. Sometimes two or more names were applied to a muscle to indicate several of these factors. Thus trapezius and triangularis indicate the shape of the corresponding muscles; biceps or triceps indicates the origin by two or three heads; rectus, obliquus, and irans- versus represent the direction taken by a muscle or its constituent fibre-bundles; viagnus and minimus indicate size; sublimis (superficial) and profundus (deep) represent the relative positions occupied; sterno-cleido-mastoid indicates structures to which the muscle is attached; flexor and extensor indicate function; and sar- torius indicates that the corresponding muscle was supposed to be of use to tailors. Since careful study has been devoted to the comparative anatomy of the muscles in various vertebrates, it has become apparent that a simple and more consistent nomenclature applicable to corresponding muscles found in various animals would be of great value. A satisfactory nomenclature of this sort has not, however, as yet been devised and adopted in comparative anatomy, and the established usage of the terms now familiarly apphed to the muscles of the human body makes it seem improbable that even if such a system were devised for comparative anatomy it could be brought into extensive use in human anatomy. For many of the muscles in the human body various synonyms have been in use in different countries. The Anatomical Congress assembled at Basel in 1895, to simpUf}' the nomenclature of human anatomy, adopted in large part the terms in familiar use in England and America. In the following pages the terms approved by the Congress wiU be employed, but where they differ materially from those previously in use, the synonym wUl be given in parentheses. Classification. — The muscles are usually treated strictly according to the region of the body in which they are found. This method of consideration is still of value in a dissector's guide and in text-books of topographical anatomy. But in studying the muscles scientifically it is of importance also to consider them in their more fundamental genetic relationships to one another and to the nervous system. Embryology and comparative anatomy have proved of the greatest value in revealing these relationships. Studies of this nature have revealed well-marked rela- tionships in the adult human musculature which are of practical as well as scientific importance The voluntary musculature may be broadly divided into that of the skeletal axis, the limbs, and the visceral orifices. The musculature of each of these divisions has a different and in general simpler form in the lower than in the higher vertebrates, and in the embryos of the higher vertebrates than in the adult. The musculature of the spinal region of the body axis of fishes, the tailed amphibia, and all vertebrate embryos is metamerically segmented; that is, it is divided along the axis of the body into a series of components corresponding with the segmentation of the vertebral column. Although marked alterations take place in the subsequent ontogenetic differentiation in higher vertebrates, traces of this primitive segmentation are still to be found in the adult; in man, for instance, in the intercostal muscles and the segments of the rectus ab- dominis. In the region of the head conditions are complex, owing to the concurrent presence of muscles which primitively correspond in nature with the segmental spinal musculature, and muscles non-segmental in character, which surround the visceral orfices. This also is true of the anus and external genitalia, where, however, the conditions are simpler. Embrj'ology and comparative anatomy have done much to clear up puzzling features in both regions. ■ The muscles of the hmbs are metamerically arranged in no adult vertebrate. In some of the lower forms a series of axial muscle segments, myotomes, fm-nishes material from which the 320 THE MUSCULATURE musculature of the limbs is differentiated. In the mammals this appears not to be the case, and the muscles are differentiated from the non-segmental tissue of the hmb-buds. Where mammalian musculature is primitively segmental, each segment becomes associated with a corresponding spinal nerve or, in the head, with a nerve which corresponds in series with a spinal nerve. Even when subsequent differentiation brings about marlied alterations in the axial musculature, the nerves maintain to a considerable degree a segmental distribution. Into each of the limbs, where the intrinsic musculature is at no time segmental, there extends during embryonic development a series of segmental spinal nerves, so that in them, as in the region of the body axis, a certain segmentation in the nerve-supply can be made out in the adult. That part of the limb nearest the head in early embryonic development has its muscles supplied by the most cranial, that part nearest the caudal extremity of the body by the most caudal, of the nerves which supply the hmb musculature. There is here, however, considerable over- lapping of the segmental areas. Variation. — In man some variation in the arrangement of the muscles is met with in every individual, and often marked deviations from the normal conditions are found. The muscles vary in their mode of origin or insertion, and in the ex- tent to which muscles of a given group are fused with one another or to which the chief parts of a complex muscle are isolated from one another. Some muscles, like the palmaris longus and the plantaris, are frequently entirely absent, and other muscles generally absent are frequently present. In addition to these frequent variations there are others so rare that many authors prefer to speak of them as anomalies rather than variations. Sometimes muscles may be found doubled by longitudinal division, or two or more muscles normally present may be fused into a single indivisible muscle. Occasionally there occur muscles constantly present in some of the lower animals, but normally not met with in the human body (anomalies of reversion or of convergence). In such instances the muscle may be normally represented by a tendon or fascia. At times the anomalies are supposed to be not a reversion to an ancestral condition, but a dis- tinct step in advance. This, however, is difficult to prove. At other times no phylogenetic relation is apparent, and the anomaly is looked upon as a monstrous sport or as the result of somepathological condition. The nerve-supply of the muscles is of value in the study of muscle variations. There is, however, not infrequent variation in the nerves with relation to the supply of the muscles. Physiology. — From the standpoint of morphology the muscles are grouped according to their intimate relations to one another and to the peripheral nerves, relations, as noted above, that are made more clear by a study of comparative anatomy and embryology. From the physiological aspect a different grouping of the muscles is required, because muscles belonging morphologically in one group may have different physiological functions in the animal body. The chief features of the mechanical action of muscles may be briefly considered here. Most muscles act on the bones as levers. In physics three types of levers are recognised In levers of the first type (fig. 339, I) the fulcrum (F) lies be- tween the place where power (P) is exerted on the lever and the point of resist- ance or load (L) . Levers of this kind are frequently met with in the body. A good example is seen in the attachment of the skull to the vertebral column. The fulcrum lies at the region of attachment; the weight of the skull tends to bend the head forward, while the force exerted by the dorsal muscles of the neck serve to keep the head upright or to bend it back. In levers of the second class (fig. 339 II) the point on which power is exerted moves through a greater distance than the point of resistance. Speed of move- ment is thus sacrificed to power. Levers of this type are exceedingly rare in the animal body. An example in the human body is the foot when the body is raised on the toes. In levers of the third class (fig. 339, III) the point on which force is exerted moves a less distance than the point of resistance. Power is thus sacrificed to speed. This is the common form of leverage found in the body. A good ex- ample is found in the action of the muscles which flex the forearm on the arm. The region in which the biceps and brachialis are attached is but a short dis- tance from the elbow-joint or fulcrum, while the hand may be looked upon as the region of resistance to the force exerted. A movement of the point P through a short distance will cause L to move through a great distance. The more the angle between a muscle or its tendon and the bone on which it acts approaches a right angle, the greater is the power of movement exerted by the muscle. The arm in fig. 339, III, is in the position of greatest advantage for the action of the biceps on the forearm. All boys know that it is easier to 'chin' oneself after the arm is partly bent than when hanging PHYSIOLOGY 321 straight from a bar. Many of the muscles run nearly parallel with the parts on which they act, but the tendons before their attachment are usually either carried over a bony prominence or some fascia or hgament acts as a pulley so that tlie tendon is inserted at an oblique angle. At other times a process for the attachment of the tendon projects from the bone and causes the force of the contracting muscle to be more advantageously exerted on the bone. It may, of course, readily be seen that the greater the distance of the attachment of a muscle from the joint over which it acts, the greater will be the power exerted by the muscle. In considering the movements of the body, it is convenient to recognise two groups, simple and complex. To the former, which alone can be considered in a text-book of anatomy, belong such movements as flexion, extension, adduc- tion, rotation, etc., while to the latter belong those associated movements which give rise to changes in the positions of the body as a whole or of extensive regions of the body. In flexion the extremities of the trunk or limbs or special portions of these regions are bent near to one another; in extension the reverse movement is brought about. The parts are straightened or even bent beyond the straight position (over-extension). Fig. 339. — Thbee Diagrams (after Testut) to Illustrate Different Types of Levers in THEIR Relations to the Mechanical Action of the Muscles. m In abduction transverse movements are made, a part being bent away from the median line of the body or limb; in adduction the reverse movement is brought about. In rotation a part is turned on its longitudinal axis. The rotation of the femur at the hip-joint is called medial rotation when the toes are turned medial- ward, lateral rotation when the toes are turned lateralward. Rotation at the shoulder-joint is called medial when the thumb is turned forward and medial- ward toward the body, lateral when the reverse movement takes place. These movements are also carried out at the elbow-joint, but here medial rotation is called pronation, lateral rotation, supination. Fick prefers these terms also for the rotation at other joints as at the shoulder, hip and knee. At the shoulder- joint the swinging of the arm toward the back is called exten- sion; toward the front, flexion; and from the side, abduction. Moving the arm toward the mid-dorsal or mid-ventral line is called adduction. Taking the body as a whole the musculature may be divided into two main divisions, an ex-pander division and a, contractor division. In general the extensors, abductors and lateral rotators expand, the flexors, adductors and medial rota- tors contract. In the most expanded condition the head and spine are extended or even sUghtly hyper- extended (flexed dorsally), and the limbs project laterally from the body with the backs of the hands and feet facing dorsalward, the palms and soles ventral ward, and the digits spread out. In the fully formed human body it is not possible to put the lower extremity in the completely expanded position, although it is in this position early in embryonic development. As develop- ment proceeds the lower extremity is adducted and rotated medialward and the girdle is so fixed that full abduction becomes no longer possible. In many of the lower vertebrates full abduction is possible throughout life in the lower extremities just as it is throughout life in the upper extremities in man. Full extension of the spinal column in man is also hindered in the thoracic region by the thorax, and in the sacro-coccygeal region by the osseous union of the vertebrae with one another as well as by the attachment of the hip girdles. The lumbar region in man is in a condition of permanent hyper-extension. 322 THE MUSCULATURE In the fully contracted condition the head and spinal column are strongly flexed, and the digits are adducted, the various segments of the Hmbs are flexed and the Umbs are adducted, flexed and rotated medialward toward the middle of the trunk. The body approaches a ball in form. It is the position taken by a gymnast when turning a somerset in the air, and is in marked contrast to the fuUy expanded condition which would be assumed could man fly Mke a bat or glide Uke a flying squirrel. In general, the muscles which tend to put the body or a part of the body into the expanded position form a distinct group as contrasted with those which tend to put the body into the contracted position. The chief musculature which extends the head and trunk lies dorso-lateral to the spinal column and is supplied by the dorsal divisions of the spinal nerves. The chief musculature which flexes the head and trunk lies ventro-lateral to the spinal column and is supplied by ventro-lateral divisions of the spinal nerves. The chief muscles which abduct, extend and rotate the limbs lateralward arise during embryonic development on the dorsal sides of the limb buds and are innervated by branches from the dorsal sides of the brachial and lumbo-sacral nerve plexus. The chief muscles which flex, adduct and rotate the Hmbs medialward arise on the ventral sides of the Umb buds and are supphed by nerves which arise from the ventral sides of the hmb plexuses. To these general rules there are some exceptions, the most marked of which is at the hip-joint where rotation of the girdle has brought about a condition in which the primitive action of the flexor and extensor groups is partly reversed. The chief flexors (the ilio-psoas and rectus femoris) belong to the dorsal division and some of the chief extensors (the hamstring muscles) belong to the ventral division. At the ankle-joint the ex- ception is more apparent than real. What is usually called flexion at the ankle-joint is really hyper-extension and the reverse movement is the nearest we can come to real flexion. In the extremelj' contracted position of the body as a whole the feet are extended (flexed plantar- ward) at the ankle-joint. Muscles which produce a movement in a common direction are called S3aiergists, while those whose contraction produces opposite movements are called antagonists; e. g., the flexors and extensors are antagonists. In the actual working of the muscular system, however, when a set of muscles is contracting to produce a movement, the antagonists also contract to a .;ertain degree. The movement is the result of nerve /^impulses^ sent simultaneously to all the muscles which act on the part moved. | The relation of the internal architecture of a muscle to the movements to which its contrac- tion gives rise is a complex subject, the details of which cannot be entered into here. In general it may be said that when the fibre-bundles run directly from one attachment to the other, as in fig. 338, a and f, the force exerted by the contraction of the individual muscle-fibres is most efficiently utilised and the extent of the movement varies directly as the length of the fibres, while the force exerted varies directly with the number of the fibres. In muscles of the types indicated in fig. 338, g, h, i, a certain amount of the extent of move- ment and of the force exerted by the contraction of the individual fibres is not effectively exerted on the parts moved by the muscles, as may be seen by applying to this action the laws of the parallelogram of forces. In such muscles, however, the great number of short muscle- fibres composing them makes possible the exertion of great power with some loss of speed of contraction in the muscle as a whole. The direction of the movements which result from muscular contraction is in large part determined by the shape of the articular surfaces, none of which are to be looked upon as simple fulcra, but instead, during a given movement, the fulcrum shifts from one region to another of the joint. In different muscles the extent of contraction of the constituent fibre-bundles during activity varies considerably. While usually the length of the contracted fibre-bundles is half that of those in the extended state, the amount of shortening in some muscles is only 25 to 35 per cent. Functional activity is necessary for the fuU development or for the maintenance of develop- ment in muscles. Muscles atrophy if their nerve supply is injured or if they are passively prevented from contracting. Order of treatment. — The muscles and fascia are here treated in the following order : — (1) those of the head and neck and shoulder girdle (p. 323) ; (2) those of the upper extremity (p. 360); (3) those of the back (p. 410); (4) those of the thorax and abdomen (p. 422); (5) those of the pelvic outlet (p. 439); (6) those of the lower extremity (p. 452). The reason for taking up the musculature in the order named is, that during embryonic development musculature belonging primitively to the head comes to overlap that of the neck; that of the neck spreads over the region of the back and thorax, and becomes attached to the shoulder girdle; that of the arm extends over the region of the thorax, abdomen, and back; that of the back partially over the region of the thorax; while that of the abdomen enters into intimate relation with the pelvic girdle. So far as practicable the musculature of these various regions will be taken up according to fundamental morphological relationships. Since a morphological grouping of the muscles does not accord perfectly with a physiological grouping, there is given at the end of this section a table showing what muscles are concerned in performing the simpler voluntary movements. HEAD, NECK AND SHOULDER GIRDLE 323 The topographical relations of the muscles in various regions of the body are illustrated in the series of cross-sections given for each region. Tables illustrating the relations of the central nervous system and the per- ipheral nerves to the muscles are given in the section on the nervous system (Section VI). Fig. 340.— Human Embryo (Le) 42 mm. Long. (After His.) Auditory sac Branchial clefts Upper limb First thoracic myotome Sixth thoracic myoton First Ijimbar myotome I. MUSCULATURE OF THE HEAD, NECK AND SHOULDER GIRDLE PHYSIOLOGICAL AND MORPHOLOGICAL ASPECTS The head, situated at the anterior end of the trunk in bilaterally symmetrical animals, is primitively that part of the body first brought into contact with new surroundings as the animal moves forward. We therefore find developed here the most highly differentiated organs of .special sense, those of vision, hearing, and smell, through which the animal is put in touch with an environment more or less removed from immediate contact with the body. In connection with these 324 THE MUSCULATURE organs of special sense, the brain is developed. In most animals the head also is the chief organ for the prehension of food and for attack and defense. The neck is a part of the trunk differentiated to give freedom to the movements of the head. The forelimbs, relatively unimportant as the forefins in the fishes, become important organs of locomotion in the land animals. In the fishes there is no true neck, but the forefins are developed at the sides of the cervical part of the trunk. In the higher vertebrates the forelimbs are also first differentiated at the sides of the cervical region (fig. 340) but, as embryonic development goes on, they shift caudalward to the sides of the cranial (anterior) part of the thorax. The cervical region is thus left free for movement but the musculature and nerves of the upper extremity remain intimately related to it. In man, with the assumption of the erect posture, the head no longer has to bear the brunt of the new surroundings as the body moves forward. There is, however, a distinct advantage in having those organs of special sense, which put the individual into touch with the more distant parts of the environment, situated high above the ground, and a motile neck is of great value in directing the organs of special sense toward various parts of the environment. The develop- ment of the superior extremities as organs for the prehension of food and as organs of attack and defense reduces the value of the head for these purposes, but still leaves it the important functions of the reception of food and air and the preparation of food for gastric and intestinal digestion. The head, furthermore, assumes a new and most important function as an organ for the expression of the emotions and of speech. The expression of the emotions, such as anger, fear, affection and the like,* is brought about largely through the action of flat, subcutaneous "facialis" muscles which underlie most of the skin of the face and head and extend down under that of the neck (figs. 341 and 344). They also line the mucous membrane of the lips and cheeks. Most of them arise from the surface of the skull and are inserted into the skin, which they pull in various directions causing it to become smooth or twinkled, according to the direction of the pull. The various muscles are grouped about the buccal, nasal and aural orifices and about the orbit of the eye. Some of the fibre-bundles are arranged so as to constrict the orifices, others radiate out so as to dilate them. The chief groups of muscles of the head and neck, in addition to the facialis group just mentioned, are the muscles of the orbit and middle ear, the muscles used in mastication and swallowing (cranio-mandibular, supra- and infrahyoid groups, muscles of the tongue, soft palate and pharj^nx), the muscles of the larynx, and the ventral and dorsal groups of muscles which lie in the region of neck, extend over the thorax and move the head, neck and shoulder girdle. A brief summary of these groups will be given before proceeding to a more detailed account. Facialis group. — The muscles are especially well developed about the mouth, a sphincter muscle {orbicularis oris) serving to close, the radiating muscles to open the lips {quadratus labii superioris and inferioris), to pull the corners ot the mouth in various directions, as, for instance, upward to express bitterness {caninus) or pleasure {zygomaticus) , or lateral- ward and downward to express grief or pain (risorius, triangularis, plalysma) or to protrude the lips as in pouting {mentalis and incisive muscles). The buccinator, which radiates out from the corner of the mouth and hues the mucous membrane of the cheek, is used in mastication and whisthng. About the orbit and in the eyelids a circulai- musculature {orbicularis oculi) is broadly developed. It is usedto close the eyes, and to contract the skin about the orbit. Associated with the orbicularis are muscles which produce perpendicular furrows in the skin of the fore- head above the nose (procerus, corrugator). The skin is drawn upward from the orbit and horizontal furrows are caused in the skin ot the forehead by muscles attached to the scalp (epicranius). Two of these muscles, the occipitales, arise one on each side from the occipital bone and are attached to an aponeurosis which lies beneath the scalp to which it is firmly united. Two of the muscles, the frontales, extend one on each side from this aponein-osis to the skin above the eyebrows. About the nasal orifices there are weak constrictors (alar part of the nasalis, depressor aloe nasi) and dilators (dilator naris anterior and posterior, transverse part of the nasalis, angular head of the quadratus labii superioris). From the ear (auricle) three flat muscles radiate, one backward (auricularis posterior), one upward (auricularis superior) and one forward (auricularis anterior). These muscles are seldom functionally developed. They pull the auricle in their respective directions. They may be looked upon as (primitively) dilators of the aural orifice. On the cartilage of the auricle are several rudimentary " intrinsic " muscles which may be looked upon as remnants of a constrictor of this orifice. *See Darwin: The Expression of the Emotions in Man and Animals. GROUPS OF MUSCLES 325 In the orbital cavity there are six muscles which are attached to and move the eyeball and one muscle (the levator palpehroe superioris) which extends into and raises the upper lid (fig. 341) . Of the muscles which move the eyebaU five arise hke the levator of the lid, from the back of the orbit. Four of these, the rectus muscles, are inserted respectively into the superior, inferior, medial and lateral sides of the eyeball and direct the pupil upward, downward, medialward and lateralward. One, the superior oblique, sends a tendon through a loop at the upper, front part of the nasal side of the orbit and thence to the upper surface of the eyeball. Another muscle, the mferior oblique, arises from the nasal side of the front of the lower part of the orbit and is attached to the lower part of the eyebaU. The obUque muscles prevent the rectus muscles from rotating the eyeball. These muscles are supphed by the third, fourth and sixth cranial nerves. They are described in the section on the eye, p. 1067. In the middle ear are two small muscles (the tensor tympani and the stapedius) attached respectively to the malleus and stapes and supplied by fifth and seventh cranial nerves. They are described in the section on the ear, p. 1091. Mastication and swallowing. — The complex musculature used in biting, masticating and swallowing food is used also in speech in conjunction with the muscles of the larynx and the lips. The two movable bones of the skull concerned with these functions are the mandible and the hyoid bone. The mandible articulates with the skull on each side, just in front of the external audi- tory meatus. The hyoid bone is connected on each side by the stylo-hyoid ligament with the styloid process of the temporal bone, which descends just behind the external auditory meatus. A powerful group of muscles, the cranio -mandibular muscles (figs. 344, 345, 346, 347 c), or muscles of mastication, arise from the temporal fossa {temporal muscle), the zygomatic arch [masseter muscle) and the pterygoid process (external and internal pterygoid muscles) and are inserted into the coronoid process of the mandible [temporal muscle), the outer side of the ramus {masseter muscle), the inner side of the ramus {internal pterygoid), and into the condyle of the jaw {external pterygoid). These muscles raise the jaw, move it forward and from side to side, and are used in biting and chewing the food. They are innervated by the fifth cranial (masticator) nerve. Another less powerful group of muscles, the suprahyoid group (fig. 348), is divisible into two subdivisions, hyo-mandibular which extends in front between the hyoid bone and the ramus of the jaw (anterior belly of the digastric, genio-hyoid, mylo-hyoid) and a hyo-temporal group which extends between the hyoid bone and the temporal bone back of the external audi- tory meatus {stylo-hyoid, posterior belly of the digastric). Two of the hyo-mandibular muscles (the anterior belly of the digastric and the mylo-hyoid) are innervated by the trigeminal; the genio-hyoid by the hypoglossal nerve. The two hyo-temporal muscles (posterior belly of the digastric and stylo-hyoid) are innervated by the facial nerve. Morphologically therefore, as indicated by this innervation, the muscles of this group are diverse. Physiolog- ically they are closely united. The group, acting as a whole, elevates the hyoid bone and with this the larynx and the tongue. If, however, the hyoid bone be fixed by contraction of the neck muscles (infrahyoid muscles) attached to its lower border, the suprahyoid muscles act as antagonists of the cranio-mandibular muscles and depress the jaw. The hyo-mandibular muscles form, together with the tongue, the muscular floor of the mouth. When acting with the hyo-temporal muscles they help the tongue to pass food into the pharynx. When acting alone the hyo-mandibular muscles draw forward the hyoid bone and with it the base of the tongue and the larynx and thus open the passage from the pharynx into the oesophagus. The two hyo-temporal muscles, acting in conjunction with the middle and inferior constrictors of the pharynx, draw the hyoid bone and larynx backward, as well as upward, and thus constrict the pharynx while giving free passa'_e for air from the naso-pharynx into the larynx. The chief functions of the suprahyoid group are, therefore, to play a part in deglutition and respiration. Closely associated with the muscles of the suprahyoid group in the performance of these important functions are the muscles of the tongue, the pharynx and the soft palate. The bulk of the tongue (fig. 349) is made up of muscles which have their origin on each side from the inner surface of the front part of the mandible {genio-glossus) , the hyoid bone {hyo-glossus and chondro-glossus) and the styloid process of the temporal bone {stylo-glossus) . Muscles also connect the tongue with the palate (glosso-palatinus) and with the pharynx {glosso-pharyn- geus). These muscles, together with intrinsic longitudinal, transverse and perpendicular fibre-bundles, enable the tongue to perform the complex activities associated with mastication and swallowing and with speech. During mastication the tongue passes the food from side to side between the teeth. When the food has been masticated the tongue forms a bolus of it and then this is passed into the pharynx by a sudden elevation of the dorsum of the tongue produced in part by the muscles of the tongue, in part by the suprahyoid group of muscles. The muscles of the tongue are described on p. 345. The pharynx is the dilated upper part of the alimentary canal into which open the Eus- tachian tubes, the nasal passages, the mouth and the larynx. The walls of the side and back of the pharynx are composed mainly of muscular tissue. The chief muscles are three " con- strictor " muscles on each side, a superior, a middle and an inferior, and an elevator and dilator, the stylO'pharyngeus (fig. 894). The three constrictor muscles are attached to the median raphe* which extends in front of the spinal column from the base of the occipital bone to the sixth cervical vertebra. The superior constrictor muscle is attached to the pterygoid process, the pterygo-mandibular ligament, the mandible and the side of the root of the tongue (fig. 343) ; the middle constrictor to the hyoid bone ; and the inferior constrictor to the larynx. These muscles constrict the pharyngeal orifice and thus force food into the oesophagus. The stylo-pharyngeal muscle, which extends from the styloid process into the lateral wall of the pharynx, serves to * The attachments to the raphe are usually spoken of as the insertions, those to the bones in front as the origins of these muscles. The raphe is, however, a more fixed structure than most of the structm'es to which the constrictors are attached in front. 326 THE MUSCULATURE elevate and dilate the pharynx and elevate the larynx. The muscles of the pharynx are de- scribed on page 1134. The orifices of the various passages into the pharynx are dilated or constricted by muscular action. The orifices of the nasal passages, the Eustachian tubes, and the mouth are controlled mainly by the musculature of the soft palate and pharynx. The orifice of the larynx is con- trolled by special muscles which act in conjunction with those of the suprahyoid group, the tongue, and the pharynx. The soft palate is a muscular partition which is continued backward from the hard palate between the buccal cavity and the naso-pharyngeal orifice and then bends downward between the back part of the mouth and the nasal part of the pharynx, terminating in a median pro- jection, the uvula. Above, on each side, back of the fold of tissue {plica salpingo-palatinus) which descends from the ventral border of the orifice of the Eustachian tube and which marks laterally the passage from the nose into the pharynx, there is a muscle,- the levator veli palatini (fig. 343~>. This arises from the petrous portion of the temporal bone and from the Eustachian tube descends to the middle of the side of the soft palate and then spreads out broadly on its dorsal side. The muscle from each side interdigitates to some extent with that of the other side. These muscles raise the soft palate toward the upper part of the posterior wall of the naso- pharynx and thus shut off the nose from the buccal portion of the pharynx during deglutition. The sides of this portion of the pharynx are, meanwhile, constricted by the superior constrictors of the pharynx and by the pharyno-palatinus muscles described below. Contraction of the levator veli palatini tends to cause folds of tissue to close firmly the opening of the Eustachian tube. This is counteracted by the tensor veli palatini muscles (fig. 343). One of these arises on each side from the pterygoid region of the sphenoid bone, and is inserted into the anterior part of the soft palate by a tendon which passes beneath the hamular process of the pterygoid process. Contraction of this pair of muscles flattens the anterior part of the soft palate and exerts a traction which dilates the orifice of the Eustachian tube. Most authorities state that the Eustachian tube is thus opened each time we swaUow. As air is admitted into the middle ear the tensor tympani muscle contracts so as to prevent too sudden an effect on the ear drum (Jonnesco.) Dorsal to the fibres of the elevator of the palate in the soft palate next the median line on each side there extends from the hard palate into the uvula a small muscle, the muscle of the uvula, which lifts the tip of this and shortens the soft palate from front to back thus enlarging the opening from the mouth into the pharynx. On each side of the uvula the posterior edge of the soft palate is continued backward and downward into a fold, the arcus pharyngo-palatinus, which contains a muscle, the pharyngo-palatinus (fig. 865). This arises from the soft palate, gasses downward and backward on the inner side of the lateral wall of the pharynx and divides iato two fasciculi, one of which is attached to the larynx, the other to the median raphe. The muscle constricts the pharynx at the junction between the nasal and buccal portions and elevates the larynx. As the bolus of food is passed from the dorsum of the tongue into the pharynx the bucco-pharyngeal opening is dilated by the contraction of the elevators of the palate and uvular muscles and the opening into the naso-pharynx is closed not only by the soft palate being raised against the posterior wall of the naso-pharynx but also by the lateral folds raised on each side by the pharyngo-palatinus against the uvula. Meanwhile the larynx is raised by the pharyngo-palatinus and the stylo-pharyngeus, as well as by the suprahyoid muscles, and carried forward by the hyo-mandibular subdivision of the latter muscles so that the opening from the pharynx into the cesophagus is dilated for the passage of food. At the same time the opening into the larynx is constricted from above, the larynx being carried forward beneath the tongue so that the epiglottis slants somewhat backward. This backward slant is aided by the constriction of the thjTeo-hyoid muscle which raises the thyreoid cartilage toward the hyoid bone and by the stylo-glossus muscle whioh pulls the tongue backward over the larynx. The opening into the larynx is constricted at the sides and behind by the contraction of muscles which run in the aryepiglottic folds and by the thyreo-arytenoid and transverse arytenoid muscles. At the end of deglutition the larynx is puUed back from beneath the base of the tongue by the middle and inferior constrictors of the pharynx and the opening is again dilated. The buccal cavity may be shut off from the pharynx by the action of the muscles which pass in the glosso-palatal folds from the soft palate to the mouth in front of the tonsils. These glosso-palatal muscles elevate the folds in which they he, depress the soft palate, and, if the dorsum of the tongue be raised, shut oft' the buccal cavity. The muscles of the soft palate are described on p. 1134. The uvular muscle, the levator veU palaini, the glosso-palatinus and the pharyngo- palatinus muscles are supphed by the pharyngeal plexus. The tensor veU palatini is sup- plied by the mandibular division of the fifth nerve. The pharyngeal muscles are supplied by the glosso-pharyngeal, the vagus, and the spinal accessory cranial nerves. The larynx lies in the neck, but since the intrinsic muscles of the larynx from the standpoint of embryology and comparative anatomy belong with the musculature of the head, it is con- venient to refer to them briefly here rather than to treat of them with the intrinsic muscles of the neck. A full description of the laryngeal muscles is given in the section on the larynx (fig. 981) . They develop from tissue which corresponds with that which in fishes gives rise to the muscles of the gills and are innervated by the nerves which in the fishes innervate the gills, the tenth pair (vagus) of cranial nerves. The movements of the laryngeal cartilages are such as to approximate or draw apart the vocal cords and to loosen or make them tense. The approxi- mation of the vocal cords is produced by the rotation medialward of the vocal processes of the arytenoid cartilages brought about by the lateral crico-arytcnoid and transverse arytenoid muscles. The drawing apart of the vocal cords is produced by the posterior crico-arytenoids. The vocal cords are made long, thin and tense by the crico-thyreoid. They are shortened and thickened by the thyreo-arytenoid (externus) and the vocalis. The inferior laryngeal branch of GROUPS OF MUSCLES 327 the vagus supplies all the muscles but the crioo-thyreoid. This is supplied by the superior laryngeal branch of the vagus. Metamerism. — The muscles thus far considered are essentially visceral muscles, although all are composed of striated muscle cells and all are more or less directly under the control of the will. From the morphological standpoint the muscles of the orbit, the tensor tympani, the muscles of mastication, the hyo-mandibular muscles and the muscles of the tongue have been grouped with the ordinary voluntary skeletal muscles while the facialis musculatm'e, the stapedius, the hyo-temporal muscles and the muscles of the soft palate, pharyn.x and larynx are looked upon as of a more purely visceral origin. A primitive characteristic of the voluntary skeletal muscles is metameric segmentation. This is maintained through life in the trunk musculature of fishes and of tailed amphibia and is passed through as a temporary stage in aU the higher vertebrates. The embryonic segmented muscles are caDed myotomes (see fig. 340). In some regions the metamerism is retained throughout life even in the higher forms, as, for instance, in the intercostal muscles and the intertransverse muscles. But for the most part the primitive metamerism is so lost during the differentiation of the definitive trunk musculature that only traces of it remain here and there as, for instance, in the segments of the rectus abdominis muscle. In the lower forms the myotomes give rise during embryonic development to material utilized in the formation of the limb musculature, but even in the fishes all traces of trunk metamerism are lost in the differentiated limb musculature and in the higher forms, as in man, the limb musculature appears to differentiate directly from the un- segmented tissue in the hmb-buds. In the head the musculature is differentiated directly, as in the limbs, without undergoing a preliminary metameric or myotomic stage. Attempts have been made to show that in primitive forms the cranial voluntary skeletal musculature, in the narrower morphological sense mentioned above, passes through a metameric stage com- parable with the myotomic metamerism of the trunk. This attempt has been partially success- ful as regards the development of the muscles of the eye in some of the lower forms. There is also good evidence that the spinal region of the skull and associated structures represent a part of the metameric trunk fused with a more primitive head so that the musculature of the tongue and the hyo-mandibular muscles belongs morphologically with the primitively metameric trunk musculature. The rest of the cranial musculature gives little evidence of a primitive metameric segmentation and hence is probably to be classed morphologically with the unseg- mented visceral musculature. Of the muscles of the neck, the most superficial, the platysma (fig. 341), is a subcutaneous muscle belonging to the facialis group of the head from which it grows down during embryonic development. It is supplied by the seventh cranial (facial) nerve. It extends from the corner of the mouth and the side of the mandible over the clavicle. It depresses the corner of the mouth, wrinkles up the skin of the neck and aids the circulation by reUeving pressure on the uiiderlying veins. Beneath the platysma there lies a layer composed of two flat muscles (fig. 344) which extend from the base of the skull behind the ear to the shoulder girdle. One of these muscles, the sterno-cleido-mastoid, arises in front from the sternum and clavicle and is inserted into the m.istoid process of the temporal bone and the skull behind this. The other, the trapezius, arises from the base of the skull, and from the ligamentum nuohfe and vertebral spines of the cervical and thoracic regions, and is inserted into the spine of the scapula, the acromion and the lateral third of the clavicle. These two muscles constitute the superficial shoulder -girdle musculature. They extend the head, bend it toward the same side and rotate it toward the opposite side. The sterno-cleido-mastoid and the upper part of the trapezius raise the shoulder girdle and thorax and hence are of use in forced inspiration. The trapezius draws the scapula toward the spine and rotates the inferior angle of the scapula lateralward. The lower part of the trapezius acting alone draws the scapula downward and dorsalward while rotating the inferior angle lateralward. The trapezius is therefore used when the arm is raised high or carried backward. The two muscles of this group are innervated partly by the spinal accessory, and partly by the ventral divisions of the second, third and fourth cranial nerves. They represent in part musculature which in the lower vertebrates is associated with the visceral musculature of the gills (hence the innervation by the spinal accessory, a derivative of the vagus nerve) and in part metameric musculature of the second, third, and fourth cervical segments. During embryonic development this musculature therefore spreads out widely from its origin, the upper cervical region. The lower part of the trapezius varies greatly in the extent of its development caudalward. It may reach only half way down the thoracic region or it may extend into the lumbar region. The deeper musculature of the neck is derived from the cervical myotomes. The primitive segmental musculature of the neck, hke that of the whole trunk, becomes divided at an early embryonic stage into two divisions, a dorsal, supplied by the dorsal divisions of the spinal nerves, and a ventro-lateral supplied by the ventral divisions. The trapezius, although it covers the intrinsic dorsal musculature of the cervical region, insofar as it is of cervical origin, belongs to the ventro-lateral musculature and is derived, apparently, from the first three cervical myotomes. There is also a deeper layer of muscles attached to the shoulder girdle which arise from the ventro-lateral divisions of the lower five or six cervical myotomes but which, with one exception, the levator scapulm (fig. 353), wander over the thorax during embryonic development. This group is described below as the deep shoulder-girdle muscula- ture. The rest of the muscles derived from the ventro-lateral divisions of the cervical myo- tomes are divisible into three gi'oups, the infra-hyoid, the scalene and the prevertebral. The infra-hyoid group hes at the front of the neck, superficial to the larynx and trachea (fig. 348), and is composed of four flat muscles, the sterno-hyoid, sterno-thyreoid, thyreo-hyoid and omo-hyoid (scapulo-hyoid), the names of which indicate the origin and insertion. The chief function of this group of muscles is to depress the hyoid bone, the larynx and the as- sociated structures. When the supra-hyoid group of muscles contracts at the same time, the infra-hyoid muscles help to depress the lower jaw, or if this in turn is fixed by the cranio-man- dibular group, to flex the head. The muscles of this group are derived from the ventral portions 328 THE MUSCULATURE of the first three cervical myotomes and are innervated by the first three cervical nerves through the ansa hypoglossi. The primitive segmental origin of these muscles is frequently indicated by transverse tendons (inscriptiones tendineae). They correspond morphologically with the rectus abdominis musculature. The scalene group (fig. 352) lies at the side of the neck and extends to the first and second ribs from the transverse processes of the lower six cervical vertebrae. The muscles of this group bend the neck toward the side, or if the neck be fixed, elevate the thorax. They come from the lateral parts of the ventro-lateral divisions of the lower five cervical myotomes and are innervated by the lower five cervical nerves. They correspond morphologically with the intercostal and with the lateral abdominal musculature. The prevertebral group lies back of the pharynx and oesophagus and in front of the bodies and transverse processes of the cervical veitebrae. The muscles of this gi-oup arise not only from the transverse processes and bodies of the cervical vertebrae, but also in part from the bodies of the first three thoracic vertebrae and are inserted in part into the cervical vertebrae (?or!(/MS coiM) and in part into the base of the occipital bone {longus capitis). This musculature flexes the neck and the head. When acting on one side it rotates the head toward the same side. It is innervated by the first six cervical nerves. The deep shoulder-girdle musculature. — This becomes differentiated from the ven- tro-lateral divisions of the lowei five or six cervical myotomes. Like the muscles of the superficial layer those of the deeper layer spread out widely from their origin. There are four muscles in the deeper group, all of which become attached to the dorsal border of the scapula. Of these, one, the levator scapulce (fig. 353), remains in the cervical region, extending from the upper cervical transverse processes to the medial angle of the scapula. Two, the rhomboids (fig. 353), extend over the intrinsic dorsal musculature and are attached to the upper thoracic and lower cervical vertebral spines; while the fourth, the serratus anterior (fig. 354), extends over the side of the upper part of the thorax beneath the scapula and is attached to the first nine ribs. These muscles all, however, through their innervation, reveal in the adult their primitive cervical origin. They are supplied by branches from the third to the seventh cervical nerves. The levator scapulae elevates the scapula, the rhomboid muscles retract it and the serratus anterior draws it forward. The levator and rhomboid muscles rotate the shoulder girdle so as to depress the shoulder, the serratus anterior, like the trapezius, rotates it so as to raise the shoulder. The two former muscles are an aid in extending the arm, the latter in flexing and abducting it. When the group, as a whole, contracts action is exerted on the ribs so that the group is of use in forced inspiration. The intrinsic dorsal musculature of the neck, innervated by the dorsal divisions of the cervical nerves, is separated from the scalene muscles by the levator scapula. Dorsally it is covered by the trapezius and the rhomboid muscles. It is to be looked upon as a specialized portion of the system of intrinsic dorsal muscles which extend from the sacrum to the base of the skull on each side of the vertebral column. The primary function of this muscle system is to extend and to rotate the spine and the skuU. In the thoracic region three main subdivi- sions may be recognised, a lateral, the ilio-costal; an intermediate, the longissimus; and a medial, the transverse-spinal group (fig. 381). In the cervical region these three groups may hkewise be recognised and, in addition, there is a superficial group, the splenius (fig. 380) , not represented in the lower thoracic region. The splenius arises from the upper thoracic and lower cervicla spines and is inserted into the transverse processes of the upper cervical vertebrae and into the mastoid processes of the temporal bone and the neighbouring part of the occipital. It acts with the sterno-cleido-mastoid, by which it is crossed near the head, in extending the head, bending it toward the side, but tends to rotate it toward the same side instead of toward the opposite side. Laterally beneath the splenius the ilio-costalis cervicis extends from the upper part of the thorax to the transverse processes of the sixth to the fourth cervical vertebrae, and the longissimus cervicis and capitis extend from the same region to the transverse processes of the mid-cervical vertebrae and to the mastoid process of the temporal bone (fig. 381). These muscles likewise extend and bend the head and neck laterally and rotate it toward the same side. Medially on each side the strong semispinalis capitis (fig. 381), arises from the upper thoracic and the lower cervical vertebrae, spreads out and is inserted into the squamous portion of the occipital bone. It is a powerful extensor of the head. Beneath it numerous fasciculi extend from the transverse proceses to the spines of the cervical vertebrae. These fascicuh, the more superficial of which are the Ion', est, constitute the Scmispinales cervicis, muliifidus, and roiatores muscles. They extend and rotate the neck. Between the successive spines and the transverse process there are short muscles (inler- spinales, intertransversares) . The rectus capitis anterior and the rectus capitis lateralis between the transverse process of the atlas and the lateral part of the occipital belong with the latter series. Between the base of the skull behind and the first two vertebrae there are four deep-seated specialized muscles which constitute the suboccipital group (fig. 382). The rectus capitis posterior major and minor spread out respectively from the spines of the atlas and epistropheus and are inserted beneath the inferior nuchal line of the occipital. The obliquvs capitis inferior arises from the spine of the epistropheus and is inserted into the transverse process of the atlas; the obliquvs capitis superior arises from this and is inserted into the lateral part of the inferior nuchal line of the occipital. These muscles extend and rotate the head. A detailed de- scription of the intrinsic muscles of the back is given on page 410. The muscle fasciae in the head and neck are well developed in connection with most of the groups of muscles except the facialis group and are described in detail in connection with each of these groups. In the head we may here call attention merely to the dense temporal fascia which covers over the temporal fossa and hides from view the temporal muscle. In the neck the fasciae are of considerable practical importance. It is convenient to think of them as divisible into several layers although the various layers fuse to some extent. The external layer (fig. 350) may be looked upon as completely ensheathing the neck and as dividing on each FACIALIS MUSCULATURE 329 side into two layers which ensheath the sterno-cleido-mastoid and trapezius muscles. As a free fascia it is attached to the lower jaw, to the clavicle and sternum, and to the hyoid bone which divides it into a submaxillary and an infra-hyoid portion. It is connected with the fibrous sheath of the parotid and submaxillary glands. The middle layer of cervical fascia is composed of two laminae, one extending between the sterno-hyoid and omo-hyoid and another more deli- cate one beneath this, ensheathing the thyreo-hyoid and sterno-thyreoid muscles and fused with the fibrous sheath which encloses the carotid artery, internal jugular vein and the vagus nerve. The deeper muscles of the side and front of the neck and the intrinsic muscles of the back of the neck are hkewise ensheathed by muscle fasciae. Of the various groups of muscles mentioned above, some, for the sake of con- venience, are treated in connection with the organs to which they belong. Thus the muscles of the eye and ear are taken up in Section VIII; those of the palate, pharynx and larynx in Sections IX and X; the deep dorsal musculature of the neck will be taken up in the section on the intrinsic muscles of the back, p. 410, The remaining groups of muscles will be taken up in the following order: — 1. The facial group p. 329. 2. The cranio-mandibular group p. 338. 3. The supra-hyoid musculature p. 343. 4. The muscles of the tongue p. 345. 5. The superficial shoulder-girdle musculature p. 347. 6. The infra-hyoid musculature p. 350. 7. The scalene musculature p. 353. 8. The prevertebral musculature p. 355. 9. Anterior and lateral intertransverse muscles p. 356. ■ 10. Deep musculature of the shoulder girdle p. 356.* 1. THE FACIALIS MUSCULATURE (Figs. 341, 344) The muscles of this group are intimately connected with the scalp, with the skin of the face and neck, and with the mucous membrane lining the lips and the cheeks. Most of the muscles have an osseous origin and a cutaneous insertion, but there are exceptions. Both origin and insertion may be cutaneous, or the attachment may be to an aponeurosis instead of directly to the skin. The deeper musculature about the mouth is attached to the mucous membrane. The muscles are composed of interdigitating muscle-fibres which are grouped in bundles that take a nearly parallel or slightly converging course and give rise to thin muscle-sheets. The extent of development of the various muscles of the group and their independence varies greatly in different individuals. The region from which the facial musculature originates in the embryo is, in the main at least, that of the hyoid arch immediately below the ear. From here the musculature spreads with the development of the facial nerve, dorsally to the occipital region behind the ear, distally over the neck, ventrally over the face, and upward toward the eye, forehead, and the side of the skull. The course of the development is indicated by the branches of the facial nerve. A somewhat similar phylogenetic development is indicated by conditions found in the inferior mammals and lower vertebrates. According to Ruge and Gegenbam-, the facial musculature is to be looked upon as derived from two muscle-sheets, of which in man the deeper has dis- appeared in the region of the neck while it is differentiated into the deeper facial muscles in the region of the head. The deeper layer of transverse fibres in the neck, the sphincter colli, is found in several of the mammals. The complex development of the facial muscles in man is char- acteristic of the human species, and is associated with the use of these muscles as a means of expression of the emotions, a physiological function superadded to the primitive function of opening and closing visceral orifices. There is much individual variation in the differentiation of the muscles. Fasciae. — The skin of the head and neck is, in most regions, firmly fused with the tela subcutanea. This is composed of a dense fibrous tissue united by a looser areolar tissue to the underlying structures. But a slight amount of fat is embedded in the subcutaneous ti.ssue of the scalp, forehead, and nose. Considerable fat may be embedded in the region of the cheeks, the back of the neck, and the under surface of the chin (double chin). The constantly repeated action of various muscles of the facialis group usually results by middle Hfe in the production of permanent wrinkles due to alterations in the structure of the tela subcutanea and the cutis. The subcutaneous muscles of the cranial vault and the neck are invested with fascial membranes. That covering the cranial musculature externally is firmly fused to the subcutane- * The pectoral muscles and the latissimus dorsi, which extend from the skeleton of the hmb to the front and side of the thorax and the lower part of the back, arise from the hmb-bud during embryonic development, are innervated through the brachial plexus, and wiU, therefore, be taken up in considering the intrinsic musculature of the upper Imrb, p. 360. 330 THE MUSCULATURE ous tissue of the scalp. That covering the subcutaneous muscle of the neck is less firmly fused with the subcutaneous tissue. In the facial region the more superficial muscles are so closely embedded in the subcutaneous tissue that no distinct fasciae intervening between the muscles and the skin can, as a rule, be distinguished. Of the deeper muscles of the facialis group, the buccinator alone possesses a distinct fascia. This muscle lies upon the mucous membrane of the lateral wall of the mouth, and is covered externally by a fascia continued into the fascia investing the superior constrictor of the pharynx. Bursse. — Bursa subcutanea prementalis. Between the periosteum at the tip of the chin and the overlying tissue. Bursa subcutanea prominentias laryngese. In front of the junction of the right and left laminae of the thyreoid cartilage. Fig. 341.^The Superficial Muscles of the Head and Neck. Orbicularis oculi Procerus Quadr. labii sup caput angulare Nasalis, pars transversa Dilator naris anterior-, Dilator naris posterior^ Quadr. labii sup. caput infraorbitale Caput zygomaticum Orbicularis oris Quadratus labii infenoris Triangularis Auricularis superior MUSCLES The muscles of the faciahs group may be conveniently subdivided as follows: — (a) Cervical : the platysma. (&) Oral : the orbicularis oris and the incisivus labii superioris and inferioris; the quadratus labii superioris and inferioris; the caninus, zygomaticus, risorius, and triangularis; and the buccinator, (c) Mental, (d) Nasal: the nasalis, depressor septi, and the dilatores naris. (e) Periorbital: the orbicularis oculi, corrugator, and procerus. (/) Epicranial: the frontalis and occipitalis, with the galea aponeurotica. (g) Auricular: anterior, superior, and posterior. With these the temporalis superficialis is also described. (o) CERVICAL MUSCLE The platysma is a large, thin, quadrangular muscle which runs obliquely from the chin, the corner of the mouth, and the lower part of the cheek across the ORAL MUSCLES 331 mandible and the neck to the proximal part of the thorax and shoulder. The muscles of each side interdigitate across the chin. A short distance below the chin, in the neck, the ventral margins diverge (fig. 341). Origin. — From the tela suboutanea by somewhat scattered bundles — (1) along a Une ex- tending from the cartilage of the second rib to the acromion, and (2) along the dorsal margin of the muscle. Insertion. — Into — (1) the mental protuberance of the mandible and the inferior margin of the mandible; and (2) into the skin of the lower part of the cheek and at the corner of the mouth, where it fuses more or less with the quadratus labii inferioris and the orbicularis oris. Nerve-supply. — The cervical branch (ramus colh) of the seventh cranial nerve forms beneath the muscle a plexus to which the cutaneus colh nerve contributes sensory branches. Relations. — The muscle is situated beneath the panniculus adiposus, to which in the neck it is not very firmly attached. For the most part it is separated from the external layer of the cervical fascia by loose areolar tissue. The main cutaneous rami of the cervical plexus and the external jugular vein lie beneath the muscle. Action. — It wrinkles up the skin of the neck, depresses the corner of the mouth, and thus plays a part in expression of sadness, fright, and suffering. It aids the circulation by relieving pressure on the underlying veins. Variations. — Either the facial or the distal development of the muscle may be more exten- sive than that described above. On the other hand, it ma.y be less developed than usual, and rarely it is absent. Accessory shps have been seen going to the zygoma, the auricle, or the mastoid process, etc., and to the clavicle and sternum. Rarely a deep transverse layer is found in man. Fig. 342. — Diagram to Illustkate the Architecture op the Orbicularis Oris. (After T. D. Thane.) Depressor septi nasi-^ Incisivus sup. ~ (b) ORAL MUSCLES The muscles of the mouth belonging to the facialis system include several intralabial muscles: — a sphincter, the orbicularis oris; a transverse, the com- pressor labii; and four deep submucous muscles which pass from the sides of the lips to the alveolar juga of the upper canine and lower lateral incisor teeth, the incisivi labii superioris and inferioris. From each corner of the mouth there radiate out several muscles; the caninus and zygomaticus upward to the maxilla and zygomatic bone; the risorius lateral ward over the cheek; the platysma and the triangularis downward over the side of the jaw; and the buccinator, lateral- ward over the side of the oral cavity. From each of these fibre-bundles are continued into the more peripheral and superficial portions of the orbicularis. In addition to these muscles there are two retractors or quadrate muscles, one of which, the quadratus labii superioris, extends from the upper lip medial to the angle to the bridge of the nose, the lower margin of the orbit, and the zygo- matic bone; while the other, the quadratus labii inferioris, extends from a corre- sponding position in the lower lip to the side of the chin. The orbicularis oris, compressor labii, and incisive muscles close the lips; the other muscles open them and pull them in various directions. The buccinator, however, plays a part in the closing of the mouth by offering support for the orbicularis. Intralabial Muscles The orbicularis oris (figs. 308, 341, 342, 343) is a complex muscle which surrounds the oral orifice and forms the chief intrinsic musculature of the Ups. Immediately about the orifice, and on the deep surface of the muscle, is a fairly well-defined sphincter, although at the corners of the mouth the fibre-bundles of one hp cross those of the other and are inserted into the mucosa, and to a less extent into the skin. In the mid-line the fibre-l^undles end partly in the perimysium, partly in the skin. About this sphincter area and between its outer margin and 332 THE MUSCULATURE the skin is a complex musculature comprised partly of fibre-bundles prolonged from the muscles which radiate from the corners of the mouth. The more superficial portion of the muscle in the upper Up is composed of fibre-bundles from the triangularis (depressor anguU oris), the more superficial portion of that in the lower lip by fibre-bundles from the caninus (levator anguli oris). These fibre-bundles form commissures at the angles of the mouth and extend toward the median line, where many of them interdigitate with those of the opposite side, and are attached to the skin of the lips. The deeper portions are partly formed by fibre-bundles prolonged from the buccinator, the mandibular fibre-bundles of the latter muscle going mainly to the upper lip, the maxillary fibre-bundles mainly to the lower hp. These fibre-bundles are attached chiefly to the mucosa, near the corners of the mouth. The compressor labii, or muscle of Klein, is composed of bundles of fibres which take a course transverse to those of the orbicularis, and pass obhquely from the skin surrounding the oral orifice toward the mucosa which bounds its inner margin. It is said to be best marked in infants. The incisivus labii superioris is a small muscle-bundle which passes from the alveolar jugum of the upper canine tooth to the back of the orbicularis near the corner of the mouth. The incisivus labii inferioris passes similarly from the alveolar jugum of the lower lateral incisor tooth to the back of the orbicularis in the lower lip. Nerve-supply. — These muscles are suppUed by the buccal branches of the facial nerve which enter the orbicularis on the lateral border. Relations. — The main mass of intrinsic musculature of the lips is placed slightly nearer the mucosa than the skin. On its deep surface lie the labial arteries. Action. — The orbicularis draws the upper lip downward, the lower lip upward. The incisive muscles draw the corners of the lips medialward, and the compressor flattens the lips. Together they serve to close the mouth. Acting separately they may draw different parts of it in the directions indicated by their structure. The circumferential portion of the orbicularis acting with the incisive muscles makes the lips protrude. The central portion of the orbicularis draws the lips together, and when the buccinator also acts, draws them against the teeth. It is this portion of the muscle that has chiefly to do with nutritive functions. The more peripheral parts of the muscle are chiefly utilised in the expression of the emotions. Retractors op the Lips or Quadrate Muscles (Fig. 341) The quadratus labii superioris is a thin, quadrangular muscle with three heads, all of which are inserted into the skin and musculature of the upper lip. The caput zygomaticum (zygomaticus minor) is long and slender and arises from the lower part of the external surface of the zygomatic bone beneath the lower border of the palpebral portion of the orbicularis oculi. It passes obliquely forward over the caninus and orbicularis oris muscles, and extends to a cutaneous and muscular insertion in the upper hp medial to the corner of the mouth. It lies medial to the zygomaticus. The caput infraorbitale (levator labii superioris), a broad, flat muscle, arises from the infra- orbital margin of the maxilla, where it is concealed by the orbicularis oculi. It extends obhquely forward over the caninus and beneath the caput angulare to the skin and musculature of the lateral half of the upper hp. The caput angulare (levator labii superioris alseque nasi) arises from the root of the nose, where it is fused with the frontalis. As it descends it divides into two fasciculi, one of which is attached to the skin and the alar cartilage of the nose; the other passes obliquely downward over the caput infraorbitale to the skin and musculature of the lateral half of the upper hp. Nerve-supply. — The zygomatic ramus of the seventh nerve sends branches to enter the deep surface of each of the divisions of the muscle. Actions. — It raises the lateral hah of the upper lip and the wing of the nose. It is of value in inspiration, serves to express the emotion of discontent, and comes into play in violent weep- ing. Variations. — The caput zygomaticum is often absent. It may be fused with the zygoma- ticus (major). It may be doubled. Its origin may extend to neighbouring structures. The other heads, though more stable, vary considerably, especiafly in the extent of their fusion with neighbouring muscles. The quadratus labii inferioris (depressor labii inferioris) is a thin, rhomboid muscle which arises below the canine and bicuspid teeth from the base of the mandible, between the mental protuberance and the mental foramen, and extends obhquely upward in a medial direction to the orbicularis oris, through which its fibre-bundles pass. Its more medial fibres cross at their insertion with those of the muscle of the other side. It is attached to the skin and mucosa of the lower lip. It is essentially a part of the platysma, and is superficially united to the skin except where covered by the triangularis (depressor anguh oris). It crosses the mental vessels and nerves and a part of the mentalis (levator menti). Nerve-supply. — The mandibular branch of the facial sends twigs into its deep surface near the lateral border. Action. — It draws down and everts the lower Up. It is an antagonist of the mentahs (levator menti). It plays a part in the expression of terror, irony, great anger, and similar emotions. Muscles of the Angle of the Mouth (Figs. 341, 342, 344, 345) The caninus (levator anguli oris) is a flat, quadrilateral muscle which arises from the canine fossa of the maxilla and runs beneath the quadratus (levator) labii superioris to the corner of ORAL MUSCLES 333 the mouth, where it becomes attached to the skin and sends some fasciculi into the orbicularis of the lower lip. Between the caninus and the quadratus labii superioris there is a certain amount of fatty areolar tissue through which the infraorbital vessels and nerves run. Its deep surface extends over the canine fossa, the buccinator muscle, and the mucosa of the Up. The external maxillary (facial) artery passes over its inferior extremity. The zygomaticus (z. major) is a long, ribbon-shaped muscle which arises by short tendinous processes from the zygomatic bone near the temporal suture under cover of the orbicularis oculi. It passes obliquely to the corner of the mouth, where it is attached to the skin and mucosa. The body of the muscle is subcutaneous and is usually surrounded by fat. It crosses the masseter and buccinator muscles and the anterior facial vein. The risorius is a thin, triangular, subcutaneous muscle which extends across the middle of the cheek and lies in a more superficial plane than the platysma, with which it is often fused. It arises from the tela subcutanea above the parotid fascia. Its fibres converge across the masseter muscle toward the angle of the mouth and are attached to the skin and mucosa in this vicinity. It lies above the anterior facial vein and external maxillary artery. The platysma has been described above. The triangularis (depressor anguli oris) is a broad, flat, well-developed, subcutaneous muscle which arises from the base and external surface of the body of the mandible below the canine, bicuspid, and first molar teeth. From here its fibres converge toward the corner of the mouth, where they are in part inserted into the skin and in part are continued into the orbicularis oris of the upper hp. It overUes the buccinator and the quadratus (depressor) labii inferioris muscles. Not infrequently (58 out of 92 bodies — LeDouble) some fascicuh are continued into Fig. 343. (After Eisleh.) Buccinator Muscle and Ptertgomandibular Raphe, as seen from the buccal side. The alveolar processes of both jaws have been removed in the region of the molar teeth. The soft palate and its muscles have been removed. Auditory (Eustachian) .tube Mylo-hyoid Buccinator Internal pterygoid the neck as the transversus menti, a fibro-musoular band formed by the interdigitation of the slips prolonged from each side below the chin and superficial to the platysma. Santorini described the transversus menti as an independent though inconstant muscle. According to Eisler the true transversus menti muscle is to be distinguished from aberrent slips of the tri- angularis or of the platysma in this region. In one instance Eisler found a slender nerve emerging through the platysma and passing to this muscle. Nerue-supply. — The zygomatic branch of the seventh nerve supphes the canine (levator anguli oris) and zygomatic (major) muscles. Branches enter the middle of the deep surface of the latter muscle and the superficial surface of the former near its lateral border. The risorius is suppUed by branches from the buccal rami of the seventh nerve, which enter its deep sur- face. The triangularis (depressor anguh oris) is supplied by the buccal branch through branches which enter its deep surface near the posterior margin. Action. — The caninus (levator anguli oris) and zygomatic (z. major) muscles raise the corner of the mouth, the former at the same time drawing it medially, the latter, laterally. The caninus gives rise to expression of bitterness or menace. The zygomaticus is active in smihng or laughing. When contracted greatly it elevates the cheek and the lower eyehd and produces crow's-foot wrinkles at the corner of the eye. The risorius draws the angle of the mouth later- ally. ^ In spite of its name it is not used to express pleasure, but instead gives rise to an expression of pain. The triangularis (depressor anguli oris) depresses the corner of the mouth and draws it laterally, giving rise to the expression of grief. 334 THE MUSCULATURE Variations. — The risorius is very inconstant in its development, and in its relations to- neighbouring muscles, and is not infrequently quite small. The zygomaticus is rarely absent Its origin may extend to the temporal or masseteric fascias. It may be doubled throughout its length or at one extremity. Frequently the triangularis is divided into three fasciculi. The buccinator (fig. 343) arises from — (1) the molar portion of the alveolar process of the maxilla; (2) the buccinator crest of the mandible, and (3) the pterygo-mandibular raphe of the bucco-pharyngeal fascia. This narrow fibrous band, which separates the buccinator from the superior constrictor of the pharynx, extends from the pterygoid hamulus to the buccinator crest of the mandible. The fibre-bundles are divisible into four sets. The most cranial extend directly into the orbicularis of the upper lip. The next pass through the commissure at the corner of the lips into the orbicularis of the lower lip; the third through the commissure into the orbicularis of the upper hp, and the fourth directly into the orbicularis of the lower lip. The muscle is attached chiefly to the mucosa of the lips near the angle of the mouth. Some fibre- bundles extend to the more medial portion of the mucosa and some through the orbicularis to the skin. Nerve-supply. — By the buccal branch of the facial nerve through filaments which enter the posterior half of its outer surface. Relations. — The muscle is covered externally by the thin bucco-pharyngeal fascia; internally by the mucosa of the mouth. Above its outer surface lie the zygomatic (z. major), risorius, and masseter muscles." Between the last and the buccinator lies a large pad of fat (the buccal fat pad). The parotid duct passes forward over the muscle, and slightly in front of its centre pierces it and passes into the mouth. It is crossed by the external maxillary (facial) artery and anterior facial vein and by the buccal artery and nerve. Actions. — It draws the corner of the mouth laterally, pulls the lips against the teeth, and flattens the cheek. It is of use in mastication, swallowing, whistling, and blowing wind- instruments. Variations. — Occasionally it consists of two laminse, a condition found in many mammals. It may be continuous in part with the superior constrictor of the pharynx, as in the cat. (c) MENTAL MUSCLE The mentalis (levator menti) (fig. 343) is a short, thick muscle which arises from the alveolar jugum of the lower lateral incisor tooth and the neighbouring region of the mandible under cover of the quadratus (depressor) labii inferioris and beneath the oral mucosa, where this is reflected from the lips to the gums. It extends to the chin, where it is fused with the muscle of the opposite side and is attached to the skin of the chin. Nerve-supply. — The mandibular branch of the seventh nerve sends terminal twigs into this muscle. Actions. — It draws up the skin of the chin and thus indirectly causes the lower lip to pro- trude. It is of use in articulation, in forcing bits of food from between the gums, and in the expression of various emotions (muscle of pride) . Variations. — It varies greatly in size and generally is fused with the platysma. {d) NASAL MUSCLES (Figs. 341 and 344) Toward the nasal apertures several muscles converge. Those extending from above elevate and dilate, those from below depress and contract, the nostrils. To the former belongs the pars transversa of the nasalis (compressor naris), a triangular muscle extending from the bridge of the nose to the naso-labial sulcus; the caput angulare of the quadratus labii superioris (levator labii superioris alaeque nasi), which arises from the root of the nose and sends a fasciculus to the wing of the nose; and the dilatores naris, described below; to the latter, the pars alaris of the nasalis (depressor alas nasi), which extends from the alveolar juga of the upper lateral incisor and canine teeth to the dorsal margin of the nostril; and the small depressor septi nasi. The nasalis consists of two parts, the pars transversa and the pars alaris. The pars trans- versa (compressor naris) is triangular. It lies on the side of the nose above the wing. Its fibre-bundles arise from an aponeurosis which overlies the bridge of the nose, is adherent to the skin, and is not closely attached to the underlying cartilage. From this aponeurosis the fibre- bundles converge toward the back of the wing, where they are attached to the skin along the fine which separates the wing from the cheek (naso-labial sulcus). Its insertion is covered by the nasal proce.ss of the caput angulare (levator labii superioris alseque nasi) of the quadratus labii superioris (p. 332), with which its fibres interdigitate. An attachment (origin) is also described by many as taking place in the lower part of the canine fossa of the maxilla. The pars alaris (depressor ala; nasi) (fig. 343), is a small quadrangular muscle situated below the aperture of the nose, between this and the alveolar portion of the maxilla. It is covered by the mucosa of the gum, by the orbicularis oris and the quadratus (levator) labii superioris, aad laterally is fused with the pars transversa (compressor naris). It arises from the alveolar juga of the lateral incisor and the canine teeth. Its fibre-bundles extend vertically to the skin of the dorsal margin of the nostril, from the dorsal part of the cartilage of the wing to the septum The depressor septi is a flat, triangular muscle which extends from the orbicularis oris to the lower edge of the nasal septum. It may arise from the jugum alveolare of the medial PERIORBITAL MUSCLES 335 The dilator naris posterior is a thin, triangular muscle which lies on the side of the wing of the nose. It arises from the skin of the naso-labial groove and is attached to the inferior border of the wing of the nose. The dilator naris anterior is a very small, thin muscle which runs from the lower margin of the cartilage at the front of the wing of the nose to the skin. It is not usually clearly marked. Nerve-supply. — The muscles of this gi'oup are supphed by the infra-orbital and buccal branches of the facial nerve. Actions. — The transverse portion of the nasalis (compressor naris) acts with the angular head (levator labii superioris alaeque nasi) of the quadratus labii superioris in drawing lateral- FiG. 344. — The Deeper Muscles op the Face and Neck. Procerus Quadr. labii sup. caput angulare Caput infra- orbitale Nasalis, pars transversa Cani Depressor septi nasi Nasalis, pars alaris Orbicularis oris Buccinator Triangularis Quadratus la- bii inferions M entails Mylo-hyoid Anterior belly of digastric - Temporal _ Posterior belly of digastric ' Splenius capitis - Stylo-hyoid Scalenus anterior • '■ %\ ward and up the lateral margin of the wings of the nose, and gives rise to the expression of sen- suaUty. (Poirier.) This accords with the electrical experiments of Duchenne. However, acting in conjunction with the alar portion, the transverse portion of the nasalis may constrict the nostrils. The alar portion (depressor alae nasi) of the nasalis and the depressor septi nasi draw down the nostril. The former tends to contract it from side to side, the latter from front to back, and at the same time to depress the tip of the nose. They play a part in the expression of anger and of pain. The functions of the other muscles are indicated by then' names. Variations. — The muscles of the nose vary considerably in extent of development, and one or more may be absent. Authors differ considerably in their description of several of the muscles. The anomalus is a longitudinal muscle strip occasionally found running from the frontal process to the body of the maxilla near the lateral margin of the nasal aperture. (e) PERIORBITAL MUSCLES (Figs. 341, 344) The muscles which encircle the orbit constrict the entrance of the orbit so as to shut out light and protect the eye against foreign bodies. To these belong 336 THE MUSCULATURE the orbicularis oculi, the corrugator, and the procerus. The orbicularis oculi is a large, flat, elliptical muscle which lies in the eyelids and over the bone surrounding the orbit. Three parts are recognised, a palpebral, an orbital and a lacrimal. The quadrangular corrugator extends from the nasal portion of the frontal bone to the skin of the middle half of the eyebrow; the narrow procerus (pyramidaHs nasi) from the bridge of the nose to the skin at the root. The muscles which have an antagonistic action are the levator palpebrse superioris and the epicranius. The levator palpebrse is described in the chapter on the Eye (see Section VIII), the epicranius in the following subsection. The orbicularis oculi. — The palpebral portion arises from the ventral surface and margins of the lateral portion of the medial palpebral hgament (tendo oculi), and from the covering of the lacrimal sac. The fibre-bundles spread out as they pass into the eyelids and again are con- centrated toward their insertion into the outer surface of the lateral palpebral ligament. Many of the fibre-bundles interdigitate here without being inserted into the ligament. The muscle in each eyelid lies between the tarsal plate and the skin, separated from both by loose tissue. The superficial muscle-fibres nearest the margin of the hds constitute the ciliary muscle, or muscle of Riolan. They are very small fibres and probably act on the eyelashes and Meibomian glands. The orbital portion arises by a superior origin from the medial palpebral ligament (tendo ocuU), the nasal portion of the frontal bone, and the anterior lacrimal crest of the maxilla, and by an inferior origin from the medial palpebral hgament and the medial portion of the inferior rim of the orbit. The fibre-bundles form a flat ring which surrounds the orbit for a consider- able distance, especially inferiorly. The muscle is adherent to the overlying skin. It hes over the bones surrounding the margin of the orbit and over the attachments of several of the facial muscles attached to these bones. With these muscles some of the fibre-bundles are usually continuous. The lacrimal portion (tensor tarsi or Horner's muscle) arises from the posterior lacrimal crest of the lacrimal bone and passes down on the dorsal surface of the lacrimal sac and the medial palpebral ligament (tendo oculi). It bifurcates and furnishes a fasciculus attached to each tarsal plate. Some of the fibre-bundles surround the lacrimal canaliculi and some surround the ducts of the tarsal glands and the roots of the eyelashes. The corrugator arises from the frontal bone near the fronto-nasal suture. It extends obliquely upward to be inserted into the skin of the middle half of the eyebrow. The fibre- bundles of insertion interdigitate with those of the frontahs. The muscle hes relatively deep. It is covered by the procerus (pyramidahs nasi), the frontalis, and the orbicularis. Under it lie the supra-orbital vessels and nerves. The procerus (p3rramidalis nasi) overlies the nasal bone. It arises from the lateral cartilage of the nose through a fibrous membrane and also directly from the nasal bone, and is attached to the skin over the root of the nose, where its fibres interdigitate with those of the frontalis. The medial margins of the muscles on each side are more or less fused. Nerve-supply. — The muscles of this group are supphed by temporal and infraorbital branches of the facial nerve which enter the deep surfaces near the lateral margins. Action. — The palpebral portion of the orbicularis closes the eyehds, of which the upper moves more freely than the lower. It also serves to dilate the lacrimal sac and allow the tears to flow away readily. The tensor tarsi probably contracts the sac and forces the tears into the nose. The upper half of the orbital portion of the orbicularis contracts and depresses the tissue overhanging the orbit, and stretches the skin of the forehead. The corrugator draws the skin of the brow downward and medially, thus aiding the preceding muscle. It causes the perpendicular furrows characteristic of frowning. The procerus (pyramidahs nasi) draws down the skin of the forehead and wrinkles the skin across the root of the nose. The lower half of the orbital portion of the orbicularis raises the skin of the cheek, causing the wrinkles seen to radiate from the corner of the eye. The whole set of muscles comes into play in the forcible closure of the eyes. In case of violent expiratory efforts, as in shouting, sneezing, coughing, etc., the eye is thus usually forcibly closed. The pressure thus exerted on the eyeball prevents a too violent flow of blood to the vessels of the eye. Pressure is thought at the same time to be exerted on the lacrimal gland so as to cause the excessive flow of tears often experienced at such times. Variations. — The muscles of this group vary in extent and differentiation, and may be more or less fused with one another or with neighbouring muscles. The orbital portion of the or- bicularis, the corrugator, and the procerus have been found absent. (/) THE EPICRANIAL MUSCULATURE (Fig. 341) The epicranius (occipito-frontalis) is formed of the two frontal muscles, which lie on each side of the forehead, the two occipital muscles, which occupy corre- sponding positions on the occipital bone, and of the epicranial aponeurosis, the galea aponeurotica, which extends between these. The occipital muscles arise from the supreme nuchal line and are inserted into the galea aponeurotica. The frontal muscles arise from the latter and are inserted into the skin near the eye- brows. The chief function of these muscles is to elevate the brows. The AURICULAR MUSCLES 337 muscles and the intervening aponeurosis lie between two layers of fascia, the external of which is fused to the skin, while the internal moves freely over the periosteum, to which it is loosely attached. Hsemorrhages and abscesses spread freely between the deep layer of fascia and the periosteum. The frontalis is a large, thin muscle with convex upper and concave lower border. It arises from the epicranial aponeurosis midway between the coronal suture and the orbital arch, and is inserted into the skin of the eyebrow and of the root of the nose. The medial fibre-bundles take a sagittal direction; the lateral converge obhquelj' toward the brow. The medial margins of the muscles of each side are approximated near the attachment. The more medial fibre-bundles are continuous with those of the procerus (pyramidahs nasi) and the angular portion (levator labii superioris alasque nasi) of the quadratus labii superioris; the more lateral interlace with those of the corrugator and orbicularis muscles. The branches of the vessels and nerves of the frontal region pierce the muscle and are distributed between it and the skin. The occipitalis, flat and quadrangular, lies on the occipital bone above the supreme nuchal line. It rises by tendinous fibres from the lateral two-thirds of this line and from the posterior part of the mastoid process of the temporal bone, and is inserted into the epicranial aponeurosis. The medial fibre-bundles run sagitaUy, while the lateral run obliquely forward. The occipital artery and nerve lie between the muscle and the skin. The lateral border of the muscle comes in contact with the posterior auricular muscle. The muscles of each side are usually separated by a strip of aponeurosis. The galea aponeurotica (epicranial aponeurosis) is a fibrous membrane which extends be- tween the occipital muscles and from them anteriorly to the frontal muscles. In the area be- tween these two sets of muscles it is composed largely of sagitahy running fibres into which coronal fibres radiate from the region of the muscles of the ear. Between the two occipital muscles the aponeurosis is attached to the supreme nuchal line and external occipital protuber- ance. Laterally the fascia covering it is continued as a special investment of the auricular muscles, beyond which it is attached to the mastoid process, the zygoma, and to the external cervical and the masseteric fasciae. Nerve-supply. — The frontahs is suppUed by the temporal branches of the facial nerve, the occipitalis by the posterior auricular branch. The branches enter the deep surface of each of these muscles near its lateral border. Action. — The occipitalis serves to draw back and to fix and make tense the epicranial ap- oneurosis. The frontalis, with its aponeurotic extremity fixed, elevates the brows and throws the skin of the forehead into transverse wrinkles as in the expression of attention, surprise, or horror. When both muscles contract forcibly there is, in addition, a tendency to make the hair stand on end because the hair-bulbs of the occipital region slant forward, those of the frontal region backward. The frontalis when fixed below puUs the scalp forward. Variations. — The ocoipitahs is occasionally absent, a condition normal in ruminants. The muscles of the two sides may be fused in the median line (normal in dogs). It may be fused with the posterior auricular. The frontalis is rarely missing. The frontalis may send shps to the medial or lateral angles or the orbital arch of the frontal bone, to the nasal process of the maxilla or to the nasal bone. The fibre-bundles of the frontalis may interdigitate across the median line. The transversus nuchas, or occipitaUs minor, is a small muscle, frequently present (27 per cent., Le Double), which runs from the occipital protuberance toward the posterior auricular muscle, with which it may be fused. It may He over or under the trapezius. (g) AURICULAR MUSCLES (Fig. 341) The intrinsic muscles of the auricle are described in Section VIII. There are three 'extrinsic^ auricular muscles which converge from regions anterior, superior, and posterior to the auricle and are inserted into it. The auricularis anterior (attrahens aurem) is a small, flat, triangular muscle which arises between the two layers of the fascia of the galea aponem-otica, extends over the zygomatic arch, and is attached to the ventral end of the helix. The fibre-bundles converge from the origin toward a tendon of insertion. The area of origin of this muscle is often marked by a fibrous band tangential to its component fibres. From this band muscle fibre-bundles radiate out toward the frontal region of the skull. To the muscle formed of these radiating fibres the names epicranio-temporalis (Henle), temporalis superficialis (Sappey) and auriculo-frontalis (Gegen- baur) have been given. The auricularis superior (attoDens aurem) is a large, tliin, triangurar muscle which, from its tendinous insertion on the eminence of the triangular fossa of the ear, radiates upward into ' the fascia of the galea aponeurotica, between the layers of which it takes oigin near the temporal ridge. It lies over the temporal fascia and the periosteum of the parietal bone. The auricularis posterior (retrahens aurem) is a thin, band-like muscle which extends over the insertion of the sterno-cleido-mastoid from the base of the mastoid process and the ap- oneurosis of the sterno-cleido-mastoid muscle to the convexity of the concha, where it has a ten- dinous insertion. It is usually composed of two fasciculi, and is contained between two layers of fascia derived from the galea aponeurotica. Nerve-supply. — The aiu-icularis anterior and superior are supphed by the temporal branch of the facial, the auricularis superior and posterior by the posterior am-icular branch. The twigs of supply run to the deep surface of the muscles. 338 THE MUSCULATURE Relations. — The superficial ascending branch of the auriculo-temporal nerve usually runs superficial to the anterior and superior auricular muscles. The superficial temporal vessels run at first beneath these muscles and the lateral expansion of the galea aponeurotica, then between the two fascial layers which enclose the muscles. Their branches of distribution finally come to lie between the muscles and aponeurosis and the skin. The posterior auricular artery and nerve usually run under cover of the auricularis posterior. Action. — The anterior muscle is a protractor, the superior an elevator, and the posterior a retractor of the ear, but usually in man they are inactive. Variations. — These muscles vary much in development. The most constant of them is the superior. The posterior frequently is increased in size and may be fused with the occipitalis, which originally was probably an ear muscle. From the anterior muscle a special deep fasciculus is occasionally isolated. Each of the muscles is occasionally, though rarely, absent, the anterior most frequently. An inferior auricular muscle is very rarely found in man, though present in many of the lower mammals. A slip of the posterior auricular may run beneath the ear to the parotid fascia. Fig. 345. — The Temporal Muscle. 2. CRANIO-MANDIBULAR MUSCULATURE (Figs. 344, 345, 346, and 347) The cranio-mandibular muscles, or muscles of mastication, pass from the base of the skull to the lower jaw. They are represented in the selachians by a single muscle mass, the adductor mandibulee (Gegenbaur), but in the higher vertebrates this muscle mass becomes variously subdivided during embryonic development. The muscles are innervated by the masticator nerve (motor root of the tri- geminal cranial nerve, the nerve of the mandibular arch). In man four muscles are recognised, the temporal, masseter, and internal and external pterygoids. The temporal and masseter muscles are situated on the lateral sm-face of the skull, partly under cover of muscles of the facialis group. The temporal muscle (fig. 345), which resembles the quadrant of a circle, arises from the temporal fossa and is inserted into the coronoid process of the mandible; the thick, quad- rilateral masseter (fig. 344) muscle arises from the zygomatic arch and is in- serted into the lateral surface of the ramus and angle of the mandible. The pterygoids (fig. 346) are more deeply seated. The cone-shaped external pterygoid arises from the lateral side of the pterygoid process and lower surface of the great wing of the sphenoid and is inserted into the condyloid process of the mandible and the capsule of the joint. The thick, quadrilateral internal pterygoid parallels the masseter. It arises from the pterygoid fossa of the sphenoid and is inserted into the inner side of the angle of the mandible. It will be noted that the tem- FASCIJE 339 poral, masseter, and internal pterygoid muscles have approximately vertical axes of contraction and adduet the lower jaw, while the external pterygoid- has an approximately horizontal axis of contraction and draws the jaw forward and, when acting on one side, toward the opposite side. Fig. 346. — The Pterygoid Muscles. External pterygoid Internal pterygoid FASCI.E The temporal fascia arises from the temporal line of the frontal bone and from the superior temporal line of the parietal and the periosteum immediately below this. It extends to the zygomatic arch. In its inferior quarter the fascia divides into two lamellae, one of which passes to the outer, the other to the inner, surface of the arch, but at the superior margin of the arch these two lamelte are united by dense fibrous tissue. Between the two lamella? above the arch hes a fatty areolar tissue in which the middle temporal artery often runs. The outer sur- face of the fascia is covered by the superficial temporal and anterior and superior auricular muscles, and by a thin layer of fascia from the galea aponeurotica, with which, toward the zygo- matic arch, it becomes merged. The superficial temporal artery and auriculo-temporal nerve cross it. The masseteric fascia represents essentially a continuation of the temporal fascia from the inferior margin of the zygomatic arch over the masseter muscle which it covers. It is less thick than the temporal fascia, but is firm and strong. It is attached dorsally to the dorsal margin of the mandible, mferiorly to the inferior margin, and ventrally to the body and to the ventral majgin of the ramus and the coronoid process of the mandible. In part it extends over the fat pad of the cheek to the buccinator fascia. The parotid gland, covered by the parotid extension of the external cervical fascia, extends over the posterior portion of this fascia. The parotid fascia becomes fused to its external surface at the anterior margin of the gland. Over it lie the parotid duct, the transverse facial artery, branches of the facial nerve, the zygomaticus (major), risorius, and platysma muscles. The pterygoid muscles are each surrounded by a dehcate membrane. In addition an mterpterygoid fascia separates the two muscles. This arises from the sphenoidal spine and toUows the internal surface of the external pterygoid to the mandible. MediaUy it is attached to the lateral lamella of the pterygoid process; posteriorly and laterally it presents a free margin which forms with the neck of the mandibular condyle, an orifice for the passage of the internal maxillary artery, the auriculo-temporal nerve, and several veins. Its posterior margin is strengthened into the spheno-mandibular ligament, which runs from the spine of the sphenoid to the lingula of the mandible. The pharyngeal region is separated from the pterygoid by a dense membrane, the lateral pharyngeal fascia. This extends from the depth of the pterygoid fossa to the prevertebral tascia, a,nd separates the tensor veh palatini from the internal pterygoid muscle. It is attached above along a Ime extending from the external margin of the carotid canal to the internal margin ot the oval foramen. i 340 THE MUSCULATURE Fig. 347. CRANIO-MANDIBULAR MUSCLES 341 The sigmoidal septum is a thin membrane which occupies the incisura mandibulae and sepa- rates the masseter from the external pterygoid muscle. MUSCLES The temporalis (fig. 345). — Origin. — (1) From the whole of the temporal fossa, with the exception of that part formed by the body and temporal process of the zygomatic (malar) bone; and (2) from the fascia covering the fossa. Insertion is into the tip, dorsal and ventral borders, and the whole internal surface of the coronoid process of the mandible and the ventral portion of the medial surface of the ramus. In structure, the muscle is thin near its superior margin, but becomes thick as its insertion is approached. The fibre-bundles arising from the medial surface of the fossa and from the fascia converge upon the medial and lateral surfaces and the margins of a thick, broad tendon which begins very high in the muscle, becomes visible laterally some distance above the zygo- matic arch, and is inserted into the tip, edges, and internal surface of the coronoid process. On the ventral and dorsal margins of the tendon the insertion of fibre-bundles continues to the coro- noid process, while medially the insertion of the fibre-bundles is continued on the medial surface of the coronoid process and often on the ramus as far as the body of the bone. Nerve-supply. — Usually three branches from the anterior branch of the mandibular division of the fifth nerve curve upward over the temporal surface of the great wing of the sphenoid and enter the deep surface of the muscle. The posterior and middle nerves pass above the external pterygoid; the anterior, which springs from the buccinator nerve, passes between the two heads of the external pterygoid before curving upward. Relations. — The muscle is covered by the temporal fascia and the zygomatic arch. Below the temporal fossa the pterygoid muscles and the buccinator lie medial to it. The temporal fossa in front of the muscle is filled with a fatty areolar tissue and this also extends between the muscle and the temporal fascia. Fatty tissue hkewise lies between the muscle and the buccina- tor. Medial to the muscle run the deep temporal vessels and nerves, the buccinator nerve and the spheno-mandibular ligament. The masseteric nerve passes lateralward behind and below the tendon. The masseter (fig. 343) is composed of two layers. The superficial layer arises by an apo- neurosis from the anterior two-thirds of the lower border of the zygomatic (malar) bone. The fibre-bundles arise from the deep surface of this aponeurosis and its tendinous prolongations pass obliquely downward and backward, and are inserted into the lower half of the external surface of the ramus, into the angle, and into the neighbouring portion of the body of the man- FiG. 347.* — A AND B ARE Transvehsb Sections and C (after Testut), a Frontal Section THROUGH the LeFT SiDE OF THE HeAD, IN THE REGIONS INDICATED IN THE DIAGRAM. a and b in the diagram indicate the regions through which pass sections A and B, fig. 351; and a', section A, fig. 357. 1. Adipose tissue. 2. Arteria temporalis superfioialis. 3. A. carotis externa. 4. A. car- otis interna. 5a. A. maxillaris externa (facial). 56. A. maxillaris interna. 6. A. verte- bralis. 7. Atlas. 8. Cerebellum. 9. Epistropheus (axis). 10. Fascia buccopharyngea. 11. F. cervicalis, a (superficial layer), 6, deep parotid process. 12. F. interpterygoidea. 13. F. masseterioa. 14. F. nuchie. 15. F. pharyngobasilaris. 16. F. pharyngis lateralis. 17. F. temporaHs. 18. Galea aponeurotica. 19. Glandula parotica. 20. Ligamentum stylo- mandibularis. 21a. Mandible, capitulum; b, coronoid process. 22. Meatus acusticus ext. 23. Medulla oblongata. 24. MeduUa spinalis (spinal cord). 25. Musculus auricu- laris posterior (retractor auris). 26. M. buccinator. 27. M. caninus (levator anguli oris). 28. M. constrictor pharyngis medius. 29. M. constrictor pharyngis superior. 30. M. digastricus. 31. M. genio-glossus. 32. M. hyo-glossus. 33. M. incisivus labii inferioris. 34. M. levator veli palatini. 35. M. longus capitis (rectus capitis anticus major). 36. M. longissimus capitis (trachelo-mastoid). 37. M. longitudinalis inferior. 38. _M. masseter. 39. M. mylo-hyoideus. 40. M. nasalis (alar portion). 41. M. obhquus ca,pitis inferior. 42. M. obUquus capitis superior. 43. M. pterygoideus externus — a, superior fasciculus; 6, inferior fasciculus. 44. M. pterygoideus internus. 45. M. quadratus (levator) labii superioris. 46. M. rectus capitis anterior (minor). 47. M. rectus capitis posterior major. 48. M. rectus capitis posterior minor. 49. M. rectus capitis laterahs. 50. M. semispinalis capitis (complexus). 51. M. splenius capitis. 52. M. sterno-cleido-mastoideus. 53. M. stylo-glossus. 54. M. stylo-hyoideus. 55. M._ stylo-pharyngeus. 56. M. temporalis (a, fasciculus from zygoma). 57. M. tensor veli palatini. 58. M. trapezius. 59. M. zygomaticus (major). 60. Nervus accessorius (spinal accessory). 61. N. alveolaris inferior (dental). 62. N. alveolaris posterior superior (dental). 63. N. auriculo-temporalis. 64. N. buccinatorius. 65. N. canalis pterygoidei (Vidian nerve). 66. N. glosso-pharyngeus. 67. N. hypoglossus. 68. N. Ungualis. 69. N. mandibularis. 70. N. masseteric nerve. 71. N. maxillary nerve. 72. N. mylo- hyoid nerve. 73. N. palatinus. 74. Sympathetic trunk. 75. N. temporalis profundus. 76. N. vagus. 77. Os occipitale — a, basilar portion; b, external protuberance. 78. Os sphenoidale. 79. Os temporale — o, processus zygomaticus; b, tubercle. 80. Os zygo- maticum (malar). 81. Pharyngeal orifice of tuba auditiva (Eustachian tube). 82. Palatum durum (hard palate). 83. Pharynx — a, oral portion; b, nasal portion. 84. Pharyngeal recess. 85. Sinus maxillaris (antrum of Highmore). 86. Sinus transversus (lateral). 87. Tonsila palatina. 88. Uvula. 89. Vena facialis posterior (temporo- maxillary). 90. V. jugularis interna. * This and the following series of cross-sections are taken from a thin, not very muscular, adult male. The fasciae are represented in most instances disproportionately thick. 342 THE MUSCULATURE dible — the more anterior directly, the posterior by means of an aponeurosis. The deep layer arises from the lower border and internal surface of the zygomatic arch. The fibre-bundles pass neai'ly vertically downward, and are inserted upon the upper hah of the external surface of the ramus. The origin and insertion are by tendinous bands, to which the fibre-bundles are attached in a multipenniform manner. The two layers are fused near the origin and insertion and in front. From the temporal surface of the zygomatic bone and the neighbouring part of the deep layer of the temporal fascia there arises a fasciculus which is separated by a pad of fat from the main body of the temporal muscle, and is inserted into the lateral sm-faoe of the lower extremity of the tendon of the temporal muscle and into the ventro-lateral surface of the tip of the coronoid process. This fasciculus, sometimes described as a part of the temporal muscle, is innervated by the masseteric nerve. Nerve-supply. — The branch arises in common with the posterior nerve to the temporal muscle from the motor root of the trigeminal (the masticator nerve). It passes above the external pterygoid, through the mandibular (sigmoid) notch, and enters the deep surface of the muscle near the dorsal margin. • I Relations. — It is covered by the masseteric fascia (see above). It lies upon the ramus of the jaw and ventrally is separated by a pad of fat from the buccinator muscle. At the mandibu- lar (sigmoid) notch the sigmoid septum separates it from the external pterygoid muscle. The parotid gland partly overlaps its posterior border. The pterygoideus externus (figs. 343-346) consists of two fasciculi. Each is thick and tri- angular. The superior is flattened in a horizontal, the inferior in a vertical, plane. At their origin they are separated by a narrow cleft. Near the insertion they become more or less fused. The superior fasciculus arises by short tendinous processes from the infratemporal (pterygoid) crest and from the neighbouring portion of the under surface of the great wing of the sphenoid. Its fibre-bundles converge toward the insertion, which takes place by short tendinous processes into — (1) the capsular ligament in front of the articular disc and (2) the upper third of the front of the neck of the condyle. The inferior fasciculus is the larger. It arises by short tendinous processes from the lateral surface of the lateral lamina of the pterygoid process, from the pyrami- dal process of the palate bone, and from the adjacent portions of the maxillary tuberosity. The fibre-bundles converge toward their insertion into a depression on the front of the neck of the condyle. Nerve-supply. — A branch from the masticator nerve (mot6r root of the trigerninus) ap- proaches the muscle near the upper border of the medial surface of the superior fasciculus and gives branches to both portions. Relations. — It is partly covered by the maxillary fasciculus of the internal pterygoid and by the temporal and masseter muscles. Medial to it lies the chief fasciculus of the internal ptery- goid muscle. The masseteric and the posterior and middle temporal nerves usually pass above the muscle, the anterior temporal and the buccinator nerves and frequently the internal maxil- lary artery between the two fasciculi. The internal maxillary vessels usually pass below the lower border of the muscle and across its external surface; and the auriculo-temporal, lingual, and infei-ior alveolar (dental) nerves cross the deep surface of the muscle. The pterygoideus internus (fig. 346). — Origin. — From (1) the pterygoid fossa, and (2) from the maxillary tuberosity and the pyramidal process of the palatine, where these adjoin. Structure and Insertion. — From the medial and lateral lamins of the pterygoid process there ai-ise aponeuroses and from the palatine bone at the lower margin of the fossa, and from the maxillary tuberosity and palatine bone in front of the external pterygoid, there arise short tendons. From these aponeuroses and tendons and directly from the fossa the fibre-bundles take a nearly parallel course downward, backward, and outward, and are inserted in part in a multi-penniform manner into the lower half of the internal surface of the ramus of the mandible. The insertion extends to the mylo-hyoid ridge. The muscle is divided at its origin into two fascicuh by the distal margin of the external pterygoid. Nerve-supply. — The internal pterygoid nerve arises from the back of the mandibular nerve near the foramen ovale. It passes near or through the otic ganglion, and thence to the medial surface of the muscle near the dorsal edge. Both the buccinator and lingual nerves are also described as sending filaments to this muscle. Relations. — Laterally the muscle is covered by the interpterygoid fascia and the spheno- mandibular ligament, the external pterygoid, temporal, and masseter muscles, and the ramus of the mandible. The inferior alveolar (dental) and Ungual nerves and the corresponding vessels run across this surface. Medial to the muscle lie the lateral pharyngeal fascia, the tensor veh palatini muscle, and the superior constrictor of the pharynx. Action. — The muscles of this group adduct the lower jaw and serve to carry it forward and backward and from side to side. The elevation is produced by the masseter, temporal, and internal pterygoid muscles. The suprahyoid muscles and the external pterygoid are the feeble antagonists. T?he forward movement of the jaw is produced by the simultaneous action of the two external pterygoids (slightly by the superficial layer of the masseter, and the anterior fibres of the temporal) while the inferior posterior portions of the temporal muscles carry the jaw at the temporo-discoidal joint somewhat backward. Oblique lateral rotator}' movements are produced chiefly by the action of one of the external pterygoids. The alternate action of these two msucles associated with the elevating action of the other muscles of the group, gives rise to the grinding movement of the molar teeth. Purely lateral movements of the jaw may be produced by the internal pterygoids, acting alternately. Lord (Anat. Rec, vol. 7, p. 355, 1913) states that in ordinary opening of the mouth the external pterygoids pull the articular discs and condyles forward while the jaw rotates about an axis passing through the insertions of the stylo-mandibular ligaments. Variations. — The temporal muscle may have a more extensive cranial origin than usual. It may be formed of two superimposed layers. It may be more or less fused with the external pterygoid, or send a fasciculus to the coronoid process. The masseter may be completely SUPRAHYOID MUSCULATURE 343 divided into two fasciculi, a condition normal in many mammals. A special fasciculus may arise from the temporo-mandibular articulation or from the zygomatic (malar) bone. Its deepest fibres may be fused with the temporal muscle. The two fasciculi of the external pterygoid may be distinct, as in the horse. It has been seen fused with the temporal and with the digastric muscle. The internal pterygoid may send a fasciculus to the masseter. It may give origin to the stylo-glossus. Inconstant fasoiouh (accessory pterygoids) extending from the body of the sphenoid to the pterygoid process represent perhaps remnants of the muscles which act on the movable pterygoids possessed by many inferior vertebrates. 3. SUPRAHYOID MUSCULATURE (Fig. 348) From the hyoid bone there extend to the base of the skull on each side four muscles which form a fairly well-defined group. They are situated external to Fig. 348. — Antebioe and Lateral Cervical Muscles. stylo-glossus Hyo-glossus Mylo-hyoid Anterior belly of_£j digastric Raphe of mylo-, hyoid Inferior constrictor Anterior belly of omo- hyoid Sterno-hyoid Sterno-thyreoid Thyreo-hyoid the musculature of the tongue and pharynx. They elevate the hyoid bone and larynx and depress the mandible. The most superficial of the group is the slender, fusiform stylo-hyoid, which arises from the styloid process of the temporal bone and is inserted into the body of the hyoid. Immediately behind this is the flattened posterior belly of the digastric, which extends from its origin in the mastoid notch to a tendon that runs between two divisions of the tendon of the stylo-hyoid and is attached to the hyoid bone by an aponeurotic process. From the digastric tendon the flat, triangular anterior belly is continued to the back of the ventral portion of the inferior margin of the mandible. Internal to this anterior belly the thin, quadrangular mylo-hyoid arises from the inner surface of the body of the mandible and is inserted into a median raphe extending from the mandible to the hyoid. Still more internally the triangular genio-hyoid extends from the hyoid to the mental spine of the mandible. The last two muscles form the muscular floor of the mouth. The motor innervation of the posterior belly 344 THE MUSCULATURE of the digastric and of the stylo-hyoid is from the seventh cranial nerve, the sensory innervation probably from the glosso-pharyngeal cranial nerve. The mylo-hyoid and the anterior belly of the digastric are supplied by the masticator (fifth) cranial nerve; the genio-hyoid from the hypoglossal by a branch, the fibres of which are possibly derived through anastomosis from the first cervical nerve. From the morpliological standpoint, therefore, the stylo-hyoid and the posterior belly of the digastric belong to the faciahs group; the anterior belly of the digastric and the mylo-hyoid to the group of mandibular muscles, and the genio-hyoid to the muscles of the tongue inner- vated by the hypoglossal, or, if we consider the nerve-fibres of the nerve to the genio-hyoid as derived from the first cervical nerve, to the same group as the infra-hyoid muscles. It is con- venient, however, to follow the usual custom of considering these muscles as a suprahyoid group. FASCIA The muscles of this group he internal to that portion of the external cervical fascia which extends above the hyoid bone. This fascia, which is described on p. 347, comes into contact merely with the tendon, the anterior belly, and to a slight extent with the posterior belly of the digastric muscle. Above the tendon it sends inward a process which curves down internal to the tendon, and is inserted into the external surface of the hyoid bone. The individual muscles of the group are covered by dehcate adherent membranes. An aponeurotic membrane usually extends between the anterior bellies of the digastric muscles of each side. MUSCLES (Fig. 348) The stylo-hyoideus. — Origin. — From the lateral and dorsal part of the base of the styloid process by a rounded tendon which soon becomes a hollow cone to the internal surface of which the fibre-bundles of the muscle are attached. Structure and Insertion. — The fibre-bundles are inserted on both sides of a slender tendon which divides to let the tendon of the digastric pass through and then is attached to the ventral surface of the body of the hyoid bone near its junc- tion with the great cornu. Nerve-su-pply. — From the facial nerve as it emerges from the stylo-mastoid foramen a small twig is given off which enters the proximal third of the deep surface of the muscle. The glosso- pharyngeal nerve also gives to it a small twig, probably sensory. Relations. — It descends immediately in front of the posterior belly of the digastric. Ex- ternally lie the parotid and submaxillary glands. Medially it crosses the internal and ex-ternal carotid artery, the hypoglossal nerve, the stylo-pharyngeus muscle, the superior constrictor of the pharynx, and the hyo-glossus muscle. The posterior auricular artery passes between it and the posterior belly of the digastric and the external maxillary artery crosses over it. The digastricus. — The posterior belly arises by tendinous processes from the mastoid (digastric) notch of the temporal bone. The fibre-bundles form a ribbon-)ike belly which con- verges on the intermediate tendon. This begins as a semiconical laminar process on the outer surface of the muscle a short distance above the hyoid bone. The anterior belly arises by short tendinous processes from the digastric fossa of the mandible. This attachment is often de- scribed as an insertion. The fibres converge on both surfaces of the flattened anterior end of the intermediate tendon. The intermediate tendon hes a variable distance above the hyoid bone, usually less than a centimetre. It curves upward toward each belly of the muscle. It is united to the outer surface of the body and to the base of the great cornu of the hyoid bone by an aponeurotic expansion from its inferior margin. Other expansions are usually continued into the interdigastric aponeurotic membrane. Occasionally the intermediate tendon of the digastric is bound to the hyoid bone by a fibrous loop which allows the tendon free play. Nerve-supply. — The facial nerve near the stylo-mastoid foramen gives off a branch which enters the proximal third of the anterior margin of the muscle. From this a ramus may be continued through the muscle to the glosso-pharyngeal nerve. The anterior belly is supplied by a branch of the nerve to the mylo-hyoid muscle. This enters the middle of the lateral part of the deep surface. Very rarely the vagus may supply the anterior belly, the hypoglossal, the posterior belly. Relations. — The posterior belly of the digastric lies internal to the mastoid process and the longissimus capitis (trachelo-mastoid), splenius, and sterno-cleido-mastoid muscles. Pos- teriorly near its origin are the rectus capitis lateralis and obliquus cap. sup. muscles, the occip- ital artery and the spinal accessory nerve. It helps to form the deep wall of the cavity in which the parotid gland is placed. Internally it crosses the origin of the styloid muscles, the carotid arteries, the internal jugular vein, and the twelfth cranial nerve. The intermediate tendon of insertion hes below the inferior margin of the submaxillary gland, and crosses the hyo- glossus and mylo-hyoid muscles. The relations to the stylo-hyoid muscle have been described above. The anterior belly lies on the mylo-hyoid and is covered by the external cervical fascia and the platysma. The mylo-hyoideus. — Origin. — From the mylo-hyoid ridge of the mandible. Structure and Insertion. — Its fibre-bundles take an oblique course and are inserted into — (1) a median raphe extending from the middle of the ventral surface of the hyoid bone nearly or quite to the MUSCLES OF THE TONGUE 345 dorsal surface of the inferior margin of the mandible, and (2) into the ventral surface of the hyoid bone. Some of the fibre-bundles may cross the median line. The muscles of the two sides form a sheet with a downward convexity which lies between the inner surface of the body of the mandible and the hyoid bone. On the diaphragm thus formed rests the tongue. Nerve-supply. — From the mylo-hyoid branch of the inferior alveolar (dental) nerve several filaments enter the under surface of the muscle. Relations. — The mylo-hyoid muscle is covered externally by the submaxillary gland, the anterior belly of the digastric, and the external cervical fascia. It is crossed by the submental artery. With the genio-hyoid and the genio-glossus muscles it helps to bound a cornpartment in which are lodged the sublingual gland, the duct of Wharton, and the deep portion of the submaxillary gland. Its deep surface also faces the stylo-glossus and hyo-glossus muscles, the lingual and hypoglossal nerves, and to a slight extent the buccal mucosa. The genio-hyoideus (fig. 349). — Origin. — By short tendinous fibres from the mental spine of the mandible. Structure and Insertion. — The fibre-bundles diverge and are inserted into the ventral surface of the body of the hyoid bone. Usually a special fasciculus goes to the great cornu of the hyoid bone. Nerve-supply. — The hypoglossal nerve sends a filament to the middle third of the deep surface of the muscle. The nerve-fibres are thought to be derived chiefly from the first cervical nerve. Relations. — It lies between the genio-glossus and mylo-hyoid muscles. It adjoins its fellow of the opposite side and is often fused with it. Lateral to it he the subhngual and sub- maxillary glands and the hypoglossal nerve. Action. — The muscles of this group all elevate the hyoid bone and, through this, the larynx and inferior part of the pharynx, and thus play a part in the act of swallowing. The stylo- hyoid and posterior belly of the digastric serve also to draw the hyoid bone in a dorsal direction; the ventral belly of the digastric and the genio-hyoid, in a ventral direction. The digastric, genio-hyoid, and mylo-hyoid depress the mandible, when the hyoid bone is fixed. The posterior belly of the digastric has a slight power to bend the head backward. Variations. — The stylo-hyoid tendon frequently passes entirely in front of and less frequently entirely behind the digastric muscle. Its insertion may be of greater extent than usual. A special fasciculus to the lesser cornu is not very infrequent; more rarely one extends to the angle of the jaw or to other regions. The muscle may arise from the petrous portion of the tem- poral or from the occipital bone, as in some lower vertebrates. It may be doubled or absent, or fused with the posterior belly of the digastric. The anterior belly of the digastric may be missing; the posterior belly may be inserted into the angle of the jaw. The intermediate ten- dons of the digastric of each side may be connected by a fibrous arch. The anterior bellies of the muscles of each side may be united by a fasciculus or fused. The anterior belly is frequen tly doubled. The posterior belly may be divided by a tendinous inscription. Fasciculi may pass from either belly to neighbouring structures. The mylo-hyoid may not extend quite to the hyoid bone. It may be more or less fused with neighbouring muscles. Rarely it is absent. The genio-hyoid is frequently more or less fused with the muscles of the tongue or with the genio- hyoid of the opposite side. A considerable number of infrequently found muscles have been described superficial to the stylo-hyoid and digastric muscles. Most of them are innervated by the glosso-pharyngeal nerve or by the facial nerve. 4. MUSCLES OF THE TONGUE (Fig. 349) The tongue is a flexible organ, composed chiefly of various muscles, some of which lie entirely within its substance, while others extend to be attached to neighbouring parts of the skeleton. To the former the term intrinsic, to the latter the term extrinsic, is frequently applied. In this section the extrinsic muscle will alone be taken up. The intrinsic muscles are described in the section on the Digestive System. Certain pharyngeal and palatal muscles which are continued into the tongue are described in connection ^vith the pharynx. The extrinsic musculature of the tongue is concealed below by the suprahyoid musculature and the sublingual gland. It is covered on the free surface of the tongue by the mucosa. The musculature of the tongue is supplied by the hypoglossal nerve, which is in series with the motor roots of the spinal nerves. It is, primitively at least, derived from the ventral portion of mj'^otomes in series with the spinal myotomes. Four extrinsic muscles are recognised on each side. The stylo-glossus is a slender muscle, which arises from the styloid process and is inserted into the side of the tongue. It is cylindrical near its origin, flat and triangular near its inser- tion. The thin, quadrilateral hyo-glossus arises from the body and great cornu of the hyoid bone and is inserted into the dorsum of the tongue. The chondro- glossus arises from the lesser cornu of the hyoid bone and joins the superior and inferior longitudinal muscles of the tongue. The genio-glossus (genio-hyo- glossus), which forms the main part of the body of the tongue, arises from the mental spine of the mandible, from which the fibre-bundles radiate out toward the whole length of the dorsum of the tongue and to the hj'oid bone. 346 THE MUSCULATURE Under the mucous membrane of the tongue is a dense layer of fibrous tissue, the lingual fascia. In the body of tlie tongue there is a sagittal septum linguae, which separates the two genio-glossus muscles. A transverse fibrous lamella, the hyo-glossal membrane, helps to unite the tongue to the hyoid bone. Delicate membranes invest the free portions of the extrinsic muscles of the tongue. MUSCLES The stylo -glossus. — This arises from the front of the lower end of the styloid process of the temporal bone and from the upper part of the stylo-mandibular ligament. Insertion. — It runs obliquely downward, forward, and medially, with slightly diverging fibre-bundles, to the lateral margin of the tongue, where it gives rise near the anterior pillar of the fauces to two fasciculi. The larger, lateral, longitudinal fasciculus runs superficially along the lateral margin of the tongue to the tip. The fibre-bundles are attached to the overlying mucosa and under- lying musculature. The smaller, inferior, transverse fasciculus gives rise to diverging fibre- bundles which pass medially through the hyo-glossus into the base of the tongue. The most posterior of these diverging bundles may extend to the hyoid bone. The hyo-glossus. — This arises from — (1) the lateral part of the ventral surface of the body of the hyoid bone and (2) from the upper border of the great cornu. The fibre-bundles take a nearly parallel course upward, diverging, however, slightly. Near the upper margin of the back Fig. 349. — Side View op the Muscles op the Tongue. > Glosso-palatinus Stylo-glossus -hyoid Anterior belly of - digastric part of the tongue they curve mcdianward and interlace with the intrinsic musculature of this region. The dorsal fibre-bundles pass transversely, the middle obliquely, the ventral longi- tudinally. They are inserted into the fibrous tissue which forms the skeletal framework of the tongue. The chondro-glossus is a small muscle which arises from the lesser cornu of the hyoid bone and gives rise to fasciculi which join the longitudinalis inferior and the longitudinalis superior of the tongue described in Section IX. The genio-glossus. — This arises from the mental (genial) suine of the mandible partly directly, partly by means of a short, triangular tendon. The more inferior fibre-bundles radiate toward the tip of the tongue; the intermediate extend directly toward the dorsum of the tongue, where they are inserted into the lingual fascia and skeletal framework. The inferior curve back to be inserted on the median part of the superior border of the hyoid bone. Nerve-supply. — Twigs from the hypoglossal nerve enter the lateral surfaces of the muscles of this group. Action. — The chief of the muscles, the genio-glossus, performs various services according to the part which contracts. The anterior portion serves to withdraw the tongue into the mouth and depress the tip; the middle portion to draw the base of the tongue forward, depress the median portion of the tongue, and make the tongue protrude from the mouth; the inferior fibres to elevate the hyoid bone and carry it forward. The stylo-glossus retracts the tongue, elevates its margin, and raises the hyoid bone and base of the tongue. The hyo-glossus draws down the sides of the tongue and is also a retractor. The chondro-glossus aids in both these movements. Relations. — The main portion of the tongue is composed of the two genio-glossus muscles, which are separated in the median line by the hngual septum. The genio-glossus is covered inferiorly by the genio- hyoid and the mylo-hyoid muscles; along the lateral margin of the tongue by the glosso-palatinus, the stylo-glossus, the longitudinalis inferior, and the glosso-pharyngeus CERVICAL FASCIA 347 muscles; and posteriorly by the hyo-glossus, and the chondro-glossus. Below it forms a part of the medial wall of the space in which the sublingual gland is lodged. Over the dorsum and tip of the tongue it is covered by the mucosa. This likewise covers laterally, in the region of the base of the tongue, the stylo-glossus, hyo-glossus, and the longitudinalis inferior. The lingual artery runs between the hyo-glossus and the genio-glossus, and along the boundary between the longitudinalis inferior and the genio-glossus to the tip of the tongue. The lingual vein, which lies lateral to the hyo-glossus muscle, takes a similar although much more irregular course. The glosso-pharyngeal nerve passes down medial to the stylo-glossus muscle to the root of the tongue. The hngua! nerve passes along the lateral margin of the tongue external to the stylo- glossus, hyo-glossus, and inferior longitudinal muscles. The hypoglossal nerve hes lateral to the inferior portion of the hyo-glossus muscle and then sinks into the genio-glossus. The hyo-glossus muscle is covered laterally below the free portion of the tongue by the mylo- hyoid, digastric, and stylo-hyoxd muscles and by the deep part of the submaxillary gland. Medially it covers in part the middle constrictor of the pharynx. The stylo-glossus muscle above the tongue hes medial to the stylo-hyoid and the internal pterygoid muscles and the parotid gland, and between the internal and external carotid arteries. It lies lateral to the superior constrictor of the pharynx. Variations. — The genio-glossus often sends a slip to the epiglottis (levator epiglottidis) . It may send some bundles into the superior constrictor of the pharynx (genio-pharyngeus) or to the stylo-hyoid hgament. Various parts of the muscle may be more or less, isolated. Of these, a fasciculus from the mental (genial) spine to the tip of the tongue is the most frequent (longitudinalis linguae inferior medius). The hyo-glossus exhibits considerable variation in structure. Some authors consider the chondro-glossus but a portion of this muscle, while Poirier considers it merely the origin of the longitudinalis inferior. The stylo-glossus may be absent on one side or on both. Its origin varies considerably and may be from the angle of the jaw. The muscle may be doubled. 5. SUPERFICIAL MUSCULATURE OF THE SHOULDER GIRDLE AND THE EXTERNAL CERVICAL FASCIA (Figs. 348, 355) The stemo-cleido-mastoid is a strong, band-shaped muscle, bifurcated below, which arises from the medial third of the clavicle and the front of the manubrium and is inserted into the mastoid process of the temporal bone and the neigh- bouring part of the occipital. The large, fiat, triangular trapezius arises from the occipital bone and the spines of the cervical and thoracic vertebrae and is in- serted into the lateral third of the clavicle and into the acromion and spine of the scapula. The two muscles lie in a well defined layer of fascia which ensheaths the neck beneath the platysma, the external cervical fascia. Both muscles bend the head and neck toward the shoulder, rotate and extend the head, and raise the shoulder. The sterno-cleido-mastoid also elevates the thorax and flexes the neck. These two superficially placed muscles represent differentiated portions of a musculature found in elasmobranchs and in the amphibia and all higher vertebrates. In sharks this muscula- ture is associated with the musculature of the branchial arches, and, hke them, is innervated by the vagus nerve. In the higher vertebrates it is innervated by the vagus or by the spinal accessory nerve, developed in connection with the vagus. To this innervation by a cranial nerve, innervation by cervical nerves is added in those higher vertebrates in which the muscula- ture is more extensively developed. In the human embryo the muscles migrate from their origin in the upper lateral cervical region to the positions found in the adult. FASCIA The fascise of the neck and the relations of the muscles are shown in cross-section in figs. 347, and 351. The tela subcutanea of the head and neck in the upper dorsal region is thick, fibrous, and closely adherent to the underlying muscle fascia. Ventrally in the cervical region it contains the platysma. The external cervical fascia (fig. 350) lies beneath the subcutaneous tissue and the platysma, completely invests the neck and extends cranialward over the parotid gland to the zygoma and the masseteric fascia. The trapezius hes between two closely adherent lamince of the fascia. From the ventral margin of the trapezius it is continued as a thin but strong membrane across the posterior triangle of the neck, between this muscle and the sterno- cleido-mastoid, and is attached below to the clavicle. It invests the sterno-cleido-mastoid with two adherent laminse and extends from the ventral margin of this muscle across the anterior triangle to the mid-line where it is continued into that of the opposite side. In this triangle the fascia is bound to the hyoid bone, and is thus divided into a submaxillary and an infrahyoid portion. The infrahyoid portion is simple and is attached below to the front of the manubrium. The submaxillary portion is attached to the inferior margin of the mandible. It covers the submaxillary gland, and along the inferior margin gives rise to a strong, membranous 'process which passes inward below the gland and, after extending around the tendon of the digastric muscle, becomes united 348 THE MUSCULATURE to the superior margin of the hyoid bone. This process ventrally becomes fused with the peri- mysium of the ventral belly of the digastric. Dorsally it extends over the posterior end of the submaxillary gland and becomes attached to the angle of the jaw. Here it is strengthened by fibrous tissue which extends in from the ventral margin of the sterno-cleido-mastoid and serves to separate the parotid from the submaxillary gland. This 'mandibular process' is continued into the stylo-mandibular ligament. Fig. 350. — Fascia op the Neck. (After Eisler.) The superficial fascia has been removed in places in order to show the deeper fasciaj; the sterno-cleido-mastoid has been partly removed; the submaxillary gland, almost wholly; the parotid gland, as far as the duct. 1. Submaxillary space. 2. Parotid space. 3. Sterno-cleido-mastoid. 4 Supra-clavicular fossa. 5. Supra-sternal space. 6. External jugular vein. 7. Anterior jugular vein. 8. Median colU vein. 9. N occipitaUs minor. 10. N. aurioularis magnus. 11. Deltoid. 12.^Proc. coracoideus. 13, Fascia ooraco-clavieularis. The parotid gland is enclosed between two laminae of the external cervical fascia. These are continued over the gland from the fascial investment of the sterno-cleido-mastoid, and unite ventrally to become fused to the masseteric fascia along the anterior margin of the gland. They unite below the inferior margin of the gland, and are continued into the rnandibular process mentioned above. The external layer, which is the thicker and stronger, is attached above to the cartilage of the auditory canal and to the zygoma. The inner lamina is attached above TRAPEZIUS 349 to the base of the temporal bone. It is incomplete and is more or less fused to the posterior belly of the digastric muscle, the styloid process, and the muscles arising from this process. Between the styloid process and the angle of the jaw this lamina is strengthened to form the stylo-mandibular ligament. In the back, beyond the spine of the scapula, the fascia arising from the investing adherent fascial sheath of the trapezius muscle is continued laterally across the fascia investing the infra- spinatus muscle, and becomes fused with the most superficial layer of this fascia and more djstally with that of the latissimus dorsi muscle. Near this lateral line of fusion it is usually closely adherent to the tela subcutanea. MUSCLES The sterno-cleido-mastoideus (fig. 348). — Origin. — By a medial (sternal) head from the front of the manubrium and by a lateral (clavicular) head from the upper border of the median third of the clavicle. Between the two origins there intervenes a triangular area covered by the external cervical fascia. Its insertion is — (1) on the anterior border and outer surface of the mastoid process, and (2) on the lateral half of the superior nuchal line of the occipital bone. Structure. — The tendons are comparatively short, the longest being that on the anterior surface of the sternal attachment. The fibre-bundles of the muscle take a nearly parallel course from origin to insertion. Five fasciculi may be more or less clearly recognised. In a superficial layer — (1) a superficial sterno-mastoid; (2) a sterno-occipital; and (3) a cleido- occipital. In a deep layer — (4) a deep sterno-mastoid and (5) a cleido-mastoid. Nerve-supply. — (1) From the spinal accessory nerve, which gives it branches during its course through the deep portion of the muscle, and (2) by branches from the anterior primary divisions of the second and third (?) cervical nerves. These branches enter the deep surface of the upper half of the muscle. Action. — To bend the head and neck toward the shoulder and rotate the head toward the opposite side. When both muscles act, the neck is flexed toward the thorax and the chin is raised; or, with fixed head, the sternum is raised, as in forced respiration. When the head is bent back, the two muscles may further increase the hyperextension. Relations. — The muscle and its sheath are covered externally by the tela subcutanea, which here contains the platysma and the external jugular vein, as well as the superficial branches of the cervical plexus. Beneath the muscle lie the sterno-hyoid, sterno-thyreoid, omo-hyoid. levator scapuliE, scaleni, splenius, and digastric muscles, the cervical plexus, the common carotid artery, internal jugular vein, and the vagus nerve. The spinal accessory nerve usually runs through its deep cleido-mastoid portion. Variations. — There is considerable variation in the extent of independence of the main fasciculi of the muscle. In many of the lower animals the cleido-mastoid portion of the muscle is quite distinct from the sterno-mastoid portion, and this condition is frequently found in man. The cleido-occipital portion of the muscle is that most frequently absent (Wood found it present in 37 out of 102 instances). The clavicular portion of the muscle varies greatly in width. The sternal head has been seen to e.xtend as far as the attachment of the fifth rib. Slips from the muscle may pass to various neighbouring structures. The main fascicuU of the muscle may be doubled. Sometimes one or more tendinous inscriptions cross a part or the whole of the superficial layer of the muscle. The trapezius (fig. 355). — Origin. — By aflat aponeurosis from the superior nuchal fine and external protuberance of the occipital bone, the ligamentum nuchte, and the vertebra! spines and supraspinous ligament from the seventh cervical to the twelfth thoracic vertebra. The aponeuroses of the right and left muscles are continuous across the middle fine. Between the middle of the ligamentum nuchae and the second thoracic vertebra, the aponeuroses give rise to an extensive quadrilateral tendinous area. At the distal extremity of the muscle they are also weU developed. Structure and Insertion. — The superior fibre-bundles pass obliquely downward, lateralward, and forward to the postero-superior aspect of the lateral third of the clavicle; the middle fibre- bundles, transversely to the medial edge of the acromion and the upper border of the spine of the scapula; the lower fibre-bundles, obliquely upward and laterally to terminate thi'ough a flat, triangular tendon on a tubercle at the medial end of the spine of the scapula. Nerve-supply. — The external branch of the spinal accessory nerve descends for a distance near the superior border of the trapezius muscle and then along the ventral surface. Soon it gives rise to ascending branches for the superior portion of the muscle and descending branches for the middle and inferior portions. The main branches of distribution run about midway between the origin and insertion of the fibre-bundles. The branches from the second (?), third and fourth cervical nerves anastomose with the trunk of the spinal accessory, sometimes as it passes along the margin of the muscle, at other times within the substance of the upper portion of the muscle. Action. — When the whole muscle contracts, it draws the scapula toward the spine and turns it so that the inferior angle points laterally, the lateral angle upward. In addition the upper portion draws the point of the shoulder upward, and with the scapula fixed extends the head, bends the neck toward the same side, and tm'ns the face to the opposite side. The lower portion of the muscle tends to draw the scapula downward and inward and at the same time to rotate the inferior angle of the scapula outward. Relations. — It is covered merely by skin and fascia. It Ues external to the semispinahs, splenii, rhomboidei, latissimus dorsi, levator scapute, supraspinatus, and a small portion of the infraspinatus muscles. Variations. — The lower limit of attachment of the muscle may be as high as the fourth thoracic vertebra. The right and left muscles are seldom symmetrical. The upper attach- ment may not extend to the skull. The clavicular attachment may be much more extensive > 350 THE MUSCULATURE than normal or may be missing. The attachments to the scapula show considerable variations. Occasionally the cervical and thoracic portions are separate, a condition normal in many mammals. VentraUy the trapezius may become continuous with the sterno-cleido-mastoid in the neck, or send a fasciculus to it or to the sternum. Aberrant fasciculi are not infrequent. Rarely a transverse tendinous inscription is found in the cervical or in the thoracic portion of the muscle. Sometimes a fasciculus is sent into the deltoid. The innervation of either the sterno-cleido-mastoid or the trapezius may be by cervical nerves only. The omo-cervicalis {levator claviculce) is a fasciculus frequent in the lower mammals, but rarely found in man. It usually extends from the acromial end of the clavicle to the atlas and axis, but may extend to more distal cervical vertebrae. It is innervated by a ramus from the cervical branches to the trapezius. The supra-clavicularis proprius is a muscle rarely found. It extends on the cranial surface of the clavicle from the sternal to the acromial end and is innervated by the third cervical nerve. It is said to make tense the superficial layer of the cervical fascia. A bursa is often found between the base of the spine of the scapula and the tendon of inser- tion of the thoracic portion of the trapezius. Another bursa is also frequently found between the insertion of the transverse portion and the supraspinous fascia. 6. INFRAHYOID MUSCULATURE (Figs. 348 and 351) The four infrahyoid muscles constitute a well-defined group of muscles which depress the hyoid bone, the larynx, and the associated structures. They lie beneath the sterno-cleido-mastoid muscle and the external cervical fascia. Two strata may be recognised. In the superficial stratum are comprised the omo- hyoid, a narrow, ribbon-like digastric muscle which arises from the superior margin of the scapula and is inserted into the hyoid bone; and the thin, quad- rangular sterno-hyoid, which arises from the superior margin of the sternum and the medial end of the clavicle and is inserted into the hyoid bone. Between these two muscles is an aponeurotic membrane which constitutes the main part of the middle layer of the cervical fascia, and represents possibly a retrograde portion of a single muscle, of which the two above named are but the ventral and dorsal margins. Beneath this superficial musculature the thin, quadrangular thyreo-hyoid descends from the hyoid bone to the thyreoid cartilage, and the ribbon-like stemo-thyreoid arises from the dorsal surface of the manubrium and is inserted into the thyreoid cartilage. All these muscles are supplied by branches from the ansa hypoglossi. The nerve-fibres arise from the first three cervical nerves. The muscles of this group are derived from the ventral portions of the ventro-lateral divi- sions of the first three cervical myotomes, and correspond with the rectus abdominis muscle, which is derived from the ventral portions of the eighth to the tweUth thoracic myotomes. This musculature is characterised by metameric segmentation, which may be more or less ob- scured, and by a general longitudinal direction taken by the component fibre-bundles. The course of the fibres in the omo-hyoid may be looked upon as a secondary condition due to the shifting laterally of the distal attachment of the muscle. Musculature of this nature is not derived from the lower cervical and upper thoracic myotomes in man, but in some of the lower vertebrates it forms a continuous ventral band. Even in man occasional traces of this ventral musculature may, however, be seen as muscular and aponeurotic slips on the upper part of the thoracic wail, above the ribs and the aponeurosis of the external intercostal muscles. FASCIA (Figs. 351 and 357) The middle cervical fascia is composed of two laminae. Of these, the superficial, which ensheaths the sterno-hyoid and omo-hyoid muscles and fills in the intervening area, is much the stronger and better differentiated. The more delicate deep lamina ensheaths the thyreo-hyoid and sterno-thyreoid muscles, and laterally extends out to become fused with the superficial lamina. It is also more or less closely bound to the sheath which covers the internal jugular vein, carotid artery, and vagus nerve. The middle cervical fascia is attached above to the hyoid bone. Beyond the lateral edge of the omo-hyoid it becomes fused with the deep lamina of the external layer of the cervical fascia, beneath the sterno-cleido-mastoid. Posterior to this muscle it usually terminates along the cranial margin of the omo-hyoid in the areolar tissue of the neck. Its distal attachment takes place into the dorsal surface of the upper margin of the sternum, and from here a process is sent over the left innominate vein to the pericardium. Lateral to the sternum the fascia is attached for some distance to the inner margin of the clavicle, and gives rise to processes, one of which extends to the fascia of the subclavius muscle, while the others pass on each side of the subclavian vein to the first rib. Still more laterally the fascia is fused along the lower margin of the scapular belly of the omo-hyoid to the underlying dense, fatty areolar tissue. INFRA-HYOID MUSCLES 351 MUSCLES (Figs. 348 and 351) The sterno-hyoideus. — Origin. — From (1) the deep surface of the medial extremity of the clavicle; (2) the costo-clavicular (rhomboid) ligament; and (3) the neighbouring part of the sternum. The origin may extend to the cartilage of the first rib. Structure and insertion — The fibre-bundles take a nearly parallel course upward. The muscle belly, however, contract, slightly in width and increases slightly in thickness and slants somewhat toward the median Hne. The insertion takes place directly upon the inferior margin of the body of the hyoid lateral to the mid-line. Not infrequently a tendinous inscription near the junction of the middle and inferior thirds more or less completely divides the muscle into two portions. A second inscription is sometimes found at the level of the oblique line of the thyreoid cai'tilage. Nerve- supply. — One or more branches from the ansa hypoglossi enter the lateral margin of the muscle. Frequently one goes to the upper third, another to the lower third, of the muscle. The omo-hyoideus. — Origin. — From the superior margin of the scapula near, and occa- sionally also from, the superior transverse ligament of the scapula. Insertion. — The lower border of the hyoid bone lateral to the sterno-hyoid muscle. Structure. — The inferior belly of the muscle near its origin is thick and fleshy. It contracts as it passes ventrally across the posterior triangle of the neck. Beneath the sterno-cleido-mastoid it is attached to a short ten- don from which, as it bends upward toward the hj-oid bone, the superior belly takes origin and thence expands toward the insertion. The tendon of attachment is short. The fibre-bundles of both bellies take a nearly parallel course. The central tendon of the muscle is held in place by a strong process in the middle layer of the cervical fascia. This process is attached to the dorsal surface of the clavicle and to the first rib. Nerve-supply. — The superior belly is supphed by a branch which enters its deep surface near the medial margin somewhat below the centre; the inferior by a branch which enters the proximal third of its deep surface. These branches arise from the ansa hypoglossi. jjThe sterno-thyreoideus. — Origin. — Partly directly, partly by tendinous fibres, from — (1) the dorsal surface of the manubrium from the middle line to the notch for the first rib; (2) the dorsal surface of the cartilage of the first rib. Occasionally also from the back of the cartilage of the second rib or from the clavicle. Structure and insertion. — The fibre-bundles take a nearly parallel course upward and shghtly lateralward. The muscle is inserted by short tendinous fibres into the oblique hne on the lamina of the thyreoid cartilage. A transverse tendinous inscription near the upper border of the interclavicular hgament not infrequently divides the belly of the muscle more or less completely into two parts. Sometimes a second transverse inscription is found at the level of the lower margin of the thyreoid cartilage. Nerve-supply. — By one or two branches from the ansa hypoglossi, which enter the ventral surface of the muscle near the lateral margin. One branch usually goes to the upper, another to the lower, third of the muscle. The thyreo-hyoideus. — Origin. — From the oblique line on the lamina of the thyreoid cartilage. Structure and insertion. — The fibre-bundles take a parallel course and are inserted on the inferior margin of the lateral third of the body of the hyoid bone and the external surface of the great cornu. Many fibre-bundles are continuous with those of the sterno-thyreoid. Nerve-supply. — By a branch of the hypoglossal which enters the muscle near the middle of its lateral border. The fibres are said to be derived from the first cervical nerve. Action. — The sterno-hyoid and omo-hyoid depress the hyoid bone; the sterno-thyreoid depresses the thyreoid cartilage; and the thyreoid-hyoid approximates the bone to the cartilage. The omo-hyoid tends to draw the hyoid bone somewhat laterally. In this it is aided by the posterior bell}' of the digastric and the stylo-hyoid and is opposed by the sterno-thyreoid and thyreo-hyoid muscles, and the anterior belly of the digastric. Relations. — The muscles of this group he beneath the external cervical fascia. The sterno- cleido-mastoid muscle crosses the omo-hyoid, the sterno-hyoid, and sterno-thyreoid muscles. The latter two'muscles extend for a distance behind the manubrium of the sternum. The omo- hyoid is partly covered by the trapezius, crosses the scalene muscles, the brachial plexus, the internal jugular vein, carotid artery, and the sterno-thyreoid and thyreo-hyoid muscles. The sterno-hyoid extends over the sterno-thyreoid muscle, the thyreoid gland, crico-thyreoid muscle, and the thyi'eoid cartilage. The sterno-thyreoid Ues over the innominate veui, the trachea, and thyreoid gland. It is partly covered by the sterno-hyoid and omo-hyoid muscles. The thyreo-hj'oid is largely covered by the omo-hyoid and sterno-hyoid muscles, and lies upon the hyo-thyreoid membrane and the upper part of the thyreoid cartilage. Variations. — The muscles vary in extent of development and may be more or less fused with one another. The sternal attachment of the sterno-hyoid is more frequently absent than the clavicular attachment. The region between the omo-hyoid and sterno-hyoid may be com- posed of muscle instead of fascia. Each of the muscles may be longitudinally divided into two distinct fascicuh, may send fascicuU to one another or to the middle layer of the cervical fascia, or may have an abnormal origin or insertion. The omo-hyoid is the one of the group most frequently absent. One of the bellies is much more frequently absent than both. The inter- mediate tendon of the omo-hyoid may be reduced to a tendinous inscription or even disappear entirely. The distal attachment maj' take place on the scapular spine, the acromion, the cora- coid process, or even the first rib or clavicle. An extra fasciculus from the clavicle is found in 3 per cent, of instances. (Le Double.). Not very infrequently a muscle innervated by a branch of the descendens hypoglossi is found extending from the sternum to the clavicle behind the origin of the sterno-cleido-mastoid. It may also extend from the sternum or clavicle in various directions upward toward the head. 352 THE MUSCULATURE Fig. 351, A and B. — Tbansverse Sections Through the Left Side of the Neck and Shoulder in the Regions indicated in the Diagram. a and 6 in the diagram indicate sections A and B of fig. 347 (p. 340). a, that of section A, fig. 357 (p. 366). 41 63 35 5G 36 60 30 H 28 29 SCALENE MUSCLES 353 BURS^ The bursa m. sterno-hyoidei is in constantly found between the lower margin of the hyoid bone and median hyo-thyreoid ligament and the sterno-hyoid muscle and external cervical fascia. It is better developed in men than in women and is found either on each side of the median line or fused in the median line. The bursa m. thyreo-hyoidei is frequently found between the greater cornu of the hyoid bone and hyo-thyreoid membrane and the thyreo-hyoid muscle. 7. SCALENE MUSCULATURE (Figs. 348 and 352) The three muscles which form this group constitute a triangular mass which extends in front of the levator scapulae and intrinsic dorsal musculature and behind the prevertebral musculature from the first two ribs to the transverse processes of the cervical vertebrae. They cover laterally the apex of the pleural cavity. They bend the neck and fix the first two ribs or raise the thorax. In front lies the scalenus anterior, which extends from the first rib to the fourth to skth vertebrae. Behind this the scalenus medius extends from the first rib to the lower six vertebrae. The most dorsal of the group, the scalenus posterior, extends from the second rib to the fifth and sixth vertebrae. These muscles are supplied by direct branches of the cervical nerves. They are probably derived from the lateral portions of the cervical myotomes. According to Gegenbaur, the two more ventral are homologous with intercostal muscles, the dorsal with the levatores costarum. It is to be noted, however, that the anterior muscle lies in front of the brachial plexus, i. e., in a position similar to that of the subcostal musculature. The scalene musculature is morpho- logically closely related to the deep shoulder-girdle musculature, p. 356. FASCIA (Figs. 351, 357) From the front of the bodies of the cervical vertebrae the prevertebral fascia is continued laterally over the longus colli and the scalene muscles, and extends dorsally into the fascia covering the levator scapulae. Between the muscles fascial processes are sent in to become attached to the cervical vertebras. Interiorly the fascia extends to the outer surface of the thorax. MUSCLES (Fig. 352) The scalenus anterior. — This arises from the ventral part of the inferior border of the transverse processes of the fourth, fifth, and sixth cervical vertebrae, usually also from the third, rarely from the seventh, by means of long, slender tendinous processes. From each tendon arises a fasciculus composed of nearly parallel fibre-bundles. The fasciculi soon fuse to form a muscle belly which contracts somewhat toward the insertion. This takes place by means of 1. Arteria carotis communis. 2a. A. cervicalis profunda. 2b. A. cervicalis superficiaUs 3. A. thoracoacromialis (acromial branch). 4a. A. thyreoidea inferior. 4b. A. thyreoidea superior. 5. A. transversa colli. 6. A. transversa scapulae. 7. A. vertebralis. 8. Bursa m. subscapularis. 9. Cartilago arytenoidea. 10. Cartilago thyreoidea. 11. Clavicle. 12. Costa I. 13. Costa II. 14. Fascia cervicalis — a, superficial layer; b, middle layer. 15. Deep or prevertebral layer. 16. Fascia coraco clavicularis. 17. Fascia nuchas. IS. Glandula thyreoidea. 19. Humerus. 20. Ligamentum coracohumerale. 21. Med- ulla spinalis (spinal cord). 22. Musculus arytenoideus transversus. 23. M. biceps brachii, tendon long head. 24. M. constrictor pharyngis inferior. 25. M. deltoideus. 26. M. Uio-costalis. 27. M. infraspinatus. 28. M. levator scapulae. 29. M. longissimus capitis (trachelo-mastoid). 30. M. longissimus cervicis. 31a. M. longus colli. 31b. M. longus capitis (rectus capitis anticus major). 32. M. omo-hyoideus. 33. M. platysma. 34. M. rhomboideus minor. 35. M. scalenus anterior. 36. M. scalenus medius. 37. M. semi' spinalis capitis (oomplexus). 38. M. serratus anterior. 39. M. serratus posterior superior. 40. M. splenius. 41. M. sterno-cleido-mastoideus. 42. M. sterno-hyoideus. 43. M. sterno-thyreoideus. 44. M. subclavius. 45. M. subscapularis; a, tendon. 46. M. thyreo-arytenoideus (and vocalis). 47. M. thyreo-hyoideus. 48. M. transverso-spinales. 49. M. trapezius. 50. Nervous accessorius. 51. N. cervicalis IV. 52. N. laryngeus inferior. 53. N. descendens hypoglossi. 54. Sympathetic trunk. 55. N. thoracaUs I. 56. N. vagus. 57. (Esophagus. 58. Plexus brachialis. 59. Scapula — a, glenoid cavity; b, ooracoid process; c, spine. 60. Trachea. 61. Vena transversa colli. 62. V. jugularis externa. 6.3. V. jugularis interna. 64. Vertebra cervicalis V. 65. Vertebra cervicalis VII. 66. Vertebra thoracalis I, arch. 67. Vertebra thoracalis II — a, spine; b, transverse process. 354 THE MUSCULATURE a tendon which sends a fibrous lamina a short distance upward on the outer surface of the muscle. The tendon is inserted into the scalene tubercle on the upper surface of the body of the first rib. The scalenus medius. — This arises usually from the third to the seventh, sometimes from aU seven or from merely the last four or five cervical vertebrrs. The origin takes place from the posterior part of the lateral border of the transverse processes by means of a slender tendon from each of the upper and directly by a muscular fasciculus from each of the lower vertebrae. The .fasciculi become combined into a compact muscle belly which is inserted in a manner similar to the scalenus anterior into the upper surface of the fu-st rib behind the subclavian groove. The insertion usually extends to the second rib. The scalenus posterior arises by short tendons from the posterior tubercles of the transverse processes of the fifth and sixth cervical vertebrae. The origin may extend as high as the fourth vertebra, or as low as the seventh. It is inserted by a short tendon into the lateral surface of the second rib. Occasionally it extends to the third rib. Fig. 352 — The Deep Ventral Muscles op the Neck. Rectus capitis anterior Rectus capitis lateralis Orgin of tlie longus capitis Scalenus medius Scalenus anterior Scalenus posterior Rectus capitis la- teralis Rectus capitis anterior Intertransversus posterior Nerve-supply. — The scalenus anterior is innervated by branches from the'fifth, sixth, and seventh cervical nerves; the middle by the fourth, fifth, sixth, seventh, and eighth cervical nerves; the posterior by the seventh or eighth nerves. Action. — With the thorax fixed the scalene muscles bend the neck to the side and sUghtly forward and turn it sUghtly toward the opposite side. With the neck fixed they serve to lift the first two ribs and are of use in enforced inspiration. In quiet inspiration they serve to fix the first two ribs. Relations. — The longus colli lies medial to the scalenus anterior. DorsaUy the scalene muscles; medially the pharynx, thyreoid gland, and trachea; ventro-lateraUy the sterno-cleido- mastoid, infra-hyoid, and subclavius muscles and the clavicle bound a space filled with dense fatty areolar tissue in which are contained the subclavian and carotid arteries, the subclavian and internal jugular veins, the vagus, phrenic, and sympathetic nerves, and numerous smaller blood-vessels and nerves. The main branches of the lower five cervical nerves pass laterally between the scalenus anterior and medius. The subclavian artery passes behind, the sub- clavian vein in front, of the attachment of the scalenus anterior. The scalenus medius above and the scalenus posterior below enter into relations dorsally with the levator scapulae and the intrinsic dorsal musculature, from which they are separated by fascial septa. PREVERTEBRAL MUSCLES 355 Variations. — The scaleni present numerous variations in the extent of the costal and ver- tebral attachments. The degree of fusion of the various fasciculi likewise varies so much that diiferent authors have described varying numbers of muscles into which the scalenus mass should be subdivided. A muscle frequently present is the scalenus minimus. This arises from the anterior tubercle of the sixth or sixth and seventh cervical vertebrte, and is inserted into the first rib behind the sulcus for the subclavian artery. It sends a process (Sibson's fascia) to the pleural cupola and serves to make the pleura tense. Zuckerkandl found it in 22 out of 60 bodies on both sides; 12 times on the right side only, 9 times on the left. It is innervated by the eighth cervical nerve. When absent, a ligamentous band takes its place. An intertransversarius lateralis longus, may extend from the posterior tubercles of the 3-5 transverse processes to the tip of the seventh transverse process and divide the muscle fasciculi near their origin into dorsal and ventral divisions. 8. THE PREVERTEBRAL MUSCULATURE (Fig. 352) This deep-seated musculature extends along tiie ventro-Iateral sm-faces of the three upper thoracic and the cervical vertebrEe to the skull. It is composed of two muscles. The longus colli arises from the bodies of the three thoracic and from the bodies and transverse processes of the third to the sixth cervical verte- brae, and is inserted into transverse processes and bodies of the cervical vertebrae. The longus capitis (rectus capitis anterior major) arises from the transverse processes of the fourth, fifth, and sixth cervical vertebrae, and is inserted into the basilar process of the occipital bone. These muscles flex, abduct, and rotate the head and neck. All of them are supplied by direct branches from the anterior divisions of the cervical nerves. They are probably specialised from the ventro- lateral portions of the cervical myotomes. Similar muscles are found in all vertebrates with well-developed necks. The rectus capitis anterior (minor) represents an anterior cervical intertransverse muscle. FASCIA (Figs. 351, 357) The muscles are firmly bound to the vertebral column by the prevertebral fascia described in connection with the scalene muscles and by the septa which extend in between the muscles of this group and between them and the scalenus anterior. MUSCLES (Fig. 352) The longus colli. — This muscle may be compared to a triangle, the base of which extends from the anterior tubercle of the atlas to the body of the third thoracic vertebra and the apex of which is the transverse process of the fifth cervical vertebra. The complex construction of the muscle makes it advisable to consider it as divided into three parts. The supero-lateral portion consists of fasciculi which arise from the anterior tubercles of the transverse processes of the third, fourth, fifth, and sixth cervical vertebrse and from the body of the third thoracic and become fused into a belly which is inserted into the anterior tubercle of the atlas. The median portion is formed of muscle fasciculi which arise from the antero-lateral p.irts of the bodies of the first three thoracic vertebrae and the last three cervical vertebrae by tendin- ous processes. These fasciculi fuse into a belly which terminates by three flat tendinous fas- ciculi on the antero-lateral surfaces of the bodies of the second, third, and fourth cervical vertebras. The infero -lateral portion is applied to the inferior lateral surface of the median portion. It arises from the lateral parts of the bodies of the first three thoracic vertebrae and is inserted by tendinous processes into the transverse processes of the fifth and sixth cervical vertebrae. Nerve-supply. — By branches from the second to sixth cervical nerves which send rami to the various constituent fasciculi of the muscle. The longus capitis (rectus capitis anterior major). — Origin. — By cylindrical tendons from the tips of the anterior tubercles of the third, fourth fifth, and sixth cervical vertebras. The tendons send up aponeurotic expansions on the outside of the fasciculi, which arise from them. These fasciculi fuse into a dense muscular belly to which is usually added a fasciculus from the longus colli. The insertion takes place into the impression on the inferior sui'face of the basilar portion of the occipital bone, extending lateral to the pharyngeal tubercle outward and for- ward. The insertion of the fibre-bundles from the third vertebra is direct; the other fibre- bundles are inserted largely into a tendinous lamina which covers the middle of the ventral surface of the muscle and from which, in turn, other fibre-bundles arise. It is an incomplete digastric muscle. Nerve-supply. — The first, second, third, and fourth cervical nerves send branches into the ventral surface of the muscle. 356 THE MUSCULATURE Actions. — The longus colli serves to bend the neck forward; the supero-lateral portion, when acting on one side only, serves slightly to bend the neck toward that side and to rotate it; the infero-lateral portion serves especially to prevent hyperextension. The longus capitis bends the head forward; one side acting alone rotates the head toward that side. Variations. — There is considerable variation in the number of vertebrje to which the ten- dons of origin and insertion of the longus colh and longus capitis may be attached and in the extent of fusion of the different fasciculi composing them. There may be fusion with the scale- nus anterior. The atlantico-hasilaris internus in 4 per cent, of cases extends from the anterior tubercle of the atlas to the base of the skull. 9. ANTERIOR AND LATERAL INTERTRANSVERSE MUSCLES (Fig. 352) The anterior intertransverse muscles extend successively between the anterior tubercles of the cervical vertebrte. They lie in front of the anterior divisions of the cervical nerves and are supplied by branches from these divisions. They are usually more or less bound up with the insertions of the scalene and pre- vertebral muscles into these tubercles. The muscle between the atlas and epi- stropheus is frequently missing; when present, it passes in front of the lateral articulation between these vertebrte. The rectus capitis anterior (minor) may be considered a continuation of the series. The lowest muscle may extend between the seventh cervical vertebra and the first rib. The lateral intertrans- verse muscles lie immediately behind the ventral divisions of the spinal nerves and lateral to the dorsal divisions and are supplied by branches from the ventral divisions. The rectus capitis laterahs belongs to this series. The rectus capitis anterior (minor) arises from the lateral mass of the atlas and is inserted into the base of the occipital bone. The rectus capitis lateralis runs from the transverse process of the atlas to the lateral part of the occipital. For the posterior intertransverse muscles see p. 417. The rectus capitis anterior (minor). — This arises from the upper surface of the lateral mass of the atlas in front of the articular process and partly from the neighbouring transverse proc- ess. From a tendon the fibre-bundles extend in a nearly parallel direction upward and medially to be inserted on the inferior surface of the basilar portion of the occipital bone in front of the condyle Nerve-supply. — From the first (and second) cervical nerves. Action. — The rectus capitis anterior (minor) serve to bend the head forward and, when the muscles on one side only are contracted, to rotate the head toward the same side. Relations. — The muscles of this group are closely apphed to the vertebral column. Be- tween the fascia covering them and the fascia surrounding the pharynx which lies in front is a region in which merely a slight amount of loose areolar tissue is found. Dorso-mediaUy the longus colli below and the longus capitis above help to bound the space in which the chief ves- sels and nerves extend between the thorax and the head. The rectus capitis lateralis (fig. 352). — Origin. — From the upper surface of the transverse process of the atlas. Structure and insertion. — The fibre-bundles give rise to a quadrilateral sheet which passes upward to be inserted on the under surface of the pars lateralis of the occipital bone. Nerve-supply. — The ventral branch of the suboccipital (first cervical) nerve gives twigs to its ventral surface. Action. — To flex the head laterally. Relations. — In front lie the anterior primary division of the suboccipital nerve and the internal jugular vein. Behind the muscle lie the superior oblique and the longissimus capitis (trachelo-mastoid) muscles and the atlanto-occipital joint. 10. DEEP MUSCULATURE OF THE SHOULDER GIRDLE (Figs. 348, 353, 354, 388) To this group belong four muscles which arise in the lateral cervical region during embryonic development and become secondarily attached to the vertebral margin of the scapula. One of these muscles, the band-like levator scapulae (fig. 353), remains in the cervical region. It extends beneath the sterno-cleido- mastoid, the trapezius, and the intervening fascia from the transverse processes of the first four cervical vertebrae to the medial angle of the scapula. A second, the large, quadrilateral serratus anterior (magnus) (fig. 354), comes to lie beneath the blade of the scapula and wanders with this to the thoracic region. It arises, in the adult, from the first nine ribs and is inserted into the vertebral margin of the scapula. The flat, quadrangular rhomboideus major and rhomboideus DEEP SHOULDER MUSCLES 357 minor (fig. 353) arise from the spines of the last cervical and first four or five thoracic vertebrae, pass obliquely downward across the deep dorsal muscles beneath the trapezius and are inserted into the vertebral margin of the scapula. The third to the seventh cervical nerves supply this set of Fig. 353. — The Levator Scapul* and Rhomboidbi. Semisplnalis capitis Spleiiius capitis Levator scapulae Serratus posterior superior Rhomboideus minor Splenius cervicis Rhomboideus major Supraspinatusp"" Serratus posterior inferior Obliquus internus' muscles. The levator scapulae is supplied by the third and fourth cervical nerves, the rhomboids by the fifth (dorsal scapular), the serratus anterior by the fifth to the seventh (long thoracic nerve). The muscles of this group ele- vate the scapula, rotate it, and draw it backward (rhomboidei) or forward (serratus anterior). When all contract together they raise the thorax. 358 THE MUSCULATURE The levator soapulse and the serratus anterior (magnus) are two differentiated parts of a muscle which is a continous mass in many of the lower mammals. A muscle corresponding to the rhomboideus is found in some of the reptiles and many of the higher vertebrates. In some of the mammals it has a more extensive cervical attachment than in man. FASCIiE The fasciae investing these muscles are shown in cross-section in fig. 357. The levator seapulEc is invested by fascial membranes, the external and stronger of which is continued dorsaUy from the fascial investment of the scalene muscles. The thinner layer on^its deep surface Hes next the fascial investment of the intrinsic muscles of the back. Cranial- ward from the rhomboid muscles the fascial investment of the levator scapulse is fused dorsally with the fascia covering the splenius cervicis. Where the dorsal margin of the levator comes in contact with the rhomboideus minor, the fascia is continued over into the thin fascial mem- FiQ. 354, — SERKATtrs Anterioh. brane which invests both surfaces of the rhomboidei. Similarly the investing fascia of the leva- tor is continued ventrally into the fascia investing both sm'faces of the serratus anterior (mag- nus). Within the internal fascial investment of this group of muscles, near the insertion of the levator, run the transversa coUi artery and the dorsal scapular nerve. MUSCLES The rhomboideus minor (fig. 353). — Origin. — ^Lower part of the ligamentum nuchse, the spines of the seventh cervical and first thoracic vertebrae, and the intervening supraspinous Uga- ment. Insertion. — Vertebral border of the scapula near the spine. The rhomboideus major (fig. 353). — Origin. — Spines of the fii'st four or five thoracic ver- tebrae. Insertion. — Vertebral border of the scapula opposite the infraspinous fossa. Structure. — The two muscles are included between two adherent fascial layers which bridge over the greater or less space that may intervene between them. The fibre-bundles take a parallel course obliquely downward and lateralward from the vertebrae. From the vertebral spines the muscles arise by an aponeurosis which varies in width. The attachment to the scap- ula is by short tendinous processes. The attachment of the rhomboideus major is firmest to- ward the inferior angle of the scapula. Nerve-supply. — The dorsal scapular nerve, which usually arises chiefly from the fifth cervical nerve, enters the superior margin of the rhomboideus minor and then courses distaUy near the deep ventral surface of the two muscles and about midway between the tendons of origin and insertion. SERRATUS ANTERIOR 359 Action. — The two muscles draw the scapula upward and medialward toward the spine and rotate it so as to depress the shoulder. Relations. — Over the muscles lies the trapezius. Under them he the serratus posterior superior and the splenius cervicis, the longissimus dorsi, the iho-costalis, serratus posterior superior and external intercostal muscles. The descending ramus of the transversa ooUi artery descends on the deep surface. Blood-vessels for the trapezius pass to this muscle between the two rhomboids. Variations. — There is much variation in the extent of the vertebral attachment. The minor is frequently, the major occasionally, absent. The two rhomboids are frequently fused with one another or may be divided into several distinct fascicuU. Frequently (SO per cent., Balli) a fasciculus extends obliquely on the deep surface of the R. major from the cranial part of the origin to the distal part of the insertion. Shps may be sent to the latissimus dorsi or the teres major. An accessory slip may pass between the trapezius and splenius muscles to the occipital bone (occipito-scapularis). A muscle corresponding to this fasciculus is normally found in many mammals. The levator scapulae (figs. 353, 388). — Origin. — By short tendons from the dorsal tubercles of the transverse processes of the first four cervical vertebras, between the attachments of the splenius cervicis and scalenus medius muscles. The tendons from the third and fourth cervical vertebrae are fused for a short distance with those of the longissimus cervicis. Structure and insertion. — The fibres run in parallel bundles in a dorso-lateral direction downward to the ver- tebral border of the scapula opposite the supraspinous fossa. The fibre-bundles are inserted directly into the periosteum. As a rule, the flat fasciculi arising from the different vertebrae are easily separated. Nerve-supply. — By rami chiefly from the third and fourth cervical nerves. These rami enter the ventral margin of the muscle and extend obhquely across the dorsal surface of the constituent fascicuh about midway between the tendons of origin and insertion. Frequently anastomosing branches pass between the nerves. The lowest fasciculus is usually supplied by branches from the nerve to the rhomboid muscles (dorsal scapular). Action. — Draws the scapula upward and tends to rotate it so that the inferior angle approaches the spine. When the scapula is fixed, the muscle serves to bend the neck laterally and slightly to rotate it toward the same side and extend it. Relations. — Externally the sterno-cleido-mastoid and, in part, the splenius capitis cover it above; the trapezius, below; and the external cervical fascia, its middle portion. Internally lie the splenius cervicis, longissimus and ilioeostaUs cervicis (transversalis cervicis), and serratus posterior superior muscles and the ramus descendens of the transversa colU artery. In front lie the scalene muscles. Variations. — The number of cervical vertebrae from which the muscle springs varies from two to seven. The most constant are the slips of origin from the fii'st two vertebrae. The muscle may send slips to the temporal or the occiptal bone or to the trapezius, the serratus anterior (magnus), serratus posterior superior, and other muscles, or to the clavicle, first or second rib, etc. Often the parts of the muscle running to each vertebra are separated for the whole distance. A bundle of fibres that appears to be a detached shp of the levator scapulae may run from the first two or from lower cervical vertebrae to the lateral end of the clavicle and to the acromion. This represents the levator claviculae found normally in many vertebrates. According to Le Double, it is innervated by a branch from the cervical branches to the trapezius group. The serratus anterior (magnus) (figs. 354, 388). — First Pari. — The origin is by two digita- tions from the first and second ribs and from a fibrous arch uniting these two attachments. The fibre-bundles converge to be inserted on an oval space on the costal surface of the scapula near its medial angle. Second Part. — This arises by two or three digitations from the second, third, and sometimes the fourth ribs. The fibre-bundles spread out into a thin sheet which is inserted along the vertebral border of the scapula. Third Part. — This, the strongest part of the muscle, arises by digitations from the fourth or fifth to the eighth or ninth ribs. The attach- ments of the digitations are longest on the upper border of each rib. The interdigitate with the attachments of the external oblique muscle of the abdomen. The fibre-bundles converge to be inserted on the large oval space on the costal surface near the inferior angle of the scapula. Nerve-supply. — From the proximal portions of the anterior divisions of the fifth, sixth, seventh, and sometimes the eighth cervical nerves branches arise which fuse into the long thoracic nerve. This nerve usually passes laterally through or behind the scalenus medius muscle, courses along the outer surface of the serratus anterior midway between the origin and insertion, and gives rise to numerous twigs to supply the various divisions. The fibres to the upper portion come mainly from the fifth cervical nerve; those to the middle from the fifth and sixth; and those to the lower from the sixth and seventh. Action. — -The muscle holds the scapula against the thorax and draws it forward and later- ally and, by its highly developed inferior portion, rotates the bone so as to raise the point of the shoulder. It is of especial importance in abduction of the arm. It also aids, to a slight degree, in forced inspiration. Relations. — Superficial to the muscle lie the peotoralis major and minor, subscapularis, teres major, and latissimus dorsi muscles, the subclavian and axillary vessels, and the brachial plexus. Between the latissimus dorsi and pectoral muscles it is covered by skin and fascia inferiorly, and superiorly by the fatty areolar tissue of the axiUary fossa. Under it he the ex- ternal intercostal, serratus posterior superior, and the lower extremity of the scalenus medius and posterior muscles. Variations. — -The digitations may extend to the tenth or only to the seventh rib. The muscle may be continuous with the levator scapulae as it is in the carnivora, or some of its upper digitations may be wanting. Slips may be continued into neighbouring muscles. The lower digitations may be partially replaced by digitations innervated by intercostal nerves. 360 THE MUSCULATURE II. MUSCULATURE OF THE UPPER LIMB The upper limbs in man, relieved of the function of locomotion which is their chief office in most of the lower mammals, have become endowed with great Fig. 355. — First Layer of Muscles of the Back. Sterno-cleido-mastoid Triceps Rhomboideus major Pectoralis major Gluteus medius Gluteus maximus MUSCLES OF UPPER LIMB 361 freedom of movement which permits their developing many important functions. Primitively of value in climbing, in seizing food, preparing it for eating and carrying it to the mouth, in attack and defense, their importance has been greatly increased through the invention and use of tools, at first simple but constantly increasing in complexity. They are also used as a means of social expression, as seen primitively in the shrugging of the shoulders, or in the varied movements of the arms which accompany heated discourse, and as finally developed in the art of writing. In order to understand the muscles which are called into play in the performance of these varied functions it is necessary to consider the various types of movement which take place at each of the joints. Since, however, most muscles act on more than one joint and the different parts of a muscle may act differently on the same joint, it is convenient to take up the muscles of each region of the limb in groups, based not so much upon the action of the muscles on any one joint as upon the development of the group and the innervation of the muscles composing it. Movement of the scapula is of essential importance in the movements of the arm. The scapula is kept against the thorax by muscular attachments and atmospheric pressure, but it may be moved forward, backward, upward, and downward, and may be rotated so that the glenoid fossa, with which the head of the humerus articulates, is pointed forward when the arms are carried forward, lateralward when the arms are abducted, upward when the arms are raised high and somewhat downward when the arms are carried backward, thus greatly increasing the extent of movement in these various directions. The acromio-clavicular, and sterno-clavieular joints both allow hmited movements in various directions so that they resemble physiologically limited ball and socket joints. The part played by the superficial and deep shoulder-girdle muscles in the various movements has been described above, p. 356, in connection with these groups of muscles. The action of these muscles is aided by the "pectoral muscles," (figs. 360, 388) and by the latissimus dorsi (fig. 355) described below. These muscles depress the scapula* At the humero-scapular or shoulder-joint the arm may be carried outward or abducted, bodyward or adducted, forward or flexed and backward or extended. The last is much more hmited in degree than the other two. The arm may also be partially rotated at this joint. These various movements are brought about by the scapulo-humeral muscles (figs. 355, 356, 363) and by the latissimus dorsi (fig. 355) and the pectoralis major, (fig. 360) assisted by the muscles of the arm which arise from the scapula. They are produced in association with the movements of the scapula described above. At the ulno-humeral joint the movements are relatively simple, consisting of flexion and extension. Extension is produced at the elbow by the dorsal muscles of the arm (fig. 363), flexion is produced not only by the ventral muscles of the arm, which are inserted into the radius and ulna (fig. 364), but also by the more superficial of both the main groups of muscles of the forearm. The pronation of the forearm, whereby the palm is turned downward, and supination, whereby it is turned upward, take place in the joints be- tween the radius and ulna at each extremity and between the radius and the lower end of the humerus. At the upper radio-ulnar joint the radius is turned on its long axis, at the lower joint it is carried about the lower end of the ulna. Pronation is produced chiefly by muscles belonging to the ulno-volar group of forearm muscles (fig. 370) ; supination is produced by the biceps of the arm (fig. 364) in conjunction with some of the muscles of the radio-dorsal group of the forearm (fig. 367). At the wrist joints (radio-carpal, intercarpal), the movements are those of flexion, extension, radial abduction and ulnar abduction. Volar flexion takes place chiefly at tlie radio-carpal joint, dorsal flaxion at the intercarpal joint (Frohse). Extension is produced by those muscles of the radio-dorsal group of the forearm, which send tendons to the wrist and digits, flexion by the corresponding muscles of the ulno-volar group, radial abduction is produced by the radial carpal extensors (fig. 367), and flexor ulnar abduction by the ulnar carpal extensor and flexor (fig. 370). The varied movements of the thumb and fingers, flexion, extension, abduction, and adduction are produced partly by muscles of the two chief groups of forearm muscles, partly by the intrinsic muscles of the hand. Of chief interest here are the free movements of the metacarpal of the thumb and the hmited movements of the other metacarpals, that of the little fingers being the most movable, as seen in spreading or cupping the hand. In flexion and extension of the metacarpal of the thumb the movement is such as to bring the thumb into opposition to the fingers. In the metaoarpo-phalangeal joints those of the fingers admit of much greater freedom of movement, flexion, extension, abduction, and adduction, than that of the thumb. The interphalangeal joints are pure hinge joints and permit merely flexion and extension. Divisions. — The muscles described in this section as the muscles of the upper limb are all differentiated from the blastema of the embryonic limb bud. Most of them are differentiated in connection with the skeleton of the limb and extend between the various bones which compose it, but a few grow out from the limb bud over the trunk and become secondarily attached at one extremity to the trunk, while the other extremitj' remains attached to the skeleton of the limb. Thus the pectoral muscles (fig. 360), extend from the limb bud over the front of the thorax and the latissimus dorsi extends over the side and back of the trunk * The upper sternal part of the pectoralis major, however, acting alone elevates the scapula, and the glenoid fossa, the latissimus dorsi draws the scapula backward, tlie pectoral muscles draw it forward. 362 . THE MUSCULATURE as far as the iliac crest (fig. 355). The muscles of the limb may be divided into two great divisions, a dorsal division, innervated by nerves arising from the back of the brachial plexus (supra- and subscapular, axillary and radial nerves) and a ventral division innervated by nerves arising from the front of the plexus (sub- clavian, anterior thoracic, musculo-cutaneous, median and ulnar). The former, which correspond with the musculature on the back of the shark's fin, are in the main extensors; the latter, which correspond with the musculature on the front of the shark's fin are in the main flexors. The bellies of the muscles of each division are found in the region of the shoulder and thorax, the arm, the forearm, and the hand. The shoulder muscles belong to the dorsal division. They arise from the lateral third of the clavicle and from both surfaces of the scapula and are inserted into the upper part of the humerus. They include the deltoid (fig. 355), the chief abductor of the arm; the supraspinatus, the infraspinatus and the teres minor (fig. 363), all lateral rotators; the subscapularis (fig. 356), the chief medial rotator; and the teres major (fig. 355) , a medial rotator and adductor. With these may be classed the latissimus dorsi (a medial rotator, adductor and extensor) (fig. 355), which arises from the dorsolumbar fascia and the crest of the ilium and is inserted into the upper part of the shaft of the humerus. These muscles are sup- plied by the suprascapular, the subscapular, and the axillary nerves. The pectoral group belongs to the ventral division. It includes the pedoralis major (fig. 360) , a powerful flexor and adductor of the arm arising from the anterior chest wall and inserted into the shaft of the humerus; the pectoralis minor (fig. 388), which arises from the chest wafl and is inserted into the coracoid process of the scapula, and the subclavius (fig. 361), which extends from the first rib to the clavicle. These muscles are supplied by the subclavian and the anterior thoracic nerves. In the arm the dorsal division is represented by the triceps and anconeus, (fig. 363). The triceps arises from the scapula and the back of the humerus and is inserted into the olecranon process of the ulna. The anconeus arises from the radial epicondyle of the humerus and is inserted into the olecranon process. Both muscles extend the forearm. The triceps also adducts the arm. They are supplied by the radial nerve. The ventral division is made up of the coraco-brachialis (fig. 365) ; the biceps (fig. 364); and the brachialis (fig. 365). The coraco-brachialis (fig. 365), arises from the tip of the coracoid process of the clavicle and is inserted into the shaft of the humerus. It adducts and flexes the arm. The biceps (fig. 364), arises by a short head from the coracoid process and by a long head from the scapula above the glenoid fossa and is inserted into the radius and the fascia of the forearm. It flexes and supinates the forearm. The long head is an abductor, the short head an adductor and flexor of the arm. The brachialis (fig. 365), arises from the lower part of the shaft of the humerus and is inserted into the ulna. It is a flexor of the forearm. The two main divisions of the musculature of the forearm give rise to the prominences on each side of the elbow-joint. Their peculiar arrangement with respect to the humerus is because in man, as in most tetrapods, the normal posi- tion of the forearm is one of pronation and in this position the back of the forearm is in line with the radial epicondyle, the front with the ulnar epicondyle. The dorsal or extensor muscles, springing from the lower end of the humerus (fig. 367), get the most direct purchase when attached to the radial epicondyle, and the ventral or flexor muscles (fig. 370), the most direct purchase when attached to the ulnar epicondyle. The two divisions of the musculature may therefore here be designated the radio-dorsal and the ulno-volar or volar divisions. The main bulk of the musculature is found in the upper part of the forearm. At the wrist numerous tendons pass over to the wrist, palm and digits. This arrangement facilitates movement of the hand. The muscles of the dorsal division (figs. 367, 368, 369), are divisible into two groups, a superficial and a deep group. Those of the superficial group arise from the radial side of the lower end of the humerus and are inserted into the dorsal end of the radius (brachio-radialis) , the radial and ulnar sides of the metacarpus {extensor carpi radialis longus and b7-evis and extensor carpi ulnaris) and into the backs of the digits {extensores digitorum) . The deeper muscles arise chiefly from MUSCLES OF SHOULDER 363 the ulna and are inserted into the radius (supinator), the thumb (abductor pollicis longus, extensor pollicis loncjus and brevis) and index-finger (extensor indicis pro- prius, fig. 369) . All are supplied by the radial nerve. The chief function of the brachio-radialis is to flex the forearm. The chief functions of the other muscles are indicated by their names. The volar musculature (figs. 370, 371, 372, 375) arises from the medial side of the lower end of the humerus and from the front of the radius and ulna and is divisible into four planes. The muscles of the most superficial plane, pronator teres, flexor carpi radialis, palmaris longus, and flexor carpi ulnaris, arise from the humerus and are inserted respectively into the radius, the radial side of the meta- carpus, the palmar fascia and the ulnar side of the metacarpus. In the second layer the flexor digitorum sublimis arises from the humerus and the upper part of the radius and ulna and sends tendons to the second row of phalanges of the fin- gers. In the third layer the flexor digitorum profundus and flexor pollicis longus arise from the radius and ulna and send tendons to the terminal row of phalanges. In the fourth layer a single muscle, the pronator quadratus (fig. 377), extends in the lower part of the forearm from the radius to the ulna. These muscles are supplied mainly by branches of the median nerve but the ulnar nerve supplies the flexor carpi ulnaris and a part of the flexor profundus digitorum. The chief functions of these muscles are indicated bj^ their names. In the hand (figs. 368, 375, 376, 377, 379) there are several sets of intrinsic muscles. About the metacarpal of the thumb is grouped a set of muscles which arise from the carpus and metacarpus and are inserted into the metacarpal and first phalanx of the thumb (flexor brevis pollicis, opponens pollicis, abductor pollicis brevis, adductor pollicis) . A similar set of muscles is grouped about the metacarpal of the little finger (abductor digiti quinti, opponens digiti quinti, flexor brevis digiti quinti) . These sets of muscles give rise respectively to the thenar and hypothenar eminences. Between the metacarpals two sets of interosseous muscles arise; a volar, adductor toward the middle finger and a dorsal, abductor group. They are inserted into the sides of the bases of the first row of phalanges and into the extensor tendons. They also flex the first row of phalanges and extend the other two rows. From the tendons of the deep flexor muscle of the fingers, a series of lumbrical muscles extends to the radial sides of the extensor tendons. They flex the first row of phalanges and extend the other two. Over the thenar emi- nence there is a subcutaneous muscle, the palmaris brevis. The muscles of the hand are supplied by the ulnar nerve, with the exception of the two more radial lumbricals and the abductor, opponens, and flexor brevis of the thumb, which are supplied by the median nerve. Fasciae. — The muscle fascise of the upper extremities are well developed. The deltoid and latissimus dorsi are contained in a fascial sheet which extends between them. The deeper muscles which arise from the scapula are covered by strong fascia. Of the pectoral muscles the pectorahs major is covered by a delicate fascia, while the subclavius and pectoralis minor are contained within the dense cosio-coracoid membrane (fig. 358) which extends into the fascia covering the axillary fossa. The latter (fig. 359), is thin and is intimately fused to the tela subcutanea. The muscles of the arm are enveloped in a cylindrical sheath which in the lower half of the arm is united to the humerus by intermuscular septa. In the forearm near the wrist and on the back of the hand the tela subcutanea contains little fat. The antibrachial fascia forms a cylindrical enclosure for the muscles of the forearm. Near the wrist it becomes strengthened dorsally to form the dorsal ligament of the carpus (posterior annular ligament). This ligament converts the grooves on the back of the radius into canals for the tendons of the extensors of the wrist and fingers. On the back of the hand and fingers the fascia is intimately connected with these tendons. On the volar side near the wrist the fascia is strengthened to form the volar hgament of the carpus. Beneath the ligament hes the transverse hgament of the carpus which extends from the pisiform and hamate bones to the tuberosities of the navicular and greater multangular bones. It completes an osteo-fibrous canal for the tendons of the long flexors of the fingers. On the palm of the hand the fascia is firmly bound to the bones by intermuscular septa, which separate the thenar and hypothenar regions from a central palmar region. On the volar sides of the fingers the fascia forms the vaginal ligaments of the flexor tendons. A. MUSCULATURE OF THE SHOULDER (Figs. 355, 356, 357, 363, 388) The muscles belonging to this group are the deltoid, the teres minor, the infra- and supraspinatus, the latissimus dorsi, the teres major, and the subscapularis. 364 THE MUSCULATURE The deltoid (fig. 355) is a large, shield-shaped muscle which covers the shoulder. It arises from the spine of the scapula, the acromion, and lateral third of the clavicle and is inserted into the deltoid tubercle of the humerus. It abducts the arm. The teres minor, infra- and supraspinatus form a group of muscles (fig. 363) which arise from the back of the scapula, pass over the capsule of the shoulder- joint, to which their tendons are adherent, and, under cover of the deltoid, are inserted into the top and the dorsal margin of the great tubercle of the humerus. The band-like teres minor arises from the upper two-thirds of the axillary border of the scapula, and has the lowest insertion on the tubercle. The triangular infraspinatus (fig. 363) arises from the whole infraspinous fossa except the axillary border, and is inserted above the teres minor. The pyramidal supraspinatus (fig. 363) arises under cover of the trapezius from the supraspinous fossa, and has the highest insertion on the tubercle. The teres minor, supraspinatus and infraspinatus act as lateral rotators of the arm, the supraspinatus also as an abductor. The latissimus dorsi, the teres major, and the subscapularis form a group of muscles attached to the lesser tubercle of the humerus and to the crest which Fig. 356. — Front View of the Scapular Muscles. Clavicle Coracoid process Supraspinatus Deltoid Coraco bracliialis and sliort head of biceps Pectoralis major extends distally from this on the medial side of the intertubercular (bicipital) groove. The latissimus dorsi (figs. 355, 356) is a large, flat, triangular muscle, which arises from an aponeurosis covering the lumbar and the lower half of the thoracic regions of the back and from the posterior part of the iliac crest, and is inserted into the intertubercular (bicipital) groove. The teres major (figs. 355, 356) is a thick, ribbon-shaped muscle which arises from the dorsal surface of the inferior angle of the scapula and is inserted behind the latissimus dorsi into the distal two-thirds of the crest of the small tubercle of the humerus. The subscapularis (fig. 355) is a thick, triangular muscle which extends from the subscapular fossa to the small- tubercle of the humerus. These muscles adduct the arm and rotate it medialward. The latissmus dorsi is also the chief extensor of the arm. Near their humeral attachments these two groups of muscles are separated below by the long head of the triceps. The supraspinatus is separated from the subscapularis by the base of the coracoid process and by the intertubercular (bicipital) groove. The tendons of the latissimus dorsi, teres major, and sub- scapularis are crossed ventrally by the main vessels and nerves of the arm and by the short head of the biceps and the coraco-brachialis. The supra- and infraspinatus muscles are supplied by the suprascapular nerve. The deltoid and the teres minor are supplied by the axillary (circumflex). The subscapularis, the teres major, and the latissimus dorsi are supplied by subscapular nerves. That to the latissimus dorsi is called the dorsal thoracic nerve. DELTOIDS us 365 The deltoid in many of the mammals and the lower vertebrates is represented by separate scapulo-humeral and cleido-humeral portions. The cleido-mastoid in some mammals is con- tinued into the deltoid. The teres minor, which is innervated by the same nerve, may be looked upon as a derivative of the deltoid, although in man it is anatomically more intimately connected with the infraspinatus. The teres major may be looked upon as a speciahsed portion of the more primitive latissimus dorsi. The comparative anatomy of the shoulder muscles through- out the vertebrate series is a somewhat intricate subject, owing to the great variations exhibited in the form and attachment of the shoulder girdle. The muscles of this group show more or less marked resemblances to certain muscles of the lower limb. The deltoid and the teres minor probably represent the tensor fascise latEe, the glu- teal fascia, and the upper part of the gluteus maximus; the latissimus dorsi and teres major, the lower portion of the gluteus maximus; and the subscapularis, the gluteus medius and mini- mus, and the piriformis. The subscapular and axillary nerves, which supply the arm muscles mentioned, therefore represent in the main the nerves to the gluteal muscles, and the gluteal branch of the posterior cutaneous nerve of the thigh. The infraspinatus muscle probably represents the ihacus; the supraspinatus possibly the pectineus muscle of the lower limb. FASCIA (Figs. 351, 357, 359, 362) The tela subcutanea covering the regions occupied by these muscles contains considerable fat. In most regions it is not readily separable into two distinct layers. In the neighbourhood of the shoulder-joint it is adherent to the underlyingmusculatureand the axillary fasciie. Over the acromion there is a well-marked subcutaneous bursa, bursa subcutanea acromialis. Muscle fasciae. — The deltoid and latissimus dorsi muscles are throughout the greater part of their extent superficially placed. They are covered by an adherent fascial layer, which, above, is attached to the clavicle and to the spine of the scapula. VentraUy it is continued over and fuses with the fascia covering the pectoralis major, serratus anterior, and external oblique muscles. On the back it extends as a thin sheet between the dorsal margin of the deltoid and the upper margin of the latissimus dorsi, and is continued dorsaUy into the fascial investment of the rhomboid muscles. The lateral fascial extension of the trapezius becomes fused to the dorsal surface of this sheet. Toward the armpit the fascial investment of the deltoid and latiss- imus dorsi muscles is continued into the axillary fascia, and on the back of the arm it is con- tinued into the fascial investment of the triceps. The supraspinatus muscle lies beneath the trapezius. It is covered by a dense adherent fascial layer which is separated from the trapezius by loose connective tissue which usually contains a considerable amount of fat. The infraspinatus and the two teres muscles lie beneath the musculo-fascial layer composed of the deltoid, the latissimus dorsi, and the fascial sheet described above. Each of the three muscles has a special fascial investment which is bound to the scapula about the region of attach- ment of the muscle to the bone. Where two of the muscles adjoin, their fasciae gives rise to intermuscular septa. Septa of this nature are found between the infraspinatus and each of the teres muscles, and between the teres minor and the teres major. The intermuscular septum between the infraspinatus and teres minor muscles is often incomplete. The fascia covering the teres major is so delicate as hardly to deserve the name, except near the origin of the muscle. Near the spine the fascia covering the deep surface of the deltoid is often fused to that covering the infraspinatus. The subscapularis muscle is invested by a moderately dense fascia which is bound to the scapula along the periphery of the attachment of the muscle. For a short distance this fascia is fused with the fascial investment of the teres major near the origin of the latter muscle, so that an intermuscular septum is formed. From the ventro-lateral margin of the fascia covering the subscapularis muscle a sheet of fascia is continued below the axillary fascia into the fascia cover- ing the serratus anterior (magnus). MUSCLES The deltoideus (figs. 355, 356, 360). — Origin. — Fleshy from the lateral border and upper surface of the acromion and from the ventral border and upper surface of the lateral third of the clavicle, and tendinous from the spine of the scapula. Some fibre-bundles also at times arise from the deep fascia of the muscle where it overlies and is fused to the fascia of the infraspinatus muscle near the spine. Insertion. — Into the deltoid tuberosity of the humerus by a strong tendon arising from numerous tendinous bands within the muscle (fig. 364). Structure. — In structure the deltoid muscle is complex. Three portions may be recognised: — a clavicular, an acromial, and a spinous. The first and last are composed of long fibre-bundles which take a slightly converging course and are inserted by aponeurotic tendons respectively on the front and back of the V-shaped area of insertion of the muscle. The acromial portion, on the other hand, is multipenniform in composition. Four or five tendinous expansions descend into the muscle from the acromion, and three up into the muscle from the tendon of insertion. From the acromion and from the descending tendinous processes fibre-bundles run to be inserted on the sides of the ascending processes and into the tendons of insertion of the clavicular and spinous portions of the muscle. N eroe-supply . — The axillary (circumflex) nerve passes across the costal surface of the muscle near the tendon of insertion and gives off rami which enter lateral to the middle of the muscle. The nerve fibres are derived from the (foiu-th), fifth, and sixth cervical nerves. Action. — When the whole muscle contracts, the arm is abducted (raised lateralhO to a 366 THE MUSCULATURE TERES MINOR 367 horizontal position. When the clavicular and acromial parts act, the arm is raised and flexed (brought forward toward the chest). When the acromial and spinous parts act, the arm is raised and extended (carried toward the back), but in this instance the arm is not brought to a level with the shoulder-joint, but only about 45° from the hanging position. The inferior part of the serratus anterior and the trapezius act in conjunction with the deltoid in abduction. Abduction is greatest when the arm is rotated lateralward. The ventral portion rotates the arm medially, the dorsal portion laterally. When the arm is fixed, the deltoid tends to carry the inferior angle of the scapula toward the spinal column and away from the thorax. Relations. — On its ventral border the deltoid is in contact with the pectoralis major muscle. Near the clavicle the cephalic vein and a small artery pass between the two muscles. Its dorsal border is continued into a dense fascial sheet which overlies the infraspinatus muscle. Its tendon of insertion passes between the biceps and triceps muscles. The deltoid overhes the coracoid process and upper extremity of the humerus, the coraco-olavicular and coraco-acromial hgaments, and the insertions of the supraspinatus, infraspinatus, and teres minor muscles, the origins of the biceps and coraco-brachiahs, and a part of the long and lateral heads of the triceps. Beneath it run the posterior circumflex artery and axillary (circumflex) nerve. Variations. — The clavicular portion is frequently separate from the rest of the muscle. The three portions may be distinctly separate — a condition normal in some of the lower mammals. The clavicular and acromial portions have been found missing. The deep portion of the muscle may be separated as a distinct layer and inserted either into the capsule of the joint or into the humerus. Accessory fasciculi may pass into the muscle from the fascia over the infraspinatus and from the vertebral and axillary borders of the scapula. Not infrequently fasciculi are con- tinued into the muscle from the trapezius — a condition normal in animals with ill-developed clavicles. An accessory tendon of insertion may extend to the radial side of the forearm. Bundles of fibres from the axillai'y border of the scapula have been seen to cross the deep sm^face of the deltoid and be inserted into the deltoid fascia. The deltoid may be fused with neighbour- ing muscles, the pectoralis major, trapezius, infraspinatus, brachialis, brachio-radiahs. The teres minor (fig. 363). — Origin. — From the upper two-thirds of the axillary border of the infraspinous fossa, and from the septa lying between it and the infraspinatus on the one side and the teres major and subscapularis on the other. The origin is in part fleshy, in part from an aponeurotic band on its ventral surface toward the subscapularis muscle. Structure and insertion. — The fibre-bundles from this origin take a slightly converging course toward a tendon of insertion which extends for some distance on the dorsal surface of the muscle. The muscle is adherent to the capBule of the joint, and terminates on the inferior of the three facets of the great tubercle of the humerus and the postero-lateral aspect of that bone for two or three centimetres below the facet. Nerve-supply. — From a branch of the axillary (circumflex) nerve which enters the muscle on its lateral margin about midway between its extremities. A 'ganglion' is usually found upon this nerve. A branch from the nerve to the teres major has also been reported. The nerve fibres are derived from the fifth cervical nerve. Action. — It acts conjointly with the infraspinatus to rotate the arm laterally. It is a flexor when the arm is down and an extensor when it is abducted. It is also an adductor. Relations. — The muscle is in part covered by the deltoid. Ventrally it enters into relations with the long head of the triceps, the teres major, and the subscapularis. Superiorly, the cir- cumflex (dorsal) scapular vessels run between it and the axillary border of the scapula. Fig. 357. A and B. — Transverse Sections through the Left Shoulder in the Regions INDICATED IN THE DIAGRAM. In the neighbourhood of the brachial plexus in each section some of the adipose and lymphatic tissue has been removed. In section B the fascia covering the apex of the axillary fossa is thus revealed from above, a and 6 in the diagram indicate the regions through which pass sections A and B, fig. 351 (p. 352); a' and b', the regions through which pass sections A and B, fig. 362 (p. 375). 1. Aorta. 2. Arteria brachiaUs. 3. A. circumflexa scapulae (dorsahs scapulse). 4. A. carotis communis. 5. A. mammaria interna. 6. A. subclavia. 7. A. thoracahs lateralis (long thoracic). 8. Costa I. 9. Costa II. 10. Costa III. 11. Costa IV. 12. Costa V. 13. Costa VI. ' 14. Clavicle. 15. Fibrocartilago intervertebrahs (intervertebral disc). 16. Fascia axillaris. 17. Fascia cervicalis (superficial layer). 18. Middle layer. 19. F. coraco-clavicularis. 20. F. lumbo-dorsahs. 21. Fascia of posterior serrati. 22. Humerus. 23. Medulla spinalis (spinal cord). 24. Musculus biceps — a, long head; 6, short head; c, tendon of short head. 25. M. coraco-brachialis. 26. M. deltoideus. 27. M. infraspin- atus. 28. M.iho-costahsdor^i (accessorius). 29.M.intercostalesexterni. 30. M.intercostales interni. 31. M. latissimus dorsi, tendon. 32. M. levator costs. 33. M. longissimus dorsi. 34. M. longus oolU. 35. M. pectorahs major. 36. M. pectorahs minor. 37. M. platysma. 38. M. rhomboideus major. 39. M. scalenus anterior. 40a. M. serratus anterior. 406, M. serratus posterior superior. 41. M. sterno-mastoideus. 42. M. cleido-mastoideus. insertion. 43. M. sterno-hyoideus. 44. M. sterno-thyreoideus. 45. M. subclavius. 46. M. subscapularis. 47. M. teres major. 48. M. teres minor. 49. M. trapezius. 50. M. transverso-spinales. 51. M. triceps — a, long head; 6, lateral head. 52. Nervus axillaris 53. N. cutaneus antebrachii medialis (internal cutaneous). 54. a-e, Nn. intercostales I-V. 55. N. medianus. 56. N. phrenicus. 57. N. musculocutaneus. 58. N. radiaUs (musoulo-spiral). 59. N. recurrens. 60. N. subscapularis. 61. Sj'mpathetic trunk. 62. N. thoracalis anterior. 63. N. thoracalis longus. 64. N. thoracodorsaUs (long subscapular). 65. N. ulnaris. 66. N. vagus. 67. CEsophagus. 68. Plexus brachialis — a, lateral fasciculus; 6, medial; c, posterior. 69. Scapula. 70. Sternum. 71. Trachea. 72. Venae brachiales. 73. V. cephaUca. 74. V. jugularis anterior. 75. V. jugularis inferior. 76. V. subclavia. 77. Vertebra I. 78. Vertebra II. 79. Vertebra III. 80. Vertebra IV. 81. Vertebra V. 82. Vertebra VI. 368 THE MUSCULATURE Variations. — Aside from its frequent fusion with the infraspinatus, there has also been reported an isolation of a special fasciculus to the subtubercular attachment. The infraspinatus (fig. 363). — Origin. — From the vertebral three-fourths of the infra- spinous fossa, from the under surface of the spine, from the enveloping fascia and from inter- muscular septa between it and the two teres muscles. Structure and insertion. — The fibre-bundles converge toward the lateral angle of the scapula to be attached to a deep-seated tendon which is adherent to the capsule of the joint and is attached to the middle facet of the great tubercle. The fibre-bundles arising from the inferior surface of the spine and the fascia near this form a distinct fasciculus which descends on and covers the tendon of insertion. Nerve-supply. — From the suprascapular nerve, which passes beneath the supraspinatus muscle and enters the deep surface of the infraspinatus in the lateral part of the midde third of its upper margin. From here rami spread out toward the vertebral border of the muscle and toward the humeral insertion. The nerve fibres are derived from the fifth and sixth cervical nerves. Action. — This muscle is the chief lateral rotator of the arm, a movement that can be carried through 90°. The upper part of the muscle is an abductor, the lower part an adductor of the arm. The muscle is also a flexor. Relations. — The deltoid and trapezius, and sometimes the latissimus dorsi muscles, cover a portion of the dorsal surface. Over most of it extends the complex fascia described above. Laterally it adjoins the teres minor and major muscles. Under the muscle he the transverse (suprascapular) and circumflex (dorsal) scapular vessels. Variations. — These are rare, aside from a greater or less independence of the bundles arising from the spine and a greater or less complete fusion with the teres minor. A fasciculus has been seen extending to the muscle from the deltoid. The supraspinatus (fig. 363). — Origin. — Fleshy from the medial two-thirds of the supra- spinous fossa and from the deep surface of the enveloping fascia near the vertebral end. Structure and insertion. — The fibre-bundles converge upon a deep-seated tendon nearly to its attachment into the highest of the three facets on the great tubercle of the humerus. Nerve-supply. — Two branches from the suprascapular nerve enter the middle third of the deep surface of the muscle. The nerve fibres are derived from the fifth cervical nerve. Action. — It aids the deltoid in abducting the arm. It is also a weak lateral rotator and flexor. It keeps the head of the humerus in place during abduction of the arm. Relations. — The muscle is covered by the trapezius, the acromion, and the coraco-acromial hgament. Beyond the base of the spine of the scapula it comes into contact with the infra- spinatus muscle. Beneath the muscle pass the suprascapular nerve and transverse scapular (suprascapular) vessels. Variations. — The muscle shows slight variations. Its tendon may be fused with that of the infraspinatus. Its belly may be reinforced by fibre-bundles from the coraco-acromial ligament. The latissimus dorsi (figs. 355, 356, 387, 388). — Origin. — (1) From an aponeurosis at- tached to the spines and interspinous ligaments of the five or six last thoracic and the upper lumbar vertebra, to the lumbo-dorsal fascia, and to the posterior third of the external lip of the crest of the ilium; (2) from the external surface and upper margin of the last three or four ribs by muscular slips which interdigitate with those of the external oblique. In the lumbar region the aponeuroses of the right and left muscles are connected by fibrous fascicuh which cross the mid-dorsal line above the supraspinous ligament. Structure and insertion. — From this extensive area of the origin fibre-bundles converge toward the tendon of insertion. In the region of the dorsal wall of the axillary fossa the muscle is concentrated into a thick, ribbon-like band which winds about the teres major and passes to the ventral surface of that muscle. As this takes place the fibre-bundles become apphed to each surface of a flat tendon, which, after emerging from the muscle, is six to eight cm. long and three to five cm. broad, and is inserted into the ventral side of the crest of the lesser tubercle of the humerus and into the depth of the intertubercular (bicipital) groove immediately ventral to the tendon of the teres major. With this it is more or less closely bound, although between the tendons there lies a serous bursa. Some of the fasciculi of the tendon extend to the crest of the greater tubercle. Frequently a tendon slip passes from the inferior margin of the ten- don to the tendon on the posterior surface of the long head of the triceps or into the brachial fascia (see lalissirno-condyloideus, p. 379). Like the teres major, with which it is closely associated, the latissimus dorsi muscle under- goes a torsion between its origin and its insertion, so that the dorsal surface of the muscle is continued into the ventral surface of the tendon and the most cranially situated of the fibre- bundles are most distally attached to the humerus, and vice versa. The muscle either directly or through its fascial extension is often adherent to the inferior angle of the scapula. Nerve-supply. — From the dorsal thoracic (long subscapular) nerve (from the sixth, seventh and eighth cervical nerves) . This nerve, which may arise in conjunction with the axillai'y nerve, passes to the deep surface of the muscle in the lower part of the axilla, and here gives rise to rami which diverge as the muscle expands toward its tendons of origin. Though soon embedded in the muscle substance, two main branches may be followed for a considerable distance near the deep surface of the muscle. One usually extends near the lateral, the other near the supe- rior, border of the muscle, and from these large rami pass into the intervening region. Branches of the dorsal thoracic artery and vein accompany the nerve. Action. — With the trunk fixed, the latissimus dorsi draws the raised arm down and back- ward and rotates it medialward (swimming movement). When the arm is hanging by the side, the action of the muscle is on the scapula. The upper third of the muscle draws the scapula toward the spine, the inferior two-thirds depress the shoulder. When the humerus is fi^ed, the latissimus serves to lift the trunk and pelvis forward, as in climbing. It also aids in forced inspiration through its costal attachments. BURSJE 369 ^Relations. — The trapezius covers a small portion of the muscle in the mid-thoracic region of the back. Over a large area it is subcutaneous, and its fascial investment is adherent to the skin. As it winds about the teres major its tendon comes to lie behind the coraco-brachialis muscle. The main nerves and vessels of the arm here pass across its ventral surface. The muscle covers in part the rhomboideus major, the infraspinatus, teres major, serratus posterior inferior, the lower ribs, the external intercostal muscles, the dorsal border of the external and internal oblique muscles, and the lower dorsal part of the serratus anterior (magnus). Variations. — It may show considerable variation in the extent of its fleshy portion and in the attachment of its aponeurosis to the vertebral column, crest of the ilium, the ribs, and the scapula. Its origin may be merely from the ribs. It maj' be divided into separate fasciculi. Frequently a fasciculus arises from the inferior angle of the scapula. The muscle is often inti- mately united to the teres major. For an account of the muscular slip which extends from the latissimus dorsi across the axillary fossa to the tendon of the pectoralis major near the inter- tubercular (bicipital) groove see the latter muscle (p. .374); and for the slip continued from the tendon of the latissimus dorsi to the olecranon see the Triceps Muscle (p. .379). The teres major (figs. 356, 388). — Origin. — Directly from the dorsal surface of the inferior angle of the scapula and from the septa which lie between this muscle and the subscapularis, teres minor, and infraspinatus muscles. Insertion. — For about five or six cm. from the lower border of the small tubercle of the humerus, along the medial lip of the intertubercular (bicipital) groove. ProximaUy the fibre- bundles are attached directly to the tubercle; more distally the attachment is by means of a flat tendon which extends for some distance on the dorsal surface of the muscle. Structure. — The nearly paraOel fibre-bundles pass upward in a spiral direction so that the muscle undergoes a torsion on its axis. The fibre-bundles which have the highest attachment to the scapula have the lowest humeral attachment, and vice versa. Nerue-supply. — By a branch of the lower subscapular nerve which enters the muscle near the middle of its scapular border. The nerve fibres are derived from the fifth, sixth (and seventh) cervical nerves. Action. — It aids the latissimus dorsi in adducting the arm, and in some positions of the arm acts as a medial rotator and as an extensor. Relations. — Dorsally the muscle is covered by the latissimus dorsi and by the fascia which extends from this muscle to the deltoid and rhomboid muscles. It is also crossed by the long head of the triceps. Its lower border and ventral surface are largely covered by the latissimus dorsi and its tendon. Its upper border helps to bound a triangular space the other sides of which are the borders of the scapula and the humerus. In front lies the subscapularis, and behind, the teres minor. Across this space passes the long head of the triceps. Lateral to this head lie the humeral circumflex vessels and axillary (circumflex) nerve; and medial, the circum- flex (dorsal) scapular artery. Variations. — The teres major may be connected with the latissimus dorsi by a fasciculus, or it may be fused with that muscle or its tendon. Slips have also been seen extending to the triceps and into the fascia of the arm. The muscle is rarely absent. The subscapularis (figs. 356, 388). — Origin. — The fibre-bundles spring — (1) directly and by means of tendinous bands from the costal surface of the scapula, except near the neck and at the upper and lower angles; and (2) from intermuscular septa between it and the teres major and teres minor muscles. Insertion. — The tendon of insertion as it passes over the capsule of the joint is intimately bound to this. It is inserted into the lesser tubercle of the humerus and into the shaft im- mediately below this. Structure. — The fibre-bundles arising from the tendinous bands attached to the bone con- verge upon several tendinous laminee which extend into the muscle from the tendon of insertion, thus forming small pennif orm fasciculi. The fibre-bundles arising directly from the bone con- verge toward the extremities of the tendinous lamina;, thus forming triangular bundles inter- digitating with the penniform fasciculi. The fasciculus which arises highest on the axillary border goes directly to the humerus. Nerve-supTply. — By two or three subscapular branches from the back of the brachial plexus. One or more of these may arise in association with the axillary (circumflex) nerve. From the main nerves rami spread out to enter the ventral surface of the muscle near the junction of the lateral and middle thirds. The nerve fibres come from the fifth and sixth cervical nerves. Action. — It is the chief medial rotator of the arm. It strengthens the shoulder-joint by drawing the humerus against the glenoid cavity. It is an extensor when the arm is at the side, a flexor when the arm is abducted. The upper portion of the muscle, however, acts as a flexor in both positions. The upper part acts as an abductor but when the arm is abducted the muscle is an adductor. Relations. — Ventrally it forms the greater part of the posterior wall of the axillary fossa, and enters into relation with the serratus anterior (magnus) and the combined tendon of the coraco-brachiaUs and biceps. On it lie the axillary vessels, the brachial plexus, and numerous lymph-vessels and glands. At its lateral border lie the teres major, the humeral cu-cumflex vessels, axillary (circumflex) nerve, and circumflex (dorsal) scapular vessels. Behind it he the long head of the triceps and the teres minor muscle. Variations. — It may be divided into several distinct segments. A fasciculus may be sent to the tendon of the latissimus dorsi and another to the brachial fascia. The subscapularis minor arises from the axillary border of the scapula and is inserted into the articular capsule (capsular hgament) of the shoulder-joint or into the crest of the lesser tubercle of the humerus. BURS^ B. subacromialis. — A large bursa, nearly constantly found, between the acromion and coraco-acromial ligament and the insertion of the supraspinatus muscle and capsule of the joint. 370 THE MUSCULATURE Processes extend over the greater and lesser tubercles. B. supracoracoidea. — A bursa sometimes found between the coracoid process and the clavicle and the deltoid muscle. B. m. subscapularis. — Between the glenoid border of the scapula and the subscapularis muscle. Communicates with the joint cavity. A small portion of this bursa may be isolated adjacent to the base of the coracoid process (6. subcoracoidea) . B. m. infraspinati. — Between the tendon of the infraspinatus and the capsule of the joint or the great tubercle. B. m. latissimi dorsi. — Constant between the tendons of the latissimus dorsi and the teres major. B. m. teretis majoris. — Under the insertion of the tendon of the teres major muscle. B. PECTORAL MUSCLES AND AXILLARY FASCIA (Pigs. 357, 358, 360, 361, 388) The muscles belonging to this group are the pectoralis major, pectoralis minor, and the subclavius. Of these, the largest and most superficial is the Fig. 358. — Deep Fascia of the Breast. (After Eisler). The Pectoralis Major Has Been in Large Part Removed. 1, Deltoid; .2, Pectoralis Major, Abdominal Past; 3, Pectoralis. Minor; 4, Coraco-Brachialis. triangular pectoralis'major (fig. 360), which arises from the second to the sixth ribs, the sternum, and the medial half of the clavicle and is inserted into the crest of the greater tubercle of the humerus (pectoral ridge). Its lateral margin adjoins the ventral margin of the deltoid. Beneath this muscle the much smaller triangu- lar pectoralis minor (fig. 388) extends from near the ends of the second, third, fourth, and fifth ribs to the tip of the coracoid process, while the small subclavius (fig. 361) extends from the first rib upward and lateralward to the clavicle. The pectoral muscles and the subclavius play a part in forced inspiration. The pectoralis major also serves to adduct and flex the arm- and rotate it medialward. Of the muscles included in this group, the two pectoral muscles are morphologically the most closely related. They receive a nerve-supply from the same set of nerves, the anterior thoracic With them the subclavius, which has a separate nerve of its own, is closely associated. Cor- F ASCIIS 371 responding musculatui-e, although variously modified in different forms, is found tlii'oughout the vertebrate series. In the lower forms it se"ems to be differentiated directly from the segmental trunk musculature and secondarily attached to the shoulder girdle, like the superficial and deep musculature of the shoulder girdle previously described. In man, however, the muscle mass from which these muscles arise is at all times in intimate union with the skeleton of the upper limb, and the nerves which supply it are in much more intimate union with the brachial plexus than are those of the shoulder-girdle muscles. For these reasons the three muscles are classed with the intrinsic muscles of the arm. They have no certain representatives in the lower hmb, although the clavicular portion of the pectoralis major is considered by some to represent certain adductor muscles of the thigh. Possibly they correspond in their embryonic origin with the obturator internus group of the lower hmb. In many of the mammals a subcutaneous muscle arises from the pectoral muscle mass and extends over the axUla and the trunk. In man this musculature is frequently represented by abnormal shps of muscles, of which the 'axillary arch' and possibly the 'sternalis' are representa- tives. A list of some of the abnormal muscles which are innervated from the anterior thoracic nerves and are evidently derivatives of the pectoral muscle mass is given at the end of this section Fig. 359. — (After Eisler). Fascia of the Axillary Fossa. FASCIiE In the tela subcutanea of the pectoral region the mammary gland is embedded between two layers which ensheath the gland and are connected by dense fibre-bands. To a greater or less extent the platysma extends into the tela of this region from above the clavicle. Muscle fasciae. — The pectorahs major is invested with a thin, adherent membrane, fascia pectoralis, attached to the clavicle and the sternum and continued into the fascial invest- ment of the external obUque, the serratus anterior (magnus), and the deltoid muscles, and in to the axillary fascia. More important is the coraco-clavicular (costo-coracoid) fascia fig. 358. This arises from two fascial sheets which invest the subclavius muscle and are at- tached to the clavicle. From the inferior margin of this muscle the membrane is continued to the superior margin of the pectoralis minor. Between the coracoid process and the first costal cartilage it is strengthened to form the costo-coracoid ligament. Between this and the pectorahs minor it is thin. At the superior margin of this muscle it again divides to form two adherent fascial sheets, which, at the axillary margin of the muscle, once more unite to form a fii'm membrane continued into the fascial investment of the coraco-brachiahs and short head of the biceps and into the axiUai'y fascia. Above, dorsally, the membrane is adherent to the sheath of the axillary vessels and nerves. Axillary fascia (fig. 359). — The arm-pit, or axillary fossa, is a pyramidal space bounded by the pectoralis major and minor and coraco-brachialis muscles in front; by the latissimus 372 THE MUSCULATURE dorsi, teres major, and subsoapularis muscles behind; by the subscapularis muscle toward the joint; and by the serratus anterior (magnus) toward the thoracic wall. In the groove between the coraco-brachiaUs and the subscapularis and tendons of the latissimus dorsi and teres major muscles run the main nerves and vessels of the arm. These are surrounded by a considerable amount of connective tissue in which numerous blood- and lymph-vessels, lymph-nodes, nerves, and masses of fat are embedded. Fig. 360. — The Pectoralis Major and Deltoid. Sterno-cleido- mastoid ■Aponeurosis of external oblique External intercostal Over this connective tissue the fascia covering the musculature of the neighbouring portion of the shoulder and thorax is continued into the fascia covering the musculature of the medial side of the arm. Thus the fascia covering the pectoralis minor, the coraco-clavicular fascia, strengthened by a reflection of the fascial investment of the pectorahs major and deltoid muscles- is continued across the ventral margin of the arm-pit into the fascia which covers the coraco- brachialis and biceps muscles in the arm. Similarly, dorsally, the fascia Covering the latissimus dorsi and teres major is continued over the arm-pit into that covering the long head of the triceps in the arm. The ventral is connected with the dorsal fascia by a thin membrane which is adherent to the connective tissue filling the axillary space and to the subcutaneous tissue. On the trunk this membrane, the fascia axillaris, becomes fused below the axillary fossa with the fascia of the serratus anterior (magnus). In the arm it becomes fused with the fascia over the biceps muscle. Owing to its adherence to the skin and the connective tissue of the axillary fossa, investigators have dissected out and figured the axillary fascia in different ways. MUSCLES The pectoralis major (fig. 360). — Origin. — (1) From the medial half of the clavicle; (2) from the side and front of the sternum as far as the sixth costal cartilage; (3) from the front of the cartilages of the second to the sixth ribs; and (4) from the upper part of the aponeurosis of the external oblique where this extends over the rectus abdominis muscle. The costal origin may in part take place from the osseous extremities of the sixth and seventh ribs. Insertion. — Crest of the greater tubercle (outer lip of the bicipital groove) of the humerus from the tubercle to the insertion of the deltoid (fig. 174). Some of the tendon fibres are also continued into the tendon of the deltoid and adjacent fibrous septa and into the fibrous lining of the intertubercular sulcus. Structure. — The muscle is divisible into a series of overlapping layers spread out hke a fan. Of these, the clavicular portion forms the most cranial and superficial layer, and the portion of the muscle springing from the aponeurosis of the external oblique, the most caudal and deepest layer. This last layer has a special tendon, while the other layers are inserted into a combined SUBCLAVIUS 373 tendon lying ventral to this. The two tendons are continuous at their distal margins. (W. H. Lewis.) Neroe-supply. — From the external and internal anterior thoracic nerves, branches of which enter the sterno-costal portion of the muscle about midway between the tendons of origin and insertion, and the clavicular portion in the proximal third. The nerve fibres are derived from the (fifth), si.xth, seventh and eighth cervical and first thoracic nerves. Action. — With the thorax fixed, the muscle adducts and flexes the arm and rotates it medial- ward. The clavicular portion draws the arm forward, upward, and medialward; the sterno- costal portion draws the arm downward, medialward, and forward. When the arm is pendent, the upper portion elevates, the lower depresses, the shoulder. With the arm fixed, the muscle draws the chest upward toward it. It is of value in forced inspii'ation. Relations. — It lies over the coracoid process, the subclavius, pectoralis minor, intercostal, and serratus anterior (magnus) muscles, the coraco-clavicular (costo-coracoid) fascia, and the thoraco-aoromial vessels. It forms the main part of the ventral wall of the axillary fossa, and laterally it enters into relation with the deltoid, biceps, and coraco-brachialis muscles. Variations. — In considering variations the muscle may be looked upon as composed of four portions — a clavicular, a sternal, a costal, and an abdominal, the last being that portion which arises from the aponeurosis of the external obhque. These portions vary in the extent of their attachments and in the degree of separation which they present. The abdominal por- tion may extend to the umbilicus. Huntington considers this portion a derivative of the pan- nicular muscle of the lower mammals. On the sternum the muscles of the two sides may de- cussate across the middle line. The sterno-costa! portions of the muscle are more frequently deficient or missing than the clavicular, but in rare cases the entire muscle is absent. The clavicular portion of the muscle may be fused with the deltoid. The sterno-costal may extend laterally to the latissimus dorsi. There may be an intimate fusion of the abdominal portion with the rectus abdominis or the external oblique. Sometimes a slip may run from the pec- toralis major to the biceps, the pectoralis minor, coracoid process, capsule of the joint, or brachial fascia. The pectoralis minor (fig. 388). — Origin. — By aponeurotic slips from the second, third, fourth, and fifth ribs near the costal cartilages. Fig. 361. — The Subclavius and the Upper Portion op the Serratus Anterior. Serratus anterior Structure and insertion. — The fibre-bundles converge upward and outward to a flattened tendon which is attached to the medial border and upper surface of the coracoid process of the scapula. Nerve-supply. — From the internal anterior thoracic nerve which enters the upper part of the middle third of the deep surface by several branches. Some of the branches extend through to the pectoralis major. The nerve fibres arise from the seventh and eighth cervical nerves. Action. — When the thorax is fixed, the pectoraUs minor pulls the scapula forward, the lateral angle of the bone downward, and the inferior angle dorsalward and upward. When the scapula is fixed, the muscle aids in forced inspiration. Relations. — It is covered by the pectorahs major. Near its insertion the fibrous investment of the chief nerves and vessels of the arm is adherent to its enveloping fascia. Variations. — The origin may extend to the sixth rib or may be reduced to one or two ribs. In the primates below man the insertion of the muscle takes place normally into the humerus. In man its insertion may be continued (in more than 15 per cent, of bodies — Wood) over the coracoid process to the coraco-acromial or coraco-humeral ligaments, to the tendon of the sub- scapularis muscle, or to the great tubercle of the humerus. It may be divided into two super- imposed fasciculi. Fasciculi may extend from the muscle to the subclavius or the pectoralis major. The subclavius (fig. 361). — Origin. — From a flat tendon attached to the fii-st rib and its cartilage near their junction. Structure and insertion. — The fibre-bundles arise in a penniform manner from the tendon of origin which extends for some distance along the lower border of the muscle. They are inserted in a groove which lies on the lower sm'face of the clavicle between the costal tuberosity and the coracoid tuberosity. The medial fibre-bundles are inserted directly, the lateral by a strong tendon. Nerve-supply. — By a branch which arises usually from the fifth or fifth and sixth cervical nerves and enters the middle of the back part of the muscle. Action. — When the first rib is fixed, the subclavius depresses the clavicle and the point of 374 THE MUSCULATURE the shoulder. When the clavicle is fixed, the muscle aids in forced inspiration. It also serves to keep the clavicle against the sternum. Relations. — It is concealed by the clavicle and peotorahs major muscle. Behind it lie the subclavian vessels and the brachial plexus. Variations. — It may be replaced by a ligament or by a peotoralis minimus muscle (see below). It may be doubled or may be inserted into the coracoid process, ooraco-aoromial hgament, the acromion, or the humerus. The subclavius posticus arises near the subolavius, passes backward over the subclavian vessels and brachial plexus and is inserted into the cranial margin of the scapula near the base of the coracoid process. Abnormal Muscles of the Pectoral Group The following muscles are usually innervated by the anterior thoracic nerves and are probably generally abnormal derivatives of the pectoral mass. Frequently they represent muscles normally found in lower mammals. The sternalis. — A flat muscle somewhat frequently seen on the surface of the pectoralis major, usually nearly parallel to the sternum. It arises from the sheath of the rectus and from some of the costal cartilages (third to seventh) and terminates on the sterno-oleido-mastoid, on the sternum, or on the fascia covering the pectoraUs major. When present on both sides, the two muscles may be fused across the sternum. This muscle is found in 4 per cent, of normal individuals and 48 per cent, of anencephalic monsters. (Eisler.) Rarely, corresponding muscle slips have been found innervated by the intercostal nerves. These probably represent remains of a thoracic 'rectus' muscle. The pectoro-dorsalis (axillary arch). — This muscle in its most complete form extends from the tendon of the pectoralis major over the axillary fossa to the tendon of the latissimus dorsi, to the fascia covering the latissimus dorsi, to the teres major or even more distaUy. It may, however, be more or less fused with either of the last two muscles mentioned, and it presents a great variety of forms. It may extend from the latissimus dorsi to the brachial fascia over the coraco-brachialis or biceps, to the long tendon of the biceps, to the axillary fascia, to the axillary margin of the pectoralis minor, or to the coracoid process, etc. It is found in about 7 per cent, of bodies. (Le Double.) When supplied from the anterior thoracic nerves, it probably rep- resents a portion of the thoraco-humeral subcutaneous (pannicular) muscle of the lower primates. It is also sometimes supplied by the medial brachial cutaneous or the intercosto- brachial (humeral) nerve and frequently is partly or wholly supplied by the dorsal thoracic (long subscapular) nerve. The part of the muscle supphed by the dorsal thoracic nerve is probably derived from the latissimus dorsi musculature. The costo-coracoideus. — A muscular slip which arises from one or more ribs or from the aponeurosis of the external oblique between the pectoralis major and latissimus dorsi muscles, and is inserted in the coracoid process. The chondro-humeralis (epitrochlearis). — This is a slip which springs from one or two rib cartilages or from the thoraco-abdominal fascia beneath the pectoralis major, or from its lower border or tendon, and extends on the medial side of the arm to the intertubercular (bicipital) groove, the brachial fascia, the intermuscular septum, or the medial epicondyle. It is found in 12 to 20 per cent, of bodies (Le Double), and occurs normally in many of the lower mammals. The pectoralis minimus (sterno-chondro-scapularis). — From the cartilage of the first rib and sternum to the coracoid process. The sterno-clavicularis. — From the manubrium of the sternum to the clavicle between the pectoralis major and the coraco-clavicular (costo-coracoid) fascia. In 2 per cent, to 3 per cent of bodies. (Gruber.) The scapulo-clavicularis. — From the coracoid process of the scapula to the outer third of the clavicle. The infra-clavicularis. — From above the clavicular part of the pectoralis major to the fascia over the deltoid. BURSiE B. m. pectoralis majoris. — Between the tendon of insertion of the pectoralis major and the long head of the biceps. Frequent. C. MUSCULATURE OF THE ARM (Figs. 355, 356, 362, 363, 364, 365, 367, 370, 372) The muscles included in this section are the triceps and anconeus, coraco- brachialis, biceps, and brachialis. The triceps and anconeus (fig. 363) constitute a mass of musculature extending along the back of tlie arm from the scapula and humerus to the olecranon of the ulna. The coraco-brachialis, biceps, and brachialis (figs. 364, 365) constitute a similar mass of musculature extending along the front of the arm from the scapula and the humerus to the humerus, and to the radius and ulna near the elbow. In the upper half of the arm the two groups are separated on the lateral side of the arm by the deltoid, pectoralis major, teres minor, supra- and infraspinatus muscles, and by the greater tubercle of the humerus. On the medial side they are separated the by chief nerves and blood- MUSCLES OF THE ARM 375 Fig. 362, A-D. — Transverse Sections through the Left Arm in the Regions shown in THE Diagram. o and 6 in the diagram indicate the regions through which pass sections A and B, fig. 351 (p. 352); a' and b', the regions through which pass sections A and B, fig. 367 (p. 366); and a" the region thi-ough which passes section A, fig. 366 (p. 385). 1. Arteria brachialis. 2. Bursa subcutanea olecrani. 3. Fascia brachiahs. 4. Humerus. 5. Musculus anconeus. 6. M. biceps — a, long head; b, short head; c, tendon of insertion. 7. M. brachiahs. 8. M. brachio-radialis. 9. M. coraco-brachialis. 10. M. deltoideus. 11. M. e.xtensor carpi radiahs brevis. 12. M. extensor carpi radialis longus. 13 M. extensor digitorum communis. 14. M. flexor carpi radialis. 15. M. flexor carpi ulnaris.. 16. M. flexor digitorum subhmis. 17. M. flexor digitorum profundus. 18. M. palmaris longus. 19. M. pronator teres. 20. M. triceps — a, lateral head; b, long head; c, medial head. 21a. N. cutaneus antibrachii medialis (internal cutaneous). 216. N. cutaneus antibrachii dorsalis. 22. N. musculo-cutaneus. 23. N. medianus. 24. N. radialis^a, muscular branch. 25. N. ulnaris. 26. Lymphatic gland. 27. Olecranon. 28. Septum intermusculare laterale. 29. Septum intermusculare^mediale. 30. Vena cephalica. 31. V. basilica. 32. Vv. brachiales. 9 2,1'' 23 32.2,5 24°- 376 THE MUSCULATURE MUSCLES OF THE ARM 377 vessels of the arm and by the tendons of the latissimus dorsi, teres major, and subscapularis muscles. In the distal half of the arm they are separated medially by the medial intermuscular septum (described below) and by the medial epicon- dyle and the ulno-volar group of muscles of the forearm. On the lateral side of the arm they are separated by the lateral intermuscular septum, by the lateral epicondyle, and by the brachio-radialis and the extensor muscles of the forearm which take origin from the lateral epicondyle. FASCIA The fasciae and the general relations of the muscles of the arm are shown in the cross- sections in fig. 362. The tela subcutanea of the arm is fairly well developed and contains a considerable amount of fat, especially near the shoulder. It is but loosely bound to the muscle fascia, except near the insertion of the deltoid, where the union may be more intimate. Bursse. — B. subcutanea epicondyli lateralis. — Between the lateral epicondyle and the skin. Rare. B. subcutanea epicondyli medialis. — Between the medial epicondyle and the skin. Inconstant. B. subcutanea olecrani. — Between the olecranon process of the ulna and the skin. Nearly constant. The brachial fascia forms a cylindrical sheath about the muscles of the arm. It contains circular and longitudinal fibres, the former being the better developed. The fascia is strong over the dorsal muscles, especially near the two epicondyles of the humerus. Proximally the fascia of the arm is continued into the axillary fascia and into the fascial investment of the pec- toralis major, deltoid, and latissimus dorsi muscles; distally it is continued into the fascial investment of the forearm. It is intimately bound to the epicondyles and to the dorsal surface of the olecranon. It is separated by loose areolar tissue from the beUies of the muscles which it covers. From the tendons of the deltoid, pectoralis major, teres major, and latissimus dorsi muscles, however, fibrous bundles are continued into the brachial fascia. There are a number of orifices in the fascia for the passage of nerves and blood-vessels. Of these, the largest is that for the basilic vein and two or three large branches of the medial antibrachial (internal) cutaneous nerve. This lies on the ulnar margin of the arm in the lower third. On the radial margin lie the cephalic vein in a double fold of the fascia, orifices for branches of the musculo- cutaneous nerve, and more dorsally orifices for branches of the radial. From the fascia septa descend between the muscles which it invests. Of these septa, the most important are the medial and lateral intermuscular septa, which separate the dorsal group of muscles from the ventral in the distal half of the arm. The medial intermuscular septum is the stronger. It is attached to the medial epicondyle and to the medial margin of the humerus proximal to this, It is continued proximally into the tendon of insertion of the coraco-brachialis and the investing fascia of this muscle. Into it longitudinal bundles of fibres descend from the tendon. It separates the brachiaUs and pronator teres muscles from the medial head of the triceps. The lateral intermuscular septum is attached to the lateral epicondyle and to the lateral margin of the humerus. It is continued proximally into the dorsal surface of the tendon of insertion of the deltoid muscle, and into the septa between the deltoid and the triceps. It separates the triceps from the brachialis in the third quarter of the arm and from the brachio-radi- alis and extensor carpi radialis longus in the distal quarter. The median nerve and brachial vessels lie in front of the medial septum. The ulnar nerve and the superior ulnar collateral (inferior profunda) artery are bound to its dorsal surface. MUSCLES 1. Dorsal or Extensor Group Two muscles are included in this group, the triceps brachii and the anconeus. The triceps is a complex muscle in which proximally three heads, a long or scapu- lar, a lateral humeral, and a medial humeral, may be distinguished. The long head arises from the infraglenoid tuberosity of the scapula, the lateral head from the humerus above and laterally to the groove for the radial nerve fmusculo- spiral groove), the medial head from the lower half and medial margin of the posterior surface of the humerus. Distally these heads fuse and are inserted by a common tendon into the olecranon of the ulna. The anconeus lies chiefly in the forearm, but physiologically and morphologically it belongs with the triceps, and hence is described in connection with the muscles of the arm. It is a tri- angular muscle, which arises from the lateral epicondyle and is inserted into the olecranon and adjacent part of the shaft of the ulna. Both muscles are supplied 378 THE MUSCULATURE by branches of the radial (musculo-spiral) nerve. They extend the forearm. The long head is also an adductor of the arm. The triceps, variously modified, is found in the amphibia and all higher vertebrates. The anconeus is found in the prosimians and all higher forms. The triceps muscle is homologous with the quadriceps of the thigh. The long head is equivalent to the rectus femoris. The anconeus is not represented in the lower limb. The triceps brachii (figs. 355, 356, 363). — The long head arises from the infraglenoid tuber- osity of the scapula by a strong, broad tendon, some of the fibres of which are connected with the inferior portion of the capsule of the shoulder-joint. The tendon soon divides into two lamellse, which extend distally, one a short distance on the deep surface, the other much farther Fig. 363. — Dorsal View op the Scapular Muscles and Triceps. Supraspinatus Infraspinatus Teres minor Long bead of triceps Lateral head of triceps Medial head of triceps on the superficial surface of this head. The parallel fibre-bundles which arise from these lamellae form a thick muscle-baud which twists upon itself so that the ventral surface at the origin becomes dorso-medial at the insertion. At the insertion the long head becomes ap- plied to an aponeurosis which extends upward from the main tendon of insertion of the triceps. The fibre-bundles extend for some distance on the medial side of this tendon and terminate about three-fourths of the way down the arm. ' The lateral head has a tendinous origin from the superior lateral portion of the posterior surface of the humerus along a line extending from the insertion of the teres minor as far as the groove for the radial (musoulo-spkal) nerve, and from the aponeurotic arch formed by the lateral intermuscular septum as it crosses this groove. The constituent fibre-bundles descend, the superior vertically, the inferior obliquely, to be inserted on the dorsal and ventral surfaces of the proximo-lateral margin of the common tendon of insertion of the triceps. The medial head has a fleshy origin from the posterior surface of the humerus below the radial (musculo-spiral) groove and from the dorsal surfaces of the medial and lateral intermus- cular septa. The greater part of the fibre-bundles arising from this extensive area are inserted into the deep surface of the common tendon, but some extend directly to the olecranon and the articular capsule of the elbow. The slip attached to the capsule is sometimes called the subanconeus muscle. FLEXORS OF THE ARM 379 Insertion. — The tendon of insertion of the triceps forms a flat band covering the dorsal surface of the distal two-fifths of the muscle. It also extends proximally between the long and lateral heads and on the deep surface of the former. This tendon is inserted into the olecranon and laterally, by a prolongation over the anconeus, into the dorsal fascia of the forearm. Neroe-supply. — From the radial (musculo-spiral) nerve. The branch to the long head arises in the arm-pit and enters that margin of the muscle which is prolonged down from the lateral edge of the tendon, but which, because of the torsion of the muscle, comes to he on the medial side. The nerve usually enters through several rami about the middle of the free portion of the long head. Somewhat more distally the radial nerve gives off a branch that enters, by two or three branches, the proximal portion of the medial head. A similar branch is given to the lateral head and other branches are given to the lateral and medial heads from that portion of the radial (musculo-spiral) nerve lying in the radial (musculo-spiral) groove." The nerve fibres arise from the sixth, seventh, and eighth cervical nerves. Relations. — Near the shoulder the triceps is covered by the deltoid muscle. The long head passes between the teres major and teres minor muscles. The circumflex (dorsal) scapular vessels here pass medial, the circumflex humeral vessels and the axillary (circumflex) nerve lateral, to this head. More distally the muscle lies beneath the brachial fascia. It covers the radial groove of the humerus, in which run the radial (musculo-spiral) nerve and (superior) pro- funda brachii artery. Ventro-lateral to the muscle he the deltoid, brachialis, brachio-radialis, and extensor carpi radiaUs muscles; ventro-medial, the coraco-brachiahs, biceps, and brachialis muscles. Action. — It extends the forearm. The leverage is of such a nature that force is sacrificed for speed of movement. The long head of the triceps also serves to extend and to adduct the arm and to hold the head of the humerus in the glenoid cavity. Variations. — The scapular attachment may extend for a considerable distance down the axillary border of the scapula. Each of the heads may be more or less fused with neighbouring muscles. Frequently a fourth head is found. This may arise from the humerus, from the axillary margin of the scapula, from the capsule of the shoulder-joint, from the coracoid process, or from the tendon of the latissimus dorsi. The latissimo-condyloideus (dorso-epitrochlearis).^This muscle is found in about 5 per cent, of bodies. When well developed, it extends from the tendon of the latissimus dorsi to the brachial fascia, the triceps muscle, the shaft of the humerus, the lateral epicondyle, the olec- ranon, or the fascia of the forearm. It is innervated by a branch of the radial (musculo-spiral) nerve. It is a muscle normally present in some one of the forms above mentioned or in some similar form, in a large number of the inferior mammals. In the human body it is normally represented by a fascial slip from the tendon of the latissimus to the long head of the triceps or the brachial fascia. The anconeus. — Origin. — By a short narrow tendon from the distal part of the back of the lateral epicondyle and the adjacent part of the capsular hgament of the elbow-joint. Structure and insertion. — The tendon of origin is prolonged on the deep surface and lateral border of the muscle. From this the fibre-bundles spread, the proximal transversely, the more distal obliquely, to be inserted into the radial side of the olecranon and an adjacent impres- sion on the shaft of the ulna. Its superior fibre-bundles are usually continuous with those of the medial head of the triceps. Nerve-supply. — By a long branch which arises in the radial (musculo-spiral) groove from the radial (musculo-spiral) nerve, passes through the medial head of the triceps, to which it gives branches, and enters the proximal border of the anconeus. The nerve fibres arise from the seventh and eighth cervical nerves. Action. — It aids the triceps in extending the forearm and draws the ulna laterally in prona- tion of the hand. Relations. — The muscle hes immediately beneath the antibrachial fascia. It extends over the head of the supinator (brevis) and the elbow-joint and upper radio-ulnar joint. Variations. — The extent of fusion of .the muscle with the medial head of the triceps varies a good deal. It may also be fused with thfe extensor carpi ulnaris. It has been reported missing. P^P^*^ ^>> B. intratendinea olecrani. — Within the tendon of the='triceps near its insertion. JVIore frequent than the following: — - ,' B. subtendinea olecrani. — Between the tendon of the trffeopS; and the olecranon and dorsal ligament of the elbow-joint. Inconstant. B. epicondyli medialis dorsalis. — Between the medial epicondyle, the edge of the triceps, and the ulnar nerve. Rare. jiC- B. m. anconei. — Between the tendon of origin of the muscle and the head of the raditi^'* Frequent. 2. Ventral or Flexor Group (Figs. 364, 365, 370, 372) The muscles of this group are the coraco-brachialis, the biceps, and the brachi- alis. The coraco-brachialis (fig. 365) is a band-like muscle which arises from the coracoid process and is inserted into the middle third of the shaft of the humerus. The biceps (fig. 364) arises by two heads: a short head, closely as- sociated with the coraco-brachialis, fi"om the coracoid process; a long head, by an 380 THE MUSCULATURE extended tendon, from the supraglenoid tuberosity of the scapula. The fusiform belly whicli arises from the fusion of these two heads is inserted into the radius and into the fascia of the forearm. The brachialis (fig. 365) extends under cover of the biceps from the lower three-fifths of the shaft of the humerus to the coronoid process of the ulna. The muscles of this group are supplied by the musculo- cutaneous nerve. The brachialis also usually receives a branch from the radial nerve. The coraco-brachialis and short head of the biceps flex and adduct the arm at the shoulder; the biceps and brachialis flex the forearm at the elbow. The long head of the biceps abducts the arm at the shoulder. Fig. 364. — Superficial Muscles of the Front of the Ahm. Pectoralis minor Coraco-brachiali; Long head of triceps Tendons of insertion of _ pectoralis major and deltoid Lateral head of triceps Medial head of triceps Semilunar fascia (lacertus fibrosus) Extensor carpi radialis iongus Brachio-radialis The muscles of this group are found in most of the hmbed vertebrates. In many of the lower forms the coraco-brachialis, which appears farther down in the vertebrate series than the biceps, has a more extensive insertion than in man. It may extend to the ulna (lizards) and may be subdivided into various muscles which correspond with the adductors of the thigh. The biceps, the place of which is taken in the lower vertebrates by a coraco-radial muscle, in most of the mammals presents two heads, the more lateral of which is attached by a tendon to the scapula above the shoulder-joint. This long tendon of the biceps lies primitively outside the capsule of the shoulder-joint, but in some of the higher mammals has come to lie within the capsule. In the biceps four elements mayberecogni.sed; — a coraco-radial, coraco-ulnar, gleno- radial, and gleno-ulnar. (Krause.) The development of these elements varies in different mammals CORA CO-BRA CHIALIS 381 The coraco-brachialis (fig. 365). — Origin. — (1) By a short tendon from the tip of the cora- coid process of the scapula and (2) from the tendon of the short head of the biceps. Insertion. — (1) By means of a strong tendon into the medial surface of the humerus im- mediately proximal to the middle of the shaft, and (2) often above this also into an aponeurotic band which e.xtends from the tendon along the medial margin of the humerus, arches over the tendons of the latissimus dorsi and teres major, and is attached to the lesser tubercle of the humerus. When the attachment to the tubercle does not take place, the band becomes closely applied to the deep surface of the muscle. Structure. — From the tendons of origin, which are usually closely associated, the fibre- bundles take an oblique, nearly parallel, course and are attached to the aponeurotic band above Fig. 365. — Deep Muscle.? of the Front of the Arm. Pectoralis minor Short head of biceps Coraco-brachiahs Long head of triceps Medial head of triceps Medial intermuscular septi rLong head of biceps — r~ — -Insertion of pectoralis major Insertion of deltoid J- Lateral part of brachialis Insertion of biceps mentioned and to both surfaces of the flat tendon of insertion. This extends high into the muscle. The belly of the muscle usually shows some separation into a superficial and a deep portion, between which runs the musculo-cutaneous nerve. When this separation is well marked, the tendon of origin of the superior fasciculus may be distinct from that of the inferior fasciculus and the short head of the biceps, and the tendon of insertion may give a separate lamina to each fasciculus. Nerve-supply. — A branch of the musculo-cutaneous nerve, or of the brachial plexus near the origin of this nerve, enters the upper third of the medial border of the muscle, and passes across the constituent fibre-bundles about midway between their attachments. The nerve fibres arise from the sixth and seventh cervical nerves. Action. — Adducts and flexes the arm at the shoulder and helps to keep the head of the humerus in the glenoid fossa. When the arm has been rotated lateralward, it acts as a medial rotator. Relations. — The coraco-brachialis is largely covered by the deltoid and pectoralis major muscles. Below the inferior border of the latter it becomes superficial. Near its origin it lies 382 THE MUSCULATURE between the pectoralis minor and the subscapularis muscles. More distally it lies medial to the humerus and in front of the chief brachial vessels and nerves. The musculo-cutaneous nerve usually runs through it. Variations. — The humeral insertion of the muscle varies considerably. According to Wood, the coraco-braohialis consists primitively of three parts, which arise from the coraooid process and are inserted respectively into the upper, the middle, and the distal part of the humerus along the medial side. The superior division is most deeply, the inferior the most superficially, placed. In man the muscle is composed of parts of the middle and inferior divisions. The inferior division may be completely developed as far as the medial epicondyle. The superior division of the muscle is occasionally found. Slips from the coraco-brachialis to the brachiahs have been seen. Complete absence of the muscle has been recorded. The biceps brachii (figs. 364, 370). — The short head arises by a flat tendon closely asso- ciated with that of the coraco-brachialis from the coracoid process. From the dorso-medial surface of this tendon the fibre-bundles descend nearly vertically, though increasing in num- ber, toward their attachment to the tendon of insertion. The fibre-bundles which arise highest on the tendon of origin are inserted highest on the tendon of insertion, while those which have the lowest origin have the lowest insertion. The long head arises from the supraglenoid tuberosity and from the glenoid ligament by a long tendon (9 cm.) bifurcated at its origin. The tendon at first passes over the head of the^humerus within the capsule of the joint, and then passes into the intertubercular (bicipital) groove, which is covered by the capsule of the joint and an expansion from the tendon of the pectoralis major. To this point the tendon is surrounded by the synovial membrane of the joint. After emerging from this the tendon slowly expands and from its dorsal concave surface arise fibre-bundles which, increasing in number, extend, somewhat obliquely, toward the ten- don of insertion. As in case of the short head, here also the fibre-bundles which arise highest on the tendon of origin have the highest insertion. Insertion. — The tendon of insertion begins usually in the distal quarter of the arm as a vertical septum between the two heads of the muscle. More distally this broadens out on each side into a flattened aponeurosis. The fibre-bundles are inserted into the sides of the septum and on each surface of the aponeurosis — those of the long head chiefly on the deep surface, those of the short head chiefly on the superficial surface. The aponeurosis is continued into a strong, flattened tendon which descends between the brachio-radialis and pronator teres muscles to be inserted on the dorsal half of the bicipital tuberosity of the radius. From the medial border of the tendon an aponeurotic expansion, the lacertus fibrosus (semilunar fascia), is continued into the fascia of the ulnar side of the forearm. Nerve-supply. — By a branch from the musculo-cutaneous nerve for each head. These branches may be bound in a common trunk for some distance. They enter the deep surface of the muscle in the proximal part of the middle third of each belly often by several rami. Usually there is a distinct intramuscular fissure for the reception of the branches to each head and the blood-vessels which accompany them. The nerve fibres come from the fifth and sixth cervical nerves. Action. — It is a chief flexor of the arm at the elbow and is also a supinator of the forearm. This last action is most marked when the forearm is flexed and pronated. Both heads are flexors and medial rotators of the arm at the shoulder. The long head is an abductor and so also is the short head when the arm is greatly abducted, otherwise the short head is an adductor. Relations. — The tendons of origin are concealed by the pectoralis major and deltoid muscles. Beyond this the muscle is covered by the fascia brachii. In the lower part of the ai-m it lies upon the brachialis muscle. Upon the medial margin lie the coraco-brachialis muscle, the brachial vessels, and the median nerve. Variations. — Variations are frequent. The whole muscle or either head may be missing, but such cases are rare. The long head may extend only to the bicipital groove. Frequently the muscle is partially divided into the four primitive portions mentioned above. The two heads may be separate from origin to insertion. There may be an accessory head (1 in 10 subjects — Le Double) which arises from the coracoid process, the capsule of the joint, the tendon of the pectoralis major, or the shaft of the humerus near the insertion of the coraco-brachialis. In most instances the origin takes place above the origin of the brachialis from the humerus. Sometimes several accessory heads are seen. Marked vai-iation of insertion is less frequent, but occasionally a supernumerary slip may go to the medial intermuscular septum or the medial epicondyle. The fusion of the biceps with neighbouring muscles (pectoralis major and minor, coraco-brachialis, brachialis, palmaris longus, pronator teres, brachio-radialis) by means of tendinous or muscular slips has been frequently reported. The brachialis (fig. 365). — Origin. — (1) From the distal three-fifths of the front of the humerus, (2) from the medial intermuscular septum, and (3) from the lateral intermuscular septum proximal to the heads of the brachio-radialis and extensor carpi radiaUs longus. Proxi- mally it sends up a pointed process on the lateral side of the insertion of the deltoid and another between the insertions of the deltoid and the coraco-braohiahs. Distally the area of origin stops a little above the capitulum and the trochlea. Structure and Insertion. — The fibre-bundles arise directly from this area of origin, except near the insertion of the deltoid and on the medial margin, where tendinous bands are developed. The fibre-bundles descend, the middle vertically, the medial obliquely lateralward, the lateral still more obliquely medialward. The tendon of insertion appears on the dorsal side of the lateral edge of the muscle in its lower fourth. Continuous with this stronger lateral portion of the tendon more distally a thinner band appears upon the ventral surface of the muscle above the joint. The tendon becomes thick as it passes distally, is closely united to the capsule of the elbow-joint, and is attached to the ulnar tuberosity. In addition to the main tendon, some of the deeper fibre-bundles of the muscle and some of those coming from the lateral intermuscular septum are attached by short tendinous bands to the coronoid process. MUSCLES OF FOREARM AND HAND 383 Neri/e-supply. — From the museulo-cutaneous nerve by a branch which enters the ventral surface of the muscle near the junction of the upper and middle thirds of the medial border. In addition the radial (musculo-spiral) nerve usually sends a small branch into the distal lateral portion of the muscle. A branch from the median nerve frequently supplies the medial side of the muscle near the elbow-joint (Frohse). Action. — To flex the forearm. Relations. — It lies behind the biceps, on each side of which it projects. The distal lateral portion of the muscle is grooved by the brachio-radialis, which here is closely apphed to it. The radial (musculo-spiral) nerve runs between these two muscles. On the medial side run the brachial vessels and median nerve. Variations. — It may be divided into two distinct heads continuous with the projections on each side of the deltoid tuJjerosity. A great number of supernumerary slips have been recorded. These may be attached to the radius, ulna, fascia of the forearm, capsule of the joint, brachio- radialis, and extensor carpi radialis muscles. It may be partially fused with neighbouring muscles. It has also been reported absent. BURS^ B. m. coraco-brachialis. — Between the subscapularis muscle, the tendon of the coraco- brachialis, and the coracoid process. Frequent. B. bicipito-radialis. — Between the ventral half of the radial tuberosity and the tendon of the biceps. Constant. B. cubitalis interossea. — Between the tendon of the biceps and the ulna and the neighbour- ing muscles. Frequent. D. MUSCULATURE OF THE FOREARM AND HAND (Figs. 366-379) The muscles of the forearm arise in part from the humerus, in part from the radius and ulna. Their bellies lie chiefly in the proximal half of the forearm. They are divisible into two groups: — a radio-dorsal, composed of extensors of the hand and fingers and supinators of the forearm; and an ulno-volar, composed of flexors of the hand and fingers and pronators of the forearm. The brachio- radialis, which belongs morphologically with the former group, is physiologically a flexor of the forearm. The two groups are separated on the medial side of the back of the forearm by the dorsal margin of the ulna (figs. 366, 369). Ventrally they are separated by the insertions of the biceps and brachialis and by an intermuscular septum (figs. 366, 370). In the hand, in addition to the tendons of the muscles of the forearm mentioned above (fig. 376), there are several sets of intrinsic muscles. About the meta- carpal of the thumb (figs. 375, 376, 377) is grouped a set of muscles which arise from the carpus and metacarpus and are inserted into the metacarpal and first phalanx of the thumb. A similar set of muscles is grouped about the metacarpal of the little finger (figs. 375, 376). These sets of muscles give rise respectively to the thenar and hypothenar eminences. Between the metacarpals lies a series of dorsal and palmar interosseous muscles (figs. 377, 378, 379) which are inserted into the first row of phalanges and into the extensor tendons. From the tendons of the deep flexor of the fingers a series of lumbrical muscles passes to the radial side of the extensor tendons (figs. 373, 375). These various muscles abduct, adduct, flex, and extend the digits. In addition to these deeper skeletal muscles of the hand there is a subcutaneous muscle over the hypothenar eminence (fig. 375). Of the muscles of the hand, all are supplied by the ulnar nerve except most of those of the thumb and the two more radial lumbricals, which are supplied by the median nerve. An arrangement of the muscles of the forearm in which the dorsal extensor-supinator mus- culture extends proximally on the radial side of the arm to the distal extremity of the humerus, and the volar flexor-pronator musculature similarly on the ulnar side, is characteristic of all limbed vertebrates and is associated with the pronate position of the forehmb characteristic of quadrupeds. In ampliibia and reptiles the musculature terminates distaUy on the carpus and in the aponeuroses of the hand. In the higher forms special tendons are differentiated for those muscles of the forearm which act on the fingers. On the back of the hand in many vertebrates short extensor muscles are found running from the carpus to the phalanges. On the volar surface a complex musculature is found in all forms which have freely movable fingers. In animals which walk on the ends of the fingers, especially in the hoofed animals, the intrinsic musculature of the hand is greatly reduced. The phylogenetic development of the muscles of 384 THE MUSCULATURE the forearm and hand is too complex a subject to be briefly summarised. The phylogeny of the forearm flexors and the palmar musculature has been studied by McMurrich. In his papers a summary of the hterature on the subject may be found. FASCIA The fasciae and the general relations of the musculature of the forearm and hand may be followed in the cross-sections fig. 366. The tela subcutanea contains a moderate amount of fat in the upper part of the forearm. This grows less in amount as the wrist is approached. On the back of the hand it contains little fat. In the palm and on the volar surface of the fingers a moderate amount of fat is embedded between dense vertical bundles of fibres which unite the skin to the fascia. Except on the volar surface of the hand and on the backs of the terminal phalanges, the tela is but loosely united to the underlying fascia. The bursa subcutanea olecrani lies over the dorsal surface of the olecranon. Subcutaneous bursiE are also frequently found over the knuckles (b. subcutanese metacarpophalangeae dorsales) and the proximal joints of the fingers (b. subcutanese digitorum dorsales). The antibrachial fascia encloses the muscles of the forearm in a cylindrical sheath, composed in the main of circular fibre-bundles, but strengthened by longitudinal and obhque bundles extending in from the epicondyles of the humerus, the olecranon, the lacertus fibrosus of the bi- ceps, and the tendon of the triceps. The fascia of the forearm is attached to the dorsal surface of the olecranon and to the subcutaneous margin of the ulna. Above, it is continued into the fascia of the arm; below, into the fascia of the hand. From the antibrachial fascia in the upper half of the foreai-m a fibrous septum extends between the radio-dorsal and the ulno-volar muscle group to the radius. In the radial septum below the elbow a branch of communica- tion extends between the superficial and deep veins of the arm. That part of the fascia over- lying the radio-dorsal group of muscles is much denser than that covering the volar group, except where the latter is strengthened by the lacertus fibrosus. In addition to the main radial septum other septa descend between the underlying muscles from the antibrachial fascia. These septa are best marked near the attachment of the muscles to the humerus. Here the fascia is firmly fused to the muscles. Dorsally the antibrachial fascia is strengthened at the wrist by transverse fibres which extend from the radius to the styloid process of the ulna, the triquetrum (cuneiform), and pisiform, and give rise to the dorsal ligament of the carpus (posterior annular ligament). From this ligament septa descend to the radius and ulna and convert the grooves in these bones into osteo-fibrous canals which lodge the tendons of the various muscles extending to the wrist and hand. On the back of the hand there is spread a fascia composed of two thin fascial sheets between which the extensor tendons are contained. Between the tendons these sheets are more or less fused. On the backs of the fingers the fascia blends with the extensor tendons and.the associated aponeurotic expansions from the interosseous and lumbrical muscles. Between the fingers it is continued into the transverse fasciculi of the palmar aponeurosis. At the sides of the hand the fascia is continued into the thenar and hypothenar fasciae. Each dorsal interosseous muscle is covered by a special fascial membrane which is separated by loose tissue from the fascia investing the e.xtensor tendons. Fig. 366, A-H. — Transverse Sections through the Llpt Forearm and Hand. H. Transverse section through the first phalanx of the middle finger, diagrammatic, with the cavity of the synovial sheath of the flexor tendons distended. The regions through which these sections pass are indicated in the diagram, c and d in the diagram show the regions through which pass sections C and D, fig. 362 (p. 375). 1. Aponeurosis palmaris. 2. Arteria radialis. 3. A. ulnaris. 4. Bursa bicipito-radiahs. 5 Discus articularis. 6. Ligamentum carpale dorsale. 7. L. carpi transversum. 8. L. carpi volare. 9. Fascia antibrachii. 10. Musculus abductor pollicis brevis. 11. M. abductor pollicis longus — a, tendon. 12. M. abductor digiti quinti. 13. M. adductor polhcis. 14. M. anconeus. 15. M. biceps, tendon. 16. M. brachialis, tendon. 17. M. braohio-radialis — a, tendon. 18. M. extensor carpi radiahs brevis — a, tendon. 19. M. extensor carpi radiahs longus — a, tendon. 20. M. extensor carpi ulnaris. 21. M. ex- tensor digitorum communis — a, tendon for second finger; b, tendon for the third finger; c, tendon for fourth finger; d, tendon for fifth finger; e, digital aponeurosis. 22. M. extensor digiti quinti proprius. 23. M. extensor indicis proprius. 24. M. extensor polhcis brevis — a, tendon. 25. M. extensor poUicis longus — a, tendon. 26. M. flexor carpi radialis — a, tendon. 27. M. flexor carpi ulnaris — a, tendon. 28. M. flexor digitorum profundus — a, tendon for second finger; b, tendon for third finger; c, tendon for fourth finger; d, tendon for fifth finger. 29. M. flexor digitorum sublimis — a, tendon for second finger; b, tendon for third finger; c, tendon for fourth finger; d. tendon for fifth finger. 30. M. flexor digiti quinti brevis. 31. M. flexor pollicis brevis. 32. M. flexor pollicis longus — a, tendon. 33. M. interossei dorsales. 34. M. intero.ssei volares. 35. M. lumbricales. 36. M. op- ponens polhcis. 37. M. opponens digiti quinti. 38. M. palmaris brevis. 39. M. palmaris longus — a, tendon. 40. M. pronator quadratus. 41. M. pronator teres. 42. M. supi- nator. 43. N. cutaneus antibrachii lateralis. 44. N. medianus. 45. N. radialis — a, deep radial nerve; b, superficial radial nerve. 46. N. ulnaris. 47. Os capitatum (magnum). 48. Os hamatum (unciform). 49. Os lunatum (semilunar). 50. Os meta- carpal, I. 51. Os metacarpale, II. 52. Os metacarpale. III. 53. Os metacarpale, IV. 54. Os metacarpale, V. 55. Os multangulum majus (trapezium). 56. Os naviculare. 57. Ossa sesamoidea of fifth digit. 58. Radius. 59. Ulna. 60. Vagina fibrosa (tendon- sheath) of the long digital flexors. 61. Vagina fibrosa (tendon-sheath) of the flexor pollicis longus. 62. Vagina fibrosa (tendon-sheath in digit). 63. Vena cephalica. MUSCLES OF FOREARM AND HAND 385 44 2 9 d A -~. 4^i 42 ^1 4-5»2a JO 9 H 386 THE MUSCULATURE D 28° 28* 28' 2t2Z ai' 3f 2\^ F RADIO-DORSAL DIVISION 387 On the volar side of the forearm for some distance above the wrist the tendons of the flexor carpi radialis, tlie palmaris longus, and the flexor carpi ulnaris run between two layers of the fascia. The fascia is much strengthened at the wrist by transverse fibres which give rise to the volar ligament of the carpus. Beneath it hes the transverse ligament of the carpus (anterior annular hgament). This dense band is broader than the volar ligament but like it extends from the pisiform bone and the hamulus of the hamatura (unciform) to the tuberosity of the navicular and the tuberosity of the greater multangular (trapezium). It serves to complete an osteo-fibrous canal through which pa.ss the flexor tendons of the fingers. Between the two ligaments which are partially fused with one another run the ulnar artery and nerve. On the palm of the hand the ensheathing fascia presents three distinct areas — a central, a lateral, and a medial. The central portion, the palmar aponeurosis, is composed chiefly of bundles of fibrous tissue which radiate superficially toward the fingers from the tendon of the palmaris longus or from a corresponding region of the forearm fascia when this muscle is absent. Between these bundles are others which arise from the transverse ligament. The deep surface of the fascia is composed of a thin incomplete layer of transverse fibres which continue the transverse fibres of the forearm fascia. Near the capitula of the metacarpals this layer becomes much stronger and constitutes a ligamentous band (superficial transverse ligament of Poirier). Near the bases of the digits bundles of transverse fibres (fasciculi transversi) lie in the webs of the fingers and constitute an incomplete transverse ligament separated by a distinct interval from the super- ficial transverse ligament. From the palmar aponeurosis processes are sent in toward the deeper structures. Of these, the most important are those continued into a fibrous sheath which surrounds the space con- taining the long flexor tendons and the lumbrical muscles. This dense fibrous sheath is united by fibrous processes to the third, fourth, and fifth metacarpals. As the flexor tendons diverge and the ends of the metacarpals are approached, numerous processes descend from the palmar aponeurosis to the transverse capitular ligament. These hold the tendons in place. On the volar surface of the fingers the fascia serves to complete osteo-fibrous canals for the long flexor tendons. The ventral surface of the first and second phalanges of each finger is slightly grooved. The fascia is firmly united on each side to the margin of the groove, and over the groove forms a semicyhndrical, strong, fibrous sheath, the vaginal ligament of the finger. This sheath is strengthened by transverse bands over the bases of the first and second phalanges (annular ligaments) and by cruciate bands over the shafts of the phalanges (cruciate ligaments). Over the interphalangeal joints the sheath is thin, but is strengthened by crucial bands which permit of freedom of motion. The thenar fascia is a thin membrane covering the short muscles of the thumb. It is con- tinued above into the fascia of the forearm, medially is fused with the tendon of the palmaris longus and the palmar aponeurosis, and extends as a septum to be attached to the third meta- carpal. Laterally it is attached to the first metacarpal and is continued into the dorsal fascia of the hand. It is fused with an aponeurosis from the tendon of the abductor poUicis longus. Distally it is continued into the vaginal ligament of the long flexor of the thumb. Superficially it is closely adherent to the skin. The hypothenar fascia invests the palmar muscles of the little finger. It is continued from the ulnar margin of the fifth metacarpal over the muscles of the little finger to the palmar aponeurosis, and, by means of a septum, to the radial side of the fifth metacarpal. Proximally, it is attached to the hamatum (unciforn?^ and extends into the fascia of the forearm, distally, it extends into the vaginal ligament of the tendon of the fifth digit. A deeply seated suprametacarpal fascial layer, or deep palmar fascia, covers the inter- osseous muscles and is attached to the volar surface of the metacarpal bones. In addition to the fasciae mentioned, intermuscular septa serve to separate mjre or less completely the various intrinsic muscles of the hand. MUSCLES 1. Radio-Dorsal Division The muscles of this group lie in two chief layers, a superficial and a deep. a. Superficial Layer (Figs. 367, 370, 371), The muscles of this laj^er, closely associated at their origins, extend from the radial .side of the distal end of the humerus to the distal extremity of the radius, the carpus, and the fingers. They are divisible into a radial, an intermediate, and an ulnar set. Radial set. — To this belong three muscles, the brachio-radialis, extensor carpi radialis longus and brevis. The brachio-radialis (fig. 370), a forearm flexor, is a superficial fusiform muscle which arises from the lateral epicondylar ridge of the humerus and is inserted into the base of the styloid process of the radius. The extensor carpi radialis longus (fig. 371) is a narrow, fusiform muscle which extends 388 THE MUSCULATURE along the radial margin of the forearm, partly under cover of the brachio-radialis. It arises from the lateral epicondylar ridge of the humerus, and is inserted into the second metacarpal bone. The extensor carpi radialis brevis (fig. 367) is a band-like muscle more dorsally placed than the last at the radial side of the arm. It arises from the lateral epicondyle and is inserted into the bases of the second and third metacarpals. These muscles are supplied by branches of the radial nerve which arise proximal to the passage of the deep radial (posterior inter- osseous) through the supinator muscle. Distally this set of muscles is separated from the intermediate set by the long abductor and the extensors of the thumb, which pass from an origin under the latter set over the tendons of the radial extensors to the thumb. The intermediate set. — This consists of the thick, flattened extensor digitorum communis and the slender extensor digiti quinti proprius (fig. 367). They arise from the lateral epicondyle, and are inserted into the backs of the fingers. The ulnar set consists of one muscle, the fusiform extensor carpi ulnaris, which arises from the lateral epicondyle of the humerus and is inserted into the back of the base of the fifth metacarpal. The intermediate and ulnar sets of muscles are supplied by branches from the ramus profundus of the radial nerve after this has passed through the supinator muscle. In the leg the lateral set of the superficial layer is represented by the tibialis anterior. The intermediate set is represented by the long extensors of the toes. The single muscle which constitutes the medial set is represented by the peroneal muscles. The brachio-radialis (supinator radii longus) (figs. 367, 370). — Origin. — From the upper two-thirds of the lateral epicondylar ridge of the humerus and from the front of the lateral intermuscular septum. Insertion. — Into the lateral side of the base of the styloid process of the radius. Structure. — The constituent fibre-bundles arise directly from the septum and by short tendinous bands from the epicondylar ridge, extend downward and ventrally, and terminate in a penniform manner on a tendon which extends high on the deep surface of the muscle. This tendon becomes free about the middle of the forearm as a broad, flat band. This be- comes narrow as the tendon winds about the radius from the volar to the lateral surface. Before its insertion it expands laterally and is connected with neighbouring ligaments. The free surface of the muscle faces laterally at its origin, but, owing to the torsion, ventrally in the forearm. The tendon, however, is turned again so that at the insertion it faces laterally once more. Nerve-supply. — From a branch of the radial nerve (musculo-spiral) which enters the proximal third of the muscle on its deep surface. The nerve fibres arise from the fifth and sixth cervical nerves. Action. — To flex the forearm. This action is strongest when the forearm is pronated. It acts as a supinator only when the arm is extended and pronated. It then serves to put the arm in a state of semi-pronation. When the forearm is flexed, it acts as a pronator. Relations. — The muscle is superficially placed on the ventro-lateral surface of the forearm. Its tendon of insertion, however, is covered by the long abductor and the short extensor of the thumb. Near its origin (fig. 367) it lies lateral to the brachialis. In the intervening tissue run the radial nerve and the terminal branch of the profunda brachii artery. Dorsally and laterally lieslthe medial head of the triceps. More distally the muscle overlies the extensor carpi radialis longus. It crosses the supinator, pronator teres, and flexor pollicis longus muscles. Beneath its medial edge lie the radial vessels and nerve. Variations. — The humeral origin may extend half-way up the shaft. The radial insertion may be as high as the middle of the shaft or descend to the lesser multangular, navicular, or third metacarpal. In about 7 per cent, of bodies (Le Double) the tendon of insertion divides into two or three slips which are inserted on the styloid process of the radius. Occasionally the radial nerve passes between these slips. An accessory slip may pass to the fascia of the forearm. The muscle may be doubled throughout its length and it may be missing. It may be connected by accessory slips with neighbouring muscles, the deltoid, brachialis, long abductor of the thumb, or long radial carpal extensor. The slip most frequently found goes to the brachiahs. The extensor carpi radialis longus (figs. 367, 368, 371.) — Origin. — From the lower third of the lateral epicondylar ridge, the lateral intermuscular septum, and from the front of the tendons of the extensor carpi radialis brevis and the extensor communis digitorum which arise from the lateral epicondyle. Structure and insertion. — The fibre-bundles are inserted in a penniform manner on both surfaces of a tendon which first appears on the lateral border of the deep surface of the muscle, becomes free above the middle of the forearm, and descends, closely applied to the tendon of the short radial carpal extensor, to the second compartment beneath the dorsal carpal ligament, through which it passes to its insertion into the base of the second metacarpal near the radial border. The outer surface of the muscle faces at first laterally, then ventrally. Nerve-supply. — By one or two branches which arise from the radial (musculo-spiral) nerve as it passes between the brachialis and brachio-radialis. The nerve enters the deep surface of the muscle in the proximal third. The nerve fibres arise from the (fifth), sixth and seventh cervical nerves. Action. — To extend and abduct the hand. It steadies the wrist when the flexors act on EXTENSOR CARPI RADIALIS BREVIS 389 the fingers. It is a flexor of the forearm; a supinator when the forearm is extended, a pronator when it is flexed. Relations. — It is covered by the brachio-radialis near the elbow. Below it becomes super- ficial except where crossed by the tendons of the muscles of the thumb. (For the relations to the short radial carpal extensor see below.) Fig. 367. — Muscles of the Radial Side and the Back of tee Foeearm. Brachlalis Brachio-radialis Extensor carpi radialis longus Extensor digitorum communis Extensor carpi radialis brevis Abductor pollicis longus Extensor pollicis brevis Extensor pollicis longus Flexor carpi ulnaris Extensor carpi ulnaris Extensor digiti quinti propnus Variaiions. — The humeral attachment may be more extensive than that indicated above. The tendon of insertion may send a band to the third or to the fourth metacai'pal or to the mul- tangulum majus (trapezium). The muscle may be fused, partly or completely, with the short radial extensor. It may send a slip to the abductor pollicis longus or to some of the interossei. The extensor carpi radialis brevis (figs. 367, 368). — Origin. — From a band which descends on its deep surface from the common extensor tendon attached to the lateral epicondyle, from the intermuscular septa surrounding its head, and from the radial collateral ligament of the elbow-joint. 390 THE MUSCULATURE Structure and insertion. — The fibre-bundles converge obliquely toward a tendon which appears high up on the dorso-lateral surface of the muscle. Toward the lower third of the forearm this tendon becomes a free, strong band closely apphed to the under surface of the tendon of the long radial extensor, and with this passes through the second compartinent be- neath the dorsal ligament of the carpus, diverging as it does so toward its insertion into the back of the bases of the second and third metacarpal bones. Fig. 368 — Tendons upon the Dobsum of the Hand. Abductor poUicis longus Extensor polUcis brevii Dorsal carpal ligament Extensor carpi ulnans ^^^ Extensor digitorum communis Extensor digiti quinti Extensor indicts proprius Attachment of extensor digitorum to third phalanx Nerve-supply. — A branch is supplied to the muscle from the deep radial (posterior interos- seous) nerve before this enters the supinator (brevis). The branch enters the middle third of the medial margin of the muscle by several rami. The nerve fibres arise from the (fifth), sixth and seventh cervical nerves. Action. — To extend the hand and, to a slight extent, to flex the forearm. Relations. — In its proximal portion the muscle is placed with a medial surface toward the common extensor, a deep toward the supinator (brevis) and pronator teres, and a dorso- lateral toward the long radial extensor. More distally the muscle and its tendon become flattened about the radius and partly covered by the long radial extensor and its tendon. EXTENSOR CARPI ULNARIS 391 In the distal quarter of the forearm the tendons of these two muscles are crossed by the long abductor and the short extensor of the thumb. Beneath the dorsal carpal ligament the tendon of the short radial extensor is crossed by the tendon of the long extensor of the thumb. Variations. — The tendon often sends no slip to the second metacarpal. Fusion of the two radial extensors is frequent. The fused muscle may have from one to four tendons. The extensor carpi radialis intermedius of Wood is a muscle which arises, rarely directly from the humerus, but not infrequently as a slip from one or both radial extensors. It is inserted into the second or third metacarpal bone or into both. The extensor carpi radialis accessorius is a muscle which has an origin like the extensor intermedius, but which terminates on the base of the metacarpal or first phalanx of the thumb, the short abductor of the thumb, or some neigh- bouring structure. The extensor digitorum communis (figs. 367, 368). — Origin. — From a tendon attached to the lateral epicondyle, and from intermuscular septa which lie between the head of the muscle and the short radial extensor, the extensor of the Uttle finger, and the supinator muscle. Insertion. — By four tendons into the bases of the phalanges of the fingers. Structure. — The fibre-bundles arise from the interior of the pyramidal case formed by the tendon, the fascia, and intermuscular septa, and pass distally to converge on four tendons which begin in the middle of the forearm, become free a little above the wrist, pass under the dorsal carpal ligament in a groove common to them and the tendon of the extensor indicis proprius, and diverge to the backs of the fingers. Opposite the metacarpo-phalangeal joint each tendon gives rise on its under surface to a band which becomes attached to the base of the first phalanx of its respective digit. The tendon is also closely bound to the joint by fibrous bands connected with the palmar fascia. On the dorsum of the first phalanx the tendon expands and is bound to an aponeurotic extension from the interosseous and lumbrical muscles. The tendon divides into three bands. The middle band passes to the base of the second phalanx, the lateral bands pass laterally around the joint to be inserted into the back of the base of the third phalanx. The lateral bands are bound to the second joint by a thin layer of transverse and oblique fibres. An obliquely transverse band usually passes from the tendon of the index to that of the middle finger above the heads of the metacarpals. The tendon to the index finger is united to the tendon of the extensor indicis proprius opposite the metacarpo-phalangeal articulation. The tendon to the ring finger usually sends a slip to join the tendon of the middle finger. The fourth tendon lies near that of the ring finger and divides into two shps, one of which joins the tendon of the ring finger and one goes to the little finger to join the tendon of the extensor digiti quinti proprius. Nerve-supply. — From a branch which arises from the deep radial (posterior interosseous) nerve as it emerges from the supinator (brevis) muscle. From this several twigs enter the deep surface of the middle third of the belly. Often the nerve is bound up with the nerve to the extensor of the little finger and the ulnar extensor. On the other hand, there may be several separate branches to the muscle. The nerve fibres arise from the sixth, seventh, and eighth cervical nerves. Action. — The muscle extends the two terminal phalanges on the basal, the basal on the metacarpus, and the hand at the wrist. The extensor action is strongest on the first phalanx. The cross-bands between the tendons hinder ^Jie independent extension of the middle and ring fingers, while the special extensors of the index and little fingers makes the movements of these fingers freer. When the hand is abducted toward the radial side, the extensor muscles tend to draw the fingers ulnarward. When the hand is abducted toward the ulnar side, the muscles tend to draw the fingers toward the thumb. When the hand is in the mid-position the ring finger and little finger are abducted and the index-finger is adducted. (Frohse.) Relations. — It is superficially placed. Under it lie the deep muscles of the back of the forearm, the interosseous vessels, and the deep radial (posterior interosseous) nerve. It lies between the short radial carpal extensor and the extensor of the little finger. Variations. — There is considerable variation in the extent of isolation of the parts going to the various fingers. That to the index-finger is the one most frequently isolated. At times the tendon to the index or httle finger may be wanting. More frequently one or more of the tendons subdivides to be attached to two or more fingers or to the thumb. The connections between the tendons on the back of the hand vary greatly. The extensor digiti quinti proprius (extensor minimi digiti) (figs. 367, 368). — Origin. — Chiefly from the septum between it and the common extensor, but also in part from the septum between it and the extensor ulnaris and from the overlying fascia. Structure and insertion. — The fibre-bundles descend in a narrow band which begins near the neck of the radius. They are inserted into the side of a tendon which begins high on the ulnar margin of the muscle. The most distal fibre-bundles extend nearly to the wrist-joint. The tendon passes through the fifth compartment beneath the dorsal carpal ligament, and extends on the back of the fifth metacarpal to the base of the first phalanx of the little finger, where it is joined by a shp from the fourth tendon of the common extensor. The insertion of the tendon is Uke that of the tendons of the common extensor. Nerve-supply. — By a branch or branches from the deep radial (posterior interosseous), nerve. The nerve filaments enter the middle third of the fleshy portion of the muscle on its deep surface. The innervation of this muscle is intimately related to that of the preceding. Action. — It acts as a portion of the common extensor, but, owing to its separation, in- dependent movement of the Little finger is possible. Relations. — It Ues between the common extensor and the ulnar extensor and upon the deep muscles of the back of the forearm. Variations. — Absence is not very frequent; blending with the common extensor is frequent. Its tendon often divides into two or more slips. The belly may also be doubled. It may have a supplementary origin from the ulna. A tendon shp to the ring-finger is frequently found. The extensor carpi ulnaris (figs. 367, 368). — Origin. — By two heads: one from the inferior dorsal portion of the epicondyle by an aponeurotic band attached below the tendon of the 392 THE MUSCULATURE common extensor, from the enveloping fascia, and from the septa between it and the extensor digitiquinti, anconeus, and supinator (brevis); the other from the proximal three-fourths of the dorsal border of the ulna. Structure and insertion. — The fibre-bundles descend in an osteo-fascial compartment bounded by the dorsal surface of the ulna, the fascia of the forearm, the dense fascia overlying the ulnar origin of the muscles of the thumb, and the origin of the extensor indicis. The tendon commences high in the muscle and appears on the radial border of the middle third of the back of its belly. The fibre-bundles are inserted in a penniform manner on the ulnar border and deep surface of the tendon as far as the wrist. Here the tendon enters the sixth osteo-fibrous canal beneath the dorsal carpal Ugament in a special groove on the outer side of the styloid process of the ulna. It is inserted into the base of the fifth metacarpal. Nerve-supply. — By a branch which arises from the deep radial (posterior interosseous) nerve as this emerges from the supinator (brevis) muscle. Several filaments enter the deep surface of the muscle in the middle third. The nerve fibres arise from the sixth, seventh and eighth cervical nerves. Action. — To extend and abduct the hand ulnarward. Relations. — It occupies a superficial position on the ulnar side of the extensors of the fore- arm. Beneath it he the deep muscles of the back of the forearm and the posterior surface of the ulna. Variations. — It may receive a slip from the triceps or be fused with the anconeus or with the extensor of the little finger. More frequently it is doubled, partially or completely. An accessory tendon may go to the first phalanx of the little finger, to the head of the fifth meta- carpal, to the fourth metacarpal, to the extensor tendon of the little finger, or to the fascia over the opponens digiti quinti. The muscle may be reduced to a fibrous band. The ulnaris digiti quinti is a rare muscle arising from the dorsal surface of the ulna and inserted into the base of the first phalanx of the httle finger. It may be represented by a fasciculus or an extra tendon from the ulnar extensor. b. Deep Layer (Fig. 369) The muscles of this group extend from the ulna to the radius, thumb, and index- finger. They are the supinator, abductor pollicis longus, extensor pollicis longus and brevis, and extensor indicis proprius. The supinator is a rhomboid muscle which arises from the lateral epicondyle of the humerus and the supinator crest of the ulna winds laterally around the radius and is inserted into its volar surface. The abductor pollicis longus is a fusiform muscle which arises from the middle third of the ulna, the interosseous membrane, and the radius, and is inserted into the base of the first metacarpal. The extensor pollicis brevis arises from the radius distal to the preceding muscle, and is inserted into the base of the first phalanx of the thumb. The extensor pollicis longus is a narrow muscle which arises from the middle third of the dorsal surface of the ulna and is inserted into the base of the second phalanx of the thumb. The extensor indicis proprius is a narrow, fusiform muscle arising from the shaft of the ulna and inserted into the dorsal aponeurosis of the index-finger. These muscles are supplied from branches of the deep radial (posterior interosseous) nerve while this is passing through or after its exit from the supinator. The extensor pollicis longus is represented by the extensor hallucis longus of the leg. The abductor pollicis longus and extensor pol'icis brevis are represented by the abnormal abductor hallucis longus and extensor primi internodii hallucis muscles, the rudiments of which are perhaps normally present in the tibialis anterior. The supinator and the extensor indicis muscles are not represented in the leg. On the other hand, the extensor digitorum brevis, norma! in the foot, is only occasionally found on the back of the hand. The supinator (brevis) (figs. 366, 369, 372). — Origin. — From (1) the inferior dorsal portion of the lateral epicondyle by a tendinous band which is adherent to the deep surface of the tendons of origin of the radial and common extensors and to the radial collateral ligament of the joint; and (2) the ulna by a superficial aponeurosis and by fibre-bundles attached directly to the depression below the radial notch and to the supinator crest. Insertion. — The lateral and volar surfaces of the radius from the tuberosity to the attach- ment of the pronator teres. Structure. — From their origin the fibre-bundles descend spirally in a muscular sheet which enwraps the radius (fig. 366). The attachment extends to the oblique Une. The muscle is divided into a superficial and a deep plane by a septum in which the deep radial (posterior interosseous) nerve runs. The radial attachments of these two portions are separated by an osseous area into which no fibre-bundles are inserted. The fibre-bundles of the superficial layer have a much more vertical course and are longer than those of the deep layer. Nerve-supply. — By branches which arise from the deep radial (posterior interosseous) nerve before it passes between the two layers of the supinator muscle. The nerve fibres arise from the fifth, sixth, and seventh cervical nerves. Action. — To supinate the forearm. Relations. — The supinator is covered by the superficial group of extensor muscles above described and by the anconeus. ABDUCTOR POLLICIS LONGUS 393 ' Variations. — The extent of separation of the muscles into two portions varies. Accessory fasciculi of origin are not uncommon. These may spring from the annular ligament, tensor liga- menti annularis anterior (5 per cent, or more of bodies — Le Double), the lateral epicondyle, the tendon of the bi ceps, the tuberosity of the radius, etc. A sesamoid bone may lie in the tendon of origin. The tensor ligamenti annularis posterior is a sUp generally present and often independent of the supinator. It runs from the ulna behind the radial notch to the annular ligament of the radio-ulnar joint. The abductor polUcis longus (extensor ossis metacarpi poUicis) (fig. 369). — Origin. — From (1) the lateral margin of the dorsal surface of the ulna in the proximal portion of the middle third. Fig. 369. — The Deep Muscles of the Back of the Forearm. Abductor pollicis longus Extensor poUicis brevis Extensor poUicis longus Radial extensors Flexor carpi ulnaris Flexor digitorum profundus Extensor indicis proprius Extensor carpi ulnaris and the adjacent interosseous membrane, (2) the dorsal surface of the radius distal and medial to the attachment of the supinator, and (3) at times, from the septa lying between it and the supinator, extensor carpi ulnaris, and extensor polUcis longus. Structure and insertion. — The fibre-bundles from this extensive area of origin converge in a bipenniform manner upon a tendon which appears as an aponeurosis on the deep surface of the muscle about the middle of the forearm. The tendon as it descends becomes rounded. The insertion of fibre-bundles continues nearly to the wrist. Here, together with the tendon of the short extensor, it enters the first osteo-fibrous canal beneath the dorsal carpal ligament upon the lateral surface of the distal extremity of the radius. Upon leaving this canal the tendon extends to be inserted on the radial side of the base of the first metacarpal bone. Nerve-supply. — By one or more branches from the deep radial (posterior interosseous) nerve 394 THE MUSCULATURE after it has emerged from the supinator. The branches enter the muscle on the superficial surface in the proximal third. The nerve fibres come from the sixth, seventh (and eighth) cervical nerves. Action. — It carries the first metacarpal radialward and forward. At the height of its contraction it flexes and abducts the hand at the wrist. Relations. — Near its origin the muscle is covered by the superficial extensors of the forearm. More distally, accompanied by the short extensor, it passes radially, becomes superficial, and crosses the tendons of the two radial carpal extensors. Variations. — The muscle or its tendon may be doubled. An accessory tendon may be applied to the multangulum majus (trapezium), the transverse ligament of the carpus, the superficial muscles of the thenar eminence, or the first metacarpal. Of these, the attachment to the short abductor and short flexor is the most frequent (7 out of 36 bodies — Wood). There may be three or more tendons. The muscle may be fused with the short extensor. The extensor poUicis brevis (fig. 369). — Origin. — From the distal part of the middle third of the medial portion of the dorsal surface of the radius and from the neighbouring portion of the interosseous membrane. Rarely its origin extends to the ulna. Structure and insertion. — The fibre-bundles converge on a tendon which appears on the radial border. The fibres are inserted as far as the dorsal carpal (posterior annular) ligament. The tendon hes parallel to the ulnar side of that of the abductor poUicis longus, and, in close connection with it, passes through the first compartment beneath the dorsal carpal ligament, and crosses the metacarpo-phalangeal joint on the radial side of the long extensor tendon. It is inserted on the base of the first phalanx of the thumb or into the capsule of the metacarpo- phalangeal joint. Nerve-supply. — From a branch derived from the deep radial (posterior interosseous) nerve. This branch is usually given off in common with or near the nerve to the abductor pollicis longus, and many traverse that muscle to reach the extensor pollicis brevis, which it enters in the proximal third of its radial border. The nerve fibres come from the sixth, seventh (and eighth) cervical nerves. Action. — To extend the thumb at the metacarpo-phalangeal joint and to abduct the first metacarpal. It likewise acts as a weak supinator of the forearm. Relations. — It hes between the abductor pollicis longus and the extensor pollicis longus, by which its origin is partly overlapped. In company with the former muscle it passes medially from beneath the common extensor of the fingers and over the tendons of the radial carpal extensors to reach its osteo-fibrous canal under the dorsal carpal hgament. Variations. — The head of the mu3cle may be fused with the long abductor. Its tendon of insertion may give rise to a sUp inserted on the first metacarpal (in 2 out of 85 bodies — Le Double) or into the terminal phalanx. Its tendon is often united with that of the long extensor. It may be fused with the long abductor of the thumb and has been found missing. It may be doubled. The extensor pollicis longus (fig. 369). — Origin. — From the middle third of the lateral part of the dorsal surface of the ulna; from the neighbouring part of the interosseous membrane; and from the septa between it and the extensor indicis proprius, and the extensor carpi ulnaris. Structure and insertion. — The fibre-bundles converge in a bipenniform manner on the two sides of a tendon which appears high on the dorsal surface of the muscle. They extend as far as the dorsal carpal (posterior annular) hgament. The fusiform body of the muscle descends somewhat obliquely on the dorsal surface of the forearm. The tendon enters the third osteo- fibrous canal beneath the dorsal carpal (posterior annular) Hgament. On emerging from the canal it passes very obliquely across the dorsal surface of the carpus, over the tendons of the radial extensors, to the ulnar side of the first metacarpal. It passes along this and on the dorsal surface of the first phalanx, expands to be inserted into the base of the second phalanx. The aponeurosis of insertion receives tendinous slips from the short muscles of the volar surface of the thumb. Nerve-supply. — By a twig from the deep radial (posterior interosseous) nerve. The branch gives rise to twigs which enter the proximal third of the radial border of the muscle. The fibres arise from the sixth, seventh, and eighth cervical nerves. Action. — To extend the second phalanx on the first, and this on the metacarpal. It also draws the whole thumb when extended toward the second metacarpal. It may have a sUght supinator action on the forearm. Relations. — The head of the muscle is partly overlapped by the long abductor of the thumb. It lies between this and the extensor pollicis brevis on one side, and the extensor indicis proprius on the other. Over it lie the extensors of the fingers and the ulnar carpal extensor. Variations. — The tendon may give a slip to the base of the first phalanx of the thumb, to the dorsal carpal hgament, or to the index finger. It may receive an accessory slip from the common extensor of the fingers or the short extensor of the thumb. It is frequently! doubled. An additional extensor is found in about 6 per cent, of bodies between the extensor! of the index finger and that of the thumb. It has a double tendon and insertion into both digits (extensor communis pollicis et indicis). The extensor indicis proprius (fig. 369). — Origin. — From the proximal part of the distal third of the posterior surface of the ulna, medial and distal to that of the preceding muscle, from the adjacent interosseous membrane, and from the septum between it and the extensor pollicis longus. Structure and insertion. — The fibre-bundles are inserted on a tendon which first appears on the radial border of the muscle. The insertion of fibre-bundles extends nearly to the dorsal carpal (posterior annular) ligament. Here the tendon passes beneath that of the extensor of the little finger and enters the fourth osteo-fibrous canal beneath the lateral tendons of the common extensor. It passes across the wrist beneath the tendon from the extensor communis to the index finger, and is inserted on the ulnar side of this into the dorsal aponeurosis of the index finger opposite the base of the first phalanx. ULNO-VOLAR DIVISION 395 Nerve-supply. — By a twig from the deep radial (posterior interosseous) nerve. This twig enters the proximal third of the radial border of the muscle. It frequently arises from a branch to the extensor pollicis longus. The nerve fibres come from the sixth, seventh, eighth cervical nerves. Ac! ion. — To extend the first phalanx on the metacarpal. Like the common extensor it has a limited action on the two terminal phalanges. It also adducts the index finger and is a weak supinator of the forearm. Relations. — It is covered by the superficial extensor group. Variations. — These are frequent. It may be absent. There may be two heads, or the muscle may be completely doubled. It may receive an accessory slip from the ulna or the carpus. The tendon may give accessory slips to the middle finger, the ring finger, or the thumb. The accessory tendon to the middle finger is the most frequent. The tendon to the index finger may be inserted on the metacarpus. Abnormal Muscles of the Back of the Wrist and Hand The extensor medil digiti is a small muscle which arises from the ulna beneath the extensor of the index finger, with which it is more or less fused. It sends a tendon to the extensor aponeurosis of the middle finger or slips both to this finger and the index finger. It is present in about 10 per cent, of bodies (Le Double). The extensor digiti annularis is a muscle similar to the extensor medii digiti, but much rarer . The extensor digitorum brevis, which resembles the muscle of corresponding name on the dorsum of the foot, may have from one to four fascicuU, but most frequently one. The most common fasciculus is one which sends a tendon to the extensor tendon of the index finger. One for the middle finger is nearly as frequent. Others are rare. A fasciculus for the thumb has not been reported. (Le Double.) The fasciculi usually arise from the bones of the ulnar half of the carpus — lunatum (semilunar), triquetrum (cuneiform), hamatum (unciform), and capitatum (magnum), and from the dorsal ligaments uniting these bones. The tendons are inserted either into the corresponding extensor tendons or into the metacarpals. The muscle is found in about 10 per cent, of bodies (Wood). BurSjB B. m. extensoris carpi radialis brevis. — Between the tendon and the base of the third metacarpal. B. m. abductoiis pollicis longi. — Between the tendons of the long and short radial extensors and the tendons of the abductor pollicis longus and extensor pollicis brevis. Another bursa lies beneath the tendon of insertion of the abductor. B. intermetacarpo-phalangeae. — Between the laXeral surfaces of the heads of the meta- carpal bones of neighbouring fingers dorsal to the transverse capitular ligament. B. tendinum m. extensoris digitorum communis. — Small bursae are sometimes found beneath the tendons to the index and little fingers near where they begin to diverge from the common tendon. B. m. extensoris carpi ulnaris. — A small bursa may be found under the tendon of origin of this muscle. B. m. supinatoris. — Between the supinator and the tendon of the extensor muscles. B. m. extensoris pollicis longi. — Between the tendon and the first metacarpal. Synovial Tendon-sheaths Vagina tendinum mm. extensorum carpi radialium. — Synovial sheaths cover the tendons of the two radial carpal extensors as they pass beneath the dorsal carpal (posterior annular) ligament. In the adult these sheaths usually are more or less fused and communicate with the sheath of the extensor pollicis longus where this crosses them. Vagina tendinum mm. extensoiis digitorum communis et extensoris indicis. — A synovial sheath surrounds the tendons of these muscles as they pass beneath the dorsal carpal (posterior annular) ligament. This sheath extends for some distance on the tendons as they diverge. Vagina tendinis m. extensoris digiti quinti. — A synovial sheath extends on the tendon of this muscle from above the dorsal carpal (posterior annular) ligament to the base of the meta- carpal. Vagina tendinis m. extensoris carpi ulnaris. — This sheath commences above the carpal (posterior annular) ligament and extends to the insertion of the tendon. Vagina tendinum mm. abductoris pollicis longi et extensoris pollicis brevis. — The sheaths which surround these two tendons beneath the dorsal carpal (posterior annular) Ugament usually communicate freely. Vagina tendinis m. extensoiis pollicis longi. — A long synovial sheath surrounds this tendon. Where it crosses the tendons of the radial extensors, a communication is found with the sheath of the latter. 2. Ulno-Volar Division The muscles on the volar side of the forearm lie in four layers. a. First Layer (Fig. 370) Of the four muscles of associated ulnar epicondylar origin which constitute this layer the pronator teres is a strong, band-like muscle which is inserted into 396 THE MUSCULATURE the lateral surface of the middle third of the shaft of the radius; the fusiform flexor carpi radialis sends a tendon to the base of the second metacarpal; the slender palmaris longus is inserted into the palmar fascia; and the medially situated, fusiform flexor carpi ulnaris into the pisiform bone and the palmar fascia. The pronator teres is the most powerful pronator of the forearm. When Fig. 370. — Front of the Forearm First Laier of Muscles. Pronator teres Flexor carpi radialis — Palmaris longus Flexor carpi ulnaris Flexor digitorum sublimis Brachio-radialis Flexor poUicis longus the hand is slightly flexed the ulnar carpal flexor abducts ulnarward. When the hand is greatly flexed lateral movement is difficult. The ulnar flexor is supplied by the ulnar nerve, the other muscles by the median. The pronator teres probably corresponds with the pophteus of the leg. The flexor carpi radialis and flexor carpi ulnaris probably represent in the main the two heads of the gastroc- nemius, and the palmaris longus, the plantaris. The pronator teres (fig. 370}. — Origin. — By two heads: — (1) The humeral or chief head arises by a tendon from the superior half of the ventral surface of the medial epioondyle and directly from the overlying fascia and from the intermuscular septa between it and the medial PRONATOR TERES 397 head of the triceps and the flexor carpi radialis. (2) The ulnar, deep or accessory, head arises by an aponeurotic band attached to the inner border of the coronoid process medial to the tendon of the brachialis. Between the humeral and ulnar heads is a fibrous arch beneath which the median nerve passes. Structure and insertion. — The fibre-bundles of the humeral head are inserted in a penniform manner on a tendon which begins near the middle of the belly of the muscle on the superficial Fig. 371. — Front of the Forearm: Second Layer op Muscles. Muscles of first layer Brachialis Flexor digitorum subli: Flexor carpi ulnans Flexor carpi radialis Palmaris longus Brachio-radialis Extensor carpi radialis longus Supinator Brachio-radialis Flexor pollicis longus Abductor pollicis longus Extensor pollicis brevis surface along the radial border. The tendon gradually becomes broader, winds about the volar surface of the radius, and is inserted into the middle third of its lateral surface. The attach- ment of fibre-bundles continues nearly to this insertion. The fibre-bundles of the ulnar head form a slender fasciculus which is inserted into the radial side of the deep surface of the humeral head. Nerve-supply. — By a branch derived from the median nerve before it passes between the two heads of the muscle. The nerve enters the proximal part of the middle third of the main belly of the muscle on its deep surface near the radial border. The branch to the ulnar head usually enters this portion of the muscle somewhat proximal to its fusion with the humeral head. The nerve fibres arise from the sixth and seventh cervical nerves. Action. — To pronate and flex the forearm. 398 THE MUSCULATURE Relations. — The muscle is superficially placed. Near its origin it is covered by the lacertus fibrosus of the biceps, and near its insertion by the radial vessels and nerve and the brachio- radialis and radial extensor muscles. It is the most radial of the group of muscles under con- sideration. The radial border helps to bound an angular space, the cubital fossa, in which lie the brachial vessels, median nerve, and the tendon of the biceps. The median nerve passes between its humeral and ulnar heads. The muscle overlies the supinator, the brachialis, and the radial origin of the flexor digitorum sublimis muscles and the ulnar artery. Variations. — Supplementary fasciculi may arise from the humerus, the medial intermuscular septum of the arm, the flexor carpi radialis, the flexor sublimis, or the brachiahs muscles. The two portions of the muscle may be distinct from origin to insertion. Either part of the muscle may be doubled. The ulnar head may be absent. The radial insertion may be extensive. Fasciculi may extend to the long flexor of the thumb. There may be a sesamoid bone in the tendon of origin from the humerus. The flexor carpi radialis (fig. 370). — Origin. — From (1) the common tendon attached to the medial epicondyle; and (2) the septa between its head and the pronator teres, the flexor sublimis, and the palmaris longus. Structure and insertion. — The fibre-bundles descend to converge upon a tendon at first intra- muscular, but which in the middle of the arm appears on the vblar surface of the muscle and soon becomes free from the attachment of fibre-bundles. The fibre-bundles from the epicondyle descend nearly vertically to the front and sides of the tendon, while those from the intermus- cular septa take an oblique course to the deep surface of the tendon. The tendon is at first flat, but soon becomes cylindrical, bound to the superficial muscle fascia, and enters the hand through a special osteo-fibrous canal formed mainly by the groove in the os multangulum majus (trapezium) and the transverse carpal (anterior annular) ligament. It is inserted into the base of the second metacarpal. It usually also sends a tendon slip to the third. Nerve-supply. — By a branch from the median nerve which divides into several twigs that enter the muscle near the junction of its proximal and middle thirds on the deep surface. The nerve usually arises near the elbow. The nerve fibres arise from the sixth, seventh (and eighth) cervical nerves. Action. — To flex the hand at the wrist. To a slight extent it may also act as a pronator of the forearm and a flexor of the forearm on the arm. Relations. — It is superficial except near its insertion. The belly of the muscle lies between the pronator teres and the palmaris longus and upon the flexor digitorum sublimis. The tendon of the muscle passes over the flexor poUicis longus, and near the wrist is a guide to the radial artery, which here lies lateral to it. In the hand the tendon lies beneath the thenar muscles and is crossed by the tendon of the long flexor of the thumb. Variations. — It may receive a fasciculus from the brachiahs or biceps muscles or from the radius or ulna. It may send tendon slips to the multangulum majus (trapezium), navicular, the transverse carpal (anterior annular) hgament, or the fourth metacarpal. The insertion may take place variously into these structures. The palmaris longus (fig. 370). — Origin. — From the common tendon attached to the medial epicondyle and from the surrounding intermuscular septa. Structure and insertion. — The fibre-bundles take a nearly parallel course to a tendon which appears high in the middle third of the forearm on the volar surface of the muscle. In the middle of the forearm the attachment of fibre-bundles usually ceases, the tendon becomes bound to the overlying fascia, and descends paraUel with that of the radial flexor. Near the proximal border of the transverse carpal (anterior annular) ligament the tendon expands into radiating bundles of fibres of which the medial and lateral are attached to the fascia over the intrinsic muscles of the thumb and little finger, while the middle, much more developed, con- stitute the chief portion of the palmar aponeurosis. Nerve-supply. — From a branch which usually arises in company with the nerve to the proximal part of the flexor sublimis. It frequently traverses the superficial fibres of the flexor sublimis. The nerve enters the middle third of the muscle. Action. — To flex the hand. It is also a weak flexor and pronator of the forearm. Relations. — It is placed between the radial and ulnar flexors over the flexor sublimis. In the distal part of the forearm the tendon lies over the median nerve. Variations. — It is absent in 11.2 per cent, of instances (Le Double). It may be highly developed or reduced to a tendinous band. The belly of the muscle may lie in the distal instead of in the proximal part of the forearm. It may be digastric. It may be fused with neighbouring muscles. It may arise from the medial intermuscular septum of the arm or from the lacertus fibrosus, from the radius, from the coronoid process, from the radial or ulnar flexor, or from the flexor sublimis muscles. The tendon may terminate in the fascia of the forearm, the thenar eminence, the carpus, or the abductor of the thumb. The muscle may be partly or wholly doubled. The flexor carpi ulnaris (fig. 370). — Origin. — By two heads: — (1) the humeral head arises from the common flexor tendon attached to the lower ventral part of the medial epicondyle Fibre-bundles of this head are also attached to the surrounding intermuscular septa and the deep fascia of the forearm. (2) The ulnar head arises by short tendinous fibres from the medial side of the olecranon and by an aponeurotic band common to it and the flexor digitorum pro- fundus from the upper two-thirds of the dorsal border of the ulna. Proximally the two heads of the muscle are united by a fibrous arch extending from the olecranon to the medial epi- condyle. Beneath this band pass the ulnar nerve and the dorsal recurrent ulnar artery. (See Epitrochleo-olecranonis, p. 402.) Structure and insertion. — The fibre-bundles of the humeral head descend nearly vertically, those of the ulnar head obliquely distally in a radial direction. They are iiiserted in a penniform manner on a tendon which appears in the proximal part of the middle third of the belly of the muscle on the radial margin of the deep surface, and in the distal third of the forearm forms the radial border of the muscle. On the ulnar side the insertion of fibre-bundles continues nearly FLEXOR DIGITORUM SUBLIMIS 399 to the pisiform bone. The insertion of the tendon takes place chiefly into the pisifoi'in bone, but from it tendinous bundles extend to the palmar aponeurosis, volar ligament of the carpus, to the pisohamate ligament (pisi-unciform), and to the bases of the fifth, fourth, and third metacarpals. Nerve-supply. — From two or three branches of the ulnar nerve, the most pro.ximal of which arises near the elbow-joint. These branches, which may arise by a single trunk, enter the deep surface of the proximal third of the muscle and send long twigs distally across the middle third of the constituent fibre-bundles. The nerve fibres arise from the seventh and eighth cervical and first thoracic nerves. Action. — To flex the hand and to abduct the hand ulnarward. Relations. — It is superficially placed. Its aponeurotic origin is adherent to the fascia of the forearm. It lies medial to the palmaris longus and flexor sublimis and upon the flexor profundus. Beneath the muscle lies the ulnar nerve. The ulnar artery extends along the radial border of the tendon near the wrist. Variations. — These are rare. Slips from the tendon may pass to the metacarpo-phalangeal articulation of the little finger. (See, however. Abnormal Muscles, p. 402.) b. Second Layer This is composed of one muscle, the flexor digitorum sublimis, which, although in part covered by the muscles of the preceding layer, is in part super- ficial. It arises from the medial epicondyle of the humerus, and from the radius and the ulna, and sends tendons to the second row of phalanges of the fingers. It corresponds probably with the soleus and the tendons of the flexor digitorum brevis in the leg and foot. The flexor digitorum sublimis (figs. 371, 373, 375). — Origin. — By two heads: the ulnar or chief head arises (1) by the tendon common to it and the superficial group of muscles from the medial epicondyle, and by short tendinous bands from the ventral surface of the epicondyle; (2) from the ulnar collateral ligament of the elbow, the ulnar tuberosity, the medial border of the coronoid process, and the inferior extremity of the tendon of the brachialis; and (3) from the intermuscular septum between the flexor subhmis and the overlying muscles. The radial head arises from an oblique line on the volar surface of Ijje radius, and from the middle third of the anterior border. Insertion. — Into the sides of the volar surface of the shafts of the second row of phalanges of the fingers. Structure. — The fibre-bundles of the ulnar head and the upper part of the radial head con- verge, the ulnar fibre-bundles nearly vertically, the radial obliquely, to form a common belly the deep surface of which on the ulnar side is backed by a dense tendinous band. On the radial side of this a less dense membrane covers over an oval canal which passes distally along the line of junction of the two heads and lodges the ulnar artery and the median nerve. The fibre-bundles of the ulnar head form a superficial and a deep group. The superficial portion near the middle of the forearm divides into a lateral and a medial division, the former being inserted on a tendon that goes to the middle and the latter on one that goes to the ring finger. The fibre-bundles of the radial head join with the lateral division of the superficial layer of the ulnar head and are inserted on the tendon of the middle finger nearly as far as the wrist. A small muscle fasciculus of the superficial portion of the ulnar head is usually united by a tendon to the long flexor of the thumb. The deep portion of the ulnar head about the middle of the forearm terminates in large part on the volar surface of the dense tendinous band above mentioned. From this in turn two muscle bellies arise. One of these is inserted in a bipenniform manner on a tendon going to the index finger, the other on a tendon going to the little finger. A muscle fasciculus also usually passes from the region of the tendon band to that portion of the superficial fasciculus which terminates on the tendon of the ring finger. The four tendons pass together through the carpal canal under the transverse carpal (anterior annular) ligament, those to the middle and ring fingers lying at first superficial to the other two. The tendons then diverge, and each tendon, together with and above a tendon of the flexor profundus, passes over the metacarpo-phalangeal joint into an osteo-fibrous canal on the palmar surface of the first phalanx of the finger for which it is destined. Here the tendon becomes flattened about the round tendon of the flexor profundus. Opposite the middle of the phalanx the tendon divides into two slips, between which the tendon of the flexor profundus passes. The divided halves of the sublimis tendon fold about the profundus tendon so that their lateral edges come to meet in the mid-line beneath this tendon opposite the phalangeal joint (figs. 375, 376). They then again separate, extend distally, and are attached one on each side into a ridge at the middle of the lateral border of the second phalanx. The tendons are also attached by vincula tendinum, a ligamentum breve, between the tendon and the head of the first phalanx and the joint, and a ligamentum longum, between the tendon and the volar surface of the first phalanx. Nerve-supply. — Before the median nerve passes between the two heads of the pronator teres a branch arises which accompanies the nerve through the pronator and sends several branches into the proximal third of the ulnar head of the muscle. As the median nerve passes beneath the muscle, one or more branches are given to the radial head, and a long branch is given to the fasciculus of the second and from this one to that of the fifth digit. Occasionally, the median nerve in the distal third of the forearm gives rise to branches for these fasciculi. The nerve fibres arise from the seventh and eighth cervical and first thoracic nerves. Action. — Chiefly to flex the second phalanx of each finger on the first; secondarily, to flex the fingers on the hand and the hand on the forearm. 400 THE MUSCULATURE Relations. — The belly of the muscle is covered by the pronator teres, flexor carpi radialis, and palmaris longus, but is superficial along a narrow strip between the flexor carpi ulnaris and the palmaris longus, and on each side of the tendon of the flexor carpi radialis. The muscle rests on the flexor pollieis longus and flexor digitorum profundus, the median nerve (see de- scription given above) and ulnar vessels. The median nerve emerges from beneath the radial border of the muscle in the lower third of the forearm. In the palm the tendons lie beneath the Fig. 372. — Front of the Forearm: Third Later of Muscles. Brachio-radialis Muscles of the first and second ,^ Tendon of flexor digitorumlongus Flexor digitorum brevis Abductor hallucis Flexor hallucis longus Flexor hallucis brevis First lumbrical Tendon of adductor hallucis ^-i-W...!.^ the tendon of the long flexor passes, while the tendon of the short flexor becomes attached to the base of the second phalanx. The arrangement is essentially Uke that described at length for the flexors of the fingers (p. 401). Nerve-supply. — From the medial plantar nerve by a branch which enters the middle third of the deep surface near the medial margin of the muscle. Action. — It is a strong flexor of the second row of phalanges. Relations. — The short flexor is sejiarated from the abductors of the big toe and little toe by strong intermuscular septa (p. 492), and from the long flexor tendons and the quadratus plantaj (flexor accessorius) by a transverse septum in which the lateral plantar vessels and nerve cross the foot. In its distal two-thirds it is separated from the plantar fascia by loose tissue. Variations.— The muscle shows a tendency toward reduction, one or more of its fasciculi being frequently absent, and occasionally the whole muscle. The fasciculus for the fifth toe is absent in about 20 per cent, of bodies (Le Double). When a fasciculus is absent, its tendon is usually replaced by an accessory tendon from the long flexor. The muscle or its tendons may be more or less fused to the tendons of the flexor digitorum longus. MUSCLES OF GREAT TOE 495 b. Muscles Attached to the Tendons op the Flexor Digitoeum LoNGUs (fig. 420) The muscles belonging in this group are the quadratus plantae (flexor ac- cessorius), a flat, quadrangular, bicipital muscle which runs from the medial and plantar surface of the body of the calcaneus to the dorso-lateral margin and deep surface of the long flexor tendon; and the lumbrlcales, four slender bipinnate muscles which run from the medial sides of the digital slips of the tendon to the medial sides of the four more lateral toes. The quadratus aids the long flexor muscle; the lumbricales extend the last two phalanges and flex the first phalanx of each of the digits to which they pass. The lumbrical muscles correspond to those of the hand. The quadratus is not there represented. The nerve-supply is from the lateral (external) plantar nerve except that for the first lumbrical muscle which gets its supply from the medial (internal) plantar. The quadratus plantae (flexor accessorius) (fig. 420). — This muscle arises by two heads- The lateral head springs by an elongated tendon from the calcaneus in front of the lateral process of the tuber, and from the lateral margin of the long plantar hgament. The medial head arises directly from the medial surface of the body of the calcaneus as far back as the medial process of the tuber calcanei, and from neighbouring hgaments. Structure and insertion. — The two heads are separated at their origin by a short triangular space. They soon fuse to form a single beUy, but the fibre-bundles of each head in the main are separately inserted. Those from the lateral head diverge to be attached to the lateral margin of the flexor tendon. Those from the medial head are inserted on a tendon that begins on the medial margin and deep surface of this head, becomes broader, and is inserted as a flat aponeurosis on the deep surface of the flexor tendon. There are great individual varia- tions in the structure of this muscle. The flbres of either part may be inserted with those of the other part. Nerve-supply. — From a branch of the lateral plantar nerve which passes obliquely across the superficial surface of the muscle parallel with the tendon of the flexor digitorum longus. _ Relations. — The muscle Ues in a fascial compartment with the long flexor tendons. This compartment is bounded on each side by intermuscular septa, deeply by the tarsus, and plantar- ward by a septum which intervenes between it and the flexor digitorum brevis, and in which the lateral plantar nerve and vessels cross to the lateral side of the foot. Action. — It assists the long flexor tendon in flexing the toes. It makes the direction of traction on the toes parallel with the long axis of the foot. Variations. — It is frequently reduced in size. The lateral head is not infrequently missing, the medial head or the whole muscle much more rarely. The mode of attachment to the tendon varies. It may be inserted in part or wholly into the long flexor of the great toe. It may receive, in about one body in twenty (Wood), an accessory slip of origin from the fibula, one of the muscles of the leg, the fascia of the leg or foot, or the medial surface of the calcaneus, etc. The lumbricales. — The three lateral muscles arise from the contiguous sides of the digital tendon-slips of the flexor digitorum longus in the angles of division. The first lumbrical arises on the medial margin of the tendon to the second toe. The fibre-bundles of each muscle con- verge on both sides of a tendon which becomes free near the metatarso-phalangeal joint and is attached to the medial side of the first phalanx of the toe to which the muscle belongs. A tendi- nous expansion is sent into the aponeurosis of the extensor muscle. Nerve-supply. — The three lateral lumbrical muscles are most frequently supplied by branches of the deep ramus of the lateral plantar nerve, the medial by the first common plantar digital branch of the medial plantar nerve. The latter nerve may supply the two more medial muscles or the more medial muscles may receive a double supply. The branches of the lateral plantar nerve enter the deep surfaces of the muscles in the middle third. The branches of the medial plantar enter the medial borders of the muscles near the junction of the proximal and middle thirds. Relations. — The lumbrical muscles lie in a plane with the long flexor tendons deeper than the flexor brevis tendons and superficial to the adductor hallucis. The deep branches of the lateral plantar nerve and vessels pass across their deep surface; superficial branches of both plantar nerves across the superficial surface. Action. — To extend the last two phalanges of the toes and to flex the first. Variations. — One or more of the muscles may be absent. Sometimes a muscle is doubled. This is more frequently the case with the third and fourth muscles. The first may arise wholly from the tendon of the posterior tibial muscle or from this and the Ions flexor of the big toe. The third lumbrical may arise from the flexor digitorum brevis. The second and fourth lumbricals may be inserted into the tendons of the flexor digitorum brevis. c. Intrinsic Muscles of the Great Toe (figs. 419-421) These muscles are the abductor, flexor brevis, and adductor. Of the three muscles, the first two lie in the medial fascial compartment, while the last lies in the middle compartment covered by the flexor digitorum longus and its associated muscles. 496 THE MUSCULATURE The abductor hallucis (fig. 419), the largest and most superficial of these muscles, lies on the border of the sole medial to the short flexor muscle. It passes from|the calcaneus across the tendons of the long flexor muscles, and is inserted into the medial side of the base of the first phalanx of the great toe and into the medial side of the long extensor tendon. It is partly fused to the medial belly of the flexor hallucis brevis. The flexor hallucis brevis (fig. 421) is a bicaudal muscle which lies over the first metatarsal. It arises in the region of the cune- iform bones and is inserted on each side of the base of the first phalanx. Between Fig. 420. — Second Layer of the Muscles op the Sole. Origin of abductor digit! V Part of abductor digiti V Flexor digiti V \<\ Abductor digiti V Lumbricales Flexor digitorum brevis Abductor hallucis Quadratus plantEe Flexor digitorum longus Flexor hallucis longus Flexor hallucis brevis Adductor hallucis Abductor hallucis Tendon of flexor digitorum brevis its two bellies and insertions runs the tendon of the long flexor of the great toe. Proximally and medially the flexor brevis is crossed by the abductor hallucis. Its tendons are fused with those of the abductor and the oblique head of the ad- ductor. The adductor hallucis (fig. 421) is composed of two distinct heads, an oblique and a transverse. The oblique head extends from the long plantar liga- ment under cover of the tendons of the flexor digitorum longus and the lumbrical muscles to the lateral side of the base of the first phalanx of the great toe. Its tendon of insertion is joined by the transverse head, which arises from the capsules of the third to the fifth metatarso-phalangeal joints. Beneath the adductor lie the more medial interosseous muscles. These muscles perform not only the functions indicated by their names, but also extend the second phalanx. They correspond fairly well with those of the thumb. The opponens is not normally present in the foot. The nerve supply for the adductor is from the lateral (external) plantar nerve; that for the other muscles is from the medial (internal) plantar. The abductor hallucis (fig. 419). — Origin. — From (1) the medial process of the tuber calcanei; (2) the deep surface of the neighbouring plantar fascia; (3) the laoiniate (internal FLEXOR HALLUCIS BREVIS 497 annular) ligament; (4) the septum between the muscle and the flexor digitorum brevis; and (5) a fibrous arch which extends on the deep surface of the muscle over the plantar vessels and nerves and the long flexor tendons from the calcaneus to the navicular bone. Structure. — From the medial process of the tuber calcanei a tendinous band passes to the deep, lateral side of the muscle. Numerous tendinous bands arise from the other areas of origin. The fibre-bundles arise from these tendons and directly from the fibrous arch. They are attached in a penniform manner to numerous tendinous slips which extend far up in the muscle. These slips become graduahy fused into a tendon which appears on the superficial plantar aspect of the muscle. Opposite the distal half of the first metatarsal bone the tendon leaves the belly of the muscle and becomes closely bound to the medial belly of the flexor hallucis brevis. Fig. 421. — Third Layer of the Muscles op the Sole. Part of abductor digiti V Flexor digiti V brevi: Tendon of flexor digitorum longus. Flexor hallucis longus Flexor digitorum longus Tibialis posterior Flexor hallucis brevis Adductor hallucis (caputobliquum) Insertion. — In conjunction with the tendon of the medial belly of the flexor brevis into the base of the first phalanx. It usually sends an expansion to the extensor tendon. Nerve-supply. — A branch from the medial plantar nerve usually enters near the middle of the lateral border of the muscle. Relations. — It is covered by the plantar fascia and is separated from the muscles of the median compartment by the medial intermuscular septum. It crosses the tendons of the tibialis anterior, tibiahs posterior, flexor digitorum longus, and flexor hallucis longus muscles and the plantar vessels and nerves. The flexor hallucis brevis (fig. 421). — Origin. — From a tendon attached to the first (in- ternal), second and third cuneiform bones. The more lateral of its fibres are continued into the plantar calcaneo-cuboid Ugament and the more medial into the expansion of the tendon of the posterior tibial muscle. Structure and insertion. — The fibre-bundles give rise to two belHes, a medial and a lateral. Those of the medial belly pass obUquely medially to be inserted into the tendon of the abductor hallucis, and by a short tendon fused with this into the medial side of the plantar surface of the base of the first phalanx. This tendon contains a sesamoid bone. Those of the lateral converge upon the tendon of the oblique head of the adductor, and the two muscles are inserted by a common tendon, which contains a sesamoid bone, into the lateral side of the plantar surface of the base of the first phalanx. 498 THE MUSCULATURE Nerve-suy-ply. — A branch from the medial plantar (or first plantar digital) nerve divides over the plantar surface of the muscle and gives a twig to each belly near the middle third. Rarely the lateral belly may receive a branch from the lateral plantar nerve. Relations. — The abductor halluois covers it medially; the tendon of the flexor hallucis longus passes between its two heads. Branches of the medial plantar vessels and nerve lie on its superficial surface. The adductor hallucis (fig. 421). — The oblique head. — Origin. — From (1) the tuberosity of the cuboid and the sheath over the tendon of the peroneus longus muscle; (2) the plantar calcaneo-cuboid hgament; (3) the third cuneiform; (4) the bases of the second and third meta- tarsals and (5) a fi^brous arch which extends from the plantar calcaneo-cuboid Ugament to the interosseous fascia. Structure and insertion. — From short tendon-slips the fibre-bundles pass forward to form a thick, fusiform belly which is attached in a bipeuniform manner to a flat tendon. The tendon begins about the middle of the plantar surface of the muscle and is inserted in common with that of the flexor brevis into the lateral side of the plantar surface of the base of the first phalanx, and by a sUp into the aponeurosis of the long e.xtensor muscle on the back of the big toe. Nerve-supply. — A branch from the deep ramus of the lateral plantar nerve enters the middle third of the lateral border of the muscle on its deep surface. The transverse head arises from the joint-capsules of the third, fourth, and fifth metatarso- phalangeal joints and from the transverse capitular hgaments. Structure and insertion. — Of the three fasciculi, that to the little toe Hes nearest the heel, that to the middle toe the most distally. The fibre-bundfes take a nearly parallel course to be attached to tendon-shps which are fused into a common tendon that sphts and passes on each side of the tendon of the obUque head and is inserted into the sheath of the tendon of the long flexor of the great toe (Leboucq). Nerve-supply. — A branch from the deep ramus of the lateral plantar nerve enters the middle third of the deep surface of the muscle. Relations. — The adductor hallucis is crossed superflciaUy by the tendons of the flexor digitorum longus and by the lumbrical muscles. On its deep surface he the interosseous muscles, and the deep plantar vessels and nerves. Action. — The actions of the muscles of this group are indicated by the names of the individ- ual muscles. The abductor and the obhque head of the adductor are also flexors of the first phalanx. All the muscles of the group aid in extending the second phalanx. The transverse head of the adductor serves to draw together the heads of the metatarsals after they have been separated by the weight of the body during the tread. Variations. — The extent of fusion of the abductor and adductor with the two heads of the short flexor varies considerably. The' abductor may receive an accessory fasciculus from the medial border of the foot. Either the adductor or the flexor brevis may send a tendon to the base of the first phalanx or to the short flexor tendon of the second toe. The adductor shows frequent variations in relation to its metatarsal attachments, owing to the fact that originally a fasciculus from the body of the second (and third) metatarsal was probably normally present and the transverse head was more developed (Leboucq). The opponens hallucis is a fasciculus occasionally found which extends from the short flexor or the medial intermuscular septum to the body of the first metatarsal. This muscle is normal in some monkeys. An adductor digiti secundi has been seen to arise from various sources and become attached to the lateral side of the plantar sm-face of the base of the first phalanx of the second toe. This muscle may be fused with the oblique adductor. A corresponding muscle is found normally in some apes, and in some of the lower animals there is a special adductor for each toe. d. Intrinsic Muscles of the Little Toe (figs. 419-421) In this group belong three muscles, an abductor, a flexor and an opponens. The largest of these, the abductor digiti quinti (fig. 419), extends superficially over the lateral margin of the foot from the lateral side of the tuber calcanei to the base of the little toe. The flexor digiti quinti brevis (fig. 421) is a small, flat muscle ,which lies on the plantar surface of the fifth metatarsal. The opponens is a small muscle lying lateral to this. The two, which are often fused, arise from the cuboid. The flexor brevis is inserted into the plantar side of the base of the first phalanx of the little toe. The opponens is inserted into the lateral surface of the metatarsal. The abductor corresponds with the abductor of the little finger. The opponens and flexor brevis correspond probably with the deep part of the opponens of the little finger. The nerve supply is from the lateral plantar nerve. The abductor digiti quinti (fig. 419). — -Origin. — From (1) the lateral process of the tuber calcanei and the lateral and plantar surface of the body of the bone in front of this; (2) the lateral intermuscular septum; (3) the deep surface of the lateral plantar fascia, including the fibrous band extending from the calcaneus to the lateral side of the base of the fifth metatarsal bone. Structure. — The fibre-bundles run obhquely to a flat tendon of insertion. This begins within the muscle near the calcaneo-cuboid joint, soon emerges on the medial side of the deep surface, and becomes free near the metatarso-phalangeal joint. Considerable individual variation in structure is found. Insertion.- — On the lateral surface of the first phalanx of the httle toe and the metatarso- phalangeal capsule. Often a shp is sent to the extensor tendon. While usually the muscle INTEROSSEUS MUSCLES 499 glides over the tuberosity of the fifth metatarsal, it frequently sends a second fasciculus to be attached to this bone (abductor ossis metatarsi quinti) . A special fasciculus from the tuberosity often constitutes the lateral margin of the muscle. Nerve-supply. — The nerve arises from the lateral plantar. It may be distributed either near the deep or the superficial surface of the muscle. The former appears to be the case when the muscle is slightly developed. The chief intramuscular branches then extend across the middle third of the constituent fibre-bundles near the deep surface. In case the calcaneo-meta- tarsal bundles are well developed, the nerve enters the proximal margin of the muscle and its chief branches extend across the middle third of the more superficial muscle-bundles, finally terminating in the distal margin of the muscle. Relations. — It is ensheathed by the plantar fascia and the lateral intermuscular septum. It lies superficial to the quadratus plantoe (flexor accessorius), the opponens and flexor Ijrevis of the Mttle toe, the long plantar hgament, and the tendon of the peroneus longus muscle. The flexor digiti quinti brevis (fig. 421). — Origin. — From the sheath of the peroneus longus, the tuberosity of the cuboid, and (3) the base of the fifth metatarsal. Structure and insertion. — The fibre-bundles take a nearly parallel course, although the belly is slightly fusiform. They are attached by short tendinous bands to the base of the first phalanx of the little toe, the capsule of the corresponding joint, and the aponeurosis on the dorsal surface of the toe. Nerve-supply. — A branch of the superficial ramus of the lateral plantar nerve sends twigs to the middle third of the plantar surface of this and the following muscle. Relations. — It is covered medially by the plantar fascia, laterally by the abductor of the fifth toe. Medially it lies superficial to the third plantar interosseous muscle. The opponens digiti quinti. — This muscle arises from the sheath of the peroneus longus and the tuberosity of the cuboid by a slender tendon which passes over the tuberosity of the fifth metatarsal and gives rise to fibre-bundles which are inserted on the lateral surface of the fifth metatarsal. Nerve-supply. — From branches of the nerve to the flexor brevis. Relations. — It is covered by the abductor of the fifth toe. Actions. — The abductor and flexor brevis abduct the little toe and flex the first phalanx. They act as extensors of the second phalanx. The opponens serves to draw the little toe medi- ally in a plantar direction. Variations. — The muscles of this group may be more or less completely fused. The abduc- tor, in addition to the variations mentioned above, may send tendons to the third and fourth metatarsals. The opponens is frequently missing. The abductor accessorius digiti quinti is a rare muscle which arises from the lateral process of the tuber of the calcaneus and is inserted into the lateral surface of the base of the first phalanx of the httle toe. e. The Interosseous Muscles (fig. 422) Two groups of interosseous muscles are recognised, a dorsal and a plantar. The dorsal are the larger and fill the interspaces. The first two are inserted into each side of the base of the first phalanx of the second toe; the third and fourth into the lateral sides of the bases of the first phalanges of the third and fourth toes. The plantar interossei lie on the medial side of the ventral surfaces of the third, fourth, and fifth metatarsals, and are inserted each on the medial side of the base of the first phalanx of the corresponding toe. In the hand the axis about which the interosseous muscles are arranged passes through the middle finger, in the foot through the second toe. The nerve-supply is from the lateral plantar nerve. The interossei dorsales. — Each of the three lateral dorsal interosseous muscles arises from — (1) the sides of the shaft and the plantar surface of the bases of the metatarsal bones bounding the space in which it lies; (2) from the fascia covering it dorsally; and (3) from fibrous prolonga- tions from the long plantar hgament. The first has a similar origin except that it is attached medially to the base of the first metatarsal and to a fibrous arch extending from the base to the head. Structure. — The component fibre-bundles of each muscle are inserted bipinnately on a ten- don which begins high in the muscle and becomes free near the metatarso-phalangeal joint. Insertion. — The first and second on each side of the base of the first phalanx of the second toe. The third and fourth on the lateral side of the bases of the proximal phalanges of the third and fourth toes. Each tendon is adherent to the capsule of the neighbouring joint. They send no well marked processes to the extensor tendons, as do those of the hand. The interossei plantares. — Each plantar interosseus arises — (1) from the proximal third of the medial plantar surface of the shaft and from the base of the metatarsal on which it Ues; and (2) from expansions of the long plantar hgament. Structure and insertion. — The obliquely placed fibre-bundles are longer than those of the dorsal interossei, and are inserted in a tendon which hes near the medial border of the muscle, becomes free near the metatarso-phalangeal joint, and is inserted into a tubercle on the medial side of the base of the first phalanx of the digit to which it goes. Nerve-supply. — From the deep branch of the lateral plantar nerve several rami are given ofi for the interossei. The nerve of each muscle enters the plantar surface in the proximal third. The interosseous muscles of the foiirth interspace, however, are usually supplied by a branch from the superficial ramus of the lateral plantar nerve. 500 THE MUSCULATURE Relations. — -The interosseous muscles are covered on the plantar surface by a thin fascia on which the deep branches of the lateral plantar nerve and vessels run. The first dorsal inter- osseous adjoins mediaOy the flexor hallucis brevis and laterally on the plantar surface of the second metatarsal, adjoins the second dorsal interosseous. Dorsal and plantar interossei then alternate across the plantar surface of the foot until the fifth metatarsal is reached. Here the third plantar interosseous adjoins the flexor brevis of the little toe. Fig. 422. — Fourth Layer op the Muscles op the Sole. Peroneus longus Plantar interossei Dorsal interossei Action. — The chief axis of the foot may be taken to extend through the second toe. The dorsal interosseous muscles abduct — pull the digits to which they are attached away from this axis; the plantar interosseous muscles adduct — pull the digits toward the axis. The interossei all flex the first row of phalanges. Variations. — The second dorsal interosseous may have no attachment to the third metatarsal. BURS^ B. intermetatarsophalangeae. — Four bursse between the neighbouring sides of the heads of the metatarsal bones and dorsal to the transverse capitular ligaments. B. mm. lumbricalium. — Between the ends of the tendons of the lumbrioal muscles and the transverse capitular hga- ments. The three medial are more constant than the lateral. For other bursas in the foot, see pp. 483 and 491. MUSCLES GROUPED ACCORDING TO- FUNCTION The exact functions of many of the muscles have not yet been decisively determined. Anatomical studies, the construction of mechanical models, the electrical stimulation of the musculature, and observation of the muscular activities of normal individuals and of individuals in whom given muscles or sets of muscles are absent or paralysed, have all proved valuable methods of investigation, but each method has its drawbacks, and knowledge of the part actu- ally played by individual muscles in the normal activities of the body is as yet merely approxi- FUNCTIONS OF MUSCLES 501 mate. Owing to the influence of gravity, the relations of other muscles to the skeleton, and similar factors, a given muscle may perform functions which would not be deduced from a simple study of the relations of the muscle to the skeleton. Thus the ihacus serves to flex not only the hip, but also the knee, and the hamstring muscles may flex the hip while flexing the knee. The functions ascribed to various muscles in the following tables, although an attempt has been made to base them upon the more recent work on the action of the muscles, must be taken to be merely approximately correct. So far as possible the muscles are given in order of their power in effecting the various movements. In this we have utilized chiefly the work of R. Fiok: "Anatomie und Mechanik der Gelenke unter Berticksichtigung der bewegenden Muskeln" in von Bardeleben's Handbuch der Anatomie des Menschen. (In this table have been included not only the voluntary muscles, described in the preceding section, but also several described in other parts of the book. 1. Facial muscles. These serve essentially to contract the various visceral orifices of the head or to retract the tissue surrounding them. Ear. Retractors: auricularis anterior, superior, and posterior. Orbit. (a) Retractor: Epicranius (occipito-frontalis). The levator palpebrse superioris, innervated by the third cranial nerve, serves to raise the upper lid of the eye. (6) Contractors: orbicularis oculi, corrugator, and procerus. Nasal orifice. (o) Dilators: angular head of the quadratus labii superioris, transverse portion of the nasahs, and the dilatores naris. (6) Contractors: pars alaris of the nasalis and the depressor septi nasi. Oral orifice. (a) Retractors: Upward: zygomaticus, quadratus labii superioris, caninus. Lateralward: zygomaticus, risorius, platysma, triangularis, bucci- nator. Downward: triangularis, quadratus labii inferioris, platysma. (6) Contractors: orbicularis oris, compressor labii, incisivus labii inferioris and superioris. (c) Protractors of the lips : incisivus labii inferioris and superioris, mentalis. 2. Muscles acting on the eyeball (see Section on Eye). To adduct the pupil: rectus medialis. To abduct the pupil: rectus lateralis. To direct the pupil upward: rectus superior, in association with the obhquus inferior. To direct the pupil downward: rectus inferior, in association with the obliquus superior. 3. Muscles acting on the lower jaw. (a) To raise it: masseter, temporal, internal pterygoid. (6) To lower it: external pterygoid, digastric, mylo-hyoid, genio-hyoid, and the infrahyoid muscles. The weight of the jaw also plays a part in this movement. (c) To protract it: external pterygoid, internal pterygoid, masseter and the ante- rior part of the temporal. (d) To retract it: the inferior dorsal portion of the temporal and the digastric. (e) To produce lateral movements: the external pterygoid acting on one side rotates the chin and carries the jaw toward the opposite side. The rotation may be aided by the digastric of the opposite side. The masseter draws it slightly toward the side on which the muscle lies. This action of the masseter is counterbalanced by the internal pterygoid (Riegner). 4. Muscles acting on the hyoid bone. (a) To elevate it: digastric, stylo-hyoid, stylo-glossus, mylo-hyoid, genio-hyoid, genio-glossus, hyo-glossus, and the middle constrictor of the pharynx. (6) To depress it: thyreo-hyoid, sterno-hyoid, omohyoid, sterno-thyreoid. (c) To protract it: genio-glossus (inferior portion), genio-hyoid, anterior belly of digastric, and the mylo-hyoid. (d) To retract it: posterior belly of digastric, stylo-hyoid, and the middle con- strictor of the pharynx. 5. Muscles acting on the larynx (see Section IX). (o) To elevate it: thyreo-hyoid, stylo-pharyngeus, pharyngo-palatinus, the in- ferior constrictor of the pharynx, and the elevators of the hj'oid bone. (6) To depress it: sterno-thyreoid, sterno-hyoid, and omo-hyoid. (c) To approximate the vocal cords: crico-arytenoideus lateralis; vocalis; thjTeo-arytenoideus, arytenoideus transversus. (d) To make the vocal cord tense: crico-thj'reoideus. (e) To widen the rima glottidis: crico-arytenoideus posterior. (/) To shorten and thicken the vocal cords: thyreo-arytenoideus (externus), vocalis. 502 THE MUSCULATURE (g) To constrict the aditus and vestibule of the larynx: aryepiglotticus, thyreo-arytenoideus. (h) To widen the aditus and vestibule of the larynx: thyreo-epiglottideus 6. IMuscles acting on the tongue (see Section IX). (o) To elevate it: stylo-glossus (especially along the sides), glosso-palatinus, glosso-pharyngeus, and the elevators of the hyoid bone. (6) To depress it: genio-glossus (in the centre), hyogiossus (at the sides), chondroglossus, and the depressors of the hyoid bone. (c) To protrude it: geniq-glossus (middle and inferior portions). (d) To retract it: genio-glossus (anterior portion), stylo-glossus, chondro- (e) To shorten it and make it bulge upwards: longitudinalis superior and inferior. (/) To narrow it and make it bulge upwards: transversus Unguse. (g) To flatten it: verticalis linguse. When the muscles work symmetrically, these movements are symmetrical; when they do not work symmetrically, the tongue is moved from side to side, rotated, etc. 7. Muscles acting on the palate and pharynx (see Section IX). (a) To narrow the pharyngeal opening of the tuba auditiva (Eustachian tube) : levator veli palatini. (6) To widen the isthmus of the tuba: levator veli palatini. (c) To open the tube: tensor veli palatini, pharyngo-palatinus. (d) To raise and shorten the uvula: m. uvulae. (e) To depress the soft palate: glosso-palatinus, pharyngo-palatinus. (f) To make tense the soft palate: tensor veli palatini. (g) To lift the soft palate: levator veli palatini. (h) To approximate the glosso-palatine arches (anterior pillars of the fauces): glosso-palatinus. (i) To approximate the pharyngo-palatine arches (posterior pillars of the fauces): pharyngo-palatinus, superior constrictor of the pharynx. {j) To constrict the pharynx: superior, middle, and inferior constrictors. (k) To widen the pharynx: stjdo-pharyngeus and the muscles which protract the hyoid bone. (I) To elevate the pharynx: stylo-pharyngeus, pharyngo-palatinus. 8. Muscles acting on the head. (a) To flex it: the supra- and infrahyoid muscles, rectus capitis anterior, longus capitis, rectus capitis lateralis. (6) To extend it: sterno-cleido-mastoid, trapezius, splenius capitis, longissimus capitis, semispinalis capitis, obliquus capitis superior, rectus capitis posterior major and minor. When the hyoid bone and lower jaw are fixed by contraction of the hyomandibular and infrahyoid muscles, the posterior beUy of the digastric aids the extensors of the head in opening the mouth. (c) To bend it laterally: sterno-cleido-mastoid, rectus capitis lateralis, splenius capitis, longissimus capitis, semispinalis capitis, obliquus capitis superior. (d) To rotate it: sterno-cleido-mastoid, trapezius, splenius capitis, longissimus capitis, semispinalis capitis, obhquus capitis superior and in- ferior, rectus capitis posterior major. 9. Muscles acting on the spinal column. (o) To flex it: sterno-cleido-mastoid, longus colli, longus capitis, psoas major and minor, scaleni, rectus abdominis, obhquus abdominis externus and internus, the crura of the diaphragm, levator ani, and the coccj'geus. . (6) To extend it: splenius capitis, splenius cervicis, spinahs, sacro-spinaHs, semispinalis dorsi, cervicis and capitis, multifidus, rotatores, interspinales, intertransversarii, levatores costarum, quadratus lumborum. (c) To bent it laterally and extend it: quadratus lumborvim, splenius, iliocostalis, longissimus dorsi, cervicis and capitis, semispinales, multi- fidus, rotatores, levatores costarum, intertransversarii. (d) To bend it laterally and flex it: scalene, sterno-cleido-mastoid, obliquus abdominis externus and internus, intercostales, psoas major and minor. When the arm and shoulder girdle are fixed the trapezius, levator scapulae, latissimus dorsi and rhomboids aid abduction. (e) To rotate it to the right: r. internal oblique, 1. external oblique, r. splenius, 1. sterno-cleido-mastoid, r. longissimus capitis, r. ilio-costalis, 1. semispinahs, 1. multifidus, 1. rotatores (except the lumbar) , longus colli (r. above, 1. below), 1. serratus anterior and rhom- boids, r. levatores costarum. FUNCTIONS OF MUSCLES 503 10. Muscles of respiration. Quiet inspiration: the external intercostals, interoartilaginous parts of internal interoostals, diaphragm. Enforced inspiration: in addition to the muscles mentioned above, the scaleni, sterno-cleido-mastoid, serratus posterior superior and inferior, rhomboids, serratus anterior, latissimus dorsi, subclavius, pectoralis major and minor, and the extensors of the spinal column, the trapezius and the levator scapuli. Quiet expiration: interosseous pai'ts of internal intercostals, subcostales, and transversus thoracis. Enforced expu-ation: in addition to the muscles mentioned above, the abdominal muscles, ilio-costalis lumborum and dorsi, longissimus dorsi, and the quadratus lumborum. The chief muscles of respiration are the intercostals; the diaphragm plays a minor part (Fick). 11. Muscles acting on the abdomen. (a) Constriction of the abdominal cavity: obliquus abdominis externus and internus, the transversus and rectus abdominis, and the dia- phragm, levator ani, and coccygeus. (6) Reduction of pressure in the abdominal cavity: the muscles of inspiration, with the exception of the diaphragm, serve to lessen the com- pression of the abdominal viscera. 12. Action of the muscles of the perineal region. (a) To close anal canal: sphincter ani externus. (&) To constrict the anal portion of the rectum: levator ani (pubo-coccygeal portion). (c) To constrict the bulbus urethrae and the corpus cavernosum urethrse (corpus spongiosum) : bulbo-cavernosus. (d) To elevate the prostate gland: levator ani. (e) To constrict the vagina: bulbo-cavernosus, levator ani (pubo-coccygeal por- tion), constrictor vaginse. (f) To cause erection of penis and clitoris: ischio-cavernosus, bulbo-cavernosus, and sphincter urethrae membranaceaj. (g) To compress the urethra and the bulbo-urethral (Cowper's) or the great ves- tibular (Bartholin's) gland: sphincter urethrae membranaceae and the transversus perinei profundus. (h) To support and Uft the pelvic floor : levator ani, coccygeus, transversus perinei profundus and superficialis. 13. Muscles acting on the shoulder-girdle. The two joints acted upon are the sterno-clavicular and the acromio-clavicular. The movements produced consist in lifting and lowering the scapula, carrying it forward and backward and rotating it. (o) Elevation: trapezius (upper portion), levator scapulae, sterno-cleido-mastoid, rhomboidei, pectoralis major (upper sternal part), serratus anterior (middle portion), omo-hyoid. (6) Depression: trapezius (lower portion), pectoralis major (lower portion), pectoralis minor, subclavius, latissimus dorsi, serratus anterior (lower part). The weight of the limb is likewise a factor. (c) Forward movement: serratus anterior, pectorales major and minor. (d) Backward movement: trapezius, rhomboidei, latissimus dorsi. (e) Rotation: Associated with abduction of the arm : serratus anterior" (inferior portion), trapezius. Associated with adduction of the arm: rhomboidei, pectoralis major (pectoral portion), latissimus dorsi, pectoralis minor, levator scapulae. 14. Muscles acting on the arm at the shoulder-joint. (o) To flex it, When the arm is at the side: pectoralis major (upper part), deltoid (anterior part), short head of biceps, coracobrachialis, infraspinatus, long head of biceps, teres minor, subscapularis (upper part), supraspinatus. When the arm is abducted 60°: pectoralis major, deltoid, subscapularis, short head of biceps, coracobrachialis, long head of biceps, infraspinatus, supraspinatus. The movement is aided by the trapezius and the serratus anterior. (6) To extend it, When the arm is at the side: latissimus dorsi, deltoid (posterior part), teres major, subscapularis (lower part), triceps. When the arm is abducted 60°: latissimus dorsi, deltoid, teres major, triceps, teres minor. The upper and middle portions of the trapezius and the levator scapulae play an important part in extension of the arm. (c) To abduct it, When the arm is at the side: deltoid, supraspinatus, long head of biceps, subscapularis, infraspinatus (upper part). When the arm is abducted 60°: deltoid, supraspinatus, infraspinatus (upper part), long head of biceps, short head of biceps. 504 THE MUSCULATURE The siibscapularis is an adductor when the arm is abducted. The inferior part of the serratus anterior and the trapezius are important in abduction of the arm. (d) To adduct it, When the arm is at the side: pectoralis major, latissimus dorsi, deltoid (pos- terior and anterior parts), teres major, triceps, coraoobrachialis, short head of biceps, teres minor, infraspinatus. When the arm is abducted: pectoralis major, latissimus dorsi, teres major, triceps, subscapularis, deltoid (dorsal and ventral parts), coracobrachialis. (e) To rotate it lateral ward (supinate). When the arm is at the side: infraspinatus (upper part), the dorsal part of the deltoid, teres minor, supraspinatus. When the arm is abducted 60°: teres minor, infraspinatus, deltoid (dorsal part), coracobrachialis. (/) To rotate it medialwai-d (pronate). With the arm at the side: latissimus dorsi, pectoralis major, subscapularis, deltoid (ventral part), long head of biceps, teres major, short head of biceps. With the arm abducted 60°: latissimus dorsi, pectoralis major, subscapularis, teres major, deltoid (ventral part). When the arms are raised high the power of rotation at the shoulder becomes slight. 15. Muscles acting on the forearm at the elbow-joint (arranged according to R. Fick). (a) Fle-xion at elbow. Forearm supinated: brachialis, long head of biceps, short head of biceps, brachio-radialis, pronator teres, extensor carpi radiahs longus, flexor carpi radialis, extensor carpi radialis brevis, palmaris longus. Forearm in mid-position or pronated: brachiaUs, long head of biceps, short head of biceps, brachio-radialis, extensor carpi radialis longus, pronator teres, flexor carpi radialis, extensor carpi radialis brevis, palmaris longus. (6) Extension at elbow: triceps (lateral, medial, and long heads), anconeus. (c) Pronation of forearm. Forearm extended: flexor carpi radiahs, pronator teres, pronator quadratus, palmaris longus. Forearm at right angles: pronator teres, flexor carpi radiahs, brachio-radialis, pronator quadratus, extensor carpi radialis longus, palmaris longus. Forearm flexed: pronator teres, brachio-radiahs, flexor carpi radialis, pro- nator quadratus, extensor carpi radiahs longus, palmaris longus. {d) Supination. Forearm extended: short head of biceps, supinator, long head of biceps, brachio-radiahs, extensor carpi radialis longus, abductor poUicis longus, extensor pollicis brevis, extensor pollicis longus, extensor indicis proprius. Forearm at right angles: short head of biceps, long head of biceps, supina- tor, abductor poUicis longus, extensor polhcis brevis, brachio- radialis (in pronation), extensor pollicis longus, extensor indicis proprius. Forearm flexed: short head of biceps, long head of biceps, supinator, ab- ductor pollicis longus, extensor polhcis brevis, extensor pollicis longus, extensor indicis proprius. 16. Muscles acting on the hand at the wrist (arranged according to R. Fick). (o) To flex it: flexor digitorum sublimis, flexor digitorum profundus, flexor carpi ulnaris, flexor pollicis longus, flexor carpi radialis, ab- ductor pollicis longus, palmaris longus. (6) To extend it: extensor digitorum communis, extensor carpi ulnaris, extensor carpi radialis longus and brevis, extensor indicis proprius, extensor pollicis longus. (c) Radial abduction: extensor carpi radialis longus, extensor carpi radialis brevis, abductor pollicis longus, flexor carpi radialis, extensor indicis proprius, extensor pollicis longus, extensor polhcis brevis. (d) Ulnar abduction: extensor carpi ulnaris, flexor carpi ulnaris. 17. Muscles acting on the palm : (a) To_flex the ulnar side: opponens, long and short flexors of the little finger. (h) To extend the ulnar side: extensor carpi ulnaris, extensor digiti quinti. (c) To adduct the ulnar side: third volar interosseous. {d) To abduct the ulnar side: abductor digiti quinti. For action on the radial side see " muscles adting on the thumb." Move- ments of the second, third and fourth metacarpals are produced by the long flexors and the dorsal interosseous muscles. 18. Muscles acting on the thumb. (a) To oppose the thumb: adductor, opponens, flexor brevis, flexor longus, ad- ductor brevis. (6) To repose the thumb: long abductor, short extensor. FUNCTIONS OF MUSCLES 505 (c) To flex all joints: flexor poUicis longus; the carpo-metacarpal and metacarpo- phalangeal joints; flexor brevis, the adductors, abductor brevis; thecarpo-metacarpaljoints: opponens poUicis, abductor longus. (d) To extend: all joints, extensor pollicis longus; the carpo-metacarpal and metacarpo-phalangeal joints, extensor poUicis brevis; the inter- phalangeal joint, abductor brevis, flexor brevis. (e) To adduct: the adductor, flexor brevis, opponens, first dorsal interosseous, extensor longus. (/) To abduct: the long and short abductors. 19. Muscles acting on the fingers. (a) To flex: all the joints, flexor digitorum profundus; all but the last, flexor digito- rum subhmis; the metacarpo-phalangeal joint only, flexor digiti quinti brevis, the lumbrieales, and interossei. (6) To extend the fingers: extensor digitorum communis, extensor indicis pro- prius, extensor digiti quinti proprius; to extend the two inter- phalangeal joints: the lumbrieales, interossei, and frequently the flexor digiti quinti brevis. (c) To abduct from the axis passing through the centre of the middle finger: dorsal interossei, first two lumbrieales, abductor digiti quinti, the long extensor of the fingers. (d) To adduct toward this axis : volar interossei, last two lumbrieales, opponens and flexor digiti quinti brevis. 20. Muscles acting on the pelvis. (o) To flex it: rectus abdominis, obliquus abdominis externus and internus, psoas major and minor. (6) To extend it: sacro-spinalis, multifidus, latissimus dorsi and quadratus lumborum. (c) To bend it laterally and rotate it: abdominal muscles, quadratus lumbo- rum, psoas muscles, and latissimus dorsi acting on one side. 21. Muscles acting on the thigh at the hip-joint (arranged according to R. Fiok). (a) To flex it: ilio-psoas, rectus femoris, adductor longus, adductor brevis, obturator externus, tensor fasciae latae, pectineus, sartorius, gluteus minimus, adductor magnus (upper part), gracilis, quadratus femoris. (6) To extend it: gluteus maximus, adductor magnus (posterior lower part), biceps, semitendinosus, semimembranosus, gluteus medius, piriformis, obturator internus. (c) To adduct it: adductor magnus, gluteus maximus, adductor brevis, adductor longus, quadratus femoris, obturator externus, gracilis, ad- ductor magnus (upper part), pectineus, biceps, semitendinosus, obturator internus and gemelU, semimembranosus. (d) To abduct it: gluteus medius and minimus, the piriformis, rectus femoris, tensor fasciiB latte, sartorius; and when the hip is flexed, the gluteus maximus, obturator internus, and gemeUi. (e) To rotate it medialward: gluteus medius (anterior portion), gluteus minimus, ilio-psoas, adductor magnus (upper part), pectineus, adductor longus, semitendinosus, semimembranosus, tensor fasciae latae. (/) To rotate it lateralward: gluteus maximus, quadratus femoris, obturator internus, piriformis, rectus femoris, adductor brevis, adductor magnus (lower part), biceps, sartorius, obturator externus gracilis, gluteus medius (posterior part). 22. Muscles acting on the leg at the knee-joint (arranged according to R. Fick). (o) To flex it: semimembranosus, semitendinosus, biceps, gastrocnemius, gracilis, sartorius, popHteus. (6) To extend it: quadriceps femoris (the tensor fasciae latae and gluteus maxi- mus through the ilio-tibial band keep the extended leg fixed). (c) To rotate it medialward (when flexed): semimembranosus, semitendinosus, sartorius, popliteus, gracilis. (d) To rotate it lateralward (when flexed) : biceps, tensor fasciae latae. 23. Muscles acting on the foot at the ankle-joint (arranged according to R. Fick). (a) To flex it: tibialis anterior, extensor digitorum longus, peroneus tertius, extensor hallucis longus. (6) To extend it: gastrocnemius, soleus, flexor hallucis longus, peroneus longus, tibialis posterior, flexor digitorum longus, peroneus brevis. (c) To Invert the foot at the inferior articulation of the talus (art. talo-calcanea and talo-calcaneo-navicularis) : gastrocnemius, soleus, tibialis posterior, flexor hallucis longus, flexor digitorum longus, tibialis anterior. (d) To evert the foot at the inferior articulation of the talus : peroneus longus, peroneus brevis, extensor digitorum longus, peroneus tertius, extensor hallucis longus, tibialis anterior. (e) To invert the foot at Chopart's (talo-navicular-calcaneo-cuboid) joint: tibialis anterior, tibiaUs posterior, flexor digitorvmi longus, flexor hallucis longus, extensor hallucis longus. (J) To evert the foot at Chopart's joint: peroneus longus, peroneus brevis, extensor digitorum longus, peroneus tertius. 506 THE MUSCULATURE 24. Muscles acting on the toes (arranged according to R. Fick). (a) To flex: all the joints, flexor hallucis longus, quadrat us plantse, and flexor digitorum longus; the first interphalangeal and the metatarso- phalangeal joints of the four lateral toes, flexor digitorum brevis; the metacarpo-phalangeal joints, the lumbricales, interossei, abductor hallucis, adductor hallucis (oblique head), flexor hallucis brevis, abductor digiti quinti, flexor digiti quinti brevis. (6) To extend; all joints, extensor digitorum longus, extensor hallucis longus, extensor digitorum brevis; the interphalangeal joints, the lumbricales, and the adductors and abductors of the big and little toes. (c) To abduct from an axis passing through the second toe; abductor hallucis, dorsal interossei, abductor digiti quinti, first lumbrical. (d) To adduot toward this axis : adductores hallucis, plantar interossei, three more lateral lumbricals. (e) To draw together the ends of the metatarsals : the transverse head of the ad- ductor of the big toe. References. — For development of the muscular system, consult the list given by W. H. Lewis, Development of the Muscular System, in Keibel and Mall's Human Embryology; for variations: Le Double, Traite cles variations du systeme musculaire de I'homme; for action of muscles: R. Fick, Handbuch der Anatomic und Mechanik der Gelenke unter Berticksichtigung der bewegenden Muskeln, in von Bardeleben's Handbuch, and H. Strasser, Lehrbuch der Muskel und Gelenkmechanik; for the extremities: Frohse und Frankel, Die Muskeln des menschlichen Armes und Beines, in von Bardeleben's Handbuch; for the head and trunk: Eisler, Die Muskeln des Stammes, in von Bardeleben's Handbuch; for the pelvis: Holl, Die Muskeln und Fascien des Beckenausganges. Further references to the literature upon the muscular system may be found in Poirier- Charpy's Traite d'anatomie humaine. SECTION V THE BLOOD- VASCULAR SYSTEM Revised for the Fifth Edition By H. D. senior, M.B., F.R.C.S. PROFESSOR OF ANATOMY, NEW YORK UNIVERSITY THE organs of circulation consist of a system of tubes or vessels which during life are filled with fluid constantly moving in one direction. The major portion of the system is concerned with the continuous distribution of blood throughout the body and is called the haemal or blood-vascular system. A circumscribed part of the hismal circulation is differentiated into a rhythmically contracting propulsory organ called the heart. The minor portion of the system is called the lymphatic system. The lymphatic vessels convey fluid, the lymph, from the tissues to the haemal system. The essential functions of the blood-vascular system are performed by the smallest of all the blood-vessels, the capillaries [vasa capillaria], which form a network pervading practically all the tissues of the body. Blood is carried to and from the capillaries by larger vessels called the arteries and veins respectively. The heart receives blood from the veins and propels it, in turn, into the arteries. One of the primary functions of the blood is the transmission of oxygen from the atmosphere to the tissues. In order to do this the blood must of necessity pass through the respiratory organ before being deUvered to the body at large. In gill-breathing vertebrates, the blood, having received oxygen in its passage through the giUs, passes on directly to the tissues._ The entire circuit is here accomplished by a single continuous chain of vessels in which capillaries occur twice, once in the gills and again in the organs and tissues in general. In man, as in other higher vertebrates, lungs assume the function of the gills. Having received oxygen in the lungs the blood is returned again to the heart before being redistributed throughout the body. There are thus in man two separate circuits or systems of blood-vessels, one traversing the lungs and a second ramifying throughout the body. The former is known as the pulmonary circula- tion; the latter as the systemic. Each has its own arteries, capillaries and veins; the heart is common to both. From the time of birth the heart is longitudinally divided into right and left halves, each of which contains its own independent stream of blood. The blood entering the left side of the heart has issued from the pulmonary circulation and is driven into the systemic; that in the right side, having traversed the systemic circuit, is returned again to the lungs. The heart and blood-vessels have a continuous lining of flattened cells called endothelium ; the hsemal system is, therefore, a closed circuit.* The main thickness of the heart,_ arteries and veins consists of additional tissue developed around the endothelial lining. It is due to this tissue that the blood is continuously delivered to and withdrawn from the capillaries under suitable pressure and velocity. The heart is mainly composed of rhythmically contracting muscle and its valves are so arranged that the contained blood is driven intermittently in one direction only. The walls of the largest arteries are formed to a great extent of elastic tissue, and, being constantly under tension from within, are instrumental in converting the stream, intermittently received from the heart, into a continuous flow. The walls of the medium sized to smallest arteries are mainly muscular. The smallest arteries are microscopic in size and known as arterioles [arteriote]. The muscular arteries are capable of general or local alterations of calibre regulated by the nervous system; they are thus largely concerned in the maintenance of the blood pressure and in the regulation of the volume of blood entering given localities under varying conditions. The veins have much thinner walls than the arteries; the blood in them is under low tension upon which they e.xercise little or no control. When an artery divides, the combined calibre of its branches is greater than that of the vessel itself. Since the arteries divide repeatedly the bed of the blood-stream increases in proportion as the vessels diminish in size. The rate of increase, slow at first, becomes enormous in the arterioles. Conversely, the bed of flow undergoes contraction as the heart is approached from the venous side. The velocity of flow in the capillaries must necessarily be much lower * In the spleen and bone marrow the blood-channels intermediate between the arteries and veins are possible exceptions to this statement, but the essential conditions here are still imper- fectly understood. 507 508 THE BLOOD-VASCULAR SYSTEM than in the great arteries and veins. From the relative slowness of the blood flow in the sys- temic capillaries, it has been estimated that then- total bed is eight hundred times greater than the bed of the main arterial stem. Variations in the course and arrangement of the adult arteries and veins, originally studied by the surgeon for utihtarian purposes only, now furnish one of the most stimulating fields for anatomical research. Text-books can provide, at best, catalogues of the arrangement commonly found in the adult body and of the most ordinary variations. That no text-book description can fit any individual case in all particulars, and that unusual distribution of vessels does not necessarily shorten hfe are among the earhest lessons learned in the anatomical laboratory. The adult vascular pattern is derived from a symmetrical arrangement in the early embryo of which scarcely a trace remains. The intervening changes are so numerous and profound that the general uniformity of vascular distribution Ln different individuals is more remarkable than the occurrence of occasional wide variations from the usual type. In early stages of development all vessels have a similar structure ; they consist, in fact, of a single layer of endothehum. Some vessels, however, are larger than others; these act as arteries or veins (according to the direction of flow) while the smaller channels perform the office of capillaries. The early principal vessels do not necessarily persist, for many of these dwindle or are lost. New channels are meanwhile in continuous process of formation and some of these may, in turn, become main channels. It thus follows that the main vessels of the adult must be looked upon rather as selected channels through a plexus of possible pathways, than as sepa- rate entities which must necessarily conform to given rules of distribution and branching. In time, no doubt, most of the commoner variations from the usual adult type wUl receive a rational explanation; at present enough has been done to indicate the value of the embryo- logical method. The Ust of v.ariations in the arteries and veins respectively is preceded by a brief account of the morphogenesis of these vessels. In the case of the heart anomalies frequently result in early death, so that subjects of devel- opmental irregularities are seldom seen in the anatomical laboratory. The anomahes usually consist in improper development of the septa which normally divide the heart and main ar- terial trunk into their pulmonary and systemic halves. A short account of the morphogenesis of the heart is appended to the description of the adult organ. In the following section the heart and pericardium will first be considered followed by the arteries and veins. A. THE HEART AND PERICARDIUM 1. THE HEART The heart [cor] is a hollow organ principally composed of muscle, the myo- cardium. It is lined internally by endocardium which is continuous with the intima of the blood-vessels. Externally, it is covered by the epicardium, a serous membrane continuous with the serous Hning of the pericardium. The form of the heart, when removed from the body without previous hardening, is that of a fairly regular truncated cone. The base [basis cordis] is poorly circumscribed but corresponds, in a general way, to the area occupied by the roots of the great vessels and the portion of the heart-wall between them. The base of the heart is held in position* chiefly by the great vessels, which are attached to the peri- cardium; the remainder of the organ is capable of free movement within the pericardial cavity. The interior of the heart is longitudinally divided, into right and left cavities, by a septum passing from base to apex. Each cavity is subdivided into an atrium [atrium cordis] and a ventricle [ventriculus cordis], the former receiving the ultimate venous trunks and the latter giving rise to the main arteries. Thus the left atrium receives the four pulmonary veins, and the right atrium the superior and inferior vena cava and the coronary sinus; the aorta issues from the left ventricle and the pulmonary artery from the right. The ventricles, which constitute the major portion of the heart, may be recognised by their very thick walls. The atria have thinner walls and are less capacious than the ventricles; projecting from each is a diverticulum or auricle [auricula cordis]. The auricles (which receive their name from their resemblance to dog's ears) partially embrace the roots of the pulmonary artery and aorta. Orientation of the heart. — The apex of the heart [apex cordis] points forward, to the left and downward. The base is directed backward, to the right and up- ward. The longitudinal axis of the heart forms an angle of about 40° with the horizontal plane and also with the median sagittal plane of the body. * Not necessarily fixed, for during systole the base performs a greater excursion than does the apex. EXTERIOR OF THE HEART 509 The long axis of the heart is therefore slightly more horizontal than vertical, and slightly- more antero-posterior than transverse. The atria are posterior to rather than above the ven- tricles. To arrive approximately at the longitudinal axis, it is necessary to select the central point of the base. By cutting the vessels short in several hearts, hardened by formalin before removal, a point immediately to the left of the left lower pulmonary vein was selected in deter- mining the data above given. A steel pin was passed through this point to the apex cordis, and the angles controlled by frontal and transverse sections of the thorax. Mention of angular measurements of the axis of the heart could be found only in the text-books of Testut and Luschka; the former gives 40° to the horizontal plane, the latter 60° to the mid-sagittal. Luschka's angle appear to be too large; but further investigation in this direction is desirable. Fig. 423. — Steeno-costal Surface op the Heart. Left subclavian artery Left inferior thyreoid vein Left innominate vein Left superior intercostal vein Vestige of left common cardinal Left pulmonary artery Vena cava superior Conus arteriosus Margo obtusus Left ventricle Incisura apicis cordis Size and weight. — In the adult the heart measures about 12.5 cm. (5 in.) from base to apex, 8.7 cm. (31 in.) across where it is broadest, and 6.2 cm. (24 in.) at its thickest portion. In the male its weight averages about 312 gm. (eleven ounces), and in the female about 255 gm. (nine ounces). It increases both in size and weight up to advanced life, the increase being most marked up to the age of twenty-nine years. The proportion of heart-weight to body-weight is about 1:205 in the adult. EXTERIOR OF THE HEART In hearts which have been hardened by injection before removal from the bod}^, the regularity of the heart-cone is disturbed by a well-marked triangular facet, imparted by contact with the diaphragm. This facet is the diaphragmatic surface [facies diaphragmatica], which is directed downward and slightlj- back- ward (fig. 424). It ends abruptly along a sharp margin extending from the apex 510 THE BLOOD-VASCULAR SYSTEM toward the right. This margin is the margo acutus (fig. 423) ; it separates the diaphragmatic surface from the sternocostal surface. The other margin of the diaphragmatic surface is more rounded and shades gradually into the very wide margo obtusus (fig. 423), which passes almost insensibly into the sternocostal surface. The convex sternocostal surface [facies sternocostalis] (fig. 423), directed forward and somewhat upward and to the right, is triangular and bounded below by the margo acutus. To the left it goes over into the margo obtusus along a line extending from the apex of the heart to the root of the pulmonary artery. The margo obtusus corresponds to the rounded left side of the left ventricle. The interventricular sulcus is a slightly marked groove indicating the separa- tion of the ventricles upon the exterior of the heart. It lodges coronary blood- vessels and a moderate quantity of fat which can be seen through the epicardium. Fig. 424. — Base and Diaphragmatic Surface op the Heart. (After His.) Left pulmonary ^ artery Left superior pul- monary vein Left inferior pul- monary vein ^Reflexion of pericardium Coronary sinus ■ Aorta . Superior vena cava . Right pulmonary artery Margo obtusus ^ The anterior part of this groove, sulcus longitudinalis anterior, beginning poste- riorly, runs obliquely over the upper part of the margo obtusus on to the sterno- costal surface. Crossing the margo acutus to the right of the apex, it is continuous with the sulcus longitudinalis posterior upon the diaphragmatic surface. The diaphragmatic surface is formed about equally by the right and left ventricles, and the sterno-costal surface mainly by the right. Where the longitudinal sulcus crosses the margo acutus it produces a slight notch, the incisura (apicis) cordis. The atria are separated externally from the ventricles by the sulcus coronarius. This is a horseshoe-shaped groove well marked below and laterally, and inter- rupted above by the roots of the pulmonary artery and aorta. It lodges the coronary sinus, smaller coronary vessels and fat. ATRIAL PORTION 511 ATRIAL PORTION The atrial portion of the heart is situated behind, and shghtly to the right of and above, the ventricular portion. The separation between the right and left atrium is not indicated behind except in distended hearts (such as that shown in fig. 424) ; in these it is marked by a slight groove connecting the left sides of the superior and inferior venae cavse. In front, the auricles are separated by the deep notch which lodges the aorta and pulmonary artery. A slight groove on the back of the right atrium which connects the right sides of the superior and inferior vense cavse, is the sulcus terminalis (figs. 424, 425) . This represents the right limit of what was, in the embryo, the sinus venosus. It also indicates that the embryonic sinus venosus has become an integral part of the adult right atrium. The superior and inferior cavae have each a nearly vertical direction and join the posterior part of the right atrium above and below, respectively. The coronary sinus runs downward, backward and to the right to join the lower part of the right atrium anterior to the inferior vena cava. The four pulmonary veins run nearly transversely and somewhat forward into the right and left sides of the left atrium. Fig. 425. — Atria Opened Posteriorly to show the Septum Atriorum. Pulmonary artery Aorta Vena cava superior Crista terminalis I ^ ^^ Sulcus terminalis Limbus fossae ovalis (.section) Vena cava inferior Facies diaphragmatica The interior of the atrial portion of the heart is divided into right and left cavities by the septum atriorum. This septum is a composite structure, having been developed (see morphogenesis of the heart) in two independent parts, each forming an incomplete septum in itself. The two incomplete septa, however, partly overlap one another so that, by the lateral fusion at the time of birth, they together produce the impervious structure of the adult heart (fig. 425). Of these septa, the first to be formed is the membranous septum [pars membranacea septi atriorum]. Later there is formed to the right of this the muscular septum, the margin of which forms, in the adult atrium, the greater part of the limbus fossae ovalis. The margin of the membranous septum is recognizable as a fold 512 THE BLOOD-VASCULAR SYSTEM of endocardium on the septal wall of the left atrium; it is called the valvula foraminis ovjilis. Posteriorly into the right atrium [atrium dextrum (fig. 425)], above and below, respectively, open the superior and the inferior vena cava. Upon the septal wall, immediately above the inferior cava is the fossa ovalis, a depression of Fig. 426. — Section op the Ventricles in Systole and Diastole. (After Krehl.) > which the floor is formed by the membranous septum. Surrounding the fossa ovalis except below (indeed producing the fossa) is the limbus fossae ovalis which is continuous anteriorly and below with the valvula venae cavae (inferioris Eustachii). Just anterior to the fossa ovalis is the orifice of the coronary sinus guarded by the valvula sinus coronarii (Thebesii) (fig. 428). Leading from the ATRIAL PORTION 513 front of the atrium forward and slightly downward and to the left is the ostium venosum (right atrio-ventricular orifice) guarded by the tricuspid valve. Above and behind this is the auricle, the exterior of which is in contact medially with the root of the aorta. To the right of the superior and inferior caval orifices there is a vertical ridge, the crista terminalis, which corresponds to the sulcus terminalis on the exterior (figs. 425, 428). The portion of the atrium medial to the crista is smooth and is called the sinus venarum; in the embryo it is separated from the atrial cavity proper by the right and left sinus valves. The crista terminalis marks the original line of attachment of the right sinus valve. The valve itself has disappeared, except at the lower part where it persists as the caval and coronary valves. These valves vary in size considerably in different specimens, and are frequently nethke from numerous perforations. The conversion of a portion of a single valve into two separate valves, which meet at an acute angle, is brought about by an attachment between the sinus valve and an embryonic structure called the sinus-septum. This septum is a ridge dividing the right horn of the sinus venosus from the transverse portion of the sinus (the coronary of the adult) ; it probably con- FiG. 427. — The Interiok op the Ventricles, Anteriok Half. (After His.) ilmonary artery Aortic semilunar valves Anterior papillary of left vent. Muscular ventricu- lar seplum 'Opening into ventricle 'Conus arteriosus Membranous ven- ■ tricular septum, 'Crista supra ven- \ tricularis ■Papillary of conus -Right ventricle Anterior papillary muscle tributes somewhat to the formation of both the coronary and caval valves. The left sinus valve usually disappeai's by blending with the septum atriorum on which it unites with the limbus fossae ovalis; it ooeasionaUy remains partially separate in the adult. The interior of the right auricle and of the portion of the atrium lateral to the crista terminalis is thrown into ridges (musculi pectinati) by prominent bands of the atrial myocardium. The musculi pectinati end abruptly by joining the crista. The orifice of the superior cava has no valve and is directed downward and somewhat forward; below it, on the posterior wall of the atrium, there has been described a tubercle or ridge, the tuberculum intervenostun (Loweri). Apart from the posterior circumference of the superior cava itself and the limbus fossae ovalis, the hiunan heart appears to contain nothing in this region that could be described as a tubercle. With regard to the segregation of the streams entering the foetal right atrium from the superior and inferior cavae, respectively, in which the tubercle of Lower has been supposed to participate, it is to be noted that the fossa ovalis is just above (almost within) the inferior 514 THE BLOOD-VASCULAR SYSTEM caval orifice. Also that the caval opening and the fossal ovalis (containing the foetal foramen ovale) are, in hearts well hardened before removal, situated in a distinct diverticulum to the left of the remainder of the atrium. Between this diverticulum and the atrium proper, the caval valve and the limbus fossa? ovalis form a prominent flange, better marked in the foetus than the adult. Opening into the right atrium, particularly upon the septal and right lateral walls, are numerous /orowiraa venarum minimarum (Thebesii). The left atrium [a. sinistrum] (fig. 425) is to the left and somewhat posterior to the right. It is behind the root of the aorta and its auricle is to the left of the Fig. 428. — Interior of the Right Atrium and Ventricle. The atrio-ventricvdar bundle is dissected out. • Left common carotid artery - Innominate artery Vena cava superior Reflexion 'of pericardium Pulmonary artery Ascending aorta Left pulmonary valve Conus arteriosus Vena cava inferior Part of posterior tricuspid cusp Posterior papillary pulmonary root. Opening into it posteriorly on the right and left sides, re- spectively, are the right and left upper and lower pulmonary veins. The valvula foraminis ovalis forms a more or less distinct crescentic ridge on the septal wall (fig. 425). This may not be attached to the limbus fossas ovalis, in which case there is a communication between the two atria. Absence of lateral adhesion between the two septa atriorum does not necessarily lead to admixture of arterial and venous blood during life. The left ostium venosum (atrio-ventricular orifice) ATRIO-VENTRICULAR VALVES 515 guarded by the mitral valve leads from the anterior part of the atrium forward and shghtly downward and to the left. The interior of the left atrium is smooth ex- cept in the auricle, in which musculi pectinati are well marked. Fig. 429. — Left Ventricle and Part op the Atrium. The aorta is opened through the anterior cusp of the mitral valve. The plainly visible left limb of the atrio-ventricular bundle has been accentuated. Aorta Pulmonary artery Apex of the left ventricle ATRIO-VENTRICULAR VALVES The atrio-ventricular valves (figs. 427, 428, 429, 431) are attached around the venous ostia of the ventricles in such a way as to open freely into the ventricles, but to prevent regurgitation of the blood into the atria during ventricular systole. Each valve is continuous along its line of attachment, but its free edge is notched so as to produce an irregular margin; some of the notches are so deep as to partially divide the valve into cusps. The right atrio-ventricular valve is commonly divided by three deep notches into three cusps; this valve is therefore called the tricuspid [valvula tricuspidalis]. The left is similarly divided into two cusps and is called the bicuspid [v. bicuspidalis] or mitral. The depth of the notches, however, is very variable and there may be an increase or (more rarely) a diminution in the number of cusps; the addition of small subsidiary cusps is quite common. Each valve cusp is tied down to the papillary muscles [mm. papillares] of the ventricle by chordae tendinese. The latter are fibrous cords, generally branched, of varying thickness. The thinnest cords are attached to the free margin of the cusp; those of intermediate thickness to the ventricular surface a few millimetres from the margin, and the thickest to the ventricular surface 516 THE BLOOD-VASCULAR SYSTEM near the attached margin. The valves are smooth and glistening on the atrial aspect, but rough and fasciculated, from the attachment of the chordae, on the ventricular. The cusps of the mitral valve are called anterior and posterior; those of the tricuspid, anterior, posterior and medial. Each cusp receives chorda from more than one papillary muscle and each papillary muscle sends chordse to more than one cusp. The chordse tendinese of the mitral valve are thicker than those of the tricuspid (figs. 428, 429). VENTRICULAR PORTION The ventricles form the greater portion of the heart. In the adult the relation of the ventricles to one another is as follows. The left [ventriculus sinister] has the form of a narrow cone, the apex of which is the apex of the heart. The right ventricle [ventriculus dexter] is crescentic in section and appears to be partially wrapped around the right or lower wall of the left ventricle which forms the septum ventriculorum (fig. 426). The left ventricle forms the margo ob- tusus of the heart, about half the diaphragmatic surface, and a shght part of the sterno-costal surface. The right ventricle forms about half the diaphragmatic surface and the major part of the sterno-costal surface; it takes no share in the formation of the apex of the heart. The interventricular septum [septum ventriculorum] is thick and muscular except for a small area near the root of the aorta which is membranous [septum membranaceum ventriculorum]. The latter can be seen from the left ventricle in the angle between the attached edges of the right and posterior aortic valves (fig. 429). The membranous septum is partly concealed from the right heart by the medial cusp of the tricuspid valve which is attached to it near its upper part. The portion of the membranous septum above the medial tricuspid cusp is therefore atrio-ventricular, i. e., between the right atrium and left ventricle. The membranous septum is the extreme lower part of the independent septum (s. aorticum) which divides the aortic root from the pulmonary artery and conus arteriosus (and partially subdivides, also, the right ventricle by separating the conus arteriosus from the remainder of the ventricle). The relation of the part of the aortic septum between the conus arteriosus and aortic root to the septum ventriculorum is beautifully shown by His, in fig. 427. The greater part of the interior of the ventricles is thrown into ridges by myocardial bundles of large size. These fasciculi [trabeculae cordis] either stand out in rehef only, or, by being undermined, form bands covered except at either end by endotheUum. A careful exam- ination of the endocardium of fresh hearts will reveal a plexiform network of Purkinje fibres. These fibres, belonging to the atrio-ventricular conducting system, become very obvious when the endocardium has been exposed to the air long enough to become partially dry. The wall of the right ventricle [ventriculus dexter] (figs. 427, 428) is much thicker than that of the atria, but less so than that of the left ventricle. The upper and anterior part of the right ventricle is in relation posteriorly with the root of the aorta. This portion of the ventricle is called the conus arteriosus and is separated from the remainder of the right ventricle by a muscular spur which extends from the back of the conus to the right venous ostium. The spur is the crista supraventricularis ; its relation to the partition between the conus and aorta, and to the septum membranaceum, shows that it is the free edge of the embryonic aortic septum (see morphogenesis of the heart). Two papillary muscles in the right ventricle are constant in position, the large anterior papillary muscle, and the small papillary muscle of the conus (Luschka). The anterior papillary is situated on the sterno-costal wall, near the junction of this with the septal wall. The papillary of the conus is placed just below the septal end of the crista supraventricularis. The posterior papillary muscles form an irregular group springing from the diaphragmatic wall. Some chordae tendinese stretch directly from the septal wall (with or without small muscular elevations at their bases) to the medial cusp of the tricuspid valve. The chordae tendinese from the anterior papillary go to the anterior and posterior cusps; those from the conus papillary to the medial and anterior, and those from the posterior papillary muscles to the medial and posterior cusps of the tricuspid valve, respectively. There is frequently a band of myocardium extending from the septal wall of the right ven- tricle to the anterior papillary muscle near its middle. This is the moderator band, which contains a part of the right limb of the atrio-ventricular bundle. If the moderator band joins SEMILUNAR VALVES 517 the anterior papUlary near its base, as it frequently does, it is difficult to distinguish it from the ordinary trabeoulae in this situation. The term moderator band was originally applied to this bridge or band of muscle under the impression that it prevented overdistention of the ventricle. Subsequent discovery of the conducting system of the heart makes it plain that there is always a band conducting the right limb of the atrio- ventricular bundle from the septum to the anterior papillary muscle. Whether the band is isolated from the other trabecules, and therefore readily recognizable, appears to depend somewhat upon the relation of the base of the papillary muscle to the septum ventriculorum. The wall of the left ventricle [veiitriculus sinister] (figs. 427, 429) is very thick except at the extreme apex, and at the membranous septum. In the left ventricle are two large papillary muscles, generally known as anterior and posterior; both send chordae tendineae to each cusp of the mitral valve. On the septal wall of the ventricle the left limb of the atrio-ventricular bundle can usually be seen as a broad, flattened band beneath the endocardium. The band appears just below the septum membranaceum and divides into strands which go to the two papillary muscles. The strands in many places bridge across part of the ventricle to reach the papillary muscles covered only by tubes of endocardium. These bridging strands connecting the papillary muscles with the septum ventriculorum, which were formerly called "false chordas tendinese," are exactly comparable to the moderator band of the right ventricle which occasionally consists of atrio-ventricular bundle and endo- cardium only. SEMILUNAR VALVES The semilunar valves [valvulse semilunares] guard the arterial ostia of the ventricles. The aortic ostium is directed upward and slightly forward and to the right; the pulmonary backward and slightly upward and to the left. Each valve, of which there are three to each ostium, is a pocket-like fold of endocardium strengthened by fibrous tissue (fig. 430) . The free edge of each valve is directed away from the ventricle, so that excess of pressure within the great vessels brings Fig. 430. — Intbrigh View of the Aortic Semilunar Valves. Aortic sinus Section of fibrous ring Free edge of valve i Nodulus Arantii Lunula the three valves of either ostium into mutual apposition. In the middle of the free edge of each valve there is a small fibro-cartilaginous nodule; radiating from this toward the entire fundus, and along the extreme free edge of the valve, are fibrous thickenings. On either side of the nodule, between the thicker margin and fundus, the valve is thin over a crescentic area called the lunula. The aortic valves are called the right, left, and posterior; the pulmonary valves, the right, left, and anterior.* The aortic semilunar valves are stronger than the pulmonary; opposite them there are three dilatations in the aortic wall, the aortic * The BNA names of the aortic and pulmonary valves are not based upon their relative positions in the body. From transverse sections through the thorax (see any good atlas) it may be seen that one aortic valve is anterior, one pulmonary valve posterior, and the other aortic and pulmonary valves are right and left. If the removed heart is held so that the ven- tricles are on the right and left of the septum, respectively, the valves take the positions indi- cated by the BNA. The names given by the BNA to the valves, although conventional (Uke many other terms of orientation applied to parts of the heart), are convenient, particularly from a developmental standpoint. 518 THE BLOOD-VASCULAR SYSTEM sinuses [sinus aortae] or sinuses of Valsalva. From the right and left sinuses the right and left coronary arteries, respectively, arise. After ventricular systole the increased pressure in the great vessels distends the valves with blood. The noduli meet in the centre and the lunulas, coming into mutual contact, produce a tri-radiate line of contact between the valves. ARCHITECTURE OF THE MYOCARDIUM In the adult heart the myocardium of the atria is separate from that of the ventricles. There is, between the atria and ventricles, a fibrous partition, the upper and lower surfaces ol which give attachment to the muscle fibres of these cavities, respectively. The fibrous partition (fig. 431) is thickest in the triangle formed by the meeting of the aortic, and right and left atrio-ventricular ostia. This interval is filled by a mass of fibrous tissue, which in the angles between the aortic and the left atrio-ventricular ostium forms two thickened triangular masses, the trigona fibrosa. The fibrous mass is continued to the pulmonary ostium as the tendon of the conus. Below the point of junction of the trigona and the tendon of the conus these structures blend with the septum membranaceum ventriculorum. The septum membranaceum, tendon of the conus, and part of the trigona are derived from the aortic septum (pp. 516, 527). The trigona give off laterally, on either side, atrio-ventricular rings which en- circle the venous ostia and give attachment to the atrio-ventricular valves. There are also weak Fig. 431. — Base op a Well Developed Heart showing the Coubse op the Superficial Muscle Fibres. From X to jX' around the front of the aorta indicates the course of the aortic septum. (Mall, I nat. size.) rings surrounding the pulmonary and aortic orifices; the aortic and left atrio-ventricular rings being partly confluent. The rings surrounding the arterial and venous ostia axe the annuli fibrosi. The atrial musculature is attached to the trigona and atrio-ventricular rings only. The superficial fibres are attached to both rings and either encircle both atria in one loop, or enter the septum and form a figure 8. The deeper fibres are attached to one ring and encircle one atrium only; some fibres encircle only the auricle. The ventricular musculature is very complex and consists of numerous superimposed layers distinguished from one another by the direction taken by the muscle fibres. In a general way, the fibres of the deepest layer have a direction crossing those upon the surface of the same area at a right angle. The intervening layers of fibres pass through all stages of obhquity. Recent work upon the origin and distribution of the ventricular fibres has resulted in the recognition of a certain uniformity of behavior, thus: — 1. AH fibres arise from, and are inserted into, the fibrous partition at the base. The at- tachment may be directly to the trigona or annuli, or indirectly to them by means of the chordse tendineae and atrio-ventricular valves. 2. The more superficial fibres (fig. 432) tend to encircle the entire heart, passing over the longitudinal sulci. If they enter the septum they do so by passing into the vorte.x or whorl at the apex of the left ventricle. These fibres have always a definite direction upon the sur- face, i. e., from right to left upon the sterno-costal surface and from left to right on the dia- phragmatic (fig. 431). 3. The deeper fibres all enter the septum in a direction oblique or perpendicular to its longitudinal axis. In addition they completely encircle one or both ventricles forming, in the latter case, double loops (fig. 433). VESSELS AND NERVES OF THE HEART 519 During systole, as a result of this arrangement: — (1) The papillary muscles and the longi- tudinal and antero-posterior axes of the ventricles are simultaneously shortened. (2) There is a movement of torsion or "wringing" which I'educes the ventricular cavities to their minimum dimensions. Conducting system. — Although the ordinary myocardium of the atria is distinct from that of the ventricles there is, at one place, a connection between them. This connection is by means of a small band of muscle which differs histologically from ordinary heart muscle. It is known as the atrio-ventricular bundle, and serves to transmit the atrial rhythm of contraction to the ventricles. The atrio-ventricular bundle begins in the septal wall of the atrium a short distance in front of the coronary orifices (fig. 428). It has an e.xpanded free end, the atrio-ventricular node, from which branches pass to be quickl}' lost in the atrial myocardium. The bundle passes forward covered by endocardium and by one or two millimetres of mj'ocardium, and passes beneath the medial cusp of the tricuspid valve. In passing from the atrium to the ventricle, the bundle skirts the lower margin of the septum membranaceum. Immediately in front of the septum membranaceum it divides into a left and right limb, of which the former pierces the muscular interventricular septum . The right limb now passes beneath the crista supra ventricul- aris and above the papillary muscle of the conus, giving off branches to the latter and to other small papillaries on the septum (fig. 428). Bending somewhat toward the apex, it enters the moderator band which conducts it to the large anterior papillary muscle. From here it passes along one of the trabeculae connected with the sterno-oostal wall of the ventricle, or in the wall itself, to reach the posterior papillary muscle or muscles. The right limb is compact and rounded and in the intact heart is usually invisible except, sometimes near the root of the moderator band or in the band itself. The left limb of the bundle appears in the left ventricle a little below the septum mem- branaceum. It is a wide band immediately beneath the endocardium, which cannot usually be Fig. 432. — Diagram of one Anterior AND ONE Posterior Superficial Bundle OP Cardiac Muscle Fibres seen from Behind. (After MacCallum.) Fig. 433. — Diagram of a Deeper Bundle of Muscle Fibres. (After MacCallum.) Conus arteriosus Tendon of the conus V ""^r^ «\ Right atrio-ven- •^^ -3 ' ■■' x tncular ring stripped off without injuring the bundle (fig. 429). It passes along the septal wall toward the apex and divides into two parts, which again subdivide to be distributed to the anterior and the posterior papillary muscles. The branches for the papillary muscles may reach them through thick trabecula;, or they may form thin strands which, covered only by endocardium, bridge from septum to papillary muscle. In addition to the comparatively distinct branches to the papillary muscles of both ventricles, the bundle gives off finer fibres which form a sub-endocardial plexus. This plexus, visible to the naked eye (p. 516) is made up of fibres having a structure similar to those of the ventricular portion of the bundle. The fibres were described by Purkinje as long ago as 1845,* but it was not until 1906, thirteen years after the discovery of the bundle by W. His, Jr., that Tawaraf recognised their significance. There is another node of muscle having characters similar to that of the conducting system, although not connected with it except by myocardium of the ordinary character. This is the sinus-node which is situated at the upper end of the crista terminaUs of the right atrium. Una- nimity is still lacking with regard to the physiological significance of this structure. Vessels and Nerves of the Heart The arteries. — The two coronary arteries arise from the right and left sinuses of the aorta. The right coronary artery [a. coronaria dextraj passes forward between the pulmonary artery and the right atrium, and then follows the right coronary sulcus to the diaphragmatic surface of the heart (fig. 435), to anastomose with the left coronary artery. The posterior descending branch [ramus descendens posterior] arises at the posterior longitudinal sulcus. It * Arch. f. Anat., Physiol, u. wissenschafthche Medizin. t Das Reitungssystem des Saiigertierherzens, Fischer, Jena, 1906. 520 THE BLOOD-VASCULAR SYSTEM E asses in the furrow between the ventricles toward the apex, near which it anastomoses with ranches derived from the left coronary artery. In this course the right coronary artery supplies branches to the right atrium and roots of the pulmonary artery and aorta, as well as one that descends near the margo acutus (right marginal), and a second (preventricular) to the anterior wall of the right ventricle. It supplies both ventricles and the septum. The left coronary artery [a. coronarius sinistra] passes for a short distance forward, between the pulmonary artery and the left auricle, and then divides into two principal branches, one of which runs in the anterior longitudinal sulcus to the apex of the heart, the anterior descending branch [r. descendens anterior], around which it sends branches to anastomose with the right coronary; whilst the other, the circumflex [ramus circumflexus], winds to the diaphragmatic surface in the coronary groove, to anastomose with the corresponding twigs of the right artery. In this course it gives off a branch which follows the margo obtusus (left marginal) as well as smaller branches to the left atrium, both ventricles, and the commencement of the aorta and pulmonary vessels. Fig. 434. — Stebno-costal Surface of the Heart, showing its Arteries and Veins. (After Spalteholz.) Innominate artery Left subclavian artery Superior vena cava Left common carotid artery _ Pulmonary artery Conus arteriosus - Left auricle Rightcoronary. artery Right ventricle The cardiac or coronary veins accompany the coruuary arteries and return the blood from the walls of the heart. The great cardiac vein [v. cordis magna], (fig. 434) runs in the anterior longitudinal sulcus, passing round the left side of the heart in the coronary sulcus to terminate in the commence- ment of the coronary sinus. Its mouth is usually guarded by two valves, and it receives in its course the posterior vein of the left ventricle, with other smaller veins from the left atrium and ventricle, all of which are guarded by valves. The middle cardiac vein (v. cordis media], sometimes the larger of the two chief veins, com- municates with the foregoing at its commencement above the heart's apex. It ascends in the posterior longitudinal groove, receiving blood from the ventricular walls, and joins the coronary sinus through an orifice guarded by a single valve, close to its termination. VESSELS AND NERVES OF THE HEART 521 The posterior vein of the left ventricle [v. post, ventriculi sinistri], lies upon the posterior surface of the ventricle and, receiving branches from it, passes upward to terminate directly in the coronary sinus. The anterior cardiac veins [vv. cordis anteriores] consist of several small branches from the front of the right ventricle, which vary in number and either open separately into the right atrium or join the lesser cardiac vein (fig. 434). The small cardiac vein [v. cordis parva] is a small vessel which receives branches from both the right atrium and ventricle, and winds around the right side of the heart, in the coronary sulcus, to terminate in the coronary sinus. The coronary sinus [sinus coronarius] (fig. 435) may be regarded as a much dilated terminal portion of the great cardiac vein. It is about 2.5 cm. (1 in.) in length, is covered by muscular fibres from the atrium, and hes in the coronary sulcus below the base of the heart. Its cardiac orifice, with the coronary (Thebesian) valve, has already been described. Besides the tributary veins already named, a small oblique vein [v. obUqua atrii sinistri] of the left atrium may some- FiG. 435. — Base and' Diaphragmatic Surface op the Heart, showing its Arteries and Veins. (After Spalteholz.) Kigtit pulmonary artery Left pulmouary artery Left atrium Great cardiac vein Posterior 'vein of tlie left ven- tricle Right pulmonary veins Left ventricle- Middle cardiac vein . Posterior descending branch of the right coronary artery Posterior longitudinal sulcus times be traced, on the back of the left atrium, from the ligament of the left vena cava (Marshall) to the sinus. This httle vein, which is not always pervious or easy of demonstration, never possesses a valve at its orifice, and, Uke the coronary sinus, formed a part of the left superior vena cava of earlyfoetal life. The smallest cardiac veins [vv. cordis minima;] drain blood from septum and lateral walls of the atria, particularly the right; also from the conus arteriosus. They open directly into the right atrium. Although anastomoses occur between the two coronary arteries, these are by no means extensive, and are not sufficient to allow of the estabhshment of a satisfactory collateral cir- culation in the case of the blocking of one coronary artery. Consequently such interference with the cardiac circulation produces rapid pathological changes in the heart musculature, provided it is sudden in occurrence. If the obhteration of the artery take place gradually, however, some rehef may be afforded by the estabhshment of a collateral circulation through the vense minimse, which open out from both the atrial and ventricular cavities and communicate 522 THE BLOOD-VASCULAR SYSTEM with the finer branches of the cardiac veins, and also with the general capillary network in the heart's walls. The lymphatic vessels of the heart pass chiefly through the anterior mediastinal lymph- nodes into the broncho-mediastinal trunk. (See Section VI.) The cardiac nerves, derived from the vagus and the cervical sympathetic, descend into the superior mediastinum, passing in front of and behind the arch of the aorta; they unite in the formation of the superficial and deep cardiac plexuses. The superficial plexus lies above the right pulmonary artery as the latter passes beneath the aortic arch. The deep plexus lies be- tween the trachea and the arch of the aorta, above the bifurcation of the pulmonary trunk. For the connections of the plexuses see section on Nervous System. 2. THE PERICARDIUM The pericardium is a cone-shaped, fibro-serous sac which surrounds the heart and contains a small amount of fluid [liquor pericardii]. Its apex is above at the root of the great vessels, and its base below, adherent to the diaphragm. Its connection with the diaphragm is in part to the central tendon and in part to the muscle, especially on the left side. It consists of an outer fibrous layer and an inner serous layer. The virtual space between the serous pericardium and the epicardium is commonly called the pericardial cavity. Fia. 436. — ^Lept Posteriok View of the Heart to show the Reflections of the Peri- cardium. Pulmonary artery Left pulm. artery Ligament of left superior cava Morgo obtusus Coronary sinus Vena cava inferior The fibrous layer is strong and inelastic, made of interlacing fibres. Its connection with the central tendon of the diaphragm is intimate, particularly in the region of the caval opening, but elsewhere it is attached loosely by means of areolar tissue. Above, it is lost on the sheaths of the great vessels, all of which receive distinct investments, with the single exception of the inferior vena cava, which pierces it from below. The aorta, superior vena cava, the pulmonary artery, and the four pulmonary veins, are all ensheathed in this manner. The pericardium is connected above with the deep cervical fascia. Two variable bands of fibrous tissue, the sterno-pericardial ligaments [ligg. sterno-pericardiaca], connect the front of the pericardium, above and below, with the posterior surface of the sternum. RELATIONS OF HEART AND PERICARDIUM 523 The serous layer is smooth and ghstening and consists of connective tissue, rich in elastic fibres, covered by endotheUum. It lines the interior of the fibrous layer and is continuous with the epicardium or serous covering of the heart. The reflexion of the serous layer from the heart to the fibrous layer of the pericardium occurs at both the arterial and venous attachments of the heart. At the arterial attachment a simple tube of epicardium is reflected along the pul- monary artery and aorta. At the venous attachment the serous layer is reflected from the front of the pulmonary veins on the left, and from the front of these and from the roots of the venae cavae on the right. This reflexion is separated above from that around the aorta and pulmon- ary artery (figs. 424, 436). Around the lower margin of the left lower pulmonary vein (fig. 436) and the root of the inferior vena cava, this reflexion is continuous with an arched refle.xion from the back of the atria (figs. 424, 436). The latter reflexion forms a pocket posterior to the atria which is sometimes called the oblique sinus of the pericardium. Between the reflexions of the epicardium at the arterial and venous attachments of the heart there is a dorsal communication between the right and left sides of the pericardial cavity. This is the transverse sinus of the pericardium [s. transversus pericardii]; it passes behind the aorta and pulmonary artery and in front of the superior cava and left atrium. During early embryonic life the sinus transversus is closed by the dorsal mesocardium (see p. 527). The primitive ventral mesocardium, which divides the right and left sides of the pericardial cavity ventrally, is lost very early. The ligament of the left superior cava [lig. vense cavae sinistrse] (figs. 423, 436) is a doubling of the serous layer which passes between the left pulmonary artery above and the left superior pulmonary vein below. It contains, besides some fatty and areolar tissue, the shrunken remains of the left superior vena cava. It is usually connected above with the left superior intercostal vein by means of a small tributary of the latter. Passing from its lower end to the left end of the coronary sinus is the small vena obliqua atrii sinistri (oblique vein of Marshall). The root of the left superior intercostal (and the adjacent part of the left innom- inate) vein; the vein passing from the super or intercostal to the lig. venae cavae sinistrse; the obhque vein of the left atrium, and the coronary sinus all represent parts of the embryonic left vena cava superior. Relations. — In front of the pericardium are found the thymus gland or its remains, areolar tissue, the sterno-pericardial ligaments, the left transversus thoracis muscle, the internal mammary vessels, the anterior margins of the pleural sac and' lungs, and the sternum. Later- ally, it is overlapped by the lungs with their pleural sacs, and it is in contact with the phrenic nerves and their accompanying vessels. Posteriorly, it is in relation with the cesophagus and vagus nerves, the descending aorta, the thoracic duct and vena azygos, and the roots of the lungs. Below it is separated by the diaphragm from the stomach and the left lobe of the fiver. Vessels. — The arteries of the pericardium are derived from the pericardiac, oesophageal, and bronchial branches of the thoracic aorta and from the internal mammary and phrenic arteries. RELATIONS OF THE HEART AND PERICARDIUM TO THE THORACIC WALL Heart (fig. 437 A and B). — The base of the heart corresponds posteriorly to the fifth, to the ninth thoracic vertebra. Anteriorly the apex is in the fifth intercostal space, 7.5 to S cm. (3 to 3i in.) from the medan line. The base (above) corresponds to a line (A) drawn from a point 1 cm. (= in.) below the second left chondro-costal articulation, and 3 cm (Ij in. from the median line, to another point (the same distance from the median line) 1 cm. above the right third ehondro-sternal articulation. The marge acutus, or lower border corresponds to a line (B) drawn from the apex through the xiphi-sternal articulation, to a point on the sixth costal cartilage 2 cm. to the right of the median line. The right border of the heart may be indicated approximately by a fine (shghtly convex to the right) joining the right ends of A and B. The left border corresponds to a fine (slightly convex to the left) joining the left end of A to the apex. If a line be drawn from the upper margin of the left third ehondro-sternal articulation to the right edge of the sternum in the fifth intercostal space, the upper end of the line wiU he over the centre of the pulmonary ostium, and the lower two-thirds of it (approximateljO will overlie the main axis of the tricuspid ostium. The aortic ostium is immediately to the left of the above line with its centre at the left edge of the sternum opposite the third space. The mitral ostium is very largely behind the third left interspace; its upper end is behind the third cartilage, its lower behind the left margin of the sternum opposite the fourth cartilage and space. Of the ostia of the heart, the pulmonary is nearest the anterior thoracic wall, the aortic is slightly in advance of the mitral, and the tricuspid is the deepest of all. The pericardium follows the heart closely. The upper end (apex) in the subject used in preparing fig. 437 extended up, behind the sternum, to the lower margin of the first costal cartilage on the right and the upper margin of the second on the left. MORPHOGENESIS OF THE HEART AND PERICARDIUM The heart is formed by the blending in the median fine of two longitudinal endothehal tubes lying ventral to the fore-gut of the early embryo. Each tube is partially surrounded laterally by the splanchnic mesoderm which forms a septum between the right and left sides of 524 THE BLOOD-VASCULAR SYSTEM Fig. 437. — A, Telebobntgenogham of a Formalin Preparation or the Anterior Thoracic Wall with the Heart, Pericardium and Diaphragm in situ. (Le Wald, X i). B, Explanatory Outline Drawing, Traced from the Negative and Con- trolled BY Stereoscopic Views. The ostia have been accurately fitted with wire rings. P, pulmonary ostium; M, mitral; T, tricuspid; aortic ostium is unlabelled; I- VII, right costal cartilages. I MORPHOGENESIS OF THE HEART AND PERICARDIUM 525 the ccelomic cavity. The blended endothehal tubes form the endocardium. The splanchnic mesoderm in relation to the endocardium becomes the myoepicardium, and the double layer connecting the heart dorsally and ventrally with the somatic mesoderm becomes the (temporary) dorsal and ventral mesocardia. The somatic mesoderm of the heart region becomes the peri- cardium. The originally straight heart-tube grows rapidly and becomes tortuous on account of its increasing length between the hmits assigned by its fixed arterial and venous ends. Its arterial end is continued into the truncus arteriosus, which is later divided into the pulmonary artery and the ascending aorta. Its venous end receives the vitehine and umbihcal veins, and, later on, the common cardinals also. By the formation of a series of alternate bulgings and constric- tions the heart becomes differentiated into the sinus venosus, atrium, ventricle and conus arte- riosus, counting from the venous to the arterial end. These parts, after going through a process of progressive differentiation and shifting (fig. 438) take up relative positions somewhat ap- proaching those of the adult. Fig. 438. — Models showing the Development of the Heart. (After His.) Conus arteriosus Conus arteriosus The sinus venosus hes on the dorsal wall of the atrium, and is composed of right and left horns united by a transverse portion. The sinus is separated from the atrium by a sagitaUy directed sHt-Uke opening, guarded by right and left lateral valves which project into the atrium. The atrium is wide, being prolonged into a ventrally projecting pouch on either side, the future right and left auricles. The ventricle is situated caudal and somewhat ventral to the atrium. The right Umb of the common ventricle, which leads into the conus arteriosus, is the future right ventricle; the left limb, connected with the atrium, is the future left ventricle. The Fig. 439. — Sagittal Section throtjgh a Reconstrttction of the Heart of a 9 mm. Human Embryo seen FROir the Left Side. (Tandler, X 75.) Septum =«''""1'"° Foramen ovale Conus arteriosus- Septum prinum Sinus venosus communication between the atrium and the ventricle, known as the atrial canal, is indicated on the exterior by a constriction; its interior consists of a transversely placed slit. The conus arteriosus is continued from the ventricle without obvious constriction and passes over into the truncus arteriosus. The sinus venosus early loses its bilateral symmetry owing to the rapid enlargement of the right horn. This horn soon receives, through the proximal portion of the right vitelline vein {inferior vena cayo), all the blood coming from the left vitelline and both umbihcal veins. The right common cardinal also gains ascendency over the left and becomes the superior vena cava. 526 THE BLOOD-VASCULAR SYSTEM The left horn and transverse part, now only draining the dwindling left common cardinal, (left superior cava) and the coronary veins, become the coronary sinus. The right horn gradually becomes absorbed into the right end of the atrial cavity until the superior and inferior cava; and the coronary sinus acquire separate openings into that chamber. Between the opening of the coronary sinus and that of the inferior cava there is a ridge, the sinus-septum (between the right horn and transverse parts of the sinus), which becomes attached to the lower part of the right sinus valve. In the atrium a septum begins early to grow from the ventro-cephaUc wall of the atrium, toward the atrial canal. As the interatrial communication around the edge of the septum (ostium primum) is becoming narrow, a perforation occurs near the attached margin of the septum (ostium secundum). This fii-st septum (septum primum) is incomplete because when its edge reaches the atrial canal the atria stiU communicate through ostium secundum. To the right of the septum primum another septum (s. secundum) is formed later; this never stretches completely across the atrium and is rather a crescentic ridge than a true septum. Until the free edges of the two septa overlap one another there is a direct passage leading from one side of the atrium to the other; eventually they do overlap and the communication becomes oblique but persists until birth. (For adult relations of septa, see p. 511.) The cavities resulting from the division of the common atrium are the right and left atria of the adult. The obUque channel connecting the atria (foramen ovale) is bounded on the right side by the s. secundum the free edge of whicli forms the limbus fossae ovalis. The channel is bounded on the left by the s. primum which slants into the left atrium. The free edge of the s. primum becomes the valvula foraminis ovalis; the remainder, the membranous atrial septum of the adult.' Fig. 440. — Reconstkuction op the Heart of an 11 mm. Human Embryo viewed from Below. (Mall, 50.) The lower part of the ventricular portion has been cut off. Connective tissue septa colored yellow. Ao, aorta; Ap, anterior papillary muscle; La, left atrium; Lo, left venous ostium; Lp, large (anterior) papillary muscle of right ventricle; Mpm, medial papillary muscle; PP, pos- terior papillary muscle; P, pulmonary artery; RA, right atrium. i The portion of the dorsal wall of the right atrium immediately adjoining the septa is derived from the sinus venosus. Tliis part of the atrium (the sinus venarum) receives the great venous openings. The left side of the left sinus-valve is attached to both septa and assists the septum secundum in the formation of the limbus foraminis ovalis. The cephalic part of the right sinus- valve disappears along the line of the (adult) crista ierminalis, which therefore hmits the right portion of the right atrium derived from the sinus venosus. The caudal portion of this valve persists as the inferior caval and coronary valves. These are drawn out of their original ahgn- ment by the adhesion between the caudal part of the right sinus-valve and the sinus-septum. The left atrium receives, through the dorsal mesocardium, the originally single pulmonary vein. This common stem is absorbed into the atrial wall; later, the primitive right and left tributaries are absorbed in a similar way, leaving the four pulmonary veins of the adult open- ing separately into the left atrium. The area of the left atrium adjacent to the pulinonary veins, therefore, is not part of the original atrial waU. The ventricles are divided by a septum (s. musculare ventriculorum) growing from the caudal wall of the common ventricular cavity toward the atrial canal. The canal moves to the right, and the dorsal part of the septum blends with the dorsal lip of the canal. The free ventral edge of the interventricular septum helps to bound the foramen through which blood from the left ventricle must enter the right on its way to the conus arteriosus. The foramen persists until (the free margin of the interventricular septum having been joined by the aortic septum) it becomes the circumference of the aortic ostium. THE ARTERIES AND VEINS 527 The aortic septum is a composite structure formed partly by a septum growing between tlie fourth and sixth pairs of aortic arches, and partly by sweUings growing in the interior of the conus and truncus arteriosus. When fully formed it extends spirally along the truncus and conus, and enters the right half of the common ventricular cavity, where it joins the right side of the free edge of the interventricular septum. The septum is arranged in such a way that the blood from the left ventricle passes no longer through the right ventricle but along its own channel {the aorta) through the conus and truncus to the first four pairs of aortic arches. The blood from the right ventricle passes through the pulmonary division of the conus and truncus arterio- sus, anterior and to the left of the aorta, into the sixth arches. Further differentiation brings about the external separation of the aorta from the pulmonary artery, but their common cover- ing of epicardium persists as such in the adult. The lower end of the aortic septum persists in the adult as the septum membranaceum ventriculorum and the crista supraventricularis, the relations of which to the septum musculare are well shown in fig. 428. During the formation of the aortic septum four endocardial swelhngs appear at the distal part of the interior of the conus. These are arranged as smaller and larger opposite pairs; the smaller and larger swellings, therefore, alternating around the lumen. The larger pair of swellings assists (by partial blending) in the formation of the aortic septum. When the septum is complete, half of each of the larger sweUings is contained in the aorta and half of each in the pulmonary artery. One of the smaller swelhngs remains in the aorta and one in the pulmonary artery, so that there are now three sweUings in each vessel. Each of the six swellings becomes undermined to form a semilunar valve of the adult. The atrio-ventricular valves. — The interior of the ventricular cavity, which is at first smooth, becomes undermined in an irregular way, to form a system of myocardial trabeculse. The Ups of the transversely directed atrial canal become thickened into prominent anterior and posterior endocardial cushions; these project into the ventricular cavity and become involved in its myocardial trabecular system. The atrial canal, which has now moved to the right, be- comes divided sagittaUy, into right and left venous osiia, by the septum primum. The inter- ventricular septum joins the ventricular side of the posterior endocardial cushion. The anterior and posterior endocardial cushions, where they blend with one another and with the septum primum on the medial side of each venous ostium, form an atrio-ventricular valve-cusp on either side, viz., the anterior cusp of the mitral in the left ostium, and the medial cusp of the tricuspid in the right. The posterior cusp of the mitral and the anterior and posterior of the tricuspid are formed later, partly, by lateral tubercles developing in either ostium, and partly by undermining of the ostia from the ventricular side. The atrial musculature extends into the atrio-ventricular valves and, until a late stage, is continuous with the trabecular system of the ventricles. GraduaUy, however, this connection between atrial and ventricular musculature is lost, leaving only the chordae tendinese connecting the papillary muscles with the valves Muscle is found at the basal region of the valve-cusps in the adult, and occasionally persists in the chordae tendinese. The connection between the atrial and ventricular musculature is not confined to that occurring by means of the valves and trabecular system. The original myocardial connection between the atrial and ventricular portions of the heart remains complete until the embryo has reached the length of about 11 mm. From that time on the epicardium begins to blend with the fibrous annuh of the venous ostia. MeanwhUe the atrial musculature rapidly loses its connection with that of the ventricles until they are connected in one place only, i. e., the site of the atrio-vetitricular bundle. The pericardial cavity is the original cephalic end of the intraembryonic ccelom. The somatic mesoderm of the pericardial region forms the adult pericardium. The splanchnic mesoderm persists only in the part which furnishes the myo-epicardium. The ventral and dorsal mesocardia, both of which are formed by the splanchnic mesoderm, are, in the main, transitory. The early disappearance of the ventral mesocardium unites the right and left sides of the peri- cardial ccelom ventral to the heart. The dorsal mesocardium persists at the arterial and venous ends of the heart only. The loss of the dorsal mesocardium between the latter points gives rise to the sinus transversus pericardii of the adult. During development, the heart and pericardium migrate from a point opposite the cephahc end of the pharynx to one opposite the caudal end of the oesophagus; in fact, from the neck well into the thorax. In the adult, instead of being at the cephahc end of the ccelom, the heart and pericardium are contained between the right and left layers of the ventral mesentery of the oesophagus; the pericardial pleura of the adult. The cranio-caudal migration is evidenced in the adult by the course of the recurrent and of the cardiac nerves, and also by the apparent migration of the vessels derived from some of the dorsal segmental arteries. B. THE ARTERIES AND VEINS The arteries [arteriae], proportionately to their size, have much thicker walls than the veins. After death they retain their natural form, but are contracted and contain usually a small amount of pale clot. In a very general way the thickness of wall is proportional to cahbre. Some arteries, however, are con- stantly thicker or thinner than could be predicted from size alone. The larger arteries usually take a direct course and branch dichotomously. In descriptive anatomy if dichotomous branches are of nearly equal size it is common for each to take another name; if one branch preponderates in size, it is apt to retain the name of the parent trunk while the smaller is regarded as a collateral branch [vas coUaterale] . There are numerous 528 THE BLOOD-VASCULAR SYSTEM exceptions to dichotomous branching; branches may run perpendicularly or recurrently to the vessel from which they arise; or several branches may arise simultaneously. There is less tendency to anastomosis between large or medium sized arteries than in veins of corresponding magnitude. Anastomoses do occur, however, particularly in the form of arches, such as the palpebral, plantar and volar arches, or the arches between the intestinal arteries. This form of anastomosis is sometimes called inosculation. Between smaller arteries anastomosis is usually free as in the case, for instance, of the articular retia. In some organs anastomosis (excepting capillary) between neighbouring arteries can scarcely be said to exist at all; the a. centralis retinae affords a good example of this, as do the arteries of the brain, spleen, and kidney; such arteries are called terminal. The larger arteries are supplied by vasa vasorum, frequently arising from their own recurrent branches. The veins [venae] have thin walls, and after death are either collapsed or filled with clot or stained serum. They are characterized by the presence of valves and frequent anastomoses. Frequent anastomoses occur between veins of all sizes; plexuses are common, such, for instance, those of the pelvis. Venm comitantes are veins which, usually in pairs, accompany many arteries; they communicate with one another, around the artery, very freely. Veins do not primitively accompany arteries. In the case of the extremities the primitive veins are superficial. The deep veins of the hmbs are of later formation and to them the superficial veins subsequently become tributary. The veins from the stomach, spleen, pancreas and intestine are collected into a large trunk, the portal vein. This does not open into the inferior vena cava directly, but breaks up into numerous smaller vessels in the Hver. From these the blood is returned, through the hepatic veins, to the inferior cava. Many veins are provided with valves, the free borders of which are directed toward the heart. In the small veins the valves are single; in the larger veins they are usually double, rarely treble. Valves are much more numerous in the veins of infants than those of the adult, they seem to disappear progressively with advancing age. The venous valves are most numerous in the superficial veins, and in the deep veins of the extremities; in many veins of the head and neck they occur only at their point of termination in a larger trunk. The cranial venous sinuses are modified veins, consisting of intima only which lines channels in the fibrous dura mater. The venous spaces in cavernous tissue, such as the corpora cavernosa, may be looked upon as specially modified veins. The larger veins, hke the arteries, have vasa vasorum. The arteries and veins will be considered in the following order: 1, pulmonary artery and veins; 2, the systemic arteries; and, 3, the systemic veins. At the ends of the second and third divisions, the development and variations are considered. 1. THE PULMONARY ARTERY AND VEINS The pulmonary artery [a. pulmonahs] (fig. 441) passes from the right ventricle to the lungs. It differs from all other arteries in the body in that it contains venous blood. It arises as a short, thick trunk from the conus arteriosus of the right ventricle, and, after a course of about 5 cm. (2 in.) within the pericar- dium, divides into a right and a left branch. These branches pass to the, right and the left lung respectively. The trunk of the pulmonary artery at its origin is on a plane anterior to the ascending aorta, and slightly overlaps that vessel. Thence it passes upward, backward, and to the left, forming a slight curve around the front and left side of the ascending portion of the aorta; and, having reached the concavity of the aortic arch, on a plane posterior to the ascending aorta, it divides into its right and left branches, which diverge from each other at an angle of about 130°. The division of the pulmonary artery occurs immediately to the left of the second left chondrosternal articulation. In the foetus, the pulmonary artery continues its course upward, backward, and to the left under the name of the ductus arteriosus (Botalli), and opens into the descending aorta just below the origin of the left subclavian artery. After birth, that portion of the pulmonary artery which extends to the aorta becomes obhterated, and remains merely as a fibrous cord, the ligamentum arteriosum (fig. 436). Relations. — In front, the trunk of the pulmonary artery is covered by the remains of the thymus gland, and the pericardium. The artery Ues, at its commencement, behind the upper margin of the third left chondro-sternal articulation. The right margin of the artery is behind the second piece of sternum but the greater part of the vessel is behind the medial end of the second intercostal space. Behind, it lies successively upon the ascending aorta and the left atrium. To the right are the ascending aorta, the right atrium, the right coronary artery, and the cardiac nerves. THE SYSTEMIC ARTERIES 529 To the left are the pericardium, the left pleura and lung, the left auricle, the left coronary artery, and the cardiac nerves. The right pulmonary artery [ramus dexter] longer than the left, passes almost horizontally under the arch of the aorta to the root of the right lung, where it divides, either directly or after repeated division, into three branches, one for each lobe. These branches follow the course of the bronchi, dividing and sub- dividing for the supply of the lobules of the lung. The terminal branches do not anastomose with each other. Relations. — In its course to the lung it has in front of it the ascending aorta, the superior vena cava, the phrenic nerve, the anterior pulmonary plexus, and the reflexion of the pleura. Behind are the right bronchus and the termination of the azygos vein. Above is the arch of the aorta, and below are the left atrium and the upper right pulmonary vein. At the root of the lung it has the right bronchus above and behind it; the pulmonary veins below and in front. Crossing in front of it and the other structures forming the root of the lung are the phrenic nerve and the anterior pulmonary plexus; behind are the azygos vein, the vagus nerve, and the posterior pulmonary plexus. The left pulmonary artery, shorter and slightly smaller than the right, passes in front of the descending aorta to the root of the left lung, where it divides into two branches for the supply of the upper and lower lobes respectively. These divide and subdivide as on the right side. Relations. — At the root of the lung it has the left bronchus behind and also below it, in consequence of the more vertical direction taken by the left bronchus than by the right. Below and in front are the pulmonary veins, while passing from the artery and the upper left pulmonary vein is the hgament of the left superior cava. Crossing in front of it and the other structures forming the root of.the lung are the phrenic nerve, the anterior pulmonary plexus, and the reflex- ion of the left pleura; crossing behind, are the descending aorta, the left vagus nerve, and the posterior pulmonary plexus. The pulmonary veins [vv. pulmonales] (figs. 424, 441) return the aerated blood from the lungs to the heart. They are usually four in number, superior and inferior, of the right and left sides. Occasionally, however, there are three pulmonary veins on the right side, the result of the vein from the middle lobe of the right lung opening separately into the left atrium instead of joining as usual the upper of the two right pulmonary veins. The relations of the pulmonary veins to the pulmonary arteries and bronchi in the lungs- are given with the anatomy of the lungs (Section X). The pulmonary veins are about 15 mm. in length. In the pericardium the right pulmonary veins [vv. pulmonales dextrse] both pass behind the superior vena cava. The superior vein receives the vein from the right middle lobe and runs below and in front of the right pulmonary artery. The left pulmonary veins [vv. pulmonales sinistrse] enter the left atrium about 3 cm. in front of the veins of the right side. The superior vein is below the left pulmonary artery. 2. THE SYSTEMIC ARTERIES THE AORTA The aorta (fig. 442) is the main systemic arterial trunk, and from it all the systemic arteries are derived. It begins at the left ventricle of the heart, and ascends near the anterior thoracic wall as high as the second right chondro-sternal articulation [aorta ascendens]. It then turns backward and to the left forming an arch [arcus aortas] which reaches the posterior thoracic wall at the left side of the fourth thoracic vertebra. From here it runs downward along the vertebral column [aorta descendens] through the thorax and abdomen and ends by dividing, opposite the fourth lumbar vertebra, into the right and left common iliac arteries. From the point of bifurcation a small vessel, the middle sacral, is continued down the middle line in. front of the sacrum and coccyx. The midclle sacral represents the sacral and coccygeal aorta. The Ascending Aorta The ascending aorta [aorta ascendens] (fig. 442) begins at the upper part of the left ventricle, on a level with the third intercostal space, and ascends behind I 530 THE BLOOD-VASCULAR SYSTEM the sternum to the upper border of the right second chondrosternal articulation. It measures about 5 to 5.5 cm. (2 to 2i in.), forming, as it ascends, a gentle curve with its convexity to the right. It is enclosed for the greater part of its length in the pericardium, being invested, together with the pulmonary artery, in a com- mon sheath formed by the serous layer of that membrane. A dilatation known as the bulbus aortse occurs immediately above the heart upon which are three locaHzed bulgings, known as the aortic sinuses (sinuses of Valsalva); they are placed, one to the right, one to the left, and one posteriorly. From the right and eft are derived the coronary arteries of the heart. (See Heart.) Fig. 441. — The Gkeat (Modified from a dissection in St, Internal jugular vein Transverse cervical artery Transverse scapular artery Vessels of the Thorax. Bartholomew's Hospital Museum.) Inferior thyreoid ■ Right inferior laryn- Right common carotid artery Subclavian vein' Innominate artery Left innominate vem Phrenic nerve Superior vena cava Arch of aorta Right bronchus Branch of right pul- monary artery Branch of right pul- monary vein Right pulmonary artery Branch of right pul- monary artery Branch of right pul- monary vein Right coronary artery Thoracic vertebra Azygos vein Intercostal veins Intercostal arteries --Thyreoid gland Left internal jugular vein , Vagus nerve Left common carotid artery Left inferior laryngeal nerve -Left subclavian artery Left subclavian vein Left internal mammary vein Left superior inter- costal vein Phrenic nerve Vagus nerve Recurrent nerve Ligamentum arteri- osum Left pulmonary artery Left pulmonary vein Left bronchus Branch of left pulmon- ary artery Pulmonary artery Left pulmonary vein Left coronary arteiy Conus arteriosus Thoracic duct Thoracic aorta Relations. — In front, it is overlapped at its commen-cement by the right auricle, conut arteriosus and pulmonary artery. Higher up, as the pulmonary artery and auricle diverge, is is separated from the manubrium by the pericardium, the remains of the thymus gland, and by the loose tissue and fat in the superior mediastinum, and is here shghtly overlapped by the right pleura and by the edge of the right lung in full inspiration. The root of the right coronary artery is also in front. Behind are the left atrium of the heart, the right pulmonary artery, the right bronchus, and the anterior right deep cardiac nerves. On the right side it is in contact, below with the right atrium, and above with the superior vena cava. On the left side are the pulmonary artery and the branches of the right superficial cardiac nerves. Branches. — The right and left coronary arteries have already been described (p. 519). The Arch of the Aorta The arch of the aorta [arcus aortse] (figs. 441, 442), extends in a gentle curve upward, backward, and to the left, from the level of the upper border of the THE ARCH OF THE AORTA 531 second right costal cartilage to the lower border of the fourth thoracic vertebra. Attached to the concavity of the arch, just beyond the origin of the left sub- clavian artery, is the ligamentum arteriosum (vestige of the dorsal part of the left sixth arch). Between the left subclavian artery and the ligamentum arterio- sum there is sometimes a definite constriction of the arch (isthmus aortse) situated opposite the third thoracic vertebra. When the isthmus is well marked, it is succeeded by a dilatation (aortic spindle) which begins in the neighbourhood of the ligamentum arteriosum and passes over into the descending aorta. Passing under the arch are the left bronchus, the right pulmonary artery, and the left recurrent (inferior laryngeal) nerve. It measures about 4.5 cm. (14- in.). Fig 442 — ^The Thoracic and Abdominal Aorta. Right common carotid artery Right internal jugular vein Right lymphatic duct Innominate artery Right vagus nerve Right innominate vein Internal mammary vein Trunk of the pericardiac and thymic veins Superior vena cava Hemiazygos vein^ cross- ing spine to enter vena azygos Inferior vena cava Right inferior phrenic artery Cceliac artery Right middle suprarenal artery Right internal spermatic artery Right spermatic vein Left common carotid artery Left vagus nerve Thoracic duct Left innominate vein Left subclavian artery Left superior intercostal Recurrent (laryngeal) Accessory hemiazygos vein (Esophagus Left upper azygos vein (Esophageal branches from aorta Hemiazygos vein Thoracic duct Left inferior phrenic artery Left middle suprarenal artery Receptaculum chyli Superior mesenteric artery Left ascending lumbar Left internal spermatic artery Inferior mesenteric artery Relations. — In front and to the left, it is slightly overlapped by the right pleura and lung, and to a greater extent by the left pleiu-a and lung. It is crossed in the following order from right to left, by the left phrenic nerve, by the cardiac branches of the vagus nerve, the cardiac braUches of the sympathetic nerve, by the left vagus nerve, and by the left superior intercostal vein as it passes up to the left innominate vein. Behind and to the right are the trachea, the oesophagus, the thoracic duct, the deep cardiac plexus which is situated on the trachea just above its bif.urcation, and the left recurrent (inferior laryngeal) nerve. Above it are the three chief branches for the head, neck, and upper extremities, namely, the innominate, the left carotid, and the left subclavian arteries, and the left innominate vein. 532 THE BLOOD-VASCULAR SYSTEM Below it — that is, in its concavity — are the bifurcation of the pulmonary artery, the left bronchus, the left recurrent (inferior laryngeal) nerve, the ligamentum arteriosum, the super- ficial cardiac plexus, two or more bronchial lymphatic glands, and the reflexion of the pericardium. The branches of the aortic arch are: — the inDominate, the left common caro- tid, and the left subclavian arteries. The innominate and left carotid arise close together — indeed, so close that, when seen from the interior of the aorta, the orifices appear merely separated by a thin septum. The left subclavian arises a little less close to the left carotid. THE INNOMINATE ARTERY The innominate [a. anonyma] or brachio-cephalic artery (fig. 441), the largest branch of the arch of the aorta, extends from near its commencement upward and a little forward and to the right, as high as the upper limit of the right sterno-clavicular joint where it bifurcates into the right common carotid and right subclavian arteries. It lies obliquely in front of the trachea, and measures from -3.7 to 5 cm. (1| to 2 in.). Fig. 443. — -The Thykeoidea Ima. (After Henle.) fiight carotid artery Sight subclavian artery Innominate artery Superior vena cava Left carotid artery Left subclavian ai'tery Pulmonary artery Relations. — In front of the artery are the manubrium, the origins of the sterno-hyoid and sterno-thyreoid muscles, the right sterno-clavicular joint, and the remains of the thymus gland. The left innominate vein crosses the root of the vessel, and the inferior thyreoid and thyreoidea ima veins descend obliquely over it to end in the left innominate vein. The inferior cervical cardiac branches of the right vagus nerve pass in front of it on their way to the deep cardiac plexus. Behind, it hes on the trachea, crossing that tube obhquely from left to right, and coming into contact above with the right pleura. To the right side are the right innominate vein, the right vagus, and the pleura. To the left side are the left common carotid, the remains of the thymus gland, the right inferior thyreoid vein; and, higher, the trachea. The branches of the innominate artery are: — (1) The right common carotid; and (2) the right subclavian. These are terminal branches. There are usually no collateral branches from this vessel, but at times the thyreoidea ima may arise from it. THE COMMON CAROTID ARTERY 533 The thyreoida ima artery, which occurs in about 10 per cent, of subjects, ascends on the front of the trachea to the thyreoid gland. It may be large in which case it might complicate the low operation of tracheotomy. It does not always arise from the innominate, but occa- sionally from the arch of the aorta (fig. 443) or from the right common carotid. THE COMMON CAROTID ARTERIES The common carotid arteries [aa. carotides communes] pass up deeply from the thorax on either side of the neck to about the level of the upper border of the thyreoid cartilage, where they divide into the external and internal carotid arteries. The external carotid supplies the structures at the upper part of the front and side of the neck, the larynx, pharynx, tongue, face, the upper part of the back of the neck, the structures in the pterygoid region, the scalp, and in chief part the membranes of the brain. The internal carotid gives off no branch in the neck, but enters the cranium and supplies the greater part of the brain, the structures contained in the orbit, and portions of the membranes of the brain. The common carotid artery on the right side arises from the bifurcation of the innominate at the upper limit of the sterno-clavicular joint; on the left side from the arch of the aorta a little to the left of the innominate artery, and on a plane somewhat posterior to that vessel (fig. 441). The portion of the left common carotid artery which extends from the arch of the aorta to the upper limit of the sterno-clavicular articulation lies deeply in the chest, and requires a separate description; but above the level of the sterno-clavicular joint the relations of the right and left carotids are practically the same, and are given under the account of the right common carotid. THORACIC PORTION OF THE LEFT COMMON CAROTID ARTERY Within the thorax the left common carotid is deeply placed behind the manubrium of the sternum, and is overlapped by the left lung and pleura. It arises from the middle of the aortic arch, close to the left side of the innominate artery, and a little posterior to that vessel, and ascends obliquely in front of the trachea to the left sterno-clavicular articulation, above which its relations are similar to those of the right common carotid (fig. 442). Relations. — In front, but at some httle distance, are the manubrium and the origins of the left sterno-hyoid and sterno-thyreoid muscles, whilst in contact with it are the remains of the thymus gland, and the loose connective tissue and fat of the superior mediastinum. Crossing its root is the left innominate vein. Behind, it lies successively upon the trachea the left recurrent (inferior laryngeal) nerve, the oesophagus (which here inclines a little to the left), and the thoracic duct. To its right side is the root of the innominate artery, and higher up are the trachea and the inferior thyreoid veins. To its left side, but on a posterior plane, are the left subclavian artery and the left vagus nerve; and, shghtly overlapping it, the edge of the left pleura and lung. THE COMMON CAROTID ARTERY IN THE NECK The common carotid artery in the neck extends from the sterno-clavicular articulation to the upper border of the thyreoid cartilage on a level with the fourth cervical vertebra, where it divides into the external and internal carotid arteries. A line drawn from the sterno-clavicular joint to the interval between the mastoid process and the angle of the jaw would indicate its course. The artery is at first deeply placed beneath the sterno-mastoid, sterno-hyoid, and sterno-thyreoid muscles, and at the level of the top of the sternum is only 2 cm. (f in.) distant from its fellow of the opposite side, and merely separated from it by the trachea. As the carotid arteries run up the neck, however, they diverge in the form of a V and become more superficial, though on a plane posterior to that in which they lie at the root of the neck, and are separated from each other by the larynx and pharynx. At their bifurcation they are about 6 cm. (2j in.) apart. The com- mon carotid is contained in a sheath of fascia common to it and the internal jugular vein and vagus nerve. The artery, vein, and nerve, however, are not in contact, but separated from one another by fibrous septa, which divide the com- mon sheath into three compartments: one for the artery, one for the vein, and one 534 THE BLOOD-VASCULAR SYSTEM for the nerve. The vein, which is larger than the artery, lies to the lateral side, and somewhat overlaps it. The vagus nerve lies behind and between the two vessels. The artery on the right side measures about 9.5 cm. (3f in.) ; on the left side, about 12 cm. (4J in.) in length. Fig. 444. — The Collateral Circulation after Ligature op the Common Carotid and Subclavian Arteries. (A ligature is placed on the common carotid and on the third portion of the subclavian artery.) Right anterior cerebral - Internal carotid - Right posterior cerebral - Occipital Descending branch of occipital External carotid — ^■ Superficial branch of descending occipital Deep branch Transverse cervical Descending branch Acromial branch. Subscapular branch Anterior circumflex tnfraspinous branch Posterior circum flex Lateral thorucli Subscapular Circumflex scapulai Infrascapul: Subscapular Left anterior cerebral Anterior communicating Posterior communicating Left posterior cerebral Anterior spinal Vertebral External maxillary Lingual Superior thyreoid .Inferior thyreoid Common carotid Thyreo- cervical trunk Costo-cervical trunk Innominate Superior intercostal ^■T Left common carotid -j Left subclavian 7 Superior thoracic Internal mammary Anterior intercostal First aortic inter- costal Second aortic inter- costal ■Anterior intercostal Relations. — In front the artery is covered by the skin, superficial fascia, platysma, and deep fascia, and is more or less overlapped by the sterno-mastoid muscle. At the lower part of the neck it is covered in addition by the sterno-hyoid and sterno-thyreoid muscles, and is crossed by the anterior jugular vein, and is often overlapped by the thyreoid gland. _ Opposite the cricoid cartilage it is crossed obliquely by the onio-hyoid muscle, and, above this spot, by the superior thyreoid vein, and the sterno-mastoid artery. Along the anterior border of the sterno-mastoid there is a communicating vein between the facial and anterior jugular veins, which, as it crosses the line of the carotid artery, is in danger of being wounded in the operation THE COMMON CAROTID ARTERY 535 of tying the carotid. The ramus descendens n. hypoglossi generally descends in front of the carotid sheath, being there joined by one or two communicating branches from the second and third cervical nerves. At times this nerve runs within the sheath. There are usually two lymphatic glands about the bifurcation of the artery. These are often found enlarged and infiltrated in cancer of the lip and tongue. Behind, the common carotid lies on the longus colli and scalenus anterior below, and longus capitis (rectus capitis anterior major) above. Posterior to the artery, but in the same sheath, is the vagus nerve; and posterior to the sheath, the cervical sympathetic and the cervical Fig. 445. — Artebies or the Head and Neck. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Transverse facial artery Supraorbital artery ^ -•^^'"'t^^^'^S^^^^^ /' Frontal artery / 0<=iS^r*^i^ / Dorsal nasal artery Superficial temporal artery ^ ~^^-^T^S^ ' Infraorbital — Angular artery Superior labial artery -^ At — Inferior labial artery J y Mental artery - Submental artery Glandular branches External maxillary artery Lingual artery Auricular branch Stylomastoid arterj Posterior auricular artery ^ y Descending branch of occipital artery Splenius capitis muscle Internal carotid artery Transverse cervical artery Trapezius muscle"" Ascending branch — Descending branch — Axillary artery Acromial branch -^ Superior Hyoid branch Anterior branch I Vh/re'crd Posteriorbranch artery Thyreoid gland Common carotid artery Inferior thyreoid artery Ascending cervical artery Superficial cervical artery Th3n:eocervical trunk V Subclavian artery ^^ 'm^" Pleura Internal mam- "" mary artery "-Transverse scap- ular artery Deltoid branch I Pectoral branches Thoracoacromial artery cardiac branches of the sympathetic and vagus nerves. At the lower part of the neck the inferior thyreoid artery courses obliquely behind the carotid, as does Hkewise the inferior (recurrent) laryngeal nerve. Medially, from below upward, are the trachea and oesophagus, with the inferior (recurrent) laryngeal nerve in the groove between them, and the terminal branches of the inferior thyreoid artery, the lateral lobe of the thyreoid gland, the cricoid cartilage, the thyreoid cartilage, and the lower part of the pharynx. At the angle of bifurcation is the carotid gland [glomus caro- ticumj. Laterally are the internal jugular vein and the vagus nerve. On the right side, at the root of the neck, the vein diverges somewhat from the artery, leaving a space in which the vagus ) 536 THE BLOOD-VASCULAR SYSTEM nerve and vertebral artery are exposed. On the left side the vein approaches and somewhat overlaps the artery, thus leaving no interval corresponding to that on the right side. The cricoid cartilage is, as a rule, taken as the centre of the incision in the operation for ligature of the common carotid artery. The incision is made in the line of the vessel parallel to the anterior margin of the sterno-mastoid muscle. The omo-hyoid forms one of the chief rallying points in the course of the operation for ligature of the artery above that muscle, the usual situation. The artery is found beating at the angle formed by the omo-hyoid with the sterno-mastoid. Branches. — (1) External and (2) internal carotid arteries. The common carotid gives off no lateral branch, and consequently does not diminish in size as it runs up the neck. It is often a little swollen just below its bifurcation, a condition that should not be mistaken for an aneurismal dilation. The collateral circulation (fig. 444), after Hgature of the common carotid, is carried on chiefly by the anastomosis of the internal carotid with the internal carotid of the opposite side through the circle of Willis; by the vertebral with the opposite vertebral; by the inferior thy- reoid with the superior thyreoid; by the deep cervical branch of the costo-cervical trunk (superior intercostal) with the descending branch of the occipital; by the superior thyreoid, hngual, external maxillary (facial), occipital, and temporal, with the corresponding arteries of the oppo- site side, and by the ophthalmic with the angular. The anastomosis between the deep cervical branch of the costo-cervical trunk with the descending branch of the occipital is an important one; it is situated deeply at the back of the neck, and is to be found lying between the semi- spinaUs capitis (complexus) and cervicis muscles. THE EXTERNAL CAROTID ARTERY The external carotid artery [a. carotis externa] (fig. 445), the smaller of the two branches into which the common carotid divides at the upper border of the thyreoid cartilage, is distributed to the anterior part of the neck, the face, and the cranial region, including the skin, the bones, and the dura mater. It is at first situated medial to the internal carotid; but as it ascends in the neck it forms a gentle curve, with its convexity forward, and, running slightly backward as well as upward, terminates opposite the neck of the mandible just below the condyle, by dividing into the internal maxillary and superficial temporal arteries. It here lies superficial to the internal carotid, from which it is separated by a portion of the parotid gland. At its origin it is overlapped by the anterior margin of the sterno-mastoid, and is covered by the superficial fascia, platysma, and deep fascia. Higher up the neck it is deeply placed, passing beneath the stylo-hyoid muscle, the posterior belly of the digastric muscle, and the hypoglossal nerve; and finally becomes embedded in the parotid gland, where it divides into its terminal branches. It is separated from the internal carotid artery posteriorly by the stylo-pharyngeus and stylo-glossus muscles, the glosso-pharyngeal nerve, the pharyngeal branch of the vagus nerve, a portion of the parotid gland, and the stylo-hyoid ligament; or, if the styloid process is abnormaUy long, by that process itself. It measures about 6.5 cm. (2| in.). Relations. — In front, in addition to the skin, superficial fascia, platysma, and deep fascia, it has the hypoglossal nerve, the hngual, common facial and posterior facial veins, the posterior belly of the digastric and stylo-hyoid muscles, the superior cervical lymphatic glands, branches of the facial nerve, and the parotid gland. The sterno-mastoid also overlaps it in the natural state of the parts. Behind, it is in relation with the internal carotid, from which it is separated by the stylo- glossus and stylo-pharyngeus muscles, the glosso-pharyngeal nerve, the pharyngeal branch of the vagus nerve, the stylo-hyoid hgament, and the parotid gland. The superior laryngeal nerve crosses behind both the external and internal carotid arteries. Medially, it is in relation with the hyoid bone, the pharyngeal wall, the ramus of the mandible, the stylo-mandibular ligament which separates it from the submaxillary gland, and the parotid gland. Laterally, in the first part of its course, it is in contact with the internal carotid artery. The branches of the external carotid are usually given off in the following order, from below upward: — 1. Ascending pharyngeal. 2. Superior thyreoid. 3. Lingual. 4. External maxillary (facial). 5. Sternocleidomastoid. 6. Occipital. 7. Posterior auricular. 8. Superficial temporal. 9. Internal maxillary. THE ASCENDING PHARYNGEAL ARTERY 537 1. THE ASCENDING PHARYNGEAL ARTERY The ascending pharyngeal artery [a. pharyngea ascendens] (fig. 446) is usually the first or second branch of the external carotid. Occasionally it comes off at the bifurcation of the common carotid from the common carotid itself. It is a long slender vessel which runs deeply seated up the neck to the base of the skull, having the walls of the pharynx and the tonsil medially, the internal carotid artery laterally, and the vertebral column, the longus capitis (rectus capitis anterior major), and the sympathetic nerve posteriorly. In front it is crossed by the stylo-glossus (fig. 446) and the stylo-pharyngeus muscles and the glosso- pharyngeal nerve. Branches of the Ascending Pharyngeal Artery The branches of the ascending pharyngeal artery are small and variable. They supply the longus and rectus capitis muscles, the upper cervical sympathetic ganglion and adjacent lymph-nodes, as well as the pharynx, soft palate, ear, cranial nerves, and meninges. The pharyngeal branches [rami pharyngei] supply the superior and middle constrictor muscles and the mucous membrane lining them. These vessels anastomose with branches Fig. 446. — Scheme op Right Ascending Pharyngeal Abteey. The internal carotid artery is hooked aside. Meningeal branch passing through lacerated foramen Inferior tympanic branch Meningeal branch passing through jugular foramen Meningeal branch passing through hypoglossal canal (Walsham.) Stylo-pharyngeus Glosso-pharyngeal nerve Occipital artery Longus capitis Ascending pharyngeal artery Middle constrictor of pharynx Sympathetic nerve Internal carotid artery External carotid artery Levator veli palatini Palatine branch Buccinator muscle Superior constrictor of pharynx Pterygo-mandibular raphe Stylo-glossus Ascending palatine branch of ext. maxillary artery Tonsillar branch of ext. maxil- lary artery xillary artery Lingual artery Superior thyreoid artery Common carotid artery of the superior thyreoid. One branch (the palatine) passes over the upper edge of the superior constrictor to the soft palate and its muscles. This branch follows a course similar to that taken by the ascending palatine artery, and when the latter is small may take its place. It generally gives off small twigs to the Eustachian tube and tonsil. The inferior tympanic artery [a. tympanica inferior] accompanies the tympanic branch of the glosso-pharj'ngeal nerve through the tympanic canaliculus into the tympanum, and anastomoses with the other tympanic arteries. The posterior meningeal artery [a. meningea posterior] is distributed to the membranes of the brain. Some twigs pass with the jugular vein through the jugular foramen into the cranium, and supply the dura mater in the posterior fossa of the skull. Others occasionally reach the same fossa through the hypoglossal (anterior condyloid) canal in company with the hji^oglossal nerve; while others pass through the cartilage of the lacerated foramen and supply the middle fossa of the skull. 538 THE BLOOD-VASCULAR SYSTEM 2. THE SUPERIOR THYREOID ARTERY The superior thyreoid artery [a. thyreoidea superior] (figs. 445, 447) arises from the front of the external carotid a little above the origin of that vessel, and, coursing forward, medially, and then downward, in a tortuous manner, supplies the depressor muscles of the hyoid bone, the larynx, the thyreoid gland, and the lower part of the pharynx. The arterj' at first runs forward and a little upward, just beneath the greater cornu of the hyoid bone. In this part of its course it lies in the superior carotid triangle, and is quite superficial, being covered only with the integument, fascia, and platysma. It next turns downward, and passes beneath the omo-hyoid, sterno-hyoid, and sterno-thyreoid muscles, and ends at the upper part of the thyreoid gland by breaking up into terminal glandular branches. The superior thyreoid vein passes beneath the artery on its way to the internal jugular vein. The superior thyreoid is the artery most commonly divided in cases of suicidal wounds of the throat. Branches of the Superior Thyreoid Artery The named branches of the superior thyreoid artery are: — (1) The hyoid; (2) the sterno-mastoid; (3) the superior laryngeal; (4) the crico-thyreoid; (5) anterior; (6) posterior; and (7) glandular. Fig. 447. — Scheme of Left Superior Thyreoid Artery. (Walsham.) External maxillary artery Hyoid branch of lingual Superior laryngeal branch j- — Crico-thyreoid branch External carotid artery Ascending pharyngeal artery Internal carotid artery Sterno-mastoid branch Superior thyreoid artery Common carotid artery Inferior thyreoid artery (1) The hyoid [ramus hyoideus] is usually a small twig which passes along the lower border of the hyoid bone, lying on the thyreo-hyoid membrane under cover of the thyreo-hyoid and sterno-hyoid muscles. It supplies the infra-hyoid bursa and the thjo-eo-hyoid muscle, and anastomoses with its fellow of the opposite side, and with the hyoid branch of the lingual. When the latter artery is small, the hyoid branch of the superior thyreoid is usually com- paratively large, and vice versa. (2) The sterno-mastoid [ramus sternocleidomastoideus] (fig. 447) courses downward and backward across the carotid sheath, and entering the sterno-mastoid supphes the middle portion of that muscle. It gives off slender twigs to the thyreo-hyoid, sterno-hyoid, and omo-hyoid muscles, and the platysma and integuments covering it. At times the vessel arises directly from the external carotid. It hes usually somewhere in the upper part of the incision for tying the common carotid above the omo-hyoid muscle. (3) The superior laryngeal [a. laryngea superior] (fig. 447) passes medially beneath the BRANCHES OF THE LINGUAL ARTERY 539 thyreo-hyoid muscle, and, perforating the thyreo-hyoid membrane along with the internal branch of the superior laryngeal nerve, suppUes the intrinsic muscles and mucous lining of the larynx. Its further distribution within the larynx is given with the description of that organ. This branch sometimes arises from the external carotid direct. It may enter the larynx by passing through a foramen in the thyreoid cartUage. (4) The crico -thyreoid [ramus cricothyreoideus] passes across the crico-thyreoid membrane immediately beneath the lower border of the thyreoid cartilage. It anastomoses with its fellow of the opposite side, and usually sends a small branch through the membrane into the interior of the larynx. Occasionally a considerable twig descends over the cricoid cartilage to enter the isthmus of the thyreoid gland. The crico-thyreoid has, however, frequently been seen of comparatively large size — once as large as the radial, and crossing the membrane obliquely. In order to avoid injuring the crico-thyreoid artery in the operation of laryngot- omy, it is usual, if the operation has to be done in a hurry, to make the incision through the crico-thyreoid membrane in a transverse direction, and as near to the cricoid cartilage as possible. (5) The anterior branch [ramus anterior] is the terminal branch supplying the isthmus and the neighbouring part of the lateral lobe of the thyreoid gland. (6) The posterior branch [ramus posterior], the other terminal, supplies the posterior part of the lateral lobe, and sends branches to the inferior constrictor of the pharynx and to the oesophagus. It anastomoses with the ascending branches of the inferior thyreoid artery. (7) The glandular branches [rami glandulares] are the ultimate twigs, arising from the ante- rior and posterior terminal branches, for the supply of the thyreoid gland. 3. THE LINGUAL ARTERY The lingual artery [a. lingualis] (fig. 448) arises from tiie front of the external carotid, between the superior thyreoid and external maxillary (facial) arteries, often as a common trunk with the latter vessel, and nearly opposite or a little below the greater cornu of the hyoid bone. It may, for purposes of description, be divided into three portions: the first, or oblique, extends from its origin to the posterior edge of the hyo-glossus muscle; the second, or horizontal, lies beneath the hyo-glossus; the third, or ascending, beneath the tongue. The first or oblique portion is situated in the superior carotid triangle, and is superficial, being covered merely by the integument, platysma, and deep fascia. Here it lies on the middle constrictor muscle and superior laryngeal nerve. After ascending a short distance, it curves downward and forward beneath the hypoglossal nerve, and, in the second part of its course, runs horizontally along the upper border of the hyoid bone, beneath the hyo-glossus, by which it is separated from the hypoglossal nerve and its vena comitans, and the posterior belly of the digastric and the stylo-hyoid muscles. In this part of its course it lies successively on the middle constrictor of the pharj^nx and the genio-glossus muscle, and crosses a small triangular space known as 'Lesser's triangle,' the sides of which are formed by the tendons of the digastric, the base by the hypoglossal nerve, and the floor by the hyo-glossus muscle, in which situation it is usually tied. In the third part of its course it ascends tortuously, usually beneath the anterior margin of the hyo-glossus, to the under surface of the tongue, and is thence continued to the tip of that structure lying between the lingualis and the genio-glossus muscles. From the anterior edge of the hyo-glossus to its termination it is only covered by the mucous membrane of the under surface of the tongue. This part of the vessel is sometimes called the ranine artery. The lingual artery is accompanied by small vense comitantes. Branches op the Lingital Artery The named branches of the lingual artery are: — (1) The hyoid; (2) the dorsal lingual; (3) the sublingual; and (4) the deep lingual (ranine). (1) The hyoid branch [ramus hyoideus] (fig. 448) is a small vessel which arises from the first part of the lingual, and courses along the upper border of the hyoid bone, superficial to the hyo- glossus, but beneath the insertion of the posterior belly of the digastric and the stylo-hyoid. It anastomoses with its fellow of the opposite side, and with the hyoid branch of the superior thyreoid artery, and supphes the contiguous muscles. (2) The dorsalis linguse (fig. 448) arises from the second portion of the Ungual artery, usually under cover of the posterior edge of the h}'o-glossus muscle. It ascends to the back of the dorsum of the tongue, and, dividing into branches, supplies the mucous membrane on each side of the V formed by the vallate papillae. It also supplies the pillars of the fauces and the tonsil, where it anastomoses with the other faucial and tonsillar arteries. Instead of a single artery, as above described, there may be several small vessels running directly to the parts mentioned. The artery anastomoses in the mucous membrane by very small branches with the 540 THE BLOOD VASCULAR-SYSTEM vessel of the opposite side; but the anastomosis is so minute that when one Hngual artery is injected the injection merely passes across to the opposite side at the tip of the tongue; and when the tongue is divided accurately in the middle line, as in the removal of one-half of that organ, practically no haemorrhage occurs. (3) The sublingual artery [a. sublingualis] (fig. 448) usually comes off from the lingual at the anterior margin of the hyo-glossus. It passes beneath the mylo-hyoid to the subhngual gland, which it supplies, and finally it usually anastomoses with the submental artery, a branch of the external maxillary (facial). It also supplies branches to the side of the tongue, and gives off a terminal twig, which anastomoses beneath the mucous membrane of the floor of the mouth (to which it also gives twigs) with the artery of the opposite side. The artery of the frgenum is usually derived from this vessel (fig. 448). (4) The deep lingual [a. profunda hnguai], the termination of the hngual, courses forward beneath the mucous membrane, on the under surface of the tongue, to the tip. It lies lateral to the genio-glossus, between that muscle and the inferior lingualis, and is accompanied by the lingual vein and terminal branch of the lingual nerve. It follows a very tortuous course, so that it is not stretched when the tongue is protruded. Branches are given off from it to the contiguous muscles and mucous membrane. Near the tip of the tongue it communicates with its fellow of the opposite side, as shown by the fact that when the lingual artery of one side is injected, the injection fluid passes into the branches of the artery of the other side. Fig. 448. — Scheme of the Right Lingual Artery. Glosso-palatinus Descending palatine artery Pharyngo -palatinus Palatine tonsil Ascending palatine branch of external maxillary Tonsillar branch, of dorsal lingual Tonsillar branch of external maxillary Stylo -glossus Dorsal lingual artery Middle constrictor Hypoglossal nerve External maxillary artery Posteriorbelly of digas- tric and stylohyoid Hyoid branch of lingual Sup. laryngeal n Hyoid branch of sup thyreoid Internal carotid artery Common carotid (Walsh am.) Deep lingual artery Artery of frsenulum Hyo-glossus Subungual artery Genio -hyoid Anterior belly of digastric Submental artery Superior thyreoid artery 4. THE EXTERNAL MAXILLARY (FACIAL) ARTERY The external maxillary or facial artery [a. maxillaris externa] (fig. 449) arises immediately above the lingual from- the fore part of the external carotid, at times as a common trunk with the lingual. It courses forward and upward in a tortuous manner to the mandible, and, passing over the body of this bone at the anterior edge of the masseter muscle, winds obliquely upward and forward over the face to the medial angle of the eye, where it anastomoses, under the name of the angular artery, with the dorsal nasal branch of the ophthalmic. It is usually divided into two portions — the cervical and the facial. The cervical portion (fig. 449) ascends tortuously from its origin from the external carotid upward and forward beneath the posterior belly of the digastric and stylo-hyoid muscles, and usualty also beneath the hypoglossal nerve, and then, making a turn, runs horizontally forward for a short way beneath the jaw, either imbedded in or lying under the submaxillary gland. It has here the mylo-hyoid and stylo-glossus beneath it. On leaving the cover of the gland it forms a loop passing first downward and then upward over the lower border of the jaw imme- diately in front of the masseter muscle, where it is superficial, being merely cov- ered by the integument and platysma. Here it can be felt beating, and can be readily compressed. In the above course it lies in the posterior part of the sub- maxillary triangle, and, in addition to the structures already mentioned as cross- ing it, is covered by the skin, superficial fascia, and platysma, and by one or two submaxillary lymphatic nodes. The vein is separated from the artery by the BRANCHES OF THE EXTERNAL MAXILLARY ARTERY 541 submaxillary gland, the posterior belly of the diagastric muscle, the stylo-hyoid muscle, and the hypoglossal nerve. The facial portion (fig. 449) of the external maxillary artery ascends tortuously forward toward the angle of the mouth, passing under the platysma (risorius), the zygomatic muscle, the zygomatic head of the quadratus labii superioris (zygomaticus minor), and the zygomatic and buccal branches of the facial nerve. It here lies upon the jaw and the buccinator muscle. Thence it courses upward by the side of the nose toward the medial angle of the eye, passing over or under the infraorbital and angular heads of the quadratus labii superioris, and under the infraorbital branches of the facial nerve. It lies on the caninus (levator anguli oris) and the infraorbital branches of the fifth nerve. The anterior facial vein takes a straighter course than the external maxillary artery, is separated from it by the zygomatic muscle, and lies lateral to it. Branches of the External Maxillary Artery of the Neck The branches of the external maxillary artery in the neck are: — (1) The ascending palatine; (2) the tonsillar; (3) the glandular; (4) the submental. (1) The ascending palatine [a. palatina ascendens] (figs. 448, 449) — the first branch of the external maxillary, but often a distinct branch of the external carotid — ascends between the internal and external carotids, and then between the stylo-glossus and stylo-pharyngeus mus- cles, and on reaching the wall of the pharynx is continued upward between the superior constrictor and internal pterygoid muscles toward the base of the skull as high as the levator veli palatini, where it divides into two branches, a palatine and a tonsillar. One of these branches, the pala- tine, passes with the levator veU palatini over the curved upper margin of the superior constrictor to the soft palate, where it is distributed to the tissues constituting that structure, and anasto- moses with its fellow of the opposite side and with the descending palatine branch of the internal maxillary, and the ascending pharyngeal, which vessel often to a great extent supplies the place of this artery. The other branch, the tonsillar, supplies the tonsil and the Eustachian tube, anastomosing with the tonsillar branch of the external maxillary (facial) and ascending pharyn- geal arteries. The ascending palatine artery supphes the muscles between which it runs on its way to the palate. (2) The tonsillar branch [ramus tonsillaris] (fig. 449) ascends between the stylo-glossus and internal pterygoid muscles to the level of the tonsil, where it perforates the superior constrictor muscle of the pharynx, and ends in the tonsil, anastomosing with the tonsillar branch of the ascending palatine and with the other tonsillar arteries (fig. 448). It gives branches also to the root of the tongue. (3) The glandular branches [rami glandulares] are distributed to the submaxillary gland as the artery is passing through or beneath that structure. A small twig from one of these branches usually supplies the submaxillary (Wharton's) duct. (4) The submental artery [a. submentahs] (fig. 449) comes off from the external maxillary as the latter vessel lies under cover of the submaxillary gland, and, passing forward on the mylo-hyoid muscle between the base of the jaw and the anterior belly of the digastricus, supphes these structures and the overlying platysma and integuments. It anastomoses with the sub- lingual artery. The external maxillary also supphes the adjacent muscles of the neck. Branches of the External Maxillary Artery on the Face From the lateral or concave side of the artery are given off branches which supply the masseter muscle and anastomose with the masseteric and buccinator branches of the internal maxillary artery, the transverse facial artery, and the infraorbital arteries. From the medial or convex side the following larger and named vessels are given off : — (1) The inferior labial; (2) the superior labial; and (3) the angular. (1) The inferior labial artery [a labiahs inferior] arises at the angle of the mouth and runs in the under Up within the substance of the orbicularis oris, close to the mucous membrane. It anastomoses with the artery of the other side. Frequently an additional branch passes from the external maxillary to the lower lip. (2) The superior labial artery [a. labialis superior] arising from the facial a httle higher than the inferior, passes forward beneath the zygomaticus, and then, hke the inferior labial, courses tortuously along the lower margin of the upper hp between the orbicularis oris and the mucous membrane, about 1.2 cm. (i in.) from the junction of the mucous membrane and the skin. It is usually larger than the inferior labial. It anastomoses with its fellow of the opposite side, and gives off a small artery to the septum — arteria septi nasi. Compression of this vessel will sometimes control hiemorrhage from the nose. (3) The angular artery [a. angularis] (fig. 449) is the terminal branch of the external max- illary. It supplies the nose and anastomoses at the medial angle of the eye with the dorsal nasal branch of the ophthalmic. It is accompanied by the anterior descending vein from the scalp. 542 THE BLOOD-VASCULAR SYSTEM- It lies to the medial side of the lacrimal sac and supphes that structure and the lower part of the orbicularis oculi, beneath which a branch anastomoses with the infraorbital artery. The situation of the artery to the medial side of the lacrimal sac should be borne in mind in opening a lacrimal abscess. Fig. 449. — Scheme of the Right External Maxillary Artery. (Walsham.) Orbicularis oculi muscle Transverse facial artery Quad, labii sup., zygomatic head Zygomaticus muscle Buccinator muscle Masseteric branch Masseter muscle Stylo-pharyngeus muscle Stylo-glossus muscle Ascending palatine branch Tonsillar branch External maxillary artery External carotid artery Posterior belly of digastric muscle Lingual artery Frontal branch of ophthal- mic artery ■Dorsal nasal branch of ophthal- mic artery Angular artery Quad, labii sup., angular head Infraorbital artery Quad, labii sup., infraorbital head i-at. nasal artery Caninus muscle .Artery of septum Superior labial artery Risorius muscle Inferior labial artery Mental branch of inferior alveolar artery Quadratus labii inferioris muscle -Inferior labial artery .Triangularis muscle ■Submental artery .Branches to submaxillary gland Anterior belly of digastric muscle Mylo-hyoid muscle ■Hyo glossus muscle 'Hypoglossal nerve 5. THE STERNOCLEIDOMASTOID The sternocleidomastoid artery [a. sternocleidomastoidea] arises from the posterior side of the external carotid at the point where the carotid is crossed by the digastric muscle. It is distributed to the sternocleidomastoid muscle, and is frequently represented by one of the muscular branches of the occipital artery. 6. THE OCCIPITAL ARTERY The occipital artery [a. occipitalis] (fig. 450) is usually a vessel of considerable size. It comes off from the posterior part of the external carotid opposite the external maxillary (facial), or else a little higher than that vessel. It then winds THE POSTERIOR AURICULAR ARTERY 543 upward and backward to the interval between the mastoid process of the temporal bone and transverse process of the atlas, and, after running horizontally backward in a groove on the mastoid portion of the temporal bone, again turns upward, and ends by ramifying in the scalp over the back of the skull, extending as far forward as the vertex. The vessel may be divided into three parts — viz., that anterior to the sterno- mastoid muscle; that beneath the sterno-mastoid; and that posterior to the sterno-mastoid. In the first part of its course the occipital artery is covered by the integuments and fascia, and is more or less overlapped by the posterior belly of the digastric muscle, the parotid gland, and posterior facial (temporo-maxillary) vein. It is crossed by the hypoglossal nerve as the latter winds forward over the carotid vessels to reach the tongue. It successively crosses in front of the internal carotid artery, the hypoglossal nerve, the vagus nerve, the internal jugular vein, and tlie spinal accessory nerve. In the second part of its course it sinks deeply beneath the digastric muscle into the interval between the mastoid process of the temporal bone and the transverse process of the atlas. It is here covered by the sterno-mastoid, splenius capitis, and longissimus capitis muscles and by the origin of the digastric; and lies, first on the rectus capitis laterahs, which separates it from the vertebral artery, then in a groove, the occipital groove, on the mastoid portion of the tem- poral bone, and then on the insertion of the superior oblique muscle. In the third part of its course it enters the triangular interval formed by the diverging borders of the splenius capitis and the superior nuchal line of the occipital bone. Here it lies beneath the integuments and the aponeurosis uniting the occipital attachments of the sterno-mastoid and trapezius, and rests upon the semi-spinalis capitis (complexus) just before tlie insertion of that muscle into the occipital bone. In company with the greater occipital nerve, it perforates either this aponeurosis, or less often the posterior belly of the epicranius (occipito-frontaHs), and follows roughly, but in a tortuous course, the line of the lamboid suture, lying between the integument and the cranial aponeurosis. In the scalp it divides into several large branches, which ramify over the back of the skull and reach as far forward as the vertex. They anasto- mose with the corresponding branches of the opposite side, and with the posterior auricular and the superficial temporal arteries. Branches of the Occipital Arteey (Fig. 450) The branches of the occipital artery are : — (1) The muscular; (2) the menin- geal; (3) the auricular; C4) the mastoid; (5) the descending; (6) the occipital. (1) The muscular branches [rami musculares] (fig. 450) supply the sternocleidomastoid and adjacent muscles. One of these branches may take the place of the sterno-mastoid branch of the external carotid. The hypoglossal nerve then, as a rule, loops round it instead of round the occipital. (2) The meningeal branches [rami meningei] (fig. 450), one or more in number, are long slender vessels which leave the occipital artery as it crosses the internal jugular vein and, ascend- ing along the vessel, pass with it through the jugular or hypoglossal foramen, and are distributed to the dura mater lining the posterior fossa of the skull. (3) The auricular branch [ramus auricularis] ascends over the mastoid process to the back of the ear, and supphes the pinna and concha. It sometimes takes the place of the posterior auricular artery (fig. 450). (4) The mastoid branch [ramus mastoideus] is a small twig that passes into the skull through the mastoid foramen, supplying the dura mater, the diploe, the walls of the transverse sinus, and the mastoid cells. (5) The descending or princeps cervicis [ramus descendens] (fig. 450), the largest of the branches of the occipital, arises from that artery just before it emerges from beneath the splenius, and, descending for a short distance between the splenius and semi-spinalis capitis (complexus), divides into a superficial and a deep branch. The superficial branch perforates the splenius, supplies branches to the trapezius, and anastomoses with the ascending branch of the transverse cervical artery. The deep branch passes downward between the semi-spinahs capitis (com- plexus) and colli, and anastomoses with the deep cervical branch of the costo-cervical trunk and with branches of the vertebral. The anastomoses between the above-mentioned arteries form important collateral channels after hgature of the common carotid and subclavian arteries (fig. 444). (6) The occipital or terminal branches [rami occipitales] (fig. 450), usually two in number, named from their position medial and lateral, ramify over the scalp, and have already been described. The medial branch generally gives off a twig which enters the parietal foramen (parietal artery) and is distributed to the dura mater. The occipital artery may also give off the stylo-mastoid, the posterior auricular, or the ascending pharyngeal arteries. 7. THE POSTERIOR AURICULAR ARTERY The posterior auricular artery [a. auricularis posterior] (fig. 450) arises from the posterior part of the external carotid artery, usually immediately above the 544 THE BLOOD-VASCULAR SYSTEM posterior belly of the digastric, about the level of the tip of the styloid process. Occasionally it arises under cover of the digastric, quite close to, or as a common trunk with, or as a branch of, the occipital. It courses upward and backward in the parotid gland to the notch between the margin of the external auditory meatus and the mastoid process, where it divides into branches. In this course it rests on the styloid process, crosses the spinal accessory nerve, and is crossed by the facial nerve. Fig. 450. — Scheme of Left Occipital and Posterior Auricular Arteries. (Walsham.) Occipital branch of pos- terior auricular Parotid gland Sterno -mastoid, cut Auricular branch of occipital Post, auricular artery Rectus capitis lateralis Spinal accessory Occipital artery Internal jugular vein Ext. maxillary artery ^ Hypoglossal n Lingual artery Vagus nerve Superior thyreoid Common carotid ^^ \IM/''^_ Lateral branch of occipital '" Medial branch of occipital ■Semi-spinalis capitis Descending branch of occipital ■Superior oblique Longissimus capitis, cut Splenius capitis, cut Meningeal branches Sternocleidomastoid branch of occipital -Internal carotid - Sterno-mastoid - External carotid - Trapezius Branches of the Posterior Auricular Artery The branches of the posterior auricular artery are: — (1) the stylo-mastoid; (2) the auricular; (3) the occipital ffig. 450). The posterior auricular also gives branches to the parotid gland and the adjacent muscles, namely, the posterior belly of the digastric, the stylo-hyoid, and auricularis posterior (retrahens aurem) . (1) The stylo-mastoid artery [a. stylomastoidea] comes off from the posterior auricular artery just before it reaches the notch between the margin of the external auditory meatus and the mastoid process, and, following the facial nerve upward, enters the stylo-mastoid fora- men in the temporal bone. In the facial canal (aqueduct of Fallopius) it gives off the following named twigs: — (a) meatal, to the external auditory meatus; (6) mastoid [rami mastoidei], to the mastoid cells and tympanic antrum; (c) stapedic [ramus stapedius], which runs forward to the stapedius muscle; (d) posterior tympanic [a. tympanica posterior], which anastomoses with the anterior tympanic branch of the internal maxillary, forming with it in the foetus a vascular circle around the membrana tympani; (e) vestibular, to the vestibule and semicircular canals; and (J) terminal, a small twig which leaves the facial canal (by the hiatus) with the great super- ficial petrosal nerve, and anastomoses with the superior petrosal branch of the middle meningeal artery. (2) The auricular branch [ramus auricularis] passes upward behind the ear and beneath the auricularis posterior (retrahens aurem), supplying the medial surface of the pinna and adjacent THE INTERNAL MAXILLARY ARTERY 545 skin. It anastomoses with the posterior branch of the superficial temporal artery. The branches to the pinna not only supply the back of that structure, but some perforate the cartilage, and others turn over its free margin to supply the lateral surface; there they anasto- mose with the anterior auricular branches from the temporal. (3) The occipital branch [ramus ooeipitahs] passes upward and backward, crossing the aponeurotic insertion of the sterno-mastoid muscle. It gives a branch to the posterior belly of the epioranius (occipito-frontaHs), and anastomoses with the occipital artery. 8. THE SUPERFICIAL TEMPORAL ARTERY The superficial temporal artery [a. temporalis superficialis] (fig. 445), is the smaller of the two terminal divisions of the external carotid, though apparently the direct continuation of that vessel. It arises opposite the neck of the man- dible and, under cover of the parotid gland, passes upward in the interval be- tween the condyle and the external auditory meatus to the zygoma, lying on the capsule of the temporo-mandibular joint. Thence it ascends over the posterior zygomatic root and the temporal aponeurosis for about 4 or 5 cm. (1| or 2 in.), and there divides into frontal and parietal branches. It is surrounded by a dense plexus of sympathetic nerves, and is accompanied by the auriculo-temporal nerve, which lies beneath and generally a little behind it. It is crossed by the temporal and zygomatic branches of the facial nerve, and by the auricularis anterior (attra- hens aurem) muscle. As it crosses the zygoma it can be readily felt pulsating immediately in front of the ear, and in this situation can be compressed against the bone. It is here quite superficial, being merely covered by the integuments and a delicate prolongation from the cervical fascia (fig. 445) . Branches of the Superficial Temporal Artery The branches of the superficial temporal artery are: — (1) The parotid; (2) the transverse facial; (3) the anterior auricular; (4) the zygomatico-orbital; (5) the middle temporal; (6) the frontal; (7) the parietal. (1) The parotid branches [rami parotidei] are small twigs given off in the substance of the parotid gland. (2) The transverse facial [a. transversa faciei] is the largest branch of the temporal. It sometimes arises from the external carotid as a common trunk with the temporal. It is at first deeply seated in the substance of the parotid gland, but soon emerging from the upper part of the anterior border of the gland known, courses transversely across the masseter muscle about a finger's breadth below the zygoma. The parotid duct runs below it, and the zygomatic (infraorbital) branches of the facial nerve above it. It supphes the parotid gland, the masseter muscle, and the skin of the face, and anastomoses with the infraorbital, the buccal, and the ex- ternal maxillary (facial) arteries. (3) The anterior auricular branches [rami auriculares anteriores] are three or four in number and supply the tragus, the pinna, and the lobule of the ear, and to some extent the external auditory meatus. (4) The zygomatico-orbital artery [a. zygomaticoorbitahs] (fig. 445), at times a branch of the deep temporal, passes forward along the upper border of the zygoma, in the fat between the superficial and deep layers of the temporal aponeurosis, and, after giving branches to the orbicularis oculi, sends one or more twigs into the orbit through foramina in the zygomatic (malar) bone to anastomose with the lacrimal and palpebral branches of the ophthalmic. (5) The middle temporal artery [a. temporahs media] (fig. 453), arises just above the zygoma, and, perforating the temporal aponeurosis and temporal muscle, ascends on the squa- mous portion of the temporal bone, and anastomoses with the posterior deep temporal artery. (6) The frontal or anterior terminal branch [ramus frontalis] ramifies tortuously in an up- ward and forward direction over the front part of the skull. It hes first between the skin and temporal fascia and then between the skin and epicranial aponeurosis. It supphes the anterior belly of the epicranius (occipito-frontahs) and the orbicularis ocuh muscles, and anastomoses with the supraorbital and frontal branches of the ophthalmic, and with the corresponding artery of the opposite side. The secondary branches given off from this vessel to the scalp run from before backward. (7) The parietal or posterior terminal branch [ramus parietahs] ramifies on the side of the head between the skin and temporal fascia. Its branches anastomose, in front with the anterior terminal branch; behind, with the posterior auricular and occipital arteries; and above, across the vertex of the skull, with the corresponding artery of the opposite side. 9. THE INTERNAL MAXILLARY ARTERY The internal maxillary artery [a. maxillaris interna] (fig. 451) is the larger of the two terminal divisions of the external carotid. It arises opposite the neck of the mandible in the substance of the parotid gland, and, passing first between the mandible and the spheno-mandibular ligament and then between the external 546 THE BLOOD-VASCULAR SYSTEM and internal pterygoid muscles, sinks deeply into the pterygo-palatine (spheno- maxillary) fossa, and there breaks up into its terminal branches. It is divided into three portions: a mandibular, a pterygoid, and a pterygo-palatine. (1) In the first part of its coixrse (the mandibular portion) the artery lies between the neck of the mandible and the spheno-mandibular ligament, taking a horizontal course forward, nearly parallel to and a httle below the auriculo- temporal nerve and the external pterygoid muscle. It is here embedded in the parotid gland, and usually crosses in front of the inferior alveolar (dental) nerve. (2) In the second part of its course (the pterygoid portion) the artery may be placed superficial or deep to the external pterygoid muscle. In the first case it passes between the two pterygoid muscles and the ramus of the jaw, and then turns upward over the lateral surface of the external pterygoid, medial to the tem- poral muscle to gain the two heads of the external pterygoid, between which it Fig. 451.' — Scheme of Left Internal Maxillary. (Walsham.) Infraorbital artery and nerve Spheno-palatine branch Descending palatine branch Naso-palatine branch Artery of the pterygoid canal (Vidian) Anterior deep temporal artery External pterygoid branch Orbital branch Nasal branch--^ Anterior alveolar-/- branch Labial branch- Posterior alve-, olar branch Alveolar branch- Mental branch Submental branch Posterior deep temporal artery Small meningeal artery Middle meningeal artery Temporal artery Anterior tympanic Deep auricular branch Auriculo-temporal Masseteric branch External carotid artery \Spheno-mandibu- lar ligament .Inferior alveolar artery and nerve Internal pterygoid branch Mylo-hyoidean branch sinks into the pterygo-palatine fossa. In the second case it passes medial to the external pterygoid, and is covered by that muscle till it reaches the interval be- tween its two heads, where it then often forms a projecting loop as it turns into the pterygo-palatine fossa. (3) In the third part of its course (the pterygo-palatine portion) the artery lies in the pterygo-palatine fossa beneath the maxillary division of the fifth nerve and in close relationship with the spheno-palatine (Meckel's) ganglion, and there breaks up into its terminal branches. Bhanches of the Internal Maxillary Artery The branches of the internal maxillary artery are: — (A) From the first part : — (1) The deep auricular; (2) the anterior tympanic; (3) the middle meningeal; (4) the inferior alveolar (dental); (5) the accessory meningeal (sometimes). All these vessels pass through bony or cartilaginous canals. FIRST PART OF THE INTERNAL MAXILLARY ARTERY 547 (B) From the second part : — fl) The masseteric; (2) the posterior deep tem- poral; (3) the pterygoid; (4) the buccal; and (5) the anterior deep temporal. All these branches supply muscles. (C) From the third part: — (1) The posterior superior alveolar (dental); (2) the infra-orbital; (3) the descending palatine; (4) the a. canalis pterygoidei or Vidian; and (5) the spheno-palatine. All these branches pass through bony canals. Branches of the First Part of the Internal Maxillary Artery (1) The deep auricular artery [a. auricularis profunda] (fig. 451) passes upward in the sub- stance of the parotid gland behind the capsule of the temporo-mandibular joint, and, perforating the bony or cartilaginous wall of the external auditory meatus, supplies the skin of that passage and the membrana tympani. It at times gives a branch to the joint as it passes behind the temporo-mandibular articular capsule. Fig. 452. — The Middle Meningeal Arteet within the Skull. Middle meningeal artery Anterior meningeal artery (After Spalteholtz.) Anterior etIi-_ V moidal artery , ^^j^^ Posterior eth- / _>^*^w moidal artery ' ■ .. ■ ■ Mastoid branch .- ^^ of occipital artery !r_^=;^ — Occipital artery , • Internal jugular vein , ^ Posterior auricular artery \ Superficial temporal artery , . Deep auricular artery \ \ Anterior tympanic artery Middle meningeal artery Internal maxillary artery Accessory meningeal branch External pterygoid branch Inferior alveolar artery I Artery of the pterygoid canal (Vidian) Posterior lateral ' Mylohyoid branch nasal arteries , , Major palatine artery ' Spheno-palatine artery Major and minor palatine arteries (2) The anterior tympanic artery [a. tympanica anterior] is a long slender vessel, which runs upward behind the condyle of the jaw to the petro-tympanic (Glaserian) fissure, through which it passes to the interior of the tympanum. Here it supphes the fining membrane of that cavity and anastomoses with the other tympanic arteries, forming with the posterior tympanic branch of the stylo-mastoid artery a vascular circle around the membrana tympani. This circle is more distinct in the foetus than in the adult. (3) The middle meningeal artery [a. meningea media] is the largest branch of the internal ma.xillary artery. It comes off from the vessel as it hes between the spheno-mandibular liga- ment and the ramus of the jaw, and under cover of the external pterygoid passes directly up- ward to the foramen spinosum, through which it enters the interior of the cranium. In this part of its course it is crossed by the chorda tympani nerve; and just before it enters the foramen is embraced by the two heads of origin of the auriculo-temporal nerve (fig. 451). The trunk of the mandibular division of the fifth nerve, as it emerges from the foramen ovale, lies in front of the artery. As the artery passes upward it is surrounded b3' filaments of the sympathetic nerve, and is accompanied by two veins. On entering the skull it ramifies between the bone and dura mater, supplying both structures. It at first ascends for a short 548 THE BLOOD-VASCULAR SYSTEM distance in a groove on the greater wing of the sphenoid, and then divides into two branches, an anterior and a posterior. The anterior branch passes upward, in the groove on the greater wing of the sphenoid, on to the parietal bone at its anterior and inferior angle; at this spot the groove becomes deepened and often bridged over by a thin plate of bone, being converted for 6 to 12 mm. (j to I in.) or more into a distinct canal. The situation of the artery is here indicated on the exterior of the skull by a spot 3.7 cm. (Ij in.) behind, and about 2.5 cm. (1 in.) above, the zygomatic process of the frontal bone. The anterior branch is continued along the anterior border of the parietal bone nearly as far as the superior sagittal sinus, and gives off in its course, but especially poste- riorly, large branches which ramify in an upward and backward direction in grooves on the pari- etal bone (fig. 452). The posterior branch passes backward over the squamous portion of the temporal bone; and thence on to the parietal bone, behind the anterior branch. This branch and its collaterals extend upward as far as the sagittal sinus, and backward as far as the transverse (lateral) sinus. In addition to its terminal anterior, and terminal posterior branches, the middle meningeal gives off: — (a) Ganglionic branhecs to the semOunar (Gasserian) gangUon and its sheath of dura mater, (b) A superficial petrosal branch [ramus petrosus superficiahs], which enters the hiatus of the facial canal in company with the large superficial petrosal nerve and anasto- moses with the terminal branch of the stylo-mastoid artery, (c) A superior tympanic artery [a. tympanica superior], which enters the canal for the tensor tympani, and supplies that muscle. (d) An orbital or lacrimal branch, which enters the orbit at the outermost part of the superior orbital (sphenoidal) fissure, or sometimes through a minute foramen, just lateral to that fissure, and anastomoses with the lacrimal branch of the ophthalmic, (e) Anastomotic or perforating branches which pierce the greater wing of the sphenoid bone, and anastomose with the deep temporal arteries. (4) The inferior alveolar artery [a. alveolaris inferior] (fig. 451), arising from the internal maxillary as it lies between the spheno-mandibular hgament and neck of the jaw, courses downward to the mandibular foramen, which it enters in company with, and a little behind and lateral to, the inferior alveolar nerve. It then passes along the canal in the interior of the bone, giving off branches to the molar, premolar, and canine teeth. On reaching the mental foramen it divides into two branches, the incisive and the mental. The incisive continues its course in the bone, supplies branches to the incisor teeth, and anastomoses with the artery of the opposite side. The mental branch [ramus mentahs] passes through the mental foramen in company with the mental branch of the inferior alveolar (dental) nerve, and emerges on the chin under cover of the quadratus labii inferioris. It anastomoses above with the inferior labial (coronary), and below with the submental, and also with the inferior labial. Near its origin the artery gives off (a) a lingual or gustatory branch, which accompanies and supplies the lingual nerve, and ends in the mucous membrane of the mouth; and, just before it enters the man- dibular (dental) foramen in the lower jaw, (6) a mylo-hyoidean branch [ramus mylohyoideus], which accompanies the nerve of that name along the groove in the lower jaw, and, after supply- ing the mylo-hyoid muscle, anastomoses with the subhngual and submental arteries. (5) The accessory or small meningeal branch [ramus meningeus aocessoria] arises either from the internal maxillary a little in front of the middle meningeal, or as a branch of the latter vessel. It passes upward along the com'se of the mandibular division of the fifth nerve, and, entering the skull through the foramen ovale, is distributed to the semilunar (Gasserian) ganglion, and to the waUs of the cavernous sinus and the dura mater in the neighbourhood. Branches op the Second Part of the Internal IMaxillary Artery The branches of the second portion of the internal maxillary all supply muscles. They are: — (1) The masseteric; (2) the posterior deep temporal; (3) the pterygoid; (4) the buccal; and (5) the anterior deep temporal. (1) The masseteric artery [a. masseterica] comes off from the internal maxillary as the latter is passing from between the neck of the jaw and the spheno-mandibular ligament. It passes, with the masseteric nerve tln-ough the mandibular (sigmoid) notch in the mandible and supplies the masseter muscle. Some filaments perforate the muscle and anastomose with the transverse facial and with the masseteric branches of the external maxillary (facial). (2) The posterior deep temporal artery [a. temporalis profunda posterior] arises, as a rule, from the internal maxillary in common with the masseteric for a little be3'ond that branch. It passes upward beneath the temporal muscle in a slight groove on the anterior margin of the squamous portion of the temporal bone, supplying the temporal muscle, the pericranium and the external layer of the bone. It anastomoses with the other temporal arteries. (3) The pterygoid branches [rami pterygoidei] are short trunks which pass into and supply the internal and external pterygoid muscles. (4) The buccal artery [a. buccinatoria] (fig. 451) courses forward and downward with the buccal nerve to the buccinator muscle, lying in close contact with the medial side and anterior margin of the tendon of the temporal muscle and coronoid process of the lower jaw. It supplies the buccinator muscle and mucous membrane of the mouth, and anastomoses with the external maxillary (facial), transverse facial, and infraorbital arteries. (5) The anterior deep temporal artery [a. temporalis profunda anterior] ascends beneath the temporal muscle in a slight groove on the greater wing of the sphenoid bone. It supplies the muscle, pericranium, and subjacent bone, and gives off small branches which pass through minute foramina in the zygomatic (malar) bone. Some of these last branches enter the orbit and anastomose with the lacrimal artery; others emerge on the face and anastomose with the transverse facial artery. THE INTERNAL CAROTID ARTERY 549 Branches of the Third Part of the Internal Maxillary Artery The branches of the third part of the internal maxillary artery, like those of the first part, all pass through bony canals. They are the following: — (1) The posterior superior alveolar (dental); (2) the infraorbital; (3) the descending palatine; (4) the artery of the pterygoid canal (Vidian); and (5) the sphenopalatine. (1) The posterior superior alveolar (dental) artery [a. alveolaris superior posterior] arises from the internal maxiUary as the latter is passing into tlie pterygo-palatine (spheno-maxillary) fossa, and descends in a tortuous manner in a gi'oove on the back of the body of the maxilla. It gives off branches to the maxillary sinus, to the molar and premolar teeth, the gums, and to the buccinator muscle. (2) The infraorbital artery [a. infraorbitalis] arises from the internal maxillary, generally as a common trunk with the posterior alveolar (dental). It passes forward and a little upward through the pterygo-palatine (spheno-maxillary) fossa; then forward in company with the infraorbital branch of the fifth nerve, first along the groove, and then tlirough the canal in the orbital plate of the maxilla; and finally, emerging on the face at the infraorbital foramen, under cover of the quadratus labii superioris, is distributed to the structures forming the upper Up, the lower eyeUd, the lacrimal sac, and the side of the nose. It anastomoses with the superior labial (coronary) and angular branches of the external maxillary (facial), with the nasal and lacrimal branches of the ophthalmic, and with the transverse facial. It gives off small branches supplying the fat of the orbit and the inferior rectus and inferior oblique muscles. The anterior superior alveolar branch [a. alveolaris superior anterior] passes downward through a groove in the anterior wall of the maxilla, together with the anterior alveolar branch of the infraorbital nerve, and supplies branches to the incisor and canine teeth and the mucous membrane of the maxillary sinus. It has also nasal branches which pass through the foramina in the nasal process of the maxiUa. (3) The descending palatine artery [a. palatina descendens] descends in the pterygo- palatine canal with the anterior palatine branch of the spheno-palatine ganglion. On emerging on the palate at the greater (posterior) palatine foramen, it divides into the following branches; — (a) The major palatine artery [a. palatina major], which courses forward in the muco-perios- teum at the junction of the hard palate with the alveolar process as far as the incisive (anterior palatine) foramen, where it anastomoses with the spheno-palatine artery; and (b) minor palatine arteries [aa. palatina; minores], which pass backward and downward into the soft palate, contributing to the supply of that structure, and anastomosing with the ascending palatine artery. After the operation for cleft palate, serious heemorrhage occasionally occurs from the descending palatine artery. The foramen is situated a little behind, and medial to, the last molar tooth, and almost immediately in front of the hamular process (fig. 452). (4) The arteria canalis pterygoidei or Vidian artery is a long slender branch which passes backward through the pterygoid (Vidian) canal in company with the nerve of tlie same name into the cartilage of the lacerated foramen. It gives off branches which supply the roof of the pharynx, and anastomose with the ascending pharyngeal and spheno-palatine arteries; also a branch which is distributed to the Eustachian tube; and one which enters the tympanum, and anatomoses with the other tympanic arteries. (.5) The spheno-palatine [a. sphenopalatina], the terminal branch of the internal maxillary, passes with the naso-palatine branch of the spheno-palatine ganglion from the pterygo-palatine (spheno-maxillary) fossa into the nose through the spheno-palatine foramen. Crossing the roof of the nose in the muco-periosteum, it passes on to the septum, and then runs forward and downward in a groove on the vomer toward the incisive (anterior palatine) foramen, where it anastomoses with the anterior palatine artery, which enters the nose through the lateral com- partment of that foramen (the canal of Stenson). In this course it gives off branches to the roof and contiguous portions of the pharynx, and to the sphenoidal cells. It has also posterior lateral nasal branches [aa. nasales post, laterales], which ramify over the nasal conchse (tur- binate bones) and lateral walls of the nose, and give twigs to the ethmoidal and frontal sinuses and the Uning membrane of the maxillary sinus; and posterior septal branches [aa. nasales post, septi], which run upward and forward, giving small twigs to the mucous membrane cover- ing the upper part of the septum, and which pass through the cribriform plate of the ethmoid, and anastomose with the ethmoidal arteries (perforating or meningeal branches). THE INTERNAL CAROTID ARTERY The internal carotid artery [a. carotis interna] (figs. 453 and 454) arises with the external carotid at the bifurcation of the common carotid, opposite the upper border of the thyreoid cartilage, on a level with the fourth cervical vertebra. It is at first placed a little lateral to the external carotid, but as it ascends in the neck the external carotid becomes more superficial and in front of the internal. The internal carotid passes up the neck, in front of the transverse processes of the upper cervical vertebrae, lying upon the longus capitis (rectus capitis ant. major), to the carotid foramen, thence through the carotid canal in the petrous portion of the temporal bone, making at first a forward and medial turn and then a second turn upward, and enters the cranium through the foramen lacerum. It makes a sig- moid curve on the side of the body of the sphenoid bone, and terminates, after perforating the dura mater, by dividing opposite the anterior clinoid processes { 550 THE BLOOD-VASCULAR SYSTEM in the lateral fissure (fissure of Sylvius) j into the anterior and middle cerebral arteries. In its course up the neck it often forms one or more curves, especially in old people. Between the internal and the external carotids, at their angle of diver- gence, is situated the carotid body or gland [glomus caroticum]. The internal carotid is the continuation upward of the primitive dorsal aorta, and supplies the greater part of the brain, the contents of the orbit, and parts of the internal ear, forehead, and nose. It is divided into three portions: — (1) a cervical; (2) a petrosal; and (3) an intracranial. 1. The Cervical Portion Relations. — In the neck (fig. 453) the artery is at first comparatively superficial, having in front of it, as it lies in the superior carotid triangle, the skin, superficial fascia, platysma and Fig. 453. — The Carotid Arteries. (After Toldt, ''Atlas of Human Anatomy," Rebman Lon- don and New York.) Anterior deep temporal artery Lacrimal gland Posterior deep temporal artery Lateral palpebral arteries Temporal muscle \ \ *, \ Supraorbital artery Frontal artery Dorsal nasal artery Masseteric artery External pterygoid muscle Middle tem- poral artery Middle men ingeal artery "^-.^V Superficial tern- \^ poral artery Internal maxil- , lary artery - \ Inferior alveolar artery Spheno-mandibular ligament Stylomastoid artery Inferior alveolar Posterior auricular artery Mylohyoid branch. Posterior belly of digastric muscle Internal pterygoid muscle Lingual nerve Buccinator artery Occipital artery '' External carotid artery External maxillary artery Sternocleidomastoid artery ,' Lingual artery '' /'' Hyoglossus muscle'' ^ Hyothyreoid membrane ' / Superior thyreoid artery ' / Internal carotid artery Posterior branch Anterior branch Common carotid artery Thyreohyoid muscle Infraorbital artery Superior pos- terior alve- olar artery Inferior labial artery ~~^ Mylohyoid muscle ■-^External maxillary artery Submental artery ^ ThiiTreohyoid muscle .^ Hyoid branch of the lingual artery Superior laryngeal artery Crico-thyreoid branch Middle crico-thyreoid ligament deep fascia, and the overlapping edge of the sterno-mastoid muscle. Higher up, as it sinksHDe- neath the parotid gland, it becomes deeply placed, and is crossed by the posterior belly of the digastric and stylo-hyoid muscles, the hypoglossal nerve, and the occipital and posterior auricu- lar arteries; whilst still higher it is separated from the external carotid artery, which here gets THE INTRACRANIAL PORTION 551 in front of it, by the stylo-glossus and stylo-pharyngeus muscles, the glosso-pharyngeal nerve, the pharyngeal branch of the vagus nerve, and by the stylo-hyoid ligament. Behind, it hes upon the longus capitis (rectus capitis anticus major), which separates it from the transverse processes of the three upper cervical vertebrae, on the superior cervical ganglion of the sympathetic nerve, and on the vagus nerve. Near the base of the skull, the hypofilossal, vasus, glosso-pharyngeal, and spinal accessory nerves cross obhquely behind it, separating it here from the internal jugular vein, which, as the artery is about to enter the carotid canal, also forms one of its posterior relations. On its lateral side are the internal jugular vein and vagus nerve. On its medial side it is in relation with the pharynx, the superior constrictor muscle separat- ing it from the tonsil. The ascending pharyngeal and ascending palatine arteries, and at the base of the skull the Eustachian tube and levator palati muscles, are also medial to it. 2. Thf Petrosal Portion The petrosal portion (fig. 454) is situated in the carotid canal in the petrous portion of the temporal bone. It is here separated from the walls of the canal by a prolongation downward of the dura mater. In this part of its course it first ascends in front of the tympanum and cochlea of the internal ear; it then turns forward and medially, lying a little medial to and behind the Eustachian tube, and enters the cranial cavity by turning upward through the fora- FiG. 454. — The Internal Carotid Artert in the Canal. Superficial petrosal branch (After Spalteholz.) Superior ophthalmic vein Cavernous sinus Superior tympanic artery Anterior tympanic artery _« Jugular fossa — -Longus capitis muscle Inferior tympanic artery .^Internal carotid artery Ascending pharyngeal artery men lacerum, lying upon the Ungula of the sphenoid bone. In this part of its course it is accom- panied by the ascending branches from the superior cervical ganghon of the sympathetic. These form a plexus about the artery, but are situated chiefly on its lateral side. It is also surrounded by a number of small veins, which receive tributaries from the tympanum and open into the cavernous sinus and internal jugular vein. 3. The Intracranial Portion On entering the cranium through the foramen lacerum, the internal carotid first ascends to reach the lateral part of the body of the sphenoid medial to the hngula. It then follows the carotid sulcus forward and slightly downward along the medial waU of the cavernous smus (fig. 454). Here it has the sixth nerve immediately lateral to it, and is covered by the hning membrane of the sinus. Again turning upward, it pierces the dura mater on the medial side of the anterior clinoid process, and, passes between the second and third nerves to the anterior perforated substance. At the medial end of the lateral (Sylvian) fissure it pierces the arachnoid and divides into its two terminal branches, the anterior and middle cerebral. As it hes in the 552 THE BLOOD-VASCULAR SYSTEM foramen laoerum the artery is crossed on its lateral side by the great superficial petrosal nerve as the latter goes to join the great deep petrosal from the carotid plexus to form the nerve of the pterygoid, canal (Vidian). Branches of the Internal Carotid Artery The cervical portion gives off no branch. The petrosal portion gives off the caroticotympanic. The branches of the intracranial portion are : — (2) ophthalmic ; (3) posterior communicating; (4) chorioid; (5) anterior cerebral; (6) middle erebral. As the internal carotid artery lies on the medial side of the cavernois sinus, it also gives off the following small branches — branches to the walls of the cavernous inus; to the pituitary body; to the semilunar (Gasserian) ganglion; to the dura mater. These anastomose with anterior branches of the middle meningeal. 1. THE CAROTICOTYMPANIC ARTERY The caroticotympanic enters the tympanum through a small foramen in the posterior wall of the carotid canal, and contributes its quota to the blood-supply of that cavity. It anastomoses with the tympanic branches of the stylo-mastoid, internal maxillary, and middle meningeal arteries. 2. THE OPHTHALMIC ARTERY The ophthalmic artery (fig. 455) comes off from the internal carotid immedi- ately below the anterior clinoid process just as the latter vessel is passing through the dura matter. Entering the orbit through the optic foramen below and lateral to theo ptic nerve, it at once perforates the sheath of dura mater which is prolonged through the optic foramen on both artery and nerve. It then runs in a gentle curve with a lateral convexity below the optic nerve and lateral rectus, being here crossed by the naso-ciliary (nasal) nerve. Turning forward and upward, it passes over the optic nerve, to its medial side. Thence it runs obHquely beneath the superior rectus in front of the naso-ciliary (nasal) nerve under the lower border of the superior oblique, but above the medial rectus, and continues its course under the pulley for the superior oblique and reflected tendon of that muscle to the medial palpebral region, where it divides into the frontal and nasal branches. Branches of the Ophthalmic Artery The branches of the ophthalmic artery are: — (1) the lacrimal; (2) the supra- orbital; (3) the central artery of the retina; (4) the muscular; (5) the ciliary; (6) the posterior ethmoidal; (7) the anterior ethmoidal; (8) the medial palpe- bral; (9) the frontal; and (10) the dorsal nasal. (1) The lacrimal artery [a. laorimalis], is usually the first and often the largest branch 9f the ophthalmic. It arises between the superior and lateral rectus on the lateral side of the optic nerve from the ophthalmic, soon after that vessel has entered the orbit. At times it is given off from the ophthalmic outside the orbit, and then usually passes into that cavity through the superior orbital (sphenoidal) fissure. It runs forward along the lateral waO of the orbit with the lacrimal nerve, above the upper border of the lateral rectus, to the lacrimal gland, which it supplies. In this course it furnishes the following branches: — (a) Recurrent, one or more branches which pass backward through the superior orbital (sphenoidal) fissure, and anasto- mose with the lacrimal branch of the middle meningeal artery. The anastomosis is sometimes of large size, and then takes the chief share in the formation of the lacrimal artery, (b) Mus- cular branches, distributed chiefly to the lateral rectus, (c) Zygomatic branches — small twigs, which pass through the zygomatico-orbital (malar) canals, and anastomose with the orbital branch of the middle temporal, and with the transverse facial on the cheek, (d) Lateral palpebral arteries [aa. palpebrales laterales] which are distributed to the upper- and lower eyelids and to the conjunctiva, (e) Ciliary. See Ciliary Arteries, page 553. (2) The supraorbital artery [a. supraorbitaHs] usually arises from the ophthalmic as the latter vessel is about to cross over the optic nerve. Passing upward to the medial side of the superior rectus and levator palpebrse, it runs along the upper surface of the latter muscle with the frontal nerve in the orbital fat, but beneath the periosteum, to the supraorbital notch. On emerging on the forehead beneath the orbicularis ocuU, it divides into a superficial and deep branch, the former ramifies between the skin and epicranius (occipito-frontahs), the latter BRANCHES OF THE OPHTHALMIC ARTERY 553 between the epicranius and the pericranium. Both branches anastomose with the anterior branches of the superficial temporal, the angular branch of the external maxillary (facial), and the transverse facial artery. The branches of the supraorbital are: — (o) periosteal, to the periosteum of the roof of the orbit; (6) muscular, to the levator palpebra; and superior rectus; (c) diploic, given off as the artery is passing through the supraorbital notch and, entering a minute foramen at the bottom of the notch, is distributed to the diploe and frontal sinuses; (d) trochlear, to the pulley of the superior obhque; (e) palpebral, to the upper eyehd. (3) The arteria centralis retinae, a small but constant branch, comes off from the oph- thalmic close to the optic foramen, and, perforating the optic nerve about 6 mm. (\ in.) behind the globe, runs forward in (the substance of the nerve) to the eyeball, supplying the retina. Its further description is given in the section on the Eye. (4) The muscular branches [rami musculares] are very variable in their origin and distri- bution. They may be roughly divided into superior and inferior sets. The superior or smaller set supply the superior oblique, the levator palpebra3, and superior rectus. The inferior pass forward, between the optic nerve and the inferior rectus, supplying that muscle, the medial rectus, and the inferior oblique. From the muscular branches are given off the anterior ciliary arteries. (See Ciliary Arteries.) (5) The ciliary arteries are divided into three sets: — The short posterior, the long posterior, and the anterior, (i) The short posterior [aa. oiliares posteriores breves], five or six in number, come off chiefly from the ophthalmic as it is crossing the optic nerve. They run forward about Fig. 45.5. — The Left Ophtii.'vlmic Artery and Vein. Supraorbital artery Lacrimal gland Superior rectus, cut — pr; Eyeball Lateral rectus Lacrimal artery Superior rectus, cut Inferior ophthalmic Superior ophthalmic Optic nerve Superior ophthalmic Commencement of superior ophthalmic vein Reflected tendon of superior oblique Ophthalmic artery Anterior ethmoidal artery Posterior ethmoidal artery Ciliary arteries Levator palpebrse, cut Annulus communis (of Zinn) Ophthalmic artery Optic commissure Internal carotid artery the nerve, dividing into twelve or fifteen smaU vessels, which perforate the sclerotic around the entrance of the optic nerve, and are distributed to the chorioid coat, (ii) The long posterior ciUary arteries [aa. ciliares posteriores longte], usually two, sometimes three, in number, come off from the ophthalmic on either side of the optic nerve, and run forward with the short ciliary to the sclerotic. On piercing the sclerotic, they course forward, one on either side of the eyeball between the sclerotic and the chorioid to the ciliary processes and iris. Their further distribu- tion is given under the anatomy of the Eye. (iii) The anterior ciliary arteries [aa. ciliares an- teriores] are derived from the muscular branches and from the lacrimal. They run to the globe along the tendons of the recti, forming a zone of radiating vessels beneath the conjunctiva. Some of them, the episcleral arteries [aa. episclerales] ; perforate the sclerotic about 6 mm. (-f in.) behind the cornea, and supply the iris and ciUary processes. It is these vessels that are enlarged and congested in iritis, forming the circumcorneal zone of redness so characteristic of that disease. They then differ from the tortuous vessels of the conjunctiva in that they are straight and parallel. The remainder constitute the anterior conjunctival arteries [aa. oon- junctivales anteriores]. (6) The posterior ethmoidal artery [a. ethmoidalis posterior] (fig. 455) runs medially be- tween the superior oblique and medial rectus, and, leaving the orbit by the posterior ethmoidal canal, together with the posterior ethmoidal branch of the naso-ciliary (nasal) nerve, enters the posterior ethmoidal cells, whence it passes through a transverse slit-hke aperture between the sphenoid bone and cribriform plate of the ethmoid bone into the cranium. It gives off (a) ethmoidal branches to the posterior ethmoidal cells; (6) meningeal branches to the dura mater lining the cribriform plate; and (c) nasal branches, which pass through the cribriform plate to ( \ 554 THE BLOOD-VASCULAR SYSTEM the superior meatus and upper spongy bones of the nose, and anastomose with the nasal branches of the spheno-palatine artery (fig. 452). (7) The anterior ethmoidal artery [a. ethmoidahs anterior] (fig. 452), a larger branch than the posterior ethmoidal, arises in front of the latter, passes medially between the superior obhque and medial rectus, and, leaving the orbit through the anterior ethmoidal canal, in com- pany with the anterior ethmoidal nerve, enters the cranial cavity. After running a short dis- tance beneath the dura mater on the cribriform plate of the ethmoidal bone, it passes into the nose through the horizontal slit-hke aperture by the side of the crista gaUi. Its terminal branch passes along the groove on the under surface of the nasal bone, and emerges on the nose between the bone and lateral cartilage, terminating in the skin of that organ. It gives off the following branches in its course: — (i) Ethmoidal, to the anterior ethmoidal cells; (ii) anterior meningeal artery, [a. meningea anterior] to the dura mater of the anterior fossa; (iii) nasal, to the middle meatus and anterior part of the nose; (iv) frontal, to the frontal sinuses; (v) cutaneous, or terminal, to the skin of the nose. (8) The medial palpebral arteries [aa. palpebrales mediales] arise either separately or by a common trunk from the ophthalmic artery opposite the pulley for the superior obhque, just as the latter vessel is about to divide into its terminal branches. They pass, one above and one below, the medial palpebral hgament and then skirt along the upper and lower eyelids respectively, near the free margin between the palpebral tarsi and the orbicularis muscle, and form a superior and an inferior tarsal arch [arcus tarsus superior et inferior] by anastomosing with the lateral palpebral branches of the lacrimal. The upper also anastomoses with the supra- orbital artery and orbital branch of the temporal artery; the lower with the infraorbital, the angular branch of the external maxillary (facial), and the transverse facial arteries. A branch from the lower palpebral passes with the ductus nasolacrimalis as far as the inferior meatus. Small twigs, the posterior conjunctival arteries [aa. conjunctivales posteriores], are also given to the caruncula lacrimahs and conjunctiva. (9) The frontal artery [a. frontalis], the upper of the terminal branches of the ophthalmic, pierces the superior tarsus at the medial angle of the orbit, passes upward over the frontal bone .beneath the orbicularis ocuh, supphes the structures in its neighbourhood, and anastomoses with its feUow of the opposite side, with the supraorbital, and with the anterior division of the superficial temporal artery. (10) The dorsal nasal [a. dorsahs nasi], the lower of the terminal branches of the ophthalmic, leaves the orbit at the medial angle by perforating the tarsus above the medial palpebral liga- ment. It then descends along the dorsum of the nose, beneath the integuments, and anasto- moses with the angular and lateral nasal branches of the external maxillary (facial). It gives off a lacrimal branch as it crosses the lacrimal sac, and a transverse nasal branch as it crosses the root of the nose; the latter vessel anastomoses with its fellow of the opposite side. 3. THE POSTERIOR COMMUNICATING ARTERY The posterior communicating artery [a. communicans posterior] (fig. 456) is given off from the internal carotid just before the division of that vessel into the anterior and middle cerebral arteries; occasionally it arises from the middle cere- bral itself. It is as a rule a slender vessel which runs backward over the optic tract and pedunculus cerebri along the side of the hippocampal gyrus to join the posterior cerebral. At times, how- ever, it is of considerable size, and contributes chiefly to form the posterior cerebral, the portion of the latter vessel between the basilar and posterior communicating being then as a rule reduced to a mere rudiment. It gives off the following branches: — (a) the hippocampal, to the gyrus of that name; and (6) the middle thalamic, to the optic thalamus. 4. THE CHORIOID ARTERY The chorioid artery [a. chorioidea] is a small but constant vessel which arises as a rule from the back part of the internal carotid just lateral to the origin of the posterior communicating. It passes backward on the optic tract and the pedunculus cerebri, at first lying parallel and lateral to the posterior communicating artery. It then dips under the edge of the uncinate gyrus and, entering the chorioid fissure at the lower end of the inferior cornu of the lateral ventricle, ends in the chorioid plexus and supplies the hippocampus and fimbria. 5. THE ANTERIOR CEREBRAL ARTERY The anterior cerebral artery [a. cerebri anterior] (figs. 456, 459), one of the terminal branches into which the internal carotid divides in the lateral fissure (fissure of Sylvius), supplies a part of the cortex of the frontal and parietal lobes of the brain and a small part of the basal ganglia. It passes at first anteriorly and medially across the anterior perforated substance between the olfactory and optic nerves to the longitudinal fissure where it approaches its fellow of the opposite side CIRCULUS ARTERIOSUS 555 and communicates with it by a short transverse trunk, about five mm. long, known as the anterior communicating artery [a. communicans anterior] (fig. 456). On- ward from this point it runs side by side with its fellow in the longitudinal fissure round the genu of the corpus callosum; then, turning backward, it continues along the upper surface of that commissure, and, after giving off large branches to the frontal and parietal lobules, anastomoses with the posterior cerebral artery. 6. THE MIDDLE CEREBRAL ARTERY The middle cerebral artery [a. cerebri media] (figs. 456, 460), the larger of the terminal divisions of the internal carotid, supplies the basal ganglia and a part of the cortex of the frontal and parietal lobes. It passes obliquely upward and lateralward into the lateral (Sylvian) fissure, and opposite the insula divides into cortical branches. CiEcuLus Arteriosus The four arteries which supply the brain, namely, the two internal carotid arteries and the two vertebrals (which unite to form the basilar), form a remark- FiG. 456. — -The Arteries of the Brain. (The cerebellum has been out away on the left side to show the posterior part of the cere- brum. From a preparation in the Museum of St. Bartholomew's Hospital.) Anterior cerebral, artery Middle cerebral artery Internal carotid. artery Postero-median perforating Posterior cere- bral artery Superior cerebel- lar artery Anterior inferior cerebellar artery Vertebral artery Anterior commu- nicating artery Antero-lateral perforating Chorioid Posterior com- municating artery Posterior chorioid Basilar artery Hum, cut Anterior spinal artery able anastomosis at the base of the brain known as the circle of Willis [circulus arteriosus (WilHsi)]. This so-called circle, which has really the form of a heptagon, is formed, in front, by the anterior communicating artery uniting the anterior cerebral arteries of opposite sides; laterally, by the internal carotids and the posterior communicating arteries stretching between these and the posterior cerebrals; behind, by the two posterior cerebrals diverging from the bifurcation of the basilar artery (fig. 456). This free anastomosis between the two internal carotid and the two vertebral arteries serves to ecjuaUse the flow of blood to the various portions of the brain; and, should one or more of the arteries entering into the formation of the circle be temporarily or permanently obstructed, it ensures a flow of blood to the otherwise deprived part through some of the collateral arteries. Thus, if one carotid or one vertebral is obstructed, the parts suppHed by that vessel receive their blood through the circle from the remaining pervious vessels. Indeed, one vertebral artery alone has been found equal to the task of carrying sufBcient blood for the supply of the > 556 THE BLOOD-VASCULAR SYSTEM brain after ligature of both the carotids and the other vertebral artery. Further, the circle of Willis is the only medium of communication between the ganglionic or central and the peripheral or cortical branches of the cerebral arteries, and between the various ganglionic branches them- selves. The ganglionic and the cortical branches form separate and distinct systems, and do not anastomose with each other; and the ganglionic, moreover, are so-called end-vessels, and do not anastomose with the neighbouring ganglionic branches. The three cerebral arteries, anterior, middle, and posterior may be regarded as branches of the circle of Willis. (For details concerning the distribution of the cerebral arteries see p. 562.) THE SUBCLAVIAN ARTERY The subclavian artery on the right side [a. subclavia dextra] arises at the bifur- cation of the innominate opposite the upper limit of the right sterno-clavicular articulation. On the left side it arises from the arch of the aorta, and, as far as the medial border of the scalenus anterior, is situated deeply in the chest. The first portion of the left subclavian artery is described separately. Beyond the medial border of the scalenus anterior the artery has the same rela- tions on both sides. It courses from this point beneath the clavicle in a slight curve across the root of the neck to the lateral border of the first rib, there to end in the axillary artery. Thus the course of the artery in the neck will be indicated by a line drawn from the sterno-clavicular joint in a curve with its convexity upward to the middle of the clavicle. The height to which the artery rises in the neck varies. It is perhaps most commonly about 1.2 cm. (| in.) above the clavicle. If the cm-ved line above mentioned is drawn to represent part of the circumference of a circle having its center at a point on the lower margin of the clavicle 3.7 cm. d^ in.) from the sternal end of that bone, the line of the artery will be sufficiently well indicated for all practical purposes. In its course the artery arches over the dome of the pleura and gains the groove on the upper surface of the first rib by passing between the scalenus anterior and medius muscles. The artery is accom- panied by the subclavian vein, the latter vessel lying in front of the scalenus anterior, anterior to the artery, and on a slightly lower plane. The subclavian artery is divided into three portions — as it lies medial to, pos- terior to, or lateral to, the scalenus anterior muscle. THE FIRST OR THORACIC PORTION OF THE LEFT SUBCLAVIAN ARTERY The left subclavian artery [a. subclavia sinistra] (fig. 457) arises from the left end of the arch of the aorta. The first part of the left subclavian is consequently longer than the first part of the right, which arises at the bifurcation of the innominate artery. The artery at its origin is situated deeply in the thorax, and as it arises from the aorta is on a plane posterior to and a little to the left of the thoracic portion of the left common carotid. It first ascends almost vertically out of the chest, and at the root of the neck curves laterally over the apex of the left plem-a and lung to the interval between the anterior and middle scalene mus- cles. Beyond the medial border of the scalenus anterior — that is, in the second and third portions of its course — its relations are similar to those of the right sub- clavian artery. Relations. — In front it is covered by the left pleura and lung, whilst more superficial are the sterno-thyreoid, sterno-hyoid, and sterno-mastoid muscles. It is crossed a Uttle above its origin by the left innominate vein, and higher in the neck near the scalenus anterior by the internal jugular, vertebral, and subclavian veins. The phrenic nerve crosses the artery imme- diately medial to the scalenus anterior, and then descends parallel to it, but on an anterior plane, to cross the arch of the aorta. The vagus nerve descends parallel to the artery between it and the left common carotid, coming into contact with its anterior surface just before crossing the arch of the aorta. The left cervical cardiac nerves of the sympathetic also descend in front of it on their way to the cardiac plexus. The left ansa subclavia also loops in front of the subclavian artery. The left common carotid is situated anteriorly and to its right. The thoracic duct arches over the artery just medial to the scalenus anterior, to empty its contents into the confluence of the internal jugular and subclavian veins (fig. 442). Behind and somewhat medial to it are the oesophagus, thoracic duct, inferior cervical gang- lion of the sympathetic, longus coUi muscle, and vertebral column. To some extent it is over- lapped posteriorly by the left pleura and lung. On its right side are the trachea and the inferior laryngeal nerve, and, higher up, the oesopha- gus and thoracic duct. On its left side are the left pleura and lung. THE FIRST PORTION OF THE RIGHT SUBCLAVIAN ARTERY 557 Branches. — The vertebral, internal mammary^ and thyreo-cervical trunk (thyreoid axis) usually arise from the first portion on the left side. (See p. 559.) THE FIRST PORTION OF THE RIGHT SUBCLAVIAN ARTERY The first portion of the right subclavian artery (fig. 457) extends from its origin at the bifurcation of the innominate, behind the ui3per margin of the right sterno- FiG. 457. — The Subclavian Artery. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Medial palpebral arteries Tarsal . / Superior . /, *^i Inferior s/yl/ Lateral palpebral arteries Infra -orbital artery Superior labial artery Anterior auricular brancbes -^ Perforating branches of the posterior auricular artery Supra-orbital artery Frontal artery ,Dorsal nasal artery Zygomatico-orbital artery Left naris ..^Frontal branch ) of the superficial Parietal branch J temporal artery Zygomatic muscle Transverse facial artery .. — "Superficial temporal artery of the superior thyreoid artery Inferior labial artery Mental artery -- Submental artery ,-. t J i. [ Internal Carotid artery I j.^j^^^^, Superior th3Teoid artery — Levator scapulee muscle Common cartoid artery A^^s '^f Inferior thyreoid artery //^m^ ,« -^ Phrenic nerve Vertebral artery Transverse scapular artery Subclavian artery Serratus anterior muscle Internal mammary _ artery ( Innominate artery"" Pericardico-phrenic — artery _ vena dSerrT^M?* V-^^ Thymus- j:^m^' Intercostal £ branches "^T^bm**- -« Costal pleura -~-^ / S^^, Perforating branches Anterior medi astinal artery Superior phrenic , artery Superio; epigastric artery Musculo phrenic artery clavicular joint, upward and laterally in a gentle curve over the apex of the right lung and pleura to the medial border of the scalenus anterior. It measures about 3 cm, {\\ in.). In this course it ascends in the neck a variable distance above the clavicle, but is so deeply placed, so surrounded by important structures, and gives > 558 THE BLOOD-VASCULAR SYSTEM off so many large branches, that it is now seldom or never selected for the applica- tion of a ligature. Relations. — In front it is covered by the integuments, the superficial fascia, the platysma, the anterior layer of the deep fascia, the clavicular origin of the sterno-mastoid, the sterno-hyoid and sterno-thyreoid muscles, and the deep cervical fascia. It is crossed by the commencement of the innominate, by the internal jugular, and by the vertebral veins; and, in a medio-lateral direction, by the vagus and phrenic nerves, and the superior cardiac branches of the sympathetic nerve. A loop of the sympathetic nerve itself also crosses the artery, and forms with the trunk of the S3'mpathetic a ring around the vessel known as the ansa subclavia (annulus of Vieussens). Behind, but separated from the artery by a cellular interval, are the longus coUi muscle, the transverse process of the seventh cervical or first thoracic vertebra, the main chain of the sympathetic nerve, the inferior cardiac nerves, the recurrent laryngeal nerve, and the apex of the right lung and pleura. Below, it is in contact with the pleura and lung and the loop of the recurrent laryngeal nerve, which winds round the artery from the vagus and ascends behind it to the larynx. The subclavian vein is below the artery and on an anterior plane. Branches. — The vertebral, internal mammary, superficial cervical, and thyreo- cervical trunk (thyreoid axis) arise from this part of the vessel on the right side. (See p. 559.) Not uncommonly a small aberrant artery also takes origin from this portion of the artery and descends to the left behind the oesophagus to join a branch of the aorta opposite the third or fourth thoracic vertebra. This vessel is probably the remains of the right dorsal aorta. THE SECOND PORTION OF THE SUBCLAVIAN ARTERY The second portion of the subclavian artery lies behind the scalenus anterior muscle. It measures about 2 cm. ff in.) in length and here reaches highest in the neck. The subclavian vein is separated from the artery by the scalenus anterior, and lies on a lower and anterior plane (fig. 463) . Relations. — In front it is covered by the skin, superficial fascia, platysma, anterior layer of deep fascia, the clavicular origin of the sterno-mastoid, posterior layer of deep fascia, and by the scalenus anterior. The phrenic nerve — which, in consequence of its oblique course medially downward, crosses a portion of both the first and second part of the subclavian — is separated from the second portion by the scalenus anterior muscle, as is also the subclavian vein which courses on a somewhat lower plane. Behind the artery are the apex of the pleura and lung, and a portion of the scalenus medius; also the scalenus minimus (partially or entirely fibrous, known as Sibson's fascia, see p. 355). Above is the brachial plexus. Below are the pleura and lung. One branch only — the costo-cervical trunk (superior intercostal) — is, as a rule, given off from this portion of the subclavian; occasionally the transverse cervical or the descending branch of the transverse cervical (posterior scapular artery) arises from it. THE THIRD PORTION OF THE SUBCLAVIAN ARTERY The third portion of the subclavian artery extends from the lateral margin of the scalenus anterior muscle to the lateral border of the first rib. It is more super- ficial than either the first or second portions; it is in relation with less important structures, and as a rule gives off no branch, and for these reasons is the part selected when practicable for the application of a ligature. It is the longest of the three portions of the subclavian artery, and lies in a triangle — the subclavian triangle — bounded by the sterno-mastoid, the omo-hyoid, and the clavicle (fig. 445). Relations. — In front it is covered by skin, superficial fascia, platysma, supra-clavicular nerves (descending superficial branches) of the cervical plexus; the anterior layer of deep fascia which descends from the omo-hyoid to the clavicle; and the posterior layer of deep fascia which descends from the omo-hyoid to the fu'st rib and passes over the scalenus anterior and phrenic nerve. Between the two layers of fascia is a variable amount of cellular tissue and fat, and running in this is the transverse scapular (supra-scapular) artery. The subclavian is crossed by this artery unless the arm is drawn well downward. Close to the lateral margin of the sterno-mastoid, the external jugular vein pierces the fascia, and crosses the subclavian artery to open into the subclavian vein. As this vein hes between the two layers of fascia, it receives on its lateral side the transverse scapular (supra-scapular), transverse cervical, and other veins of the neck, which together form a plexus of large veins in front of the arterj'. The nerve to the subclavius, and, when present, the accessory branch from this nerve to the phrenic, also THE VERTEBRAL ARTERY 559 here cross in front of the artery. In very muscular subjects the clavicular head of the sterno- mastoid may be larger than usual, and in such a case wiU form one of the coverings of the artery. Behind, the artery is in contact with the scalenus medius, and with the lower trunk of the brachial plexus. Below, the artery rests in the posterior of the two grooves on the upper surface of the first rib. Above is the brachial plexus of nerves and the posterior beUy of the omo-hyoid muscle. The trunk formed by the fifth and sixth cervical nerves is also above the artery, but on a some- what anterior plane. It is close to the vessel, and has been mistaken for the artery in the appU- cation of a Kgature. As a rule there is no branch given off from the third portion of the subclavian. At times, however, the transverse cervical or the descending branch of the transverse cervical (posterior scapular artery) may arise from the third portion of the subclavian instead of from the thyreo-cervical trunk (thyreoid axis) and from the transverse cervical respectively, as here described. There is considerable variation in the branches of the subclavian artery and Bean (Am. Jour. Anat., Vol. 4, p. 303) has shown that the branches are arranged in a different way on the two sides of the body. The usual form on the right side is for the vertebral, internal mammary, the superficial cervical and the common trunk of the inferior thjTeoid and transverse scapular arteries to arise from the first part of the subclavian. In this case the ascending cervical is a branch of the inferior thyreoid, while the transverse cervical and costo-cervical arise from the second portion. There are no branches from the third portion. On the left side the usual form is for the vertebral and internal mammary, and thyreo-cer- vical trunk, to arise from the first part. The thyreo-cervical trunk divides into inferior thyreoid, transverse scapular, and transverse cervical arteries; the super- ficial cervical is absent, and the costo-cervical trunk arises from the first part. There are three more types of origin of the branches; in one, the vertebral, internal mammary, costo-cervical, and inferior thyreoid come from the first part, while the transverse cervical arises from the second part, and the transverse scapular comes either from the third part or the axillary artery; in the second, the inferior thyreoid, transverse scapular and transverse cervical arise in a com- mon stem from the first part; while in the third, which is the rarest form, the in- ferior thyreoid and superficial cervical arteries come by a common trunk from the first part, while the transverse scapular artery arises from the internal mammary. 1. THE VERTEBRAL ARTERY The vertebral artery [a. vertebralis] (fig. 458) the first, largest, and most con- stant branch, arises from the upper and posterior part of the first portion of the subclavian, on the right side, about 2 cm. (f in.) from the origin of the latter ves- sel from the innominate, on the left side, from the most prominent part of the arch of the subclavian, close to the medial edge of the scalenus anterior muscle. It first ascends vertically to the foramen transversarium of the sixth cervical vertebra, and, having passed through that foramen and those of the next succeed- ing cervical vertebrae as high as the epistropheus (axis), it tmns laterally and then ascends to reach the foramen in the transverse process of the atlas; after passing through that foramen it turns backward behind the articular process, lying in the groove on the posterior arch of the atlas. It next pierces the posterior occipito-atlantoid membrane and the dura mater, and enters the cranium through the foramen magnum. Here it passes upward, at first lying by the side of the medulla, then in front of that structure, and terminates at the lower portion of the pons by anastomosing with the vertebral of the opposite side to form the basilar. The vertebral artery may be divided for purposes of description into four parts: the first, or cervical, extending from its origin to the transverse process of the sixth cervical vertebra; the second, or vertebral, situated in the foramina trans- versaria; the third, or occipital, contained in the suboccipital triangle; and the fourth, or intracranial, within the cranium. The first or cervical portion. — The artery here lies between the scalenus anterior and longus colli muscles. In front it is covered by the vertebral and internal jugular veins, and is crossed by the inferior thyreoid artery, and on the left side, in addition, by the thoracic duct, which runs over it medio-laterally. Behind, the artery hes on the transverse process of the seventh cervical vertebra and the sympathetic nerve. To its medial side is the longus coUi. To its lateral i 560 THE BLOOD-VASCULAR SYSTEM side is the scalenus anterior. It gives off as a rule no branch in this part of its course. Occa- sionally, however, a small branch passes into the foramen tranversarium of the seventh cervical vertebra. The second or vertebral portion. — As the artery passes through the foramina transversaria, it is surriunded by a plexus of veins and by branches of the sympathetic nerve. The cervical nerves lie behind it. Between the transverse processes it is in contact with the intertransverse muscles. The third or occipital portion. — The artery here hes in the suboccipital triangle, bounded by the superior oblique, inferior oblique, and rectus capitis posterior major muscles. As it winds round the groove on the atlas, it has the rectus capitis laterahs, the articular process, and the posterior ocoipito-atlantoid membrane in front of it; the superior oblique, the rectus capitis posterior major, and the semispinalis capitis (complexus) behind it. Separating it from the arch of the atlas, is the first cervical or suboccipital nerve. The fourth or intracranial portion extends from the aperture in the dura mater to the lower border of the pons, where it pierces the arachnoid and unites with its fellow to form the basilar artery. It here winds round from the side to the front of the medulla, lying in the Fig. 458. — Scheme op the Left Veetebeal Aeteey. (Walsham.) The internal jugular and vertebral veins are hooked aside to expose the artery. Risht posterior cerebral artery Left posterior cerebral " artery Basilar artery " Basilar part, occipital Intracranial portion of verte bral artery Rectus capitis lateralis muscl Second cervical nerve Vertebral plexus of veins Third cervical Vertebral portion of vertebral artery Fourth cervical nerve Vertebral plexus of veins Fifth cervical nerve Sixth cervical Inferior thyreoid artery Longus colli muscle Cervical portion of vertebral artery Internal jugular vein, hooked a little aside Vertebral vein, cut Subclavian artery :ipital bone Occipital portion of vertebral artery Descending branch of occipital artery Semispinalis colli muscle Deep cervical artery Scalenus anterior muscle, cut Subclavian vein vertebral groove on the basilar part of the occipital bone. In this course it passes beneath the first process of the hgamentum denticulatum, and between the hypoglossal nerve in front, and the anterior roots of the suboccipital nerve behind. Branches of the Vertebral Artery The first part of the vertebral artery gives no branches. The second and third parts give off muscular branches to the semispinalis and posterior recti and oblique muscles. The second part also gives off five or six, (1) Spinal branches. The fourth part gives off the following: (2) Posterior meningeal; (3) posterior spinal; (4) anterior spinal; and (5) posterior inferior cerebellar. (1) The spinal branches [rami spinales] run through the intervertebral foramina into the vertebral canal, and there divide into two branches: one of which ramifies on the ba,cks of the bodies of the cervical vertebra;; while the other runs along the spinal nerves, supphes the cord and its membranes, and anastomoses with the arteries above and below. (2) The meningeal [ramus meningeus] is a small branch given off as the vertebral artery pierces the dura mater to enter the cranium. It supplies the bone and dura mater of the posterior fossa of the skull, and anastomoses with the posterior meningeal branches derived from the occipital and ascending pharyngeal arteries. It gives branches to the falx cerebelli. THE BASILAR ARTERY 561 (3) The posterior spinal artery [a. spinalis posterior] runs downward obliquely along the side of the medulla to the back of the cord, down which it passes behind the roots of the spinal nerves, being reinforced by spinal branches accompanying these nerves, in the neck, the thoracic, and in the lumbar region. It can be traced as low as the end of the spinal cord. (4) The anterior spinal artery [a. spinalis anterior] comes off from the vertebral a little below its termination in the basilar artery. Descending with a medial slant in front of the medulla, it unites on a level with the foramen magnum with its fellow of the opposite side. The single vessel thus formed runs downward in front of the spinal cord beneath the pia mater as far as the termination of the cord, being reinforced by the spinal branches on the way down. The spinal arteiies are described in detail with the anatomy of the spinal cord. (5) The posterior inferior cerebellar [a. cerebeUi inferior posterior] (fig. 456) — the largest branch of the vertebral — arises from that vessel just before it joins its fellow to form the basilar artery. At times it may come off from the basilar itself. It runs, at first laterally across the restiform body between the origin of the vagus and hypoglossal nerves, and, descending toward the vallecula, there divides into two branches, medial and lateral, (a) The medial branch runs backward between the vermis and the lateral hemisphere of the cerebellum. It supplies the vermis, and anastomoses with the artery of the opposite side, and with the superior vermian of the superior cerebellar. (6) The lateral branch runs laterally and, ramifying over the under surface of the cerebellar hemisphere, supplies its cortex and anastomoses along its lateral margin with the superior cerebellar arteries. From the undivided trunk of the posterior inferior cerebellar artery branches are given to the medulla oblongata, supplying the chorioid plexus and the fourth ventricle. THE BASILAR ARTERY The basilar artery [a. basilaris] is formed by the confluence of the right and left vertebral arteries, which meet at an acute angle at the lower border of the pons. It runs forward and upward in a slight groove in the middle line of the pons, and divides at the upper border of that structure at the level of the tentorial notch into the two posterior cerebral arteries, which take part in the formation of the circle of Willis (fig. 456) . Branches of the Basilar Artery The branches of the basilar artery are: — 1. Pontine; 2. internal auditory; 3. anterior inferior cerebellar; 4. superior cerebellar; 5. posterior cerebral. (1) The pontine branches [rami ad pontem] are numerous small vessels which come off at right angles on either side of the basilar artery, and, passing laterally over the pons, supply that structure and adjacent parts of the brain. (2) The internal auditory artery [a. auditiva interna], a long slender vessel, accompanies the auditory nerve into the internal auditory meatus (fig 514). It here lies between the facial and auditory nerves, and at the bottom of the meatus passes into the internal ear, and anastomoses with the other auditory arteries. (See Internal Ear.) (3) The anterior inferior cerebellar [a. cerebelU inferior anterior] arises from the basilar soon after its origin, passes laterally and backward across the pons, and then over the brachium pontis to the front part of the under surface of the cerebellum. It anastomoses with the posterior inferior cerebellar artery (fig. 456). (4) The superior cerebellar [a. cerebelli superior] comes off from the basilar immediately behind its bifurcation into the posterior cerebral arteries. It courses laterally and backward over the pons, in a curve roughly corresponding to that of the posterior cerebral artery, from which it is separated by the third cranial nerve; but, soon sinking into the groove between the pons and the pedunculus cerebri, it curves round the latter onto the upper surface of the cerebellum, lying nearly parallel to the fourth nerve. Here it divides into two branches medial and lateral, (o) The medial branch courses backward along the superior vermis, anas- tomosing with its fellow of the opposite side, and, at the posterior notch of the cerebellum, with the inferior vermian branch of the posterior inferior cerebellar artery. (6) The lateral runs to the circumference of the cerebellum, anastomosing with the lateral branch of the inferior posterior cerebellar artery. Branches are given off from the main trunk of the superior cerebellar artery, or from its medial branch to the anterior velum (valve of Vieussens), the corpora quadrigemina, the pineal body, and the chorioid plexus. (5). The posterior cerebral arteries [aa. cerebri posteriores] are the two terminal branches into which the basilar bifurcates at the upper border of the pons, immediately behind the posterior perforated substance. Each artery runs at fii'st laterally and a little forward across the pedunculus cerebri immediately in front of the third nerve, which separates it from the superior cerelsellar artery. After receiving the posterior communicating artery, which runs backward from the internal carotid, the posterior cerebral turns backward onto the under surface of the cerebral hemisphre, where it breaks up into branches for the supply of the temporal and occipital lobes. The branches of the posterior cerebral artery are described below in connection with those of the other cerebral arteries. 562 THE BLOOD-VASCULAR SYSTEM Distribution of the Cerebral Arteries Although the brain receives its blood supply from two distinct sources, namely, from the internal carotids and from the vertebrals, it is convenient to consider together the dis- tribution of the various cerebral branches derived from these stems. The formation of the circulus arteriosus (circle of Willis) and the origin of the anterior, middle and posterior cerebral arteries has already been described (pp. 554, 561). The detailed distribution of these vessels will now be considered. In general, their branches may be divided into central or ganglionic and per- ipheral or cortical. The anterior cerebral artery has but a hmited central distribution. It gives off a few inconstant branches which enter the anterior perforated substance and supply the anterior end of the caudate nucleus. One or two of these run to the corpus callosum and septum peUucidum. The anterior communicating branch is a transverse trunk which connects the two arteries and thereby completes the circulus arteriosus in front. It hes in front of the optic chiasm, and varies considerably in length and size. It may give off some of the branches to the anterior perforated substance. The cortical branches supply the gyrus rectus, the olfactory lobe and a part of the orbital gyri on the ventral surface. On the medial surface branches supply the cortex as far back as the parieto-occipital fissure. These branches are given off as the artery Fig. 459. — The Arteries or the Mesial Surface op the Brain. (After Spalteholz.) Sulcus cinguli Corpus callosum Anterior cerebral artery Anterior communicating artery ' Internal carotid artery I Posterior cerebral artery Posterior communicating artery curves around the corpus callosum and some of them curve over onto the lateral surface and supply the superior and middle temporal convolutions. Branches from the anterior cerebral artery also supply the corpus callosum (fig. 459). The middle cerebral artery gives off most of the branches to the basal gangha and supplies the greater part of the lateral surface of the brain. It runs through the lateral fissure (fissure of Sylvius) (fig. 460). The branches of the middle cerebral include the following: The central branches are: — (i) The caudate, two or three small branches, which arise from the medial aspect of the artery and pass through the medial part of the floor of the lateral fissure (fissure of Sylvius) to the head of the caudate nucleus, (ii) The antero -lateral are numerous small arteries which pass through the anterior perforated substance and supply the caudate nucleus (except its head), the internal capsule, and part of the optic thalamus, (iii) The lenticulostriate, a larger branch of the antero-latera! set, passes through a separate aperture in the lateral part of the anterior perforated substance, runs upward between the lenticular nucleus, which it supplies, and the external capsule, perforates the internal capsule, and terminates in the caudate nucleus. It has been so frequently found ruptured in apoplexy that it is called by Charcot the 'artery of cerebral haemorrhages.' (iv) Sometimes a more or less distinct branch, called lenticulo-optic, is distributed to the lateral and hinder portion of the lenticular nucleus and the lateral portion of the optic thalamus. The cortical branches come off opposite the insula. They supply the insula, the inferior frontal gyri, the central gyri (anterior and posterior), the parietal lobules, superior and in- ferior, the supra-marginal, angular, and superior temporal g}T:i. The posterior cerebral give off both central and cortical branches. The central branches are the postero-median, posterior chorioid, and the postero-lateral. The postero-median THE CEREBRAL ARTERIES 563 enter the posterior perforated substance and supply the medial portion of the optic thalamus, and the walls of the third ventricle; the posterior chorioid pass through the transverse fissure to the tela chorioidea (velum interpositum) and chorioid plexus; the postero-lateral run to the posterior part of the optic thalamus and give branches to the cerebral peduncles and the corpora quadrigemina. The cortical branches of the posterior cerebral supply the entire occipital lobe and all of the temporal lobe except the superior temporal gj'rus (fig. 459). In regard to the cerebral arteries in general it may be said that there is no anastomosis between the cortical and central branches, the two forming distinct and separate systems. The cortical may or may not anastomose with each other, but the communication between the neighbouring cortical branches is seldom sufficient to maintain the nutrition of an area when the vessel that normally supphes it is obstructed. The central branches are so-called end- vessels and do not anastomose with each other. Hence obstruction of the middle cerebral artery leads to softening of the area suppUed by its central branches, but not always to softening of the region suppHed by its cortical branches. Indeed, the cortical region may escape com- pletely, although the central area is irreparably disorganised. The gross anastomosis of the posterior cerebral with the anterior cerebral arteries through the circulus arteriosus has already been described. To sum up the distribution of the cerebral arteries, the branches of each are divided into the central, or ganglionic and the peripheral or cortical. The central branches arise at the commencement of the cerebral arteries about the cireulus arteriosus whilst the cortical are derived chiefly from the termination of these vessels. Fig. 460. — The Arteries of the Lateral Surface of the Brahst. (After Toldt, Human Anatomy," Rebman, London and New York.) Central sulcus (Rolandi) ' Atlas of Branches of the anterior cerebral artery Branches of the posterior cerebral artery Branches of the anterior cere bral artery Optic nerve Branch of the posterior cerebral artery Middle cerebral artery (A) The central branches are divided into four sets — two median and two lateral. 1. The two median are — (1) The antero-median, which arise from the anterior cerebral and the anterior communicating, and supply the fore end of the caudate nucleus, and (2) the postero- median, which arise from the posterior cerebral and supply the medial part of the optic thalamus and neighbouring wall of the third ventricle. 2. The two lateral are: — (1) The antero -lateral arise from the middle cerebral, and, passing through the anterior perforated substance, supply the lenticular nucleus, the posterior part of the caudate nucleus, the internal and external capsules, and the lateral part of the optic thalamus. (2) The postero-lateral arise from the posterior cerebral, and supply the hinder part of the optic thalamus, the pedunculus cerebri, and the corpora quadrigemina. (B) The cortical branches ramify in the pia mater, giving off branches to the cortical substance, some of which extend through it to the underlying white substance. It will be seen that the middle cerebral supphes the somaesthetic area of the cortex. It also supphes the cortical auditory centre, and, in part, the higher visual centre. The anterior cerebral supphes only a small part of the somtesthetic area, namely, the part of the leg centre that occupies the paracentral lobule and the highest part of the anterior central gyrus. The posterior cerebral supphes the visual path from the middle of the tract backward, and the half vision centre in the occipital lobe. It supphes also the corpora quadrigemina and the sensory part of the internal capsule. The branches which supply the cerebellum and brain stem are given in connection with the vertebrals on page 561. 564 THE BLOOD-VASCULAR SYSTEM 2. THE THYREOCERVICAL TRUNK The thyreocervical trunk [truncus thyreocervicalis] or thyreoid axis arises from the upper and front part of the subclavian artery, usually opposite the internal mammary, and slightly medial to the scalenus anterior. It is a short thick trunk, and divides almost immecUately into three radiating branches — namely, the inferior thyreoid, the transverse scapular, and the transverse cervical (figs. 444, 457). This is the usual form only on the left side (see page 559). It may give off also the ascending cervical. THE INFERIOR THYREOID ARTERY The inferior thyreoid artery [a. thyreoidea inferior] is the largest of the three branches into which the thyreocervical trunk (thyreoid axis) divides, and may arise in a common trunk with the transverse scapular, or as a branch of the sub- clavian. It ascends tortuously passing medially in front of the vertebral artery, the inferior laryngeal nerve and the longus colU muscle, and behind the common carotid and the sympathetic nerve or its middle cervical ganglion, to the thyreoid gland, where it anastomoses with the superior thyreoid artery and the artery of the opposite side. The branches of the inferior thyreoid artery are : — (1) Muscular; (2) oesophageal and pharyngeal; (3) tracheal; (4) inferior laryngeal; (5) glandular; and (6) as- cending cervical. (1) The muscular branches supply the scalenus anterior, longus coUi, sternohyoid, sterno- thyreoid, and omo-hyoid muscles, and the inferior constrictor muscle of the pharynx. (2) The oesophageal and pharyngeal branches [rami oesophagei et pharyngei] of the inferior thyreoid artery supply the oesophagus and pharynx and anastomose with the other arteries supplying those structures. (3) The tracheal branches [rami tracheales] ramify on the trachea, where they anastomose with the tracheal branches of the superior thyreoid and bronchial arteries. (4) The inferior laryngeal artery [a. laryngea inferior] passes along the trachea to the back of the cricoid cartilage in company with the inferior laryngeal nerve. It enters the larynx beneath the inferior constrictor. Its further distribution in that organ is described under Larynx. (5) The glandular branches [rami glandulares] supply the thsrreoid gland. (6) The ascending cervical artery [a cervicalis ascendens] (figs. 444, 457) is given off from the thyreocervical trunk or from the inferior thyreoid as that vessel is passing beneath the carotid sheath. It ascends between the scalenus anterior and the longus capitis (rectus capitis anterior major), lying parallel and medial to the phrenic nerve and behind the internal jugular vein. It anastomoses with the vertebral, ascending pharyngeal, and occipital arteries, and supphes branches to the deep muscles of the neck [rami musculares], to the spinal canal [rami spiuales], and to the phrenic nerve. Two veins accompany the ascending cervical artery and end in the innominate vein. THE TRANSVERSE SCAPULAR ARTERY The transverse scapular or suprascapular [a. transversa scapulae] artery passes laterally across the root of the neck, lying first beneath the sterno-mastoid, and then in the subclavian triangle behind the clavicle and subcalvius muscle. At the lateral angle of this space it is joined by the suprascapular nerve, sinks beneath the posterior belly of the omo-hyoid, and passes over the hgament bridg- ing the scapular notch, the nerve passing through the notch (fig. 461). It then ramifies in the supraspinous fossa of the scapula, and, winding downward round the base of the spine over the neck of the scapula, enters the infraspinous fossa, and terminates by anastomosing with the circumflex (dorsal) scapular artery, and the descending branch of the transverse cervical (posterior scapular) artery. As it lies under cover of the sterno-mastoid muscle, it crosses the phrenic nerve and the scalenus anterior; and as it courses through the subclavian triangle, it is separated by the cervical fascia which descends from the omo-hyoid to the first rib, from the subclavian artery and brachial plexus of nerves. If this artery is seen in tying the subclavian it should not be injured, as it is one of the chief vessels by which the collateral circulation is carried on after ligature of the subclavian in the third part of its course. At the lateral part of the subclavian triangle it is covered by the trapezius, and after passing over the transverse scapular Mgament it pierces the supraspinous fascia and passes beneath the supra-spinatus muscle, ramifying between it and the bone. In the infraspinous fossa it hes between the infra-spinatus and the bone. The artery is accompanied by two veins. THE TRANSVERSE CERVICAL ARTERY 565 The branches of the transverse scapular are: — (1) the nutrient, to the clavicle; (2) the acromial [ramus acromialis] to the arterial rete or plexus on the acromial process, to reach which it pierces the trapezius; (3) the articular, to the acromio-clavicular joint and shoulder- joint; (4) the subscapular, given off as the artery is passing over the transverse scapular liga- ment, descends to the subscapular fossa between the subscapularis and the bone, and anas- tomoses with the infrascapular branch of the circumflex (dorsal) scapular artery, and with the subscapular and transverse cervical arteries; (5) the supraspinous branches, which ramify in the supraspinous fossa, and supply the supra-spinatus muscle and the periosteum, and the nutrient artery to the bone; (6) the infraspinous branches, which ramify in a similar way in the infraspinous fossa, giving off twigs to the infra-spinatus muscle, the periosteum, and the bone. Fig. 461. — Scheme of Anastomoses of the Right Scapular Arteries. (Walsham.) Subscapular branch of transverse scapular artery Supraspinous branch of transverse scapular artery Descending branch of transverse cer^ vical artery Branch of inter costal artery Branch of inter- costal artery Continuation of de- scending branch of transverse cer- vical artery Transverse scapular artery -. ^^y7 Acromial branch of ;^/ A thora CO -acromial -Acromial rete Subscapular branch of transverse scapular artery Infraspinous branch of transverse scapular artery Subscapular branch of axillary artery Circumflex scapular artery branch of cir apular artery Dorsal thoracic branch o£ subscapular artery THE TRANSVERSE CERVICAL ARTERY The tranverse cervical artery [a. transversa colli], somewhat larger than the transverse scapular (suprascapular), runs like the latter vessel laterally across the root of the neck, but on a slightly higher transverse plane, and a little above the clavicle. At its origin from the thyreo-cervical trunk (thyreoid axis) it lies under the sterno-mastoid; on leaving the cover of this muscle, it crosses the upper part of the subclavian triangle, lying here only beneath the platysma and cervical fascia; further laterally, it passes beneath the anterior margin of the trapezius and omo-hyoid muscle, and at the lateral margin of the levator scapulse divides into a descending (posterior scapular) and an ascending (superficial cervical) branch. In this course it crosses the phrenic nerve, the scalenus anterior, the brachial plexus, and the scalenus medius. Sometimes it passes between the cords of the brachial plexus. The branches of the transverse cervical artery are: — (1) a descending (posterior scapular) ; and (2) an ascending (or superficial) cervical. The descend- ing branch occasionally arises from the third portion of the subclavian artery. (1) The descending branch, or posterior scapular [ramus descendens] the apparent continua- tion of the transverse cervical artery, begins at the lateral border of the levator scapula;, and, continuing its course beneath this muscle to the upper and posterior angle of the scapula, turns downward and skirts along the posterior border of the scapula, between the serratus anterior 566 THE BLOOD-VASCULAR SYSTEM (magnus) in front and the levator seapulEe and rhomboideus minor and major behind, to the inferior angle, where it anastomoses with the subscapular artery. It gives off the following branches: — (a) Supraspinous, which ramifies between the supraspinous muscle and the trapezius, and sends branches through the muscle into the fossa, to anastomose with the transverse scapular artery. (6) Infraspinous branches, one or more of which enter the infraspinous fossa, and anastomose with the circumflex (dorsal) scapular, (c) Subscapular branches, which enter the subscapular fossa, and anstomose with the branches of the transverse scapular and subscapular arteries, (d) Muscular branches, to the muscles between which it runs and to the latissimus dorsi. These branches anastomose with the posterior divisions of the intercostal arteries. (2) The ascending branch or superficial cervical artery [r. asoendens], smaller than the descending branch, ascends under the anterior margin of the trapezius, lying upon the levator scapulae and splenius muscles. It supplies branches to the trapezius, levator scapulae, and splenius muscles, and the posterior chain of lymphatic glands. It anastomoses with the superficial branch of the descending branch of the occipital between the splenius and semi- spinahs capitis (complexus) . It is accompanied by two veins. This artery may arise directly from the thyreoid axis, or from the third part of the subclavian artery. 3. THE INTERNAL MAMMARY ARTERY The internal mammary artery [a. mammaria interna] (figs. 457, 462) comes off from the lower part of the first portion of the subclavian, usually opposite the Fig. 462. — Scheme of the Right Internal Mammary Artery. (Walsham.) _^ Common carotid artery Phremc nerve Subclavian artery Subclavian vein, cut Anterior intercostal branch ■ intercostal branch Musculo-phrenic artery Deep circumflex iliac artery Internal jugular vein Subclavian vein, cut Scalenus anterior muscle Sternum Transversus thoracis muscle Perforating branch Superior epigastric artery -Inferior epigastric artery thyreo-cervical trunk (thyreoid axis), close to the medial edge of the scalenus anterior, occasionally opposite the vertebral, or at a spot between these two ves- sels. It descends with a slight inclination forward and medialward, under cover of the clavicle, and enters the thorax behind the cartilage of the first rib, and thence passes down behind the cartilages of the next succeeding ribs, about 1.2 cm. (I in. ) from the lateral margin of the sternum, to the sixth interspace, where it divides into the superior epigastric and musculo-phrenic. It is accompanied by two veins, which unite into one trunk behind the first intercostal muscle; this THE INTERNAL MAMMARY ARTERY 567 passes to the medial side of the artery into the corresponding vena innominata, or occasionally on the right side into the vena cava superior direct. The artery may be divided into two portions, the cervical and the thoracic. The cervical portion is covered by the sterno-mastoid muscle, subclavian vein, and internal jugular vein, and is crossed obliquely, in the latero-medial direction, by the phrenic nerve. It rests upon the pleura and courses around the upper part of the innominate vein. There is no branch from this part of the artery. The thoracic portion lies behind the cartilages of the six upper ribs, and in the interspace between the ribs has in front of it the pectoralis major and the internal intercostal muscles and external intercostal hgaments. Behind, it is in contact above with the pleura, but it is separated from it lower down by shps of the transversus thoracis (triangularis sterni). On the left side, the artery between the fourth and sixth ribs may be said to be in the anterior mediastinum, the pleura here forming a notch for the heart. In the first, second, and third spaces the artery, if wounded, can be easily tied; but in the fourth space the operation is at- tended with more difficulty. The remaining spaces are so narrow that a portion of the cartilage would have to be removed to expose the vessel. The branches of the internal mammary artery are: — (l) The pericardio- phrenic; (2) the anterior mediastinal and thymic; (3) the bronchial; (4) the peri- cardiac; (5) the sternal; (6) the anterior intercostals; (7) the perforating; (8) the lateral costal; (9) the superior epigastric; and (10) the musculo-phrenic. (1) The pericardio-phrenic artery [a. pericaridiophrenica], is a long slender vessel which comes off from the internal mammary just after it has entered the chest, and descends with the phrenic nerve, at first between the pleura and innominate vein; then (on the right side) between the pleura and the vena cava superior ; and lastly, between the pleura and the pericardium to the diaphragm, where it anastomoses with the other diaphragmatic arteries. It gives branches both to the pleura and pericardium. (2) The anterior mediastinal and thymic arteries [aa. mediastinales anteriores et thymicae] come off irregularly from the internal mammary. They are of small size, and supply the con- nective tissue, fat, and lymphatics in the superior and anterior mediastina and the remains of the thymus gland. (3) The bronchial branches [rami bronchiales] are often wanting. When present they are supphed to the bronchi and the lower part of the trachea. (4) The pericardiac branches are distributed to the anterior surface of the pericardium. (5) The sternal branches [rami sternales] enter the nutrient foramina in the sternum, and also supply the transversus thoracis (triangularis sterni). (6) The anterior intercostal branches [rami intercostales] (figs. 463, 478) — two in each of the five or six upper intercostal spaces — run laterally from the internal mammary artery, along the lower border of the rib above and the upper border of the rib below, and anastomose with the corresponding anterior and collateral branches of the aortic intercostals. Each pair of branches sometimes arises by a common trunk from the internal mammary, which in this case soon divides into an upper and a lower branch, as above described. They lie at first between the internal intercostal muscles and the pleura; afterward between the external and internal intercostal muscles. They supply the contiguous muscles, the pectoralis major, and the ribs. (7) The perforating or anterior perforating branches [rami perforantes] — five or six in number, one corresponding to each of the five or six upper spaces — come off from the front of the internal mammary, between the superior and inferior anterior intercostals, and, perforating the internal intercostal muscles, pass forward between the costal cartilages to the pectoralis major, which they supply [rami musculares]. The terminal twigs perforate that muscle close to ttie sternum, and are distributed to the integument [rami cutanei]. The second, third, and fourth perforating supply the inner and deep surface of the mammary gland, and become greatly enlarged during lactation [rami mammaria]. They frequently require ligation in excision of the breast. (8) The lateral costal branch [ramus costales lateralis] is given off close to the first rib, and descends behind the ribs just external to the costal cartilages. It anastomoses with the upper intercostal arteries. This vessel is often of insignificant size, or absent. (9) The superior epigastric artery [a. epigastrica superior] (fig. 462), or medial terminal branch of the internal mammary artery, leaves the thorax behind the seventh costal cartilage by passing through the costo-xiphoid space in the diaphragm. It is the direct prolongation of the internal mammary downward. In the abdomen it descends behind the rectus muscle, between its posterior surface and its sheath, and, lower, entering the substance of the muscle, anastomoses with the inferior epigastric, a branch of the external iliac. It gives off the following small branches: — (o) The phrenic, to the diaphragm; (b) the xiphoid, which crosses in front of the xiphoid cartilage, and anastomoses with the artery of the opposite side; (c) the cutaneous, which perforate the anterior layer of the sheath of the rectus and supply the integuments; (d) the muscular, to the rectus muscle, some of which perforate the rectus sheath laterally, and are distributed to the obhque muscles; (e) the hepatic (on the right side only), which pass along the falciform ligament to the liver, and anastomose with the hepatic artery; (/) the peritoneal, which perforate the posterior layer of the sheath of the rectus, and ramify on the peritoneum. (10) The musculo-phrenic artery [a. musculophrenica], or lateral terminal branch of the internal mammary artery, skirts laterally and downward behind the costal cartilages of the false ribs along the costal attachments of the diaphragm, which it perforates opposite the ninth rib. It terminates, much reduced in size, at the tenth or eleventh intercostal space by anasto- mosing with the ascending branch of the deep circumflex iUac artery. It gives off in its course the following small branches: — (a) The phrenic for the supply of the diaphragm; (b) the an- terior intercostals, two in number for each of the lower five or six intercostal spaces, are dis- 568 THE BLOOD-VASCULAR SYSTEM tributed like those to the upper spaces, aheady described, and anastomose like them with the corresponding anterior branches of the lower aortic intercostals; (c) the muscular for the supply of the oblique muscles of the abdomen. 4. THE COSTO-CERVICAL TRUNK The costo-cervical trunk [truncus costocervicalis] (figs. 444, 463) is a short stem which arises usually from the back part of the second portion of the sub- clavian artery, behind the scalenus anterior on the right side, but commonly just medial to that muscle on the left side. Its course is upward and backward above the dome of the pleura and then downward toward the thorax, before entering which it divides into its two terminal branches. The branches of the costo-cervical trunk are : — (1) the superior intercostal and (2) the deep cervical. (1) The superior intercostal [a. intercostahs suprema] (fig. 463) continues the direction of the costo-cervical trunk, passing downward into the thorax in front of the neck of the first rib. It sometimes terminates opposite the first intercostal space by becoming the first intercostal artery. Usually, however, it is prolonged downward over the neck of the second rib and supplies the second intercostal space in addition. It communicates with the highest aortic intercostal artery. As it crosses the neck of the first rib the superior intercostal lies anterior (ventral) to the first intercostal nerve and lateral to the superior thoracic ganghon of the sympathetic. Fig. 463. — Scheme of the Right Costo-cervical Trunk. (Walsham.) Scalenus anterior muscle Deep cervical branchi First thoracic nerve First intercostal nerve. Subclavian artery. Second intercostal nerve Anterior intercostal artery Third intercostal^ nerve Anterior intercostal artery Internal mammary artery Intercostal vessels of, third space Sympathetic nerve Costo-cervical trunk Arteria aberrans Arteria aberrans Intercostal vessels of fourth space The branches to the first and second intercostal spaces resemble in course and distribution the succeeding intercostals derived from the thoracic aorta (see p. 588). Like the aortic inter- costals they give off dorsal [rr. dorsales] and spinal branches [rr. spinalesj. An arteria aberrans, when present, arises from the medial side of the right superior intercostal, or occasionally from the right subclavian itself. It descends as a slender vessel into the thorax, passing downward and medially behind the oesophagus as far as the third or fourth thoracic vertebra, where in some cases it anastomoses with a similar slender branch arising from the aorta below the hga- mentum arteriosum. This anastomosis represents the remains of the embryonic right dorsal aortic arch, and it is by its occasional enlargement that the anomaly of the right sub- clavian artery rising from the descending portion of the aortic arch occurs (see p. 637). (2) The deep cervical artery [a. cervicahs profunda] passes directly backward, first between the seventh and eighth cervical nerves, and then between the transverse process of the seventh cervical vertebra and the neck of the first rib, having the body of the seventh cervical vertebra to its medial side, and the intertransverse muscle to its lateral side. It then tm'ns upward in the groove between the transverse and spinous processes of the cervical vertebrae lying upon the semispinaUs colh. It is covered by the semispinahs capitis (complexus). Between these muscles it anastomoses with the deep branch of the descending branch (princeps cervicis) of the occipital artery. It gives off a spinal branch which enters the vertebral canal through the intervertebral foramen with the eighth cervical nerve. THE AXILLARY ARTERY 569 THE AXILLARY ARTERY The term axillary is applied to that portion of the maia arterial stem of the upper limb that passes through the axillary fossa. The axillary artery [a. axillaris] (fig. 464) therefore is continuous -with the subclavian above and with the brachial below. It extends from the lateral border of the first rib to the lower edge of the teres major muscle, and has the shoulder-joint and the neck of the humerus to its lateral side. When the arm is placed close to the side of the body, the artery forms a gentle curve with its convexity upward; but when the arm is carried out from the side at right angles to the trunk in the ordinary dissecting position, the vessel takes a nearly straight course, which will then be indicated by a Hne drawn from the middle of the clavicle to the groove on the medial side of the coraco- brachialis and biceps muscles. The axillary artery is at first deeply placed beneath the pectoral muscles, but in its lower third it is superficial, being covered Fig. 464. — The Axillary Artery. (After Spalteholz.) Axillary artery Thoraco-acromial artery I . I Axillary vein Acromial branch I , J Deltoid branch Musculo-cutaneous j Circumflex humeral artery Coraco brachial muscle Deltoid muscle Pectorahs major muscle ( ' Deltoid branch^ . Median ! Ulnar nerve / / / nerve I Brachial cutaneous/ ' / Brachial vein and medial anti- / / brachial nerves / Axillary nerve / Subscapular artery Latissimus dorsi muscle ' Pectoralis minor muscle '■< y^^ Pectoral branches umflex scapular artery Lateral thoracic artery sal thoracic artery only by the skin and the superficial fascia and deep fascia. It is divided into three parts, first, second, and third, according as it lies respectively above, beneath, or below the pectoralis minor. The First Part of the Axillary Artery The first part of the axillary artery extends from the lateral border of the first rib to the upper border of the pectorahs minor. It measures about 2.5 cm. (1 in.) in length. Relations. — In front it is covered by the skin, superficial fascia, lower part of the platysma, the deep fascia, the pectorahs major, the coraco-clavioular (costo-ooracoid) fascia, the sub- clavius muscle and the clavicle when the arm hangs down by the side. The cephalic and thoraco-acromial veins, the external anterior thoracic nerve, and the axillary lymphatic trunk, cross over it. A layer of the deep cervical fascia which has passed under the clavicle also descends in front of it. 570 THE BLOOD-VASCULAR SYSTEM Behind, it rests upon the first intercostal space and first intercostal muscle, the first digita- tion and sometimes a portion of the second digitation of the serratus anterior (magnus) muscle, and a part of the second rib. The long thoracic nerve, on its way to the serratus anterior muscle, passes behind it. To its lateral side, and somewhat on a higher plane, are the cords of the brachial plexus. To its medial side, and on a slightly anterior plane, is the axillary vein. The internal anterior thoracic nerve courses between the vein and the artery. The Second Part of the Axillary Artery The second part of the axillary artery (fig. 464) lies beneath the pectoralis minor deep in the axilla. It measures 3 cm. (a little more than 1 in.) in length. Relations. — In front, in addition to the pectorahs minor, it is covered by the pectoralis major and the integuments. Behind, it is separated by a considerable interval, containing loose connective tissue and fat, from the subscapularis muscle; whilst behind, and in contact with it, is the posterior cord of the brachial plexus. To the medial side, but separated from the artery by the medial cord of the brachial plexus, is the axillary vein. To the lateral side is the lateral cord of the brachial plexus, and at some little distance the coracoid process. It is thus seen that the second portion of the auxiliary artery is surrounded on three sides by the cords of the brachial plexus — one behind, one medial, and one lateral. The Third Part of the Axillary Artery The third part of the axillary artery (fig. 464) extends from the lower border of the pectoralis minor to the lower border of the teres major. Its upper half lies deeply placed within the axilla, beneath the lower edge of the pectoralis major muscle, but its lower half is in the arm external to the axilla, and is uncovered by muscle. It measures about 7.5 cm. (3 in.) in length. Relations. — In front it has, in addition to the skin and superficial fascia, the pectorahs major above, and lower down the deep fascia of the arm. It is crossed obhquely by the medial root of the median nerve and by the lateral brachial vena comitans. Behind, it lies successively upon the subscapularis, the latissimus dorsi, and teres major muscles. From the first-named muscle it is separated at first by a considerable mass of fat and cellular tissue. The radial (musculo-spiral) and axillary (circumflex) nerves intervene between the artery and the muscles. On its lateral side it is separated from the bone by the coraco-brachialis, by which it is partly overlapped, this muscle and the short head of the biceps serving as a guide to the artery in hgature. For a part of its course it has also the musculo-cutaneous nerve and the lateral root of the median nerve to its lateral side. To its medial side it has the axillary vein, the ulnar nerve, the medial antibrachial (internal) and brachial (lesser internal) cutaneous nerves, and the medial root of the median nerve. The ulnar nerve is between the artery and the vein. The medial antibrachial (internal) cutaneous nerve is a httle in front of the artery as well as medial to it. Branches of the Axillary Artery The branches of the axillary artery are exceedingly variable. In fig. 465 is shown what Hitzrot has found the usual type, in which the second portion of the artery has no named branches. The figure brings out the segmental relation of the branches of the axillary artery to the chest wall and suggests how one of the branches may supply the place of another. If the lateral thoracic arises directly from the axillary, it is generally from the second part as described below. In addition to the larger branches of the artery small twigs are supplied to the ser- ratus anterior, coraco-brachialis, and subscapularis; also to the axillary lymph- nodes. The first part gives off. — ^(1) The superior thoracic; and (2) the thoraco- acromial. The second part gives off: — (3) The lateral thoracic. The third part gives off: — (4) The subscapular; (5) the anterior humeral circumflex; and (6) the posterior humeral circumflex. Branches of the Axillary Artery 1. The superior thoracic [a. thoracalis suprema] is variously given off from the axillary artery, usually either as a common trunk' with the next branch, the THE AXILLARY ARTERY 571 thoraco-acromial, or a little above. It passes behind the axillary vein across the first intercostal space, supplying the intercostal muscles and the upper portion of the serratus anterior, and anastomoses with the intercostal arteries. At times it sends a branch between the pectoralis major and minor, which then, as a rule, more or less takes the place of the pectoral branch of the thoraco-acromial (figs. 464 and 465). 2. The thoraco-acromial or acromio-thoracic axis [a. thoracoacromialis] arises from the front part of the axillary just above the upper border of the pectoralis minor. It is a short trunk, and, coming off from the front of the artery, pierces the coraco-clavicular fascia, and then divides into three or four small branches, named from their direction: — (a) the acromial; (b) the deltoid; (c) the pectoral, and {d) the clavicular. Fig. 46.5. — The Branches of the Axillary Artery. (After Hitzrot.) The numbers 1-5 indicate the intercostal spaces. Thoraco-acromial Superior thoracic Clavicular branch /M/,:^ Acromial branch Pectoral branch Deltoid branch Anterior circumflex humeral Posterior circumflex humeral Branch to teres major Branches to latissimus do Branch to serratus anterior (a) The acromial branch [r. acromiaUs] or branches pass laterally across the coracoid process, frequently through the deltoid muscle, which they in part supply, to the acromion, where they form, by anastomosing with the anterior and posterior circumflex and transverse scapular (suprascapular) arteries, the so-called acromial rete, or plexus of vessels on the surface of that process. (6) The deltoid branch [r. deltoideus] runs downward with the cephalic vein in the interval between the pectorahs major and the deltoid, and, supplying lateral ofTsets to these muscles and the adjacent integument, anastomoses with the anterior and posterior circumflex humeral arteries. (c) The pectoral branch [r. pectorahs] passes between the pectorahs major and minor muscles, both of which it supplies. In the female, one or more branches which perforate the pectoralis major are often of large size, and supply the superimposed mammary gland. (d) The clavicular branch passes upward beneath the clavicle, supphes the subclavius muscle, and anastomoses with the transverse scapular artery. 3. The lateral thoracic artery [a. thoracalis lateralis] descends along the lower border of the pectoralis minor, under cover of the pectoralis major, to the chest wall. It supplies both pectoral muscles and the serratus anterior fmagnus), sends branches around the lower border of the pectoralis major to the mammary gland, and terminates in the intercostal muscles by anastomosing with the aortic intercostals and the internal mammary. It also furnishes branches to the lymph-nodes of the axillary fossa. The branches to the mammary gland in the female are often of large size. 4. The subscapular artery [a. subscapularis] is the largest branch of the axillary. It arises opposite the lower border of the subscapularis, and runs in a 572 THE BLOOD-VASCULAR SYSTEM downward and medial direction along the anterior border of that muscle under cover of the latissimus dorsi. It supplies the subscapularis, teres major, latissimus dorsi, and serratus anterior (magnus) muscles, and gives branches to the nodes in the axillary fossa. The course of this large vessel along the posterior border of the axillary fossa should be remembered in opening abscesses in the fossa, and in removing enlarged nodes from it. It is accompanied by two veins, which usually unite and then receive the circumflex (dorsal) scapular vein, and open as a single vein of large size either into the axillary or at the confluence of the medial brachial vena comitans with the basilic vein. About 2.5 or 3.7 cm. (1 or 1| in.) from its origin, the subscapular artery divides into two end branches, (1) the circumflex (dorsal) scapular, and (2) the dorsal thoracic. Fig. 466. — The Anastomoses about the Scapula. Subscapular branch of transverse scapular artery Supraspinous branch of transverse scapular artery Descending branch of transverse cer- vical artery Transverse scapular artery Acromial branch of thoraco-acromial Acromial rete Subscapular branch of transverse scapular artery Infraspinous branch of transverse scapular artery Subscapular branch of axillary artery Circumflex scapular artery Infrascapular branch of cir- cumflex scapular artery Branch of inter costal artery Branch of inter- costal artery Continuation of de- scending branch of transverse cer- vical artery (1) The circumflex scapular artery [a. circumflexa scapulae], or dorsal scapular, arising from the subscapular, usually at the point above mentioned, passes backward through the trian- gular space bounded by the subscapularis above, the teres major below, and the long head of the triceps laterally, and then between the teres minor and the axiUary border of the scapula, which it commonly grooves. It thus reaches the infraspinous fossa, where, under cover of the infra-spinatus, it anastomoses with the transverse scapular (suprascapular) artery and the descending branch of the transverse cervical (posterior scapular) (fig. 466). As it passes through the triangular space, it gives off a ventral branch which ramifies between the subscapularis and the bone, supplying branches to the subscapularis, to the scapula, and to the shoulder- joint. A second branch is often given off near the triangular space and passes downward between the teres major and teres minor, supplying both muscles (fig. 467). (2) The dorsal thoracic artery [a. thoracodorsahs] continues in the course of the subscapular as far as the angle of the scapula, where it anastomoses with the circumflex scapular, the descending branch of the transverse cervical (posterior scapular), the lateral thoracic, and intercostal arteries. 5. The anterior circumflex humeral artery [a. circumflexa humeri anterior], usually quite a small vessel, comes off from the lateral side of the axillary artery, generally opposite the posterior circumflex. It passes beneath the coraco- brachialis and short and long heads of the biceps, winding transversely round the front of the surgical neck of the humerus, across the intertubercular (bicipital) groove, and anastomoses ^vith the posterior circumflex and thoraco-acromial arteries. It gives off the following small branches: THE BRACHIAL ARTERY 573 (o) The bicipital or ascending, which runs up the intertubercular groove to supply the long tendon of the biceps and the shoulder-joint; and (h) a pectoral or descending branch, which runs downward along the insertion of the pectorahs major, and supplies the tendon of that muscle. The anterior circumflex artery, in consequence of its being close to the bone, is sometimes difficult to secure in the operation for excision of the shoulder-joint. 6. The posterior circumflex humeral artery [a. circumflexa humeri posterior] (fig. 467) arises from the posterior aspect of the axillary, just below the lower border of the subscapularis muscle. It passes through the quadrilateral space, bounded by the teres minor above, the latissimus dorsi and teres major below, the humerus laterally, and the long head of the triceps medially, and, winding round the back of the humerus beneath the deltoid, breaks up under cover of that muscle into a leash of branches, which for the most part enter its substance. The axillary (circumflex) nerve and two vense comitantes run with it. It anastomoses with the anterior circumflex, the arteries on the acromion, and the profunda artery. Fig. 467. — The Arteries of the SHOtiLDER. (After Spalteholz.) Transverse cervical artery Ascending branch 1 Superior transverse scapular Ugament Descending branch ! ' ' Transverse scapular artery —Acromion ^^_^ «„_^ -Acromial branch /A '__'__ __ ; _'^. _ ^^ ■Deltoid muscle Infraspinatus muscle CIrcumSex scapular artery Teres minor muscle i Posterior circumflex Teres major humeral artery muscle Triceps muscle (lateral head) Triceps muscle (long head) In addition to the leash of vessels to the deltoid, it gives off the following small branches: — (a) nutrient, to the greater tuberosity of the humerus; (b) articular, to the back of the shoulder- joint; (c) acromial, to the plexus on the acromion; and [d) muscular, to the teres minor and long and short heads of the triceps. One or more of these branches to the triceps descend either between the lateral and long head or in the substance of that muscle, to anastomose with an ascending branch from the profunda artery. It is by means of this anastomosis that the collateral circulation is chiefly carried on when the axillary or the brachial artery is tied between the origins of the posterior circumflex and profunda arteries. THE BRACHIAL ARTERY The brachial artery [a. brachialis] (fig. 468), the continuation of the axillary, extends from the lower border of the teres major to a little below the centre of the crease at the bend of the elbow, where it divides, opposite the junction of the head with the neck of the radius, into the radial and ulnar arteries. The artery is situated at first medial to the humerus; but as it passes down the arm it gradually gets in front of the bone, and at the bend of the elbow lies midway between the two epicondyles. Hence, in controlling hiemorrhage, the artery should be com- pressed laterally against the bone in its upper third, laterally and backward in its middle third, and directly backward in its lower third. Throughout the greater part of its course the artery is superficial, being merely overlapped slightly on 574 THE BLOOD^VASCULAR SYSTEM its lateral side by the coraco-brachialis and biceps muscles; but at the bend of the elbow it sinks deeply beneath the lacertus fibrosus of the biceps into the triangular interval (antecubital space) bounded on either side by the brachio- FiG. 468. — The Brachial Artery. (After Toldt, "Atlas of Human Anatomy" Rebman, London and New York.) Subscapular artery Deltoid pectoral triangle Thoraco- f Acromial branch acromial ] artery [ Deltoid branch Axillary lymph-nodes ''y- Dorsal thoracic artery Circumflex scapular artery Cutaneous branch— V Coraco-brachiahs Brachial artery - Deltoid muscle — t Lateral antibrachial cutaneous nerve f™"-^' / ^ Brachial artery Lacertus fibrosus Brachio-radialis muscle- — ' Radial recurrent artery-^ Cutaneous branches v. |"~ Antibrachial fascia radialis and pronator teres, and at its bifurcation is more or less under cover of these muscles (fig. 469). The sheath of the brachial artery is closely incor- porated with the fascia covering the biceps muscle, and it is for this reason that in the operation for hgaturing the vessel is apt to be retracted with the muscle. THE BRACHIAL ARTERY 575 A line drawn from the groove medial to the coraco-brachialis and biceps muscles to midway between the epicondyles of the humerus will indicate its course. It is accompanied by two veins which frequently communicate across the artery. In addition to the branches named below the iDrachial artery gives off numerous muscular branches and, occasionally, the nutrient artery to the humerus. The muscular branches usualty come off from the lateral side of the artery; one in particular, which supplies the biceps muscle, is frequently of large size. Relations. — In front, the artery is covered by the integument and superficial and deep fasciae, and at the bend of the elbow by the lacertus fibrosus of the biceps, and in muscular subjects by the overlapping margins of the brachio-radialis and pronator teres. In the middle third of the arm it is crossed obliquely from the lateral to the medial side by the median nerve, and at the bend of the elbow by the median cubital vein, the bicipital fascia intervening (fig. 475). Behind, it lies successively on the long head of the triceps (from which it is separated by the radial (musculo-spiral) nerve and profunda artery), on the medial head of the triceps, on the insertion of the ooraco-braohialis, and thence to its bifurcation on the brachiahs muscle. Fig. 469. — The Brachial Ahteey at the Bend of the Elbow, Left Side, Front View. (From a mounted specimen in the Anatomical Department of Trinity College, Dublin.) Posterior branch of medial antibracliial cutaneous nerve Anterior branch of medial antibrachial cutaneous nerve Brachial artery Branch to pronator teres Lacertus fibrosus, cut Pronator teres muscle Median nerve Ulnar artery Superficial radial nerve Radial recurrent artery and deep radial nerve Tendon of biceps Musculo-cutaneous nerve Brachio-radialis muscle * — Radial artery Lateral to the artery is the coraco-brachialis above, and the muscular belly of the biceps below, both of which shghtly overlap the vessel, and at the bend of the elbow the tendon of the biceps. The lateral vena comitans is also to its lateral side. The median nerve is in close contact with the lateral side of the artery in the upper third of its course, but in the middle third crosses the artery obliquely to gain the medial side. Medial to the artery in the upper part of its course are the medial antibrachial (internal) cutaneous and the ulnar nerves; the latter nerve, however, leaves the artery about the origin of the ulnar collateral (inferior profunda) branch, to make, with that vessel, for the medial epicondyle. Lower down, the medial antibrachial cutaneous nerve also leaves the artery, by piercing the deep fascia. The median nerve is in close contact with the medial side of the artery in its lower third and at the bend of the elbow. The basilic vein is superficial to it, and a Uttle to its medial side in the greater part of its course, but separated from it by the deep fascia. The medial vena comitans runs along its medial side. Branches of the Brachial Artery The branches of the brachial artery are: — (1) The profunda brachii; (2) the superior ulnar collateral (inferior profunda); (3) the inferior ulnar collateral 576 THE BLOOD-VASCULAR SYSTEM (anastomotica magna); and (4) the terminal branches — the radial and ulnar arteries. (1) The Profunda Artery The profunda brachii (superior profunda) is the largest branch of the brachial. It arises from the medial and hinder aspect of that artery, a Httle below the in- ferior border of the tendon of the teres major. It at first lies to the medial side of the brachial, but soon passes behind that vessel, and, sinking between the medial and long heads of the triceps with the radial (musculo-spiral) nerve, curves around the humerus in the groove for the nerve, lying in contact with the bone between the medial and lateral heads of the triceps. On reaching the lateral supracondyloid ridge of the humerus it perforates the lateral intermuscular septum, and, continuing forward between the brachio-radialis and brachialis to the front of the lateral epicondyle, ends by anastomosing with the radial re- current artery (figs. 468 and 474). It gives off the following branches: — (a) The deltoid branch [r. deltoideus] which may also arise from the brachial itself or from the superior ulnar collateral. It runs across the anterior surface of the humerus, under cover of the coraco-brachialis and biceps, and suppUes the brachiahs and deltoid. (6) The middle collateral artery [a. coUaterahs media] runs in the substance of the middle head of the triceps as far as the elbow, where it terminates in the articular rete. (c) The radial collateral artery [a. collateralis radialis] arises about the middle of the upper arm, and runs behind the lateral intermuscular septum to the rete at the elbow-joint. (d) A nutrient humeral artery [a. nutritia humeri], which may come from the brachial itself or from a muscular branch, enters a canal in the humerus. (2) The Superior Ulnar Collateral Artery The superior ulnar collateral artery [a. collateralis ulnaris superior] (inferior profunda) arises from the medial side of the brachial, usually about the level of the insertion of the coraco-brachialis, at times as a common trunk with the profunda. It passes with the ulnar nerve medially and downward through the medial intermuscular septum, and then along the medial head of the triceps to the back of the medial epicondyle, where, under cover of the deep fascia and the origin of the flexor carpi ulnaris from the olecranon and medial epicondyle, it enters into the anastomoses around the elbow-joint. It frequently supplies the nutrient artery to the humerus. It gives branches to the triceps, to the elbow- joint, and a branch which passes in front of the medial epicondyle to anastomose with the anterior ulnar recurrent. (3) The Inferior Ulnar Collateral Artery The inferior ulnar collateral artery [a. collateralis ulnaris inferior] or anasto- motica magna arises from the medial side of the brachial, about 5 cm. (2 in.) above its bifurcation into the radial and ulnar arteries, and, running medially and down- ward across the brachialis, divides into two branches, a posterior and an anterior. The posterior pierces the medial intermuscular septum, winds round the medial condyloid ridge of the humerus, and pierces the triceps, between which and the bone it anastomoses with the articular branch of the profunda artery, and to a lesser extent with the interosseous recurrent, forming an arterial arch or rete around the upper border of the olecranon fossa. The anterior branch passes medially and downward between the brachialis and pronator teres, and anas- tomoses in front of the medial epicondyle, but beneath the pronator teres, with the anterior ulnar recurrent. From this branch a small vessel passes down behind the medial epicondyle to anastomose with the posterior ulnar recurrent and superior ulnar collateral arteries (fig. 474). THE ULNAR ARTERY The ulnar artery [a. ulnaris] (fig. 470) the larger of the two terminal branches of the brachial, begins opposite the lower border of the head of the radiusin the middle fine of the forearm. Thence through the upper half of the forearm it runs THE ULNAR ARTERY 677 beneath the pronator teres and superficial flexor muscles, and, having reached the ulnar side of the arm about midway between the elbow and the wrist, it passes directly downward, being merely overlapped by the flexor carpi ulnaris. Crossing the transverse carpal (anterior annular) ligament immediately to the radial side of the pisiform bone, it enters the palm, where it divides into two branches, which enter respectively into the formation of the superficial and deep volar arches. The artery is accompanied by two veins, which anastomose with each other by frequent cross branches, and usually terminate in the brachial venae comitantes. The ulnar nerve is at first some distance from the artery, but approaches the vessel at the junction of its upper and middle thirds, and then lies close to its medial or ulnar side. The course of the artery in the lower two-thirds of the forearm is indicated by a line drawn from the front of the medial epicondyle to the radial side of the pisiform bone; and in the upper third of the forearm by a line drawn in a gentle curve with its convexity to the medial side from 2.5 cm. (1 in.) below the centre of the bend of the elbow to a point in the former line at the junction of its upper with its middle third. The artery throughout its course is best reached through the interval between the flexor carpi ulnaris and the flexor digitorum sublimis. The relations of the artery will be given in detail in the forearm, and in the palm of the hand. The relations in the forearm are: — In front. — In the upper half of the forearm the ulnar artery is deeply placed beneath the pronator teres, the flexor carpi radialis, the palmaris longus, and the flexor digitorum sublimis. In the lower half it is comparatively superficial, being merely overlapped above by the tendon of the flexor carpi ulnaris, whilst the last inch or so of the vessel is only covered as a rule by the skin and superficial and deep fasciae. As the artery hes beneath the pronator teres, it is crossed from the medial to the lateral side by the median nerve, the deep head of origin of the muscle usually separating the nerve from the artery. The lower part of the artery is crossed by the palmar cutaneous branch of the ulnar nerve. Behind. — For about 2.5 cm. (1 in.) of its course the artery lies upon the brachialis; but thence, as far as the transverse carpal (anterior annular) ligament, upon the flexor digitorum profundus, which separates it above from the interosseous membrane and bone, and at the wrist from the pronator quadratus. The artery is bound down to the flexor digitorum pro- fundus by bands of fasciae. To the lateral side in the lower two-thirds of its course is the flexor digitorum subMmis. To the medial side in the lower two-thirds is the flexor carpi ulnaris, the guide to the vessel. The ulnar nerve, as it enters the forearm from behind the medial epicondyle, is at first some distance from the artery, being separated from it in its upper third by the flexor digitorum subhmis, but in its lower two-thirds is in close contact with the vessel and on its ulnar side. The branches of the ulnar artery in the forearm are: — 1. The ulnar recurrent arteries. 2. The common interosseous. 3. Muscular. 4. Dorsal ulnar carpal. 5. Volar ulnar carpal. 1. The ulnar recurrent arteries [aa. recurrentes ulnares] are two, the volar, and dorsal. The volar is a small branch which arises from the medial side of the ulnar artery, or the dorsal ulnar recurrent, and, running between the lateral edge of the pronator teres and the brachiahs. anastomoses in front of the medial epicondyle with the inferior and superior ulnar collaterals. It supphes branches to the muscles between which it runs, and to the skin. The dorsal, larger than the volar, comes'off from the medial side of the ulnar artery, either a little below the latter branch, or else as a common trunk with it, and, passing between the flexores digitorum subhmis and profundus, turns upward to the back of the medial epicondyle, where it Ues with the ulnar nerve between the two heads of origin of the flexor carpi ulnaris. It supplies the contiguous muscles — the flexor carpi ulnaris, the palmaris longus, and the flexores digitorum sublimis and profundus — the elbow-joint, and the ulnar nerve, and anastomoses with the inferior and superior ulnar collaterals, and with the interosseous recurrent forming the so-called rete olecrani. 2. The common interosseous artery [a. interossea communis] is a short thick trunk 1.2 cm. (| in.) or so in length, which comes off from the lateral and back part of the ulnar artery about 2.5 cm. ( 1 in.) from its origin, and just before that artery is crossed by the median nerve. It passes backward and downward between the flexor pollicis longus and the flexor digitorum profundus, toward the triaagular interval bounded by the upper border of the interosseous membrane, the oblique hgament, and the lateral border of the ulna, where it divides into the volar and dorsal interosseous arteries. (a) The volar interosseous artery [a. interossea volaris], smaller than the dorsal, but apparently the direct continuation of the common trunk, courses downward in front of the . interosseous membrane. It lies under cover of the overlapping edges of the flexor digitorum profundus and flexor poUicis longus, to both of which muscles it supphes branches. At the 578 THE BLOOD-VASCULAR SYSTEM upper border of the pronator quadratus it divides into two branches, an anterior terminal and a posterior terminal (fig. 473). The volar interosseous artery is accompanied by two veins and by the deep branch of the median nerve which hes to its radial side. The artery is bound down to the interosseous membrane by aponeurotic fibres. Fig. 470. — The Volar Arteries of the Forearm and Hand. (After Toldt, "Atlas of Human Anatomy/' Rebman, London and New York.) Biceps brachii — Inferior ulnar collateral artery — Brachial artery — Tendon of the biceps brachn — Brachio-radiah: Radial recurrent artery Ulnar recurrent artery Supinator interosseous artery f longus Extensor carpi radialis ] [ brevis Flexor digitorum sublimis^- Brachio -radialis Flexor digitorum profundus 1 Median nerve Pronator quadratus ^-. Flexor carpi radiahs ' Ir- _ Radial artery — -vflfll Superficial volar branch — Transverse carpal ligament Abductor brevis pollicis Flexor brevis pollicis Common volar digital arteries .e^^^- Adductor pollicis — tj—/-' First dorsal interosseii ' ^'j, LumbricaIes-^--r. Superior ulnar collateral artery Medial intermuscular septum Bracbialis Median nerve Pronator teres Flexor carpi radialis Palmaris longus Ulnar artery Flexor carpi ulnaris Flexor profundus digitorun Deep volar branches of ulnar artery Superficial volar arch Flexor digiti V brevis Abductor digiti V Proper volar digital arteries The branches of the volar interosseous artery are: — (i) The median artery [a. mediana] is a long slender vessel which arises from the volar interosseous immediately after the latter is given off from the common trunk. It passes forward between the flexor digitorum profundus and the flexor pollicis longus to the median nerve, with which it descends beneath the transverse carpal (anterior annular) ligament into the palm, and when of large size sometimes enters into the formation of the superficial palmar arch. At times the artery arises from the common THE ULNAR ARTERY 579 interosseous before its division, (ii) The nutrient arteries of the radius and uhia are usually derived from this vessel, (iii) The volar terminal division of the volar interosseous artery passes either in front of or behind the pronator quadratus, but in either case in front of the interos- seous membrane, and anastomoses with the volar carpal branches of the radial and ulnar arteries, and with the recurrent branches from the deep volar arch, forming the so-called volar carpal rete. (iv) The dorsal terminal, the larger division, pierces the interosseous mem- brane, and continues its course downward behind the interosseous membrane, under cover of the extensor muscles, to the back of the wrist, where it ends by anastomosing with the dorsal Fig. 471. — The Back of the Left Forearm, with the Dorsal Interosseous Artery AND Branches of the Radial at the Back of the Wrist. (From a dissection in the Hunterian Museum.) Articular branch of the profunda Brachialis Brachio-radialis, cut Common extensor tendon Supinator Dorsal interosseous artery Abductor pollicis longus Brachio-radialis, cut Extensor pollicis brevis Dorsal carpal ligament Extensor carpi radialis longus Radial artery First dorsal metacarpal artery Extensor pollicis longus First dorsal interosseous muscle First dorsal metacarpal artery Princeps pollicis artery Dorsal digital artery Rete over olecranon Interosseous recurrent artery Anconeus, cut Extensor carpi ulnaris Flexor carpi ulnaris Origin of extensor pollicis longus and indicis proprius Dorsal branch of volar interosseous artery Interosseous membrane Dorsal ulnar carpal artery Extensor carpi radialis brevis Dorsal radial carpal artery Fourth dorsal metacarpal artery Third dorsal metacarpal artery Second dorsal metacarpal artery carpal branches of the radial and ulnar arteries, forming the so-called dorsal carpal rete. This branch anastomoses, as soon as it pierces the interosseous membrane, with the dorsal interosseous artery. (6) The dorsal interosseous artery [a. interossea dorsalis], the larger division of the com- mon interosseous, turns backward through the triangular interval bounded by the interosseous membrane below, the oblique hgament above, and the ulna on the medial side, and emerging at the back of the forearm between the abductor pollicis longus and the supinator, under cover of the superficial extensors of the forearm, descends between the superficial and the deep muscles, crossing in this course the abductor polhcis longus, the extensor pollicis brevis, the extensor pollicis longus, and the extensor indicis proprius (fig. 471). It anastomoses at the lower border 580 THE BLOOD-VASCULAR SYSTEM of this muscle and just above the wrist joint, with the dorsal branch of the volar interosseous which here, as above described, has perforated the interosseous membrane. It is separated from the deep radial nerve at first by the radius and supinator, and on the back of the forearm by the extensores polUcis longus and indicis proprius. The chief branch of the dorsal interosseous artery, the interosseous recurrent artery [a. interossea recurrens] arises from the dorsal interosseous as the latter emerges from beneath the supinator. It runs upward between the anconeus and supinator, usually under cover of the former, to the interval between the lateral epicondyle and the olecranon, where it anas- tomoses with the profunda, inferior ulnar collateral, radial recurrent, and dorsal ulnar recurrent arteries, and gives branches to the retiform plexus over the olecranon — the rete olecrani. Fig. 472. — Anastomoses and Distribution of the Arteries of the Hand, Volar interosseous - Radial artery - Volar radial carpal Superficial volar Dorsal radial carpal Radial artery at wrist First dorsal metacarpal Second dorsal metacarpal Princeps polUcis First dorsal meta- carpal (branch to index) Radialis indicis Dorsal digital Volar digital First dorsal branch of volar digital Second dorsal branch of volar digital Anastomosis of volar digital arteries about matrix of nail and pulp of finger Ulnar artery Volar ulnar carpal Dorsal ulnar carpal Deep ulnar Superficial arch Carpal re- current Dorsal per- forating Volar meta- carpals Common volar digitals Dorsal meta- carpals Common volar digital 3. The muscular branches [rami musculares] are numerous. * They supply the deep and superficial flexors of the fingers, the flexor carpi radialis and ulnaris, and the pronator radii teres. 4. The dorsal ulnar carpal [ramus carpeus dorsafis] comes off from the ulnar artery a little above the transverse carpal (anterior annular) ligament, and, winding medially round the end of the ulna or the ulnar collateral ligament of the wrist, beneath the flexor carpi ulnaris, ramifies on the back of the carpus beneath the extensor tendons. It forms by its anastomosis with the dorsal radial carpal, with the dorsal terminal branch of the volar interosseous and with the dorsal interosseous arteries a plexus or rete, the so-called dorsal carpal rete. The branches given off from this plexus or arch are described with the dorsal carpal branch of the radial artery. THE ULNAR ARTERY 581 5. The volar ulnar carpal [ramus carpeus volaris] is a small branch given off from the ulnar artery opposite the carpus. It passes beneath the flexor digitoruro profundus to anastomose with the volar radial carpal, with terminal twigs of the volar branch of the volar interosseous, and with recurrent branches from the deep volar arch, forming an anastomotic arch across the front of the carpus — the volar carpal arch or rete. Fig. 473. — The Arteries op the Right Forearm and the Deep Volar Arch. -Superior ulnar collateral -Inferior ulnar collateral Brachial artery - Radial recurrent artery. Brachio-radialis - Flexor pollicis longus muscle - -Brachialis muscle - Volar ulnar recurrent -Dorsal ulnar recurrent -Volar interosseous artery -Flexor carpi ulnaris -Flexor digitorum profundus muscle -Volar interosseous artery Transverse carpal ligament, cut- "Volar branch of ulnar artery, cut "Deep volar arch 'H\ fe^^Vc— Volar metacarpal arteries Volar digital artery, cut short Volar digital artery" The Ulnar Artery at the Wrist The ulnar artery at the wrist may be said to extend from the upper to the lower border of the transverse carpal (anterior annular) ligament upon which it rests. It here lies immediately to the radial side of the pisiform bone, and to the ulnar side of the hook of the hamate (unciform), the two bones forming for the vessel a protecting channel, which is further converted into a short canal by the expansion of the flexor carpi ulnaris passing from the pisiform to the hook of the hamate (unciform). The ulnar nerve in this situation is immediately to the ulnar side of the artery. 582 THE BLOOD-VASCULAR SYSTEM The Ulnae Artery in the Palm (Superficial Volar Arch) The ulnar artery, on entering the palm, divides into two branches, the super- ficial and deep. The superficial branch (fig. 472) , the direct continuation of the vessel, anasto- moses with the superficial volar, a branch of the radial, forming what is then known as the superficial volar arch. After descending a short distance toward the cleft between the fourth and fifth fingers, it turns toward the thumb, forming a curve with its convexity toward the fingers and its concavity toward the muscles of the thumb, and anastomoses opposite the cleft between the index and middle fingers, at the junction of the upper with the middle third of the palm, with the superficial volar branch of the radial artery to complete the arch. A line drawn transversely across the palm on a level with the metacarpo-phalangeal joint of the thumb will roughly indicate the situation of the arch. Relations. — In front: in addition to the skin and superficial fascia, the vessel is crossed successively, by the palmaris bevis, the palmar branch of the ulnar nerve, the palmar aponeuro- sis and the palmar branch of the median nerve. Behind, it rests successively upon the short muscles of the little finger, the digital branches of the ulnar nerve, the flexor tendons, and the digital branches of the median nerve. The branches of the superficial volar arch. In addition to small muscular and cutaneous branches the superficial volar supplies: — The common digital arteries [aa. digitales volares communes]. These, usually four in number, arise from the conve.xity of the superficial arch and, running downward through the palm, give off the digital arteries proper to both sides of the httle, ring, and middle fingers, and the ulnar side of the index finger. The radial side of the index finger and the thumb are supplied by the first volar metacarpal branch" of the radial artery. The most ulnar of the common digital arteries passes distally over the muscles in the ulnar border of the palm, and thence along the ulnar bordet of the httle finger. The remaining arteries pass distaUy in the three ulnar intermetacarpal spaces to within about 6 mm. (j in.) of the clefts between the fingers, where they divide into branches, the digital arteries proper [aa. digitales volares proprise], which supply the sides of contiguous fingers. As the common digital arteries pass through the palm, they lie between the flexor tendons, on the digital nerves and lumbrical muscles, and beneath the palmar aponeurosis. Just before bifurcating they pass under the transverse fasciculi, and are joined b}^ the volar metacarpal branches from the deep volar arch (fig. 472). At this spot they also receive the volar perforating branches from the dorsal metacarpal vessels. On the sides of the fingers the proper digital arteries lie between the palmar and dorsal digital nerves. They anastomose by small branches, forming an arch across the front of the bones on the proximal side of each interphalangeal joint. They supply the flexor tendons and the integuments, and terminate in a plexiform manner beneath the pulp of the finger and around the matrix of the nail. A dorsal digital branch is given off to the back of the fingers about the level of the middle of the first phalanx, and a second but smaller dorsal digital branch about the level of the middle of the second phalanx. The deep branch of the ulnar artery, also called the communicating artery, sinks deeply into the palm between the abductor and flexor quinti digiti brevis, and joins the radial to form the deep volar arch. (See The Radial Artery.) THE RADIAL ARTERY The radial artery — the smaller of the two arteries into which the brachial divides at the bend of the elbow — appears as the direct continuation of the brachial. It runs, at first curving laterally, along the radial side of the forearm as far as the styloid process, then, coiling over the radial collateral ligament and the lateral and back part of the wrist, enters the palm of the hand from behind be- tween the first and second metacarpal bones, and ends by anastomosing with the deep branch of the ulnar to form the deep volar arch. Hence the artery is divisible into three parts: that in the forearm, that at the wrist, and that in the palm of the hand. The course of the artery is indicated by a line drawn from a point 2.5 cm. (1 in.) below the centre of the elbow to a point situated just medial to the styloid process of the radius. I. The Radial Artery in the Forearm In its course through the forearm (fig. 470) the radial artery is found in the most lateral of the intermuscular spaces, and it is only necessary to divide the. THE RADIAL ARTERY 583 skin, superficial and deep fascia, to expose the vessel, and in addition in the upper third to separate the brachio-radialis from the pronator teres. Relations. — In front, the artery is at first overlapped by the brachio-radialis, but for the rest of its course it is merely covered by the slcin, superficial and deep fascise, by some cutaneous veins, and by cutaneous branches of the musculo-cutaneous nerve. Behind, it lies successively from above downward on the tendon of the biceps, the supinator, from which it is separated by a layer of fat, the insertion of the pronator teres, the radial origin of the flexor digitorum sublimis, the flexor poUicis longus, the pronator quadratus, and the volar surface of the lower end of the radius. It is in this last situation, where the artery Ues upon the bone and can therefore be easily pressed against it, that the pulse is usually felt. Fig. 474. — Diagram of the Relation of the Arteries of the Left Forearm to THE Bones. (Walsham.) Superior ulnar collateral artery Brachial artery Inferior ulnar collateral artery Volar ulnar recurrent Dorsal ulnar recurrent - Ulnar artery interosseous artery Volar interbsseous artery Volar ulnar carpal Superficial branch of ulnar artery (superficial volar arch) L volar digital artery Profunda artery Lateral epicondyle Articular branch of profunda artery Radial recurrent artery Interosseous recurrent artery Radial artery Oblique ligament Interosseous membrane Dorsal interosseous artery Volar radial carpal Radial artery of wrist Superficial volar branch of radial artery Deep volar arch On its lateral side it has, throughout the whole of its course, the braohio-radiahs muscle, the guide to the artery in ligature, and the lateral vena comitans; in its middle third, the superflcial radial nerve as well. In its lower third the superficial radial nerve is to its lateral side, but separated from it by the brachio-radialis and fascia. On its medial side, in the upper third is the pronator teres, in the lower third the tendon of the flexor carpi radialis, and throughout the whole of its course the medial vena comitans. The branches of the radial artery in the forearm are: — (1) The radial re- current; (2) the muscular; (3) the volar radial carpal; (4) the superficial volar. (1) The radial recurrent [a. recurrens radialis] usually arises from the lateral side of the radial just below its origin from the brachial. It at first runs laterally on the supinator and then divides into three chief branches (fig. 475). One of these continues laterally through the fibres of the radial (musculo-spiral) nerve, or between the superficial (radial) and deep radial (posterior interosseous) nerves when the radial (musculo-spiral) divides higher than usual, into the brachio- radiaUs and extensor carpi radiahs longus and brevis, and anastomoses with the interosseous recurrent. A second ascends between the brachiahs and braehio-radiahs, with the radial 584 THE BLOOD-VASCULAR SYSTEM (musculo-spiral) nerve, and anastomoses with the profunda artery. A third descends with the superficial radial nerve under cover of the brachio-radialis, supplying that muscle. The radial recurrent also gives off branches to the elbow-joint. (2) The muscular branches [rami musculares] come off irregularly to supply the contiguous muscles on the lateral side of the forearm. (3) The volar radial carpal branch [ramus carpeus volaris] arises from the rnedial side of the radial artery about the level of the lower border of the pronator quadratus. It crosses the front of the radius beneath the flexor muscles, and anastomoses with the volar carpal branch of the ulnar, forming the volar carpal rete. This plexus is joined above by terminal twigs from the volar interosseous artery, and below by recurrent branches from the deep volar arch. It sup- plies branches to the lower end of the radius, and to the wrist and carpal joints. (4) The superficial volar branch [ramus volaris superficialis] leaves the radial artery as the lat- ter vessel is about to turn over the radial collateral ligament to the back of the wrist. It courses forward over the short muscles of the ball of the thumb, and anastomoses with the superficial. Fig. 475. — The Bend op the Elbow, Left Side. (From a dissection by Dr. Alder Smith in the Museum of St. Bartholomew's Hospital.) Median nerve Posterior branch of in- ferior ulnar collateral Branches of medial a nti -brachial cutaneous nerve Basilic vein Brachialis Volar branch of inferiori ulnar collateral Median antibrachial vein Median cubital vein Tendon of biceps Lacertus fibrosus Deep median vein Ulnar artery Pronator teres Vena comitans of brachial artery Basilic vein Brachialis Cephalic vein Brachial artery Dorsal anti- brachial cuta- neous nerve Radial n. and as- cending branch of radial recur- rent artery 'Accessory ceph- -~ alio vein Cephalic vein Ascending br. of radial recurrent Deep radial nerve Radial recurrent artery Brachio-radialis Superficial radial nerve branch of the ulnar artery to complete the superficial volar arch. It supplies small branches to the muscles of the ball of the thumb, and frequently terminates in these muscles without ioining the arch. Occasionally it passes beneath the abductor poUicis brevis. II. The Eadial Artery at the Wrist The radial artery at the wrist winds over the radial side of the carpus, under the extensor tendons of the thumb, from a spot a little below and medial to the styloid process of the radius to the base of the first interosseous space, where it sinks between the two heads of the first dorsal interosseous muscle into the palm, to form, by anastomosing with the deep branch of the ulnar artery, the deep volar arch. A line drawn from 1.2 cm. (| in.) medial to the styloid process to the base of the first interosseous space, which can be distinctly felt on the back of the hand, will roughly indicate the course of the artery (fig. 476). THE RADIAL ARTERY 585 Relations. — The artery is covered successively by the abductor poUicis longus and extensor pollicis brevis, by branches of the superficial radial nerve and veins, and, just before it sinks between the two heads of the interosseous muscle, by the tendon of the extensor pollicis longus. The branches of the superficial radial nerve to the thumb and index finger cross it. It is at first somewhat deeply placed beneath the first-mentioned extensor muscles of the thumb; but subsequently it lies quite superficial, and can be felt pulsating in a fittle triangular depression bounded on either side by the extensores pollicis longus and brevis, and above by the lower end of the radius. The artery lies successively on the radial collateral ligament of the wrist, on the navicular (scaphoid), the greater multangular (trapezium), the base of the first meta- carpjal bone, and on the dorsal ligaments uniting these bones. It has usually with it two com- panion veins, and a few branches of the musculo-cutaneous nerve. Fig. 476. — The Radial Artery at the Wrist, Left Forearm. (From a dissectionjn the Hunterian^Museum.) Articular branch of the profunda Brachialis Brachio-radialis, cut Common extensor tendon Supinator Dorsal interosseous artery Abductor pollicis longus Brachio-radialis, cut Extensor pollicis brevis Borsal carpal ligament Extensor carpi radialis longus Radial artery First dorsal metacarpal artery Extensor pollicis longus First dorsal interosseous muscle First dorsal metacarpal artery Princeps pollicis artery Dorsal digital artery Triceps Rete over olecranon Interosseous recurrent artery Anconeus, cut Extensor carpi ulnaris Flexor carpi ulnaris Origin of extensor pollicis longus and indicis proprius Dorsal branch of volar interosseous artery Interosseous membrane Dorsal ulnar carpal artery Extensor carpi radialis brevis Dorsal radial carpal artery Fourth dorsal metacarpal artery Third dorsal metacarpal artery ■^^^ — ' Second dorsal metacarpal artery -(1) The dorsal radial The branches of the radial artery at the wrist are: carpal; (2) the first dorsal metacarpal, (1) The dorsal radial carpal branch [ramus carpeus dorsaUs] arises from the radial as the latter vessel passes under the abductor pollicis longus, and runs medially beneath the ex- tensor carpi radiahs longus and brevis, and the extensor pollicis longus, across the dorsal surface of the carpus, to anastomose with the dorsal ulnar carpal and with the terminal twigs of the posterior branch of the volar interosseous artery. This anastomosis is called the dorsal carpal 586 THE BLOOD-VASCULAR SYSTEM rete [rete carpi dorsale]. From this rete are given oif the second, third, and fourth dorsal metacarpal arteries to the second, third, and fourth intermetacarpal spaces respectively. These vessels run downward on the dorsal interosseous muscles as far as the flexure of the fingers, and there divide into two branches (dorsal digital), which run along the sides of the contiguous fingers on their dorsal aspect. Near their proximal ends they anastomose with the dorsal perforating branches of the deep volar arch. Distally they are connected by volar perforating branches with the digital arteries or the corresponding spaces. The branches which run along the backs of the fingers anastomose with the dorsal branches of the first dorsal digital arteries derived from the volar common digital vessels (fig. 476). (2) The first dorsal metacarpal (figs. 472, 476) is given off by the radial shortly before it passes between the two heads of the first dorsal interosseous muscle. It quickly divides into two branches which supply the dorsal surface of the thumb and the radial side of the index- finger toward its dorsal surface. III. The Radial Artery in the Palm (Deep Volar Arch) The radial artery enters the palm between the first and second metacarpal bones at the base of the first interosseous space, by passing between the two heads of the first dorsal interosseous muscle. It then runs medially between the transverse and oblique heads of the adductor pollicis muscle and continuing its course in a slight curve with the convexity forward, across the base of the meta- carpal bones and interosseous muscles, it anastomoses with the deep branch of the ulnar, forming the deep volar arch [arcus volaris profundus]. The arch may be said to extend from the first interosseous space to the base of the meta- carpal bone of the little finger, and is a finger's breadth nearer the wrist than the superficial arch. It is covered by the superficial and deep fiexor tendons, by the superficial head of the flexor pollicis brevis, and by part of the flexor quinti digiti brevis. It is accompanied by the deep branch of the ulnar nerve, and two small venae comitantes (figs. 472, 473). The branches of the deep volar arch are: — (1) The princeps pollicis; (2) the radialis indicis; (5) the volar metacarpals (three in number); (4) the recurrent carpal; (3) the dorsal perforating. The first two are usually spoken of as coming off from the radial artery in the palm; the last three from the deep volar arch. (1) The arteria princeps pollicis arises from the radial artery as it enters the palm between the two heads of the first dorsal interosseous muscle. It passes downward between the adductor pollicis transversus and the first dorsal interosseous muscle, parallel to the metacarpal bone, and between the two portions of the flexor polhcis brevis under cover of the flexor polUcis longus. Opposite the metacarpo-phalangeal joint it usually divides into two branches, one of which is distributed to each side of the thumb on its volar aspect. These vessels anasto- mose with each other at the end of the thumb, like the other digital arteries. (2) The arteria radialis indicis comes off from the radial artery a little lower than the former vessel, or as a common trunk with it, and passes forward between the first dorsal interosseous and adductor pollicis transversus, parallel to the radial side of the second metacarpal bone. After emerging from beneath the adductor poUicis transversus it continues its course along the radial side of the index-finger, on its volar aspect, as far as the tip, anastomosing in this course with the digital artery on the opposite side of the finger in a way similar to that of the other digital arteries. It frequently communicates, at the lower border of the adductor pollicis, with the superficial volar arch and princeps pollicis. It gives off a dorsal branch, which anasto- moses with the branch fron the fu-st dorsal metacarpal to the index finger. (3) The volar metacarpal arteries [aa. metacarpex volares], three in number, come off from the convexity of the deep arch, and, coursing downward in the centre of the second, third, and fourth interosseous spaces on the interosseous muscles, terminate near the cleft of the fingers by anastomosing with the digital arteries from the superficial arch. These vessels supply the interosseous muscles and the bones, and the second, third, and fourth lumbricales. (4) The recurrent branches come off from the concavity of the arch, and consist of two or three small vessels which run upward toward the wrist, and anastomose with the volar branch of the volar interosseous, and the volar radial and ulnar carpal arteries. (5) The dorsal perforating brandies (rr. perforantes), which are usnally three in number, pass from the arch directly through the second, third, and fourth interosseous spaces between the two heads of the corresponding dorsal interosseous muscle, and join the proximal ends of the first dorsal interosseous, and the second, third, and fourth dorsal metacarpal arteries re- spectively. THE THORACIC AORTA The thoracic aorta [aorta thoracalis] (fig. 477) is the thoracic portion of the aorta descendens. It extends from the termination of the aortic arch at the lower border of the body of the fourth thoracic vertebra to the lower border of the body of the twelfth thoracic vertebra, where it passes between the medial THE THORACIC AORTA 587 crura of the diaphragm, and is thence continued under the name of the abdominal aorta. It is at first situated a little to the left of the vertebral column, but as it descends, approaches the front of the column, at the same time following the back- ward curve of the spine, and at the diaphragm is almost in the middle line. It lies in the posterior mediastinum, having the oesophagus at first a little to the right of it, then in front of it, and just above the tenth thoracic vertebra, where this tube pierces the diaphragm, a little to its left side. Fig. 477. — The Arch of the Aorta, the Thoracic Aorta, and the Abdominal Aorta, WITH THE Superior and Inferior Vena Cava and the Innominate and Azygos Veins. Right common carotid artery Right internal jugular Right lymphatic duct Innominate artery Right vagus nerve Right innominate vein Internal mammary vein Trunk of the pericardiac and thymic veins Superior vena cava Azygos vein Hemiazygos vein, cross- ing spine to enter vena azygos Inferior vena cava Coeliac artery Right middle suprarenal artery Right internal spermatic artery Right spermatic vein Left common carotid artery Left vagus nerve Thoracic duct Left innominate vein Left subclavian artery Left superior intercostal Recurrent (laryngeal; nerve Accessory hemiazygos vein (Esophagus Left upper azygos vein (Esophageal branches from aorta _^ Hemiazygos vein Thoracic duct Left inferior phrenic artery Left middle suprarenal artery Receptaculum chyH Superior mesenteric artery Left ascending lumbar Left internal spermatic vessels Relations. — In front it is crossed from above downward by the root of the left lung, by the oesophagus, which separates it from the pericardium and heart, and by the diaphragm. Behind, it hes upon the lower seven thoracic vertebrae, and is crossed obhquely opposite the seventh or eighth thoracic vertebra by the the vena hemiazygos (azygos minor) and op- posite the fifth or sixth vertebra by the accessory hemiazygos vein, or by one or more of the intercostal veins. On the right side it has, above, the oesophagus and vertebral column; lower down the right pleura and lung. The vena azygos and thoracic duct also lie to the right, but on a some- what posterior plane. On the left side it has the left lung and pleura above, and the oesophagus below. The vena hemiazygos and the accessory hemiazygos vein are also to the left, but on a posterior plane. 588 THE BLOOD-VASCULAR SYSTEM Branches of the Thoracic Aorta The branches of the thoracic aorta may be divided into the visceral and the parietal. The visceral are: — (1) The pericardiac; (2) the bronchial; and (3) the oesophageal. The parietal are: — (1) The intercostal; (2) the superior phrenic; and (3) the arteria aberrans. A. Visceral Branches (1) The pericardiac branches [rami pericardiaci] — two or three small branches, irregular in their origin, course, and distribution — pass to the posterior surface of the pericardium to supply that structure, and anastomose with the other peri- cardiac branches. They give small twigs to the posterior mediastinal glands. (2) The bronchial arteries [aa. bronchiales] supply the bronchi and the lung substance. They vary considerably in their origin, course, and distribution; they are usually three in number — one on the right side, and two on the left. (a) The right bronchial generally arises either from the first right aortic intercostal, or else as a common trunk witli the left upper bronchial from the front of the aorta just below the level of the bifurcation of the trachea. It passes laterally on the back of the right bronchus, and is distributed to the bronchi and lung substance, (b) The left upper bronchial arises from the front of the aorta just below the bifurcation of the trachea, or as a common trunk with the right bronchial, (c) The left lower bronchial arises from the front of the aorta just below the level of the left bronchus. Like the corresponding artery on the right side, the left bronchial arteries run laterally on the left bronchus, and, after dividing and subdividing on the back of the bronchi, supply the bronchi themselves and the lung substance. Small twigs are given off from the bronchial arteries to the bronchial glands and to the oesophagus. (3) The oesophageal arteries [aa. oesophageae], four or sometimes five in number, arise at intervals from the front of the descending thoracic aorta, the first coming off just below the left lower bronchial. They usually increase in size from above downward, the upper coming off more toward the right side of the aorta, the lower more toward the left side. They pass forward to the oesophagus, supplying that tube and anastomosing with each other and with the descending oesophageal branches of the inferior thyreoid above, and with the ascending oesophageal branches of the phrenic and gastric arteries below, thus forming a chain of anastomoses along the whole length of the tube. B. Parietal Branches (1) The intercostal arteries [aa. intercostal es], usually ten in number on each side, supply the lower intercostal spaces, the two upper spaces (occasionally the first only) being supplied from the costo-cervical trunk of the subclavian artery. The lowest artery accompanies the twelfth thoracic nerve below the last rib and is therefore called the subcostal artery. Its distribution is similar to that of the lumbar arteries (p. 593) except that it commonly crosses the anterior surface, rather than the posterior, of the quadratus lumborum. The intercostals arise in pairs from the back part of the aorta, and at once turning, the one to the right, the other to the left, wind backward over the front and sides of the vertebral bodies to reach the intercostal spaces. In foetal life these arteries run almost transversely backward, or even with a slight inclination downward, to the intercostal spaces; but after the first year, in consequence of the disproportionate growth of the aorta and vertebral column, the upper int-er- costals have to ascend to reach their respective spaces. The arteries in their course around the vertebrae differ on the two sides of the body. On the right side the arteries — and especially the upper, in consequence of the aorta lying a little to the left side of the spine in the upper part of its course — are longer than the left. They wind over the front and right side of the vertebrae, being crossed by the thoracic duct and vena azygos (major), and covered by the right pleura and lung. The upper are also crossed by the oesophagus. They give off small branches to the bodies of the vertebrae and anterior longi- tudinal Hgament. On the left side, as the intercostals wind around the sides of the bodies of the vertebrae, the lower are crossed by the vena hemiaz3rgos (azygos minor), the two upper by the left superior intercostal vein, and the two next by THE THORACIC AORTA 589 the accessory hemiazygos vein when this is present. They are all covered by the left pleura and lung (fig. 478). The branches of the intercostal arteries are: — (a) anterior, (b) posterior. (a) The anterior branches [rami anteriores] at first cross the intercostal space obliquely, in consequence of the downward direction of the ribs, toward the angle of the rib above, and thence are continued forward in the costal groove, and anastomose with the superior branches of the anterior intercostals from the internal mammary in the upper spaces, and from the musculo-phrenic in the lower spaces. They he at first on the external intercostal muscles, being covered in front by the pleura and lung, the endothoracic fascia, and the subcostal muscles. Opposite the heads of the ribs they are crossed by the sympathetic nerve. At the angle of the ribs they pass under cover of the internal intercostal muscles, and thence to their termination he between the two intercostal muscles. Their situation in the midspace as far as the angle of the rib should be remembered in performing paracentesis thoracis. To avoid the risk of injuring the vessels, the puncture should not be made further back than the angle of the ribs. They are accompanied by a nerve and vein, the vein lying above and the nerve below, except in the upper spaces, where the artery, having to ascend to reach the space, at first Mes below the nerve which runs more horizontally. The uppermost branch anastomoses with the costo-oervical artery from the subclavian, and at times supplies almost entirely the second intercostal space. The arteries to the tenth and eleventh spaces on reaching the end Fig. 478. — Scheme op Intercostal Abtebt. (Walsham.) Longissimus dorsi Medial cutaneous branch Semlspinalis dorsi and multifidus spinse Prelaminar branch Neural branch Postcentral branch Spinal cord Anterior spinal artery Lateral cutaneous branch llio-costalls Intercostal artery Vena hemiazygos Vena azygos Thoracic duct (Esophagus Anterior intercostal Internal mammary artery Anterior cutaneous branch' Posterior branch Sympathetic Collateral branch Medial mammary branch ^ Upper or main branch of anterior intercostal of their respective ribs pass between the abdominal muscles, and anastomose with the inf. epigastric artery from the external ihac, and with the lumbar arteries from the abdominal aorta. The artery beneath the twelfth rib anastomoses with the lumbar arteries and with the external circumflex ihac. Each anterior branch gives off the following: — (i) The collateral branch which comes off near the angle of the rib and runs forward, between the external and internal intercostals, along the upper border of the lower rib enclosing the space. It is smaller than the main anterior branch and anastomoses with tlie lower anterior intercostal in each space, (ii) Muscular branches [rami nmsculares] supply the intercostal, pectoral and abdominal muscles, (iii) The lateral cutaneous branches [rami cutanei laterales], both pectoral and abdominal, run with the corresponding branches of the intercostal nerves through the external intercostal and ser- ratus anterior muscles. They then divide into anterior and -posterior branches which turn for- ward and backward, respectively, to supply the integument. The anterior branches from the third, fourth and fifth spaces supply lateral mammary branches [rr. mammarii laterales] to the lateral region of the breast, (iv) Anterior cutaneous branches [rami cutanei anteriores] pierce the external intercostal ligament and the pectorahs major just lateral to the sternum. 590 THE BLOOD-VASCULAR SYSTEM They are distributed to the skin and give medial mammary branches [rr. mammarii mediales] to the medial region of the breast. (b) The posterior branches [rami posteriores]. — These large branches are given oil from the intercostals opposite the quadrilateral space bounded by the transverse process of the vertebra above, the neck of the rib below, the body of the vertebra medially, and the anterior costo- transverse ligament laterally. Passing backward toward this space with the dorsal branch of the corresponding intercostal nerve, they divide opposite the intervertebral foramen into a muscular and a spinal branch, (i) The muscular branch [r. muscularis] passes backward through the quadrilateral space, and soon subdivides into a medial and a lateral branch. The former passes between the longissimus dorsi and iUo-costaUs, and, after supplying these muscles, gives off medial cutaneous branches [rr. cutanei mediales]. The latter branch pierces the multi- fidus spinas, and, emerging between the longissimus dorsi and semispinahs dorsi near the spinous processes, gives off lateral cutaneous branches [rr. cutanei laterales]. It suppHes the muscles ■ in its course. (ii) The spinal branch [r. spinalis] enters the intervertebral foramen with the spinal nerve of the corresponding segment. The disposition of the spinal branch is similar to_ that of the spinal branches entering the canalis vertebralis in other regions and may be described here: — ARTERIES OF THE VERTEBRAL CANAL Spinal arteries are derived from the vertebral, ascending cervical and costo-cervical arteries, from the dorsal rami of the intercostal (fig. 478) and lumbar arteries, and from the ilio-lumbar and lateral sacral arteries. The spinal branch in each case divides into three branches, post- central, prelaminar and neural. Each post-central branch divides on the lateral part of the posterior longitudinal ligament into an ascending and a descending branch by which means a bilateral series of anastomosing arches are formed throughout the length of the canal. From the concavities of the opposite arches transverse connecting stems are formed which are again connected by a median longitu- dinal channel. The pre-laminar branches also divide and form an anastomosis in front of the laminse and ligamenta flava. This is similar in character to the post-central, but much less regular. The neural branches enter the dura mater and are usually small and end by supplying the nerve roots. A variable number of these (5-10 on a side) are larger than the others and rein- force the longitudinal anterior and posterior spinal arteries given off from the vertebrals within the cranium. (For arteries of the spinal cord, see Section VII.) (2) The superior phrenic arteries [aa. phrenicse superiores], are small twigs coming off from the thoracic aorta immediately above the diaphragm. They are distributed to the vertebral portion of the diaphragm on its upper surface. (3) The arteria aberrans is a small twig which, arising from the thoracic aorta near the right bronchial artery, passes upward and to the right behind the oesophagus and trachea, and is occasionally found to anastomose on the oesophagus with the arteria aberrans of the superior intercostal artery (see p. 568). It is regarded as the remains of the right aortic dorsal stem (fig. 506). (4) The mediastinal branches [rami mediastinales], numerous, but small, are distributed to the pleura, and the vessels, nerves and lymph-nodes of the posterior mediastinum. THE ABDOMINAL AORTA The abdominal aorta [aorta abdominalis] (fig. 479), the abdominal portion of the descending aorta, begins at the aortic opening in the diaphragm opposite the lower broder of the twelfth thoracic vertebra, and ends usually opposite the middle of the body of the fourth lumbar vertebra by dividing into the right and left common iliac arteries. It is at first centrally placed between the medial crura of the diaphragm, but as it descends in front of the lumbar vertebrse it leaves the middle line, and, at its bifurcation, lies a little to the left side of the spine. The place at which the aorta bifurcates may be somewhat roughly indicated on the surface of the abdomen by a point about 2.5 cm. (1 in.) below and a little to the left of the umbilicus. The level of its bifurcation may be more accurately determined by drawing a straight line across the front of the abdomen joining the highest points of the iliac crests. The inferior vena cava, which accompanies the abdominal aorta, lies to its right side. Below, the vein is in contact with the artery and on a somewhat posterior plane; but above, it is separated from the aorta by the right medial crus of the diaphragm, and, in consequence of the caval opening in the diaphragm being placed further forward than the opening for the aorta, is on an anterior plane. THE ABDOMINAL AORTA 591 Relations. — In front, the aorta is successively crossed from above downward by the right lobe of the liver, the cceHac (solar) plexus, the lesser omentum, the termination of the oesophagus in the stomach, the ascending layer of the transverse meso-colon, the splenic vein or commence- ment of the portal vein, the pancreas, the left renal vein, the third portion of the duodenum, the mesentery, the aortic plexus of the sympathetic nerve, the internal spermatic or ovarian arteries, the inferior mesenteric artery, the median lumbar lymphatic nodes and lymphatic vessels, and the small intestines. Of these structures the cceliac (solar) plexus, the aortic plexus, the splenic vein or the commencement of the portal vein, the pancreas, the left renal vein, the duodenum, the lym- phatics, the spermatic or ovarian arteries, and the peritoneal reflexions are in contact with the aorta. Behind, the aorta hes upon the bodies of the lumbar vertebrae and intervening intervertebral cartilages, the anterior longitudinal ligament, the origin of the left medial crus of the diaphragm, and the left lumbar veins. Fig. 479. — The Abdominal Aorta and its Branches, with the Inferior Vena Cava and ITS Tributaries. Cystic arterj Hepatic duct — Cystic duct Commoa duct Portal vem_ Gastro-duodenal br __ Right gastric artery_ Hepatic artery^ Right suprarenal vein Inferior suprarenal artery Renal artery Renal vein Vena cava inferior Kidney Right spermatic \ Right internal spermatic artery Quadratus lumborum muscle Right lumbar artery and left lumbar vein Ureteric branch of — spermatic artery Middle sacral vessels. Left lobe of liver (Esophagus Left inferior phrenic artery Right inferior phrenic artery Superior suprarenal Left gastric artery Inferior suprarenal Splenic artery — — • Left phrenic vein — — Left suprarenal vein ,. . \— Superior mesenteric ir^., ^''"^ Kidney Ureteric branch of renal Left spermatic vein Left internal spermatic artery Inferior mesenteric artery Ureteric branch of spermatic Ureteric branch of common iliac Common iliac artery External iliac artery Hypogastric artery On the right side from above downward are the right medial crus of the diaphragm, the great splanchnic nerve, the caudate lobe of the liver, tlie receptaculum chyU and beginning of the thoracic duct (the two latter structures are on a posterior plane), the right coeHac (semi- lunar) gangUon, and the inferior vena cava. On the left side are the left medial crus of the diaphragm, the left splanchnic nerve, and the left cocliac (semilunar) ganghon. The pancreas is also in contact with the aorta on the left side, and the small intestines are separated from it only by peritoneum. Branches of the Abdominal Aorta The branches of the abdominal aorta usually arise in the following order from above downward (figs. 479, 480) : — ■ (1) Right and left inferior phrenic; (2) coeliac; (3) right and left middle suprarenal; (4) right and left first lumbar; (5) superior mesenteric; (6) right and 592 THE BLOOD-VASCULAR SYSTEM left renal; (7) right and left internal spermatic; (8) right and left second lumbar; (9) inferior mesenteric; (10) right and left third lumbar; (11) right and left fourth lumbar; (12) right and left common iliac; (13) middle sacral. The above branches may be divided into the parietal, the visceral, and the terminal. The parietal branches are distributed to the abdominal walls. They are the right and left phrenics, and the four right and left lumbars. The visceral branches supply the viscera. Three of these are given off singly from the front of the aorta, namely, the cceliac, the superior mesenteric, and the inferior mesenteric; and three are given off in pairs, namely, the two suprarenals, the two renals, and the two spermatics. The terminal branches are the middle sacral and the right and left common iliac arteries. Fig. 480. — Scheme of the Abdominal Aorta. (Walsham.) Lesser nmpntnm^ *'*^ Pancreas Left renal vein Superior mesenteric artery Transverse meso-colon Inferior part of duodenum Transverse colon Mesentery Small intestines Great omentum' Inferior mesenteric artery Thoracic duct Cceliac artery First lumbar vein Cisterna chyli Second lumbar vein Peritoneum Third lumbar vein Fourth lumbar vein A. The Parietal Branches of the Abdominal Aorta 1. THE INFERIOR PHRENIC ARTERIES The inferior phrenic artery [a. phrenica inferior] usually arises from the aorta as it passes between the medial crura of the diaphragm. At times it comes off from the cceliac artery; or when it arises as two separate vessels, either the right or left vessel may come from this artery, or from other of the upper branches of the abdominal aorta. The right phrenic passes (fig. 480) over the right medial crus of the diaphragm behind the vena cava, and then upward and to the right between the central and right leaflets of the central tendon of the muscle, where it divides into an anterior and a posterior branch. The former courses anteriorly and medially and anastomoses with the anterior branch of the left phrenic, with the musculo-phrenio branches of the internal mammary, and with the pericardio- phrenic arteries; the latter passes posteriorly and laterally toward the ribs, and anastomoses with the intercostal arteries. Besides the two terminal branches and branches for the supply of the diaphragm itself the right phrenic gives off the right superior suprarenal [ramus supra- renaUs superior], to the right suprarenal gland, as well as branches to the vena cava,- to the hver, and to the pericardium. The left phrenic crosses the left medial crus of the diaphragm behind the CESophagus, and, like the right artery, divides into an anterior and posterior branch and gives off a left suprarenal branch. The distribution and anastamoses are similar on the two sides. THE LUMBAR ARTERIES 593 2. THE LUMBAR ARTERIES The lumbar arteries [aa. lumbales] (fig. 479), usually eight in number, four on each side, come off in pairs from the posterior aspect of the abdominal aorta, opposite the bodies of the four upper lumbar vertebrae. A fifth pair of lumbar arteries, generally of small size, frequently arises from the middle sacral artery opposite the fifth lumbar vertebra. The lumbar arteries, which are rather longer on the right than on the left side, in consequence of the aorta lying a little to the left of the median line, wind more or less transversely around the bodies of the vertebrae to the space between the transverse processes, where they give off each a dorsal branch, and then, coursing forward between the abdominal muscles, termi- nate, by anastomosing with the other arteries of the abdominal wall. Relations. — As they wind around tlie bodies of the vertebra they pass beneath the chain of the sympathetic nerve trunk, and the upper two beneath the crura of the diaphragm. The right arteries also pass beneath the vena cava inferior, and the two upper on that side beneath the receptaculum chyli. The arteries on both sides then dip beneath the tendinous arch thrown across the sides of the bodies of tlie vertebrae by the psoas, and continue beneath this muscle until they arrive at the interval between the transverse processes of the vertebrae and the medial edge of the quadratus lumborum. While under cover of the psoas they are accompanied by two slender filaments of the sympathetic nerve and by the lumbar veins. A httle anterior to the transverse processes they are crossed by branches of the lumbar plexus, and here usually cross in front of the ascending lumbar vein. They now pass behind the quadratus lumborum, with the exception sometimes of the last, which ma}' pass in front of the muscle. At the lateral edge of the quadratus they run between the transversus and the internal oblique, and then, after perforating the internal oblique between the internal and external oblique. Finally, much diminished in size, they enter the rectus, and give off one or more anterior cutaneous branches, which accompany the last thoracic and the ilio-hypogastric nerves to the skin. They anastomose with the lower intercostals, ilio-lumbar, deep ckcumflex iliac, and inf. epigastric arteries. The branches of the lumbar arteries are ; — (a) Vertebral branches which supply the bodies of the vertebrae and their connecting ligaments. (6) Muscular branches to the psoas, quadratus lumborum, and obUque muscles of the abdomen. (c) The dorsal branch [r. dorsahs]. This is of large size, and passes backward in company with the dorsal nerve between the transverse processes above and below, the intertransversalis medially and the quadratus lumborum laterally, to the muscles of the back. On reaching the interval between the longissimus dorsi and multifidus spinae, it divides into a lateral and a medial branch. The former ends in the multifidus, the latter and larger supphes the sacro- spinalis, and gives branches which accompany the termination of the dorsal nerves to the skin. Just before the artery passes between the transverse processes it gives off a spinal branch fr. spinalis], which accompanies the lumbar nerve through the intervertebral foramen into the vertebral canal (see p. 590). (d) Renal branches of small size pass forward in front of the quadratus lumborum to the capsule of the kidney. They anastomose with the renal artery. A communication is thus established between the renal arteries and the arteries supplying the lumbar region. B. The Visceral Branches of the Abdominal Aorta THE CCELIAC ARTERY The coeliac artery [a. coeliaca] — or coeliac axis, as it is commonly called, because it breaks up simultaneously into three branches which radiate from it like the spokes of a wheel from the axle — is a short thick trunk given off from the front of the aorta between the medial crura of the diaphragm a little below the aortic opening. It passes horizontally forward above the upper margin of the pancreas for about half an inch, and then breaks up into three branches for the supply of the stomach, duodenum, spleen, pancreas, liver, and gall- bladder (fig. 481). Relations. — In front is the lesser omentum; behind, the aorta; above, the right lobe of the liver; below, the pancreas; to the right, the right coeliac (semilunar) ganghon and caudate lobe of the liver; to the left, the left cceliac (semilunar) ganglion and the cardiac end of the stomach. It is closely surrounded by the dense coeliac (solar) ple.xus of sympathetic nerves. Branches of the coeliac artery. — The ccehac artery divides into the left gastric, the hepatic, and the splenic arteries. 1. The Left Gastric Artery The left gastric [a. gastrica sinistra] (fig. 481), the smallest of the three branches into which the coeliac artery divides, courses at first upward and to the 594 THE BLOOD-VASCULAR SYSTEl left toward the cardiac end of the stomach, where it turns sharply round, and then, following the lesser curvature of the stomach, descends from left to right toward the pylorus. It anastomoses with the right gastric branch of the hepatic artery, which has proceeded from the opposite direction, the two branches thus forming a continuous arterial arch corresponding to the lesser curvature of the stomach. The artery at first lies behind the posterior layer of the omental bursa of peritoneum (fig. 480), but on reaching the cardiac end of the stomach it passes, between the layers of peritoneum reflected from the diaphragm onto the oesophagus, into the lesser omentum in which it then runs to its terminal anastomosis with the pyloric. It is surrounded by a plexus of sympathetic nerves. It supplies both surfaces of the stomach around the lesser curvature and gives off email CBSophageal branches [rami oesophagei] which anastomose with the oesophageal branches from the thoracic aorta. Fig. 481. — -The Cceliac Artery and its Branches. Abdominal aorta Right medial crus of diaphragm Cystic artery Right inferior phrenic artery Hepatic duct Cystic duct Splenic artery Common bile duct Right gastric v artery "^ Gastro-duod- enal artery Superior pan- creatico - du- odenal artery Head of ^ pancreas Inferior pan- creatico - du- Left crus of diaphragm (Esophageal branch Coeliac artery Left gastnc artery Vasa brevia odenal artery _^ Right gastro- epiploic artery 2. The Hepatic Artery Left gastro-epiploic artery The hepatic artery [a. hepatica], the largest branch of the coeliac artery in the foetus, but intermediate in the adult between the left gastric and the splenic, comes off on the right side of the coeliac artery, and, winding upward and to the right to the porta (portal fissure) of the liver, there breaks up into two chief branches for the supply of the right and left lobes of that organ. It at first courses forward and to the right along the upper border of the head of the pancreas, behind the posterior layer of the peritoneal omental bursa, to the upper margin of the duodenum, where it passes forward beneath the layer of peritoneum forming the floor of the epiploic foramen (of Winslow). It thus runs between the two layers of the lesser omentum, and ascends along with the hepatic duct which lies to its right, and with the portal vein which lies behind it (figs. 480, 481). The branches of the hepatic artery are: — (1) The right gastric; (2) thegastro- duodenal; (3) the hepatic proper. (1) The right gastric artery [a. gastrica dextra] comes off from the hepatic just as the latter vessel enters the lesser omentum, and, descending between the two layers of that fold of peritoneum to the pylorus, there turns to the left, and, ascending from right to left, anastomoses along the lesser curvature of the stomach, as already mentioned, with the left gastric artery, which descends from the opposite direction. (2) The gastro-duodenal artery [a. gastroduodenalis] arises from the hepatic THE SPLENIC ARTERY 595 a little beyond the pyloric. It descends behind the superior portion of the duodenum to the lower border of the pylorus, where it divides into the right gastro -epiploic and the superior pancreatico-duodenal. It varies from 1.2 to 2.5 cm. (I to 1 in.) in length. (a) The right gastro-epiploic artery [a. gastroepiploica dextra] passes from right to left along the greater curvature of the stomach between the laj;ers of the great omentum, and anastomoses with the left gastro-epiploic branch of the splenic. From this anastomotic arch are given oS: — (i) Ascending or gastric branches, which supply the anterior and posterior surfaces of the stomach, and anastomose with the descending gastric branches of the arteries along the lesser curvature, (ii) Epiploic [rami epiploici] or omental branches — long slender vessels which descend between the two anterior layers of the great omentum, and then, looping upward, anastomose with similar slender branches given off from the middle and left colic, and passing down in Uke manner between the two posterior layers of the great omentum. (6) The superior pancreatico-duodenal [a. pancreaticoduodenaUs superior] — the smaller division of the gastro-duodenal — arises from that vessel as it passes behind the first portion of the duodenum, and courses downward behind the peritoneum, in the anterior groove between the second portion of the duodenum and the pancreas, to anastomose with the inferior pan- creatico-duodenal, a branch of the superior mesenteric. Both the inferior and superior pan- creatico-duodenal give off duodenal [rami duodenales] and pancreatic branches [rami pancreatici] to supply these organs. (3) The hepatic artery proper [a. hepatica propria] is the continuation of the hepatic after the gastro-duodenal has arisen. It ascends between the layers of the lesser omentum, preserving the relations of the main artery to the portal vein and common bile (and hepatic) duct, and divides, near the porta hepatis, into right and left branches. (a) The right branch [r. dexter], given off at the porta (portal fissure) of the liver, runs to the right either behind the hepatic and cystic ducts, or between these strucures. At the right end of the porta it divides into or more branches, which again subdivided as they enter the hver sub- stance for the supply of the right lobe. As it crosses the cystic duct it gives off the cystic artery. The cystic artery [a. cystica] courses forward and downward through the angle formed by the union of the hepatic and cystic ducts, and just before it reaches the gall-bladder divides into a superficial and deep branch. The former breaks up into a number of small vessels, which ramify over the free surface of the gall-bladder beneath the peritoneal covering, and furnish branches to the muscular and mucous coats. The deep branch ramifies between the gall- bladder and the liver^ubstance, supplying each, and anastomosing with the superficial branch. (b) The left branch [r. sinister], the smaller division of the hepatic artery, runs medialward toward the left end of the porta hepatis, and, after giving off a distinct branch to the caudate (Spigelian) lobe, enters the left lobe of the liver. 3. The Splenic Artery The splenic artery [a. lienalis] — the largest branch of the cceliac artery — arises from the left side of the termination of that vessel below the left gastric, and passes along the upper border of the pancreas in a tortuous manner to the spleen. It at first lies behind the ascending layer of the transverse meso-colon, but on nearing the spleen enters the lieno-renal ligament, and there breaks up into numerous branches, which enter the hilus and supply the organ. In this course it crosses in front of the left medial crus of the diaphragm and the upper end of the left kidney and is placed above the splenic vein. The branches of the splenic artery are: — (1) The pancreatic; (2) the left gastro-epiploic; (3) the vasa brevia; and (4) the terminal. (1) The pancreatic branches (rami pancreatici) come off from the splenic at varying intervals as that vessel courses along the upper margin of the pancreas. They enter and supply the organ. One larger branch usually arises from the splenic about the junction of its middle with its left third. Entering the pancreas obUquely, it runs from left to right, commonly above, and a httle behtad, the pancreatic duct, whidh it supplies together with the substance of the organ. (2) The left gastro-epiploic [a. gastroepiploica sinistra] arises from the splenic near the greater curvature and below the fundus of the stomach, and, passing between the anterior layers of the great omentum, descends along the greater curvature of the stomach from left to right, and anastomoses with the right gastro-epiploic. Like that vessel, it gives off ascend- ing or gastric branches to the anterior and posterior surfaces of the stomach respectively, and long slender descending epiploic or omental branches to the great omentum which anastomose with like branches from the right and left colic arteries. (3) The vasa brevia [aa. gastrics breves] come off from the splenic just before it divides into its terminal branches, oftentimes from some of these terminal branches themselves. Passing from between the folds of the Ueno-renal ligament into those of the gastro-henal, they thus reach the fundus of the stomach, where, ramifying over both its anterior and posterior surfaces, they anastomose with the left gastric and left gastro-epiploic arteries. 596 THE BLOOD-VASCULAR SYSTEM (4) The splenic or terminal branches, five to eight or more in number, are given off from the splenic as it lies in the lieno-renal ligament, and, entering the spleen at the hilum, are distributed in the way mentioned in the description of that organ. THE SUPERIOR MESENTERIC ARTERY The superior mesenteric artery [a. mesenterica superior] is given off from the front of the aorta a little below the cojliac, which it nearly equals in size; some- times it forms a common trunk with the coehac. Lying at first behind the pan- creas and splenic vein, it soon passes forward between the lower border of that gland and the upper border of the inferior portion of the duodenum, and, crossing in front of the duodenum, enters the mesentery, in which it runs from left to' right, in the form of a curve with its convexity to the left, to the caecum, where it anastomoses with its ileo-colic branch. Its vein Hes to its right side above, having Fig. 482. — The Supekior Mesbntekic Artery and Vein. (The colon is turned up, and the small intestines are drawn over to the left side.) Middle colic artery Inferior pancre atico-duodenal ^ artery Right colic artery \ Ileo-colic artery Left colic artery Superior mes- enteric artery previously crossed obhquely in front of the artery from left to right. It is sur- rounded by the mesenteric plexus of nerves. The accessory portion of the head of the pancreas dips in behind the vessel. The branches of the superior mesenteric are, in their primitive order: — (1) the inferior pancreatico-duodenal; (2) the intestinal arteries; (3) the ileo- colic; (4) the right colic; and (5) the middle colic. (1) The inferior pancreatico-duodenal [a. pancreatico duodenaUs inferior] arises either from the superior mesenteric as that vessel emerges from the contiguous margins of the pancreas and inferior part of the duodenum or from its first intestinal branch. Crossing behind the superior mesenteric vein, it courses upward and to the right between the head of the pancreas and the duodenum, and beneath the ascending layer of the transverse meso-colon, to anas- tomose with the superior pancreatico-duodenal. (2) The intestinal arteries [aa. intestinales] arise from the convex side of the superior mesenteric, and, varying from twelve to sixteen in number, radiate in the mesentery, where THE SUPERIOR MESENTERIC ARTERY 597 Fig. 483. — The Blood-vessels of the Ileo-c^cal Region. (From Kelly.) (Arteries red, veins blue.) The peritoneal covering is removed so as to show the vessels more clearly. Above and to the right are seen the cut ends of the ileo-cohc artery and vein. This artery gives off a branch to the ascending colon and a posterior and anterior ctecal artery, the latter descending through the ileo-colic fold. A short anastomosis connects the ileo- cohc with the mesenteric. The artery of the vermiform process (appendix) is seen to arise from the posterior cfecal artery, 2 cm. above the ileum. It passes behind the ileum in the free border of the mesappendix and gives off five branches (long appendices have 8-12, short appendices, 2-3), which traverse the mesappendix at fairly regular intervals in the direction of the hilus of the appendix, where they divide into anterior and posterior branches. The branches in the me.sappendix are sometimes seen to anastomose, forming loops of varying size. The terminal branch curves around the tip. The CEeco-appendicular junction is supplied by a separate branch arising likewise from the posterior ileo-caecal trunk. This branch may or may not anastomose with the proximal appendicular twig and while in some cases it supplies only the caecum, in others, as in the present case, it sends a few dehcate branches into the appendix. At the place where this caeco-appendicular artery crosses the ileo-caecal fold it is seen to give off a dehcate recurrent twig to this structure. Throughout their entire course the arteries are accompanied by veins. 598 THE BLOOD-VASCULAR SYSTEM each divides into two branches, which inosculate with similar branches given oS from the branch above and below. From the primary loops thus formed, secondary loops are derived in Hke manner, and from these tertiary, and at times quaternary, or even quinary loops. From the ultimate loops terminal jejunal and iliac branches [aa. jejunales et iliea;] pass on to the muscu- lar coat of the gut. These terminal vessels bifurcate, the two branches encircling the intestine, and thus forming with those above and below a series of vascular rings surrounding the small intestine throughout its whole length. The first intestial artery anastomoses with the pancre- atico-duodenal arteries, and the last (the continuation of the main artery) with the Ueo-coUc. These branches of the superior mesenteric in their course to the intestine also supply the mesentery and the mesenteric glands. (3) The ileo-colic [a. ileocolica] descends behind the peritoneum toward the caecum, where it divides into a cohc branch which tracks upward beneath the peritoneum to anastomose with the descending branch of the right cohc; and into an ihac branch which passes between the layers of the mesentery and anastomoses with the termination of the superior mesenteric artery. Near the site of division the ileo-colic gives off anterior and posterior csecal branches. From the latter of these arises a caeco-appendicular artery, to the caecum and root of the vermi- form process, and a main appendicular artery [a. appendicularis] (fig. 483). (4) The right colic [a. colica dextra] — sometimes given off as a common trunk either with the middle colic or with the ileo-colic — passes to the right behind the peritoneum to the back of the ascending colon, where it divides into an ascending branch, which anastomoses with the descending branch of the middle cohc, and a descending branch which anastomoses with the ascending or colic branch of the ileo-cohc. (5) The middle colic [a. colica media], arising from the concavity of the superior mesenteric a little below the pancreas, enters the transverse meso-colon, and divides into two branches — one of which passes to the left and anastomoses with the ascending branch of the left colic; the other, winding downward and to the right, anastomoses with the ascending branch of the right colic. THE RENAL ARTERIES The renal arteries [aa. renales] come off one on each side of the abdominal aorta, a little below the superior mesenteric and first lumbar arteries, on a level with the first lumbar vertebra. They pass laterally across the crura of the diaphragm to the kidneys, the right being on a slightly lower plane and somewhat longer than the left, and passing behind the inferior vena cava. In front of each is the corresponding renal vein, and behind, at the hilus of the kidney, is the com- mencement of the ureter. Each artery as it enters the hilus usually divides into three main stems, one of which passes toward the upper part of the pelvis, a second to its middle portion, and a third to its lower. Each of these primary stems then divides so that there result from seven to nine secondary branches, the majority of which pass anterior to the pelvis, while the remainder are posterior to it (fig. 484). No anastomoses take place between the branches of the anterior and posterior secondary stems and hence a longitudinal incision into the kidney along its curved border, half way between the anterior and posterior calices, will cut only terminal arteries. The branches of the renal arteries are : — (1) The inferior suprarenal [a. suprarenahs inferior] which ascends to the suprarenal body. (2) The capsular or peri-renal branches to the capsule of the kidney and peri-renal fat. (3) The ureteral branch to the upper end of the ureter. THE MIDDLE SUPRARENAL ARTERIES The middle suprarenal artery [a. suprarenahs media] comes off, one on each side from the aorta, just above the first lumbar artery, and passes laterally to the suprarenal body, across the medial crura of the diaphragm a little above the renal arteries. In the foetus they equal the renals in size. In the adult they are much smaller. They anastomose with the superior and inferior suprarenal arteries from the inferior phrenic and renal arteries respectively. For the distribution of the suprarenal vessels within the suprarenal bodies, see Section XII. THE INTERNAL SPERIVIATIC ARTERIES The internal spermatic arteries [a. spermatica interna], (fig. 479), right and left, come off from the front of the abdominal aorta. They diverge from each other as they descend over the aorta and psoas muscle to the abdominal inguinal (internal abdominal) ring, where they are joined by the ductus deferens, and, pass- THE INTERNAL SPERMATIC ARTERIES 599 ing with it through the inguinal canal and out of the subcutaneous inguinal (ex- ternal abdominal) ring, run downward into the scrotum in a tortuous course to the testes. They terminate in branches to the epididymis and body of those organs. Within the abdomen they lie beneath the peritoneum, and cross in their descent over the ureters and distal ends of the external iliac arteries; the right being super- FiG. 484. — A. The Renal Artery and the Distribution of its Branches in Relation TO THE Pelvis. B. Transverse Section through the Middle op the Same Kidney. (After Brodel, Johns Hopkins Hospital Bulletin.) o, renal artery; a' and a", its anteiior and pubtenor branches, 6, branches to pyramids; c, line of division between anterior and po&tenoi pyi imids The arrow and dotted Una indicate the line of separation between tin fi lunn iK ot the anterior and posterior branches. ficial to the vena cava, and behind the termination of the ileum; and the left beneath the sigmoid colon. In the inguinal canal and in the scrotum the sper- matic veins lie in front of the artery, and the ductus deferens lies behind it. In the foetus these vessels pass in a transversely lateral direction to the testis, which in early foetal life lies in the loin in front of the kidney; but as the testes 600 THE BLOOD-VASCULAR SYSTEM Fig. 485. — The Vascular Trunks of iiii: Li>wi:k Ahimi.mf.x. (From l\f'lly, by Brodel.) THE INTERNAL SPERMATIC ARTERIES 601 descend to the scrotum, the vessels become elongated, and are drawn with the testis into the scrotum. The branches of the internal spermatic artery are: — (1) Ureteral; (2) cre- masteric; (3) epididymal; and (4) testicular. (1) The ureteral are small branches given off to the ureter as the spermatic artery crosses it. They anastomose with the other ureteral branches derived from the renal, common ihac, and vesical arteries. (2) The cremasteric are small branches given off to the cremaster muscle; they anastomose with the cremasteric branch of the inf. epigastric. Fig. 486. — The Ovakian Vessels. (After Clark.) 1 (3) The epididynal are distributed to the epididymic, and anastomose with the deferential artery. (4) The testicular arteries [aa. testiculares] are the terminal branches of the spermatic; they perforate the tunica albuginea posteriorly, and are distributed to the body of the organ in the way mentioned in the section on the Testis. The e.xternal spermatic artery is a branch of the inferior epigastric artery (p. 614). 602 THE BLOOD-VASCULAR SYSTEM THE OVARIAN ARTERIES The ovarian arteries [aa. ovaricse], are the homologues of the internal sper- matic arteries in the male, and correspond in their relations in the upper part of their course. They diverge somewhat less, however, and, on reaching the level of the common iliac artery, turn medialward over that vessel and descend tor- tuously into the pelvis between the folds of the broad ligament to the ovaries. In the broad hgament the ovarian artery lies below the Fallopian tube, and on reaching the ovary turns backward and supplies that organ. In fig. 486 is shown how the artery enters the hilus of the ovary and breaks up into_branches which determine the lobules of the organ. The branches of the ovarian arteries are: — (1) Ureteral; (2) tubal; (3) uterine; and (4) ligamentous. (1) The ureteral is distributed, as in the male, to the ureter. F(2) The tubal suppKes the isthmus and ampulla of the tuba uterina (Fallopian tube) and its fimbriated extremity. (3) The uterine runs beneath the tuba uterina (Fallopian tube) to the uterus, supplying the upper part of the fundus, and anastomosing with the uterine arteries from the hypogastric. (4) The ligamentous is distributed to the round ligament, passing with that structure through the inguinal canal, and anastomosing with the superficial external pudendal artery. Like the spermatic, the ovarian arteries in the foetus come off at right angles to the aorta, and pass transversely lateralward to the ovaries, which are formed, as are the testes, in the right and left loin in front of the kidneys. They elongate as the ovaries descend into the pelvis. During pregnancy these arteries undergo great enlargement. THE INFERIOR MESENTERIC ARTERY The inferior mesenteric artery [a. mesenterica inferior], smaller than the superior, arises from the front of the abdominal aorta about 3.7 cm. (1| in.) Fig. 487. — The Inferiob Missenteeic Artery and Vein. (The colon is turned up, and the small intestines me drawn to the right side.) Middle colic artery Inferior pancreatico- duodenal artery Superior mesenteric artery Right colic artery Abdominal aorta Vena cava inferior Right common iliac artery Middle sacral artery and vein Left colic artery teric artery Left colic artery Inferior mesen- teric artery Sigmoid artery Superior haemor- rhoidal artery above the bifurcation of that vessel. It runs obliquely downward and to the left, behind the peritoneum, across the lower part of the abdominal aorta a,nd then over the left psoas muscle and left common iliac artery. It descends into the THE COMMON ILIAC ARTERIES 603 pelvis between the layers of the sigmoid meso-colon, and terminates on the rectum in the superior hsemorrhoidal artery. It supplies the lower half of the large in- testine. Its vein lies at first close to the left side, but soon passes upward on the psoas, away from the artery, to end in the splenic vein (fig. 487). The branches of the inferior mesenteric are: — (1) The left colic; (2) the sigmoid; and (3) the superior haemorrhoidal. (1) The left colic artery [a. colica sinistra] runs transversely to the left, beneath the peri- toneum, and divides into two branches, one of which, entering the transverse meso-colon, as- cends upward and to the right, to anastomose with the middle colic. The other descends, and, entering the sigmoid meso-coion anastomoses with tlie ascending branch of the sigmoid artery. The distribution of this artery, and of the next, to the colon is similar to that of the cofie branches of the superior mesenteric, and does not require a separate description. (See pp. 597, 598.) (2) The sigmoid artery [a. sigmoidea] runs downward and to the left over the psoas mus- cle and, entering the sigmoid meso-colon, divides into two branches; the upper anastomosing with the left cohc, the lower with the superior hemorrhoidal. (3) The superior haemorrhoidal artery [a. hasmorrhoidaUs superior] is the continued trunk of the inferior mesenteric. It descends into the pelvis, behind the rectum, between the layers of the sigmoid meso-colon. On reaching the wall of the bowel it bifurcates, one branch proceeding on either side of the gut, to within 10 or 12 cm. (4 or 5 in.) of the anus. Here each again divides, and the branches, piercing the muscular coat, descend between that coat and the mucous mem- brane, forming with each other, and with the middle haemorrhoidal arteries — derived from the hypogastric (internal ihac) — a series of small vessels, running longitudinally to the rectum, and parallel to each other as far as the level of the internal sphincter, where, by their anastomosis, they form a series of loops around the lower part of the rectum. C. The Terminal Branches of the Abdominal Aorta THE MIDDLE SACRAL ARTERY The middle sacral artery [a. sacralis media], is, anatomically, the continuation of the aorta. The coccygeal glomerulus [glomus coccygeum], in which it ter- minates, is believed to contain the rudiments of the caudal aorta. The artery extends from the bifurcation of the aorta to the tip of the coccyx. As it passes downward into the pelvis, it runs behind the left common iliac vein, the hypo- gastric plexus of the sympathetic nerve, and the peritoneum. It lies successively upon the intervertebral disc between the fourth and fifth lumbar vertebrse, the fifth lumbar vertebra, the intervertebral disc between that vertebra and the sacrum, and lower down upon the anterior surface of the sacrum and coccyx. Branches. — The branches of the middle sacral artery are : — (1) The lowest lumbar artery [a. lumbahs ima], which, when present, usually comes off from the middle sacral artery. Each vessel of this pair runs laterally beneath the common ihac artery and vein; and, after giving off a dorsal branch, ramifies over the lateral part of the sacrum, and ends in the iliacus muscle by anastomosing with the circumflex Oiac artery. The dorsal branch passes to the back between the last lumbar vertebra and the sacrum and ramifies in the gluteus maxiraus, anastomosing with the lumbar arteries above, and the superior gluteal artery below. (2) Lateral sacral branches, are usually four in number. They are serially homologous with the intercostal and lumbar arteries given off by the aorta. They run laterally, and anastomose with the lateral sacral branches of the hypogastric (internal iliac) artery. They give off small spinal branches, which pass through the sacral foramina, and supply the sacral canal and back of the sacrum. (3) Rectal or haemorrhoidal branches pass forward beneath the peritoneum or in the sig- moid meso-colon to the rectum, which they help to supply, and anastomose with the other haemorrhoidal or rectal arteries. THE COMMON ILIAC ARTERIES The common iliac arteries [aa. iliacse communes] arise opposite the left side of the middle of the body of the fourth lumbar vertebra, at the bifurcation of the abdominal aorta, and, diverging from each other in the male at about an angle of 60°, and in the female at an angle of 68°, terminate opposite the lumbo-sacral articulation by bifurcating into the external iliac, which is continued along the brim of the pelvis to the lower hmb, and into the hypogastric (internal iliac), which passes through the superior aperture of the pelvis and descends into that cavity (fig. 488). The relations differ slightly on the two sides, and maj^ be considered separately. 604 ■THE BLOOD-VASCULAR SYSTEM Fig. 488. — The Relations of the Common Anatomy," Rebman, Internal jugular vein Thyreoidea ima vein Subclavian vein Right innominate vein Thymic veins //j/^ Superior vena cava Iliac Arteries. (Alter Toldt, "Atlas of Human London and New York.) Thyreoid gland ., Left innominate vein Internal mammary artery and Suprarenal gland ^__ /"/ Superior teric artery Inferior vena cava Spermati Internal spermatic artery Common iliai artery and vein ^ Anterior sacral, / ■" plexus '"' 1^ Deep circumflex iliac artery and , vein I Inferior epigas- / N^' trie artery and / \ vein ' External sper- matic artery Femoral artery Femoral vein' \ I External puden- '" dal veins '' Anterior scrotal veins Common tunica vaginali THE HYPOGASTRIC ARTERY 605 The Right Common Iliac Artery The right common iliac measures about 5 cm. (2 in.) in length, and is rather longer than the left, in consequence of the aorta bifurcating a little to the left of the median line. Relations. — In front it is covered by the peritoneum, and is crossed by the right ureter a little before its bifurcation, by the ovarian artery in the female, by the termination of the ileum, by .the terminal branches of the superior mesenteric artery, and by branches of the sympathetic nerve descending to the hypogastric plexus. Behind, it hes on the right common iliac vein, the end of the left common ihac vein, and the commencement of the inferior vena cava, which separate it from the fourth and fifth lumbar vertebrae and their intervening disc, the psoas muscle, and the sympathetic nerve; whilst still deeper in the groove between the fifth vertebra and the psoas are the lumbo-sacral trunk, the obturator nerve, and the ilio-lumbar artery. To the right side are the beginning of the inferior vena cava, the end of the right common iliac vein, and the psoas muscle, which, however, is separated from the artery by the vena cava inferior at its upper part. To the left side are the right common iliac vein, the termination of the left common Uiac vein, and the hypogastric plexus. The Left Common Iliac Artery The left common iliac artery, 4 cm. (14 in.) in length, is a little shorter and thicker than the right. Relations. — In front it is covered by the peritoneum, which separates it from the intestines, and is crossed by the ureter, the ovarian artery in the female, branches of the sympathetic nerve descending to the hypogastric plexus, the termination of the inferior mesenteric artery, the sigmoid colon, and the sigmoid mesocolon. Behind are the lower border of the body of the fourth lumbar vertebra, the disc between the fourth and fifth lumbar vertebra, the body of the fifth lumbar vertebra, and the disc between it and the sacrum. Crossing deeply behind the artery between the fifth lumbar vertebra and the psoas, is the obturator nerve, the lumbo-sacral trunk, and the ilio-lumbar artery. To the left side is the psoas muscle. To the right side are the left common ihac vein, the hypogastric plexus, and the middle sacral artery. Collateral Circulation The collateral circulation after obstruction or ligature of the common ihac artery is carried on chiefly (fig. 497) by the anastomosis of the middle sacral with the lateral sacral; the internal mammary with the epigastric; the lumbar arteries of the aorta with the iho-lumbar and deep circumflex iliac; the pubic branch of the epigastric with the pubic branch of the obturator; the posterior branches of the sacral arteries with the superior gluteal (gluteal) ; the superior hem- orrhoidal from the inferior mesenteric, with the hfemorrhoidal branches of the hypogastric (in- ternal iliac) and pudic; the ovarian arteries from the aorta with the uterine branches of the hy- pogastric (internal iliac) ; and by the anastomosis across the middle line of the pubic branch of the obturator with the like vessel of the opposite side; the lateral sacral with the opposite lateral sacral; and the vesical, hemorrhoidal, uterine, and vaginal branches of the hypogastric with the corresponding branches of the opposite hypogastric (internal iliac). Branches of the Common Iliac Artery The branches of the common iliac artery are: — (1) The hypogastric (internal iliac); and (2) external iliac. There are a few small, unimportant branches distributed to the peritoneum and subperi- toneal fat. They anastomose with vessels given off from the lumbar, inferior phrenic, and renal arteries, forming a subperitoneal arterial anastomosis. The ureter receives small insignificant twigs as it crosses the artery. They anastomose with the ureteral arteries given off from the internal spermatic above, and with those derived from the vesical arteries below. THE HYPOGASTRIC ARTERY The hypogastric or internal iliac artery [a. hypogastrica], arises at the bifur- cation of the common iliac opposite the lumbo-sacral articulation. It descends into the pelvis for about 3 cm. (1| in.) and then divides, opposite the upper margin of the great sciatic foramen, into an anterior and a posterior division. The anterior divisio?i commonly gives off the obturator, inferior gluteal, umbilical, 606 THE BLOOD-VASCULAR SYSTEM inferior vesical, deferential, middle hsemorrhoidal, uterine fin the female), and internal pudendal arteries. From the posterior division the ilio-lumbar, lateral sacral, and superior gluteal arteries arise. These vessels are classified, for description, as parietal and visceral. In the adult the hypogastric is smaller than the external ihac; in the foetus it is much larger and through it the foetal blood is returned to the placenta. The adult hypogastric and common ihac arteries of either side represent the proximal portion of each of the embryonic umbilical arteries. The remainder of the umbUical artery within the body is represented by the umbiMcal branch of the hypogastric which runs to the navel. At birth, when the circulation in the um- bihcal cord ceases, the lumen of the umbihcal branch of the hypogastric becomes obhterated except a small channel which remains pervious as the superior vesical of tlie adult. Relations. — Behind, the hypogastric artery rests on the termination of the external iliac vein, the hypogastric vein, the medial margin of the psoas muscle, the lumbo-sacral trunk, the obturator nerve, and the sacrum. In front, it is covered by the peritoneum, and is crossed by the ureter. Fig. 489. — The Htpogastbic Artery. (After Henle.) ExternI iliac artery Hypogastric artery Deep circumflex, iliac artery Ilio-lumbar artery Lateral sacral artery Inferior epigastric, artery Ascending branch ^Internal pudic artery Internal ves- ical artery Hsemorrhoidal artery Coccygeus muscle Bladder Internal obturator muscle The branches of the hypogastric artery may be divided into parietal and visceral sets. The parietal branches are: — -(1) The ilio-lumbar; (2) the lateral sacral; (3) the obturator; and (4) the gluteal arteries. The visceral branches are: — (1) The umbilical; (2) the inferior vesical; (3) the middle haemorrhoidal; (4) the uterine; and (5) the internal pudendal. Parietal Branches of the Hypogastric Artery 1. THE ILIO-LUMBAR ARTERY The ilio-lumbar artery [a. iliolumbalis] — a short vessel coming off from the posterior part of the hypogastric artery — -runs upward and laterally beneath the , common iliac artery, first between the lumbo-sacral trunk and obturator nerve, THE LATERAL SACRAL ARTERIES 607 and then between the psoas muscles and the vertebral column. On reaching the superior aperture of the pelvis it divides into two branches, an iliac and a lumbar (fig- 489). The iliac branch [ramus iliaous] passes laterally beneath the psoas and the femoral (anterior crural) nerve and, perforating the iUacus, ramifies in the iliac fossa between that muscle and the bone. It supphes a nutrient artery to the bone, and then breaks up into several branches which radiate from the parent trunk, upward toward the sacro-iUac synchondrosis, laterally toward the crest of the Uium, downward toward the anterior superior spine, and medially toward the pelvic cavity. The first anastomoses witli the last lumbar; the second with the external circum- flex and gluteal; the third with the deep circumflex iUac from the external ihac; the fourth with the Uiac branch of the obturator. The lumbar branch [ramus lumbalis] ascends beneath the psoas, and, supplying that muscle and the quadratus lumborum, anastomoses with the last lum- bar artery. It sends a spinal branch (ramus spinalis) into the vertebral canal through the inter- vertebral foramen between the last lumbar vertebra and the sacrum; this branch anastomoses with the other spinal arteries. The Qio-lumbar artery is serially homologous with the lumbar arteries. Hence the similarity in its course and distribution. 2. THE LATERAL SACRAL ARTERIES The lateral sacral artery [a. sacralis lateralis], commonly arises as two vessels from the posterior division of the hypogastric. The superior artery, when two Fig. 490. — The Gluteal Artehies. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) ^ Glutaeus medius muscle Inferior branch - Superior brancli- Superior gluteal artery - Piriformis muscle- Inferior gluteal artery — Internal pudendal artery, A. comitans nervi ischiadici Obturator fascia Inferior h£e rhoidal artery / Sacro-tuberous ,' ligament ~^ Perineal artery Hedial circumflex femoral artery (deep branch) ■ Glutseus minimus muscle ^ Obturator internus muscle /\ Biceps femoris muscle • (long head) Attachment of the ilio- psoas muscle to the trochanter minor Adductor minimus muscle First perforating artery Adductor magnus muscle Second perforating artery are present, runs downward and medially to the first anterior sacral foramen, through which it passes; and, after supplying the spinal membranes and anas- tomosing with the other spinal arteries, passes through the first posterior sacral 08 THE BLOOD-VASCULAR SYSTEM foramen, and is distributed to the skin over the back of the sacrum, there anas- tomosing with branches of the superior and inferior gluteal arteries. The inferior lateral sacral descends on the side of the sacrum, lateral to the sacral chain of the sympathetic, and medial to the anterior sacral foramina, crossing in its course the slips of origin of the piriformis muscle and the first anterior sacral nerve. On reaching the coccyx it anastomoses in front of that bone with the middle sacral artery, and with the inferior lateral sacral of the opposite side (fig. 489). In this course it gives off: — Spinal branches [rami spinales], which enter the second, third and fourth anterior sacral foramina, and, after supplying the spinal membranes and anastomos- ing with each other, leave the spinal canal by the corresponding posterior sacral foramina, and are distributed to the muscle and skin over the back of the sacrum; and rectal branches which run forward to the rectum. At times the lateral sacral arteries are exceedingly small, the spinal branches then coming chiefly from the middle sacral. The anastomosing branches between the lateral sacral and middle sacral are usually regarded as sacral arteries diminished in size, and serially homologous with the lumbar and intercostal arteries. 3. THE OBTURATOR ARTERY • The obturator artery [a. obturatoria], usually arises from the anterior division of the hypogastric. It runs forward and downward a Httle below the brim of the pelvis, having the obturator nerve above and the obturator vein below. It here lies between the peritoneum and the endo-pelvic fascia, but later it passes through the obturator canal, the aperture in the upper part of the obturator membrane. In this course it is crossed by the ductus deferens. On emerging from the obturator canal the artery divides into two branches, anterior and posterior, which wind around the margin of the obturator foramen beneath the obturator externus muscle. The branches of the obturator artery are: — (1) The iliac or nutrient branch; (2) a vesical branch; (3) the pubic branch; (4) the anterior, and (5) posterior terminal branches. (1) The iliac or nutrient branch ascends to the iliac fossa, passing between the iUacus muscle and the bone. It suppUes a nutrient vessel to the ihum, and anastomoses with the medial branch of the iliac division of the ilio-lumbar artery. (2) The vesical branch or branches are smaU vessels which run in the lateral false ligament of the bladder to that organ, where they anastomose with the other vesical arteries. (3) The pubic branch [ramus pubicus] comes off from the obturator as that vessel is leaving the pelvis by the obturator canal. It runs upward and medially behind the pubis, anastomosing with its feUow of the opposite side of the body, and with the pubic branch of the inferior epi- gastric artery. One of the anastomosing channels between the pubic branch of the obturator and pubic branch of the inferior epigastric arteries is sometimes of large size, a fact of surgical interest in that the enlarged vessel may then run around the medial side of the femoral ring (pp. 615 and 636). (4) The anterior branch [ramus anterior] runs around the medial margin of the obturator foramen, and anastomoses with the posterior branch and with the medial circumflex artery. It supplies branches to the obturator and adductor muscles. (5) The posterior branch [ramus posterior] skirts the lateral margin of the obturator fora- men, lying between the obturator externus and the obturator membrane. At the lower margin of the foramen it divides into two branches. One branch continues its course around the lower margin of the foramen, and anastomoses with the anterior branch of the obturator and with the medial circumflex. The other branch turns laterally below the acetabulum, and ends in the muscles arising from the tuberosity of the ischium. It anastomoses with the inferior gluteal artery. This branch gives off a small twig, the acetabular artery [a. acetabuli], which passes under the transverse Ugament into the hip-joint, where it suppUes the synovial membrane, the hgamentum teres, and the fat in the fossa at the bottom of the acetabulum. 4. THE GLUTEAL ARTERIES There are two gluteal arteries, the superior and inferior. The superior gluteal artery [a. glutea superior], the largest branch of the posterior division of the hypogastric comes off as a short, thick trunk from the lateral and back part of that vessel, of which indeed it may be regarded as the continuation. Passing backward between the first sacral nerve and the lumbo-sacral trunk through an osseo-tendinous arch formed by the margin of the bone and the upper edge of the endo-pelvic fascia, it leaves the pelvis through the great sciatic foramen above the piriformis muscle in company with its vein and the superior gluteal nerve. At its exit posteriorly from the great sciatic foramen it lies under cover of the gluteus THE INFERIOR VESICAL ARTERY 609 maximus and beneath the superior gluteal vein, and in front of the superior gluteal nerve. It here breaks up into two chief branches, a superficial and a deep. Its emergence from the pelvis is indicated on the surface by a point situated at the junction of the posterior with the middle third of a line drawn from the anterior superior to the posterior superior spine of the ilium. The branches of the superior gluteal artery are : — (o) Within the pelvis, branches are distributed to the obturator internus, the piriformis, the levator ani, the coccygeus, and the pelvic bones. (h) External to the pelvis, the artery divides into a superior and an inferior branch. (i) The superior branch [ramus superior] breaks up into a number of large vessels for the supply of the upper portion of the gluteus maximus, some of them piercing the muscle and supply- ing the skin over it, and anastomosing with the posterior branches of the lateral sacral arteries; whilst one of larger size, emerging from the muscle near the ihao crest, anastomoses with the deep circumflex iliac artery. The lower branches to the muscle anastomose with branches of the inferior gluteal (sciatic). (ii) The inferior branch [ramus inferior] subdivides into two branches — One skirts along the lane of origin of the gluteus minimus (fig. 490), between the gluteus medius and the bone, and, emerging in front from beneath these muscles under cover of the tensor fascite lata:, anas- tomoses with the ascending branch of the lateral circumflex and the deep circumflex iliac arter- ies. The other passes forward between the gluteus medius and minimus, accompanied by the branch to the tensor fasciae lata; of the inferior division of the superior gluteal nerve, toward the greater trochanter, where it anastomoses with the ascending branch of the lateral circumflex. It supphes branches to the contiguous muscles and to the hip-joint. The inferior branch before its division gives off the external nutrient artery of the ilium. The inferior gluteal [a. glutea inferior], is one of the terminal branches of the anterior division of the hypogastric artery. It leaves the pelvis below the piriformis muscle, and immediately breaks up into a number of diverging branches. The largest enter the gluteus maximus muscle, where they anastomose with the superior gluteal branches. Others pass to the hip-joint and the deep muscles around it; a third group passes downward to the hamstring muscles and anas- tomoses with the medial and lateral circumflex and first perforating; a fourth slender branch, the sciatic artery [a. comitans n. ischiadici], accompanies the sciatic nerve (fig. 490). Visceral Branches of the Hypogastric Artery 1. THE UMBILICAL ARTERY The umbilical artery in the fcetus is the continuation of the hypogastric. Passing forward along the side of the pelvis, it runs beneath the lateral reflexion of peritoneum from the bladder, where, after giving off one or more vesical branches, it ceases to be pervious and passes on to the side and upper part of the bladder. Thence it ascends in the lateral umbilical fold, as a fibrous cord [ligamentum umbilicale laterale], to the umbilicus, where it is joined by its fellow of the opposite side. As it lies lateral to the bladder it is crossed by the ductus deferens. The branches of the umbilical artery are: — (1) Superior vesical arteries, the lowest of which is sometimes called (2) the middle vesical artery (fig. 489). The superior vesical arteries [aa. vesicales superiores] ramify over the upper surface of the bladder, anastomosing with the artery of the opposite side and with the middle and inferior vesical below. They give off the following branches: — (a) The urachal branches which pass upward along the urachus. (h) The ureteric branches pass to the lower end of the ureter, and anastomose with the other ureteric arteries, (c) The middle vesical may come off from one of the superior vesicals or from the umbilical. It is distributed to the sides and base of the bladder, and anastomoses with the other vesical arteries. 2. THE INFERIOR VESICAL ARTERY The inferior vesical artery [a. vesicahs inferior] arises from the anterior division of the hypogastric, frequently in common with the middle haemorrhoidal, and passes downward and medially to the fundus of the bladder, where it breaks up into branches which ramify over the lower part of the viscus. It gives off branches to the prostate, which supply that organ and anastomose with the arteries of the opposite side by means of descending arteries which pass through 610 THE BLOOD-VASCULAR SYSTEM the prostatic plexus of veins, but outside the capsule of the prostate, and with the inferior hsemorrhoidal branches of the internal pudic. At times one of these prostatic branches is of large size, and supplies certain of the parts normally supplied by the int. pudendal. It is then known as the accessory pudendal and most commonly terminates as the dorsal artery of the penis. The inferior vesical usually gives off the deferential, or artery of the ductus deferens [a. deferentialis]. This vessel, which may come off from the superior vesical, divides, on the ductus deferens, into an ascending and a descending branch. The ascending branch follows the ductus through the inguinal canal to the testis, where it anastomoses with the internal spermatic artery. The_ descending branch passes downward to the dilated portion of the ductus and vesiculse seminales. 3. THE MIDDLE HEMORRHOIDAL ARTERY The middle hsemorrhoidal artery [a. hsemorrhoidals media], variable in origin, perhaps most commonly arises from the anterior division of the hypogastric along with the inferior vesical. It runs medially to the side of the middle portion of the rectum, dividing into branches which anastomose above with the superior hsemorrhoidal derived from the inferior mesenteric, and below with the inferior hsemorrhoidal derived from branches of the internal pudendal. Its corre- sponding vein terminates in the inferior mesenteric vein. In the female it also sends branches to the vagina. 4. THE UTERINE ARTERY The uterine artery [a. uterina], arises from the anterior division of the hypo- gastric close to or in conj unction with the middle hsemorrhoidal or inferior vesical. It runs downward and medially through the pelvic connective tissue, crossing the ureter about 12 mm. (| in.) from the cervix uteri. It then turns upward and ascends in the parametrium between the layers of the broad ligament at the side of the uterus in a coiled and tortuous manner, and, after giving off a number of tortuous branches which ramify horizontally over the front and back of the uterus, supplying its substance, anastomoses with the uterine branch of the ovarian artery. In addition to the branches to the uterus the branches of the uterine artery are: — (1) Cervical. — This branch comes off from the uterine as the latter artery crosses the ureter to turn upward on to the uterus. It is directed medially, and divides into three or four branches which pass on to the cervix at right angles to it; one branch anastomosing with its fellow of the opposite side in front and behind the neck, forming the so-caUed coronary artery of the cervix. (2) Tubal [ramus tubarius]. — Tliis courses along the lower surface of the tuba uterina (FaUopian tube) as far as its fimbriated extremity, and may also send a brancli to the ligamentum teres. (3) Ovarian [ramus ovarii]. — This runs along the attached border of the ovary, sending branches to that structure, and terminates by anastomosing widely with the ovarian artery. Usually the vaginal artery also arises from tlie uterine. (4) The vaginal artery [a. vaginaUs] corresponds to the inferior vesical artery of the male, and may arise directly from the hypogastric artery, close to the origin of the uterine, or from the superior vesical. It passes medially, behind the ureter, to the upper part of the vagina, and sends numerous branches to that structure and also some iio the posterior part of the fundus of the bladder. The branches to the vagina tend to anastomose with one another and with the cervical branch of the uterine, to form a more or less perfect vertical stem in the median Une of the vagina, both back and front. This stem is sometimes termed the azygos artery of the vagina. Branches also pass to the vagina from the middle hsemorrhoidal artery. 5. THE INTERNAL PUDENDAL ARTERY The internal pudendal (pudic) artery [a. pudenda interna] (figs. 492, 493, 494) is one of the terminal branches of the anterior division of the hypogastric artery (the inferior gluteal being the other) . It arises opposite the piriformis muscle and accompanies the inferior gluteal downward to the lower border of the great sciatic foramen. It leaves the pelvis between the piriformis and coccygeus and winds over the ischial spine to enter the ischio-rectal fossa through the small sciatic foramen. Running forward in the ischio-rectal fossa medial to the lower part of the obturator internus it ends by dividing into the perineal artery and the artery of the penis (or clitoris). INTERNAL PUDENDAL ARTERY 611 Relations. — Within the -pelvis, the artery is anterior to the piriformis muscle and the sacral plexus of nerves, and lateral to the inferior gluteal artery. It passes between the piriformis and coccygeus, with the gluteal artery and pudendal nerve medial to it, and the nerve to the ob- turator internus lateral. The sciatic and posterior femoral cutaneous (lesser sciatic) nerves are still more lateral. On, the ischial spine the artery retains its relations to the pudendal nerve (which often divides in this situation into its two terminal branches) and the nerve to the ob- turator internus. It is accompanied by venae comitantes and covered by the gluteus maximus muscle. In the ischio-rectal fossa the artery is placed on the lateral wall about 3.5 cm. (IJ in.) above the tuberosity of the ischium. It is accompanied in a canal in the obtm-ator fascia (Alcock's canal) by the dorsal nerve of the penis and the perineal nerve, which are respectively above and below the artery. The branches of the internal pudendal artery are: — (1) Small branches to the gluteal region; (2) the inferior hsemorrhoidal arteries; and the terminal branches (3) perineal; and (4) artery to the penis or clitoris. 612 THE BLOOD-VASCULAR SYSTEM Fig. 492. — The Internal Pudendal Artery. (From Kelly, by Brodel.) Dorsal artery of clitoris Inferior hasmorrhoidal artery Internal pudic artery Sacro-spinous ligament Fig. 493. — The Perineal and Hemorrhoidal Branches of the Internal Pudendal Arteries. (From Kelly, by Brodel.) INTERNAL PUDENDAL ARTERY 613 (1) The branches of the gluteal region are: (a) twigs to the gluteus maximus; (6) branches accompanying the nerve to the obturator internus; (c) a sacral branch which pierces the sacro- tuberous ligament, and anastomoses with the inferior gluteal artery. (2) The inferior hemorrhoidal artery (a. haemorrhoidalis inferior] (figs, 493, 494) arises at the posterior part of the ischio-rectal fossa and, perforating the obturator fascia, at once breaks up into several branches. These, rumiing medially toward the anus, traverse the ischio-rectal fat and supply the fascia, skin and the levator ani and external sphincter muscles. The in- ferior hEemorrhoidal branches anastomose with those from the middle and superior hemor- rhoidal, and from the gluteal and perineal arteries. (3) The perineal artery [a. perinei] (figs. 493, 494), one of the terminal arieries of the in- ternal pudendal, arises at the anterior part of the ischio-rectal fossa. It pierces the base of the urogenital diaphragm (triangular hgament) anterior or posterior to the superficial transverse perineal muscle, and enters the space deep to CoUes's fascia. Here it runs forward between the ischio- and bulbo-cavernosus muscles to the scrotum or labium majus and divides into numer- ous terminal branches. Immediately after piercing the diaphragm, the perineal artery gives off a constant transverse perineal branch which runs toward the median Une along the super- ficial transverse perineal muscle. The terminal branches of the perineal are the posterior scrotal or labial arteries [aa. scrotales, or labiales posteriores] which ramify on the scrotum or labia majora (according to sex) and anastomose with external pudendal arteries. (4) The artery of the penis, or clitoris [a. penis or clitoridis] (figs. 493, 494) pierces the free border of the urogenital diaphragm and runs forward between the layers of the diaphragm with the dorsal nerve of the penis along the inferior ramus of the pubis. It traverses the fibres of the deep transverse perineal muscle and of the sphincter of the membranous urethra and Fig. 494. — The Arteries op the Male PERiN.ffi;uM. On the right side CoUes's fascia has been turned back to show the perineal artery. On the left side the perineal vessels have been cut away with the inferior layer of the urogenital dia- phragm to show the artery of the penis. Posterior sacral artery Bulbo-cavernosus CoUes's fascia, turned back Dorsal artery of penis Deep artery of penis Ischio-cavernosus Transverse perineal vessels Cut edge of urogenital diaphragm Perineal nerve giving oB transverse branch Internal pudendal artery Inferior hemorrhoidal artery Artery of bulb Bulbo-urethral gland Artery of the penis Sacro-tuberous ligament — Levator ani External sphincter ani Gluteus maximus ends by dividing into deep and dorsal arteries of the penis, or clitoris, according to sex. The branches of the artery of the penis (or clitoris) are: (a) The artery to the bulb; (b) the uretliral artery; and (c) the terminal, deep artery of the penis or clitoris. (a) The artery of the bulb [a. bullii urethras or vestibuli vaginas] takes a medial direction through the fibres of the m. transversus perinei profundus. It then pierces the inferior fascia of the urogenital diaphragm to reach the bulb, the erectile tissue of which it supplies, in either sex. This vessel also suppUes branches to the bulbo-urethral gland (Cowperi) or the gland of the vestibule (Bartholini). The situation of the artery to the bulb should be remembered in performing the operation of lateral lithotomy, particularly as it may arise far back. When the artery arises, as it occa- sionally does, from the accessory pudendal it pierces the urogenital diaphragm further forward and is out of danger in the ordinary low operation. (6) The urethral artery [a. urethralisj.is a small branch which passes into the corpus spongi- osum and anastomoses with branches from the artery of the bulb. 614 THE BLOOD-VASCULAR SYSTEM (c) The deep artery of the penis or clitoris [a. profunda penis or clitoridis], larger in the male sex, pierces the inferior layer of the urogenital diaphragm near the inferior ramus of the pubis. It enters the crus of the penis (fig. 494) or clitoris, and is distributed in the corpus cavernosum urethrae. (d) The dorsal artery of the penis or clitoris [a. dorsalis penis or clitoridis] (figs. 492, 494), perforates the inferior fascia of the urogenital diaphragm near its apex. The dorsal nerve is lateral to the artery and both join the dorsal vein (which hes between the arteries of either side) on the dorsum of the penis or clitoris. The artei-y is much larger in the male than the female; in either sex it supphes the glans, corona, and prepuce and anastomoses with the external pudendal artery. THE EXTERNAL ILIAC ARTERY The external iliac artery [a. iliaca externa] — the larger in the adult of the two vessels into which the common iliac divides opposite the lumbo-sacral articulation — extends along the superior aperture of the pelvis, lying upon the medial border of the psoas muscle, to the lower margin of the inguinal ligament, where, midway between the anterior superior spine of the ilium and the symphysis pubis, it passes into the thigh, and takes the name of the femoral. It measures 8.5 to 10 cm. (3| to 4 in.) in length. The course of the vessel is indicated by a line drawn from 2.5 cm. (1 in.) below and a little to the left of the umbilicus to a spot midway between the symphysis pubis and the anterior superior spine of the ilium. If this line is divided into thirds, the lower two-thirds indicate the situation of the external iliac, the upper third the common iliac. The external iliac vein, the continuation upward of the femoral vein from the thigh, lies to the medial side of the artery, but on a slightly lower plane, and, just before its termination, gets a little behind the artery on the right side. Relations. — In front, the artery together with the vein is covered by the parietal per- itoneum descending from the abdomen into the pelvis, and by a layer of condensed subperitoneal tissue (Abernethy's fascia). It is crossed by the termination of the ileum on the right side, and by the sigmoid colon on the left. The external spermatic (genital) branch of the genito- femoral (genito-crural) nerve runs obhquely over its lower third, and just before its termination it is crossed transversely by the deep circumflex iliac vein. The internal spermatic or ovarian vessels lie for a short distance on the lower part of the artery, and the ductus deferens in the male curves over it to descend to the pelvis. It is sometimes crossed at its origin by the ureter. The external iliac lymphatic nodes lie along the course of the artery. The commencement of its inferior epigastric branch is also in front. Behind. — At first the artery lies partly upon its own vein; lower down upon the medial border of the psoas; and just before it passes through the lacuna vasorum, beneath Poupart's ligament, upon the tendon of the psoas. The continuation of the ihac into the endo-pelvic fascia is also below it. To its medial side is the external iliac vein, the peritoneum, and the ductus deferens in the male, or the ovarian vessels in the female. To its lateral side is the psoas muscle and the iliac fascia. The collateral circulation is carried on (fig. 497) when the external ihac is tied, by the anas- tomosis of the iUo-lumbar and lumbar arteries with the circumflex ihac; the internal mammary with the inferior epigastric; the obturator with the medial circumflex; the inferior gluteal with the medial circumflex and superior perforating; the gluteal with the lateral circumflex; the arteria comitans nervi ischiadici from the inferior gluteal, with the perforating branches of the profunda; the external pudenal with the internal pudendal; the pubic branch of the obturator with the pubic branch of the epigastric. The branches of the external iliac artery are: — (1) The inferior epigastric; (2) the deep circumflex iliac; and (3) several small and insignificant twigs to the neighbouring psoas muscles and lymphatic gland. (1) The Inferior Epigastric Artery The inferior or deep epigastric artery [a. epigastrica inferior] (fig. 495) usually comes off from the external iliac just above the inguinal (Poupart's) ligament. Immediately after its origin, the ductus deferens in the male, and the round ligament in the female, loop around it on their way to the pelvis. It here lies medial to the abdominal inguinal (internal abdominal) ring, behind the inguinal canal, and a little above and lateral tc the femoral ring. Thence it ascends with a slightly medial direction passing above and to the lateral side of the subcu- taneous inguinal (external abdominal) ring, lying between the fascia transversalis and the peritoneum. Having pierced the fascia transversalis at this point, it THE INFERIOR EPIGASTRIC ARTERY 615 passes in front of the linea semicircularis (Douglas' fold) and turns upward be- tween the rectus and its sheath. Higher, it enters the substance of the muscle, and anastomoses with the superior epigastric, descending in the rectus from the internal mammary. The situation of the artery between the two inguinal rings should be borne in mind in the operation for strangulated inguinal hernia, and its near proximity to the upper and lateral side of the femoral ring should not be forgotten in the operation for femoral hernia. The arter3r is accompanied by two veins which end in a single trunk before opening into the external iliac vein. The branches of the inferior epigastric are small and include: — (a) The external spermatic [a. spermatica externa], which runs with the ductus through the inguinal canal, supplies the cremaster muscle, and anastomoses with the internal spermatic, external pudendal, and perineal arteries. In the female a corresponding artery [a. hg. teretis uteri] accompanies the round liga- FiG. 495. — The Inferior (Deep) Epigastric Artery. (From Kelly, by Brodel). l^ectus A " Ovarian vessels External iliac artery ^External iliac ment of the uterus through the inguinal canal and anastomoses in a similar manner. (6) The pubic [ramus pubicus], which passes below, or sometimes above, the femoral ring to the back of the pubis, where it anastomoses with the pubic branch of the obturator. This branch, though usually small, is occasionally considerably enlarged, when its exact course becomes of great interest to the surgeon. Thus it may descend immediatelj' medial to the vein, and there- fore lateral to the femoral ring, or it may course medially in front of the femoral ring and turn downward either behind the os pubis or immediately behind the free edge of the lacunar (Gim- bernat's) ligament, in which situation it would be exposed to injury in the operation for the re- lief of a strangulated femoral hernia. In such cases the obturator may lose its connection with the hypogastric and actually arise from the inferior epigastric. Very rarely the inferior epi- gastric loses its connection with the external iUac and arises from the obturator. This abnormal origin of the obturator is said to occur once in every three subjects and a half; but the abnormal 616 THE BLOOD-VASCULAR SYSTEM artery only courses around the medial side of the ring — in which situation it is liable to injury in the operation for femoral hernia — in exceptional cases. According to Langton (Holden's 'Anatomy'), the chances are about seventy to one against this occurring. But even when it takes the abnormal course, it lies 3 mm. or so from the margin of the ring, and will probably escape injury in the division of the stricture if several short notches are made in place of a single and longer incision. (2) The Deep Circumflex Iliac Artery The deep circumflex iliac artery [a. circumflexa ilium profunda], arises from the lateral side of the external iliac artery either opposite the epigastric or a little below the origin of that vessel. It courses laterally just above the lower margin of Poupart's ligament, lying between the fascia transversahs and the peritoneum, or at times in a fibrous canal formed by the union of the fascia transversahs with the iliac fascia. Near the anterior superior spine of the ihum, it perforates the transversus, and then courses between that muscle and the internal oblique, along and a little above the crest of the ilium. It finally gives off an ascending branch, which anastomoses with the lumbar and lower intercostal arteries,, and runs backward to anastomose with the ilio-lumbar artery. It is accompanied by two veins. These unite into one trunk, which then crosses the external iliac artery to join the external iliac vein. The branches of the deep circumflex iliac artery are as follows: — (a) Muscular branches which supply the psoas, iliacus, sartorius, tensor fasciae latse, and the oblique and transverse muscles of the abdomen. One of these branches, larger than the rest, usually arises about 2.5 cm. (1 in.) behind the anterior superior spine of the ilium and ascends perpendicularly be- tween the transversus muscle and the internal oblique. It has received no name but is impor- tant to the surgeon, as it indicates the intermuscular plane between the two muscles. (6) Cutaneous branches, which supply the skin over the course of the vessel, and anastomose with the superficial circumflex ihac, the superior gluteal, and the ascending branch of the lateral circumflex. THE FEMORAL ARTERY The femoral artery (fig. 496) is the continuation of the external iliac, and extends from the lower border of Poupart's ligament, down the anterior and medial aspect of the thigh, to the tendinous opening in the adductor magnus, through which it passes into the popliteal space, and is then known as the pop- liteal. The femoral artery is at first quite superficial, being merely covered by the skin, and superficial and deep fascia; but, after thus passing abo.ut 13 cm. (5 in.) downward through the space known as the femoral trigone (Scarpa's triangle), it sinks at the apex of that triangle beneath the sartorius muscle, and thence to its termination continues beneath the sartorius, coursing deeply between the vastus medialis and adductor muscles in the space known as the adductor (Hunter's) canal. It at first rests upon the brim of the pelvis and head of the thigh bone, from which it is merely separated by the capsule of the hip-joint and the tendon of the psoas. Here it can be readily compressed. Owing to the obliquity of the neck of the femin- and the direct course taken by the artery, it lies lower down on muscles only, at some little distance from the bone. At its termination, in consequence of the shaft of the femur inclining toward the middle line of the body, the artery lies close to the bone, but to the mechal side. The course of the vessel when the thigh is slightly flexed and abducted — the position in which the Hmb is placed when the vessel is hgatured — is indicated by a line drawn from a spot midway between the anterior superior spine of the ilium and the symphysis pubis to the adductor tubercle. When the thigh is in the extended position and parallel to its fellow, the course of the artery will correspond to a hne drawn from the spot above mentioned to the medial border of the patella. About 4-5 cm. (li-2 in.) below the inguinal ligament the femoral artery gives off a large branch called the profunda femoris. The portion of the artery proximal to the origin of the profunda is sometimes called the common femoral, and the continuation of the vessel the superficial femoral. The superficial femoral varies in length according to the distance that the profunda is given off from the common femoral below Poupart's ligament. As a rule, it measures 9 cm. (Ss in.), the common 4 cm. (IJ in.). But the profunda may come off 5 cm. (2 in.) or more below Pou- part's ligament, in which case the superficial femoral will be shorter to this extent; or it may THE FEMORAL ARTERY 617 come off less than 3.7 cm. (IJ in.) below Poupart's Ugament, or even from the external ibac above Poupart's ligament, when the superficial will be longer than normal. The practical point to remember is that it is more usual to meet with a short than with a long common femoral and that if the superficial femoral is tied at the apex of the femoral trigone— i. e., the spot where the sartorius comes into contact with the adductor longus— there is nearly always a sufficient Fig. 496.— The Femoral Artert. (After Toldt, "Atlas of Human Anatomy," Rebman London and New York.) Superficial epigastric artery- Tensor of fascia lata Femoral nerve. Femoral artery. Femoral vein Sartonus. Deep femoral artery- (Ascending , branch Descending, branch Fascia lata First perforating artery- Deep femoral artery Vastus medialis Femoral i Saphenous nerve- t B.i Femoral artery " Rectus femons Articular rate of the knee- External spermatic artery — Medial circumflex artery Superficial branch — Adductor brevis Adductor longus Gracilis Ventral wall of adductor canal Muscular branch Saphenous nerve Sartorius Genu suprema artery - Superior medial articular artery Articular branch Saphenous branch length of that vessel above the ligature to ensm-e a firm internal clot and consequently, as far as this point is concerned, a successful result. The relations of the femoral artery in the femoral trigone.— In front, the femoral artery (fig. 496) is covered by the skin, the superficial fascia, the iUac portion of the fascia lata, and the lumbo-inguinal (crural) branch of the genito-femoral nerve. The superficial cu-cumflex ihao vein, and sometimes the superficial epigastric vem, descend over the artery from the medial to 618 THE BLOOD-VASCULAR SYSTEM the lateral side. Just above the sartorius, the artery is crossed by the most medial of the anterior cutaneous branches of the femoral nerve. The fascia transversahs, which is continued down- ward into the thigh beneath the inguinal ligament, is also in anterior relation, but it soons be- comes indistinguishable from the sheath of the vessel. Behind, the artery rests from above upon the tendon of the psoas muscle, which separates it from the brim of the pelvis and capsule of the hip-joint; the pectineus, and adductor longus. The artery is partially separated from the pectineus by the femoral vein and the profunda vein and artery, and from the adductor longus by the femoral vein which is almost directly behind the artery near the apex of the femoral trigone. The small nerve to the pectineus crosses behind the artery to reach its medial side. A similar prolongation to that derived from the fascia transversaUs in front, descends be- hind the vessel from the iliac fascia; but this, lil^e the anterior prolongation or fascia, soon blends with the sheath of the vessels. To the medial side is the femoral vein. This is separated above from the artery, where the two vessels he in the femoral sheath, by a thin fascial septum. Below, the vein is some- what behind the artery. To the lateral side. — Above, the common stem of the femoral (anterior crural) nerve ia about 1 cm. (J in.) lateral to the artery. When the femoral nerve gives off its branches, the saphenous nerve and the nerve to the vastus mediaUs accompany the artery on the lateral side. The adductor canal is the somewhat triangularly shaped space bounded by the vastus medialis on the lateral side, the adductors longus and magnus posteriorly, and by an aponeurosis thrown across from the adductors to the vastus medially and in front. Below, the canal terminates at the tendinous opening in the adductor magnus; above, its Umit is less well defined, as here the aponeurosis between the muscles becomes less tendinous, and gradually fades away into the perimuscular fascia. The transverse direction of the fibres of the aponeurotic covering at the lower two-thirds of the canal is characteristic, and serves as a raUying-point in tying the artery in this part of its course. Lying superficial to the aponeurosis is the sartorius muscle. The femoral artery, in the adductor (Hunter's) canal, has the following relations :■ — In front, in addition to the skin, superficial and deep fascia, are the sartorius muscle and the aponeurotic fibres of the canal. The saphenous nerve crosses in front of the artery from the lateral to the medial side, lying in the wall of the canal. Behind, the artery is in contact with the adductor longus, and just above the opening in the adductor magnus, usually with the latter muscle. The femoral vein lies behind the artery, but gets a httle lateral to it at the lower part of the canal. It is here very firmly and closely attached to the artery, embracing it as it were on its posterior and lateral aspect. Hence it is very hable to be punctured on ligaturing the artery in this part of its course. Such an accident is best avoided by opening the sheath of the vessels well to the medial side of the front of the artery, and by keeping the point of the aneurysm needle closely applied to the vessel in passing it between the vein and the artery. There are some- times two veins, which then more or less surround the artery. To the lateral side are the vastus mediaUs, the nerve to the vastus medialis, and at the lower part of the canal, the femoral vein. Branches of the Femoral Artery The branches of the femoral artery are: — (1) The superficial epigastric; (2) the superficial circumflex iUac; (3) the external pudendal; (4) the inguinal; (5) the profunda; (6) muscular branches; and (7) the suprema genu (anastomotica magna). (1) the superficial epigastric artery [a. epigastrica superficialis], comes_ off from the femoral about 1.2 cm. (| in.) below the inguinal ligament. At its origin it is beneath the fascia lata, but almost at once passes through this fascia, or else through the fossa ovalis, and courses in an upward and slightly medial direction in front of the external oblique muscle almost as far as the umbilicus. It ends in numerous small twigs, which anastomose with the cutaneous branches from the inferior epigastric and internal mammary. In its course it gives off small branches to the in- guinal glands and to the sldn and superficial f ascifs. Running with it is the superficial epigastric irein, which ends in the great saphenous just before the latter passes through the fossa ovalis (saphenous opening). (2) The superficial circumflex iliac artery [a. circumflexa ilium superficialis], (fig. 496), usually smaller than the superficial epigastric, arises either in common with that vessel, or else as a separate branch from the femoral. It passes laterally over the ihacus, and, soon perforating the fascia lata a Httle to the lateral side of the fossa ovalis, runs more or less parallel to the inguinal ligament about as far as the crest of the ihum, where it ends in branches which anastomose with the deep circumflex iliac artery. In its course it gives off branches to the iliacus and sartorius muscles, to the inguinal glands, and to the fascia and skin. Its companion vein ends in the great saphenous vein just before the latter passes through the fossa ovaUs (saphenous opening). BRANCHES OF THE FEMORAL ARTERY 619 (3) the external pudendal arteries [aa. pudendae externse], arise from the medial side of the femoral. Some of them pass either through the fascia lata, or Fig. 497. — To show the Anastomoses of the Arteries of the Lower Extremity. (After Smith and Walsham.) Inferior epigastric artery Ilio-lumbar artery Deep circumflex iliac artery Superior gluteal artery Common femoral artery Profunda artery Lateral circumflex artery Crucial anastomosis ' Popliteal artery Superior lateral articular Anterior tibial artery Inferior lateral articular - Fibular collateral ligament ^ U^" Tibial recurrent - Peroneal artery - Lateral anterior malleolar artery . Perforating peroneal artery - Posterior peroneal artery - Lateral plantar artery Abdominal aorta Common iliac artery Middle sacral artery Hypogastric artery External iliac artery Obturator artery Inferior gluteal artery Internal pudendal artery Medial circumflex artery Superficial femoral artery Perforating branches of profunda Genu suprema Terminal branch of profunda anasto- mosing with popliteal Superior medial Eirticular Tibial collateral ligament Inferior medial articular Posterior tibial artery Anterior msdial malleolar artery lateral tarsal artery Dorsalis pedis artery Arcuate artery through the fascia covering the fossa ovalis (saphenous opening) and cross the spermatic cord in the malCj or round ligament in the female, to reach and supply the integument above the pubes. One branch descends along the penis lateral 620 THE BLOOD-VASCULAR SYSTEM to the dorsal artery, with which, and with the corresponding artery of the opposite side, it anastomoses at the corona. In the female, this branch terminates in the preputium clitoridis, anastomosing with the dorsal artery of the clitoris. Other branches run medially beneath the deep fascia, across the pectineus and adductor longus muscles, and, perforating the fascia close to the ramus of the pubis, supply the skin of the scrotum or the labium majus, in the female [aa. scrotales or labiales anteriores] anastomosing with the posterior scrotal or labial branches of the perineal artery. The external pudendal supplies small twigs to the pectineus and adductor muscles. Its companion veins terminate as a single trunk in the great saphenous. (4) The inguinal branches [rami inguinales], a series of five or six small branches arise a short distance below the inguinal Hgament. They supply the subinguinal lymph-nodes, and the skin and muscles in this region. (5) The profunda artery [a. profunda femoris] (figs. 496, 497), is the chief nutrient vessel of the thigh. It is usually given off from the back and lateral part of the common femoral, about 4 cm. (1| in.) below the inguinal fPoupart's) ligament. At first it is a little lateral to the femoral, but as it runs downward and backward it gets behind that artery and closer to the bone. On reaching the upper border of the adductor longus muscle, it leaves the femoral, and, passing beneath the muscle, pierces the adductor magnus. Finally, much reduced in size, it ends in the hamstraing muscles, anastomosing with the third perforating and muscular and articular branches of the popliteal. Jlelations. — Behind, the artery Hes successively upon the iKacus, the pectineus, the adduc- tor brevis, and adductor magnus muscles. In front, at first it is superficial, being merely covered by the skin, superficial and deep fascise, and branches of the femoral (anterior crural) nerve; but as it sinks behind the femoral artery, it has in front of it both the femoral and the profunda veins and lower down the adductor longus muscle. Laterally is the femur at the angle of union of the adductors longus and brevis. Medially is the pectineus at the upper part of its course. Branches of the profunda. — The profunda gives off the following branches: — (a) The lateral circumflex; (h) the medial circumflex; and (c) the three per- forating. The termination of the artery is sometimes called the fourth perforating branch. (a) The lateral- circumflex [a circumflexa femoris laterahs] a short trunk, but the largest in diameter of the branches of the artery, arises from the lateral side of the profunda as it hes on the iUacus muscle, about 2 cm. (f in.) below the origin of that vessel from the femoral. It passes in a transversely lateral direction over the iliacus, under the sartorius and rectus, and between the branches of the femoral (anterior crural) nerve. In this course it gives off branches to the rectus and vastus intermedins (crureus), and then divides into two chief sets of branches — ascending and descending. The ascending branch [ramus ascendeus] either breaks up at once into numerous branches or it may arise as several vessels some of which are apt to come from the profunda itself or even from the femoral. These run upward under the sartorius and tensor facise latse or laterally under the rectus femoris. The highest branches reach the gluteus medius and minimus and anastomose with the gluteal and deep circumflex ihac arteries; one branch runs beneath the rectus femoris to the hip-joint, and the others cross the vastus intermedins and pierce the vastus lateralis to anastomose with the first perforating and the medial circumflex. The descending branches [rami descendentes] run directly downward along with the nerve to the vastus laterahs muscle. They lie beneath the rectus muscle and on the vastus intermedins (crureus) or vastus laterahs, some of them being j ust under cover of the anterior edge of the latter muscle. They are distributed to the vastus lateralis, vastus intermedins, and rectus, one branch usually running along the anterior border of the vastus laterahs as far as the knee-joint, where it anastomoses with the superior lateral articular branch of the pophteal (fig. 499); another, enter- ing the vastus intermedius, anastomoses with the termination of the profunda and with the genu suprema (anastomotica magna). (6) The medial circumflex artery [a. circumflexa femoris medialis] comes off from the back and medial aspect of the profunda artery on about the same level as the lateral circumflex; sometimes as a common trunk with that vessel. As it winds around the medial side of the femur to reach the region of the trochanters, it lies successively, flrst, between the psoas and pectineus, then between the obturator externus and adductor brevis; finaUy, between the adductor mag- nus and quadratus femoris, where it anastomoses with the lateral circumflex, with the inferior gluteal (sciatic), and with the superior perforating, forming the so-called crucial anastomosis. While still in the femoral trgione it gives off a superficial branch [r. superfioialis] which runs in a transversely medial direction to supply the pectineus adductor longus and brevis, and the gracilis. The remainder of the artery is designated as the deep branch [r. profundus]. An acetabular branch (r. acetabuli] courses upward beneath the tendon of the psoas, and enters the hip-joint beneath the transverse ligament, and, together with the articular branch of the obtura- tor, supplies the fatty tissue in the acetabulum, and sends branches to the synovial membrane. The medial circumflex veins join the profunda vein. (c) The perforating arteries of the profunda are so called because they perforate, in a more or less regular manner from above downward, certain of the adductor muscles. They form a series THE POPLITEAL ARTERY 621 of loops by anastomosing with one another (fig. 497), and with the superior gluteal, medial cir- cumflex, and inferior gluteal arteries above, and with the muscular and articular branches of the popliteal below. They are distributed chiefly to the hamstring muscles, but send twigs along the lateral intermuscular septum to supply the integuments at the back and lateral parts of the thigh. Other branches perforate the lateral intermuscular septum and the short head of the biceps, and, entering the vastus intermedins (crureus) and vastus laterahs, anastomose with the descending' branch of the lateral circumflex. All the perforating arteries, moreover, contribute to reinforce the artery of the sciatic nerve, a branch of the inferior gluteal (sciatic) artery. They are each accompanied by two veins which terminate in the profunda. The first perforating artery [a. perforans prima] is given off from the profunda as that vessel sinks beneath the adductor longus. It either pierces the adductor brevis, or else runs between the pectineus and adductor brevis, and then passes through a small aponeurotic opening in the adductor magnus close to the medial lip of the hnea aspera. In this course it supphes branches to the adductors, and, after perforating the adductor magnus, is distributed to the lower part of the gluteus maximus and the hamstring muscles, one branch commonly running upward beneath the gluteus maximus to anastomose with the lateral circumflex, medial circumflex, and inferior gluteal (sciatic) arteries, forming the crucial anastomosis at the junction of the neck of the femur with the great trochanter (flg. 497). A second branch descends to anastomose with the ascend- ing branch of the second perforating. The second perforating artery [a. perforans secunda] which is given off from the profunda as it lies behind the adductor longus, pierces the adductor brevis, and then passes through a second aponeurotic opening in the adductor magnus a httle below that for the first perforating artery, and also close to the linea aspera. It supplies the hamstring muscles, sends a branch upward to anastomose with the descending branch of the first perforating, and another downward to anas- tomose in hke manner with the ascending branch of the third perforating. The third perforating artery [a. perforans tertia] also arises from the profunda as it hes under the adductor longus, usually about the level of the lower border of the adductor brevis. It turns beneath this border, and then, like the first and second perforating, passes through an aponeu- rotic opening in the adductor magnus close to the linea aspera. It also supplies the hamstring muscles, and divides into two branches, which anastomose above with the second perforating, and below with the termination of the profunda. Two nutrient arteries to the femur [aa. nutritiae femoris superior et inferior] arise from the perforating arteries. The superior generally arises from the first perforating, the inferior usually from the third. (6) The muscular branches [rami musculares], of the femoral artery supply the sartorius, the rectus, the vastus medialis, the vastus intermedius (crureus), and the adductor muscles. (7) The genu suprema (or anastomotica magna) arises from the front and medial side of the femoral just before the latter perforates the adductor magnus muscle, and almost immediately divides into branches, (a) saphenous, {h) muscu- lar, and (c) articular. These branches may sometimes come off separately from the femoral. (a) The saphenous branch [a. saphena] pierces the aponeurotic covering of the adductor canal, passes between the sartorius and gracilis muscles along with the saphenous nerve, and, perforating the deep fascia, suppUes the skin of the upper and medial side of the leg and anasto- moses with the inferior medial articular branch of the popUteal and the other vessels forming the plexus or rete at the medial side of the knee. In its course it gives twigs to the lower part of the sartorius and gracihs muscles. (6) The muscular branches [rr. musculares] run downward in front of the adductor magnus tendon, burrowing amongst the fibres of the vastus mediahs as far as the medial condyle. They break up into numerous twigs which supply the lower ends of the vasti muscles and adductor magnus. One branch runs laterally across the lower end of the femur to end in the vastus laterahs. (c) The articular branches [rr. articulares] come off from the saphenous and muscular branches and enter the arterial rete on the medial and lateral sides of the knee. They anas- tamose with the medial and lateral superior articular branches of the popHteal and the ante- rior tibial recurrent and, Uke other vessels of the rete, supply branches to the joint. THE POPLITEAL ARTERY The popliteal artery [a. poplitea] (fig. 498) runs through the pophteal space or ham. It is a continuation of the femoral, and extends from the aponeurotic opening in the adductor magnus at the junction of the middle with the lower third of the thigh to the lower border of the popliteus muscle, where it terminates by dividing into the anterior and posterior tibial arteries. This division is on a level with the lower border of the tuberosity of the tibia. As the artery passes through the opening in the adductor magnus, it is accompanied by the pophteal vein, and at times by the branch of the obturator nerve to the knee-joint. The vein throughout is behind the artery, at first lying a little lateral to it, but as the vessels pass through the popliteal space the vein crosses obliquely over the artery. 622 THE BLOOD-VASCULAR SYSTEM and at the termination of the artery lies a little to its medial side. The tibial (internal popliteal) nerve is superficial to both artery and vein. As it enters the space it is well to the lateral side of the vessels, but as it descends it gradually approaches them, crosses behind them, and at the lower part of the space lies to their medial side. The artery in the whole of its course is deeply placed and covered by a considerable amount of fat and cellular tissue. Relations (fig. 498). — In front, the artery lies successively on the pophteal surface of the femur (from which it is separated by a httle fat and sometimes one or two small glands); on the posterior ligament of the knee; on the hinder edge of the articular surface of the head of the tibia; and on the pophteus muscle. From the latter muscle it is separated by the expansion from the semi-membranosus which covers the muscle, and is attached to the popUteal line on the tibia. Behind, the artery is covered, above by the semi-membranosus; in the centre of the space by the skin, superficial and deep fascia; and below, by the medial head of the gastrocnemius. The Eopliteal vein is behind it in the whole of its course. The tibial (internal popliteal) nerve crosses ehind it obUquely, from the lateral to the medial side, about the centre of the space. As the artery divides into the anterior and posterior tibial, it is crossed by the aponeurotic arch of the soleus which stretches between the tibial and fibular origins of that muscle. To the medial side are the semi-membranosus above, and the medial head of the gastrocne- mius and the tibial (internal pophteal) nerve below. To the lateral side are the biceps and the tibial (internal popliteal) nerve above, and the lateral head of the gastrocnemius and the plantaris below. Branches of the Popliteal Artery The branches of the popliteal include the following: — (1) the sural; (2) the articular; and (3) the terminal. (1) The sural arteries [aa. surales] arise irregularly from the popliteal and supply the muscles of the calf, sending branches upward to the muscles bound- ing the upper part of the popliteal space. From the sural arteries also arise the superficial sural or cutaneous branches which pass downward between the two heads of the gastrocnemius, and, perforating the deep fascia, supply the skin and fascia of the calf. A branch, usually of moderate size, accompanies the small saphenous vein, and is sometimes called the posterior saphenous artery. (2) The articular, five in number, are divided into two superior (medial and lateral), two inferior (medial and lateral), and the middle or azygos. The superior and inferior come off transversely in pairs from either side of the popliteal, the superior above, the inferior below the joint. Winding round the bones to the front of the knee, they form — by anastomosing with each other and with the genu suprema (anastomotica magna) , the termination of the profunda, the descend- ing branch of the lateral circumflex, and the anterior tibial recurrent — a super- ficial and deep arterial rete (fig. 499). The superficial anastomosis or rete lies between the skin and fascia round about the patella (patellar rete), which it supplies, the larger branches entering it from above. The deep anastomosis or articular rete [rete articularis genu] lies on the surface of the bones around the articular surfaces of the femur and tibia, supplying branches to the contiguous bones and to the joints. The middle articular is a single short trunk coming off from the deep surface of the popliteal artery. It at once passes through the posterior ligament into the joint. (o) The superior lateral articular artery [a. genu superior lateralis], the larger of the two superior articular branches, runs in a lateral direction above the lateral head of the gastrocne- mius, and, passing beneath the biceps and through the lateral intermuscular septum and vastus lateralis, enters the substance of the vastus intermedins (erureus), and anastomoses, above with the descending branch of the lateral circumflex, below with the inferior lateral articular, and across the front of the femur with the superior medial articular, the genu suprema (anastomot- ica magna), and termination of the profunda, forming with them, as already described, the deep articular rete. Branches are given off to the patella, to the upper and lateral part of the joint, to the bone, and to the contiguous muscles. (6) The superior medial articular artery [a. genu superior mediaUs] (fig. 499) runs medially just above the medial head of the gastrocnemius, beneath the semi-membranosus, and, after perforating the tendon of the adductor magnus, enters the substance of the vastus medialis. Here it anastomoses with the deep branch of the genu suprema (anastomotica magna) and ter- mination of the profunda above, with the inferior medial articular below, and with the superior lateral articular across the front of the femur. It supphes small branches to the contiguous muscles, to the femur, to the patella, and to the joint. (c) The inferior medial articular artery [a. genu inferior mediaUs], the larger of the two in- ferior articular arteries, passes in an obliquely medial direction across the pophteus, below the medial condyle (tuberosity) of the tibia and beneath the tibial collateral ligament to the front and POPLITEAL ARTERY 623 medial side of the knee-joint. Here it anastomoses (fig. 499), above witli the superior medial articular and the superficial branch of the genu suprema (anastomotica magna), and across the front of the tibia with the inferior lateral articular. It supphes branches to the lower and medial part of the joint. (d) The inferior lateral articular artery [a. genu inferior lateralis] passes laterally above the head of the fibula, along the tendon of the popliteus muscle, beneath the lateral head of the gas- trocnemius, and then under the tendon of the biceps, and between the long and short fibular Fig. 498. — Relations of the Popliteal Artery to Bones and Muscles, Left Side. Superior lateral articular artery - Fibular lateral ligament llj IK Inferior lateral articular artery {i- Popliteus Muscular branch to soleus Soleus Anterior tibial artery Peroneus longus ■ Peroneal artery ■ Flexor hallucis longus Cutaneous branch of peroneal artery Peroneus brevis . Continuation of peroneal artery Superior medial articular artery Popliteal artery Posterior ligament of knee ■ Azygos articular artery — 14 Semi-membranosus Inferior medial articular artery Muscular branch . Tibialis posterior ■ Tibial nerve Flexor digitorum longus Posterior tibial artery Tibialis posterior Communicating brauch Laciniate ligament Internal calcaneal artery collaterallligaments. Then winding to the front of the joint, it anastomoses above with the superior lateral articular, below with the anterior tibial recurrent, and across the front of the tibia with the inferior medial articular. It also supplies branches to the lateral and lower part of the joint. (e) The middle or azygos articular artery [a. genu media] arises from the deep surface of the popliteal artery, and passes, with the articular branch of the obtiu*ator nerve, through the 624 THE BLOOD-VASCULAR SYSTEM popliteal ligament, directly into the knee-joint, where it supplies the crucial ligaments, and the patellar synovial and alar folds. It anastomoses with the intrinsic branches of the other articu- lar arteries. (3) The terminal branches of the popliteal are the posterior and the anterior tibial arteries. Fig. 499. — The Anastomosis about the Left Knee-joint. (Walsham.) (Semi-diagrammatic. ) Deep branch of genu suprema Superficial branch of genusuprema . . Adductor magnus Superior medial articular artery piercing tendon of adductor magnus Tibial collateral ligament Inferior medial articular artery passing under tibial collateral ligament Posterior tibial artery Descending branch of lateral circum,flex artery Superior lateral articular artery passing through external inter- muscular septum Lateral epicondyle Fibular collateral ligament Inferior lateral articular artery passing under fibular collateral ligament Anterior tibial recurrent artery ■~ Anterior tibial artery THE POSTERIOR TIBIAL ARTERY The posterior tibial artery [a. tibialis posterior] (fig. 500) , the larger of the two branches into which the popliteal divides at the lower border of the popliteus muscle, runs downward on the flexor aspect of the leg between the superficial and deep muscles to the back of the medial malleolus. Midway between the tip of the malleolus and the calcaneus, and under cover of the origin of the abductor hallucis as it arises from the laciniate (internal annular) ligament, it divides into the medial and lateral plantar arteries. The artery is first situated midway between the tibia and fibula, and is deeply placed beneath the muscles of the calf. As it passes downward it inclines to the medial side and at the lower third of the leg is superficial, being only covered by the skin and fasciae. At the ankle it lies beneath the laciniate ligament, and at its bifurcation also beneath the abductor hallucis. A line drawn from the centre of the popliteal space to a spot midway between the medial malleolus and point of the heel will indicate its course. In addition to the branches named below it supplies the muscles between which it passes, and the integument of the lower medial region of the leg. Relations. — Anteriorly, from above downward, it lies successively on the tibialis posterior, the flexor digitorum longus, the posterior surface' of the tibia, and the deltoid ligament of the ankle-joint. Posteriorly, it is covered by the skin and fascia, the gastrocnemius and soleus, and the deep or intermuscular fascia of the leg, by which it is tightly bound down to the underlying muscles. It is crossed by the tibial nerve about 4 cm. (If in.) below its origin, after it has given off its POSTERIOR TIBIAL ARTERY 625 peroneal branch; the nerve first lies on the medial, and for the rest of its course on the lateral side of the vessel. It is accompanied by two veins, which send numerous anastomosing branches across it. In the lower third of the leg the artery is superficial, being covered only by the skin and^by the superficial and deep fascia?. Fig. 500. — The Popliteal, the Posterior Tibial, and the Peroneal Arteries. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Adductor magnus - ;nu suprema artery- Vastus medialis -^ z: Superior medial articular artery — - Superior lateral articular artery a Popliteal artery Middle articular artery '^ , Semimembranosus — i Inferior medial articular artery ~ Popliteal artery — - Sural arteries Collateral fibular ligament Inferior lateral articular artery Fibular branch Anterior tibial artery _,-Interosseous membrane .^Tibial nutrient artery Posterior tibial artery - Flexor longus digitorum- Flesor hallucis longus b » Peroneal artery -^ — ■ Fibtilar nutrient artery > Flexor hallucis longus Communicating branches , ~^, I Posterior tibial muscle'- ^«3( Posterior medial malleolar artery- v^^nm^j Flexor longus hallucis- Communicating branches- Tendo Achllli; Medial calcanean branches tt/V^ aPeroneus brevis - Perforating branch ^ Peroneus longus - Posterior lateral malleolar artery — Lateral calcanean branche ■•Calcanean rete At the medial malleolus it lies beneath the laciniate (internal annular) ligament and abduc- tor hallucis upon the deltoid ligament of the ankle-joint. Here it has the tibialis posterior and flexor digitorum longus in front of it, and the tibial nerve and the flexor haUucis longus be- hind and to its lateral side. At times the tibial nerve divides higher than usual, when one branch lies on the medial side of the artery and the other branch on the lateral side. 626 THE BLOOD-VASCULAR SYSTEM The branches of the posterior tibial artery are: — (1) The fibular; (2) the peroneal; (3) the tibial nutrient; (4) the communicating; (5) the posterior medial malleolar; (6) the medial calcanean, and (7) the terminal, medial and lateral plantar. (1) The fibular or superior fibular branch [ramus fibularis], which frequently arises from the beginning of the anterior tibial, runs upward and laterally toward the head of the fibula. It is small and gives twigs to the soleus, peroneus longus, and extensor digitorum longus, and anasto- moses with the inferior lateral articular and the lateral sural arteries. (2) The peroneal artery [a. peronea] is a large vessel which (figs. 498, 500), arises from the posterior tibial about 2.5 cm. (1 in.) below the lower border of the popliteus muscle. At first forming a gentle curve convex laterally, it approaches the fibula, and continues its course downward close to that bone as far as the lower end of the interosseous membrane, where it gives off a large branch, the perforating (anterior peroneal), and then, passing over the back of the inferior tibio-fibular joint, terminates by breaking up into a network, which is distributed over the back of the lateral malleolus and lateral surface of the calcaneus (figs. 500, 504). It is accompanied b}^ two vense comitantes. Besides the named branches it supplies twigs to the flexor hallucis longus, tibialis posterior, tibialis anterior, peronei and soleus; also to the integument on the lateral side of the leg. Relations. — At its upper part it is deeply placed between the tibialis posterior and soleus muscles, and beneath the deep or intermuscular fascia. For the rest of its course to the ankle it Ues beneath, or sometimes in the substance of, the flexor hallucis longus in the angle between the fibula and interosseous membrane. After giving off the perforating branch, it is only cov- ered, as it lies behind the tibio-fibular articulation, by the integuments and deep fascia, and in this part of its course is sometimes called the posterior peroneal. The branches of the peroneal artery are: — (a) The perforating (anterior peroneal) ; (b) the fibular nutrient; (c) the communicating; (d) the lateral malleolar; (e) the lateral calcanean; and (/) the terminal. (o) The perforating (or anterior peroneal) branch [ramus perforans] arises from the front of the peroneal artery at the lower part of the interosseous space, and, passing through the interosseous membrane, runs downward over the front of the inferior tibio-fibular joint, beneath the peroneus tertius, and supplies this muscle and the inferior tibio-fibular joint. It anasto- moses with the tarsal, arcuate (metatarsal) and lateral malleolar branches of the anterior tibial artery, and with the lateral plantar artery on the lateral side of the foot, forming a plexus over the ankle (fig. 503). (b) The fibular nutrient [a. nutritia fibula;] enters the nutrient foramen of the fibula. (cj The communicating branch [ramus communicans] passes medially in front of the tendo Achillis to anastomose with the communicating branch of the posterior tibial. The usual situation of this communication is from 2.5 to 5 cm. (1 to 2 in.) above the ankle-joint. (d) The lateral posterior malleolar artery [a. malleol.aris poster, lateralis] anastomoses on the lateral malleolus with the anterior lateral malleolar of the anterior tibial artery to form the lateral malleolar rete. (e) The lateral calcaneal branches [rami calcanei laterales] come off from the peroneal below the point at which the perforating is given off, and are distributed over the lateral surface of the calcaneus. (/) The terminal branch or posterior peroneal, the continuation of the peroneal artery, anastomoses with the other arteries distributed to the lateral malleolus and heel. (3) The tibial nutrient artery [a. nutritia tibiae], a vessel of large size, leaves the posterior tibial at its upper part, pierces the tibialis posterior, and enters the nutrient foramen in the upper third of the posterior surface of the tibia. In the interior of the bone it divides into two branches: an ascending or smaller, which runs upward toward the head of the bone; and a de- scending or larger, which courses downward toward the lower end. It gives off two or three muscular twigs to the tibialis posterior before it enters the foramen. The nutrient artery of the tibia is the largest nutrient artery of bone in the body, and is accompanied by a nerve given off by the nerve to the popliteus. (4) The communicating branch [ramus communicans] arises from the posterior tibial about 5 cm. (2 in.) above the medial malleolus, and, passing transversely across the tibia beneath the flexor hallucis longus and tendo Achillis, anastomoses with the communicating branch of the peroneal. Frequently an inferior communicating branch between the posterior tibial and peroneal arteries is hkewise present in the loose connective tissue beneath or behind the tendo Achillis. (5) The posterior medial malleolar branch [ramus maUeolaris posterior medialis] divides for distribution over the medial malleolus, anastomosing with the other arteries entering into the medial malleolar rete [rete m.iUeolare mediale] which is formed over the portion of bone. In its course to the malleolus it runs beneath the flexor digitorum longus and tibiaUs posterior muscles. (6) The medial calcanean branches [rami calcanei mediales] are distributed to the soft parts over the medial side of the calcaneus. These branches come off from the posterior tibial just before its bifurcation, and anastomose with the medial malleolar and pei'oneal arteries. (7) The terminal branches are the lateral and medial plantar arteries. ANTERIOR TIBIAL ARTERY 627 THE LATERAL PLANTAR ARTERY The lateral plantar artery [a. plantaris lateralis] (figs. 501, 502) — the larger of the two branches into which the posterior tibial divides beneath the laciniate (internal annular) ligament — passes at first laterally and forward across the sole of the foot to the base of the fifth metatarsal bone, where it bends medially, and still running forward sinks deeply into the foot and terminates at the proximal end of the first interosseous space by anastomosing with the deep plantar (com- municating) branch of the dorsal artery of the foot. In its course to the fifth metatarsal bone the artery runs in a more or less straight line obliquely across the foot ; whilst its deep portion, extending from thefif th metatarsal bone to the proximal Fig. 501. — The Plantar Arteries, Left Foot. (From a dissection in the Museum of St. Bartholomew's Hospital.) Lateral calcanean branch Anastomosing branch of lateral plantar Abductor digiti quinti — Medial calcane Cutaneous branch of medial plantar Plantar aponeurosis, cut Abductor hallucis Anastomotic branch Lateral plantar artery Digital to lateral side of little toe Lumbrical muscle Fourth metatarsal Third metatarsal Second metatarsal Anastomosis about interpha- langeal joint Dorsal branch of plantar digital Anastomosis of plantar digital arteries around matrix of nail and pulp of toe Medial plantar artery Flexor digitorum brevis Superior branch of medial plantar Flexor hallucis brevis First plantar metatarsal artery Plantar digital branch of first meta- tarsal to toe Plantar digital branch of first meta- tarsal to medial side of great toe Plantar digital branch of first meta- tarsal to lateral side of great toe end of the first interosseous space, forms a slight curve with the convexity forward, and is known as the plantar arch. The plantar arch is comparable to the deep volar arch formed by the deep branch of the ulnar anastomosing with the radial through the first interosseous space. This homology is at times more complete in that the deep plantar (communicating) branch of the dorsalis pedis, the homologue of the radial in the upper limb, takes the chief share in forming the arch. The lateral plantar artery is accompanied by two veins. The course of the artery is indicated by a line drawn across the sole of the foot from a point midway between the tip of the medial malleolus and the medial tubercle of the calcaneus to the base of the fifth metatarsal bone, and thence to the lateral side of the base of the first metatarsal. The lateral plantar artery, besides the branches named below gives twigs to supply the muscles between which it passes, and the tarsal joints. It also gives 628 THE BLOOD-VASCULAR SYSTEM branches to the integument of the lateral side of the sole, some of which anasto- mose with arteries on tlie lateral side of the dorsum. Relations. — In the first part of its course from the medial malleolus to the base of the fifth metatarsal bone, the artery is covered successively by the abductor hallucis and the flexor digitorum brevis, by which it is separated from the plantar aponeurosis, and may be slightly overlapped in muscular subjects by the abductor quinti digiti. As it approches the base of the fifth metatarsal bone it Ues, as it turns medially before sinking into the foot, in the interspace between the flexor digitorum brevis and the abductor quinti digiti, and is here covered only by the skin and superficial fascia and the plantar aponeurosis. It hes upon the calcaneus, the quadratus plantse (flexor accessorius), and the flexor digiti quinti brevis. It is accompanied by the lateral plantar nerve, the smaller of the two divisions into which the tibial nerve divides. In this part of its course it gives off small branches to the contiguous muscles and to the heel. Fig. 502. — Plantae Arteries (Deep). (After Henle.) Anterior perforating branch First dorsal interosseous muscle Metatarsal artery Deep plantar b"°'=h\J^>«MMi ]l||, I m\miiii^-\^^^^''^ metatarsal artery Plantar metatarsal artery Perforating branch Branch of the medial plantar artery Abductor hallucis muscl Tendon of the posterior tibial muscle Medial plantar artery Tendons of the flexor digitorum longus Quadratus plant£e Abductor of the fifth digit Lateral plantar artery tibial artery In the second part of its course the artery, which is here known as the plantar arch [arcus plantaris], sinks into the sole, and is covered, in addition to the skin, superficial fascia, plantar aponeurosis, and flexor digitorum brevis by the tendons of the flexor digitorum longus, the lumbricales, branches of the medial plantar nerve, and the adductor hallucis. It lies upon the proximal ends of the second, third, and fourth metatarsal bones and the corresponding interos- seous muscles. The branches of the lateral plantar artery are: — (1) Perforating; and (2) plantar metatarsal (digital). (1) The perforating branches [rr. perforantes], three in numbers, ascend through the proximal end of the second, third, and fourth spaces, between the two heads of the correspond- ingly named dorsal interosseous muscles, and communicate with the proximal ends of the first, second, and third dorsal metatarsal (interosseous) arteries (fig. 502). (2) The plantar metatarsal arteries [aa. metatarsete plantares] are usually four in number, and pass forward in the four intermetatarsal spaces, which are numbered from the medial side. They rest upon the interosseous muscles of their spaces, and are at first under cover of the lum- bricals, but as they approach the clefts of the toes each divides into two branches, the plantar digital arteries [aa. digitales plantares], which supply the contiguous sides of the toes. The plantar digital branch for the medial side of the great toe is usually given off by the first plantar metatarsal; that for the lateral side of the Uttle toe is usually a separate branch from the lateral end of the plantar arch. ANTERIOR TIBIAL ARTERY 629 The plantar metatarsal arteries, immediately before they bifurcate, send to the dorsum of the foot a perforating branch each to the corresponding dorsal metatarsal arteries. They anastomose by many small twigs with the dorsal metatarsal arteries, which also run along the sides of the metatarsal bones, but more toward the dorsal aspect. Immediately above each phalangeal joint the plantar digital vessels communicate by cross branches, forming a rete for the supply of the articular end of the phalanges and the contiguous joints. At the distal end of the toes they also freely anastomose with each other, forming a rete beneath the pulp and around the matrix of the nail. The metatarsal and digital arteries are each accompanied by two small veins. THE MEDIAL PLANTAR ARTERY The medial plantar artery [a. plantaris medialis] (figs. 501, 502) — much the smaller of the two divisions into which the posterior tibial divides, passes forward along the medial side of the sole of the foot usually to the first interosseous space. Here it ends by anastomosing either with the first plantar metatarsal artery derived from the plantar arch, or with the branch given off by the first plantar metatarsal to the medial side of the great toe. Relations. — The artery is at first under cover of the abductor hallucis, but afterward Ues in the interval between that muscle and the flexor digitorum brevis. It is covered by the skin and superficial fascia, but not by the plantar aponeurosis, since it lies between the central and medial portions of that structure. The branches of the medial plantar are: — (1) The deep and (2) the superficial branches. (1) The deep branch [ramus profundus], which at once divides — or it may come off as several branches — to supply the muscles, articulations,and integument of the medial side of the sole. Some of these branches form an anastomosis aroundthe medial margin of the foot, with branches of the dorsahs pedis. (2) The superficial branch [ramus superficialis] breaks up into very small twigs which ac- company the digital branches of the medial plantar nerves, and anastomose with the plantar metatarsal arteries in the first, second, and third spaces. At times a twig from one of these branches joins the lateral plantar artery to form a superficial plantar arch. THE ANTERIOR TIBIAL ARTERY The anterior tibial artery [a. tibialis anterior] fig. 503 — the smaller of the two branches into which the popliteal artery divides at the lower border of the popliteus muscle — at first courses forward between the two heads of origin of the tibialis posterior, and, after passing between the tibia and fibula above the upper part of the interosseous membrane, runs downward on the front and lateral aspect of the leg, between the anterior muscles, as far as the front of the ankle-joint. Below the joint it is known as the dorsalis pedis. The course of the vessel is indicated by a line drawn from the front of the head of the fibula to a point mid- way between the two malleoli. The artery is accompanied by two veins which communicate with each other at frequent intervals across it. It is also accompanied in the lower three-fourths of its course by the deep pei'oneal nerve. The nerve, which winds round the head of the fibula, and pierces the extensor digitorum longus, first comes into contact with the lateral side of the artery about the upper third of the leg; in the middle third it is a little in front of the artery, and in the lower third again lies to its lateral side. In addition to the named branches the anterior tibial artery supplies muscular twigs to the extensors of the toes and the tibiahs anterior. Relations. — The artery at first Ues in the triangle formed by the two heads of the tibiahs posterior and the popliteus muscle; and, as it passes above the interosseous membrane, it has the tibia on one side and the fibula on the other. It is separated from the deep peroneal (ante- rior tibial) nerve at its commencement by the neck of the fibula and the extensor digitorum longus. This arrangement is homologous with that met with in the forearm in the case of the posterior interosseous artery and deep radial (posterior interosseous) nerve. Posteriorly in its course down the leg it lies in its upper two-thirds upon the interosseous membrane, to which it is closely bound by fibrous bands; and in its lower tliird upon the front of the tibia and the ankle-joint. To its medial side along its upper two-thirds is the tibialis anterior muscle; but at the lower third it is crossed by the tendon of the extensor hallucis longus and then for the rest of its course has this tendon overlapping it or to its medial side. On its lateral side it is in contact in its upper third with the extensor digitorum longus muscle; in its middle third with the extensor hallucis longus; but, as this muscle crosses to the medial side of the artery, the vessel usually for a very short part of its course comes again 630 THE BLOOD-VASCULAR SYSTEM into contact with the extensor digitorum longus. At the upper and lower thirds of its course on the front of the leg the artery has the deep peroneal (anterior tibial) nerve to its lateral side. In front the artery is covered by the skin, superficial and deep fascia. In its upper two- thirds it is deeply placed in the cellular interval between the tibiahs anterior on the medial side and the extensor digitorum longus and extensor hallucis longus on its lateral side; and in .its lower third it is crossed in the latero-medial direction by the tendon of the extensor Fig. 503. — The Anterior Tibial Artery, Dorsal Artery op the Foot, and Perforatinq (Anterior) Peroneal Artery, and their Branches, Left Side. Superior medial articular artery Inferior medial articular artery Anterior tibial recurrent artery Anterior tibial artery Tibialis anterior muscle Extensor hallucis longus' Medial malleolar artery Crucial ligament- Dorsalis pedis artery. Most medial tendon of extensor digi torum brevis Deep plantar branch' First dorsal metatarsal artery Superior lateral articular artery — -Inferior lateral articular artery ^Extensor digitorum longus Peroneus tertius ^ Perforating peroneal artery Lateral malleolar artery Peroneus brevis muscle — Extensor digitorum brevis, cut — Lateral tarsal artery Arcuate artery Dorsal metatarsal artery hallucis longus, and lies beneath the cruciate (anterior annular) ligament of the ankle-joint The deep peroneal nerve is usually in front of the artery in the middle third of the leg. The branches of the anterior tibial artery are: — (1) The posterior tibial recur- rent: (2) the anterior tibial recurrent; (3) the medial malleolar; and (4) the DORSALIS PEDIS ARTERY 631 Fig. 504.^Scheme of the Distribution and Anastomoses op the Arteries of the Right Foot. (Walsham.) (The plantar arteries are shown in dotted outHne; the dorsal in solid red.) Peroneal artery Perforating peroneal branch Lateral malleolar branch Posterior peroneal artery Dor sails pedis artery Lateral plantar artery Lateral tarsal branch Lateral plantar artery forming plantar arch r -| Posterior perforating \\, |"^' branches "^^^^5^^_ I "^ Plantar digital artery to lateral side of Uttle toe Second, third, and fourth dorsal metatarsal ar- teries given off from arcuate artery Second, third, and fourth plantar metatarsal ar- teries Branch of third dorsal metatarsal artery to lateral side of little toe Anterior tibial artery Medial malleolar branch Malleolar branch of pos- terior tibial artery Communicating branch between posterior tibial and peroneal arteries Medial plantar artery Medial tarsal branch ■Arcuate artery ■Deep plantar artery First dorsal metatarsal First plantar metatarsal artery Dorsal digital branch of first dorsal metatarsal to medial side of great 632 THE BLOOD-VASCULAR SYSTEM lateral malleolar. In addition, ten or twelve muscular branches are given off irregularly to the adjacent muscles along the artery. (1) The posterior tibial recurrent artery [a. recurrens tibialis posterior] is occasionally absent. It ascends between the popliteus muscle and the popliteal ligament of the knee-joint, supplying these structures and the superior tibio-fibular joint. It anastomoses with the inferior lateral articular branch of the pophteal, and to a less extent with the inferior medial articular branch. (2) The anterior tibial recurrent [a. recurrens tibiahs anterior] is given off from the anterior tibial artery immediately after that vessel has passed above the interosseous membrane. It winds tortuously through the substance of the tibialis anterior muscle, over the lateral condyle (tuberosity) of the tibia close to the bone; and, perforating the deep fascia, ramifies on the lower and lateral part of the capsule of the knee-joint. It anastomoses with the inferior and superior lateral articular branches of the pophteal, with the descending branch of the lateral circumflex, and somewhat less freely with the medial articular branches of the pophteal and with the genu suprema (anastomotica magna). It gives off small branches to the tibialis anterior, the extensor digitorum longus, the knee-joint, and the contiguous fascia and skin. It forms one of the col- lateral cliannels by which the blood is carried to the hmb below in obstruction of the pophteal artery (fig. 503). (3) The medial malleolar [a. maUeolaris anterior medialisj, the smaller of the two malleolar branches, arises from the lower part of the anterior tibial artery a httle higher than the lateral, usually about the spot where the tendon of the extensor haUucis longus crosses the anterior tibial artery. It winds over the medial malleolus, passing beneath the tibiaUs anterior, and joins the medial malleolar rete anastomosing with branches from the posterior tibial artery. (4) The lateral malleolar artery [a. maUeolaris anterior lateralis], larger than the medial, arises from the lateral side of the anterior tibial artery, usually on a lower level than the medial malleolar. It winds downward and laterally round the lateral malleolus, passing beneath the extensor digitorum longus and peroneus tertius, and joins the lateral malleolar rete by anas- tomosing with the perforating peroneal, the termination of the peroneal, and the lateral tarsal branch of the dorsahs pedis (fig. 503). The anastomosis between the lateral malleolar and perforating peroneal is sometimes of considerable size, supplying the blood to the dorsal artery of the foot; the anterior tibial, then much reduced in size, usually ends at the place of origin of the lateral malleolar. THE DORSALIS PEDIS ARTERY The dorsalis pedis artery [a. dorsalis pedis] (fig. 503) is a continuation of the anterior tibial. It extends from the front of the ankle-joint to the proximal end of the first interosseous space, where it ends, as the deep plantar branch, by joining the lateral plantar artery to complete the plantar arch. It is accompanied by two venae comitantes. The course of the artery is indicated by a fine drawn from a point midway between the two malleoli to the proximal end of the first metatar- sal space. Relations. — Behind, the artery from above downward Ues successively on the talus (astrag- alus), navicular, second cuneiform, and the base of the second metatarsal bones, and the hga- ments uniting these bones. At times its course is a little more lateral, lying either partly on the second cuneiform bone, or on the dorsal ligaments uniting the second cuneiform to the first cuneiform. It is more or less bound down to the bones by aponeurotic fibres derived from the deep fascia. In front, the artery is covered by the crucial (anterior annular) hgament, sometimes by the extensor hallucis longus, by the skin, the superficial and deep fascia, and, just before its termi- nation, by the tendon of the extensor hallucis brevis. The angle formed by this tendon with the extensor hallucis longus is the best guide to finding the artery in the process of Ugature (fig. 503). To its lateral side is the most medial tendon of the extensor digitorum longus, and lower down the tendon of the extensor hallucis brevis. The deep peroneal (anterior tibial) nerve is also to its lateral side. To its medial side is the extensor hallucis longus, except at times for about half an inch below, where the tendon of the extensor haUucis brevis, having crossed the artery, may he between it and this tendon. The branches of the dorsalis pedis artery are: — (1) The tarsal; (2) the arcu- ate; and (3) the deep plantar. (1) The tarsal branches may be divided into (a) the lateral and (6) the medial, (a) The lateral tarsal artery [a. tarsea lateraUs] runs laterally over the navicular and cuboid bones beneath the extensor digitorum brevis. It supplies branches to that muscle, and to the bones and the articulations between them, and anastomoses above with the lateral malleolar and perforating (anterior) peroneal, below with the arcuate (metatarsal) and, over the lateral border of the foot, with the anastomotic branches of the lateral plantar artery. (6) The medial tarsal arteries [aa. tarseai raediales] consists of a few small branches which run over the medial side of the foot, supplying the skin and articulations, and anastomose with the medial malleolar. (2) The arcuate (metatarsal) artery Ja. arcuata] (figs. 503, 504) runs laterally across the foot, in a shght curve with the convexity forward, over the bases of the metatarsal bones, and beneath the e.xtensor tendons and the extensor digitorum brevis. At the lateral border of the foot it anastomoses, with the lateral tarsal, and with branches of the lateral plantar. MORPHOGENESIS OF THE ARTERIES 633 lYom the oonvexity of the arch it gives off four dorsal metatarsal (interosseous) arteries, which run forward on the dorsal interosseous muscles in the centre of the four interosseous spaces to the cleft of the toes, where they bifurcate for the supply of the contiguous sides of the toes. The artery to the first space is large, and gives off the digital artery to the medial side of the great toe. This vessel continues the direction of the dorsalis pedis and is commonly known as the dorsalis hallucis artery. The most lateral of the interosseous branches gives off a small vessel for the supply of the lateral side of the little toe. At the proximal end of the second, third, and fourth interosseous spaces each artery receives a perforating branch from the lateral plantar artery, and immediately before they bifurcate a second perforating artery through the distal end of the interosseous space from the corresponding digital. The dorsal digital arteries [aa. digitales dorsales], into which the dorsal metatarsal arteries divide at the cleft of the toes, run along the side of each toe toward the dorsal aspect, anas- tomosing with each other across the dorsum of the toes and by frequent branches with the digital branches of the plantar metatarsal arteries, which also run along the sides of the toes, but nearer the plantar surface. At the end of the toes they anastomose with each other around the quick of the nail. (3) The deep plantar branch [ramus plantaris profundus] comes off from the dorsaUs pedis with the first dorsal metatarsal (into which arteries indeed the dorsalis pedis may be said to divide). At the back of the first interosseous space it dips into the sole between the two heads of the first dorsal interosseous muscle, and communicates with the termination of the lateral plantar artery, completing the plantar arch, in a manner similar to that in which the radial artery, passing through the first dorsal interosseous muscle in the hand, completes by anastomos- ing with the ulnar the deep palmar arch. MORPHOGENESIS AND VARIATIONS OF THE ARTERIES A. ARTERIES OF THE HEAD AND TRUNK 1. MORPHOGENESIS In conformity with the branchiomeric and metameric development of the head and trunk (see p. 15) the arteries are developed in two sets, the branchiomeric (aortic arches) and metameric (segmental arteries). Fig. 505. — Model of the Pharynx and Aortic Arches op a Human Embryo 5 mm. Long. (Tandler, X75.) Second aortic arch Dorsal aorta Third aortic arch Sixth aortic arch (1) The system of aortic arches consists of five pairs of arteries which spring from the ven- tral aorta, or aortoe, and pass around the pharynx in the branchial arches to join the paired dorsal aorta;. Some of the arches are veiy transitory, but all those that give rise to permanent vessels are present in embryos about five miUimetres in length. Fig. 505 shows their distri- bution and rlations to the pharyngeal pouches at this stage; the arches which appear fifth in order are regarded as the sixth because (like the sixth arches in lung-fish and amphibia) they give 634 THE BLOOD-VASCULAR SYSTEM off the pulmonary arteries. The true fifth arches are probably not always developed, but when they occur they are later in development, imperfect, and very transitory. The dorsal aortEe, originally paired, are now united to form a single vessel as far forward as a place slightly caudal to the sixth arches. During the separation of the heart into right and left halves (p 526.), the primitive ventral aorta is divided by the aortic septum into two vessels, the main pulmonary artery and the as- cending aorta of the adult. The pulmonary trunk becomes connected with the sixth pair of arches only; the other arches then communicate, by means of the aorta, with the left ventricle. The further changes which occur in the arches to bring about the conditions found in the adult are shown diagrammatioally in fig. 506. The right and left pulmonary arteries arise from the corresponding sixth arches. The portion of the sixth arch dorsal to the pulmonary artery dis- appears on the right, on the left it persists until birth as the ductus arteriosus (lig. arteriosum of the adult). The fourth arch, including the short ventral stem between the fourth and sixth arch, becomes the permanent aortic arch on the left side, and the innominate and proximal por- tion of the subclavian upon the right. The dorsal longitudinal stem disappears on both sides between the third and fourth arches, and on the right side from the sixth arch back to the un- paired dorsal aorta. A trace of the latter portion of the right dorsal stem frequently persists in the adult as a small vessel (a. aberrans) connecting the dorsal aorta, directly or indirectly, with the right subclavian artery (p. 590). The ventral stems between the fourth and third arches form the common carotids; those between the third and first become the external carotids. The internal carotids are formed by the third arches and tlie dorsal stems between the third and first arches. The first and second arches disappear early, contributing somewhat to the formation of the branches of the internal and external carotids. Fig. 506. — -Diageams showing the Method of Normal Development op the Aoetic (Arches, and Indicating the Mechanism op Some Variations.) The primitive aortic arches (1-6), and some of the cervical dorsal segmentals (V-VIII) are shown in all the diagrams but numbered in Y only. X., abnormal: the aortic arch is on the right; the left subclavian takes the dorsal course; the right vertebral arises direct from the aortic arch. Y., normal; Z., abnormal: the right subclavian arises from the sixth cervical dorsal segmental; the left from the sixth and seventh. A, ascending aorta; AA, aortic arch; AD, dorsal 'aorta ; CC, common carotid; CE, external carotid; CI, internal carotid; D, ductus arteriosus; IN, innominate; S, subclavian; T, costo-cervical; V, vertebral. X In early development the segmental arteries are caudally placed with regard to the aortic arch vessels. As the latter, however, become shifted following the migration of the heart from the neck into the thorax, the persistent seventh dorsal cervical segmental (subclavian) reaches the neighbourhood of the sixth aortic arch. Little is known of the share taken by the first and second aortic arches in the formation of the branches of the internal and external carotid arteries. It has been shown by Tandler that the internal maxillary is prirnarily a branch of the internal carotid, (the first and second arches tak- ing a share in its formation). The primitive vessel is known as the stapedial since it passes be- tween the crura of the developing stapes. It gives off supraorbital, infraorbital, and mandibular branches; the latter two arising from the main artery by a common trunk. The common trunk is later joined by a branch from the external carotid and, together with the supraorbital, becomes the middle meningeal. An anastomosis between the supraorbital and the ophthalmic persists 80 that in the adult the anterior branch of the meningeal frequently takes a considerable share in the blood-supply of the orbit. The stapedial trunk undergoes retrogression and is represented in the adult by the carotico-tympanic of the internal carotid and by the superior tympanic of the middle meningeal. The infraorbital branch of the stapedial becomes the second and third parts of the internal maxillary and gives off branches accordingly. The mandibular branch becomes the inferior alveolar of the adult. (2) The segmental system (fig. 507) consists of arteries primarily arising from the aorta in three longitudinal series, dorsal, lateral, and ventral on either side. The segmental arrange- ment is much less perfect in the ventral and lateral groups than in the dorsal. So much so, in fact, that the term segmental is used for the ventral and lateral groups rather as a matter MORPHOGENESIS OF THE ARTERIES 635 of convenience than as indicating a strict numerical correspondence between segments and The dorsal segmental arteries primarily supply the central nervous system but later give off two sets of vessels to the body wall; these persist in the adult as the anterior and posterior main branches of the intercostal and lumbar arteries. The remainder of each segmental artery is represented in the adult by the spinal ramus which accompanies the corresponding nerve root through the intervertebral foramen. The tendency to form intersegmental anastomoses between these vessels (and their branches) gives rise to many of the important longitudinal stems of adult anatomy. Thus, the spinal ramus gives rise to a pre- and postneural anastomosing channel on either side, the (primarily paired) anterior and posterior spinal arteries. The anterior branches have each a longitudinal precostal anastomosis, and, as they grow forward with the developing body wall, their ends are connected to form the mammary anastomosis. Between the posterior rami, a postoostal and a postvertebral anastomosis may be formed. In addition, the anterior rami give off lateral and anterior perforating branches (fig. 507). Two dorsal segmental arteries have been recognized in the occipital region, the first dis- appears and the second, the hypoglossus artery, follows the hypoglossal nerve to the ventral sur- face of the brain where it is connected with the termination of the internal carotid of its own side by means of a longitudinal stem the a. vertebralis cerebralis. The hypoglossus artery, by shift- ing forward to the third aortic arch, itself acquires a secondary origin from the internal carotid. In the cervical region, the spinal ramus of segmental cervical I forms the third, or sub' occipital, part of the vertebral artery. Cervical segmentals I to VI lose their connection with the aorta and a postcostal anastomosis between them forms the second part of the same artery. The first part of the vertebral is formed by the posterior ramus of cervical VI and its precostal anastomosis with cervical VII (subclavian) (fig. 508). Fig. 607. — Scheme of the Typical Arrangement of the Branches op the Aorta. (After Quaim) Longitudinal anastomoses: 1, precostal; 2, postcostal; 3 postvertebral; 4, preneural; 5, post- neural; 6, mammary. , Posterior branch Anterior branch Lateral perforating branch Anterior perforating branch The anterior ramus of cervical VII forms the entire first part of the subclavian on the left, and the distal portion of it upon the right (see system of aortic arches). The second part of the subclavian is formed by the lateral branch of the anterior ramus of cervical VII, while the portion of the anterior ramus ventral to this becomes the root of the internal mammary. The anterior ramus of cervical VIII disappears, but the pi'ecostal anastomosis connecting it with the subclavian (cervical VII) persists to form the costo-cervical of the adult. The posterior ramus of cervical VIII forms the root of the deep cervical, and, by a postvertebral anastomosis with the other posterior cervical rami and with the occipital, forms the remainder of the deep cervical and the descending branch of the occipital artery. In the thoracic and lumbar regions, the embryonic conditions very largely persist (fig. 508). The anterior rami of thoracic segmentals I and II, however, lose their connection with the aorta and, by a precostal anastomosis with cervical VIII, become secondarily connected (through the costo-cervical trunk) with the subclavian. The superior intercostal of the adult is thus formed. The fifth lumbar segmental apparently joins the umbihcal artery (of the ventral segmental series) to form the external ihac which, in the adult, provides the chief arterial supply to the lower extremity. The inferior gluteal (sciatic), which is the primitive artery of supply for the lower extremity, if it is segmental at all, belongs to the sacral region. The free ends of the anterior rami of all the thoracic and the upper four lumbar segmentals become united, as they grow out with the body wall, to form the longitudinal mammary anastomosis (fig. 508). This anastomosis, by its connection with the anterior ramus of cervical 636 THE BLOOD-VASCULAR SYSTEM yil (subclavian) and with the anterior ramus of lumbar V (external iliac), forms the internal matnmary (with its superior epigastric branch) and the inferior {deep) epigastric arteries of the adult. In the sacral region, the adult shows evidence of segmental vessels in branches of the middle and lateral sacral arteries; the latter probably representing a precostal anastomosis. Whether the parietal branches may be derived directly from segmental sources, or whether they are vessels of new formation, has not been determined embryologicaUy. The obturator would appear to be segmentalifor it contributes a branch to the mammary anastomosis which persists in the adult (pubic brandies of obturator and inferior epigastric). If the connecting branch with the inferior epigastric is large, the obturator may lose its connection with the hypogastric, in which case the latter is said to arise from the former, or from the external iliac, One of the most interesting of the longitudinal anastomoses in connection with the dorsal segmentals is the primitively bilateral preneural anastomosis extending ventral to the spinal cord 'and connected, beyond the first spinal segment, with each internal carotid by means of the right and left aa. cerebrales vertebrales. The hypoglossus artery (p. 635) having lost its con- nection with the internal carotid, leaves the spinal ramus of cervical I (third part of the subclavian) to take over the major share of the cerebral supply. A process of blending by anas- FiG. 508. — Diagram to Show the Development of the Arteries or the Trunk prom the Aortic Arches and Segmental Arteries. The arteries which persist are black; those which degenerate are in outhne; those newly formed are shaded. (After Mall.) txternal Cl Bulbus Arteriosus'; fulmooaryArleij ' SabclariaffArterCffs ' J)eep£plgastricAtterK. femora t Artery ,^ Umbilical Artery, tomosis now occurs resulting in the single basilar and anterior spinal arteries of the adult. The posterior communicating, proximal portions of the posterior cerebrals, the fourth part of the vevte- brals, and the right and left roots in the anterior spinals of the adult alone retain the primitive arrangement and testify to the double nature of the original anastomosis. Asymmetry in the vertebrals and other irregularities in the adult can usually be explained on developmental grounds. The postneural anastomosis, which joins the preneural at about the first cervical seg- ment, retains its bilaterality throughout to form tlie paired posterior spinal arteries of the adult. The lateral segmental arteries take origin from the aorta in series, intermediate in position between the dorsal and ventral segmentals. They reach their fullest development in embryos of about 8 mm., when they extend from the seventh cervical to the twelfth thoracic segment and supply the mesonephros. At this stage Broman found twenty arteries on each side, many of which were non-segmental. As the suprarenals and gonads develop, they each receive branches from several mesonephric arteries. The latter arteries now undergo rapid retrogression and the suprarenal and gonadie branches are shifted caudally through the mesonephric series to newly formed (non-segmental) arteries opposite the upper lumbar segments. Finally there remain three suprarenal arteries opposite the twelfth thoracic and first and second lumbar segments and a gonadie artery {ovarian or internal spermatic of the adult) opposite the third lumbar segment. AU of these vessels now appear to be direct branches from the aorta. Of the three suprarenal branches, the upper and lower each gives a large branch to the diaphragm and kidney respectively and become the inferior phrenic and renal arteries of the adult. The middle becomes the middle suprarenal of the adult. Felix puts a somewhat different interpretation upon the origin of the vessels persisting in the lumbar region after the disappearance of the thoracic mesonephric arteries. He finds in an embryo of 18 mm. nine arteries on either side, extending from the ninth thoracic to the third lumbar segment, all of which he looks upon as mesonephric. These he classifies into tlxree groups: — Cranial, which reach the mesonephros by passing dorsal to the suprarenal; caudal which pass ventral to the suprarenal, and middle which pass through it. Inasmuch as the arteries anastomose in the mesonephros there is great liability to variation in the number and position of the stems which persist in the adult. The suprarenal arteries VARIATIONS OF THE ARTERIES 637 are usually derived from the caudal group, the renals from the caudal or middle and the sper- matics from the middle. When accessory renals or spermatics occur in the adult their place of origin and course will generally indicate the group from which they are derived. The ventral segmental arteries appear very early. In an embryo of seven somites (ca. 2 mm.) described by Dandy* there was a right and a left series of twelve arteries, each arising from the still ununited dorsal aortce, the artery at the caudal end of each series being the um- bihcal, and the remainder vitelline arteries. In an embryo of 4.9 mm. (35 somites) described by IngaUst the originally paired viteUine arteries had united (as had the dorsal aortffi in part) to form unpaired vessels. There were unpaired vessels as follows: one opposite the seventh cervical segment (co^hac); five opposite the first four thoracic (omphalo-mesenterics, united by a longitudinal anastomosis), and one vessel of doubtful significance opposite the fifth and sixth thoracic segments. The paired umbiUoal arteries were opposite the first lumbar segment. No other ventral arteries were present. It has been found from more fully developed stages that the inferior mesenteric artei-y is distinguishable at a stage of 8 mm. opposite the second lumbar segment. Also that the ventral segmental vessels undergo a process of migration until they reach their definitive positions, i. e., the coeliac opposite the twelfth thoracic segment, the superior mesenteric opposite the first, the inferior mesenteric opposite the third, and the umbilicals opposite the fourth lumbar seg- ments, respectively. The cesophageal arteries of the adult do not belong to this series; but seem to be vessels of later formation. The umbilical arteries, by means of secondary anastomosis, move laterally upon the aorta so as to pass lateral to the Wolffian ducts instead of medial . The proximal portion of each um- bilical artery becomes the common iliac of the adult; its continuation is represented by the hypo- gastric and its umbilical branch. The external iliac appears to be derived from the dorsal seg- mental artery of the fifth lumbar segment, and the parietal branches of the hypogastric from corresponding sacral segmentals acquired by anastomosis. How such anastomoses be- tween the umbihcals and the dorsal segmentals come about has not been ascertained. 2. VARIATIONS Aorta and pulmonary artery. — The variations met with in the arch of the aorta are usually to be explained as persistent foetal conditions, and are often associated with abnormahties of the heart. Many of the variations are due to different modes of transformation of the primitive system of aortic arches. Since the aorta and pulmonary artery develop from a common conus and truncus arteriosus, irregular and imperfect development of the aortic septum may also produce numerous variations. It has been seen that at one stage of development two fourth arches, a right and a left, are present, and such a condition is occasionally persistent in the adult. In such cases, owing to the portion of the aorta derived from the bulbus arteriosus being directed upward and to the right and the descending aorta lying in the left side of the vertebral column, the right arch passes from right to left behind the oesophagus, which thus seems to perforate the aortic arch. Another variation occasionally seen is the occurrence of an aortic arch curving to the right instead of the left. This may be due to a persistence of the lower portion of the right dorsal longitudinal stem and the disappearance of the left, as shown in fig. 506; or it may be associated with a complete inversion of all the viscera, a situs inversus. If the lower portion of the right dorsal longitudinal trunk should persist, and the part of it which normally forms the proximal part of the right subclavian should disappear, the right subclavian would arise from the descending portion of the aortic arch. It is to be noted that in such cases the subclavian passes behind the oesophagus and below the right inferior laryngeal nerve. Partial persistence of the lower portion of the right dorsal longitu- dinal trunk is represented in the arteria aberrans (see p. 590). Another group of variations is based on the persistence of the ductus arteriosus, which is derived from the sixth aortic arch. With this group belong the cases in which the pulmonary artery arises from the aorta; that is, where the blood of the pulmonary arteries passes from the aorta through the ductus arteriosus. Variations in the number and the position of the vessels arising from the arch are extremely great, and many of these conditions are found normally in other mammals or birds. There may be from one to six branches. The case of one branch is the normal in the horse. It involves the fusion of the two aortic stems and the shortening of the fourth arch so that the left subclavian joins with the common stem. The avian form with trto innominate arteries is extremely rare. A more common form is the one found in most apes, in which the innominate and left carotid form one branch ; in rare instances the three branches are the two subclavians and a general carotid artery. When there are more than three branches the vertebral arteries are added, or the extra branch may be the thyreoidea ima (fig. 443). The commonest form with four vessels is the one in which the left vertebral arises between the left carotid and subclavian. A rarer form is to be found when the order is right subclavian, right carotid, left carotid, and left sub- clavian. Where there are five arteries, the extra ones are the right subclavian and left vertebral. The case of six branches is due to the separate origin of both vertebrals and both subclavians. The manner in which the vertebral artery may arise from the adult aortic arch is indicated in fig. 506. The innominate artery may be absent, or may give off additional branches (see Aokta). It may be longer than usual and, bending to the left, ascend in front of the trachea (or more rarely behind the trachea and oesophagus) to turn again to the right. The thyroidea ima has been referred to (p. 532). Carotid arteries. — The common carotid may be absent or bifurcate higher or lower than usual. * Am. Journ. Anat., Vol. 10, 1910. t Arch. f. mikr. Anat., Bd. 70, 1907. 638 THE BLOOD-VASCULAR SYSTEM Itjmay not bifurcate at all, in which case the branches usually arising from the external car- otid are derived from the common. The ascending pharyngeal and superior thyreoid occa- sionally arise from an otherwise normal common carotid. Unusual origin ^of the common carotids has been referred to (see Aorta). Branches of the carotid arteries. — The superior thyreoid, lingual and external maxillary sometimes have a common stem of origin. The superior thyreoid artery varies in size inversely with the inferior. The external maxillary occasionally terminates in its submental branch. In such cases the main supply of the face is taken over by an abnormally large dorsal nasal branch of the ophthalmic, or transverse facial branch of the temporal artery. The occipital sometimes arises from the internal carotid or from the ascending cervical. The ascending pharyngeal is very variable in its place of origin from the external carotid, it may arise from the common or internal. Out of 447 arteries examined, the second portion of the internal maxillary passed lateral to the external pterygoid muscle in 55 per cent., and medial to it in 45 per cent, of cases. When medial to this muscle the internal maxillary sometimes passes medial to the inferior alveolar and lingual nerves and occasionally between them. The variability in the course of this artery appears to depend on a tendency to reduplication of the infraorbital branch of the stapedial artery (p. 634) in the neighbourhood of the mandibular nerve. Such a condition was found by Thyng in a 17 mm. human embryo. When the internal maxiUary passes medial to the ex- ternal pterygoid there is often a parallel anastomosing channel between the posterior deep temporal and buccal branches. The ophthalmic artery may arise, wholly or in part, from the middle meningeal, or vice versa. This is due to the anastomosis between the supraorbital branch of the stapedial and the oph- thalmic in the embryo. Subclavian artery. — Irregularities of origin have been referred to (see Aorta). The branches of the subclavian artery are very variable in their place of origin (p. 559). The vertebral may arise directly from the arch of the aorta (p. 537) or take an unusual course in the neck. It may enter the foramen transversarium of the fourth or fifth cervical vertebra instead of the sixth; this arises from substitution of an embryonic precostal anastomosis in these segments for the usual postcostal. By a converse substitution it may enter the seventh. The aa. transversa colli and scapulas vary inversely in size. The arteria aberrans connecting the right subclavian with the dorsal aorta has been referred to (p. 634). The thoracic aorta. — Transposition, and the arteria aberrans have been referred to above. Branches of the thoracic aorta. — The intercostal arteries are hable to numerical variation, evidently owing to the occurrence of precostal intersegmental anastomoses between the embry- onic dorsal segmentals. A common longitudinal stem may even take over the vessels of both sides. The anterior spinal artery usually shows lack of median symmetry which indicates the bilaterality of its origin (p. 636). The arrangement of the bronchial arteries is hable to, much variation; this has not received adequate explanation. The abdominal aorta sometimes divides as low as the fifth lumbar vertebra, occasionally higher than usual, depending upon the definitive position taken by the umbiUcal arteries (p. 637). Cases are on record of accessoiy pulmonary arteries arising by a single stem from the abdommal aorta, which passes into the thorax along the oesophagus. The aorta and vena cava inferior may be transposed either as a part of situs inversus or as an abnormality of the venous system. Branches of the abdominal aorta. — The lumbar arteries are subject to the same type of variation as occurs in the intercostals. There may be a loop connecting the caeliac and superior mesenteric arteries. Any or all of the branches of the coeUac may arise from the superior mesenteric (coelio-mesenteric in the latter case) or directly from the aorta. The instabiUty of the coeUac and superior mesenteric branches is favored by the rapid cranio-caudal migration of the two trunks; intersegmental anastomosis, in some cases, may be a factor also. There is very great variation in the number of branches given off by the superior mesenteric and in the details of their arrangement. This is a natural result of the number of possible routes which may be taken by the blood; these resemble, in their variety, those of an embryonic circulation. The region of supply of the inferior mesenteric artery is sometimes taken over entirely or in part (e. g., middle colic) by the superior mesenteric. An omphalo-mesenteric artery, in rare cases, arises from the superior mesenteric or one of its branches. It passes to the navel and anasto- moses with inferior epigastric and with the small arteries accompanying the round ligament of the liver or the urachus. Accessory renal arteries are very common; as many as six have been recorded. These may arise from the aorta, middle sacral, inferior phrenic, middle suprarenal or internal spermatic. According to Felix, these are to be regarded as persistent mesonephric arteries. Those arising above the regular renal frequently enter the kidney dorsal to the hilum. Those below it are more apt to be ventraUy placed. Nearly all possible varieties of origin are met with in the inferior phrenic, middle supra- renal, internal spermatic and accessory renal arteries which find explanation in the caudal migra- tion of, and anastomosis between, the embryonic representatives of these vessels. The oc- casional origin of the inferior phrenic from the coeUac (or its branches) or from the superior mesenteric; of the internal spermatic or the middle suprarenal from the lumbar arteries, or of an accessory renal from the inferior mesenteric must be taken as indicating embryom'c anastomoses between the dorsal, lateral, or ventral segmental arteries, as the case may be. The iliac and hypogastric arteries. — The length of the common iZiac depends upon the site of aortic bifurcation (p. 590) ; also upon the site of division of the common iliac into external iliac and hypogastric. If these spring directly from the aorta (as they do in rare cases) the common iliac is absent. The trunk formed by the common iliac and hypogastric is the proximal portion of the embryonic umbilical artery. The manner in which tliis takes over a dorsal segmental artery (probably the fifth lumbar) to become the external iliac is not sufficiently undersood to account for variations in this region. VARIATIONS OF THE ARTERIES 639 The branches of the hypogastric artery show great variation in their origin, and there is frequently no separation of the hj'pogastrio into anterior and posterior divisions. Rarely the branches all take origin from the external iUao, in which case the hypogastric (as such) is absent. The obturator artery may arise from the inferior epigastric, or vice versa (p. 615). The arleria comitans n. ischiadici may be larger than usual and form a very pronounced anas- tomosis with the popliteal. In rare cases the main blood-supply of the lower limb is thus derived from the inferior gluteal which is the primitive embryonic condition (p. 640). .The vesical and vaginal arteries are liable to variation in their relative areas of distribution. The internal pudendal is sometimes small and maj' terminate as the perineal artery, in these cases the urogenital region is supplied largely by the accessory pudendal (p. 610). B. ARTERIES OF THE EXTREMITIES 1. MORPHOGENESIS The arteries of the adult extremities represent surviving chaimels resulting from the selection of a chosen path traversing the perineural arterial plexuses of the early embryonic limb. At present there is little unanimity of opinion as to whether the pattern of the developing nerve trunks is specifically reproduced by the primitive arterial plexuses or whether the un- doubted similarity between the two is of a more general nature. There occurs in either ex- tremity one case in which an artery of fundamental importance follows a course practically independent of nerve distribution. The volar interosseous, in the forearm, and the peroneal, in the leg, are accompanied by insignificant nerves (n. to pronator quadratus, and n. to fie.xor hallucis longus respectively) which, moreover, do not ex-tend the full length of the arteries in question. The blood of a developing limb, having traversed the proximal segment by means of the arterial plexus around a single nerve, has the choice of several possible paths by which to reach the digits. The selected channel becomes, for the time, the principal artery of the distal segment. This presently gives way to a second favoured route, which may persist or again give way to a third. Thus, finally, the adult arrangement is established. This process of alternation is the cause of many of the commoner variations for, if it does not proceed to its usual termination, a small vessel, commonly rated as a branch, may testify to its earher im- portance by appearing as one of the chief vessels of the part. In the upper extremity the blood first traverses the peri-median plexus (which becomes later the axillo-brachial trunk) and flows to the digits mainly by the volar interosseous route. Next the volar interosseous d-nandles in favour of the median. The median afterward relin- quishes its function to the radial and ulnar. In the lower extremity the main blood-flow at first follows the peri-sciatic plexus from which it is dehvered to the digits chiefly by the peroneal artery. The peroneal artery passes from the sole to the dorsum of the foot through the sinus pedis, and from here suppUes the digits. The anterior and posterior tibial are at first small, the latter supplj-ing the plantar digital arteries. At a stage of 10 millimetres the femoral artery is represented by a peri-saphenous plexus which anastomoses with the peri-sciatic plexus near the knee. The peri-femoral plexus rapidly consoUdates into the femoral and genu suprema arteries. The femoral later takes over the pophleal as its direct continuation, and the origin of the genu suprema marks the boundary between the femoral and ischiadic zones of the main trunk. Finally the peroneal gives place to the anterior and posterior tibial arteries. The portion of the peroneal perforating the tarsus disappears. In so doing it leaves the original termination of the peroneal artery connected with the dorsalis pedis to become the arcuate branch of the latter. 2. VARIATIONS The variations of the arteries of the upper extremity may be divided into two categories, A certain number of them, particularly those occurring in the forearm and hand, are directly traceable to the unusual persistence of one or more of the embryonic channels; or, when varia- tion involves magnitude only, to reciprocal variations in the size of the normal vessels. The commoner and more important variations of the arterial distribution, however, arise in a manner much less susceptible to ready explanation. They depend, in fact, upon variations in the course taken by the single or double route which, surviving from the intricacies of the peri-median plexus, persists to maturity. These will be referred to later. The volar interosseous artery maj' be unusually large. It may reinforce a deficient radia or ulnar through the volar carpal arterj% or its dorsal carpal branch may join the radial at the back of the wrist. In very rare cases the volar interosseous, together with a large ulnar artery, replaces the radial altogether. A large median artery may participate in the palmar supply of the fingers, either b}' joining the superficial volar arch or (the arch being absent) by breaking directly into digital branches. The median, when large, occasionally replaces the ulnar, verj' rarely the radial, and frequently the superficial volar. The superficial volar arch may be small, with compensation by the deep, or absent. In the latter case the digital arteries may come directly from the ulnar and radial, ulnar and median or median and radial. In the absence of the superficial volar, which is ver3- frequent, the super- ficial arch is completed by the princeps pollicis or the volaris radiahs indicis. 640 THE BLOOD-VASCULAR SYSTEM Cases are on record in which the ulnar artery, arising in the middle of the arm passes behind the medial epicondyle to follow the nerve in the forearm as usual. The ulnar artery here replaces the superior ulnar collateral and the ulnar recurrent. This anomaly is explained in a striking way by the account given by de Vriese of the development of the vessels of the upper extremity. Several important variations in the distribution of the main vessels belong to the second category. It is not uncommon for tioo arteries to arise from the primitive peri-median plexus of the arm. In such cases one artery usuaUy takes a course dorsal to the median nerve, i. e., it is crossed medio-lateraUy by the medial head of the nerve and in the contrary direction by the nerve itseh. Its course corresponds to that taken by the ordinary axiUo-brachial trunk; it is known as the deep brachial artery. The other vessel takes a course ventral to the median, nerve, and is known as the superficial brachial. The superficial brachial may join its com- panion artery, at or above the elbow, or one of the forearm vessels arising from it. In either case the superficial brachial is referred to as a "vas aberrans." Persistence of the superficial brachial further operates as a frequent cause of abnormality in the forearm in that it is often continued directly into one or moi-e of the chief arteries of the latter, the deep brachial taking the remainder. This condition is classified as a high origin of the radial, ulnar, etc., as the case may be. There is another type of variation belonging to the same category. In this, one large artery only occurs above the elbow which, instead of following the normal course of the brachial, passes, entirely or in part, ventral to the median nerve. In the first case this vessel represents the superficial brachial, the deep being absent. In the second it corresponds in its upper part to the deep brachial and in its lower to the superficial, the two components varying in inverse proportion. E. MiiUer*, who has made a study of the variations belonging to this category, classifies the abnormal artery occurring in cases of vas aberrans, of high origin of fore arm- vessels, and of single abnormal brachial, according to the proportion of superficial brachial present in any particular example, as a. brachialis superficialis superior media, inferior, or ima. In an embryo of 11.7 milhmetres he found a system of arterial channels in relation with the median nerve out of which any variation of this category might have been produced during further development. In cases in which the superficial brachial alone persists, the branches of the axillary (and sometimes the profunda brachii and superior ulnar collateral) arise from a common (deep brachial) trunk called the profunda axillaris. In cases in which the deep and superficial brachial co-exist examples of continuation of the superficial brachial into the radial are rather common, continuation into the ulnar less so. Continuation of the superficial brachial into the median, interosseous, or of posterior interosseous arteries occasionally occur, but they are rare. In any case of high origin a cross branch may connect the high vessel with the deep brachial in the neighbourhood of the elbow. The ulnar artery when arising high is often superficial to the forearm flexors (a fact which has not been explained on embryological grounds), the inter- osseous arising from the radial. The variations occurring in the arteries of the lower extremity are usually compensatory, or due to persistence of alternative embryonic channels. The sciatic (inferior gluteal) very rarely persists as the main artery of supply. In such cases the small femoral ends as the genu suprema which then appears to be a branch of the profunda. The profunda is irregular; its origin may occur anywhere between the inguinal Ugament and a point four inches below it. The median or lateral circumflex may arise from the femoral. The branches of the latter commonly arise separately from the profunda, or from the femoral. The popliteal does not vary much in its point of division. High division is commoner than low, but is never higher than the lower epiphyseal fine of the femur. The anterior tibial may be small and only reach the middle or lower part of the leg. In such cases an enlarged anterior peroneal may end as the dorsahs pedis, or the dorsal metatarsal arteries may be supphed from the plantar arch. Cases in which the anterior peroneal supplies the dorsum of the foot do not represent a dkect inheritance of the embryonic method by which the peroneal artery performs this office. The embryonic route of the peroneal to the dorsum of the foot is transtarsal. The anterior tibial artery may reach the extensor surface of the leg by accompanying the peroneal nerve. This case, hke that of the ulnar artery passing around the medial epicondyle, is interesting in connection with the work of de Vriese. ^ . c ■ The posterior tibial artery may be absent or small, the peroneal replacing it, or remforcmg it by means of the ramus communicans. Absence of the peroneal has been recorded by Otto and W. Krause, but these cases are explained by Barkow as being suppression of the posterior tibial artery between the origin of the peroneal and the communicating branch (Quain). The lateral plantar is sometimes very small, in which case the plantar arch may be supphed by a large deep plantar. In rare cases there is a superficial plantar arch as in the embryo. 3. THE SYSTEMIC VEINS The systemic veins are naturally divided into three groups — (1) the veins of the heart; (2) the vena cava superior and its tributaries, namely the veins of the head, neck, upper extremity, and thorax; and (3) the vena' cava inferior and its tributaries, namely, the portal system, and the veins of the abdomen, pelvis, and lower extremity. * E. Miiller, Anat. Hefte, No. 22, 1903. THE INNOMINATE VEINS 641 I. THE VEINS OF THE HEART The veins of the heart have already been described (p. 520). II. THE VENA CAVA SUPERIOR AND ITS TRIBUTARIES THE VENA CAVA SUPERIOR The vena cava superior (fig. 509) carries to the heart the blood returned from the head and neck and upper extremities through the right and left innominate veins, and from the walls of the thorax, either directly through the azygos vein, or indirectly through the innominate veins. It is formed (fig. 509) by the con- fluence of the right and left innominate veins behind the first right sterno-chondral articulation. Descending from its origin in a gentle curve with its convexity to the right and in a direction slightly backward behind the sternal end of the first and second intercostal spaces and second costal cartilage, it terminates in the right atrium of the heart on a level with the third right costal cartilage in front and the seventh thoracic vertebra behind. It measures about 7 to 8 cm. (3 in.) in length. A little more than its lower half (4 cm.) is contained within the pericar- dium, the serous layer of that membrane being reflected obliquely over it imme- diately below the spot where it is joined by the vena azygos, and on a lower level than the reflexion of the pericardium on the aorta. The superior vena cava contains no valves. Relations. — In front, in addition to the first and second intercostal spaces and the second costal cartilage, it is covered by the remains of the thymus gland, the intrathoracic fascia, and the pericardium, and is overlapped by the right pleura and lung. Behind (fig. 609) are the vena azygos (major), the right bronchus, the right pulmonary artery, and the superior right pulmonary vein; and below, the fibrous layer of the pericardium. The serous layer is reflected over the front and sides of the vessel, but not over its posterior part. To the right side are the right lung and pleura and the phrenic nei've. To the left side are the innominate artery and the ascending aorta. Tributaries. — In addition to the right and left innominate veins and the vena azygos it receives small veins from the mediastinum and pericardium. THE INNOMINATE VEINS The innominate or brachio-cephalic veins [vv. anonymae] return the blood from the head and neck and upper extremity. They are formed on each side by the confluence of the internal jugular and subclavian veins behind the sternal end of the clavicle. They terminate behind the first costal cartilage on the right side by uniting to form the vena cava superior. The innominate veins have no valves. The right innominate vein [v. anonyma dextra] (fig. 509) measures about 2 to 3 cm. (1 to H in-) in length, and descends from its origin behind the sternal end of the clavicle, very slightly forward and medially, along the right side of the sub- clavian and innominate arteries, to its junction with the left vein behind the first costal cartilage close to the sternum. It is superficial to the innominate artery. Relations. — In front are the origins of the sterno-hyoid and sterno-thyreoid muscles, the clavicle, the first costal cartilage, and the remains of the thymus gland. Behind are the pleura and lung. To the right are the right pleura and lung and the phrenic nerve. To the left (fig. 509) are the right subclavian artery, the innominate artery, the right vagus nerve, and the trachea. The left innominate vein [v. anonyma sinistra] (fig. 509) measures 6 to 7.5 cm. (2| to 3 in.) in length, and extends from its origin behind the sternal end of the left clavicle obHqueljr across the three main branches of the arch of the aorta, to unite with the right innominate vein behind the cartilage of the first rib close to the sternum to form the vena cava superior. In this course it runs from left to right with an inclination downward and slightly backward. A line drawn obliquely across the upper half of the manubrium of the sternum, from the sterno- 642 THE BLOOD-VASCULAR SYSTEM clavicular articulation on the left side to the lower border of the first costal carti- lage at its junction with the sternum on the right side, will indicate its course. The left innominate vein is on a level with the top of the sternum at birth. Relations. — In front, in addition to the manubrium of the sternum, it has the origins of the sterno-hyoid and sterno-thyreoid muscles, and the remains of the thymus gland, the sternal end of the left clavicle, and the sterno-clavicular articulation. Behind are the three chief arteries arising from the arch of the aorta, the trachea, and the left phrenic and left vagus nerves. Below it is the arch of the aorta. Above it are the cervical fascia, the inferior thyreoid, and thyreoidea ima veins. Tributaries. — In addition to the internal jugular and subclavian veins, by the confluence of which the innominate veins are formed, each vein receives on its upper aspect the vertebral, the deep cervical, and inferior thyreoid veins; and Fig. 509. (Modified Internal jugular vein- Transverse cervical Transverse scapular artery Right recurrent nerve Right common carotid artery Subclavian vein Vagus nerve Innominate artery *^ I* Left innominate vein Phrenic nerve Superior vena cava Arch of aorta Right bronchus Branch of right pul monary artery Branch of right pul monary vein Right pulmonary artery Branch of right pul- monary artery Branch of right pul monary vein Right coronary artery Thoracic vertebra Azygos vein Intercostal veins Intercostal arteries — The Vena Cava Supeeior and the Innominate Veins. from a dissection in St. Bartholomew's Hospital Museum.) Inferior thyreoid ' -Thyreoid gland Left internal jugular Vagus nerve Lett common carotid artery Left recurrent nerve Left subclavian artery Left subclavian vein Left internal mammary Phrenic nerve Vagus nerve Recurrent nerve Ligamentum arteri- osum Left pulmonary artery Lett pulmonary vein Left bronchus Branch of left pulmon- ary artery Pulmonary artery Lett pulmonary vein Left coronary artery Conns arteriosus CEsophagus Thoracic duct Thoracic aorta on its lower aspect the internal mammary vein. The left vein, moreover, is joined by the thyreoidea ima, the left superior intercostal, and by the thymic, tracheal, oesophageal, superior phrenic, anterior mediastinal, and pericardiac veins. At the confluence of the internal jugular and subclavian veins on the right side the three lymphatic trunks or the right lymphatic duct open; on the left side the thoracic duct. THE VEINS OF THE HEAD AND NECK The veins of the head and neck may be divided for purposes of description into the superficial, which return the blood from the external parts of the head and SUPERFICIAL VEINS OF HEAD AND NECK 643 neck; and the deep, which return the blood from the deeper structures. All the veins, whether superficial or deep, terminate in the internal jugular or sub- clavian, or open directly into the innominate veins at the root of the neck. Through the latter all the blood from the head and neck ultimately passes on its way to the heart. THE SUPERFICIAL VEINS OF THE HEAD AND NECK The venous blood from the anterior part of the scalp and integument of the face is returned, through the anterior and posterior facial veins, to the common facial, a tributary of the internal jugular vein. From the posterior part of the scalp and from the integument of the neck venous blood is returned, through the external jugular and its tributaries, to the subclavian vein. A. The Antehior Facial Vein The anterior facial vein [v. facialis anterior] (fig. 510) begins a little below the medial end of the eyebrow where it is formed by the union of the frontal and Fig. 510. — The Supeepicial Veins of the Face and Scalp. (After Quain.) Superficial tem- poral Nasal branch of igular vein Posterior facial Posterior exter^ nal jugular vein" External jugula: Communicating branch with an- terior jugular Anterior jugtUar vein Transverse scapular i supraorbital veins. It descends near the medial angle of the orbit, and then by the side of the nose to the cheek, which it crosses obliquely, to the anterior edge of the massetpr muscle. Thence it passes through the digastric triangle to the upper border of the hyoid bone, where it terminates in the common facial vein. In this course it is reinforced by numerous collateral veins, and gradually increases in size. It has, moreover, numerous communications with the deep veins. The portion of this vein above the lower margin of the orbit is called the angular [v. 644 THE BLOOD-VASCULAR SYSTEM angularis]. In the remainder of its course over the face and neck it is termed the anterior facial vein. The angular vein skirts around the medial margin of the orbit, lying with the angular artery on the frontal (nasal) process of the maxillary bone slightly medial to the lacrimal sac. Branches pass from the posterior part of the angular vein into the orbit to join the ophthalmic. The angular, the facial, and the ophthalmic veins contain no valves. The blood, therefore, can' pass either forward from the ophthalmic into the angular, or backward through the facial and angular into the ophthalmic, and so on to the cavernous and other venous sinuses of the cranium. Hence in certain tumours in the orbit and cranium, the congestion of the angular and facial veins; and the danger in facial carbuncle and anthrax of septic thrombi spreading backward through the angular and ophthalmic veins to the cranial sinuses. The anterior facial vein runs in a more or less direct line behind its corre- sponding artery, the external maxillary (facial), which itself pursues a tortuous course. It usually passes deep to the zygomatic muscle, the zygomatic head of the quadratus labii superioris, and the risorius, but superficial to the other muscles. At the anterior edge of the masseter it meets the external maxillary artery, lying immediately posterior to it. In the neck it lies beneath the platysma and cer- vical fascia, and is usually separated from the external maxillary artery by the submaxillary gland and the stylo-hyoid and posterior belly of the digastric muscles, below which it is joined by the posterior facial, to form the common facial vein. Tributaries. — It receives, from above downward: — fa) the frontal vein; (b) the supraorbital vein; (c) the superior palpebral veins; (d) the external nasal veins; (e) the inferior palpebral veins; (f) the superior labial vein; (g) the inferior labial vein; (h) the masseteric veins; (i) the anterior parotid veins; (j) the pala- tine vein and (k) the submental vein. (a) The frontal vein [v. frontalis] (fig. 510) begins about the level of the coronal suture in a venous plexus which communicates with the anterior division of the temporal vein. Soon forming a single trunk, it passes vertically downward over the frontal bone, a short distance from the middle line and parallel to its feUow of the opposite side, to the medial end of the eye- brow where it terminates in the angular vein. (b) The supraorbital vein [v. supraorbitalis] begins over the frontal eminence by inter- communication with the middle temporal vein. It receives tributaries from the forehead and eyebrow, and, running obliquely, medially and downward, opens into the termination of the frontal vein to form the angular. It communicates with the ophthalmic vein, and receives the frontal vein of the diploe as the latter vein issues from the bone at the bottom of the supraorbital notch. (c) The superior palpebral veins [vv. palpebrales superiores] arise in the upper eyeMd and open into the lateral side of the angular vein. They communicate with the middle temporal vein. (d) The external nasal veins [vv. nasales externae] form three or four stems on either side. The upper veins run upward into the angular and the lower, from the ala, pass more hori- zontally into the anterior facial vein. (e) The inferior palpebral veins [vv. palpebrales inferiores] arise in the lower eyelid, and, passing medially and downward over the cheek from which they receive tributaries, open into the later.ll side of the anterior facial vein. They communicate with the infraorbital vein. (f) Tlie superior labial vein [v. labialis superior] and (g) the inferior labial vein [v. labialis inferior] arise from venous plexuses in the upper and lower lips. They run laterally to open into the medial side of the facial vein. (h) The masseteric veins [vv. masseterioae] and (i) the anterior parotid veins [vv. parotidae anteriores], of small size, drain the cheek over the masseteric and parotid regions. (j) The palatine vein [v. palatina] accompanies the ascending palatine or tonsillar artery from the venous plexus about the tonsil and soft palate, and joins the anterior facial vein just below the body of the mandible. (k) The submental vein [v. submentalis] lies on the mylo-hyoid muscle superficial to the submental artery. Running back in the submental triangle, it joins the anterior facial vein just after the latter has passed over the body of the mandible. It communicates with the anterior jugular vein. Communications. — The tributaries of the anterior facial vein comrnunicate freely with the anterior and middle temporal, ophthalmic, infraorbital and anterior jugular veins. The main trunk has a large communicating branch with the pterygoid plexus. This vein, some- times known as the deep facial, opens into the anterior facial Ijelow the zygomatic bone under cover of the zygomaticus muscle. B. The Posterior Facial Vein The posterior facial (temporo-maxillary) vein [v. facialis posterior] is formed in in the region of the root of the zygoma by the union of the superficial and middle temporal veins. It passes downward behind the ramus of the mandible POSTERIOR FACIAL VEIN 645 through the substance of the parotid gland— here lying lateral to the super- ficial temporal and external carotid arteries. At the angle of the mandible it runs medially and somewhat forward, and, passing either deep or superficial to the stylo-hyoid and digastric muscles, joins the anterior facial to form the common facial vein. The tributaries received by the posterior facial vein are: — (a) the superficial -The Veins of the Head, Neck, and Axilla. ^ (Aft^er Toldt, 'Atlas of Human Anatomy," Rebman, London and New York.) Frontal diploic veins Supraorbital vein Middle temporal vein Superficial temporal artery and vein Articular mandibular veins ^^^/ Posterior facial veins External nasal veins Angular vein Anterior facial vein Submental vein Occipital artery and Hypoglossal nerve ''^ and venee comitans Superior thyreoid artery and vein \ Superior laryngeal , artery and vein Circumflex hum- / Anterior \ 15, ' 1 Posterior \ v;' Circumflex scapular Lateral thoracic artery and vein temporal veins; (b) the middle temporal vein; (c) the transverse facial vein; (d) the articular veins; fe) the posterior parotid veins; (f) the anterior auricular veins; (g) the stylo-mastoid vein; and (h) the internal maxillary vein through which occurs the principal drainage of the pterygoid plexus. 646 THE BLOOD-VASCULAR SYSTEM _ (a) The superficial temporal vein [v. temporalis superficialis] returns the blood from the parietal region of the scalp. It is formed by the union of an anterior and a posterior branch: theformer communicates with the supraorbital and frontal veins; the latter with the posterior auricular and occipital veins and the temporal vein of the opposite side. These branches lie superficial to the corresponding branches of the superficial temporal artery, which they roughly though not accurately follow. Like the artery, they lie between the skin and the cranial aponeurosis, and descend over the temporal fascia to unite a Uttle above the zygoma, and just in front of the auricle of the ear, to form the superficial temporal trunk. The vein thus formed continues its course downward with the trunk of the temporal artery, and opposite the zygoma is joined by the middle temporal vein to form the common temporal vein. (b) The middle temporal vein [v. temporaUs media] corresponds with the orbital branch of the temporal arterj', and communicates in front with the ophthalmic vein, the external palpebral veins, and the infraorbital veins, and then runs backward between the layers of the temporal fascia to join the superficial temporal vein. The middle temporal vein communicates with the deep temporal veins, and through them with the pterygoid venous plexus. (c) The transverse facial vein [v. transversa faciei] corresponds to the transverse facial artery, (d) Articular veins [vv. articulares mandibute] form the plexus around the temporo- mandibular joint; this plexus receives the tympanic veins [w. tympanicae), which, together with its corresponding artery, passes through the petrotympanic fissure, (e) Posterior parotid veins [w. parotidese posteriores] emerge from the substance of the parotid gland, (f) Anterior auricular veins [w. auriculares anteriores], from the auricle of the ear. (g) Stylo-mastoid vein [v. stylomastoidea] from the facial canal, (h) The internal maxallary vein accompanies the first part of the internal maxillary artery. It begins at the posterior confluence of the veins forming the pterygoid plexus, and passes backward between the stylo-mandibular ligament and the neck of the mandible. It ends by joining the posterior facial vein. The pterygoid plexus [plexus pterygoideus] is formed by the veins which correspond to the branches of the internal maxillary artery. It is situated, partly on the medial surface of the internal pterygoid muscle, and partly around the external pterygoid muscle. The veins entering into this plexus are: — the two middle meningeal veins [w. meningeae mediae], which accompany the artery of that name; the posterior superior alveolar (dental); the inferior alveolar (dental); the masseteric; the buccal; the pterygoid veins from the pterygoid muscles; the deep temporal veins [vv. temporales profundae], by which the plexus communicates with the temporal plexus; the spheno -palatine vein; the infraorbital; the superior palatine; a branch of commu- nication with the lower branch of the ophthalmic vein, which courses through the inferior orbital (spheno-maxillary) fissure; and the rete foraminis ovalis and Vesalian vein, through which the plexus communicates with the cavernous sinus. The plexus ends posteriorly in the internal maxillary vein, which joins the posterior facial vein, and anteriorly in a com- municating vessel (the deep facial vein), which passes forward and downward between the buccinator and masseter muscles to join the anterior facial vein. The above-mentioned veins, forming by their confluence the pterygoid plexus, correspond in then- course so nearly with that of their companion arteries that a detaOed description is not necessary. Although for convenience described with the superficial veins, they are all deeply placed. Near the angle of the mandible there is almost always a communicating branch between the posterior facial and the external jugular veins. When large, this branch may drain the greater part of the blood from the posterior facial. C. The Common Facial Vein The common facial vein [v. facialis communis] is a short thick stem contained within the carotid triangle. It is formed, just below the angle of the mandible, by the union of the anterior and posterior facial veins. It ends opposite the hyoid bone, by opening into the internal jugular vein. In addition to the vessels which form it, sometimes it receives the superior thyreoid, the pharyngeal, and the lin- gual or the subHngual veins. D. The External Jugular Vein The external jugular vein [v. jugularis externa] (fig. 510) is formed by the con- fluence of the posterior auricular and a short communicating trunlc from the posterior facial near the angle of the mandible. It runs obliquely downward and backward across the sterno-mastoid muscle to a point opposite the middle of the clavicle, where it terminates as a rule in the subclavian vein. A line drawn from a point midway between the mastoid process and angle of the jaw to the middle of the clavicle will indicate its course. It is covered by the skin, superficial fascia, and platysma, and is crossed by a few branches of the cervical plexus, the great auricular nerve running parallel to it at the upper part of the neck. It is separated from the sterno-mastoid by the anterior layer of the deep cervical fascia. Just above the clavicle it perforates the cervical fascia, by which it is prevented from readily collapsing, the fascia being attached to its walls. It then opens into the subclavian vein, oc- casionally into the internal jugular, or into the confluence of the subclavian and internal jugular THE EXTERNAL JUGULAR VEIN 647 veins. It contains a pair of valves about 2.5 to 5 cm. (1 to 2 in.) above the clavicle, and a Becond'pair where it enters the subclavian vein. Neither of these valves is sufficient to prevent the blood from regurgitating, or injections from passing from the larger vein into the external jugular. Tributaries and communications. — These include; — (a) The posterior auricular vein; (b) the occipital vein; (c) a branch of communication with the posterior fa- cial vein; (d) the posterior external jugular vein; (e) the transverse scapular vein; and (f) the anterior jugular vein. (a) The posterior auricular vein [v. auricularis posterior] begins in a venous plexus on the posterior part of the parietal bone. This plexus communicates with the vein of the opposite side across the sagittal suture, and with the posterior branch of the superficial temporal vein in front, and with the occipital vein behind. It descends over the back part of the parietal bone and the mastoid process of the temporal bone, lying with its artery behind the ear, and joins a branch from the posterior facial vein to form the external jugular. Fig. 512. — The Veins of the Face. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Deep temporal veins Infraorbital artery and i Lateral lacuna of the superior sagittal sinus Sphenoparietal sinus Middle temporal vein Articular man- dibular veins Superficial temporal art* ry Pterygoid pi. Internal maxillary arter> Inferior alveolar nerve Posterior facial vein ^ Inferior alveolar artery and vein Jugular Common facial vein (6) The occipital vein [v. occipitalis] begins at the back of the skuU in a venous plexus which anastomoses with the posterior auricular and the posterior branch of the superficial temporal veins. It passes downward over the occipital bone, and usually perforates the trapezius with the occipital artery, to join a plexus drained by the deep crevical and vertebral veins. It also communicates with the posterior auricular, and in many cases this forms the chief path of drainage. One of its branches, usually the most lateral, receives a mastoid em- issary vein [emissarium mastoideum] which issues through the mastoid foramen of the tem- poral bone, and in this way forms a communication with the transverse sinus. (c) The branch of communication with the posterior facial vein occurs a short distance below the point at which the posterior facial receives the internal maxillary vein. It is very constant and is placed immediately behind the angle of the mandible. Through it the external jugular 648 THE BLOOD-VASCULAR SYSTEM usually receives a considerable proportion of the blood returning from the temporal and ptery- goid regions. (d) The posterior external jugular vein (fig. 512) descends from the upper and back part of the neck, receiving small tributaries from the superficial structures and muscles. At times it communicates with the occipital, or may appear as a continuation of that vein. It opens into the external jugular as the latter vein is leaving the sterno-mastoid muscle. (e) The transverse scapular vein [v. transversa scapulae] corresponds to the transverse scapular (suprascapular) artery. If double, these venae comitantes usually form one trunk before they open into the external jugular vein. They contain well-marked valves. (/) The anterior jugular vein [v. jugularis anterior] begins below the chin by communicating with the mental, submental, inferior labial, and inferior hyoid veins. It descends a little lateral to the middle line, receiving branches from the superficial structures at the front and side of the neck, and occasionally a branch from the larynx and thyreoid body. Just above the clavicle it turns laterally, and, piercing the fascia, passes beneath the sterno-mastoid muscle and opens into the external jugular vein just before the latter joins the subclavian; at times it opens into the subclavian vein itself. In its course down the neck it communicates with the external jugular; and, as it turns laterally beneath the sterno-mastoid, sends a branch across the trachea, between the layers of cervical fascia, to join the anterior jugular of the opposite side. This communicating vein, the jugular venous arch [arcus venosus juguli], may open directly into the external jugular or into the internal jugular vein; occasionally one or both ends may open into the subclavian or innominate vein. It may be divided in the operation of tracheotomy, and is then often found greatly engorged with blood. Another branch, often of considerable size, courses along the anterior margin of the sterno-mastoid and joins the anterior facial vein. When the anterior jugular vein is large, the external jugular is small, and vice versa. It is usually also of large size when the corresponding vein on the opposite side is absent, as is frequently the case. It contains no valves. THE DEEP VEINS OF THE HEAD AND NECK The deep veins of the head and neck may be divided into: — (1) the veins of the diploe; (2) the venous sinuses of the dura mater encephah; (3) the veins of the brain; (4) the veins of the nasal cavities; (5) the veins of the ear; (6) the veins of the orbit; (7) the veins of the pharynx and larynx; and (8) the deep veins of the neck. The veins of the diploe terminate partly in the superficial veins already described, partly in the venous sinuses of the cranium, and partly in the deep veins of the neck. The venous sinuses open into the deep veins of the neck. The veins of the brain terminate in the venous sinuses. The veins of the nasal cavities terminate partly in the deep, and to some extent in the superficial veins. The veins of the ear join both the superficial and deep veins and the venous sinuses. The veins of the orbit terminate partly in the superficial veins, but chiefly in the venous sinuses. The veins of the pharynx and larynx enter the deep veins of the neck. 1. THE VEINS OF THE DIPLOE The veins of the diploe [venae diploicse] (fig. 513) are contained in bony chan- nels in the cancellous tissue between the external and internal laminae of the skull. They are of comparatively large size, with very thin and imperfect walls, and form numerous irregular communicating channels. They have no valves. They ter- minate in four or five main and descending channels, which open, some outward through the external cranial lamina into some of the superficial and deep veins of the head and face, and some inward through the internal lamina into the venous sinuses. They are divided into the frontal, anterior temporal, posterior temporal, and occipital. The frontal diploic veins are contained in the anterior part of the frontal bone. They converge anteriorly to a single vein [v. diploica frontalis] which passes downward, perforates the external table through a small aperture in the roof of the supraorbital notch, and terminates in the supraorbital vein. They also communicate with the superior sagittal sinus. The anterior temporal [v. diploica temporahs ant.] are contained in the posterior part of the frontal and in the anterior part of the parietal bone. They pass downward, and end, partly in the deep temporal veins by perforating the greater wing of the sphenoid bone, and partly in the spheno-parietal sinus. The posterior temporal [v. diploica temporalis post.] ramifies in the parietal bone, and, coursing downward to the posterior inferior angle of that bone, passes either through a foramen in its inner table, or through the mastoid foramen into the transverse sinus. The occipital [v. diploica occipitalis] ramifies chiefly in the occipital bone, and opens into the occipital vein or into the transverse sinus. The diploic veins freely anastomose with one another in the adult; but in the foetus, before the bones have united, each system of veins is distinct. VENOUS SINUS OF THE DURA MATER 649 2. THE VENOUS SINUSES OF THE DURA MATER The venous sinuses of the dura mater [sinus durse matris] are endothelially lined blood-spaces, situated between the periosteal and meningeal layers of the dura mater. They are the channels by which the blood is conve3red from the cerebral veins, and from some of the veins of the meninges and diploe, into the veins of the neck. The sinuses at the base of the skull also carry the chief part of the blood from the orbit and eyeball to the jugular veins. At certain spots the sinuses communicate with the superficial veins by small vessels known as the emis- sary veins, which run through foramina in the cranial bones. The venous sinuses are sixteen in number, six being median and unpaired, the remaining ten consisting of five lateral pairs. The median sinuses are: — (1) the superior sagittal; (2) the inferior sagittal; (.3) the straight; (4) the occipital; (5) the circular; and (6) the basilar plexus. The lateral and paired sinuses are: — • (7) the two transverse; (8) the two superior petrosal; (9) the two inferior petro- sal; (10) the two cavernous; and (11) the two spheno-parietal. Occasionally there are two additional sinuses, the two petro-squamous. (1) The superior sagittal (or longitudinal) sinus [sinus sagittalis superior] (fig. 515) lies in the median groove on the inner surface of the cranium along the attached margin of the falx cerebri. It extends from the foramen caecum to the Fig. 513. — The Veins op the Diploe. (From a specimen in St. Bartholomew's Hospital Museum.) The occipital diploic vein The posterior temporal diploic internal occipital protuberance. It grooves from before backward the frontal bone, the contiguous sagittal margins of the parietal bones, and the squamous por- tion of the occipital bone In the foetus, and occasionally in the adult, it commu- nicates (through the foramen caecum) with the nasal veins. It communicates throughout life with each superficial temporal vein by means of a parietal emis- sary vein [emissarium parietale] which passes through the parietal fora- man. It is triangular on section, the base of the triangle corresponding "to the bone. Crossing it are a number of fibrous bands known as the chords of Willis, and projecting into it in places are the arachnoidal (Pacchionian) granulations. The parts of the sinus into which the arachnoidal granulations project are irregu- lar lateral diverticula from the main channel known as the lacimce laterales ffig. 517). In front the sinus is quite small, but it increases greatly in calibre as it runs backward. It receives at intervals the superior cortical cerebral veins and the veins from the falx. The former, for the most part, open into it in the direc- tion opposite to that in which the blood is flowing in the sinus. They pass for some distance in the walls of the sinus before opening into it. Posteriorly, at the internal occipital protuberance, the superior sagittal sinus usually turns sharply to 650 THE BLOOD-VASCULAR SYSTEM the right, and ends in the right transverse (lateral) sinus; the straight sinus then usually terminates in the left transverse (lateral) sinus. Occasionally, however, the superior sagittal sinus ends in the left transverse sinus, the straight then passing into the right. At the angle of union between the superior sagittal sinus and the transverse sinus into which it empties there is a dilation, the confluens sinuum or torcular Herophih. At this point there is a communication between the right and left trans- verse sinuses. In some cases the communication is so free that the blood from the sagittal sinus flows almost equally into each transverse sinus. The confiuens may communicate with the occipital vein through the occipital emissary vein [emissarium occipitale], which, when present passes through a minute foramen in the occipital protuberance. (2) The inferior sagittal (or longitudinal) sinus [sinus sagittalis inferior] (fig. 515) is situated at the free margin of the falx cerebri. Beginning about the junction of the anterior with the middle third of the falx, it is continued backward along the concave or lower margin of that process to the junction of the falx with the tentorium, where it ends in the straight sinus. The sinus is cylindrical in Fig. 514. — The Venous Sinuses. (From a dissection by W. J. Walsham in St. Bartholomew's Hospital Museum.) Meningeal branch of pos- terior ethmoidal aitery Middle meningeal artery Ophthalmic division of trigeminus Oculomotor nerve Cavernous sinus Trochlear nerve Auditory & facial nerve! Superior petrosal sinus Inferior petrosal sinus Petro-squamous sinus Spinal accessory nerve Sigmoid portion of transverse sinus Posterior meningeal branch of vertebral artery Left marginal sinus '\f'iV\ — Circular sinus Left transverse sinus Superior sagittal sinus Carotid artery -Abducens nerve Basilar artery Basilar plexus of veins Auditory artery Vertebral artery — Glosso - pharyngeal —J and vagus nerves I' / Anterior spinal , artery /_ Hypoglossal nerve / Spinal accessory nerve Right marginal sinus Occipital sinus Right transverse sinus shape and of small size, and receives some of the inferior frontal veins of the brain, some of the veins from the medial surface of the brain, and some of the veins of the falx. . (3) The straight sinus [sinus rectus] lies along the junction of the falx cerebri with the tentorium cerebelli. It is formed by the union of the great cerebral vein (of Galen) and the inferior sagittal sinus. It receives in its course branches from the tentorium cerebelh and from the upper surface of the cerebellum. _ It runs downward and backward to the internal occipital protuberance, where it ends in the transverse sinus opposite to that joined by the superior sagittal sinus. On section it is triangular in shape, with its apex upward. (4) The occipital sinus [sinus occipitaHs] (fig. 514) ascends at the attached margin of the falx cerebelli, along the lower half of the squamous portion of the occipital bone from near the posterior margin of the foramen magnum to the internal occipital protuberance. It usually begins in a right and a left branch, known as the marginal sinuses. These proceed from the termination of each VENOUS SINUSES OF THE DURA MATER 651 transverse sinus, run around the foramen magnum, where they communicate with the venous vertebral retia, and unite at a variable distance from the internal oc- cipital protuberance to form the single occipital sinus. Sometimes they re- main separate as far as the occipital protuberance, then forming two occipital sinuses. One of the two marginal sinuses may be much smaller than the other, or be entirely absent. At the point where the marginal sinuses unite to form the single occipital sinus, there is a communication with the venous vertebral retia. The occipital sinus ends in the confluens sinuum. It receives in its course veins from the tentorium cerebelli, and from the inferior surface of the cerebellum. It communicates through the plexus of veins which surrounds the hypoglossal nerve [rete canalis hypoglossi] in the hypoglossal (anterior condyloid) canal with the vertebral vein and the longitudinal vertebral venous sinuses. (5) The circular sinus [sinus circularis] (fig. 516) encircles the hypophysis cerebri. It consists of the two cavernous sinuses and their communications across Fig. 515. — The Venous Sinuses. (Longitudinal section.) Abducens. aerve Oculomotor nerve Superior sagit- Vein of Galen Middle meningeal artery Internal carotid artery Superior petrosal sinus Fabr cerebell Facial and auditory nerves Glossopharyngeal, vagus and accessory Hypoglosaal Second cervical nerve Ligamentum denticulatum petrosal sinus the median line by means of the anterior and posterior intercavernous sinuses. The intercavernous sinuses are small and cross the median line in front of and behind the hypophysis, respectively. (6) The basilar plexus [plexus basilaris] is a venous plexus in the substance of the dura mater over the basilar part of the occipital bone. It extends from the cavernous sinus to the margin of the foramen magnum below. It communi- cates laterally with the inferior petrosal sinus, and inferiorly with the internal vertebral venous plexuses. One of the larger of the irregular venous channels forming the plexus passes transversely from one inferior petrosal sinus to the other. This venous plexus is serially homologous with the longitudinal vertebral venous sinuses on the posterior surfaces of the bodies of the vertebrae. (7) The transverse (or lateral) sinus [sinus transversus] (figs. 514, 516) extends from the internal occipital protuberance to the jugular foramen. In this course it lies in the groove (which has been named after it) along the squamous portion of the occipital bone, the posterior inferior angle of the parietal bone, the mastoid portion of the temporal bone, and the jugular process of the occipital bone. It at first runs laterally and forward horizontally between the two layers of the tentorium cerebelli, following the curve of the groove on the occipital and on the mastoid angle of the parietal bone. On reaching the groove in the mas- 652 THE BLOOD-VASCULAR SYSTEM 1. toid portion of the temporal bone it leaves the tentorium and curves medially |/ and downward and then forward over the jugular process of the occipital bone, and ends in the posterior compartment of the jugular fossa in the superior bulb of the internal jugular vein. The S-shaped part of the sinus which hes on the mas- toid portion of the temporal and jugular portion of the occipital bone is sometimes known as the sigmoid sinus. The transverse sinus receives the internal auditory veins [vv. auditivse internfe] from the labyrinth, which emerge from the internal auditory meatus. It also receives veins from the temporal lobe of the cerebrum, some of the superior and inferior cerebellar veins, some of the veins of the medulla and pons, the occipital, and the posterior temporal and occipital veins of the diploe. At the point where it leaves the tentorium it drains the superior petrosal sinus and, when present, the petro-squamous sinus. It communicates with the occip- ital and vertebral veins through the mastoid and posterior condyloid foramina by means of the mastoid and condyloid emissary veins. As the transverse sinus lies between the layers of the tentorium it is on section prismatic in shape. The sigmoid portion is semicylindrical. The right transverse sinus is usually the larger and the direct continuation of the superior sagittal sinus, and hence conveys the chief part of the blood from the cortical surface of the brain and vault of the skull. The left transverse sinus is usually the smaller and the direct con- tinuation of the straight sinus, and hence returns the chief part of the blood from the central ganglia of the brain. The right and left sinuses communicate opposite the internal occipital protuberance. The relation of the lateral sinus to the outside of the skuU, especially to the mastoid process of the temporal bone, is of importance with reference to the operations of trephining the mastoid cells, opening the tympanum, and exposing the sinus itself, in septic thrombosis, etc. The course of the sinus corresponds to a hne drawn from the external occipital protuberance to the base of the mastoid process, or to the asterion, and thence over the back of the mastoid process in a curved line toward its apex. (8) The superior petrosal sinus [sinus petrosus superior] (figs. 514, 515) runs at the attached margin of the tentorium cerebelli, along the upper border of the petrous portion of the temporal bone. It connects the cavernous with the transverse sinus. Leaving the lateral and back part of the cavernous sinus just below the fourth nerve, it crosses the fifth nerve, and, after grooving the petrous bone, ends in the transverse sinus as the latter turns downward on the mastoid portion of the temporal bone. It receives veins from the temporal lobe of the cerebrum, veins from the cerebellum, veins from the tympanum through the squamo-petrosal fissure, and sometimes the anterior temporal veins of the diploe. (9) The inferior petrosal sinus [sinus petrosus inferior] (figs. 514, 516) runs along the line of the petro-occipital suture, and connects the cavernous sinus with the commencement of the internal jugular vein. It is shorter than the superior petrosal, but considerably wider. As it crosses the anterior compartment of the jugular foramen, it separates the glosso-pharyngeal from the vagus and accessory nerves. It receives veins from the inferior surface of the cerebellum, from the medulla and pons, and from the internal ear. The last, the vein of the cochlear canaliculus [v. canaliculi cochleae], issues through the canaliculus cochleae. (10) The cavernous sinus [sinus cavernosus] (fig. 516) is an irregularly shaped venous space situated between the meningeal and periosteal layers of the dura mater on the side of the body of the sphenoid bone. It extends from the medial end of the superior orbital (sphenoidal) fissure in front to the apex of the petrous bone behind. Its lateral wall is the more distinct, and contains the third and fourth nerves, and the ophthalmic division of the fifth nerve. The nerves take the above-mentioned order from above downward, and in the medio-lateral direc- tion. The internal carotid artery and the sixth nerve also pass through the sinus, being separated from the blood by the endothelial lining. The right and left cavernous sinuses communicate across the middle line with the opposite sinus in front and behind the hypophysis cerebri as before mentioned. The cavernous sinus is traversed by numerous trabeculae or fibrous bands, so that there is no central space, but rather a number of endotheUal-lined irregular lacunar cavities commu- nicating one another. Hence its name cavernous, from its resemblance to cavernous tissue. In front it receives the ophthalmic vein, with which it is practically continuous, and just above the third nerve the spheno-parietal sinus. Medially it communicates with the opposite sinus, and posteriorly it ends in the superior and inferior petrosal sinuses. It also receives veins from the inferior surface of the frontal lobe of the brain, and some of the middle cerebral veins. Through the Vesahan vein, which runs in a minute foramen in the spinous process of THE VEINS OF THE BRAIN 653 the sphenoid bone, the sinus communicates with the pterygoid plexus of veins; through the venous plexus around the petrosal portion of the internal carotid [plexus venosus caroticus internus], with the internal jugular vein; and through a venous rete which leaves the cranium by the foramen ovale [rete foraminis ovalis] and by small veins passing through the foramen lacerum medium, with the pterygoid and pharyngeal plexuses. (11) The spheno-parietal sinus [sinus sphenoparietalis] runs in a slight groove on the under surface of the lesser wing of the sphenoid bone. It originates in one of the meningeal veins near the apex of the lesser wang, and, running roedially, passes through the sphenoidal fold of dura mater above the third nerve into the front part of the cavernous sinus. It generally receives the anterior temporal veins from the diploe. ( Fig. 516. — The Venous Sinttses at the Base of the Brain. The dura mater has not been removed. (After Toldt, ''Atlas of Human Anatomy," Rebman, London and New York,) Position of crista gall: Circular sinus \ Circular sinus \ Process of dura in foramen cEecum Eyeball Ophthalmic vein Connection the rete foraminis ovalis Middle meningea: artery Internal carotid _ artery Superior T>ulb of the __ internal jugular vein Transverse sinus Mastoid vein Vertebral artery ._- Maxillary nerve -^ V^ ~ Facial nerve ■"Acoustic nerve Vagus nerve Accessory nerve Fold of dura mater Hypoglossal nerve First spinal nerve The petro-squamous sinus is occasionally present. It hes in a groove along the junction of the petrous and squamous portions of the temporal bone. It opens posteriorly into the trans- verse sinus at the spot where the latter enters on its sigmoid course. In front it sometimes, though very rarely, passes through a foramen in the squamous portion of the temporal bone between the mandibular fossa and the external auditory meatus into the temporal vein. 3. THE VEINS OF^THE BRAIN The veins of the brain present the following peculiarities: — (a) They do not accompany the cerebral arteries, (h) Ascending veins do not, as in other situ- ations, run with descending arteries, but with ascending arteries, and vice versa. (c) The deep veins do not freely communicate, {d) The veins have very thin walls, no muscular coat, and no valves, ie) The veins opening into the sagittal, and some of those opening into the transverse (lateral) sinus pour in their blood in a direction opposite to the current in the sinuses, so impeding the flow in both 654 THE BLOOD-VASCULAR SYSTEM vein and sinus. (/) The flow of blood in the sinuses is further retarded by the trabeculfe stretching across their lumen, and in the sagittal sinus by the blood having to ascend, when the body is erect, through the anterior half of its course. The veins of the brain may be divided into the cerebral and the cerebellar. Fig. 517.- -The Veins of the Brain, Superior Surface. (After Toldt, Anatomy," Rebman, London and New York.) 'Atlas of Human Superior sagittal sinus Lateral protrusion (lacuna) of superior sagittal sinus Un- \ jected) — Superior cerebral veins Lateral lacuna of su.* perior sagittal sinus (opened) Arachnoidal (Pacchionian) Lateral lacuna of superior sagit- (opened) Venous orifice The Cerebral Veins The cerebral veins, like the cerebral arteries, may be divided into the cortical and the central. The cortical or superficial veins ramify on the surface of the brain and return the blood from the cortical substance into the venous sinuses. The}^ lie for the most part in the sulci between the gyri, but some pass over the gyri from one sulcus to another. They consist of two sets : a superior and an inferior. (1) The superior cerebral veins [vente cerebri superiores] (fig. 517), some eight to twelve in number on each side, are formed by the union of branches from the convex and medial surfaces of the cerebrum. Those from the convex surface pass medially and forward toward the longitudinal fissure, where they are joined by the branches coming from the medial surface. After receiving a sheath from the arachnoid, they enter obliquely into the superior sagittal THE CEREBRAL VEINS 655 sinus, running for some distance in its walls. These veins freely communicate with each other, thus differing from the cortical arteries. They also communicate with the inferior cortical veins. They may be roughly divided into (a) frontal; (6) paracentral; (c) central; (d) occipital. (2) The inferior cerebral veins [venec cerebri inferiores] (fig. 518), ramify on the base of the hemisphere and the lower part of its lateral surface. Those on the inferior surface of the frontal lobe pass, in part into the inferior sagittal sinus, and in part into the cavernous sinus. Those on the temporal lobe enter in part into the superior petrosal sinus, and in part into the transverse sinus, passing into the latter from before backward. A large vein from the occipital lobe winds over the cerebral peduncle and joins the great cerebral vein (of Galen) just before the latter enters the straight sinus. One of the inferior cortical veins is called the middle cerebral vein [v. cerebri media] ; it runs in the lateral fissure (of Sylvius) and ends in the cavernous sinus. This vein is sometimes called the superficial Sylvian vein. Another, the great anasto- FiG. 518. — The Veins op t^e Brain, Inpehior Sttepace. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Roots of the superior cerebral veins Opening of the in- f e r i 0 r cerebral veins into the transverse sinus Inferior cerebellar veins Opening of the superior sagittal sinus -" into the right transverse sinus Inferior cere- ^/ bral veins Anterior external spinal ^ Opening of the straight sinus into the left transverse sinus Occipital sinus mosing vein of Trolard, a branch of the middle cerebral, estabhshes a communication between the superior sagittal and cavernous sinuses by anastomosing with one of the superior cortical veins. A second anastomotic vein, that of Labb6, is also a tributary of the middle cerebral, and connects the veins over the temporal lobe with the transverse sinus. A small inferior cerebral vein, the ophthalmomeningeal vein, estabhshes a communication between the cerebral veins and those of the orbit. It communicates with the veins of the base and is usually drained by the superior ophthalmic vein. It occasionally opens into the superior petrosal sinus. The central or deep (ganglionic) veins return blood from the internal parts of the cerebrum, and converge to the great cerebral vein. 656 THE BLOOD-VASCULAR SYSTEM Fig. 519. — The Veins of the Brain, Lateral Surface. (After Toldt, "Atlas of Human Anatomy/' London and New York.) Superior cerebral veins Dura mater Lateral lacuna of the superior ^ r__^ » sagittal sinus _ ^. ^y'7^^t0'^^mK~^ J^ Middle cerebral vein Transverse sinus Middle temporal vein External carotid artery Palatine vein Internal pterygoid muscle Posterior facial vein Internal carotid artery Hypoglossal nerve ' Internal jugular vein ^^^ ^f Internal maxillary artery &g?"**5^<^ Vena comitans of hypo- **-^ ■* glossal nerve Submaxillary duct External maxillary artery ;X ''^N^ Anterior facial vein Y \ 2»B Lingual artery Superior thyreoid vein Superior oph thalmic vein Inferior oph- thalmic vein Pterygoid plexus Temporal Fig. 520. — The Ophthalmic Veins. (After Quain.) Posterior ciliary vein Superior ophthalmic vein Supraorbital vein communicating with nasofrontal Frontal vein Lacrimal gland Maxillary sinus •Anterior facial vein THE VEINS OF THE EAR 657 (3) The internal cerebral veins [vv. cerebri internee] are two large venous trunks (the vense Galeni) which leave the brain at the transverse fissure, that is, between the splenium of the corpus callosum and the corpora quadrigemina. In this region they unite to form the great cerebral vein [v. cerebri magna, Galeni], which opens into the anterior end of the straight sinus. The internal cerebral veins are formed by the union of the chorioid vein with the vena terminalis near the interventricular foramen. From this spot they run backward parallel to each other, between the layers of the tela chorioidea, and terminate in the way above mentioned. Tributaries of the internal cerebral veins. — In addition to the vena terminalis and the chori- oidal, the internal cerebral veins also receive the basal vein, the veins of the thalmus, the vein of the chorioid plexus of the third ventricle, and veins from the corpus callosum, the pineal body, the corpora quadrigemina, and posterior horn of the lateral ventricle. The united trunk, or great cerebral vein, receives veins from the upper surface of the cerebellum, and one of the posterior inferior cerebral veins. The chorioid vein [v. chorioidea] runs with the chorioid plexus. It begins in the inferior cornu of the lateral ventricle, and ascends on the lateral side of the chorioid plexus along the margin of the tela chorioidea to the interventricular foramen, where it unites with the vena terminalis to form the internal cerebral vein. It receives tributaries from the hippocampus, corpus callosum, and fornix. The terminal vein (or vein of the corpus striatum) [v. terminalis], formed by veins from the corpus striatum and thalamus, runs forward in the groove between those structures, passing in its course beneath the stria terminalis, and joins the chorioid (choroid) vein at the inter- ventricular foramen. Tributaries. — It receives, in addition to the veins from the corpus striatum, thalamus and fornix, the vena septi pellucidi which receives blood from the septum peUucidum, and anterior cornu of the lateral ventricle. The basal vein [v. basalis], runs backward over the cerebral peduncle, and enters the internal cerebral vein near the union of that vessel with the vein of the opposite side. Tributaries. — A vein, the deep Sylvian, from the insula and surrounding convlutions; the inferior striate veins from the corpus striatum, which they leave through the anterior perforated substance; and the anterior cerebral veins from the front of the corpus callosum. It is also joined by interpenduncular veins from the structures in the interpeduncular space; ventricular veins from the inferior cornu of the lateral ventricle; and by mesencephalic veins from the mid-brain. The Cerebellar Veins The cerebellar veins are divided into the superior and inferior. The superior [vv. cerebeDi superiores] ramify on the upper surface of the cerebellum; some of them run medially over the superior vermis to join the straight sinus and great cerebral vein; others run laterally to the transverse and superior petrosal sinuses. The inferior [vv. cerebeUi inferiores], larger than the superior, run, some forward and laterally to the inferior petrosal and transverse sinuses, and others directly backward to the occipital sinus. The Veins of the Medulla and Pons The veins from the medulla oblongata and the pons terminate in the inferior petrosal and transverse sinuses. 4. THE VEINS OF THE NASAL CAVITIES The venous plexuses on the inferior nasal concha (turbinate bone) and back of the septum are described with the Nose. The veins leaving the nasal cavities follow roughly the course of their corresponding arteries. Thus the spheno- palatine veins pass through the spheno-palatine foramen into the pterygoid plexus; the anterior and posterior ethmoidal veins join the ophthalmic. Small veins accompany branches of the external maxillary artery through the nasal bones and frontal processes of the maxillary bones, and end in the angular and anterior facial veins; and other small veins pass from the nose anteriorly into the superior labial, and thence to the anterior facial. 5. THE VEINS OF THE EAR The veins from the external ear and external auditory meatus join the posterior facial and posterior auricular veins. The veins from the tympanum open into the superior petrosal sinus and posterior facial vein. The blood from the laby- rinth flows chiefly through the internal auditory veins [vv. auditivse internse], which lie with the internal auditory artery in the internal auditory meatus, and enters the transverse or inferior petrosal sinus. Some of the blood from the laby- rinth, however, passes through the vestibular vein which Hes in the aquseductus 658 THE BLOOD-VASCULAR SYSTEM vestibuli, into the inferior petrosal sinus. Some also passes through the vena canalicuU cochleae which traverses the canal of the same name and empties into the commencement of the internal jugular vein. 6. THE VEINS OF THE ORBIT The blood from the eyeball and orbit is returned by the superior ophthalmic vein into the cavernous sinus. This vein and its tributaries have no valves, and communicate with the frontal, supraorbital, inferior cerebral, and other veins. Hence under certain conditions, as from pressure on the cavernous sinus, the blood Fig. 521. — The Veins of the Orbit. Supraorbital artery Lacrimal gland Superior rectus, cut Eyeball Lateral rectus Lacrimal artery Superior rectus, cut Inferior ophthalmic vein Superior ophthalmic vein Optic nerve Superior ophthalmic ^ Commencement of superior H^l ophthalmic vein Reflected tendon of superior obUque Ophthalmic artery Anterior ethmoidal artery Posterior ethmoidal artery Ciliary arteries Levator palpebrae, cut Annulus communis of Zinn Ophthalmic artery Optic chiasma Internal carotid artery may flow in the contrary direction to the normal — i. e., from behind forward into the frontal and supraorbital, and thence through the angular vein into the anterior facial; or upward into the cerebral venous system. In this way pressure on the retinal veins is quickly relieved, and little or no distension occurs in cases of obstruction in the cavernous sinus. The superior ophthalmic vein [v. ophthalmica superior] begins at the medial angle of the eyelid by a free communication with the frontal, supraorbital, and angular veins, and thence runs backward and laterally with the ophthalmic artery across the optic nerve to the medial end of the superior orbital (sphenoidal) fissure, where it is usually joined by the inferior ophthalmic vein. It then passes backward between the two heads of the lateral rectus muscle below the sixth nerve, leaves the orbit through the medial end of the superior orbital (sphenoidal) fissure and enters the front part of the cavernous sinus. In this course it lies anterior and superficial to the ophthalmic artery. Tributaries. — (1) The naso-frontal vein; (2) the superior muscular veins; (3) the veins of the lids and conjunctiva; (4) the ciliary veins; (5) the anterior and posterior ethmoidal veins; (6) the lacrimal vein; (7) the central vein of the retina; and (8) the inferior ophthalmic vein. (1) The naso-frontal vein [v. naso-frontalis] begins by a free communication with the supra- orbital vein and enters the orbit through the frontal notch or foramen. It frequently joins the superior ophthalmic vein quite far back in the orbit (see fig. ,520). (2) The muscular veins [vv. musculares] are derived from the levator palpebrse, superior rectus, superior oblique, and medial rectus. (3) The palpebral and conjunctival veins [vv. palpebrales; vv. conjunctivales ant. et post.], both anterior and posterior, open into the superior ophthalmic. (4) The ciliary veins, the veins of the eyeball, are divided into two sets. An anterior [vv. cihares ant.] emerge from the eyeball with the anterior ciliary arteries, and open THE INTERNAL JUGULAR VEIN 659 into the muscular veins returning the blood from the four recti. They form a circumcorneal ring of episcleral veins [w. episclerales]. The posterior set, which drain the venae vorticosae, leave the globe midway between the cornea and the entrance of the optic nerve. The latter veins are four or five m number, the upper ending in the superior, the lower in the inferior ophthalmic vein (fig. 520). (5) The anterior and posterior ethmoidal veins [w. ethmoidales ant. et post.), correspond in their course with the arteries of the same name. They enter the orbit through the anterior and posterior ethmoidal foramina, and join either the ophthalmic direct, or one or other of the superior muscular branches. (6) The lacrimal vein [v. lacrimalis] retm-ns the blood from the lacrimal gland, and corre- sponds in its course to the lacrimal artery. (7) The central vein of the retina [v. centrahs retinse] runs with the central artery in the optic nerve. It joins the superior ophthalmic at the back of the orbit. (8) The inferior ophthalmic vein [v. ophthalmica inferior], smaller than the superior, is formed near the front of the orbit by the confluence of the inferior muscular with the lower posterior ciliary veins. It runs backward below the optic nerve, along the floor of the orbit, and either joins the superior ophthalmic vein, or opens separately into the cavernous sinus. A large communicating branch passes downward through the inferior orbital (spheno-maxillary) fissure to join the pterygoid plexus of veins. It receives muscular twigs from the inferior and lateral rectus and from the interior oblique, and some posteior ciliary veins. 7. THE VEINS OF THE PHARYNX AND LARYNX The pharyngeal veins [vv. pharyngeee] are arranged in the form of a plexus, between the constrictor muscles and the pharyngeal or prevertebral fascia. The pharyngeal plexus receives branches from the mucous membrane, the pterygoid canal [vv. canalis pterygoidei] from the soft palate, the Eustachian tube and the anterior recti and longus colli muscles. Above, it communicates with the ptery- goid plexus of veins; below it drains into the internal jugular vein. The veins of the larynx end partly in the superior laryngeal vein [v. laryngea superior], which opens into the internal jugular vein, and partly in the inferior laryngeal vein [v. laryngea inferior], which terminates in the plexus thyroideus impar. The laryngeal plexus of veins communicates with the pharyngeal plexus. 8. THE DEEP VEINS OF THE NECK The deep veins of the neck include the internal jugular, vertebral, deep cervical, erior thyreoid, thyreoidea ima, thymic, tracheal, and oesophageal veins. The Internal Jugular Vein The internal jugular vein [v. jugularis interna] begins at the jugular fossa, and is the continuation of the transverse sinus. It passes down the neck, in company first with the internal carotid artery and then with the common carotid artery, to a point a little lateral to the sterno-clavicular articulation, where it joins the subclavian to form the innominate vein. At its commencement in the larger, posterior and lateral part of the jugular foramen, it is somewhat dilated, forming the superior bulb of the jugular vein [bulbus v. jugularis superior] (fig. 522). This dilated part of the internal jugular vein lies in the jugular fossa of the temporal bone and is therefore in immediate relation to the floor of the tympanum. At first the internal jugular lies in front of the rectus capitis lateralis, and behind the internal carotid artery, from which it is separated by the hypoglossal, glosso- pharyngeal, and vagus nerves, and by the carotid plexus of the sympathetic. As it descends it passes gradually to the lateral side of the internal carotid, and re- tains this relation as far as the upper border of the thyreoid cartilage. Thence it runs to its termination along the lateral side of the common carotid artery, being contained in the same sheath with it and the vagus nerve, but separated from these structures by a distinct septum. The vein generally overlaps the artery in front. About 2.5 cm. (1 in.) above its termination it contains a pair of imperfect valves below which a second dilation usually occurs in the vein. This, the inferior bulb [bulbus v. jugularis inferior], extends as low as the junction of the internal jugular with the subclavian. It not infrequently receives the termination of the external jugular vein. Tributaries. — At the superior bulb the internal jugular vein receives the inferior petrosal sinus; the vein of the cochlear canaliculus, and a meningeal 660 THE BLOOD-VASCULAR SYSTEM vein; opposite the angle of the jaw, veins from the pharyngeal plexus, and often a communicating branch from the external jugular vein; opposite the bifurcation of the carotid it is joined by the common facial, and a little lower down by the lingual, sternomastoid, and the superior thyreoid veins. At the level of the cricoid cartilage by the middle thyreoid when this vein is present. The inferior petrosal sinus is described with the other sinuses of the brain (p. 652) ; the pharyngeal plexus with the veins of the pharynx (see p. 659) ; and the common facial vein with the superficial veins of the scalp and face (p. 646). The lingual vein [v. lingualis], begins near the tip of the tongue, where it accompanies the arteria profunda linguEe. It lies at first beneath the mucous membrane covering the under surface of the tongue. It then passes backward medial to the hyo-glossus, and in company with the lingual artery. After receiving the sublingual vein [v. sublingualis] and the dorsal Fig. 522. — The Internal Jugular Vein. (After Henle). Branches of the anterior facial vein Superficial temporal vein Styloglossus muscle Sublingual gland Hyoglossus muscle Geniohyoid muscli Sternohyoid muscle Thyreohyoid muscle Omohyoid muscle Temporal vein Stylopharyngeus Pterygoid plexus Superficial branches ^Styloglossus muscle ^Posterior facial vein Pharyngeal vein Stylohyoid muscle Anterior facial i Common facial vein Superior thyreoid vein Internal jugular vein lingual veins [w. dorsales linguae], which roughly correspond to their respective arteries, it is joined by the small v. comitans nervi hypoglossi which follows the upper border of the hypo- glossal nerve. The trunk finally crosses the common carotid artery and opens into the internal jugular vein. The lingual vein communicates with the pharyngeal veins and with tributariesof the anterior facial. It occasionally terminates in the posterior or in the common facial vein. The sternomastoid vein [v. sternocleidomastoidea] accompanies the artery of the same name and empties into the internal jugular. The superior thyreoid vein [v. thyreoidea superior] emerges from the upper part of the thyreoid gland, in which it freely anastomoses with the other thyreoid veins. This anas- tomosis, the plexus thyreoideus impar, occurs both in the substance of the organ and on its surface beneath the capsule. The vein then passes upward and laterally into the interna] jugular vein, crossing the common carotid artery in its course. At times it forms a common trunk with the common facial vein. Its tributaries are the sterno-hyoid, sterno-thyreoid, and thyreo-hyoid veins from the muscles bearing those names; and the crico-thyreoid and superior laryngeal veins which correspond with the crico-thyreoid and superior laryngeal arteries respectively. These require no special description. THYMIC, TRACHEAL AND (ESOPHAGEAL VEINS 661 A separate vein frequently passes out from the capsule of the thyreoid gland near the lower part of the lateral lobe, crosses the common carotid, and opens into the main superior thyreoid vein or into the internal jugular vein a little below the cricoid cartilage. In the former case it is regarded as part of the superior th3Teoid vein system ; in the latter it is generally known as the middle, thyreoid vein. The Vertebral Vein The vertebral vein [v. vertebralis] does not accompany the vertebral artery in its fourth stage, that is, within the skull, but begins in the posterior vertebral venous plexus of the suboccipital triangle. It then enters the foramen in the transverse process of the altas, and passes with the vertebral artery through the foramina in the transverse processes of the cervical vertebrae, forming a plexus around the artery. On leaving the transverse process of the sixth cervical verte- bra it crosses in front of the subclavian artery and opens into the innominate vein. It has one or two semilunar valves at its entrance into the innominate vein. In the suboccipital triangle it communicates with the internal vertebral venous plexuses, with the deep cervical, and occipital veins, and is joined by veins from the recti and oblique muscles and the pericranium. Tributaries. — -As it passes down the neck it receives (1) intervertebral veins, which issue along with the cervical nerves, from the spinal canal; (2) tributaries from the anterior and posterior vertebral venous plexus from the bodies of the cervical vertebrse and their transverse processes; and (3) tributaries from the deep cervical muscles. Just before it terminates in the innominate it is joined by (4) the anterior vertebral vein, a small vein which accompanies the ascending cervical artery, and, sometimes, by the deep cervical vein. The Deep Cervical Vein The deep cervical vein [v. cervicahs profunda], larger than the vertebral, passes down the neck posterior to the cervical transverse processes. It corre- sponds to the deep cervical artery from which it is separated by the semispinalis eervicis muscle. It begins in the posterior vertebral venous plexus and receives tributaries from the deep muscles of the neck. It communicates with, or enthely drains, the occipital vein by a branch which perforates the trapezius muscle. The deep cervical vein then passes forward beneath the transverse process of the seventh cervical vertebra to open into the innominate vein near the vertebral, or into the latter near its termination. Its orifice is guarded by a pair of valves. The Inferior Thyreoid and Thyreoidea Ima Veins The inferior thyreoid veins [vv. thyreoidea inferiores] descend from the lower part of the thyreoid gland obliquely lateralward to the innominate veins. The right vein crosses the innominate arteiy just before its bifurcation, and ends in the right innominate vein a little above the superior vena cava. It receives inferior laryngeal veins and veins from the trachea, and has valves at its termina- tion in the innominate. The left vein passes obliquely over the trachea behind the sterno-thyreoid muscle, and opens into the left innominate vein. It also receives laryngeal and tracheal veins, and sometimes the thyreoidea ima; it is guarded by valves where it opens into the innominate trunk. The thyreoidea ima vein [v. thyreoidea ima] is single and placed approximately in the median line. It begins in the thj'reoid isthmus from the plexus thyreoideus impar, runs downward upon the anterior surface of the trachea, and opens into the left innominate vein or into the left inferior thja-eoid. The Thymic, Tracheal and CEsophageal Veins These small veins usually open into the left innominate vein. The thymic veins [vv. thymicae], small in the adult, open into the left innominate or into the inferior thyreoid or thyreoidea ima vein. The tracheal veins [vv. tracheales] anastomose with the laryngeal and bronchial veins. The oesophageal veins [vv. cesophagese] from the upper part of the oesophagus, anastomose with the lower oesophageal veins and with the pharyngeal plexus. 662 THE BLOOD-VASCULAR SYSTEM THE VEINS OF THE THORAX THE SUPERFICIAL VEINS OF THE THORAX The superficial veins of the front of the thorax can be seen in fig. 537. They form a plexus over the entire chest which the portion over the mammary gland is called the mammary plexus. The laterally placed lateral thoracic and costo- axillary veins drain the mammary plexus and communicate with the thoraco- epigastric vein. These three veins terminate in the axillary vein (p. 671). The veins nearer the median line are drained by the internal mammary vein and its anterior intercostal and superior epigastric tributaries. The veins over the entire thorax are in free communication with the superficial veins of the abdominal wall (p. 683). THE DEEP VEINS OF THE THORAX The deep veins of the thorax are: — the pulmonary veins, and the vena cava superior and its innominate and other tributaries. Of these veins, the pulmonary, the vena cava superior, and the innominate veins have already been described, as have the tributaries of the latter arising in the neck. The following veins are described below: — (1) The azygos and ascending lumbar veins, which discharge their blood into the vena cava superior; (2) the veins of the vertebral column, which are tributary to the azygos veins through the intercostals; (3) the internal mammary veins, and (4) the superior phrenic, an- terior mediastinal and pericardiac veins, all of which open into the innominate veins. I. THE AZYGOS AND ASCENDING LUMBAR VEINS The azygos veins are longitudinal veins, the remnants of the posterior cardi- nals, which are the main collecting trunks for the posterior part of the body in the embryo. They lie along the sides of the thoracic vertebrae, and collect the blood from the intercostal veins; they are the upward continuation of longitudinal anastomotic trunks, the ascending lumbar veins which take origin in the abdomen. The azygos veins are three in number, the azygos (azygos major) on the right side, and the hemiazygos (azygos minor) and accessory hemiazygos (azygos tertia) on the left. The azygos vein [v. azygos] begins in the abdomen as a continuation .upward of the ascending lumbar vein. Through this means it connects with the iliac veins and it has also an anastomosis with the vena cava inferior which may become very important in cases of obstruction of the vena cava. It runs up through the pos- terior mediastinum on the right side of the front of the bodies of the thoracic vertebrte as high as the fourth thoracic vertebra, in this part of its course lying to the right of the aorta and thoracic duct; it then curves forward over the root of the right lung, and opens into the vena cava superior immediately before the latter pierces the pericardium. It usually contains an imperfect pair of valves at the point where it turns for- ward from the fourth thoracic vertebra to arch over the root of the lung; and still more imperfect valves are found at varying intervals lower down the vein. It receives the intercostal veins of the right side, except the first two or three. These veins (usually excepting the first) are collected into a common trunk before joining the azygos vein. It also receives the hemiazygos and accessory hemiazygos, the right posterior bronchial vein, and small oesophageal and pos- terior mediastinal veins. The hemiazygos vein [v. hemiazygos] begins in the abdomen by communicat- ing, like the azygos vein, with the ascending lumbar vein of its own side. It courses up the posterior mediastinum to the left of the bodies of the lower thoracic vertebrae as high as the eighth or ninth, where it turns obliquely to the right, and, crossing in front of the vertebral column behind the aorta and the oesophagus, opens into the vena azygos. In its course it crosses over three or four of the lower left intercostal arteries, and is covered by the pleura. AZYGOS AND ASCENDING LUMBAR VEINS 663 Tributaries. — (1) The lower four or five left intercostal veins; (2) the lower end of the accessory hemiazygos vein (sometimes); (3) small left mediastinal veins; and (4) the lower left oesophageal veins. The accessory hemiazygos [v. azygos accessorial varies considerably in size, position, and arrangement, and is often continuous with, or drained by, the left superior intercostal vein. It hes in the posterior mediastinum by the left side of the bodies of the fifth, sixth, and seventh or eighth thoracic vertebrae, and is more Fig. 523. — The Superior and Inferior Ven^ Cav.e, the Innominate Veins, \ND THE Azygos Veins Right common carotid .rtery Right internal jugular - Right lymphatic duct Innominate artery Right vagus nerve Right innominate vein Internal mammary vein Trunk of the pericardiac and thymic veins Vena cava superior Vena hemiazygos, cross- ing to enter vena azygos Hepatic veins Right inferior phrenic artery Coeliac artery iddle suprarenal artery Right Right spermatic vein Left common carotid artery Left vagus nerve Thoracic duct Left innominate vein Left subclavian artery Recurrent nerve Accessory hemiazygos CEsophagus Accessory hemiazygos vein (Esophageal branches from aorta Vena hemiazygos Thoracic duct Left inferior phrenic artery Left middle suprarenal artery Cisterna chyli Superior mesenteric artery Left ascending lumbar or less vertical in direction. It communicates above with the left superior in- tercostal vein, and below either joins the hemiazygos or passes obliquely across the seventh or eighth thoracic vertebra to join the azygos vein. It crosses the corresponding left intercostal arteries, and is covered by the pleura. Tributaries. — (1) The fourth, fifth, sixth, seventh, and sometimes the eighth intercostal veins; and (2) the left posterior bronchial vein. The ascending lumbar vein [v. lumbalis ascendens] begins, on either side, in the neighbourhood of the sacral promontory. It is here in free communication, by 664 • THE BLOOD-VASCULAR SYSTEM means of the anterior sacral plexus, with the middle and lateral sacral veins, and with the common iliac, hypogastric and ilio-lumbar veins. It ascends in front of the lumbar transverse processes communicating with the lumbar veins, the vena cava inferior and, usually, with the renal vein. The right vein enters the thorax between the aorta and the right medial crus of the diaphragm, and is continued upward as the vena azygos. The left vein pierces the left medial crus and becomes the hemiazygos. The intercostal veins [vv. intercostales]. — The intercostal veins are twelve in number on each side, the last one being subcostal. They correspond to the inter- costal arteries. There is one vein to each artery, the vein lying above the artery whilst in the intercostal space. Each vein receives a dorsal tributary which accompanies the posterior ramus of an intercostal artery between the transverse process of the vertebrae and the neck of the rib. These dorsal branches not only return the blood from the muscles of the back, but receive a spinal branch from the vertebral venous plexuses. The intercostal veins also receive small tributaries from the bodies of the vertebrae. The termination of the intercostal veins is different on the two sides and also varies greatly in different individuals. The intercostal vein from the first space on either side may join the superior inter- costal vein, but commonly opens directly into the innominate or one of its tribu- taries, most frequently the vertebral. On the right side. — The second intercostal vein joins with the third or with the third and fourth to form the right superior intercostal vein [v. intercostalis suprema dextra]. This vein opens into the azygos vein as the latter is arching over the root of the right lung. The rest join the azygos directly. The upper of these liave well-marked valves where they join the azygos vein; in the lower veins these valves are imperfect. All the intercostal veins are pro- vided with valves in their course between the muscles. On the left side the second intercostal vein joins the third and fourth to form a single trunk, the left superior intercostal vein [v. intercostalis suprema sinistra]. This vein passes upward across the arch of the aorta and opens into the left innominate vein. The left superior intercostal frequently communicates at its lower end with the accessory hemiazygos vein, which is occasionally tributary to it. In most oases a small tributary runs up over the front of the aortic arch to join the superior intercostal vein; it is a vestige of the left common cardinal and from it a small fibrous cord can often be traced through the vestigial fold of the pericardium to the oblique vein of the left atrium (p. 523). The left fifth, sixth and seventh intercostal veins commonly open into the accessory hemiazygos, and the eighth or ninth and succeeding veins into the hemiazygos. The method of termination of the intercostal veins of the left side is subject to such variation that a normal arrangement can scarcely be said to exist at all. The eighth may open directly into the azygos, as may the seventh and ninth or even more of the veins; the hemiazygos and accessory hemi- azygos being correspondingly reduced in size. The posterior bronchial veins [vv. bronchiales posteriores] correspond to the bronchial arteries, but do not return the whole of the blood carried to the lungs by those vessels — that part which is distributed to the smaller bronchial tubes and the alveola; being brought back by the pulmonary veins. The posterior bronchial veins issue from the lung substance behind the structures forming the root of the lung. The right vein generally joins the vena azygos just before the latter vein enters the superior vena cava. The left vein opens into accessory hemi- azygos vein. The bronchial veins at the root of the lung receive smaU tributaries from the bronchial glands, from the trachea, and from the posterior mediastinum. The oesophageal veins [vv. oesophagefe] from the thoracic portion of the oesophagus end in part in the vena azygos, and in part in the vena hemiazygos. They anastomose with the upper oesophageal veins, and with the coronary vein. The posterior mediastinal veins, small and numerous, open into the azygos and hemiazygos veins. 2. THE VEINS OF THE VERTEBRAL COLUMN The venous plexuses around and within the vertebral column extending from the cranium to the coccyx may be divided into two categories: — (1) the external and (2) the internal vertebral venous plexuses. The external plexuses consist of two parts, the anterior vertebral venous plexuses situated on the anterior aspect of the vertebral bodies and the posterior vertebral venous plexuses ramifying over the posterior aspect of the vertebral arches, spines, and transverse processes. The internal plexuses consist of two longitudinal venous sinuses situated between the vertebrae and the posterior longitudinal ligament, and of two vertebral venous retia placed immediately external to the dura mater. The sinuses of the internal plexuses communicate freely with one another and with the internal retia and external plexuses. They receive the external spinal veins and the basivertebral veins from the bodies of the vertebrae. The venous circulation of the vertebral VEINS OF THE VERTEBRAL COLUMN 665 column is drained by the vertebral, intercostal, lumbar and sacral veins either directly or by means of (3) the intervertebral veins. 1. The external vertebral venous plexuses [plexus venosi vertebrales externi] include the following : (a) The anterior vertebral venous plexuses [plexus venosi vertebrales anteriores] (fig. 524) consist of small veins ramifying in front of the bodies of the vertebrae. These veins com- municate with the basivertebral veins and are larger in the cervical region than elsewhere. (6) The posterior vertebral venous plexuses [plexus venosi vertebrales posteriores] (fig. 524) are situated around the transverse, articular, spinous processes and laminae of the vertebrae. Communications take place between the plexuses of each segment and with the veins of the neighbouring muscles and integuments. Branches are also sent, through the ligamenta flava, to the internal vertebral venous plexuses, and, between the transverse processes, to the inter- vertebral veins. 2. The internal vertebral venous plexuses [plexus venosi vertebrales interni] (fig. 524) : — (a) The two longitudinal vertebral sinuses [sinus vertebrales longitudinales] run through- out the entire length of the vertebral canal. They are situated behind the bodies of the vertebrae on either side, between the bone and the posterior longitudinal hgament. The sinuses have Fig. 524. — The Veins op the Vertebral Column. { Mammillary process Accessory process or tip of the true transverse process Costal elem Posterior transverse branch Ejrternal spinal veins Intervertebral vei Anterior transversi Lumbar vein Posterior vertebral plexus Basivertebral veins ertebral plexu extremely thin walls, and their interior is made irregular by numerous folds but no true valves are present. The calibre of the longitudinal sinuses is reduced by constrictions opposite the intervertebral discs; the consti'ictions alternating with dilatations opposite the vertebral bodies. At each dilatation there occurs a cross communication between the longitudinal sinuses of either side, and each receives a basivertebral vein from the corresponding vertebral body. Opposite every intervertebral foramen and anterior sacral foramen each longitudinal sinus is joined by the corresponding intervertebral vein. The longitudinal sinuses communicate very freely with one another, and with the vertebral retia. At the foramen magnum they communicate with the basilar plexus and, by means of the rate canalis hypoglossi, with the internal jugular vein. (6) The venous rete of the vertebrae [retia venosa vertebrarum] (fig. 524) extend from the foramen magnum to the coccyx. They consist of two main retia situated posteriorly and lateraOy to the dura between the latter and the vertebral arch. They communicate very freely with one another across the median line; with the posterior external plexus by means of twigs perforating the ligamenta flava; and with the longitudinal vertebral sinuses by means of lateral branches. At the foramen magnum they communicate with the occipital sinus. (c) The external spinal veins consist of two sets — anterior and posterior — which are drained by means of veins following the nerve roots, into the internal vertebral venous plexus. The anterior external spinal veins [w. spinales externa; anteriores] form a tortuous anas- tomosing vessel in the region of the anterior median fissure. The posterior external spinal ^•eins [vv. spinales externse posteriores], smaller than the an- terior run longitudinally on the posterior surface of the cord. The external spinal veins form a wide-meshed plexus in the pia mater which drains the internal spinal veins [vv. spinales internae] (see Spinal Cord). 666 THE BLOOD-VASCULAR SYSTEM {d) The basivertebral veins [vv. basivertebrales] (fig. 524) collect the blood from the cancellous tissue of the bodies of the vertebra;, and consist of a tunica intima only. They take a radial direction converging to the transverse vessels connecting the longitudinal vertebral sinuses. They communicate with the anterior external plexus and with the intercostal veins. 3 The intevertebral veins [vv. intervetebrales] (fig. 524), emerge from each longitudinal Fig. 525. — The Vertebral Venotts Plexuses. (After Henle.) Occipital vein Venous rete Dura mater spinalis sinus and pass out through the intervertebral or anterior sacral foramina. They open into the vertebral, intercostal, lumbar or sacral veins according to region and receive numerous tribu- taries from the anterior and posterior external vertebral venous plexuses. They are instru- mental in draining the venous system of the vertebral column and spinal cord. 3. THE INTERNAL MAMMARY VEIN The internal mammary vein [v. mammaria interna] is formed by the union of the vena3 comitantes corresponding to the superior epigastric and musculo-phrenic arteries. The right and left internal mammary veins pass upward, in company with the corresponding arteries, to open into the right and left innominate respectively. Tributaries. — In addition to the superficial veins of the thorax, the internal mammary veins receive the anterior intercostal, anterior bronchial and peri- cardiac veins. The superior epigastric vein [v. epigastrica superior] assists in the drainage of the subcu- taneous abdominal veins [vv. subcutanCEe abdominis]. The anterior bronchial veins [w. bronchiales anteriores] arise in the bronchial walls and communicate with the tracheal and posterior bronchial veins. THE VEINS OF THE UPPER EXTREMITY 667 4. THE SUPERIOR PHRENIC, ANTERIOR MEDIASTINAL, AND PERICARDIAC VEINS The superior phrenic [vv. phreniese superiores], the anterior mediastinal [w mediastinales anteriores], and pericardiac [w. pericardiacae] veins are small vessels, corresponding to the ar- teries of those names. They pass over the arch of the aorta and open into the lower and an- terior part of the left innominate. THE VEINS OF THE UPPER EXTREMITY The veins of the upper limb consist of two sets — a superficial and a deep. The superficial veins ramify in the subcutaneous tissue above the deep fascia, and they do not accompany arteries. The deep veins accompany the arteries, and have practically the same relations as those vessels. The superficial and deep veins communicate at frequent intervals through the intermuscular veins which run between the muscles and perforate the deep fascia. Both sets of veins are provided with valves, but the valves are more numerous in the deep than in the superficial. There are usually valves where the deep veins join the superficial. The superficial veins are larger than the deep, and take the greater share in returning the blood. I. THE SUPERFICIAL VEINS OF THE UPPER EXTREMITY The superficial veins begin in two irregular plexuses, one in the palm and the other on the back of the hand. The plexus in the palm is much finer, and com- municates with the superficial volar veins of the fingers. The latter discharge their blood into the dorsal venous rete by means of the veins of the folds between the fingers, or the intercapitular veins [vv. intercapitulares] (fig. 426). The veins of the back of the hand begin in a longitudinal plexus over the fingers, and at the bases of the fingers the veins of the adjacent digits are con- nected by digital venous arches [arcus venosi digitales], from which arise the dorsal metacarpal veins [vv. metacarpese dorsales]; these form upon the back of the hand a dorsal venous rete [rete venosum dorsale manus] (fig. 427). Of the veins of the arm, two stand out prominently, the basilic and the cephalic. Both of these arise from the veins of the back of the hand, curve around to the volar surface of the forearm, and pass to the upper arm (fig. 426). The basilic vein [v. basilica],* arises on the back of the hand from the ulnar end of the dorsal venous rete, which usually forms an arch. It curves around the ulnar side of the forearm to the volar surface and passes to the elbow and the upper arm, where it lies in the median bicipital sulcus. It extends up to about the middle third of the sulcus, and, piercing the brachial fascia, joins the brachial vein. The cephalic vein [v. cephalica],* begins at the radial end of the dorsal venous rete or arch and curves around the radial border of the forearm to the volar surface not far above the thumb. It passes to the elbow and the upper arm, but, unlike the basilic, it maintains its superficial course up to the shoulder, lying first in the lateral bicipital sulcus and then in the groove between the pec- toralis major and the deltoid. Just below the clavicle it turns into the depth, and empties into the axillary vein. In the forearm plexus one or more longitudinal veins besides these are usually distinct. One lateral to the cephalic is known as the accessory cephalic [v. cephalica accessoria] (formerly the radial) vein; one near the centre is known as the median antibrachial [v. mediana antibrachii], (formerly the anterior ulnar) vein. At the elbow there is usually an obhque connecting branch, the median cubital vein [v. mediana cubiti] (formerly termed median basilic) which extends *Tlie basilic vein here described corresponds to tlie posterior ulnar and basilic; the cephalic corresponds to the median, median cephalic and cephalic of the older terminology employed in English text-books. The BNA terminology has the gi-eat advantage that it can be readily used to desci'ibed any form of venous pattern. The English terminology applies only to cases in which the M-shaped arrangement occurs upon the volar surface of the elbow. Berry and Newton find the latter arrangement in only 13 per cent, out of 300 cases examined. 668 THE BLOOD-VASCULAR SYSTEM from the cephalic up to the basilic. In some cases this anastomosis is made by a division of the median antibrachial into two branches, a median cephalic and Fig. 526.- -The Superficial Veins of the Akm and Forearm. (After Toldt, "Atlas of Human Anatomy," Rebman, rondon and New York.) Cephalic / vein I Conaecting branches between the superfi- cial and deep veins Brachial fascia Accessory median cubital (var; Median cubital — .- Intercapitular veins Cephal: vein -Proper volar --^ digital Connec- veins tion with deep veins Accessory cephalic Antibrachial fascia > Basilic vein Note. — In the limb here represented the direct venous channel on the radial side of the forearm, the accessory cephalic (formerly radial) vein, is continued directly into the cephalic above the elbow. The cephalic in the forearm (formerly median) is mainly drained by the basilic through the median antecubital. The vein opposite the bend of the elbow, which usu- ally forms the segment of the cephalic formerly known as the median cephalic vein, is here a small channel draining into an accessory median cubital. The basilic vein of the forearm (formerly posterior ulnar) is represented by a plexus of small venous channels. SUPERFICIAL VEINS OF THE ARM 669 median basilic. Occasionally the cephalic in the upper arm is reduced to a small tributary, which takes the course of the cephalic in the forearm, but bends ulnar- ward at the elbow to form the basilic. Numerous connections occur between the deep and the superficial veins at the elbow. The superficial plexus of veins in the upper arm consists of small vessels that pass to the cephalic vein. Fig. 527. — Veins op the Back op the Forearm. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Cephalic vein — Accessory median cubital vein Median cubital vein Subcutaneous venous / network v. Accessory cephalic vein Basilic vein Dorsal venous rete . Digital venous arch 670 THE BLOOD-VASCULAR SYSTEM II. THE DEEP VEINS OF THE UPPER EXTREMITY The deep veins of the upper extremity accompany their corresponding arteries. There are two veins to each artery below the level of the axilla, known as the vense comitantes. The deep veins all contain numerous valves, and Fig. 528. — Deep Veins of the Ahm and Axilla. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Internal jugular vein Transverse scapular vein / Transverse cervical artery Axillary artery and vein \ m^^ / Transverse cervical vein Anterior circumflex humeral artery and vem \ ^.^^^H^^^^L * External jugular vein Subclavian vein Jugular venous arch Right innominate vein Posterior cir< umflex humeral artery and Circumflex scapular vem Biceps muscle Basilic vein Biceps muscle Brachial veins Ulnar nerve Dorsal thoracic artery and vein ^Median cubital vein L^^^^^Inferior ulnar collateral artery and vein . v^Connection of radial with superficial veins -Ulnar artery and veins Radial artery and veins communicate at frequent intervals through intermuscular veins with the super- ficial vessels. DEEP VEINS OF THE UPPER EXTREMITY 671 Beginning at the fingers, two minute proper volar digital veins [venae digitales volares proprise], accompany each digital artery along the sides of the fingers, and uniting at the cleft, form common volar digital veins [vv. digitales volares communes], which join the vense comitantes of the arteries, forming the super- ficial palmar arch. In like manner the veins accompanying the arteries forming the deep arch receive tributaries, the volar metacarpal veins [vv. metacarpese volares], corresponding to the branches of that arch. A superficial and a deep volar venous arch [ arcus volaris venosi superficialis et profundus] are thus formed accompanying the arterial arches. The venae comitantes from the ulnar side of the superficial and deep arches unite at the spot where the ulnar artery divides into the superficial and deep branch to form two ulniar venae comitantes [vv. ulnares] ; whilst those on the radial side of the superficial and deep arch accompan}^ the superficial volar artery and the termination of the radial artery respectively, and unite at the spot where the superficial volar is given off from the radial artery, to form the radial venae comitantes [vv. radiales]. The ulnar and radial venae comitantes thus formed course up the forearm with their respective arteries, receiving numerous tributaries from the muscles amongst which they run, and giving frequent communications to the superficial veins. They finally unite at the bend of the elbow to form the brachial venas comitantes [vv. brachiales]. The ulnar venae comitantes receive, before joining the radial, the companion veins of the interosseous arteries. At the bend of the elbow the deep veins are connected with the basilic or with the median antibrachial vein by a short, thick trunk (fig. 528). The brachial venae comitantes accompany the brachial artery. At the lower border of either the teres major or subscapularis muscle, the more medial vein receives the more lateral and the basilic vein, to form a single axillary vein. The venae comitantes of the arteries of the arm anastomose with one another by frequent cross branches. The axillary vein [v. axillaris], is formed by the junction of the medial brachial vena comitans with the basilic vein at the lower border of either the teres major or subscapularis muscle. It is a vessel of large size, conveying as it does nearly the whole of the returned blood from the upper extremity. It accompanies the axillary artery through the axillary fossa, lying to its medial side and, at the upper part of the space, on a slightly posterior plane. At the lateral border of the first rib it changes its name to the subclavian. It has one or two axillary lymphatic nodes in close connection with it, and is liable, if care is not taken, to be wounded in removing these glands. The vein contains a pair of valves, usually placed near the lower border of the subscapularis muscle. Tributaries : — (1) The subscapular veins which accompany the subscapular artery; (2) the circumflex veins accompanying the circumflex arteries; (3) the lateral thoracic vein [v. thoracalis lateralis] a large vein which accompanies the lateral thoracic artery and receives numerous thoraco-epigastric veins [vv. thoracoepigastricse] from the epigastric and lower thoracic regions; (4) the costo- axillary veins [vv. costoaxillares] the radicles of which arise in the pectoral region from the mammary plexus [plexus venosus mamillae] ; and (5) the cephalic vein. The subclavian vein [v. subclavii] (fig. 528), is the continuation of the axillary. It begins at the lateral border of the first rib, and terminates by joining the internal jugular to form the innominate vein opposite the lateral end of the sterno-clavicular articulation. It lies anterior to the subclavian artery and on a lower plane, and is separated from the artery in the second part of its course by the scalenus anterior muscle. The subclavian vein, just before it is joined by the external jugular, contains a pair of valves. Tributaries. — The subclavian vein receives the thoracoacromial vein near its distal end, and the external jugular vein near the lateral border of the sterno- mastoid muscle. The transverse cervical veins terminate in the subclavian near the external jugular, or in the latter vein, or in a plexiform arrangement formed between the transverse scapular, transverse cervical and external jugular veins. The external jugular vein is described with the superficial veins of the head and neck (p. 646). The thoracoacromial vein [v. thoracoacromiahs], receiving tributaries cor- responding to the branches of the artery of the same name, terminates near the lateral border of the first rib. 672 THE BLOOD-VASCULAR SYSTEM The transverse cervical veins [vv. transversae colli] receive tributaries cor- responding in distribution to the branches of the transverse cervical artery. They emerge from beneath the trapezius muscle, cross the posterior triangle, and usually terminate in the subclavian vein. They usually terminate as a single vein the orifice of which is guarded by a pair of valves. Occasionally the cephahc vein, or a branch from the cephalic (the jugulo-cephalic), passes over the clavicle to the subclavian. III. THE VENA CAVA INFERIOR AND ITS TRIBUTARIES All the veins of the abdomen, pelvis, and lower extremities, with the exception of the superior epigastric (p. 666), and ascending lumbar vein (p. 521), which join with the superior caval system, enter directly or indirectly into the vena cava inferior. The veins corresponding to the parietal branches of the abdominal aorta, except the middle sacral vein, open directly into the vena cava inferior; the middle sacral vein only indirectly through the left common iliac vein. Of the visceral veins corresponding to the visceral branches of the abdominal aorta, those which return the blood from the stomach, intestines, pancreas, and the spleen end in a common trunk called the portal vein. The portal vein [vena portae] enters the liver and there breaks up into a net- work of smaller vessels somewhat after the manner of an artery. This network contains venous blood, and is moulded upon the tissue-elements of the organ itself. The smaller vessels consist, like capillaries (from which they differ in developmental history) of intima only; they are called sinusoids. The venous blood is returned from the sinusoidal plexus by the hepatic veins which open into the vena cava inferior as that vessel lies in the fossa venae ca,v£e of the liver. Of the other visceral veins, both renals, the right suprarenal, and the right spermatic or ovarian open directly into the vena cava inferior; whilst the left suprarenal and left spermatic or ovarian are drained through the left renal. Two of the superficial veins of the lower part of the anterior abdominal wall, the superficial epigastric and superficial circumflex iliac, enter the great saphenous vein; and two of the deep veins from the like situation, the inferior epigastric and deep circumflex iliac, enter the external iliac vein. The blood in these vessels, however, can flow upward as well as in the normally downward direction. In obstruction of the vena cava inferior they become greatly enlarged, and form, with the superior epigastric vein and with other superficial veins of the thorax with which they anastomose, one of the chief channels for the return of the blood from the lower limbs. The veins of the pelvis, which receive the veins from the perinseum and gluteal region, join the hypogastric vein. THE VENA CAVA INFERIOR The vena cava inferior (fig. 529) is the large vessel which returns the blood from the lower extremities and the abdomen and pelvis. It is formed by the con- fluence of the right and left common iliac veins opposite the body of the fifth lumbar vertebra, ascends in front of the lumbar vertebrae to the right of the ab- dominal aorta, passes through the caval opening in the diaphragm, and ends in the lower and back part of the right atrium of the heart on a level with the lower border of the ninth thoracic vertebra. At its origin it lies behind the right common iliac artery on a plane posterior to the aorta, but as it ascends it passes slightly forward and to the right, reaching a plane anterior to the aorta, and becoming separated from that artery by the right medial crus of the diaphragm and the caudate lobe of the liver. While in contact with the liver it lies in a deep groove [fossa venae cavje] on the posterior surface of that organ, the groove being often converted into a distinct canal by a thin portion of the hepatic sub- stance bridging across it. As it passes through the diaphragm its walls are attached to the tendinous margins of the caval opening, and are thus held apart when the muscle contracts. On the thoracic side of the diaphragm it Hes for about 1.2 cm. (I in.) within the pericardium, the serous layer of that membrane being reflected over it. THE VENA CAVA INFERIOR 673 Relations. — In front it is covered by the peritoneum, and crossed by the right spermatic artery, branches of the aortic plexus of the sympathetic, the transverse colon, the root of the mesentery, the duodenum, the head of the pancreas, the portal vein, and the liver. The median gi'oup of the lumbar lymphatic nodes are also in front of it below, and at its com- mencement the right common iliac artery rests upon it. Behind, it hes on the lumbar vertebrae, the right lumbar arteries, the right renal artery, the right coehao (semilunar) ganglion, and the right medial crus of the diaphragm. To the right are the peritoneum, liver, and psoas muscle. To the left is the aorta, and higher up the right medial crus of the diaphragm. Tributaries. — The vena cava inferior receives the following veins: — ■(!) the renal veins; (2) the right suprarenal vein; (3) the right spermatic or the right Fig. 529. — The Abdominal Aorta and Vena Cava Inferior. i Cystic artery Hepatic duct Cystic duct Common bile duct Portal vein Gastro-duodenal br. Right gastric arterj Hepatic artery Right suprarenal vein Inferior suprarenal artery Renal artery Renal vein Vena cava inferior Kidney Right spermatic vein Right internal sper- matic artery Quadratus lumborum muscle Right lumbar artery and left lumbar vein Ui eteric branch of spermatic artery Middle sacral vessels, Left lobe of liver (Esophagus Left inferior phrenic artery Right inferior phrenic artery Superior suprarenal Left gastric artery Inferior suprarenal Splenic artery Left inferior phrenic vein Left suprarenal vein Superior mesenteric artery Kidney Ureteric branch of renal Left spermatic vein Left internal spermatic artery Inferior mesenteric artery Ureteric branch of spermatic Ureteric branch of common iliac Common iUac artery External iliac artery Hypogastric artery ovarian vein; (4) the lumbar veins; (5) the inferior phrenic veins; (6) the hepatic veins; and (7) the right and left common iliac veins. (1) The renal veins [vv. renales] (fig. 529) return the blood from the kidneys. They are short but thick trunks, and open into the vena cava nearly at right angles to that vessel. The vein on the left side, like the kidney, is a little higher than on the right, and is also longer, in consequence of its having to cross the aorta. Each renal vein lies in front of its corresponding artery. The left vein crosses in front of the aorta, just below the origin of the superior mesenteric artery. It is covered by the inferior portion of the duodenum, and receives the left spermatic, or the left ovarian in the female, and usually the left suprarenal, and sometimes the left phrenic. There are rudiments of valves in each vein where it joins the vena cava. Those on the right side, however, are less well marked. (2) The suprarenal veins [vv. suprarenales] (fig. 529). — ^There is usually only one suprarenal vein on each side to return the blood brought to the suprarenal body by the three suprarenal arteries. On the right side the vein opens directly into the vena cava, above the opening of the right renal vein. On the left side, it opens into the left renal. 674 THE BLOOD-VASCULAR SYSTEM (3) The spermatic veins [vv. sperraaticaj] (fig. 529) retui-n the blood from the testis. They begin by the confluence of small branches from the body of the testis and epididymis. As they proceed up the spermatic cord, in front of the internal spermatic artery and ductus deferens, they become dilated and plexiform, constituting the pampiniform plexus [plexus pampiniformis] (fig. 541). After passing through the subcutaneous inguinal ring, the inguinal canal, and the abdominal inguinal ring, the plexus communicates with the inferior epigastric vein and is continued as two veins. Along with the artery the veins pass up beneath the peritoneum, and on the left side also beneath the sigmoid colon, across the psoas muscle and ureter. They receive small tributaries from the ureter and peritoneum, and proceed as a single trunk, on the right side to the vena cava inferior, and on the left side to the left renal vein. There are commonly a number of imperfect valves in the spermatic plexus and a perfect pair at the termination of each spermatic vein. On the left side, however, the terminal valve may be wanting. Fig. 530. — The Veins op the Female Pelvis. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Right common iliac artery and vein Right external iliac artery Left common iliac artery and vein Edge of the suspensory ligament / Hypogastric artery and vein of the ovary , / / Ovarian vein / — «^' , Left external iliac artery and vein -^' ^ Sacrotu- berous ligament Obturator in- ternus muscle Utero-vaginal plexus ; behind the bulbus vestibuli The ovarian veins [vv. ovarica3[ begin at the plexus pampiniformis near the ovary, between the layers of the broad ligament. This plexus is larger than in the male and com- municates freely with the utero-vaginal plexus of veins, and with the plexus of veins which ex- tends from the hilus of the ovary into the ovarian ligament (fig. 486). After passing from between the layers of the broad Ugament, the plexus unites to form at first two and then a single vessel, which accompanies the ovarian artery, following a course similar to that of the spermatic veins in the male. The right ovarian veins open into the vena cava inferior, the left into the left renal. They usually contain imperfect valves in their plexiform part, and a perfect valve where they join the vena civa and renal vein respectively. THE PORTAL VEIN 676 (4) The lumbar veins [vv. lumbales], four to five on either side accompany the lumbar arteries and collect venous blood from the muscles of the back and abdomen. They terminate by passing beneath the tendinous arches of the psoas major, along the sides of the lumbar vertebrae, and opening into the vena cava inferior. The veins of the left side are longer than those of the right and pass behind the aorta. Each vein receives a dorsal tributary corre- sponding in distribution to the dorsal branch of the lumbar artery. Between the dorsal tribu- taries and the posterior vertebral venous plexus there occurs a free communication. There is also an anastomosis between the main lumbar veins and the anterior vertebral venous plexus around the bodies and transverse processes of the lumbar vertebrae. By means of these communications the intervertebral veins, the internal and external vertebral and spinal plexuses are partly drained. In addition to these anastomoses the lumbar veins are connected with one another and with common iliac, hypogastric, ilio-lumbar, renal, azygos and hemiazygos veins by means of the ascending lumbar vein (p. 66.3). (5) The inferior phrenic veins [v. phrenica inferior] follow the course of the inferior phrenic arteries; the right opens into the vena cava direct; the left into the suprarenal, the left renal, or the vena cava. (6) The hepatic veins [vv. hepaticse], the largest tributaries of the vena cava, return the blood from the liver. Commencing in the substance of the liver (see Liver), they converge as they approach its posterior surface, and unite to form two or there large trunks, which open into the vena cava as it lies in the fossa vense cavae. Some smaller vessels from the caudate lobe, and other parts of the liver in the nighbourhood of the caval fossa, open directly into the vena cava. The hepatic veins contain no valves, but, in consequence of opening obliquely into the vena cava, a semilunar fold occurs at the lower magin of each orifice. THE PORTAL VEIN The veins corresponding to the inferior mesenteric, the superior mesenteric, and to some of the branches of the coeliac artery, do not join the vena cava in- ferior direct, but unite to form a common trunk — the portal vein. This vein enters the liver, and breaks up in its substance into sinusoids from which the blood is again ultimately collected by the hepatic veins, and carried by them into the vena cava inferior. The terminal branches of the hepatic artery also empty into the hepatic sinusoids, and their blood likewise finds its way finally into the hepatic veins, and thence into the vena cava inferior. The portal vein and its tributaries have no valves. The portal vein [v. portae] (fig. 531), is a thick trunk 7 or 8 cm. (3 in.) in length. It is formed behind the head of the pancreas, opposite the right side of the body of the second lumbar vertebra, by the union of the superior mesenteric with the splenic veins. It passes upward and to the right behind the superior part of the duodenum, and then between the layers of the lesser omentum. In the latter situation it passes in front of the foramen epiploicum and is accompanied by the hepatic artery and the hepatic duct. Finally it enters the porta of the liver, and there divides into a right and a left branch. In this course the hepatic artery and the common bile duct are in front, the former to the left, the latter to the right. It is surrounded by branches of the hepatic plexus of the sympathetic nerve, and by numerous lymphatic vessels and some glands. The connective tissue sheath enclosing these structures is called the fibrous capsule of Glisson [capsula fibrosa, Glissoni]. Just before it divides it is somewhat dilated, the dilated portion being called the sinus of the portal vein. The division into right and left branches takes place toward the right end of the porta of the liver. The right branch is shorter and thicker than the left, and supplies the right lobe of the liver and a branch to the quadrate lobe. The left branch is longer and smaller than the right, and supplies the left lobe, and gives a branch to the caudate (Spigelian) and quadrate lobes. It is joined, as it crosses the left sagittal fossa, by a fibrous cord, known as the ligamentum teres hepatis (obUterated vena umbilicalis), and posteriorly by a second fibrous cord, the ligamentum venosum (ob- lietrated ductus venosus). The position of the original course of the umbilical vein across the left portal is marked, in. adult life, by a dilation of the latter vein, called the umbilical recess. Tributaries. — ^The pyloric, the coronary (gastric), the cystic, the superior mesenteric, and the splenic. The pyloric vein begins near the pylorus in the lesser curve of the stomach, and, running from left to right with the right gastric artery, opens directly into the lower part of the portal vein. It receives branches from the pancreas and duodenum. The coronary vein [v. coronaria ventriculi] (fig. 533) runs with the left gastric artery at first from right to left, among the lesser curvature of the stomach, toward the cardiac end, and then, turning to the right, passes across the spine from left to right to end in the portal trunk a 676 THE BLOOD-VASCULAR SYSTEM Fig. 531. — The Portal Vein. (From Kelly, by Brodel.) TRIBUTARIES OF THE PORTAL VEIN 677 little higher than the pyloric vein. At the cardiac end of the stomach it receives small branches from the oesophagus. The cystic vein [v. cystica] (fig. 533) returns the blood from the gall-bladder. It usually opens into the right branch of the portal vein. The superior mesenteric vein [v. mesenterica superior] (fig. 534) begins in tributaries whichi correspond witli the branches of the superior mesenteric artery. It courses upward a little in front and to the right of the artery, passing with that vessel from between the layers of the mesentery. It passes in front of the inferior portion of the duodenum, and behind the pancreas, where it joins the splenic vein to form the portal trunk (fig. 531). Tributaries. — In addition to the tributaries corresponding to the branches of the superior mesenteric artery — viz. the ileo-colica, colica dextra, colica media, and vence intestinales (fig. 534) — it receives the right gastro-epiploic and the pan- creatico-duodenal veins just before its termination in the portal vein. The right gastro-epiploic vein [v. gastroepiploica dextra] (fig. 533) accompanies the artery of that name. It runs from left to right along the greater curvature of the stomach, receiving branches from the anterior and posterior surfaces of that viscus, and from the great omentum, and, passing behind the superior portion of the duodenum, ends in the, superior mesenteric vein just before that vessel joins the portal trunk. Fig. 532. — The Portal Vein within the Lr^ee. Ascending branch (After Rex.) Vena cava inferior' Falci- form liga- ment Right main branch Left Round ' branch lig. Gall-bladder Trunk of por- Umbilical tal vein recess The pancreatio-duodenal veins [vv. pancreatico-duodenales] (fig. 531) run with the superior and inferior pancreatico-duodenal arteries between the head of the pancreas and the second portion of the duodenum. They receive pancreatic and duodenal veins [vv. pancreaticiE et duodenales] and are collected into a single stem which follows the inferior pancreatico-duodenal artery and ends in the superior mesenteric vein a little below the right gastro-epiploic vein. .The splenic vein [v. lienalis] (fig. 531) issues as several large branches from the hilus of the spleen. These soon unite to form a large trunk, which passes across the aorta and spine in company with the splenic artery, below which it lies, to join at nearly a right angle the superior mesenteric vein. In this course it lies behind the pancreas; and at its union with the superior mesenteric to form the vena portse in front of the vena cava inferior. Tributaries. — It receives the short gastric veins [vv. gastricse breves], from the fundus of the stomach, the left gastro-epiploic vein, and the inferior mesenteric vein. As it lies in contact with the pancreas it receives some small pancreatic veins [vv. pancreaticse]. The left gastro-epiploic vein [v. gastroepiploica sinistra] (fig. 533) accompanies the left gastro-epiploic artery. It runs from right to left along the greater curvature of the stomach, receives branches from the stomach and omentum, and opens into the commencement of the splenic vein. 678 THE BLOOD-VASCULAR SYSTEM The inferior mesenteric vein [v. mesenterica inferior] (fig. 531) begins at the rectum as the superior hgemorrhoidal vein. This emerges from the hsemor- rhoidal plexus in which it communicates freely with the middle and inferior haemorrholdal veins. It passes out of the pelvis with the inferior mesenteric artery; but, after receiving the sigmoid and left colic veins [vv. sigmoideee et V. colica sinistra] which accompany the arteries of the same names, it leaves the artery and runs upward on the psoas to the left of the aorta and behind the peritoneum. On approaching the pancreas it turns medially, and passes obliquely behind that gland to join the splenic vein just before the latter unites with the superior mesenteric to form the vena portse. Fig. 533.- -The Veins of the Stomach and the Portal Vein. (From a dissection by W. J. Walsham.) Right branch of portal vein Hepatic artery Hepatic artery proper Gastro-duodenal branch of hepatic artery Pyloric vein Right gastro- epiploic vein' Omental veins Left branch or portal ^ 5 corres- ponding to short gastric arteries Left gastric artery Hepatic artery The adult portal vein and its tributaries contain no valves, a circumstance which adversely affects the circulation of blood within this system. The liability to excessive pressure in the most dependent part of the portal system is evidenced by the great frequency of the condition known as piles, due to dilatation of the veins of the internal hsemorrhoidal plexus. In earrly life valves are present in the veins of the stomach and of the intestinal wall but these undergo retrogression. The accessory portal veins. — Since the blood returning from the abdominal portion of the digestive tract and spleen must pass through the hepatic-capillaries before returning to the heart, extensive obliteration of these capillaries, such as occurs in certain diseases of the liver, would prevent the return of the portal blood to the heart were it not for anastomoses between tribu- taries of the portal vein and those of the caval systems, constituting what have been termed accessory portal veins. Some of the more important of these are — (1) between the branches of the coronary vein of the stomach and the oesophageal veins which open into the vena azygos; (2) between the parumbilical veins [vv. parumbilicales], which communicate with the portal vein above and descend upon the ligamentum teres to the anterior abdominal wall to anastomose with the superior and inferior epigastric and superior vesical veins; (3) between the superior and middle hsemorrhoidal veins, the latter opening into the hypogastric, and (4) between a wide-meshed retro-peritoneal plexus of veins which communicates with the portal vessels over the posterior surface of the liver and the veins of the pancreas, duodenum and ascending and descending colon on the portal side, and with the phrenic and azygos veins on the systemic. THE HYPOGASTRIC VEIN THE COMMON ILIAC VEINS 679 The common iliac veins [vv. iliacae communes], (fig. 536) are formed opposite the sacro-iliac articulation by the confluence of the external iliac and hypo- gastric (internal iliac) veins. They converge as they ascend, and unite oppo- site the upper border of the fifth lumbar vertebra and a little to the right of the median line to form the vena cava inferior. Fig. 534. — The Superior Mesenteric Vein. (The colon is turned up, and the small intestines are drawn over to the left side.) Middle coin artery Inferior pancre Left colic artery Superior mes- enteric artery and vein Ileo-colic artery Vermiform process The right vein, shorter and more vertical in direction than the left, passes obliquely behind the right common iliac artery to its lateral side, where it is joined by the left common iliac vein. The left vein lies to the medial side of the left common iliac artery, and, after crossing in front of the promontory of the sacrum and the fifth lumbar vertebra below the bifurcation of the aorta, passes beneath the right common iliac artery to join the right vein and form the vena cava inferior. The left vein may contain an imperfect valve. Tributary. — The ilio-lumbar veins may enter the lower part of the common iliac, or open into the hypogastric vein. The left vein receives the middle sacral vein. The middle sacral vein [v. sacralis media] opens usually as a single trunk into the left common liiac vein. The venae comitantes which form it ascend on either side of the middle sacral artery in front of the sacrum. They communicate with the lateral sacral veins, forming the anterior sacral plexus [plexus sacralis anterior] which receives the sacral intervertebral veins, and anastomoses freely with the neighbouring lumbar and pelvic veins. Below, the middle sacral veins communicate with the hsemorrhoidal veins. THE HYPOGASTRIC VEIN The hypogastric (internal iliac) vein [v. hypogastrica] (fig. 536) is formed by the confluence of the veins (except the umbilical) corresponding to the branches 680 THE BLOOD-VASCULAR SYSTEM of the hypogastric artery. It varies considerably in length, but is usually quite a short trunk, extending from the upper part of the great sciatic foramen to the sacro-liac articulation, where it joins the external iliac to form the common iliac vein. It lies behind and a little medial to the hypogastric artery. It con- tains no valve. Tributaries. — The hypogastric vein receives directly or indirectly the following vessels; the superior gluteal, ilio-lumbar, lateral sacral, obturator, inferior Fig. 635. — The Inferior Mesenteric Vein. (The colon is turned up, and the small intestines are drawn to the right side.) Middle colic artery - — Inferior pancreatico- duodenal artery Superior mesenteric artery Right coUc artery Abdominal aorta /ena cava inferior Right common iliac artery Middle sacral artery and vein Left colic artery Inferior mesen- teric artery Left colic artery Inferior mesen- teric artery Sigmoid artery Superior hasmor- rhoidal artery gluteal (sciatic), internal pudendal, and (in the female) the uterine veins; also branches from the pudendal, vesical, and haemorrhoidal plexuses. The single umbilical vein-^the vein corresponding to the right and left hypogastric arteries and their continuation, the umbilical arteries — does not enter the pelvis, but, leaving the umbihcal arteries at the navel, passes along the falciform ligament to the liver. After birth it is converted into the hgamentum teres hepatis. (See Portal Vein, p. 675.) The superior gluteal veins [vv. glutete superiores] accompany the superior gluteal artery and, passing through the upper part of the great sciatic foramen, open into the hypogastric vein near its termination, either separately or as a single trunk. The ilio-lumbar veins [vv. ilio lumbales] open into the hypogastric a little higher than the superior gluteal. At times they join the common iliac vein. The lateral sacral veins [vv. sacrales laterales] (fig. 536) join the superior gluteal or the hypogastric at or about the same situation as the gluteal. They form with the middle sacral veins a ple.xus in front of the sacrum, which receives tributaries from the sacral canal. The obturator vein [v. obturatoria] (fig. 536), which lies below the obturator artery as it crosses the side of the pelvis, opens into the front of the hypogastric vein a little below the su- perior gluteal. Its branches correspond to those of the artery. The inferior gluteal veins [vv. giuteae inferiores] accompany the inferior gluteal (sciatic) artery, and, as a rule, unite to form a single trunk before joining the hypogastric a little below the obturator vein. All the above veins so closely follow the ramifications of their respective arteries that no further special description of them is required. They all contain valves. THE DORSAL VEIN OF THE PENIS 681 The internal pudendal vein [v. pudenda interna] (fig. 536) begins at tlie termination of the deep veins of the penis [w. profundae penis] which issue from the corijus coavernosum penis with the artery of that body. Tliese veins communicate with the dorsal vein at the root of the penis In its course the internal pudendal vein runs with the internal pudendal artery, receiving tributaries corresponding to the branches of that vessel. It. terminates in the lower part of the hypogastric vein. Fig. 536. — The Veins of the Pelvis, Male. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Abdominal aorta Ascending lumbar vein External iliac artery and vein Ductus deferens Inferior gluteal vein Internal pudendal artery and vein Vems from pudendal plexus Obturator fascia Crus of the perns L of the penis Corpus cavernosun Deep artery of penis The dorsal vein of the penis [v. dorsalis penis] (fig. 536) begins in a plexus around the corona glandis, then runs along the centre of the dorsum of the penis between the two dorsal arteries. In this course it receives large tributaries from the interior of the organ, which, emerging for the_ most part between the corpus cavernosum lu-ethrai and corpus cavernosum penis, wind obliquely over the lateral surface of the latter structure to the dorsum of the penis to end in the dorsal vein. At the root of the penis the dorsal vein communicates with the subcutaneous veins of the dorsum of the penis and, leaving the arteries, passes straight backward between the two layers of the fundiform (suspensory) ligament. It then goes between the subpubic linament 682 THE BLOOD-VASCULAR SYSTEM and the upper part of the fascia of the urogenital diaphragm (fig. 542). Here it bifurcates, each branch passing backward and downward to the pudendal plexus of veins. At times the dorsal vein begins as two branches, which run between the dorsal arteries and only unite to form a single trunk about 3.7 cm. (Ij in.) from the symphysis. After dividing into a right and a left branch within the pelvis, each vessel generally communicates with the obturator vein by a branch passing over the back of the pubis to the obturator foramen. Fig. 537. — The SuBcrrTANEOus Arteries and Veins op the Anterior Body Wall. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) venous net of the neck Anterior jugular vein Edge of superficial cervical fascia Superficial cervical artery and vein Cephalic vein opening into the deep vein of neck (variation) Subcutane Arch of the jugular vein Pectoral venous rete Mammillary venous plexus Connections with th internal mammar veins and with tht perforating branches of the internal mam- mary arteries Connections with the su- perior epigastric veins and chief branches of the superior epigastric arteries Venous rete of the umbilicus Connections with the infer- ior epigastric veins and>^. the chief branches of the inferior epigastric ar- teries Superficial epigastn artery and veins Superficial iUac artery and vem Superficial subingxii- nal lymph-nodes Subcutaneous dor^ sal vein of thi penis The pudendal plexus [plexus pudendalis] surrounds the prostate and the neck and fundus of the bladder. It receives in front the right and left divisions of the dorsal veins of the penis, and communicates with the posterior scrotal veins [vv. scrotales posteriores] and with the hasmor- rhoidal plexus. The prostatic veins and the vesical plexus open into it, and it also communi- cates with the internal pudendal vein. The veins forming the plexus are of large size, especially in old men, in whom they often become varicose, and contain phleboliths, or vein-stones VEINS OF THE LOWER EXTREMITY 683 The plexus is surrounded by a kind of capsule formed by the superior fascia of the pelvic diaphragm. It terminates in a single stem on each side which opens into the hypogastric vein. In the female the smaller pudendal plexus surrounds the urethra and receives the dorsal and deep veins of the clitoris [vv. dorsales et profunda clitoridis], veins from the vestibule, and the posterior labial veins [w. labiales posteriores]. It communicates freely with the utero- vaginal plexus and is drained by the hypogastric veins. The vesical plexus [plexus vesicalis] surrounds the apex, the sides, and the anterior and posterior surfaces of the bladder. It is situated between the muscular coat and the peritoneum, and where the bladder is uncovered by peritoneum external to the muscular coat in the pelvic cellular tissue. It opens into the pudendal plexus. The utero-vaginal plexus [plexus uterovaginalis] connects with the haemorrhoidal, vesical, and uterine plexuses. Its lower part drains thi'ough the internal pudendal veins and the pudendal plexus, and its upper protion largely through the ovarian veins, and partly through the uterine veins [vv. uterinae] to the hypogastric (fig. 530). The hEemorrhoidal plexus [plexus haemorrhoidalis] surrounds the rectum, and is situated at the lower part of that tube. It consists of two portions, one of which, the internal haemor- rhoidal plexus, is situated between the muscular and mucous coats, while the other, the external hsemorrhoidal plexus, rests upon the outer sui-face of the muscular coat. The veins of this latter plexus terminate in the inferior, middle, and superior hsemorrhoidal veins. The inferior [w. hiemorrhoidales inferiores] join the internal pudendal; the middle [v. haemorrhoidalis media] accompanies the middle hsemorrhoidal artery and opens into the hypogastric and superior haemorrhoidal veins; the superior (p. 678) forms the commencement of the inferior mesenteric vein, and through this the blood gains the portal vein. None of these veins have any valves, hence the enlargement of the inferior htcmorrhoidal veins, when the portal vein is obstructed, as in cirrhosis of the liver. Through the haemorrhoidal veins a free communication is established between the systemic and portal system of veins. THE EXTERNAL ILIAC VEIN The external iliac vein [v. iliaca externa] (fig. 536), is the upward continuation of the femoral. Beginning at the lower border of the inguinal ligament, it accompanies the external iliac artery medially upward along the brim of the mi- nor pelvis, lying at first on the superior ramus of the pubis, and then on the psoas major muscle. It terminates by joining the hypogastric vein behind the hypo- gastric artery, opposite the lower border of the sacro-iliac articulation, to form the common iliac vein. It lies at first medial to the external iliac artery, and on the left side remains medial to the artery throughout its course. On the right side, however, as it ascends, it gradually gets behind the artery. It contains one or two valves. In addition to the femoral, the external iliac receives the inferior epigastric vein [v. epigastrica inferior] (fig. 536) and the deep circumflex iliac vein [v. cir- cumflexa ilium profunda] (fig. 541), which accompany the arteries of the same name. THE SUPERFICIAL VEINS OF THE ABDOMINAL WALL The plexus of superficial veins of the anterior abdominal wall is continuous with that of the thorax (fig. 537). Its main channels are the superficial circumflex ihac, the superficial epigastric, and the external pudendal, all of which open into the great saphenous vein. These communicate, by means of subcutaneous abdominal veins, with the superior epigastric vein, and, by means of the thoraco- epigastric veins, with the lateral thoracic and costo-axillary. The superficial veins communicate verj' freely with the deeper veins of the abdominal wall, and, by means of parumbilical veins, they communicate to a slighter extent with the portal system. The superficial veins of the lumbar region form an abundant plexus which drains through the dorsal and lateral perforating branches of the intercostal, lumbar, and sacral veins. THE VEINS OF THE LOWER EXTREMITY The veins of the lower extremity are divided into the superficial and the deep. The superficial veins lie in the subcutaneous tissue superficial to the deep fascia, through which they receive numerous communicating branches from the deep veins. They are collected chiefly into two main trunks, which, beginning on the foot, extend upward, one, the great saphenous, lying antero-medially, and the 684 THE BLOOD-VASCULAR SYSTEM other, the small saphenous, postero-laterally. The former finally joins the femoral vein by passing through the deep fascia at the groin; the latter, the pop- liteal by perforating the fascia at the ham. The deep veins, on the other hand, accompany their corresponding arteries. All the veins of the lower limb have valves which are more numerous than in the veins of the upper extremity and in the deep than in the superficial veins. I. THE SUPERFICIAL VEINS OF THE LOWER EXTREMITY The superficial veins of the lower limb begin in the plexuses of the foot. The dorsal digital veins [vv. digitales pedis dorsales] collect blood from the dorsal surfaces of the toes and unite in pairs, around each cleft, to form the dorsal metatarsal veins [vv. metatarsese dorsales pedis]. The dorsal metatarsal veins, of which the first and fifth are larger than the others, join the dorsal venous arch [arcus venosus dorsalis pedis]. This arch is convex toward the toes and crosses near the bases of the metatarsal bones. From the medial and lateral ends of the arch the great and small saphenous veins, respectively, take origin. The area of the dorsum of the foot contained between the arch and the two saphenous veins is covered by the dorsal venous rate [rete venosum dorsale pedis] which extends as high as the ankle-joint (fig. 539). On the plantar surface the plantar digital veins [w. digitales plantares] return the venous blood to the clefts of the toes and unite to form the common digital veins [vv. digitales communes pedis]. The common digital veins join freely with one another on the sole to form the plantar venous rete [rete venosum plantare]. There are numerous communications between the superficial veins of the dorsum and sole. These occur both in the clefts of the toes, by means of the intercapitular veins [vv. intercapitulares], and around the margins of the foot. Communications between the superficial and deep veins of the foot are very free (fig. 540). The great (or internal) saphenous vein [v. saphena magna] (fig. 538) com- mences as the medial end of the dorsal venous arch, and, after receiving branches from the sole which join it by turning over the medial border of the foot, passes upward in front of the medial malleolus, and then obliquely up- ward and backward about a finger's breadth from the posterior border of the tibia in company with the saphenous nerve, which becomes superficial just be- low the knee. Continuing its course upward, it passes behind the medial epi- condyle, and then runs upward on the medial side of the front of the thigh to about 3.7 cm. (li in.) below the inguinal Hgament, where it dips through the fossa ovalis (saphenous opening) in the fascia lata, and ends in the femoral vein. Tributaries. — In its course up the leg and thigh it receives numerous unnamed cutaneous tributaries. As it passes up the thigh it often receives a large vein, the femoro-popliteal which communicates with the small saphenous, and several of the cutaneous veins on the lateral part of the thigh, and a second vein, the accessory saphenous [v. saphena accessorial, formed by the union of the cutaneous veins from the medial and back part of the thigh (fig. 538). The great saphenous vein contains from ten to twenty valves. Immediately before entering the fossa ovalis the great saphenous vein receives the super- ficial epigastric, superficial circumflex iliac, and external pudendal veins, though any of these veins — or all of them — may pierce the fascia separately and enter the femoral vein. The superficial epigastric vein [v. epigastrica superficialis] anastomoses with the superficial abdominal, and parumbUical veins. The superficial circumflex iliac vein [v. circumflex ilium superficiahs] anastomoses with the thoraco-epigastric and the superficial circumflex iliac veins. The external pudendal veins [vv. pudenda^ externaj] collect venous blood from the anterior scrotal or labial veins, which anastomose with the posterior scrotal or labial veins, and from the subcutaneous veins of the dorsum of the penis [vv. dorsales penis subcutanese]. The small saphenous vein [v. saphena parva] (fig. 539) begins at the lateral end of the venous arch on the dorsum of the foot. After receiving branches from the sole, which turn over the lateral border of the foot, it passes behind the lateral malleolus, and then upward and, lying at first along the lateral side of the tendo Achillis, afterward along the back of the calf, in company with the sural (short saphenous) nerve, to about the lower part of the centre of the popliteal space, where it perforates the deep fascia, and, sinking between the two heads of the gastrocnemius, opens into the popliteal vein. SUPERFICIAL VEINS OF THE LOWER LIMB 685 Tributaries.^As it passes up the calf between the superficial and deep fascia, it receives numerous cutaneous veins from the heel, and the lateral side and back part of the leg, and Fig. 538. — The Superficial Veins and Lymphatics of the Left Lower Limb. (Walsham.) Superficial epigastric vein Lymphatics from penis and scrotum Femoral vein Superficial femoral lymphatic glands External pudendal vein Superficial lymphatics from lateral wall of abdomen Superficial lymphatics from lower and anterior walls of abdomen Accessory saphenous vein. Great saphenous vein' Femoro-popliteal vein, Medial malleolus' Dorsal venous arch Superficial inguinal lym- phatic glands Superficial circumflex iliac vein communicates at intervals, through transverse or intermuscular branches, with the deep veins accompanying the peroneal artery. Just before perforating the deep fascia, it receives a large descending branch, the vena femoropoplitea, from the lower and back part of the thigh. This 686 THE BLOOD-VASCULAR SYSTEM communicates with a plexus of veins upon the posterior and lateral regions of the thigh and with the great saphenous. In many cases the small saphenous vein is entirely drained, by means of the femoro-popliteal, into the great saphenous. Under these circumstances the usual place of termination of the small saphenous is marked by a small vein opening into the popliteal. A small offshoot from the inferior sural branch of the popliteal artery accompanies this vein for a Fig. 539. — The Veins op the Dorsum op the Foot. (After Toldt, "Atlas of Human Anat- omy," Rebman, London and New York.) Great saphenous vein Anterior tibial muscle Dorsal pedal artery and vein Extensor hallucis longus tendon Dorsal venous arch Dorsal digital vein - Anterior tibial artery i=— Anterior tibial veins ^ Dorsal venous rete of foot ^Dorsal metatarsal arteries -Dorsal metatarsal vein Intercapitular veins short distance down the back of the calf. The small saphenous vein contains from nine to twelve valves. II. THE DEEP VEINS OF THE LOWER EXTREMITY The deep veins of the lower extremity accompany the arteries, and have received corresponding names. From the foot to the knee there are two veins to each artery. These veins run on either side of the corresponding artery, and com- DEEP VEINS OF THE LOWER LIMB 687 municate at frequent intervals with each other across it. They are known as the venae comitantes. From the knee upward there is a single main vein to each artery, except at the back of the thigh and in the gluteal region, where there are commonly two. Fig. 540.- -The Veins op the Sole of the Foot. (After Toldt, "Atlas of Human Anatom}',' Rebman, London and New York.) Intercapitular veins Posterior tibial veins 7 / Posterior tibial muscle— -| t Posterior tibial artery Great saphenous vein — Flexor digitorum ^^ longus tendon ^^V ^ - Plantar digital ^ .-i- Plantar venous arch Lateral plantar artery and accompanying veins Deep branch of the medial plantar and veins Venous rete of the heel Small saphenous vein The veins of the foot and leg. — The deep veins of the foot become separated from the superficial where the plantar metatarsal veins [vv. metatarsese plantares] leave the plantar digital and intercapitular veins to accompany the plantar meta- tarsal arteries. The plantar metataisal veins empty into the plantar venous arch [arcus venosus plantaris] which accompanies the arterial plantar arch in the depth of the sole. (fig. 540) THE BLOOD-VASCULAR SYSTEM The posterior tibial veins [vv. tibiales posteriores] drain the plantar venous arch and the superficial rete (fig 542). They follow the posterior tibial artery up the leg, receiving tributaries corresponding to its branches, the largest of which are the peroneal veins [vv. peronefe]. They unite with the anterior tibial vense comitantes at the lower border of the popliteus muscle. The anterior tibial veins [vv. tibiales anteriores] begin in the dorsal venous rete and accompany the anterior tibial artery up the leg receiving tributaries cor- responding to branches of the artery. Fig. 541. — The Femoral Vein. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Deep circumflex iliac artery and v Inferior epi- gastric ar- tery and vein Fundiform ligament of penis Vastus medialis Second per- forating artery and Adductor longus Tunica vaginalis propria testis Deep femoral artery and vein They pass backward between the interosseous membrane and the tibia and fibula to unite with the posterior tibial veins. The posterior and anterior tibial veins unite at the lower border of the popliteus muscle to form the popliteal vein. All these veins contain numerous valves, and communicate, by means of intermuscular branches, with the superficial veins. The popliteal vein [v. poplitea] (fig. 542), is formed by the confluence of the venae comitantes of the anterior and posterior tibial arteries at the lower border of the popliteus, and extends upward to the opening in the adductor magnus at the junction of the middle and lower third of the thigh, where it changes its name to femoral. TEE POPLITEAL VEIN It accompanies the popliteal artery, lying superficial to it in the whole of its course, and tightly bound down to it by its fascial sheath. At the lower part of the space it is a little medial to the artery, but, crossing the vessel obliquely as it ascends, lies a little lateral to it at the upper part of the space. The tibial (internal popliteal) nerve lies superficial to the vein, being lateral to it above, then posterior to it, and then a little to its medial side. The popliteal vein contains two or three valves. Fig. 542. — The Deep Veins of the Leg. (After Toldt, *' Atlas of Human Anatomy," Rebman. London and New York.) Semimenibraaosus .^ Semitendinosus Popliteal artery Medial sural artery and veins Popliteal veins <->_- Gastrocnemius (medial head) Deep layer of the crural fascia - Flexor digitorum longus Posterior tibial artery and veins Flexor hallucis longu: - Popliteal vein Lateral sural artery and veins al artery and Flexor digitorum longus -. Posterior tibial Posterior medial malleolar artery Medial calcanean branches——- Venous rete of the heel — _ Peroneal artery and Flexor hallucis longus Posterior lateral malleolar artery and veins Lateral calcanean branches and veins The popliteal receives the small saphenous vein. It is also joined on its lateral and medial sides by the accessory popliteal veins [vv. popliteoe accessorise] which form common trunks of termination of the sural and articular veins of the respective sides. The medial vein receives in addition, through a plexus extending as high as the opening in the adductor magnus, the veins accompanying the a. genu suprema. 690 THE BLOOD-VASCULAR SYSTEM The femoral vein [v. femoralis], the continuation of the popliteal upward, extends from the tendinous opening in the adductor magnus to the inguinal ligament. In this course its relations are similar to those of the femoral artery. As the vein passes through the adductor canal, it lies behind and a little lateral to the artery. At the apex of the femoral trigone (Scarpa's triangle) it is still posterior to the artery, but gradually passes to the medial side as it ascends through the trigone (fig. 541). In the neighbourhood of the inguinal hgament the femoral vein hes on the same plane as the artery from which it is separated by a delicate prolongation of the fascia stretching be- tween the front and back layers of the femoral sheath. On the medial side the vein is sepa- rated by a similar septum from the femoral canal. The femoral vein contains five pairs of valves. Tributaries. — The femoral vein receives (in addition to the great saphenous vein, and, in some cases the superficial veins of the epigastrium and groin) the profunda veins and a variable number of small femoral vense comitantes. The profunda femoris veins [vv. profunda femoris) arise from the vense comitantes corre- sponding to branches of the profunda femoris artery. The medial and lateral circumflex veins [w. circumflex femoris mediales et laterales] collect blood from the muscles of the adductor and lateral rotator regions. The perforating veins anastomose with femoro-popliteal and other veins of the posterior femoral region, and with the circumflex and accessory popUteal veins. They return blood from the femur and the adductor, hamstring and vasti muscles. The venae comitantes, much smaller than the main femoral vein, accompany the femoral artery on either side. They anastomose with one another, with the femoral, and often with the popliteal vein. They terminate in the femoral a short distance above the profunda veins. MORPHOGENESIS AND VARIATIONS OF THE VEINS The veins of the adult human body tend to accompany the arteries; this tendency is more pronounced in the trunk, neck, and extremities than in the cranium. Developmental history shows that the primitive distribution of the veins of the trunk resembles that of the arteries of the same region in its bilateral symmetry only. Also that the changes which modify the primitive bilateral symmetry of the chief veins are not only more extensive but of a different nature from those producing a similar effect upon the arteries. In both cases the main body- vessels begin as a pan- of main longitudinal trunks and end as a main unpaired channel (or channels in the case of the venous system) situated near the median plane of the body. In the ease of the venous system the change results from wholesale destruction of the vessels on the left of the body accompanied by enlargement of those upon the right. In the arterial system destruction occurs to a much more limited extent; the definitive channel results mainly from blending of the two primitive aortse. The main venous channels of the cranium and extremities are primitively superficial; in the cranium they remain so. In the extremities new veins are formed which follow the main arteries; to these the more primitive channels become tributary. The heart, as soon as it assumes the simple tubular form is found to receive four veins. These, the two vitelline and two umbilical veins, enter the sinus venosus, a vitelline and an umbilical vein on either side. The umbilical veins are lateral to the vitellines, and are paired within the body only; they arise from the placenta, and traverse the belly-stalk as a single trunk. The vitelline veins return blood from the yolk sac, and, at first, are independent throughout. At a later period two other pairs of veins arise for the venous drainage of the embryonic body. They are the pre- and post-cardinals which drain the cephalic and caudal regions respectively. The right pre-cardinal vein unites with the right post-cardinal to form the right common cardinal (duct of Cuvier). The latter runs in a medial direction to join the sinus venosus lateral to the right umbilical. On the left side the arrangement matches that on the right to produce a primitively symmetrical pattern. During development changes are brought about in the primitive veins which end in the production of the adult venous system as follows: the common and pre-cardinals, together with the subclavian veins and the cephalic ends of the post-cardinals, are transformed into the vena cava superior and its larger tributaries. The remainder of the post-cardinal system is instrumental in the production of the vena cava inferior and its tributaries. FinaUy the intra-embryonic portions of the vitelline and umbilical veins participate in the formation of the portal and hepatic systems of veins together with the proximal end of the vena cava inferior. The following brief account of morphogenesis and variations is divided into three headings (1) vena cava superior and its tributaries; (2) vena cava inferior and its tributaries, and (3) the portal system. A. THE VENA CAVA SUPERIOR AND ITS TRIBUTARIES 1. MORPHOGENESIS The pre-cardinal veins at first return blood from the head only, but as the heart recedes into the thorax the cardinal veins migrate with it. In so doing the common cardinals lag somewhat behind and in consequence their direction, primitively transverse, approaches the Ion- THE VENA CAVA SUPERIOR 691 gitudinal. The pre-cardinals, which have increased in relative length, now course symmet- rically along the neck into the thorax. At a stage of 16 mm., the definitive subclavian vein has migrated from the common to the pre-cardinal, which henceforth receives the main ven- ous flow from the upper extremity as well as from the head. The symmetrical arrangement of the cardinal veins is disturbed at a stage of about 18 mm., by the development of a transverse connection between the right and left pre-cardinals (fig. 544). This connection, the left in- nominate vein, arises, probably, by the development of cross-anastomoses uniting the lateral veins draining the developing thymus and thyreoid glands. On the right side of the embryo the veins of the adult are now recognisable as follows: — the vein (pre- and common cardinal) extending from the left innominate to the heart becomes the vena cava superior. The pre- cardinal, from the left innominate to the subclavian, becomes the right innominate. From the subclavian to the cranium it becomes the internal jugular. The vessel of the left side corresponding to the vena cava superior now rapidly diminishes in size. It extends from the left innominate vein (the extreme left end of which corresponds in its method of formation to the entire right innominate) to the right atrium. In so doing it passes ventral to the aortic arch and the foot of the left lung, dorsal to the left artium, and through part of the coronary sulcus. Fig. 543. — Semidiagrammatic Reconstructions of the Cranial Venous System. (Mall.) A, 4 Weeks; B, 5th Week; C, Beginning op 3rd Month; D, An Older Fcetus. A.c.v; pre-cardinal vein; A.V., otic vesicle; Inf. Pet., inferior petrosal sinus; L., eye; O.V., superior ophthalmic vein; S.L.S., superior sagittal sinus; S.P.S. sphenoparietal sinus; S.R., sinus rectus; S.S., middle cerebral vein; T.H., confluens sinuum; V., semilunar ganglion; V.C.A., v. cerebralis anterior; V.J., internal jugular vein; V.C.L., v. capitis lateralis; V.O.M. or sup. pet., v. cerebralis media and superior petrosal sinus; V.C.P. or L.S., v. cerebralis pos- terior and transverse sinus. The segmental veins draining the second, third and fourth intercostal spaces of the left side open, by a common stem formed by the left pre-cardinal, into the left innominate. The cor- responding segmental veins of the right side open, by a common stem, into the vena azygos. The collecting stem, on either side, is the vena intercostais suprema. The method of origin of the azygos, hemiazygos and accessory hemiazygos veins is treated with the inferior caval system. Below the superior intercostal tributary, the left superior cava is lost to within a short distance of the sinus venosus. Here its lower end persists as the oblique vein of the left atrium and the left end of the coronary sinus. The former course of the left superior cava is often indicated in the adult by a small fibrous cord, uniting the extremities of the persisting veins and passing through the ligamentum v. cavoe sinistrae (p. 523). Within the cranium the pre-cardinal veins are primitively in close contact with the brain and medial to the semilunar, acustico-facial, glossopharyngeal and vagus ganglia. The portion of each vein extending from the semilunar ganglion to the facial canal (its exit from the cranium) early becomes involved in a process of anastomosis-migration which eventually places it lateral to the ganglia and to the otocyst. The new vein formed in the latter situation is called the vena capitis laterahs (fig. 543). The portion of the pre-cardinal vein which remains medial to the semilunar ganglion persists as the adult cavernous sinus and receives a primitive vein (v. cerebralis anterior) which drains the orbit and the mid- and forebrain. The forebrain tributaries of 692 THE BLOOD-VASCULAR SYSTEM the right and left v. cerebralis anterior unite to from a median vein, the definitive superior sagittal sinus, wliicli at first drains into the cavernous sinus. There are two other primitive cerebral veins; the v. cerebralis media and v. cerebralis posterior. The first receives blood from the cerebellar region and drains into the cavernous sinus. The second, the v. cerebralis posterior, also receives blood from the hind-brain and, leaving the skull through the jugular fora- men, joins the pre-cardinal (internal jugular) vein m the neck. Several changes occur from now on (fig. 543) which bring about the definitive relations of the dural sinuses and transfer the main venous exit from the stylomastoid to the jugular foramen. The right v. cerebralis posterior joins the superior sagittal sinus and this becomes the right transverse sinus. The left V. cerebralis posterior communicates with the junction of the superior sagittal and right transverse sinuses (now the confluens sinuum) and becomes the left transverse sinus. The confluens receives the sinus rectus, which forms its adult connections with the inferior petrosal sinus and great cerebral vein. The v. cerebralis media joins the transverse sinus to become the superior petrosal sinus. The latter forms a new (intracranial) means of drainage for the caver- nous sinus and its tributaries. The original drainage channel of the cavernous sinus (v. capitis lateralis), having been supplanted, disappears. The superior cerebral veins drain into the superior sagittal sinus. The remaining portion of the interrupted v. cerebrah's anterior drains the middle cerebral vein and spheno-parielal sinus. The inferior petrosal sinus arises de novo. In the upper extremity the venous drainage is at first superficial and opens into the post- cardinal and umbilical veins. The ulnar limb of the loop-like early venous channel (marginal vein) becomes the primitive ulnar vein, but does not open into the pre-cardinal until a stage later than that of 10 millimetres. The primitive ulnar forms the basilic, part of the brachial, the axillary, and subclavian veins. It receives the large thoraco-epigastric trunk. The cephalic vein, which at first joins the external jugular, is of secondary formation. The venoe comitantes are formed later still. 2. VARIATIONS The great veins of the thorax may present variations from the normal as a result of absence of the left innominate vein. In this case there are two superior cavse, not necessarily of equal size, each of which receives an internal jugular and subclavian vein. Persistence of the left Fig. 544. — The Transformation of the Postcardinal System of Veins, C representing THE Adult. The Wolffian Body is Dotted. (Lewis.) a.c, precardinal; as. 1., ascending lumbar; az., azygos; c, caudal; c.h., common hepatic; c. il., common iliac; C.S., coronary sinus; d.C, common cardinal; g., spermatic or ovarian; h., hepatic; h.-az., hemiazygos; h.-az. ac, accessory hemiazygos (here draining into the intercostalis suprema); i. j., internal jugular; l.c.i., left common iliac; 1. in., left innominate; m.s., middle sacral; p.c, posterior cardinal; r., renal; r.a., renal anastomosis; r.c.i., right common iliac; r. in., right innominate; s., suprarenal; s-c, subcardinal; s-cl., subclavian; s.l., sinusoids; v.c.i., vena cava inferior; v.c.s., vena cava superior. ^i JL vena cava superior without failure of the left innominate may occur in three classes of cases: (a) In which both cavse are present, equal in size or asymmetrical, (b) In which the left cava only occurs, associated with situs inversus, (c) In which the left cava only is present, without situs inversus. The left vena cava superior, when present, crosses in front of the aortic arch and THE VENA CAVA INFERIOR 693 enters the right atrium by way of the coronary sinus, collecting the coronary veins. Cases are • on record of a left superior cava terminating in the left atrium. The azygos weins.^Variations of these veins and of the intercostal veins have been dealt with on pp. 663-664. For their morphogenesis, see under vena cava inferior. The veins of the neck, face, and scalp. — These veins have so many variations in detail that it is difficult, in the case of some veins, to assign their normal distribution. The external jugular, for instance, is usually described in Enghsh text-books as a tributary of the subclavian vein; it is assigned by the BNA to the internal jugular. It is frequently found to open into the angle between the two, or, forming a plexus with its tributaries, drain into both. The origin of the external jugular vein is also exceedingly variable. The external jugular may be small, or absent, in which case the anterior jugular is large. The reverse may be the case since the external jugular frequently receives the posterior, and sometimes the common facial. Fortu- nately venous variations are not of prime surgical importance. Veins of the cranium. — The venous sinuses of the dura mater are not subject to important variations. Variations in the relative size of the transverse simises have been referred to on p. 651. The petrosquamous sinus, occasionally present, is described on p. 653. The occipital and inferior sagittal sinuses are frequently absent. The cerebral veins are liable to great variation in detail: the great cerebral vein may be absent, as a single trunk, in which case the internal cerebral veins open directly into the sinus rectus. The middle cerebral vein may open into the sphenoparietal, or superior petrosal sinus or into the basilar plexus. Veins of the upper extremity. — The subclavian vein is occasionally posterior to the artery, or spUts to enclose the latter and the anterior scalenus. Either case represents a partial re- tention of the early condition in which the vein passes behind the brachial plexus. Variations in the superficial veins have been referred to on p. 668. The question of the most common distribution of these vessels has lately been fully reviewed by Berry and Newton. The cephalic vein occasionally opens into the external jugular by persistence of the embryonic jugulo-cephahc vein. B. THE VENA CAVA INFERIOR AND ITS TRIBUTARIES 1. MORPHOGENESIS The right and left post-cardinal veins (fig. 544) are at first symetrical in size and position. Early in development each posterior cardinal vein becomes involved in the growth of the cor- responding mesonephros, and the original venous channel is converted into a system of sinusoids. In the sinusoidal circulation of each mesonephros two main longitudinal venous channels soon make their appearance. One lies ventro-medial to the mesonephros and is called the sub-cardinal vein. The other, which lies dorsal to the mesonephros, receives the segmental veins and is frequently called the post-cardinal. Since the mesonephric segment of the post-cardinal vein has obviously passed out of existence, the vein in question (unlabelled in fig. 544) wQl be here distinguished as the dorsal trunk. The sub-cardinals communicate freely between themselves and with the dorsal trunks, lie ventral to the mesonephric arteries, and are at first symmetrical. The cephalic end of the right sub-cardinal now acquires a communication with the common hepatic vein, thus providing a new means of drainage for the sub- and post-cardinal systems (fig. 544) . The rapidly enlarging main venous channel resulting from this alternative niethod of drainage follows the right dorsal trunk as far as the level of the permanent renal veins. It is then transferred, by means to an anastomosing channel, to the right sub-cardinal and, through this, to the common hepatic vein; it becomes the vena cava inferior. From now on the portions of the sub-cardinal veins not participating in the formation of the cava dwindle rapidly. A cross anastomosis between the right and left sub-cardinals persists as the portion of the adult left renal vein which crosses ventral to the aorta. By means of it the remainder of the left renal; thfe left internal spermatic and left suprarenal veins are connected with the vena cava. The left lumbar and left common ihac veins are also transferred to the vena cava, probably by direct anastomosis with the left post-cardinal vein. The vena cava inferior is at first lateral to the right ureter, its transference to the medial side occurs through anastomosis. The portion of the right posterior cardinal vein above the mesonephric region, together with its continuation into the dorsal trunk, becomes the azygos vein (fig. 544). The corresponding vessel upon the left side is transformed into the accessory hemiazygos and hemiazygos veins. The hemiazygos vein is drained into the azygos by means of an anastomosing channel which may also drain the accessory hemiazygos. The variability of the means of drainage of the accessory hemiazygos vein, by means of anastomosing channels, is referred to onp. 663. The ascending lumbar veins are anastomosing channels of new formation. In the lower extremity, as in the upper, the original superficial plexus is gradually drained by a loop-Uke marginal vein. The fibular limb of this loop, the primitive fibular vein, becomes small saphenous; it follows the sciatic nerve and opens into the post-cardinal. The next vein to be developed is the great saphenous; the small saphenous is transferred to this by an anastomos- ing vein which is usually present in the adult — the femoropopliteal vein. The deep veins are of later formation. The drainage of the small saphenous is usually taken over by the popliteal vein. 2. VARIATIONS In determining the probable embryonic cause of variations of the vena cava inferior the possibility of abnormal persistence of the sub-cardinal veins must be remembered. The posi- tion of transverse anastomoses with regard to the aorta is often the key to diagnosis. Instruc- 694 THE BLOOD-VASCULAR SYSTEM tive cases of abnormalities of the vena cava inferior have recently been pubhshed by v. Alten and by Neubei-ger (see References). Both articles contain bibUographies. The chief varia- tions are as follows: — (1) The inferior vena cava, in cases of transposition of the viscera, may he on the left side of the aorta. (2) Without transposition it may also lie to the left of the aorta, crossing to the right to gain the caval opening immediately below the diaphragm, or after receiving the left renal vein. (3) It may be double, the left cava than usually passing across the aorta into the right after receiving the left renal vein. A communication between the right and left veins in the position of the normal left common iliac vein may or may not then exist. (4) The inferior vena cava may be absent, the blood from the lower extremities passing by a large vein in the position of the ascending lumbar and azygos veins through the diaphragm to open into the superior vena cava. The hepatic veins then open directly into the right atrium through the normal caval opening in the diaphragm. (5) The inferior vena cava may receive the left sper- matic vein. (6) It may receive a left accessory renal vein passing behind the aorta, and into this the usual tributaries of the left renal vein may open. (7) It may receive several accessory renal veins; as many as seven on each side have been met with. (8) The lumbar veius may enter it on one or both sides as a common trunk. The variations in the veins of the lower extremity are for the most part unimportant. They have been mentioned in the description of the corresponding veins. 3. THE PORTAL SYSTEM OF VEINS The portal system arises by transformations in the vitelline and umbilical veins. The proximal ends of the vitelline veins, where they lie between the umbilicals, are early enveloped in, and invaded by, the growing liver. The columns of liver cells, while not penetrating the endothelium, subject the vitelline veins to a process of fenestration by which the original channels are subdivided into innumerable smaller vessels or sinusoids. The sinusoids arising from the two vitelline veins intercommunicate to form one continuous network in which the vessels are larger in the afferent (portal) and efferent (hepatic) areas than in the intermediate zone. Fig. 545. — Sbmidiagrammatic Reconstructions of the Veins of the Liver, Ventral Aspect (Mall). A, Embryo of 4.5 mm. Long; B, 4 mm. (more advanced than A); C, 7 mm. d.v., ductus venosus; I., intestine; L., liver; m., superior mesenteric (continued as portal) vein; r.a., ramus angularis; r. a'., right branch of portal vein; r.h.d., right hepatic vein; r.h.s., left hepatic vein; r.u., recessus umbilicahs; u.v., left umbilical vein (the right umbihcal vein is not labelled); v.o.m., vitelline veins. The two umbilical veins now form communications with the portal area of the sinusoidal network and eventually lose their original connections with the sinus venosus (fig. 545). The fate of the umbilical veins differs on the two sides; the right degenerates, from the sinus venosus to the common umbilical vein, and leaves the left to receive all the blood flowing from the pla- centa. The left, having lost its connection with the sinus venosus, discharges its blood partly into the portal sinusoidal zone, and partly, by means of the newly formed direct channel, the ductus venosus, into the right vitelline (fig. 545). The hepatic end of the right vitelline vein enlarges considerably, for the left vitelline loses its original connection with the sinus venosus. It transmits blood both from the sinusoids and from the ductus venosus to the sinus venosus, and is called the common hepatic. The vitelline veins are not only connected within the liver, but their distal ends become united upon the yolk-stalk to form a single trunk. A third communication between them is effected by a transverse vessel passing dorsal to the duodenum. The portion of the right vitelline below the transverse vessel disappears, as does the portion of the left between it and the liver. A tortuous vitelline vein is thus produced which enters the liver by passing dorsal to the intestine from left to right. This vessel is joined, to the left of the intestine, by the superior mesenteric vein and, dorsal to it, by the splenic. When the portion of the vitelline below the termination of the superior mesenteric finally disappears the vessel extending from the splenic vein to the liver becomes the portal vein of the adult. Important variations of the portal system are rarely found in the adult. The mechanism of anomalies found in the embryo have been investigated by Begg (Anier. Jour. Anat., Vol. 13). THE FCETAL CIRCULATION 695 FGETAL CIRCULATION The changes which accompany the transformation of the foetal type of circulation into that of the adult are initiated by the first inspiration. Prior. to this act the functions of external respiration and digestion are performed by the Fig. 546.^The Heart, with the Arch op the Aorta, the Pulmonary Artery, the Ductus Arteriosus, and the Vessels concerned in the Fcetal Circulation. (From a preparation of a fcetua in the Museum of St. Bartholomew's Hospital.) Right innominate vein Superior vena cava Right pulmonary artery Inferior vena Left branch of portal vein Ductus venosus Arch of aorta Ductus arteriosus Left pulmonary artery Descending aorta Umbilical vein Portal vein Right branch of, portal vein Umbilical Umbilical arteries Umbilical -artery mesenteric vein Inferior senteric artery eft common iliac artery Hypogastric artery External iliac artery mother; the foetal venous blood passing to the placenta through the umbilical arteries and returning through the umbilical vein. At the time of birth the right and left chambers of the heart communicate only by means of an oblique passage between the overlapping atrial septa (p. 511) . The pulmonary artery and descending aorta communicate by means of the ductus arteriosus (p. 508). 696 THE BLOOD-VASCULAR SYSTEM Arterial blood, transmitted from the placenta through the umbilical vein, passes almost entirely by way of the ductus venosus to the vena cava inferior. From here it passes through the right atrium; then, obliquely between the atrial septa into the left atrium, from which it passes through the left ventricle and into the ascending aorta. Escaping largely through the branches of the aortic arch, it is distributed to the head and upper extremities, and returned to the vena cava superior. Having reached the right atrium it passes, to the right of the stream from the vena cava inferior fp. 513), through the atrio-ventricular ostium into the right ventricle. The blood issuing from the right ventricle into the pulmonary artery goes almost entirely (the lungs being functionless) into the ductus arteriosus and so into the descending aorta. Having performed two circuits, the blood returns to the placenta through the umbilical branches of the. hypogastric arteries. The two streams, arterial and semi-venous, cross one another in the right atrium. The degree of intermixture, if any, which occurs in this cavity has been the subject of much discussion; for literature and experimental evidence on this point see Pohlmann, A. (Johns Hopkins Hosp. Bui., Vol. 18, 1907.) When the lungs assume their function at birth the pressure in the left atrium is suddenly raised by an inrush of blood. The overlapping atrial septa (primum and secundum) are brought into lateral apposition and thus the blood entering the right atrium finds but one exit — the atrio-ventricular ostium. Since the vessels of the expanded lungs now transmit a greatly increased volume of blood, the stream passing through the ductus venosus is diminished proportionately. The blood traversing the aortic arch, released from the check exerted by the lateral stream pouring from the ductus arteriosus, passes more readily into the descending aorta; thus the adult equilibrium is established. References for blood-vascular system. — A. Heart: (Development) Born, Archiv f. mikr. Anat., Bd. 33, 1889; His, Anatomie menschl. Embryonen, 1880-85, Anatomie des menschl. Herzens, 1886; Tandler, in Keibel and Mall's Human Embryology. (Morphology) MacCallum, Johns Hopkins Hospital Reports, vol. 9, 1900; Mall, Amer. Jour. Anat., vol. 11, 1911, vol. 13, 1912; (Atrio-ventricular bundle) Keith and Flack, Jour. Anat. and Physiol., vol. 41, 1907. B. Arteries. (Development) Evans, in Keibel and Mall's Human Embryology; (Pulmonary) Bremer, Anat. Rec, vol. 3, 1908; (Internal mammary) Mall, Johns Hopkins Hospital Bui., 1898; (Cephalic) Tandler, Morph. Jahrb., Bd. 30, 1902; (C celiac) Tandler, Anat. Hefte, Bd. 25, 1904; (Extremities) Miiller, Anat. Hefte, Bd. 22, 1903; de Vriese, Arch, de Biol., T. 18, 1902; (Variations) Goppert, Morph. Jahrb., Bd. 40, 1909; C. Veins. (Development) Davis, Amer. Jour. Anat., vol. 10, 1910; (Brain) Mall, Amer. Jour. Anat., vol. 4, 1904; (Liver) Mall, Amer. Jour. Anat., vol. 5, 1905; (Cervical) Lewis, F. T., Amer. Jour. Anat., vol. 9, 1909; (Upper extremity) Berry and Newton, Anat. Anz., Bd. 33, 1908; (Vena cava inferior) Neuberger, Anat. Anz., Bd. 43, 1913; v. Alten (ibid): (Sinusoids) Minot, Proc. Boston Soc. Nat. Hist., vol. 29, 1900. S E C T 1 O N V [ THE LYMPHATIC SYSTEM Revised for the Fifth Edition By ELIOT R. CLARK, A.B., M.D. ASSOCIATE IN ANATOMY, JOHNS HOPKINS MEDICAL SCHOOL I. GENERAL ANATOMY OF THE LYMPHATIC SYSTEM THE blood-vascular system has, as a part of its function, the collection of substances from the various tissues of the body which are to be conducted to the other tissues. In carrying on this function it is assisted by a second system of collecting vessels, the lymphatics. This second system resembles the blood-vascular system in many ways, but differs markedly in others. Like the tslood-vascular system, it is made up of minute endothehal-Uned capillaries, where the absorption of substances occurs, and of larger conducting vessels. It differs from the blood-vascular system' in two important particulars. While the blood-vascular system is pro- vided with a pumping'mechanism by which its fluid content is driven through a complete circuit from the heart, through artery, capillary, vein and back to the heart, the lymphatics merely conduct fluid from, the capillaries to the larger vessels, which eventually empty their contents into the large veins of the neck. The second important difference between the two systems is found in the presence, along the course of the lymphatic vessels, of glands or nodes (fig. 553) [lymphoglandulee] in which the vessels branch out into lymph capillaries. These are lined, as are the absorbing capillaries, with a single layer of endothehal cells, thus permitting an interchange of substances between the contents of the lymph capillaries and the lymphoid tissue around them. Our present knowledge does not permit an exact statement of the complete extent of the lymphatic system. While, in a general way, the lymphatics may be said to be present where- ever blood-capillaries occur, there are certain tissues where lymphatics have not been definitely demonstrated. The general constitution of the lymphatic system will be considered under three heads — (1) the capillaries, (2) the collecting vessels and (3) the lymphoid organs. I. THE LYMPHATIC CAPILLARIES The lymphatic capillary, like the blood-capillary, is the portion of the lymph- atic system which is chiefly concerned in the specific function of this system. In the blood-capillaries, where the blood is separated from the outside tissues by a single layer of flat endothehal cells, there occurs the interchange of fluid substances and of cells, while the heart, arteries and veins serve to transport the blood, modi- fied in the capillaries, to other parts of the body. Similarly in the lymphatic system, it is in the capillaries, both those most peripheral and those in the lymph nodes, where the absorption and interchange of fluid substances and of cells takes place. Consequently it becomes of prime importance to obtain a clear under- standing of the structure of the lymphatic capillaries, their relation to the other tissues, and their mode of functioning. At the outset, however, it must be admitted that our knowledge on this subject is far from complete. Historical. — Previous to the development of microscopic anatomy, in the middle third of the 19th century, there was no accm-ate knowledge of such small structures as the lymphatic capil- lary. In order to explain the absorption of substances by the lymphatics, as well as the passage of substances from the blood-vessels through the tissues, various theories were invented. Promi- nent among such theories was that of the "vasa serosa," of H. Boerhaave and other 18th century anatomists and physiologists, which was perhaps most elaborately developed by Bichat, 1801-03. According to this theory there are two sets of minute vessels, too small for the passage of cellu- lar elements. The one set leads from the blood-capillaries onto the various surfaces of the body and into the loose spaces in the tissues — the "exhalants. " The other set leads from the body surfaces (including the serous cavities) and the loose spaces in the tissues to the lymphatics — the "inhalants" or " absorbants, " which take in fluids by a sucking action. 697 698 THE LYMPHATIC SYSTEM This theory was somewhat shaken by the discovery of Magendie, in the first decade of the 19th century, that absorption may take place by the veins, as well as the lymphatics, and by the criticism of early 19th centmy anatomists who developed the teohnio of injection of lymphatics to a high point. Our present conception of the lymphatic capilJaries may be said to have started with KoUiker who, in 1846, saw, with the aid of the microscope, the lymphatic capillaries in the trans- parent tails of living frog larvae. He found them to be definite structures made up of a thin wall, from which projected fine-pointed processes, and in which were nuclei. Like Schwann who, in 1837, had studied the blood-capillaries in the tail of the frog larva, he erroneously sup- posed that the fine processes of the lymphatic capillaries were continuous with similar proc- esses of the surrounding connective-tissue cells. Since, according to the conception current at the time, cells were thought to be hollow structures, with a membranous wall and fluid content, it was concluded that the mode of transmission of fluid from blood to lymphatic capillary took place through canaliculi inside these cells. This conception was elaborated by Virchow, in his CeUular-Pathologie. In 1862 von Recklinghausen by means of the silver nitrate staining method discovered that the lymphatic vessels are lined with an endothelium made up of flattened cells whose outlines show as fine dark Knes after this treatment. Again, however, as a result of the eagerness to find open passages through the tissues from blood to lymphatic capillary, an erroneous interpretation was made, von Recklinghausen held that the unstained parts outside the lymph vessels rep- resent a system ofj irregularly shaped lymph-canaliculi ("Saftkanalchen") which are in open communication on the one hand with the blood-capiUaries, and on the other with the lymphatics This conclusion has since been disproved by numerous investigators. In a second series of observations, von Recklinghausen brought evidence in favor of open communications between the lymphatics and the peritoneal cavity. He watched, under the microscope, the passage into lymphatics, through minute openings, of milk, placed on a portion of the central tendon of the diaphragm. These minute openings he termed "stomata. " Cohn- heim described similar though smaller openings in blood-capillaries, and His described them in other lymphatic capillaries. Arnold termed the openings in the vessels "stigmata," as dis- tinguished from the openings into the peritoneal cavity, or "stomata." With the advent into microscopical technic of the various dyes for staining cell-nuclei and protoplasm, and the more precise methods for making histological studies, the endothelial wall of the lymphatic capillary has been definitely established, although much remains to be learned concerning the differences between the lymphatics of the various tissues. Moreover, recent investigators have failed to find open connections between the lumen of the lymphatic vessel and the tissue outside. Kolossow failed to find the "stomata" of von Recklinghausen and the "stigmata" of Cohnheim, His and Arnold. The "stomata" have been carefully studied by a number of other recent investigators. All agree in finding a complete endothelial lining for the lymphatic capillaries lying underneath the peritoneum and pleura, with no openings or "stomata." Careful studies of the lymphatic capillaries in the transparent tails of living frog larvae, which may be clearly seen with the higher magnifications of the micro- scope, show that the endothelial lining of these capillaries is complete, with no trace of an open- ing into the spaces in the tissue outside (E. R. Clark). Form. — The shape of the lymphatic capillaries has been found to vary enormously in the different parts of the body, where they have been studied. In general they form richly anas- tomosing plexuses, from which may extend cul-de-sacs, which end bUndly. Such cul-de-sacs are especially noticeable in the dermal papillae, in the filiform papillse of the tongue, and in the intestmal villi. The plexuses are often present in two layers — a superficial and a deep. The vessels of the superficial plexus are of smaller calibre than those of the deep. These two sets of plexuses are particularly well seen in the skin and the gastro-intestinal tract. In relation to the blood-capiUaries, the lymphatic capillaries are generally the more deeply placed. In cahbre, unlike the comparatively uniform diameter of blood-capillaries, the lymphatics vary enormously. In the same capillary a very narrow part may be succeeded by a very wide one (figs. 547, 548). Teichmann found lymphatic capillaries varying in diameter from a few thousandths of a millimetre to one millimetre. In the capsule of the spleen of the cow some meas- ured more than 1.5 mm.! The capillaries are without valves. Activity. — That the lymphatic endothelium is not exclusively a passive membrane has been shown by Clark in studies on the lymphatics in the transparent tails of living frog larvae. The lymphatics here are seen to send out protoplasmic processes which, somewhat like an amoeba, actively take into the interior of the lymphatic red blood-cells accidentally forced from the blood-capiUaries into the tissue-spaces. The mode of passage of leucocytes into or out of the lymphatics offers no such difiiculties as that of the fluids, for they are able, through their power of amoeboid movement, to pass independently through the endothelium — a process first directly observed by Cohnheim. 1. The Extent and Chabacter of Lymphatic Capillaries The skin over the entire surface of the body is richly provided with lymphatic capiUariea. They form two sets of plexuses in the dermis, a superficial and a deep. The superficial set sends out bhnd cul-de-sacs into the dermal papillae. The richest skin plexuses are found in the scrotum, the palms of the hand and palmar side of the fingers and in the soles of the feet and plantar side of the toes. In the loose subcutaneous fascia, according to Teichmann, there are present only the larger collecting vessels, with no lymphatic capillaries. Lymphatic capillaries of the scrotum are shown in Fig. 547. The conjuntiva, both the sclerotic and corneal, is supplied with a rich plexus of capillaries, which are narrower in the corneal than in the sclerotic portion. At the corneal border the LYMPHATIC CAPILLARIES 699 capillaries form a fairly regular ring which has been called by Teichmann a ciroulus lymphaticus. At the various orifices of the body, the skin plexuses go over into the mucous plexuses, forming anastomoses with them. Tiiroughout the entire alimentary tract, including the nasal cavities, the lymphatic capillaries form extensive plexuses which are in many places divided into a superficial plexus in the mucosa and a deeper plexus in the submucosa. In portions pro- vided with a peritoneal covering, there is a third rich subserous plexus. In the tongue and the small intestine the plexus in the mucosa sends out blind cul-de-sacs; in the tongue into the filiform papilla?; in the small intestine into the villi. Where muscle is present along the ali- mentary tract, the lymphatics pass between the muscle bundles, but form no plexuses around them. The lining of the tracheal and bronchial passages is supplied with a double plexus of lym- phatic capillaries, a mucous and a submucous set, which vary in richness according to the loose- ness of the tissue. In the smaller bronchi but a single layer of capillaries is present, and, ac- cording to Miller, no capillaries are present around the air cells. Plexuses surround the pul- FiG. 547. — The Lymphatics of the Scrotum. (After Teichmann.) Showing the transition of the capillaries to the vessels with valves (o, a, a). monary arteries and veins. Under the pleura lie rich plexuses which connect with the deeper lymphatics around the veins only in places where the veins reach the surface of the lung. Concerning the arrangement of the lymphatic capillaries in the glands derived from the alimentary tract much remains to be learned. The salivary glands have been recently studied anew by Aagaard, who has found lymphatic capillaries accompanying the blood-vessels into the interior of the lobules, and forming here irregular plexuses. The thyreoid gland contains lymphatic plexuses which lie in relation to the colloid-con- taining alveoli. Direct connection between the lymphatics and the alveoli has lately been described by Matzunaga, but this observation needs verification. The lymphatics are apparently concerned in the absorption of the colloidal secretion, for traces of it have been found in the lymphatics draining the gland. Concerning the lymphatics of the parathyreoids nothing is known. The course of the lymphatics draining the thymus has been recently described, but the nature of the capillaries in this gland is unknown. The lymphatic capillaries of the liver are of great importance, for the lymph which flows from this organ forms a very considerable part of the total lymph which is collected into the thoracic duct. And yet very little is definitely knowm about the natm'e and distribution of the lymphatic capillaries in the interior of the organ. In the capsule there is a rich plexus, lying under the peritoneum, in which very large widenings have been described (called bj^ Teichmann "Lymphbehalter"). In the interior rich plexuses surround the branches of the hepatic artery and portal vein (fig. 549), and plexuses have been described accompanying the branches of the portal vein into the lobules. The linings of the large bile-ducts and the gall-bladder are provided with a submucous network of lymphatics (Sudler and Clermont). The gall-bladder has also a rich subserous plexus. Concerning the lymphatic capillaries of the pancreas Bartels notes briefly that they form richly branched plexuses in the interlobular connective tissues, which surround larger or smaller parts of whole lobules, not the single gland elements. The mucous lining of the genito-urinary tract, wherever- it has been carefully studied 700 THE LYMPHATIC SYSTEM has been found provided with plexuses of lymphatics. In the bladder they form a rich plexus of irregular capillaries which lie immediately under the almost intraepithelial blood-capiUaries. They connect, through the muscular layer, with a subserous plexus. The lymphatic plexus of the urethra anastomoses \vith the capillaries of the base of the bladder, and in the male with those of the glans penis. The lymphatic capillaries of the ductus deferens and of the seminal vesicles have not been studied. In the prostate (Camineti) the lymphatics form rich plexuses surrounding the glands, which connect with a very wide meshed subcapsular plexus, surrounding the entire gland. In the testis there is a rich superficial plexus, lying directly beneath the tunica albuginea. Concerning the deep lymphatics of the testis there has been much dispute. Ludwig and Thomsa Fig. 548. — Surface View and Section of Lymph-nodes op the Intestine. A. Solitary folhcle. B. Pej'er's patch. (After Teiohmann.) found the lymphatic capillaries going over into lacunse, without endothelium. This has been disputed by Tommasi and Gerster, who find, in the septa, capillaries with endothelial wall, which they consider the beginnings of the lymphatics. In the female, lymphatic plexuses have been found in the mucosa of vagina and hymen, anastomosing with those of the vulva. In the uterus, capillaries in the mucosa are very difficult to demonstrate. Definite lymphatics, however, have been found passing through the mus- cularis, and under the peritoneum a rich subserous plexus of capillaries is present. In the preg- nant uterus these subserous capillaries are much distended (Schick). The Fallopian tubes are provided v?itb lymphatics, but they have not been carefully described. LYMPHATIC CAPILLARIES 701 The ovary has a rich superficial lymphatic plexus. In the iaterior of the gland, according to His, the capUlaries form networks in the connective- tissue framework. In the tunica externa of the follicles there is a rich plexus. The kidney has two sets of lymphatics, a superficial, capsular set, and a deep set. The cap- sular set is divided into two layers, one lying directly beneath the peritoneum made up of a wide meshed plexus, and the other in the fibrous capsule of the kidney, with finer capillaries and narrower meshes, which anastomose with the deeper capillaries. The lymphatic capillaries of the kidney parenchyma have recently been described by Kumita. He found rich plexuses in both cortex and medulla, surrounding the straight and convoluted tubules, the loops of Henle and the collecting tubules. He also found a plexus surrounding and accompanying the blood- vessels into the interior of the glomeruli. The lymphatic capillaries of the adrenal have also been described recently by Kumita. His results agree with those of Stilling, who studied the lymphatics of the adrenal of horse, cow and calf. Like the kidney, the adrenal possesses a superficial and a deep set. The superficial set Fig. 549. — ^Lymphatic Plexus ahound the PortaljVein in"' an Adult Man. (After Teich- mann.) Showing the supporting relation of the vein. is in two layers, as in the kidney, the outer lying in the looser tissue around the adrenal and the inner lying within and just under the capsule. The latter is made up of a rich lymphatic plexus, which anastomoses with the capillaries of the parenchyma. The parenchymatous lymphatics are present in the form of plexuses which surround the groups of cells. In spite of numerous investigations, endothelial-lined lymphatics have not been definitely found in the central nervous system, or in the peripheral nerves. The subarachnoid and similar spaces, including the perineural spaces, do not form parts of the lymphatic system. Rich plexuses of lymphatic capillaries are present in the tendons of muscles (Schweigger- Seidel and Ludwig). In muscles, themselves, the question of the presence of lymphatics has long been disputed, sometimes answered in the affirmative, more often in the negative. A re- cent study by Aagaard, however, would seem to place beyond doubt the presence of lymphatic capillaries in striated muscles. By long continued injection, he was able to find Ij'mphatics in the intramuscular portions of the tendons, which extended out among the muscle fibres themselves. He also found capillaries in the tongue musculature. The heart is provided with a subpericardial plexus of lymphatic capillaries. A subendocardial plexus has also been described (Sappey, Rainer). Bock has recently found that there is an ex- tremely rich lymphatic network throughout the substance of the heart. According to his de- scription, the lymphatic capillaries are more numerous than the blood-capillaries. *~, kThe periosteum of bones is provided with a rich plexus of lymphatic capillaries. They are present in 'several layers, of which the outermost form the richest plexus. Lymphatic capillaries 702 THE LYMPHATIC SYSTEM have also been described accompanying the blood-vessels in the Haversian canals in bones (Rauber, Schwalbe, Budge). Nothing is known concerning the lymphatics of the bone marrow. Cartilage lacks both blood and lymphatic capillaries. The capsular membranes of joints are richly provided with lymphatic capillaries (Tillmanns) . They are arranged in two layers — an inner layer made up of a rich plexus of wide capillaries, lying just outside the subendothelial blood-capillaries, and an outer layer, consisting of a rich plexus in the subsynovial tissue. The lymphatic capillaries have no open connection with the joint cavity. The membranes suiTounding the pleural, pericardial and peritoneal cavities are richly sup- plied with lymphatic capillaries, which form here thick plexuses outside the endotheUum. These plexuses are usually described with the underlying organ, as the subserous lymphatic capillaries of the intestine, etc. In the central tendon of the diaphragm the subperitoneal lymphatics are extremely rich. They widen out here to form very large endotheUal-lined cavities which, in the spaces between the connective-tissue bundles, lie directly in contact with the peritoneal epithelium. The existence of open connections between these capillaries and the peritoneal and pleural surfaces (the "stomata" of von Recklinghausen) has recently been disproven. The capillaries on the two surfaces of the central tendon communicate freely with one another. 2. THE LYMPHATIC VESSELS The lymph which enters the lymphatic capillaries passes over into collecting vessels (ducts), which carry it through the lymph-glands (nodes) to the large veins at the base of the neck. The lymph-vessels course in the loose subcutaneous tissues, in the connective tissues between muscles and organs, often accompanying the arteries and veins, sometimes forming networks around them. An idea of their arrangement can be best obtained by glancing at the illustrations of the lymphatics of special regions. In general they are made up of numerous long, narrow vessels, rarely more than half or three-fourths of a millimetre in diameter, which occasionally communicate with one another, and which radiate toward groups of lymph-glands placed in certain definite regions. In the lymph-glands the afferent lymph-vessels break up into capillaries, which again collect into efferent vessels. Several of these efferents from each lymph-gland may pass to a second lymph-gland, where they undergo a second widening into capillaries. In this way the lymph, passing through one, two, three or more lymph-nodes in succession, eventually reaches the thoracic duct, or one of the short ducts, all of which empty into the large veins at the base of the neck. The thoracic duct, which receives, at its lower end, the lymph from the lower half of the body, is the only lymphatic vessel which attains any considerable size (four to six millimetres in diameter) and is usually the only one large enough to be seen readily without injection. In structure the lymphatic vessels much resemble the veins. They possess an intima, a media and an adventitia, although the line of demarcation between the different layers is not sharp. In the thoracic duct, the endothelium of the intima is succeeded by a delicate layer of fibres, mainly elastic; outside of this is the media, made up mainly of circular smooth muscle- cells, interspersed with elastic and connective-tissue fibres; then follows a layer of coarse elastic and connective-tissue fibres, which is succeeded by the adventitia, containing longitudinal and transverse bundles of smooth muscle-ceUs, as well as blood-vessels and nerves. The other lym- phatic vessels possess the three layers, which, however, toward the capillaries, grow thinner, and eventually reach a stage in which, outside the endothehum, there are found only single musole- ceUs, or muscle-ceUs in groups of two or three. The lymphatic vessels are characterised by their great richness in valves, which are present throughout their entire course, from their beginnings in the capillary region to their openings into the veins of the neck. The valves are bi- or tri-cuspid, and are always arranged so as to prevent the flow of lymph back to the capillaries. They thus aid indirectly in the movement of the lymph, in that any external pressure on the vessels must always force the lymph onward. Nerves of lymphatic vessels. — That the thoracic duct and the smaller lymphatic vessels are provided with nerves has been shown by several observers. According to Kytmanoff (in dogs) the nerves to the lymphatics are mainly non-medullated, and are both motor and sensory They form four sets of plexuses — adventitial, supramuscular, intermuscular and subendotheUal. Sensory nerve-endings (fig. 550) are found in adventitia and media, in the form of free-ending threads, and bush-like endings. Motor endings are present in connection with the smooth muscle cells of the media. In the intima there is a plexus of extremely fine varicose threads. The physiological action of the nerves supplying the receptaculum chyli has been tested by Camus and Gley who found in dogs a dilatation of the receptaculum as the result of electrical stimulation of the splanchnic nerve. Movement of the lymph. — It has been estimated (Ludwig) that the amount of lymph which passes through the lymphatic ducts of a dog aggregates, during the twenty-four hours, one-third the body-weight. In the thoracic duct the lymph is under a sufficient pressure to burst the duct behind a ligature. In the absence of any especial propulsive organ, such as the heart for the blood-circulation, what are the forces which move the lymph? There must be recognised pri- mary and accessory forces. As accessory forces there are the movement of the muscles and the LYMPHATIC VESSELS 703 general pressure of the organs on the lymph-ducts. Since these are provided with valves, all preventing the lymph from flowing backward, any such pressure causes the lymph to move on- ward. As accessory agents must also be reckoned the smooth muscle and elastic tissue which is present in the walls of the lymph-vessels and in the lymph-gland. That these forces, however, are not primary is shown by numerous facts. There is an active circulation in the lymphatics of Fig. 650. — A. The Adventitial and SuPKA-MusctrLAR Nerve Plexuses, together with Sensory Endings in the Thoracic Duct of a Dog. (Methylene-blue method.) B. Nerve-fibres on the Endothelium op a Lymphatic Capillary of a Dog. (After Kytmanoff.) U^:^^^^ ^^^'\r^i*.I^ ~'^"'*J^ iXiatmrft'^-:^: ^■S53*K*^?.>S5„W^'^- ^ ■/' embryos long before valves develop. In many lower animals no valves develop save at the entrance of the lymphatics to the veins. That neither valves nor muscular movements are es- sential is shown by the fact that, in the tails of frog larvae, where no valves are present and where the muscle movements have been completely paralysed by an anesthetic, the circular- tion of lymph continues unchecked. The primary cause, therefore, for the movement of lymph is to be sought in the capillary region, in the force produced by the passage of lymph through the endothelial wall, whether this 704 THE LYMPHATIC SYSTEM process be a filtration and diffusion — -in which case the causes would he in the pressure and mo- lecular condition of the tissue fluid outside the lymphatic — or whether it be an active secretion by the endothelium — in which case the driving force would be this secretory power of the endothelium. 3. THE LYMPHOID ORGANS Closely associated with the lymphatic capillaries and vessels is a group of glandular structures known as lymphoid organs. They consist, essentially, of groups of round lymphoid cells, lying in a meshwork of reticulum fibres, and hav- ing often a definite relationship to the blood or lymph vessels. The group of lymphoid organs includes, in addition to the lymph-glands [lymphoglandulse] or lymph-nodes, which are particularly related to the lymphatic vessels, the spleen, thymus and bone-marrow, which are also largely made up of lymphoid tissue. The spleen and thymus, however, are considered separately with the Ductless Glands. Fig. 551. -Diagram op a Ltmph-nodb. (After Toldt, "Atlas of Human Anatomy, "Rebman, London and New York.) Capsule Medullary cords Deep lymph vessels Anastomosis between afiferent and efferent vessel -^ Superficial y lymph-paths In their most simple form, the lymphoid organs form mere irregular accumulations or patches of lymphoid cells, whioh^iave been termed lymphoid infiltrations. Such patches are frequent in mucous membranes especially along the intestinal tract (fig. 549) and the air-passages in the lungs. Larger accumulations of lymphoid cells produce definite round nodules, which may occur singly, as solitary follicles or in groups, as aggregated follicles (Peyer's patches) (fig. 548). In the sohtary foLhcle the lymphoid ceSs are arranged concentrically, with a region in the centre where the cells are less closely packed together. This is called the germinal centre, and contains numerous cells undergoing mitotic division. The sohtary folhole contains blood-capiUaries. Lymph-capiUaries, however, do not enter the follicle but form a rich plexus about it. The lymph-glands or nodes (fig. 551) are larger lymphoid structures, which are developed along the course of the lymph-vessels. They vary much in size, shape, and colour, and may occur singly or in small or large groups. The size varies from the size of a pin-head to that of an oUve, or larger. In skape'they may be spherical, oval, or flattened on one or more sides, according to their relations to other organs. Each gland has an indentation or hilus, where the arteries enter, and where the veins and efferent ducts emerge. Their colour depends upon position and state of function. The glands along the respiratory tract are black, due to the presence of car- bon granules. The mesenteric glands are milk-white during digestion, and other nodes are pale and translucent when their sinuses are filled with fluid, and pink or even red when red-blood LYMPHOID ORGANS 705 cells are present in the sinuses. The lymph-gland is made up of four distinct elements : lymphoid elements, lymphatic capillaries, supporting structures, and blood-vessels. The lymphoid elements (fiji. .551) are arranged as follicles and as cell-strings. The follicles lie around the circumference of the gland, and form the cortex [substantia corticalis]. The cell- strings or meduUary cords are irregular cords of cells which extend from the follicles through the central or medullary portion [substantia medullaris] of the gland. The follicles and medullary cords are made up, as are the solitary follicles, of round lymphoid cells. Fig. 552.- -SuRFACE View and Section op a Lymph-node showing the Peripheral and Cen- tral, Sinuses. (After Teichmann.) The lymphatic vessels (tig. 551) enter the lymph-gland as several vasa afferentia, and leave it, at the hilus, as the vasa efferentia. The vasa afferentia spread out in the cortical portion of the gland into an extremely rich plexus of wide capillaries which surround the follicles, forming the peripheral sinus. The capillaries do not enter the follicle. This plexus continues, around the foUicles, into the medullary portion where it forms again a rich plexus, the medullary sinus, in the spaces around the meduUary cords (fig. 552). At the hilus the medullary capil- laries collect into larger vessels and emerge as the vasa efferentia. The supporting structures consist of a fibrous capsule surrounding the gland, from which trabecula3 or septa pass in, around and between the foUicles and cords. From the septa, a fine reticulum passes into the foUicles and cords, where it forms a rich dense meshwork, in the interstices of which lie the Ij'mphoid cells. The capsule and trabeculse are made up of white fibres, elastic fibres and smooth muscle-fibres. i 706 THE LYMPHATIC SYSTEM The blood-vessels, which enter and leave at the hilus, send branches into the follicles and into ihe meduUary cords. The enormous widening of the lymph-stream in the lymph-node from the vasa afferentia to the capillaries — like a brook widening out into a pond — causes a very great diminution in the rate of flow of the lymph. Thus there is present in the gland a very slowly moving stream of lymph, which is separated from the lymphoid tissue outside by a single layer of flattened endotheh'al cells. There is thus possible an easy interchange of substances, and an opportunity for the passage, through the endothelium, of wandering cells. While the entire mode of func- tioning of the lymph-gland is not clear, it is known that lymphocytes, formed here, enter the lymph-stream, and that substances such as, for instance, carbon granules, or leucocytes laden with bacteria, are checked in their course by the lymph-gland. Arrangement. — The lymph-glands are so arranged throughout the body that all the lymph which enters the lymphatic capillaries must pass through one or more lymph-glands on its way to the veins. It is possible that this rule may have exceptions, although none have yet been definitely proved. Thus, some of the small lymphatics which join the thoracic duct may enter it without having passed through a gland. Moreover, there is often found (fig. 551) a direct anastomosis between an afferent and an efferent lymphatic vessel. Most of the glands are collected in certain regions, where they form centers toward which the lymphatic vessels radiate. Such groups are termed regional glands. The glands forming such a group are connected with one another by numerous anastomoses, which are termed lymphatic plexuses [plexus lymphatici]. In addition to the regional glands there are many isolated glands which lie along the course of the lymph-vessels, and through which pass the vessels draining a much more limited capillary area. Such glands are termed intercalated glands. 4. THE DEVELOPMENT OF THE LYMPHATIC SYSTEM Our knowledge of the lymphatic system has been very greatly increased during the past ten years by studies on its mode of development. Previous to 1902 nothing definite was known about the primary development or the mode of growth of the lymphatic system. It was concluded by some (Budge, GuUard and Saxer) that the lymphatics arise from undifferentiated mesenchyme cells; Ranvier believed that they arise from veins by budding of the endothelium; while Sala described them as arising partly from the mesenchyme and partly from venous endothelium. Regarding the mode of growth and spreading of the lymphatics, various theories were like- wise held. Kolliker, His, Goethe and, later, Sala held that growth takes place by the suc- cessive addition of mesenchyme cells; Langer, Rouget, and Ranvier maintained that growth takes place by sprouting of the endothelium (fig. 553). S. Mayer thought that new lymphatics are derived from transformed blood-capillaries. Miss Sabin in 1902 gave the first clear picture of the mode of origin and growth of the lymphatic system, and our present knowledge is largely based upon her discoveries. She showed by injections of embryo pigs that the lymphatics of the skin appear first in four regions of the body — two on each side at the base of the neck, and two in the inguinal region — in the form of sacs which are connected with the veins. From these four regions the lymphatics spread out step by step over the skin of the entire body, in the form of a richly anastomosing capillary plexus. Since the publication of Miss Sabin's paper, numerous studies have been made on the mode of development of lymphatics in many different animals, including man. The results of these studies indicate that the lymphatic endothelium first appears in the form of buddings-out from the veins in certain well-defined regions of the embryo. As to the exact manner of this primary origin views differ. Miss Sabin, in her first paper, held that it arises by budding from the veins. F. T. Lewis held that it is formed by the transformation of plexuses of blood-capillaries. This view was accepted by Miss Sabin, and verified by Huntington and McClure. Stromsten recuiTi'd to Sala's view that the first lymphatic endothehum arises in part from venous endothelium, and in part from the mesenchyme cells. Hoyer and his pupila find that the first lymphatics arise as buds from the veins. This has also been found (1912) by E. R. and E. L. Clark in chick embryos. Thus far six regions have been found, in which lymphatics develop from the veins — in the neck, on each side, at the angle formed by the internal jugular and subclavian veins; in the pelvis, on each side, along the iliac veins; and two unpaired sets in the region of the renal veins, one ventral to the aorta, the mesenteric, and one dorsal to the aorta, retroperitoneal. In these six regions the lymphatics soon coalesce to form large sacs, the jugular, iliac, mesenteric and retroperitoneal. The sacs are later broken up into the primary sets of lymph-nodes. The receptaculum chyli develops in the region of the retroperitoneal sac. From these primary anlages derived from the veins the lymphatics spread out into the various organs and tissues of the body. The cutaneous lymphatics spread out from the two jugular and two iliac regions (Sabin), the lymphatics of the intestine from the mesenteric sac (Heuer). The method by which this extension of the primary lymphatics occurs is still in dispute, but there seems to be conclusive evidence that it takes place by the sprouting of the endothehum (fig. 553) ; that the endothehum of the lymphatics, derived from the veins, is a specific, inde- pendent tissue, and that all new lymphatic endothehum is formed from lymphatic endothehum, DEVELOPMENT OF THE LYMPHATICS 707 and not from blood-vessels or mesenchyme cells. This view is supported especially by the work of Sabin, MacCaUum, Hoyer and his pupils and E. R. Clark. On the other hand, F. T. Lewis has suggested that the spreading of lymphatics occurs by the transformation of blood-vessels into lymphatics; while Huntington and McClure and their pupils maintain that it occurs by the continued transformation of mesenchyme cells. The lymphatics growing from the various primary centres meet and anastomose with one another, and gradually lose aU connections with the veins save those at the base of the neck Sylvester has found, however, that in South American monkeys the connections with the veins in the region of the renal veins are maintained in the adult. Valves do not appear in the lym- phatic vessels until quite late, in human embryos about 5 or 6 cm. long. (Sabin.) The lymphatic nodes do not make their appearance until the system of vessels is well established. They are at first represented by masses of lymphoid tissue in the meshes of a lymphatic network. Later the lymphoid mass breaks up into smaller portions, into which the blood-vessels and branches from the surrounding network penetrate; and each mass, together Fig. 553. — The Speouting of Lymphatic Capillaries in the Pig. (After MacCaUum.) The lymphatics are injected and the sprouts are both single cells and clumps of cells. with the portions of the network surrounding it, becomes enclosed in a connective-tissue capsule. The original lymphoid tissue becomes transformed into the medullary cords and cortical nodules of the node, while the enclosing lymphatic capillaries form its peripheral lymph-sinus. The earhest nodes appear in the places occupied by the primary Ij'mphatic plexuses or sacs (Miss Sabin, F. T. Lewis, JoUy), and have been termed the "primary nodes" (Miss Sabin). Secondary and tertiary sets of nodes develop later at places of confluence of many Ivmohatics (cf. A. H. Clark.) • ^ f ^^ Regeneration and new growth of lymphatic vessels and glands. — While blood-vessels are known to possess throughout life the capacity for regeneration and new growth, this process in lymph-vessels has been very little studied. Yet enough has been learned from the work of Coffin and Evans to justify the statement that lymphatic vessels also possess the capacityFfor new growth. Evans made the interesting observation that lymphatic vessels grow into a tumor of connective-tissue origin (a round-celled sarcoma), while they fail to grow into a tumor of epithelial origin (an experimentally-produced peritoneal carcinoma in mice). 708 THE LYMPHATIC SYSTEM The question as to whether lymph-glands may form anew is not yet entirely settled. The study of the problem is extremely difficult, because very small lymph-nodes may be normally present in a csrfcain region, yet they may escape observation untQ they become hypertrophied under certain conditions. A. W. Meyer in a careful experimental study found no evidence of new-formation of lymph glands. On the other hand, there is considerable evidence for the new- formation of lymph-glands under pathological conditions. The haemolymph nodes. — In addition to the ordinary lymph-nodes, there occur along the course of certain veins small nodes which are either red or brown in colour, according to their state of functional activity. These have been termed haemolymph nodes. The red nodes closely resemble in structure an ordinary lymph-node, except that the sinuses are filled with blood, while the brown nodes show not blood, but blood pigment, both free in the sinuses and in the phagocytic cells of the sinuses. In certain respects these nodes resemble the spleen, there being a reduction of the medullary cords and an increase in the amount of the sinuses, which resemble those of the spleen-pulp rather than the more open lymphatic sinuses; and their trabeculae are also like those of the spleen in having numerous smooth muscle-cells. Some of these hsemolymph nodes have lymphatic Fig. 554. — A Developing H^moltmph Node. Central blood-vessel vessels, but whether, as in the spleen, these are limited to the capsule, or whether they open into the blood-sinuses, making true hsemolymph nodes, is not yet clear. A difficult point in connection with the structure of the hfemolymph nodes is the relation of the blood-sinuses to the blood-vessels. The greater weight of evidence seems to favour the view that the sinuses are connected with the veins rather than that the arteries open directly into them, although one observer fails to find any connection between the blood-vessels and the central sinus (Schumacher). In fig. 554 is shown a hsemolymph node in the neck of a pig 24.5 cm. long. This stage marks the first appearance of the hsemal node in the neck, and shows the node in its simplest form, the foUicle and its peripheral blood-sinus (Miss Sabin). There are wide variations in the distribution and number of the haemolymph nodes; indeed sufficient observations have not yet been made to determine their complete distribution. They have been divided into three groups, the prsevertebral, the renal, and the splenic. In one subject, in which they were very numerous, they occurred at the root of the lung, near the bronchi, and bronchial vessels, a few near the oesophagus, a continuous praevertebral chain in the abdomen extending from the diaphragm to the upper two or three sacral vertebra, as well as a few along the ccefiac axis and its branches, the superior mesenteric, renal, and iliac vessels (Lewis). Schumacher, from a study of lymph-glands and haemolymph glands of various stages, concludes that the haemolymph glands are not to be considered as organs sui generis, but that they represent rudimentary forms of ordinary lymph-glands, which have lost their connections with the lymphatic vessels. Further investigations are needed to clear up this subject. NODES OF THE HEAD AND NECK 709 II. SPECIAL ANATOMY OF THE LYMPHATIC SYSTEM The lymphatic system will be considered by regions as follows: A, head and neck; B, upper extremity; C, thorax; D, abdomen and pelvis; E, lower ex- tremity. A. THE LYMPHATICS OF THE HEAD AND NECK The lymphatics of the head and neck may be divided into two sets. One set is superficial, draining the entire skin sin-face, and has its nodes, for the most part, in the neck, the principal group lying along the external jugular vein. The other set is deeper and drains the mucous membrane of the upper part of the digestive and respiratory tracts, together with the deep organs, such as the thyreoid gland and the tendons of the muscles. The nodes of this set are deeply placed, being situated along the carotid arteries, with outlying retro-pharyngeal nodes. 1. THE SUPERFICIAL NODES OF THE HEAD AND NECK Lymph-nodes appear first in the neck in the process of development. In the pig the first node to appear develops from the lymph heart, which is in the supra- clavicular triangle behind the sterno-cleido-mastoid muscle. From here ducts grow across the muscle and give rise to a chain of nodes along the external jugular vein. This chain is to be considered as the main chain of superficial nodes in the neck. From it lymphatic vessels grow over the back of the head, the side of the head, the face, and the front of the neck, and in their course groups of secondary nodes develop. The nodes of the main chain are known as the superficial cervical nodes, and are from four to six in number. The secondary groups are — (1) the occipital; (2) the posterior auricular; (3) the anterior auricular; (4) the parotid; (5) the submaxillary, with the facial as a tertiary set, and (6) the submental. 1. The occipital nodes [lymphoglandulse occipitales]. — The lymphatics of the skin of the back of the head collect into a few trunks that either empty into from one to three small nodes near the occipital insertion of the semispinalis capitis muscle, or pass by the secondary group and empty directly into the upper nodes of the main superficial cervical chain (fig. 555). 2. The posterior auricular nodes [Igl. auriculares posteriores]. — A portion of the temporal part of the scalp, together with the posterior surface of the ear, except the lobule, and the posterior surface of the external auditory meatus, drain into two small nodes on the insertion of the sterno-cleido-mastoid muscle. The effer- ent vessels of these nodes pass to the upper part of the superficial cervical chain. 3. The anterior auricular nodes [Igl. auriculares anteriores] are few innumber — from one to three — and are situated immediately in front of the tragus of the ear. They receive vessels from the anterior surface of the auricle and the external audi- tory meatus, from the integument of the temporal region and the lateral portion of the eyelids. Their efferents pass to the parotid and superior deep cervical nodes. 4. The parotid nodes. — The parotid group of nodes is considerably larger than the two preceding, containing from ten to sixteen nodes, and the group drains a more complex area. It receives vessels from the adjacent surface of the external ear, the external auditory meatus, the skin of the temporal and frontal regions, and the eyelids and nose. The deeper nodes of this set receive vessels from the parotid gland. In the embryo these nodes He in the pathway of the lymph- vessels that grow to the scalp; many of these vessels, however, pass the parotid group and empty into the superficial cervical chain. The nodes of the parotid group lie embedded in the substance of the parotid gland, and their efferents pass to the submaxillary and the superior superficial and deep cervical nodes. As "inferior auricular nodes" Bartels designates one or two small glands of the parotid group which lie below the ear, and receive afferent vessels from the lower part of the ear. 5. The submaxillary [Igl. submaxillares] and facial [Igl. faciales profundae] nodes. — The submaxillary (perhaps better "mandibular") group consists of a i 710 THE LYMPHATIC SYSTEM chain of from three to six nodes, resting on the submaxillary (salivary) gland, along the inferior border of the mandible. They lie usually on the submaxillary gland, but may extend from the insertion of the anterior belly of the digastric to Fig. 555. — The Lymphatics of the Head and Neck. (After Toldt, "Atlas of Human Anatomy " Rebman, London and New York ) Occipital lymph-nodes Posterior auricular lymph-nodes Superficial cervical lymph-nodes \ ► Axillary lymph-nodes .i.„z:^^=^ the angle of the jaw. They are about the size of a pea, and the largest is near the point where the external maxillary (facial) artery crosses the mandible. The sub- maxillary nodes, together with the next group, the facial, drain a complex area, THE FACIAL NODES 711 including not only skin, but mucous membrane. They receive lymph-vessels from the nose, cheek, upper lip, the external part of the lower lip, together with almost all those from the gums and teeth and from the anterior third of the lateral portions of the tongue. In agreement with the fact that these nodes, though lying superficially and draining the skin, drain also the mucous membrane, their vessels empty not only into the superficial cervical chain, but also into the deep carotid chain. The facial nodes are evidently outlying nodes of the submaxillary group. They are in two main sets — (1) the supra-maxillary set, which consists of from one to thirteen nodes, resting on the mandible near the point where it is crossed by the external maxillary (facial) artery. (2) The buccinator set, lying on the Fig. 556. — Lymphatics or the Outer Nose and Face. (After Ktittner.) Submax- illary node line connecting the lower margin of the ear and the angle of the jaw. Of these latter nodes, some lie near the point where the parotid duct perforates the buc- cinator muscle; the others are farther forward, between the external maxillary artery and the anterior facial vein. Additional nodes belonging to the group may occur near the nose and in the suborbital region. These facial nodes receive affer- ents from the outer surface of the nose, the lips, eyelids, cheek, temporal part of the face, the mucosa of the mouth, the teeth of the upper jaw, the gums, the tonsils, and the parotid gland. Their efferents pass to the submaxillary and parotid nodes. 6. The submental nodes [Igl. submentales], usually two in number, lie in the triangle bounded by the anterior bellies of the two digastric muscles and the hyoid bone (fig. 559). They are usually near the median line, and drain the skin of the chin, the skin and corresponding mucous membrane of the central part of the lower 712 THE LYMPHATIC SYSTEM lip and jaw, the floor of the mouth, and the tip of the tongue. The efferent vessels pass either to the submaxillary nodes or to the deep cervical chain. 2. THE LYMPHATIC VESSELS OF THE FACE The different parts of the face and their lymphatic relation to these groups of superficial nodes will now be considered. The lymphatics of the scalp form a rich network in the neighbourhood of the vertex, from which vessels pass in various directions. From the frontal region a Fig 557. — Lymphatic Nodes and Vessels of the Ear, Eyelids, Nose and Lips. New- born child. P, parotid. M, submaxillary gland. B, buccal fat ("sucking pad"). Supero- lateral deep cervical lymph nodes are not labelled. (After Bartels.) Ant. auricular lymph nodes Ant. submaxillary /' lymph nodes Middle submaxillary/ lymph nodes Inferior submental lymph nodes (var ) Posterior submaxillary lymph nodes number of ducts pass downward and backward to the parotid nodes; those from the parietal and temporal regions pass to the anterior auricular, parotid, and pos- terior auricular nodes; and those from the occipital region pass partly to the occi- pital nodes and partly to the superior deep cervical group, while a single large vessel descends along the posterior border of the sterno-mastoid muscle to ter- minate in one of the inferior deep cervical nodes. The lymphatics of the eyelids and conjunctiva. — The capillary plexus of the eyelids and the conjunctiva is an abundant one, and at the free border of the eyelids becomes extremely close. The lymphatics from the lateral three-fourths of the lids pass to the anterior auricular and parotid groups of nodes, while those from the medial one-fourth pass obliquely across the cheek with the facial vein to terminate in the facial and submaxillary nodes (figs. 556, 557, 561). The lymphatics of the nose. — The lymphatics of the nose (fig. 556) form a net- work which is coarse at the root of the organ, but dense over the alar region. The vessels run in three sets — (1) one set passing over the eye to the parotid nodes; (2) a set passing under the eye to the same nodes; and (3) the most important LYMPH-VESSELS OF THE FACE 713 group, consisting of from six to ten trunlts, passing to the facial and submaxillary nodes. There are some anastomoses between the capillaries of the skin and those of the mucous membrane of the nose. Fig. 558. — The Facial Nodes. (After Buchbinder.) ll -Suborbital nodes "Node of nasogenial fold - Supra maxillary ] ' Inframaxillary n( The lymphatics of theUps (fig. 559). — -The capillary plexuses of the skin and mucous membrane are continuous at the free border of the lips. The vessels of the upper lip, of which there are about four on each side, pass to the submaxillary Fig. 559. — The Lymphatics op the Lips. Newborn child. Dorendorf.) (From Bartels after Superior submental lymph nodes Ant. submaxillary lymph Deep cervical lymph node nodes. From the lower lip the trunks from near the angle of the mouth pass to the submaxillary nodes, while those from the centre of the lip pass to the submental nodes. There are from two to four subcutaneous vessels and from two to three submucous vessels on either side. The collecting trunks passing to the submaxillary nodes do not anastomose, and 714 THE LYMPHATIC SYSTEM the same is true of the submucous vessels of the lower lip. The subcutaneous vessels, on the other hand, passing to the submental nodes, anastomose freely, an important fact in connection withthe extension of cancer of the lower lip. The lymphatics of the auricle and external auditory meatus. — The lymphatic plexus in the auricle, external auditory meatus, and the outer side of the tympanic membrane is an abundant one. An anastomosis has been described between a scanty plexus on the inner side of the tympanic membrane and the plexus on the outside. The collecting vessels pass to three sets of nodes: — (1) those from the external and internal surface of the auricle and the posterior part of the external auditory meatus pass to the posterior auricular nodes; (2) those from the lobule, the helix, a part of the concha and the outer portion of the external auditory mea- tus pass to the inferior auricular and superficial cervical chain; some of the vessels from the first and second areas also run to the deep cervical group; (3) an anterior group from the tragus and part of the external auditory meatus consisting of from four to six trunks, pass to the anterior auricular nodes, which are connected with the parotid nodes. 3. THE DEEP LYMPHATIC NODES OF THE HEAD AND NECK The deep cervical chain is the largest mass of nodes in the neck. It consists of from fifteen to thirty nodes, which lie along the entire course of the carotid artery and internal jugular vein. This chain receives vessels from all the super- ficial nodes, also directly from the skin, as well as from the entire mucous mem- brane of the respiratory and alimentary tracts in the head and neck. Thus it drains both the superficial and the deep structures. For convenience of description this long chain, though usually continuous, is divided into two groups — (1) a superior group, lying above the level at which the omo-hyoid muscle crosses the carotid artery, and (2) an inferior or supra-clavicular group, lying below that level. (1) The superior deep cervical nodes [Igl. cervicales profundae superiores]. — This group of nodes extends from the tip of the mastoid process to the level at which the omo-hyoid muscle crosses the common carotid artery. The dorsal and smaller nodes of the chain lie on the splenius, levator scapulae, and scalene mus- cles. They drain the skin of the back part of the head, both indirectly and directly, and receive (1) efferents from the occipital and posterior auricular nodes, (2) a large vessel from the skin of the occipital part of the scalp, (3) some trunks from the auricle, and (4) cutaneous and muscular vessels from the neck. The ventral nodes of the chain lie on the internal jugular vein. They drain the face both directly and indirectly, as well as the deeper structures of the head and neck. They show especially well in fig. 563 in connection with the tongue. (2) The inferior deep cervical [Igl. cervicales profundse inferiores] or supra- clavicular nodes lie in the supra-clavicular triangle. In the upper part of the tri- angle the nodes rest on the splenius, the levator scapulae, and the scalene muscles, while at the base of the triangle they are related to the subclavian artery and the nerves of the brachial plexus. They drain a wide area, receiving vessels from the head, neck, arm, and thoracic wall. They are connected with the superior deep cervical chain, and receive afferents from the axillary nodes, and, in addition, they receive vessels directly from the back of the scalp, from the skin of the arm, and from the pectoral region. Thus it will be seen that a large part of the lymph of the head and neck, as well as some from the arm and thorax, passes through these nodes. Their efferents unite to form the jugular trunk, which ends at the junction of the internal jugular and subclavian veins. In the descriptions of the deep lymphatic vessels certain additional groups of nodes will be considered, which may be regarded as outlying groups from the deep cervical chain. 4. THE DEEP LYMPHATIC VESSELS OF THE HEAD AND NECK The lymphatics of the brain. — It is now recognised that there are no lymph- atics in the brain and cord, so that the function of absorption must be accom- phshed by means of the veins. There is an abundant exudation of lymph around the nervous system into the subdural space, which is connected with the central LYMPHATICS OF THE MOUTH 715 canal of the nervous system, and which is to be considered as a zone in which the tissue-spaces are especially large. Along the arteries of the brain the adventitia is loose and open, possessing tissue-spaces which have received the confusing name of perivascular lymphatics. It would be better to name them perivascular tissue- spaces. The lymphatics of the eye. — No lymphatic vessels have as yet been discovered either in the eyeball or in the orbit. In both, however, there are abundant tissue- spaces, the most noteworthy of the orbit being the interfascial space (space of Tenon), which communicates by a space between the optic nerve and its sheath with the subarachnoid spaces of the cranial cavity. In the eyeball the tissue- spaces are abundant, even if the vitreous and aqueous chamber be omitted from the category. Numerous spaces exist in the chorioid coat, especially in the lamina supra-chorioidea, and in the sclerotic, both sets communicating by perivascular spaces surrounding the venae vorticosae with the interfascial space. In the cornea there are abundant lacunae, united by their anastomosing canaliculi, to form a network of lymph-spaces which come into close relation with the conjunctival lymphatics at the corneal margin. Fig. 560. — The Deep Ceevical Chain (After Poirier.) Mastoid node Internal jugular chain The conjunctiva, being a portion of the integument, does possess lymphatic vessels ffig. 562), arranged in a double network whose collecting vessels accompany those of the eyelids, and terminate with them in the submaxillary, anterior auricular, and parotid nodes. The Lymphatics of the Digestive Tract in the Head and Neck The lymphatics of the gums. — ^The lymphatics from the mucous membrane of the gums pass to the submaxillary nodes. The capillary plexus is abundant; the collecting vessels arise from it on the inner surface of the gum, and pass between the teeth to reach a common semicircular collecting vessel on the outer surface. Lymphatics have recently been demonstrated in the pulp of the tooth (Schweitzer). The lymphatics of the tongue. — -There is a rich lymphatic plexus throughout the entire extent of the submucosa of the tongue, but that portion lying in the basal part of the tongue seems to be more or less independent of the rest. Accord- ing to Aagaard the tongue muscles are provided with lymphatics which are drained by the ducts of the submucosal plexuses. There are four groups of collecting vessels — (1) apical; (2) marginal; (3) basal; and (4) central. (1) The apical vessels are usually four in number, two on each side. One pair perforates the mylo-hyoid muscle and ends in a supra-hyoid median node, while the other pair pass to the deep cervical chain. The latter are long, slender vessels, which run along the frenum of the tongue to the surface of the mylo-hyoid muscle, cross the hj'oid bone just behind the pulley of the digastric, and then run downward in the neck to a node of the deep cervical chain, just 716 THE LYMPHATIC SYSTEM above the omo-hyoid. It will be noted in fig. 563 that the most anterior vessels end in the lowest nodes, while those from the back of the tongue end in higher nodes, (2) The marginal vessels are from eight to twelve in number. They all pass to the superior Fig. 561. — Lymphatics of the Head, Neck, and Axilla. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Lymph-vessels of the breasts deep cervical nodes, a part of them passing external to the sublingual gland, while the larger number pass internal to it. There is one large and constant node at the point where the digastric muscle crosses the jugular vein, to which a large number of the vessels converge. LYMPHATICS OF NASAL CAVITIES 111 (3) The hasal vessels are seven or eight in number, and drain the basal portion of the tongue. Some end in the large node just mentioned, while others run backward close to the median line, where they anastomose, as far as the glosso-epiglottidean fold, when they separate and join the tonsillar vessels to pass outward to the superior deep cervical nodes. (4) The central vessels, arising from the central portion of the tongue, pass backward in the median line on the ventral surface of the tongue. They lie upon the mylo-hyoid muscle, cross the hyoid bone, and end in the superior deep cervical chain. The lymphatics of the palate. — The lymphatics from the palate pass to the deep cervical chain. The trunks from the hard palate run in the submucosa as far as the last molar tooth, where they pass in front of the anterior pillars of the fauces and end in the superior deep cervical nodes beneath the digastric muscle. In the soft palate the capillary plexus is very rich, reaching a maximum in the uvula. From the inferior surface of the soft palate and the pillars of the fauces vessels pass directly to the superior deep cervical chain, but some of the vessels Fig. 562. — The Lymphatics of the Conjunctiva. (After Teichmann.) from the upper surface of the soft palate run forward with the pharyngeal vessels and end in the retro-pharyngeal nodes. It will be seen from fig. 564 that the retro- pharyngeal nodes are simply outlying nodes from the deep cervical chain. The lymphatics of the pharynx. — As has just been stated, there are certain outlying nodes of the deep cervical chain which lie behind the phaiynx. They receive some of the ducts from the submucosa of the roof of the pharynx, but many of the pharyngeal vessels pass by these nodes and end directly in the superior deep chain. The tonsil is especially rich in lymphatics, and its ducts, together with those from the middle and inferior portions of the pharynx, end in the superior deep cervical chain. The lymphatics of the Eustachian tube run to the lateral retro-pharyngeal lymph-nodes or, passing these, to the deep cervical nodes. The lymphatics of the nasal cavities. — The mucous membrane of the nose contains a rich lymphatic plexus whose main ducts pass to the retro-pharyngeal nodes. An anterior set, however, anastomoses with the subcutaneous vessels, and through these their lymph is conveyed to the facial and submaxillary nodes. The posterior vessels run either to the deep cervical chain or to the retro-pharyn- geal nodes. Key and Retzius have shown that an injection of the Ij^mphatics of the nose may be made by injecting the subarachnoid spaces at the base of the 718 THE LYMPHATIC SYSTEM brain, although there is presumably no direct connection between the spaces and the lymphatic vessels. The lymphatics of the nasal sinuses end in the retro- pharyngeal nodes. Fig. 563. — The Lymphatics of the Tongite. (Poirier and Charpy.) Basal trunks ir^- . Marginal collecting trunks / with hypoglossal nerve — Marginal trunk V>___ ' Submen- j^y' ^l^ '"" ^ ' tal node "5^^-^- CoUecting ~ trunks frora margin of — tongue Node inter- calated in these ducts Vessel from margin of tongue ending in in- ternal jugular chain _ ^""Intercalated node Central vessel passing to node above the omo-hyoid Inferior node of m ternal jugular chain (above omo hyoid muscle) > ] Collecting f trunks from tip of tongue 1 Retro-pharyngeal J nodes Intercalated node CoUecting vessels of pharynx to deep ; cervical chain [ NODES OF THE UPPER LIMB 719 The lymphatics of the larynx. — The larynx is, for the most part, drained by the deep cervical nodes, although its lymph may also pass through certain out- lying nodes situated upon its ventral surface. The mucous membrane is divided into two zones by the ventricular folds, the mucous membrane of these structures possessing but a scanty lymphatic plexus. The vessels from the upper part of the lar3'nx, four or five in number, pass to the nodes of the superior deep cervical chain, situated near the digastric muscle; those from the lower part pass to the lower nodes of the same chain, some even descending as far as the supra-clavicular nodes. The lymphatics of the trachea pass, on each side, to the paratracheal and inferior deep cervical nodes. The lymphatics of the thyreoid body. — The lymphatics of the thyreoid body pass either to the small nodes situated in front of the larynx and trachea, or to nodes of the deep cervical chain, a part of them ascending and a part descending. It will thus have been seen that the lymphatics of the mucous membrane of the head and neck all end in the deep cervical chain of nodes or in the outlying nodes from it. Some of the vessels pass by the outlying nodes, but since the nodes of the chain are so closely connected, the lymph must pass through several nodes before entering the veins. The main tonsils, the numerous lingual and pharyngeal tonsils, together with small lymph-follicles in the submucosa of the respiratory tract, represent lymph-nodes in the capillary zone. B. THE LYMPHATICS OF THE UPPER EXTREMITY 1. THE LYMPHATIC NODES OF THE UPPER EXTREMITY The lymph-nodes of the arm lie, for the most part, in the axilla, where thpre is a large group of nodes which receive almost the entire drainage of the arm and the thoracic wall. In addition, there is in the arm a set of outlying superficial nodes, the superficial cubital (supra-trochlear) , while small isolated nodes are often intercalated along the course of the deep lymphatic vessels which accompany the radial, ulnar, anterior interosseus and brachial arteries, the cephalic vein, and the deep cubital vessels. (1) The antibrachial nodes are very small, pin-head sized nodes which are intercalated along the deep lymphatics which accompany the radial, ulnar, ante- rior and posterior interosseus arteries. (2) The deep cubital nodes [Igl. cubitales profundse] are also very small nodes, one or two in number, intercalated along the ducts, near the deep vessels at the bend of the elbow. (3) The superficial cubital node [Igl. cubitales superficiales] (or supratrochlear) is situated three or four centimetres above the medial epicondyle of the humerus. It lies in the superficial fascia on the medial side of the basilic vein near the place where it passes through the deep fascia. It is usually single, but may be absent or represented by a chain of from two to five nodes. Its eflerents follow the basilic vein. (4) The delto-pectoral nodes are very small intercalated nodes from one to three in number, and are situated in the groove between the deltoid and pectoral muscles. Their vessels follow the cephalic vein. (5) The axillary nodes [Igl. axillares], from twelve to thirty-six in number, may be divided into groups according to the areas which they drain (fig. 566). In addition to the upper extremity, they receive lymphatic drainage from the thoracic walls, including dorsal, lateral and ventral (mammary) regions. (1) The subclavian group consists of four or five nodes, situated in the apex of the axillary fossa. They receive the efferent vessels of all the other groups, and their efferent vessels in turn unite to form a single trunk, the subclavian, which empties into the thoracic duct on the left side and on the right side either into the vein directly or else after uniting with the jugular trunk. (See pp. 726-728.) (2) The central group. A little lower along the axillary artery is a group of three to five nodes, which makes a second centre for the vessels of the other groups, and sends its efferents to the subclavian group. It will be clear from the figure that the separation of groups 1 and 2 is arbitrary. (3) The brachial group. — This consists of four or five nodes, and, as its position toward the junction of the axillary and brachial arteries indicates, is the main station for the lymphatics of the arm proper. It receives almost all the superficial and deep lymphatics of the arm, and its efferents pass to the central and subclavian groups, although a few pass directly to the 720 THE LYMPHATIC SYSTEM suprascapular group. Small, outlying nodes of this group may be intercalated along the vessels following the brachial artery throughout its course. (4) The subscapular group [Igl. subscapulares]. — In this group are six or seven nodes, which follow the subscapular artery and its branch, the circumflex (dorsal) scapular. Belonging Fig. 565. — The Lymphatics op the Uppeb Extremity. (After Toldt, Anatomy," Rebman, London and New York.) 'Atlas of Human Axillary lymph nodes — to it there are usually two or three sjnall nodes on the dorsal surface of the scapula, in the groove which separates the teres major and minor. This group receives vessels from the dorsal surface of the thorax, aa well as from the arm, and its efferents pass to the brachial group. (5) The anterior Jpeclmal'^group [Igl. peotorales]. — This group consists of four or five nodes which lie along the lower border of the peetorahs major and drain the mammary gland and front of the chest. Their efferent vessels pass to the central and subclavian groups. LYMPH-VESSELS OF THE LOWER LIMB 721 (6) The posterior pectoral group [Igl. pectorales] consists of small nodes situated on the inner wall of the axiUa, along the course of the long thoracic artery. They receive afferents from the lateraljntegument of the thorax and drain into the nodes of the central group. ^[2. THE LYMPHATIC VESSELS OF THE UPPER EXTREMITY The lymphatic vessels of the upper extremity are divided into two sets — -a superficial and a deep set. The superficial vessels. — The superficial lymphatic vessels of the arm course in two layers, the one quite subcutaneous, the other next the deep fascia, with frequent anastomoses between the two sets. The majority of these vessels remain superficial throughout the arm, but some of them pass through the deep fascia in the upper arm especially where the basilic vein pierces the deep fascia, Fig. 566. — The Axillary Ltmph-nodbs. (After Poirier and Cuneo.) Brachial group Central group Nodes connect- ing the central and subscapu- lar groups Subscapular group Subclavian ?S^^ group Vessel from the mammary gland Anterior pec- toral node Vessel from the mammary gland Collecting trunk Subareolar plexus Vessel from lateral thoracic wall Vessel passing to internal mammary node Collecting vessels Vessel passing to internal mammary node to join the deep lymphatics accompanying the brachial artery. The general distribution of the superficial lymphatics and their relations with the lymph- nodes are shown in figs. 565 and 567. The capillary plexus is most dense in the palmar sm-faces of the fingers, where the meshes are so fine that they can only be seen with a lens. On the dorsal surface of the fingers and hand the plexus is less dense. From the plexus on the palmar side of the fingers vessels come together at the base of the fingers where they pass dorsally to be joined by the dorsal vessels of the finger. They now follow two rather distinct curves: (1) those from the thumb and index finger and a part of the middle finger pass upward along the radial side of the forearm, com-se medially over the lower part of the biceps muscle, and empty into the axillary lymph-nodes. One or two vessels follow the cephalic vein and, after traversing the delto-peotoral node, pierce the costo-eoracoid membrane to enter the subclavian nodes, or pass over the clavicle into the inferior deep cervical nodes. (2) Those from the rest of the fingers course for a short stretch on the dorsum of the forearm, when they turn toward the ulnar side, wind around to the volar side and either continue superficially along the upper arm to the axillary nodes, or pass into the superficial cubital node, or, joining the efferents from these nodes, pass through the deep fascia to unite with the deep lymphatics. (3) A set of vessels from the palm of the hand passes upward along the volar side of the forearm. Anastomoses are frequent between these groups of lymphatic vessels, particularly in the cubital region. It will thus be seen that the superficial cubital nodes receive lymph from the ulnar digits and from the palm of the hand, but not from the thumb and forefinger. The superficial lymphatics from the rest of the arm join these thi'ee main groups at various levels. The deep vessels. — ^The deep lymphatic vessels of the upper extremity drain the joint capsules, periosteum, tendons, and (if the recent work of Aagaard is 722 THE LYMPHATIC SYSTEM correct) the muscles. They collect into vessels which, in general, accompany the arteries, in the forearm, the radial, ulnar, anterior and posterior interosseous, and in the arm the brachial. Above the elbow they are joined by numerous super- FiG. 567. — The Lymphatics op the Forearm. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Brachial fabcia Brachial artery and veins ^Superficial lymphatic vessels Superficial cubital lymph-nodes Tendon of the biceps muscle ■^ Deep cubital lymph-nodes Deep lymphatic vessels AntibracMal fascia— - ■ Superficial lymphatic vessels Lymph-vessels of the hand fj / / i/ ^^ ^ ^ Lymph-vessels of the thumb *^ Lymph-vessels of the finger Lymphatic network --- Superficial volar arch ^--- Palmar aponeurosis — Lymphatic network Subcutaneous fat of the finger ficiall lymphatic vessels including efferents from the superficial cubital nodes. Along their course in the forearm are intercalated small nodes (pin-head size), radial, ulnar, anterior and posterior interosseous (Mouchet) and deep cubital; and, in the arm, small brachial intercalated nodes. The deep vessels in the main enter the brachial group of axillary lymph-glands which lie behind the large vessels LYMPHATICS OF THE MAMMARY GLAND 723 and nerves, the efferents from which nodes pass either into the lower deep cer- vical lymph-nodes or directly into the subclavian trunk. The lymphatics of the shoulder-joint have recently been described by Tananesco. He finds a ring of lymphatics in the joint capsule, whose efferents, in the main, following the arteries, run to the central and subclavian groups of axillary nodes. C. THE LYMPHATICS OF THE THORAX The lymphatics of the thorax will be considered under the following divisions: the superficial vessels, the deep nodes, and the deep vessels. 1. THE SUPERFICIAL LYMPHATIC VESSELS OF THE THORAX The superficial lymphatics of the thorax pass almost exclusively to the axillary nodes, and may be regarded as forming three sets, a ventral, a lateral, and a dorsal. The ventral set drains the thoracic integument, which extends form the median line and the clavicle over to the lateral border of the chest, and includes the vessels of the mammary gland, which will, however, be described separately. The majority of the vessels from this area end in the anterior pectoral group of axillary nodes, a few, which arise beneath the clavicle, passing to the supra- clavicular nodes, and a few perforating the intercostal spaces and ending in the chain of nodes along the internal mammary artery. It has been shown that an injection into the subcutaneous plexus near the median line passes to the opposite side, and that, in addition to the anastomosis between the networks of the two sides of the thorax which this result manifests, there may also be a few collecting trunks crossing the median line, and, furthermore, anastomoses occur between the superficial networks of the anterior thoracic and abdominal walls. Thus while the main channel of lymphatic drainage is through the axiUa, there are minor accessory channels to (1) the supraclavicular nodes, (2) to the axilla of the opposite side, (3) to the internal mammary chain, and (4) in iso- lated cases even to the inguinal nodes. These accessory channels may become more open in cases of obstruction to the main channel. The lateral set of superficial thoracic lymphatics is much less extensive than the anterior, and its collecting vessels pass upward to open into the posterior pectoral group of axillary nodes. The dorsal set, which occupies the subcutaneous tissue of the dorsal thoracic wall, sends its vessels to the subscapular group of axillary nodes. The Lymphatics of the Mammary Gland (Figs 566, 568) The lymphatic network over the peripheral portions of the mammary gland is like that of the rest of the thoracic wall. In the areola, however, the capillaries are far more abundant, forming a double subareolar plexus. The superficial plexus is so dense that its meshes can be seen only with a lens. The deeper plexus not only drains the superficial plexus, but receives the vessels from the mammary gland itself, and from it arise two large trunks, one from the inferior and one from the superior part of the plexus. These two vessels pass to one or two of the nodes belonging to the anterior pectoral group of axillary nodes. In addition there may be — (1) one or two vessels passing to the nodes along the axillary artery; (2) in rare cases a vessel passing directly to the subclavian nodes. There is also a defi- nite channel from the medial margin of the gland to the internal mammary nodes, the ducts following the perforating branches of the internal mammary vessels, and it may be noted that the crossed anastomosis and that with the abdominal network, mentioned in connection with the superficial thoracic vessels, may, on occasions, serve as channels for the mammarj^ drainage. There is also clinical evidence indicating that lymphatic vessels from the lower and medial aspect of the mammary gland may pass through the abdom- inal wall in the angle between the xiphoid process and the costal cartilages, establishing a communication with the lymphatics of the abdomen in the diaphragmatic region. Lymphatics of the thoracic muscles. — The recent studies of Aagaard make it probable that muscles are provided with lymphatics. Whether his findings will be substantiated or not, however, it is unquestioned that lymphatic vessels course through the pectoral muscles — some passing to the axillary, others to the subclavian, and still others to the internal mammary chain of nodes. This would suffice to explain the fact that cancer of the breast may extend into and through the pectoral muscles. 724 THE LYMPHATIC SYSTEM 2. THE DEEP LYMPHATIC NODES OF THE THORAX The lymphatic nodes of the thoracic cavity may be divided into the parietal and the visceral. The parietal nodes are arranged in two sets, the internal mammary chain and the intercostal nodes (fig. 570) . Along the internal mam- mary artery are from four to sLx small nodes, [Igl. sternales] which receive ducts from the anterior thoracic and the upper part of the abdominal walls, from the anterior diaphragmatic nodes which drain the liver, and from the medial edge of the mammary gland. The efferent vessels usually unite with the vessels of the anterior mediastinal and bronchial nodes, to form the broncho-mediastinal trunk, which may join the thoracic duct on the left and the jugular or subclavian trunk on the right or may empty separately into the subclavian vein on both sides. Fig. 568.- -Lymphatics of the Subareolar Plexus of the Breast. (After Sappey.) Vessels from network Lobuleof gland, uninjected Subareolar network Vessel from , . ( network n ^ Lobule of gland uninjected Superficial *:i— network Vessels from network The intercostal nodes [Igl. intercostales] lie along the intercostal vessels, near the heads of the ribs. There are usually one or two in each space, and occasiona,lly a node is placed where the perforating lateral artery is given off. They receive afferents from the deeper part of the thoracic wall and costal pleura. Their efferents enter the thoracic duct, those from the nodes of the lower four or five interspaces uniting usually to form a common duct on each side, but more marked on the left side, which descends to the receptaculum chyh. The efferent lymph-vessels from the upper intercostal nodes often unite into common trunks which drain several interspaces, and which may pass through a large gland near the thoracic duct before emptying into it. Occasionally such collecting vessels from the right side cross the mid-Une behind the aorta to reach a large gland to the left of the aorta. The visceral nodes of the thorax are arranged in three groups : — ■ 1. The anterior mediastinal nodes [Igl. mediastinales anteriores] are situated, as their name indicates, in the anterior mediastinum, and are arranged in an upper and a lower set. The upper set is situated upon the anterior surface of the arch of the aorta, and consists of eight or ten nodes, which receive afferents from the pericardium and the remains of the thymus gland. Their efferent vessels pass upward to join the broncho-mediastinal trunk. The lower set consists of from LYMPH-VESSELS OF THE THORAX 725 three to six nodes, situated in the lower part of the mediastinum. They receive afferent ducts from the diaphragm, hence they are sometimes termed the dia- phragmatic nodes, and also from the upper surface of the liver. Their efferents pass upward to open into the upper anterior mediastinal nodes. 2. The posterior mediastinal nodes [Igl. mediastinales posteriores] eight or ten in number, are situated along the thoracic aorta, and receive vessels from the medi- astinal tissue and from the thoracic portion of the oesophagus. Their efferents open directly into the thoracic duct. 3. The bronchial nodes [Igl. bronchiales] form an extensive group lying along the sides of the lower part of the trachea, and along the bronchi as far as the hilus Fig. 569. — The Tracheal and Bronchial Nodes. (Sukiennikow.) Inferior laryngeal nerve — Tracheal nodes Trachea Inierior laryngeal nerve Tracheo-bronchial node Bronchial nodes Connecting chain Pulmonary nodes Pulmonary nodes Connecting chain Pulmonary nodes of each lung, those lying in the hilus being termed the pulmonary nodes, and others, according to their position, lateral tracheo-bronchial, inferior tracheo- bronchial (nodes of the bifurcation) and tracheal (paratracheal). Thej'' receive the drainage of the lower part of the trachea, the bronchi, the lungs, part of the oesophagus, and, to a small extent, the heart. Thek efferent vessels unite with those from the upper anterior mediastinal and internal mammarj^ nodes to form the broncho-mediastinal trunk. 3. THE DEEP LYMPHATIC VESSELS OF THE THORAX In following the deep lymphatics of the thorax the course of development will be followed in describing first the thoracic duct and right lymphatic ducts, second the parietal vessels, and third the visceral vessels. 726 THE LYMPHATIC SYSTEM The Thoracic Duct The thoracic duct [ductus thoracicus] (fig. 570), which is the main collecting duct of the lymphatic system, extends from the second lumbar vertebra along the spinal column and course of the aorta to the junction of the left internal jugular and subclavian veins. It receives all the Ij^mphatics below the diaphragm, and the deep lymphatics from the dorsal half of the chest wall; and also, when joined, near its cephalic end, by the left broncho-mediastinal, subclavian and jugular trunks, from the remainder of the left half of the body, above the diaphragm. At the caudal end the duct is formed usually by the union of three collecting ducts, one from each of the lumbar groups of nodes, and an unpaired intestinal Fig. 570. — The Thokacic Duct. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Thoracic duct Internal jugular vein Jugular trunk Subclavian trunk Subclavian vein Right innominate vein — >^~.-^.n,^, .— ,.^^^^_^ — ^, .. Axillary lymph -nodes Intercostal lymph-nodes ■*^ iSi^^ y/i To inferior gastric node partly dorsalward to the anterior mediastinal group of nodes on the upper surface of the diaphragm, and to the nodes around the vena cava, and partly ventral- ward to the hepatic nodes of the portal fissure. The collecting vessels of the inferior surface pass to the nodes situated in the portal fissure, either along the artery or the bile-ducts. The lymphatics of the gall-bladder join the hepatic nodes along the cystic and common bile-ducts, and also the superior pancreatic nodes. Lymphatics of the pancreas. — The lymph-vessels which drain the pancreas fall, according to Bartels, into four groups: left, anterior (upper), right and posterior (lower). (1) The left group drain the tail of the pancreas and pass to the splenic lymph-nodes, at the hilus of the spleen. (2) Anteriorly lymphatics pass to "superior pancreatic lymph-nodes," superior gastric and hepatic nodes. (3) To the right, lymphatics pass to " pancreatico-duodenal lymph-nodes." (4) Posteriorly lymphatics pass to the aortic, mesenteric, meso-colic, and inferior pancreatic nodes. The siDlenic, superior pancreatic, inferior pancreatic, and pancreatico-duodenal nodes are usually grouped together as " lymphoglandulse pancreatico-l'enales." Anastomoses exist between the lymphatics of the pancreas and those of the duodenum. The lymphatics of the spleen (fig. 582) are found only in the form of a sub- capsular plexus, there being no deep network (Mall). They pass to the splenic nodes [Igl. pancreatico-lienales], which are variable in number and are situated LYMPHATICS OF THE KIDNEY 737 along the course of the splenic vessels. In addition to the spleen they drain the fundus of the stomach and a part of the pancreas. Fig. 578.— Lymphatics op the Small Intestine. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) { The Lymphatics of the Excretory Organs and of the Suprarenal The lymphatics of the kidney.— The lymphatic vessels from the deep capsular and parenchymatous lymphatics of the kidney run to the nodes of the lumbar cham (fig. 583). On the right side, part of the nodes concerned lie ventral and I 738 THE LYMPHATIC SYSTEM part dorsal to the renal vein; one of the nodes lies as far caudalward as the bifurca- tion of the aorta; and one or two vessels may pass to pre-aortic nodes. On the left side the vessels end in four or five nodes of the lumbar group. The efferents of these nodes pass through the diaphragm and end in the thoracic duct. The lymphatics of the Suprarenal. — The lymphatic vessels coming from the capsular and parenchymatous plexuses pass, on the right side, into two or three anterior para-aortic nodes, and a small retro-venous gland, near the pillar of the diaphragm; on the left side, into para-aortic nodes, and, in part, through the diaphragm, in company with the splanchnic nerve, to a posterior mediastinal Fig. 579. — The Lymphatic Circulation of the Ileo-c^cal Region, Anterior View. (After Kelly.) gland, lying between the ninth thoracic vertebra and the aorta. Anasto- moses occur with the lymphatics of the kidney. In addition to the capsular lymphatics proper, Kumita describes a subserous plexus, which is present over both kidney and adrenal, which anastomoses with the lymphatics of the liver and diaphragm. The efferents of this plexus collect, on the right side, to a gland placed to the right of the inferior vena cava, anterior to the right renal vein, and on the left side to a gland anterior to the left renal vein. The lymphatics of the ureter. — Sakata has recently studied the lymphatics of the ureter. They fall into three groups: (1) An anterior (upper) group, which run to the anterior lumbar nodes, or join the renal lymphatics; (2) a middle group which pass to the posterior lumbar and interiliac nodes; (3) a posterior (lower) group which pass to hypogastric nodes and which anastomose with lym- phatics of the bladder. LYMPHATICS OF PROSTATE 739 The lymphatics of the bladder. — The collecting vessels from the lower part of the ventral surface pass to a node of the external iliac group, situated near the femoral ring and the obturator nerve; those from the upper part of the ventral and dorsal surfaces pass to the middle node of the middle group of the external ihac chain, and from the rest of the dorsal surface they pass either to the hypogastric i Fig. 580.- -The Lymphatic Circulation op the Ileo-c^cal Region Posterior View. (After KeUy.) nodes or beyond these to the nodes at the bifurcation of the aorta (fig. 584). In this latter group end also the vessels from the neck of the bladder. Along some of the lymphatics of the bladder are intercalated lymph-nodes, which have been termed anterior and lateral vesical nodes. The lymphatics of the prostate. — The lymphatics of the prostate have been studied in the dog by Walker and in man by Bruhns. The collecting vessels, sbc to eight on each side, pass along the prostatic artery to the nodes along the ex- ternal border of the hypogastric artery. These nodes are connected with those along the external and common iliac arteries, and it is possible, from an injection of the prostate, to fill the entire chain of nodes as far as the renal artery. A trunk from the posterior surface runs up over the bladder and curves outward to 740 THE LYMPHATIC SYSTEM the middle node of the middle group of the external iliac chain, and still other vessels from the posterior surface run first downward, pass around the rectum, and then ascend to the lateral sacral nodes. From the anterior surface a descending duct may follow the deep artery of the penis, and the internal pudic to the hypogastric Fig. 581. — The Superficial Lymphatic Netwoek of the Liver. (After Teichmann). Fig. 682. — Lymphatics of the Periphery of a Pig's Spleen. (After Teichmann.) nodes (fig. 585) . The lymphatics of the prostate anastomose with those of the bladder, ductus deferens and rectum. The lymphatics of the urethra. — 1. In the Male. — The capillary plexus of the urethra is in the mucous membrane. The collecting vessels from the mucous LYMPHATICS OF URINARY TRACT Fig. 583. — Lymphatics of the Kidney. (After Poirier and Cunfio.) 741 Suprarenal artery- Pre-aorticnode i Fig. 584. — Lymphatics of the Bladder. (After Cunco and Marcille.) External iliac node- Collecting trunks of upper dorsal surface Collecting trunk of upper dorsal surface Collecting trunk of , inferior ventral surface Hypogastric node Hypogastric node Ureter Collecting trunks along inferior vesical artery Collecting trunks to end in the node of the promontory 742 THE LYMPHATIC SYSTEM membrane of the glans follow the dorsal vein. Those from the penile and^mem- branous portions of the urethra start from the inferior surface and curve around the corpora cavernosa, as seen in fig. 586, to join the others along the dorsal vein. These vessels run with the vein to the symphj^sis, where the}' form a plexus in which there may be some small intercalated nodes. From this plexus vessels pass in two directions: — (1) Three or four vessels, the crural trunks, pass to the deep inguinal and external iliac nodes, and (2) one vessel enters the inguinal canal and ends in one of the external iliac nodes. The vessels from the bulbar and membranous portions either follow the internal pudic arterj', or pass to the symphj-sis and end in the external iliac nodes, or pass onto the surface of the bladder and thence to the external iliac chain. The Fig. 585. — The Lymphatics of the Prostate. (After Ciin^o and Marcille.) External iliac / — nodes | Retro prostatic lymphatics Collecting vessels from prostate to Node of the pro- montory Lateral sacral Collecting vessels from prostate to node of pro- montory Middle hamor- rhoidal node and trunks Ijinphatics of the prostatic portion run with the prostatic ducts. The lymphatics of the urethra anastomose with those of the bladder and those of the glans. 2. Inthe female the Ij-mphatic vessels of the urethra end in the external iliac and hypogastric nodes. Lymphatics of the Rephoductive Org.vns In the Male (figs. 585, 586, 587) The IjTQphatics of the external genitaha will be first described and then those of the internal organs (fig. 589). The lymphatics of the scrotum form a rich plexus which has been pictured by Teichmann (fig. 547). The collecting vessels, ten to fifteen on either side, arise near the raphe and pass to the root of the penis, where some curve lateralward to the superior medial superficial inguinal nodes; while others, coming from the lateral surface of the scrotum, pass to the corresponding inferior nodes. LYMPHATICS OF REPRODUCTIVE ORGAXS 743 Fig. 586. — ^Lymphatics of the Penile axb Membraxous Portioxs of the Urethra. (After Cuneo and Marcille.) Collecting trunk in front of — symphysis { Vessel along inter- nal mdic artery Vessel from anterior — surface of the prostate Collecting trunk behind the symphysis Vessel along inter- nal pudic artery Fig. 5S7. — ^Ltmphatics of the Glaxs Pexis ix a Xew-borx Child. (Cuneo and Marcille.) External iliac node Node in abdominal inguinal ring Presymphysial' node Network ofr^fg^"'-- glans penis '"' { 744 THE LYMPHATIC SYSTEM The lymphatics of the penis.— (1) The cutaneous lymphatics form a plexus from which collecting vessels follow the dorsal vein and end in the superficial mguinal nodes. (2) The lymphatics of the glans form an exceedingly rich plexus from which vessels follow the dorsal vein of the penis, as described under the urethra, and end in the deep inguinal and external iliac nodes. (3) The lymphatics of the erectile structures are little known. The lymphatics of the testis are both superficial and deep, the latter being exceedmgly hard to inject. The collecting vessels follow the spermatic cord and artery and end in the lumbar nodes. .—Lymphatics of the Pemnedm. (After Toldt, "Atlas of Human Anatomy," Reb- man, London and New York.) Dorsal lymph-vessels of the clitoris Glans clitoridis Fig. 688, Superficial epigastric vein \ Superficial inguinal lymph-nodes Labium majus Region of the tuberosity of the ischium / Fat of ischio -rectal fossa Anus The lymphatics of the ductus deferens and vesiculse seminales. — In the ductus deferens only a superficial set has been injected, and its vessels passlto the external ihac nodes. The plexus of the vesiculaj seminales is double, super- ficial and deep, and its vessels pass to the external iliac and hypogastric nodes. In the Fernale (Figs. 588, 589, 590) The lymphatics of the vulva.— Throughout the vulva there is an exceedingly rich, superficial lymphatic plexus, from which collecting vessels pass to the symphysis and there turn lateralward to the medial superficial inguinal' nodes. The fact that the capillary plexus is continuous from side to side and that there is a plexus of the vessels in front of the symphysis, makes the nodes of both sides liable to infection from a unilateral lesion. LYMPHATICS OF VAGINA 745 The lymphatics of the clitoris. — The lymphatics of the glans of the clitoris form an abundant network from which collecting vessels pass toward the symphy- sis pubis, and thence principally to the deeper inguinal nodes, one or two, however, passing through the inguinal canal to terminate in the lower external iliac nodes. The lymphatics of the ovary. — The ovary has a remarkably rich lymphatic plexus, from which from four to six vessels leave the hilus and follow the ovarian artery to the lumbar nodes. One vessel may run in the broad ligament to the internal iliac group. The lymphatics of the Fallopian tube form three capillary networks from which collecting vessels run in part with those of the ovary, and in part with the uterine lymph-vessels. The lymphatics of the uterus. — According to Poirier, the lymphatics of the uterus arise from three capillary plexuses, a mucous, a muscular, and a peritoneal. The collecting vessels from the body of the uterus are in three sets: — (1) Those from the fundus, consisting of four or five vessels, run lateralward in the suspen- FiG. 589. — Lymphatics op the Internal Genital Organs in the Female. (After Poirier. Vena cava- Kidney Right renal vein' ( Right spermatic artery Lumbar node Lumbar node — Anterior crural nerve- Peritoneum- Lymphatics in utero-sacral ligament Cervical lymphatics—- Ovary — Parovarium — Lymphatics of round ^ ligament / — ^Lumbar vein Spermatic artery Ureter Inferior mesenteric artery Middle lumbar node Middle sacral artery Ovarian lymphatics Pelvic colon — Lymphatics of the tube „nterine tube (Falloppii) sory ligament of the ovary and follow the ovarian vessels to the lumbar and pre- aortic nodes. They anastomose with the lymphatics from the ovary opposite the fifth lumbar vertebra; (2) some small vessels from the fundus follow the round ligament of the uterus and terminate in the inguinal nodes; and (3) others from the body of the uterus pass laterally with the uterine vessels and terminate in the iliac nodes. The collecting vessels from the cervix, five to eight in number, form a large lymphatic plexus just after leaving the cervix. From this plexus run three sets of vessels. Two or three vessels pass lateralward with the uterine artery in front of the ureter, and end in the external iliac nodes; a second set passes behind the ureter and ends in a node of the hypogastric group, and a third set from the posterior surface runs downward over the vagina and then backward and upward to end in the lateral sacral nodes and node of the promontory of the sacrum. The lymphatics of the vagina (fig. 590) . — -There are two lymphatic plexuses in the vagina, a superficial and deep — the latter, the mucosal plexus, being ex- ceedingly rich. The collecting vessels are in three groups. The superior set drains the upper third of the vagina and takes the same course as those from the lower cervical portion of the uterus; the middle set follows the vaginal artery to 746 THE LYMPHATIC SYSTEM the hypogastric nodes; and the inferior set runs to the lateral sacral nodes and to those of the promontory. The capillary network of the lower part of the vagina is continuous with the plexus of the vulva, which drains to the inguinal nodes. Fig. 590. — ^Lymphatics of the Vagina. (After Poirier.) Utero-vaginal lymphatics Vaginal lymphatics (middle) E. THE LYMPHATICS OF THE LOWER EXTREMITY 1. THE LYMPHATIC NODES OF THE LOWER EXTREMITY The principal group of nodes of the lower extremity is situated in the in- guinal region, and hence is known as the inguinal group. It is in many respects similar to the axillary group, although it is not quite equivalent to it develop- mentally. The nodes composing it are divisible into a superficial and a deep group, the former containing many more and larger nodes than the latter. Furthermore, it is convenient to divide each of these groups into an upper and a lower set, the dividing line being an arbitrary line drawn horizontally through the point where the saphenous vein pierces the fascia of the fossa ovalis. The nodes above this line are termed collectively the inguinal nodes, while those below it are known as the subinguinal nodes. The superficial inguinal nodes [Igl. inguinales superficiales] (fig. 591), lie along the base of the femoral trigone immediately below Poupart's ligament, superficial to the fascia lata. Then number varies from ten to twenty. They receive the subcutaneous drainage of the abdominal walls, the gluteal region, and the perineal region, and their efferents descend to the fossa ovalis, which they perforate along with the saphenous vein and terminate in the lower external iliac nodes. The superficial subinguinal nodes [Igl. subinguinales superficiales], occupy the lower part of the femoral trigone and receive the entire superficial drainage of the leg, as well as a few vessels from the gluteal region and from the perineum. Thek efferents pierce the fossa ovalis and pass partly to the deep subinguinal nodes and partly directly to the lower external ihac nodes. LYMPH-NODES OF LOWER LIMB 747 The deep nodes. — The deep nodes are small, and vary from one to three. They lie medial to the femoral vein, the highest one (node of Cloquet or of Rosenmiiller) being placed in the femoral ring and being of especial surgical { Fig. 591.- -The Sttpebficial Inguinal Nodes. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Inguinal 1 \ ligament ft vs (Poupart s) Inguinal fc\ lymph-nodes^^ ) /^""^ Femoral artery Femoral vein Falciform margin Superficial ^ ' \ subinguinal nod Great saphen- Tjj^^ ous vein lH IH \i interest in that, when enlarged, it may simulate a strangulated hernia. The lowest node is below the point where the lesser saphenous joins the femoral vein. These deep nodes receive the deep lymphatics of the leg, the vessels from the glans penis in the male, and the clitoris in the female, and some of the vessels from the superficial subinguinal nodes. Their efferent vessels enter the external iliac nodes. In addition to the inguinal group of nodes there are some other nodes in the lower limb situated along the course of the deep vessels. Thus there is a node in the course of the anterior tibial vessels below the knee, and there is a small ( 748 THE LYMPHATIC SYSTEM group of popliteal nodes [Igl. popliteae], in the popliteal space, which are in the course of the lesser saphenous vessels, and receive the vessels which accompany the posterior tibial and peroneal vessels and those which drain the knee-joint. Fig. 592. — The Superficial Lymphatics op the Lowee Extremity. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Superficial epigastric vein Inguinal node: Superficial subinguinal nodes Great saphenous vein Accessory saphenous ' 2. THE LYMPHATIC VESSELS OF THE LOWER EXTREMITY As in the upper extremity, the subcutaneous capillary plexus of the lower varies greatly in complexity, being most abundant in the soles of the feet. The collecting vessels form two main groups. The medial, larger group follows the saphenous vein, and ends in the superficial subinguinal nodes, while the lateral LYMPH-VESSELS OF LOWER LIMB 749 group curves around to join the medial, partly in the leg and partly in the thigh. Two or three vessels from the heel follow the lesser saphenous vein to the popliteal space. The vessels from the upper and dorsal part of the thigh curve around on both sides to reach the superficial inguinal nodes. The vessels of the anus and Fig. 593. — The Lymphatics of the Back of the Lower Extremity. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Popliteal lymph-nodes— Small saphenous Deep lymphatic vessels perineum, as well as those from the external genitalia, except from the glans penis or the clitoris, pass to the medial nodes of the superficial inguinal group. The deep vessels follow the course of the arteries of the leg, those accompany- ing the dorsalis pedis and anterior tibial arteries coming into relation with the ( 750 THE LYMPHATIC SYSTEM anterior tibial node, when it is present, and then passing backward to join the vessels which accompany the posterior tibial and peroneal arteries. These terminate in the popliteal nodes, from which efferents follow the com-se of the femoral artery and terminate in the deep inguinal nodes. The deep lymphatic vessels accompanying the gluteal and obturator arteries pass to the hypogastric nodes. Lymphatics of the hip-joint. — According to Clermont, they accompany, in the main, the arteries about the joint. (1) Satellites of the anterior circumfle.x artery, draining almost the entire ventral surface, pass to the lateral inferior external iliac node. (2) Satellites of the pos- terior circumflex artery, draining the dorsal and medial surfaces, empty into the medial inferior external iliac node, occasionally into one of the deep inguinal nodes. (3) Satellites of the obturator vessel, draining the round ligament, empty into the obturator or hypogastric nodes. (4) Satellites of the inferior gluteal vessels, draining the dorsal surface, empty into three small nodes along the internal pudic and inferior gluteal arteries. Less important ("accessory") vessels are: satellites of the superior gluteal artery leading to a gluteal node; vessels from the dorsal surface which cross the lateral border of the pectineus to reach the medial inferior external iliac node; and vessels from the ventral surface, crossing parallel to the cotyloid notch, passing under the psoas to the lateral inferior external Uiae or one of the deep inguinal nodes. Lymphatics of the knee-joint. — According to Tanasesco the lymphatics draining the struc- tures around the knee-joint in the main follow the arteries about the joint and pass largely to the more deeply placed of the popliteal nodes. Some (superficial) follow the great saphenous vein to the subinguinal nodes, and sometimes deep vessels pass the pophteal nodes and, ac- companying the femoral artery, run to the deep inguinal or inferior external iliac. References for lymphatic system. — (Development) : Sabin, Amer. Jour. Anat., vols. 1, 3, 4, 9, also in Keibel and Mall's Human Embryology; Lewis, Amer. Join-. Anat., vols. 5, 9; Huntington and McClure, Amer. Jour. Anat., vol. 10; Clark, E. L., Anat. Record, vol. 6; Clark, E. R., Amer. Jour. Anat., vol.13. (Regeneration): Meyer, Johns Hopkins Hosp. Bui., vol. 17. (General): Bartels, in von Bardeleben's Handbuch d. Anatomic; Sappey, "Description et Iconographie des Vaisseaux Lymphatiques," Paris, 1885; Teichmann, "Das Saugadersystem," Leipzig, 1861. (Muscle, etc.): Aagaard, Anat. Hefte, Bd. 47. (Connective tissue): von Recklinghausen, "Die Lymphgefasse u. ihre Beziehung zum Bindegewebe," Berhn, 1862. (Stomata): Walter, Anat. Hefte, Bd. 46. (Lung): Miller, Anat. Rec, vol. 5. (Teeth): Schweitzer, Arch. f. mikr. Anat., Bd. 74. (Hoemolyinph glands): von Schumacher, Arch. f. mikr. Anat., Bd. 81. Tumors): Evans, Beitr.z. klin. Chir., Bd. 78. i SECTION VII THE NERVOUS SYSTEM Revised for the Fifth Edition Bt IRVING HARDESTY, A.B., Ph.D. PBOPESSOR OP ANATOMY, THE TDLANE UNIVERBITT OP LOUISIANA THE nervous system of man, both anatomically and functionally, is the most highly developed and definitely distributed of all the systems of the body. It consists of an aggregation of peculiarly differentiated tissue-elements, so arranged that through them stimuli may be transmitted from and to all the other tissue systems or functional apparatuses. It is a mechanism with parts so adjusted that stimuli affecting one tissue may be conveyed, controlled, modified, and distributed to other tissues so that the appropriate reactions result. While protoplasm will react without nerves, while muscle will contract without the mediation of nerves, yet the nervous system is of the most vital importance to the higher organisms in that the stimuli required for the functioning of the organs are so distributed throughout their component elements that the necessary harmonious and coordinate activities are produced. For this purpose the nervous sj^stem permeates every organ of the body; nerve cell-bodies, accu- mulated into groups, receive impulses and give rise to the nerves which ramify and divide into smaller and smaller branches till the division attains the individual nerve-fibres of which the nerves are composed, and even the fibres bifurcate repeatedly before their final termination upon their allotted elements. So intimate and extensive is the distribution throughout that could all the other tissues of the body be dissolved away, still there would be left in gossamer its form and proportions — a phantom of the body composed entirely of nerves. The parent portion or axis of the system extends along the dorsal mid-line of the body, surrounded by bone and, in addition, protected and supported by a series of especially constructed membranes or meninges, the outermost of which is the strongest. The cephalic end of the axis, the encephalon, is remarkably enlarged in man, and is enclosed within the largest portion of the bony cavity, the cranium, while the remainder of the central axis, the spinal cord, continues through the foramen magnum and lies in the vertebral canal. The intimate connection of the axis with all the parts of the body is attained by means of forty-six pairs of nerves, which are attached to the axis at somewhat regular intervals along its extent. They course from their segments of attach- ment through the meninges and through their respective foramina in the bony cavity to the periphery. Of these craniospinal nerves, fifteen pairs pass through the cranium and are attached to the encephalon, and thirty-one pairs to the spinal cord. Some of the cranial nerves and all of the thirty-one pairs of spinal nerves contain both afferent fibres, which convey impulses from the per- ipheral tissues to the central axis, and efferent fibres, which convey impulses from the axis to the peripheral tissues. The different pans of nerves possess the two types of fibres in varying proportions. Upon approaching the spinal cord, each spinal nerve is separated into two roots ■ — its posterior or dorsal root and its anterior or ventral root. The afferent fibres enter the axis by way of the dorsal roots, which are, therefore, the sensory roots, and the efl^erent fibres leave the axis by way of the ventral or motor roots. As usually studied, the nervous sj'stem is referred to in two main divisions : — (1) The central nervous system, composed of — (a) The spinal cord, or medulla spinalis, and (6) the brain or encephalon. 751 752 THE NERVOUS SYSTEM Fig. 594. — Showing the Ventral Aspect of the Central Nervous System, with the Proxi- mal Portions of the Cranio-spinal Nerves attached and the Relation op the Proximal Portion (Gancliated Cord) of the Sympathetic Nervous System. The Encephalon or Brain is Straightened Dorsalward prom its more Horizontal Position with Reference to the Spinal Cord. The Spinal Ganglia and the Dorsal and Ventral roots of the Spinal Nerves may be noted. (Composite drawing in part after Allen Thompson from Rauber — modified.') Superior cervical sympathetic ganglion Middle cervical sympathetic ganglion Inferior cervical sympathetic ganglion n I Thoracic nerve Gangliated cord ~/-~t Cervical nerve I Lumbar nerve -] Sacral nerve VJ Coccygeal nerve Filum terminale DEVELOPMENT OF NERVOUS SYSTEM 753 Neurenteric canal Primitive groove Body-stalk 754 THE NERVOUS SYSTEM (2) The peripheral nervous system, composed of — (a) The cranio-spinal nerves, and (6) the sympathetic nervous system. All these parts are so intimately connected with each other that the division is purely arbitrary. The cranio-spinal nerves are anatomically continuous with the central system; their component fibres either arise within or terminate within the confines of the central system, and thus actually contribute to its bulk. The sympathetic system, however, may be more nearly considered as having a domain of its own. By communicating rami, it is intimately associated with the cranio-spinal nerves and thus with the central system, both receiving impulses from the central system and transmitting impulses which enter it. But, while its activities are largely under the control of the central system, it is possible that impulses may arise in the domain of the sympathetic system and, mediated by its nerves, produce reactions in the tissues it supplies without involving the central system at all. For this reason, as well as because of the structural peculiarities of the sympathetic system, the nervous system is sometimes divided into — (1) the cranio-spinal system, consisting of (a) the central system and (b) the cranio-spinal nerves; (2) the sympathetic nervous system, consisting of its various peripheral ganglia and their outgrowths forming its plexuses. Within and closely pro.ximal to the central system or axis are grouped the parent cell-bodies whose processes comprise the nerve fibres of the cranio-spinal nerves. Other groups of nerve cell-bodies, distributed in the periphery without the bounds of the central system,, give rise to the fibres of the sympathetic nerves and plexuses. Any group of such cell-bodies situated in the periphery, whether belonging to the cranio-spinal or sympathetic system, is known as a ganglion. THE DEVELOPMENT OF THE NERVOUS SYSTEM The essential elements of the nervous system, the nerve cell-bodies and the essential portion of all nerve fibres, central, cranio-spinal and sympathetic, de- velop from one of the embryonic germ layers, the ectoderm, and all arise from a given region of that germ layer. Further a small portion of the supporting tissue of the nervous system, the neuroglia, is of the same origin. In its development the nervous system is precocious. It is the first of the functional apparatuses to begin differentiation and is the first to acquire its form. The first trace of the embryo appears on the developing ovum as the embryonic area, and the rapidly proliferating cells of this area shortly become arranged into the three germinal layers: — the outer layer or ectoderm, the middle layer or mesoderm, and the inner layer or entoderm. Early in the process of this arrangement there is formed along the axial fine of the embryonic area a thickened plate of ectodermal cells, the neural plate. In the further proliferation of these cells, the margins of the neural plate, which he parallel with the long axis of the embryonic area, rise shghtly above the general surface, forming the neural folds, and the floor of the plate between the folds under- goes a slight invagination, the process resulting in the neural groove (fig. 595, A, A', B and B^). As development proceeds and the embryonic area assumes the form of a distinct embryo, the neural folds or lips of the groove graduaUy converge, and beginning at the oral end, finally unite. Thus the groove is converted into the neural tube, extending along the dorsal mid-hne and en- closed within the body of the embryo by the now continuous ectoderm above (fig 595, C^, D and D'). For a time the neural tube remains connected with the inner surface of the general ectoderm along the line of fusion by a residual lamina of ectodermal cells. This lamina is known as the ganglion crest (neural crest). It is a product of the proliferation of the ectoderm during the process of fusion, consists of the cells which composed the transition between the closing lips of the original groove and the general ectoderm or skin, and whose fusion aided in the closure of the tube. The ectoderm soon becomes separated from the ganghon crest and the cells of the crest become distinctly differentiated from the cells of the neural tube. The essential elements of the entire nervous system together with the neuroglia are derived from the cells of the neural tube and the cells of the ganglion crest. Fig. 595. — Dorsal Surface Views of Human Embryos and Diagrams of Transverse Sections Illustrating the Development or the Neural Tube. A, dorsal view of human embryo at beginning of infolding of neural plate to form neural groove. Amnion partly removed. (Graf Spee, from Keibel and Mall.) A', diagram of portion of a transverse section of an embryo as though taken through A at the fine a'. B, dorsal view of human embryo of 7 somites, neural tube not yet closed, Mall Collection. (Dandy, from Keibel and Mall.) B', diagram of portion of a transverse section of an embryo as though taken through B at the line b'. C'-, diagram of portion of a transverse section of an embryo as though taken through D at fine c'. D, dorsal view of human embryo of 8 somites, 2.11 m.m. long, neural tube closed except at caudal end. (KoUmann, from Keibel and Mall.) D', diagram of a portion of a transverse section of an embryo as though taken through D at^line d^ DEVELOPMENT OF NERVOUS SYSTEM 755 Before the caudal extremity of the tube is entirely closed, its oral end undergoes marked enlargement and becomes distended into three vesicular dilations, the anterior, middle, and posterior primary brain vesicles. The anterior of these primary vesicles give off a series of secondary vesicles and by these, followed by further dilations, flexures of its axis, and by means of locahzed thickenings of its walls, the portion of the tube included in the three primary vesicles develops into the encephalon or brain of the adult. The remainder of the tube becomes the spinal cord. This latter portion retains the simpler form. By the proliferation and migra- tion laterally of the cells lining this portion of the tube, there results a comparatively even bilateral thickening of its walls so that the mature spinal cord retains a cylindrical form through- out its length. The proliferating and migrating cells of the wall of the neural tube are known as germinal cells. The products of their division are apparently indifferent at first, but later they become differentiated into two varieties: (1) spongioblasts, or those cells which will develop into neu- roglia, and (2) neiiroblasts, or those which will increase in size, develop processes and become nerve cell-bodies.' As described below, the processes given off by a neuroblast are of two general characters: (1) a long process or axone which goes to form nerves, nerve roots, and nerve fasciculi, and (2) dendritic processes which are numerous, branch much more frequently and extend but a short distance from the cell-body. An adult cell-body with all its processes is known as a neurone and the neuroblasts of the developing system become transformed into the neurones Fig. 596. — Diagrams of Tkansvebse Sections or Embryonic Spinal Cords showing the Migration of the Cells op the Ganglion Crest to form the Spinal and Sympathetic Ganglia and the Origin of the Dorsal and Ventral Roots of the Spinal Nerves. A, a- stage following D' of fig. 595. B, a later stage in which the ganglia and the components of the nerve are assuming their form resulting from the further migration and from processes being given off by the neuroblasts. — Spinal ganglion Sympatheti of the varying sizes, shapes, and arrangements of processes characteristic of different divisions and localities of the nervous system. Usually the fii-st process to be noted is that which will become the axone or nerve fibre. Neurones whose cell-bodies belong to the peripheral nervous system are not developed within the walls of the neural tube or central nervous system at all. These, comprising the spinal ganglion neurones and those of the sympathetic system, are derived from the cells of the ganglion crest. The wedge-shaped lamina of cells, comprising the ganghon crest, through rapid cell division, gradually extends outward and ventralward over the surface of the neural tube along either side. Soon the prohferation becomes most active in regions corresponding to the mesodermic somites or primitive body segments and this, together with the stress of the growing length of the body, results in the ganghon crest (originally a lamina) becoming seg- mented also. The segments or locahsed cell masses thus formed are the beginning not only of the spinal ganglia, but also of the ganglia of the entu-e sympathetic system. The cells of the crest migrate to assume a more lateral position, and then occurs a separation of their ranks. A portion of them remain in a dorsolateral position near the wall of the neural tube and develop into the neurones of the spinal ganglia (the sensory neurones of the spinal nerves), but others wander further out into the periphery and become the neurones of the sympathetic. Certain of those of this more nomadic group of cells settle within the vicinity of the vertebral column and by sending out their processes, form the gangliated cord or the proximal chain of sj^mpathetic ganglia; others migrate further, but in more broken rank, and become the gangha of the pre- vertebral plexuses (as the cardiac, coeliac and hypogastric plexuses), or the scattered intermediate chain of ganglia; while still others wander into the very walls of the peripheral organs and 756 THE NERVOUS SYSTEM Fig. 597. — ^Diagram Showing the Chief Paths of Migration of the Cells from THE Ganglia of the Spinal and Cranial Nerves to form the Adult Sympathetic System (After Schwalbe, modified.) Carotid plexus Vagus I. cervical spinal Middle cervica' Inferior cervical ganglion Sympathetic trunl I. lumbar spinal ganglion I. sacral spinal ganglion Ciliary ganglion Otic ganglion Spheno-palatine Submaxillary Pharyngeal plexus Pulmonary plexus Cardiac plexus (Esophageal plexus Coronary plexus Gastric plexus Cceliac (solar) plexus Submucous and myenteric plex- uses (Meissner and Auerbach) Aortic plexus Inferior mesenteric plexus Pelvic plexuses Coccygeal ganglion DEVELOPMENT OF NERVOUS SYSTEM 757 occur singly or in groups in such plexuses as those of Auerbach and Meissner, within the tunics of the walls of the alimentary canal. Scattered along between these proximal, intermediate, and distal groups there are to be found small straggling gangha, many of which contain so few cell-bodies that they are indistinguishable with the unaided eye. All these sympathetic neu- rones, however, are always either directly or indirectly anatomically associated with and Fig, 598. — Diagrams of Oral Portion of Human Neural Tube Showing the Three Primary Brain Vesicles and Some of the Secondary Vesicles Derived from Them. A, diagram of dorsal view of early stage. B, lateral view at about the third week. C, lateral view at about the eighth week. After His, modified, m, mamillary vesicle; i, infundibular recess; o, oKactory vesicle. Anterior primary veeicle ^ optic veeic] "middle primary vesicle -'Posterior primary vesicle Auditory vesicl Middle primary vesicle ^ epiphysis Anterior primary Telencephalon^ spinal cord -cerebellum ^ ;*Posteriorprimary vesicle medulla olfactory vesicle- -^'•'' optic vesicle"' / Pontine fltaure cervical flexure Fig. 599. — Diagrammatic Sagittal Section of a Vertebrate Brain. (After Huxley.) 4, fourth ventricle; s, cerebral aqueduct; 3, third ventricle. Corpora quadrigemina Mid -brain Epiphysis Lateral ventricle Cerebral hemisphere Corpus striatum Pons Varoli (.hind -brain J Cerebral peduncle Thalamus [ Hypophysis Foramen of Monro Hypothalamus Fig. 600.— Diagrammatic Horizontal Section of a Vertebrate Brain. (Afte Huxley.) 4, fourth ventricle; 3, third ventricle. Metencephalon Thalamus Medulla oblongata ^^ Cerebellum —Lateral ventricle Lamina terminalis Corpus striatum Mid-brain Epiphysis Foramen of Monro largely under the control of the neurones of the central system through central visceral eferent fibres passing to them by way of the rami communicantes or by way of the peripheral distri- bution of the spinal nerves. The ganglia of the sensory portions of all those cranial nerves attached to the inferior of the main divisions of the brain and all the sympathetic ganglia of the head have an origin similar to that of the spinal and sympathetic gangha in the remainder of the body. The behavior of the walls of the three primary vesicles, into which the oral end of the neural tube is converted, is much more complex than in case of the spinal cord. Their walls do not 758 THE NERVOUS SYSTEM thicken uniformly and, to give rise to the form of the adult brain, the anterior and the posterior of the three vesicles give off secondary vesicles. The walls of the posterior primary vesicle give rise to the posterior of the main divisions of the brain, the hind brain or rhombencephalon, the cerebellum developing from the anterior portion only of its dorsal wall, and the medulla oblongata and pons from its ventral wall. Its cavity persists and enlarges into the fourth ventricle of the adult, while the posterior portion of its dorsal wall does not develop functional nervous tissue at all but persists as a thin membrane known as the chorioid tela of the fourth ventricle. The cells which form the ganglia of the audi- tory and vestibular nerves arise from the dorsolateral regions of this vesicle. From the middle primary vesicle comes the mid-brain or mesencephalon, the corprora quad- rigemina [colliculi] developing from its entire dorsal wall and the cerebral peduncles occupying its ventral wall. The constriction between the middle and posterior vesicles becomes the isthmus of the rhombencephalon. The anterior or first primary vesicle undergoes greater elaboration than either of the other two. At an early period it gives off a series of secondary vesicles or diverticula. First, two ventrolateral outpouchings occur, the optic vesicles, which later become the optic stalks and optic cups of the embryo. A medial protuberance becomes evident in its antero-dorsal wall and from each side of this quickly starts a lateral diverticulum. The two lateral diverticula thus arising from the protuberance are the beginning of the two cerebral hemispheres or the telencephalon, and the vesicular cavities contained persist as the two lateral ventricles of the brain. Soon, each of these vesicular rudiments of the hemispheres gives off ventrally from its anterior part a narrow tube-like diverticulum, each continuous into the parent primary vesicle. These are the olfactory vesicles which are transformed into the olfactory bulbs and olfactory tracts^ of the adult encephalon. (See fig. 598, B. and C.) As development proceeds, the cavities of the olfactory vesicles become occluded in man. However, in many of those animals Fig. 601. — Diagram op Mesial Section op the Human Beain showing the Segments and THE Flexures and the Expansion of the Cebebral Hemispheres over the Other Portions op the Beain. The Thalamus is not shown. Cerebral hemisphere Corpus callosum i- Septum pellucidum Third ventricle Fourth ventricli Hypophysis Cerebral peduncle Pons 1 ( Medulla oblongata ! Spinal cord in which the olfactory apparatus attains greater relative development than in man, these cavi- ties persist as the olfactory ventricles. The cavities of the optic vesicles never persist as ven- tricles in the adult. They form stalks which represent the future courses of the optic nerves, while from their extremities are developed the retina;, portions of the ciliary bodies and portions of the iris of the ocular bulbs. In addition to that which forms the cerebral hemispheres, the remaining portion of the anterior primary vesicle becomes the diencephalon or inter-brain. The lateral walls of this part thicken to form the tiialami, the posterior end of its dorsal wall gives off a secondary vesicle which becomes the pineal body or epiphysis, and from its ventral waU projects the infundibular recess which becomes the posterior lobe of the hypophysis with its infundibulum and tuber cinereum. The adult human brain is characterised by the preponderant development of the cerebral hemispheres. The secondary vesicles forming these expand till, held within the cranial cavity, the hemispheres come to extend posteriorly completely over the thalamencephalon and the mesencephalon and even overlap the cerebellum to its posterior border. Their cavities, which persist from their origin from the anterior primary vesicle, are correspondingly large (the lateral ventricles) and comprise two of the four ventricles of the adult brain. The third ventricle be- comes a narrow cavity situated between the two thalami. It represents the original cavity of the anterior primary vesicle from which the structures above mentioned arose as secondary vesicles. It remains continuous with the lateral ventricles by the two inter-ventricular foramina, known also as the /ora?«ma of mom'o, one into each cerebral hemisphere. The fourth ventricle of the adult represents the cavity of the posterior primary vesicle and comes to he between the cerebellum and medulla oblongata, since the cerebellum likewise extends posteriorly from its region of origin. The cavity of the middle primary vesicle becomes the cerebral aqueduct, or aqueduct of Sylvius, passing under the corpora quadrigemina and connecting the fourth or posterior ventricle with the third. Development of the nerve fibres. — All axones begin as outgrowths or processes of the cyto- plasm of neuroblasts. Most of such processes are sent out at a very early stage in the develop- ment of the nervous system and extend to the tissues they are to innervate when these tissues are as yet quite near the neural tube. Then, as the structures of the body elaborate and assume DEVELOPMENT OF NERVOUS SYSTEM 759 their final forms and positions more remote from the central nervous system, the axones ter- minating in them must necessarily grow and be drawn out with the structures. At need, later axones are sent out by neurones developing later to supply the growth demands. Such axones follow the general paths made by those aheady extending to the tissues requiring them. Being processes of the cytoplasm of the cell-body, the growth and Ufe of all axones (and dendrites) is under the control of the nucleus in the cell-body. They grow by absorbing nourishment, or having added to them substances, from the tissue stroma through which they pass, which stroma may be either ectodermal or mesodermal in origin. The great majority of axones in the central nervous sytem and all in the peripheral system have sheaths about them. The sheath is an acquired structure and is not added till a rela- tively late period of development. These sheaths are of two general varieties, sheaths con- FiG. 602. — Diagram illusteating the Gross Divisions of the Central Nervous System. Olivary body— --,___ Mesencephalon j (mid-brain) J ^« Pons (Varoli) Myelencephalon (medulla oblongata) //-"•Pars cervicalis -Pars thoracalis -""Pars lumbalis Spinal cord (medulla spinalis) sisting merely of a fibrous coat with the nuclei belonging to it, and sheaths in which there has been added a coating of fat or myeUn, medullary sheaths. A nerve fibre consists of an axone and its sheath whether meduUated or non-medullated. In the embryo, axones are given off from the developing neurones at a time when the entire ectodermic neural tube and embryonic ganglia and the mesodermic tissue surrounding them are each void of definite cell boundaries, each being a continuous mass of nucleated protoplasm, a syncyiium. From these syncytia are developed the fibrous connective tissues of the later framework supporting the nervous system. Of this, the fibrous tissue, neuroglia, is derived from the ectodermal syncytium, while the white and elastic fibrous tissues are derived from the mesodermal or mesenchymal syncytium. Before any connective tissue fibrils are developed in either syncytium, before and at the time of the ingrowth of blood-vessels into the developing gangha and the neural tube from the mesenchyme about them, there occurs an invasion of the mesenchymal syncytium into the ectodermal sjmcytium. This invasion occurs both as independent ingrowths and fusions at the periphery of the neural tube and by 760 THE NERVOUS SYSTEM the mesenchymal tissue being carried in by the ingrowing blood-vessels. After the mixture of the nuclei resulting from this fusion of the syncytia from the two sources, nuclei of mesodermal origin cannot be distinguished from those of ectodermal origin. Further, axones outgrowing from the embryonic ganglia and neural tube carry with them adhering portions of the ectodermal syncytium into the surrounding mesenchymal (fig. 603). As development proceeds further, each syncytium becomes resolved into a reticulum of granular endoplasmic processes, containing the nuclei, with transparent exoplasm occupying its meshes. Fibrils soon form in the exoplasm and from these develop the connective-tissue fibres, whether neurogha in the central nervous system or mesenchymal fibrous tissue both without and within it. Certain of these fibrils of course surround the axones imbedded among them and from condensations of such fibrils are derived the fibrous sheaths of the axones, the sheath nuclei being acquhed from the adjacent nuclei of the original syncytium. These sheaths become more dense or pronounced as the axones extend and the fibrous tissue increases with growth, but there are always present fine marginal fibrils by which the sheaths grade into the looser fibrous tissue about them. It is generally beUeved that the tissue giving rise to these Fig. 603. — Drawings Illustrating the Origin of the Axone and the Development of THE Medullary Sheaths. A, ventral portion of transverse section of an embryonic spinal cord involving portion of periphery of future ventral horn and part of the mesenchymal (mesodermal) syncytium out- side the external limiting membrane of the cord. B, later stage of ventral root (peripheral) axone with myehn droplets adhering to it and fibrillated stroma surrounding it. C, stage in which myehn droplets, supported by fibrils of stroma, have increased and accumulated to form a practically continuous myehn or meduUary sheath. D, final stage with medullary sheath of even thickness, showing a node, and showing a neurilemma, sheath nucleus and fibrous framework of the myehn ("neurokeratin") derived from the fibrils of the original stroma. Myel'n - Neurilemma Mesenchymal syncytium axone sheaths is of mesodermal origin. However, in amphibian larvae, Harrison has shown that some sheath nuclei at least are derived from the nuclei of the ectodermal syncytium of the ganghon crest, and Neal has noted in elasmobranchs the fact that nuclei migrate from the ven- tral waU of the neural tube along with the axones growing out to form the ventral roots of the spinal nerves. Whether aU or any of these nuclei are originally ectoderrnal, and, if so, whether such ectodermal tissue gives rise to all axone sheaths, especiaUy in the higher animals, are questionable contentions. Axones possessing only fibrous sheaths comprise the non-meduUated nerve fibres. The majority of the sympathetic fibres are of this variety, and Ranson has found numerous non- meduUated fibres present in the spinal nerves. The generally accepted form of non-medullated sympathetic fibres may be seen in fig. 609, C. MeduUated fibres are those which possess an investing coat of fat or myehn in addition to the fibrous sheath. Most of the fibres in the central nervous system and most of those belong- ing to the cranio-spinal nerves proper acquire myehn sheaths. Myehn begins to appear upon axones shortly after the beginning development in the syncytium of the fibrils of the fibrous connective tissue, and thus after the beginnings of what will become the fibrous sheaths. The fibrous portions of the sheaths in the central nervous system develop less rapidly and are far more scant than those of the medullated fibres of the peripheral nerves. Probably because of this, it has been claimed that myehn begins to appear on the axones of the central system before the appearance of the fibrous sheath. In man, the first appearance of myelin occurs at about the fourth month, but myelinisation is not completed tiU after birth. The cranio-spinal nerves contain completely meduUated fibres before the central system does. Myehn first appears as small droplets adhering to the axone at irregular intervals. These droplets increase in size and number and gradually accumulate to form a practicaUy continuous sheath of fat immediately investing the axone. They probably result from the coalescence of finer droplets floating in the surrounding fibrillated stroma. However, coUecting upon the axone, DEVELOPMENT OF NERVOUS SYSTEM 761 the myelin retains the form of an emulsion, and as it increases in amount it incloses the adjacent fibrils which serve as a framework supporting the droplets of the emulsion in its meshes. Thus supported, the increasing myelin does not inclose the adjacent nuclei and endoplasm of the original syncytium. Probably because of the fibrous support of the myehn thus obtained, medullating fibres may be often seen presenting the beaded appearance shown in fig. 603, C, instead of an even distribution of the emulsion after it has become continuous along the axone. The "beads" probably represent the uneven beginning of the accumulation indicated in B of this figure. Increasing further, the myelin becomes a cyhnder of even thickness, the adjacent nuclei being pressed away against its surface and the adjacent fibrils also condensed upon it. There is good reason to believe that the fibrous portion of the sheath, the primilive sheath or neurilemma, of the meduUated axone arises as a condensation of the fibrils of the surrounding stroma during development, that the sheath cells represent certain of the nearest nuclei in- corporated from the original syncytium, and that the so-called neuro-keralin of the myehn represents the fibrous framework of the myehn inclosed by it during its accumulation upon the Fig. 604. — Showing Some of the Varieties op the Cell-bodies op the Neurones OP the Human Nervous System, including the Dendrites and Small Portions op THE Axones. Axone Sheaths not included. A. From spinal ganghon. B. From ventral horn of spinal cord. C. Pyramidal cell from cere- bral cortex. D. Purkinje cell from cerebellar cortex. E. Golgi cell of type II from spinal cord. E. Fusiform cell from cerebral cortex. G. Sympathetic, a, axone; d, dendrites; c, collateral branches; ad, apical dendrites; hd, basal dendrites; c, central process; p, peripheral process. axone. The theory that the myehn arises as a differentiated portion of the axone and the theory that it is formed by the neurilemma have been advanced. That it is accumulated from the immediately surrounding fluid of the stroma and adheres to the axone, added droplets coalescing there, in preference to other tissue elements because of some physical or chemical peculiarity of the axone, is more probably correct. As the medullary sheath approaches completeness, constrictions may be observed at more or less regular intervals at which the myelin emulsion is absent. There are the nodes of Ranvier. The process by which they arise is not clearly understood. While the fibre is growing in length, new myehn is added at the nodes. The internodal segments of the sheath increase in length with age, and each segment may possess from one to several sheath nuclei. In adolescence, fibres whose medullary sheaths are in various stages of completeness may be found both in nerve bundles in the central system and in the cranio-spinal nerves, and in both, the sheaths of some axones certainly never acquire mj'ehn. Also, in the adult, fibres whose medullary sheaths present the beaded appearance may be observed, probably repre- senting cases of arrested accumulation of myelin. According to Westphal there is a slight in- crease in the thickness of the sheath with age. Larger axones acquire thicker sheaths of myeUn than smaller ones. Some fibres of the sympathetic system are meduhated but in such the myelin sheath is relatively thinner than in the cranio-spinal system. Beaded sheaths are frequent in sympathetic rami, though non-meduUated fibres are most abundant. 762 THE NERVOUS SYSTEM FUNDAMENTALS OF CONSTRUCTION The functionally mature nervous system consists of peculiarly differentiated essential cell elements held in place by two forms of supporting tissue and supplied with abundant blood-vessels. The nervous element is distinguished from all other units of the structure of organs in that its cell-body gives off outgrowths or processes of peculiarly great length and characteristic form. Knowledge of the possible lengths and com- plexity of these processes is comparatively recent and, to include them together with their parent cell-body, which has long been known as the 7ierue cell, the term neurone is used. The neurone, therefore, may be defined as the nerve cell- bodj' with all its processes, however numerous and far reaching they may be. As a class of tissue elements, all neurones possess characteristics distinguishing them from other tissue elements, but the varieties within this class vary greatly. They vary in form both according to function and according to their locality in the nervous sj^stem. They vary in different animals, those in the higher animals being more complex in form. Fig. 604 gives illustrations of the external form of the cell-body of a few of the types found in the human nervous system. The cell-body of the neurone gives off two general types of processes, ■dendrites and axones: (1) The dendritic processes or dendrites. These are the more numerous, the shorter, and the more frequently branching processes. They branch dichotomously and with rapid decrease in diameter as tliey branch. They serve to increase the absorbing surface of the cell-body for purposes of nutrition. Nerve impulses transmitted to the neurone are received by them and, therefore, they also serve to increase the recipient surface of the neurone. They never acquire meduUary sheaths. Since they convey impulses toward the cell-body, they are known as cellipital processes. Their absorbing and receptive surfaces are further increased by the presence of thickly placed, very minute projections known as "pin-head processes" or gemmules. (2) The axone (neuraxis). Each neurone possesses properly but one of these processes. It arises from the cell-body more abruptly and quickly becomes smaller in diameter than are most dendrites before the latter decrease by branching. It is the longest process, in most cases very much longer than dendrites. Computation shows that some axones may contain nearly 200 times the volume of the parent cell-body of the neurone. Occasionally the axone gives off a few small branches near the cell-body. These are known as collaterals and are given off at practically right angles instead of dichotomously. Regardless of its branching, the axone maintains a practically uniform diameter throughout its long course. Its usual nervous func- tion is to convey the impulses away from the cell-body, either to transmit them to other neu- rones by contact upon their dendrites, etc., or to appropriate elements of the other tissue systems of the body. Thus the axones are the cellifugal processes. There is one weU-known partial exception to this, namely, a part of the axone of the spinal ganglion type of neurone, the peripheral sensory neurone. The axone of this bifurcates a short distance from the cell- body into a peripheral and a central branch. See fig. 604, A, and fig. 610. The peripheral branch collects sensory impulses from the tissues of the body, the skin, etc., and, in conveying them to the central system, must necessarily convey them toward the cell-body as far as the point of bifurcation. Thence the impulse goes on in the central branch, stiU toward the central system but now, in conformity, away from the cell-body of the neurone. While the continued vitality of the axone is dependent upon the cell-body, in the peculiar case of the spinal ganglion neurone the impulse does not necessarily pass through the ceU-body. Experiments with the lower animals have shown that the impulses pass in the fibre from the peripheral tissues to the central system when the cell-bod^' has been cut away. Terminations of axones. — At its final termination, well beyond its collateral branches and usually a considerable length from its ceU-body, the axone practically always divides into two or more terminal branches, and each of these breaks up, now dichotomously, into numerous terminal twigs. These terminal twigs are known as telodendria. Telodendria vary in number and characterof form according to the tissues in and upon which they terminate. Functionally, they are of three classes: Those terminating upon and in the other (peripheral) tissues of the body are either (1) sensory or (2) motor. In order to transmit impulses from one neurone to another, telodendria of the axone of one neurone are placed in contact with the dendrites or cell-body of another neurone forming (3) synapses. Upon approaching its termination, every axone loses its sheath, its telodendria being necessarily bare. Sensory or afferent axones, receiving impulses from the skin or other epithelial surfaces, break up into very numerous telodendria each of which terminates directly upon the surface of the epitheUal cell, such as the cells of the germinative (Malpigin) layer of the skin or those of its basal or columnar layer. Such telodendria are known as free terminations. Free terminations are also to be found in the connective tissues of the body. A second varietj' of peripheral termination of afferent axones is the encapsulated for jn. These are known as 'end organs' and 'corpuscles' and are named according to their complexity and position. Three of the different forms of them are shown in fig. 605, B, C, and D. These are always situated in fibrous connective tissue from which their capsules are derived. Their most elaborate form is the lamellated or Pacinian corpuscle. Besides the motor axones terminating upon the fibres of voluntary or skeletal muscle, sensory impulses are carried from this tissue and one of the forms of telodendria for this purpose terminates upon the muscle fibre. This is known as PERIPHERAL TERMINATIONS OF AXONES 763 Fig. 605.— Showing Some Varieties op Pekipheeal Terminations of Axones. 'Free termination' in epithelium (after Retzius). B. Krause's corpuscle from conjunctiva (after Dogiel). C. Meissner's corpuscle from skin (after Dogiel). D. Pacinian corpuscle (after Dogiel). E. Termination upon tendon sheath (Huber and DeWitt). F. Neuro- mus- cular spindle (after Ruffini). G. Motor termination upon smooth muscle-cell. H. Motor 'end-plate' on skeletal muscle fibre (after Bohmandvon Davidoff). a, axone; t, telodendria. a yf:._ 764 THE NERVOUS SYSTEM the 'neuromuscular spindle.' In it, the axone penetrates the sarcolemma and breaks into telodendria which coil spirally about the muscle fibre. The most extensive and elaborate form of sensory telodendria are those which spread out in plate-form upon tendons sheaths. Fig. 606. — Schemes showing Two Forms of Synapses or the Termination of Axones upon Cell-bodies of other Neurones. A. In ventral horn of spinal cord. B. In spinal ganglia. Fig. 607. — Drawings Illustrating two General Types of Arrangement op Neuro- FIBRILL^ IN the CeLL-BODIES OF NeURONES. A, cell-body of spinal-ganglion neurone. B, selected "giant pyramidal cell" from cerebral cortex, human, a, axone. Motor peripheral axones terminate upon muscle and upon the secretory cell of glands (secretory axones). The motor cranio-spinal axones terminate upon skeletal (voluntary) muscle fibres and upon the cell-bodies of sympathetic neurones, the axones of which latter termmate upon cardiac muscle, smooth muscle fibres, and (secretory) in glands. Upon skeletal muscle, the terminal branch of the axone loses its sheath and breaks up into numerous telodendria which themselves branch and show very evident, irregular varicosities, the whole of which spread out STRUCTURE OF THE NEURONE 765 in plate-form, and lie in contact with the substance of the muscle fibre. In man and all mammals, the area covered is usually somewhat oval and is marked by a granular differentiation of the muscle substance. This with the telodendria is known as a motor end-plate. The telodendria of sympathetic axones ending upon cardiac and smooth muscle fibres are fewer and simpler than those of cranio-spinal axones upon skeletal muscle. They consist of a few fine fibrils, with very small varicosities along them and at their ultimate terminations, which run longitudinally along the muscle fibre in close relation with its substance. Those upon gland cells are similar in character except that they often form a loose pericellular plexus about and upon the cell. The varicosities of telodendria are sometimes called end-feet and closer study of them has shown that they themselves consist of fine plexuses of the neuro-fibrils described below as contained in the cell-body of the neurone and extending throughout all its processes. Quite recently Boek has found that a sympathetic axone may sometimes accompany a cranio-spinal axone to an end plate on a skeletal muscle fibre. ^Synapses. — Every functionally complete nerve pathway consists of two or more neurones arranged in series. Very often, the series consists of many more than two, the impulses being transmitted from neurone to neurone. The axone, bearing the impulse away from the cell-body of one neurone, gives off terminal branches, each of which loses its sheath and breaks up into telodendria which twine themselves upon the dendrites or cell-body of another neurone. The mpulse is transferred from one neurone to another by means of contact rather than by direct anatomical continuity of the parts of the two neurones. Such terminations of axones are known as synapses. Fig. 608. — Drawings Illustrating the Abundance and General Arrangement op the Tigroid Masses in Cell-bodies of Neurones in Resting Condition. A, cell-body from spinal ganglion. B, large cell-body from ventral horn of spinal cord, a, axone. d, dendrites. Capsule 'd a- B In the terminal arrangement of the telodendria, synapses assume forms varying from com- pact "pericellular basketa" and "climbing fibres" to the more open arborisations composed of fewer twigs in simpler arrangements, "end-brushes." In case of the spinal ganghon type of neurone, the cell-body of the majority of which has no dendritic processes, the telodendria of the visiting axone form an anastomosing pericellular plexus inclosing the entire cell-body. This and the simple end-brush form of synapses are illustrated in fig. 606. It should be mentioned that, contrary to the general belief that impulses are transmitted by simple contact of the neurones in the series, it has been claimed that the ultimate twigs of the telodendria frequently penetrate the substance of the receiving cell-body and are fused in continuity. If during the processes of growth this becomes true, instead of being an appearance produced by the technique employed, it is better considered as merely an exception to the general rule. Internal structure of the neurone. — The ceU-body of the neurone consists of a large, spherical, vesicular nucleus and a cytoplasm continuous into its axone and dendritic outgrowths. Its nucleus is further characterized by having most usually but one nucleolus, large, spherical and densely staining, situated in a karyoplasm containing otherwise a remarkably small amount of chromatin. Of the cytoplasm, the two most interesting structures are its fibrillar and its gran- ular components. The fibrillar structure, known as the neuro-fibrillce, represents a growth and elaboration of the spongioplasniic reticulum of the original, embryonal cell. The filaments increase in thick- ness during the development of the neurone, and, in the sending out of its processes, the meshes of the original reticulum become so drawn out in the processes as to give the appearance of a more or less parallel arrangement of threads. The reticular or net-like arrangement is usuallj- more nearly retained in the cytoplasm immediately about the nucleus, since here the stress of the out- growing processes is less directly applied. In the cell-body of the spinal ganglion type of neu- rone, when no dendrites are given off, the net-like arrangement is apparent tlu-oughout the cyto- plasm except in that region giving rise to the axone. On the other hand, in the typical so-called "pyramidal cell" of the cerebral cortex, from which two chief processes, the axone and the apical 766 THE NERVOUS SYSTEM dendrite, are given off from opposite poles, the more reticular arrangement about the nucleus is often practically obliterated by the opposing growth stress. So manifest does the parallel appearance of the neuro-fibrillfe in the processes often become that it has been interpreted as a series of individual and independent fibrils. In the application of gold chloride and similar methods to the neurones of lower forms, the reduced reagent is often precipitated upon the fibrils in parallel, seemingly independent lines. And, assuming the ex- istence of independent fibrils, it has been contended that the neurone is not the functional unit of the nervous system but is itself composed of numerous functional units, individual fibrils, each for the conduction of nerve impulses. More recent and trustworthy methods, however, show that the neuro-fibrillaj retain their original reticular form, the threads anastomosing in all planes, and that the meshes of the net may, in the processes, be so drawn in one direction that a parallel appearance predominates. Further, it is now held that the neuroplasm, or the more fluid substance in which the fibrils lie throughout, is capable, and probably fully as cap- able, of conducting impulses as the fibrils. Of the granules in the cytoplasm, the most interesting are those first described in detail by Nissl. These are the most abundant of those in the cell-body and are known as tigroid masses or Nissl bodies. They consist of numerous basophilic granules collected into clumps or masses of varying size. They are known to disappear during fatigue of the nervous system and they are more abundant in animals after a period of rest. They are distributed throughout the cyto- plasm of the cell-body with the interesting exception that they are not found in the axone nor in the immediate vicinity of its place of origin from the cytoplasm, leaving a free region known as the axone hillock. As accumulated masses, they show characteristic shapes and arrangement Fig. 609. — Showing Pieces of Axones. A. From a cranio-spinal nerve. B. From the spinal cord. C. From the sympathetic, a, axones; m, medullary sheath; w, nodeof Ranvier;s, neurilemma or sheath of Schwann with occasional sheath-nuclei. which are interpreted as signifying the shapes and arrangement of the spaces or meshes they occupy in the reticulum of the neuro-fibriUai. In cell-bodies of the varieties found in the ventral horns of the spinal cord or in the cerebral and cerebellar cortex, for example, the masses situated immediately about the nucleus are smaller, more numerous and of irregular shape. Nearer and in the beginnings of the dendrites, they are larger and mostly of fusiform or diamond shape. Farther out in the dendrites, they become more and more thin and attenuated; and in the dis- tant reaches of the dendrites they are invisible or absent. In the cell-body of the spinal ganglion they are of irregular shape, smaller and more numerous throughout the cytoplasm, being slightly smaller and more thickly placed in the immediate vicinity of the nucleus. In all neurones several hours post-mortem, they appear in fewer and larger masses and it was in this condition that Nissl originally described them in man. Closely examined, the masses of all sizes are found to be accumulations of finer granules. Functionally they are supposed to be of nutritive signi- ficance, substances in unstable chemical equiblibrium, energy stored in the cytoplasm, capable at need of being split into simpler forms usable in the activities of the neurone. The fact that tigroid masses are absent from the axone hillock, the axone, and the distant reaches of the den- drites may signify that the substance is chiefly present here only in the spUt and usable form. Also, in the axone especially, the neurofibrilla? are so closely arranged that the meshes of their net here are too small to contain masses of appreciable size. Close examination of the axone hillock and longitudinal sections of the axone in deeply stained preparations usually show a few very minute basophilic granules. Sheaths of the axone. — The great majority of axones acquire sheaths about them which isolate and protect them in their course through other tissues or in company with other axones. A nerve fibre is an axone together with its sheath. In transverse sections, the axone comprises CONNECTIVE TISSUE OF NERVOUS SYSTEM 767 the central portion of the nerve fibre or its so-called "axis-cylinder." It is of course the essen- tial portion of the fibre. As noted above in describing their development, nerve fibres are classified according to the character of the sheaths. Those which possess sheaths of myehn, a peculiar form of fat, are known as medullaled fibres, and those in which the sheaths are merely mem- branes of condensed fibrous tissue, void of myelin, are non-medullated fibres. A medullated fibre also possesses a fibrous membrane outside its myeUn sheath, known as the neurilemma or sheath of Schwann. The neurilemma is of the same origin and general structure as the sheath of the non-medullated fibre, and both possess nuclei scattered along thern. Medullated fibres, at more or less regular intervals, show constrictions at which the myelin sheath ceases, but over which the neurilemma continues. These constrictions are the 7iodes of Ranvier. The mye- lin is in the form of an emulsion, whose fat droplets are supported in a fine fibrous reticulum (neurokeratin), while the neurilemma without serves to hold it in place. The neurilemma pos- sesses from one to three or four sheath nuclei between adjacent nodes of Ranvier. There is no sharp line of separation between medullated and non-medullated fibres, for in any locality there may be found axones in all degrees of medullation. Most of the fibres Fig. 610. — Diagram op Transverse Section op Spinal Cord with Roots of Spinal Nerve AND Neighbouring Ganglia Attached, Illustrating Simplest Forms op Neurone Chains. Fasciculus cuneatus Cephalic branch of spinal ganglion neurone belonging to the sympathetic system (processes of sympathetic neurones) are non-medullated, but both partially medullated and completely medullated sympathetic fibres may be found. (See fig. 609.) The myehn sheaths of completely medullated sympathetic fibres are always thinner and less well developed than those of meduUated cranio-spinal fibres. Most of the fibres belonging to the cranio-spinal nerves and to the central nervous system are medullated, but among the fibres belonging to either there are to be found numerous non-medullated fibres. As indicated in fig. 609, nodes of Ranvier are absent in the medullated fibres of the central system. In all the higher vertebrates, the myehn sheath always begins on the axone a short distance from its parent cell-body. The neurilemma of the medullated and the fibrous membrane of the non-medullated fibre are each faintly continuous with the fibrous connective tissue sur- rounding it, and, in the cranio-spinal and sympathetic ganglia, in which each cell-body of the neurone has a fibrous capsule about it, the fibrous membrane or the neurilemma, as the case may be, is directly continuous into the capsule of the ceU-body. Upon approaching its final termination, in other tissues or upon the dendrites or cell-body of other neurones, the nerve fibre always loses its sheath, the telodendria of the axone always being bare when placed in contact with the other element. In losing the sheath, the myelin sheath, if present, always ceases and the fibrous membrane becomes continuous with the tissue investing the receiving element, whether the capsule of the ganglion cell, the sarcolemma of the skeletal muscle fibre, the corium of the skin, or the connective-tissue capsule of the encapsulated terminal corpuscle, The connective tissue of the nervous system is of two main varieties — while fibrous connec- tive tissue and neuroglia. White fibrous tissue alone supports and binds together the peripheral system, and it is the chief supporting tissue of the central system. As connective tissues, these two varieties are quite similar in structure, each consisting of fine fibriUiE, either dispersed or in bundles, among which are distributed the nuclei of the parent syncytium. In both tissues nuclei are frequently found possessing varying amounts of cytoplasm which has not yet been transformed into the essential fibrils. In addition to its enveloping membranes, the three meninges, which are of white fibrous tissue, the white fibrous tissue supporting the central system within is quite abundant. It is aU 768 THE NERVOUS SYSTEM sent in from without, either as ingrowths of the developing pia mater, the most proximal of the membranes, or is carried in with the blood-vessels, of the walls of which it is an abundant component. Practically, the neuroglia as a connective tissue proper differs from white fibrous tissue only in origin and in its chemical or staining properties. Based upon the latter, there are methods of technique by which the two may be distinguished. White fibrous tissue is derived from the middle germ layer or the mesoderm, while neurogha comes from the ectoderm. The epithelium lining the central canal of the spinal cord and the ventricles of the encephalon, with which the canal is continuous, is the remains of the mother tissue of the neuroglia, and in the adult is the only vestige representing its origin. The cells of this epithelium are known as ependymal cells, and they are usually classed as a variety of neuroglia. Axones, with their meduUated or non-meduUated sheaths (nerve fibres) comprise all nerves in the periphery and all nerve tracts in the central system. White substance [substantia alba] ("white matter") consists of a portion of nervous tissue in which medullated fibres predominate. The myelin sheaths, being in the form of a fat emulsion, reflect the entire spectrum and thus appear white. Grey substance [substantia grisea] ("grey matter") is a portion of nervous tissue in which medullated axones do not predominate. Thus sympathetic ganglia and sympathetic nerves may be grey, though the term is usually applied to grey portions of the central system, such as the cerebral cortex, the central grey column of the spinal cord, etc. Such grey regions contain more cell-bodies of neurones than other regions, though at least half of their volume may consist of neuroglia, white fibrous connective tissue, blood-vessels, and axones of both varieties. Neurone chains. — As noted above, the numerous neurones comprising the nervous system are functionally and anatomically related to aU the other tissues of the body and to each other. A functionally complete nerve pathway extends from the tissue in which the nerve impulse is aroused to the tissue in which a resultant reaction occurs. It is known that the simplest possible of such paths necessarily comprises at least two neurones. The great majority involve a greater number. The axone of one neurone bearing impulses from the peripheral tissue transfers the impulses to the dendrites or cell-body of another by synapsis, and the axone of this, in the same way, transfers them to another and so on till the final neurone receives the impulses and the telodendria of its axone transfer the impulse to the tissue element which reacts in re- sponse to the stimulus brought. Neurones are thus linked together in chains. A neurone chain may be defined, therefore, as a number of neurones associated with each other in series to form a functionally complete nerve pathway. Examples of the simplest forms of neurone chains as contained in the spinal cord are illustrated in fig. 610. An impulse aroused in the skin is borne by the spinal ganglion neurone to the spinal cord where, in the left half of the figure, telodendria of one of the terminal branches of its axone form synapses with a neurone in the ventral horn, and the axone of this bears the impulse out of the spinal cord to transmit it proba- bly direct to skeletal muscle. This arrangement involves but two neurones and is supposed to be relatively rare. In the right half of the figure, a third neurone is seen interposed. This is a neurone, numerous in grey substance everywhere, whose axone is relatively short and branches frequently, making possible several synapses in the near neighbourhood of its parent cell-body. Its type is referred to as the Golgi neurone of type II. This interposed, gives a chain of three neurones between the origin of the impulse in the periphery and the contraction of muscle in response. Simple chains like these can result only in reflex activities and such chains are often called reflex arcs. Another chain is indicated in the figure in which the reflex action involves involuntary or smooth muscle. This must involve at least one sympathetic neurone, and, should the Golgi neurone of type II form synapses with the ventral horn neurone involved, a chain composed of four neurones results. In the more extensive and complex neurone chains, such as those in which the impulse from the skin, as above, ascends to the cerebral cortex and the resultant muscular contraction is thrown under cerebral control, each of the several neurones or links in the series is not only referred to by name according to the position of its cell-body, but each is often called according to its order in the series, as "neurone of first order," "second order," "third order," etc. A given axone may break into a considerable number of branches each of which forms synapses with a different second neurone, or, if peripheral, the telodendria of each branch may terminate upon a separate peripheral tissue element. Thus, a given impulse aroused in a peripheral tissue element may be transmitted to an ever increasing number of neurones, and the initial neurone may comprise the first link in a number of neurone chains. Such is quite general in the structural plan of the nervous system throughout. It is thought possible to consider each neurone interposed in a chain as a separate source of energy, a sort of relay in the nerve path; that the impulse passing through the axone is gradually weakened in over- coming resistance, but, when transferred to another neurone, it incites a splitting into usable form of the substance represented by the tigroid masses and thus a liberation of energy or a reinforcement of the impulse. Further, thus is made possible the economy of one neurone serving as a hnk in a number of nem-one chains. The axones (nerve fibres) taking part in the various neurone chains course in bundles of varying size, the larger of which have names. And there is a general tendency with axones of the same function and the same origin to course in company with each other. A fibre bearing impulses from the peripheral tissues to the central system is an afferent fibre or sensory fibre. A fibre bearing impulses out of the central system to peripheral tissues is an efferent fibre or motor RELATIONS OF NEURONES 769 fibre. Efferent fibres which bear impulses to skeletal muscle are known as somatic ejferent fibres, while those which terminate upon the cell-bodies of sympathetic neurones and thus bear impulses destined for smooth muscle, cardiac muscle and glands (secretory) are visceral or splanchnic efferent fibres. A nerve is a closely associated aggregation of parallel nerve fibres coursing in the periphery. It may be spinal, cranial or sympathetic according to its attachment or according to the origin of the majority of its fibres. It may contain several functional and structural varieties of fibres. The spinal nerves contain all structural varieties. Nerve roots are those bundles of fibres which join to form a nerve. Most of the cranial nerves have but one root of origin. Nerve roots, in their turn, are formed by the junction of smaller root-filaments. Nerve branches result from the division of the nerve, the separation of its component fibres into separate bundles. Some branches are of sufficient size and significance to be called nerves and given separate names. The smaller branches are called rami, twigs, etc. In the central system, a given bundle of fibres is called a fasciculus, while two or more adja- FiG. 611. — Diagram of.Transveese Section op Medulla Oblongata, Illustrating Nuclei OF Termination and Nuclei or Origin. cent fasciculi com'sing parallel to each other comprise a funiculus, a bundle of bundles. The. central nervous system is bilaterally symmetrical throughout its length. A bundle of fibres arising from cell-bodies situated on one side and crossing the mid-line transversely to terminate in the opposite side is a commissure. The commissures vary greatly in size and contain fibres crossing in both directions. Scattered fibres which cross the mid-line are commissural fibres. Fibres of varying lengtli, arising from cell-bodies situated in one locality of the central sj-stem, which do not cross the mid-Une, but terminate in other localities of the same side, above and below the level of their origin or in a different region of the same level, form association fasciculi. The shortest association fasciculi, not extending bejj^ond the bounds of a given division of the central sj-stem, are known as fasciculi proprii. When bundles of the same origin, functional direction and significance, running one on either side of the mid-line, cross the mid-line they are said to decussate and the crossing is known as a decussation. In the decussations, the direc- tion of the crossing is oblique rather than transverse. The cell-bodies of neurones whose axones go to form certain nerve roots, fasciculi and certain commissures show a tendency to accumulation in localized masses. In the peripheral system, such an accumulation of cell-bodies is known as a ganglion; in the central system such is distin- guished as a nucleus. Thus, there are the sympathetic ganglia which give rise to sympathetic nerves and sympathetic roots of nerves; and on the beginning of each spinal nerve there is a spinal ganglion which gives rise to the afferent fibres of its dorsal root and in its nerve trunk. There are ganglia on the cranial nerves which give rise to the afferent or sensory axones in them and which are of the same significance as the spinal ganglia. Every ganglion, therefore, has 770 THE NERVOUS SYSTEM connected with it bundles of nerve fibres. Some of these fibres bear impulses from neighboring ganglia or from the tissues of the neighboring organs and transmit them to the cell-bodies of the ganglion ; others arise from the cell-bodies in the ganglion and bear impulses to the central system or, in case of the sympathetic, to other ganglia or to the tissues of the peripheral organs. Nec- essarily, the larger the ganglion, the larger will be the bundles of fibres connected with it. Nuclei may be considered in two general classes: (1) Recipient nuclei or nuclei of termina- tion, and (2) Nuclei of origin. A nucleus of termination is an accumulation of cell-bodies in which the axones of a given fasciculus or of a nerve root terminate, that is, ceU-bodies which, by synapses, receive the im- pulses borne by the terminating axones. In most cases the impulses transferred to a nucleus so named are sensory in character. The nucleus may be considered as a defined region in which neurones of the next order are interpolated in a given nerve pathway or system of neurone chains. Fasciculi in the spinal cord which bear impulses to the cerebrum have their nuclei of termination in the meduUa oblongata, and the sensory or afferent axones of the cranial nerves find their nuclei of termination upon entering the central system. A nucleus of origin is an accumulation of ceU-bodies of neurones which give origin to the axones going to form a given nerve root or a fasciculus. Strictly speaking, a nucleus of ter- mination for one nerve tract is the nucleus of origin for another, the next link in the neurone chain. However, the term is commonly used to distinguish a group of cell-bodies giving rise to a motor nerve tract. Thus each motor cranial nerve has its nucleus of origin within the central system. The central grey substance of the spinal cord is in the form of a column continuous throughout the length of the cord and so the cell-bodies in the ventral horns of this column which give rise to the motor or afferent roots of the spinal nerves are not considered as grouped into nuclei of origin, one for each of the motor roots. The dorsal root of each spinal nerve is afferent or sensory in function and its axones arise as processes of cell-bodies comprising the spinal ganglion of the nerve. The afferent or sensory fibres of the cranial nerves arise as processes of ceU-bodies comprising the gangha of the cranial nerves, which ganglia are, in development and character, exactly homologous to the spinal ganglia. The ventral root of each spinal nerve is efferent or motor in function and its fibres arise as processes of cell-bodies situated in the ventral horn of the grey substance of the spinal cord. The efferent or motor fibres of the'cranial nerves arise as processes of ceU-bodies accumulated as nuclei of origin in the grey substance of the encephalon, and homologous with those cell-bodies of the ventral horns of the spinal cord which give origin to the ventral-root fibres. The general relation of the cerebrum (which includes the mesencephalon) to the remainder of the nevous system is a crossed relation. Neurone chains from the general body to the cere- brum, via the spinal nerves and cord and via the cranial nerves and medulla oblongata and pons of one side, cross the mid-line to terminate in the opposite side of the cerebrum. Axones, and neurone chains, arising in response in one side of the cerebrum, likewise usually decussate in descending to terminate in the respective regions of the opposite side. Many of the names given nervous structures, prior to 1850 especially, instead of suggesting something of their functional or anatomical significance, indicate nothing more than active imaginations for accidental resemblances between the various structures of the nervous system and objects in ordinary domestic environment. Also, quite often the name given a structure is merely the name of some anatomist associated with it. The much needed elimination of these old non-descriptive names is proving a very slow process. Attempts have often increased the difficulty by making necessary the use of several names for a given structure instead of one. The most recent and concerted attempt, the nomenclature known as the BNA (anatomical names chosen by a commission appointed for the purpose which convened in Basle in 189.5), has been adopted by modern text-books. It is here used in the form of the English equivalents of the Latin terms, except in cases of those Latin terms which have become so commonly used as to be considered words incorporated into the English language. The BNA has retained manj' of the old names and, since a name should indicate something of the locality and significance of the structure to which it is applied, it is not yet wholly satisfactory throughout. In applying the names of a few fasciculi, the BNA in the following pages is slightly modified by so compounding the name that the first word in the compound indicates the locality of origin of the fasciculus and the second, the locahty of its termination. Thus, "Dorsal spino-cerebellar fasciculus" indicates the more dorsally coursing of the fasciculi which arise from cell-bodies in the spinal cord and terminate in the cerebellum. This principle appUes to many of the BNA names without change, as "lateral cerebrospinal fasciculus." THE CENTRAL NERVOUS SYSTEM The central nervous system [systema nervorum centrale] or organ is an aggregation of nuclei, fasciculi and commissures — a large axis of grey and white substance situated in the dorsal mid-line of the body — and the bundles of fibres connecting it with the tissues of other systems and with the peripheral ganglia are of necessity correspondingly large. So numerous are the axones connecting it and so intimately are its neurones associated that a disturbance affecting any one part of the system may extend to influence all other parts. The enlarged cephalic extremity of this central axis, the brain or encephalon, is a special ag- gregation of nuclei and masses of grey substance, many of which are much larger than any found in the periphery. MORPHOLOGY OF SPINAL CORD 771 In the study of the central nervous system its enveloping membranes or meninges are met with first, and logically should be considered first, but since a comprehensive description of these membranes involves a foreknowledge of the various structures with which they are related, it is more expedient to consider them after making a closer study of the entire system they envelop. For convenience of study, the central nervous system is separated into the gross divisions, spinal cord and brain (encephalon) as illustrated in fig. 602. Each of these divisions will be subdivided and considered with especial reference to its anatomical and functional relations to the other divisions and the inter- relations of its component parts. I. THE SPINAL CORD The spinal cord [medulla spinalis] is the lower (caudal) and most attenuated portion of the central nervous system. It is approximately cylindrical in form and terminates conically. Its average length in the adult is 45 cm. (18 in.) in the male and 42 cm. in the female. It weighs from 26 to 28 grams or about 2 per cent, of the entire cerebro-spinal axis. After birth it grows more rapidly and for a longer period than the encephalon, increasing in weight more than sevenfold, while the brain increases less than half that amount. Its specific gravity is given as 1.038. The Line of division between the spinal cord and the medulla oblongata is arbitrary. The outer border of the foramen magnum is commonly given, or, better, a transverse line just below the decussation of the pyramids. Lying in the vertebral canal, the adult cord usually extends to the upper border of the body of the second lumbar vertebra. However, cases may be found among taller individuals in which it extends^'no farther than the last thoracic vertebra. With increase in stature, its actual length increases, but the extent to which it may descend the verte- bral canal decreases. Up to the third month of intra-uterine life it occupies the entire length of the vertebral canal, but owing to the fact that the vertebral column lengthens more rapidly and for a longer period than does the spinal cord, the latter, being attached to the brain above, soon ceases to occupy the entire canal. At birth its average extent is to the body of the third lumbar vertebra. External Morphology of the Spinal Cord In position in the body, the spinal cord conforms to the curvatures of the canal in which it lies. In addition to the bony wall of the vertebral canal, it is enveloped and protected by its three membranes or meninges, which are con- tinuous with the like membranes of the encephalon: first, the pia mater, which closely invests the cord and sends ingrowths into its substance, contributing to its support; second, the arachnoid, a, loosely constructed, thin membrane, separated from the pia mater by a considerable subarachnoid space ; thnd, the dura niater, the outermost and thickest of the membranes, separated from the arachnoid by merely a sHt-hke space, the subdural space. The intimate association of the central system with all the peripheral organs is attained chiefly through the spinal cord, and this is accomplished by means of thirty-one pairs of spinal nerves, which are attached along its lateral aspects. The nerves of each pair are attached opposite each other at more or less equal intervals along its entire length, and in passing to the periphery they penetrate the men- inges, which contribute to and are continuous with the connective-tissue sheaths investing them. Each nerve is attached by two roots, an afferent or dorsal root, which enters the cord along its postero-lateral sulcus, and an efferent or ventral root, which makes its exit along the ventro-lateral aspect. With its inequahties in thickness and its conical termination the spinal cord is subdivided into four parts or regions: — (1) The cervical portion, with eight pairs of cervical nerves; (2) the thoracic portion, with twelve pairs of thoracic nerves; (3) the lumbar portion, with five pairs of lumbar nerves; and (4) the conus meduUaris, or sacral portion, with five pairs of sacral and one pair of coccygeal nerves. From the termination of the conus meduUaris, the pia mater continues below in the subarachnoid space into the portion of the vertebral canal not occupied by the spinal cord, and forms the non-nervous, slender, thread-like terminus, the filu7n terminale. This becomes continuous with the dura mater at its lower extremity. 772 THE NERVOUS SYSTEM In the early fetus the spinal nerves pass from their attachment to the spinal cord outward through the intervertebral foramina at right angles to the long axis of the cord, but, owing to the fact that the vertebral column increases consider- ably in length after the spinal cord has practically ceased growing, the nerve-roots become drawn caudad from their points of attachment, and, as is necessarily the case, their respective foramina are displaced progressively downward as the termination of the cord is approached, until finally the roots of the lumbar and sacral nerves extend downward as a brush of parallel bundles considerably below the levels at which they are attached. This brush of nerve-roots is the Cauda equina. The dura mater, being more closely related to the bony wall of the canal than to the spinal cord, extends with the vertebral column and thus en- velops the Cauda equina, undergoing a slightly bulbous, conical dilation which decreases rapidly and terminates in the attenuated canal of the coccyx as the coccygeal ligament. The enlargements. — Wherever there is a greater mass of tissue to be in- nervated, the region of the nervous system supplying such must of necessity possess a greater number of neurones. Therefore, the regions of the spinal cord associated with the skin and musculature of the regions of the superior and Fig. 612.— Dorsal View of Portion of Spinal Cord in Position in Vertebral Canal Dura mater spinalis — -^fe^V{?/ "^T^felf^'" ■^^"^chnoidea spinalis ■ --■* Lower cervical region ^ Spinal nerve Thoracic region inferior limbs are thicker than the regions from which the neck or trunk alone are innervated. Thus in the lower cervical region the spinal cord becomes broadened into the cervical enlargement, and likewise in the lumbar region occurs the Imnbar enlargement. The spinal nerves attached to these regions are of greater size than in other regions. The cervical enlargement [intumescentia cervicalis] begins with the third cervical vertebra, acquires its greatest breadth (12 to 14 mm.) opposite the lower part of the fifth cervical vertebra (origin of the sixth cervical nerves), and extends to opposite the second thoracic vertebra. Unlike the lumbar enlargement, its lateral is noticeably greater than its dorso-ventral diameter. The lumbar enlargement [intumescentia lumbalis] begins gradually with the ninth or tenth thoracic vertebra, is most marked at the twelfth thoracic vertebra (origin of the fourth lumbar nerves), and rapidly diminishes into the conus medullaris. Both the lumbar and thoracic regions are practically circular in transverse section. Neither diameter of the lumbar is ever so great as the lateral diameter of the cervical enlargement. The thoracic part attains its smallest diameter opposite the fifth and si.xth thoracic vertebrae (attachment of the seventh and eighth thoracic nerves.) The enlargements occur with the development of the upper and lower limbs. In the embyro they are not evident until the limbs are formed. In the orang-utan and gorilla the cervical enlargement is greatly developed; the ostrich and emu have practically none at all. Surface of the spinal cord. — The cord is separated into nearly symmetrical right and left halves by the broad anterior median fissure into which the pia mater is duplicated, and opposite this, on the dorsal surface, by the posterior median sulcus. Along the lower two-thirds of the cord this sulcus is shallowed to little SURFACE OF SPINAL CORD 773 more than a line which marks the position of the posterior median septum; in the medulla oblongata it opens up and attains the character of a fissure. Each of the two lateral halves of the cord is marked off into a posterior, lateral, and anterior division by two other longitudinal sulci. Of these, the postero-lateral sulcus occurs as a shght groove 2 to 3| mm. lateral from the posterior median sulcus, and is the groove in which the root filaments of the dorsal roots enter the cord in regular linear series. The ventral division is separated from the lateral Fig. 613. — Drawing prom Specimen showing Cauda Equina, the Roots op Certain of THE Spinal Nerves which form it, and its Accompanying Dura Mater. (Dorsal aspect.) V / -Dura mater spinalis I Lumbar enlargement Conus meduUaris Filum terminale Coccygeal ligament (filum matris spinalis) by the antero -lateral sulcus. This is rather an irregular, linear area than a sulcus. It is from 1 to 2 mm. broad, and represents the area along which the efferent fibres make their exit from the cord to be assembled into the respective ventral roots. This area varies in width according to the size of the nerve-roots, and, like the postero-lateral sulcus, its distance from the mid-line varies according to locality, being greatest on the enlargements of the cord. In the cervical region, and along a part of the thoracic, the posterior division is subdivided by a delicate longitudinal groove, the postero-intermediate sulcus, which becomes more evident 774 THE NERVOUS SYSTEM towardjthe medulla oblongata and represents the line of demarcation between the fasciculus gracihs and the fasciculus cuneatus. Occasionally in the upper cervical region a similar line may be seen along the ventral aspect close to the anterior Fig. 614. — Posterior and Anterior Views of the Spinal Cord. (Modified from Quain.) Clava ^, Funiculus cuneatus' Postero -median sulcus f Postero-Iateral sulcus Postero-lateral sulcus- - Postero-median sulcus ^l}-i Cervical enlargement I/Umbar enlargement Olivary body Lateral funiculus Decussation of pyramids I- ^U Anterior median fissure Antero-Iateral sulcus (Line of ventral nerve- roots) Anterior median fissure median fissure. This is the antero-intermediate sulcus, forming the lateral boundary of the ventral cerebro-spinal fasciculus. Collectively, the entire space between the posterior median sulcus and the line of attachment of the dorsal roots is occupied by the posterior funiculus; the lateral space between the line of attachment of the dorsal and that of the ventral GREY SUBSTANCE OF SPINAL CORD 775 roots, by the lateral funiculus; and the space between the ventral roots and the anterior median fissure, by the anterior funiculus. Each of these funiculi is subdivided within into its component fasciculi. The dorsal and ventral nerve-roots are not attached to the cord as such, but are first frayed out into numerous thread-like bundles of axones which are distributed along their lines of entrance and exit. These bundles are the root filaments [fila radicularia] of the respective roots. The fila of the larger spinal nerves are fanned out to the extent of forming almost continuous lines of attachment, while in the thoracic nerves there are appreciable intervals between those of adjacent roots. Throughout, the intervals are less between the fila of the ventral than between those of the dorsal roots. Internal Structure of the Spinal Cord By reflected light masses of medullated axones appear white in the fresh, and such masses are known as white substance. The spinaal cord consists of a continuous, centrally placed column of grey substance surrounded by a variously thickened tunic of white substance. The closely investing pia mater sends Fig. 615.- -A, Ventral, and B, Dorsal, Views op Portion op Spinal Cord showing Modes op Attachment op Dorsal and Ventral Roots. Antero-Iateral sulcus (line of ventral roots) /'^Anterior median fissure Posteriormedian sulcus / Posterior in- numerous ingrowths into the cord, bearing blood-vessels and contributing to its internal supporting tissue. The volume of white and of grey substance varies both absolutely and relatively at different levels of the cord. The absolute amount of grey substance increases with the enlargements. The absolute amount of white substance also increases with the enlargements coincident with the greater amount of grey substance in those regions. The relative amount of white substance increases in passing from the conus medullaris to the medulla oblongata, due to the fact that the ascending and descending axones associating the cord with the encephalon are the one contributed to the cord and the other gradually terminating in it at different levels along its entire descent. The grey substance. — In the embryo all the nerve-cells of the grey substance are derived from the cells lining the neural tube, and in the adult the column of grey substance, though greatly modified in shape, still retains its position about the central canal. In transverse section the column appears as a grey figure of two laterally developed halves, connected across the mid-line by a more attenu- ated portion, the whole roughly resembling the letter H. The cross-bar of the H is known as the grey commissure. Naturally, it contains the central canal, which is quite small and is either rounded or laterally or ventrally oval in section, according to the level of the cord in which it is examined. The canal continues upward, and in the medulla oblongata opens out into the fourth ventricle. Downward, in the extremity of the conus medullaris, it widens slightly and forms the rhomboidal sinus or terminal ventricle, then is suddenly constricted into an extremely small 776 THE NERVOUS SYSTEM canal extending a short distance into the filum terminale, and there ends blindly. The grey commissure always lies somewhat nearer the ventral than the dorsal surface of the cord, and itself contains a few medullated axones which vary in amount in the different regions of the cord. The medullated axones crossing the mid-line on the ventral side of the central canal form the ventral or anterior white commissure ; those, usually much fewer in number, crossing on the dorsal side of the central canal, form the dorsal or posterior white commissure. These two commissures comprise fibres crossing in the grey substance as distinguished from others which cross in the white substance dorsal and ventral to them. The axones of these commissures serve in functionally associating the two lateral halves of the grey, column. Each lateral half of the grey column presents a somewhat crescentic or comma- shaped appearance in transverse section, which also varies at the different levels of the cord. At all levels each half presents two vertical, well-defined horns, themselves spoken of as columns of grey substance. The dorsal horn [columna posterior] extends posteriorly and somewhat laterally toward the surface of the cord along the line of the postero-lateral sulcus. It is composed of an apex and a neck [cervix columnse posterioris]. In structure the apex is peculiar. The greater portion of it consists of a mass of small nerve-cells and neurogha tissue, among which a gelatinous substance of questionable origin predominates, giving the horn a semi-translucent appearance. This is termed the gelatinous substance of Rolando, to distinguish it from a similar appearance immediate^ about the central canal, the central gelatinous substance. The apex of the dorsal horn is widest in the regions of the enlargements, especially the lumbar, and the gelatinous substance of Rolando is most marked in the cervical region. In these regions the cervix consists of a slight constriction of the dorsal horn between the apex and the line of the grey commissure. In the thoracic region, however, the base of the cervix is the thiclcest part of the dorsal horn. This thickness is due to the presence there of the nucleus dorsalis, or Clarke's column — a column of grey substance containing numerous nerve-cells of larger size than elsewhere in the dorsal horn, and extending between the seventh cervical and third lumbar segments of the cord. Tapering finelj' at its ends, this nucleus attains its height in the lower thoracic or first lumbar segment. About the ventro-lateral periphery of the nucleus dorsalis are scattered nerve-cells of the same type as contained in it. These cells ai'e sometimes distinguished as Stilling's nucleus, though Clarke's column was also described by Stilling. They are more numerous about the lower extremity of the nucleus dorsalis, and they continue to appear below its termination in the lumbar region. The ventral horn [columna anterior] of each lateral half of the grey figure is directed ventrally toward the surface of the spinal cord, pointing toward the antero-lateral sulcus. It contains the cell-bodies which give origin to the efferent or ventral root axones, and these axones make their emergence from the spinal cord along the antero-lateral sulcus. The ventral horns vary markedly in shape in the different regions. In certain segments each ventral horn is thickened later- ally and thus presents its two component columns of grey substance : the lateral horn [columna laterahs], a triangular projection of grey substance into the surrounding white substance, in line with or a little ventral to the line of the grey commissure; and the ventral horn proper [columna anterior], projecting ventrally. In the mid-thoracic region the lateral horn is relatively insignificant, and the anterior horn is quite slender; in the cervical and lumbar enlargements both horns are considerably enlarged. The grey substance is not sharply demarcated from the white. In the blending of the two there are often small fasciculi of white substance embedded in the grey, and likewise the grey substance sends fine processes among the axones composing the white substance. Such processes or grey trabeculse are most marked along the lateral aspects of the grey figure and present there the appear- ance known as the reticular formation. The reticular formation of the spinal cord is most evident in the cervical region (fig. 616). Minute structure. — The large cell-bodies of the ventral horn as a whole are divisible into four groups, only three of which are to be distinguished in the mid-thoracic region of the spinal cord: — (1) A ventral group of cells, sometimes separated into a ventro-lateral and a ventro- medial portion (see figs. 616, 619), occupies the ventral horn proper, is constant throughout the entire length of the cord, and contributes axones to the ventral root, most of which probably supply the muscles adjacent to the vertebral column; (2) a dorso-medial group of cells, situated in the medial part of the ventral horn, just below the level of the central canal, gives origin to axones some of which go to the ventral root of the same side, but most of which cross the mid- line vi& the anterior white commissure, either to pass out in the ventral root of the opposite side or to enter the white substance of that side and course upward or downward, associating with other levels of the cord. Some of its axones terminate among the cells of the ventral horn WHITE SUBSTANCE OF SPINAL CORD 111 in the same level of the opposite side; (3) a lalEral group of cells, sometimes separated into a dorso- lateral and a ventro-lateral portion, occupies the lateral column or horn, and is best differentiated in the cervical and lumbar enlargements. Most of the axones arising from its larger cells are contributed to the ventral root of the same side, and such axones probably supply the muscles of the extremities. Some of those from its ventral portion are distributed to the muscles of the body-wall; the dorso-lateral portion is that part of the lateral column \vhich persists throughout the cord, and is considered as supplying the visceral efferent fibres in the ventral roots. (4) an intermediate group, occupying the mid-dorsal portion of the ventral horn. Axones arising from its cells are probably seldom contributed to the ventral root, but instead course wholly within the central nervous system. Some pass to the opposite side of the cord, chiefly via the anterior and possibly the posterior white commissure, to terminate either in the same or different levels of the grey column. Others of longer course pass to the periphery of the cord, join one of the spino-cerebellar fasoicuh, and pass upward to the cerebellum. Furthermore, there are scattered throughout the grey substance many smaller cell-bodies of neurones. These give rise to axones of shorter course, either commissural or associational proper. Of such axones many are quite short, coursing practically in the same level as that in which their cells of origin are located, and serve to associate the different parts of the grey sub- stance of that level. Others course varying distances upward and downward for the association of different levels of the grey column. It is evident from the above that in addition to the various nerve-ceUs it contains, there is also to be found a felt-work of axones in the grey substance. Many of these axones are meduUated, though not in sufficient abundance to destroy the grey character of the substance. The felt-work is composed of three general varieties of fibres: — (1) The terminal branches of axones entering from the fasciculi of the white substance and forming end-brushes about the various cell-bodies in the grey substance (partly meduUated) ; (2) axones given off from the cells of the grey substance and which pass into the surrounding white substance either to enter the ventral-roots or to join the ascending and descending fasciculi within the spinal cord (partly meduUated); (3) axones of Golgi neurones of type 11, which do not pass outside the confines of the grey substance (non-meduUated). Some axones of any of these varieties may cross the mid-line and thus become commissural. In general all fibres of long course acquire medullary sheaths a short distance from then- cells of origin, and lose them again just before termination. The white substance of the spinal cord. — The great mass of the axones of the spinal cord course longitudinally and form the thick mantle surrounding the column of grey substance. This mantle is divided into right and left homo- lateral halves by the anterior median fissure along its ventral aspect, and along its dorsal aspect by the posterior median septum, which is for the most part a connective-tissue partition derived from the pia mater along the line of the posterior median sulcus. The mantle is supported internally by interwoven neuroglia and white fibrous connective tissue, the latter, derived chiefly from the pia mater, closely investing it without. The axones of the white substance belong to three general neurone systems: — (1) The spino-cerebral and cerebrospinal system, which consists of axones of long course, one set ascending and another descending, forming links in the neurone chains between the cerebrum and the peripheral organs. The ascending axones of this system collect the general bodily sensations which are conve.yed to the cerebrum, the cells of which in response contribute axones which descend the cord, conveying efferent or motor impulses. (2) The spino-cerebellar and cerebellospinal system consists of conduction paths, one set ascending and another descending, which are connections between cerebellar structures and the grey substance of the spinal cord. (3) The spinal association and commissural system of axones which serve to associate the different levels and the two sides of the spinal cord and which are proper to the spinal cord, i. e., they do not pass outside its confines. Both the first and second systems increase in bulk as the cord is ascended. The ascending axones of each system are contributed to the white substance of the cord along its length, and therefore accumulate upward; the axones descending from the encephalon are distributed to the different levels of the cord along its length, and therefore diminish downward. The mass of the third system of axones varies according to locality. Wherever there is a greater mass of neurones to be associated, as there is in the enlargements of the cord, a greater number of these axones is required. Their cells of origin, being in the grey substance of the cord, contribute to its bulk and thus both the cells and the axones of this S3^stem serve to make the enlargements more marked. In the lumbar and sacral regions the greater mass of the entire white substance consists of axones belonging to this system. It forms a dense felt-work about the grey column throughout the cord. Necessarily this system contains axones of various lengths. Some merely associate different levels within a single segment 778 THE NERVOUS SYSTEM Fig. 616. — Transverse Sections prom Different Segments of the Spinal Cord, show- ing Shape and Relative Proportions of Grey and White Substance in the Various Regions. Posterior funiculus Fasciculus cuneatus Anterior funiculus Cervical I Fasciculus gracilis Posterior septum ^ Dorsal (posterior) root D erior) horn Thoracic \ III CONDUCTION PATHS 779 of the cord; others associate the different segments with each other. Axones which associate the structures of the spinal cord with those of the medulla ■ oblongata may be included in this system. Many of these axones cross the mid- line both in the grey and in the white substance to associate the neurones of the two sides of the grey column. For purposes of distinction, such as cross the mid- line are called commissural fibres, while those which course upward and down- FiG. QilG— Continued. Sacral IV Coccygeal ward on the same side are association fibres. Coursing in longitudinal bundles about the grey figure, the latter compose the fasciculi proprii or ' ground bundles ' of the spinal cord. METHODS BY WHICH THE CONDUCTION PATHS HAVE BEEN DETERMINED A purely anatomical examination of a normal adult cord, prepared by whatever means, gives no indication of the fact that the mass of longitudinally coursing fibres of the white sub- 780 THE NERVOUS SYSTEM stance is composed of more or less definite bundles or fasciculi, each having a definite course, and whose axones form links (conduction paths) in a definite system of neurone chains. Present information as to the size, position, and connections of the various fascicuH is based , upon evidence obtained by three different lines of investigation: — (1) Physiological investigation. — (a) Direct stimulation of definite bundles or areas in section and carefully noting the resulting reactions which indicate the function and course of the axones stimulated, (b) 'WaUerian degeneration' and the application of such methods as that of Marchi. When an axone is severed, that portion of it which is separated from its parent cell-body degenerates. Likewise a bundle of axones severed from their cells of origin, whether by accident or design, will degenerate from the point of the lesion on to the locality of their termination in whichever direction thisimay be. This phenomenon was noted by Waller in 1852 and is known as WaUerian degeneration. By the application of a staining technique which is differential for degenerated or degenerating axones and a study of serial sections con- taining the axones in question, their course and distribution may be determined. The locality of their cells of origin, if unknown, may be determined by repeated experiment till a point of lesion is found not followed by degeneration of the axones under investigation, (c) The axonic reaction or 'reaction from a distance.' Cell-bodies whose axones have been severed undergo chemical change and stain differently from those whose axones are intact. Thus cell-bodies giving origin to a bundle of severed axones may be located in correctly stained sections of the region containing them. (2) Embryological evidence. — In the first stages of their development axones of the cere- bro-spinal nervous system are non-medullated. They acquire their sheaths of myelin later. Axone pathways forming different chains become medullated at different periods. Based upon this fact a method of investigation originated by Flechsig is employed, by which the posi- tion and course of various pathways may be determined. A staining method differential for medullated axones alone is apphed to the nervous systems of foetuses of different ages, and path- ways meduUated at given stages may be followed from the locality of their origin to their termination. In the later stages, when most of the pathways are medullated and therefore stain alike, the less precocious pathways may be followed by their absence of meduUation. (3) Direct anatomical evidence. — (a) Stains differential for axones alone are applied to a given locality to determine the fact that the axones of a given bundle actually arise from the cell-bodies there, or that axones traced to a given locality actually terminate about the cell- bodies of that looahty. For example, it may be proved anatomically that the axones of a dorsal root arise from the cells of the corresponding spinal ganglion, and then these axones may be traced into the spinal cord and their terminations noted either by collateral or terminal twigs, or the fasciculus they join in their cephalic course may be determined. (6) The staining prop- erties and the size and distribution of the tigroid masses in the cell-bodies of sensory neurones differ from those in the motor neurones, and recently Malone has claimed that, in the central system, the cell-bodies in the nuclei of sensory neurone chains, those ascending toward the cere- bral cortex, may be distinguished from the cell-bodies of the motor or descending chains by the arrangement and size of their tigroid masses. He claims further that in the same way, the cell- bodies of the somatic efferent neurones may be distinguished from those of the visceral efferent neurones. In this way the locaUty of origin of certain physiologically known paths may be determined. (4) The so-called paihologico-anatomical method is based upon the same general principles as is the physiological (or experimental) method. A pathological lesion, a local infection or a tumor for example, may destroy a nucleus of cell-bodies or sever a bundle of axones, and the resulting degeneration of the axones may be followed through serial sections suitably prepared. The locahty of the lesion known, the path may be followed to determine the locality of its ter- mination; its locality of termination known from the symptoms resulting, the path may be fol- lowed to its cells of origin, or to determine whatever be the locality of the lesion. Funiculi. — In order that the various fasciculi may be referred to with greater ease, the white substance of the spinal cord in section is divided into three areas known as funiculi or columns and which correspond to the funiculi already mentioned as evident upon the surface of the cord when intact. The funiculi are outlined wholly upon the basis of their position in the cord and with reference to the median line and the contour of the column of grey substance; their component fascicuh are defined upon the basis of function. (1) The 'posterior funiculus or column is bounded by the posterior median septum and the line of the dorsal horn; (2) the lateral funiculus or column is bounded by the lateral concavity of the grey column and the lines of entrance and exit of the dorsal and ventral roots; (3) the ventral funiculus or column is bounded by the Hne of exit of the ventral roots, and by the anterior median fissure. The posterior funiculus or column [funiculus posterior]. — This funiculus is composed of two general varieties of axones arranged in five fasciculi. First, and constituting the predominant type in all the higher segments of the cord, are the afi'erent or general sensory axones, which arise in the spinal ganglia, enter the cord by the dorsal roots, assume their clistribution to the neurones of the cord, and then take their ascending course toward the encephalon. The axone of the spinal ganglion neurone undergoes a T-shaped division a short distance from the cell- body, one limb of this division terminating in the peripheral organs and the other going to form the dorsal root. Upon entering the cord the dorsal root axones POSTERIOR FUNICULUS 781 undergo a Y-shaped bifurcation in the neighbourhood of the dorsal horn, one branch ascending and the other descending. Their ascending branches form the fasciculus gracilis (Goll's column) and the fasciculus cuneatus(Burdach's column). These fasciculi are the chief ascending or sensory spino-cerebral connections, the direct sensory path to the brain. The neurones represented in them con- stitute the first link in the nem-one chain between the periphery of the bodj'- and the cerebral cortex. Fig. 617. — Showing Disposition or the Dorsal Root Fibres Upon Entering the Spinal Coed. (From Edinger, after Cajal.) A, shows dorsal root axones DR, entering the spinal cord, bifurcating at B, and giving off collat- erals C to the neurones of the cord. B shows the telodendria of these axones or of their collaterals displayed upon cell-bodies of the grey substance of the cord. In threading their way toward the brain, these sensory axones tend to work toward the mid- line. Therefore tliose of longer course are to be found nearer the posterior septum, in the upper segments of tlie cord, than those axones which enter the cord by the dorsal roots of the upper segments. Thus it is that the fasciculus gracilis, the medial of the two fasciculi, contains the axones which arise in the spinal ganglia of the sacral and lumbar segments. In other words, it ia the fasciculus bearing sensory impulses from the lower limbs to the brain, while the fasciculus cuneatus, the lateral of the two, is the corresponding pathway for the higher levels. Naturally, there is no fasciculus cuneatus as such in the lower segments of the spinal cord. The axones being mucli blended at first, it is only in the upper thoracic and cervical region that there is any anatomical demarcation between the two fasciculi. In this region the two become so dis- tinct that there is in some cases an apparent connective-tissue septum between them, continuing inward from the postero-intermediate sulcus — the surface indication of the hne of their junction (fig. 616). Upon reaching the medulla oblongata the fibres of the fasciculus gracilis and the fasciculus cuneatus terminate about cells grouped to form the nuclei of these fasciculi. The nucleus of the fasciculus gracilis is situated medially and begins just below the point at which the central canal opens into the fourth ventricle; the nucleus of the fasciculus cuneatus is placed laterally and ex- tends somewhat higher than the other nucleus. The neurones whose cell-bodies compose these 782 THE NERVOUS SYSTEM nuclei constitute the second links in the neurone chains conveying sensory impulses from the periphery to the cerebral cortex. The descending or caudal branches of the dorsal root axones are concerned wholly with the neurones of the spinal cord. They descend varying distances, some of them as much as four segments of the cord, and give off numerous col- laterals on their way to the cells of the grey column. Those terminating about cell-bodies of the ventral horn which give rise to the ventral or motor root-fibres, are responsible for certain of the so-called 'reflex activities' and thus contribute to the simplest of the reflex arcs. In descending they serve to associate different levels of the grey substance of the cord with impulses entering by way of a single dorsal root. Some of their collaterals cross the mid-line in the posterior white commissure, and thus become connected with neurones of the opposite side. The caudal branches of longer course are scattered throughout the ventral portion of the fasciculus cuneatus {middle root zone) , and the longest show a tendency to collect along the border-line between the fasciculus cuneatus and the fasciculus gracilis, and thus contribute largely to the comma-shaped fasciculus. Also some of the longest of them in the lower levels course in the oval bundle or septo- marginal root zone. The ascending branches of the dorsal root axones also give off collaterals to the grey sub- stance of the cord, thus extending the area of distribution of a given dorsal nerve-root to levels of the cord above the region at which the root enters. The greater number of the terminations of dorsal root axones within the spinal cord are concerned first with neurones other than those contributing ventral root- fibres. The greater mass of the neurones concerned are those of the Golgi type II and those contributing the fasciculi proprii or ground bundles of the spinal cord, or the second variety of axones composing the posterior funiculus. The latter fasciculi arise from the smaller cells of the grey column. These axones pass from the grey substance to enter the surrounding white substance, bifurcate into ascending and descending branches, which in their turn give off numerous collaterals to the cells of the grey substance of the levels through which they pass. The cell-bodies giving origin to such axones are so numerous that the entire column of grey substance is surrounded by a continuous felt-work of axones of this variety. The dorsal fasciculus proprius (anterior root zone of posterior column) arises chiefly from cells situated in the dorsal horn (slraium zonale). Coincident with the ingrowth and arrange- ment of the fasciculi gracilis and cuneatus many fibres of the dorsal fasciculus proprius go to form both the oval bundle and the comma-shaped fasciculus. Thus these two bundles are mixed, being fasciculi proprii which contain caudal branches of dorsal root axones. The association fibres in the oval bundle are the longest of any belonging to the dorsal fasciculus proprius. The cephalic and caudal branches combined of some are said to extend more than half the length of the cord and it has been claimed that some even associate the cervical region with the conus meduUaris. Based upon this claim, Obersteiner has called the oval bundle, the "dorso-medial sacral field" and Edinger has referred to the most dorsal part of it as the "tractus cervico-lum- balis dorsalis." The 'median triangle' is formed by the continuation of the dorsal fasciculi proprii with the oval or septo-marginal fasciculus. Some of the axones of the dorsal fasciculus proprius cross the midline to distribute impulses to the neurones of the opposite side. These commissural axones, together with certain collaterals of the dorsal root axones, which cross the mid-line out- side the dorsal white commissure, compose the so-called cornu-commissural tract at the base of the posterior septum. The lateral funiculus or column [funiculus lateralis]. — Not all the axones of the posterior or dorsal nerve-roots extend to the encephalon. Estimation shows that the sum of all the dorsal roots is greatly in excess of the sum contained in the fasciculi cuneatus and gracilis just before these enter their nuclei of termination. Therefore many of the ascending dorsal root axones are concerned with spinal- cord relations wholly. The marginal zone of Lissauer, situated along the lateral margin of the postero-lateral sulcus. is composed largely of dorsal root axones. Many of these finally work across the line of the sulcus into the posterior funiculus. Many of the dorsal root-fibres which do not reach the brain occur in Lissauer's zone. Many others of course occur throughout the posterior column. Lissauer's zone also contains some fibres arising from the small cells of the dorsal horn, and to this extent corresponds to a fasciculus proprius. Ranson has found that large numbers of the non-meduUated dorsal root axones which enter the cord are contributed to Lissauer's zone. The lateral fasciculus proprius (lateral ground bundle, lateral limiting layer) is situated in the lateral concavity of the grey column and is continuous with the other fasciculi proprii both dorsal and ventral. Beyond that it probably contains LATERAL CEREBROSPINAL FASCICULUS 783 fewer commissural axones, it is of the same general significance as the others. It is frequently divided into small bundles by the reticular formation (see fig. 616). The lateral cerebro-spinal fasciculus (crossed p.yramidal tract). In contrast to the sensory fibres passing through the spinal cord conveying impulses destined to reach the cerebral cortex, axones are given off from the pyramidal cells of the Fig. 618. — Diageam Illustrating the Formation of the Fasciculi Proprii (association fasciculi) and the Commissural Fibres of the Spinal Cord, and the General Archi- tecture OF THE Cord as a Mechanism for Reflex Activities. The ventral fasciculus proprius is omitted and the lateral is shown on one side only. The lower spinal ganglion neurone shown illustrates the type whose ascending branch is of much longer extent than that of the upper one. -* Dorsal fasciculus proprius Commissural neurone in ventral fas- *— - ciculus proprius Lateral fasciculus 'i^ proprius cortex, which descend to terminate about the cells of the grey substance of the spinal cord, chiefly the cells which give origin to the ventral root-fibers. Upon reaching the medulla oblongata in their descent, these axones are accumulated into two well-defined, ventrally placed bundles, the pyramids, one from each cerebral hemisphere. In passing through the brain stem the pyramids contribute many fibres which cross the mid-line to terminate in the motor nuclei of the cranial nerves of the opposite side, and thus decrease appreciably in bulk. According to the estimate of Thompson, only about 160,000 of the pyramidal fibres are destined to enter the spinal cord. Upon reaching the lower part of the medulla, the greater mass of the fibres of each pyramid, which are destined to enter the cord, suddenly cross the mid-line in the 'decussation of the 784 THE NERVOUS SYSTEM pyramids.' The remainder retain their ventral position in their descent decussating gradually in the cord itself. The pyramidal fibres which cross in the medulla course in the lateral column ventral to Lissauer'sjzone, and lateral to the lateral fasciculus proprius, and form the lateral cerebrospinal fasciculus (crossed pyramidal tract). It is a large fasciculus, oval shaped in transection, and since its axones terminate in the grey column of the cord all along its length, it decreases in bulk as the cord is descended. In addition to the three dispositions of the dorsal root axones given above, certain of them, either by collaterals or terminal twigs, form telodendria about the cells of the dorsal nucleus (Clarke's column), which nucleus extends from about the seventh cervical to the third lumbar segment of the cord. The axones given off by these cells pass to the dorso-lateral periphery of the lateral funiculus, and there collect to form the dorsal spino-cerebellar fasciculus (direct cerebellar tract of Flechsig). As such they ascend without interruption, and in the upper level of the medulla oblongata pass into the cerebellum by way of the inferior cerebellar peduncle or restiform body. Necessarily, this fasciculus is not evident in levels below the extent of the nucleus dorsalis. Also situated superficially in the lateral funiculus is another ascending con- duction path, and, like the dorsal spino-cerebellar fasciculus, to which it is ad- jacent, it is also in part at least a cerebellar connection. Its position suggests its name, superficial ventro-lateral spino-cerebellar fasciculus (Gowers' tract). This tract at'present'does not include as great an area in transverse section as when originally described. The more internal portion of the original Gowers' tract is now given a separate sig- nificance, and will be considered separately. While the exact location in the grey column of all the cell-bodies giving origin to the superficial ventro-lateral spino-cerebellar fasciculus is un- certain, it is known that certain ventral horn cells contribute their axones to it. Many of its cells of origin are scattered in the area immediately ventral to the nucleus dorsalis, others in the intermediate and mesial portion of the lateral group of ventral horn cells. In the lumbar region these cells are quite numerous, and, therefore, the fasciculus begins at a lower level in the spinal cord than does the direct cerebellar tract. In degenerations it becomes visible in the upper seg- ments of the lumbar region, and has been proved to increase notably in volume as the cord is ascended. Its axones arise for the most part directly from cell-bodies of the same side of the cord, though it has been shown by several investigators that many of its axones come from the grey substance of the opposite side by way of the ventral white commissure. Terminal twigs and collaterals of the dorsal root-fibres, mostly of the same side, but occasionally from the opposite side, terminate about its cells of origin. At one time Gowers' tract was considered an entity, but now, even in the more Umited area it occupies, it must be considered a mixture of axones of several terminal destinations or distinct neurone systems. The destination of some of its axones has not been determined with certainty. A portion, the spino-cerebellar fasciculus proper, go to the cerebellum, and there have been traced to the cortex of the superior vermis. Most of these reach the cerebellum not by way of the restiform body, as does the dorsal spino-cerebellar tract, but pass on in the brain-stem to the level of the inferior corpora quadrigemina, and there turn back£to join the brachiumjconjunctivum or superior cerebellar peduncle. (Auerbach, Mott, Hoche.) Only a few of its_ axones leave the fasciculus lower down in the medulla, to enter the cerebellum by way of the restiform body, in company with the dorsal spino-cerebellar tract. (Rossolimo, Tschermak.) Another portion of its axones are thought to reach the cerebrum, probably the nucleus lentiformis, though it has not been positively traced further than the superior corpora quadrigemina. Many axones in Gowers' tract of the cord correspond to those of the fasciculi proprii, and merely run varying distances in the cord, to turn again into its grey substance. Schaeffer followed some of these from the lumbar region up to the level of the second cervical nerve. In the ventro-mesial border of Gowers' tract and immediately upon the periphery, near the antero-lateral sulcus (exit of ventral nerve-roots), there is found in the higher segments of the cord a small oval bundle, the spino-olivary fasciculus or Helweg's (Bechterew's) bundle. The functional direction of its fibres has not been settled. It is asserted to arise from cell-bodies of the ohve in the medulla oblongata, and in the cord is beheved to be associated with the cells of the ventral column of grey substance, probably those of the lateral; horn. More recent claims assert that it arises fron cell bodies inithe cord and thus is spino-olivary. By some observers it has been traced as far down as the mid-thoracic region; by others, however, only as far as the third cervicalfsegment. The olives being nuclei largely concerned with cerebellar connections, Helweg's fasciculus is probably an indirect cerebellar association with the spinal cord neurones. It is composed of axones of relatively very small diameter, andjt is one of the last fasciculi of the spinal cord to become meduUated. Situated between the superficial ventro-lateral spino-cerebellar fasciculus and the lateral fasciculus proprius is an area which, in transverse sections, may be, by position, referred to collectively as the intermediate fasciculus. So intermingled are the axones comprising it that it has been called the mixed lateral zone. It contains fibres of at least five functional varieties: FASCICULI OF SPINAL CORD 785 786 THE NERVOUS SYSTEM (1) Fibres belonging to the lateral fasciculus proprius which are of longer extent gradually course farther away from the grey substance of the cord and such mix into the intermediate fasciculus. (2) It is said to contain fibres descending from the cerebellum to associate with the neurones of spinal cord, probably directly with the ventral root or motor neurones. (3) The rubro-spinal fasciculus. — This arises from cell-bodies in the red nucleus of the tegmentum (in the mesencephalon) and is a crossed fasciculus. Axones arising from the red nucleus of one side cross the mid-Une while yet in the mesencephalon and descend in the lateral funiculus of the cord to terminate gradually about ceU-bodies of the ventral horn, both those which give rise of ventral root fibres and those which contribute to the fascicuU proprii. Its fibres are more thickly bundled in a crescentic area fitting onto the ventral side of the lateral cerebro-spinal fasciculus, and some are said to mix into the area of this latter. (4) The vestibulo-spinal fasciculus. — This is sometimes called the lateral vestibulo-spinal fasciculus from the fact that there is a tract of similar significance in the ventral funiculus of the cord. It arises from some of the ceU-bodies comprising Deiter's nucleus, the lateral nucleus of termination of the vestibular nerve, and from some of those of the spinal nucleus (nucleus of the descending root) of this nerve, all of which is in the medulla. _ It descends the cord, un- crossed, to terminate gradually about ventral horn cells, thus comprising a part of the apparatus for the equilibration of the body. . Its fibres are thought to be more closely collected in the area immediately ventral to the rubro-spinal fasciculus, but of course commingle with the latter. (5) The corpora-quadrigemina-thalamus path. The most lateral portion of the intermediate fasciculus, a small area once included in Gower's tract, contains fibres both ascending and de- scending, connecting the spinal cord with the thalamus (diencephalon) and the quadrigeminate bodies of the mesencephalon. These are crossed paths. The ascending fibres arise from ceU- bodies in the ventral horn of one side, cross in the ventral white commissure (commissural neurones) and course upward in the intermediate fasciculus to their termination in the opposite side. Those terminating about cell-bodies in the thalamus form what is known as the spino- thalamic tract, while those terminating in the nuclei of the quadrigeminate bodies are called the spino-mesencephalic or spino-tectal tract (Iradus spino-tectalis) . It is not known in which region of the cord most of these fibres arise but it is quite probably the cervical region. The fibres which arise from cell-bodies of the thalamus and nuclei of the quadrigeminate bodies cross the mid-line in the mesencephalon and descend the cord to terminate graduaDy about cell- iDodies in the ventral horn ol the opposite side. Those from the thalamus are known as the thalamo-spinal tract and those from the quadrigemina, as the mesencephalo- or tecto-spinal tract. The latter is thought to be the larger. By the fibres of the above tracts general sensory impulses from the body (skin, etc.) are carried to the central portion of the optic apparatus, and the descending fibres give a simple anatomical possibility for the movements of the body in response to visual and auditory im- pulses. The descending fibres are thought to terminate chiefly in contact with association neurones of the fasciculi proprii, these transferring the impulses to the neurones giving origin to the ventral or motor root fibres, but some are thought to terminate directly about the cell- bodies of ventral-root neurones. A portion of the intermediate fasciculus, most adjacent to Gower's tract, has been designated as Loewenthal's tract. The anterior funiculus or column [funiculus anterior]. — The intermediate fasciculus is continued ventrally and mesially across the line of exit of the ventral root axones, and thus into the anterior funiculus. This portion is also mixed, but its axones of long course associate somewhat different portions of the nerve axis from those connected by the more lateral portion. According to the studies of Flechsig, von Bechterew, and Held, this mesial portion contains fibres, both ascending and descending, which associate the various levels of the grey substance of the spinal cord with the neurones in the reticular formation of the medulla oblongata. The levels to which they have been traced comprise the olivary nuclei, which are largely concerned in cerebellar connections, and the nuclei of the vagus, glosso-pharyngeal, auditory, facial and the spinal tract of the trigeminus. Also some of the ascending fibres are probably associated with the nuclei of the eye-moving nerves. This portion of the intermediate fasciculus also grades into and is mixed with the axones of the ventral fasciculus proprius, as is its lateral portion with the lateral fasciculus proprius. In other words, the fasciculi proprii proper, the axones nearest the grey substance, serve for the intersegmental association of the different levels ol the grey substance of the cord, while the intermediate fasciculus contains axones of longer course which serve to associate more distant levels of the grey substance of the nerve axis — that of the spinal cord with its upward continuation into the medulla oblongata, pons and mesencephalon. The anterior marginal fasciculus, ventral vestibulo-spinal tract (Loewenthal's tract) forms the superficial boundary of the mesial portion of the intermediate fasciculus. It is a narrow band, parallel with the surface of the cord, and extends mesially from the mesial extremity of Gowers' tract (from Helweg's bundle) to the beginning of the anterior median fissure. The axones belonging to it proper are descending from the recipient nuclei of the vestibular nerve. Of these nuclei it has been held by some investigators that only Deiters' nucleus (the lateral nucleus of termination in the upper extremity of the medulla oblongata) gives origin to the axones of the anterior marginal fasciculus. Others agree with Tschermak that the superior and more laterally situated Bechterew's nucleus of the vestibular nerve also contributes axones ANTERIOR MARGINAL FASCICULUS 787 to it, and quite probably the nucleus of the spinal root of the vestibular adds further axones. Still other investigations have shown that a part at least of the fasciculus comes from the nucleus fastigius (roof nucleus) of the cerebellum. Since many axones from both Deiters' and Beehterew's nucleus terminate in the nucleus fastigius, the ventral vestibulo-spinal fasciculus Fig. 620.— Diagram of Spinal Cord Illustrating the Two Chief Varieties of Spino- CEREBRAL AND Cerebro-spinal Neurone Chains. The Ventral tecto-spinal (sulco- marginal) fasciculus, fibres descending from the superior quadrigeminate bodies, is not filled in. Soni£esthetic i Optic thalamus . of cerebral cortex Tecto-spinal tract Decussation of 1 emnisci Decussation of pyramids Cervical region of spinal cord Superior quadrigeminate body 1 1 ,-. Inferior quadrigeminate body 'i. Nucleus of fasciculus cuneatus TT- Nucleus of fasciculus gracilis ! j ^> Spino -thalamic and spino-mesencephalic paths ~__ Fasciculus cuneatus Posterior (dorsal) root Spinal ganglion Lumbar region of spinal cord IS, in any case, a conduction path from the nerve connections for equilibration to the grey sub- stance of the spinal cord. The fasciculus is said to extend as far as the sacral region of the cord, its axones terminating about the cells of the ventral horns. The term "ventral" is added to its name to distinguish it from the vestibulo-spinal tract described above as coursing in the lateral funiculus. It is considered an uncrossed pathway. 788 THE NERVOUS SYSTEM The ventral cerebro-spinal fasciculus (anterior or direct pyramidal tract), as stated above, is the uucrossed portion of the descending cerebro-spinal system of nem-ones. It is a small, oblong bundle, situated mesially in the anterior funiculus, parallel with the anterior median fissure. Like the lateral cerebro-spinal fasci- culus (crossed pyramidal tract), its axones arise from the large pyramidal cells of the motor area of the cerebral cortex, and transmit their impulses to the neu- rones of the ventral horns of the grey substance of the spinal cord, and almost entirely to those ne.urones which give origin to the ventral or motor root fibres. It represents merely a delayed decussation of the pyramidal fibres, for instead of crossing to the opposite side in the lower portion of the medulla oblongata, as do the fibres of the lateral fasciculus, its fibres decussate all along its course, crossing in the ventral white commissure and in the commissural bundle of the cord to terminate about the ventral horn cells of the opposite side. Hoohe, employing Marchi's method, found that a few of its fibres terminate in the ven- tral horn of the same side. This conforms to the pathological and experimental evidence that there are homolateral or uncrossed fibres in the crossed pyramidal tracts also. Like the crossed tract, the ventral pyramidal tract diminishes rapidly in volume as it descends the cord. Its loss is greatest in the cervical enlargement, and it is entirely exhausted in the thoracic cord. With the exception of the anthropoid apes and certain monkeys, none of the mammalia below man, which have been investigated, possess this ventral pyramidal tract Lying between the ventral cerebro-spinal fasciculus and the pia mater of the anterior median fissure is a thin tract of descending axones continuous ventrally with the anterior marginal fasciculus. From its position it is known as the sulco- marginal fasciculus; functionally it is the ventral mesencephalo-spinal (tecto- spinal) tract. The extent of its course in the spinal cord is uncertain. It arises from the cells of the grey substance of the superior pair of the quadrigeminate bodies, and there, in largest part at least, it crosses the mid-line, and in the so-called 'optic acoustic reflex path' descends through the medulla oblongata into the spinal cord of the opposite side. The superior quadrigeminate bodies having to do with sight, this tract forms a second path conveying visual impulses to the neurones of the spinal cord. The commissural bundle is situated about the floor of the anterior median fissm-e, and is the most dorsal tract of the anterior funiculus. It contains decus- sating or commissural axones of three varieties. (1) It contains the decussating axones of the ventral cerebro-spinal fasciculus throughout the extent of that fasciculus; (2) it is chiefly composed of the axones of the ventral fasciculus proprius which arise in the grey substance (ventral horn) of one side, cross the mid-line as com- missural fibres, and course both upward and downward to be distributed to the neurones of different levels of the grey substance of the opposite side; (3) it contains decussating axones which arise from cell-bodies in the grey substance of one side and cross the mid-line to terminate about cell-bodies in practically the same level of the opposite side. The latter are merely axones belonging to the ventral white commissiu-e which course without the confines of the grey figure. The commissural bundle is present throughout the length of the spinal cord, and is largest in the enlargements, i. e., where the association and commissural neurones occur in greater number generally. In its two last-mentioned varieties of axones it corresponds to the commissural portion of the dorsal fasciculus proprius (the cornu-commissural bundle). The ventral fasciculus proprius is but a continuation of the lateral fasciculus proprius, and is composed of ascending and descending association fibres of the same general significance. SUMMARY OF THE SPINAL CORD The spinal cord contains two general classes of axones arranged into three general systems. It contains axones which — (a) enter it from cell-bodies situated outside its boundaries, i. e., in the spinal ganglia and in the encephalon, and (b) axones which arise from cell-bodies situated within its own grey substance, some of which axones pass outside its boundaries both to the periphery and into the encephalon; some of which remain wholly within it. Its axones comprise — (1) a system for the intersegmental association of its grey substance, both ascending and descending, association proper and commissural; (2) a spino-cerebral and cerebro-spinal system, ascending and descending; and (3) a spino-cerebellar and cerebello-spinal system, ascending and descending. For these relations the grey substance of the cord contains three general classes of nerve-cells: — those which give rise to the peripheral efferent or motor axones of the ventral roots; those which give rise to central axones of long course, going to the encephalon; and those which supply its central axones of shorter course, the association and commissural systems. SUMMARY OF SPINAL CORD 789 The three systems : (1) Association and commissural. — Axones of spinal ganglion (afferent) neurones bifurcate within the cord into cephalic and caudal branches which extend varying distances upward and downward and terminate, (a) about cell-bodies whose axones are short and terminate within the grey substance of the same side and in the same level as their cell- bodies {Golgi neurones of type II); (b) about ceO-bodies whose axones pass without the grey sub- stance, bifurcate into cephalic and caudal branches to terminate in the grey substance of the same side but in various levels above and below (association fibres in the dorsal, lateral and ven- tral fasciculi proprii); (c) about cell-bodies whose axones cross the mid-line to terminate either in the same level of the grey substance of the opposite side, or bifurcate and the cephalic and caudal branches pass in the fasciculi proprii to terminate in various levels of the grey substance of the opposite side. The longer cephalic branches of (b) and (c) may terminate in the meduUa oblongata. All, associated with ventral root (efferent) neurones, belong to the neurone chains for the so-oaOed reflex activities. (2) The cerebral system. — (a) The cephalic branches of certain spinal ganglion neurones ascend beyond the bounds of the spinal cord to terminate within the medulla. Those ascend- ing from the spinal ganglia of lower thoracic and lumbo-sacral segments accumulate mesiaUy to form the fasciculus gracilis which terminates in the nucleus of this fasciculus; those arising from the upper thoracic and cervical segments accumulate more laterally in the posterior funi- culus to form the fasciculus cuneatus which terminates in the nucleus of the fasciculus cuneatus. (6) The impulses transferred to the neurones of these nuclei are borne across the mid-line and finall}' reach the sensory-motor area of the cerebral cortex, and cell-bodies here give rise to axones which descend, some decussating in the medulla to form the lateral cerebrospinal fasciculus, others form the uncrossed ventral cerebrospinal fasciculus which crosses the mid-line as it de- scends the cord. Both of these fasciculi transfer their impulses either directly to efferent ven- tral horn neurones, or to association neurones and these to the efferent neurones, (c) The cephalic and caudal branches of spinal ganglion neurones terminate about cell-bodies in the grey substance of the cord whose axones cross the mid-line and ascend laterally to terminate either in the quadrigeminate bodies {spino-mesencephalic tract), or in the thalamus (spino-thalamic trad), (d) Cell-bodies in thalamus and superior quadrigeminate bodies (receiving optic im- pulses) and in the inferior quadrigeminate bodies (probably mediating auditory impulses), give axones which cross the mid-line in the mesencephalon and descend, forming the thalamo- spinal and mesencephalospinal tracts, to terminate in contact with the efferent neurones of the cord. Axones from both sources descend in the lateral funiculus, while from the superior quadrigeminate body, a separate bundle descends in the ventral funiculus as the sulco-marginal {ventral mesencephalospinal) fasciculus, (e) The rubrospinal tract arises from cell-bodies in the red nucleus (in the mesencephalon), crosses the mid-line and descends in the lateral funiculus to transfer (probably cerebellar) impulses to the efferent neurones of the spinal cord. (.3) The cerebellar system. — (a) The cephalic and caudal branches of spinal ganglion neurones give telodendria about the cell-bodies forming the dorsal nucleus of the cord (Clarke's column) and about cell-bodies situated in grey substances ventral to the dorsal nucleus ("Still- ing's nucleus") and in the lateral horn. Axones arising from the cells of the dorsal nucleus pass laterally to form the dorsal spino-cerebellar fasciculus which ascends into the cerebellum by way of its inferior peduncle of the same side and terminates about cell-bodies of its cortex. Axones arising from Stilling's nucleus and the lateral horn cells, of both the same and opposite sides of the cord, accumulate to form the superficial venlro-lateral spino-cerebellar fasciculus, which ascends to enter the cerebellum by way of its superior peduncle and terminate about the cells of the cerebellar cortex, (b) A few axones arising in the roof nucleus of the cerebellum probably descent? in the animor marginal fasciculus in company with the ventral vestibulospinal tract to terminate upon the efferent neurones of the cord, (c) The inferior olivary nucleus, in the medulla, is a cerebellar relay and its cell-bodies are associated with the neurones of the upper por- tion of the same side of the spinal cord. Whether the axones arise in the olivary nucleus or in the grey substance of the cord is uncertain, but the more usual supposition favours the cord and thus the name, spino-olivary fasciculus is given them, (rf) Among its other functions, the cerebellum is concerned with equilibration. The vestibular nerve is the afferent nerve of equilibration and a large mass of the axones arising from its nuclei of termination terminate in the cerebellum, in the roof nuclei especially. Axones arising from cell-bodies in Deiters' nucleus (its lateral nucleus of termination) and in the nucleus of its descending root descend the cord in the lateral funiculus to form the (lateral) vestibulospinal tract, and also in the anterior marginal fasciculus to form ventral vestibulospinal tract. Impulses borne by these axones reach the efferent or motor root neurones. The rubro-spinal fasciculus, mentioned above also may be possibly considered as belonging to the cerebellar system. Sympathetic relations. — The cell-bodies of the efferent neurones in the ventral horns are of two general varieties: (a) those whose axones terminate upon skeletal muscle (somatic efferent), and (6) those whose axones terminate in contact with cell-bodies of sympathetic neurones, the splanchnic or visceral efferent neurones. The axones of the sympathetic neurones, in their turn, terminate upon cardiac and smooth muscle (motor) and in glands (secretory). Like the somatic, the visceral efferent neurones receive impulses within the ventral horns (a) from the cephalic and caudal branches of spinal ganglion neurones, (b) the descending cere- bro-spinal fasciculi, and (c) from either, by way of the fasciculi proprii and Golgi neurones of type II. Their cell-bodies are situated for the most part in the dorsal portion of the lateral horn (dorso-lateral group of cells), which is the only portion of the lateral horn present in the thoracic region of the cord. Many of the visceral efferent fibres leave the spinal nerves distal to the spinal ganglia and make the white communicating rami, thus going to the nearest sym- pathetic ganglia; others pass on in the spinal nerve and its branches to terminate in more distal sympathetic ganglia. Dogiel has described axones which arise in sympathetic ganglia and termi- nate upon the ceU-bodies of the spinal ganglia. Such convey sensory impulses which, however, enter the spinal cord by way of the dorsal root branch of the spinal ganglion neurone. Such afferent sympathetic neurones are relatively rare, the peripheral distribution of the ordinary 790 THE NERVOUS SYSTEM Fig. 621. — Schematic Representation op the More Important Architectural Relations OF Neurones in the Spinal Cord, Omitting those Involving the Mesencephalon AND Thalamus. a, afferent (spinal ganglion) axone of spino-oerebral chain with bifui'cation and caudal branch; b, afferent axone coursing in Lissauer's zone and distributed wholly within the cord; c, collaterals of a and b disposed in three ways; p, pyramidal axone in lateral (crossed) cerebro-spinal fasciculus distributed to levels of grey substance; pa, axone in ventral cerebro- spinal fasciculus decussating before termination; v, ventral root or motor neurones; n, nucleus dorsalis giving axone to dorsal spino-oerebellar fasciculus; g, ascending neurones of Gowers' tract; d, descending axone from cerebellum (probable); fp, neurones of fasciculi proprii, association proper; h, commissural neurones; e, Golgi cell of type II. ORDER OF MEDULLATION 791 spinal ganglion neurone in the domain of the sympathetic supplying the needs for sensory axones. In transverse sections of the spinal cord, the relative area of white substance as compared with that of grey increases as the cord is ascended. The absolute area of each varies with the localitj^, both being greatest in the enlargements. The grey substance predominates in the conus medullaris and lower lumbar segments. The white substance begins to predominate in the upper lumbar segments, not because of the increased presence of ascending and descending cerebral and cere- bellar axones, but because of the increased volume of the fasciculi proprii coinci- dent with the greater mass of grey substance to be intersegmentally associated in this region. In the thoracic region the greatly predominating white substance Fig. 622. — Graphic Representation of the Varying Amounts of Grey and White Sub- stance AND OF THE VARIATIONS IN AbEA OF ENTIRE SECTIONS OP THE DIFFERENT SEGMENTS OF THE Spinal Cord. (From Donaldson and Davis.) (Based upon measurements from several adult human spinal cords.) Curves showinO area of cross seel ion of human spinnl cord. -Whife ma\ter Grey matter. -Entire section. In ra IF ¥ w Mnn I n m w v yj yh yjii ix x xi xii i ii m ivyi iiiiiivn CERVICAL THORACIC LUMBAR SACRAL is composed mostly of the axones of long course. The greatly increased absolute amount of white substance in the cervical region is due both to the greater ac- cumulation of cerebral and cerebellar axones in this region and to the increased volume of the fasciculi proprii of the cervical enlargement. ORDER OF MEDULLATION OF THE FASCICULI OF THE CORD The axones of the spinal cord begin to acquire their myehn sheaths during the fifth month of intra-uterine hfe and myehnization is not fuUy completed till between the fifteenth and twentieth years. In general, axones which have the same origin and the same locality of termination — ■ the same function — acquire their sheaths at the same time. While it has been proved that the medullary sheath does not necessarily precede the functioning of an axone, it may be said that those fasciculi which first attain complete and definite functional ability are the first to become medullated. At birth all the fascicuh of the spinal cord are meduUated except Helweg's fasci- culus, and occasionally the lateral and ventral cerebro-spinal tracts. The latter tracts vary considerably and in general may be said to become medullated between the ninth month (before birth) and the second year. As indicated by their meduUation, those axones by which the cord is enabled to function as an organ per se, that is, the axones making possible the simpler reflex activities, complete their development before those axones which involve the brain with the activities of the cord. According to Flechsig and van Gehuohten, and investigators succeeding them, the following is the order in which the axones of the cord become medullated: — (1) The afferent and efferent nerve-roots and commissural fibres of the grey substance. (2) The fasciculi proprii, first the ventral, then the lateral, and last the dorsal, fasciculus proprius. (3) The fasciculus cuneatus (Burdach's column) and Lissauer's zone — the area of tho.se ascending spino-cerebral fibres which run the shorter course and which convey impulses from the upper limbs, thorax and neck. (4) Fasciculus gracilis (GoU's column). (5) The dorsal spino-cerebeUar fasciculus (direct cerebellar tract). (6) The superficial antero-lateral spino-cerebeUar fasciculus (Gowers' tract). 1(7) The lateral cerebro-spinal fasciculus (crossed pyramidal) and the ventral cerebro- spinal fasciculus (direct pyramidal tract). (8) The spino-olivary or Helweg's (Beohterew's) fasciculus. 792 THE NERVOUS SYSTEM The axones descending from the cerebellum and the brain-stem are so mixed with other axones that it is difficult to determine the sequence of their medullation. The fasciculi contaia- ing them also contain axones of the variety in the fasciculi proprii and so show medullation early. It is probable that the ascending, spino-cerebellar, fibres acquire their myeUn earlier than the descending, if descending exist. Blood Supply of the Spinal Cord The spinal rami of the sacral, lumbar, intercostal, or vertebral arteries, as the case may be, accompany the spinal nerves through the intervertebral foramina, traverse the dura mater and arachnoid, and each divides into a dorsal and a ventral radicular artery. These accompany the nerve-roots to the surface of the cord, and there break up into an anastomosing plexus in the pia mater. From this plexus are derived three tortuously coursing longitudinal arteries and! numerous independent central branches, which latter penetrate the cord direct. Of the longitudinal arteries, the anterior spinal artery zigzags along the anterior median fissure and gives off the anterior central branches, which pass into the fissure and penetrate the cord. These branches give ofT a few twigs to the white substance in passing, but their most partial distribu- tion is to the ventral portion of the grey substance. The two posterior spinal arteries, one on each side, course near the hnes of entrance of the dorsal root-fibres. They each branch and anastomose, so that often two or more posterior arteries may appear in section upon either side Fig. 623. — Semi-diagrammatic Representation of the Blood Supply op the Spinal Cobd, Posterior external spinal veins Posterior radicular vein ,'~ ' " . ..^^^ Posterior central artery and vein Posterior spinal artery /PeripKeral arterial plexus Posterior radicular artery Intercostal artery Anterior radicu- Spinal ramus \ "x lar artery V Internal spinal vein i Anterior central artery Anterior spinal artery Anterior central vein of the dorsal root. These give off transverse or central twigs to the white substance, but espe- cially to the grey substance of the dorsal horns. Of the remaining central branches many enter the cord along the efferent fibres of the ventral roots, and are distributed chiefly to the grey substance; others from the peripheral plexus throughout penetrate the cord and break up into capillaries within the white substance. Some of the terminal twigs of these also enter the grey substance. The blood supply of the grey substance is so much more abundant than that of the white substance that in. injected preparations the outline of the grey figure may be easily distinguished by its abundance of capillaries alone. The central branches are of the terminal variety. In the white substance the capillaries run for the most part longitudinally, or parallel with the axones. The venous system is quite similar to the arterial. The blood of the central arteries is col- lected into corresponding central venous branches which converge into a superficial venous plexus in which are six main longitudinal channels, one along the posterior median sulcus, one along the anterior median fissure, and one along each of the four lines of the nerve-roots. These comprise the posterior and anterior external spinal veins (fig. 623). The internal spinal veins course along the ventral surface of the grey commissure, and arise from the convergence of certain of the twigs of the anterior central vein. The posterior central vein courses along the posterior median septum in company with the posterior central artery, and empties into the median dorsal vein. The venous system communicates with the coarser extra-dural or internal vertebral plexus chiefly by way of the radicular veins. II. THE BRAIN OR ENCEPHALON The brain is that greatly modified and enlarged portion of the central nervous system which is enclosed within the cranial cavity. It is surrounded and sup- ported by the same three membranes (meninges) that envelop the spinal cord. GENERAL TOPOGRAPHY 793 While there is a considerable subarachnoid space, the brain more nearly fills its cavity than does the spinal cord. The average length of the brain is about 165 mm. and its greatest transverEe diameter about 140 mm. It averages longer in the male than in the female. Exclusive of its dura mater, the normal brain weighs from 1100 to 1700 gm. (40-60 oz.), varying in weight with the stature of the individual or with the bulk of the tissues to be innervated. Its average weight is 1360 gm. (48 oz.) in males and 1260 gm. (44 oz.) in females. It averages about fifty times heavier than the spinal cord, or about 98 per cent, of the entire cerebro-spinal axis. In its precocious growth it is at birth relatively much larger than at maturity. At birth it comprises about 13 per cent, of the total body-weight, while at maturity it averages only about 2 per cent of the weight of the body. Its specific gravity averages 1.036. In proportion to the body- weight the brain-weight averages somewhat higher in smaller men and women. Some very small dogs and monkeys and some mice have brains heavier in proportion to body-weight than man. The minimal weight of the adult brain compatible with human intelligence may be placed at from 950 to 1000 grams. Above the minimal, there is only a general relation between the degree of intelligence and the weight of the brain, owing to the fact that several factors may be coincident with large brains. It may be said in general, however, that the average brain weight of eminent men is above the general average. Some men judged eminent have had brains weigh- ing less than the general average. Of the records generally accepted, the greatest brain weight Fig. 624. — Mesial Section of the Head of a Female Thirty-five Yeaks Old . Corpus callosuiu Septum pellucidum Thalamus Vein of Galen - - Epiphysis Posterior cere- bral artery Corpora ^ quadrigemina Third nerve " ^V Straight sinus Cerebellum Occipital sinus Fourth ventricle Sulcus cinguli Fornix Crista galli Anterior cere- bral artery Optic chiasma Sphenoidal Pons Medulla ob- for eminent men is 2012 grams, recorded for the poet and noveUst, Ivan Tourgenieff. The trust- worthiness of this weighing is doubted by some authorities. From the undisputed records the following may be taken: Cuvier, 1830 grams; John Abercrombie, 1786 grams; Thackery, 1658 grams; Kant, 1600 grams; Spurzheim, 1559 grams; Daniel Webster, 1518 grams; Louis Agassiz, 1495 grams; Dante, 1420 grams; Helmholtz, 1440 grams; Goltz, 1395 grams; Liebig, 1352 grams; Walt Whitman, 1282 grams; Gall, 1198 grams. In the average brain weights for the races that for the Caucasian stands highest, the Chinese standing next, then the Malay, followed by the Negro, with the AustraUan lowest. The differences between the meninges of the brain and those of the spinal cord occur chiefly in the dura mater. (1) The dura maler is about double the thickness of that of the spinal cord, and consists of two closely adhering layers, the outermost of which serves as the internal peri- osteum of the cranial bones, while that of the cord is entirely separate from the periosteum lining the vertebral canal. (2) The inner layer is duplicated in places into strong partitions which extend between the great natural divisions of the encephalon. Of these, the sickle- shaped ialx cerebri extends between the hemispheres of the cerebrum, the crescentic tentorium cerebelli extends between the cerebellum and the overlapping posterior portion of the cerebrum, and the smaller falx cerebelli occupies the notch between the hemispheres of the cerebellum. Contained within these partitions of the dura mater are the great collecting venous sinuses of the brain. These will be considered in the more detailed description of the cranial meninges. General topography. — In its superior aspect or convex surface the encephalon is oval in contour, with its frontal pole usually narrower than its occipital pole. 794 THE NERVOUS SYSTEM Viewed from above, the cerebrum comprises almost the entire dorsal aspect, the occipital lobes overlapping the cerebellum to such an extent that only the lateral and lower margins of the cerebellar hemispheres are visible. The great longitu- dinal fissure of the cerebrum separates the cerebral hemispheres. Laterally the temporal lobes, with their rounded anterior extremities, the tem- poral poles, are each separated from the frontal and parietal lobes above by the lateral cerebral fissure (fissme of Sylvius) . In the depths of this fissure and over- lapped by the temporal lobe is situated the insula, or island of Reil (central lobe). The surface of each cerebral hemisphere is thrown into numerous folds or curved elevations, the gyri cerebri or convolutions, which are separated from each other by slit-like fissures, the sulci cerebri. The gyri (and sulci) vary greatly in length, in depth, and in their degrees of curvature. The larger and deeper of them are similar in the two hemispheres; most of them are individually variable, but each gyrus of one hemisphere is homologous with that of the like region of the other hemisphere. By gently pressing open the great longitudinal fissure, the corpus callosum, the chief commissural pathway between the cerebral hemi- spheres, may be seen. The occipital margin of this large transverse band of white substance is rounded and thickened into the splenium of the corpus callosum, while its frontal margin is curved ventrally into its genu and rostrum. The base of the encephalon (fig. 625) is more irregular than the convex surface, and consists of a greater variety of structures. In the mid-line between the frontal lobes appears the anterior and inferior extension of the great longitudinal fissure. When the margins of this are separated, the outer aspect of the rostrum of the corpus callosum, the downward continuation of the curve of the genu, is exposed. The inferior surface of each frontal lobe is concave, due to its compression upon the superior wall of the orbit. The orbital gyri with their respective orbital sulci occupy this concave area. The cranial nerves [nervi cerebrales]. — Along the mesial border of each orbital area, and parallel with the great longitudinal fissure, lie the olfactory bulbs con- tinued into the olfactory tracts. Each olfactory bulb is the first central connection or the ' nucleus of reception' of the olfactory nerve, the first of the cranial nerves. A few fine filaments of this nerve may often be discerned penetrating the ventral surface of the bulb. The olfactory bulb and tract lies in the olfactory sulcus, which forms the lateral boundary of the gyrus rectus, the most mesial gyrus of the inferior surface of the frontal lobe. Upon reaching the area of Broca (area parol- factoria), or the region about the medial extremity of the gyrus rectus, each olfactory tract undergoes a slight expansion, the olfactory tubercle, and then divides into tliree roots or olfactory striae — a medial, an intermediate, and a lateral, which comprise the olfactory trigone. The striae begin their respective courses upon the anterior perforated substance, an area which contains numerous small foramina through which the antero-lateral group of central cerebral arteries enters the brain. This region forms the anterior boundary of that area of the base of the encephalon in which the substance of the brain becomes continuous across the mid-line. At the medial boundary of the anterior perforated substance the optic nerves come together and fuse to form the optic chiasma. Thence the optic tracts dis- appear under the poles of the temporal lobes in their backward course to the thai- ami and the geniculate bodies or metathalami. Immediately behind the optic chiasma occurs that diverticulum from the floor of the third ventricle known as the tuber cinereum. It is connected by its tubular stalk, the infundibulum, with the hypophysis or pituitary body, which occupies its special depression (sella turcica) in the floor of the cranium and is usually torn from the encephalon in the process of its removal. Behind the tuber cinereum are the two mammillary bodies (corpora albicantia), each of which is connected with the fornix, one of the larger association fasciculi of the cerebrum. The peduncles of the cerebrum (crura cerebri) are the two great funiculi which asso- ciate the cerebral hemispheres with all the structm-es below them. They diverge from the anterior border of the pons (Varoli) and, one for each hemisphere, dis- appear under the poles of the temporal lobes. The pons (brachium pontis or middle cerebellar peduncle) is chiefly a bridge of white substance or a commissure between the cerebellar hemispheres. CRANIAL NERVES 795 The oculomotor or third pair of cranial nerves make their exit from the poste- rior perforated substance in the interpeduncular fossa just behind the corpora mammillaria. Tlie trochlear nerves emerge around the lateral aspects of the pedunculi cerebri along the anterior border of the pons. The trochlear is the smallest of the cranial nerves, and the only pair arising from the dorsal aspect of the brain. The trigeminus, or fifth cranial nerve, is the largest. It penetrates the pons to find its recipient nuclei in the depths of the brain-stem. It is a purely sensory nerve, but it is accompanied by the much smaller masticator nerve which is motor and is usually referred to as the motor root of the trigeminus. Fig. 625. — View of the Base op the Beain. (After Beaunis.) Gyri orbitales Anterior perfor- ated substance Hypophysis tuber Inferior vermis Five pairs of cranial nerves are attached to the brain-stem along the inferior border of the pons: — the abducens nerve, which is motor, emerges near the mid-line; the facial, motor, emerges from the more lateral aspect of the brain- stem ; the glosso-palatine or the intermediate nerve of Wrisberg, largely sensory, is attached in company with the facial; and, entering the extreme lateral aspect of the stem are the cochlear and vestibular nerves. These latter two, when taken together as one, are known as the acoustic (auditory) or eighth cranial nerve. They are both purely sensory. The cochlear courses for the most part laterally and dorsally around the inferior cerebellar -peduncle, giving it the appearance from which it derives its name, 'restiform body.' The remaining four pairs of the cranial nerves are attached directly to the medulla oblongata. This comprises that portion of the brain-stem beginning at the inferior border of the pons above, and continuous with the first segment of the spinal cord below. On its ventral surface the pyramids and the olives (olivary bodies) are the two most prominent structures. The pyramids, which are con- tinuous below into the pyramidal (cerebro-spinal) tracts of the spinal cord, form the two tapering prominences along either side of the anterior median fissure; the olives are the oblong oval elevations situated between the pyramids and the resti- 796 THE NERVOUS SYSTEM form bodies, and each is the superficial indication of the inferior 'olivary nucleus. The glosso-pharyngeal, the vagus (pneumogastric), and the spinal accessory cranial nerves are attached along the lateral aspect of the medulla oblongata in line with the facial nerve and between the olive and the restiform body. The spinal accessory, purely motor, is assembled from a series of rootlets which emerge from the lateral aspect of the first three or four cervical segments of the spinal cord, as well as from the medulla. It becomes fully formed before reaching the level of the olive, and passes lateralward in company with the vagus and fur- ther on joins the latter in part. The root filaments of the vagus and glosso- pharyngeal are arranged in a continuous series, and, if severed near the surface of the medulla, those belonging to the one nerve are difficult to distinguish from those belonging to the other. Both of these are mixed motor and sensory. The hypoglossal, purely motor, emerges as a series of rootlets between the pyramid and the olive. Thus it arises nearer the mid-line, and in line with the abducens, trochlear, and oculomotor. If the occipital lobes be lifted from the superior surface of the cerebellum and the tentorium cerebelli removed, the quadrigeminate bodies of the mid-brain or mesencephalon may be observed. These are situated above the cerebral pedun- cles, in the region of the ventral appearance of the oculomotor and trochlear nerves. Resting upon the superior pair of the quadrigeminate bodies [colliculi superiores] is the epiphysis or pineal body, and just anterior to this is the cavity of the third ventricle, bounded laterally by the thalami and roofed over by the tela chorioidea of the third ventricle (velum interpositum) . By separating the inferior margin of the cerebellum from the dorsal surface of the medulla oblongata the lower portion of the fourth ventricle (rhomboid fossa) may be seen. The cisterna cerebello-meduUaris, the subarachnoid space in this region, is occupied in part by a thickening of the arachnoid. This is continuous with the tela chorioidea (ligula) and chorioid plexus of the fourth ventricle. The former roofs over the lower portion of the fourth ventricle, and, passing through it in the medial fine, is the lymph passage, the foramen of Magendie, by which the cavity of the fourth ventricle communicates with the subarachnoid space. The fourth ventricle, as it becomes continuous with the central canal of the spinal cord, terminates in a point, the calamus scriptorius. From the inferior surface, the cerebellar hemispheres are more definitely demarcated, and between them is the vermis or central lobe of the cerebellum. Divisions of the encephalon. — The encephalon as a whole is developed from a series of expansions, flexures, and thickenings of the wall of the cephalic portion of the primitive neural tube, the three primary brain vesicles. Being continuous with the spinal cord, it is arbitrarily considered as beginning just below the level of the decussation of the pyramids, or at a line drawn transversely between the decussation of the pyramids and the level of the first pair of cervical nerves. In its general conformation four natural divisions of the brain are apparent: the two most enlarged portions — (1) the cerebral hemispheres and (2) the cere- bellum; (3) the mid-brain (mesencephalon) between the cerebral hemispheres and the cerebellum, and (4) the medulla oblongata, the portion below the pons and above the spinal cord (fig. 602). However, the most logical and advantageous arrangement of the divisions and subdivisions of the encephalon is on the basis of their development from the walls of the embryonic brain vesicles. (See fig. 598.) On this basis, for example, both the medulla oblongata and the cerebellum with its pons are derived from the posterior of the primary vesicles, and are, therefore, included in a single gross division of the encephalon, viz., the rhomben- cephalon. In the following outline the anatomical components of the enceph- alon are arranged with reference to the three primary vesicles from the walls of which they are derived, and the primary flexures and thickenings of the walls of which they are elaborations. During the early growth of the neural tube its basal or ventral portion and the lateral por- tions acquire a greater thickness than the roof of the tube, and thus the tutpe is longitudinally divided into a basal or ventral zone and an alar or dorsal zone. This is especially marked in the brain vesicles. Structures arising from the dorsal zone begin as localised thickenings of the roof. For example, in the rhombencephalon the greater part of the medulla oblongata and of the pons region is derived from the ventral zone, while the cerebellum is derived from the dorsal zone. The first of the flexures occurs in the region of the future mesencephalon, and is known as the cephalic flexure; next occurs the cervical flexure, at the junction with the spinal cord; DIVISIONS OF THE ENCEPHALON 797 O O W H O CO O h-l 02 I— I > i=< d gs 798 THE NERVOUS SYSTEM Fig. 626.— Median Sagittal Section theough Embryonic Human Bbain at End of Fiest Month. (After His.) (Showing the locahties of origin of the derivatives of the three primary vesicles named in outline on p. 797.) Hypophysis (anterior sii Ventral zone Dorsal zone Fig. 627. — Sagittal Section op Brain of Human Embryo of the Third Month. (After His) (Reference numerals correspond with those of fig. 626 and those after names of parts in outline on p. 797.) MEDULLA OBLONGATA 799 third, the pontine flexure, in the region of the future fourth ventricle. Both the cervical and pontine flexures, while having a significance in the growth processes, are almost entirely ob- literated in the later growth of the encephalon. The location of the development of the various parts of the encephalon may be determined, and their elaboration and changes in shape and positionmay be traced by comparing the accompanying figs. 626, 627, 628. The reference numbers in Fig. 628. — Median Sagittal Section op Adult Human Brain. (Drawing of model by His.) (Reference numerals same as in figs. 626 and 627.) Olfactory bulb Optic chiasma Infundibulum the last three figures correspond with the like numerals after the names of the parts on p. 797 in the outline of the divisions of the encephalon. The more detailed subdivisions of the parts will be met with in their individual descriptions. THE RHOMBENCEPHALON 1. THE MEDULLA OBLONGATA The medulla oblongata [myelencephalon] is the upward continuation of the spinal cord. It is only about 25 mm. long, extending from just above the first cervical nerve (beginning of the first cervical segment of the spinal cord) to the inferior border of the pons. It lies almost wholly within the cranial cavity, resting upon the superior surface of the basal portion of the occipital bone, with its lower extremity in the foramen magnum. Its weight is from 6 to 7 gm. or about one- half of one per cent of the whole cerebro-spinal axis. It is a continuation of the spinal cord, and more. It contains structures continuous with and homologous to the structures of the spinal cord, and in addition it contains structures which have no homologues in the spinal cord. Due in part to these additional struc- tures, the medulla, as it approaches the pons, rapidly expands in both its dorso- ventral and especially in its lateral diameters. With it are associated nine of the pairs of cranial nerves. On its anterior or ventral aspect the anterior median fissure of the spinal cord becomes broader and deeper because of the great height attained by the pyramids. At the level at which the pyramids emerge from the pons, the region in which they are largest, the fissure terminates in a triangular recess so deep as to merit the name foramen caecum. The pyramids are the great descending cerebral or motor funiculi. In the medulla oblongata they decrease in bulk in passing toward the spinal cord, for the reason that many of the pyramidal axones are contributed to structm-es of the medulla, chieflj^ after crossing the mid-line. At the lower end of the medulla occurs the decussation of the pyramids, by which the anterior median fissure is almost obliterated for about 6 mm., and which, upon removal of the pia mater, may be easily observed as bundles of fibres interdigitating obliquely across the mid-line. Not aU the p)Tamidal fibres cross to the opposite side at this level in man, but a portion of those coursing in the lateral portion of the pyramid maintain their ventro-mesial position 800 THE NERVOUS SYSTEM and continue directly into the spinal cord, to form there the ventral cerebro-spinal fasciculus or direct pyramidal tract. However, most of such fibres finally cross the mid-line during their course in the spinal cord. The exact proportion of the direct fibres is variable, but always the greater mass of each pjrramid crosses to the opposite side at the level of the decussation of the pyramids, and descends the cord as the lateral cerebro-spinal fasciculus or crossed pyramidal tract. Both of these pjnramidal tracts are described in the discussion of the fascicuU of the cord. Fig. 629. — Semi-diagbammatic Representation of the Ventral Aspect of the Rhomben- cephalon AND Adjacent Portions of the Cerebrum. _ (Modified from Quain.) Insula Olfactory tract Hypophysis — Optic nerve Optic tract Mammillary bodies Cerebral peduncle Semilunar (Gasser ian) ganglion Oblique fasciculus of pons Tuber cinereum Oculomotor nerve ,-- (in) Lateral geniculate body - Trochlear nerve (IV) / ~~- Trigeminus (V) . Abducens (VI) — Brachlum of pons Facial nerve (Vn) ~ Glosso-palatine nerve (intermediate part of X facial) Cochlear and vestibular \ nerves (Acoustic or VIII) \ Glosso-pharyngeal nerve (IX) Vagus nerve (XJ \ Accessory nerve (XI) (spmal accessory) Decussation of pyramids Each pyramid is bounded laterally by the antero-lateral sulcus, also continu- ous with that of the same name in the spinal cord. Toward the pons this sulcus separates the pyramid from the olive [oliva] (inferior olivary nucleus), and in the region of the olive there emerge along this sulcus the root filaments of the hypo- glossal nerve. These are in line with the filaments of the ventral roots of the spinal nerves. The olives, as their name implies, are oblong oval eminences about 1.2 cm. in length. They extend to the border of the pons, and are somewhat thicker at their upper ends. Their surfaces are usually smooth, except at their lower ends, where they frequently appear ribbed, owing to bundles of the external arcuate fibres passing across them to and from the restiform body, which occupies the extreme lateral portion of the medulla. Along the line between the restiform body and the olive are attached .the root filaments of the vagus, glosso-'pharyngeal, and spinal accessory nerves. Both the abducens and the facial nerve emerge along the inferior border of the pons, the facial in line with the glosso-pharyngeal, but the abducens in line with the hypoglossus. Dorsal aspect. — The increased lateral diameter of the medulla oblongata is contributed to a great extent by the restiform bodies. These are the inferior cere- MEDULLA OBLONGATA 801 bellar peduncles (crura cerebelli ad medullam oblongatam) and contain the major- ity of the ascending fibres, which associate the cerebellum with the structures below it. In toto, the restiform bodies are much larger than could be formed by the combined cere- bellar fasciculi of the spinal cord, their great size being due to their receiving numerous axones coursing in both directions, which connect the cerebellum with structures contained in the medulla oblongata alone, so that in the medulla they increase as they approach the cerebellum. Their mesial borders form the lateral boundaries of the fourth ventricle. Their name (resliform, meaning rope-hlie) was suggested from the appearance frequently given them by the fibres of the cochlear (acoustic division of the eighth) nerve, which course around their lateral per- iphery to become the strice medullares in the floor of the fourth ventricle. Fia. 630. — Diagram Showing the DBctrssATioN op the Pyramids. The uppermost level represented is near the inferior border of the pons. Chorioid tela of fourth ventricle Solitary tract --Nucleus of vestibular nerve y--' Restiform body . Spinal tract of trigeminus •Nucleus of cochlear nerve -Vagus nerve Hypoglossal nerve Pyramid Spinal tract of trigeminus Decussation of pyramids Lateral cerebro-spinal fasciculus ^crossed pyramidal tract) Ventral cerebro-spinal fasciculus (direct pyramidal tract) Upon removal of the cerebellum it may be seen that below the calamus scrip- torius (inferior terminus of the fourth ventricle) the structures manifest in the dor- sal surface of the medulla are directly continuous with those of the spinal cord. The fasciculus gracilis (Goll's column) of the spinal cord acquires a greater height and volume and becomes the funiculus gracilis of the medulla, and because of this increased height the posterior median sulcus of the cord becomes deepened into the posterior median fissure. The posterior intermediate sulcus is also accentuated by the fasciculus cuneatus (Burdach's column) likewise now enlarged into the funiculus cuneatus of the medulla. The lateral funiculus of the medulla, of course, does not contain the lateral or crossed pyramidal tract present in the spi- nal cord. At the border of the calamus scriptorius the funiculus gracilis terminates in a slight elevation, the clava, which is the superficial indication of the nucleus of the fasciculus gracilis. Beginning somewhat more anteriorly, and having a somewhat greater length, is a similar enlargement of the funiculus cuneatus, the tuberculum cuneatum or nucleus of the fasciculus cuneatus. 802 THE NERVOUS SYSTEM These nuclei are the groups of nerve cell-bodies about which the ascending or sensory axones of the respective fasciculi terminate or where the sensory impulses are transferred to a second neurone in their course to the structui-es of the encephalon. These cell-bodies in their turn give off axones which immediately cross the mid-line and assume a more ventral position, contributing largely to the lemniscus or fillet of the opposite side, and thus such axones are the encephalic continuation of the central sensory pathway conveying impulses from the periphery of one side of the body to the opposite side of the cerebrum. The crossing of these axonesjis known as the decussation of the lemnisci. Fig. 631. — Dohsal Aspect op Medulla Oblongata and Mesencephalon, Showing the Floor of the Fourth Ventricle (Rhomboid Fossa). (Modified from Spalteholz.) aedullaiis of thalamus \ r ^ . , Internal capsule Habenular commisbur \ Trigonum habenuls v / \ Epiphysis Brachium of infErior quadrigeminate todv Cerebral pi dund Anterior medullary velu Brachium conjunctiva m Brachium of pons " Restiformbodj ""-y Calamus scriptorms Funiculus gracilis Funiculus cuneatus Lateral funiculus ~ Caudate nucleus .^j^— Taenia chorioidea Stria terminalis ~ ~ of thalamus ^1£4.S.l i^' tnaiamus Quadrigeminate bodies Trochlear nerve ^~ Lingula cerebelli Trigonum of vagus (ala cinerea) "-- Nucleus of fasciculus cuneatus - Obex Nucleus of fasciculus gracilis (clava) ■Posterior median fis •Posterior intermediate sulcus^ With the termination of the dorsal funiculi and the ventral course of the fibres of the lemnisci in their decussation, the central canal of the spinal cord loses its roof of nervous tissue in the medulla and comes to the surface as the fourth ven- tricle. The floor of the fourth ventricle, which corresponds to the floor of the central canal, is considerably widened into two lateral recesses opposite the junc- tion of the inferior and middle cerebellar peduncles of either side, and, being pointed at both its superior and inferior extremities, it is rhomboidal in shape and thus is the rhomboid fossa. The pia mater of the spinal cord is maintained across the tip of the calamus scriptorius to form the obex, a small, semilunar lamina roofing over the immediate opening of the central canal. The obex carries a few medullated commissural fibres. . ' MEDULLA OBLONGATA 803 Fia. 632. — Diagram of the Spino-cerebellar FAscicuiii and the Origin and Decussa- tion OF the Lemnisci. Nucleus of spinal tract of trigeminus^ Spinal tract o£ \ trigeminus \ Root filaments of glosso- pharyngeal ] Nucleus of ala cinerea 804 THE NERVOUS SYSTEM. 2. THE PONS The pons (Varoli) is, for the most part,- a great commissure or 'bridge' of white substance coursing about the ventral aspect of the brain-stem, and connect- ing the cerebellar hemisphere of one side with that of the other. In addition it contains fibres passing both to and from the structures of the brain-stem and the grey substance of the cerebellum, and fibres descending from the cerebral cortex. Each of its lateral halves forms the middle of the three cerebellar peduncles, the hrachium pontis of either side. In size it naturally varies directly with the development of the cerebellum, both in a given animal and relatively throughout the animal series. In man it attains its greatest relative size, and possesses a median or basilar sulcus in which lies the basilar artery. Its sagittal dimension varies from 25 to 30 mm., while its transverse dimension (longitudinal with the course of its fibres) is somewhat greater. It is a rounded white prominence interposed between the visible portion of the cerebral peduncles (crura) above and the medulla oblongata below. Its inferior margin is rounded to form the inferior pontine sulcus, which, between the points of the emergence of the pyramids, is continuous with and transverse to the foramen cjecum. Its superior margin is thicker and is rounded to form the superior pontine sulcus, which, between the cerebral peduncles, is continuous with and transverse to the interpeduncular fossa. (See fig. 629.) It is bilaterally sym- metrical. The ventro-lateral bulgings of its sides (and, therefore, the basilar sulcus) are produced by the passage through it of the fibres of the cerebral pedun- cles from above, to reappear as the pyramids below. Its ventral surface rests upon the basilar process of the occipital bone and the dorsum sellse of the sphenoid, while its lateral surfaces are adjacent to the posterior parts of the petrous portions of the temporal bones. The fibres of the thicker superior portion of the pons (Jasciculus superior pontis) course obliquely downward to their entrance into the brachium of the pons and the cerebellar hemis- phere; those of the lower and mid-portions (Jasciculus medius pontis) course more transversely, naturally converging upon approaching the cerebellum. Certain fibres of the upper mid- portion course at first transversely and then turn abruptly downward across the fibres above them, to join the inferior portion of the brachium pontis. This bundle is termed the oblique fasciculus (fig. 629). The trigeminus or fifth cranial nerve penetrates the superior lateral por- tion of each brachium pontis near the point of the downward turn of the obhque fasciculus; its large afferent root and the masticator nerve (its small efferent root) accompany each other quite closely. On either side of the basal surface of the pons usually may be seen a small bundle of fibres which begins in the interpeduncular fossa, near or in the sulcus of the oculomotor nerve. It passes laterally along or under the superior border of the pons, loses some of its fibres in the lateral sulcus of the mesencephalon, then runs inferiorly between the superior cerebellar peduncle and the brachium of the pons to disappear in the junction of these. Being sometimes double, it is known as the lateral filaments of the pons {fila lateralia pontis or Icenia pontis). The location of the cell-bodies giving origin to it is uncertain. That portion of the rhombencephalon overlying the pons and forming the floor of the fourth ventricle is not really a part of the pons at aU. It is merely a continuation of the brain- stem from the meduOa below to the structures above. Therefore on the dorsal surface there is no line of demarcation between the pons and medulla below or between the pons and isthmus above. The fibres of the trigeminus and masticator nerve pass through the pontine fibres to and from their nuclei in the brain-stem. 3. THE CEREBELLUM The cerebellum or hind brain is the largest portion of the rhombencephalon. It lies in the posterior or cerebellar fossa of the cranium, and dorsal to the pons and medulla oblongata, overhanging the latter. It fits under the occipital lobes of the cerebral hemispheres, from which it is separated by a strong dupUcation of the inner layer of the dura mater, the tentorium cerebelli. Its greatest diameter Ues transversely, and its average weight, exclusive of the dura mater, is about 140 gm., or about 10 per cent, of the entire encephalon. It varies in development with the cerebrum, and, like it, averages larger in the male. It is relatively larger in adults than in children. Its development begins as a thickening of the anterior portion of the roof (dorsal zone) of the posterior of the three primary brain vesicles. Resting upon the brain- stem, it roofs over the fourth ventricle and is connected with the structures anterior, below, and posterior to it by its three pairs of peduncles. The surface of the cerebellum is thrown into numerous narrow folia or gyri, which in the given locaHties run more or less parallel with each other. They are THE CEREBELLUM 805 separated by narrow but relatively deep sulci. Unlike the spinal cord and medulla, in which the grey substance is centrally placed and surrounded by a mantle of white substance, the surface of the cerebellum is itself a cortex of grey substance, the cortical substance [substantia corticalis], enclosing a core of white substance, the medullary body [corpus medullare]. However, within this central core of white substance are situated definite grey masses, the nuclei of the ere bellum. The gross divisions of the cerebellum are three: the two larger lateral portions, the hemispheres, and between these the smaller central portion, the vermis. The demarcation between these gross divisions is not very evident from the dorsal surface, because the hemispheres in their extraordinary development in man encroach upon the vermis, and, being pressed under the overlapping occipital ends of the cerebral hemispheres, they become partially fused upon the vermis Fig. 633. — Section of Head Passing Through the Mastoid Processhs op the Temporal Bones and Behind the Medulla Oblongata. Showing the Position op the Cere- bellum. (From a mounted specimen in the Anatomical Department of Trinity College, Dublin.) Corpus callosum Chorioid pli Veins of Galen Tentoriun cerebel] Transverse sinus Dentate nucleus Caudate nucleus Lateral ventricle Superior petrosal Mastoid antrum Transverse sinus Mastoid process along the dorsal mid-line. Though differentiated simultaneously with the cere- bellar hemispheres in the human fcetus, in most of the mammalia the vermis is the largest and most evident of the parts, and it is practically the only part which exists in the fishes, reptiles, and birds. In man, owing to the fact that the vermis does not keep pace in development with the hemispheres, there results a very decided notch between the two hemispheres along the line of the entire ventral and inferior aspect of the cerebellum, the floor of this notch being the surface of the vermis. The inferior portion of the notch is the posterior cerebellar notch (incisura marsupialis) ; its prolongation above is wider than below, and is termed the superior cerebellar notch. It is occupied by a fold of the diu'a mater, the falx cerebelli. With the variations in contour of the cerebellum, certain of its sulci are broader and deeper, and merit the name fissures. These are more or less definitely placed, and subdivide the hemispheres into lobes'and the vermis (the median lobe) into lobules. Superior surface. — The superior surface is bounded from the inferior sm-face by the horizontal fissure (fig. 635) which extends ventrolaterally, to the entrance of the brachium of the pons. Between this and the extreme anterior border of the dorsal surface are two other fissures, the posterior and anterior semilunar fissures. These, Hke the horizontal fissure, may be traced, with slight interruptions, across the mid-line, and consequently mark off not onl}^ the two hemispheres but also the vermis into corresponding divisions. 806 THE NERVOUS SYSTEM The superior semilunar lobe [lobulus semilunaris superior] (postero-superior lobe) of each hemisphere lies between the horizontal and the posterior semilunar fissm-es. It largely composes the outer border of the cerebellum, and, therefore, is the longest of the lobes. The adjacent surface of the hemispheres, because of the frequently less com- plete development of the anterior semilunar fissure, is sometimes referred to as the quadrangular lobe, with its posterior and its anterior portions. On the other hand, especially when the anterior semilunar fissure is well marked, this area may be divided into — (1) the posterior semilunar lobe, between the posterior and anterior semilunar fissures, and (2) the anterior seynilunar lobe, anterior to the anterior semilunar fissure (fig. 635). Anterior to the quadrangular lobe on each hemisphere is the ala of the central lobule, bounded by the postcentral and the precentral sulcus. Anterior to this, on the anterior margin of the hemisphere, is the vinculum lingulae, a slender process continuous with the lingula of the vermis (fig. 658). Fig. 634. — Median Section Through Cerebellum and Brain-stem. (Allen Thompson, after Reiohert.) 1. culmen monticuli; 2, superior semilunar lobe; 3, inferior semilunar lobe; 4, slender lobe; 5, biventral lobe; 6, tonsil. Cerebral peduncle Massa intermedia Thalamus Epiphysis (pineal body) Corpora quadrigemina Derive r- The monticulus proper is divided into an inferior lobule, the declive, and a superior lobule, the culmen. These appear as continuations across the mid- line of the posterior and anterior semilunar lobes of the hemispheres, and are separated by the corresponding fissures (fig. 635). At the extreme anterior part of the superior surface and in the bottom of the anterior cerebellar notch lies a more definitely defined portion of the vermis. This is the central lobule (fig. 635). It is broadened laterally into two pointed wings, the alee of the central lobule, the folia of which, if present, are parallel with those of the anterior semilunar lobes and separated from them by the post- central sulcus. If the anterior margin of the central lobule be lifted, the lingula cerebelli THE CEREBELLUM 807 {lingula vermis) will appear separated from the central lobule by the pre-central sulcus. It is a thin, tongue-like anterior projection of the cortical substance comprising four to eight folia adhering upon the anterior medullary velwm, the roof of the superior portion of the fourth ventricle. Inferior surface. — ^The three cerebellar peduncles of each side join to form a single mass of white substance, and enter the ventral aspect of each hemisphere at the medial and ventral extremity of the horizontal fissure. The inferior surface of the cerebellum is less convex than the superior surface. The hemispheres are decidedly separated by a continuation of the posterior cerebellar notch, which becomes broader, the vallecula of the cerebellum, which contains the inferior portion of the vermis, vermis inferior, and whose margins embrace the medulla oblongata. The inferior surfaces of the hemispheres are each divided by the intervening fissures into four lobes (fig. 636). Fig. 635.— Diagram op the Superior Surface of the Cerebellum. Tegmentum Frenulum veil Ala of central lobuli Cerebral peduncle Substantia nigra Inferior quadrigemmate body Central lobule /f"X^, Culmen of Posterior cerebellar notcb Declive of monticulus Folium of vermis Below, the inferior semilunar lobe (postero-inferior lobe) is separated from the superior semilunar lobe of the superior surface by the horizontal fissure. It is the largest of the inferior lobes, and is broader at its medial extremity. Frequently two and sometimes three of its curved sulci appear deeper than others, and sep- arate it into two or three slender lobules [lobuli graciles]. More commonly there are two of these, the lobulus gracilis posterior and lobulus gracilis anterior, separated by the postero-inferior sulcus. The biventral lobe is smaller and more curved than the inferior semilunar lobe, from the anterior margin of which it is separated by the curved antero -inferior sulcus. Its medial extremity is pointed and does not extend to the vermis; its lateral extremity is broader and curves anteriorly to the ventral extremity of the horizontal fissure — the line of outer termination of the inferior semilunar lobe. The tonsil [tonsilla cerebelli] (amygdala) is a rounded, triangular mass, placed mesially within the inner curvature of the biventral lobe, and separated from it by the retrotonsillar fissure. Its inferior mesial border slightly overlaps the vermis. The smallest of the lobes is the flocculus. It lies adjacent to the inferior and lateral surface of the mass of white substance produced by the confluence of the three cerebellar peduncles, and extends into the mesial extremity of the horizon- tal fissure. It is so flattened that its short folia give it the appearance suggesting its name. Occasionally there is added a second, less perfectly formed portion, the secondary flocculus. From each floccular lobe there passes toward the mid- line a thin band of white substance, the peduncle of the flocculus ; these extend 808 THE NERVOUS SYSTEM to meet each other at the most anterior portion of the inferior vermis, and thus form the narrow posterior medullary velum. The inferior vermis (figs. 634, 636) is more definitely demarcated than the superior. Lying in the floor of the vallecula cerebelli, it is separated on each side from the adjacent lobes of the hemispheres by a well-marked sulcus about it, the nidus avis. By contour and by deeper transverse fissures (sulci) occurring at intervals across it, four divisions or lobules of the inferior vermis are recognised. These lobules, like those of the superior vermis, are each in intimate relation with the pair of lobes of the hemispheres adjacent to it on either side. 1. The tuber vermis is adjacent to the folium vermis of the superior aspect, and thus is the most inferior lobule of the inferior vermis. It is a short, somewhat pyramidal-shaped division, whose four or five transversely arranged folia are con- tinuous with the folia of the inferior semilunar lobes on either side. 2. The pyramid is separated from the tuber vermis by the post-pyramidal sulcus. Its several folia cross the vallecula cerebelli and curve to connect with the biventral lobes on either side. 3. The uvulva is separated from the pyramid by the prepyramidal sulcus. It is triangular in shape. Its base or broader inferior portion appears as two laterally projecting ridges of grey substance, the furrowed bands or alee uvulce, which extend across the floor of the nidus avis and under the mesial margins of the tonsils on either side. In these bands its folia curve and become continuous with the tonsils. The uvula and the two tonsils are sometimes referred to collectively as the uvular lobe. 4. The nodule is the smallest and most anterior division of the inferior vermis. It is separated from the uvula by the post-nodular sulcus, and is closely associated anteriorly with the posterior medullary velum, the transverse continuation of the peduncles of the floccular lobes. StTMMAET OF EXTERNAL FEATURES OP CEREBELLUM Superior Surface. Hemisphere Vermis Anterior border — Anterior medullary velum — Anterior border Vinculum of Lingula Lingula Precentral sulcus Ala of central lobule Central lobule Post-central sulcus C Anterior semilunar lobule Culmen Quadran- I Anterior semilunar fissure [ Monticulus gular lobe ] Posterior semilunar lobule Declive [ Posterior semilunar fissiire Superior semilunar lobe Folium. Horizontal Fissure Inferior Surface Horizontal Fissure Inferior f Posterior slender lobule 1 semilunar -j Posterior-inferior sulcus [ Tuber lobe [ Anterior slender lobule J Anterior-inferior sulcus Post-pyramidal sulcus Biventral lobe Pyramid Retro-tonsillar fissure Prepyramidal sulcus Tonsil Uvula Horizontal Fissure Post^nodular sulcus Flocculus Nodule Posterior medullary velum Internal structure of the cerebellum (fig. 637). — The white substance of the cerebellum is continuous with its peduncles and forms a compact central mass. Over the surface of this the grey substance or cortex is spread in a thin but uniform and much folded layer. Upon section of the cerebellum certain of the sulci as well as the fissures are shown to be much deeper than is apparent from the surface. The deeper sulci separate the lobes into divisions, the medullary laminae, each of which is composed of a number of folia and each of which has its own core of white substance. The folia of the laminae line the sulci (and fissures), and also comprise their surface aspect, and are separated by the shallow, secondary sulci. The larger NUCLEI OF THE CEREBELLUM 809 laminae are subdivided into from two to four secondary laminae of varying size. Such subdivision is especially marked in the vermis. Here each lamina comprises a lobule and is, therefore, separated by a fissure, and each lobule is usually sub- divided with the exception of the nodule, the folium, and the lingula. In sagittal sections, or sections transverse to the general direction of the sulci, this arrange- ment of the laminae gives a foliate appearance, which, especially in sagittal sec- tions of the vermis, is termed the arbor vitae (see fig. 634). IThe cerebellar cortex consists of three layers and contains four general types of cell-bodies of_neurones, aD of which possess features pecuHar to the cerebellum. The outermost or molecular layer contains small stellate cells, "basket cells," with rel- atively long dendrites. These serve to associate the different portions of a given fohum. The axones of the largest of them give off branches which form pericellular baskets about the bodies of the cells of Purkinje, each axone contributing to several baskets. The layer of Pur- kinje cells, or the middle layer, is quite thin. The bodies of the cells of Purkinje are arranged in a single layer, and their elaborate systems of dendrites extend throughout and largely compose the molecular layer. The dendrites of these, the most essential cells of the cortex, are displayed in the form of arborescent fans (see fig. 604), arranged parallel with each other and transverse Fig. 636. — Diagram of the Inperioe Surface op the Cerebellum after the Removal OF the Medulla Oblongata, Pons, and Mesencephalon. The tonsil of the right side is omitted in order to display the connection of the pyramid with the biventral lobe, the furrowed band of the uvula, and more fuUy the posterior meduUary velum. The anterior notch is less evident than in the actual specimen. Superior cerebellar peduncle Posterior medullary velum Middle cerebellar peduncle (brachium of pons) Flocculus Biventral lobe Anterior slender lobule Posterior _J slender \ , , lobule \\\ Inferior semilu- . — ^ nar lobe Anterior Fourth medullary ventricle velum Lingula Tuber vermis 1 Pyramid Posterior cerebellar notch to the long axis of the folium containing them. Their axones are given off from the base of the ceU-body and acquire their medullary sheaths quite close to the ceU-body, and, after giving off several collaterals in the inner layer, pass into the general white substance and thence to other laminae or lobes. Certain of them go to structures outside the cerebellum. The inner layer is the granular layer. It contains numerous small nerve-cells or " granule-ceUs " which pos- sess from two to five radiating dendrites, unbranched except at their termination, which occurs suddenly in the form of three to six claw-hke twigs. Thek axones are given off either from the ceU-body direct or more often from the base of one of the dendrites, and pass outward into the molecular layer, where they bifurcate and course in both directions parallel to the long axis of the folium, to become associated with the dendrites of the cells of Purkinje. In the layer of the cells of Purkinje there is situated at intervals a neurone of the Golgi type II (see fig. 604). The short, elaborately branched a.xone of this neurone is distributed among the cells of the granular layer. Axones conveying impulses to the cerebellar cortex terminate in the granular layer as 'moss fibres,' or directly upon the cells of Purkinje as 'climbing fibres,' and probably upon the cells of the Golgi type II. Thus the neurones which receive impulses coming to the cortex are the cells of Purkinje, probably the Golgi cells of type II, and the granule-cells; those which distribute these impulses to other neurones of the folium are the Golgi cells of type II, the granule-ceUs, and the basket- cells (association neurones), and the collaterals of the cells of Purkinje. Impulses are conveyed from the cortex of a folium to that of other folia, lamina, lobules or lobes, or to the nuclei of the cerebellum, or to structures outside the cerebellum by the axones of the cells of Purkinje. The nuclei of the cerebellum (fig. 637) are in its central core of white substance. They are four in number, and all are paired, those of each pair being situated opposite each other on either side of the mid-line. 810 THE NERVOUS SYSTEM 1. The largest of them is the dentate nucleus. This is an isolated mass of grey substance situated in the core of white substance of each hemisphere. It is in the form of a folded or corrugated cup-shaped lamina, with the opening of the cup (hilus) directed anteriorly and obliquely toward the mid-line. It contains a mass of white substance and possesses a capsule. Its cell-bodies give rise to most of the fibres forming the superior cerebellar peduncles. 2. The nucleus emboliformis is an oblong and much smaller mass of grey substance, which lies immediately medial to the hilus of the dentate nucleus. It is probably of the same significance as the dentate nucleus, being merely a portion separated from it. 3. The nucleus globosus, the smallest of the cerebellar nuclei, is an irregular horizontal mass of grey substance with its larger end placed in front. It lies close to the medial side of the nucleus emboliformis, and often appears separated into two or more rounded or globular masses. 4. The roof nucleus [nucleus fastigii] is the second largest of the cerebellar nuclei, and is the most mesially placed. The pair is situated in the roof of the Fig. 637. — Section op Cerebellum and Brain-stem Passing Obliquely Through Inferior Portion of Cerebellum to Superior Margin op Pons. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Posterior cerebellar notch Medullary lami Cortical substance Corpus medullare Vermis (superior) Nucleus globosus Capsule of dei tate nucleus Dentate nucleus Core of the dentate nucleus Hilus of dentate nucleus Brachium conjunctivum Fourth ventricl Fossa rhomboidea (pars superior) Stratum nucleare Decussation of brachium conjunctivum Roof nucleus Nucleus emboliformis Lingula cerebelli Anterior medullary velum Substantia ferruginea Lateral lemniscus Medial longitudinal fasciculus Raphe of medulla oblongata Cerebral peduncle Interpeduncular fossa fourth ventricle, and so near the mid-line that both nuclei are in the white sub- stance of the vermis. They are ovoid in shape, and the nucleus of one side receives axones from the nucleus of the vestibular nerve chiefly of the opposite side, the decussation of these axones taking place in the vermis. Its cells are larger than those of the two first-mentioned nuclei. The peduncles of the cerebellum. — The peduncles consist of three pairs — the inferior, middle, and superior. The three peduncles of each side come together at the level of the lower border of the pons, and the entering and emerging fibres of which they are composed become continuous with the central core of white sub- stance of the cerebellar hemispheres. (Fig. 631, 638, 639.) The restiform body of the medulla oblongata is the inferior peduncle. It forms the lateral boundary of the inferior portion of the fourth ventricle, and upon reaching the level of the pons turns sharply backward into the cerebellum. In the region of the turn it is encircled externally by fibres of the cochlear nerve. It contains fibres, both ascending and descending, between the cerebellar cortex and the structures below the cerebellum. Its fibres include: (1) fibres from the spinal cord including the dorsal spino-cerebellar fasciculus (direct cerebellar tract) and probably a small proportion of the ascending fibres of the superficial ventro-lateral spino-cerebeUar fasciculus (Cowers' tract); (2) fibres from the PEDUNCLES OF THE CEREBELLUM 811 olive of the same and opposite side of the medulla oblongata; (3) fibres from the nuclei of the funiculus gracilis and cuneatus of the same and opposite sides; (4) fibres to and from the olive of the opposite side; (5) fibres to the nuclei of the motor cranial nerves; (6) fibres descending to the ventral horn cells of the spinal cord. The ascending or afferent fibres of the spino-cerebellar and cerebeUo-olivary fasciculi are the principal components of the inferior ped- uncle; the existence of fibres (5) and (6) is not weU estabhshed. Of these, the fibres of the direct cerebellar tract terminate in the cortex of the superior vermis of both sides of the mid-hne, but, for the most part, in that of the same side. The olivary fibres end in the cortex of both the su- perior vermis and the adjacent cortex of the hemispheres, and some of them terminate in the nucleus dentatus. The brachium pontis'or the middle peduncle is the largest of the three cere- bellar peduncles. In it the pons fibres pass slightly downward and into the cere- bellar hemisphere, between the lips of the anterior part of the horizontal fissure, entering lateral to the inferior peduncle. Fig. 638. — Transparency Drawing Showing the Origin, Course, and Connections op the Sttperior Cerebellar Peduncles (Brachia Conjunctiva) in the Formation op 'Stilling's Scissors.' Thalamus -\- - Internal capsule * Bundle from red nucleus to internal capsule "* Red nucleus Decussation of brachia conjunctiva Brachium conjunctivum (supenor peduncle) Inferior peduncle (restiform body) Bundle to cerebellar cortex Dentate nucleus Medulla oblongata It consists of the transverse fibres of the pons, and within the cerebellum its fibres are dis- tributed in two main groups — the upper transverse fibres of the pons apparently pass downward to radiate in the lower portion of the hemisphere, whUe the lower transverse fibres pass upward and medialward to radiate in the superior part of the hemisphere and vermis. For the most part the fibres of the middle peduncle may be considered as commissural fibres, passing from one side of the cerebellum to the other. Each peduncle contains fibres coursing in opposite directions. Many of these fibres are interrupted in their course to the opposite side by cells scattered throughout the pons, nuclei of the pons, and, therefore, in each brachium pontis some of the fibres are processes of the cells of the cerebellum and course toward the opposite side, while others are processes of the cells of the pontine nuclei and course to the cerebellar hemis- phere of the same side. Many cell-bodies of the nuclei of the pons whose axones terminate in the cerebellum receive impulses from fibres descending from the cerebral cortex of the opposite side — coriico-pontine fibres. Furthermore, there are evidences after degeneration that the brachium pontis also contains a few fibres from the cerebellum to the structures of the brain- stem and spinal cord. 812 THE NERVOUS SYSTEM The brachium conjunctivum or superior cerebellar peduncle emerges from the cerebellum on the medial side of the brachium pontis and also on the superior and medial side of the course of the restiform body. It forms the lateral boundary of the superior portion of the fourth ventricle and is the cerebello-cerebral peduncle. Its transverse sectioii appears semilunar in shape, with the concave side next to the cavity of the ventricle. The medial border, which inclines toward the mid-line, is connected with that of the corresponding peduncle of the opposite side by the anterior medullary velum, which thus roofs over the superior part of the fourth ventricle. The lateral border is distinguished from the pons by an open furrow or lateral sulcus. The superior cerebellar peduncles are almost entirely efferent pathways as to the cerebellum and form the chief connections between the cerebellum and the cerebrum. They arise almost wholly from the dentate nuclei. As they course forward they slightly converge and disappear under the inferior quadrigeminate bodies. Here, in the tegmentum of the mesencephalon, they undergo an almost total decussation, and then the majority of the fibres of each peduncle, having thus crossed the mid-line, terminate in the red nucleus of the opposite side. The red, nucleus lies in the tegmentum of the mesencephalon, below the superior quadrigeminate bodies, and therefore quite close to the decussation. The cells of the red nucleus, about which the fibres of the peduncle terminate^ in their turn send processes (axones) into (1) the rubro-spinal tract of the spinal cord and (2) mto the prosencephalon, most of which latter terminate in the thalamus whose ceU-bodies give fibres to the cerebral cortex by way of the internal capsule; but some pass from the red nucleus under the thalamus to join the internal capsule. In addition to the fibres having the origin and course described above, and which constitute the greater mass of the superior cerebellar peduncle, each peduncle is said to contain fibres which — (1) arise in the cerebellar cortex of the same and opposite sides of the mid-line, instead of from the dentate nucleus, and which join the peduncle at the side of the dentate nucleus, between it and the restiform body; (2) fibres which do not cross the mid-line in the decussation, but terminate in the red nucleus of the same side; (3) some fibres are not interrupted in the red nucleus, but pass directly into the thalamus; (4) a small proportion of fibres afferent as to the cerebellum, which arise in the structures of the cerebrum and pass in to the cerebellum; and (5) the greater part, if not all, of the ascending fibres of the superficial ventro-lateral spino- cerebellar fasciculus (Gowers' tract) of the spinal cord. The latter, instead of entering the cerebellum by way of the restiform body, are deflected in the upper medulla and pass in the lateral tegmentum of the pons to the anterior medullary velum, where they turn back- ward to enter the cerebellum in its superior peduncle and pass to its cortex, probably from the lateral side of the dentate nucleus (see fig. 656). The anatomy of the fourth ventricle. — The fourth ventricle is rhomboidal in shape, being considerably widened at the level of the brachia pontis and pointed at each end. Its floor consists of a slight depression in the brain-stem, the fossa rhomboidea, and corresponds to the floor of the central canal. Its pointed inferior end, the calamus scriptorius, is directly continuous with the central canal, and its narrowed superior end is continued into the aquseductus cerebri (Sylvii) of the mesencephalon, which is nothing more than a resumption of the tubular form of the canal. The entire cavity of the ventricle is lined with an epithelium which is continuous with the epithehum, or ependyma, of the central canal below and the aqueduct above. The entire ventricle involves the isthmus of the rhombencephalon, the metencephalon and a portion of the medulla oblongata. It is divided for study into an inferior, an intermediate and a superior part. The roof of the superior portion of the fourth ventricle is nervous, consisting of a thin lamina of white substance, the anterior (superior) inedullary velum, thickened at the sides by the brachia conjunctiva. At its extreme mesencephalic end (in the isthmus of the rhombencephalon) the anterior medullary velum is slightly thick- ened by a continuation of the white substance of the inferior quadrigeminate bodies, forming the frenulum veil. The inferior portion of the velum is contin- uous with the white substance of the cerebellum, and is covered by the lingula cerebelli, an extension of the cortical substance of the superior vermis (fig. 631). The roof of the intermediate portion of the fourth ventricle is formed by the cerebellum proper, the vermis and the mesial portions of the hemispheres. The nervous portion of the roof terminates with the posterior (inferior) medullary velum, a thin, narrow band of white substance which is the continuation of the peduncles of the fioccular lobes, and which connects them at the mid-line with the nodule of the inferior vermis. The roof of the inferior portion of the fourth ventricle is non-nervous. It is the chorioid tela of the fourth ventricle, a semilunar lamina consisting of the epi- thelial lining of the ventricle, reinforced by a continuation of the connective tissue of the pia mater and the adjacent portion of the arachnoid. Along the line of its THE FOURTH VENTRICLE 813 attachment to the surface of the medulla it is thickened, and in sections this por- tion bears the name ligula {toRiiia ventriculi quarti). The thickest portion spans the tip of the calamus scriptorius and is termed the obex. The width of the ven- tricular cavity is extended laterally from its widest part into the lateral recesses. narrow pockets on each side and around the upper parts of the restiform bodies. In the mid-Hne of the lower part of the chorioid tela there is a more or less well- marked opening, the foramen of Magendie (medial aperture of the fourth ventricle), which is a lymph-channel connecting the cavity of the ventricle with the subarach- noid space. There is a similar opening from each lateral recess {lateral apertures of Key and Retzius). The chorioid plexuses of the fourth ventricle consist of highly vascular, lobular, villus-like processes of the ventricular lining (and pia-mater) of the chorioid tela. They are reddish in the fresh specimen, and the epithelial lining of the ventricle is closely adapted to the unevennesses of their surfaces. From below they run as Fig. 639. — Diagram of the Roop and Lateral Boundaries of the Fourth Ventricle. The trochlear nerve should be shown emerging from the lateral boundary of the frenulum veli. Ii.ferior quadrigeminate body Trochlear nerve Axilerior medullary velum Biachium coniunctivum Brachlum of pOQS Restiform body Ligula teenia Chorioid tela of fourth ventricle Cuneate tubercle Clava Tubercle of Rolando Frenulum veli Lateral lemniscus Lingula of vernis Fourth ventricle Posterior medullary velum Chorioid plexus Foramen of Magendie two parallel masses on either side of the mid-line, which become united above, and then are separated again into two lateral processes which bend at right angles and project into the lateral recesses. Portions frequently protrude through the three openings of the ventricle into the subarachnoid space. The floor of the fourth ventricle [fossa rhomboidea] (fig. 640). — This is thrown into eminences and depressions indicative of the internal structures of the brain-stem subjacent to it. Its inferior portion is the dorsal surface of the upper portion of the medulla oblongata; its intermediate portion is the dorsal surface of the pons region, while its superior portion belongs to the isthmus of the rhombencephalon. Its triangular lower e.xtremity terminates as the opening of the central canal of the spinal cord. This portion is deepened at the obex and shows furrows which point downward and converge medialward, giving the appearance known as the calamus scriptorius. The mid-line of the floor is sharply distinguished by the well-marked median sulcus, which becomes shallower above than below. In the tip of the calamus scriptorius, immediately anterior to the obex, the median sulcus deepens to become continuous into the central canal. This terminal depression is known as the ventricle of Arantius. Throughout the length of the floor on either side of the median sulcus is a continuous ridge, the medial eminence, which is bounded laterally by the limiting sulcus. Underlying the floor of the ventricle is a layer of grey substance of varying thickness, which is continuous with that surrounding the central canal of the cord. The medial eminence is subdivided into portions of unequal width and elevation, and the limiting sulcus accordingly shows fovesE of different depths. 814 THE NERVOUS SYSTEM Beginning at the calamus soriptorius, the following areas of the floor of the fourth ventricle are usually distinguished (fig. 640) : — The area postrema of Retzius is a superficial vascular structure bounded inferiorly by the tEenia and overlying the terminal portion of the nucleus of the fasciculus gracilis (clava) and a portion of the nucleus of termination of the vagus nerve. The funiculus separans, a short oblique fold of the floor, composed chiefly of neurogUa, separates the area postrema from the ala cinerea (irigonum vagi), which is an oblique, grey-coloured, wing-shaped eminence indicating the middle third of the nucleus of termination (recipient nucleus) of the vagus and glosso- pharyngeal nerves. At the superior extremity of the ala cinerea is a well-marked triangular depression of the limiting sulcus known as the inferior fovea. Mesial to and extending above the ala cinerea is a narrow triangular eminence lying close to the median sulcus, which represents the nucleus of origin of the hypoglossal nerve, the hypoglossal eminence [trigonum n. hypoglossi]. The lateral field of this eminence shows small oblique rugse, giving it a "feathery" appearance, the area plumiformis of Retzius. The nucleus intercalatus of Van Gehuchten is a wedge- shaped portion very slightly demarcated from the hypoglossal eminence, and intercalated between it and the inferior fovea. This nucleus is considered by some observers as an inferior Fig. 640. — Dohsal Surface of the Brain-stem Showing the Anatomy of the Flock op the Fourth Ventricle. (Modified from Spalteholz.) Median sulcus Limiting sulcus ^ Aqueduct of cerebrum Nucleus incertus ^^ Locus cffiruleus Medial eminence ^■'^^ Acoustic medullary striae ■ Inferior fovea - ' Nucleus of fasciculus cuneatus — ' Taenia of fourth ventricle ^' Area postrema^' Nucleus of fasciculus gracilis (clava) Posterior median fissure. Nucleus of coch- *'^^^ ^ learis (tuberculum '' ^ ' acusticum) Acustic area (nucleus vestibularis) ^ Nucleus intercalatus "~ Hypoglossal eminence (trigone) ^^ Irigonum vagi (ala cinerea) ^ Funiculus separans Obex medial extension of the nucleus of termination of the vestibular nerve (area acustica), but Streeter, who has made a detailed study of the floor of the fourth ventricle by means of serial sections, doubts that it is a part of this nucleus. It is much more probable that it supplies visceral efferent flbres to the vagus and is thus a continuation of the dorsal efferent nucleus of the vagus. Superior to the inferior fovea, and crossing each half of the floor of the fourth ventricle, are the acoustic striae. These are bundles of axones arising in the dorsal nuclei of termination of the cochlear or auditory nerve, which are situated in the lateral periphery of each restiform body. The bundles course around the dorsal periphery of the upper portion of the restiform body, then across each half of the floor of the ventricle to the median sulcus, in which they suddenly turn ventrally into the substance of the medulla oblongata, and in doing so they cross the mid-line to enter the substance of the opposite side. The striie vary greatly in different individuals, both in the degree of their prominence and their direction. Sometimes no striae are visible from the surface. Frequently a bundle may be discerned which courses obliquely upward and lateralward from the median sulcus to disappear in the floor further away from the mid-Une and again, a bundle may depart from the transverse course before reaching the median sulcus. Such a bundle ascending is sometimes called conductor sonorus. The acoustic striae cross the acoustic area. This is the flattened elevation which occupies the whole lateral portion of the intermediate portion of the floor of the ventricle, lateral to the limiting sulcus, and extends into the inferior portion lateral to the inferior fovea. It represents the subjacent STRUCTURE OF MEDULLA OBLONGATA 815 nucleus of termination of the vestibular nerve. The dorsal and ventral nuclei of the cochlear nerve {iuberculum acusticum) are indicated by the ventro-lateral fullness in the contour of the restiform body. In many of the mammals they produce a well-marked protuberance. In its superior portion the medial eminence occupies the greater part of the floor of the fourth ventricle, and in the upper part of the intermediate portion of the floor it presents a broader, well-marked, elongated elevation, the eminence of the facial and abducens or the colliculus facialis. This represents the mesiaOy placed nucleus of origin of the abducens and the genu of the root of the facial nerve, which root courses around and above the nucleus of the abducens. The nucleus of the facial is too deeply situated to produce an eminence. Lateral to this eminence is a depression of the limiting sulcus, which overUes the mesial part of the region of the larger portion of the nucleus of termination of the trigeminus, and is the fovea trigemini or superior fovea. The strip of the floor above the superior fovea and lateral to the medial eminence often appears greyish blue or dark brown, owing to pigmented cells subjacent to it, and is known as the locus caeruleus. It also represents a portion of the nucleus of the trigem- inus. The most superior portion of the medial eminence becomes narrow and lies close to the mid-line. The function of the underlying grey substance producing it is uncertain, and for this reason Streeter has named the elevation nucleus incertus, noting that by position it is closely related to the upper portion of the nucleus of the trigeminus. Internal Structure of the Medulla Oblongata and Pons The finer detail of the internal structure lies within the scope of microscopic rather than of gross anatomy. However, the significance and relations of certain of the more important and larger of the internal structures of the meduUa and pons as observed in sections may be considered. The entire brain-stem may be regarded as an upward continuation of the spinal cord, to which structures are added giving each part its peculiar character and conformation, and in which the structures characteristic of the spinal cord are modified in varying degrees. The pyramids, the great descending or motor cerebro-spinal fasciculi, are directly con- tinuous into the pyramidal fasciculi of the spinal cord. They form the extreme ventro-medial portion of the medulla, and from the fact that they contribute numerous fibres to the efferent nuclei (nuclei of origin) of the cranial nerves and to other portions of the grey substance of the brain-stem, they decrease appreciably in bulk in descending toward the spinal cord. Most of the fibres contributed to the medulla, as well as to other divisions of the brain-stem, decussate as they leave the pyramids, and terminate in the grey substance of the opposite side. However, the chief decussation of the pyramids occurs in the lower end of the medulla. Here usually about three-fourths of the fibres then comprising the pyramids cross the mid- line to form the lateral cerebro-spinal fasciculus (crossed pyramidal tract) of the spinal cord immediately below. The remaining fourth, comprising the more lateral fibres or those furthest away from the mid-line, continues uncrossed into the spinal cord as the ventral cerebro-spinal fasciculus or direct pyramidal tract. The majority of the latter fibres decussate gradually in the commissural bundle and in the ventral white commissure of the cord as they approach the levels of their termination. In practically all vertebrates except man and the apes there are no ventral pyramidal fasciculi, the decussation in the medulla being a total one. In man, the proportion of fibres crossing in the chief decussation varies. Cases have been noted in which apparently the entire pjTamids decussate at this level. In other cases the direct or ventral pyramidal tract may be much larger than usual, at the expense of the lateral. The decussation usuaUy appears to be symmetrical and it occurs so suddenly that the fibres, in coursing from the ventral to the lateral positions, detach the tips of the ventral horns of the spinal cord from the remainder of the grey figure, and these appear as isolated, irregularly shaped masses of grey substance in transverse sections of the medulla. From this level upward the outline of the grey figure of the cord is lost, and the cell-columns of the ventral horns occur in more or less detached groups as the motor nuclei of the cranial nerves. The origin and decussation of the lemnisci (fillet) begins immediately above the decussa- tion of the pyramids, and here the arrangements characteristic of the spinal cord are further modified. The dorsal portion of the grey figure of the cord is manifest up to this level, but here, after a considerable increase in its thickness, the grey commissure gives rise to two thick dorsal outgrowths on each side of the mid-hne. These dorsal projections of grey substance comprise the nuclei of termination (relays) of the chief ascending or sensory spino-cerebral fasciculi of the spinal cord. The nucleus of the fasciculus gracilis (nucleus of GoU's column) arises a little before the nucleus of the fasciculus cuneatus (nucleus of Burdach's column). The former extends slightly downward from its point of origin, so that its inferior extremity is included in sections through the decussation of the pyramids (fig. 6il). It produces a slight bulbous enlargement (the clava) of the end of the funiculus gracihs, while the nucleus of the fasciculus cuneatus corresponds to the cuneate tubercle of the external contour of the meduUa (figs. 632, 640). From the cells of these nuclei arise the lemniscus — the cephalic continuation of the spino-cerebral pathway which conveys the general bodily sensations to the cerebrum. In passing out of the nuclei the fibres of the lemniscus course in a ventro-medial direction. Curving around the region of the central canal, they contribute largely to the internal arcuate fibres, then, sweeping across the mid-line, they convert it into the raphe, and immediately after crossing (decussating) they turn cephalad and collect to form the bundle known as the lemniscus. In the medulla, the lemnisci are two thin bands of fibres spread vertically on each side of the raphe, with their lower or ventral edges thicker than their dorsal edges. In their course toward the cerebrum they increase in bulk, owing chiefly to fibres being added to them from the nuclei of termination of the aiferent roots of the cranial nerves, which fibres likewise cross the mid-line as internal arcuate fibres to join the lemniscus of the opposite side. In passing 816 THE NERVOUS SYSTEM through the pons, the lemnisci gradually become spread horizontally, and beyond the pons their then more lateral portions are further displaced and come to course in the lateral borders of the isthmus rhombencephali and mesencephalon, while the medial portions remain nearer the mid-line. This lateral spreading of each lemniscus produces the lateral lemniscus and the medial lemniscus, distinguished in transverse sections of the superior pons and mesencephahc Fia. 641. — Transverse Section of Medulla Oblongata at the Level of the Decussation OF THE Pyramids. Central grey substance Nucleus of fasciculus gracilis Funiculus cuneatus j^^^-Substantia gelatinosa (Rolandi) Spinal tract of trigeminus if' ' Gowers' tract » Lateral cerebro-spinal fasciculus V '^ Ventral horn \ Decussation of pyramids Pyramid regions of the brain stem (fig. 660). The lateral lemniscus is contributed very largely by the cell-bodies of the nuclei of termination of the cochlear nerve of the opposite side. The reticular formation of the medulla and pons region is considerably more abundant than in the spinal cord. As in the spinal cord, it consists of grey substance through which nerve-fibres, singly and in small bundles, course in all directions, and more sparsely than in other regions. In the medulla it is traversed by the internal arcuate fibres. It may be con- FiQ. 642. — Transverse Section of Medulla Oblongata at Level of the Decussation of THE Lemnisci, Posterior median fissure Central grey substance Nucleus of hypogl Internal arcuate fibers Root filum of hypoglossus Nucleus of inferior olivi Medial accessory olivary nucleu Nucleus of fasciculus gracilis * Commissural nucleus of ala i ' / Nucleus of fasciculus cuneatus Dorsal external arcuate fibres is of spinal tract of trigemi-nus -- Spinal tract of trigi Raphe' '-- -' Restiform body ■Nucleus lateralis V Substantia reticularis Ventra.1 external arcuate fibres Decussation of lemnisci sidered an enlarged continuation of the middle portion of the grey column of the cord, dispersed by numerous fibres, giving it the reticulated appearance which suggests its name. Its numer- ous nerve-cells belong, for the most part, to the association and commissural systems of the brain stem, and, therefore, the fibres arising in it correspond largely to the fasciculi proprii of the spinal cord. As in the cord, most of the fibres are of short course, serving to associate different portions of the same level and adjacent levels with each other. Those of long course show a tendency to collect into a small, well-marked bundle which courses one on each side close_ to the mid-line, ventral to the central canal in the closed part of the medulla, and near the median sulcus of the floor of the fourth ventricle, in the open part. In the mesencephalon this bundle is again situated closely ventral to the aquaeductus cerebri. STRUCTURE OF MEDULLA OBLONGATA 817 This bundle is known as the medial longitudinal fasciculus (posterior longitudinal bundle). It corresponds more nearly to the ventral fasciculus proprius of the spinal cord than to others of the fasciculi proprii. In the medulla it appears as the dorsal edge of the lemniscus, but in the shifting of the position of the lemniscus in the pons region, it retains its medial position and thus becomes isolated. By position it is especially adapted for the association of the nuclei of the cranial nerves. Evidence has been found that those fibres which arise in the corpora quadrigemina and descend the spinal cord in its sulco-marginal or ventral mesencephalo-spinal fasciculus, pass through the medulla in the medial longitudinal fasciculus. The nuclei of termination of the vestibular nerve are said also to contribute many fibres to it. The inferior olivary nucleus is an added structui-e in the medulla oblongata, i. e., it has no homologue in the spinal cord. The two of them occupy the olivary prominences, the olives of the exterior, and constitute the most conspicuous and striking isolated masses of grey sub- stance in sections of the medulla. They appear as crenated laminae of grey substance folded so as to encup a dense mass of white substance, and in actual shape the entire nucleus has the form of an irregular corrugated cup with the opening or hilus on the side toward the mid- line. The mass is so crumpled that the diameter of the hilus is appreciably less than the length of the nucleus, and thus transverse sections of either extremity of it appear as closed capsules. Fig. 643. — Transverse Section op Medulla Oblongata Through Nuclei of Vagus and HyPOGLOSSUS AND THROUGH THE MlDDLE OP THE OlIVES. Medial longitudinal fasciculus Chorioid tela of fourth ventricle Nucleus of hypoglossus Medial nucleus of vestibular nerve "** Descending (spinal) nucleus of vestibular nerve Nucleus ambiguus Dorsal accessory olivary nucleus Root filum of hypo glossus Nucleus of ala cinerea (trigonum vagi) / Dorsal efferent nucleus of vagus ' ' Solitary tract Nucleus of solitary tract __ / '^j^J/' /^"s^ ' — Nucleus of fasciculus ^"^'^ ''< -^ ^^' cunatus ■^ ^ ^^^*^ ^ Nucleus of spinal tract ^ ""^ \ ./Jal^^r °^ trigeminus Restiform body Spinal tract of trigeminus Cerebello-olivary fibres Root filum of vagus — Nucleus lateralis Thalamo-olivary tract ' '' Pyramid Lemniscus Raphe There are several small detached portions of the olivary nucleus known as the accessory olivary nuclei. These are named according to their position with reference to the chief portion or olive proper. They are plates less corrugated than the chief nucleus, and appear rod-like in sections. The largest is the dorsal accessory olivary nucleus. The medial accessory olivary nucleus is widest at its inferior end, which extends a little below the inferior extremity of the chief nucleus. The lateral accessory olivary nucleus is the smallest. In serial sections the accessory nuclei are found to be plates of grey substance usually continuous with one another. The oUvary nuclei are mainly cerebellar connections. By both ascending and descending fibres each cerebellar hemisphere is connected with the olivary nucleus of the same and opposite sides. Serial sections of a human brain with congenital absence of one cerebellar hemisphere, described by Strong, show that the chief connection of a hemisphere is with the olive of the oppo- site side. These fibres necessarily pass between the cerebellum and the olives by way of the restiform body, and, in so doing, form an obliquely coursing bundle in the lateral border of the medulla known as the cerebello-olivary fibres (fig. 643). The olivary nuclei also comprise a secondary relay between the spinal cord and the cerebellum by way of the spino-olivary fas- ciculus of the cervical cord, and it will be noted that they receive fibres from the thalami. The latter fibres, the thalamo-olivary tract, approach the olive at its lateral periphery, while upward through the brain-stem the tract courses in a more medial position. This tract comprises one of the cerebro-cerebellar paths. Arising in the thalamus and terminating in the olive, its impulses reach the opposite cerebellar hemisphere by way of the cerebeUo-ohvary fibres. The arcuate fibres are referred to as internal and external, according as they course dorsal or ventral to the inferior ohvary nucleus. The internal arcuate fibres comprise fibres destined for both the cerebellum and cerebrum, and also for the association of the tegmental grey substance of the two sides in which they course. Certain of the fibres passing between one restiform body (cerebellar hemisphere) and the olive of the opposite side course internal to the olive of the same side, and thus form the ventral portion of the internal arcuate fibres. As noted above, the internal arcuate fibres consist in 818 THE NERVOUS SYSTEM greatest part of fibres being contributed to the lemnisci, arising from the cells of the nucleus of the fasciculus gracOis and fasciculus cuneatus and sweeping downward and decussating to form the lemniscus of the opposite side. However, all the fibres arising in these nuclei do not enter the lemniscus. A few of them cross the mid-line with the internal arcuates, but pass on to enter the restiform body (cerebellar hemisphere) of the opposite side. Some of these course ventraUy and, upon approaching the olive of the opposite side, are deflected around the ventral side of both the olive and the pyramid, and thus pass to the restiform body as external arcuate fibres also. Certain of the internal arcuate fibres arise from the cells of the nuclei of termina- tion of the cranial nerves and from small cells situated in the grey substance of the reticular formation. These, in crossing the mid-line, correspond to the white commissures of the spinal cord. Some of them terminate in the meduUa; others, especially those from the nuclei of termination of the cranial nerves, join the lemniscus and pass toward the cerebrum; others reach the cerebellar hemisphere of the opposite side. The external arcuate fibres, in addition to those mentioned above, comprise certain fibres which arise in the nuclei of the fasciculus gracilis and cuneatus and pursue a dorso-lateral course to enter the restiform body (cerebellar hemisphere) ol the same side. These form the dorsal segment of the external arcuates. The greater mass of the external arcuates are cerebello- oHvary fibres. Certain of those passing from one olive to the restiform body of the opposite side are deflected at the raphe, and course on the ventral side of both the other olive and the pyramid in order to reach the opposite cerebeUo-ohvary bundle. Likewise, those passing from the restiform body to the opposite olive are deflected by the olive of the same side and pursue a similar course to the raphe. While out of the hilus of each olive streams a dense mass of white substance, yet many of the fibres concerned with the olive pierce its walls from all sides. Many of the external arcuate fibres are said to be interrupted in the nucleus arcuatus. This is a thin sheet of grey substance, variable in amount, which lies on the ventral aspect of Fig. 644. — Reconstruction of the Inferior Olivary Nucleus, Dorso-lateral Surface. (After Sabin.) each pyramid, and, though it decreases inferiorly, it may be evident down to the decussation of the pjTamids. The nucleus receives its name from the fact that its larger portion is inter- polated in the course of the external arcuates. It is continuous anteriorly with the grey substance or nuclei of the pons. The external arcuate fibres of longer course, like the olives with which they are largely concerned, have no homologues in the spinal cord. The central canal of the closed portion of the meduUa is surrounded by a greater amount of central grey substance, substantia grisea centralis, than is the canal in the spinal cord. This is largely gelatinous substance, the central gelatinous substance, and the nerve-fibres in coursing through the grey substance are partially deflected by it, leaving it as a cyhndrical, more evident area of grey substance than in other regions. In the open portion of the meduUa the central grey substance naturally forms a more transparent lamina just under the floor of the fourth ventricle. In the mesencephalon it again surrounds the reformed canal or aque- duct of the cerebrum. The central connections of the cranial nerves are most easily homologised with spinal-cord structures. Functionally the cranial nerves are of three varie- ties:— (1) the motor or efferent nerves, comprising the oculomotor, the trochlear, masticator, the abducens, the facial, the spinal accessory, and the hypoglossus; (2) the sensory or afferent, comprising the olfactory, the optic, the trigeminus, the vestibular, and the cochlear and (3) the mixed, motor and sensory nerves, comprising the glosso-palatine, the glosso-pharyngeal, and the vagus. The nuclei of origin of the motor or efferent cranial nerves and the efferent portions of the mixed nerves are directly continuous with the cell columns of the ventral horns of the spinal cord, while the emerging root filaments and roots of these nerves correspond to the ventral roots of the spinal nerves. The nuclei of ter- STRUCTURE OF MEDULLA OBLONGATA 819 mination of the afferent or sensory cranial nerves and of the sensory portions of the mixed nerves correspond directly to the nuclei of the fasciculus gracilis and fasciculus cuneatus, and to the cell-bodies of association and commissural neu- rones of the medulla and cord and, functionally, are merely anterior continua- tions of these. The nuclei of the efferent or motor cranial nerves lie in two parallel lines, one near the mid-line arid the other more laterally placed. The nuclei giving origin to the oculomotor, the trochlear, the abducens, and the hypoglossus are near the mid-line, and correspond to the ventro-medial and dorso-medial cell groups of the ventral horns of the spinal cord; the nuclei of origin of the masticator (motor Figs. 645 and 646. — Diagrams showing the Composition op the Cerebellar Portions OF the Internal and External Arcuate Fibres. Nucleus of Commissural nucleus fasciculus of ala cinerea gracilis Spinal tract of trigemi] Dorsal external arcuate fibres -Restiform body Ventral external arcuate fibers Nucleus of tractus solitarius Nucleus of ala cinerea ; Medial nucleus and descending root ot vestibular nerve Nucleus of fasciculus cuneatus ^Nucleus ambiguus -\ — Restiform body Root filum of vagus Cerebello-olivary fibres Ventral external arcuate fibres root of the trigeminus) of the facial, and the nucleus ambiguus: giving origin to the motor portions of the glosso-pharyngeal and vagus nerves, together with the nucleus of the spinal accessory, correspond to the ventro-lateral and dorso-lateral cell-groups of the ventral horns of the spinal cord. The nerve-roots having medial nuclei of origin are those which make their exit from the brain-stem along tlie more media,l superficial line, while those having the more lateral nuclei comprise the more lateral hne of roots apparent on the surface of the stem. Some of the effer- ent fibres of the vagus, supposedly visceral efferent, arise from a small nucleus dorso-medial to the nucleus ambiguus, the dorsal efferent nucleus of the vagus. i he first two pau-s of cranial nerves, the olfactory and optic, are attached to the 820 THE NERVOUS SYSTEM prosencephalon. These are purely sensory, and make their entrance near the mid-line of the brain, both having superficially placed nuclei of termination. Of the other nerves, all having sensory or afferent functions enter the brain along the lateral or more dorsal line, and the ganglia giving origin to their afferent axones correspond directly to the spinal ganglia of the dorsal or afferent roots of the spinal nerves. Commissural and associational neurones are much more numerous in the brain-stem than in the spinal cord. Their axones serve to connect the struc- tures on the two sides of the mid-line and to associate the different levels of the same side. Just as in the spinal cord, those of longer com-se correspond to the fasciculi proprii. Many of their axones descend into the spinal cord. Of the fifteen pairs of cranial nerves, eleven pairs are attached to the medulla oblongata and pons, viz., the trigeminus, the masticator, abducens, facial, glosso-palatine, vestibular, cochlear, glosso-pharyngeal, vagus, spinal accessory, and hypoglossus. The hypoglossus, the motor nerve of the tongue, has its nucleus of origin beginning in the lower portion of the floor of the fourth ventricle at the level of the acustic striae. It ' is a long nucleus, lying close to the mid-line and just under the floor of the ventricle (hypoglossal eminence) and extending down to the region of the funiculus separans. Here it curves ventrally to a slight degree, and below the obex assumes a position ventro-lateral to the central canal, and thus extends a short distance below the level of the inferior tip of the olive. The nerve arises as a series of rootlets which traverse the entii-e thickness of the medulla (fig. 643), to emerge in line in the furrow between the olive and the pyramid and fuse to form the trunk of the nerve. The lowermost of the rootlets usually emerge below the ohve. The nucleus receives impulses — (1) from the cerebrum by way of divergent fibres from the pyramid of the opposite side (voluntary); (2) impulses brought in by the sensory fibres of the cranial nerves (reflex); and (3) by axones from other levels of the medulla (associational). None of its axones are supposed to decussate, though numerous commissural fibres are known to pass between the nuclei of the two sides. The spinal accessory is likewise a purely motor nerve, and has a laterally placed, long, and much attenuated nucleus of origin. Above, its nucleus is in line with and practically continu- ous with the nucleus giving motor fibres to the vagus and glosso-pharyngeus (nucleus ambiguus). Below, it consists of the lateral and dorso-lateral groups of cells of the ventral horn of the first five or six segments of the spinal cord. The nerve arises as a series of rootlets which emerge laterally and join a common trunk, which passes upward between the dorsal and ventral roots of the upper cervical nerves and parallel with the meduOa to turn lateralward in company with the vagus. (See fig. 629). The upper rootlets arise from that part of the nucleus con- tiguous to the inferior end of the nucleus ambiguus, and are described as comprising the medullary or accessory part of the nerve; those which arise from the ventral horn cells below are described as the spinal part. The trunk of the spinal accessory fuses with the vagus in the region be- tween its two ganglia, and, before separation, contributes fibres (the accessory part) to the trunk of the vagus. Some of the accessory fibres are distributed as motor fibres to the muscles of the larynx and some of them are visceral efferent fibres. The latter probably terminate chiefly in sympathetic ganglia which send axones to the heart. The spinal part is distributed to the sterno-mastoid and trapezius muscles. The nucleus of the spinal accessory receives termi- nal twigs of pyramidal fibres from the opposite side and is otherwise subjected to influences similar to those afi'ecting the cells giving origin to the motor roots of the spinal nerves. The vagus or pneumogastric and the glosso-pharyngeus, though they have widely different peripheral distributions, are so similar in origin and central connections that they may be described together. Both contain efferent fibres, though both are in greater part sensory. They are similar as to the origin of both their efferent and afferent components. The afferent fibres of the vagus arise in its jugular gangUon and its nodosal ganghon (ganglion of the trunk); the afferent fibres of the glosso-pharyngeus arise in its superior ganghon and its petrosal ganghon. In both nerves these fibres enter the lateral aspect of the medulla and bifurcate into ascending and descending branches, similar to those of the dorsal root-fibres in the spinal cord. Some of these branches terminate in practically the same level of the medulla about cell-bodies situated on the same and the opposite sides. Such branches end chiefly in the nuclei of the hypoglossal and spinal accessorj^, and about the cells giving origin to the efferent components of the vagus and glosso-pharyngeus themselves — short reflex arcs. However, most of the afferent fibres terminate in the nucleus of termination of the vagus and glosso-pharyngeus: — (1) the nucleus of the ala cinerea, the middle portion of which is indicated in the floor of the fourth ventricle by the ala cinerea; (2) in the closed portion of the medulla, the lower end of the nucleus of the ala cinerea comes to lie in the dorso-lateral proximity of the central canal, and this portion is known as the commissural nucleus of the ala cinera (figs. 642 and 645) from the fact that fibres may be seen which pass directly from it across the mid-line; (3) the longer of the descending branches of the bifurcated fibres collect to form the solitary tract, a compact bundle situated dorsaUy just ventro-lateral to the nucleus of the ala cinerea and quite con- spicuous in sections of the medulla. The fibres of this bundle terminate in the nucleus of the solitary trad, which is but a ventro-lateral and downward continuation of the nucleus of the ala cinerea enclosing the bundles forming the tract. It is most probable that the fibres of the solitary tract are chiefly from the vagus (pneumogastric), though Bruce has found evidence that the glosso-pharyngeal contributes to it appreciably. It decreases rapidly in descending the medulla, owing to the rapid termination of its fibres about the cells of its nucleus. It, NUCLEI OF CRANIAL NERVES 821 with the axones given by the cells of its nucleus, is believed to extend as far downward as the level of the fourth cervical segment of the spinal cord. This being in the level of origin of the phrenic nerve, the tract forms a link in the respiratory apparatus which aids in the co- ordinated respiratory movements. The axones given off by the cells of the nucleus of the ala cinerea (terminal nuclei of the vagus and glosso-pharyngeus) course on both sides of the Fig. 647. — Scheme showing the Relative Size and Position op the Nttclei of Origin (Red) of the Motor and the Nuclei op Termination (Blue) op the Sensory Cranial Nerves. Nucleus of olfactory nerve Nucleus of oculomotor nerve " Nucleus of trochlear nerve Nucleus of mesencephalic root of masticator Chief motor nucleus of masticator Nucleus of facial' Nucleus of abducens*' Nucleus ambiguus (vagus and glosso-pharyngeus) Nuclei of optic Nucleus of hypoglossus " Nucleus of spinal accessory nerve ^ Pulvinar o \ thalamus Lateral genic- ulate body I nerve Nucleus of supe- rior colliculus I - Sensory nucleus of trigeminus , Nucleus of vestibular nerve ~ Dorsal nucleus of cochlear nerve Nucleus alSE cinerege (vagus and glosso-pharyngeus) Solitary tract (vagus and glo pharyngeus) --Nucleus of spinal tract of trigeminus mid-line, associating nuclei of other cranial nerves with vagus and glosso-pharyngeal impulses, many decussating to be distributed to the structures of the opposite side. Many join the lemnis- cus of the opposite side and pass into the cerebrum; others are distributed to the motor neu- rones of the cervical cord of the same and opposite sides (reflex axones), and no doubt others form central connections with the cells of the reticular formation of the medulla, though their precise relations have not been determined. ' ' 822 THE NERVOUS SYSTEM Cell-bodies in the nucleus of the ala cinerea, the nucleus of the solitary tract and in the commissural nucleus of the ala cinerea comprise the so-called respiratory and vaso-motor nuclei ("centres") of the medulla. Some of the caudal branches of the axones given off by the cells of these nuclei descend the spinal cord, not only to the segments giving origin to the phrenic nerve, but also to those supplying the intercostal and levatores costarum muscles. Some of these augment the solitary tract; most of them descend in the reticular formation of the meduUa and cord. Further, axones given off by these cells convey vaso-motor impulses which are distributed to visceral efferent neurones throughout the cord. Fig. 648. — Diagbam illustrating Principal Central Relations op the Vagus Nerve, EXCLUSIVE OF RELATIONS TO DESCENDING CeREBBAL OR PYRAMIDAL FIBRES. Medial lemniscus Dorsal efferent nucli of vagus Nucleus of hypogli , Nucleus of ala cinerea Nucleus anbiguus — p# Ganglia of vagus Solitary tract and nucleus of solitary tract The nuclei of origin of the motor fibres of the vagus and glosso-pharyngeus are the dorsal efferent nucleus of the vagus and the nucleus ambiguus. The cells of the dorsal nucleus of the vagus lie somewhat clustered in the ventro-mesial side of the nucleus of the ala cinerea and lateral to the nucleus of the hypoglossus. Their axones pass outward among the entering or afferent vagus fibres, and it is suggested that most of them are visceral efferent fibres of the vagus, i. e., they terminate about sympathetic neurones. The nucleus ambiguus or ventral efferent nucleus of both nerves hes in the lateral half of the reticular formation, about mid-way between the olive and the line traversed by the rootlets of the two nerves. Its upper end is larger. Its cells are considerably dispersed by the fibres of the reticular formation. The axones arising from its cells course at first dorsalward and then turn abruptly outward to join NUCLEI OF VESTIBULAR NERVE 823 the rootlets of the vagus or glosso-pharyngeus, as the case may be. The vagus is thought to receive more efferent fibres from the nucleus ambiguus than does the glosso-pharyngeus, and Cunningham notes that it may be questioned whether the latter nerve contains any motor fibres at all, there being paths by which the fibres of its motor branch (to the stylo-pharyngeus muscle) might enter it other than direct from motor nuclei. The oesiibtdar and cochlear nerves are usually considered as one nerve and together are designated as the acoustic or eighth cranial nerve. While both are purely sensory, are similar in development and course together, they are distinct as to function and their nuclei of termina- tion differ. They are here described as separate cranial nerves. The two nerves approach the brain stem together and enter it at the lateral aspect of the junction of medulla oblongata and pons. The vestibular nerve arises as the central processes of the bipolar cells of the vestibular ganglion, and passes into the brain-stem on the ventro-mesial side of the restiform body to find its nucleus of termination (nucleus vestibularis) in the floor of the fourth ventricle. This nucleus occupies a triangular area of considerable extent (area acustica, fig. 640), and is usually subdivided into a lateral nucleus (Deiters'), a medial 7iucleus (Schwalbe's), a superior nucleus (Bechterew's), and an inferior nucleus (nucleus spinaUs). The latter is a downward pro- longation of the general nucleus vestibularis which accompanies the descending or spinal root of the nerve. Fig. 649. — Transverse Section of Medulla at Inferior Border of Pons. Medial longitudinal fasciculus Nucleus of medial ^ eminence Acoustic medullary ^ \ stria Descending root of i fibular I ^Dorsal root of coch- ■^ Restiform body Dorsal nucleus of cochlear nerve ^ Cochlear nerve 'Vestibular nerve Root filum of glosso pharyngeus Cerebello-olivary fibres Thalamo-oUvary tract Nucleus of inferior olive '^ External arcuate fibres Nucleus arcuatas From the cells of the lateral and inferior nuclei axones are given off which form paths to the lateral funiculus of the spinal cord (vestibulo-spinal fasciculus, fig. 619) and to its anterior marginal fasciculus (ventral vestibulo-spinal tract). From both the lateral nucleus and the superior nucleus a special path is given off which passes upward and terminates in the roof nucleus of the cerebellum (nucleus fastigii) of the opposite side and in the nucleus dentatus and the cortex of the vermis. Also, fibres arising in the nuclei fastigii are said to terminate in the lateral (Deiters') nucleus in addition to those which probably descend into the anterior marginal fasciculus of the spinal cord. From the medial and also from the superior nucleus fibres pass to the medial longitudinal fasciculus of both sides, and are distributed to the nucleus of the abducens of the same side and to the nuclei of the trochlear and oculo- motor nerves of the opposite side and of the masticator nerve of the same and opposite sides. From the lateral and medial nuclei, and probably from aU, fibres arise which cross the mid- line to enter the lemniscus and ascend to the cerebrum (lateral portion of the thalamus) on the opposite side. The lateral (Deiters') nucleus is said to contribute more fibres to the medial longitudinal fasciculus than does a nucleus of any other cranial nerve. If any of these fibres descend the cord, they must do so in its anterior marginal fasciculus. The inferior nucleus is accompanied by the descending or spinal root of the vestibular nerve, which begins to assemble in the nuclei above. This root is composed of both caudal branches of' the entering fibres of the nerve and chiefly of fibres arising from the cells of its nuclei. Thus for the vestibular nerve it corresponds in every way to the solitary tract for the vagus, and to the spinal tract of the trigeminus. Such of its fibres as descend into the spinal cord most probably do so in the lateral vestibulo-spinal fasciculus. Many of the anatomical details of the central connections of the vestibular nerve have not yet been determined with exactness. In addition to whatever other functions it may have, 824 THE NERVOUS SYSTEM it is considered to be the nerve of equilibration, and the connections noted above may be considered the pathways by which it exercises this function. The fibres of the apparatus which are represented in the spinal cord are supposed to convey impulses to the ventral horn (motor) cells of the cord as far down as the lumbar region. The cochlear nerve, the auditory nerve proper, arises as the central processes of the bipolar cells of the spiral ganglion of the cochlea. In the lateral periphery of the restiform body, just before the latter enters the cerebellum, the nerve finds its two nuclei of termination, the ventral nucleus and the dorsal nucleus (tuberculum acusticum, fig. 640). From the dorsal nucleus arise the acoustic medullary strice. These bundles pass around the dorsal aspect of the restiform body and course just under the ependyma of the floor of the fourth ventricle to the mid-line, where they suddenly turn downward into the substance of the medullsa and in doing so, cross to the opposite side and join the lemniscus. As the lemniscus becomes separated higher up into a medial and lateral portion, these fibres course in the lateral lemniscul and are distributed chiefly to the grey substance of the inferior quadrigeminate and media, Fig. 650. — Scheme showing Some of the Central Connections op the Acoustic Nerve. (In part after Edinger.) Medial geniculate body Inferior quadrigeminate body Nucleus of trochlear nerve Nucleus fastigii Nucleus emboUforniis ,' Dentate nucleus Lateral nucleus of vestibular nerve Restiform body Dorsal nucleus of cochlear nerve Ventral nucleus of cochlear nerve Cochlear nerve Peduncle of superior olivei ^ Vestibular nerve Superior olivary nucleus Trapezoid body geniculate body of that side. At the mid-line some of their fibres join the median longitudinal fasciculus and by way of it are distributed to the nuclei of origin of other cranial nerves. In frequent cases, the acoustic striae course so deeply beneath the ependyma as not to be super- ficially visible in the floor of the fourth ventricle. From the ventral nucleus of termination fibres arise which terminate about the cells of the superior olivary nucleus of the same and opposite sides. The superior olive is a small accumu- lation of grey substance which lies in the level of the inferior portion of the pons, and in line with the much larger inferior ohvary nucleus of the medulla. However, it is not analogous to the latter in any sense. The two superior olives form links in the central acoustic chain. From cells of the superior ohvary nucleus of the same and opposite sides, fibres arise which pass by way of the lateral lemniscus and terminate in the grey substance of the inferior quadri- geminate body and in the medial geniculate body, thus associating these bodies with the ventral nucleus of cochlear termination of the opposite side. From the medial geniculate body fibres arise which pass to the cortex of the superior temporal gyrus. This path is supplemented by fibres arising in the inferior quadrigeminate body, which likewise go to the temporal lobe. In the lateral lemniscus some of the acoustic fibres are interrupted by cells of the nucleus of the lateral lemniscus. In crossing the mid-line, between the superior olives, the fibres from the two sources form a more or less compact bundle, the corpus trapezoideum (trapezium). To this are added fibres crossing between the nuclei trapeozidei, smaller masses of grey substance just ventral to the superior olives and probably of the same significance. Also, some fibres arising in the nuclei of termination of the cochlear nerve pass to the in- ferior quadrigeminate body of the same side. On the other hand, the connection with the medial NUCLEI OF CRANIAL NERVES 825 geniculate body is thought to be wholly a crossed one. Further, some fibres are described aa terminating in the superior quadrigeminale body of both the same and the opposite side. These, forming the stratum lemnisci of this body, are especially suggestive of associating auditory impulses with eye movements. All the fibres arising in the superior ohvary nucleus do not enter the corpus trapezoideum and the lateral lemniscus. A small bundle, the peduncle of the superior olive, arises in each nucleus and courses dorsally to the region of the nucleus of the abducens. Here certain of its fibres terminate about the cells of the nucleus of the abducens, while others enter the medial longitudinal fasciculus and pass to the nuclei of the trochlear and oculomotor nerves, thus further establishing connections between auditory impulses and eye movements. The facial nerve is commonly described as consisting of the "facial proper" and its so-called sensory root or pars intermedia, the two together being designated as the seventh cranial nerve. However, the pars intermedia neither serves as a sensory root for the facial nor is it purely sensory. Many years ago Sapolini considered it a separate nerve and later it was called the intermediate nerve of Wrisberg. More recent investigations of its development and distribution, especially those of Streeter and Sheldon, further indicate that it merits a separate description Fig. 651. — Transverse Section through Inferior Border op Pons and Portion of Overlying Cerebellum (From ViUiger.) Nucleus of roof Nucleus globosus Nucleus emboliformis- Dentate nucleus Superior nucleus of vestibular (Becht Lateral nucleus of vestibular (Deiters') Spinal tract of trigeminus ' \\ Nucleus of facial M|fw^»~~ K estif orm body Superior olive Thalamo-ohvans tract and a separate name, and, indicative of its distribution, it is here described as the glosso-palatine nerve. The facial, the glosso-palatine and the abducens all have their nuclei within the level of the pons though the roots of all appear from under its inferior border. The facial [nervus faciahs] has its nucleus (of origin) in the ventro-lateral region of the reticular formation, superior to and in line with the nucleus ambiguus. The axones given off by the cell-bodies of the nucleus collect into a bundle which, instead of passing ventrally and directly to the exterior of the pons, courses at first dorso-mesially to the mesial side of the nucleus of the abducens (ascending root of the facial) ; then it turns and courses superiorly for a few milli- metres, parallel with the nucleus of the abducens and immediately beneath the floor of the fourth ventricle {genu internum); then it turns abruptly and pursues a ventro-lateral and inferior direction to its point of exit at the inferior border of the pons, just lateral to the olive and mesial to the entrance of the vestibular nerve. Its exit usually involves a few pons fibres. In transverse sections through the middle of the nucleus of the abducens the genu of the facial appears as a compact transversely cut bundle at the dorso-medial side of this nucleus. The nucleus of the facial is described as consisting of two chief groups of cells, an anterior and a posterior group which give rise respectively to the axones of the superior and inferior branches of the facial nerve. It receives cortical impulses from the lower portion of the anteiior central gjTus of the cerebral cortex, from the root fibres of the trigeminus of the same side, which serves as its sensory root, and (chiefly) fibres arising from the nuclei of termination of the trigeminus. The nuclei of termination of the optic and the auditory nerves of the same and opposite sides give rise to fibres which terminate about its cells. The fibres from the cerebral cortex descend in the pyramidal fasciculi and cross by way of the raphe and arcuate fibres to terminate in the nucleus of the opposite side. The anterior group of the cells of the facial nucleus must receive cortical fibres not only from the cerebral hemisphere of the opposite but also from that of the same side, evidenced by the fact that the superior branch of the nerve is but little affected in facial paralysis resulting from a lesion in the cerebral cortex of one side. A lesion destroying the root of the nerve or its nucleus of origin will of course give total facial paralysis in the side of the lesion. 826 THE NERVOUS SYSTEM The glosso-palatine nerve {nervus intermedius, sensory root of facial, etc.) is a mixed nerve but largely sensory. It accompanies the facial from a short distance beyond the geniculum (genu externum) of the facial to its attachment to the brain stem. Its sensory fibres arise as T-fibres of the cells of the geniculate ganglion (at the geniculum of the facial) . The peripheral processes go aa the chorda tympani to supply the epitheUum of the anterior part of the tongue and that of the palate, especially of the palatine arches. The central processes enter the brain stem, bifurcate into caudal and cephahc branches, and find their nucleus of termination in a superior extension of the nucleus of the solitary tract (the ventral portion of the nucleus of the ala cinerea). The geniculate ganghon contains some ceU-bodies of sympathetic neurones, left over in it during the period of migration form its homologue of the ganglion crest. The efferent fibres of the glosso-palatine arise from ceU-bodies lying dorso-medial to the nucleus of the facial and in the level between this and the nucleus of the masticator nerve superior to it. Its cells are usually scattered in the reticular formation in Mne with the dorsal efferent nucleus of the vagus. Since most of its fibres, at least, are concerned with sympathetic neurones (terminate in sympathetic gangha) and convey secretory impulses destined for the salivary glands, it has been called the nucleus salivatorius. Fig. 652. — Transverse Section through Pons and Portion of CEREBELLtrM at Level OP Nuclei and Root Filaments of Abducens and Facial Nerves. (From Villiger.) Nucleus globosus Nucleus emboliformis Brachium conjunctivum Restiform body Tractus thalamo-olivaris Corpus trapezoideum and medial Fourth ventricle Brachium conjunctivum Genu of facial nerve (pars ascendens n. facialis) Tractus nucleo-cerebellaris Nucleus of abducens Nuclei and root of ~ trigeminus Brachium pontis Nucleus reticularis tegmenti Beep stratum of pons Superficial stratum of pons Pyramid Medial stratum of pons The abducens is a smaU, purely motor nerve, which suppUes the lateral rectus muscle of the eye. Its nucleus of origin Hes close to the mid-line in the medial eminence of the floor of the fourth ventricle, and in line with that of the hypoglossus. Its root-fibres, uncrossed, pursue a ventral course, inclining a Httle laterally and curving inferiorly to emerge from under the inferior border of the pons. They pass lateral to the pyramid, and often between some of its fascicuh. The nucleus receives cortical or voluntary impulses by way of the pyramidal fascicuU chiefly of the opposite side. Its connection with the auditory apparatus and the medial longitudinal fasciculus has already been noted. It probably receives afferent impulses through the fibres of the trigeminus as well as by fibres descending from the nuclei of termi- nation of the optic nerve. It is also associated, by way of the medial longitudinal fasciculus, with the nucleus of the oculomotor nerve of the same and opposite sides. The trigeminus is considerably larger than any of the nerves inferior to it, and has the most extensive central connections of any of the cranial nerves. It is a purely sensory nerve which enters through the brachium pontis in line with the facial nerve. It serves as the nerve of general sensibility for the face from the vertex of the scalp downward, and thus it corresponds to the afferent fibres (dorsal root) for all the nerves giving motor supply to structures underlying its domain. Its fibres arise from its large, trilobed, semilunar (Gasserian) ganglion, situated outside the brain. This corresponds to the dorsal root ganglion of a spinal nerve, and its cells give off the characteristic T-fibres with peripheral and central branches. The central or afferent branches upon entering the brain-stem bifurcate into ascending and descending divi- sions, just as the entering dorsal root-fibres of the spinal nerves, and find their nucleus of ter- mination in a dorso-lateral column of grey substance, lying deeply and extending longitudinally through the brain stem, and consisting of the upward continuation of the gelatinous substance of Rolando of the spinal cord. Opposite the entrance of the nerve is a considerably thickened portion of this column of grey substance, known as the sensory nucleus of the trigeminus, and the remainder below is called the nucleus of the spinal tract (fig. 647). Both parts are equally "sensory." After bifurcation the branches of the entering fibres of the trigeminus terminate about the cells of these nuclei. The descending branches are much longer than the ascending, NUCLEI OF CRANIAL NERVES 827 Fig. 653. — Dkawing of Model of Bbain-stem showing the Nuclei of Origin of the Motor Cranial Nerves. (After Sabin.) 828 THE NERVOUS SYSTEM and in passing downward form the spinal tract of the trigeminus, weU marked in aU transverse sections of the meduDa oblongata figs. 641, 642, 643, 649). The spinal tract decreases Snfdfv m descendmg the medulla, owing to the rapid termination of its fibr1L"n the nucleus ofthetmct^^ ^'^■fi^'^^''*'^'''^'^ Illustrating the Principal Central Connections of the Trigeminus orP™lMIDAL°FlBRET'''' ^""^^^'^^ °^ ^HEIR RELATIONS TO DESCENDING CeR^rIl Mesencephalic nucleus and root of masti- cator nerve Medial lem- niscus Medial longi- tudinal fasciculus \ Masticator nerve \ Semilunar ganglion ■Fasciculus proprius It has been traced as far down as the second cervical segment of the spinal cord. The ascending Pvt.n«i^n ^^^ f^'^l' T'* °^ *^^'^, terminate in the 'sensory nucleus,' and, therefore, the extension upward into the mesencephalon of the nucleus of termination of the trigeminus is both shorter and more scant than the spinal extension. Axones from the nucleus of termination of the trigeminus are distributed— (1) to the nuclei 01 masticator nerve of the same and opposite sides (short or simple reflex fibres); (2) to the INTERNAL STRUCTURE OF THE PONS 829 nuclei of the other motor cranial nerves, especially of the facial; (3) to the thalamus of the same and chiefly the opposite side, and thus, through interpolation of thalamic neurones, their impulses reach the somaisthetio area of the cerebral cortex. These fibres ascend in the recticular formation of the opposite side, most of them finally coursing strictly withia the medial lemniscus. In crossing the mid-line they contribute to the internal arcuates. (4) Some fibres of both the trigeminus direct and from its nucleus pass laterally into the cerebellum. The longer of the reflex or association axones arising in the nucleus of termination may contribute to the medial longitudinal fasciculus; many of them descend to terminate in the grey substance of the spinal cord below the levels in which the fibres of the spinal tract proper terminate. The nucleus of termination is directly homologous to the nuclei of the fasciculus graciUs and fasci- culus cuneatus, and, like the nuclei of termination of all sensory cranial nerves, it contains cell-bodies homologous to those which give rise to the fasciculi proprii and commissural fibres of the spinal cord. The masticator nerve [porlio minor n. irigemini] is a purely motor nerve, usually called the motor root of the trigeminus from the fact only that it makes its exit from the pons by the side of the entering fibres of the trigeminus, passes outward over the ventro-mesial side of the semilunar ganglion and accompanies the inferior maxiUary division (mandibular nerve) of the trigeminus till it divides totally into its branches for the motor supply of the muscles of mastica- tion. It serves, therefore, as but a relatively small part of the "motor root" of the trigeminus. The nucleus of origin of the masticator nerve is attenuated into two parts: (1) The chief nucleus (nucleus princeps) lies on the dorso-medial side of the larger portion (sensory nucleus) of the nucleus of termination of the trigeminus. It is the larger of the two parts and gives origin to much the greater part of the masticator. (2) Scattered anteriorly and continuous Fig. 655. — Transverse Section Through i Upper Part of Pons at the Level of the Entrance op the Trigeminus. (From Villiger.) Anterior medullary velum Gowers' tract- Fourth ventricle Fasc. long, dorsalis (Schiitz) Medial longitudinal fasciculus Corpus trapez. and medial lemniscus Deep stratum of pons Brachium conjunctivum Sensory nucleus of trigeminus Chief nucleus of ma ticator nerve Thalamo- olivary tract Lateral aJ lemniscus JS^ Brachium pontis Superficial stratum of pons with the chief nucleus, in line with the locus coci'uleus, are the cell-bodies usually described as the nucleus of the mesencephalic (descending) root. These cells lie in decreasing linear distribu- tion, through the mesencephalon, as far anterior as the posterior commissure of the cerebrum, and the mesencephalic root of the nerve accumulates as it descends to join the exit of the fibres arising from the chief nucleus. The average diameter of its cells is somewhat less than for the chief nucleus. It is not clearly settled that the fibres arising from the mesencephahc nucleus of the masti- cator nerve go to the muscles of mastication. As suggested by KoUiker, some of these may supply the tensor veli palatini and tensor tympani muscles. Recent investigations of lower ani- mals by Johnston and Willems indicate that the mesencephalic root may contain no motor fibres at all, representing instead a portion of the sensory trigeminus fibres. It is claimed that some fibres in descendtug give off collaterals which terminate about cells in the chief nucleus, and thus an impulse descending by them is given a wider distribution and also reinforced by the interpolation of another neurone. Such fibres, however, maj' be the sensory fibres just mentioned terminating upon the cells of the nucleus to form simple reflex arcs. It is claimed that each masticator nerve receives a few fibres arising from the cells of the nucleus of that of the opposite side. Both parts of the nucleus of the masticator receive afferent impulses brought in by the trigeminus of the same (chiefly) and of the opposite side, and both receive cortical impulses by fibres from the inferior portion of the precentral gyrus which descend in the cerebral ped- uncles and cross to terminate in the nucleus of the opposite side. The internal structure of the pons. — The nuclei and roots of the trigeminus, masticator, abducens, facial, glosso-palatine, cochlear and vestibular nerves are extended within the level 830 THE NERVOUS SYSTEM of the pons, and their position and course have been described above. The pons proper (the bridge) consists of a mass of transversely running fibres continuous on either side into the brachia pontis or middle cerebellar peduncles. In the animal series the relative amount of these fibres varies with the size of the cerebellum upon which they are dependent. They are relatively more abundant in man than in other animals. In transverse sections the pons fibres are seen to course ventrally about the main axis of the brain-stem, making it possible to divide the section into a basilar or ventral part and a dorsal part {tegmentum). The fibres in their transverse and ventral course around the medulla oblon- gata involve the pyramids. At the inferior border of the pons the fibres little more than separate the pyramids as such from the main axis of the brain-stem, but more superiorly the pons fibres pass through the pyramids, splitting them into the pyramidal fasciculi. These pyramidal or chief longitudinal fibres of the pons are the continuation of the basal portion of the cerebral peduncles through the pons, to emerge as the pyramids proper at its inferior border. They occupy an intermediate or central area among the pons fibres of either side, leaving the periphery of the pons uninvaded. The superficial pons fibres form the solid bundle of its ventral and lateral periphery and the deep pons fibres form similar bundles dorsaUy enclosing the area of pyramidal fasciculi (fig. 655). In transverse sections through the inferior portion of the pons, the dorsal or tegmental part consists of structures continuous with and analogous to the structures of the meduUa oblongata immediately below, exclusive of the pyramids. In addition, this region contains the superior ohvary nucleus and the corpus trapezoideum. The significance of these structures and their relation to the nucleus of termination of the cochlear nerve is shown in figs. 650, 651 and 652. In this region the lemniscus (fillet) changes from the sagittal to the coronal plane, and its Fig. 656.- -DiAGBAM SHOWING THE RhOMBENCEPHALIC CoUBSE OP GOWEBS' TrACT AND THE Direct Cerebellar Tract. Brachium conjunctivum Dorsal spino-cerebellar fasciculus (direct cerebellar tract) Superficial antero-lateral spino-cerebellar fasciculus (Gowers' tract) lateral edges are becoming drawn outward and carry the lateral lemniscus of the regions superior to this. The medial longitudinal fasciculus, left alone by the change in the arrangement of the leminscus, maintains its dorsal position throughout the pons and into the mesencephalon above. The thalamo-olivary tract appears loosely collected in the dorsal part of the pons, dorso-medial to the nucleus of the superior olive. The restiform body acquires in this inferior region a more dorso-lateral position than in the medulla below. Its fibres are beginning to turn upward in their course to the cerebellum mesial to the brachium pontis. Here the restiform body is nearing completion, and the fibres now contained in it may be summarised as foUows: — (1) The fibres of the dorsal spino-cerebellar fasciculus (direct cerebellar tract) of the same side. (2) Fibres from the nuclei of the fasciculus gracilis and fasciculus cuneatus of the same and opposite side (external arcuate fibres). (3) Fibres to and from the inferior olives of the same and (chiefly) the opposite side (cere- bello-olivary fibres). (4) Sensory cerebellar fibres from the nuclei of termination of the vagus, glosso-pharyngeus, vestibular and trigeminus, vestibular especially, and from the cells of the reticular formation. (5) Descending fibres to the motor nuclei of the vagus and glosso-pharyngeal, and fibres descending into the anterior marginal fasciculus of the spinal cord, the latter, however, being in large part interrupted by cells in the nuclei of the vestibular nerve. (6) A few fibres arising from the arcuate nuclei. These nuclei are continuous superiorly with the nuclei of the pons and some of their fibres are described as entering the cerebellum by way of the restiform body instead of by way of the brachium of the pons as in the levels above. The ascending fibres of the restiform body are distributed to the cortex of the vermis, the nucleus of the roof (fastigii), the nucleus dentatus, nucleus emboliformis, and nucleus globosus. Very few if any of the fibres ascending the cord in Gowers' tract enter the cerebellum by way of the restiform body. This tract (the superficial antero-lateral spino-cerebellar fasciculus) GREY SUBSTANCE OF THE PONS 831 ascends the medulla, dispersed in the reticular formation, and therefore in a more ventral posi- tion than that of the direct cerebellar tract. In this position it becomes enclosed by the fibres of the pons, and so it passes upward, beyond the pons, around the lateral lemniscus to the brachium conjunctivum, and there turns back to enter the cerebellum by way of its supe- rior peduncle. Certain clinical phenomena, probably purely psychological, have been alleged to indicate that some of the fibres of Gowers' tract pass on to the cerebrum instead of turning in the medullary velum to enter the cerebellum. The dorsal part of a transverse section through the upper part of the pons contains the superior cerebellar peduncles [brachia conjunctiva] instead of the restiform bodies or inferior peduncles. Instead of the cerebellum forming the roof of the fourth ventricle, in this region the roof is formed by the anterior medullary velum bridging the space between the two brachia conjunctiva. Adhering upon the meduUary velum is the lingula cerebelli — the superior and ventral extremity of the superior vermis. This is the only portion of the cerebellum attached to this region. The lemniscus (fUlet) is found more lateral than at the inferior border of the pons, and is divided into the medial lemniscus and lateral lemniscus proper. The lateral lemniscus has shifted dorsally until in this region it courses in the dorso-lateral margin of the section external to the brachium conjunctivum. The mesencephalic root of the masticatornerve occurs in the dorso- FiG. 657. — Diagram showing Connections op the Fibres of the Pons. The plane of the section is obliquely transverse or parallel with the direction of the brachia pontis J]^ —— Restiform body Medial descending cerebro-pontile path •^Medial lemniscus Longitudinal (pyramidal) fasciculi lateral margin of transverse sections through this region, and this and the trigeminus are the only cranial nerves represented here. The transverse fibres of the ventral part of the section (pons proper), and therefore the brachia pontis, consist of fibres coursing in opposite directions. Many are fibres which are out- growths of the Purkinje cells of the cortex of the cerebellar hemispheres, and pass either directly to the cerebellar hemisphere of the opposite side or turn dorsalward in the raphe to course longitudinally in the brain-stem both toward the spinal cord and toward the mesencephalon. Others terminate in the grey substance (nuclei) of the pons. Others are fibres which arise in the grey substance of the pons and pass to the cerebellar hemispheres, and still others are the cerebro-pontile fibres, from the temporal, occipital and frontal lobes. The grey substance of the pons [nuclei pontis 1 occurs quite abundantly. At the inferior border of the pons it is found concentrated about the then more accumulated bundles of the emerging pyramids, and serial sections show it to be a direct upward continuation of the arcuate nuclei of the medulla oblongata below. Higher up it is dispersed throughout the central area in the interspaces between the transverse pontile and longitudinal pyramidal fasciculi. A large portion of the nerve-fibres passing through it are thought to iDe interrupted by its cells, which thus serve as links in some of the neurone chains represented by the fibres of the pons. Of the more important of such relations, the following are said to exist: — (1) Fibres which arise in the cortex of one cerebellar hemisphere and terminate about cells of the nucleus pontis of the same and opposite side of the mid-line. These cells give off axones which pass to the other cerebellar hemisphere. In this relation the nuclei of the pons are analogous to the arcuate nuclei, save that the cerebellar fibres interrupted in the former are connected with the cerebellum by way of the brachia pontis instead of the restiform bodies. 832 THE NERVOUS SYSTEM (2) Certain of the descending oerebro-pontile fibres terminate about cells of the nuclei of the pons. Such cells give off fibres which probably, for the most part, pass to the cerebellar hemispheres, the impulses from the cerebral hemisphere of one side being conveyed to the opposite cerebellar hemisphere. Most of the descending cerebro-pontile fibres are thought to cross the mid-line to terminate about cells of the nuclei of the pons of the opposite side, a rela- tion not sufficiently emphasised in the accompanying diagram (fig. 657). Of the cerebro-pontile paths, the frontal pontile path (Ai-nold's bundle) is described as arising in the cortex of the frontal lobe (frontal operculum) passing in the anterior portion of the internal capsule down into the medial part of the base of the cerebral peduncle, and terminat- ing in the grey substance of the pons. The descending temporal pontile path, sometimes caOed Turk's bundle, arises in the cortex of the temporal lobe, traverses the posterior portion of the internal capsule, lies lateral in the pyramidal portion of the cerebral peduncle, and termi- nates in the grey substance of the pons. In the posterior part of the internal capsule, the tem- poral pontile path is joined by a small bundle arising in the occipital lobe and going to the pons nuclei. This, supposedly smaller than the other two, adds an occipito-pontile path. The total area in cross section of the pyramidal fasciculi as they enter the pons above is considerably greater than that which they possess as they emerge as the pyramids of the medulla below. The difference is considered very appreciably greater than can be explained as due to the loss of pyramidal fibres supplied to the nuclei of origin of the cranial nerves lying within the level of the pons, and the additional difference is explained as due to the termination within the pons of the oerebro-pontile paths. THE ISTHMUS OF THE RHOMBENCEPHALON The isthmus of the rhombencephalon is nothing more than the transition of the metencephalon into the mesencephalon above. It is quite short and com- prised of only the structures which run through it, namely, the brachia conjunc- tiva (superior peduncles of the cerebellum), the anterior medullary velum, the lateral sulcus of the mesencephalon, the cerebral peduncles, and the inferior end of the interpeduncular fossa. It surrounds the superior extremity of the fourth ventricle. The lateral and medial lemnisci, the superior extension of the nucleus of the trigeminus, the mesencephalic nucleus and root of the masticator nerve and Gowers' tract extend through it. At the mid-line, just inferior to the inferior quadrigeminate bodies is the frenulum of the anterior medullary velum and the trochlear nerves, emerging at the sides of this, course ventrally around the sides of the isthmus. In the lateral sulcus, the isthmus shows usually a small triangular elevation known as the trigonum lemnisci from the fact that the lateral lemniscus tends toward the surface in this region. Functions of the cerebellum. — From the above descriptions involving the structures of the metencephalon, it may be noted (1) that a given side of the cerebellum is associated chiefly with the same side of the general body and with the opposite side of the cerebrum. (2) That it receives afferent impulses from the spinal cord (brought into the cord by the dorsal roots of the spinal nerves) by way of the direct cerebellar fasciculus of the same side, and by Gowers' tract and from the nuclei of the fasciculus gracilis and cimeatus of the same and opposite sides. It further receives afferent impulses from the nuclei of termination of the trigeminus, glosso- pharyngeal and vagus of the same side chiefly, and especially does it receive afferent impulses from the nuclei of the vestibular nerve of the opposite and same side. (3) That the cerebellum sends impulses to the red nucleus, the thalamus and the cerebral cortex of the opposite side, and some of its fibres terminate in the nuclei of termination of the vestibular nerve and probably some fibres arising in its roof nuclei descend into the spinal cord direct. (4) That the cerebel- lum receives impulses from the thalamus of the opposite side by way of the thalamo-olivary tract and the inferior olive, and especially from the cerebral cortex of the opposite side by way of the frontal, temporal and occipital pontile paths and the nuclei of the pons. Further, fibres from the general pyramidal fascicuh are described as terminating about ceUs of the nuclei of the pons. Taking into consideration these known associations of the cerebellum, the anatomically possible paths which in part may distribute cerebellar impulses to the grey substance sending efferent fibres to the peripheral tissues are (1) the general pyramidal fasciculi whose cortex of origin may receive impulses by fibroi proprioe from the cortical areas receiving impulses from the cerebellum. The pyramidal fasciculi, decussating, distribute impulses to the grey substance of i the medulla and cord of the same side as that from which the cerebeUo-cerebral impulses passed to the cortex. (2) The lateral vestibulo-spinal and the anterior marginal fasciculi to the ventral horn of the spinal cord of the same side, probably carrying impulses descending from the cerebellum as well as impulses brought in by the vestibular nerve and descending direct from its nuclei of termination into the spinal cord. (3) The rubro-spinal tract of the cord and probably some of the thalamo-spinal fibres (corpora-quadrigemina-thalamus path), the red nuclei and thalami being associated abundantly with the cerebellum. These tracts Hkewise decussate in descending but likewise do the cerebellar impulses ascending to their cells of origin. Whatever other functions it may possess, developmental defects and pathologic lesions show that the cerebellum has to do with the equilibration of the body and the finer coordinations, adjustive control of the contractions of functionally correlated groups of muscles. Making this THE MESENCEPHALON 833 possible, in part at least, it is seen above that is it associated (1) directly with the special nerve of equihbration, the vestibular; (2) with the optic apparatus by way of the thalamus, and (3) with the afferent impulses from the general body, by way of the direct cerebellar and Gowers' tracts, by way of the nuclei of the fasciculus gracilis and cuneatus, and the nuclei of termination of the trigeminus, glosso-pharyngeal and vagus. It has been suggested that by way of these latter paths the cerebellum deals especially with those general afferent impulses which arise within the muscles of the body (neuro-musoular spindles, etc.) and which are grouped under the name "muscular sense." The cerebellum can be considered as an enlarged and modified por- tion of the grey substance of the spinal cord, receiving a greater number and variety of afferent impulses and with them mediating more comprehensive and complicated reflex activities than is possible with the less abundant grey substance of a given portion of the cord proper. SUMMARY OF PRINCIPAL STRUCTURES IN RHOMBENCEPHALON A. Gross Exterior. 1. Medulla Oblongata (Myelencephalon). f Cerebellum I Hemispheres — lobes and lobules. I I Vermis — lobules and lingula. 2. Metencephalon \ Pons { Dorsal part (preoblongata). ^ y Ventral part (pons proper). I superior — brachium conjunctivum. [ Cerebellar peduncles \ middle — brachium of pons. [ inferior — restiform body. 3. Isthmus of Rhombencephalon. 4. Fourth Ventricle and its Chorioid tela. 5. Anterior and Posterior Medullary Vela. B. Grey and White Substance. 1. Funiculus gracilis, nucleus of fasciculus gracihs, funiculus cuneatus, nucleus of fasciculus cuneatus. 2. Internal and external arcuate fibres, decussation of lemnisci, lemniscus, medial lemniscus, lateral lemniscus. 3. Cerebral peduncles, pyramidal fasciculi, pyramids, decussation of pyramids, arcuate nuclei. 4. Superficial and deep strata of pons, nuclei of pons, branchia of pons. 5. Inferior olivary nuclei, cerebello-olivary fibres, thalamo-olivary tract, spino-olivary tract. 6. Nuclei emboliformis, globosus and fastigii (of the roof), and nucleus dentatus with bra- chium conjunctivum of cerebellum. 7. Central gelatinous substance and gelatinous substance of Rolando. 8. Reticular formation. 9. Hypoglossal nerve and nucleus of hypoglossal. 10. Spinal accessory nerve and lateral nucleus. 11. Vagus and glossopharyngeal nerves, nucleus of ala cinerea, solitary tract and nucleus of solitary tract, commissural nucleus of ala cinerea, nucleus ambiguus, dorsal efferent nucleus of vagus. 12. Vestibular nerve — its superior nucleus (Bechterew), its medial nucleus (Schwalbe), its lateral nucleus (Deiters), and the nucleus of its descending (spinal) root. 13. Cochlear nerve, dorsal nucleus and ventral nucleus of cochlear, acoustic medullary striae, nucleus of superior olive, trapezoid body, nucleus trapezoidei, lateral lemniscus, nucleus of lateral lemniscus. 14. Facial nerve and nucleus of facial nerve. 15. Glosso-palatine nerve, nucleus of glosso-palatine and nucleus salivatorius. 16. Abducens and nucleus of abducens. 17. Trigeminus, "sensory nucleus" of trigeminus, spinal tract and nucleus of spinal tract of trigeminus. 18. Masticator nerve, chief nucleus and (so-called) mesencephaUc nucleus and root of masticator. 19. Medial longitudinal fasciculus. 20. Nucleus intercalatus, nucleus of median eminence, nucleus incertus. THE CEREBRUM 1. THE MESENCEPHALON The mesencephalon or mid-brain is that small portion of the encephalon which is situated between and connects the rhombencephalon below with the prosen- cephalon above. It is continuous with the isthmus rhombencephali, and occupies the tentorial notch, the aperture of the dm-a mater which connects the meningeal cavity containing the cerebellum with that occupied by the prosencephalon. Its greatest length is about 18 mm., and it is broader ventrally than dorsally. Its dorsal surface is hidden by the overlapping occipital lobes of the cerebral hemis- pheres. It consists of — (1) the lamina quadrigemina, a plate of mixed grey and white substance which goes over lateralward and below into (2), the cerebral 834 THE NERVOUS SYSTEM peduncles (crura) and their tegmental structures, and it contains (3), the nuclei of origin of the trochlear and oculomotor nerves. It arises from thickenings of the walls of the middle cerebral vesicle of the embryo, the lamina quadrigemina arising from the dorsal or alar lamina of this portion of the neural tube, while the basal lamina thickens to form the nuclei of the nerves, the substantia nigra, etc., and by the ingrowing of the cerebral peduncles. By means of the lamina quad- rigemina roofing it over, the neural canal throughout the mesencephalon retains its tubular form and is known as the aquaeductus cerebri (Sylvii) , connecting the cavity of tlie fourth ventricle below with that of the third ventricle above. External features. — Dorsal surface. — The lamina quadrigemina shows four well-rounded elevations, the quadrigeminate bodies [corpora quadrigemina], divided by a flat median groove crossed at right angles by a transverse groove. The anterior pair of these, the superior quadrigeminate bodies [colliculi], are Fig. 668. — Dorsal Surface op Mesencephalon and Adjacent Parts. (After Spalteholz.) Epiphysis (lifted) Taenia cliorioidea ■Camina affiza Supi Brachium quadn geminum superiu Bracliium quadn geminum Infenus ^ Medial genicu late body lateral genicu- late body Cerebral peduncle Inferior colhculus Frenulum of anterior med ullary velum Trigone of lemniscus Trochlear nerve Brachium conjunctivum Lateral filaments of pons- " Trigeminus — Lingula of vermis Vinculum of lingula Brachium of pons Cerebellum (cut) larger though less prominent than the inferior pair or inferior colliculi. Each colliculus is continued laterally and upward into its arm or brachium. The inferior brachium proceeds from the inferior colliculus, disappears beneath and is continuous into the medial geniculate body, and enters the thalamus. The supe- rior brachium proceeds from the superior colliculus, disappears between the medial geniculate body and the overlapping pulvinar of the thalamus, and becomes con- tinuous with the lateral geniculate body and thus with the lateral root of the optic tract. The geniculate bodies are rounded elevations of grey substance which arise as detached portions of the thalami, and therefore belong to the thalamencephalon rather than to the mesencephalon. The superior quadrigeminate body or superior colliculus and the lateral gen- iculate body are a part of the optic apparatus, while the inferior colliculus and the medial genicu- late body belong chiefly to the auditory apparatus (see Central Connections of Cochlear Nerve). Just as the terminal cochlear nuclei are connected by a few fibres with the superior colliculus, so do some fibres from the optic tract pass mto the inferior colliculus. Also some fibres form the optic tract (mesial root) are said to terminate in the medial geniculate body. Resting in the broadened medial groove between the superior quadrigeminate bodies lies the non-nervous epiphysis or pineal body. This also belongs to the thalamencephalon. Under the stem of the epiphysis is a strong transverse band of white substance crossing the THE MESENCEPHALON 835 mid-line as a bridge over the opening of the cerebral aqueduct into the third ventricle. This is the posterior commissure of the cerebrum, and contains commissural fibres arising in both the thalamencephalon and mesencephalon. The triangular area bounded by the stem of the epi- physis, the thalamus, and the superior coUiculus with its brachium, is known as the habenular trigone. Inferiorly, the lamina quadrigemina is continuous with the isthmus of the rhombencephalon by way of the brachia conjunctiva or superior cerebellar pedun- cles, and the anterior medullary velum which bridges between the mesial margins of these peduncles. The narrowed upper end of the velum, the part directly below the inferior quadrigeminate bodies, is thickened into a well-defined white band known as the frenulum veil. From the lateral margins of this band on each side and just below the inferior quadrigeminate bodies emerge the trochlear nerves (the fourth pair of cranial nerves), and the increased thickness of the band is largely due to the decussation of this pair of nerves taking place within it. The brachium conjunctivum, together with the inferior and superior colliculi of each side, form a marked ridge which results in the lateral sulcus of the mesen- cephalon, a lateral depression between the base of this ridge and the cerebral peduncle below and continuous into the transverse sulcus at the superior border Fig. 659. — Diagram op Lateral View of Mesencephalon and Adjacent STRtrcTURES. (After Gegenbaur, modified.) Pulvinar of thalamus Lateral geniculate body Cerebral peduncle Epiphysis Medial geniculate body Quadrigeminate bodies iuJ ^ Lateral lemniscus Superior cerebellar peduncle Middle cerebellar peduncle Inferior cerebellar peduncle of the pons. The ridge is thickened laterally by the lateral lemniscus, which is disposed as a band of white substance passing obhquely upward from under the brachium pontis, applied to the lateral surface of the brachium conjunctivum and which enters the lateral margin of the mesencephalon. The region at which the lateral lemniscus approaches nearest the surface and in which the largest portion of its nucleus lies is the slightly elevated trigone of the lemniscus. The ventral surface of the mesencephalon is formed by the cerebral peduncles (crura), two large bundles of white substance which are close to one another at the superior margin of the pons, but immediately diverge somewhat, producing the interpeduncular fossa, and in so doing pass upward and lateralward to disap- pear beneath the optic tracts (fig. 629) . The posterior recess of the interpeduncu- lar fossa extends slightly under the superior margin of the pons, while its anterior recess is occupied by the corpora mammillaria of the prosencephalon. The tri- angular floor of the fossa is the posterior perforated substance, a greyish area presenting numerous openings for the passage of blood-vessels. It is divided by a shallow median groove and is marked off from the medial surface of each peduncle by the oculomotor sulcus, out of which emerge the roots of the oculomotor nerves. The ventral surface of each peduncle is rounded and has a somewhat twisted appearance, indicating that its fibres curve from above medialward and downward. Sometimes two small, more or less transverse bands of fibres may be noted crossing the peduncle — an inferior, the tcenia pontis, and a superior, the transverse pedun- 836 THE NERVOUS SYSTEM cular tract. The inferior represents detached fibres of the pons; the superior, running from the brachium of the inferior quadrigeminate body and disappearing in the oculomotor sulcus, appears to be derived from the quadrigeminate bodies. Since it is well developed in the cat, dog, sheep, and rabbit, but is absent or little marked in the mole, it is supposed to be concerned with the optic apparatus. Internal structure. — Transverse sections of the mesencephalon throughout are composed of — (1) a dorsal -part, consisting of the lamina quadrigemina or the grey sulDstance of the corpora quadrigemina, with the strata and bundles of nerve-fibres connected with them, and the abundant central grey .substance sm-rounding the aqueduct; (2) a tegmental part, consisting of the upward con- tinuation of the reticular formation of the medulla oblongata and that of the Fig. 660. — Transverse Section Through the Inpekior Quadrigeminate Bodies. Central grey substance Stratum zonaIe-~, Aqueduct of-^ & cerebrum / ~ - Nucleus of mesen- cephalic (descend- , ing) root of masti- y't^ ^ cater ■'^ »■ Nucleus of trochlear - nerve of lateral lemniscus Lateral lemniscus (acoustic) Thalamo-olivary tract Medial lemniscus Decussation of brachia conjunctiva Posterior recess of in^ terpeduncular fossa Substantia nigra Basis of cerebral peduncle Superficial stratum of pons dorsal (tegmental) portion of the pons region, to which are added the superior cerebellar peduncles and the red nuclei of the tegmentum in which these peduncles terminate; (3) a paired ventral part, the cerebral peduncles, each of which consists of a thick, pigmented stratum of grey substance, the substantia nigra, spread upon the large, superficial, and somewhat crescentic tract of white substance known as the basis of the peduncle. The cerebral peduncles correspond to the longitudinal or pyramidal fasciculi of the pons and medulla. Likewise the lemniscus and the medial longitudinal fasciculus of the medulla and pons continue through all sections of the mesencephalon. The central grey substance is a continuation of the central gelatinous substance of the spinal cord and the similar stratum of the medulla and that which immediately underlies the ependyma of the fourth ventricle. As in the spinal cord and medulla, it is largely composed of gelatinous substance. It is much more abundant in the mesencephalon, and in sections appears as a cir- cumscribed area comparatively void of nerve-fibres. The nucleus of the mesencephalic root of the masticator nerve may likewise be traced through- out the mesencephalon. It consists of a few small bundles of fibres surrounding a thin strand THE MESENCEPHALON 837 of nerve-cells which give origin to its fibres. It courses caudalward close to the lateral margin of the central grey substance, and is quite small at its beginning in the extreme superior part of the mesencephalon, but as it descends toward the exit of its fibres from the pons, it increases slightly in size, due to the progressive addition of fibres. Its nucleus also increases sUghtly in bulk in approaching the region of the chief motor nucleus of the nerve. As mentioned above, the investigations of Johnston and Willems in lower animals suggest that the cells of the mesencephalic nucleus may be sensory instead of motor in character. The sensory nucleus (nucleus of termination) of the trigeminus tapers rapidly and probably does not extend throughout the mesencephalon. The nuclei of the trochlear and oculomotor nerves form a practically continuous column of nerve-cells extending close to the mid-line and ventral to the aqueduct of the cerebrum. They are in hne with the nuclei of origin of the abducens and hypoglossus, and, like them, may be regarded as an upward continuation of the ventral group of the cells of the ventral horn of the spinal cord. The portion of the column giving origin to the oculomotor nerve is considerably larger than that for the trochlear. Fig. 661 . — Diagrams showing the Course op Origin of the Trochlear Nerves. (Stilling. The upper figure shows roughly the entire central course of the trochlear nerves; the lower rep- resents their region of exit in transverse section. Aquasductus cerebri of trochlear, nerve TT'^A (^■' Decussation of trochlear nerves \ , Trochlear nerve ^- — - — ' i-i — — -V Aquaeductus cerebri r w. 'X — Mesencephalic root \ \\ \ of masticator "' ^'- ■■ Brachium conjunctivum Lateral lemniscus A transverse section through the inferior quadrigeminate bodies involves a portion of the decussation of the brachia conjunctiva and the nuclei of origin of the trochlear nerves, while a transverse section through the superior quadri- geminate bodies passes through the red nuclei of the tegmentum and the nuclei of origin of the oculomotor nerves. The latter section will also involve the brachia of the inferior quadrigeminate bodies and the medial geniculate bodies connected with them, and, if slanting slightly forward it will involve the pul- vinars of the thalami and the lateral geniculate bodies. The trochlear or fourth nerve is the smallest of the cranial nerves, and is the only one which makes its exit from the dorsal surface of the brain, as well as the only one whose fibres undergo a total decussation. Its nucleus of origin is situated beneath the inferior quadrigeminate bodies in the ventral margin of the central grey substance, quite close to the mid-line and to its fellow nucleus of the opposite side, and it is closely associated with the dorso-mesial margin of the medial longi- tudinal fasciculus. Its root-fibres pass lateralward and dorsalward, curving around the margin of the central grey substance, mesial to the mesencephalic root of the masticator nerve. As the root curves toward the mid-line in the dorsal region just beneath the inferior quadrigeminate bodies, it turns sharply and courses inferiorly to approach the surface in the superior portion of the anterior medullary velum, the frenulum veli. In this it meets and undergoes a total decussation with the root of its fellow nerve, and then emerges at the medial margin of the supe- rior cerebellar peduncle of the opposite side. Having emerged, it then passes ventraUy around the cerebral peduncle, and thence pursues its course to the superior obhque muscle of the eye. It receives optic impulses from the superior quadrigeminate bodies and impulses from the cerebral cortex of chiefly the same side, and it is associated with the nuclei of other cranial nerves by way of the medial longitudinal fasciculus. 838 THE NERVOUS SYSTEM The oculomotor or third nerve, like the trochlear, is purely motor. It is the largest of the eye-muscle nerves. It supplies in all seven muscles of the optic apparatus: — two intrinsic, the sphincter iridis and the ciliary muscle, and five extrinsic. Of the latter, the levator palpebrse superioris is of the upper eyelid, while the remaining four, the superior, medial, and inferior recti and the obliquus inferior, are attached to the bulb of the eye. As is to be expected, its nucleus of origin is larger and much more complicated than that of the trochlear nerve. Practically continuous with that of the trochlear below, the nucleus is 5 or 6 mm. in length and extends anteriorly a short distance beyond the bounds of the mesencephalon into the grey substance by the side of the third ventricle. It hes in the ventral part of the central grey substance, and is very intimately associated with the medial longitudinal fasciculus. Its thickest Fig. 662. — Transverse Section Through Level op Superior Quadrigbminate Bodies. Stratum zonale of thalamus N Stratum zonale / Nucleus of superior colliculus Epiphysis (pineal ^'—'^—•" bodyj ^^ Central grey ^^^Va - "^ ~ " substance Optic-acoustic reflex path f — ^ Aquasductus cerebri Nucleus of mes- — encephalic (de- scending) root of masticator nerve Nucleus of ^ oculo-motor Fila of oculomotor nerve Substantia nigra portion is beneath the summit of the superior quadrigeminate body. The root-fibres leave the nucleus from its ventral side and collect into bundles which pass through the medial longitudinal fasciculus and course ventrally to the mesial portion of the substantia nigra, where they emerge in from six to fifteen rootlets which blend to form the trunk of the nerve in the oculomotor sulcus of the cerebral peduncles. Those bundles which arise from the more lateral portion of the nucleus course in a series of curves through and around the substance of the red nucleus below and, in the substantia nigra, join those which pursue the more direct course. The trunk thus assembled passes lateralward around the mesial border of the cerebral peduncle. A portion of the fibres of the oculomotor nerve upon leaving the nucleus decussate in the tegmentum immediately below and pass into the nerve of the opposite side, in which they are beUeved to be distributed to the opposite medial rectus muscle. The ceUs of the nucleus have been variously grouped and subdivided with reference to the difTerent muscles supphed by the nerve. Perlia has divided them into eight cell-groups. The nucleus may be more easily con- sidered as composed of an inferior and a superior medial group. The inferior group consists of a long lateral portion continuous with the nucleus of the trochlear nerve below, and a smaller medial portion, situated in the medial plane and continuous across the mid-line with its fellow of the opposite side. The superior medial group consists of cells of smaller size than the inferior, and is known as the nucleus of Edinger and Weslphal. It is believed to give origin to THE LEMNISCUS 839 the fibres (visceral efferent fibres) which terminate in the ciliary ganglion, axones from which supply the two intrinsic muscles concerned, viz., the ciliary muscle and the sphincter iridis. The nucleus of the oculomotor is associated with the remainder of the optic apparatus — (1) by way of the neurones of the superior quadrigemtnate body with the optic tract (retina) and it receives impulses from the occipital part of the cerebral cortex of the same and the opposite sides, and probably from the motor cortex of the frontal lobe; (2) by way of the medial longitudi- nal fasciculus with the nuclei of the trochlear and abducens (the latter making possible the co- ordinate action of the lateral and medial recti for the conjugate eye movements produced by these muscles), and with the nucleus of the facial (associating the innervation of the levator palpebrifi with that of the orbicularis oculi); (3) with the nuclei of termination of the sensory nerves, especially the auditory, by way of the lateral lemniscus and medial longitudinal fasciculus. It is probably connected with the cerebellum by way of the brachia conjunctiva and red nuclei. Fig. 663. — Diagram of Longitudinal Section of NtrcLEus of Oculomotoe Neeve. (After Edinger.) Nucleus of posterior com- missure and med. longit. fasc. Medial longitudinal fasciculus Ciliary muscles (a) and sphincter of iris (b) Levator palpebrse Superior rectus Medial rectus Inferior oblique Inferior rectus Superior group(nucleus of Edinger and West- phal) .--Inferior group The eminence representing the inferior quadrigeminate body proper consists of an oval mass of grey substance, the nucleus of the inferior coUiculus, containing numerous nerve-cells, most of which are of small size. A thin superficial lamina of white substance, the stratum zonale, forms its outermost boundary, and fibres from the lateral lemniscus enter it laterally and from below {stratum lemnisci). Near the lateral margin of the central grey substance occurs the beginning of the inferior brachium, a bundle containing fibres to and from the medial geniculate body and the inferior quadrigeminate body. The lemniscus in the mesencephalon is considered in two parts. The more lateral portion of the lemniscal plate occuring in the pons has here spread dorso-latorally, and occupies a position in the lateral margin of the section, and is known as the lateral lemniscus, while the medial portion which remains practically unchanged in the tegmentum is distinguished as the medial lemniscus. (See fig. 660). In the upper portion of the lateral lemniscus occurs a small, scattered mass of grey substance, the nucleus of the lateral lemniscus, in which manj' of its fibres are interrupted. The upper and greater portion of the lateral lemniscus with its nucleus belongs to the auditory apparatus, being connected with the nucleus of termination of the cochlear nerve, chiefly of the opposite side. (See fig. 650.) A large part of the fibres of this portion terminate in the inferior quadrigeminate bodies. Many of the latter enter at once the nucleus of the body 840 THE NERVOUS SYSTEM (nucleus of inferior colliculus) of the same side, and disappear among its cells; others cross the mid-line to the quadrigeminate body of the opposite side. In crossing, some pass superficially and thus contribute to the stratum zonale, while others pass either through the nucleus or below it and cross beneath the floor of the mecUan groove between the stratum zonale and the dorsal surface of the central grey substance, forming there an evident decussation with similar fibres crossing from the opposite side. Most of the fibres arising from the cells of the nucleus of the inferior quadrigeminate body pass by way of the inferior brachium to the medial geniculate body and the thalamus; some pass ventrally to terminate in the nucleus of origin of the trochlear nerve and some pass forward and laterally to terminate in the cortex of the superior gyrus of the temporal lobe, the cortical area of hearing. Another portion of the lateral lemniscus passes obliquely forward in company with the inferior brachium, and terminates in the medial gen- iculate body. Thus a large portion of the lateral lemniscus, the inferior quadrigeminate bodies with their brachia and the medial geniculate bodies are concerned with the sense of hearing. The nucleus of the inferior quadrigeminate body receives fibres which arise in the cortex of the superior temporal gyrus of chiefly the same side. Practically all the remainder of the lateral lemniscus terminates in the nucleus, or stratum cinereum, of the superior quadrigeminate body of the same and opposite sides. They approach the nucleus from below, and contribute to the well-marked band of fibres coursing on the dorso- lateral margin of the central grey substance, and known as the 'optic-acoustic reflex path' or stratum lemnisci (fig. 662). The medial lemniscus arises in the medulla oblongata from the nuclei (of termination) of the funiculus gracilis and funiculus cimeatus of the opposite side, and likewise from the nuclei of termination of the sensory roots of the cranial nerves of the opposite side. It is, therefore, a continuation of the central sensory pathway conveying the general bodily (including the head) sensations into the prosencephalon. CoursLag still more laterally than in the pons below, it passes into the hypothalamic grey substance, in the lateral portion of which most of its fibres terminate. By axones given off from the cells of the hypothalamic nucleus the impulses borne thither by the lemniscus are conveyed by way of the internal capsule and corona radiata to the gyri of the somsesthetic area of the cerebral cortex. The basis (pes) pedunculi comprises the great descending pathway from the cerebral cortex, and thus is continuous with the internal capsule of the telen- cephalon. The principal components of each basis pedunculi are as follows: — (1) The pyramidal fibres, which occupy the middle portion of the peduncle and comprise three-fifths of its bulk, and which are outgrowths of the giant pyramidal cells of the somaesthetic area of the cerebral cortex, chiefly the anterior central gyi'us. These supply ' voluntary ' impulses to the motor nuclei of the cranial nerves on the opposite side, form the pyramids of the medulla, and are distributed to the ventral horn cells of the spinal cord of the opposite side. (2) The frontal pontile fibres, which course in the mesial part of the peduncle from the cortex of the frontal lobe to their termination in the grey substance of the pons. (3) The occipital and temporal pontile fibres. which run in the ventral and lateral portion of the peduncle from their origin in the occipital and temporal lobes to their termination in the grey substance of the pons. The substantia nigra is continuous with the grey substance of the pons and that of the reticular formation below, and with that of the hypothalamic region above. Its remarkable abundance begins at the superior border of the pons, and it conforms to the crescentic inner contour of the cerebral peduncle, sending numerous processes which occupy the inter-fascicular spaces of the latter. It contains numerous deeply pigmented nerve-cells, which in the fresh specimen give the appearance suggesting its name. Its anatomical significance is not well understood. It is known that some fibres of the medial lemniscus terminate about its ceUs instead of in the hypothalamus higher up, and Melius has found in the monkey that a large portion of the pyramidal fibres arising in the thumb area of the cerebral cortex are interrupted in the substantia nigra. It is probable that other fibres of the peduncle also terminate here. The brachia conjunctiva or superior cerebellar peduncles, in passing from their origin in the dentate nuclei, lose their flattened form and enter the mesencephalon as rounded bundles. In the tegmentum, under the inferior colliculi, the two brachia come together and undergo a sudden and complete decussation. Through this decussation the fibres of the brachium of one side pass forward to terminate, most of them, in the red nucleus [nucleus ruber] of the tegmentum of the opposite side (fig. 589). Some fibres are said to pass the red nucleus and terminate in the ventrolateral part of the thalamus. The red nuclei are two large, globular masses of nerve-cells situated in the tegmentum under the superior quadrigeminate bodies. At all levels they are considerably mixed with the entering bundles of the brachia conjunctiva, and they contain a pigment which in the fresh condition gives them a reddish colour, suggesting their name. They receive in addition descending fibres from the cerebral cortex (frontal operculum) and from the nuclei of the corpus striatum. From the cells of each red nucleus arise fibres THE MESENCEPHALON 841 which pass — (1) into the thalamus and to the telencephalon (prosencephalic continuation of the cerebellar path), and (2) fibres which descend into the spinal cord, the 'rubro-spinal tract,' in the lateral funiculus (fig. 619). The latter cross from the red nucleus of the opposite side and descend in the tegmentum. The red nuclei are also in relation with the fasciculus relroflexus of Meynert, which belongs to the inter-brain. Fig. 664. — Scheme to Illustrate the Principal or Crossed Relations op the Descend- ing Cortical (Pyramidal) Fibrbs to the Nuclei op Origin op the Cranial Nerves. '^ Motor gyri of cerebral cortex Corona radiata ^Internal capsule ^ -Cerebral peduncle ^ -Nucleus of oculomotor nerve .-■Nucleus of trochlear nerve Nucleus of mesencephalic ' " root of masticator nerve Nucleus of facial nerve Nucleus of glosso-palatine : of abducens ^ _. Nucleus ambiguus .Dorsal efferent nucleus of vagus ^Nucleus of hypoglossal nerve -Nucleus of accessory nerve _ --Decussation of the pyramids The thalamo -olivary tract courses in the mesencephalon more dorsally than in the pons region. It runs in the ventro-lateral boundary of central grey substance just lateral to the nuclei of the trochlear and oculomotor nerves. A small guadrigemino-pontile strand of fibres has been described as arising in the quadri- gemina, especially the inferior pair, and terminating in the nuclei of the pons. Impulses carried by these fibres are probably destined for the cerebellar hemisphere of the opposite side. The superior quadrigeminate bodies (superior colliculi) are phylogenetically more important than the inferior. In certain of the lower vertebrates they are 842 THE NERVOUS SYSTEM enormously developed and in most of the mammals they are relatively larger and appear more complicated in structure than in man. They are concerned almost wholly with the visual apparatus, mediating most of the reflexes with which it is concerned. The nucleus of the superior colliculus is of somewhat greater bulk than that of the inferior. It is capped by a strong stratum zonale (fig. 662), which has been described as composed chiefly of retinal fibres, passing to it from the optic tract by way of the superior brachium, but, since Cajal found in the rabbit that extirpation of the eye is followed by very slight degeneration of the stratum zonale, it is probable that it is composed of other than retinal fibres — possibly fibres from the occipital cortex and fibres arising within the nucleus itself. The nucleus is separated from the central grey substance by a weU-marked band of fibres, the stratum album profundum. This contains fibres from two sources: — (1) fibres from the lateral lemniscus which approach the nucleus from the under side, some to terminate within it, others to cross to the nucleus of the opposite side; (2) fibres which arise within the nucleus and course ventrally around the central grey substance, both to terminate in the nucleus of the oculomotor nerve and to join the medial longitudinal fasciculus and pass probably to the nuclei of the trochlear and abducens. The lemniscus fibres often course less deeply than (2) and give the stratum lemnisci. The optic fibres proper approach the nucleus by way of the superior brachium, and are dispersed directly among its cells; only a small proportion of them cross over to terminate in the nucleus of the opposite side. They consist of two varieties: — (1) retinal fibres which arise in the gang- lion-cell layer of the retina and enter the superior brachium at its junction with the lateral root of the optic tract, and (2) fibres from the visual area of the occipital lobe of the cerebral hemi- sphere. Sometimes the optic fibres in their course within the nucleus of the superior coUiculus form a more or less evident stratum near the stratum album profundum. This is known as the stratum oplicum (stratum album medium). The portion of the nucleus between this stratum and the stratum zonale is called the stratum cinereum. The fibres entering the nucleus from the lateral lemniscus probably all represent auditory connections. The stratum album profundum, composed of the lemniscus fibres and fibres from cells of the nucleus, and the stratum opticum together, form the so-caOed 'optic-acoustic reflex path' (fig. 662). The mesencephalo-spinal amd the spine -mesencephalic (spino-tectal) paths course together ventro-lateral to the nuclei of the coUiculi. In the superior quadrigeminate bodies they course in the dorsal edge of the median lemniscus, between the stratum opticum and stratum album profundum. From the various studies that have been made it appears that the superior coUiculus of the corpora quadrigemina is merely the central reflex organ concerned in the control of the eye muscles — eye muscle refle.xes which result from retinal and cochlear stimulation, and from some general body sensations by way of the spinal cord. Fibres from its nucleus to the visual area of the occipital cortex have been claimed for certain mammals, but in man the superior colliculus may be entirely destroyed without disturbance of the perception of light or color and flbres arising from its nucleus to terminate in the cerebral cortex are denied. In the level of the anterior part of the superior colliculus the fibres which arise from the cells of its nucleus and course ventrally in the stratum album profundum ooUect into a strong bundle. This bundle passes ventral to the medial longitudinal fasciculus and, in the space between the two red nuclei, it forms a dense decussation with the similar bundle from the opposite side. In decussating the fibres turn in spray-like curves downward and soon join the medial longitudinal fasciculus. This is the 'fountain decussation' of Forel. It is said to be augmented by decus- sating fibres from the two red nuclei. There is abundant evidence that fibres arising in the corpora quadrigemina descend into the spinal cord. Various studies make it appear that at least part of these are fibres from the fountain decussation, and that these course through the medulla oblongata in the ventral part of the medial longitudinal fasciculus, and thence descend into the cord in the 'quadrigemino- thalamus path' (lateral mesencephalo-spinal tract) (fig. 619). The medial longitudinal fasci- culus is continuous with the ventral fasciculus proprius of the spinal cord and most of these fibres arising in the superior quadrigeminate bodies retain their ventral position in the cord as the sulco-marginal fasciculus of the opposite side. Their termination about those ventral horn cells of the cervical cord which send fibres through the rami communicantes probably establishes the pathway by which the superior quadrigeminate bodies are connected with the cervical sympathetic ganglia, and by which may be explained the disturbances in pupillary contraction induced by lesions of the lower cervical cord. The medial geniculate body and the medial root of the optic tract, which runs into the former, probably have nothing to do with the functions of the optic apparatus. Both remain intact after extirpation of the eyes. The medial root of the optic tract is apparently nothing more than the beginning of the inferior cerebral (Gudden's) commissure, a bundle passing by way of the optic tract, connecting the medial geniculate body of one side with that of the other side, and probably with the inferior colliculus. The medial longitudinal fasciculus (posterior longitudinal fasciculus), con- tinuous into the ventral fasciculus proprius and the sulco-marginal fasciculus of the spinal cord, extends throughout tlae rhombencephalon and mesencephalon, and is represented in the hypothalamic region of the prosencephalon. Deserted by the lemniscus at the inferior border of the pons, it maintains its closely medial position and courses throughout in the immediate ventral margin of the central grey substance of the medulla and floor of the fourth ventricle, and likewise in the ventral margin of the central grey substance of the mesencephalon. THE PROSENCEPHALON 843 The two fasciculi constitute the principal association pathways of the brain-stem, and, true to their nature as such, they are among the first of its pathways to acquire medullation. In the mesencephalon they become two of its most conspicuous tracts, and their course, in most inti- mate association with the nuclei of origin of the nerves supplying the eye muscles, suggests what is probably one of their most important functions, viz., that of associating these nuclei with each other and of bearing to them fibres from the nuclei of the other cranial nerves neces- sary for the co-ordinate action of the muscles of the optic apparatus associated with the functions of these other nerves. Fibres from each medial longitudinal fasciculus terminate either by collaterals or terminal arborisations about the cells of the motor nuclei of aU the cranial nerves, and each nucleus prob- ably contributes fibres to it. It also receives fibres from the nuclei of termination of the sensory nerves especially the vestibular. Thus it contains fibres coursing in both directions, and, while it is continually losing fibres by termination, it is being continually recruited and so maintains a practically uniform bulk. Thus, a given lesion never results iu its total degenera- tion. Many of the fibres coursing in it arise from the opposite side of the mid-line. A special contribution of fibres of this kind is received by way of the fovmtain decussation from the nucleus of the superior coUiculus of the opposite side. As noted above, it is in part continu- ous into the spinal cord as the ventral fasciculus proprius. It receives some fibres by way of the posterior commissure of the prosencephalon from a small nucleus common to it and the posterior commissure situated in the superior extension of the central grey substance of the mesencephalon. Van Gehuchten and Edinger describe for it a special nucleus of the medial longitudinal fasciculus situated beyond this commissure in the hypothalamic rsgion. This nucleus may be explained as an accumulation of the gray substance of the reticular forma- tion below and as receiving impulses from the structures of the prosencephalon which are dis- tributed by its axones to the structures below by way of the medial longitudinal fasciculus. Scattered in the posterior part of the posterior perforated substance, near the superior border of the pons, is a small group of ceU-bodies forming the inter -peduncular nucleus (inter- peduncular gangUon of von Gudden). Fibres arising in the habenular nucleus of the diencepha- lon curve posteriorly, forming the fasciculus retroflexus of Meynert, and terminate about its cells. Fibres arising from its cells course dorsalward and terminate about association neurones in the ventral periphery of the central grey substance. It is concerned with olfactory impulses. SUMMARY OF THE MESENCEPHALON 1. Quadrigeminate bodies: (a) Inferior coUicuU, their nuclei and brachia. (6) Superior colhculi, their nuclei and brachia. 2. Pedimcles of the cerebrum 3. Aqueduct of the cerebrum. 4. Central grey substance. 5. Substantia nigra. 6. Decussation of superior cerebellar peduncles and the red nuclei. 7. Medial lemniscus, lateral lemniscus and nucleus of lateral lemniscus. 8. Mesencephalic nucleus and root of masticator nerve. 9. Trochlear nerve and its nucleus. 10. Oculomotor nerve and its nucleus. 11. Mesencephalo-spinal and rubro-spinal tracts. 12. Medial longitudinal fasciculus, its nucleus, the nucleus of the posterior commissure. 13. The fountain decussation. 14. Interpeduncular nucleus. As frequently reaUzed in the above, the structures of the mesencephalon are both overlapped by, and are of necessity functionally continuous with, the structures of the next and most ante- rior division of the encephalon, the prosencephalon. 2. THE PROSENCEPHALON The prosencephalon or fore-brain includes those portions of the encephalon derived from the walls of the anterior of the three embryonic brain-vesicles. In its adult architecture it consists of — (1) the diencephalon (interbrain), comprising the thalamencephalon or the thalami and the structm-es derived from and immediately adjacent to them, and, in addition, the mammillary portion of the hypothalamic region; (2) the telencephalon (end -brain), comprising the optic portion of the hypothalamic region and the cerebral hemispheres proper. The last mentioned consist of the entire cerebral cortex or superficial mantle of grey substance, including the rhinencephalon, and also the basal ganglia or buried nuclei (corpus striatum), together with the tracts of white substance connecting and associating the different regions of the hemispheres with each other and with the structures of the other divisions of the central nervous system. EXTERNAL FEATURES OF THE PROSENCEPHALON A. THE DIENCEPHALON. — The basal surface of this division of the brain consists of only the mammillary portion of the hypothalamic region (fig. 668). 844 THE NERVOUS SYSTEM This comprises — (1) the mammillary bodies [corpora mammillaria] (albicantia) , the two rounded projections situated in the anterior part of the interpeduncular fossa, and (2) the anterior portion of the posterior perforated substance or the small triangle of grey substance forming the floor of the posterior part of the third ventricle, and which represents numerous openings for the passage of branches of the posterior cerebral arteries (fig. 668) . The hypothalamic portions of the cerebral peduncles might be included. The structures of the optic or re- maining portion of the hypothalamus belong to the telencephalon. The upper or dorsal surface of the diencephalon is completely overlapped and hidden by the telencephalon, and covered by the intervening ingrowth of the Fig. 665. — Doesal Surface of Diencephalon with Adjacent Structukes. (After Obersteiner.) Coipus callosum Fifth ventricle Septum pellucidum Caudate nucleus Lateral sul encephalon Eminence of hypoglossal Restifcrm body Clava Posterior fissure Postero-intermediate sulcus Postero-lateral sulcus Habenular commissure Epiphysis Sulcus cor] media Inferior coUiculus Frenulum veli Lingula cerebelli Acoustic area vagi Tuberculum cuneatum Funiculus gracilis Funiculus cuneatus Lateral funiculus cerebral meninges, the tela chorioidea of the third ventricle (velum interpositum). These removed (fig. 665), it is seen that the thalami on either side are by far the most conspicuous objects of the diencephalon. They, together with the parts developed in connection with them, are distinguished as the thalamencpehalon. The thalamencephalon consists of — (1) the thalami; (2) the metathalamus or geniculate bodies; and (3) the epithalanius, comprising the epiphysis with the posterior commissure below it and the habenular trigone on either side. The thalami are two ovoid, couch-like masses of grey substance which form the lateral walls of the third ventricle. The cavity of the ventricle is narrow, and quite frequently the thalami are continuous through it across the mid-hne by a small but variable neck of grey substance, the massa intermedia ("middle com- missure"). The upper surfaces of the thalami are free. The edges of the tela chorioidea of the third ventricle are attached to the lateral part of the surface of each thalamus, and, when removed, leave the taenia chorioidea lying in the chori- THE DIENCEPHALON 845 oidal sulcus. Each thalamus is separated laterally from the caudate nucleus of the telencephalon, by a linear continuation of the white substance below, known as the stria terminalis thalami (taenia semicircularis). Like the quadrigemina, each thalamus is covered by a thin capsule of white substance, the stratum zonale. The average length of the thalamus is about 38 mm., and its width about 14 mm.; its inferior extremity is directed obliquely lateralward. The dorsal surface usually shows four eminences, indicating the position of the so-called nuclei of the thalamus within. These are the anterior nucleus or anterior tubercle, the medial nucleus or tubercle, the lateral nucleus, and the pulvinar, the tubercle of the posterior extremity. The pulvinar of the human brain is peculiar in the fact that it is so developed as to project inferiorly and slightly overhang the level of the quadrigeminate bodies. The projecting portion assumes relations with the optic tract and the metathalamus. Fig. 666.- -DissECTioN OF Brain showing Metathalamus and Pulvinar with Adjacent Structures. Caudate nucleus Stria terminalis of thalamus Pulvinar Optic tract Inferior quadrigemi nate body Medial geniculate body Lateral geniculate body Mammillary body Optic tract Olfactory buib Insula (central lobe) Tail of caudate nuclei Both the structures of the metathalamus, the lateral and medial geniculate bodies, are connected with the optic tract, but it is thought that actual visual axones terminate only in the lateral genticulate body. As the optic tract curves around the cerebral peduncle it divides into two main roots. The lateral gen- iculate body receives a small portion of the fibres of the lateral root of the optic tract; the remainder pass under this body and enter the pulvinar of the thalamus. The medial geniculate body is connected with the medial root of the optic tract, which root consists largely, not of retinal fibres, as does the lateral root, but of the fibres forming Gudden's commissure (the inferior cerebral commissure). The retinal fibres contained in the medial root pass to terminate in the superior quadrigeminate bodies. Of the epithalamus, the epiphysis (pineal body, conarium) is the most con- spicuous external feature. This is an unpaired, cone-shaped structure, about 7 mm. long and 4 mm. broad, which also projects upon the mesencephalon so that its body rests in the groove between the superior quadrigeminate bodies. Its stem is attached in the mid-line at the posterior extremity of the third ventricle, and therefore just above the posterior commissure of the cerebrum (fig. 658). It is covered by pia mater, and is involved in a continuation of the tela chorioidea 846 THE NERVOUS SYSTEM of the third ventricle. Though it develops as a diverticulum of that portion of the anterior primary vesicle which gives origin to the thalamencephalon, it is wholly a non-nervous structure, other than the sympathetic fibres which enter it for the supply of its blood-vessels. It consists of a dense capsule of fibrous tissue (pia mater) from which numerous septa pass inward, dividing tlie interior into a number of intercommunicating compartments filled with epithelial (ependymal) cells of the same origin as the ependyma lining the ventricles and aque- duct below. Among these cells are frequently found small accretions (brain-sand, acervulus cerebri), consisting of mixed phosphates of lime, magnesia, and ammonia and carbonates of lime. The compartments form a closed system. In function the epiphysis ranks as one of the glands of internal secretion of the body, and it is often referred to as the 'pineal gland.' How- ever, it is perhaps funotionless in man. Fig. 667. — Mesial Section of Entire Brain, showing Mesial Surface of Diencephalon _^'7' ; AND Telencephalon. (After Henle.) Massa Hypothalamic sulcus intermedia Interventricular foramen (Monroi) Posterior commissure \ i . / Sulcus of corpus callosum Epiphys Splemum of corpus callos Lamina quadrigemina Anterior commissure Sub-callosal gyrus Aqueduct of cerebrum (Sylvii) Anterior medullary velum Genu of corpus V callosum Rostrum of corpus callosum Lamina terminalis Cerebellum Fourth ventricle Hypo- \ Optic 1 Medulla / / I Physis Qptic chiasma Pons Mammil- Tuber lary body cinereum Apparently arising from the base of the epiphysis, but having practically nothing to do with it, are the striae meduUares of the thalamus (striae pineales, pedunculi conarii, taenia thalami, habenulse) . These are two thin bands of white substance which extend from under the epiphysis anteriorly upon the thalamus, along the superior border of each lateral wall of the third ventricle, and thus form the boundaries between the superior and mesial surfaces of each thalamus. They have been called the habenulce, from their relation to the habenular nucleus, situated in the mesial grey substance at their inferior ends. They are continuous across the mid-line in the habenular commissure, just below the neck of the epiphysis, and between it and the pos- terior cerebral commissure, or, rather the superior part of the latter (figs. 631, 665). It will be seen below that each habenula contains olfactory fibers from the fornix, the anterior perfor- ated substance and the septum pellucidum, as well as fibres out of the thalamus, and that most of its fibres terminate in the habenular nucleus. The ventro-lateral surface of the thalamencephalon is continuous into the hypothalamic tegmental region, the upward continuation of the tegmental grey substance of the mesencephalon. It is also adjacent to a portion of the internal capsule. Both these relationships, as well as the fibre connections of the dien- cephalon with the structures above and below it, are deferred until the discussion of the internal structure of the prosencephalon. The mesial surface of the diencephalon (fig. 667), allows a better view of the shape and relations of the third ventricle. Below the line of the massa inter- media the ventricle is usually somewhat wider than it is along the upper margins of THE TELENCEPHALON 847 the thalami. This greater width is occasioned by a groove in the ventromesial surface of each thalamus, known as the hjrpothalamic sulcus (sulcus of Monro). It is along the line of this sulcus that the third ventricle is continuous with the aqueduct of the cerebrum, and thus with the fourth ventricle below, and, likewise, with the two lateral ventricles of the cerebral hemispheres at its anterior end. The latter junction occurs through a small oblique aperture, the interventricular foramen (foramen of Monro), one into each lateral ventricle. The dorsal or upper portion of the third ventricle extends posteriorly beneath its chorioid tela Fig. 668. — Ventral Aspect of Brain-stem Including Mammillaht and Optic Portions OF THE Hypothalamus. Insula Anterior perforated substance ^^| nillary bodies, Cerebral peduncle Semilunar (Gasser ian) ganglion Oblique fascicul of pons Hypophysis 1 TN Optic nerve Optic tract Oculomotor nerve Hypoglossal nerve Decussation of pyramids _-- Cervical II (velum interpositum) to form a small postfiiur n^ccss about the epiphysis. This is known as the supra-pineal recess. The anterior and ventral extremity of the third ventricle involves the pars optica hypothalami, which belongs to the telencephalon. B. THE TELENCEPHALON. — External features. — The optic portion of the hypothalamus consists of that small central area of the basal surface of the telen- cephalon which includes and surrounds the optic chiasma, and comprises the structures of the floor of the anterior and ventral portion of the third ventricle. The area extends anteriorly from the mammillary bodies in the interpeduncular fossa, and includes the tuber cinereum and hypophysis behind the optic chiasma, and some of the anterior perforated substance in front of it. The most anterior portion of the third ventricle is in the form of a ventral ex- tension. The wall of this portion is almost wholly non-nervous and quite thin, and thus the cavity of the ventricle is but thinly separated from the exterior of 848 THE NERVOUS SYSTEM the brain. The front portion of this wall is the lamina terminalis and in the ven- tricular side of the upper part of this lamina the anterior commissure of the cerebrum is apparent. The optic chiasma lies across and presses into the lower portion of the lamina terminalis, and in so doing produces an anterior recess in the cavity of the ventri- cle known as the optic recess. Behind the optic chiasma the floor of the third ventricle bulges slightly, giving the outward appearance known as the tuber cinereum, and the cavity bounded by this terminates in the infundibular recess. The tuber cinereum then is a hollow, conical projection of the floor of the third ventricle, between the corpora mammillaria and the optic chiasma. Its wall is continuous anteriorly with the lamina terminalis and laterally with the anterior perforated substance. The infundibulum is but the attenuated apex of the conical tuber cinereum, and forms the neck connecting it with the hypophysis. It is so drawn out that it is referred to as the stalk of the hypophysis. The cavity of the tuber cinereum (infundibular recess) is sometimes maintained throughout the greater part of the length of the infundibulum, giving it the form of a long-necked funnel. Near the hypophysis the cavity is always occluded. Fig. 669. — Diagrams op the Hypophysis Cerebri. (After Testut.) A, posterior surface; B. transverse section; C, sagittal section; 1, anterior lobe; 2, posterior lobe; 3, infundibulum; 4, optic chiasma; 5, infundibular recess; 6, optic recess. In C the infundibulum is relatively much shorter than in the actual specimen. The hypophysis cerebri (pituitary body or gland) is an ovoid mass terminating the infundibulum. It lies in the sella turcica of the sphenoid bone, where it is held down and roofed in by the diaphragma selloe, a spheroid pocket of the dura mater. It consists of two lobes, a large anterior lobe, the glandular or buccal lobe, and a smaller posterior or cerebral lobe. The posterior lobe is usually enclasped in a concavity of the anterior lobe. Development. — The posterior or cerebral lobe alone is originally continuous with and a part of the infundibulum. It alone represents the termination of the hollow diverticulum which, in the embryo, grows downward from that part of the anterior cerebral vesicle which later becomes the third ventricle. The driginal cavity afterward becomes obliterated except in the upper part of the infundibulum. It is, therefore, of cerebral origin. The anterior or buccal lobe arises quite differently. It is developed from an upward tubular diverticulum (Rathke's pouch) of the primitive buccal cavity. In the higher vertebrates, including man, its connection with the buccal cavity becomes obliterated as the cartilaginous base of the cranium is consoli- dated, but in the myxinoid fishes the connection remains patent in the adult. Cut off within the cranial cavity, the embryonic buccal lobe assumes its intimate association with the cerebral lobe. In about the second month of fetal life it begins to develop numerous secondary diverti- cula which become the epithelial structures evident in the adult human subject. Structure. — The posterior or cerebral lobe retains no organized structure. It may be said to consist of a mass of neuroglia and other fibrous connective tissue with the cells belonging to these and a moderate suppl}' of blood-vessels, with some sympathetic cell-bodies and fibres for the blood-vessels. The anterior or glandular lobe is probably the functional part of the organ. In addition to its abundant supporting tissue, it consists of compartments lined with two kinds of ouboidal cells — cells of different size and different staining properties. The principal or more numerous cells are smaller, with thicldy granular cytoplasm. In mi.xtures containing orange G and fuchsin these cells stain orange, while the chromophile cells, the larger and less numerous variety, take the fuchsin deeply. The compartments have an abundant blood supply. Near the interlobar septum, the cells frequently are arranged to form small vesicles which contain colloid substance, resembling the typical structure of the thyreoid body. Like the epiphysis, the hypophysis must be regarded as glandular — a gland with internal secretion. In the case of giants and in acromegaly it is usually greatly enlarged. The principal cells increase greatly in number after removal of the thyreoid body. The fundaments of the optic nerve are derived from this portion of the telen- cephalon, though the nuclei of termination of its fibres are located in the thalam- THE OPTIC TRACTS 849 encephalon and mesencephalon. The optic apparatus consists of the retinae and optic nerves, the optic chiasma, the optic tracts, the superior quadrigeminate bodies with their relations with the nuclei of the eye-moving nerves, the meta- thalamus, the pulvinar of the thalamus, and the visual area of the cerebral cortex of the occipital lobe. The fibres of the optic nerves arise from the cells of the ganglion-cell layer of the retinae. The fibres which arise in the mesial or nasal halves of each retina cross the mid-line to find their nuclei of termination in the central grey substance of the opposite side, while those from the outer or lateral halves terminate on the same side (fig. 670.) The optic chiasma (optic commissure) is functionally independent of the struc- tures of the optic portion of the hypothalamus adjacent to it. It is formed by the Fig. 670. — Diagram of the Principal Components op the Optic Apparatus. (After Cunningham.) approach and fusion of the two optic nerves, and is knit together by the decussat- ing fibres from the nasal halves of each retina, and, in addition, by the fibres of Gudden's commissure which is contained in it. Beyond the chiasma the optic fibres continue as the optic tracts which course posteriorly around the cerebral peduncles to attain their entrance into the thalam- enchephalon and mesencephalon. Upon reaching the pulvinar of the thalamus each optic tract divides into two roots, a lateral and mesial. The lateral root contains practically all of the true visual fibres — fibres arising from the latera half of the retina of the same side and the nasal half of the retina of the opposite side. These fibres are distributed to three localities: — (1) part of them terminate in the lateral geniculate body; (2) the greater portion pass over and around the lateral geniculate body and enter the pulvinar; (3) a considerable portion enter the superior quadrigeminal brachium and course in it to terminate in the nucleus of the superior quadrigeminate body. The most evident function of this latter portion is to bear impulses which, by way of the neurones of the quadrigeminate body, are distributed to the nuclei of the oculomotor, trochlear, and abducent nerves, and thus mediate eye-moving refiexes. The cells of the lateral geniculate body and the pulvinar, about which the retinal fibres terminate, give off a.xones which terminate in the cortex of the visual area, chiefly the gyri about the calcarine fissure of the occipital lobe. In reaching this area they curve upward and backward, coursing in a compact band of white substance known as the optic 850 THE NERVOUS SYSTEM radiation (radiatio oocipito-thalamica, fig. 699). Whetlier any fibres of the optic radiation arise in tlie superor quadrigeminate body is doubtful. It also is in large part composed of fibres arising from the cells of the visual area, which pass from the cortex to the pulvinar, superior quadrigeminate bodies, and possibly some to the medulla oblongata and spinal cord. The mesial root of the optic tract contains few true visual fibres. It runs into the medial geniculate body, and neither it nor this body are appreciably affected after extirpation of both eyes. It may be considered as largely representing the fibres of Gudden's commissure (infe- rior cerebral commissure). This commissure consists of fibres which connect the medial genicu- late bodies of the two sides with each other, and which, instead of crossing the mid-line through the mesencephalon, course in the optic tracts and cross by way of the posterior portion of the optic chiasma. It consists of fibres which both arise and terminate in each of the bodies, and, therefore, of fibres coursing in both directions. It is also claimed that the fibres of Gudden's commissure connect the medial geniculate body of each side with the inferior colliculus of the opposite side. THE CEREBEAL HEMISPHERES The cerebral hemispheres in man form by far the largest part of the central nervous system. Together, when viewed from above, they present an ovoid surface, markedly convex upward, which corresponds to the inner surface of the vault of the cranium. The greater transverse diameter of this surface' lies posteriorly in the vicinity of the parietal eminences of the cranium. The outline of the superior aspect varies according to the form of the cranium, being more spheroidal in the brachycephalic and more ellipsoidal in the dolichocephalic forms. The hemispheres are separated from each other superiorly by a deep median slit, the longitudinal fissure, into which fits a duplication of the inner layer of the dura mater known as the falx cerebri. The posterior or occipital extrem- ities of the hemispheres overlap the cerebellum, and thus entirely conceal the mesencephalon and thalamencephalon. They are separated from the superior surface of the cerebellum and the corpora quadrigemina by the deep transverse fissure. This is occupied by the tentorium cerebelli, which is similar to and con- tinuous with the falx cerebri and is connected with the tela chorioidea of the third ventricle below. Each of the hemispheres is usually described as having three poles or projecting extremities, and three surfaces bounded by intervening borders. The most anterior projection is the frontal pole. This is near the mid-line, and with its fellow of the other hemisphere, forms the frontal end of the ovoid contour of the cerebrum. The occipital pole is the most projecting portion of the posterior and inferior end, and is more pointed than the frontal pole. The infero-lateral por- tion of the hemisphere is separated anteriorly by the deep lateral fissure (fissure of Sylvius) into a distinct division, the temporal lobe, and the anterior portion of this lobe projects prominently forward and is known as the temporal pole. The surfaces of the hemisphere are — (1) the lateral or convex surface; (2) the medial surface; and (3) the hasal surface. The convex surface comprises the entire rounded aspect of the hemisphere visible previous to manipulation or dissection, and is the surface subjacent to the vault of the cranium. The mesial surface is perpendicular, flat, and parallel with that of the other hemisphere, the two bounding the longitudinal fissure and for the most part in contact with the falx cerebri. The superomesial border intervenes between the convex and medial surfaces, and is thus convex and extends from the frontal to the occipital pole. The more complex hasal surface fits into the anterior and middle cranial fossae, and posteriorly rests upon the tentorium cerebelh. Thus it is subdivided into — (a) an orbital area, which is slightly concave, since it is adapted to the orbital plate of the frontal bone, and is separated from the convex surface by the necessarily arched superciliary border and from the mesial surface by the medial orbital border, the latter being straight and extending from the frontal pole mesial to the olfactory bulb and tract; (fo) a tentorial area or surface, which is arched in conformity with the dorsal surface of the cerebellum. This is separated from the convex surface by the infero-lateral border, which runs from the occipital to the temporal pole; and from the mesial surface by the medial occipital border, which is a more or less rounded ridge extending from the occipital pole obliquely upward in the angle formed by the junction of the perpendicular falx cerebri and the horizontal tentorium cerebeUi. This border is best seen in brains which have been hardened with the membranes in situ. The remainder of the basal surface includes the ojDtic portion of the hypothalamus already considered, and the small THE CORPUS CALLOSUM 851 depressed and punctate area, the anterior perforated substance, which is pene- trated by the antero-lateral group of the central branches of the anterior and middle cerebral arteries and into which the striae of the olfactory trigone disappear. In addition to the orbital area the basal surface of the hemisphere shows signs of the impress of the petrous portion of the temporal bone and of the great wing of the sphenoid. The corpus callosum. — In their early development as lateral dilations of the anterior primary brain-vesicles, the hemispheres are connected with each other only at the anterior end of the thalamencephalon, where they are both continuous with the lamina terminalis. As development proceeds and the hemispheres extend upward, backward, forward, and laterally to completely conceal the base,, and as the palhum, or cortex, thickens and its folds begin to appear, the two hemi- spheres become united across the mid-hne above the thalamencephalon and the third ventricle by the inter-growth of the great cerebral commissure, the corpus callosum. After removal of the falx cerebri from the longitudinal fissure, the Fig. 671. — Mesial and Tentorial Surfaces op Right Cerebral Hemisphere, Viewed from THE Left. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Sulcus oi corpus callosum Body of fornix J Body of corpus callosum ' ' Thalamus Interventricular foramen \^,.-»— -«-s..^--''^-w/ Crus of fonux Cut surface of cerebral peduncle Genu of corpus callosum of corpus callo Columns of formx Anterior comnussure/ Optic chiasma Columns of formx' Corpus mammillare '^' Isthmus of gyrus fornicatus ^ * Chorioid fissure , \ Fimbria I * Hippocampal fissure 1 I Impressure for petrous bone Mammillo-thalamic fasciculus Dentate fascia dorsal surface of the corpus callosum 'may be exposed by drawing apart the contiguous mesial surfaces of the hemispheres. It consists of a dense mass of pure white substance coursing transversely, and arises as out-growths from the cortical cells of both hemispheres. Thus it is the great pathway which associates the cortex of the two sides of the telencephalon. Only the smaller medial portion of the body lies free in the floor of the longitudinal fissure, by far the greater part being concealed in the substance of the hemispheres, where its fibres radiate to and from different localities of the pallium, forming the radiation of the corpus callosum. Its surface shows numerous transverse markings, the transverse strice, which indicate the course of its component bundles of fibres. In addition there may be seen two delicate, variable longitudinal bands running over its surface on each side of the mid-line. The medial longitudinal stria {stria Lancisii) runs close to the median plane, around the anterior end from the gyrus subcallosus (fig. 672), and over the posterior end downward and lateralward to disaiipcai' in the hippocampal gyrus of the base of the telencephalon. The lateral longitudinal stria is more delicate than the mesial stria, courses lateral to the medial stria, and can be seen only within the sulcus of the corpus callosum (fig. 672). Both striae are composed largely of axones having to do with the olfactory apparatus. When severed along the median plane, it may be seen that the anterior margin of the corpus callosum is turned abruptly downward, forming the genu, and that this turn continues, so that the tapering edge of the body points posteriorly and 852 THE NERVOUS SYSTEM constitutes the rostrum (figs. 667, 671). The rostrum is in contact with the lamina terminalis of the third ventricle below by a short, thin, dorso-frontal continuation of this lamina, linown as the rostral lamina. The rostral lamina may be considered as beginning at the anterior cerebral commissure with the anterior aspect of which it is in contact, and extending to the rostrum. Beginning with the rostrum and genu, the corpus callosum arches backward as the body of the corpus callosum, and ends over the quadrigeminate region in its rounded, thickened posterior margin, the splenium. It is bounded above by the sulcus of the corpus callosum, and, attached to its concave inferior surface, are the chorioid tela of the third ventricle, the fornix, the septum pellucidum, and the medial walls of the lateral ventricles. Each cerebral hemisphere includes — -(1) a superficial and much folded mantle or pallium, divided into lobes and gyri, and consisting of grey substance, the cortex, covering an abundant mass of white substance; (2) a modified portion, the Fig. 672. — Diagram of Convex Surface of Right Ceeebral Hemisphere and Part of Upper Surface of Corpus Callosum. Paramesial sulcus Superior frontal sulcus M iddle frontal sulcus Inferior frontal sulcus Precentral sulcus Lateral longitudinal stria Medial longitudinal stria Corpus callosum Central sulcus (Rolandi) Postcentral sulcus Lateral fissure (Sylvii) Intraparietal sulcus .Lateraroccipital sulcus Transverse occipital sulcus rhinencephalon, having especially to do with the impulses brought in by the olfac- tory nerve; (3) a cavity , the lateral ventricle; and (4) a buried mass of grey sub- stance, the caudate and lenticular nuclei, which together with the internal capsule of white substance, are known as the corpus striatum. Gyri, fissures, and sulci. — The cerebral pallium is thrown into numerous and variable folds or gyri (convolutions). These are separated from each other by corresponding furrows, tlie deeper and most constant of which are called fissures; the remainder, sulci. All the fissures and the main sulci are named. There are, however, numerous small and shallow sulci to which names are seldom given. These occur as short branches of main sulci or as short, isolated furrows bounding small gyri which connect adjacent gyri. These small gyri are likewise seldom given individual names. They are very variable both in different specimens and in the two hemispheres of the same specimen. Collectively, they are the so-called transitory gyri (gyri transitivi). Certain groups of them are named according to their locahty, such as orbital gyri and lateral occipital gyri. Even the main gyri [gyri profundi] (and sulci) are very irregular in detail. Some of the main and deeper fissures are considerably deeper than others. Some are infoldings of the grey cortex so deep that a portion of their course may be indicated as slight bulgings in the walls of the lateral ventricles, e. g., the hippocampal and collateral fissures. While the general surface pattern is similar for all normal human brains, yet when a detailed comparison is made, the given gyri of different specimens are found to LOBES OF THE TELENCEPHALON 853 vary greatly. The main gyii of the two hemispheres of the same brain, how- ever, are nearly alike. Origin of the gyri. — The gjrri (and sulci) are the result of processes of unequal growth — folds necessarily resulting from the surface portion of the hemispheres increasing mucli more rapidly than the central core. In the early periods of fetal life the surfaces of the hemispheres are quite smooth. In many of the smaller mammals this condition is retained throughout life, but in the larger mammals, including man, as development proceeds the cerebral cortex becomes thrown into folds. The absolute amount of the grey substance of the hemispheres varies with the bulk of the animal, and apparently with its mental capabihties. This is especially true of the cortex, for in the larger brains, and that of man especially, by far the greater amount of the cerebral grey substance lies on the surface. Therefore, in either the growth or evolution of a smaU animal into a large one the amount of cerebral grey substance is increased, and in this increase the surface area of the brain is necessarily enlarged. It is a geometrical law that in the growth of a body the surface increases with the square, while the volume increases with the cube of the diameter. The cerebral hemisphere is a mass the increase of whose volume does not keep the required pace with the increase of its surface area or cortical layer. The white sub- stance which forms the palUum arises in large measure as outgrowths from the cells of the cortical layer, and thus it can only increase in a certain proportion to the grey substance. Therefore, the surface mantle of grey substance of a hemisphere, enlarged in accordance with an increased bulk of body, is greater than is necessary to cover the surface of the geometrical figure formed by the combined white and grey substance. Consequently, in order to possess the preponderant amount of grey substance, the surface of the hemisphere is of necessity thrown into folds. It follows also that the thinner the cortical layer in proportion to the volume of the hemisphere, the greater and more folded will be the surface area. In accordance with this theory small animals have smooth or relatively smooth hemispheres, and that independently of their position in the animal scale or the amount of their inteUigence, while large animals have convoluted brains. The sulci in general begin to appear with the fifth month of fetal life, the larger of them, the fissures, appearing first and in a more or less regular order. Up to the fifth month the en- cephalon, due to its rapid growth, closely occupies the cranial capsule. During the fifth month the cranium begins to grow more rapidly than the encephalon, and a space is formed between the cerebrum and the inner surface of the cranium. This space allows further expansion of the palUura, and at the time the space is relatively greatest (during the sixth month) the form and direction of the principal gyri and sulci begin to be indicated. As growth proceeds the unre- stricted expansion of the pallium results in the gyri again approaching the wall of the cranium, and during the eighth month of fetal life they again come in contact with it. Finally, the later relative growth of the cranium results in the space found between it and the cortex in the adult. It is obvious that the relation of the cranium may be a factor in the causation of the gyri, for the increase of surface area necessitated by the increased amount of cortical grey substance might be limited by a cranial cavity of small size. It is probable that the second contact of the cortex with the cranium (during the eighth month) may at least cause a deepening and accentua- tion of the gyri already begun. Evidently the form of the cranium modifies the gyri, and to a certain extent probably determines their direction, for in long, dolichocephahe crania the an- tero-posterior gyri are most accentuated, and in the wide, brachycephalic crania the transverse gyri are most marked. At birth all the main fissures and sulci are present, but some of the smaller sulci appear later. In the growing pallium both the bottoms of the sulci as well as the summits of the gyri move away from the geometrical center of the hemisphere, the summits more rapidly, and hence the sulci or fissures first formed grow gradually deeper as long as growth continues. The mechanical factors in the growth processes which result in the more or less regular arrangement of the gyri of the hemispheres of a given group of animals have not been satis- factorily determined. It has been suggested that the differences in arrangement of the gyri in different groups of animals may be in part dependent upon the functional importance of the various regions — the amount of grey substance of a region varying with the functional impor- tance, and the consequent local increases being accompanied by resultant local foldings. This idea is supported by the fact that while the soma^sthetic (sensory-motor) area of the cortex varies with the bullc of the body, the frontal gyri, so much developed in man and which are one of the chief regions of the assooiational phenomena, are relatively independent of and do not vary with the weight of either the body or the brain. Surface area. — The total surface area of the adult human telencephalon is about 2300 sq. cm. Of this area almost exactly one-third is contained on the outer or exposed surfaces of the gyri, while the other two-thirds is found in the walls of the sulci and fissures. Lobes of the Telencephalon and the Gyri and Sulci The folded pallium of each hemisphere is arbitrarily divided into lobes, partly by the use of certain of the main fissures and sulci as boundaries and partly by the use of imaginary Hues (figs. 672, 673). These divisions are sbc in number, them- selves subdivided into their component gyri: — (1) Temporal lobe. (2) Insula (Central lobe or Island of Reil). (3) Frontal lobe. (4) Parietal lobe. (5) Occipital lobe. 854 THE NERVOUS SYSTEM (6) Olfactory brain or rhinencephalon (including structures comprised in the other lobes and often grouped under the two names olfactory lobe and limbic lobe) . This division of the cortex of the hemisphere is largely a merely topographical one. With the exception of the temporal lobe and the rhinencephalon, it has little of either morphological or functional value. The occipital lobe contains the recognised visual area of the cortex, but this area, as such, does not involve all of the lobe. In their functional significance, the frontal and parietal lobes, especi- ally, overlap each other. The temporal lobe. — This is the first lobe whose demarciition is indicated. During the second month of intra-uterine life there appears a slight depression on the lateral aspect of the then smooth hemisphere. As the pallium further grows, this depression deepens into a well-marked fossa with a relatively broad floor. This fossa marks the beginning of the lateral cerebral fissure or fissure of Sylvius, and is, therefore, known as the Sylvian fossa. As the pallium continues to project outward, the folds which form the margins of the Sylvian fossa increase in size and height and begin to overlap and conceal its broad floor, which is the beginning Fig. 673. — Diagram of the Convex Surface of the Left Cerebral Hemisphere showing THE Five Principal Lobes op the Pallium. The opercular regions of the frontal, parietal, and temporal lobes are removed to show the cen- tral lobe or island of Reil. Central sulcus (Roland!) Parietal lobe Central lobe (insula) Central sulcus of insula of the insula. The overlapping folds thus become the opercula, and as their lips approach each other, there results the deep fissure of Sylvius, which marks off anteriorly an infero-lateral limb of the pallium, termed by position the temporal lobe. As growth proceeds further, the temporal lobe thickens, the temporal pole extends further forward and becomes a free projection, thus lengthening the fissure of Sylvius and resulting in the inferior extension or stem of this fissure, which runs between the temporal pole and the frontal lobe and curves under so as to appear on the basal surface of the hemisphere. Finally the cortex of the lobe itself is thrown into folds or gyri. Its posterior end is never marked off from the lobes above and behind, except by arbitrary fines which will be mentioned in con- nection with those lobes. The temporal lobe forms part of the lateral convex and tentorial surfaces of the hemisphere, and its anterior portion is adapted to the surface of the middle cranial fossa. It thus has a superior and lateral surface and a basal and tentorial surface. In these surfaces are the following gyri with their intervening and bounding sulci (fig. 674) : — The superior temporal gyrus is bounded by the posterior ramus of the lateral fissure, and extends from the temporal pole backward into the supra-marginal region of the parietal lobe above. The upper margin of this gyrus constitutes the temporal operculum, in that it aids in overlapping and enclosing the insula in the floor of the lateral fissure. This margin is for the most part smooth, being THE TEMPORAL LOBE 855 occasionally interrupted by a few weak twigs of the lateral fissure. It is separated from the gyrus below by the superior temporal sulcus, which is parallel with the posterior ramus of the lateral fissure and is frequently called the parallel sulcus. The posterior extremity of this sulcus divides the angular gyrus of the parietal lobe, and its anterior end disappears in the temporal pole, sometimes as a continu- ous groove, sometimes in isolated pieces. The middle temporal gyrus likewise begins in the temporal pole and is con- tinuous backward into the angular gyrus of the parietal lobe. The inferior temporal gyrus forms the infero-lateral border of the temporal lobe, and is usually more broken up than the two gyri above it. It begins continuous with them in the frontal pole, and extends horizontally backward into the lateral gyri of the occipital lobe. It is separated from the middle gyrus by the middle temporal sulcus, which likewise is never so continuous a furrow as the superior temporal sulcus. Frequently this sulcus occurs in detached portions and often terminates within the temporal lobe. Fig. 674. — Outline Dkawing of Convex Surface of Left Cerebral Hemisphere. (After Toldt, "Atlas of Human .^atomy," Rebman, London and New York.) Precentral sulcus Central sulcus (RolandiJ Inferior frontal sulcus\ y^ ^ \/^ ^ f vj? . ^ > ,^,^ Horizontal ramus " of interparietal sulcus Superior ex- tremity of parieto-occi- pital tissure Gyri, LpitalesI Transverse Inferior frontal gyrus The fusiform gyrus is in the basal and tentorial surface of the temporal lobe (fig. 676). Its usual somewhat spindle shape suggests its name, and it is con- tinuous backward into the occipital gyri, or its posterior end may be completely isolated by a union of the inferior temporal sulcus and the collateral fissure, which two furrows separate it from its neighbours on either side. Anteriorly the fusiform gyrus runs into the common substance of the other three gyri at the temporal pole. The lingual gyrus is usually included in the tentorial surface of the temporal lobe, though in some texts it is regarded as a part of the occipital lobe. Its larger, posterior portion lies within the boundaries of the occipital lobe. Bounded laterally by the collateral fissure, it is continuous anteriorly into the hippocampai gyrus of the rhinencephalon (fig. 676). All of the sulci give off occasional lateral twigs {transverse temporal sulci) which themselves may or may not branch, and which tend to divide the main gyri into transverse temporal gyri. The lateral fissure (fissure of Sylvius). — -As promised in its origin by the over- lapping and enclosing of the broad floor of the Sylvian fossa by the adjacent folds of the pallium, the lateral fissure is the deepest and most conspicuous fissure of the cerebral hemisphere. Its main divisions are a short stem and three main branches. The stem lies in the basal surface of the hemisphere, where it begins 856 THE NERVOUS SYSTEM in a depression in the anterior perforated substance, the vallecula Sylvii, and passes forward and upward between and separating the temporal pole and the super- ciliary border of the frontal lobe. It corresponds in direction with the posterior border of the lesser wing of the sphenoid bone, which projects backward into it, and it contains the middle cerebral artery, the Sylvian vein, and the sinus alse parvse. It appears on the upper surface at a point known in cranial topography as the Sylvian point, where it divides into its three main branches : — (1) The posterior ramus is the linear continuation of the fissure, and runs horizontally backward and upward to terminate in the supra-marginal gyrus of the parietal lobe. (2) The anterior ascending ramus passes upward for about 10 mm., sub- dividing the inferior gyrus of the frontal lobe. (3) The anterior horizontal ramus passes forward from the stem of the fissure about 10 mm., and likewise into the' inferior frontal gyrus, but parallel with the superciliary border. Fig. 675. — The Insula with its Gtki and StrLCi. (Shown by widely separating the opercula.) Gyri breves ) Operculum ' I „ t of insula C^yrus longus J Circular sulcus Transverse -W — J> temporal " gyri Central sulcus of Superior temporal gyrus These branches, together with certain smaller collateral twigs, divide the over- lapping or opercular portions of the adjacent pallium into (a) the tem-poral opercu- lum, which lies below the posterior ramus; {h) the fronto-parietal operculum, or operculum proper, which lies above and behind the anterior ascending ramus; (c) the frontal operculum,, between the latter and the anterior horizontal ramus; {d) and the orbital operculum, below the anterior horizontal ramus. Collectively the opercula are known as the opercula of the insula. The insula (central lobe). — The insula or island of Reil is a triangular area of the cerebral cortex lying in the floor of the lateral fissure, and concealed by the opercula. Of these, the temporal operculum overlaps the insula to a greater extent than either the frontal or parietal. More than half of it may, therefore, be exposed, by gently pressing away the temporal lobe. The insula corresponds to the broad floor of the Sylvian fossa of the embryonic brain. In the developed condition its surface is convex lateralward and is itself folded into gyri. The apex of the triangle appears upon the basal surface of the hemisphere, and is the only portion which may be seen without disturbing the specimen. The apex appears as the end of a small gyrus under the temporal pole, and in close relation with the THE FRONTAL LOBE 857 anterior perforated substance and the vallecula Sylvii, and is known as the limen of the insula. In the folding process by which the opercula accomplish the overlapping and enclosing of the island, there results a deep sulcus which sur- rounds its entire area except at the limen insulse. This is known as the circular sulcus, or limiting sulcus of Reil. The gyri (and sulci) of the insula radiate from the apex of the triangle. The central sulcus of the insula is the deepest. It runs from below backward and upward, parallel with the central sulcus of Rolando above and divides the insula into a larger anterior and a smaller posterior portion. The anterior portion consists of from three to five short irregular gyri breves or precentral gyri, separated by sulci brevis ; the posterior portion consists of a single, slightly furrowed gyrus, which is long and arched and extends from the apex to the base of tlTe triangle, the gyrus longus. In a recent study of the insula of more than 200 human brains, including a few of idiots and paralytics and a series of young fcetuses, Nelidoff finds that the left island is more deeply marked by sulci and averages 11 mm. longer than the right; that, of the sulci in the island, the central sulcus is the first to appear, is the most persistent sulcus in defective brains, though occasionally absent in microcephalic idiots, and that in the average it is more pronounced in males than in females. The frontal lobe. — This is the most anterior of the lobes of the hemisphere, and hke the two lobes behind, it has a convex or lateral, a basal, and a mesial surface. The convex surface begins with the frontal pole, and is bounded posteriorly by the central sulcus {Rolandi). The basal surface extends backward to the stem of the lateral fissure, covered by the frontal pole. The mesial surface is separated from the gyrus cinguli of the rhinencephalon (limbic lobe) by the sub- frontal part of the sulcus cinguli (calloso-marginal fissure), and from the parietal lobe by a line drawn perpendicularly from the upper extremity of the central sulcus (Rolandi) to the sulcus cinguli. These surfaces include the following gyri and sulci: — • Convex surface Basal surface Mesial surface Gyri. Anterior central gyrus. Superior frontal gyrus. Middle frontal gyrus < Inferior frontal gyrus \ Sulci. Precentral sulcus Superior portion. Inferior portion. Opercular portion. Triangular portion. Orbital portion. Orbital gyri Lateral. Anterior. Posterior. Medial. Gyrus rectus. Superior frontal gyrus. Marginal gyrus. Paracentral lobule (anterior part). Superior. Inferior. Superior frontal sulcus. Middle frontal sulcus. Inferior frontal sulcus. Anterior ascending ramus of lateral fissure. Anterior horizontal ramus of lat- eral fissure. Lateral. Orbital sulci \ Medial. Transverse. Olfactory sulcus. Rostral sulci. Many of the sulci, especially the superior frontal and the rostral sulci, often give off twigs or are broken up into short furrows which give rise to small folds [gyri transitivi], too inconstant to be given special names. The anterior central gyrus (ascending frontal convolution) is the only gyrus of the frontal lobe having a vertical direction. It lies parallel to the central sulcus (Rolandi), and thus extends obliquely across the convex surface from the posterior ramus of the lateral fissure (frontal operculum) to the supero-mesial border, and is continuous on the mesial surface with the anterior portion of the para-central lobule. It comprises the larger part of the motor portion of the somsesthetic (sensory-motor) area of the cerebral cortex. It is separated from the horizontal frontal gyri in front of it by the precentral sulcus. This sulcus is developed in three parts, but the upper and middle parts in the foetal brain usually fuse together, so that in the later condition it consists of a superior and an inferior segment. The superior cuts the supero-mesial border of the hemisphere and appears on the mesial surface in the paracentral lobule. On the convex surface it is usually cormected with the posterior end of the superior frontal sulcus (fig. 674). The superior frontal gyrus is a relatively broad, uneven convolution, com- prising the anterior portion of the supero-mesial border of the hemisphere, and therefore extends horizontally from the precentral sulcus to the frontal pole. It is sometimes inperfectly divided into a superior and an inferior part by a series of 858 THE NERVOUS SYSTEM detached, irregular furrows, spoken of collectively as the para-medial sulcus. The resulting transitory gyri are of considerable interest in that they are peculiar to the human brain, and are said to be more marked in the higher than in the lower types. The middle frontal gyrus is likewise a broad strip of pallium extending from the precentral sulcus to the temporal pole. It is separated from the superior frontal gyrus by the superior frontal sulcus, which is usually continuous into the superior section of the precentral sulcus and thence extends horizontally to the frontal pole. The middle frontal gyrus is in most cases subdivided anteriorly into a superior and an inferior portioii by a middle frontal sulcus. This sulcus begins above and runs into the frontal pole, where, upon reaching the superciliary border, it frequently bifurcates into a transverse furrow, known as the Jronto-marginal sulcus. The inferior frontal gyrus forms the superior wall of the lateral fissure, and is separated from the middle frontal gyrus by the inferior frontal sulcus. This sulcus usually begins continuous with the inferior section of the precentral sulcus, and extends, very irregularly and frequently interrupted, toward the frontal pole. The gyrus abuts upon the anterior central gyrus, and its posterior portion is divided into three parts (the frontal opercula) by the anterior ascending and horizontal rami of the lateral fissure. The part behind the anterior ascending ramus is the opercular portion (a part of the fronto-parietal operculum or opercu- lum proper), sometimes referred to as the basilar portion. In most brains this part is traversed by a short oblique furrow, the diagonal sulcus. The part be- tween the two anterior rami of the lateral fissure is the cap-shaped triangular portion. This portion frequently involves one and sometimes two descending twigs of the inferior frontal sulcus. The part below the anterior horizontal ramus is by position the orbital portion. It is seen that the inferior frontal gyrus gives rise to the whole of the frontal operculum and the antei'ior half of the fronto-parietal operculum. The opercular portion is of special interest in that in the left hemisphere it constitutes the celebrated convolution of Broca, the motor area for the function of speech. The area controlling speech, however, involves that part of the triangular portion bounding the anterior ascending ramus of the lateral fissure as well, and both these parts often appear more developed on the left hemisphere. The development of the opercula of the inferior frontal gyrus is a distinctive characteristic of the human brain. This gyrus does not develop opercula even in the highest varieties of apes. The development of the function of speech in man no doubt influences the development of the frontal opercula. On the basal surface (fig. 676) of the frontal lobe is the orbital area and the gyrus rectus. The more pronounced of the orbital sulci are often so joined with each other as to form an H-shaped figure standing parallel to the mesial plane, and thus they comprise a medial, a lateral and a transverse orbtial sulcus. This figure naturally divides the orbital area into four gyri: — (1) The lateral orbital gyrus is tlie basal continuation of the inferior frontal gyrus, and is thus related to the orbital portion of the frontal operculum; (2) the anterior orbital gyrus is continuous at the pole with the middle frontal gyrus; (3) the posterior orbital gyrus is closely related to the limen insulse and the stem of the lateral fissure, and its outer part is in relation with the orbital portion of the operculum ; (4) the medial orbital gyrus is continuous over the superciliarj^ border with the superior frontal gyrus. It frequently contains one or two short, isolated sulci. Its mesial boundary is the straight olfactory sulcus, in which lies the olfactory bulb and tract of the rhinencephalon. This sulcus marks off a narrow straight strip of cortex between it and the mesial border of the lobe known as the gyrus rectus. The posterior portion of the gyrus rectus comprises a part of the parol- factory area or Broca's area, which functionally belongs to the rhinencephalon. As an area or field, this appears mesially lying between the anterior and posterior parolfactory sulci. On the mesial surface (fig. 679), of the frontal lobe the superior frontal gyrus is separated from the gyrus cinguli of the rhinencephalon (limbic lobe) by the well- marked sulcus cinguli. Anteriorly the superior frontal gyrus is subdivided by the main stem of the rostral sulci into a marginal gyrus, and what may be termed a sub'marginal gyrus. The marginal gyrus is usually broken into smaller parts by twifi's of the rostral sulci, most of which are perpendicular to the main stem, while the submargJnal gyrus is less frequently interrupted. Posteriorly the superior frontal gyrus constitutes the anterior portion of the paracentral lobide, a part of THE CENTRAL SULCUS 859 the somsesthetic area of the mesial surface of the hemisphere. This lobule is usually marked off anteriorly by a vertical twig from the sulcus cinguli. The sulcus cinguli (calloso-marginal fissure) is the longest and one of the most prominent sulci on the mesial surface of the hemisphere. It divides the anterior portion of the mesial surface into a marginal part above and a callosal part below — in other words, it separates the superior frontal gyrus from the gyrus cinguli. Its subfrontal portion begins below the rostrum of the corpus callosum and curves forward and upward around the genu, and then turns backward above the body of the corpus callosum. Before it reaches the level of the splenium, it turns up- ward and cuts and terminates in the supero-mesial border of the hemisphere, as the next sulcus behind the upper termination of the central sulcus. This upward Fig. 676. — Basal Surface of the Cehebbal Hemisphebes. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Longitudinal fissure Frontal pol Olfactory sulcus Orbital sulci Olfactory bulb Olfactory tract Medial, intermediate, and lateral olfactory strige Temporal pole Olfactory trigone^ I ^ Optic chiasma ~4-A^ Chorioid fissure -^[ Collateral fissure Isthmus of gyrus fornicatus Substantia nigra Tegmentum of mesencephalon Gyrus fornicatus Occipital pole Aquseductus cerebri (Sylvu) Lamina quadrigemina of corpus callosum Longitudinal fissure turn is the marginal portion of the sulcus cinguli. It is sometimes an abrupt curve and sometimes curves gradually, but its marginal relation to the upper end of the central sulcus is so constant that it serves as a means by which either of the sulci may be identified. The marginal portion separates the paracentral lobule from the precuneus (quadrate lobule), and is wholly within the parietal lobe. One of the most constant twigs of the sulcus cinguli is that which marks off the paracentral lobule from the superior frontal gyrus. Another sometimes divides the paracentral lobule into its frontal and parietal portions. The sulcus cinguli is developed from two and sometimes three (anterior, middle, and pos- terior) separate furrows, which later extend and fuse into continuity. This metliod of its development may explain the irregularities frequently met with and the fact that sometimes in the adult the sulcus occurs in separate pieces. The central sulcus (fissure of Rolando) (figs. 674, 678) is one of the principal land- marks of the convex surface of the hemisphere. It separates the frontal from the parietal lobe, and likewise divides the somsesthetic area of the palUum. Its 860 THE NERVOUS SYSTEM upper end terminates in and usually cuts the supero-mesial border of the hemis- phere immediately in front of the termination of the marginal portion of the sulcus cinguli. Thence it pursues an oblique though sinuous course forward across the convex surface of the hemisphere, forming on the average an angle of about 72° with the supero-mesial border (Rolandic angle), and terminates in the fronto- parietal operculum immediately above the posterior ramus, and about 2.5 cm. be- hind the point of origin of the anterior rami of the lateral fissure. It rarely cuts through the fronto-parietal operculum. In its sinuous course, varying from the line of its supero-mesial end, two bends are marked (fig. 677) : — (1) The superior genu occurs at about the junction of the upper and middle thirds of the sulcus and is concave forward. It accommodates the greater part of that portion of the cor- tex which is the motor area for the muscles of the leg and trunk, and the develop- ment of this area in man probably aids in producing it. (2) The inferior genu occurs below, is concave forward and is commonly a little more marked than the superior genu. It is probably in part a result of the superior genu — the turn of the sulcus in resuming its general course, but it may further result from the develop- ment of the shoulder and arm area of the cortex which occupies its concavity. Fig. 677. — Diagram Representing the Most Common Form of the Central Sulcus and Indicating the Regions of Junction upon it of the Areas of the Peecenteal Gyrus Devoted to the Dipfeeent Regions of the Body, as Estimated by Symington and Crymble. Superior-mesial border of hemisphere ' ^'''' ^^ Regionof junctionof legand trunk areas Region of junction of trunli and Lateral end of sulcus , Operculum The central sulcus (Rolandi) appears in the pallium of the fcetus during the latter part of the fifth month. It then consists of a lower longer and an upper shorter part. Usually these two parts become continuous before birth; very rarely do they remain separate in the adult. The point of their fusion is sometimes manifest within the depth of the sulcus. If the lips of the sulcus be pressed widely apart at about the region of the junction of its middle and upper thirds, it will be found that the opposing walls give off a number of protuberances or lateral gyri, which dovetail into each other when the sulcus is closed. Sometimes two of these lateral gyri appear fused across the floor of the sulcus, so as to form a bridge of grey substance known as the deep annectant gyrus. This interruption of the continuity of the sulcus, when present, repre- sents the point at which the two parts of the sulcus in the fcctal brain joined each other without the continuity becoming wholly completed in the adult. The genua of the adult sulcus may often be due to the precedent parts not being ia hne at the time of their fusion. From a special study of the central sulcus of 237 normal adult hemispheres, Symington and Crymble (1913) give the following details: (1) that the most common course of the sulcus is that illustrated in fig. 677, above; (2) that it varies in depth both in a given specimen and in different specimens — the greatest variations in depth reported for a given sulcus being from 22 to 12 millimeters, the shallowest part being in the region of the deep annectant gyrus; (3) that the average length from the supero-mesial border of the hemisphere to the opercular end of the sulcus is about 9 cm. in direct line and 10.4 cm. following the curves of the sulcus. The average length of the curved floor is 7.9 cm. (4) From the supro-meisal end of the sulcus to the points of junction of the general areas of the precentral gyrus, direct line measurements give averages, (a) to the junction of leg and trunk areas, 3.5 cm.; (b) to junction of trunk and arm areas, 4.5 cm.; (c) to junction of arm and face areas, 7.5 cm. The parietal lobe. — The parietal lobe occupies a somewhat smaller area of the human telencephalon than either the frontal or the temporal lobe. It has a convex and a mesial surface, but no basal surface. It is separated from the frontal lobe in front by the central sulcus; from the occipital lobe behind, on the mesial surface by the parieto-occi-pital fissure (fig. 650), and, on the convex surface, THE PARIETAL LOBE 861 by an arbitrary line drawn transversely around the convex surface of the hemi- sphere from the superior extremity of this fissure to the infero-lateral border; and it is separated from the temporal lobe below by the horizontal part of the posterior ramus of the lateral fissure, and by a line drawn in continuity with this horizontal part to intersect the transverse line drawn to limit it from the occipital lobe. . The preoccipital notch. — In situ, the infero-lateral border of the posterior portion of the hemisphere rests over a small portion of the parieto-mastoid suture of the cranium, and upon this structure occurs a fold or vertical thickening of the dura mater, which slightly indents the infero-lateral border. This indentation occurs about 4 cm. from the occipital pole, and is con- sidered one of the points of hmitation of the parietal from the occipital lobe, and is therefore called the preoccipital notch. While during late foetal Ufe and early childhood it is well marked, it is usually very shght in the adult bram, and is, as a rule, evident only in brains hardened Fig. 678. — Convex Surface of the Cerebral Hemispheres as Viewed prom Above. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Frontal pole Supero-mesial border ^5^- Longitudinal fissure Precentral sulcus Central sulcus Interparietal sulc Superior occipital sulci ,^ Occipital pole in situ. When it is visible, the arbitrary transverse line from the superior extremity of the parieto-occipital fissure, used as a boundary, between the convex surfaces of the parietal and occipital lobes, should be so drawn as to bisect the preoccipital notch. The convex surface of the parietal lobe comprises the following gyri and sulci : — The posterior central gyrus (ascending parietal) extends obliquely across the hemisphere parallel with the anterior central gyrus of the frontal lobe, from which it is separated by the central sulcus. Its inferior end is bounded by the posterior ramus of the lateral fissure, and constitutes the posterior or parietal portion of the fronto-parietal operculum. Its upper end takes part in the supero-mesial border of the hemisphere, and is bounded posteriorly by the tip end of the marginal portion of the sulcus cinguli. Its postero-lateral boundary consists of the two more or less vertical rami or factors of the interparietal sulcus, viz., the inferior and superior portions of the postcentral sulcus, either continuous -nith each other or detached. The interparietal sulcus (intraparietal) is often the most complicated sulcus of the pallium. Its development usually begins as four different furrows in the foetal brain, and the difficulty with which it is traced in the adult brain depends 862 THE NERVOUS SYSTEM upon the extent to which these four factors become continuous in the later de- velopment. When continuity of the furrows is well established, the entire sulcus may be described as consisting of a convex horizontal ramus, which gives off a few short collateral twigs and wliose either end is in the form of an irregular, reclining -\ . The transverse bar of the anterior end arises fron two of the four factors of the entire sulcus: — (1) an inferior furrow, the inferior postcentral sulcus, commenc- ing above the posterior ramus of the lateral fissure and ascending as the boundary of the lower half of the posterior central gyrus, and (2) a superior furrow, the superior postcentral sulcus, lying behind the upper portion of the posterior central gyrus, and which, upon approaching the supero-mesial border, may turn back- ward a short distance parallel with the horizontal ramus, as in fig. 674. When confluent, these two factors form together a continuous postcentral sulcus. In the adult the inferior of the two is always continuous with the horizontal ramus; when confluent, the two figures join so as to form the transverse bar of the anterior end of this ramus. The horizontal ramus, which represents the Fig. 679. — Outline Drawing op Mesial Surface of Left Cerebral Hemisphere. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Sulcus cinguli (marginal portion) Parieto-occipital fissun Calcarine fissure Sulcus cinguli (subfrontal portion) Sulcus corporis callosi '. Genu of corpus callosum \ \ \ Rostum of corpus callosum , v^ \ Anterior parolfactory sulcus \ \ Parolfactory area (Broca's area) \ Posterior parolfactory sulcus Sub-callosal gyrus (peduncle of / corpus callosum) Tuber cinereum Infundibulum third of the primary furrows, is continued backward past the superior extremity of the parieto-occipital fissure into the occipital lobe, where it usually joins the occipital ramus, the fourth of the primary furrows. This ramus divides shortly into two branches which run at right angles to the stem, forming the transverse occipital sulcus, and thus arises the transverse bar of the posterior end of the inter- parietal sulcus. The occipital ramus may, however, consist of little more than the transverse bar, which may or may not be joined by the horizontal ramus. The occipital ram.us is more frequently separate from the horizontal than is the postcentral sulcus. In their development the inferior postcentral sulcus appears first (during the latter part of the sixth month), the occipital ramus second, the horizontal ramus third, and last, the superior postcentral sulcus. The superior parietal lobule (gyrus) is the area of the supero-mesial border of the parietal lobe. It is limited in front by the superior postcentral sulcus, below by the horizontal ramus of the interparietal sulcus, and posteriorly it is continuous around the superior end of the parieto-occipital fissure into the cortex of the occipital lobe. It is a relatively wide area (lobule),' always invaded by collateral twigs of its limiting sulci, and usually contains a few short, isolated furrows. When the parieto-occipital fissure is considerably prolonged over the supero-mesial border (external parieto-occipital fissure), the continuation of the THE OCCIPITAL LOBE 863 lobule about the end of this fissure presents the appearance described as the parieto-occipital arch. The inferior parietal lobule is limited in front by the inferior postcentral sulcus, and above by the horizontal ramus of the interparietal sulcus. It is con- tinuous with the cortex of the temporal lobe below, and with that of the occipital lobe behind, and is therefore invaded by the ends of the sulci belonging to these lobes. Its anterior portion is separated from the temporal lobe by the horizontal portion of the posterior ramus of the lateral fissure. The upturned end of this ramus invades the anterior portion of the lobule and the broad fold, arched around this end and continuous behind it into the superior temporal gyrus, is known as the supramarginal gryus — the area to which auditory word- and tone-images are attributed. The angular gyrus is the portion which embraces the posterior end of the superior temporal sulcus, and is continuous behind this into the middle temporal gyrus and in front with the superior temporal gyrus. It is the area for visual word images. Its shape is usually such as to suggest its name. The most posterior part of the inferior parietal lobule, when arching in a similar way about the end of the middle temporal sulcus and continuous with the temporal gyri on its either side, is known as the post -parietal gyrus. This is a smaller area than either of the other two, and, owing to the variability of the end of the middle tem- poral sulcus, is not always evident. The mesial surface of the parietal lobe is divided into two parts by the marginal portion of the sulcus cinguli. The anterior and smaller part is the mesial con- tinuation of the posterior central gyrus, and comprises the posterior portion of the paracentral lobule. It is limited from the part of this lobule belonging to the frontal lobe by a vertical line drawn from the marginal extremity of the central sulcus. The praecuneus {quadrate lobule) is the posterior and larger part of the mesial surface of the parietal lobe. It is separatd from the cuneus of the occipital lobe by the parieto-occipital fissure, and is imperfectly separated from the gyrus cinguli (limbic lobe) below by the sub-parietal sulcus (postlimbic fissure), branches of which invade it extensively. The occipital lobe. — This is a relatively small, trifacial, pyramidal segment, comprising the posterior extremity of the hemisphere, its apex being the occipital pole. Though one of the natural divisions of the cerebral hemisphere, it is very indefinitely marked off from the lobes anterior to it. Though it contains the cortical area of the visual apparatus, only in the brains of man and the apes does it occur as a well-defined posterior projection. In most of the mammalia it is not differentiated at all. Its three surfaces comprise a convex, a mesial, and a tentorial surface. Its convex surface is separated from that of the parietal and temporal lobes by the superior and external extremity of the parieto-occipital fissure, and by an arbitrary line drawn transversely from this extremity to the infero-lateral border of the hemisphere, or so drawn as to bisect the pre-occipital notch when this is evident. The sulci which occur on the convex surface may be described as two, though both of these are very variable in their e.xtent and shape, and their branches are inconstant both as to number and length. (1) the transverse oc- cipital sulcus is the most constant in shape. It extends a variable distance transversely across the superior portion of the lobe, and, as noted above, it is frequently continuous with the interparietal sulcus through its occipital ramus, and when so, it appears as the posterior terminal bifurcation of this sulcus (fig. 674). When detached, it often occurs merely as a definite furrow with few rami, and sometimes the ramus by which it otherwise would join the inter- parietal sulcus is entirely absent. (2) The lateral occipital sulcus is always short, and has its deepest portion below the transverse sulcus. It usually has a somewhat oblique course toward the supero-mesial border. Sometimes it occurs in several detached pieces, then known collectively as the lateral occipital sulci. Therefore, the gyri of the convex surface of the lobe are also variable. They are not sufficiently constant to merit individual names. The lateral occipital sulcus or sulci roughly divide them into an inferior and lateral area, known as the lateral occipital gyri, and into a uperior larea, the superior occipital gyri. The lateral area is continuous into the gyri of the temporal lobe, while the superior area is continuous into the gyri of the parietal lobe. The mesial surface of the occipital lobe is separated from that of the parietal lobe (precuneus) and from the gyrus cinguh of the limbic lobe by the well- 864 THE NERVOUS SYSTEM marked parieto-occipital fissure. It comprises the constantly defined, wedge- shaped lobule known as the cuneus, and the posterior and mesial extremitj'- of the lingual gyrus. Since the greater portion of the length of the lingual gyrus is involved in the basal surface of the temporal lobe, this gyrus as a whole has been considered as belonging to the temporal lobe (see figs. 671, 676). The cuneus is separated from the hngual gyrus by the posterior portion of the calcarine fissure, which always terminates in a bifurcation, one limb of which invades the cuneus near the superomesial border. In addition the cuneus may contain other twigs from both the fissures bounding it, and also, when wide, may contain one or more short, detached sulci cunei. The calcarine fissure and the parieto-occipital fissure are almost invariably joined in the human brain, forming a Y-shaped figure, the prongs of which give the cuneus its shape. The calcarine fissure begins on the tentorial surface in the posterior portion of the hippocampal gyrus of the Umbic lobe, below the splenium of the corpus callosum, and extends backward across the internal occipital border of the hemisphere. It then bends downward and proceeds to its terminal bifurcation in the polar portion of the occipital lobe. The stem or hippocampal portion of the fissure is deeper than the posterior or occipital portion. It produces a well- marked eminence in the medial wall of the posterior cornu of the lateral ventricle, known a^ the calcar avis or hippocampus minor. It is developed separately from the posterior portion, which itself first appears as two grooves. All three parts are usually continuous with each other before birth. The parieto-occipital fissure usually appears from the first as a continuous groove. It begins in the supero-mesial border of the hemisphere, rarely extending into the convex surface more than 10 mm. (external parieto-occipital fissure), thence it extends vertically downward across the mesial surface (internal parieto-occipital fissure), and terminates by joining the cal- carine fissure at the region of the downward bend of the latter, or at about the junction of its anterior and middle thirds. In certain of the lower apes and in the brain of the chimpanzee there is no junction between the two fissures, they being kept apart by a narrow neck of cortex, the gyrus cunei. Neither are they joined in the human foetus. If in the adult human brain the region of their'junction be opened widely, there will be found a submerged transitory gyrus (deep annectant gyrus), which is the gyrus cunei, superficial in the fcetus. In the higher apes and in micro-cephalic idiots this gyrus may be on the surface or partially submerged. Two other transitory gyri (annectant gyxi) are to be found by pressing open the calcarine fissure, and they mark the points at which its three original grooves became continuous during its development into a boundary between the cuneus and the lingual gyi'us. Of these, the anterior cuneo-lingual gyrus crosses the floor of the calcarine fissure on the posterior side of its junction with the parieto-occipital fissure, and therefore near the gyrus cunei. The posterior cuneo- lingual gyrus occurs near the region of the terminal bifurcation of the fissure. The tentorial surface of the occipital lobe is blended intimately with that of the temporal lobe, from which it is separated only by an arbitrary line drawn to join the line of demarcation for the convex surface, at the region of the pre- occipital notch, and thence to the isthmus of the gyrus fornicatus — the narrow neck of cortex connecting the gyrus cinguh with the hippocampal gyrus, just below the splenium of the corpus callosum (see fig. 671). The gyri blending the occip- ital and temporal lobes across this fine are the lingual gyrus, already mentioned, and the fusiform gyrus (occipito-temporal convolution). In fact, the tentorial surface of the lobe may be considered as nothing more than the posterior ex- tremity of the fusiform gyrus, and the inferior portion of the same extremity of the lingual gyrus. The former is often somewhat broken up and is then continuous into the lateral occipital gyri. The two gyri are separated by the collateral fissure the posterior end of which extends into the occipital lobe. The fusiform gyrus is bounded laterally by the inferior temporal sulcus, which sometimes is continuous by a lateral twig, across the posterior end of this gyrus, with the collateral fissure. The Rhinencephalon The rhinencephalon or olfactory brain includes those portions of the cerebral hemisphere which are chiefly concerned as the central components of thie olfactory apparatus. Owing to the preponderant development of the other divisions of the hemisphere, the parts comprising this division appear relatively but feebly de- veloped in the human brain. In most of the mammals the sense of smell is relatively much more highly developed, and in many of the larger mammals the parts comprising the rhinencephalon are of greater absolute size than in man, though their cerebral hemispheres may be considerably smaller. In the human foetus the parts of the rhinencephalon are relatively much more prominent than after the completed differentiations into the adult condition. In the broader THE RHINENCEPHALON 865 sense of the term the rhinencephalon includes those parts of the hemisphere usually classed as comprising two lobes, viz., the olfactory lobe and the limbic lobe. Neither of these is a 'lobe' in the sense of comprising a definite segment of the hemisphere, as do the other lobes, and therefore the rhinencephalon cannot be called a distinct lobe. It is so strung out that by one or the other of its parts it is either in contact or continuity with each of the other lobes of the hemisphere. Morphologically, the rhinencephalon may be divided into an anterior and a posterior division. The anterior division. — the olfactory lobe proper, belongs almost wholly to the base of the encephalon, and consists of the following parts: — (1) The olfactory bulb is an elongated, oval enlargement of grey substance which lies upon the lamina cribrosa of the ethmoid bone, and, practically free, it presses under the anterior end of the olfactory sulcus in the basal surface of the frontal lobe. The numerous thin filaments of nonmeduUated axones of the olfactory nerve enter the cranium through the foramina of the lamina cribrosa and pass into the ventral surface of the bulb. Fig. 680. — Brain of Human Fcbtus of 22.5 Cm. (Beginning of Fifth Month), showing THE Parts of the Developing Rhinencephalon Apparent on the Basal Surface. (After Retzius.) dial olfactory gyrus (stria) Lateral olfactory gyrus (stria) Posterior parolfactory sulcus Uncus (hippocampal gyrus) Limen insulae ■Anterior perforated substance Hippocampal gyrus (2) The olfactory tract is a triangular band of white substance which arises in the olfactory bulb, and continues backward about 20 mm. to the region of the anterior perforated substance. It appears triangular in transverse section from the fact that its upper side fits into the olfactory sulcus. It becomes somewhat broader at its posterior end. (3) The olfactory trigone {olfactory tubercle) is the small triangular ridge, the posterior continuation of the olfactory tract joining the anterior perforated sub- stance. In it the olfactory tract breaks up into three roots, the lateral, in- termediate, and medial olfactory strice {gyri). The lateral olfactory stria em- phasizes the lateral portion of the trigone into the lateral olfactory gyrus, a portion of which is directly continuous into the lijnen insulce (figs. 676, 680). While a few of the fibres of the lateral stria penetrate this region, the greater mass of them pass obhquely lateralward over it and gradually disappear in the antero-lateral portion of the anterior perforated substance, in which some of them terminate, but through which most of them pass to curve into the anterior end of the hippocampal gyrus and terminate there, chiefly in the uncus. In most of the mammals the lateral stria is so strong that it appears as a super- ficial white band passing directly into the uncus. In the early foetus it is seen to enter the uncus in two branches, forming the medial semilunar gyms and the lateral gyrus ambiens upon the uncus. A portion of the limen insulce belongs to the rhinencephalon. (4) The parolfactory area (Broca's area) involves the mesial extension of the olfactory trigone, and is concerned with the medial olfactory stria. On the basal surface of the hemisphere this area involves the posterior extremity of the gyrus rectus — a portion of which is sometimes separated from the remainder of the gyrus by a ventral prolongation of the anterior parolfactory sulcus of the medial surface (see figs. 679, 706). This prolongation when present has been called the fissura serotina. On the medial surface the parolfactory area appears as a 866 THE NERVOUS SYSTEM definite gyrus. In front this is separated from the superior frontal gyrus by the anterior -parolfactory sulcus, and from the subcallosal gyrus behind by the deeper posterior parolfactory sulcus (fig. 679) . It is continuous above into the gyrus cin- guli of the limbic lobe, a portion of the posterior part of the rhinencephalon. A large portion of the fibres of the medial stria are lost in the parolfactory area, and are known to terminate about the cells there. This stria or root of the olfactory tract forms a slight ridge on the ventral surface of the area, which is frequently pi-ominent enough to retain the name medial olfactory gyrus appUed to it in the foetal brain (fig. 680). (5) The subcallosal gyrus (peduncle of the corpus callosum) is the narrow fold of the pallium which lies between the posterior parolfactory sulcus and the rostral lamina and the ventral continuation of the latter into the lamina terminalis. It begins above, in part fused to the rostrum of the corpus callosum, and in part continuous with the gyrus cinguli, and ventrally it goes over lateral ward and posteriorly into that portion of the anterior perforated substance known as the diagonal band of Broca, and in this way it extends into the uncus. Mesially, it approaches its fellow of the opposite side so closely that the groove separating the two is known as the median subcallosal sulcus of Retzius. Some fibres of the medial olfactory stria disappear in the substance of the subcallosal gyrus. (6) The anterior perforated substance must be considered with the rhinen- cephalon, but, like the limen insulae, it can only be considered as belonging in part to this division of the brain. It comprises the basal region between the optic chiasma and tract and the olfactory trigone. Usually the posterior parolfactory sulcus (fissura jmnia of the embryo) is sufficiently evident to more or less distinctly separate it from the latter. Its postero-lateral area is occupied by the diagonal band of Broca. A few fibres from the medial stria are known to dis- appear within its depths, and, as mentioned above, many fibres from the lateral stria also pass into it. The intermediate olfactory stria is always much the weakest of the three striae, and in many specimens is apparently absent. The fibres of this stria run almost straight backward and plunge directly into the anterior area of the anterior perforated substance, where some of them are known to terminate, while others continue into the uncus. On embryological grounds, the subcallosal gyrus and the anterior perforated substance are classed with the posterior division of the 'olfactory' lobe or anterior division of the rhinen- cephalon. The olfactory bulb and tract arise as a hollow outgrowth from the lower and anterior part of the anterior of the three primary vesicles. It is a tubular structure at first, and in many of the mammals the cavity maintains throughout hfe as the olfactory ventricle. In man the cavity becomes occluded and the ependyma and gelatinous substance which surround it become the grey core of the bulb and tract of the adult. The grey substance persists and develops chiefly in the bulb, and in fact produces it as such. It is much thicker on the inferior surface of the bulb than on the superior surface, and in section shows definite layers. From within outward, the principal of these layers are — (1) the layer of large cells whose shape suggests their name, mitral cells; (2) large dendrites of the mitral cells project toward the inferior surface of the bulb and there break up into numerous telodendria which copiously form synapses with like telodendria of the entering fibres of the olfactory nerve, thus forming rounded, much tangled glomeruli and the layer containing these, the glomerular layer; (3) the superficial layer, or olfactory layer, consists of the fibres of the olfactory nerve which form a dense interlacement with each other on the inferior surface of the bulb before they pass into its interior. The superior surface of the bulb becomes formed almost wholly of the fibres which arise as axones of the mitral cells and pass backward to form the olfactory tract, and thence to their localities of termination, chiefly by way of the three striiE. Along the dorsal, covered, aspect of the olfactory tract the gelatinous substance of the core may show through as a grey ridge. The posterior division of the rhinencephalon or the so-called limbic lobe (a name introduced by Broca in 1878) takes part in both the medial and tentorial surfaces of the hemisphere (fig. 681). Seen from the medial surface, it forms an irregular eUiptical figure which encloses the corpus callosum and the extremities of which approach each other at the anterior perforated substance, where they are continuous with the structures of the anterior division of the rhinencephalon. The figure is bounded externally by the sulcus cinguU above, by the subparietal sulcus (postlimbic sulcus) and the anterior limb of the calcarine fissure behind, and by the collateral fissure below. These respectively separate it from the frontal, parietal, occipital, and temporal lobes. It comprises the following THE RHINENCEPHALON 867 structures which are either wholly or in part devoted to the functions of the olfactory apparatus: — Part of gyrus cinguli and cingulum. Isthmus of the gj^rus fornicatus. 1. Gyrus fornicatus i f hippocampal gyrus. TT- uncus. Hippocampus ^^^^^^^ ^^^^^ ^^^^^.^^ [ fimbria. 2. The medial and lateral longitudinal strise upon the corpus callosum. 3. The fornix. 4. The mammillary body, the mammillo-thalamic fasciculus to the anterior nucleus of the thalamus and the mammillo-peduncular fasciculus. 5. Part of anterior cerebral commissure. 6. Part of septum pellucidum. 7. Most of medullary stria of thalamus. 8. Most of habenular nucleus. The gyrus fornicatus comprises the greater mass of the limbic lobe. As seen above, it is a term used to collectively represent a number of conjoined structures. Fig. 681. — Diagram showing Position of Structures Comprising the Limbic Lobe as Seen from the Mesial Aspect of the Cerebral Hemisphere. Fasciola cinerea Mammillo-thalamic fasciculus (Vicq d'azyri) ^V ^ Gyrus cinguli X \ Medial and lateral .' \ V — longitudinal striae of \ \ corpus callosum Septum pellucidum Subcallosal gyrus Olfactory bulb Medial olfactory stria Mammillary body Lateral olfactory stria Dentate fascia or gyrus Being an incomplete ellipse in form, its two ends are united to form a closed ring by means of the connection of the parolfactory area with the gyrus cinguli and the connection of the anterior perforated substance with the uncus of the hippo- campal gyrus. It is best described in terms of its three component parts indi- cated above: The gyrus cinguli begins in junction with the area parolfactoria below the anterior end of the corpus callosum, and curves above so as to entirely embrace the upper surface of the latter. It is separated from the frontal lobe by the sulcus cinguli (calloso-marginal fissure), from the parietal lobe by the subparietal sulcus, and from the corpus callosum below by the sulcus of the corpus callosum. By the latter it is separated from the longitudinal strite of the upper surface of the corpus callosum. The gyrus cinguli covers over, and its cells are closely associated with, the cingulum, a well- marked arcuate band of white substance, which follows the gyrus in its bend around the rostrum and backward to turn around the splenium of the corpus callosum in the isthmus of the gjTus fornicatus, and then to course forward into the hippocampal gyrus and the uncus. The cingulum is largely an association fasciculus between the gjTi of the temporal lobe and those gyri on the mesial surface of the cerebral hemisphere, its fibres for the most part running short courses, being continually added to it and continually leaving it. However, it contains olfactory axones running in two directions: (1) fibres from the medial olfactory stria and fibres arising in the parolfactory area, the gyrus subcaDosus and the anterior perforated substance which course posteriorly for distribution in the cortex of the gjTUs cinguli and hippocampal gyrus; (2) fibres arising in the hippocampal gyrus, especially the uncus, to course dorsalward through the isthmus and then forward as association fibres. Some fibres arising from the cortical cells of the g3TUS cinguli pass inferiorly through the cingulum, through the corpus callosum and, anteriorly, through the septum pellucidum to join the fornix below {perforating fibres of Ike fornix). The isthmus of the gyrus fornicatus is the constricted portion connecting the posterior end of the gja-us cinguli with that of the hippocampal gyrus (fig. 619 868 THE NERVOUS SYSTEM and 671). It is bounded externally by the anterior end of the calcarine fissure, and incloses the posterior turn of the cingulum. The hippocampus is the name applied to the curved appearances produced in the floor of the lateral ventricle by the peculiar foldings of this part of the cerebral cortex. The hippocanipal gyi'us (gyrus of the hippocampus) is the main gyrus of the tentorial surface of the hmbic lobe. Externally it is separated from the fusi- form gyrus by the collateral fissure, and it is bounded internally by the hippo- campal or, more inclusive, the chorioid fissure. Posteriorly it is partially divided by the calcarine fissme into the lingual gyrus (of the temporal lobe) and the isthmus of the gyrus fornicatus. Its anterior extremity is hooked backward and is known as the uncus {gyrus uncinatus) . This is almost entirely separated from the temporal lobe by a groove, the temporal notch. If the hippocampal fissure be opened up, the dentate gyrus or fascia and the fimbria will be seen. These lie side by side, separated by the shallow fimbrio -dentate sulcus (fig. 690.) The free edge of the dentate gyrus presents a peculiarly notched appearance, produced by numerous parallel grooves cutting it transversely. Its posterior end, sometimes called the fasciola cinerea, continues backward over the splenium of the corpus callosum, and upon the upper surface of the corpus callosum appears as a thin strip of grey substance which contains embedded in it the medial and lateral longitudinal strice. This thin strip is sometimes called the supracallosal gyrus (gyrus epicallosus, induseum griseum), and is thought to represent a ves- tigial part of the hippocampal gyrus. Closely beneath the splenium of the corpus caUosum, on the supero-mesial side of the hippocampal gyrus and mesial to the dentate gyrus, there sometimes occur suggestions of round or oval elevations of the grey substance which have been called the "callosal convolutions" or gyri Andrece Retzii. Rarely are they strongly developed, but when so they often produce a spiral appearance. The fimbria is but the fimbriated, free border of the posterior end or origin of the fornix, so folded as to project into the hippocampal fissure, parallel with the dentate gyrus (fig. 690). It is a conspicuous iDand composed almost entirely of white substance, continuous laterally with the thick stratum covering the ven- tricular surface of the hippocampus. It begins anteriorly in the hook or recurved extremity of the uncus. Traced backward, it is seen so curve upward, and within the ventricle it becomes part of the general accumulation of the white substance (alveus) of the surface of the hippocampus, which accumulation is the beginning of the fornix. The free border of the fimbria (seen in section) is known as the tcenia fimhrim. The fimbria is separated from the cerebral peduncles by the chorioid fissure, the thin, non-nervous floor of which alone intervenes between the exterior of the brain and the cavity of the lateral ventricle within. The hippocampal fissure attains its greatest depth between the dentate gyrus and the hippocampal gyrus, and the resulting eminence produced in the floor of the lateral ventricle is known as the hippocampus major, as distinguished from the lesser eminence produced posteriorly by the end of the calcarine fissme and known as the hippocampus minor [calcar avis]. The collateral fissure may like- wise produce a bulging in the wall of the ventricle, the collateral eminence. In transverse sections of the hippocampus major, the layers of grey and white sub- stance present a coiled appearance known as the cornu ammonis. Externally the medial surface of the hippocampal gyrus adjoining the dentate gyrus has reflected over it a delicate reticular layer of white substance known as the sub- stantia reticularis alba (Arnoldi). The fornix is the great association pathway of the limbic lobe, and appears to be wholly concerned in the apparatus of the rhinencephalon. It is a bilateral structure arched beneath the corpus callosum, with which it is connected ante- riorly by the septum pellucidum. Posteriorly it passes in contact with the splenium. It consists of two prominent strips of white substance, one for each hemisphere, the ends of which are separate from each other, while their inter- mediate parts are fused across the mid-line. These run above the chorioid tela of the third ventricle, and their lateral edges (tcenice fornicis) rest, on each side, along the line of the taenia chorioidea. The posterior, separate ends are known as the posterior pillars or crura of the fornix; the fused, intermediate portion is the body, and the separate, anterior ends are the anterior pillars or columns of the fornix. The posterior pillars [crura] of the fornix. — When seen from the medial aspect of the hemisphere, the fused portion of the fornix, in the separation of the hemispheres, is split along the mid-line (fig. 671). The half under examination THE FORNIX 869 may be seen to course obliquely lateralward under the splenium of the corpus cal- losum, and then, continuous into the fimbria, to curve forward and ventralward toward the uncus. The greater mass of the fibres coursing in the fornix arise as outgrowths of the cells of the uncus, hippocampal gyrus, and dentate gyrus. They accumulate as a dense stratum on the ventricular surface of these gyri, termed the alveus, which crops outward as the fimbria and which passes backward and up- ward; upon reaching the region of the splenium it turns obliquely forward under Fig. 682. — Diagram Showing Fornix and its Connections as seen from Above. olfactory bulb - Medial olfactory stria Subcallosal gyrus Column (anterior pillar) Fimbria Mammillo-thalamic fasciculus Stria terminalis of thalamus Stria meduUaris of thalamus Crus (posterior pillai) Epiphysis (below) Amygdaloid nucleus Hippocampus major Hippocampal commissure (lyra) it and approa(3hes the mid-line, to fuse with the hke bundle from the gyri of the hippocampus of the opposite side. The bundles thus arising from the two sides are the pillars or crura of the fornix. They appear as two flattened bands of white substance which come in close contact with and even adhere to the splenium. The angle formed by the mutual approach of the posterior pillars of the fornix is crossed by a lamina of commissural fibres connecting the hippocampal gyri of the two hemispheres (fig. 684). This lamina is the hippocampal commissure or transverse fornix. Like those of the fornix, its fibres arise from the cortex of the hippocampal gyri, but they serve as commissural fibres between the hippocampal gyri of the two hemispheres. Being of a different functional direction, it should not be considered a part of the fornix. The angle formed by the two pos- FiG. 683. — Diagram Illttsteating the Origin and Course of Forndc as viewed from the Side. Gyrus cinguli - Cinguli Longitudinal stris-- Fornix Perforating fibres Thalamic medullary stria Habenular nucleus Olfactory bulb and tract Anterior perforated substanci Uncus - ---Longitudinal strise Calcarine fissure ^Fimbria Hippocampal gyrus Mammillary body terior pillars of the fornix as traversed by the hippocampal commissure gives a picture named the psalterium or lyra. Usually the hippocampal commissure and the posterior pillars (crura) are in close contact with the under surface of the splenium. When occasionally they do not adhere, the space between is known as Verga's ventricle. According to recent studies of brains with degenerated corpus callosum, further commissural fibres between the limbic lobes course in the posterior angle of the septum pellucidum, and all along, transverse to the body of the fornix. The body of the fornix appears as a triangular plate of white substance produced by the fusion of the pillars. Its base or widest portion is behind. It is not always bilaterally symmetrical. Its upper surface is attached by the septum 870 THE NERVOUS SYSTEM pellucidum to the lower surface of the corpus callosum. Below, it lies over the chorioid tela of the third ventricle, which separates it mesially from the cavity of the third ventricle and laterally from the upper surfaces of the thalami. Its sharp lateral edge or margin (taenia fornicis) projects into the lateral ventricle of either side in relation with the chorioid plexus of that ventricle, and thus the lateral portion of its upper surface forms part of the floor of the lateral ventricle — an arrangement to be expected, since the posterior pillars arise from the floor of Fig. 684. — Horizontal Section of Telencephalon showing Bodt of Fornix and Hippo- CAMPAL Commissure as seen from Below and the Anterior Commissure in Section. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Genu of corpus callosum Parolfactory area (Broc^) ^ ^^^ ^„:,.-^ ^/ ^^^^^^^ „f ^^^^^^ ^^^^^^^ Triangular recess /f^ if \\\ TVX. ^^^^ ^^ caudate nucleus Putamen of lenticular nucleus Temporal lobe ^ Lateral cerebral fissure (Sylvii) Claustrum External capsule Internal capsule — Interventricular fora- men (MonroiJ Crus of fornix Gyrus cinguU ' Parieto-occipital fissure Globus pallidus Habenular nucleus fTail of caudate nucleus ^ — Inferior cornu of lat- eral ventricle Longitudinal fissure Medial surface of hemisphere Cuneus Calcarine fissure the ventricle, viz., the hippocampus. The ventricular portion is covered by a layer of ependyma in common with that lining the rest of the ventricle. Along its body the fornix receives fibres arising from the cells of the cortex of the gjTus cinguli and fibres from the longitudinal striaj upon the dorsal surface of the corpus callosum. These are known as the perforating fibres of the fornix. In their ventral course, they pass ob- liquely forward through the corpus callosum and, anteriorly, through the posterior angle of the septum pellucidum to join the fornix and course in its functional direction. Tlie fibres arising in the cortex of the gyrus cinguli may course short distances in the cingulum before perforating the corpus callosum. The columns or anterior pillars of the fornix [coluranse fornicis], are two separ- ate, cyhndrical bundles which pass forward from the apex of the body of the fornix and then turn sharply downward along the anterior boundary of the third ven- tricle, just behind the anterior cerebral commissure. A part of each column, the /ree portion [pars libera], forms the anterior boundary of the interventricular foramen (Monroi). Thence the covered portion [pars tecta] sinks into the grey ANTERIOR CEREBRAL COMMISSURE 871 substance of the lateral wall of the third ventricle, and passes downward to the base of the brain, where it appears on the exterior as the mammillary body [corpus mammillare] (fig. 671). Some of its fibres are interrupted in the nuclei of the mammillary body, chiefly in its lateral nucleus; probably most of them merely double back, forming a genu. From the mammUlary body the fibres are disposed in at least three ways: — (1) The greater part perhaps pass directly upward and are lost in the anterior nucleus of the thalamus, where they ramify freely and term- inate about its cells. These fibres form the bundle known as the mammillo-thalamic fasciculus, or bundle of Vicq d'Azyr; (2) A portion of the fibres go to form a mammillo-mesencephalic fas- ciculus (tegmento-mammiilary fasciculus, mammillo-peduncular fasciculus. This begins in the mammillary body and passes caudalward into the mesencephalon to terminate about cell-bodies in or in the region of, the so-called nucleus of the medial longitudinal fasciculus and posterior com- missure. Fibres given by these cell-bodies may convey impulses by way of the medial longi- tudinal fasciculus or the general reticular formation to the nuclei in the mesencephalon, rhomb- encephalon and perhaps into the spinal cord. Some of this portion of the fibres from the mam- millary body are said to pass caudalward through the mesencephalon without interruption there. (3) A portion of the fibres decussate in the superior parts of the mamillary bodies and are distributed to both the thalamus and the mesencephalon of the opposite side. This decussation is the supraraamillary commissure. As seen above, the fornix as a whole is composed of longitudinally directed fibres, some of which, however, cross the mid-line in the region of its body and course in the columns of the opposite side. For the greater part, its fibres rise from the cells of the hippocampal gyri, but it is known to contain some fibres which arise in the anterior perforated substance and sub- callosal gyrus and course through the fornix to the hippocampal gyri. The medial and lateral longitudinal striae upon the corpus callosum consist of olfactory fibres coursing in both directions: (1) fibres arising in the parolfactory area, the subcallosal gyrus and the anterior perforated substance (diagonal band of Broca) course posteriorly and then inferiorly in them to the grey substance of the gryi of the hippocampus; (2) and chiefly, fibres from the hippocampal gyri course in them anteriorly and inferiorly around the rostrum of the corpus callosum, through the ventral part of the septum pelluoidum, to join the fornix. It is suggested that the strise, especially the medial, may be considered as a part of the fornix detached upon the dorsal surface of the corpus callosum during the projection of the latter between the cerebral hemispheres. The medial stria is often called the stria Lancisii. The anterior cerebral commissure is only in part concerned in the rhinenceph- alon; it consists in greater part of commissural fibres connecting the two temporal lobes. It forms one of the four commissures of the telencephalon, the other three being the corpus callosum, the hippocampal commissure and the inferior cerebral commissure. It is a bundle of white substance with a slightly twisted appearance, which crosses the mid-line in the anterior boundary of the third ventricle be- tween the lamina terminalis and the columns of the fornix (figs. 671 and 684), just below the interventricular foramen (foramen of Monro). In each hemis- phere its main or temporal portion passes lateralward and slightly backward beneath the head of the caudate nucleus and through the anterior end of the lenticular nucleus, and thence is dispersed to the grey substance of the temporal lobe. It contains fibres both to and from the temporal lobe of each side. In addition to these fibres the anterior commissure carries in its frontal side two sets of fibres belonging to the ol- factory apparatus: — (1) fibres arising in the olfactory bulb of one side, which pass by way of the medial olfactory striae through it to the olfactory bulb of the opposite side; (2) fibres which pass through it from the medial stria (olfactory bulb) of one side to the uncus of the opposite side. The anterior commissure is a more primitive commissure than the corpus callosum, in that it is present in the lower forms when the latter is absent, and diminishes in relative size and importance as the corpus callosum appears and increases in size. In man the appearance of the anterior commissure precedes but little that of the corpus callosum. During the fifth month the lamina terminalis, which then alone unites the anterior ends of the two hemispheres, develops a thickening of its dorsal portion. In a part of this thickening, transverse fibres begin to appear and their increase in number results in the partial separation posteriorly of the part containing them from the rest of the lamina, and then follows the differentiation of this part into the anterior commissure. The remainder of the thickening of the lamina continues to increase in size with the increase of the hemispheres; its upper edge is directed posteriorly, and fibres begin to appear in it which arise in the cortex of one side and cross over to that of the other side. These fibres form the corpus callosum. The corpus callosum, a development of fibres in the upper, expanded portion of the lamina terminalis, thus bridges over a portion of the longitudinal fissure between the hemispheres. In the mean time, the /ornts arises as two bundles of fibres, one from the hippocampus of each side. In the complex mechanics of the development of the cerebrum these two bundles approach each other under the corpus callosum, fuse for a certain distance, and together arch the cavity of the third ventricle and come to acquire their adult position. There results from these processes of growth a completely enclosed space, a portion of the longitudinal fissure, the roof of which is the corpus callosum, its floor, the body of the fornix, and its lateral walls, portions of the mesial surfaces of the two cerebral hemispheres. The lateral walls of this space do not thicken 872 THE NERVOUS SYSTEM as do the other regions of the pallium, but remain thin and constitute the septum pellucidum of the adult, the space itself being the so-called fifth ventricle or cavity of the septum pellucidum. The septum pellucidum is a thin, approximately triangular, vertically placed partition which separates the anterior portions of the two lateral ventricles from each other. Its widest portion lies in front, bounded by the genu and rostrum of the corpus callosum, the rostral lamina, and the anterior pillars of the fornix, to all of which it is attached. Prolonged backward under the body of the corpus callosum, it narrows rapidly and terminates at the line of adherence be- tween the posterior portion of the fornix and the splenium of the corpus callosum. It consists of two thin layers, the laminae of the septum pellucidum, arrested developments of portions of the pallium of the hemispheres. The laminae enclose a narrow median cavity known as the fifth ventricle [cavum septi pellucidi]. This cavity is of very variable size, is completely closed, and does not merit the term ' ventricle, ' as apphed to the other cavities of the brain, in that it has no communication with the ventricular system and has a different lining from the other ventricles. Fig. 685. — Diagram showing Some of the Pkincipal Tracts and Synapses of the Ol- factory Apparatus. Perforating fibre Fornix Anterior commissure '. Medullary stria of thalamus Subcallosal gyrus Parolfactory are ^ Longitudinal strise on corpus callosum Hippocampal com- (Lyre) *" Habenular nucleus , Habenulo-pedun- cular tract (fasci- culus retroflexus) ^* Mammillo-mesen- ^"^0^^ cephalic fasciculus ^ ,---"^^ Penduculo-tegmental '"^^ tract Interpeduncular nucleus Uncinat' fasciculus ' Uncus \ Fimbria hippocampi Mammillary body Anterior perforated substance Olfactory epithelium Each lamina of the septum pellucidum consists of a layer of degenerated grey substance next to the fifth ventricle and a layer of white substance next to the lateral ventricle, the latter covered by a layer of ependyma common to that ventricle. The white substance consists in part of fibres belonging to the general association systems of the hemispheres, and in part of four varie- ties of fibres concerned with the rhinencephalon: — (1) fibres from each medial olfactory stria are known to reach the septum pellucidum and thence go by way of the fornix to the hippo- campus major; (2) fibres are thought to be contributed by the fornix to the septum pellucidum, and through it reach the subcallosal gyrus and perhaps the parolfactory area and even the ol- factory bulb ; (3) the posterior angle of the septum pellucidum is preforated by some commissural fibres passing from the body of the fornix and by some perforating fibres of the fornix, passing from above through it to the fornix below; (4) anteriorly, some fibres from the longitudinal strife upon the corpus callosum pass tlirough its inferior portion to join the fornix. The medullary stria of the thalamus [stria meduUaris thalami] {striai pinealis, lamia thalami), already described as to position, receives fibres from three sources, the majority at least of which belong to the rhinencephalon: (1) fibres from the fornix near-by and thus from the cor- tex of hippocampal gyrus and gryus cinguli (a cortico-habenular tract) ; (2) fibres from the parol- factory area and the anterior perforated substance, through the septum pellucidum and lamina terminahs (a more direct olfaoto-habenular tract) ; (3) fibres arising from the cell-bodies in the thalamus, supposedly chiefly from its anterior (olfactory) nucleus. These latter fibres make a thalamo-habenular tract. The majority of the fibres of the medullary striae terminate in the habenular nuclei, situated at the two sides of the stalk of the epiphysis. Most terminate in the habenular nucleus of the same side. Some cross in the habenular commissure (dorsal part of the posterior cerebral com- missure) and terminate in the nucleus of the opposite side. A few are claimed to pass to the nuclei of the quadrigeminate bodies and a few others to join the association tracts of the mesen- cephalon. Axones given off by the cells of the habenular nucleus curve anteriorly, inferiorly, and then course posteriorly (fasciculus retroflexus) to terminate in the interpeduncular nucleus THE LATERAh VENTRICLES 873 (a hahenulo-peduncular tract), and fibres arising in this latter nucleus pass to the cells about the central grey substance of the mesenecphalon (an inter-pedunculo-tegmental tract). The two mesencephalic paths here noted and the mammillo-mesencephalic fasciculus noted above give three anatomical possibilities for olfactory reflex activities, visceral (or sympathetic) and somatic, involving the motor cranial nerves and possibly the spinal nerves. Fibres arising in the cortex of the hippocampal gyrus, uncus especiaDy, may pass by way of the cingulum and thence by any suitable association fasciculus of the cerebral hemisphere to the motor area of the cere- bral cortex; also fibres may arise from the anterior nucleus of the thalamus and pass to the motor cortex by way of the internal capsule. From the motor cortex, the descending pyramidal fibres give the possibihties for any higher cortical activities induced by smell. A more direct mesencephahc path has been suggested by Wallenberg, namely, that cells in the olfactory trigone and anterior perforated substance, about which terminates fibres of the olfactory tract, send axones directly postei-iorly, ai'ound the tuber cinereum, to terminate in the mammiUary body and thence the impulses may go to the mesencephalon. Such fibres, if they exist, would form an olfacto-mammillary tract. A path is described in the hedge-hog which arises from cells in the olfactory trigone and passes directly posteriorly to terminate in the grey substance of the mesencephalon — an olfacto-mesencephalic tract. To the complicated central connections of the sense of smell, Dejerine adds yet another path, namely, a portion at least of the terminal stria [stria terminalis] of the thalamus (taenia semi- circularis). This contains fibres arising from cells in the anterior perforated substance and in the septum pellucidum and fibres from the opposite side by way of the anterior commissure. It runs a crescentic course posteriorly, bounding the thalamus from the caudate nucleus, turning downward and then anteriorly in the wall of the inferior cornu of the lateral ventricle to termi- nate in the amygdaloid nucleus, which latter is a more or less detached bit of the cortex of the extreme anterior portion of the hippocampal gyrus (uncus). The stria is said also to contain fibres which arise in the amygdaloid nucleus and course in it forward to be given off to the thala- mus and probably to the internal capsule and thence to the cerebral cortex above. SUMMARY OF THE OLFACTORY APPARATUS I. Peripheral part. (1) Olfactory area of nasal epithelium containing the cell-bodies and peripheral processes of olfactory neurones (olfactory ganglion). (2) Non-meduIIated central processes of olfactory neurones, the olfactory nerve, passing as numerous filaments through the cribriform plate of the ethmoid, to terminate in contact with the dendrites of the "mitral cells" (stratum glomerulosum) in the olfactory bulb. II. The Rhinencephalon. A. The anterior division. (1) Olfactory bulb, olfactory tract, olfactory trigone (tubercle), lateral olfactory stria (gyrus), medial and intermediate olfactory stria;. (2) The parolfactory area, subcallosal gyi'us, anterior perforated substance including the diagonal band of Broca. B. The posterior division. (1) Part of anterior commissure, septum pellucidum, uncinate fasciculus, hippocampal gyrus (uncus especially), dentate g3Tus, gyrus cinguU and cingulum. (2) Fimbria, hippocampal commissure, fornix, longitudinal strise upon corpus callosum, mammiUary body, mammillo-thalamic fasciculus, mammiUo-mesencephahc fasciculus. (3) The anterior nucleus of the thalamus. (4) The medullary stria of the thalamus, habenular nucleus, fasciculus retroflexus, inter- peduncular nucleus, and Lnterpedunculo-tegmental tract. (5) Probably an olfacto-mammillary and an olfacto-mesencephalic tract, and a part of the terminal stria of the thalamus with the amygdaloid nucleus. THE LATERAL VENTRICLES Two of the four cavities of the ventricular system of the brain are in the telen- cephalon. From their position, one in each cerebral hemisphere, they are known as the lateral ventricles. They arise as lateral dilations of the cavity of the anter- ior of the prhnary vesicles, and, just as the fourth ventricle remains in communi- cation with the third by way of the aqueduct of the cerebrum, so the lateral are connected with the third by the two interventricular foramina (Monroi). The whole ventricular system, including the central canal of the spinal cord, is Hned by a continuous layer of ependyma and contains a small quantity of liquid known as the cerebro-spinal fluid. Each lateral ventricle is of an irregular, horseshoe shape. It consists of a central portion or body and three cornua, which correspond to the three poles of the hemisphere. The portion projecting into the frontal lobe is known as the anterior cornu, that projecting into the occipital lobe is the posterior cornu, and the portion which sweeps anteriorly downward into the temporal lobe is the inferior cornu. The ventricles of different individuals vary considerably in capac- ity, and the cavity of a given ventricle is not uniform throughout. In some 874 THE NERVOUS SYSTEM localities the space may be quite appreciable, while in other places the walls may be approximate or even in apposition. Each lateral ventricle is a completely closed cavity except at the interventricular foramen. However, a strip of the floor of the inferior cornu is separated from the exterior of the brain by only the thin, non-nervous lamina forming the floor of the chorioid fissure. The interventricular foramen (foramen of Monro), by which the lateral ven- tricle is continuous with the cavity of the third ventricle, is a small, roundish chan- FiG. 686. — A Cast of the Four Ventricles of the Encephalon. (After Weloker.) Anterior cornu of lateral ventricle " Interventricular foramen (Monro!) Third ventricle Inferior cornu of lateral ventricle Aqueduct of cerebrum Fourth ventricle Posterior cornu of lateral ventricle' nel, 2 to 4 mm. wide, which opens into the mesial side of the posterior end of the anterior cornu. It is bounded in front by the free portion of the anterior pillars of the fornix, and behind by the anterior tubercle of the thalamus. That the greater part of the lateral ventricle is posterior to it is due to the backward extension of Fig. 687. — Di.4.gram of Sagittal Section through Lateral Part of Right Hemisphbke SHOWING Lateral Ventricle from the Mesial Side of the Section. Chorioid plexus Septum pellucidum Fornix Caudate nucleus Interventricular foramen Caudate nucleus Hippocampus major Chorioid plexus of inferior cornu Internal capsule Lenticular nucleus Anterior commissure the hemispheres during their growth and elaboration. Through the two foramina indirectly, the cavities of the two lateral ventricles are in communication with each other. The walls of the lateral ventricle. — The anterior cornu is a bowl-like cavity, convex forward and extending downward and medial ward into the frontal lobe. Above and anteriorly it is bounded by the under surface of the corpus callosum and the radiations of its genu into the substance of the frontal lobe. Its median bound- ary is the septum pellucidum; the head of the caudate nucleus (part of the corpus striatum) gives it a bulging, infero-lateral wall, and the balance of its floor is formed by the white substance of the orbital part of the frontal lobe. THE LATERAL VENTRICLES 875 The central portion or body is more nearly horizontal. It lies within the parietal lobe and extends from the interventricular foramen to the level of the splenium of the corpus callosum. Its roof is formed by the inferior surface of the body of the corpus callosum, and its mesial wall consists of the posterior part of the septum pellucidum, attaching the fornix to the under surface of the corpus callosum. Like the anterior horn, it is given an oblique, infero-lateral wall by the narrower, middle part of the caudate nucleus. Several structures contribute to its floor: — (1) the stria terminalis of the thalamus, a hne of white substance conforming to the genu of the internal capsule without, and constituting the Fig. 688. — Horizontal Dissection of the Cerebral Hemispheres. The fornix has been removed to show the relation of the tela chorioidea of the third ventricle to the chorioid plexus of the lateral ventricles. (From a mounted specimen in the Anatomical Department of Trmity College Dulilin ) Corpus callosum (dissected) Veins of Galen Crus of fornix Straight sinus. boundary between the caudate nucleus and the thalamus, and containing (2) the vena terminalis (vein of the corpus striatum); (3) the lamina affixa, a mesial continuation of the stria terminalis upon the surface of (4) the lateral part of the thalamus; (5) the medial edge of the lamina affixa, the tsenia chorioidea, and the chorioid plexus continuing under (6) the edge (taenia) of the body and the begin- ning crura (posterior pillars) of the fornix (fig. 688). The chorioid plexus of the lateral ventricle is continuous with that of the third ventricle. The chorioid tela of the third ventricle (velum interpositum) con- tinues under the taenia of the fornix into the lateral ventricle, and there, along the line of the taenia chorioidea, becomes elaborated into a varicose, convoluted, villus-like fringe, rich in venous capillaries and lymphatics. This fringe is the chorioid plexus. It is continuous anteriorly, at the interventricular foramen, with the corresponding plexus of the opposite lateral ventricle and with the chorioid plexus of the third ventricle. The latter consists of two similar but smaller fringes, which project close together into the cavity of the third ventricle from the median portion of the ventral surface of the chorioid tela. Behind, the chorioid 876 THE NERVOUS SYSTEM plexus of the lateral ventricle curves posteriorly and inferiorly into the inferior cornu, being especially well developed at the region of its entrance into the latter, into what is called the chorioid glomus. Though apparently lying free in the ventricle, the chorioid plexus is invested throughout by a layer of epithelium, the epithelial chorioid lamina, which is adapted to all its unevennesses of surface and which is a continuation of the ependymal lining of the remainder of the ventricle — continuous, on the one hand, with that of the lamina affixa and thalamus, and, on the other, with the epithehal covering upon the upper surface of the tania of the fornix and fimbria. The posterior cornu of the lateral ventricle is a crescentic cleft of variable length, convex lateralward, which is carried backward from the posterior end of the body of the ventricle and, curving medialward, comes to a point in the occipital lobe. Its roof and lateral wall are formed by a portion of the posterior radiation of the corpus callosum, which forms a layer, from its appearance known as the tapetum. In transverse sections of the occipital lobe (fig. 699) the tapetum appears as a Fig. 689. — Diagrammatic Transverse Section op Prosencephalon through Bodies of Lateral Ventricles and Middle op Thalamencephalon. Fifth ventricle . Fornix Caudate nucleus Lamina affixa Vena ter- minalis Stria ter- minalisof / /«i\ \ "^ T "^1^ < ! // \ -Chorioid tela thalamus «v.smwa \ \ \ # ^ i-ii»i«t-^ f Puta- /^#%*^\ \ \ / VlliH ^ I / I i _\ 'Thalamus §» men /*' ^ \\ W / ili Oii \m \ // // \ Third Globus pallidus Caudate nucleus Chorioid plexus Inferior cornu of lateral ventricle Fimbria Mammillo- thalamic fasciculus Internal capsule thin lamina of obliquely cut white substance immediately bounding the cavity, while outside the tapetum occurs a thicker layer of more transversely cut fibres, the occipito-thalamic radiation. In the medial or inner wall of the posterior horn run two variable longitudinal eminences: — (1) The superior of these is the bulb of the posterior cornu, and is formed by the occipital portion of the radiation of the corpus callosum (splenium), which bends around the impression of the deep pa- rieto-occipital fissure, and, hook-like, sweeps into the occipital lobe. In horizontal sections these fibres, together with the splenium and the similar fibres into the opposite occipital lobe, form the figure known as the forceps major. (2) The inferior and thicker of the eminences is the hippocampus minor [calcar avis] (cock's spur), and is due to the anterior part of the calcarine fissure, by which the wall of the hemisphere is projected into the ventricle. The posterior horn, like the anterior, is not entered by the chorioid plexu i. The inferior cornu. — In its inferior and slightly lateral origin from the region of junction between the body of the ventricle and the posterior cornu, the inferior horn aids in producing a somewhat triangular dilation of the cavity known as the collateral trigone. Beginning as a part of the trigone, the cavity of this horn at first passes posteriorly and lateralward, but then suddenly curves anteriorly and THE CAUDATE NUCLEUS 877 inferiorly into the medial part of the temporal lobe nearly parallel wdth the supe- rior temporal sulcus. Above, it follows the curved crura (posterior pillars) of the fornix and fimbria; below, it does not extend to the temporal pole by from 2 to 3 cm. The roof and lateral wall are, for the most part, like those of the posterior horn, being formed by the tapetum, but medialward a strip of the roof is formed by the attenuated, inferior prolongation, or tail, of the caudate nucleus, together with the inferior extension of the stria terminalis of the thalamus. At the end of the inferior horn the roof shows a bulging, the amygdaloid tubercle, situated at the termination of the tail of the caudate nucleus. This bulging is produced by the amygdaloid nucleus, an accumulation of grey substance continuous with that of the cortex of the hippocampal gyrus, and which gives origin to part of the longitudinal fibres coursing in the stria terminalis of the thalamus. In the medial wall and floor of the inferior horn the follo'ning structures are shown: — (1) In the posterior or trigonal part of the floor is the longitudinal collateral eminence, a bulging, very variable in development in different speci- mens, produced by the collateral fissure. This is often pronouncedly in two parts, a posterior prominence corresponding to the middle portion of the collateral fissure and an anterior prominence (less frequent) produced by the anterior part of the Fig. 690. — Dissection of Right Temporal Lobe showing the Medial Wall op the End OP the Inperior Horn op the Lateral Ventricle. (From Spalteholz.) Digitations of hippocampus Fimbria of hippocampus Hippocampal fissure Dentate gyrus or fascia ^ ^ Substantia reticularis i alba (Arnoldi) I Hippocampal gyrus ■■ Hippocampus Collateral eminence Tffinia fimbriae j Collateral fissure fissure. (2) Medial to this eminence lies the inferior extension of the chorioid plexus, usually more voluminous than the part in the bodj^ of the ventricle. (3) Partly covered by the chorioid plexus is the hippocampus major, a prominent, sickle-like ridge corresponding to the indentation of the hippocampal fissure. It begins as a narrow ridge posteriorly, at the end of the body of the ventricle, as the extension of the posterior pillar of the fornbc, and expands anteriorly as the ven- tricular surface of the uncus. Its surface is not regular, but shows a concave medial margin as distinguished from a wider, convex, lateral sm'face. Its ter- mination in front (pes hippocampi) is divided by two or three flat, radial grooves into a corresponding number of short elevations known as the hippocampal dig- itations. It is covered by a thick stratum of white substance, the alveus, arising from its depths and continued mesially into the fimbria. (4) The fimbria is so folded that its margin, ta:nia fimhrice, lies in the cavity of the inferior horn attached to the chorioid plexus and the thin, non-nervous floor of the chorioid fissure. The caudate nucleus (fig. 691). — As realised in the study of the lateral ven- tricle, the caudate nucleus is a comma-shaped mass of grey substance with a long, much-curved, and attenuated tail. Its head forms the bulging lateral wall of the anterior horn; thence it proceeds posteriorly in the lateral wall of the body of the ventricle and, at the collateral trigone, curves downward and its tail becomes 878 THE NERVOUS SYSTEM a medial portion of the roof of the inferior horn. It is separated from the thala- mus adjacent to it by the stria terminalis of the thalamus (taenia semicircularis). The end of its tail extends anteriorly below to the level of the anterior horn of the ventricle above. Owing to its much curved shape, both horizontal and vertical sections of the hemisphere passing through the inferior horn may contain the nucleus cut at two places (see figs. 694 and 698.) The caudate nucleus is the intraventricular of the two masses of grey substance which together are sometimes referred to as the basal ganglia. The extraventri- cular of these masses is the lenticular nucleus, which is bmied in the substance of the hemisphere, laterally and inferior to the caudate nucleus. The two masses Fig. 691. — Diageams of Lateral View and Sections op the NtrcLEi of the Corpus Stria- tum WITH THE Internal Capsule Omitted. A and B below represent horizontal sections along the lines A and B in the figure above. The figure also shows the relative position of the thalamus and the amygdaloid nucleus. date nucleus Lenticular nucleus Amygdaloid nucleus Caudate nucleus ^^^7 Thalamus Tail of caudate Internal capsule Lenticular nucleus Caudate nucleus Tail of caudate nucleus Internal capsule are separated by the internal capsule, a thick band of nerve-fibres continuous into the cerebral peduncles, and connecting the grey cortex of the hemisphere with the structures inferior to it. Anteriorly and below, the two nuclei become continuous and the white substance of the internal capsule, in separating them posteriorly, contributes to the striated appearance in sections, known collectively as the corpus striatum (figs. 692, 695) . The corpus striatum as such is described below. INTERNAL STRUCTURE OF THE PROSENCEPHALON From the above examinations of their external and ventricular sinfaces, it is apparent that the cerebral hemispheres consist of a folded, external mantle of grey substance, the cortex cerebri, spread more or less evenly over an internal mass THE LENTICULAR NUCLEUS 879 of white substance which contains embedded within it certain masses of grey sub- stance, the chief of which are known as the caudate and lenticular nuclei of the corpus striatum. In addition, the hemispheres of the telencephalon overlie and are in functional connection with the structures of the diencephalon below, the chief of which are the thalamencephalon and the bases of the cerebral peduncles. The grey substance of the telencephalon. — The grey substance is in intimate relation with the white substance, and in fact its cells give origin to the greater part of the fibres composing the white substance. The accumulations of grey substance to be considered are the cerebral cortex, with its variations in thickness and arrangement, the corpus striatum, the claustrum, and the amygdaloid nucleus. The cerebral cortex [substantia corticalis] is distributed over the entire surface of each hemisphere except the peduncular region of the base and the region of the corpus callosum and fornix of the medial surface. Numerous measmrements have been made to determine its average thickness. These have shown that the mantle is not uniformly distributed: — (1) that it is thicker on the convex surface than on the basal and medial surfaces; (2) that on the convex smrface it is thicker on the central region of the hemisphere, somsesthetic area, than at the poles; (3) that in the average normal specimen it averages somewhat thicker on the left than on the right hemisphere; (4) that its average thickness varies greatly in different individuals, and that the thickness decreases with old age; (5) that it is probably somewhat thicker in males than in females, and (6) that in a given specimen it averages thicker on the summits of the gyri than in the floor of the corresponding sulci. In the normal adult conditions it averages about 4 mm. thick on the ante- rior and posterior central gyri, in the somsesthetic area, while it attains its mimi- mum thickness of about 2.5 mm. on the basal surface of the occipital and frontal lobes. Its total average thickness is about 2.9 mm. The practically non- nervous floor of the third ventricle and that of the chorioid fissure are very much thinner but are not considered in these measurements. The cerebral cortex consists of layers of the cell-bodies of neurones, chiefly of the pyramidal type (fig. 604), which receive impulses from the structures below and from other regions of the cortex by way of fibres reaching them through the internal mass of white substance, and which in turn contribute fibres to the white substance. Certain fibres of shorter course and numerous collateral branches of fibres passing out of the cortex are devoted to the association of the region of their origin with the cortex of the immediate vicinity of their origin, and most of these course within the grey cortex itself. In certain gyri, such as the anterior central gyri and those of the medial surface of the occipital lobe, these short association fibres accumulate into strata, and in vertical sections give the cortex a stratified appearance. Two such strata of white substance may be noted in the above localities, one lying about midway in the thickness of the cortex and one slightly internal to this. They are known as the inner and outer stripes of Baillarger. In addition, a thin, superficial or tangential layer of fibres may often be distinguished lying in the surface of the cortex. Transverse sections through the anterior end of the hippocampus show a coiled arrangement of the layers of white substance, to which has been given the name cornu ammonis. The peculiar structure and appearance of the olfactory bulb and tract, parts of the cortex, have already been mentioned. The corpus striatum is so called on account of the appearance in section of its component parts, the caudate and lenticular nuclei (basal ganglia) and the internal capsule between them. The two nuclei are directly continuous with each other at their anterior ends (fig. 691), and in addition they are connected by numerous small bands of grey substance which pass from one to the other through the internal capsule, especially its anterior part. Also each nucleus contributes numerous fibres to, and receives fibres from, the internal capsule. These bundles of fibres both arising and terminating within the nuclei, together with the grey substance among the fibres of the capsule, produce the ribbed and striped appear- ance suggesting the name, corpus striatum. The caudate nucleus — the intra- ventricular part of the corpus striatum — hes with its thicker anterior part (head) closely related to the internal capsule, but its tail passes posteriorly around the posterior border of the capsule and curves downward and anteriorly into the roof of the inferior cornu of the lateral ventricle. The lenticular nucleus [nucleus lentiformis] — the extraventricular part of the corpus striatum — is embedded in the white substance of the cerebral hemi- sphere. It is somewhat pyriform in shape, not being so long as the caudate nucleus, and neither having a tail nor extending so far anteriorly. Its lower sur- face is separated from the inferior cornu of the lateral ventricle by the white sub- stance of the roof of that cornu, and by the tail of the caudate nucleus, and, fur- 880 THE NERVOUS SYSTEM ther forward, the anterior commissure passes through its base. Its lateral sur- face is rounded and conforms both in extent and curvature with the surface of the insula, from which it is separated by the fibres of the external capsule and the intervening claustrum. Its oblique superior and mesial surface is adapted to the lateral surface of the internal capsule, and it comes to a rounded apex in the angle formed by the internal capsule and a plane parallel with the base of the hemi- sphere. In both horizontal and coronal (transverse) sections through its middle it resembles a compound biconvex lens. Internally this appearance is produced by two vertically curving laminae of white substance, an external and an internal medullary lamina, which divide its substance into three zones: — the two medial zones together form an area, triangular in section, known as the globus pallidus ; the lateral, larger and more grey, concavo-convex zone is the putamen. Radiat- ing fibres from the medullary laminae extend into the zones, especially those of the globus pallidus. These zones disappear in transverse sections of the anterior Fig. 692. — Coronal Section of Telencephalon Passing Through Fbontal Lobes and Anterior Portion of Corpus Striatum. (From mounted specimen in the Anatnmiral Department of Trinity College, Dublin.) Longi- tudin fissure Olfactory tract' portion of the lenticular nucleus (fig. 692), due to the fact that the larger putamen alone comprises this portion and alone becomes continuous with the caudate nucleus. (See figs. 691, 696.) Connections. — Both nuclei of the corpus striatum become continuous with the cortex in the region of the anterior perforated substance, and the putamen of the lenticular nucleus may blend with the anterior part of the base of the claustrum. The following are the principal fibre connections: — (1) Fibres arising in the nuclei which join the internal capsule to reach the cerebral cortex, and fibres arising in the cortex which descend by the same course to the cells of the nuclei. (2) Fibres which pass in both directions between the thalamus and the corpus striatum (caudate nucleus especially). These are more abundant anteriorly, and necessarily pass through the internal capsule. (3) The ansa lenticularis, or strio-subthalamio radiation, a usually distinct lamina, composed largely of fibres passing inferiorly between the thalamus and lenticular nucleus. It passes from the basal aspect of the anterior tubercle of the thalamus and curves below through the internal capsule to the basal surface of the lenticular nucleus, and there its fibres are distributed upward through its medullary lamina to the globus pallidus and putamen. Some enter the internal capsule and reach the cortex, chiefly that of the tem- poral lobe. The ansa lenticularis also contains fibres from the cortex of the temporal lobe to terminate in the inferior and mesial parts of the thalamus. The fibres associating the thalamus with the temporal lobe belong to the so-called inferior peduncle of the thalamus. (4) Fibres connecting both nuclei (chiefly the caudate) with the red nucleus and substantia nigra of the mesencephalon. These pass through the hypothalamic region and along the cerebral peduncle. No definitely localised functions have been with certainty ascribed to either nucleus. They serve as 1-elays in the pathways associating the cortical grey substance with the structures below and in them the neurones concerned in these pathways are greatly increased. The claustrum is a triangular plate of grey substance which is embedded in the white substance between the lenticular nucleus and the insula. Its medial THE THALAMUS 881 surface is concave, conforming to the convexity of the putamen. The sheet of white substance intervening between it and the putamen is known as the external capsule. Its lateral surface shows ridges or projections in section which conform to the neighbouring gyri of the insula, and it is spread through an area which quite closely coincides with that of the inusla. Below and anteriorly it becomes con- tinuous with the cortex of the anterior perforated substance and with the lenticu- lar nucleus at the region of the junction of these. Above and posteriorly it gradu- ally becomes thinner, and finally disappears in the white substance about it. In origin it is thought to be a detached portion of the cortical grey substance of the insula. The amygdaloid nucleus [nucleus amygdalae] is represented by the amygda- loid tubercle, which has already been described in the extremity of the inferior cornu of the lateral ventricle (figs. 666 and 691). It is an almond-shaped mass of cells joined to the tail of the caudate nucleus, continuous above with the putamen and anteriorly continuous with the cortex of the hippocampal gyrus. Fig. 693. — Coronal Section op Telencephalon through the Anterior Commissure, Optic Chiasma, and Trunk op Corpus Callosum. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Caudate nucleus (head) Internal capsule (frontal portion ^,' Longitudinal fissure Corpus callosum Anterior cornu of lateral ven- tricle Chorioid plexus of lateral i The chief connections of the amygdaloid nucleus by way of the stria tertjiinalis of the thalamus are noted above under the description of the posterior division of the rhinencephalon. The amygdaloid nucleus, like the claustrum, is thought to represent a detached portion of the cortex, it being detached from the uncus. Considering this and its chief connections, it, with the stria terminahs of the thalamus, are concerned in the central portion of the olfactory apparatus. The thalamus and hypothalamus. — The external features of these portions of the prosencephalon have been described in their natural place, but inasmuch as they contain the chief relays between the telencephalon and the divisions of the nervous system caudal to the prosencephalon, the consideration of their internal structure has been deferred till now. The principal grey masses to be considered are the thalamus and the hypothalamic nucleus. The structures comprising the metathalamus and epithalamus have already been mentioned in their relations with the mesencephalon and the optic and auditory apparatus. The thalamus has upon its upper surface, under its ependyma, a thin stratum zonale of white substance, derived in part from the incoming fibres and in part from its own cells. Its oblique lateral surface conforms to the medial surface of the internal capsule; its vertical medial surface forms the lateral wall of the third ventricle, and below it is continuous into the hypothalamic (tegmental) region. 882 THE NERVOUS SYSTEM Its upper surface shows a middle, an anterior, and a posterior prominence or tuber- cle. The anterior tubercle (nucleus) forms the posterior boundary of the inter- ventricular foramen; the posterior tubercle is the cushion-like pulvinar which projects backward over the lateral geniculate body and the brachium of the superior quadrigeminate body. A horizontal section through the supero-medial edge, spHtting the stria medul- laris of the thalamus and thus passing above the massa intermedia, shows the grey mass of the thalamus divided into segments or nuclei by a more or less distinct internal medullary lamina. This extends the whole length of the thalamus, dividing its middle and posterior portion into the medial and the lateral nucleus. Fia. 694. — HoKizoNTAii Dissection showing the Grey and White Substance op the Telencephalon Below the Corpus Callosum and the Relative Position of the Thalamencephalon. (After Landois and Stirling.) Gyrus cinguU Genu of corpus callosum Anterior cornu Caudate nucleus Internal capsule (Frontal portion) External capsule _ ^ . f Putamen Lenticular Globus. nucleus | palUdus Claustrum Internal capsule (occr pital portion) Medial geniculate body Tail of caudate nucleus Hippocampus major' Hippocampus minor' Septum pellucidum Corpus striatum Column of fornix Clava Funiculus cuneatus Funiculus gracilis Anteriorly the lamina bifurcates into a medial limb, extending to the medial sur- face of the thalamus, and a lateral limb, extending forward to join the genu of the internal capsule (figs. 695, 700). This bifurcation results in a cup-like sheet of white substance which encloses the anterior nucleus. On the lateral surface of the section, next to the internal capsule, there may usually be distinguished an external medullary lamina, separated from the white substance of the capsule by a reticular layer of mixed white and grey substance. The anterior nucleus, lying partially encapsulated in the bifurcation of the internal medullary lamina, is somewhat wedge-shaped and points backward be- tween the anterior portions of the lateral and medial nuclei. It is composed chiefly of large cells, and constitutes the anterior tubercle of the superior aspect. Its principal connection from below is with the nuclei of the mammillary body of the same and opposite sides, and with uninterrupted fibres derived from the columns of the forni.x. THE THALAMUS 883 The fibres from both sources enter it by way of the mammillo-thalamic fasciculus (figs. 671 and 695). The significance of this connection is mentioned in the description of the limbic lobe. The lateral nucleus, lying between the external and internal medullary lam- inae, extends posteriorly to include the entire pulvinar. The pulvinar, as already noted, together with the lateral geniculate body, constitutes the prosencephalic nucleus of termination of the optic tract, and the stratum zonale upon the surface of this nucleus might be called the stratum opticum. The anterior portion of the lateral nucleus receives fibres inferiorly from the red nucleus, from the brachium conjunctivum (cerebellum direct), and some fibres of the medial lemniscus terminate about its cells. The medial nucleus lies medial to the internal medullary lamina and forms the posterior portion of the lateral wall of the third ventricle. It is shorter than the lateral nucleus, and is less extensively pervaded by fibres. Fig. 695. — Coronal Section of Prosencephalon through Thalamencephalon at Region OP Corpora Mammillaria. (Seen from in front.) (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Lateral ventricle ^ __.._-^ , ^ , . , , , Corpus callosum (central portion) Chorioid plexus of lateral ven- tricle Caudate nucleus ^ Massa inter- ~,- media Internal capsule Lenti- [ (Puta cular ! men nu- I Globus cleus I pallidus External capsule Claustrum Ansa peduncu- laris Optic tract Inferior peduncle ^ of thalamus Inferior cornu of lateral ventricle Hippocampal ^ digitations Oculomotor nerve Fornix It is thought to receive fibres from the red nucleus, and perhaps some from the lemniscus, and is usually continuous across the third ventricle with the opposite medial nucleus by the massa intermedia. In comparative anatomy, the nuclei of the thalamus have been variously subdivided by the different investigators. All the nuclei are connected with the lenticular nucleus by fibres passing between the two through the internal capsule directly, and by fibres curving from below, chiefly from the anterior, lateral and medial nuclei, and passing in the ansa lenticularis. The cortical connections of the thalamus are abundant. They consist of fibres both to and from the cortex of the different lobes of the hemisphere, the greater part arising in the thalamus and terminating in the cortex. These fibres collect in the internal and external medullary laminae and the stratum zonale; most of them enter the internal capsule and thence radiate to the different parts of the cortex. They form the so-called peduncles of the thalamus, which have been distinguished both by the Flechsig method of investigation and by the degeneration method. The anterior or frontal peduncle passes from the lateral and anterior part of the thalamus through the frontal portion of the internal capsule, and radiates to the cortex of the frontal lobe. (See fig. 700.) The middle or parietal peduncle passes from the lateral surface of the thalamus through the inter- mediate part of the internal capsule, and upward to the cortex of the parietal lobe. The pos- terior or occipital peduncle passes chiefly from the pulvinar, through the occipital portion of the internal capsule, and radiates backward to the occipital lobe by way of the occipito-thalamic (optic) radiation (fig. 699). The inferior peduncle passes from the medial and basal surface of the thalamus (from the anterior and medial nuclei chiefly), turns outward to course beneath the lenticular nucleus, and radiates to the cortex of the temporal lobe and insula. The fibres of this peduncle course chiefly in the ansa lenticularis (fig. 695). Some turn upward in the external capsule to reach the cortex above the insula; others pass upward through the medullary laminae of the lenticular nucleus. 884 THE NERVOUS SYSTEM The h3rpothalamic nuclues (fig. 698) , or body of Luys, is the principal nucleus of termination of the medial lemniscus, the great sensory spino-cerebral pathwayl It is a biconvex plate of grey substance situated on the basal aspect of the latera. and anterior nuclei of the thalamus, and between these and the basis of the cerebral Fig. 696. — Horizontal Sections of the Peosencephalon through the Thalamus and Corpus Striatum. The plane of the section of the left hemisphere splits the medullary stria of the thalamus and is about 15 millimeters superior to the plane through which the right hemisphere is cut. (After Toldt.) Trunk of corpus caliosum Septum pellucidum Genu of corpus caliosum Anterior cornu of lateral ventricle Head of caudate nucleus Column of fornix Internal capsule Island of Reil (insula) Chorioid glomu: Occipito- thalamic radiation Splenium of corpus caliosum Calcarine fissure peduncle, or rather the substantia nigra, which is spread upon the dorsal surface of the peduncle, and which, though greatly diminished, extends into the hypo- thalamic region. The hypothalamic nucleus presents a brownish-pink colour in fresh material, due to pigment in its cells and to its abundant blood capillaries. It contains the cell-bodies of the neurones of the third order in this pathway, those of the first order being situated in the spinal ganglia, and those of the second order in the nuclei of the fasciculus gracilis and fasciculus cimeatus. It is enclosed by a thin capsule of white substance, some of the fibres of which seem to decussate with those of the opposite side in the floor of the third ventricle, above and just behind the region of the corpora mammiUaria. By far the greater part of the fibres arising from the nucleus join the internal capsule, and through it ascend to WHITE SUBSTANCE OF TELENCEPHALON 885 radiate to the cortex of the pre- and post-central gyri, the sensory-motor or somsesthetic area of the hemisphere. The majority terminate in the post-central gyrus. All the fibres connecting the cerebral cortex with both the thalamus and the hypothalamic nucleus belong to the so-called projection fibres of the cerebral hemisphere. The habenular nucleus and the fasciculus relroflexus of Meynert have been noted in the de- scription of the rhinencephalon. The habenular nucleus, a part of the epithalainus, is a small group of nerve cells situated in the habenular trigone just infero-lateral to the epiphysis. The fibres of the medullary stria of the thalamus (habenula) terminate about its cells. A small bundle of fibres crossing the mid-hne under the epiphysis in the superior aspect of the posterior cerebral commissure is called the commissure of the habenuloe, from the fact that it connects the habenular nuclei of the two sides. Fig. BOy.' — Oblique Feontal Section through the Brain in the Direction of the Cerebral Peduncles and the Pyramids. (Seen from in front.) (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Longitudinal fissure Radiation of corpus callosum Septum pE llucidum Superior frontal gyrus Body of corpus callosum Anterior horn of lateral ventricle Head of caudate nucleus Corona radiata Column of formz Internal capsule Thalamus ~ Third ventricle - Cerebral peduncle Brachium pontis Longitudinal pyramidal fasciculi of pons Superficial fibres of pons /' Pyramid External capsule Globus pallldus Optic tract Mammillary body Oculo-motor nerve Trigeminal nerve Facial and cochlear Glosso-pharyngeal nerve Vagus nerve Inferior ohvary nucle Decussation of pyramids The fasciculus retroflexus (Meynerti) is a relatively strong bundle of medullated fibres which runs downward and then turns caudalward from the habenular nucleus toward the inferior portion of the interpeduncular fossa. It has been shown that many, at least, of the fibres of this bundle arise from the cells of the habenular nucleus. In its slightly caudad course, the bundle passes obliquely through the red nucleus, entering the medial superior aspect and making its exit from the ventro-mesial side of the inferior extremity of this nucleus. In the animals in which it has been studied, the bundle ends in the interpeduncular nucleus (ganglion), a group of nerve cells lying in the floor of the interpeduncular fossa at the level of the inferior quadrigemina. In man, the interpeduncular nucleus is not definitely assembled and the bundle seems to dis- appear in the posterior perforated substance. However, the microscope shows cells dispersed among the fibres of the bundle and these cells probably represent the nucleus. The white substance of the telencephalon. — A horizontal section through the upper part of the trunk of the corpus callosum will pass above the basal grey substance of the corpus striatum, and, aided by the corpus callosum, each hemi- sphere in such a section will appear as if consisting of a solid, half-oval mass of white substance, bounded without by the grey layer of the cortex (fig. 672). As 886 THE NERVOUS SYSTEM seen at this level, the white substance of each hemisphere is known as the centrum semiovale. Horizontal sections passing below the body of the corpus callosum involve the corpus striatum and thalamus, and the appearance of the white sub- stance is modified accordingly (fig. 694). In the white substance of the cerebral hemispheres as a whole three main sys- tems of fibres are recognised: — projection fibres, commissural fibres, and associa- tion fibres. The projection fibres are those of a more or less vertical course, which pass to and from the cortex of the hemisphere, associating it with the structures below the confines of the hemisphere. The commissural fibres are those of a transverse or horizontal course, which cross the mid-line and functionally connect the two hemispheres with each other. The association fibres are those which neither cross the mid-line nor pass beyond the bounds of the hemisphere in which they arise, but instead associate the different parts of the same hemisphere — lobes with lobes and gyri with gyri. The fibres which associate the cortex with the Fig. 698. — Coronal Section op Brain Passing Through the Pulvinah of the Thalamus AND the Uncus of the Hippocampal Gyrus. (After Toldt.) Chorioid tela of ■ third ventricle \ \ I r'n/n "'/'/" ~'»*ip''/^>' '^ Chorioid plexus of third ven- tricle Internal capsult Habenular nucleus Tail of caudate nucleus Optic tract Fimbria of hippocampus Peduncle of cerebrum Post, recess of interpeduncular Red nucleus nuclei of the corpus striatum must also be classed as association fibres, since these masses of grey substance are a part of the telencephalon, while by definition those which associate the thalamus and hypothalamus with the cortex belong to the projection system. Some of the fibre bundles of the above systems have already been described in connection with the parts with which they are concerned. The projection fibres of the hemisphere comprise both ascending and descend- ing fibres between the cerebral cortex and structures below the bounds of the hemi- sphere, i.e., some arise in the structures below and terminate in the cortex; others arise from the cortical cells and terminate in the structures below, including the grey substance of the thalamencephalon, mesencephalon, rhombencephalon, and spinal cord. The projection fibres are given different names in the hemisphere according to their arrangement and the appearances to which they contribute in the dissections. Beginning with the pyramidal fasciculi and the basis of the peduncle, they contribute — (1) to the internal capsule and some to the external capsule and (2) to the corona radiata. The internal capsule [capsula interna] is a band of white substance, consisting of the ascending fibres from the nuclei of the thalamus, hypothalamus, and corpus striatum, reinforced by the descending fibres from the cortex to these nuclei and by those descending in the cerebral peduncle to terminate in the mesencephalon, rhombencephalon and spinal cord. It is a broad, fan-like mass of fibres, which increases in width from the base of the hemisphere upward, and which is spread between the lenticular nucleus on its lateral aspect and the caudate nucleus and THE CORONA RADIATA 887 thalamus on its medial side. To reach the cortex above, the course of its fibres necessarily intersects that of the radiations of the corpus callosum, and thus, together with the corpus callosum, the fan-like bands of the two hemispheres form a capsule containing the thalami, the third ventricle, the caudate nuclei, and the anterior and central portions of the lateral ventricles. In horizontal sections, each internal capsule appears bent at an angle, the genu, which approaches the cavity of the lateral ventricle along the line of the boundary between the thalamus and the caudate nucleus. Along the genu runs the stria terminalis of the thala- mus, and through the genu the capsule receives fibres from the internal medullary lamina of the thalamus, from the stratum zonale of the thalamus and from that of the caudate nucleus. At the genu each capsule is separable into two parts: — (1) the anterior (frontal) portion, spreading between the caudate and lenticular nuclei; (2) the posterior (occipital) portion, between the lenticular nucleus and the thalamus (fig. 700.) Fig. 699. — Coeonal Section THROtroH the Splenium op the Corpus Callosum and the Posterior Cornua op the Lateral Ventricles. (Viewed from behind.) (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Radiation of, corpus callosum Bulb of posterioi Splen Corpora quadri- gemina L of corpus callosum Tela chorioidea of third ven- tricle Medial longitu. L dinal fasciculus Cerebellum Brachium pontis Flocculus Epiphysis Posterior cornu ^ ^ ^ of lateral ven- tiicle ^ Glomus chori- ^ ^ oideum Tapetum _ Occipito-thalamic radiation Collateral emin- en:e Collateral fissure Lateral Lemniscus Brachium con- junctivum Central grey substance Medial lemniscus Pyramid FunctionaOy, the internal capsule may be divided into a frontal, a fronto-parietal and an occipital part. The frontal part consists of (1) an anterior segment, carrying chiefly fibres coursing in both directions between the thalamus and the cortex of the frontal lobe, and (2) a posterior segment carrying the frontol-pontUe tract. The fronto-parietal part may be considered in four segments; — (1) An anterior segment, the genu, carrying fibres from the cortex to the nuclei of the motor cranial nerves; (2) posterior to this is the corticospinal segment for the arm and thorax, descending cortical fibres to the regions of the spinal cord supplying these; (3) next is the corticospinal segment }or the lower extremity; (4) a posterior segment carrying the general sensory path ascending from the hypothalamic nucleus, the infero-lateral part of the thalamus and the red nucleus to the cortex. All the segments of the fronto-parietal part carry in addition, fibres in both directions between the cortex above and the thalamus and the nuclei of the striate body. The occipital part consists (1) of an anterior segment which carries the temporal and occipital pontile paths, and (2) a posterior segment carrying the visual fibres between the occipital cortex and the nuclei of termination of the optic nerve. This segment also carries the auditory fibres passing between the cortex of the superior temporal gyrus and the regions of termination of the lateral lemniscus. Thus it carries a visual and an auditory path. The corona radiata. — Above the corpus callosum and laterally joining its radiations, the fibres of the internal capsule are dispersed in all directions. The appearance known in coronal sections of the hemispheres as the corona radiata is produced by the ascending and descending fibres of the internal capsule combined with the radiations of the corpus callosum. The radiations related to the internal THE NERVOUS SYSTEM capsule may be divided into a frontal, a parietal and an occipital part, corres- ponding to the frontal, parietal and occipital peduncles of the thalamus, or to the parts of the internal capsule. The radiation derived from the posterior segment of the occipital part of the internal capsule, the visual path, accumulates into a well-defined band of fibres which passes posteriorly into the occipital lobe, spreading in the lateral wall of the posterior cornu of the lateral ventricle immediately lateral to the tapetum. This band consists for the most part of fibres arising in the pulvinar of the thalamus and Fig. 700.- -DiAGBAM TO Indicate the Relative positions of the Projection Fibees in THE Intehnal Capsule. (In part after VilEger.) yy4 y Stria terminalis of '/^j / thalamus «?■,////'/ •• Fronto-pon- -™ Cortico-spinal path (arm) ~~ ^ Cortico-spinal path (leg) "^ General sen- sory path ■ ^ Temporal 1 and occipital pontile path I ■^ visual and auditory path J Fronto- parietal part in the lateral geniculate body and going to the visual area of the occipital cortex, and of fibres arising in this cortex to terminate in the thalamus and mesenceph- alon. Being thus concerned with the optic apparatus, it is known as the occipito- thalamic radiation or optic radiation (fig. 699). The external capsule is, as already noted, a thin sheet of white substance spread between the claustrum and the lenticular nucleus. It owes its appearance as such to the presence of the claustrum. It joins the internal cap- sule at the upper, posterior, and anterior borders of the putamen, and below the claustrum it is continuous with the general white substance of the temporal lobe. Thus it contributes to an encapsulation of the lenticular nucleus by white substance. Most of the fibres contained in it belong to the association system. Its projection fibres consist of those of the inferior peduncle of the thalamus, which pass from the basal surface of the thalamus and, instead of continuing below to the cortex of the temporal lobe and insula, turn upward, around the lenticu- lar nucleus to the cortex above the insula. Some of these thalamus fibres are known to pass upward through the lamina; of the lenticular nucleus instead of through the external capsule. DESCENDING PROJECTION FIBERS 889 The ascending projection fibres arise mostly from the cells of the nuclei of the thalamus and hypothalamic nucleus; some arise from nuclei in the mesencephalon and from the red nucleus. They may be summarised as follows: — (1) The terminal part of the general sensory pathway of the body. The portion of the medial lemniscus which arises in the nuclei of the fasciculus gracilis and cuneatus, of the opposite side, terminates in the hypothalamic nucleus and the inferior portion of the lateral nucleus of the thalamus. The projection fibres given off by the latter nuclei pass chiefly through the posterior segment of the fronto-parietal part of the internal capsule and radiate to and terminate in the somaesthetic area of the cortex, chiefly in the posterior central gyrus. Some few pass outside around the lenticular nucleus, and ascend by way of the external capsule. (2) The terminal part of the general sensory pathway of the head and neck. The nuclei of termination of the sensory portions of the cranial nerves of the rhombencephalon (except the nuclei of the cochlear nerve) give fibres which course upward in the medial lemniscus (fillet) and reticular substance of the opposite side and terminate in the infero-lateral portions of the thalamus and in the h3rpothalamic nucleus. Thence arise projection fibres which ascend to the somaesthetic area by practically the same route as those of the general sensory system for the body. ' (3) The terminal part of the auditory pathway. The ventral and dorsal nuclei of termina- tion of the cochlear nerve send impulses which, by way of the lateral lemniscus, are distributed to the inferior quadrigeminate body, the medial geniculate body, and the nucleus of the lateral lemniscus of the opposite side. These nuclei send projection fibres through the posterior segment of the fronto-parietal part of the internal capsule, and thence by the temporal portion of the corona radiata to the cortex of the superior temporal gjrrus (auditory area). Probably some of these fibres pass by way of the inferior peduncle of the thalamus. Some of the fibres arising in the nuclei of termination of the vestibular nerve convey impulses which reach the somaesthetic area, but the origin of the terminal portion of this system is uncertain. (4) The terminal part of the visual pathway. The cells of the pulvinar and the lateral geniculate body, serving as nuclei of termination of the optic tract, give off projection fibres which pass by way of the posterior segment of the occipital portion of the internal capsule and the occipito-thalamic radiation to the cortex of the occipital lobe, chiefly the region about the posterior end of the calcarine fissure — the visual area. (5) The terminal ascending cerebellar pathway. The fibres of the brachium conjunctivum, after decussating, terminate both in the red nucleus and in the lateral nucleus of the thalamus. Some fibres from the red nucleus become projection fibres direct, others terminate in the medial and anterior portion of the lateral nucleus of the thalamus. From the thalamus the projection fibres of this system pass in the parietal peduncle of the thalamus to the somaesthetic area. The descending projection fibres arise as outgrowths of the pyramidal cells of the cerebral cortex. Practically all of them cross to the opposite side in their descent to the structures of the brain stem and spinal cord. The majority of them arise near and within the gyri in which the respective ascending fibres terminate. Those transmitting cortical impulses to the cells giving origin to the motor fibres of the cranial and spinal nerves arise chiefly from the giant pyramidal cells of the precentral (anterior central) gyrus, the paracentral lobule and the posterior ends of the superior, middle, and inferior frontal gyri. These latter occupy nearly three-fourths (the anterior three segments) of the fronto-parietal part of the inter- nal capsule and the middle three-fifths of the basis of the cerebral peduncle, and are usually called 'pyramidal fibres (fig. 700). The principal descending projection fibres may be grouped as follows: (1) The pyramidal fibres to the spinal cord (cortico-spinal or pyramidal fascicuh proper). These arise from the giant pyramidal cells of the upper two-thirds of the precentral gyrus, the anterior portion of the paracentral lobule and the posterior third of the superior frontal gyrus. Those for the lumbo-sacral region of the spinal cord arise nearest the supero-mesial border of the cerebral hemisphere. The tract descends through the two middle segments of the fronto-parietal part of the internal capsule. Those carrying cortical impulses for the muscles of the arm and shoulder course in the segment anterior to the course of those for the muscles of the leg. Both continue through the cerebral peduncles and the pons and through the pyramids of the medulla, and then decussate, passing down the spinal cord to terminate about the ventral horn ccUs (the origin of the motor nerve roots) of the opposite side. (2) The pyramidal fibres to the nuclei of origin of the motor cranial nerves arise from the pyramidal cells in the inferior third of the precentral gyrus, the posterior end of the inferior frontal gyrus, the opercular margin of the posterior central gyrus, and probably some (for eye movements) in the posterior end of the middle frontal gyrus. The locality of the origin of the pyramidal fibres terminating in the nuclei of the facial and hypoglossal nerves only has been determined with certainty. The general tract passes in the genu of the internal capsule, through the cerebral peduncle, and, gradually decussating along the brain stem, terminates in the nuclei of the motor cranial nerves of the opposite side. (3) The frontal pontile path (Arnold's bundle) arises in the cortex of the frontal lobe, anterior to the precentral gyrus, descends through the frontal part of the corona radiata and posterior segment of the frontal portion of the internal capsule into the fronto-mesial portion of the cerebral peduncle, and terminates in the nuclei of the pons. 890 THE NERVOUS SYSTEM (4) The temporal pontile path (Turk's bundle) arises in the cortex of the superior and middle temporal gyri, passes through the posterior segment of the occipital part of the internal capsule, enters the cerebral peduncle postero-lateral to its pyramidal portion, and terminates in the nuclei of the pons. An occipito-pontile path is described as arising in the occipital cortex and joining the temporal pontile path in the internal capsule to pass to the nuclei of the pons. (5) The occipito-mesencephalic path (Flechsig's secondary optic radiation) arises in the cortex of the visual area of the occipital lobe (cuneus and about the calcarine fissure), passes forward through the occipito-thalamic radiation, downward in the posterior segment of the occipital portion of the internal capsule, and terminates in the nucleus of the superior quadri- geminate body and the lateral geniculate body. It is probable that some of its fibres terminate directly in the nuclei of the eye-moving nerves. (6) Those fibres of the fornix which arise in the hippocampus and terminate in the corpus mammiUare or pass through it to the anterior nucleus of the thalamus of the same and opposite side (mammiUo-thalamic fasciculus) or pass into the mescencephalon and probably to structures lower down. The commissural system of fibres. — ^The commisstiral fibres of the telenceph- alon serve to connect or associate the functional activities of one hemisphere with those of the other. They consist of three groups: — The corpus callosum, the anterior commissure and the hippocampal commissure. (1) The corpus callosum, the great commissure of the brain. A general description of this with the medial and lateral striae running over it has aheady been given. It is a thick band of white substance, about 10 cm. wide, which crosses between the two hemispheres at the bottom of the longitudinal fissure. Its shape is such that in its medial transverse section its parts are given the names splenium, body, genu, and rostrum (figs. 667 and 679). Its lower surface is medially joined to the fornix, in part by the septum peUucidum and in part directly. Laterally it is the tapetum of the roof of the lateral ventricle of either side. The majority of its fibres arise from the cortical cells of the two hemispheres, and terminate in the cortex of the side opposite that of their origin. In dissections, its fibres are seen to radiate toward all parts of the cortex — the radiation of the corpus callosum. These radiations may be divided into frontal, parietal, temporal and occipital parts. The occipital parts curve posteriorly in two strong bands from the splenium into the occipital lobes, producing the figure known as the forceps major. Anteriorly, the frontal parts are two similar but lesser bands which curve from the genu forward into the frontal lobe, producing the forceps minor. (2) The anterior commissure has been described in connection with the rhinencephalon. In addition to the ohactory fibres coursing through it from the olfactory bulb and parolfactory area of one hemisphere to the uncus of the opposite hemisphere, its greater part consists of fibres which arise in the cortex of the temporal lobe, the uncus chiefly, of one side and terminate in that of the opposite side. It crosses in the substance of the anterior boundary of the third ventricle, and through the inferior portions of the lenticular nuclei, and can be seen only in dissections (figs. 684, 693). It is a relatively small, round bundle, and its mid-portion between its terminal radiations presents a somewhat twisted appearance. (3) The hippocampal commissure (transverse fornix) belongs wholly to the limbic lobe (rhinencephalon), and has been described there. It connects the hippocampal gyri of the two sides, and crosses the mid-Mne under and usually adhering to the under surface of the splenium of the corpus callosum. Crossing the body of the fornix, it thins anteriorly and ceases in the posterior angle of the septum peUucidum. With these three commissures of the telencephalon, the three other commissures of the prosencephalon should be called to mind. The inferior cerebral commissure (Gudden's commissure), while occurring in the optic chiasma and allotted by position to the telencephalon, really belongs to the diencephalon since it connects with each other the medial geniculate bodies of the two sides. The supra-mammillary commissure, connecting the nuclei of the mam- miUary bodies of the two sides, is allotted to the diencephalon. The posterior cerebral com- missure, situated just below the stalk of the epiphysis, belongs to both the diencephalon and mesencephalon. Its superior part, the habenular commissure, connecting the two nuclei of the habenulae, belongs wholly to the diencephalon. In its inferior part, the fibres arising in the thalamus of one side and terminating in that of the other side belong likewise to the diencephalon, but those passing between the superior quadrigeminate bodies of the two sides and between the so-called nuclei of the medial longitudinal fasciculi belong to the mesencephalon. The association system of the hemisphere. — The possibilities for association bundles connecting the different parts of the same hemisphere with each other are innumerable, and a large number are recognised. They serve for the distribution or diffusion of impulses brought in from the exterior by the ascending projection system, and it is by means of them that the different areas of the cortex may function in harmony and coordination. Most of the association bundles are supposed to contain fibres coursing in both directions. Several of them have already been described in company with the grey masses with which they are concerned. They may be summarised as follows (see figs. 683, 701 and 702) : — ■ (1) Those of short course, the fibrse propriae, which associate contiguous gyri with each other. These arise from the ceUs of a gyrus and loop around the bottoms of the sulci, continu- ally receiving and losing fibres in the cortex they associate. The stripes of BaiUarger within the cortical layer might be included among the short association bundles. (2) The cingulum (girdle) lies in the gyrus cinguli and is shaped correspondingly. It ASSOCIATION FIBRES 891 extends from the anterior perforated substance and the subcallosal gyrus around the genu of the corpus callosum, then, under cover of the gyrus cinguU and around the splenium, and thence downward and forward in the hippocampal gyrus to the uncus. It is chiefly an aggregation of fibres of short course — fibres which associate neighbouring portions of the cortical substance Fig. 701. — Photogeaph of "Torn Preparation " op Cerebral Hemisphere showing SOME OP THE Association Fasciculi. (After R. B. Bean.) Central sulcus External capsule Superior and inferior longitudinal fasciculi and temporal pontile path External capsule, posterior part Fig. 702. — Schematic Representation op Certain op the Association Pathways of the Cerebral Hemisphere. Fibrse proprise Superior longitudinal ,'j fasciculus ^ ' ■, Stria terminalis \ ^' '; of thalamus \ ^— *w^ "y-^ "^ ,'' '; Cingulum Uncinate fasciculus Inferior longitudinal fasciculus beneath which they course, and which, by continually overlapping each other, form the bundle. (3) The uncinate fasciculus is a hook-shaped bundle which associates the uncus and anterior portion of the temporal lobe with the olfactory bulb, parolfactory area and anterior perforated substance and perhaps the frontal pole with the orbital gyri. Its shape is due to its having to curve medialward around the stem of the lateral cerebral fissure. 892 THE NERVOUS SYSTEM (4) The superior longitudinal fasciculus is the longest of the association paths, and asso- ciates the frontal, occipital, and temporal lobes. From the frontal lobe it passes laterally in the frontal and parietal operculum, transverse to the radiations of the corpus callosum and the lower part of the corona radiata, and above the insula to the region of the posterior end of the lateral fissure, and thence it curves downward and forward to the cortex of the temporal lobe. Some of its fibres extend to the cortex of the temporal pole. The occipital portion consists of a loose bundle given off from the region of the downward curve, which radiates thence to the occipital cortex. (5) The inferior longitudinal fasciculus associates the temporal and occipital lobes and extends along the whole length of these lobes parallel with their tentorial surfaces. Posteriorly it courses lateral to the lower part of the oceipito-thalamic radiation, from which it differs by Fig. 703. — Diagrams Suggesting the General Motor, General and Special Sensory AND THE Association Areas of the Convex and Mesial Surfaces of the Cerebral Hemisphere. Parietal *' association area Temporo-occlpifal association area Frontal -association area Temporo- occipital association area the fact that its fibres are less compactly arranged. It associates the lingual and fusiform gyri and the cuneus with the temporal pole. (6) The medial and lateral longitudinal striae of the upper surface of the corpus caUosum may be considered among the association pathways, since most of their fibres associate the grey substance of the hippocampal gyrus with the subcallosal gyrus and the anterior perforated substance of the same hemisphere. Their significance as parts of the rhinencephalon has already been given. (7) Likewise the longitudinal fibres in the stria terminalis of the thalamus (taenia semi- circularis) may be considered among the association pathways, since these connect the amyg- daloid nucleus with the anterior perforated substance. (8) The numerous fibres passing in both directions between the cerebral cortex and the nuclei of the corpus striatum belong to the association system. These do not form a definite bundle, but, instead, contribute appreciably to the corona radiata. However, a pathway described as the occipito-frontal fasciculus probably consists largely of the more sagittally running fibres of this nature. The existence of this fasciculus has been noted in degenerations and in cases of arrested development of the corpus callosum. Its fibres are described as con- tributing greatly to the tapetum, and as coursing beneath the corpus callosum immediately FUNCTIONAL AREAS OF CORTEX 893 next to the ependyma of the lateral ventricle. As a mass, they appear in intimate connection with the caudate nucleus, and are spread toward both the frontal and the occipital lobes (chiefly the latter), in the mesial part of the corona radiata of those lobes. It is described as also con- taining fibres in both directions associating the occipital with the temporal lobe. Vertical association fibres pass through the caudate and lenticular nuclei between the cortex above and that of the temporal lobe below. (9) Since the olfactory bulb is a part of the hemisphere proper, the olfactory tract may be considered an association pathway connecting the olfactory bulb with the parolfactory area, the subcallosal gyrus, the anterior perforated substance, and the uncus. As already shown, a portion of the fibres of the tract belongs to the commissural system. THE FUNCTIONAL AREAS OF THE CEREBRAL CORTEX The definitely known areas of specific function of the human cerebral cortex are relatively small. They comprise but little more than a third of the area of the entire hemisphere. They are — (1) the general sensory-motor or somaisthetic area, and (2) the areas for the organs of special sense. They represent portions of the cortex in which terminate sensory or ascending projection fibres bearing impulses from the given peripheral structures, and in which arise motor or descending projection fibres bearing impulses in response. Knowledge of the location of the areas has been obtained — (1) by the Flechsig method of investigation, and to a considerable extent by Flechsig himself; (2) from clinico-pathological observations, largely studies of the phenomena resulting from brain tumors and traumatic lesions; (3) by experimental excitation of the cortex of monkeys and apes, the resulting phe- nomena being correlated with the anatomical findings and compared with the observations upon the human brain. The remaining larger and less known areas of the cortex are referred to as 'association centres' or areas of the 'higher psychic activities.' In development, the sensory fibres to the specific areas acquire their medullary sheaths first, before birth, and then the respective motor fibres from each become medullated. It ia not till a month after birth that the association centres show medullation and therefore acquire active functional connection with the specific areas. In defining an area it is not claimed that all the fibres bearing a given type of impulse terminate in that area, nor that all the motor fibres leading to the given reaction originate in the area. It can only be said that of the fibres concerned in a given group of reactions, more terminate and arise in the areas cited than in any other areas of the cortex. The corresponding motor fibres arise both in the region of the termination of the sensory fibres (sensory area) and also in a zone (motor area) either partially surrounding or bordering upon a part of the region of termination. The different areas are as follows: — (1) The somaesthetic (sensory-motor) area, the area of general sensibility, and the area in which arise the larger part of the cerebral motor or pyramidal fibres for the cortical control of the general muscular system. As is to be expected, it is the largest of the specific areas. It includes the anterior central gyrus, posterior central gyrus, the posterior ends of the superior, middle, and inferior frontal gyri, the paracentral lobules, and the immediately adjacent part of the gyrus cinguli. The ascending or sensory fibres are found to terminate most abundantly in the part posterior to the central sulcus (Rolandi), the posterior central gyrus being the special area of cutaneous sensibility, and the adjacent anterior ends of the horizontal parietal gyri have been designated as the area of 'muscular sense.' Both these areas are carried over upon the medial surface to involve the lower part of the paracentral lobule and a part of the gyrus cinguli. The anterior central gyrus gives origin to relatively more motor fibres than the other portions of the somffisthetic area. In distribution, the muscles furthest away from the cortex are innervated from the most superior part of the area, the leg area being in the supero-mesial border of the hemisphere, while that from the head is in the anterior and inferior part of the area (fig. 703). The muscles of mastication and the laryngeal muscles are controlled from the fronto-parietal operculum. Broca's convolution, the opercular portion and part of the triangular portion of the inferior frontal gyrus, of the left hemisphere, constitutes the especial motor area of speech, and Mills has extended this area to include the supero-anterior portion of the insula below. The various authorities differ considerably as to the exact locations of many of the areas for the cortical control of given sets of muscles. Further observations must be skillfully made tor localisation of areas of the human cortex in detail and further correlations must be deter- mined between the experiments upon the cortex of anthropoid apes and the functions of that of man. The accompanying diagrams are compiled from several of the diagrams more usually given and must be considered as only approximately correct. (2) The visual area. — The especial sensory portion of this area is that immediately border- ing upon either side of the posterior part of the calcarine fissure. The entire area, motor and sensory overlapping each other, includes the whole of the cuneus. The motor visual area proper is described as the more peripheral portion of the entire area. In addition, an area producing eye movements is described as situated in the posterior end of the middle frontal gyrus. (3) The auditory (cochlear) area comprises the middle third of the superior temporal gyrus and the transverse temporal gyri of the temporal operculum. The motor portion of this area hes in its inferior border. The fibres arising in the area course downward ia the temporal pontile path to the motor nuclei of the medulla. (4) The olfactory area consists of the olfactory trigone, the parolfactory area, the sub- callosal gyrus, part of the anterior perforated substance, the hippocampal gyrus (especiaUj' the uncus), and the callosal half of the gyrus cinguli. Its motor or efferent area lies chiefly in the hippocampal g3T.'us, the fibres from which pass out from the telencephalon by way of the fornix and cingulum. 894 THE NERVOUS SYSTEM (5) The gustatory area is supposed to comprise the anterior portion of the fusiform gyrus and the zone (motor portion) about the anterior extremity of the inferior temporal sulcus. (6) The assocaition areas. — The relatively large areas allotted at present to the so-called higher psychic activities are indicated in fig. 703. The great relative extent of these is one of the characteristics of the human brain. They probably merely represent the portions of the cortex of which httle is known, and may eventually be subdivided into more specific areas. They are considered to be connected with the structures below by fewer projection fibres than are the recognised areas named above, while, on the other hand, they are rich in association fibres. By means of the latter they are in intimate connection with the specific areas and have abundant means of correlating and exercising a controlhng influence upon the functions of these areas. According to Flechsig, they consist of — (1) a parietal association area, comprising that part of the parietal cortex between the somaesthetic area and the visual area; (2) an occipito- temporal association area, including the unspecified portions of the temporal lobe and the ad- joining portion of the occipital lobe not included in the visual area; (3) a frontal association area, including all the frontal lobe anterior to the somesthetic and olfactory area. In the folds of the inferior parietal lobule of the parietal association area such intellectual activities as the optic discrimination of words, letters, numbers, and objects generally are supposed to Fig. 704. — Convex Surface op left Cebebral Hemisphere with Diagrammatic Presenta- tion OF the Areas Suggested as Concerned with Speech. Area for coordination of muscles producing speech f (Broca's convolution) I Motor area for hand (graphic) Motor area for mouth and larynx ^ Auditory word images Visual word ' images Auditory area Word understanding take place, while the superior parietal lobule continued into the posterior part of the praecxmeus is the general region for the perception of form and solidity of objects — the stereognostic centre. The insula is suggested as the area in which auditory, olfactory and gustatory impulses are associated with the motor areas beginning in the operculum dorso-laterally adjacent to it. Observations of symptoms and the position of lesions accompanying them have made it possible to arrive at some trustworthy conclusions regarding the cortical areas controlling speech. Broca announced in 1861 that the inferior frontal gjTus of the left hemisphere was peculiarly concerned with speech. This area was later confined to the posterior end or opercular portion of this gyrus and the name "Broca's Convolution" was given it. It is now known that Broca's convolution and the adjacent portion of the triangular part of the inferior frontal gyrus as well comprise the motor area or emissive speech area — the area especially devoted to the control of that coordinated action of the muscles concerned which makes possible articulate speech. Patients in whom this area is impaired are unable to give utterance to words though they may understand them both written and spoken, and though they may give utterance to sound. This inability is known as motor aphasia. Results of observed lesions have further shown that the area in which the auditory images of words are retained (word memories) com- prises the posterior end of the superior temporal gyrus and the adjoining portion of the supra- marginal gyrus. Injury to this area is accompanied by inability to recognise spoken words although the patient hears them and may recognise and understand written words, a phe- nomenon known as "word-deafness" or sensory aphasia. This area may be considered as continuous with the superior portion of the posterior end of the middle temporal gyrus which has been suggested as the area of "word-understanding," or "lalognosis." On the other hand, the area in which visual images of words are retained is located as the angular gyrus. Injury to this results in an inability to recognise printed or written words although the patient CONDUCTION PATHS 895 may hear, understand and speak them. This is called "word-Uindness." This area is nearest the special area of vision on the one hand and on the other hand, is continuous into the area to which word-understanding is attributed. For purposes of writing, it must be associated with the motor area for the muscles of the hand in the precentral gyrus. While the motor area for speech is most functional in the left hemisphere, the remaining areas concerned are probably equally developed in the two hemispheres. III. GENERAL SUMMARY OF SOME OF THE PRINCIPAL CONDUCTION PATHS OF THE NERVOUS SYSTEM In the following summary the arabic numerals indicate paragraphs in which are mentioned the nuclei or ganglia containing the cell-bodies of the neurones interposed in the chains; the small letters indicate the different names given to the different levels of the pathways through which their fibres run. For detailed descriptions of either nuclei or pathways see pages de- scribing them. Only the more common neurone chains are followed here. I. The Spino-cbrebhal and Cerebro-spinal Path A. The ascending system of neurones, (fig. 706) 1. Spinal ganglion — neurone of first order. (a) Terminal corpuscles and peripheral process of T-fibre. (6) Dorsal or afferent root of spinal nerve. (c) Ascending branch of bifurcation of dorsal root fibre in fasciculus gracihs, or fasciculus cuneatus of spinal cord. 2. Nucleus of fasciculus gracilis or nucleus of fasciculus cuneatus in meduUa oblongata — neurone of second order, (a) Internal arcuate fibres. (6) Decussation of lemniscus. (c) Interolivary stratum of lemniscus of opposite side. (d) Medial lemniscus. 3. Hypothalamic nucleus and lateral nucleus of thalamus — neurone of third order. (a) Internal capsule, posterior segment of fronto-parietal portion. (6) Corona radiata, fronto-parietal part. (c) Posterior central gyrus of somsesthetic area of cerebral cortex. B. Descending system of neurones (fig. 706). 1. Giant pyramidal cells of precentral g}TUS of somaesthetic area. (o) Corona radiata, fronto-parietal part. (6) Internal capsule, middle segments of fronto-parietal portion. (c) Basis of the cerebral peduncle and the peduncle. (d) Pyramid of medulla oblongata. (el) Decussation of pyramids. (/') Lateral cerebro-spinal fasciculus (crossed pyramidal tract), (e^) Ventral cerebro-spinal fasciculus (direct or uncrossed pyramidal tract). (P) Gradual decussation of latter in cervical and upper thoracic regions of spinal cord. 2. Cells of ventral horn of spinal cord of opposite side, (o) Ventral or efferent roots of spinal nerves. (6) Peripheral nerve-trunks directly to skeletal muscles or indirectly to smooth muscle or glands by way of sympathetic neurones. II. Short 'Reflex' Paths of Spinal Cord 1. Spinal gangha. (o) Terminal corpuscles and peripheral process of T-fibres. (6) Dorsal root of spinal nerve. (c) Collaterals and descending branches of bifurcation of dorsal root fibres in spinal cord (d) Directly to ventral horn cells of same level of spinal cord. (e) Or, more commonly, to same through intermediation of Golgi cell of type II. (/) Or to neurones of fasciculi proprii to ventral horn cells of other levels of spinal cord. 2. Ventral horn cells of same (chiefly) and opposite side and thence by way of ventral roots and peripheral nerve trunks directly to muscles. 3. Dorso-lateral group of ventral horn cells of same (chiefly) and opposite sides and thence by ventral root fibres to cell-bodies in sympathetic gangha. 4. Sympathetic axones to smooth muscle or glands. III. Cerebral Path for the Cranial Nerves, ExcLusrvE of Those of Special Sense A. Ascending system of neurones. 1, Ganglia of origin of sensory components of vagus, glossopharyngeus, glosso-palatine and trigeminus. (a) Peripheral arborisations and afferent peripheral branches of T-fibres of same. (6) Central branches of T-fibres of same (sensory nerve roots). 2. Nuclei of termination of central branches (bifurcated and imbifurcated) in meduUa oblongata, (a) Reticular formation, internal arcuate fibres and medial lemniscus of the opposite side. 896 THE NERVOUS SYSTEM 3. Hypothalamic nucleus and lateral nucleus of thalamus. (a) Internal capsule, posterior segment of fronto-parietal portion. (6) Corona radiata, fronto-parietal part. (c) Cerebral cortex — chiefly lower third of posterior central gyrus. Fig. 705. — Scheme of Ascending or Spino-cerebeal Conduction Pathways. -Fibrse propriEe P3Tamidal fibre Corona radiata ■Internal capsule -Hypothalamic nucleus .Nuclei of termination of sensory cranial ] Ganglia of sensory cranial nerves Nucleus of spinal tract of trigeminus .Nucleus of fasciculus cuneatus ■Nucleus of fasciculus gracilis ^N. Posterior root ' Spinal ganglion 'Fasciculus cuneatus •Fasciculus gracilis B. Descending system of neurones. 1. Pyramidal cells of opercular region of soma^sthetic area. (a) Corona radiata, fronto-parietal. (b) Internal capsule, genu chiefly. (c) Basis of cerebral peduncle and peduncle. (d) Decussation in brain stem. CONDUCTION PATHS 897 2. Nuclei of origin of motor cranial nerves and motor components of mixed cranial nerves, of opposite side chiefly and thence by way of these nerves to the respective muscles supplied. Notes: (1) Most of the descending cortical fibres to the nucleus of origin of the trochlear Fig. 706. — Scheme of Descending Ceeebeo-spinal Conduction Pathways. Caoidate nucleus' Internal capsule Cerebral peduncle Trochlear nerv Medulla oblongati Ventral roots of spinal nerves Ventral white commissure nerve and that portion of the nucleus of the oculomotor which supplies the internal rectus muscle apparently do not decussate but terminate in the nuclei of the same side. (2) The efferent nucleus of the glosso-palatine (salivatory nucleus) and the dorsal efferent nucleus of the vagus give rise to visceral efferent fibres, i.e., carry impulses destined for smooth muscle and glands by way of sympathetic neurones. The same is true for the supero-median part of the nucleus of the oculomotor. 898 THE NERVOUS SYSTEM (3) The nuclei of termination of the cranial nerves, especially those of the vestibular and trigeminus, send fibres also into the cerebellum. IV. The Short 'Reflex' Paths of the Cranial Nehves These consist of the central branches of their afferent or sensory fibres, bearing impulses to the nuclei of origin of both their own motor components and to the nuclei of origin of other Fig. 707. — Scheme of Principal Ascending Cerebellar Conduction Paths. -*• Corona radiata Thalamus Lateral nucleus of thalamus - Internal capsule Red nucleus Decussation of brachia conjunctiva Nucleus fastigii Dentate nucleus 3 v^eicuciiuut (displaced) --._ Ganglia of afferent cranial nerves --'' (vestibular chiefly) — • Nucleus of funiculus cuneatus ' Nucleus of funiculus gracilis > Spinal ganglia motor nerves. Fibres to the more distant nuclei pass to them by way of the medial longi- tudinal fasciculus. Instead of terminating in the motor nuclei directly, the sensory fibres are usually interrupted by a third or intermediate neurone interposed in the chain. The vagus and glosso-pharyngcus are connected by way of the solitary fasciculus and its nucleus with the structures below their level of entrance, even with the ventral horn cells of the upper segments of the cervical cord, and through these with the muscles of respiration. CONDUCTION PATHS 899 V. Conduction Paths Involving the Cerebellum A. Ascending cerebellar pathways. 1. Spinal ganglia. (a) Dorsal roots of spinal nerves. (6) Collaterals and descendiag branches of bifurcation of dorsal root fibres in spinal cord, chiefly those conveying impulses of muscle-sense. 2x. Dorsal nucleus (Clarke's column). (o) Dorsal spino-cerebellar fasciculus (direct cerebellar tract). (6) Restiform body (inferior cerebellar peduncle) — (c) Joined in meduUa by external arcuate fibres (crossed and uncrossed fibres arising in nuclei of funiculus gracilis and cuneatus) ; (d) Joined in medulla by fibres arising in nuclei of termination of afferent vagus, glosso-pharyngeal, vestibular, and trigeminal nerves; (e) Joined by fibres both to and from (ascending and descending) the inferior olivary nucleus of the same and opposite sides (cerebello-olivary fibres). 2y. Nerve-cells in base of ventral horn of same and opposite side. (a) Superficial antero-lateral spino-cerebellar fasciculus (Gowers' tract), ascending through spinal cord and reticular formation' of medulla and pons. (6) Anterior meduUary velum and brachium conjunctivum to cerebellar cortex (vermis). 3. Cerebellar cortex (vermis), dentate nucleus, nucleus fastigii, nucleus emboliformis, and nucleus globosus. (a) White substance (corpus medullars) of cerebellum, associating various regions of its cortex and its nuclei with each other. (6) Brachium conjunctivum (superior cerebellar peduncle) arising chiefly from dentate nucleus, (c) Decussation of brachium conjunctivum. 4. Red nucleus and ventral portion of lateral nucleus of thalamus. Most fibres of the brachium conjunctivum terminate in the red nucleus; many merely give off collaterals to it in passing to their termination in the thalamus. Most of the ascending fibres arising in the red nucleus also terminate in the ventral part of the thalamus; some ascend to the cerebral cortex direct. (a) Internal capsule, middle third, and fronto-parietal part of corona radiata. (6) Somsesthetic area of cerebral cortex and cortex of frontal lobe anterior to it. (c) Inferior peduncle of thalamus to cortex of temporal lobe. B. Descending cerebrocerebellar paths. 1. Pyramdial cells of somsesthetic area send fibres through corona radiata, internal capsule, and cerebral peduncle to nuclei of pons and arcuate nucleus of same and opposite side. 2. Gelt of cortex of posterior part of frontal lobe give fibres to form frontal pontile path through frontal parts of corona radiata and internal capsule and through medial part of cerebral peduncle to nuclei of pons of opposite side. 3. Cells of cortex of temporal lobe (superior and middle gyri) give fibres to form temporal pontile path which passes under the lenticular nucleus into anterior segment of occipital portion of internal capsule and lateral part of cerebral peduncle to nuclei of pons of opposite side. This path is joined in the internal capsule by a small occipito- pontile path. 4. Cells of nuclei of pons send fibres by way of brachium pontis (middle cerebeOar peduncle) to cortex of cerebellar hemisphere, of side opposite to that of the origin of the cei-ebral fibres making synapses with the cells of the pons. C. Descending cerebellospinal paths. 1. From cells of nucleus fastigii of same and opposite sides and probably from other nuclei of cerebellum arise fibres which terminate in the nuclei of termination of the vestib- ular nerve and these send fibres into the intermediate and anterior marginal fasciculi of spinal cord (fig. 619), and thence to the cells of the anterior horn. 2. Probably connected with the cerebellum is the pathway arising in the red nucleus of the opposite side and descending in the rubro-spinal tract of the lateral funiculus of the spinal cord (fig. 619). The rubro-spinal tract decussates in the ventral portion of the tegmentum of the mesencephalon and is said to pass through the medulla oblon- gata in the medial longitudinal fasciculus. It must be noted here that some fibres arising in the cortex of the frontal lobe terminate in the red nucleus. VI. The Vestibular Conduction Paths (Equilibration) 1. Vestibular ganglion gives origin to the peripheral utricular and three ampullar branches and to the combined and centrally directed vestibular nerve. 2. Lateral vestibular nucleus (Deiters'), medial nucleus, superior nucleus, and nucleus of descending or spinal root (nuclei of termination) give origin to fibres as follows: — (a) From lateral and superior nuclei to nucleus fastigii of opposite side and to cortex of vermis and to dentate nucleus (cerebellar connection). (6) From medial and superior nuclei to nuclei of origin of eye-muscle nerves of same and opposite sides, by way of medial longitudinal fascicuh. (c) From lateral nucleus and nucleus of descending root through reticular formation into_lateral and ventral vestibulo-spinal tracts of spinal cord. 900 THE NERVOUS SYSTEM (d) The nuclei receive fibres from the grey substance of the vermis. It is probable that all the nuclei of termination give off fibres bearing ascending impulses which ultimately reach the somresthetic area, but the course pursued and neurones involved in such a chain are uncertain. VII. The Auditory Conduction Path (Cochlear Nerve) 1. Spiral ganglion of the cochlea gives origin to short peripheral fibres to organ of Corti, and to the centrally directed cochlear nerve. 2. Dorsal and ventral nuclei of the cochlear nerve (nuclei of termination). (o) Striae medullares arise from dorsal nucleus and pass around outer side of resti- form body (acoustic tubercle), then medianward under ependyma of floor of fourth ventricle to mid-line, then ventralward into tegmentum, where they decussate and join trapezoid body and lateral lemniscus of opposite side. Fig. 708. — -Diagram Showing Some op the Connections op the Vbstibxjlar and Cochlear Nerves. Medial geniculate body Nucleus of lateral lemmscus Medial longitudinal fasciculus Lateral lemniscus. Peduncle of superior olive. ^Inferior quadngeminate body Nucleus of trochlear nerve Nucleus fastigii Nucleus emboliformis Dentate nucleus ^ Lateral nucleus of "■' vestibular nerve _^Restiform body Dorsal nucleus of ^'^ cochlear nerve ^^Ventral nucleus of '' cochlear nerve .Cochlear nerve Superior olivary nucleus Trapezoid body (6) Fibres arising in ventral nucleus pass ventraDy medianward and some termi- nate in the superior ohvary nucleus of same side; others pass by way of trapezoid body and lateral lemniscus to terminate in superior olivary nucleus, nucleus of lateral lemniscus, medial geniculate body and nucleus of inferior quadri- geminate body of the opposite side. 3. Nuclei of superior olives of both sides and nucleus of lateral lemniscus send fibres by way of lateral lemniscus to inferior quadrigeminate body and through inferior brachium to medial geniculate body, and some may pass uninterrupted to the cortex of the temporal lobe. 4. Fibres from medial geniculate body and probably from nucleus of inferior quadri- geminate body pass into internal capsule and through temporal part of corona radiata to middle third of superior temporal gyrus and adjacent portions (auditory area). 6. From strife medullares and from superior ohvary nucleus (peduncle of superior olive) arise fibres which terminate in nucleus of abducens or pass by way of the medial longitudinal fasciculus to other motor nuclei of cranial nerves. It is probable that fibres from the auditory area of the cerebral cortex are also distributed to nuclei of the cranial nerves. VIII. Conduction Paths op the Optic Apparatus . Oplic impulses. 1. 'Bipolar' cells of retina with short (peripheral) processes to layer of rods and cones (neuro-epithehum) and short centrally directed processes to ganglion-cell layer of retina (nucleus of termination). CONDUCTION PATHS 901 2. Ganglion-cells of retina give origin to — (o) Optic stratum of retina. (6) Optic nerve. (c) Optic chiasma; fibres from nasal side of retina cross in chiasma to opposite side; fibres from lateral side of retina continue on same side in— (d) Optic tract to — 3. Pulvinar of thalamus, lateral geniculate body, and nucleus of superior quadrigeminate body. (o) Fibres from nucleus of superior quadrigeminate body pass ventrally, to nuclei of origin of oculomotor and trochlear nerves and to medial longitudinal fasciculus of same and opposite sides, and from it are distributed to nucleus of origin, of abducens. (6) Fibres from lateral geniculate body and pulvinar pass through occipitafportion of internal capsule and oocipito- thalamic radiation (optic radiation) to cortex of occipital lobe (visual area). Fig. 709. — Diagram of Principal Pathways of Optic Apparatus. (After Cunningham,) CORP. GEN. M 4. Cells of visual area of cortex send fibres through occipito-thalamic radiation and occipital portion of internal capsule to nucleus of superior quadrigeminate body (oocipito-mesencephalic fasciculus), and thence, probably interrupted by cells of this nucleus, to nuclei of eye-muscle nerves. 5. Cells of nucleus of superior quadrigeminate body and pulvinar send fibres by way of medial longitudinal iasciculus into lateral and ventral funicuU of spinal cord (see fig. 619), chiefly of the opposite side. Fibres from the quadrigeminate body cross mid-line chiefly in decussation of 'optic-acoustic reflex path' (fig. 662). 6. The smaller cells of the supero-mesial group of the nucleus of the oculomotor nerve (nucleus of Edinger and Westphal) send axones, by way of the trunk of the nerve and the short root of the ciliary ganglion, which terminate about cells in — 7. The ciliary gangUon, whose cells send axones to enter the ocular bulb and termi- nate upon the smooth muscle fibres of the cihary body and iris. B. Skin-pupillary reflexes. 1. Peripheral processes of spinal gangUon cells terminating in the skin and central processes of same entering by way of dorsal roots of cervical nerves to bifurcate in spinal cord and give terminal twigs about — • 2. Cells of the dorso-lateral group of the ventral horn of the same and opposite sides. These cells send (visceral efferent) axones to terminate about cells in — 902 THE NERVOUS SYSTEM 3. The superior cervical sympathetic ganglion, which cells send axones chiefly by way of the carotid plexus and the sympathetic roots of the ciUary ganglion to terminat about cells in — 4. The ciliary ganglion. Such cells send axones into the ocular bulb to terminate in the ciliary body and radial muscle fibres of the iris, producing dilation of the pupil. C. Auditory-eye reflexes. 1. Cells of the nuclei of termination of the cochlear nerve and superior olive send fibres by way of the medial longitudinal fasciculus (some to this by way of the peduncle of the superior olive) to the nuclei of origin of the eye-moving nerves. 2. The same nuclei of the cochlear nerve send axones by way of the lateral lemniscus to terminate in the superior quadrigeminate body and thence may be sent impulses which are distributed to the nuclei of the eye-moving nerves. IX. Principal Conduction Paths op Olfactoky Apparatus 1. Bipolar cells of olfactory region of nasal epithelium send short (peripheral) processes toward surface of nasal cavity and centrally directed processes, the olfactory nerve, through lamina cribrosa of ethmoid bone into olfactory bulb (glomerular layer). 2. 'Mitral cells' of olfactory bulb give fibres which form — (a) The olfactory tract which divides into — ■ Fig. 710.- -Diagram SHcmNG Some of the Principal Tracts and Synapses op the Olpac- TORY Apparatus. Anterior Subcallosal gyrus Parolfactory area Gyrus rectus ^ Olfactory tract Olfactory bulb Perforating fibres \ Medullary stria of thalamus ^ Longitudinal striae on corpus callosum Hippocampal com- (Lyre) ~* Habenular nucleus _ . Habenulo-pedun- cular tract (fasci- culus retroflexus) Mammillo-mesen- o cephalic fasciculus ■ ^x Penduculo-tegmental tract Interpeduncular nucleus Fimbria hippocampi Uary body Anterior perforated substance Olfactory epithelium (6) Medial olfactory stria through which fibres pass — (1) into parolfactory area (Broca's area); (2) into subcallosal gyrus; and (3) by way of anterior cerebral commissure to olfactory bulb and uncus of hippocampal gyrus of opposite side. (c) Intermediate olfactory stria to anterior perforated substance. (d) Lateral olfactory stria, which terminates to some extent in anterior perforated substance, but chiefly in uncus, hippocampal gyrus, and gyrus cinguU (olfactory area) of same side. 3. Cells of uncus and hippocampal gyrus give fibres which form — (a) The cingulum (in part), by which they are associated with the cortex of the gyrus cinguli and other areas of the cerebral cortex. (b) The hippocampal commissure (in part), by which they are connected with the grey substance of the opposite side. (c) The fornix, which, interrupted in part in the nuclei of the corpus mammUlare, conveys impulses — (1) to the anterior nucleus of thalamus of the same (chiefly) and opposite sides (mammillo-thalamic fasciculus), and (2) into the mesencephalon and substantia nigra (mammillo-mesencephalic fasciculus), and by way of this tract probably to the nuclei of the mesencephalon and medulla oblongata. 4. The parolfactory area, anterior perforated substance, anterior portion of thalamus and fornix give fibres which form the medullary stria of the thalamus and which terminate in the habenular nucleus. 5. Habenular nucleus sends fibres in fasciculus retroflexus to terminate in interpeduncular nucleus. 6. Interpeduncular nucleus sends fibres to nuclei of mesencephalon and probably to structures below it. RELATIONS OF BRAIN AND CRANIUM 903 The Relations of the Brain to the Walls of the Ceanial Cavity The precise methods by which the exact positions of the most important fissures, sulci, gyri, and areas can be ascertained and mapped out on the surface of the head in the living subject are fully described in Section XIII. Here, only a very general survey of the relations of the brain to the cranial bones is given and from a purely anatomical standpoint. The parts of the brain which lie in closest relation with the walls of the cranial cavity are the olfactory bulb and tract, the basal and lateral surfaces of the cerebral hemispheres, the inferior surfaces of the lateral lobes of the cerebellum, the ventral surfaces of the medulla and pons, and the hypophysis. Certain of these portions of the brain lie in relation with the basi-cranial axis, that is, with the basi-oGcipital, the basi-sphenoid, and the ethmoid bones, while others are associated with the sides and vault of the cranial cavity. Considering the former portions first, the ventral surface of the medulla oblongata, which is formed by the pyramids, lies upon the upper surface of the basi-occipital bone. More superiorly the ventral surface of the pons rests upon the basi- Fig. 711. — Drawing of a Cast of the Head op an Adttlt Male. (Prepared by Professor CuiininKliam to illustrate cranio-cerebral topography.) Position of frontal eminence Transverse (lateral) sinus sphenoid, from which it is partly separated by the basilar artery and the pair of abducens nerves. In front of the dorsum sella3 the hypophysis (pituitary body) is lodged in the hypophyseal fossa. Still further forward the olfactory tracts he in grooves on the upper surface of the pre- sphenoid section of the sphenoid bone; and in front of the sphenoid the olfactory bulbs rest upon the cribriform plates of the ethmoid. Posterior and lateral to the posterior part of the foramen magnum the lateral lobes of the cerebellum are in relation with the cranial wall, resting upon the lower parts of the supra- occipital and the posterior parts of the ex-occipital portions of the occipital bone, while anteriorly each lobe is in relation with the inner surface of the mastoid process and the posterior surface of the petrous portion of the temporal bone. The area of the skull wall which is in close re- lationship with the cerebellar hemispheres may be indicated, on the external surface of the skull, by a line which commences at the inferior part of the external occipital protuberance and thence runs upward and lateralward. It crosses the superior nuchal line a httle beyond its centre, and, continuing in the same direction, crosses the inferior part of the lambdoid suture and reaches a Eoint directly above the asterion (the meeting-point of the occipital, temporal, and parietal ones) ; thence it descends, just in front of the occipito-mastoid suture, to the tip of the mastoid process, and there turns medialward to its termination at the margin of the foramen magnum, immediately behind the posterior end of the oociptal condyle. The basal surface of each cerebral hemisphere may be said to consist of two parts, an anterior and a posterior, separated by the stem of the lateral cerebral fissure. The anterior part, formed 904 THE NERVOUS SYSTEM by the orbital surface of the frontal lobe, rests upon the upper surfaces of the orbital plate of the frontal bone and the lesser wing of the sphenoid. It is, therefore, in close relation with the upper wall of the orbital cavity. The posterior part, behind the stem of the lateral fissure, begins with the anterior portion of the temporal lobe, including its pole. The pole itself projects against the orbital plate of the great wing of the sphenoid bone, and it is in relationship with the posterior part of the lateral wall of the orbit. The basal surface of the hemisphere, behind the pole of the temporal lobe is in contact with the upper surfaces of the great wing of the sphenoid and the petrous part of the temporal bone. The convex surfaces of the cerebral hemispheres have the most extensive relationships with the cranial wall, and it is more especially to these surfaces that the surgeon turns his attention. The general area in which the convex surface of each cerebral hemisphere is in relation with the skuU bones is readily indicated by a series of lines which correspond with the positions of its superciliary, infero-lateral, and supero-mesial borders. The line marking the superciliary margin of the hemisphere commences at the nasion (the mid-point of the fronto-nasal suture) ; it passes lateralward above the superciliary ridge, crosses the temporal ridge, then, turning posteriorly in the temporal fossa, it reaches the parieto- sphenoidal suture, and continues backward along it to its posterior extremity. Fig. 712. — Drawing op a Cast of the Head of a Newly Born Male Infant. (Prepared by Professor Cunningham to illustrate cranio-cerebral topography.) Interparietal sulcus External part of parieto-occip- ital fissure Position of frontal eminence Lateral fissure The line marking out the infero-lateral border commences at the posterior end of the parieto- sphenoidal suture, whence it passes downward, in front of the spheno-squamous suture, to the infra-temporal ci-est (pterygoid ridge) ; there it turns posteriorly and, running parallel with and mesial to the zygomatic arch, it crosses the root of the zygoma, and, ascending slightly, it passes above the external auditory meatus. Continuing backward with an incliriation upward it reaches a point immediately above the asterion; thence it descends, and, crossing the inferior part of the lambdoid suture and the superior nuchal line, it passes medialward to the inferior part of the external occipital protuberance. The supero-mesial border of the hemisphere is defined by a line which runs from the nasion to the inion. This line should be drawn about 5 mm. lateral to the sagittal suture, because the mesial area is occupied by the superior sagittal sinus, and it should be further away from the middle line on the right than on the left side, because the sinus tends to he more to the right side. The area of the skull wall enclosed by the three lines which mark the positions of the super- ciliary, infero-lateral, and the supero-mesial borders of the cerebral hemisphere is formed by the vertical plate of the frontal bone, the parietal bone, the great wing of the sphenoid, the squamous part of the temporal, and the upper section of the supra-occipital segment of the occipital bone. It covers the outer surfaces of the frontal, parietal, temporal, and occipital lobes of the cerebrum and the fissures and sulci which bound and mark them. In every consideration of the topographical relations of the cerebral g3Ti to the walls of the cranial cavity it must be borne in mind that the conditions are not constant, and that, therefore, the relations are variable. The three main factors upon which this variability depends are age, sex, and the shape of the skull. As examples of the variations which occur it may be mentioned that the lateral cerebral fissure is relatively higher in the child than in the adult (compare figs. 711 and 712). The supero-mesial end of the central sulcus is further away from the coronal suture in the female and in the child than in the adult male, and in dolichocephalic than in BLOOD-SUPPLY OF BRAIN 905 braohycephalic heads. The angle formed between the Hne of the central fissure and the mid- sagittal plane, which averages about 68° in the adult, is more acute in dolichocephalic heads, and the external part of the parieto-occipital fissure is further forward in the child, and possibly in the female, than it is in the adult male. The position of the posterior horizontal limb of the lateral fissure varies even in the adult. Its posterior part is always under cover of the parietal bone, and it terminates either in front of or inferior to the parietal eminence, but the anterior part may be above, parallel with, or inferior to the squamo-parietal suture. In the adult the anterior part of the fissure runs upward and backward from the posterior end of the spheno-parietal suture along the anterior part of the squamo-parietal suture to its highest point; thence it continues in the same direction beneath the parietal bone toward the lambda, terminating either in front of or below the parietal eminence. In the child, however, the fissure is considerably above the hne of the squamo-parietal suture (fig. 712), which it gradually approaches, attaining its adult position about the ninth year. This change of position, which occurs during the first nine years, is due partly to the ascent of the sutural hne and partly to the descent of the fissure on the surface of the brain. The frontal bone always covers the superior, middle, and inferior frontal gyri, except their posterior extremities, which are beneath the parietal bone (fig. 711). The ascending limb (ramus anterior ascendens) of the lateral fissure, which cuts into the posterior part of the inferior frontal gyrus, runs parallel with and under cover of the lower part of the coronal suture, or immediately in front of it, and the anterior horizontal hmb is parallel with and beneath the upper margin of the great wing of the sphenoid. The parietal bone is in relation with the convex surfaces of four lobes of the brain. Speaking very generally, it may be said that the anterior third covers the posterior part of the frontal lobe, including the anterior central gyrus, and the posterior ends of the superior, middle, and in- ferior frontal gyri and the precentral sulcus. The posterior two-thirds of the bone are superficial to the perietal lobe, the posterior part of the temporal lobe, the anterior part of the occipital lobe, the posterior part of the horizontal limb of the lateral fissure, the superior and inferior parts of the post-central sulcus, the interparietal sulcus, the posterior sections of the superior and middle temporal sulci, and the external part of the parieto-occipital fissure. The central sulcus is beneath the parietal bone at the junction of its middle and anterior thirds (fig. 711). In the adult, the upper end of the central sulcus is situated at about 55 per cent, of the whole length of the naso-inionic hne posterior to the nasion. It is about 4 or 5 cm. from the coronal suture. The inferior end of the sulcus, which extends to near the posterior horizontal limb of the lateral fissure, lies beneath the point of intersection of the auriculo-bregmatic line with a hne drawn from the stephanion (the point where the temporal ridge cuts the coronal suture) to the asterion. This point is about 46 per cent, of the horizontal arc measured from the glabella to the inion. The superior end of the parieto-occipital fissure usually lies about 6 mm. in front of the lambda, and the course of the fissure may be indicated by a line drawn from 5 mm. in front of the lambda to a point immediately above the asterion, and, as the latter point corresponds with the pre-occipital notch on the infero-lateral border of the hemisphere, the line in question will indicate the adjacent margins of the parietal, temporal, and occipital lobes. The occipital bone is in close relation with the cerebellum, as already pointed out, but it also covers the posterior part of the lateral surface of the occipital lobe of the cerebral hemisphere. The great wing of the sphenoid covers the outer surface of the pole of the temporal lobe, and the squamous part of the temporal bone covers the anterior parts of the superior, middle, and inferior temporal gyri and the sulci which separate them. The Blood Supply of the Encephalon The double origin of the continuous arterial system of the brain given by the confluence of the two vertebral arteries and the two internal carotid arteries, together with the description of the general distribution of the different cerebral, mesencephalic, and cerebellar arteries into which the system is divided, and the origin and course of the corresponding veins, are fuUy dealt with in Section V. Here attention may be called briefly to the abundant and systematic internal distribution of the terminal branches of the system and their intimate arrangement for the actual nourishment of the nervous tissues within. The general plan of the blood supply for the entire encephalon may be summarised as fol- lows:— (1) At their origin the different arteries are so connected, directly or indirectly, on the base of the encephalon, that the blood approaching the brain by way of the vertebral and internal carotid arteries is practically a common supply for all the arteries of the encephalon, and a given part of it may possibly pass mto any one of them. (2) In the pia mater of each gross division of the encephalon the different arteries again become coimected with each other in a superficial, freely anastomosing plexus, contmuous thi'oughout. (3) From this plexus of the surface, naturally composed in part of the trunks of the different arteries themselves, arise branches which enter directly into the nervous substance and which break up into twigs that are terminal; i. e., twigs that do not anastomose with each other. (4) The arterial capillary system arising from the terminal twigs passes over into venous capillaries which converge to form corresponding venous twigs which in their turn pass to the sm-face and join in forming a peripheral, anastomosing venous plexus superimposed upon the similar arterial plexus. (5) From this venous plexus arise the different veins of the encephalon which may or may not accompany the arteries for a short distance, and which finaUy empty into the sinuses in the cranial dura mater. These, likewise confluent, empty into the internal jugular veins. The chorioid plexuses of the ventricles of the brain are modifications of the general anastomosing peripheral plexuses. The chorioid plexuses of the lateral and third ventricles are derived largely from branches of the chorioid arteries, which arises separately from the internal carotid artery. 906 THE NERVOUS SYSTEM The blood supply of the cerebrum may best be taken as an illustration of the general plan of the blood-vascular system of the encephalon. The terminal or internal branches of the surface plexus, derived from the posterior, middle, and anterior cerebral arteries, are arranged into two groups, a central or ganglionic and a cortical group. The central branches themselves form four groups in each hemisphere: — (1) The antero-mesial group consists of terminal branches from the plexus of the domain of the anterior cerebral artery, which pass through the medial part of the anterior perforated substance and supply the head of the caudate nucleus, the septum peUucidum, the columns of the fornix, and the lamina terminaUs. (2) The antero-lateral group consists of terminal branches from the domain of the middle cerebral artery. These pierce the anterior perforated substance in two sub-groups — (a) the internal and (6) the external striate arteries (fig. 713). The internal striate arteries pass thi'ough the segments of the globus paUidus of the lenticular nucleus and through the internal capsule, to both of which they give branches, and they terminate in the caudate nucleus and thalamus. The external striate arteries are larger and more numerous. They pass upward between the external capsule and the putameu, and then through or around the upper part of the putamen into the internal capsule, where they form two groups, the lenticulo-lhalamic and the lenticulo-caudate groups. The former terminate in the thalamus and the latter in the caudate nucleus. On account of its larger size at its origin and its direct linear continuation with the internal carotid, emboU {thrombi) pass more frequently into the middle cerebral artery Fig. 713. — Diagram Showing the Manner of Distribution of the Cortical and Central Branches of the Cerebral Arteries. Cortical arteries. External striate arteries- Middle cerebral artery Caudate nucleus Thalamus Tuber cinereum Internal striate arteries than into the anterior cerebral artery. One of the lenticulo-caudate arteries which is larger and longer than the others and which is a direct branch from the middle cerebral artery has been called the 'artery of cerebral hemorrhage' (Charcot), on account of the greater frequency with which it is ruptured. (3) The postero-medial central arteries are terminal branches of the posterior cerebral artery. They also enter the anterior perforated substance, but supply the floor of the third ventricle, the posterior part of the thalamus, and the hypothalamic region. (4) The postero-lateral group are also terminal branches of the posterior cerebral artery. They supply the posterior part of the internal capsule, the pulvinar of the thalamus, the gen- iculate bodies, the corpora quadrigemina and their brachia, the epiphysis, and the cerebral pedunces. The cortical group of the cerebral arteries arise from the anastomosing plexus in the pia mater of the cortical surfaces of the hemisphere. They pass into the cortical substance both from the summits of the gyri and from the walls of the sulci. They consist of short, medium, and long branches, and pass at right angles into the gyri. The short branches terminate in the cortical substance; the medium branches supply the more adjacent white substance, and the longer branches pass more deeply into the general medullary centre of the hemisphere. All of both the central or ganglionic and the cortical arteries are terminal in the sense that they do not anastomose in the substance of the cerebrum. The blood-vascular system of the other divisions of the encephalon is in accordance with the same general plan of that of the cerebrum. Slight individual modifications of the general plan are to be expected. BLOOD-VESSELS OF CEREBELLUM 907 The blood-vessels of the mesencephalon, in addition to the supply derived from the postero- lateral group of central arteries, include the vessels of the quadrigeminate bodies and those of the cerebral peduncles. The arteries of the quadrigeminate bodies are usually six in number, three for each side — the superior, middle, and inferior quadrigeminate arteries. The superior and middle are branches of the posterior cerebral arteries, and the inferior are branches of the superior cerebellar arteries. The superior supply the superior quadrigeminate bodies and the epiphysis; the middle supply both the superior and inferior quadrigeminate bodies, and the inferior the inferior quadrigeminate bodies. They all anastomose in the pia on the surface of the stratum zouale, forming a fine-meshed plexus, and from this superficial plexus the terminal branches pass into the substance of the bodies. The veins terminate in the vein of Galen (v. cerebri magna.) The arteries of the cerebral peduncles form two groups, mesial and lateral. The mesial peduncular arteries are branches of the basilar and the posterior cerebral arteries. They pass to the medial sides of the pendunoles and supply the superior and medial part of the tegmentum. The vessels of this group which accompany the fibres of the oculomotor nerves are known as the radicular arteries; they supply the root-fibres and the nuclei of the nerves, which receive no other branches. The lateral peduncular arteries are branches of the posterior cerebral and Fig. 714.- -Showing the Capillary Supplt op the Cerebellar Cortex. "Journal of Comparative Neurology," Vol. IX.) (After Aby, Capillaries of molecu- lar layer Line of the Purkinje cells Recurrent capillaries to granular layer Arteriole through cortex to medulla Recurrent capillaries to granular layer Line of the Purkinje cells Arteriole passing through cortex to medulla Recurrent capillary to granular layer Recurrent capillaries to molecu- lar layer Junction of cortex and meduUa Capillaries of molecu- lar layer Junction of cortex and medulla Arteriole passing through cortex to medulla superior cerebellar arteries. They supply the lateral portions of the peduncles and the lateral part of the tegmentum. The veins of the mid-brain terminate in the basilar veins and the vein of Galen. The blood-vessels of the cerebellum. — Six arteries supply the cerebellum; two, the posterior inferior cerebellar, are derived from the vertebral arteries, and the remaining four, two anterior inferior and two superior cerebellar, from the basilar artery. The course and general distribution of the arteries are described m Section V, but here it must be noted that the branches of these six vessels form a rich network in the pia mater on the surfaces of the cerebellar lobes, and that extensions of the plexus pass with the folds of the pia mater into the sulci and fissures. From the superficial plexus terminal branches pass mto the interior of the cerebellum and their collaterals form capillary plexuses in the white and grey substance. The extensions of the surface plexus are of three lengths: — (1) a longer set, which pass through the cortex of the cerebellum and supply the white substance of the corpus meduUare; (2) a set of shorter arterioles which pass through the molecular layer of the cortex and break up in its granular layer; (3) the shortest set pass into the cortex and immediately break up in its molecular layer. The meshes of the capillary plexuses in the grey susbtance are ovoidal and their axes run radially. The meshes of the plexuses in the white substance are parallel with the nerve-fibres. In addition to the vessels mentioned, a distinct branch is distributed to each dentate nucleus. This springs either from the superior cerebellar or from the anterior inferior cerebellar artery of the corre- sponding side. 908 THE NERVOUS SYSTEM The efferent veins of the cerebellum do not accompany the arteries; they spring from a plexus in the pia mater which receives tributaries from the interior, and they form three groups on each cerebellar surface, the vermian veins and the lateral veins. The superior vermian vein runs forward on the superior surface of the vermis and terminates in the vein of Galen. The inferior vermian vein runs posteriorly and ends in one of the transverse sinuses. The superior lateral veins open into the superior petrosal or transverse sinuses, and the inferior lateral veins into the inferior petrosal and transverse sinuses. The vein from the dentate nucleus usuaDy joins the inferior lateral veins. The blood-vessels of the pons. — The arteries to the pons are branches of the basilar artery, and of its anterior inferior and superior cerebellar branches. The plexus in the pia mater is comparatively unimportant, and the branches which enter the substance of the pons form two main groups, the central and the peripheral. The central arteries spring directly from the basilar. They pass backward along the raphe, giving branches to the adjacent parts, and they terminate in the nuclei of the pons and those in the floor of the fourth ventricle. The peripheral arteries are radicular and intermediate. The radicular branches spring from the peripheral plexus and from the anterior inferior cerebellar arteries; they accompany the roots of the trigeminus, abducens, facial, vestibular, and cochlear nerves, supply their fibres and the adjacent parts, and they end in the grey nuclei with which the nerve-fibres are connected. The inter- mediate arteries enter the surfaces of the pons irregularly and break up into capillaries in its substance. The veins form a plexus on the surface. The dorsal and lateral part of this plexu- is drained into the basilar vein on each side, and the inferior part is connected by efferent channels with the inferior petrosal sinus and the cerebellar veins. The blood-vessels of the medulla oblongata. — The arteries of the medulla are derived directly from the vertebral arteries, from their anterior and posterior spinal and posterior inferior cerebellar branches, and from the basilar artery. The branches of these vessels form a plexus in the pia mater from which, and from the arteries themselves, three main groups of vessels pass into the medulla — the chorioidal, the central, and the peripheral. The chorioidal arteries are derived chiefly from the posterior inferior cerebellar arteries. They supply the chorioid plexus of the fourth ventricle. The anterior central arteries rise from the anterior spinal artery, from the basilar artery, and from the peripheral plexus; they pass caudalward along the raphe, supplying the adjacent parts of the ventral funicuh and the olivary bodies, and they break up into fine terminals in the grey substance of the floor of the fourth ventricle around the nuclei of the cranial nerves. The posterior central arteries spring from the posterior spinal arteries; they pass down the median septum of the inferior part of the medulla and supply the adjacent nervous substance. The peripheral arteries, like those of the spinal cord, are separable into radicular and intermediate groups. The radicular arteries pass from the anterior and posterior spinal branches and from the trunks of the vertebral arteries and accompany the fibres of the last six cranial nerves into the substance of the medulla. They supply the nerve-roots and adjacent white substance and they terminate in capillaries in the grey substance of the lateral part of the floor of the ventricle. The intermediate peripheral arteries spring from the arteries previously named and from the peripheral plexus, and they pass directly into the funiculi of the meduUa, where they terminate in a capillary plexus which supplies the white substance and the grey nuclei; some of these arteries, more especially those derived from the posterior inferior cerebellar and the posterior spinal arteries, extend inward to the lateral part of the floor of the fourth ventricle. The veins which issue from the medulla form a peripheral plexus in the pia mater in which there are two main longitudinal channels, an anterior median and a posterior median vein. The former communicates posteriorly with the anterior median vein of the cord, and anteriorly with the veins of the pons and with the veins which accompany the hypoglossal nerves. The latter veins empty into the internal jugular veins. The posterior median vein is continuous caudally with the corresponding vein of the cord, and anteriorly, in the region of the calamus scriptorius, it divides into branches which join the radicular veins. The blood is carried away from the peripheral plexus mainly by the radicular veins, which pass along the roots of the last six cranial nerves. Those which accompany the hypoglossal nerves have already been referred to. The others end in the terminal parts of the transverse sinuses, the inferior petrosal sinuses, or the inferior part of the occipital sinuses. The nerve supply of the blood-vessels of the brain consists of a perivascular plexus of sympa- thetic nerve-fibres upon the walls of the vessels and meduUated fibres which accompany the vessels and apparently terminate, for the most part, in the connective tissue about them. The former are thought to be vaso-motor in function; the latter probably sensory fibres of the cranio-spinal type. Nerves have been described only for the larger vessels. IV. THE MENINGES Three membranes, collectively called the meninges, envelope the entire cen- tral nervous system, separate it from the walls of the bony cavities in which it lies, and aid in its protection and support. They consist of feltworks in which white fibrous connective tissue predominates, and through them pass the blood-vessels which supply the central nerve-axis and the nerves by which the axis is connected with the periphery. Though there are definite spaces or cavities between them, the membranes are not wholly separated from each other, and they are both continuous with and contribute to the walls of the blood-vessels and the sheaths (epineurium) of the nerves passing through them. Beginning with the outermost, they are — (1) the dura mater, the thickest, most dense and resistant of the mem- THE DURA MATER 909 Fia. 715. — Showing the Spinal Dura Mater Exposed in situ. (Dorsal aspect.) (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Foramen magnum Vertebral artery , Transverse process of atlas" ■ Cervical nerve I Spinal dura mater^^ Epidural cavity,^ f-j ^^?]^ii-) Thoracic nerve I ^Spinal ganglion ^Anterior ramus ^Posterior ramus Posterior costotransverse ligament**' Costal process of lumbar vertebrae*. . Lumbar nerve I Sacrum (dorsal surface) Anterior sacral foramina^: - Sacral nerve I Posterior ramus of sacral nerve I Filum of dura mater (coccygeal ligament) Sacral canal- , Continuation of spinal dura mater upon the roots of the sacral nerves. ' Coccygeal nerve 910 THE NERVOUS SYSTEM branes; (2) the arachnoid, the much less dense, web-hke middle membrane; and (3) the pia mater, a thin, compact membrane, closely adapted to the sm-face of the central system, into which it sends numerous connective-tissue processes. It is highly vascular in that it contains the rich superficial plexuses of blood- vessels from which the intrinsic blood supply of the central system is derived. The space between the dura mater and the arachnoid is known as the sub-dural Fig. 716. — Dorsal Aspect of the Medulla Oblongata and Spinal Cord with the Dura Mater Partially Removed. (Hirschfeld and Leveill6.) A B Superior peduncle of the cerebellum Median sulcus ot 4tli ventricle Glosso-pharyngeus Vagus Spinal accessory A ventral root A dorsal root lllfnrrfc^^-^-^^ Fiium terminale surround- ed by Cauda equina ni.— (.^1 IV.-.r^ 1 -Spinal ganglion cavity, and that between the arachnoid and the pia mater is the sub-arachnoid cavity. The Duea Mater In the fresh condition the dura mater appears as a bluish-white, exceedingly resistant membrane, forming the outermost envelope of the entire central nervous system. Its external surface or that next to the bony wall is rough, while its internal surface appears smooth, due to the fact that the subdural cavity partakes of the nature and has the hning of a lymph-space. The cranial dura mater consists of two distinct, closely associated layers, the outermost of which serves as the internal periosteum of the cranial bones. The spinal dura mater is described as consisting of but one layer. The internal periosteum of the spinal SPINAL DURA MATER 911 canal, though continuous at the foramen magnum with the outer layer of the cranial dura mater, is not considered a part of the spinal dura mater, from the fact that it is so widely separated from the layer actually investing the spinal cord. Thus, since the cranial and spinal portions of the dura mater differ, they are described separately. The spinal dura mater is a fibrous tube with funnel-shaped caudal end which encloses and forms the outermost support of the spinal cord. It consists of but one layer and this corresponds to the inner layer of the cranial dura mater. It begins at the foramen magnum and terminates in the spinal canal at about the level of the second piece of the os sacrum. It is firmly attached to the periosteum of the surrounding bones only in certain localities: — (1) The upper end of the tube blends intimately with the periosteum of the margin of the foramen magnum, and thus in this locality it becomes continuous with the outer layer of the cranial dura mater. Also in this locahty it is attached firmly, though less intimately, to the periosteum of the posterior surfaces of the second and third cervical vertebrae. This locahty may be considered the upper fixation-point of the spinal dura mater. (2) It extends laterally and contributes to the connective tissue investments of each pair of spinal nerves, and as such it passes into the intervertebral foramina and becomes continuous with the periosteum lining each. (3) Along its ventral aspect the spinal dura mater is attached by numerous proc- FiG. 717. — View of Membranes op Spinal Cord from Ventral Aspect. (EUis.) Spinal dura mater' Spinal arachnoid Dorsal root Ventral root Ligamentum denticulatum esses to the posterior longitudinal ligament of the vertebral canal. These attachments are more or less delicate, loose, and irregular, and are easily torn or cut in removing the speci- men. They are stronger and more numerous in the cervical and lumbar regions than in the thoracic. (4) In the space between the dura and the walls of the vertebral canal (epidural cavity) lies the rich internal vertebral venous plexus, and along the lateral aspect the dura is occasionally connected with the periosteum through the tissue of the walls of the vessels of this plexus, especially in case of the vessels which penetrate the dura. Along its dorsal aspect the spinal dura mater is practically free from the wall of the vertebral canal. (5) At its lower and funnel-shaped extremity, opposite the second sacral vertebra, the tube suddenly contracts into a filament extending into the coccyx and breaking up into a number of processes which become continuous with the periosteum of the dorsal surface of the coccyx. This filament is the coccygeal ligament or filum of the dura mater, and its attachment may be considered the lower fixation-point of the spinal dura mater. (See figs. 613 and 715). The extent of the tube is maintained chiefly by means of the two fixation-points, for all the other_ attachments are sufficiently loose to permit of the movements of the vertebral column. The inner surface of the spinal dura mater appears smooth, but upon closer examination it is found to be connected with the arachnoid by a few delicate sub- dural trabeculse — occasional fine strands of connective tissue bridging the sub- dural space (fig. 725). Along its lateral aspects the inner sm-face is at intervals quite firmly attached to the pia mater by the dentations of the ligamenta dentic- ulata, which are prolonged through the arachnoid. 912 THE NERVOUS SYSTEM Further, it is continuous at intervals with both the pia mater and arachnoid by way of the connective-tissue sheaths of the nerve-roots which are prolonged from the pia and blend with the dura mater in the passage of the nerve-roots through it. The dura is also pierced by the spinal rami of the vertebral arteries, and the connective tissue of the outer walls of these vessels blends with aU three of the meninges. The filum terminate of the pia mater extends below the termination of the spinal cord into the point of the funnel-shaped end of the dura mater, and there blends with it in line with the coccygeal ligament of the outer surface. The tube of the spinal dura mater varies in calibre with the variations in the diameter of the spinal cord. However, the termination of its cavity occurs about seven segments below the termination of the spinal cord. This extension con- tains the long intra-dural nerve-roots forming the cauda equina, and the calibre of this part, before its sudden contraction, is about as great as that found in any Fig. 718. — The Dura Mater Encephali of the Base op the CRANitrM. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Position of crista galli Process of dura in foramen csecum Circular sinus Circular sinus \ Olfactory bulb Eyeball Ophthalmic vein Cavernous sinus Connection with the rete f oraminis ovalis Internal carotid artery Bulb of the internal jugular vein Transverse sinuS' Vertebral artery "" Fold of dura mater^ Vrt«^ Maxillary nerve \ i « Mandibular i Jl-»" nerve Abducens nerve Acoustic nerve jlossophar; nerve Vagus nerve Accessory nerve Hypoglossal nerve First spinal nerve / Dura mater other region. As each pair of nerve-roots of the cauda equina passes outward, they lie free for a variable distance in a tubular extension of the dura before the latter blends with and contributes to the thickness of their sheath. The subdural cavity, the space between the dura mater and the arachnoid, is the thinnest of the meningeal spaces. Along the ventral aspect especially, the spinal arachnoid is quite closely applied to the inner surface of the dura mater. It contains a small amount of cerebro-spinal fluid (lymph) which prevents friction between the opposing surfaces, and is continuous with the fluid in the like space of the cranial meninges. The space communicates with the venous sinuses of the cranium in the region of the Pacchionian bodies, and its fluid is likewise in contact with the blood-vessels passing through it. It is probably continuous with the lymph-spaces of the nerve-roots passing through it, for colored fluids injected into it pass into the nerve-roots. The arachnoid is so thin and gauze- Uke that a ready interchange of fiuids between this space and the subarachnoid space is possible by simple filtration. CRANIAL DURA MATER 913 The cranial dura mater [dura mater encephali]. — The dura mater investing the brain performs a double function — it serves as an internal periosteum for the cranial bones and gives support and protection to the brain. In conformity with its double function it consists of two layers, easily separable in the child, but closely adhering to each other in the adult, except in occasional localities, where there exist small clefts lined with endothelium. The large blood sinuses and ven- ous lacunse, corresponding to the internal vertebral venous plexus of the vertebral canal, are placed between the two layers and the semilunar ganglia of the trigem- ini also lie between them. The cranial dura begins with the adhesion of the spinal dura mater to the periosteum at the foramen magnum, and it forms a sac- like envelope about the entire encephalon. Consisting of two layers, it is a much thicker membrane than that of the spinal cord. The outer surface of the cranial dura mater when torn away from the cranial bones appears very uneven, and when placed in water presents a flocculent appearance. G. 719. — CoBONAL Section of the Head, Passing through the Posterior Horns of THE Lateral VENTRicLEb From a mounted specimen m the Anatomical Department of Trinity College, Dublin. Inferior long itudinal fas ciculus Transverse sinus Dentate nucleus Tentorium cerebelli This is due to the many fine bundles of connective tissue and the blood-vessels which pass between the dura and the cranial bones and which are partially pulled out of their openings in the latter in the process of separation. The abundance of these connections, and, therefore, the degree of adhesion to the bones, varies in different localities. The separation is much less difficult from the inner table of the bones of the vault of the cranium than from the bones of the base of the cavity. The adhesions to the vault of the cranium are most firm along the lines of the sutures. This is due to the fact that during the period before the sutures are closed the outer layer of the dura mater is directly continuous with the external periosteum, and, in consequence of this condition during development, the connective-tissue connection is more abundant along these lines and some is even caught in the closure of the sutures. Along the vault there are occasionally noticed small lymph-spaces between the bone and the dura mater. The stronger adherence to the base of the cranial cavity is due to the numerous foramina in the floor, through which all the larger cranial blood-vessels and the cranial nerves pass, and the dura mater is continuous with the connective-tissue investments of these as well as with the periosteum lining the foramina. Also the floor of the cavitj' is more uneven than the vault, and the projections of the bones here tend to increase the firmness of attachment. The weight of the brain upon the floor probably contributes to the result. The inner surface of the inner layer of the cranial dura mater forms the outer boundary of the subdural cavity. Except for the occasional delicate subdural trabeculse and the passage of blood-vessels and nerve-roots, this surface appears 914 THE NERVOUS SYSTEM smooth and glistening, being lined by a layer of endothelium and containing a small amount of the cerebro-spinal lymph. The subdural cavity of the base of the brain is prolonged a short distance outward along the roots of the various cranial nerves before it is obUterated by the blending of the dura mater with the sheaths of the nerves. This outward extension of the space is most marked about tlie optic and auditory nerves. In the optic especially, the dura mater remains separate from the nerve throughout its length, only fusing with its sheath upon the posterior surface of the ocular bulb (fig. 718). One of the most striking differences between the cranial dura mater and that of the spinal cord is that the inner layer of the former undergoes striking septa-like duplications or folds, forming exceedingly strong partitions which project between the larger subdivisions of the encephalon. These are four in number, two large and two small — the falx cerebri and the tentorium cerebelli; the falx cerebelli and the diaphragma sellse. The larger enclose within their folds the great venous sinuses, into which most of the spent blood of the encephalon collects to pass out- ward by way of the internal jugular veins (figs. 720, 721). Fig. 720. — The Cranium with Encephalon Removed to show the Falx Cerebri, the Tentorium Cerebelli, and the Places where the Cranial Nerves pierce the Dura Mater. (Sappey.) Trochlear nerve Oculomotor nerve Falx cerebri Superior sagit- tal sinus Inferior sagit- tal sinus Vein of Galen artery Internal carotid artery Falx cerebelli Facial and auditory nerves Glassopharyngeal, vag:us and accessory nerves Hypoglossal nerve Second cervical nerve First Inferior Abducens Trigeminus cervical petrosal nerve nerve Ligamentum denticulatum nerve sinus The falx cerebri is the most striking of these partitions. It is a sickle-shaped fold which projects vertically from the vault into the longitudinal fissure between the cerebral hemispheres. It begins attached to the crista galli in front, and arches to terminate by blending with the superior surface of the hirozontally placed tentorium cerebelli. Its convex, superior border joins the outer layer of the dura along the medial plane of the vault, and encloses the superior sagittal sinus. Its concave border is free and contains in its posterior two-thirds the smaller inferior sagittal sinus. The anterior and narrower end is often perforated and occasionally so much so as to appear as a coarse, fibrous reticulum. The pos- terior part of the concave border touches the upper surface of the corpus callosum, but the anterior part, which does not descend so low, is separated from the corpus callosum by a part of the subarachnoid space. The base of the fold which slopes downward and blends with the upper surface of the tentorium cerebelli, contains the straight sinus running along the line of junction. The tentorium cerebelli is a large transverse, semilunar fold, concave forward. It descends from its central part which is elevated, and consequently it forms a i THE DURA MATER 915 tent-shaped covering. Its superior surface is in relation with the tentorial surfaces of the hemispheres, and its inferior surface conforms accurately to the superior surface of the cerebellum. The outer or convex border of the fold is attached on each side to the posterior clinoid process, the superior border of the petrous portion of the temporal bone, the mastoid portion of the temporal bone, the pos- terior inferior angle of the parietal bone, and the horizontal ridge of the occipital bone. The transverse sinus lies in this border. From the internal occipital pro- tuberance to the mastoid portion of the temporal bone and along the petrous part of the temporal bone it encloses the superior petrosal sinus. The greater part of the inner or anterior border of the tentorium is free, and it forms the superior and lateral boundaries of an arched cavity, the tentorial notch or foramen ovale of Pacchioni, which encloses the mesencephalon, and through which ascend the cerebral peduncles and the posterior cerebral arteries. The anterior extremities of the inner border cross the outer border, and they are attached to the anterior clinoid processes. A depressed angle is formed between Fig. 721.— Showing the Upper Surface op the Tentorium Cbrebelli and the Tentorial Notch through which the Mid-bkain and Posterior Cerebral Arteries enter the Middle Fossa of the Cranium. Infundibulum _ Crista galli Optic nerve Middle cerebral artery Arterior cerebral artery Posterior commu- nicating artery Cavernous sinus Superior cerebel- lar artery Posterior cerebral artery Superior petrosal sinus Free border of tentorium bound- ing tentorial notcb Optic tract Oculomotor nerve Cerebral peduncle Aqueduct of cerebrum Mesencepbalon Falx cerebri Transverse sinus Superior sagittal sinus the inner and outer borders of the tentorium in the middle fossa of the skull at the lateral portion of the posterior clinoid process, and in this angle the root of the oculo-motor nerve pierces the inner layer of the dura mater. The falx cerebelli is a small, sickle-shaped, triangular fold which projects forward into the small groove {-posterior cerebellar notch), between the hemispheres of the cerebellum. Its base is attached to the tentorium; its postero-inferior border, along which runs the occipital sinus, is attached to the internal occipital crest. Its anterior border is free, and its apex, which lies immediately above the foramen magnum, usually bifurcates as it disappears anteriorly, grasping the foramen magnum from behind. Bifurcation is always the case when the internal occipital crest splits below to enclose a vermiform fossa. The diaphragma sellae is a small circular fold, deficient in the centre, which projects horizontally from the margins of the hypophyseal fossa or sella turcica. Its lateral border is attached to the clinoid processes and the limbus of the sphe- 916 THE NERVOUS SYSTEM noid, and its medial border forms the boundary of the foramen of the diaphragma sellce and surrounds the infundibulum. Its superior surface is in relation with the base of the brain, and its inferior surface is in relation with the hypophysis, which it binds down in the hypophyseal fossa. The spaces which lie between the layers of the cranial dura mater are Meckel's caves, the spaces which lodge the endolymphatic sacs, and the blood sinuses and lacunae. Meckel's caves are two cleft-like spaces or niches which lie, one on each side, in the trigeminal impression on the apex of the petrous portion of the temporal bone. Each space lodges the semilunar (Gasserian) ganglion and the trigeminus and masticator nerves of the corresponding side, and it communicates with the subdm-al space in the posterior fossa of the cranium by an oval opening, which lies above the superior border of the petrous portion of the temporal bone and inferior to the superior petrosal sinus. Fig. 722. — Showing Blood-vessels of Cranial Dura Mater and Cranial Nerves in the Base op the Skull. (On the left side the dura mater has been removed from the middle fossa.) Meningeal branch of an- terior etlunoidal artery Meningeal branch of pos terior ethmoidal artery Middle meningeal artery Ophthalmic division of trigeminus Oculomotor nerve Cavernous sinus. Trochlear nerve Auditory and facial nerves Superior petrosal sinus Inferior petrosal sinus Petro-squamous sinus Spinal accessory nerve Sigmoid sinus Posterior meningeal branch of vertebral artery Left marginal sinus Left transverse sinus Superior sagittal sinus Circular sinus Carotid artery Abducens ^....ilar artery Basilar plexus of veins -^ —j- Auditory artery —L Vertebral artery — j-Glosso -pharyngeal , and vagus nerves ^Anterior spinal py artery ' ^Hypoglossal nerve Spinal accessory Right marginal sinus Right transverse sinus The space which contains the endolymphatic sac on each side hes behind the petrous portion of the temporal bone and communicates with the aquseductus vestibuli. The venous sinuses and lacunae. — The cranial blood sinuses have already been fully described in the account of the vascular system, and it is sufficient to note here that they are continuous, on the one hand, with the meningeal veins, and, on'the other, with the veins outside the cranial waDs. The vessels which establish communication between the blood sinuses and the extracranial veins are referred to collectively as emissary veins. They possibly help to maintain the regularity of the cranial circulation, and they have therefore a certain amount of practical importance. The sinuses which are connected with the extracranial^veins by emissary veins are the superior sagittal, the transverse (lateral), and the cavernous. Three or four emissary veins pass from the superior sagittal sinus; — one passes through the foramen caecum and communicates with the veins of the roof of the nose, or, through the nasal bones, with the angular veins. Two pass through the parietal foramina and establish communications with the occipital veins, and a fourth, which is very inconstant, pierces the occipital protuberance and joins the tributaries of the occipital veins. Connecting each lateral sinus with the extracranial veins THE ARACHNOID 917 there are, as a rule, two emissary veins: — one, the mastoid emissary vein, which passes through the mastoid foramen to the occipital or posterior auricular vein; and the other, the post-condy- loid vein, which traverses the condyloid (posterior condyloid) foramen and joins the suboccipital plexus. The cavernous sinus is in communication anteriorly with the superior ophthalmic vein, and through the latter with the angular vein; it is connected with the pterygoid plexus by emissary veins which pass either through the foramen ovale or the foramen Vesalii, and with the pharyngeal plexus by small venous channels which accompany the internal carotid artery through the carotid canal. The venous lacunae or spaces are small clefts lined by endotheUum which communicate with the meningeal veins and with the blood sinuses. They also have communications with the emissary veins and the diploic veins. They lie between the outer and inner layers of the dura mater, the majority of them at the sides of the superior sagittal sinus, but others are found in the tentorium associated with the transverse sinuses and the straight sinus. Blood-vessels. — The blood supply of the cranial dura mater is derived from the meningeal arteries, which ramify in its outer layer. The more important of these arteries have already been described in the account of the vascular system, and it is only necessary here to recall the fact that the greater part of the dura mater above the tentorium cerebelli is supplied by branches of the middle meningeal arteries. These are reinforced — (1) at the vertex by branches of the occipital arteries which enter through the parietal foramina; (2) in the middle fossa by the small meningeal arteries' and by meningeal branches of the internal carotid, lacrimal, and ascending pharyngeal arteries; and (3) in the anterior fossa by meningeal branches of the anterior and posterior ethmoidal arteries. The dura mater in the posterior fossa of the skull, below the tentorium cerebelU, also re- ceives branches from the middle meningeal arteries, but its blood supply is derived mainly — (1) from the meningeal branches of the vertebral arteries which enter- the fossa through the foramen magnum, (2) from meningeal branches of the occipital arteries which enter through the mastoid and hypoglossal foramina, and (3) from meningeal branches of the occipital and ascending pharyngeal arteries which enter through the jugular and hypoglossal (anterior condyloid) foramina. The meningeal veins accompany the arteries as vena comitantes, usually one vein with each artery. The middle meningeal artery usually has two venae comitantes. The meningeal veins communicate with the venous sinuses and with the diploic veins, and, unlike ordinary veins, they do not increase much in calibre as they approach their terminations. The nerves of the dura mater are partly derived from the sympathetic filaments which accompany the arteries and partly from the cranial nerves. The nerves, other than sympathetic filaments, which supply the cranial dura mater are sensory fibres derived from the trigeminus and vagus nerves, and possibly from the first cervical nerves. The branches from the trigeminus are derived from the three divisions of that nerve on each side, and it has been stated that branches are given from the nasal branch of the ophthalmic division to the dura mater in the anterior fossa. The meningeal branch of the ophthalmic division of the trigeminus supplies the tentorium ; that from the maxillary division accompanies the branches of the middle meningeal artery. The meningeal branch of the mandibular division (nervus spinosus) passes into the skull through the foramen spinosum and is distributed to the dura mater over the great wing of the sphenoid and to the mastoid ceOs. The "recurrent branch of the hypoglossal nerve" passes to the dura mater of the posterior fossa of the cranium. This recurrent or meningeal branch of the hypo- glossal nerve really consists of fibres derived from the superior cervical ganglion of the sympa- thetic, and contains sensorj' fibres from the first and second cervical nerves. The meningeal branch of the vagus springs from the ganglion of the root of that nerve, and is distributed in the posterior cranial fossa. The sympathetic filaments are distributed to the smooth muscle of the walls of the blood-vessels. The cranial subdiiral cavity is not of uniform thickness throughout, being thinner along the basal aspect of the encephalon. The lymph contained in it is usually but little more than is sufficient to keep moist its bounding surfaces. It is continuous with the lymph capillaries of the nerves and those of all the tissues it bathes, and it is continuous with the similar cavity of the spinal canal. Its lymph is in free contact with the blood-vessels passing through it and with those in the tissues it bathes, and it is replenished by filtration through their walls. Though extensive, the subdural space is thin at best, for the dura mater is quite closely applied to the second of the three meninges. The Arachnoid The arachnoid or ' serous ' membrane is the middle of the three meninges of the central nervous system. As in the case of the other two, an attempt is made to give this membrane a name descriptive of its texture. It is a gauzy reticulum of almost web-like delicacy, which in reality pervades the space it occupies. Its outer surface, or that closely related to the dura mater and bounding the subdural cavity alone shows a sufficiently organized structure to merit the name of membrane. This surface is covered by a layer of endothehum which is identical with that lining the inner surface of the dura mater and is continuous with it by way of the endothehal cells covering the blood-vessels, 918 THE NERVOUS SYSTEM the nerve-roots, the ligamenta dentioulata of the spinal cord, and the occasional delicate tra- beculae passing between the dura mater and the arachnoid. Immediately under the endothehum, the connective-tissue fibres of the arachnoid are woven into a very thin, more or less compact web. This, however, quickly grades into a loose, spongy reticulum which pervades the thick subarachnoid cavity throughout, and the strands of which are directly continuous into the more compact tissue of the pia mater. Thus an inner surface can hardly be claimed. This loose, sponge-like arachnoid tissue holds the cerebro-spinal fluid of the subarachnoid cavity, the meshes of the sponge constituting a reticular web of intercommunicating spaces hned by endothehoidal cells covering the strands of the web. The cranial subarachnoid cavity is larger, and the strands of the web are relatively more abundant than in that of the spinal canal. In addition, the cavity is traversed by the spinal and cranial nerves, by the blood-vessels passing to] and from the pia, and, in the spinal canal distinctively, it is traversed by the ligamenta denticulata and the filum terminale. Through these the arachnoid is further continuous with the pia mater. The cranial arachnoid is directly continuous into that of the spinal cord, and in the two localities does not differ as much as does the dura mater. Within the cranium, the arachnoid does not closely follow the surface of the encephalon. It is folded in between the cerebellum and cerebral hemispheres, following the con- tour of the tentorium cerebelli, but it does not dip into the fissures and sulci except the anterior part of the longitudinal fissure and slightly into the lateral (Sylvian) fissure. Otherwise it fills in the inequalities of surface of the encephalon, its outer surface forming a sheet enveloping the whole and bridging over the sulci and the deeper grooves between the gross divisions. Upon the summits of the gyri it is more closely applied to the pia mater, and there its reticulum becomes so dense Fig. 723. — Diagram showing the Relations op the Pia Mater, the Arachnoid, and the Stibarachnoid Cavity to the Brain. Pia mater Subarachnoid cavity Third ventricle Infundibulum Clsterna basalis Cisterna pontis Fourth ventricle Cisterna cerebello- medullaris Foramen of Magendie that the two membranes almost appear as one. The sulci, occupied by looser reticulum, form a continuous system of channels filled more abundantly by the cerebro-spinal fluid. The arachnoid folds in between the cerebellum and medulla oblongata, and at the base of the brain it ensheathes the olfactory bulbs and tracts, and its outer surface forms a continuous sheet stretching from one temporal lobe to the other and bridging over the interpeduncular fossa and the inequahties of surface in the region of the optic chiasma and the stems of the lateral fissures. Obviously, therefore, the subarachnoid cavity between its outer surface and the pia mater is of considerable depth in certain localities. These localities comprise the subarach- noid cisternoe. These occur where the cavity at the base of the brain is especially large, and make possible a 'water-bed' which serves to protect the brain from injurious contact with the bones. The foUowing cisternae are distinguished (fig. 723) : — (1) The cisterna basalis lies at the base of the cerebrum and is divided by the optic chiasma into two parts — (a) the cisterna chiasmatis and (b) the cisterna interpeduncularis. (2) The cisterna pontis is situated about the pons, especially in its basilar sulcus and the THE SPINAL ARACHNOID 919 transverse fissures of either border, and is continuous anteriorly with the cisterna basalis and posteriorly with the subarachnoid cavity about the medulla. (3) The cisterna superior Ues in the angle between the splenium of the corpus callosum and the superior surfaces of the cerebellum and the mesencephalon, and is connected ventrally, around the cerebral peduncles, with the cisterna basalis. (4) The cisterna cerebello-medullaris (cisterna magna) is the cavity between the inferior surface of the cerebellum and the dorsal surface of the medulla oblongata. It is continuous below into the spinal subarachnoid space. The fluid in this cavity is directly continuous with that in the fourth ventricle by way of the foramen of Magendie (median aperture of the fourth ventricle). Pacchionian bodies [granulationes arachnoideales] (fig. 724.) — In certain situ- ations, more particularly along the margins of the longitudinal fissure, particu- larly in the frontal region, and to a much less extent upon the superior surface of the vermis of the cerebellum, the subarachnoid tissue elaborates numerous small, ovoid or spherical nodules, the Pacchionian bodies. Each body or arachnoid villus consists of a retiform network of subarachnoid substance and its meshes are filled with cerebro-spinal fluid. The Pacchionian bodies on the vertex of the brain project through the inner layer of the dura mater, both into the superior sagittal sinus and into the venous spaces or parasinoidal sinuses which lie at the sides of that sinus, and, as they become larger, they press against the outer layer of the dura mater and produce ovoid depressions in the inner plate of the cranium. Fig. 724. — Coronal Section transverse to the Great Longitudinal Fissure, Showing THE Meninges. (Key and Retzius.) Subarachnoid space Superior sagittal sinus Pacchionian body -Corpus callosum They probably facihtate the passage of lymph from the subarachnoid cavity into the blood sinuses, and thus may aid in relieving pressure within. On the other hand, through them the cerebro-spinal fluid is replenished at need from the blood plasma. They are not present at birth, but they appear at the tenth year and increase in number and size with advancing age. They are less marked in the female than in the male. The spinal arachnoid (figs. 725, 726) is a loose, reticular sac which is most capacious about the lumbar enlargement of the spinal cord and about the Cauda equina. Like that of the encephalon, the portion next to the dura mater alone resembles a membrane, being a loosely organized feltwork, covered on the side of the subdural cavity by a layer of endothelium common to that cavity. Through- out its length the spinal subarachnoid cavity is relatively wide, and, as in the cranium, contains a fine, spongy, web-like reticulum, numerous threads of which are continuous with the pia mater. This spongy tissue is the inner modification of the arachnoid, and its meshes are occupied by the cerebro-spinal fluid. It is not so abundant as in the cranial subarachnoid cavity. In addition to the delicate threads, the arachnoid is more firmly attached to the pia mater by three incomplete partitions. The most continuous of these is arranged along the dorsal mid-line and is known as the septum posticum of Schwalbe (subarachnoid septum). This may be described as a linear accumulation of the spongy tissue which pervades the subarachnoid space. It is most incomplete in the upper cervical region, where it becomes merely a line of threads connecting with the pia. It is most complete as a septum in the lower cervical and in the thoracic region, but at best it maintains a spongy character. The other two partitions are 920 THE NERVOUS SYSTEM formed by the denticulate ligaments, which extend laterally from either side of the spinal cord, connecting the pia and dura mater and involving the arachnoid in passing through it. Within the subarachnoid cavity these form more or less complete septa, though outside the arachnoid they are attached to the dura only at the intervals of their pointed dentations. They belong to the pia mater and will be described with it. The arachnoid is further continuous with the pia by way of the connective-tissue sheaths of the roots of the spinal nerves and the blood- vessels passing through the subarachnoid cavity. Vessels and nerves. — The arachnoid has no special blood supply and probably no special nerves other than those supplying the walls of the blood-vessels passing through it. The cerebro-spinal fluid. — The subarachnoid cavity is the great lymph-space of the central nervous system. That of the spinal region is directly continuous into that of the cranium, and the fluid contained communicates freely with that in the ventricles of the brain and the central canal of the meduUa and spinal cord by way of the foramen of Magendie or medial aperture into the fourth ventricle. In addition, there are the lateral apertures into the fourth ventricle and there is possible an interchange of fluid between the lateral ventricle and the subarachnoid cavity of the base of the brain by diffusion through the thin floor of the chorioid fissure. The arachnoid throughout is not a membrane sufficiently compact to seriously oppose diffusion between the fluid contained in its cavity and that contained in the subdural cavity, and the endotheUum covering it probably even facilitates such activities. The cerebro-spinal fluid occupying the cavities is a transparent fluid of a slight yellow tinge, characteristic of the Fig. 725. — Diagram op Transverse Section op Upper Thoracic Region of the Spinal Cord showing the Relations op the Spinal Meninges and their Cavities. Dura mater Arachnoidea ( Pia mater Septum posticum Subdural trabeculee Subdural space Fila of dorsal root ^^Subarachnoid cavity Denticulate ligament §*1 =* Fila of ventral root ^ * ^ * Linea splendens with anterior ^ "- ^ \ spinal artery Epidural trabecule to periosteum lymph in other lymph-spaces of the body. It is not very great in amount, probably never exceeding 200 c.c. in normal conditions. It is greatest in amount in old age, when the cavities are larger, due to atrophy and shrinkage of the nervous tissues. It collects from the lymph spaces in the meninges, and from exudation through the walls of the vascular chorioid plexuses and sinuses of the system it bathes. Its amount may be temporarily increased by a period of increased blood-pressure in the cranial vessels. Pressure due to its abundance may be relieved by diffusion through the membranes containing it, and especially through the viUi of the Pacchionian bodies into the venous sinuses and lacunae and thence into the venous system through the internal jugular veins. The Pia Mater The pia mater, the third of the meninges, is a thin membrane which envelopes and closely adheres to the entire central nervous system and sends numerous proc- esses into its substance. It likewise contributes the most proximal and compact portion of the sheaths worn by the nerve-roots in their passage through the menin- geal spaces. It is very vascular in that the superficial plexuses of blood-vessels of THE PI A MATER 921 both the brain and spinal cord ramify in it as they give off the central branches into the nervous substance. The structure and arrangement of the membrane vary somewhat in the cranial and spinal regions. The spinal pia mater consists of two layers, an inner and an outer. It is thicker and more compact than that of the encephalon, due to the extra develop- ment of its outer layer, which is in the form of a strong, fibrous layer with the fibres arranged for the most part longitudinally. The spinal pia mater also appears less vascular than the cranial from the fact that the blood-vessels composing the plexus lying in it are obviously much smaller than those of the encephalon. Its inner layer is a thin feltworlt of fibres which is closely adherent to the surface of the spinal cord throughout, sending numerous connective-tissue processes into it which contributes to the support of the nervous tissues. The larger of these processes carry with them the numerous intrinsic blood-vessels from the superficial plexus. The two layers are closely connected with each other, and are distinguished by the difference in the arrangement of their fibres. The membrane dips into the anterior median fissure and bridges it over by forming an extra thickening along it. This thickening appears as a band along the mid-line of the ventral surface of the cord, the linea splendens (fig. 717). It carries, or ensheathes, the anterior spinal artery, the largest of the arterial trunks of the superficial ple.xus (fig. 725). Fig. 726. — Diagram showing Rel.ations op Meninges to Spinal Nekve-hoots. Denticulate ligament Body of vertebra Periosteum Bura mater Subdural cavity Arachnoid Subarachnoid cavity Pia mater Intervertebral foramen- The pia mater contributes the innermost and most compact portion of the epineurium of each of the nerve-roots, and thus, upon the roots, it is prolonged laterally into the intervertebral foramina, where the dura mater blends with it in producing the increased thickness of the epineurium. From each side of the cord the pia mater gives off a leaf-like fold, the den- ticulate ligament, which spreads laterally toward the dura mater midway between the lines of attachment of the dorsal and ventral nerve-roots. The outer border of this fold is dentate or scalloped into about twenty-one pointed processes, which extend through the arachnoid and are attached to the inner surface of the dura mater. The dentations are usually inserted between the levels of exit of the roots of the spinal nerves, the uppermost one a little cephalad to the first cervical nerve and the region where the vertebral artery perforates the dura mater; the most caudal one between the last thoracic and first lumbar nerves, or, between the last two thoracic nerves. The ligaments, aided slightly by the septum posticum, serve to hold the spinal cord more or less suspended in the subarachnoid cavity. Below, at the sudden, conical termination of the spinal cord in the lumbar portion of the spinal canal, the pia mater is spun out into a thin, tubular filament, the filum terminale, which continues caudalward into the sac formed by the dura mater about the cauda equina, and at the end fuses with the dura mater in line with the filum of the spinal dura mater (coccygeal ligament) of the outside (figs. 613, 715). 922 THE NERVOUS SYSTEM The cranial pia mater is closely applied to the external surface of the brain, dipping into all the fissures, furrows, and sulci. It is connected with the arach- noid by numerous filaments of the spongy subarachnoid tissue and by the blood- vessels traversing the subarachnoid cavity. It is also pierced by the cranial nerves, and furnishes them their sheaths, which become continuous with the arachnoid and dura mater. Its outer surface bounds the subarachnoid cavity. It is with difficulty separable into two layers of mixed white fibrous and elastic connective tissue, with slightly pigmented con- nective-tissue cells enmeshed between them. Its inner surface sends a large number of fibrous processes into the nervous substance, which blend with the neuroglia and aid in the support of the nervous elements. The larger of these processes accompany the central arterial and venous branches of the rich superficial plexuses of blood-vessels contained in the pia on the surface of the brain. Pieces of the pia when pulled off and placed in water present a flocculent appearance as to their inner surfaces, due to these processes having been pulled out. The cranial pia mater sends strong, vascular duplications into two of the great fissures of the encephalon; viz., the transverse cerebellar fissure, between the cere- bellum and the medulla oblongata, and the transverse cerebral fissure, between the cerebellum, mesencephalon, and thalamencephalon, and the overhanging cerebral hemispheres. These duplications are spread over the cavities of the fourth and third ventricles, and are known as the chorioid telce of these ventricles respectively. Fig. 727. — Diagram showing Chorioid Tela of Fourth Ventricle after Removal of Cerebellum. (The trochlear nerve should be shown emerging from the frenulum veli.) Inferior quadrigeminate body Trochlear nerve Superior medullary velum Brachium conjunctivuMl Brachium of pons Restiform body Ligula (taenia) Chorioid tela of fourth ventricle Cuneate tubercle Clava Tubercle of Rolando Frenulum veil Lateral lemniscus Lingula of cerebellum Fourth ventricle VeBsels to chorioid plexus Inferior medullary velum Chorioid plexus The tela chorioidea of the fourth ventricle lies in the transverse cerebellar fissure, between the inferior surface of the cerebellum (vermis chiefly) and the dorsal surface of the medulla (fourth ventricle). The two layers of this fold of the pia remain separate and a portion of the cisterna posterior of the subarachnoid cavity lies between them. The inferior of the layers is the tela chorioidea (fig. 727.) It is triangular in shape, with its base cephalad at the nodule of the vermis and its apex below at the level of the tuber vermis. The superior layer of the fold is the pia mater of the vermis. The tela chorioidea is strengthened by the epithelial roof (ependyma) of the fourth ventricle and is continuous with the pia mater of the medulla oblongata and spinal cord. In roofing over the fourth ventricle the tela chorioidea of the fourth ventricle constitutes the ligula and the obex. A little above the calamus scriptorius it is pierced by the foramen of Magendie and the two lateral apertures into the fourth ventricle. In front of the foramen of Magendie the vessels of the chorioid tela, which are derived from the posterior inferior cerebellar arteries, form two longitudinal, lobulated strands which invaginate the epithelial roof of the ventricle, one on either side of the mid-hne, and project into its cavity. These form the chorioid THE CHORIOID TELA 923 plexus of the fourth ventricle. At the base of the tela the two chorioid plex- uses join each other and then turn transversely lateral ward into the lateral re- cesses of the ventricle, where they pass behind the restiform bodies and form the ' cornucopicB.' The chorioid tela of the third ventricle, or velum interpositum, is a triangular duplication of the pia mater which extends between the fornix above and the thai- ami and third ventricle below, and in front fuses with the brain substance at the interventricular foramina. In the transverse cerebral fissure the layers of pia forming this tela are separate, the upper being the pia of the under surface of the corpus caUosum and continuous with that of the ten- torial surfaces of the occipital lobes; the lower being continuous into the pia enfolding the epiphysis, and covering the mesencephalon, anterior medullary velum, and cerebellum. The Fig. 728. — Hokizontal Dissection op the Cerebrum showing the Tela Chorioidea of THE Third Ventricle. (From a mounted specimen in the Anatomical Department of Trinity College, DubUn.) The fornix has been removed to show the chorioid tela of the third ventricle. Corpus caUosum (dissected) Veins ofGalei Crura of fornix. Septum pellucidum Thalamus Chorioid tela (velum inter- positum) Chorioid plexus Fimbria Hippocampus major Collateral eminence layers forming the portion of the dupUcation which roofs over the third ventricle are loosely adherent to each other and form the tela chorioidea proper of that ventricle. The upper surface of this portion is in relation with the fornix and its lower surface, covered by the epithelial chorioid lamina, lies laterally over the superior surfaces of both thalami, and mesiaUy forms the roof of the third ventricle between them. The epitheUum or ependyma is continuous with that covering the thalami and lining the ventricles. Between the two layers of this portion, and embedded in a small amount of the spongy subarachnoid tissue retained between them, are the two veins of Galen, the internal cerebral veins. Posteriorly these veins unite in the region of the epiphysis to form the single great cerebral vein (vena cerebri magna) which empties into the straight sinus. Anteriorly the veins of Galen receive the veins of the septum pellucidum from each lamina of the septum pellucidum above, and also the terminal vein (vein of corpus striatum), lying in the stria terminahs of the thalamus, empties into them from each side. The chorioid tela of the third ventricle or velum interpositum extends laterally between the fornix and fimbria above and the stria terminalis of the thalamus be- 924 THE NERVOUS SYSTEM low into each lateral ventricle. The blood-vessels of the border proj ecting into the lateral ventricle are amplified into a plexus which appears as a strip of reddish, lobulated, villus-like processes known as the chorioid plexus of the lateral ven- tricle. The plexus, being in the border of the tela, begins at the interventricular foramen, extends through the body or central portion of the ventricle, and down- ward into its inferior cornu. It is most developed at the junction of the body with the inferior cornu, and is there known as the glomus chorioideum. From the under surface of the chorioid tela of the third ventricle, hanging down on either side of the mid-line into the cavity of the ventricle, are two other longitudinal, lobulated strands of blood-vessels which are the chorioid plexuses of the third ventricle. At the anterior end of the third ventricle these two plexuses join with each other and also with the plexus of the lateral ventricle of each side through the interventricular foramina. The chorioid plexuses of both the ventricles are covered by a layer of ependyma, epithelial chorioid lamina, which is but a reflexion of the ependyma lining the cavities throughout and represents the remains of the germinal layer of the embryonic brain vesicles. The blood-vessels Fig. 729. — Diagram op Coronal Section of Cerebrum through Middle of Thalamen- CEPHALON SHOWING RELATIONS OF PlA MaTER EnCEPHALI AND ChORIOID PlEXUSES OP Third and Lateral Ventricles. Fifth ventricle Fornix of the chorioid plexus of the lateral ventricle receive blood by the chorioid artery (a direct branch of the internal carotid), which enters the plex-us through the chorioid fissure immediately mesial to the uncus, and also by the chorioidal branches of the posterior cerebral artery, which supply the plexus of the body of the ventricle. The chorioid plexuses of the third ventricle receive blood chiefly by branches from the superior cerebellar arteries. The greater part of the blood of both plexuses passes out by way of the tortuous chorioid veins, which, at the interventricular foramen, empty into the vense terminates (veins of the corpus striatum), which, in their turn, go to form the greater part of the veins of Galen. Thence the blood passes by way of the vena cerebri magna into the straight sinus. It is probable that a large part of the oerebro-spinal fluid of the third and lateral ventricles is derived by diffusion through the walls of the vessels of the chorioid plexuses. THE PERIPHERAL NERVOUS SYSTEM The intimate connection and consequent control exercised by the central nervous system over all the tissues and organs of the body is attained through the THE PERIPHERAL NERVOUS SYSTEM 925 Fig. 730. — Showing the Relation between the Central and the Peripheral Nervous Systems. (Combination drawing, spinal part after Allen Thompson, from Rauber.) -/" - I Cervical nerve Gangliated cord vi Coccygeal nerve Filum terminale 926 THE NERVOUS SYSTEM peripheral nervous system. This system, abundantly attached to the central system, consists of numerous bundles of nerve-fibres which divide and ramify throughout the body, anastomosing with each other and forming various plexuses, large and small. The terminal rami divide and subdivide until the divisions attain the individual nerve-fibres of which they are composed, and finally the nerve- fibres themselves divide and terminate in relations with their allotted peripheral elements. It is by means of this system that stimuli arising in the peripheral tissues are conveyed to the central system, and that impulses in response are borne from the central system to the peripheral organs. For pm-poses of description, as well as upon the basis of certain differences in structm-e, arrangement, and dis- tribution, the peripheral nervous system is separated into two main divisions: — (1) the cranio-spinal and (2) the sympathetic system. Both of these divisions include numerous ganglia or peripheral groups of nerve- cells from which arise a considerable proportion of the fibres forming their nerve- trunks, but neither of the divisions may be considered wholly apart from the central system nor are they independent or separate from each other. The sen- sory or afferent fibres of the cranio-spinal nerves pass by way of the afferent nerve- roots into the central system and contribute appreciably to its bulk, and the motor or efferent fibres of these nerves have their cells of origin (nuclei) situated within the confines of the central system. The sympathetic system is intimately asso- ciated with the cranio-spinal, and consequently with the central system — (1) by means of fibres which enter and terminate in the cranio-spinal gangha and transfer impulses which enter the central system; (2) by efferent fibres of central origin which com'se in the nerve-trunks and terminate in the ganglia of the sym- pathetic system; (3) also, the sympathetic trunks usually contain numerous afferent cranio-spinal fibres which thus course to their peripheral termination, usually in the so-called 'splanchnic area,' or domain of the sympathetic, in company with the sympathetic fibres. Likewise the peripheral branches of the cranio-spinal nerves often carry for varying distances numerous sympathetic fibres which are on their way to terminate either in other sympathetic ganglia or upon their allotted peripheral tissue-elements. The following differences between the cranio-spinal and sympathetic systems of nerves may be cited: — (1) The cranio-spinal nerves are anatomically continuous with the brain and spinal- cord; probably no fibres arising in the sympathetic gangha actually enter the central system other than for the innervation of its blood-vessels, (2) The gangha of the cranio-spinal nerves all lie quite near the central axis, in hne on either side of it, and at more or less regular intervals; the sympathetic gangha are scattered throughout the body tissues, are far more numerous and more variable in size, and probably only the larger of them are symmetrical for the two sides of the body. (3) The cranio-spinal nerves are paired throughout, and the nerves of each pair are symmetrical as to their origin and also, with certain exceptions (notably the vagus), in their course and distribution; most of the larger and more proximal of the sym- pathetic nerve-trunks are symmetrical for the two sides of the body; many of them are not, and many of the smaller and most of the more peripheral nerves and gangha, large and srnall, are not paired at all. (4) Even in their finer twigs, the cranio-spinal nerves of the two sides probably do not anastomose with each other across the mid-hne of the body; the sympathetic nerves do so abundantly, especially within the body cavity. (5) The cranio-spinal nerve; are distributed to the ordinary sensory surfaces of the body and the organs of special sense and to the somatic, striated or 'voluntary' muscles of the body; the sympathetic fibres are devoted chiefly to the supply of the so-caUed involuntary muscles of the body, including the smooth muscle in the walls of the viscera and in the walls of the blood and lymph vascular-systems, while others serve as secretory fibres to the glands. (6) Cranio-spinal nerve-fibres are char- acterized in general by well-developed medullary sheaths, making the nerves appear as white strands; most of the sympathetic fibres are non-medullated, some are completely and some partially medullated, but none possess as thick medullary sheaths as those of the cranio-spinal nerves. Thus sympathetic nerves appear as grey strands. The cranio-spinal nerves.^ — There are forty-six pairs of cranio-spinal nerves, of which thirty-one pairs are attached to the spinal cord (spinal nerves) and fifteen pairs to the encephalon (cranial nerves) . The spinal nerves are the more primi- tive and retain the typical character, i. e., each is attached to the spinal cord by two roots, a dorsal or sensory ganglionated root, and a ventral, which is motor, and thus not ganglionated. Most of the cranial nerves have only one root, which in come cases corresponds to a dorsal root and therefore has a ganglion, and in other cases corresponds, physiologically at least, to a ventral root of a spinal nerve. Among other differences, the fibres of the first cranial nerve, for example, do not collect to form a distinct nerve-trunk. THE CRANIAL NERVES 927 I. THE CRANIAL NERVES Customarily, the cranial nerves are described as comprising twelve pairs and each is referred to by number. However, present knowledge of their origin, central connections and peripheral distribution suggests that those enumerated as the fifth, seventh, and eighth pairs under the old nomenclature are better each separated into its two component nerves, each of which merits a separate descrip- tion and a separate name. None of the cranial nerves corresponds closely to a typical spinal nerve with its motor and sensory root. The so-called motor por- tion of the fifth is no more its motor root than is the seventh nerve. The sensory portion of the seventh is not wholly sensory and rather resembles the ninth pair in distribution, and it has long been commonly referred to as a separate nerve. The two parts of the eighth nerve, both sensory, are known to be wholly different in functional character and are so named. Further, the names of the nerves, descrip- tive of their function, are pedagogically much more eflacient than the use of num- bers in referring to them. Separating the three pairs mentioned, each into its two nerves, gives fifteen pairs instead of twelve. Their names and functional nature are given in the fol- lowing table. The Roman numerals given in parentheses correspond to the serial numbers given when twelve pairs only are considered. It is also customary to enumerate the cranial nerves from in front backward and caudalward, and this custom is followed here, but again it would be pedagogically better to take them in the reverse order. Then each in its turn could be directly considered as in continuous series with the spinal nerves below and the similarities to and progres- sive modifications from the spinal type could be better realized. It will be remem- bered that somatic motor or efferent fibres are those which terminate directly upon the fibres of skeletal muscle while visceral motor fibres transfer their impulses to sympathetic neurones, and the axones of the latter terminate upon gland cells and upon the fibres of cardiac and smooth muscle. Name Nature General Distribution Olfactory (I) Sensory Olfactory region, nasal epithelium. Optic (II) Sensory Retina. Oculomotor (III) Motor { |-^- ; ; ■ ; ; ; ; if.tr/bt/y.Tif "' Trochlear (IV) Motor-somatic Eye-moving muscles. Abducens (VI) Motor-somatic Eye-moving muscles. Trigeminus (V) Sensory Face, mouth, and scalp. Masticator (minor part or Motor-somatic Muscles of mastication. motor root of trigeminus). T?„„;„i /^7TT^ A/r„i„> / Somatic Facial muscles. Facial (VII) Motor '^ visceral (?) Sahvary glands, vessels(?). Glossopalatine. (Intermedi- ( Sensory Tongue, palate. ate pari of facial). \ Motor- visceral Sahvary glands. Cochlear (auditory) (VIII).. Sensory Internal ear. Vestibular (equilibrator) Sensory Semicircular canals, utriculus, sac- (VIII). cuius. i Sensory Tongue, palate, pharynx. ,;,„.„,/ Somatic Pharynx. Motor| yjgj.gj.^j Glands and vessels. Sensory Alimentary canal, lung, heart. Motor I Somatic Larynx, pharynx. \ Visceral Alimentary canal, heart, larjmx, tra- chea, lung. Hypoglossal (XII) Motor-somatic Tongue-moving muscles. Q„;„„i „„„„„ cvTN A/i«t„. /Somatic Neck and shoulder muscles. Spmal acessory (XI) Motor | visceral Pharynx, larynx, heart. The cranial nerves, like the spinal nerves, are developed from cells of the primi- tive neural tube and, beginning with the fifth pair downward, all the sensory nerves are developed from the cells corresponding to those of the ganglion crest which give origin to the spinal ganglia with the sensory components or dorsal roots of the spinal nerves. Otherwise between the cranial nerves and the spinal nerves there are many important differences. Each spinal nerve has a dorsal or sensory root, which springs from the cells of a spinal ganglion; a ventral or motor root, whose fibres are processes of the nerve-cells which are situated in the walls of the central system, and at their attachment to the surface of the cord the two roots are some distance apart. Only one of the (usually considered) twelve pairs of cranial 928 THE NERVOUS SYSTEM nerves corresponds at all closely with typical spinal nerves. This one is the trigeminus which possesses a sensory ganglionated root and near its attachment is accompanied by a small motor nerve, the masticator, which serves in very small part as a corresponding motor root of the trigeminus. But even in this case where the similarity between the cranial and spinal nerves is greatest, there are still points of anatomical difference, which if not essential are very obvious, for the so-called motor root joins not the whole but only with one branch of the sen- sory portion. The two are only slightly separated from each other at their attach- ment to the surface of the brain. All the other cranial nerves differ in a still more marked manner from typical spinal nerves. The first nerve is an afferent nerve whose cells of origin (olfactory ganglion) are scattered in the mucous membrane Fig. 731. — -Subface Attachment op the Cranial Nerves. (After Allen Thomson, modified.) Insula / Olfactory tract Hypophysis Anterior perforated substance"^^^^J Corpora mammillai N. opticus (II) Optic tract Cerebral peduncl Oblique fasciculus — Tuber cinereum N. oculomotorius (m) -- N. trochlearis (IV) \ "N. masticatorius "^ N. trigeminus (V) ,___.. N abducens (VI) ,' Brachium pontis N. facialis (VH) N. glossopalatinus ^ N. cochlearis and N, vestibularis (VM) N- glosso-pbaryngeus (IX) N. vagus (X) N. accesfeorius (XI) (spinal accessory) N. Hypoglossus (XU) Pyramid Decussation of pyramids' _ Cervical II of the nose, an organ of special sense, and its fibres are not collected together into a nerve-trunk, but pass, as a number of small bundles, through the lamina cribrosa of the ethmoid bone directly into the olfactory bulb. The optic nerve is also a nerve of special sense. Its fibres form a very distinct bundle, similar in appear- ance to an ordinary nerve, from which, however, it differs essentially, both with regard to structure and development; for, unlike an ordinary nerve, its connective tissue consists to a large extent of neurogha instead of ordinary connective tissue, and its component nerve-fibres are of much smaller calibre than those of an ordi- nary nerve. It represents the location of the original optic stalk, a diverticulum from the neural tube and it associates the retina (optic cup) , a bit of modified cor- THE TERMINAL NERVE 929 tex, with the encephalon. The optic nerve, therefore, corresponds more closely with an association tract of the central system than with an ordinary nerve. The oculomotor, trochlear, abducens and hypoglossal nerves are purely motor nerves, and thus correspond only with the ventral roots of spinal nerves. The spinal accessory is also purely motor. Its fibres arise from the cells of the anterior horn of the spinal cord and from a nucleus of the medulla which represents a dis- placed portion of that horn, but they do not leave the surface of the spinal cord and brain in the usual situation of ventral roots. On the contrary, they emerge in a series of rootlets from the lateral funiculus of the cord on the dorsal side of the ligamentum denticulatum, and from the upward prolongation of this funiculus. The cochlear and vestibular are nerves of special sense, and in some respects both correspond closely with the dorsal root of a typical spinal nerve, and the gan- glia of both represent spinal ganglia, but their distribution is limited to the mem- branous labyrinth. The vagus and glosso-pharyngeal nerves contain both motor and sensory fibres, but they differ from typical spinal nerves in that the motor fibres, in company with the sensory, issue from the postero-lateral sulcus of the medulla, and they are intimately intermingled, from their origin, with the sensory fibres, which latter arise from ganglia interposed in the trunks of the nerves and otherwise correspond with the fibres of the dorsal root of a typical spinal nerve. Superficial attachments and origins. — It is customary to speak of the area where the nerve-fibres leave or enter the brain substance as the superficial attachments of the cranial nerves, and the groups of cells from which the fibres spring, and about which they terminate, as their nuclei of origin or termination, respectively. THE OLFACTORY NERVES The olfactory nerve-fibres are the central processes of the bipolar olfactory nerve cell-bodies situated in the olfactory region of the nasal mucous membrane. In man, the olfactory region comprises the epithelium upon the superior third of the nasal septum and that upon practically the whole of the superior nasal concha. The area is relatively small as compared with that of other mammals and, as in other mammals, is characterized by an increased thickness of the epithelium and a yellowish brown colour in the fresh. The peripheral processes of the olfactory cell-bodies (the olfactory gangUon) are short and extend only to the surface of the olfactory epithehum. As the central processes pass upward from their cells of origin they form plexuses in the mucous membrane, and from the upper parts of these plexuses, immediately below the lamiiia cribrosa of the ethmoid, about twenty filaments issue on each side. These filaments comprise the olfactory nerve. They are non-medullated. They pass upward, through the foramina in the lamina cribrosa, into the anterior fossa of the cranium in two rows, and after piercing the dura mater, the arachnoid, and the pia mater, they enter the inferior surface of the olfactory bulb. They contribute to the superficial stratum of nerve- fibres on the inferior surface of the olfactory bulb and end in the glomeruli, which are formed by the terminal ramifications of the olfactory nerve-fibres intermingled with the similar ramifications of the main dendrites of the large mitral cells which lie in the deeper part of the grey substance of the olfactory bulb. The olfactory nerve-fibres are grey fibres, since they do not possess medullary sheaths, and they are bound together into nerves by connective-tissue sheaths derived from the pia mater, from the subarachnoid tissue, and from the dura mater. Prolongations of the subarach- noid space pass outward along the nerves for a short distance. Central connections. — The olfactory impulses are transmitted by way of the peripheral proc- esses of the olfactory neurones through the cell-bodies and the olfactory nerve-fibres and through the glomeruli to the mitral cells. Thence they are carried by the central processes (axones) of the mitral cells, which pass backward along each olfactorj' tract and its three olfac- tory strise (see Rhinencephalon, p. 864). THE TERMINAL NERVE (Nervus Terminalis) In lower vertebrates and recently in those mammals whose sense of smell is relatively much more developed than in man, three nerves have been found concerned with the olfactorj' appara- tus:— ■(!) The olfactory nerve proper whose fibres, as noted above, are the central processes of 930 THE NERVOUS SYSTEM the nerve cell-bodies situated in the epithelium of the olfactory region of the nasal mucosa, and which terminate in the olfactory bulb; (2) The vomero-nasal nerve, whose fibres are the central processes of nerve cell-bodies situated in the epithelium of the vomero-nasal (Jacobson's) organ and which pass caudalward in the submucosa and upward to join the filaments of the olfactory nerve proper and which, in the dog, cat, rabbit, rat, etc., terminate in the accessory olfactory bulb — a small protuberance possessed by these animals on the postero-median aspect of the olfactory bulb proper; (3) The terminal nerve, a small plexiform nerve, which unlike the other two, is ganglionated. In man, the vomero-nasal (Jacobson's) organ is rudimentary after birth and, therefore, the vomero-nasal nerve is not present, the only fibres for the vomero-nasal region being those of gen- eral sensibility from the trigeminus and sympathetic fibres common to the epithelium of the entire nasal fossa. The terminal nerve has been recently described as present in the human foetus and it is men- tioned here because of the expressed belief that it is present in the adult. From the observations recorded for human and rabbit foetuses and the adult dog and cat, the following description may be given: It is variably plexiform throughout its course. Its peripheral twigs are distributed to the mucosa of the nasal septum, some to the mucosa joining the olfactory region while other and larger twigs extend further forward and are distributed to mucosa of the vomero-nasal organ, accompanying and sharing in the distribution of the vomero-nasal nerve when this is present. Its central connections are in the form of two or three small roots which pass through the cribri- form plate of the ethmoid bone in company with and mesial to the vomero-nasal nerve and then, still plexiform, extend caudalward over the infero-mesial aspect of the olfactory bulb and upon the olfactory peduncle or stalk (olfactory tract) beyond, a root often extending to near_the lamina terminalis and optic chiasma. The roots disappear in the mesial and infero-mesial aspect of the frontal portion of the brain at different localities caudal to the olfactory bulb and usually near the olfactory peduncle, but often one may disappear in the region corresponding to the anterior perforated substance of the adult human brain. Numerous small groups of ganglion cells are found interposed along both the peripheral and intracranial course of the terminal nerve. A group, larger in size than the others and situated in the intracranial course of the nerve, is called the ganglion ierminale. The fibres of the nerve are non-medullated. Both the ganglion cells and the fibres of the nerve are described as having more the appearances characteristic of sympathetic neurones than of cranio-spinal. On the other hand, our conceptions of sympathetic neurones do not permit of their terminating within the central system except for the innervation of its bloodvessels. It may result that, instead of being an independent nerve as now claimed, the nervus terminalis is a part of the forward exten- sion of the cephalic sympathetic, the larger ganglia and plexuses of which latter are well known, and that its neurones receive and convey impulses to the gland cells of the nasal mucosa and to the muscle of the blood-vessels of the mucosa and those supplying the infero-mesial part of the frontal end of the cerebrum. THE OPTIC NERVES The fibres of the optic nerve are the central processes of the ganglion cells of the retina. Within the ocular bulb they converge to the optic papilla, where they are accumulated into a rounded bundle, the optic nerve. The nerve thus formed pierces the chorioid and the sclerotic coats, and, at the back of the bulb, enters the orbital fat, in which it passes backward and medialward to the optic foramen. After traversing the foramen it enters the middle fossa of the cranium, and anas- tomoses with its fellow from the opposite side, forming the optic chiasma. It may, therefore, for descriptive purposes, be divided into four portions — the intra-ocular, the intra-orbital, the intra-osseous, and the intra-cranial. The total length of the nerve varies from forty-five to fifty millimetres. The intra-ocular part is rather less than one millimetre in length. It passes backward from the optic papilla through the chorioid and through the sclerotic coats of the bulb. As it passes through the latter coat of the bulb in many sep- arate bundles, the area it traverses has a cribriform appearance when the nerve is removed, and consequently is known as the lamina cribrosa sclerce. The intra-orbital part of the nerve emerges from the sclerotic about three milli- metres below and to the median side of the posterior pole of the bulbus, and it is about thirty millimetres long. It passes backward and medialward, surrounded by the posterior part of the fascia bulbi (Tenon's capsule) and by the orbital fat, to the optic foramen. As it runs backward in the orbit it is in relation above with the naso-ciliary (nasal) nerve and the ophthalmic artery which pass obliquely from behind and laterally, forward and medialward across the junction of its posterior and middle thirds, and also in relation with the superior oph- thalmic vein, the superior rectus muscle, and the upper branch of the oculo-motor nerve. Below it are the inferior rectus muscle, and the inferior division of the oculo-motor nerve. To its lateral side, near the posterior part of the orbit, are the ophthalmic artery, the ciliary ganglion, the abducens nerve,, and the external rectus muscle. The anterior two-thirds of this portion of the optic nerve are surrounded by the ciliary arteries and the ciliary nerves and it is penetrated on its THE OCULO-MOTOR NERVES 931 medial and lower aspect by the central artery of the retina. As it enters the optic foramen to become continuous with the intra-osseous part, it is in close relation with the ligaments of Lock- wood and Zinn (annulus tendineus communis) and with the four recti muscles which arise from them. The intra-osseous portion is from six to seven millimetres long. It lies be- tween the roots of the small wing of the sphenoid and the body of that bone, and it is in relation below and laterally with the ophthalmic artery. The intra-cranial portion, which is from ten to twelve millimetres long, runs backward and medialward, beneath the posterior end of the olfactory tract, and above the ophthalmic artery, the medial border of the internal carotid artery and the diaphragma sellse to the chiasma. From the chiasma to the central connections of the nerve, the path is known as the optic tract. Central connections. — The central connections of the fibres of the optic nerve have been considered with the optic chiasma and the optic tract (see p. 849). Fig. 732. — Nerves op the Nasal Cavitt. Nasal branch ^ ^ , . "' ethmoidal Olfactory ^"' * " nerve plexus Superior nasal co: Sphenoidal sinus Spheno-palatine ganglion Palatine nerves — Nasal branches Posterior palatine Anterior palatine Middle palatine The sheaths of the optic nerve. — The optic nerve receives a sheath from each of the membranes of the brain, and prolongations of the subdural and sub- arachnoid cavities also pass outward along it to the posterior part of the sclera. THE OCULO-MOTOR NERVES The oculo-motor or third cranial nerve is a purely motor nerve. Each sup- plies seven muscles connected with the eye, two of which, the sphincter of the iris and cihary muscle, are within the ocular bulb. The remaining five are in the orbi- tal cavity, and four of them — the superior, inferior, and medial recti and the inferior oblique — are attached to the bulb, while the fifth, the levator palpebrje superioris, is inserted into the upper eyelid. The fibres of the oculo-motor nerve spring from their nucleus of origin situated in the grey substance of the floor of the cerebral aquteduct in the region of the superior quadrigeminate body (fig. 662). The cells of tliis nucleus are divided into two main groups, a superior and an inferior (fig. 663). The superior group includes two nuclei, a medial and a lateral. The latter, besides being lateral, is also somewhat dorsal to the former. The inferior group has been divided into five secondary nuclei, according to the eye-muscles the cells of each group innervate. Three of the five lie lateral to the others and somewhat dorsally, and of the remaining two, which are placed more medially, one encroaches upon the mid-line (nucleits mediaiis) and is con- 932 THE NERVOUS SYSTEM tinuous with the corresponding group of the opposite side and is common to the oculo-motor nerves of both sides. It has been foimd, by the study of diseased conditions and by experiments with animals, that the centres of innervation of the eye-muscles suppUed by the nerve correspond to the above divisions of both the superior and inferior group of cells into a medial and lateral series. The relative position of the divisions of each group and the muscles they are thought to innervate are shown in the following diagram devised by Starr: — Mesial Plane. StrPBRIOR Grotip. Inferior Group. Sphincter of Iris. Ciliary Muscle. Ciliary Muscle. Sphincter of Iris. Levator Palpcbrae Superioris. Medial Rectus. Medial Rectus. Levator Palpebrse Superioris. 1 Superior Rectus. Inferior Rectus. Inferior Rectus. Superior Rectus. Inferior Oblique. Inferior Oblique. As they leave their nucleus of origin in the mid-brain, the fibres of the oculo- motor nerve form a series of fasciculi, which curve ventrally around and through the red nucleus and the medial part of the substantia nigra, to the oculo-motor sulcus on the medial surface of the cerebral peduncle, where they emerge in from six to fifteen small bundles which pierce the pia mater and collect into the trunk of the nerve. Immediately after its formation along the oculo-motor sulcus, the trunk of the nerve passes between the posterior cerebral and the superior cere- bellar arteries, and, running downward, forward, and laterally in the posterior part of the cisterna basalis, it crosses the anterior part of the attached border of the tentorium cerebelli at the side of the dorsum sellse, and, piercing the arachnoid and the inner layer of the dura mater, it enters the wall of the cavernous sinus about midway between the anterior and posterior clinoid processes. Immediately after its entry into the wall of the sinus it lies at a higher level than the trochlear nerve, but the latter soon crosses on its lateral side and gets above it, and directly afterward the oculo-motor nerve divides into a smaller superior and a larger inferior branch (fig. 734). Before its division communications join it from the cavernous plexus of the sympathetic about the internal carotid artery, and from the ophthalmic division of the trigeminus. Both branches proceed forward, and the nasal branch of the trigeminus, which has passed upward, on the lateral side of the inferior branch of the oculomotor lies between them. At the anterior end of the cavernous sinus the two branches pass through the superior orbital (sphe- noidal) fissure, between the heads of the lateral rectus muscle, and enter the or- bital cavity. In the orbit, the superior branch hes between the superior rectus and the optic nerve; it supplies the superior rectus and then turns round the medial border of that muscle and terminates in the levator palpebrse superioris. The inferior branch runs forward, beneath the optic nerve, and divides into three branches which supply the inferior and medial recti and the inferior oblique. The branch to the inferior oblique muscle is connected with the ciliary ganglion by a short thick offset, the short root of the ciliary ganglion, by mediation of the sympathetic neurones of which the oculo-motor nerve sends impulses to the ciliary muscle and the sphincter muscle of the iris. The inferior branch also gives some small twigs to the inferior rectus. The branches of the oculo-motor nerve, which supply the recti muscles, enter the muscles on their ocular surfaces, but the branch to the inferior oblique muscle enters the posterior border of that muscle. THE TROCHLEAR NERVES 933 Some of the fibres which spring from the medial portion of the oculo-motor nucleus do not pass into the nerve of the same side, but into that of the opposite side, and it is beheved that they are distributed to the opposite medial rectus muscle. Other fibres which arise from the nucleus descend in the medial longitudinal fasciculus and either terminate about the cells of the nucleus of the facial or join the facial nerve, in which they pass to the upper part of the orbicularis palpebrarum. The eye is opened by the oculo-motor and closed by the facial nerve. Central connections. — The nucleus of the oculo-motor is associated with the middle portion of the anterior central gyrus, the posterior end of the middle frontal gyrus and with the cortex about the visual area of the occipital lobe of the opposite side of the brain by the pyramidal fibres. It is probably associated with the cerebellum by the fibres in the superior cerebellar peduncles, with the superior calliculus, and with the sensory nuclei of the other cranial nerves by the medial longitudinal fasciculus. To produce the coordinated activities of the eye-moving muscles, it must be associated with the nuclei of the trochlear and abducens. THE TROCHLEAR NERVES The fibres of each trochlear or fourth nerve (or patheticus) spring from the cells of a nucleus which lies in the grey substance of the floor of the cerebral aquse- duct in hne with the oculo-motor nucleus, but in the region of the inferior quadri- geminate bodies. As the fibres pass from their origins they rim ventrally and lat- erally in the substance of the tegmentum for a short distance, then they curve medianward and dorsalward, and, in passing through the anterior end of the supe- rior medullary velum they decussate totally with the fibres of the trochlear nerve Fig. 733. — Diagrams op Sections through the Origin op the Trochlear Nerve. (Still- ing.) (The upper figure is an obUque section, the lower is a coronal section.) Cerebral aqueduct- Nucleus of trochlear nerve Trochlear nerve Trochleai nerve ■Cerebral aqueduct Nucleus of masticator Brachium conjunctivum •Lateral lemniscus of the opposite side. After the decussation the fibres emerge from the surface of the superior medullary velum, at the side of the frenulum veli, usually in two small bundles, which pierce the pia mater and join together to form the slender trunk of the nerve. This trunk curves forward and ventralward to the base of the brain around the sides of the superior peduncle of the cerebellum and cerebral peduncle of the side opposite to that in which the nerve originates, running parallel with and between the superior cerebellar and posterior cerebral arteries. As it reaches the base of the brain behind the optic tract the nerve enters the cisterna basalis, in which it runs forward, immediately beneath or piercing the free border of the ten- torium cerebelli, to the superior border of the petrous portion of the temporal bone, where it pierces the arachnoid and the dura mater and enters the posterior end of the lateral wall of the cavernous sinus. In the wall of the cavernous sinus it receives communications from the cavernous plexus of the sympathetic and bj' a small filament from the ophthalmic division of the trigeminus. It gradually ascends, as it passes forward in the lateral wall of the sinus, and, beyond the middle of the sinus, it crosses the lateral side of the trunk of the oculo-motor nerve and gains a higher position. At the anterior end of the sinus the nerve 934 THE NERVOUS SYSTEM enters the orbit above the lateral rectus and immediately turns medialward between the periosteum of the roof of the orbit and the levator palpebrae superioris. At the medial border of the roof it turns forward to its termination, and enters the orbital or superior surface of the superior oblique muscle to which its fibres are distributed. The central connections of the nucleus of the trochlear nerve are similar to those of the oculo-motor save that its cells probably do not send fibres which connect with the facial nerve. The trochlear is peculiar in that — (1) it is the smallest of the cranial nerves; (2) it is the only nerve having its superficial attachment upon the dorsal aspect of the euoephalon; (3) it is the only cranial nerve whose fibres undergo a total decussation, and (4) in that it terminates in a muscle of the side of the body opposite that in which it has its origin. GaskeU has suggested that this latter condition has probably been brought about, phylogenetically, by the trans- ference of the muscles which have carried their nerves with them. It should be remembered that most of the fibres arising from the medial group of the cells of the nucleus of the oculo-motor, cross the opposite side. This is thought to be especially true for those supplying the medial rectus muscle. THE ABDUCENS The abducens (or sixth nerve) on each side arises from the cells of a nucleus which lies in the grey substance of the floor of the fourth ventricle in the region of the inferior part of the pons. The nucleus is situated close to the middle line, ventral to the acoustic medullary strise and beneath the colliculus facialis and it is in direct linear series with the nuclei of the oculo-motor, trochlear and hypo- glossal nerves. It is the third of the eye-moving nerves. The fibres which pass from the nucleus into the nerve run inferiorly and ventralward through the ret- icular formation, the trapezium, and the pyramidal fasciculi, and they emerge from the ventral surface of the medulla in the sulcus at the inferior border of the pons and the upper end of the pyramid of the medulla. From this superficial attachment the nerve runs upward and forward in the subarachnoid space between the pons and the basisphenoid and at the side of the basilar artery. A little below the level of the upper border of the petrous portion of the temporal bone it pierces the dura mater, passes beneath the petro-sphenoidal hgament, at the side of the dorsum sellte, and enters the cavernous sinus, in which it runs forward along the lateral side of the internal carotid artery. At the anterior end of the sinus it passes through the superior orbital (sphenoidal) fissure between the heads of the rectus lateralis, below the inferior branch of the oculo-motor nerve, and above the ophthalmic vein. In the orbit it runs forward on the inner or ocular surface of the rectus lateralis, and finally it pierces this muscle and terminates upon its fibres. While it is in the cavernous sinus it receives communications from the carotid plexus of the sympathetic and from the ophthalmic nerve. All the fibres arising in the nucleus of the sixth nerve do not pass into the sixth nerve. Some of them ascend in the medial longitudinal fasciculus of the same and opposite sides, and ter- minate about cells of the medial group of the nucleus of the oculo-motor nerve, by which the impulses are conveyed to the opposite medial rectus muscle. Thus impulses reaching the abdu- cens nucleus can throw into simultaneous action the lateral rectus of the same side and the medial rectus of the opposite side, and thus turn both ej'es in the same direction. Central connections. — The nucleus of the abducens receives impulses from the anterior central gyrus of the opposite side by the pj'ramidal fibres, and it is associated with the sensory nuclei of other nerves by way of the medial longitudinal fasciculus, and that of the trigemiuus especially through the reticular formation. THE TRIGEMINUS The trigeminus is the largest of the cranial nerves with the exception of the optic. It is usually described as the fifth cranial nerve and as possessing both a sensory and a motor root. For reasons already given, the "motor root" is here described separately and given the separate name, masticator nerve. The fibres of the trigeminus, which are all sensory, spring from the cells of the semi- lunar (Gasserian) ganglion, which corresponds with the ganglion of the dorsal root of a spinal nerve, and they enter the brain stem through the side of the anterior third of the pons. BRANCHES OF THE TRIGEMINUS 935 The semilunar (Gasserian) ganglion is a semilunar mass which lies in Meckel's cave, a cleft in the dura mater above a depression in the medial part of the upper surface of the petrous portion of the temporal bone. The convexity of the ganglion is turned forward, and from it three large nerves, the ophthalmic, the maxillary, and the mandibular, are given off. From the concavity, which is directed backward, springs the root of the nerve. The medial end of the ganglion is in close relation with the cavernous sinus and the internal carotid artery at the foramen lacerum, and the lateral end lies to the medial side of the foramen ovale. The surfaces of the ganglion are striated, due to bundles of fibres traversing them. The upper surface is separated by the dura mater from the temporal lobe of the brain, and the lower rests upon the masticator nerve and the outer layer of dura mater upon the petrous portion of the temporal bone. The fibres of the trigeminus root as they leave the semilunar (Gasserian) ganglion, form from thirty to forty fasciculi which are bound together into a flat band, from six to seven millimetres broad, which passes backward over the upper border of the petrous portion of the temporal bone and below the superior petrosal sinus into the posterior fossa of the cranium. In the posterior fossa it runs backward, medialward, and downward, and passes into the pons through its continuation into the middle peduncle of the cerebellum. In the tegmentum of the pons region, the fibres bifurcate into ascending and descending branches which terminate about the cells of the nucleus of termination of the trigeminus. This nucleus, large at the level of the entrance of the root, has tapering superior and inferior e.xtremities. The inferior ex- tremity of the nucleus, which is much the longer, descends as low as the upper portion of the spinal cord and the fibres of the root terminating about the cells of this extremity are known as the spinal tract of the trigeminus. Central connections. — The nuclei of termination of the trigeminus send impulses to the somaesthetic area of the cortex of the opposite side by the fibres of the medial lemniscus (fillet) and, for reflex actions, to the motor nuclei of other cranial nerves by the medial longitudinal fasciculus and by fascicuU propri in the reticular formation of the same, and opposite sides. THE BRANCHES OF THE TRIGEMINUS The main branches of the trigeminus, given off by the front side of the semi- lunar ganglion, are three in number (ophthalmic, maxillary, and mandibular) , each of which is referred to as a nerve and each of which is purely sensory, though the third branch, or mandibular nerve, is joined by the fibres of the masticator nerve which is motor. (1) The Ophthalmic Nerve or First Division The ophthalmic nerve, the first division of the trigeminus, is the smallest of the three branches which arise from the semilunar (Gasserian) ganglion. It springs from the medial part of the front of the ganglion and passes forward, in the lateral wall of the cavernous sinus, where it lies below the trochlear nerve and lateral to the abducens nerve and the internal carotid artery (fig. 734). A short distance behind the superior orbital (sphenoidal) fissure the nerve divides into three ter- minal branches — the frontal, lacrimal, and naso-ciliary (nasal) nerves. They pierce the dura mater, which closes the fissure, and pass forward into the orbit. Before its division the ophthalmic nerve receives filaments from the cavernous plexus of the sympathetic and it gives off, soon after its origin, a tentorial (recur- rent meningeal) branch which runs backward, in close association with the troch- lear nerve, and ramifies between the layers of the tentorium cerebelli. Further forward three branches spring from the ophthalmic nerve which contribute sen- sory fibres to the oculo-motor, trochlear, and abducens nerves. The terminal branches. — (a) The frontal nerve is the largest terminal branch. It pierces the dura mater and passes into the orbit through the superior orbital (sphenoidal) fissure, above the rectus lateralis and a little below and to the lateral side of the trochlear nerve. In the orbit it runs forward, between the levator palpebrse superioris and the periosteum, and breaks up into three branches, the supra-orbital, frontal proper, and supratrochlear. The supra-orbital nerve, the largest of the three branches, leaves the orbit at the supra- orbital notch (fig. 734). As it passes thi-ough the notch it gives off a small branch which enters the bone and supphes the diploe and the mucous membrane of the frontal sinus. Its terminal branches give twigs to the pericranium and to the skin of the scalp, the upper ej-eUd, the frontal 936 THE NERVOUS SYSTEM region, and the parietal region almost as far as the lambdoid suture (fig. 740). One branch running at the upper margin of the orbital cavity unites with a branch of the facial nerve. The frontal branch, given off at a variable point, lies medial to the supra-orbital, passes through the frontal foramen, and is distributed to the skin of the forehead and upper eyehd (fig. 734). The supratrochlear branch runs forward and medialward toward the upper and medial angle of the orbit, where it passes above the pulley of the superior obhque muscle, pierces the palpebral fascia, and ascends to the lower and middle part of the forehead, accompanied by the frontal artery (fig. 734). Before it leaves the orbit it sends a branch downward behind or in front of the pulley of the obliquus superior which joins with the infratrochlear nerve, and as it leaves the orbit it gives off filaments to supply the skin and conjunctiva of the medial third of the upper eyelid. Its terminal branches pierce the orbicularis and frontalis, and, as they pass to the skin of the forehead, they communicate with branches of the facial nerve. (b) The lacrimal nerve [n. lacrimalis] is the smallest of the three branches of the ophthalmic division. It passes through the superior orbital (sphenoidal) fissure lateral to and slightly below the frontal nerve, and is directed forward and lateral- FiG. 734. — Nerves op the Orbit from Above and Behind. (Schematic.) Infratrochlear 1 Supratrochlear I 1 Frontal branch of frontal , Supraorbital Superior ob-^ lique muscle"" Trochlear Naso-ciliary (nasal) " Annular com- mon tendon of Zinn Optic nerve - Internal car- otid artery Abducens ^-r Semilunar ^ (Gasserian) "^ j ^ Levator palpebrse superioris Superior rectus Lacrimal gland Frontal Short ciliary nerves Anastomosing branch with zygomatic Lacrimal Long ciliary nerves Inferior rectus Branch to internal oblique Lateral rectus Ciliary ganghon Sympathetic ] Roots of Short } ciliary Long J ganghon Abducens Inferior branch of oculo-motor Superior branch of oculo-motor Lateral rectus (lat. head) Ophthalmic Maxillary Mandibular A' — Foramen spinosum ward, along the upper border of the rectus lateralis to the lacrimal gland (fig. 734) . On the lateral wall of the orbit it receives a small branch from the zygomatic nerve (the orbital branch of the maxillary nerve). This branch brings to the lacrimal nerve secretory fibres for the lacrimal gland. A small twig passes beyond the gland, pierces the palpebral fascia, supplies filaments to the conjunctiva, and is then distributed to the integument at the lateral angle of the eye and to the skin over the zygomatic process of the frontal bone. (c) The naso-ciliary (nasal) nerve enters the orbit between the two heads of the rectus lateralis and between the superior and inferior branches of the oculo-motor nerve. In the orbit it lies at first lateral to the optic nerve, but, as it runs obliquely forward and medialward to the medial wall of the orbital cavity, it crosses above the optic nerve and between it and the rectus superior, and near the border of the rectus medialis it divides into its terminal branches, the chief of which are the infratrochlear and anterior ethmoidal nerves (fig. 734). In addition to those received from the cavernous plexus before the division of the ophthalmic nerve , THE MAXILLARY NERVE 937 the naso-ciliary nei've itself receives numerous sympathetic (secretory and vaso- motor) fibres. Its several branches are: (i) The long root of the ciliary ganglion which is given off at the superior orbital (sphenoidal) fissure. It is a slender filament which runs forward on the lateral side of the optic nerve to the superior and posterior part of the ciliary ganglion (fig. 734). (ii) The long ciliary nerves, usually two in number, which arise from the naso-cihary nerve as the latter is crossing above the optic nerve. They run forward, on the medial side of the optic nerve, pierce the sclerotic, and are distributed with the lower set of short ciliary nerves (fig. 734). The long root of the cihary ganglion and the long ciUary nerves carry sensory fibres which belong to the naso-ciliary nerve proper, most of which merely pass through the ganglion, and it carries sympathetic fibres, added to it, most of which may terminate about the cell-bodies of the ganglion. (iii) The posterior ethmoidal (spheno-ethmoidal) branch springs from the posterior border of the naso-ciUary nerve near the upper border of the rectus medialis. It passes through the posterior ethmoidal canal and is distributed to the mucous membrane of the posterior ethmoidal cells and the sphenoidal sinus. (iv) The infratrochlear nerve passes forward between the obhquus superior and the rectus medialis, and under the pulley of the former muscle divides into two branches: — The superior palpebral branch helps to supply the eyehds with sensory fibres and usually anastomoses with the supratrochlear nerve. The inferior palpebral branch is distributed to the lacrimal sac, the conjunctiva and skin of the medial part of the upper eyehd, the caruncle, and the skin of the upper part of the side of the nose. (v) The anterior ethmoidal (distal part of the nasal) nerve, passing forward and medial- ward between the obhquus superior and the rectus medialis, leaves the orbit through the anterior ethmoidal foramen, accompanied by the anterior ethmoidal vessels, and enters into the anterior fossa of the cranium (fig. 734). It then crosses the lamina cribrosa of the ethmoid, lying outside the dura mater, which separates it from the olfactory bulb, and descends into the nasal fossa through the ethmoidal fissure, a slit-like aperture at the side of the crista galli. In the sub- mucosa of the nasal fossa it terminates by dividing into two sets of anterior nasal branches: the internal nasal branches and the external nasal branch (fig. 732). The internal nasal branches divide into the medial nasal branches (the septal branches of the nasal nerve), which run downward and forward on the upper and front part of the septum, and the lateral nasal branches (the external terminal branch of the nasal nerve), which give twigs to the anterior extremities of the superior and middle nasal conchae (turbinated bones), and to the mucous membrane of the lateral wall of the nose (fig. 732). The external nasal branch (the anterior terminal branch of the nasal nerve) runs downward in a groove on the inner surface of the nasal bone. It pierces the wall of the nose between the nasal bone and the upper lateral cartilage, and supphes the integument of the lower part of the dorsum of the nose as far as the tip. (2) The Maxillary Nerve or Second Division of the Trigeminus The maxillary nerve is entirely sensory in function and it is intermediate in size between the ophthalmic and mandibular nerves. It springs from the middle of the anterior border of the semilunar (Gasserian) ganglion and runs forward in the lower and outer part of the lateral wall of the cavernous sinus (fig. 735). Leaving the middle fossa of the cranium, by passing through the foramen rotundum, it enters the pterygo-palatine (spheno-maxillary) fossa (fig. 734), where it is joined by twigs with the spheno-palatine ganglion; then, changing its name, it passes forward, as the infra-orbital nerve, through the inferior orbital (spheno-maxillary) fissure into the infra-orbital sulcus in the floor of the orbit; continuing forward it traverses the infra-orbital canal accompanied by the infra-orbital artery, and appears in the face, beneath the levator labii superioris (quadratus) and above the levator anguli oris (caninus) where it divides into four sets of terminal branches which anastomose more or less freely with branches of the facial nerve to form the infra-orbital plexus. Branches. — The branches of the maxillary nerve are — (a) branches given off in the middle fossa of the cranium; (6) branches given off in the pterygo-palatine (spheno-maxillary) fossa; (c) branches given off in the infra-orbital sulcus and canal; and (d) terminal branches. (a) The middle (recurrent) meningeal branch, given off in the middle fossa of the cranium, breaks up into numerous branches which supply the dura mater with sensory fibres, reinforce the sympathetic plexus on the middle meningeal artery, and anastomose with the spinous nerve (the recurrent branch of the man- dibular nerve). (b) The branches given off in the pterygo-palatine (spheno-maxillar}^ fossa are the spheno-palatine nerves, the zygomatic branch of the maxillary nerve, and the posterior superior alveolar nerves. 938 THE NERVOUS SYSTEM The spheno -palatine nerve has two or three branches which descend in the pterygo- palatine fossa and give a small part of their fibres to the spheno-palatine (Meckel's) ganghon (fig. 735), the larger part of their fibres passing tlirough the ganghon into its orbital, nasal, and palatine branches. (See Spheno-p.\l.\tine Ganglion, p. 962.) The zygomatic (orbital or temporo-malar) branch, given off from the upper surface of the maxiUary nerve, passes forward and lateralward, and, at the end of the inferior orbital (spheno- maxillary) fissure, passes through it into the orbit and divides into two branches, facial and temporal. The zygomatico -facial (malar) branch runs forward, passes through a zygomatico-orbital foramen, then thi-ough the zygomatico-facial (malar) foramen, pierces the orbicularis palpe- brarum, communicates with the zygomatic (malar) branch of the facial nerve, and supplies the skin of the prominence of the cheek. The zygomatico -temporal (temporal) branch runs upward in a groove in the lateral wall of the orbit, passes through a zygomatico-orbital foramen, then through the zygomatico-temporal (spheno-malar) foramen, and enters the temporal fossa. It turns around the anterior border of the temporal muscle, pierces the deep layer of the temporal fascia, and runs backward for a short distance in the fat between the superficial and deep lam- ellae, then, turning lateralward, it pierces the superficial lamellae about an inch above the zygoma, anastomoses with the temporal branch of the facial nerve, and supphes the skin of the anterior part of the temporal region. The infra-orbital nerve, that part of the maxiUary nerve lying distal to the spheno- palatine ganghon, enters the orbit through the inferior orbital (spheno-maxiUary) fissure, accompanied by the infra-orbital artery, and with it passes through the infra-orbital canal (fig. 735) to the face, where it divides into four sets of terminal branches, some of which, by anastomoses with the branches of the facial nerve, form the infra-orbital plexus. Three sets of superior alveolar nerves arise from the maxillary and the infra-orbital nerves, namely, the posterior superior alveolar branches, the middle superior alveolar branch, and the anterior superior alveolar branches. Fig. 735. — Lateral View of the Maxillary Nerve. Mandibular Ophthalmic MaxiUary Zygomatic lunar- \ <• (Gasser- V,, ian) r ^ ganglion ^ • y Anterior \^,' superior v*s^ alveolar branches Vidian Spheno-palatine ganglion Spheno-palatine nerves/ Posterior inferior nasal Posterior superior alveolar branches Middle superior alveolar branch The posterior superior alveolar (dental) nerves are usually two in number, but sometimes arise by a single trunk. They pass downward and lateralward through the pterygo-maxillary fissure into the zygomatic fossa, where they give branches to the mucous membrane of the gums and the posterior part of the mouth; then they enter the posterior alveolar (dental) canals and unite with the other alveolar branches to form the superior dental plexus, through which they give branches to the roots and pulp cavities of the molar teeth and to the mucous membrane of the maxillary sinus (fig. 735). (c) The branches given off in the infra-orbital sulcus and canal are the middle and anterior superior alveolar (dental) nerves. (i) The middle superior alveolar (dental) nerve leaves the infra-orbital nerve in the pos- terior part of the inlVa-orliital sulcus, and, pa.ssing downward and forward in a canal in the max- illa, it divides into terminal branches that anastomose with the other alveolar branches to form the superior dental plexus. Through the plexus it supplies the bicuspid teeth and gives branches to the mucous membrane of the maxillary sinus and also to the gums (fig. 735). THE MANDIBULAR NERVE 939 (ii) The anterior superior alveolar (dental) nerve is the largest of the superior alveolar nerves. It is given off by the infra-orbital nerve in the anterior part of the infra-orbital canal, and passes downward in a bony canal in the anterior wall of the maxilla. After uniting with the other alveolar nerves to form the superior dental ple.xus, it supplies the canines and the incisors and gives branches to the mucous membrane of the maxillary sinus and the gums (fig. 735). It also gives off a nasal branch which enters the nasal fossa through a small foramen, and supphes the mucous membrane of the anterior part of the inferior meatus and the adjacent part of the floor of the nasal cavity. (iii) The superior dental plexus is formed in the bony alveolar canals by the three superior alveolar nerves. It is convex downward and anastomoses across the mid-line with the corre- sponding plexus of the other side (fig. 735). From it arise the superior dental branches supply- ing the superior canines and incisors, superior gingival branches supplying the gums, and also branches to the mucous membrane of the maxiUary sinus and to the bone. On the plexus are two gangliform enlargements, one, called the ganglion of Valentine, situated at the junction of the middle and the posterior branches, and the other, called the ganglion of Bochdalek, at the junction of the middle and anterior branches. (d) The terminal branches of the maxillary nerve are the inferior palpebral, the external and internal nasal (nasal), and the superior labial. The inferior palpebral branches, usually two, pass upward and supply sensory fibres to all the skin and conjunctiva of the lower eyelid (fig. 740). The external nasal branches pass medialward under cover of the levator labii superioris (quadratus), and supply the skin of the posterior part of the lateral aspect of the nose. The internal nasal branches pass downward and medialward under the lateral wall of the aose, and then turn ujnvard to supply the skin of the vestibule of the nose. The superior labial branches, three or four in number, as a rule are larger than the palpebral and nasal branches. They pass downward to supply the skin and mucous membrane of the upper Up and the neighbouring part of the cheek. (3) The Mandtbular Nerve or Third Division of the Trigeminus The mandibular division is the largest of the three divisions of the trigeminus (figs. 736 and 740). As a nerve, it is usually described as formed by the union of two distinct nerves, namely, the entire masticator nerve and the large bundle of sensory fibres derived from the semilunar (Gasserian) ganglion which pass peripherally as the third division of the trigeminus. These two nerves remain separate until they pass through the foramen ovale and then unite immediately outside the skull to form a large trunk which almost directly after its formation divides into a small anterior and a larger posterior portion. The trunk is situated between the pterygoideus externus, laterally, and the otic ganglion and the tensor palati medially. In front of it is the posterior border of the pterygoideus internus, and behind it, the middle meningeal artery. Two branches arise from the trunk of the nerve before its division, namely, the spinous (recurrent) nerve and the nerve to the pterygoideus internus. The spinous (recurrent) nerve, after receiving a vasomotor filament from the otic ganglion, enters the cranium through the foramen spinosum, accompanying the middle meningeal artery, and divides into an anterior and a posterior branch. The anterior branch communicates with the meningeal branch of the maxillary division of the trigeminus, furnishes filaments to the dura mater, and ends in the osseous substance of the great wing of the sphenoid. The posterior branch traverses the petrosquamous suture and ends in the Uning membrane of the mastoid ceUs. The fibres going to form the neriie to the internal pterygoid muscle are almost wholly motor fibres and therefore comprise a branch of the masticator nerve and are described as such under the description of the masticator (fig. 737). The anterior portion of the mendibular nerve is smaller than the posterior and is chiefly composed of motor fibres which form branches of the masticator nerve and supply the muscles of mastication, the temporalis, masseter, and pteryg- oideus externus. Practically all of the sensory fibres of the anterior portion (fibres of the mandibular nerve proper) form the buccinator (long buccal) nerve. The latter is accompanied, in the first part of its course, by a small strand of motor or masticator fibres which leaves it to end in the anterior part of the temporal muscle. The buccinator (long buccal) nerve, entirely sensory, passes between the two heads of the external pterygoid muscle and runs do\\Tiward and forward under cover of or through the ante- rior fibres of the temporahs to the cheek (fig. 736). As it passes forward it emerges from under cover of the anterior border of the masseter and lies on the superficial surface of the buccinator, where it interlaces with the buccal branches of the facial nerve and gives off filaments to supply the superjacent skin; finally it pierces the buccinator and supphes the mucous membrane on its 940 THE NERVOUS SYSTEM inner surface as far forward as the angle of the mouth. The fibres of the anterior deep temporal nerve, a branch of the masticator, are frequently associated with the buccinator until the latter has passed between the heads of the external pterygoid; then the anterior deep temporal nerve separates from the buccinator and passes upward on the lateral surface of the upper head of the external pterygoid. The posterior portion of the mandibular nerve divides into three large branches. Two of these, the lingual and the auriculo-temporal nerves, are exclusively- sensory; the third, the inferior alveolar (dental) nerve, contains a strand of motor fibres, the mylo-hj^oid nerve, which comprise a branch of the masticator nerve. The lingual nerve is the most anterior branch of the mandibular nerve (figs. 736, 743) . It lies in front and to the medial side of the inferior alveolar (dental) nerve and descends at first on the medial side of the pterygoideus externus, then between the pterygoideus internus and the ramus of the mandible to the posterior part of the mylohyoid ridge, where it passes off the anterior border of the ptery- goideus internus; at this point it is situated a short distance behind the last Fig. 736. — DisTRiBTrTioN of the Mandibular Division op the Trigeminus combined with Branches op the Masticator Nerve. (Henle.) Auriculo-temporal nerve Posterior deep temporal nerve Nerve to masseter Mylo-hyoid ne Lingual nerve molar tooth and is covered in front by the mucous membrane of the posterior part of the mouth cavity. After leaving the pterygoideus internus it crosses the fibres of the superior constrictor, which are attached to the mandible, and turns forward toward the tip of the tongue, crossing the lateral surfaces of the stylo- glossus, hyoglossus, and genioglossus. In its com-se across the hyoglossus it lies first above, then to the lateral side of, and finally below Wharton's duct, and as it ascends on the genioglossus it lies on the medial side of the duct. Communications and branches. — While it is on the medial side of the pterygoideus externus the lingual nerve is joined, at an acute angle, by the chorda tympani (figs. 736, 743), a branch of the glosso-palatine nerve, and as it hes between the ramus of the mandible and the pterygoid- eus internus it is connected by a branch with the inferior alveolar (dental) nerve, and gives off one or two small branches, the rami isthmi faucium, which are ditributed as sensory fibres to the tonsil and the mucous membrane of the posterior part of the mouth (fig. 743). While it is above the duct it gives a branch, which contains many sensory and visceral motor chorda tympani fibres, to the submaxillary ganghon (.seep. 963), and it receives branches, chiefly sympathetic, from that ganglion. A little further forward it is connected by one or two branches, which run along the anterior border of the hyoglossus, with the hypoglossal nerve THE MANDIBULAR NERVE 941 (fig. 743). It then gives off the sublingual nerve, which runs forward to supply the subHngual gland and the neighbouring mucous membrane (fig. 74.3). Its terminal (lingual) branches are derived chiefly from the glosso-palatine nerve. They pierce the muscular substance of the tongue and are distributed to the mucous membrane of its anterior two-thu-ds. They interlace with similar branches of the other side and with branches of the glosso-pharyngeal nerve. The inferior alveolar (dental) nerve is the largest branch of the posterior portion of the mandibular nerve. It commences on the medial side of the ex- ternal pterygoid muscle and descends to the interval between the spheno-man- dibular ligament and the ramus of the mandible, where it receives one or two communicating branches from the lingual nerve. Opposite the middle of the medial surface of the ramus it enters the mandibular (inferior dental) canal, ac- companied by the inferior alveolar (dental) artery, which lies in front of the nerve, and it runs downward and forward through the ramus and the body of the mandible (fig. 736). At the mental foramen it divides into two parts, one of which, the mental nerve, passes out through the mental foramen, the other, com- monly called the incisive branch, continues forward in the canal, and supplies, through the inferior dental plexus, the inferior canine and incisor teeth and the corresponding regions of the gums. Branches. — ^The branches of the inferior alveolar (dental) nerve are branches forming the inferior dental plexus, and the mental branch. A bundle of motor fibres, the mylohyoid nerve, a branch of the masticator nerve, is given off just before the inferior alevolar nerve enters the mandibular canal. The inferior dental plexus is formed by a series of branches which communicate with one another within the bone, giving rise to a fine network. From this plexus two sets of branches are given off: — the inferior dental branches, corresponding in number to the roots of the teeth, enter the minute foramina of the apices of the roots and end in the pulp; the second set, the inferior gingival branches, supply the gums. The mental nerve is a nerve of considerable size which emerges through the mental foramen (fig. 736). It communicates, near its exit from the bone, with branches of the facial nerve, and then divides into three branches. The smallest branch, turning downward, divides into several twigs, the menial branches, which supply the integument of the chin. _ The other two, inferior labial branches, pass upward, diverging as they ascend, and divide into a number of twigs. The stoutest twigs ramify to the mucous membrane which lines the lower hp. Other twigs are distributed to the integument and fascia of the hp and chin. The auriculo -temporal nerve usually arises from the posterior portion of the mandibular nerve by two roots which embrace the middle meningeal artery and unite behind it to form the trunk of the nerve. The trunk passes backward on the medial aspect of the pterygoideus externus, and between the spheno-man- dibular ligament and the temporo-mandibular articulation, lying in close relation with the capsule of the joint. Behind the joint it enters the upper part of the parotid gland, through which it turns upward and lateralward. It emerges from the upper end of the gland, crosses the root of the zygoma close to the posterior border of the superficial temporal artery, and divides into auricular and temporal terminal branches at the level of the tragus of the pinna (fig. 736) . Communications. — (a) Each of the two roots of the nerve receives a communication from the otic ganglion containing fibres derived from the glosso-pharyngeal nerve. These fibres have passed from the glosso-pharyngeal through the tympanic plex-us and the smaU superficial petrosal nerve and through the otic ganglion. (b) Sensory filaments pass from the auriculo-temporal nerve to the temporo-facial branch of the facial nerve. (c) Filaments of connection with the sympathetic plexus on the internal maxiUary artery. (d) A communication to the inferior alveolar (dental) nerve. Branches of the auriculo-temporal nerve. — (a) An articular branch to the temporo-man- dibular joint, given off as the nerve lies on the medial side of the capsule. (6) Branches to the external auditory meatus. Two branches, as a rule, are given off in the parotid gland. They enter the meatus by passing between the cartilage and the bone and supply the upper part of the meatus, the membrana tympani by a fine branch, and occasionally the lower branch gives twigs to the skin of the lobule of the pinna. (c) Parotid branches are distributed to the substance of the parotid gland. Sensory or trigeminal fibres for the gland spring either directly from the nerve or from the communicating branches previously given by it to the glosso-palatine nerve. The parotid branches also con- tain filDres derived from the glosso-pharyngeal nerve which pass successively through its tym- panic branch, the tympanic plexus, the small superficial petrosal nerve, the otic ganglion, and the communicating twigs from the otic ganglion to the roots of the auriculo-temporal nerve. The parotid branches are later again mentioned as concerned chiefiy with the ganglialed cephalic plexus. (d) The anterior auricular branches, usually two in number, are distributed to the skin of the tragus and the upper and outer part of the pinna. 942 THE NERVOUS SYSTEM (e) The superficial temporal branches supply the integument of the greater part of the tem- poral region, and anastomose with the temporal branch of the facial nerve. THE MASTICATOR NERVE (Fig. 737) The masticator nerve (motor root or portio minor of trigeminus) . The fibres of the masticator nerve spring from two nuclei, a slender upper or mesencephalic nucleus and a clustered lower or chief nucleus. The fibres arising in the mesen- cephalic nucleus descend along the lateral aspect of the nucleus to the pons as the descending or mesencephalic root;* here they join the fibres from the chief motor nucleus and issue with them from the side of the pons in from six to ten root filaments. These blend to form the nerve, which is from one and a half to two millimetres broad. At the point where it emerges from the pons the nerve is in front of and ventral to the root of the trigeminus and it is separated from the latter by a few of the transverse fibres of the pons which constitute the lingula oj Wrisberg. From its superficial exit from the pons, the masticator nerve passes upward, lateralward, and forward in the posterior fossa of the cranum, and along the medial and anterior aspect of the trigeminus, to the mouth of Meckel's cave. In this cavity it runs lateralward below the semilunar (Gasserian) ganglion to the foramen ovale, through which it passes to join the mandibular division of the Fig. 737. — Schematic Representation of the Masticator Nerve and its Branches (in Black). Lateral view. Modified from Spalteholz. Gasserian ganglion Masticator nerve / External pterygoid nerve Auriculo-temporal i 1 \ 1 Internal maxillary artery\ Posterior deep temporal nerve Anterior deep temporal nerve Internal pterygoid nerve Masseter nerve Buccinator nerve External carotid artery -■' Mylo-hyoid nerve ^ " trigeminus immediately outside and below the base of the skull. The nerve is purely motor and its fibres are devoted almost wholly to the muscles having to do with mastication. Central connections. — The nuclei of origin of the masticator nerve are connected with the lower part of the somaesthetic area of the cerebral cortex of the opposite side by the p}Tamidal fibres descending in the genu of the internal capsule, and they are associated with the sensory nuclei of other cranial nerves through the reticular formation and by the medial longitudinal fasciculus. Branches. — Almost immediately after joining the trunk of the mandibular nerve, most of the fibres of the masticator leave it to form the greater part of the so-called anterior portion of the mandibular. However, one branch of masticator fibres, the nerve to the internal pterygoid muscle, is given off from the mandibular just before its division into anterior and posterior portions. The masticator * Recent investigations indicate that the mesenephalic root is not wholly motor but at least in part sensory in character, and thus belongs partly to the trigeminal nerve. (See page 829.) THE FACIAL NERVE 943 branches derived from the anterior portion are the deep tem-poral nerves, the masseteric nerve, and the nerve to the external -pterygoid. One branch, the mylo-hyoid nerve, is carried in the posterior portion of the mandibular and is given off from its inferior alveolar branch. The nerve to the internal pterygoid passes under cover of a dense layer of fascia derived from an expansion of the ligamentum pterygo-spinosum, and enters the deep surface of the muscle. Near its commencement this nerve furnishes a visceral motor root to the otic ganglion, and small twigs to the tensor tympani and tensor palati. The deep temporal nerves, usually two in number, posterior and anterior, pass between the bone and the upper border of the external pterygoid muscle, and turn upward around the infra- temporal crest of the sphenoid bone to end in the deep surface of the temporalis (fig. 736). The posterior of the two often arises in common with the masseteric nerve. The anterior is frequently associated with the buccinator (long buccal) nerve till the latter has passed between the two heads of the pterygoideus externus. There is frequently a third branch, the medius, which passes lateralward above the pterygoideus externus, and turns upward close to the bone to enter the deep surface of that muscle. A small strand of masticator fibres accompanies the buccinator nerve to enter and end in the anterior part of the temporal muscle. The masseteric nerve, which frequently arises in common with the posterior deep temporal nerve, passes between the bone and the pterygoideus externus, and accompanies the masseteric artery through the notch of the mandible to be distributed to the masseter (fig. 736). It is easily traced through the deeper fibres nearly to the anterior border of the masseter. As it emerges above the pterygoideus externus it gives off a twig to the temporo-mandibular articulation. The nerve to the external pterygoid, after a course of about 3 mm. (an eighth of an inch), divides into twigs which enter the deep surface of the two heads of the muscle. It is usually adherent at its origin to the buccinator nerve. The mylo-hyoid branch, carried in the posterior portion of the mandibular nerve, is given off immediately before the inferior alveolar (dental) nerve enters the mandibular (inferior dental) canal. It pierces the lower and back part of the spheno-mandibular ligament and runs down- ward and forward in the mylo-hyoid groove between the mandible on the lateral side, and the internal pterygoid muscle and the lateral surface of the submaxillary gland on the medial side. In the anterior part of the digastric triangle it is continued forward between the anterior part of the submaxillary gland and the mylo-hyoideus, and it breaks up into branches which supply the mylo-hyoideus and the anterior belly of the digastric (fig. 736). THE FACIAL NERVE The facial or seventh nerve is purely motor. It is accompanied a short distance by a bundle usually called its sensory root or the intermediate nerve. This latter, however, on the Ijasis of its origin, distribution, and mixed instead of sensory character, is described separately below as the glosso-palatine nerve. It is smaller than the facial, is fused to the trunk of the facial and the ganglion giving rise to its sensory fibres is situated upon the external genu of the facial (figs. 738 and 741). The fibres of the facial nerve (fig. 738) spring from a nucleus of cells situated laterally in the reticular formation at the level of the lower pons, dorsal to the supe- rior olive, and between the root fibres of the abducens nerve and the laterally placed spinal tract of the trigeminus. From this nucleus the fibres of the nerve pass medially and dorsalward to the floor of the fourth ventricle and, just under the floor, they turn anteriorly, passing dorsal to the nucleus of the abducens (fig. 653, p. 827). At the anterior end of this nucleus they turn sharply ventralward and lateralward, and at this point it is claimed that fibres descending in the near-by medial longitudinal fasciculus from the nucleus of the oculo-motor nerve of the same side become intermingled with the fibres of the facial nerve and pass outward with them. This, however, is uncertain. Continuing ventralwai'd through the reticular formation the fibres of the facial emerge from the brain-stem at the inferior border of the pons, lateral to the superficial attachment of the abducens. At the point of its emergence, the facial nerve pierces the pia mater, from which it receives a sheath, and then proceeds forward and lateralward in the posterior fossa of the cranium to the internal auditory meatus, which it enters in company with the glosso-palatine nerve and with the cochlear and vestibular nerves. As it lies in the meatus it is situated above and in front of the latter nerves, from which it is separated by the glosso-palatine, and it is surrounded, together with these three nerves, by sheaths of both the arachnoid and the dura mater and by prolongations of the subarachnoid and sub-dural spaces. While it is still in the meatus it blends with the glosso-palatine and thus the combined trunk is formed. At the outer end of the meatus the trunk pierces 944 THE NERVOUS SYSTEM the arachnoid and the dura mater and enters the facial canal (aqueduct of Fallo- pius), in which it runs forward and slightly lateralward to the hiatus Fallopii, where it makes an angular bend, the external genu [geniculum], around the anterior boundary of the vestibule of the inner ear; this bend is enlarged by the adhesion of the geniculate ganglion (of the glosso-palatine) upon its anterior border. From the geniculum the facial nerve runs backward in the facial canal along the lateral wall of the vestibule and the medial wall of the tympanum, above the fenestra vestibuli (ovalis), to the junction of the medial and posterior walls of the tympanic cavity; then, bending downward, it descends in the posterior wall to the stylo-mastoid foramen. As soon as it emerges from the stylo-mastoid foramen it turns forward around the lateral side of the base of the styloid process. Fig. 738.- Fibres from oc- ulomotor nerve Nucleus of abducens Diagram of the Facial (Yellow) and Glosso-palatine Nerve (Blue). Facial i Glosso- palatine Internal auditory meatus Small superficial petrosal nerve Fenestra vestibuli Tympanic plexus Chorda tympani Communication to auricular branch of vagus Fenestra cochlese Posterior auricular Communication to glosso-pharyngeal Nerve to post, belly of diagastric Nerve to stylo- hyoideus Styloid process Tympanic branch of facial nerve Hilary Spheno- palatine ganglion Vidian nerve Great deep petrosal nerve Middle memng( Foramen ovale artery Otic ganglion Spine of sphenoid Communication fron temporal Chorda tympani Communication from auricular branch of glosso-pharyngeal Lingual nerve Small deep petrosal nerve and plunges into the substance of the parotid gland, where it divides into its cervico-facial and temporo-facial terminal divisions. Before its terminal divisions, the nerve gives off three, and sometimes four, small branches: one, the nerve to the stapedius muscle, before it leaves the skull, the others after it leaves the skull. The nerve to the stapedius is given off from the facial nerve as it descends in the posterior wall of the tympanum behind the pyramidal eminence. It is stated that filaments are also given off from the facial to the auditory artery (probably visceral motor from the glosso-palatine) while the nerve is passing through the internal auditory meatus. After it leaves the skull the facial nerve gives off two or three coll terai branches and its two terminal divisions, the temporo-facial and cervico-facial. The collateral branches are the posterior auricular nerve, a branch to the posterior belly of the digastric, and sometimes a lingual branch. (1) The posterior auricular nerve is the first branch of the extracranial portion of the facial nerve. It passes between the parotid gland and the anterior border of the sterno-mastoid muscle and runs upward in the deep interval between the external auditory meatus and the mastoid process. In this situation it communicates with the auricular branch of the vagus. It supplies the auricularis posterior, sends a slender twig upward to the am-ioularis superior, and ends in a long slender branch, the occipital branch, which passes backward to supply the occipitalis muscle. It also receives filaments from the small occipital and great auricular nerves, and supplies the intrinsic muscles of the auricle (pinna). (2) The nerve to the posterior belly of the digastric arises from the facial nerve close to the stylo-mastoid foramen and enters the muscle near its centre, or sometimes near its origin. It usually gives off two branches: the nerve to the stylo-hyoid, which sometimes arises directly from the facial nerve and passes to the upper part of the muscle that it supplies, and the anas- tomotic branch, which joins the glosso-pharyngeal nerve below its petrous ganglion. (3) The lingual branch, first described by CruveiUiier, is not commonly present. It arises a little below the nerve to the stylo-hyoideus and runs downward and medialward to the base of the tongue. In its course it passes to the medial sides of the stylo-glossus and stylo-pharyn- THE FACIAL NERVE 945 geus, and runs downward along the anterior border of the latter muscle to the wall of the pharynx. It pierces the superior constrictor, insinuates itself between the tonsil and the anterior piUar of the fauces, and it is stated that it gives filaments to the base of the tongue and to the stylo-glossus and glosso-palatinus (palato-glossus) muscles. The terminal divisions. — In the substance of the parotid gland the two terminal divisions of the facial nerve he superficial to the external carotid artery and to the posterior facial (temporo-maxillary) vein. The way in which these terminal divisions give off their branches varies much in different subjects and often on the opposite sides of the same subject. One of the more common forms is here described. The temporo-facial or upper division runs upward and forward, and, after receiving communicating twigs from the auriculo-temporal nerve, gives off tem- poral and zygomatic (malar) branches. The cervico -facial or lower division runs downward and forward, receives branches from the great auricular nerve, and Fig. 739. — The Right Facial Nekvb, within the Skull, and the Relations op the Glosso-palatine and Glosso-pharyngeal Nerves with the Tympanic and Internal Carotid Plexuses. (From Sobotta's Atlas, modified.) Tensor tympani muscle Deep petrosal nerve Auditory (Eustachian) tubi Superior carotico-tympanic n. Great superficial petrosal n Ramus anastomotic with tympanic plexus Geniculate gangli' Glosso-palatine n Stapes Facial n Tympanic sinus Stapedius muscl stapedius, nerve Maxillary nerve (lifted) ' Nerve of pterygoid canal (Vidian) Spheno-palatine ganglion Mastoid cells Chorda tympani Stylo-mastoid foramen Tympanic Petrosal ganglion of glosso pharyngeal ^ Nodosal ganghon of vagus . Superior cervical sympathetic ganghon gives off — (1) buccal branches, comprising what have been called infraorbital and buccal branches; (2) the marginal mandibular (supra-mandibular) branch; and (3) the ramus colli (infra-mandibular branch). These branches from the two terminal divisions anastomose freely to form the parotid plexus (pes anserinus). The temporal branches passing upward communicate freely with each other and with the zygomatic branches. They also communicate with the zygomatico-temporal branch of the zygomatic nerve (the orbital branch of the maxillary nerve) and with the supra-orbital nerve. They supply the frontalis, orbicularis oouli, corrugator supercilii, and auricularis anterior and superior (fig. 740). The zygomatic (malar) branches passing upward and forward, communicate with the buccal branches of the facial nerve; with the zygomatico-facial branch of the zygomatic nerve (the orbital branch of the maxillary nerve) ; with the supraorbital and lacrimal branches of the oph- thalmic nerve, and with the palpebral twigs of the maxillary. They supply both ej'ehds, the orbicularis oculi, and tlie zygomaticus (fig. 740). The buccal (infra-orbital and buccal) branches arise sometimes from the lower terminal division and sometimes from both the upper and the lower terminal divisions. The buccal branches, passing forward upon the masseter and underneath the zygomaticus and quadratus labii superioris, interlace with the zygomatic and marginal mandibular (supra-mandibular) branches of the facial nerve, with the buccinator (long buccal) branch of the trigeminus, and with the terminal branches of the maxillary nerve, forming with the last-named nerve the infra- orbital plexus. They supply the zygomaticus, risorius, quadratus labii superioris, caninus. 946 THE NERVOUS SYSTEM buccinator, inoisivi, orbicularis oris, triangularis, quadratus labii inferioris, and the muscles of the nose (fig. 740). The marginal mandibular (supra-mandibular) branch, passing downward and forward under cover of the risorius and the depressors of the lower hp, commimicates with the buccal branches and with the ramus colli of the facial nerve, and with the mental branch of the mandibular nerve. It supplies the quadratus labii inferioris and mentalis. The ramus colli (infra-mandibular branch) runs downward and forward under cover of the platysma, which muscle it innervates (fig. 740). Beneath the platysma it forms one or more communicating loops, near its commencement, with the great auricular nerve, and longer loops, lower down, with the superficial cervical nerve. Central connections. — The nucleus of origin of the facial in the rhombencephalon includes an anterior and a posterior group of cells which give rise respectively to its upper and lower ter- minal divisions. They are associated with the somaesthetic area (lower third of the anterior central gyrus) by way of the pyramidal fasciculi of the opposite and same sides, and with the nuclei of the other cranial nerves, including the nucleus of termination of the glosso-palatine, by way of the reticular formation and the medial longitudinal fasciculus. Fig. 740. — S"0pekpicial_ Distribution of the Facial and other Nerves of the Head. (After Hirschfield and Leveill(5.) Supra-orbital Palpebral twig of lacrimal Infratrochlear Temporal braacli of facial Zygomatic br. of facial Maxillary div. of trigeminus Posterior auricular Auriculo-temporal Lesser occipital Great auricular Cervical cutaneous GLOSSO-PALATINE NERVE The glosso-palatine nerve (sensory root or pars intermedia of facial, nerve of Wrisberg) contains both sen.sory and motor fibres. While it has a separate attachment to the medulla, it courses in close company with the facial and, in the internal auditory meatus, it is involved in the same sheath with the facial, which relation is maintained by its larger part thence through the facial canal till a short distance above the stylo-mastoid foramen. Here this larger part leaves the trunk of the facial as the chorda tympani nerve. The origin, central connec- tions and peripheral distribution of the glosso-palatine are similar to those of the THE GLOSSO-PALATINE NERVE 947 glosso-pharyngeal nerve and suggest that it may be considered an aberrant portion of that nerve. The sensory portion is much greater than the motor. Its fibres arise from cells situated in the geniculate ganglion which thus corresponds to a spinal ganglion. The central processes from these cells pass medialward in the facial canal (aqueduct of Fallopius) enclosed in the sheath of the facial nerve, which they leave in passing through the internal auditory meatus, to turn slightly downward in the posterior fossa of the cranium and enter the medulla at the inferior border of the pons, be- tween the attachments of the facial and vestibular nerves. They com-se through the reticular formation of the medulla, medianward and dorsalward to terminate about cells which comprise a superior extension of the nucleus of termination of the glosso-pharyngeal nerve (nucleus of ala cmerea). The peripheral processes from the geniculate ganglion are distributed chiefly to the epithelium covering the soft palate, portions of the glosso-palatine arches, and the anterior two thirds of the tongue. The geniculate ganglion is so named from the fact that it is embedded upon the anterior border of the external genu {geniculum, great bend) of the facial nerve, behind the hiatus Fallopii. It is somewhat triangular in form. From its supero- medial angle leave the central processes of its cells, the root of the nerve; from its infero-lateral angle leave the fibres which later leave the sheath of the facial as the chorda tympani, and its anterior angle is connected with the great superficial petrosal nerve (figs. 738 and 741). The geniculate ganglion contains a rel- atively large number of cell-bodies of sympathetic neurones many of whose processes run in this latter nerve, a relation mentioned below with the gangliated cephalic plexus. The motor portion of the glosso-palatine consists for the most part of visceral efferent fibres, chiefly secretory. These arise in the medulla oblongata from a small group of cells scattered in the reticular formation dorso-medial to the nucleus of the facial and in line with the dorsal efferent nucleus of the vagus below. It is called the salivaiory nucleus. The fibres course ventralward and lateralward to their exit, mingle with the entering sensory fibres of the glosso- palatine in the sheath of the facial and, through the branches of the glosso- palatine, pass to terminate in sympathetic ganglia of the head, large and small. These gangfia send axones which terminate in the smooth muscle of vessels and about the cells of the glands of the lingual and palatine mucous membrane and of the salivary glands proper. Some of the motor fibres of the nerve terminate in contact with the sympathetic cells remaining in the geniculate ganglion and which give rise to sympathetic fibres issuing from it. Most of the motor fibres pass into the great superficial petrosal nerve and the chorda tympani to terminate in (chiefly) or pass through the spheno-palatine and submaxillary ganglia re- spectivelJ^ Some may pass by the geniculo-tympanic branch and tympanic plexus to end in the otic ganghon. Many no doubt end in the smafler ganglia involved in the various sympathetic plexuses. It is suggested that the motor part carries secretory impulses destined chiefly for the sub-maxillary and sublin- gual glands. A small gangliated plexus on the capsule of the medial side of the parotid gland has been frequently dissected and found to communicate freely with twigs from the facial nerve and twigs concerned with the trigeminus. It is possible that some glosso-palatine visceral motor fibres terminate in these ganglia for secretory impulses to the parotid gland as well. Central connections. — The nucleus of termination of tlie glosso-palatine nerve (superior extension of the nucleus of termination of the sensory portion of the glosso-pharyngeal) is associated with the somffisthetic area of the cerebral cortex of the opposite and same sides by way of the medial lemniscus, and with the saUvatory nucleus and motor nuclei of other cranial nerves by way of the reticular formation and medial longitudinal fasciculus. The nucleus of origin of the motor portion (sahvatory nucleus) may be associated not only with the nucleus of termination of the sensory part, but with the nuclei of termination of other cranial nerves, and perhaps with the motor area of the cortex of the opposite side by way of the pjTamidal fascicuh. Branches and communications. — Aside from its two or three small collateral twigs of communication, the fibres of the glosso-palatine course in two main branches or nerves: (1) the great superficial petrosal nerve, continued through the Vidian nerve, and extended through and beyond the spheno-palatine ganglion as the palatine portion of the glosso-palatine (palatine nerve) ; (2) the chorda tym- 948 THE NERVOUS SYSTEM pani, the larger branch, which extends to join and contribute its quota of fibres to the lingual nerve, a branch of the trigeminus. In the internal auditory meatus, the glosso-palatine gives two delicate collaterals to the vestibular nerve, and some filaments (visceral motor probably) are described as given to the auditory artery and to the temporal bone. A small geniculo-tympanic branch is given, in the facial canal, from the geniculate ganglion to the small superficial petrosal nerve. This is probably aU visceral motor and sympathetic fibres (fig. 741). There may occur a twig arising from or near the beginning of the chorda tympani and form- ing a cormnunicatio?i vnih the auricular branch of the vagus. A large part of the great superficial petrosal nerve is formed of glosso-palatine fibres. This nerve is further described below in its relation to the spheno-palatine ganglion. It arises from the anterior angle of the geniculate ganglion, enters the middle fossa of the cranium through Fig. 741. — Diagram of the Glosso-palatine Nekve (Black) and the Relations op the Gangliated Cephalic Plexus to otheb Cbanial Nebves. (After Bean.) Broken Mnes, motor; continuous hues, S3'mpathetic; glosso-palatine in solid black. Medial view. Left side. Superior cervical sympathetic gangli Ciliary ganglion -- Ophthalmic nerve kw "\ X Maxillary nerve i\i) - - -V^N.^-- Mandibular nerve -\V -^V^V^^^-^-v^ Great deep jV ' \ ^^M~^ petrosal nerve '^\.\N^^^^~- Sphenopalatine 'A\'\\\rl^ ganglion Palatine portion of glosso-palatine nerve Nerve of pterygoid canal (Vidian nerve) Otic ganglion Middle meningeal . , artery ( Submaxillary ganglion External maxillary artery the hiatus FaUopii, and passes beneath the semilunar ganglion into the foramen lacerum, where it joins with the great deep petrosal nerve to form the Vidian nerve. Thence the glosso- palatine portion passes over or through the spheno-palatine ganglion to form the greater part of the small and middle palatine nerves which are distributed to the epithelium and glands of the soft palate, some of the sensory fibres probably terminating in the taste organs found there; the remainder serving as fibres of general sensibility. It is probable that most of the motor glosso-palatine fibres in the great superficial petrosal nerve terminate in the spheno-palatine ganglion; some may pass to the carotid plexus and to smaU gangUa elsewhere. The chorda tympani consists to a very large extent of sensory fibres (peripheral processes of the cells of the geniculate ganglion), but it also contains motor fibres and is thus also a mixed nerve. It leaves the trunk of the facial nerve a short distance above the stylo-mastoid foramen, and pursues a slightly recurrent course upward and forward in the canaliculus chorda tympani (iter chordae posterius), a minute canal in the posterior wall of the tympanic cavity, and it THE VESTIBULAR NERVE 949 enters that cavity close to the posterior border of the membrana tympani. It crosses the cavity, running on the medial surface of the tympanic membrane at the junction of its upper and middle thirds, covered by the mucous membrane lining the tympanic cavity, and passes to the medial Bide of the manubi-ium of the malleus above the tendon of the tensor tympani. It leaves the tympanic cavity and passes to the base of the skull through a smaU foramen (the iter chordae anterius) at the medial end of the petro-tympanic (Glaserian) fissure. At the base of the skull it inclines downward and forward on the medial side of the spine of the sphenoid, which it frequently grooves, and, on the medial side of the pterygoideus externus, it joins the posterior border of the hngual nerve at an acute angle. Some of its fibres (motor chiefly) leave the lingual nerve and pass to the sub-maxillary ganglion, and others (sensory) continue forward to the tongue, where, in company with fibres of the lingual nerve, they terminate in the epithehum covering the anterior two-thirds of the tongue. Some probably serve to convey sensations of taste, most of them are fibres of general sensibility. Before it joins the lingual nerve the chorda tympani receives a communicating twig from the otic ganglion (figs. 738, 741). THE VESTIBULAR NERVE The vestibular nerve is purely sensory. With the peripheral processes of its cells of origin terminating in the neuro-epithelium of the semicircular canals and Fig. 742. — The Left Membeanoits Labyrinth of a Human Fcetus-of lO Weeks (30 mm.), Lateral Aspect. Vestibular ganglion and nerve, red; cochlear nerve, yellow. (Streeter, American Journal of Anatomy.) a. 3omm. lateral. the vestibule, and their central processes conveying impulses which are dis- tributed to the gray substance of the cerebellum and spinal cord, the nerve com- prises a most important part of the apparatus for the equilibration of the body. It has been customary to describe the vestibular [radix vestibularis] and the coch- lear [radix cochlearis] nerves combined as the acoustic (auditory) or eighth cranial nerve. While the two are blended in a common sheath from near the medulla to the bottom of the internal auditory meatus, they are likewise partty enclosed in the same sheath with the facial and glosso-palatine nerves and the internal audi- tory artery which accompany them in this meatus. At the bottom of the meatus 950 THE NERVOUS SYSTEM the vestibular and the cochlear are separate; they are separate at their entrance into the lateral aspect of the medulla oblongata; and their central connections, peripheral distributions and functions are different. The vestibular nerve arises as processes of the cells of the vestibular ganglion (ganglion of Scarpa), situated upon and blended within the nerve at the bottom of the internal auditory meatus. Unlike the ordinary spinal ganglion, to which it corresponds, the cells of the vestibular ganglion retain an embryonal, "bipolar," form. The central processes course v/ith the cochlear nerve in the internal auditory meatus medialward, caudad and slightly downward, inferior to the accompanying' if acial and glosso-palatine nerves, and, arching ventrally around the restiform body, they enter the medulla at the inferior border of the pons, lat- eral to the glosso-palatine and facial and medial to the entrance of the cochlear nerve. They find their nucleus of termination spread in the floor of the fourth ventricle and grouped as the median, the lateral (Deiters'), the superior, and the nucleus of the spinal root of the vestibular nei've. In the internal auditory mea- tus, the vestibular nerve is connected by two small filaments of fibres with the glosso-palatine nerve. These are either visceral motor fibres for the vessels of the domain of the vestibular or are aberrant fibres which course only temporarily with the vestibular and return to the glosso-palatine. The peripheral processes of the cells of the vestibular ganglion terminate in the specialised or neuro-epithelium comprising the maculm in the sacculus and the utriculus and the cristce in the ampullte of the three semicircular canals. Thus there are five terminal branches of the nerve. None of its fibres terminates in the cochlea. The vestibular ganglion has a lobar form, one lobe giving rise to a superior utriculo-ampuUar division which divides into three terminal branches; the other giving a sacculo-ampuUar division which gives two terminals. The superior or utriculo -ampullar branch divides into the following terminal branches: — (1) The utricular branch passes through the superior macula cribrosa of the vestibule and terminates in the macula acustica of the utriculus. (2) Accompanying the utricular branch through the superior macula cribrosa is a branch, the superior ampuUar, to the crista acustica of the ampulla of the superior semicircular canal, and — (3) A similar branch, the lateral ampullar, to the ampulla of the lateral semicircular canal. The inferior or saccule -ampullar branch accompanies the cochlear nerve a short distance further than the superior, and divides into — (4) A branch, the posterior ampullar, which passes through the foramen singulare and the inferior macula cribrosa and tormiiiatcs in the ampulla of the posterior semicircular canal, and — (5) A branch, the saccular, which passes through the middle macula cribrosa and terminates in the macula acustica of the sacculus. The central connections of the vestibular nerve are described in detail on pages 823, 824. Its large nucleus of termination, spread through the area acustica in the floor of the fourth ventricle, and divided into four sub-nuclei, is associated with the nuclei fastigii, globosus, and emboliformis of the cerebellum, with the nuclei of the eye-moving nerves, with the spinal cord, and probably with the cerebral corte.x. THE COCHLEAR OR AUDITORY NERVE The fibres of the cochlear nerve are distributed to the organ of Corti in the cochlea, and so are considered as comprising the auditory nerve proper. They arise from the long, coiled spiral ganglion of the cochlea, the cells of which, like those of the vestibular ganglion, are bipolar. The peripheral processes of these cehs are shorter than those of the vestibular ganglion. They terminate about the auditory or hair-ceUs of the organ of Corti and thus collect impulses aroused by stimuli affecting these cells. The central processes of the ganglion cells continue through the modiolar canal and the tractus spiralis foraminosus of the cochlea, and thence, joining the vestibular nerve through the internal auditory meatus, accompanying the facial nerve and internal auditory artery, they course medial- ward and downward, approach and enclasp the restiform body (fig. 665) and enter the lateral aspect of brain-stem to terminate in their dorsal and ventral nuclei. A description of these nuclei and the further central connections of the cochlea with the superior olive, the nuclei of the eye-moving nerves, the inferior quadrigeminate bodies, the medial geniculate bodies, and with the cerebellum and temporal lobes of the cerebral hemispheres is given on pages 824, 839. THE GLOSSO-PHARYNGEAL NERVE 951 The cochlear nerve is separate from the vestibular at the bottom of the internal auditory meatus and at its entrance into the medulla. THE GLOSSO-PHARYNGEAL NERVE The glosso-pharyngeal or ninth cranial nerves are mixed nerves and each is attached to the medulla by several roots which enter the posterolateral sulcus, dorsal to the anterior end of the olivary body and in direct line with the facial nerve. The filaments, when traced lateralward, are seen to blend, in front of the flocculus, into a trunlc which hes in front of the vagus nerve, but which passes through a separate opening through the arachnoid and the dura mater and through the jugular foramen. In the foramen this trunk hes in front, and lateral to the vagus nerve in a groove on the petrous portion of the temporal bone; and in this situation two ganglia are interposed in it, a superior or jugular, and an inferior or petrosal. After it emerges from the jugular foramen the glosso-pharyngeal nerve descends at first between the internal carotid artery and the internal jugular vein and to the lateral side of the vagus; then, bending forward and medialward, it descends medial to the styloid process and the muscles arising from it, and turning around the lower border of the stylo-pharyngeus it passes between the internal and the external carotid arteries, crosses the superficial surface of the stylo-pharyngeus, and runs forward and upward medial to the hyoglossus muscle and across the middle constrictor and the stylo-hyoid ligament, to the base of the tongue (fig. 743). Ganglia. — The superior or jugular ganglion (ganglion of Ehrenritter), is a small, ovoid, reddish-grey body which lies on the back part of the nerve-trunk in the upper part of the jugular foramen. No branches arise from it. It is sometimes continuous with the petrosal ganglion or it may be absent. The inferior or petrosal ganglion, (ganglion of Andersch), is an ovoid grey body which lies in the lower part of the jugular foramen, and appears to include all the fibres of the nerve. Branches and communications. — (1) The petrosal ganglion is connected with the superior cervical ganglion of the sympathetic by a fine filament. (2) It also has a filament of communication with the auricular branch of the vagus which varies inversely in size with the latter branch and sometimes entirely replaces it. This filament may be absent. (3) An inconstant communication with the ganglion of the root of the vagus. (4) A short distance below the petrous gangUon the trunk of the nerve is connected by a twig with that branch of the facial nerve which supplies the posterior belly of the digastric muscle. There is also a small twig (probalily sensdryl to the stylo-hyoid. (5) From the petrosal ganglion : The tympanic branch (nerve of Jacobson) arises from the petrosal ganglion and passes through a foramen, which lies in the ridge of bone between the car- otid canal and the jugular fossa, into the tympanic canahculus (Jacobson's canal), where it is surrounded by a small, fusiform mass of vascular tissue, the iniumesceniia tympanica. After traversing the tympanic canaliculus it enters the tympanum at the junction of its lower and medial walls, and, ascending on the medial wall, breaks up into a number of branches which take part in the formation of the tympanic plexus on the surface of the promontory (fig. 739). The continuation of the nerve emerges from this plexus as the small superficial petrosal nerve, which runs through a small canal in the petrous portion of the temporal bone, beneath the canal for the tensor tympani, and appears in the middle fossa of the cranium through a foramen which lies in front of the hiatus Fallopii. From this foramen it runs forward and passes through the fora- men ovale, the canaliculus innominatus, or the spheno-petrosal suture, and enters the zygomatic fossa, where it joins the otic ganghon. While it is in tlie canal in the temporal bone the small superficial petrosal nerve is joined by a geniculo-tympanic branch from the geniculate gangUon of the glosso-palatine nerve. (6) Branches from the tympanic plexus : — (a) The tubal branch (ramus tubae), a dehcate branch, which runs forward to the mucous membrane of the tuba auditiva (Eustachian tube) and sends filaments backward to the region of the fenestra vestibuli (ovahs) and the fenestra cochleaj (rotunda). (6) The superior and inferior carotico-tympanic (carotid) branches pass medianward to the internal carotid plexus (fig. 741). The above communications carry fibres almost entirely concerned with the sympathetic plexuses of the head and they will be again mentioned below with the gangUated cephalic plexus. Branches from the trunk of the nerve : — (1) Pharyngeal branches, which may be two or three in number, arise from the nerve a short distance below the petrosal ganglion. The prin- cipal and most constant of these passes on the lateral side of the internal carotid artery, and after a very short independent course joins with the pharyngeal branch of the vagus and with branches of the superior cervical ganglion to form the pharyngeal plexus (fig. 743). 952 . THE NERVOUS SYSTEM (2) A muscular brancli is distributed to the stylo-pharyngeus muscle. This branch re- ceives a communication from the facial nerve (fig. 743). (3) The tonsillar branches are a number of small twigs which arise under cover of the hyo- glossus muscle; they proceed to the tonsil, around which they form a plexus, the circulus tonsillaris. From this plexus fine twigs proceed to the glosso-palatine arches (pillars of the fauces) and to the soft palate. (4) The lingual branches are the terminal branches of the nerve and supply the mucous membrane of the posterior half of the dorsum of the tongue, where, chiefly as taste-fibres, they are distributed to the vallate papillae. Some small twigs pass backward to the follicular glands of the tongue, and to the anterior surface of the epiglottis. Other twigs are distributed around the foramen officum, where they communicate with the corresponding twigs of the opposite side. The sensory fibres. — The sensory fibres of the glosso-pharyngeal nerve spring from the supe- rior and petrosal ganglia and pass peripherally and centrally. The peripheral processes of the ganglion cells are those which are distributed to the mucous membrane (taste-buds) of the tongue and pharynx, and the central processes pass medialward to the medulla. In the medulla they pass dorsalward and medianward through the reticular formation and, bifurcating into ascend- ing and descending branches, they end in the nucleus of termination of the glosso-pharyngeal nerve, that is, in the superior part of the nucleus alae cinereae and in the nucleus of the tractus solitarius. The motor fibres arise from the nucleus ambiguus in the lateral funiculus of the medulla, in fine with the nucleus of origin of the facial nerve. From this nucleus they pass at first dorsalward and then, turning lateralward, they emerge and join the sensory fibres and run with them in the trunk of the nerve (fig. 646). Van Gehuchten's observations point to the conclusion that one motor nucleus of the glosso- pharyngeal nerve is separate from and Kes above and to the medial side of the nucleus ambiguus, and that a portion of the nucleus of the ala cinerea is also a motor nucleus common to the glosso-pharyngeal and vagus nerves. It is quite probable that the former motor nucleus is that now considered as the dorsal motor nucleus of the vagus. An unknown proportion of the motor fibres are visceral motor and course in the various communications of the glosso- phar3mgeal nerve with cephalic plexus. Central connections. — The nuclei of termination of the glosso-pharyngeal nerve are asso- ciated with the motor nuclei of other cranial nerves by the medial longitudinal fasciculus, and with the somaesthetic area of the cortex cerebri of the opposite side by the medial lemniscus (fillet). The motor nucleus of the nerve is associated with the somaesthetic area by the pyra- midal fibres. THE HYPOGLOSSAL NERVE The hypoglossal nerves are exclusively motor; they supply the genio-hyoidei and the extrinsic and intrinsic muscles of the tongue except the glosso-palatini. They are usually designated as the twelfth pair of cranial nerves. The fibres of each nerve issue from the cells of an elongated nucleus which lies in the floor of the central canal in the lower half of the medulla and in the floor of the fourth ventricle in the upper half beneath the trigonum hypoglossi. This nucleus is the upward continuation of the ventro-medial group of cells of the ventral horn of the spinal cord. From their origin the fibres run ventralward and somewhat lateral- ward, probably joined in the medulla by a few fibres from the nucleus ambiguus which is a segment of the upward prolongation of the lateral group of cells of the ventral horn. The conjoined fibres issue from the medulla in the sulcus between the pyramid and the olivary body, in a series of from ten to sixteen root filaments, which pierce the pia mater and unite with each other to form two bundles (fig. 731). These bundles pass forward and lateralward to the hypoglossal (anterior condyloid) foramen, where they pierce the arachnoid and dura mater. In the outer part of the foramen the two bundles unite to form the trunk of the nerve. At its commencement, at the base of the skull, the trunk of the hypoglossus lies on the medial side of the vagus, but as it descends in the neck it turns gradually around the dorsal and the lateral side of the latter nerve, lying between it and the internal jugular vein, and a little above the level of the hyoid bone it bends for- ward, and crosses lateral to the internal carotid artery, the root of origin of the occipital artery, the external carotid, and the loop formed by the first part of the lingual artery (fig. 743). After crossing the lingual artery it proceeds forward on the lateral svnface of the hyo-glossus, crossing to the medial side of the posterior belly of the digastric, and the stylo-hyoid muscles. It disappears in the anterior part of the submaxillary region between the mylo-hyoid and the hyo-glossus, and divides into its terminal branches between the latter muscle and the genio-glossus. As it descends in the neck the trunk lies deeply between the internal jugular vein and the internal carotid artery under cover of the parotid gland, the styloid muscles, and the pos- terior beUy of the digastric, and it is crossed superficially by the posterior auricular and the occip- ital arteries. As it turns forward around the root of the occipital artery the sterno-mastoid branch of that vessel hooks downward across the nerve, and as it turns forward on the hyo- THE HYPOGLOSSAL NERVE 953 glossus muscle it lies immediately above the ranine vein. It is crossed by the posterior belly of the digastric and the stylo-hyoid muscle, and it is covered superficially, behind the mylo- hyoid, by the lower part of the submaxillary gland. Communications. — The hypoglossus is connected with the first cervical gan- glion of the sympathetic, with the ganglion nodosum of the vagus, with the loop between the first and second cervical nerves, and with the lingual nerve; the latter communication is established along the anterior border of the hyo-glossus muscle (figs. 743 and 744). Terminal branches. — These include (1) a meningeal branch; (2) branches from the cervical plexus; and (3) branches from the hypoglossus proper. (1) A meningeal branch, frequently represented by two filaments, is given off in the hypo- glossal (anterior condyloid) canal. It passes backward into the posterior fossa of the cranium and is distributed to the dura mater. It was believed at one time that the fibres of the meningeal branch were derived from the lingual nerve, but it is now deemed more probable that they are either sensory or visceral motor fibres from the cervical nerves, or from the vagus. Fig. 743. — The Hypoglossal, Glosso-phartngeal, and Lingual Nerves. (Spalteholz.) Ganglion nodosum Cut surface of the styloid process ._- Internal jugular vein Facial nerve (cut off) Spinal accessory (external branch ) Transverse proc- ess of atlas Anterior branch of first cervical Glosso- Internal pharyngeal carotid Semilunar nerve artery ganglion ^ Pharyn- r Of vagus Of glos- branches | fy^l^l{ Anterior branch of second cervical nerve 'Stylo -pharyngeal branch Stylo-pharyngeus Hypoglossal nerve External carotid artery Anterior branch of third cervical nerve Descendeus cervicalis (hypoglossi) Anterior branch of fourth cervical nerve Steruo-mastoideus i Ansa cervicalis (hypoglossi) Ophthalmic _ Maxillary nerve ' Mandibular — nerve Lateral plate — of pterygoid process ,, Chorda tympani ^ensor veli palatini Lingual nerve Buccinator Branches to isthmus of fauces ff- Stylo- glossus Vagus i Lingual branches of lingual nerve Sublingual nerve Anastomotic "^N-.branch to ., hypoglossal Genio-glossus Lingual branches \ \ of hypoglossal N Genio-liyoideus Hyoglossus Thyreo-hyoid branch Lingual artery Phrenic nerve ~ Superior thyreoid artery Thyreo-hyoideus Branch to the sterno-hyoideus Common carotid artery (2) Branches which consist of fibres derived from the cervical plexus. — The descendens cervicalis (hypoglossi) and the muscular twig to the thyi'eo-hyoid muscle, though apparently arising from the hypoglossal nerve, consists entirely of fibres which have passed into the hypo- glossal nerve from the loop between the first two cervical nerves. Therefore, neither of them are branches of the hypoglossus proper. (See fig. 752.) (a) The descendens cervicalis (hypoglossi) parts company with the hypoglossus at the point where the latter hooks around the occipital artery (fig. 743). It runs downward and slightly medialward on the sheath of the great vessels (occasionally within the sheath), and is joined at a variable level by branches from the second and third cervical nerves, forming with them a loop, the cervical loop [ansa hypoglossi] (fig. 743). The cervical loop rnay be placed at any level from a point immediately below the occipital artery to about four centinietres above the sternum. From this loop aU the muscles attached to the hyoid bone are supphed. A twig to the anterior belly of the omo-hyoid arises from the descendens cervicalis in the upper part of its course. The nerves which supply the sterno-hyoid, sterno-thyreoid, and posterior belly of the omo- hyoid are given off by the cervical loop. Twigs from the first two nerves pass downward in the muscles behind the manubrium sterni and •in rare cases communicate with the phrenic 954 THE NERVOUS SYSTEM nerve within the thorax. The nerve to the posterior belly of the omo-hyoid runs in a loop of the cervical fascia below the central tendon of the muscle. (b) The nerve to the thyreo-hyoid leaves the hypoglossus near the tip of the great cornu of the hyoid bone, and runs obhquely downward and medialward to reach the muscle. AU the fibres in (a) and (b) are derived from the first, second and third cervical nerves. (c) The nerve to the genio-hyoid arises under cover of the mylo-hyoid, where loops are formed with the lingual nerve from which loops branches pass into the muscle. It probably contains some true h}fpoglossal fibres. (3) The branches of the hypoglossus proper, the rami linguales, supply the stylo-glossus, hj'O-glossus, genio-glossus, and the intrinsic muscular fibres of the tongue. The nerve to the stylo-glossus is given off near the posterior border of the hyo-glossus. It pierces the st3'lo-glossus, and its fibres pursue a more or less recurrent course within the muscle. The nerves to the hyo-glossus are several twigs which are supphed to the muscle as the hypoglossal nerve crosses it. The nerve to the genio-glossus arises under cover of the mylo-hyoid in common with the ter- minal branches to the intrinsic muscles of the tongue. It communicates freely with branches of the lingual, forming long loops which lie on the genio-glossus. From these loops twigs pass into the genio-glossus and into the muscular substance of the tongue. Central connections. — The nucleus of origin of the hypoglossus is associated with the som- Eesthetic area (operculum) of the cortex cerebri of the opposite side by the pyramidal fibres, and it is connected with the sensory nuclei (nuclei of termination) of other cranial nerves by way of the reticular formation and the medial longitudinal fasciculus. THE VAGUS OR PNEUMOGASTRIC NERVE The vagus or pneumogastric nerves are the longest of the cranial nerves, and they are remarkable for their almost vertical course, their asymmetry, and their extensive distribution, for, in addition to supplying the lung and stomach, as the name ' pneumo-gastric ' indicates, each nerve gives branches to the external ear, the pharynx, the larynx, the trachea, the oesophagus, the heart, and the abdominal viscera. They are commonly referred to as the tenth pair of cranial nerves. Each nerve is attached to the side of the medulla, in the postero-lateral sulcus, dorsal to the olivary body, by from twelve to fifteen root filaments which are in linear series with the filaments of the glosso-pharyngeal nerve. The filaments contain both sensory and motor fibres. They pierce the pia mater, from which they receive sheaths, and, traced outward, they pass into the posterior fossa of the cranium toward the jugular foramen and unite to form the trunk of the nerve, which passes through openings in the arachnoid and the dtira mater which are common to it and to the spinal accessory nerve. In the jugular foramen a small spherical ganglion, the jugular ganglion (ganglion of the root) , is interposed in the trunk which here turns at right angles to its former course and descends through the neck. As it leaves the jugular foramen it is joined by the internal or accessory portion of the spinal accessory nerve, and immediately below this junction it enters a large ovoid ganglion, the ganglio7i nodosum or ganglion of the trimk (fig. 743). As it descends through the neck the nerve passes ventral and somewhat lateral to the superior cervical sympathetic ganglion, and in front of the longus capitis and longus colh, from which it is separated by the prevertebral fascia. In the upper part of the neck it is placed between the internal carotid artery and the internal jugular vein, and on a plane dorsal to them, the artery being ventral and mesial, and the vein ventral and lateral. In the lower part of the neck it occupies a similar position in regard to the common carotid artery and the internal jugular vein, and the three structures are enclosed in a common sheath derived from the deep cervical fascia, but within the sheath each structure occupies a separate compartment (fig. 743) . In the root of the neck and in the thorax the relations of the nerves of the two sides of the body differ somewhat, and they must, therefore, be considered separately. The right vagus passes in front of the first part of the right subclavian artery in the root of the neck and then descends in the thorax, passing obliquely downward and backward on the right of the trachea, and behind the right innominate vein and the superior vena cava, to the back of the root of the right lung. Just before it reaches the right bronchus it lies close to the medial side of the vena azygos as the latter hooks forward over the root of the lung. At the back of the right bronchus the right vagus breaks up into a number of branches which join with the branches of tlie sympathetic to form the right posterior pulmonary plexus, and from this plexus it issues in'the form of one or more cords, combined .sensory, visceral motor and sympathetic, which de- scend on the cesophagus and break up into branches which join with branches of the left vagus, forming the posterior oesophageal plexus. At the lower part of the thorax fibres of this plexus become again associated in one trunk which passes througli the diaphragm on the posterior THE VAGUS NERVE 955 surface of the oesophagus, and is distributed to the posterior surface of the stomach and to the coeliac (solar) plexus and its offsets. The left vagus descends through the root of the neck between the carotid and subclavian arteries and in front of the thoracic duct. In the upper part of the superior mediastinum it ia crossed in front by the left phrenic nerve, and in the lower part of the same region it crosses in Fig. 744. — Diagram of the Branches of the Vagus Nerves. Auricular branch Meningeal branch Ganglion of root Spinal accessory nerve ' Hypoglossal nerve Loop between first two cervical External carotid artery Cardiac branch from recurrent nerve Thoracic cardiac branch (right vagus) Hepatic plexus Coeliac plexus front of the root of the subclavian artery and the arch of the aorta and behind the left superior intercostal vein. Below the aortic arch it passes behind the left bronchus and divides into branches which unite with twigs of the sj'mpathetic to form the left posterior pulmonary plexus. Prom this plexus the fibres of the left vagus issue as one or more cords that break up into anas- tomosing branches to form the anterior oesophageal plexus. At the lower part of the thorax this plexus becomes a single trunk, which passes through the diaphragm on the anterior surface of the oesophagus, and it is distributed to_the anterior surface of the stomach and tothe liver. 956 THE NERVOUS SYSTEM The jugular ganglion (ganglion of the root) is a spherical grey mass about five miUimetres in diameter which lies in the jugular foramen (fig. 744). It is connected with the spinal accessory nerve and with the superior cervical sympa- thetic ganglion, and it gives off an auricular branch, by means of which it becomes associated with the facial and glosso-pharyngeal nerves, and a recurrent meningeal branch. The ganglion nodosum (ganglion of the trunk) lies below the base of the skull and in front of the upper part of the internal jugular vein. It is of flattened ovoid form and about seventeen miUimetres long and four millimetres broad (figs. 744 and 743). It is joined by the accessory part of the spinal accessory nerve, and is associated with the hypoglossal nerve, with the superior cervical ganglion of the sympathetic, and with the loop between the first two cervical nerves, and it gives off a pharyngeal, a superior laryngeal, and a superior cardiac branch. Both ganglia and especially the nodosal retain numerous cell-bodies of sympathetic neurones and the twigs issuing from the ganglia thus contain sympa- thetic fibres. The greater part of the cell-bodies are of sensory neurones. Communications. — The vagus nerve is connected with the glosso-pharyngeal, spinal accessory and hypoglossal nerves, with the sympathetic, and with the loop between the first and second cervical nerves. (1) Two communications exist between the vagus and glosso-pharyngeal nerves: one between their trunlis, just below the base of the skull, and one, in the region of their gangha, consisting of one or two filaments. When two filaments are present one passes from the jugular gangUon and the other from the auricular nerve to the petrosal ganghon of the glosso-pharyngeal nerve. Either or both of these filaments may be absent. (2) Two twigs pass from the spinal accessory nerve to the ganglion nodosum, and at a lower level the accessory part of the spinal accessory nerve also joins the same gangUon (fig. 744). The majority of the fibres of the accessory part of the spinal accessory nerve merely pass across the surface of the ganglion and are continued into the pharyngeal and superior laryngeal branches of the vagus, but a certain number blend with the trunk of the vagus and are continued into its recurrent laryngeal and cardiac branches. (3) Two or three fine filaments connect the ganghon nodosum with the hypoglossal nerve as the latter turns around the lower part of the gangUon (fig. 744). (4) Fibres pass from the superior cervical ganghon of the sympathetic to both ganglia of the vagus (fig. 744). (5) A twig sometimes passes from the loop between the first two cervical nerves to the gangUon nodosum (fig. 744). Terminal branches. — These are the meningeal, auricular, pharyngeal, superior laryngeal, recurrent (inferior laryngeal), cardiac, bronchial, pericardial, oesopha- geal, and the abdominal branches. (1) The meningeal or recurrent branch is a slender filament which is given off from the jugular ganglion. It takes a recurrent course through the jugular foramen, and is distributed to the dura mater around the transverse (lateral) sinus. (2) The auricular branch, or nerve of Arnold, arises from the jugular gangUon in the jugular foramen. It receives a branch from the petrosal gangUon of the glosso-pharyngeal, enters the petrous part of the temporal bone through a foramen in the lateral wall of the jugular fossa, and communicates with the facial nerve or merely Ues in contact with it as far as the stylo- mastoid foramen. It usually leaves the temporal bone by the stylo-mastoid foramen, but it may pass through the tympano-mastoid fissure, and it divides, behind the pinna, into two branches, one of which joins the posterior auricular branch of the facial while the other suppUes sensory fibres to the posterior and inferior part of the external auditory meatus and the back of the pinna. It also suppUes twigs to the osseous part of the external auditory meatus and to the lower part of the outer surface of the tympanic membrane. (3) The pharyngeal branches may be two or three in number. The principal of these joins the pharyngeal branch of the glosso-pharyngeal on the lateral surface of the internal car- otid artery, and after passing with the latter medial to the external carotid artery it turns downward and medialward to reach the posterior aspect of the pharynx. Here the two nerves are joined by branches from the superior cervical ganglion of the sympathetic, with which they form the pharyngeal plexus (figs. 743, 744). Branches from this plexus supply sensory fibres to the mucous membrane of the pharynx and motor fibres to the constrictores pharyngis, levator palatini, uvulae, glosso-palatinus, and pharyngo-palatinus. (4) The superior laryngeal nerve arises from the lower part of the ganghon nodosum, and passes obliquely downward and medialward behind and medial to both internal and external carotid arteries toward the larynx. In this course it describes a curve with the convexity downward and lateralward and divides into (i) a larger internal and (ii) a smaller external branch (fig. 744). Before its division it is joined by twigs with the sympathetic and with the pharyngeal plexus, and it gives a small branch to the internal carotid artery. THE VAGUS NERVE 957 (a) The internal branch accompanies the superior laryngeal artery to the interval between the upper border of the thyreoid cartilage and the great cornu of the hyoid bone. It passes under cover of the thyreo-hyoid muscle and pierces the hyo-thyreoid membrane to gain the interior of the pharynx, where it hes in the lateral wall of the sinus piriformis and divides into a number of diverging branches. The ascending branches supply the mucous membrane on both surfaces of the epiglottis, and probably that of a small part of the root of the tongue. The descending branches ramify in the mucous membrane lining the larjmx, and supply the mucous membrane which covers the back of the cricoid cartilage. One of the descending branches passes downward on the internal muscles of the larynx to anastomose with the terminal part of the inferior (recurrent) laryngeal nerve. (b) The external branch runs downward on the inferior constrictor to the lower border of the th}Teoid cartilage, where it ends, for the most part, in the crico-thyreoid muscle. A few filaments pierce the crico-thyreoid membrane and are distributed to the membrane lining the larynx. It occasionally gives off a cardiac branch which joins one of the cardiac branches of the sympathetic; it also furnishes twigs to the inferior constrictor, and communicating twigs to the pharyngeal plexus, and it receives a communication from the superior cervical gangUon of the sympathetic. (5) The recurrent (inferior or recurrent laryngeal) nerve of the right side arises from the vagus at the root of the neck in front of the right subclavian artery. It hooks around the artery, passing below and then behind that vessel, and runs upward and slightly medialward, crossing obliquely behind the common carotid artery (fig. 744). Having gained the side of the trachea, it runs upward in the groove between the trachea and the CBsophagus, accompanying branches of the inferior thja-eoid artery, and, near the level of the lower border of the cricoid car- tilage, becomes the inferior laryngeal nerve. In its course the right recurrent nerve gives off branches to the trachea, cesophageal branches to the ojsophagus and pharynx, and, near its commencement, one or more inferior cardiac branches. It communicates with the inferior cervical sympathetic ganghon and with the superior laryngeal nerve. The inferior laryngeal nerve, the continuation of the recurrent, ascends between the trachea and oesophagus, enters the larynx under cover of the inferior constrictor of the pharynx, and divides into two branches, anterior and posterior. The anterior branch passes upward and for- ward on the crico-arytajnoideus lateralis and thyreo-arytajnoideus, and supplies these muscles and also the vocalis, arytsenoideus obliquus, ary-epiglotticus, and thyreo-epiglotticus. The posterior branch, passing upward, supplies the crico-arytaenoideus posterior and arytsenoideus obliquus, and anastomoses with the medial branch of the superior laryngeal nerve. On the left side the recurrent nerve arises in front of the aortic arch and winds around the concavity of the arch lateral to the ligamentum arteriosum. It crosses obliquely behind the root of the left common carotid artery, gains the angular interval between the oesophagus and trachea, and corresponds with the nerve of the right side in the remainder of its course and distribution (fig. 744). (6) Cardiac branches. — Of these branches of the vagus, there are two sets, the superior and inferior. All the branches of both sets pass to the deep part of the cardiac plexus except a superior branch on the left side that passes to the super- ficial part of the cardiac plexus. All contain visceral motor, sympathetic and sensory fibres. (a) The superior (superior and inferior cervical) cardiac nerves arise from the vagus and its branches in the neck (figs. 744, 786). Some of these branches on both sides join with the cardiac branches of the sympathetic in the neck and pass with them to the cardiac plexus. Some on the right side pass independently through the thorax to the deep part of the cardiac plexus, and a branch on the left side passes through the thorax to the superficial part of the cardiac plexus. (b) The inferior (thoracic) cardiac branches. — These branches on the right side arise in part from the recurrent nerve and in part from the main trunk of the vagus, while on the left side they usually arise entirely from the recurrent. AU these branches pass to the deep part of the cardiac plexus (figs. 744, 786). (7) The bronchial (pulmonary) branches are anterior and posterior (fig. 744) . (a) The anterior bronchial (pulmonary) branches consist of a few small branches which arise at the upper border of the root of the lung. They pass forward to gain the anterior aspect of the bronchus, where they communicate with the sympathetic and form the anterior pulmonary plexus, from which fine twigs pass along the bronchus. (b) The posterior bronchial (pulmonary) branches. — Almost the entire remaining trunk of the vagus usuallj' divides into these branches, which join with branches from the second, third, and fourth thoracic ganglia of the sympathetic to form the posterior pulmonary plexus (fig. 744). The plexuses of the two sides join freely behind the bifurcation of the trachea, and branches from the plexus pass along each bronchus into the lung. (8) The pericardial branches pass from the trunk of the vagus or from the bronchial or oesophageal plexuses to the anterior and posterior surfaces of the pericardium. They are chiefly sensory. 958 THE NERVOUS SYSTEM (9) CEsophageal branches, given off by the trunk of the nerve above the bronchial plexuses and from the oesophageal plexuses lower down, pass to the wall of the oesophagus. (10) Abdominal branches. — The terminal part of the left vagus divides into many branches, some of which communicate freely along the lesser curvature of the stomach with filaments from the gastric plexus of the sympathetic, and to some extent with branches of the right vagus, to form the elongated anterior gastric plexus (fig. 744). From this plexus as well as from the nerve-trunk, gastric branches are given to the anterior surface of the stomach. Hepatic branches from the trunk or from this plexus pass in the lesser omentum to the hepatic plexus (fig. 744). The terminal part of the right vagus divides into many branches, and forms along the lesser curvature of the stomach an elongated posterior gastric plexus by communications with branches from the gastric plexus of the sympathetic and with branches from the right vagus. Gastric branches are given off by the trunk of the nerve and from this plexus. Coeliac branches are given by the trunk to the cceliac (solar) plexus, and splenic and renal branches, either directly or through the coeliac (solar) plexus, are given to the splenic and renal plexuses (fig. 744) . Central connections. — The sensory fibres of the vagus are processes of the cells of the jugular ganglion and the ganglion nodosum. The peripheral fibres from these cells bring in sensory impulses from the periphery, and their central fibres convey the impulses to the brain. The latter fibres enter the medulla in the filaments of attachment in the postero-lateral sulcus, and, in the reticular formation, they bifurcate into ascending and descending branches which end in the nuclei of termination of the vagus, namely, in the nucleus alae cinerese in the floor of the fourth ventricle and in the nucleus tractus solitarii. The tractus solitarius consists largely of the descending branches. These and the axones arising from the nuclei of termination of the vagus descend the spinal cord to terminate about ventral horn cells which give origin to the phrenic nerve and to motor fibres supplying other muscles of respiration, and they also convey impulses which are distributed to visceral motor neurones along the spinal cord. The motor fibres spring from the nucleus ambiguus and from the dorsal efferent (motor) nucleus of the vagus, described on page 820. They join the sensory fibres in the reticular formation. Some of the motor fibres, especially those from the dorsal efferent nucleus, are visceral motor fibres. The central connections of the vagus are similar to those of the glosso-pharyngeal nerve (fig. 647). Van Gehuchten's observations point to the conclusion that the chief nucleus of termination of the vagus nerve is that of the tractus solitarius. THE SPINAL ACCESSORY NERVE The spinal accessory nerve [n. accessorius] is exclusively motor. It consists of two parts, the accessory or superior, and the spinal or inferior part. The fibres of the accessory or superior portion [ramus internus] ("accessory vagus") spring chiefly from the inferior continuation of the nucleus ambiguus, in common with the motor fibres of the vagus above, and they pass through the reticular formation to the postero-lateral sulcus of the medulla, where they emerge as a series of filaments, below those of the vagus. The filaments pierce the pia mater and unite, as they pass outward in the posterior fossa of the cranium, to form a part of the nerve which enters the apertm-e in the dura mater common to the vagus and spinal accessory nerves. In the aperture this trunk is joined by the spinal portion of the nerve. The spinal or inferior portion [ramus externus] arises from the ventro-lateral cells of the ventral horn of the cord as low as the fifth, and rarely the seventh, cervical nerve. The fibres pass dorsalward and lateralward from their origins through the lateral part of the ventral horn and through the lateral funiculus of white substance, and they emerge from the lateral aspect of the cord behind the ligamentum denticulatum, along an oblique line, the lower fibres passing out immediately dorsal to the ligament, and the upper close to and sometimes in association with the dorsal roots of the upper two spinal nerves. As the spinal fibres pass out of the surface of the cord they unite to form an ascending strand which enters the posterior fossa of the cranium, through the foramen magnum, and, turning lateralward, blends more or less intimately with the accessory por- tion. Thus combined, the nerve enters the jugular foramen in company with the vagus, but here it is again separated into its two branches, which contain chiefly the same fibres as the original superior and inferior parts. The superior branch, or accessory portion of the nerve, gives one or more filaments to the jugular ganghon (ganglion of the root of the vagus), and then joins either the trunk of the vagus directly or its ganglion nodosum, the fibres of the branch being contributed to the pharyngeal, laryngeal, and cardiac branches of the vagus. Fibres corresponding to the white rami communi- cantes, absent in the cervical nerves, probably enter the cervical sympathetic ganglion through this ramus of the spinal accessory nerve. The fibres from the accessory to the vagus therefore probably include visceral motor and cardio-inhibitory fibres. The inferior branch or the spinal portion runs backward and downward under cover of the posterior belly of the digastric and the sterno-mastoid. It usually crosses in front of and to the lateral side of the internal jugular vein and between it and the occipital artery; then it GANGLIATED CEPHALIC PLEXUS 959 pierces the slerno-mastoid, supplies filaments to it, and interlaces in its substance with branches of the Second cervical nerve. It emerges from the posterior border of the sterno-mastoid slightly above the level of the upper border of the thyreoid cartilage, passes obliquely downward and backward across the occipital portion of the posterior triangle, and disappears beneath the trapezius about the junction of the middle and lower thirds of the anterior border of that muscle (fig. 743). In the posterior triangle it receives communications from the third and fourth cervical nerves, and beneath the trapezius its fibres form a plexus with other branches of the same nerves. Its terminal filaments are distributed to the trapezius and they can be traced almost to the lower extremity of that muscle. Central connections. — The nuclei of origin, like other motor nuclei, are connected with the somsesthetic area of the cerebral cortex of the opposite side by the pyramidal fibres, and they are associated with the sensory nuclei of other cranial nerves by the medial longitudinal fasciculus, and with sensations brought in by the spinal nerves by the fibres of the fasciculi proprii. THE GANGLIATED CEPHALIC PLEXUS The Sympathetic Ganglia of the Head and Their Associations with THE Cranial Nerves The sympathetic system of the head, like that of the remainder of the body described below, is arranged in the form of a continuous gangHated plexus subdi- vided into sub-plexuses. Unlike the great unpaired prevertebral plexuses in the thoracic and abdominal cavities, all the larger sympathetic ganglia of the head are paired, gangha corresponding to each other being found on either side. Thus they may be considered as an upward extension of the series of paired lumbar, thoracic and cervical ganglia belonging to the sympathetic trunks lying along either side of the vertebral column. Numerous small ganglia, many of them microscopic, occur in the sub-plexuses throughout the head. These are irregular in size and position and those in the region of the median line are no doubt unpaired. In origin, the ganglia of the cephalic plexus consist of cell-bodies which, in the early stages of development, migrated from the fundaments of the ganglia of the vagus, glosso-phar3mgeal and glosso-palatine nerves, and most especially from that of the semilunar (Gasserian) ganglion of the trigeminus — a developmental relation identical with that of the remainder of the sym- pathetic system to the ganglia of the spinal nerves. Just as is known for the spina! ganglia, some cell-bodies destined to develop into sympathetic neurones, instead of migrating, remained within the confines of the ganglia of the above nerves, in company with the cell-bodies of their sensory neurones. This is thought to be especially true for the geniculate, the petrosal and the jugular ganglion. Therefore these ganglia must be considered as in small part sympathetic ganglia. The gangliated cephalic plexus could properly be included as a division of the general sym- pathetic system described later. However, because its larger ganglia are so intimately asso- ciated with branches of the oculomotor, trigeminal, masticator, glosso-palatine, glosso-pharyngeal and vagus nerves, it is customary to describe it in connexion with the cranial nerves. The larger ganglia, one on either side of the head, comprise the ciliary ganglion, the spheno-palatine (Meckel's) ganghon, the otic and the submaxillary ganglion. To these must be added portions of the geniculate, petrosal, jugular and the gan- ghon nodosum, and a part of the superior cervical sympathetic ganglion. The chief relations of the gangliated cephalic plexus to the cranial nerves are shown in fig. 741. The so-called roots and branches of the ganglia carry three varieties of fibres: (1) Sensory, (2) Motor (visceral motor or preganglionic), and (3) Sympathetic. Most roots and branches are mixed, the name of a root being determined only by the variety of fibres predominating in it. A bundle of sensory fibres going to a ganghon is called its sensory root. Such, however, cannot comprise a true root since none of its fibres arises in the ganghon and very few or none may terminate in it. The only sensory fibres terminating in a ganghon are the few which may ap- proach it in any of the roots to terminate in its capsule or the capsules of its cells and convey impulses of general sensibility from the ganghon to the central nervous system. Almost all of the fibres of a "sensory root" merely pass around or through a ganglion and into its branches beyond, which they borrow as paths for reaching their allotted fields of distribution. In this relation it should be realized that while the cihary, spheno-palatine, otic and submaxillary ganglia are customarily described under the discussion of the trigeminus, this nerve has func- tionally less to do with them than any of the other cranial nerves with which they are associated. Bundles of trigeminal (sensory) fibres, traceable in gross anatomy because meduUated and of appreciable size, pass to the gangha, but only to pass through them as continuations of the ter- minal branches of the trigeminus. The so-called motor root of a ganglion may carry two kinds of fibres: (a) visceral motor (preganglionic) fibres, arising in the nuclei of origin in the central system and passing in the trunk 960 THE NERVOUS SYSTEM and branches of a cranial nerve (oculomotor, masticator, etc.) to enter and terminate in contact with the ceU-bodies of the ganglion, which, in their turn, give fibres to the branches of the gang- lion; (b) fibres of the same origin, name and course but which may pass thi-ough the ganglion to terminate in contact with the cells of a more distant ganglion. Any root, the motor especially, may contain somatic motor fibres, that is, fibres of central origin which pass through the gang- lion uninterrupted and into its branches to terminate upon the fibres of skeletal (voluntary) muscle. A sympathetic root likewise may carry two and perhaps three varieties of fibres conforming to the name: (a) fibres arising from the cells of other sympathetic gangha and terminating in the ganghon in question; (b) fibres arising in other ganglia which pass through the gangfion in question to enter its branches and terminate either in other ganglia or upon their allotted mus- cular or glandular elements. A third is the fibre of the sensory sympathetic neurone, probably quite rare, which may arise from a cell-body in the ganglion and pass centralward in its root and in the appropi'iate cranial nerve to terminate about a cell-body of the dorsal-root or spinal gang- hon type, the central process of which latter conveys this sensory impulse of sympathetic origin into the central system just as sensory oranio-spinal impulses are conveyed. Fig. 745. — Diagram to Illtjsteate the Sthtjctural Relations op the Roots and BsANCHES OF A CEPHALIC SYMPATHETIC GANGLION. Sensory fibres, blue; motor, red; sympathetic, black. Sensory fibre terminating in capsule of ganglion and capsule of its cells Sensory root Sympathetic root Branches of distribution The branches of distribution of the gangha, the larger of them often called nerves, are those bundles in which the fibres, both arising in or passing through the gangha, course toward their terminations upon their allotted tissue elements of the head. The larger gangha of the head are described as each possessing the three roots above mentioned. In the branches pass fibres motor to the vessels of the head, to the intrinsic muscles of the eye bulb, to the [lacrimal glands, the mucous membranes (gland cells) of the nasal and oral cavities and the salivary glands, and sensory fibres conveying impulses from these structures. The plexuses into which the gangliated cephalic plexus is divided and which connect the ganglia to form it, are numerous and vary greatly in size. They underlie the mucous membranes and they surround all the vessels and glands. They are named according to their locahty. The largest of them are the tympanic plexus and the carotid and cavernous plexuses. They have been repeatedly referred to in their relations to the branches of the cranial nerves. Of the numerous branches described from the superior cervical sympathetic ganglion, the two large ones which pass upward associate it especially with the gangliated cephalic plexus. That branch known as the internal carotid nerve may be considered as the direct continuation upward of the gangUated sympathetic trunk of the body. Through the branches of this, the carotico-tympanic and the deep petrosal nerves, and through the plexuses derived from it, the superior cervical ganghon may be associated with practically all the other sympathetic gangha of the head (figs. 7.39 and 741). The other branch from the superior cervical ganghon, the jugular nerve, associates it with the ganglia of the glosso-pharyngeal and vagus nerves, with the petrosa ganghon by a direct branch and with the gangha of the vagus through the nodosal plexus. These latter gangha (and the nerves to which they belong) are connected, chiefly by THE CILIARY GANGLION 961 way of the tympanic nerve, which is from the petrosal ganghon, with the tympanic plexus (fig. 741). The tympanic plexus serves as a common point of distribution of fibres from the superior cervical sympathetic ganglion, the gangha of the vagus, the petrosal ganghon, and the geniculate ganglion, to the cavernous and carotid plexuses and to the spheno-palatine and otic gangha. The superior cervical ganglion is associated with the cavernous and carotid plexuses direct by the internal carotid nerve and with the tympanic plexus by the Inferior and superior carotico- tympanic nerves. The tympanic plexus receives fibres from the geniculate ganghon by a small geniculo-tympanic branch and it is connected with the spheno-palatine ganghon by a small anastomotic or tympano-petrosal branch to the great superficial petrosal nerve, and with the otic ganglion by the small superficial petrosal nerve. It is not directly connected with either the cihary or the submaxillary ganglion. However, these ganglia, as well as the sphenopalatine and otic, are connected with the carotid plexus either directly by named branches or indirectly by way of plexuses derived from the carotid. The geniculo-tympanic branch, the tympanic nerve and twigs of the nodosal plexus may be considered as analogous to the rami oommunicantes of^the spinal nerves. The parotid branches, described above as branches of the auriculo-temporal nerve (from the trigeminus) and as containing fibres from the glossopharyngeal, should be mentioned here as belonging to the gangliated cephalic plexus. These branches are sympathetic fibres arising in the otic ganglion and passing as branches of the ganglion to the auriculo-temporal in which they remain till this nerve enters the parotid gland and then they are distributed to the gland. The visceral motor or preganglionic fibres which terminate about their cells of origin in the otic ganglion are derived from the glosso-pharyngeal nerve and pass successively through the tym- panic nerve, the tympanic plexus, and the small superficial petrosal nerve to the otic ganglion. The tympanic nerve (tympanic branch of the glosso-pharyngeal, or nerve of Jacobson), the branch to the Eustachian tube (ramus tubes), and the superior and inferior carotico-lympanic branches are also described as branches of the glosso-pharyngeal nerve. These must hkewise be considered as belonging to the gangliated cephahc plexus. For purposes of dissection, it may be more expedient to consider separately, with its roots and branches, each of the larger ganglia of the gangliated cephalic plexus. Under this heading belong in part the geniculate ganglion of the glosso- palatine nerve, and the ganglia of the glosso-pharyngeal and vagus, especially the petrosal ganglion of the former and the jugular ganglion of the latter, from the fact that these ganglia contain numerous cell-bodies of sympathetic neurones as well as those of the sensory neurones of their nerves. These ganglia, however, have been described with their corresponding cranial nerves. The sensory and motor roots of their sympathetic portions are contained in the roots of their nerves. The geniculate probably has no sympathetic root. The sympathetic roots of the petrosal and jugular ganglia are contained in the branches of the jugular nerve. The chief branches of distribution of the geniculate are the geniculo-tympanic branch, the great superficial petrosal nerve, and the external superficial petrosal nerve. The branches of the petrosal ganghon are the tympanic nerve and its branches of the tympanic plexus. The chief branch of distribution from the jugular ganglion is contained in the auricular branch of the vagus, or nerve of Arnold, supplemented by sympathetic fibres in the trunk of the vagus itself. The principal cephalic sympathetic ganglia are the ciliary, the spheno-palatine (Meckel's), the otic and the submaxillary. The Ciliary Ganglion The ciliary, lenticular, or ophthalmic ganglion lies in the posterior part of the orbital cavity, about 6 mm. in front of the superior orbital (sphenoidal) fissure, to the lateral side of the optic nerve, and between the optic nerve and the external rectus muscle. It is a small, reddish, quadrangular body, compressed laterally, and it measures about two millimetres from before backward (fig. 734). Roots. — (o) Its motor or short root enters its lower and posterior angle and is a visceral motor branch derived from the branch of the inferior division of the oculomotor nerve which supplies the inferior oblique muscle. The fibres of the motor root probably all terminate in the ciliary ganglion in connection with motor sympathetic neurones. (6) The sensory or long root passes through the upper and back part of the ganglion. It is a branch of the naso-oiliary (nasal) nerve and is, therefore, composed of fibres from the trigeminus passing through the ganglion. (c) The sympathetic root consists of fibres derived from the cavernous plexus of the sympathetic; it passes to the ganglion with the long root. Branches. — From three to six short ciliary nerves emerge from the anterior border of the ganglion ; they divide as they pass forward and eventually form about twenty nerves which are arranged in aii upper and a lower group, and the latter group is joined by the long ciliary branches of the naso-ciliary (nasal) nerve, now sensory and sympathetic (fig. 73-1). When they reach the eyeball, the ciliary nerves pierce the sclerotic around the optic nerve, and pass forward in grooves on the inner surface of the sclera. The sympathetic fibres contained are dis- tributed as motor fibres to the ciliary muscle, the sphincter of the iris, and to the vessels of these and of the cornea. 962 THE NERVOUS SYSTEM The Spheno-palatine or Meckel's Ganglion This ganglion is associated with the maxillary nerve (fig. 743). It is a small reddish-grey body of triangular form, which is flattened at the sides, and measiu-es about five millimetres from before backward. It lies deeply in the pterygo- palatine (spheno-maxillary) fossa at the lateral side of the spheno-palatine fora- men and in front of the anterior end of the pterygoid (Vidian) canal. It is attached to the maxillary nerve, from which it receives its sensory root, and it is connected with the Vidian nerve, which furnishes it with motor and sympathetic filaments (fig. 739). The exact position of the ganghon depends upon the size and shape of the sphenoidal air cells. When these are small, or high and narrow, the ganglion lies lateral to them; when they are large, or broad and fiat, the ganglion lies inferior to them. Sometimes it may lie anterior to them if the cells are short from in front backward. The ganglion may be reached with ease by chipping away the bone around the sphenoidal air cells after the skull is divided sagitally. Roots. — (a) Its motor root, consisting of visceral motor fibres of the glosso-palatine nerve, is contained in the great superficial petrosal nerve which is incorporated in the Vidian nerve. It springs from the anterior angle of the geniculate ganglion and passes through the hiatus of the facial canal (hiatus Fallopii) into the middle fossa of the cranium, where it runs forward and medialward, in a groove on the upper surface of the petrous part of the temporal bone, to the foramen laoerum, and in this part of its course it passes beneath the semilunar (Gasserian) ganghon and the masticator nerve. In the foramen lacerum it joins with the great deep petrosal nerve to form the Vidian nerve (nerve of the pterygoid canal), which passes forward through the pterygoid (Vidian) canal and its motor and sympathetic fibres terminate in the spheno-palatine ganglion in the pterygo-palatine (spheno-maxillary) fossa. The great superficial petrosal nerve contains sensory as well as sympathetic and motor fibres. The sensory fibres pass through the ganghon and, in the small palatine nerve, descend to the soft palate, where they terminate in the epithelium covering it and some are probably concerned with peripheral taste organs found there. They arise from the cells of the geniculate ganglion and therefore belong to the glosso-palatine nerve. (6) The sympathetic root is the great deep petrosal portion of the Vidian nerve. This root, which is of reddish colour and of soft texture, springs from the carotid plexus which lies on the outer side of the internal carotid artery in the carotid canal. It enters the foramen lacerum through the apex of the petrous portion of the temporal bone, and unites with the great superficial petrosal branch of the facial nerve to form the Vidian nerve. The great superficial petrosal nerve also carries sympathetic fibres to the spheno-palatine ganglion, derived from the geniculate ganglion and from the tj'mpanic plexus. The Vidian nerve [n. canalis pterygoidei] commences by the union of the great superficial and deep petrosal nerves in the foramen lacerum, and runs forward through the pterygoid (Vidian) canal to the pterygo-palatine (spheno-maxillary) fossa to the spheno-palatine ganglion. The Vidian nerve often may be seen in a ridge of bone along the floor of the sphenoidal cells and its direction there depends upon the position of the spheno-palatine ganglion. While it is in the pterygoid canal the Vidian nerve is joined by a sphenoidal filament from the otic ganghon, and it gives branches to the upper and back part of the roof and septum of the nose, and to the lower end of the Eustachian tube. (c) The sensory roots consist of the sensory fibres mentioned above in the great superficial petrosal nerve and of usually two spheno-palatine branches from the maxillary nerve. The majority of the fibres of these roots do not join the ganghon, but pass by its medial side and enter the palatine branches. Branches. — The branches of the ganghon, containing sensory, vaso-motor and secretory fibres, are orbital or ascending, internal or nasal, descending or palatine, and posterior or pharyn- geal. Ascending branches. — The orbital or ascending branches are two or three small twigs which enter the orbit through the inferior orbital (spheno-maxillary) fissure and proceed, within the periosteum, to the inner wall of the orbit, where they pass through the posterior ethmoidal foramen and through the foramina in the suture behind that foramen to be distributed to the mucous membrane which lines the posterior ethmoidal cells and the sphenoidal sinus. Internal branches. — The internal or nasal branches are derived in part from the medial side of the ganglion, but are also largely made up of fibres which pass from the spheno-palatine branches of the maxillary nerve without traversing the ganglionic substance. They are dis- posed in two sets, the lateral and the medial (septal) posterior superior nasal branches. The lateral posterior superior nasal branches are six or seven small twigs which pass through the spheno-palatine foramen, and are distributed to the mucous membrane covering the poster- ior parts of the superior and middle nasal conchae (turbinated bones) (fig. 732). They also furnish twigs to the lining membrane of the posterior etlimoidal cells. The medial posterior superior nasal (septal) branches, two or three in number, pass medial- ward through the spheno-palatine foramen. They cross the roof of the nasal fossa to reach the back part of the nasal septum, where the smaller twigs terminate. The largest nerve of the set, the naso-palatine nerve, or nerve of Cotunnius, runs downward and forward in a groove in the vomer between the periosteum and the mucous membrane to the incisive (anterior palatine) canal, where it communicates with the nasal branch of the anterior superior alveolar nerve. The two naso-palatine nerves then pass through the foramina of Scarpa in the intermaxillary suture, the left nerve passing through the anterior of the two foramina. In the lower part of the incisive (anterior palatine) canal the two nerves form a plexiform communication (for- THE SUBMAXILLARY GANGLION 963 merly described as Cloquet's ganglion) and they furnisli twigs to the anterior or premaxillary part of the hard palate behind the incisor teeth. In this situation they communicate with the anterior palatine nerves. Descending branches. — The descending branches are the great or anterior, the posterior, and the middle (external) palatine nerves. Like the internal set of branches, they are in part derived from the ganglion and in part are directly continuous with the spheno-palatine nerves (fig. 732). The great or anterior palatine nerve, its sensory fibres derived from the maxillary nerve, arises from the inferior angle of Meckel's ganglion, and passes downward through the pterygo- palatine canal, accompanied by the descending palatine artery. Emerging from the canal at the greater (posterior) palatine foramen it divides into two or three branches, which pass for- ward in gi-ooves in the hard palate and supply the glands and mucous membrane of the hard palate and the gums on the inner aspect of the alveolar border of the upper jaw. During its cour.se through the pterygo-palatine canal the anterior palatine nerve gives off the posterior inferior nasal nerves. These nerves pass through small openings in the perpendicular plate of the palate bone to supply the mucous membrane covering the posterior part of the inferior nasal concha (turbinated bone) and the adjacent portions of the middle and inferior meatuses of the nose. The posterior or small palatine nerve passes downward through a lesser palatine foramen (accessory palatine canal), and enters the soft palate, distributing branches to that organ, to the uvula, and to the tonsil. Its sensory fibres are derived from the glosso-palatine nerve, through the great superficial petrosal nerve and through the spheno-palatine ganglion. It was formerly believed to convey motor fibres from the facial nerve to the levator palati and azygos uvulae, but it is now beheved that these muscles are supplied by the spinal accessory nerve through the pharyngeal plexus (fig. 732). The middle (external) palatine nerve, the smallest of the three, in part, likewise from the glosso-palatine nerve, traverses a lesser palatine foramen and supplies twigs to the tonsil and to the adjacent part of the soft palate (fig. 732). Posterior branch. — The pharyngeal branch, which is of small size, passes backward and somewhat medialward through the pharyngeal canal accompanied by a pharj'ngeal branch of the spheno-palatine artery. It is distributed to the mucous membrane of the uppermost part of the pharynx, to the upper part of the posterior nares, to the opening of the Eustachian tube, and to the lining of the sphenoidal sinus. Its sensory fibres are derived from the maxillary nerve. The Otic Ganglion The otic or Arnold's ganglion is a small reddish-grey body which is associated with the mandibular nerve. It lies deeply in the zygomatic fossa, immediately below the foramen ovale, on the inner side of the trunk of the mandibular nerve. It is in relation internally with the tensor palati, which separates it from the Eusta- chian tube. In front of it is the posterior border of the pterygoideus internus, and behind it lie the middle and small meningeal arteries. It is compressed laterally, and its greatest diameter, which lies antero-posteriorly, is about three millimetres. Roots. — The ganglion is closely connected with the nerve to the pterygoideus internus, through which it may receive a motor root from the masticator nerve. Through the small superficial petrosal nerve, which joins the upper and back part of the ganglion, it receives a motor root from the glosso-palatine nerve and sensory and motor fibres from the glosso- pharyngeal nerve. It receives also a slender sphenoidal filament from the Vidian nerve. The sympathetic roots are derived from the small superficial petrosal nerve and from the sympathetic plexus on the middle meningeal artery. Branches. — The communicating branches which pass from the ganglion are: — (1) The filaments to the chorda tympani; some of whose fibres probably terminate in the submaxillary ganglion; (2) filaments to the auriculo-temporal nerve; (3) filaments to the spinous nerve (the recurrent branch of the mandibular nerve). The branches of distribution are sympathetic to the vessels and somatic motor branches to the tensor tympani, and tensor veli palatini. The Submaxillary Ganglion The submaxillary ganglion is suspended from the lingual division of the man- dibular nerve by anterior and posterior branches. It is a small reddish body, of triangular or fusiform shape, which lies between the mylo-hyoideus and hyo- glossus and above the duct of the submaxillary gland. Roots. — The sensory root is received from the lingual nerve. The motor root is from both the masticator nerve by way of the lingual nerve, and from the glosso-palatine nerve by way of the chorda tympani. The motor fibres pass from the chorda tympani after it has joined the lingual, and the sensory fibres come directly from the lingual nerve. The sympathetic root is formed by filaments from the sympathetic plexus on the facial artery. Branches. — (a) Five or six glandular branches are given to the submaxillary gland and to Wharton's duct. (6) Branches to the lingual nerve and the sublingual gland. (c) To the mucous membrane of the floor of the mouth. 964 THE NERVOUS SYSTEM II. THE SPINAL NERVES The spinal nerves are arranged in pairs, the nerves of each pair being symmet- rical in their attachment to either side of their respective segment of the spinal cord, and, in general, symmetrical in their course and distribution. There are usually thirty-one pairs of functional spinal nerves. For purposes of description these are topographically separated into eight pairs of cervical nerves, twelve pairs of thoracic nerves, five pairs of lumbar, five pairs of sacral, and one pair of coccygeal nerves. Occasionally the coccygeal or thirty-first pair is practically wanting, while, on the other hand, there may be frequently found small filaments represent- ing one or even two additional pairs of coccygeal nerves below the thirty-first pair. These rudimentary coccygeal nerves are probably not functional. They never pass outside the vertebral canal, and often even remain within the tubular portion of the filum terminale. There sometimes occurs an increase in the number of vertebrae in the vertebral column and in such cases there is always a correspond- ing increase in the number of the spinal nerves. Origin and attachment. — Each spinal nerve (unlike the cranial nerves) is attached to the spinal cord by two roots: — a sensory or afferent dorsal root [radix posterior] and a motor or efferent ventral root [radix anterior]. Each dorsal root has interposed in its course an ovoid mass of nerve-cells, the spinal ganglion, and the nerve-fibres forming the root arise from the cells of this ganglion and are thus of peripheral origin. The fibres composing the ventral root, on the other hand, are of central origin; they arise from the large motor cells of the ventral horn of the grey column within the spinal cord. Each dorsal root-fibre upon leaving its cell of origin pursues a short tortuous course within the spinal ganglion and ^hen undergoes a T-shaped bifurcation, one product of which passes toward the periphery, where it terminates for the collection of sensations and is known as the peripheral branch, or, since it conveys impulses toward the cell-body, the dendrite of the spinal Fig. 746. — Ventral and Dohsal Views op Spinal Cord showing Manner of Attachment OF Dorsal and Ventral Roots. Antero-lateral sulcus (line of ventral i /"Anterior median fissure Posterior median sulcus /Posterior in- ganglion neurone. It is more correct, however, to consider the T-fibre as a bifurcated axone. The other product of the bifurcation, the central branch, passes into the spinal cord and in its course toward the cord contributes to form the dorsal root proper. The central branches, upon emerging from the spinal ganglia, form a single compact bundle at first, which passes through the dura mater of the spinal cord and then breaks up into a series, of root-filaments [fila radicularia]. These thread-like bundles of fibres spread out vertically in a fan-like manner and enter the cord in a direct linear series along its postero-lateral sulcus. The fibres of the ventral root emerge from the cord in a series of more finely divided root fila- ments, which, unlike the entering filaments of the dorsal root, are not arranged in direct linear series, but make their exit over a strip of the ventro-lateral aspect of the cord in some places as much as two millimetres wide. As they enter the spinal cord the fibres of the dorsal roots undergo a Y-shaped division, both products of which course in the cord longitudinally, an ascending and a descending branch. The descending or caudal branches are shorter than the ascending, and soon enter and terminate THE SPINAL NERVES 965 about the cells within the grey column of the cord, forming either associational, commissural, or reflex connections, or about cells whose fibres form cerebellar connections. The ascending or cephalic branches are either short, intermediate, or long. The short and intermediate branches are similar in function to the descending branches, save that they become associated with the grey substance of segments of the cord above rather than below the level of their en- trance. The long branches convey impulses destined for the structures of the brain, and pass upward in the fasciculus gracilis or fasciculus cuneatus of the cord, and terminate in the nuclei of these fasciculi in the meduUa oblongata (figs. 618 and 620). Aberrant spinal ganglia. — In serial sections on either side of the spinal ganglion of a nerve there may often be found outlying cells either scattered or in groups of sufficient size to be called small gangUa. Such are more often found in the dorsal roots of the lumbar and sacral nerves. These cells are nothing more than spinal ganghon-cells displaced in the growth processes, and have the same nature and function as those in the ganghon. In some animals occasional cells very rarely have been found in the outer portion of the ventral root. These probably represent afferent fibres which enter the cord by way of the ventral root. Likewise, especially in the birds and amphibia, it has been shown that occasional efferent fibres may pass from the grey substance of the cord to the periphery by way of the dorsal instead of the ventral root. Relative size of the roots. — The sensory or dorsal root is larger than the ventral root, indicating that the sensory area to be supplied is greater and perhaps more abundantly innervated than the area requiring motor fibres. It has been shown that in the entire thirty-one spinal nerves of one side of the body of man the dorsal root-fibres number 653,627, while all the corresponding ventral roots contain but 233,700 fibres, a ratio of 3.2 : 1. (Ingbert.) In the increase in the size of the nerves for the supply of the limbs the gain of dorsal root or sensory fibres is far greater than the gain of ventral root-fibres. The first cervical or the sub-occipital nerve is always an exception to the rule; its dorsal root is always smaller than its ventral, and in rare cases may be rudimentary or entirely absent. The spinal ganghon and, therefore, the sensory root of the coccygeal nerve, is also quite frequently absent. The dorsal and ventral root-fibres of each spinal nerve proceed outward from their segment of attachment to the spinal cord, pierce the pia mater and arachnoid, collect to form their respective roots, and pass into their respective intervertebral foramina. On the immediate peripheral side of the spinal ganglion the two roots blend, giving origin to the thus mixed nerve-trunk. As the trunk, the sensory and motor fibres make their exit from the vertebral canal through the interverte- bral foramen. Relation to the meninges. — The root filaments of each nerve receive connec- tive-tissue support from the pia mater and arachnoid in passing through them. In the sub-arachnoid cavity they become assembled into their respective nerve-roots; and the roots, closely approaching each other, pass into the dura mater, from which they receive separate sheaths at first, but at the peripheral side of the ganglion these sheaths blend into one, which, with the subsequent blending of the roots, becomes the sheath or epineurium of the nerve trunk. By means of the sheaths derived from the meninges, especially the dura, the nerve-roots and the trunk are attached to the periosteum of the margins of the intervertebral foramina and thus are enabled to give some lateral support to the spinal cord in the upper por- tion of the canal. The majority of the spinal ganglia lie in the intervertebral foramina, closely ensheathed, and thus outside the actual sac or cavity of the dura mater. The gangha of the last lumbar and first four sacral nerves he inside the vertebral canal, but since the sheath derived from the dura mater closely adheres to them, they are still outside the sac of the dura mater. The gan- gha of the last sacral and of the coccygeal nerves (when present) lie in tubular extensions of the sub-dural cavity, and thus not only within the vertebral canal, but actually within the sac of the dura mater. The trunk of the first cervical nerve is assembled within the sac of the dura mater, and, therefore, the spinal ganghon of this nerve, when present, may he within the sac. Course and direction of emergence. — Invested with the connective-tissue sheath derived from the meninges, each thoracic, lumbar and sacral nerve emerges from the vertebral canal through the intervertebral foramen below the correspond- ing vertebra, and all the nerves are in relation with the spinal rami of the arteries and veins associated with the blood supply of the given localities of the spinal cord. The first cervical nerve does not pass outward in an intervertebral foramen proper, but between the occipital bone and the posterior arch of the atlas and beneath the vertebral artery. Thus the eighth or last cervical nerve emerges between the seventh cervical and the first thor- acic vertebra. The first and second pairs of cervical nerves pass out of the vertebral canal almost at right angles to the levels of their attachment to the spinal cord. During the early periods of develop- ment the level of exit of each pair of spinal nerves is opposite the level of its attachment to the 966 THE NERVOUS SYSTEM cord, but, owing to the fact that in the later periods the vertebral column grows more rapidly than the cord and increases considerably in length after the cord has practically ceased growing, all the spinal nerves, with the exception of the first two, pass downward as well as outward. The obhquity of their course from the level of attachment to the level of exit increases progres- sively from above downward, and, as the cord ends at the level of the first or second lumbar vertebra, the roots of the lower lumbar and of the sacral nerves pass at first vertically downward within the dura mater, and form aroimd the filum terminale a tapering sheaf of nerve-roots, the Cauda equina (horse's tail) (fig. 613, p. 773). Topography of attachment. — The relations between the levels of attachment of the spinal nerves to the cord and the spinous processes of the vertebrae situated opposite these levels have been investigated by Nuhn and by Reid. The follow- ing table compiled by Reid gives the extreme limits of attachment as observed in six subjects. Table of Topogkaphy of Attachment of Spinal Nerves to the Spinal Cord. (Reid.) (A) signifies the highest level at which the root filaments of a given nerve are attached to the cord, and (B) the lowest level observed. For example, the root filaments of the sixth thoracic nerve may be attached as high as the lower border of the spinous process of the second thoracic vertebra, or some may be attached as low as the upper border of the spinous process of the fifth thoracic vertebra, but in a given subject they do not necessarily extend either as high or as low as either of the levels indicated. Nerves Second cervical (A) A httle above the posterior arch of atlas. (B) Midway between posterior arch of atlas and spine of epistropheus. Third " (A) A Uttle below posterior arch of atlas. (B) Junction of upper two-thirds and lower third of spine of epistropheus. Fourth " (A) Just below upper border of spine of epistropheus. (B) Middle of spine of third cervical vertebra. Fifth " (A) Just below lower border of spine of epistropheus. (B) Just below lower border of spine of fourth cervical vertebra. Sixth " (A) Lower border of spine of third cervical vertebra. (B) Lower border of spine of fifth cervical vertebra. Seventh " (A) Just below upper border of spine of fourth cervical vertebra. (B) Just above lower border of spine of sixth cervical vertebra. Eighth " (A) Upper border of spine of fifth cervical vertebra. (B) Upper border of spine of seventh cervical vertebra. First thoracic (A) Midway between spines of fifth cervical and sixth cervical vertebra. (B) Junction of upper two-thirds and lower third of interval between seventh cervical and first thoracic vertebra. Second " (A) Lower border of spine of sixth cervical vertebra. (B) Just above lower border of spine of first thoracic vertebra. Third thoracic (A) Just above middle of spine of seventh cervical vertebra. (B) Lower border of spine of second thoracic vertebra. Fourth " (A) Just below upper border of spine of first thoracic vertebra. (B) Junction of upper third and lower two-thirds of spine of third thoracic vertebra. Fifth " (A) Upper border of spine of second thoracic vertebra. (B) Junction of upper quarter and lower three-quarters of spine of fourth thoracic vertebra. Sixth " (A) Lower border of spine of second thoracic vertebra. (B) Just below upper border of spine of fifth thoracic vertebra. Seventh " (A) Junction of upper third and lower two-thirds of spine of fourth thoracic vertebra. (B) Just above lower border of spine of fifth thoracic vertebra. Eighth " (A) Junction of upper two-thirds and lower third of interval between spines of fourth thoracic and fifth thoracic vertebra. (B) Junction of upper quarter and lower three-quarters of spine of sixth thoracic vertebra. Ninth " (A) Midway between spines of fifth thoracic and sixth thoracic vertebra. (B) Upper border of spine of seventh thoracic vertebra. Tenth " (A) Midway between "spines of sixth thoracic and seventh thoracic vertebra. (B) Middle of the spine of eighth thoracic vertebra. Eleventh " (A) Junction of upper quarter and lower three-quarters of spine of seventh thoracic vertebra. (B) Just above spine of ninth thoracic vertebra. Twelfth " (A) Junction of upper quarter and lower three-quarters of spine of eighth thoracic vertebra. (B) Just below spine of ninth thoracic vertebra. First lumbar (A) Midway between spines of eighth thoracic and ninth thoracic vertebrae. (B) Lower border of spine of tenth thoracic vertebra. Second " (A) Middle of spine of ninth thoracic vertebra. (B) Junction of upper third and lower two-thirds of spine of eleventh thoracic vertebra. PRIMARY DIVISIONS OF SPINAL NERVES 967 Nerves Third Fourth Fifth First sacral Fifth Coccygeal (A) Middle of spine of tenth thoracic vertebra. (B) Just below spine of eleventh thoracic vertebra. (A) Just below spine of tenth thoracic vertebra. (B) Junction of upper quarter and lower three-quarters of spine of twelfth thoracic vertebra. (A) Junction of upper third and lower two-thirds of spine of eleventh thoracic vertebra. (B) Middle of spine of twelfth thoracic vertebra. (A) Just above lower border of spine of eleventh thoracic vertebra. (B) Lower border of spine of first lumbar vertebra. (A) Lower border of spine of first lumbar vertebra. (B) Just below upper border of spine of second lumbar vertebra. Relative size of the nerves. — The size of the different spinal nerves varies greatly. Just as the spinal cord shows marked enlargements in the cervical and lumbar regions necessitated by the greater amount of innervation required of these regions for the structures of the upper and lower limbs, so the nerves attached to these regions are considerably larger than elsewhere. The smaller nerves are found at the two extremities of the cord and in the mid-thoracic region. The smallest nerve is the coccygeal, and the next in order of size are the lower sacral and the first two or three cervical nerves. The largest nerves are those which contribute most to the great nerve trunks for the innervation of the skin and muscles of the limbs: — the lower cervical and first thoracic for the upper limbs and the lower lumbar and first sacral for the lower Umbs. The nerves gradually increase in the series in passing from the smaller toward the larger. Fig. 747. — Diagrams Illustrating the Origin and DisTRiBtrTioN op a Typical Spinal Nerve. A, in thoracic region; B, in region of a limb (highly schematic). Medial branch ' Lateral branch Posterior primary division Anterior primary division Lateral branch Anterior or ventral branch Medial branch Lateral branch Posterior primary \ division Anterior primary division Lateral or dorsal \ branch Alimentary canal The primary divisions of the nerve-trunk. — A typical spinal nerve (middle thoracic, for example), just as it emerges from the intervertebral foramen, divides into four branches: — the two large primary divisions; viz., the posterior primary division [ramus posterior] and the anterior primary division [ramus anterior]; third, the small ramus communicans, by which it is connected with the sympa- thetic; and fourth, the smaller, ramus meningeus {recurrent branch), which im- mediately turns centralward for the innervation of the membranes and vessels of the spinal cord. In general, the posterior primary division passes dorsalward between the arches or transverse processes of the two adjacent vertebrae in relation with the anterior costo-transverse ligament, and then divides (with the exception of the first cer- vical, the fourth and fifth thoracic, and the coccygeal nerves) into a medial (inter- nal) branch and a lateral (external) branch. The medial branch turns toward the spinous processes of the vertebrse, and supplies the bones and joints and the mus- cles about them, and may or may not supply the skin overlying them. The lateral branch turns dorsalward and also supplies the adjacent muscles and bones, and, if the medial branch has not supplied the overlying skin, it also terminates in cutaneous twigs. 968 THE NERVOUS SYSTEM In the upper half of the spinal nerves the medial branches supply the skin; in the lower half, it is the lateral branches which do so. Both branches of almost aU the posterior divisions, espe- cially those of the lower nerves, show a tendency to run caudalward and thus are distributed to muscles and skin below the levels of their respective intervertebral foramina. They never supply the muscles of the limbs, though their cutaneous distribution extends upon the buttock, the shoulder, and the skin of the back of the head as far upward as the vertex. The posterior primary divisions, with the exception of those of the first three cervical nerves, are much smaller than the anterior primary divisions. As their mixed function suggests, the posterior primary divisions contain both nerve-fibres from the ventral roots and peripheral processes of the spinal ganghon-cells. If the nerve-trunk on the immediate peripheral side of the spinal ganghon be teased, bimdles of ventral root-fibres may be seen crossing the trunk obliquely to enter the posterior division, and fibres from the spinal ganghon may be also traced into it. Also a few sympathetic fibres, derived chiefly by way of the ramus communicans, are known to course in it for distribution in the walls of the blood-vessels, etc., of the area it suppUes. The anterior primary divisions run lateralward and ventralward. With the exception of the first two cervical nerves, which contribute the hypoglossal loop, they are larger than the posterior primary divisions, and appear as direct continu- ations of the nerve-trunks. Only in case of most of the thoracic nerves do thej^ remain independent in their course. In these they run lateralward and ventral- ward in the body-wall. In general, these divisions supply the lateral and ventral Fig. 748.- -DlAGBAM IlLTJSTRATING THE OrIGIN OF THE COMPONENT NEEVE-FrBKES OF THE Pbimaey Divisions of a Typical Spinal Nerve. Spinal ganglion neurone to capsule of ganglion ^ Gray ramus communicans — White ramus com Sympathetic ganglion \ Gangliated Sympathetic trunk j trunk Sympathetic cell body in spinal ganglion Posterior primary division \ Spinal Anterior primary division J nerve ^>^ ^Gray ramus communicans \ ^White ramus communicans Sensory sympathetic neurone Branch to prevertebral ganglion parts of the body, the limbs, and the perineum. In the cervical, lumbar, and sacral regions they lose their anatomical identity by dividing, subdividing, and anastomosing with each other so as to give rise to the three great spinal plexuses of the body — the cervical, the brachial, and the lumbo-sacral plexuses. The major- ity of the thoracic nerves retain the typical or primitive character in both their anterior and posterior primary divisions. In them the anterior division (inter- costal nerve) divides into a lateral or dorsal and an anterior or ventral branch, both of which subdivide. The lateral branch is chiefly cutaneous; it pierces the superficial muscles and, in the subcutaneous connective tissue, divides into a smaller posterior and a larger anterior ramus, which respectively supply the skin of the sides and the lateral part of the ventral surface of the body. The anterior branch continues ventralward iii the body-wall, giving off twigs along its course to the adjacent muscles and bones, and, as it approaches the ventral mid-fine of the body, it turns sharply lateralward and sends rami medialward and lateralward to supply the skin of the ventral aspect of the bodjr. In the region of the limbs the typical arrangement is interfered with in that what corresponds to the lateral and anterior branches of the division are carried out into the limbs for the skin and muscles there, instead of supplying the lateral and ventral parts of the body-wall. RAMI COMMUNICANTES 969 Nerve-fibres arising in the spinal ganglion and fibres from the ventral root pass directly from the nerve-trunk into the anterior primary division of the spinal nerve. This division also receives sympathetic nerve-fibres by way of the ramus communicans. These latter accompany the division and are distributed to their allotted elements in the territory it supplies. Fig. 749. — Table Giving the Approximate Areas of Distribution of the Different Spinal Nerves with a Diagram showing Their Respective Levels of Exit from the Vertebral Column. (Arranged by Dr. Gowers.) MOTOR SENSORY REFLEX Sterno -mastoid Trapezius \ Serratus j Shoulder Arm } muse. Flexors, hip Extensors, knee Extensors (?■) Flexors, knee (?) Muscles of leg m( ing foot J Perineal and anal muscles Neck and scalp 1 Neck and shoulder I Shoulder Arm [ Front of thorax Abdomen (.Umbilicus 10th) I- Groin and scrotum I (front) ■ Cremasteric I [ Lateral side ! | | I Knee-joint j ( Medial side ' Leg, medial side Buttock, lower Back of thigh Leg 1 and } except medial I [ foot j part I Perineum and anus Foot-clonus Plantar The rami communicantes are small, short, thread-like branches by which the nerve-trunks are connected with the nearest ganglion of the vertically running gangliated cord of the sympathetic (sympathetic trunk). The trunk or anterior primary division of every spinal nerve has at least one of these; most of the nerves have two, and sometimes there are three. The nerves of the cervical region usu- ally have but one, and this is composed largely of sympathetic fibres (grey 970 THE NERVOUS SYSTEM ramus). Where there are two, one usually contains medullated fibres, chiefly from the ventral root, sufficient to give it a whiter appearance (white ramus). In the upper cervical and in the sacral regions one sympathetic ganglion may be connected with two or more spinal nerves, and sometimes one nerve is connected with two ganglia. The rami communicantes of the spinal nerves are equivalent to the communicating rami connecting certain of the cranial nerves with the sympathetic system (trigeminus, glosso-pharyngeus, vagus) . The medullated fibres of the rami and, therefore, the white rami consist chiefly of fibres from the spinal nerves, viz., fibres from the spinal ganglion-cells which enter and course to their distri- bution through branches of the sympathetic nerves, visceral afferent fibres, and fibres from the ventral roots of the spinal nerves which terminate in the sympathetic ganglia, visceral efferent (preganghonic) fibres. Thus the white rami have been termed the visceral divisions of the spinal nerves. The grey rami consist chiefly of sympathetic fibres, most of which are non-meduUated or partially medullated, and which course to their distribution by way of the spinal nerves. Some of the sympathetic fibres terminate in the spinal ganghon, afferent sympathetic fibres (fig. 748). The usual absence of white rami communicantes from the cervical nerves is explained on the grounds — (1) that probably relatively few efferent visceral fibres are given to the sympathetic from this region of the cord; (2) that many of the visceral efferent fibres which do arise from this region of the cord probably join the rootlets of the spinal accessory nerve and pass to the sympathetic system through the trunk of this nerve, and through the vagus with which it anastomoses; and (3) that such of these fibres as are given off from the lower segments of the cervical region, descend the cord and pass out by way of the upper thoracic nerves which give very evident white rami to the sympathetic. The meningeal or recurrent branch (figs. 747, 748, and 762) is very small and variable, and is often difficult to find in ordinary dissections. It is given off from the nerve-trunk just before its anterior and posterior primary divisions are formed. It consists of a few peripheral branches of spinal ganglion-cells (sensory fibres) which leave the nerve-trunk and re-enter the vertebral canal for the sensory innervation of the meninges, and which are joined by a twig from the grey ramus or directly from the nearest sympathetic ganglion (vaso-motor fibres). There is considerable evidence, both physiological and anatomical, obtained chiefly from the animals, which shows that at times certain of the peripheral spinal ganghon or sensory fibres may turn backward in the nerve-trunk and pass to the meninges within the ventral root instead of contributing to a recurrent branch. The occurrence of such fibres in the ventral root explains the physiological phenomenon known as 'recurrent sensibility.' Likewise, sympathetic fibres entering the trunk through the grey ramus may pass to the meninges by way of the ventral root, and at times the recurrent branch is probably absent altogether, its place being taken entirely by the meningeal fibres passing in the ventral root. Areas of distribution of the spinal nerves. — Both the posterior and anterior primary divisions divide and subdivide repeatedly, and their component fibres are distributed to areas of the body more or less constant for the nerves of each pair, but the distribution of the different nerves is very variable. Corresponding to their attachment, each to a given segment of the spinal cord, the nerves have pri- marily a segmental distribution, but, owing to the developmental changes and displacement of parts during the growth of the body, the segmental distribution becomes greatly obscured and in some nerves practically obliterated. Naturally it is more retained by the nerves supplying the trunk than by those contributing to the innervation of the limbs and head, and the areas supplied by the posterior primary divisions are less disturbed than those supplied by the anterior. The segmental areas of cutaneous distribution of the posterior divisions are more evi- dent than the areas of muscle supplied by these divisions, from the fact that the segmental myotomes from which the dorsal muscles arise fuse together and over- lap each other considerably during development. No nerve has a definitely pre- scribed area of distribution, cutaneous or muscular, for its area is always consider- ably overlapped by the areas of the nerves adjacent to it. The mid-thoracic nerves more nearly supply a definitely prescribed belt of the body. A. POSTERIOR PRIMARY DIVISIONS The posterior primary divisions of the spinal nerves spring from the trunks immediately outside the intervertebral foramina, and they pass dorsalward between the adjacent transverse processes. With the exceptions of the first and second cervical nerves they are smaller than the corresponding anterior primary divisions, which in these nerves is smaller from the fact that a large portion of them go over into the hypoglossal or cervical loop. The posterior primary divi- sions, after passing between the transverse processes into the region of the back, divide into medial and lateral branches. This division, however, does not occur in the cases of the first cervical, the last two sacral, and the coccygeal nerves. THORACIC NERVES 971 1. Cervical Nerves The posterior primary division of the first cervical or sub -occipital nerve springs from the trunk, between the vertebral artery and the posterior arch of the atlas, passes dorsalward into the sub-occipital triangle, and breaks up into branches which supply the superior oblique, the inferior oblique, and the major rectus capitis posterior muscles, which form the lateral boundaries of the triangle. It also gives a branch across the posterior surface of the major rectus capitis pos- terior to the minor rectus capitis posterior, and a branch to the semispinalis capitis (complexus) in the roof of the triangle. It communicates with the medial branch of the posterior primary division of the second cervical nerve, either through or over the inferior obUque muscle, and it occasionally gives a cutaneous branch to the skin of the upper part of the back of the neck and the lower part of the scalp. The posterior primary division of the second cervical nerve is the largest pos- terior division of all the cervical nerves. It divides into a small lateral branch and a very large medial branch. The lateral branch gives a twig to the inferior oblique and terminates in branches which supply the splenius and longissimus capitis (trachelo-mastoid) muscles. The medial branch is the greater occipital nerve. It turns around the lower border of the inferior oblique, crosses the sub-occipital triangle obliquely, pierces the semispinalis capitis (complexus), the tendon of the trapezius, and the deep cervical fascia, passing through the latter immediately below the superior nuchal line of the occipital bone, and it divides into several terminal sensory branches which ramify in the superficial fascia of the scalp. It gives one or two motor twigs to the semispinalis capitis (complexus), and its terminal branches which are accompanied by branches of the occipital artery supply the skin of the scalp, above the superior nuchal Une, as far forward as the vertex. Occasionally one branch reaches the pinna and supplies the skin on the upper part of its medial aspect. As it turns around the inferior oblique it gives branches which join with the medial branches of the posterior primary divisions of the first and third cervical nerves, and in this manner a small looped plexus is formed beneath the semispinalis capitis (complexus) muscle, the posterior cervical plexus of Cruveilhier. The posterior primary branches of the third, fourth, and fifth cervical nerves divide at the lateral border of the semispinalis colli into medial and lateral branches. The medial branches of the third, fourth, and fifth nerves run backward between the semispinalis colli and capitis (complexus), supplying both muscles. Then, after passing backward between the semispinalis capitis and the ligamentum nuchse, they pierce the origin of the trapezius and supply the skin of the back of the neck. The greater part of the medial branch of the third nerve, which runs upward in the superficial fascia to the scalp, is called the third or smallest occipital nerve ; it interlaces with the greater occipital nerve, and it supplies the skin of the upper part of the back of the neck, near the middle line, and the skin of the scalp in the region of the external occipital protuberance. The medial branches of the posterior primary divisions of the sixth, seventh, and eighth cervical nerves pass to the median side of the semispinalis colli, between it and the subjacent multifidus spinse, and they end in the neighbouring muscles. The lateral branches of the posterior primary divisions of the last five cervical nerves are small and they are distributed to the longissimus capitis (trachelo- mastoid), the ilio-costalis cervicis (cervicalis ascendens), the longissimus cervicis (transversalis cervicis), the semispinalis capitis (complexus), and the splenius muscles. 2. Thohacic Nerves The posterior primary divisions of all the thoracic nerves divide into medial and lateral branches while in the vertebral groove. The medial branches of the upper six thoracic nerves pass dorsalward between the semispinalis dorsi and the multifidus spinje; they supply the spinalis dorsi, the semispinahs dorsi, the multi- fidus spinse, the rotatores spinse, the intertransversales, and the interspinales muscles; and they end in cutaneous branches which, after piercing the trapezius, turn lateralward in the superficial fascia of the back, and supply the skin as far as the middle of the scapula. The cutaneous branch of the second nerve is the larg- est; it can be traced lateralward as far as the acromion process. The medial branches of the lower six thoracic nerves run dorsalward, between the longissi- 972 THE NERVOUS SYSTEM mus dorsi and the multifidus spinae; they chiefly end in twigs to the adjacent muscles, but not uncommonly they give small cutaneous twigs which pierce the latissimus dorsi and the trapezius and end in the skin near the mid-line of the back. The lateral branches of the upper six thoracic nerves pass between the longis- FlG. 750. DlSTRLBCTION OF THE POSTERIOR PRIMARY DIVISIONS OP THE^SPINAL NeRVES. (Henle.) Semispinalis colli- Multifidus spinx Gluteus mazimus simus dorsi and the ilio-costalis dorsi (accessorius) and end in those muscles, but the lateral branches of the six lower nerves are longer; they pass into the interval between the longissimus dorsi and the ilio-costalis dorsi and give branches to them, and then they pierce the latissimus dorsi and are distributed to the skin of the lower and lateral part of the back. ANTERIOR PRIMARY DIVISIONS - 973 3. Lumbar Nerves The medial branches of the posterior primary divisions of all the lumbar nerves end in the multifidus spinse and those of the three lower nerves send very small branches to the skin of the sacral region. The lateral branches of the upper three nerves pass obliquely lateralward, supplying twigs to the adjacent muscles, pierce the posterior layer of the lumbar aponeurosis at the lateral bord^' of the sacro-spinalis (erector spinse) and enter the subcutaneous tissue. They are, for the most part, cutaneous, forming the superior clunial nerves, which cross the crest of the iUum and pass downward to occupy different planes in the thick superficial fascia which covers the upper part of the gluteus medius. The branch from the first lumbar nerve is comparatively small, and occupies the most super- ficial plane. The second occupies an intermediate position. The lateral branch from the third nerve is the largest of the three, and occupies the lowest position; it distributes branches over the gluteus maximus as far as the great trochanter. The three nerves anastomose with one another and also with the cutaneous branches from the posterior primary divisions of the two upper sacral nerves. The lateral branch of the fourth lumbar nerve is of small size and ends in the lower part of the sacro-spinalis (erector spinas). That of the fifth lumbar is distributed to the sacro-spinalis and communicates with the first sacral nerve. 4. Saceal Nerves The posterior primary divisions of the upper four sacral nerves escape from the vertebral canal by passing through the posterior sacral foramina; those of the fifth sacral nerve pass out through the hiatus sacralis between the posterior sacro- coccygeal ligaments. Those of the upper three sacral nerves divide in the ordi- nary manner into medial and lateral branches. Those of the lower two sacral nerves remain undivided. The medial branches of the upper three sacral nerves are of small size, and are distributed to the multifidus spinse. The lateral branches anastomose with one another and with the lateral branch of the last lumbar nerve, forming loops on the posterior surface of the sacrum from which branches proceed to the posterior surface of the sacro-tuberous (great sacro-sciatic) ligament, where they anasto- mose and form a second series of loops, from which loops two or three branches are given off. These branches pierce the gluteus maximus and come to the surface of that muscle in a line between the posterior superior spine of the ilium and the tip of the coccyx. Then, as the middle clunial nerves, they are distributed to the integument over the medial part of the gluteus maximus, and communi- cate, in their course through the superficial fascia, with the posterior branches of the lumbar nerves. The posterior divisions of the lower two sacral nerves unite with one another, with the posterior branch of the third sacral, and with the coccygeal nerve, form- ing loops from which twigs pass to the integument over the lower end of the coccyx. The posterior primary division of the coccygeal nerve is also undivided. It separates from the anterior division in the sacral canal and emerges through the hiatus sacralis, pierces the hgaments which close the lower part of that canal, receives a communication from the posterior division of the last sacral nerve, and ends in the skin over the dorsal aspect of the coccyx. B. ANTERIOR PRIMARY DIVISIONS The anterior primary divisions of the spinal nerves are larger than the pos- terior primary divisions, and each is joined near its origin bj^ a grey ramus commu- nicans from the sympathetic gangUated cord (figs. 751, 752, 762). Beginning with the first or second thoracic nerve and ending with the second or third lumber nerve, each anterior division sends to the gangliated cord a white ramus communi- cans. The same is true of the second and third or of the third and fourth sacral nerves. These white rami are appropriately designated the visceral branches of 974 THE NERVOUS SYSTEM the spinal nerves. The anterior primary divisions of the cervical, lumbar, sacral, and coccygeal nerves unite with one another to form plexuses, but the anterior primary divisions of the thoracic nerves, except the first and last, remain separate, pursue independent courses, and each divides, in a typical manner, into a lateral and an anterior or ventral branch. The separation of the anterior primary divi- sion into lateral and anterior branches is not confined to the thoracic nerves; it occurs also in the lower cervical, the lumbar, and the sacral nerves, but such a divi- sion cannot be clearly distinguished either in the upper cervical nerves, or in the coccygeal nerve. 1. CERVICAL NERVES The anterior primary divisions of the upper four cervical nerves unite to form the cervical plexus, and each receives a communicating branch from the superior cervical sympathetic ganglion. The anterior divisions of the lower four cervical nerves are joined by the greater part of the first thoracic nerve and they unite to form the brachial plexus (figs. 751, 754, 755). The fifth and sixth cervical nerves receive communicating branches from the middle cervical sympathetic ganglion, and the seventh and eighth from the inferior cervical ganglion, while the first thoracic nerve is always connected with the first thoracic sympathetic gang- lion by a grey ramus (figs. 751, 786) and in most cases also by a white ramus communicans. THE CERVICAL PLEXUS The cervical plexus (figs. 751, 752) is formed by the anterior primary divisions of the upper fom- cervical nerves which constitute the roots of the plexus. It lies in the upper part of the side of the neck, under cover of the sterno-mastoid, and upon the levator scapulse and the scalenus medius. It is a looped plexus, consisting of three loops. A large part of the anterior primary division of the first cervical nerve is given to the hypoglossal or cervical loop; the remainder passes to the cervical plexus and in doing so it runs lateralward on the posterior arch of the atlas beneath the verte- bral artery, then it turns forward, between the vertebral artery and the outer side of the upper articular process of the atlas, and finally it descends, in front of the transverse process of the atlas, and unites with the upper branch of the second nerve, forming with it the first loop of the plexus. It gives branches to the rectus capitis lateralis, longus capitis (major rectus capitis anterior), and to the rectus capitis anterior (minor). The division communicates with the ganglion of the trunk of the vagus and with the superior cervical ganglion of the sympathetic system (fig. 752) . From the first loop of the plexus, two branches of the division pass over into the sheath of the hypoglossal nerve and descend with it to contrib- ute to the hypoglossal loop [ansa hypoglossi] or better, the cervical loop. The fibres entering the sheath of the hypoglossus, after giving a few twigs to the gpnio-hyoid and thyreo-hyoid muscles, leave the sheath as the descendens cer- vicalis (hypoglossi) and this latter joins the communicans cervicalis, (the portion of the loop from the second and third cervical nerves) and thus completes the cervical or hypoglossal loop. This loop usually may be found between the sheaths of the sterno-mastoid muscle and the carotid artery, superficial to the internal jugular vein; sometimes it may lie in the carotid sheath between the carotid artery and the internal jugular vein; rarely it may lie dorsal to both the artery and vein. Sometimes it is relatively long, descending toward the sternum below the level of the thyreoid cartilage; again it is quite short and occurs near the level of the hyoid bone. The descendens cervicahs (hypoglossi) parts company with the hypoglossal nerve at the level at which the nerve curves around the occipital artery. It runs downward and shghtly medialward on the sheaths of the great vessels and occasionally within the sheath of one of them. The second cervical nerve (anterior primary division) passes behind the upper articular process of the axis and the vertebral artery, and between the inter- transverse muscles extending from the first to the second cervical vertebrse, to the interval between the scalenus medius and the longus capitis (rectus capitis anterior major), where it divides into two parts. The upper part ascends and unites with the first nerve to form the first loop of the plexus, and the lower branch passes downward and dorsalward and joins the upper branch of the third nerve in CERVICAL PLEXUS 975 the second loop of the plexus (figs. 751, 752). This branch gives off the small occipital nerve and a filament to the sterno-mastoid, which communicates with the spinal accessory nerve in the substance of the muscle, and it gives branches which assist in forming the hypoglossal or cervical loop (ansa hypoglossi) the cer- vical cutaneous and the great auricular nerves (fig. 752). Fig. 751. — Origin of the Cervical and Brachial Plexus. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Anatomy," Rebman Muscular branch to rectus capitis anterior and lateralis and longus capitis m^ \ Rectus capitis lateralis s^^W, Muscular branch to longus capitis and longus colli eating branch to descendens 2rvicalis (hypoglossi) Small occipital Communicating branch to spinal accessory Great auricular -,^ Cervical cutaneous Muscular branch Supra -da viculaiis -v;- Phrenic .-i^ Dorsal scapul Supra-scapular Axillary Internal carotid artery Rectus capitis anterior Radial Musculo-cutaneous . Medial ulnar Anti -brachial cutaneous Internal car- otid nerve First cervical nerve Ramus communi- cans Second cervical nerve Superior cervical ganglion Third and fourth cervical nerves Ramus communi- cans Vertebral artery Ganglia ted trunk ^ Fifth, sixth and seventh cer- vical nerves Middle cervical ganglion Eighth cervical nerve Inferior cervical ganghon First thoracic nerve Vertebral exus Subscapular ^'''''' Long thoracic Serratus anterior Anterior thoracic Scalenus medius Subclavian artery The third and fourth cervical nerves pass behind the vertebral artery (fig. 751) and between the intertransverse muscles to the interval between the scalenus medius and the longus capitis (rectus capitis anterior major), where the third unites with the second and fourth nerves and completes the lower two loops of the plexus. The anterior primary divisions of these nerves are about double the size of the preceding. The third gives off branches to the hypoglossal loop, to the 976 THE NERVOUS SYSTEM larger part of the great auricular and cervical cutaneous nerves, a branch to the phrenic, a branch to the supra-clavicular nerves, and muscular branches to the scalenus medius, levator scapulse, longus capitis, and trapezius (fig. 752). The trapezius branch joins the spinal accessory nerve beneath the muscle. The fourth nerve gives a branch to the phrenic, a branch to the supra-clavicular nerves, and muscular branches to the scalenus medius, levator scapulae, longus colli, and trapezius (fig. 752). The branch to the trapezius unites with the one from the third nerve and joins the spinal accessory nerve beneath the muscle. The fibres forming the cervical (hypoglossal) loop innervate all the muscles of the infra-hyoid group, though twigs to the genio-hyoid and thyreohyoid seemingly enter these muscles from the trunk of the hypoglossus (fig. 752). Fig. 752. — Diagram op the Cervical Plexus. Ganglion of trunk of vagus Sterno-mastoid Small occipital Great auricular Scalenus medius Spinal accessory Cervical cutaneous Scalenus medius Levator scapulae - Sympathetic - Longus capitis Rectus capitis anterior Rectus capitis lateralis Hypoglossal nerve Superior cervical sympathetic ganglion Scalenus anterior S t e r n o -thyreoid Trapezius Posterior Middle _ Anterior supraclavicular supraclavicular supraclavicular The nerve to genio-hyoid is given off from the trunk under cover of the mylo-hyoid in com- mon with the terminal branches of the hypoglossal proper going to the intrinsic muscles of the tongue. The nerve to the thyreo-hyoid muscles leaves the trunk of the hypoglossal near the tip of the great cornu of the hyoid bone, running obUquely downward and medianward to reach its muscle. A twig to the anterior belly of the omo-hyoid is given from the upper part of the descendens cervicalis and the nerves for the sterno-hyoid, the sterno-thyreoid and the pos- terior belly of the omo-hyoid are supplied from the turn of the loop (fig. 7.52). The nerves to the sterno-hyoid and sterno-thyreoid send twigs downward in the muscles behind the manubrium sterni and fibres from these in rare cases join the phrenic nerve in the thorax. The nerve to the posterior belly of the omo-hyoid courses as a loop in the cervical fascia below the central tendon of its muscle. Each root of the cervical plexus receives a communicating grey ramus from the superior cervical ganglion of the sympathetic, and from the roots and loops of BRANCHES OF CERVICAL PLEXUS 977 the plexus a number of branches arise which form two main groups, the superficial and the deep. Superficial Branches of the Cervical Plexus The superficial branches are described, according to the direction in which they run, as ascending, transverse, and descending branches. The ascending branches are the small occipital and the great auricular nerves. There is only one transverse branch, the cervical cutaneous (transverse cervical), and the descending branches are distinguished as the supraclavicular nerves and the cervical (hypo- glossal) loop. The ascending branches. — (1) The small occipital nerve (fig. 751) arises from the second and third cervical nerves, or from the loop between them, and runs Fig. 753.- -SuPEHFiciAL Branches op the Cervical Plexus. (After Hirschfeld and Leveill6.) Posterior auricular nerve Auricular br of great auricular V* Cervical brauch of facial Cervical cutaneous- ^ Branches of cervical f cutaneous nerve \ Great occipital Great auricular Mastoid br. or 2nd small occipital Spinal accessory Twigs from the mastoid branch Br. to levator scapulse Posterior supra- clavicular Middle supra- clavicular upward and^dorsalward to the posterior border of the sterno-mastoid, where it hooks around the lower border of the spinal accessory nerve and then ascends along the posterior border of the muscle to the mastoid process. It pierces the deep cervical fascia and passes across the posterior part of the insertion of the sterno-mastoid into the superficial fascia of the scalp, in which it breaks up into auricular, mastoid, and occipital terminal branches. (a) The auriculax branch runs upward and slighly forward to reach the integument on the upper median part of the auricle (pinna), wliioh it supphes. (6) The mastoid branch is distrib- uted to the slvin covering the base of the mastoid process, (c) The occipital branches ramify over the occipitaUs muscle and are distributed to the skin of the scalp ' they communicate with one another and with the great occipital nerve. The branches of the small occipital nerve 978 THE NERVOUS SYSTEM anastomose with twigs of the posterior auricular, great auricular, and great occipital nerves (fig. 753). (2) The great atiricular nerve arises from the second and third cervical nerves (figs. 751, 752). It accompanies the small occipital to the posterior border of the sterno-mastoid, but at that point it diverges from the small occipital (fig. 753) and runs upward and forward across the sterno-mastoid toward the angle of the mandible. When it is about half-way across the muscle it begins to break up into its terminal branches, which are named, according to the area of their distribution, mastoid, auricular, and facial. As the nerve ascends obliquely across the sterno-mastoid it is embedded in the deep cervical fascia, is covered by superficial fascia and the platysma, and it lies parallel with and slightly dorsal to the external jugular vein, (a) The mastoid branch is small, and is distributed to the integument covering the mastoid process. It anastomoses with the posterior auricular and small occipital nerves. (6) The auricular branches are three or four stout twigs which interlace with the branches of the posterior auricular nerve; they cross the superficial surface of the posterior auricular branch of the facial, and are distributed to the skin on the back of the auricle with the exception of its uppermost part. One or two twigs pass through fissures in the cartilage of the auricle, and are distributed to the integument on the lateral surface of the lobule and the lateral surface of the lower part of the helix and anthelix. (c) The facial branches pass upward and forward among the superficial lobules of the parotid gland, and supply the skin over that gland and immediately in front of it, and they anastomose in the substance of the gland with the cer- vico-facial division of the facial nerve. In some cases fine twigs may be traced forward nearly to the angle of the mouth. Transverse branch of the plexus. — The superficial cervical cutaneous nerve (transverse cervical) arises from the second and third cervical nerves (figs. 751, 752), and appears at the posterior border of the sterno-mastoid, a little below the great auricular nerve. It passes transversely across the sterno-mastoid under cover of the integument, platysma, and external jugular vein, and divides into a number of twigs which spread out after the manner of a fan, and, as they approach the middle line, extend from the chin to the sternum (fig. 753). The upper two or three of these twigs unite, beneath the platysma, with the cervical (infra- mandibular) branch of the facial and thus form loops. From the terminal branches of the nerve numerous twigs arise which pierce the platysma and end in the skin of the front part of the neck. The descending or supra-clavicular branches. — These are derived from the third and fourth cervical nerves (figs. 751, 752), and arise under cover of the sterno-mastoid. At their commencements they are usually united with the mus- cular branches destined for the trapezius. They become superficial at the middle of the posterior border of the sterno-mastoid, and as they pass downward they pierce the deep cervical fascia. They include the following: (1) The anterior supra-clavicular (suprasternal) branches (fig. 753) are small, and cross over the clavicular attachment of the sterno-mastoid to reach the integument over the upper part of the manulDrium sterni. They also supply the sterno-clavicular joint. (2) The middle supra-clavicular (supra-clavicular) nerves are of considerable size. They cross in front of the middle third of the clavicle under cover of the platysma, and are distributed to the skin cover- ing the upper part of the pectoralis major as low as the third rib. (3) The posterior supra- clavicular (supra-acromial) branches (fig. 753) cross the clavicular insertion of the trapezius and the acromion process. They are distributed to the skin which covers the upper two-thirds of the deltoid muscle and they supply the acromio-clavicular joint. Deep Branches of the Cervical Plexus The deep branches of the plexus pass lateralward and dorsalward, or ventral- ward and medialward; therefore they form two series, the lateral and the medial. The lateral branches of the deep series include communicating branches from the second, third, and fourth cervical nerves to the spinal accessory nerve, and muscular branches to the sterno-mastoid and the scalenus medius, levator scap- ulse, and trapezius. The communicating branches. — The communicating branch from the second cervical nerve is ultimately distributed to the sterno-mastoid, and those from the third and fourth nerves end in the trapezius. 1. The nerve to the sterno-mastoid arises from the second cervical nerve (fig. 753). It pierces the deep surface of the sterno-mastoid, and coinmunicates within the muscle with the spinal accessory nerve. 2. The nerves to the scalenus medius (fig. 752) are derived from the third or fourth to the eighth cervical nerves close to their exit from the intervertebral foramina. BRANCHES OF CERVICAL PLEXUS 979 3. The nerves to the levator scapulae (fig. 752) are derived from the third and fourth cervical nerves, and occasionally from the second or fifth. They pierce the superficial surface of the levator scapute, and supply the upper three divisions of that muscle. 4. The branches to the trapezius (fig. 752) are usually in the form of two stout twigs which are given off by the third and fourth cervical nerves. They emerge from under cover of the sterno-mastoid at its posterior border and cross the posterior superior triangle of the neck at a lower level than the spinal accessory nerve (fig. 753). They pass under cover of the trapezius in company with the last-named nerve, and communicate with it to form the subtrapezial plexus, from which the trapezius is supplied. The medial branches of the deep series also comprise communicating and mus- cular branches. The communicating branches (figs. 751, 752) include (1) branches which connect each of the first four cervical nerves with the superior cervical ganghon of the sympathetic; (2) a branch to the vagus; (3) a branch to the hypoglossal; and (4) branches which pass from the second and third cervical nerves to the descendens cervicalis (hypoglossi) . The ultimate dis- tribution of the twigs connected with the sympathetic and the vagus nerves is not known, but the fibres which pass to the hypoglossal nerve pass from it to the thyreo-hyoideus muscle, and to the descendens cervicalis and the latter joins with the branches from the second and third cervical nerves, forming with them the cervical or hypoglossal loop [ansa hypoglossi] which lies on the carotid sheath. From this loop the two beUies of the omo-hyoid muscle and the sterno-hyoid and sterno-thyreoid muscles are supphed as described above. The muscular branches supply the rectus capitis lateralis, the longus cap'tis (rectus capitis anterior major), the rectus capitis anterior (minor), the scalenus anterior, and the diaphragm. The nerve to the latter muscle is the phrenic. 1. The branch to the rectus capitis lateralis is furnished to that muscle by the first cervical nerve as it crosses the deep surface of the muscle. 2. The nerve to the rectus capitis anterior (minor) is given off by the first nerve at the upper part of the loop in front of the transverse process of the atlas. 3. The longus capitis (rectus capitis anterior major) receives twigs from the upper four cervical nerves. 4. The longus colli receives branches from the second, third, and fourth cervical nerves, and additional branches also from the fifth and sixth nerves. 5. The phrenic nerve (fig. 752) springs chiefly from the fourth cervical nerve, but it usually receives a twig from the third and another from the fifth cervical nerve, a small communicating branch from the sympathetic, and, rarely, a branch from the vagus. The twig from the fifth cervical nerve is frequently connected with the nerve to the subclavius. After the union of its roots the phrenic nerve passes downward and medialward on the scalenus anterior (fig. 755). In this part of its course it is crossed by the tendon of the omo-hyoid and by the trans- verse cervical and transverse scapular (suprascapular) arteries. It is overlapped by the internal jugular vein, and it is covered by the sterno-mastoid muscle. At the root of the neck the left phrenic nerve lies behind the terminal portion of the thoracic duct, and each nerve passes off the anterior border of the scalenus anterior and descends in front of the first part of the subclavian artery and the pleura imme- diately below that artery; each nerve passes dorsal to the terminus of the sub- clavian vein, crosses either in front of or dorsal to the internal mammary artery and gains the medial surface of the pleural sac. From the root of the neck the rela- tions of the phrenic nerves differ. The right phrenic nerve descends along the medial surface of the right pleural sac and crosses in front of the root of the lung. It is accompanied by the pericardiaco-phrenic artery (comes nervi phrenici), and it is in relation medially, and from above downward, with the right innominate vein, the superior vena cava, and the pericardium, the latter membrane separating it from the wall of the right atrium (auricle) . The left phrenic nerve descends along the medial surface of the left pleural sac accompanied by the pericardiaco-phrenic (comes nervi phrenici) artery. In the superior mediastinum it lies between the left common carotid and the left subclavian arteries, and it crosses in front of the left vagus, the left superior intercostal vein, and the arch of the aorta. Below the arch of the aorta it crosses in front of the root of the left lung, and then hes along the left lateral surface of the pericardium, which separates it from the wall of the left ventricle. Branches. — Both phrenic nerves distribute branches to the pericardium and to the pleura. The right nerve gives off a branch, pericardiac, which accompanies the superior vena cava and supplies the pericardium. Each phrenic nerve divides into numerous terminal phrenico- abdominal branches. As a rule, the right phrenic nerve divides into two main terminal branches, an anterior and a posterior. The anterior branch runs forward and one of its terminal filaments 980 THE NERVOUS SYSTEM anastomoses with the phrenic of the opposite side in front of the pericardium; others descend between the sternal and costal attachments of the diaphragm into the abdomen, where some of them supply the diaphragm and others descend in the falciform Ugament to the peritoneum on the upper surface of the liver. The posterior branch passes through the vena caval opening and ramifies upon the lower surface of the diaphragm, anastomosing with the diaphragmatic plexus of the sympathetic, and its terminal branches supply the muscular fibi-es of the right half of the diaphragm, the inferior vena cava, and the right suprarenal gland. The left phrenic nerve divides into several branches. One of the most anterior branches anastomoses with the right phrenic nerve; the others pierce the diaphragm and ramify on its under surface, where they anastomose with filaments of the left diaphragmatic plexus of the sympathetic and supply the left half of the diaphragm and the left suprarenal gland. The left phrenic nerve is considerably longer than the right nerve, partly on account of the lower level of the diaphragm on the left side, and partly on account of the greater convexity of the left side of the pericardium. THE BRACHIAL PLEXUS The brachial plexus (figs. 751, 754, 755) is formed by the anterior primary divisions of the four lower cervical nerves and the greater part of that of the Fig. 754. — Diagbam op a Common Form op Bbachial Plexus. The posterior cord of the plexus is darkly shaded. Fifth cervical — ^j\ \( From fourth cervical Sixth cervical Seventh cervic; Eighth cervical Long thoracic. First thoracic. First intercostal Second thoracic Second intercostal Third thoracic Third intercostal ical^^ -Nerve to subclavius - Suprascapular Anterior thoracic nerves Lateral cord of plexus N.^ = — Radial (musculo-spiral) — ;_: ■• Transverse carpal ligament ^ Volar antibrachial interosseous - Palmar cutaneous branch (cut short) Median nerve Pisiform bone _ Deep branch of ulnar Abductor digiti quinti , Flexor digiti quinti brevis '*-* Palmaris brevis between the flexor carpi ulnaris and flexor digitorum sublimis, and is covered only by skin and fascia. At a variable point in this part of the forearm, usually about 5 to S cm. (2 to 3 in.) from the carpus, the nerve divides into its two terminal branches, a dorsal branch to the dorsal aspect of the hand, and a volar branch to the volar aspect. 990 THE NERVOUS SYSTEM Branches. — ^The ulnar resembles the median nerve in not furnishing any branches to the upper arm. As it passes between the olecranon process and the medial condyle it gives off two or three fine filaments to the elbow-joint. In the upper part of the forearm it supplies the flexor carpi ulnaris and the medial portion of the flexor digitorum profundus, and in the lower half it gives off the three cutaneous branches. In the palm of the hand it supplies the integument of the hypothenar eminence, the fifth digit, and half of the fourth digit, and part of the skin of the dorsum. It also supplies the short intrinsic muscles of the hand with the exception of the abductor poUicis, the opponens, the lateral head of the flexor poUicis brevis, and the two lateral lumbricales. The nerves to the flexor carpi ulnaris and to the medial two divisions of the flexor digitorum profundus arise from the ulnar nerve in the upper third of the forearm. Cutaneous branches. — About the middle of the forearm the ulnar nerve gives off two cutaneous branches: — one pierces the fascia and anastomoses with the volar branch of the medial antibrachial (internal) cutaneous nerve, and the other, the palmar cutaneous branch, runs downward in front of the ulnar artery (fig. 759) and is conducted by this vessel into the palm Fig. 760. — Diagrams Illustrating a Common Distribution op Cutaneous Nerves op Ulnar branch of medial anti- ' brachial cutaneous Dorsal cutane- ous branch' of ulnar Dorsal digital nerves (ulnar) Forearm. A, dorsum; B, volar aspect Dorsal antibrachial...// \ cutaneous (radial) l/j \ Dorsal antibrachial ' ' ^ cutaneous (radial) \ Lateral antibrachial '* cutaneous (musculo.. cutaneous) Lateral antibrachial cutaneous (musculo- cutaneous Median nerve .-Superficial radial Superficial radial From lateral anti- brachial Dorsal cutaneous digital branches of radial Dorsal branches of radial Dorsal branches of proper volar dii^tal Dorsal nerves (median)' -^*» branches of proper volar digital nerves (median) Ulnar branches dial anti- brachial cuta- neous Volar branches of medial anti- brachial cutaneus -.-Volar branch of ulnar .^Cutaneous branches of common volar digital nerves Proper volar digital nerves (ulnar) (fig. 756). It furnishes some filaments to the vessel, supplies a few twigs to the skin of the hypo- thenar eminence, and ends in the integument covering the central depressed surface of the palm. The dorsal or posterior cutaneous branch, usually the smaller of the terminal branches, arises about 5 cm. (2 in.) above the wrist-joint, and passes backward under cover of the flexor carpi ulnaris to reach the dorsal aspect of the wrist (fig. 761), where it gives off dehoate branches to anastomose with branches of the medial antibrachial (internal) cutaneous, the dorsal anti- brachial (external) cutaneous branch of the radial (musculo-spiral), the lateral antibrachial cutaneous of the musculo-cutaneous nerve, and with branches of the superficial radial, and then divides into five branches, the dorsal digitals (fig. 757), which are distributed to the ulnar sides of the third, fourth, and fifth digits and the radial sides of the fourth and fifth digits. These branches usually extend on the fifth digit only as far as the base of the terminal phalanx, and on the fourth digit as far as the base of the second phalanx. The more distal parts of these digits are supplied by palmar digital branches of the ulnar nerve. The volar branch, the other terminal branch of the ulnar nerve, continues its course between the flexor carpi ulnaris and flexor digitorum sublimis, on the medial side of the ulnar artery, to the wrist, where, on the lateral side of the pisiform bone, it divides into a superficial and a d£ep branch (figs. 759 and 761). The latter accompanies the deep branch of the ulnar artery into the interval between the abductor digiti quinti and flexor digiti quinti brevis, and then THE MEDIAN NERVE 991 passes through the fibres of the opponens digiti quinti to reach the deep surface of the flexor tendons and theu- synovial sheaths. It supphes the abductor and opponens digiti quinti, the flexor digiti quinti brevis, the third and fourth lumbricales, all the interossei, the adductors of the thumb, and the medial head, and occasionally the lateral head, of the flexor poUicis brevis. The superficial branch gives off a branch to supply the palmaris brevis muscle, an anastomosing branch to the median nerve, and then divides into two branches, the proper volar digital branch, which is distributed to the medial side of the fifth digit on its volar aspect, and the common volar digital branch, which passes underneath the palmar aponeurosis and divides into two branches, which supply the contiguous margins of the fourth and fifth digits. These branches usually supply also the dorsal surface of the second and third phalanges of the same digits. The median nerve contains fibres of the sixth, seventh, and eighth cervical nerves and of the first thoracic, and sometimes of the fifth cervical nerve. The trunk is formed a little below the lower margin of the pectorahs minor, by the Fig. 761. — Nerves op the Palmar Surface op the Hand. (Testut.) The transverse carpal (anterior annular) ligament, superficial palmar arch, the flexor tendons of the digits, and the proximal portions of the lumbrical muscles have been removed. Superficial radial Palmar branch of median Branches of superficial radial Branch to adductor polhi Proper volar digital -y^ Deep branch of ulnar Dorsal branch of ulnar — Superficial branch -Muscular branch 'almar cutaneous brancb — Branch to lumbrical IV ■Common volar digital •Proper volar digital union of two components, one from the medial and one from the lateral cord "of the brachial plexus (fig. 755). The medial component passes obliquely across the third part of the axillary artery, and in the upper part of the trunk the fibres of the two components are felted together. From its commencement the median nerve runs almost vertically through the lower part of the axillary fossa and through the arm and forearm to the hand. In the fossa it hes lateral to the axillary artery and it is overlapped, on its lateral side, by the cqraco-brachiahs muscle. In the upper half of the arm it lies along the lateral side of the brachial artery, and it is overlapped by the medial border of the biceps. At the middle of the arm it passes in front of the brachial artery, and then it descends, on the medial side of the artery, to the elbow. In the upper part of the antecubital fossa it is still at the medial side of the bra- chial artery, but separated from it by a small interval, and in the lower part of the fossa it Lies 992 THE NERVOUS SYSTEM along the medial side of the ulnar artery. In case of the high division of the brachial artery, when the radial and the ulnar arteries lie together in the upper arm, the median nerve may pass between them and then one or the other of the arteries will be superficial to the nerve. As it leaves the antecubital fossa it passes between the two heads of the pronator teres, and it crosses in front of the ulnar artery (fig. 759), from which it is separated by the deep head of the pronator. In the forearm it passes vertically downward, accompanied by the median (comes nervi mediani) artery. In the upper two-thirds of this region it lies deeply, between the flexor digitorum sublimis and the flexor digitorum profundus, but in the lower third it becomes more superficial, and is placed beneath the deep fascia, between the flexor carpi radialis on the radial side and the palmaris longus and flexor digitorum sublimis tendons on the ulnar side. It crosses beneath the transverse carpal (anterior annular) ligament, in front of the flexor tendons, and in the palm at the lower border of the ligament it enlarges and divides into three branches, the common volar digital nerves (fig. 760). Branches. — The median nerve does not supply any part of the upper arm. In front of the elbow-joint it furnishes one or two filaments to that articulation. In the forearm it supplies all the superficial anterior muscles (with the exception of the flexor carpi ulnaris) directly from its trunk, and it supplies the deep muscles (with the exception of the ulnar half of the flexor digitorum profundus) by its volar (anterior) interosseous branch. Thus in general it supplies the pronator and flexor muscles of the forearm (radial side). In the hand it supplies the group of short muscles of the thumb, which are placed on the radial side of the tendon of the flexor pollicis longus, the two lateral lumbricales, the integument covering the central, part of the palm and ulnar aspect of the thenar eminence, and the palmar aspect of the first, second, third, and radial half of the fourth digits. It also sends twigs to the dorsal aspect of these digits. The nerve to the pronator teres usually arises a little above the bend of the elbow, and pierces the lateral border of the muscle (figs. 759 and 761). It may arise in a common trunk with the following nerves: — The nerves to the flexor carpi radialis, palmaris longus, and flexor digitorum sublimis arise a Uttle lower down, and pierce the pronator-flexor mass of muscles to end in the respective members of the group for which they are destined (fig. 758). The volar (anterior) interosseous nerve arises from the median at the level of the bicipital tubercle of the radius (fig. 759), and runs downward, on the interosseous membrane, accom- panied by the volar (anterior) interosseous artery. It passes under cover of the pronator quad- ratus, and pierces the deep surface of that muscle, which it supplies. The volar interosseous nerve also furnishes a twig to the front of the wrist-joint, and supphes the flexor digitorum profundus and the flexor poUicis longus. The nerve to the former muscle arises from the volar interosseous near its commencement; it supplies the outer two divisions of the muscle, and it communicates within the substance of the muscle with twigs derived from the ulnar nerve. It also supphes a branch to the interosseous membrane which runs downward upon, or in, the membrane, supplying it and giving branches to the volar (anterior) interosseous and nutrient arteries and to the periosteum of the radius, the ulna, and the carpus. The palmar cutaneous branch arises immediately above the transverse carpal (anterior annular) ligament and passes between the tendons of the flexor carpi radialis and the palmaris longus (fig. 759). It then crosses the superficial surface of the transverse carpal ligament, and is distributed to the integument and fascia on the central, depressed surface of the palm. It also supplies a few twigs to the medial border of the thenar eminence; these twigs commu- nicate with the musculo-cutaneous and superficial radial nerves. The three common volar digital nerves pass in the palm of the hand dorsal to the superficial palmar arch and its digital branches, while the proper volar digitals, branches of these nerves, lie on the volar side of the digital arteries. The first of the common volar digital nerves gives off a branch to supply the abductor pollicis, the opponens, and the superficial head of the flexor pollicis brevis, and joins by a delicate branch with the deep branch of the ulnar nerve. It then divides into three proper volar digitals (fig. 761). The lateral of these passes obhquely across the long flexor tendon of the thumb and runs along the radial border of the thumb to its extremity. It gives numerous branches to the pulp of the thumb, and a strong twig which passes to the dorsum to supply the matrix of the nail. The second of these proper volar digitals supplies the medial side of the volar aspect of the thumb and gives off a twig to the matrix of the thumb nail. The third supplies the radial side of the second digit and gives a twig to the flrst lumbrical muscle. The second common volar digital sends a twig to the second lumbrical muscle, and divides a httle above the metacarpo-phalangeal articulation into two proper volar digitals, which respectively supply the adjacent sides of the second and third digits. The third common volar digital communicates with the ulnar nerve, often gives a branch to the third lumbrical muscle, and divides into two proper volar digitals which supply the adja- cent sides of the third and fourth digits. As the proper volar digitals pass along the margins of the fingers they give off twigs for the innervation of the skin on the dorsum of the second and third phalanges and the matrix of their nails. Each of the nerves terminates in filaments to the pulp of the finger. RELATIONS OF NERVES 993 Table Showing Relation op Cervical and Thoracic Nerves to Branches op Brachial Plexus Nerves Contributing. Nerves, Branches op Plexus. 5C f Dorsal scapular (nerve to rhomboids) \ Nerve to subclavius ( Suprascapular 5 and 6 C J ^erve to subclavius 1 Upper subscapular Lower subscapular *■ Axillary (circumflex) 5 6 and 7 C I ^°"S (posterior) thoracic ' ' I Lateral anterior thoracic 5, 6, and (7) C Musculo-cutaneous (5), 6, 7, 8 C Radial (musculo-spiral) (5), 6, 7, 8 C, and 1 T Median 7 and 8 C Thoraco-dorsal (middle or long subscapular) f Medial anterior thoracic 8 C. andl T \ Uhiar [ Medial antibrachial (internal) cutaneous IT Medial brachial (lesser internal) cutaneous Table Showing the Relations op the Cervical Nerves to the Muscles OF the Upper Extremity Nerves Contributing. Accessory, 2 C 3, 4C... 3 and 4 C Muscles. 5 and 6 C. 6C. 6 and 7 C. 5, 6, and;i;7 C. 7C. 7 and 8 C 5, 6, 7, andSC. 8 C 7, 8 Cand'l T. 8C.and IT. Sterno-mastoid Trapezius Levator scapulae Subclavius Supraspinatus Infraspinatus Subscapularis Teres major Teres minor Deltoid Brachiahs ^ Biceps Braohioradialis Supinator ■I Pronator teres Fle.xor carpi radialis I Palmaris longus I Ext. carpi radialis longus I " " brevis \ Abductor pollicis brevis Opponens " I Flexor poUicis brevis (superf. head) Serratus anterior Coraoo-brachialis Ext. digitorum coram. " digiti quinti proprius " carpi ulnaris Abductor pollicis longus Extensor pollicis brevis Extensor pollicis longus Ext. indicus proprius Latissimus dorsi Triceps Anconeus Pectoralis major Dorsal inteross. Palmar " Add. pollicis " pollicis trans. Flex, polhois brev. (deep) Pectoralis minor Flex, digit, subl. Lumbricalis Flex, carpi ulnaris " digit, prof. " pollicis long. Pronator quadratus Nerves to Muscles. Spinal accessory " , 3 and 4 C. 3 and 4 C. Nerve to subclavius !• Suprascapular Upper and lower subscapular Lower subscapular Axillary (circumfle.x) Musculo-cutaneous Radial (musculo-spiral) Deep radial (posterior interosseous) Median Radial (musculo-spiral) Deep radial (posterior interosseous) Median Long (posterior) thoracic Musculo-cutaneous Deep radial (posterior interosseous) Thoraco-dorsal (long"subscapular) Radial (musculo-spiral) Lat. and med. ant. thoracic Ulnar ■ Med. ant. thoracic Median " and ulnar Ulnar " and median Median 994 THE NERVOUS SYSTEM 2. THE THORACIC NERVES The anterior primary divisions of the thoracic nerves, with the exception of the first, retain, in the simplest form, the characters of anterior primary divisions of the typical spinal nerve. They do not form plexuses, but remain distinct from each other. Each divides into an easily recognisable lateral or dorsal and anterior or ventral branch (figs. 762 and 763), and they are not distributed to the limbs. The first, second, and last thoracic nerves, on account of their pecuUarities, require separate description. The remainder are separable into two groups, an upper and a lower. The upper group consists of four nerves, the third to the sixth inclusive, which are distributed entirely to the thoracic wall. The lower group contains five nerves, the seventh to the eleventh inclusive, which are distributed partly Fig. 762. — Diagram of the Distribution of a Typical Thoracic Nerve. Longissimus dorsi Semispinalis dorsi Medial branch' i y Superior costo-transversf~ ' ligament Dorsal root Ventral root Recurrent branch' Sympathetic ganglion- Viceral branch Branch to aorta' (Esophagu Internal mammary artery Transverse thoracic muscle Ilio-costalisldorsi Lateral branch Posterior primary division Anterior primary division Internal intercostal muscle External intercostal muscle ■Lateral cutaneous bianch Anterior branch Anterior intercostal membrane to the thoracic and partly to the abdominal wall. The upper group is therefore purely thoracic in distribution, and the lower thoraco-abdominal. The first thoracic nerve is connected with the first thoracic sympathetic gang- lion, and it frequently is joined by a small branch with the second nerve. It is distributed chiefly to the upper limb. Opposite the superior costo-transverse ligament of the second rib it divides into a larger and a smaller branch; the larger passes upward and lateralward, between the apex of the pleura and the neck of the first rib, and on the lateral side of the superior intercostal artery, to the root of the neck, where it joins the brachial plexus. The smaller branch con- tinues along the intercostal space, below the first rib and between the intercostal muscles in which, as a rule, all its fibres terminate. However, the smaller branch may give off a lateral cutaneous branch which connects with the medial brachial (lesser internal) cutaneous nerve and with the intercosto-brachial nerve in the axillary fossa; and occasionally it terminates in an anterior cutaneous branch at the anterior extremity of the first intercostal space. The second thoracic nerve, as it lies between the pleura and the superior costo-transverse ligament of the third rib, gives a branch to the first nerve, then it pierces the posterior intercostal membrane and passes between the external and internal intercostal muscles in the second intercostal space. In the dorsal part of the space it sends branches backward, through the external intercostal muscle, THE THORACIC NERVES 995 to supply the second levator costse and the serratus posterior superior, and then it divides into a lateral and an anterior branch. The two branches run forward together to the mid-axillary line, where the lateral branch pierces the external intercostal muscle and passes between two digitations of the serratus anterior (magnus) into the axillary fossa; the anterior branch enters the substance of the internal intercostal muscle. The lateral branch, the intercosto-brachial (intercosto-humeral) , may divide into a small anterior and a large posterior division, or the anterior division may be absent. In either case the lateral branch anastomoses with the medial brachial (lesser internal) cutaneous nerve, and usually with the lateral branch of the third intercostal nerve; it also anastomoses with the lateral branch of the first nerve, if the latter is present. After forming these junctions it passes out of the axillary fossa, pierces the deep fascia, and supplies the integument in the upper and pos- terior half of the arm. It also gives off a few filaments which terminate in the skin over the ajdllary border of the scapula. The size of the intercosto-brachial nerve and the extent of its distribution are usually in inverse proportion to the size of the other cutaneous nerves of the upper arm, especially the middle brachial (lesser internal) cutaneous. When the latter nerve is absent, the intercosto-brachial usually takes its place. The course and distribution of the anterior branch, when it is present, being similar to the course and distribution of the anterior branches of the next four nerves, do not require a separate description. The thoracic intercostal nerves (upper group). — The third, fourth, fifth, and sixth thoracic nerves, in the posterior parts of the intercostal spaces, give muscu- lar branches to the levatores costarum, the first to the fourth also giving branches to the serratus posterior superior. They pass forward a short distance between the external and internal intercostals, giving twigs to these muscles, and divide into two branches, lateral and anterior. The lateral cutaneous branches continue forward between the intercostal muscles, and, near the mid-axillary line, pierce the external intercostals and serratus anterior (magnus) and divide into two branches, posterior and anterior. The posterior branches pass backward over the latissimus dorsi to supply the skin in the lower part of the scapular region. The anterior branches, in the four nerves, increase in size from above downward. They pass around the lateral border of the great pectoral muscle and are distributed to the integument over the front of the thorax and m'anima, sending filaments, the lateral mammary branches, into the latter organ. The lowest two nerves also supply twigs to the upper digita- tions of the external oblique muscle. The anterior branches run obliquely forward and medialward through the substance of the internal intercostal muscles, reaching the deep surface of these muscles at the extremity of the costal cartilages (fig. 762). They continue forward between these muscles and the pleura, pass in front of the internal ■ mammary artery, turn abruptly ventralward a short distance from the sternum, pierce the internal intercostals, the anterior intercostal membrane, and the pec- toralis major, and give off three sets of terminal branches. One set supplies the transverse thoracic muscle and the back of the sternum. A second set, cutaneous, runs mesially. The third set passes laterally over the pectoralis major, supplying the skin in that region, and, in the female, the mammary gland through the medial mammary branches. The anterior branches in their course supply the intercostal and subcostal muscles and give filaments that supply the ribs, the periosteum, and the pleura. The thoraco-abdominal nerves (lower group). — The relations of the posterior portions of the seventh, eighth, ninth, tenth, and eleventh thoracic nei'ves to the thoracic wall are similar to those of the upper thoracic intercostal nerves. Each divides in a similar manner into a lateral and an anterior branch, but these branches are distributed partly to the abdominal and partly to the thoracic wall, and the smaller muscular branches have also different distributions. The lateral branches, lateral cutaneous nerves of the abdomen, pierce the external intercostal muscles and pass through or between the digitations of the external oblique into the subcutaneous tissue, where they divide in the typical way into anterior and posterior branches. The posterior branches pass backward over the latissimus dorsi. The anterior branches give filaments to the digitations of the external oblique and extend forward, medialward and downward to the outer border of the sheath of the rectus. The anterior branches pass forward between the external and internal intercostal muscles, to the ends of the intercostal spaces; there they insinuate 996 THE NERVOUS SYSTEM themselves between the interdigitating slips of the diaphragm and the transversus abdominis and enter the abdominal wall. The seventh, eighth, and ninth nerves, in their transit from the thoracic to the abdominal wall, pass behind the upturned ends of the eighth, ninth, and tenth rib-cartilages respectively. Having entered the abdominal wall the nerves run forward between the transversus abdominis and the internal oblique, muscles to the outer border of the rectus abdominis, where they pierce the posterior lamella of the internal oblique aponeurosis and enter the sheath of the rectus. In the sheath they pass through the substance of the rectus. Finally they turn directly forward, pierce the anterior part of the sheath, and become anterior cutaneous nerves of the abdomen. The muscular branches. — Muscular branches from all the thoraco-abdominal nerves are distributed to the levatores costarum, the intercostal muscles, the transversus abdominis, the internal oblique, and to the rectus abdominis, and the ninth, tenth, and eleventh nerves gives branches also to the serratus posterior inferior. Branches are also distributed from a variable number of the lower nerves to the costal portions of the diaphragm. The last thoracic nerve. — The anterior primary division of the last thoracic nerve is distributed to the wall of the abdomen and to the skin of the upper and front part of the buttock. It appears in the thoracic wall immediately below the last rib, where it communicates with the sympathetic cord and gives off a com- municating branch to the first lumbar nerve. It passes from the thorax into the abdomen beneath the lateral lumbo-costal arch (external arcuate ligament), accompanied by the subcostal artery, and it runs across the upper part of the quadratus lumborum dorsal to the kidney and to the ascending or the descending colon according to the side considered. At the lateral border of the quadratus lumborum it pierces the aponeurosis of attachment of the transversus abdominis muscle and divides, between the transversus and the internal oblique muscle, into a lateral and an anterior branch. It gives branches to the transversus abdominis, the quadratus lumborum, and the internal oblique muscles. The anterior branch passes forward, between the internal oblique and the transversus abdominis, to which it suppUes twigs. It enters the sheath of the rectus, turns forward through that muscle, and terminates in branches which become cutaneous midway between the umbilicus and the symphysis. Before it becomes cutaneous it supplies twigs to the transversus abdominis, the internal oblique, the rectus abdominis, and the pyramidalis muscles. The lateral branch pierces the internal obhque; it supplies the lowest digitation of the external obhque, and then pierces the latter muscle from 2.5 to S cm. (1 to 3 in.) above the iliac crest, and descends in the superficial fascia of the anterior part of the gluteal region, crossing the ihac crest about 2.5 cm. (1 in.) behind its anterior extremity and reaching as far down as the level of the great trochanter. Occasionally this branch is absent and its place is taken by the iliac branch of the ilio-hypogastric. In such oases, however, the branch from the last thoracic to the first lumbar nerve is larger than usual. THE LUMBO-SACRAL PLEXUS The lumbo-sacral plexus is formed by the union of the anterior primary divisions of the lumbar, sacral, and coccygeal nerves. In about 50 per cent, of cases it receives a branch from the twelfth thoracic nerve. Its components are distributed to the lower extremity in a manner homologous and similar to the distribution of the parts of the brachial plexus to the upper extremity; the lumbar nerves are distributed similarly to the nerves formed from the anterior (medial and lateral) cords of the brachial plexus, and the sacral nerves are distributed in a manner similar to the distribution of the nerves from the posterior cord of the brachial plexus. Partly for convenience of description and partly on account of the differences in position and course of some of the nerves arising from it, this plexus is sub- divided into four parts — the lumbar, sacral, pudendal, and coccygeal plexuses. These plexuses overlap so that there is no definite line of demarcation between them. However, they will be considered separately. 3. THE LUMBAR NERVES The anterior primary divisions of the five lumbar nerves increase in size from the first to the last. Each lumbar nerve is connected by one or two long, slender THE LUMBAR NERVES 997 rami with a lumbar sympathetic ganglion. The first three nerves and the greater part of the fom-th enter into the formation of the lumbar plexus, and the smaller Fig. 763. — Cutaneous Nerves of the Thorax and Abdomen, viewed prom the Side. (After Henle.) PectoraliB major Supraclavicular branch of cervical plexus Pectoralis minor Sheath of rectus _- Ilio-hypogastric Brachial plexus Intercosto-brachial part of the fourth and the fifth nerve commonly unite to form the lumbo-sacral cord which takes part in the formation of the sacral plexus (figs. 764, 765) . When the fourth nerve enters into the formation of both lumbar and sacral plexuses, 998 THE NERVOUS SYSTEM it may be called the furcal nerve, but this name is also applied to any of the nerves that enter into the formation of both plexuses, so there may be one or more furcal nerves. THE LUMBAR PLEXUS Although the lumbar plexus is ordinarily formed by the first three lumbar nerves and a part of the fourth, yet it is subject to considerable variation in the manner of its formation. Owing to this variation three general classes of plexuses may be found, proximal or pre- fixed, ordinary, and distal or post-fixed. The basis of classification is the relation of the nerves of the limb to the spinal nerves which enter into their formation. The intermediate or slighter degrees of variation may consist only of changes in the size of the portions contributed by the diHerent spinal nerves to a given peripheral nerve, for a given nerve may receive a larger share of its fibres from a more proximal spinal nerve, and a smaller share from a more distal nerve, or vice versd. However, in the more marked degrees of variation the origin of a given peripheral nerve may vary in either direction to the extent of one spinal nerve. The more extreme types of the plexuses are sometimes associated with abnormal conditions of the vertebral column. It has been suggested that when the prefixed or proximal condition occurs, it indicates that the lower limb is placed a segment more proximal than in the ordinary cases, and when the distal condition is present, that the limb is arranged a segment more distal. Three types each of the proximal and the distal classes and one type of the ordinary class have been described by Bar- deen. His statistics are made use of in the compilation of the following tables, in which are shown the range of variation and the common composition of each class of plexus: — Composition of the Nerves of the Lumbar Plexus Range of Variation Nerve. Proximal. Ordinary. Distal. Lateral (external) cutaneous 12 T, 1, 2, 3 L. 1, 2, 3, 4 L. 1, 2, 3, 4 L. Femoral (anterior crural) ... 12 T, 1, 2, 3, 4 L. 1, 2, 3, 4 L. 1, 2, 3, 4, 5 L. Obturator 1, 2, 3, 4 L. 1, 2, 3, 4 L. 2, 3, 4, 5 L. Furcal 3 or 3, 4 L. 4 L. 4, 5 or 5 L. Common Composition Nerve. Proximal. Ordinary. Distal. Lateral (external) cutaneous 1, 2 L. 1, 2, 3 L. 2, 3 L. Femoral (anterior crural) . . 1, 2, 3, 4 L. 2, 3, 4 L. 2, 3, 4, 5, L. Obturator 1, 2, 3, 4 L. 2, 3, 4 L. 2, 3, 4 L. Furcal 4 L. 4 L. 4 L. The lumbar plexus lies in the posterior part of the psoas muscle (fig. 765), in front of the transverse processes of the lumbar vertebrae and the medial border of the quadratus lumborum, and its terminal branches are distributed to the lower part of the abdominal wall, the front and medial part of the thigh, the external genital organs, the front of the knee, the medial side of the leg, and the medial side of the foot. The first and second of the lumbar nerves give collateral muscular branches to the quadratus lumborum muscle, and the second and third nerves give similar branches to the psoas. The remaining branches of the plexus are terminal branches. The first lumbar nerve, after it has been joined by the branch from the last thoracic nerve, divides into three terminal branches, the ilio-hypogastric nerve, the ilio-inguinal nerve, and a branch which joins the second nerve. The fibres of this latter branch pass mainly into the genito-femoral (genito-crural) nerve, but occasionally some of them enter the femoral (anterior crural) and obturator nerves. The remaining nerves divide into anterior or ventral and posterior or dorsal divisions. The anterior divisions form a portion of the genito- femoral (genito-crural) nerve and the obturator nerve, and the posterior divisions enter the lateral (external) cutaneous and femoral (anterior crural) nerves. All the terminal branches of the plexus are formed in the substance of the psoas muscle; four of them, the ilio-hypogastric, the ilio-inguinal, the lateral (external) cutaneous, and the femoral (anterior crural), leave the muscle at its lateral border. The genito-femoral (genito-crural) passes through its anterior surface, and the obturator through its medial border. Terminal branches. — The ilio-hypogastric nerve springs from the first lumbar nerve, after the latter has been joined by the communicating branch THE LUMBAR PLEXUS 999 from the last thoracic nerve, as it is in about 50 per cent, of the cases, and it thus contains fibres of both the last thoracic and the iirst lumbar nerves. It pierces the lateral border of the psoas and crosses in front of the quadratus lumborum (fig. 765), and behind the kidney and the colon. At the lateral border of the quadratus it pierces the aponeurosis of origin of the transversus abdominis and enters the areolar tissue between the transversus and the internal oblique, where it frequently communicates with the last thoracic and with the ilio-inguinal Fig. 764. — Diagram of a Common Form of Lumbo-saceal Plexus. (Modified from Paterson.) From last thoracic nerve •< - r — First lumbar Genito-femoral lUo-hypogastrici Ilio-inguinal> Lateral cutaneo Obturator Accessory obturator. To superior gluteal To inferior gluteal --- To piriformis - Sciatic _ ^^ J/ To quadratus femons Common peroneal section - — •Second lumbar — —Third lumbar Fourth lumbar Fifth lumbar - Second sacral - Third sacral J • Visceral branches - Fourth sacral . Visceral branches ■• Perineal * Fifth sacral - To coccygeus - To levator ani To hamstrings ' Fosterior femora] Perforating t cutaneous cutaneous To obturator internus nerve, and it divides into an iliac and a hypogastric branch, which correspond, respectively, with the lateral and anterior branches of a typical spinal nerve. The anterior cutaneous (hypogastric) branch passes forward and downward, between the transversus abdominis and the internal oblique muscles, giving branches to both; it communi- cates with the ilio-inguinal nerve, and, near the anterior superior spine of the ilium, it pierces the internal oblique muscle and continues forward beneath the external obhque aponeurosis toward the middle line. About 2. .5 cm. (1 in.) above the subcutaneous inguinal ring it pierces the aponeurosis of the external oblique, becomes subcutaneous, and supplies the skin above the symphysis. The lateral cutaneous (iliac) branch pierces the internal and external obhque muscles, emerging through the latter above the iUac crest at the junction of its anterior and middle thirds (fig. 769). It is distributed to the integument of the upper and lateral part of the thigh, in the neighborhood of the gluteus medius and tensor fasciae latae muscles (fig. 768). 1000 THE NERVOUS SYSTEM The ilio-inguinal nerve arises principally from the first lumbar nerve, but it frequently contains fibres of the last thoracic nerve. It emerges from the lateral border of the psoas, at a lower level than the ilio-hypogastric nerve, and passes across the quadratus lumborum (figs. 765, 766). As a rule, it is below the level of the inferior end of the kidney, but it passes dorsal to the ascending or the descending colon according to the side considered, and crosses the posterior part of the inner lip of the iliac crest; it then runs forward on the upper part of the iliacus, pierces the transverus abdominis near the anterior part of the crest, and communicates with the anterior cutaneous (hypogastric) branch of the ilio- hypogastric nerve. A short distance below the anterior superior spine it passes through the internal oblique muscle, and then descends in the inguinal canal to the subcutaneous inguinal (external abdominal) ring, through which it emerges into the thigh on the lateral side of the spermatic cord (fig. 763). It is distributed to the skin of the upper and medial part of the thigh, in the male to the root of the penis and to the skin of the root of the scrotum through the anterior scrotal nerves (fig. 768), and in the female to the mons veneris and labium majus through the anterior labial nerves. Not uncommonly the iho-inguinal nerve is blended with the iho-hypogastric nerve and separates from the latter between the transversus abdominis and the internal obUque muscles. It may be replaced by branches of the genito-femoral (genito-orural) nerve, or it may replace that nerve or the lateral cutaneous nerve. cs The genito-femoral (genito-crural) nerve is connected with the first and second lumbar nerves, but the majority of its fibres are derived from the second nerve. It passes obliquely forwarcl and downward through the psoas and emerges from the anterior surface of that muscle, close to its medial border, at the level of the lower border of the third lumbar vertebra. After emerging from the sub- stance of the psoas it runs downward on the anterior surface of the muscle (fig. 765), to the lateral side of the aorta and the common iliac artery, passes behind the ureter and divides into two branches, an external spermatic or genital, and a lumbo-inguinal or crural (fig. 766). Occasionally it divides in the substance of the psoas, and then the two branches issue separately through the anterior surface of the muscle. The external spermatic (genital) branch runs downward on the psoas muscle, external to the external iliac artery; it gives a branch to the psoas, and at Poupart's hgament it turns around the inferior epigastric artery and enters the inguinal canal, accompanjdng the spermatic cord in the male or the round hgament in the female. It suppUes the cremaster muscle, and gives twigs to the integument of the scrotum (fig. 766) or the labium majus. The lumbo-inguinal (crural) branch passes downward along the external ihac artery and beneath Poupart's hgament into the thigh, which it enters to the lateral side of the femoral artery. A short distance below Poupart's ligament it pierces the fascia lata or passes through the fossa ovalis (saphenous opening) and supplies the skin in the middle of the upper part of the thigh. A short distance below Poupart's hgament it sometimes sends branches to the anterior branch bf the lateral cutaneous nerve, and about the middle of the thigh it often joins with the cutaneous branches of the femoral (anterior crural) nerve. The lateral cutaneous nerve receives fibres from the dorsal branches of the anterior primary divisions of the second and third lumbar nerves, and frequently some fibres from the first lumbar (fig. 769). It emerges from the lateral border of the psoas and passes obliquely across the iliacus dorsal to the iliac fascia, and dorsal to the caecum on the right side and the sigmoid colon on the left side, to a point immediately below the anterior superior spine of the ilium, where it passes below Poupart's ligament into the lateral angle of the femoral trigone (Scarpa's triangle). Leaving the trigone at once it passes through, behind, or in front of the sartorius and divides into two branches, anterior and posterior, which enter the deep fascia (fig. 766). The posterior branch of the lateral cutaneous nerve breaks up into several secondary branches which become subcutaneous, and they supply the integument of the lateral part of the thigh, from the great trochanter to the level of the middle of the femur. The anterior branch runs downward in a canal in the deep fascia, for three or four inches, before it becomes sub- cutaneous. It usually divides into two branches, a lateral and a medial. The lateral branch supplies the skin of the lower half of the lateral side of the thigh, and the medial branch is dis- tributed to the skin of the lateral side of the front of the thigh as far as the knee (fig. 766). Its lower filaments frequently unite with the cutaneous branches of the femoral (anterior THE FEMORAL NERVE 1001 crural), and with the patellar branch of the saphenous nerve in front of the patella, forming with them the patellar plexus. The femoral (anterior crural) nerve is the largest terminal branch of the lum- bar plexus. It is formed chiefly by fibres of the dorsal branches of the anterior primary divisions of the second, third, and fourth lunibar nerves, but it sometimes receives fibres from the first nerve also (figs. 765 and 769). It emerges from the lateral border of the psoas a short distance above Poupart's ligament, and descends in the groove between the psoas and the iliacus, behindPoupart's ligment, into Fig. 765. — Lumbo-sacral Plexus. (After Toldt, 'Atlas of Human Anatomy,' Rebman, London and New York.) Lumbar vertebrae Medial crus of diaphrag: Rib XU Psoas minor Intercostal XII /I Q jadratus lumborum -^ /? I lUo-hypogastnCs^/^/' '-J, ''j Ilio-mgumal v.^ MMtjK') Psoas major Transversus v// '^ /A abdominis " ^ Genito-femoral-' ' Lumbar I (anterior bran::h) /Muscular branch -■ Ilio -hypogastric 'Psoas minor *^ //Ifa^W ^<*|^^-=' R^mi communicantes ^\^j^^p^.^ Sympathetic trunk Lumbar II Muscular branche V^ Gemto-femoral Obturator fascia Piriformis with its muscular branch j^y s. Muscular branches for J iliacus 'J> Fe J ^Obturator ^Lumbo-sacral trunk g!^^ \ \ '^^^^^ ^ Piriformis |_^A^/l " ' ^P// \ Y*^ \Sciatic V7 J; ^/Mt \ \ \ Sacral pie ~^ N ^v Posterior cutaneo Ganghon coccygeum impar / / jj Coccygeal ' / Ano-coccygeal Middle h£emorrhoidal and \ inferior ve; Pudendal plexus the femoral trigone (Scarpa's triangle), where it lies to the lateral side of the femoral artery (fig. 767) , from which it is separated by some of the fibres of the psoas. In this situation it is flattened out and it divides into two series of ter- minal branches, the superficial and the deep. In general, they supply the muscles and skin on the anterior aspect of the thigh. Branches. — The branches of the femoral nerve are collateral and terminal. The collateral branches are twigs of supply to the ihacus, and a branch to the femoral artery; they are given off before the nerve enters the femoral trigone. 1002 THE NERVOUS SYSTEM The terminal branches form two groups, the superficial and the deep. The superficial terminal branches are two muscular branches, the nerve to the pectineus, and the nerve to the sartorius, and two anterior cutaneous branches. Fig. 766. — Cutaneous Nerves of the Right Thigh, (Spalteholz.) (The iliac fascia has been removed, the fascia lata retained.) Ilio-hypogast: Ilio -inguinal Transversus abdominis. Obliquus internus abdom- inis Obliquus externus ab- • dominis Lateral cutaneous branch •■ of inter- costal XU Intercostal XII Lateral cutaneous Lumbo-inguinal nerve - Psoas minor Genito-femoral nerve _N Psoas major ^j Lateral cutaneous nerve ' Iliacus ... External iliac artery ., External spermatic nerve -^„^ ,. Lumbo-inguinal nerve .•^1^. _ Femoral nerve ( Internal spermatic artery and — Ductus deferens --y,-- Rectus abdominis Anterior cutaneous branch of ilio-hypogastric nerve Fossa ovalis External spermatic nerve Anterior scrotal nerves Ixii.... Spermatic cord Great saphenous vein Anterior cutaneous branches '' of femoral nerve (Anterior cutaneous branches of femoral nerve 'The nerve to the pectineus passes medially and downward behind the femoral sheath and in front of the psoas to the anterior surface of the pectineus, in which it terminates. The nerve to the sartorius accompanies the middle cutaneous nerve; it leaves the latter nerve above the sartorius and ends in the upper part of the muscle. THE OBTURATOR NERVE 1003 The anterior (middle and internal) cutaneous nerves are best described separately. The middle cutaneous nerve soon divides into two branches, medial and lateral. The lateral branch pierces the sartorius and both branches become cutaneous about the junction of the upper and middle thirds of the tliigh (figs. 766, 768). They descend along the medial part of the front of the thigh to the knee, supplying the skin in the lower two-thirds of the medial part of the front of the thigh, and their terminal filaments take part in the formation of the patellar plexus. About the middle of the thigh the middle cutaneous is often joined by a twig with the lumbo- inguinal nerve (crural branch of the genito-crural nerve). The medial or internal cutaneous nerve runs downward and medialward along the lateral side of the femoral artery, to the apex of the femoral trigone (Scarpa's triangle), where it crosses in front of the artery and divides into an anterior and a posterior terminal branch. Before this division takes place, however, two or three collateral branches are given off from the trunk. The highest of these passes through the fossa ovalis (saphenous opening), or it pierces the deep fascia immediately below the opening, and supplies the skin as low as the middle of the thigh. The lowest pierces the deep fascia at the middle of the thigh and it descends in the subcutaneous tissue, supplying the skin on the medial side of the thigh from the middle of the thigh to the knee (figs. 768, 769). This nerve frequently varies in size inversely with the cutaneous branches of the obturator and saphenous nerves. The anterior branch of the internal cutaneous nerve passes vertically downward to the junction of the middle and lower thirds of the thigh, where it pierces the deep fascia. It still continues downward for a short distance, then it turns lateralward and passes to the front of the knee, where it enters into the patellar plexus. The posterior branch descends along the dorsal border of the sartorius, and it gives off a branch which passes beneath that muscle to unite with twigs from the saphenous and from the superficial division of the obturator nerve, forming with them the subsartorial plexus which lies on the roof of the adductor (Hunter's) canal. At the medial side of the knee the nerve pierces the deep fascia and it descends to the middle of the calf (figs. 766, 768). The deep terminal branches of the femoral nerve are six in number, one cutaneous branch, the saphenous, and five muscular branches. The branches radiate from the termination of the trunk of the femoral nerve, and thej^ are arranged in the following order from medial to lateral: — the saphenous nerve, the nerve to the vastus medialis, the nerve to the articularis genu (subcrureus) , the nerve to the vastus intermedins (crureus), the nerve to the vastus lateralis, and the nerve to the rectus femoris. The saphenous nerve passes down through Scarpa's triangle along the lateral side of the femoral artery. At the apex of the triangle it enters the adductor (Hunter's) canal and descends through it, lying first to the lateral side, then in front, and finally to the medial side of the artery (fig. 767). After emerging from the lower end of the canal, accompanied by the superficial branch of the genu suprema (anastomotic) artery, it passes between the dorsal border of the sartorius and the anterior border of the tendon of the gracihs, and, becoming superficial, it enters into relationship with the great saphenous vein and descends with it along the inner border of the upper two-thirds of the tibia (fig. 768). It crosses the medial surface of the lower third of the tibia, passes in front of the internal malleolus, and runs forward along the medial border of the foot to the ball of the great toe. While it is in the adductor (Hunter's) canal it gives off a twig to the subsartorial plexus. Before it passes from under cover of the sartorius it gives off an infra-patellar branch, which Eierces the sartorius just above the knee and passes outward to the patellar plexus. After it ecomes superficial it supphes the integument on the medial side of the leg and foot, and it anastomoses, in the foot, with the medial dorsal cutaneous branch of the superficial peroneal (musculo-outaneous) nerve. The nerve to the vastus medialis accompanies the saphenous nerve in the femoral trigone (Scarpa's triangle), lying to its outer side. At the upper end of the adductor canal it passes beneath the sartorius, external to the roof of the canal, and enters the medial surface of the vas- tus medialis. It sends a twig down to the knee-joint. The nerve to the articularis genu (subcrureus), usually a terminal branch of the femoral, frequently arises from the nerve to the vastus intermedins. It passes between the vastus medialis and the vastus intermedins to the lower third of the thigh, where it supplies the artic- ularis genu and sends a branch to the knee-joint. The nerve to the vastus intermedins (crureus) is represented by two or three branches which enter the upper part of the muscle. One of them frequently sends a twig to the knee-joint. The nerve to the vastus lateralis pas.ses downward behind the rectus and along the anterior border of the vastus lateralis accompanied by the descending branch of the lateral circumfiex artery. It also sends a branch to the knee-joint. 'The nerve to the rectus femoris (fig. 767) enters the deep surface of that muscle, having previously given off a twig to the hip-joint which accompanies the ascending branch of the external circumflex artery. The obturator nerve contains fibres from the anterior primary divisions of the second, third, and fourth lumbar nerves, but its largest root is derived from the third nerve (figs. 765, 769). It sometimes receives fibres from the first and third lumbar nerves. It emerges from the medial border of the psoas at the dorsal part of the brim of the pelvis, where it lies in close relation with the lumbo-sacrai trunk of the plexus, from which it is separated by the iho-lumbar artery. Im- mediately after its exit from the psoas it pierces the pelvic fascia, crosses the 1004 THE NERVOUS SYSTEM lateral side of the internal iliac vessels and the ureter, and runs forward in the extraperitoneal fat, below the obliterated hypogastric artery and along the upper part of the medial surface of the obturator internus to the upper part of the obturator foramen, where it passes through the obturator canal below the so- called horizontal ramus of the pubis and above the obturator membrane, into the upper part of the thigh. It is accompanied in the pelvis and the obturator canal by the obtm-ator arterj^, which lies at a lower level than the nerve, and it divides Fig. 767. — Femoral and Obtubator Nerves. (Ellis.) Femoral vein Femoral artery Pectineus Obturator (anterior div.) Adductor longus Adductor brevis Adductor magnus Geniculate branch of obturator Semi-membranosus Tensor fasciae latffi Profunda artery Pectineus Rectus femoris Saphenous Nerve to vastus medialis Adductor longus Femoral artery Genu suprema artery Patellar branch of saphenous in the obturator canal into two branches, an anterior and a posterior, which supply the adductor group of muscles, the hip and knee-joints, and the skin on the medial aspect of the leg. The anterior branch of the obturator has a twig joining it with the accessory obturator nerve, if that nerve is present, and then descends behind the pectineus and adductor longus and in front of the obturator externus and adductor magnus muscles (fig. 767). Its branches are: — 1. A twig to the accessory obturator nerve if the latter is present. 2. An articular branch to the hip-joint. 3. Muscular branches to the gracihs, adductor longus, and, usuaOy, to the adductor brevis. 4. Two terminal branches, of which one is distributed to the femoral artery and the other communicates with the subsartorial plexus. The subsartorial branch is occasionally longer THE LUMBOSACRAL TRUNK 1005 than usual, and it then descends, along the dorsal border of the sartorius, to the medial side of the knee, where it enters the subcutaneous tissue, and, proceeding downward, supplies the skin on the medial side of the leg as far as the middle of the calf. Twigs join it with the saphenous. The posterior branch of the obturator (fig. 767) pierces the upper part of the obturator externus and passes downward between the adductor brevis and adduc- tor magnus. Its branches are: — 1. Muscular branches to the obturator externus, to the oblique fibres of the adductor magnua and to the adductor brevis when the latter is not entirely suppUed by the anterior branch. The branch to the obturator externus is given off in the obturator canal. 2. An articular branch to the knee-joint which appears in some cases to be the continuation of the trunk of the posterior branch (fig. 767). It either pierces the lower part of the adductor Fig. 768. — Distribution op Cutaneous Nerves on the Postebior and Anterior Aspects OF the Inferior Extremity. Middle clunial Infra-patellar branch of saphenous Superficial peroneal Deep peroneal magnus, or it passes through the opening for the femoral artery. In the popliteal space it descends on the popUteal artery to the back of the joint, where it pierces the posterior hgament, and its terminal filaments are distributed to the crucial ligaments and the structures in their immediate neighbourhood. This branch is not uncomraoulj' absent. Occasionally the posterior branch of the obturator nerve also supples a twig to the hip-joint. The accessory obturator nerve arises from the third or fourth or from the third and fourth lumbar nerves, in the angles between the roots of the femoral (anterior crural) and obturator nerves. It is present in about twenty-nine per cent, of all cases (Eisler). It is often closely associated with the obturator nerve to the level of the brim of the pelvis, but instead of passing through the obturator foramen, it descends along the medial border of the psoas, crosses the anterior part of the brim of the pelvis, passes beneath the pectineus, and terminates in three main branches. One of these branches joins the anterior division of the obturator nerve, another supplies the pectineus, and the third is distributed to the hip-joint. The Lumbo-sacral Trunk The trunk of the plexus usually formed by the union of the smaller part of the fourth and the entire fifth lumbar nerves is called the lumbo-sacral trunk 1006 THE NERVOUS SYSTEM (figs. 765, 769). Sometimes the larger part of the fourth nerve may help to form the trunk. It may receive fibres from the third lumbar nerve or be formed entirely from the fifth. At its formation it is situated on the ala of the sacrum under cover of the psoas. It descends into the pelvis, and, as it crosses the anterior border of the ala of the sacrum, it emerges from beneath the psoas at the medial side of the obturator nerve, from which it is separated by the ilio-lumbar artery. It passes behind the common iliac vessels and unites with the first and second sacral nerves, forming with them the upper trunk of the sacral plexus. 4. SACRAL NERVES The anterior primary divisions of the upper four sacral nerves enter the pelvis through the anterior sacral foramina and they diminish in size progressively from above downward. The first sacral is the largest of the spinal nerves, the second is slightly smaller than the first, while the third and fourth are relatively small. The fifth sacral nerve is still smaller than the fourth; it enters the pelvis between the sacrum and the coccyx. The anterior divisions of these nerves enter into the formation of three parts of the lumbo-sacral plexus, the sacral, pudendal, and coccygeal. Sacral Plexus The sacral plexus shows in its formation variations similar to those of the lumbar plexus; hence there are also seven types of this plexus, three of them belonging to the prefixed or proximal class, three to the postfixed or distal class, and one to the ordinary class. The following tables show the range of variation and the common arrangement in these classes: — • Composition of the Nerves of the Sacral Plexus Range of Variation Nerve. Proximal. Furcal 3 or 3, 4 L. Common peroneal (exter- nal popliteal) 3, 4, 5 L. 1, 2 S. Tibial (internal popliteal) 3, 4, 5 L. 1, 2, S. Posterior femoral cutane- ous (smaU sciatic) 5 L. 1, 2, 3 S. 5 L.l, 2, 3, 4 S. 5 L. 1, 2, 3, 4 S. Common Composition Nerve. Proximal. Ordinary. Distal. Furcal 4 L. 4L. 4L. Common peroneal (exter- nal popliteal 4, 5 L. 1, 2 S. 4, 5 L. 1, 2 S. 4, 5 L. 1, 2 S. Tibial (internal popliteal) . 4, 5 L. 1,2 S. 4, 5 L. 1, 2, 3 S. 4, , 1^. 1, 2, 3, 4 S. Posterior femoral cutane- ous (small sciatic) 1, 2, 3 S. 1, 2, 3 S. 2, 3 S. The ordinary type of sacral plexus is commonly formed by the smaller part of the anterior division of the fourth lumbar nerve and the entire anterior division of the fifth lumbar nerve, together with the first and parts of the second and third sacral nerves. The plexus lies in the pelvis on the anterior surface of the piriformis (fig. 765) and behind the pelvic fascia and the branches of the hypogastric (internal iliac) artery. It is also dorsal to the coils of intestine, the lower part of the ilio-pelvic colon lying in front of the left plexus, and the lower part of the ileum in front of the right plexus. The branches given off by this plexus are : — visceral, cutaneous, and muscular. Visceral branches are given off from the second, third, and fourth sacral nerves to the pelvic viscera. The visceral branches correspond to white rami communicantes, through not joining the sympathetic trunk. The branches from the second and fourth sacral nerves are inconstant. Ordinary. Distal. 4L. 4, 5 or 5 L. 4, 5 L. I, 2 S. 4, 5, L. 1, 2, 3 S. 4, 5 L. 1, 2, 3 S. 4, 5 L. 1, 2, 3, 4, S. THE SACRAL PLEXUS 1007 Cutaneous branches. — (a) The posterior femoral cutaneous (small sciatic) nerve arises partly from the anterior and partly from the posterior branches of the anterior primary divisions of the first, second, and third sacral nerves. It lies on the back of the plexus (figs. 765, 769), leaves the pelvis at the lower border of the piriformis, and descends in the buttock between the gluteus maxi- mus and the posterior surface of the sciatic nerve (fig. 770). At the lower border of the gluteus maximus it passes behind the long head of the biceps femoris, and descends, immediately beneath the deep fascia, through the thigh and the upper part of the popliteal space (fig. 740). At the lower part of the popliteal region it perforates the deep fascia, and it terminates in branches which are dis- tributed to the skin of the calf. Branches of the small sciatic. — 1. Perineal branches are distributed in part to the skin of the upper and medial sides of the thigh on its dorsal aspect. One of the branches, kno\\Ti as the long pudendal nerve, runs forward and medialward in front of the tuberosity of the ischium to the lateral margin of the anterior part of the perineum, where it perforates the fascia lata and CoUes' fascia and enters the anterior compartment of the perineum. In the perineum twigs join it with the superficial perineal nerves, and its terminal filaments are distributed to the skin of the scrotum in the male, and to the labium majus in the female. 2. Inferior clunial (gluteal) branches, two or three in number, are given off beneath the gluteus maximus; they turn around the lower border of this muscle and are distributed to the skin of the lower and lateral part of the gluteal region. 3. Femoral cutaneous branches are given off as the nerve descends through the thigh. They perforate the deep fascia and are distributed to the skin of the back of the thigh, especially on the medial side. In case of the separate origin of the tibial (internal popliteal) and common peroneal (external popliteal) nerves, the posterior femoral cutaneous (small sciatic) also arises from the sacral plexus in two parts. The ventral portion descends with the tibial nerve below the piriformis and gives off the perineal branches and medial femoral branches, while the dorsal portion passes through that muscle with the common peroneal nerve, and furnishes the gluteal and lateral femoral branches. (6) The inferior medial clunial (perforating cutaneous) nerve arises from the posterior portion of the second and third sacral nerves (figs. 765, 769). It perforates the lower part of the sacro-tuberous (great sciatic) ligament, turns around the inferior border of the gluteus maximus, and is distribtued to the skin over the lower and medial part of that muscle. It is sometimes associated at its origin with the pudic nerve. It is not always present. Its place is sometirnes taken by a small nerve (the greater coccygeal perforating nerve of Eisler), arising from the third and fourth or fourth and fifth sacral nerves, and sometimes it is represented by a branch of the posterior femoral cutaneous. Muscular branches of the sacral plexus. — (a) One or two small nerves to the piriformis pass from the posterior divisions of the first and second sacral nerves. (b) The superior gluteal nerve receives fibres from the posterior branches of the fourth and fifth lumbar, and the first sacral nerves. It passes out of the pelvis through the great sciatic foramen, above the upper border of the piriformis, and it is accompanied by the superior gluteal artery. As soon as it enters the buttock it divides into two branches, an upper and a lower. 1. The upper branch is the smaller. It accompanies the upper branch of the deep division of the superior gluteal artery below the middle curved line of the ihum, and it ends entirely in the gluteus medius (fig. 770). 2. The lower branch, larger than the upper, passes forward across the middle of the gluteus minimus, with the lower branch of the gluteal artery; it supphes the gluteus medius and the gluteus minimus, and it ends in the medial and posterior part of the tensor fasoias latse. (c) The inferior gluteal nerve is formed by fibres from the posterior branches of the fifth lumbar, and the first and second sacral nerves. It passes through the great sciatic foramen, below the piriformis, and divides into a number of branches which end in the gluteus maximus (figs. 765, 769). (d) The nerve of the quadratus femoris is formed by the anterior branches of the fom'th and fifth lumbar and the first and second sacral nerves. It lies on the front of the plexus and issues from the pelvis below the piriformis. In the buttock it lies at first between the sciatic nerve and the back of the ischium, and, at a lower level , between the obtxu-ator internus with the gemelli and the ischium . It terminates in the anterior surface of the quadratus femoris, having previouslj^ given off a branch to the hip-joint and another to the inferior gemellus. (e) The nerve of the obturator internus is formed by the anterior branches of the fifth lumbar, and the first and second sacral nerves (figs. 765, 769). It leaves the pelvis below the pii-iformis, and crosses the spine of the ischium on the 1008 THE NERVOUS SYSTEM lateral side of the internal pudic artery and on the medial side of the sciatic nerve. It gives a branch to the gemellus superior, and turns forward through the small sciatic foramen into the perineum, where it terminates in the inner surface of the obturator internus. The sciatic nerve [n. ischiadicus]. — -The sciatic is not only the largest nerve of the sacral plexus, but it is also the largest nerve in the body. Its terminal branches are chiefly muscular, though some of its fibres are cutaneous. Although it is referred to as one trunk, it consists in reality of peroneal (lateral) and tibial (medial popliteal) portions, which are bound together by a sheath of fibrous tissue as far as the upper end of the popliteal space. In about 10 per cent, of the cases the two parts remain separate, and in such cases the peroneal (lateral popliteal) Fig. 769. — A Dissection op the Lumbar and Saceal Plexuses, from Behind. (The anterior crural nerve is placed between the external cutaneous and obturator nerves.) Dura mater of cord Last thoracic nerve Ilio -hypogastric Iliac branch of ilio hypogastric Gluteus medius Superior gluteal artery Superior gluteal Sciatic nerve Inferior gluteal nerve G eni to -femoral Cauda equina Filum terminale Lateral cutaneous Obturator \^ ' — Lumbo-sacral trunk -^i First sacral nerve Fifth sacral nerve Visceral branches Inferior gluteal artery Sacro-spinous ligament Pudic nerve Inferior medial clunial of second and third sacral i part usually pierces the piriformis. The peroneal portion of the nerve consists of fibres derived from the dorsal branches of the anterior primary divisions of the fourth and fifth lumbar and the first and second sacral nerves, while the tibial part is formed by the fibres from the anterior branches of the fourth and fifth lumbar, and the first, second, and third sacral nerves (figs. 765, 769). ^ The com- mon trunk leaves the pelvis by passing through the great sacro-sciatic foramen, usually below the piriformis, and descends through the buttock, running midway between the tuber ischii and the great trochanter (fig. 770). Passing down the thigh, the trunk terminates at the upper angle of the popliteal space by dividing THE SCIATIC NERVE 1009 into the common peroneal (external politeal) and the tibial (internal popliteal) nerves (fig. 771). The relation of the trunk to the piriformis muscle is more or less unique. It may pass either above or below the muscle, it may spht and pass around the muscle, or the muscle may be spUt and surround the nerve. Again, there may be a sphtting of both the muscle and the nerve, in which case any possible combination of the four parts may occur; a portion of the nerve may be above and a portion between the parts of the muscle, or a portion may be below and a portion between. The trunk of the nerve hes deeply in the thigh, and it is covered posteriorly by the skin and fascia, the gluteus maximus and the long head of the biceps femoris. Anteriorly it is in relation, from above downward, with the following structures: — the posterior surface of the ischium and the nerve to the quadratus femoris, the gemellus superior, obturator internus, gemellus inferior, quadratus femoris, and adductor magnus muscles. Muscular branches of the sciatic are given off at the upper part of the thigh to the semitendinosus, to the long head of the biceps femoris, to the semi membranosus, Fig. 770. — A Dissection op the Nerves in the Gluteal Region. (The gluteus maximus and gluteus medius have been divided near their insertions, and thrown upward.) Inferior gluteral artery -Gluteus maximus Inferior gluteal nerve Gluteal artery Sacro-tuberous ligament Comes nervi ischiadici Gemellus inferior Tuberosity of ischium Long pudendal \ Adductor ^ magnus Sciatic nerve Posterior cutaneous nerve Tendon of obturator externus Vastus externus Gluteus maximus and to the adductor magnus, and, about the middle of the thigh, a branch is fur- nished to the short head of the biceps. The branch to the short head of the biceps femoris is derived from the peroneal (lateral popliteal) portion of the nerve, while all the other muscular branches are given off by the tibial (medial pophteal) part. The semitendinosus receives two branches, one which enters it above and another which passes into it below its tendinous intersection. The nerve to the long head of the biceps descends along the sciatic trunk and enters the middle of the deep surface of the muscle. The nerves to the semimembranosus and adductor magnus arise by a common trunk ' which divides into three or four branches. One branch ends in the adductor, and the others are distributed to the semimembranosus. The branch to the adductor magnus supplies only those fibres of the muscle which begin from the tuberosity of the ischium and descend vertically to the medial condyle of the femur. At the apex of the popliteal space the two component parts of the common trunk of the sciatic become distinct. The tibial nerve (internal popliteal) , formed by fibres from the anterior branches of the fourth and fifth lumbar and first, second, and third sacral nerves, passes vertically through the popliteal space, descends through the leg to a point midway between the medial malleolus and the most prominent part of the medial tubercle of the os calcis, where it divides into its terminal branches, the lateral plantar and the medial plantar nerves. The part of the nerve from the point of bifurcation to the lower border of the popliteus muscle is sometimes called the internal popliteal; the part of the nerve in the dorsum of the leg being then designated the posterior tibial nerve. 1010 THE NERVOUS SYSTEM In the upper part of the pophteal space the tibial nerve lies relatively superficially, being covered dorsally by the skin and fascia, while in the lower part of the space it is overlapped by the heads of the gastrocnemius and is crossed by the plantaris. In the upper part of the space it lies in front of the posterior femoral cutaneous (small sciatic) nerve and to the lateral side of the vein and artery; at the middle of the space it is dorsal and in the lower part of the space it is medial to both of them. The branches given off by the tibial nerve in the popliteal space are articular, cutaneous, and muscular. The articular branches are usually three in number, a superior and an inferior internal articular and an azygos articular. They accompany the corresponding arteries, and, after piercing the ligaments, are distributed in the interior of the joint. The superior branch is often wanting. The cutaneous branch, the medial sural cutaneous (tibial communicating) nerve, descends between the heads of the gastrocnemius, beneath the deep fascia, to the middle of the calf, where it pierces the fascia and unites with the peroneal anastomotic branch of the lateral sural cutaneous to form the sural (external saphenous) nerve, through which its fibres are distributed to the skin of the lower and dorsal part of the leg and the lateral side of the foot. The muscular branches are distributed to both heads of the gastrocnemius, to the plantaris, soleus, and popliteus. The nerve io the soleus is relatively large, and passes between the lateral head of the gastroc- nemius and the plantaris before it reaches its termination (fig. 771). The nerve to the popliteus descends on the posterior surface of the muscle, turns around its lower border, and is distributed on its anterior aspect. In addition to supplying the popliteus, it gives articular branches to the knee and superior tibio-fibular joints, a branch to the tibia which accompanies the medullary artery, and a long, slender twig which gives filaments to the anterior and posterior tibial arteries, and it descends as the interosseous crural nerve on the interosseous membrane to the inferior tibio-fibular joint. It also gives branches to the interosseous membrane and to the periosteum of the lower part of the tibia. Relations. — In the upper part of the leg the tibial nerve is placed deeply, under the gas- trocnemius and soleus, but in the lower half it is merely covered by the deep fascia, which is thickened between the medial maleolus and the calcaneus to form the lacinate (internal annular) ligament, and the termination of the nerve lies either under cover of this hgament, or under the attachment of the abductor hallucis. The anterior relations of the nerve are, from above down- ward, the tibialis posterior, the flexor digitorum longus, the lower part of the tibia, and the pos- terior ligament of the ankle-joint. For a short distance after its commencement the nerve lies to the medial side of the posterior tibial artery; then it crosses behind the artery and runs down- ward along its lateral aspect. The branches of the lower part of the tibial nerve (below the popliteal space) are likewise muscular, cutaneous, and articular. They are supplied to the deep muscles of the dorsum of the leg, to the fibula, to the skin of the heel and foot, and to the ankle-joint. Several of the terminal branches are important enough to receive special names and special treatment. The muscular branches pass from the upper part of the nerve to the tibiahs posterior, flexor digitorum longus, soleus, and flexor haUuois longus. The fibular branch arises with the nerve to the flexor hallucis longus, and accompanies the peroneal artery. It supplies the peri- osteum and gives filaments which accompany the medullary artery. The articular branches arise from the lower part of the nerve, immediately above its terminal branches, and they pass into the ankle-joint through the deltoid ligament. The medial calcaneal (calcaneo-plantar cutaneous) nerves ai-ise from the trunk of the tibial nerve in the lower part of the leg. They pierce the laciniate (internal annular) ligament, and are distributed to the integument of the medial side and plantar surface of the heel and the adjoining part of the sole of the foot (fig. 771). Terminal branches of tibial nerve. — The medial plantar nerve is the larger of the two terminal branches of the tibial nerve. It commences under cover of the lower border of the laciniate (internal annular) ligament, or under the posterior border of the abductor hallucis, and passes forward, accompanied by the small internal plantar artery, in the inter-muscular septum between the abductor hallucis and the flexor digitorum brevis. At the middle of the length of the foot it becomes superficial, in the interval between the two muscles, and divides into four sets of terminal branches (fig. 772) : — (a) Muscular branches pass from the trunk of the nerve to the abductor hallucis and the flexor digitorum brevis. (6) Articular branches are distributed to the talo-navicular (astragalo- sacphoid) and the naviculari-cuneiform'joint. (c) Plantar cutaneous branches are supplied to the skin of the medial part of the sole. THE TIBIAL NERVE 1011 {d) The digital branches are four in number, the first, a proper plantar digital, the secondj third, and fourth, the common plantar digitals. Near the bases of the Fig. 771. — Muscle Nerves of the Right Leg, viewed from Behind. (Spalteholz.) The semitendinosus, semimembranosus, biceps femoris, gastrocnemius, plantaris, soleus, and flexor hallucis longus have been wholly or in part removed. Sciatic nerve ■ Popliteal vein — Popliteal artery -- Adductor magnus -- J Vastus medialis ^'-'^■r ., ■ -- > ; ■ ' i Articular branch - - -j.-^r ;- ^r ^j^ , "1 Tibial nerve 1 Semimembranosus — r-? Medial head of gastrocnemius — Jf- Lateral head of gastrocnemius ■' Popliteus ■"Biceps f' —Medial sural cutaneous nerve — Common peroneal nerve ~ Articular branch ■- Lateral sural cutaneous nerve /^M^--^-"***" Muscular branches Plantar muscle Head of fibula — Interosseus cruris nerve — Popliteal artery Soleus (cut) — - -Muscular branch Posterior tibial artery ■ Tibial nerve Muscular branch * Flexor digitorum longus Posterior tibisil artery — g Tibialis posterior \Jd |--PeroneaI artery — Muscular branch Flexor hallucis longus — Peroneus longus 5--Peroneal artery Tendo calcaneus (Achillis) Articular branch • Medial calcaneal nerves Posterior tibial artery ' Laciniate ligament |--- Articular branch — Flexor hallucis longus (cut) ^---Sural nerve -Lateral calcaneal branches metatarsal bones, the second, third and fourth common plantar digital divide into proper plantar digital nerves. The first proper plantar digital nerve becomes subcutaneous farther back than the others, and, after sending a branch to the flexor hallucis brevis, passes to the medial side of the great 1012 THE NERVOUS SYSTEM toe. The second (common digital) nerve gives a twig to the first lumbrical and bifurcates to supply the adjacent sides of the first and second toes. The third supplies the adjacent sides of the second and third toes, and the fourth, after connecting with the superficial branch of the lateral plantar nerve, divides to supply the adjacent sides of the third and fourth toes. All the proper digital nerves run along the sides of the toes and he below the corresponding arteries; they supply the joints of the toes, and each gives off a dorsal branch to the skin over the second and terminal phalanges and to the bed of the nail. All of them give fibres terminating in numerous Pacinian corpuscles. The lateral plantar nerve is the smaller of the two terminal branches of the tibial nerve. It commences at the lower border of the laciniate (internal annular) Fig. 772. — Superficial Nerves in the Sole op the Foot. (Ellis.) Abductor hallucis- Flexor digitorum brevis" Medial plantar Medial plantar artery. Proper plantar digital nerve to medial side of hallux Abductor minimi digit! Lateral plantar artery Lateral plantar nerve Proper plantar digital branches of the lateral plantar .ti^- Proper plantar digital branches of the 11 J medial plantar ligament, or under cover of the origin of the abductor hallucis, and passes forward and lateralward to the base of the fifth metatarsal bone, where it divides into a superficial and a deep branch (fig. 772). As it runs forward and lateralward it it is superficial to the tendon of the flexor hallucis longus and to the quadratus plantse (flexor accessorius), and deep to the flexor digitorum brevis. At its ter- mination it lies in the interval between the flexor digitorum brevis and abductor digiti quinti. Branches. — -From the trunk of the lateral plantar nerve muscular, superficial and deep, and articular branches are given off. THE COMMON PERONEAL NERVE 1013 The muscular branches arise from the commencement of the nerve and are dis- tributed to the abductor digiti quinti and quadratus plantse. The articular branches supply the calcaneo-cuboid joint. The superficial branch supplies muscular filaments to the flexor digiti quinti brevis, the opponens, the third plantar and fourth dorsal interosseous muscles, and divides into two common plantar digital nerves, each of which subdivides to form proper plantar digital nerves. The lateral of the two common branches supplies the lateral side of the fifth digit; the medial connects with the lateral digital branch of the medial plantar nerve (fig. 772) and divides into proper plantar digital nerves for the adjacent sides of the fourth and fifth digits. The digital branches of the superficial division of the lateral plantar, like those of the medial plantar, supply the skin of the toes and the beds of the nails, and their fibres terminate in numerouos Pacinian corpuscles. The deep branch passes forward and medialward into the deep part of the sole with the plantar arterial arch. It runs deep to the quadratus plantse, the long flexor tendons and the lumbricals, and the oblique adductor of the great toe. It lies, therefore, immediately beneath the bases of the metatarsal bones and it supplies the following muscular and articular branches: — • Muscular branches to the lateral three lumbricals, the interossei of the medial three inter- metatarsal spaces, and the transverse and oblique adductor muscles of the great toe. Articular branches to the intertarsal and to the tarso-metatarsal joints and not uncommonly to the metatarso-phalangeal joints also. Filaments from the deep branch frequently pass through the interosseous spaces and join with the interosseous branches of the deep peroneal (anterior tibial) nerve. The common peroneal (external popliteal) nerve. — ^At the apex of the pop- liteal space, where the two component parts of the sciatic trunk usually become distinct, the lateral portion receives the name common peroneal nerve. It de- scends along the posterior border of the biceps femoris, which forms the upper part of the lateral boundary of the space (fig. 771). It leaves the space at the lateral angle, crosses the plantaris, the lateral head of the gastrocnemius, the pop- liteus, and the inferior external artery, and descends behind the upper part of the soleus, to the neck of the fibula, where it turns forward between the peroneus longus and the bone, and breaks up into its three terminal branches, the recurrent articular, the superficial peroneal (musculo-cutaneous), and the deep peroneal (anterior tibial) nerves (fig. 773). Upper branches. — While it is in the popliteal space the common peroneal (external popliteal) nerve gives off two articular branches and a cutaneous branch. The superior articular branch accompanies the superior external articular artery. The lateral head of the gastrocnemius, and it joins the inferior external articular artery behind the tendon of the biceps femoris. Both the upper and lower articular branches pierce the ligaments and are distributed in the interior of the knee joint. The cutaneous branch {communicans fibularis) , lateral sural cutaneous, is extremely variable both as to the number of its branches and as to the place of its anastomosis with the medial sural cutaneous. Leaving the common peroneal (external popliteal) in the popliteal space, it descends between the deep fascia and the lateral head of the gastrocnemius to the middle of the calf, where it pierces the fascia and unites with the medial sural cutaneous to form the sural (external saphenous) nerve. In its course it may give off no branches; or it may give off several, some of which supply the skin of the dorsum of the leg, while one of them, the peroneal anastomotic branch, unites with the medial sural cutaneous to form the sural (short saphenous) nerve. The junction of the peroneal anastomotic branch with the medial sural cutaneous may take place at any point between the popliteal space and the lower third of the leg. The sural (external or short saphenous) nerve is formed by the union of the lateral sural cutaneous nerve either directly, or tlu-ough a connecting branch, the peroneal anastomotic, with the medial sural cutaneous (fig. 771). It descends along the lateral border of the tendo Achillis, giving branches to the lower and lateral part of the leg, and lateral calcaneal branches to the lateral side of the heel. It passes dorsal to the lateral malleolus, turns forward across the lateral surface of the cruciate (external annular) ligament, and becomes the lateral dorsal cutaneous nerve. Continuing along the lateral side of the foot it divides into two branches, the dorsal digitals, one of which supplies the lateral side of the fifth digit, while the other anastomoses with or takes the place of a branch of the superficial peroneal (musculo-cutaneous) nerve, which is distributed to the adjacent sides of the fourth and fifth digits (fig. 773). The terminal branches of the common peroneal. — (1) The recurrent articular nerve passes medialward, around the neck of the fibula, and through the upper 1014 THE NERVOUS SYSTEM part of the attachment of the extensor digitorum longus. At the medial border of the fibula it becomes associated with the anterior tibial recmrent artery, with which it ascends through the upper part of the tibialis anterior to the head of the Fig. 773. — Distrebtjtion of the Superficial and Deep Peroneal Nerves on the Ante- rior Aspect of the Leg and on the Dorsum of the Foot. (Hirschfeld and Leveill^.) Common peroneal nerve- Recurrent articular' Superficial peroneal Branch to peroneus longus' Branch to external digitorum longus Branch to peroneus brevis' Superficial peroneal' Intermediate dorsal cutaneous- Lateral dorsal cutaneous' Deep peroneal nerve ■Anterior tibial artery Tibialis anterior 'Deep peroneal nerve Medial dorsal cutaneous Deep peroneal (lateral division) Deep peroneal (medial division) tibia and the knee-joint. It supplies the tibialis anterior, the superior tibio- fibular joint, and the knee-joint. (2) The superficial peroneal (musculo-cutaneous) nerve arises from the com- mon peroneal between the peroneus longus and the neck of the fibula and de- scends in the intermuscular septum between the long and short peronei on the I THE DEEP PERONEAL NERVE 1015 lateral side, and the extensor digitorum longus on the medial side. It gives off muscular and cutaneous branches in its descent, and at the junction of the middle and lower thii-ds of the leg it pierces the deep fascia and divides into a medial and a lateral branch (fig. 773). Muscular branches are given off from the superficial peroneal to the peroneus longus and peroneus brevis before the nerve pierces the deep fascia. Cutaneous branches pass from the trunk of the superficial peroneal to the skin of the lower part of the front of the leg. The medial dorsal cutaneous (internal cruciate branch of the superficial peroneal), passes downward and medialward across the transverse and the cru- ciate (anterior annular) ligament of the ankle and subdivides into two branches. The medial branch passes to the medial side of the great toe; it also supplies twigs to the skin of the medial side of the foot, and it anastomoses with the deep saphen- ous nerve and with the medial terminal branch of the deep peroneal (anterior tibial) nerve. The lateral branch passes to the base of the cleft between the second and third toes and divides into two dorsal digital branches which supply the adjacent sides of the cleft. The lateral branch (intermediate dorsal cutaneous) of the superficial peroneal, in separating from the medial, crosses in front of the cruciate ligament and divides into two dorsal digital branches, which pass beneath the dorsal venous arch. The medial of these branches supplies the adjacent sides of the third and fourth toes (fig. 773). The lateral branch communicates with the sural (external saphen- ous) nerve and is distributed to the adjacent sides of the fourth and fifth toes. This latter branch is frequently replaced by the sural nei-ve. (3) The deep peroneal (anterior tibial) nerve springs from the end of the common peroneal (external popliteal) nerve between the peroneus longus muscle and the neck of the fibula. It passes forward and medialward through the upper part of the origin of the extensor digitorum longus, to the interval between that muscle and the tibialis anterior; then it descends, in the anterior compartment of the leg, to the ankle, where it divides into a medial and a lateral terminal branch (fig. 773). In the upper part of the leg the deep peroneal nerve lies between the extensor digitorum lon- gus and tibialis anterior and lateral to the anterior tibial artery. In the middle of the leg it is in front of the artery and between the extensor hallucis longus and tibiaMs anterior; then it crosses beneath the extensor hallucis, and in the lower third of the leg it is again to the lateral side of the artery, but between the extensor hallucis longus and the extensor digitorum longus. Branches furnished from the trunk of the deep peroneal are muscular, articu- lar, and terminal. The muscular branches supply the tibialis anterior, extensor digitorum longus, extensor hallucis longus, and peroneus tertius. Articular filaments are given to the ankle-joint and the inferior tibio-fibular articulation. Terminal branches. — The medial terminal branch passes downward along the side of the dorsalis pedis artery and divides into two dorsal digital branches which supply the adjacent sides of the first and second toes. It also gives fila- ments to the periosteum of the adjacent bones, to the metatarso-phalangeal and interphalangeal articulations, a twig to the dorsal interosseous muscle of the first space, and a perforating twig which connects with the lateral plantar nerve. The lateral terminal branch passes lateralward, beneath the extensor digitorum brevis, and it ends in a gangliform enlargement from which branches are dis- tributed to the extensor digitorum brevis, the tarsal joints, and to the three lateral intermetatarsal spaces. The latter branches supply the neighbouring bones, periosteum, and joints. They give off perforating twigs, which pass through the spaces and anastomose with branches of the lateral plantar nerve, and the most medial also gives a twig to the second dorsal interosseous muscle. 1016 THE NERVOUS SYSTEM Table Showing Ordinary Relations op Lumbar and Sackal Nerves to Branches op the Lumbar and Sacral Plexuses and to the Pudic Nerve Neeves Contributing. Nerves. Nerves. Femoral Obturator 1 L, / Ilio-hypogastric \ Ilio-inguinal 1 and 2 L Genito-femoral 1, 2, and 3 L Lateral cutaneous 2, 3, and 4 L ( Femoral 1 Ubturator 4, 5 L., and 1 S / Superior gluteal ( JNerve to quadratus lemons 4, 5 L., 1 and 2 S Sciatic (peroneal part) 4, 5 L., 1, 2, and 3 S Sciatic (tibial part) 5 L., 1 and 2 S . . I Inferior gluteal 1 Nerve to obturator internus 1 and 2 S Nerve to piriformis 2 and 3 S Medial inferior clunial 1, 2, and 3 S Posterior femoral cutaneous 2, 3, and 4 S Pudic Table Showing Relations op Muscles op Lower Extremity to Nerves op Lumbar and Sacral Plexuses Nerves Contributing. Muscles. Illio-psoas Sartorius rectineus Adductor longus 2, 3, and 4 L 19^"'^'! u ■ I Adductor brevis 3 and 4 L < Quadriceps femoris \ Obturator externus 3, 4, and 5 L _ Adductor magnus ' Gluteus medius " minimus Tensor fasc. latae Semimembranosus Plantaris Popliteus Quadratus femoris Inferior gemellus ' Flex, digit, long. Tibialis posterior Flexor digit, brev. " haUucis brev. Abductor hallucis First lumbrical Superior gemellus Obturator internus Gluteus maximus Semitendinosus Soleus I Flex, hallucis long. I Piriformis I Gastrocnemius I Flexor quadratus plantse 1 and 2 S ] ^*"^- 1^?^*^ '^^^iti I Plantar interossei I Dorsal " I Add. haUucis trans. l " " obliq. 1, 2, and 3 S Long head of biceps femoris f Ext. haU. long. " digit. " " digit, brev. 4, 5 L., and IS \ Tibialis anterior 4, 5L., and 1 S. 5L., and 1 S. 5L., 1 and2S. Peroneus tertius longus brevis THE PUDENDAL PLEXUS Femoral Obturator Obturator and sciatic Superior gluteal Sciatic Tibial Nerve to quad. fern. Tibial Posterior medial Plantar Nerve to obt. int. Inferior gluteal Sciatic Tibial Tibial Lateral plantar Sciatic Deep peroneal Superficial peroneal " peroneal The pudendal plexus, like the parts of the lumbo-sacral plexus ah-eady described, varies in its formation. The accompanying tables show the extreme THE PUDENDAL PLEXUS 1017 range of variation and the common method of formation of the large nerve of this plexus in each of the three classes. COMPOSITION OF THE NERVES OF THE PUDENDAL PLEXUS Range of Variation Nerve. Proximal. Ordinary. Distal. Pudic nerve 1,2,3,4,5 8. 1,2,3,4 8. 2,3,4,5 8. Common Composition Nerve. Proximal. Ordinary. Distal. Pudic nerve 2,3 8. 2,3,4 8. 3, 4 S. The pudendal plexus is commonly formed by parts of the anterior divisions of the second, third, and fourth sacral nerves. It lies in the lower part of the back of the pelvis, and gives off visceral, muscular, and terminal branches. Visceral branches (pelvic splanchnics) arise from the third and fourth sacral nerves especially, and enter branches of the sympathetic plexus. They are distributed both directly (their afferent or sensory fibres terminating in the pelvic viscera) and by their visceral efferent fibres terminating in the ganglia of the sympathetic plexus to the pelvic viscera (figs. 765, 791). The middle hsemor- rhoidal nerves pass to the rectum, the inferior vesical nerves to the bladder, and, in the female, the vaginal nerves to the vagina fsee Sympathetic System). Muscular branches are given by the fourth sacral nerve to the coccygeus, levator ani, and sphincter ani externus (fig. 765). The nerves to the two former muscles pass into the pelvic surfaces of the muscles, but that to the last-named muscle, called the perineal branch, passes backward between the levator ani and the coccygeus, or through the posterior fibres of the latter muscle, into the posterior part of the ischio-rectal fossa, and, in addition to supplying the sphincter ani, it gives cutaneous filaments to the skin between the anus and the coccyx. Terminal branches. — The pudic nerve [n. pudendus] rises usually from the anterior primary divisions of the second, third, and fourth sacral nerves (fig. 765). It emerges from the pelvis below the piriformis, crosses the spine of the ischium, lying to the medial side of the internal pudic artery (fig. 769), and accompanies the artery, through the small sciatic foramen, into Alcock's canal in the ob- turator fascia on the lateral wall of the ischio-rectal fossa, where it terminates by dividing into three branches, the inferior hsemorrhoidal, the perineal, and the dorsal nerve of the penis. The inferior haemorrhoidal nerves frequently arise independently from the third and fourth sacral nerves, pierce the medial wall of Alcock's canal, and pass forward and medialward through the ischio-rectal fat to supply the sphincter ani externus and adjacent skin. They anastomose with branches of the perineal nerve. The perineal nerve runs forward for a short distance in Alcock's canal and divides into a deep and a superficial branch. The deep branch breaks up into filaments, one or two of which pierce the medial wall of the canal and pass medialward to the anterior fibres of the sphincter and levator ani. The re- maining part of the nerve pierces the base of the m-o-genital trigone (triangular ligament), and enters the superficial pouch of the urethral triangle, where it is distributed to the bulb of the urethra, and to the transversus perinei, bulbocaver- nosus, and ischiocavernosus. It also sends some sensory filaments to the mucous membrane of the urethra. The superficial branch almost at once divides into medial and lateral branches, the posterior scrotal (labial) nerves. Both branches pass through the wall of Alcock's canal into the anterior part of the ischio- rectal fossa, then they pierce the base of the uro-genital trigone, and enter the superficial pouch of the urethral triangle. The lateral branch usually passes below the transversus perinei, and the medial branch above the muscle or through its fibres. The lateral branch connects with the long pudendal nerve, and with the inferior hsemorrhoidal nerve, and both branches end in terminal filaments which anastomose and which are distributed to the skin of the scrotum and the anterior part of the perineum in the male, and to the labium majus in the female. 1018 THE NERVOUS SYSTEM The dorsal nerve of the penis runs forward in Alcock's canal above the internal pudic artery. It pierces the base of the uro-genital trigone, continues forward between the layers of the trigone, embedded in the fibres of the con- strictor urethrse, and it gradually passes to the lateral side of the internal pudic artery. A short distance below the pudic arch it pierces the anterior layer of the uro-genital trigone, gives a branch to the corpus cavernosum penis, passes forward between that structure and the bone, and turns downward on the dorsum of the penis, passing between the layers of the fundiform (suspensory) ligament and along the outer side of the dorsal artery of the penis. It supplies the skin of the dorsum of the penis, and, having given branches to the prepuce, it breaks up into terminal filaments which are distributed to the glans penis. The dorsal nerve of the clitoris is much smaller than the dorsal nerve of the penis to which it corresponds. Is is distributed to the clitories. THE COCCYGEAL PLEXUS This plexus is frequently, and with some reason, considered as a subdivision of the pudendal plexus, and sometimes it is described with the coccygeal nerves. It is formed chiefly by the anterior division of the fifth sacral nerve and the coccygeal nerve, but it receives a small filament from the anterior division of the fourth sacral nerve (figs. 765, 769). These constituents unite to form plexiform cords lying on either side of the coccyx. From these cords arise the ano-coccygeal nerves, which pierce the sacro-tuberous (great sacro-sciatic) ligament and supply the skin in the neighbourhood of the coccyx. III. THE DISTRIBUTION OF THE CUTANEOUS BRANCHES OF THE SENSORY AND MIXED CRANIAL AND SPINAL NERVES The cutaneous filaments of the sensory and mixed nerves are distributed to definite regions of the surface of the body which are known as 'cutaneous areas.' Each cutaneous area has one special nerve of supply and the central part of the area receives that nerve alone, but wherever the borders of two areas meet they reciprocally overlap, therefore each margin of every cutaneous area has two nerves of supply, its own nerve and that of an adjacent area, and of these, some- times one and sometimes the other preponderates. The Cutaneous Areas of the Scalp The limits of the cutaneous areas in the scalp region are indicated in figs. 774, 776, but in general terms it may be said that the skin of the scalp in front of the pinna is supphed by four cutaneous nerves, viz. , the mesial part by the supratrochlear and the supra-orbital branches of the ophthalmic division of the trigeminus, and the lateral part by the temporal branch of the maxillary division, and the auriculo-temporal branch of the mandibular division of the same nerve. The portion of the scalp behind the pinna also receives four cutaneous nerves; laterally it is supplied by the great auricular and small occipital branches of the cervical plexus which contain filaments from the second and third cervical nerves, and medially it receives the great and smallest occipital nerves which are derived from the internal branches of the posterior primary divisions of the second and third cervical nerves respectively. The Cutaneous Areas of the Face With the exception of the skin over the posterior part of the masseter muscle, the whole of the skin of the face is supplied by the branches of the trigeminus. The nose is supplied medially by the supratrochlear, the infratrochlear, and the nasal branches of the ophthalmic division, and laterally by the infra-orbital branch of the maxillary division. The upper eyelid is supplied by the supratrochlear, the supra-orbital, and the lacrimal branches of the ophthal- mic division; the lower eyelid by the infratrochlear branch of the ophthalmic division and by the infra-orbital and the zygomatico-facial (malar) branches of the maxillary division. The skin over the upper jaw and the zygomatic (malar) bone is supplied by the infra-orbital and zygomatico-facial branches of the maxillary division, that over the buccinator by the buccal branch of the mandibular division, and that over the lower jaw, fiom in front backward, by the mental, buccal, and auriculo-temporal branches of the mandibular division, except a small part near the posterior border which receives its supply from the great auricular nerve. CUTANEOUS AREAS OF THE NECK The Cutaneous Areas of the Auricle (Pinna) 1019 The upper two-thirds of the outer surface of the pinna are suppUed by the auriculo-temporal branch of the mandibular division of the trigeminus, and the lower third by twigs of the great Fig 774— Diageam of the Cutaneous Nerve Areas of the Head and Neck. Red— ophthalmic division of trigeminus. White-maxillary division of trigemmus. Blue— mandibular division of trigemmus. Dotted shading— Posterior primary divisions of cervical nerves. . Obhque shading— Ascending and transverse superficial branches of cervical plexus. Transverse shadmg— Descending superficial branches of cervical plexus. It i^ult be remembered that the boundaries of each area are not distmct; wherever two areas meet they overlap. Supra-trochlear Lacrimal Infra -trochlear Smallest occipital ^\-*V/.' auricular nerve. The lower three-fourths of the cranial surface of the pinna are supphed by the great auricular nerve, and the upper fourth by the small occipital nerve. The posterior surffce of the external auditory meatus receives filaments from the auricular branch of the vagus. The Cutaneous Areas of the Neck The skin over the anterior part of the neck is supplied by the superficial cervical branch of the cervical plexus, which contains fibres from the second and third cervical nerves and in the lower part of its extent, by the anterior supra-clavicular nerves (suprasternal branches). 1020 THE NERVOUS SYSTEM which convey twigs of the third and fourth cervical nerves (fig. 774). The lateral part of the neck receives filaments from the second, third, and fourth cervical nerves by way of the great auricular, small occipital, and middle supraclavicular (supra-clavicular) branches of the cervical plexus, and posteriorly the skin of the neck is suppUed by the small occipital nerve and by the medial branches of the posterior primary divisions of the cervical nerves from the second to the sixth inclusive (fig. 776). The Cutaneous Areas of the Trunk The skin over the ventral aspect of the trunk as far down as the third rib is supphed by the anterior supra-clavicular (suprasternal) and middle supra-olavicular (supra-clavicular) branches of the cervical plexus, which contain filaments from the third and fourth cervical nerves (fig: 776). From the third rib to tlie lower part of the abdominal wall the skin receives the anterior cutaneous branches, and the anterior divisions of the lateral cutaneous branches of Fig. 775. — Diagram of the Cutanbotts Areas of the Side of the Body and Part of the Limb. (After Head.) the thoracic nerves except the first, second, and twelfth (fig. 776). The skin over the lower and anterior part of the abdominal wall is supplied by the iho-hypogastric branch of the first lumbar nerve. The cutaneous supply of the lateral aspects of the body is derived from the lateral branches of the anterior primary divisions of the thoracic nerves from the second to the eleventh, and the skin over the dorsal aspect of the body is supplied laterally by the posterior divisions of the lateral branches of the thoracic nerves from the third to the eleventh, and medially by the posterior primary divisions of the thoracic nerves, in the upper half by their medial branches and in the lower half principally by their lateral branches. THE CUTANEOUS AREAS OF THE LIMBS The areas of skin of the upper and lower limbs which are supplied by the branches of the brachial, lumbar, and sacral plexuses are indicated in fig. 776, and the spinal nerves which con- tribute to each nerve area are noted. The question of the skin areas supplied by any given spinal nerve is one of great chnical importance, in connection with the diagnosis of injuries of nerves and of pathological conditions affecting them. Therefore, considerable attention has been directed to the matter and it has been found that the areas which become hypersensitive when certain spinal nerve-roots are irritated, or anaesthetic when the roots are destroyed, do CUTANEOUS AREAS OF THE BODY 1021 Fig. 776. — Diagram showing Areas op Distriution of Cutaneous Nerves. Head : — Red — Ophthalmic division of trigeminus. White — maxillary division of trigeminus. Blue — mandibular division of trigeminus. Dotted area — Posterior primary divisions of cervical nerves. Oblique and transverse shading — Branches of cervical plexus. Body and Limbs : — Red — Anterior branches of anterior primary divisions.. Blue — Posterior branches of anterior primary divisions. Two colours in one area indicate that the area is supplied by two sets of nerves, and it should be remembered that wherever two nerve areas approach each other they overlap. The dotted blue area of the posterior femoral cutaneous (small sciatic) indicates that the nerve comes from the posterior as well as from the anterior parts of the anterior primary divisions of the sacral nerves, but it supplies a flexor area. The area of the inferior medial cluneal nerve is left uncoloured, because its true nature is uncertain. Dotted shading — posterior primary divisions. The numbers and initial letters refer to the respective spinal nerves from which the nerves are derived. Ophthalmic division of trigeminus - - Mandibular division of trigeminus Maxillary division of trigeminus Supraorbital Great auricular - Cutaneous colli, 3, 3 C -. Supra -clavi cular Axillary Lateral cutaneous nerves Anterior cutaneous nerves Medial brachial cutaneous and intercosto- brachial, 1,2 T Posterior brachial, cutaneous Medial antibrachial cutaneous Musculo-cutaneous (Lateral antibrachialj Lateral femoral cutaneous Geni to -femoral Superficial radial, 6 C Ilio-inguinial, i L Median, 6,7, C. i T Ulnar, i T Supra-clavicular, 3, 4 C Axillary, 5, 6 C Lateral branches of thoracic nerves Posterior brachial cutaneous Medial and intercosto- brachial cutaneous Medial antibrachial cutaneous Dorsal antibrachial cutaneous, 6, 7, 8 C Medial antibrachial cutaneous Superior clunial Lateral cutaneous of ilio-hypogastric Musculo-cutaneous, 5, 6 C Middle clunial Inferior medial clunial 2, 3 S Ulnar, 8 C Superficial radial, 6, 7 C Area supplied by superficial radial and ulnar Median, 6,7, 8 C, i T Common peroneal — Saphenous — Superficial peroneal Deep peroneal Medial plantar Lateral femoral cutaneous Posterior femoral cutaneous Common peroneal, 5 L, i, 2 S Saphenous, 3, 4 L Medial calcaneal of tibial, i, 2 S ■ J'-ii Lateral plantar, i, 2 S V... Medial plantar, 4, 5 L, 1022 THE NERVOUS SYSTEM not correspond exactly with the regions to which the fibres of the roots can apparently be traced by dissection. Moreover, it has been discovered, partly by clinical observations on the human subject and partly by experiment on monkeys, that the nerves of the hmbs have a more or less definite segmental distribution. To understand clearly this segmental arrange- ment the reader must remember that in the embryonic stage when no limbs are present the body is formed of a series of similar segments, each of which is provided with its own nerve. At a later stage when the limbs grow outward, each limb is formed by portions of a definite number of segments which fuse together into a common mass of somewhat wedge-hke outline. Each rudimentary limb possesses a dorsal and a ventral surface. The dorsal surfaces of both the upper and the lower limbs are originally the extensor surfaces, and the ventral surfaces the flexor surfaces, but, as the upper limb rotates lateralward and the lower limb rotates median- ward as development proceeds, in the adult, the extensor surface of the upper Umb becomes the posterior surface, and the extensor surface of the lower limb, the anterior surface. The preaxial border of the upper limb is the radial or thumb border, and the postaxial border, the ulnar or little finger border. The preaxial border of the lower hmb is the tibial or great toe border, and the postaxial border, the fibular or little toe border. As projections of the segments of the body grow out to form the limb-buds and limbs each projection carries with it the whole or part of the nerve of the segment to which it belongs, and therefore the number of body segments which take part in a hmb is indicated by the number of spinal nerves which pass into it. If these facts are remembered it will naturally be expected (1) that the highest spinal nerves passing into a hmb will be associated with its preaxial portion and the lowest with its post- FiG. 777. — Diagrams A, B, and C, Illustrating Stages in the Projection op the Limb- BDDS FOR THE IJPPER EXTREMITY, AND THE DRAWING OUT OF THE NeRVBS OF THE CORKESPOND- ing Body SegmentsfoetheCutanbous Areas of the Preaxial and Postaxial Border of THE Limb. Postaxial border shaded. axial portion; (2) that only the nerves of those segments forming middle or central portions of the limbs will extend to the tips of the hmbs; (3) that the highest and lowest segments in each hmb area wiU take a smaller part in the formation of the limb that the -middle segments; and (4) that, consequently, the highest and lowest nerves wiU pass outward into the limb for a shorter distance than the middle nerves. Observers are not yet in perfect agreement as to the exact distribution of each nerve, but the diagrams in figs. 775 to 781 show the embryonic derivation of the cutaneous areas and the adult dorso-ventral segmental arrangement in the projected portions of both the upper and lower limbs as assumed from clinical observations. In the upper parts of the lower limbs, the original segmental distributuion appears to be masked. This may be due (1) partly to the fact that the areas recognisable by clinical phenomena do not correspond exactly with the areas to which definite dorsal root-fibres are distributed, but rather to definite segments of the grey substance of the spinal cord with which the root-fibres are connected; (2) partly to the overlapping of segments and the acquired preponderance of one nerve over another in the overlapping areas, and (3) partly to the fact that in the lower hmb there has been a greater amount of shifting of parts to result in the fixed fiat position of the sole of the foot; (4) and partly to the incompleteness of the data which are at our disposal in the case of the human subject. Sherrington has proved that in the monkey the sensory areas of the limbs are arranged in serial correspondence with the spinal nerves, the middle nerves of each limb series passing to the distal extremity while the higher and lower nerves are limited to the proximal regions. Thorburn's observations, which differ from Head's, are, especially as regards the upper limb, in close conformity with the results obtained by Sherring- ton's experiments on monkeys. Each limb may be divided into its preaxial and postaxial borders by a line drawn longi- tudinally along the middle of both its anterior and posterior surfaces (compare figs. 777 and 779) The cutaneous nerves to the preaxial border are from the cephalic portion of the hmb plexus, and those to the postaxial are from the caudal components of the plexus. Thus the thumb and index finger are cephalad. The Cutaneous Areas of the Upper Limb A line passing along the middle of both the anterior and posterior surfaces of the upper ex- tremity to the tip of the middle finger (fig. 779) separates the preaxial from the postaxial border and passes longitudinally along the area of the cutaneous fibres derived from the seventh cervical nerve. CUTANEOUS AREAS OF THE LIMBS 1023 The skin over the upper third of the deltoid muscle is supplied by the posterior supra- clavicular (supra-acromial) and middle supra-clavicular (supra-clavicular) nerves, which are branches of the cervical plexus containing fibres of the third and fourth cervical nerves, and that over the lower two-thirds by the axillary (circumflex) nerve which conveys fibres of the fifth and sixth cervical nerves (fig. 776). The skin over the lateral surface of the upper arm is supphed externally by the axillary (circumflex) nerve above, and below by the superior branch of the dorsal antibrachial cutaneous, Fig. 778. — Diagram of the Cutaneous Areas op the Upper Extremity. (Modified from Head.) the external cutaneous branch of the radial (musculo-spiral) nerve. The former contains filaments of both the fifth and sixth cervical nerves, and the latter filaments of the sixth alone. The skin of the medial side of the upper arm is supplied by the medial antibrachial cutaneous (internal cutaneous) nerve with fibres of the eighth cervical and first thoracic nerves, and by the medial brachial cutaneous (lesser internal cutaneous) and intercosto-brachial (intercosto- humeral) nerves which are derived from the first and second thoracic nerves. The dorsal side of the upper arm is supphed, laterally, by the fifth and sixth cervical nerves through the axillary Fig. 779. — Diagram of the Cutaneous Areas op the Upper EIxtremitt. The solid middle lines are drawn to separate preaxial (radial) borders from postaxial borders. (After Thorburn, modified.) (circumflex) nerve and by the dorsal antibrachial cutaneous; the middle portion, by the seventh cervical nerve through the posterior brachial cutaneous, the internal cutaneous branch of the radial (musculo-spiral) nerve; and the medial portion by the first and second thoracic nerves through the medial brachial cutaneous (lesser internal cutaneous) nerve, and the intercosto- brachial (intercosto-humeral) nerve (fig. 776). The front of the forearm is divided into three areas, a lateral which is supphed by the fifth, sixth, and possibly the seventh cervical nerves, through the musculo-cutaneous branch of the 1024 THE NERVOUS SYSTEM brachial plexus; a middle which is supplied by the seventh cervical nerve as above, and a medial area supplied by the eighth cervical and first thoracic nerve through the medial antibrachial cutaneous (internal cutaneous) nerve. On the dorsal side of the forearm there are three areas: — (1) a lateral suppUed by fibres of the fifth and sixth cervical nerves through the musculo- cutaneous nerve; (2) a middle, which receives fibres of the seventh, and probably some from the sixth and eighth cervical nerves through the lower branch of the dorsal antibrachial cutaneous of the radial (inferior external cutaneous branch of the musculo-spiral nerve), and (3) a medial which receives the eighth cervical and first thoracic nerves through the medial antibrachial cutaneous (figs. 776, 779). The palm of the hand is supplied by the sixth, seventh, and eighth cervical nerves through the superficial radial (radial) nerve, and through the median and ulnar nerves. The super- ficial radial supplies the radial side of the thumb by its palmar cutaneous branch. The re- mainder of the palm and the palmar aspects of the fingers are supplied by the median and ulnar nerves through their palmar cutaneous and digital branches, the median supplying three and a half digits and the ulnar the remaining one and a half (figs. 776 and 779). The dorsal aspect of the hand is suppUed by the sixth, seventh, and eighth cervical nerves, which reach it through the superficial radial( radial) and through the median and ulnar nerves. The superficial radial supplies the lateral part of the dorsum and the lateral three and a half digits, except the lower portions of the second, third, and half of the fourth digits, which ■receive twigs from the median nerve; the ulnar nerve supplies the ulnar half of the dorsum of Fia. 780.— Diagram op the Cutaneotts Areas op the Lower Extremity. (After Head.) the hand, including the medial one and a half digits. The areas supplied by definite spinal nerves, according to the observations of Head and Thorburn, are shown in figures 778 and 779 respectively. The Cutaneous Areas of the Lower Extremity The segmental arrangement of the cutaneous areas of the lower extremity is not so well retained as in the upper, due largely to a greater amount of developmental shifting of the parts. Both of the lines separating the areas of the lumbar (cephalic) and the sacral (caudal) parts of the lumbo-sacral plexus he on the dorsal aspect of the limb. The nerves from the lumbar part of the plexus are distributed to the entire anterior and the medial and lateral surfaces of the hmb and to the muscles of the anterior and medial portions of the thigh and the anterior portion of the leg, whereas the cutaneous nerves from the sacral part of the plexus are con- fined to a narrow strip along the dorsal aspect of the limb (fig. 781). However, the muscular distribution of the sacral part is as much expanded as its cutaneous area is contracted; it supplies the muscles in the dorsal portions of the hip, thigh and knee, the whole of the dorsal part of the leg and ankle and the plantar muscles of the foot. There are six cutaneous areas in the region of the buttock, three upper and three lower. Of the upper areas the lateral is supplied by the anterior primary divisions of the last thoracic and first lumbar nerves through the iliac branches of the last thoracic and the iho-hypogastric nerves; the middle upper area receives the lateral divisions of the posterior primary branches of the upper three lumbar nerves, and the medial upper area is supplied by twigs from the lateral branches of the posterior primary divisions of the upper two or three sacral nerves (figs. 776, 780). CUTANEOUS AREAS OF THE LIMBS 1025 Of the lower three areas, the lateral receives filaments from the second and third lumbar nerves through the lateral femoral cutaneous (external cutaneous) branch of the lumbar plexus; the middle area is supplied by the first, second, and third sacral nerves through the posterior femoral cutaneous (small sciatic) nerve; and the medial area by the second and third sacral nerves through the medial inferior clunial (perforating cutaneous) branch of the sacral plexus (fig. 776). On the back of the thigh there are three areas. According to Head, the medial and lateral areas are supphed by the second and third lumbar nerves, the former through the lateral femoral cutaneous (external cutaneous) branch of the lumbar plexus, and the latter through the anterior cutaneous branches of the femoral (internal cutaneous branch of the anterior crural) nerve. The middle area receives twigs from the first, second, and third sacral nerves through the posterior femoral cutaneous (small sciatic), a branch of the sacral plexus. The front of the thigh is supplied by the first, second, and third lumbar nerves, and, according to Head, there are five cutaneous areas. The lateral area receives twigs of the second and third lumbar nerves through the lateral (external) cutaneous nerves. There are two medial areas, an upper and a lower. The former is supplied by the lumbo-tnguinal (crural) branch of the genito-femoral (genito- crural), which conveys twigs of the first and second lumbar nerves; the latter receives fibres of the second and third lumbar nerves through one of the an- FiG. 781. -Diagram op the Cutaneous Areas of the Lower Extremity (After Thorburn, modified.) t'W terior (middle) cutaneous branches of the femoral (anterior crural) nerve. The small upper and medial area is supplied by the first lumbar nerve through the iUo-inguinal, and the lower medial area receives twigs of the second and third lumbar nerves through one of the anterior cutaneous branches (internal cutaneous) of the femoral (anterior crural) nerve (fig. 776). The front of the knee is supplied by the second, third, and fourth lumbar nerves through the anterior (middle and internal) cutaneous and saphenous (long saphenous) branches of the femoral (fig. 776). Of the skin over the region of the popliteal space, the medial portion receives fibres from the second, third, and fourth lumbar nerves through the anterior (internal) cutaneous branch of the femoral (anterior crural) nerve and through the superficial division of the obturator nerve; the middle and lateral portion receives twigs of the first three sacral nerves through the pos- terior cutaneous (small sciatic) nerve (fig. 776). The skin over the front and medial side of the leg is supplied by the fourth lumbar nerve through the saphenous nerve, and the skin of the front and lateral side receives nerve-fibres from the fifth lumbar nerves through the sural cutaneous (fibular communicating) branch of the common peroneal (external popliteal) nerve. In the skin of the back of the leg four areas can be distinguished, a medial, two middle, upper and lower, and a lateral area. The medial area is supphed by the fourth lumbar nerves through an anterior cutaneous branch (internal cutaneous) of the femoral (anterior crural) 1026 THE NERVOUS SYSTEM nerve and the superficial branch of the obturator nerve. The upper middle area is supplied by the second, and third sacral nerves through the posterior femoral cutaneous (small sciatic) nerve, and the lower middle area by the first sacral nerve through the sural (external saphenous) nerve. The lateral area is supphed by the fifth lumbar nerve through the lateral sural cutaneous (fibular communicating) branch of the common peroneal (external popliteal) nerve (fig. 776, 780, 781). The skin of the dorsum of the foot is supplied principally by the fifth lumbar and by the first sacral nerves," the majority of the nerve-fibres travel by the superficial peroneal (musculo- cutaneous) nerve, but the adjacent sides of the first and second toes are supplied by the femoral (anterior crural) nerve and the side of the dorsum of the httle toe is supplied through the sural (external saphenous). The skin of the region of the heel is supplied by the first sacral nerve, the medial surface and medial part of the under surface by the medial calcaneal branches of the tibial (calcaneo- plantar) nerve and the posterior, external, and lower aspects by the sural (external saphenous) nerve (fig. 776). The sole of the foot in front of the heel receives cutaneous fibres from the fifth lumbar and the first sacral nerves; the medial area, which includes the medial three and a half digits, being supplied by the medial plantar nerve which conveys fibres of the fifth lumbar and the first sacral nerves; and the lateral area by the fifth lumbar nerve through the lateral plantar nerve. The medial side of the foot is supphed by the first sacral and fourth lumbar nerves through the saphenous nerve and the lateral side by the fifth lumbar nerve through the sural (external saphenous) nerve. The skin of the scrotum and penis is supphed by the first lumbar nerve through the iho- inguinal nerves, and by the second and third sacral nerves through the perineal and dorsal penile branches of the pudendal (pudic) nerve. The cutaneous areas of the lower extremity which have been demarcated by Head and Thorburn are shown in fig. 780. These do not conform wholly with each other nor with the areas given in more detail in fig. 776, due probably to individual differences in subject and observer and to the difficulties coincident with the overlapping of the areas. Fig. 781 is more general in character and is considered more approximately correct. The homology of the parts of the plexuses of the upper and lower extremities is not well carried out in the distribution of the nerves. The radial and great sciatic nerves are similar to the extent that the one arises from the posterior cord of the brachial plexus and the other from the sacral ple.xus, and that the one is distributed to the dorsal aspect of the arm and the other to the dorsal surface of the lower extremity, but the great sciatic supplies the sole of the foot, and the plantar muscles, whereas the radial does not supply the palm of the hand and the palmar muscles. THE SYMPATHETIC SYSTEM The so-called sympathetic system is that portion of the peripheral nervous system which is especially concerned in the distribution of impulses to the Fig. 782. — Diagram showing two stages of the Migration op the Primitive Ganglia PROM THE Ganglion Crest; A. the Division of the Primitive Ganglia into Spinal AND Sympathetic Portions, and B. the Formation op the Nerves. ~-^ Ectoderm ganglion glandular tissues, to the muscle of the heart and blood-vessels, and to the non- striated muscular tissue of the body wherever found. Since these tissues are most THE SYMPATHETIC SYSTEM 1027 Fig. 783. — Diagram Showing the Chief Paths of Migration op the Cells from THE Ganglia of the Spinal and Cranial Nerves to form the Adult Sympathetic System (After Schwalbe, modified.) Carotid plexus Closso-pharyngeal Vagus nerve I. cervical spinal ganglion Superior cervical ganglion Inf. Middle cervical ganglion Tior cervical ganglion I. thoracic spinal ganglion Sympathetic trunk I, lumbar spinal ganglion I. sacral spinal ganglion Pharyngeal plexus Coccygeal spinal ganglion Aortic plexus Inferior mesenteric plexus Pelvic plexuses Coccygeal ganglion 1028 THE NERVOUS SYSTEM abundant in and largely comprise the viscera or splanchnic organs of the body, the largest and most evident of the structures comprising the sympathetic system are found either in or near the cavities containing the viscera. However, the Fig. 784. — Scheme showing General Plan of the Coarser Portions op the Sympa- thetic Nervous System and its Principal Communications with the Cbrebro-spinal System. (After Flower, modified.) Intgrfta! CttToUd pU J^ami communicantes Jittuieen ^anffUated cord and Jniular G(imlion of vafju-f *' To Petrosal ganglion o/^_ glossopharyngeal Cervical nerve J JI- m " Ciliary ganafien ^ . &7jjy/imM)doium^.Vayi^ ' Spfieno-palatine^eckl'syanaiion . mpocAsmic piekus Ga/iff//on Cocci/ffeum impar finer divisions of the system ramify throughout the whole body, supplying vaso- motor fibres to the blood-vessels throughout their course, controlling the glands of the skin, and supplying pilo-motor fibres for the hairs, forming intrinsic plexuses within the walls of the viscera, and it is claimed that a few of its neurones THE SYMPATHETIC SYSTEM 1029 convey inpulses toward the central system (sensory sympathetic neurones). While it is very probable that certain of the simpler reflexes of the splanchnic organs may be mediated by the sympathetic system alone, yet the sympathetic is by no means independent of the cranio-spinal system, but is rather, both ana- tomically and functionally merely a part of one continuous whole. Throughout, it shares its domain of termination with cranio-spinal fibres, chiefly of the sensory variety, and most of its rami and terminal branches carry a few cranio-spinal fibres toward their areas of distribution. Likewise the cranio-spina,l nerves carry numerous sympathetic fibres gained by way of rami connecting the two systems. Like the cranio-spinal system, the sympathetic consists of cell-bodies, each of which gives off one axone. In addition, the cell-bodies give off numerous dichotomously branched den- drites by which their receptive surfaces are increased, and they are accumulated into ganglia, large and small. The larger ganglia have more or less constant positions, shapes, and arrange- ments, while the smaller, some of which are microscopic, are scattered throughout the body in a seemingly more indefinite manner. The axones or fibres arising in these gangha are given off in trunks and rami which associate the ganglia with each other or with the cranio-spinal system, or which pass from the ganglia to be distributed directly upon their allotted elements. The sympathetic fibres arising from the ganglia are, for the most part, either totally non- medullated or partially medullated. Some fibres are completely medullated near their cells of origin, but lose their meduUary sheaths before reaching their terminations. Some of them possess complete medullary sheaths throughout, but in no cases are the sheaths as thick or well developed as is the rule with the cranio-spinal fibres. Thus, nerve-trunks and rami in which sympathetic fibres predominate appear greyish in colour and more indefinite, as dis- tinguished from those of the cranio-spinal nerves, which always appear a glistening white, due to hght being reflected from the emulsified myelin of the sheaths of their fibres. Origin of the S3rmpathetic system. — Not only must the cranio-spinal and sympathetic systems be considered anatomically continuous and dependent, but ako the neurones of the two systems have a common origin, namely, the ectoderm of the dorsal mid-line of the embryo. The cells of the ganglion crest (see p. 754) become arranged in segmental groups and soon separate into two varieties: — those which will remain near the spinal cord and develop into the spinal ganglia, and those which, during the growth processes, migrate and become displaced further into the periphery and form the sympathetic gangha. Fig. 785. — Scheme showing the Connection between the Sympathetic and the Cranio- spinal AND Central Nbrvous Systems. Spinal ganglion neurone to capsule of ganglion Meningeal ramus Dorso-Iateral group of ' ventral horn ceUs Ventral root / J Gray ramus communicans ~yt^y White ramus co mmunicans Sympathetic ganglion 1 Gangliated ^ Sympathetic trunk / trunk ' Sympathetic cell body in spinal ganglion Posterior primary division 1 Spinal Anterior primary division J nerve ^^^ ^Gray ramus communicans \ ^White ramus communicans Sensory sympathetic neurone Branch to prevertebral ganglion In the development of the sympathetic system the migration from the vicinity of the central system occurs to varying extents, so that in the adult the cells comprise three general groups of ganglia situated different distances away from the central nerve axis. — (1) A large portion of the cells remain near the central system and form a linear series of ganglia which, with the trunks con- necting them, become two gangliated nerve trunks extending along each side, proximal to and parallel with the vertebral column; (2) a still larger portion of the cells migrate further toward the periphery and are accumulated into ganglia which assume an intermediate position and which, with the rami associating them with each other and with other structures, form a series of great prevertebral 1030 THE NERVOUS SYSTEM plexuses; (3) still other cells wander even further away from the locality of their origin and invade the very walls of the organs innervated by the sympathetic system. The latter cells occur as numerous small terminal ganglia, most of which are microscopic and which, with the twigs connecting them, form the most peripheral of the sympathetic plexuses. Examples of these are the intrinsic ganglia of the heart and pancreas and the plexuses of Auerbach and Meissner in the walls of the digestive canal. Small, straggling ganglia may be found scattered between these three general groups. In the head, the gangliated trunks and great prevertebral plexuses are represented by the ciliary, sphenopalatine, otic and submaxillary ganglia and the plexuses associated with these. The supporting tissue of the sympathetic system accumulates early and is probably all of meso- dermic origin. Construction of the sympathetic system. — The sympathetic ganglia may be considered as relays in the pathways for the transmission of impulses from the region in which they arise to the tissues in which they are distributed; the cells composing the ganglia are the cell-bodies of the neurones interposed in the various neurone chains performing this function. A fibre arising from a cell-body in a given ganglion may pass out of the ganglion and proceed directly to its termination upon a smooth muscle-fibre or gland-cell, or it may pass through a connecting trunk to another ganglion and there terminate about and thus trans- mit the impulse to another cell, which, in its turn, may give off the fibre which bears the impulse to the appropriate tissue-element. Fibres arising in given ganglia may pass uninterrupted through other ganglia and proceed to their re- spective destinations. On the other hand, several neurones may be involved in the transmission of a given impulse when sent from a region distant from the tissue to which it is distributed. Communication between the central nervous system and the sympathetic is established through both efferent and afferent fibres. In the region of the spinal cord both varieties of fibres pass from one system to the other by way of the rami communicantes, delicate bundles of fibres connecting the nearby sympa- thetic trunk with the respective spinal nerves (fig. 785). The efferent fibres of the rami arise in the ventral horn (dorso-lateral cell-group chiefly) of the spinal cord, emerge through the ventral roots, enter the rami, and terminate chiefly about the cells of the nearest sympathetic ganglion; some, however, may pass through or over the ganglion of the sympathetic cord and terminate about cells in more distant ganglia. Since these fibres transmit impulses from the central to the sympathetic system, they are known as visceral efferent fibres. They are of smaller size than is the average for the cranio-spinal effer- ent or motor fibres of the ventral root. The visceral afferent fibres are of two varieties: — (1) Peripheral processes of the spinal ganglion-cells which run outward in the nerve-trunk, enter the rami communicantes, pass through the various connecting trunks and terminal rami of the sympathetic and terminate in the tissues supplied by these rami. . Such are merely sensory fibres of the cranio-spinal type which collect impulses in the domain of the sympathetic and convey them to the central system by way of the sympathetic nerves and the dorsal roots of the spinal nerves. (2) Afferent sympathetic fibres proper. The actual existence of these has not been long established, and their relative abundance is as yet uncertain. They consist of fibres arising in the sympathetic ganglia which enter the spinal ganglia by way of the rami commnicantes and the cranio-spinal nerve-trunk and terminate in arborisations about the spinal ganglion-cells (fig. 785). The afferent impulses transmitted by these sympathetic fibres are borne into the spinal cord or brain by way of the cranio-spinal fibres of the dorsal roots. These sensory sympathetic fibres must necessarily either receive the impulses they bear from sympathetic neurones having both peripheral and central processes or they themselves must be axones or central processes of neurones having also processes terminating in the peripheral tissues. Doubtless the variety of visceral afferent fibres first mentioned greatly predominates. The thoracic and the lumbar spinal nerves are connected with the sympathetic trunk (gangliated cord) by two rami communicantes. Most of both the visceral efferent and also the visceral afferent fibres (which arise in the spinal ganglia) pass by way of a separate ramus. Both these varieties being of the cranio-spinal type, and, therefore, medullated, they give the ramus a white appearance meriting the name white ramus communicans. Fibres of the sympathetic type predomi- nate in the second ramus and thus it is the grey ramus communicans. The latter consists of: — (1) afferent sympathetic fibres and (2) of sympathetic fibres which join the primary divisions of the spinal nerves and course in them to their allotted tissues (fig. 785). In the sacral region, most of the visceral efferent fibres pass over the ganglia of the sympa- thetic trunk and terminate in the more peripheral ganglia of the plexuses of this region. This is THE SYMPATHETIC SYSTEM 1031 especially true for the fibres passing from the second, third, and fourth sacral nerves. In the cer- vical region white rami are not in evidence, a fact probably exphcable as due to an arrangement by which at least most of the visceral efferent fibres arising in the cervical segments of the spinal cord pass downward in these segments and join the sympathetic tlirough the white rami of the upper thoracic nerves; others may enter the cervical portion of the gangliated cord through the spinal accessory or eleventh cranial nerve, rather than through individual white rami, while others pass into the nerves of the brachial plexus to terminate in the minute ganglia of the plex- uses upon the blood-vessels of the limb. All the spinal nerves are joined by grey rami communi- cantes from the sympathetic trunk. Vaso-motor fibres to the meninges and intrinsic blood-vessels of the spinal cord pass to the spinal nerves by way of the grey rami. Thence they may reach the meninges by one of three ways: — (1) through the delicate recurrent or meningeal branch of the spinal nerve (fig. 785) ; (2) through the trunk and ventral Fig. 786. — Diagram suggesting the Origin, Course and Connections of Sympathetic Nerve-fibres. Spinal ganglion •- Sympathetic trunk SympatliQtic ganglion Grey ramus communicans White ramus communicans White ramus communicans Grey Sympathetic trunk communicans ^ root of the spinal nerve; (3) probably more rarely, through the trunk and dorsal root of the spinal nerve (fig. 786). Corresponding communications exist between the cranial nerves and the sympathetic, but the corresponding rami usually extend further toward the periphery and in not so regular a manner as the communications between the spinal nerves and the sympathetic system. The mesencephalon, for example, is chiefly connected with the ciUary ganglion of the sympathetic by_ fibres which are sent through the oculo-motor nerve and which enter this ganghon by way of its short root and terminate about its cells. Visceral efferent fibres from the rhombencephalon pass outward to the sympathetic in the roots of the facial, glosso-palatine, glosso-pharyngeal. 1032 THE NERVOUS SYSTEM vagus, and spinal accessory nerves, all of which have more or less irregularly disposed com- municating rami. The ganglia of origin of the vagus, more than perhaps any other nerve, both receive impulses from visceral efferent fibres and give origin to sympathetic fibres. Likewise twigs of other cranial nerves, especially of the trigeminus, connect with (pass through) the small sympathetic ganglia of the head. The meningeal branches given by certain of the cranial nerves contain vaso-motor fibres, and these correspond to the sympathetic fibres in the recurrent branches and in the roots of the spinal nerves. It is known that spinal ganglia and certain of the ganglia of the cranial nerves contain cell-bodies of sympathetic neurones — cell-bodies which, during the period of the migration peripheralward, remained within the confines of these ganglia (fig. 785). These cell bodies receive efferent impulses from ventral root fibres and send their axones further into the periphery just as if in the sympathetic ganglion. Their relative abundance is not known. It is supposed that the ganglia of the vagus, glosso-pharyngeus, trigeminus and the geniculate ganglion contain a considerable proportion of such sympathetic cell-bodies. From the above it may be seen that the ganglia and connecting trunks and rami of the sympathetic system may be divided as follows: — (1) The two sympathetic gangliated trunks lying proximal to and parallel with the vertebral column; (2) the great prevertebral plexuses, of which there are roughly four, one in the head, one in the thorax, one in the abdomen, and one in the pelvic cavity (fig. 784), each of which is subdivided; (3) the numerous terminal ganglia and plexuses situated either within or close to the walls of the various organs; (4) the trunks and rami associating the ganglia with each other and thus contributing to the plexuses, or connecting the ganglia with other nerves or with the organs with whose innerva- tion they are concerned. The trunks and rami may be divided into — (a) the rami communicantes, or central branches, connecting the sympathetic with the cranio-spinal and central systems; (Ja) associative trunks, best considered as those which associate sympathetic ganglia situated on the same side of the body; (c) commissural branches, or those which associate ganglia situated on opposite sides of the mid-line of the body, such as the transverse connecting branches between the sympathetic trunk in the lumbo-sacral region (fig. 787) , or all the associating trunks between the ganglia of plexuses occupying the mid-region of the body; {d) terminal or peripheral branches, or those which pass from the ganglia to their final distribution apparently uninterrupted by other ganglia. THE SYMPATHETIC TRUNKS The sympathetic gangliated trunks, or gangliated cords, of the sympathetic system are two symmetrical trunks with ganglia interposed in them at intervals of varying regularity, and extending vertically, one on each side of the ventral aspect of the vertebral column, from the second cervical vertebra to the first piece of the coccyx. Upon the coccyx the two trunks unite and terminate in a single medial ganglion, the ganglion coccygeum impar. The various ganglia are connected with the cranio-spinal nerves by the rami communicantes. Mor- phologically, each trunk might be expected to possess thirty-one ganglia, one for each spinal nerve, but, owing to the fusion of adjacent ganglia in certain regions, especially in the cervical, there are in the adult only twenty-one or twenty-two ganglia in each trunk. These occur as three cervical ganglia, ten or eleven thoracic ganglia, four lumbar and four sacral ganglia, and the ganglia n coccygeum impar, which is common to both trunks. In the cervical region the sympathetic trunks lie in front of the transverse processes of the vertebra3, from which they are separated by the longus capitis (rectus capitis anticus major) and longus colli; in the thoracic region they he at the sides of the bodies of the vertebrae and on the heads of the ribs; in the lumbar region they are placed more ventraUy with reference to the spinal nerves and more in front of the bodies of the vertebrte and along the anterior borders of the psoas muscles; in the pelvis the ganglia lie between and ventral to the openings of the sacral foramina. In the lower lumbar and sacral region one gangUon may send rami commu- nicantes to two spinal nerves and one spinal nerve may be connected with two gangha. The ganglia of the trunks throughout give off associative branches to the gangha of the prevertebral plexuses and branches to the nearby viscera and blood-vessels. These branches may appear either white or grey according to the predominance of meduUated or non-medullated fibres in them. In the lumbo-sacral region commissural or transverse branches between the gangha of the two trunks are especially abundant. In trunks having a whiter appearance, the greater part of the meduUated fibres producing it are sensory and visceral motor fibres from the spinal nerves which have passed through the sympathetic ganglia without termination. The nerve trunks connecting the ganglia of the sympathetic trunks all contain three varieties of fibres: — (1) THE SYMPATHETIC TRUNK 1033 visceral motor fibres which have entered them in the white rami communicantes from the spinal nerves of higher or lower levels, and which are coursing in them to terminate in other gangUa, either in the trunks above or below or in ganglia not belonging to the trunks; (2) fibres arising in sympathetic ganglia of a higher or lower level and passing upward or downward to terminate in other ganglia of the trunk or to issue from the trunk and proceed to more peripheral ganglia or to ganglia of the opposite trunk (both associative and commissural fibres); (3) afferent fibres or sensory fibres arising either in the spinal ganglia, or sensory sympathetic fibres arising in sympathetic ganglia and coursing in the trunk to pass into spinal ganglia above or below by way of the grey rami communicantes. THE CEPHALIC AND CERVICAL PORTIONS OF THE SYMPATHETIC TRUNK The cephalic portion of the sympathetic system consists of numerous small ganglia and of numerous plexuses connected with the internal carotid nerve, the ascending branch given off by the superior cervical sympathetic ganglion. The cephalic ganglia are all relatively small. There are four considered in the ordinary macroscopic dissections, namely, the ciliary or ophthalmic, the spheno- palatine or Meckel's ganglion, the otic, and the submaxillary. To these may be added a portion of the superior cervical sympathetic ganglion, the sympathetic portions of the nodosal, petrous, geniculate and semilunar ganglia, and the var- ious small ganglia dispersed in the plexuses. These ganglia with their roots or communicating branches have been described in their relations with the divisions of the trigeminus and with the oculo-motor, glosso-palatine, vagus and facial nerves. The internal carotid nerve, the ascending branch from the superior cervical sympathetic ganglion, may be regarded as an upward prolongation of the primi- tive sympathetic trunk. It arises from the upper end of the superior cervical ganglion and passes through the carotid canal into the cranial cavity. It divides into two branches which subdivide to form a coarse plexus, the internal carotid plexus, which partly surrounds the internal carotid artery before the latter enters the cavernous sinus (fig. 787 and 788). It passes with the artery to the caver- nous sinus, where it forms the finer meshed cavernous plexus. The internal carotid plexus supplies offsets to the artery and receives branches from the tympanic plexus through the inferior carotico-tympanic nerve and from the spheno-palatine ganglion through the great deep petrosal nerve. It also communicates by fine branches with the semilunar (Gasserian) ganglion and with the abducens nerve. The cavernous plexus gives branches of communication to the oculo-motor and trochlear nerves and to the opthalmic division of the trigeminus. According to Toldt and Spalteholz, it communicates with the tympanic plexus through the superior carotico-tympanic (small deep petrosal) nerve. It also communicates with the ciliary ganglion through the long root of the ciliary ganglion and usually through a separate sympathetic root of this ganglion. These branches may pass through the superior orbital (sphenoidal) fissure either separately or with the naso- ciliary (nasal) nerve. The cavernous plexus also gives branches to the carotid artery and filaments of the plexus accompany small branches of the artery to the hypophysis (pituitary body) and to the dura mater on the sphenoid bone. The terminal branches of the cavernous plexus consist of delicate filaments that anastomose freely, forming fine plexuses, and pass from the cavernous plexus along the terminal divisions of the internal carotid artery and their branches. These fine plexuses take the name of the artery on which they lie. The four larger of them are the plexuses of the anterior and middle cerebral arteries, the plexus of the chorioid artery, and the ophthalmic plexus. The cervical portion of the sympathetic cord extends upward along the great vessels of the neck. No white rami communicantes connect it directly with the spinal cord, but instead it receives visceral efferent fibres from the upper thoracic spinal nerves through the sympathetic trunk, and probably also from the cervical spinal cord through the spinal acessory nerve and the connections with the vagus. It sends grey rami communicantes to each of the cervical nerves. It extends from the subclavian artery to the base of the skull, lying dorsal to the sheath of the great vessels and in front of the longus capitis and longus colli, which separate is from the transverse processes of the cervical vertebrae (fig. 787). It usually 1034 THE NERVOUS SYSTEM Fig. 787. — Showing the Sympathetic Trunks in their Relation to the Vertebral Column, to the Spinal Nerves, and to each Other. (Modified from^Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Cavernous plexus Internal carotid plexi Internal carotid nerve Jugular nerve Vagus Superior cervical ganglion - rical plexus Cervical portion of sympathetic trunk Superior cardiac nerve' Rami communicantes Middle cervical ganglion Brachial plexus Inferior cervical ganghon .First thora.,ic ganghon' Ansa subclavia (Vieussenii) Inferior cardiac or and middle c nerves Pulmonary branches Twigs to aortic plexus Splanchnic gangUons. Last thoracic ganghon^ Splanchnic minor nerve Medial part of lumbo costal arch Lateral part of lumbo-costal arch Psoas major- Second lumbar nerve Twelfth intercostal nerve Lumbar plexus Li Glossopharyngeus ..- Jugular nerve --—Pharyngeal plexus ■"-» Pharyngeal branches **Vagus External carotid nerves ylnfenor thyreoid plexus Vertebral plexus Subclavian plexus Rami communicantes Thoracic portion of sympathetic trunk Thoracic ganglia .-.Intercostal nerves — Greater splanchnic nerve /^„- Lesser splanchnic nerve >-^ /^ I -Thoracic aortic plexus splanchnic nerve Greater splanchnic nerve Branches to phrenic plexus ..•Branches to coeliac ganglia **Rami communicantes Rami communicantes Lumbo-sacral trunk Rami communicantes Branches to abdominal aortic plexus Branches to hypogastric plexus ^. Fifth lumbar ganglion ._ Commissural branches ■First sacral ganglion U V '"-^^Rami communicantes Ganghon coccygeum impar SUPERIOR CERVICAL GANGLION 1035 has but three ganglia, one at each end, the superior and inferior, and one between these two, called the middle ganglion. The latter varies somewhat in position and is sometimes absent. 1. Superior Cervical Ganglion The superior cervical ganglion is usually fusiform in shape and is sometimes marked by one or more constrictions. There is ground for the belief that it is formed by the coalescence of four ganglia corresponding to the first four cervical nerves. It varies from an inch to one and one-half inches (2.5 to 3.7 cm.) in length, lying dorsal to the upper part of the sheath of the great vessels of the neck and in front of the transverse processes of the second and third cervical vertebrae. Fig. 788. — Diagram op the Glosso-palatine Nerve and the Relations op the Gangli- ATED Cephalic Plexus to other Cranial Nerves. (After Bean.) Broken lines, motor; continuous lines, sympathetic; glosso-palatine .in solid black. Medial view. Left side. £ > en d S a « 3 Glosso-palatine ." g « S " a ° 3 -g p, ' ' ' Carotid _ ^ artery Oculomotor nerve Chorda tympani Ciliary ganglion — Ophthalniic nerve .1 i V ^ Maxillary nerve 4^i)--\-TX— Mandibular nerve jV/^wSj^^^::^;^^ Great deep \\ » \ » "'^"^yi^ petrosal nerve W'W^^^^""' Sphenopalatine 'A ^ ^ \r\^ ganglion Palatine portion of glosso-palatine nerve Nerve of pterygoid canal (Vidian nerve) Otic ganglion • Middle meningeal ([l\ artery \ i^ r Submaxillary ganglion )nr\rr External ma^llaiy artery It occasionally extends upward as high as the transverse process of the first vertebra (fig. 787). It is connected with the middle cervical ganglion by the intervening trunk, and it gives off a large number of communicating branches. Rarely, the ganglion may be double or split with a ventral portion lying superfi- cial to the carotid sheath and a dorsal portion dorsal to the sheath, connected by sympathetic filaments near the superior and inferior extremities of the ganglion. Communications: — (1) Four grey rami communicantes associate the ganglion with the anterior primary divisions of the first four cervical nerves. (2) Communicating branches to the cranial nerves. — An iiTegular number of small twigs pass between the superior cervical gangUon and the hypoglossal nerve and to the ganghon nodo- sum of the vagus. A named branch, the jugular nerve, runs upward to the base of the skull and divides into two branches, one of which enters the jugular foramen and terminates in the jugular ganghon of the vagus, and the other ends in the petrous ganghon of the glosso- pharyngeus. (See fig. 788). 1036 THE NERVOUS SYSTEM (3) Four or five laryngo -pharyngeal branches come from the superior ganglion and the plexus extending downward from it, and pass forward and medialward, lateral to the carotid vessels, to the wall of the pharynx, where they unite on the middle constrictor with the pharyn- geal branches of the glosso-pharyngeus and vagus, forming with them the pharyngeal plexus, from which branches are distributed to the walls of the pharynx and to the superior and external laryngeal nerves (fig. 787). (4) The superior cervical cardiac nerve springs from the lower part of the ganglion or from the trunk immediately below it. It passes downward behind the carotid sheath, either in front of or dorsal to the inferior thyreoid artery, and in front of the longus colli, and establishes communications with the upper cervical cardiac branch of the vagus, the middle cervical cardiac branch of the sympathetic, and with the inferior and external laryngeal nerves. At the root of the neck the nerve of the right side passes in front of or behind the first part of the right sub- clavian artery, and is continued along the innominate artery to the front of the bifurcation of the trachea, where it ends in the deep part of the cardiac plexus. The left nerve passes into the thorax along the front of the left common carotid artery, crosses the front of the arch of the aorta immediately anterior to the vagus, and terminates in the superficial part of the cardiac plexus (fig. 789). Filaments from both the right and left nerves pass to the inferior thyreoid plexus. (5) The external carotid nerves (fig. 787) pass forward from the .superior cervical ganglion to the external carotid arlcry, where they divide into branches which anastomose freely to form around the artery the external carotid plexus. This plexus extends to the beginning of the artery, and is continued upon the common carotid artery as the common carotid plexus. From the external carotid plexus, filaments pass to form secondary plexuses around each of the branches of the external carotid artery. These plexuses take the names of the arteries which they follow, namely, the superior thyreoid plexus, lingual plexus, etc. Filaments pass from the external carotid plexus to the glomus caroticum (the carotid gland), and from the superior thyreoid plexus to the thyreoid gland. From the external maxillary (facial) plexus passes the sympathetic root of the submaxillary glion. A part of the internal maxillary plexus is continued upon the middle meningeal artery as the meningeal plexus. From this plexus filaments pass to the otic ganglion, and sometimes a branch, called by English anatomists the external superficial petrossal nerve, passes to the geniculate ganglion. (6) Small branches to the ligaments and bones of the upper part of the vertebral column. (7) The internal carotid nerve (ascending branch) and plexus have been described with the cephalic portion of the sympathetic system. 2. The Middle Cervical Ganglion The middle cervical ganglion is small and somewhat triangular in outline. It is sometimes absent. Its position is variable, but it commonly lies about the level of the cricoid cartilage, in front of the bend of the inferior thyreoid artery (fig. 787), and it is associated with the superior cervical ganglion and with the inferior cervical ganglion by the trunk of the gangliated cord. From the lower part of the middle ganglion some filaments pass dorsal to the subclavian artery, while others pass in front of and beneath that artery and anastomose with the first-mentioned filaments to form a loop, the ansa subclavia {ansa Vieussenii) (figs. 751, 787). Filaments from this loop to the inferior cervical ganglion thus form another communication between the middle and inferior cervical ganglia. Connections. — The middle cervical ganghon gives off four or more rami. Two (a and h) are grey rami communicantes which connect the middle ganglion with the anterior primary iDranches of the fifth and sixth cervical nerves. (c) One or more peripheral branches pass along the inferior thyreoid artery and anastomose with branches from the superior and middle cardiac nerves and from the inferior cervical ganghon, thus taking part in the formation of the inferior thyreoid plexus, from which branches pass to the thyreoid gland. {d) The middle cardiac nerve arises by one or more branches from the ganghon, or from the trunk of the cord, and passes downward dorsal to the common carotid artery and, on the right side, either in front of or dorsal to the subclavian artery, and then along the innominate artery to the deep part of the cardiac plexus (figs. 787 and 789). It is frequently larger than the superior cardiac nerve. On the left side the nerve runs between the subclavian and common carotid arteries. On both sides the nerve communicates with the inferior laryngeal nerve and external laryngeal nerve. The middle cervical ganglion also gives branches to the common carotid plexus. 3. The Inferior Cervical Ganglion The inferior cervical ganglion is irregular in form. It is larger than the middle cervical ganglion, and it lies deeply in the root of the neck dorsal to the vertebral artery or the first part of the subclavian artery, and ventral to the interval between the transverse processes of the last cervical and the first thoracic vertebrse (figs. 759, 761). It is connected with the middle cervical ganglion by THE SYMPATHETIC TRUNK 1037 the sympathetic trunk, and by filaments passing to the ansa subclavia (Vieussenii), and it is either blended directly with the first thoracic ganglion or connected with it by a short stout portion of the trunk. It gives rami to the last two cervical nerves and peripheral branches to the vertebral and internal mammary arteries, to the heart, and to the inferior thyreoid plexus. Connections. — (1) The rami to the seventh and eighth cervical nerves are grey rami communicantes. (2) The branches to the vertebral artery are large and they unite with similar branches from the first thoracic ganglion to form a plexus, the vertebral plexus (fig. 787), which accom- panies the artery into the posterior fossa of the cranium, where it is continued on the basilar artery. The plexus communicates in the neck by delicate threads with the cervical spinal nerves. These are probably meningeal rami. (3) The branches to the internal mammary artery form the internal mammary plexus. (4) The inferior cardiac nerve may arise from the inferior cervical ganglion, from the first thoracic ganglion, or by filaments from both these ganglia (figs. 787 and 789). It communicates with the recurrent laryngeal nerve and with the middle cardiac nerve, and passes to the deep part of the cardiac plexus. On the left side it frequently joins the middle cardiac nerve to form a common trunk. Construction of the cervical portion of the sympathetic trunk. — This portion of the trunk contains both meduUated and non-medullated fibres, and a large part of the former are of cranio-spinal origin. In the absence of white rami communicantes to this portion of the sym- pathetic trunk, it is evident that few if any of the cranio-spinal or efferent visceral fibres are contributed to it below the superior ganglion by the cervical region of the spinal cord. Instead, such fibres are known to enter by way of the white rami from the upper thoracic nerves, and to ascend to this portion of the sympathetic trunk. Most of these fibres terminate about the cells of the superior, middle, and inferior cervical ganglia, and these cells in their turn give off sympathetic fibres which pass by way of the branches mentioned above for the cephalic and cervical portions, to their distribution in the structures of the head, neck, and thorax. The efferent visceral fibres which terminate in the superior ganghon especially are among those which mediate — (1) vaso-motor impulses for the head; (2) secretory impulses for the submaxil- lary gland; (3) pilo-motor impulses for the hairs of the face and neck; (4) motor impulses for the smooth muscle of the eyelids and orbit, and (5) dilator impulses for the pupil. The sympathetic or grey fibres in the cervical portion of the sympathetic trunk arise from the cells of the upper thoracic and the cervical ganglia, and are passing either to connect the ganglia with each other or to enter the peripheral branches and proceed to their terminal distribution. THE THORACIC PORTION OF THE SYMPATHETIC TRUNK The thoracic part of the gangliated trunk runs downward on the heads of the ribs from the first to the tenth, and then passes a little ventralward on the sides of the bodies of the lower two thoracic vertebrse. Above it is continuous with the cervical portion at the root of the neck, dorsal to the vertebral artery. Below it leaves the thorax dorsal to the medial lumbo-costal arch (arcuate ligament), or sometimes dorsal to the lateral lumbo-costal arch, and continues into the lumbar portion of the trunk. It lies behind the costal pleura and crosses over the aortic intercostal arteries. The number of ganglia in this part of the trunk is variable. There are usually ten or eleven, but the first is sometimes fused with the inferior cervical ganglion and occasionally other ganglia fuse. The ganglia are irregularly angular or fusiform in shape, and lie on the head of the ribs, on the costo-vertebral articulations, or on the bodies of the vertebrae. The portions of the trunk connecting the ganglia usually are single, but sometimes they are composed of two or three small cords in juxtaposition. Each ganglion, with the possible exception of the first, receives a white ramus comnmnicans from a thoracic nerve and all give off grey rami communicantes to these nerves. The white rami communicantes, as they approach the sympathetic trunk, quite often appear double, due to the separation of a large portion of their fibres into two main streams, one passing upward in the sympathetic trunk, and one passing downward. Of the white rami from the upper five thoracic nerves, the upward stream of fibres is much larger than the downward, due to the fact that a greater part of the efferent visceral fibers from these nerves are distributed through the cervical portion of the sympathetic trunk, as noted above in the construction of that portion. Usually the white rami from the spinal nerves pass directly to the corresponding ganglia of the trunk, and thus lie in company with the corre- sponding grey rami. Sometimes, however, they may join the intermediate por- tions of the trunk, and in the lower thoracic region especially, a ramus may pass from a nerve to the ganglion corresponding to the nerve above or below. The 1038 THE NERVOUS SYSTEM fibres of the white rami from the lower thoracic nerves are in greater part directed downward in the sympathetic trunk, and also downward in its peripheral branches, to be distributed to the abdominal viscera. In all cases, however, some of the fibres of the thoracic white rami terminate in the ganglia nearest their junction with the trunk, while others pass into the nearest peripheral branches. In this way the white rami from all the thoracic spinal nerves, especially those of the mid-region, are directly concerned in the innervation of the thoracic viscera, lungs, oesophagus, aorta, etc. The first thoracic ganglion is larger than the other ganglia of this region and is irregular in form. It may be narrowly ovoid or semilunar. It lies in front of the neck of the first rib, behind the pleura, and on the medial side of the costo- cervical trunk (superior intercostal artery), which vessel separates it from the prolongation of the portion of the first thoracic nerve which passes to the brachial plexus. It sometimes fuses with the inferior cervical ganglion, and, on the other hand, sometimes extends to the upper part of the second rib to fuse with the second thoracic ganglion. The result of the latter fusion resembles the stellate ganglion of the carnivora, and when it occurs, is sometimes referred to as the ganglion stellatimn. When well developed, the first ganglion sends a branch to the cardiac plexus, forming the fourth cardiac nerve of Valentin. ^ The second thoracic ganglion, triangular in shape and almost as large as the preceding, is sometimes placed on the costo-vertebral articulation, and is some- times partly concealed by the first rib. The third to the ninth thoracic ganglia are usually placed opposite the heads of the corresponding ribs, but the tenth and eleventh may lie on the bodies of the vertebrae. The fibres passing from the ganglia form two groups of branches, the central and the peripheral. The central branches are the grey rami communicantes, which pass from the ganglia to the corresponding spinal nerves. After they have joined with the anterior primary divisions of the nerves, the fibres of these rami divide into four groups: — (1) Fibres which pass medialward along the roots of the nerves to supply vessels of the membranes of the spinal cord, or enter a meningeal or recurrent branch for the same purpose; (2) fibres which enter the spinal ganglion and terminate there (sensory sympathetic fibres) ; (3) fibres which pass dorsalward into the posterior primary divisions of the nerves; (4) fibres which pass lateral- ward in the anterior primary divisions of the nerves. The last two groups of fibres are distributed to the muscle of the blood-vessels of the body-walls, to the skin-glands, and to the muscles of the hairs of the body. The peripheral branches of the ganglia form two series, an upper and a lower. Those of the upper' series pass from the upper four or five ganglia ventralward to be distributed as follows: — (1) Pulmonary branches which accompany the intercostal arteries toward their aortic origin without forming plexuses around them, and pass to the posterior pulmonary plexus (fig. 789). (2) Aortic branches, some of which arise directly from the gangha and some from the pulmonary branches, and unite with branches from the cardiac plexus and from the splanchnic nerves to surround the aorta as the thoracic aortic plexus (fig. 789). This plexus accompanies the aorta into the abdomen and there joins with the coehac (solar) plexus. (3) (Esophageal branches join with the oesophageal plexus of the vagus. (4) Vertebral branches, some of which pass with the nutrient arteries into the bodies of the vertebra; and some of which pass to the median line and there anastomose with similar branches from the opposite side (commissural branches). The peripheral ganglionic branches forming the lower series consist largely of efferent and afferent fibres from the spinal nerves, which pass through the gangha and reinforce the sympathetic filaments proper. Thus composed, these branches run ventralward and medialward on the sides of the bodies of the vertebrae and unite to form the splanchnic nerves which supply the abdominal organs, the afferent fibres serving to collect sensory impulses in this domain of the sym- pathetic. (1) The great splanchnic nerve may be formed by branches from all the thoracic ganglia from the fifth to the tenth inclusive, or it may receive fibres from only two or three of these THE SYMPATHETIC TRUNK 1039 ganglia (fig. 787). It is usually formed by branches from the fifth to the tenth. The superior branch, usually the largest, receives smaller inferior branches from the lower ganglia as it passes downward on the sides of the bodies of the vertebrae in the posterior mediastinum. The nerve enters the abdominal cavity bypassing through the crus of the diaphragm, and joins the upper end of the coeliac (semilunar) ganglion of the coeliac (solar) plexus. Near the disk between the eleventh and the twelfth thoracic vertebra there is formed on the nerve the splanchnic ganglion. Filaments from the nerve and from this ganglion pass along the intercostal arteries to the aorta, oesophagus, and the thoracic duct, and some fibres from the right side pass to the vena azygos (major). Sometimes this nerve divides into two cords, giving off numerous branches which anastomose with each other and with the lesser splanchnic nerve to form a plexus, in the meshes of which are found some small ganglia. (2) The lesser splanchnic nerve receives fibres from the ninth and tenth gangha. Its course is similar to that of the great splanchnic nerve (fig. 787), but on a more dorsal plane, and it terminates in the cceliac (solar) and renal plexuses. (3) The least splanchnic nerve, not always present, arises from the last thoracic ganghon or sometimes from the small splanchnic nerve. It passes through the crus of the diaphragm and ends in the renal plexus. Construction of the thoracic portion of the cord. — The majority of the visceral efferent fibres which pass from the central nervous system enter the thoracic portion of the sympathetic trunk; some end there in ramifications around the cells of its ganglia, while others merely pass through on their way to more distant terminations. With regard to those which terminate in the gangha, it has been shown that in the dog and cat many end in the ganglion stellatum which corresponds with the last cervical and the upper three or four thoracic ganglia in man. Among these are the fibres conveying secretory impulses to the sweat-glands of the upper hmb, which emerge from the spinal cord in the thoracic nerves from the sixth to the ninth, and, in the dog, those which convey and transfer vaso-constrictor impulses to the sympathetic neurones supplying the pulmonary blood-vessels. These visceral efferent fibres leave the spinal cord in the second to the seventh thoracic nerves. Other fibres which terminate around the thoracic sympathetic ganglion-cells in the dog and cat are the vaso-constrictor fibres for the upper limbs and some of the vaso-constrictor fibres for the lower limbs. Of the fibres which traverse the thoracic portion of the sympathetic trunk to gain more distant terminations, some ascend to the cervical region (p. 1033), others descend to the lumbar region, and many pass by the immediate peripheral branches to the splanchnic nerves. Among those which descend to the lumbar region are pilo-motor fibres, vaso-motor fibres, and secretory fibres to the lower limb, some vaso-constrictor fibres to the abdominal blood- vessels, motor fibres to the circular, and inhibitory fibres to the longitudinal muscle of the rectum. The latter enter the sympathetic trunk by the lower thoracic nerves and pass in the lumbar peripheral branches to the aortic plexus, and terminate around the cells of the inferior mesenteric ganglion. The visceral efferent fibres which pass through the thoracic ganglia to the splanchnic nerves are mainly vaso-motor fibres to the abdominal blood-vessels; the majority of them probably terminate around the cells of the ganglia in the coelio (solar) plexus, but those for the renal blood- vessels no doubt end in the renal ganglia. In addition to all the above-mentioned fibres there are in the thoracic part of the sympathetic trunk afferent fibres of both sympathetic and cere- bro-spinal type, passing toward the spinal ganglia and the latter, greatly predominating, pass into the dorsal roots of the thoracic spinal nerves. THE LUMBAR PORTION OF THE SYMPATHETIC TRUNK The lumbar portion of each trunk lies on the fronts of the bodies of the verte- brae along the anterior border of the psoas muscle, and nearer to the median line than the thoracic portion. It is connected with the thoracic portion of the sympathetic trunk by a slender intermediate portion of the trunk that may pass through the diaphragm or dorsal to it (fig. 787). The continuation of the lumbar into the sacral portion is also slender, and descends dorsal to the common iliac artery. The right trunk is partly covered by the vena cava inferior and the left by the aorta. The ganglia, which are small and oval, vary in number from three to eight, but are usually four. Rarely they are so fused as to form one continuous ganglion. White rami communicantes pass to the ganglia from the first two or three lumbar nerves only. This portion of the sympathetic trunk also receives visceral efferent and afferent fibres which are derived from the white rami communicantes of the lower thoracic nerves and continue downward in the trunk. Branches. — As in the thoracic region, the branches from the gangha are central and per- ipheral. The central are grey rami communicantes. There may be two branches to a nerve or one ramus may divide so as to join two adjacent spinal nerves. Sometimes a spinal nerve may receive as many as five grey rami from the sympathetic trunk. The peripheral branches include; — (a) Branches passing to the aorta and taking part in the formation of the aortic plexus; (6) branches which descend in front of the common ihac artery to the hypogastric plexus; and (c) branches to the vertebrse and ligaments. 1040 THE NERVOUS SYSTEM THE SACRAL PORTION OF THE SYMPATHETIC TRUNK The sacral part of each truak passes downward in front of the sacrum, imme- diately lateral to the medial borders of the anterior sacral foramina. It is continuous above with the lumbar portion of the trunk, and below it anastomoses freely in front of the coccyx with the trunk of the other side to form a plexus in the terminus of which is the coccygeal ganglion {ganglion coccygeum impar) (fig. 787). Like the cervical and lower lumbar portions of the sympathetic trunk, the sacral part receives no white rami communicantes from the spinal nerves. The sacral ganglia are small in size, and usually four in number. The varia- tion both in size and number is more marked in this portion of the trunk than in the two parts above. Branches. — The branches of the sacral gangha include: — (1) Grey rami communicantes to the sacral nerves. (2) Branches to the front of the sacrum which anastomose with their fellows of the opposite side (commissural branches). (3) Branches which enter into the formation of the plexus on the middle sacral artery. (4) Branches which join the pelvic plexuses. (5) Branches given off by the ganglion coccygeum impar to the coccyx and its ligaments and to the glomus coccygeum (coccygeal gland). Construction of the lumbar and sacral portions of the gangliated trunk. — The ganglia of both these portions of the trunk are very variable in shape, size, position, and number. There are usually four gangha belonging to each portion, but sometimes as many as eight may be distinguished in the lumbar and at other times there may be as many as six in the sacral portion. In the majority of cases, especially in the sacral region, these masses of cells are so fused that their number is less than the number of the spinal nerves with which they are associated. As noted above, only the first two or three lumbar spinal nerves send white rami which enter these ganglia directly as such. However, visceral efferent fibres descend this entire stretch of the trunk, through both the lumbar and sacral portions, from the white rami of the lower thoracic and the upper lumbar nerves above. These fibres either terminate in the various gangha or pass uninterrupted to the more distant sympathetic cell-bodies which are concerned in impulses that are vaso-motor to the genital organs, motor for the uterus, the vas deferens, and the mus- cular coats (circular coat especially) of the bladder. Also, some of them convey secretory, pilo- motor, and vaso-motor impulses for the glands, skin, and vessels of the lower extremity in addition to the similar impulses conveyed in the peripheral branches from the lower part of the thoracic portion of the sympathetic trunk. The motor impulses for the uterus or vas deferens and for the bladder pass, in most part probably, by way of the peripheral branches from the lumbar portion of the cord, through the aortic plexus to the inferior mesenteric gang- lion; others, the vaso-motor impulses to the genital organs especially, pass by way of the sacral ganglia and the peripheral branches from them to the hypogastric or pelvic plexus and the appro- priate subplexuses of this region. Of the vaso-motor fibres for the penis, some of the constrictor fibres pass down the sacral portion of the sympathetic trunk and terminate about the cells of the sacral ganglia, and these cells send out sympathetic fibres which join and course in the pudic nerve (n. pudendus). All of both the lumbar and sacral spinal nerves receive grey rami from the gangliated trunk. These, just as those from the other portions of the trunk, consist of — (1) vaso-motor fibres to vessels of the meninges and the vertebral canal; (2) sympathetic fibres which join the divisions of the spinal nerves and course in them to their distribution, and (3) afferent sympathetic fibres terminating in the spinal ganglia. In addition to the visceral efferent fibres, the branches of the lumbo-sacral portion of the sympathetic trunk carry cerebro-spinal fibres of general sensibility — sensory fibres arising in the spinal gangha of this and the lower thoracic region. There are no white rami proper passing from the sacral spinal nerves to course or terminate in the sympathetic trunk. Visceral efferent fibres are given off by these nerves in abundance, but, instead of entering the trunk and its ganglia, they form bundles which pass over the trunk and directly into its peripheral branches and to the more distant ganglia. The bundles passing from the second, third, and fourth sacral nerves are large and especially definite. While homologous to white rami, such bundles are better known as the visceral branches of the sacral nerves or the plevic splanchnics. They contain some spinal sensory fibres, but consist for the most part of visceral efferent, conveying impulses, vaso-motor (vaso-dilator, chiefly) to the gen- ital organs, both motor and inhibitory for the rectum, uterus, and bladder (longitudinal coat especially), and secretory for the prostate gland. These fibres contribute to the hypogastric plexus and are interrupted in the small gangUa of its sub-plexuses, named according to the various urino-genital organs concerned. THE GREAT PREVERTEBRAL PLEXUSES The great prevertebral plexuses, in the body cavities, are three in number — the cardiac, the coeliac (solar or epigastric), and the hypogastric or pelvic. The cardiac plexus lies behind and below the arch of the aorta, and the coeliac and THE CARDIAC PLEXUS 1041 hypogastric plexuses are situated in front of the lumbar vertebrae. Each plexus receives not only sympathetic fibres which have passed from or through the ganglia of the sympathetic trunks of either side, but also both afferent and efferent cranio-spinal nerve-fibres derived directly from the cranio-spinal nerves. In addition the cardiac and coeliac plexuses receive both efferent visceral and cranio- spinal sensory or afferent visceral fibres from both vagus nerves. It should be clearly understood that the branches which run from the sympathetic gangliated trunks to the prevertebral plexuses contain meduUated fibres which are passing, like the fibres from the sacral nei'ves, directly from the spinal cord to terminate about the cells of the plexuses. 1. The Cardiac Plexus The cardiac plexus is formed by the cardiac branches from both vagus nerves and from both sympathetic trunks. It lies beneath and dorsal to the arch of the aorta, in front of the bifurcation of the trachea, and extends a short distance upward on the sides of the trachea. It is composed of a superficial and a deep part (fig. 789). The superficial part of the cardiac plexus is much smaller than the deep part, and lies beneath the arch of the aorta in front of the right pulmonary artery. It is formed chiefiy by the cardiac branches of the left vagus and by the left superior cardiac nerve, but sometimes receives filaments from the deep cardiac plexus. The cardiac ganglion (ganglion of Wrisberg,) usually found connected with this plexus, lies on the right side of the ligamentum arteriosum. Branches. — From this plexus some branches pass to the left half of the deep cardiac plexus, and others accompany the left pulmonary artery to the left anterior pulmonary plexus. It also sends branches to the right anterior coronary plexus. , The deep portion of the cardiac plexus lies dorsal to the arch of the aorta at the sides of the lower part of the trachea and in front of its bifurcation. It consists of two lateral parts, more or less distinct, connected by numerous branches, which pass around the lower part of the trachea. It is formed by the superior, middle, and inferior cervical cardiac branches from the right sympathetic trunk, the mid- dle and inferior cervical cardiac branches from the left trunk, and all the cervical and thoracic cardiac branches of the vagus except the superior cervical cardiac branch of the left vagus. It also receives branches from the superficial cardiac plexus. The left part of the deep cardiac plexus gives branches to the left atrium (auricle) of the heart, to the left anterior pulmonary plexus, to the left coronary plexus, and sometimes to the super- ficial part of the cardiac plexus. The right part of the deep cardiac plexus gives branches to the right atrium, to the right an- terior pulmonary plexus, and to the right and the left coronary plexuses (fig. 789). The branches to the left coronary plexus pass behind the pulmonary artery. Some of those to the right coro- nary plexus pass anterior and some posterior to the right pulmonary artery. The coronary plexuses are formed by branches given off by the cardiac plexus. They accompany the coronary arteries and are right and left. The right {anterior) coronary -plexus receives filaments from the superficial part of the cardiac plexus, but is formed chiefiy by filaments from the right portion of the deep cardiac plexus (fig. 789). Its distribution to the heart follows that of the right coronary artery. The left {posterior) coronary plexus is larger than the right plexus, and is formed for the most part by filaments from the left portion of the deep cardiac plexus, but it receives some filaments from the right portion of the deep cardiac plexus (fig. 789). Its distribution to the heart follows that of the left coronary artery. The cardiac plexus and the network of nervous structures in the walls of the atria are the remains of the primitive plexuses found in the embryo, which are called the bulbarj the inter- mediate, and the atrial plexuses, terms which sufficiently indicate their relative positions. The bulbar plexus gives off the coronary nerves and is transformed into the superficial part of the deep cardiac plexus; the remainder of the deep cardiac plexus is formed by the intermediate plexus, and the atrial plexus becomes the network of the atrium. The fibres which pass to the cardiac plexus are meduUated and non-meduUated; the former 1042 THE NERVOUS SYSTEM Fig. 789. Caediac, Pulmonary, and Coronary Plexuses. (Schematic.) (Modified from Cunningham.) Superior cardiac nerve- Middle cardiac nerve' Cervical cardiac branches of vagus Inferior cardiac nerve- Recurrent nerve^ Thoracic cardiac branches, of vagus Right coronary plexus— — Middle cervical ganglion _ Inferior cervical ganglion Deep cardiac plexus Superficial cardiac plexus NLeft posterior pulmonary plexus - Left coronary pie: THE C (ELI AC PLEXUS 1043 are the so-called inhibitory, the latter motor. The inhibitory impulses leave the central nervous system by the spinal accessory and vagus nerves. The motor iibres leave the spinal cord by the ventral roots and white rami communicantes of the thoracic nerves and terminate about the cells of the intervening sympathetic ganglia. From the cells of these gangha arise the non-meduUated (grey) fibres of the plexus. These fibres terminate directly upon the fibres of cardiac muscle or about the cells of the minute intrinsic cardiac ganglia which in their turn give axones to the muscle. 2. The Pulmonary Plexuses The pulmonary plexuses are a continuation of the cardiac plexuses. The two are so intimately joined that it is difficult to distinguish them as separate plexuses. The pulmonary are formed by fibres from both the vagus and sympa- thetic nerves. The anterior and posterior pulmonary branches of the vagus unite, dorsal to the bifurcation of the trachea, with fibres from the second, third and fourth ganglia of the thoracic portion of the sympathetic trunk to form the anterior and posterior pulmonary plexuses that lie ventral and dorsal to the bifurcation of the trachea. Here the pulmonary plexuses of both sides connect with each other freely. Leaving the trachea, the plexuses pass into the lungs along the pulmonary arteries (figs. 744, 789) . The parts of the plexus of each side are named according to their position anterior or posterior to the right and left pulmonary arteries; thus, there is a right anterior and a right posterior, a left anterior and a left posterior pulmonary plexus. 3. The C celiac Plexus The coeliac (solar or epigastric) plexus is the largest of the prevertebral plexuses. It is unpaired, and is continuous above with the aortic plexus of the thorax and below with the abdominal aortic and superior mesenteric plexuses. It lies in the epigastric region of the abdomen behind the bursa omentalis (lesser sac of the peritoneum) and the pancreas, upon the crura of the diaphragm and over the abdominal aorta, and around the origin of the coeliac and the superior mesen- teric arteries. It occupies the interval between the suprarenal bodies and extends downward as far as the renal arteries. It is formed by the great and the lesser splanchnic nerves of both sides, by coeliac branches of the right vagus, and by filaments from the upper lumbar ganglia of the sympathetic trunlc. It sometimes receives coeliac branches from the left vagus. It contains two large ganglia, the right and left coeliac (semilunar) ganglia (fig. 790). The coeliac (semilunar) ganglia are two large, flat, irregularly shaped masses, separable into a varying number of ganglia. These two masses, or rather the smaller ganglia which compose them, are associated by a varying number of com- municating branches. Each mass, right and left, lies upon the corresponding crus of the diaphragm, at the medial border of the corresponding suprarenal body, being sometimes overlapped by this body. The right mass lies behind the inferior vena cava. Each coeliac ganglion receives at its upper border the greater splanchnic nerve, and, near its lower border, lying over the origin of the renal artery, is a more or less detached part, known as the aortico-renal ganglion. This ganglion receives the lesser splanchnic nerve and may seemingly give origin to the greater part of the renal plexus. Another part of the cceliac ganglion, often found dorsal to the origin of the superior mesenteric artery, is known as the superior mesenteric ganglion (fig. 790) . From the coeliac plexus and its ganglia subordinate plexuses are continued upon the aorta and its branches. These comprise both paired and unpaired plexuses. The paired plexuses are the phrenic, suprarenal and renal, the sper- matic in the male, and, in the female, the ovarian plexuses. The unpaired plex- uses are the aortic, hepatic, splenic, superior gastric, inferior gastric, superior mesen- teric, and inferior mesenteric. That part of the coeliac plexus surrounding the coeliac artery was formerly described as the coeliac plexus. It is better considered as an unnamed part of the larger coeliac (solar) plexus. This part of the plexus receives fibres from both vagus nerves, and gives filaments that form plexuses around the branches of the cceliac artery and their ramifications. 1044 THE NERVOUS SYSTEM The paired subordinate plexuses of the coeliac. — (1) The phrenic (diaphragmatic) plexuses consist of fibres from the upper part of the cceliac ganglia, which follow the inferior phrenic arteries and their branches on the under surface of the diaphragm (fig. 790). Filaments are given off by the roots of the plexuses to the suprarenal bodies, and others unite with the ter- minal branches of the phrenic nerves. The point of junction with the right phrenic nerve is marked by the phrenic ganglion, from which branches are distributed to the inferior vena cava, to the right suprarenal body, and to the hepatic plexus. (2) The suprarenal plexuses are comparatively large plexuses, formed mainly by branches from the cceliac (semilunar) ganglia. However, fibres come to them from the coeliac plexus Fig, 790. — Abdominal Plexuses of the Sympathetic. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Coeliac plexus Left vagus nerve Phrenic pie ..-, X"* hypogastric plexus *^ *»t,^ V — Sympathetic trunk '^"■f^-^^X Superior ~ *'^^^ -^K--^ — h£emorrhoidal Sacral plexus Visceral branches of pudendal plexus - Middle hsEmorrhoidal plexus "- Pudic nerve "Ureter Vesicula seminalis Prostatic plexus Rectum Levator am Cavernous plexus of penis Great cavernous nerve third or third and fourth sacral spinal nerves. Each pelvic part of the plexus accompanies the corresponding hypogastric (internal ihac) artery, and gives off secondary plexuses that continue on the branches of the artery to the pelvic viscera. Of these secondary plexuses, the middle hsemorrhoidal and the vesical plexus are common to both sexes and are paired. The middle hsemorrhoidal plexus passes on each side along the middle hsemorrhoidal artery to the rectum, where it receives the superior hsemorrhoidal nerves and sends filaments into the wall of the rectum (fig. 791). REFERENCES FOR NERVOUS SYSTEM 1047 The vesical plexus receives some branches from the pelvic parts of the hypogastric plexus, but is largely reinforced by way of the pelvic splanchnios, from the third and fourth sacral nerves. Each part passes along the corresponding vesical arteries to the bladder, and gives off two sets of branches, namely, the superior vesical nerves (fig. 791), which supply the upper part of the bladder-waU and send some branches to the ureter, and the inferior vesical nerves, which supply the lower part of the bladder and, in the male, give secondary deferential plexuses to the vas deferens. These plexuses surround the vasa deferentia and the vesiculse seminales and anastomose with the spermatic plexuses. The prostatic plexus, found only in the male, is formed in two parts by nerves of con- siderable size, and lies chiefly on the sides of the prostate gland between it and the levator ani (fig. 791). Each of the.se parts supplies the gland and the prostatic part of the urethra^ and sends offsets to the neck of the bladder and the vesioute seminales. This plexus is contmued forward on either side to form the cavernous plexus of the penis (fig. 791), which anastomoses with branches of the dorsal nerve of the penis, gives off branches to the membranous part of the urethra, and also gives origin to two sets of nerves, namely, the large and the small cavernous nerves of the penis. The large cavernous nerve, one on each side, runs forward to the middle of the dorsum of the penis, where it anastomoses with the dorsal nerve of the penis on the corresponding side, and ends in twigs which are distributed chiefly to the walls of the sinuses of the corpus caver- nosum penis, but some of the terminal filaments supply the corpus cavernosum urethrte (corpus spongiosum) (fig. 791). The small cavernous nerves are small filaments which pierce the uro-genital trigone (tri- angular ligament) and the compressor urethra;, and enter the posterior part of the corpus cavernosum. The utero-vaginal plexus, found in the female, is formed in its upper part on each side largely by fibres clerived from the pelvic part of the hypogastric plexus, but it receives some fibres from the pelvic splanchnics of the third and fourth sacral nerves. The nerves from this part of the plexus accompany the uterine arteries as they pass between the layers of the broad ligament. Some accompany each uterine artery and its branches to their termination, but a considerable number of fibres leave the artery and pass into the body of the uterus to supply its lower part and cervix. Between the layers of the broad ligament this plexus anastomoses with the ovarian plexus and sends some filaments to the uterine tube (Fallopian tube). The lower part of the plexus ulero-vaginalis receives some fibres on each side from the pelvic part of the hypogastric plexus, but it is formed chiefly by efferent visceral fibres from the second, third, and fourth sacral nerves. These fibres terminate in contact with intrinsic cell-bodies whose axones supply the wall and mucous membrane of the vagina and urethra. From the plexus on the anterior surface of the vagina fibres pass to form the cavernous plexus of the clitoris, which gives off the great and lesser cavernous nerves of the clitoris for the supply of the clitoris. The utero-vaginal plexus of the female corresponds to the prostatic plexus of the male. References for the Nervous System. A. General. Barker, Nervous System, 1899; Edinger, Vorlesungen, 1908; Johnston, Nervous System, 1906; (phylogeny) Parker, Anat. Eec, vol. 4; {develo-pment) Streeter, in Keibel and Mall's Human Embryology. B. Brain and Spinal Cord. Bechterew, Funktio- nen der Nervencentra, 3 vols., 1908; {cell-structure) Malone, Anat. Rec, vol. 7; {axone-sheaths) Hardesty, Amer. Jom*. Anat., vol. 4; (cortical localization) Donaldson, Jour. Nerv. and Mental Dis., vol. 13; Smith, Jour. Anat. and Physiol., vol. 41; Israelsohn Ai'b. Wien. neurol. Inst., vol. 20; (central fissure) Symington and Crymble, Jour. Anat. and Physiol., vol. 47; (brain-weight) Pearl, Jour. Comp. Neurol., vol. 25; Spitzka, Phila. Med. Jour., 1903; (ventricles Harvey, Anat. Rec, vol. 4; (mid-brain and medulla) Sabin, Atlas, 1901; (tri- geminal nuclei) Willems, Nevraxe, T. 12; (spinal cord, cornparative) BuUard, Amer. Jour. Anat., vol. 14. C. Peripheral. (Histogenesis) Bardeen, Amer. Jour. Anat., vol. 2; (experimental) Harrison, Amer. Jour. Anat., vol. 5; Jour. Exper. ZooL, vol. 9; (phylogeny of facial) Sheldon, Anat. Rec, vol. 3; (trigeminus) Symington, Jour. Anat. and Physiol., vol. 45; (nervus termnialis) Johnston, Anat. Rec, vol. 8. (afferent spinal neurones) Ranson, Jour. Comp. Neurol., vol. 18; (structure) Ranson, Anat. Rec, vol. 3; (brachial plexus) Todd, Anat. Anz., Bd. 42; (abdominal, statistical) Bardeen, Amer. Jour. Anat., vol. 1 (sympathetic termina- tions) Boeke, Anat. Anz., vol. 44. SECTION YIII SPECIAL SENSE OEGANS Revised for the Fifth Edition By DAVID WATERSTON, M.A.,M.D., F.R.C.S.E., King's College, London PROFESSOR OF ANATOMY IN THE UNrVERSITT OF LONDON GENERAL CONSIDERATIONS THE term "special sense organs" indicates those structures situated on or near the surface of the body which receive the impressions of sound, light taste and smell, and transmit them to the brain in the form of nerve impulses. The essential difference between what is termed general sensibility and the special senses lies in the fact that the organs of special sense are each sensitive to a specific stimulus which does not affect the general sensory apparatus of the body surface to an appreciable degree. Thus, the waves of light or of sound, flavoured substances which have a taste, and the minute particles which stimulate the sensory organ for smell — all these varied stimuli create no impression when they come into contact with the sensitive general surface of the body. The vibration of sound waves present in an organ pipe may indeed be felt by the hand, but the sensation is that of vibration and not of sound. This difference in function between the ordinary and the special senses as well as the difference between the individual organs of special sense, is as- sociated with a difference in structure; for each special sense organ has a charac- teristic receptive mechanism of cells highly specialised in form and structure, which receive the stimuli coming from without, and transmit them to the brain in the form of a nerve-current. These cells may be derived by the specialisation of certain cells coming directly from the surface of the body, or they may be cells derived from the central nervous system — as in the case of the eye. In this case, the cells are placed in close relation to the terminals of a special cranial nerve. Many of the sense organs, and especially the eye and ear, are highly com- plex in structure. The complexity is due largely to the elaborate mechanical arrangement for receiving the external stimulus, and for conveying it to, or focussing it upon, the sensory cells proper. It must always be borne in mind that sensation itself is a function of the brain — it is the response in consciousness to the afferent impressions transmitted to the brain by the sensory nerves. Further, the quality of the sensation does not arise in the sense organ, but in the brain itself. Thus, stimulation of the trunk of the optic nerve by mechanical means produces sensations of light, apart from stimulation of the retina. In the following account, the organs of smell, taste, vision and hearing will be successively considered. I. THE OLFACTORY ORGAN The olfactory apparatus [organon olfactus] in man does not reach the high development which is found in many of the lower animals. In them, not only is the sensory apparatus found distributed over a large area of the nasal mucous membrane, but the central connections of the olfactory nerves make up a considerable portion of the brain, including all those structures known under the name of rhinencephalon. In man, sensibility to smell is localised to a compara- tively limited area in the upper part of the nasal cavity, known as the olfactory area. The structure of the nose in all its parts has been fully dealt with in the 1049 1050 SPECIAL SENSE ORGANS section on the Respiratory System — and hence it is not necessary to describe the whole nasal cavity. The olfactory area of the nose includes the uppermost part of the nasal fossae on the lateral wall above the superior concha, and a slightly larger area of the septum. Fig. 792 shows the size of this area, and it will be noticed that the area on the lateral wall of the nose does not coincide with the area of the superior concha, but is rather smaller. It should be added that the olfactory nerves can be traced to a somewhat larger area of the mucous membrane, to the middle concha; it is, therefore, possible that the area indicated is too small. The mucous membrane in the olfactory area has special characters, both naked eye and microscopic, which distinguish it from the rest of the nasal mucous Fig. 792. — Diagram op the Distribution op the Nerves in the Nasal Cavity. (Poirier and Charpy.) The olfactory area is represented by dots. A, septum. B, lateral wall. Posterior su- , , , t . A Afiterior perior nasal Posterior superior nasal / [ r \ • \ ethmoid - , ^ — "^'W membrane. It is usually of a yellowish colour, and is soft and pulpy in consistence It is covered by a columnar ciliated epithelium and contains numerous glands (glands of Bowman) . The olfactory apparatus within it consists of the olfactory cells. These cells are elongated spindle-shaped structures, lying between the deeper parts of the investing columnar cells. From each a slender process passes to the surface of the mucosa, and terminates in a group of short hair-like processes, the olfactory hairs (v. Bumm), while from the deep portion of the cell a long slender process passes deeply into the mucosa. These processes resemble nerve filaments, with no medullary sheath, and they pass in the olfactory nerves to the olfactory bulb, in which they terminate in arborisation around the dendritic enlargements of the mitral cells of the olfactory bulb (see fig. 795; also Olfactory Nerve, p. 929). Fig. 793. — Section Showing the Development op the Olpactort Pit. The connections of the olfactory bundle and tract with the brain are fully dealt with in the section on the Nervous System. The development of the olfactory organ is connected with the development of the nose, which represents at first only the olfactory portion. About the third week, a localised thicken- ing of the surface epithelium occurs on the antero-ventral aspect of the head in the region of the fore-brain, forming on each side an olfactory plate. These plates become depressed from the sur- face by the growth of the margins, giving rise to the olfactory pits. The further changes are THE EYE 1051 associated with the formation of the face and nose (see Morphogenesis). The cells of the sur- face epithelium on the olfactory pits in part form olfactory cells, and send processes inward which pass to the olfactory lobe of the brain, and form the olfactory nerve. The organ of Jacobson is a small rudimentary structure in man. It is represented by a minute canal, 2 to 9 mm. long, placed on each side in the lower portion of the nasal septum, opening on the surface slightly above the orifice of the naso-palatine canal. Below it lies a small piece of cartilage, lying below the cartilage of the septum, and known as Jacobson's carti- lage. The canal is lined by epithelium, but contains no olfactory cells. It is developed from a small portion of the olfactory plate which becomes separated from the area which gives rise to epithelium of the olf actor j' region. II. ORGAN OF TASTE The taste organs [organon gustus] consist of minute epithelial structures, the taste buds [calyculi gustatorii], situated mainly in the epithelial covering of the tongue and also in the epiglottis. In the tongue, the taste buds are found mainly on the walls of the vallate papillse (see p. 1106), but they are found to a slight extent scattered over the whole area of distribution of the glosso-pharyngeal nerve, on the surface of the foliate and fungiform papillse, and on the plicse fimbriatse on the lower surface of the tongue. Tigs. 794 and 795. — Diagrams Illustrating the Structure of the Taste Buds AND the Olfactory Mucosa. In the foetus, the distribution is even wider, and they have been described as occurring on the soft palate, palatine arches, uvula, and in the mucous membrane covering the medial surfaces of the arytenoid cartilages. It is possible that such structures, though found in these regions in the foetus, usually disappear in the adult. Each taste bud is a hollow conical or oval structure, measuring .07-.08 mm. in length. At one end it opens by a small channel, termed the pore canal, which passes to the surface between adjacent epithelial cells. The surface opening is termed the outer -pore and the opening at the taste bud the inner taste pore. The taste bud consists of epitheUal supporting, of gustatory and of basal cells, arranged as seen in figure 794. The gustatory cells are long slender fusiform cells. The free end of each passes to the inner taste pore, and terminates in stiff hair-like processes, which project toward the pore canal. The deep end of each is connected with a basal cell. Terminal branches of the glosso-pharyngeal nerve ramify around the gustatory cells, and convey to the brain the impulses generated by contact of the ends of these cells with sapid particles. The epithelial supporting cells line the taste buds, and also project into the interior between the olfactory cells. Development. — The taste buds appear comparatively late in embryonic life — about the third month. They arise mainly from the entodermal portion of the tongue, b}' differentiation of the deeper cells of the epithelial covering over localised areas. Around these cells terminations of the glosso-pharyngeal nerve are found. These cells assume the characteristic shape and arrangement of the adult to form a taste bud. At first the opening of the bud lies upon the surface, but as the surrounding epithelial cells increase in size and thickness, the pore-canal is formed as a space between adjacent epithelial cells on the summit of the bud. III. THE EYE The sensory portion of the eye is the retina, a cup-shaped membrane, which lines the posterior half of the eyeball. It is formed of layers of nerve cells, from 1052 SPECIAL SENSE ORGANS which processes pass to the brain in the optic nerve. The eyeball is a hollow spher- ical structure, whose wall is formed externally by a fibrous tunic including the sclera (the white of the eye), and the cornea (the transparent area in the anterior aspect of the eyeball). Internal to the tunic formed by these membranes is a pigmented vascular membrane, the chorioidal membrane, of which the anterior part forms the iris, or the coloured part of the eye. Within these tunics is formed a cavity, in which lies the crystalline lens of the eye. In front and behind the lens are two chambers; that in front of the lens contains the aqueous humour and that behind it the vitreous. The study of the eye is best undertaken by examining the eye in the living, and subsequently by the dissection of specimens, and that order is followed in this account. General Surface View The two eyes are situated nearly in the line where the upper and middle thirds of the face meet; they lie right and left of the root of the nose, the most prominent part of the front of each globe being about 3 cm. (1 J in.) from the mid-line of the face. Each eye is overshadowed by the corresponding eyebrow, and is capable of being concealed by its eyehds, upper and lower. The orbital margin may be traced all round with the finger. At the junction of the medial and intermediate thirds of the upper margin the supraorbital notch (incisura supraorbitalis) can usually be felt, and the supraorbital nerve passing through it can sometimes be made to roll from side to side under the finger. The medial margin is the most difficult to trace in this way, partly because it is more rounded ofi' than the others, partly because it is bridged over by a firm band (medial palpebral ligament), passing medially from the medial angle of the eyelids; below this band, however, a sharp bony crest is felt, which lies anterior to the lacrimal sac. Note how the eye is protectedby the rim of the orbit, above and below; if we lay a hard flat Fig. 796. — View of the Eye with Eyelids Open. Palpebra superior (pars tarsalis) Cilia I Sulcus orbitopalpebralis superior Sclera r ' I Angulus oculi medialis ' Medial palpebral commissure Ins I ^ Pupil Caruncula lacrimalis Palpebra inferior body over the orbital opening, it will rest upon the upper and lower bony prominences, and will not touch the surface of the globe. Medially, the eye is protected from injury mainly by the bridge of the nose; laterally it is most readily vulnerable, as here the orbital rim is comparatively low. With one finger placed over the closed upper lid, press the eyeball gently backward into the orbit, and observe the elastic resistance met with, due to the fact that the globe rests pos- teriorly on a pad of fat. The space between the free edges of the upper and lower lids is known as the palpebral aperture [rima palpebrarum]: it is a mere slit when the lids are closed; but when they are open its shape is, roughly, that of an almond lying with its long axis horizontal, and about thirty millimetres in length. When the eyes are directed to an object straight in front of them, this aperture is about twelve millimetres wide, but its width varies with upward and downward movements of the eyeball, being greatest on looking strongly upward, diminishing gradually as the eye looks progi'essively lower. The angles formed by the meeting of the lids at each end of the palpebral aperture are named respectively the lateral and medial angles (or canthi) [angulus oculi later- alis, medialis], of which the lateral is sharp, while the medial is rounded off. On a closer in- spection, it will be found that, for the last five millimetres or so before reaching the medial angle the edges of the lids run an almost parallel course, and are here devoid of lashes. Through the open palpebral aperture the front of the eyeball comes into view, extending quHe to the lateral, but not reaching as far as the medial, angle; just within the latter we find a small reddish promi- nence, the lacrimal caruncle [caruncula lacrimalis] ; and between this and the eyeball a fold of SURFACE VIEW OF THE EYE 1053 conjunctiva known as the plica semilunaris. While the eye is open, press one finger on the skin, a little beyond the lateral angle, and draw it firmly away from the middle line; observe that the upper lid then falls over the eyeball, and that the outline of a firm band already referred to (the medial palpebral ligament) becomes evident, passing between the medial angle and the nose. The falling of the lid is caused by our dragging upon a ligament (the lateral palpebral raph6) to which the lateral end of its tarsus is attached, and so putting the lid itself upon the stretch. If, while the eyeball is directed downward, we place one finger on the lateral end of the upper eyelid and draw it forcibly upward and laterally, we can usually cause the lower division of the lacrimal gland to present just above the lateral angle. Fig. 797. — View op the Eye with Eyelids Closed. Sulcus orbitopalpebralis superior Angulus oculi medialis Cilia Palpebra Medial palpebral commissure inferior The upper eyelid [palpebra superior] is much broader than the lower, extending upward as far as the eyebrow. The skin covering it is loosely attached to the subjacent tissues above, but more firmly below, nearer the free margin, where it overlies a firm fibrous tissue called the tarsus superior. When the eye is open, a fold is present at the upper border of this lower more tightly applied portion of skin, called the superior palpebral fold, and by it the lid is marked off into an upper or orbital, and a lower or tarsal, division. The presence of the tarsus can be readily appreciated on our pinching horizontally the entire thicloiess of the eyelid below the palpebral fold. The lower eyelid [palpebra inferior] is similarly divided anatomically into a tarsal and an orbital part, but the demarcation is sometimes unrecognisable on the surface, Fig. 798. — View of Medial Region op the Eye, with the Eyelids Widely Separated AND THE Eyeball Turned Laterally. Edge of palpebra superior Tarsal (Meibomian) glands though a fold or groove (the inferior palpebral) is usually visible when the eye is widely opened. There is no precise limit of this lid below, but it maybe regarded ase.xtending to the level of the lower margin of the orbit. Numerous very fine short hairs are seen on the anterior surface of both eyelids. Each eyelid presents an anterior and a posterior surface, separated by a free margin with two edges: — (a) An anterior, rounded edge [limbus palpebralis anterior] along which the stiff cilia, or eyelashes, are closely placed in a triple row; and (b) a sharp posterior edge [limbus palpetjralis posterior] which is applied to the surface of the globe (see fig. 813). The cilia of both eyeUds have their points turned away from the palpebral aperture, so that the upper ones curve upward, and the lower downward; the oiha of the upper lid are the stronger, 1054 SPECIAL SENSE ORGANS and those in the middle of each row are longer than those at each end. Between the two edges just described, the Ud-margin has a smooth surface, on which is a single row of minute apertures, the openings of large modified sebaceous glands, the tarsal or Meibomian glands. It is by these glistening, weU-lubricated surfaces that the opposite lids come into apposition when they are closed. The secretion of these glands is known as the sebum palpebrale. The sharp posterior edge of the lid-margin marks the situation of the transition of skin into mucous membrane. Near the medial end of the margin of the lids we find a prominence, the lacrimal papilla, on the summit of which is a small hole [punctum lacrimale], the opening of the lacrimal duct (ductus lacrimaUs) for the passage of tears into the lacrimal sac. The lower punctum is rather larger than the upper, and is placed further from the medial angle of the eye. If we now examine the posterior surface of the eyelids — e. g., of the lower — we observe that it is lined by a soft mucous membrane, the palpebral conjunctiva [tunica conjunctiva palpebrarum]. Over the tarsal part of the lid the conjunctiva is closely adherent, but beyond this it is freely movable along with the loose submucous tissue here present. On tracing it backward, we find that it covers the whole posterior surface of the hds, and is then continued forward over the front of the eyeball, forming the conjunctival tunic of the globe [tunica con- junctiva bulbi]. The bend it makes as it changes its direction here is called the conjunctival fornix [fornix oonjuuotivEe superior or inferior]. Numerous underlying blood-vessels are visible through the palpebral conjunctiva, and under cover of its tarsal part we can see a series of nearly straight, parallel, light yellow lines, arranged perpendicularly to the free margin of the hd — the tarsal glands. The conjunctiva over the medial and lateral fourths of each lid is not quite so smooth as elsewhere, and is normally of a deeper red colour; we shall find later that there are glands well developed in these positions. When the eyelids are opened naturally, we see through the palpebral aperture the following: the greater part of the transparent cornea, and behind it the coloured iris with the pupil in its centre; white sclera to the medial and lateral sides of the cornea; the semilunar fold and lacrimal caruncle at the medial angle. The extent of the eyeball visible in this way varies according to its position. Thus, with the eyes looking straight forward, the lower margin of the upper Ud is nearly opposite to the top of the cornea, or, more strictly, to a line midway between the top of the cornea and the upper border of the pupil, while the lower lid corresponds with the lower margin of the cornea. When the eyes are directed strongly upward, the upper lid is relatively on a slightly higher level, as it is simultaneously raised, but the lower lid now leaves a strip of sclera exposed below the cornea. On looking downward the upper lid covers the upper part of the cornea as low down as the level of the top of the pupil, while the lower hd is about mid- way between the pupil and the lower margin of the cornea. If we draw the eyelids forcibly apart, we expose the whole cornea, and a zone of sclera about eight and a half milhmetres in breadth above and below, and ten milHmetres in breadth to the lateral and medial sides — altogether about one-third of the globe; all the eyeball thus exposed is covered by the ocular conjunctiva [tunica conjunctiva bulbi]. Over the sclera the conjunctiva is freely movable, and through it we see superficial blood-vessels that can be made to slip from side to side along with it (episcleral vessels). Occasionally other deeper vessels may also be seen which do not move with the conjunctiva, but are attached to the sclera (an- terior ciliary arteries and veins). Near the corneal border the conjunctiva ceases to be fieely movable, and it is closely adherent to the whole anterior surface of the cornea, giving the latter its characteristic bright, reflecting appearance; no blood-vessels are visible through it here in health. When the lids are shut, the space enclosed between their posterior surfaces and the front of the eyeball is thus everywhere lined by conjunctiva, and is known as the con- junctival sac. Not unfrequently the tendinous insertions of some or aU of the recti muscles into the sclera may be seen through the conjunctiva, each insertion appearing as a series of whitish parallel lines running toward, but terminating about seven mUhmetres from, the corresponding corneal border. The cornea appears as a transparent dome, having a curvature greater than that of the sclera; the junction of the two unequally curved surfaces is marked by a shallow depression running around the cornea, known as the scleral sulcus [sulcus sclerse]. In outline the cornea is nearly circular, but its horizontal diameter is slightly greater than its vertical. Between it and the iris a space exists, whose depth we can estimate roughly by looking at the eye from one side; this space, or anterior chamber [camera ocuh anterior] is occupied by a clear fluid, the aqueous humour. Almost the whole anterior surface of the iris is visible, its extreme periphery only being concealed by sclera. In colour the iris varies greatly in diiferent individuals. Near its centre (really a little up and in) a round hole exists in the iris, the black pupil [pupUla], whose size varies considerably in different eyes, and in the same eye according to temporary conditions, such as exposure to light, etc. On the surface of the iris we see a number of ridges [plicae iridis] running more or less radially ; adjoining ones occasionaUy unite and interlace to some extent, so as to leave large depressed meshes at intervals. These are the crypts of the iris. The radial ridges coming from the edge of the pupil, and those coming from the more peripheral part of the iris, meet in a zigzag ele- vated ridge concentric with the pupil, called the corona iridis, and by this ridge the iris is roughly marked off into two unequal zones — an outer, the greater [annulus U'idis major] and an inner, the lesser [annulus iridis minor]. The border next the pupil [margo pupillaris] is edged with small, roundish, bead-like prominences of a dark brown colour, separated from one another by depressions, so that it presents a finely notched contour. Not infrequently, in a light-coloured iris, we may see the sphincter muscle through the anterior layers, in the form of a ring about one millimetre in breadth around the pupil. The annulus iridis major may be described as consisting of three parts: — (a) A comparatively smooth zone next the zigzag ridge; (6) a middle area, showing concentric but incompletely circular furrows; (c) a small per- ipheral darker part, presenting a sieve-like appearance. On the floor of the large depressed THE EYEBALL 1055 meshes, or crypts, parallel radial vessels can be traced, belonging to the iris-stroma. The zig- zag line mentioned above corresponds to the position of the circulus arteriosus minor. Occa- sionally, especially in a hght iris, superficial pigment spots of a rusty brown colour occur. (In examining the living eye, the ophthalmoscope may now be used, so as to gain a view of the fundus, and to study the termination of the optic nerve, the distribution of the larger retinal vessels, etc.) The general red reflex obtained from the fundus is due to the blood in a capillary network (chorio-capillaris) situated in the inner part of the chorioid. To the nasal side of the centre of the fundus is a paler area of a disc shape corresponding to the intraocular end of the optic nerve, and known as the papilla of the optic nerve [papilla n. optici]. This papilla (or 'optic disc') is nearly circular, but usually slightly oval vertically; it is of a light orange-pink colour, with a characteristic superficial translucency; its lateral third segment is paler than the rest as nerve- fibres and capillaries here are fewer in number. About its centre we often observe a weU- marked whitish depression [excavatio papillae n. optici], formed by the dispersion of the nerve- fibres as they spread out over the fundus; at the bottom of this depression a sieve-like appearance may be seen, due to the presence of the lamina cribrosa sclerae, which consists of a white fibrous tissue framework, with small, roundish, light-grey meshes in it, through which the nerve-fibre bundles pass. Also near the centre of the papiUa, the retinal blood-vessels first come into view, the arteries narrower in size and lighter in colour than the veins; they divide dichotomously as they are distributed over the fundus. The retina proper is so transparent as to be ophthal- moscopically invisible, but its pigment-epithelium gives a very finely granular or darkly stippled appearance to the general red reflex. In the centre of the fundus, and therefore to the lateral side of the papilla, the ophthalmoscope often shows a shifting halo of light playing round a Fig. 799. — The Normal Fundus op the Eyeball. (Parsons.) horizontally oval, comparatively dark enclosed area; this latter corresponds to the yellow spot [macula lutea] region, and about its centre a small pale spot usuafly marks the position of the fovea centralis. Two structures visible at the nasal end of the palpebral aperture have been previously mentioned, and should now be examined more narrowly. The lacrimal caruncle is an island of modified skin, and fine hairs can commonly be detected on its surface, and it contains sebaceous and sweat glands. Lateral to it and separated from it by a narrow groove, is the semilunar fold of conjunctiva; it rests on the eyeball, and is a rudiment of the third eyelid or nictitating membrane, present in birds and well represented in many other vertebrates. Examination of the Eyeball (In the following account, the structure of the eyeball is described as it would appear upon dissection.) The eyeball [bulbus oculi] is almost spherical, but not perfectly so, mainly be- cause its anterior, clear, or corneal segment has a greater curvature than the rest of the eye. Considering it as a globe, it has an anterior pole [polus anterior] and a posterior pole [polus posterior]; the former corresponding to the centre of the front of the cornea, the latter to the center of the posterior curvature. An imag- inary straight line joining the two poles is called the axis of the eyeball. The equator of the eye is that part of its surface which lies midway between the two poles. The various meridians are circles which intersect the poles. The sagittal axis of the globe is the greatest (about 24 . 5 mm.), the vertical equatorial the least 1056 SPECIAL SENSE ORGANS (about 23.5 mm.), and the transverse equatorial axis is intermediate in length (about 23 . 9), so that the eyeball is in reality an ellipsoid, flattened slightly from above downward. These figures refer to the adult male; in the female the eyeball is . 5 mm. smaller in aU axes. Again, if the globe is divided in its mid-sagittal plane, the nasal division will be found to be slightly smaller than the temporal. The optic nerve joins the globe three or four millimetres to the nasal side of the posterior pole. The shape of the eye depends on, and is preserved by, the outermost tunic, formed conjointly by the cornea and sclera, the entire outer surfaces of which are now in view. The anterior or corneal part has already been examined. All around the cornea there remains a little adherent conjunctiva; elsewhere, the sclerals directly exposed, except for some loose connective tissue which adheres to it, especially around the optic nerve entrance. In front of the equator we see the tendinous insertions of the four recti muscles. Behind the equator are the inser- tions of the two oblique muscles — that of the superior oblique tendinous, and further forward; that of the inferior more fleshy, and placed between the optic nerve and the lateral rectus. Fig. 800. — Diagrammatic View of the Insertions of the Ocular Muscles. Superior rectus Lareral rectus Inferior rectus It is difficult to recognise the different recti muscles by their insertions if we do not know whether the eye examined is a right or a left one. To determine this we should hold the globe with the optic nerve toward us, and in the natural position with the superior oblique tendon uppermost. The inferior oblique tendon will now point to the side to which the eye belongs, and we can consequently determine the difTerent recti muscles. The medial [m. rectus medialis] rectus is inserted nearest (5.5 to 7 mm. from) the corneal border; the superior [m. rectus superior] rectus commonly, sometimes the lateral [m. rectus laterahs], is inserted furthest from it (7.7 to 8 mm.). All the recti tendons are broad and thin, but that of the medial is the broadest (8 to 10.3 mm.); those of the lateral and inferior the narrowest (6 to 9.2, or 9.8 mm., respectively). The greatest interval between two neighbouring tendons is that between the superior and medial recti (about 12 mm.); the least is between the superior and lateral (7 mm.). The form of the lines of insertion of the different tendons varies considerably, the inferior being almost straight, the superior and lateral convex forward, the medial further removed from the corneal border below than above. The insertions of the oblique muscles [mm. obliqui] are at more than double the average distance of the insertions of the recti from the corneal border. That of the superior oblique is found on the superior surface of the sclera, about sixteen millimetres from the corneal edge, in the form of a line 10.7 mm. long sloping from before backward and medially. The inferior oblique has a long fleshy insertion lying between the lateral rectus and the optic nerve entrance; the posterior end of the insertion, which is also the higher, is only about five to six millipietres from the optic nerve, and from this point it slopes forward, laterally, and slightly downward. Several small nerves and two arteries may be seen running forward and ulti- mately perforating the sclera not far from the entrance of the optic nerve. The two arteries are the long posterior ciliary [aa. ciliares posteriores longi] ; they both perforate the globe in the horizontal meridian, 3.5 mm. from the optic nerve, one on the lateral, the other on the medial, side. The short ciliary arteries [aa. ciliares THE EYEBALL 1057 posteriores breves] are too small to be seen in an ordinary examination. The nerves are the long and short ciUary [nn. ciliareslongi, breves]. Nearer the equator large venous trunks emerge; they can be traced for some distance in front of their exit as dark lines, running antero-posteriorly internal to the sclera. The optic nerve is seen in section, surrounded loosely by a thick outer sheath; in the centre of the nerve-section a small red spot indicates the position of the central retinal blood-vessels [a. et v. centralis retinae]. (The following structures appear in an eyeball divided into fore and hind halves by cutting through it in the equatorial plane.) 1. Posterior hemisphere seen from in front. — This is much the same view that the ophthal- moscope affords us. Unless the eye be very fresh, however, the retina will have lost its trans- parency, and will now present the appearance of a thin whitish membrane, detached in folds from the external coats, but still adherent at the optic papilla. The vitreous jelly lying within the retinal cup may be torn away. In the human eye the retina next the posterior pole is stained yellow [macula lutea]. On turning the retina over, a little pigment may be seen adhering to its outer surface here and there. Cut through the retina close to the optic disc all around and remove it: note how easily it is torn. We now see a dark brown surface, consisting of the retinal pigment layer [stratum pigmenti retinas] adherent to the inner surface of the chorioid. Brush off the retinal pigment under water. The chorioid thus exposed can for the most part be fairly easily torn away from the thick sclera, as a lymph-space exists between them, but the attachment is firm around the optic nerve entrance, and also where the arteries and nerves join the chorioid after penetrating the sclera. The chorioid is darkly pigmented, of a brown colour, with markings on its surfaces corresponding to the distribution of its large veins. The inner Fig. 801. — Anteeiob Hemisphere of Eyeball, Viewed from Behind. Pupil Ciliary processes surface of the sclera is of a light brownish colour, mainly from the presence of a delicate pig- mented layer, the lamina suprachorioidea, which adheres partly to it, partly to the chorioid, giving to their adjacent surfaces a flocculent appearance when examined under water. 2. Anterior hemisphere viewed from behind. — The round opening of the pupil is visible in the middle, in front of the large clear crystalline lens. The retina proper extends forward a little way from the line of section, and then ends abruptly in a wavy line called the era serrata, beyond which it is only represented by a very thin membrane [pars ciliaris retinae]. Outside the periphery of the lens are a number of ciliary processes arranged closely together in a circle concentric with the pupil, and each radially elongated; posteriorly they are continuous with n umerous fine folds, also radial, which soon get very indistinct as they pass backward, but reach almost to the ora serrata [plicae ciliares]. Between the front of the ciliary processes and the edge of the pupU lies the iris. On removal of the retina the inner surface of all this region is seen to be darkly pigmented, but especially dark in front of the position of the ora serrata. Vitreous probably still adheres to the back of the lens, and by pulhng upon it the lens can be removed along with its capsule and suspensory ligament; some pigment will now be found adhering to the front of the vitreous, torn from the ciliary processes, which are consequently now lighter in colour than before. The lens-capsule is transparent, and has a smooth glistening outer surface; through it a greyish, star-shaped figure may be observed on the anterior and posterior surfaces of the lens. The suspensory ligament is a transparent membrane attached to the capsule of the lens about its equator, and is best seen by floating the lens in water in a glass vessel placed on a dark ground. On opening the capsule we expose the lens itself, which is superficially soft and glutinous to the touch, but becomes firmer as we rub off its outer laj-ers and approach its centre. Carefully tear the chorioid and iris from the sclerotic as far as possible; a firm adhesion exists just behind the corneal periphery. The outer surface of the chorioid thus exposed is found to be also rather darkly pigmented, taut it shows a white ring corresponding to the adhesion just mentioned, and a pale area behind this ring indicates the position of the ciliary muscle [m. ciharis]. On this surface numerous white nerve-cords are visible running 1058 SPECIAL SENSE ORGANS forward. Observe that the iris, the ciliary processes, etc., and the chorioid are all different parts of the same ocular tunic — mere local modifications of it. Similarly the sclera and cornea are seen to blend together to form one outer coat. An eyeball should now be placed for half an hour in a freezing mixture of crushed ice and salt. It will thus become quite hard, and should at once be divided into two parts by cutting it antero-posteriorly through the centre of the cornea and the optic nerve. We thus gain another view of the relations of parts, the position of the lens between the aqueous and vitreous chambers, etc. On removing the lens, vitreous, and retina, and brushing off its pigment, the light markings corresponding to the chorioidal veins (venae vorticosse) should be noted, and their distribution studied. Usually four vortices or fountain-like markings are found in the whole chorioid, Fig. 802. — Horizontal Section of the Eyeball. X 4. Anterior surface of lens Optic axil Corneal epithelium Posterior surface of cornea '^^ Cornea Crystalline lens Zonula ciliaris Posterior surface of lens Sulcus sclerse / Lig. pectinatum iridis I Posterior chamber / /Sinus venosus scle___ / yScleral conjunctiva ^Anterior chambe ^^^^_- Angulus indis Ciliary body Ciliary processes - Zonular fibres Papilla of optic nerve Lamina cribrosa scleras A. Centralis retinse Retina dea Macula latea and fovea centralis Sclera their points of junction situated at approximately equal distances from one another at about the hne where the posterior and middle thii-ds of the globe meet. These sections should be kept for reference while following the further description of the ocular tunics. The coats of the eyeball. — 1. The outer, fibrous coat of the eye [tunica fibrosa oculi] is formed by the sclera and cornea, which pass into one another at the scleral sulcus. It consists throughout mainly of fine connective-tissue fibres, arranged in interlacing bundles, with small lymph-spaces at intervals between them. The naked-eye appearance of the two divisions of this fibrous coat is, however, quite different, the cornea being transparent, while the sclera is white and opaque. The sclera encloses the posterior five-sixths or so of the eyeball. It is perfo- THE CORNEA 1059 rated bj'' the entrance of the optic nerve, and the opening in the sclera, only partially bridged across by fibres from the inner layers, forms the lamina cribrosa. The fibre-bundles composing the solera are arranged more irregularly than in the cornea, and run mainly in two directions, viz., antero-posteriorly and circularly; the circular fibres are particularly well developed just behind the sulcus. It is thickest (about 1 mm.) posteriorly, where it is strengthened chiefly by the outer sheath of the optic nerve, and partly also by the tissue surrounding the ciliary vessels and nerves. It becomes gradually thinner as it passes forward, up to the line of insertion of the I'ecti muscles, where it is .3 mm. thick. In front of that line it is again reinforced by their tendinous fibres becoming incorporated with it and its thickness increases to .6 mm. In children the sclera is often so thin as to allow the underlying chorioidal pigment to show through, its colour then appearing bluish white. In the aged, again, it is sometimes yellowish. It always contains a few pigment cells, but these are in the deep layer termed the lamina fusca, and only become visible externally where the sclera is pierced by vessels and nerves going to the chorioid. It is almost non-vascidar, but quite at its anterior end a large venous sinus [sinus venosus sclerse; canalis Schlemmi (Lauthi)], (canal of Schlemm) runs in its deeper layers circularly around the cornea. Just in front of this sinus, at the corneal limbus, the sclera merges into the cornea, its inner layers changing first, and finally the outer ones. Fig. 803.— Portion op Fig. 802, Enlarged. Anterior surface of lens Crystalline lens Iris / Sulcus sclerEQ t Lig, pectinatum iridis I ^Posterior chamber ; venosus sclerae / Scleral conjunctiva Anterior chamber Angulus iridis ;.'*Circulus arteriosus majo Ciliary muscle Ciliary muscle, circular fibres Ciliary processes . Zonular fibres Ora serrata Insertion of tendon of rectus lateralis The cornea forms the anterior sixth of the eyeball. It is thickest ,'at its periphery (1.1 mm.) and becomes gradually thinner toward its centre (0.8 mm.); the curvature of its posterior is consequently greater than that of its anterior surface, but even the latter is more curved than the surface of the sclera. In the cornea proper, fibre-bundles are arranged so as to form a series of superposed lameUse, each of which is connected here and there to the adjacent ones by fibres passing from one to the other, so that they can only be torn apart with difficulty. The corneal lymph-spaces communi- cate with one another by very fine canals, and thus not only is a thorough lymph-circulation provided for, but the protoplasm with which these spaces are partially occupied may be also regarded as continuous throughout. It contains no blood-vessels, with the exception of a rich plexus at its extreme periphery, on which its nutrition is ultimately dependent. The sinus venosus o} Schlemm is an important channel for the return of blood and also of fluid which transudes into it from the anterior chamber. It consists of a network of venous spaces, formed of a principal vessel accompanied by several smaller ones, which unite with it and with one another in a plexiform manner. -They commence indirectly with the spaces of the angle of the iris and they are in direct communication with the anterior ciliary veins. 1060 SPECIAL SENSE ORGANS The outer surface of the cornea is covered by an extension of the ocular conjunctiva, in the form of an epitheUum several layers deep. The most external part of the true cornea appears homogeneous, even when highly magnified and constitutes the anterior elastic lamina, Bow- man's membrane, though there is reason to believe that its structure only differs from that already described in the closeness of its fibrous texture; the two parts are certainly connected by fine fibres. Posteriorly, the cornea is lined by a fu-m, thin, glass-hke layer (posterior elastic lamina, membrane of Descemet), distinct from the corneal tissue both anatomically and chem- ically. At the periphery this membrane breaks up into a number of fibres, which mainly arch over to join the base of the iris and form part of the ligamentum pectinatum iridis. The pectin- ate ligament is an open network of interlacing fibres, directly continuous with the circular and longitudinal bundles of sclera surrounding the venous sinus of Schlemm (Henderson). The interstices between these fibres constitute spaces (spaces of Fontana) [spatia anguli iridis (Fontanse)] freely communicating with the aqueous chamber on the one hand, and indirectly with the venous sinus of the sclera on the other. The posterior elastic lamina is in turn lined by a single layer of flat cells, which are continuous peripherally with cells lining the spaces of the angle and the anterior surface of the iris which form the endothelium of the anterior chamber. The cornea is richly supplied with nerves, particularly in its most superficial layers. 2. The dark, middle, or vascular coat of the eye [tunica vasculosa oculi] i? formed by the iris, ciliary body, and chorioid. It is closely applied to the sclera, but actually joins it only at the anterior and posterior limits of their course to- gether, viz., at the scleral sulcus, and around the optic nerve entrance. It is separated from the sclera between these two points by a narrow slit-like lymp- space [spatium perichorioideale]. In front of the sulcus, the middle coat is sepa- rated from the outer (i. e., the iris from the cornea) by a considerable space filled with fluid, caUed the anterior aqueous chamber. The vascular coat has two open- ings in it; a larger one in front, the pupil, and a smaller one behind, for the passage of the optic nerve. Its structure is that of a pigmented connective tissue, support- ing numerous blood-vessels and containing many nerves and three deposits of smooth muscle-fibres. The chorioid [chorioidea] forms the posterior part of the vascular coat, and extends, with slowly diminishing thickness, forward as far as the ora serrata. Its outer and inner surfaces are botli formed by non-vascular layers; that covering the outer, the lamina suprachorioidea, is pigmented, arranged in several fine loose lamelte; that covering the inner surface is a thin, transparent, homogeneous membrane, called the basal lamina of the chorioid. The inter- vening chorioidal stroma is very rich in blood-vessels, which are of largest size next its outer surface constituting the lamina vasculosa. These become progressively smaller toward the basal lamina, next to which is a layer of closely placed wide capillaries, called the lamina chorio- capillaris. The pigment becomes less in amount as we pass inward, and finally ceases, being absent entirely from the choriocapillary and basal laminae. In front of the ora serrata the vascular coat becomes considerably modified' and the part reaching from the ora serrata of the retina to the iris is termed the ciliary region of the tract, or ciliary body [corpus ciliare]. Its superficial aspects have been already briefly described. In front, the cihary processes, about seventy in number, project toward the interior of the eye, forming the corona ciliaris. Be- hind this part lies the orbiculus ciliaris, whose inner surface is almost smooth, faint radial folds [plic£e ciliares] only being present, three or four of which join each ciliary process. The more minute structure of this ciliary region resembles closely that of the chorioid, except that the chorio-capillaris is no longer present, that the stroma is thicker and richer in blood- vessels, and that a muscular element (ciliary muscle) exists between the vascular layer and the lamina suprachorioidea. On antero-posterior section the ciliary body is triangular; the shortest side looks forward, and from about its middle the iris arises; the two long sides look respectively inward and outward, the inner having the ciliary processes upon it, while the outer is formed by the ciliary muscle. This muscle possesses smooth fibres and consists of an outer [fibrfe me- ridionales (Brueckei)] and an inner division [fibra; circulares (Muelleri)]. The meridional fibres take origin from the outer fibrous coat of the eye at the sclero-corneal junction in front, and pass- ing backward to join the outer layers of the orbiculus ciliaris and chorioid; the circular fibres are situated next to the ciliary processes. The entire muscle is destitute of pigment, and there- fore is recognisable in the section by its light colour. The whole thickening of the vascular tunic in this region, muscle and folds and processes together, is named the ciliary body. It includes the corona ciliaris, formed of the ciliary processes and folds, and the orbicularis ciliaris containing the ciliary muscle. The iris projects into the interior of the front half of the eye in the form of a circular disc perforated in the middle. The appearance of its anterior surface has already been described. The anterior surface is covered with a layer of endothe- lium except at the crypts near the cihary border. Thus the lymph spaces between the stroma cells communicate directly with the anterior chamber. Its posterior THE RETINA 1061 surface exhibits numerous radial folds running from the ciliary processes to near the pupillary margin; a thick layer of black pigment covers it and curls around this edge, so as to come into view all around the pupil as seen from in front. The ciliary border of the iris is continuous with the front of the ciliary body, and there it also receives fibres from the ligamentum pectinatum iridis; in other respects the iris is quite free, merely resting on the front of the lens-capsule near the pupil. Its stroma [stroma iridis] is spongy in character, being made up of vessels covered by a thick adventitia, running from the periphery to the pupillary border, with interspaces filled by branch- ing pigment cells, which are particularly abundant near the front surface. Deep in the stroma, running around near the pupillary border, we find a broad flat band of smooth muscle-fibres, constituting the m. sphincter pupillse. Immediately behind the vascular tissue hes a thin membrane, consisting of fine, straight fibres running radially from the ciliary border to the stroma behind the sphincter. The nature of these fibres was long in dispute, but they are now accepted as being undoubtedly smooth muscular — and comprise the m. dilatator pupillae. Fig. 804. — Diagrammatic Horizontal Section of Eyeball and Orbit. (After Fuchs, much modified.) Periorbita green; muscle-fascia red; Tenon's capsule yellow. Lower lacrimal punctum Cornea \ . Caruncle Opening of Meibo: Anterior chamber Iris Corona ciliaris Orbiculus cili Outer check ligament Fovea centralis retina Muscle-fascia Orbital blood-vessel. Central retinal vessels optic nerve External rectus muscle_ Inner palpebral ligament Nasal process of upper jaw Anterior limb of inner palpebral ligament Lacrimal sac Posterior limb of inner palpebral ligament with Horner's muscle springing from it Lacrimal bone Process of muscle-fas- cia to under surface of conjunctiva Ora serrata Tendon of insertion of internal rectus Inner check ligament Periorbita Orbital plate of ethmoid bone Posterior lamina of muscle-fascia lined by Tenon's capsule Internal rectus muscle The m. sphincter pupiUos and the ciliary muscle are supplied indirectly by the oculomotor nerve through the ciliary ganglion. The dilatator pupillae is supplied by sympathetic fibres , which have their origin from the cells of the superior cervical ganghon. Thence they ascend in the carotid and cavernous plexuses, and join the ophthalmic division of the trigeminal nerve, passing to the eyeball by way of the long ciliary nerves. The pre-ganglionic sympathetic fibres leave the spinal cord by the motor roots of the first two or three thoracic nerves, and ascend the sympa- thetic trunlv to the superior cervical ganglion without interruption. The posterior surface of the iris is lined by pigment already mentioned, consisting of two layers of pigmented cells, each layer representing the extension forward of one subdivision of the retina. The anterior surface of the iris is covered by a delicate epithehal layer, continuous with the ceils of the posterior elastic lamina of the cornea. The colour of the iris in different individuals depends upon the amount of stromal pigment. 3. The retina. — The inner surface of the vascular coat is everywhere lined by a layer of pigment of corresponding extent, which usually adheres to it closely on dissection. 1062 SPECIAL SENSE ORGANS Developmentally this general pigment lining is quite distinct from the vascular coat, and represents the outer wall of the secondary optic vesicle or embryonic retina; it consists of a single layer of pigmented epithelial cells. It is known as the slratum pigmenti. The amount of pigment is greatest anteriorly, over the ciliary region and iris, and there is again a small local increase posteriorly, corresponding to the macula lutea and to the edge of the optic nerve en- trance. In the ciliary region these cells have recently been described as Uning numerous nar- row tubular depressions in the inner part of the vascular tract, and they are said to have here a special function, viz., that of secreting the intraocular fluid. From the manner in which the secondary optic vesicle, or optic cup, is formed, its two walls are necessarily continuous in front, at what may be termed the lip of the cup; we have just observed that the outer wall lines the vascular coat every- where and corresponds in extent; consequently, the lip must be looked for at the edge of the pupil, i. e., at the termination of this coat anterorly. The inner wall of the cup, consequently, reaches from the lip, or pupillary edge, in front to the optic stalk or nerve behind, and is in close apposition to the pigment-epithelium; unlike the outer, however, this wall is represented in the developed eye by tissues very dissimilar in structure in different parts of its extent. Tracing it backward from the pupillary edge, we find that over the whole posterior surface of the iris it exists as a single layer of pigmented epithelium, the two layers of the cup having here produced a double layer of pigment cells. At the root of the iris the single inner layer of cells still exists; but now they become destitute of pigment, and this con- dition obtains over the entire ciliary region, constituting what is known as the pars ciliaris retinae. At the l^ne of the ora serrata the tissue derived from the inner wall abruptly increases in thickness, and rapidly acquires that complexity of structure characteristic of the retina proper, which extends from here to the optic nerve and is termed the pars optica retinas. It consists of several layers — nerve- fibres, nerve-cells, and nerve-epithelium — held together by a supporting frame- work of delicate connective tissue. The nerve-epithelium is on the outer surface, immediately applied to the pigment-epithe- lium; at the posterior pole of the eye a small spot [fovea centralis] exists, where this is the only retinal layer represented, and where consequently the retina is extremely thin. The nerve- fibres run on the inner surface of the retina and are continuous with those of the optic nerve; they constitute the only retinal layer that is continued into the intraocular end of the nerve. The nerve-cells are found between these surface layers. The larger blood-vessels of the retina run in the inner layers, and none encroach on the layer of nerve-epithelium. Fig. 805. — The Lens. (Side view; enlarged.) Within the coats mentioned, the interior of the eyeball is fully occupied by con- cents, which are divided into three parts, which are named according to their consistence and anatomical form. They are all transparent, as through them the light has to pass so as to gain the retina. Of these, the only one that is sharply and independently outlined is the lens, which is situated in the anterior half of the globe at the level of the ciliary processes, where it is suspended between the other con- tents, which fill respectively the space in front of it and the space behind it. The space in front of the lens called the aqueous chamber; that behind the lens is the vitreous chamber. The lens [lens crystallina] is a biconvex disc, with its surfaces directed ante- riorly and posteriorly; these surfaces meet at its rounded-off edge or equator [sequator lentis] which is near (but does not touch) the adjacent ciliary processes. The posterior is considerably more convex than the anterior surface; the central part of each surface is called its pole [polus anterior; polus posterior]. The lens is closely encased in a hyaline elastic capsule [capsula lentis] thicker over the an- terior than over the posterior surface. Thus enclosed, it is held in position in the globe by a suspensory ligament, attached to the lens capsule near the equator of the eye, and swung from the ciliary region. Posteriorly, the lens rests in a cup THE LENS 1063 formed by the front part of the vitreous, while its anterior capsule is in contact with the aqueous fluid and lies close against the back of the pupillary margin of the iris. When in position the lens measures nine millimetres across, and about four millimetres between its poles. On each surface a series of fine, sinuous, grey lines can be seen radiating from the pole to- ward the equator, called respectively the anterior and posterior stellate figures. The liiies observable on the posterior are always so placed as to be intermediate with those on the anterior surface, so that on viewing them through the lens they occupy a position corresponding to the Fig. 806. — Diagrammatic Representation op the Blood-vessels of the Eyeball. (Parsons, after Leber.) Arteries red; veins blue. s.p., Short posterior ciliary arteries, l.p.c, Long posterior ciliary artery, a.c, Anterior ciliary vessels. C of S., Canal of Schlemm. c.a.i.ma., Circulus arteriosus iridis rnajor. v.v,. Venae vorticosEe. a. conj., Anterior conjunctival vessels, p. conj., Posterior conjunctival vessels. intervals between the lines on the anterior surface. The lens-capsule is comparatively brittle, and can be readily cut through when scraped with a sharp-pointed instrument; on doing so the divided edges curl outward, away from the lenticular substance. When removed from its capsule, the outer portion of the lens is found to be soft and glutinous, but its substance gets progressively firmer as we approach the centre. This harder central part is known as the nucleus [nucleus lentis], and the surrounding softer matter as cortex [substantia corticahsj. The cortical part shows a tendency to peel off in successive layers. It consists of long fibres, the ends of which meet in front and behind at the anterior and posterior stellate figures. 1064 SPECIAL SENSE ORGANS Histologically the capsule is not in immediate contact with the cortex over the front surface of the lens, a single layer of cells intervening, called the epithelium lentis. The zonula ciliaris or suspensory ligament of the lens is formed by a number of fine zonular fibres [fibrse zonulares] passing from the ciliary body. They are attached to the lens-capsule a little in front of and behind the equator, and the spaces included between the fibres of the ligament are termed the zonular spaces [spatia zonularia]. A continuous space, which can.be injected after death, round the margin of the lens is known as the canal of Petit. It is probably an artefact. This space is bridged across by fine intermediate suspensory fibres, and is occupied by fluid. The vitreous body [corpus vitreum] is a transparent, colourless, jelly-like mass, the vitreous humour, enclosed in a delicate, clear, structureless membrane, called the hyaloid membrane. This latter is closely applied to the back of the posterior lens-capsule and of the suppensorj^ ligament, and to the inner surface of the pars ciliaris retinse, retina proper, and optic papilla. Although possessing some degree of firmness, the vitreous humour contains quite 98 per cent, of water, and has no definite structure. Fig. 807. — Blood-vessels of the Eyeball, Lateral View. Cornea Anterior chamber Sclero-corneal junction g Anterior ciliary artery Long posterior "* ciliary artery 4 J'7~ """■■• V. Vorticosa Optic nerve ---- Arteria centralis retinse Membranes have been described in it, but these are really artificial products. In certain situations spaces e.xist in the vitreous mass, the most determinate of which runs in the form of a canal from the optic papilla to the posterior pole of the lens, corresponding to the position of the foetal hyaloid artery (hyaloid canal or canalis hyaloidea). Other very fine spaces are de- scribed running circularly in the peripheral part of the vitreous concentric with its outer sur- face. Microscopically, wandering cells are found in the vitreous, which often here assume pecuhar forms which the observer can, not infrequently, study subjectively. The aqueous humour is a clear, watery fluid, occupying the space between the cornea on the one hand, and the ciliary body, zonula ciliaris, and lens on the other. The iris, projecting into this space, has both its surfaces liathed in the aqueous; but, as its inner part rests on the lens, it is regarded as mums (Zinni) ^ Lesser wing of sphenoid \ Sheath of optic nerve Rectus inferior Lateral rectus Inferior oblique tion. In upward and downward movements of the cornea the eye rotates on its horizontal equatorial axis. The other principal axis of rotation is the sagittal, which we have previously described as corresponding to the line joining the anterior and posterior poles of the globe (page 1055). In rotation of the eye on its sagittal axis, therefore, the cornea may be said to move as a wheel on its axle, for its centre now corresponds to one end of the axis; in other words, this is a rotation of the cornea. Such movements may, consequently, be expressed with refer- ence to their effect on an imaginary spoke of the corneal wheel — e. g., one- running vertically Fig. 814. — Dissection of the Mttsclbs of the Left Okbit, From Above. Lateral rectus Inferior oblique J Rectus medialis Rectus superior , Tendon of superior oblique ' ! ; Trochlea of superior oblique Levator palpebrae superioris Levator palpebrae superioris Periorbita upward from the corneal centre. Thus we may say 'rotation of the cornea laterally' when this part of the wheel moves toward the lateral angle, or 'medially' when toward the nose. The only two muscles that rotate the eyeball merely on one axis are the lateral rectus and the medial rectus ; the former abducting, and the latter adducting, the cornea. The action of the superior and inferior recti is complicated by the obliquity of the axes of muscles and globe previously mentioned. ORBITAL FASCIM 1071 The chief action of the superior rectus is to draw the cornea upward, but at the same time it adducts and rotates the cornea medially. The inferior rectus mainly draws the cornea downward, also adducting it and rotating it laterally. The chief action of the superior oblique is to rotate the cornea medially, also drawing it downward and slightly abducting it. The inferior oblique mainly rotates the cornea laterally, also drawing it upward and slightly abducting it. The fasciae of the orbit [fascise orbitales]. — The orbital contents are bound to- gether and supported by fibrous tissues, which are connected with each other, but which may conveniently be regarded as belonging to tliree systems. These are : — • (1) Those lining the bony walls; (2) those ensheathing the muscles; and (3) the tissue which partially encapsules the eyeball. 1. The orbital periosteum [periorbita], is closely applied to the bones forming the walls of the cavity, but may be stripped off with comparative ease. It pre- sents openings for the passage of vessels and nerves entering and leaving the orbit. Periorbita Fig. 815. — Diagram Representing the Orbital Fasciss in Vertical Section. black; muscular sheaths violet; Tenon's capsule green. Tbicularis oculi ' Periorbita and septum orbitale ' Anterior insertion of levator palpebrae Process from periorbita to slieatli of lacrimal gland Sheath of levator palpebrse Periorbita . levator palpebrse superioris . rectus superior Space filled by orbital fat Fascial sheath of optic ic nerve M. rectus inferior M. obliquus inferior Posteriorly this tissue is very firm, being joined by processes of the dura mater at the optic foramen and superior orbital fissure; at the optic foramen it is also connected with the dm'a sheath of the optic nerve. As it covers the inferior orbital (spheno-maxillary) fissure its fibres are interwoven with smooth muscle, forming the orbital muscle of MtiUer. From its inner sur- face processes run into the orbital cavity, separating the fat lobules. One important process comes from the periorbita about midway along the roof of the orbit, runs forward to the back of the upper division of the lacrimal gland, and there spUts, helping to form the gland-capsule: this capsule is joined at its medial border by other periorbital bands coming off near the upper orbital rim, and forming the suspensory ligament of the gland. On the side of the orbit the peri- orbita sends fibrous processes to the trochlea of the superior obUque, which keep it in position. On arriving at the lacrimal groove the periorbita divides into two layers, a thin posterior one continuing to line the bone forming the floor of the groove, whilst the thicker anterior layer bridges over the groove and the sac which lies in it, forming the limbs of the medial palpebral ligament (p. 1052). Quite anteriorly, at the rim of the orbit, the periorbita sends off a membranous process which aids in forming the fibrous tissue of the eyelids (orbito -tarsal ligament, or palpebral fascia), and is itself continuous with the periosteum of the bones outside the orbital margin. 2. The orbital muscles are connected by a common fascia, which splits at their borders and furnishes a sheath to each. Processes of this fascia give membranous investments for the vessels and nerves (including the optic nerve), splitting simi- 1072 SPECIAL SENSE ORGANS larly to enclose them; these membranous processes also assist in separating the fat lobules. Posteriorly, this fascia is thin and loose, and blends with the periorbita at the origin of the muscles. Anteriorly, it becomes thicker and firmer, accompanies the muscles to near the equa- tor of the eyeball, and there divides into two laminte, an anterior and a posterior; the former continues a forward course, forming a complete funnel-shaped investment all around, passing ultimately to the eyelids and orbital margin — whilst the latter turns backward, covering the hinder third of the globe. The anterior lamina is a well-marked membrane everywhere, but in certain situations it presents special bands of thickening, corresponding to the direct continuation forward of the sheath of each rectus muscle. Above and below, this lamina spreads out in the form of two large membranes, which are finally applied to the deep surface of the palpebral fascia; the lower membrane constitutes what has been described as the suspensory hgament of the eyeball.' The upper membrane requires a fuller description, as its distribution is modified by the presence of the levator palpebrae muscle. Fig. 816. — Hokizontal Section Through Left Orbit, viewed prom above. (After von Gerlach. To show check ligaments, etc.) Conjunctival fornix Lacrimal gland Palpebral raphe Lateral check ligament- Lateral orbital wall Lateral rectus Orbital fat Space occupied by subconjunctival tis- ^_^_^ sue, and by fascia YhH bulbi further back ' Upper part of Horner's muscle Palpebral fascia Medial check ligament Medial wall of orbit Medial rectus Ethmoidal cells The upper part of the sheath of the superior rectus (along with the adjoining membrane on each side of it) passes to the deep surface of the levator, to which it closely adheres, and com- pletely ensheaths this tendon by extending round its borders to its upper surface. The lower part of this levator sheath is applied to the inferior surface of the deeper of the two divisions of the levator muscle, superior tarsal muscle, and is attached to the upper border of the tarsus of the upper lid, reaching on each side to the lateral and medial angles of the orbit. The upper part of the sheath of the superior tarsal muscle reaches to the middle of the palpebral fascia, and is mainly continued forward between the muscle and the fascia to the anterior surface of the tarsus. The lower membrane (suspensory ligament of the eyeball), joined by the sheath of the inferior rectus, reaches forward to the attached (posterior) border of the tarsus of the lower lid, where it is mainly attached, while a part of it extends to the lower palpebral fascia. To understand the special bands of the anterior lamina mentioned above, we must follow the sheath of each rectus muscle forward, when we find that, while it is rather loosely applied to the muscular belly in its posterior two-thirds, it then suddenly becomes thicker, and is firmly attached to the muscle for some distance before finally leaving it, and is thereafter often accompanied by some muscle-fibres. The best developed of these bands, the lateral check ligament, passes anteriorly and laterally to the lateral angle of the orbit, helping to support the lacrimal gland on its way, and is inserted near the orbital edge immediately behind the lateral palpebral raphe. The medial band, or medial check ligament, is larger than the lateral, but not so thick; it passes forward and medially to be inserted into the upper part of the lacrimal crest and just behind it. These two bands, lateral and medial, come from the sheaths of the THE OPTIC NERVE 1073 corresponding recti muscles. From the sheath of the superior rectus come two thin bands, one from each border. The medial joins the sheath of the tendon of the superior obhque; the lateral goes to the lateral angle of the orbit, assisting in the support of part of the lacrimal gland. The sheath of the inferior rectus is thickened in front, and, on leaving the muscle, goes to the middle of the inferior oblique, splitting to enclose it; it then passes to be inserted into the lower medial angle of the orbit close behind its margin, about midway between the medial check ligament and the orbital attachment of the inferior obhque. 3. In addition to its partial investment by the muscle-fascia, the eyeball has a special membrane enclosing its hinder two-thirds, the fascia bulbi ("Tenon's capsule"). This is a thin, transparent tissue, situated immediately internal to the posterior lamina of the muscle-fascia. It follows the curve of the solera from the insertion of the recti to about 3 mm. from the optic nerve entrance. There it leaves the eyeball and blends with the posterior lamina of the muscle-fascia; the combined membrane may be traced backward, enveloping the optic nerve-sheath loosely, approaching it as it nears the optic foramen, but never actually joining it. The interval between it and the nerve-sheath is called the supravaginal lymph-space. The fascia bulbi first comes into relation with the muscles at the point where they are left by their proper sheaths; it there invests their tendons, forms a small serous bursa on the anterior surface of each, and adheres to the sclera along a line running around the globe, just anterior to the insertions of the four -recti muscles. Between this line and the corneal border, the con- junctiva is separated from the sclei'a by the subconjunctival tissue, strengthened by a fine expansion of the muscle-fascia. The inner surface of the fascia is smooth, and is onlj^ connected with the sclera by a loose, wide-meshed areolar tissue. This interval between the sclera and fascia, known as the interfascial (Tenon's) space, is a Ij^mph cavitJ^ and permits free movements of the eyeball within the capsule. Relation of the Fascia Bulbi to the Oblique Muscles. — The fascia surrounds the posterior third of the inferior oblique and its tendon, running along its ocular sm'face till it meets the fascial band coming from the inferior rectus (see above), and forming a serous bursa on the superficial surface of the oblique near its insertion. The tendon of the superior oblique for about its last five milhmetres is invested solely by the fascia bulbi; in front of this, as far as the trochlea, the tendon lies in a membranous tube derived from the muscle fascia, the inner lining of which is smooth, and may be considered as a prolongation of the fascia bulbi. The Optic Nerve The part of this nerve with which we have here to do lies within the orbit, ex- tending from the optic foramen to the eyeball (fig. 813). The length of this portion of the nerve is from 20 to 30 mm. and its diameter about 5 mm. Its course is somewhat S-shaped; thus, on entering the orbit, it describes a curve, with its convexity down and laterally, and then a second slighter curve, convex medially. Finally, it runs straight forward to the globe, which it enters 3 to 4 mm. to the medial side of its posterior pole. In its passage through the optic foramen the nerve is surrounded by a prolongation of the meninges. The dura mater splits at the optic foramen, part of it joining the periorbita, while the remainder continues to surround the nerve loosely as its outer or dural sheath. The nerve is closely enveloped by a vascular covering derived from the pia mater, named accordingly the pial sheath. The space between these two sheaths is subdivided by a fine prolongation of the arachnoid (the arachnoidal sheath) into two parts, termed the intervaginal spaces [spatia inter- vaginalia], viz., an outer, narrow, subdural, and an inner, wider, subarachnoid space, communi- cating with the coiTesponding intracranial spaces. The arachnoidal sheath is connected with the sheath on each side of it by numerous fine processes which bridge across the intervening spaces. The pial sheath sends processes inward, which form a framework separating the bundles of nerve-fibres; between the enclosed nerve-fibres and each mesh of this framework there is a narrow interval occupied by lymph. The nerve-fibres are medullated, but have no primitive sheath. About fifteen or twenty millimetres behind the globe the central vessels enter, piercing obliquely the lower lateral quadrant of the nerve, and then run forward in its axis. They are accompanied throughout by a special process of the pial sheath, which forms a fibrous cord in the centre of the nerve. On reaching the eyeball, the dural sheath is joined by the arachnoid, and turns away from the nerve to be continued into the outer two-thirds of the sclera. Similarly the pial sheath also here leaves the nerve, its greater part running into the inner third of the sclera, while a few of its fibres join the chorioid; the intervaginal spaces consequently end abruptlj' in the sclera around the nerve-entrance. In this locality the connective-tissue framework of the nerve becomes thicker and closer in its meshwork, and has been already alluded to as the lamina cribrosa sclerae. It is formed by processes passing out from the central fibrous cord at its termination and by processes passing inward from the pial sheath, sclera, and chorioid. It does not pass straight across the nerve, but follows the curve of the surrounding sclera, being therefore slightly convex backward. The nerve-trunk here quickly becomes reduced to one-half its former diam- 1074 SPECIAL SENSE ORGANS eter, the fibres losing their medullary sheath, and being continued henceforward as mere axis- cylinders. Apart from the consequent loss of bulk, this histological change may be readUy recognised macroscopicaUy in a longitudinal section of the nerve, its aspect here changing from opaque white to semi-translucent grey. The part of the nerve within the lamina cribrosa has aheady been noted in the ophthalinoscopic examination of the Uving eye (p. 1055). The optic nerve is mainly nourished by fine vessels derived from those of the pial sheath, which run into the substance of the nerve in the processes above mentioned. In front of the entrance of the central retinal artery this vessel aids to some extent in the blood-supply of the axial part of the nerve. Fig. 817. — Tkansvehse Section through Optic Nerve, showing the Relations of its Sheaths and Connective-tissue Framework. Dural sheath Arachnoidal sheath Suharachnoid space Subdural space -; Central retinal artery Central retinal vein Connective-tissue frame- work, with meshes in which the nerve-fibre bundles lie Fig. 818. — ^Longitudinal Section through Termination of Optic Nerve. "Pit in optic papilla Chorioid ~;;^^5!i3?i,-__r""^^^^S?r^^S>k /a0^^-^ s.— ^m, ""^^i Retina Short posterior^ ciUary artery Central retinal vessels Dural sheath Arachnoidal sheath Optic nerve with connective-tiss framework Pigment epithelium Suprachorioidal space Lamina cribrosa Sclera The Blood-vessels and Nerves of the Orbit As these structures will be more particularly described in other sections of this work, a very short general account will suffice here. Arteries. — The main blood-supply is afforded by the ophthalmic artery, a branch of the internal carotid, which gains the orbit through the optic foramen, where it lies below and lateral to the nerve. On entering the orbit it ascends, and passes obliquely over the optic nerve to the medial wall of the orbit; in this early part of its course it gives off most of its branches, which vary much in their manner of origin and also in their course. The arteries of the orbit are remarkable for their tortuous course, for their delicate walls, and for their loose attachment to the surrounding tissues. The ophthalmic artery gives off special branches in the orbit to the lacrimal gland, the muscles, the retina (through the optic nerve), and the eyeball, as well as to the meninges, the ethmoidal cells, and the nasal mucous membrane. Twigs from all the different branches go to supply the fat, fasciae, and ordinary nerves of the orbit. Branches which leave the orbit anteriorly ramify on the forehead and nose, and also go to the supply of ORBITAL VESSELS AND NERVES 1075 the eyelids and the tear-passages. The ophthalmic artery has many anastomoses with branches of the external carotid. The contents of the orbit are also supplied in part by the Infraorbital artery, a branch of the internal maxillary; in particular this artery supplies part of the inferior rectus and inferior oblique muscles in the cavity, and also gives a branch to the lower eyelid. Veins. — Branches, corresponding generally to those of the artery, unite to form the superior and inferior ophthalmic veins, which ultimately, either separately or united into one trunk, pass through the superior orbital fissure and empty into the cavernous sinus. The inferior vein is connected with the pterygoid plexus by a branch which leaves the orbit by the inferior orbital fissure. Nerves of the orbit. — These are (A) motor, (B) sensory, and (C) sympathetic, and aU enter the orbit by the superior orbital fissure, with the exception of one small sensory branch passing through the inferior orbital fissure. (The optic nerve has been already described, and is not included in this account.) A. The motor nerves are the oculomotor, trochlear, and abducens. 1. The oculomotor nerve enters the orbit in two parts, an upper smaller, and a lower larger, division. The upper division [ramus superior] gives off two branches: one suppHes the superior rectus, entering its lower surface far back; the other branch goes to the levator pal- pebra?, entering its lower surface in its posterior third. The lower division [ramus inferior] divides into three branches, of which one supplies the inferior rectus, entering its upper surface Fig. 819. — The Blood-vessels of the Left Orbit, viewed from above. Supraorbital artery- Lacrimal gland' Superior rectus, cut' Eyeball Lateral rectus Lacrimal artery Superior rectus, cut Inferior ophthalmic vein Superior ophthalmic vem Opt] Superior ophthalmic vein Commencement of superior ophthalmic vein Reflected tendon of superior oblique Ophthalmic artery 7] Anterior ethmoidal artery Posterior ethmoidal artery* Ciliary arteries Levator palpebr^e, cut Common tendon ring (of Zinn) Ophthalmic artery Optic chiasma Internal carotid artery far back, and another supplies the medial rectus, entering its medial surface a little behind its middle. The third branch of the lower division gives (1) the short root to the cihary ganglion, and (2) one or more twigs to the inferior rectus, and the remainder of this branch then enters the lower surface of the inferior oblique muscle about its middle. 2. The trochlear nerve supplies the superior oblique muscle, entering its upper surface about midway in its course. 3. The abducens nerve supplies the lateral rectus, entering its medial surface about the junction of the posterior and middle thirds of the muscle. As regards the manner of termination of these motor nerves, it is found that in aU the ocular muscles the nerve on its entrance breaks up into numerous bundles of fibres, which form first coarse and then fine plexuses, the latter ultimately sending off fine twigs supplying the muscle throughout with nerve-endings. The posterior third of these muscles is, however, comparatively poorly supplied with both kinds of plexuses and with nerve-endings. B. The sensory nerves are supplied by the ophthalmic and maxillary divisions of the trigeminal cranial nerve. The ophthalmic division is chiefly orbital; while the maxillary sends only a small branch to the orbit. 1. The ophthalmic division of the trigeminal nerve enters the orbit in three divisions, namely: — (1) Frontal, spUtting subsequently into supratrochlear and supraorbital, both passing out of the orbit. It is distributed to the corresponding upper eyehd, and the skin over the root of the nose, the forehead, and the hairy scalp as far back as the coronal suture on the same side. It also gives branches to the periosteum in this region, and to the frontal sinus. (2) Lacrimal, supplying the lacrimal gland, anastomosing with a branch of the maxillary 1076 SPECIAL SENSE ORGANS in the orbit, and finally piercing the upper eyelid. Outside the orbit it is distributed to the lateral part of the upper lid, the conjunctiva at the lateral angle, and the skin between this and the temporal region. (3) Naso-ciliary [n. naso-ciUaris] giving off — (a) a branch to the ciliary gangUon, constituting its long root ; (6) two or three long ciliary nerves; and (c) the injratrochlear, passing out of the orbit. The nerve then leaves the orbit as the anterior ethmoidal nerve [n. ethnioidaUs anterior], re- entering the cranial cavity before being finally distributed to the nose. The infratroohlear branch [n. infratrochlearis], supplies the eyehds and skin of the side of the nose near the medial angle of the eye, the lacrimal sac, caruncle, and plica semilunaris. The anterior ethmoidal nerve, after its course in the cranial cavity, passes through an aperture in the front of the lamina cribrosa of the ethmoid bone, and is ultimately distributed to the nasal mucous membrane, and to the skin of the side and ridge of the nose near its tip. 2. The maxillary division of the fifth nerve gives a branch, called the zygomatic nerve, which passes into the orbit through the inferior orbital fissure, anastomoses with the lacrimal, and leaves the orbit in two divisions. These are distributed to the skin of the temple and of the prominent part of the cheek. A few minute twigs from the spheno-palatine ganghon, and sometimes from the maxillary division of the fifth nerve, also pass through the inferior orbital fissure to supply the periorbita in this neighbourhood. C. The sympathetic nerves of the orbit are mainly derived from the plexus on the internal carotid arterj'. With the exception of branches accompanying the ophthalmic artery, and of the distinct sympathetic root of the ciUary ganghon, they enter the orbit in the substance of Fig. 820. — Section through Contents op Right Orbit, 1-2 mm. in front of the Optic Foramen, viewed from behind. (After Lange.) Trochlear nerve Superior rectus and levator palpe-. bras superioris muscles ■ oblique musclC' Ophthalmic vein ve (frontal, liary, and lacrimal branches) Medial rectus muscle— -^^ \ Inferior rectus muscle '' \m — "'^'^ Ophthalmic vein 117. Ophthalmic artery Abducens nerve Oculomotor nerve Lateral rectus muscle the other nerve-cords. The connections between the ocular nerves and the carotid plexus are recognisable as fibres going to the oculomotor, abducens, and ophthalmic nerves; as a rule, the comparatively large twigs going to the abducens join it furthest back, and those to the oculo- motor furthest forward. Sympathetic connections with the trochlear nerve are very doubt- ful. The special courses of the motor fibres to the dilatator pupillae muscle have already been described. The ciliary ganglion is situated between the optic nerve and lateral rectus far back in the orbit. Its three roots — motor, sensory, and sympathetic — have been already mentioned. Anteriorly, it gives off three to six smaU trunks, which subdivide to form the short ciliary nerves [nn. cihares breves] about twenty in number, piercing the sclera around the optic nerve entrance. The lymphatic system of the orbit. — Although there are no lymphatic vessels or glands in the orbit, the passage of lymph is nevertheless well provided for. We have already observed the lymph channels within, between, and outside the sheaths of the optic nerve, and have seen how these communicate anteriorly with the lymph channels of the eyeball, and posteriorly with the intracranial meningeal spaces. In addition, there are lymph-spaces around the blood-vessels, situated between the outer coat and the loose investment furnished by the muscle fascia. The nerves of the orbit (apart from the optic) are probably similarly surrounded by lymph-spaces. In the absence of lymphatic vessels it is difficult to trace the circulation thoroughly; much of the lymph from the orbital cavity is said to pass into the parotid nodes. The Eyelids The cutaneous and conjunctival surfaces of the eyelids [palpebras] have al- ready been examined (p. 1053), and the position of the tarsus has been indicated. We have now to ascertain the nature and relations of the tarsus, and describe the other tissues entering into the formation of the eyelids (fig. 821). THE EYELIDS 1077 The skin here is thin, bearing fine hairs, and having small sebaceous and nu- merous small sweat-glands. Immediately beneath it is a loose subcutaneous tissue, destitute of fat, separating the skin from the palpebral part of the orbicu- laris muscle. The lid-fibres of this muscle arise from the medial palpebral liga- ment, and course over the whole upper and lower eyelids in a succession of arches, so as to meet again beyond the lateral angle; there they in part join one another, in part are inserted into the lateral palpebral raphe. The muscular fibres are arranged in loose bundles, with spaces between them occupied by connective tissue; in the upper lid these connective-tissue fibres may be traced upward and backward into the fibrous expansion of the tendon of the levator palpebree supe- FiG. 821. — Sagittal Section op the Upper Eyelid. (After Waldeyer and Fuohs.) Orbicularis oculi - Sweat gland ■ -!:• Sebaceous gland — Cross section of orbicularis oculi ^^Sltt/ Ciliary gland (of Moll) Ciha ^ :i Anterior insertion of leva- tor palpebree superioris Superior tarsal muscle of MuUer - Fibres from levator to skin 7' ^ Mucous glands (Krause) Conjunctival papillse over attached border of tarsus Mucous glands (of Krause) ^_ Tarsal (Meibomian) glands M. ciliaris (Riolani) Posterior edge of lid-margin Opening of duct of tarsal gland rioris. One strong bundle of orbicularis fibres, called the musculus ciliaris Riolani, is found near the edge of the lid, in front of and behind the efferent ducts of the tarsal glands (fig. 821). A central connective tissue separates the orbicularis muscle from the tarsus in the tarsal division of the lids. In the upper Ud this is to be regarded as mainly the anterior or fibrous expansion of the tendon of the levator palpebrse, which sends connective-tissue septa between the bundles of the overlying orbicularis (as just mentioned) going to the skin. In the orbital part of this hd the central connective tissue includes also the palpebral fascia, lying here immediately beneath the orbicularis muscle; but this soon thins off and fades into the more deeply placed levator expansion. This latter is strengthened by an extension of the sheath of the superior rectus, by which this muscle is enabled to influence the elevation of the Ud indirectl.y. In the lower lid the central connective tissue similarly consists of palpebral fascia, blended with a thin fibrous extension of the sheath of the inferior rectus. Immediately in front of each tarsus is a little loose connective tissue, which contains the large blood-vessels and nerves of the hds. The tarsus of each lid is a stiff plate of close connective tissue, with its sur- faces directed anteriorly and posterior^; in its substance the tarsal glands are 1078 SPECIAL SENSE ORGANS embedded. One tarsal border is free, viz., toward the edge of the lid, the other is attached; the former is straight, while the latter is convex, especially in the upper lid. The length of each tarsus is about twenty millimetres. Its breadth is greatest in the middle of the hd, and becomes gradually smaller toward 'each angle, where the tarsi are joined to the lateral raphe and medial palpebral ligament. The breadth of the upper tarsus (10 mm.) is about twice that of the lower. The thickness of each is greatest, and its texture closest, at the middle of its length, thinning off toward the angles of the eye and toward both borders. Into the superior anterior border of the upper tarsus the lower layer of the levator expansion is attached, consisting of smooth muscle-fibres constituting the superior tarsal muscle of Mtiller. In like manner, at the inferior border of the lower tarsus, bundles of smooth muscle-fibre are inserted (the inferior tarsal muscle of Miiller), developed in what has been regarded as part of the extension of the sheath of the inferior rectus. The palpebral conjunctiva is firmly adherent to the posterior aspect of the tarsus; but in the orbital part of the lid loose subconjunctival tissue intervenes between it and Miiller's tarsal muscle. Lymphoid tissue occurs in the substance of the conjunctiva, especially in its orbital division. Near the upper fornix, the conjunctiva receives expansions of the tendon of the levator palpebrse and of the sheath of the superior rectus, and, at the lower fornix, of the sheath of the inferior rectus. The surface of the tarsal conjunctiva shows small elevations or papillae everywhere; but these are particularly well marked over the attached border of the tarsus. Glands of the eyelids. — From its manner of formation the eyelid may be regarded as consisting of two thicknesses of skin, the posterior having been doubled back upon the anterior at the edge of the lid; thus the epidermis and corium of the skin proper are represented respectively by the conjunctiva (epi- thelium) and tarsus of the inner thickness. At the free border of the lid, accord- ingly, we find glands corresponding to the sebaceous and sweat-glands of the skin, viz., large sebaceous glands of the cilia (Zeiss's glands) and the ciliary glands of Moll, which are modified sweat-glands. Again, in the inner skin-thickness of the lid, the tarsal (Meibomian) glands are sebaceous. Acino-tubular mucous glands occur at the attached border of the tarsus (Krause's or Waldeyer's glands), and similar glands also occur at the fornix, and are especially abundant near the outer angle of the upper lid, close to the efferent ducts of the lacrimal gland; from their structure and the character of their secretion, these acinous or acino-tubular glands have been termed by Henle 'accessory lacrimal glands.' Other simple tubular glands (Henle), formed merely by the depressions between the papiUae, are best developed in the medial and lateral fourths of the tarsal conjunctiva of both hds. Blood-vessels. — The arteries run in the central connective tissue of the lids, mainly in the form of arches near the borders of the tarsus, from which twigs go to the different pal- pebral tissues. They are supplied by the lacrimal and palpebral branches of the ophthalmic, and by small branches derived from the temporal artery. The veins are more numerous and larger than the arteries, and form a close plexus beneath each fornix. They empty themselves into the veins of the face at the medial, and into the orbital veins at the lateral angle of the eye. The lymphatic vessels of the lids are numerous, and are principally situated in the con- junctiva. Lymph-spaces also surround the follicles of the tarsal glands. The palpebral lymphatic vessels from the lateral three-fourths of the lid pass through the anterior auricular and parotid nodes; those from the medial fourth of the lower lid go to the facial and submaxil- lary lymphatic nodes. Nerves. — (a) Sensory. The upper lid is chiefly supplied by branches of the supraorbital and supratrochlear nerves, the lower Ud by one or two branches of the infraoibital. At the medial angle the infratrochlear nerve also aids in the supply, and, at the lateral angle, the lacrimal, (b) Motor. The palpebral part of the orbicularis is suppKed by branches of the facial nerve, which mainly enter it near the lateral angle. The tarsal muscles are suppUed by the sympathetic nervous system. The medial palpebral ligament has been referred to previously. Arising from the frontal process of the maxilla, it extends laterally over the front wall of the lacrimal sac, bends round the lateral wall of the sac, and then passes backward to the posterior crest on the lacrimal bone. It is thus U-shaped, having its limbs anterior and posterior, embracing the lacrimal sac; the anterior limb lies immedi- ately beneath the skin, and is visible in the living. The palpebral fibres of the orbicularis are inserted into the anterior surface of both limbs, those attached to the posterior limb constituting the pars lacrimalis of the orbicularis palpebrarum (Horner's muscle). The lateral palpebral raphe is merely a stronger development of connective tissue in the orbicularis. Both ligaments are connected with the tarsi as already mentioned. LACRIMAL APPARATUS 1079 The Lacrimal Apparatus The tears are secreted by an acinous gland, and flow through fine ducts to the upper lateral part of the conjunctival sac, whence they pass over the cornea and are drained off through the puncta, pass along the canaliculi into the lacrimal sac, and ultimately down the naso-lacrimal duet to the inferior meatus of the nose. The lacrimal gland is situated near the front of the lateral part of the roof of the orbit, lying in a depression in the orbital plate of the frontal bone. It consists of two very unequal parts, one placed above and the other beneath the tendinous expansion of the levator palpebree superioris, but small gaps in the expansion per- mit of connections between these two parts of the gland. The upper and larger subdivision (superior lacrimal gland) is a firm elongated body, about the size of a small almond; it has a greyish-red colour, and is made up of closely aggregated lobules. The upper surface (next the orbital roof) is convex, and its lower surface is slightly concave. Anteriorly, the gland almost reaches the upper orbital margin, and it extends backward for approximately one-fourth the depth of the orbit, measuring about twelve mUlimetres in this direction. The lateral border of the gland descends to near the insertion of the fascial expansion of the lateral rectus, while its medial border almost reaches the lateral edge of the superior rectus; its transverse measurement is about twenty millimetres. It is enveloped in a capsule, which is slung by strong fibrous bands passing to its medial border from the orbital margin (suspensory hgament of the gland). Fig. 822. — Dissection of the Eye to Show the Lacrimal Appakatus, Anterior View. Inferior lacrimal gland Excretory ducts/ Superior lacrimal gland i I Palpebra superior Tendon of superior oblique } Superior lacrimal duct ^ Lacus lacrimalis y Medial palpebral commissure - Fornix of lacrimal sac - Junction of lacrimal ducts - Inferior lacrimal duct - Nasolacrimal duct ^ I-- i' Lacrimal papilla and punctum Inferior oblique Palpebra inferior The lower subdivision of the gland (^inferior lacrimal gland) is composed of loosely applied lobules, and lies immediately over the lateral third of the upper conjunctival fornix, reaching lateralward as far as the lateral angle. Each subdivision of the gland possesses several excretory ducts, which all open on the lateral part of the upper fornix conjunctivae, about four millimetres above the upper border of the tarsus. Those of the superior gland, three or four in number, pass betweefi the lobules of the lower gland; the most lateral duct is the largest, and opens at the level of the lateral angle of the eye. The ducts of the inferior gland in part discharge themselves into those of the upper, but there are also several fine ducts from this subdivision that run an independent course. Near the medial angle are the two puncta lacrimalia, upper and lower, each situated at the summit of its papilla. The top of each papilla curves backward toward the conjunctival sac, so that the puncta are well adapted for their function of draining off any fluid collecting there. The ductus (canaliculi) lacrimales extend from the puncta to the lacrimal sac. The lumen at the pmrctum is horizontally oval, from its lips being slightly com- pressed antero-posteriorly; the lumen of the lower punctum is somewhat larger than that of the upper. As the lower papilla is a little further from the medial angle of the eye than the upper, the corresponding canaliculus is longer. On tracing either ductus from its origin, we flnd that at first it runs nearly vertically for a short distance, then bends sharply toward the nose, and finally 1080 SPECIAL SENSE ORGANS courses more or less horizontally, converging slightly toward its fellow, and not infrequently joining it before opening into the sac. The calibre varies consider- ably in this course, being narrowest a short distance from the punctum, and widest at the bend, from which point it again narrows very gradually as it nears the sac. The wall of the ductus consists mainly of elastic and white fibrous tissue, lined internally by epitheUum, and covered externally by striated muscle (part of the orbicularis). The muscle- fibres run parallel to the ductus in the horizontal part of its course; but they are placed, some in front and some behind, around the vertical part, acting here as a kind of sphincter. Just before their termination, the ducts pierce the periosteal thickening that constitutes the posterior limb of the medial palpebral ligament. The lacrimal sac [saccus lacrimalis] lies in a depression in the bone at the medial angle of the orbit (the lacrimal fossa). It is vertically elongated, and narrows at its upper and lower ends; the upper extremity or fundus is closed, while the lower is continuous with the naso-lacrimal duct. Laterally, the sac is somewhat com- pressed, so that its antero-posterior is greater than its transverse diameter. The ducts, either separately or by a short common tube, open into a bulging on the lateral surface of the sac near the fundus. As has previously been mentioned, the sac is surrounded by periosteum, but between this and the mucous membrane forming the true sac-wall there is a loose connective tissue, so that the cavity is capable of considerable distention. The relations of the medial palpebral Ligament have already been described; it is to be noted that the fundus of the sac extends above this ligament. The naso-lacrimal duct [ductus naso-lacrimalis] reaches from the lower end of the sac to the top of the inferior meatus of the nose, opening into the latter just beneath the adherent border of the inferior nasal concha. Traced from above, its main direction is downward, but it has also a slight inclination backward and laterally. It lies in a bony canal, whose periosteum forms its outer covering. Between this and the mucous membrane of the duct there is a little intermediate tissue, in which run veins of considerable size connected with the plexus of the inferior concha. The duct does not usually open directly into the nasal cavity at the lower end of the bony canal, but pierces the nasal mucous membrane very obliquely, so that a flap [plica lacrimalis (Hasneri)] of mucous membrane covers the lower border of the opening in the bone, upon which flap the tears first trickle after escaping from the duct proper. The sac and naso-lacrimal duct together constitute the lacrimal canal, lined throughout by a continuous mucous membrane. This membrane presents folds in some situations, especially near the opening of the canaliculi, at the junction of the sac and duct, and at the lower end of the duct. That at the top of the duct is the most important, as it sometimes interferes with the proper flow of tears out of the sac. The total length of the lacrimal canal is roughly twenty-four millimetres, half of this being sac, and half naso-lacrimal duct. If, however, we reckon as duct the obUque passage through the nasal mucous membrane, this measurement may occasionally be increased by eight or ten millimetres. The lacrimal sac, when distended, measures about six millimetres from before backward, by four millimetres transversely. The naso-lacrimal duct is practically circular, and has a diameter of about three millimetres, rather less at its junction with the sac, where we find the narrowest part of the whole lacrimal canal. Development of the ■ Eye The eye is developed from the three sources involving two fundamental embryonic layers — the retina from a portion of the ectodermal wall of the forebrain on each side; the lens from the ectodermal surface epithelium; and the sclera, cornea (except epithelium) and chorioidal coat from the mesoderm which surrounds the former structures. The process of development is, briefly, as follows: — The site of the eye is marked by a sUght depression on the surface of the forebrain on either side. There later an outgrowth occurs from the ventro-lateral aspect on each side of the forebrain, in the form of a hoUow vesicle, whose cavity is continuous with that of the forebrain. This outgrowth is termed the •primary optic vesicle [vesicula ophthalmicaj. The lateral surface of the vesicle comes into contact with the surface epithelium of the head and this epithelium becomes thickened at the area of contact. The superficial portion of the vesicle expands, while its connection with the brain remains slender; becoming depressed on the surface, it forms a cup-shaped hollow, the secondary optic vesicle or optic cup [caliculus ophthalmicus] whose wall is formed of two layers, an outer investing layer and an inner inverted one. The chorioidal fissure is present almost from the first stages, as a cleft on the ventral aspect of both the distal portion of the vesicle, or cup, and of the stalk; and it is formed by an infolding of the surface into the cavity of the vesicle along a narrow linear area. In this cleft are found vessels which pass to the hollow of the optic cup. The margins of the cleft meet and fuse, and enclose the vessels in the interior — hence the enclosure of the a. centralis retina within the optic nerve, and of the hyaloid artery in the interior of the vitreous. Should the margins of the cleft remain separate, the. condition of coloboma results. DEVELOPMENT OF THE EYE 1081 From the optic cup is formed the whole of the retinal or nervous tunic. It will be noticed that this tunic is composed of two layers, with a narrow sUt-like interval between them, but that the layers are continuous with one another at the margin of the cup. This margin is afterward found, in the fully developed eye, at the pupillary margin of the iris. The outer investing layer forms the pigment layer, and the inner inverted layer gives rise to the other parts of the retina, viz., the pars optica, over the bottom of the cup, the pars ciliaris, in the ciliary region, and the pars iridica, near the margin of the original cup, including the dilatator and sphincter pupillae muscles of the iris. The lens is formed as a hollow invagination from the surface epitheKum, which sinks into the hoUow of the optic cup. The margins meet and fuse, enclosing a cavity, and the lens mass sinking more deeply in, loses its connection with the surface, and a layer of mesoderm passes in between them. The anlages of the lens and the primitive retina are at first in contact with one another. They graduaUy draw apart, and the intervening space is filled by the vitreous humour. The origin of the vitreous humour is not yet fully understood, but it appears to be developed from the adjacent ectoderm of the optic cup, and in part from the surrounding mesoderm. Figs. 823, 824, 825 and 826. — Sections Representing Four Successive Stages in the Origin op the Optic^ Vesicle and the Development op the Eyeball. ■W The optic cup and the lens are surrounded by mesoderm and from it are formed the struc- tures of the tunica vasculosa (middle coat) in its different parts, viz., chorioid, ciliary body and ins, and also the sclera and cornea (fibrous portion). Bii I^^- f" n®''J5'" <'lia'»ber is formed by cleavage of the mesoderm, a space appearing in it, hUed with fluid. The mesoderm surrounding this space forms the endothehum Hning the anterior chamber. The mesoderm also forms a vascular covering for the front of the lens, termed the capsula vasculosa leniis, or pupillary membrane, which disappears from the sur- face of the lens in the later months of development. The eyehds and conjunctiva are formed from the integumentary covering of the eye. 1 he former are mostly skin folds, which, at first separate, meet and fuse with one another along their margin. Subsequently they become undermined by the ingrowth of epithelium from a central horizontal sht, the rima palpebrarum ; the central part of the invading epithehum breaks down, and the free folds are formed. The lacrimal gland is developed from a series of tubular outgrowths from the conjunctival sac. 1082 SPECIAL SENSE ORGANS The lacrimal canals and naso-lacrimal duct are formed by the growth of an epithelial band which passes through the mesoderm to the nasal cavity along the naso-lacrimal groove. This band loses its primitive connection with the groove, and is reunited to the lid margins by secondary epithelial bands which grow from the naso-lacrimal duct to the lid margin. Simi- larly a secondary connection is later made with the nasal cavity at the lower end of the duct. The position of the naso-lacrimal duct corresponds to the line of union of the nasal and maxillary processes; but the duct does not represent a portion of the cleft between these processes, and is formed secondarily between them. IV. THE EAR Under the name of the ear [organon auditus] there is included a number of structures of which some, the ear proper, constitute the auditory mechanism — that is, an apparatus for the collection, transmission and reception of the waves of sound; while others — the semicircular ducts and associated structures — are concerned in receiving and transmitting impressions produced by movements of the head. These impressions constitute the basis of what may be termed the static or equilibratory sense, and afford data employed in estimating movements of the body in relation to surrounding objects. The former of these, the ear proper, consists of three main parts, each possess- ing distinct structural and functional characters. The first portion, often known as the external ear, consists of a receptive organ placed upon the surface of the head, the auricle or pinna, and of a short tube, the external auditory meatus, which leads into the interior, and is closed at its deep end by the tympanic membrane. The second portion, known as the middle ear, consists of the tympanic cavity, a small air-containing chamber in the petrous portion of the temporal bone, con- nected with the nasal part of the pharynx by a tube, the auditory (or Eustachian) tube. From the tympanic chamber a recess passes posteriorly and leads to a cavity in the mastoid portion of the temporal bone, the mastoid or tympanic antrum. A chain of three small bones transmits the sounds across the middle ear. The third part, or internal ear which contains the essential sensory apparatus, lies within the complex cavities in the interior of the petrous temporal bone known as the osseous labyrinth. It consists of (1) the utricle and saccule, two small ves- icular structures lying in the bony vestibule, and (2) the membranous semicir- cular ducts and (3) the membranous cochlea, which lie within the corresponding bony canals. These structures are filled with fluid, the endolymph, and communicate with one another. They are largelj' separated from the bony walls by fluid, perilymph, and they are lined by sensory epithelium. Closely related to the epithelial sensory cells are found the terminal branches of the cochlear and vestibular nerves. The description of the three divisions of the ear is taken up in order from the surface inward. 1. THE EXTERNAL EAR The external ear consists of the auricle attached to the side of the head, and the external auditory meatus leading from it to the middle ear (flg. 829). THE AURICLE The auricle, or pinna, is an irregular oval plate-like structure which lies upon the lateral surface of the head. It presents a lateral and a medial surface. The lateral surface is irregularly concave (fig. 827). The deepest part of its concavity situated near the centre, is termed the concha, and it is partially divided by a prominent oblique ridge, the crus of the helix, into a superior part, the cymba conchae, and a large inferior part, the cavum conchae. The cavum conchse leads into the external auditory meatus, and is bounded ventrally by a prominent proc- ess, the tragus, which projects posteriorly over the entrance to the meatus. The tragus, is separated from the crus of the helix by a well-marked depression, the anterior incisure and has a small tubercle on it superiorly, the supratragic tuber- cle. Bounding the cavum conchte posteriorly and inferiorly is a projection, the antitragus, lying opposite, but inferior, to the tragus, and between the two is a deep notch, the intertragic notch [incisura intertragica]. A prominent semicircular THE AURICLE 1083 ridge, the anthelix, bounds the concha posteriorly and superiorly. Inferiorly it is separated from the antitragus by a slight depression, the posterior auricular sulcus. Superiorly the anthelix divides into two ridges, the crura of the anthelix, and between these is a shallow depression, the triangular fossa. The superior and dorsal margin of the auricle is inverted and forms a prominent rim, the helix, which Fig. 827 — ^Lateral Surface or the Left Auriole. Crura of anthelix Crus of tne helix- Anterior incisure- Supratragic tubercle Tragu; Intertragic incisure- HeUx Auricular tubercle Triangular fossa Scapha Cavum J Anthelix Posterior auricular sulcus is continued anteriorly into the crus of the helix, and inferiorly into the lobule. An elongated depression, partly overlapped by the helix, termed the scapha (scaphoid fossa) separates the helix and the anthelix. Superiorly and dorsally the free margin of the helix frequently presents a slight projection, the auricular, tubercle (tubercle of Darwin). Fig. 828. — Lateral and Medial Surface of the Cartilage of the Right Auricle and its Muscles, etc. Helicis major Obliquus Transversus Helicis minor' Ebrous band pleting fore part of meatus l.yy Antitrago-helicin Terminal fissure Isthn Antitragicus , Tragicus Spine of Fissure of Santorini Lamina tragi helix Cartilage of meatus Upon the medial surface of the auricle the depressions of the lateral surface are represented by elevations, viz., the eminence of the concha, the eminence of the scapha, and the eminence of the triangular fossa, respectively; and the elevations by depressed areas, viz., the fossa of the anthelix, transverse sulcus of the anthelix. 1084 SPECIAL SENSE ORGANS and the sulcus of the crus of the helix. The attachment of approximately one- third of the medial surface covers up the two latter depressions. The cephalo-au- ricular angle, between the dorsal free part of the auricle and the side of the head, averages 20 to 30 degrees. Structure of the Auricle The features of the auricle just described are mainly produced by a plate of yellow elastic cartilage, the auricular cartilage. In addition to the elevations and depressions already noted, it presents the following additional features. Projecting anteriorly from the helix, near the crus is a small tubercle, spine of the helix (fig 828) ; while the posterior margin of the helix terminates in a pointed tail-like process, the cauda helicis which is separated inf eriorly from the antitragus by the deep antitrago-helicine fissure. Another deep fissure, the terminal notch [incisura terminalis auris], separates the cartilage of the auricle from that of the meatus, leaving only a narrow strip, the isthmus, connecting the two. The cartilage of the tragus, the lamina tragi, is separated from that of the auricle and is attached to the lateral margin of the cartilage of the meatus. The auricle is covered on both its medial and lateral aspects by skin which closely follows the irregularities of the cartilage. Thus it is tightly bound to the perichondrium of the lateral surface by the subcutaneous areolar tissue, but much more loosely attached to the medial surface, and in the subcutaneous tissue there is little fat except in the lobule, which is made up almost entirely of fat and tough fibrous tissue. Hairs are abundant but rudimentary, except in the region of the tragus and antitragus, where they may be large and long, particularly in males and in the aged. Sebaceous glands are found on both surfaces, and are especially well developed in the concha and triangular fossa, but sudoriferous glands are few and scattered. Ligaments and muscles. — The auricle is attached to the side of the head by the skin, by the continuity of its cartilage with that of the acoustic meatus, and by certain extrinsic ligamente and muscles. Three ligaments may be distinguished in the connective tissue: — The anterior ligament, stretching from the zygoma to the helix and tragus; the superior ligament, from the superior margin of the bony external acoustic meatus to the spine of the helix; and the posterior ligament, from the mastoid process to the eminence of the concha. There are also three ex- trinsic muscles, the anterior, superior, and posterior auricular (see p. 337, fig. 341). Six intrinsic muscles are distinguished. These are poorly marked in man and vary much in development. Upon the lateral surface (fig. 828) the helicis major stretches from the spine of the helix to the ventral superior margin of the helix; the helicis minor overlies the crus helicis; the tragicus runs vertically upon the tragus; and the antitragicus stretches from the antitragus to the cauda helicis. Upon the medial surface (fig. 828) the transversus auriculae stretches between the eminences of concha and scapha, and the obliquus between the eminences of the concha and the triangular fossa. Two small muscles occasionally present are the m. pyramidalis auriculse (Jungi) and the m. incisurse heUcis (Santorini). Vessels and Nerves of the Auricle The arteries are the auricular branch of the posterior auricular and the anterior auricular branches of the superficial temporal arteries. The veins are the anterior auricular vein of the posterior facial (temporal) and the auricular branches of the posterior auricular veins. The latter vessels sometimes join the transverse (lateral) sinus through the mastoid emissary vein. The lymphatics empty into the anterior, posterior and inferior auricular lymph-nodes. The sensory nerves of the auricle are the branches of the great auricular, small occipital (p. 977, fig. 753), and auriculo-temporal (p. 941, fig. 740). The muscles are suppUed by the posterior auricular branch of the facial (p. 944, fig. 740). Variations There are many variations in the size, shape, and conformation of the auricle and in the cephalo-auricular angle. These are associated not only with differences in sex, age, and race, but are also found in individuals of the same family. THE EXTERNAL AUDITORY MEATUS The external auditory (acoustic) meatus [meatus acusticus externus] extends medially and somewhat anteriorly and inf eriorly from the concha to the tympanic membrane (fig. 829). It is about twenty-five mm. (1 in.) long, and, owing to the obliquity of the tympanic membrane, its anterior and inferior wall is 5-6 mm. EXTERNAL AUDITORY MEATUS 1085 longer than the posterior and superior. It consists of a lateral cartilaginous and a medial osseous portion. The canal describes an S-shaped curve in both hori- zontal and vertical directions. Near the auricular end it is convex anteriorly and inferiorly, while at the tympanic end the curve is reversed, and is concave in the same direction. The lumen is irregularly elliptical in outhne, the longer axis being vertical at the auricular, but nearly horizontal at its tympanic end. The meatus is constricted at about its centre, and also near the tympanum. Fig. 829. — -Vertical Section of the Middle and External Ear. Semi circular Glands in oq canals (ducts) secus meatus Tympanic membrane ^ Cochlea \ \ Cavity of tympanum \ f '' Cartilaginous tuba auditiva Cartilagp — Osseous meatus Cartilage of external meatus Parotid gland Styloid process Osseous tuba auditiva Relations. — The anterior loall is in relation with the condyle of the mandible medially, and with the parotid gland laterally; the inferior wall is closely bound to the parotid gland; and the 'posterior tuall of the bony part is separated by only a thin plate of bone from the mastoid cells. The superior loall is separated at its medial end by a thin plate of bone from the epi- tympanic recess, and laterallj' a thicker layer of bone separates it from the cranial cavity. Structure of the meatus. — The walls of the meatus are formed laterally of fibro-cartilage and medially of bone, lined internally by skin. The cartilage is folded upon itself to form a groove, deficient in its dorsal part, where the edges of the cartilage are united by dense connective tissue. The cartilaginous groove is thus converted into a canal. Medially, the cartilage forms about one-third of the circumference; laterally, two-thirds. Two fissures (incisures of Santbrini) usually occur in its anterior wall (fig. 828). Laterally the cartilage is directly continuous with the cartilage of the auricle and medially it is firmly connected with the lateral lip of the osseous portion. The osseous portion, which forms slightly more than half the canal, is formed by the tympanic portion of the temporal bone; it is described in connection with that bone. The skin of the meatus forms a continuous covering for the canal and tympanic membrane. It is thick in the cartilaginous, but very thin in the bony, part of the meatus, especially near the tympanic end, where it is tightly bound to the perios- teum . In the cartilaginous meatus it contains numerous fine hairs and sebaceous glands, but neither hairs nor sebaceous glands are found in the bony meatus. Tubular ceruminous glands, which secrete the cerumen (ear wax) , form a nearly continuous layer throughout the cartilaginous, but occur on onlj- a small part of the posterior and superior wall of the bonj', meatus. The openings of their ducts appear as dark points to the naked eye (fig. 829). 1086 SPECIAL SENSE ORGANS The arteries are branches from the posterior auricular, superficial temporal, and deep auricular arteries (q.v.)- The veins and lymphatics connect with those of the auricle and empty similarly. The nerves are branches from the auriculo-temporal and the auricular ramus of the vagus. 2. THE MIDDLE EAR Under the term middle ear there are included the tympanic cavity (tym- panum), the tympanic antrum and the auditory (Eustachian) tube. These form a continuous irregular passage, filled with air, and located within and upon the surface of the temporal bone. The tympanum is shut off from the external ear Fig. 830. — Frozen Coronal Section op the Right Ear. (Somewhat Enlarged.) Chorda tympani Manubrium mallei / Capitulum maUei j Tympanic cavity Stapes / Facial nerve Tympani membrane Promontorium 1 Lamina spiralis Modiolus ' \ I Tempoial bone \ I Dura mater / Temporal bone Temporal muscle Cochlea Internal carotid Internal jugular vein Internal carotid artery Cartilage of meatus ' External auditory meatus (cartilaginous) Parotid gland by the tympanic membrane; and from the chamber which forms the internal ear by the structures which fill in the cochlear and vestibular fenestra. It commu- nicates with the pharynx by the auditory (Eustachian) tube. _ The structures of the middle ear are of importance, and the study is somewhat difficult, on account of the small size of the structures, the depth at which they lie, and the hard charac- ter of the surrounding bone. The illustrations (figs. 829, 830, 831, 833, 834) will help to explain the text and should be constantly referred to. Figs. 830 and 831 are taken from frozen sections traversing the right ear in the coronal planes; while figs. 833, 834 represent dissections. The parts to be considered in order are the tympanic rnembrane, the tympanic cavity, the tympanic antrum and the auditory (Eustachian) tube. The Tympanic Membrane The tympanic membrane [membrana tympani] (fig. 835) is elliptical in shape, its long axis nearly vertical, measuring 9 to 10 mm., its short axis, 8 to 9 mm. It slopes medially from the superior and posterior to the inferior and anterior THE TYMPANIC MEMBRANE 1087 wall of the meatus, forming, as a rule, with the superior wall, an angle of 140 degrees. It varies, however, greatly in form, size, and obliquity. Viewed from the meatus, it appears as a semitransparent membrane, which sometimes has a reddish tinge. It is drawn medially and made funnel-shape by the manubrium of the malleus, but the walls of the funnel bulge toward the meatus (fig. 834) . The most depressed point at its centre, the umbo, is slightly inferior and posterior to the centre of the membrane, and corresponds to the tip of the manubrium (fig. 832). From it a whitish streak, the malleolar stria, caused by the manubrium shining through, passes superiorly toward the circumference. At the superior end of the stria is a slight projection, the malleolar prominence, formed by the lateral process of the malleus. From it two folds, the anterior and posterior Fig. 831. — Frozen Coronal Section op the Right Ear. (Somewhat Enlarged.) Prominence of facial canal Medial tympanic wall Tegmen tympani Recessus epitympanicus \ Stapes I Facial nerve ^ Fenestra vestibuli ; Cochlea , Facial, and cochlear vestibular nerves Cavum conchse Internal carotid artery Cartilage of meatus j Parotid gland plicffi, stretch to the extremities of the tympanic sulcus (fig. 832). The small triangular area of the membrane bounded by the plicae, is termed the pars flaccida (Shrapnell's membrane). It is thin and flaccid, and is attached directly to the petrous bone in the tympanic notch (notch of Rivinus). The larger part of the tympanic membrane, the pars tensa, is inferior to the plicae and is tightly stretched. Its thickened margin, the limbus, is attached by a fibro -cartilaginous annulus to the tympanic sulcus, and at the spines of the tympanic ring is continuous with the plicae. Structure of the tympanic membrane. — The tympanic membrane is about .1 mm. thick, and consists of four layers. The lateral cutaneous layer, relatively thick, is a continuation of the skin lining the external auditory meatus. Next to it is a radiate fibrous layer, composed of connective tissue, the fibres of which are attached to the manubrium of the malleus and radiate from it. Medial to it is the circular fibrous layer, which has its fibres arranged concentrically and is esijecially thick at the cncumference. It is closely bound to the rachate layer. The mucous layer, which is a continuation of the mucosa of the tympanic cavity, covers the medial surface of the membrane smoothl}', except where the manubrium of the malleus causes a pro- jection. The fibrous layers are attached to the fibro-cartilaginous ring and are not present in the pars flaccida. 1088 SPECIAL SENSE ORGANS The Tympanic Cavity The tympanic cavity [cavum tympani], as has been stated, is an air-space, lined with mucous membrane, situated between the external and the internal ear. It is of irregular outline, but, roughty, it is a slit-like cavity, lying in an oblique antero-posterior plane. Its transverse diameter measures only from 2-4 mm., while the vertical and antero-posterior diameters measure about 15 mm. (fig. 834). It is narrowest at the centre, and wider superiorly than inferiorly. The bony walls have already been partly described with the temporal bone, and hence the description given here will refer to the appearance found in the fresh, or un- macerated condition. It will be noticed (see fig. 829) that the floor of the space is on very much the same horizontal plane as the floor of the external meatus, and the lower margin of the tympanic membrane. The roof, on the other hand, lies at a much Fig. 832. — ^Lateral Surface op the Left Membhana Tympani. (Enlarged from life.) Pars flaccida or Shrapnell's membrane Posterior plica Malleolar prominence caused by' lateral process of malleus Long process of incus Malleolar stria 7 Pars tensa of tympanic membrane higher level than the upper margin of that membrane. Hence the cavity may be divided into two regions, a loiver part, corresponding in extent to the tym- panic membrane, and an upper, above the upper border of the membrane, known as the epitympanic recess. This division forms a definite chamber, and con- tains the head of the malleus and the body and short process of the incus. It is on the posterior part of this chamber that the communication with the tympanic antrum is found (fig. 835). As the shape of the tympanum is irregular, its walls are not everywhere clearly marked off from one another, but there may be recognized (figs. 829 and 835) a roof, or tegmental wall, a floor, or jugular wall, a medial or labyrin- thine wall and a lateral or membranous wall, an anterior or carotid, and a pos- terior or mastoid boundary or wall. The roof, or tegmental wall, is formed by a portion of the tegmen tympani, a thin plate of bone which is continued backward to form the roof of the tympanic antrum. This plate is formed by the petrous part of the temporal bone, and at its lateral margin is the petro-squamous suture, where a slight deficiency in the roof may occur. The floor, or jugular wall is very narrow transversely, and is in intimate relation to the internal jugular vein (fig. 831). As shown in fig. 833, the surface is frequently very irregular from stalactite-lilve projections between which are the tympanic cellulas (air cells), while near the back there is occasionally a marked projection corresponding externally to the root of the styloid process. The posterior or mastoid wall presents at its lower part, many additional tympanic ceUulse, and higher up, an elevation, the pyramidal eminence, on whose apex is an aperture transmitting the tendon of the stapedius muscle. The fleshy beUy of that muscle is contained in a cavity in, the interior of the bony pyramid of the posterior wall. Lateral to this is an aperture, the aperiura tympanica canaliculm chorda, through which the chorda tympani nerve enters the tym- panum, covered by a reflexion of the mucous membrane. Between this opening and the pyra- mid is a slight elevation; and above it is a fossa, termed the sinus posterior. Above this again is a recess, where the posterior ligament of the incus is attached, known as the fossa incudis. This portion of the posterior wall forms the boundary of the epitympanic recess. Here the ■cavity of the tympanum is continued with that of the antrum tympanicum, or mastoid antrum, THE TYMPANIC CAVITY 1089 a large irregular space into which open the mastoid cells (see p. 1092). The boundaries of the orifice are formed above by the tegmen tympani, medially by the prominences of the lateral semicircular canal and facial nerve, and laterally by a plate of bone termed the scutum. The carotid (anterior) wall presents superiorly the tensor tympani muscle in its canal, and at a lower level the opening of the tuba audiliva (Eustachian tube) (fig. 835). Inferiorly, a thin, bony wall, covered with tympanic cellulse and pierced by the carotico-tympanic nerves, separates the tympanic cavity from the carotid canal. The membranous (lateral) wall is formed mainly by the tympanic membrane, with the small rim of bone to which it is attached, but superiorly the lateral wall of the epitympanic recess is formed by a plate of bone termed the scutum. The labyrinth (medial) wall (fig. 833) presents inferiorly the promontory, produced by the first turn of the cochlea with the tympanic plexus (Jacobson's nerve) lodged in grooves upon its surface. Inferior and posterior to the promontory is a depression or fossula at the bottom of Fig. 833.- -The Labyrinth (Medial) Wall op the Right Tympanum with the Tympanic Ossicles in Position. Short process of incu: Long process of incus Chorda tympani Facial nerve Pyramidal eminence Tendon of stapedius Stapes Cochlear fossula — Torn edge of mucosa of superior liga- ment of incus Body of incus Neck of malleus Anterior malleolar ligament Lateral process of malleus Chorda tympani j"" Tympanic pies Promontory Tympanic cellulae which is the cochlear fenestra (fenestra rotunda), closed by the secondary tympanic membrane, and posterior to the promontory is a smooth projection, the subiculum of the promontory, which forms the inferior border of a rather deep depression known as the tympanic sinus. Anteriorly and superiorly is the cochleariform process, and superiorly and posteriorly are a depression or fossula leading to the vestibular fenestra (fenestra ovalis), which is closed by the base of the stapes, the prominence of the facial (Fallopian) canal, and the prominence of the lateral semicii'oular canal, the two latter being formed in the medial wall of the entrance to the mastoid antrum. The tympanic mucous membrane forms a complete covering for the walls and contents of the tympanic cavity. It is continuous anteriorly with the mucosa of the tuba auditiva (Eustachian tube) and posteriorly with that of the tympanic (mastoid) antrum and mastoid cells. It is a thin, transparent, vascular membrane intimately united to the periosteum. As it passes from the walls to the contents of the tympanic cavity, besides covering the ligaments of the malleus and the incus and the tendons of the tensor tympani and stapedius muscles, it forms a number of special folds and pouches. The anterior malleolar fold is reflected from the tympanic membrane over the anterior process and ligament of the malleus and the adjacent part of the chorda tympani, and the posterior malleolar fold stretching between the manubrium and the posterior tympanic wall, surrounds the lateral ligament of the malleus and the posterior part of the chorda tympani. Each of these folds presents inferiorly a concave free border, and between them and the tym- panic membrane are two blind pouches, the anterior and posterior malleolar recesses or pouches 1090 SPECIAL SENSE ORGANS of Troltsch. Connected with the posterior recess is a third cul-de-sac, the superior recess of the tympanic membrane, or pouch of Prussak, situated between the pars flaccida of the tym- panic membrane and the neck of the malleus. The floor of this recess is formed by the lateral process of the malleus, and is lower than its outlet; therefore, the recess may serve as a pocket in which pus or other fluid may accumulate. A somewhat variable fold of mucosa, the plica incudis, passes from the roof of the tympanic cavity to the body and short process of the incus. The body and short process of the incus, the head of the malleus, and this fold incompletelj separate off a lateral cupular portion of the epitympanic recess, and a stapedial fold stretches from the posterior wall of the tympanic cavity and surrounds the stapes, including the oburator membrane, which stretches between its crura. Other inconstant folds have been described. The mucosa of the typanic cavity, except over the tympanic membrane, promontory, and ossicles, is covered by a columnar ciliated epithelium. Fig. 834. — The Tympanic Cavity, Antehiob Wall Removed, Epitympanic recess Lateral malleolar ligament Pars flaccida Superior recess Lateral process of Anterior malleolar ligament Insertion of tensor tampani Manubrium of malleus External acoustic meatus Umbo and tip of manubrium of malleus Tympanic cellula Head of malleus Neck of malleus Facial nerve Long process of incus Pyramidal eminence Tendon of stapedius Bones. — The tympanic cavity contains three small movable bones, joined to- gether and to the walls of the cavity, and having attached to them special muscles and ligaments. These auditory ossicles form a chain across the tympanic cavity connecting the tympanic membrane and the vestibular (oval) fenestra. They are the malleus, the incus, and the stapes, and are described in the section on Oste- ology on p. 79. Articulations of the ossicles. — The manubrium and lateral process of the maUeus are im- oedded in the tympanic membrane. The margin of the irregularly elliptical articular surface bn the posterior side of the head of the malleus is bound to the body of the incus by a thin capsular ligament, forming a diarthrodial joint, the incudo-malleolar articulation. From the inner surface of the capsular ligament, a wedge-shaped rim projects into the joint cavity and incompletely divides it. The long crus of the incus lies parallel to the manubrium of the malleus and on its superior and medial aspect (figs. 833 and 835). It ends in the lenticular process. The convex extremity of this fits into the concavity on the head of the stapes, to form a diarthrodial joint, the incudo-stapedial articulation. From its articulation with the incus, the stapes passes almost horizontally across the tympanic cavity to its junction with the medial wall. The cartilage-covered edge of the base is bound to the cartilage-covered rim of the vestibular (oval) fenestra by the annular ligament of the base of the stapes, thus forming the tympano-stapedial syndesmosis. Ligaments of the ossicles. — In addition to the attachment of the manubrium of the malleus and the base of the stapes to the walls of the tympanic cavity, the bones have additional ligamentous attachments. The superior malleolar liga- THE TYMPANIC CAVITY 1091 ment runs almost vertically from the superior wall of the epitympanic recess to the head of the malleus (fig. 834) . The anterior malleolar ligament extends from the angular spine of the sphenoid bone through the petro-tympanic (Glaserian) fissure to the anterior or long process of the malleus, which it surrounds, and is inserted with it into the neck of the malleus. The lateral malleolar ligament is short and thick, and runs from the margins of the tympanic notch (notch of Rivinus) to the neck of the malleus (fig. 834) . The posterior ligament of the incus passes from the fossa on the posterior tympanic wall to the crus brevis of the incus (fig. 835) . The superior ligament of the incus is little more than mucous membrane; it runs from the tympanic roof to the body of the incus. Muscles of the ossicles. — Each of the muscles of the ossicles is contained in a bony canal. The tensor tympani is a pinniform muscle about 2 cm. long. It arises from the cartilaginous part of the tuba auditiva (Eustachian tube), from the Fig. 835. — Medial Surface op Right Membrana Tympani. (Enlarged.) Superior malleolar ligament Incus Head of malleus Chorda tympani nerve Tendon of tensor tympani Manubrium of malleus Tensor tympani muscle Tuba auditiva Posterior ligament of incus Posterior portion of epitympanic recess ■Base of stapes 'Lenticular process of incus Posterior portion of membrana tympani adjacent part of the great wing of the sphenoid, and from the bony walls of the semicanal which encloses it. It ends in a round tendon which turns almost at right angles over the cochleariform process and passes laterally across the tympanic cavity to be attached to the manubrium of the malleus near the neck. It draws the manubrium medially and tightens the tympanic membrane, and is supplied by the motor division of the trigeminal cranial nerve, through the tensor tympani branch from the otic ganglion. The stapedius arises in the interior of the hollow pyramidal eminence. The tendon escapes through the openings at the apex and then turns inferiorly and is inserted on the posterior surface of the neck of the stapes. It draws laterally the ventral border of the base of the stapes and is supplied by the facial nerve. Vessels and nerves. — The arteries of the tympanic cavity are the anterior tympanic from the internal maxillary artery (fig. 451), the stylo-mastoid from the posterior auricular artery, the superficial petrosal from the middle meningeal artery, the inferior-tympanic from the ascending pharyngeal (fig. 446), and the carotio-tympanic branch from the internal carotid. The veins empty into the superior petrosal sinus and into the posterior facial (temporo- maxillary vein). The nerves are the tympanic plexus formed by the tympanic branch of the glosso-pharyngeal (p. 951), and the inferior and superior carotico-tympanic nerves which join the internal carotid plexus of the sympathetic (p. 960). The small superficial petrosal nerve takes its origin from the tympanic plexus, and the chorda tympani crosses the t)"mpanic cavity from the posterior to the anterior wall (p. 948, figs, 738 and 835). 1092 SPECIAL SENSE ORGANS The Antrum Tympanicum The aperture {aditus) in the upper part of the posterior wall of the tympanum leads into the chamber termed the antrum tympanicum. This is a comparatively large cavity, of irregular form, lying mainly behind but also somewhat above and lateral to the tympanum, and extends to the medial end of the external auditory meatus. It is lined by mucous membrane, continuous with that of the tympanic cavity, and into it open the mastoid cells (cellulse mastoidese). These cells are small, irregular cavities in the interior of the mastoid process and they com- municate with one another freely. They vary exceedingly in their size and asrangement. The antrum tympanicum has a roof, formed by the tegmen tympani, a posterior wall, separating it from the bend of the transverse sinus, a lateral wall, lying about 10 mm. from the surface of the head, a inedial wall, and an anterior wall (see also p. 78). The Auditory (Eustachian) Tube The auditory tube [tuba auditiva] (Eustachian tube) (fig. 829) extends from the carotid (anterior) wall of the tympanic cavity inferiorly, medially, and anteriorly to the pharynx. It is about 37 mm. (1.5 in.) long. In the lateral one-third of its length it has a bony wall, while in the medial two-thirds this wall is cartilaginous. The osseous part (see p. 74) begins at the tympanic ostium on the anterior wall of the tympanic cavity. It is in relation medially and inferiorly with the carotid canal, and gradually contracts to its irregular medial extremity, which is the narrowest point in the tube, and is termed the isthmus. The cartilaginous part is firmly attached to the osseous and hes in a sulcus at the base of the angular spine of the sphenoid bone. It gradually dilates in its passage to the lateral wall of the pharynx, where its opening, pharyngeal sotium, is just posterior to the inferior nasal concha (turbinated bone). The walls of the cartilaginous part are formed by a cartilaginous plate which is folded so as to form a trough-like structure, consisting of a medial and a lateral lamina, completed inferiorly by a membranous lamina formed of connective tissue. A small portion of the lumen in the superior part of the cartilaginous tube remains per- manently open; elsewhere the walls are in contact, except during deglutition, when they are opened by the tensor veli palatini muscles. The mucosa of the osseous part is thin, and firmly attached to the bony wall, but in the cartilaginous part it becomes thicker, looser, and folded, and contains mucous glands, especially near the pharynx, where there is also some adenoid tissue. 3. THE INTERNAL EAR The internal ear [auris interna] is the essential part of the organ of hearing. It consists of a cavity, the osseous labyrinth, contained within the petrous portion of the temporal bone, and enclosing a membranous labyrinth. The osseous labyrinth is divided into cochlea, vestibule, and semicircular canals (seep. 80), and the accompanying figures (338-838 )show their position and relations. It will be noticed that the vestibule forms a central chamber, from which the semicircular canals and the cochlea branch off; the former from the superior and dorsal portion, and the latter from the ventral and inferior. It will further be noticed that the bony wall of this vestibule shows depressions and ridges on its interior, which are associated with parts of the membranous labyrinth, viz., an upper recess for the utricle (fovea hemielliptica) and a lower recess for the saccule (foyea hemispherica). There are openings in the bony wall for the entrance of nerves to the different parts of the membranous labyrinth, and for the transmission of the ductus endolymphaticus, as well as the small openings of the semicircular canals (ducts) and the opening of the cochlear canal (or duct). The membranous labyrinth, in which the auditory (acoustic) nerves (cochlear and vestibular) end, lies within the osseous labyrinth, the form of which it more or less closely resembles. Thus the membranous semicircular ducts lie within the bony semicircular canals, the membranous cochlear duct within the bony cochlea; while the vestibule contains two small membranous sacs, the utricle and saccule, with their connections. The membranous structures are much smaller in diameter than the osseous, and are partially separated from the bone by an endothelial-Hned space which is filled with a fluid, the perilymph. The THE MEMBRANOUS LABYRINTH 1093 membranes are in contact, however, with the bony wall along their convex margin, and the utricle, saccule and cochlear canals are in contact with the bony walls over the areas where the nerves enter them. The fluid which fills the mem- branous labyrinth is termed the endolymph. Fig. 836. — The Osseous Labyrinth of the Right Side. (Modified from Soemmerring. Enlarged.) Superior semicircular caiial< Posterior semicircular canal Lateral semicircular canal Vestibule and fenestra ovahs' Second turn of cochlea Cupula of cocMea Ampulla Fenestra cochleari: Commencement of first turn of the cochlea The utricle is an oval tubular sac, whose rounded end lies in the superior and dorsal portion of the vestibule. It is here tightly bound to the elliptic recess (fovea hemielliptica) by connective tissue and by the entrance of the filaments of the utricular division of the vestibular nerve as they pass from the superior 837. — Interior of the Osseous Labyrinth of the Left Side. (Modified from Soemmerring. Enlarged.) -Superior semicircular canal Elliptic recess (fovea hemielliptica) Superficial recess (fo hemispherica Lamina spirali Scaia tympani of cochlea. •Posterior semicircular canal Lateral semicircular canal .Opening common to superior and posterior semicircular canal Internal aperture of vestibular aquseduct ■Internal aperture of cochlear canaliculus macula cribrosa to the wall of the utricle. In the anterior part of the interior of the utricle, an oval, whitish, thickened area, macula acustica utriculi, marks the terminal distribution of the nerve, and posteriorly the utricle is joined by the orifices of the semicircular ducts. Fig. 838. — Interior of the Osseous Cochlea. (Enlarged.) Lamina spiralis Modiolus The saccule is a flattened, oval sac, smaller than the utricle, and situated in the anterior and inferior part of the vestibule. It is bound to the spherical recess (fovea hemisphserica) by connective tissue and by the saccular division of the 1094 SPECIAL SENSE ORGANS vestibular nerve, filaments of which extend from the middle macula cribrosa to the anterior and medial wall of the saccule, to be distributed over a thickened area, macula acustica sacculi. Anteriorly and inferiorly the saccule gradually passes into a short canal, the ductus reuniens, which connects it with the cochlear duct, and posteriorly the very small endolymphatic duct is attached (fig. 839). Fig. 839. — Diagram of the Left Membranous Labyrinth. (Deaver.) Superior and lateral membranous ampullje Superior semicircular duct Cupular CEecum Cochlear duct Dtricle Lateral semicircular duct Posterior membranous ampulla Ductus endolymphaticus This extends through the aquseductus vestibuli to the posterior surface of the petrous portion of the temporal bone, where it ends in a dilated blind pouch, the endolymphatic sac, situated just beneath the dura. Just beyond the saccule, the endolymphatic duct is joined at an acute angle by a short canal of minute calibre, the utriculo-saccular duct, which opens into the utricle through its anterior medial wall and, with the endolymphatic duct, connects it with the saccule. Fig. 840. — Right Membranous Labyrinth of a Newborn Child. Exposed by Partial Removal OF THE Bony Labyrinth. Dorsal view. (Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Facial nerve Osseous lamina spiralis Lamina basilans (membranous *• lamina spiralis) Scala tympani Supenor semicircular duct Common crus Saccule i Posterior membranous ampulla Posterior ampuUary nerve The semicircular ducts (membranous semicircular canals) are situated within the osseous semicircular canals and are, therefore, known as the lateral, superior, and posterior semicircular ducts. They connect with the utricle by five openings, the posterior and superior ducts uniting to form a common crus before their THE MEMBRANOUS LABYRINTH 1095 termination. Each duct is less than a third of the diameter of the bony canal, from which it is separated by a large perilymphatic space, except along the greater cm*vature, where it is attached. The ducts are dilated in the bony Fig. 841. — Schematic Representation of the Right Membranotjs Labyrinth and the Divisions of the Acoustic Nerve. Dorsal view. (Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Utriculo-saccular duct Macula acustica of utricle Macula acustica of saccule Vestibular ganglion Vestibular nerve Saccular nerve \ Cochlear nerve.^^ Cochlear duct " Saccule Ductus reuniens (of Hensen) Posterior ampullary nerve --Superior semicircular duct Ampullary cristae of the superior and lateral semi-circular ducts — , Endolymphatic duct Posterior semicir- cular duct Ampullary crista of the posterior semi- circular duct -" Endolymphatic ; ampullse, producing the lateral, superior, and posterior membranous ampullae, and on the attached surface of each of these there is a transverse groove, the ampullary sulcus, for the ampullary division of the vestibular nerve, and corre- sponding to the sulcus a ridge, the ampullary crista, projects into the interior. Fig. 842. — Axial Section Through the Decalcified Cochlea of a Newborn Child (Toldt, '* Atlas of Human Anatomy," Rebman, London and New York.) Hamulus of lamina spirahs^ Apical spiral'^;;; Helicotrema Modiolus Scala vestibuli Cochlear duct Lamina basilans (membranous lamina' spiralis) Osseous lamina spirabs Spiral ganglion of cochlea Base of modiolus Cochlear nerve Internal acoustic meatus Acoustic nerve (cochlear division) rl^V^ Spiral ligament of cochlea jj;^v^ScaIa tympan f Macula acustica sacculi Wall of saccule Saccular nerve :tibular ganglion Acoustic nerve (vestib- ular division) The cristse in the ampullee of the membranous semicircular ducts and the maculae in the saccule and utricle are superficially covered with fine crystals of calcium carbonate, otoconia (otohths). 1096 SPECIAL SENSE ORGANS The cochlear duct (membranous cochlea or scala media) begins within the cochlear recess of the vestibule in a blind pouch, the vestibular caecum, and traversing the spiral canal of the cochlea, ends just beyond the hamulus of the lamina spiralis in a second blind pouch, the cupular caecum. Close to the ves- tibular caecum it is joined to the saccule by the ductus reuniens. It is lined throughout by epithelium and is somewhat triangular in cross-section. Its floor is formed by thickened periosteum over part of the osseous lamina spiralis and by a fibrous membrane, the lamina basilaris, which stretches from the free border of the lamina spiralis to a thickening of the periosteum, the spiral ligament of the cochlea, on the peripheral wall. The epithelium of this floor is greatly modified, forming the spiral organ (organ of Corti) in which the fibres of the cochlear nerve terminate. The periplieral wall is formed by the thickened periosteum upon the peripheral wall of the cochlear canal, while the third waU is Figs. 843 and 844. — Sections Showing Early Stages in the Development op the Otic Vesicle. fomed by a thin vestibular membrane (membrane of Reissner) which passes from the periphera wall to the osseous lamina spiralis near its free margin, forming with the lamina spiralis an angle Ff 45 degrees. The cochlear duct and the osseous spiral lamina divide the cochlear spiral canal into two parts, one next to the basilar membrane, the scala tympani, and one next to the vestibular membrane, the scala vestibuli. The scala tympani unites with the scala vestibuli at the helicotrema, and from the scala tympani a minute canal, the perilymphatic duct, passes through the cochlear canaliculus and connects with the subarachnoid space. A thin fibrous layer, the secondary tympanic membrane, closes the cochlear fenestra (fenestra rotunda) and thus separates the scala tympani from the tympanic cavity, and the vestibular perilym- phatic space (scala vestibuli) is separated from the tympanic cavity by the base of the stapes in the vestibular fenestra (fenestra ovalis). Vessels and nerves. — The internal auditory artery , fig. 514), a branch of the basilar artery, accompanies the cochlear and vestibular nerve. It supplies the vestibule, semicircular canals, and cochlea, and their membranous contents. The blood is returned by the internal auditory vein into the inferior petrosal sinus, and by small veins which pass through the cochlear and vestibular aqueducts to the inferior and superior petrosal sinuses. The acoustic nerve (p. 949, figs. 841 and 842) consists of a vestibular and a cochlear division. The membranous ampuUse of the semicircular ducts and the acoustic maculae of the utricle and saccule are supplied by the vestibular nerve. The spiral organ (organ of Corti) in the cochlear duct is supphed by the cochlear nerve. Development of the Ear The external and middle ears have a common origin quite distinct frorn that which gives rise to the internal ears, and are to be regarded as portions of the branchial arch apparatus secondarily adapted to auditory purposes. The sensory epithelium lining the internal ear is derived from the otic vesicle, a structure formed from the surface epithelium of the head, while the membrane and bones surrounding it are formed from the mesoderm which surrounds the vesicle. DEVELOPMENT OF THE EAR 1097 Internal ear. — The process of development is as follows (fig. 843-845) : — By invagination from the surface, an epithelial-lined vesicle, termed the primitive otocyst or otic vesicle, is formed dorsal to the extremity of the second branchial cleft. It is at first merely a pit on the surface, but eventually it loses its connection with the surface epithe- lium and sinks into the interior. It then undergoes the alterations in shape and form shown in the accompanying fig. 845. The vesicle is at first somewhat oval, and a small hollow stalk arises from it, the recess of the labyrinth, which forms the ductus endolymphaticus in the adult. The ventral and dorsal portions of the cyst become enlarged. From the former two hoUow plate-like projections arise, one placed vertically, the other horizontally, and along the free margins of these plates are formed the semicircular ducts, the superior and posterior from the vertical, and the lateral duct from the horizontal one. The central part of each plate be- comes peforated, and the periphery is thus altered to the characteristic loop form of the adult semicircular ducts. The portion of the vesicle lying between the dorsal and ventral enlarge- ments forms the primitive atrium. It becomes divided into two chambers, an upper dorsal connected with the semicircular ducts, forming the utricle, and an inferior ventral, the saccule, which is connected with that portion of the ventral expansion from which the cochlea is formed. The recess of the labyrinth retains its connection with the cavity of the vesicle at the narrow stalk connecting utricle and saccule, (fig. 845). The cochlea is formed by an outgrowth from the saccule, at first straight, and later coiled in the fashion formed in the adult. Fig. 845. — Diageams Illustrating Successive Stages in the Development of the Membranous Ear. Semicircular canals Ductus endolym- Semicircnlar Ductus endo- •i^^HSBmiiN. I canal lymphaticus Vestibular pouch Recessus Cochlear pouch Ductus reuniens Saccule Utricle Ductus reuniens Cochlea External and middle ear. — The external auditory meatus is formed from the dorsal part of the first (external branchial) pouch, and the tympanic membrane from the membrane which forms the floor of that pocket and separates it from the corresponding pharyngeal (internal) pouch. Its outer surface is thus formed from ectoderm and the inner from endoderm. The internal (pharyngeal) groove gives origin to the tympanic cavity and tuba auditiva, the margins of the groove uniting. The auricle is formed from nodular thickening of the tissue bounding the outer end of the first branchial cleft. Three nodules are formed on the first (mandibular) and three on the second (hyoid) arch. Behind the latter, the free margin of the auricle is formed by a folding off of the integument. Later an additional tubercle is formed dorsally between the two sets of nodules. From the mandibular nodules are formed mainly the tragus and the crus of the helix — from the hyoid tubercles the scaphoid fossa, antitragus and the crus of the anthchx. The auditory ossicles, and their muscles are formed from the neighbouring arches, the malleus and incus, together with the tensor tympani, being derived from the first arch, while the stapes and stapedius probably are derived from the second arch. The tympanic cavity is at first quite small, but later increases greatly, partly by the con- densation bf the loose areolar tissue which underlies its mucous membrane, the auditory ossicles and their muscles being thus apparently brought within the cavity, and partty by the absorption of the neighbouring bone. By this latter process the antrum and the tympanic and mastoid cells are formed, all these depressions or cavities being lined by mucous membrane continuous with that of the tj'mpanic cavit}'. The Ear in the Child. — The ear in the newborn child shows several marked differences from the adult ear. Among the principal differences are the following: — 1. The external auditory meatus is very short, since the bony portion is undeveloped, and is represented only by the tympanic ring. As a result of this, the tympanic membrane is placed on a level with the surface of the head, and looks very much downward. 2. The mastoid or tympanic antrum is relatively very large, and lies above and behind the tympanum. Its lateral wall is only about 1 mm. in thickness. 3. The mastoid process is not developed, and hence the stylomastoid foramen opens on the surface behind the lower part of the tympanic ring. The exit of the facial nerve is therefore much more upon the surface, and higher up than in the adult. 4. The auditory (Eustachian) tube is nearly horizontal in direction. 5. The ossicles are of nearly the] same size as in the adult. 1098 SPECIAL SENSE ORGANS References for the Special Sense Organs. — For the development of the various sense organs, see article by Keibel in Keibel and Mall's Human Embryology, vol. 2. A. Visual. Graefe-Saemisch, Handbuch d. ges. Augenheilkunde; Salzmann, Anat. u. Histol. d. Augapfels, 1912; various papers in Archiv f. Oph- thalmologic; (Anterior chamber, etc.) Henderson, Ophthalmic Review, 1910-11; {Optic disc) Johnson, Phil. Trans. Royal Soc. B. vol. 194; B. Auditory. Gray, Labyrinth of Mammals, 1910; (Tectorial membrane, etc.) Hardesty, Amer. Jour. Anat., vol. 8; (Auditory nerve, comparative) Holmes, Trans. Royal Irish Acad., vol. 32, ser. B; (Experimental embryology) Lewis, Amer. Jour. Anat., vols. 3, 7; C. Olfactory. Read, Amer. Jour. Anat., vol. 8. D. Taste. Von Ebner, in Koel- liker's Handbuch d. Gewebelehre; Graberg, Anat. Hefte, Bd. 12. SECTION IX DIGESTIVE SYSTEM Revised for the Fifth Edition By C. M. JACKSON, M.S., M.D., PROFESSOR OF ANATOMY IN THE UNIVERSITY OF MINNESOTA IN order to furnish the living protoplasm with the materials necessary for energy, growth and repair, a constant supply of food must be provided. Most foods must be rendered soluble, and must undergo certain preliminary chemical changes, in order to render them suitable for absorption and assimilation by the cells of the body. For this preparation of the food-supply, the digestive system [apparatus digestorius] is provided, which includes the alimentary canal and certain accessory glands (salivary glands, liver and pancreas) . The alimen- tary canal is divided into a number of successive segments, varying in size and structure according to their function. These segments (fig. 846) include the mouth, pharynx, oesophagus, stomach, small and large intestines. Typical structure. — The most important layer of the tubular alimentary canal is the inner mucous memhrane [tunica mucosa]. From its epithelial lining, the various digestive glands are derived, and through it the process of absorption takes place. The epithelium is supported by a fibrous tunic [lamina propria mucosa;] beneath which is a thin layer of smooth muscle [lamina muscularis mucosae]. The layer next in importance is the muscular coat [tunica muscu- laris] which propels the contents along the canal. It is typically composed of two layers of smooth (involuntary) muscle, the inner circular and the outer longitudinal in arrangement. Between the mucosa and the muscularis is a loose, fibrous submucous layer [tela submucosal, which allows the folds in the mucosa to spread out when the canal is distended. Finally, there is an outer fibrous coat [tunica fibrosa], which in the abdominal cavity becomes the smooth serous coat [tunica serosa], or visceral layer of the peritoneum, which eliminates friction during movements. The variations in the structure of the aUmentary canal in different regions are due chiefly to differences in the mucosa. Glands. — Since the glands form an important part of the digestive system, the classifica- tion of glands in general will be discussed briefiy. A gland may be somewhat loosely defined as an organ which elaborates a definite substance which is either a waste product to be eliminated (excreted), or a secretion to be further utilized by the organism. Glands may be divided into (a) ductless glands (e. g., spleen, thyreoid gland), which pour their secretions directly into the blood or lymph; and (b) glands with ducts, which open upon an epithelial surface. Some organs, however, belong in both classes (e. g., liver, pancreas). The glands with ducts (the so-called true' glands) are always derived from an epithelial surface and may be further subdivided upon the basis of either (1) form or (2) cell-structure. According to form, glands are classified as either retromandibular fossa (fig. 863), extending from the zygomatic arch above to the angle of the mandible below. Form and relations. — The parotid is somewhat prismatic or wedge-shaped (figs. 863, 864), with three surfaces and three borders or angles. The lateral sur- face is covered by skin and superficial fascia, and in its lower part by the platysma. The anterior surface overlaps the masseter and extends medialward in contact 1114 DIGESTIVE SYSTEM with the posterior border of the mandibular ramus and with the posterior aspect of the internal pterygoid muscle. An irregular "pterygoid lobe" may extend between the internal and the external pterygoid muscles. The posterior surface is in contact with the sternomastoid muscle laterally, and with the styloid process and associated muscles medially. Between the sternomastoid and styloid process it touches the posterior belly of the digastric, and is in relation with the internal carotid and jugular vessels. The various structures in contact with the parotid gland often make more or less distinct grooves upon its posterior and anterior surfaces. Borders. — -The anterior border usually extends from below obliquely upward and forward so as to give the whole superficial surface a triangular appearance. Near the upper end of the anterior border, the parotid duct leaves the gland, and just above this there is usually a small separate accessory lobe [gl. parotis acces- soria], of variable form and size. The branches of the facial nerve also emerge from the anterior border. The posterior border extends along the anterior aspect of the sterno-mastoid muscle up to the mastoid process. The medial border is deeply placed (at the junction of the anterior and posterior surfaces), and approaches the wall of the pharynx. The upper extremity of the parotid sends a process into the posterior part of the manibular fossa, behind the condyle of the mandible, and is related with the Fig. 865. — Diagram op Horizontal Section Showing the Parotid Compartment and Relations. Arrow indicates opening in sheath. (Modified from Woolsey after Testut.) EXTERNUi CAROTI9 ARTERY l»HAHYN- FACIAL . -, , —»,, NER\ PAROTID APONEU- ROSIS _ SUPERFIC t M ■ LAYER ^ ^^=>, \STYLOII 'LAYER 1 I ' \yif^ ^~S!K) ^PROCESS AND ITS MUSCLES external auditory meatus. From the upper extremity emerge the superficial tem- poral vessels and the auriculo-temporal nerve. The lower extremity is separated by the stylo-mandibular ligament from the posterior end of the submaxillary gland. Fascia. — As shown in fig. 865, the parotid gland is enclosed in a sheath (called the parotid fascia or aponeurosis) derived from the deep fascia of the neighbourhood. The superficial layer of the sheath covers the lateral surface of the gland, while the deep layers correspond to the anterior and posterior surfaces of the gland. The sheath is very feeble or deficient at the medial angle. The superficial and deep layers of the parotid sheath unite below to form a thick fascial band extending from the angle of the mandible to the sterno-mastoid muscle. Contents. — Within the sheath, the parotid gland is in intimate relation with numerous important structures. Extending along the medial border, and partly embedded in the gland, is the external carotid artery, dividing above into the superficial temporal and internal maxillary (including the origins of the deep auricular and transverse facial); and the posterior facial (temporo-maxillary) vein and branches. The auriculo-temporal nerve passes through the upper part of the gland, while the facial nerve passes somewhat horizontally through it, dividing into its temporo-facial and oervico-facial divisions. Finally, there are embedded m the gland two or three deep lymphatic nodes, which receive lymphatic vessels from the external auditory meatus, the soft palate and the posterior part of the nasal fossa; and several superficial_ nodes, which receive lymphatic vessels from the temple, eyebrows and eyelids, cheek and auricle. Structure. — The parotid is a racemose gland of the serous type. THE SUBMAXILLARY GLAND 1115 Duct, vessels and nerves. — The duct of the parotid (Stenson's) issues from tlie anterior bor- der of the gland, crosses the masseter a finger's breadth below the zygoma, and turns abruptly medialward round its anterior border. It penetrates the fat of the cheek and the fibres of the buccinator muscle, between which and the mucous membrane it runs for a short distance before it terminates, sometimes on the summit of a little papilla, by a minute orifice. This opening is placed opposite the crown of the second upper molar tooth. The duct commences by numerous branches, which converge toward the anterior border of the gland, and receives in its passage across the masseter the duct of the accessory parotid gland. The canal is about the size of a crow-quill, length about 35 to 40 mm., diameter 3 mm. Its mucous membrane is covered for a short distance, beginning with its oral termination, by stratified pavement epitheUum, for the remainder of the distance by columnar epithelium. The coat of the duct is thick and tough, and consists of fibrous tissue intermixed with nonstriated muscle-fibres. The arteries are derived from those lying in the gland substance and from the posterior auricular artery. The veins terminate in the posterior facial (temporo-maxillary) trunk. The nerves. — The parotid gland receives its secretory fibres from the otic ganglion, con- veying impulses from the glosso-pharyngeal via the lesser petrosal and the auriculo-temporal; its sensory supply through branches of the fifth nerve; and its sympathetic supply from the carotid plexus. The lymphatics from the parotid gland terminate in the superficial and deep cervical glands, especially in the deeper group of parotid nodes embedded in the substance of the gland. Variations. — The parotid is quite variable in size and in the form of its various processes, especially of the accessory lobe, as already mentioned. The lobulations are less distinct in infancy. Rarely the parotid is confined to the masseteric region, the retro-mandibular fossa being filled with a fatty tissue enclosing the vessels and nerves normally found with the gland. THE SUBMAXILLARY GLAND The submaxillary gland [gl. submaxillaris] weighs 7 to 10 grams, and is of about the form and size of a flattened walnut. It consists of a chief or superficial part, and a smaller deep process. The chief portion is located in the digastric triangle, and presents three surfaces — superficial, deep and lateral (figs. 847, 866). Fig. 866. — Medial View of the Submaxillary and Sublingual Glands. (Sobotta — McMurrich's Atlas.) Sublingual caruncle Ductus sublingualis major Orbicularis Labial glands Minor sublingual ducts ^Submaxillary ducts ---Lingual nerve ,Deep process of ^ submaxillary / 'A Genio-glossus Gemo-hyoideus Mylo-byoideus Submaxillar; gland Surfaces. — The superficial or latero-inferior surface is covered by skin, super- ficial fascia, platysma and deep fascia (which forms an incomplete capsule around the gland). It is crossed by the facial vein and by cervical branches of the facial nerve. Several lymphatic glands, which receive vessels from the anterior facial region, lie upon or embedded in this surface. The lateral surface is the smallest of the three. It is in contact with the sub- maxillary fossa of the medial surface of the mandible, and with the lower part of the internal pterygoid muscle. The posterior aspect of the gland is deeply grooved by the external maxillary (facial) artery and is separated from the parotid gland by the stylo-mandibular ligament. The deep or medio-superior surface is in contact with the lower surface of the mylohyoid, and behind this with thehyo- 1116 DIGESTIVE SYSTEM glossus, stylohyoid and posterior belly of the digastric. Between this surface and the mylohyoid muscle are the mylohyoid nerve and artery and the sub- mental artery. The deep portion is a tongue-like process which passes from the deep surface of the submaxillary gland around the posterior border of the mylohyoid muscle, and extends forward in company with the duct, under cover of (above) the mylo- hyoid, and in relation with the hyoglossus and genioglossus muscles. At its commencement, the deep process lies just below the submaxillary ganglion and ■ anteriorly it gives off the submaxillary duct as it approaches the sublingual gland. Structure. — The submaxillary is a racemose gland belonging to the mixed type, some of the acini being serous, others mucous (fig. 867). The submaxillary (Wharton's) duct springs from the deep surface of the superficial part of the gland; it passes forward and inward, along the medial surface of the deep lobe, and opens by a small orifice on the summit of a papilla [caruncula sublinguahs] by the side of the frenulum of the tongue. It is crossed superficially by the lingual nerve. It hes at first between the mylo- FiQ. 867. — Section op the Submaxillary Gland op an Adult Man. X 252. (Lewis and Stohr.) Mucous gland cells Connective tissue Secretory duct hyoid and hyoglossus; next, between the mylohyoid and genioglossus; and lastly, under cover of the mucous membrane of the mouth, between the genioglossus and the sublingual gland. The duct is about 5 cm. in length, and has comparatively thin walls. It is lined by columnar epithelium. Vessels and nerves. — The arteries to the gland are derived from the external maxillary (facial) and lingual, and they are accompanied by corresponding veins. The nerves. — The submaxillary gland receives its secretory fibres from numerous small sympathetic ganglia situated on the submaxillary duct and in the hilus of the gland, these conveying impulses from the chorda tympani; its sensory branches probably come from the geniculate ganglion, and its sympathetic branches from the cervical sympathetic. Variations. — Absence of the gland is a rare anomaly. A case is recorded (Turner) where the submaxillary was placed entirely under cover of the mylohyoid, being closely associated with the sublingual gland. THE SUBLINGUAL GLAND The sublingual gland [gl. sublingualis] — the smallest of the salivary glands (2 to 3 gm.) is in reality a group of glands forming an elongated mass in the floor of the mouth under the tongue (fig. 847) . Above, it forms a distinct ridge, covered by a fold of mucosa (plica sublingualis) upon which its ducts open (fig. 866). It is flattened from side to side, its loioer border resting upon the upper surface of the mylohyoid, its lateral surface in contact with the sublingual fossa of the mandible, and its medial surface with the geniohyoid, geniohyoglossus, lingual nerve, deep lingual artery and submaxillary duct (fig. 863). Anteriorly it touches its fellow of the opposite side, while 'posteriorly it is often related with the deep process of the THE TEETH 1117 submaxillary gland. It has no distinct capsule, thus differing from the submaxil- lary and parotid glands. In structure, it is a racemose mixed gland, but predomi- inantly mucous. Ducts. — The minor sublingual duels [ductus sublinguales minores], ducts of Rivinus, vary from five to fifteen or more in number, and open on minute papillae along the crest of the plica sublingualis (fig. 858). The anterior portion of the gland often forms a larger [Bartholin' s) duel [ductus sublingualis major] which opens alongside the submaxillary duct on the caruncula sublingualis (figs. 858, 866). Vessels and nerves. — The arteries are derived from the sublingual and submental, with corresponding vci^is. The lymphatics are tributaries of the superior deep cervical nodes. Nerves. — The sublingual glands receive their secretory fibres from the subma.xillary and associated sympathetic ganglia, conveying impulses from the chorda tympani; sympathetic, branches come from the cervical sympathetic and sensory fibres probably from the geniculate ganglion, although this question needs further investigation. Development of the salivary glands. — The salivary glands appear early as buds from the ectodermal epithelium extending into the adjacent mesenchyme of the mouth cavity. The parotid appears first on the side of the mouth cavity in an embryo of 8 mm., as a groove which becomes tubular and pushes back over the masseter to the ear region, developing branches (at first solid). Around the gland and between the branches is mesenchyme which becomes condensed to form the peripheral capsule. The submaxillary gland appears in the 13 mm. embryo as a ridge in the epithelium of the alveolo-lingual groove. The solid cord (lumen appearing later) grows forward to the region of its adult orifice. Its posterior end extends backward and gives off solid branches which later form the acini and duct system of the mature gland. The sublingual glands appear somewhat later (24 mm. embryo) as a series of separate anlages of variable number, budding off in the positions where the adult ducts empty. The major sublingual gland, if present, appears fii'st. The histogenetic development of the salivary glands is not completed until some time after birth, probably about the time of weaning. However, mucin cells appear in the sublingual glands in the foetus of four months and serous cells in the parotid of five months. Variations. — The duct of Bartholin is present in about half of the cases, and the corre- sponding anterior part of the gland may be more or less separate [gl. sublingualis major]. The number of ducts may reach thirty (TiUaux). Rarely processes from the gland may penetrate the mylohyoid, appearing on its lower surface in one or more places (Moustin). Most of the variations in this and the other salivary glands are due to developmental irregularities. Comparative. — Oral glands are not found in the lower aquatic vertebrates. Mucous glands occur in all terrestrial vertebrates, but true sahvary (digestive) glands appear only in mammals. Although great variations occur in the different species of mammals, those in man (excepting the anterior lingual) are typical for the order. The sublingual gland, however, often occurs as two separate glands, corresponding to the sublinguaUs major and minor. The parotid gland apparently has no representative in forms below mammals. In some mammals (e. g., monkey) it has two main lobes — a larger superficial and a smaller deeper lobe between which lies the facial nerve (Gregoire). Other oral glands (e. g., orbital, zygomatic) appear in some mammals. THE TEETH The teeth [dentes] are highly specialized structures developed in the oral mucosa as organs of mastication and also (in man) of speech. The adult indi- vidual with perfect dentition has thirty-two teeth, arranged arch-like in the sock- ets (alveoli) of the maxilla and the mandible. Sixteen belong to the upper or maxillary arch; and sixteen to the lower or mandibular. The four central teeth in each dental arch are the incisors; the tooth next to these on each side is the canine; behind these are the two premolars (bicuspids) ; and lastly the three molars. This relation of teeth is expressed by the following dental formula: .21 2 3 „„ i2,Cj-,pm2,m3 = 32. Form. — Each tooth [dens] has a crown [corona dentis], the portion exposed beyond the gum, and covered with enamel (figs. 871, 872). The root [radix den- tis] is the portion covered with cementura and embedded in the bony socket. At the line of union of crown and root is the slightly constricted neck [coUum dentis]. The surface of the tooth directed toward the lip (or cheek) is termed the labial (or buccal) surface [facies labialis; f. buccalis]; while that toward the tongue is the lingual surface [f. lingualis]. The crowns of the opposite arches meet at the masticating surface [f. masticatoria]. The surfaces in contact with the adjacent teeth of the same arch [facies contactus] are, for the incisors and canines, termed medial and lateral, while those for the premolars and molars are termed anterior and posterior. 1118 DIGESTIVE SYSTEM Structure. — As shown in longitudinal section (fig. 873), each tooth has a central cavity [cavum dentis] or pulp cavity, which is filled with pulp [pulpa dentis]. The pulp is a soft fibrous tissue richly supplied with vessels and sensory nerves which enter the root canal through the apical /orame?i [foramen apicis dentis]. The body of the tooth, both crown and root, is composed of a dense modified variety of bone called dentine [substantia eburnea]. It is yellowish in colour. The striated appearance of the dentine is due to numerous fine canals, the dentinal ; ' ':■ Fig. 868. — Teeth of an Adult, Exteknal View. Incisors Canine Premolar Molars Wisdom tooth Fig. 869. — Teeth of Adult, Lingual Fig. 870. — Teeth of Adult, Labial and Surfaces. (Broomell and Fischelis.) Buccal Surfaces. (Broomell and Fische- lis.) Fig. 871. — Canine Tooth, Lingual Surface. Fig. 872. — A Molar Tooth in Section. n* Root Cusp fP^^^^) ~ -Pulp cavity Neck Cingulum tubules. These contain 'Tomes' fibrils,' which are long protoplasmic branches of the odonto- blasts, a layer of cells on the surface of the pulp. At the outer surface of the dentine are numer- ous small, irregular interglobular spaces, corresponduig in the root to Tomes' 'granular sheath' (fig. 873). The dentine of the crown is covered with a layer of white enamel [substantia adamantina], which is the hardest substance in the body. It is composed of numerous mmute THE TEETH 1119 hexagonal -prisms [prismata adamantina] which are arranged perpendicular to the surface and are of epithelial origin. In adult teeth, the enamel is often worn through in places, exposing the yellowish dentine. The dentine of the root is covered by a thin layer of cementum [sub- stantia ossea], a layer of bone which is very thin at the neck, but becomes thicker toward the root apex (fig. 873). Surrounding the root is the aUeolar periosteum, a fibrous membrane connecting the cementum firmly with the bony lining of the socket. For further details of the minute structure of teeth, works on histology may be consulted. Gums. — Covering the alveolar portions of the maxilla and mandible are the gums [gingivae]. They are continuous with the mucosa of the vestibule exter- FiG. 873. — Vertical Section op an Inferior Canine Tooth, in Situ. Toldt's Atlas.) X 4. (From Transition from mandibular to i^\ ^ alveolar periosteum Pulp capillaries Alveolar periosteum Cementum Compact bone of mandible Marrow spaces of mandible nally and of the palate or floor of the mouth internally. Like the mucosa of the mouth elsewhere, they are covered with stratified squamous epithelium. The lamina propria is especially thick and strong, and is firmly attached to the sub- jacent bone. Around the neck of each tooth, the epithelium of the gum forms an overlapping collar and the lamina propria is continuous with the alveolar perios- teum (fig. 873). The incisors.— (Figs. 868, 869, 870, 874.) The incisor teeth [dentes incisivi] are so named on account of then: function in cutting the food. The crown has a 1120 DIGESTIVE SYSTEM characteristic chisel shape. The masticating surface is narrow and chisel-edged. In recently erupted teeth, the cutting edge is elevated into three small cusps, which soon wear down, leaving a straight edge. These cusps correspond to three indistinct ridges on the labial surfaces. The lateral angle of the crown is usually more rounded than the medial. The labial surfaces are slightly convex, the lin- FiG. 874. — Cross-Section of the Medi ^i. Upper Incisor, in Situ. X 4. (From Toldt's \tl IS 1 Dentine of root of tooth Root canal of tooth' Alveolar periosteum Wall of dental alveolus gual slightly concave. The contact surfaces are somewhat triangular. The roots of the incisors are single, though often longitudinally grooved, indicating traces of a division. They are somewhat conical, but flattened from side to side, expecially the lower set, and are slightly curved lateralward. The upper or maxillary incisors are much larger than the lower. They are lodged in the premaxilla, and are inclined downward and forward. They overlap the lower incisors in masti- cation, hence the masticating surface is worn off and rounded at its posterior edge, while the anterior edge becomes sharp and chisel-hke. The lingual surfaces of the crowns terminate near the gum in a low, inverted V-shaped ridge, the basal ridge or cingulum. At the apex of Fig. 875. — Variations in the Form of the Upper Third Molar. (BroomellandFischelis.) the V, near the gum, there is often (especially on the lateral incisor) a smaU lingual cusp. The medial upper incisor is distinguished from the lateral by its much larger size. The lower or mandibular incisors are smaller than the upper, the cutting edges being only about half as wide. Being overlapped by the upper set, the lower incisors have the masti- cating surface worn ofT anteriorly, leaving a sharp cutting edge posteriorly. The lower mcisors are vertically placed, and the crown becomes narrower toward the neck. A cingulum is rarely visible. The medial lower incisor, unlike the upper, is slightly smaller than the lateral. The canines.— (Figs. 868, 869, 870, 871.) The canine teeth [dentes canini] so-called from their prominence in the dog-tribe, are the longest of all the teeth (fig. 868). The crown is thicker and more conical than in the mcisors. The mas- ticating surface forms a median angular poi nt, on either side of which the cutting THE TEETH 1121 edge slopes to the lateral angle. The medial limb of the cutting edge is usually somewhat shorter than the lateral, rendering the crown asymmetrical. The labial surface is convex, the lingual somewhat concave. The root is single, long, flattened from side to side and grooved on the sides as in the incisors. The canine root is usually slightly curved lateralward. The bony alveolar protuberances [juga alveolaria] are more prominent than those of any other teeth. The upper canine slants forward and overlaps the lower, as in the incisors. The upper canine also presents a well-marked cingulum, and usually a distinct lingual cusp (fig. 871) below which a slight median ridge extends along the lingual surface. On the lower canine, these structures are poorly marked or absent. The lower canine is somewhat smaller than the upper, and its root is occasionally bifid. The premolars.— (Figs. 868, 869, 870, 876, 877.) The premolars [dentes premolares] are so named on account of their position in front of the molars. The Fig. 876. — Dissection Showing the Roots op the Teeth. Teeth in Occlusion. X 1 (From Toldt's Atlas.) Buccal surface Wisdom tooth Premolar teeth Mental foramen crown presents on the masticating surface two prominent cusps, on account of which the premolars are often called 'bicuspids.' The buccal and lingual sur- faces are convex especially from side to side, so that the crown is somewhat cylindrical in form, with flattened, quadrilateral anterior and posterior contact surfaces. The root is (usually) single and more or less flattened antero-posteriorly, and usually somewhat curved backward. The upper premolars are distinguished from the lower by a greater antero-posterior flatten- ing of the crown and by a deep groove separating the cusps (excepting at their anterior and posterior margins) on the masticating surface. In the first upper premolar the lingual cusp and surface are decidedly smaller than the buccal; and the root is frequently bifid or double (occasionally even triple). In the second upper premolar the lingual cusp and surface are as large as the buccal; and the root, though deeply grooved, is rarely bifid. In the lower premolars, the crowns are more cylindrical in form, and the cusps are united by a median ridge so that the masticating surface presents two small pits. The roots are more rounded and tapering, and rarely grooved. In the first lower premolar (like the corresponding upper) the lingual cusp and surface are much smaller than the buccal, the lingual cusp some- times being rudimentary; while in the second they are more nearly equal. The second lower premolar is often slightly larger than the first, while in the upper premolars the converse is true. It should be noted, however, that the premolars are quite variable in all respects, and it is therefore often difficult to identify the individual isolated teeth. The molars.— (Figs. 868, 869, 870, 872, 875, 876.) The molars [dentes mol- ares] or 'grinders' are characterized by their large size, and by the presence of 1122 DIGESTIVE SYSTEM three to five masticating cusps (hence sometimes called 'multicuspids')- The crowns are massive, somewhat resembling rounded cubes, and the lingual and buc- cal surfaces present vertical grooves continuous with the fissures separating the cusps. The pulp cavity (fig. 872) has slight extensions corresponding to the cusps, and also communicates with the canals of the roots, which are usually two or three in number, and more or less curved. Fig. 877. — Diagram Showing the Articulation of the Teeth. (Poirier-Charpy.) labial-!/, WcalA Vlmgual ^"8"^^ buoci -lingual The upper molars are most easily distinguished from the lower by the presence of a triple root. The masticating surface is nearly square with rounded angles. They each have typically four cusps, separated by grooves resembling a diagonally placed H (fig. 852). The crowns of the upper molars are obliquely placed so as to slant downward and slightly lateralward. Each upper molar has three roots, two buccal and one Ungual or palatal. They are aU (especially the buccal) in more or less close relation with the floor of the maxillary antrum (of Highmore) (fig. 876). The buccal roots are flattened antero-posteriorly, and longitudinally grooved, and bent backward. The palatal root is more rounded, with a groove on the hngual surface, and usually bent medialward. Either of the buccal roots may fuse with the palatal, or there may be an extra fourth root. As to the individual upper molars, the first has almost invariably four typical cusps (rarely only three, or with an additional fifth rudimentary). The second upper molar has only three cusps in about half of the cases (in Europeans), and four in the remainder. The third, or wisdom tooth [dens serotinus] is exceedingly variable in size and form (fig. 875). It has three cusps much more frequently than four, and its three roots are often more or less fused into a conical mass. It is usually much smaller than the other molars, and is absent in nearly one-fifth of all cases. Fig. 878. — Diagrams Showing the Early Development or Three Teeth, One of which IS Shown in Vertical Section. (Lewis and Stohr.) Epithelium of the margin Enamel Dental of the jaw organs groove Dental ridge Z^-'''^ Papillae A B Enamel organs Necks of enamel organs C D The lower molars have usually four or five cusps (two lingual, and two or three buccal) the fissures separating them being cross-shaped or stellate (fig. 864). The crowns incUne upward and slightly medialward. They have each two roots, anterior and posterior, flattened antero-posteriorly, and usually somewhat curved backward. The roots, especially the anterior, may be longitudinally grooved. The anterior has two root-canals, the posterior usually only one. The apices of the roots of the lower molars, especially of the third, approach the man- dibular (inferior dental) canal (fig. 876). Of the individual lower molars, the first is usually slightly the largest, and has five cusps in the great majority of cases (variously estimated at from 60 to 95 per cent.), otherwise four. The four main cusps (two buccal and two lingual) are separated by a cruciform fissure, which bifurcates posteriorly to embrace the small fifth cusp (which is placed shghtly to the buccal THE TEETH 1123 side) when present. The second lower molar has usually four cusps (75 to 85 per cent, of cases) , otherwise five, the fifth usually small or rudimentary. The roots are sometimes confluent. The lower third or wisdom tooth, like the upper, is usually small and exceedingly variable (fig. 875). It has usually four or five cusps; but the number may be increased to six or seven, Fig. 879.^Modei, of Ectoderm op Jaw of Hitman Embryo 40 mm. Long, Showing Dental Ridge with Enamel Organs for the First Teeth. (Kingsley, after Rose.) , or reduced to three, two, or one. The roots are often short and fused into a conical mass in which sometimes only a single canal is present. The dental arches. — On comparing the upper and the lower dental arches, it is seen that the upper (fig. 852) forms an elliptical curve, while the lower (fig. 864) resembles a parabola. Fig. 880. — Section Showing Later Stages op Tooth Development. (Szymonowicz.) ^^ ^ .Epithelium of oral cavity Enamel - pulp Inner _ enamel'" cells Neck of enamel organ Dental ridge of permanent tooth , Bone trabecu- l3s of lower jaw The upper arch is slightly larger (due chiefly to the slant of the teeth, as previously explained) so that it shghtly overlaps the lower when the teeth are in occlusion. Thus, as showli in fig. 876, the upper incisors (and canines) overlap the lower. The buccal cusps of the lower pre- molars and molars fit into the groove between the upper buccal and lingual cusps; while the upper lingual cusps correspond to the groove between lower buccal and lingual cusps. This arrangement favors a more perfect mastication (see fig. 877). Moreover, when viewed from the side (fig. 876), it is seen that in general, the corresponding teeth of the upper and the lower arches are not opposite, but alternate with each other. This is 1124 DIGESTIVE SYSTEM due chiefly to the great width of the upper central incisor. The lower molars, however, es- pecially the third, are wider (antero-posteriorly) than the upper, so that the two arches are nearly equal in length. The interdental line between the two arches is not straight, but shghtly convex downward (fig. 876). In both arches, the crowns of the incisors and canines are taller than those of the premolars and molars. Vessels and nerves. — The vessels and nerves of the teeth are distributed partly to the pulp and partly to the surrounding alveolar periosteum. The arteries are all derived from the internal maxillary. Those for the upper teeth are the posterior superior alveolar and the anterior superior alveolar (from the infraorbital). Similar branches to the lower jaw are given off by the inferior alveolar. They give off twigs to the gums (rami gingivales), the alveolar Fig. 881. — Hard Palate op a Child of Five Years, Showing Decidtjous Teeth. Gubernacular canal _ Palate process of maxilla Greater palatine foramen palatine foramea periosteum (rr. alveolares), and the pulp cavities (rr. dentales). A dental branch enters each root canal through the apical foramen, and breaks up into a rich peripheral capillary plexus under the odontoblast layer. From this plex-us, the corresponding veins arise. There is a plex-us of peridental lymphatics, which anastomose with those of the surrounding gums, and drain chiefly into the submaxillary nodes. Lymphatics have also recently been demonstrated in the pulp of the tooth (Schweitzer). The nerves are sensory branches derived from the trigeminus. Those for the upper teeth are from the anterior, middle, and posterior superior alveolar (fig. 735); while those for the lower teeth are from the inferior alveolar (fig. 736). These nerves give numerous branches to Fig. 882. — The Deciduous Teeth, External View. Incisors Canine Deciduous molars Maxillary or upper set Mandibular or lower set the gums, alveolar periosteum, and pulp cavities. The latter enter with the corresponding vessels, and their distribution within the tooth is a subject of controversy. They may be followed easily to a plexus under the odontoblasts; but whether they end freely, or in connection with the odontoblasts (which by some are considered as peripheral sensory cells), or send fine terminal branches out into the dentinal canals is still uncertain. Development of the teeth. — The teeth represent calcified papillae of the oral mucosa, the enamel being a derivative of the ectodermal epithehum, and the remainder of the tooth coming from the underlying mesenchyme. The first trace of the teeth appears in the human embryo of about 11 mm., in the form of an epithelial shelf, the dental ridge, extending into the mesen- chyme corresponding to the future alveolar portions of the jaws (figs. 878, 879). From the dental ridge there is later produced a series of cup-shaped enlargements, the enamel organs, which become constricted off except for a slender neck attaching each to the common ridge. By the end of the third foetal month, the twenty enamel organs of the temporary or deciduous teeth are formed. The concavity of each enamel organ is filled by the dental papilla of mesen- chyme. THE TEETH 1125 A somewhat later stage in the organogenesis of a tooth is shown in fig. 880. The mesen- chymal cells on the surface of the dental papilla, next to the enamel organ, form a single layer of columnar cells, the odontoblasts. These cells form the dentine upon their outer surfaces, gradually retreating toward the center of the tooth as the dentine increases in thickness. The first dentine formed is irregular, enclosing the spatia interglobularia. The odontoblasts re- main through life just beneath the dentine on the surface of the pulp, sending slender processes, up into the dentinal tubules as previously noted in the structure of the adult tooth. The re- mainder of the dental papilla becomes the pulp, receiving its vascular and nerve supply at the point opposite the enamel organ, corresponding to the future root. The enamel organ (fig. 880) is differentiated into three layers: a thin outer layer attached by the neck to the dental ridge; a thick middle layer (forming the spongy "enamel pulp"); and a single inner layer of cylindrical enamel cells, the adamantoblasts. The latter form the prisms, which are deposited gradually upon the outer surface of the dentine. Fig. 883. — Dissection Showing the Teeth at about Six Years. Fischelis.) (Broomell and 4^;,,>.^/,tijf|. Surrounding the entire developing tooth there is formed a strong, fibrous connective- tissue membrane, the tooth-sac. The deeper part of this sac later becomes the alveolar periosteum around which the bony alveoli are formed. This bone may entirely surround the tooth-sac, excepting at the summit, where a foramen persists through which a process of connective tissue {gubernanilnm dentis) connects the tooth-sac with the overlying gum (see figs. 114, 881). Upon the inner surface of the tooth-sac, next to the root, the bony cemenlum is deposited upon the dentine. The root gradually elongates, and is usually not completed until long after the eruption. The remaining superficial portion of the tooth-sac undergoes pressure atrophy and absorption. The remnants of the enamel organ, however, persist and form a thin tough cuticle [cuticula dentis], Nasmyth's membrane, which is soon worn off when the crown is exposed at the surface. From the remainder of the dental ridge, which lies on the lingual side of the deciduous teeth (fig. 878), the permanent teeth are later derived in a very similar manner. (Rudimentary indications of a prelacteal dental ridge have also been described.) The anlages of the per- manent teeth therefore lie to the lingual side of the deciduous (fig. 883). From the posterior end of the dental ridge a process extends into the jaw behind the deciduous teeth, and from this process the permanent molars (which have no deciduous predecessors) are formed. At birth, although no teeth have yet been cut, there are present in the gums the anlages of not only all of the deciduous teeth, but also all of the permanent teeth, with two exceptions. Those of the second molars do not appear until six weeks after birth, and of the third molars not until the fifth year. The remnants of the dental ridges become broken up into small masses of epithehal cells, which persist for a variable time. 1126 DIGESTIVE SYSTEM The deciduous teeth. — The deciduous [dentes decidui], temporary or milk teeth are twenty in number, corresponding to the following formula: di|, dc[, dm| = 20. The deciduous teeth (figs. 882, 883) are much smaller in size than the perma- nent teeth, and their necks are more constricted. The enamel of the crown cap is thicker. In general, their form and structure otherwise is very similar to that Fia. 884. — Pulp-cavity op the Upper First Molar, From the Fifth to the Ninth Year (Broomell and Fischelis.) already described in the case of the permanent incisors and canines. The molars, however, are different. Their cusps on the masticating surface are very sharp and irregular. There are usually three 'cusps on the first upper molar and four on the second; four cusps on the first lower molar and five on the second. The roots Fig. 885. — Showing the Extent of Calcification op Deciduous Teeth. (Peirce.) 40weeks(newli.} 30weel(S(foe 18weeks(foetslX 17wee]i5(&etal> correspond to those of the permanent molars (three above and two below), but they are much more divergent, to allow room for the development of the corre- sponding subjacent permanent premolar teeth. The first molar is always con- siderably smaller than the second. Fig." 886. — Showing the Extent op Calcification op the Permanent Teeth. (Peirce.) Calcification in the dentine and enamel of the teeth does not begin until the anlages of the crowns are well formed. The process of calcification follows that of the development of the tooth in general, beginning in the superficial portion of the crown and gradually spreading toward the root. Calcification in the deciduous teeth begins during the fifth foetal month, and at birth the crowns are nearly completed (fig. 885). Of the permanent set of teeth, only the first molar has begun to calcify at birth (fig. 886). Calcification of the other permanent teeth begins during the second year; excepting the second molar, which begins during the fifth, and the third molar, which begins about the eighth year. There are, however, great variations THE TEETH 1127 in the time at which the caloificatioa of the various teeth begins. As a rule, the calcification of the roots is not completed at the apices until some time after the crowns are exposed in eruption. Eruption of the teeth. — -Oa account of pressure due to growth and expansion at the root of the tooth (and probably other obscure factors), the crowns are pushed toward the surface. The overlying portion of the tooth-sac, together with corresponding portions of the temporary alveolar bone, are absorbed, and the crown is "cut," i. e., breaks through the surface of the gum in eruption. In the case of the permanent teeth, this is normally preceded by a shedding of the deciduous teeth. The latter have been loosened by the absorption of their roots, which is perhaps due largely to the activity of certain odontoclasts (like the osteoclasts of bone) which are found in the region of absorption. Time and order of eruption. — The time of the eruption of the various teeth is subject to great variation, so that no two investigators agree upon it. Aside from the wisdom teeth, the time of eruption is most variable in the canines and premolars, and least variable in the first permanent molars (Rose). The eruption averages four and one-half months earliei in the male, and is also earlier in well-to-do and city children (Rose). The order in which the teeth appear is less variable. The average time at which the various deciduous and permanent teeth appear is indicated approximately in the following table. A. Deciduous Teeth Months after Birth (Average) Lower central incisors 7 (6-8) Upper central incisors 8-9 Upper lateral incisors 9-10 Lower lateral incisors 12-14 First molars 14 Canines 18 Second molars 22-24 B. Permanent Teeth The average time at which the teeth in the lower jaw undergo eruption is shown in the table below. The corresponding teeth in the upper jaw appear a little later : — Years First molars 6-7 Central incisors 7 Lateral incisors 8 First premolars 9-10 Second premolars 9-10 Canines 11 Second molars 12 Third molars (wisdom teeth) 17-25 Variations. — The great variabihty of the teeth has already been emphasized, and numerous variations described in connection with the various individual teeth and their development. In number, the teeth may be reduced, due to absence (oftenest of the third molar) or incom- plete development with failure of eruption. An increase in the normal number is less common' It may be only apparent, due to the retention of a deciduous tooth. There may rarely, however, be a true extra third incisor or premolar, or a fourth molar. Aberrant teeth may occur either on the labial or palatal side of the dental arch. A third dentition appears rarely in old age. In form, there is much greater variation as before mentioned. All intermediate forms between rudimentary and fully developed teeth may occur. Fusion between neighbouring teeth is sometimes found, and deformities in the dental arches necessarily accompany palatal defects involving the alveolar arches. Comparative. — As the oral mucosa represents an invagination of the integument, so the teeth are morphologically equivalent to dermal papilliE. The close relationship between the teeth and the dermal appendages is clearly shown among many of the lower vertebrates, but most clearly in the Selachians (which include sharks and allied forms). In fig. 887, which illustrates a sagittal section through the lower jaw of a young dogfish, it is clearly evident that the external placoid scales or 'dermal teeth' are continuous with the equivalent oral teeth at the oral margin of the jaw. Both the dermal teeth and the oral teeth are composed of dentine which presents an enlarged base and a somewhat conical apex. The base is embedded in the fibrous lamina propria (often in bony plates) while the apex projects through the epithehum and is covered with a thin cuticular layer the "enamel membrane." True enamel is usually rudimentary or absent in the primitive teeth of lower vertebrates, and represents a secondary acquisition. The dentine is in aU cases derived from the connective tissue, and the enamel from the epithelium . The process of development of the primitive oral teeth is also iDustrated in fig. 887. Just within the oral margin there is a shelf-like downgrowth of the ectodermal epithelium, forming a primitive germinal ridge. Along this ridge may be seen the anlages of several rows of teeth in various stages of development. As fast as the mature teeth at the oral margin are worn off, new teeth pass up from below to replace them. Thus the primitive form of dentition is polij- ■phyodont, with many sets of teeth developed successively thi'oughout hfe. As we pass up the vertebrate scale there is a tendency to a reduction in the number of sets, although there is a 1128 DIGESTIVE SYSTEM wide variation among the various forms. In most mammals, as in man, the number of sets of teeth has been reduced to two, or diphyodojit dentition, with only traces of an earher (pre- lacteal) and also a later (post-permanent) set. In some mammals (monotremes, oetacea) the dentition has been reduced to a single set, jnonophyodont, while in birds all except rudi- mentary traces of dentition have been lost. pAs may be further observed in fig. 887, the primitive teeth are of a recurved conical form, and serve primarily for grasping and holding the food. The speciahzation of the teeth for purposes of mastication is in general a secondary acquisition amongst higher vertebrates. It is also noteworthy that the primitive teeth, as found among nearly all forms below the mammals, are practicaOy alike in form, i. e., homodont. Among mammals, however, there is a marked speciahzation of the teeth, or helerodont dentition. The mammalian teeth are usually differentiated into four distinct classes, incisors, canines, premolars and molars, similar to those found in man. The typical or complete mammalian dentition, however, contains a larger number of teeth than found in man, and is represented by the formula • 31 43 1—, c -, pm-, m-=44 3' 1' ^ 4' 3 **• Thus it is evident that there has been a reduction in the incisors and premolars in the human species, and there has been considerable discussion of the question as to which teeth of the Fig. 887. — Section through Lower Jaw op Dog-fish, Showing the Development of the Oral Teeth, and the Transition to Dermal Teeth. M, mandible. (After Gegenbaur.) Intermediary forms — *- - ^,' Developing tooth Skin of lower jaw Dermal tooth ^ „ Dental epithelial ridge ... Epithelium of oral mucosa «. Anlage of tooth primitive series have been lost. This reduction in the number of teeth is probably correlated with the general reduction in the jaws, which are relatively much larger and stronger in the savage races and lower animals. The third molar, or wisdom tooth, is probably now on the road to extinction, due to a continuation of the same evolutionary process. Another interesting problem, concerning which there has been much speculation, is the origin of the multicuspidate mammalian molar. It has clearly been derived from the primitive conical type of the homodont dentition, but as to the method of evolution there is a difference of opinion. According to one view (the 'concrescence' theory), the molar has been derived by a process of fusion, each cusp representing a primitive conical tooth. Another view (the 'differentiation' theory) is that the molar represents a single primitive tooth, upon the crown of which the various cusps have been differentiated. According to a third view, which is a compromise, the tritubercular (tricuspid) form of tooth, which is that found in the earliest fossil mammals, was derived by a process of concrescence of three primitive teeth, while from this tricuspid form the multicuspidate molar has been derived by a process of differentiation. THE PHARYNX The pharynx is a vertical, tubular passage, flattened antero-posteriorly, and extending from the base of the cranium above to the beginning of the oesophagus below. Posteriorly, it is in contact with the bodies of the upper six cervical verte- brae. Laterally, it is in relation with the internal and common carotid arteries, THE PHARYNX 1129 the internal jugular vein, the sympathetic and the last four cranial nerves. Anteriorly, it communicates above with the nasal cavity, beneath this with the oral cavity, and below with the laryngeal cavity. The pharynx is correspondingly divided into three parts: the nasal -pharynx [pars nasalis], which is exclusively respiratory in function; the oral pharynx [pars oralis], which is both respiratory and alimentary; and the laryngeal pharynx [pars laryngea], which is almost entirely alimentary. Size and form. — The average length of the pharynx is about 12 cm. (5 inches). It is widest at the nasal pharynx, with a constriction (isthmus) connect- (Sobotta-McMurrioh.) 1. — The Interior op the Pharynx, Viewed prom Behind. Pharyngeal tonsil geptum Torus tubarius L Pharyngeal recess Glossopalatine arch Styloid process Styloid muscles Salpingopharyngeal fold Parotid gland Pharyngopalatine arch Pharyngo epiglottic fold Aryepiglottic fold Aditus laryngis Cuneate tubercle "^S Corniculate tubercle ^\ Fold of laryngeal l Thyreoid gland ing it with the widened oral pharynx, and is again somewhat narrowed at the junc- tion of oral and laryngeal pharynx (fig. 888) . It is narrowest at the point where it joins the oesophagus below. In sagittal section (fig.' 848), it is evident that the anterior and posterior walls are closely approximated in the laryngeal pharynx, and have only a small space between them in the oral pharynx. The nasal pharynx, however, has a considerable antero-posterior depth, and by its bony walls is always kept open for respiratory purposes. Structure. — The pharynx approaches the typical structure of the alimentary canal, yet differs from it in several important respects. The lining mucosa is continuous with that of the various cavities which open into the pharynx. Above, it is closely adherent to the base of the cranium, where it is thick and dark in colour. It becomes thinner where it approaches the open- ings of the auditory tubes and choana;; and below it is paler and thrown into longitudinal folds. The epithehum of the greater part of the nasal pharynx (from the orifice of the auditory tube upward) is stratified cihated columnar, while that of the remainder of the pharynx is stratified squamous. 1130 DIGESTIVE SYSTEM External to the mucosa, there is a characteristic fibrous membrane, the pharyngeal apo- neurosis [fascia pharyngobasilaris], which is well marked above, but below it loses its density and gradually disappears as a definite structure. Above, it is attached to the basilar portion of the occipital bone in front of the pharyngeal tubercle. Its attachment may be traced to the apex of the petrous portion of the temporal bone, and thence to the auditory (Eustachian) tube and medial lamina of the pterygoid process. It descends along the pterygo-mandibular ligament to the posterior end of the mylohyoid ridge of the lower jaw, and passes thence along the side of the tongue to the stylohyoid ligament, the hyoid bone, and thyreoid cartilage. External to the pharyngeal aponeurosis is a thick muscular layer, made up of various cross- striated muscles, as will be described later. Outside of the muscular layer is a thin fibrous tunica adventitia, connected with the adjacent prevertebral fascia by a loose, areolar tissue. This loose tissue allows movement of the pharynx, and also favours the spreading of post- pharyngeal abscesses. The nasal pharynx (figs. 848, 888) belongs, strictly speaking, with the nasal fossa as a part of the respiratory rather than the digestive system. Its anterior wall is occupied by the two choance (posterior nares), with the nasal septum between them. The floor is formed by the upper surface of the soft palate and in a direct posterior continuation of the floor of the nasal fossae. Posteriorly, how- ever, the floor presents a more or less narrowed opening, the pharyngeal isthmus, which communicates with the oral pharynx below. The isthmus is formed ante- riorly by the uvula, laterally by the posterior (pharyngo-palatine) arches. These slope backward and downward to the posterior wall of the pharynx, which forms the posterior boundary of the isthmus. The floor and isthmus change their form and position greatly during the action of the palatal muscles, as will be mentioned later. The lateral wall of the nasal pharynx presents above and behind, correspond- ing to its widest point, a wide, slit-like lateral extension, the pharyngeal recess [recessus pharyngeus] or fossa of Rosenmueller (fig. 888). Below and in front of this recess, the greater part of the lateral wall is occupied by the aperture of the auditory (Eustachian) tube [ostium pharyngeum tubse]. This is a somewhat triangular, funnel-shaped opening, with an inconspicuous anterior lip [labium anterius], a more distinct posterior lip [labium posterius], which presents poste- riorly a rounded prominence (due to the projecting cartilage of the auditory tube), called the torus tubarius. The prominence of the posterior lip facilitates the intro- duction of the Eustachian catheter, in connection with which the location of the aperture in the mid-lateral wall just above the level of the floor of the nasal fossa should be carefully noted. On the lower aspect of the triangular apertm-e is a slightly rounded fold, the levator cushion, which is a prominence caused by the levator palati muscle. A fold of mucosa descending from the posterior lip of the aperture to the lateral pharyngeal wall is the plica salpingo-pharyngea (due to the m. salpingo-pharyngeus). An inconspicuous plica salpingo-palatina descends from the anterior lip to the soft palate. The posterior wall (fig. 848) of the nasal pharynx slopes from below upward and forward, passing (at the level of the anterior arch of the atlas) into the roof [fornix pharyngis]. The roof is attached chiefly to the basi-occipital and basi- sphenoid bones, extending laterally to the carotid canal of the pyramid, and ante- riorly to the base of the nasal septum. In the posterior wall of the nasal pharynx there is found in the mucosa a variable and inconstant blind sac, the pharyngeal bursa. The mucosa of the roof, and to a certain extent also of the posterior wall, especially in children, is thrown into numerous folds, which may be irregular or radiate from the neighbourhood of the bursa. There is often a median longitu- dinal groove (or sometimes ridge) at the posterior (inferior) end of which is the bursa. These folds of the mucosa contain much lymphoid tissue, both diffuse and in the form of numerous characteristic lymphoid nodules, with crypt-like invaginations of the surface epithelium. This area constitutes the pharyngeal tonsil [tonsilla pharyngea] (fig. 890), which is well-developed in children (often abnormally enlarged, producing 'adenoids'), but usually, though not always, atrophied in the adult. According to Symington, the involution of the pharyn- geal tonsils begins at 6 or 7 years, and is usually completed at 10 years. In the region of the pharyngeal tonsil and elsewhere, the mucosa presents numerous small racemose mucous glands, especially thick in the palatal floor of the nasal pharynx and similar to those of the oral cavity. The oral pharynx (figs. 848, 864, 888) is continuous above through the pharyn- THE PHARYNX 1131 geal isthmus with the nasal pharynx and below with the laryngeal pharynx. Its posterior wall presents no special features. The anterior wall is deficient above, where there is a communication with the mouth cavity through the isthmus Fig. 889. — Vertical Section op a Human Palatine Tonsil, a, Stratified epithelium; b, basement membrane; c, tunica propria; d, trabeculse; e, diffuse lymphoid tissue; /, nodules; h, capsule; i, mucous glands; k, striated muscle; I, blood vessel; q, pits. (From Radasch.) faucium. The faucial isthmus is bounded above by the uvula, laterally by the anterior (glosso-palatine) arches, and below by the dorsum of the tongue in the region of the sulcus terminalis. Below the faucial isthmus, the anterior wall of Fig. 890. — Portion op a Cobonal Section through the Pharyngeal Region, Showing Waldbyer's Tonsillar Ring. (Palatine tonsils hypertrophied. ) Temporal lobe External pterygoid - Tensor veli palatinJ Levator veli palatini ^ ^.^ ^ yr - Internal {[ V-i-Z^ maxillary art ,^ f "^^t^^^^ Neck.of mandible Internal pterygoid Superior constrictor and capsule of tonsil Styloglossus Stylohyoid Lymph node Hypoglossal nerve Lingual artery -^ Epiglottis Cavity of larynx V_^3 — J — ^ Palatine tonsil (hypertrophied) Angle of mandible External maxillary j~ artery \ Lingual tonsil "* M. hyoglossus — Vallecula -> . Platysma the oral pharynx is formed by the root of the tongue, which has been described previously. The lateral wall of the oral pharynx on each side presents the pala- tine tonsil, enclosed in a somewhat triangular tonsillar fossa [sinus tonsillaris] 1132 DIGESTIVE SYSTEM limited anteriorly and posteriorly by the anterior and posterior palatine arches, and below by the root of the tongue. The palatine arches are folds of the mucosa formed at the sides of the free posterior border of the soft palate, as already mentioned in connection with that organ. The anterior arch (or pillar) [arcus glossopalatinus] extends from the soft palate downward and forward to the lateral margin of the tongue, just behind the papillfe foliatse. It is a fold of mucosa due to the underlying glosso-palatine muscle, and inconspicuous except when this muscle is in action, or when the tongue is depressed. It forms the lateral boundary of the faucial isthmus. The posterior arch [arcus pharyngopalatinus] is a more prominent fold which extends from the soft palate in the region of the uvula downward and backward to join the postero-lateral aspect of the pharyngeal wall. It forms the lateral boundary of the pharyngeal isthmus, and encloses the pharyngo-palatine muscle, whose actior will be explained later. The palatine tonsil [tonsilla palatina] (figs. 864, 889, 890, 891) is a flattened ovoidal body, usually visible through the mouth cavity and faucial isthmus, and located on each side of the oral pharynx. The tonsil is extremely variable in size, but in the young adult averages about 20 mm. in height, 15 mm. in width (antero-posteriorly) and 12 mm. in thickness. The lateral or attached surface of the tonsil is covered by a thin but firm fibrous capsule, which is continuous with the pharyngeal aponeurosis, and in contact with the middle constrictor muscle of the pharynx (fig. 864). Just out- side the constrictor, the tonsil is in relation with the ascending pharyngeal and ascending palatine arteries, but is separated by a considerable space from the external and internal carotids. Rarely, however, the lingual or external maxil- lary may extend up higher than usual, so as to be in close relation with the lower aspect of the tonsil. Further lateralward, the palatine tonsil is in relation with the internal pterygoid muscle, and on the surface corresponds to a point somewhat above and in front of the angle of the mandible. The posterior border of the tonsil is thicker than the anterior, and forms a somewhat flattened surface in con- tact with the pharyngo-palatine muscle (fig. 891). The medial or free surface of the tonsil is covered with mucosa and presents a variable number (12 to 30) small pits which are the openings into the tubular or slit-like crypts [fossulse tonsillares]. These crypts are somewhat more numerous in the upper part of the tonsil, and are sometimes branched or irregular in form. Usually they end blindly in the substance of the tonsil, surrounded by lymphoid tissue in characteristic nodular masses (fig. 889). The lymphocytes normally migrate through the stratified squamous epithelium lining the crypts (occasion- ally eroding passages of considerable size), and escape into the pharyngeal and mouth cavities, where they form the so-called salivary corpuscles. Around the periphery of the palatine tonsil, within the capsule, are many mucous glands (fig. 889), similar to those described in connection with the lingual and pharyngeal tonsils. The ducts of the mucous glands sometimes enter the crypts, but usually pass to the surface chiefly around the margins of the palatine tonsil. Tonsillar plicae and fossae. — Connected with the tonsil are certain important folds and fossse. The plica triangularis (fig. 891) is a fold of variable extent and appearance, placed just behind the anterior arch, wider below and narrower above. According to Fetterolf, it is a prolongation of the tonsillar capsule, cov- ered with mucosa. It may be adherent to the anterior part of the medial surface of the tonsil, or it may be free, in which case it covers a recess called the anterior tonsillar fossa. Occasionally there is a similar plica and fossa at the posterior border of the tonsil. Above the tonsil there is similarly a supratonsillar fossa [fossa supratonsillaris], which is also inconstant and exceedingly variable in size and shape. Killian found a supratonsillar fossa or canal in 41 of 105 cadavers. Tonsillar vessels. — The arteries to the tonsil include the anterior tonsillar (from the dorsalis linguEe); the inferior tonsillar (from the external maxillary); the -posterior tonsillar (from the ascending pharyngeal) and the superior tonsillar (from the descending palatine). These pierce the capsule and supply the gland. The veins form a plexus around the capsule and empty into the lingual vein and the pharyngeal plexus. The lymphatic relations of the palatine tonsil are important. Afferent vessels are received from adjacent areas of the mucosa in the pharynx, mouth and lower part of the nasal cavity (v. Lenart). These are connected with an extensive lymphatic plexus around the lymph follicles within the tonsil. Efferent lymphatic vessels pass chiefly to the upper deep cervical lymphatic nodes. One of these, located just behind the angle of the mandible, is so closely connected with the tonsil, and so constantly THE PALATINE TONSIL 1133 enlarged following tonsillar infection, that it has been called the tonsillar lymph gland (Wood). There are also communications with the submaxillary and superficial cervical lymphatic nodes. The tonsillar lymphatic vessels connect also with those of the lingual tonsil in the root of the tongue. The tonsillar ring. — The two palatine tonsils, together with the lingual tonsil below and the pharyngeal tonsil above, form an almost complete ring of characteristic tonsillar tissue sur- rounding the pharynx and known as Waldeyer's 'tonsillar ring' (fig. 890). It is a highly specialized development of the diffuse lymphoid tissue which is found everywhere in the mucosa of the alimentary and respiratory tracts. It may be noted that the 'tonsillar ring' corre- sponds to the anterior limit of the embryonic foregut, hence the epithehum is of endodermic origin. The arrangement of the tonsils, together with their lymphatic connections, has sug- gested the widely accepted view that they are to be considered as protective mechanisms whose function is to intercept infectious material which has entered the mouth or nasal cavities. This theory is supported by the experiments of v. Lenart, who found that substances injected into the nasal mucosa are intercepted partly in the tonsils, and partly in the cervical lymph Fig. 891. — The Left Palatine Tonsil, Showing the Arterial Supply. 1, Mesial aspect. 2, Postero-lateral aspect. E, lateral surface. B, posterior surface. T, medial surface. G, groove for pharyngo-palatine muscle. C, capsule. PT, plica triangu- laris. Arteries: AA, anterior tonsillar (from dorsal lingual); PA, posterior tonsillar (from ascending pharyngeal) ; SA, superior tonsillar (from descending palatine) ; lA, inferior tonsil- lar (anterior from dorsal lingual; posterior from tonsillar branch of internal maxillary). (Fet- terolf : Amer. J. Med. Sc, 1912.) nodes. Oppel, however, opposes this view, holding that the function of the tonsils, as of lym- phoid tissue elsewhere, is merely the production of lymphocytes. Development of the tonsil. — According to Hammar, the palatine fossa (sinus tonsillaris) is a derivative of the second inner branchial groove and is visible in the human embryo of 17 mm. There appears in the floor of the fossa a tubercle (tuberculum tonsillare) which later becomes atrophied, excepting a portion which is converted into the plica triangularis. The primitive tonsil becomes divided into two lobes, upper and lower, by a fold (plica intratonsillaris) which later usually disappears. In the fojtus of about 100 mm. (crown-rump length) the epithelium of the floor grows into the subjacent mesenchyme in the form of somewhat irregular solid sprouts of epithelium. These later become hollow and form the crypts. Ai'ound them, in about the sixth fa-tal month, the lymphoid tissue begins to accumulate, at first diffusely, later forming characteristic follicles. The lymphocytes arise in situ from the connective- tissue cells (Hammar) or by immigration from the blood-vessels (Stohr). Retterer's claim that the tonsillar lymphoid cells are derived from the epithelial cells has not been confirmed. The later fcetal development of the tonsil is subject to considerable individual variation. The supratonsillar fossa is a remnant of the upper part of the primitive sinus tonsillaris, which may be transformed into a canal by growth of adenoid tissue around it. It is inconstant and quite variable in size and extent. A portion of the sinus may likewise persist anteriorly (an- terior tonsillar fossa) between the tonsil and the plica triangularis, but this portion is usually obliterated by fusion of the plica with the tonsil. The occasional retro-tonsillar fold and fossa are said to arise secondarily (Hammar). Variations in the tonsil. — The palatine tonsil, like the lingual and pharyngeal tonsils, is an exceedingly variable organ. Many of the variations are developmental in origin, as above indicated, and ai-e therefore congenital. Furthermore, the tonsils, hke all lymphoid structures, are subject to marked age variations. Though fairly well formed at birth, they are yet some- what undeveloped. They rapidly increase in relative size and complexity, however, being 1134 DIGESTIVE SYSTEM best developed in childhood. After the age of puberty, they usually undergo certain retro- gressive changes, become smaller in size, and in old age become almost entirely atrophied and lost. They are also markedly subject to inflammatory hypertrophy, especially in children. Variations in the relations of the blood-vessels were mentioned above. The laryngeal pharynx (fig. 848) is the lower portion leading from the oral pharynx above into the oesophagus below (at the level of the lower border of the cricoid cartilage, usually opposite the sixth cervical centrum). It is wide above Fig. 892. — The Muscles of the Soft Palate and the Palatal Arches as Seen fbom in Front. (After Toldt, "Atlas of Human Anatomy," Rebman, London and New York.) Incisive papilla Upper bp Second molar Maxillary tuberosity Hamulus of internal pterygoid plate Transverse palatine ridges ^ Angle of mouth - X^^^v. So^* parts of cheek (cut) Oral vestibule Palatine glands Palatine foramen with anterior palatine nerve -Posterior nasal spine '^^j^m/'^ Buccinator X— . Pterygo-mandibular raphe Levator veli palatini Constrictor pharyngis superior Pharyngo-palatinus Glosso-palatinus Bucco-pharyngeal fascia Palatine tonsil ''^W'W-^^ Stylo-glossus fa ~^^^ Isthmus of the fauces Dorsum of tongue and narrow below (fig. 888) . Its posterior walls are continuous with those of the oral pharynx and in relation with the vertebral centra. Its lateral walls are attached to the hyoid bone and the posterior part of the medial surface of the thyreoid cartilage. Anteriorly it is in relation with the larynx. In the median line above is the epiglottis, below which is the superior aperture of the larynx. Still lower is the posterior wall of the larynx, containing the arytenoid and lamina of the cricoid cartilage. Laterally, are the pharyngo-epiglottic folds, and below these on each side a deep, elongated fossa, the recessus piriformis, bounded laterally by the medial surface of the thyreoid cartilage. The mucosa of the laryn- geal pharynx is similar to that of the oral pharynx, and contains racemose mucous glands, which are especially numerous in its anterior wall. Muscles of the pharynx and soft palate. — These muscles (figs. 892, 893, 894), which are here grouped together for convenience of description, are chiefly sphincter-hke constrictors in function. They include the constrictors of the faucial isthmus (mm. glossopalatini), the constrictors of the pharyngeal isthmus MUSCLES OF PHARYNX AND PALATE 1135 (mm. pharyngopalatini) , the three pharyngeal constrictors, and also the levator and the tensor veil palatini, the m. uvulae and the stylo-pharyngeus. The stylo- pharyngeus and pharyngo-palatine muscles form an incomplete longitudinal layer within the more circularly arranged constrictors of the pharynx. Fig. 893. — View of Muscles of Soft Palate, as Seen feom Behind, Within the Pharynx. (Modified from Bourgery.) PharyngeaT "'' \ll aponeurosis — ^ M. uvulae Hamular process Pharyngo-palatinus Constrictor pharyngis superior Crico-arytaenoideus posterior Thyreoid cartilage Cncoid cartilage The muscles are arranged in layers either behind or in front of the aponeurosis, and in a horizontal section of the soft palate the following layers are met with from behind forward: (1) The mucous membrane on the pharyngeal surface; (2) the posterior layer of the pharyngo-palatinus (palato-pharyngeus) ; (3) the m. uvulae; (4) the levator veli palatini; (5) the anterior layer of the pharyngo-palatinus; (6) the palatal aponeurosis with the tensor veli palatini; (7) the glosso-palatinus palato-glossus) ; and (8) the mucous membrane on the oral aspect. The glosso-palatinus (palato-glossus) is a cylindrical muscle extending between the soft palate and the lateral border of the tongue. Origin. — From the oral surface of the palatal apo- neurosis. Insertion. — (1) The superficial layer of muscles which covers the side and adjacent part of the under surface of the tongue; (2) the transversus linguae. Structure. — At its origin the muscle forms a thin sheet, but the fibres, passing lateralward, quiclcly concentrate to form a cylindrical bundle, which passes downward beneath the mucous membrane of the pharynx 1136 DIGESTIVE SYSTEM and in front of the tonsil, forming the glosso-palatine arch of the fauces. It reaches the side of the tongue at the junction of its middle and posterior thirds, and some of its fibres continue forward to join with those of the stylo-glossus and hyo-glossus, while the majority pass medially to become continuous with the transversus linguse. Nerve-supply. — From the pharjmgeal branches (plexus) of the vagus. Action. — (1) To draw the sides of the soft palate downward; (2) to draw the sides of the tongue upward and backward. The combination of these actions tends to constrict the faucial isthmus. (The origin and insertion of the glosso-palatinus as given above are often described as reversed.) The pharyngo-palatinus (palato-pharyngeus) — named from its attachments — is a thin sheet. Origin. — (1) From the aponeurosis of the soft palate by two heads which are separated by the insertion of the levator veli palatini; (2) by one or two narrow bundles from the lower part of the cartilage of the auditory (Eustachian) tube (salpingo-pharyngeus) . Insertion. — (1) By a narrow fasciculus into the posterior border of the thyreoid cartilage near the base of the superior cornu ; (2) by a broad expansion into the fibrous layer of the pharynx at its lower part . Fto. 894. — Thk Musrir=i op the Pharynx, Lateral View. Medial lamina of pterygoid process Constrictor pharyngis superior Pterygo-mandibular raphe Stylo-hyoid ligament Stylo-pharyngeus Crico-thyreoideus Cricoid cartilage Structure. — The upper head of the muscle consists of scattered fibres which blend with the oppo- site muscle across the middle line; the lower head is thicker, and foUows the curve of the posterior border of the palate. The two heads with the fasciculus from the auditory (Eustachian) tube form a compact muscular band in the posterior palatine arch; the fibres mingle with those of the stylo-pharyngeus, at the lower border of the superior constrictor, and then expand upon the lower part of the pharynx. Nerve-supply. — From the pharyngeal branch (plexus) of the vagus. Action. — (1) Approximates the posterior arches of the fauces; (2) depresses the soft palate; (3) elevates the pharynx and larynx. (The origin and insertion above given are often described as reversed.) The inferior constrictor is thick and strong. It arises from the thyreoid cartilage im- mediately behind the oblique hne and superior tubercle (thyreo-pharyngeus), and from a tendinous arch extending between the inferior tubercle of the thyreoid and the cricoid cartilage and also from the lateral surface of the cricoid cartilage (cricopharyngeus) (fig. 894). The fibres spread backward and medialward, the lowest horizontally, whilst those above ascend more and more obUquely, and are inserted into the fibrous raph6 of the pharynx. Some of MUSCLES OF PHARYNX AND PALATE 1137 the lowest fibres are continuous with the muscular fibres of the oesophagus, and the upper over- lap the middle constrictor (fig. 894). The nerve-supply of all three constrictors is from the pharyngeal nerve. Near the upper border the superior laryngeal nerve and artery pierce the thyreo-hyoid membrane to reach the larynx. The inferior laryngeal nerve ascends beneath the lower border immediately behind the crico-thyreoid articulation. The middle constrictor is a fan-shaped muscle which arises from the lesser cornu of the hyoid bone and from the stylo-hyoid Ugament (chondro-pharyngeus), and from the whole length of the greater cornu (cerato-pharyngeus). The diverging fibres are inserted into the median raphe, and blend with those of the opposite side. The lower fibres of the muscle descend, beneath the inferior constrictor, to the lower part of the pharynx; the upper overlap the superior constrictor, and reach the basilar process of the occipital bone, whilst the middle fibres run transversely (fig. 894). The glosso-pharyngeal nerve passes downward above its upper border, the stylo-pharyngeus passes between it and the superior constrictor, and near its origin it is overlapped by the hyo- glossus and crossed by the lingual artery. The superior constrictor is quadrilateral in shape, pale, and thin (fig. 894). It arises from the lower third of the hinder edge of the median lamina of the pterygoid process and its hamular process (pterygo-pharyngeus), from the pterygo-mandibular ligament (buoco-pharyn- geus), from the posterior fifth of the mylo-hyoid ridge of the mandible (mylo-pharyngeus), and from the side of the root of the tongue (glosso-pharyngeus) . The fibres pass backward to be inserted into the median raphd, the highest reaching the pharyngeal tubercle. The Eu- stachian tube and the levator veli palatini are placed above the superior arched border, and the space {sinus of Morgagni) between this and the basilar process, devoid of muscular fibres, is strengthened by the pharjmgeal aponeurosis, this portion of it being semilunar in shape. The stylo-pharyngeus arises from the base of the styloid process internally. It passes down- ward and medialward to reach the pharynx between the superior and middle constrictors. Its fibres spread out as it descends beneath the mucous membrane. At the lower border of the superior constrictor some of its fibres join fibres of the pharyngo-palatinus (palato-pharyn- geus), and are inserted mto the posterior border of the thyreoid cartilage (fig. 894); the rest blend with the constrictors. The nerve-supply of the stylo-pharyngeus is from the glosso-phar- yngeal nerve. The levator veli palatini — named from its action on the velum of the soft palate — is some- what rounded in its upper, but flattened in its lower, half. Origin. — (1) The inferior surface of the petrous portion of the temporal, anterior to the orifice of the carotid canal; (2) the lower margin of the cartilage of the auditory (Eustachian) tube. Insertion. — The aponeurosis of the soft palate; the terminal fibres of the muscles of each side meet in the middle line in front of the m. uvulae. Structure. — Its origin is by a short tendon; the muscle then becomes fleshy, and continues so to its insertion. Nerve-supply. — From a pharyngeal branch (plexus) of the vagus. Action. — (1) To raise up the velum of the soft palate, and bring it in contact with the posterior wall of the pharynx; (2) to narrow the pharyngeal opening and to widen the isthmus of the auditory (Eustachian) tube. (According to Cleland, it closes the pharyngeal opening of this tube.) The tensor veli palatini — named from its action on the velum of the soft palate — is a thin, flat, and narrow sheet. Origin. — (1) The scaphoid fossa of the sphenoid; (2) the angular spine of the sphenoid; (3) the lateral side of the membranous and cartilaginous wall of the auditory (Eustachian) tube. Insertion. — (1) Into the transverse ridge on the under surface of the hori- zontal plate of the palate bone; (2) the aponeurosis of the soft palate. Structure. — Its belly as it descends between the pterygoideus internus and the internal pterygoid plate is muscular. On approaching the hamular process it becomes tendinous, and continues so to its insertion. A bursa is interposed between the hamular process and the tendon. The belly of the muscle is at nearly a right angle with its tendon. Nerve-supply. — From the mandibular division of the trigeminus through the tensor palati branch of the otic ganglion. Actions. — (1) Tightens the soft palate; (2) opens the auditory (Eustachian) tube during deglu- tition. The m. uvulse. — so named by reason of its position in the uvula. Origin. — (1) From the aponeurosis of the soft palate and tendinous expansions of the two tensores veli palatini. In- sertion.— Into the uvula. Structure. — The muscle consists of two narrow parallel strips lying on each side of the middle Une of the palate. Nerve-supply. — From the pharyngeal branch of the vagus. Action. — To draw up the uvula. Origin of the muscles. — According to W. H. Lewis, the tensor palati is a derivative of the mandibular arch (probably split off from the pterygoid mass) ; the levator palati and m. uvulae come with the facial musculature from the hyoid arch; the glosso-palatine, stylo-pharyngeus and pharyngeal constrictors probably from the third visceral arch, in a pre-muscle mass visible in a 9 mm. embryo. The adult innervation of the pharyngeal muscles does not agree entirely with this, however. The pharyngeal muscles (as above stated) are innervated chiefly from the vagus, whereas if derived from the third arch their innervation from the glosso-pharyngeus would be expected. Process of swallowing. — In the act of swallowing, practically aU of the muscles of the mouth, tongue, palate and pharynx are involved. By compression of the hps and cheeks, together with elevation of the tongue, the food is forced backward through the faucial isthmus into the oral pharynx. Constriction of the faucial isthmus by the glosso-palatine muscles assists in preventing a return to the mouth. By the action of the levator palati, tensor palati, and pharyngo-palatine muscles, the soft palate is retracted and tightened, with constriction of the pharyngeal isthmus, so as to prevent the passage of the food upward into the nasal pharynx. The pharynx is dra-nm upward by the stylo-pharyngeus, and the pressure produced by the pharyngeal constrictors (the contraction beginning above and extending downward) forces the food dowTiward through the laryngeal pharynx and into the oesophagus. Passage of the food into the larynx is prevented by constriction of the superior aperture of the larynx. 1138 DIGESTIVE SYSTEM Vessels and nerves. — The vessels of the tonsil and the motor nerves of the various muscles have aheady been mentioned. In general, the arteries to the pharynx are derived chiefly from the ascending pharyngeal, the ascending palatine branch of the external maxillary, and the descending palatine and pterygo-palatine branches of the internal maxillary. The veins form a venous plexus between the pharyngeal constrictors and the pharyngeal aponeurosis, and also an external plexus, communicating with the pterygoid plexus above and with the posterior facial or internal jugular vein below. The lymphatic vessels pass chiefly to the deep cervical nodes, those from the upper portion (including the pharyngeal tonsil) ending partly in the retro-pharyngeal glands. The nerves of the pharynx, both motor and sensory, are derived chiefly from the glosso-pharyngeal and vagus, by way of the pharyngeal plexus. The development of the pharynx. — The pharynx is developed chiefly (if not entirely) from the anterior end of the archenteron. In this portion of the archenteron, with the develop- ment of the branchial arches, there are formed on each side four entodermal pouches or grooves (with a rudimentary fifth), the branchial clefts (see p. 17). With further development the first pair of branchial clefts form the tympanic cavities and the auditory or Eustachian tubes; the lower portion of each second branchial cleft persists as a fossa in which a palatine tonsil is developed ; the remains of the third and fourth pairs are found on each side in the vaUecula and piriform sinus of the larynx. The origin of the pharyngeal tonsil may be observed in the ■third month of foetal life in the form of small folds of mucous membrane which, during the sixth month, become infiltrated with diffuse adenoid tissue, lymph-nodules differentiating in this toward the end of foetal life. The pharyngeal bursa, which is not a constant structure (Kilr lian), may be observed as a small diverticulum of the pharyngeal waU, closely connected with the anterior extremity of the notochord. The diverticulum develops independently of Rathke's pouch (which gives rise to the anterior portion of the hypophysis), and is also apparently distinct from Seesel's pocket. The entire pharynx, like the associated facial region, is relatively small and undeveloped in the foetus and newborn, but develops rapidly during infancy. The development of the muscles and of the palatine tonsils has already been considered. Variations. — Variations in the palatine and pharyngeal tonsils and in the pharyngeal bursa have already been mentioned. Remnants of the visceral clefts may persist as aberrant diver- -ticula or as 'branchial fistulae' connected with the pharynx. Many additional muscles have been described, chiefly longitudinal muscles arising from the base of the cranium either by spUt- •ting of those normally present, or as separate slips. A detailed description of these may be found in Poirier-Charpy's work. Abnormally extensive fusion of the posterior arches of the ■palate with the walls of the pharynx may produce a congenital stenosis of the pharyngeal isthmusi Comparative. — The pharynx is not distinctly separated from the mouth cavity in the .lower vertebrates. It is the region containing the branchial or visceral clefts and is thus both .respiratory and aUmentary in function. The nasal pharynx, including the apertures of the •auditory tubes, becomes distinct along with the nasal cavity when the palate is formed (from the reptiles upward). In the air-breathing vertebrates, the laryngeal aperture appears in the ventral wall of the pharynx just anterior to the beginning of the cesophagus. Of the tonsils, the pharyngeal are the most primitive, being present in the roof of the pharynx in amphibia, weU-developed in reptiles, birds, and mammals (Killian). The palatine tonsils, on the other hand, are characteristic of mammals, being rarely absent, however (e. g., rat, guinea pig). From the embryological point of view, Hammar has classified the palatine ^tonsils in the various mammals under (1) the primary type (including rabbit, cat, and dog), in which the tonsil is formed from the embryonic tonsillar tubercle (described above under development of tonsil); and (2) the secondary type (including pig, ox, sheep and man), in which the tonsilt lar tubercle disappears and the tonsil is developed from the wall of the surrounding tonsillar sinus. Typical epithelial crypts (highly branched in the ox) are found only in the secondary •type. The tonsil may form a single (lymphoid) lobe (cat, pig, rabbit) or may develop typi- cally two lobes (ox, sheep, man), separated by the intratonsillar fold. There are great varia- tions among difl'erent species as to relative size, number and character of folds, crypts, «tc. The intimate relation of the epithelium with the underlying lymphoid tissue is charac- teristic and constant. THE (ESOPHAGUS The cesophagus (figs. 895, 896) is that portion of the alimentary tract which! extends between the pharynx and the stomach. It is more constricted than the rest of the canal, being narrowest at its commencement opposite the lower border of the cricoid cartilage. It is again somewhat contracted behind the left bronchus, and at its passage through the diaphragm, which is opposite the tenth or eleventh thoracic vertebra. It has an average length of 25 cm. (varying from 20 to 35 cm.). The average distance from the rima oris to the beginning of the cesophagus is about 15 cm. In its course downward the oesophagus follows the curves of the vertebral column until it finally passes forward in front of, and slightly to the left of, the aorta to gain the oesophageal opening in the diaphragm. In addition to these curves it presents two lateral curvatures, one convex toward the left side at the root of the neck and in the upper part of the thorax, and the other concave toward the left in the lower part of the thorax where it leaves the vertebral column. It lies in the middle line at its commencement (usually opposite the sixth cervical vertebra), and again, at a lower level, opposite the fifth thoracic vertebra. THE (ESOPHAGUS 1139 After death the oesophagus is somewhat flattened from before backward, but it is more rounded during life. It is closed except during the passage of food, etc. The -peristaltic movements of the oesophagus can readily be observed by means of the Roent- gen-rays. Solids often lodge a short time at the level of the arch of the aorta, but pass quickly through the cardiac orifice. A swallow of liquid, on the other hand, is usually detained at the lower end of the oesophagus (probably by sphincteric action of the cardia) for about seven seconds before passing into the stomach (Pfahler). Fig. 895. — The CEsophagus and Stomach. (Testut.) Thyreoid cartilage' Trachea Left flexure of cesophagus Aortic arch Right flexure of oesophagus Descending aorta Hiatus (Esophagus (Esophagus, pars abd Lesser curvature Pars pylorica Descending duodenum Inferior duodenu: Fundus of stomach — Greater curvature Bifurcation of aorta The oesophagus is divided into three parts: cervical, thoracic and abdominal. Cervical portion. — The oesophagus has anteriorly the trachea, the posterior portion of the left lateral lobe of the thyreoid gland, and the left recurrent nerve, branches of the inferior thyreoid artery, and the carotid sheath. Posteriorly, it rests upon the vertebral column, the longus colli muscles, and prevertebral fascia. On its right side are placed the right carotid and right recurrent nerve; and on the left side the left inferior thyreoid vessels, left carotid artery, left sub- clavian, and the thoracic duct. The recurrent nerves pass upward on each side to gain the interval between the trachea and oesophagus. The left nerve, as already described, lies in front of the tube, and the right along its right border. Thoracic portion. — The oesophagus descends in the thorax through the super- ior and the posterior mediastina. In the superior mediastinum its anterior rela- tions are the trachea, with the deep cardiac plexus in front of its bifurcation, the left subclavian and carotid arteries crossing its left border obliquely, the left recurrent nerve, and the arch of the aorta. To the left are the left carotid- and subclavian arteries, the end of the arch of the aorta, and the left pleural sac. To the right it is in relation with the right vagus nerve and the right pleural sac. Posteriorly, it rests upon the vertebral column, the left longus colli muscle, and it overlaps the thoracic duct. As it enters the posterior mediastinum, it passes behind the left bronchus (or bifurcation of the trachea) and the right pulmonary artery, resting posteriorly on the vertebral column and thoracic duct. In the posterior 1140 DIGESTIVE SYSTEM mediastinum it has anteriorly the pericardium, which separates it from the left atrium and a portion of the diaphragm; posteriorly it rests upon the vertebral column, accessory hemiazygos and hemiazygos veins, the right aortic intercostal arteries, the thoracic duct, and the descending aorta. To the right is the right pleural sac, the vena azygos, which it partly overlaps, and below, the thoracic duct. To the left in the upper part is the descending thoracic aorta, and, below, the left pleural sac is separated from it by a little loose areolar tissue. It is surrounded by the oesophageal ple.xus formed by the vagi nerves, and, as they emerge from the lower part of the plexus, the left vagus lies in front of the oesophagus and the right vagus behind. Fig. 896. — Cross-sections Illustrating the Relations of the CEsoPHAGtrs at Various Levels. Abdominal portion. — The oesophagus lies in the epigastric region of the abdo- men. Anteriorly is the left lobe of the liver. To the left the left lobe of the liver and the fundus of the stomach. To the right the caudate (Spigelian) lobe of the liver, and posteriorly the decussating fibres of the crura of the diaphragm and the left inferior phrenic artery. The abdominal portion is very short, usuallj^ not more than 2 cm. (4/5 inch) in length (see figs. 896 D, 907). Structure. — The thick-walled oesophagus presents the four typical tunics of the alimentary canal (fig. 897). The mucosa and the muscularis are the most important, the submucosa and the external adventitia being accessory layers. The mucosa (fig. 897) is thick and strong, of reddish colour in its upper portion and more greyish below. It presents deep longitudinal folds to allow for distention, and when empty the lumen is therefore stellate in cross sections. The hning epithelium is stratified squamous. The lamina propria presents numerous papiUse, and is limited externally by a muscularis mucosm. This is a comparatively thick layer (except at the upper end) and is composed of smooth muscle fibres, longitudinally arranged. THE (ESOPHAGUS 1141 The submucosa (fig. 897) is a thick, very loose fibrous layer connecting the mucosa with the muscularis. It contains numerous vessels and nerves, and mucous glands. The latter [gl. oesophageae] are of the racemose type, Uke those of the mouth, and are variable in number. There are also two sets of superficial glands, confined to the lamina propria, and resembling the fundus glands of the stomach. The upper set (Rtidinger-Sohaffer glands) are found in 70 per cent, of oases, occurring above the level of the fifth tracheal ring. The lower set (ojsophageal cardiac glands) form a ring around the ccsophagus just above the cardiac aperture. A few small lymph nodes also occur in the submucosa, often around the ducts of the mucous glands. The muscularis (fig. 897) is a thick reddish tunic with two distinct layers, approximately equal in thickness. The fibres of the inner layer are arranged circularly and are continuous with the inferior constrictor above and with the obhque fibres of the stomach below. The fibres of the outer layer are longitudinal and commence above as three flattened bands: a strong anterior band arising from the ridge on the back of the cricoid cartilage, and two lateral bands blending with the fibres of the stylo-pharyngeus and the pharyngo-palatine. These all unite into a continuous layer which below passes into the muscular coat of the stomach. The upper third or fourth of the oesophagus contains e.xclusively cross-striated muscle fibres, like those of the pharynx. Below this, there is a zone of intermingled smooth and cross-striated fibres. The lower half of the cesophagus muscle is usually composed exclusively of smooth fibres. Around the muscular coat is a thin loose fibrous layer [tunica adventitial connecting the oesophagus with neighbouring structures. Vessels and nerves. — The arterial supply of the oesophagus is derived from the inferior thyreoid, the oesophageal branches of the aorta, the intercostals, the inferior phrenic and the Fig. 897.- -Transveesb Section of the Uppee Third of the Human CEsophagus. (Lewis and Stohr.) Stratified epithelium X5. Group of fat-cells'^^JI *^^\ Circular muscles | Muscu- ■^''''^ Longitudinal muscles J laris Lymph nodule ' "'^A Tunica adventitia Mucous gland left gastric arteries. Branches pierce the wall and supply the various coats. The veins accompany the arteries. They form on the outer surface of the ccsophagus a venous plexus opening into the gastric coronary vein below and the azygos and thyreoid veins above (thus estabUshing a communication between portal and systemic veins). There are also numerous lymphatics in the cesophagus arising chiefly in the mucosa and draining into the lower deep cervical, posterior mediastinal and superior gastric nodes. The nerves form two sympathetic plexuses, the submucous and the myenteric, from which the walls are supphed as will be de- scribed later for the stomach and intestine. Branches are received from the sympathetics, and from the vagus, including the recurrent nerve. Development. — The embryonic oesophagus is at first relatively very short, but lengthens rapidly in connection with the descent of the stomach. The upper end is still high in children, corresponding to the higher vertebral level of the larynx. The lining epithehal cells are primi- tively cylindrical in form, and irregular ciliated areas are found from the third foetal month up to birth (F. T.Lewis). In the embryo of about 20 mm., there is a proHferation of the epithelium, associated with the formation of vacuoles, but the lumen does not appear to be normally oc- cluded. The primary longitudinal folds of the mucosa appear early (third month) and at the lower end seem to participate in the rotation of the stomach (F. P. Johnson). The superficial oesophageal glands appear about the fourth month (78 mm.), the deep glands at 240 mm. (Johnson). Of the muscular layers, the circular appears first (at about 10 mm.) the longi- tudinal shghtly later (17 mm.). Variations. — Usually a bundle of smooth muscle connects the oesophagus with the left bronchus [m. broncho-oesophageus], and another similarly with the left mediastinal pleura [m. pleuro-oesophageus]. More rarely there are similar bands connecting with the trachea, peri- 1142 DIGESTIVE SYSTEM cardium, etc. Pouch-like dilatations of the oesophagus may occur, especially in the upper part of its posterior wall or at the lower end. According to C. R. Robinson, the latter include (1) ampulla phrenica, just above the diaphragm, and (2) antrum cardiacum, in the abdominal portion of the oesophagus. Diverticula also occur, some of which may be derived from the embryonic vacuolization of the epithehum previously described, as may likewise the occasional congenital atresia. Abnormal strictures of the ccsophagus may occur, oftenest at the upper end, at the left bronchus, and near the lower end. Finally, the oesophagus may be in part either double or absent, and may communicate by fistula with the trachea. Comparative. — The length of the oesophagus varies with the length of the neck, being shortest in fishes and amphibia where the cesophagus is not well marked off from the stomach. The lining epithelium is stratified squamous in mammals and birds, but often ciliated in lower forms. Mucous glands are absent in fishes, but occur typically m all higher forms. They are found best developed toward the lower end of the cesophagus, except in mammals, where they are usually more numerous at the upper end. Dilatations may occur normally, as in the crop of birds, which is richly supphed with glands. The musculature of the oesophagus is primitively entirely smooth (Oppel) as found in amphibia, reptiles and birds. A secondary replacement by cross-striated muscle is found to a variable extent in the majority of mammals and fishes. THE ABDOMEN The abdomen properly consists of that part of the body situated between the thorax and the pelvis. It is bounded above by the diaphragm; below, by the brim of the true pelvis; behind, by the vertebral column, diaphragm, quadratus lum- borum and psoas muscles, and by the posterior portions of the ilia. At the sides it is limited by the anterior parts of the ilia and the hinder segments of the muscles which compose the anterior abdominal wall, viz., the transversus, internal oblique. Fig. 898. — Diagram of the Abdominal Regions. Joint between meso-sternum and ensiform cartilage Tip of ensiform cartilage Costal border ■TJpper horizontal plane Lower horizontal plane A, at "level of tubercles of iliac crest Lower horizontal plane B, at ' level of anterior iliac spines Vertical plane A, from middle of inguinal ligament .Vertical plane B, at lateral bor- der of rectus (semilunar line) Summit of symphysis pubis and external oblique. In front, besides these muscles, there are the two recti and pyramidales muscles. External to the peritoneum the abdomen is hned by a special layer of fascia. It is customary for anatomists and physicians to divide, for purposes of descrip- tion, the ventral surface of the abdomen, by means of two horizontal and two ver- tical lines, into nine regions (fig. 898). A complete uniformity in the use of the boundary hues marking these regional subdivisions has not as yet been attained, although the variations in the schemes used are not marked as concerns the main features. It should be borne in mind that it is necessary that the boundary lines used should be converted into planes carried through the whole depth of the abdo- men and defined on the dorsal as well as the ventral surface, and that the relations defined can only be approximate, owing to the wide range of the physiological variation in the position of the abdominal contents. The nine regions or subdivi- sions may be outhned as follows: — The upper horizontal line or plane passes through the lowest point of the tenth costal cartilages, about 5 cm. above the um- bihcus, and dorsally through the second or third lumbar vertebra. The lower THE ABDOMEN 1143 horizontal line and plane passes through the level of the anterior superior iliac spines, and dorsally about 2.5 cm. below the promontory of the sacrum. Cun- ningham has proposed that this hne be passed through the tuberculum cristse, therefore in a plane slightly higher than the interspinous plane. For the longitu- dinal hnes and planes it has been customary to run vertical hnes parallel with the mid-body line or mid-sagittal plane, and from the middle of the inguinal Ugaments. The outer border of each rectus would seem, however, preferable as a guide for these longitudinal lines and planes, which may be easily locahsed above by the lateral infra-costal furrow and below by the pubic spines, leaving thus on each side an inguinal region which includes the whole of the inguinal canal. The boundary lines here indicated may be made intelligible by a reference to fig. 898. The regions thus outhned are known as the right and left hypochondriac and epigas- tric regions, found above the upper horizontal line; the right and left lumbar and the umbiUcal regions, found between the two horizontal lines; the right and left Fig. 899. — The Adbominal Visceea in Situ, after Removal of the Anterior Abdom- inal Wall (After Sarazm ) Transverse colon Great omentum Small intestine Sigmoid coloDJ inguinal or iliac and the hypogastric regions, found below the lower horizontal lines. (According to the BNA, the lumbar regions are termed 'lateral abdominal'.) On freely laying open an abdomen from the front, the general form of the space is seen to be an irregular hexagon, the sides of which are formed as follows: — The upper two by the margins of the costal cartilages with the ensiform cartilage between; the two lateral sides by the edges of the lateral boundary; and the two lower by the two inguinal ligaments which meet at the pubes. In this irregular hexagon the following organs can be observed without dis- arranging their normal position (fig. 899). Above, on the right side, under the costal cartilages, can be seen the liver, which extends from the right across the median line to a point below the left costal cartilages. Below the liver, and lying to the left side, can be seen the anterior surface of the stomach; from the lower border of the stomach the omentum extends downward, and shining through it can be seen the middle part of the transverse colon. On each side and below the 1144 DIGESTIVE SYSTEM irregularly folded omentum are exposed the coils of the small intestine; in the right iliac fossa a part of the csecum appears;- and in the left iliac fossa the lower (iliac) part of the descending colon and the beginning of the sigmoid colon. To the left of the stomach and under cover of the lower ribs of the left side the edge of the spleen may possibly be observed; and just below the edge of the liver, and about the level of the tip of the ninth rib, the gall-bladder may be seen. The dome of the urinary bladder may be noticed just behind the symphysis pubis and in the median line. The disposition of the viscera in the foetus is shown in fig. 953. General morphology — Before taking up the various individual organs included in the abdominal and pelvic portions of the alimentary canal, a brief consideration of their general morphology is desirable. The primitive canal, as already described in the embryo (in the Fig. 900. — Digeammatic Representation of an Early Stage in the Development of THE Alimentary Canal and the PERiTONEtrM. (After Sobotta-McMurrich.) Lesser curvature CEsophagus Ventral mesogastrium "v y^ Stomach (lesser omentum) \ _^.?^=:S^r-_ / Greater curvature Ventral mesogas- trium (falciform lig.) Falciform lig. Umbilical vein Omphalo-mesenteric duct Umbilical Dorsal meso- / gastrium Sup. mesenteric art. Left colic flexure Inf. mesenteric art. Distal limb of intestinal loop section on Morphogenesis), and as found in the lower vertebrates is a comparatively straight, simple tube extending ventral to the body axis from mouth to anus. In the abdominal region (and primitively throughout the whole trunk), the canal lies within the body cavity, which is lined by parietal peritoneum. The visceral peritoneum is reflected from the mid-dorsal line as a double layer, the ■primiiive dorsal mesentery, within which the vessels and nerves pass to the walls of the canal. Within the dorsal mesentery are also the spleen and pancreas. In the anterior (upper) region of the abdomen there is also a similar primitive ventral mesentery, which contains the liver. The relations above mentioned are indicated diagrammatically in fig. 900, which represents a comparatively early stage in the development of the intestinal canal. The hver is already almost completely separated from the diaphragm (with which it was intimately associated in the earher septum transversum). The ventral mesentery persists in the form of (1) the gastro- THE PERITONEUM 1145 hepatic or lesser omentum, connecting the stomach with the hver; and (2) the falciform ligament, connecting the hver with the ventral body wall. The stomach undergoes a rotation on its longitudinal axis so that its anterior border (lesser curvature) is turned to the right, and its posterior border (greater curvature) to the left (fig. 901). Thus the posterior mesentery of the stomach [mesogastrium], bulges to the left and forward, carrying with it the spleen and pancreas. The portion of the mesentery corresponding to the pancreas, and that from the spleen to the root of the mesentery, become fused with the posterior body wall. The portion of the primitive mesogastrium between the stomach and spleen persists as the gastro-splenic omentum (or ligament), while the lower portion arches forward and downward as an extensive fold, the great omentum. The portion of the peritoneal cavity left behind the stomach is termed the bursa omentalis, or lesser sac, the remainder of the peritoneal cavity being the greater sac. Along with the pancreas, the duodenum becomes adherent to the posterior wall. The remainder of the intestine forms a loop (fig. 901), the upper portion of which forms the jejuno- ileum, the lower portion the large intestine. The intestinal loop rotates counter-clockwise, so that the csecum and ascending colon are carried over to the right side of the body cavity, where (with the corresponding portion of the primitive mesentery) they become adherent to the posterior body wall (fig. 901). The mesentery of the transverse colon persists (though fused partly with the great omentum, as explained later under development). The descending colon becomes displaced to the left side, and (together with its mesentery) becomes adherent to the posterior wall of the abdomen. The mesentery of the sigmoid colon usually persists (in part), whUe that of the rectum is obhterated. Through these modifications of the peri- FiG. 901. — Diagrams Illustrating the Development of the Great Omentum, Mesentery, ETC. A, Earlier Stage; B, Later Stage. bid, caecum; dd, small intestine; dg, yolli-stallc; di, colon; du, duodenum; gc, greater curvature of the stomach; gg, bile duct; gn, mesogastrium; k, point where the loops of the intestine cross; mo, mesocolon; md, rectum; mes, mesentery; wf, vermiform appendix. (McMurrich after Hertwig.) mS toneum, and through unequal growth in the different regions, the simple primitive intestinal tube is transformed into the complicated adult canal. The details of the transformation will be more fuUy discussed later. Under certain rare conditions, the developmental process is modified so as to produce a situs inversus, which may be partial or complete, involving both thoracic and abdominal viscera. Under these circumstances, the viscera are transposed, the right and left sides being reversed. THE PERITONEUM The peritoneum, as has been shown, is a serous membrane which lines the cav- ity of the abdomen from the diaphragm to the pelvic floor, and invests or covers to a varying extent the viscera which that cavity contains. Viewed in its very sim- plest condition, it may be regarded as a closed sac, the inner surface of which is smooth, while the outer surface is rough and is attached to the tissues which sur- round it. In the male subject the peritoneum forms actually a closed sac; but in the female its wall exhibits two minute punctures, which correspond to the openings of the Fallopian tubes. That part which lines the walls of the abdomen is termed the parietal peritoneum; that which is reflected on to the viscera is the visceral peritoneum. The disposition of the peritoneum may first be studied by noting 1146 DIGESTIVE SYSTEM its arrangement as made evident in transverse sections of the abdomen at certain levels. The first section to be described shows the peritoneum in its simplest condition. This is a transverse section through the body, at about the level of the upper sur- face of the fourth lumbar vertebra, and therefore about the site of the umbilicus (fig. 902). Starting on the inner surface of the anterior abdominal wall, the peritoneum is seen to cover the transversalis fascia, and indirectly the anterior abdominal muscles; then, passing Fig. 902. — Diagram of Cross-section of the Abdomen, Showing the Peritoneal Belations AT THE Level OF THE Umbilicus. A 0, Aorta. AS. COL., Ascending colon. DES. COL., Descending colon. MES., Mesentery. M. COL., Descending mesocolon. »S/, Small intestine. V.C., Vena cava inferior. to the left, it lines the side of the abdomen, until it reaches the descending colon. This it covers, as a rule, in front and on the sides, though occasionally it forms a mesocolon. Then it passes over the bodies of the vertebrae with the large vessels upon them, and leaves the back of the abdo- men to run forward and enclose the small intestine, returnuig again to the spine. The two layers thus form the mesentery, having between them a middle layer [lamina mesenterii propria] containing the terminal branches of the superior mesenteric vessels. It then passes over the right half of the posterior abdominal wall, covering the ascending colon in front and at the sides only (unless there be a mesocolon), and then passes on to the side and front of the abdomen to the point from which it was first traced. Fig. 903. — Diagram of Cross-section of the Abdomen, Showing the Peritoneal Rela- tions AT THE Level of the Foramen op Winslow. (P. of W.) Gastro-hepatic omeatum In tracing the peritoneum in a section of the body opposite the stomach (fig. 903), on a level with the first lumbar vertebra, its course becomes more com- plicated and difficult to follow. In the section already given the peritoneum as a simple closed sac can be readily con- ceived; but at the level now exposed the serous membrane has been so introverted that there appear to be two sacs, one leading from the other, and known respectively as the greater and the lesser sac of the peritoneum. They communicate through the epiploic foramen (of Winslow) . The le.sser sac [bursa omentahs] is situated behind the stomach, so that on first opening the abdomen no trace of it is to be seen. It extends downward [recessus inferior] between the layers of the great omentum (though this part of the lesser sac is largely obliterated by adhesion THE PERITONEUM 1147 in the adult). It extends upward [recessus superior] beiiind tlie caudate lobe of the liver. The vestibule [vestibulum bur.sse omentalis] is the portion which lies just behind the lesser omentum, and communicates with the greater sac through the epiploic foramen. In general, the lesser sac is Umited anteriorly by the liver, stomach, and omenta; posteriorii/ by the posterior abdominal wall, and below, behind the great omentum, by the transverse meso-colon. Its disposition on vertical section is shown in fig. 904. The epiploic foramen (foramen of Winslow) (figs. 903, 906) is situated just below the liver; it looks toward the right, and will readily admit one or two fin- gers. It is bounded superiorly by the caudate lobe of the liver; inferiorly, by the duodenum (pars superior); posteriorly, by the vena cava; and anteriorly by the right margin of the gastro-hepatic or lesser omentum, containing the struc- tures passing to and from the hver. Starting at the epiploic foramen, the lesser sac will be found to turn to the left. Fig. 904. — DiAGEAM OP A Sagittal Section of the Trunk, Showing the Relations op the Peritoneum. (Allen Thompson.) Gastro-hepatic omentum Stomach Transverse colon Mesentery Smairintestine Uterus Epiploic foramen Pancreas Duodenum ■Transverse meso-colon Aorta If, now, the peritoneum be viewed in a transverse section of the body at the level named, viz., through the first lumbar vertebra, it will be found that the section has probably passed through the epiploic foramen (fig. 903). Starting at the front of the abdomen and- going to theright, the peritoneum is seen to line the anterior abdominal wall, to pass over the side of the abdomen, and to cover the front of the right kidney; it then extends on to the vena cava, when it becomes a part of the lesser sac; then along the back of the lesser sac, over the aorta and pancreas, which separate it from the vertebral column ; next it reaches the anterior of the two internal surfaces of the spleen internal to the hilus. Here it meets with another layer of peri- toneum, and helps to form the gastro-splenic ligament [lig. gastrolienale]. Leaving the spleen, it changes its direction forward and to the right, and runs to the stomach, forming the posterior, layer of the gastro-splenic hgament; it covers the posterior surface of the stomach, and leaves its mesial border (lesser curvature) to form the posterior layer of the lesser omentum, and then passes upward and to the right to the liver. In this transverse section it is only seen passing on the right margin of the lesser omentum, where it forms the anterior boundary of the epiploic foramen. Here it bends sharply around the omental margin enclosing the hepatic vessels continuing to the left as the anterior layer of the lesser omentum; and then passing to the left reaches the stomach, which it covers in front. It then forms the anterior layer of the gastro- 1148 DIGESTIVE SYSTEM splenic ligament, and once more reaches the spleen. It passes right around the spleen to the back of the hilus, where it is reflected on to the left kidney as the lieno-renal hgament (fig. 903). Hence the peritoneum passes along the side and front of the abdomen to the point from which it started. In this section the liver is so divided as to appear separated from all connection with the other viscera and the abdominal wall, and to be surrounded by peritoneum. The course of the peritoneum in a longitudinal section of the body will now be considered (fig. 904). Starting at the umbilicus and passing downward, the peritoneum is seen to line the anterior abdominal wall. Before reaching the pelvis it covers also the urachus, the deep epigastric arteries, and obliterated hypogastric arteries, which form ridges beneath it. For some little way above the os pubis the peritoneum is loosely connected with the abdominal wall, a circumstance which is made use of in supra-pubic cystotomy. Moreover, as the distended blad- der rises from the pelvis it can detach the serous membrane to some extent from the anterior abdominal wall. In extreme distension of the bladder the peritoneum may be lifted up for some 5 cm. vertically above the symphysis. On reaching the OS pubis it is reflected on to the upper part of the bladder, covering it as far back as the base of the trigone; thence it is reflected on to the rectum, wihch it covers in front and at the sides on its upper part, rarely forming a distinct mesorectum. Between the bladder and rectum it forms in the male the recto-vesical pouch. The mouth of this pouch is bounded on either side by a crescentic fold, the plica semilunaris. In the female the peritoneum is reflected from the bladder on to the uterus, which it covers; it then extends so far down in the pelvis as to pass over the upper part of the vagina behind; thence it extends to the rectum. The peri- toneum which invests the uterus is reflected laterally to form the broad ligaments. The fold between the vagina and rectum forms the recto-vaginal pouch, or pouch of Douglas. The membrane has now been traced back to the spine. Following it upward, the sigmoid colon wifl be found to be completely covered by peritoneum, a mesocolon attaching the gut to the abdominal wall (shown in fig. 905). A little higher up in the median line the peritoneum passes forward, to enclose the small intestine, and, returning to the spine, forms the mesentery (fig. 904). It now passes over the third part of the duodenum to the pancreas, from which point it again passes forward to form the lower layer of the transverse mesocolon. It invests the transverse colon below and partly in front, and then leaves it to pass downward to take part in the great omentum. Running down- ward some distance, it returns and forms the anterior layer of the omentum. On reaching the stomach it goes over the anterior surface, and at the upper border forms the anterior layer of the lesser or gastro-hepatic omentum, which extends between the stomach and the liver. It invests the inferior surface of the liver in front of the transverse fissure, and, turning over its anterior border, covers the upper surface. At the posterior limit of the upper surface it leaves the liver and goes to the diaphragm, forming the superior layer of the coronary ligament. It covers the anterior part of the dome of the diaphragm, and, once more reaching the anterior abdominal wall, can be followed to the umbilicus, where it was first described. This completes the boundary of the greater sac. On reference to the diagram (fig. 904) the student might be led to suppose that the two sacs are quite separate. This, of course, is not the case; but in a longitudinal section of the body made anywhere to the left of the epiploic foramen (foramen of Winslow), it is impossible to show the direct connection between the two sacs. (See fig. 905.) The peritoneum has only been traced in this longitudinal section so far as it concerns the greater sac. It now remains to follow upon the same section (fig. 904) such part of the membrane as forms the lesser sac. The peritoneum here will be seen to cover the posterior surface of the stomach; thence from the lesser curvature it runs upward to the liver, forming the posterior layer of the lesser or gastro-hepatic omentum. It reaches the liver behind the transverse fissure. It covers only a part of its posterior surface (caudate lobe), and is reflected on to the diaphragm, forming the lower layer of the coronary ligament. It now goes down- ward over the posterior part of the dome of the diaphragm to the spine, separated from the latter by the great vessels. On reaching the anterior border of the pan- creas it passes forward, and forms the upper layer of the transverse meso-colon. It then covers the upper half of the transverse colon, and, descending, forms the innermost layer of the great omentum. (The inner layers of the great omentum are usually fused in the adult, however, thus obliterating this portion of the lesser sac.) It now ascends, and, arriving at the greater curvature of the stomach, THE PERITONEUM 1149 passes on to its posterior wall. At this point its description was commenced. The general relations of the greater and the lesser sac are also evident in fig. 905 showing the hnes along which the parietal peritoneum is reflected from the pos- terior abdominal wall as the visceral peritoneum, forming the various mesenteries and covering the various abdominal organs. Fig. 905. — Reflections of the Peritoneum on the Posterior Abdominal Wall. (From Rauber-Kopsch, modified.) T.. . „ Falciform lig. Recessus superior omentalis ; Lig. triangulare sinistrum Opening of hepatic veins into V. cava inferior Lig. coronarium Epiploic foramen (of Winslowj Hepato -duodenal lig. and root struc- tures of livei Duodenum, parb sup Duodenum, pars faoriz, Radix mesenterii Uncovered area for ascending colon Plica gastro- pancreatica .,— Gastro-lienal lig. Bursa omen- — talis, recessus lienalis Phreno-colic lig. Duodeno- jejunal flexure Uncovered area for descending colon The precise manner in which certain organs — such as the hver, the caecum, the duodenum, and the kidneys — are invested by peritoneum is described in the accounts of those viscera. To such accounts the reader is referred for a description of the many 'ligaments' (such as those of the bladder and liver) which are formed by the peritoneum. The great omentum. — As is evident from its development, the great omentum [omentum majus] is formed of four layers of peritoneum, though this is quite impossible to demonstrate in an adult, the individual layers having become adherent. The great omentum acts as an apron, protecting the intestines and providing 1150 DIGESTIVE SYSTEM them with a heat-economising covering of fat. It is nearly quadrilateral in shape, and is variable in extent. In fig. 904 the great omentum is shown to be connected with the greater curvature of the stomach, on the one hand, and the transverse colon, on the other. Originally it extended backward above the transverse colon and mesocolon to the posterior abdominal wall. The line along which it fuses with the transverse colon and mesocolon during development is shown in fig. 904. Mr. Lockwood has made some investigations on the lengths of the transverse meso-colon and great omentum in thirty-three cases. In twenty, under the age of forty-five, only one sub- ject had a great omentum long enough to be drawn beyond the pubic spine; in five, the omentum reached as far as the pubes. In the cases beyond forty-five years it was the exception rather than the rule to find an omentum which could not be puUed beyond the lower Umits of the abdomen. The lesser omentum [omentum minus] consists of a double layer of peritoneum extending between the stomach and the liver. If the two anterior layers of the great omentum are traced upward, they are seen to enclose the stomach, and then Fig. 906. — Abdominal Visceka, Anterior View, after Removal of a Part of the Liver AND Intestines. (Rauber-Kopsch.) Right lung lesser jOas|-:^epa t"™ [ denallig. Foramen epiploicum mm.! "t Fundus of gall bladder SHSSu. Right colic flexure Duodenum Right kidney Radix mesenteni Appendices epiploicee Ileo-colic fold and fossa Processus vermiformis Phreno- r^f~ ""'"^- Duodeno- / jejunal flexure Superior II J mesenteric \^ vessels ■ r~f1 Left kidney \_M Abdominal 'M aorta J^ Inf mesenteric join together again at the lesser curvature to form the lesser omentum (fig. 904). It is connected above with the portal (transverse) fissure and the fissure for the ductus venosus; below, with the lesser curvature of the stomach; the left extrem- ity encloses the oesophagus; the right border contains the hepatic vessels and is free, forming the anterior boundary of the epiploic foramen (see fig. 906). The lesser omentum is divided into two parts. The portion connecting the portal fissure of the hver with the first part of the duodenum, and enclosing the root structures of the liver, is called the hepalo-duodenal ligament [fig. hepatoduodenale]. The portion of the lesser omentum connecting the lesser curvature of the stomach with the fissure of the ductus venosus is the gastro-hepatic hgament [lig. hepatogastricum]. The gastro-splenic ligament [fig. gastrolienale] connects the left extremity of the stomach with the spleen, continuing the layers of peritoneum which enclose the stomach (fig. 903). The gastro-phrenic and phreno-colic ligaments. — As the peritoneum passes from the diaphragm to the stomach it forms a small fold just to the left of the THE STOMACH 1151 oesophagus. This is the gastr o-phrenic ligament. A strong fold of the membrane also extends from the diaphragm (opposite the tenth and eleventh ribs) to the splenic flexure of the colon, and is knoM'n as the phreno-colic (costo-colic) hgament [lig. phrenicolienale]. (See figs. 905, 906.) Minute anatomy. — The peritoneum, like all serous membranes, consists of two layers; a lining layer composed of simple squamous epithelium (mesothelium), and an underlying layer of fibrous connective tissue. The latter is highly elastic, and denser in the parietal than in the visceral layer. It often contains fat. In mesenteries and similar structures, the con- nective tissue is usually very scanty, except surrounding the vessels and nerves. Ruptures often occur in the omenta, which thus become fenestrated in structure. The visceral peritoneum is usually closely attached to the organs for which it forms the outer serous tunic, but the pa- rietal peritoneum is often loosely attached to the adjacent wall by a fatty subserous layer [tela subserosa]. Smooth muscle occurs frequently in the various peritoneal folds. The peritoneal cavity contains normally a very sUght amount of watery fluid, which serves to lubricate the smooth peritoneal surface and thus to ehminate friction between adjacent surfaces during the movements of the alimentary canal. Vessels and nerves. — The peritoneum is in general somewhat sparsely supphed with blood- vessels from various adjacent trunks. Lymph-vessels also occur, but they probably do not connect directly with the peritoneal cavity by stomata (as is found in the frog and as claimed by some to occur in man). They communicate with the lymphatics of neighbouring i-egions. The nerves are also comparatively scarce. They are partly of sympathetic origin (vasomotor), and partly sensory nerves from the intercostal (7th to 12th), and lumbar nerves. The sensory nerves are more frequent in the parietal peritoneum and end in the connective tissue, either freely or in special end-organs (varying from simple end-bulbs to Pacinian corpuscles). Development. — The principal features in the development of the peritoneum have already been mentioned in the section on Morphogenesis and in the remarks on the general morphology of the intestinal canal (p. 19). Further details will be included later under the development of the intestine, etc. Variations. — Variations in the form and relations of the peritoneum are exceedingly common, and are most commonly of developmental origin. Variations in the form and re- lations of the various abdominal organs necessarily involve corresponding modifications in the peritoneum. The diaphragm may be incomplete!}' formed, leaving the peritoneal cavity in communication with the pleural, or more rarely the pericardial cavity. The primitive dorsal mesentery of the intestine [mesenterium commune] may persist unmodified (in about 2 per cent, of adults), or the various secondary changes may be inhibited at any stage. Thus the'stomach or the intestinal loop may fail, either wholly or partly, to undergo their character- istic rotations. The adhesions of the various mesenteries may be incomplete, or they may be more extensive than usual. For example, the sigmoid mesocolon may be more or less com- pletely obliterated by adhesion, and numerous unusual peritoneal pockets or hgamentous bands may be formed in this way in various localities. Variations thus due to extensions of the normal developmental process are sometimes difficult to distinguish from pathological adhesions caused by peritonitis. Comparative. — As previously mentioned, the primitive body cavity in vertebrates extends throughout the trunk region. In the oyclostomata, this primitive relation persists, the peri- cardial cavity remaining in communication with the general body cavity. In all higher forms, however, the pericardial cavity becomes entirely separated. In amphibia the lungs he in the general (pleuroperitoneal) body cavity; in the reptiles and birds, they are partially separated; but a complete separation of the pleural cavities occurs only with the formation of the definite diaphragm in mammals. The formation in the peritoneal cavity of a complete dorsal mesentery, and an incomplete ventral mesentery (in the hepatic region) is typical for all classes of vertebrates. Slight modifications in the form of the mesenteries depend chiefly upon the diiJerent degrees of com- ple.xity in the development of the various parts of the intestinal tract. The marked changes associated with extensive secondary adhesions of the primitive peritoneal structures are found only among the higher mammaha, especially in man. THE STOMACH The stomach [ventriculus ; gaster] is a dilation of the alimentary canal suc- ceeding the oesophagus. In the stomach the food is mixed with the gastric juice and reduced to a viscid, pulpy liquid, the chyme [chymus], which undergoes a certain amount of digestion and absorption before passing into the duodenum. The stomach (figs. 906, 907) is a somewhat pear-shaped organ located in the upper, left side of the abdominal cavity. It presents a body [corpus ventricuh], with an enlarged upper end or fimdus, on the right side of which is the cardia, the aperture communicating with the oesophagus. The body of the stomach is extremely variable in form, as will be explained later, but is in general divisible into a more expanded upper two-thirds, the cardiac portion [pars cardiaca], which is nearly vertical, and a more constricted lower third, the pyloric portion [pars pylorica], which tm-ns horizontally toward the right. The pyloric portion often presents toward its lower end a slight, variable dilation, the antrum pylori, 1152 DIGESTIVE SYSTEM succeeded by a short constricted pyloric canal (Jonnesco) . At the lower end of this canal the pylorus forms the aperture leading into the duodenum, and contains a thick sphincter derived from the circular fibres of the muscular layer. The stom- ach has two borders and two surfaces. The medial (or upper) border forms the lesser curvature [curvatura ventriculi minor], which is concave (except near the pylorus) and gives attachment to the lesser omentum. The lateral (or lower) border forms the greater curvature [curvatura ventriculi major], which is convex, and gives attachment to the great omentum. The curvatures separate the anterior surface [paries anterior], which faces forward and upward, from the posterior surface [paries posterior], which is placed backward and downward. Dimensions. — The dimensions of the stomach are subject to great variation and therefore only a gross approximation can be given. The length of the lesser curvature averages about 10 cm. (7.5 cm. to 15 cm.), and that of the greater Fig. 907. — ^Longitudinal Section op Stomach, Showing the Interior of the Posterior Half. (Rauber-Kopsoh.) Fundus of stomach. i ^~- / f\ Notch |> * H ^ _8. _7. .6. .5. .4. i^ "~. / 7^ " -s- — ^ i ^=M::_ ^^^1 I- T Ai ■ ' ~^ ~> ^ ' "^^Ms V . / 1 -^ .aC^ s \ / \ f i -- -_ -" J^ /. , ^ A r - /rip of 9th c c ^ 1 .2. J- Eg -xi -2- .3- .4^ _5. .6 _7 -8 _9 .IQ )'' Cl _1. k' 4 -^-~. ■ —- ' -— ^' X / ^ CI" r^ "■", T'e..°5 9tti C. C r ^ y \ w\ — " ^ .> ^ - 'h. n ,_ .F V di3c between! ptebraQiVT^ fe IP ~ "7~f 55 ?\ 1^ T ~ ■ %i Jr k i* i k / F' ^ 'm % «j '% *f / [>an<.,.,=.. ■^ c / (Ty' V^ --/ r / y ts- f ii-' \ y ' '' Meso-Colon / / -— ~^ -^ \u p i: -X J ^ ir / >^ MesoC )lor / ^ / \ ^ oe ' iL ^ ^ : I < '■ Irest of Iliun »»- — » — .1 ^ ^ n * J ^ "-• 1 .i "^ -~^ -^1 \ ly - ^ t^ \ ' *■ / p^ N S < ^ } 1 M ,so-S V / 4. n/ \ // ^\ — begin. \ y .^^ — / ^ t) K // \ V / '^ \ ill -^ H- ^ \ '( / ' .5 -6 -7 _8 _9 10 11 12 13 y s r 'sa^ V / / p'^ s. S ' Promontory \ * / / \ •^ 1 n of- /luscle ^ \ / / ^ 1 Anterior _ Superior- llac Spine \ 'aoas" \ \ ^ ^ / \ * ^ \ / \ \ / ^ / ■s / Poupart \ Pubes / ... 1.. en 1 1 and its relations to surrounding organs undergo considerable change. Even in the foetus it is quite variable, but its general form and position do not differ essentially from the adult condition. Glands. — According to Johnson, in an embryo of 16 mm., the lining epitheUum shows the primitive foveols as pit-hke depressions which become elongated, forming irregular anasto- mosing grooves, separated by vilJus-like projections. The pits multiply and deepen, and from their bottoms the gastric glands bud off (at 120 mm.). The parietal cells appear very early in the gland fundus, but the differentiation of gland cells is still incomplete at birth. 1158 DIGESTIVE SYSTEM Figs. 915 and 916. — Diagrams of the Contact Areas of the Stomach, Anterior and Posterior Views. cardia Mid- line of body Fig. 917. — ^The Abdominal Viscera, From Behind. (Riidinger,) Larynx Lung Diaphragm Pancreas Spleen Stomach Descending colon Inferior mesenteric vein Superior mesenteric vein Ascending colon THE STOMACH 1159 ^The circular layer of muscle is indicated at 16 mm.; the longitudinal much later, about 90 mm., and not completed before 240 mm. (F. T. Lewis). Variations. — The great variability of the stomach in form, position and relations has already been repeatedly emphasized. These variations have been most carefully studied recently by various observers in the living body by means of the Roentgen-rays. Some of the results of study by this method are sho\vn in figs. 918, 919. Peristalsis. — It would appear that most of the variations in the form of the stomach that have been described are merely various phases in the series of changes undergone by the stomach during the normal process of physiological digestion. The following account of these changes is based largely upon the radiographic observations of Cole. Earlier observations by various investigators upon the Uving stomach of man and lower animals (and especially the radiographic study of the cat by Cannon) have shown that the cardiac portion of the stomach is the first to become distended with food (and gas). Until a considerable degree of distention is reached, the pyloric portion usually remains a somewhat narrow contracted canal, along which distinct peristaltic contractions pass pylorusward. Under favorable conditions, however, the peristaltic contractions may be observed to begin in the cardiac portion, although they are usually most distinct in the pyloric portion. Each individual contraction travels at the rate of about 2,5 cm. (1 inch) per second, so that it requires several seconds for a contraction to travel from fundus to pylorus. The number of simultaneous Fig. 918. — Different Forms of the Stomach as Shown by The Rcentgen Rats. Fundus not represented. (Cole.) C — "Drain-trap D — "Fish-hook" contractions present in the stomach varies from 1 to 6 or 7, 3 or 4 being the most common. In fig. 919, a series of 10 successive radiographs show the progression in a stomach with four simultaneous individual peristaltic contractions. The peristaltic movements are further com- phcated by the appearance (simultaneously in all) of successive periods of 'systole,' during which the peristaltic contractions become stronger and deeper, and ' diastole,' in which the contractions relax and become less distinct (Cole). In fig. 919, phases 1 to 6 represent the 'systole,' and 7 to 10 the 'diastole.' A 'systole' and a 'diastole' together make up a ' gastric cycle.' During the entire progress of an individual peristaltic contraction from fundus to pylorus, the number of 'cycles' appears to correspond to the number of peristaltic con- tractions present. Thus the figure represents a stomach of the 4-cyole type. The time required for a ' cycle ' varies widely, the average (in the 3- or 4-cycle type) being about 2 or 3 seconds. In the earlier stages of gastric digestion the pylorus usually remains closed, but after a variable time it relaxes slightly (lumen about 3 mm. in diameter) at intervals, allowing the chyme to be spurted into the duodenum. Thus the various constrictions often found in the formalin-hardened stomachs, and the pyloric antrum, appear to be merely transient phases of the digestive process. The 'hour- glass' stomach is in many cases to be explained in this way; in others, however, the constriction is pathological and permanent. Various forms of abnormal lobulations and dilations also rarely occur. 1160 DIGESTIVE SYSTEM Gastroptosis is a very common abnormality in which the body of the stomach extends vertically downward to the umbilicus, or lower, forming a sharp bend beyond which the pyloric portion turns upward to reach its termination. This form is especially common in women, due to tight lacing. Fig. 919. — Serial Radiographs Taken at Short Intervals, Showing Diastole (Phases 7-10) and Systole (Phases 1-6), and the Progression toward the Pylorus op a Four-cyclBjType of Gastric Peristalsis. Fundus of the stomach not shown. (Cole.) Comparative. — The primitive stomach is perhaps merely a receptacle for food, true'digestive glands being absent in many of the fishes. The vertebrate stomach is a dilated sac of variable form, but is typically somewhat looped, with cardiac and pyloric segments. In birds, there is a peculiar arrangement, correlated with the absence of teeth. The stomach is divided into an THE DUODENUM 1161 anterior glandular proventriculus, and a posterior muscular gizzard with a homy lining serving to grind the food. The mammalian stomach is the most variable in form and structure which are correlated with the method and character of alimentation. The cardiac end of the stomach is often hned to a variable extent with a prolongation of the oesophageal stratified squamous epithelium. The three kinds of glands, cardiac, fundic and pyloric, are typically present. In general, the stomach is larger and more complicated in herbivora than in carnivora. Instead of being a single sac, the stomach may be more or less divided into chambers. An incomplete division into cardiac and pyloric portions is so common that it may be considered typical. The most extreme specialization is found in the ruminants. In these the stomach has four chambers, the first two of which, however, are expansions of the oesophagus. THE SMALL INTESTINE The small intestine [intestinum tenue] extends from the pylorus to the ileo- csecal orifice, and occupies most of the abdominal cavity below the liver and stomach. It is a cylindrical tube whose diameter decreases from about 4 cm. above to about 2.5 cm. at the lower end. Its length, when removed from the body and measured fresh, averages about 7 metres (23 ft.) ; but when formalin- hardened in situ, the length (which is probably nearer that during life) is only about 4 metres. The length does not seem to vary according to sex, height or weight in the adult, but it is said to be relatively longer in the child. The small intestine includes two main divisions, the duodenum and the mesenteric small intestine, the latter being further subdivided into jejunum and ileum. THE DUODENUM The duodenum is the first part of the small intestine, and is very definite in position and extent. It is firmly attached to the posterior abdominal wall, being almost entirely retroperitoneal. It is the widest part of the small intestine, the Fig. 920. — The Duodenum and Pancreas, Anterior View. Superior layer of transverse meso-colon Inferior layer of transverse meso-colon Inferior part of duodenum Superior mesenteric i average width being 4 cm. or more, and is also the shortest segment, being only about 25 cm. in length. In general, it is somewhat C-shaped, the concavity enclosing the head of the pancreas (figs. 920, 921, 922). Parts. — For convenience of description, the duodenum is divided into the following parts: (1) the first or superior portion [pars superior] which is short (5 cm. or less), leading from the pylorus and forming the superior flexure [flexura duodenalis superior]; (2) the descending portion [pars descendens], about 7 or 8 cm. in length, which receives the bile and pancreatic ducts and joins the inferior portion at the inferior flexure [flexm-a duodenalis inferior]; and (3) the inferior portion [pars inferior], which is again subdivided into (a) transverse portion [pars horizontaHs], about 10 cm. long, which usually ascends slightly and passes gradually into (b) the ascending portion [pars ascendens], 2 or 3 cm. long, ter- minating in the duodeno-jejunal flexure [flexura duodenojejunalis]. 1162 DIGESTIVE SYSTEM Position and relations. — As shown in fig. 914, the duodenum usually lies chiefly in the lower part of the epigastric region, only the inferior (transverse) portion extending into the umbilical region. All but the terminal (ascending) portion of the duodenum lies to the right of the mid-line. The superior portion usually lies at the level of the first lumbar vertebra (or the disk below). It is covered anteriorly, and to a variable extent posteriorly, by a prolongation of the peritoneum from the corresponding surfaces of the stomach. It is somewhat freely movable. When the stomach is empty, it extends from the pylorus almost horizontally to the right and backward. As the stomach becomes distended, however, the pylorus is carried to the right and downward for a variable distance, and the position of the superior part of the duodenum is correspondingly altered. Superiorly it is in contact with the hver (quadrate lobe) and the neck of the gall-bladder and forms the lower boundary of the epiploic foramen; anteriorly, with the liver and (often) the transverse colon; inferiorly and posteriorly, with the head of the pancreas below, and with the common bile duct, hepatic vessels and portal vein above. The second or descending portion of the duodenum extends along the right side of the first to the third lumbar vertebra. It is covered antero-laterally by peritoneum, excepting (usually) the area of contact with the transverse colon (figs. 906, 920). Posteriorly (fig. 956) it is in contact with the right kidney, ureter and renal vessels, and below with the psoas muscle. Anteriorly (fig. 906) it is crossed by the transverse colon (the layers of the transverse mesocolon usually separated by an area of direct contact); above the colon, it may be in contact with the gall-bladder, and below the colon with coils of small intestine. The Fig. 921. — The Duodenum and Pancbeas, Posterior View. Portal vein Terminal part of duodenum Head of pancreas left or medial aspect of the descending duodenum (figs. 920, 921, 922) is in contact with the head of the pancreas, and some fibres from the muscular tunic are said to become intermingled with the pancreatic lobules. Somewhat posteriorly the common bile duct descends between pancreas and duodenum, and enters the descending duodenum, in common with the pancreatic duct, about 10 cm. below the pylorus. The loop formed by the pancreatico-duodenal arteries also runs along the descending duodenum. The third or transverse portion of the duodenum usually crosses the body of the third lumbar vertebra, ascending slightly from the right to the left side (figs. 920, 921). It is covered anteriorly with peritoneum, excepting a small space where the superior mesenteric vessels enter the root of the mesentery. Anteriorly it is further in contact with coils of smaU intestine; superiorly, with the head of the pancreas, and the inferior pancreatico-duodenal vessels; posteriorly, with the vena cava. The terminal or ascending portion is covered anteriorly and laterally by peritoneum, and is in contact with coils of the ileum. To the right it is in rela- tion with the head of the pancreas (processus uncinatus) and the superior mesen- teric vessels; and posteriorly with the psoas muscle, aorta and left renal vessels. The duodeno-jejunal flexure usually lies opposite the second lumbar vertebra, and is in contact above with the inferior surface of the body of the pancreas, and the root of the transverse mesocolon. THE DUODENUM 1163 Fig. 922. — ^Dissection op the Duodenum and Pancreas, Anterior View. (Rauber-Kopsch.) 1164 DIGESTIVE SYSTEM The end of the duodenum is firmly fixed in its place by the suspensorius duodeni. This name has been given to a fibro-muscular band that contains, according to Treitz, non-striated muscular fibres, and descends to the terminal part of the duodenum from the lumbar part of the diaphragm, passing to the left of the cceliac artery and behind the pancreas. Lockwood points out that this band is continued on, after being inserted into the duodenum, between the layers of the mesentery. He suggests the name of the 'suspensory muscle of the duodenum and mesentery,' and says, 'together with the other constituents of the root of the mesentery, it forms a band of considerable strength, sufficient not only to support the weight of the intestines and mesentery, but also to resist the pressure of the descent of the diaphragm.' In connection with this fourth portion of the duodenum, mention may be made of certain peritoneal folds and fosste which are of some surgical interest by reason of their being associated with retro-peritoneal hernia. Four such fossEE may be mentioned, namely, the superior and in- ferior duodenal fossa:, paraduodenal and the retroduodenal,; f osste. On drawing the terminal portions of the duodenum to the right, two triangular folds of peritoneum, the superior and in- ferior duodenal folds, which extend from the wall of the duodenum to the posterior abdominal wall may be observed. Each fold has a free edge. Beneath each fold is found a pouch of peri- toneum, constituting the superior and inferior duodenal fossae. The former, the smaller, opens downward and is present in about 50 per cent., while the latter opens upward and is present in about 75 per cent., of the subjects examined (Jonnesco). The paraduodenal fossa (fossa of Landzert) is not often found in the adult; when present, it is situated to the left of the last part of the duodenum, and is formed by a fold of peritoneum enclosing the inferior mesen- teric vein. The retroduodenal fossa is a rare form extending from below upward behind the transverse portion of the duodenum. Interior of the duodenum. — -The interior of the first part of the duodenum is smooth. The pylorus is often somewhat invaginated, much in the same way that the uterus projects into the vagina (fig. 908). On account of this arrange- FiG. 923. — Duodenal Foss^ and Folds. Paraduodenal fossa is not shown. (After Cunningham.) Transverse meso-colon Transverse colon Superior duodenal fossa Inferior duodenal fossa The mesentery Inferior mesenteric vein Inferior mesenteric artery ment fwhich renders the complete emptying of the cavity somewhat difficult) and also on account of the distensibility of this portion, it usually shows up very distinctly in radiographic pictures as a ' cap ' to the pyloric end of the stomach during digestion. In the lower portions of the duodenum, transverse ridges or folds of the mucosa appear (fig. 922) which are also apparent in radiographs occasionally. On the medial wall of the descending portion, posteriorly, about half-way down, is a more or less distinct longitudinal fold [plica longitudinahs duodeni], toward the lower end of which is a small elevation, the bile papillaj'or papilla major [papilla duodeni], upon which open the common bile duct and the pancreatic duct, either separately or by a common aperture (fig. 922). Above the papilla there is usually a prominent hood-like fold (valvula connivens), and below it a variable fold or frcenum which forms a continuation of the plica longi- tudinahs. About 2 cm. (.9 to 3.5 cm., Baldwin) above and in front of the bile papilla there is a second, smaller, rounded papilla minor, upon which the ac- cessory pancreatic duct (of Santorini) ends. The minute structure, vascular relations, development, variations, etc., of the duodenum will be considered later, with those of the small intestine as a whole. THE JEJUNUM AND ILEUM 1165 THE JEJUNUM AND ILEUM The mesenteric portion of the small intestine is divided into an upper half (or two-fifths) , the jejunum, and a lower half (or three-fifths) , the ileum. Although the character of the gut changes considerably from the upper end of the jejunum to the lower end of the ileum, the transition is gradual, and there is no definite line of demarcation. In general, the jejunum is somewhat wider, has thicker walls, is more vascular and has a more complicated mucosa. The lymphoid organs (Peyer's patches) are, however, characteristic of the ileum. The jejunum begins at the duodeno-jejunal flexure. The first coil is variable in direction, being found (in order of frequency) as follows: (1) downward, for- ward and to the left; (2) directly forward and downward; (.3) to the left, then downward; (4) forward and to the right (Harman). Some further details as to the position of the various succeeding coils are given later under the development of the intestine (figs. 930, 931). While there is considerable individual variation, it is true in general that the coils of jejunum occupy the upper and left portion of the body cavity, while those of the ileuyn occupy the lower and right side, the lower portion lying in the pelvic cavity. The ileum finally passes upward over the pel- vic brim to the right iliac fossa where it terminates in the ileo-csecal orifice. Fig. 924. — Pohtion of the Small. Intestine, Laid open to Show the Plic.e Circtj- LARBS. (Brinton.) The mesentery [mesenterium] is a fan-shaped fold extending from the duodeno- jejunal flexure to the ileo-csecal junction. It is composed of a double layer of peritoneum which encloses and supports the jejunum and ileum and their vessels, connecting them with the abdominal wall. The root of the mesentery [radix mesenterii] or parietal attachment, is only about 15 cm. long, corresponding to a line extending from the duodeno-jejunal flexure obliquely downward and to the right, across the transverse duodenum, the great vessels and the vertebral column to the ileo-csecal junction (fig. 905). The visceral attachment of the mesentery to the intestine, corresponding to the length of the jejuno-ileum, is nearly 7 metres long, and is thinner than at the root. The loidth of the mesentery, measured from parietal to visceral attachment, varies somewhat in different parts of the canal, the average being 18 or 20 cm. (ranging from 15 to 22.5 cm.). It is narrow above (also at the lower end), but reaches its full width about 30 cm. below its upper end. Between the two peritoneal layers of the mesentery is a third layer [lamina mesenterii propria] con- taining the superior mesenteric vessels (arteries, veins and lymphatics) with their branches and accompanying nerves, the small mesenteric lymph-nodes (50 to 100 in number), and a variable amount of fibro-adipose connective tissue. Minute anatomy. — The small intestine has the four typical layers, — mucosa, submucosa, muscularis and serosa (figs. 927, 928). They are, in general, somewhat similar in structure to those of the stomach (fig. 910), excepting the mucosa. The mucosa is lined with a simple cyhndrical epithehum, underneath which is a fibrous lamina propria, limited externally by a muscularis mucosoe, as in the stomach. The muscularis mucosae sends slender muscular bundles upward into the villi. The inner surface of the mucosa (fig. 924) presents numerous coarse, closely set, transverse folds [plicaj circulares]. These are permanent, crescentic folds, involving both mucosa and submucosa, and usually extending one- half to two-thirds of the way around the lumen. They often branch and anastomose, sometimes forming circles or spirals. The largest exceed 5 cm. in length and 3 mm. in width. The plicae 1166 DIGESTIVE SYSTEM circulares are absent from the first part of the duodenum, but become well-marked in the descend- ing portion (fig. 922). They are largest and best developed in the lower duodenum and upper half of the jejunum, below which they graduaUy become smaller (fig. 924) and disappear at the lower end of the ileum. The digestive and absorptive surface of the small intestine is further greatly increased by multitudes of small processes, the villi (figs. 925, 927), which give the mucosa a velvety appear- ance. They are largest (.5 to .7 mm. in height) and most numerous in the duodenum and jejunum, where they are typically leaf-shaped, and gradually become smaller, scattered and conical in the ileum. The villi are much reduced in distention of the intestine, and may even be temporarily obliterated. Between the bases of the vilh there open short, simple tubular glands — the crypts of Lieberkuehn [gl. intestinales], whose fundus cells (of Paneth) probably secrete digestive enzymes. In the duodenum there are found, in addition, the larger tubulo- FiG. 925. — A, Surface View op the Hardened Mucosa op the Small Intestine. (After Kolliker.) B, Side View of a Wax Reconstruction op the Epithelium in the Human Duodenum. (Huber.) i g , Intestmal gland v , Villus racemose glands of Brunner [gl. duodenales], which occupy the submucosa, and are especially numerous in the upper portion of the duodenum. They are purely mucous in character ac- cording to Bensley, although Oppel describes granular cells, similar to Paneth cells, which may secrete digestive enzymes. Scattered over the whole of the mucous membrane of the small intestine are numerous small lymph-nodules, the larger of which extend into the submucosa; these are the so-caUed solitary glands [noduli lymphatici solitarii]. Aggregations of lymph-nodules, known as Peyer's patches [noduli lymphatici aggregati], situated in the mucosa and submucosa, are found in the ileum especially toward the lower end (fig. 926). They are oval, from 1.2 to 7.5 cm. in length and about 1 to 2.5 cm. in breadth, and are placed in the long axis of the bowel along a line most remote from the mesentery. They are variable in number, the average being about 20 to 30. Fig. 926.- -SuRF.\CE View op the Mucosa op the Ileum, Showing Aggregated Lymph Nodes (Peyer's Patch). (From Toldt's Atlas.) Aggregated lymph nodes Solitary lymph nodes (Peyer's patch) The submucosa is in general a loose areolar layer containing vascular and sympathetic plexuses (figs. 927, 928). The muscularis is composed of smooth muscle arranged in the two typical layers, — a thinner, outer longitudinal and a thicker, inner circular, — both of which become thinner toward the lower end of the ileum. The serosa is typical in structure, the squamous epithelial covering being absent in the retroperitoneal areas of the duodenum. Blood-supply of the small intestine. — The small intestine receives its blood from the superior mesenteric artery and a branch coming indirectly from the hepatic, the superior pancreatico- duodenal. The superior mesenteric artery runs between the layers of the mesentery and gives off six or seven relatively large branches and a variable number of smaller branches. The first two or three of the larger branches divide into an ascending and a descending branch, which join above and below with the corresponding branches of the continguous arteries, form- ing thus a single row of arches. From about the beginning of the second quarter of the small THE JEJUNUM AND ILEUM 1167 Fig. 927. — Cross-section op Ileum (contracted), a, b, c, Villi, d,- Intestinal gland, e, Tunica propria. /, /., Muscularis mucosa, g, Blood-vessel, h, Submucosa. i, Circular muscle, k, Longitudinal muscle. I, Serosa, m, Subserosa. n, Aggregated lymph nodules (Peyer's patch). (Radasch.) '^^\ ^ ^ x^.^; ) /I I 41 J '%— & / V XJ^ t Fig. 928. — Diagrams op the Vascular Supply and Nerves op the Small Intestine. A, Blood vessels; arteries as coarse black lines, capillaries as fine Hnes, veins shaded (after.Mall). B, Lymphatics (after Mall). C, Nerves, based on Golgi preparations (after Cajal). m, Mucosa. mm., Muscularis mucosae, s.m., Submucosa. cm., Circular muscle, i.e.. Intermuscular connective tissue. Z.m., Longitudinal muscle, s. Serosa, c.i., Central lymphatic. n.,"Nodule. s.pl. Submucous plexus, m.pl.. Myenteric plexus. (Lewis and Stohr.) m.m. s.m. ^^^ '■'' m.pl,^=Af_ >. 1168 DIGESTIVE SYSTEM intestine a second tier of arches, formed in a similar manner, is often noted, and below the middle of the jejuno-ileum more than two tiers of arches may be present the complexity of the arches increasing, while the size of the vessels diminishes. From the convex border of the most dis- tally placed arches there pass to the intestine straight branches, so-called vasa recta. Near the beginning of the jejunum these are numerous and large, and have a length of about 4 cm., and are quite regular. After the first third of the intestine is passed the vasa recta become smaller and shorter, and toward the lower end of the ileum they become short and irregular and are often less than 1 cm. in length. (Dwight.) The blood is returned by means of the superior mesenteric vein, which, with the splenic vein, forms the portal. The vascular ar- rangement in the intestinal wall is shown in fig. 928. The lymphatic vessels form a continuous series, which is divided into two sets — viz., that of the mucous membrane and that of the muscular coat. The lymph-vessels of both sets form a copious plexus (fig. 928). The efferent lymphatic vessels form the so-called laoteals, which pass through the mesenteric lymph-nodes, finally reaching the cisterna (receptaculum) chyli. The nerves. — The small intestine is supplied by means of the superior mesenteric plexus which is continuous with the lower part of the cceUac (solar) plexus. The branches follow the blood-vessels, and finally form two plexuses: one (Auerbach's or myenteric) which lies between the muscular coats; and another (Meissner's) in the submucous coat. The nerve fibres are chiefly from the sympathetic, partly from the vagus. Development of the small intestine. — As the intestine is being separated from the yolk- vesicle it forms at first a relatively straight tube, and as the tube elongates there is formed a single primary loop, situated in the sagittal plane of the embryo, which loop extends into the coelom of the umbilical cord; to its summit is attached the constricted attachment of the yolk- vesicle, the yolk-stalk (fig. 929). This primary loop of the intestine, as it elongates, turns on an axis, so that its caudal portion turns toward the left and its cephalic portion toward the right. We may then speak of a right and a left half of the loop. Near the top of the left half of the loop, there is noted an enlargement which marks the caecum, the greater part of the left Fig. 929. — Model of Stomach and Intestine of Human Embhyo 19 mm. Long. The figures on the intestine indicate the primary coils (X 16). (Mall.) half of the loop forming, therefore, the large intestine, while the right half of the loop forms the small intestine. In the further growth of the loop the right half elongates more rapidly than the left half, so that the caecum is no longer found in the middle of the loop. In an embryo of the fifth week, as noted by Mall, whose account is here followed closely, 'the right half of the loop has a number of small bends in it, which are of great importance in the further develop- ment of the intestine.' These small bends or loops he has marked with the numbers 1, 2, 3, 4, 5, 6. (See figs. 929, 930, 931.) The first of these bends is primarily not clear, appearing as a portion of the pyloric end of the stomach; however, it is recognised by the fact that the ducts of the liver and pancreas terminate in it, marking it as the duodenum. The omphalo-mesenteric veins and arteries, the future superior mesenteric vessels, pass through the middle of the mesentery of the large primary loop and pass over the sixth bend or secondary loop, to which is also attached the yolk-stalk. With the elongation of the intestine these six bends or loops become accentuated and acquire secondary loops or coils, nearly all of which are still found in the ccelorn of the umbihcal cord, but even with this more complicated coiling of the intestine the six primary divisions may be clearly made out. (See fig. 929.) The large mtestine, the left half of the large primary loop, lies in the sagittal plane of the embryo and does not grow as rapidly as the small intestine, and while this is acquiring the secondary coils, the whole mass rotates about the large intestine as an axis. 'By this process the small intestine is gradually turned from the right to the left side of the body, and in so doing is rolled under the superior mesenteric artery. This takes place while the large intestine has an antero-posterior direction and before there is a transverse colon.' (Mall.) With the return of the small intestine from the umbilical coelom to the peritoneal cavity, which occurs apparently quite suddenly and during the middle of the fourth month, the caecum comes to lie in the right half of the abdominal cavity, just below the liver; the greater portion of the remainder of the large intestine then lies transversely across the abdominal cavity as the transverse colon. The six groups of loops of the small intestine may still be recognised, the loops of the upper part THE SMALL INTESTINE 1169 of the small intestine having roOed to the left of the superior mesenteric artery, while the loops which were formerly in the cord are found in the right side of the abdominal cavity. It is not difficult to trace these six groups of loops through the later stages of foetal life to the new- born, and thence to the adult stage. In the adult, as also through the various stages of develop- ment, loop 1 forms the duodenum. From the primary groups of coils marked 2 and 3 are developed the greater part of the jejunum, arranged in two distinct groups of loops, situated in the left hypochondriac region. The part of the intestine developed from group 4 of the primary coils passes across the umbilical region to the right upper part of the abdomen. That part developed from group 5 of the primary coils recrosses the median line to the left iliac fossa, whUe that part derived from group 6 of the primary coils is found in the false pelvis and the lower part of the abdominal cavity between the psoas muscles. (Mall.) Figs. 900, 901, 930 may serve to make clear these statements. They present what may be regarded as the normal arrangement of the small intestine, having been found 21 times in 41 cadavers examined. Variations from this arrangement occur; the great majority of such variations are, however, not of sufficient importance to require special mention. According to Johnson (upon whose descriptions the following account is based), there is in embryos of 13 mm. to 23 mm. a formation of vacuoles in the duodenal epithelium, which Fig. 930. — Model Showing Course OF Intestine, Made phom Same Ca- daver FROM WHICH Fig. 931 was Drawn. (MaU.) Fig. 931. — The Usttal Position of the Intestine in the Abdominal Cavity. The numbers in the figure mark the parts which are homologous with the primary bends and groups of coils numbered from 1 to 6. (Mall.) leads to complete temporary occlusion of the lumen. A persistence of this condition may cause permanent atresia. In the epithelium of the small intestine numerous pockets or cysts occur, which usually disappear, but may persist and form permanent diverticula or accessory pancreas. The villi begin to appear at 19 mm., first in the mucosa of the upper portion of the intestine, as localized outgrowths which become arranged in longitudinal rows. The crypts of Lieberkuehn bud off from the epithehum at 55 mm., and from those in the duodenum, the duodenal (Brun- ner's) glands begin to bud off at 78 mm. The plicte circulares begin to appear at the mid- region of the small intestine at 73 mm. The circular muscle layer begins to appear at about 12 mm., the longitudinal at 75 mm. Variations in the small intestine. — Although relatively fixed in position, the duodenum is quite variable in form. The C-shape previously described is the most common. When the pylorus and the duodeno-jejunal flexure are approximated, the form is nearly circular. When the two ends are more widely divergent, it approaches a U-form. Not infrequently, the inferior portion ascends abruptly from the inferior angle, giving a V-form. Finally, the terminal ascending portion may be very small or absent, in which case the duodenum ap- proaches an L-form. Variations in the position of the various coils of the jejunum and ileum have already been discussed. The lymph-nodules, including Feyer's patches, like all lym- phoid structures, are prominent during youth, but become atrophied in old age. Meckel's diverticulum, which represents a derivation from the embryonic yolk stalk and sac, is found in about 2 per cent, of all adults. It is a blind tube or diverticulum of variable 1170 DIGESTIVE SYSTEM size, usually approaching the intestine in width and averaging 5 cm. in length (ranging from 1 cm. to 13 cm.). Its attachment to the intestine varies from 15 cm. to 360 cm. (average 80 cm.) above the caecum. It is usually attached opposite the mesentery. It may end freely, but is occasionally adherent to adjacent intestinal coils or connected with the anterior abdominal wall by a cord or band-hke process. Other diverticula of variable size and number may occur, usually along the mesenteric border of the intestine. They may be either congenital (probably from the embryonic pockets previously mentioned) or acquired. They occur most frequently in the duodenum (found by Baldwin in 15 of 105 cases) where they are usually associated with the openings of the bile and pancreatic ducts. Comparative. — The comparative anatomy of the small intestine will be discussed later together with that of the large intestine. THE LARGE INTESTINE The large intestine [intestinum crassum] is that part of the alimentary canal which extends between the ileum and the anus. It is divided into the following parts: Csecum, ascending, transverse, descending, and sigmoid colon, and rec- tum. It is so arranged as to surround the small intestine, making a circuit around the abdominal cavity from right to left (fig. 899). The caecum lies in the right iliac fossa; thence the colon passes vertically upward on the right side (ascending colon) until the liver is reached. Here it forms a more or less rectangular bend (the right colic or hepatic flexure), and then passes transversely across the belly (transverse colon) below the stomach. It then reaches the spleen, where it makes a second sharp bend (the left colic or splenic flexure), and, passing vertically down- ward on the left side (descending colon), reaches the left iliac fossa. At this point it forms the loop of the sigmoid colon, and finally passes through the pelvis as the rectum (fig. 906). The large intestine is much larger in diameter than the small intestine, and is not so much convoluted. Excepting the dilated portion of the rectum, it is wider at the beginning than at the end. It varies in width at different parts from 3 to 8 cm. The length from the root of the appendix or tip of the cse- cum to the point where the meso-colon ends is, in the male, about 140 cm., and in the female about 130 cm. The average total length, including the rectum, is about 150 cm. (5 ft.). The extremes found are 100 to 200 cm. The large intestine, in all parts except the rectum, has a peculiar arrangement of its walls, which gives it a very different appearance from the small intestine. It is sacculated, and the sacculations [haustra] are produced by the gut having to adapt its length to three shorter muscular bands which run the course of the intes- tine. These bands, which are about 12 mm. wide and 1 mm. thick, aie really the longitudinal fibres of the muscular wall, which are chiefly collected along three lines (fig. 935). One band [taenia mesocolica], corresponding to the attachment of the mesocolon, is posterior on the transverse colon, and postero-median on the ascending and descending colons. A second band [taenia omentalis] is antero- superior on the transverse colon, elsewhere postero-lateral. The third band [taenia libera] is free; it is inferior on the transverse colon, anterior elsewhere. All these bands start on the caecum at the vermiform process, and spread out to form a uniform layer on the rectum. Between the sacculations are semilunar folds [plicae semilunares coli], which involve the entire thickness of the intestinal wall, forming crescentic ridges of the mucosa which project into the lumen (figs. 932, 935) . Along the free surface of the colon, especially near the taeniae, are numerous small appendages [appendices epiploicae], which are pouches of peritoneum con- taining fat (fig. 906). The caecum. — The caecum [intestinum caecum] is a cul-de-sac forming the first part of the large intestine. It is defined as that part of the colon which is situated below the entrance of the ileum. Its breadth is about 7.5 cm., and its length about 6 cm. (Fig. 932). There is usually a more or less well-marked constriction opposite the ileo- caecal orifice marking the boundary between caecum and colon. The caecum itself also frequently presents a constriction dividing it into two sacculations. It lies in the right iliac fossa, and is usually situated upon the iHo-psoas muscle, and so placed that its apex or lowest point is just projecting beyond the medial border of that muscle (figs. 899, 906). It is usually entirely enveloped in periton- eum, and is free in the abdominal cavity, but more or less attached in about 10 per cent, of all cases. The apex of the caecum usually corresponds to a point a THE LARGE INTESTINE 1171 little to the medial side of the middle of the inguinal ligament. Less frequently the caecum will be found to be in relation with the iliacus muscle only; or the bulk of it will lie upon that muscle, while the apex rests upon the psoas. In a number of cases the caecum is entirely clear of both psoas and iliacus muscles, and hangs over the pelvic brim, or is lodged entirely within the pelvic cavity. Sometimes the caecum may pass even to the left of the median line of the body. This part of the colon is liable to considerable variation. Fig. 932. — Interior of the Caecum, Anterior View. (Rauber-Kopsch.) -.-PUcEe semilunares coli Frenulum (siaistrum) valvule coli Frenulum (dextrum) , valvulse coli Ostium et valvula processus vermiformis Its variations in form may be described under four types: 1. The foetal type is conical in shape, the appendix arising from the apex, and forming a continuation of the long axis of the colon. The three muscular bands which meet at the appendix are nearly at equal distances apart (fig. 933, A). When the cascum is empty and contracted it tends to approach this type. 2. The second form is more quadrilateral in shape than the last; the three bands retain their relative positions; the appendix appears between two bulging saccuU, instead of at the summit of a cone (fig. 933, B). Fig. 933. — The Four Types op C^cum. A B C (Treves.) 3. In the third type, that part of the caecum lying to the right side of the anterior band grows out of proportion to that part to the left of the band. The anterior wall becomes more developed than the posterior, so that the apex is turned so much to the left and posteriorly that it nearly meets the ileo-cajcal junction. A false apex is formed by the highly developed part to the right of the anterior band. This is the usual caecum found (fig. 933, C). 1172 DIGESTIVE SYSTEM 4. In the fourth type, the development of the part to the right of the anterior band is excessive, while the segment to the left of the band has atrophied. In this form the anterior band runs to the inferior angle of junction of the ileum with the ciecum. The root of the appendix is posterior to that angle. There is no trace of the original apex, and the appendix appears to spring almost from the ileo-cscal junction (fig. 933, D.) The ileo-csecal valve. — The ileo-caecal valve [valvula coli] is situated at the entrance of the ileum into the large intestine at the upper border of the caecum, on the posterior aspect and toward the medial side (fig. 932). The valve usually lies nearly opposite the middle of a line from the anterior superior iliac spine (left) to the umbilicus. The ileum passes from below upward and toward the right, and terminates with a considerable degree of obliquity. The valve is formed by two lip-like folds projecting into the large intestine, the upper [labium superius], and the lower [labium inferius]. They are a little oblique. The opening between them takes the form of a narrow transverse slit about 1.2 cm. in length. At the ends of the slit the valves unite and are prolonged at either end as a ridge [frenu- lum valvula; coli] partially surrounding the intestine. Villi cover that surface of the folds looking toward the ileum; the surface toward the large intestine is free from villi. In the formation of this valve the longitudinal muscular fibres pass across from the ileum to the large intestine without dipping down between the two layers of each fold. The circular muscular fibres, on the other hand, are contained between the mucous and submucous layers which form these folds. The efficiency of the valve in preventing the return of faeces is due largely to its oblique position. (Symington.) Fig. 934. — C^ctjm, Vermiform Process, and End of Ileum, with the Blood-supply and THE Neighbouring Foss.e. (Woolsey, after Merkel.) Sup. ileo-caec. fossa Plic. ileocsec. ant. T.V ,- imnmim'r^^ \ \ -^£r^ \ >. Vertex of bladder ^ \ ^ Middle umbilical ligament Parietal peritoneum uteri Recto-uterine fold , Recto-uter- \ / ine (recto- vaginal) pouch TJrachus Symphysis pubis Labium majus Body of uterus Labium minus External orifice of urethra Urethra' , Internal orifie of urethra / Orifice of vagina Rectum Posterior labium External os uteri Anterior labium Anus Vagina ' Vesico-uterine pouch Vestibule The upper or first portion of the rectum is about 10 cm. long, and is concave forward [fiexura sacralis] except at the lower end where it curves backward and downward [flexura perinealis] to join the second portion. The lower part of the first portion often presents a dilation [ampulla recti], due to accumulation of faeces. This part is sometimes described as the infra-peritoneal portion of the rectum proper. Anteriorly, the rectum is in contact with coils of ileum and, in the male, with the trigone of the bladder, the vesiculse seminales, ductus deferentes, and posterior aspect of the prostate (fig. 937). In the female, it is in contact anteriorly with the vagina and the cervix uteri (fig. 938). Posteriorly, it is in contact with the sacrum, coccyx and ano-coccygeal body. In the male, a small band of muscle fibres, the recio-urethral muscle, extends from the per- ineal flexure of the rectum to the membranous urethra. THE RECTUM 1177 The peritoneum is reflected anteriorly from the rectum to the bladder in the male (recto-vesical pouch) and to fornix of the vagina in the female (recto-vaginal pouch). In the newborn, the peritoneum reaches to the base of the prostate (Symington). On the posterior surface of the gut, there is no peritoneum below a point about 12.5 cm. from the anus. Thus the peritoneum at the upper end of the rectum entirely surrounds the gut. Lower down it covers only the sides and anterior wall, and lower still the anterior wall only, where it is reflected upon the bladder or vagina. The second portion of the rectum, or anal canal [pars analis recti] is from 2.5 cm. to 3.5 cm. in length. From the lower end of the first portion, it turns at right angles downward and backward, passing through the pelvic floor, and ending at the anus. It is entirely below the peritoneum, and is surrounded by the two sphincter muscles (figs. 936, 937). Anteriorly is the bulb of the urethra and the posterior margin of the urogenital trigone in the male (fig. 937), while in the female it is separated from the vestibule and the lower part of the vagina by the 'perineal body' (fig. 938). Posteriorly it is connected with the tip of the coccyx by the ano-coccygeal body. Laterally it is in contact with the margins of the levatores ani, which act as an acoessory_ sphincter, and help to support the ampulla recti. The anus. — The anus is the aperture by which the intestine opens externally. During life it is contracted by the sphincters, so as to give the surrounding skin a wrinkled appearance. Around the lower part of the rectum and anus certain muscles that are connected with its proper function are situated. They are the internal sphincter, the levator ani, and the external sphincter. The levator ani and external sphincter will be found described in the section on Musculature. The internal sphincter is a thickening of the circular fibres of the intestine, situated around the second portion or anal canal. It forms a complete muscular ring, 2 to 3 mm. thick, and is composed of non-striated muscle. The rectum differs from the rest of the colon in having smoother walls and no appendices epiploicse. At the upper end of the rectum, the taenia libera and taenia omentalis join to form a broad band which spreads out, covering the entire anter- ior aspect of the rectum. Similarly the taenia mesocolica spreads out upon the posterior aspect. Thus the rectum has a complete longitudinal muscle layer, which, however, is thicker anteriorly and posteriorly than laterally. It sends a bundle of fibres to the coccyx [m. recto-coccygeus]. Below, the longitudinal layer passes between the two sphincters and breaks up into numerous bundles which are interwoven with the external sphincter and levator ani, some of them terminating in the circumanal skin. Its mucous membrane is thicker than that of the rest of the large intestine. Certain folds, chiefly longitudinal in direction, are seen in the lax state of the tube, which disappear when distended, but Houston had described three permanent oblique transverse folds [plicae transversales recti] (fig. 936), containing bundles of non-striated muscle-cells, which project into the lumen of the tube: one is on the right at the level of the reflection of the peritoneum from the rectum; and two are on the left, one above and one below the right fold. That upon the right side is the largest and most constant, and its muscular bundle is sometimes called the sphincter tertius. It is located about 7.5 cm. above the anus. These folds, like the corre- sponding semilunar folds of the colon, when well marked involve the entire wall. The mucous membrane of the upper portion of the anal canal presents a series of vertical folds known as rectal columns [columnae rectales] (columns of Morgagni), containing bundles of non-striated muscle longitudinally arranged. These columns become more prominent as they extend downward. Just above the anus each two adjacent columns are united by an arch-hke fold of mucous membrane, these folds forming what are known as the anal valves, while the small fossse behind them are known as the rectal sinuses. The area below the valves and extending to the anus is termed the annulus hcemorrhoidalis (fig. 936). This is lined by a modified skin, while the area above the valves forms a transition to the typical mucosa of the rectum. Minute structure of the large intestine. — In general, the large intestine has the four coats (fig. 939) — mucosa, submucosa, muscularis, and serosa — characteristic of the alimentary canal. The mucosa lacks the villi and plicae circulares characteristic of the small intestine. It contains many solitary lymphatic nodules, but no Peyer's patches. It differs from the stomach in the absence of foveolse, and in the presence of large numbers of mucous 'goblet cells' found both on the surface and along the numerous crypts of Lieberkuehn (which con- tain no cells of Paneth). The subrnucosa is much as in the small intestine. The muscularis has a continuous inner circular layer, the outer longitudinal fibres being chiefly gathered into the three bands, the teniae coh, as above mentioned. The serosa is typical, excepting extra- peritoneal areas where the epithehum is lacking. The appendices epiploicae were also mentioned above. The caecum and colon present no special features worthy of mention, beyond the typical structure above outlined. 1178 DIGESTIVE SYSTEM The vermiform process, however, differs in several important respects (fig. 940). The walls are relatively thick and the lumen small. The solitary lymph nodules are closely packed or confluent (especially in young people). They occupy the greater part of the sub mucosa, and somewhat resemble the Payer's patches of the ileum. They, like all the lymphoid structures Fig. 939. — Cross-section of the Large Intestine, a, Mucosa. 6, Submucosa. c, Mus- cularis. d, Serosa. (Radasch.) in general, tend to become atrophied in old age. Fat cells are usually abundant in the sub- mucosa. The muscularis presents an inner circular layer and also a thin but complete outer longitudinal layer. The serosa is typical. The lumen shows a progressive tendency to ob- literation as age advances (Ribbert). This condition is never found in infancy but occurs Fig. 940. — Transverse Section of the Human Vermiform Process. (X 20). (Stohr and Lewis, from Sobotta.) Note absence of villi and abundance of lymph nodules. F, Clusters of fat cells in submucosa. Only the inner part of the circular muscle is shown. usually only partial) in over 25 per cent, of adults and in 50 per cent, of all cases over 50 years of age. It is, however, somewhat uncertain whether this represents a normal process. In obliteration, the glands and lymphoid nodules disappear, and the entire mucosa is transformed into an axial mass of fibrous connective tissue. The rectum also presents several peculiarities of structure. Attention has already been / THE LARGE INTESTINE 1179 called to the transverse folds (of Houston) and the rectal columns, sinuses and valves. Just above the valves, the mucosa is transitional, the epithelium being partly stratified, and the crypts of Lieberkuehn few and scattering. Below the valves, the annulus hEemorrhoidalis is lined by a modified slcin. Hairs and sebaceous and sweat glands do not appear until just outside the anal orifice. The thickening of the circular muscle to form the internal sphincter, and the somewhat uniform disposition of the longitudinal muscle have already been mentioned, as well as the absence of a serous coat in the lower portions. Blood-vessels. — The large intestine is supplied with blood by the branches of the superior mesenteric and inferior mesenteric arteries, while it also receives a blood-supply from the internal iliac at the rectum. The vessels form a continuous series of arches from the caecum, where the vasa intestini tenuis anastomose with the ileo-colic, the first branch of the superior mesenteric given to the large intestine. The blood-supply of the rectum is from the inferior mesenteric by the superior ha^morrhoidal, from the hypogastric (internal ihac) by the middle haemorrhoidal, and from the internal pudic by the inferior hEemorrhoidal. The vessels at the lower end of the rectum assume a longitudinal direction, communicating freely near the anus, and less freely above. The blood of the large intestine is returned into the portal vein by means of the superior mesenteric and inferior mesenteric veins. At the rectum a communication is set up between the systemic and portal system of veins, since some of the blood of that part of the intestine is returned into the hypogastric (internal ihac) veins. In the lower end of the rectum the veins, like the arteries, are arranged longitudinally. This arrangement is called the haemorrhoidal plexus. The vermiform process is supphed by a special branch of the ileo-colic artery (fig. 934). This branch, the appendicular artery, crosses behind the terminal portion of the ileum (where pressure may obstruct the circulation) to enter the mesenteriolum. An accessory artery of small size also descends along the medial margin of the colon and caecum, entering the base of the appendix. The nerves and lymphatics of the large intestine differ in no important particular from those of the small intestine, so far as their relations within the intestinal wall are concerned. The efferent lymphatic vessels in general follow the blood-vessels and pass through cor- responding lymph nodes in the various regions (see p. 734). Those of the caecum and vermi- form process pass through the appendicular and ileo-caecal nodes; those of the colon through mesocolic and mesenteric nodes. Those of the descending and sigmoid colons connect with the inferior mesenteric and lumbar nodes. The superior zone of the rectum is drained by lymphatics passing to the ano-rectal and inferior mesenteric nodes; the middle zone (region of rectal columns) to nodes along the three haemorrhoidal arteries; the inferior zone (anal in- tegument) chiefly to the superficial inguinal nodes. Development of the large intestine. — At an early stage in the development of the intestinal . canal, when this presents a single primary loop and soon after this loop has turned on its axis, there is observed on the left half of the loop, near its top, an enlargement which marks the be- ginning of the large intestine. With further growth this enlargement develops a lateral out- growth on the side opposite to that to which the mesentery is attached, therefore free from the mesentery. A conical projection of the large intestine or colon beyond the place where this is joined to the small intestine is thus formed. This conical projection or pouch of the large in- testine, which continues the colon somewhat beyond the insertion of the small intestine, develops into the caecum and the vermiform process. It does not present, in its further growth, a uniform enlargement. The portion nearest the colon grows in size more rapidly than the terminal por- tion, this difference in size becoming more apparent as development proceeds, the smaller terminal portion forming the vermiform process. On the return of the intestine to the peritoneal cavity (in embryos of about 40 mm.) the csecum lies on the right side, immediately below the liver. During the later fcetal months the caecum gradually descends into the right iliac fossa, and there is thus established an ascending colon. The caecum may, however, even in the adult, retain its embryonic position on the right side immediately beneath the liver, or may descend farther than usual. The ascending and descending colons, the sigmoid meso-colon (in part), and the rectum with corresponding portions of the mesorectum, become adherent to the posterior body wall during the fourth and fifth fcetal months. At the same time, the posterior layer of the great omentum becomes fused with the upper (anterior) surface of the transverse meso-colon. The layer of retroperitoneal fascia corresponding to the obliterated mesocolon is shown in fig. 1005. Variations in the process of fusion give rise to numerous peritoneal variations in the adult. The sigmoid colon is relatively long at birth. On account of the relatively small size of the true pelvic cavity, both sigmoid colon and coils of ileum are usually excluded from it in the foetus and infant. In fcetuses of four to six months (length 100 mm. to 240 mm.) transitory viUi appear in the mucosa throughout the large intestine, including the vermiform process. They appear in rows, corresponding to longitudinal folds. Their early obliteration is possibly due to dis- tention of the gut by the meconium.-' The glands bud off like those of the small intestine. Lymphoid nodules are present abundantly in the vermiform process at birth (Johnson). The circular muscular layer begins to appear in the lower part of the large intestine at 23 mm.; the tenia at 75 to 99 mm. (F. T. Lewis). Development of the rectum and anus. — The posterior end of the primitive intestine or arch- enteron, designated the hind-gut, presents a terminal portion which is somewhat dilated and known as the cloaca, into the lateral and ventral portions of which open the Wolffian ducts, and from the ventral portion of which arises the allantois. The ventral portion of the cloaca, which is an entodermal structure, comes in contact with the ectoderm to form the cloacal membrane, and this forms the floor of a slight depression. For a time the cloaca or hind-gut extends for some distance caudal to the cloacal membrane, forming what is known as the post anal gut; this, however, soon disappears. Early in the development of the human embryo 1180 DIGESTIVE SYSTEM when this has attained a length of about 6.5 mm., the fold which separates the cloaca and hind, gut from the allantois deepens, and folds develop from the lateral walls of the cloaca which meet and gradually separate the cloaca into a dorsal portion, which forms the rectum, and a ventral portion which forms the uro-genital sinus. This uro-rectal septum extends in its further growth until the cloacal membrane is reached, separating it into a ventral portion known as the uro- genital membrane, and a dorsal portion known as the anal membrane. The anal membrane ruptures comparatively late in development, establishing thus a communication between the hind-gut (rectum) and the exterior. The mesoderm develops around the lower end of the rectum, so that the ectoderm becomes slightly invaginated and hnes the portion of the anal canal below the valves. A want of ruptui-e of the anal membrane constitutes an arrest of devel- opment known as atresia of the anus. Folds of the mucosa representing the rectal columns, valves and sinuses appear in embryos during the third month, and are well developed during the latter half of the foetal period (Johnson). Variations. — The large intestine is exceedingly variable in its structure and relations, especiaUy with reference to the peritoneum — so much so that it has been found more convenient to include a consideration of the variations along with the preceding description of the individual parts. The content of faeces (and gas) is as a rule relatively greatest in the csecum, decreasing in ascending and transverse colons. The descending colon is usually empty, or nearly so, the sigmoid colon and rectum somewhat variable. The rectal ampulla is usually more dilated in women. Comparative. — The morphology of both small and large intestines will be briefly considered here. As previously mentioned, the primitive form of intestine is a comparatively straight tube extending from stomach to anus, and connected by a primitive mesentery to the mid- dorsal line of the body cavity. There is in many of the lower forms no clear division into small and large intestine, though the rectal region is usually more dilated, and opens into a cloaca. Diverticula often occur in the region between large and small intestine. In many fishes, numerous "caeca" occur just below the pylorus, and in others an extensive spiral valve projects into the lumen of the intestine. The absorptive and digestive surface of the mucosa is further increased by the formation of various kinds of folds, and (beginning in amphibia) of villi. Lymphoid tissue is typically present in the mucosa, often locaUzed in definite masses. Solitary nodules appear in amphibia, and Peyer's patches in birds. Tubular mucous glands occur in the lower forms, but Brunner's glands and crypts of Lieberkuehn with Paneth cells apparently only in mammals. A cmcum is usually present from the reptiles upward (double in birds), and often forms an important organ of digestion. The bile and pancreatic ducts open constantly a short distance below the pylorus. The small intestine is always longer than the large, but there is extreme variation in length among the various species. The four tunics — mucosa, submucosa, muscularis and serosa — are tjqDical for vertebrates, the muscularis consisting of inner circular and outer longitudinal smooth muscle fibres. Among mammals, the divisions of the intestine correspond in general to those found in the human species, but there is exceedingly great variation in the relative development of the various parts. In general, the length, size and complexity of structure is relatively greatest in the herbivora (whose food is more difficult of digestion), least in the carnivora, and intermediate in the omnivora. Even in the same species, the structure of the intestine may be appreciably modified according to habitual diet. The large intestine varies, but is always shorter and wider than the small intestine. In mammals the rectum only is said to be homologous with the large intestine of lower vertebrates. The cmcum is rarely absent and is enormously developed in herbivora. It often contains large amounts of Ij'mphoid tissue, which, in pig and ox forms a so-called 'intestinal tonsil. ' The vermiform process (found typically developed in man and higher anthropoids) apparently represents a retrogressive evolutionary change in the cffical apex, although this interpretation is denied by some (Berry), who interpret the appendix as a progressive, functional lymphoid organ. THE LIVER The liver [hepar] is tiie largest gland in the body. Its secretion, the bile [bills ; fel], is poured into the duodenum through the common bile duct. In addition it has important functions as a 'ductless gland' in connection with the nitrogenous and carbohydrate metabolism. In form it is a variable somewhat irregular mass, roughly comparable to a modified hemisphere occupying the upper right portion of the abdominal cavity (figs. 899, 914). It presents a convex, rounded upper or parietal aspect, which is in contact with the diaphragm and adjacent body walls, and a lower, flattened visceral surface, in contact with the abdominal viscera. When viewed from the front, it is somewhat triangular in outline, occupying the right hypochondriac, the epigastric and (slightly) the left hypochondriac regions. Physical characters. — In weight, the liver averages about 1500 gm. (3| lbs.), but it is exceedingly variable, commonly ranging from 1000 gm. to 2000 gm. Its relative weight is also variable, averaging about 2.5 per cent, of the body in the adult male (somewhat higher in the female). Its specific gravity averages 1.056, so that the average weight of 1500 gm. would correspond to a volume of 1420 cc. Its dimensions are also quite variable. Its greatest depth (antero-posterior) averages about 15 cm., and its greatest height (vertical) is about the same. Its THE LIVER 1181 width (horizontal) is about 20 cm., while its greatest length (measured obliquely from side to side) averages about 25 cm. The colour of the liver is a reddish- brown. It is firm in consistency, but friable, so that it is easily ruptured. Surfaces and borders. — The most general division of the surface of the liver, Fig. 941 — Superior Surface op the Liver. Site of the caudate (Spigelian) lobe as above stated, is into two — the parietal and the visceral. The parietal surface is again subdivided, usually into two surfaces — posterior and superior. The posterior surface [facies posterior] is triangular (fig. 943). It is wide on the right, where the right lobe is in contact with the diaphragm (corresponding Fig. 942. — Inferior Surface of the Liver. Vena cava inferior Common bile-duct Portal Hepatic artery Caudate (Spigelian) lobe Umbilical fissure chiefly to the 'uncovered area' of the coronary ligament), and narrow on the left side, where the posterior margin of the left lobe is likewise attached to the dia- phragm. At the lower, left hand corner of the right lobe is a small triangular area of contact with the suprarenal body [impressio suprarenalis]. Near the mid-line 1182 DIGESTIVE SYSTEM is the caudate (Spigelian) lobe, opposite the tenth and eleventh thoracic vertebral bodies, from which it is separated by the diaphragm (chiefly the right crus). On the right of the caudate lobe is the fossa lodging the vena cava (sometimes bridged over), while to the left is the fissure of the ductus venosus, giving attach- ment to the upper portion of the lesser omentum (relations in cross-section shown in fig. 945). The superior surface [facies superior] is in general convex and moulded to the inferior surface of the diaphragm (fig. 941). Tne relations in cross-section of the Fig. 943.- -PosTEEioE Surface of the Livdr. Vena cava inferior Tuber omentale Papillary process of caudate (Spigelian) lobe Impression for right kidney body are shown in fig. 945. It extends downward upon the anterior abdominal wall to a variable extent in the epigastric region, including the entire area of the liver visible from the front (fig. 941). It also presents a broad area extending downward on the right side. Symington accordingly distinguishes three surfaces corresponding to the superior surface above described, viz., right surface, anterior surface and superior surface. The superior surface is related above, through the diaphragm, with the base of the right lung, the pericardium and heart, and (on the extreme left) with the base of the left lung. Where it rests upon the liver, the heart forms a shallow fossa [impressio cardiaca]. Fig. 944. — Diagram Showing Ligaments on the Dorso-inferior Aspect of the LrvER. (Lewis and Stohr.) c.l., Coronary lig. f.l. Falciform lig. g.b., Gall bladder, l.o., Lesser omentum, l.t.l., Left triangular lig. o.b., Caudate lobe, p.v., Portal vein, r.l., Lig. teres, r.t.l., Right triangular lig. v.c.i., Vena cava inf. .Itl The inferior or visceral stxrface [facies inferior] (fig. 942) faces downward and backward. It is irregularly concave, with impressions due to contact with the underlying viscera. It is divided into three lobes, right, left, and quadrate, whose relations will be described later. Of the borders, the anterior [margo anterior] is the best marked. It forms the inferior boundary of the triangular anterior view of the liver (figs. 899, 914, 941), and separates the superior from the inferior surface. Slightly to the left of the mid-line, it often presents a slight umbilical notch [incisura umbilicalis], where it THE LIVER 1183 is crossed by the falciform ligament. The posterior surface is separated from the superior and inferior surfaces by ill-defined postero-superior and postero-inferior borders. Surface outline. — The average position of the hver may be outlined upon the anterior surface of the body as follows (fig. 914): Locate one point on the right mid-clavicular (mid- Poupart) line opposite the fifth rib; a second point on the left mid-clavicular line about 2 cm. lower, in the fifth interspace; and a third point about 2 cm. below the costal arch (10th rib) on the right lateral wall. A line slightly concave upward, joining the first and second points defines the uppermost aspect of the lever. A line, strongly convex laterally, joining the first and third points, defines the right side of the liver. Finally, a third line, joining the second and third points, corresponds to the anterior border and defines the lowermost portion of the liver. This line is subject to many individual variations. In general, it is usually slightly convex downward as it crosses the epigastric region. It usually presents a slight umbilical notch, as before mentioned, and frequently a notch for the fundus of the gall-bladder, which is placed near the right mammarj' (mid-Poupart) line. The lower and right portion of the anterior border of the liver runs somewhat parallel with the infracostal margin. In the upright position, and in livers larger than usual, it extends about 2 cm. below the hypochondrium into the right lateral abdominal (lumbar) region (fig. 914). In the supine position, however, the liver recedes about 2 cm. toward the head. The liver of course participates also in the respiratory movements of the diaphragm. Fig. 945.- -Ceoss-section of Body at Level op the Eleventh Thoracic Vertebra. (Poirier-Charpy.) Caudate lobe of liver Suprarenal gl. Vena cava inf. 1 I Aorta Spleen Falciform lig. Lobes and fissures. — The superior surface is divided by the falciform ligament into two areas, corresponding to a larger right and a smaller left lobe (fig. 941). On the posterior and inferior surfaces of the liver (figs. 942, 943), an H-shaped arrangement of fossae and fissures completes the demarcation of lobes. The left upright of the H [fossa sagittalis sinistra] corresponds to the prolongation of the line of attachment of the falciform ligament. It is made up of the umbilical fissure [fossa venae umbilicalis], containing the round ligament, on the inferior surface; and of the fossa ductus venosi, containing the ligamentum venosum (obliterated ductus venosus) and the upper part of the lesser omentum, on the posterior surface of the liver. This left sagittal fossa separates the left lobe of the liver from the right lobe (in the wider sense of the term). The right lobe is further subdivided by the right upright and cross-bar of the H. The right upright [fossae sagittales dextrae] is made up of the broad fossa for the gall-bladder [fossa vesicae felleae] on the inferior surface, and the broad fossa vence cavce on the posterior sur- face (fig. 943. These two fossae are not continuous, but are separated by a narrow strip of liver, the caudate process of the caudate lobe (fig. 942). The cross-bar of the H is formed by the transverse or portal fissure [porta hepatis], which encloses the root structures of the liver, within the lower part of the lesser omentum (fig. 942). The area anterior to the cross-bar of the H corresponds to the quadrate 1184 DIGESTIVE SYSTEM lobe of the inferior surface; that posterior to the cross-bar to the caudate lobe of the posterior surface; while the remainder of the liver, to the right of the H, is the right lobe (in the narrower sense). The right lobe [lobus hepatis dexter] makes up the greater part of the hver. Its relations on the superior and posterior surfaces have already been mentioned. On the inferior or visceral surface (fig. 942), there appears posteriorly a large concavity [impressio renalis] for the right kidney; medially a faint impression [impressio duodenalis] for the descending duodenum; and antero-inferiorly a variable area [impressio coHca] of contact with the right (hepatic) flexure of the colon. The caudate process joins the right with the caudate lobe. The left lobe [lobus hepatis sinister] lies to the left of the left sagittal fissure and the falci- form ligament. It is flattened but variable in form and size, and makes only about one-fifth of the entire liver. In children and especially in early foetal life, it is relatively much larger. At the left extremity, there is usually found in the adult liver a variable fibrous band [appendix fibrosa hepatis] representing the atrophied remnant of the more extensive gland in earlier life. In this fibrous appendix (and in other parts of the liver) the bile ducts of the atrophied liver substance persist as vasa aberrantia hepatis. The left lobe is related superiorly, through the diaphragm, with the heart and the base of the left lung. Injeriorly (fig. 942) it presents a large concavity [impressio gastrioa] which is in contact with the anterior surface of the stomach. Above and behind the gastric impression is the rounded tuber omentale which is placed above the lesser curvature of the stomach and re- lated, through the lesser omentum, with a corresponding tuberosity on the pancreas. To the left of the tuber omentale, and near the posterior aspect of the liver, is a small inconspicuous groove [impressio cesophagea] for the abdominal part of the oesophagus. The quadrate lobe [lobus quadratus] lies, as before mentioned, on the inferior surface of the liver (fig. 942) in the anterior or inferior area of the H. It is in contact with the pylorus and the first part of the duodenum. Pig. 946. — Relation op STBucTtrRBs at and Below the Teansvekse or Portal PissuHE. Anteioe view. (Thane.) Common bile-duct- The caudate or Spigelian lobe [lobus caudatus; SpigeU] was described on the posterior sur- face of the liver (fig. 943). Inferiorly, the caudate lobe, behind the portal fissure, is divided by a notch into two processes. The left or papillary process [processus papillaris] is short and rounded, and lies opposite the tuber omentale. In the fcetus it is relatively much larger and ia in contact with the pancreas. The right or caudate process [processus caudatus] is of variable size, and joins the caudate with the right lobe of the hver. It is usually small and inconspicuous. In the foetus, however, it is relatively much larger, and extends downward to a variable extent behind the duodenum and head of the pancreas. In the adult, it forms the upper boundary of the epiploic foramen (of Winslow). Peritoneal relations. — -The liver in the adult is almost entirely surrounded by peritoneum. Although it develops together with the diaphragm in the common septum transversum (as explained previously, see figs. 951,952), the peritoneum soon extends in between liver and diaphragm, so that they remain in immediate contact only in the so-called 'uncovered area.' This is an irregular area on the posterior surface of the liver (chiefly on the right lobe), the margins of which cor- respond to the coronary ligament (figs. 905, 944). The posterior surface of the liver is therefore chiefly retroperitoneal, excepting the caudate (Spigelian) lobe, which is in contact with the recessus superior of the bursa omentalis (fig. 905). The superior and inferior surfaces of the liver are entirely covered with peritoneum, excepting the lines of attachment of the various peritoneal ligaments, and the fossa for the gall-bladder, which is usually directly in contact with the gall blad- der with no intervening peritoneum. Ligaments. — The liver is attached by five peritoneal ligaments — coronary, right and left triangular (lateral) and falciform ligaments and lesser omentum—" and two accessory ligaments — teres and venosum. The coronary ligament [lig. coronarium hepatis], as before mentioned, corre- THE LIVER 1185 sponds to the reflections of peritoneum from the liver to the diaphragm at the mar- gins of the 'uncovered area' (fig. 944) on the posterior surface of the liver. Within this uncovered area the hepatic veins join the inferior vena cava. The coronary ligament, though somewhat irregular and variable in form, is elongated laterally and roughly quadrangular. At the four angles, the peritoneal layers come together and are prolonged into four ligaments — right and left triangular (lateral) and falciform hgaments and lesser omentum. There is often also a special prolongation of the coronary ligament downward upon the right kidney, forming the hepato-renal ligament [lig. hepatorenale]. This lies to the right of the fora- men epiploicum. The right triangular (or lateral) ligament [hg. triangulare dextrum] is a short but variable prolongation of the coronary ligament to the right and downward (figs. 905, 944) . It connects the posterior surface of the right lobe of the liver with the corresponding portion of the diaphragm. The left triangular (lateral) ligament [lig. triangulare sinistrum] is a longer, narrower pro- longation of the coronary ligament to the left (figs. 905, 944). It connects the posterior as- pect of the left lobe of the hver with the corresponding portion of the diaphragm. The falciform ligament [lig. falciforme hepatis] is a double layer of peritoneum representing (as before mentioned) the ventral portion of the primitive ventral mesogastrium. Its upper end is continuous posteriorly with the coronary ligament. It passes forward and downward over the superior surface of the liver. From its line of attachment to the liver (between right and left lobes) it passes forward and slightly to the left to the attachment on the anterior body wall. This attachment extends downward slightly to the right of the mid-line to the umbilicus. The lower margin of the falciform ligament is free, and encloses the roimd ligament. The round ligament [lig. teres hepatis] is a fibrous cord representing the obliter- ated foetal left umbilical vein. It extends upward from the umbilicus enclosed in the lower margin of the falciform ligament. At the anterior margin of the liver it passes backward on the inferior surface, enclosed in a slight peritoneal fold at the bottom of the fossa vense umbilicalis (sometimes bridged over by liver tissue). It ends by joining the left branch of the portal vein. The ligamentum venosum [lig. venosum; Arantii] similarly represents the obliterated fcetal ductus venosus. It is a fibrous cord lying in the fossa ductus venosi, and e.xtends from the left branch of the portal vein upward to the left hepatic vein near its opening into the vena cava. The ligamentum venosum lies within the hepatic attachment of the lesser omentum. The lesser omentum [omentum minus] has already been discussed in connec- tion with the peritoneum. It represents the dorsal part of the primitive ventral mesogastrium, extending from the stomach to the liver. It includes two parts, as shown in fig. 906. The upper and larger part forms the gasiro-hepalic ligament [lig. hepato-gastricum], connect- ing the liver (fossa ductus venosi) with the lesser curvature of the stomach. The upper part of this ligament is somewhat thicker, the lower part thinner and more transparent. The rela- tions of the lesser omentum in cross-section of the body are shown in fig. 903. The lower and right portion of the lesser omentum extends beyond the pylorus and connects the portal fissure with the duodenum, forming the hepalo-duodenal ligament [lig. hepatoduodenale] (fig. 905). Its right margin forms the anterior boundary of the epiploic foramen (of Winslow). Between its layers are located the root structures of the hver, as follows: hepatic artery to the left, common bile duct to the right, portal vein behind and between. A special prolongation of the hepato-duodenal ligament frequently extends downward to the transverse colon, forming the hepato-colic ligament [lig. hepatocoHcum]. Fixation of the liver. — The liver is to a certain extent fixed in place by means of its various ligaments, and especially through the attachment of the hepatic veins to the inferior vena cava. On account of the close apposition of the liver to the diaphragm, the atmospheric pressure also helps in its support. Finally, the sup- port of the liver, as well as of the abdominal viscera in general, is dependent to a considerable extent upon the tonic contraction of the abdominal muscles, which exerts a constant pressure upon the abdominal contents. Blood-vessels. — The liver receives its arterial supply of blood from the hepatic artery, a branch of the coeliac, which passes up between the two layers of the lesser omentum, and dividing into two branches, one for each lobe, enters the liver at the portal fissure. The right branch gives off a branch to the gall-bladder. The liver receives a much larger supply of blood from the portal vein, which conveys to the liver blood from the stomach, intestines, pancreas, and spleen. It enters the portal fissure, and there divides into two branches. Below this fissure the hepatic artery lies to the left, the bile-duct to the right, and the portal vein behind and between the two (fig. 946). These three structures ascend to the liver between the layers of the lesser omentum in front of the epiploic foramen. At the actual fissure the order of the three structures from before backward is — duct, artery, vein. 1186 DIGESTIVE SYSTEM The hepatic veins, by which the blood of the hver passes into the inferior vena cava, open usually by two large and several small openings into that vessel on the posterior surface of the gland at the bottom of the fossa venae cavoe. Lymphatics. — The lymphatics are divided into a deep and a superficial set. The deep set runs with the branches of the portal vein, artery, and duct through the liver, leaving at the portal fissure, where they join the vessels of the superficial set. The efferent deep vessels after leaving the portal fissure pass down in the lesser omentum in front of the portal vein, through the chain of hepatic lymphatic nodes, and ultimately end in a group of nodes at the upper border of the neck of the pancreas, in which the pyloric lymphatics also terminate. The superficial set begins in the subperitoneal tissue. Those of the upper surface consist: — (1) Of vessels which pass up, principally, in the falciform ligament and right and left triangular ligaments, through the diaphragm, and so into the anterior mediastinal nodes, and finally into the right lymphatic duct. Some lymphatics of the right triangular ligament pass to the posterior mediastinal lymph-nodes and into the thoracic duct. (2) Of a set passing downward over the anterior border of the liver to the hepatic nodes in the portal fissure, and over the pos- terior surface to reach the superior gastric and coeliac nodes. On the lower surface, the lym- phatics to the right of the gall-bladder enter the lumbar nodes. Those around the gall-bladder enter the hepatic nodes of the lesser omentum. Those to the left of the gall-bladder enter the superior gastric nodes. Nerves. — The nerves of the liver are derived from the vagi (those from the left vagus entering from the stomach through the lesser omentum), and from the coehac plexus of the sympathetic (including right vagus branches) through a plexus accompanying the hepatic artery. The terminations, so far as known, are chiefly to the walls of the vessels and of the bile ducts. Structure of the liver. — The liver is, for the greater part, covered by peritoneum, beneath which is found the fibro-elastio layer known as Glisson's capsule. At the portal fissure, Ghsson's capsule passes into the substance of the liver, accompanying the portal vessels, the branches of the hepatic artery, and the bile-ducts. The hver substance is composed of vascular units measuring from 1 to 2 mm., and Icnown as hver lobules. These are in part (man) separated by Fig. 947. — Section of a Portal Canal. (Quain.) Branch of porl'al vein I I -^ Lymphatics in Glisson's capsule Lymphatics in Glisson's capsule -r^^ I -Branch of hepatic artery a small amount of interlobular connective tissue, which is a continuation of Ghsson's capsule. In this interlobular connective tissue are found the terminal branches of the portal vessels; the hepatic artery, and the bile-ducts (figs. 947, 948). The branches of the portal vessels which encircle the liver lobules are known as the interlobular veins. From these are given off hepatic capillaries, which anastomose freely, but have in general a direction toward the centre of the lobule, and unite to form the central or intralobular veins, which in turn unite to form the sub- lobular veins, and these the hepatic veins. The intralobular branches of the hepatic arteries form capillaries which unite with the capillaries of the intralobular portal veins. The liver is a modified compound tubular gland. The liver-cells are arranged in anas- tomosing cords and columns occupying the spaces formed by the hepatic capillaries. The bile-ducts have their origin in so-called bile-capillaries [ductus biliferi], situated in the columns of liver-cells; they anastomose freely and pass to the periphery of the lobules to form the pri- mary divisions of the bile-ducts, and these unite to form the larger bile-ducts. The branches of the portal vessel are accompanied in their course through the liver by the branches of the hepatic artery and the bile-ducts, surrounded by extensions of Ghsson's capsule forming the so-called 'portal canals' (fig. 947). The branches of the hepatic vein are solitary, their walls are thin and closely adherent to the liver substance, whence they remain wide open on sectioning the liver. While it is customary to describe thus the hver lobules, it would be more logical to con- sider as the real lobules what Mall has described as the 'portal units.' Each portal unit includes the territory supplied by one interlobular branch of the portal vein, and drained by the accompanying bile-duct. The relations of the ordinary lobules and the portal units are evident in fig. 948. The portal unit corresponds more nearly to the lobule of other glands, where the duct is in the centre of the lobule. THE LIVER 1187 Bile passages. — The bile passages, which transmit the bile from the liver to the duodenum, include the gall-bladder, the cystic duct, the hepatic ducts, and the common bile duct. The gall-bladder [vesica fellea], which retains the bile, is situated between the right and quadrate lobes on the lower surface of the liver. It is pear-shaped, and when full, is usually seen projecting beyond the anterior border of the liver, coming in contact with the abdominal wall opposite the ninth costal cartilage at the lateral margin of the right rectus muscle (fig. 914). It extends back as far as the portal fissure. It measures in length, from before backward, 7 to 10 cm. It is 2.5 to 3.5 cm. across at the widest part, and will hold about 35 cc. (Ij oz.). The broad end of the sac is directed forward, downward, and to the right, and is called the fundus. The narrow end, or neck [collum vesicae fellete], which is curved first to the right, then to the left, lies within the gastro-duodenal Ugament at the portal fissure. The intervening part is called the body [corpus vesicae felleae]. Fig. 948.- -Diagram of the Portal Unit and Vascular Relations of the Hepatic Lobule. (After Szymonowicz.) PORTAL UNIT PORTAL UNIT Its upper surface is in contact with the liver, lying in the fossa of the gall-bladder. It is attached to the liver by connective tissue. The lower surface is covered by peritoneum, which passes over its sides and inferior surface, though occasionally it entirely surrounds the gall- bladder, forming a sort of mesentery attaching to the liver. The lower surface comes into con- tact with the first part of the duodenum and the transverse colon, and occasionally with the pyloric end of the stomach or small intestine, which post mortem are often found stained with bile. The neck of the gall-bladder opens into the cystic duct [ductus cysticus]. This is a tube about 3.5 cm. long and 3 mm. wide, which unites with the hepatic duct to form the ductus choledochus; it is directed backward and to the left as it runs in the gastro-hepatic ligament, the common hepatic artery being to the left and the right branch of the artery and portal vein behind. It joins the hepatic duct at an acute angle, and is kept patent by a spiral valve [valvula spiralis; Heisteri], formed by its mucous coat (fig. 949). The hepatic duct [ductus hepaticus] Ijegins with a branch from each lobe, right and left (that from the left receiving also the ducts from the caudate lobe), in the portal fissure, and is directed downward and to the right within the portal fissure and the hepato-duodenal ligament, the right branch of the hepatic artery being behind and the left branch to the left. It is from 3 to 5 cm. long; its diame- ter is about 4 mm. Uniting with the cystic duct, it forms the common bile-duct [ductus choledochus]. 1188 DIGESTIVE SYSTEM The ductus choledochus or common bile-duct is about 7.5 cm. in length and 6 mm. in width. It passes down between the layers of the lesser omentum, in front of the portal vein, and to the right of the hepatic artery (fig. 946) ; it then passes behind the first part of the duodenum, then between the second part and the head of the pancreas, being almost completely embedded in the substance of the pancreas, and ends a little below the middle of the descending duodenum by open- ing into that part of the intestine on its left side and somewhat behind (figs. 921, Fig. 949.- -Intekior of the Gall Bladder and Ducts. (From Toldt's Atlas.) Tunica mucosa of gall bladder Plicae tunicse mucosae / Spiral valve (of Heistet) Common bile duct (ductus choledochus) Biliary mucous glands 922, 957). It pierces the intestinal wall very obliquely, running between the muscular layers for a distance of about 1 to 2 cm. There is a slight constriction at its termination. The pancreatic duct is generally united with the ductus choledochus just before its termination, and there is a slight papilla at their place of opening on the mucous surface of the duodenum. This papilla is about 8 or 10 cm. from the pylorus. After the pancreatic duct has entered the bile-duct there is (in about half the cases) a dilatation of the common tube called the ampulla of Vater. THE LIVER 1189 In its oblique course through the duodenal wall, the common bile duct is accompanied by the pancreatic duct, the two together usually causing the pUca longitudinalis duodeni (fig. 922). Circular muscle fibres join with bundles of longitudinal fibres at the lower part of the ducts and form a sphincter around each (fig. 950). Contraction of the sphincter probably closes the orifice of.'the common bile duct, so that (except during digestion) the bile is backed up into the gall-bladder. Structure of the gall-bladder. — The wall of the gall-bladder is made up of three coats — mucosa, fibro-muscular and serosa. Fig. 950. — Macerated Duodenal Portion op the Common Bile Duct, Showing Musculature. B, Common bile duct. TT^, Pancreatic duct (of Wirsung). iS, Tij, Sphincter fibres of Isile duct. H, Fibres of pancreatic duct. (Hendrickson.) 1. The mucosa is raised into folds bounding polygonal spaces, giving the interior a honey-* comb appearance. It is lined with columnar epithelium, and contains a few tubular mucous glands and lymph-nodules, and is hmited externally by a poorly developed muscularis mucosae. At the neck the mucous membrane forms valve-like folds which project into the interior. This layer contains an anastomosis of blood-vessels, the capillaries being most numerous in the folds of the mucosa, and a fine plexus of lymphatics. 2. The fibro-muscular coat consists of interlacing bundles of non-striated muscle and fibrous tissue not definitely arranged, the muscular bundles running longitudinally and obliquely This layer contains the principal blood-vessels and lymphatics, and also a nerve plexus. Fig. 951. — Diagrams op the Development op the Liver. (Lewis and Stbhr.) A, The condition in a 4.0 mm.- human embryo. B, A 12 mm. pig. C, The arrangement of ducts in the human adult, c. d., Cystic duct; c. p., cavity of the peritoneum; d., duodenum; d.c, ductus choledochus; dia., diaphragm; div., diverticulum; /. I., falciform ligament; g. b., gall bladder; g. a., greater omentum; h. d., hepatic duct; ht., heart; int., intestine; li., liver; I.O., lesser omentum; to., mediastinum; on., cesophagus; p. c, pericardial cavity; p. d. pan- creatic duct; ph., pharynx; p. v., portal vein; st , stomach; Ir., trabecula; v. c. i., vena cava in- ferior; v.v. vitelline vein; y. s., yolk sac. v.v. ml. B 3. The serosa being formed by the peritoneum, is only found on the lower surface and part of the sides. The ducts consist of a fibro-muscular and a mucous layer. In the fibro-muscular layer are non-striated muscle-cells which are chiefly circular, together with white fibrous tissue and elastic fibres. The mucous layer is lined with columnar epithehum, and has manj' mucous glands. In the cystic duct the mucous membrane is raised into folds, which are crescentic in form, and directed so obUquely as to seem to surround the lumen of the tube in a spiral manner. The development of the liver. — The relations which the liver bears to the diaphragm, to its vessels and more especially the veins, and to its so-called hgaments, may be understood by a reference to its development (figs. 951, 952). In discussing the development of the peritoneum and the mesenteries it was shown that the liver has its origin in a bud of entoderm, which grows 1190 DIGESTIVE SYSTEM into the transverse septum in the region where this is attached to the ventral mesoderm of the developing intestine; and that, with further development, the transverse septum differentiates into an upper thinner portion, inclosing the Cuvierian ducts, and destined to form the diaphragm, and a lower thicker portion in which the liver develops. Shortly after the formation of the entodermal bud which forms the liver this mass of epithelium taecomes penetrated by out- growths from the omphalo-mesenteric veins, reducing the epithelial mass to anastomosing trabeculae separated by blood-spaces forming a sinusoidal circulation. The definite hepatic lobules are not differentiated until after birth. The process of the development of the lobules is very complicated, the vascular arrangement being shifted repeatedly (Mall). The liver rapidly enlarges, filling the upper portion of the abdominal cavity, and extending along its ventral wall to the region of the umbilicus. During the enlargement it in a measure outgrows the transverse septum, and there are developed grooves which result in an infolding of the peritoneum covering the transverse septum, and which in part separate the developing liver from that part of the septum destined to form the diaphragm_, and also from the ventral abdominal wall. These grooves appear at the sides and also ventral to the hver, but do not completely separate the liver from the diaphragm, nor do they meet in the median line. A portion of the liver, therefore, remains uncovered by peritoneum, and remains attached to the diaphragm; this area may be known as the uncovered or phrenic area of the hver. Around this area the peritoneum of the hver is reflected on to the diaphragm, forming the coronary ligament, with right and left extensions, designated as the right and left triangular hgaments. Owing 'to the fact that the grooves which develop on the sides of the liver do not meet in the median line, there persists a fold of peritoneum which attaches the Hver to the ventral abdominal Fig. 952. — Diagram (A) : A Sagittal, Section of an Embryo showing the Liver en- closed WITHIN THE Septum Transversum; (B) AFbontal Section of the same; (C) Fron- tal Section of a Later Stage when the Liver has separated from the Diaphragm. All, Allantois; CI, cloaca; D, diaphragm; Li, liver; Ls, falciform ligament of the liver, M, mesentery; Mg, mesogastrium; Pc, pericardium; iS, stomach; ST, septum transversum; U, umbilicus. (McMurrich.) wall; this forms the falciform ligament, which divides the superior surface of the hver into a right and a left lobe. The region of the attachment of the ventral mesentery (mesogastrium) into which grows the entodermal liver bud, forms the lesser omentum. The developing liver early comes into intimate relation with the omphalo-mesenteric veins, and a little later the um- bilical veins. The developmental history of these veins and their relation to the developing liver is discussed elsewhere (see Development of the Portal Vein and Inferior Vena Cava, p. 694). After birth the left umbilical vein forms the hepatic ligamentum teres, situated in the free edge of the falciform hgament. The ductus venosus likewise atrophies to form the ligamentum venosum. The gall-bladder has its origin in a groove lined by entoderm, which appears on the ventral surface of the primitive intestine or archenteron, between the stomach and the yolk-vesicle. From the cephalic end of this groove grows out the bud destined to form the liver; the caudal end of the groove becomes gradually separated from the developing intestine to form a pouch, lined by entoderm, which forms the beginning of the gall-bladder. With further growth the attachment to the intestine of both the liver and the gall-bladder becomes narrowed to form the ductus choledochus. During development, the liver undergoes marked changes in form and relative size. It grows with great rapidity in the embryo, its maximum relative size reaching 7 to 10 per cent, of the entire body about the third prenatal month. At this time, the hver is globular in form, the visceral surface very small, and the left lobe more nearly approaching the right in size. During the later foetal months (fig. 953) and at birth, the liver forms about 5 per cent, of the whole body. It stiU remains relatively large in infancy, but decreases to about 2.5 per cent, in the adult. From the beginning, the relative weight of the liver averages slightly higher in the female. Variations of the liver and bile passages. — Many variations of the liver have already been mentioned. In size, both relative and absolute, it is subject to marked individual varia- tions, as well as according to age and sex (previously described). Inform, the liver is also quite variable. There are two extreme types: (1) in which the liver is very wide, extending far over into the left hypoohondrium, but relatively flattened from above downward; and (2) in which it THE LIVER 1191 extends but slightly to the left, being somewhat flattened from side to side, and elongated vertically. This type may occur as a result of tight lacing, in which the liver is frequently deformed. The part projecting below the right costal margin may form the so-called 'Riedel's lobe.' All intermediate forms between these two types occur. Its position and relations will also vary necessarily according to differences in size and shape. For example, in the wide type and also in enlarged livers, the left lobe may extend over upon the spleen, a relation which is constant during prenatal life. There may be supernumerary fissures, dividing the hver into additional lobes, as many as 16 having been described in an extreme case (Moser). These extra fissures often correspond to fissures which are normal in other mammals. There may also be accessory lobes, usually small, and connected with the main gland by stalks. Any one of the normal lobes may be atrophied or absent. There may also be abnormal grooves on the parietal surface of the liver. Of these, there are two varieties: (1) costal grooves, due to impressions of the overlying ribs and costa! cartilages; and (2) diaphragmatic grooves, due to wrinkles in the diaphragm. These Fig. 953. — The Viscera op the Fcettjs. (Rudinger.) Thyreoid Liver Falciform ligament Small intestine Right ventricle Stomach Part of transverse colon Hypogastric artery grooves most frequently occur in females, as a result of tight lacing. The appendix fibrosa has already been mentioned. There are numerous variation in the vascular arrangements, as well as in the psritoneal relations (particularly in connection with the coronary ligament). The bile passages are even more variable than the liver proper. The gall-bladder is variable in size and capacity (25 cc. to 50 oc. or more), as well as in its position, and relations. The fundus projects to a variable extent beyond the anterior margin of the liver so as to come into contact with the abdominal wall in a little more than half the cases, but is often retracted. The fossa of the gall-bladder is of variable depth, rarely so deep that it reaches the superior surface of the liver. The peritoneum usually covers only the sides and inferior surface of the gall- bladder, but occasionally surrounds it entirely, forming a short 'mesentery.' In rare cases the gall-bladder is bilid or double, and is occasionally absent. There are numerous variations in the bile-ducts. Rarely the hepatic ducts may communicate directly with the gall-bladder. The point at which hepatic and cystic ducts unite is variable, which affects the relative lengths of these and the ductus choledochus. The latter may open into the duodenum separately, instead of with the pancreatic duct. 1192 DIGESTIVE SYSTEM Comparative. — The liver arises in all vertebrates as an outgrowth of the entodermic epi- thelium of the intestine just beyond the stomach. In amphioxus it remains a simple saccular diverticulum, but in aU higher forms becomes a compound tubular gland. The tubular char- acter becomes masked, however (in amniota, and especially in mammals), by the abundant anastomosis between the tubules, forming what is called a 'solid' gland. The relations with the portal venous system are constant. The liver frequently stores large quantities of fat, and may even undergo a complete fatty metamorphosis (lamprey). The colour of the liver is usually reddish-brown, but may be yellow, purple, green or even vermillion (due to bile pigments). In size, the liver is variable, but is usually relatively larger in anamniota. Among mammals, there is great variation according to diet, the liver being relatively larger in carnivora, smaller in herbivora, and intermediate in omnivora (including man). It is also relatively larger in small animals (including young and foetal stages), probably on account of their more intense metabo- lism. There are typically two lobes, right and left, in the vertebrate hver. These are frequently subdivided, however, especially in mammals, which often present numerous lobes. The gall-bladder is typically present, as in man, but varies in form, size and position. It may be completely buried in the fiver. In some species it is absent, in which case the hepatic ducts open directly into the duodenum by one or more apertures. The hepatic and cystic ducts typically unite to form a common bile-duct, as in man, but there are numerous variations in the detailed arrangement of the ducts. THE PANCREAS The pancreas (figs. 922, 954, 955, 956) is an elongated gland extending trans- versely across the posterior abdominal wall behind the stomach from the duode- num to the spleen. Through the pancreatic duct, opening into the descending duodenum, flows its secretion [succus pancreaticus], which is of importance in digestion. The pancreas also has a very important internal secretion. Fig. 954. — The Duodenum and Pancreas, Anterior View. Superior layer of transverse meso-colon Duodeno-jejunal Sesure Inferior layer of transverse meso-colon Inferior part of duodenum Superior mesenteric vessels The pancreas is greyish-pink in colour; average length {in situ), 12 cm. to 15 cm.; average weight about 80 gm. (extremes 60 gm. to 100 gm. or more); specific gravity, 1.047, which is about the same as that of the salivary glands. In position, the pancreas lies in the epigastric and left hypochondriac regions. In form, it somewhat resembles a pistol, with the handle placed to the right and the barrel to the left. The pancreas is accordingly divided into a head, lying within the duodenal loop; a body, extending to the left; and a tail, or splenic extremity. The head [caput pancreatis] is a discoidal mass somewhat elongated vertically and flattened dorso-ventrally. It forms the enlarged right extremity of the pan- creas and lies within the concavity of the duodenum (flgs. 922, 954, 955). Its relations are as follows (figs. 954, 955, 956) : Its posterior surface is placed opposite the second and third lumbar vertebrae, and is in contact with the aorta, the vena cava, the renal veins and right renal artery. The common bile-duct is also partly embedded in this surface. Its anterior surface is crossed by the transverse colon, above which is the pyloric extremity of the stomach, and below which are coils of THE PANCREAS 1193 Fig. 955. — The Duodenum and Pancreas, Posterior View. Portal vein Terminal part of duodenum Head of pancreas Fig. 956. — Outline Showing the Average Position op the Deeper Abdominal Viscera in 40 Bodies, on a Centimetre Scale (reduced to .36 natural size). AB, anterior mid-line. EF, horizontal line half way between pubes and suprasternal margin. CD, line half way between pubes and line EF. (Addison.) 13 12 11 10 9 a 7 6 FT 4 3 2 1 All 21 3 1 4 1 5 1 6 1 7 8 9 10 11 12 13 r f "'*""" Co 5ta At '\ \ -X — . V \, ■' / \ .' ••. ■. r- ■ri :v.-' \ '?• ^. ^■^ \ n^ ^ / • ""i p^ if ,, • -3. -' f~ I ^ "T ^ •. ■■.:t: 1 1 ^ /- , \ 1 ^ " ■* i -^'V \ ! / \ ^ >^ * ' \ h Bvv^?* EO / \y '/ |» \ r ir ^fe w^ \\'r ■f? !S» ^ W ^^ "? The ri /• A f J the 1st dfeand 2nd / ,f ^ ^ J r ■T \ ; ^3. 4- .5. Lumbarx 1 1 ; t .,'- f i N. / N / ■«• ■■■^ / / 1 j y \ / ^ y V* ,.^ V 1 / \ s It ^, fp V / \ .7. .8. -■^ — ,/- n •^ / — : ^ — s f \ i J ^ >- _ — "' JO 'cr II 0 ^ nbilicua Cl .1. -2 ^ \ / ^ \ / \ \ / \ / "> L_Ant 1 1 1 erior Superior i1 1 ac Sd no *. s'. s. / Sacral Promon °7 y ; -8. -7- _8 9f 10 .11 ~^ \ ^ \ /" \ "^ ^ / % Psoas M iscle / ou :a -ig y tib / \ / \ y J13 \ Pubes / P 1 1194 DIGESTIVE SYSTEM small intestine. Upon this surface are also the pancreatico-duodenal and (in part) the superior mesenteric vessels. The margin of the head of the pancreas is C-shaped, corresponding to the inner aspect of the duodenal loop, with which it is closely related. Superiorly the margin is in contact with the pylorus and first part of the duodenum; on the right, with the descending duodenum and the ter- minal portion of the common bile duct ; inferiorly, with the horizontal, and on the left, with the terminal ascending portion of the duodenum. The lower and left portion of the head of the pancreas is hooked around behind the superior mesenteric vessels, forming the processus uncinatus or pancreas of Winslow (fig. 922). A groove, the pancreatic notch [incisura pancreatis], is thus formed for the vessels. The morphology of this process is explained later under development (fig. 958). In the adult condition, the head of the pancreas is largely retroperitoneal. The only portions covered by peritoneum are (1) a small area above the attach- ment of the colon, and in relation with a pocket-like recess of the bursa omentalis, and (2) a small area below the transverse colon, which is in relation with coils of small intestine. The mesentery of the small intestine begins where the superior mesenteric vessels pass downward from in front of the processus uncinatus. The junction of the upper and left aspect of the head with the body of the pancreas is called the neck. This is a somewhat constricted portion grooved posteriorly by the superior mesenteric vessels, the vein here joining with the splenic to form the portal vein (fig. 955). Anterior to the neck is the pyloric portion of the stomach. The upper portion of the neck (together with a variable area on the left end of the body) projects above the lesser curvature of the stomach. This projection [tuber omentale] is related, through the lesser omentum, with a similar tuberosity on the left lobe of the liver. The anterior aspect of the neck is covered with peritoneum of the bursa omentalis (lesser sac), and is continuous with the anterior surface of the body of the pancreas (fig. 922). The body [corpus pancreatis] is the triangularly prismatic portion of the pan- creas extending from the neck on the right to the tail on the left. Its direction is transversely to the left and (usually) somewhat upward. It is therefore usually placed at a somewhat higher level than the head, opposite the first lumbar verte- bra. It presents three surfaces — anterior, posterior, and inferior — and three borders — superior, anterior, and posterior. Of the surfaces, the anterior [facies anterior] faces forward and somewhat upward. It is covered with the peritoneum of the posterior wall of the bursa omentalis (lesser sac), and forms a slightly concave area which is in contact with the posterior surface of the stomach (figs. 904, 906). The posterior surface [f. posterior] of the body of the pancreas is flattened and retroperitoneal. From right to left it crosses the anterior aspect of aorta, left suprarenal body and left kidney. The splenic vessels also run along the posterior surface, the artery, which is above, corresponding more nearly with the superior border. The inferior surface [f. inferior] is usually the narrowest of the three. It is covered by peritoneum (con- tinuous with the lower layer of the transverse mesocolon) and is in contact with the duodeno-jejunal angle medially and with coils of jejunum laterally. Of the borders, the superior [margo superior] is related with the splenic artery along its whole length from its origin in the coeliac, and the posterior [margo posterior] separates posterior and inferior surfaces. The anterior border [margo anterior] is sharp and prominent. It gives attachment to the transverse meso- colon, whose upper layer (belonging to the lesser sac) is continuous with that on the anterior surface of the pancreas, and whose lower layer (belonging to the greater sac) is continuous with that on the inferior surface. The tail of the pancreas [cauda pancreatis] is at the left extremity of the body. It is variable in form, but usually somewhat blunted and upturned. It is almost invariably in contact laterally with the medial aspect of the spleen, and inferiorly with the splenic flexure of the colon. The splenic vessels often cross from above in front of the tail of the pancreas on their way to join the spleen. Ducts. — The pancreas has usually two ducts, the main pancreatic duct and the accessory duct. The main pancreatic or duct of Wirsung [ductus pancreaticus; Wirsungi] begins in the tail of the pancreas, and extends to the right within the body of the pancreas, about midway between upper and posterior borders, but nearer the posterior surface (figs. 922, 957). It runs a slightly sinuous course THE PANCREAS 1195 receiving branches all along, which enter nearly at right angles. It is largest in the head of the pancreas (diameter about 3 mm.) where it turns obliquely down- ward. As it approaches the duodenum, it is joined by the common bile duct, the two running side by side. They pass obliquely through the wall of the duodenum for a distance of about 15 mm. (usually causing a fold of the mucosa, the plica longitudinalis duodeni). They terminate finally, usually by a common aperture, but sometimes separately, on the duodenal papilla major, as described in connec- tion with the interior of the duodenum. The common aperture is somewhat nar- row, but just preceding this the duct is frequently dilated, forming what is called the ampulla of Vater. The accessory pancreatic duct (duct of Santorini) is nearly always present (figs. 922, 957), but variable. This duct is small, and lies within the head of the pancreas. At its left end, it usually joins the main duct in the neck of the pan- creas. From here it extends nearly horizontally across to the upper part of the descending duodenum and, piercing its wall, usually ends upon the small papilla minor, about 2 cm. above and slightly ventral to the papilla major. The relations of the ducts are explained later under development. Fig. 957. — The Pancreas and its Ducts, Dissected from Behind. Duct of pancreas Accessory duct of Santorini Common bile-duct Blood-vessels. — The pancreas receives blood chiefly from the splenic artery through its pancreatic branches, and from the superior mesenteric and hepatic by the inferior and superior pancreatico-duodenal arteries, which form a loop running around, below, and to the right of its head. The blood is returned into the portal vein by means of the splenic and superior mesenteric veins. Lymphatics. — ;The lymphatics terminate in numerous glands which lie near the root of the superior mesenteric artery, above and below the neck of the pancreas. All the lymphatics drain ultimately into the cceliac glands. Nerves. — These are branches of the coeliac plexus which accompany the arteries entering the gland. The main part of the coehac plexus lies behind the gland. Minute anatomy. — In many respects, the pancreas resembles the salivary glands in struc- ture, hence its German name 'Bauchspeicheldrtise' ('abdominal sahvary gland'). The gland proper is racemose (or tubulo-racemose) in structure, the secreting cells characteristically granular and 'serous' in type. The thin-walled 'intercalary ducts,' often invaginated to form 'centroacinar' cells, are characteristic. The lobules are very loosely joined by areolar tissue, and there is no distinct fibrous capsule around the gland. 'The most important of the distinctive characters of the pancreas is the presence throughout the gland of numerous small interlobular ceU-masses of varied form and size — the islets of Langerhans (fig. 959). These have no ducts, but are richly supplied with blood-vessels. They are ductless glands of great import- ance in sugar metabolism, and their removal or disease produces diabetes. While derived embryologically from the same entodermal anlage which gives rise to the pancreas gland proper, they apparently have no direct connections with it in the adult. The question as to the possible metamorphosis of acini into islets, or vice versa, under certain conditions (e. g., hunger) in the adult has been much disputed. Bensley, however, has recently presented strong evidence against this view. Development of the pancreas. — The pancreas has its origin in three entodermal buds, one of which (the dorsal anlage) grows from the dorsal portion of the duodenum, the other two (ventral anlages) from either side of the bile-duct. Of the two latter, only that growing from the right side of the bile-duct needs further consideration, as the other soon disappears. The dorsal anlage grows at first more rapidly than the ventral, which arises from the bile-duct. In their further growth both the dorsal and ventral anlages become lobed, these lobes dividing further to form the ducts and the alveoh of the gland. By about the end of the second month the distal end of the ventral portion comes in contact with the dorsal portion at a short distance 1196 DIGESTIVE SYSTEM from the latter's connection with the duodenum. A fusion of the two portions thus takes place in this region, and at the same time there is estabhshed by anastomosis a connection be- tween the terminal branches of the main duct of the dorsal portion — duct of Santorini — and the branches of the main duct of the ventral portion — the duct of Wirsung. With further devel- opment the duct of Wirsung develops into the main pancreatic duct, the duct of the dorsal Fig. 958.- -DiAGEAM Showing the Relations of the Pancreas to the Primitive Mesen- tery. (Poirier-Charpy.) Aorta Left gastric art. Dorsal mesogastrium (pr.rtion becoming adherent) Tail of pancreas Splenic art. Right gastro-epiploic art. Superior pancre- atico-duodenal art. Head of pancreas Mesentery at duodeno-jejunal fle ''Processus uncinatus Body of pancreas Dorsal mesogastriu (portion fusing w transverse meso- colon) portion (duct of Santorini) either losing its connection with the duodenum or remaining as the accessory pancreatic duct. Thus of the adult gland, only the lower portion of the head is derived from the primitive ventral anlage, although the duct of the latter drains nearly the entire adult gland. The upper part of the head of the pancreas, and all of the body and tail are derived from the dorsal anlage; although most of its duct joins with the duct of Wirsung to form the main pancreatic duct, only a small part persisting as the accessory duct of Santorini. Fig. 959. — Section op Human Pancreas, Magnified, Showing Several Islets of Langerhans. (Radasch.) a, Interlobular connective tissue, containing an interlobular duct, c, b. Capillary, d, Interlobular duct, e, Alveoli. /, Islet of Langerhans. During the early stages in the development of the pancreas the entodermal buds from which it forms grow into the mesoduodenum, and later the dorsal mesogastrium. With the rotation of the stomach and the consequent change in the position of the mesogastrium and its partial fusion with the abdominal wall, the pancreas assumes a retroperitoneal position. This is illustrated by fig. 958. The head of the pancreas is involved in the rotation of the primitive REFERENCES FOR DIGESTIVE SYSTEM 1197 intestinal loop counter-clockwise around the superior mesenteric artery. This accounts for the position and the hook-like form of the processus uncinatus. Following this rotation, the duodenum and the head of .the pancreas become pressed backward against the posterior ab- dominal wall, where they become adherent, with fusion and obliteration of the primitive peri- toneum. The body of the pancreas, extending mto the dorsal mesogastrium (fig. 900), is simi- larly caught in the pouch-like downgrowth of the latter to form the bursa omentahs (lesser sac), and is thereby carried over to the left side. When the posterior layer of the primitive bursa fold becomes fused with the posterior abdominal wall, the enclosed pancreas is likewise fixed and becomes retroperitoneal. Of these obUterated peritoneal layers of the embryo, only certain layers of fascia remain as their representatives in the adult. From the lower aspect of the pan- creas downward, the posterior layer of the bursa fold becomes fused with the transverse meso- colon, so that in the adult the latter appears to arise from the anterior border of the pancreas (fig. 904). Variations. — Aside from minor fluctuations in size and form, the variations of the pancreas are chiefly congenital and of embryonic origin. Cases of accessory or supernumerary pancreas are not rare. They are usually of small size and have separate ducts. They may occur along the wall of the duodenum, or even in the stomach or jejunum. They are perhaps m some way con- nected with the numerous intestinal diverticula which occur in the embryo. Divided pancreas differ from the accessory in that a mass of the pancreas becomes separated from the main gland, connected only by a duct. This occurs oftenest in the region of the tail (sometimes extending into the spleen) or of the processus uncinatus, forming what is termed a 'lesser pancreas.' Sometimes a ring of glandular tissue from the head of the pancreas surrounds the descending duodenum, forming an annular pancreas. Variations in the direction of the body are numerous; it may be horizontal, ascending or bent in various ways. These are doubtless congenital vari- ations, as similar types have been described in the foetus (Jackson). It has been experimentally demonstrated that varying degrees of distention of the stomach and intestines affect profoundly the form of the body of the pancreas. When the stomach alone is distended, the pancreas is flattened antero-posteriorly, the inferior surface being practically obliterated. When both stomach and intestines are distended, the pancreas is flattened from above downward, and e.xtends forward hke a shelf, the posterior surface being much reduced (Jackson). Numerous variations in the ducts are easily understood from their complicated development. The acces- sory duct (of Satorini) is in the foetus as large as the main duct (of Wirsung), the preponderance of the latter being established later. The accessory duct in the adult may be larger than usual, and retain its primitive drainage, or even drain the entire gland in rare cases where the duct of Wirsung is absent. Or the accessory duct may be rudimentary or (rarely) absent. Similar variations occur in the main duct of Wirsung. Rarely the pancreas may open into the duo- denum by three ducts, probably representing three embryonic anlages. Abnormalities of the pancreas are often associated with duodenal diverticula. Comparative. — The pancreas, like the liver, is constant throughout the vertebrates. It always arises by budding off from the endodermal epithelium of the intestine, closely associated with the Uver. There is typically a triple anlage (rarely multiple, which is perhaps the ancestral type), with one dorsal and two ventral outgrowths. These fuse and form the adult pancreas in a variety of ways. In many of the fishes, the pancreas is very small, diffuse and incon- spicuous, sometimes embedded in the liver or intestinal wall. Of the three primitive ducts, usually only two persist (as in man), but often only one, or all three (in birds). All three types occur in mammals. The islets of Langerhans arise from the epithelial pancreas anlage, and ap- pear to be constantly present, even in the lowest vertebrates. Laguesse even considers that phylogeneticaUy they form the most primitive part of the pancreas, but this is doubtful. References for digestive system. — General and Co7nparative: Quain's Anat- omy, 11th ecL; Poirier-Charpy, Traits d'anatomie; Rauber-Kopsch, Lehrbuch der Anatomie, 9te Aufl.; Oppel, Mikroskopische Anatomie, Bd. 1-3; also 'Ver- dauungsapparat ' in Merkel and Bonnet's 'Ergebnisse'; Wiedersheim, Bau des Menschen. Topography: (adult) Merkel, Topographische Anatomie; (develop- mental) Jackson, Anat. Rec, vol. 3. Development: Keibel and Mall's Manual. Teeth: Tomes, Dental Anatomy. Tonsils: (lingual) Jurisch, Anatomische, Hefte, Bd. 47; (pharyngeal) Symington, Brit. Med. Jour. (Oct., 1910); (palatine) Killian, Archiv f. LaryngoL, Bd. 7. (Esophagus: Goetsch, Amer. Jour. Anat., vol. 10. Stomach: (structure), Bensley, Buck's Ref. Handb. Med. Sc, vol. 7 (1904); (form) Cunningham, Trans Royal Soc. Edinb., vol. 45; (radiography) Cole, Archives Roentgen Rays, 1911; also Journal Amer. Med. Assn., vol. 59. Duodenum: (diverticula), Baldwin, Anat. Rec, vol. 5. Vermiform process: Berry and Lack, Jour. Anat. and Phys., vol. 40. Rectum: Symington, Jour. Anat. and Phys., vol. 46. Liver: Mall, Amer. Jour. Anat., vol. 5. Pancreas: (islets) Bensley, Amer. Jour. Anat., vol. 12; (ducts) Baldwin, Anat. Rec, vol. 5. SECTION X THE RESPIRATOEY SYSTEM Revised fob the Fifth Edition By R. J. TERRY, A.B., M.D., PHOFESSOR OF ANATOMY IN WASHINGTON UNIVERSITr R ESPIRATION consists in the absorption by the organism of oxygen and the discharge of a waste-product, carbon dioxide. Among unicellular animals the oxygen is taken up directly from the medium — water or air — in which they Hve, and the carbon dioxide given off into it. With the cells which make up the body of higher animals the principle is the same, but the interchange of gases is indirect. The blood stands as an intermediate element between the cells of the body and the medium inhabited Fig. 960. — Dissection of a Male Negro, Age 43 Years, to Show the Organs of Res- piration in Situ. Frontal sinus' Nasal cavityj Thyreoid gland Left bronchus by the animals, and serves as a carrier of the gases between them. Moreover, special organs are provided for the rapid interchange between air and blood, which constitute the so-caUed respiratory system. The respiratory system of air-breathing vertebrates consists of tubular and cavernous organs constructed so as to permit of the atmospheric air reaching the 1199 1200 THE RESPIRATORY SYSTEM blood circulating in the body. The essential organs in the system are the paired lungs located in the thoracic cavity. Air is carried to and from the lungs by the trachea and bronchi, and these simple transmitting tubes are in turn put into communication with the exterior by the mediation of other organs. The latter are, however, specially constructed in adaptation to other functions in addition to those relating to respiration: the larynx for the production of the voice, the pharynx and mouth in connection with alimentation, the nasal cavity and external nose functioning in the sense of smell. (For the description of the mouth and pharynx see Section IX; for the olfactory organ see Section VIII.) The organs of circulation are always adapted to the form of the respiratory apparatus, and among all higher animals a connection is established between heart and lungs by the pulmonary artery, which carries venous blood to the latter, and by the pulmonary veins, which convey arterial blood from the lungs to the heart, whence the aorta takes it into the general circulation. In their origin and development the respiratory organs are closely associated with or differentiated from the beginnings of the digestive apparatus. Thus the processes of the early development of the nasal cavity and mouth are interdependent; the origin of the greater part of the larynx, the trachea and lungs is by ventral outgrowth of the entodermal canal. THE NOSE The external nose [nasus externus] (fig. 961), shaped like a triangular pyramid, is formed of a bony and cartilaginous framework covered by muscles and the in- tegument of the face externally and lined within by periosteal and perichondral layers overspread by mucous membrane. At the forehead, between the eyes, is Fig. 961. — The Left Side of the External Nose, showing its Cartilages, etc. Nasal bone Nasal process of the maxilla Lateral nasal cartilage Nasal septal cartilage Lateral cms of greater alar cartilage Medial crus of greater alar cartilage Sesamoid cartilages Fibrous tissue Lesser alar cartilages Cellular tissue forming ala the root of the nose [radix nasi], and from this, extending inferiorly and anteriorly, is a rounded ventral border, the dorsum of the nose [dorsum nasi], which may be either straight, convex, or concave, and which ends inferiorly at the apex of the nose [apex nasi]. The superior part of the dorsum is known as the bridge. Inferi- only, overhanging the upper lip, is the base of the nose [basis nasi] which presents two orifices, the nares or nostrils, separated from one another by the inferior mov- able part of the nasal septum [septum mobile nasi]. The nostril of man is remarkable on account of its position, facing as it does almost directly downward. It is oval in form, with the long axis directed antero-posteriorly, or approximately so, in Europeans. The size of the nostril is under the control of muscles (see p. 334) and may be dilated or constricted by their action. The sides of the nose slope from the dorsum laterally and posteriorly, and THE NOSE 1201 below ferminate on each side in the margin of the nose [margo nasi]; posteriorly and interiorly the sides are expanded and more convex, forming the alae nasi. Each of these is separated from the rest of the lateral surface by a sulcus, and the inferior free margin of each bounds a naris laterally. Three types of nose, distinguished by differences in the proportion of breadth and length are recognised by anthropologists: the leptorrhine or long, high nose; the platyrrhine or short, low nose; the mesorrhine, a form intermediate between the other two. The leptorrhine type prevails among white races, the platyrrhine in the blaeli peoples and the mesorrhine in the red and yellow races. Fig. 962. — Anterior View op the External Nose, showing its Cartilages, etc. Lacrimal groove — 7 — Groove on anterior border of nasal septal cartilage jid cartilages Lesser alar cartilages Cellular tissue of ala Nasal process of the maxilla Lateral nasal cartilage Lateral crus of greater alar cartilage The framework of the external nose is formed partly of bone and partly of hyaline cartilage The bones, which form only the smaller superior part, are the two nasal bones and the fronta processes and anterior nasal spines of the two maxillae (pp. 87, 108). The nasal cartilages [cartilagines nasi] are located about the piriform aperture and constitute the larger part of the nasal framework. There are five principal cartilages: superiorly, the two lateral nasal cartilages, interiorly the two greater Fig. 963. — Inferior View op the External Nose, showing its Cartilages, etc. ITasal septal cartilage - Medial crus of greate: alar cartilage Nasal septal cartilage Cellular tissue of ala alar cartilages, and the single median nasal septal cartilage. Beides these there are the lesser alar cartilages, the sesamoid cartilages, and the vomero-nasal carti- lages of Jacobson. The lateral nasal cartilages [cartilagines nasi laterales] are triangular and nearly flat lateral e.xpansions of the septal cartilage, placed one on each side of the nose just inferior to the nasal bone. Each presents an inner and an outer surface and three margins. The medial margin is continuous in its supe- rior third with the anterior margin of the septal cartilage, and through this with its 1202 THE RESPIRATORY SYSTEM fellow of the opposite side, but it is separated inferiorly from the septal cartilage by a narrow cleft. The curved supero-lateral margin is firmly attached b}^ strong fibrous tissue to the nasal bone and frontal process of the maxilla, and underlies these bones for a considerable distance, especially near the septum. The inferior margin is connected by fibrous tissue to the greater alar cartilage. The greater alar cartilages [cartilagines alares majores], variable in form, are situated one on each side of the apex of the nose (figs. 961, 963). Each is thin, pliant, curved, and so folded that it forms a medial and a lateral crus, which bound and tend to hold open each naris. The medial crus [crus mediale] is loosely attached to its fellow of the opposite side, the two being situated inferior to the septal cartilage and forming the tip of the nose and the inferior part of the mobile septum. The lateral crus [crus laterale] joins the medial crus at the apex of the nose; it is somewhat oval in shape, and curves dorsally in the superior and anterior portion of the ala. It is connected posteriorly to the nasal margin of the maxilla by a broad mass of dense fibrous and fatty tissue, and helps to maintain the contour of this part of the nose. Fig. 964. — Medial Wall of the Nasal Cavity, the Mucotts Membrane Being Removed. The dotted line indicates the course of the incisive canal. Nasal bone Frontal i Lateral nasal Groove between septal and lateral nasal cartilage Thickened bord' resting upon anterior papilla Septal cartilage Orifice of tuba auditiva Soft palate The angle formed by the crura (angulis pinnahs) varies with the shape of the nose; it aver- ages 30°. The greater and lesser alar cartilages together form an incomplete ring arotmd the naris. A variable number of small cartilages, lesser alar cartilages [cartilagines alares minores] are found in the fibrous tissue of the ala, and in the interval between each greater alar and lateral cartilage occur one or more small plates, sesamoid cartilages [cartilagines sesamoidese] (fig. 961). The septal cartilage [cartilago septi nasi] (fig. 964) forms the anterior part of the septum. It is quadrilateral in shape and fits into the triangular interval of the bony septum. Its antero-superior margin in its upper part meets the inter- nasal suture. Inferior to the nasal bone it presents a shallow groove which gradu- ally narrows toward the tip of the nose, and whose borders are continuous supe- riorly with the lateral nasal cartilages, but are separated from their inferior two- thirds by a narrow slit. The most inferior part of this margin of the septal car- tilage is placed between the greater alar cartilages. The antero-inferior margin extends backward from the rounded anterior angle to the anterior nasal spine. Inferiorly it is attached to the medial crus of the greater alar cartilage and to the THE NASAL CAVITY 1203 mobile nasal septum. The postero-superior margin is attached to the perpen- dicular plate of the ethmoid, and the postero-inferior margin joins the vomer and the ventral part of the nasal crest of the maxilla, the cartilage broadening out to obtain a wide though lax attachment to the nasal spine. The shape of the septal cartilage varies with the extent of the ossification of the bony septum. Even in the adult a strip of cartilage may extend for a varying distance postero- superiorly between the vomer and perpendicular plate of the ethmoid, sometimes reaching the body of the sphenoid; it is known as the sphenoidal process of the septal cartilage [proc- essus sphenoidalis septi cartilaginei]. The vomero-nasal cartilage [cartilago vomero-nasalis Jacobsoni*] is a narrow strip of cartilage firmly attached to each side of the septal cartilage, where this joins the anterior portion of the vomer. Muscles. — The muscles are grouped according to function as dilators and contractors, the latter being comparatively feeble in their action. They are described on p. 334. The skin covering the external nose is thin and freely movable upon the sub- jacent parts, except at the tip and over the cartilages, where it is much thicker, Fig. 965. — Obliqite Section passing through the Nasal Cavity just in Front of the CHOANiE. (Seen from behind.) Crista galli Front wall of left ' •>!/\ sphenoidal sinub with orifice belov Orifice of righl sphenoidal sinus Superior nasal concha Middle nasal concha' Upper surface of. soft palate more adherent, and furnished with numerous exceptionally large sebaceous glands. At the nares it is reflected into the nasal cavity, where it passes into the mucous membrane. The hairs on the skin of the nose are very fine, except in the nares, where they may be strongly developed. Vessels and nerves. — The arteries of the external nose are derived from the external maxil- lary (facial) artery (pp. 540 and 541), the ophthalmic artery (p. 554), and the infra-orbital artery (p. 549). The veins terminate in the anterior facial vein and the ophthalmic vein (p. 644). The lymphatics pass to the submaxillary lymphatic nodes (p. 712). The motor nerves are branches of the facial (p. 946). The sensory nerves are derived from the trigeminal through the frontal and naso-cihary branches of the ophthalmic (p. 936) and infra-orbital branch of the maxiUary (p. 939). The nasal cavity [cavum nasi] is the ample space situated between the floor of the cranium and the roof of the mouth extending forward into the external nose and backward to the nasal part of the pharynx. With the exception of the inferior part of the nose its walls are of bone as already described (pp. 110, 112). The cartilages and membranes of the nose complete the boundaries anteriorly. Here the cavity opens to the exterior by the nares. At the back a free communi- *Jaeobson: Danish anatomist. B. 17S3, D. 1843. 1204 THE RESPIRATORY SYSTEM cation with the pharynx is established through the paired ehoana;. Furthermore accessory nasal cavities, the paranasal sinuses, open into the cavum nasi. The walls of the nasal cavity are covered with periosteum and mucosa, the latter pre- senting important differences in the respiratory and olfactory regions. The organ of smell, included in the nasal cavity, is described on p. 1049. The cavum nasi is divided into right and left symmetrical parts, called the nasal fossae, by the septum of the nose [septum nasi]. The latter is supported by a framework composed of the osseous septum [septum nasi osseum] posteriorly, and the cartilaginous septum [septum cartilagineum] anteriorly. Antero-inferiorly, the small movable part of the septum is also called the membranous septum [septum membranaceum]. The nasal septum is almost always straight in primitive races and Caucasian children; but in a large proportion of Caucasian adults it is deflected to one side or the other. Fig. 966. — Sagittal Section through the Facial Part op the Head and the Bodies OP THE UPPER THREE Cervical Vertebrae. The section lies to the right of the median plane. The nasal septum has been removed. (Rauber-Kopsch.) Cribriform plate Spheno-ethmoidal , Hypophysis Dorsum sellae Choanal arch .. Nasopharyngeal - meatus Pharyngeal tonsil Torus tubarius Levator cushion Anterior lip of tubal aperture Salpingopharyn goal fold Uvula Foramen cgecum Palatopharyngeal fold Incisive canal Upper lip Vestibulum oris Mouth cavity proper Lower lip Sublingual mucosa Hyoid bone Mental spme In the septum, upon each side, just superior to the nasal spines of the maxillas, there is frequently a minute opening leading superiorly and posteriorly and ending blindly. This cavity is closely related to the vomero-nasal cartilage and is a rudimentary representative of the vomero- nasal organ (of Jacobson) [organon vomero-nasale], which in some animals is well developed and receives a branch of the olfactory nerve. On the floor of the nasal cavity about 2 cm. from the posterior margin of the naris and near the nasal septum a small depression, the nasopalatine recess, is often seen. This is the mouth of the incisive duct [ductus incisivus] which leads into the incisive canal for a greater or less distance and may even extend to the mouth, where its termination is marked by the incisive papilla. The incisive duct indicates the position of a foramen which in the embryo connected the mouth and nose. The naris leads upward into the vestibule of the nose [vestibulum nasi], the small cavity within the compass of the greater alar cartilage. Its walls are lined with skin beset with the large hairs called vibrissas and containing many seba- ceous glands. The vibrissae serve to protect the nasal cavity from the entrance of foreign matter. On the lateral wall, the vestibule is marked off from the rest of the nasal cavity by a cUstinct ridge, the limen nasi, corresponding to the superior margin of the greater alar cartilage. On the lateral wall of the cavity within the limen nasi are three antero-posterior ridges, the superior, middle, and inferior I THE NASAL MEATUSES 1205 conchae (fig. 966). These have a bony framework (described on pp. 83, 110) and are covered by the mucous membrane of the nose. The conchje are not parallel to one another but converge in a backward direction. The superior nasal concha [concha nasaUs superior] is the smallest, projects only slightly medialward and downward from the upper, posterior part of the lateral wall, overhanging the groove called superior meatus of the nose. The middle nasal concha [concha nasalis media] is extensive, reaching from the fore part to the posterior confines of the lateral wall. Its free margin is nearly vertical in its anterior one-fourth, hori- zontal and laterally rolled in the rest of its extent. Under cover of this concha runs the middle meatus. The inferior nasal concha, [concha nasalis inferior] is the longest, has a lateral attached and an inferior laterally rolled free margin running near the floor of the nasal cavity. Beneath it lies the inferior meatus. Meatuses of the nose [meatus nasi] (figs. 966, 968). The name common meatus of the nose [meatus nasi communis] is given to that part of the nasal cav- FiG. 967. — Frontal Section through the Facial Portion op the Head of a White Man, Age 28 Years. lofundibulum - Ethmoidal cell — Middle meatus Maxillary sinus Inferior meatus ity which lies between the septum nasi and the nasal conchas and stretches from floor to roof. The three meatuses under cover of the nasal conchae have been mentioned. These passages all communicate freely with the common meatus, extend antero- posteriorly and have a greater capacity in front than behind. The superior meatus [meatus nasi superior] is the smallest of the three. Into it open the posterior ethmoidal cells by one or two small foramina. The spheno- palatine foramen, which communicates with the meatus in the dry skull, is entirely covered up bj^ mucous membrane. The middle meatus [meatus nasi medius] is a much larger passage. Upon its lateral wall is a rounded eminence, the ethmoidal bulla, caused by the middle ethmoidal cells and perforated by the open- ing into them. Inferior to this is a deep curved groove, the hiatus semilunaris, which is continued superiorly by the ethmoidal infundibulum [infundibulum eth- moidale] into the frontal sinus. It also receives the openings of the anterior eth- moidal cells and the maxillary sinus. The inferior meatus [meatus nasi inferior] is the longest of the three. Upon its lateral wall, just inferior to the attachment of the inferior concha, is the slit-like opening of the naso-lacrimal duct [ductus naso-lacrimalis], around the opening of which the mucous membrane forms a valve, the plica lacrimalis (Hasneri). Recent investigation of the nasal conchae indicates that two upper conchae (concha nasalis superior and concha nasalis suprema [Santorini]) are more often present than one. Three upper conchae are not rare. 1206 THE RESPIRATORY SYSTEM The attached margins of the middle and inferior conchse are both arched, the convexities being upward. The highest point of the convexity is near the middle of the attached margin in the inferior concha and lies about 17 mm. above the floor of the nose; the anterior end of this concha is approximately 25-35 mm. distant from the apex of the nose (KaUius). From the anterior end of the middle concha a slight variable elevation of the mucous mem- brane of the nose extends forward and downward. This, the agger nasi, which is regarded as of constant occurrence in the new-born, appears to be a rudimentary representative of the naso- turbinale of mammals (Schwalbe). Below the agger nasi a broad depression of the lateral wall, the atrium meatus medii, leads posteriorly beneath the anterior free margin of the middle concha to the middle meatus, while above the agger, between it and the roof of the nasal cavity, the slight olfactory groove [sulcus olfactorius] ascends upon the lateral wall to the olfactory region. In this region, above the superior concha, is a corner of the nasal cavity of interest on account of the sphenoidal sinus opening into it: this is the spheno-ethmoidal recess [recessus spheno-ethmoidalis]. Variation in the number and position of the openings into the meatuses is of practical inter- est. An accessory mouth of the maxillary sinus is rather frequently met with, especially in old people; it lies most commonly behind the hiatus semilunaris. The infundibulum ethmoidale may open independently of the hiatus semilunaris at a spot beneath the anterior end of the at- tached margin of the middle concha. In the inferior meatus the mouth of the naso-laorimal duct, which is found 22-25 mm. behind the posterior margin of the nares, may have one or more accessory openings associated with it; these are perforations of the plica lacrimalis. Communication between the nasal cavity and the nasal part of the pharynx is effected by means of the paired posterior apertures [choanse]. These are oval in form, their height greater than their width. They are located at either side of the posterior edge of the nasal septum and are limited above by the body of the sphenoid, below by the line of junction of the hard and soft palate. From the plane of the choana forward a rather constricted portion of the nasal cavity ex- tends for a short distance to reach the level of the posterior ends of the middle and inferior con- chse. Into this region, which is known as the meatus naso-pharyngeus, open posteriorly the superior, middle and inferior meatuses. Posterior rhinoscopic examination reveals the choanse, the naso-pharyngeal meatus, the posterior extremities of the three conchse and of the meatuses beneath them. Dimensions of the nasal cavity. — The length of the floor averages approximately 40 mm., the width 32 mm., the height from floor to lamina cribrosa 47 mm. The length of the lateral wall is about 63 mm. The choana measures 29.8 mm. high and 15.5 mm. broad. The area of the two nares is 2 sq. cm. Paranasal sinuses [sinus paranasales] (figs. 964-968). — The location, form and relations of the bony-walled spaces connected with the nasal cavity have been fully described in the section on Osteology. The conditions observed in the living subject differ in certain respects from those present in the macerated skull; the spaces are lined by a mucous membrane which, though affecting but slightly the form of these chambers, modifies considerably the openings by which they communicate with the nasal cavity. These openings permit the entrance and exit of air and to some extent the escape of fluids which may accumulate in the sinuses. While the significance of these spaces is not at present clear it is, how- ever, certain that they function in lightening the weight of the skull, and probable that indirectly they serve in connection with the sense of smell. Maxillary sinus (of Highmore*) [sinus maxillaris Highmori] (figs. 965, 966, 967). Entrance into the maxillary sinus is offered through the middle part of the hiatus semilunaris, that is, the deep, narrow notch between the ethmoidal bulla and un- cinate process of the ethmoid. Viewed from within the sinus, the opening appears as an oval window in the upper part of the medial wall — a position unfavourable to the discharge of matter, when the body is in the upright posture. An accessory opening, situated behind the normal ostium, is present in about 10 per cent, of cases. Measurements of 90 specimens of the adult sinus maxiUaris gave as the average the following (Schaeffer) : Dorsosuperior diagonal 38 mm. Ventrosuperior diagonal 38.5 mm. Superoinferior 33 mm. Ventrodorsal ". 34 mm. Mediolateral 23 mm. Increase in capacity of the maxillary sinus is sometimes observed as the result of more or less extensive excavation of the bony processes of the maxilla adjacent to it, viz. : the alveolar, palatal, frontal and zygomatic. On the other hand narrowing of the cavity is encountered, * Highmore, Nathaniel: English physician. B. 1613, D. 1685. THE NASAL CAVITY 1207 caused by unusually thick walls of bone, bulging inward of the facial or nasal walls, and through retention of teeth. Incomplete division into two parts through the presence of a septum has several times been observed. Communication with ethmoidal cells and with the cavity of the orbital process of the palate bone sometimes exists. Frontal sinus [sinus frontalis] (figs. 78, 964, 968). — The paired frontal sinuses, separated from each other by a bony septum, have in general the shape of a three- sided pyramid with the base below and the apex formed above in the frontal squama. In the base near the septum is located the superior aperture of the infundibulum which, it will be recalled, opens inferiorly at the anterior extremity of the hiatus semilunaris. The form and size of the frontal sinuses are exceedingly variable. They may extend back- ward in the orbital part of the frontal bone as far as the suture between it and the small wing of the sphenoid; laterally into the zygomatic process; upward toward the coronal suture. The capacity of the sinus, as determined in a small number of cases, varied from 3 to 7.8 ccm. (Brvihl). Asymmetry of the septum is frequently observed. Absence of one of the sinuses is not a rare condition; absence of both is occasionally encountered. Fig. 968. — ^Left Nasal Cavity. (Rauber-Kopsch.) Opening of sphe- Hypophysis noidal sinus Choanal arch Pharyngeal tonsil — Torus tubanus" Levator cushion Anterior lip of tubal aperture Salpingo- pharyngeal fold w Naso-pharyngeal ! meatus Sound Uvula in naso- lacrimal „ canal •- S Ethmoidal cells [cellulse ethmoidales] (figs- 965, 968). — The openings of the anterior cells into the semilunar hiatus and infundibulum, and of the posterior cells at the superior meatus have already been described. Communications between the ethmoidal cells and the sphenoidal and maxillary sinuses are not rare; the cavity in the orbital process of the palate bone may open into the posterior cells. In old age, foramina through the lamina papyracea may appear, leading to the introduction of air into the orbit. Sphenoidal sinus [sinus sphenoidalis] (figs. 964, 965, 966). — The apertures of the paired sphenoidal sinuses are, on account of the mucous membrane covering, much smaller than they are in the dried skull. They lie in the anterior wall near the septum, nearer the roof than the floor, and open into the spheno-ethmoidal recess. Extension of the sphenoidal sinuses backward and also into neighbouring processes, and communication with ethmoidal cells and with the small cavity of the orbital process of the palate are not unusual. The capacity of the sinus varies between 1 and 4.2 ccm. (Briihl). Functions of the paranasal sinuses. — Various functions have been attributed to the sinuses near the nose, none of which is entirely satisfying. Medieval anatomists proposed that these cavities contributed to the resonance of the voice, or that they supplied the mucus by which the nasal cavity is kept moist. Lightening the skull, warming the inspired air and taking part, indirectly, in the sense of smell are functions assigned by anatomists of later times. The mucous membrane of the nose [membrana mucosa nasi]. — The nasal cav- ity is completely lined with mucous membrane, which inferiorly, at the limen nasi blends with the skin covering the walls of the vestibule (p. 1204). Posteriorly it joins the mucous membrane of the pharynx and palate. It covers some of the 1208 THE RESPIRATORY SYSTEM openings which are seen in the bony walls; those apertures, however, which lead into the paranasal-sinuses and into the naso-lacrimal duct remain patent, although as already stated the bony openings are much reduced in size. In the nasal cavity the bright rose-red vascular mucous membrane is tightly bound to the periosteum and perichondrium, and is covered with a cihated columnar epithelium. Numerous large mucous nasal glands [glandules nasales] pour their more or less watery secretion over the entire surface. A very considerable venous plexus is found in many parts of the nasal mucosa. Over the inferior concha and to a less extent in the mucosa of the middle and superior conchEB, it forms the cavernous plexuses of the conchse [plexus cavernosi concharum] contributing to build up about these bodies a true erectile tissue. The thickness which these glands and venous plexuses give to the mucous membrane of the conchoe causes the marked increase in size of these bodies over that of their bony supports. The region covered by the mucous membrane just described forms the greater part of the nasal cavity, and is loiowTi as the respiratory region [regio respiratoria]. The mucous membrane of a small area over the superior concha and the adjacent septal wall (fig. 969) has a somewhat different structure. In this area the olfactory nerves are distributed, whence it is known as the olfactory region [regiojolfactoria] and its mucous membrane, compared with that of the respiratory region, is less vascular, yellow or yellowish- brown in colour, and covered by a non-ciliated epitheUum. Its cells, specially modified, some of which are directly connected with the olfactory nerve, form the olfactory organ [organon olfactus]. Small mucous olfactory glands [glanduloe olfactoria;] occur in the region. The mucous membrane which lines the paranasal sinuses throughout is a continuation of the nasal mucosa; it is, however, paler, less vascular, somewhat thinner, and more loosely attached to the bones. Mucous glands are numerous. The waving of the ciha in the nasal cavity is such as to sweep foreign matter toward the choanje; in the paranasal sinuses, toward the nasal cavity. Fig. 969. — Diagram of the Distribution of the Nerves in the Nasal Cavity. (Poirier and Charpy.) The olfactory area is represented by dots. Posterior superior nasal Posterior su- Anterior perior nasal ethmoid ant pal Vessels and nerves. — The arteries of the nasal cavity are the spheno-palatine artery from the internal maxillary which, through its posterior lateral nasal branches, supplies the middle and inferior conchfe (p. 549), the anterior and posterior ethmoidal arteries from the ophthalmic (p. 553), the descending palatine artery from the internal maxiUary (p. 549), and the superior labial branch of the external ma.xiUary to the vestibule. The venous plexuses of the mucous membrane are drained posteriorly by the spheno-palatine to join the pterygoid plexus, superiorlj by the anterior and posterior ethmoidal veins to join the superior ophthalmic vein, and ante- riorly by small branches to join the facial. The lymphatics form a weU-developed plexus which is said to communicate indirectly, through the lymphatics surrounding the olfactory nerves, with the subdural and subarachnoid spaces. Posteriorly two or more well-developed trunks communicate with the pharyngeal lymphatics, and anteriorly the nasal lymphatics join with the lymphatics of the face. The olfactory nerves pass through the cribriform plate of the ethmoid bone and are distributed to the olfactory area (p. 929). The trigeminal nerve furnishes the following branches to the nasal cavity: — branches from the naso-ciliary branch of the oph- thalmic nerve ; the Vidian nerve ; the posterior superior and posterior inferior nasal and the ante- rior palatine from the spheno-palatine ganglion (p. 962); the anterior superior alveolar from the infra-orbital division of the maxillary nerve (p. 938). The development of the nose. — The nasal cavity malves its appearance as a depression of the ectoderm on either side of the median line, immediately in front of the oral fossa, with which the depressions are at first continuous. Later, by the union of the maxillary and globular processes (see p. 18), the depressions are separated from the anterior part of the oral fossa, and this separation is continued by the formation of the palatal processes of the maxillas and palatine bones, so that finally the nasal cavities communicate posteriorly only with the pharynx. The cartilage which forms the lateral walls of the nasal fossas is at first quite smooth, but later it becomes eroded by absorption, whereby the nasal concha; are formed. The erosion also extends into the ethmoid bone, forming the ethmoidal cells, and into the neighbouring bones to form the frontal, sphenoidal, and maxillarjf sinuses. CARTILAGES OF THE LARYNX THE LARYNX 1209 The larynx (figs. 960, 970, 971,), is a tubular organ, the framework of which is made of cartilages joined together and of elastic membranes. Its inner surface is covered by mucosa. From the membranes are formed a pair of vocal folds which, by the passage of air through the larynx, are thrown into vibration and so function in the generation of sound. These folds are affected in respect to their Fig. 970. — View of Interior op Larynx as seen from above during Inspiration. "Base of tongue Median glo Epiglottis Tubercle of epiglotti Ventricular fold Ary-epiglottic fold Cuneiform tubercle Corniculate tubercle Arytenoid commissure Pharynx tension and in their mutual relation by the actions of a system of laryngeal muscles under the control of the vagus nerve and are made thereby, on the one hand, to produce those modifications of the sound involved in the voice and on the other hand to regulate the amount of air passing through the cavity of the larynx. The latter communicates above with the pharynx by means of the opening called the laryngeal aperture, and below with the cavity of the trachea. Figure 970 shows the laiyngeal aperture with its boundaries, the epiglottis and Fig. 971. — View of Interior of Larynx as seen from above during Vocalisation. Base of tongue Median glosso-epiglottic fold Ventricular fold Vocal fold Piriform recess Vocal process. Epiglottis Tubercle of epiglottis Ventricle Ary-epiglottic fold the aryepiglottic folds ; also the cavity of the larynx where, on the walls right and left, appear the ventricular and vocal folds with the chink called rima glot- tidis separating them. The position of the larynx and some of its important parts can be well seen in a median section (fig. 972). THE CARTILAGES OF THE LARYNX The number of cartilages entering into the framework of the larj^nx is nine, three of which are single and the rest in pairs. Their forms and positions are shown in fig. 973. 1210 THE RESPIRATORY SYSTEM The cricoid cartilage [cartilago cricoidea] (figs. 973, 974, 975, 978), single, has been compared in its shape to a signet ring. Its position is at the lower end of the larynx, where it is connected with the first ring of the trachea. Posteriorly the cricoid cartilage expands into a broad lamina [lamina cartilaginis cricoidese] which enters into the posterior boundary of the laryngeal cavity, while laterally and in front it forms a narrow arch [arcus cartilaginis cricoideae]. On either side of the upper margin of the lamina is the elliptical arytaenoid articular surface [facies articularis arytsenoidea] its long axis parallel with the margin of the cricoid, its steeply sloping surface convex for articulation with the arytsenoid cartilage. The hinder surface of the lamina presents a median ridge and lateral impressions for the attachment of the posterior crico-arytsenoid muscles. The arch, weakest Fig. 972.- -Median Section op a Man 21 Years of Age, showing the Position of Larynx AND Trachea. (After W. Braune, from Poirier and Charpy.) Epiglottis — Hyoid bone^ Laryngeal aperture Fat mass' Laryngeal ventricle Thyreoid cartilage Lamina of cricoid Arch of cricoid Trachea (Esophagus Thyreoid body Sterno- thyreoid m.' Sternum' Left innominate. vein Innominate, artery Ascending aorta Right lung — Right auricle — Pharynx Arytaenoid . cartilage WW '„ ~"" Ventricular fold ^ \\\' ^ Vocal fold \YI cervical vertebra in its middle part, presents concave upper and straight lower margins. A circular, elevated thyreoid articular surface [facies articularis thyreoidea] for articulation with the inferior cornu of the thyreoid cartilage is situated upon the side of the cricoid where arch and lamina are continuous. The internal surface is covered by the laryngeal mucosa. The thyreoid cartilage [cartilago thyreoidea] (figs. 973, 974, 975, 977), single and the largest in the laryngeal skeleton is composed of two broad laminae, right and left, which meet and are fused anteriorly in the mid-line in a right angle, partly covering the other cartilages laterally and in front. The laminae are stout, but their connection at the angle is through a weak strip of cartilage. The upper margin of each lamina is convex, and in front drops abruptly to form in the median line the superior thyreoid notch [incisura thyreoidea superior] . The anterior edges CARTILAGES OF THE LARYNX 1211 meeting in the angle produce the laryngeal prominence [prominentia laryngea] ("Adam's apple"), which is seen on the front of the neck. The horizontal in- ferior margin presents near its middle the inferior thyreoid tubercle [tuberculum thyreoideum inferius], and in the median line the inferior thyreoid notch [incisura thyreoidea inferior]. The thick posterior margin of each lamina is continued above the superior edge in the long superior cornu [cornu superius], and below the inferior margin in the short inferior cornu [cornu inferius]. The former is directed slightly backward and medial ward, and joins with the end of the greater cornu of the hyoid by ligament. The inferior cornu, curving medialward as it descends, articu- lates by a flat, circular facet upon the medial side of its extremity with the thy- reoid articular surface of the cricoid cartilage. The external surface of the lamina affords attachment for muscles and presents in its upper posterior part the Fig. 973. — Caetilaqes op the Labynx seen prom behind in Their Natural Positions. The CtTNEiFORM Cartilage is Somewhat Higher than Normal. (Merkel.) Epiglottic cartilage Corniculate cartilage Arytaenoid cartilage I — Superior cornu of thyreoid Cuneiform cartilage Thyreoid cartilage Inferior cornu of thyreoid Median crest superior thyreoid tubercle [tuberculum thyreoideum superius] ; in its lower part the inferior thyreoid tubercle. The internal surface of the thyreoid cartilage is smooth. A thyreoid foramen [foramen thyreoideum], sometimes seen in the upper part of the lamina, giving passage to the superior laryngeal artery, results from the incomplete union of the fourth and fifth branchial cartilages from which the lamina are derived. The oblique line [lines obUqua], extending between the thyreoid tubercles, is commonly present and is regarded by many anatomists as a normal feature of the external surface of the thyreoid cartilage. It marks the attachment of the sternohyoid and thyreohyoid muscles. At the insertion of the vocal ligaments in the angle of the laminae a small perichondral process is often observed. The arytaenoid cartilages [cartilagines arytsenoidese] (figs. 973, 977, 978, 979), paired, surmount the lamina of the cricoid cartilage and give attachment to the vocal ligaments, whose relations and state of tension are altered by the changes in position which these cartilages are almost constantly undergoing. Each cartilage is pyramidal in form, and moulded for the attachment of several muscles. The apex, which is above, is bent backward and medialward and is connected with a corniculate cartilage. The base, somewhat triangular in shape, presents at the lateral and posterior part an oval or circular concave articular surface [facies articularis], directed medialward and downward to meet the aryteenoid articular surface of the cricoid cartilage. The lateral angle of the base is prolonged into a stout muscular process [processus muscularis] for the attach- 1212 THE RESPIRATORY SYSTEM ment of the crico-arytsenoid muscles, while the anterior angle is extended as a sharp projection, the vocal process [processus vocalis], which serves for the attachment of the vocal ligament. The surfaces of the arytsenoid are named medial, posterior, and antero-lateral. The narrow medial surface, covered by the mucosa of the larynx, is nearly vertical, and faces the corresponchng side of the opposite arytsenoid, from which it is separated by a small space. The posterior surface is concave for muscular attachment. The antero-lateral surface is the largest, and presents an irregular contour. On this surface a ridge, the arcuate crest [crista arcuata], extends horizontally between two hollows — the triangular fovea [fovea triangularis] above, which lodges some mucous glands, and a larger depression below, the oblong fovea [fovea oblonga] for the vocal muscle. The colliculus is a small eminence found upon the anterior margin and antero-lateral surf ace. Fig. 974. — Fkont View of the Laryngeal Skeleton. (Modified from Bourgery and Jacob.) Greater corau of hyoid* Body of hyoid Lateral hyo-thyreoid ligament Triticeous cartilage Foramina for superior laryngeal vessels and internal laryngeal n. Median hyo-thyreoid ligament Superior cornu of thyreoid Superior thyreoid notch Lamina of thyreoid Oblique line Median crico-thyreoid ligament. Inferior cornu of thyr Crico-thyreoid joint" Crico-tracheal ligament Tracheal cartilagt The corniculate cartilages (of Santorini) [cartilagines corniculatse (Santorini*)] (figs. 973, 977). — This pair of small conical cartilages is set upon the bent apices of the arytsenoids, continuing their curves backward and mechalward. The corniculate cartilage is not an independent structure in many lower animals, and its continuity with the arytsenoid is sometimes met with in man where the two cartilages are normally developed in a continuous mass of tissue. The epiglottic cartilage [cartilago epiglottica] (figs. 973, 977, 981, 987), unpaired, invested by mucosa behind and partly in front, thin and leaf-shaped, stands behind the root of the tongue and the body of the hyoid. It lies above the thyreoid cartilage, in front of the entrance of the larynx. The free upper margin is convex, or notched; the lower end tapers to a short stalk, the petiole of the epiglottis [petiolus epiglottidis], to which the thyreo-epiglottic ligament is attached. The anterior surface is free above and covered by mucosa; in its lower part it is bound to the body of the hyoid, and is separated by a mass of fat from * Santorini: Venetian anatomist. B. 1681, D. 1737. JOINTS OF THE LARYNX 1213 the hyo-thyreoicl ligament. Its posterior surface above is saddle-shaped; below, it is convex, presenting the epiglottic tubercle [tuberculum epiglotticum]. To the margins are attached the ary-epiglottic folds. The epiglottic cartilage presents numerous small holes and depressions for the accommodation of glands. The cuneiform cartilages (of Wrisberg) [cartilagines cuneiformes (Wrisbergi*)] (fig. 973) lie as small, rod-like bodies in the ary-epiglottic folds anterior to the corniculate_ cartilages. They are variable in form and size and not rarely absent altogether. These cartilages are parts of the epiglottic cartilage in some mammals where, as in man, they he in the ary-epiglottic folds. Their relations to the arytEcnoids are regarded as secondary. Sutton has shown that in the ant-eater a continuous rim of yellow elastic cartilage extends from the sides of the epiglottic cartilage to the summits of the aryttenoids. A minute unpaired inlerarylmnoid or procricoid cartilage is rarely present imbedded in the cricopharyngeal ligament and covered by the pharyngeal mucosa. It is a constant structure in certain mammals. A pair of small sesamoid cariilages, also constantly present in some mammals, is occasionally found in man at the lateral margins of the arytaenoids, connected with them and with the corniculate cartilages by elastic ligaments. Structure of the cartilages. — The thyreoid, cricoid, and greater part of the aryta;noid are composed of hyaline cartilage; the epiglottic, corniculate, and cuneiform cartilages, as well as the ape.x and vocal process of the arytsenoid, are of elastic cartilage. Certain parts of the laryn- geal skeleton normally undergo calcification and subsequent ossification. Calcification begins at about twenty years of age in the thyreoid and cricoid cartilages, and later in the arytenoid. The process begins a little later in the female than in the male, and does not extend so rapidly. The extent to which the cartilages are ossified and the time occupied in the process vary con- siderably. The elastic elements are not involved in the process. Fig. 975.- FiG. 976.- -Cricoid AND Arytenoid Cartilages seen prom Before. -Cricoid and Arytenoid Cartilages seen erom the Left. (Rauber-Kopsch.) (Rauber-Kopsch.) Corniculate cart. Apex of arytjenoid CoUiculus " Arcuate crest ^ Muscular process ■ Vocal process Ary-corniculate synchondrosis Corniculate Colliculus..- g, ^ Arcuate Tnangular pit ** crest Oblong pit "■■■■/"'^W^^ft- Muscular Vocal process .— *''^^^ait^9*'^^SS|^H process - . ^™-|..., Lamina of .^'^ HIh cricoid -Thyreoid A 1. £ / w^mobUr't' nMMMjcffi^ artlcular Arch of ...4i^mi!,,..: "mai surface THE JOINTS AND FIBROUS MEMBRANES OF THE LARYNX (1) Connections between the Laryngeal Cartilages The crico-thyreoid articulation (figs. 973, 974, 975). — The articular surfaces concerned are the thyreoid articular surface on the side of the cricoid and the articular surface on the inferior cornu of the thyreoid cartilage. The crico- thyreoid articular capsule [capsula articularis cricothyreoidea] attached around the margins of these surfaces and certain accessory bands serve to bind the carti- lages together. The accessory bands, cerato-cricoid ligaments fall into three groups radiating from the inferior cornu: the ligamenta ceratocricoidea posteriora upward and medialward to the superior margin of the cricoid; tlie ligamenta ceratocricoidea lateralia downward at the side and back of the capsule; the ligarnentum ceratocricoideum anterius downward and forward. The capsule possesses a synovial layer. A rotary movement about a transverse axis of the cricoid upon the thyreoid or vice versa and a slight backward and forward gliding are permitted at this joint. * Wrisberg: German anatomist. B. 1737, D. 1808. 1214 THE RESPIRATORY SYSTEM The crico-arytaenoid articulation [articulatio cricoarytsenoidea (figs. 973, 977, 978). — The articular surface of the cricoid cartilage and the articular surface of the arytsenoid which enter into this articulation are so disposed that at no time do they meet in complete apposition. A loose capsule [capsula articularis crico- FiQ. 977. — The Laryngeal Skeleton seen from Behind. (Poirier and Charpy.) — ____ Epiglottic cartilage — . — ^Greater cornu of hyoid -Triticeous cartilage Hyo-thyreoid membrane——. Posterior crico-arytae ligament Inferior comu of thyreoid Lamina of cricoid Membranous wall of trachea Body of hyoid Superior comu of thyreoid "Thyreo-epigottic ligament Corniculate cartilage Corniculo- and crico- geal ligaments 'ArytEenoid cartilage Crico-aryt£enoid joint Posterior cerato-cricoid ligament Crico-thyreoid joint ^Lateral cerato-cricoid ligament Fig. 978. — The Larynx with its Ligaments, viewed from the Right. (The right lamina of the thyreoid cartilage has been removed.) (Spalteholz.) Eoiglottis Ary-epiglo tti fold (section through the mucous mem- brane) Arytenoid cartilage Muscular process — Crico-arytEenoid joint '^ Vocal process Theyreoid articular surface''' Tracheal cartilages <^ epiglottic ligament —Median hyo-thyreoid ligament '/'—Quadrangular membrane — Thyreoid cartilage Ventricular ligament 'Vocal ligament "Elastic cone Median crico-thyreoid ligament - Arch of cricoid — Cnco-tracheal ligament — Annular ligament arytaenoidea] of fibrous and synovial strata attached around the edges of the joint surfaces unites the cartilages. Posterior crico-arytsenoid ligament [Hg. cricoarytsenoideum posterius], attached above„ to the medial surface of the base and muscular process of the arytainoid, and below to the lamina MEMBRANES OF THE LARYNX 1215 of the cricoid, is important in helping to fix the former cartilage in place upon the sloping arytaenoid articular surface of the cricoid and in limiting its movements. Motion at this articulation is very free. The following simple movements of the arytaenoid are best under- stood:— (1) gliding of the arytaenoid toward or away from its fellow; (2) inclining forward and backward; (3) rotating on a vertical axis, so that the vocal process sweeps medialward or lateral- ward and also a little downward or upward. The union of the corniculate cartilage with the apex of the arytsenoid cartilage [synchondrosis arycorniculata] is usually by connective tissue; rarely is there a joint cavity. The petiole of the epiglottic cartilage is connected with the thyreoid, below and behind the superior notch, by a strong, elastic thyreo-epiglottic ligament [lig. thyreoepiglotticum] (fig. 977). (2) The Elastic Membrane of the Larynx [Membrana elastica laryngis] This name is given to a more or less continuous sheet of elastic fibres connected with the deeper parts of the laryngeal mucosa. Its upper part is known as the quadrangular membrane, the lower part as the elastic cone. A middle region of the elastic membrane lies opposite the ventricle of the larynx. The quadrangular membrane (figs. 978, 981, 988) extends from the ary-epi- glottic folds above to the level of the ventricular folds (false vocal cords) below. The lateral parts of this membrane are widely separated superiorly, but they con- verge toward the middle line as they descend. Anteriorly, the membrane is fixed in the angle of the thyreoid laminae and to the sides of the epiglottic car- tilage; posteriorly, to the corniculate cartilages and to the arytaenoids. The superior edge on either side lies within the ary-epiglottic fold, which it supports; it slopes downward and backward and includes the cuneiform cartilage. The inferior edge, horizontal and in a sagittal plane, is best developed in front, where it is attached in the angle of the thyreoid a little way from the middle line ; behind, it is fixed to the medial margin of the triangular fovea of the arytsenoid. This inferior free margin, differentiated as the ventricular ligament [lig. ventriculare], is enclosed within, and is the support for the ventricular fold. Fia. 979. — The Elastic Cone seen from Above. (Modified from Luschka.) Nodule of elastic tissue ^„..^I'erichondraI insertion of vocal ligaments Nodule of elastic tissue .Vocal ligament Elastic I tilage Arytaenoid cartilage in transverse section Posterior crico-arytaenoid ligament The elastic cone [conus elasticus] (figs. 978, 979). — -This part of the elastic membrane extends from the level of the vocal folds to the superior margin of the cricoid cartilage. Its component fibres are attached in the re-entrant angle and adjacent lower margin of the thyreoid cartilage, whence they spread downward and backward to the upper edge of the cricoid arch and to the arytsenoid carti- lages. The strong anterior portion, perforated by vessels, is the median crico- thyreoid ligament [fig. cricothyreoideum (medium)] (figs. 974, 975). The lateral parts (lateral portions of the crico-thyreoid membrane) present superior free edges, somewhat thickened, which, running horizontally near the middle line from the thyreoid angle to the vocal processes, constitute the vocal ligaments. These are inserted anteriorly into a perichondral process in the thyreoid angle; poster- iorly, they have a wide area of attachment to the upper and medial surfaces of the vocal processes of the arytaenoids with the elastic fibres of which they are in part continuous. A yellowish, cellular nodule (sometimes cartilage) occurs in the 1216 THE RESPIRATORY SYSTEM anterior end of each ligament. The vocal ligaments enter into the formation of the vocal folds (true vocal cords). Fig. 980. — The Larynx seen from the Left Side. (Modified from Luschka.) Epiglottis J Hyoid bone Thyreo-hyoid musclo— ^ Thyreoid cartilage- Median crico-thyreoid ligament' Crico-thyreoid muscle (straight part) Tracheal cartilage Internal laryngeal nerve Hyo-thyreoid membrane Superior laryngeal artery Superior laryngeal vein Cricothyreoid muscle (oblique part) ry — Posterior crico-arytsenoid muscle Cricoid cartilage Fig. 981. — The Muscles and Ligaments of the Larynx seen from the Side. (The left lamina of the thyreoid cartilage has been removed.) Hyo-epiglottic ligament- Body of hyoid. Fat mas?. Hyo-thyreoid membrane — Thyreo-epiglottic muscle Quadrangular membrane — Thyreoid cartilage External thyreo-arytaenoid muscle Elastic cone Lateral crico-arytaenoid muscle Median crico-thyreoid ligament Cricoid cartilage ■Ary-epiglottic fold Ary-epiglottic and ary- _| -'--• membranosus muscles Posterior crico-arytaenoid muscle -Thyreoid articular surface Lamina of cricoid Inferior laryngeal nerve The median crico-thyreoid ligament is incised m the operation of laryngotomy. It is crossed by the anastomotic arch of the crico-thyreoid arteries, which, however, can be avoided in the operation by making a transverse cut through the ligament close to the superior margm of the arch of the cricoid cartilage. LIGAMENTS OF THE LARYNX 1217 (3) Connections between the Larynx and Neighbouring Structures The hyo-thyreoid membrane [membrana hyothyreoidea] (figs. 977, 980, 981) is a loose, fibrous, elastic sheet, binding together the thyreoid cartilage and hyoid bone. It extends from the superior margin of the former to the greater cornua and Fig. 982. — Scheme of Rima, showing Action of Posterior Crico-aryt^noid Muscle, WHICH DRAWS THE ArttjEnoid Cartilage PROM I TO II. (Modified from Stirling.) superior margin of the body of the latter. The superior laryngeal artery and vein and the internal laryngeal nerve pass through it from the side. Its posterior and lateral edge is cord-like, consisting of elastic fibres which stretch as the lateral Fig. 983. — Scheme showing Action of the Transverse Arytenoid drawing Arytenoid Cartilage from Neutral Position I to II. (Modified from Stirling.) hyo-thyreoid ligament [lig. hyothyreoideum laterale] from the superior cornu of the thyreoid to the greater cornu of the hyoid. A small cartilago triticea is sometimes present in this band. The middle part, median hyo-thyreoid ligament [hg. Fig. 984. — Scheme showing Action of Thyreo-arty^noid drawing the Vocal Processes and the Vocal Ligaments from II to I. (Modified from Stirling.) hyothyreoideum medium] thick and elastic, extends from the superior thyreoid notch upward behind the body of the hyoid to be attached to its superior margin, the hyoid bursa being interposed between the bone and the membrane. 1218 THE RESPIRATORY SYSTEM The cartilage tritioea is the remains of a connection between the thyreoid and hyoid present in the embryo. It persists in adult hfe in some lower animals. The hyo-epiglottic ligament [lig. hyoepiglotticum] (figs. 978, 981) connects the anterior surface of the epiglottic cartilage with the superior margin of the body and the greater cornua of the hyoid. It is a broad sheet, lying above a mass of fat which stands between the median hyo-thyreoid membrane and the epiglottis and spreading laterally to join the pharyngeal aponeurosis in the region of the piriform recess. The name glosso-epiglottic ligament is given to the elastic fibres extending between the root of the tongue and the epiglottis within the median glosso-epi- glottic fold. The corniculo -pharyngeal ligament (fig. 977) extends from the corniculate cartilage down- ward and toward the median hne, attaching to the mucosa of the pharjoix and joining its fellow behind the arytaenoid muscle. From this point a single band, the crico -pharyngeal liga- ment [hg. oricopharyngeum], which may enclose a nodule of cartilage (the interarytsenoid or procricoid cartilage), descends in the middle line, to be fixed to the cricoid lamina and into the pharyngeal mucosa. The larynx and trachea are united by fibrous membrane, the crico-tracheal ligament [lig. cricotracheale] (figs. 974, 978), between the inferior margin of the cricoid cartilage and the upper margin of the first tracheal ring. Posteriorly the ligament is continued into the membranous wall of the trachea. MUSCLES OF THE LARYNX Of the many muscles connected with the larynx, two groups may be recog- nised, the members of one coming from neighbouring parts, fixing themselves to the larynx and acting upon the organ as a whole; the members of the other group confining themselves exclusively to the larynx and acting so as to affect its parts. The muscles composing the first group are described elsewhere. (See Section IV.) The muscles of the second group are composed of striated fibres and are supplied by the vagus nerve through its laryngeal branches. These muscles are all more or less under cover of the thyreoid cartilage, with one ex- ception, the crico-thyreoid. The crico-thyreoid muscles [m. cricothyreoideus] (fig. 980) are placed one on either side of the outer surface of the larynx in its lower part. Each muscle is partially separated into an anterior straight [pars recta] and a posterior oblique portion [pars obliqua], which together arise from the arch of the cricoid. The fibres of the straight part ascend steeply and are inserted into the inferior margin of the thyreoid cartilage. The oblique portion is inserted into the inferior cornu and into the lower margin and inner surface of the thyreoid cartilage. The straight part elevates the arch of the cricoid, causing the lamina, and with it the arytsenoid cartilages, to sLuk, while the obhque part draws forward the thyreoid; thus the vocal ligaments are made tense. The muscle is supplied by the external branch of the superior larjTi- geal nerve. A connexion between the posterior part of this muscle and the inferior constrictor of the pharynx and their common nerve-supply indicate their genetic relationship. The posterior crico-arytffinoid muscle [m. cricoarytasnoideus posterior] (figs. 980, 981, 982), paired, is situated at the back of the larynx, covered by the submu- cous coat of the pharynx. It is a thick, triangular mass which takes origin from the posterior surface of the cricoid lamina, the two muscles being well separated by the median crest of the cartilage. The lower fibres ascend and the upper ones pass horizontally lateralward and are inserted into the muscular process of the arytaenoid cartilage on its posterior surface and tip. When these muscles contract, the muscular processes of the arytsenqids are puUed back- ward and downward, while the vocal processes travel lateralward and a Uttle upward, so that the rima glottidis is widened and the vocal hgaments made tense (fig. 982). The innervation is by the posterior branch of the inferior laryngeal nerve. In ether narcosis the dilator muscle is later paralyzed and afterward earlier restored than the constrictors of the larynx. At the lower margin of this muscle a small slip, the cerato-cricoid muscle [m. ceratocri- coideus], is sometimes found, extending between the lamina of the cricoid and the inferior cornu of the thyreoid cartilage. The constrictor laryngis. — Whereas the crico-arytgenoideus posterior is a dila- tor of the larynx, the several muscles now to be considered are in the main con- MUSCLES OF THE LARYNX 1219 strictors. They form a ring, the constrictor laryrigis, around the laryngeal cavity, interrupted, however, by the cartilages. In the larynx of amphibia and reptiles a complete sphincter guards the entrance to the air-passages. The following muscles are included in the constrictor group: — The transverse arytaenoid muscle [m. arytaenoideus transversus] (figs. 981) 983, 985) is. a single muscle of quadrilateral form, extending across the middle line from the posterior concave surface of one arytaenoid cartilage to that of the other. Its anterior surface, between the cartilages, is covered by the laryngeal mucosa; its posterior surface, crossed by the arytaenoideus obliquus, is clothed by the submucous coat of the pharynx. The arytaenoideus transversus approximates the arytenoid cartilages and their vocal proc- esses, which are at the same time elevated, and the vocal Ugaments made tense. It is supplied by the posterior branch of the inferior laryngeal nerve. Fig. 985. — -The Nerves of the Larynx seen from Behind. Greater cornu of hyoid Triticeous cartilage Ary-epiglottic fold Superior cornu of thyreoid orniculate cartilage Anterior branch of in- ferior laryngeal nerve Posterior branch of in- ferior laryngeal nerve Posterior crico-arytas- noid muscle Crico-thyreoid joint Base of the tongue Epiglottis External branch of su- perior laryngeal nerve Internal branch of su- perior laryngeal nerve Cut edge of hyo-thy- reoid membrane Cuneiform tubercle Oblique arytagnoid Arytsenoid cartilage Lamina of cricoid Inferior laryngeal The lateral crico -arytaenoid muscle [m. cricoarytaenoideus lateralis] (fig. 981) arises from the upper margin and outer surface of the cricoid arch and from the elastic cone, whence the fibres extend backward and upward to an insertion on the anterior surface of the muscular process of the arytaenoid cartilage. This muscle is inseparable from the thyreo-arytsenoideus in about half the cases. The lateral oricoarytsnoids by their contraction cause the vocal processes to move toward the median line and a little downward, so that the vocal Ugaments are approximated and shghtly stretched. They antagonise the posterior crico-arytaenoids. The anterior branch of the in- ferior laryngeal nerve supphes these muscles. The external thyreo-arytaenoid muscle [m. thyreoarytsenoideus (externus)] (figs. 981, 984, 988), variable in form and in the disposition of its fibres, is closely connected with the preceding. It Hes under cover of the thyreoid lamina lateral to the laryngeal saccule (ventricular appendix) and elastic cone. Arising within the angle of the thyreoid laminae the muscle extends upward and backward to its insertion on the lateral margin of the arytaenoid cartilage. 1220 THE RESPIRATORY SYSTEM It draws forward the arytsenoid cartilage (and also tilts the cricoid), and rotates it so that the vocal process passes medialward and downward, relaxing the vocal ligament. It is the antagonist of the crioo-thyreoid (fig. 984). Its nerve-supply is the anterior branch of the in- ferior laryngeal. The vocal muscle [m. vocalis], (fig. 988), prismatic in form, is tiie inner con- stant part of tlie thyreo-arytasnoideus. It lies in tiie vocal lip lateral to the vocal ligament. Its fibres run from their origin in the angle of the thyreoid laminse to their insertion in the vocal process and oblong fovea of the arytaenoid cartilage. It draws forward the vocal process, relaxing the vocal ligament. Its nerve comes from the anterior branch of the inferior laryngeal. The insertion of certain fibres of this muscle into the elastic vocal ligament has been observed (ary-vocalis muscle of Ludwig). D. Lewis has shown that some of the elastic fibres in the vocal ligament are derived from the perimysium of the vocal muscle. The ventricular muscle [m. ventricularis] consists of a few fibres derived from the thyreo- arytffinoideus which reach the back of the laryngeal saccule and enter the ventricular fold. The small thyreo-arytwnoideus superior extends from the angle of the thjrreoid to the muscular process of the arytaenoid upon the lateral surface of the main muscle. The oblique arytsenoid muscle [m. arytsenoideus obhquus] is a slender band lying at the back of the larynx and under the pharyngeal submucosa. It arises from the muscular process of the arytsenoid posteriorly, and, ascending obliquely, crosses its fellow in the median line. Some fibres are inserted into the apex of the opposite arytsenoid cartilage; other fibres sweep around the apex and accom- pany the thyreo-arytsenoid to an insertion in the angle of the thyreoid cartilage, constituting the thyreo-arytcenoideus obliquus. This muscle contracts the laryngeal aperture and vestibule of the larynx. Its nerve is derived from the anterior branch of the inferior laryngeal. Closely connected with the thyreo-arytsenoideus is a bundle of fibres of fairly regular occurrence, called the thyreo-epiglottic muscle [m. thyreoepiglotticus] (fig. 981). It originates from the inner surface of the thyreoid lamina and pro- ceeds upward and backward to end in the quadrangular membrane and to become attached to the lateral border of the epiglottis. The ary-membranosus and ary-epiglotlic muscles are inconstant fascicles of the constrictor group which run in the ary-epiglottic fold and become fixed into the quadrangular membrane and margin of the epiglottic cartilage. Summary of the Actions of the Laryngeal Muscles According to their actions, the laryngeal muscles may be divided into — (a) those which effect the tension of the vocal folds; (b) those which control the rima glottidis; (c) those which effect the closure of the laryngeal aperture and vestibule. (a) The vocal ligaments are made tense by the action of the crico-thyreoid, the lateral and posterior cricoarytsenoid and the transverse arytaenoid muscles. The vocal ligaments are re- laxed as the result of the action of the external thyreo-arytaenoid and vocal muscles. (6) The rima glottidis is widened by the crico-arytajnoideus posterior and made narrow by the contraction of the arytaenoids. The crico-arytaenoideus lateralis also assists in closing the rima glottidis by rotating the vocal processes medialward, and if the crico-arytsenoideus posterior contracts simultaneously, it aids in the closure. The vocal hgaments are approxi- mated also by the thyreo-arytaenoideus [externus]. (c) The laryngeal aperture and vestibule are closed mainly by the arytsenoideus transversus and thyreo-arytsenoideus (externus), by which the arytaenoid cartilages are brought into apposi- tion and drawn toward the epiglottis. Other muscles derived from the constrictor group, arytaenoideus obliquus and ary-epiglotticus assist in closing the laryngeal aperture. CAVITY OF THE LARYNX AND LARYNGEAL MUCOSA The cavity of the larynx [cavum laryngis] is relatively narrow and does not correspond in shape with the outer surface of the organ. Its form is shown in fig. 986 taken from a cast of the laryngeal cavity and the spaces continuous with it. Its walls are covered throughout by the mucous membrane of the larynx (figs. 987, 988). The mucosa of the larynx is continuous above with the mucous membrane of the pharynx, below with that of the trachea (figs. 970, 971). At the root of the tongue the pharyngeal mucosa is reflected backward to the anterior surface of the epiglottis, presenting the median and lateral glosso-epiglottic folds [plica CAVITY OF THE LARYNX 1221 glosso epiglottica medianaet lateralis]. From the sides of the pharynx it passes medialward, first sinking between the thyreoid cartilage laterally and the aryt- senoid and cricoid medially, entering into the walls of the piriform recess; then passing over the superior margin of the quadrangular membrane to form the ary- epiglottic fold. At the medial side of the piriform recess a slight fold of the mucosa [phca nervi laryngei) corresponds to the superior lar3Tigeal nerve. Between the root of the tongue and the epiglottis is a depression subdivided in the middle line and limited laterally by the median and lateral Fig. 986. — Cast of the Vestibulum and Cavum Oris, op the Phahtnx, Laeynx, op the Upper Part op the Trachea and (Esophagus. Seen from in front And below. (Rauber- Kopsch.) Rima oris Alveolar part of mandible *■ --^'tf'-ymM Tongue Glosso-epiglottic vallecula S Vestibule of larynx Piriform recess Laryngeal ventricle Cavum laryngis inferius (Esophagus glosso-epiglottic folds; this is the epiglottic vallecula [vallecula epiglottica]. The piriform recess and the epiglottic vallecula are favorite sites for the lodgment of foreign bodies. The ary-epiglottic fold [plica aryepiglottica] extends from the side of the epiglottis to the apex of the aryt:rnoid cartilage; within it are fibres of the ary-epiglottic and thyreo-epiglottic muscles and the cuneiform and corniculate cartilages. These cartilages correspond to two rounded eminences on each side of the laryngeal entrance, the cuneiform and corniculate tubercles [tuberculum cuneiforme (Wrisbergi); tubereulum corniculatum (Santorini)], respec- tively. Of these, the former is often small and inconspicuous, the latter usually well developed and prominent. The cavity of the larynx above the level of the ventricular folds is known as the vestibule [vestibulum laryngis]. This is wide in its upper part, but the sides incline toward the median line in descending, and the cavity becomes narrow 1222 THE RESPIRATORY SYSTEM transversely in approaching the region of the glottis. Here the cavity has received the special name, superior entrance to the glottis [aditus glottidis superior]. The parts of the framework of the larynx which enter into the walls of the vestibule are : in front, the epiglottic and thyreoid cartilages with the thyreo-epiglottic hgament; at the side, the quadrangular membrane, the cuneifoi-m and corniculate cartilages, and the medial surface of the arytsenoid cartilage; behind, the anterior surface of the transverse arytsenoid muscle. The vestibule communicates with the pharynx by the laryngeal aperture [aditus laryngis] (figs. 970, 971, 972, 987), which looks upward and backward. The form of the aperture is oval or triangular, with the base in front; here it is bounded by the epiglottis; laterally by the ary- epiglottic fold of the mucosa. Posteriorly the laryngeal aperture is prolonged as a little notch between the corniculate cartilages and the apices of the arytsenoids [incisura interarytsenoidea] limited behind by a commissure of the mucosa. The high anterior waU of the vestibule presents a marked convexity, the tubercle of the epiglottis [tuberculum epiglotticum], over the thyreo-epiglottic ligament. The lateral walls, Fig. 987. — Median Section op the Larynx. (Merkel.) Median glosso-epiglottic fold Cuneiform tubercle' Corniculate tubercle Arytaenoid muscles' Lamina of cricoid' — Epiglotti:: cartilage — ^Appendix of the ventricle -/^ — Ventricular fold Ventricle Vocal fold Thyreoid cartilage Median crico-thyreoid ligament Arch of cricoid Crico-tracheal ligament First tracheal cartilage higher in front than behind, show two slight ridges, separated by a shallow groove, extending downward from the cuneiform and corniculate tubercles. The posterior wall, very low, corre- sponds to the commissure connecting the arytsenoid cartilages. On either side of the vestibule, toward its inferior end, is the sagittally running ventricular fold [plica ventricularis] (false vocal cord) (figs. 970, 971, 987, 988). This appears as an elevation of the mucous coat of the lateral wall, prominent in its middle and anteriorly, fading away posteriorly. The ventricular fold contains the inferior free edge of the quadrangular membrane, that is, the ventricular liga- ment, and numerous glands. Wylie's experiments with the ventricular folds led him to conclude that the closure of the glottis in defaecation and vomiting is mainly effected by the apposition of these folds. (Quain.) The interval between the right and left ventricular folds, the vestibular slit [rima vestibuli] leads downward to a space between the planes of the ventricular and vocal folds, which extends on each side into the laryngeal ventricle [ventricu- lus laryngis (Morgagni*)] (figs. 970, 971, 987, 988). The latter is a little antero- posterior pocket of the mucosa reaching from the level of the arytsenoid nearly to the angle of the thyreoid cartilage, and undermining the ventricular fold; it opens into the cavity of the larynx by a narrow mouth limited above and below by the ventricular and vocal folds. From its anterior part a small diverticulum, * Morgagni. ItaUan anatomist. B. 1682, D. 1771. THE VOCAL FOLDS 1223 the ventricular appendix [appendix ventriculi laryngis] extends upward between the ventricular fold medially and the thyreo-arytsenoid muscle and thyreoid car- tilage laterally. Many mucous glands open into it. The appendix is occasionally so large as to reach the level of the upper margin of the thyreoid cartilage or even the great cornu of the hyoid bone. The laryngeal pouches of some of the apes are remarkably developed and appear to serve in affecting the resonance of the voice. In man, their function, besides that of pouring out the secretion of the glands located within their walls, is not known. The vocal fold [plica vocalis] (or true vocal cord) (figs. 970, 971, 987, 988) is the thin edge of a full, lip-like projection, the vocal lip. The vocal folds cor- respond in antero-posterior extent to the vocal hgament, and stand nearer the median line than the ventricular fold. In colour the vocal folds are pearly white, excepting the anterior end of each, where there is a yellow spot [macula flava] produced by a little mass of elastic tissue (sometimes cartilage) in the ligament. The vocal lip [labium vocale] forms the floor of the ventricle and contains the upper part of the elastic cone, whose thickened free edge, the vocal ligament, lies in the Fig. 988. — Fbontal Section op a Larynx Hardened in Alcohol. B. Anterior segment. (Poirier and Charpy.) A. Posterior segment. Cunei- form tubercle Ventri- cular muscle Appen- dix Thy- . reo- arytae- noid (ext.) Cricoid .Crico- thyreoid B. vocal fold and along the vocal muscle. The two vocal lips with the vocal folds and the intervening space, the rima glottidis, together constitute the sound- producing apparatus, the glottis. Below the vocal folds and the medial surfaces of the arytenoid cartilages is a slit, the rima glottidis (figs. 970, 971, 988), the narrowest part of the laryngeal cavity, extending from the arytsenoideus transversus muscle posteriorly to the thyreoid cartilage in front. The portion of the rima between the vocal folds is known as the pars intermembranacea ; that between the arytsenoids the pars intercartilaginea. The rima glottidis in easy respiration is narrow and has the form of a long triangle; in laboured breathing it is widely open and lozenge-shaped. Below the level of the vocal folds is the space called the inferior entrance to the glottis [aditus glottidis inferior] (fig. 988), which is narrow from side to side above, wide and circular in section below — altogether somewhat funnel-shaped. Its walls are formed by the elastic cone and by the arch and lamina of the cricoid cartilage. The lining mucosa is separated from the elastic cone by numerous glands and loose connective tissue, a condition favorable to the development of oedema; below it is continuous with the mucosa of the trachea. By means of the laryngoscope a more or less complete picture of the laryngeal aperture and the cavity of the larynx can be obtained (figs. 970, 971). There appear, highest up, the 1224 THE RESPIRATORY SYSTEM root of the tongue with the epiglottic valleculse and glosso-epiglottic folds leading backward to the epiglottis; behind the latter, the triangular aperture of the larynx, bounded at the sides by the ary-epiglottic folds. Further lateralward appear the piriform recesses, the laryngeal portions of which lie as transverse fissures behind the laryngeal aperture. Within the ary- epiglottic folds are seen the prominent corniculate tubercles on either side of the inter- arytaenoid commissure and just anterior, the variable cuneiform tubercles. Within the vesti- bule the epiglottic tubercle rises upon the anterior wall, while at the sides appear the ventricular folds overhanging the slit-like openings of the laryngeal ventricles. Below this level the vocal folds stand out on either side approaching nearer the median plane than do the ventricular folds and conspicuous by their pearly whiteness. The form and extent of the rima glottidis and of its divisions, the intermembranous and intercartilaginous parts, can be inspected. Far down, the cricoid cartilage and anterior wall of the trachea may appear and under favourable conditions a glimpse of the bifurcation of the latter can be obtained. The mucous coat of the larynx [tunica mucosa laryngis] in general is covered by a ciliated epithelium; the vocal lips, and, exceptionally, small areas of the mucosa of the laryngeal surface of the epiglottis and the ventricular folds possess a covering of flat, non-ciliated cells. The attachment of the mucosa to the underlying parts is very firm about the vocal folds and dorsal side of the epiglottis, and loose in the ary-epiglottic folds, where much areolar tissue is present. In general the mucosa is pink in colour, becoming bright red over the epiglottic tubercle and edges of the epiglottis and fading over the vocal folds, which appear almost white. Numerous mucous glands [glandulse laryngeal] occur about the larynx and are aggregated into groups in certain places. One cluster of anterior glands [gl. laryiifjoa- nnteriores] is found in front of and on the posterior side of the epiglottis; another, the middle glands [gl. laryngeae media;], is in the ventricular fold, in the triangular fovea of the arytfonoid curtilage and clustered about the cuneiform cartilage, while a third set, the posterior glands [gl. laryngea; posteriores], is disposed about the transverse arytajnoid muscle. Many glands pour their secretion into the appendix of the laryngeal ventricle, but there are none on or about the vocal folds. Lymph- nodules of the larynx [noduli lymphatici laryngei] occur in the mucosa of the ventricle and on the posterior surface of the epiglottis. Position and relations. — The larynx opens above into the pharynx by the aditu and in thiss region is connected with the hyoid bone. Below, its cavity leads into the trachea. Its position in the neck is indicated on the surface by the laryngeal prominence (Adam's apple). It stands in front of the fourth, fifth, sixth, and seventh cervical vertebrae; from these it is separated by the prevertebral muscles and the pharynx, into the anterior wall of which it enters. The integument and cervical fascia cover the larynx anteriorly in the middle line, while toward the side are the sterno-hyoid, sterno-thryeoid, and thyreo-hyoid muscles. The lateral lobe of the thyreoid gland and the inferior constrictor of the pharynx are in relation to it laterally, while further removed are the great vessels and nerves of the neck. Peculiarities of age and sex. Position. — The larynx is placed high in the neck in foetal and infantile life and descends in later life. In a six-months foetus the organ is two vertebra higher than in the adult. (Symington.) The descent of the larynx has-been attributed to the vertical growth of the facial part of the skull, but this cause is questioned by Cunningham, who points out the high position of the larynx in the anthropoid apes, where the facial growth is more striking than in man; it appears also that the larynx follows the thoracic viscera in their subsidence, which, according to Mehnert, continues until old age. At birth the interval between the hyoid bone and thyreoid cartilage is relatively very small and increases but little during early life. Growth and form. — The larynx of the new-born is relatively large and in contour more rounded than that of the adult. The organ continues to grow until the third year, when a resting period begins, lasting until about twelve years of age, during which time there appears to be no difference between the larynx of the male and that of the female. At puberty, while no marked change is observable in the larynx of the female, rapid growth accompanied by modification of form of the larynx is initiated in the male. The laryngeal cavity is enlarged, the antero-posterior diameter markedly increased; the whole framework becomes stronger; the thyreoid cartilage especially increases greatly in its dimensions, giving rise to the laryngeal prominence; the vocal folds are lengthened and thickened, the voice changing in quality and pitch. These changes are, for the most part, effected in about two years, but complete develop- ment is not attained before twenty to twenty-five years of age. Castration is known to in- fluence the development of the larynx, for in the eunuch it has been found to resemble that of a young woman. The changes in the structure of the cartilages have already been described. Dimensions. — In the male the distance from the upper edge of the epiglottis to the lower margin of \\u: cricoid is 70 mm.; in the female, 48 mm. The transverse diameter is 40 mm. in the nial(\ 'Ao mm. in the female. The greatest sagittal diameter is 40 mm. in the male, 37 mm. in the female. The vocal folds in the male measure relaxed about 15 mm., in the female, but 11 mm.; when stretched, about 20 mm. and 15 mm. respectively. ' The length of the rima glottidis in the quiescent state is on the average 23 mm. in' the male; 17 mm. in the female. In the male the pars intermembranacea measures 15.5 mm., the pars intercartilaginea, 7.5 mm. In the female these are 11,5 mm. and 5.5 mm. respectively. The rima may be lengthened by stretching of the vocal folds to 27.5 mm. in the male and 20 mm. in the female. (Moura.) In the male the width of the rima glottidis is 6-8 mm. in its widest part, but may be increased nearly to 12 mm. Vessels and nerves (figs. 980, 985), — The arteries supplying the larynx are the superior and inferior laryngeal, which accompany the internal and inferior laryngeal nerves respectively, and the crico-thyreoid arteries (see pp. 538, 564). The superior and inferior laryngeal veins join the superior and inferior thyreoid veins re- spectively. The lymph vascular system is well developed throughout the larynx generally, but in the THE TRACHEA AND BRONCHI 1225 vocal folds where the mucosa is thin and tightly bound down the vessels are scarce and small in size (see p. 719). The nerves of the larynx are the superior and inferior laryngeal branches of the vagus and also certain branches of the sympathetic. Taste-buds occur and are abundant in the mucosa of the posterior surface of the epiglottis. The innervation of the muscles has already been in- dicated, and the description of the course and relations of these nerves will be found in the chapter on the Peripheral Nervous System. It should be mentioned here, however, that the idea of sharply limited territories of innervation, not only for the mucosa, but for the muscles as well, has been brought into question by the researches of Semon and Horsley, E.xner, and others, which show that the distribution and functions of the laryngeal nerves are e.xtremely complex. The development of the larynx. — The larynx is developed partly from the lower portion of the embryonic pharynx and partly from the upper portion of the trachea. The .cricoid carti- lage represents the uppermost tracheal cartilage, while the thyreoid is formed by the fusion of four cartilages representing the ventral portions of the cartilages of the fourth and fifth branchial arches. The laryngeal muscles are derived from the musculature of these arches and conse- quently their nerve-supply is from the vagus. Whether or not the arytenoid and epiglottic cartilages are also derivatives of the branchial arches is uncertain, although it seems probable that they are. THE TRACHEA AND BRONCHI The tubular trachea (figs. 972, 989), or windpipe, extends from the larynx downward through the neck and into the thorax to end by dividing into two branches, the right and left bronchi [bronchus (dexter et sinister)], which lead to Fig. 989 — Trachea and Bronchi in Their Relations to the Great Vessels as seen from Behind. (After Gegenbaur.) Left subclavian artery Superior vena cava Right pulmonary veins Inferior vena cava the lungs. These tubes are simple transmitters of the respiratory air. Their walls are, for the most part, stiff and elastic, consisting in large part of cartilage. While the_ general form of these tubes is cyhndrical, a rounded contour is presented by their walls only in front and at the sides, the posterior surface being flat. The inner surface of the walls of the tubes presents a succession of slight annular pro- jections caused by the cartilaginous rings which enter into their structure. The calibre of the trachea varies at different levels, a cast of the lumen being in gen- eral spindle-shaped. Its sectional area is less than the combined sectional areas of the two bronchi. When the bifurcation of the trachea [bifurcatio tracheae] is viewed by looking down into its cavity, a sagitally directed keel, the carina tracheae (fig. 990), is seen standing between the openings which lead into the bronchi. Its position is a httle to the left of the mid-plane of the trachea in a slight majority of cases, or in the mid-plane in a large percentage. 1226 THE RESPIRATORY SYSTEM Position and relations (figs. 972, 989, 1000). — The trachea lies in the median plane, extending from the level of the sixth cervical vertebra downward and backward, receding from the surface in following the curve of the vertebral col- umn, and deviating a little to the right in approaching the level of the fourth thoracic vertebra, where it divides. Its lower end is fixed so that with elevation and descent of the larynx the tube is stretched and contracted, ■ changes in length which also result from extension and flexion of the head and neck. The mobility of the trachea is favored by its loose investment of connective tissue. About half of the trachea lies in the neclj, but the extent varies with the length of the neck, the position of the head and with age; the trachea holds a lower position in adult life than in childhood and a still lower one in old age when the bifurcation may be as low as the sixth or seventh thoracic vertebra. In front and closely connected with it is the isthmus of the thyreoid gland, covering usually the second to fourth cartilages; anterior to this the cervical fascia and integuments. The cervical aponeurosis is attached to the upper margin of the sternum in two lamellae, with an interspace containing the venous jugular arch, a lymph gland, and some fat. Between these aponeuroses and the trachea is another space containing the inferior thyreoid veins and some tracheal lymph-glands, and sometimes a thyreoidea ima artery. The innominate artery occasionally crosses the trachea obUquely in the root of the neck. Behind the trachea, in its whole length, Ues the oesophagus, which in this part of its course inclines to the left. On either side are the great vessels and nerves of the neck, and the lobes of the thyreoid gland. The inferior laryngeal nerve lies in the angle between the (Esophagus and trachea. Fig. 990. — Bifurcation op the Trachea showing the Tracheal Keel. R. L. Right and left bronchi. (Heller and von Schrootter, from Poirier and Charpy.) Within the thorax the trachea lies in the mediastinum, enveloped in loose areolar tissue and fixed through strong fibrous connections with the central tendon of the diaphragm. The innominate artery and the left common carotid are at first in front and then at its sides as they ascend, while the left innominate vein and the remains of the thymus are further forward. The aortic arch is in contact with the anterior surface of the trachea near the bifurcation. On the right side are the vagus nerve, the arch of the vena azygos, the superior vena cava, and the mediastinal pleura; on the left, the arch of the aorta, the left subclavian artery, and the recurrent laryngeal nerve. A large group of bronchial lymph-glands [lymphoglandulae bron- chiales] lies below the angle of bifurcation. The oesophagus is behind and to the left. The bronchi take an obfique course to the hilus of the lung, where they branch. The right bronchus is nearer to the vertical in its course than is the left; it is also shorter and broader. These conditions, together with the position of the tracheal keel, explain the more frequent entrance of foreign bodies into the right than into the left bronchus. The asymmetrical course of the two bronchi is probably genetically associated with the position of the heart and aorta. The azygos vein arches over the right bronchus, the vagus passes behind, and the right branch of the pulmonary artery crosses anteriorly below the level of the first (eparterial) branch of the bronchus. The aorta arches over the left bronchus and gains its posterior surface along with the cesophagus; the left branch of the pulmonary artery passes at first in front and then above the bronchus. Dimensions. — On account of their elasticity considerable difficulty is met with in obtaining accurate measurements of the air-tubes. The length of the trachea is given at 95-122 mm.; its transverse diameter 20-27 mm. ; the sagittal diameter 16-20 mm. The right bronchus has a length of 25-34 mm.; the left, 41-47 mm. The transverse diameter of the right is 18 mm.; of the left, 16 mm. The angle of bifurcation of the trachea varies from 56° to 90°, the mean being 70.4° a wide angle corresponding to the breadth of the thorax of man. The right bronchus makes an angle of 24.8° with the median plane; the left, 45.6°. According to Tillaux the length of that portion of the trachea between the superior edge of the sternum and the cricoid cartilage varies with age and sex as follows: — Adult male, from 4.5 to 8.5 cm average, 6.5 cm. Adult female, " 5 to 7.5 cm " 6.4 cm. Boys 2| to 10 years, " 2.7 to 6.5 cm " 4.4 cm. Girls 3i to 101 " " 4 to 6.5 cm " 5.1 cm. THE TRACHEA AND BRONCHI 1227 The diameter of the lumen of the trachea when distended to a cylindrical form has been measured by S&: — New-born 4.12 to 5.6 mm. Infant 2 years 7.5 to 8 mm. Infant 4 to 7 8 to 10.5 mm. Over 20 years, male 16 to 22.5 mm. Over 20 years, female 13 to 16 mm. Structure of the trachea and bronchi (figs. 978, 988, 989, 991).— The walls of the trachea and bronchi are composed of a series of cartilages having the form of incomplete rings, held together and enclosed by a strong and elastic fibrous mem- brane. Posteriorly, where the rings are deficient, this membrane remains as the membranous wall [paries membranacea] ; between the cartilages it constitutes the annular ligaments [ligg. annularia (trachealia)]. Fig. 991. — Schematic Longitudinal Section of the Wall op the Trachea. (Gegenbaur.) Fibrous membrane^ Annular ligament Tracheal glandS' Tracheal cartilage A tracheal cartilage [cartilago trachealis] comprises a little more than two- thirds of a circle. Its ends are rounded, its outer surface flat, while the inner sur- face is convex from above downward; the upper and lower margins are nearly parallel. The cartilages are from sixteen to twenty in number. The first is usually broader than the type, and is connected by the crico-tracheal ligament with the cricoid cartilage. Sometimes these two cartilages are in part continuous. The last cartilage is adapted to the bifurcation of the trachea and presents at the middle of its lower margin a hook-hke process. This turns backward between the origins of the bronchi, and in the majority of cases gives a cartilaginous basis to the tracheal carina. Some of the tracheal cartilages vary from the type by bifurcating at one end. The cartilages keep the lumen of the trachea patent for the free passage of the air. Calcification occurs as with the laryngeal cartilages, but much later in life. A mucous coat [tunica mucosa], soft and pinkish-white in colour, covers the inner surface of the trachea; posteriorly it is thrown into longitudinal folds. Mucous secreting tracheal glands [gl. tracheales] are present in the elastic sub- mucous coat [tela submucosa] between the cartilages and at the back of the trachea. A thin layer of transversely disposed smooth muscle-fibres, stretching between the ends of the cartilages in the posterior wall, constitutes the muscular 1228 THE RESPIRATORY SYSTEM coat [tunica muscularis]. Contraction of this trachealis muscle, as it is more prop- erly named, causes the ends of the tracheal cartilages to be approximated and the lumen of the wind-pipe to be diminished. The structure of the walls of the bronchi is similar to that of the trachea. The right bronchus possesses six to eight cartilages; the left, nine to twelve. An inconstant broncho-asophageal muscle may connect the back of the left bronchus with the gullet. Vessels and nerves. — The arteries supplying these air-tubes come from the inferior thyreoid and from the internal mammary by its anterior mediastinal or broncliial branches. Venous radicles come together in the annular ligaments and join lateral veins on either side, which empty the blood into the plexuses of the neighbouring thyreoid veins. Lyinph-vessels are abundant, and are disposed in two sets, one in the mucosa, another in the submucosa. They drain into the tracheal, bronchial and oesophageal lymph-glands. Neri'es are provided by the vagus direct, by the inferior laryngeal, and by the sympathetic. THE LUNGS The lungs [pulmones], the essential organs of respiration, are constructed in such a way as to permit the blood to come into close relation with the air (fig. 992). Their genetic connection with the entodermal canal has already been indi- cated (see also p. 1099). In plan of structure the lung has been compared with Fig. 992. — Schematic Section of a Lobule of the Lung showing the Relation of the Blood-vessels to the Air-spaces. (After Miller, from the 'Reference Handbook of the Medical Sciences.') b.r. Respiratory bronchiole, d.al. Alveolar duct; a second alveolar duct is shown cut off. a,a. Atria, s.al. Alveolar saccule, a.p. Alveolus, art. Pulmonary artery with its branches to the atria and saccules, v. Pulmonary vein with its tributaries from the pleura (1), the alveolar duct (2), and the place where the respiratory bronchiole divides into the two alveolar ducts (3). )sa/ a gland, since it is composed of a tree-like system of tubes terminating in expanded spaces. Closely associated with the system of tubes are certain blood-vessels, some of which take part in nourishing the organ, others participate in its special mechanism. The lungs are two in number, and lie one on either side of the thoracic cavity, separated by a partition known as the mediastinum (figs. 993, 997, 1000). Serous membranes covering the latter right and left are parts of two closed sacs, the pleurse, each of which is reflected about a lung and the neighbouring chest-wall after the manner of serous membranes in general. The space enclosed within the sac-walls is the pleural cavity, genetically a subdivision of the ccelom. Form (figs. 994, 998). — The lung is pyramidal or conical in form, with the base [basis pulmonis] below and resting on the diaphragm, and with apex [apex pul- moni.s] above, in the root of the neck. Two surfaces, costal and mediastinal, are described. The broad convex costal surface [fades costalis] is directed against THE LUNGS 1229 the thoracic wall in front, laterally and behind, and is marked by grooves corre- sponding to the ribs. The mediastinal surface [f acies mediastinalis] is concave and presents a contour adapted to structures of the mediastinum (fig. 994). A special concavity on this surface, known as the cardiac fossa, corresponds to the promi- nence of the heart and is deeper in the left lung than in the right. Above and behind the cardiac fossa is a depression, the hilus of the lung [hilus pulmonis], where the bronchus and pulmonary vessels and nerves together constituting the root of the lung [radix pulmonis], enter and leave. Near the posterior edge of the mediastinal surface is a groove, which ascends and turns forward over the hilus ; the groove of the left lung is adapted to the cylindrical surface of the aorta; that of the right, the vena azygos. A well-marked subclavian sulcus [sulcus sub- FiG. 993. — Horizontal Section of the Thorax op a Man, aged Fifty-seven, at the Level OP the Roots of the Lungs, seen prom Above. (J. S.) (Quain.) X 1. A. A. Ascending aorta. A.M. Anterior mediastinum. A.V. Azygos vein. D.A. Descend- ing aorta. E. Eparterial bronchus. I. Superior lobe of lung. L.B. Left bronchus. L.P. Left phrenic. L.P.V. Left pulmonary vein. L.V. Left vagus. (Es. CEsophagus. P A. Pulmonary artery. P.C. Pericardial cavity. R.B. Right bronchus. R.P.A. Right branch of pulmonary artery. R.P.C. Right pleural cavity. R.P.N. Right phrenic. R.P.V. Right pulmonary vein. R.V. Right vagus. S. Inferior lobe of lung. Sc. Scapula. T.D. Thoracic duct. 3, 4, .5, 6, 7. Corresponding ribs. clavius] extends upward on this surface to the apex, corresponding on the right side to the lower part of the trachea and right subclavian artery, on the left tothe left subclavian artery alone. Further forward is a groove adapted in the right lung to the superior cava; in the left to the left innominate vein. The lung is not in actual contact with these several structures, but is separated from them by the mediastinal pleura. The mediastinal surface passes gradually into the costal surface posteriorly, there being no proper posterior edge. Where the mediastinal and costal surfaces meet in front, a sharp anterior margin [margo anterior] exists (fig. 997). In the right lung this runs down in a gentle curve to turn lateralward in the inferior margin. In the left lung the anterior margin is cut into by a wide cardiac notch [incisura cardiaca], which is occupied bj' the heart in the pericardium as it is pressed toward the anterior thoracic wall. The cardiac notch is separated from the inferior margin by a little tongue of lung substance, the pulmonary lingula [lingula pulmonis]. The base of the lung (fig. 994) presents the diaphragmatic surface [facies diaphragmatica] concave and oblique in adaptation to the dome of the diaphragm. It is limited by a sharp inferior margin [margo inferior], which follows the curves of the mediastinal and costal surfaces, and fits into the angle between the dia- phragm and thoracic wall. 1230 THE RESPIRATORY SYSTEM The apex (figs. 994, 997, 998) is rounded and points upward with an inclination forward and medially, accommodating itself to the structures within and about the superior aperture of the thorax. A deep interlobar fissure [incisura interlobaris] (figs. 994, 998), reaching through the lung substance nearly to the hilus, divides each organ into a smaller superior lobe [lobus superior] and a larger inferior lobe [lobus inferior]. The interlobar fissure runs downward and forward beginning a short distance below the apex, and reaching the base near the anterior margin in the left lung, somewhat further back in the right lung. From the obliquity of the plane of the fissure it will be noticed that the inferior lobe reaches posteriorly to within a short distance of the apex, and includes the greater part of the back and base of the lung, while the superior lobe takes in the anterior margin and apex. The presence of a mid- dle lobe [lobus medius] disturbs the symmetry of the right lung. This results from a deep, nearly horizontal incisure cutting through the lung somewhat below its middle, and extending between the anterior margin and the main interlobar fissure, which it reaches at about the level of the axillary line. Fig. 994. — Left Lung, viewed pbom the Mediastinal Surface. Apex Subclavian groove I (Spalteholz.) Costal surface Hilus, with line of section of the pleura Interlobar fissure — ' Left branch of puln nary artery Left bronchus- Mediastinal surface ^^Left pulmonary veins -Cardiac fossa Pulmonary ligament — -Anterior margin Inferior lobc_.- Inferior margin - Interlobar fissure Diaphragmatic surface Besides possessing the individual peculiarities mentioned, the two lungs further differ from each other in general form and weight, the right lung being considerably broader and heavier than the left. The difference in length maintained by some anatomists, even if it prove constant, must be slight and of httle practical importance. These difJerenoes seem to foUow the asym- metry of the vault of the diaphragm and the position of the heart. The hilus (fig. 994), already mentioned as situated on the mediastinal surface, presents in the left lung a raquette-shaped outline. Its average height is about 8.8 cm. (Luschka);it extends over both lobes. The hilu of the right lung, rather four-sided in outline and shorter than that of the left, is related to the three lobes. The entering structures, constituting the root of the lung (figs. 989, 993, 994), include the bronchus, pulmonary artery and veins, bron- chial vessels, lymphatic vessels and glands, and pulmonary nerves. These are bound together by connective tissue and invested by the pleura. The bronchus is in the posterior and upper part of the root; the pulmonary vessels he anteriorly, the veins below the arteries. The surface of the lung is marked off in polygonal areas of different sizes (secondary lobules) by lines containing pigment. The pigmentation is especially deep on the lateral surface along the furrows corresponding to the ribs. THE BRONCHIAL TUBES 1231 Branching of the bronchial tubes (fig. 995) . — Each bronchus, from its origin at the bifurcation of the trachea, takes an oblique course to the hilus, and then con- tinues in the lung as a main tube, extending toward the posterior part of the base. These stem-bronchi are curved, probably in adaptation to the heart, the right hke the letter C and the left like an S. Throughout their course the stem-bronchi give off in monopodic fashion collateral branches, the bronchial rami [rami bronchiales], and these, branching in a similar way, reach all parts of the lung. The first bronchial ramus of the right stem-bronchus arises above the place where the latter is crossed by the pulmonary artery and is named the eparterial bronchial ramus [ramus bronohialis eparterialis]; it supphes the superior lobe of the right lung, sending a special branch to the apex. All other bronchial rami, whether in the right or left lung, take origin from the Fig. 995. — Cast of the Air-tubes and Their Branches, viewed from in Front. (Spalteholz.) Ttachea (also the position of tlie median plane) I Bifurcation of trachea /^ Left bronchus Main bronchus Hyparterial branch to middle lobe Hyparterial branch to superior lobe Position of median plane stem-bronchi below the level of the crossing of the pulmonary artery and are called hyparterial bronchial rami [rami bronchiales hyparterialesj. The second bronchial branch of the right lung goes to supply the middle lobe, while several bronchial branches enter the inferior lobe. On the left side, the first bronchial branch arises below the crossing of the pulmonary artery, and goes to supply the supei-ior lobe, providing it with an apical ramus. The other branches are given to the inferior lobe. Structure of the bronchial rami. — The larger bronchial rami contain in their walls both C-shaped and irregular plates of cartilage, the latter gradually replacing the former as the branches become smaller. The membranous wall is lost and plates of cartilage are disposed on all sides. The mucosa, with ciUated epithehum, is thrown into longitudinal folds covering bundles of elastic fibres of the membrana propria. Next to the latter is a continuous layer of smooth muscle-fibres circularly arranged. Mucous secreting bronchial glands [gl. bronchiales] are present as far as tubes of 1 mm. diameter; here the cartilages also disappear. To W. S. IVIiller is due the credit of having greatly increased our knowledge of the finer structure of the lung and for having presented the conception of the primary lung lobule now generally accepted by anatomists. Some of the chief results of MiUer's work are embodied in 1232 THE RESPIRATORY SYSTEM the following descriptions pertaining to the termination of the air-tubes and to the blood and lymph vascular systems of the lungs and pleurse. Through further branching of the bronchial rami a great number of very fine bronchioles [bronchioli] are reached, whose walls possess a weak muscle layer and are lined by mucosa having an epithelium of flattened non-ciliated cells. These, subdividing, give rise to the respiratory bronchioles [bronchioh respiratorii], the walls of which are beset with alveoli (fig. 992). From the respiratory bronchioles arise the alveolar ducts [ductuli alveolares], or terminal bronchi, each of which leads to a group of air-spaces, called atria, each of which again communicates with a second series of air-spaces, tlie air-sacs (alveolar sacs or infundibula), whose walls are pouched out to form numerous pulmonary alveoli [alveoli pulmonum]. A terminal bronchus with its air-spaces and blood-vessels, lymphatics and nerves, together form a pulmonary lobule [lobulus pulmonum], the unit of lung structure. Aeby divided the bronchial branches into two sets, according to their relation to the pul- monary artery. The branch arising above the place where the pulmonary artery crosses the stem-bronchus he named the eparterial bronchus, and those arising below the crossing he called hyparterial. An eparterial bronchus exists only on the right side ; all other branches are hy- parterial. Since the eparterial supplies the superior lobe of the right lung and no eparterial branch is present on the left side, Aeby concluded that the left lung had no lobe homologous with the superior lobe of the right lung. He compared the middle lobe of the right with the superior lobe of the left lung. The collateral branches of the stem-bronchi arise in a dorsal and ventral series in the lower mammals, and the same arrangement, though less obvious, obtains in man. According to the views of Aeby and Hasse, the first ventral branch of the right side is distributed to the middle lobe, while the remaining three ventral and all the dorsal lateral branches are given to the inferior lobe. On the left side, the first ventral branch is given to the superior lobe; the other ventral branches and the dorsal branches are distributed to the inferior lobe. Fig. 996. — Scheme of the Bbonchial Tree According to Narath. A. Anterior view. B. Right lateral view. (Poirier and Charpy.) A. Apical bronchus, collateral of the first ventral and susceptible of becoming eparterial, Ap in migrating to the bronchial trunk. Narath considers the division of bronchial branches in accordance with their relation to the pulmonary artery as of no great morphological significance. He attributes the apparent differences on the two sides to a shifting in position of homologous branches. Thus, Narath considers that the eparterial bronchus of Aebj' has become the first dorsal lateral branch by displacement above the pulmonary artery and that it is homologous with an apical branch of the left side, which retains its primitive origin from the first ventral branch (fig. 996) . Narath's conception of the migration of the bronchial branches is supported by the results of Hunting- ton's extensive stiulii's of the bronchial tree in mammals. The physical properties of the lungs. — The average dimensions in the adult male are as follows: Height of the lung is given at 2.5-27 cm., the greatest sagittal diameter at 16-17 cm., and the greatest transverse measurement as 10 cm. for the right and 7 cm. for the left. The volume of the lungs when well expanded is 6500 c.c. (Merkel.) The loeight of the lungs can be found only approximately on account of the presence of blood and mucus. In the adult male the weight of both lungs is given as 1300 gm.; female, 1023 gm. The weight of the right lung compared with the left is as 11 is to 10. Ried and Hutchinson found the weight of the lungs compared with that of the body as 1 :37 (male), 1 :43 (female); in the foetus at term, 1 : 70. After respiration has been established, the lung, if placed in water, will float. Its specific gravity is between 0.345 and 0.746, (Rauber.) The fcetal lung contains no air and is heavier than water. Its specific gravity is 1.045 to 1.056. (Ivrause.) Lung tissue, free of air, with vessels moderately filled, has likewise a specific gravity of 1.045 to 1.056. (Vierordt). The colour of the lung result sfrom the presence of blood, pigment, and the air in the alveoli. It varies therefore as these constituents are all or in part present and with differences in their TOPOGRAPHY OF THE LUNGS 1233 proportions. Thus the general colour is red in the fcetus, pink, in the infant, and grey mottled with black in the adult. The dark colour is traceable to the carbonaceous matter carried into the lungs from the atmosphere. In consistence the lung is soft and spongy, and when compressed between the fingers, emits a crackling sound. Among the physical properties the elasticity of the lung is quite remarkable: Under ordinary conditions the pressure of the air in the lung keeps the alveoli and the organ as a whole distended, but when the pleura has been opened and the air pressure equalised without and within, the lung collapses. Topography. — The apices of the lungs extend upward as high as the first thoracic vertebra- a level considerably higher than the superior margin of the sternum (figs. 997, 998). The sub, clavian vein and artery and the brachial plexus, together with the anterior scalene muscle, control to a certain degree the height reached. There seems to be no constant difference be- tween the levels attained by the apices of the two lungs. The extent to which the apex rises above the clavicle is rarely more than 3.5 cm. (Merkel), and will, of course, vary with individual differences in the position and form of this bone. The average is not over 2.5 cm. (1 in.). The base of the lung, resting on the diaphragm, is separated by that thin partition from the underlying abdominal viscera: thus beneath the base of the right lung is the right lobe of the liver, while under the left lung are the left lobe of the liver, the fundus of the stomach, and the spleen. The position of the apex changes very little in respiration, and the same holds true for Fig. 997. — Position of the Lungs from Before. (Merkel.) , The parietal pleura is shaded and outlined in black. the hinder bulky part of the lung. The latter rests against the side of the vertebral column in the deep hollow of the angles of the ribs, and reaches below to the level of the eleventh costo- vertebral joint (fig. 998). The anterior margins (fig. 997) descend in curves from behind the sterno-clavicular joints, and run near together a little to the left of the median line. At the level of the sixth costo-sternal junction the anterior margin of the right lung turns lateral- ward to follow the sixth costal cartilage. The anterior margin of the left lung turns lateralward a,long the fourth costal cartilage as far as the para-sternal line, descending in .a curve to the lingula and thus forming the cardiac incisure. The positions of the inferior margins (figs. 997, 998) of the two lungs are practically alike in their positions. Each extends in a curve cov- yex downward, behind the sixth costal cartilage in its entire length, crosses the costo-chondral junction of the sixth rib to the superior margin of the eighth rib in the axillary hne, and so to the ninth or tenth rib in the scapular line, whence they run horizontally medialward to the eleventh costo-vertebral joint. * * These relations are the mean between the conditions observed in the cadaver and as found by physical examination of the hving. In old age the inferior margins of the lungs reach a level one or two intercostal spaces lower than is the case in adult life (Mehnert). 1234 THE RESPIRATORY SYSTEM The interlobar fissure (fig. 998) begins about 6 cm. below the apex of the lung at the level of the head of the third rib. With the arm hanging at the side, a hne drawn across the back from the third thoracic spine to the root of the scapular spine would indicate the course of the upper part of this fissure. (Merkel.) Thence it passes downward and around the chest to the end of the sixth bony rib in the mammillary line. Merkel points out the use of the root of the scapular spine as a landmark for finding the limits of the lobes posteriorly: with the arm hanging at the side all above this spot is superior lobe; aU below it the inferior. The short fissure of the right lung begins at the main interlobar fissure in the axillary line, about the level of the fourth rib or fourth interspace, and passes nearly horizontally to the anterior margin of the lung at the level of the fourth costal arch. The roots of the lungs are placed opposite the fifth, sixth, and seventh thoracic vertebrae. The right root lies behind the inferior vena cava and under the arch of the azygos vein; the left root is beneath the aortic arch and in front of the thoracic aorta. The phrenic nerve passes in front of each root, the vagus behind. On the front and back are the pulmonary plexuses, anterior and posterior. The ligament of the pleura goes from the lower edge of the root. Vessels and nerves of the lungs. — The bronchial arteries (see p. 588), belonging to the systemic system, carry blood for the novirishment of the lungs. They arise from the aorta or from an intercostal artery, two for the left lung and one for the right, and, entering at the hilus, Fig. 998. — Position of the Lungs from Behind. (Merkel.) The pleura is represented as in Fig. 997. reach the hinder wall of the main bronchus. The bronchial arteries accompany the bronchi, whose walls they supply, as far as the distal ends of the alveolar ducts, beyond which they do not go. These vessels also supply the lymph glands of the hilus, the walls of the large pulmonary vessels, and the connective-tissue septa of the lung. Bronchial veins (see p. 664), anterior and posterior, arise from the walls of the first two or three divisions of the bronchi and end in the innominate and the azygos or in one of the intercostal veins; those arising from the walls of the smaller tubes, including the alveolar ducts, join the pulmonary veins. The pulmonary artery (see p. 528), entering the hilus in a plane anterior to the bronchus, tm-ns to the posterior aspect of the main-stem, following its branches and their subdivisions to the lobules. Entering the lobule, the last branch of the vessel gives off as many twigs as there are atria (fig. 992), and these twigs end in dense capillary nets in the walls of the alveoli. Here the venous blood brought by the pulmonary artery, separated from the air in the alveolus only by a thin septum, is changed to arterial blood in the respiratory process. According to Miller, anastomosis between the branches of the pulmonary artery are exceptional. Anastomosis between the bronchial and pulmonary arteries has been claimed, but the connection apparently existing between these vessels is through the radicles of the bronchial veins which join the pulmonary veins. The pulmonary venous radicles begin at the capillary networks and drain the arterial blood into the pulmonary veins, which run between adjacent lobules and which receive also THE THORACIC CAVITY 1235 blood coming from the capillary network of the pulmonary pleura and from the capillary net- work of the bronchi (fig. 992). Thus it wiU be seen that while the pulmonary vein carries mainly arterial blood, it carries also some venous blood. The pulmonary veins (see p. 529) follow the bronchial tree on the side opposite the arteries to the hilus, where, having converged to two large trunks located in the root of the lung below the plane of the artery, they pass to the left atrium. The pulmonary veins have no valves. Lymphatics. — Miller has found the lymphatic vessels forming a closed tube system in the walls of the bronchi, in the pleura, and along the branches of the pulmonary artery and veins. Within the lung numerous pulmonary lymph-glands [lymphoglandulse pulmonales] are found chiefly at the places of branching of the larger bronchi [lymphoglandulae bronchiales[. Scat- tered along the latter, as well as associated with the branches of the pulmonary artery and vein, are found masses of lymphoid tissue. Deposits of carbonaceous matter in the lymphoid structures of the lung are present, except in early infancy ; the amount increases with age. Nerves. — The vagus and sympathetic contribute to form the pulmonary plexuses in front and behind the root of the lung, from which branches go to accompany bronchial arteries; a smaller number accompany the air-tubes (see p. 957). Variations. — Congenital absence of one or both lungs has been observed. Variations in the lobes are not uncommon — four for the right and three for the left lung has been recorded. An infracardiac lobe, as found in certain mammals, sometimes occurs; an infracardiac bronchus is, however, constant in man. More or less complete fusion of the middle and upper lobes of the right lung is not rare. The lungs may be symmetrical, with two lobes each, the apical bronchus of the right springing from the first ventral bronchus, as is normal for the left lung (Waldeyer, Narath) ; or the lungs may have three lobes each, the apical bronchus of the left arising from the main bronchus. The apical bronchus of the right lung may arise from the trachea, an origin that is normal in the hog and other artiodactyls. Development of the lungs and trachea. — The first indication of the trachea and lungs appears in embryos of about 32 mm. as a trough-like groove in the ventral wall of the upper part of the oesophagus, communicating above with the pharynx. Later the groove becomes constricted oi? from the oesophagus, the constriction extending from below upward, so that a tube is formed which opens into the pharynx above. The lower end of this tube soon becomes bilobed, and the lobes, elongating, give rise to additional lobes, of which there are primarily three in the right side and two in the left. The upper unpaired portion of the tube becomes the trachea, while the lobed lower portion gives rise to the bronchi and lungs, the complicated struc- ture of the latter being produced by oft-repeated branchings of the bronchi. THORACIC CAVITY Thoracic cavity [cavum thoracis] is the term used to denote the space included by the walls of the thorax and occupied by the thoracic viscera. These are, on each side, the lung, surrounded by the pleural cavity, and in the middle the pericardium and heart, great vessels, trachea and oesophagus, all closely associated and forming a dividing wall, the mediastinal septum, standing between the right and left sides of the thoracic space. The limits of the thoracic space are given by the skeletal parts of the thorax together with the ligaments involved in the articulations and the muscles and membranes interposed between the bones. The arched diaphragm forms the inferior limit; and the barrier presented by the scalene muscles and the cervical fascia makes the superior boundary, which, it is to be observed, lies above the plane of the superior aperture of the thorax and therefore in the base of the neck. These boundaries are approached by the extension of the pleural cavities; yet there intervenes the parietal layer of the pleural sac which is connected with the thoracic walls by loose connective tissue, the endothoracic fascia [fascia endothoracica]. The form of the thoracic space departs from the external contour of the thorax chiefly through the projection into it of the ridge made by the succession of centra of the thoracic spine, and by the presence on either side of the latter of the broad, deep pulmonary sulcus. On account of these features a transverse section of the thoracic space is somewhat heart-shaped, but, however, much compressed antero- posteriorly (fig. 993). The arch of the diaphragm on the right side rises to the level of the spinous process of the seventh thoracic vertebra; on the left, to the level of the eighth thoracic spinous process. At its circumference the diaphragm is in contact to a variable extent above its origin with the inner surfaces of the costal arches. In the lower part of this zone a connection exists between the muscle and the thoracic wall through a continuation of the endothoracic fascia; in the upper part, the phrenico-costal sinus (see p. 1237) intervenes. The level reached by this deepest part of the pleural cavity is lower than the summit of the peritoneal cavity, so they overlap to a considerable extent. 1236 THE RESPIRATORY SYSTEM THE PLEURA The pleura (fig. 993) is a closed serous sac, which invests the lung (pulmonary pleura), and lines the inner surface of the thoracic walls (parietal pleura). The pleural cavity [cavum pleurae] is the capillary space enclosed by the walls of the sac containing a little fluid which lubricates the apposed surfaces of the pulmonary and parietal membranes. There are two pleurae, one in relation to each lung, completely separated by a sagittal partition, the mediastinum. FiQ. 999. — Plettral Cavity Opened From in Front. 1, first rib; 2, manubrium sterni; 3, acromial extremity of clavicle; 4, xiphoid process, 5, linea alba; 6, m. transversus abdominis; 7, seventh rib; 8, sternocleidomastoid m.; 9, anterior scalene m.; 10, larynx; 11, thyreoid gland; 12, deep layer of cervical fascia in front of the trachea; 13, corresponds to upper part of anterior mediastinal cave; 14, pleural cupola; 15, mediastinal pleura; 16, lower margin of costal pleura; 17, pericardium; 18, superior lobe of lung; 19, middle lobe of right lung; 20, inferior lobe of lung; 21, diaphragm. (Rauber- Kopsch.) The pulmonary pleura [pleura pulmonalis] forms a smooth glistening coat over the outer surface of the lung, with the tissue of which it is inseparably connected. At the hilus the pulmonary pleura passes from the mediastinal surface of the lung to cover the root above, in front, and behind, and becomes continuous medialward with the parietal pleura of the mediastinum. Below the root of the lung the pleura is reflected medialward in a double layer as the pulmonary ligament [Hg. pulmonale] (fig. 994). This presents anterior and posterior surfaces and three margins; the base is mostly free, and directed toward the diaphragm, with which it is connected at its medial end; the apex is at the lung root, one margin is next to the lung, and the other joins the mediastinal pleura. THE PLEURA 1237 The parietal pleura [pleura parietalis] is divided, according to the regions of the chest with which it is associated, into the costal, diaphragmatic, and mediastinal pleura. The costal pleura [pleura costahs] hnes the thoracic wall, to which it is bound not very firmly by the endothoracic fascia. It covers incompletely the back of the sternum and extends laterally upon the ribs and "intercostal muscles. Posteriorly beyond the angles of the ribs it passes over the anterior rami of the thoracic nerves and intercostal vessels, the heads of the ribs, and the sympathetic trunk to the vertebral column; here it becomes continuous with the mediastinal pleura. Above, the pleura reaches beyond the superior margin of the sternum into the root of the neck, and in the form of a dome, the cupola of the pleura [cupola pleurae], is adapted to the ape.x of the lung. It is supported by processes of the deep cervical fascia, and by a fibrous aponeurosis known as Sibson's fascia, coming from the scalenus minimus muscle and connected with the inner margin of the first rib. In relation to the pleural cupola are those structures already described as grouped about the lung apex: the brachial plexus, subclavian artery, ante- rior scalene muscle, and the subclavian vein, and, on the left side, in addition, the thoracic duct. Below, the costal pleura is continuous with the diaphragmatic pleura [pleura diaphragmatica], which adheres closely to the thoracic surface of the diaphragm and covers it, excepting the pericardial area and where the diaphragm and thoracic wall are in contact. The mediastinal pleura [pleura mediastinalis] is reflected from before backward at the right and left sides of the mediastinum as the laminEB mediastinales, covering the pericardium Fig. 1000. — Right Lateral Surface op the Mediastinum after Removal op the Pleura. (Poii-ier and Charpy.) Trachea . — Phrenic nerve [pleura pericardiaca], to which it is closely adherent, and also the other structures of the mediastinum, with which the two layers are less firmly connected. Above the lung root the mediastinal pleura stretches directly from the spine to the sternum; but at the level of the root and below it, it is reflected laterally to the pulmonary pleura covering the root in front and behind and forming the pulmonary ligament. The right mediastinal lamina covers (fig. 1000) the right innominate vein, the superior vena cava, the vena azygos, the trachea, the innominate artery, the right vagus and phrenic nerves, and the oesophagus. The left lamina lies against the left innominate vein, the arch of the aorta the left subclavian artery, the thoracic aorta, the left phrenic and vagus nerves, and the cesoph- agus. About the base of the heart-sac are a number of adipose folds [plica? adiposis) projecting from the pleura, the surfaces of which present some villous processes, the pleural villi [villi pleurales] ; the latter also occur on the pulmonary pleura along the inferior margin of the lung. The lines of pleural reflexion are of practical importance (figs. 997, 998, 1003). Posteriorly, the costal pleura simply turns forward in a gentle curve to become the mediastinal pleura, but anteriorly and inferiorly the membrane is folded upon itself, leaving intervening capiUary spaces, the sinuses of the pleura [sinus pleurtT;]. Such a space is present where the costal pleura is reflected upon the diaphragm, the sinus phrenicocostalis, the fold of the pleura occupying the upper part of the angle between the thoracic wall and diaphragm, the endothoracic fascia 1238 THE RESPIRATORY SYSTEM filling the lower part. The inferior margui of the lung enters this sinus a variable distance in iuspiration. The line of the costo-diaphragmatio reflexion begins in front on the sixth costal cartilage, which it follows, descending obliquely to cross the seventh interspace in the mam- millary line. The greatest depth reached is at the tenth rib or interspace in the axillary line. The line of reflexion then continues around the thorax ascending slightly to the twelfth costo- vertebral joint. The Ime of reflexion behind is sometimes found as low as the level of the transverse process Figs. 1001 and 1002. — Boundaeibs op the Pleura and Lungs. Lines of pleural reflection red, boundaries of the lungs and pulmonary lobes black. 1, sixth cervical vertebra; 2, first thoracic vetebra; 3, twelfth thoracic vertebra; 4, first lumbar vertebra; 5, manubrium sterni; 6, body of sternum; 7, xiphoid process; 8, first rib; 9, cartilage of seventh rib; 10, 11, 12, tenth, eleventh and twelfth ribs. (Rauber-Kopsch.) of the first lumbar vertebra. Such a possibility must be considered in operating upon the kidney. The lines of reflexion of the costal pleura backward to the mediastinal pleura behind the sternum begin opposite the sterno-clavicular joints, descend obhquely medialward to the level of the second costal cartilage, whence they run near together or in contact, but to the left of the medianHline, to the level of the fourth cartilage. The reflexion on the right side continues from the sternum as far as the sixth rib cartilage, there turning laterally into the costo-dia- phragmatic reflexion. The line on the left side, in the region of the cardiac notch (from the fourth Fig. J103. — Schematic Drawing to Represent the Maximum op Fluctuation in the Position op the Anterior Lines op Pleural Reflexion. (Tanja.) to the sixth cartilages), is a little to the left of the sternal margin. From this position of the line of reflexion it happens that there is left uncovered by pleura a small area of the pericardium which is in contact immediately with the chest-wall. A reduplication of the pleura takes place along the anterior line of reflexion, and into the sinus costomediastinalis so formed the thin anterior margin of the lung advances in inspiration. That part of the left costo-mediastinal sinus which is in front of the pericardium is not completely filled by the margin of the lung. Although the positions of the lines of reflexion of the mediastinal pleura here described are those THE MEDIASTINAL SEPTUM 1239 usually encountered, it should be noted that they are subject to variation. The extremes of variation of the anterior lines, as determined by Tanja, are indicated in fig. 1003. Blood-vessels. — The vascular networks of the pulmonary pleura are derived from the bronchial artery and probably to some extent from the pulmonary artery which in the dog, is the only source of blood supply. The venous radicles arising from the network enter the lung. (See radicles of the pulmonary vein on page 1235.) The parietal pleura is supplied by arteries from several sources: internal mammary, intercostals, phrenics, mediastinal, and bronchial. The veins correspond to the arteries. The lymphatics of the pulmonary pleura form rich networks without definite relations to the lobules of the lung. They accompany the radicles of the pulmonary veins and drain into the bronchial lymph-glands. In the parietal pleura lymph-vessels are present most abundantly over the interspaces; they empty into the sternal and intercostal glands. (See p. 728.) The nerves supplied to the pulmonary pleura are branches from the pulmonary plexus; to the parietal pleura, from the intercostals, vagus, phrenic, and sympathetic. MEDIASTINAL SEPTUM The two pleural cavities are separated from each other by the mediastinal sep- tum [septum mediastinale] (fig. 1000). This is a sagittal partition extending from the superior aperture of the thorax to the diaphragm between the thoracic vertebrae and the sternum, its free surfaces, right and left, formed by the mediast- inal layers of the pleurae. It is composed of the pericardium and heart and of structures which, for the most part, extend in a longitudinal direction through the thoracic cavity. These include the oesophagus together with the vagus nerves, the thoracic duct, thoracic aorta and azygos vein; the trachea, the pulmonary vessels and the arch of the aorta with its great branches, the superior vena cava and its tributaries and the phrenic nerves; the thymus gland, internal mammary vessels and many lymph glands throughout the septum. These structures are packed together and supported by intervening connective tissue. Moreover, the connection of the sheaths of the great vessels with processes of the cervical fascia and the fixation of the pericardium to tlie diaphragm, give to the latter a strong support. Owing to the position of the heart, the two sides of the septum are not symmetrical, and it follows from the bulging of the left surface of the mediastinal septum that the left pleural cavity is encroached upon. The name mediastinal cavity has been applied to the two regions of the medi- astinal partition which find themselves located, the one in front, the other behind the plane of the heart. There is in reality no cavity, the term being used in this connection merely to donate space. Between the two spaces are interposed the pericardium and heart, the great vessels, trachea and bronchi. The anterior mediastinal cavity [cavum mediastinale anterius] is small. Its lateral limits are formed by the mediastinal layers of the pleurse, right and left, which are reflected backward from the costal pleurae of the anterior thoracic wall. The space is occupied by loose connective tissue, surrounding the thymus gland, the internal mammary vessels and a number of lymph-glands. Recalling the lines of reflexion of the mediastinal pleurfe as above described, the form, position and extent of this space as observed from in front, will be understood; it is widest behind the inferior end of the body of the sternum and fifth and sixth costal cartilages of the left side {area inlerpleurica inferior) ; narrowest where the mediastinal layers are approximated behind the body of the sternum, broader again where the laminae deviate posterior to the manubrium sterni {area inlerpleurica superior). In the latter space lies the thymus gland and the superior portions of the internal mammary vessels. In the area interpleurica inferior the pericardium comes into immediate contact with the anterior thoracic wall, and here the inferior portions of the left internal mammary vessels are found. The lymphatic vessels and glands of the anterior mediastinal space belong to the anterior mediastinal and sternal groups. The posterior mediastinal cavity [cavum mediastinale posterius] (fig. 1000), hmited behind by the thoracic vertebrae and laterally by the mediastinal layers of the pleurae where they are reflected forward from the costal plem-ae of the pos- terior thoracic walls, is elongated and of more regular form than the anterior space. It includes the thoracic aorta, the oesophagus and vagi, the thoracic duct, azygos vein and lymph glands. Within this space are also to be found the origins of the right intercostal arteries, the hemiazygos and, when present, the accessory hemiazygos veins, terminations of some of the left intercostal veins and the greater splanchnic nerves. The lymph glands belong to the posterior mediastinal group. (Pigs. 993, 994). — A subdivision of the mediastinal septum into anterior, middle, posterior, and superior mediastinal spaces has long been customary, and is useful for descriptive purposes. The superior mediastinum is that part of the mediastinum which Ues above the level of 1240 THE RESPIRATORY SYSTEM the pericardium. It extends" between the first four thoracic vertebrse behind and the manu- brium sterni in front, and contains the arch of the aorta and the great vessels arising from it, the innominate veins, and the upper part of the superior vena cava, the thoracic duct, the lower portion of the trachea, and a portion of the oesophagus, the phrenics, vagi, left recurrent and cardiac nerves, and the thymus gland. From the superior mediastinum the other three divisions of the space extend downward. The anterior mediastinum is identical with that part of the anterior mediastinal cavity which is below the level of manubrium sterni. The middle mediastinum lies between the layers of the mediastinal pleura? in front of the root of the lungs; it contains the heart, enclosed in the pericardium, and the phrenic nerves. The posterior mediastinum corresponds to that portion of the posterior mediastinal cavity which extends below the plane of the fifth intervertebral fibro-cartilage. References for Respiratory System. A. External nose and nasal cavity. Kallius, in von Bardeleben's Handbuch; Zuckerkandl, Normale u. path. Anatomie d. Nasenhohle, Bd. 1, Wien, 1893; {Develo-pvient) His, Archiv f. Anat. u. Phys., 1892; Killian, Arch. f. LaryngoL, Bd. 4, 1896; Schaeffer, Jour. MorphoL, vol. 21, 1910; {Concha) Peter, Arch. f. mikr. Anat., Bd. 60, 1902; {Paranasal sinuses) Bartels, Zeitschr. f. Morph. u. Anthrop., Bd. 8; Turner, Accessory Sinuses of the Nose, Edinburgh, 1901; {Anthropology) Hoyer, Morph. Arbeiten, vol. 4, 1894. B. Larynx. Gerlach, Anat. Hefte, H. 56; {Development) Lisser, Amer. Jour. Anat., vol. 12; {Ossification) Scheier, Arch. f. mikr. Anat., Bd. 59. C. Lungs. {Structure; vascular supply) Miller, Arch. f. Anat. u. Entw., 1900; Amer. Jour. Anat., vol. 7; Schultze, Sitzb. AkadWiss., Berlin, 1906; {Develop- ment) Flint, Amer. Jour. Anat., vol.6 {Topographical) Mehnert, Topogr. Alters- veranderungen d. Atmungsapparatus, Jena, 1901. D. Pleura. Ruge Morph. Jahrb. Be. 41. SECTION XI UEOGENITAL SYSTEM Revised foe the Fifth Edition By J. PLAYFAIR McMURRICH, A.M., Ph.D., LL.D. PROFEasOR OF ANATOMY IN THE UNIVERSITY OP TORONTO The urogenital system [apparatus urogenitalis] includes (A) the urinary organs and (B) the reproductive organs. A. THE URINARY ORGANS THE organs forming the urinary apparatus [organa uropoetica] are the kidneys, by which the secretion is produced; a duct, the ureter, proceeding from each kidney and convejdng the secretion to the bladder, which serves as a reservoir for the urine and from which, by a single duct, the urethra, the secretion is carried to the exterior. Fig. 1004. — Postero-medial Aspect of the Right Kidney. THE KIDNEYS The kidneys [renes] are paired organs situated in the abdominal region and each is composed of a very great number of minute tubules, the renal tubules, enclosed within a definite and firm fibrous capsule. Each kidney is somewhat bean-shaped (fig. 1004) and is situated on the dorsal wall of the body, behind the parietal peritoneum, in such a way that the ventral or visceral surface [facies ante- rior] which is convex, looks obhquely ventrally and laterally, while the dorsal or parietal surface [facies posterior], usually less convex, looks dorsally and somewhat medially (fig. 1005). The upper extremity {extremitas superior] is usually larger 1241 1242 UROGENITAL SYSTEM than the lower [extremitas inferior] and is about 1 cm. nearer the median sagittal plane of the body, owing to the long axis of the organ being directed obliquely downward and laterally. The lateral border [margo lateralis] is narrow and con- vex, and the medial border [margo medialis], which looks medially and ventrally, is concave, its middle third presenting a slit-hke aperture, the hilus. This opens into a cavity, called the sinus (fig. 1006), which is about 2.5 cm. in depth and is occupied mainly by the dilated upper extremity of the ureter, known as the renal pelvis, the interval between this and the actual kidney substance containing adi- pose tissue in which are imbedded the renal vessels and nerves. Size. — The length of the kidney in the male averages 10-12 cm., its breadth about 5.5 cm. and its thickness 3 cm.; it weighs 115-150 grams. The dimensions of the female kidney are nearly as great, but its weight is from one-seventh to one-fifth less. In the child the organ is relatively large, its weight compared with that of the entire body being about 1 : 133 at birth; but its permanent relation, which is about 1:217, is usually attained at the end of the tenth year. Fig. 1005. — Diagram showing Relation of Kidnet to Capsule. (Gerota.) Aorta Pararenal adipose — body Aponeurosis of trans- Fascia of quadratus versus abdominis lumborum Renal fascia (posterior layer) Fascia of psoas Investment and fixation. — The surface of the kidney is covered by a thin but strong ^??roMs capsule [tunica fibrosa], which turns inward at the hilus to line the walls of the sinus (fig. 1006). It may readily be peeled off from a healthy kidney, except at the bottom of the sinus, where it is adherent to the blood-vessels entering the kidney substance and to the terminal portions of the pelvis. External to the capsule is a quantity of fat tissue, the adipose capsule [capsula adiposa], which forms a complete investment for the organ and is prolonged through the hilus into the sinus. The peritoneum, which covers the ventral surface of the adipose capsule, has usually been regarded as the principal means of fixation of the kidney, but in reality this is accompHshed by means of a special renal fascia (fig. 1005), developed from the subperitoneal areolar tissue (Gerota). Renal fascia. — Lateral to the kidney there occurs between the transversalis fascia and the peritoneum a subperitoneal fascia, which, as it approaches the convex border of the kidney, divides into two layers, one of which passes in front of and the other behind the kidney, enclos- ing the adipose capsule. Traced medially, the anterior layer of the renal fascia passes in front THE KIDNEY 1243 of the renal vessels, and, over the aorta, becomes continuous with the corresponding layer of the opposite side; upward, it passes over the suprarenal gland and at the upper border of that organ becomes continuous with the posterior layer; and downward, it is lost in the adipose tissue intervening between the iliac fascia and muscle. The posterior layer, which is the thicker of the two, passes medially behind the renal vessels and is lost in the connective tissue in front of the vertebral column, and below it is lost, like the anterior layer, in the ihac region. Behind the posterior layer, between it and the quadratus lumborum, is a mass of adipose tissue, the pararenal adipose body, and both layers are united to the fibrous capsule of the kidney by trabeculae of connective tissue which transverse the adipose capsule. Each kidney is, accordingly, supported by these trabecute in a space bounded laterally and above by the layers of the renal fascia, and open medially and below. Should these trabeculse become atrophied by wasting disease or ruptured by the pressure of the pregnant uterus, by the improper use of corsets, or by any other cause, the phenomenon of movable or wandering kidney may be set up by slight external violence, the organ tending to shift its place as far as the attachment of its vessels to the main trunks and the arrangement of the renal fascia will permit. Position and relations. — The kidney is said to lie in the lumbar region. It is, however, intersected by the horizontal and vertical planes which separate the hypochondriac, lumbar, epigastric and umbilical regions from each other, and hence belongs to all these segments of the abdominal space. Its vertical level may be said to correspond to the last thoracic and upper two or three lumbar Fig. 1006. — Section of Kidney showing the Sinus. (After Henle.) Cortex- Vessels Bottom of Attachment of calyx Apex of papilla with orifices of — ( -=r^ ■ papillary ducts Margin of hilus " vertebrffi, the right lying in most cases from 8 to 12 mm. (| to \ in.) lower than the left; but exceptions to this rule are not infrequent. The posterior surface (figs. 1007, 1008), with the corresponding portion of the fatty capsule and the pararenal adipose body, rests against the posterior ab- dominal wall extending upward in front of the eleventh and twelfth ribs, and medialward to overlap the tips of the transverse processes of the first and second lumbar vertebrae; the left kidney usually reaches as high as the upper border of the eleventh rib, the right only to its lower border. The only visceral relation pos- teriorly is on the left side, where the spleen slightly overlaps the kidney opposite the upper half of its lateral border, the adjacent surfaces of the two organs loeing, however, covered by peritoneum. The parietal relations (fig. 1008) on both sides are as follows: (1) the diaphragm, the left kidney, on account of its higher position, entering more extensively into this relation than the right ; (2) the por- tion of the transversalis fascia covering the ventral surface of the quadratus lumborum; (3) the lateral border of the psoas; and (4) the last thoracic, ilio- 1244 UROGENITAL SYSTEM hypogastric and ilio-inguinal nerves and the anterior divisions of the subcostal and first lumbar vessels, all of which run obhquely downward and laterally in front of the quadratus lumborum. The upper extremity of each kidney is crowned by the suprarenal gland (figs. 1007, 1009), which encroaches also upon its ventral surface and medial border and is fixed to it by fibres derived from the subperitoneal tissue. The anterior surface of each kidney was primarily completely covered by peritoneum that separated it from neighboring viscera, but, owing to secondary changes whereby the ascending and descending colons, the duodenum and the pancreas become retro-peritoneal organs, these come into direct relation with one or the other of the kidneys and separate portions of them from actual contact with the peritoneum. Thus, in the case of the right kidney (fig. 1009), the Fig. 1007. — The Abdominal Viscera, seen from Behind. (From the model of His.) The kidneys are somewhat lower than usual in their relations to the ribs. Caudate lobe of liv Aorta Outline of last nb ^ Spleen Left kidney, with L SUprarenal body j ^ ^A Duodenum \— Descending colon Cut edge of i % . peritoneum ^ Outline of iliac crest - -^Lung ^eJ 1 ^^~^\^"*s^^~-. ~ "T Suprarenal body "^ S^^ymmmmd- Outline of last rib — r^i^irJi — Vena cava Right kidney with ureter medially Small intestine Outline of iliac crest Colon ascendens Termination of colon Small intestine •Bladder mpulla of rectum portion of the anterior surface immediately adjacent to the medial border has the descending portion of the duodenum in direct contact with it, and throughout a zone extending downward and laterally from the middle of the duodenal area to the lateral border the ascending colon and right colic flexure. Almost the entire upper half, however, and a small portion of the lower pole are covered directly by peritoneum, the upper peritoneal area having an indirect relation with the lower surface of the liver, upon which it produces the renal impression. Similarly the anterior surface of the left kidney (fig. 1009) is in direct contact with the pancreas throughout a broad transverse band situated a little above the middle of the organ, and the splenic artery pursues its tortuous course along the upper border of this pancreatic area, while the corresponding vein is interposed between the pancreas and the surface of the kidney. The lateral portion of the lower extremity is in direct contact with the descending colon and its splenic THE KIDNEY 1245 flexure, but the remainder of the lower extremity and the whole of the upper one- fourth of the organ is directly covered by peritoneum, the upper peritoneal area having, as an indirect relation, the posterior surface of the stomach medially, and the spleen laterally (figs. 956, 1009). The medial border of the right kidney approaches the vena cava inferior very closely, especially above; that of the left is separated from the aorta by an inter- val of about 2.5 cm. Fig. 1008. — Diagram of Relations of Posterior Suepace of Left Kidney. 1 Lower border of eleventh j and twelfth ribs Medial lumbo-costal arch Lateral lumbo-costal arch Variation in position. — The position of the kidneys in the abdominal cavity is subject to considerable variation. Thus while the upper pole of the right kidney may be said to lie typically opposite the lower half of the eleventh thoracic vertebra, it may be placed as high as the lower part of the tenth thoracic or as low as the upper half of the fii'st lumbar. Similarly while the upper pole of the left kidney is as a rule opposite the middle of the eleventh thoracic vertebra it may lie half a vertebra higher or as low as the lower part of the second lumbar vertebra. The lower poles are distant from the crests of the ilia anywhere from 1.0 cm.-3.0 Fig. 1009. — Diagram showing Anterior Relations of Kidneys and Suprarenal Bodies. Duodenal area Hepatic area Gastric area (non-peritoneal) (non-peritoneal) Caval area (peritoneal) Duodenal area (non-peritoneal) /ul'||i]|| Colic area [^ (non-peritoneal Colic area (non-peritoneal) Peritoneal 'ixea wih right coUc vessels Pentoneal area with left cohc vessels cm., the distance being, as a rule, somewhat less in females than in males. Occasionally the lower pole may even extend below the iliac crest, especially on the right side. The lateral border of each kidney lies 8.5-10.0 cm. lateral to the spines of the lumbar vertebrae, a distance that brings them lateral to the lateral edge of the sacro-spinahs muscle and even to the lateral edge of the quadratus lumborum, so that this border may be readily approached through the posterior wall of the body. It must be remembered, however, that the upper part of the kidney rests upon the diaphragm, so that in the event of the twelfth rib being very short there may be danger of the incision being carried too far upward, resulting in injury to the diaphragm and pleura. It is also worthy of note that the diaphragmatic. area of 1246 UROGENITAL SYSTEM the kidney corresponds with the region where a hiatus diaphragmaticus between the costal and lumbar portions of the muscle may occur and if this be pronounced the upper part of the pos- terior surface of the kidney may come into more or less direct relations to the pleura (fig. 1008). Just as there may be variation in the position of the kidneys, so too there may be con- siderable variation in the extent to which they are in relation to the various structures men- tioned above. And this is especially true as regards their relations to the colons; for if the kidneys were lower than usual they might lie entirely beneath the line of attachment of the transverse mesocolon and thus have no direct relations with either colon, or on the other hand either the ascending or descending colon, or both, may be provided with a mesentery, whereby they would be removed from direct contact with the kidney. Structure. — A section through the kidney shows its substance to be composed of an ex- ternal or cortical [substantia corticalis] and an internal or medullary portion [substantia medullaris] (fig. 1010). The medulla consists of a variable number (eight to eighteen) of conical segments termed renal pyramids [pyramides renales (Malpighii)], the apices of which project into the bottom of the sinus (fig. 1006) and are received into the primary segments (calyces) of the pelvis, while their bases are turned toward the surface, but are separated from it and from each other by the cortex. The pyramids are smooth and somewhat glistening in section and are marked with delicate striae which converge from the base to the apex and in- dicate the course of the renal tubules. The blunted apex, or papilla, of each pyramid, either singly or blended with one or even two of its fellows, is embraced by a calyx (fig. 1006), and, if examined with a hand-lens, will be seen to present a variable number (twelve to eighty) of minute apertures, the foramina papillaria, which represent the terminations of as many papillary ducts (of Bellini) through which the secretion escapes into the pelvis. Fig. 1010. — Hohizontal Section of Kidney showing the Sinus. Pyramid of Malpighi Column of Bertin Interlobar artery Artery Cortex with pyramids Branch of artery Irregular branch of artery Ureter Portion of fatty capsule The cortex may be regarded as composed of two portions, (1) a peripheral layer, the cor- tex proper, which is about 12 mm. in thickness and extends from the fibrous capsule to the bases of the pyramids, and (2) processes termed renal columns [columnse renales (Bertini)] which dip inward between the pyramids to reach the bottom of the sinus (fig. 1010). In section the cortex is somewhat granular in aspect, and when examined closely shows a differen- tiation into a number of imperfectly separated portions termed cortical lobules [lobuli oorticales]. Each of these is composed of a convoluted portion [pars convoluta], surrounding an axial radiate portion (pyramid of Ferrein) [pars radiata (processus Ferreini)]. The latter consists of a group of tubules which extend from the cortex into the base of one of the medullary pyramids, whence it is also termed a medullary ray; and each medullary pyramid is formed from the rays of a number of cortical lobules, these structures, therefore, greatly exceeding the pyramids in number. Renal tubules (fig. 1011). — The structure described above is the result of the arrange- ment of the renal tubules, which constitute the essential units of the kidney. Each of these com- mences in a spherical glomerular capsule (fig. 1011), one wall of which is invaginated by a small glomerulus of blood-vessels, the combination of glomerulus and capsule forming what is termed a renal (Malpighian) corpuscle. These corpuscles are situated in the convoluted portions of the cortical lobules, and from each of them there arises by a narrow neck a tubule, which quickly becomes wide and convoluted, this fiortion being termed the first convoluted tubule. This enters a medullary ray, where it narrows again and descends as a straight tubule, the de- scending limb of Henle's loop, into the subjacent medullary pyramid, and, turning upon itself, forming the loop of Henle, ascends to the cortex, where it again becomes wide and contorted, forming the second convoluted tubule. This again lies in the convoluted portion of the cortical lobule, and, becoming narrower, opens with other similar tubules into a straight or collecting THE URETERS 1247 tubule, which occupies the axis of the medullary ray. Then, descending into the subjacent medullary pyramid, it unites with other collecting tubules, and finally opens into the renal pelvis at the summit of a papilla. The tubules are hned with epithelium throughout, the cells being tesselated in the capsule, irregularly cubical in the convoluted tubules and ascending limbs, flattened on the descending limbs and loops of Henle, and columnar in the cortical collecting tubules and in the straight tubules of the medulla. Vessels (fig. 1011). — The kidney is very vascular. The larger arterial branches, arranged in the sinus as has already been described, enter the substance of the kidney and pass up as the interlobar arteries in the renal columns. On reaching the bases of the pyramids they bend so as to run horizontaUy between these and the cortex, forming the arcuate arteries [arterife arciformes] from which interlobular branches pass up into the cortex and supply afferent branches to the Malpighian glomeruh. From the arcuate arteries numerous branches, the arterioloe rectces, Fig. 1011. — Scheme of Tubules and Vessels op the Kidney. Renal corpuscle Cortical vein Arcuate artery Medullary artery Efferent vessel forming medullary plexus Papillary pli surrounding th foramina papill; Renal corpuscle Duct of Bellini open- ing atthefora- papillare pass down into the pyramids, supplying the tubules of which these are composed. Efferent stems which issue from the Malpighian glomeruli break up into capillaries which supply the tubules contained in the cortex. Veins corresponding to the arteriolse rectce and to the inter- lobular, arcuate and interlobar arteries occur, opening into the renal veins, and, at the surface of the kidney, arranged in star-like groups, are the stellate veins [vense steUatae], which open into the interlobular veins and also communicate with the veins of the adipose capsule. The renal lymphatics may be divided into two sets, capsular and parenchymatous. They terminate in the upper lumbar nodes. Nerves. — The nerves form a plexus accompanying the vessels, and are derived from the sympathetic and vagus through the renal plexuses. Variations. — The kidney of a foetus differs from that of the adult in being divided into a number of distinct renal lobes, each of which corresponds to the base of a renal pyramid and 1248 UROGENITAL SYSTEM is capped by a thin layer of cortex. Such a condition is permanent in some of the lower animals; but in man the superficial indications of morphological segmentation usually become obliterated during the progress of growth of the cortical tissue, and are seldom visible after the age of ten. Development. — In the development of the embryo, representatives of three different sets of excretory organs occur, the permanent kidney (metanephros) being the last to form. The two earlier sets (pronephros and mesonephros) have a common duct, the Wolffian duct, and from the lower end of this an outgrowth develops, which extends upward on the posterior abdominal wall and comes into connection with a mass of embryonic tissue known as the metanephric blastema. The outgrowth gives rise to the ureter, pelvis and collecting tubules, while the remaining portions of the tubules are formed from the blastema. Various abnormalities may result from modifications of the development of the kidneys. (1) Occasionally the ureteric outgrowth of one side fails to develop, the result being the occur- rence of a single kidney. (2) The blastema may fail to attain its normal position, in which case the kidney may be situated in the iliac region or even in the pelvis; or the blastema may be drawn into an unusual position, the kidney resting on the vertebral column, or even on the opposite side of the abdomen; (3) or the two blastemas may fuse to a greater or less extent, forming a "horse-shoe kidney," extending across the vertebral column; or, if the fusion be more extensive, an apparently single kidney, which may rest upon the vertebral column, or to one side of it. Such fused kidneys may be distinguished from single kidneys by the fact that they possess two ureters opening normally into the bladder. (4) In rare cases, a blastema may be- come divided, an accessory kidney of varying size being thus produced. (5) Finally, in one or more of the tubules there may be a failure of the union of the portion derived from the blas- tema with the collecting tubule derived from the ureteric upgrowth, and the secretion having no means of escape from such malformed tubules, they become greatly dilated, producing a cystic kidney. THE URETERS The ureter (figs. 1004, 1007, 1012, 1015), which serves as the excretory duct of the kidney, is a canal, expanded and irregularly branched above, but narrow and of fairly uniform dimensions throughout the rest of its course. At its origin in the renal sinus it consists of a number of short tubes, usually eight or nine, called calyces minores (fig. 1012), each of which embraces a renal papilla, or occasionally two papillae may be connected with a single calyx. These calyces minores open directly or by means of short intermediate tubes (infundibula) into two short passages, the superior and inferior calyces majores, which in turn unite after a longer or shorter course to form the pelvis. Occasionally a third or middle calyx major is present. The pelvis [pelvis renalis] (fig. 1012) is usually more or less funnel-shaped, being wider above, where it lies between the two lips of the hilus, and narrower below, where it arches downward and medially to become continuous with the ureter proper. It is, however, very variable in shape and in some cases is hardly larger than the ureter. Usually it is flattened dorso-ventrally so that its anterior and posterior walls are in contact and its cavity represented merely by a fissure. The majority of the branches of the renal vein and artery lie in front of it, im- bedded in fat tissue, and anterior to these are the descending portion of the duo- denum on the right side and the pancreas on the left. The intra-renal portions of the ducts, including the pelvis, are considered parts of the kidney. The ureter proper (fig. 1007) extends from the termination of the pelvis to the bladder, its course lying in the subperitoneal tissue. It is a tube about 5 mm. in diameter when distended and it is fairly uniform in size, except that a slight con- striction occurs where it enters the pelvis and a second one occurs at about the middle of its abdominal portion. Its length is variously stated, but the average in the male adult may be taken as about 30 cm., the right being usually a little the shorter. Course and relations. — The course of each ureter may be conveniently divided into three portions, abdominal, pelvic, and vesical. The abdominal portion [pars abdominalis] runs downward and shghtly medially and is in relation pos- teriorly with the psoas muscle and its fascia; it crosses the genito-femoral nerve obhquely and in the lower part of its course passes in front of the common iliac artery near its bifurcation. Anteriorly it is covered by peritoneum and is crossed by the spermatic or ovarian vessels. Medially it is in relation on the right side with the inferior vena cava and on the left with the aorta, the vein being almost in contact with the right ureter, while the artery is separated from the left one by an interval that diminishes from 2.5 cm. above, to 1.5 cm. opposite the bifurcation of the vessel. The pelvic portion [pars pelvina] passes in front of the sacro-ihac articulation THE URINARY BLADDER 1249 and then forward and downward upon the obturator internus and its fascia behind and below the psoas, crossing the obturator vessels and nerve and having anterior to it in the female the posterior border of the ovary. It thus reaches the level of the floor of the peritoneal cavity, whereupon, at about the level of the ischial spine, its course is directed forward and medially toward the bladder. In this part of its course in the m.ale, it is crossed superiorly and medially by the ductus deferens, and then passes under cover of the free extremity of the vesicula seminalis, separated from its fellow by a distance of 37 mm. In the female it runs parallel with, and 8 to 12 mm. distant from, the cervix uteri, passes behind the uterine artery, through the uterine plexus of veins, and beneath the root of the broad ligament, and finally crosses the upper third of the lateral wall of the vagina to reach the vesico-vaginal interspace and enter the substance of the bladder at about the junction of its posterior, superior and lateral surfaces. The vesical portion, about 12 mm. in length, runs obliquely downward and medialward through the coats of the bladder, and opens on its mucous surface about 20 to 25 mm. from both its fellow and the internal urethral orifice. Structure. — The wall of the ureter is about 1 mm. (jV in.) in thickness, and consists of a mucous membrane, a muscular coat, and an external connective-tissue investment. The mucous membrane is longitudinally plicated, and is lined by transitional epithelium, continuous with that of the papillse above and with that of the bladder below. Mucous follicles of simple form have been found in the upper part of the canal. The muscularis is about 0.5 mm. (1/50 in.) in thickness, and consists of two layers, an external, composed of annular fibres, and an internal, Fig. 1012. — Pelvis and Upper Portion op Ureter. (After Henle.) Calyx minor Infundibulum Superior calyx nxajor Inferior calyx major of fibres longitudinally disposed. After the tube has entered the bladder the circular fibres form a kind of sphincter around its vesical orifice; while the longitudinal fibres are continued onward through the wall of the bladder and terminate beneath its mucous membrane. Vessels and nerves. — The arteries supplying the pelvis and upper part of the ureter come from the renal; the rest of the abdominal portion of the ureter is supplied by the spermatic (or ovarian), and its pelvic portion receives branches from the middle haemorrhoidal and in- ferior vesical; the veins terminate in the corresponding trunks; and the lymphatics pass to the lumbar and hypogastric nodes. The nerves are supplied by the spermatic, renal, and hypo- gastric plexuses. Variations. — Occasionally the depression which separates the two calyces majores extends through the pelvis, so that the calyces appear to open directly into the ureter. The fission may also affect the ureter to a greater or less extent, in extreme cases producing a duplication of the tube throughout its entire length. THE URINARY BLADDER The urinary bladder [vesica urinaria] is a receptacle, whose form, size, and position vary with the amount of its contents. The adult organ in its empty or moderately filled condition Hes entirely below the level of the obhque plane of the pelvic inlet; but when considerably distended it rises into the abdomen and shows itself beneath the parietes as a characteristic mesial projection above the symphysis, a projection which in extreme distention of the bladder may extend nearly to the level of the umbilicus. 1250 UROGENITAL SYSTEM Form. — When distended it assumes in the male an ovoid shape with its longest diameter directed from above downward and backward; but in the female the transverse diameter is the greatest, in accordance with the greater breadth of the pelvic cavity. In the child it is somewhat pear-shaped, the stalk being represented by the urachus. Parts. — ^For convenience in description five surfaces may be recognized, but they are but indistinctly separated from each other. One, the anterior or pubic surface, is directed forward and downward; second, the superior or intestinal surface, looks upward; the third, the posterior surface, looks backward; and the other two are the lateral surfaces. The anterior, superior, and lateral surfaces meet at the vertex of the bladder, from which the middle umbilical ligament (urachus) extends to the umbilicus; the posterior surface, sometimes flat and some- times, especially in old age, convex, forms what is known as the base or fundus [fundus vesicae] ; and the portion of the viscus intervening between the vertex and Fig 1013 — Median Sagittal Section op the Male Pelvis (From a prepaiation in the Museum of St Thomas's Hospital ) Small intes- tine fundus is termed the body [corpus vesicae]. In the centre of the line between the anterior and posterior surfaces is the internal urethral orifice [orificium urethrae internum], by which the bladder communicates with the urethra, and the portion of the organ immediately surrounding this is sometimes spoken of as the neck. When the bladder is empty and relaxed, the superior surface sinks down upon the anterior and posterior surfaces, thus becoming concave, and the cavity of the organ is reduced to a T- or Y-shaped fissure. In the female, the cavity of the empty bladder in mid-sagittal section often more nearly resembles a figure 7 (see fig. 1014). Relations. — The anterior surface looks downward and forward toward the symphysis pubis (figs. 1013, 1014). It is uncovered by peritoneum, but is sepa- rated from the pubic bones and anterior attachments of the obturatores interni and the levatores ani by a space known as the prevesical space (cavum Retzii), THE URINARY BLADDER 1251 which contains a variable quantity of loose fat continuous with the pelvic and abdominal subperitoneal tissue. Each lateral surface is covered by peritoneum down to the level at which it is crossed obliquely from behind forward and upward by the obUterated hypogastric artery. Below this level it is separated from the levator ani and obturator internus by subperitoneal tissue, which usually bears much fat in its meshes and ensheaths the vesical vessels and nerves. It is also crossed by the ductus deferens, which passes between the ureter and the wall of the bladder, a little above the level at which the former enters the wall of the bladder, at the junction of its lateral and posterior surfaces and about 3.5'^cm. above the fundus. The posterior surface may be divided into two portions, an upper covered by the peritoneum of the recto-vesical or vesico-uterine pouch (fig. 1013), and a lower in direct contact in the male with the anterior wall of the Fig. 1014. — Mid-sagittal Section of the Female Pelvis. (Spalteholz.) Hypogastric artery ^t Hypogastric vein Promontory / / Infundibulum of tuba uterina Suspensory ligament of ovary External ihac vein Ovary Ampulla of tuba utenua Ovarian ligament Fundus uteri \ , Parietal peritoneum Uterus k. / Interna! orifice of V / uterus \/ y Recto uterine fold X , Recto uterine \ / muscle Ligamentum teres Transverse fold of bladder Vertex of bladder . ^\ Middle umbilical \ ligament Urach Symphysis pub Labium majus Body of uterus Labium minus External orifice of urethra Urethra /' / Internal orifice of urethra / Orifice of vagina Coccyx Recto coccy- \ geus muscle Rectum Posterior labium External orifice of uterus Anterior labium Vagina a.yuiKu. Vesico-uterine pouch Vestibule rectum and with the lower part of the ductus deferentes and the vesiculse semin- ales. Between the diverging ductus deferentes there is a triangular space, whose base is formed by the line of reflexion of the recto-vesical pouch of peritoneum and the apex by the meeting of the ejaculatory ducts at the summit of the prostate. It represents the area of direct contact of the posterior wall of the bladder withjthe rectum. In the female the posterior surface is adherent in its lower part to the cervix of the uterus and the upper part of the anterior wall of the vagina (fig. 1014), but it is separated above from the body of the uterus by the shallow vesico- uterine pouch of peritoneum. The superior surface is entirely covered by peritoneum. It looks almost 1252 UROGENITAL SYSTEM directly upward into the abdominal cavity and has resting upon it coils of the small intestines and sometimes a portion of the sigmoid colon behind these. Variation in position. — In the normal condition the bladder of the adult lies below the upper border of the symphysis pubis, but if fully distended it may rise above this level, carrying with it the reflexion of peritoneum from its upper surface to the anterior abdominal wall. The anterior surface of the bladder is thus brought into relation with the anterior abdominal wall, being separated from it only by the enlarged prevesical space, and it is thus possible to enter the bladder above the symphysis pubis without penetrating the peritoneum. In the infant, owing to the smaller extent of the pelvic cavity, the bladder hes at a some- what higher level than in the adult and rises into the abdominal cavity. Indeed the entire bladder is above the horizontal level of the pubic crests, the urethral orifice being behind the upper margin of the symphysis pubis. As the child learns to walk, however, this position gradually alters and usually by the age of six years the adult relations have been acquired. The fixation of the bladder. — The reflections of the peritoneum from the superior surface of the bladder to the anterior abdominal wall and from the sides and back to the corresponding walls of the pelvis are sometimes described as the superior, lateral and posterior false ligaments. Furthermore there extends from the apex of the bladder to the umbilicus a fibrous cord, the urachus, the remains of the embryonic allantois; this is described as the middle umbilical ligament of the bladder (fig. 1014), and lateral umbilical ligaments are formed by the obliter- ated hypogastric arteries which carried the foetal blood to the placenta and in the Fig. 1015. — The Posterior Wall of the Bladder. (After Henle.) Ductus deferens Plica ureterica Vesical aperture Colliculus seminalis- Opening of ejaculatory duct Prostatic utriculu Prostatic adult are represented by fibrous cords passing over the sides of the bladder and ascending to the umbilicus. In addition to these structures certain thickenings of the endopelvic fascia, where it comes into relation with the base of the bladder and prostate gland, constitute what are termed the true ligaments. Two such thickenings extend from the anterior surface of the capsule of the prostate gland, or from the lower part of the anterior surface of the bladder in the female, to the pubic bones and constitute what are known as the middle pubo-prostatic {pubo-vesical) ligaments, with which muscle fibres [m. pubovesicahs] are usually associated. Similarly, thickenings of the fascia extending from the sides of the prostate gland or from the sides of the base of the bladder to the lateral walls of the pelvis form the lateral true ligaments. Muscle fibres [m. rectovesicahs] also occur in the subperitoneal tissue contained within the peritoneal folds (posterior false ligaments) extending from the back of the bladder to the posterior wall of the pelvis and bounding the recto-vesical pouch of peritoneum in the male. They correspond to the mm. redouterini of the female. The internal surface. — The mucous membrane lining the internal surface of the bladder is soft and rose-coloured during life, and in the empty bladder is thrown into irregular folds which become effaced by distention. It is modified over a triangular area at the base of the bladder, termed the trigone [trigonum vesicae (Lieutaudi)] (fig. 1015) whose three angles correspond with the orifices of the urethra and of the two ureters, and are separated from one another by a MALE REPRODUCTIVE ORGANS 1253 distance of 20 to 25 mm. This area is paler in colour and free from the plication that characterizes the rest of the mucous membrane; it is bounded posteriorly by a transv.erse ridge, the plica ureterica, extending between the orifices of the ureters, and toward the urethral orifice presents a median longitudinal elevation, the uvula vesicae, which is apt to be especially prominent in aged persons. The internal urethral orifice is normally situated at the lowest point of the bladder, at the junction of the anterior and posterior surfaces. It is surrounded by a more or less distinct circular elevation, the urethral annulus, and is usually on a level with about the center of the symphysis pubis and from 2.0 to 2.5 cm. behind it. Structure. — The general characteristics of the mucous membrane of the bladder, which is lined by epithelium of the transitional variety, have already been described. It rests upon a loose submucous tissue, which contains numerous elastic fibres. The greater part of the thick- ness of the waU is formed, however, of the muscular coal, consisting of non-striped muscle tissue, the fibres of which are arranged in three more or less distinct layers. The outer layer is composed mainly of longitudinal fibres, some of which are continued forward to the pubis from the neck of the bladder to form the mm. pubovesioales and others backward to form the mm. rectovesicales. To this outer layer the term m. detrusor uriruB has been applied, but it should be noted that it does not contract independently of the circular layer. The middle ayer is thicker than the outer and more uniformly developed. It consists of fibres having for the most part a circular direction and is well developed over all the upper portion of the bladder, but becomes thinner in the region corresponding to the trigone. It is here that the inner layer is chiefly developed, consisting of fibres, which are situated partly in the submucous tissue and have a general longitudinal direction throughout the region of the trigone. At the neck of the bladder, however, they form a strong circular bundle, which is continued into the prostatic portion of the urethra and forms what is termed the internal sphincter of the bladder. Vessels. — The arteries of the bladder are usually two in number, the superior and inferior vesical, branches of the hypogastric artery; the fundus also receives branches from the middle hsemorrhoidal and in the female twigs are also sent to it from the uterine and vaginal arteries. The veins form an extensive plexus at the sides of the bladder, from which stems pass to the hypogastric trunk. The lymphatics accompany the veins and communicate with the hypo- gastric nodes, some of those from the fundus passing to nodes situated at the promontory of the sacrum. Nerves. — -The nerves are derived partly from the hypogastric sympathetic plexus and partly from the second and third sacral nerves. The fibres from the latter constitute the nervi erigentes, stimulation of which produces contraction of the general musculature and rela.xation of the internal sphincter. On each side of the bladder there is formed a sympathetic vesical plexus, from which superior and inferior vesical nerves pass to the corresponding parts of the bladder. Development. — In the earlier stages of development the urogenital ducts and the digestive tract open below into a common cavity, the cloaca, from the ventral portion of which a long tubular outgrowth, the allantois, extends out to the placenta through the umbilical cord. Later the cloaca becomes divided in the frontal plane into a ventral portion which receives the urogenital ducts, and a dorsal portion, which becomes the lower end of the rectum. From the upper part of the ventral portion the bladder is developed. Since the cloaca is fined by endoderm the mucous membrane of the bladder is mainly derived from that embryonic layer, but it is worthy of note that portions of the lower ends of the ureters are taken up into the wall of the bladder, giving rise to the area of the trigone, whose mucous membrane is thus of meso- dermal origin. The portion of the allantois within the body of the foetus is transformed after birth into a fibrous cord, the urachus. The urethra will be considered later in connection with the reproductive organs. B. THE REPRODUCTIVE ORGANS The reproductive organs include those of the male [organa genitalia viriHa] and those of the female [organa genitalia muliebria]. THE MALE REPRODUCTIVE ORGANS The reproductive organs of the male consist of (1) two testes in which the spermatozoa are formed, (2) their ducts, the ductus def erentes ; enclosed through- out a portion of their course in the spermatic cord; and the seminal vesicles, reservoirs for the semen, connected with the ductus def erentes; (3) the penis, the organ of copulation, which is traversed by the urethra; (4) the urethra, a canal into which the ductus deferentes open and which also gives exit to the contents of the bladder; (5) the prostate gland, a musculoglandular structure surrounding the beginning of the urethra; (6) the bulbo-urethral glands which open into the urethra. { 1254 UROGENITAL SYSTEM 1. The Testes and Their Appendages The scrotum. — The two testes, together with the beginning of the ductus deferentes, are contained within a pouch, the scrotum, which is divided into two compartments by a median sagittal septum, the edge of which is indicated on the surface by a ridge-hke thickening of the integument, termed the raphe. This double condition of the scrotum is explained by its origin from the fusion of two out- pouchings of the lower portion of the abdominal wall, the inguinal canals forming, as it were, the necks of the outpouchings. The testes are primarily retroperitoneal abdominal organs, but later they descend through the inguinal canals into the scrotal outpouchings, where they lie between the peritoneal sac which each of these contains and the remaining layers of the wall, thus retaining their retroperitoneal position. The peritoneal sacs are at first in communication with the abdominal cavity, but after the descent of the testes each undergoes degeneration in its upper part, the cavity disappearing and the peritoneal tissue becoming converted into a portion of the connective tissue in which the ductus deferens and the vessels and nerves asso- ciated with it are imbedded in their course through the spermatic cord. The portion of the sac in relation with each testis persists, however, and wrapping itself around that structure forms for it a serous investment, the tunica vaginalis propria (fig. 1016). The integument oi the scrotum is more or less pigmented and presents numerous transverse ridges extending laterally on either side from the raphe. It is furnished in the adult with coarse, scattered hairs and its sebaceous and sudoriparous glands are well developed. The deeper layers of the dermis, have a pinkish colour, and form what is termed the dartos (fig. 1016), the colouration being due to the Fig. 1016. — Horizontal Section op the Sceotum and Testis. (Diagrammatic.) Skin Dartos Cremasteric fascia Cremaster muscle Septum scroti Mediastinum testis Ductus deferens Parietal layer of tunica vaginalis propria Tunica vaginalis communis Cavity of tunica vaginalis Visceral layer of tunica vaginalis propria Tunica albuginea Sinus epididymidis Epididymis presence in it of numerous non-striated muscle fibres, which are for the most part arranged at right angles to the wrinkles of the surface and are the cause of these. The more superficial fibres of the dartos, hke the rest of the integument, form a common investment for both testes, but the deeper ones of either side bend inward at the raphe and assist in the formation of the septum. Internal to the dartos and closely related to it is a layer of laminated con- nective tissue, the cremasteric fascia. It is destitute of fat and is continuous at the subcutaneous inguinal ring with the intercrural fibres, being probably the scrotal representative of the external oblique muscle. It is succeeded by a strong sheet of fascia containing longitudinal bands of striated muscle tissue, forming what is termed the cremaster muscle (figs. 389, 1016) and being con- tinuous above with the fibres of the internal oblique muscle of the abdomen. Internal to this is a thin layer of connective tissue, the tunica vaginalis communis, which is continuous with the transversalis fascia at the inguinal ring, and, finally, there is the tunica vaginalis propria, which forms the serous investment of the testis and, as has been stated, is of peritoneal origin. Like other similar serous investments it has the form of a double sac, the outer or parietal layer of which is closely adherent to the tunica vaginahs communis and contains numerous non- striped muscle fibres forming what has been termed the internal cremaster muscle. The inner or visceral layer is thinner and closely invests the testis and a THE TESTIS AND EPIDIDYMIS 1255 portion of the epididymis, being reflected from the inferior and posterior parts of the latter to be continuous with the parietal layer. Toward the upper part of the lateral surface of the testis it is folded in between that structure and the epididy- mis, forming a well-marked pocket, the sinus eipididymidis (digital fossa) (fig. 1017), whose upper and lower lips form what are termed the ligamentaepididymidis. Vessels and nerves. — The skin and dartos of the scrotum are supplied partly by the peri- neal branch of the internal pudendal artery and partly by the external pudendal branches of the femoral. The deeper layers are supplied by the spermatic branch of the inferior epigastric. The veins accompany the arteries, the external pudendals opening into the internal saphenous vein near its termination. The lymphatics terminate in the more medial inguinal nodes. Several nerves take part in the supply of the scrotum. The external spermatic branch of the genito-femoral gives sensory branches to the anterior and lateral surfaces and also supplies the external cremaster muscle; the posterior surface is supplied by the periaeal branch of the pudendal nerve; and the inferior surface by the perineal branches of the posterior femoral Fig. 1017. — The Left Testis with Vessels and Duct. (After Sappey.) Internal spermatic artery' Internal spermatic veins- Branch of spermatic artery Head of epididy Appendix testi Lateral wall of body of testi Ductus deferens with deferential artery Vein Ductus deferens Body of epididymis Sinus epididymidis Vessels of epididymis Tail of epididymis cutaneous. The anterior aspect of the scrotum is also supplied by anterior scrotal branches of the ilio-inguinal. The non-striped musculature is probably supplied by the internal spermatic nerve from the hypogastric plexus. Hernia. — The communication of the tunica vaginaUs propria vrith the abdominal perito- neum is usually obliterated within a few days after birth, but sometimes the process of oblitera- tion is more or less incomplete. If the communication remains open there is a free passage for a loop of the intestine to enter the cavity of the tunica vaginalis, such a condition consti- tuting what is known as the congenital variety of inguinal hernia. If the communication be interrupted only at the upper part of the original sac, so that the cavity of the tunica vagin- alis propria extends a considerable distance up the spermatic cord a hernia, passing through the inguinal canal, may invaginate the upper part of the tunica vaginalis into the lower, pro- ducing what is termed the encysted variety of hernia. Or if, finally, the obliteration of the communication begins in the neighbourhood of the testis, a funnel-shaped prolongation of the peritoneal cavity may extend downward into the spermatic cord, and hernia into this con- stitutes the variety known as hernia i^ito the funicular process. The testis and epididymis. — The testes (fig. 1017) are the essential male organs of reproduction and are contained within the scrotum. They are two in number, 1256 UROGENITAL SYSTEM each being of a flattened oval form, with two surfaces, medial and lateral, two borders, anterior and posterior, and two extremities, superior and inferior. To the whole of the posterior border there is attached the epididymis, formed by the efferent ducts. The testis is obliquely placed, so that the medial surface also looks somewhat forward and downward. The surface of the testis is covered by the visceral layer of the tunica vaginalis propria except where it is in contact with the epididymis, and is formed by a dense white inelastic capsule, the tunica albuginea, beneath which is a looser and more vascular layer known as the tunica vascidosa. From the inner surface of the albuginea, lamellae of connective tissue, known as septula, converge toward the posterior border of the testis and toward its upper part unite together to form a network (fig. 1018), the mediastinum testis (or corpus Highmori), through which blood-vessels and lymphatics enter and leave the testis, while by the interspaces of the network, known as the rete testis, the tubules of the testis are placed in com- munication with the epididymis. The septula divide the substance of the testis into a number of compartments or lohules, each of which is occupied by a number of slender, greatly contorted canals, the seminiferous tubules [tubuli seminiferi], from whose epithelial lining the spermatozoa are formed. The tubules of each lobule converge to form a single, almost straight duct and these tubuli recti pass Fig. lOlS. — Diagram of the Testicular Tubules. Ductus epididymidis ua Lobulus epididymidis Efferent ducts Tunic albuginea receiving attacli- ment of septula Tubulus rectus Rete testis in mediastinum testis Ductus epididymidis Ductulus aberrans Ductus deferens toward the mediastinum, where they open into the rete testis. In the lobules the seminif- erous tubules are imbedded in a loose connective tissue that contains certain pecuhar cells, the interstitial cells, to which has been attributed the formation of an internal secretion. The epididymis (fig. 1017), which lies along the posterior border of the testis, is an elongated structure with a body [corpus epididymidis], enlarged above to form the head [caput] and to a less extent below to form the tail [cauda]. It is invested by a tunica albuginea, continuous with, but much thinner than that of the testis, and is formed mainly by the greatly contorted duct of the epididymis, which represents the beginning of the ductus deferens. The head is formed by 12-14 tubules, the efferent ducts (fig. 1018), which take their origin from the rete testis as almost straight tubules, but gradually become greatly coiled, so that each duct has the form of an elongated cone, its coiled portion forming what is termed a lobulus epididymidis. At their coiled ends the various efferent ducts open into a single tube, the ductus epididymidis. Its diameter is only about 0.4 mm., but it measures 6.0-7.0 metres (18-21 feet) in its entire length, being coiled so extensively as to be contained within the body and tail of the epididymis. In this latter region it passes over into the ductus deferens. Vessels. — The principal artery supplying the testis is the internal spermatic, from which branches are also sent to the epididymis. The deferential artery, a branch of the superior vesical, also sends branches to the epididymis and enters into extensive anastomoses with the testicular branches of the internal spermatic, and anastomoses also occur with the vessels supplying the scrotum. The veins correspond with the arteries. The lymphatics of the testis and epididymis unite to form four to six large stems which pass upward in the spermatic cord to terminate in the lower lumbar nodes. Morphology. — The testis is primarily an abdominal organ and is developed in close relation- ship with the provisional kidney [mesonephros] whose duct, indeed, becomes the ductus deferens DUCTUS DEFERENS AND SEMINAL VESICLE 1257 and some of whose tubules, becoming the efferent ducts, place the seminiferous tubules in com- naunioation with the ductus deferens. The epididymis may therefore be said to be developed from the mesonephros. The portions of this structure that are not concerned in the formation of the efferent ducts disappear for the most part; a few of the tubules persist, however, as rudimentary organs associated with the epididymis. Among these may be mentioned one or more blindly ending, coiled tubules, varying from 5-30 cm. in length, which are connected with the ductus epididymidis usually in the tail of the epididymis. They are knowTi as the ducluli aberrantes (fig. 1018) and may be regarded as persistent excretory mesonephric tubules. Another of the rudimentary organs is the paradidymis {organ of Giraldes), which is a whitish body, situated immediately above the head of the epididymis, and is composed of irregularly coiled tubules, which terminate blindly at both extremities. They may be regarded as efferent ducts that have failed to connect with the testis and are of interest in that they sometimes develop into cysts connected with the epididymis. In addition there is frequently attached to the upper pole of the testis a sohd oval body composed of connective tissue, known as the appendix testis {hydatid of Morgagni) (fig. 1017). It measures from 3 to 8 mm. in length and its significance is doubtful. A similar, though smaller structure, the appendix epididymidis, is attached less frequently to the head of the epididymis. It is usually provided with a distinct stalk and contains a cavity; it is believed to represent the upper end of the Miillerian duct, present in the embryo and giving rise to the tuba uterina in the female, but almost completely degenerating in the male. The testis begins its descent from the abdominal cavity into the scrotum at the third month of fetal life and reaches the abdominal inguinal ring at about the sixth month, but it is not until shortly before birth that it arrives at its final location in the scrotum. The cause of the descent is stiU uncertain, but it is supposed to be partly due to the failure of a band of connective tissue, which extends from the lower pole of the embryonic testis to the bottom of the scrotal pouch, to keep pace with the growth of the body walls. This hgament, which is known as the gubernac.ulum testis, thus becomes relatively shorter and draws the testis downward toward the point of its attachment to the scrotum. There are various features in the descent, however, that cannot be explained by the simple traction of the gubernaculum and it must be regarded as a complicated growth process whose meaning is yet uncertain. The gubernaculum testis apparently undergoes degeneration after the testis has reached its definitive location and cannot be recognized in connection with the adult testis. Occasionally the descent of the testis is interrupted, the organ remaining either in the abdomen or in the inguinal canal. This condition of cryptorchism is always associated with a suppression of the function of the organ. 2. The Ductus Deferentes and Vesicul^ Seminales Each ductus deferens is the continuation of a ductus epididymidis and ex- tends from the tail of the epididymis to the prostatic portion of the urethra. At its beginning it ascends along the posterior border of the epididymis (testicular portion) and is at first slender and tortuous (fig. 1018), but before reaching the level of the head of the epididymis it becomes straighter and thicker (fig. 1017), owing to the development in its walls of strong layers of longitudinal and circular non-striated muscle tissue. Thence it is continued almost vertically upward as one of the constituents of the spermatic cord {funicular portion) to the subcu- taneous inguinal ring, and, entering this, traverses the inguinal canal {inguinal portion), still forming a portion of the cord. At the abdominal ring it separates from the other constituents of the cord and, looping over the inferior epigastric artery near its origin, passes downward and backward over the lateral surface of the bladder {pelvic portion). At the junction of the posterior and lateral surfaces of the bladder it passes medially to the ureter and is then continued downward, forward and medially upon the base of the bladder until it reaches the prostate gland (fig. 1019), whose substance it traverses, as the ductus ejaculatorius, to open into the prostatic portion of the urethra (see p. 1263). Just before it reaches the prostate gland each ductus deferens presents an irregular spindle-shaped enlargement, the ampulla (figs. 1019, 1020), whose walls are somewhat sacculated. Just beyond this it is joined upon its lateral surface by a club-shaped lobulated structure, the vesicula seminalis (fig. 1019). Each vesicle measures 4.5-5.5 cm. in length and has a greatest diameter of about 2 cm. It rests upon the posterior surface of the bladder, lying parallel with and lateral to the corresponding ductus deferens, and in its upper one-third is in relation posteriorly with the peritoneum which forms the anterior wall of the recto- vesical pouch, while below it is in contact with the anterior wall of the lower part of the rectum, through which it may be palpated. Indeed, the two vesiculee, together with the ductus deferentes, form the lateral boundaries of the triangular area at the base of the bladder, throughout which that organ is in relation to the rectum. 1258 UROGENITAL SYSTEM Each vesicle is enclosed within a fine capsule of connective tissue, which contains numerous non-striated muscle fibres and is continuous below with the capsule of the prostate gland. On removing this capsule the vesicle will be found to consist of a greatly coiled tube, 10-12 cm. Fig. 1019. — Ductus Depeeentes and Vesicul^ Seminales. (After Sappey.) Ejaculatory duct Prostatic utriculus — CoUiculus seminali Orifice of ejaculatory duct -J'- — Ampulla of ductus deferens Ejaculatory duct entering prostatic fissure Membranous urethra Ductus deferens Orifice of prostatic utriculus Vesicula seminalis Fig. 1020. — Ductus Deferens and Vesicula Seminalis dissected. (After Sappey.) Diverticula! '"\^ ^ p^ Sacculi of ampulla of ductus deferens Junction of ductus deferens and vesicula seminalis Ejaculatory duct in length, which ends blindly and has attached to it on either side a number of short diverticula (fig. 1020). The walls of the tube and diverticula are formed of smooth muscle tissue, arranged in layers similar to those of the ductus deferentes, and are lined by a much folded mucous THE SPERMATIC CORD 1259 membrane, whose cells contain considerable quantities of a yeUowish-brown pigment, and also contribute a secretion to the seminal fluid. In addition to having this function the vesiculse also serve as receptacles for the spermatozoa. They arise as diverticula from the embryonic ductus deferens, and it is worthy of note that a number (4 or 5) of similar but quite small diver- ticula arise from the upper part of each ductus ejaculatorius. Vessels and nerves. — The artery supplying the ductus deferens is the a. deferentialis, a branch of the superior vesical. It accompanies the ductus to the tail of the epididymis and also gives a branch to the vesicula seminalis. The latter also receives branches from the middle haemorrhoidal and inferior vesical arteries. The deferential vein accompanies the ductus deferens to the base of the bladder where it breaks up into a plexus that communicates with the seminal venous plexus formed by the veins from the seminal vesicles. This joins with the vesical and pudendal ple.xus and so communicates with the hypogastric vein. The lymphatics of the ductus deferentes and seminal vesicles pass to the external iliac and hypogastric nodes. The nerves of both structures are derived from the hypogastric plexus. The spermatic cord. — In its descent through the inguinal canal into the scrotum the testis necessarily drags after it the ductus deferens and the testicular vessels and nerves, these structures coming together at the abdominal inguinal Fig. 1021. — Ceoss-section of the Spermatic Cord. A. spermatica interna N. spermaticus int. Lympli vessel Vv. spermaticae int. Fascia cremasterica Lymph vessel Ductus deferens Vv. spermaticse int A. et V. deferentialis V. spermatica ext. ring to form what is termed the spermatic cord [funiculus spermaticus]. This structure extends, therefore, from the abdominal inguinal ring, through the in- guinal canal and the neck of the scrotal sack to the testis, and is enclosed within the same investing layers as the testis. Thus as it emerges from the subcutaneous inguinal ring it receives an investment of con- nective tissue continuous with the intercrural fibres and the aponeurosis of the external oblique muscle. This cremasteric fascia has beneath it bands of striated muscle tissue, the external cremaster muscle (fig. 1021), especially developed on the posterior surface of the cord and con- tinuous with the internal oblique muscle of the abdomen, and within these is an indistinct layer of connective tissue, the tunica vaginalis communis, which is received at the abdominal inguinal ring where it is continuous with the fascia transver.saUs. Within the sheath thus formed there is a matrix of connective tissue, usually containing considerable amounts of fat and strands of non-striated muscle tissue, which form what is termed the internal cremaster muscle {funicular portion), and imbedded in this connective tissue are the various essential constituents of the cord. These are as follows (figs. 1017, 1021) : (1) the ductus deferens, occupy- ing the posterior surface of the cord and having associated with it the deferential artery and veins and the deferential plexus of nerve fibres; (2) the internal spermatic artery, which occupies the axis of the cord and is surrounded by (3) the internal spermatic veins, which form a complicated network, known as the pam- 1260 UROGENITAL SYSTEM piniform plexus; (4) the testicular lymphatics; and (5) the internal spermatic plexus of nerves from the hypogastric plexus; and (6) branches of the genito- femoral nerve for the supply of the external cremaster muscles. 3. The Penis The penis is composed of three rod-like bodies composed of erectile tissue (fig. 1023), firmly united together and invested by fascia and integument (fig. 1022). When this erectile tissue becomes engorged with blood the organ assumes an erect position, but otherwise it is pendulous, hanging downward in front of the scrotum from its attachment to the symphysis pubis. The erectile bodies are, however, prolonged backward beyond the symphysis pubis into the perineal re- gion, and it is customary to speak of this perineal portion as the root of the penis [radix penis] or pars fixa in contrast to the body of the penis [corpus penis] or pars libera. The body of the penis in its flaccid condition is almost cylindrical, but in erection it becomes somewhat triangular in section, what was the anterior surface or dorsum penis* becoming flattened, while the opposite one, the urethral surface [facies urethralis], becomes more sharply rounded. At the free extremity of the penis there is a blunt conical enlargement, the glans penis (fig. 1023), at the apex of which is the external orifice of the methra. The glans is separated from the body by a constriction, the ?ieck [coUum glandis], and from this region a fold of integument arises, which more or less completely encloses the glans, forming the prepuce [prseputium] (fig. 1024). The prepuce is quite free from the glans dorsally but in the ventral mid-line it is attached to it, almost to the urethral Fig. 1022. — Transverse Section through the Bodt op the Penis. Superficial dorsal vein of penis Dorsal artery ^ | /Deep dorsal vein Tunica albuginea Tunica albuginea- Skin Dartos Septum .Corpus cavernosum penis Fascia penis Artery Urethra Corpus cavernosum urethrs orifice, by a narrow fine of adhesion, the frenulum [frenulum prseputii], which contains blood-vessels of considerable size. The base of the glans has a well- marked rounded border, the corona [corona glandis], and is deeply concave for the reception of the distal ends of the corpora cavernosa penis. The integument of the penis is continuous with that of the scrotum and like it is pigmented and contains no fat. Immediately below it there is a layer of non- striated muscular tissue, the dartos, and beneath this a layer of loose connective tissue, containing the superficial vessels and nerves of the penis; beneath this again is a denser, elastic sheet of connective tissue, the fascia penis (fig. 1022), which encloses the erectile bodies as far as the base of the glans and is continuous with the superficial fascia of the perineum and inguinal region. Where it passes beneath the symphysis pubis it receives from the anterior surface of the latter a strong band of fibrous tissue, which forms the suspensory ligament of the penis [Hg. suspensorium penis]. Two of the erectile bodies of the penis, the corpora cavernosa penis, are paired (fig. 1023). They are attached at their proximal ends to the base of the tuberosity of the ischium, and in this part of their extent are termed the c7-ura penis, being * It should be noted that the terms "dorsum" and "dorsal" are used for the penis in a sense directly opposite their usual meaning. THE PENIS 1261 composed of fibrotis connective tissue, whicli lias resting upon it the m. ischio- cavernosus (see Section IV). The two crura are situated in the lateral portions of the superficial perineal interspace and pass forward parallel with the rami of the ischia and pubis, gradually becoming transformed into cavernous erectile tissue. Shortly before they reach the level of the symphysis pubis the two corpora come into contact in the median hne, their medial walls fusing to form a septum, and thus united they extend throughout the entire length of the body of the penis, occupying the dorsal portion of the space enclosed by the fascia penis (fig. 1022) . They terminate at the posterior surface of the glans, where they taper Fig. 1023. — Dissection of the Perineum Showing the STRtrcTTTBE and Relations op the Penis. Corona glandis — Corpus cavernosum xirethr^ Corpus cavernosum penis ■ ■ M, ischio-cavernosus . Urogenital trigone (diaphragm) Prostate gland - somewhat to be received into its basal concavity (fig. 1024). The septum in its proximal part forms a complete partition between the two bodies, but distally it is broken through by numerous clefts by which the blood lacunse of the two bodies are placed in communication. Each corpus cavernosum penis consists of a strong elastic fibrous sheath, the tunica albu- ginea, from which trabeculiB extend into the substance of the organ, dividing it into a network of communicating cavities, into which open terminal branches of the a. profunda penis, which traverses the axis of the corpus. These cavities consequently are to be regarded as vascular lacunae, which, becoming engorged with blood, produce the enlargement and erection of the organ. The third erectile organ is the corpus cavernosum urethra (formerly "corpus spongiosum") (fig. 1023), so called because it is traversed throughout its entire length by the urethra (fig. 1024). It is an unpaired, median structure, having no 1262 UROGENITAL SYSTEM bony attachments and begins posteriorly in the superficial perineal interspace with an enlargement, the bulb [bulbus urethrae] (fig. 1023), whose posterior surface rests on the superficial fascia of the urogenital trigone and is enclosed by the m. bulbo-cavernosus. Anteriorly the bulb gradually tapers to a rather slender cylindrical portion, the body, very uniform in diameter, which extends throughout the entire length of the body of the penis, lying in the median hne beneath the fused corpora cavernosa penis (figs. 1022, 1023). At the neck of the penis it undergoes a sudden enlargement to form the glans, the whole of that structure, which has already been described, being formed by the corpus cavernosum urethras. The structure of the corpus cavernosum urethrae is essentially the same as that of the corpora cavernosa penis, the tunica albuginea, however, being much thinner. Vessels and nerves. — The principal arterial supply of the penis is derived from the internal pudendal artery (see p. 610), although the proximal portion of its integument is also supplied by the external pudendal branches of the femoral artery. The veins from the integument Fig. 1024. — Mid-sagittal Section (diagrammatic) Showing Male Bladder, Ukethba, etc. Symphysis pub: Subpubic lig. Suspensory lig. Urogenital trigone (diaphragm) Bladder Seminal vesicle Ampulla Prostate middle lobe Ejaculatory duct Prostatic utriculus Prostate gland Bulbo-iurethral (Cowper's) gland Ductus deferens Prepuce. Fossa navicularis collect into one or more stems, the superficial dorsal veins, which run along the dorsal mid-line and, diverging, open into the great saphenous vein. The deep veins from the corpora cavernosa open into a median deep dorsal vein, which connects partly with the internal pudendal veins and partly with the pudendal plexus. Both the superficial and deep lymphatics terminate in the superficial inguinal nodes. The lymph-vessels from the glans are said to follow those of the urethra and end in the deep inguinal and external iliac nodes. The nerves supplying the penis are the anterior scrotal branches of the ilio-inguinal and the perineal branches and dorsal nerve of the penis from the pudendal. Sympathetic fibres also pass to the penis from the hypogastric plexus and with these fibres from the third and fourth sacral nerves, which constitute what is termed the nervus erigens, since stiinulation of it pro- duces erection of the organ. An anatomical provision for the production of this phenomenon has been found in the occurrence of peculiar thickenings of the intima of the arteries of the penis, by which the lamina of the vessels are greatly diminished or even occluded when in a state of moderate contraction, as when the organ is flaccid. When the arteries are dilated the intimal thickenings become reduced in height and the blood is afforded a free passage into the lacunar spaces of the corpora cavernosa, which thus become engorged. 4. The Male Urethra The urethra is the canal which extends from the bladder to the extremity of the glans penis and serves for the passage of both the urine and the seminal fluid. THE MALE URETHRA 1263 In its course (fig. 1024) it traverses first the prostate gland, then the urogenital diaphgram and then the entire length of the corpus cavernosum urethrse, and may thus be regarded as being composed of three portions. The prostatic portion [pars prostatica] (fig. 1024) extends almost vertically downward from the neck of the bladder, traversing the substance of the prostate gland. In its proximal part there is on its posterior wall a median longitudinal ridge, the crista urethralis, which below dilates into an oval enlargement, the colliculus seminalis (figs. 1015, 1025), to accommodate which there is a marked Fig. 1025. — The Male Urethra, cleft anteriorly to show the Mucous Coat. Ureter , -^r * ^ Section of bladder Internal urethral onfice Openings of prostatic glands' Prostatic utricnlus '^m ©j^ Follicular glands of dorsal wall — VmL ;. ' Bulbo-urethral gland Septum of penis Section of prostate Colliculus seminalis Ejaculatory duct Openings of prostatic glands "7 Membranous uerthra Section of corpus cavernosum penis Orifice of bulbo-urethral gland Section of corpus cavernosum penis '^ ^ 1' Bulbous portion of urethra Mucous membrane Fossa navicularis External urethral orifice widening of the lumen of the urethra in this part of its course. At the centre of the colliculus there is an elongated opening of a pouch of varying depth, termed the utricnlus prostaticus ("uterus masculinus"), which corresponds to the lower part of the vagina in the female (see p. 1279). Situated one on either side of this are the much smaller openings of the ejaculatory ducts. Owing to the prominence formed by the coUiculus a section of the urethra in this region is somewhat fl-shaped, and at the bottom of the furrows on either side of the median eleva- 1264 UROGENITAL SYSTEM tion are the minute openings of the numerous ducts of the prostate gland (fig. 1025). ^ ^ On its emergence from the prostate gland the urethra at once penetrates the deep layer of fascia of the urogenital trigone and enters the deep perineal inter- space, this portion of its course being known as the membranous portion [pars membranacea]. Its direction is now downward and slightly forward, curving beneath the subpubic ligament, from which it is separated by a plexus of veins and by the fibres of the sphincter urethras membranaceae, which form an almost complete investment for it. The lumen of this part of the urethra is much narrower than that of the prostatic portion, and since it traverses the rather unyielding fasciae of the urogenital trigone it is less dilatable than in other parts of its extent, with the exception of the external orifice. Passing through the superficial layer of fascia of the urogenital trigone the urethra then enters the bulb of the corpus cavernosum urethrae (fig. 1024) and is invested throughout the remainder of its extent by this structure, whence this portion is known as the cavernous portion [pars cavernosa]. In its proximal part this hes in the superficial interspace of the perineum and passes almost directly forward; but more distally, where it enters the body of the penis, it accommodates itself to the position of that organ, which it traverses lengthwise, lying in the mid- line near its ventral surface (fig. 1022). Thus the proximal portion of the cavernous and the whole of the membranous and prostatic portions have a fixed position, whence they are sometimes associated as the pars fixa of the urethra, while the penial portion forms the pars mobilis. On entering the bulb the lumen of the urethra dilates somewhat and in this region has opening into it the ducts of the bulbo-urethral glands (fig. 1025), but as it enters the body of the corpus caver- nosum it diminishes again and maintains a uniform diameter throughout the extent of that structure. When it reaches the glans penis it undergoes another dilation, which is known as the fossa navicularis (fig. 1025), beyond which it diminishes to the slit-hke external orifice, situated at the extremity of the glans and forming the least dilatable portion of the entire urethral canal. Throughout the greater part of its extent the cavernous portion of the urethra shows upon its dorsal wall the openings of numerous tubular depressions of the mucous membrane, the urethral lacunm [lacunas urethrales (Morgagnii)]. One of these, the lacuna magna, situated m the mid-dorsal line of the proximal part of the fossa navicularis, has its orifice guarded by a valve-hke fold [valvula fossEe navicularis] of the mucous membrane and is sufficiently large to receive the point of a small catheter. Numerous minute glands [gl. urethrales] open upon the surface of the urethral mucosa. They are most abundant in the anterior wall, but occur also on the sides and floor. ,.„ Dimensions of the urethra.— The entire length of the urethra is somewhat variable in ditterent individuals, the greatest variation being in the length of the pars mobihs. Of the pars fi^a the prostatic portion is 2.5-3.0 cm. in length, the membranous portion about 1.0 cm., and the fixed part of the cavernous portion 6.5 cm., the entire pars fixa having thus a length of some- what over 10.0 cm. (4 in.). The average diameter of the urethra is 5.0-7.0 mm., but it will be noted that the canal presents in its course three dilatations; namely, (1) at the fossa navic- ularis, which begins about 0.5 cm. from the external orifice; (2) the bulb of the corpus caverno- sum urethras; and (3) in the prostatic portion. Furthermore there are two regions in which it is distinctly narrowed; namely, at the external orifice and in the memjjranous portion. While the remaining portions are capable of considerable distention, these are relatively indistensible, the maximum diameter to which they may be dilated being about 10 mm. Arranged in an ascending order according to their capability for distention the parts would have the followmg order: external orifice, membranous portion, penial portion, prostatic portion, bulbar portion. 5. The Prostate Gland The prostate gland [prostata] (figs. 1013, 1019, 1024 and 1025) is a mass of glandular and muscular tissue surrounding the proximal portion of the male urethra, and may, indeed, be regarded as a special development of the wall of this portion of the canal. It is a more or less flattened conical structure whose base [basis prostatse] is in contact with the lower surface of the bladder and the apex [apex prostatse] with the deep fascia of the urogenital trigone. Its anterior surface [facies anterior] is in relation with the symphysis pubis, from which it is separated by the pudendal plexus of veins, and posteriorly [facies posterior] it is separated from the lower portion of the rectum only by some loose connective tissue; laterally it is in relation with the levatores ani, receiving an investment from the endopelvic fascia covering these. i THE FEMALE REPRODUCTIVE ORGANS 1265 The urethra enters the base of the gland near its anterior border and traverses it almost vertically, so that the greater portion of the gland is posterior to the canal. On the posterior surface of the gland is a more or less distinct median vertical groove, which serves to separate the lateral portion as the lateral lobes [lobus dexter et sinister], although the demarcation is merely a superficial one. The groove terminates above in a well-marked notch on the posterior border of the base, and immediately in front of this there is a deep funnel-shaped depression of the surface, which receives the ejaculatory ducts. Beginning at this depression two grooves pass forward and slightly lateralward across the surface of the base, marking off a more or less pronounced median elevation, which constitutes what is termed the middle lobe [lobus medius] (fig. 1024); since this lies beneath the trigone of the bladder behind the internal orifice of the urethra its enlargement may produce more or less occlusion of the latter. Dimensions. — The longest axis of the prostate, which is almost vertical in the erect posture measures 2.5-3.0 cm., the transverse diameter at the base is 4.0-4.5 cm. and the thickness 2.0-2.5 cm. Its iveight is normally 20-25 grms. but in old age it may be double that, its dimensions having correspondingly increased. Structure. — The prostate consists of some 15-30 branched tubular glands imbedded in a matrix of connective tissue, containing a large amount of non-striped muscle tissue and form- ing at the surface of the gland a strong fibro-muscular capsule from which prolongations are contributed to the pubo-vesical ligaments and muscles. The glands, which vary greatly in their development, are outgrowths from the mucous membrane of the urethra, into which their ducts open at the bottom of the grooves that lie lateral to the colliculus seminahs; similarly, the matrix with its muscle tissue is evidently the modified muscular coat of the urethra. Con- sequently there is no distinct demarcation between the wall of the urethra and the substance of the gland, and from the developmental standpoint the gland is to be regarded as the modified wall of the urethra. The facts that the prostate shows a special development at puberty and undergoes more or less extensive degenerative changes with the cessation of the reproductive function, as seen in old age and in castrates, indicate that it is associated physiologically with the reproductive organs. Its secretion is a thin alkaline fluid, which may contain round or elongate, concen- trically layered bodies, measuring 0.3-0.5 mm. in diameter and known as amyloid bodies, although they are really albuminous in chemical composition. They are constantly found in adults in the lumina of the glands and may become calcified. The secretion has been found to have a stimulating effect upon the spermatozoa, and this may be its principal function. Vessels and nerves. — The arterial supply of the prostate is derived from the inferior vesical and middle hemorrhoidal branches of the hypogastric artery. The veins form a rich prostatic plexus in the immediate vicinity of the gland, this being part of the general plexus at the base of the bladder and communicating posteriorly with the seminal plexus and anteriorly with the pudendal plexus. It drains finally into the hypogastric vein. The lymphatics are very abun- dant and form a network on the posterior surface of the gland -from which four principal vessels pass to the hypogastric nodes. The nerves are derived from the hypogastric plexus. 6. The Bulbo-urethral Gl.inds The bulbo-urethral glands [gl. bulbo-urethralis (Cowperi)] or Cowper's glands (figs. 1024, 1025) are two small tubulo-alveolar glands which fie one on either side of the membranous portion of the urethra, imbedded among the fibres of the sphincter urethrse membranacete, between the two layers of fascia of the uro- genital trigone. Each is a rounded body with a diameter of 4.0-9.0 mm. and is drained by a duct [ductus excretorius] which perforates the superficial fascia of the trigone and, entering the substance of the bulb of the corpus cavernosum urethrse, traverses it to open on the floor of the bulbar portion of the urethra after a total course of 3.0-4.0 cm. Nothing is definitely known as to the nature of the secre- tion or the functions of the glands. THE FEMALE REPRODUCTIVE ORGANS The organs of reproduction in the female consist of (1) the ovaries, the essential organs of reproduction; (2) the tubce uterince (Fallopian tubes), which serve as ducts for the conveyance of the ova to (3) the uterus, in which the embryo normally undergoes its development; (4) the vagina, a canal by which the uterus is placed in communication with the e.xterior; and (5) the external genitalia. In addition it will be necessary to consider here the female urethra, although it differs from that of the male in that it serves merely as a passage for the contents of the bladder and does not transmit the reproductive elements. i { 1266 UROGENITAL SYSTEM Fig; 1026. — The Female Organs of Generation. (Modified from Sappey.) (Vagina divided and laid open behind.) Posterior surface of body of uterus Ovarian ligament Ovary Tuba uterina Mesosalpinx Fimbriated extremity of tube Fimbria ovarica Mesometrium Supravaginal zone of cervix External orifice of uterus Vaginal wall, divided and reflected Vagina, anterior wall iG, 1027. — Diagrammatic Sagittal Section of the Broad Ligament. Tuba uterina Mesometriu: Posterior surfac Connective tissue and unstriped muscle (utero-pelvic band) Uterine veins -Uterine artery Ease of ligament THE BROAD LIGAMENT 1267 Broad ligament. — ^The first three of these structures are entirelj^ contained within the true pelvis and are associated with a transverse fold of peritoneum which rises from the floor of the pelvic cavity between the bladder and the rectum, incompletely dividing the cavity into an anterior and a posterior compartment. It is known as the hroad ligament of the uterus [lig. latum uteri] (fig. 1026). The broad ligament appears to extend laterally from the sides of the uterus to the lateral walls and floor of the pelvis, although in reality it extends across the pelvic cavity from side to side and encloses the uterus between the two layers of which it is composed. It is attached to the floor of the pelvis below, where the two layers are reflected, the one upon the anterior wall of the pelvis and the posterior and superior surfaces of the bladder, and the other posteriorly over the floor of the pelvis to the posterior pelvic wall and the rectum, forming the anterior wall of a deep depression between the rectum and uterus, known as the recto-uterine pouch (of Douglas) [excavatio rectouterina (cavum Douglasi)] (fig. 1035). Its lower border also passes upward upon the sides of the pelvis, resting upon the pelvic fascia, but its lateral borders are free, extending between the lateral wall of the pelvis and the extremity of the tuba uterina on each side and forming what are termed the infundibulo-pelvic ligaments. The upper border is also free and con- tains the tuba uterina on either side, and the fundus of the uterus in the midline (fig. 1027). Fig. 1028. — Cross-sections of the Body Illustrating the Development of the Female Urogenital system. A, at Higher Level. B, at Lower Level. Epodpliorou Attached to the posterior layer of the broad hgament a httle below its upper border and therefore projecting into the posterior compartment of the pelvis, there is a horizontal shelf, termed the mesovarium, since it has the ovary attached to its free edge (fig. 1027). The portion of the broad hgament above this is known as the mesosalpinx (salpinx = tuba), while that below istermed the mesometrium (metra= uterus). The remaining structm-es that occur between the two layers of the broad ligament will be described with the organs with which they are associated, but it is to be noted that the ligament in its upper part is broader than the transverse diameter of the pelvic cavity and its sides are accordingly folded back upon the lateral walls of the cavity, following the course of the tuba uterina. The broad ligament is the adult representative of the fold of peritoneum which encloses the embryonic excretory organ, the mesonephros. This is for a time a voluminous organ, projecting under cover of the peritoneum from the dorsal wall of the abdomen and bearing upon its medial wall a thickening, the genital ridge (fig. 1028 A), from which the reproductive gland develops. In the free edge of the peritoneum enclosing it two ducts occur, the Wolffian duct, which is the duct of the excretory organ and becomes the ductus deferens of the male, and the Miillerian duct. With the progress of development the two MuUerian ducts fuse in the lower portions of their course to form the uterus and vagina (prostatic utriculus of the male), while in their upper parts they remain separate and form the tubs uterinae. By this fusion the two peritoneal folds are brought into continuity at their edges, and (the mesonephros de- generating on the formation of the permanent kidney) constitute the broad ligament (fig. 1028 B). This structure therefore contains between its two layers the uterus and the remains of the mesonephros, and has the ovary attached to its posterior surface. In the male what corresponds to the broad hgament fuses with the peritoneum covering the posterior surface of the bladder. i ( 1268 UROGENITAL SYSTEM 1. The Ovaries Form and position. — The ovarie,s [ovaria] are two whitish organs, situated one on either side of the pelvic cavity. Each has somewhat the shape of an almond (fig. 1026). It is attached by one of its edges [margo mesovaricus] to the border of the mesovarium, and since it is along this line of attachment that the vascular and nerve supply enters the substance of the organ, this border is spoken of as the hilus [hilus ovarii]. The opposite border is free [margo liber]. The larger rounded end is directed toward the free extremity of the tuba uterina and hence is known as the tubal extremity [extremitas tubaria], while the other, the uterine extremity [extremitas uterina], is directed toward the uterus; the two surfaces, owing to their topographic relations, are known as the lateral and medial surfaces [facies mediahs et lateralis]. Fig. 1029. — The Female Pelvic Organs Viewed from Above. (Spalteholz.) Sigmoid colon ' ~ Recto-uterine pouch Rectum Ureter \. ;-fflffs?r Recto-uterine fold / Parietal peri- / . / toneum / Ureter ' •/ Suspensory / ligament of / ovary ! Ampulla of tuba / uterina ^ ^i Isthmus of tuba uterina ^Ligamen- tum teres Transverse vesical fold The exact position of the ovary in the pelvis is subject to some variation, but typically it hes almost in a sagittal plane (fig. 1029) against the lateral wall of the pelvis, resting in a distinct depression, the /ossa ovarica, lined by peritoneum and bounded above by the external iliac vessels and behind by the ureter and uterine artery, while beneath its floor are the obturator vessels and nerve. The long axis of the ovary is almost vertical when the body is erect, the tubal pole being upward; the mesovarial border is directed forward and laterally, its free border dorsally and medially while its surfaces look almost laterally and medially. Frequently, however, the uterus is displaced to one side, dragging the uterine extremity of the opposite ovary (by the attachment of the ovarian ligament) toward the mid-plane. The long axis of the ovary thus becomes oblique, approaching more or less the horizontal. The as- cending portion of the tuba uterina rests upon its mesovarial border and the fimbriated mouth THE UTERINE TUBES 1269 of the tube is in contact with its medial surface. When enlarged the ovary may be felt through lateral wall of the vagina and, better, through that of the rectum; and its position with regard to the surface may be indicated by a point midway between the anterior superior spine of the ilium and the symphysis pubis or the opposite pubic tubercle. The position assumed by the ovary is due to its attachment to the edge of the mesovarium and to the upper portion of the broad hgament being broader than the diameter of the pelvis, so that it is folded back upon the lateral walls of the cavity. In addition to its attachment to the broad hgament through the mesovarium, the ovary is also connected to the side of the uterus by the ovarian ligament [hg. ovarii proprium] (fig. 1026), a' band of connective tissue with which numerous non-striped muscle fibres are intermingled. It lies between the two layers of the broad hgament, on the boundary line between the mesosalpinx and the mesometrium, and extends from the uterine pole of the ovary to the side of the uterus. Here it is attached just below the origin of the tuba uterina and above the point of attachment of the round hgament of the uterus, with which it is primarily continuous. Another Hgament, termed the suspensory ligament of the ovary (figs. 1029, 1034), extends laterally between the two layers of the broad hgament from the tubal extremity of the ovary to the pelvic walls, forming the lateral portion of the lower boundary of the mesosalpinx. It is formed by the vessels and nerves (internal spermatic) passing to and from the ovary, and from the point where it meets the lateral pelvic wall it may be traced upward for some distance upon the posterior wall of the abdomen, behind the peritoneum, which it elevates into a more or less distinct fold, whose lateral wall on the right side becomes continuous above with the peritoneum lining the subccecal fossa. Size. — The size of the ovary varies considerably, that of the right side being as a rule somewhat larger than that of the left. The length may be anywhere from 2.5 cm. to 5.0 cm., the breadth about half the length and the thickness half the breadth. Its average weight in the adult is from 6.0 to 8.0 grms., but in old age it may fall to 2.0 grms. Structure. — The ovary is covered by a layer of columnar epithehum which is continuous with the peritoneal epithelium along the line of the attachment of the mesovarium; the ovary consequently is not covered by peritoneum, but is rather to be regarded as a local thickening of the peritoneum. Its substance is a network of connective tissue, in which non-striped muscle fibres also occur, and is known as the stroma. The more central portions of this are largely occupied by blood-vessels but in the cortical portions are multitudes of immature ova, surrounded by their follicle cells [follicuU oophori primarii]; and also numbers of cavities of various sizes, lined with foUicle cells and filled with fluid, each containing an ovum [ovulumj in a more or less advanced stage toward maturity. These are the Graafian follicles [follicuU oophori vesiculosi (Graafi)], and as they ripen they increase in diameter and approach the surface, upon which they may form marked prominences. When mature the follicles burst, allowing the escape of the ovum, scars being thus formed upon the surface of the ovary that are known as corpora albicantia. If, however, the ovum becomes fertilized and pregnancy results the walls of the follicle undergo a remarkable development, forming what is known as a corpus luteum. Epoophoron and paroophoron. — Closely associated with the ovaries are two rudimentary organs situated between the layers of the mesosalpinx and representing remains of the meso- nephros of the embryo. The larger of these is the epoophoron (fig. 1030). It consists of a longi- tudinal duct [ductus epoophori longitudinalis (Gartneri)], lying parallel with the tuba uterina and closed at either extremity, and 10-15 transverse ducts [ductuli transversi], which open into the longitudinal duct. It is the remains of the upper or reproductive portion of the meso- nephros and therefore is the homologue of the epididymis of the male. In addition there is fre- quently to be found in the neighbourhood of the epoophoron and close to the mouth of the tuba uterina one or more stalked, oval cysts, the appendices vesiculosi {hydatids of Morgagni), which may reach the size of a small pea. The other organ is the parobphoron; it is much smaller than the epoophoron and usually disappears before adult life, but when present consists of a small group of coiled tubules, more or less distinct, representing a portion of the excretory portion of the mesonephros. Its equiva- lent in the male is therefore the paradidymis. Vessels and nerves. — The chief artery is the ovarian, which together with the ovarian veins and lymphatics passes to the ovary in the suspensory ligament. An additional blood supply is furnished by the ovarian branch of the uterme artery. The veins follow the course of the arteries. As they emerge from the hilus they form a weU-developed plexus (pampiniform plexus) between the laj'ers of the mesovarium. Unstriped muscle fibres occur in the meshes of the plexus and the whole structure has much the appearance of erectile tissue. The lym- phatics accompany the blood-vessels and terminate in the lumbar nodes. Nerves pass to the ovary with the ovarian artery from the renal and aortic sympathetic plexus. 2. The Titb^ Uterine The tubae uterinse or Fallopian tubes (figs. 1026, 1030) serve to convey the ova to the uterus. They are two trumpet-shaped tubes, structurally continuous 1270 UROGENITAL SYSTEM with the superior angles of the uterus and running in the superior border of the broad hgament (mesosalpinx) to come into relation with the ovaries at their distal extremities. Each tube opens proximally into the uterine cavity and dis- tally communicates witli the pelvic portion of the peritoneal cavity by a funnel- shaped mouth, the ostium abdominale, which under normal conditions is closely applied to the surface of the ovary, so as to receive the ova as they are expelled from the Graafian follicles. Each tube is from 7 to 14 cm. in length and con- sists of a narrow straight portion, the isthmus, immediately adjoining the uterus, followed by a broader, more or less flexuous portion, the mnpulla, which terminates in a funnel-like dilatation, the infundibulum. The margins of the infundibulum are fringed by numerous diverging processes, the fimbria, one of which, the fimbria ovarica, is much longer than the rest and extends along the free border of the mesosalpinx (the infundibulo-pelvic ligament) to reach the tubal pole of the ovary. The course of each tube is at first almost horizontally laterally and backward from its attachment to the uterus, until it reaches the lateral wall of the pelvis and there comes into relation with the uterine extremity of the ovary (figs. 1029, 1034). It then bends at right angles and passes almost vertically upward 1030. — The Broad Ligament and its Contents, seen prom the Front. (After Sappey.) EpoCphoron Ampulla of Fallopian tube Tuba uterina External angle of uterus Fimbriated extremity of tube Fimbria ovarica Round ligament Ovarian ligament Anterior peritoneal lamina along the mesovarial border of the ovary until it reaches its tubal extremity, where it curves downward and backward so that the mouth of the infundibulum and the fimbriae rest upon the medial surface of the ovary. Structure. — The tubas occupy the upper free edge of the mesosalpinx and are therefore enclosed within a peritoneal covering [tunica serosa] except a small strip along their lower surface (fig. 1027), and hence a rupture of one of them may lead to the escape of its contents either into the peritoneal cavity or into the subserous areolar tissue between the two laj'ers of the broad ligament. At the margins of the infundibulum and the borders of its fimbrite the peritoneal epithelium becomes directly continuous with the mucous membrane lining the interior of the tube. The subserous areolar tissue [tunica adventitial in the immediate vicinity of the tube is lax and contains the blood-vessels and nerves by which the tube is supplied; it forms a loose connection between the peritoneum and the muscular wall [timica muscularis] of the tube. This consists of two layers of non-striped muscle fibres, an outer longitudinal and an inner circular one, and reaches its greatest development toward the uterine end of the tube. The inner layer [tunica mucosa] of the tube is hned by a columnar cihated epithelium which is raised into numerous folds, simple in the region of the isthmus, but becoming higher and more complex in the ampulla, where, in transverse sections, the lumen seems to have a lab3Tinthine form. The beat of the cilia is toward the uterus. Vessels and nerves. — The arteries of the tubaj are derived from the ovarian and uterine, each of which gives off a tubal branch, which pass between the two layers of the mesosalpinx, the one medially and the other laterally, and anastomose to form a single stem. The veins accompany the arteries. The lymphatics accompany those from the ovary and fundus uteri and terminate chiefly in the lumbar nodes. The nerves of the ampuUa are given off from the branches passing to the ovary, while those of the isthmus come from the uterine branches. THE UTERUS 1271 3. The Uterus The uterus (fig. 1031) is an unpaired organ, situated between the two layers of the broad ligament and communicating above with the tubse uterinse and below with the vagina. It is pyriform in outhne, although flattened antero-posteriorly (fig. 1032) and it is divided into two main portions, the body [corpus uteri] and the cervix by a transverse constriction, the isthmus. The body is the portion above the isthmus and in adults, especially in women Fig. 1031. — The Posterior Surface of the Uterus. (After Sappey.) ---.__ — Tuba uterina Supra-vaginal cervix External orifice Vaginal wall \ \ ^Edge of peritoneum Cervical attaciiment of vagina who have borne children, is much larger than the cervix, although the reverse is the case in children. In young girls the two parts are about equal in size. The anterior or vesical surface [fades vesicalis] is almost flat (fig. 1032), while the pos- terior or intestinal surface [facies intestinalis] is distinctly convex, the two surfaces meeting in well-marked rounded borders, at the upper extremities of which the tubas uterinse are attached. The superior border which extends be- tween the points of attachment of the two tubse is thick and rounded and forms Fig. 1032. — -Sagittal Section op the Virgin Uterus. (After Sappey.) 'A Internal orifice Canal of cervix Posterior fornix Posterior lip Reflection of peritoneun Anterior lip Anterior forni: External orifice what is termed the fundus uteri. The cavity [cavum uteri] of the body is reduced to a fissure by the antero-posterior flattening of the walls and has a triangular form (fig. 1033), broad above where it communicates on either side with the cavity of a tuba uterina and narrow below where it communicates with the cavity of the cervix, this communication, which corresponds in position with the isthmus, form- ing what is known as the internal orifice [orificium internum] (internal os uteri). The cervix is more cj'lindrical in form, though slightly expanded in the middle 1272 UROGENITAL SYSTEM of its length, and is divided into a suTpravaginal [portio supravaginalis] and a vaginal -portion [portio vaginalis] by the attachment to it of the vagina (fig. 1031). The line of this attachment is obhque, about one-third of the anterior surface of the cervix and about one-half of the posterior surface belonging to the vaginal portion. At the lower extremity of the cervix is the external orifice [orificium externum] (external os uteri), which is round or oval before parturition has taken place and is bounded by two prominent labia, anterior and posterior, the anterior one [labium anterius] being shorter and thicker than the posterior [labium pos- terius] and reaching a lower level (fig. 1032). In women who have borne children the external orifice assumes a more slit-like form and the labia become notched and irregular. The cavity of the cervix, known as the canal of the cervix [canaHs cervicis], is fusiform in shape, and extends from the internal to the external orifice. On its anterior and posterior walls are folds known as the plicce palmatce (fig. 1033), consisting of a median longitudinal ridge from which shorter elevations extend laterally and slightly upward; these are most distinct in young individuals and are apt to become obliterated by parturition. Fig. 1033. — Frontal Section of the Vihgin Uterus. (After Sappey.) Uterine wall Cavity of body Internal orifice Uterine wall : with plicEe palmatse External orifice Vaginal wall Position and relations. — The direction of the axis of the uterus is apparently variable within considerable limits, not only in different individuals, but also in any one individual in correspondence with the degree of distention of the bladder anteriorly and the rectum posteriorly. In what may be regarded as the typical condition (fig. 1034) the external orifice lies at about the level of the upper border of the symphysis pubis and in the plane of the spines of the ischia. From this point the axis of the cervix is directed upward and slightly forward, the lower level of the anterior labium being thus brought about. The entire uterus is, accordingly, anteverted, and, furthermore, the body is bent forward (anteflexed) upon the cervix at the isthmus, the axis of the two portions making an angle, open anteriorly, of from 70° to 100°. Frequently, also, the body is sHghtly in- clined either to the right or to the left. The anterior surface of the uterus rests upon the upper and posterior surfaces of the bladder (fig. 1029), from which the body is separated by the utero-vesical pouch of peritoneum. The anterior layer of the broad ligament as it passes over the anterior surface of the uterus forms the posterior wall of this pouch and is reflected forward to the superior surface of the bladder at about the level of the isthmus (fig. 1034), so that the whole of the anterior wall of the cervix is below the floor of the pouch and is separated from the posterior surface of the bladder only by connective tissue. Posteriorly, however, the peritoneal covering of the uterus, which here forms the anterior wall of the recto-uterine pouch, e.xtends down as far as the uppermost portion of the vagina and consequently invests the entire surface of the uterus, whose convex posterior wall is thus separated from the rectum by the recto-uterine pouch (figs. 1029, 1035). Coils of the small intestine rest upon the posterior surface of the body and may also be inter- posed between the cervix and the rectum. An important relation is that of the ureters to the cervix, these ducts, as they pass to the bladder, running parallel with the cervix at a distance of from 8 to 12 mm. from it. Ligaments. — The broad ligament between whose layers the uterus is situated has already been described (p. 1267). In addition there is attached to each border THE UTERUS 1273 Fig. 1034 — Mid-sagittal Section of the Female Pelvis (Spalteholz.) Hypogastric artery , Hypogastric vein Promontory / / Infundibulum of tuba uterina Ureter Parietal pentoneum Suspensory ligament of ovary External iliac vein Ovary Ampulla of tuba utenna Ovarian ligament Fundus uteri \ Ligamentum teres \ Transverse fold of \ \ bladder >. \ Vertex of bladder v \ \ Middle umbilical \ \ ligament Recto-uterine fold Urach Symphysis pubis Labium maju Body of uterus Labium minus External orifice of urethra / Urethra Internal orifice of urethra Orifice of vagina Rectum Posterior labii External orifice of uterus Anterior labium Hymen Anus Vagina Vesico-uterine pouch Vestibule Fig. 1035. — Section of the Pelvis showing the Ligaments of the Uterus. Symphysis Prevesical fat Bladder-waU Obturator inter nus Obturator fascia Subperitoneal tissue Broad ligament Peritoneum Sacro-tuberous ligament Utero-sacral ligament running forward into recto-uterine Ugament Vesical cavity Peritoneum of utero- vesical pouch Utero-vesical ligament Broad ligament Recto-uterine pouch of Douglas '^^5o ] ^^^^®^® 1274 UROGENITAL SYSTEM of the uterus, immediately below the point of attachment of the ovarian ligament, the ligamentum teres (round ligament) (fig. 1030), which is a fibrous cord con- taioing non-striped muscle tissue. It extends downward, laterally and forward between the two layers of the mesometrium toward the abdominal inguinal ring, and, traversing this and the inguinal canal, it terminates in the labium majus by becoming continuous with its connective tissue. It is accompanied by a funicular branch of the ovarian artery and a branch from the ovarian venous plexus, and in the lower part of its course by a branch from the inferior epigastric artery, over which it passes as it enters the abdominal ring. In its course through the inguinal canal it is accompanied by the iho-inguinal nerve and the external spermatic branch of the genito- femoral. The utero-sacral ligaments are flat fibro-muscular bands which extend, one on each side, from the upper part of the cervix uteri to the sides of the sacrum op- posite the lower border of the sacro-iliac articulation. They produce the recto- uterine folds (fig. 1029) of peritoneum, which form the lateral boundaries of the mouth of the recto-uterine pouch (of Douglas) and their muscle fibres [m. rec- touterinus] are continuous at one extremity with the muscular tissue of the uterus and at the other with that of the rectum. Structure. — The portion of the broad ligament that invests the uterus forms the serous covering [tunica serosa] of the organ and is sometimes termed the perimetrium. Over the fundus and the greater portion of the body it is thin and firmly adherent to the subjacent muscular substance of the uterus, so that it cannot readily be separated from it. Over the posterior surface of the cervix and the lower part of the anterior surface of the body, however, it is thicker, and is separated from the muscular substance by a layer of loose connective tissue, the para- metrium, which also extends upward along the sides of the uterus between the two layers of the broad hgament, with whose subserous areolar tissue it is continuous. Owing to this disposition of the parametrium the whole of the cervix may be amputated without encroaching upon the peritoneal cavity. The main mass of the uterus is formed by the muscle tissue [tunica muscularis] or myome- trium, whose fibres have a very complicated arrangement. Two principal layers may be distinguished, an outer, wealv one, composed partly of longitudinal fibres continuous with those of the tub® uterinje, and of the round and utero-sacral hgaments, and a much stronger inner one, whose fibres run in various du-ections and have intermingled with them in the body of the uterus large venous plexuses. The inner surface of the myometrium is hned by a mucous membrane [tunica mucosa] or endometrium, which has a thickness of from 0.5 to 1.0 mm. and is composed of tissue resembling embryonic connective tissue, bearing upon its free surface a single layer of cihated columnar epithelium. On account of its structure the tissue is rather delicate and friable, and numerous simple tubular glands, which open into the cavity of the uterus, traverse its entire thickness. In the cervix the mouths of some of the glands may become occluded, produci^g retention cysts, which appear as minute vesicles projecting from the surface between the plicse palmatae; they are known as ovula Nabothi, after the anatomist who first described them. Vessels and nerves. — The principal artery of the uterus is the uterine, whose terminal portion ascends along the lateral border of the uterus in a tortuous course through the para- metrium, giving off as it goes lateral branches to both surfaces of the uterus. Above, it anasto- moses with the ovarian artery, which thus forms an accessory source of blood supply during pregnancy. The veins form a plexus that is drained by the ovarian and uterine veins, a com- munication with the inferior epigastric being also made by way of the vein accompanying the round ligament. The lymphatics from the greater portion of the body pass to the iliac nodes: those of the fundus accompany the ovarian vessels to the lumbar nodes. A vessel also accompanies the round hgament to terminate in one of the superficial inguinal nodes. The lymph-vessels from the cervix terminate in the external iliac, hypogastric and lateral sacral nodes. The nerves of the uterus pass to it from two sympathetic gangha, situated one on either side of the cervix, whence they are termed the cervical gangha, and forming part of the plexus utero-vaginalis. Branches pass to the ganglia from the hypogastric plexus and also from the second, third and fourth sacral nerves. 4. The Vagina The vagina (fig. 1034) is a muscular, highly dilatable canal lined by mucous membrane, and extends from the uterus to the external genitaUa, where it opens to the exterior. Its long axis is practically parallel with that of the lower part of the sacrum and it therefore meets the cervix uteri at a wide angle which is open anteriorly. Its anterior wall is, accordingly, somewhat shorter than the posterior, measuring 6.0-7.0 cm., while the posterior one is about 1.5 cm. longer. It becomes continuous with the cervix uteri some distance above the lower extremity of that structure, which thus projects into the lumen of the vagina, and there is so formed a narrow circular space between the wall of the vagina and THE VAGINA 1275 the vaginal portion of the cervix uteri. The roof of the space is formed by the reflection of the vagina upon the cervix and is termed the fornix. Owing to the greater length of the posterior wall of the vagina the portion of the circular space below the posterior fornix is considerably deeper than that below the anterior. In its ordinary condition the lumen of the vaginal canal is a fissure, which in transverse section resembles the form of the letter H with a rather long trans- verse bar (fig. 1036). On both the anterior and the posterior wall there is in the median line a well-marked longitudinal ridge, the columna rugarum, which is especially distinct in the lower part of the anterior wall, where it lies immediately beneath the urethra and forms what is known as the urethral carina. From both columnse other ridges pass laterally and upward on either side, forming the rugw vaginales. Both these and the columnee diminish in distinctness with ad- vance in age and with successive parturitions. Toward its lower end the vagina traverses the urogenital trigone, being much less dilatable in this region than elsewhere, and it opens below into the vestibule of the external genitalia. Its orifice is partially closed by a fold of connective tissue, rich in blood-vessels, and lined on both surfaces by mucous membrane. This membrane, known as the Fig. 1036. — Horizontal Section of Vagina and adjacent Structures. (After Henle.) hymen, has usually a somewhat semilunar form, surrounding the posterior border of the orifice, but it may take the form of a circular curtain pierced by one or several apertures. It varies greatly in strength and development and although it is nearly always ruptured by the first act of sexual congress, it may remain unbroken until parturition. Rarely it takes the form of a complete imperforate curtain and may necessitate a surgical operation at the commencement of the menstrual periods. After rupture the remains of the hymen persist as small lobed or wart-like structures, the carunculoe hymenales, around the vaginal orifice. Relations. — The uppermost part of the posterior wall of the vagina is in relation with the peritoneum forming the floor of the recto-uterine pouch (of Douglas), but elsewhere the canal is entirely below the floor of the peritoneal cavity. Posteriorly it rests almost directly upon the rectum (flg. 1036), and the contents of that viscus may be readily felt through its walls. Anteriorly it is in intimate relation with the urethra and the posterior wall of the bladder (figs. 1034, 1036), while laterally it is crossed obliquely in its upper third by the ureters as they pass to the base of the bladder, and in its lower two-thirds by the edges of the anterior portion of the levatores ani. The duct of Gartner, the remains of the lower portion of the Wolffian duct, may occasionally be found at the side of the 1276 UROGENITAL SYSTEM upper half of the vagina as a minute tube or fibrous cord. The external orifice is surrounded by the fibres of the bulbo-cavernosus muscle, which may be re- garded as forming a sphincter {s-phinder vagince) . Structure. — The wall of the vagina is formed mainly of non-striped muscle tissue, whose fibres are indistinctly arranged in two layers, an outer longitudinal and a less distinct inner circular one. Above, this tissue is continuous with that of the cervix uteri, as is also the mucous membrane which lines the lumen. This differs from that of the cervix in having a stratified squamous epithelium and in being destitute of glands. Vessels and nerves. — The arteries of the upper part of the vagina are derived from the vaginal branch of the uterine; its middle portion is supplied by a vaginal branch from the inferior vesical and its lower part by the middle hssmorrhoidal and internal pudendal. The veins form a rich plexus on the surface and drain into the hypogastric vein. The lymphalics are very numerous and drain for the most part to the hypogastric and lateral sacral nodes; some of those from the lower portion of the canal joining with those from the external genitalia to pass to the inguinal nodes. The nerves passing to the vagina are derived from the utero-vaginal and vesical plexuses. 5. The Female External Genitalia and Urethra The female external genitalia [pudendum muliebre] (vulva) present an elon- gated depression, occupying the entire perineal region and bounded laterally by Fig. 1037. — The External Genitals op the Female. Corpus clitoridis Labium majus Labium minus Fossa navicularis — ~ Frenulum labiorum pudendi Posterior commissure two folds of integument, the labia majora (fig. 1037). These anteriorly are continued into the mojis pubis, an eminence of the integument over the symphysis pubis due to a development of adipose tissue. The medial surfaces of the two labia are normally iii contact, the fissure between them being termed the rinia pudendi, and where they meet anteriorly and posteriorly they form the anterior and posterior commissures [commissura labiorum anterior et posterior]. Just anterior to the latter is an inconstant transverse fold, the frenuhim labiorum pudendi ("fourchette") (fig. 1037). The mons and the outer sm-faces of the labia are covered by short crisp hairs, but tlie medial surfaces of the labia are smooth, possessing only rudimentary hairs, but beset with large sebaceous and sudoriparous glands. The interior of the labia is occupied by a mass of fat tissue in which the distal extremity of the round ligament of the uterus breaks up. FEMALE EXTERNAL GENITALIA 1277 Within the depression bounded by the labia majora is a second pair of integu- mental folds, the labia yninora (fig, 1037), which difTer from the labia majora in being destitute of hairs and fat. They are usually concealed by the labia majora, but are sometimes largely developed and may then project through tlie rima pudendi, assuming a dried and pigmented appearance. The labia minora divide and unite anteriorly over the distal extremity of the clitoris, form- ing the prcepuiiuni cliioridis in front of the clitoris, and the frenulum diloridis behind it. Pos- terior to this they diverge and reach their greatest height, gradually diminishing as they pass backward to terminate in a slight, inconstant, transverse fold, the frenulum labiorum pudendi, situated just anterior to the posterior commissure of the labia majora. Anterior to the frenu- lum is the fossa navicularis of the vestibule. The vestibule. — The space between the two labia minora is termed the vestibule, and into its most anterior portion there projects the extremity of an erectile organ, the clitoris (fig. 1037), which is comparable to the penis of the male. It is, however, relatively small and is not perforated by the urethra, which lies below it. It is composed of two masses of erectile tissue, the corpora cavernosa clitoridis, which differ from the corresponding structures of the penis only in size. They are attached posteriorl3^ to the rami of the pubis by the cr^ira clitoridis (fig. 1038), and as they pass forward they converge and meet together to form the body of the organ, which, beneath the symphysis pubis, bends sharply upon itself Fig. 1038. — Diagrammatic Repkesentation of the Pehin^al Structures in the Female. Glans clitoridis Pars intermedialls Mucous membrane of vestibule Urethral orifice Ischio-pubic arch Bulbo-cave covering bulb' vestibuU Inferior layer of uro genital trigone Bulbus vestibuli Greater vestibular (Bartholin's) gland External sphincter < and passes posteriorly beneath the anterior commissure of the labia majora. Distally the corpora cavernosa abut upon another mass of erectile tissue, which fits hke a cap over their extremities; it is formed by an anterior prolongation of the bulbi vestibuli and is termed the glans clitoridis, being comparable to the glans penis, from which it differs only in not being perforated by the urethra. A short distance posterior to the glans chtoridis is the opening of the urethra [orificium urethrse externum], situated upon the summit of a slight papilla-like elevation. Lateral to this orifice are sometimes found the openings, one on either side, of two elongated slender ducts, the 'paraurethral ducts (ducts of Skene). Still more posteriorly is the external orifice of the vagina [orificium vaginae], partially closed in the virgin bj^ the hymen. Lateral to this, in the angles between the hymen and the labium minus on either side, is the opening of the greater vestibular gland, while the lesser glands open at various points on the floor of the vestibule, sometimes at the bottom of more or less distinct depressions. Beneath the floor of the vestibule and resting upon the superficial layer of the urogenital trigone are two oval masses of erectile tissue, the hidbi vestibuli (fig. 1038), homologous with the corpus cavernosum urethriE of the male. They con- sist principally of a dense network of anastomosing blood-vessels, enclosed within 1278 UROGENITAL SYSTEM a thin investment of connective tissue. From the main mass of each bulbus a slender prolongation, the pars intermedia, extends anteriorly past the side of the urethra, to form the glans clitoridis. The greater vestibular glands [gl. vestibularis major (Bartholini)] or glands of Bartholin (fig. 1038) represent the bulbo-urethral glands of the male. They are two small, compound tubular glands, situated one on either side immediately posterior to the bulbi vestibuli. The single duct of each gland opens on the floor of the vestibule in the angle between the hymen and the orifice of the vagina and a httle posterior to the mid-transverse line of the latter. Numerous small tubular glands occur in the integument forming the floor of the vestibule; they are termed the lesser vestibular glands and are especially developed in the interval between the urethral and vaginal orifices. The muscles of the female external genitalia (fig. 1038) correspond to the perineal muscles of the male (see Section IV). There are two transverse perineal muscles, which have the same relations as in the male, and two ischio-cavernosi, which are related to the crura clitoridis just as those of the male are to the crura penis. The bulbo-cavernosi, however, present somewhat different relations, each being band-like in form, arising from the central point of the perineum and ex- tending forward past the orifice of the vagina, over the greater vestibular gland and the bulbus, to form with its fellow of the other side a tendinous investment of the body of the clitoris. The two muscles act as a sphincter to the vagina and are sometimes termed the sphincter vagince. The urethra. — The urethra of the female [urethra muKebris] (figs. 1034, 1036) corresponds only to the prostatic and membranous portions of the male and is a relatively short canal, measuring from 3.0 to 4.0 cm. in length. At its origin from the bladder it lies about opposite the middle of the symphysis pubis and thence extends downward and slightly forward to open into the vestibule between the glans clitoridis and the orifice of the vagina. Its posterior wall is closely united with the anterior wall of the vagina, especially in the lower part of its course where it forms the urethral carina of the vaginal wall; laterally and anteriorly it is sur- rounded by the pudendal plexus of veins. Structure. — Its walls are very distensible, and are lined by a mucous membrane with numerous longitudinal folds, one of which on the posterior side is more prominent and is termed the crista urethralis. The mucosa contains numerous small glands [gl. urethrales], a group of which on each side is drained by the inconstant ductus paraurethrahs. External to the loose submucosa is a sheet of smooth muscle, whose fibres are arranged in an outer circular and an inner longitudinal layer, a rich plexus of veins lying between the two and giving the entire sheet a somewhat spongy appearance. The circular fibres are especially developed at the vesical end of the canal, forming there a strong sphincter, and striped muscle fibres, derived from the bulbo-cavernosus, form a sphincter around its vestibular orifice. The female urethra differs from that of the male in not being enclosed within a prostate gland; but what are probably rudiments of this structure are to be found in the groups of urethral glands drained by the paraurethral ducts. Vessels and nerves. — The arteries supplying the external female genitalia are the internal and external pudendals, and the veins terminate in corresponding trunks. The lymphatics, which are very richly developed, drain for the most part to the inguinal nodes; those from the urethra pass to the iliac nodes. The nerves are partly sympathetic and partly spinal; the former are derived from the hypogastric plexus, the latter principally from the pudendal, the anterior portions of the labia majora being supplied by the iUo-inguinal and the external spermatic branch of the genito-femoral. DEVELOPMENT OF THE REPRODUCTIVE ORGANS It has already been pointed out (p. 1267) that during development a transitory excretory organ, the mesonephros or WolfEan body, reaches a high degree of development, and its duct, the Wolffian duct, opens into a cloaca or common outlet for the intestinal and urinary passages. The mesonephros forms a strong projection from the posterior wall of the abdomen into the body cavity, and on the medial surface of the peritoneum which covers it a thickening appears which is termed the genital ridge. The upper part of this ridge becomes the ovary or testis, as the case may be, while the remainder of it becomes the ovarian and round ligaments in the female and the gubernaculum testis in the male. As the ovary or testis develops the tubules of the upper part of the Wolffian body enter into relation with it, forming, indeed, in the case of the testis, a direct union with the semin- ferous tubules. The Wolffian body then becomes divisible into a reproductive and an excretory portion, and, when the metanephros or permanent kidney develops, the latter portion degene- rates, leaving only a few rudiments, such as the paroophoron in the female (p. 1269) and the vas aberrans and paradidymis (p. 1257) in the male. The reproductive portion also becomes much reduced in the female, persisting as the tubules of the epoophoron (p. 1269), but in the male it DEVELOPMENT OF THE REPRODUCTIVE ORGANS 1279 forms the lobules of the epididymis and serves to transmit the spermatozoa to the Wolffian duct. In addition to the Wolffian duct, a second duct, the Miillerian, occurs in connection with the genito-urinary apparatus, and, like the Wolffian duct, it opens below into the cloaca. The history of the two ducts is very different in the two sexes. In the male the Wolffian duct persists to form the vas deferens, of which the seminal vesicle is an outgrowth and the ejaculatory duct the continuation, while the MilUerian duct degenerates, its lower end persisting as the prostatic utriculus and its upper end as the appendix of the epididymis. In the female, on the contrary, it is the Miillerian duct which persists, its lower portion fusing with the duct of the opposite side to form the vagina and uterus, while its upper portion forms the tuba uterina. Inhibition of the fusion of the lower ends of the two Miillerian ducts gives rise to the bihorned or divided uteri, or the bilocular uteri and vaginse which occasionally occur. The Wolffian duct in the female almost completely disappears, persisting only as the longitudinal tube of the epoophoron and as the rudimentary canal of Gartner (p. 1275) . With the degenera- tion of the mesonephros the peritoneum which covered it becomes a thin fold, having in its free edge the Miillerian duct and, on the fusion of the lower ends of the ducts, the two folds also fuse and so give rise to the broad hgament. Fig. 1039. — Development of the Reproductive Organs. Epoophoron Wolffian body Epididymis SinuB pocu- laris INDIFFERENT The developmental relations of the male and female organs may be seen from figure 1039 and also from the following table: — Female Ovary f Ovarian ligament , Round ligament Epoophoron Paroophoron Longitudinal tubule of epoophoron Canal of Gartner Uterine (Fallopian) tube Uterus Vagina Genital ridge Wolffian body Wolffian duct Miillerian duct Testis Gubernaculum testis Head of epididymis -j Paradidymis 1 I Vas aberrans / j Body and tail of epididymis i Ductus deferens ! Ejaculatory duct f Appendix of epididymis (?) Prostatic utriculus The development of the external organs of generation in the two sexes presents a similar differentiation from a common condition. The division of the cloaca to form a urogenital sinus and the terminal part of the rectum has already been noted (p. 1253). In the floor of the sinus, to the sides of and above the urethral orifice, erectile tissue develops, forming a genital tubercle. An outpouching of that portion of the anterior abdominal wall to which the round ligament of the uterus or the gubernaculum was attached occurs to form the genital swellings. 1280 UROGENITAL SYSTEM lying one on either side of the sinua, and medial to these a pair of folds develop at the borders of the sinus, enclosing the genital tubercle above and forming the genital folds. This condition practically represents the arrangement which persists to adult life in the female. The genital tubercle becomes the clitoris, the genital swellings the labia raajora, the genital folds the labia minora, and the urogenital sinus, into which the urethra and Miillerian ducts (vagina) open, is the vestibule. In the male tlie development proceeds farther. The genital tubercle elongates to form the penis, and the free edges of the genital folds meet together and fuse, closing in the urogenital sinus and transforming it into the cavernous portion of the urethra, thus bringing it about that the male urethra subserves both reproductive and urinary functions. The genital swellings also meet and fuse together below the root of the penis, form- ing the scrotum. The homologies of the parts in the two sexes may be seen from the following table: — Male Female Urogenital sinus Cavernous portion of urethra Vestibule Genital tubercle Penis Chtoris Genital folds Integument and prepuce of penis Prepuce of clitoris and labia minora Genital swellings Scrotum Labia majora Inhibition of the development of the parts in the male or their over-development in the female will produce a condition resembling superficially the normal condition of the opposite sex, and constituting what is termed pseudo-hermaproditism; or a failure of the genital ridges to fuse may result in what is known as hypospadias, the cavernous portion of the urethra being merely a groove in the under surface of the otherwise normal penis. References for the Urogenital System. A. Urinary tract. {General, incl. literature to 1900) Disse, in von Bardeleben's Handbuch; {Renal blood-vessels) Brodel, Proc. Ass'n Amer. Anatomists, 1901; {Renal tubules) Huber, Amer. Jour. Anat., vol. 4; Peter, Die Nierenkanalchen, etc., Jena, 1909; {Topog- raphy of female ureter) Tandler u. Halban, Monatschr. Geburtsh. u. Gynak., Bd. 15. B. Male reproductive tract. {General, incl. literature to 1903) Eberth, in von Bardeleben's Handbuch; {Histology and development) von Lichtenberg, Anat. Hefte, Bd. 31; Hill, Amer. Jour. Anat., vol. 9; {Prostate) Bruhns {lymphatics) Arch. f. Anat. u. Entw., 1904; Ferguson {Stroma) Anat. Rec, vol. 5; Thompson (topography) Jour. Anat. and Physiol., vol. 47; {External genitals) Forster, Zeitschr. f. Morph. u. Anthrop., Bd. 6. C. Female repro- ductive tract. {General, incl. literature to 1896) Nagel, in von Bardeleben's Handbuch; Waldeyer, Das Becken, Bonn, 1899; {Lymphatics) Bruhns, Arch, f. Anat. u. Entw., 1898; Polano {ovary) Monatschr. Geburtsh. u. Gynak., Bd. 17; {Nerves) Roith, Arch. f. Gynak., Bd. 81; {Histology, ovary) von Winiwarter, Anat. Anz., Bd. 33; {Develop?/ient, uterus) Hegar, Beitr. z. Geburtsh. u. Gynak., Bd. 13; Stratz, Zeitschr. Geburtsh. u. Gynak., Bd. 72; {Lig. eres) Sellheim, Beitr. z. Geburtsh. u. Gynak., Bd. 4, 1901. SECTION XII THE SKIN, MAMMAEY GLANDS AND DUCTLESS GLANDS Rewritten for the Fifth Edition By ABRAM T. KERR, B.S., M.D. PBOPESSOK OP ANATOMY IN THE UNIVERSITT MEDICAL' COLLEGE THE SKIN THE covering which envelops the whole external surface of the body is known as the common integument [integumentum commune]. This con- sists of the cutis or skin proper and of appendages, the hair, nails, and skin glands. The cutis is composed of a superficial epithelial layer, the epidermis, derived from the ectoderm, and a deep connective tissue layer developed from the mesoderm and divided into a superficial part, the corium, and a deeper part the tela subcutanea (figs. 1040, 1041). The subcutaneous tela is not usually con- sidered as a part of the skin in a restricted sense, but as a superficial fascia, which name is often applied to it. Fig. 1040. — Magnified Section of the Thickened Skin of the Palm op the Hand. X 6 Corpus papillare , l!^,_^ Retinaculum Tela Subcutanea The skin forms an encasement for the entire body broken only in the regions where it merges with the mucous membranes. It serves not only as a direct physical protection to the under- lying structures, but also, through its function as an organ of touch and of general sensibility, it indirectly protects the body by the action of the special end organs and peripheral termina- tions of the sensory nerves which thus bring the body into relations with its surroundings. Through the radiation and conduction of heat to and from the blood circulating in it, through the amount of secretion of its glands and the evaporation from its surface, the skin forms the principal organ for the regulation of the bodily heat. By means of the action of its sweat and sebaceous glands it possesses an important secretory function. It has also a minor role as an organ of respiration and absorption. The surface area of the skin corresponds approximately to the surface of the body and naturally varies with the size of the individual. It has been variously estimated at from 10,500 to 18,700 sq. cm. for a medium-sized adult male. 81 1281 1282 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS The aperturae cutis are holes through the skm where it joins with the mucous membrane, usually without sharp line of demarcation, at the nares, the rima oris, the anus, and the external urethra in the male, and at the vaginal vestibule in the female. Owing to the fact that the skin extends beyond the surface at the aperaturse cutis, and covers the major and minor pudendal labia, and the prepuce and extends into the external acoustic canal, the surface area is slightly greater than the surface of the body. The thickness of the skin varies in different regions of the body and also in different individuals. The mean thickness is between 1 and 2 mm., the extremes ranging from .3 to 4.0 mm. or more. This is exclusive of the subcutaneous tela. The thickness appears to be in direct proportion to the amount of friction and pressure to which the part is subjected. Thus it is thicker on the dorsal than on the ventral surface of the trunk and neck, and on the flexor than on the extensor surfaces of the hands and feet. Otherwise it is thicker upon the extensor than on the flexor surface of the extremities. 1041. — ^Vertical Section prom the Sole of the Foot of an Adult. Str.lir.) X 25. (Lewis and Duct of a sweat gland — stratum corneum ,^ Stratum lucidum Stratum granulosura stratum germinativum Coil of a sweat gland - [ Corpus I papillare ■ Tela subcutanea Fat tissue ■ — fe^rj^ '^ ^^^^fe.b:^i:. The thickness of the skin is least upon the tympanum and it is also thin upon the eyehds and penis. It obtains a thickness of 3 mm. on the volar surface of hands and plantar surface of the feet and gains a thicliness of about 4 mm. on the cephalic part of the back and dorsal surface of the neck. It is thinner in the aged than in the adult, thicker in men than in women, and in the same sex is subject to much individual variation depending upon exercise, occupation, etc. The vascularity of the skin also influences its thickness. Over most of the surface of the body the skin is elastic and so loosely attached that it may be stretched to a greater or less extent. The elasticity varies in different individuals. Closely associated with the elasticity is the manner of attachment of the skin to underlying structures. This varies somewhat according to the tissues which are covered but the great motility is due in the main to the very oblique arrangement of the connective tissue and elastic fibres of the deeper layers of the skin; the fixity to the more vertical arrangement of these fibres. An understanding of the looseness and elasticity of the skan is of much practical im- portance to the surgeon in certain operations. When the [traction is slow as over a slow-growing tumour, or over the abdomen and breasts in pregnancy, the skin may be stretched to a very considerable degree. In these cases there are often produced short parallel reddish streaks which when the stretching is reheved are re- THE SKIN 1283 placed by whitish, silvery lines, striae or lineae albicantes, due to atrophy of the tissues. In spite of this the skin usually retains enough elasticity to contract gradually to its former extent as it does immediately after moderate stretching. In most parts of the body the attachment is loose so that the skin is movable and may be pinched up into folds. In some places the attachment of the skin is firm and there is no slip- ping of the skin over underlying parts, as on the glans penis. In some other parts the motion is very limited as in the scalp and the volar surface of the hands and the plantar surface of the feet. • Fig. 1042. — Finger Print (Natural Size) Showing Crist* and Sulci. The colour of the skin varies greatly. It may be white, yellow, black, red, or any of the shades of these colours, and, according to the colour, the races of man- Idnd have been roughly divided. The colouration is due partly to pigment and partly to the blood within the cutaneous vessels. The amount of pigment varies with race, age, sex, and with exposure to the sun and air. In the white races the skin of the child is a pinkish white, tending to become dead white in the adult and yellowish in the aged, and it is normally more pigmented in certain regions, such as the axillary region, the scrotum, the vulva, and the mammary areola. Fig. 1043. — Diagram Showing the Arrangement of the Principal Crist.® of the Thumb The colour of the white, yellow, red, and black races is not produced by the climate, as we find different races existing under the same climatic conditions and the same coloured race under different conditions of climate. Each race presents several variations of colour; for example, in the white race we distinguish a blonde, a brimette, and an intermediate tj'pe. Anthropolo- gists distinguish twenty to thirty different shades of colour in the skin. In blondes of the white race under the action of strong sun light the skin passes from a rose white to a brick red or becomes pigmented in spots, freckles. In the first case the pigment in the skin is not increased to any great extent but the skin is affected by a superficial inflammation, erythema, associated with exfoliation and often with the formation of blisters. In brunettes of the white race the sun burns the skin a dark yellowish or reddish brown, the degree of pigmentation here being increased and is spoken of as tan. The colouration is onlj' temporary and diminishes on withdrawal from exposure. The sun darkens the skin in the yellow races also. In the newborn of the black races the skin is of a reddish colour, since the pigment although developed to some extent is at birth obscured by overlying opaque cells which later become transparent. The newborn of the yellow races are also hghter than their parents. In white races the shade of the skin is clearer on the ventral surface of the trimk and on the flexor surface of the extremities. In the black races the volar surface of the hands and the plantar surface of the feet as well as the sides of the digits are less deeply pigmented than the rest of the body. The colour of the skin is greatly influenced by the blood in its deeper layers which during life gives it a more or less distinctly reddish tinge, varying directly with the vascularity and inversely with the thickness of the epidermis. Absence i 1284 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS of the normal pigment is a not uncommon congenital anomaly producing albinism or leuko- derma. It may affect all the skin structures or it may be partial. The skin presents certain elevations and depressions due to the fact that it follows more or less closely the contour of the underlying structures, but in addi- tion to this it possesses certain elevations and depressions peculiarly its own. They are found on the skin in various parts of the body. Some are permanent, others only temporary. Large permanent folds which include all the layers of the skin are seen, as the prepuce of the penis and the pudendal labia. The most marked depression is the umbilical fovea. Other conspicuous folds and furrows are seen in the neighbourhood of the lips and eyelids. Certain other less permanent folds and furrows are produced by the action of the joints, joint-furrows, and of the muscles of expression of the skin,*'wrinkles." Fig. 1044.- -From a Photograph op the Superficial Fubhows on the Back of the Hand. (X 1.) Other minute folds and furrows which affect only the epidermis and the super- ficial layer of the corium are seen in various places. These are represented by the numerous fine superficial creases, unassociated with elevations, forming rhom- boidal and triangular figures over almost the whole of the surface of the skin (figs. 1042, 1043). They are especially numerous on the dorsal surface of the hands (fig. 1044). The fine curvilinear ridges [cristse cutis] with intervening furrows [sulci cutis] arranged in parallel lines in groups on the flexor surface of the hands and feet are also of this type. They form patterns characteristic for each individual and permanent throughout life. Fig. 1045. — From a Photograph op the Skin Ridges and Papillae op the Palm op the Hand. Epithelium Completely Removed Above; Partly Removed Below. (X 5.) --^— Corpus papillare corii ";^ Sulci cutis Among the projections are the large permanent folds of skin such as the labia pudendi, the preputium penis, the frenula preputii, clitoridis, and labiorum pudendi, and less marked ridges as the median raphe of the perineum, scrotum and penis, and the tuberculum labii superioris. Of a somewhat different sort are the touch pads (toruli tactiles] of the hands and feet. Among the larger depressions in addition to the umbilical fovea, is the coccygeal foveola, and a consider- able num))er of well-marked permanent furrows found in various places, such as the nasolabial and mentolabial sulci, the philtrum labii superioris, the infraorbital sulcus, and the infra- and supraorbitial palpebral sulci. There are numerous articular furrows on both the flexor and extensor surfaces produced by the action of the joints, and associated with intervening folds of skin, particularly on the dorsal surface. They are especially noticeable on the hands. Varia- tions of the palmar joint sulci are due to variations in opposition of the thumb and the use of the fingers and the relative arrangement of the thumb and fingers and joints. They are of THE EPIDERMIS 1285 especial medical and surgical importance as indicating topographically the position of the joints, their relation to which has been recently made clearer by means of the X-ray. The folds and furrows brought about through the action of the skin muscles run at right angles to the muscle fibres and are more or less transitory at first but become more permanent through repeated or long-continued action. They are represented by the wrinkles of the fore- head, the lines of expression of the face, the transverse wrinkles of the scrotum and the radiating folds around the anus. The more superficial cristae cutis and sulci cutis are arranged in groups within and around the touch pads, on the volar surface of the hands and the plantar surface of the feet (figs. 1042, 1043). The crista; of each group are parallel. They correspond to the rows of papillfe of the corium. Because the patterns of the crista; and sulci are characteristic for the individual, and per- manent from youth to old age, they have been classified in a number of types and are important medioolegally as a means of identification. The various systems of classification are based upon the arrangement over the distal phalanges of the fingers and make use of (1) a transverse ridge which is parallel with the articular plicae (2) a curved ridge with its convexity distally and more or less closely meeting the first, medially and laterally, and (3) the curved and concen- tric ridges between these two (fig. 1043). There are also a great number of minute depressions which mark the points where the hairs pierce the surface and where the glands open. These are popularly known as pores. Under Fig. 1046. — PAPii.i,.ffi: of the Cohium after Maceration. From Retouched Photograph. Epithelium Removed by Maceration. ( X 25.) ^>-Papinee corii the influence of cold and emotion the hair muscles contract and cause a slight elevation of the skin at the point where the hair emerges. This roughened appearance of the skin is popularly known as "goose-flesh." A complex wrinkling of the skin appears in old age, or in the course of exhausting diseases/as a result of loss of elasticity and from absorption of the cutaneous and subcutaneous fat. Rounded depressions called dimples are produced by the attachment of muscle-fibres to the deep surface of the skin, as on the chin and cheek, and are made more evident by the contraction of these fibres. Others are produced by the attachment of the skin by fibrous bands to bony eminences, as the elbow, shoulder, vertebrse, and posterior iliac spines. They are best seen when the sub- cutaneous adipose tissue is well developed. The cutis is made up of two layers which are structurally and developmentally markedly different. The superficial ectodermic portion, epidermis, is made up almost entirely of closely packed epithelial cells, the deeper mesodermic part, corium, is formed largely of connective-tissue fibres. The epidermis (cuticle, scarf-skin) is a cellular non-vascular membrane which forms the whole of the superficial layer of the skin and at the great openings through the skin, as the mouth and anus, blends gradually with the mucous mem- brane. It represents from one-tenth to over half the thickness of the skin, in different parts of the body, the usual thickness being .05 to .2 mm., ranging from .03 mm, to nearly 3 mm. The thickness varies also in different individuals. Its deep surface is molded exactly to the underlying corium but its superficial surface fails to reproduce all of the irregularities of the latter. In spite of this close association, blood-vessels never enter the epidermis. Structure of the epidermis. — The cells of the epidermis are packed together in many irregu- lar layers. The deepest cells are soft protoplasmic, somewhat elongated, perpendicular to i 1286 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS the surface of the corium and joined together by fine fibrils; more superficially they become round or polyhedral. These cells together with several more superficial layers form a stratum from which the other cells of the epidermis are developed and which therefore are laiown as the stratum germinativum (Malpighii). The cells in the superficial part of this stratum, in some situations, have a granular appearance forming a layer which is called the stratum granulosum. Superficial to this there is, also only in some places, a layer in which the cells are somewhat indistinct and transparent, and therefore known as the stratum lucidum. This is a transition between the softer and more opaque stratum germinativum and the firmer and more transparent superficial layer formed of large, flattened, dry, horny cells, known as stratum corneum. In general the stratum germinativum is thicker than the stratum corneum. In certain parts as the face, the back, the back of the hands and feet, the two layers are equal in thicloiess. In other regions, as in the volar surface of the hands and plantar surface of the feet, the stratum corneum is much thicker than the stratum germinativum varying from two to three or even five times as thick. This increased thickness of the stratum corneum is not due to pressure alone as it is well marked in the foetus, but it is not improbable that pressure may stimulate the further growth of the cells. Where the papilte of the corium are arranged in rows as on the volar surface of the hands and the plantar surface of the feet, the epidermis is molded to these so as to appear as ridges on the surface, already described as cristse. In most other places the irregularities of the papillae of the corium do not show on the sm-face. At short and regular intervals on the cristse are notches and transverse furrows which mark the openings of the sweat glands. The separation of the epidermis from the corium by the accumulation of serous fluid between the layers is known as a bUster. Sometimes it is only the separation of the superficial layers from the deeper layers of the epidermis. The skin is regenerated after a blister or a wound by growth of the cells of the stratum ger- minativum. It is probable that cells of the superficial layers take no part in this. Therefore in skin grafting the surgeon in order to transplant the cells of the stratum germinativum usually includes all the layers of the epidermis and the extreme tips of the papillae of the corium as shown by the minute bleeding points left on the surface from which the graft has been cut. The pigment which gives the main colour to the skin is caused by the accumulation of pig- ment granules, melanin, in the deepest cells of the stratum germinativum. It does not occur until after the sixth month of foetal life and develops chiefly after birth. The blackness of the skin of the negro depends almost entirely upon this pigment. Pigment granules are also found to a less extent in more superficial cells and sometimes in the corium. Development of the epidermis. — The epidermis is derived from the ectoderm, in early embryos appearing as a double stratum of cells, the superficial layer of which is known as the epitrichium or periderm, the deep layer becomes the stratum germinativum. By multiplica- tion of the deep cells a number of layers are produced and the more superficial cells tend to assume the adult characteristics. At about the sixth month of foetal hfe the epitrichial layer finally disappears. The surface layers are cast off and mixing with the secretion of the cutaneous glands form a yellowish layer over the surface of the skin of the foetus, the vernix caseosa. Growth continues throughout life. New cells are formed in the deeper layers pushing the older cells toward the surface. The character of the cells changes as they approach the surface, the change being quite abrupt at the level of the stratum lucidum. As the form of the cells changes, chemical and physical alterations of their contents occur. In most places the super- ficial cells are represented by thin scales but in the palms and soles the cells are somewhat swol- len. The superficial cells are being constantly thrown off and replaced by deeper ones. The corium (cutis, cutis vera, derma) is a fibrous vascular sh.eath composed of interwoven bundles of connective-tissue fibres intermixed with elastic fibres, connective-tissue cells, fat, and scattered unstriped muscle-fibres. It is traversed by rich plexuses of blood-vessels, lymph-vessels, and nerves, and encloses hair- bulbs and sebaceous and sudoriferous glands. It varies in thickness from .3 mm. to 3.0 mm. or more, usually ranging from .5 to 1.5 mm. It is to this layer that the strength and elasticity of the skin are due and it is also only this layer which when properly cured we know as leather. The superficial layer of the corium is of finer, closer texture, free from fat, and forms a multitude of eminences called papillae corii (figs. 1040, 1045, 1046) which project into corresponding depressions on the deep surface of the epidermis. For this reason this part of the corium although but indistinctly separated from the deeper layer is called the corpus papillare. Some of the papillae contain vessels, others nerves, hence they are known as vascular or tactile papillse. They are very closely set, varying considerably in number in different parts of the body from .36 to 130 to a square millimetre, and it has been estimated that there are about 150 million papilloe on. the whole surface. They also vary greatly in size not only in different regions but in the same region, being from .03 to .2 mm. or more in height. The deeper layer of the corium, the tunica propria (stratum reticulare), is composed of coarser and less compact bands of fibrous tissue intermingled with small fat lobules. The fibrous and elastic tissue is arranged for the most part in intercrossing bundles nearly parallel to the surface of the skin. The bundles running in some directions are usually more strongly developed and more numerous than those in others but the direction of the strongly developed bundles varies in THE TELA SUBCUTANEA 1287 different parts of the body. In general those are best developed which have a direction parallel with the usual lines of tension of the slcin, hence it results that wounds of the skin tend to gape most at right angles to these lines. The bundles take a direction nearly at right angles to the long axis of the hmbs, and on the trunk run obhquely, caudally, and laterally from the spine (figs. 1047, 1048). On the scalp, forehead, chin, and epigastrium, equally strong bundles cross in all directions, and a round wound, instead of being linear as elsewhere, appears as a ragged or triangular hole. The arrangement of the connective-tissue bundles influences the arrangement of the blood-vessels of the skin. The tela subcutanea or superficial fascia is also a fibrous vascular layer which passes as a gradual transition without definite line of demarcation from the deep surface of the tunica propria of the corium to connect it with the underlying structures. Like the tunica propria it is composed of bundles of connective tissue containing elastic fibres and fat, but the bundles are larger and more loosely arranged, and form more distinct cormeotive-tissue septa, which divide the fat, when present, into smaller and larger lobules. Where these connecting strands are especially large and well defined, they are known as re- tinacula. Over almost the whole surface of the body the connective-tissue strands of the tela Figs. 1047 and 1048. — Diagrams Showing the Arbangembnt op the Connective Tissue Bundles of the Skin on the Anterior and Posterior Surfaces of the Body. (After Langer.) are arranged nearly parallel with the surface, and bind the skin so loosely to the parts beneath that it may stretch and move freely over the deeper parts. In some situations the connective- tissue bundles of the tela subcutanea run almost at right angles to the surface and bind the skin firmly to the deep fascia, as in the flexor surface of the hands and feet and in the scalp and face. The quantity of subcutaneous fat varies considerably in different parts of the body. It is, for instance, entirely absent in the penis, scrotum, and eyeUds. When it is abundant, the subcutaneous layer is known as the panniculus adiposus. In some situations, as in the caudal portion of the abdomen and in the perineum, the connective tissue is so arranged that the panniculus may be divided into layers, so that a superficial and a deep layer of the superficial fascia may be recognised. The fat is well de- veloped over the nates, volar surface of the hands and plantar surface of the feet, where it serves as pads or cushions; in the scalp it appears as a single uniform lobulated layer between the corium and the aponeurosis of the epicranial muscle; and on other parts of the surface it is some- what unequally distributed and shows a tendency to accumulate in apparent disproportion in some localities, as on the abdomen, over the symphysis pubis, about the mammse in females, etc. Everywhere except on the scalp it may undergo rapid and visible increase or decrease under the influence of change of nutrition. 1288 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS The amount of elastic tissue mixed with the white fibrous connective tissue of which the corium and subcutaneous tela mainly consist varies in the different parts of the body. It is especially abundant in the deeper layer of the tela over the caudal part of the ventral ab- dominal wall where it forms almost a continuous sheet. Many elastic fibres also accompany the blood-vessels and are mingled with the connective-tissue sheaths around the hairs, the sweat glands, and their ducts. The papillce corii are usually simple cones but some are bulbous at their ends and others have duplicated apices. They may be perpendicular to the surface or oblique, in some places overlapping. Those on the flexor surfaces of the hands and feet are best developed and are arranged in rows so as to form long parallel curvilinear ridges, two of which are grouped together and correspond to one crista on the surface of the epidermis (figs. 1045, 1046). When there are no papillary ridges the papilte are irregularly scattered, shorter, and may disappear in places or be replaced by ridges. The papilliE serve to give a greater surface area to the corium so as to bring a greater number of blood-vessels and nerves into closer relation with the epidermis and thus with the surface of the body. They are best developed where the epidermis is thickest. Thus they are the largest on the flexor surface of the hands and feet and beneath the nails and are smallest on the face, scrotum, and mammEe. The skin, as removed in the dissecting room, usually includes the epidermis and more or less of the corium and subcutaneous tela. The cut surface is formed of connective tissue which has a shining bluish-white appearance with minute pits closely scattered over the surface. These pits are usually more or less completely filled with small yellow fat lobules. Skin muscles. — In the subcutaneous tela and the corium muscle fibres are found in large and small groups. These are of two kinds, striated muscle and unstriated muscle. Subcutaneous planes of striated muscle are relatively scanty in man when compared with the great panniculus carnosus of the lower mammalia. This is mainly represented by the platysma in the neck which has both its origin and part of its insertion in the skin. Closely associated with this are the muscles of expression of the face and the palmaris brevis muscle which have one end terminating in the deep surface of the skin. The epicranial muscle is also considered by some to belong to this group. Unstriated muscle fibres are scattered through the corium collected into bundles in the neighbourhood of the sebaceous glands and the hairs. They are described in connection with these latter (p. 1293). In addition to these unstriated muscles are found in the scrotum as the dartos, in the perineum, around the anus, and beneath the papilla and areola of the mammary gland. Burssa mucosae subcutanea. — In some situations where the integument is exposed to repeated friction over subjacent bones or other hard structures its movements are facilitated by the development of sac-like interspaces in the sub- cutaneous tissue, the subcutaneous mucous bursse. They are similar to the more deeply placed bursse which are found in relation with muscle tendons. Their occurrence is quite variable. In some individuals they are numerous, in others very few. They have a considerable practical importance from the fact that they may become greatly swollen. The most constant subcutaneous mucous bursae are the following: Bursa anguli mandibulae; B. subcutanea prementalis, between the periosteum and soft parts over the tip of the chin; B. subcutanea prominentise laryngese over the ventral prominence of the thyreoid cartilage of the larynx (often found in the male; B. subcutanea acromialis, between the acromion and the skin; B. subcutanea olecrani, beneath the skin on the dorsal surface of the olecranon; B. subcutanea epicondyli humeri lateralis, found beneath the skin over the lateral epioondyle of the humerus (occasional); B. subcutanea epicondyli humeri medialis, between the skin and the medial epicondyle of the humerus (more frequent); B. subcutanea metacarpophalangea dorsalis, between the sldn and the dorsal side of the metacarpophalangeal joints (occasional, especially the fifth); B. subcutanea digitorum dorsalis, beneath the skin over the proximal finger-joints; and rarely over the distal finger-joints; B. subcutanea trochanterica, between the skin and the great trochanter of the femur; B. subcutanea praepatellaris, beneath the skin covering the caudal half of the patella; B. subcutanea infrapatellaris, between the skin and the cephahc end of the ligamentum patella;; B. subcutanea tuberositatis tibiae ventral to the tibial tuberosity, covered by skin or by skin and crural fascia; B. subcutanea malleoli lateralis, between the skin and the point of the lateral malleolus; B. subcutanea malleoli me- dialis, between the skin and medial malleolus; B. subcutanea calcanea, in the sole of the foot between the skin and the plantar surface of the calcaneum; B. subcutanea sacralis, beneath the skin which covers the lumbodorsal fascia and the region between the sacrum and coccyx. Blood-vessels of the skin. — Both the corium and the subcutaneous tela are very vascular, but the size and number of vessels varies in different situations. Although the origin of the cutaneous arteries from the deep arteries and the positions where the subcutaneous arteries pierce the muscles vary greatly, the areas supplied by certain groups of arteries and the direc- tion in which the arteries of the skin run show much regularity. Moreover the metameric arrangement of the arteries in the skin is clearly seen, especially upon the trunk. We can recog- nise two groups of skin arteries. One group is represented by a small number of rather large branches which are distributed throughout or principally in the subcutaneous tela and corium, as the inferior superficial epigastric artery, the arteries of the scalp, etc. These arteries tend to NERVES OF THE SKIN 1289 disturb the metameric arrangement. In the other group the arteries are intrinsically for the supply of other organs but give off small end twigs to the skin, e. g., the arteries to the superficial muscles. The arteries enter the corium from the subcutaneous tela, break up into smaller branches anastomose freely and in the deepest layer of the corium form a network, the cutaneous rate (subcutaneous plexus), rete arteriosum cutaneum, from which small branches are given off to supply the fat and sweat glands and also to the papillary layer of the corium. Here another network of arteries is formed, the subpapillary rete, rete arteriosum subpapillare. From the subpapillary plexus, minute twigs pass to the papilla;, to the hair follicles, and to the sebaceous and sudoriferous glands. The cutaneous veins like the arteries may be divided into three groups: (1) small radicals which accompany the corresponding arteries and go to make up veins whose main function is to collect the blood from the muscles; (2) larger branches accompanying the arteries whose main course is in the subcutaneous tela as the inferior superficial epigastric vein; (3) large veins which run in the subcutaneous tela but have a course independent of the arteries such as those seen through the slcin on the hands and arms. These large vessels will be found described in con- nection with the general description of the veins (Section V). Minute venules arise from the capillaries of the papilla, accompany the arteries and form parallel with the surface of the skin a series of closely connected plexuses. Four such plexuses, Fig. 1049. — Cutaneous Nerves of the Middle Finger and Lamellotts (Pacinian) Cor- n s, MS ,ri(.iii T,.!,irs \ths) Twig from n. digitalis Volaris proprius LamellousCPacinian'^ puscles with nerves ■ Interdigital fold Cut edge of skin along mid-line of dorsal sur- face of finger Mid-line of volar surface of finger more distinct than the arterial, may be recognised in some situations. Of these retia venosa one is situated just beneath the papilla;, and another at the junction of the corium and subcu- taneous tela. They receive branches from the fat, hair folhcles, and glands, and empty into the large veins of the sldn situated in the subcutaneous tissue. Lymphatics of the skin. — The cutaneous lymphatic vessels are found in the skin of all parts of the body but are more abundant in certain places. The lymph-vessels of the skin are developmentally among the first lymph-vessels to appear. The larger vessels and glands of the subcutaneous tela will be found described in connection with the general lymphatic system Section VI). In the corium the lymphatics from the papillae form a subpapillary network which opens into a subcutaneous plexus connected with the larger lymph-vessels of the subcu- taneous tela. There are no lymph-vessels in the epidermis, but this is supposed to be nourished by the lymph in the tissue spaces between the cells and these spaces connect indirectly with the lymph-vessels. The nerves. — The skin has one of the richest nerve supplies of the body. The nerves are in greater proportion in those parts which are most sensitive. The various skin areas are supplied by specific (segmental) nerves with much greater regularity than in the case of the arteries. The nerves supplying adjoining areas overlap so that there is an intermediate space supphed by both. The variations consist in an extension of one area and a corresponding contraction of an adjoin- ing area. The distribution of the nerves in the skin shows, especially on the trunk and neck, a marked metameric arrangement. The arrangement of these nerves in the subcutaneous tela 1290 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS and their areas of distribution will be found described in detail in the section on the Nervous System. With the exception of the nerves to the sudoriferous and sebaceous glands, the skin-muscles and blood-vessels, all the cutaneous nerves are sensory. They have diverse modes of termina- tion. Some end in the subcutaneous tela; others, the greater number, terminate in the corium; still others extend to the epidermis. Toward their termination the nerves branch and rebranch, and just beneath the surface they form a great number of small twigs from which the terminal fibres arise. These may be divided into two groups, those that end freely and those whose termination is surrounded by a capsule. The free ends are slightly enlarged and terminate in the epidermis and in certain regions in the corium. The encapsulated terminations form special end organs and are found in the corium as the bulbous corpuscles (end-bulbs of Krause) [corpuscula bulboidea, Krauserii]; the tactile corpuscles (corpuscles of Meissner or Wagner) [corpuscula tactus, MeissneriJ; and the genital corpuscles [corpuscula nervorum genitalia[. In the subcutaneous tela the end-bulbs are seen as the lamellous corpuscles (corpuscles of Vater: Pacinian corpuscles), [corpuscula lamellosa; Vateri, Pacini[ shown in fig. 1049; the Golgi-Mazzoni corpuscles and the Rufflni corpuscles. All the terminations except the lamellous corpuscles are microscopic, not exceeding 0.2 mm. in length. The lamellous corpuscles, which are readily seen in reflecting the skin from the fingers and toes, may be as much as 2 mm. long and half as thick (fig. 1049). The exact function of each of the various endings is not known. They are undoubtedly sensory fibres except those to the glands, muscles, and blood-vessels. Development of the corium and subcutaneous tela. — The corium is developed from the superficial part of the myotome or dermo-muscular plate of mesoderm. At first it is very largely cellular but later fibres are produced. In the earlier stages the corium and tela subcutanea are not distinguishable and only in the later embryonic period may the corium be separated into the papillary stratum and the tunica propria. THE APPENDAGES OF THE SKIN The appendages of the skin include: (A) the hairs; (B) the nails; (C) the cutaneous glands; and (D) the mammary glands. A. THE HAIRS The hairs [pili] are less developed in man than in any other primate. Where well developed they in themselves serve as a protective organ and moreover through their connection with the nervous system they become in a measure organs of special sense. They are strong, flexible, somewhat elastic, and poor conductors of heat. They cover the entire surface of the body with the following exceptions: The flexor surfaces of the hands and feet; the dorsal bends and sides of the fingers and toes; the dorsal surfaces of the distal phalanges of the fingers and toes; the red borders of the lips; the glands and inner surface of the prepuce of the penis and clitoris; the inner surface of the labia majora; the labia minora and the papilla mammae. The size and length of hairs varies greatly not only in different parts of the body but also in different individuals and races. In certain situations the hairs are especially long and large and are designated by special names. Thus upon the scalp, capilli, in the axillary region, hirci, and after puberty upon the face in the male, the beard, barba, and in the pubic region in both sexes, pubes. The pubic hairs extend upon the external genital organs and upon the ventral abdominal wall toward the umbilicus. All of the hairs of these regions are not long and large but short and finer hairs are mixed with them in varying numbers. Strong, well-developed short hairs are found in connection with the organs of sense forming the eyebrows, supercilia, the eyelashes, cilia, at the entrance to the external acoustic meatus, tragi, and at the nares, vibrissse. Upon the extensor surfaces of the extremities, upon the chest, and in other situations in some individuals, especially in adult males, the hairs are also longer and stronger than upon the rest of the body, where they are, as a rule, short, fine and downy. The first hairs appearing in the foetus are very fine, and are called lanugo. The long hairs of the adult scalp may attain a length of ISO cm. or more; the short hairs average from .5 to 1.3 cm. in length, while the lanugo does not exceed 1.4 cm. Excess of long hairs, hypertrichosis, may involve the whole hairy surface of the body. It is usually inherited and affects several individuals in the same family. Local areas of long hairs also occur as over naevi and upon the sacrum. Local congestion due to inflammation, irritation, or pressure may cause hypertrichosis. In women, hair upon the upper lip or other parts of the face may be an inherited peculiarity or due to some abnormahty of the sexual organs. It is also not uncommon after the menopause. In diameter the hairs vary from .005 mm. for the finest lanugo to .203 mm. for the coarsest hair of the beard ; but they usually taper toward the tip and also are narrower toward the base. As a general rule, blonde hairs are the finest and black hairs the coarsest. THE HAIRS 1291 In colour the hairs may be either blonde, brown, black, red, or some gradation of these colours. The colour varies with the race, and also with the individual, and according to age. It is due to pigment in the cells of the hair but is also influenced by the amount of air between the cells. Greying and whitening of the hair is due not only to a decrease of pigment but also to an increase in the amount of air between the cells. Sudden blanching of the hair is thought to be due almost entirely to an increase in the quantity of this contained air. Whitening of the hair is physiological in old age and not infrequent in younger persons. This may be an inherited pecul- iarity or may follow mental overwork, nervous shock, or prolonged disease. Local blanching is also seen as the result of disease. The hair may be straight, waved, curled, or frizzled in varying degree. Here also there is not only an individual but also a racial variation, as instanced in the curled or crinkled hair of the African negro and the straight hair of the American Indian. The curliness is caused by the form and the manner of implantation in the skin. Straight hairs are round or oval in transection Fig. 1050. — Longitudinal Section of a Growing Hair of the Head. Toldt's Atlas.) (X30.) (From Epidermal coat of follicle Scapus pili (shaft) Collum foUiculi pili- Inner root sheath Outer root sheath ' Radix pili (root i ■ Substantia corticalis — " Substantia medullaris Sebaceous gland f \ Arrector pili muscle Outer fibrous layer — Dermal I , ^. , coat of 1 I°°<=' fi''""^ '^y" ~~ • follicle I Hyaline layer ; Bulbus pil Fundus folliculi pil and curled hairs are more flattened. The root of curled hair has been observed in certain instances, as in the negro, to have a curved course in the skin which may account in a measure for its curliuess. The hairs are arranged singly or in groups of from two to five and, except those of the eye- lashes, are implanted at oblique angles to the surface of the skin. The directions in which the hairs point are constant throughout life for the same individual. They are arranged in tracts in which the hairs diverge from a centre in whorls, the vortices pilorum. These vortices are found oonstantty in certain definite regions and apportion the whole hairy surface. The centres of vortices are found at the vertex (sometimes double) upon the face, around the external auditory meatus, in the axilla, in the inguinal region, and sometimes on the lateral surface of the body. These are all paired except as a rule the first. Where adjoining vortices come together the hairs are arranged in lines along which they all point in nearly the same direction, only slightly diverging, forming the hair streams, fiumina pilorum. In other lines and places the hairs point in converging directions such as at the umbihcus and over the tip of the coccyx. 1292 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS The number of hairs to the square centimetre varies in different parts of the body and also in the same situation with the individual and with differences in race, colour and diameters. The hairs are most numerous on the head, ranging from 170 to 300 to the square centimetre at the vertex. They are less numerous on other parts of the body, varying from 23 to 44 (per square centimetre) on the chin, and from 24 to 80 on the forearm. The greatest number is found with blonde hair, the next with brown, then black, and the least with red hair. The structure of the hair. — Each hair consists of a shaft [scapus pili] (fig. 1050) projecting from the free surface of the skin to end (unless broken or cut) in a conical end [apex pih], and of a root [radix pili], imbedded in the case of the lanugo hair in the corium and of the larger hairs at various depths in the subcutaneous tela. Surrounding the root is a downgrowth of the skin known as the follicle [folliculus pili]. Fig. 1051. — ^Longitudinal Section of a Hair Ready to Fall out, with Follicle roR New Haik. (X30) (From Toldt's Atlas.) , Shaft Orifice of sebace ous gland Dermal coat of hair -follicle iA Epidermal coat of hair-follicle Hair-knot (modified hair -bulb) The root of the hair at its deepest parts swells to from one and one-half to three times the diameter of the shaft forming thus the bulb [bulbus pili] (fig. 1050). The bulb is hollow and a vascular connective-tissue process, the hair papilla [papilla pili] (figs. 1050, 1051) extends from the deepest part of the follicle into the cavity in its base. The follicle consists of an external connective-tissue portion formed by the corium, the theca folliculi and an internal epithelial portion belonging to the epidermis and divided into two portions, the inner and outer root sheaths (fig. 1050). The theca of the follicle is composed of an outer loose longitudinal and a middle circular layer of connective tissue and an inner basement membrane. The outer root sheath is directly connected with the stratum germinativum of the epidermis. In its deeper part it consists of several layers of cells but of only one near the surface. The inner root sheath has been divided into three layers. At the junction of the outer and middle thirds of the follicle of most of the hairs, the ducts of usually two or more sebaceous glands connect with the space between the hair THE NAILS 1293 and its follicle (figs. 1050, 1051). Immediately beneath this is the narrowest part of the follicle the neck [collum folhcuU piU], especially important as the position of the nerve ending of the hair. The hair is formed of epithelial cells arranged in two and sometimes three layers; an outer single-celled layer of transparent over-lapping cells, the cuticle, an intermediate layer several cells thick formed of irregular fusiform horny cells containing pigment and arranged in fibrous strands, the substantia corticalis, and in some of the larger hairs an internal two or three celled layer of angular cells occupying the center of the hair shaft for only part of its length, the substantia meduUaris. Between both the cortical and medullary cells are spaces containing air. In the hair bulb, where the cells are larger and softer the layers are not distinguishable. The cells here being in process of division and being gradually transformed into the horny cells of the shaft. Many of the hairs have in connection with their follicle round or flat bundles of unstriped muscle fibres, the arrectores pilorum (figs. 1050, 1052). These are situated on the side toward which the hairs point, their deep ends being attached to the hair follicle beneath the sebaceous glands which they more or less embrace and their superficial ends connected with the papillary layer of the skin. Con- traction of the arrectores not only causes the hairs to become more erect and the skin around them to project somewhat causing "goose flesh, " but also compresses the sebaceous glands which are situated between the follicle and muscle and helps to empty the glands of their secretion. Vertical Section of the Skin fbom Scalp. — Sebaceous gland Fat and connec tive tissue The blood supply of the hairs. — The hair follicles arc surrounded by a capillary network of arteries connected with those of the corium and the papill-ae are also supplied with loops of arteries. The nerves of the corium supply branches to the hairs. Some of these branches enter the papillEE, others surround the follicle at its neck and are distributed among the cells of the outer root sheath. Development. — The hairs are developed from the epidermis by thickenings and down- growths into the corium of plugs of epithelium. The deepest parts of these plugs become swol- len to form bulbs and from these the hairs are produced. The central cells of the epithehal downgrowths disintegrate producing the lumen of the follicle. The hairs continue to grow from the deeper cells and protrude from their follicles between the fifth and seventh foetal months. Abnormally they may be scanty at birth and rarely entirely absent, alopecia. The lanugo hairs which cover all the hairy parts of the body at birth are soon shed and replaced by new hairs in- the old follicles. Throughout lite also the hairs are being constantly shed and replaced by new ones. This is accompanied by cornification of the bulb and fibrillation of the deep end of the hair (fig. 1051). Thinning of the hair and baldness occur when the shed hairs cease to be replaced. This is common in old age and a premature baldness appears to run in certain fam- ilies. The rate of growth is normally from 1 to 1.5 cm. per month, but is subject to variation. B. THE NAILS The nails [ungues] are thin, semi-transparent, horny epidermic plates upon the dorsal surfaces of the distal phalanges of the fingers and toes. Through their hardness they serve as protective organs not only by covering the nerve endings and other delicate structures of the skin; but also by acting as natural weapons. On the fingers they form useful tools. They are four-sided plates presenting a dis- 1294 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS tal free border [margo liber], which overhangs the tips of the fingers, an irregular, sharp proximal edge [margo occultus], and on each side a somewhat thinned border [margo lateralis] (fig. 1053). Fig. 1053.- -DoHSAL Surface of Isolated Finger Nail. Margo liber Corpus unguis (XI.) (From Toldt's Atlas.) ^ A ■ |l''hl,':??W- Lunula Radix unguis ---fj-'f'&Wjmil Margo occultus Each nail is composed of an exposed distal part, the body [corpus unguis], and a proximal covered part, the root [radix unguis], (fig. 1053), which ends in the margo occultus. The nail is at a slightly deeper level than the surrounding skin which overhangs the root and the lateral margins in a fold, the nail wall Fig. 1054. — Finger Nail and Nail Bed. Corpus unguis Margo lateralis Lunula Vallum unguis Radix unguis- — Matrix unguis Cristse matricis unguis Sulci matricis unguis Margo occultus [vallum unguis] (figs. 1054, 1055, 1056). The epidermis of the free edge of the nail wall, especially proximally, is thickened and often appears as a ragged edge. At a deeper level than the above and extending somewhat more distally is a vari- ably developed thin parchment-like membrane, the eponychium, closely attached to Fig. 1055. — ^Longitudinal Section Through the Tip op the Middle Finger. ( X 2) (From Toldt's Atlas.) Stratum corneum Stratum germinativum Corpus papiUare Margo liber Stratum corneum Stratum germinativum 1/ Matrix unguis . Radix unguis the superficial surface of the nail. It is the representative of the superficial layers of the embryonic epidermis which do not take part in the formation of the nail. The groove which is formed between the vallum and the underlying nail bed is known as the sulcus matricis unguis. This lodges the root and lateral margins THE NAILS 1395 of the nail and is deepest in the centre of the root, becomes shallower toward the lateral margins, and finally disappears entirely toward the free border of the nail (figs. 1055, 1056). The dorsal free exposed surface of the nail is formed by a hardened, thickened, horny layer of epithelium corresponding to the deeper parts of the stratum corneum (or the stratum lucidum) of the skin, the stratum corneum unguis (fig. 1056). It is convex from side to side (especially on the fifth finger), and also in some cases longitudinally. It presents a number of more or less well-marked fine longitudinal ridges. The stratum corneum forms the principal thickness of the nail. It is thicker and more solid on the toes than on the fingers. The portion of the nail which projects beyond the skin of the fingers and toes is greyish-white in colour. Unless broken or cut, it curves ventrally upon the ball of the finger or toe and tends to become long and claw-like. It may attain a length of 3 or more centimetres. The concave volar or plantar surface of the nail is softer and is formed of a layer of epithehal cells which corresponds to the stratum germuiativum (Malpgihii) of the skin and is known as the stratum germinativum unguis (fig. 1056). Because of the transparency of both layers of the nail the blood in the underlying matrix is seen through the body of the nail and gives to it a Fig. 1056. — Cross-section Through the Nail and Tip of the Ring Finger. (X4). (From Toldt's Atlas.) Corpus unguis Cristffi matricis unguis Vallum unguis ^ Sulcus matricis unguis Periosteum ^^^ "^ Retinacula cutis '^ ^^ CristEe cutis Volar surface of finger Stratum corneum unguis Stratum germinativum Matrix unguis pinkish colour; but toward the root of the nail there is a semilunar area convex distally, the lunula, which is less transparent and opaque whitish in color (fig. 1053). The lunula is vari- ously developed in different individuals. It is largest on the thumb and is often abssnt on the little finger. It is also smaller on the toes than on the fingers. The stratum corneum unguis consist of thin, flattened, transparent, horny scales with shrunken nuclei. These cells are intimately joined together in thin layers. The stratum germina- tivum unguis is formed of cells continuous with and resembling those of the corresponding layer of the epidermis. Air may occur between the cells as with the hair. The cells of the root are not yet cornified or dried out. The stratum germinativum unguis rests upon the corium, which here forms the so-called nail bed [matrix unguis].' This is made up of a dense feltwork of connective tissue fibres without fat. It is highly vascular and sensitive and the vertically arranged bundles bind the nails tightly to the periosteum of the termmal phalanges. The papillte of the matrix beneath the body of the nail are arranged in stronglj' marked longitudinal ridges, the cristee matricis unguis. The cristffi and papilla; of the matrix fit into corresponding depressions on the deep surface of the stratum germinativum unguis. The cristse of the matrix are small and low proximally and become larger and fewer distally. Those toward the lateral borders are somewhat oblique. The papillae of the root are not in rows but are irregularly arranged and disappear entirely near the distal border of the lunula. Toward the free border of the nail the papilte become large and change in character to that of the adja- cent skin. The best developed nails are those of the thumbs and great toes, the least developed, those of the fifth digits which on the toes are often represented only by a horny tubercle. Blood-supply of the nails. — The arteries are numerous in the matrix beneath the body of the nail but fewer beneath the root. They pass from the deep parts of the nail bed toward the sur- face, running in the main longitudinally and sending anastomosing branches to tlie papillte. The nerves beneath the nail are abundant and terminate in free sensorjf endings and in special end organs of several sorts. 1 The term nail bed is applied by some anatomists to that part of the corium beneath the body of the nail, the term matrix being reserved for the corium beneath the lunula and root. i 1296 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS Development of the nails. — The nails are developed from the epidermis. In early embryos over the dorsal surface of each distal phalanx there is seen a smoother and more adherent area of skin which becomes Umited by folds distally as well as proximally and laterally. It is also distinguished by a greater number of cell layers which later become flatter than the surrounding cells. The number of cell layers still further increases and at about the fifth foetal month the nail proper is formed by the deeper lying cells over an area extending from the proximal fold to the distal end of the lunula. The nail is pushed distally by constant formation of new cells in the same way as it continues to grow throughout life. The surface epithelial cells of the nail field cover the nail for some time as a thin layer, the eponychium, which later disappears except a small fringe near the root. Growth of the Nails. — The nail grows in length and thickness by multiplication of those cells of the stratum germinativum which are situated between the margo occultus of the root and the distal border of the lunula. The older cells are pushed distally and toward the sur- face by the deeper cells. As a result the nail becomes gradually thicker from the occult bor- der as far as the distal margin of the lunula. Over the rest of the nail bed no thickening appears to take place. The rate of growth is faster on the fingers than on the toes and varies with age, season, and the individual. When the nail is torn off, or detached through inflammation, it may be regenerated if the cells of the stratum germinativum have not been destroyed. Congenital hypertrophy of the nails sometimes occurs, but absence or imperfect development is rarely seen. The white spots so frequently seen in the nail are caused by air between the cell layers due usually to injury or impaired development. C. THE CUTANEOUS GLANDS The glands of the skin [glandulae cutis] are of two kinds: glomiform glands, and sebaceous glands. The glomiform ("skein-like") glands [glandulae glomi- formes] are of four types: sudoriferous glands, ciliary glands, ceruminous glands and circumanal glands. Fig. 1057. — Vertical Section of the Palmar Skin Showing an Isolated Sudoriferous Gland. (Testut.) 1, Stratum corneum; 2, Malpighian layer; 3. corium; 4, papilla; 5, body of sudoriferous gland; and 6, 7, its excretory duct; 8, orifice of duct on surface; 9, subcutaneous fat. The sudoriferous glands [glandulae sudoriferae] or sweat glands are modified simple tubular glands which secrete the siveat [sudor]. They are found in the skin of all parts of the body except that part of the terminal phalanges covered by the nails, the concave surface of the concha of the ear, the labia minora, and the inferior part of the labia majora in the female and the surface of the prepuce and the glans penis in the male. The number found in different parts of the body varies greatly. They are very few on the convex surface of the concha and on THE CERUMINOUS GLANDS 1297 the eyelid. They are also rather scanty on the dorsal surface of the trunk and neck, more numerous on the ventral surface of these parts and on the extensor surfaces of the extremities, still more numerous on the flexor surfaces, and most numerous on the volar surface of the hands and plantar surface of the feet. They vary from less than 57 to more than 370 to the square centimetre. The total number has been variously estimated at from two to fifteen millions. Each gland (fig. 1057) consists of a secretory portion or body [corpus gl. sudoriferae], and an excretory duct [ductus sudoriferus], which opens on the sur- face of the skin by a mouth visible to the unaided eye, the so-called 'pore' [porus sudoriferus]. Occasionally the duct opens into a hair follicle. The bodies of the glands are irregular or flattened spherical masses, yellowish or yellowish red in colour and somewhat transparent. They vary in size from .06 to 4 mm. or more with a mean diameter of .2 to .4 mm., the largest being found in the axilla. They are formed of the irregularly, many times coiled, terminal part of the gland tube. The bodies of the glands are situated in the deeper part of the corium or in the subcutaneous tela. The wall of the rather wide-lumened gland tube is formed of a single layer of cubical or col- umnar epithelium containing fat and pigment granules and surrounded externally by a basement membrane. Enclosing these is a more or less dense connective-tissue sheath. In many of the glands, especially the larger ones, there is a layer of obliquely running unstriped muscle fibres, the so-called myoepithelium, between the basement membrane and the cells. In some cases the bodies of the glands are imbedded in a more or less dense mass of lymphoid tissue. The ducts, beginning as several coils bound up with those of the bodies, extend often in a straight or sUghtly wavy course nearly at right angles to the surface as far as the epidermis. This they pierce as spiral canals of from two to sixteen turns, more marked where the epidermis is thickest (fig. 1041), and opened on the surface by somewhat widened funnel-shaped mouths. The ducts pass between the papilla? of the corium and open on the summits of the cutaneous cristae where these are present. The diameter of the ducts is distinctly smaller than that of the secreting part of the glands, and this is true of the lumen also. The ducts are lined by a stratified epithelium composed of two, three, or more layers of cella resting on a basement membrane without any intervening layers of muscle-cells, and surrounded by a connective-tissue sheath. This latter as well as the basement membrane ceases at the epidermis and the epithelial cells of the duct walls join those of the stratum germinativum. The duct for the rest of its course to the surface is merely a canal through the cells of the epidermis. The degree of development of the sweat glands varies with the situation, the individual, and also racially, as instanced by their great development in the negro. In some individuals the perspiration is much more profuse than in others. The glands are smaller in the aged than in the young. The odour of the sweat is peculiar and more or less characteristic, varying with the individual. The sudoriferous glands in the axillary region seem to be in some way connected with the sex- ual function for although a large number persist as small glands, others undergo further develop- ment beginning about the ninth year in the female and at puberty in the male. These glands in places form almost a continuous layer and are formed of large partly branched tubules with high secreting cells. The reddish colour of the sweat in the axillary and some other regions, especially in certain individuals, is probably derived from the pigment granules which are found in the glands here. The oil in the secretion lubricates the skin and keeps it soft and supple. Blood-supply of the sudoriferous glands. — The sudoriferous glands are supplied from the deep cutaneous plexus by an abundant network of arteries which surround and penetrate between the coils of the gland tubules. Nerves. — There is an enclosing network of nerve fibres some of which have been traced to the gland cells. Development. — The sudoriferous glands are seen first in the fourth or fifth foetal month. The anlages resemble closely those of the hair, but the cells are not so loosely packed. They project down as solid plugs which become long, slender, and tortuous rods. In the seventh foetal month the rods begin to develop a lumen in the deeper parts, which also now begin to coil. A lumen soon develops also in the superficial parts and joins that in the deeper part of the gland. The outer of the two layers of epitheUum in the ducts becomes transformed at its transi- tion into the gland proper into the myoepithelial layer. The ciliary glands [gl. ciliares; Molli] are modified sudoriferous glands of the branched tubo-alveolar type. They have simpler coils but are larger than ordi- nary sweat glands. They are situated in the eyelids near their free borders and open into the follicles of the cilia or close to them (see Section VIII). The circumanal glands [gl. circumanales] are found in a circular area about 1.5 cm. wide which surrounds the anus, a short distance from it. These glands are several times the size of the ordinary sweat glands and resemble the glands found in the axilla, their secretion likewise having a strong odour. They are branching tubular glands. The other kinds of glands which are found in this same area are ordinary sweat glands, glands with straight duets, with saccules and secondary alveoli, and tubo-alveolar glands. Cerumimous glands [gl. ceruminosse] are glomiform glands somewhat modi- fied from the sudoriferous type. They are branched tubo-alveolar glands ( 1298 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS with relatively large lumina in the coils and narrow short ducts, and occur only in the external acoustic (auditory) meatus. They are very abundant on the dorsal and superior part of the acoustic meatus in the region of the cartilaginous part, where in the adult most of them open on the surface of the skin close to hairs. Others open into the hair follicles as they all do in the foetus and child. Their secretion, the cerumen, is, when freshly secreted, a fluid or semifluid oily material of a yellowish-brown colour, which on exposure to the air becomes solid like wax. The sebaceous glands [gl. sebaceae] are simple branched or unbranched alveolar glands distributed over nearly the whole surface of the body. Nine- tenths of them are closely associated with the hairs, into the follicles of which they empty (figs. 1050, 1051), and are therefore absent from certain of the non- hairy parts of the body, as the flexor surfaces of the hands and feet, the dorsal surfaces of the distal phalanges of the fingers and toes. On the other hand, a few are found, usually much modified, opening independent of the hair follicles, as at the angles of the red margins of the lips, around the nares, around the anus, and the tarsal (Meibomian) glands in the eyelids. Modified sebaceous glands are also found upon the mammary papilla and areola in the female, and in some cases upon the superficial surface of the glans and the surface of the prepuce of the penis, here known as preputial glands ; also a few very small ones may be found upon the labia minora, the glans and prepuce of the clitoris. The glands vary in size in different situations and also in individuals and races. They range from .2 to 2.2 mm. long and nearly as broad. Among the smallest are those of the scalp. The largest are found on the alse of the nose and on the cheeks where their ducts are visible to the unaided eye. They are also large on the mons pubis, labia majora, scrotum, about the anus and on the mammary areola. Smaller glands are also found associated with these large ones. The size of the glands is independent of the size of the hairs with which they are associated but the number of glands depends upon the size of the hair. On small hairs one or more glands are always found and on large hairs there may be a whole wreath of from four to six separate glands opening into the hair follicle. The number of sebaceous glands has never been exactly estimated, although, it is known that they are less numerous than the sudoriferous glands. This is very evident on the extrem- ities, trunk, and neck, where they bear a relation of 1 to 6 or 8. On the scalp, concha of the ear, and skin of the face they are about equal in number while on the forehead, alae of the nose, free borders of the eyehds and external genital organs in the female the number of sebaceous glands is greater than the number of sudoriferous glands. Each sebaceous gland consists of a secretory portion, the body, connected with the hair follicle or the surface of the skin by a wide short duct. In the small glands, the body of the gland may consist of a single alveolus but in the larger glands there are from four to twenty of these connected by irregular ducts to a single excretory duct. The ducts open into the hair follicles near their necks between the inner root sheath and the hair or upon the surface of the skin. They are always very short, cylindrical, or infimdibuli- form, and their epithelium is directly connected with that of the outer root sheath of the hau' folhcle or with the epidermis where the hair is wanting. The glands lie in the superficial layers of the corium and where one or a few are connected to a single hair, they usually open into the hair follicles on the side toward which the hairs point. Where there are several glands for one hair they may completely surround the hairs like a rosette. The cells of the body of the gland and of the duct are surrounded by a basement membrane outside of which is a connective-tissue sheath, both of which are continuous with corresponding coverings of the hair folhcle. The periphery of the alveolus is formed of small cubical epithehal cells, the central part of larger and more rounded cells. The cells of the alveolus show all stages of fatty degeneration, the peripheral cells contain small fatty particles, those nearest the centre larger and more nu- merous fat droplets, some of them being completely broken down. There is no distinct lumen to the alveolus but this is filled with degenerated cells, fatty particles and ddbris of broken-down and cast-off cells. The deeper cells continue to multiply and push the more superficial cells toward the lumen where they in turn are cast off. The secretion thus formed is known as the sebum cutaneum. It is a whitish or whitish-yellow mass composed of fat and broken-down cells of the consistency of thick oil which spreads over the surface of the skin and hair as a lubricant. Through the decomposition of its fat more or less odour is produced. When the gland duct is blocked the secretion is retained and becomes more solid and is known as a comedo. The active secretion of the sebaceous glands does not begin before the fifth or sixth year of life. It attains its maximum in the adult and decreases in the aged. The relation of the arreotores pilorum to the sebaceous glands has been described in con- nection with the relation of these muscles to the hairs. Vessels and nerves. — The sebaceous glands are surrounded by a fine capillary plexus of blood-vessels closely associated with those of the hairs and skin. Concerning their lymph- vessels little is known. The nerves of the sebaceous glands are connected with those of the skin and hair but the exact manner of distribution is not clearly understood.] THE MAMMARY GLANDS 1299 Development. — The sebaceous glands appear lirst in the fifth foetal month as single, rarely double, buds on the anlages of the hair follicles. The distal ends of these enlarge and become lobulated. In these solid masses of cells lumina for the alveoli and the ducts later are formed, through the fatty degeneration of the central cells. The oily contents of these cells together with the debris and the cast-off surface cells of the epidermis form the vernix caseosa on the sur- face of.the foetus. D. THE MAMMARY GLANDS The mammary glands [mammae] or breasts are modified cutaneous glands. In tlie male they remain rudimentary and functionless throughout life, but in the female they are functionally closely associated with the reproductive organs since they secrete the milk for the nourishment of the newborn and are subjected to marked changes at puberty, throughout pregnancy, during and after lacta- tion, and after the menopause. Fig. 1058. — The Right Mamma op a Girl 18 Years Old. (Modified from Spalteholz.) Areolar gland' Papilla Areola The two mammffi (fig. 1058) are situated on the ventral surface of the thorax one on each side of the sternum. As examined from the surface in a well-developed nulliparous female they appear to extend from the second or third rib to the si.xth or seventh costal cartilage and from the lateral border of the sternum to beyond the ventral folds of the axillse. Separating the two mammae there is a median unraised area of variable size, the sinus mammarum. In shape they are conical or hemispherical, and in consistency somewhat firm and elastic: The size of the two breasts is seldom equal, the left, as a rule being slightly the larger. Each measures from 10 to 13 cm. in diameter being slightly longer in the direction parallel to the lateral border of the pectoralis major muscle. The weight of each gland varies from 140 to 200 grams, or more. Each mamma presents for examination a ventral surface and a dorsal surface. The ventral surface is free, covered by skin, smooth and convex. It is continuous i 1300 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS cephalically, without sharp demarcation, with the ventral surface of the thorax but laterally and caudally it is usually sharply defined (figs. 1058, 1060). It is Fig. 1059. — The Female Mamma Dt-hing Lactation. (After Luschka.) Adipose loculus Gland loculus Fig. 1060. — Sagittal Section of the Right Mamma of a Woman Twenty-two Years Old (Testut ) Pectoralis major Skin Retinaculum cutis /"^ Pyramidal process „, Pectoralis minor ■jfS^ -Intercostal muscle Pectoral fascia Connective tissue Superficial fascia --^(^ horizontal plane Fifth nb Pyramidal process Rectinaculum Fat cutis External oblique most prominent slightly meso-caudal to the centre and at this point there is a marked pigmented projection, the nipple [papilla mammse] surrounded by a THE MAMMARY GLANDS 1301 slightly raised area, also pigmented, the areola mammae. These two structures will be described separately later. The dorsal surface of the mammary gland (figs. 1060, 1061) is attached and concave. It is in relation in its cephalo-medial two-thirds with the fsacia over the pectoralis major muscle. In its caudo-lateral third it extends over the base of the axillary fossa, where it is in relation with lymphatic glands and with the ser- ratus anterior muscle, and at its most caudal part, sometimes with the external abdominal oblique muscle. The usual number of breasts in the human species is two; rarely is the number reduced, much more often do we find an increase in this number. Each of these conditions is found in both sexes and may be complete or partial. Complete suppression of both breasts, amastia, is one of the rarest anomaUes and is usually associated with other defects. Complete absence of one is less rare. A more frequent condition is arrest of development, micromastia, leading to rudimentary but functionless organs. Absence of the nipple, athelia, is much commoner and generally affects both breasts. All grades of the imperfection from complete absence to shghtly imperfect nipple may be found. When there is an increase this may include the whole breast, polymastia, or just the nipple, polythelia. The supernumerary structures [mammae Fig. 1061. — Horizontal Section of the Right Mamma or a Woman 22 Years Old. (Testut.) Pyramidal process Skin Retinaculum cutis Areola Duct -^ Retinaculum cutis ■^ Pyramidal proces ir1?X -Skin Superficial fascia Connective tissue ' Sixth rib -IntercQstals accessori8e] may be represented only bj' a pigmented area representing an areola; or by a nipple with or without an areola; by a gland with a more or less perfect nipple and areola; or with ducts opening without a nipple; or there may be no opening on the surface. The extra mamma is very rarely perfectly developed and functional. Various observers have found the super- numerary breasts or nipples occurring in from 1 to 7 per cent, of the cases examined and some- what oftener in males than in females. The extra organs are found more frequently on the left side, usually along a line extending from the axilla toward the genitalia. Tliis corresponds to the position in which the mammae occur m some other mammals and also to the milk line of the embryo. Although they are occasionally found in other situations, over 90 per cent, of them are encountered upon the ventral surface of the thorax along the above-mentioned line caudal and medial to the normal pair of breasts. They are frequently hereditary. It is doubtful whether their possessors are either more fertile or more Uable to bear twins. The shape of the breasts varies with the development and functional activity'and the amount of fat. The smooth, somewhat conical breast of the nullipara becomes hemispherical with increase in the amount of fat, while in emaciation it may be reduced to a flattened disc with an irregular surface. After lactation the breasts tend to become more pendulous with marked sulci between them and the thoracic walls, and after repeated pregnancies they may become elon- gated so as to be almost conical or even have pedunculated bases. The size of the mammary gland in girls remains relatively the same as in the infant up to puberty when it suddenly increases considerably and continues for a time to enlarge slightly at each menstrual period. There is also a temporary enlargement and soreness at each menstrual period, due perhaps to the increased vascular supply. Until the age of puberty the glands measure 8 to 10 mm. in diameter but when they have attained their complete adult development they have increased to 100 to 110 mm. in the cephalo-medial, 120 to 130 mm. in the cephalo-lateral (obliquely from above downward) direction, and 50 to 60 mm. in thickness. During pregnancy the breasts again increase in size, more especially i 1302 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS after the birth of the child. When their full functional activity is established, their volume may be two or three times as great as before pregnancy. After lacta- tion they return again nearly to their former size, which they retain until another pregnancy. After the menopause the useless glands in some cases atrophy and are reduced to small discoidal masses. In others, especially in fat individuals, although the secreting tissue disappears, it is replaced by fat so that there is little or no reduction in size. In addition to the above-mentioned variations in size, the breasts are subject to great individual differences, the cause of which is little understood. Large robust women are sometimes seen with small mammary glands, and small women with large glands. In some individuals they are espe- cially large. The weight of each mamma varies, naturally, with the volume, increasing from 30 to 60 centigrams in the small gland of a young child to 140 to 200 grams after puberty and in nursing women reaching 400 to 500 and occasionally 800 to 900 grams. The firm and elastic, well-developed breasts of young nullipara become during lactation even more firm and tense, but after lactation especially if there has been a long period of nursing they lose their consistency and after several pregnancies become soft and flabby. The sulcus which defines the caudal border of the breast is but little marked in thin nulli- para, more marked in fat women, and especially evident in some multipara. The relations of the dorsal surface of the gland vary somewhat with the position. The level varies with the stature; as a rule, in tall women it is more caudal and in short and broad-chested women it is more cephalic. The tightness of the attachment to the sheath of the pectoralis major muscle is quite variable, but even when quite loose there is some movement of the breast when the arm is raised. The glandular tissue of that part of the breast which overhangs the axilla may be in direct contact with the lymphatic glands. Structure. — The mammary glands are composed of the essential epithelial glandular tissue, the parenchyma, the supporting and enclosing connective tissue of the subcutaneous tela, the stroma, and the covering cutaneous layer. Parenchyma. — The essential part of each mamma is a flattened, circular mass of glandular tissue of a whitish or reddish-white colour, the corpus mammae. This is thickest opposite the nipple and thinner toward the periphery. The ventral surface of this mass is convex and made uneven by numerous irregular pyramidal processes which project toward the skin. The dorsal surface, or base, is flat or slightly concave and much less irregular than the ventral surface. Minute proc- esses of glandular tissue extend from the corpus mammse into the retromammary tissue, some of them accompanying the septa of the pectoral fascia between the bundles of muscle fibres of the pectoralis major muscle. The circumference of the mamma is thick and well defined, more marked caudally than cephalically, but it presents numerous irregular processes which extend beyond the limits apparent from the surface. One of these especially large and well marked extends cephalo- laterally into the axillary fossa, and there are frequently other large but less- marked projections. The corpus mammae is not a single structure but is composed of from fifteen to twenty separate lobes [lobi mammse] (fig. 1059). These are larger and smaller irregular flattened pyramidal groups of glandular tissue, with their apices toward the nipple and their bases radiating toward the periphery of the gland. Each lobe has a single excretory duct [ductus lactiferus] (figs. 1059, 1060, 1061), which opens by a contracted orifice [porus lactiferus] in a depression upon the tip of the nipple. When traced from the pore toward the circumference of the gland, the ducts are seen to run first directly dorsally through the nipple, parallel and close to one another. From the base of the nipple they diverge. Each duct is here visible to the unaided eye and measures from 1.5 to 2.5 mm. in diameter. Beneath the areola its diameter increases for a short distance to from 4 to 9 mm., forming thus a reservoir, the ampulla or sinus lactiferus, in which the secretion may accumulate for a time. Beyond this dilation the duct continues, gradually decreasing in size as it breaks up into smaller and smaller branches, There is no anastomosis between the ducts during their course, although at or beneath the pore two or more ducts may join to have a common opening. They possess no valves but when empty their inner surface is thrown into longitudinal plicse. The ducts have an external coat of white fibrous connective tissue mixed with circular and longitudinal elastic fibres. They are lined with a simple cuboidal or columnar epithelium, except near the orifice, where it is stratified squamous. External to the lining epithelium there THE MAMMARY GLANDS 1303 occurs in the smaller ducts a second layer of elongated cells resembling the myoepithelium of the sudoriparous glands. Each of the terminal branches of a duct ends in a tubulosaccular, spherical or pyriform alveo- lus. A number of these alveoli which open into a common branch of the duct, when grouped together and bound up with connective tissue, constitute a lobule of the gland (lobulus mammae). A lobe is made up of all the lobules whose ducts join one common excretory duct. The alveoli are composed typically of a single layer of epithehal cells enclosed by a basement membrane. This layer is the true secretory epithelium. It consists in the more active gland of granular polyhedral or cuboidal cells which may be so closely placed as to leave almost no lumen to the alveoh. During lactation these cells may be found in different stages of secretory activity, their central ends being filled with minute oil globules and more or less flattened accord- ing to the degree of distention of the alveoli. The alveoli and ductules now possess considerable lumina which are filled with the above-mentioned millc globules Uberated from the cells and sus- pended in a serous fluid also secreted by the cells. TMs constitutes the milk (lac femininum). Stroma. — The lobes, lobules, and alveoli are completely covered by a connective-tissue sheath too delicate to constitute a distinct capsule. Outside of this the whole gland is embedded in the subcutaneous tela which forms for it a sheath, capsula adiposa mammae. This is particu- larly well developed on the ventral surface where the fat fills in between the irregularities caused by the lobes and lobules and gives to the surface of the gland its smooth appearance. Within the corpus mammte there is little fat between the lobules in nulhpariB but much more fat is found here in the stroma in multipara;. When the fat is absorbed, as it is during lactation and in emaciation, the lobules stand out much more distinctly. There is however, no fat immediately beneath the areola and nipple. The connective tissue is here loosely arranged and allows free motility of the nipple and also permits the more easy distention of the ducts and sinuses during lactation. The connective-tissue strands, retinacula mammae, which extend from the apices of the glandular processes on the ventral surface of the mamma are connected to the cerium and correspond to the retinacula cutis found in other situations. These are sometimes particularly well developed over the cephaUc part of the mamma and have been called the suspensory liga- ment of Cooper. The dorsal surface of the mamma is bound to the pectoral fascia by loose connective tissue containing, as a rule, only a small amount of retromammary fat (figs. 1060, 1061). The attach- ment to the sheath of the pectorahs major muscle is at times so loose that the spaces between the connective tissue appear to form serous sinuses, the sub- or retromammary bursas. In addition to the axillary process or 'tail' of the gland, a projection is sometimes seen extend- ing toward the sternum and another caudolaterally; also processes extending toward the clavicle and caudomedially have been described. Besides these large projections there are numerous branched interlacing processes which combine into larger and smaller masses on the ventral surface and exist as minute extensions on the dorsal sm'face. In thin women, the parenchyma at the apex of these triangular processes reaches nearly to the surface. A mammary gland may be made up of a larger amount of stroma and a smaller amount of glandular tissue, or the reverse, and therefore a small breast may fiu-nish more milk than a large one. There is also a variation in different parts of the same breast, one lobe or section may have well-developed lobules while in another they remain almost as at puberty, merely branching ducts. The glandular tissue when sectioned is whitish with a greyish or pinkish cast and is firm and resistant, almost cartilaginous in consistency. It is thus easily distinguished from the adipose capsule. Changes due to age and functional activity. — At birth the mamma consists mainly of fifteen to twenty slightly branched ducts lined with stratified squamous or columnar epithelium. In spite of the lack of true glandular tissue, within the first few days there may be such rapid cell proliferation that the ducts become distended with cells and detritus. By pressure upon the gland a few drops of this material may be expressed which constitutes the so-called 'witches milk.' From birth until puberty the mamma remains rudimentary, simply keeping pace with the general body growth, but in the female, at puberty, an abrupt change occurs. The tubules grow rapidly into the smTOunding tissue and some acini (alveoli) appear; the stroma and fat are also greatly increased; and the breast becomes rounded and well formed but consists mainly of fatty stroma and ducts, with but a very small number (if any) of true secreting acini. At this time in both boys and girls the breast may become swollen and tender and a milk-hke secretion may be produced similar to that at birth. The great increase in volume during pregnancy and lactation is due to the increase in the size and number of the lobules and acini, and is accom- panied by a decrease in the interlobular and intralobular stroma and in the fat, so that the gland feels hard and imeven. The acini appear first in the periphery, thence along the larger ducts toward the centre of the corpus mammte. The secretion of the gland for the first two or three days after parturition until the free secre- tion of milk is established is termed the colostrum. It differs from normal milk not only in chemical composition but also in containing larger fat globules and special cells known as colostrum corpuscles. The decrease of the gland nearly to its original size after lactation is due to an involution of the parenchyma, the acini being reduced to narrow tubules, most of them completely atrophy- ing. With this is associated a development of fat and fibrous stroma. The gland does not, however, regain its virgin appearance but its main mass is looser and more irregular, less dis- tinct, and the peripheral processes larger, while the stroma contains numerous fat-lobules. This causes the breast to be less smooth, fii-m, and elastic, and it tends to become pendulous and form a sulcus where it overhangs its base. With the end of sexual activity the secreting portions of the glands gradually atrophy, finally leaving Uttle more than the ducts. Even these undergo senile atrophj', and the main mass of the gland is represented only by a flattened disc, in which the peripheral processes can scarcely be made out. In fat women there may be little reduction in size, but the breast is here transformed almost entirely into fat. i 1304 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS The skin covering the ventral surface of the breast is very white, covered with lanugo hairs associated with sebaceous glands, and contains many sweat glands of the ordinary type. It is so thin that the subjacent veins are readily seen through it. It is closely adherent to the subjacent fatty layer but its flexibility, elasticity, and motility over the deeper glandular tissue permit much stretching during the enlargement which occurs at the time of lactation. In spite of this, linea albi- cantes are often produced especially when the breasts have been unusually large. Aside from the above-mentioned particulars, it does not differ from the skin of the adjacent part of the thorax, except over the centre of the breast where it forms the areola and nipple. The areola mammae (figs. 1058, 1059, 1060, 1061) is covered by a thin, deli- cate, pigmented skin. The colour in young nulliparae is reddish, the shade varjang with the complexion. During pregnancy the colour darkens, slightly in blondes, but so as to become almost black in marked brunettes. This pigmentation serves as one of the signs of gestation. After lactation the colour fades, but little pigmentation remaining in blondes, considerable in brunettes. During pregnancy- there is sometimes seen extending more or less beyond the areola a less deeply and less uniformly pigmented ring, the secondary areola. In size, the areola is subject to considerable individual variation and is increased in pregnancy. The surface of the areola is roughened by a number of slight elevations irregu- larly arranged. These are due to underlying large sebaceous and rudimentary milk glands [gl. areolares; Montgomerii], tubercles of Montgomery. Projections caused by sebaceous glands are also found in the secondary areola. All of these tubercles enlarge greatly during pregnancy and the glands produce a slight secre- tion which is discharged through ducts that open on their summits. The sweat glands are few but large, and in addition to the lanugo hairs there are usually several well-developed hairs. The corium of the areola is devoid of fat but contains a well-developed layer of smooth muscle fibres, the fascicles of which intercross in various directions but may be seen to be mainly of two orders, circular and radial. They are continuous with those of the nipple. The circular fibres are most numerous adjacent to the nipple, where they may form a layer nearly 2 mm. in thickness. The areola varies greatly in size, measuring from 15 to 60 mm. in diameter. There is some confusion in regard to the areolar glands and the tubercles of Montgomery. Some consider the tubercles to be caused by the areolar glands, others consider them caused by the sebaceous glands. Sebaceous glands undoubtedly cause the projections in the secondary areola. The sudoriferous glands of the areola are large and compound tubular glands with a comphcated glomerulus and are considered as transitions between sweat and mammary glands. The seba- ceous glands are even more numerous than the sudoriferous and are composed of several lobes. They also have been considered by some as intermediate stages in the formation of mammary glands, but this is improbable. There are ten to fifteen very small areolar glands (though Pinard found an average of but four to each breast), whose structure is essentially identical with that of the principal mammary glands. They have dilations on their ducts and they open on the areola at times in common with a sebaceous gland. The nipple [papilla mamma] (figs. 1058, 1059, 1060, 1061) in well-developed nulliparae is situated slightly meso-caudal to the centre of the breast and on a level with the fourth rib or fourth intercostal space about 12 cm. from the median line. But its position in reference to the thoracic wall varies greatly with age, individual, and the present and past activity of the gland. The nipple is usually somewhat conical or cylindrical with a rounded fissured tip marked by fifteen to twenty minute depressions into which the lactiferous ducts empty. The average length of the nipple is 10 mm. to 12 mm. The skin is thin, wrinkled, and pig- mented like the areola, except over the tip of the nipple where there is no pigment. The corium of the nipple has many large vascular and nervous papilla; and there is no fat in it. Hairs and sudoriferous glands are absent but sebaceous glands are present in great numbers. Their secretion here and over the areola serves to keep the skin soft and to protect it from the saliva of the nursing infant. In the deeper layers of the corium smooth muscle fibres form a loose stratum continuous with that of the areola. This is made up principally of an external circular layer and to a slight extent by an internal layer whose bundles of fibres are parallel with the milk ducts. Numerous interlacing muscle fibres connected with these layers and mixed with loose connective tissue, and elastic fibres, but no fat, surround the lactiferous ducts as they pass through the axis of the nipple. The nipple usually does not project from the surface until the third year. It soon becomes conical but does not attain its full size until shortly after puberty. The size of the nipple is variable, ordinarily in proportion to the size of the gland, but large nipples are sometimes found on small breasts and small nipples on large breasts. During pregnancy the nipple increases in THE MAMMARY GLANDS 1305 size and becomes more sensitive and more easily erectile. The shape of the nipple in addition to conical or cylindrical may be hemispherical, flattened, discoidal, or slightly pedunculated. Its end may be invagtnated or the entire nipple retracted beneath the surface of the gland and pro- jecting only in response to stimuli. The circular muscle fibres of the nipple act like those at its base in the areola. By inter- mittent, rhythmic contractions they tend to empty the lactiferous ducts; by continuous and tight contraction they act as a sphincter. When contracted they also narrow the nipple, make it harder, erect, and more projecting. When the vertical fibres contract they depress the tip of the nipple or they may retract the whole nipple beneath the surface. The muscle of the areola when stimulated puckers the skin toward the nipple causing circular concentric folds in the skin of the areola. The male mammary gland [mamma virilis]. This develops exactly as with the female. From birth to puberty the glands in the two sexes have a parallel growth and development, but from this time on the glands in the male grow but slightly and reach their full development about the twentieth year. The corpus mammae in the adult male measures from 1.5 to 2.5 cm. in diametei and .3 to .5 cm. in thickness. It is whitish in colour, tough, and stringy. It is composed of the same number of lobes as in the female but these consist of little more than short ducts with no true acini and may be reduced to mere epitheUal or connective-tissue strands. The areola and nipple are present and pigmented, but the nipple averages only 2 to 5 mm. in height. The areola has a diameter of 2 to 3 cm. and is covered with hairs. The areolar tubercles may be recognised and the areolar muscle is present. The position of the nipple in relation to the chest-wall is more constant than in the female as the breast is less movable. It is seldom beyond the limits of the fourth intercostal space or the two adjacent ribs, and averages 12 cm. from the median line. Occasionally the male breast may hypertrophy on one or both sides, gynecomastia. Blood-supply. — The main arterial supply to the mammary gland is from mam- mary rami of perforating branches of the internal mammary artery (p. 567). Usually that from the second or third intercostal space is especially large. Small branches, external mammary rami, are also supplied to the caudal and lateral segments of the breast by the lateral thoracic artery (p. 571 ). Some rami from the thoracoacromial or supreme thoracic arteries (p. 571) may reach the cephalo- lateral segment of the breast and small twigs, lateral mammary rami, from the anterior branches of the lateral cutaneous rami of the aortic intercostal arteries (p. 589) supply its deep surface. These vessels anastomose freely and form a wide-meshed network in the stroma of the ventral and dorsal surfaces from which branches proceed around the lobes and lobules and finally form a close network of capillaries around the alveoli. From these, venous capillaries arise and pass in two groups, one deep, accompanying the arteries, the others superficial. These latter extend to the ventral surface of the gland to form a loose network beneath the skin. During lactation these subcutaneous veins show through the sldn as bluish lines, and frequently form a more or less complete circle around the nipple. They connect with the superficial veins of the neck superiorly, with those of the abdomen inferiorly, and with the thoracoepigastric vein laterally. The deep veins carry the blood to larger vessels, which empty into the subclavian, the inter- costal, the internal mammary, and the axillary; and the superficial group may connect with the external jugular and femoral veins. The lymphatics. — The lymphatics of the mammae are extremely numerous, forming rich plexuses and free anastomoses. Their exact origin and distribution are not yet fully understood, but it is clear that there is a rich plexus in the skin of the areola and nipple which empties mainly into a subareolar plexus. Deep lym- phatics arise in the spaces around the alveoli in all parts of the gland, and most of these converge toward the nipple where they join the subareolar plexuses. They anastomose freely with the cutaneous lymphatics and many of them empty into the subareolar plexus through large lymph-vessels which run parallel with the lacteal ducts. From the subareolar plexus usually two large lymph-vessels arise and pass toward the axilla to empty into the axillary lymph-glands (p. 719). Other lymphatic vessels of the mammary gland follow the course of the various blood-vessels. There is usually a third trunk from the cephahc part of the breast and often a fourth from the caudal segment which join with the others to the axillary glands. The lymphatics of the mammary gland also commimicate with the lymphatics of the skin, the ventral chest-wall and those of the deep fascia over the pectoral muscles, as well as the lymphatics of the opposite side. They also empty into the lymphatics which accompany the blood-vessels of this region, and thus communicate with the axillarj', subclavicular, and supraclavicular lymphatic nodes (p. 722). Moreover, those from the medial portion of the gland accompany the branches of the internal mammary artery and empty into the sternal glands along the artery within the thorax. Since cancer of the breast extends and is disseminated through Ij'mphatic channels, their distribution and connections are of great practical importance. i 1306 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS The nerves. — The gland proper receives its nerves laterally from the lateral mammary rami of the anterior rami of the lateral cutaneous branches of the fourth to sixth intercostal nerves and medially from the medial mammary rami of the anterior cutaneous branches of the second to the fourth intercostal nerves. The skin over the breast receives in addition to branches from the above nerves, branches from the supraclavicular nerves of the cervical plexus. It is alto- gether probable that sympathetic fibres reach the gland but by what course is not yet clear. The nerves are distributed in part to the sliin, in part to the plain muscle of the areola and nip- ple, some to the blood-vessels, and others to the glandular tissue. The secretion is, however, not entirely controlled by nerves as it is influenced also by hormones from other organs brought to it by the blood. Development. — In very early embryos the epithelium over an area on the side of the body extending from the fore to the hind limb (or beyond these limits) is seen to be deeper and more cubical, the mammary streak. In this area there is produced by multiplication of cells a ridge, the mammry line or ridge. In spots along this line, corresponding to the relative position of the mammary glands in some mammals and the supernumerary mammse in man, the epithelium thickens. The intervening parts of the line disappear as the spots enlarge to form transient mammary hillocks. In man ordinarily development proceeds in but one of these hillocks on each side. The deep surface of the hillock projects into the corium as the superficial surface flattens out and the mesodermic cells of the corium condense around the ingrowth producing the nipple zone. Rapid proliferation of the deeper cells produces a club-shaped stage from the deeper surface of which small bud-like masses of epithelial cells sprout and extend as solid plugs into the corium. These are the anlages of the true secreting part of tlie gland and the number of buds corresponds to the number of lobes of the future gland. The sprouts extend beyond and beneath the nipple zone and are supported by closely packed connective-tissue cells forming the stroma zone. The epithelial buds continue to grow and branch and a lumen is finally produced in the originally solid plugs. The primary epithelial ingrowth degenerates and ultimately dis- appears. A cavity is produced in it which later connects with the lumina of the gland ducts. The depressed nipple zone becomes elevated above the surface soon after birth. Further development of the mammary gland has been discussed previously under changes due to age and functional activity (p. 1303). THE DUCTLESS GLANDS Under the term ductless glands are included not only certain glandular struc- tures of epithelial origin with a more or less definitely known function and an internal secretion but also certain organs whose function is not definitely known or understood. Of the organs here considered, the function of the thyreoid gland, the parathyreoid glands, the chromaffin system, the medullary portion of the suprarenal glands, and the aortic paraganglia is somewhat definitely known. But the function of the thymus, the spleen, the cortical portion of the superenal glands, the glomus caroticum, and the glomus coccygeum is still in doubt; although probably some, if not all of them, have an internal secretion or at any rate are closely associated with the other glands of internal secretion. The hypo- physis and the pineal body are not considered in this connection but will be found described with the brain (pp. 845,848). The lymph-nodes, which may also be considered as ductless glands, are described in Section VI. Many of the true glands, such as the liver, pancreas and sexual glands, have also internal secre- tions which pass directly into the vascular system as in the ductless glands. THE SPLEEN The spleen [lien] is a large blood-vascular organ closely associated with the lymphatic system. Its exact function is still in doubt. Position. — The spleen is situated in the dorsal part of the left cephalic segment of the abdominal cavity so deeply placed against the diaphragm and dorsal to the stomach and colon as to be invisible from the ventral surface of the body when the abdominal cavity is opened. It is mainly in the left hypochondriac region but its deepest and most cephalic part extends also into the epigastric region. It is obliquely placed with its long axis corresponding approximately to the line of the caudal ribs. It tends to become more vertical when the stomach is fully distended but when the stomach is empty and the colon distended it assumes a more hori- zontal position. Changes in the attitude of the body also cause slight altera- tions in the situation of the spleen. It moves with the excursions of the dia- phragm in expiration and inspiration. The colour of the spleen is, in life, a dark bluish-red or brownish-red, but after death it becomes darker with a more bluish or violet tint. The size of the spleen is perhaps more variable than that of any other large THE SPLEEN 1307 organ in the body. Not only does the size differ in different individuals but it changes greatly with the blood content in the same individual. There is a dis- tinct expansion for a time after each meal and the spleen contracts and expands rythmically. Fig. 1062. — Wedge-shaped Spleen, Viscebal Surface. Diaphragmatic surface Margo anterior Extremitas superior Margo posterior Margo posteno. Lower end of renal surface Gastric surface Extremitas inferior In the adult it usually measures 10 to 15 cm. in length, 7.5 to 10 cm. in breadth, and 2.5 to 4 cm. in thickness. The weight usually ranges from 150 to 225 gm. At birth it represents from jitg to jjo of the total body weight and this porportion is maintained wuthout much varia- tion until the age of fifty years, when (like the lymphoid organs in general) it begins to diminish Fig. 1063. — Tetkahedral-shaped Spleen, Visceral Surface. Extremitas superior Renal surface- Margo posterior Intermediate angle Posterior extremity Gastric surface Hilus lienis Margo anterior Anterior extremity in size. This diminution continues until in the very old it represents but y J „ of the body weight- There is no great difference in relative size in the two sexes. The spleen is somewhat soft and very friable. It is elastic, extensible, contractile, and extremely vascular. Shape. — Iia form the spleen varies greatly. This is due largely to its softness which permits considerable modifications by the pressure of the distended or con- 1308 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS tracted surrounding hollow viscera. When in situ with the stomach distended, its shape may be compared to a blunt spherical wedge with a concave apex and rounded extremities, and possessing therefore three surfaces (fig. 1062); but when the stomach is contracted and the left flexure of the colon distended an addi- tional surface is produced and its shape becomes tetrahedral (fig. 1063). Inter- FiG. 1064. — Spleen Showing Tttbebcle on the Intermediate Border. -Extremitas superior Gastric surface Margo anterior Extremitas inferior mediate forms between these extremes are produced by variations in the degree of distention of stomach and colon. The spleen presents two aspects: lateral or parietal, against the diaphragm; and medial or visceral, toward the abdominal cavity. In its usual wedge form the three surfaces of the spleen are diaphrag- matic, gastric, and renal. There are three borders, anterior, posterior, and inter- mediate; and two extremities, superior and inferior. Fig. 1065.- -Cross-section op the Body at the Lower Part of the Epigastric Region. (Rtidinger.) Transverse colon Aorta Stomacli Liver Gall-bladder Kidney The diaphragmatic surface [facies diaphragmatica] is a smooth convex surface with an irregularly oval outline, in the wedge-shaped spleens wider cephalically, but in the tetrahedral-shaped spleens wider caudally. It looks dorsally toward the left and somewhat cephahcally. It lies against the diaphragm over an area opposite the ninth, tenth, and eleventh ribs and the intervening intercostal spaces, with its long axis corresponding in a general way to the course THE SPLEEN 1309 of the ribs. Although it is separated from the ribs by the peritoneum, the diaphragm, and the left pleural cavity (cephalically also by the left lung) (figs. 1065, 1066), the ribs sometimes make impressions upon it. The gastric surface [facies gastrica] is a semilunar-shaped surface, concave cephalo-caudally and from side to side, wiiich looks ventrally to the right and somewhat caudally (figs. 1062, 1065, 1066). Nearly parallel with the dorsal boundary of this surface is a narrow depression usually formed by a series of pits, as a rule six or eight, which together form the hilus of the spleen [hilus lienis]. In this situation the vessels and nerves enter and leave the spleen, the vein being dorsal. When the stomach is distended it is in contact with the major part of the gastric surface; the left flexure of the colon forming an impression upon a small area near the caudal extremity and the taU of the pancreas, as a rule, resting against a narrow area dorsal to the hilus or just Fig. 1066. — Sagittal Section through the Left Side op the Body, Showing the Relations of the Spleen. IX, X, XI, XII, corresponding ribs. 1, Left kidney; 2, spleen; 3, pancreas; 4, splenic vessels; 5, transverse colon; 6, stomach; 7, left lobe of liver; 12, lung; 14, heart; 16, diaphragm. (Testut and Jacob.) L' ' vnr cephalic to the colon. When the stomach is empty and contracted and the colon distended the size of the gastric area is considerably decreased and the relative size of the coUc impression greatly increased so as to form upon the spleen in this situation a colic or basal surface (fig. 1063). The stomach is, however, at all times in contact with some part of the spleen. The renal surface [facies renalis] the smallest of the three surfaces, shorter as well as narrower than the gastric surface, is an oblong, flat or slightly concave area, which faces dorsally, to the right and slightly caudally. It is in relation with the anterior surface of the left kidney (fig. 1066). In some cases the cephalic third of the renal surface is also in relation with the anterior sur- face of the suprarenal gland. It is separated from these latter structures, however, by the renal adipose capsule as well as by the peritoneum. The tail of the pancreas in some cases is in con- tact with a small area on the ventral part of this surface. In fat individuals these relations are not as intimate as the relations with other organs because of the large amount of suprarenal fat. The anterior border [margo anterior] is clearly defined, thin, sharp, and more or less convex. It is marked in over 90 per cent, of the cases by one or more trans- verse or oblique notches, especially in its cephalic part. It is placed between the 1310 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS diaphragm and the stomach and separates the diaphragmatic from the gastric surface (figs. 1062-1065). The posterior border [margo posterior] is rounded, shorter, and straighter than the anterior border and is notched in less than a third of the cases. It separates the diaphragmatic from the renal surface and is lodged in the angle between the left kidney and the diaphragm (figs. 1062-1065). The intermediate border is a blunt ridge dorsal to the hilus, separating the gastric from the renal surface. It may be clearly defined or more or less obscure and often shows a marked tubercle (fig. 1064). When the stomach is contracted and the colon distended this border divides caudally into ventral and dorsal limbs both of which may be well marked or either may be deficient depending on the direction and degree of pressure of surrounding organs. When well marked there is produced at the point where the two limbs diverge a more or less marked projection, the intermediate extremity or angle (fig. 1063). The superior extremity [extremitas superior], usually larger than the inferior extremity in the wedge-shaped spleens but smaller in the tetrahedral form, is rounded and bent medially. It extends as high as the tenth thoracic vertebra and lies 1 to 2 cm. from the vertebral column. The inferior extremity [extremitas inferior], also somewhat rounded, is directed toward the left and caudally. It is in relation with the phrenicocolic ligament. When the stomach is contracted and the colon distended the inferior extremity becomes much broader, in extreme cases forming a distinct inferior border ending ventrally in the anterior margin as an anterior extremity and dorsally in the posterior margin as the posterior extremity (fig. 1063). In the tetrahedral-shaped spleen the additional surface produced by the pres- sure of the colon is known as the basal or colic surface (fig. 1063). This varies in size reciprocally with the degree of pressure of colon and stomach. When well developed the cohc surface is concave and is separated from the renal and gastric surfaces by the more or less sliarply defined dorsal and ventral limbs of the intermediate border and separated from the diaphragmatic surface by an inferior margin produced from the broadened inferior extremity. The left flexure of the colon is in contact with the greater part of this sur- face, but the pancreas also usually hes against it in its cephahc part (fig. 1063). Peritoneal relations. — The surface of the spleen is completely covered, except for a small area at the hilus, by a peritoneal coat, the tunica serosa. Ventral to the hilus a double layer of peritoneum is prolonged from the spleen to the left side of the greater curvature of the stomach and the left edge of the ventral layer of the great omentum, forming the gastrolienal ligament which contains the short gastric arteries and veins. Dorsally a second double layer of peritoneum extends from the hilus to the ventral surface of the kidney and the caudal surface of the diaphragm forming the phrenicolienal (lienorenal) ligament. This ligament encloses the splenic artery and veins as they pass to and from the spleen. It is also between the two layers of peritoneum of this ligament that the tail of the pan- creas reaches the spleen (fig. 1065). Except by these two Hgaments the spleen has normally no attachment to the abdominal wall or to any of the surrounding viscera. The gastroHenal, and more especially the phrenicohenal ligament, serve in a measure to anchor the spleen in its place in the abdominal cavity but in addi- tion to these the spleen is supported by a fold of peritoneum which e.xtends from the left cohc flexure to the parietal peritoneum over the diaphragm, the phrenico- colic ligament. This serves as a shng in which the inferior extremity of the spleen rests. The spleen, however, is held in position in the abdominal cavity mainly by the intraabdominal pressure. Topography. — The superior extremity of an average-sized spleen is located between the angle and tubercle of the tenth rib on the left side and about 3 to 4 cm. from the median line on a level with the spinous process of the ninth thoracic vertebra. In the majority of cases, it does not extend more than 2 cm. either cephalic or caudal to a transverse plane at the level of the infra- sternal notch. The inferior extremity reaches nearly to the midaxillary lioe in the tenth inter- costal space and 10 to 15 cm. from the superior extremity. The long axis therefore corresponds nearly to the shaft of the tenth rib. The posterior border lies beneath the cephalic border of the eleventh rib. The whole spleen (unless enlarged) lies dorsal to a plane passed through the midaxillary lines and is lateral to a line from the left sternoclavicular joint to the tip of the left eleventh rib. In deep inspiration the spleen is greatly depressed and if enlarged may be felt beneath the ribs. Variations. — From the mean weight between 150 and 200 gm. there are wide variations. It is not rare to find spleens weighing 80 to 100 gin. and they are recorded as light as 10 and THE SPLEEN 1311 20 gm. On the other hand, spleens weighing 3000 to 4000 gm. are sometimes foimd. These are usually, however, associated with an acute infectious disease, such as malaria or typhoid fever, or a progressive metamorphosis, such as leukemia. Congenital absence of the spleen is one of the rarest anomaUes. The presence of more than one spleen is the commonest anomaly of the spleen. Adami has found accessory spleens to occur in 11 per cent, of all autopsies. They are round or oblong and vary in size from a pea, or smaller, to a walnut. There are most often one or two but there may be twenty or more. They are found near the hilus on the dorsal side of the gastroUenal ligament, less often, in the great omentum, in the mesentery, on the wall of the intestine, or in the tail of the pancreas. In certain cases the left lobe of the liver is very long and prolonged far to the left and sepa- rates the spleen from the diaphragm. This is the rule in the foetus and is often found in the infant but is exceptional in the adult. Exceptionally the spleen may be placed far caudal to the normal situation extending into the iliac region and even into the pelvis. This is due in part to congenital laxness of the supports, also to increase in weight. The spleen has been found in almost every part of the abdominal cavity and in transposition of the viscera it is upon the right side. One or more notches on the anterior border are present according to Parsons in 93 per cent, of the oases, two or more in 66 per cent., but five, six, or seven much more rarely. On the pos- terior border notches are found in 32 per cent, of the cases, and on the inferior border in 8 per cent. In 20 per cent, of the cases a marked fissure, occasionally more than one, is found on the diaphragmatic surface. Most frequently it begins at one of the notches in the posterior border and passes for a distance across the surface, rarely reaching the anterior border. Occasionally such a fissure starts from the anterior border and rarely there is such a fissure connecting with neither border. Fig. 1067. — Portion op Section op the Spleen of an Adult Man. (Lewis and Stohr.) X15. '( 1 f Splenic pulp Spindle-shaped nodule Trabeculse lienis Central arteries in splenic nodules Structure. — The peritoneal covering of tlie spleen, tunica serosa, is intimately bound to the underlying, whitish, highly elastic fibrous capsule, the tunica albu- ginea (fig. 1067). This is composed mainly of white fibrous connective tissue but contains numerous fine elastic fibers, and a few smooth muscle fibres. It is much thicker than the serous covering and completely invests the spleen. From its dee]) s\irt':ice the tunica albuginea gives off into the interior numerous trabecule, trabeculae lienis, which join with one another and form a framework in which course the blood-vessels, more especially the veins. It is through the contraction of the smooth muscle fibres in the tunica albuginea and trabeculae, that the regular periodic contraction and expansion of the spleen is produced. In the meshes of the trabecular network, lymphoid tissue which forms the proper splenic tissue, the pulpa lienis, is located. This is soft, friable, and dark brownish or bluish-red in colour. In this, in a fresh spleen, are seen small round whitish or greyish masses from .25 to 1.5 mm. in diameter, the Malpighian cor- puscles [noduli lymphatici lienales; Malpighii]. The trabecula3 are in connection with a reticular network which permeates the spleen sub- stance or spleen-pulp. Mall has shown that the trabeculse and vascular system together out- 1312 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS line masses of spleen-pulp about 1 mm. in diameter, known as splenic lobules. Each lobule is bounded by three main trabeculae, from each of which secondary trabeculoB pass into the sub- stance of the lobule incompletely subdividing it into compartments, filled with splenic pulp, arranged in the form of anastomosing columns or cords and designated as pulp-cords. The branches of the splenic artery, after coursing for a short distance in the main trabeculae, leave these, and, after further division, become surrounded with a layer of adenoid tissue, which layer presents here and there irregular thickenings forming the Malpighian corpuscles. An arterial branch, surrounded with adenoid tissue, enters the apex of a splenic lobule, constituting its intralobular vessel, which, soon after entering the lobule, loses its adenoid sheath and then sends a branch to each of the above-mentioned compartments. These branches do not anas- tomose. They give off terminal branches which course in the pulp-cords, form dilations, ampuUse, and terminate directly or indirectly in the large venous spaces found between the pulp- cords. From the latter the blood passes, by means of small intralobular veins, to interlobular veins situated in the trabeculae bounding the lobules. Some of the ampullae are connected with one another by capillary branches. Blood-supply. — The spleen receives its blood from the splenic artery, which is very large in proportion to the size of the organ it supplies. It divides in the phrenicolienal ligament into from three to six or eight branches, rami lienales (fig. 1062), which enter the spleen at the hilus. After entering the spleen the arteries divide and subdivide and run to their termination in the ampullae without anastomosing. They form what are known as terminal arteries. The main splenic artery is very tortuous. The vein, vena lienalis, leaves the spleen usually by the same number of branches as the entering artery. These imite in the phrenicohenal ligament to form a large trunk which is straighter than the splenic artery and hes caudal to it. The lymphatics. — A superficial and a deep set of lymphatics have been described in the spleen. The former is said to form a plexus beneath the peritoneum and the latter to be derived from the fine perivascular spaces in the adenoid tissue around the vessels. From these several trunks arise and joining at the hilus pass between the layers of the phrenicolienal hgament to empty into the lymph-glands dorsal to and around the cephalic border of the tail of the pancreas. The presence of both superficial and deep sets of lymphatics in the human spleen has been denied by some investigators. According to Mall, there is no deep set. The nerves. — The nerves are derived from the right vagus and from the coeliac plexus. They enter the spleen at the hilus, accompanying the branches of the lienal artery. They are composed mostly of non-medullated fibres which form a rich plexus around the arteries supply- ing the muscular fibres in the media while a second group has been traced to the muscular fibres of the trabecule. Development of the spleen. — The first anlage of the spleen is seen in the fifth week of foetal life as a swelling on the dorsal (left) surface of the mesogastrium. This is due to an increase in the mesenchymal cells as well as to a thickening of the coelomic epithelium. This latter becomes stratified, and indistinctly differentiated from the underlying embryonic connective tissue through the transformation of the deepest of the epithelial cells into mesenchymal cells. As development proceeds the thickened mass becomes entirely isolated and the ccelomic epithelium covers it as a single layer. The arteries are seen first as a capillary network throughout the organ which considerably later become arranged as tufts of widened capillaries, the anlage, of the vascular structural unit. These spherical groups of arterial capillaries leading by wide openings into a wide meshed venous plexus are boimded by trabecule from the capsule. The number of structural units in the spleen seems to be fixed fairly early but the size and complexity changes greatly. The spherical mass with a single central artery changes to the adult condition where the central artery gives off side branches, each of which has a spherical mass of capillaries, and the pulp intervenes between the artery and the vein so that the capillary circulation of the early embryo becomes the cavernous circulation of the adult. The lienal lymphatic nodules of Malpighi and the splenic pulp appear only in the latter half of embryonic life. THYREOID GLAND The thyreoid gland [glandula thyreoiclea] is an extremely vascular, ductless gland, whose internal secretion, acting as a stimulus to the tissues, has a profound influence on the nutrition of the body and on the nervous system. It is a single organ composed of two lateral, frequently unsymmetrical, masses, joined to- gether by a transverse median band. The median transverse band or isthmus [isthmus gl. thyreoidese] is thin and narrow, and often has a long slender process, ' the pyramidal lobe [lobus pyramidalis], extending from it cephalically. The lat- eral parts or lobes [lobi, dexter et sinister] form the principal mass of the gland. It is situated in the ventral portion of the middle third of the neck on both sides of the larynx and the cephalic end of the trachea, dorsal to the infrahyoid group of muscles. The consistency of the thyreoid gland is uniformly soft and compressible. The colour is reddish, with a brownish or yellowish cast, but becoming more bluish or reddish with changes in its blood content. The size is subject to considerable individual variation and is slightly greater in women than in men. The normal thyreoid gland measures from 4 to 6 cm. in width at its widest part. The lateral lobes measure from 5 to 8 cm. in length. THE THYREOID GLAND 1313 about 2 cm. in width, and from 1.5 to 2.5 cm. in thickness. The right is usually a little longer than the left. The isthmus averages from .6 to .8 cm. in thickness and from .5 to 1.5 cm. in height. The weight of the normal gland averages about 30 grams; but many specimens are found as light as 20 grams, and others weigh as much as 60 grams. When hyperemio or congested the size of the gland may be markedly augumented. This occurs normally in most women at puberty and dm-ing menstruation and pregnancy. In various abnormal conditions of the gland there is an increase in size, sometimes to a marked degree. These enlargements are ordinarily grouped under the term struma or goitre, and may be associated with either a hyper- or hyposecretion of the gland. Decrease in size is common in old age and may appear prematurely in certain diseases. The shape of the gland as viewed from the ventral surface is that of a capital U with the concavity directed cephahcally (fig. 1068). The sides of the U are formed of the more or less elongated lobes connected slightly cephahc to their Fig. 1068. — Ventral View op the Thyreoid Gland. t of hyoid bo -Body of hyoid bone Hyo-tbyreoid ligament — Thyreoid cartilage Thyreoid isthmus Hyo-thyreoid membrane Thyreo-hyoid muscle Inferior constrictor Sterno-thyreoid muscle Median portion of crico- thyreoid membrane Crico-thyreoid muscle Lateral lobe of thyreoid gland thickened caudal ends by the thin transverse isthmus. In transverse sections through the isthmus the gland is also U-shaped with the concavity directed dor- sally, the lobes being on each side and the isthmus ventral to the trachea (fig. 1068). The surface of the gland is somewhat unevenly roughened. The isthmus glandulae thyreoidae usually becomes wider laterally where it is attached by its two extremities to the lateral lobes (figs. 1068, 1069). Its ventral surface which is flat or somewhat convex is covered superficially by the sub- cutaneous tela and skin and beneath these by the superficial and middle layers of the cervical fascia. Between the layers of cervical fascia and close to the median line is the sterno-hyoid muscle and more laterally and deeper the sterno-thyreoid muscle. The dorsal surface is concave and is in relation with the first two to four rings of the trachea and sometimes with the cricoid cartilage. The size and form of the isthmus is subject to considerable variation. It may be very short. Rarely it is wanting entirely or connects with but one lateral lobe. Its superior border is, as a rule, concave and is connected in many cases with the pyramidal lobe. The caudal border, although usually on the third ring of the trachea and 2.5 to 3 cm. from the jugular notch of the sternum, may be especially developed so that it extends caudally beyond the lateral lobes and produces a process which is known as the medial lobe. i 1314 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS The pyramidal lobe is usually a narrow elongated flattened somewhat conical process of thyreoid tissue representing the persistent portion of the median embry- onic thyreoid (fig. 1069). Its base is attached ordinarily to the left side of the Fig. 1069. — Thyreoid Gland, with Pthamidal Lobe and Levator Muscle. Sterno-hyoid ligament Sterno-hyoid muscle Omo-hyoid Thyreo-hyoid Body of hyoid bone F/— Hyo-thyreoid ligament •llljl Hyo-thyreoid membrane Levator glandules thyreoidese Thyreoid cartilage Pyramidal lobe of thyreoid gland Left lateral lobe superior border of the isthmus and its apex which extends cephalically a variable distance, often to the superior border of the thyreoid cartilage, is attached by a fibrous cord, the thyreoid ligament. The pyramidal lobe is not always present. Some investigators have fomid it present in only 40 per cent of all cases ; others in as high as 90 per cent. The average is somewhere between Fig. 1070. — Cross-section op Neck Showing Relations op the Thyreoid Gland. (After Braune, from Porier and Charpy.) Sterno-hyoid --Sterno-thyroid • Trachea Omohyoid 'ni//|/ffl^ffll^^^^'^>^^.^^^ Platysma laV>Cl'^'^ ^ Sterno-mastoid ■/ \ \ ■ t /'/ij'i.MlJL -- ^-J LateraMobe of 4i' \ ^ -^ ^^1 r.^f?^Kl^X il '^y'-idsland ^^>#i"'^'-A ^*>tenD«rf!>"' )|\v. "> ;;*^ 'SfflH»^^^l&.>^ A carotiscom. ^ ^^ p^=^_=^r^#;— .t-;^__— ^ l^r ^ - N. vagus K%'''Vp'^eh"8fCSf^PfW^W^ T^ ^^'' *• ttyreoidea sup. t^^->^,'ii'^'^*i.^M^W ^ ^^- Sympathetic trunk ^t^J^^i^MmVTi^'l ^ A. thyreoideainf. A. vertebralis these extremes. It is closely adherent to the subjacent structures, usually at one side of the median line, more often the left. The superficial relations of the pyramidal lobe are similar to those of the isthmus. Its deep surface is in relation also with the cricoid and thyreoid cartilages, the crico-thyreoid muscle and the hyo-thyreoid ligament. THE THYREOID GLAND 1315 The pyramidal lobe, though usually single, may be double or bifid at its caudal end, one process joining each lateral lobe. It may be attached in the angle between the isthmus and one of the lateral lobes, or to the lateral lobe itself. It may be cylindrical, band-hke, or swollen at its centre or cephaho end and is occasionally entirely separate from the rest of the th}Teoid or divided into separate detached parts, thus forming accessory th}Teoids. The apex in some cases extends to the middle of the thyreohyoid membrane or rarely to or beyond the hyoid bone or the process may be quite short. In the thyreoid ligament, attached to the apex, muscle fibres are sometimes found, aberrant parts of the infrahyoid muscles, the levator of the thyreoid gland. The thyreoid lobes, right and left, are placed on each side of the trachea and larynx (figs. 1068, 1069, 1070). Each lobe is somewhat pyramidal in shape and presents for examination a base, an apex, a medial, a ventro-lateral, and a dorsal surface. The base is roughly convex or pointed, rarely flattened, usually at the level of the fifth or sixth ring of the trachea (figs. 1068, 1069). It is separated from the jugular notch of the sternum by a distance of 1.5 to 2 cm. but when the head is extended the distance is greatly increased. It is in relation with the inferior thy- reoid artery and numerous veins, mostly tributaries of the inferior thyreoid vein. The apex is pointed or rounded (figs. 1068, 1069). It is directed cephalo- dorsally and is situated at the dorsal border of the lateral lamina of the thyreoid cartilage at the level of its caudal, or rarely its middle, third. ' It is covered by the sterno-thyreoid muscle beneath which the superior thyreoid artery accompanied by the corresponding vein crosses the apex to reach the gland. It is also crossed in this situation by the external ramus of the superior laryngeal nerve as it passes to the crico- thyreoid muscle. The medial surface of the lateral lobe is concave and intimately bound to the trachea and cricoid cartilage (fig. 1070). Toward the apex it becomes more flattened where it comes into contact with the lateral lamina of the thyreoid cartilage. At the border where this surface joins with the dorsal surface it is in relation with the oesophagus and pharynx, and in the angle between these structures and the trachea and larynx it is close to the recurrent laryngeal nerve. The dorsal surface (fig. 1070) is broad and rounded caudally, but toward the apex is reduced to a mere border. It lies upon the fascial sheath containing the common carotid artery, the jugular vein, and vagus nerve, most intimately related to the common carotid artery which usually produces a groove in it. The inferior thyreoid artery sends large branches over this surface. The inferior thyreoid veins also have large branches here. Imbedded in the connective tissue in relation with this surface the parathyreoid bodies are found, and in some cases the recurrent nerves are placed so far laterally that they also touch this siu-face. In many cases the sympathetic trunk and the middle cervical ganglia of the sympathetic with the cardiac branches are closely related to the dorsal surface of the gland. The ventro-lateral surface is convex and is separated by loose connective tis- sue from the overlapping sterno-thyreoid, sterno-hyoid, and omo-hyoid muscles. More superficial on its lateral aspect is the sterno-cleido-mastoid muscle. The above muscles are enclosed by the superficial and middle sheets of the cervical fascia. In the subcu- taneous tela the platysma muscle spreads over the gland. This surface of the gland is covered by a plexus of veins and by branches of the superior thyreoid artery. Accessory thyreoid glands are small masses of glandular tissue one or more of which may be found situated in the median line or at one side of it anywhere between the isthmus and the root of the tongue. They vary considerably in size and represent parts of the pyramidal lobe or isthmus which have become completely separated from the rest of the gland. In structure they are composed of the same tissue as the rest of the gland. Fixation. — In addition to the connective tissue which binds the thyreoid gland to the trachea, it is attached by the connection of its capsule with the cervical fascia and by the fibrous prolongations from the capsule. These prolongations are found medially attaching the isthmus and adjoining portions of the lateral lobes to the ventral surface of the cricoid cartilage, the caudal border of the thyreoid cartilage, and the sheath of the crico-thyreoid muscles, and laterally attaching the lateral lobes to the trachea and lateral surface of the cricoid cartilage. In addition to these the connection of the vessels and nerves to the gland helps to fix it in position. Structure. — The thyreoid gland like other glands is composed of a connective- tissue stroma supporting an epithelial secreting parenchyma. 1316 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS The connective tissue which covers the surface of the gland forming for it a capsule, may be divided into two layers, superficial and deep. The superficial layer intimately connected with and derived from the fascia colli as pointed out above has an important fimotion in supporting and fixing the gland. This layer is in some cases thin and transparent; in other cases it is very tough and thick. It is connected by loose areolar tissue with the thin deep layer of the capsule. Between these two layers the larger vessels run for a space before entering the gland and the veins, particularly, form here con- siderable plexuses. From the deeper layer of the capsule numerous trabeculse and septa carrying blood-vessels, lymphatics, and nerves pass into the gland and imperfectly separate its parenchyma into irregular masses of variable size, the lobules [lobuli]. Each lobule is composed of a number of closed, non-communicating, irregular, spherical, ovoid, or sometimes branched alveoli, acini or vesicles, varying in size from .045 to .22 mm. in diameter and separated and bound together by a vascular connect- ive tissue continuous with that surrounding the lobules and with that of the cap- FiQ. 1071. — Arteries of the Thyreoid Gland, Anterior View. 1. Lateral lobe; 1' pyramidal lobe; 2, trachea; 3, thjrreoid cartilage; 4, crico-thyreoid membrane; 5, hyo-thyreoid membrane; 6, 7, 8, 9, inferior thyreoid artery and branches; 10, 11, 12, 13, 14, 15, superior; thyreoid artery and branches; 16, thyreoidea ima. (Testut and Jacob.) — I'l 4i sale. The vesicles are filled with a yellowish viscous fluid, known as coUoid, the secretion of the epithelial cells. The vesicles are lined with a single layer of epithelial cells of a fairly uniform cuboidal or columnar shape, becoming flattened in distended vesicles and ia old age. The cells are not supported by a basement membrane but are in close relation with connective tissue and capillary blood-vessels. An extremely rich lymphatic network surrounds the vesicles and the lymph-vessels come into intimate relation with the cells. Through these vessels the secretion is conveyed from the gland to the general circulation. Blood-vessels. — The thyreoid gland has an extremely abundant blood- supply. The arteries are usually four in number but occasionally five (figs. 1071-1073). The superior thyreoid arteries divide into two, three, or more main branches which reach the gland near the apex of the lateral lobes and supply mainly the ventral and medial surfaces of the cephahc portion of the lobes (fig. 1071). There is usually also a dorsal branch, which anasto- moses with a branch from the inferior thyreoid. One of the ventral branches frequently con- nects along the cephalic border of the isthmus with its fellow of the opposite side. The inferior thyreoid arteries break up into two or three main branches, occasionally into many fine twigs, which reach the dorsal surface of the lateral lobes near the eaudolateral borders and supply THE THYREOID GLAND 1317 mainly the dorsal and lateral surfaces of the caudal part of the gland (fig. 1071). There is usually a well-marked branch which passes cephalioally to anastomose with a good-sized branch from the superior thyreoid. Small branches are distributed to the ventral surface of the caudal portion of the lobes and isthmus. The small fifth artery, the thyreoid ima artery, occasionally present, ascends on the ventral surface of the trachea and reaches the gland at the caudal border of the isthmus or of either lobe. It anastomoses with the other arteries which may be correspondingly reduced in size. The above-mentioned arteries branch freely and are distributed over the surface of the gland between the two layers of the capsule where they anastomose extensively with one another and with the arteries of the opposite side. From the surface plexus branches pass with the septa and trabeculse through the gland to break up into the capillary plexuses around the vesicles. The relation of the inferior thyreoid artery to the recurrent nerve is important from a surgical point of view but unfortunately is not constant. In some cases the nerve is ventral to the artery, more often on the right, in other cases it is dorsal and often the nerve passes be- tween the branches of the artery. Their relation is most intimate close to the trachea Fig. 1073. Fig. 1072. — Vessels of the Thyreoid Gland, Anterior View. 1, 2, 3, Lateral lobes and isthmus; 4, pyramidal lobe; 5, hyoid bone; 6, thyreoid cartilage; 7, trachea; 8, common carotid;. 9, internal jugular; 10, thyreo-linguo-facial vein; 11, superior thyreoid artery; 12, inferior laryn- geal vessels; 13, middle thyreoid vein; 14, subclavian artery; 15, inferior thyreoid artery; 16^ inferior lateral thyreoid veins; 17, inferior medial thyreoid veins; 18, left innominate vein; Ift aortic arch; 20, vagus nerve. (Testut.) The veins (fig. 1072) issue from the substance of the gland along the septa which penetrate from its capsule. Between the two layers of the capsule they form a rich plexus of large vessels from which three large branches issue on each side. The superior thyreoid veins leave the capsule of the ventral surfaces of the lateral lobes near their apices and pass cephalo-laterally to empty into the internal jugular veins, sometimes with the facial veins. The middle thyreoid veins are sometimes absent, when present they^are often very small and pass from the lateral border of the lateral lobes laterally to empty in to' the internal jugular vein. The inferior thyreoid veins arise from the caudal and lateral part of the dorsal surfaces of the lateral lobes and pass caudolaterally to open into the innominate veins. Ventral to tlie trachea, caudal to the isthmus, the two inferior thyreoid veins are connected by numerous cross anastomoses and occasionally they open by a single trunk which joins the left innominate vein. A thyreoidea ima vein is sometimes present. The lymphatics of the thjTeoid gland begin as abundant plexuses arovmd the vesicles of the gland lobules. These connect with the interlobular branches which empty into radicles accompanying the blood-vessels through the septa to the surface of the gland where they join a considerable plexus placed between the two layers of the capsule. From the cephalic portion of the isthmus and lobes efferent vessels extend cephalo-medially to one or two small i 1318 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS pre-laryngeal glands and cephalo-laterally along with the superior thyreoid artery to the deep cervical glands. From the caudal part of the lateral lobes and isthmus efferent vessels pass caudally to some small pre-tracheal glands and caudolaterally to the deep cervical glands. The nerves of the thyreoid gland are probablj' all derived from the sympathetic and arise from the middle and inferior cervical ganglia and accompany the arteries to the gland. Development. — The thyreoid gland is first seen in very young embryos as a prominence on the ventral wall of the pharynx. This becomes a stalked vesicle and divides into lateral lobes. The stalk elongates forming the thyreoglossal duct of His. Later the lumen is obliterated and the duct is then represented by an epithehal cord which soon loses its connection with the pharynx. It opens at first cephalic to the regular second branchial arch on the summit of the tuberculum impar but later shifts to its caudal boundary (Grosser). It is represented in the adult only by a short blind pouch, the foramen csecum but very rarely a considerable duct may be present. The bilobed mass appears to shift caudally, increasing m size and spreading laterally and dorsally. The median cord of cells formed from the stalk becomes the isthmus and the p3rramidal lobe, when this is present, the lateral portions form the lateral lobes. The gland is now composed of irregular, in general transversely disposed cords of cells. More rapid growth later occurs in the centres of the lateral lobes and the cell cords become closely packed with,Jittle connective tissue between. Lumina appear in different places in the cell cords and the cell cords are broken up into groups of cells; in these the lumina continue to appear even up into early childhood. On each side, diverticula from the more caudal pharyngeal pouches, the ultimobranchial bodies, come into contact with the dorsal and lateral parts of the anlage of the thyreoid gland and become partly enclosed in the neighbourhood of the transversely running cell cords. This core of cells becomes either a compact body or an irregular group of cells and is probably not transformed into thyreoid tissue. THE PARATHYREOID GLANDS The parathyreoid glands are small masses of epithelial cells found in the neigh- bourhood of the dorsal surface of the thyreoid gland but quite distinct from it and Fig. 1073. — Parathteeoid Glands, Viewed Fkom Behind (Natural Size). H — Pharynz Common carotid ort. i_ Branch of sup. thyreoid art. I — Internal jugular V. Superior parathyreoid p- Vagus nerve — Lateral lobe of thyreoid — Inferior parathyreoid i I ' — Inferior thyreoid art. Recurrent (inferior 'laryngeal) nerve I — Trachea ^(Esophagus of different structure. They are ductless glands and although very small they are essential to life. The usual number is four, two on each side, in relation with the lateral lobes of the thyreoid gland (fig. 1073) . In colour they are yellowish with more or less of a reddish or brownish tint but lighter than the thyreoid gland. Their consistency varies somewhat but usually it is softer than that of the thyreoid gland. The shape of the majority of the glands is a flattened ovoid, sometimes tapering at one or both ends, rarely a flattened circular disc. At some place on the surface there is usually a depressed hilum where the artery enters and the vein leaves. The average size of the glands is 6 to 7 mm. in length; 3 to 4 mm. in width and 1 to 2 mm. in thickness. Occasionally they may be found 15 mm. in length. They THE THYMUS 1319 weigh from .01 to .1 gm. with an average of .035 gm. From their situation they have been divided into a superior, or internal, derived from the fourth branchial pouch, and an inferior, or external, derived from the third branchial pouch. The superior parathyreoid glands (fig. 1073) are found, as a rule, on the dorsal surfaces of the lateral lobes of the thyreoid gland at about the junction of the cephalic and middle thirds Occasionally they may be situated in the areolar tissue at the level of the apex of the thyreoid gland or cephalic to it. They may be ventral to the prevertebral layer of the cervical fascia, on the dorsal wall of the oesophagus or pharynx and close to the dorsomedial margin of the thy- reoid gland. They may also be placed at the level of the caudal border of the cricoid cartilagel rarely as high as the inferior cornu of the thyreoid cartilage or as low as the sixth trachea, ring. Sometimes they are imbedded completely in the thyreoid gland. As a rule, they are tightly attached to the capsule of the thyreoid gland or situated between its layers. The inferior parathyreoid glands (fig. 1073) are less constant in their situation than the superior. They usually are found in relation with the dorsal surface of the lateral lobes of the thyreoid glands, not far from their bases. They may be quite outside the region of the thy- reoid gland along the carotid arteries or tlie sides of the trachea, or they may be placed more cephalically than usual or extend caudal to the gland as far as the tenth tracheal ring, even into the thorax. They are imbedded, when caudally placed, in fatty areolar tissue in relation with the apex of the thymus gland and the inferior thyreoid veins or applied against the oesophagus. The parathyreoids are intimately related to branches of the inferior thyreoid artery, a separate branch of which supplies each of them. When there is a large branch of the inferior thyreoid artery anastomosing with the superior they are more or less in line with this. Each parathyreoid gland is surrounded by a fibrous capsule from which extremely vascular septa and trabecula; penetrate into the gland separating and binding together the masses of polyhedral cells which are arranged in solid groups or intercommunicating cords of varying sizes and shapes. The cell cords, as a rule, are not arranged like the thyreoid vesicles. At times the secretion may accumulate and produce a vesicular appearance and the secretion then closely resembles colloid. Two kinds of cells, oxyphile and principal cells, have been described; but the inter- mediate forms suggest that these are the same sort of cells in different stages of functional activity. The blood-vessels are distributed m the connective tissue of the trabeculae and thus their sinusoids are brought into close connection with the cells of the gland. The nerves are also distributed along the septa. In the highly vascular connective tissue ^between the cell cords fat cells are found separate or in groups. The number of parathyreoid glands found by different investigators varies. The average number in a series of cases is less than four. Whether this is due to a real absence of the glands or to failure to find them due to their aberrant location, their inclusion in the thyreoid gland, or the fusion of two glands, is not clear. In some cases it is the superior glands, in other cases the inferior glands, which appear to be missing. On the other hand various com- petent observers have reported finding more than four parathyreoid glands. Five or six are occasionally found; as many as eight have been recorded in one instance. In these cases the number on a side may not be symmetrical. The increased number may be due to the separation of buds in the course of development. The parathyreoid glands are liable to be associated with accessory thymus masses, with small lymphatic glands, and with fat lobules; and as they may somewhat resemble each of these, they may be mistaken unless a microscopic examination is made. Blood-supply. — Each parath3Teoid gland is supplied by a single separate artery derived, as a rule, from one of the glandular, muscular, or oesophageal branches of the inferior thyreoid artery or from the anastomosing branch between the superior and inferior thyreoid arteries. When the glands are in aberrant positions their arteries may be derived from the nearest source. The arteries are distributed along the trabeculae and septa. The veins returnmg the blood either follow the arteries or they pass to the surface of the gland where they break up into a plexus of thin-walled vessels. Upon leaving the gland the veins empty into some one of the branches of the thyreoid veins. Development. — The parathyreoids (epithelial bodies) begin as proliferations of the epi- thelium on the oral and lateral walls of the dorsal diverticulum of the third and fourth pharyn- geal pouches. The cells show early a histological differentiation with vacuolated and reticulated plasma. The common pharyngo-branchial ducts diminish in size and become constricted off and separated from the pharynx. The parathyreoid glands later become independent and separated from the thymus anlages. The epithelial cells grow out in the form of cords separated by connective tissue and in intimate relation to the blood-vessels. Different kinds of cells are not distinguishable until postfcetal life when evidence of secretion begins. THYMUS The thymus is a transitory organ of epithelial origin, but in structure resem- bling the lymphoid tissue. Its function is not clearly understood but it seems to be intimately associated with the growth and nutrition of the individual, and it is classed with the ductless glands of internal secretion. It is situated in the ventro-cephalic part of the thorax and extends into the caudal part of the neck (fig. 1074). It lies between the two pleural sacs ventral to the heart and great vessels, dorsal to the sternum and the sterno-thyreoid and sterno-cleido-mastoid muscles. 1320 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS Although arising from the branchial clefts one on each side of the neck, the two portions become so closely associated that they are usually spoken of as one. Each of these parts is ordinarily regarded as a lobe of the thymus [lobus, dexter et sinister]. In colour the thymus is pinkish or reddish grey in the foetus and newborn, becoming greyish white in the adult or yellowish as it undergoes involution. It is composed of soft, yielding tissue more friable than the thyreoid or spleen. In size the thymus varies greatly. Under normal conditions it appears to attain its maximum size at about the age of puberty, and to continue large as long as the body continues to grow and then to undergo a gradual involution. Fig. 1074. — Thymus Gland in a Child at Birth. Thyreoid cartilage./^ Sterno - thyre oi d e u s Crico-thyreoid membrane Crico-thyreoid muscle Thyreoid gland Right common carotid artery Right vagus Right internal jugu- lar vein Level of sternum Section of clavicle Section of first rib Section of sternum Thyreo-hyoideus -hyoideus Cricoid cartilage First ring of trachea Trachea Left suspensory ligament Left recurrent nerve (Esophagus Left innominate vein Left lobe of thymus Left internal mam- mary artery Left lung Section of fifth rib cartilage Xiphoid process It is, however, very sensitive to any nutritive changes of the individual and becomes very small, even in the infant, under the influence of wasting diseases. It not infrequently exists in the adult only as a vestige but in some cases it may remain large until middle age or later. At birth it is usually from 50 to 60 mm. long cephalo-caudally and about half as broad. The weight varies with the size. It is given by Hammar as over 13 gm. at birth, increasing to double this between the sixth and the tenth years and gaining its maximum of between 37 and 38 gm. between the eleventh and fifteenth years. From this time the weight decreases until between the ages of fifty-six and sixty-five it weighs between 25 and 26 gm. and at seventy- five years may be as light as 6 gm. The involution of the gland is not accompanied by a cor- responding reduction in size and weight as the thymic tissue is gradually invaded by fatty tissue which maintains to some extent the form of the organ. In shape the thymus is an elongated, spindle-shaped mass consisting of the central portion or body and two extremities (figs. 1074, 1075). The body is the THE THYMUS 1321 widest and largest part of the organ and has no distinct separation from the extremities. The inferior extremity is also broad and is known as the base. It rests on the pericardium, ordinarily extending as far caudal at birth as the atrio- ventricular furrow but rarely it may extend as far as the diaphragm. The superior extremity is much elongated and extends into the neck. It is represented by two horns nearly always unequal in size the left being usually the larger. It extends nearly to the thyreoid gland, in some cases reaching it. Relations. — Topographically the thymus when well developed is divided into cervical and thoracic parts. The cervical portion presents for examination an anterior surface and a posterior surface. The anterior surface is convex and is in relation with the sterno-thyreoid and sterno-cleido- mastoid muscle. The posterior surface is concave and rests medially upon the anterior surface of the trachea, laterally upon the common carotid artery and sometimes on the left side upon the oesophagus. The thoracic portion of the thymus is much more important representing four-fifths of the organ (fig. 1075). It presents for examination an anterior, a posterior, and two lateral surfaces. The anterior surface is dorsal to the sternum from which it is separated cephalically by the origin of the sterno-thyreoid muscle. To a less extent it is in relation with the sterno-clavicular articulation and comes into contact laterally with three or four of the cephalic sterno-costal articulations and lateral to this with the internal mammary artery. The posterior surface is largely concave and is in relation caudally with the pericardium which separates it from the Fig. 1075.- — Thymus in an Adult Superior mediastinum" Cupula pleurae... Right lung, __ I superior lobe ") (From Toldt's Atlas.) A^l^'^^ U ^'K\ — sternal end of clavicle Mediastinal ■ pleura Mediastinal. pleura -— Left lung Pleural cavity •vmsi.'\\.,^-:-\.k'l,t:: iiaiitiKv.s.'. ^Asi Anterior * mediastinal space right atrium and ventricular portion of the aorta and pulmonary artery. The middle part is in relation with the aorta and to the right of this with the superior vena cava. The cephaUc part is in relation with the branches of the aorta and superior vena cava. The lateral surfaces are somewhat flattened and are separated from the lungs by the mediastinal pleura. The phrenic nerve on the right side runs in the pleura near the dorsal border of this surface, on the left it is, as a rule, not in direct contact with the thymus. Structure. — The two lateral lobes of which the thymus is composed are rarely of the same size; the right is usually the more strongly developed. They are joined at an oblique plane so that the ventral surface of the right is narrow and its dorsal surface broader and the reverse condition is found in the left lobe. The two lobes are separated from one another by connective tissue. Rarely the two are joined by a medial portion, isthmus, near the middle or toward the caudal end (fig. 1076). Each lobe of the thymus is completely surrounded by a thin dehcate connective-tissue capsule from which numerous septa extend through the gland accompanied by the blood-vessels and nerves. The capsule is composed mainly of white fibrous connective tissue with some elastic fibres. It rarely contains much fat in the newborn but the amount of fat increases as development and involution proceed. Fibrous prolongations from the capsule may extend from the apices of the lobes to be attached to the cervical fascia in the region of the lateral lobes of the thyreoid gland, acting as suspensory ligaments for the gland. The lobes of thymus are divided into numerous small lobules [lobuli thymi] 4 to 11 mm. in diameter. These are of roundish or polyhedral shape with bases toward the surface where they show as polygonal areas. The lobules are separated and also bound together by the loose fibrous tissue septa which extend from the capsule. Each of the primary lobules of the thymus is divided into a number of secondary lobules or follicles 1 to 2 mm. in diameter. These lymphoid-like masses of tissue are composed of a reticulum containing in its meshes lymphocytes or thymus corpuscles. The tissue is denser near the surface, forming a cortex and passes gradually into a tissue with looser meshed reticulum near the centre, medulla. In the medulla there are nests of concentrically arranged de- generated epitheKal cells enclosing a central mass of granular cells containing colloid. These 1322 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS nests are termed the concentric corpuscles of Hassall. The cortex is subdivided by secondary connective-tissue septa extending in from the septa between the lobules. t,The arteries of the thymus are somewhat varied in their origin, usually derived from the internal mammary and inferior thyreoid of each side; branches are sometimes received from the innominate, subclavian, and superior thyreoid arteries. They reach the gland in various places and spreading out in the capsule pass with the trabeculae through the gland to form a plexus around each small lobule. From this capillaries pass through the cortex to the medulla. The veins issue from the thj'mus in various places and are seen as numerous branches on its surface. The efferent vessels drain into various veins, mostly into the left innominate vein, also smaller branches into the internal mammary and inferior thyreoid veins. The lymphatics arise around the small lobules and pass through the interlobular septa to the sm-face from which they are drained into small lymph nodes near the cephalic extremity, into glands ventrally between the thymus and the sternum, and into other glands dorsally be- tween the thymus and the pericardium. The nerves of the thymus are very minute. They are derived from the cervical sympa- thetic and from the vagus and reach the thymus for the most part along with the blood- vessels which they accompany through the septa. Fig. 1076. — Thymus in a Child of Two Years. Thyreoid cartilage Seventh ring of trachea Right carotid artery Right subclavian artery j]. Right innominate vein Thymus Vena cava superior Arch of aorta Central portion of crico-thyreoid membrane Crico-thyreoideus First ring of trachea Thyreoid gland Ligament connecting thyreoid and thymus gland Left carotid artery Left subclavian artery Arch of aorta Development. — The thymus arises from the endodermal portion of the third pharyngeal pouch on each side, as a thickening due to an increase in the epitheUal cells, followed by the production of a diverticulum. At about the sixth week the connections of the pouches with the branchial clefts are cut off but a strand of tissue may persist to represent the stalk. These thick-walled cylinders become sohd cords, elongate so as to extend caudally into the thorax, and enlarge by a series of secondary buddings. The glands of the two sides come into contact and become intimately associated. The cephahc portion, as a rule, later atrophies and disap- pears. Occasionally a small part of it remains near the thyreoid cut off from the rest of the gland as an accessory thymus. From the fourth pharyngeal pouch rarely a thymus bud may be developed which produces in the adult also an accessory thymus. The epithelial character of the cells remains plainly evident for a time, then the characteristic differentiation into lymphoid structure, cortex and medulla appears. The reticulum and concentric corpuscles are undoubtedly of epithelial origin; but the thymus lymphocytes are considered by Hammar and others as leucocytes which have migrated to the thymus, while they are regarded by THE SUPRARENAL GLANDS 1323 Stohr and his followers as modified epithelial elements, not true blood cells. Maurer, Bruant, and Bell regard them as modified epithelial cells which become true functional leucocytes. THE CHROMAFFIN SYSTEM It has recently been shown that in connection with the ganglia of the sympa- thetic nervous system, special cells, other than the nerve cells, are found. These differ from the nerve cells in that when subjected to the action of chromic acid salts there can be demonstrated in their protoplasm small granules which take on a darker stain. These cells are therefore known as chromaffin cells. They, with the cells of the sympathetic system, are derived from the ectoderm. They ap- pear first as indifferent cells, the sympatho-chromaffin cells. Some of these later develop into sympathetic ganglion cells, others into chromaffin cells. Some of these latter cells remain, isolated or in groups, permanently associated with the sympathetic ganglia, the paraganglia; others become separated and form the medullary portion of the suprarenal glands, the aortic paraganglia, and the glomus caroticum. THE SUPRARENAL GLANDS The suprarenal glands [glandulae suprarenales] or adrenal glands are small irregularly shaped glandular bodies composed of two quite different organs. In the lower vertebrates these two parts are entirely separated from one another Fig. 1077. — The Suprarenal Glands, Ventral View. but in man and the mammals they have become joined together one within the other. The external cortical portion, of unknown function, is developed from the mesoderm. The internal medullary portion is derived from the sympatho- FiG. 1078. — The Suprarenal Glands, Dorsal .View. Marga superior Apex suprarenalis Facies posterior, 'Facies posterior — t— Basis gl. suprarenalis chromaffin tissues and thus from the ectoderm in common with the sympathetic nervous system. This part of the suprarenal glands is known to produce an internal secretion which reaches the general circulation through the veins and 1324 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS whose principal function seems to be to aid in keeping up the tone and activity of the muscle and other tissues innervated by the sympathetic system. Situation. — The glands are deeply placed in the epigastric region (fig. 1080) lying in the dorsal and cephalic part of the abdominal cavity, one on either side of the vertebral column in variable relation with the upper extremity of the kidney of the corresponding side. Rarely they retain the fcetal relation, capping the superior extremity of the kidney and extending a little upon both medial and lateral borders. More frequently (especially on the left) they are placed more upon the medial borders of the kidneys, extending (on the left) as far caudal as the hilus, sometimes coming in contact with the renal vessels. Aii intermediate position is often found, especially on the right. In the high positions the suprarenals may be on a level with the tenth intercostal space or eleventh rib. In the low positions they may extend as far caudally as the first lumbar vertebra. The left is usually, but not always, a little higher than the right, corresponding to the position of the kidneys. Fixation. — The suprarenals, enclosed in the renal adipose capsules, are attached to the renal fascia by connective-tissue strands and are loosely bound by connect- ive tissue to the kidneys. The attachment to the kidneys is, however, so loose that the suprarenals are not dislocated when the kidneys are displaced. In addition to the attachments common to them and to the kidneys, they are joined by connective-tissue bands to the diaphragm, vena cava, and liver on the right side and to the diaphragm, aorta, pancreas and spleen on the left. They have also additional means of fixation through the arteries, veins, and nerve fibres which enter and leave them, and through the parietal peritoneum which in places covers their ventral surfaces. Fig. 1079. — Diagrammatic Section op the Suprarenal Gland. Size and weight. — The size of the suprarenals is subject to considerable variation within physiological limits, in some cases being relatively twice as large as in others. The two glands are rarely of the same size, the right being more often the smaller. Proportionately they are much larger in the foetus and embryo than in the adult, but they do not decrease in size in old age. They appear to be slightly lighter in women than in men. The average weight in the adult is from 4 to 54 grams. As a rule, they measure about 30 mm. in height; 7 or 8 mm. in thickness; and have a breadth at the base of about 45 mm. They augment in volume during digestion and also increase in size during the acute infectious diseases and in intoxications such as uremia. Colour and consistency. — The suprarenal glands as seen from the surface have a yellowish or brownish-yellow colour. Upon section the colour of the surface layer appears a little darker while the central part of the gland appears greyish or, if it contains much blood, of a reddish colour. If some httle time has elapsed since death, the central part of the suprarenal may be almost black in colour. The glands are very fragile and softer in consistency than the thyroid or thymus. As a rule, they are harder and more resistant than the fat of the adipose capsule and may be thus readily detected in it. Form. — The suprarenal glands are markedly flattened dorso-ventrally. Their surfaces are roughened by irregular tubercles and furrows. They vary consider- ably in shape (figs. 1077, 1078). The right gland is usually somewhat triangular in outline while the left is, as a rule, semilunar. Each gland has an anterior and a posterior surface, a base and an apex, a medial and a superior margin. The anterior surface [facies anterior] may be either convex or concave, and THE SUPRARENAL GLANDS 1325 look ventro-laterally. It is marked by a distinct transverse, oblique, or nearly vertical fissure, the hilus suprarenalis. At this point a small artery enters and the principal suprarenal vein takes exit from the gland. These surfaces are in relation with different organs on the right and left sides. The anterior surface of the right gland is in the greatest part of its extent in contact with the posterior surface of the hver, upon which it produces the suprarenal impression. The medial edge of -this surface is overlapped, cephalioally by the inferior vena cava and caudally by the duodenum. The gland is situated between the two layers of the coronary hgament, in most cases, in direct contact with the liver to which it is bound by loose connective tissue; but, at times, the peritoneum which covers the ventral surface of the kidney extends for a greater or less distance between the suprarenal and the liver. The anterior surface of the left gland, in some cases, may be in contact in its cephalic part with the left lobe of the liver and also, at times, with the spleen. The middle and major part lies against the fundus and cardiac end of the stomach, while caudally the suprarenal is often Fig. 1080. — Ventral View of the Supbarenal Glands, in Situ. X 3. (From Toldt's Atlas.) Hepatic veins Diaphragm, pars lumbalis Left suprarenal crossed by the tail of the pancreas and the splenic artery and vein. The whole or a large part of the anterior surface of the left suprarenal is covered by the parietal peritoneum of the omental bursa. The posterior surface [facies posterior] of both the suprarenals is distinctly smaller than the anterior surface. It is flat or convex and looks dorso-medially. It is in relation with the lumbar part of the diaphragm, to which it is bound by connective tissue, but from which it is separated by an extension of the renal adipose capsule. The base [basis gl. suprarenalis] is a narrow elongated surface distinctly hollowed out, which lies in contact with the superior extremity of the kidney or its medial margin, cephalic to the hilus. This surface looks dorsally, laterally, and somewhat caudally with the result that it extends farther on the anterior surface than on the posterior surface of the kidney. The medial border [margo medialis] is sharp, thin, and irregularly convex. It extends more or less vertically to meet the superior border. On the right it hes dorsal to the inferior vena cava cephalically and to the duodenum caudally and is close to, if not in contact with, the sympathetic cceliac ganglion. On the left the medial border lies dorsal to the stomach and caudally may be crossed by the pancreas and splenic vessels. It is in close proximity to the aorta and the coeliac sympathetic ganghon. The superior border [margo superior] is sharp and thin and differs somewhat on the two sides. 1326 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS On the right it is irregular, straight or convex, and extends, dorsal to the liver, obliquely cephalo-medially to meet the medial border in a more or less acute point, apex suprarenalis, which is directed cephaUcally and somewhat medially. On the left the superior border is irregularly convex in shape and nearly horizontal in direction. It passes gradually over into the medial border without the intervention of any distinct apex. It is dorsal to the stomach and in some cases comes into contact with the spleen. Accessory suprarenal glands [gl. suprarenales accessoriEe] are often foimd in the connective tissue in the neighbourhood of the principal organs. They are also sometimes found in the kidney near the internal spermatic veins and in the region of the sexual glands. The structures recorded as accessory suprarenal glands may be complete suprarenal glands composed of the cortex and medulla or they may be composed of the cortex only. Masses of chromaffin tissue representing the medulla are sometimes spoken of as accessory suprarenals but these more properly belong with the chromaffin system. Complete absence of the suprarenal glands has been recorded only in monsters with grave cranial and cephafic defects. Absence of one gland has been found and the fusion of the two has also been noted. Structure. — The suprarenal glands are surrounded by a thin and tough fibrous capsule composed mainly of white fibrous connective tissue. From the capsule numerous trabeculse are given off which pervade the gland and form septa between the groups and rows of cells. Within the capsule the suprarenal is composed of an external firmer yellowish layer, the cortex [substantia corticalis], and an internal softer whitish layer, the medulla [substantia meduUaris] (fig. 1079). On section the cortex is seen to form by far the greater part of the gland and it is marked radially from the centre toward the surface by darker and lighter streaks. In its deepest part it is brownish yellow or red and is usually slightly torn where it joins the medulla. As frequently found at autopsy the cortex is separated from the medulla by a sUt filled with a soft dark brown or blackish mass caused by the breaking down of the deeper layer of the cortex. The medulla is a greyish, spongy, vascular mass which often because of its blood content appears of a reddish or reddish-brown colour. The cortical portion of the gland is subdivided into a superficial, glomerular portion, zona glomerulosa; an intermediate, fascicular portion, zona fasciculata; and an internal reticular portion, zona reticulata, according to the peculiar grouping of the gland cells in these respective areas. In the glomerular zone the cells are of irregular columnar shape, and grouped in coiled columns. In the fascicular zone the cells, which are of polyhedral shape, are arranged in more or less regular parallel columns, while in the reticular zone the cells form trabecute or groups. The reticular connective-tissue framework, continuous with the capsule, surrounds the cell masses and cell columns of the several zones. The cells of the medulla show an affinity for chromic acid — chromaffin cells — and are grouped in irregular masses separated by septa of the reticulum and venous spaces. The arteries form a close-meshed plexus in the capsule from which branches run more or less parallel toward the medulla forming a network around the cell columns of the glomerular and fascicular zones. This opens into a venous plexus of wide calibre in the reticular zone, which is connected with the vessels of the medulla. Small medul- lary arteries pass through the cortex without branching to end in a venous plexus in the medulla. The abundant wide-meshed venous sinuses in the medulla (sinusoids) join to form small central veins which converge towai'd the centre of the medulla to form the large central vein. Vessels and nerves. — The suprarenal glands are richly supplied with vessels. The arteries are three — superior, middle and inferior. From the inferior phrenic artery, the superior suprarenal artery arises and passes toward the superior border of the gland. From the aorta the middle suprarenal artery takes origin between the coehac and superior mesenteric arteries and passes toward the medial border of the supra- renal. It is a branch of this artery which is usually found at the hilus along with the central vein. From the renal artery the inferior suprarenal artery arises and reaches the suprarenal near its base. These three arteries anastomose with one another and form a plexus in the capsule of the suprarenal from which the arteries for the interior of the gland are derived. The large central vein from the medulla passes through the cortex to emerge at the hilus as the suprarenal vein, vena suprarenalis. The right vein opens usually into the inferior vena cava, where there is a valve, the left into the left renal vein. There may also be small branches connecting with the phrenic or the right renal vein. The lymphatics of the suprarenals are very numerous and are represented by a superficial plexus in the capsule and a deep plexus in the medulla. These are connected by numerous anastomoses. They pass medially and converge into a number of trunks on each side which empty into lymph-glands situated along the aorta near the origin of the renal arteries. On the left side there is also the communication through the diaphragm with a posterior mediastinal gland. The nerves are derived chiefly from the coeliac and renal plexuses but include filaments from the splanchnics, and according to some authors from the phrenic and vagus nerves also. These numerous fine twigs connect with the gland in many different places and form a rich plexus. Branches are distributed to the capsule, to the cortical substance, and to the medullary substance. Groups of sympathetic ganglion cells are found in the medullary part of the gland. Development. — The suprarenal glands of mammals have their origin from two sources. The cortical mesodermic portion of the glands arises in early embryos as buds extending from THE CAROTID BODY 1327 the mesothelium on both sides of the root of the mesentery into the mesoderm ventral to the aorta. A little later these become definite organs completely separated from the coelomic epithelium and are soon vasoularised, but the central vein does not become visible until con- siderably later. The suprarenal glands after their separation from the peritoneum form a ridge on either side of the posterior wall of the ca4om medial to the mesonephros. Some little time after the origin of the cortical portion of the gland has undergone cellular differentiation and has become surrounded by a delicate capsule, the medullary portion is formed by the migration of masses of sympatho-chromaffin cells from the medial side toward the centre of the organ so that they surround the central vein as the anlage of the medullary nucleus. They penetrate the cortical portion of the gland as development proceeds and become completely surroimded by it. These migrating masses are entirely or for the most part of chromaffin formative cells derived from the ectoderm. They are clearly differentiated from the cortical cells by their small size and darker colour, in stained sections. Migration of these cell masses into the gland seems to be continued even after birth. The differentiation of the cortex into three layers occurs late in development. The suprarenal glands are relatively large in foetal life; and their relation to the kidneys is secondarily acquired. THE GLOMUS CAROTICUM The carotid bodies [glomera carotica] are small ovoid or spherical bodies found at or near the point where the common carotid arteries divide into the inter- nal and external carotids (fig. 1081). They are usually on the dorsal and medial side of the angle of bifurcation of the arteries. There is ordinarily one body on Fig. 1081. — The Glomus Caroticum (Carotid Body). (From Testut, after Prince- teau.) 1, Carotid body; 2, 3, 4, common, external and internal carotids; 5, int. jugular; 7, inf. cervical .sympathetic ganglion; 8, vagus. each side, 5 or 6 mm. in length and 2 or 3 mm. in thickness. It is reddish-yellow in colour and is attached to the carotid by fibrous tissue and by the vessels and nerves which enter it. A small special fibrous band may sometimes be recog- nised binding it to the common, external or internal carotid artery. The carotid body or gland is composed of two essential parts: (1) round, oval, or polyhedral epithelial cells which contain chromaffin granules, and are bound together by a mass of fibrous connective tissue; and (2) a rich plexus of capillaries and sinusoids forming a mesh. Large lymph-vessels surround the outside of the gland. The carotid gland has a very abundant nerve supply, mostly from the sympathetic system, and ganglion cells are foimd in it. It may receive twigs from the superior laryngeal, hypoglossal, or glossopharyngeal nerves, as recorded by some observers. The size of the carotid body varies considerably. At times the carotid bodies are absent; in other cases they are so small that they can be detected only in microscopic sections; occasionally they are 8 mm. in length by 4 or 5 mm. in thickness. Rarely the carotid bodies may be broken up into two or more smaller masses boimd together by connective tissue. The carotid body may be larger in old individuals due to an increase in the connective tissue or vascular elements with a corresponding decrease in the epithehal cells. The origin is probably from sympatho- chromaffin cells but some investigators believe that they are derived from the endothehum of the blood-vessels and others that they arise from the endoderm of a branchial pouch. 1328 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS Figs. 1082 and 1083. — Aortic Paraganglia. (Zuckerkandl.) Aorta Sympathetic trunk- Aortic paraganglia^ Left renal artery inferior mesenteric artery - — Plexus aorticus \ifc* Common iliac artery Vena cava int. Aorta «*# Right paraganglion - ■Left renal vein Ureter Left paraganglion Inferior mesenteric artery Plexus aorticus '"Common iliac artery REFERENCES FOR SKIN AND DUCTLESS GLANDS THE AORTIC PARAGANGLIA 1329 The abdominal chromaffin bodies, the paraganglia aortica, or paraganglia lumbalia, are situated on each side of the abdominal aorta near the point of origin of the inferior mesenteric artery (figs. 1082, 1083). They are elongated, flat- tened, ovoid bodies, softer and greyer than the lymphatic glands and extremely variable in size. They measure, as a rule, between 6 and 12 mm. in length, although occasionally as long as 30 mm. or as short as 1 mm. They may be connected by transverse bands in front of the aorta or occur as scattered nodules in this situation. They are intimately related to the aortic sympathetic plexus and at least one of them is uniformly found. They consist of a mass of chromaffin cells surrounded by a rich capillary plexus and contain many nerve fibres and nerve cells. THE GLOMUS COCCYGEUM The coccygeal body [glomus coccygeum] is a small, spherical greyish-red body consisting of a median unpaired mass 2 to 3 mm. in diameter, single or divided into three to six connected nodules. It is placed immediately ventral to the tip FiQ. 1084. — Coccygeal Gland, in Sittt. 1, Sacrum; 2, coccyx; 3, coccygeal gland; 4, middle sacral artery; 5, 6, sacral sympathetic; 7, ganglion impar.; 8, last sacral; 9, coccygeal nerve; 10, gluteus maximus; 11, ischio-coccygeus; 12, levator ani; 13, ano-coccygeal raphe. (Testut.) of the coccyx, imbedded in fat and in relation with the terminal branch or branches of the medial sacral artery, with the ischio-coccygeal muscles, and fibres of the sympathetic nervous system (fig. 1084). It is composed of groups of epithelial cells bound together by a mass of fibrous tissue and containing a plexus of sinusoidal capillary vessels in intimate relation with the cells. Numerous nerve fibres also enter the gland. It is not certain that the cells are chromaffin in character or that the coccygeal body has an internal secretion. A. References for the skin and mammary gland. — General and topographic: Quain's Anatomy, 11th ed., vol. ii, pt. 1; Testut, Traits d'Anatomie Humaine, 4th ed .; Poirier-Charpy, Traits d'Anatomie, vol. v; Rauber-Kopsch, Lehrbuoh der Anatomie, 9th ed.; Bardeleben, Handbuch der Anatomie, vol. v, pt. 1; Merkel, Topographische Anatomie; Corning, Lehrbuoh der topographischen Anatomie. Development: Keibel and Mall, Human Embryology. Skin: Heidenhain, Anat. Hefte., vol. xxx; Kean (finger prints), Jour. Amer. Med. Assoc, vol. xlvii; Unna (blood and lymph), Arch. f. mikr. Anat., vol. Lx.xii; Botezat (nerves) Anat. Anz., vol. xxxiii. Nails: Branca, Annales de Dermat. et SyphQis, 1910; Mammary glands; Kerr, Buck's Ref. Hand. Med. Sci. (Breast) vol. 4, 1914. B. References for the ductless glands. — General and topographic: Quain's Anatomy, 11th ed. ; Testut, Trait6 d'Anatomie Humaine, 4th ed., vol. iv; Poirier-Charpy, Traite d'Anatomie vol. iv.; Rauber-Kopsch, Lehrbuch der Anatomie, 9th ed.; Merkel, Topographische Anatomie; Corning, Lehrbuch der topographischen Anatomie, 3rd ed. Development: Keibel and Mall, Human Embryology. Spleen: Shepherd, Jour. Anat. and Physiol., vol. x.xxvii; Mall, Amer. Jour. Anat., vol. ii. Thyreoid: Marshall, Jour. Ansit. and Physiol., vol. xxix. Parathyreoids: Forsyth, Brit. Med. Jour., 1907; Rulison, Anat. Rec, vol. iii;Halsted and Evans, Annals of Surg., vol. xlvi. Thymus: Hammar, Erbge. d. Anat. u. Entwick., Bd., xix. Suprarenal glands: Gerard, Georges et Maurice, Bull. Mem. Soc. Anat. Paris, 1911, (6) T. 13; Ferguson, J. S., Amer. Jour. Anat., vol. v, 1905. Carotid body: Gomez, .L. P., Am. .tour. Med. Sci., vol. cxxxvi; Aortic paraganglia; Zuckerkandl, Verhandl. d. Anat. Gesell., 15th Versamm., 1901. I SECTION XIII CLINICAL AND TOPOGRAPHICAL ANATOMY Revised for the Fifth Edition Bt JOHN MORLEY, Ch.M., F.R.C.S. HONORARY SURGEON, ANCOAT's HOSPITAL, MANCHESTER; LECTURER IN CLINICAL ANATOMY, MANCHESTER UNIVERSITY THE HEAD IN describing the clinical and topographical relations, the divisions of the body- will be successively considered in the following order: headj neck, thorax, abdomen, pelvis, back, upper and lower extremities. The bony landmarks of the head will first be considered, followed by a separate description of the cranium and the face. Bony landmarks. — These should be studied with the aid of a skull, as well as on the hving subject. Beginning in front is the nasion, a depression at the root of the nose, and immediately above it, the glabella, a slight prominence joining the two supracihary arches. These points mark the remains of the frontal suture, and the junction of the frontal, nasal, and superior maxillary bones and one of the sites of a meningocele. In the middle line, behind, is the external occipital protuber- ance, or inion, the thickest part of the vault, and corresponding internally with the meeting-point of six sinuses. A line joining the inion and glabella corresponds to the sagittal, and occasionally the frontal, suture, the falx cerebri, the superior sagittal sinus, widening as it runs backward, and the longitudinal fissure of the brain. From the inion the superior nuchal hues pass laterally toward the upper and back part of the base of the mastoid processes, and indicate the first or so- called horizontal part of the transverse (lateral) sinus. This vessel usually presents a varying curve upward and runs in the tentorium. The second or sigmoid portion turns downward on the inner surface of the mastoid, then forward, and lastly downward again to the jugular foramen, thus describing the double curve from which this part takes its name. In the jugular foramen the vessel occupies the posterior compartment; its junction with the internal jugular is dilated and forms the bulb. A line curved downward and forward from the upper and back part of the base of the mastoid, reaching two-thirds of the way down toward the ape.x, will indicate the second part of the sinus. The spot where it finally curves inward to the bulb would be about 1.8 cm. (J in.) below and behind the meatus. The two portions of the transverse sinus meet at the asterion laterally; at the entry of the superior petrosal sinus medially. The right transverse sinus, the larger, is usually a continua- tion of the superior sagittal sinus, and, therefore, receives blood chiefly from the cortex of the brain; the left, arising in the straight sinus, drains the interior of the brain and the basal ganglia. Each transverse sinus receives blood from the temporal lobe, the cerebellum, diploe, tympanic antrum, internal ear, and two emissary veins, the mastoid and posterior condylar. About 6 . 2 cm. (2| in.) above the external occipital protuberance is the lambda, or meeting of the sagittal and lambdoidal sutures (posterior f ontanelle, small and triradiate in shape) . It is useful to remember, as guides on the scalp to the above two important points, that the lambda is on a level with the supraciUary ridges, and the external occipital protuberance on one with the zygomatic arches. Below the external occipital protuberance, between it and the foramen magnum, an occip- ital, the commonest form of cranial meningoceles, makes its appearance. It comes through the median fissure in the cartilaginous part of the squamous portion of the bone. 1331 I 1332 CLINICAL AND TOPOGRAPHICAL ANATOMY The point of junction of the occipital, parietal, and mastoid bones, the asterion, is placed about 3 . 7 cm. (1| in.) behind and 1 . 2 cm. (| in.) above the centre of the auditory meatus (fig. 1085). It indicates the site of the posterior lateral fon- tanelle and just below it the superior nuchal line terminates. The bregma, or junction of the coronal, sagittal, and, in early life, the frontal suture (anterior f on- tan elle, large and lozenge-shaped), lies just in front of the centre of a line drawn transversely over the cranial vault from one pre-auricular point to the other (fig. 1090) . The bregmatic f ontanelle normally closes before the end of the second year. The lambdoid fontanelle is closed at birth. The pterion, or junction of the frontal and sphenoid in front, parietal and squamous bones behind, lies in the temporal fossa, 3.7 to 5 cm. (IJ to 2 in.) behind the zygomatic process of the frontal, and about the same distance above the zygoma (fig. 1085). This spot also gives the position of the trunk and the anterior and larger division of the middle meningeal artery (fig. 1090), the Sylvian point and divergence of the limbs of the lateral (Sylvian) fissure, the insula (island of Reil), and middle cerebral artery. It, further, corresponds to the anterior lateral fontanelle. On the side of the skull the zygomatic arch, the temporal ridge, and external auditory meatus need atten- tion. That important landmark, the zygomatic arch, wide in front where it is formed by the zygomatic (malar), narrowing behind where it joins the temporal, gives off here three roots, the most anterior marked by the eminentia articularis, in front of the mandibular (glenoid) fossa, the middle behind this joint, while the posterior curves upward and backward to be continuous with the temporal ridge. Within the zygomatic arch lie two fossae separated by the infra-temporal (ptery- goid) ridge : above is the temporal, with the muscle and deep temporal vessels and nerves; below is the infra-temporal or zygomatic fossa, with the lower part of the temporal muscle, the two pterygoids, the internal maxillary vessels, and the man- dibular division of the fifth. To the upper border of the zygomatic arch is attached the temporal fascia, to its lower, the masseter. Its upper border marks the level of the lower lateral margin of the cerebral hemisphere. A point corresponding to the middle root of the zygoma, immediately in front of the tragus, and on a level with the upper border of the bony meatus, is called the pre-auricular point. Here the superficial temporal vessels and the auriculo-temporal nerve cross the zygoma, and a patient 's pulse may be taken by the anaesthetist. The lower end of the central (Rolandic) fissure lies 5 cm. (2 in.) vertically above this point. The temporal ridge, giving origin to the temporal fascia, starts from the zygomatic proc- ess of the frontal, and becoming less distinct, curves upward and backward over the lower part of that bone, crosses the coronal suture, traverses the parietal bone, curving downward and backward to its posterior inferior angle. Here it passes on to the temporal, and passing forward over the external auditory meatus, is continuous with the posterior root of the zygoma. Below the root of the zygoma will be felt the temporo-mandibular joint, and when the mouth is opened, the con- dyle will be felt to glide forward on the eminentia articularis, leaving a well-marked depression behind. The external auditory meatus, measured from its opening on the concha to the membrane, is about 2.5 cm. (1 in.) in length; if from the tragus, 3.7 cm. (1^ in.). Its long axis is directed medially and a little forward with a slight convex curve upward, most marked in its centre. Between the summit of this curve and the membrane is a sUght recess in which foreign bodies may lodge. The lumen is widest at its commencement, narrowest internally. To bring the cartilaginous portion in line with the bony, the pinna should be drawn well upward and back- ward. In the bony portion the skin and periosteum are intimately blended, thus accounting for the readiness with which necrosis occui's. The sensibility of the meatus is explained by the two branches sent by the auriculo-temporal nerve. The fact that the deeper part is supplied by the auricular branch of the vagus explains the vomiting and cough occasionally met with in affections of the meatus. The anterior inferior angle of the parietal bone, and its great importance as a landmark, have already been noted. The posterior inferior angle of tliis bone (grooved by the transverse (lateral) sinus) lies a httle above and behind the base of the mastoid, on a level with the roots of the zygoma (fig. 1085). Just below and in front of the tip of the mastoid the transverse process of the atlas can be made out in a spare subject. In front, the circumference of the bony orbit can be traced in its whole extent. The supraorbital notch lies at the junction of the medial and intermediate thirds of the supraorbital arch. When this notch is a complete foramen, its detection is much less easy. To its medial side the supratrochlear nerve and frontal arterd cross the supraorbital margin; like the supraorbital, this nerve and vessel lie, at THE CRANIUM 1333 first, in close relation with the periosteum. The frontal artery is one of the chief blood-supplies to flaps taken from the forehead. Owing to the paper-like thin- ness of the bones on the medial wall of the orbit, e. g., lacrimal, ethmoid, and body of sphenoid, and the mobihty of the skin, injuries which are possibly pene- trating ones, as from a slate-pencil, ferrule, etc., are always to be looked upon with suspicion. After a period of latency of symptoms, infection of the membranes and frontal abscess have often followed. Above the supraorbital margin is the supraciliary arch, and higher still the frontal eminence [tuber frontale]. FiQ. 1085. — The Skull, showing Kronlein's Method of Ckaniocerebral Topography. THE CRANIUM Under this heading will be considered the scalp, the bony sinuses, cranio- cerebral topography and the hypophysis. The scalp. — The importance of the scalp is best seen from an examination of its layers (fig. 1086). These are — (1) skin; (2) subcutaneous fat and fibrous tissue; (3) the epicranius (occipito-frontalis) and aponeurosis; (4) the sub- aponeurotic layer of connective tissue; (5) the pericranium. The first three layers are connected and move together. The thick skin supported by the dense fibrous subcutaneous layer and epicranial aponeurosis, is well adapted to protect the underlying skull from the effects of trauma, and in this connection the mobility of the first three layers on the subaponeurotic areolar tissue is important. A scalp wound does not gape widely unless it involves the epicranial aponeurosis, in which case it involves the subjacent "dangerous area" of the scalp, so-called because pus in this laj^er maj^ spread widely underneath the scalp and even give meningeal infection by spreading through the diploic or emissary veins. In the process of scalping (whether performed by the knife or by the hair being caught in machinery), separation takes place at this sub- aponeurotic layer which is loose, delicate and devoid of fat. The numerous sebaceous glands frequently give rise to cj'sts in the scalp. 1334 CLINICAL AND TOPOGRAPHICAL ANATOMY The epicranius and aponeurosis have been described elsewhere (p. 336). The pericranium differs from periosteum elsewhere in that it gives little nourishment to the bone beneath, which derives most of its blood-supply from the meningeal vessels. After necrosis of the skull there is no tendency to the formation of an involucrum of new subperiosteal bone as in the long bones. The pericranium is firmly adherent to the sutures of the skull bones, so that any subpericranial effusion of blood or pus is limited by the sutures. Of the vessels of the scalp, the arteries, arising in the anterior region from the internal, in the posterior from the external, carotid, are peculiar in their position. Thus they he superficial to the deep fascia, which is here represented by the aponeurosis (fig. 1086). From this position arises the fact that a large flap of scalp may be separated without perishing, as it carries its own blood- vessels. From the density of the layer in which the vessels run they cannot retract and are difficult to seize, haemorrhage thus being free. Finally, from their position over closely adjacent bone, ill-applied pressure may easily lead to sloughing. A practical point with regard to the veins is given below. The lymphatics from the front of the scalp drain into the anterior auricular and parotid, those behind into the posterior auricular, occipital and deep cervical nodes. The nerves are derived from all three divisions of the trigeminus, from the Fig. 1086. — Section through the Scalp, Skull, and Duka Mater. (Tillaux.) Skin and superficial fascia with ^ hair bulbs and sebace- glands / Fat pellets Epicranial aponeu- Skull: diploic tissue facial (motor) and also from three branches of the second and third cervical. The supply from the fifth explains the neuralgia in acute iritis, glaucoma, and herpes frontahs, and also the pains shooting up from the front of the ear in late cancer of the tongue. The emissary veins. — These are communications between the sinuses within, and the veins outside, the cranium. Most of them are temporary, corresponding to the chief period of growth of the brain. Thus in early life, when the develop- ment of the brain has to be very rapid, owing to the approaching closure of its case, a free escape of blood is most essential, especially in children, with their sudden explosions of laughter and passionate crying! The gravity of these emissary veins and their free communications with others are shown by the readiness Avith which they become the seat of thrombosis, and thus of blood-poisoning, in cranial injuries, erysipelas, infected wounds of the scalp, and necrosis of the skull. They include the following: 1. Vein through the foramen OEecum, between the anterior extremity of the superior sagittal sinus and the nasal mucous membrane. The value of this temporary outlet is well seen in the timely profuse epistaxis of children. Other more permanent communications between the skuD cavity arid nasal mucous membrane pass through the ethmoid foramina. The fact that the nasal mucous membrane is loose and ill-supported on the nasal conchas ( turbinate bones) allows its vessels to give way readily, and thus forms a salutary safeguard to the brain, warding off many an attack of apoplexy. 2. Vein thi-ough the mastoid foramen, between the transverse THE BONY SINUSES 1335 (lateral) sinus and the posterior auricular and occipital veins. This is the largest, the most constant, and the most superficial of the emissary veins. Hence the old rule of applying blisters or leeches over it in cerebral congestion. 3. Vein through the posterior superior angle of the parietal between the superior sagittal sinus and the veins of the scalp. 4. Vein through the condyloid foramen between the transverse (lateral) sinus and the deep veins of the neck. 5. Vein through the hypoglossal canal between the occipital sinus and the deep veins of the neck. 6. Ophthalmic veins communicating with the cavernous sinus and the angular vein. These veins may be the source of fatal blood-poisoning, by conveying out of reach septic material, in acute periostitis of the orbit, or in osteitis, of dental origin, of the jaws. 7. Minute veins through the foramen ovale between the cavernous sinus and the pharyngeal and pterygoid veins. 8. Communications between the frontal diploic and supraorbital veins, between the anterior temporal diploic and deep temporal veins, and between the posterior temporal and occipital diploic veins and the transverse sinus. In addition to the veins specially mentioned, the scalp and sinuses communicate by numerous diploic veins, by those in the inter-sutural membrane, and thi'ough sutures before their obliteration, as already explained. Structure of cranium. — Two layers and intervening cancellous tissue. Each layer has special properties. The outer gives thickness, smoothness, and uni- formity, and, above all, elasticity. The inner is whiter, thinner, less regular — e. g. the depressions for vessels. Pacchionian bodies, dura mater, and brain. The diploe, formed by absorption after the skull has attained a certain thickness, reduces the weight of the skull without proportionately reducing its strength, and provides a material which will prevent the transmission of vibrations. A blow on the head may fracture the internal layer only, the external one and diploe escap- ing. This is difficult to diagnose, and thus it is impossible to judge of the severity of a fracture from the state of the external layer. This may be whole, or merely cracked, while the-internal shows many fragments, which may set up meningitis or other mischief. It is usual to find more extensive splintering of the inner than of the outer layer (table). The average thickness of the adult skull-cap is about 5 mm. (\ in.). (Holden.) The thickest part is at the external occipital protuberance, where the bone is often 1.8 cm. (| in.) in thickness. The thinnest part of the skull vault is over the temporal part of the squamous. The extreme fragility of the skull here is partly compensated for the by thickness of the soft parts; these two facts are always to be remembered in the diagnosis of a fracture of the skull here, after a slight injury. Other weak spots are the medial wall of the orbit, the cerebellar fossae, and that part of the middle fossa corresponding to the glenoid cavity. Anatomical conditions tending to minimise the effects of violence inflicted upon the skull. — (1) The density and mobility of the scalp. (2) The dome-like shape of the skull. This is cal- culated to bear relatively hard blows and also to allow them to glide off. (3) The number of bones tends to break up the force of a blow. (4) The sutures interrupt the transmission of violence. (5) The inter-sutural membrane (remains of fcetal periosteum) acts, in early life, as a linear buffer. (6) The elasticity of the outer layer (table). (7) The overlapping of some bones, e. g. the parietal by the squamous; and the alternate bevelling of adjacent bones, e. g. at the coronal suture. (8) The presence of ribs, or groins, e. g. (a) from the crista galli to the internal occipital protuberance; (b) from the root of the nose to the zygoma; (c) the temporal ridge from orbit to mastoid; (d) from mastoid to mastoid; (e) from external occipital protu- berance to th? foramen magnum. (9) Buttresses, e. g. zygomatic processes and the greater wing of the sphenoid. (10) The mobility of the head upon the spine. THE BONY SINUSES Frontal. — When well developed, the frontal sinuses may reach 5 cm. (2 in.) upward and 3.7 cm. (1| in.) laterally, occupying the greater part of the vertical portion of the frontal bone. When very small, they scarcely e.xtend above the nasal process. In any case, they are rarely symmetrical. The average dimen- sions of an adult frontal sinus are 3.7 cm. (IJ in.) in height, 2.5 cm. (1 in.) in breadth, and 1.8 cm. (f in.) in depth. (Logan Turner.) The sinuses are sep- arated by a septum. The posterior wall is very thin. Each sinus narrows downward into the infundibulum. This is 'deeply placed, at the back of the cavity, behind the frontal (nasal) process of the maxilla and near the medial wall of the orbit. Its termination in the middle meatus is about on a level -mth the palpebral fissure.' (Thane and Godlee.) Its direction is backward. The communication of these sinuses with the nose accounts for the frontal headache, the persistence of polypi and ozsena, and the fact that a patient with a compound fracture opening up the sinuses can blow out a flame held close by. To open the frontal sinus, while the incision which leaves the least scar is one along the shaved eyebrow, superficial laterally so to avoid the supraorbital nerve and vessels, running a little downward at the medial end, it is always to be remembered that, where the sinuses are little developed, this or a median incision may open the cranial cavity. To avoid this compli- cation the sinus should always be opened at a spot vertically above the medial angle. The development of these by the twentieth or twenty-fifth year may render a fracture 1336 CLINICAL AND TOPOGRAPHICAL ANATOMY here much less grave in the adult than would otherwise be the case, the inner layer (table), if now separated from the outer, protecting the brain. Mr. Hilton showed that the absence of any external prominence here does not necessarily imply the absence of a sinus, as this may be formed by retrocession of the internal layer. In old people these sinuses may enlarge by the inner layer following the shrinking brain. Again, prominence of the supracOiary and frontal eminences does not necessarily point to the existence of a sinus at all, being due merely to a heaping up of bone. The mastoid cells are arranged in two groups, of the utmost importance in that frequent and fatal disease, inflammation of the middle ear: — (A) The upper, or 'antrum,' present both in early and late life, horizontal in direction, closely adja- cent to and communicating with the tympanum. (B) The lower, or vertical. This group is not developed in early life. A. Tympanic antrum (fig. 1088). — This is a small chamber lying behind the tympanum, into the upper and back part of which (epitympanic recess) it opens. Its size varies, especially with age. Almost as large at birth, it reaches its maxi- mum (that of a pea) about the third or fourth year. After this its size usually diminishes somewhat, owing to the development of the encroaching bone around Fig. 1087. — Tempobal Bone, showing Suprambatal Triangle. (Barr.) The lower part of the transverse sinus is here placed too far back to be relied upon with con- stant accuracy. Root of zygoma Suprameatat triangle Position for ~^ perforating vertical cells it. Its roof, or tegmen, is merely the backward continuation of the tegmen tympani. The level of this is indicated by the posterior root of the zygoma. 'The level of the floor of the adult skull at the tegmen antri is, on an average, less than one-fourth of an inch above the roof of the external osseous meatus; in children and adolescents, from one-sixteenth to one-eighth of an inch.' (Mac- ewen.) In early life, when the bony landmarks, e. g. the suprameatal crest (fig. 1087), are little marked, the level of the upper margin of the bony meatus will be the safest guide to avoid opening the middle fossa. The lateral wall of the antrum is formed by a plate descending from the squamous bone. This is very thin in early life, but as it develops by deposit under the periosteum, the depth of the antrum from the surface increases. Macewen gives the average of the depth as varying from one-eighth to three- fourths of an inch. The thinness of the outer wall in early life is of practical importance. It allows of suppuration making its way externally — subperiosteal mastoid abscess. This will be facihtated by any delay in the closure of the petro- and masto-squamosal sutures, by which this thin plate blends with the rest of the temporal bone. Further, by the path of veins running through these sutures or THE TYMPANIC ANTRUM 1337 their remnants, infection may reach such sinuses as the inferior petrosal. The sutures normally close in the second year after birth. Through the floor, the antrum communicates with the lower or vertical cells of the mastoid. This floor is on a lower level than the opening into the tympanum, and thus drainage of an infected antrum is difficult, fluid finding its way more readily into the lower cells. Behind the mastoid antrum and cells is the bend of the sigmoid part of the trans- verse (lateral) sinus, with its short descending portion (fig. 1087). The average distance of the sinus from the superior meatal triangle is 1 cm. (f in.). It may be further back; on the other hand, it may come within 2 mm. (y\ in.) from the meatus, and even overlap the outer wall of the antrum. Fig. 1088. — The Mastoid Antrum and Cells. (Jacobson and Steward.) 1. Posterior root of zygoma forming the supramastoid or suprameatal crest and upper part of Macewen's triangle. 2. Antrum, and in front of it, the epitympanic recess. 3. Vertical cells of the mastoid. 4. Ridge on the inner wall of the tympanum, caused by the facial canal. 5. Fenestrse on inner wall of tympanum, indicated in shadow. 6. A deficiency present in the tegmen tympani, enlarged with a small osteotrite to emphasise the thinness of the roof of the antrum and tympanum. 7. Cells extending, in this case, even into the root of the zygoma. The exact position of the antrum, a little above and behind the external auditory meatus is represented by Macewen's 'suprameatal triangle.' This is a triangle bounded by the posterior root of the zygoma above, the upper and posterior segment of the bony external meatus below, and an imaginary line joining the above boundaries (fig. 1087). "Roughly speaking, if the orifice of the external osseous meatus be bisected horizontally, the upper half would be on the level of the mastoid antrum. If this segment be again bisected vertically, its posterior half would again correspond to the junction of the antrum and middle ear, and immediately behind this lies the suprameatal fossa.' (Macewen.) When opening the antrum through this triangle, the operator should work forward and medially, so as to avoid the transverse sinus (fig. 1087) ; while, to avoid the facial nerve (fig. 10S7), he should hug the root of the zygoma and the upper part of the bony meatus as closely as possible. The level of the base of the brain will be a few lines above the posterior root of the zygoma (fig. 1089) and about 6 mm. (j in.) above the roof of the bony meatus. (Macewen.) 1338 CLINICAL AND TOPOGRAPHICAL ANATOMY B. The lower or vertical cells of the mastoid are developed later than is the antrum, and vary much in their contents. The condition of the mastoid cells varies very widely. They may be numerous (fig. 1088) or few. In the latter case they are replaced by diploe, or by bone which is unusually dense, without necessarily any pathological change. Hence mastoids have been classified as pneumatic, diploetic, or sclerosed. As part of the surgical anatomy of this most important region, the different paths by which infection of the tympanum and antrum may travel should be glanced at. The most important are: — (1) Upward: either by advancing caries or by infection of veins going to the superior petrosal sinus, or through the tegmina to the membranes; an abscess in the overlying temporal lobe, usually the middle and back part. (2) Backward : the transverse (lateral) sinus and cerebellum (abscess of the front and outer part of the lateral lobe) are reached in the same ways as those given above, the mastoid vein being the one chiefly affected here. Macewen has shown that the bony wall of the sinus, like those of the tegmina and the aqueduct of Fallopius, may be naturally imperfect. (3) Downward : where the vertical cells are well developed (fig. 929) mischief may reach the mastoid notch and cause deep-seated inflammation beneath the sterno- mastoid. (v. Bezold's abscess.) (4) Lateralward: the explanation of this, in early life, has been given above. (.5) Medialward : the facial nerve, or by the fenestra ovahs; the labyrinth is now in danger. When the internal ear and auditory nerve are affected, infection finds another path to the cerebellar fossa. The sphenoidal sinuses are less important surgically, but these points should be remem- bered:— (1) Fracture through them may lead to bleeding from the nose, which is thus brought into communication with the middle fossa; (2) the communication of their mucous membrane with that of the nose may explain the inveteracy of certain cases of polypi and ozaena; (3) here and in the frontal sinuses very dense exostoses are sometimes formed. Before any operative attack on these sinuses is undertaken, their most important relations should be remembered. Thus above are the olfactory and optic nerves, the pituitary body, and front of the pons. Externally lie the cavernous sinus and superior orbital (sphenoidal) fissure. Below is the roof of the nose. The ethmoidal and maxillary sinuses are considered later in connection with the Nose. See also the sections on Osteology and Respiratory System. CRANIO-CEREBRAL TOPOGRAPHY To make as clear as possible the points of practical importance which have, of late years, been put on a definite basis, and which the surgeon may have to recall and act upon at very short notice, cranio-cerebral topography will be spoken of under the following headings: A. Relation of the brain as a whole to the skull, B. Relation of the chief sulci and gyri to the skull. C. Localisation of the chief sulci and gyri. Before alluding to the above, it is necessary to say distinctly that the following surface-markings and points of guidance are only approxi- mately reliable, for the following reasons: (1) In two individuals of the same age and sex the sulci and convolutions are never precisely alike. (2) The rela- tions of the convolutions and sulci to the surface vary in different individuals. (3) That as the surface area of the scalp and outer aspect of the skull are greater than the surface area of the brain, and as the convexities do not tally, lines drawn on the scalp or skull cannot always correspond precisely to cerebral convolutions or sulci. It results from the above that when a definite area of the surface is said to correspond accurately in any individual to a definite area of the brain surface, this result has been correlated from many examinations; and that as surface- markings, shape, and processes of skull and arrangement of surface are all liable to variations in different individuals, the surgeon must allow for these variations by removing more than that definite area of skull which is said to correspond exactly to that part of the brain which he desires to expose. A. Relation of the brain as a whole to the skull (figs. 1089, 1091). — To trace the lower level of each cerebral hemisphere on the skull, the chalk would start from the lower part of the glabella; thence the line representing the lower borders of the frontal lobe pursues a course, slightly curved upward, about 0.8 cm. (^ in.) above the supraorbital margin; next, crossing the temporal crest about 1.2 cm. (i in) above the zygomatic (external angular) process, it passes not quite hori- zontally but descending slightly to a point in the temporal fossa just below the tip of the great wing of the sphenoid (pterion), 2.5 cm. (1 in.) behind the zygo- matic process. From this point the line of the level of the brain, now convex forward and corresponding to the anterior extremity of the temporal lobe, would dip down, still within the great wing of the sphenoid, to about the centre of the zygoma. Thence the line of the lower border of the temporal lobe would CRANIO-CEREBRAL TOPOGRAPHY 1339 travel along the upper border of this process about 6 mm. (J in.) above the roof of the external auditory meatus (fig. 1089), and thence just above the base of the mastoid and the posterior inferior angle of the parietal, and so along the linea nuchse suprema, and corresponding to the tentorium and horizontal part of the transverse (lateral) sinus, to the external occipital protuberance. The upper margin of each hemisphere would be represented by a line drawn from just below the glabella, sufficiently to one side of the middle line to allow for the falx and superior sagittal sinus, to one immediately above the superior external occipital protuberance and inion. B. Relation of the chief fissures and convolutions to the skull. C. Local- isation of the chief sulci and gyri. These headings will be taken together. It will be well first to indicate the position of the chief sutures which mark off the parietal bone, under which lies that part of the brain which is most important to the surgeon — the motor area. The upper limit of the bone will be indicated by the line already spoken of as giving the upper margin of the hemisphere — the sagittal line, or Sagittal suture. The anterior limit of the parietal bone, formed Fig. 1089. — The Outline of the Brain and its Fissures in Relation to the Sutures OF THE Skull. (Cunningham.) s.M. Supraciliary margin of the cerebrum, i.l.m. Infero-lateral margin of the cerebrum. L.s. Position of highest part of the arch of the transverse sinus. R. Central sulcus (Fissure of Rolando), s^. Anterior horizontal limb of lateral fissure, s^ Anterior ascending limb of lateral fissure, s^ Posterior horizontal limb of lateral fissure, p.b. Opercular portion of the inferior frontal convolution, p.t. Triangular portion of the inferior frontal 'convolution. P.O. Orbital portion of the inferior frontal convolution. by the coronal suture, may be traced thus : The point where it leaves the sagittal suture (the bregma) will be found by drawing a line from a point just in front of the external auditory meatus (the pre-auricular point) (fig. 1085) straight upward on to the vertex; from this point a line drawn downward and forward to the middle of the zygomatic arch would indicate that of the coronal suture. Under this suture lie the posterior extremities of the three frontal convolutions; for the frontal lobe lies not only under the frontal bone, but extends backward under the anterior part of the parietal, the central sulcus (fissure of Rolando) , which separates the frontal from the parietal lobe, lying from 3.7 to 5 cm. (1| to 2 in.) behind the coronal suture at its upper extremity and about 2.5 cm. (1 in.) at its lower. The squamoso-parietal suture, which marks the lower border of the anterior two-thirds of the parietal bone, is not so easy to define, owing to the irregularity and variations of its curve. Its highest point is usually 4.3 cm. (If in.) above the zygoma. The lambdoid suture, which forms the posterior boundary of the parietal bone, will be marked out by a line which starts from a point (lambda) about 6.2 cm. (2i in.) above the external occipital protuberance, and runs downward and forward to a point on a level with the zygoma, 3.7 cm. (IJ in.) behind and 1.2 cm. (J in.) above the centre of the meatus. 1340 CLINICAL AND TOPOGRAPHICAL ANATOMY The position of the chief sulci will now be given: — Lateral (Sylvian) fissure (fig. 1089). — The point of appearance of this, on the outer side of the brain, practically corresponds to the pterion (p. 1332, fig. 1085) — a point which lies in the temporal fossa, about 3.7 cm. (1| in.) behind the zygomatic process and about the same distance above the zygoma. From this point the lateral fissure, which here separates the frontal and parietal from the temporal lobe, runs backward and upward, ascending gently, at first in the line of the squamo-parietal suture, then crossing this suture about its centre and thence, ascending more rapidly, it climbs up to the temporal ridge, to end 1.8 cm. (f in.) below the parietal eminence. Its termination is surrounded by the supramarginal convolution, to which the parietal eminence corresponds with sufficient accuracy. Such being the surface-marking of the chief or posterior horizontal limb of the lateral fissure (s^, fig. 1089), it remains to indicate briefly the two shorter limbs which bound the inferior frontal convolution, which, on the left side, contains the centre for speech (Broca's convolution), and corresponds to a point l3ang three fingers' breadth vertically above the centre of the zygo- matic arch. (Stiles.) Of these, the anterior horizontal (s^, fig. 1089) runs for- ward across the termination of the coronal, just above the line of the spheno- parietal suture. The ascending limb (s^, fig. 1089) runs upward for about Fig. 1090. — Lateral View op the Skull, Showing the Topogeaphy of the Middle Meningeal Artery and the Transverse Sinus. Anterior branch of middle meningeal art. Posterior branch' of middle menin- geal art. 2.5 cm. (1 in.) just behind the termination of the coronal suture, or 5 cm. (2 in.) behind the zygomatic process. The central sulcus (fissure of Rolando). — This most important fissure, in front of which, in the precentral convolution of the frontal lobe, lie the motor centres for the opposite side of the body, is situated under the parietal bone. It may be marked out with sufficient precision in the following way (Thane): The sagittal line, from glabella to external occipital protuberance, is bisected, and a point 1.2 cm. (Jin.) behind the centre represents the superior Rolandic point. From this point a line drawn downward and forward 9 cm. (3| in.) long, at an angle of 67|° with the sagittal line (i. e., | of a right angle) will represent the central sulcus. The lower extremity of this line is known as the inferior Rolandic point. This method is open to the objection that it only apphes to the average adult skull, and not to skulls of all sizes. To obviate this difficulty the method of Kronlein may be employed in addition (fig. 1085). A base line BL is drawn through the lower border of the orbit and the upper border of the external acustic meatus. Parallel to this an upper horizontal Une UH is marked out at the level of the upper margin of the orbit. Three hues vertical to the base line are now drawn, (1) at the posterior border of the mastoid process MRi (2) through the condyle of the lower jaw (CR2), and (3) from the mid-point of the zygoma (ZS). The point Ri, where the first vertical joins the sagittal sutiu'e is the superior Rolandic point. The point S where the third vertical ZS cuts the line UH marks the junction of the three hmbs of the lateral fissure. A line joining Ri and S will cut the second vertical CR2 at the inferior Rolandic point, Rj. CRANIO-CEREBRAL TOPOGRAPHY 1341 The posterior limb of the lateral fissure also may be represented by a line bisecting the angle RiSH and ending behind at the point S^ where it cuts the vertical MRi. Some further points in the surgical anatomy of the cranium must be referred to: — The mid- dle meningeal artery. This vessel, entering the middle fossa by the foramen spinosum, grooves the great wing of the sphenoid and divides into two branches. The anterior grooves the anterior inferior angle of the parietal bone, and is then continued upward and slightly back- ward between the coronal suture and central sulcus (fig. 1090), almost to the vertex; the posterior branch takes a lower level, running backward under the squ.imous bone to supply the parietal and anterior part of the occipital bones. If a skull, bisected antero-posteriorly, be held up to the light, it will be seen how thin are the bones over the chief branches of this vessel, thus accounting for the slight violence sometimes sufficient to rupture it. The groove it occupies in the parietal is sometimes converted into a canal. A wounded artery retracting here may be very difficult to secure. The veins which accompany the artery and which lie lateral to it Fig. 1091.- — Cerebral Topography and Localization. (Gushing, prom Keen's Surgekt.) in the groove are thin-walled and sinus-like before they open into the spheno-parietal sinus, another explanation of the obstinacy of this haemorrhage. According to the point of rupture, three hsematomata should be remembered (Kronlein), anterior or fronto-temporal; middle, or temporo-parietal; and posterior, or parieto-occipital. The first two are much the most frequent, and exposure of the pterion, with free removal of the adjacent bone, will suffice for dealing with them. Drainage of the lateral ventricle. — (1) Where the anterior fontanelle is closed, Poirier and Keen have opened the inferior cornu through the middle temporal convolution, the pin of the trephine being placed 3.1 cm. (IJ in.) behind the external auditory meatus, and about the same distance above Reid's base-line which is drawn from the lower margin of the orbit through the mid-point of the external auditory meatus. The needle should here be directed to a point 1342 CLINICAL AND TOPOGRAPHICAL ANATOMY about 5 cm. (2 in.) above the opposite ear. (2) Kocher's point for draining the lateral ventricle is taken over the frontal lobe 2.5 cm. from the median line and 3 cm. in front of the upper Rolandic point. The needle is passed downward and a little backward to a depth of 4 or 5 cm. Up to this point the outside of the cranium has been mainly considered; it remains to draw attention to some of the chir.f points in the sjirgical anatomy of the interior, especially ot the base. The three fossae are of paramount importance in fracture. In the anterior fossa the delicacy of parts of the floor, the connection of this with the nose and orbit, and the exact adaptation of its irregular surface to that of the frontal lobes, no 'water-bed' intervening, are the chief points. Thus the slightness of a fatal fissure, the frequent presence of bruising after a blow perhaps on the occiput, which has been considered to have caused only concussion, the characteristic palpebral hemorrhage, and the infection of a fracture here are all explained, together with the possibility and gravity of a fracture here from a severe blow on the nose. In the middle fossa the frequency of fractures is explained by the facts that while here, as in the other fossae, a fracture often radiates down from the vertex, the overlying vault being a region often struck, the base is weakened by numerous foramina and fissures. Further, the resisting power of the petrous bone must be lessened by the cavities for the internal ear, the carotid, and, to a less degree, by the jugular fossa. For fluids to escape through the external meatus, the dura, the prolongation of the arachnoid into the internal meatus, the membrani tympani, and probably the internal ear, must all be injured. The presence of the middle meningeal artery (fig. 1090) and the cavernous sinus in this fossa must also be remembered, especially in such operations as that on the Gasserian ganglion. Posterior fossa : It is not sufficiently recognised that fractures here are, owing to the anatomy of the parts, in some respects the most important of all. It is here that a small fissure-fracture, ultimately fatal, with severe occipital and frontal bruising and some intradural hemorrhage, has been so often overlooked, especially in the drunken. This is explained by the supposed strength of the bone, this being really very thin in places, by the thickness of the soft parts, and the abundance of hair. Further, there is no very apparent escape of cerebral contents as in the anterior and middle fosse. Blood, etc., may trickle into the pharynx far back, or a deep-seated eochymosis coming up after two days, under the muscles about the mastoid process, may call attention to the damage within. Dura mater. — The outer layer of this membrane acts as a periosteum, by bringing blood- vessels to the bone while the inner layer supports the brain. The influence of its partitions and its damping effect on vibrations is great in blows on the head. Its varying adhesions, according to site and age, must be remembered. Thus while it is intimately connected over the base with its adhesions to the different foramina, it is more loosely connected with the vault, as is shown in middle meningeal hemorrhage. In early and later life the closeness of its connection with the bones is also more marked. It is united to the inter-sutural membranes. Finally, the existence of the cerebro-spinal fluid with its power of lessening the evil of vibrations and its aid in regulating infra-cranial pressure, must be borne in mind. The chief collections, in which the subarachnoid meshwork is almost absent, are met with in front and behind the medulla. That in front, also lying under the pons, Hilton's 'water-bed,' sends a prolongation forward to the optic chiasma, but does not extend under the frontal or temporal lobes. The collection behind lies between the medulla and under surface of the cerebellum. Here, by the foramen of Magendie, the intra-ventricular cavities communicate with the sub- arachnoid space of the spinal cord. THE HYPOPHYSIS CEREBRI The hypophysis (pituitary body) which has now become of great clinical importance, consists of a pars anterior and pars intermedia derived from the buccal ectoderm, and a posterior pars nervosa formed by a downgrowth from the floor of the third ventricle. The gland lies in the fossa hypophyseos of the sphenoid bone, and an enlargement of it, apart from general skeletal and nutri- tional effect due to anomalies of its internal secretions, will cause pressure on the cavernous sinus on each side, and on the optic chiasma above. It will also expand the fossa hypophyseos, pushing down its floor at the expense of the sphenoidal air sinus. Such enlargements may be detected by lateral radiograms. The normal size of the adult hypophyseal fossa (fig. 1097) is 10-12 mm. from before backward and 8 mm. from above downward (Keith). The hypophysis may be exposed surgically either by turning the nose to one side, and remov- ing the upper part of the septum and floor of the sphenoidal sinus, or by Cushing's method, in which a sublabial incision is made in the vestibule of the mouth, and through it the mucosa is then separated from each side, of the nasal septum back to the sphenoidal sinus. A strip of septum is removed, and also the floor of the sphenoidal sinus, after which the hypophyseal fossa is opened and the gland e.xposed (fig. 1097).* THE FACE The topics included under this heading are the arteries, parotid region, nerves, mandible and maxilla, orbit, mouth, palate and nose. The outhne of the different bones — nasal, upper and lower jaws, zygomatic ■* H. Gushing. The Pituitary Body and its Disorders, 1912. THE FACE 1343 and zygoma — can be readily traced. The last mentioned and the glabella are alluded to on pp. 1331 and 1332; and the canine fossa should be identified as one of the antral routes. The delicacy, laxity, and vascularity of the skin are of great importance in all operations, while the abundance of large gland orifices accounts for the frequency of lupus here. Arteries. — The supraorbital artery can be felt beating just above its notch (junction of medial with lateral two-thirds of supraorbital margin); the little frontal artery is of importance, as it nourishes the flap when a new nose is taken from the forehead; the superficial temporal, accompanied by the auriculo-temporal nerve, can be felt where it crosses the root of the zygoma just in front of the tragus, its anterior branch about 3.1 cm. (1| in.) above and behind the zygomatic process of the frontal; the occipital, accompanied by the great occipital nerve (fig. 450), pulsates to the medial side of the centre of a line drawn from the occipital protu- berance to the mastoid process; the posterior auricular, rather deeply, between the auricle and the mastoid process. The external carotid lies behind the ascending Fig. 1092. — Surface Relations of Vessels and Nerves in Lateral View op the Face AND Neck. Supraorbital n. Supratrochlear n. Infratrochlear n. External nasal n. Infraorbital n. Buccal n. Ext. maxillary art. Mental n. Post, belly of digastric Ant. belly of digastric Thyreoid cartilage Common carotid art. Thyreoid gland External auditory meatus Facial nerve (in red) Parotid gland (yellow) Sternomastoid Accessory nerve Ext. jugular vein ramus of the jaw. The external maxillary (fig. 1093) crosses the jaw just in front of the masseter; if divided, both ends must be secured here. It can be felt again a little behind the angle of the mouth, just beneath the mucous membrane (it here gives off the labial branches, which can also be felt, lying deeply, if the lip is taken between the finger and thumb) ; and again by the side of the nose, as it runs up to Ithe angulusoculi. The small angular branch is, from its position, always troublesome to secure. To trace the course of the external maxillary artery a line should be drawn from a point a little above and lateral to the tip of the great cornu of the hyoid to the lower part of the anterior border of the masse- ter, and thence to one lateral to and above the angle of the mouth, and so onward, lateral to the angle of the nose, up to the medial angle. The anterior facial vein takes a straight course behind the tortuous external maxillary artery. The absence of valves and its communication by the angular and ophthalmic veins with the cavernous sinus, and, by the deep facial, with the pterygoid plexus, are of grave importance in infective thrombosis. The external jugular vein will be mentioned later. Parotid region. — A line drawn from the lower border of the meatus to a point midway between the nose and upper lip gives the level of the parotid duct, which 1344 CLINICAL AND TOPOGRAPHICAL ANATOMY opens into the mouth opposite the second molar tooth. The level of the duct, somewhat inconstant, would be usually about a finger^s breadth below the zygoma. It is accompanied by the transverse facial artery above, and the infraorbital branch of the facial nerve below. The sheath of the parotid, continuous with those of the masseter and sterno-mastoid, is strong enough to cause most exquisitely painful tension when inflammation of the gland is present, and, together with the presence of deep processes of the gland in connection with the Fig. 1093. — Scheme op the External Maxillary (Facial) Artery. (Walsham.) Orbicularis ocuU muscl Transverse facial artery M. quadr. labii sup (caput zygom.) Zygoma ticus muscle Buccinator muscle Masseteric branch Masseter muscle Stylo -phar ynge u i Stylo-glossus muscle Ascending palatine branch Tonsillar branch External maxillary artery External carotid artery Posterior belly of digastric muscle Lingual artery Frontal branch of ophthal- mic artery Nasal branch of ophthal- mic artery -Angular artery M. quadr. labii ■ sup. (caput ang.) Infraorbital artery Caput infraorb. ■Lat. nasal artery Caninus muscle —Artery of septum Superior labial artery Risonus muscle Infenor labial artery Mental branch of inferior alveolar artery Quadratus labii inferioris muscle Inferior labial artery Triangularis muscle Submental artery branches to submaxillary Anterior belly of digastric Mylo-hyoid muscle ■Hyo-glossus muscle 'Hypoglossal nerve mandibular (glenoid) cavity and styloid process, to explain the deep burrowing of pus which may take place into the pharynx and pterygoid region. The relation of the capsule to growths, innocent or malignant, of the parotid is also important (See figs. S65, 1092). The parotid region would be thus mapped out (fig. 1096). Above by the pos- terior two-thirds of the zygoma; below, by a line corresponding to the posterior belly of the digastric (fig. 1096) ; behind, are the external auditory meatus, mastoid, and sterno-mastoid. In front the gland and socia parotidis overlap the posterior part of the masseter, to a variable degree (fig. 1096). THE FACE 1345 Sensory nerves. — -The cutaneous nerve areas of the face are shown in fig. 774. The supraorbital nerve, the main sensory branch of the ophthalmic, emerges from the orbit with its companion artery through the notch (occasionally a foramen) at the junction of the medial third and lateral two-thirds of the supraorbital margin. A line drawn from the supraorbital notch downward across the interval between the bicuspid teeth will cross the infraorbital foramen from which emerges the infraorbital nerve, the main terminal division of the maxillarj^, at a point 1 cm. below the orbital margin. The mental foramen, the point of exit of the mental nerve, a branch of the inferior alveolar, is found on a prolongation of the same line midway between the upper and lower margins of the mandible in the adult. In the infant in whom the alveolar element of the jaw is relatively large, the mental foramen is nearer the lower margin, while in the edentulous jaw of old age it is found much nearer the upper margin. In trephining to expose the inferior alveolar (dental) nerve, one of the common seats of neuralgia and one in which a peripheral operation is justified from the results, the ascending ramus is opened midway between its anterior and posterior borders, on a level with the last molar. The semilunar ganglion lies at a depth of 5.5-6 cm. (2i in.) upder the eminentia articularia at the base of the zygoma. In exposing it for the purpose of excision for intractable neuralgia the following structures are encountered: (1) Skin and superficial fascia with branches of the superficial temporal artery; (2) temporal fascia and muscle with deep temporal vessels; (3) squamous bone and great wing of sphenoid, which are trephined, the floor of the middle fossa being gouged away ; (4) middle meningeal vessels and dura mater. By elevating the dura mater and superimposed temporal lobe, and securing the middle meningeal artery, the ganglion is exposed, lying in a separate compartment [cavum Meckelii] of the dura, which contains cerebro- spinal fluid. The motor nerve of the muscles of mastication lies on the lower and medial aspect of the ganglion, and should not be divided. Injection of the mandibular nerve with alcohol, by means of a long stout hypodermic needle is practised in cases of intractable neuralgia as an alternative to excision of the semilunar gang- lion. A vertical line is drawn on the cheek downward from the junction of the posterior and middle thirds of the zygomatic arch, and the needle is entered on this line at a point 1.5 cm. from the lower border of the zygoma. It is directed upward and medially so as to pass through the lowest part of the mandibular notch. If the mouth is opened the notch is depressed and more room gained. The needle impinges first against the inferior surface of the great wing of the sphenoid bone, and when the point is lowered a little it engages in the foramen ovale at a depth of 4-4,5 cm. In most cases the needle can be passed thi'ough the foramen ovale into the semi- lunar gangUon. (Harris.)* The maxillary nerve may be injected by passing a needle along the floor of the orbit from its infero-lateral angle in a direction backward and sUghtly medially to the foramen rotundum which lies 4.5 cm. from the surface. Facial nerve. — In the petrous bone the course of this nerve is first outward and forward, then, having entered the facial canal, backward and downward along the medial wall of the tympanum, above the fenestra ovalis. Emerging from the stylo-mastoid foramen the nerve takes first the line of the posterior belly of the digastric, running forward and a little downward from the anterior border of the mastoid where this meets the auricle. (Godlee.) Entering at once the posterior part of the parotid, it crosses the neck of the mandible at the level of the lower border of the tragus. The frequent paralysis of this nerve may thus depend upon — (1) cerebral causes; (2) dis- ease of or injm-y to the petrous portion; (.3) affections after its exit— BeU's paralysis. A diag- nosis may be arrived at by attention to the following. In cerebral disease the lower part of the face is chiefly affected, the eyelids usually escaping. In aU the other forms the whole side of the face is paralysed. Hemiplegia of the opposite side of the body and paralysis of the sixth nerve are usually present. In petrous paralysis, owing to involvement of the chorda tympani, there may be interference with the saliva and taste, affecting especially the anterior part of the tongue. The auditory nerve may also be affected. Here and in (3) there will be a histor}' of disease or injury. In complete paralysis the smooth side of the face and forehead, the absence of power of expression, to frown, to blow, or whistle, the open eyelids and epiphora, and subse- quent liability to mischief in the cornea, the di-opping of the angle of the mouth and dribbling of saUva, the interference with mastication from paralysis of the buccinator, are the chief points. Mandible. — Dislocation of the temporo-mandibular joint is referred to on p. 217. In the usual dislocation, from muscular action, the jaw is suddenly brought forward against the anterior part of the capsule, which tends, bj!- the action of the depressors, to give way; the elevators then pull up the mandible, a sequence that must be remembered in reduction. In the commonest fracture of * Lancet, Jan. 23, 1912. 1346 CLINICAL AND TOPOGRAPHICAL ANATOMY the mandible — unilateral, near the mental foramen — the larger anterior fragment will be pulled by the depressors downward and medially, the smaller posterior one upward and usually lateral to the other fragment. Maxilla. — The boundaries of the maxillary sinus (antrum) are of much im- portance. The base of this irregularly pyramidal cavity corresponds to the middle and inferior meatuses on the lateral wall of the nose; toward the upper and back part is the opening into the middle meatus. The apex runs laterally toward the zygomatic process. The roof is formed by the orbital plate with the infraorbital nerve and vessels anteriorly; the floor by the junction of the alveolar arch, carrying the first molars (and often the bicuspids), with the hard palate. It may be pierced by the roots of the second bicuspid or first and second molar teeth. Anteriorly, the antrum is bounded by the canine fossa; posteriorly it is in relation with the zygomatic fossa. The cavity, present at birth, increases gradually up to the twelfth year. The chief paths of infection are through the teeth (especially the first and second molar), the nose, and frontal sinus. The obstinacy of inflammation here is explained by the site of the opening, high up on the medial wall, and thus inadequate drainage, by the imperfectly multi- locular cavity of the interior and its rigid walls. The chief sites for opening the antrum are — (a) thi'ough the sockets of the first or second molars; (b) through the canine fossa, after the reflec- tion of mucous membrane has been detached, midway between the roots of the teeth and the infraorbital foramen (this path gives more room) ; (c) through the inferior meatus of the nose. THE ORBIT AND EYE The bony orbit is a pyramidal fossa with its base at the orbital margin and its apex at the optic foramen. The medial walls of the two orbits are approximately parallel, but the lateral walls diverge as they are traced forward and lie at right angles to each other. The thin floor which is formed mainly by the maxilla and corresponds to the roof of the maxillary sinus, is readily destroyed by growths extending up from the sinus and in the process pressure on the infraorbital nerve is apt to cause pain referred to the cheek. The roof formed by the orbital plate of the frontal bone is also thin, and foreign bodies thrust into the orbit may perforate it and enter the frontal lobe of the cerebrum. The medial wall is chiefly constituted by the lacrimal and lamina papyracea of the ethmoid, both very thin bones. This wall is readily destroyed by malignant growths of the nose. Injuries of the medial wall such as may be associated with fractures of the nose bring the ethmoidal air cells into communication with the cellular tissue of the orbit. The latter may thus be distended with air on attempting to blow the nose. The lateral wall is formed in its anterior third by the zygomatic bone, which separates the or"bit from the zygomatic fossa. The posterior two-thirds formed by the sphenoid bone separate the orbit from the temporal lobe of the brain in the middle cranial fossa. The orbit communicates with the cranimn by the optic foramen, which transmits the optic nerve and ophthalmic artery and the superior orbital fissure through which pass all the other vessels and nerves of the orbit. In cases of fracture of the base of the skuU involving the anterior clinoid process, a traumatic communication (arterio-venous aneurysm) may be formed between the internal carotid artery and cavernous sinus, behind the apex of the orbit, giving rise to pulsating exophthalmos. The orbital margin is larger in the transverse than in the vertical direction, and consequently there is more space on either side than above and below be- tween it and the eyeball which is nearly spherical. The eyeball lies nearer to the medial than to the lateral margin and hence foreign bodies more commonly penetrate the orbit to the lateral side of the eye. Behind the fascia bulbi, the eyeball rests on a mass of soft loose orbital fat in which foreign bodies may be hidden for a considerable time. The structure of the eyelids. — The different layers are of much practical importance. (1) The skin is delicate and fatless, and contains pigment, the object of this being to protect the eye from bright light. It helps to explain the 'dark circles' of later life. (2) Areolar tissue. Owing to its looseness and delicacy, this is very liable to infiltration, as in oedema and erysipelas. (3) THE ORBIT AND EYE 1347 Orbicularis. Paralysis of this, tiie palpebral portion, leads to epipiiora, tiie puncta being no longer kept in their normal baclcward direction against the conjunctiva. (4) Palpebral fascia, reaching from the orbit to the tarsal cartilage. This is usually strong enough to prevent haemorrhage, due to fractured base of skull, becoming subcutaneous. (5) Levator palpebr^e. (6) Tarsal plate; in reality, densely felted fibrous tissue. (7) Tarsal (Meibomian) glands, lashes, and sebaceous follicles. I Localised inflammation starting in any of these last three structures, especially the last, will cause a 'stye.' The frequency with which the lid-border is the seat of that most troublesome chronic inflammation, blepharitis, and its result, 'blear eye,' is e.xplained by these anatomical points. Its circulation is terminal and slow; half skin and half mucous membrane, it is moister and more liable to local irritation than the skin; while its numerous glands readily partici- pate in any inflammation. Fig. 1094. — Sagittal Section Thkough the Uppek Eyelid. (After Waldeyer and Fuchs.) ^ Conjunctiva near fornix / Anterior layer of insertion "~ of levator palpebrffl superioris ■ Superior tarsal muscle * Miiller 3 from levator passing tlirough orbicularis to skin Cutaneous surface just above supe- rior palpebral fold Orbicularis fibres, r.nt_ across [\ Sweat-gland -\^ — --Supei / of I /--—Fibre Fine hair with sebaceous gland at its base Ciliary gland of MoU Cilium ^^— Mucous glands — Mucous gland _ Tarsal (Meibomian) gland - -Musculus ciliaris Riolani '""Posterior edge of lid-margin Opening of duct of tarsal gland (8) The conjunctiva. To trace this important membrane, the lids should be everted, when the following will be noted. The conjunctiva over the tarsal part of the lid is closely adherent, and through it a series of nearly straight, parallel, light yellow lines and granules, the tarsal glands, can be seen. Owing to their position here (fig. 1094) and to avoid scarring, a tarsal cyst is always opened on its conjunctival surface. Beyond the tarsi, the palpebral conjunctiva is thicker and freely movable owing to the abundant lax submucous tissue. Underlying vessels are visible here. Leaving the eyelid the conjunctiva is reflected onto the eyeball at the fornix. Into the lateral part of the upper fornix open the ducts of the lacrimal gland. The bulbar conjunctiva is continued over the front of the ej^eball to the corneal margin. It is thin and contains fine vessels which are distinguished from subjacent episcleral vessels by the fact that they move with the conjunctiva. 1348 CLINICAL AND TOPOGRAPHICAL ANATOMY These conjunctival vessels, derived from the lacrimal and palpebral arteries, become very- visible in conjunctivitis. In deep inflammation affecting .the iris and ciliary body, the episcleral branches of the anterior ciliary arteries (which are derived from the muscular and lacrimal arteries) become engorged and are visible as a pink circumcorneal zone of congestion, deeply situated under the conjunctiva. These branches take a large share in the nutrition of the cornea, and are responsible for the vascularity of pannus and the 'salmon patches' of interstitial keratitis. The conjunctival nerves for the upper lid and bulbar part of the membrane, and the nerves to the cornea, are supplied by the ophthalmic division of the trigeminal. The maxillary divi- sion of this nerve sUpphes the lower palpebral conjunctiva. The differing structure of the palpebral and ocular portions has important bearings. Thus the palpebral conjunctiva is thick, highly vascular and sensitive. To this vasovilarity we owe the chemosis, or hot, red, tense swelling of purulent ophthalmia. The exquisite suffering of the same disease, or that caused by a foreign body, is explained by the numerous nerve-papillje and end- bulbs. To the thickness and abundance of the connective tissue are due the contraction and permanent thickening which may occur in granular lids. The so-called granulations, met with in this disease on the palpebral conjunctiva, are really little nodules of hypertrophied lymphoid follicles, or mucous glands, which abound here. Immediately under the bulbar conjunctiva, between it and the sclerotic, lies the anterior part of the fascia bulbi (of Tenon). This fibrous membrane forms a sheath for the posterior Pig. 1095.- -The Lacrimal Apparatus and Naso-lacrimal Duct. (Bristles are introduced into the puncta lacrimalia.) (Bellamy.) Medial wall of maxillary sinus Lacrimal sac Medial palpebral ligament Valvular folds in naso-lacrimal duct Lower ndsiii concha Orifice of naso-lacrimal duct five-sixths of the eyeball, and is intimately connected with the sheaths of the extrinsic muscles and through the check ligaments with the orbital walls. Together with the conjunctiva it must be opened in the operation of tenotomy for strabismus, and after division of a rectus tendon the muscle retains some control over the eye through its connection with the fascia bulbi. In enucleation of the eyeball both conjunctiva and fascia bulbi are divided around the cornea, where they are intimately blended. In removal of the upper jaw the attachment of the sus- pensory ligament of this fascia must always be left if possible, for otherwise the eyeball will tend to fall forward and the cornea suffer from its exposure (Lockwood). Finally the cavity between the two layers of the capsule is continuous with the extensions of the cerebral membranes along the optic nerve, i. e., with the subarachnoid space. For an account of the intrinsic and extrinsic muscles of the eye the reader is referred to the section on the Eye. Reference may be made here, however, to the part played by certain fibres of the cervical sympathetic system. Emerging from the cord at the fh-st and second thoracic segments, the communicating fibres pass up the sympathetic chain in the neck to cell stations in the superior cervical ganglion. Thence continuing onward tltrough the carotid canal and superior orbital fissure, they supply (1) the dilator muscle of the u'is, (2) the unstriped muscle element in the eyelids, and (3) smooth muscle fibres, deoribed by Sappey, in the check ligaments and fascia bulbi. Paralysis of the cervical sympathetic nerve in the neck, usually in its lowest part, by trauma or the pressure of a malignant growth, causes therefore (1) narrowing of the pupil, (2) narrowing of the palpebral fissure (pseudo-ptosis), and (3) enophthalmos. The lacrimal gland lies in a hollow at the supero-lateral angle of the orbit, protected by the zygomatic process of the frontal bone. It is not palpable nor- mally. Its lower or palpebral portion rests on the lateral third of the fornix THE MOUTH 1349 conjunctivse, into which the numerous ducts open, and it may be seen through the conjunctiva on everting and raising the upper lid. The position of the lacrimal puncta should be noted; owing to their backward direction, the lids must be previously everted. The puncta are kept open by a minute fibrous ring. Each is situated on a minute papilla at the junction of the medial and straight third of the lid with the lateral curved two-thirds. Close to the medial angle, in addition to the puncta and papillae, should be noted the caruncula lacrimalis, with its delicate haii's, and the plica semilunaris, which corresponds to the third eyelid of certain birds. The lacrimal sac is a most important part of the lacrimal apparatus, from its disfiguring diseases; it lies in a bony groove, between the nasal process of the maxilla and the lacrimal bone. The medial palpebral ligament crosses it a little above its centre (fig. 1095) . Thus two-thirds of the sac are below the ligament, and in suppuration the opening is made below it also. The angular artery ascends on the nasal side of the sac. The manipulation of a probe along the lacrimal passages should thus be practised: — the lower lid being drawn laterally and downward by the thumb, the probe is passed vertically into the punctum, then turned horizontally and passed on till it reaches the medial waU of the sac. It is then rotated somewhat forward, raised vertically, and pushed gently along the duct down- ward, and a little lateralward and backward, till the floor of the nose is reached, the operator aiming, as it were, for the site of the first molar tooth. The naso-lacrimal duct extends from the lower end of the lacrimal sac to the inferior meatus of the nose and is about 1 . 2 cm (J in.) in length. If the eyes are opened naturally, the greatest part of the cornea, behind it the iris, with the pupU in the centre, on either side of the cornea some of the sclerotic, the semilunar fold, and caruncle can be seen. THE MOUTH The lips. — When the whole thickness of the lip is incised the labial artery will be found lying near the free margin, internal to the orbicularis muscle, and Fig. 1096.— Side op the Face and Mouth Cmiti, showing the Three Salivakt Glansd. Accessory parotii Duct of accessory parotid Duct of parotid Frenulum linguae. Sublingual gland' Duct of submaxil lary gland Mylo-hyoid muscle. Masseter muscle Posterior belly of digastric muscle Submaxillary gland, drawn backward ■Hyoid bo Deep portion of submaxillary gland between it and the mucosa. There is a very free anastomosis between the arteries of the opposite sides. If the tongue be raised, the under surface is seen to be smooth and devoid of papillse. In the middle line is the frenulum. When division of this is really required in tongue-tie, the scissors should be kept close to the bone, in order to avoid the ranine vessels. 1350 CLINICAL AND TOPOGRAPHICAL ANATOMY Of these, the veins can be seen just to one side; the arteries are close by, but deeper. Farther out are two more or less distinct fringed folds, the plica; l fimbria tse, running from behind forward and, like the frenulum, disappetiring before the tip. Between these and the frenulum are the small apical mucous glands of Nuhn or Blandin. Farther back, at the junction of the mucous membrane and the alveoli, are two other projections of the mucosa, the sublingual; under these are the sublingual glands, the ranine veins, and, more deeply, Wharton's duct and the termina- tion of the lingual nerve. The majoritj' of the ducts of the sublingual gland (Rivinian) open on the sublingual ridges. A single larger one, Bartholin's, opens with that of Wharton, or close to it, on either side of the frenulum (fig. 1096). Dilatation of one of the Rivinian ducts, more fre- quently dilatation of a muciparous gland — and, much more rarelj', dilatation of Wharton's duct — constitutes a 'ranula.' The submaxillary gland can be felt nearer the angle of the jaw, lying between its fossa and the mucous membrane, especially if pressure is made from outside. The attachment of the genio-glossi can be felt behind the symphysis: the division of the muscles allows the tongue to come well out of the mouth; but when both have to be divided, the tongue loses much of its steadiness, and may easily fall Fig. 1097. — Sebtion of the Skull and Brain in thp Median Plane. (Braune.) Falx cerebri Superior sagittal sinus Inferior sagittal sinus Corpus caUosum Optic chiasma Corpus mammillare Occipital lobe of Torcular Herophili Medulla oblongata Posterior ring of atlas Body of epistropheus (axis) Thyreoid gland Sterno-thyreoid muscle' , Body of second thoracic \ vertebra back over the larynx during the administration of the anaesthetic or, later on, in sleep. It should therefore be secured forward for a while with silk. For the same reason, in removal of one-half of the mandible, part of this muscular attachment should always be left, if possible. Turning now to the dorsum of the tongue, this shows two distinct parts: one, the anterior two-thu'ds, the buccal, is rich in papiUic; the other, the posterior, the pharyngeal, contains abun- dant lymphoid follicles like the tonsil. This part possesses peculiar sensibiUty, as shown by movements of tongue and palate when a depressor is placed too far back. The two parts are separated by the v -shaped arrangement of the vallate papillEe, with the apex turned back- ward. Immediately behind the apical vallate papilla is a small pit, the foramen cEecum which represents the upper remains of the thyreoglossal tract, and may be the seat of lingual thyreoid growths. While the tongue is mainly a muscular organ, the fine fatty connective tissue in the septum and between the muscular bundles is the seat of that dangerous condition acute glossitis, and of gummatous infiltration. While the mouth is widely open, the pterj^go-man- dibular ligament can be seen and felt beneath the mucous membrane, behind the last molar tooth. Just below and in front of the lower attachment of this ligament the lingual nerve can be felt lying close to the bone below the last molar. The simplest and surest method of dividing the nerve here, to give relief from pain in incurable carcinoma of the tongue, is to draw the tongue out of the mouth and expose the nerve where it lies superficially under the mucous membrane thus made prominent between the side of the tongue and the gums, the centre of the incision THE TONSILS 1351 being opposite to the last molar tooth. (Roser, L6ti6vant.) In cancer of the tongue pain is often referred up the aurioulo-temporal nerve to the ear and side of head. Behind the last molar tooth can be felt the coronoid process, and higher up, just behind and medial to the tooth, the pterygoid hamulus of the sphenoid. This process is a landmark to the site of the greater palatine foramen, which lies just in front of it, and which transmits the greater palatine branch of the descend- ing palatine artery, together with the anterior palatine nerve. The vessel and nerve run forward in grooves on the lower surface of the palatine process of the maxilla, giving off anastomosing branches toward the middle line, and join at the incisive foramen with the nasopalatine artery. Their position must be remembered in raising the flaps during the operation for closure of a cleft in the hard palate. To ensure the vitality of the flaps the incisions must be made lateral to the vascular arch, close to and pai'allel with the upper alveolus, and should not extend be- yond a point opposite to and just medial to the last molar tooth, for fear of encroaching upon the posterior palatine canal. When the teeth are clenched, there is still a space, communicating between the mouth and pharynx behind the molar teeth, which admits a medium-sized catheter. When a patient breathes deeply through the mouth and the head is thrown back, the soft palate is raised, the pillars (arches) separated; the uvula and fauces, with the anterior and posterior pillars, with their attachments, the tonsils, and the back of the pharynx are exposed. This portion of the pharyngeal mucous membrane would lie over the lower part of the second and the upper part of the third cervical vertebrae, the anterior arch of the atlas corre- sponding to the level of the posterior nares, and the body of the epistropheus (?ixis) to the level of the soft palate (fig. 1097). If a finger be introduced past the soft palate to this part of the spine and turned upward and downward, it is possible, with the aid of an anfesthetic, to examine the upper four or five and, in children, six vertebrse, as far as the anterior surfaces of their bodies. 'The part of the column which is accessible to a straight instrument introduced through the mouth is very hmited, extending, in the adult, from the lower border of the axis to the middle or lower part of the fourth cervical vertebra; in the child, owing to the small size of the face, it comprises the bodies of the axis and of the third cervical vertebra.' (Thane and Godlee, from Chipault.) The distance from the incisor teeth to the commencement of the oesophagus at the cricoid cartilage is 15 cm. (6 in.) in the adult, and the distance from the teeth to the cardiac orifice of the stomach is 48 to 50 cm. (16 or 17 in.). The lymphatic drainage of the face, mouth, and tongue is given on pp. 712 and 715. Tonsils. — The relations of the tonsils should be carefully examined. Thus, they are separated externally by the superior constrictor and pharyngeal aponeuro- sis from the oscending pharyngeal and internal carotid arteries. The latter vessel lies about 2.5 cm. (1 in.) behind and to the lateral side of the tonsil. When serious haemorrhage follows operations here, it usually comes from one of the numerous tonsillar branches (fig. 448). The extent to which the tonsil is covered by the anterior pillar, how far it projects upward beneath the soft palate or downward into the pharynx, have all important bearings on the mode of removal. Its position corresponds to a point a little above and in front of the angle of the jaw. The lateral surface, enclosed by an imperfect capsule and separated from the superior constrictor by connective tissue, explains how an enlarged tonsil can be dragged medialwarcl by a vulsellum, and enucleated after an incision in the mucous membrane around. It is in this connective tissue that severe infective inflammation, e. g., after scarlet fever or an imbedded pipe-stem, may set up haemorrhage or spreading cellulitis, retro-pharyngeal or otherwise. The finger introduced downward at the back of the mouth, especially if the parts are ren- dered in sensitive by local anaesthetics, feels the vallate papilla, the lingual and laryngeal surfaces of the epiglottis, the arytajno-epiglottidean folds, with the cuneiform and corniculate cartilages. If the finger be moved upward behind the soft palate and turned upward to the base of the skull, and then forward, it will feel the choanae (posterior nares), separated by the vomer. Tlie other boundaries of these are, laterally, the medial pterygoid plate and palate bones; above, the basi- sphenoid; and below, the horizontal plate of the palate bone and the inferior nasal spine. Within each nostril would be felt the posterior ends of the two lower nasal conchte (turbinate bones); above and behind is felt the basilar process of the skull, the vault of the pharynx, and the bodies of the upper cervical vertebree (fig. 1097). The size of the choanae, in the bony skull 2.5 cm. (Ijin.) vertically by 1.2 cm. (J in.), and the presence of anj^ adenoids, are especially to be noted. The richness of the naso-pharynx in glandular structures, its proneness to inflammation, and of this inflammation to spread to other parts, — e. g., the tympanum, — ^are well known. The finger should be familiar with the feel of 1352 CLINICAL AND TOPOGRAPHICAL ANATOMY adenoids — i. e., hypertrophied post-nasal lymphatic nodules — soft bodies of irregular shape blocking up the naso-pharynx. _ To make out how far this is the case, it is well to take the nasal septum as the starting-point. Pharyngeal hypophyseal remnants. — In the naso-pharyngeal mucosa, a few millimetres behind the posterior border of the vomer, a group of glandular cells may be found on micro- scopical examination in all cases (Haberfeld), corresponding in histological appearance with the pars anterior of the hypophysis. These cells are a remnant of the primitive bud that grows toward the brain in front of the bucco-pharyngeal membrane to form the pars anterior of the hypophysis. In some cases of pituitary disorder they give rise to a palpable tumour in the naso- pharynx. The palate.- — Between the diverging pillars of the soft palate is the isthmus faucium, bounded above by the free margin of the palate, and below by the dorsum of the tongue. The space between the arches (pihars), glossopalatine and pharyngo-palatine, with attachments denoted by their names, shallow above, widens and deepens below. Of its lateral boundaries, the posterior pillars come nearer each other than the anterior. The coverings of the hard palate are chiefly mucous membrane, glands, and periosteum. These are intimately blended by fibrous septa, as in the superficial layers of scalp and palm of the hand. Hence the readiness with which necrosis takes place here. Hare-lip and cleft palate. — Failure of union between the mesial nasal process and the maxillary process of the embryo gives rise to the deformity known as hare-lip. The palate is developed from three primitive processes growing down from the basis cranii, viz., (1) the mesial nasal process forming the premaxilla which lies in front of the anterior pala- tine foramen and bears the four incisor teeth, (2) and (3) the maxillary process of either side. The slighter cases of failure to unite affect only the soft palate which is the last part to fuse. Complete alveolar cleft palate, which occurs combined with hare-lip and may be unilateral or bilateral, represents more serious non-union. In this condition the lateral incisor may be found either on the medial or on the lateral side of the cleft, which is explained by the fact that thi& tooth is developed in the groove between the two processes (Keith). In paring the edges of a cleft soft palate, the following structures would be, successively, cut through: — (1) Oral mucous membrane; (2) submucous tissue, with vessels, nerves, and glands; (3) glosso-palatine muscle; (4) aponeurosis of tensor palati; (5) anterior fasciculus of pharyngo-palatine; (6) levator palati and uvular muscles; (7) posterior fasciculus of pharyngo- palatine; (8) submucous tissue, vessels, nerves, and glands; (9) posterior mucous membrane. The soft palate is thicker than it seems, the average in an adult being 6 mm. (i in.). The muscles widening a cleft are the tensor and levator, while the superior constrictor closes it in swallowing. Of the arteries of the palate, from the external maxillary (facial), ascending pharyn- geal, and internal maxillary, the largest is the descending palatine branch of the last. This emerges from the posterior palatine canal close to the inner side of the last molar tooth. THE NOSE On the face the outline of the nasal bones can be easily traced, and below them the lateral nasal cartilages, flat and also somewhat triangular. Below these are the greater alar cartilages, curved and so folded back that each forms a lateral and a medial plate. Of these, the medial meet below the septal cartilage to form the tip of the nose, while the lateral curve backward, and, together with dense masses of cellular tissue and fat and accessory cartilages, form the alse. With the speculum, especially if the head be thrown back and the tip of the nose drawn up, the lower part of the septum, floor of the nose, and greater portion of the inferior concha (turbinate bone) can be seen. On throwing the head further back, with a good light the lower margin of the middle concha can also be made out. This is much higher up and nearly on a level with the root of the nasal bone. The septum often deviates to one side. The mucous membrane over it is, in health, dull red in colour; that over the inferior concha is thicker. The anterior extremity of the latter bone is about 1.8 cm. (| in.) behind the nasal orifice, while the opening of the naso-lacrimal duct is about 2.5 cm. (1 in.) behind and about 1.8 cm. (| in.) above the floor, concealed by the anterior extremity of the inferior concha. The opening into the maxillary sinus (antrum) is situated in about the centre of the middle meatus and 2.5 cm. (1 in.) above the floor The olfactory area of the mucous membrane extends over the highest concha (possibly also somewhat lower) and corresponding portions of the septum. The respiratory portion is more vascular and thicker, especially over the conchse. It is firmly adherent to the periosteum and perichondrium. The veins, especially over the lower conchse, form a dense plexus, closely resembling cavernous tissue. THE NOSE 1353 This fact explains the severity of epistaxis, and, together with the drainage of blood into out-of-the-way veins, such as the spheno-palatine and ethmoidal, Fig. 1098. — Section of the Nose, showing the Conch.*: (Turbinate Bones) and Meatuses WITH THE Openings in Dotted Outline. Frontal sinus Orifice of middle ethmoidal cells , Superior concna Orifice of the posterior ethmoidal cells Orifice of the sphenoidal smus Sphenoidal sinus Orifice of tuba auditiva Orifice of frontal sinus Upper orifice of naso-lacrimal duct Middle concha Inferior co.ncha Orifice of the Orifice of infundibulum maxillary sinus Fig. 1099. — Section showing Bony and Cartilaginous Septum. The dotted line indicates the course of the incisive (anterior palatine) canal. Nasal bone Frontal sinus Sphenoidal sinus ve between sept; and lateral nasal cartilage Thickened border of cartilage resting upon anterior nasal spine Incisive papilla Septal cartilage Orifice of tuba auditiva Soft palate accounts for the serious results which may follow on a firmly impacted and in- fected plug. The boundaries of the posterior nares have been given above. 1354 CLINICAL AND TOPOGRAPHICAL ANATOMY About 1.2 cm. (| in.) behind tlie posterior extremities of tiie inferior conchse, just above the level of the hard palate (fig. 1097), on the side of the naso-pharynx, are the openmgs of the tubce auditivce (Eustachian tubes). Oval in shape, these are bounded above and behind by the prominence of the cartilage, which is want- ing below, thus facilitating the entry of a catheter. The lower part of the tube contains in early life lymphoid tissue; enlargement of this explains the deafness in certain cases of adenoids. At the upper part of the naso-pharynx, on the posterior wall, extending down laterally as far as the tubae auditivse, is the col- lection of lymphoid tissue known as the pharyngeal tonsil, which when hypertro- phied, plays a large part in 'naso-pharyngeal adenoids.' From the periosteum of the basi-sphenoid and basi-occipital arise naso-pharyngeal fibromata. Nasal septum. — The structure of the skeletal element of the septum, which consists of the septal cartilage, the vertical plate of the ethmoid and the vomer, is shown in fig. 1099. Slight deviations of the septum to one side are common in adults, and involve mainly the cartilage and the ethmoid bone, the vomer being but little affected as a rule. The convexity is most commonly on the right side, and occlusion of the nares on that side with unsightly deflection of the whole nose, results in some cases during the transition from the nfantile to the adult facial conformation. Too extensive removal of the bony septum in the operation of submucous resection for the relief of this condition may cause sinking in of the bridge of the nose. More often, however, this is due to the destructive effect of congenital syphilis. Accessory sinuses. — The communication of these air sinuses with the nasal fossae are of great clinical importance. The sphenoidal sinus opens high up into the spheno-ethmoidal recess. The posterior ethmoidal sinuses open into the superior meatus under cover of the superior concha. The infundibulum of the frontal sinus, the anterior and middle ethmoidal and the maxillary sinus all communicate with the middle meatus under cover of the middle concha. The orifice of the maxillary sinus lies at the lowest part of the hiatus semilunaris into the front and upper end of which the frontal sinus opens. Consequently infected fluid may trickle down from the latter into the maxillary sinus. The orifice of this sinus is placed high up in its medial wall so that fluid does not drain away from it readily in case of infection. When the head is held forward in a stooping position some of the pus or mucus may escape from the nostrils, since in this position the fluid contents more readily reach the orifice. The naso-Iacrimal duct which carries the tears into the nose opens into the front and upper part of the inferior meatus under cover of the inferior concha. THE NECK The topics considered in the neck are the landmarks, thyreoid gland, sterno- mastoid, clavicle, triangles and cervical ribs. Bony and cartilaginous landmarks. — The body of the hyoid is nearly on a level with the angles of the jaw, and the interval between the third and fourth cervical vertebrae (fig. 1097). With the head in the usual erect position it lies a little higher than the chin. It divides the front of the neck into supra- and infra-hyoid regions, convenient for remembering the distribution of the deep fascia. On either side of the body are the great cornua, with the lesser cornua attached to their upper borders at the junction with the body. The upper borders of these are the guides to the lingual arteries. The outline and mobility of the body and the great cornua are easily determined by relaxing the deep fascia and pushing the bone over to the opposite side. Below the hyoid is the thyreo-hyoid space, which corresponds with the epiglottis and the upper aperture of the larynx. Thus, if the throat be cut above the hyoid, the mouth will be opened and the tongue cut into; if the thyreo-hyoid space be cut, the pharynx would be opened and the epiglottis wounded near its base. In the former case the lingual and external maxillary are the most likely vessels to be wounded ; in thyreo-hyoid, the commonest cut-throat, the superior thyreoid vessels, and the superior laryn- geal nerve. The projection of the thyreoid notch, about 2.5 cm. (1 in.) below the hyoid, is much more distinct in men than in women or children. It does not appear before puberty, and thus flatness of the thyreoid must be expected ^ THE NECK 1355 when the landmarks for tracheotomy are sought for in children with short fat necks. The cricoid, on the other hand, is always to be made out. It corresponds in horizontal plane to the following: — (1) The sixth cervical vertebra. (2) The junction of pharynx and oesophagus: from the narrowing of the tube here, foreign bodies may lodge at this point and cause dyspncea by pressing on the air-tube in front. The cricoid is taken as the centre of the incision in cesophagotomy, and also for ligature of the common carotid. (3) The junction of larynx and trachea. (4) The crossing of the omo-hyoid over the common carotid. (5) The middle cervical ganglion. Above the cricoid is the crico-thyreoid rnembrane. In laryngotomy, the deepest part of the incision should be kept to the middle line for fear of injuring the crico- thyreoids, and as near the cricoid as possible, so as to avoid the neighbourhood of the vocal cords and the small crico-thyreoid vessels. The space is always small, and, after middle life, increasingly rigid. The distance between the cricoid and the manubrium is only about 3.7 cm. (1| in.). When the neck is stretched, about 1.8 cm. (f in.) more is gained. Thus, as a rule, there are not more than seven or eight tracheal rings above the sternum. Of these, the second, third, and fourth are covered by the thyreoid isthmus. The parts met with in the middle line — (a) above, and (6) below, the isthmus — high and low tracheotomy — should be borne in mind: (o) Skin, superficial fascia, branches of transverse cervical and infra-mandibular nerves, lymphatics, cutaneous arteries, anterior jugular veins — with their transverse branches smaller above — deep fascia, sterno-hyoids, cellular tissue, supe- rior thyreoid vessels, and pre-tracheal layer of deep fascia. The importance of this last is two- fold, as, first, the tube in tracheotomy may be passed between it and the trachea, and after a wound in this region this layer, continuous with the pericardium, may conduct discharges into the mediastina, (6) The surface structures are much the same, but the anterior jugular veins and their transverse branches are much larger. The inferior thyreoid veins are also larger. A thyreoidea ima may be present, and the innominate artery, especially in children, may be 1.2 cm. (2 in.) above the sternum. The trachea is also smaller, deeper, and less steadied by muscles. The thymus, too, in young children, may prove a difficulty. Thus, in children, the high opera- tion, incising the cricoid and crico-tracheal membrane, if needful, is to be preferred. The cricoid is, however, not to be incised, if possible; the higher the tube is inserted, the greater the irritation. The suprasternal notch, between the sternal heads of the sterno-mastoids in on a level with the disc between the second and third thoracic vertebrae. Just below the level of the cricoid cartilage, on deep pressure at the anterior border of the sterno-mastoid the transverse process of the sixth cervical vertebra may be felt. It is known as Chassaignac's carotid tubercle, and the common carotid may be compressed against it. Compression below it will command the vertebral artery as well. The thyreoid gland enclosed in a capsule of deep fascia derived from the pre- tracheal layer (fig. 1070) is closely connected by this to the upper trachea and larynx. The upper somewhat pointed extremity of each lateral lobe reaches to the upper and back part of the thyreoid cartilage; here enter the superior thyreoid vessels. The lower layer and rounded extremity reaches to the fifth or sixth tracheal ring; its posterior and lower aspect is in relation to the inferior thyreoid vessels and the recurrent nerve; the lateral lobe, posteriorly, also overlaps the carotid sheath, which may be infiltrated in malignant disease of the thyreoid. The thyreoidea ima has been mentioned above. The isthmus in the adult is opposite to the second, third, and fourth tracheal rings. At its upper border is an arterial arch formed by the superior thyreoids; over the anterior surface of the gland and isthmus the inferior thyreoid veins take origin in a plexus. The upper border of the thymus (fig. 1100) may be in relation with the lower border of the isthmus. From the upper border of the latter, the pyramidal lobe, especially on the left side, is often present, reach- ing by a pedicle to the liyoid. The pyramidal lobe, when present, is the persistent remnant of the thyreo-glossal duct, and occasionally cystic outgrowths persist obstinately as remnants of this duct, in the middle line, above, behind, and below (the commonest form) the hyoid bone. In short-necked people the thyreoid is relatively lower in relation to the sternum, and en- largements of the gland are apt to become mainly intra-thoraeic. An enlargement of the thyreoid is liable to give trouble by pressure on (1) the trachea, which is compressed laterally between the lateral lobes; (2) the oesophagus; (3) the internal jugular vein and carotid artery; (4) the reciu-rent laryngeal or cervical sympathetic nerves. Parathyreoids. — These small glands, about the size of a pea, vary somewhat in number and situation. There are usually four — t^A■o behind each lateral lobe. The upper glands lie im- bedded in the capsule of the thyreoid about the junction of the middle and upper thirds of the lateral lobes on the posterior aspect. The lower pair lie nearer the lower poles of the lateral lobes, sometimes separated from them by a distinct interval. Excision of all the parathyreoids gives rise to tetany in animals. The stemo-mastoid is the landmark for several important operations. Its medial border, the thicker and better marked of the two, overlaps the carotids; 1356 CLINICAL AND TOPOGRAPHICAL ANATOMY the common carotid corresponding, as far as the upper border of the thyreoid, with a line drawn from the sterno-clavicular joint to midway between the mastoid process and the angle of the jaw. The artery can be best compressed above the level of the cricoid, as here it is less deeply covered. The student should recall the deep relations of the sterno-mastoid, which he may classify as vessels, nerves, muscles, glands, and bones; or, according to their position, (1) those above the level of the angle of the jaw; (2) those between the angle of the jaw and the omo- hyoid; (3) those below the omo-hyoid. Of the two heads of the sterno-roastoid, the sternal is the thicker and more prominent, the clavicular the wider. A stab through the interval wliich lies between tlie two heads might wound the bifurcation of the innominate on the right side, and the common carotid on the left, the internal jugular, vagus, and phrenic veins, according to the direction of the wound. Fig. 1100. — Thymus Gland in a Child at Birth. r^~. Hyo-thyreoid membrane Thyreoid cartilage [~;^^/ Sterno-thyreoid muscle' Crico-thyreoid ■^^;^- w- membrane ^^»^* Crico-thyreoid muscle Thyreoid gland Right vagus nerve Right internal jugular, vein Level of sternu Section of clavicle Section of first rib Section of sternum ^ Thyreo-hyoid muscle I^VL Omo-hyoid muscle Cricoid cartilage First ring of trachea -r — Left suspensory \ ligament Left recurrent nerve (Esophagus Left innominate vein Left lobe of thymus Left internal mammary artery Pericardium Section of fifth costal cartilage ■Xiphoid process The anterior jugular, commencing in branches from the submaxillary and submental regions, descends at first in the superficial fascia between the middle line and anterior border of sterno-mastoid, perforates the deep fascia just above the clavicle, here entering Burns's space (p. 1361); it then curves laterally to pass beneath both origins of the sterno-mastoid a little above the clavicle, to end usually in the external jugular. When distended, a large communicating branch between it and the common facial, which runs along the anterior border of the sterno-mastoid, must always be remembered in operations for removal of glands, etc. The varying level at which the external jugular crosses the lateral THE NECK 1357 border of the clavicular origin must be remembered in such operations as tenotomy here. These veins vary in size inversely to each other; the anterior jugulars are joined by numerous trans- vesre branches and become larger below. They have no valves. Of the chief arteries to the sterno-mastoid, that from the superior thjrreoid will be divided in gature of the common carotid; that from the occipital runs with the spinal accessory nerve. Behind the stemo -clavicular joint lies the commencement of the innominate veins, the bifurcation of the innominate artery on the right, and the common carotid artery on the left; deeper still lie the pleura and lung. The clavicle. — This bone can be felt beneath the skin in its whole length. It forms the only bony connection between the upper limbs and the trunk. As one traces it laterally toward the acromial end, it rises somewhat, particularly in children and in subjects of good muscular development. The skin over it is thin but very mobile, and consequently is not often wounded. The most im- portant posterior relations of this bone are, passing from the medial end laterally, the subclavian vein, the subclavian artery, and the cords of the brachial plexus as they He on the first rib. Fig. 1101. — Anterior and Lateral Cervicai, Muscles. Stylo-glossus Hyo-glossus Mylo-hyoid Anterior belly of digastric Raphe of mylo- hyoid Thyreo-hyoid Inferior constrictor Anterior belly of omo- hyoid Sterno-hyoid Sterno-thyreoid The vein occupies the angle between the first rib and the clavicle, and hence is, as a rule, the first structure compressed in growths of this bone. The artery lies on a deeper plane be- hind the mid-point of the clavicle, and the nerve cords extend a little further laterally. The Bubclavius muscle forms a protective cushion between the bone and these important structures, and this accounts for the rarity of injury to them in fracture of the clavicle. Behind the medial half of the clavicle the apex of the lung extends upward into the neck toa height of 2. 5-3. 7 cm. (1-1 2 in.), and consequently is liable to be wounded by a stab in the root of the neck. Cervical triangles. — In front of the sterno-mastoid is the anterior triangle, which is subdivided into three smaller triangles by the digastric muscle above, and the anterior belly of the omo-hyoid below (fig. 1101). These smaller tri- angles are called, from above, the submaxillary, the superior and inferior carotid triangles. The submaxillary or digastric triangle is bounded above by the jaw, and a line drawn back to the mastoid process; below, by the digastric and stylo-hyoid muscles; and in front by the middle line of the neck. 1358 CLINICAL AND TOPOGRAPHICAL ANATOMY This space contains the submaxillary gland, and embedded in the gland is the external maxillary artery, the facial vein lying superficial to the gland; deeper than the gland are the submental vessels and the mylo-hyoid vessels and nerve. Posteriorly, and separated from the above structures by the styro-mandibular ligament, which subdivides the triangle into a sub- maxillary and parotid part, is the upper part of the external carotid artery running up into the parotid gland, where it gives off its two terminal and the posterior auricular branches. More deeply lie the internal jugular vein, internal carotid artery, and the vagus. The floor of the triangle is formed by the mylo-hyoid, hyo-glossus, and superior constrictor. The lingual artery may be tied here, or, better, in order to get behind the dorsalis linguae, close to its origin, by an incision similar to that for exposing the external carotid. The hypoglossal is a guide to the carotids and the occipital artery at the lower border of the digastric, and farther forward, to the subjacent lingual, from which it is separated by the hyo-glossus. The superior carotid triangle is bounded above by the digastric, below by the omo-hyoid, and behind by the sterno-mastoid. It contains the upper part of the common carotid and its branches, the external being at first somewhat anterior to the internal. All the branches of the external carotid, save the three just given, are found in this space, together with their veins, the internal jugular vein, the vagus and sympathetic nerves, and, for a short distance, the accessory, together with those nerves which lie in front of and behind the carotids. Ligature of the common carotid is usually performed at the 'seat of election,' where the vessel is more superficial, above the omo-hyoid. An incision with its centre opposite the cricoid is made 7.5 cm. (3 in.) long in the line of the carotid artery. The deep fascia along the an- terior border of the sterno-mastoid having been divided, the cellular tissue beneath is opened up, the omo-hyoid identified and drawn down or divided. The sterno-mastoid is next drawn well laterally, and the artery felt for. At this stage, such veins as the communication between the common facial and the anterior jugular and the superior and middle th}Teoi_ds may give trouble. The sheath is next opened well to the medial side, opposite to the cricoid cartilage, the ascending cervical, when seen, being avoided. If the internal jugular be distended, it may be drawn aside with a blunt hook, or pressure made lightly in the upper angle of the wound. The needle should be passed from the lateral side in very close proximity to the lateral and back part of the artery, so as to avoid the vein and vagus. Ligature helow the omo-hyoid is rendered more difficult by the presence of the anterior jugular, the pretracheal muscles, an overlapping thyreoid gland, especially if enlarged, the greater depth of the artery, especially pn the left side and, here also, the closeness of the internal jugular. The collateral circulation is given at p. 1360. Ligature of the external carotid, otherwise difficult, is rendered very simple by first exposing the bifurcation of the common carotid artery, the incision similar to the last being prolonged up- ward. Here the facial and lingual veins and hypoglossal nerve cross the trunk, over which also lie some of the deep cervical glands. The ligatiue is usually placed between the superior thyreoid and lingual branches. Allusion must here be made to the chief structures liable to be met with in operations on the neck. These are the internal jugular, the accessory, and phrenic nerves, the vagus and hypoglossal, the thoracic duct, low down and deep on the left side, the oesophagus and recurrent nerve in difficult operations on the thyreoid gland. Of these, the internal jugular is, in some ways, the most important. Glands, tuberculous or epitheliomatous, are often adherent to its sheath, especially those which drain the submaxillary group. When this condition is present or suspected, it is always well to begin the dissection low down in the inferior carotid triangle, where the structures are probably normal and the landmarks easy to identify. In infective thrombosis of the transverse sinus the internal jugular is often tied opposite to the cricoid cartilage, being either divided between two ligatures, or, if the thrombus has extended downward, as much of the vein as is possible is removed. This vein contains only a single pair of valves low down in the neck. In all operations here on it and the other two jugulars, the risk of entry of air is to be remembered. The accessory and phrenic nerves are alluded to on p. 1360. The inferior carotid or tracheal triangle is bounded above by the omo-hyoid, behind by the sterno-mastoid, and in front by the middle line of the neck. It contains the lower part of the carotid sheath and its contents, with, behind^ it, the inferior laryngeal nerve and inferior thyreoid vessels, and to the medial side the trachea, thyreoid gland, and oesophagus. More deeply are the vertebral vessels; on the left side is the thoracic duct. The position of the branches of the external carotid should be remembered. The great cornu of the hyoid and the ala of the thyreoid are landmarks for the origin of most of them. The superior thyreoid, arising just below the level of the great cornu of the hyoid bone, passes downward and forward to the back part of the thyreoid cartilage and upper part of the thyreoid body. Many of its branches are important in surgery. The superior laryngeal perforates the thyreo-hyoid membrane. The sterno-mastoid passes laterally into the middle of the muscle, across the carotid sheath. The crico-thyreoid crosses the space of the same name just below the lower border of the thyreoid cartilage. The small hyoid branch runs to the lower THE NECK 1359 border of the hyoid bone. Anastomosing branches of the superior thyreoid form an arch along the upper border of the isthmus. The Ungual artery arises from the parent trunk, opposite the tip of the great cornu of the hyoid, and passes forward just above the great cornu, crossed by the hypoglossal, and thence to the side of the tongue. In the first part of its course, before it reaches the hyo-glossus, it is curved, at first ascending, and then, having descended slightly, before it reaches the hyo-glossus, and while it lies under it, its curve is gentle, with the concavity upward; beyond the hyo-glossus, as it lies on the muscles of the tongue beneath the mucous membrane, it is tortuous. The lingual vein, it will be remembered, does not run with its artery, but lies superficial to the hyo-glossus. It receives the two small venae comitantes which run with the lingual itself just before it crosses the common carotid. The line of the external maxillary (facial) artery (fig. 1093), which often arises with the lingual, has been given on p. 1343. The occipital artery, starting on the same level as the facial (i. e., at a point a little above and outside the tip of the great cornu of the hyoid bone), follows a line drawn upward and laterally, first to the interval between the transverse process of the atlas and the mastoid process, the former bone being felt just below and in front of the tip of the latter; thence, lying in the occipital groove of the mastoid, the artery ascends gradually, enters the scalp, together with the great occipital nerve, a little medial to a point midway between the external occipital protuberance and the mastoid process, to follow, tortuously and superficial to the aponeurosis, the line of the lambdoid suture. The surface marking of the digastric and omo-hyoid, which subdivide the anterior triangle into the three smaller subtriangles above described, should be noted. The line of the posterior belly of the digastric corresponds to one drawn from the apex of the mastoid process to a point just above the junction of the great cornu and body of the hyoid bone; and from this spot, which gives the point of meeting of the two tendons, one slightly curving upward to a point just behind the symphysis menti, would give that of the anterior belly. To trace the omo-hyoid, a line should be drawn from the lower margin of the side of the hyoid bone obliquely downward, so as to cross the common carotid opposite the cricoid carti- lage and thence curving laterally under the sterno-mastoid at the junction of its middle and lower thirds, and then onward and still laterally parallel with and a little above the clavicle, as far as its centre. Posterior triangle. — This shows in its lower part a wide with Branches of the axillary, subclavian, J Deep cervical fascia. — The arrangement of this must be remembered — (a) above, and (5) below, the hyoid bone. The latter is far more important. (a) Arrangement above the hyoid bone. — Here two chief processes can be made out: — (i) one, continuous with that in front of the sterno-mastoid, traced upward from the hyoid bone, -encloses the submaxillary gland, passing over the mylo-hyoid, and, ascending, is connected with the lower border of the mandible, gives off the masseteric and parotid fascia, and is attached to the lower border of the zygoma, and, more posteriorly, to the mastoid and linea nuchse Buprema. (ii) A special process, which forms the stylo-mandibular ligament, is important in its power of checking over-action of the external pterygoid. By both these processes the ante- rior border of the sterno-mastoid is tied firmly forward to the mandible about its angle, and more deeply to the styloid process. This renders all operations under the upper part of the muscle, •e. g., the removal of glands, extremely difficult. THE NECK 1361 (6) Below the hyoid bone. — The importance of the fascia here is infinitely greater. Four layers must be rememhored; (i) Superficial; (ii) pretracheal; (iii) prevertebral; (iv) carotid, (i) Superficial. This starts from the ligamentum nuchee, encases the trapezius, forms the roof of the posterior triangle where it is perforated by branches of the superficial cervical nerves and the external jugular Fig. 1102. — The Collateral Circulation after Ligature of the Common Carotid and Subclavian Arteries. (A ligature is placed on the common carotid and on the third portion of the subclavian artery.) Right anterior cerebral -fLi'l ^^^* anterior cerebral J/'^\^ Anterior communicating Internal carotid -VV^ Post_ communicating Right posterior cerebral J J ?r^f\^ Left posterior cerebral Occipital Descending branch of occipital External carotid Superficial branch of descending occipital Deep branch" ~ Anterior spinal External maxillary Lingual Superior thyreoid Transverse cervical Descending branch Acromical branch Subscapular branch — Su praspinous k. .. branch Anterior circumflex Infraspini branch Post. circumflex Lateral thoracic Subscapular' Circumfl Innominate Superior intercostal Left com. carotid Left subclavian Sup. thoracic Internal mammary Anterior intercostal vein. Passing on it encloses the sterno-mastoid; and, passing over the anterior triangle, it meets its fellow in the middle line. jThin behind, it is thickened anteriorly. Behind this thickened union lie the anterior jugular veins. Below, at a varying distance below the thyreoid cartilage, this layer divides into two, attached to the front and back of the manubrium. Between these (Burns*s space) 1362 CLINICAL AND TOPOGRAPHICAL ANATOMY lie some fat, a small gland, a communicating branch between the anterior jugulars and a small portion of the veins, and the sternal heads of the sterno-mastoids. The sheath to the depressors of the hyoid bone is partly derived from this layer, partly from the next. Laterally, this layer gives a sheath to the posterior belly of the omo-hyoid, is attached to the clavicle, and passing on, is continuous with the sheath to the subclavius and coraoo-clavioular fascia. (ii) Pretracheal or middle. This lies under the depressors of the hyoid, over the trachea, also encasing the thyreoid gland. Farther laterally it helps, to- gether with the prevertebral, to form the carotid sheath. Traced downward, the pretracheal layer passes over the trachea into the thorax (middle mediastinum) As it descends, it encases the left innominate vein, and ends by blending with the fibrous layer of the pericardium. Hilton suggested that the attachment of this fascia above, and that of the central tendon of the diaphragm below, to the pericardium served to keep this sac duly stretched, and so prevented any pressure of the lungs upon the heart. Fia. 1103. — Section of Neck through the Sixth Cervical Vertebra. (Braune.) Larynx Pharynx Longns colli Inferior laryngeal Thyreo-arytaenoid Cricoarytaenoideus lateralis Penrertebral layer of deep cervical fascia FretTacheal layer of deep cervical fascia Sup. thyreoid art. DesG hypoglossi Sterno-mastoid Vagus Sym^thetic Phrenic Scale anterior Brachial plexus Scalenus medius External jugular Part of articu- lar process Spinal accessory Sterno-hyoid, just posterior are seen the thyreo- and omo-hyoid muscles Thyreoid cartilage Muscular process of arytaenoid Cervical fascia Thyreoid gland Common carotid Carotid sheath Internal jugular Brachial plexus Scalenus medius External jugular Ihocostalis cervicis Scalenus posterior Spinal accessory Splenius Semispinalis colli and multifidus Semispinalis capitis Deep cervical vessels _rficial layer of deep cervical fascia on the deep aspect of the trapezius which it here encloses Sixth cervical vertebra (iii) Prevertebral. This layer passes over the longus colli and capitis upward to the base of the skull, and downward over the longus colli behind the oesophagus into the posterior mediastinum. Laterally it helps to form the carotid sheath, and, lower down, gives a sheath to the subclavian artery and so to the axil- lary, (iv) The carotid sheath. This is formed by septa from i, ii, and iii, meeting under the sterno-mastoid (fig. 1103). The following uses and important points with regard to the anatomy of the deep cervical fascia should be noted: — (A) It forms certain definitely enclosed spaces in which pus or growths may form, and by the walls of which these morbid structures may be tied down and thus rendered difficult of diagnosis, while their increasing pressure may embarrass the air-passages, etc. Thus: (1) In the first space, which lies between No. 1 and the skin, the structures met with, the platysma and superficial branches of the cervical plexus, are unimportant. Any abscess here is prone to extend, but superficially. (2) In the second space, between the superficial and middle layers, lies a narrow space containing loose cellular tissue and lymphatic glands. Sup- puration here is very common, but usually comes forward. (3) This is the largest and most important of all. From its contents it has been called the visceral compartment. (Stiles.) THE THORAX 1363 It is bounded in front by the middle, and behind by the prevertebral layer. Its contents are — larynx, trachea, cesophagus, thyreoid, carotid sheath, glands; and below, brachial plexus, sub- clavian artery, and abundant loose cellular tissue for the movements of the neck. Suppuration is somewhat rarer here; but either pus or growths, if oonfined in this space, may have baneful effects, from pressure, or from their tendency to travel behind the sternum. (4) This space between the prevertebral layer in front and muscles behind, is very limited. Retropharyngeal abscess forms here, and the dyspnoea it causes is thus explained. The origin of such abscesses is chiefly twofold, either in one of the highest deep cervical nodes, e. g., from infection of the naso-pharynx (p. 717), or from disease of the upper cervical vertebrae. In the former cases CStiles, Chiene) the suppuration will be in front of the prevertebral fascia, pointing toward the pharynx; in the latter behind the above fascia, spreading laterally, behind the carotid sheath. In making his incision, now along the posterior border of the sterno-mastoid, the surgeon should keep close to the transverse processes of the vertebrae, to avoid!opening the visceral compartment and infecting the structures in it. (B) The deep cervical fascia gives sheaths or canals tc> certain veins which perforate it, e. g., the external jugular. These are thus kept patent, and a. ready passage of blood ensured from the head and neck. Further, this fact accounts for the readiness with which air may enter veins, in operations low down in the neck. The carotid sheath is another and different instance. (C) It helps to resist atmospheric pressure. (D) Hilton's suggestion as to its action on the pericardium has already been mentioned. The lymphatic nodes of the head and neck have already been described. (See Section VI, Lymphatic System.) THE THORAX The bony landmarks of the thorax will be discussed first, followed by the structures of the thoracic wall, the lungs and pleura, and finally the heart and pericardium. Bony landmarks. — The top of the sternum corresponds (in inspiration) to the fibro-cartilage between the second and third thoracic vertebrae, and is distant about 6.2 cm. (2| in.) from the spine. In the newborn child it corresponds to the middle of the first thoracic vertebra (Symington). If traced downward, the subcutaneous sternum presents a ridge (sternal angle of Louis) opposite to the junction of the manubrium and body, and the second costal cartilages on either side; this ridge usually corresponds to the disc between the fourth and fifth thoracic vertebrae. At the lower extremity of the sternum the xiphoid cartilage usually retires from the surface, presenting the depression of the epigastric angle or 'pit of the stomach.' This is opposite to the seventh costal cartilages and the expanded upper end of the recti, and corresponds to the tenth thoracic vertebra behind. Parts behind manubrium. — There is little or no lung behind the first bone of the sternum, the space being occupied by the trachea and large vessels, as follows; The left innominate vein crosses behind the sternum just below its upper border. Next come the great primary branches of the aortic arch. Deeper still is the trachea, dividing into its two bronchi opposite to the junction of the first and second bones of the sternum. Deepest of all is the cesophagus. About 2.5 cm. (1 in.) below the upper border of the sternum is the high- est part of the aortic arch, lying on the bifurcation of the trachea. (Holden.) (Fig. 1104). Sterno-clavicular joint. — The expanded end of the clavicle and the lack of proportion between this and the sternal facet, on which largely depends the mobility of this, the only joint that ties the upper extremity closely to the trunk, can be easily made out through the skin. Its strength, considerable when the rarity of dislocation compared with fracture of the clavicle is considered, depends mainly on its ligaments, the buffer-bond meniscus, the costo-clavicular ligament, which checks excessive upward and backward movements, and the fact that the elastic support of the first rib comes into play in strong depression of the shoulder as in carrying a weight. The relative weakness of the anterior ligament deter- mines the greater frequency of anterior dislocation of the clavicle at this joint. Behind the joint lie, on the right side, the innominate artery, right innominate vein, and pleura; on the left, the left innominate vein, the left carotid, and the pleura. Acromio -clavicular joint. — On tracing the clavicle laterally, it is found to rise somewhat to its articulation with the acromion. This joint has very little mobility, and owes its protection to the strong conoid and trapezoid ligaments hard by. Owing to the way in which the joint-surfaces are bevelled, that of the clavicle looking obliquely downward, and resting upon the acromion, it is an upward displacement of the clavicle which usually takes place. Ribs. — In counting these, the position of the second is denoted by the trans- 1364 CLINICAL AND TOPOGRAPHICAL ANATOMY verse line at the junction of the manubrium and body of the sternum. It is well always to count ribs from this point and never from below, as the twelfth rib varies in size and may be obscured by the sacro-spinalis muscles. The nipple in the male, lies between the fourth and fifth, nearly an inch lateral to their cartilages. The lower border of the great pectoral corresponds to the fifth rib. The seventh, the longest of the ribs, is the last to articulate by its cartilage with the sternum. When the arm is raised, the first three digitations seen of the serratus anterior correspond to the fifth, sixth, and seventh ribs. The ninth rib Fig. 1104. — The Abch of the Aorta, with the Pulmonary Artery and Chief Branches OF THE Aorta. (Modified from a dissection in St. Bartholomew's Hospital Museum.) Int. jugular v.^ Inferior thyreoid veins Transverse cervical a Transverse scapular a Right inf. laryng. n Right com. carotid a Subclavian v Vagus nerve Innominate a -"^^"^ Left innominate v Phrenic nerve Superior vena cava Arch of aorta Right bronchus Branch of right pul- monary a. Branch of right pul- monary V Right pulmonary a. Branch of right pul- monary a. Branch of right pul- monary V. Right atrium Right coronary a. Thoracic vertebra Azygos vein Intercostal vv. Intercostal aa. Thyreoid body Left int. jugular v. Vagus nerve Left com. carotid a. Left inf. laryng. n. Left subclavian a. Lelf subclavian v. Left int. mammary v. Left sup. intercostal v. Phrenic nerve Vagus nerve Recurrent n. Lig. arteriosum Left pulmonary a. Left pulmonary v. Left bronchus Branch of left pul- monary a. Pulmonary a. Left pulmonary v. Left coronary a. Conus arteriosus (Esophagus Thoracic duct Thoracic aorta is the most oblique. The eleventh and twelfth can be felt lateral to the sacro- spinalis. Owing to the obliquity of the ribs, their sternal ends are on a much lower level than their vertebral extremities. 'Thus the first rib in front corresponds to the fourth rib behind, the second to the si.xth, the thu-d to the seventh, the fourth to the eighth, the fifth to the ninth, the sixth to the tenth, and the seventh to the eleventh. If a horizontal line be drawn round the body from before back- ward at the level of the inferior angle of the scapula, while the arms are at the sides, the line would cut the sternum in front between the fourth and fifth ribs, the fifth rib at the nipple line, and the ninth rib at the vertebral column.' (Treves.) The most frequently broken are the sixth, seventh, and eighth. The upper four and the two lowest ribs are best covered by soft parts, and, in the case of the former, the shoulder and arm take off some of the violence that would otherwise reach them. The way in which the ribs are embedded in the soft parts (fig. 1106), and the fact that the fragments are often held in place by the periosteum, account for the diffi- culty which is often met with in detecting crepitus. The intercostal spaces are wider in front than behind. The three upper are the widest of all. THE THORAX 1365 Cervical ribs. — It occasionallj' happens that the rib element of the seventh cervical vertebra, normally fused with the true transverse process, is segmented off as a separate, though usually rudimentary, rib. This anomaly is generally bilateral. It occurred in 3 of 260 subjects (1.16 per cent.) examined by Wingate Todd.* The anterior extremity of a cervical rib may, according to the degree of its development (1) lie free amongst the scalene muscles; (2) be connected with the sternum by a hgameutous prolongation; (3) articulate with the upper surface of the first thoracic at about its centre by a synchondrosis, or (4) form a complete rib, articulating by a costal cartilage with the sternum. The lowest trunk of the brachial plexus formed by the eighth cervical and first thoracic roots, the subclavian artery and less commonly the subclavian vein, curve over the upper surface of these ribs. The abnormality owes its clinical importance to the pressure effects produced on the nerve trunk in a small proportion of the cases. This pressure is manifested by ( 1) pain, going on to anaesthesia down the medial side of arm, forearm and hand; (2) paralysis of the intrinsic muscles of the hand, producing the main en griffe, and to a less extent of the mus- cles of the forearm; (3) vascular effects (anamia, gangrene, etc.), manifested chiefly in the hand. Todd has shown that these vascular effects are not due to mechanical pressure on the subclavian artery by the cervical rib as was formerly supposed, but are trophic lesions of the sympathetic (vasomotor) nerves. The vasomotor nerves to the arm mainly come from the second thoracic root by the communication it gives to the lowest cord of the brachial plexus, and so are exposed to pressure from the rib. Fig. 1105. — Cervical Ribs, Viewed from Above. ( X i.) NN, Impression for Lowest Trunk op Brachial Plexus. AA, Impression for Subclavian Artery. (T. Wingate TODD.) The same investigator has shown that similar symptoms may be produced occasionally by a first thoracic rib in cases where the brachial plexus has migrated caudad. In the living patient, unless a radiogram be taken showing all the vertebroe up to the base of the skuU, it is not possible with precision to ascertain with which vertebra the highest rib present articulates. Structures found in an intercostal space. — (1) Skin; (2) superficial fascia, with cutaneous vessels and nerves; (3) deep fascia; (4) external intercostal; (5) cellular interval between intercostals, containing trunks of intercostal vessels and nerves; (6) internal intercostals; (7) thin layer of fascia; (8) subpleural connective tissue; (9) pleura (fig. 1106). The intercostal arteries are nine aortic and two from the superior intercostal. An aortic intercostal having given off its dorsal branch, lying beneath the pleura, crosses the space ob- liquely upward to gain the lower border of the rib above, enters the costal groove at the angle, and runs forward between the intercostal muscles to anastomose with the anterior intercostals from the internal mammary or musculo-phrenic. Hence the rule of making the incision in empyema above the upper margin of the lower rib and in front of the angle. Along the dorsal branch a vertebral abscess may track backward. Internal mammary artery.- — This descends behind the clavicle, the costal cartilages, and the first six spaces, about 1.2 cm. (| in.) from the edge of the ster- num. In the sixth intercostal space it divides into musculo-phrenic and superior epigastric acteries. Its vense comitantes uniting join the innominate vein of the same side. A punctured wound of the artery is most easily secured in the second and third spaces; below, resection of part of a costal cartilage will be needed. Structures passing through the upper aperture of the thorax. — If a section is made passing through the manubrium sterni, upper border of the first rib, and * Journal of Anatomy and Physiology, Vol. 47, 1913. 1366 CLINICAL AND TOPOGRAPHICAL ANATOMY upper part of the first thoracic vertebra, the following structures are met with : — (1) In the middle line. Sterno-hyoid and sterno-thyreoid muscles, with their sheaths of deep cervical fascia, cellular tissue in which are the remains of the thymus gland, the inferior thyreoid veins, the trachea and tracheal fascia, the oesophagus, and longus colli muscles. Between the trachea and oesophagus are the recurrent nerves. (2) On each side. The apex of the lung, covered by pleura, deep cervical fascia, and membranous cervical diaphragms ("Sibson's fascia") derived from the scalenes, rises about 3.7 cm. (1| in.) above the first rib. Between it and the trachea and oesophagus lie the following : the internal mammary artery, the phrenic nerve; on the right side, the innominate vein and artery, with the vagus between the two, the cardiac nerves, and the right lymphatic duct. On the left side are the common carotid and subclavian arteries, with the left vagus between them, the cardiac nerves and the thoracic duct. Farthest back and on each side are the trunk of the sympathetic, the superior intercostal artery, and the first thoracic nerve. The mamma. — This lies chiefly on the pectoralis major and slightly on the rectus abdominis and serratus anterior. It is usually described as reaching from the second to the sixth rib, and from the sternum to the anterior border of the axilla. It is most important to remember that the breast is often a much more extensive structure than would be included in the above very limited description. Thus — (1) the gland is not encapsuled at its periphery, its tissue branching and breaking up here to become continuous with the superficial fascia. (Stiles.) (2) Fig. 1106. — Section op the Sixth Left Intercostal Space, at the Junction of the Anterior and Posterior Thirds. (Tillaux.) Intercostal vein Intercostal artery- Intercostal nerve - Serra tus anterior" Serratus aponeurosis'" osis covering external inter--. costal muscle External intercostal muscle" — Aponeurosis covering the internal intercostal muscle Internal intercostal muscle — Pleura The retinacula cutis contain lymphatics and, sometimes, mammary tissue. (3) There is a lymphatic plexus, and, often, minute lobules of gland tissue, in the pectoral fascia. (Heidenhain.) Fully one-third of the whole mamma lies posterior and lateral to the axillary border of the pectoralis major so that it reaches almost to the mid-axillary line. That part of the upper and lateral quadrant known as the axillary lobe is of especial importance from its reach- ing into close vicinity with the anterior pectoral group of axillary nodes (p. 719). In the male the nipple is usually placed in the fourth space, nearly 2.5 cm. (1 in.) lateral to the cartilages of the fourth and fifth ribs. On the nipple itself open the fifteen or twenty ducts which dilate beneath it, and then diverge and break up for the supply of the lobules. The skin over the areola is very adherent, pig- mented, and fatless. Here also are groups of little swellings corresponding to large sebaceous follicles and areolar glands. The skin over the breast is freely movable, and united to the fascia which encases the organ, and thus to the inter- lobular connective tissue, by bands of the same structure — the retinacula cutis. Under the breast, and giving it its mobility, is a cellulo-fatty layer, the seat of submammary abscess. ' The nerves which supply the breast are the anterior cutaneous branches of the second, third,' foui'th, and fiftli intercostal nerves, and the lateral branches of the last three. The connection of tliese trunliS serves to explain the diffusion of the pain often observed in painful affections of the breast. Thus pain may be referred to the side of the chest and bacli (along the above intercostal trunks), over the scapula, along the medial side of the arm (along the inter- costo-brachial nerve), or up into the neck. The gland is supplied by the following arteries : the aortic intercostals of the second, third, fovirth, and fifth spaces, similar intercostal branches from the internal mammary, which runs outward, two small branches to each space, perforating branches from the same vessel, one or two given off opposite to each space, the long thoracic and external mammary (when present) from the axillary. THE LUNGS 1367 The lymphatics have aheady been described (p. 721, fig. 566). In removal of the breast elliptical incisions will usually suffice if employed on wide lines, and if attention be paid to the following points: — (1) Those details in the surgical anatomy already referred to, especially those bearing on the extensiveness of this organ, and the propor- tionate difference between seen and unseen disease. (2) The importance of removing in one continuous piece the whole breast, all the skin over it, the costo-sternal part of the pectoralis major, the pectorahs minor, the axillary fat, and lymi^hatics. Outline of the lungs. Their relation to the chest-wall. — To map out the lung, a line should be drawn from the apex, a point about 2.5 cm. (1 in.) above the clavicle, a little lateral to the sterno-mastoid muscle, at the junction of medial and middle thirds of clavicle, obliquely downward, behind the sterno-clavicular joint, to near the centre of the junction of the first and second bones of the ster- num. Thence, on each side, a line should be drawn slightly convex as far as a similar point on the sternum lying opposite the articulation of the fourth chondro- sternal joint. On the right side the line may be dropped as low as the sixth chon- dro-sternal joint; on the left the incisura cardiaca may be shown by drawing a vertical line along the middle line of the sternum, from the level of the medial extremities of the fourth costal cartilages to the lower end of the gladiolus, and Fig. 1107. — Outline op the Heart, its Valves, the Lungs (shaded), and the Pleura. (Holden.) (Cf. fig. 437.) by carrying two other lines, from the extremities of the first line, outward so as to meet at a point over the heart's apex (Cunningham); to mark this gap, a line should be drawn sloping laterally and downward from the fourth chondro- sternal articulation across the foui'th and fifth interspaces, to a point about 3.7 cm. (1| in.) below the left nipple (male) and 2.5 cm. (1 in.) to its medial side. This point, lying in the fifth space, marks the apex of the heart. Thence the line curves medially to the sixth costal cartilage, a little medial to its chondro- sternal junction, and in the lateral vertical line. Thus the lower part of the anterior surface of the right ventricle is not covered by lung. The lower border of the lung will be marked on the right side by a line drawn from the sixth chondro- sternal articulation across the side of the chest down to the tenth thoracic spine. The lower border of the left lung will follow a similar line, starting on a level with a similar joint (sixth chondro-sternal joint), but much farther laterally than on the right side, i. e., in the fifth space, about 7.5 cm. (3 in.) to the left of the middle line, or a point corresponding to the heart's apex. In the nipple- line the lung crosses the sixth rib, in the mid-axillary line the eighth, and opposite 1368 CLINICAL AND TOPOGRAPHICAL ANATOMY the angle of the scapula (the arms being close to the sides), the tenth rib. The position of the great fissure in each lung may be ascertained approximately by drawing a line curving downward and forward from the second thoracic spine to the lower border of the lung at the sixth costal cartilage; and the smaller fissure of the right lung extends from the middle of the foregoing to the junction of the fourth costal cartilage with the sternum. It will be seen from the above that there is little lung behind the manubrium. The connective tissue here between the lung margins contains the thymus, large up to the age of puberty, and, later, its remains. The hilus (root) of the lung is referred to on p. 1230. The pleura, following much the same line as the lung above and in front, reaches lower clown laterally and behind. Thus the two sacs starting from about 2.5 cm. (1 in.) above the medial third of the clavicle converge toward the angle of Louis (p. 1238) ; meeting here, they descend vertically, the left overlapping the right slightly, to the fourth chondro-sternal joint. Hence the right sac descends behind the sternum to the sterno-xiphoid junction and sixth chondro-sternal joint. Thence, as it curves to the back of the chest, it crosses the eighth rib close to the lateral vertical line {vide supra), the tenth in the mid-axillary, the eleventh in the line of the angle of the scapula, and thence toward the twelfth thoracic vertebra. On the left side the pleura parts company from the right at the level of the fourth chondro-sternal junction, deviating laterally and downward across the fourth and fifth interspaces; it then turns again slightly medially to meet the sixth costal cartilage. Thus, as in the case of the lung, but to a less extent, there is a small area of the pericardium, and, under it, the right ventricle uncovered by the pleura. Over the side and back of the chest, along its dia- phragmatic reflection, the left pleura reaches a little lower than the right. The deepest part of the pleural sac is where the reflection crosses the tenth rib or tenth space in the mid-axillary line. From this it ascends slightly as it curves back to the spine. (Cun- ningham.) The relations of the pleura to the last rib are of much importance to the surgeon in operations on the kidney. In the case of a twelth rib of ordinary length, the pleural reflection crosses it at the lateral border of the sacro-spinalis ; when a rudimentary last rib does not reach the lateral border of this muscle, an incision carried upward into the angle between the eleventh rib and the sacro-spinalis will open the pleural sac. (Melsome.) For tapping the pleura there are two chief sites: — (1) The sixth or seventh space in front of the posterior fold of the axilla. (2) The eighth space behind, in the line of the angle of the scapula. For the incision of an empyema the first is usually chosen. The overlying soft parts are not thick, the interspace is wide enough, drainage is sufficient (especially if part of the seventh or eighth rib be resected), and this site is free from the objection that the angle of the scapula overlaps the seventh and eighth ribs, unless the arm is raised. Outline of the heart. Its relation to the chest-wall. — The upper limit of the heart (base) will be defined by a line crossing the sternum a little above the upper border of the third costal cartilage, reaching about 1.2 cm. (J in.) to the right and about 2.5 cm. (1 in.) to the left of the sternum. Its apex point is in the fifth space, 3.7 cm. (1| in.) below the male left nipple, and 2.5 cm. (1 in.) to the medial side. This point will be at 7.5 cm. (3 in.) from the left border of the sternum. The right border (right atrium) will be given by a line, slightly convex laterally, drawn from the right extremity of the upper border to the right sixth chondro-sternal joint. If another line, slightly convex upward, be drawn onward from this point across the last piece of the sternum, just above the xiphoid cartilage, to the apex, it will give the lower border (margo acutus of right ventricle), which rests on the central tendon of the diaphragm. The left border (margo obtusus of left ventricle) will be given by a line, convex to the left, passing from the left extremity of the upper border to the apex, medial to the nipple- line. This line should be 7.5 cm. (3 in.) from the middle of the sternum at the level of the fourth costal cartilage. The base of the heart is opposite four of the thoracic vertebrae, viz., the sixth, seventh, eighth, and ninth. The apex and anterior or costo-sternal surface have been mentioned. The inferior or diaphragmatic surface (chiefly left atrium and left ventricle) rests upon the diaphragm, mainly the central tendon, to which the intervening pericardium is connected, and is thus adjacent to the liver and a small portion of the stomach. If a circle 5 cm. (2 in.) in diameter be described around a point midway between the left nipple and the lower end of the gladiolus, it will define with sufficient accuracy for practical purposes that part of the heart which lies immediately behind the chest wall, and which is uncovered by lung and (in part) by pleura. (Latham.) THE HEART 1369 The valves. — The pulmonary valves (the highest and most superficial) lie, in front of the aortic, behind the third left chondro-sternal joint, and opposite to the upper border of the third costal cartilage. The aortic valves lie behind and a little below these, opposite to the medial end of the third intercostal space, and on a level with the lower border of the third left costal cartilage. The atrio -ventricular openings lie at a somewhat lower level than that of the aortic and pulmonary. Thus the tricuspid valves lie behind the middle of the sternum at the level of the fourth intercostal space; and the mitral valves, the most deeply placed of all, lie a little to the left of these, behind the left edge of the sternum and the fourth left costal cartilage (fig. 1107; also cf. fig. 437). 'Thus these valves are so situated that the mouth of an ordinary-sized stethoscope will cover a portion of them all, if placed over the juncture of the third intercostal space, on the left side, with the sternum. All are covered by a thin layer of lung; therefore we hear their action better when the breathing is for a moment suspended.' (Holden.) The pericardium. — This fibro-serous sac, occupying the middle mediastinum, is triangular in shape, with the apex upward. Here its fibrous layer gives mvest- ment to the large vessels, except the inferior cava. It is also continuous with the deep cervical fascia. The base, connected with the diaphragm, has been referred to above. In front an area of variable size (fig. 1107), owing to the divergence of the left pleura, is in contact with the left half of the lower part of the sternum, and more or less of the medial ends of the fourth, fifth, and sixth costal cartilages, here forming the posterior boundary of the anterior mediastinum. Behind, the pericardium is the anterior boundary of the posterior mediastinum, and is in close contact with the oesophagus and aorta. Paracentesis of pericardium. — While the seat of election must here remain an open question, each case requiring a decision for itself, the one most suitable on the whole is the fifth left space, about 2.5 cm. (1 in.) from the sternum, so as to avoid injury to the internal mammary artery and the pleura, of which the line of reflection has been shown to vary. In incision of the pericardium to establish free drainage, a portion of the fifth or sixth left costal cartilage should be carefully resected, the internal mammary artery tied, the trans- versus thoracis (triangularis sterni) scratched through, and the pleural reflexion pushed aside. Relation of vessels to the wall of the thorax. — Aortic arch. — The ascending part of the aorta reaches from a spot behind the sternum, a little to the left of the centre, on a level with the third left costal cartilage, to the upper border of the second right cartilage; thus it passes up- ward, backward, and to the right, and is about 5 cm. (2 in.) long. The transverse part then crosses backward to the left behind the sternum (the highest part of the arch being about 2.5 cm. (1 in.) below the notch), reaching from the second right costal cartilage to the lower border of the fourth thoracic vertebra on the left side. This part recedes from the surface, and, with the next, cannot be marked out on the surface. The third, or descending part, the shortest of the three, reaches from the lower border of the fourth to that of the fifth thoracic vertebra. Fig. 1104 will remind the reader of many of the pressure symptoms which may accompany an aneurysm of the aortic arch; e. g., pressure on the left innominate vein, the three large arte- ries, trachea, and left bronchus, recurrent nerve, oesophagus, and thoracic duct. In aneurysm of the thoracic aorta, pain, usually unilateral, referred to the corresponding intercostal nerves, is a common pressure symptom. The pulmonary artery lies behind the left side of the sternum and its junction with the sec- ond and third costal cartilages. Innominate artery. — A line drawn from the top of the arch, about 2 . 5 cm. (1 in.) below the sternal notch, and close to the centre, to the right sterno-clavicular joint, will give the line of this vessel. Left common carotid. — This vessel will be denoted by a line somewhat similar to the above, passing from the level of the arch a little to the left of the last starting-point to the left sterno- clavicular joint. Left subclavian artery. — A line from the end of the transverse arch, behind the left of the sternum, straight upward to the clavicle, delineates the vertical thoracic course of the long left subclavian artery; its thoracic portion lies behind the left carotid. Innominate veins. — The left, 7.5 cm. (3 in.) long, extends very obliquely from the left sterno-olavicular joint, behind the upper part of the manubrium, to a point 1.2 cm. (| in.) to the right of the sternum, on the lower border of the first right costal cartilage. The right, about 2.5 cm. (1 in.) long, descends almost vertically to the above point from the right sterno- clavicular joint. Venae cavae. — The superior descends from the point above given for the meeting of the innominate veins in the first intercostal space, close to the sternum, and perforates the right atrium on a level with the third costal cartilage. The inferior vena cava. — The opening of this vein into the right atrium lies under the middle of the fifth right interspace and the adjacent part of the sternum. The oesophagus. — The relations of this tube in its cervical and thoracic portions are most important, e.g., to the trachea and left bronchus; the vagi and left recurrent nerve; the pleurae, left above and right [below, aorta, and 1370 CLINICAL AND TOPOGRAPHICAL ANATOMY pericardium. Its lymphatics go below into the posterior mediastinal and superior gastric nodes; above into the lower deep cervical nodes, a point sometimes diag- nostic in malignant disease. The lumen of the oesophagus is narrowed at three points: — (1) and best marked at the cri- coid cartilage, (2) where it is crossed by the left bronchus, (3) as it passes through the dia- phragm. The tube, 25 to 27 cm. (10 to 11 in.) long, extends from the sixth cervical to the lower ■ border of the tenth thoracic vertebra. In an adult, the distance from the incisor teeth to the cricoid is about 15 cm. (6 in.); an additional 7.5 cm. (3 in.) gives the level of the crossing of the left bronchus, while from the teeth to the opening in the diaphragm would be from 41 to 43 cm. (16 to 17 in.). To expose the tube in the neck an incision is made on the left side, much as for the higher ligature of the common carotid, but carried lower down. The depressors of the hyoid being drawn medially or divided, the pretracheal fascia is opened, which allows of the overlapping thyreoid and trachea being displaced medially, while the carotid sheath is re- tracted laterally. The tracheal rings are the best guide to the oesophagus. The recurrent nerve must be avoided. THE ABDOMEN The regions and subdivisions will first be considered, the abdominal wall next, and finally the abdominal cavity, including the peritoneum and the various organs. Subdivision of the abdominal cavity. — Certain arbitrary horizontal and vertical planes, represented by lines drawn on the ventral surface, are used to subdivide the abdomen for topographical purposes (fig. 898). A. Horizontal planes. (1) Infracostal through the lower margins of the tenth costal cartilages (the lowest part of the costal margin). This plane crosses the body of the third lumbar vertebra. (2) Intertuhercular, passing through the tubercles, prominent points of the ihac crests, which are situated about 5 cm. (2 in.) behind the anterior superior spines. This plane crosses the body of the fifth lumbar vertebra. B. Vertical planes. (1) Median vertical, drawn upward in the middle line from the symphysis pubis. (2) Lateral vertical, drawn upward on each side parallel to the former, from a point midway between the anterior superior iliac spine and the symphysis pubis. These lateral lines if prolonged upward into the thorax pass rather more than 2.5 cm. (1 in.) to the medial side of the male nipple and meet the clavicle a little medial to its mid-point. According to the BNA system, the lateral vertical lines are slightly curved, extending upward from the pubic tubercle on each side along the lateral margin of the rectus muscle (corresponding to the linea semilunaris). The infracostal and intertuhercular planes, with the two lateral vertical planes that intersect them divide the abdomen into nine regions: — three median, viz., the epigastric, umbilical, and h3rpogastric and on each side three lateral, viz., hypochondriac, lumbar, and iliac (fig. 898). Another transverse plane of practical importance, though we do not use it as a boundary of the abdominal subdivisions, is represented by Addison's transpyloric line, drawn horizontally through a point midway between the umbilicus and the sterno-xiphoid junction (or midway between the symphysis pubis and supra-sternal notch). It crosses the spine at the level of the first lumbar vertebra. It must be noted that the pylorus only lies in this plane during life when the subject is in the horizontal position. On assuming the upright position the pylorus falls at least one vertebra lower. The sterno-xiphoid plane, drawn horizontally through the junction of the body of the sternum with the xiphoid, outs the spine at the disc between the ninth and tenth thoracic vertebrte, and the umbilical plane, passing through the umbilicus, crosses the disc between the third and fourth lumbar vertebrae (though in corpulent subjects it is somewhat lower). The abdominal wall. Bony and muscular landmarks. — The linea alba forms a perceptible groove in the middle fine from the xiphoid cartilage to below the umbilicus. It is a band of interlacing fibres, mostly crossing each other at right angles, that forms the main insertion of the transversus and oblique muscles, and stretches between the two recti muscles from xiphoid cartilage to symphysis. It is on the average 1.2 cm. (| in.) wide above the umbilicus. Below the umbilicus it narrows rapidly and becomes merely a thin fibrous septum between the two recti, which in this position lie close together. In its broad supra-umbilical portion, small hernial protrusions of subperitoneal fat often force their way through interstices in the linea alba, and true peritoneal sacs may be drawn through after them. The linea alba is not very vascular, and hence was at one time the favour- THE ABDOMEN 1371 ite site of incisions in opening the abdominal cavity. Since the resulting scar is weak and yielding, however, it is now more customary to make vertical incisions through the rectus sheath, to one side of the middle line, where the abdominal wall can be sutured in layers, and an incisional hernia prevented. The umbilicus lies in the linea alba rather below its centre. It is somewhat prone to hernia formation (p. 1402) and is occasionally the site of congenital fistulas, which may originate in a Meckel's diverticulum (p. 1376) or a patent urachus. When the recti are thrown into contraction the linea semilunaris on each side is made evident as a groove, extending with a slight lateral convexity from the tip of the ninth costal cartilage, where the lateral vertical line meets the thoracic margin, to the pubic tubercle. The contraction of the recti muscles also shows up the three lineae transversae, fibrous intersections adherent to the anterior layer of the sheath of the rectus, which cros.? the substance of the muscle (1) at the umbilicus, (2) at the tip of the xiphoid, and (3) midway between the former two. A tonic contraction of one or both recti localised to one of these segments occa- sionally gives rise to the "phantom" tumors which occur in some hysterical cases. The linea semilunaris shares the disadvantages of the linea alba as a site for incisions, and there is the further danger of injury to the nerve supply of the rectus, which may involve a diffuse bulge of the atrophied muscle. In tapping the bladder above the pubes, the trocar should be introduced immediately above the pubes and driven backward and a little downward. In this operation, and in suprapubic cystotomy, the retro-pubic space or cavum Retzii is opened. This is bounded in front by the pubes and superior fascia of the urogenital diaphragm, behind by the anterior surface of the bladder. Below are the true ligaments of this viscus. The space contains fatty tissue and veins, increasing in size with the advance of life. If about ten ounces of fluid are injected into the bladder, the peritoneum will be raised sufficiently to allow of a three-inch incision being made between the recti and pyramidales immediately above the pubes. The transversalis fascia is thicker below, and is often separated from the linea alba by fat, which must not be mistaken for the extra-peritoneal layer. The peritoneal reflexion is loosely connected to the bladder and can always be peeled upward. A transverse line drawn from one anterior superior iliac spine to the other crosses at about the level of the top of the promontory of the sacrum. Such a line will always show whether the pelvis is horizontal or not. (Holden.) The inguinal (Poupart's) ligament corresponds to a line drawn with a slight curve downward between the anterior superior iliac spine and the pubic tubercle. The first of these bony prominences corresponds to the starting-point of the above ligament, the attachment of the fascia lata to the ilium, the meeting of the fleshy and aponeurotic parts of the external oblique (denoted by a line drawn upward from this spine to the ninth costal cartilage, or often a little anteriorly to these points), the point of emergence of the lateral cutaneous nerve of the thigh, and part of the origins of the internal oblique, transversus, and tensor fasciae latae. The pubic tubercle marks the lateral pillar (inferior crus) of the subcutaneous inguinal (external abdominal) ring, the mouth of which corresponds to the crest of the pubes lying between the tubercle and the symphysis. The neck of an inguinal hernia is above the tubercle and Poupart's ligament; that of a femoral hernia below and lateral to the tubercle, and below the same hgament. The ring, and especially its lateral pillar, can easily be felt by invaginating the scrotal skin with a finger, and pushing upward and laterally. In a female patient, if the thigh be abducted, the tense tendon of tlu' adductor longus will lead up to the site of the ring. The abdominal inguinal (internal abdominal) ring is situated about 1.2 cm. (J in.) above the centre of Poupart's ligament; oval in shape, and nearly vertical in direction, it has the arching fibres of the transversus above it, and to its medial side the inferior epigastric artery, lying behind the spermatic cord. The pulsations of this vessel here guide the finger in the insertion of the uppermost deep sutures in radical cure of hernia. The canal runs obliquely downward and forward between the two rings. In the adult it is about 3.7 cm. (1^ in.) long, but in early life, and in adults with a large hernia dragging upon the parts, the two rings are much nearer, and may be one behind the other. For the anatomy of inguinal hernia see p. 1304. Vessels in the abdominal wall. — The three superficial branches of the com- mon femoral, the external pudic, epigastric, and circumfiex iliac, supply the lowest part of the abdominal wall and the adjacent groin and genitals. The others that have to be remembered are the inferior epigastrics and the epigastric branch 1372 CLINICAL AND TOPOGRAPHICAL ANATOMY of the internal mammary, the deep circumflex iliacs, the last two intercostals, and the abdominal branches of the lumbar arteries. Of these, the infei'ior epigastric is the most important; its course will be marked out by a line drawn from a point just medial to the centre of the inguinal ligament, upward and medially to the medial side of the abdominal ring, and thence to a point about midway between the pubes and umbilicus, forming the lateral boundary of Hesselbach's triangle (fig. 1121). Here the vessel, which at first lies between the peritoneum and fascia transversalis, perforates the latter and, passing over the semicircular line (fold of Douglas) enters the sheath of the rectus. It then runs upward, closely applied to the back of that muscle, and, a little above the level of the umbilicus, divides into branches which anastomose with the epigastric branch of the internal mammary. One superficial vein in the abdominal wall needs especial mention, the thoraco-epigastric, joining the veins of the chest, e. g., the long thoracic above with, the superficial epigastric below. Its valves directing the blood downward below and upward above (Stiles) may be rendered incompetent when this vessel is enlarged, as in interference with the portal vein, mth which it communicates by a vein in the round ligament, or in blocking of the inferior vena cava. Lymphatics. — It is sufficiently correct to say here that those above the umbilical line go to the axillary, and those below that line to the inguinal nodes. Nerves. — The lower seven intercostals and the ilio-hypogastric and ilio- inguinal supply the abdominal wall. The sixth and seventh intercostals supply the skin over the upper epigastrium; the eighth, the area of the middle linea transversa; the tenth, that of the imibilicus ; the last thoracic, ilio-inguinal and ilio- hypogastric, the region above Poupart's ligament, and that of the pubes. The ilio-hypogastric supplies the skin over the subcutaneous inguinal (external abdominal) ring; the ilio-inguinal that over the cord and scrotum. The last thoracic and ilio-hypogastric cross the iHac crest to supply the skin of the buttock. The diaphragm. — The upper limit of the diaphragm rises to the following levels in full expiration: Its central tendon to about the lower end of the body of the sternum, or the seventh chondro-sternal joint; the right half to the fifth rib, or about 1 cm. (| in.) below the nipple; the left half not rising quite so high, i. e., to the fifth space, or 2.5 cm. (1 in.) below the nipple. Topographical relations of abdominal viscera. — These will include the peritoneum, liver and bile passages, stomach, spleen, pancreas, intestines, kidneys and ureters, and large abdominal vessels. The peritoneal spaces. — The peritoneum presents certain potential spaces, determined by its various reflections from the parietes and abdominal viscera. In these spaces collections of fluid such as abscesses or extravasations from hollow viscera or blood vessels may collect and become shut off by adhesions or overflow in various directions into neighbouring spaces. The transverse mesocolon and great omentum together form a shelf transversely placed, which divides the greater sac into two main divisions — supra-omental and infra-omental. The supra-omental region, in which the various forms of subphrenic abscess are found, con- tains the following fossa; (Barnard).* (1) Right subphrenic, between the right lobe of the liver and right cupola of the diaphi-agm, bounded toward the median line by the falciform ligament, and behind by the coronary ligament. It communicates below with (2) the subhepatic fossa or right renal pouch (Morison), which is bounded above by the visceral surface of the liver, and below by the mesocolio shelf and right kidney. It extends from the right lateral abdominal wall, its most capacious part, across the median line under the left lobe of the liver, and on its posterior aspect lie the upper pole of the right kidney, epiploic foramen, and anterior surface of small omentum. (3) The left subphrenic, also known as the anterior perigastric fossa, lies between the left dome of the diaphragm above, and the left lobe of liver, stomach, spleen and omentum below. It is bounded on the right by the falciform ligament which lies somewhat to the right of the median line. (4) The omental bursa may be regarded as a diverticulum from the subhepatic fossa with which it communicates by the epiploic foramen. Abscesses in this sac are rare, but occasionally laceration of the pancreas which is closely related to it behind gives rise to a collection of pancreatic juice and blood in the lesser sac, known as a pancreatic pseudo-cyst (Jordan Lloyd). The infra-omental region is subdivided in its abdominal part into (1) right and (2) left compartments by the attachment of the root of the mesentery to the spine, descending from the duodeno-jej unal flexure downward into the right iliac fossa. These fossae communicate with the supra-omental regions in the neighbourhood of the hepatic and splenic flexm-es of the colon respectively, and below with (3) the pelvis. The deepest level of the peritoneum lining the pelvis constitutes in the male the recto-vesioal, and in the female the recto-vaginal fossa (pouch of Douglas). It should be noted that with a patient in the supine position, owing to the contour of the psoas muscles and the anterior convexity of the lumbar spine, any fluid above the pelvic brim will tend to gravitate into the subphrenic spaces across the flexures of the colon which lie far back in the loins. This is undesii-able in view of the great absorbing power of the subphrenic lymphatics, and may be obviated by propping the patient in a half-sitting position. * Barnard, H. L., Brit. Med. Journal, Feb. 15, 1908. THE STOMACH 1373 Viscera behind the linea alba. — From above downward there are the follow- ing:— (Ij Above the umbiUcus — the left lobe of the liver, the stomach, the transverse colon, part of the great omentum, the pancreas, and cceliac (solar) plexus. (2) Below the umbilicus — the rest of the great omentum, covering in the small intestines and their mesentery. In the child, the bladder occupies a partly abdominal position; and in the adult, the same viscus, if distended, will rise out of the pelvis and displace the above structures, raising the peritoneum until, if distended half way to the umbilicus, there is an area of nearly 5 cm. (2 in.) safe for operations above the symphysis. The gravid uterus also rises behind the linea alba. The liver (figs. 914, 941, and 1125). — In the erect position, the anterior thin margin of the liver projects about 1 cm. (| in.) below the costal cartilages, but can only be made out with difficulty in this position. It may also be displaced downward by pleuritic effusion or tight lacing. The liver is also, proportion- ately, much larger in small children. Of the three more accessible surfaces, the right lateral is opposite the seventh to the eleventh intercostal arches, separated from them by the pleura, the thin base of the lung, and the dia- phragm. The superior surface is accurately fitted with its right and left portions into the hol- lows of the diaphragm, a slightly depressed area intervening which corresponds to the central tendon. Its level corresponds to that of the diaphragm given above. On the left side, in the adult, the limit of the left lobe will be in the fifth interspace, about 7.5 cm. (3 in.) from the ster- num. The antericr surface is in contact with the diaphragm, costal arches, and, between them, the xiphoid cartilage, and, below, with the abdominal wall. Both the superior and anterior siu'faoes are subdivided by the falciform ligament, an important point in subphrenic suppura- tion. In the right hypochondrium the anterior margin corresponds to the lower margin of the thorax; but in the epigastric region, running obhquely across from the ninth right to the eighth left costal cartilage, it crosses the middle line about a hand's breadth below the sterno- xiphoid articulation (Godlee), or half-way between the sterno-xiphoid j unction and umbiUcus, i.e., in the transpyloric line (fig. 914). Behind, the anterior margin, following the right lateral surface within the costal arches, crosses the last rib toward the level of the eleventh thoracic spine. In the anterior border, a little to the right of the median vertical plane, is the umbilical notch, where the falciform and round ligaments meet. Still further to the right, and just to the left of the mid-Poupart plane, is the fundus of the gall-bladder. Gall-bladder and bile passages. — The fundus of the gall-bladder, situated in a fossa on the under surface of the right lobe of the liver, and having the quadrate lobe to its left, lies opposite to the right ninth costal cartilage, close to the lateral edge of the rectus. This point corresponds to the site of intersection of the lateral vertical and transpyloric lines. It is in contact with the hepatic flexure of the colon and the first piece of the duodenum, into either of which, but particularly the latter, large gall-stones impacted in the neck of the gall-bladder occasionally ulcerate. A distended gall-bladder as it enlarges tends to take a line obliquely from the above point where it emerges from under the costal margin toward the umbilicus. The long axis of the gall-bladder is directed from the fundus backward and upward. The cystic duct runs from the neck downward and forward in the gastro-hepatic omentum, and so forms an acute angle with the gall-bladder. A spiral fold of mucous membrane at the junction of the two, which fulfils the function of keeping the lumen open for the flow of bile, adds to the difficulty of passing a bougie from the gall-bladder down into the common duct. The hepatic and cystic ducts join in the right free margin of the gastro-hepatic omentum to form the common bile-duct, 7.5 cm. (3 in.) in length, which as it runs down to open into the duodenum presents four distinct stages. (1) It first lies in the free edge of lesser omentum in front of the epiploic foramen, with the hepatic artery to the medial side, and the portal vein behind them both. (2) Behind the first part of the duodenum with the gastro-duodenal artery accompanying it. (3) In a deep groove in the head of the pancreas, between that gland and the posterior aspect of the second part of the duodenum. The pancreatic tissue siurounds it completely in 75 per cent, of cases, (Bunger) hence the jaundice that occurs in chronic inter- stitial pancreatitis. (4) Piercing the muscular waU of the duodenum obliquely it ends by joining the main duct of the pancreas at the ampulla of Vater and opening into the second part of the duodenum by a common orifice. This orifice, situated on the postero-medial aspect of the gut, rather below the centre of the second portion, is raised on a small papilla and is nar- rower than the lumen of the common duct. The stomach. — The study of this organ by rendering its contents opaque with bismuth salts and projecting its shadow by X-rays on a fluorescent screen, has greatly modified the conception of its shape and position formed from post- mortem and operative observations. Examined post-mortem, or at operations under general ansesthesia it forms a flaccid sac with its long axis directed from the fundus obliquely downward, forward, and to the right. Seen under X-rays, 1374 CLINICAL AND TOPOGRAPHICAL ANATOMY with the patient standing upright, the cardiac portion (the fundus and body together) is vertical, and the smaller pyloric portion is directed backward and to the right and slightly upward (fig. 1125). The most fixed point is the cardiac orifice. The cardiac orifice lies under the seventh left costal cartilage 2 cm. (f in.) from the sterno- xiphoid junction at a depth of about 10 cm. (4 in.) from the surface. Behind, this point corre- sponds to the tenth thoracic vertebra. The pyloric orifice hes in the transpyloric plane when the patient is recumbent,'but when the patient is standing it falls to the level of the second or third lumbar vertebra, or lower still Fig. 1108. — Photograph op an Empty Stomach. (J. S. B. Stopford.) when"any transient faintness or nausea causes loss of muscular tone (Barclay). The pylorus is slightly to the right of the middle line in the empty stomach. As the stomach fiUs it descends farther and moves a little farther to the right. The lesser curvature presents a definite notch at the junction of the cardiac and pyloric portions of the stomach — the incisura angularis.. The greater curvature reaches the umbihoal plane in the erect posture, even when the stomach is empty. When the viscus is full tliis curvature lies distinctly below this plane, being lower in women than in men (Hertz). The ■pyloric portion of the full stomach is directed backward and a httle upward, as the distended pyloric vestibule moves further to the right than the pyloric orifice and lies on an anterior plane. In the recumbent posture the greater curvature hes above the umbihcal plane, even when moderately distended, and the stomach is more obliquely placed. The fundus invariably contains gas, even when the stomach contains no food, in which case the organ forms a contracted J-shaped tube (fig. 1108). In extreme distention the left dome of the diaphragm is so pushed up by the fundus that it lies at a level as high as or even higher than the THE INTESTINES 1375 right dome (Hertz). The pressure thus exerted on the heart accounts for the dyspnoea and cardiac pain so often associated with flatulence. The position of the pyloric sphincter is shown on the outer surface by a very constant venous ring runrling toward both lesser and greater curvatures in the subserous layer at right angles to the long axis of the pyloric canal (Moynihan). In connection with the extravasation of contents that results from perforating ujcers of the stomach, a knowledge of the subphrenic peritoneal fossaj is important (p. 1372). Perforation is rare on the posterior surface since it is less mobile than the anterior, and protective adhesions form readily. When it does occur, extravasation into the omental bursa results, and suzih a perforation is exposed by turning up transverse colon and stomach and incising the transverse meso-colon. Perforation on the anterior surface usually gives rise to general peritonitis, but in the less sarious cases an abscess may form localised to (l) the right subphrenic space, (2) the subhepatic fossa, or (3) the left subphrenic space, according to the situation of the ulcer on the stomach. The Spleen (fig. 1127; see also figures in Sections IX and XII). — This lies very obliquely in the left hypochondrium, its long axis corresponds closely with the line of the tenth rib. It is placed opposite the ninth, tenth, and eleventh ribs exter- nally, being separated from these by the diaphragm; and medially it is connected with the great end of the stomach. Below, it overlaps slightly the lateral border of the left kidney (fig. 1127). Its highest point is on a level with the spine of the ninth thoracic, and its lowest with that of the eleventh thoracic vertebra. Its upper pole is distant about 3.7 (1| in.) from the median plane of the body, and its lower pole about reaches the mid-axillary line on the same rib. (Godlee.) In the natural condition it cannot be felt; but if enlarged, its notched anterior margin extends downward toward the umbilicus, and is both characteristic and readily felt. The pancreas. — The head of the pancreas lies in the hollow formed by the three parts of the duodenum, on the bodies of the second and third lumbar vertebrae. The inferior vena cava lies behind it. The neck, body, and tail of the pancreas pass obliquely to the left and slightly upward, crossing respectively the commencement of the portal vein, the aorta, and the left kidney. The root of the transverse mesocolon is attached to the anterior margin of the gland, so that its supero-anterior surface is related to the omental bursa, and its inferior surface to the greater sac. The importance of this relation in the formation of pancreatic pseudo-cysts has been referred to above. Pancreatic ducts. — The main duct, the duct of Wirsung, opens into the common ampulla of Vater with the bile duct. This ampuUa usually opens into the gut by a narrow orifice raised on a small papilla. A gaU-stone impacted in the ampulla may cause a flow of bile backward along the duct of Wirsung, and so give rise to acute pancreatitis (Opie). The small accessory duct of Santorini opens into the duodenum independently about 2 cm. higher up. It often anastomoses with the larger duct in the substance of the gland. Accessory nodules of pancreatic tissue are occasionally met with in the walls of the stomach or small intestine at diff'erent regions. A cyst originating in the pancreas may "point" toward the anterior abdominal wall by three routes: — (1) Above the stomach through the lesser omentum; (2) between stomach and transverse colon through the great omentum; (3) below the transverse colon through the trans- verse mesocolon. The posterior aspect of the head of the gland, with the third part of the common bile duct may be exposed by incising the peritoneum on the lateral margin of the second part of the duodenum, and turning the gut medially toward the middle line. Intestines. (A) Small. — The average length of the small intestine is about 6.85 m. (22| ft.), though the length as measured post mortem varies considerably with the degree of contraction of the longitudinal muscular coat. The duodentma is about 25 cm. (10 in.) in length. Of the remaining portion the upper two-fifths constitute the jejunum and the lower three-fifths the ileum, though this division is quite arbitrary. Cases are recorded in which patients have survived the re- moval of over 5 m. (16 ft.) of small intestine. The first part -of the duodenum extends from the pylorus on the first or second lumbar ver- tebra, backward and to the right. It ends near the upper pole of the right kidney and on the medial side of the neck of the gaU-bladder, by turning down to form the less mobile second -part, which descends in front of the hilum of the right kidney to the level of the third lumbar vertebra. The third part of the duodenum crosses the body of the third lumbar vertebra horizontally in the infracostal plane, and then turns up obliquely to the left side of the spine and ends at the level of the upper border of the second lumbar vertebra in the duodeno-jejunal flexure. The first part is the most mobile, since it is covered back and front by peritoneum in the first half of its course. The second part has a peritoneal covering in front onlj' and is devoid of it where it is crossed by the commencing transverse colon. The third part is covered by peritoneum in front except where the superior mesenteric vessels pass across it to join the commencement of the mesentery. It is probably the constricting effect of these vessels on the duodenum that gives rise to the acute dilatation of the stomach which occasionally follows abdominal operations. 1376 CLINICAL AND TOPOGRAPHICAL ANATOMY The duodeno-jejunal flexure, which hes on the left side of the body of the second lumbar vertebra, immediately below the body of the pancreas, is held up to the right crus of the dia- phragm by a band of fibro-muscular tissue known as the suspensory ligament of Treitz. Some of the fibres of this structui-e are continued onward into the root of the mesentery. It is not found in pronogxade animals. The duodeno-jejunal flexure is the commonest site of traumatic rup- ture of the small intestine, since it is the point of union of a fixed and a freely movable portion of the gut. In the operation of posterior gastro-enterostomy the duodeno-jejunal flexm'e is readily found by passing the hand along the under surface of the transverse meso-colon to the left side of the spine, the omentum and colon being turned upward. The first coil of the jejunum is anastomosed to the posterior wall of the stomach, which is exposed by making an opening in the transverse meso-colon. In some cases the first few centimetres of the jejunum are found to be fused between the layers of the transverse meso-colon. Certain peritoneal fossas are often found on the left side of the flexure. They may give rise to retro-peritoneal hernia and strangulation of intestine. The duodenal fossaj are described on p. 1164. Jejunum and ileum. — The mesentery contains between its two peritoneal layers the superior mesenteric vessels and their intestinal branches, the superior mesenteric plexus, lacteals and many lymph nodes on their course. These nodes are frequently enlarged in abdominal tuberculosis in children (tabes mesenterica) . The attached border of the mesentery may be marked out on the surface by a line drawn from just below the transpyloric plane and a little to the left of the middle line (the duodeno-jejunal flexure), which curves downward and to the right to end in the iliac fossa at the junction of the intertubercular and right lateral vertical lines (the ileo-caecal valve). Meckel's diverticulum which is present in about 2 per cent, of subjects (Treves) is found in the free border of the ileum 30 cm. to 1 m. (1 to 3 ft.) above the ileo-caecal valve. It is a remains of the vitello-intestinal duct. It is usually a blind conical pouch some 6 to 9 cm. long with a free extremity, but may be attached to the umbihcus by a fibrous cord. This cord may cause acute intestinal obstruction by strangulating a coil of gut, or the diverticulum may be invag- inated and form the starting-point of an intussusception. The presence of aggregated lymph nodules (Peyer's patches) in the lower part of the ileum accounts for the fact that tuberculous ulcers and perforating typhoid ulcers are almost confined to this part of the gut. Intestinal localisation. — It often happens that the surgeon wishes to ascertain roughly to what part of the small intestine a given coil presenting in a wound belongs. The variations in length of the small intestine and the considerablf range of movement of the coils during peristalsis render the problem difficult, but it may be stated as a general rule that the upper third of the intestine lies in the left hypochondrium and is not usually encountered in a wound; the middle third occupies the middle part of the abdomen, and the lower third lies in the pelvis and right iliac fossa (Monks). The jejunum is thicker walled and more vascular than the ileum. The lumen steadily diminishes as we pass downward, hence foreign bodies such as gall-stones that pass through the jeju- num are apt to become impacted in the lower ileum. The most reliable indications of the level of a given coil are found, however, on inspection of the mesentery and its blood-vessels (see fig. 482 in Section V). Opposite the upper part of the bowel the mesenteric arteries are arranged in a series of large primary anastomosing loops. From these the vasa recta run to the gut 3 to 5 cm. long, straight and unbranched. Passing downward toward the lower end, the single large primary loops give place to smaller and more numerous secondary loops arranged in layers coming nearer and nearer to the bowel. Hence the vasa recta become shorter. They become also less regular and more branched, and in the lower third of the small intestine are less than 1 cm. in length. The mesenteric fat in the upper third never reaches quite to the free edge of the meusentery, so that clear transparent spaces are left near the bowel. In the lower third the fat usually occupies the whole of the mesentery right up to the intestine, and makes it thicker and more opaque.* The average width of the mesentery, from its root at the posterior parietes to the bowel is 20 cm. (8 in.) and the longest part lies between 2 and 8 m. from the duodenum (Treves). The ileum is freely movable on a long mesentery down to the ileo-C£ecal region. In some cases however a congenital fusion of the leit half of the mesentery with the parietal peritoneum near the pelvic brim binds the bowel down a few inches above the ileo-ca3cal valve, and has been said to give rise to symptoms of intestinal stasis. (Flint,! Gray, and Anderson.) (B) Large intestine. Ileo-csecal region. — The position of the ileo-csecal valve may be marked on the surface by the junction of the intertubercular and right lateral vertical lines, though it is often found considerably lower. It is situated on the postero-medial aspect of the caecum. The caecum, which is the * Monks: Trans. Araer. Surg. Assoc, 1913. t Bulletin, Johns Hopkins Hospital, Oct., 1912. i THE INTESTINES 1377 blind extremity of the colon lying below the horizontal level of the ileo-caecal valve, is approximately 6.2 cm. (2| in.) in both vertical and transverse diameters, though its size varies much with the degree of distention. It lies usually in contact with the anterior abdominal wall above the lateral half of the inguinal ligament. The orifice of the appendix (vermiform process) lies some 2 cm. below the ileo-cEecal valve. The caecum is completely covered by peritoneum as a rule, though exceptionally its posterior surface is bound down in the right iliac fossa. The axial rotation of the midgut and descent of the OEeeum that normally take place dui'ing intra-u,terine life (p. 1168) are occasionally not completed, with the result that the cfficum and appendix may be found above and to the left of the umbilicus, or less uncommonly just below Fig. 1109. — -Blood-vessels of the Ileo-c.eal Region. (From Kelly). the right lobe of the liver (3 per cent., Alglave), when an attack of appendicitis may simulate inflammation of the gall-bladder. On the other hand certain cases occur in which the CEBCum descends unusually far, proceeding downward and medially until it becomes a pelvic organ whenever the bladder and rectum are empty. This pelvic position of the ca;cum is found in 10 per cent, of infants (G. M. Smith).* In the commonest form of intussusception, the ileo-caecal valve and lower ileum are pro- lapsed into the colon and carried down by the force of peristalsis toward the anus. The valve in these cases forms the apex of the intussusceptum, however far it travels. * Anat. Record, vol. 5, 1911, p. 549. 1378 CLINICAL AND TOPOGRAPHICAL ANATOMY The vermiform process (appendix) is developed at the apex of the caecum, and persistence of the apical appendix of foetal type, is not uncommon. The fact that all three tsenis coli converge at the base of the appendix is an anatomical reminder of its primitive position. The anterior tsenia is of great service in opera- tions on the appendix, since by following it down from the colon the base of the appendix can alwaj^s be found. The adult position of the base of the appendix on the postero-medial aspect of the caecum is due to the disproportionate growth of the lateral saccule of the caecum which comes to form the apparent caecal apex. The appendix averages 10 cm. (4 in.) in length in the adult. The position of its base only is at all constant. It lies distinctly below MoBurney's point, which is midway between the umbilicus and the right anterior superior iliac spine. This point is often the seat of greatest tenderness in appendicitis. The appendix itself may be found (1) pointing upward and to the left toward the spleen, behind the terminal ileum and mesentery; (2) hanging over the pelvic brim, in which position tenderness on rectal examination or pain on micturition results when the organ is inflamed; (3) in the retro-colic fossa; and (4) with its tip projecting to the right of the csecum in the right lateral paracolic fossa, where it causes tenderness when inflamed close to the anterior superior ihac spine. The course and to some e.xtent the gravity of abscesses originating in the appendix will depend upon the position the inflamed organ is occupying at the time of perforation. The artery of the appendix derived from the posterior branch of the ileo-eoUo reaches it by running down behind the end of the ileum. It raises a fold of peritoneum called the mesen- terioluin or mesoappendix. Very rai-ely the artery comes from the anterior branch of the ileo-colic. The tmnice coli referred to above as converging on the base of the appendix contribute its longitudinal muscular coat. The inner circular coat is thicker, but along the attachment of the mesenteriole certain gaps for the passage of lymph and blood-vessels occur in the muscular coats. Through these gaps infection may easily spread from the mucosa to the peritoneum (Lockwood). The appendix is essentially a lymph gland and has been called the "abdominal tonsil." The lymph follicles he in the submucosa. They are poorly developed at birth but reach their fuU development within the first few weeks of extra-uterine hfe (Berry).* ObUteration of the lumen is common but is inflammatory in origin, and not, as was once thought, a change normal in advanced age. Pericsecal fossa. — In addition to the mesentery of the appendix certain other folds of per- itoneum are usually present at the ileo-cffical junction: (1) the ileo-colic or anterior vascular fold (fig. 1109) containing the anterior branch of the ileo-cohc arterj^; (2) the ileo-caecal, or bloodless fold of Treves, running from the lower border of ileum onto the ciEcum. The appen- dix may be in a fossa behind either of these folds. It may also be found in the retro-colic fossa lying behind the cfficum and commencement of ascending colon. The colon is readily distinguished from the small intestine by its three lon- gitudinal taeniae and saccules and by the appendices epiploicse, which are devel- oped before birth. The ascending colon runs with a slight lateral convexity upward from its junction with the caecum to the hepatic flexure which lies under the ninth right costal cartilage at the level of the second lumbar vertebra and in contact with the anterior surface of the right kidnej^ and the lower surface of the right lobe of the liver. It lies lateral to the right lateral vertical plane. This de- scription is only true of an ascending colon examined by X-raj^s in the recumbent position. When the patient stands up, the flexure sinks to the infracostal plane (third lumbar vertebra) or even lower. As the colon ascends in the angle between the quadratus lumborum and psoas, it also passes backward at an angle of 51° ■ndth the horizontal, as may be seen in a sagittal section through the right half of the abdomen (Coffey). f The caecum and ascending colon are distended as a rule with fluid contents and gas, and form the widest part of the colon. The variations in the peritoneal attachments of the colon, which are of growing clinical importance, are explained by its mode of development (p. 1179). During intra-uterine Ufe after rotation of the midgut round an axis formed by the superior mesenteric vessels, there is a stage in which the colon has almost assumed its permanent position in the abdomen but is still provided with a free mesocolon for both ascending and descending parts. This represents the normal condition of quadruped mammals. In the normal human individual this stage is transient, and before birth the ascending and descending colons lose their mesenteries by fusion of the posterior layers with the parietal peritoneum. Meanwhile the great omentum, formed by a bulging out of the primitive dorsal mesogastrium, fuses with the transverse colon and its mesocolon. The extent of these processes of fusion varies, particularly as far as the ascending and descending colons are concerned. Thus only 52 per cent, of adults have neither ascending nor descending mesocolons (the normal condition). A mesocolon is found on the left side in 36 per cent, of all cases and on the right side in 26 per cent. (Treves). In only a * Journ. Anat. and Phys., vol. 35, 1900, S3. t Surgery, Gynecology and Obstetrics, vol. 15, 1912, p. 390. i THE KIDNEYS 1379 small proportion (1.8 per cent., however, does the true primitive type of ascending mesocolon persist, continuous with the mesentery of the small intestine (G. M. Smith). Such an anomaly renders the patient liable to volvulus of the ileo-0£ecal region. In the common types of in- complete fusion of its peritoneal attachments the colon is inadequately adapted to the upright position and is predisposed to ptosis. A layer of peritoneum sometimes found passing down- ward and medially from the parietes in the right flank onto the front of the ascending colon, known as Jackson's pericolic membrane, is probably due to persistence of an early stage in the development of the great omentum, which passes to the right across the ascending colon to join with the parietal peritoneum before the descent of the cjecum is complete, and so is the most primitive agent in fixing the proximal colon back in the right loin. This membrane is usually associated with a congenitaUy mobile ascending colon (Morle}^.* At the hepatic flexure the colon bends forward and to the left, leaving the front of the kidney to which it is fixed, and crossing the second part of the duodenum. In the region of the flexure three inconstant peritoneal folds are met with giving it additional attachment to the neigh- bouring parts, viz., (1) the phreno-colic and less commonly (2) the hepalo-colic and (3) cysto- colic hgaments (Testut). Thej' must not be confused with pathological adhesions acquired after birth. The transverse colon is freely mobile except at its extremities. It crosses the abdomen with a convexity downward and forward, being separated from the anterior abdominal wall in the middle region by the great omentum. At the mid-line it usuaUy lies near the umbihcal plane in the recumbent posture, consider- ably lower in the erect, but may be found anywhere from the infra-costal plane to the pubes, depending on the tonicity of the stomach. Its main artery, the middle colic branch of the superior mesenteric, must be avoided carefully in the operations of gastro-enterostomy and gas- trectomy, since hgature of it causes gangrene of the transverse colon. The splenic flexure lies far back in the left hypochondrium and is considerably higher than the hepatic flexure. It is in contact with the lower end of the spleen, and is almost invariably held firmly in position by its -phreno-colic ligament, derived from the left extremity of the great omentum. The descending colon is of narrower calibre than the preceding parts and usually is found firmly contracted and empty. It passes downward and forward in the angle between the psoas and quadratus lumborum and obliquely across to the right the iliac fossa to end in the sigmoid or pelvic colon. The lower part of the descending colon, from the iliac crest to the pelvic brim, is often termed the iliac colon. In its upper part it hes in front of the convex lateral margin of the left kidney. The varia- tions in its peritoneal attachments have been referred to above (p. 1242). The operation of lumbar colostomy, common in pre-antiseptic days, was performed through an incision in the back parallel with the last rib. The colon lies 2.5 cm. (1 in.) to the lateral side of the edge of the sacro-spinalis, between the twelfth rib and ihac crest. The occurrence of a mesocolon here was a common source of difficulty in gaining access to the bowel without opening the peritoneum. The pelvic colon (also known as the sigmoid or omega loop (Treves), is almost as long as the transverse colon, and forms a loop, the two ends of which, at the pelvic brim and at the front of the third sacral vertebra respectively, are placed somewhat closely together. The loop is thus anatomicallj^ predisposed to axial rotation, and is the commonest seat of volvulus in the whole intestinal tract. On the left and inferior aspect of the pelvic mesocolon near its base, a small peritoneal fossa {intersigmoid) is usually found in the angle formed by the root of the mesocolon and the parietal peritoneum. It occasionaUy contains an internal hernia which may become strangulated. The upper part of the pelvic colon is frequently brought out and opened tlirough an inci- sion in the left iliac region to form an artificial anus in cases of inoperable growth of the rectum. In advanced life, and in the chronically constipated, certain diverticula of mucous membrane are occasionally met with which project through the vascular gaps of the muscular coat into the bases of the appendices epiploicse in this region, and also between the layers of the pelvic mesocolon. They often contain foecal concretions and may become inflamed or even perforate, forming an abscess in the left ihac fossa, f The junction of pelvic colon and rectum opposite the third sacral vertebra forms a more or less acute angle and constitutes the narrowest part of the colon. It is a frequent site of stricture. The kidneys. — These lie at the back of the abdominal cavity so deeply in the hypochondriac and epigastric region as to be beyond palpation in most individuals, unless enlarged or unduly mobile. The lower end of the right being slightly lower than its fellow, encroaches in health upon the lumbar and umbilical regions, and may be palpable on deep inspiration in spare subjects. These * Lancet. Dec, 1913. t McGrath: Surgery, Gynecology and Obstetrics, vol. 15, 1912, -129. 1380 CLINICAL AND TOPOGRAPHICAL ANATOMY organs lie much higher and nearer to the vertebrae than is usually supposed to be the case, the upper two-thirds of the right and all the left kidney being behind the ribs. Relatively to the vertebra3, the kidneys lie along the sides of the last thoracic and the first three lumbar. To mark them in from the front the following points should be noted: The upper extremity of the right should reach as high up as the seventh costal cartilage, the left up to the sixth, on either side close to the costo-chondral and inter-cliondral junctions. This level will corre- spond to one half way between the sterno-xiphoid and transpyloric lines. The lower end. Fig. 1110. — Renal Fascia, as seen in Cross-section. Aorta and vena cava Anterior layer of renal fascia Peritoneum Posterior layer of renal fascia about 11 cm. (4| in.) below this point, would be opposite to the subcostal line; that of the right kidney is usually lower, and may encroach upon the umbilical line. For practical piu'poses the hilus is opposite a point on the anterior abdominal wall, a finger's breadth medial to the tip of the ninth costal cartilage (Stiles), or the junction of the transpyloric and lateral vertical lines. The importance of the relation of the last rib has been mentioned at p. 1245. The lateral vertical line has one-third of the kidney to its lateral side, and two-thirds to its medial side. The shortest distance between the two kidneys, obliquely placed so as to be closer above, 'at the upper part of their medial borders' (Thane and Godlee), measures about 6.2 cm. (2| in.). On the posterior surface of the body the ividney's boundaries are indicated by the following: — (1) A line parallel with, and 2.5 cm. (1 in.) from, the mid-line, between the lower edge of the tip Fig. 1111. — Renal Fascia, as seen in Sagittal Section. -Lung Suprarenal gland —Kidney ■Anterior layer of renal fascia Posterior layer of renal fascia of the spinous process of the eleventh thoracic and the lower edge of the spinous process of the third lumbar vertebra; (2) and (3) lines drawn from the top and bottom of this line laterally, at right angles to it, for 7 cm. (2f in.); (4) a line parallel to the first, and connecting the ex- tremities of (2) and (3). Within this parallelogram the kidney lies (Morris). The chief relations of the kidneys are: — posteriorly — quadratus lumborum, psoas, diaphragm, last thoracic, ilio-hypogastric, and ilio-inguinal nerves. The twelfth rib lies behind both, the right, as a rule, not reaching above the upper border. The left often reaches the eleventh rib. The pleural reflection usually crosses the twelfth rib obliquely reaching below its neck. Anteriorly — The liver, right colic flexure and second part of the duodenum (figs. 956 and 1009), on THE URETER 1381 the right side. The liver, and stomach above, the body of the pancreas and spleen over the centre, and the descending; colon over the lower part of the left kidney. The attachments of the specialised fibrous sheets known as the renal fascia are shown in figs. 1110 and 1111. The anterior and posterior layers are seen to be continuous above and laterally. Medially and below they remain separate and it is in this dii-ection that the abnormally movable kidney travels. The fatty tissue between the kidney and the renal fascia is known as the perinephric fat; that outside the fascia is the paranephi'ic fat. The kidneys are maintained in position by (1) the vascular pedicle; (2) fatty capsule and fascia; (3) above all by the intra-abdominal pressure. Failure to ascend during development from its original position near the pelvic brim to its normal level accounts for certain cases of movable kidney of congenital origin. In these cases Fig. 1112. — The Abdominal Aorta and Vena Cava Inferior, Gall-bladder Hepatic duct Cystic duct common bile duct Portal vein — Gastro-duodenal br Right gastric art. Hepatic artery Right suprarenal vein Inferior suprarenal artery Renal artery Renal vem Inferior vena cava Kidney ij Right spermatic vein Right spermatic artery Quadratus lumborum muscle Lumbar artery and vein Uieteric branch of — spermatic artery Middle sacral vessels. Left lobe of Uver (Esophagus Left phrenic artery Right phrenic artery Superior suprarenal Left gastric artery Inferior suprarenal Splenic artery Left phrenic vein Left suprarenal vein Superior mesenteric artery Kidney Ureteric branch of renal Left spermatic vein Ureter Left spermatic artery Inferior mesenteric artery Ureteric branch of spermatic Ureteric branch of common iliac iliac artery External iliac artery Hypogastric artery the renal artery may take origin from the common iliac artery. An accessory renal artery running into the lower end of the kidney from the aorta may cause kinking of the ureter and is a not uncommon cause of hydronephrosis. The suprarenal glands are not so firmly attached to the kidneys as to the diaphragm; hence they are not encountered in operations for movable kidney and are not removed in nephrectomy. Brode] has shown that incisions into the kidney should be made rather behind its convex border (Brodel's bloodless line). Occasionally fusion of the lower poles occurs during develop- ment across the middle hue of the body, and a single horseshoe kidney results, with double ureter and vascular supply. The ixreter. — On an average 30 cm. (12 in), long, this tube descends almost vertically in its abdominal course on the psoas muscle. It is crossed obUquely 1382 CLINICAL AND TOPOGRAPHICAL ANATOMY by the spermatic or ovarian vessels. It crosses the brim of the pelvis just in front of the bifurcation of the common iliac, and descends on the side wall of the pelvis in front of the hypogastric artery. The abdominal part of the ureter may be exposed extraperitoneally by an extension for- ward of the usual lumbar renal incision. It is found lying between peritoneum and psoas 3.7 cm. (IJ in.) from the middle line and when the peritoneum is stripped from the posterior abdominal wall the ureter is invariably carried with it. Aorta and iliac arteries. — The aorta enters the abdomen opposite the last thoracic vertebra, a point 12 to 15 cm. (5 to 6 in.) above the umbilicus, or rather above the mid-point between the infrasternal depression and the umbilicus (Thane and Godlee), and thence, lying to the left of the mid-line, divides into the two common iliacs opposite the disc between the third and fourth lumbar vertebrae, or opposite the body of the fourth lumbar vertebra. This point is about 2.5 cm. (1 in.) below and to the left of the umbilicus, and on a level with a line drawn across the highest part of the iliac crest. A line drawn from this point, with a slight curve laterally, to just medial to the centre of Poupart's ligament, will give the line of the iliac arteries; the upper third of this line giving the aver- age length of the common iliac. The relation of the common iliac veins is shown in fig. 1112. The right, much shorter than its fellow, lies at first behind and then somewhat lateral to its artery. The left is at first to the medial side of its artery, and then behind the right. At the upper part of the fifth lumbar vertebra behind and lateral to the right artery, the vena cava begins. The site of some of the branches of the aorta may be thus approximately remembered as follows: The cceliac artery is given off immediately after the aorta has perforated the diaphragm; directly below this is the superior mesenteric artery. About 2.5 cm. (1 in.) lower down, or 7.5 cm. (3 in.) above the umbilicus, the renal arteries are given off. About 2.5 cm. (1 in.) above the umbilicus would be the level of the inferior mesenteric artery. The relation of the above vessels to the transpyloric line (p. 1153) is as follows: (Stiles.) The cceliac artery is two fingers' breadth, the superior mesenteric one, above the line, the renal arteries are a finger's breadth below it. The origin of the inferior mesenteric is midway be- tween the transpyloric and intertubercular lines. Collateral circulation after ligature of the common iliac. — The chief vessels here are: — ABOVE. BELOW. Pubic branch of inferior epigastric with Pubic branch of obturator. Internal mammary and lower intercostals with Inferior epigastric. Lumbar with Ilio-lumbar and circumflex iUac. Middle sacral with Lateral sacral and superior gluteal. Superior haemorrhoidal with Inferior and middle haemorrhoidal. Ovarian with Uterine Collateral circulation after ligature of the external iliac : — Internal mammary, lower intercostals, 1 ■, . t <■ ■ • * • and lumbar. / "^'^^ Inferior epigastric. Ilio-lumbar, lumbar, and gluteal with Deep circumflex iUao. Internal and external circumflex with Superior and inferior gluteal (sciatic). Perforating branches of profunda with Inferior gluteal (comes nervi ischiadici) . Circumflex and epigastric with Obturator. External pudic with Internal pudic. Collateral circulation after ligature of the internal iliac : — Branches of profunda with Inferior gluteal (sciatic). Inferior mesenteric with Hismorrhoidal arteries. Vessel of opposite side with Pubic branch of obturator. Branches of opposite side with Branches of pudic. Superior and inferior gluteal (sciatic) with Circumflex and perforating of profunda. Middle sacral with Lateral sacral. lUo-lumbar and superior gluteal with Circumflex iUac. THE PELVIS The male pelvis will be considered first, then the female pelvis, and finally a section on hernia. The Male Pelvis The topics under this heading will be considered in the following order: boundaries and subdivisions, scrotum and testis, ductus deferens and spermatic THE MALE PELVIS 1383 cord, penis and urethra, prostate, bladder, ischio-rectal fossa, rectum and anal canal. Bony boundaries. — These are the same in either sex. Above and in front is the symphysis pubis, rounded off by the subpubic ligament; diverging downward and laterally from this point on either side are the rami of the pubes and ischia, ending at the tuberosities of the latter. In the middle line behind is the apex of the coccyx, and reaching from this to the tuberosities are the sacro-tuberous (great sacro-sciatic) ligaments, to be felt by deep pressure, with the lower border of the gluteus maximus overlapping them. The depth of the perineum varies greatly — from 5 to 7. .5 cm. (2 to 3 in.) in the posterior and lateral part to 2.5 cm. (1 in.) or less in front. In the middle hne, extending longitudinally through the perineum, is the raphe, the guide to the urethra, and 'the line of safety' (on account of the small size of the vessels here) for operations on it. Fig. 1113. — ^Thb Male Perineum. (Modified from Hirschfeld and Leveilld.) Bulbo-cavernosus Superficial layer of uro-genital trigone Ischio-cavernosus Muscles of thigh Post. fern, cutaneous ni rv Permeai nerve | i Inferior haemorrhoidal nerve Cutaneous branch of fourth sacral Gluteus maximus Tuberosity of ischium Sacro-tuberous ligament Superficial transversus perinei Sphincter ani externus Subdivisions. — An imaginary line drawn transversely across the perineum from one tuber ischii to its fellow divides the lozenge-shaped space into two triangles — (1) An anterior, or uro-genital; and 2) a posterior, or rectal. The pelvic floor includes an upper or pelvic diaphragm (formed by the levator ani and coccygeus on each side) and a lower incomplete uro-genital diaphragm (or trigone) . The pelvic diaphragm (figs. 1113, 1114, 1115; see also figs. 397, 399, 400) isYmade up of the levator ani coccygeus muscles. It is somewhat funnel- shaped. When viewed from above or below (fig. 395), its fibres are seen to form horseshoe-like loops, arising on either side anteriorly, and passing posteriorly backward around the uro-genital apertures to be inserted chiefly in the mid-line posteriorly. The pelvic diaphragm serves primarily for the support of the abdominal viscera. For a detailed description of these muscles, as well as those of the uro-genital diaphragm, see section on the Muscular System. 1384 CLINICAL AND TOPOGRAPHICAL ANATOMY The xiro-genital diaphragm (or trigone) (fig. 400), the lower diaphragm of the pelvic floor, is both morphologically and functionally different from the upper. The uro-genital diaphragm is a sphincter muscular layer, derived (with the sphincter ani externus) from the primitive sphincter cloacae. The uro-genital diaphragm is composed of superior and inferior fascial layers, enclosing the membranous urethra, the sphincter urethrae membranacese and the transversus perinei profundus. Superficial to the uro-genital diaphragm is the superficial perineal interspace (fig. 400). This is covered by the superficial perineal (CoUes') fascia, and in- cludes the crura and bulb of the corpora cavernosa, with associated muscles, vessels and nerves. The space in the pelvic floor on each side below the pelvic diaphragm is the ischio-rectal fossa (figs. 399, 400, 1114). In the posterior or rectal triangle, where the urogenital diaphragm is absent, the ischio-rectal fossae form large wedge-shaped spaces. The lowei- wall or base is formed chiefly by the corresponding skin and superficial fascia, and partly by the external sphincter ani ; the medial wall by the Fia. 1114. — Coronal Section of the Ischio-rectal Fossa. (G. Elliot Smith.) Falciform process muscles (levator ani and coccygeus) and inferior fascia of the pelvic diaphragm; the lateral wall by the obturator internus muscle, with the corresponding obturator fascia (with Alcock's canal, incluchng the pudic vessels and nerves) . The apex of the fossa is above, where medial and lateral walls meet. The narrow fibrous roof strip joining the medial and lateral walls just above the level of the internal pudic vessels and nerves has been called the lamina terminalis (Elliot Smith, fig. 1114). Posteriorly the fossa is bounded by the gluteus maximus and lig. sacro-tuberosum. Anteriorly on each side the ischio-rectal fossae extend as narrow spaces between the pelvic diaphragm above, the uro-genital diaphragm below, and the pelvic wall laterally (figs. 400, 401, 402). Contents. — The ischio-rectal fossa is filled with loose adipose tissue continuous with the subcutaneous fat of the buttock. It is traversed by the inferior htemorrhoidal branches of the internal pudic artery, with the associated veins and nerves, passing to the external anal sphincter, the skin and the adjacent mucosa. The superficial vessels and nerves, as the)' run forward to pierce the superficial perineal fascia, lie in this space, as well as the inferior clunial (perforating cutaneous) branches and branches of the fom'th sacral nerve. The inferior THE MALE PELVIS 1385 hemorrhoidal veins traverse the fossa obUquely from the lateral wall downward and medially. They are usually somewhat dilated near the anal orifice, and when morbidly enlarged constitute the condition known as htemorrhoids ("piles")- The inner opening of an ana! fistula caused by the bursting of an ischio-rectal abscess into the gut is usually within 2 cm. of the anal margin, between the internal and external sphincters. The central point of the perineum is in the adult nearly an inch (2.5 cm.) in front of the anus, or midway between the centre of the anus and root of the scro- tum. Here the following structures meet, viz., the levatores ani, the two trans- verse perineal muscles, the bulbo-cavernosus, and the sphincter ani. The comparative weakness of the attachment of the sphincter ani in front, i. e., not into a bony point, is important in the division of it, as in operation for fistula. The sphincter should never be cut through anteriorly, especially in women, where its attachment here, blending with the sphincter vaginae, is a very weak one. This point also corresponds to the centre of the lower margin or base of the uro-genital diaphi'agm (triangular ligament). Its development varies much in different bodies. A little in front of this point is the bulb, with the corpus spongiosum passing forward from it. This would also be the level of the artery of the bulb, so that in lithotomy the incision should always begin below this point. A knife introduced at the central point, and carried backward and very sUghtly upward, shoiild enter the mem- branous urethra just in front of the prostate, e. g., iu median lithotomy and Cock's external urethrotomy. If pushed more deeply, it would enter the neck of the bladder. In median lithotomy, an incision 3.7 cm. (I5 in.) long is made tlirough the central tendinous point and raphe, so as to hit the membranous urethra. The following structures are divided: — • Skin and fasciae; some of the most anterior fibres of the external sphincter ani; raphe and central tendinous point; minute branches of transverse perineal vessels and nerves; base of uro-genital diaphragm Ln centre; membranous m'ethra and constrictor urethras. The attachments and arrangements of the superficial fascia (fig. 1115) must be traced and remembered. If the two layers of which it consists, the superficial alone extends over both urethral and rectal triangles alike, and is continuous with the similar structures in adjacent regions, the only difference being that, if traced foward into the scrotum and penis, it loses its fat, and contains dartos fibres. The deeper layer, found only over the urethral triangle, is called the fascia of CoUes (fig. 1115). Attached at the sides to the rami of the pubes, behind to the base of the uro-genital trigone or diaphragm, and open in front, it forms the superficial wall of a somewhat triangular pouch, limited behind by the uro-genital trigone, and containing the superficial vessels, nerves, and muscles, the bulb, adjacent part of the urethra, and crura of the penis. Owing to this space being closed behind and open in front, and to its containing the above structures, fluids extravasated within this space will obviously tend to make their way forward into the scrotum, penis, and lower part of the abdominal wall. The uro-genital triangle is subdivided into two planes by the inferior fascia of the uro-genital diaphragm and fascia of Colles. The structures in the swperficial -plane, between the uro-genital diaphragm and the fascia of Colles, have been given above. Those in the deeper, i. e., between the two layers of fascia of the diaphragm, are — (1) The membranous urethra; (2) deep transverse perineal muscle and sphincter of the membranous urethra; (3) the bulbo-urethral (Cow- per's) glands; (4) and (5) part of the pudic artery and nerve, and branches. The scrotum. — The skin of the scrotum is thin and delicate so that when distended, as by a hydrocele in the tunica vaginalis, it is remarkably translucent. Attached to its deep aspect is a layer of involuntary muscle, the dartos. When the dartos is contracted, as under the influence of cold, the scrotal skin becomes rugose. To this tendency to wrinkling, with consequent irritation from retained dirt, and the presence of many sweat glands the frequency of epithehoma in this part is due. The dartos is apt to cause inversion of the skin in wounds of the scrotum, but this difficulty in suturing may be counteracted by the application of a hot sponge, which relaxes the muscle. The superficial fascia of the scrotum is continuous with the fascia of Colles and the super- ficial fascia of the penis. Hence extravasation of urine under the fascia of Colles's balloons the scrotum and penis. The laxity of the areolar tissue under the dartos accounts for the great swelling that occurs in cedema of this part. The lymphatics of the scrotum, important by reason of the e.\ten.sion of scrotal cancer, drain into the superficial inguinal nodes. Those from the anterior aspect nearest the median raph6 run to the supero-lateral glands of this group, within a few cm. of the anterior superior spine.* * Morley: Lancet, 1911 (ii), p. 1545. 1386 CLINICAL AND TOPOGRAPHICAL ANATOMY The numerous large sebaceous glands that are found in the skin of the scrotum may give rise to cysts or adenomata. The deeper layers of the scrotum are derived from the abdom- inal wall, being brought down by the processus vaginalis in the descent of the testis. Testis and epididymis. — The left testis, the first to descend, lies somewhat lower in the scrotum, and this fact is one reason of the frequency with which a Fig. 1115. — The Arteries of the Perineum. Perineal vesseli -cavernosus Colles's fascia, turned back Ischio-cavernosus Transverse perineal vessels Cut edge of uro-genital trigone Perineal nerve giving off transverse branch Pudic vessels Dorsal artery of penis Deep artery of penis Artery of bulb Bulbo-urethral gland Pudic artery Sacro -tuberous ligament Levator ani External sphincter ani Gluteus maximus Fig Symphysis pub: Transverse fold Vesicula seminalis rJ-Ductus ejaculatorius L Prostate ^—External sphincter f- Internal sphincter .External sphincter varicose condition of the spermatic veins occurs on the left side. On palpation the Smooth firm body of the testis, pressure on which causes the characteristic "testicular sensation" can be felt to lie in front of and rather medially to the epididymis. The three parts of the latter^ the caput above, the body, and the Cauda epididymidis below, can also be distinguished. Running upward from the THE TESTIS 1387 back of the epididymis to the subcutaneous inguinal ring the spermatic cord can be felt. The bulk of the cord is made up of its coverings, of which the cremaster muscle is the most considerable, and of the pampiniform plexus of veins. On roll- ing the cord between the finger and thumb the ductus deferens can be felt like a piece of whipcord in the posterior part. The ductus (vas) deferens is thickened and nodular in tuberculous epididymitis. In vari- cocele the dilated and elongated veins of the pampiniform plexus feel on palpation like a bag of worms in the scrotum. It is important that the student, before studying diseased con- ditions, should make himself familiar with the feel of the normal parts as mentioned above and be able to identify them. Underneath the visceral layer of the tunica vaginalis, the body of the testis is covered by a dense fibrous layer, the tunica albuginea, which accounts for the small extent of swelling in orchitis as compared with epididymitis. The lymphatics of the testis run up in the spermatic cord through the inguinal canal, and accompanying the spermatic vessels end in the lumbar lymph nodes, below the level of the renal arteries. These nodes may be reached and removed along with the vessels by making an incision in the loin above the inguinal (Poupart's) ligament, and stripping the peritoneum off the posterior abdominal wall. On the right side of the perineum (left side of this figure) CoUes's fascia has been turned back to show the superficial vessels. On the left side the superficial vessels have been cut away with the anterior layer of the uro-genital trigone to show the deep vessels. The epididymis is the convoluted first part of the duct of the testis, about 6 m. (20 feet) in length. Its three portions are in differing connection with the testis. Thus the cauda is held in place by connective tissue, the body by the same medium; the caput by the vasa efferentia. Thus, when tubercular disease begins here, the testis itself is more likely to be early involved. Ductus deferens. — -The two extremities and the course of this involve several practical points. About 4.5 cm. (18 in.) long, it begins, convoluted at first and with a distinct bend upward, in the cauda epididymidis. It thence passes almost vertically upward at the back of the testis and cord to the tubercle of the pubes. Entering the canal, it lies on the grooved upper aspect of the inguinal (Poupart's) ligament, and then under the arching fibres of the internal oblique and transversus, upon the transversalis fascia. Its position, characteristic feel, and yellowish aspect are' well-known guides in operations for varicocele and hernia, while it is always to be isolated and palpated when tubercular disease below is suspected. Leaving the canal by the abdominal inguinal ring, it hooks round the inferior epigastric artery and then descends into the pelvis over the external iliac vessels. Continuing its course downward and backward over the side of the pelvis, it arches backward over the side of the bladder, superficial to the obliterated hypogastric artery, and then deep to the ureter. The two ducts now help to form the lateral boundaries of the external trigone, between the base of the bladder and the rectum. They here become dilated and sacculated and then contract again to empty into the ejaculatory ducts. The vesiculae seminales are diverticula growing out from the lower end of the deferential ducts at an acute angle, one on each side. They lie below and lateral to the deferential ducts and are related in front to the base of the bladder and posterior surface of the prostate, behind to the rectum, and above to the reoto-vesical pouch of peritoneum, which also descends to cover the upper part of their posterior aspect. The normal vesiculae seminales can scarcely be dis- tinguished from the base of the bladder on rectal palpation, but when diseased, as in tuberculous or gonorrhoeal vesiculitis, are enlarged and indurated and can be detected readily. The ejaculatory ducts, formed by the union of the vesicular and deferential duct of each side, are 2-2. .5 cm. in length. The first few millimeters of their course is extra-prostatic, and then entering the posterior surface of the prostate they run side by side downward and forward through the gland, close to the middle line, to open into the urethra on the colliculus seminalis at either side of the opening of the prostatic sinus. It is by these little ducts that infection travels from the urethra to the vesiculas and epididymis in gonorrhoea. Descent of the testis. — -The testis is developed between the tenth and twelfth thoracic segments of the embryo, and subsequently moves downward. By the third month of intra- uterine life it descends into the iliac fossa; from the fourth to the seventh month it hes at the abdominal inguinal ring; during the seventh month it passes obliquely through the abdominal wall by the inguinal canal; by the eighth month it lies at the subcutaneous inguinal ring, and it reaches the fundus of the scrotum about the time of birth. The left testis is slightty earlier than the right in all these stages. The descent referred to is due in part to the common descent of organs, associated with the descent of the diaphragm, but mainly to the gubernaculum. This is a mass of fibro-muscular tissue that forms under the inguinal fold (or plica gubernalrix) of peritoneum below the testis as it lies in the iliac fossa, and in the mesorchium. It grows down obliquely through the abdominal wall from a point lateral to the inferior epigastric artery, and tunnels out a passage for the testis. As it travels down into the scrotum it carries in front of it three layers of investing fascia derived from the abdominal wall, viz., e.xternal spermatic fascia from the external oblique, cremasteric from internal oblique and transversus muscles, and infundibuliform fascia from the transversalis fascia. The gubernaculum is attached above to the peritoneum and the posterior aspect of the testis, and by its subsequent contraction it draws down into the scrotum first a diverticulum of peritoneum, the processus vaginalis, and secondly the testis, which projects into the processus from behind just as it did into the coelom. Shortly after birth, obliteration of the processus vaginalis should occur, commencing at the deep abdominal ring and immediately above the testis. The part of the processus between these two points disappears completely. The lowest part, surrounding the testis, persists as the tunica vaginalis. Failure of obliteration, if complete, leaves a congenital hernial sac; if 1388 CLINICAL AND TOPOGRAPHICAL ANATOMY only the upper part perists, and does not communicate with the tunica vaginalis, it is called a funicular sac. Cysts originating in the processus vaginalis between the upper and lower points of primary occlusion are known as encysted hydrocele of the cord. tTndescended testis. — It occasionally happens that descent of the testis fails on one or both sides, and in these cases the organ may remain, (1) in the iliac fossa, (2) in the inguinal canal, or (3) at the subcutaneous ring. Deprived of the protection normally afforded against injury bj^ the scrotum and tunica vaginalis, the misplaced testis is subject to trauma, shows a tendency to torsion of its pedicle owing to its long mesorohium, and sometimes becomes the seat of malignant disease. A funicular hernial sac is generally present. Such testes are atro- phic and functionally deficient, and it is probably owing to their small size at an early stage that the gubernaculum fails to gain a hold on them. It has been shown by Bevan* that in unde- scended testis the ductus deferens is usually long enough to allow the organ to be placed in the bottom of the sci-otum by the surgeon without tension provided that the spermatic artery and pampiniform plexus of veins are divided. The blood-supply of the organ is then entirely derived frotn the deferential artery, a branch of the superior vesical. In rare cases the testis descends in a wrong direction (ectopia testis) and comes to he in the perineum, over Scarpa's triangle, or on the pubes. Penis. — The subcutaneous tissue of the penis, as on the scrotum, is devoid of fat and the delicate skin is very mobile and distensible, hence the ballooning of these parts in extravasation of urine or cedema. The fascia penis is continuous with CoUes's fascia. In radical amputation of the penis for malignant disease the whole organ, including the crura, is removed through an incision that splits the scrotum, and the stump of the corpus spongiosum (corpus cavernosum urethras) is brought out into the perineum behind the scrotum. The preputial orifice varies greatly in size. Normally large enough to allow easy retrac- FiG. 1117. — Cross-section op Penis. Dorsal artery y | /Deep dorsal ^ Tunica albuginea Tunica albuginea- Corpus cavernosum penis Fibrous sheatli of penis Artery Urethra Corpus cavernosum urethrse (spongiosum) tion of the prepuce from off the glans, it is frequently so small that retraction is impossible and it may even cause difficulty in micturition. The mobility of the skin over the penis must be borne in mind in the operation of circumcision, and care taken lest too much of the prepuce be removed, leaving insufficient skin to cover the penis. In this operation the vessels from which bleeding occurs lie, (1) on the dorsum, (2) in the frenum. Congenital malformations of penis. — At an early stage of development the urethra opens on the inferior aspect of the penis behind the glans. After the ingi-owth of epithelium that forms the glandular urethi-a, this primitive meatus should close. Occasionally, however, it persists, and the glandular urethra is represented by a groove on the under aspect of the glans. In these cases of hypospadias the glans is flexed on the penis and the prepuce is deficient IdbIow and has a pecuhar "hooded" appearance. In epispadias the upper wall of the m-ethra and corresponding part of the corpora cavernosa are absent. This condition is usually present in cases of ectopia vesicas. The male urethra is about 20 cm. (8 in.) in length, consisting of the cavernous portion, 16 cm, (6| in.), membranous 1 cm. (| in.) and prostatic 3 cm. (IJ in.). The narrowest part is the external orifice, and next to it the membranous urethra. The prostatic urethra is the widest and most dilatable. The bulbous urethra, just in front of the uro-genital diaphragm, is wider than the rest of the penile portion, but since it forms the most dependent spot in the fixed part of the urethra (from bladder to suspensory ligament of penis) , it is specially prone to gonorrhoeal stricture. Behind the bulb, the urethra narrows suddenly as it passes through the uro-genital diaphragm and contraction of the sphincters of * Journ. Amer. Med. Assoc, vol. 41, 1903, p. 718. THE PROSTATE 1389 the membranous urethra may here give additional difficulty in the passage of a catheter. False passages most commonly occur through the floor of the bulb on account of this, difficulty in entering the membranous urethi-a. The point of a small catheter may also be caught in the following apertm'es: (1) The lacuna magna in the roof of the fossa navicularis of the glandular urethra; (2) other crypts or lacunae in the penile part, mostly situated in the upper wall; (3) the prostatic sinus in the floor of the prostatic urethra about its centre. With the penis raised the urethra presents a simple cm-ve under the symphysis with the proportions of an ordinary silver catheter. It is in the region of the uro-genital diaphragm that the urethra is most liable to be damaged by a fall or blow, and the urine extravasated as a result will be beneath CoUes's fascia. In rupture of the membranous urethra urine may find its way in front of the inferior fascia of the uro-genital diaphragm by coexisting injury to this, or tlirough openings in the vessels, etc.; in a few such cases urine will make its way backward behind the fascia into the space of Retzius, ascending thence between the peritoneum and transversahs fascia. The attachment of the deep layer of superficial fascia to the base of the m-o-genital diaphragm accounts for the fact that urine extravasated from a ruptured m'ethra or thi-ough an opening behind a stricture passes not backward into the anal triangle, but forward onto the scrotum and abdominal wall. The prostate consists of a mass of racemose glandular tubules imbedded in a fibro-muscular stroma, that surrounds the first part of the urethra and lies below the neck of the bladder. Its base is intimately connected with the bladder by the continuation of vesical and urethral mucous membrane and by the inser- tion of the outer longitudinal muscular coat of the bladder into the gland. The inner circular muscle fibres of the bladder become specialised round the internal urethral orifice to form the internal sphincter. Adenomatous enlargements of the gland usually grow upward through this sphincter which is thus dilated and pushed aside, so that the glandular growth is covered only by vesical mucous membrane. The apex of the prostate hes at the level of the lower border of the pubic symphysis and 1.5 cm. behind it. It is firmly fixed to the superior fascia of the uro-genital diaphragm (deep layer of the uro-genital trigone) and here the urethra leaves it to become the membranous part. The anterior surface directed vertically lies 2 cm. behind the lower part of the pubic symphysis in relation to the prostatic plexus of veins; and from it the dense pubo-prostatic ligaments run forward on either side to the pubes. The posterior surface is in contact with the rectum, through the anterior wall of which it may be palpated 4 cm. (I5 in.) above the anal margin. It is separated from the rectum by the two layers of the recto-vesical septum (Elliot Smith).* The lateral surfaces are supported by the anterior fibres of the levator ani, from which, however, they are separated on each side by a dense mass of fibrous tissue in which the pudendal (prostatic) plexus of veins is imbedded. The prostatic urethra traverses the gland nearer the anterior than the pos- terior surface, with a slight forward concavity. Its floor is placed posteriorly and presents an eminence, the colliculus seminalis, about the centre of which is the orifice of the prostatic sinus, on either side of which open the common ejacu- latory ducts. The prostate is indefinitely divided into two lateral lobes. The fissure uniting them across the middle line in front of the urethra (the anterior commissure) is fibro-muscular and contains no glandular tissue. Behind the urethra the lateral lobes are continuous and the portion of gland Ijang between bladder, ejaculatory ducts and urethra has been erroneouslj^ termed the "middle lobe." Though not a separate lobe anatomically, adenomatous hypertrophy of this part is common, when it projects up into the bladder, and prevents the proper emptying of that organ. Capsule and sheath of the prostate. — In senile enlargement of the prostate removal may be effected by the suprapubic or by the perineal route. In the former, the bladder is opened above the pubes, the mucous membrane lying over the gland as it projects into the bladder is scratched through behind, and with the finger the whole adenomatous mass is enucleated. This process usually involves tearing out the whole of the prostatic m-ethra, and the ejaculatory ducts. The parts left behind consist of (1) the "capsule" which is simply the outer part of the gland proper stretched over the adenomatous mass, and consists of fibro-muscular tissue with a few flattened glandular tubules (C. Wallace). f Outside this (2) the fibrous "sheath" is derived from the visceral layer of pelvic fascia, in which is imbedded, on the anterior and lateral aspects of the gland, the prostatic plexus. Since these veins are not torn there is com- * Studies in Anatomy of the Pelvis. Journ. Anat. and Physiol., vol. 42, 190S. t C. Wallace. Prostatic Enlargement, 1907. 1390 CLINICAL AND TOPOGRAPHICAL ANATOMY paratively little hfemorrhage. In the perineal operation the posterior surface of the gland is exposed by cutting through the perineum between the bulb and external sphincter ani, and dividing the attachment of the recto-m-ethi-al muscle to the m-o-genital diaphragm and its in- ferior fascia. This exposes the back of the recto-vesioal septum (aponeurosis of DenonvilKers) which is split at its base, opening up the reoto-prostatic space of Proust. By a longitudinal incision into the prostate on each side the adenomatous lateral lobes may be enucleated sepa- rately, and it is claimed without injury to the urethra or ejaeulatory ducts (Hugh Young).* The bladder lies above the pubic symphysis at birth and so is mainly an abdominal organ. The anterior surface, in contact with the abdominal wall, has no peritoneal covering, but posteriorly the peritoneal reflection descends to cover the posterior surface of the prostate, which is relatively lower than in the adult. The adult bladder when empty forms a pyriform contracted organ behind the symphysis, and bounding the retro-pubic space of Retzius posteriorly. Into this space urine is extrava- sated in extra-peritoneal rupture of the bladder, and may mount up behind the abdominal wall in the extra-peritoneal tissue. The space is closed below by the pubo-pro.stafic ligaments and prostatic plexus of veins. In distention, the neck of the bladder and prostate being relatively fixed and immovable, the free a-pex rises up into the abdomen. As it does so it raises the peri- toneum off the abdominal wall, so that in moderate distention 5 cm. (2 in.) of abdominal wall above the pubes are free of peritoneum, and the bladder may be tapped here safely. The upper surface and a little of the posterior are covered by peritoneum, which is also related to the upper halves of the vesiculae seminales. Below the recto-vesioal pouch the base of the bladder pre- sents a small triangular area in contact with rectum, bounded by the peritoneal cul-de-sac above, the converging deferential ducts on each side and the prostate below. Tlirough this triangle which is rather expanded in distention of the bladder, puncture per rechmi was formerly prac- tised. The infero-lateral surfaces are slung up by the levator ani as by a hammock. The inte- rior of the bladder can be examined by the cystoscope in the living patient. The mucous mem- brane is loose and ruQ;ose in contraction, except over the trigone at the base, the angles of which are formed by the ureteric orifices and the internal meatus. The mucosa here is firmly adherent to the muscular coat and smooth. In hypertrophy of the bladder-muscle from ob- struction, a fasciculated appearance of the mucosa is seen and possibly diverticula between the bands of muscle. Rectum and anal canal. — The rectum proper extends from the end of the pelvic colon, opposite the third sacral vertebra, to the upper end of the narrow anal canal, which runs downward and backward almost at right angles to the rectum and is 3-4 cm. in length. The commencement of the rectum lies 13-14 cm. (5-5| in.) above the anus in the adult. This point is marked internally by an infolding of the mucosa on the right and anterior wall and to some extent of the circular muscle fibres, due to the angle at which the free pelvic colon turns into the fixed rectum. This shelf of mucous membrane is known as the upper transverse fold (first valve of Houston). Under normal conditions the rectum does not form a reservoir for faecal material, which is stored in the lower end of the pelvic colon, above the upper transverse fold, leaving the rectum empty except in defsecation. The rectum proper is subdivided into two compartments by the inferior transverse fold on the anterior wall (third or great valve of Houston), situated 8-9 cm. (3-3i in.) above the anus at the level of the anterior cul-de-sac of the peritoneum, and resulting from the adaptation of the rectum to the hollow of the sacrum. This can usually be made out on digital examination. The other transverse folds are inconstant and only present on great distention. The rectum and anal canal may be divided into three regions: (1) peritoneal from the third sacral vertebra to the lower transverse fold and anterior reflexion of peritoneum onto bladder or vagina; (2) infraperitoneal (rectal ampulla) below this and above the levator ani; (3) anal canal, below the level of the levator ani, constriction b3r which marks it off from the ampulla and converts it into an antero-posterior slit. The mucous membrane of the rectum proper is redundant and mobUe and of a bright pink colour as seen by the sigmoidoscope. It is dotted over by rectal pits, visible to the naked eye, containing lymphoid follicles, and by the smaller and more numerous Lieberkhiin's glands. In the peritoneal chamber the mucosa is transversely plicated. In the rectal ampulla it presents longitudinal folds in which lie branches of the superior hfemorrhoidal vessels. These longi- tudinal folds, known as the rectal columns, converge into the anal canal, and end at the level of the anal valves half way down the canal, each uniting two adjacent valves. The anal valves probably represent the original cloacal membrane, dividing the proctoda^um (formed from the epiblast) from the hypoblastic hindgut, and persistence of this membrane gives one form of imperforate anus (Wood Jonesf). The tearing down of a valve by hard faeces may be a cause of anal fissure, etc. (Ball). The mucous membrane of the anal canal is more firmly adherent * Studies on Hypertrophy and Cancer of the Prostate. J. H. H. Reports, vol. 14, 1906. t Brit. Med. Journal, Dec. 14, 1904. FEMALE GENITAL ORGANS 1391 to the underlying muscular coat than that of the rectum, hence in prolapse the mucosa of the rectal ampulla is the first to be extruded. Peritoneal relations. — The peritoneal chamber of the rectum has no covering of peritoneum behind, and the peritoneum, at first covering its first aspect and sides, leaves the sides obliquely and finally is reflected onto the base of the bladder (or the vaginal fornix in the female), at the level of the inferior rectal fold, 8 cm. from the anus. Blood-supply. — (1) The superior hsemorrhoidal artery, a continuation of the inferior me- senteric, reaches the rectum behind, via the pelvic meso-colon and bifurcates at once. The two branches run round on either side below the peritoneal reflection; giving ofl^ secondary branches that pierce the muscular coat about the level of the inferior transverse fold, or anterior perit- oneal reflection. Joining the submucous layer, these arteries run down in the rectal columns to the anal canal, where they anastomose with (2) the middle hsemorrhoidal arteries, branches of the hypogastric (internal iliac) and (3) the inferior hasmorrhoidal branches of the internal pudendal. The veins correspond. Their free anastomosis in the hsemorrhoidal plexus under the rectal columns, the union afforded here between the portal and systemic veins, the absence of valves in the superior hsemorrhoidal veins, and the constriction they are subject to in passing through the muscular coat, are some of the anatomical causes of the frequency of haemorrhoids. The branches of the superior hremorrhoidal artery to the rectum anastomose but little with one another, as compared with the sigmoid arteries to the pelvic colon. The main trunk of the superior hsemorrhoidal usually receives a large anastomotic branch from the lowest sigmoid artery 1-2 cm. below the sacral promontory, upon which the upper part of the rectum is dependent for its blood-supply after ligature of the superior haemorrhoidal. Hence in high excision of the rectum it is important to place the ligature on the superior hsemorrhoidal above the sacral promontory if sloughing of the gut is to be avoided.* For lymphatics of the rectum see p. 735. Supports of the rectum. — The anal canal is fixed by its attachment to the levator ani and perineal body. After division of the perineal body and recto-urethral muscle in front, the rectum is readily separable from -the back of the prostate and recto-vesical septum. When the levator ani has been divided on each side and the peritoneum opened, as in the perineal operation for excision of the rectum, the gut cannot be pulled down freely. The hand passed up behind it in the hollow of the sacrum meets on each side with a dense fibrous layer running from the sacrum opposite the third foramen onto the side of the rectum. This is the rectal stalk (Elliot Smith) and consists of dense fibrous tissue round the nervi erigentes from second, third and fourth sacral foramina and the middle haemorrhoidal vessels. It lies about 2.5 cm. above the levator ani, and after division of it the bowel is easily freed, so that the whole of the rectum and part of the pelvic colon may be drawn out at the perineum without tension. Rectal examination. — The following points can be made out by the finger introduced into rectum: — (1) The thickened, roll-like feel of a contracted external sphincter; (2) the narrower, more expanded, internal sphincter extending upward for 2.5 cm. (1 in.) from this; (3) the rectal insertion of the levatores ani, which here narrows somewhat the lumen of the gut; (4) above the anal canal, with its contrasting capaciousness, is the more or less dilated rectum proper; (5) the condition of the ischiorectal fossse on either side; (6) the membranous urethra in front, especially if a staff has been introduced; the instrument now occupies the middle line, and has the normal amount of tissue between it and the finger, thus differing from one in a false passage (in a child an instrument is especially distinct); (7) just beyond the sphincters, or 3.7 cm. (1| in.) within the anus, lies the prostate; (8) converging toward the base of the prostate, and forming the sides of the triangular space, are the vesiculse seminales and ejaculatory ducts. These can rarely be felt unless diseased and enlarged; any enlargement of the sacculated ends of the deferential ducts is much more perceptible; (9) it is within this triangular space that the elasticity of a distended bladder can be felt. (10) Usually the lowest of the transverse folds (folds of Houston), semilunar in form and about 1.2 cm. (J in.) in width, can be made out (fig. 1116). (11) Behind, the coccyx and its degree of pliability and the lower part of the sacrum. It may also be possible to feel enlarged sacral nodes and a growth from the other pelvic bones. The above examination refers chiefly to the male.^ It remains to refer to rectal examination in the female. Anteriorly, the soft perinseal body and recto-vaginal septum will be met with, and, through the latter, the cervix and os uteri, and, higher up, the lower part of the cervix uteri. More laterally the ovaries may be felt, but the uterine or Fallopian tubes, unless enlarged and thickened, are not to be made out. The student should be familiar with the feel of a healthy recto-uterine or recto-vesical pouch, according to the sex, and the coils of intestine which it may contain, so as to be able to contrast this with any collection of inflammatory or other fluid or mischief descending from the upper pelvis, e. g., from the vermiform appendix. Pos- teriorly, certain structures are met with in either sex. After a very short interval (sphincter and ano-ooccygeal body) the finger reaches the tip of the coccyx and explores the hollow of the sacrum. On each side are the ischial tuberosity and wall of the true pelvis. The finger hooked lateralward and upward, comes on the border of the falciform process of the sacro- tuberous (great sacro-sciatic) ligament, passing between the above-mentioned bones. FEMALE GENITAL ORGANS The external organs will be considered first, followed by the internal. Under the external organs are included, for convenience sake, the labia majora and minora at the sides; and, in the middle line, from above downward — (1) The glans clitoridis with its prepuce; (2) the vestibule; (3) the urethral orifice; (4) the * H. Hartmann. Annals of Surgery, Dec, 1909. 1392 CLINICAL AND TOPOGRAPHICAL ANATOMY vaginal orifice with the hymen or its remains; (5) the fossa navicularis; (6) the fourchette; (7) the sldn over the base of the perineal body. These parts have been described elsewhere, and only those points which are of importance in a clinical examination will be alluded to here. The labia majora are two thick folds of skin, covered with hair on their outer surface, especially above, where they unite {anterior com7nissure) in the mons Veneris. They contain fat, vessels, and dartos, but become rapidly thinner below, where they are continuous at the front of the perineum (their posterior commissure). When the above folds are drawn aside, the labia minora, or nymphae, appear, not projecting, in a healthy adult, beyond the labia majora. They are small folds of skin, which meet above in the prepuce of the clitoris, and below blend with the labia majora about their centre. Sometimes, especially in nulliparae, they unite posteriorly to form a slight fold, the fourchette. The glans clitoridis, covered by its prepuce, occupies the middle line above. Below it comes the vestibule, a triangular smooth surface of mucous mem- brane, bounded above by the clitoris, below by the upper margin of the vaginal orifice, and laterally by the labia minora. In the middle line of the vestibule and toward its lower part, about 12 mm. (J in.) below the glans clitoridis, and 25 mm. (1 in.) above the fourchette, is the meatus or opening of the urethra (figs. 1034, 1037). The vaginal orifice lies in the middle line between the base of the vestibule above, and the fossa navicularis below. Its orifice is partially closed in the virgin by a fold of mucous membrane, the hymen (fig. 1037). This is usually crescentic in shape attached below to the posterior margin of the vaginal orifice, and with a free edge towards the base of the vestibule. In some cases it is diaphragmatic i. e. attached all around, but perforated in the centre (fig. 1037). The schrivelled remains of the hymen probably constitute the carunculse hymenales. On either side of the vaginal orifice, at it lower part, lie the racemose, muciparous, vestibular glands (glands of Bartholin), situated beneath the super- ficial perineal fascia and sphincter vaginae. Their ducts run slightly upward and open, external to the attachment of the hymen, within the labia minora. In relation to the upper two-thirds of the vaginal orifice, placed between the uro- genital diaphragm behind and the sphincter vaginae in front, are the vascular bulbs of the vestibule, rupture of which produces pudendal hfematocele. Fourchette and fossa navicularis. — The fourchette, as stated above, is the posterior commissure of the labia minora. Normally the inner aspect of this is in contact with the lower surface of the hymen. When the fourchette is pulled down by the finger, a shallow depression is seen, the fossa navicularis, with the fourchette for its posterior, and the hymen for its anterior, boundary. Internal organs. — The examinations through the vagina and anus will be considered first, followed by uterus and appendages, ovary and ureter. Examination per vaginam. — The finger, introduced past the gluteal cleft, perineum, and fourchette, comes upon the elliptical orifice of the vagina, and notes how far it is patulous or narrow; the presence or otherwise of any spasm from the adjacent muscles; then, passing into the canal itself, the presence or absence of rugae, a naturally moist or a dry condition are observed. In the anterior wall the cord-like urethra can be rolled between the finger and the symphysis ; and further up than this, if a sound be passed, the posterior wall of the bladder. The anterior wall of the vagina is about 6.7 cm. (2| in.) long. The posterior wall, 7.5 cm. (3 in.) long, forms the recto-vaginal septum, and through it any faeces present in the bowel are easily felt. The cervix uteri is next felt for in the roof of the vagina, projecting downward and backward in a line drawn from the umbilicus to the coccyx. Besides its direction, its size, shape, mobility, and consistence should be noted. The os uteri should form a dimple or fissure in the centre of the cervix. Of its two lips, the posterior is the thicker and more fleshy feeling of the two. The vaginal culs-de-sac or fornices are next explored. These should be soft and elastic, giving an impression to the finger similar to that when it is introduced into the angles of the mouth. Any resistance felt here may be due to scars, swellings connected with the uterus (displacements or myomata), effusions of blood or inflammatory material, and, in the case of the lateral culs-de-sac, a displaced or enlarged ovary, or dilatations of the Fallopian tubes. The posterior cul-de-sac is much deeper than the anterior, and, owing to the peritoneum THE OVARY 1393 descending upon the posterior wall of the vagina, when the finger is placed here it is only separated from the peritoneal sac by the vaginal wall and pelvic fascia. In examination of the pelvic organs the bimanual method, by which one hand on the hypogastric region, pushes them down and steadies them as well, is always to be employed to complete an examination. The uterus and appendages. — The normal non-gravid uterus is usually anteflexed and anteverted so as to lie with its long axis approximately at right angles to that of the vagina. Its position varies considerably with the degree of distention of the bladder in front and of the rectum behind. The distance from external os to fundus, as estimated by the passage of a sound is in the adult virgin uterus 5.5 cm. of which 3 cm. belong to the cervix and 2.5 cm. to the body. In the empty multiparous uterus the total length of the cavity is 6 cm., 2.5 cm. comprising the neck and 3.5 cm. the body. Peritoneal relations. — In front the peritoneum is reflected from the uterus to form the utero-vesical pouch at the level of the isthmus. Behind it covers not only the uterus but the posterior fornix of the vagina, before turning off onto the front of the rectum. Laterally the peritoneum leaves the uterus and passes on to the lateral pelvic wall as a large twofold partition fig. 1118), the broad ligament. Fig. 1118. — Sagittal Section of the Bhoad Ligament. Graafian follicles of ovary Mesovarium Mesometrium Posterior surface Uterine veins Base of ligament The broad ligament, bearing in its upper border the uterine tube, in front the round ligament and behind the ovary, consists of (1) an upper thin part, the mesosalpinx lying above the attachment of the mesovarium, and containing the ovarian vessels and the epoophoron, and below this (2) the thicker mesometrium, between the layers of which is a dense mass of fibrous tissue surrounding the uterine artery. The anterior aspect of the cervix below the utero-vesical pouch of peritoneum, is readily separable from the bladder with which it lies in contact, and the peritoneum may be raised oil the uterus with ease in the lower part of its attachment both front and back. Over the upper part of the body and fundus, however, the peritoneal covering is firmly adherent, and cannot be dissected off. The ovary, attached by its hilum to the mesovarium, lies in a fossa at the back of the lateral wall of the pelvis just between the diverging external ihac and hypogastric vessels. To feel it the finger should be pushed well up in the side of the vagina toward the lateral wall of the pelvis. On the abdominal surface its position corresponds to the middle of a line drawn from the anterior superior ihac spine of that side to the opposite pubic tubercle (Rawlings). 1394 CLINICAL AND TOPOGRAPHICAL ANATOMY The lymphatics of the ovary follow the ovarian veins (see p. 745). Supports of the uterus. — The great mobility of the body of the uterus has been referred to above. The organ derives its support almost entu'ely from the attachments of the cervix and vaginal fornices. These rest on the pelvic floor, formed by the levator ani and perineal body which support them the more efficiently since the long axis of the vagina is at right angles to that of the uterus. Above the pelvic diaphragm the cervix is held up to the pelvic walls by strong specialised bands of fibro-muscular tissue running in both antero-posterior and trans- verse directions. The chief of these, lying in the base of the broad ligaments is a fibrous sheath sm-rounding the uterine artery as it descends medially from the hypogastric. In the antero- posterior direction the utero-vesical ligaments hold up the cervix to the pubes in front and the sacro-uterine ligaments bind it to the anterior aspect of the sacrum behiind. While firmly supporting the uterus these bands are elastic, and so do not fix it rigidly, but allow of the cervix being drawn downward by traction with vulsellum forceps. For lymphatics of uterus and vagina see p. 745. The ureter. — The pelvic portion of this duct is of special importance in opera- tions on the uterus and upper vagina. It crosses the brim of the pelvis on either side at the biftu-cation of the common ihac artery, or just in front of it, and descends on the side waU in front of the hypogastric artery, crossing the ob- literated umbilical 'and obturator arteries. Curving forward and medially it passes under the base of the broad ligament, where the uterine artery crosses above it, and so gains the lateral angle of the bladder by passing across in rela- tion to the lateral fornix of the vagina. In the base of the broad ligament the ureter lies about 2 cm. (f in.) from the side of the cervix, and this relation must be borne in mind in excision of the uterus. Pelvic floor. — The pelvic floor of the female corresponds in general to that of the male (see p. 1383). There are, however, important differences, due to the sexual organs. The urogenital diaphragm is relatively smaller in area, due to per- foration by the vagina. The pelvic diaphragm is also correspondingly modified, and the pubo-coccygeus component is more strongly developed (see section on Musculature.) The ischio-rectal fossa is similar to that of the male (p. 1384). HERNIA Three varieties of hernia will be considered, inguinal, femoral, and umbilical PARTS CONCERNED IN INGUINAL HERNIA In inguinal hernia, as in femoral and umbilical, there is a weak spot in the ab- dominal wall — one weakened for the needful passage of the testicle from within to outside the abdomen (p. 1387). The parts immediately concerned are the two inguinal rings, subcutaneous (external) and abdominal (internal), and the canal. Now, it must be remembered at the outset that the rings and canal are only potential — they do not exist as rings or canal save when opened up by a hernia, or when so made by the scalpel. The canal is merely an oblique slit or flat-sided passage. The subcutaneous and abdominal rings are so intimately blended with the structures that pass through them, and so filled by them, that they are potential rings only. The subcutaneous inguinal (external abdominal) ring. — This is usually described as a ring : it is really only a separation or gap in the aponeurosis of the external oblique, by which in the male the testicle and cord, and in the female the round ligament by which the uterus is kept tilted a little foward, pass out from the abdomen. The size of this opening, the development and strength of its crura or pillars, the fascia closing the ring — all vary extremely. Formation : by divergence of two fasciculi of the external oblique aponeurosis. Boundaries : two crura — (1) Superior, the smaller, attached to the symphysis and blending with the suspensory ligament of the penis; (2) inferior, stronger, attached to the pubic tubercle and blending with the inguinal ligament, and so with the fascia lata. On this inferior, stronger crus rests the cord (and so the weight of the testicle) or round ligament. Shape : triangular or elliptical, with the base downward and medially toward the pubic crest. Intercrural fibres (intercolumnar fascia) (external spermatic fascia). — This, derived from the lower part of the aponeurosis of the external oblique, ties the two crm'a together, and, being continued over the cord, prevents there being any ring here, unless made with a scalpel. This is the rule in the body: when any structure passes through an opening in a fibrous or muscular INGUINAL HERNIA 1395 layer, it carries with it a coating of tissue froro that layer; e. g., the inferior cava passing through its foramen in the diaphi-agm, and the membranous uretlu-a thi'ough the uro-genital diaphragm. Effect of position of the thigh on the ring.— As the lower crus is blended with Poupart's hgament, and as the fascia lata is connected with this, movements of the thigh will affect the rmg much, making it tighter or looser. Thus extension and abduction of the thigh stretch the crura and close the ring. In flexion and adduction of the thigh the crura are relaxed; and this is the position in which reduction of a hernia is attempted. In flexion and abduction of the thigh, the rmg is open; and this is the position in which a patient should sit, with thighs widely apart, to try on a tru.ss, and cough or strain downward, as in rowing. If the hernia is now kept up, the truss is satisfactory. _ Helping to protect this most important spot, and preventing its being more than a potential rmg, are not only the two crura and the intercrural fibres, but also a structure which has been called a thu-d or posterior pillar, namely, the reflected inguinal ligament. This has its base above at the lower part of the linea alba, where it joins its fellow and the aponeurosis of the external oblique, and its apex downward and laterally, where, having passed behind the medial crus it blends with the lacunar (Gimbernat's) ligament. Again, the falx inguinalis (the con- FiG. 1119. — The Parts concerned in Inguinal Hernia. (From a dissection in the Hunterian Museum.) External oblique, cut and turned back Internal oblique External oblique Falx inguinalis Poupart's (inguinal) hgament Reflected inguinal ligament joined tendon of the internal oblique and transversahs), curving mediaUy and downward to be attached to the ilio-pectmeal hne and spine, is a most powerful protection, behind, to what 13 otherwise a weak spot and a potential ring. Inguinal canal.— This is not a canal in the usual sense, but a chink or flat- sided passage m the thickness of the abdominal wall. The descriptions of the canal usually given apply rather to the diseased than to the healthy state. It was a canal once, and for a time only, i. e., in the later months of fcetal life (p. 1387). It remains weak for a long time after, but only a vestige of it remains in the well- made adult. Length.— In very early life there is no canal; one ring lies directly behind the other, so as to facilitate the easy passage of the testis. In the adult it measures about 37 mm. (l^ in.) in length, this lengthening being brought about by the growth and separation of the alse of the pelvis. This increased obliquity gives additional safety. On the other hand, a large hernia has not only opened \^^dely the canal and rings, but it has pulled them close together, and one behind the other thus not only rendering repair much more difficult, but also the path to the 1396 CLINICAL AND TOPOGRAPHICAL ANATOMY peritoneal sac shorter and more direct. Direction.— From the abdominal to the subcutaneous ring, downward, forward, and medially. -^ • in , Boundaries.— For convenience sake, certain hmits (largely artifacial) have been named : — , , , i, i j. iu (1) Floor. — This is best marked near the outlet, where the cord rests on the grooved upper margin of the inguinal (Poupart's) and the lacunar (Gimbernat's) lio-ament. The meeting of the transversalis fascia with this hgament forms the floor (2) i?oo/.— The apposition of the muscles and the arched border of the internal oblique and transversus. (3) Anterior wall— Skin, superficial fascia, external oblique for all the way. Internal oblique, i. e., that part arising from Poupart's ligament, for the lateral third or so. To a slight extent, the trans- versus and the cremaster. (4) Posterior wall.—For the whole extent, transversalis fascia, extraperitoneal tissue, and peritoneum. For the medial two-thirds, con- joined tendon of internal oblique and transversus, and the lateral edge of the reflected inguinal hgament, when developed. Fig. 1120. — Dissection of Inquinai, Canal. (Wood.) ^ %%\W , ^' External oblique, (turned down) 11 > Internal oblique Transversus Falx inguinalis (con- VTMW 1 I joined tendon) \ VWi I I Reflected ligament ^■— ^-^ 1 j (triangular fascia) Cremaster The transversalis fascia is thicker and better marked at its attachments below; these are- fa) laterally, to medial lip of iliac erest; (b) to the ingmnal ligament between the anterior- superior spine and the femoral vessels, where it joins the fascia ihaca; (c) opposite the femoral vessels it Tlso joins the fascia iliaca, and forms with it a funnel-shaped sheath; (d) mecbal to the femoral vessels the fascia transversalis is attached to the terminal (.^'l°-Pe«t>,^^f ) J^^^' ^^^J^f, the conjoined tendon, with which it blends. The falx ingmnahs {conjoined tendon) needs special reference It is foriied by the lower fibres of the internal oblique and transversus (arciform fibres) arching downward over the cord to be inserted into the crest and spme and the termmai aho-pectineal) line. The fibres of the internal oblique become increasingly tendmous as they descend, and this, with the fact that below they give off the cremaster, may «ause some difficulty in theh- identification when it is desked to unite them to the upper surface of Poupart s liga- ment in the operation of radical cure. The abdominal inguinal (internal abdominal) ring.— It has already been said that the term 'ring' is here misapplied except in an artiflcial sense, as when an opening is made by a scalpel; or in abnormal conditions when a hernial sac is present. The abdominal ring is not a ring in the least, but merely a tunnel- shaped expansion of the transversahs fascia, which the cord carries on with it as it escapes from the abdomen. INGUINAL HERNIA 1397 Site. — Midway between the anterior superior iliac spine and pubic tubercle. Shape : oval, with the long diameter vertical. Boundaries : centre of inguinal (Poupart's) ligament, about 12 mm. (| in.) below. Medially, the inferior epigastric artery (fig. 1121); the position of this vessel, by its pulsation, is an im- portant guide to the insertion of the highest sutures between the arciform fibres and the inguinal ligament. Owing to the artery lying to the medial side, the incision, in cutting to relieve the deep constriction of an inguinal hernia, should always be made directly upward, so as to avoid the above vessel. A large ob- lique hernia may so have altered the relations of the parts, including the artery, that it is difficult to decide whether the hernia is oblique or direct. The above incision will be safe, because, iia either case, parallel to the vessel. Coverings. — There are two chief forms of inguinal hernia : — A. The cominon form: lateral, or oblique. — Lateral, because it appears (at the abdominal ring) lateral to the inferior epigastric artery. Oblique, because it traverses the whole of the inguinal canal, entering it at its inlet and leaving it at its outlet. This form is usually congenital in origin, and is due to non-obliteration of the processus vaginalis in infancy. Fia. 1121. — Dissection of the Lower Part of the Abdominal Wall from within, the Peritoneum having been removed. (Wood.) order of the poste- rior part of the sheath of the rec- tus (fold of Doug- Fascia transversal- -^ ■ — ^ Inferior epigastr: artery Ductus (vas) deferens Spermatic vessels Obliterated hypo- gastric artery "■ Lymphatics in femoral ring External iliac artery B. Rarer form : medial, or direct. — Medial, because it appears medial to the inferior epigastric artery. Direct, because, instead of making its way down the whole oblique canal, it comes by a short cut, as it were, only into the lower part of the canal, and then emerges by the same opening as the other. A. Oblique inguinal hernia. — This possesses its coverings as follows: — (1) At the abdominal ring, or inlet, it obtains three: — (a) Peritoneum; (6) extra-peritoneal fat; (c) iiifuiidibuliform fascia, or the vaginal process of transversalis fascia prolonged at this spot along the cord. (2) In the canal it obtains one. As it emerges beneath the lower border of the internal oblique it gets some fibres from the cremaster. (3) At the subcutaneous ring, or outlet, the hernia obtains three, viz.: (a) Intercrura fibres (interoolumnar fascia) ; (b) superficial fascia; and (c) skin. B. Direct inguinal hernia. — This does not come through the abdominal ring, but,«making its waj' through the posterior wall of the lower third of the canal, either through the medial or intermediate inguinal fossa. Its coverings, therefore, vary slightly with its mode of exit (vide infra). Hitherto the two forms of inguinal hernia have been considered from the superficial aspect, that in which they are met with in practice. The inguinal region should also be studied as to 1398 CLINICAL AND TOPOGRAPHICAL ANATOMY the posterior aspect of its so-called rings and canal, as these have to bear the early stress of a commencing hernia. It is against this aspect that a piece of omentum or intestine is constantly and insidiously pressing and endeavoui'ing to make its way out. Furthermore, when either of the above constituents of hernia have made their way a little farther, and got out into the ab- dominal ring or into the canal, the patient is no longer sound. On the posterior wall are certain cords and depressions, marking off regions which corre- spond to those on the surface. Thus, there are three prominent cords and three fossae (fig. 1121). Three cords — (1) Median, or urachus; (2) lateral, or the obliterated hypogastric arteries. (1) Median, or urachus. This interesting foetal relic, the intra-abdominal part of the allantois, passes up between the apex of the bladder and the umbilicus. (2) The obliterated hypogastric arteries. These, the remains of vessels which during foetal life carry the impure blood of the foetus out to the mother through the umbilicus, run up and join the urachus at the umbilicus. In relation to these cords are the following fossae : — (a) A medial one, between the virachus and the obliterated hypogastric artery. This corresponds, on the anterior surface, to the subcutaneous inguinal (external abdominal) ring. Through this fossa comes the commonest form of direct inguinal hernia, (ft) Between the obliterated hypogastric artery and the inferior epigastric artery, which runs upward and medially to form the lateral boundary of Hessel- bach's triangle, is an intermediate fossa. This is the smallest of all. The rarer form of direct hernia comes tlirough here, (c) The lateral fossa is lateral to the inferior epigastric artery. It is the most distinct of the three, from the way in which the cord or round ligament passes down within a glove-like vaginal process of the transversalis fascia. This fossa corresponds to the abdominal ring. The coverings of a direct hernia may now be considered, together with the two-fold manner of exit of this hernia. It only traverses the lower part of the canal, making its way through either the medial or the intermediate inguinal pouch, (i) The commonest form, coming through the medial inguinal pouch, either pushes its way through or stretches before it the falx inguinalis. Its coverings are: — (1) Peritoneum; (2) extra-peritoneal fat; (3) transversalis fascia; (4) falx inguinalis (unless this is suddenly burst through); (5) (6) (7). At the subcutaneous ring the three coverings are the same as in the oblique variety, (ii) This rarer form of direct hernia comes through the intermediate inguinal pouch. As a rule, the falx inguinalis does not reach over this fossa. The coverings will be the same as in the last, with two exceptions — there is no falx inguinalis, and the cremasteric fascia, if well developed, will be present. Varieties of inguinal hernia according to the condition of the vaginal process of peritoneum. — Inguinal herniEe have above been classified according to tlieir relation to the deep epigastric artery. It remains to allude to the arrangement of these same hernias according to the varying condition of the processus vaginalis. This pouch of peritoneum, which paves the way for the passage of the testis before this organ makes its start, eventually becomes the parietal layer (p. 1387) of the tunica vaginalis below, in this fashion: During the first few weeks after birth the process becomes obliterated at two spots — one near the abdominal ring, and one just above the testis. The obliterative process, commencing first above and descending, and then, ascending from below, the shrivelling continues until nothing is lett save the tunica vaginalis below. The following are possible hernial results of an imperfect obliteration of the process: — (1) If the process does not close at all, a descending hernia is called congenital. This may make its way into the scrotum. The testis is now enveloped and concealed by the hernia. (2) If the process is closed only above, i. e., near the abdominal ring, two varieties may be met with, the infantile and the infantile encysted. In the infantile, owing to pressure above, the weak septum gradually yields and forms a sac behind the unobliterated lower part of the pro- cessus funiculo-vaginalis. Thus three layers of peritoneum may now be met with in an opera- tion, the two of the incompletely obliterated tunica vaginalis, and the proper sac of the hernia. In the encysted infantile variety the hernial pressure causes the septum to yield and form a sac projecting into, not behind, the incompletely obliterated tunica vaginalis. Here, theoretically, two layers of peritoneum will be met with. Another variety of such an encysted hernia may be produced by rupture, not stretching, of the above-mentioned septum. (3) If the processus vaginalis be closed below and not above, a patent tubular process of peritoneum will lead down as far as the top of the testis. Any hernia into this process is called a hernia into the funicular process. All these varieties save the congenital and hernia into the funicular process are rare in practice. Other practical points are that all hernise in children and young adults are probably of congenital origin, and, therefore, the weakness is often bilateral, though it may not be so palpably. This applies to both sexes. Again in hernia of sudden origin into the funicular process with narrow surroundings, strangulation may be very acute. Inguinal hernia in the female. — The inguinal canal in women is smaller and narrower than in men. Inguinal hernia is, therefore, less common in the female sex, and occurs in patients who happen to be tlie subjects of an unobliterated processus vaginalis, which extends for a varying distance along the round ligament, and is called the canal of Nuok. Inguinal hernia in the female is, therefore, always congenital. It is, practically, always of the oblique variety, and travels along the round ligament toward the labium majus. Its coverings will be the same as those of the oblique variety in the male, save that the cremaster, as a distinct muscle, is absent, and any fibres of the internal oblique which may be present are but little developed. FEMORAL HERNIA Parts concerned in femoral hernia. — (1) Skin and superficial fascia of groin. — The latter consists of two layers: (a) Superficial layer of superficial fascia. — Fatty, met with over the whole groin, and continuous with the superficial fascia FEMORAL HERNIA 1399 of the rest of the body, (b) Deep layer of superficial fascia. — Thin and mem- branous, only met with over the lower third of the abdominal wall and to the medial side of the groin. It is continuous through the scrotum with the deep layer of the superficial fascia of the perineum. Just below the inguinal hgament it is joined to the fascia lata. From these two facts it results that in rupture or giving way of the urethra the extravasated urine may come forward by way of the genitals (p. 13S5) and from the continuity of the fascia make its way on to the abdomen, but not down on to the thigh. Between the two layers of superficial fascia lie the superficial nodes of the groin, the super- ficial branches of the common femoral artery, one or two cutaneous nerves, and some veins descending to the fossa ovahs to join the great saphenous vein. (2) Inguinal (Poupart's) ligament. — This is also known as the crural arch, a misnomer, as 'crus' means leg. A description of its shape and attachments is given on p. 1371. Owing to the connection of the fascia lata to its lower border, the fossa ovalis (saphenous opening), which is situated in the fascia lata, and has its upper cornu blending with the inguinal ligament, will be affected by movements of the thigh, much as is the subcutaneous inguinal (external abdominal) ring, being tightened and stretched when the limb is extended and abducted, relaxed when it is adducted and flexed. Fig. 1122. — The LAnrNi? ekneath the Inguinal Ligament. (Lookwood.) — ■ Inguinal ligament Muscular lacuna Ilio-pectineal Hgament^l 1 \ \ \ Vascular lacuna Hio-pectineal eminenc Cooper's ligament Lacunar ligament Spermatic cord The parts beneath the ligament which block up the gap between it and the innominate bone are of the utmost importance in preventing the escape of a femoral hernia (fig. 1122). The different structures are arranged in three compartments (fig. 1122), named latero-medially : — A. lateral, iliac, or muscular; B. central, or vascular; and C. medial, or pectineal. Of these, the first is the largest; the second or intermediate one lies slightly nearer to the inguinal ligament than the other two ; while the medial compartment differs from the other two by not communicating with the pelvis, being closed above {vide infra). (A) The lateral, or iliac, compartment is bounded in front by the inguinal ligament and the iliac fascia, which is here blending with it, behind by the ihum, laterally by this bone and the sartorius, and medially by the ilio-pectineal septum, which, descending from the blending of , the iliac fascia and the inguinal ligament above, passes down to the iUo-pectineal eminence, and thence to the medial aspect of the front of the capsule of the hip-joint. This compartment transmits the ilio-psoas and femoral (anterior crural) and lateral cutaneous nerves. (B) The vascular compartment is bounded, in front, by the inguinal ligament and the transversahs fascia, which here blends with it, forming the so-called deep crui'al arch, and at the same time 1400 CLINICAL AND TOPOGRAPHICAL ANATOMY descends on to the front of the femoral sheath. The posterior boundary, Cooper's ligament, is formed by the meeting of the ilio-pectineal septum laterally and the pectineal fascia or sheath — medially the lacunar (Gimbernat's) ligament, and laterally the ilio-pectineal septum. This intermediate compartment transmits the ex ernal iliac vessels and the lumbo-inguinal nerve. This lies to the lateral side of the artery, the vein medially. Between the vein and the base of the lacunar ligament is the femoral canal (vide infra). (C) The medial or pectineal compart- ment is bounded by the pectineal fascia, continuous with the pubic part of the fascia lata, and behind by the pubic ramus. It lodges the upper end of the pectineus muscle, and the handle of a scalpel passed upward along the muscle would be prevented from passing into the pelvis by the lacunar ligament and the blending of the pectineal fascia with the upper border of the pubic ramus. (3) Lacunar (Gimbernat's) ligament. — This is merely tlie triangular medial attachment of Poupart's ligament. Its apex is attached to the pubic tubercle; of its three borders, the base is free toward the vein and the femoral canal. Its upper border is continuous with Poupart's ligament; its lower is attached to the terminal (ilio-pectineal) line. (4) Fascia lata. — Two portions are described over the upper part of the thigh : ■ — (a) An iliac, lateral and stronger, attached to the inguinal ligament in its whole extent and lying over the sartorius, ilio-psoas, and rectus. (6) A pubic, medial, weaker, and much less well defined, is attached above to the terminal line and the tubercle of the pubes. The upper cornu of the fossa ovalis is at the lacunar ligament, and at the lower cornu the two portions of the fascia blend. Their relation to the femoral vessels. — The iliac portion, being attached along Poupart's ligament, passes over these. The pubic portion, fastened down over the pectineus, which slopes down on to a deeper plane than the adjacent muscles, passes behind the femoral vessels to end on the capsule of the hip-joint. (5) Fossa ovaUs (saphenous opening). — This is not an opening, but an oval depression, situated at the spot where the two parts of the fascia lata diverge on different levels. Though the fascia lata is wanting here, there is no real opening, as the deficiency is made up by the deep layer of superficial fascia, or cribriform fascia, which fills up the opening. Uses of the fossa ovalis {saphenous opening). — Though a weak spot, it is so on purpose to transmit the saphenous to the femoral vein, and the superficial to the deep lymphatics. The depression is present in order to allow the saphenous vein to be protected from pressure in flexion of the thigh. Site. — At the medial and upper part of the thigh, with its centre 3.7 cm. (1 J in.) below and lateral to the tubercle of the pubis. Diameters. — Vertically, 2.5 cm. (1 in.), by 1.2 or 1.8 cm. (| or f in.). Shape: oval, with its long axis downward and laterally. Two exlremities or cornua: upper blending with the lacunar ligament; lower, where the two parts of the fascia lata meet. Two borders: lateral or falci- form, also known as the ligament of Hey, or femoral ligament. Semilunar in shape, arching downward and laterally from the lacunar ligament to the inferior cornu. This lies over the femoral vessels, and is adherent to thezn; to it is fixed superficially the cribriform fascia {vide infra). The medial border is much less prominent, owing to the weakness of the pubic part of the fascia lata which forms it. (6) Femoral sheath. — This is a funnel-shaped sheath, carried out by the femoral vessels under Poupart's ligament, and continuous above (in front) with the transversalis fascia as it descends to the ligament, lining the inner surface of the abdominal wall; and (behind) with the iliac fascia, and below continuous with the proper sheath of the femoral vessels. It is not only funnel-shaped, but large and loose, for two reasons: — {a) That there be plenty of room for the femoral vein and the slowly moving venous current in it to ascend without com- pression; (b) to allow all the movements of the thigh taking place — flexion and extension — without undue stretching of the vessels. By two connective-tissue septa the sheath is divided into three compartments — the lateral for the artery, the intermediate for the vein, and the medial one for the femoral canal {vide infra). Thus one septum lies between the artery and vein, and another between the vein and the femoral canal. (7) Femoral canal. — Definition: the medial division of the femoral sheath. The fascia transversalis and fascia iliaca meet directly on the lateral side of the femoral artery, but not so closely on the medial side of the femoral vein. Hence a space exists here, perhaps to prevent the thin-walled vein, with its sluggish current, being pressed upon, but it is merely a slight gap — not a canal, unless so made by a knife or by the dilating influence of a hernia. Length: about 1.9 cm. (J in.). Limits: below, fossa ovalis; above, femoral ring {vide infra). FEMORAL HERNIA 1401 Boundaries. — Laterally, a septum between it and the vein; medially, base of the lacunar ligament and meeting of fascia iliaca and transversalis; behind, fascia iliaca; in front, fascia transversalis. Contents. — Cellular tissue and fat, continuous with extra-peritoneal fatty layer. A lym- phatic node, which is inconstant.' Lymphatics passing from inguinal nodes to those in the pelvis. (8) Femoral ring. — This is mainly an artificial product. It is the upper or abdominal opening of the femoral canal. Shape: oval, with its long axis trans- verse. It is larger in women. Boundaries: medially, the lacunar ligament; laterally, the femoral vein; in front, the inguinal ligament and the thickening of the transversahs fascia attached to it, and called 'the deep crural arch'; behind the pectineus and Cooper's ligament, a thickened fascial bundle attached Fig. 1123. — Irregulahities of the Obturator Artery. (After Gray.) A External iliac artery External iliac vein Obturator foramen — Inferior epigastric artery Lymphatic node in femoral ring The obturator artery, given off from the external iliac with the inferior epigastric, descends to gain the obturator foramen, but at a safe distance from the The obturator artery, coming off from the inferior epigastric, takes a course so near to the femoral ring that it would very likely be divided by the bis- toury introduced from without to divide the base of the lacunar ligament, the cause of the con- strictioii to the hnea terminalis (fig. 1122). It is closed by the septum crurale, which is a barrier of fatty connective tissue, continuous with the extra-peritoneal fatty layer, perforated by lymphatics passing upward to the pelvic nodes. Position of vessels around the ring. — Laterally the femoral vein; above, the epigastric vessels as they ascend from the external iliac vessels, pass close to the upper and lateral aspect of the ring; immediately in front are the cord and sper- matic vessels always to be remembered in this hernia in the male; toward the medial side there may be an unimportant anastomosis between the epigastric artery above and the obturator below. If from dilatation of the above anastomosis the obturator artery comes off abnormally from the inferior epigastric, it will descend, and usually does so, close to the junction of the ex- ternal iliac and common femoral vein, and thus to the lateral and so the safe, side of the ring (fig. 1123, A). In a very few cases it curves more mediallj', close to the lacunar ligament, and thus to the medial side of the ring, and is then in great danger (fig. 1123, B). In two out of 1402 CLINICAL AND TOPOGRAPHICAL ANATOMY every five cases the obturator arises from the inferior epigastric. In about thirty-seven per cent, of the eases with such an origin the artery either crosses or courses along the side of the ring. (Cunningham.) Course of femoral hernia. — At first this is downward in the femoral canal. A pouch of peritoneum having been gradually, after repeated straining, coughing, etc., pushed through the weak spot, the femoral ring, further weakened perhaps, together with all the parts in the fem- oral arch, by child-bearing, some extra effort will force intestine or omentum into this pouch and thus form a hernia. Thus formed, femoral hernia passes at first downward in the femoral canal as far as the fossa ovaUs, but, as a rule, does not go farther downward on the thigh, but mounts forward and upward, and somewhat laterally, even reaching the level of the inguinal ligament. The reasons for this change of position are: — (1) The narrowing of the femoral sheath, funnel- like, i. e., wide above, but narrowed below; (2) the unyielding nature of the lower margin of the fossa ovalis; (3) the fact that this margin and the lateral border are united to the femoral sheath; (4) the constant flexion of the thigh; (.5) the fact that vessels (cliiefly veins) and lymphatics descend to the fossa ovaUs, the veins to join the saphenous vein and the lymphatics to join the deeper group; these descending vessels serve to loop upward or suspend a femoral hernia, and thus prevent its further course downward. Coverings of a femoral hernia. — (A) At the upper or femoral ring it obtains peritoneum, extra-peritoneal fat, and septum femorale (crurale). (B) In the canal, a coating of the femoral sheath. (C) At the external opening, further coverings of cribriform fascia, skin, and superficial fascia are added. Some of these may be deficient by the hernia bursting through them, or they may be matted together. Sir A. Cooper thought this especially likely to occur with the layer of femoral sheath and septum crurale, to which he gave the name oi fascia propria. The relations of an inguinal and femoral hernia respectively to the pubic tubercle are of importance in distinguishing between them clinically. If a finger is placed on the pubic tubercle a hernia that lies above and medial to it will be inguinal, one below and lateral to it wiU be femoral. Radical cure of femoral hernia. — The close proximity of the femoral vein always intro- duces difficulty in the introduction of the deep sutures for closure of the crural ring. Any clo- sure below this point is certain to be inefiicient. The safest and simplest method is to feel for the pulsation of the femoral artery, and make allowance for the vein on its medial side. The latter vessel is then protected by the finger-tip passed up the femoral canal, so that its dorsum rests against the vein and its tip upon the linea terminalis. The sutures are then passed so as to pick up the ilio-peotineal fascia and its thickened part. Cooper's ligament, below, and the deep crural arch and Poupart's ligament above (fig. 1122). Thus, when tightened, they draw the anterior and posterior boundaries of the ring together. (Lockwood, Bassini.) PARTS CONCERNED IN UMBILICAL HERNIA A hernial protrusion at the umbilicus, or exomphalos, may occur at three distinct periods of life, according to the anatomy of the part. Any account of umbilical hernia would be incomplete without an attempt to explain how this region, originally a most distinct opening, is gradually closed and changed into a knotty mass of scar, the strongest point in the abdominal wall. During the first weeks of foetal life, in addition to the urachus, umbilical arteries, and vein, some of the mesentery and a loop of the intestine pass through the opening to occupy a portion of the body cavity situated in the umbilical cord, later on returning to the abdominal cavity. Occasionally this condition persists, owing to failure of development, and the child is born with a large hernial swell- ing outside the abdomen, imperfectly covered ^vith skin and peritoneum. To tlais condition the term congenital umbilical hernia should be applied. Later on in foetal life it is the umbilical vessels alone which pass through this opening. At birth there is a distinct ring, which can be felt for some time after in the flaccid walls of an infant's belly. If this condition persist, a piece of intestine may find its way through, forming the condition which should be known as infantile umbilical hernia. This condition is not uncommon. Why it is not more frequently met with is explained by the way in which this ring of infancy is closed and gradually converted into the dense mass of scar tissue so familiar in adult life. This is brought about — (1) by changes in the ring itself; (2) by changes in the vessels which pass through it. (1) Changes in the ring itself. — The umbilical ring is surrounded by a sphincter-like arrangement of elastic fibres, best seen during the first few days of extra-uterine life, on the THE BACK 1403 posterior aspect of the belly wall. In older infants these fibres lose their elasticity, become more tendinous, and then shrink more and more. As they contract they divide, as by a liga- ture, the vessels passing through the ring, thus accounting for the fact that the cord, wher- ever divided, drops off at the same spot and without bleeding. (2) Changes in the vessels themselves. — When blood ceases to traverse these, their lumen contains clots, their muscular tissue wastes, while the connective tissue of their outer coat hypertrophies and thickens. Thus, the umbilical vessels and the umbilical ring are, alike, converted into scar tissue, which blends together. This remains weak for some time, and may be distended by a hernia (infantile). Finally, we have to consider the state of the umbilicus in adult life. The very dense, unyielding, fibrous knot shows two sets of fibres: — (1) Those decussating in the middle line; and (2) two sets of circular fibrous bundles which interlace at the lateral boundaries of the ring. The lower part of the ring is stronger than the upper. In other words, umbilical hernia of adult life, when it comes through the ring itself and not at the side, always comes through the upper part. In the lower three-fourths of the umbilicus the umbihcal arteries and urachus are firmly closed by matting in a firm knot of scar tissue; in the upper there is only the umbil- ical vein and weaker scar. To the lower part run up the umbilical arteries and the urachus. Owing to the rapid growth of the abdominal wall and pelvis before puberty, and the fact that the urachus and the umbilical arteries, being of soar tissue, elongate with difficulty, the latter parts depress the umbilicus by reason of their intimate connection with its lower half. Owing to the usual exit of an umbilical hernia of adult life being through the upper part of the ring, the constricting edge in strangulation should be sought below and divided downward. As pointed out by Mr. Wood, it is here that the dragging weight of the hernial contents and the weight of the dress tend to produce the chief results of strangulation. An incision here also gives better drainage if required. Coverings of an umbilical hernia. — These, more or less matted together, are : — (1) Skin; (2) superficial fascia, which loses its fat over the hernia; (3) prolonga- tion of scar tissue of the umbilicus gradually stretched out; (4) transversalis fascia; (5) extra-peritoneal fatty tissue; (6) peritoneum. If the hernia come through above the umbilicus, or just to one side, the coverings will be much the same; but, instead of the layer from the umbilical scar, there will be one from the linea alba. Strangulated umbilical hernia of adult life. — In this, the most fatal of the strangulated hernise ordinarily met with, the following are practical points in the surgical anatomy: — 1. The coverings, including the sac, are always thin, at times so markedly so that the intra-peritoneal contents are practically subcutaneous. 2. The sac is multilocular, and one or more of its cham- bers may he very deep. 3. The contents are numerous, viz., omentum, often voluminous and adherent, transverse colon, and later in the history, small intestine. 4. The contents are often adherent to the sac and each other, thus explaining the irreduoibility. 5. The long duration of the presence of the transverse colon with its stouter walls accounts for the period, often pro- longed, in which warning evidence of incarceration precedes that of strangulation. 6. The communication with the peritoneal sac is direct, short, and during a prolonged operation, free. Infection is thus readily brought about. THE BACK The surface form and landmarks of the back will be considered first, followed by the relations of skeleton, muscles, viscera and nervous system. Median furrow. — This is more or less marked according to the muscular development, lying between the trapezii and semispinales capitis, in the cervical region, and the sacro-spinales lower down. The lower end of the furrow corre- sponds to the interval between the spines of the last lumbar and the first sacral vertebra. (Holden.) Vertebral spines. — Those of the upper cervical region are scarcely to be made out even by deep pressure. That of the axis may be detected in a thin subject. Over the spines of the middle three cervical vertebrae is normally a hollow, owing to these spines receding from the surface to allow of free extension of the neck. The seventh cervical is prominent, as its name denotes. Between the skull and atlas, or between the atlas and epistropheus, a pointed instrument might pene- trate, especially in flexion of the neck. Of the thoracic spines, the first is the most prominent, more marked than that of the last cervical; the tliird should iDe noted as on a level with the medial end of the scapular spine, and in some cases with the bifurcation of the trachea; that of the seventh with the lower angle of the scapula; that of the twelfth with the lowest part of the trapezius and the head of the twelfth rib. The obliquity and overlapping_ of the thoracic spines are to be remembered. Of the lumbar spines, the most important are the second, which corresponds to the termi- nation of the cord, and the fourth, which marks the highest part of the iliac crests and the bifurcation of the abdominal aorta. The lumbar spines project horizontally, and correspond with the vertebral bodies. The third is a little above the umbilicus. 1404 CLINICAL AND TOPOGRAPHICAL ANATOMY Owing to the obliquity of the thoracic spines, most of them do not tally with the heads of the correspondino; ribs. Thus, the spine of the second corresponds with the head of the third rib ; the spine of the third with the head of the fourth rib ; and so on till we come to the eleventh and twelfth vertebrae, which do tally with then* corresponding ribs. (Holden.) The lower ribs may be felt lateral to the sacro-spinalis but in counting them from below it must be remembered, as pointed out by Holl, that in quite a Fig. 1124. — Diagram and Table showing the Approximate Relation to the Spinal Nerves of the various Motor, Sensory, and Reflex Functions of the Spinal Cord. (Arranged by Dr. Gowers from anatomical and pathological data.) .,\^ i MOTOR SENSORY REFLEX St erno -mastoid Trapezius \ Serratus j Shoulder Arm \ muse. Flexors, Mp Extensors, knee Adductors Muscles of leg mov- ing foot I7eck and scalp Neck and shoulder I Shoulder Arm Front of thorax I Buttock, upper part [• Groin and scrotum (front) Lateral side Medial side Leg, medial side Buttock, lower Back of thigh Leg ) and > except medial [foot J part 1 Perineum and anus [Scapular ■ Cremasteric I 1 J I Knee-joint Foot-clonus Plantar considerable percentage the last rib is so abnormally short that it does not reach as far as the lateral border of the sacro-spinalis; or is so rudimentary as to re- semble a transverse process (consequently the only safe method of counting ribs is from above). In these cases the lower end of the pleura maj^ pass from the lower part of the twelfth thoracic vertebra, almost horizontally to the lower edge of the eleventh, rib. THE BACK 1405 Muscles. — The student will remember the greater number and complexity and the numerous tendons of the muscles which run up on either side of the spines; the firmness and inextensibility of their sheaths; the large amount of cellular tissue between them; and the fact that toward the nape of the neclc these muscles lie exposed instead of being protected in gutters, as is the case below: all these anatomical points explain the extreme painfulness and obstinacy of sprains here. Trapezius. — To map out this muscle, the arm should be raised to a right angle with the trunk. The external occipital protuberance should be dotted in, and the superior nuchal line passing out from this; below, the twelfth thoracic spine should be marked; and laterally, the lateral third of the clavicle and the commencement of the scapular spine. Then a line should be drawn from the protuberance vertically downward to the twelfth thoracic spine; a second from about the middle of the superior nuchal line to the posterior and lateral third of the clavicle; and a third from the last thoracic spine upward and laterally to the root of the spine of the scapula. Fig. 1125. — Relations of the Abdominal Visceba to the Antbbiob Body Wall. Lateral yertical (mid- clavicular) line Sterno-xiphoid line Addison*s "trans- pyloric" line Infracostal line Hiac colon Intertubercular line Cfficum and vermiform process Latissimus dorsi. — The arm being raised above a right angle, the spines of the sLxth thoracic and the third sacral vertebra should be marked; then the outer Up of the crest of the Uium, the lower two or three ribs, the lower angle of the scapula, and the posterior fold of the axiUa, and finally the intertubercular (bicipital) gi-oove should all be marked. A vertical line from the sixth thoracic to the thu-d sacral spine will give the spinal origin of the muscle. Another from the thu-d sacral spine to a point on the iliac crest, 2.5 cm. (1 in.) or more lateral to the edge of the sacro-spinalis, will give the origin of the muscle from the sheath of the sacro-spinalis and the ilium. A line from the sixth thoracic spine, almost transversely at first, with increasing slight obliquity over the inferior angle of the scapula to the axilla and intertubercular groove, will mark the upper border of the muscle. Another very oblique line from the point of the iliac crest upward and laterally to the axilla will give the lower border and the tapering triangular apex of the insertion. The muscle may be attached to the angle of the scaptila, or separated from it by a bursa. 1406 CLINICAL AND TOPOGRAPHICAL ANATOMY Triangle of Petit. — This small space lies above the crest of the ihum, at about its centre, bounded by the anterior edge of the latissimus behind and the posterior border of the external obhque, in front. Through this gap, when the muscles are weak, a lumbar abscess occasionally, and very rarely, a lumbar hernia, may appear. Origin of spinal nerves. — It is very important to remember the relations of these to the vertebral spines, in determining the results of disease or injury of the cord and the parts thereby affected. The above relations may be given briefly as follows: — The origins of the eight cervical nerves correspond to the cord between the occiput and the sixth cervical spine. The upper six thoracic come off between Fig. 1126. — Chief Arterial Anastomoses on the Scapula. (From a dissection in the Hunterian Museum.) Supra-spinatus Transverse scapular artery Descending branch of transversa colli artery Rhomboideus minor Levator scapulae Infra-spinatus Triceps, cut Deltoid, insertion Deltoid Trapezius Rhomboideus major Teres major I [Teres major, insertion Circumflex scapular artery Posterior circumflex artery the above spine and that of the fifth thoracic vertebra. The origins of the lower six thoracic nerves correspond to the interval between the fourth and the tenth thoracic spines. The five lumbar arise opposite the eleventh and twelfth thoracic spines; and the origins of the five sacral correspond to the first lumbar spines. The diagram and table (fig. 1124), arranged by Dr. Gowers from anatomical and pathological data, show the relations of the origins of the nerves to their exits from the vertebral canal, and the regions supplied by each. Scapula, its muscles and arterial anastomoses. — Amongst the landmarks in the back, the student should be careful to trace the angles and borders of the scapula as far as these are accessible. The upper border is the one most thickly covered. With the hands hanging down, the upper (medial) angle corresponds to the upper border of the second rib; the lower angle to the seventh intercostal space; and the root of the spine of the scapula to the interval between the third and fourth thoracic spines. THE BACK 1407 The axillary border of the scapula, covered by the latissimus dorsi and teres major, may best be palpated with the arm hanging to the side. The vertebral border is brought into prominence by placing the hand on the opposite shoulder. This border is held in apposition with the thorax by the serratus anterior; consequently in paralysis of that muscle, supplied by the long thoracic nerve (5, 6, and 7 C), it becomes unduly prominent, giving rise to "winged scapula." Fig. 1126 shows the chief arteries around the scapula. The anastomoses on the acromial process between the transverse scapular (supra-scapular) thoraoo-acromial, and circumflex humeral arteries are not shown. The numerous points of ossification, primary and secondary, by which this bone is developed explain, in part, the frequency of cartilaginous and other growths here. The anatomy of the loin behind, the ilio-costal region, is of prime importance, owing to the numerous operations here. The lateral border of the sacro-spinalis and quadratus lumborum may be indicated on the surface thus. (Stiles.) That of the sacro-spinalis by drawing a line from a point on the Oiac crest 8.2 cm. (Sj in.) (four fingers'-breadth) from the middle line up- ward and slightly laterally to the angles of the ribs. That of the quadratus passing upward and sUghtly medially Ues a little lateral to that of the sacro-spinahs (erector) at the crest, Fig. 1127. — Relations of the Abdominal Viscera to the Posterior Body Wall. and a little medial to it at the twelfth rib. The ascending and descending colon lie in the slightly depressed angle between the two muscles. The iho-costal region varies greatly in space according to the length of the lower ribs, shape of the chest, and development of the ihac crest. An incision here — that for exploration of the kidney may be taken as the type — would be an oblique one, about 10 cm. (4 in.) long, starting in the angle'between the twelfth rib and the sacro-spinahs muscle and passing forward and downward toward the anterior extremity of the iliac crest. In its upper part the incision should lie 1.2 cm. (J in.) below the tweltfh rib. The anterior fibres of the latissimus dorsi are divided behind, the posterior ones of the external oblique in front. The yellowish-white lumbar fascia now comes into view, and is the first important landmark. It and the fibres of the internal oblique and transversus which arise from it are next carefully divided. The last thoracic nerve and lowest intercostal artery may also require division. If the latter is cut close to the rib, the htemorrhage is troublesome. The transversalis fascia remains to be divided. To avoid the peritoneum, the deeper part of the 1408 CLINICAL AND TOPOGRAPHICAL ANATOMY incisions should always be made from behind forward. If more room is required, as in large growths or in exploration of the ureter, the incision must be prolonged beyond the iliac crest, the lumbo-ilio-inguinal incision of Morris. Viscera. — Several of these, which can be mapped in behind — viz., the kidneys, spleen, etc. — have been already mentioned (pp. 1375, 1379). The commencement of the trachea and oesophagus has been given in front as corresponding to the sixth cervical vertebra. If examined from behind, this point, o-sving to the obliquity of the spines, would be a httle lower down. The trachea, about 12.5 cm. (5 in.) long, descending in the middle line, bifurcates opposite to the interval between the third and fourth thoracic spines (or fourth and fifth bodies). The bronchi enter the lungs at about the level of the fifth thoracic spine, the right being the shorter, wider, and more horizontal. The root of the lung is opposite to the fourth, fifth, and sixth dorsal spines, midway between these and the vertebral border of the scapula. The structures in it are the bronchus, pulmonary artery, two pulmonary veins, bronchial vessels, lymph- atics, and nerves. The phrenic nerve is in front, the posterior pulmonary plexus behind. On the right side the superior vena cava is in front, the vena azygos (major) arching over the root at the level of the fourth thoracic vertebra. On the left side the aorta arches over the root, and the thoracic aorta descends behind it. The oesophagus, about 25 cm. (10 in.) in length, starting in the middle line, curves twice to the left, at first gradually at the root of the neck; from this point it tends to regain the middle line up to the fifth thoracic vertebra; thence finally turns again, and more markedly to the left, and passes through the diaphragm opposite to the tenth, entering the stomach here or at the eleventh thoracic vertebra (ninth or tenth thoracic spine). In the thorax this tube tra- verses first the superior, then the posterior, mediastinum. At three spots, i. e., its commencement, where it is crossed by the left bronchus, and at the cardiac orifice, it presents narrowings. The relations of this tube to the pleura, peri- cardium, aorta, vagi, and thoracic duct are important in the ulceration of malignant disease and infected bodies, and in the passage of instruments. The aorta reaches the left side of the vertebral column, with its arch just above the fourth thoracic spine, and thence descends on the front of the column, with a shght tendency to the left, to bifurcate opposite the fourth lumbar spine. The spinal cord. — This, about 45 cm. (18 in.) long, extends from the foramen magnum to the junction between the first and second lumbar vertebrae. Up to the third month of foetal life it reaches to the sacral end of the vertebral canal ; later, owing to the more rapid growth of the bony wall, its lower limit is at birth opposite the third lumbar vertebra. The dura mater is continued, as a sheath, as low as the second sacral vertebra. It is anchored above to the upper cervical vertebrae and the foramen magnum, and below, as the filum terminale, to the peri- osteum of the coccyx. The deficiency of the spinous processes and laminae of the fourth and fifth pieces of the sacrum allows of infection, e. g., of a bed-sore reach- ing the membranes, and so the cord. The arachnoid and pia of the cord are continuous above with those of the brain. The parts of the column most exposed to injury are the thoraco-lumbar and cervico-thoraoic partly because here more mobile parts are joined to those which are more fixed, and also from the amount of leverage exerted on the thoraco-lumbar region, and, in the case of the upper region, because this is affected by violence exerted on the head. The chief provisions for pro- tection of the cord are the number of bones and joints which allow of movement without serious weakening, the thi'ee om-ves and columns, cervical, thoracic, and lumbar, ensuring bending before breaking; the large amount of cancellous tissue and the number and structure of the intervertebral discs all tending to damp vibrations; the large size of the theca vertebrahs and the way in which the cord, anchored and slung by the thirty-one pairs of nerves and the Ugamenta denticulata, about twenty in number, occupies neutral ground in the centre of the canal as regards injury directly and indirectly applied. In lumbar puncture (Quincke) as a means of diagnosis or of relieving pressure advantage is taken of the fact mentioned above that the theca extends below the cord. A line drawn joining the highest points of the iliac crests crosses the fourth lumbar spine. The needle is inserted in the median line between the third and fom-th or the fourth and fifth spines, and directed forward and slightly upward. The back must be flexed as fully as possible in order to widen the interspinous spaces. The needle is passed to a depth of about 5 cm. (2 in.) in an adult, or 1.8 cm. (f in.) in an infant. In the supine position the lowest part of the sub- arachnoid space ia in the mid-thoracic region, and an anaesthetic fluid, non-diffusible and of a THE SHOULDER AND ARM 1409 higher specific gravity than the cerebro-spina) fluid, will tend to gravitate there (Barker). The level of the anaesthesia can be varied by raising the pelvis or the shoulders to diiferent levels. The following table, from Holden and Windle, with additions, will be found very useful in determining the relation of numerous viscera and other structiires to the bodies of the vertebrse. VERTEBRAL LEVELS Cervical First. Level of hard palate. Second. Level of free edge of upper teeth. Second and third. Superior cervical ganglion of sympathetic. Fourth. Hyoid bone. Upper aperture of larynx. Fifth. Thyreoid cartilage and rima glottidis. Between this and the last would be the bifurcation of the common carotid. Sixth. Cricoid cartilage. Ending of pharynx and larynx. Consisting of the fused fifth and sixth ganglia, the middle cervical ganglion is usually opposite this vertebra. Here the omo-hyoid crosses the common carotid, and at this spot, the seat of election, the centre of the incision for tying this vessel is placed. At this level the inferior thyreoid passes behind the carotid trunk. Seventh. Inferior cervical ganglion. Apex of lung. Arch of thoracic duct oyer apex of lung, outward and downward to termination. Thoracic First. Summit of arch of subclavian. (Godlee.) The height of this varies. Usually it is from 1.2 to 2.5 cm. (J to 1 in.) above the clavicle. It is always in close relation with the cervical pleura. Second. Level of episternal notch. This is usually opposite the fibro-cartilage between the second and third. Bifurcation of innominate. (Godlee.) Third. Beginning of superior cava, at junction of first right costal cartilage with sternum. Highest part of aortic arch, about 2.5 cm. (1 in.) below notch. Fourth. Bifurcation of trachea. Second piece of aortic arch, extending from upper border of second right costal cartilage, reaches spine. Arch of vena azygos. The superior medias- tinum is bounded behind by the upper four thoracic vertebrae. Louis' angle, junction of manu- brium and gladiolus. Thoracic aorta begins. Fifth to ninth. Base of heart. Sixth. Pulmonary and aortic valves, opposite third left costal cartilage at its sternal junc- tion, in front. Commencement of aorta and pulmonary artery. End of superior cava, third right chondro-sternal junction in front. Seventh. Mitral orifice. i Eighth. Tricuspid orifice. Ninth. Lower level of manubrium and sterno-xiphoid fine (at lower border). Opening in 'diaphragm for inferior vena cava (lower border). Tenth. Level of tip of xiphoid cartilage. Lower limit of lung posteriorly. Upper limit of Uver comes to the surface posteriorly. QDsophagus passes through diaphragm. Cardiac orifice of stomach (sometimes). Upper limit of spleen. . Eleventh. Lower border of spleen. Suprarenal gland. Cardia (sometimes). Twelfth. Lowest part of pleura. Aorta passes through diaphragm (lower border). Coeliac artery (lower border), tipper end of kidney. Lumbar First. Superior mesenteric arteries. Pancreas. Pelvis of kidney. Renal arteries. Transpyloric Line. (Addison.) Second. Spinal cord ends at junction of first and second. Duodeno-jejunal flexure. Re- ceptaculum (cisterna) chyli. Lower end of left kidney. Third. Umbilicus, opposite disc between third and fourth. Lower end of right kidney. Fourth. Bifurcation of aortic arch. Highest part of iliac crest. Fifth. Commencement of superior vena cava. Sacral Third. End of pelvic colon and beginning of first piece of rectum proper. Lower Umit of spinal membranes. Fifth. Reflexion of recto-vesical pouch of peritoneum 2.5 cm. (1 in.) above base of prostate. Coccyx (tip). 2.5 cm. (1 in.) below this commencement of anal canal. Termination of filum terminale. THE UPPER EXTREMITY THE SHOULDER AND ARM The surface form and landmarks of the upper extremity will first be considered followed by the various regions of the shoulder, arm, forearm and hand. 1410 CLINICAL AND TOPOGRAPHICAL ANATOMY General surface form. Landmarks. — The following surface -marks, of the greatest importance in determining the nature of shoulder injuries, can be made out here: — The clavicle in its whole extent, the acromion process, the great tuberosity, and upper part of the shaft of the humerus. Much less distinctly, the position of the coracoid process in the infraclavicular fossa and the head of the humerus through the axilla can be made out. The anterior margin of the clavicle, convex medially and concave laterally, can be made out in its whole extent, the bone, if traced laterally, being found not to be horizontal, but rising somewhat to its junction with the acromion. The stemo- and acromio-clavicu- lar joints have been referred to at p. 1363. The frequency of fracture of the clavicle is explained chiefly by its exposure to shocks of varied kinds from the upper extremity, inseparable from the out-rigger-like action of the bone and its early ossification. On the other hand, the main safeguards are the elasticity and curves of the bone, the way in which it is embedded in muscles which will damp vibrations, and the buffer- bond fibro-cartilages at either extremity. The looseness and toughness of the overlying skin explain the rarity of compound fracture here. The junction of the two curves is the weakest spot and the usual site of fracture. The weight of the limb acting through the coraco-olavicular ligaments and overcoming the trapezius is the chief factor in the downward displacement; the pectoralis minor and serratus anterior acting on the scapula draw the acromial fragment for- ward. The tip of the acromion, when the arm hangs by the side with the hand supinated, is in the same Mne as the lateral condyle and the styloid process of the radius. On the medial side, the head and medial condyle of the humerus and the styloid process of the ulna are in the same line. Thus the great tuberosity looks laterally, the head medially, and the lesser tuberosity some- what forward. Between the two tuberosities runs the intertubercular (bicipital) groove, which, Fig. 1128. — Transverse Section THRoncH the Right Shoulder-joint, showing the Stkucturbs in contact with it. (Braune.) Acromion- Supra-spinatus Trapezius Teres minor Teres major' Latissimus dorsi' Deltoid Pectoralis major ji of subscapularis blended with the scapular ligament Coraco-brachialis and short head of biceps with the arm in the above position, looks directly forward. In thin subjects its lower part can be defined. Its position can be marked with sufficient accuracy by a Hne running down- ward from the acromion in the long axis of the humerus. Besides the tendon and its synovial sheath, the insertion of the latissimus dorsi, the humeral branch of the thoraco-acromial artery, and the anterior circumflex artery run in the groove. When the fingers are placed on the acro- mion and the thumb in the axilla, the lower edge of the glenoid cavity can be felt; and if the humerus be rotated (the elbow-joint being flexed), the head of the humerus can be felt also. The characteristic roundness of the shoulder is due to the great tuberosity lying under the deltoid (fig. 1130). In dislocation the loss of this roundness is due to the absence of the head and tuberosity and consequent projection of the acromion. This normal projection of the deltoid renders it impossible to place a flat straight body in contact with both the acromion and the lateral epicondyle at the same time (Hamilton's dis- location test). Below the junction of the lateral and middle thirds of the clavicle, between the contiguous origins of the pectoralis major and deltoid, is the infraclavicular fossa, in which lie the cephalic vein, the deltoid branch of the thoraco-acromial artery, and a lymphatic node which may be involved in obstinate tuberculosis of the cervical groups. On pressing deeply here, the coracoid process can be made out if the muscles are relaxed, and the axillary artery compressed against the second rib. On raising the arm and abducting it, the different parts of the deltoid can often be made out — viz., fibres from the lower border of the spine of the scapula, the lateral edge of the acromion, and the lateral third or more of the front of the clavicle; the characteristic knitting of the surface THE AXILLARY FOSSA 1411 owing to the presence of fibrous septa continuous, alike, with the skin and the sheath of the muscle and the tendinous septa which separate the muscular bundles, will also be seen. The muscle will be marked out by a base-line reaching along the above bony points, and two sides converging from its extremities to the apex, a point on the lateral surface of the humerus, about its centre. In paralysis of the deltoid, the humerus being no longer braced up against the scapula, the finger-tips can be placed between it and the acromion. To map out the pectoralis major, a line should be drawn down the lateral aspect of the sternum as far as the sixth costal cartilage, and then two others marking the borders of the muscle — the upper corresponding to the medial border of the deltoid, the lower starting from the sixth cartilage, and the two converging to the folded tendon, which is inserted as a double Fig. 1129. — The Shoulder- joint, as shown by the Rontgen-bays. layer into the lateral tubercular (bicipital) ridge. The pectoralis minor will be marked out by two lines, from the upper border of the third and the lower border of the fifth rib, just lateral to their cartilages, and meeting at the coracoid process. The lower line gives the level of the long thoracic artery; the upper, where it meets the line of the axillary artery, that of the thoraco- acromial. When the arm is abducted and the humerus rotated a httle laterally, the prominence of a well-developed coraco-brachialis comes into view; a Une drawn from the centre of the clavicle along the medial border of this muscle to its insertion into the humerus gives the Une of the axillary artery. Axillary fossa. — The boundaries of this space anterior, posterior, medial, or thoracic, lateral or humeral, apex and base, with the structures forming them and 1412 CLINICAL AND TOPOGRAPHICAL ANATOMY the vessels and nerves in relation to them, must be remembered. The chief vessels are the axillary on the lateral wall, brought into prominence when the arm is abducted, as in removal of the mamma, and the subscapular on the posterior wall. The apex is felt, when the finger is pushed upward in an operation here, to be bounded by the clavicle in front, the first rib behind, and the coracoid some- what laterally. The base is concave, owing to the coraco-clavicular (costo- coracoid) membrane as it descends to blend with the sheath of the pectoralis minor, giving also a process to the axillary fascia which unites the anterior and posterior boundaries. This process also sends septa to the skin. An axillary abscess, always to be opened early to avoid subsequent interference with the movements of the shoulder, is reached by an incision on the medial wall, midway between the an- terior and posterior boundaries, so as to avoid the long thoracic and subscapular vessels, respec- tively, the back of the knife being directed toward the lateral wall. The only vessel on this wall is the superior thoracic, which lies high up. Additional safety is given by the use of Hilton's method. For exploration of the axilla the best incision is an angular one, the two limbs being placed in a line with the anterior margin of the great pectoral, and in the line of the axillary vessels. This runs from a point on the centre of the clavicle (the limb being at a right angle to the trunk) to the medial margin of the coraco-brachialis. If this be obliterated by swelling, the above line should be prolonged to the middle of the bend of the elbow, which will give the guide to the brachial also. Collateral circulation. If the first part of the artery be tied, the channels are the same as in ligature of the third part of the subclavian {q.v.). In ligature of the third part of the axillary, if the ligature be above the circumflex arteries, the chief vessels concerned are the transverse scapular (suprascapular) and thoraco-acromial above and the Fig. 1130. — Diagrammatic Section op Shoulder through the Intertuberculab (Bicipital) Groove. (Anderson.) Deltoid Subacromial bursa Capsule of shoulder-joint Long tendon of bicepE Synovial membrane lining cap- sule and biceps tendon Glenoid lip (ligament) Glenoid cavity Glenoid lip (ligament) Inner fold of capsule and synovial membrane — Humerus posterior circumflex below. If the ligature be below the circumflex, the anastomoses will be those concerned in ligature of the brachial above the profunda (p. 1414). The lymphatic nodes in the axilla have been mentioned at p. 719, (fig. 566). The depression of the axillary fossa is best marked when the arm is raised from the side to an angle of about 45°, and when the muscles bounding it in front and behind are contracted. . In proportion as the arm is raised, the hollow becomes less, the head of the humerus now pro- jecting into it. When the folds are relaxed by bringing the arm to the side, the fingers can be pushed into the space so as to examine it. The axiUary (circumflex) nerve and posterior circumflex vessels wind around the humerus under the deltoid; a hne drawn at a right angle to the humerus and a little above the centre of this muscle marks their position on the surface. To trace the synovial membrane of the shoulder -joint is a comparatively simple matter (fig. 11.30). Covering both aspects of the free edge of the glenoid ligament, it lines the inner aspect of the capsule, whereb.y it reaches the articular margin of the head of the humerus; there is a distinct reflection, below, from the capsule on to the humeral neck before the rim of the cartilage is reached. An extensive protrusion of synovial membrane takes place in the form of a synovial bursa, at the medial and anterior part of the capsule, near the root of the coracoid process under the tendon of the subscapularis. Another protrusion takes place between the two tuberosities along the intertubercular groove, as low as the insertion of the pectoralis major. A third synovial protrusion may be seen, but not frequently, at the lateral or posterior aspect, in the form of a bursa, under the infra-spinatus tendon. Thus the continuity of the capsule is inter- rupted by two and sometimes three synovial protrusions. THE SHOULDER-JOINT 1413 Shoulder-joint. — The frequency of dislocations here, nearly equal to those of all the other joints put together, calls attention to the points contributing to make the joint alike insecure and safe. Strength is given by (1) the intimate blending of the short scapular muscles, especially the subscapularis with the capsule; (2) the coraco-acromial vault; (3) atmospheric pressure; (4) the long tendon of the biceps; (5) the elasticity of the clavicle; (6) the mobility of the scapula. The weakness of the joint is readily explained by its free mobility, the want of corre- spondence between the articular surfaces, its exposure to injury, and the length of the humeral lever. The rent in the capsule is usually anterior and below, and to this spot the head of the humerus must be made to return. While dislocations are usually primarily subglenoid, owing to the above part of the capsule being the thinnest and least protected, they take usually a secondarily forward direction, Fig. 1131. — Posterior View of the Scapular Muscles and Triceps. Supraspinatus The X mark indicates where the radial nerve leaves the long head of the triceps and passes under the outer head to gain the groove. as the triceps prevents the head passing backward. In addition to the above features of the lower part of the capsule, laxity is here also a marked feature, to allow of free abduction and elevation. This movement wall be accordingly much checked by any inflammatory matting of this part of the capsule. The best incision for exploring the joint is one commencing midway between the coracoid and acromion processes and carried downward parallel with the anterior fibres of the deltoid. The cephaUc vein and biceps tendon are to be avoided. If drainage is needed, it must be BuppUed by a counter-incision behind. This may be made along the posterior border of the deltoid, part of its humeral attachment being detached if necessary. The axillary (circumflex) nerve must be avoided in the upper part of the incision. 1414 CLINICAL AND TOPOGRAPHICAL ANATOMY The shaft of the humerus is well covered by muscles in the greater part of its extent, especially above. Below the insertion of the deltoid, the lateral border of the bone can be traced downward into the lateral supracondyloid ridge. The medial border and ridge are less prominent. Attached to these ridges and borders are the intermuscular septa, each lying between the triceps and brachiaUs (anterior), and the lateral one giving origin to the brachio-radialis (supi- nator longus) and extensor carpi radialis longus as well. The medial extends up to the insertion of the coraco-braohialis, the lateral to that of the deltoid. The lateral septum is perforated by the anterior part of the profunda vessels and the radial (musculo-spiral) nerve, the medial by the superior and posterior branch of the inferior ulnar collateral (anastomotica magna) artery and the ulnar nerve. The biceps has a two-fold attachment above and below. The former is of much importance in steadying the various movements, especially the upward one, and in harmonising the simul- taneous flexion and extension of the shoulder- and elbow-joints. (Cleland.) The lacertus fibrosus curving downward and medially with its semilunar edge upward, across the termina- tion of the brachial artery, strengthens the deep fascia and the origin of the flexors of the fore- arm. The two heads unite in the lower third of the arm. The tendon, before its insertion, becomes twisted, the lateral border becoming anterior. Fig. 1132. — Cross-Section through the Middle of the Right Arm. (Heath.) Musculo-cutaneous nerve Brachialis Hadial nerve Profunda vessels Biceps Brachial vessels Triceps, with fibrous intersection Superior ulnar collateral vessels On either side of the well-known prominence of the biceps is a furrow. Along the lateral ascends the cephahc vein. The medial corresponds to the line of the basilic vein which lies superficial to the deep fascia below the middle of the arm, and superficial and medial to the brachial vessels and median nerve. The strength of such muscles as the deltoid, and their intimate connection with the peri- osteum of the humerus, account for fracture of this bone by muscular action being more common than elsewhere. The presence of muscular tissue between the fragments, together with de- ficient immobiUzation, explains the fact that ununited fractures are also most common in the humerus. The best incisions for exploring the humerus, e. g., in acute necrosis, etc., are (a) for the upper portion, the two already mentioned along the anterior and posterior borders of the deltoid. In the latter case the presence of the radial (musculo-spiral) nerve in the deeper part of the wound must be remembered; (6) for the lower end one parallel with the lateral inter- muscular septum, deepened between the brachialis and brachio-radialis. A line drawn along the medial edge of the biceps from the insertion of the teres major to the middle of the bend of the elbow corresponds to the brachial artery. In the upper two-thirds, this artery can be compressed against the bone by pres- sure laterally; in its lower third the humerus is behind it, and pressure should be made backward. The presence of the median nerve will interfere with any pro- longed digital pressure applied in the middle of the arm. THE ARM 1415 In ligature of the artery here the line extends from the mid-axillary region above, prolonged to the centre of the front of the elbow. The only structures seen should be the medial edge of the biceps, the basilic vein, and the median nerve. The profunda comes off 2.5 cm. (1 in.) below the teres major, having the same relation to the heads of the triceps; thus, it first lies on the long head, behind the axillary and brachial arteries, then between the long and medial heads, and next, in the groove, between the medial and lateral heads, and courses with the radial (musculo-spiral) nerve (fig. 1132); the nutrient artery arises opposite the middle of the humerus; in many cases it arises, on the back of the arm, from the profunda; the superior ulnar collateral (inferior profunda) below the middle, and courses with the ulnar nerve through the intermuscular septum to the back of the medial condyle. The inferior ulnar collateral (anastomotica magna) is given off from 2.5 to 5 cm. (1 to 2 in.) above the bend of the elbow. Fig. 1138 will show the collateral circulation after ligature of the brachial, according as the vessel is tied above or below the superior profunda, or below the superior ulnar collateral. The centre of the arm is a landmark for many anatomical structures. On the lateral side is the insertion of the deltoid; on the medial, that of the coraco- brachialis. The basilic vein and the medial brachial cutaneous nerve (nerve of Wrisberg) here perforate the deep fascia, going in reverse directions. The supe- rior ulnar collateral is here given off from the brachial and joins the ulnar nerve; the median nerve also crosses the artery, and the ulnar nerve leaves the medial side of the vessel to pass to the medial aspect of the limb. The brachialis can be mapped out by two pointed processes which surround the insertion of the deltoid, pass downward into lines corresponding to the two intermuscular septa, and then converge over the front of the elbow to their insertion into the coronoid process. The median nerve (lateral head, 5th. 6th, 7th C; medial head, Sth C. and 1st T.) can be traced by a line drawn from the lateral side of the third part of the axillary and first part of the brachial artery, across this latter vessel about its centre, and then along its medial border to the forearm, where it passes between the two heads of the pronator teres. Fia. 1133. — Cross-Section through the Elbow. ( X 1/2). (After Braune.) Tendon of biceps.- _, '^^ ;::^^^\'ff^ -Pronator teres Brachio-radiahs / [-i. ^^ \^' i 1 Adductor longus — r — f Adductor brevis Saphenous — Nerve to vastus medialis Adductor magnus 'Geniculate branch of obturator Semi-membranosus Adductor longus Femoral artery Genu suprema artery Patellar branch of saphenous along the popliteal artery to the knee, and others to the lower third of the thigh, and sometimes the upper and medial aspect of the leg (Hilton), may be of much surgical importance, e. g., in carcinoma of the bowel, disease of the sacro-iliac and hip-joints, growths of the pelvis, and the rare obturator hernia. The distribution of the cutaneous nerves is shown in fig. 1158. Lying superficially in the base of the trigone, the inguinal lymphatic nodes can be detected in a thin person (fig. 1172). The fossa ovalis (saphenous opening). — The depression corresponding to this Is placed just below the lacunar (Gimbernat's) ligament, with which its upper ex- tremity blends. Its centre is about 3.7 cm. (11 in.) below and also lateral to a THE THIGH 1441 line dropped vertically from the pubic tubercle. This and the other structures concerned in femoral hernia are fully described under this section (vide supra, p. 1398). The course of the great saphenous vein is given below, p. 1456. Line of femoral artery. — A line drawn from the mid-point between the anterior superior spine and the symphysis pubis to the adductor tubercle will correspond with the course of this vessel. The sartorius usually crosses it 10 cm. ( 3 to 4 in.) below the inguinal (Poupart's) ligament. The profunda artery arises usually 3.7-5 cm. (1| to 2 in.) below Poupart's ligament. The incision for tying tiie femoral in the femoral trigone should be about 7.5 cm. (3 in.) long, in the Kne of the artery, and begins about 7.5 cm. (3 in.) below the inguinal ligament, and runs over the apex of the triangle. The femur is flexed slightly, abducted and rotated laterally. The fascia lata being divided, the sartorius, readily recognised by its direction, is drawn later- ally. The closely subjacent sheath must be opened on its lateral side. Structures that may be seen are a vein joining the great saphenous, the anterior cutaneous, saphenous nerve, and that to the vastus medialis. The collateral circulation (fig. 1156) is mainly through the following Fig. 1160. — Section of Thigh through upper Part of Hunter's Canal. (W. A.) Saphenous nerve. Femoral artery, with small venee comit- antes (femoral vein deeper) Sheath of vessels Great saphenousvein Superficial fascia Deep fascia contin- ued over back of thigh as superficial layer of deep fascia Deep layer of deep fascia (muscular aponeurosis) Vein channels: — (1) The lateral and medial circumflex above, with the genu suprema and lower muscular branches of the femoral, and the articular of the popliteal. (2) The perforating branches of the profunda above, with the vessels below first given. (3) The comes nervi iscliia- dici with the articular of the popKteal. The femoral vein Ues, below the inguinal ligament, immediately to the medial side of the artery. From this point on the vein gets to a somewhat deeper plane, though stOl very close to the artery, and gradually inclining backward, lies behind its companion at the apex of the tri- angle, and below lies somewhat laterally to it. From the apex of the femoral trigone (Scarpa's triangle) a depression runs down along the medial aspect of the thigh, corresponding to the groove already mentioned between the vastus medialis muscle and the adductors. Along this groove lies the sartorius, and beneath it the adductor (Hunter's) canal, a triangu- lar inter-muscular gap with its apex toward the linea aspera, and its base or roof formed by the fibrous expansion which ties together its boundaries, viz., the adduc- tor longus and magnus and the vastus medialis. The vein, which in the upper part of the canal lies behind the artery, separating it from the three adductors, lower down inclines more and more to the lateral side. The saphenous nerve lies also in the canal, but not in the sheath. The above-mentioned space terminates at about the junction of the middle and lower thirds of the thigh, in the opening in the adductor magnua ( 1442 CLINICAL AND TOPOGRAPHICAL ANATOMY by which the artery enters the upper and medial part of the pophteal space. The saphenous, the largest branch of the femoral nerve, having crossed the femoral vessels latero-mediaUy, accompanies them as far as the opening in the adductor magnus. Here it perforates the aponeu- rotic roof, and is prolonged under the sartorius, accompanied by the superficial part of the genu suprema artery, to perforate the fascia lata between the sartorius and gracilis, and run with the great saphenous vein at the upper and medial part of the leg. Pressure may be applied to the femoral artery — (1) Immediately below the inguinal liga- ment: it should here be directed backward so as to compress the vessel against the brim of the pelvis and the capsule of the hip-joint; (2) at the apex of the femoral trigone the pressure here being directed laterally and a little backward, so as to command the vessel against the bone; (3) in the adductor canal the pressure should be directed laterally with the same object. Care must be taken, especially above, to avoid the vein, which lies very close to the artery, and also the femoral nerve, which enters the thigh about 1.2 cm. (J in.) outside the artery, and at once breaks up into its branches, superficial and deep. In ligature of the femoral artery in Hunter's canal, the line of the incision, in the middle third of the thigh, must exactly follow that of the vessel. It is frequently made too lateral, exposing the vastus medialis. Branches of the saphenous vein being removed, the fascia lata is slit up and the sartorius identified by its fibres descending medially. Those of the vastus medialis are less oblique and are directed downward and laterally. The sartorius having been drawn to the medial side, usually, the aponeurotic roof of the canal is opened, and the femoral sheath identified. The vein, here posterior and to the lateral side, is closely coimected to the artery. The close contiguity of the femoral artery and vein accounts for the comparative frequency of arterio-venous aneurysms especially in the upper part, where the vessels are easily wounded. Their superficial position here further accounts for the facility with which mahgnant disease, e. g., epitheKomatous glands, may cause fatal ha;morrhage. Access to the femur. This is best attained on the lateral side of the shaft along the line of the lateral intermuscular septum (fig. 1160), the biceps being pulled backward, and the vastus lateralis detached anteriorly. On the medial side the bone may be exposed by an incision starting from a point midway between the inner margin of the patella and the adductor tubercle and passing obliquely upward and laterally, but the parts here are more vascular. Fractures of the shaft usually occur about the centre. The main tendency to displacement is of the lower fragment upward by the ham- strings. The upper fragment is anterior; this is especially marked in the upper third, owing to the action of the iho-psoas, which also rotates the upper fragment laterally. In the lower third the forward curve of the femur and its more superficial position explain the fact that it is here that compound fractures of the femur may, occasionally, occur. Ossification. The unstable nature of the tissues about the upper epiphysis, which appears at the end of the first year and unites about eighteen, and the frequency of tuberculous disease in early life are well known. In the lower epiphysis ossification begins before birth, a point of medico-legal importance in deciding whether a newly born child has reached the full period of uterine gestation. From this epiphysis, the level of which is denoted by a line drawn horizontally laterally from the adductor tubercle, and the vascular growing tendon of the adductor magnus — the origin of an exostosis is not uncommon. Displacement of this epiphysis (it unites about twenty) in boj'hood and adol- escence is a grave injury from the immediate risk of the popliteal vessels. The mischief is usually done by overextension of the leg, as when this is caught in a rapidly moving carriage- wheel; the epiphysis is carried forward in front of the diaphysis, the lower end of which is directed backward, endangering the vessels which are posterior and closely adjacent. Amputation through the thigh. — This is usuaUj' performed in the lower third, by anterior and posterior flaps, the former being the longer, so as to ensure a scar free from pressure, and circular division of the muscles, vessels, and nerves. The vessels requiring attention are the femoral, which lie at the medial side, and the more posteriorly, the lower the amputation; the descending branch of the lateral circumflex, and the termination of the profunda near the linea aspera. The femoral artery has a marked tendency to retract in the adductor canal. Care should be taken not to include the saphenous nerve when the femoral vessels are tied, and to cut the sciatic cleanly and high up. When amputation has to be performed in the upper third of the thigh, the tendency of the ilio-psoas to flex the shortened limb and thus bring the sawn femur against the end of the stump must be remembered, and met by keeping the patient propped up and the stump as horizontal as possible. Some of the structures now divided are shown in fig. 1160. The buttocks. Bony landmarks. — The finger readily traces the whole outline of the iliac crest. Behind, it terminates in the posterior superior iliac spine, which corresponds in level to the second sacral spine and the centre of the sacro- iliac joint. (Holden.) The third sacral spine marks the lowest limit of the spinal membranes and the cerebro- spinal fluid; it also corresponds to the upper border of the great sacro-sciatic notch. The first piece of the coccyx corresponds to the spine of the ischium. (Windle.) Its apex is in the furrow just behind the last piece of the rectum. The tuberosities of the ischium are readily felt by deep pressure on either side of the anus. In the erect position they are covered by the lower margin of the gluteus maximus. In sitting they are protected by tough skin, fasciae, with coarse fibrous fat, and often by a bursa known, according to the patients in whom it be- comes enlarged, as weaver's, coachman's, lighterman's, drayman's bursa. The THE THIGH 1443 skin of the buttock is coarse and difficult to cleanse satisfactorily. The abun- dance of sebaceous glands accounts for the frequency of boils here. Gluteus maximus. — The 'fold of the buttock' neither corresponds accurately to, nor is caused by, the lower margin of this muscle. Thus, medially, it lies below the lower margin of the muscle, as it runs laterally it crosses it, and comes to lie on the muscle. The fold is really due to creasing of the skin adherent here to the coarsely fibro-fatty tissue over the tuber ischii during extension. But in early hip disease, in which flexion of the joint is, with wasting of the muscle, almost unvary- ingly present, the fold disappears with well-known rapidity. The prominence of the buttock is mainly due to the gluteus maximus, especially behind and below, and in less degree to the other two glutei in front. Under the lower edge of the gluteus maximus the edge of the sacro-tuberous (great sacro-sciatic) ligament can be felt on deep pressure. To mark out the upper border of the gluteus maximus a line is drawn from a point on the ihac crest 5 cm. (2 in.) in front of the posterior superior spine, downward and laterally to the back of the great trochanter. The lower border is marked out by a second hne drawn from the side of the coccyx parallel with the former, and ending over the linea aspera at the junction of the upper and middle thirds of the thigh. It must be remembered that only the lower and inter- nal fibres of the muscle are inserted into the gluteal ridge on the femur. The greater part of Fig. 1161. — Section through the Hip and Gluteal Region. (One-third.) SartoriuE Reflected tendon of rectus \ Psoas and iliacus and bursa v Femoral nerve^. Common femoral.^ artery Common femoral vein^ Profunda vessels^' y'^ Se Gracili membranosus Adductor brevls Semi-tendinosus Obturator externus Adductor magnu^-f- — Adductor longus Gluteus maximu: Gluteus medius Gluteus minimus Sciatic nerve and infe- rior gluteal vessels Biceps Quadratus femoris it is inserted into the fascia lata and ilio-tibial band and so Into the lateral condyle of the tibia. Weakness of the gluteus maximus and tensor fasciae lata;, with consequent laxity of the ilio- tibial band, gives rise to abnormal side-to-side passive mobility at the knee-joint in full extension. -The following superficial nerves can be marked in over Nerves and vessels, the buttock (fig. 1182). Behind the great trochanter, branches of the lateral cutaneous; coming down over the crest, the lateral cutaneous branch of the last thoracic (about in a line with the great trochanter), and behind this the lateral branch of the ilio-hypogastric. Two or three oiTsets of the posterior primary branches of the lumbar nerves cross the hinder part of the ihac crest at the lateral margin of the sacro-spinahs. Two or three twigs from the posterior divisions of the sacral nerves pierce the gluteus maximus close to the coccyx and sacrum, and ramify laterally. Fi- nally, over the lower border of the gluteus maximus, turn upward branches of the posterior cutaneous (small sciatic) and its perineal branch (inferior pudendal), and the fourth sacral nerve. Sciatic nerve (figs. 1162, 1163). — The point of emergence below the gluteus maximus and the track of this nerve (fourth and fifth lumbar and first three sacral nerves) will be given by a line drawn from a spot a little medial to the middle of the space between the great trochanter and the tuber ischii to the lower part of the back of the thigh, where it usualty divides into the tibial and common peroneal (internal and external popliteal) nerves. { 1444 CLINICAL AND TOPOGRAPHICAL ANATOMY To stretch the nerve, an incision about tliree inches long is made in the line of the nerve, beginning about 3.7 cm. (IJ in.) below the gluteus maximus. The long head of the biceps which covers the nerve trunk and which is descending mediolaterally, is drawn medially. If the nerve is exposed lower down, the interval between the hamstrings is identified and these muscles drawn aside. The perineal branch of the posterior cutaneous (inferior pudenal) perforates the deep fascia about 2.5 cm. (1 in.) in front of the tuber ischii, and turns forward to supply the genitals. Superior gluteal artery. — If a line be drawn from the posterior superior spine to the apex of the great trochanter, the limb being slightly flexed and rotated medially, the point of emer- gence of the artery from the upper part of the great sacro-sciatic notch will correspond with the junction of the upper and middle third of this line. (MacCormao.) The gluteal nerve emerges immediately below the artery, and sends branches into the deeper portion. Inferior gluteal (sciatic) and pudic arteries. — The limb being rotated medially, a line is drawn from the posterior superior spine to the lateral part of the tuber ischii. The point of exit of the above arteries will correspond to the junction of the middle and lower thirds of this line. (MacCormac.) THE KNEE Bony landmarks. — The patella, the condyles of the femur, the condyles and tuberosity of the tibia, the head of the fibula, are all easily examined. Fig. 1162. — The Gluteal Region, with the Superior and Inferior Gluteal and Pudic Arteries. Gluteus medius, turned up ■ gluteal nerve Gluteus maximus, cut Medial circumflex artery Obturator externus , Insertion of gluteus medius Lateral circumflex artery Gluteus minimus Muscular branches of inferior gluteal artery Deep branch of superior gluteal artery Superior gluteal nerve Piriformis perforated by peroneal portion of sciatic nerve Cut edge of gluteus Insertion of gluteus maximus First perforating artery Quadratus femoris Branch of internal circumflex artery Obturator internus with the two gemelli Pudic artery and nerve Inferior gluteal artery Biceps Semi-tendinosus Semi-membranosus Posterior cutaneous nerve comitans nervi ischiadic! Tibial portion of sciatic nerve Perineal branch of posterior cutaneous Perineal portion of sciatic (From a dissection by W. J. Walsham in St. Bartholomew's Hospital Museum.) The muscular branch of the inferior gluteal (sciatic) artery has been drawn inward over the tuber ischii with the reflected origin of the gluteus maximus muscle. The patella. — ^The limb being supported in the straight position, and the exten- sor muscles relaxed, the natural range of mobility laterally of the patella can be estimated. This is interfered with by muscular action in inflammatory conditions. J THE KNEE 1445 or by early tuberculous ulceration of the contiguous cartilages. The niunerous longitudinal strise or sulci on the anterior surface of this bone can now also be detected. In these are embedded tendinous bundles of the rectus, so as to give firmer leverage. The fact that these fibres, thus tied down, are liable after stretch- ing and tearing to fold in between the ends of the bone after fracture, is a ready explanation of the difficulty of ensuring bony union here. (Macewen.) The patella is separated from the tibia by a pad of fat and a deep bursa, save at its insertion. Owing to the lowest part of the patella being thus separated from the joint by fat, fracture here does not, necessarily, open the joint. The bone has the following relation to the femur in different positions: — (1) In extension, the patella rises over the condyles, and in full extension only the lower third of its articular surface rests upon that of the condyles; its upper two-thirds lies upon the bed of fat which covers the Fig. 1163. — Deep Dissection of the Gluteal Region. Hunterian Museum.) (From a preparation in the Gluteus medms Gluteus minimus Piriformis, divided into two by the, sciatic Great trochanter Obturator externus Quadratus femons Fascial insertion of gluteus Horizontal fibres of adductor magnus Sciatic foramen (notch) Gluteal nerve sup- plying portions of gluteus medius Gluteus ] Obturator internus. Below is the infe- rior gemellus. The superior gemellus is absent Sciatic nerve. Under it, oblique fibres of adduc- tor magnus are seen lower and front part of the femur. (2) In extreme flexion, as the prominent anterior surface of the condyles affords leverage to the quadriceps, the patella needs to project very httle; thus, only its upper third is in contact with the femur, its lower two-thu-ds now resting on the pad of fat between it and the tibia. (3) In semiflexion the middle third of the patella rests upon the most prominent part of the condyles. (Humphry.) While the bone now affords the greatest amount of leverage to the quadriceps, it is also submitted to the greatest amount of strain from this muscle, which is acting almost at a right angle to the long axis of the patella. This position may therefore be called the 'area of danger,' as, in a sudden and violent contraction, the patella may be snapped across by muscular action, aided by the resistance given by the condyles, in the same way as a stick is snapped across the knee. The amount of separation of the fragments i 1446 CLINICAL AND TOPOGRAPHICAL ANATOMY in a fracture of the patella is due chiefly to the extent to which the lateral tendinous expansions of the vasti are torn; to a less degree to the haemorrhage from the numerous articular vessels (p. 1452) and synovial effusion. The lower fragment is usually the smaller, and its fractured surface tilted forward; that of the upper one usually looks backward. The patella, the largest of the sesamoid bones, ossifies by a centre which appears from the third to the fifth year. The process is completed about puberty. The rareness with which necrosis and caries occur here, when the exposed situation of the bone is remembered, is partly Fig. 1164. — Knee-joint as Shown by the ROntgen-rays, Antero-posterior View. explained by the density of its tissue, especially in front, and the intimate blending of the rectus fibres with its periosteum. When the knee-joint is bent, the trochlear surface of the femur can be made out, with some difficulty, underneath the quadriceps expansion. The upper and lateral angle of this surface forms a useful landmark (Godlee) as a line drawn from it to the adductor tubercle marks the level of the lower epiphysis of the femur. Dislocation of the patella. — The following anatomical facts account for this taking place much more frequently laterally: — (1) The medial edge of the patella is more prominent, and thus more exposed to injury; it is also well supported, as is seen when, the parts being relaxed, the THE KNEE 1447 fingers are insinuated beneath each border. (2) The pull of the extensor upon the patella, ligamentum patella;, and tibia is somewhat laterally, as the tibia is directed a little laterally to the femur, to meet the medial direction of this bone; the femora being directed medially here, to bring the knee-joints nearer the centre of gravity, and, so, counterbalance their wide separa- tion above at the pelvis. The lateral pull of the quadriceps upon the patella is, in all normal action of the muscle, counteracted by the space taken in the trochlear surface by the lateral condyle, this being wider and creeping up higher, and having a more prominent and thus pro- tective lip. In violent contraction, however, these counteracting points may be overcome. The condyles of the femur and tibia. — It should be noted that on the medial side the prominence of the medial epicondyle of the femur is well marked, and that Fig. 1165. — Knee-joint as shown by the Rontgen-rats, Lateral View. of the tibia is less so, while on the lateral side this condition is reversed. Descend- ing to the lateral condyle of the tibia, the ilio-tibial band of the fascia lata can be traced. The more distinct lateral condyle is a good landmark for opening the joint in amputation and excision. It also indicates the lower level of the synovial membrane of the knee-joint. Farther back are the biceps and fibular collateral (long external lateral) Ugament. The gap onjthe medial side between the femoral and tibial condyles is the place for feeling for a displaced medial fibro-oartilage in 'internal derangement' of the knee, and also for 'lipping' in suspected osteoartliritis. On each femoral epicondyle, posteriorly, in a thin subject, can be felt its tubercle, which gives attachment to the collateral ligament. Owing to their being placed behind the ■ centre of the bone, these ligaments become tight in extension. On the upper and posterior { 1448 CLINICAL AND TOPOGRAPHICAL ANATOMY part of the medial femoral epicondyle the adductor tubercle and the vertical tendon of the ad- ductor magnus can be felt during flexion. This bony point is a guide to the lower epiphysis, the ossification of which and its occasional exostosis have been mentioned at p. 1442. The medial aspect of this epicondyle faces practically in the same direction as the head of the femur. Ligamentum patellae and tuberosity of tibia. — These, in a well-formed leg, should, with the centre of the ankle-joint, be all in the same straight line, a useful point in the adjustment of fractures. (Holden.) Behind the upper half of the ligament is the infrapatellar pad of fat; below, the lower half is separated from the tibia by a deep bursa. The tuberosity (tubercle) of the tibia is on a level with the head of the fibula. [Prepatellar bursa. — This usually protects the lower part of the patella and upper part of the ligamentum pateUaj. It is liable to be enlarged in those who habitually kneel much, the enlargement being either fluid or solid, and occasionally, in tertiary syphilis. Its close connec- tion with the patella and, at the sides, with the joint itself, is to be remembered in infective inflammations of the bursa. Usually the deep fascia, passing off from the sides of the patella upward to the thigh and downward to the leg, serves to conduct inflammation away from the joint. Synovial membrane (fig. 1167). — This, the largest of the synovial membranes, forms a short cul-de-sac above the patella, between the quadriceps extensor and the front of the femur, this process reaching about 2.5 cm. (1 in.) above the trochlear surface of the femur. At its highest point this cul-de-sac communicates with an- FiG. 1166. — Horizontal Section of the Knee-joint. Prepatellar bursa (One-half.) (Braune.) Fibular collateral lig. Lateral condyle of femur Tibial n. ' Semimembranosus Tibial collateral lig. Medial condyle of femur M. sartorius Great saphenous vein f!^^' ^Gastrocnemius, medial head Tendon of gracilis Tendon of semitendlnosus other synovial, bursa-like sac lying between the quadriceps and front of the femur. Thus, synovial membrane will usually be met with 6.2 cm. (2| in.) or more above the trochlear surface or the upper border of the patella when the limb is extended. Flexing the joint draws the membrane down very slightly. During extension, the above pouch is supported by the articularis genu (subcrureus) . Traced down- ward, the membrane reaches the level of the head of the tibia, being separated in the middle line from the upper part of the ligamentum patellae by fat. It here gives off to the intercondyloid notch the patellar synovial fold (ligamentum mu- cosum), with its free lateral prolongations, the alar folds (ligamenta alaria). These three so-called ligaments contain fat, the processes not only padding gaps, but also meeting concussions. The enlargement of these processes, under conditions not yet understood, may certainly be a cause of 'internal derangement,' and simulate a loosened meniscus. But the synovial membrane of this joint is not only the largest: it is also the most complicated, a fact accounting for the grave peril of infective arthritis, and the well-known difficulty of effective drainage and cleansing this joint. Thus 'it passes over the gi-eater portion of the crucial ligaments, but the posterior surface of the posterior crucial, which is connected by means of fibro-areolar tissue to the front of the ligamentum postioum, and the lower portions of both crucial ligaments, where they are united together, of course cannot receive a complete covering from the membrane., (Morris.) From the above ligaments the membrane is conducted, lining the lower part of the capsule and other ligaments, to the semilunar cartilages, first over their THE KNEE 1449 upper surfaces to their free borders, and then along their under surfaces to the tibia. Between the lateral of these and the upper and back part of the tibia is a prolongation of the synovial membrane to facilitate the play of the popliteus tendon. Finally, amid the complications of this synovial membrane, its communication with some of the bursae mentioned below, and occasionally with the superior tibio-fibular joint, is to be borne in mind. In effusion the bony prominences are obliterated, and the patella 'floats.' The knee-joint is easUy opened by free lateral incisions lying midway between the margins of the patella and the tuberosities of the condyles, drainage-tubes being passed so as to meet above the patella. The above-mentioned complications of the synovial membrane show that such drainage wiU be often inadequate. By passing a director to the back of the joint and cutting down upon it carefully from the popliteal space, better drainage will be given, but opening the joint by an anterior flap is needed where the above fail, and, even then, cleansing of the numerous deep recesses is obviously difficult. Structures on the head of the tibia. — From before backward these are: — (1) Transverse ligament. (2) Anterior end of medial meniscus (fibro-cartilage). (3) Lower attachment of anterior crucial. (4) Anterior end of lateral meniscus blending with (3). (5) Posterior extremity of lateral meniscus giving off a strong process to posterior crucial. (6) Posterior extremity of medial meniscus. (7) Posterior crucial ligament. Menisci. — These serve as buffer-bonds and cushions between the contiguous bones. The more frequent displacement of the medial is explained by — (a) its greater fixity, and, therefore, its feeling strains more. Thus, in addition to weaker attachments to the coronary and transverse ligaments, it is connected all along its convex border with the inside of the capsule, and strongly with the tibial collateral ligament. The lateral meniscus, on the other hand, is more weakly attached to the capsule, especially opposite to the popliteus tendon, and has no tie to the fibular collateral ligament. (&) When, in the erect position, the knee-joint is rotated laterally and slightly flexed, a common position, an especial strain is thrown upon the very important tibial collateral ligament, and from the above-mentioned connection, on the medial meniscus also. Position of knee-joint in disease. — In inflammatory effusion, the position which best accommodates the collection of fluid is one of moderate flexion, the ligaments being now mainly relaxed. Later on, when the ligaments are softened, the hamstrings obstinately displace the leg backward, the tibia being rotated laterally by the biceps. The antero-posterior displacement is always more marked than the lateral. In straightening an anchylosed joint, the resistance of the shortened lateral, crucial, and posterior ligaments, and the facility with which a softened upper epiph.ysial line of tlie tibia may give way, must never be forgotten. Erasion and excision. — The extent and comphcations of the synovial membrane render attention to the following points imperative: — (1) Free exposure of the joint usuaUy by an anterior curved incision, the medial extremity of which must not damage the great saphenous vein. (2) The extent of the pouch under the quadriceps, it may be for 5 cm. (2 in.) above the patella, and the lateral recesses under the vasti. The pouches at the back of the joint are far more difficult to deal with, viz., the partial covering of the posterior crucial ligament, the proximity of the popliteal artery, the pouches in relation to the popUteus, gastrocnemii, and back of the femoral condyles. In erasion, the cartilage and bone, where diseased, are removed with a gouge. Owing to the removal, in addition to the synovial membrane, of the fibro-cartilages, and crucial ligaments, and the damage to lateral and patellar ligaments, there is a most obstinate tendency to flexion afterward. In excision, to avoid injury to the epiphysis, the section of the femur should not pass higher than through the upper third of the trochlear surface. Of the tibia, only 12 mm. (J in.) should be removed. Genu valgum. — Here the natural angle at which the femur inclines medially to the tibia is increased. As shown by the late v. Mikulicz, this is due to an abnormal growth downward of the medial part of the femoral diaphysis, the epiphysial line being gradually altered from one at right angles to the shaft to one which runs obliquely from without downward and medially. The femur is not only elongated on its medial side, but bent at its lower end, the concavity of the curve being lateral. Other changes have to be remembered. Pes valgus very commonly coexists, and in the tibia there may be a compensatory curve, the concavity being medial, in the lower third, or an analogous alteration in the line of the upper epiphysis may be present, its direction being no longer at a right angle with the shaft, but obhque. In Sir W. Macewen's supra-condyloid osteotomy, a longitudinal incision, about 3.7 cm. (IJ in.) long is made where the following lines meet, viz., one transverse, a finger's breadth above the upper margin of the lateral condyle, and one longitudinal, 1.2 cm. (J in.) in front of the adductor magnus tendon. The bone is divided in front of the genu suprema and above the superior medial articular artery, above the epiphysial line and behind the upward extension of the synovial membrane under the quadriceps. The following bursae about the knee-joint must be remembered. Some, it will be seen, are much more constant than others : — ( 1450 CLINICAL AND TOPOGRAPHICAL ANATOMY A. In front. — (1) One between the patella and skin, the bursa prepatellaris subcutanea (fig. 1167); (2) a deeper one between the ligamentum patellse and the upper part of the tibia; (3) between the skin and the lower part of the tuberosity of the tibia. This is not constant. B. On the medial side. — (1) One between the medial head of the gastrocnemius and medial condyle, often extending between the above muscle and the semi-membranosus. This is the largest of the burs^ about the knee-joint, and, after adult life, usually communicates with the knee-joint. But, owing to the narrow communication, it is rarely possible, when the parts are relaxed by flexion of the joint, to empty the cyst. For its removal a straight incision is made over the most prominent part of the swelling, its neck found by drawing aside the tendons. A ligature is then pushed high up around the neck, and the cyst cut away. (2) One superficial to the tibial (collateral) ligament, between it and the tendon of the sartorius, gracilis, and semi Fig. 1167. — Vertical Section op the Knee-joint in the Anteeo-posterior Direction. (The synovial bursa usually present above the upper synovial cul-de-sac is not shown.) (The bones are somewhat drawn apart.) (After Braune.) M. vastus lateralis M. vastus inter- medius Synovial cavity Prepatellar bursa Anterior crucial lig, Lig. patella M. gastrocnemius M. tibialis post tendinosus (3) One beneath the ligament, between it and the tendon of the semi-membrano- sus. (4) One between the medial condyle of the tibia and the semi-membranosus. (5) One between the semi-membranosus and semi-tendinosus. Of the above bursae, the first two alone are constant. The second and third are often one bursa prolonged. C. On the lateral side. — (1) One between the lateral head of the gastrocnemius and the condyle; (2) one superficial to the fibular collateral ligament between it and the biceps tendon; (3) one under the ligament between it and the popliteus tendon; (4) one between the popHteua tendon and the lateral condyle of the femur. This is usually a diverticulum from the synovial membrane. The following explanations may be given of an inflamed knee-joint usually taking the flexed position: — -(1) By experimental injections, Braune found that the capacity of the synovial sac reaches its maximum with a definite degree of flexion, i. e., at an angle of twenty-five degrees. THE POPLITEAL SPACE 1451 (2) As the same nei-ves supply the synovial membrane and the muscles which act upon the joint, reflex spasm of the flexors will help to explain the flexed position. (HQton.) Anastomoses around the front and sides of the knee-joint. — The most impor- tant of these take the form of three transverse arches. (1) The highest passes through the quadriceps fibres just above the upper edge of the patella. It is formed by a branch from the deep division of the genu suprema (anastomotica magna) and one from the lateral circumflex and superior lateral articular. The middle and lowest arches lie under the ligamentum patellte. (2) The middle arch, formed by branches from the genu suprema and superior medial articular on the medial side, and the inferior lateral articular, on the lateral, runs in the fatty tissue Fig. 1168. — Side View of the Popliteal Artebt. (From a dissection in the Hunterian Museum.) Femoral artery and Branches of the med cutaneous Sartoriu Genu suprema artery Vertical fibres of the adductor magnus — Popliteal artery Vastus medialis Cut edg.^ of fascia lata close to the apex of the patella. (3) The lowest arch lies on the tibia just above its tuberosity, and results from the anastomosis of the recurrent tibial and the inferior medial articular. Seven arteries thus take place in this series of anastomoses. POPLITEAL SPACE In flexion, the hollow of this space appears; in extension it is obliterated and its boundaries are ill-defined the only ones now to be made out being the semi- tendinosus and the biceps. Popliteal tendons. — When the knee is a little bent and the foot rests on the ground, the following can be made out:— on the lateral aspect, behind the ilio-tibial band, and descending to the prominence on the lateral side of the head of the fibula, is the tendon of the biceps. This i 1452 CLINICAL AND TOPOGRAPHICAL ANATOMY prominence also gives attachment to the fibular collateral ligament, which splits the tendon into two parts. IJehind is the apex (styloid process) from which the posterior part of the fibular collateral ligament arises. Parallel and close to the medial border of the tendon, the peroneal nerve descends, as a rounded cord, to cross the neck of the fibula and enter the peroneus iongus. In tenotomy of the biceps an open incision should be employed to avoid injiary to the nerve and insure the division of any contracted fascial bands. On the medial side the ten- dons are thus arranged: Nearest to the middle of the popliteal space is the long and more slender tendon of the semi-tendinosus; next, the thicker tendon of the semi-membranosus; this and the gracilis, which comes next, appear as one tendon, but by a little manipulation the finger can be made to sink into the interval between the semi-membranosus, with its thick rounded border laterally and the gracilis medially. The sartorius can easily be thrown into relief on the medial side of the joint by telling the patient to raise the leg extended, the limb being rotated laterally and one leg crosses over the other. Popliteal vessels. — The artery traverses this space from above downward, appearing beneath the semi-membranosus, a little to the medial side of the middle line, and then passing down in the centre of the space to the interval between the gastrocnemii. Its course corresponds with a line drawn from the medial side of the Fig. 1169. — Deep View of the Popliteal Space. (Hirsohfeld and LeveiM.) Adductor magnus Popliteal vein Popliteal artery Tibial nerve Vastus medialis Superior medial articular artery Tendon of semi-membranosuE Medial h. Inferior r ad of gastrocnenuus ledial articular artery Popliteal vein Popliteus Tendon of plantaris Vastus lateralis Sciatic nerve Short head of biceps Peroneal nerve Long head of biceps, cut Lateral head of gastrocnemius Lateral cutaneous crural nerve Gastrocnemius Small saphenous vein and hamstrings to the centre of the lower part of the space. The artery bifurcates on the level of a line corresponding to the tuberosity of the tibia. It lies on the pop- liteal surface of the femur, the oblique popliteal ligament and the popliteus. It is the second of these structures which usually prevents popliteal aneurism and abscess from making their way into the joint. The popliteal vein, intimately adherent to the artery, lies to the lateral side above, but crosses to its medial side below. The popliteal sheath is also unusually strong. The tibial nerve crosses the artery in the same direction as the vein, by which it is separated from the artery. This nerve is the direct continuation of the sciatic nerve (fig. 1 169), and enters more into the space than its fellow branch. The close relation of the vein and nerve explains the early stiffness of the knee, the pains below, often called 'rheumatic,' and the oedema, in popliteal aneurism; also the pulsation of swelUngs not aneurismal. The superior articular arteries (fig. 1169) course laterally and medially immediately above the femoral condyles; the way in which they cUng closely to the bone here is one provision to pre vent overstretching of the artery; the inferior ones lie j ust above the head of the fibula and below the medial condyle of the tibia (fig. 1169). The deep part of the genu suprema artery runs in front of the tendon of the adductor magnus; the superficial with the saphenous nerve. The popliteal artery may be ligatured — (A) Behind, in the upper part of the popHteal space, just after its emergence from under the semi-membranosus. Here, for a short space THE LEG 1453 of about 2.5 cm. (1 in.), the vessel is comparatively superficial after division of the fasciae. The nerve is generally seen first, and, with the vein, must be drawn laterally. The needle should be passed from the vein. (B) From the front, at the medial side. The thigh being flexed, ab- ducted, and rotated laterally, a free incision is made parallel and just behind the adductor magnus tendon, commencing at the junction of the middle and lower third of the thigh. The sartorius and the hamstrings are drawn backward, and the adductor magnus forward. Care must be taken of the genu suprema (fig. 1168). The space between the hamstrings and the adductor magnus being carefully opened up, the artery will be found in fatty areolar tissue. The vein and tibial nerve are on the lateral side of the vessel. The needle is passed in latero- medially. The collateral circulation (fig. 1156) depends chiefly on the genu suprema. The small saphenous vein perforates the roof of the popliteal space in its lower part. As a rule, it is not visible, unless enlarged. The popliteal nodes are not to be felt unless enlarged. Bursse in the popliteal space. — These have been already spoken of (p. 1449). THE LEG The skin. — The proneness of the skin to dermatitis in the lower third of the medial and front aspect of the leg as a result of varicose veins is well known. The close contiguity of the periosteum to the skin here accounts for the difficulty in healing chronic ulcers whose callous base has become fixed to the periosteum, and the frequency with which the upper fragment of a fractured tibia perforates the skin. Bony landmarks. — From the tuberosity (tubercle) of the tibia descends the anterior border or 'shin. ' This soon becomes sharp, and continues so for its upper two-thirds ; in the lower third it disappears, to be overlaid by the extensor tendons. It is curved somewhat laterally above and medially below. The medial border can also be felt from the medial condyle to the medial malleolus. Between these two borders lies the medial surface, subcutaneous save above, where it is covered by the three tendons of insertion of the gracilis and semi-tendinosus, and, overlying them, that of the sartorius. The tibia is narrowest and weakest at the junction of the middle and lower thirds, the most common site of fracture. Behind the medial malleolus, part of the groove for and the tendon of the tibialis posterior can be felt. The head of the fibula can be felt distinctly, but the shaft soon becomes buried amongst muscles till about 7.5 cm. (3 in.) above the lateral malleolus, where the bone expands into a large triangular subcutaneous surface. This lies between the peroneus tertius and the other two peronei. The peroneus longus overlaps the brevis, especially in the upper two-thirds of the leg. In the lower thii'd the brevis tends to become anterior (fig. 1173). Behind the lateral malleolus these tendons descend to the foot in a groove on its posterior border. The shaft of the fibula is placed on a plane posterior to that of the tibia, and curves backward in a du-ection reverse to that of the tibia. Muscular compartments and prominences. — When the muscles of the leg are thrown into action by dorsi-flexion and plantar flexion of the foot or by standing on the toes, several groups of muscles stand out on the surface, owing to certain compartments, and the origin of certain muscles from, and their separation by, the deep fascia, which knits the surface into corresponding elevations and depressions. The bones and the two peroneal septa divide the leg into four compartments. These are, medio-laterally : — (1) A medial, corresponding to the medial sm-face of the tibia. (2) An anterior, between the crest of the tibia and the anterior peroneal septum, attached to the antero-lateral border of the fibula, and separating the extensors from the peronei. Its surface-marking would be a line from the front of the head of the fibula to the front of the lateral malleolus. In this anterior compartment lie the extensor muscles and origin of the peroneus tertius, and the anterior tibial vessels and nerves. (3) A lateral or peroneal com- partment, lying between the anterior and posterior peroneal septum, the latter being attached to the postero-lateral border of the fibula, and separating the peronei from the calf and deep flexors. This peroneal compartment, a narrow one, contains the two chief peronei and the peroneal (external popUteal) nerve and its three divisions. (4) Much the largest, this, the posterior, lies between the posterior peroneal septum and the medial border of the tibia, and contains the calf and deep flexor muscles, the' posterior tibial vessels and nerves, and the peroneal artery and its posterior branch. The space between the tibia and fibula in front is mainly occupied by the fleshy belly of the tibialis anterior; lateral to this, and much less prominent, is the narrower extensor digitorum longus; lateral to this, again, are the peronei longus and brevis. Lower down, in an interval between the tibialis and the extensor of the toes, the extensor hallucis, here almost entirely tendinous, comes to the surface. Behind, the prominence of the calf is mainl}' formed by the gastrocnemius. On the patient's rising on tip-toe, the tendo Achillis starts into relief { 1454 CLINICAL AND TOPOGRAPHICAL ANATOMY from about the middle of the leg. Of the two heads of the gastrocnemius, the medial is seen to be the larger. On either side of the tendon, but more distinctly on the lateral side, where it is less overlapped by the gastrocnemius, the soleus comes into view. Its muscular fibres are continued on the deep surface of the tendon to within a short distance of the heel. Between the tendon and the upper part of the os calois is a bursa, oocasionaUy the seat of effusion, as in gonorrhoea. The bones. — Their relative position and curves have been mentioned (p. 1453). Access. — That to the tibia is easy along the medial aspect. The fibula is best explored by a free incision along the line of the posterior peroneal septum, which lies between the peronei and the muscles at the back (p. 1453). The presence of the superficial peroneal (musculo-cutaneous) nerve per- forating the deep fascia in the lower third below and that of the common peroneal (external popliteal) in relation to the neck of the fibula above, must be remembered. Fractures. — When, Fig. 1170. — Anastomoses op Tibial Arteries. J Anterior tibial recurren Posterior tibial, giving off muscular and medullary branches Anastomosis of medial malleolar of — (l_\ anterior tibial with posterior medial malleolar Medial calcanean Medial and lateral plantar Popliteal Anterior tibial, giving off posterior tibial recurrent and superior fibular before piercing interosseous membrane and anterior tibial afterward Lateral malleolar of anterior tibial joining posterior peroneal as is most frequent, the tibia gives way from indirect violence, the fracture is usually at the weakest spot, or the junction of the middle and lower thirds. The line of obliquity is generally marked, and from above downward and forward. The lower fragment, pulled upward by the powerful calf muscles, rides behind the upper, which projects forward under the skin. The fibula, bending more than the tibia, snaps at a higher level. Tenderness on pressure is the best guide here, as it is in suspected fractures of the upper tibia, transverse from direct violence. The most common variety of fracture of the fibula is that called after Pott, complicated with displacement of the foot. Here, from abduction of the foot, a severe strain is thrown upon the deltoid ligament, which gives way; the talus (astragalus) is pressed against the lateral malleolus, and the inferior tibio-fibular ligaments resisting, the fibula yields 5 to 7 cm. (2 to 3 in.) above the anlde, the upper end of the lower fragment being usually displaced toward the tibia. If the deltoid ligament is strong, the strain often tears off the medial malleolus. The medial margin of the foot is turned toward the ground, the lateral raised. The foot is also displaced backward. On the medial side of the ankle there is a marked projection of the lower end of the tibia; higher THE LEG 1455 up, on the lateral side, a depression where the fibula is broken. The need of replacing the^foot and the weight-bearing talus (astragalus) accurately, the fact that the ankle-joint is opened and the numerous tendons iikety to be matted are the chief points to bear in mind. In Dupuytren^s fracture there is not only fracture of the lower end of the fibula, but the inferior tibio-fibular ligaments are now torn. The foot is displaced upward and laterally, together with the lower Fig. 1171. — The Anterior Tibial Artery, Dorsal Artery of the Foot, and Perforating Branch of the Peroneal Artery, and Their Bbanches. Superior medial articular artery Inferior medial articular artery Anterior tibial recurrent artery Anterior tibial artery Tibialis anterior muscle Deep peroneal nerve Extensor hallucis longus Medial malleolar artery Crucial ligament- Dorsalis pedis artery. Innermost tendon of extensor digi- torum brevis Deep plantar branch First dorsal metatarsal artery Superior lateral articular artery Inferior lateral articular artery —Extensor digitorum longus Perforating peroneal artery Lateral malleolar artery Peroneus brevis muscle Extensor digitorum brevis, cut Arcuate branch Dorsal metatarsal artery end of the fibula. Epiphyses.—The upper one of the tibia appears shortly before birth and includes the condyle and tuberosity. It does not fuse with the shaft till the age of twenty or later. This fact and the powerful strain of the rectus on this epiphysis explain the obscure pain sometimes complained of in young adults much given to atliletics, over the tibial tuberosity. The lower epiphysis, including the medial malleolus, appears in the second and joins about the eighteenth year. Separation here is not very uncommon up to puberty. In osteotomy of the i 1456 CLINICAL AND TOPOGRAPHICAL ANATOMY tibia, simple or cuneiform, when the curve is antero-posterior as well as lateral, the close vicinity of the tibiaUs anterior tendon to the lateral border of the crest must be remembered, and when the fibula does not yield to careful force, it, also, must be divided, or damage may be done to the superior and inferior tibio-fibular Ugaments, or to the epiphyses of the bones. Fig. 1172. — The Superficial Veins and Lymphatics of the Left Lower Limb. Superficial lymphatics from lateral wall of abdomen Superficial lymphatics from lower and anterior walls of abdomen Superficial epigastric vein' Common femoral vein Superficial subinguinal lym- phatic nodes External pudendal veir Accessory saphenous vein Great saphenous vein > Medial malleolus Dorsal venous arch Superficial inguinal lym- phatic glands Superficial circumflex iliac vein Vessels. — The saphenous veins should be carefully traced, owing to the tend- ency of these and their branches to become varicose. The great saphenous THE LEG 1457 (figs. 1158, 1172), having passed from the arch on the dorsum over the medial malleolusjf'runs up close to the medial border of the tibia, where it is to be avoided *in ligature of the posterior tibial, to the back of the medial condyle; here this ves- sel is to be remembered in operations on the knee-joint; then upward along the thigh, over the roof of the adductor (Hunter's) canal, to the fossa ovalis (saphe- FiG. 1173. — Relations of the Popliteal Artery to Bones and Muscles. Superior lateral articular artery • Tibial nerve - Fibular lateral ligament - Inferior lateral articular artery . Popliteus - Muscular branch to soleus " Soleu Anterior tibial artery Peroneus longus • Peroneal artery ■ Branch of tibial nerve to flexor hallucis longus Flexor hallucis longus —^ Cutaneous branch of peroneal artery Peroneus brevis . Continuation of peroneal artery - Superior medial articular artery ■ Popliteal artery ■ Posterior ligament of knee Azygos articular artery Semi -membrano SUB - Inferior medial articular artery - Muscular branch . Tibialis posterior ■ Tibial nerve Muscular branch of tibial nerve to flexor digitorum longus . Flexor digitorum longus Posterior tibial artery Tibialis posterior Communicating branch Laciniate ligament Calcaneus , Internal calcaneal artery nous opening) (p. 1440 and fig. 1172), where it joins the femoral by perforating the cribriform fascia and the femoral sheath. Four to six valves are present chieily in the upper part. rpntJi'nf'?hrfh^°ul^''?u'' °''-f^^ ^? T^^'^'^ thrombosis is most Hkely to occm-, reaches from the h»?„ ,f fi I ^u *° t'^l^i'ldle of the leg. (Bemiett.) The saphenous nerve joins the vein below the knee, having been under the sartorius above this point (fig. 1159 and 1160) The i 1458 CLINICAL AND TOPOGRAPHICAL ANATOMY surface-marking of the upper part of the vein is a line drawn from the posterior border of the sartorius or the adductor tubercle to the lower part of the fossa ovalis. The small saphenous vein passes behind the lateral malleolus, runs upward over the middle of the calf, and joins the popliteal by perforating the deep fascia in the lower part of the popliteal space. This vein is accompained by the medial sural cutaneous (external saphenous) nerve throughout its course. The popliteal artery bifurcates at the lower border of the popliteus, about on a level with the tuberosity of the tibia. About 5 cm. (2 in.) lower down the pero- neal artery comes off from the posterior tibial (fig. 1173). The course of the posterior tibial corresponds with a line drawn from the centre of the lower part of the popliteal space to a point midway between the tip of the medial malleolus and the medial edge of the calcaneus. In the lower third, the artery becomes more superficial, passing from beneath the calf muscles, lying between the tendo Achillis and medial border of the tibia, and covered only by the skin, deep fascia, and, lower down, by the laciniate (internal annular) ligament. It is here, in its close relation to the tendons of the tibialis posterior and flexor digitorum longiis, that it is liable to be injured in the older methods of tenotomy. The nerve is medial above, lateral below (fig. 1173). Ligature of the posterior tibial in the middle of the leg. — The following are the chief points in the technique. An incision, 7.5 to 10 cm. (3 to 4 in.) long, is made 1.2 em. (J in.) behind the Fig. 1174. — Upper Segment of a Section of the Right Leg in the Upper Third. (Heath.) Tibialis anterior Extensor digitorum longus AAnterior tibial vessels and deep peroneal nerve Peroneus longus Flexor hallucis longus Soleus with fibrous intersection. Gastrocnemius Tibialis posterior Flexor digitorum longus Lateral sural cutaneous nerve Small saphenous Posterior tibial vessesls and tibial nerve medial_border of the tibia, to avoid the trunk of the great saphenous. The deep fascia being freely opened, the medial head of the gastrocnemius is drawn backward. The tibial attachment of the soleus, thus exposed, is out through carefully, so as to allow of identification of its central membranous tendon, which must not be confused with the deep intermuscular septum over the flexor. Any sural vessels are now tied. The above-mentioned special septum is next made out, passing between the bones (vertical Une descending from oblique hne of tibia and oblique line of fibula). On division of this septum the nerve usually comes into view, the artery lying more laterally. The needle is passed from the nerve; the vense comitantes may be in- cluded. The muscles should now be fully relaxed by flexion of knee and plantar flexion of foot. The ligature will be placed below the peroneal artery. The course of the anterior tibial artery corresponds with a line drawn from a point midway between the lateral condyle of the head of the tibia and the head of the fibula to one on the centre of the ankle-joint. This line corresponds to the lateral border of the tibialis anterior and the interval between it and the extensor digitorum longus (figs. 1170 and 1171). This is shown when the first of these muscles is thrown into action. The accompanying nerve is in front in the middle third of the leg, lateral above and below. Ligature of the anterior tibial artery at the junction of the upper and middle thirds of the leg. The limb being flexed and rotated medially, an incision is made, 7.5 to 10 cm. (3 to 4 in.) long, in the line of the artery, distant 2.5 cm. (1 in.) or more (according to the size of the leg) from the crest, and beginning about 5 cm. (2 in.) below the head of the tibia. If, on exposure of the deep fascia, the intermuscular septum between the tibialis and long extensor of the toes THE ANKLE 1459 is not well defined, the fascia must be freely slit up in the line of the artery, and the sulcus felt for. A small muscular artery may lead down to the trunk. The foot is now dorsiflexed and the artery sought for deep on the interosseous membrane. The nerve should be drawn to the outer side. The venas comitantes may be included in the ligature. In senile gangrene the liabiUty of the tibial arteries to disease and consequent thrombosis and interference with the collateral cu-eulation accounts both for the extension of the disease and the difficulty in detecting pulsation. The peroneal artery, given off from the posterior tibial about an inch below the popliteus, or two inches below the head of the fibula, runs deeply along the medial border of this bone, covered by the flexor hallucis longus, the nerve to which accompanies the vessel. It gives off the anterior peroneal, through the interosseous membrane, to the front of the lateral malleolus about an inch above the level of the ankle-joint. Its continuation, as the pos- terior peroneal, runs behind the malleolus, to join the anastomosis about the ankle-joint. Tlie nutrient artery of the tibia arises from the posterior tibial near its commencement. It is the largest of all the nutrient arteries to the shafts of long bones; that for the fibula comes from the peroneal. As a general rule, in amputation 2.5 cm. (1 in.) below the head of the fibula, only one main artery — the popliteal — is divided. In amputations 5 cm. (2 in.) below the head of the fibula, two main arteries — the anterior and posterior tibials — are divided. In amputations 7.5 cm. (3 in.) below the head, three main arteries — the two tibials and the peroneal — are divided. (Holden.) In an amputation through the middle of the leg, the anterior tibial artery would be found cut on the interosseous membrane between the tibialis anterior and the extensor hallucis longus, the deep peroneal nerve here lying in front of the vessel. The posterior tibial would be between the superficial and deep muscles at the back of the leg lying on the tibialis posterior, its nerve being to the lateral side. The peroneal would be close to the fibula in the flexor hallucis longus. The superficial peroneal (musculo-cutaneous) nerve, having passed through the peroneus longus and then between the peroneus longus and peroneus brevis, perforates the deep fascia in the lower third of the leg in the line of the septum between the peronei and extensors. Directly after, it divides into its two terminal branches. Amputation of the leg. — To give one instance only, amputation 'at the seat of election, or a hand's-breadth below the knee-joint, will be alluded to. Lateral skin-flaps and circular division of the muscles give an excellent result in hospital practice where the various conditions which call for such a step are usually met with. The above name was given because the pressure of the body is well carried on the prominences about the knee-joint, especially the tuberosity of the tibia, when the patient walks with the knee flexed on a 'bucket' artificial limb. Thus the scar, being central, is here not of importance. Two broadly oval lateral flaps of skin and fasciae are raised, and the remaining soft parts severed down to the bones with circular sweeps of the knife. In sawing the bone, the smaller size of the fibula and its position behind the tibia must be remembered. It is well, in order to ensure complete division of the fibula first, to roll the limb well over on its medial side, and place the saw well down on the lateral side. The parts cut thi'ough are shown in fig. 1174. THE ANKLE Bony landmarks. — The following are the differences between the two malleoli : The medial is the more prominent, shorter, and is placed more anteriorly than the lateral, being a little in front of the centre of the joint. The lateral descends lower by about 1.2 cm. (| in.), and thus securely locks in the joint on this side; it is opposite to the centre of the ankle-joint, being placed about 1.2 cm. (| in.) behind its fellow. Owing to the lateral malleolus descending lower than the medial, in Syme's and Pirogoff's amputations the plantar incision should run between the tip of the lateral malleolus and a point 1.2 cm. (J in.) below that of the medial one. When a fracture is set, or a dislocation adjusted, the medial edge of the patella, the medial malleolus, and the medial side of the great toe are useful landmarks and should be in the same vertical plane, regard being paid at the same time to the corresponding points in the opposite limb. (Holden.) On the posterior aspect of the medial malleolus is a groove for the tibialis pos- terior and flexor digitorum longus, the first named being next the bone. The tip and borders of the process give attachment to the deltoid ligament. The anterior border and tip of the lateral malleolus give attachment to the anterior talo-fibular and calcaneo-fibular ligaments respectively, the posterior talo-fibular arising from a pit behind and below the articular facet. The posterior border is grooved for the two peronei. The line of the ankle-joint corresponds to one about 1.2 cm. (I in.) below the tip of the medial malleolus drawn across the anterior aspect. { 1460 CLINICAL AND TOPOGRAPHICAL ANATOMY Effusion or tuberculous thickening shows itself first in front, between the medial malleolus and tibialis anterior and between the peroneus tertius and lateral malleolus and then behind, where it fills up the hollow between the tendo Achillis and the two malleoli. Owing to the thin- ness of the transverse crural (anterior) ligament, the extensor sheaths are easOy affected in neglected tuberculous disease. Owing to the way in which the joint is locked in, it is not easy to open and drain an infected ankle-joint satisfactorily. Removal of a portion of the lateral Fig. 1175. — Branches of the Common Peroneal Nerve. Common peroneal nerve' Recurrent articular' Superficial peroneal Branch to peroneus longus- Branch to extensor, digitorum longus Branch to peroneus brevis Superficial peroneal- Intermediate dorsal cutaneous- Lateral dorsal cutaneous" Deep peroneal nerve Anterior tibial artery Tibialis anterior Deep peroneal nerve Medial dorsal cutaneous Deep peroneal (lateral division) — Deep peroneal (medial division) malleolus subperiosteally, leaving the tip and calcaneo-fibular, will admit of the insertion of a tube and good drainage if the foot is so slung as to keep its lateral aspect dependent. Tendons. — (A) In front of ankle. — ^Latero-medially are — (1) The tibialis anterior, the largest and most medial. This tendon appears in the lower third of the leg, lying just under the deep fascia, close to the tibia; then, crossing over the THE ANKLE 1461 lower end of this and the ankle-joint, it passes over the medial side of the tarsus, to be inserted into the medial and lower part of the first cuneiform and the ad- jacent part of the first metatarsal. (2) The extensor hallucis longus. This ten- don, concealed above, appears low down in a line just lateral to the last, and then, crossing over the termination of the anterior tibial vessels and nerves (to which its muscular part lies lateral), it descends along the medial part of the dorsum to be inserted into the base of the last phalanx of the great toe. (3) and (4) The extensor digitorum longus and peroneus tertius enter a common sheath in the transverse crural ligament. The former then divides into four tendons, which Fig. 1176. — Lateral View op the Ankle Region, as Shown by the ROntgbn-rats run to the four lateral toes. The peroneus tertius is inserted into the upper surface of the base of the fifth (often also the fourth) metatarsal bone. (B) Behind. — The tendo Achillis, the thickest of all tendons, begins near the middle of the leg, in the junction of the tendons of the gastrocnemii and, a little lower, (p. 1453) the soleus. Very broad at its commencement, it gradually nar- rows and becomes very thick. About 3 . 7 cm. (1| in.) from the heel, or about the level of the medial malleolus, is its narrowest point. After this it again expands sHghtly, to be inserted into the middle of the back part of the calcaneus. The long tendon of the plantaris runs along its medial side, to blend with it or to be at- tached to the calcaneus. On either side of the tendo Achillis are well-marked { 1462 CLINICAL AND TOPOGRAPHICAL ANATOMY furrows below. Along the medial, the tendon of the tibialis posterior and the posterior tibial vessels and nerve come nearer the surface. Along the lateral, the small saphenous vein (more superficially) ascends from behind the lateral malleolus. (C) On the medial side. — The tendon of the tibialis posterior, which has pre- viously crossed from the interspace between the bones of the leg to the medial side, lies behind the inner edge of the tibia above the medial malleolus, then behind this, being here under the flexor digitorum longus, the two tendons having become super- ficial on the medial side of the ten do Achillis. It then passes forward over the deltoid and under the laciniate (internal annular) ligament between the medial malleolus and the sustentaculum tali, and then below and close to the plantar cal- FiG. 1177. — Horizontal Section through the Lower Part of the leg. (After Braune.) Deep peroneal n. Ant. tibial vessels M. extensor digitorum com. Tendon of peroneus longus M. peroneus brevis M. flexor hailucis longus — \ Sural nerv Tendon of ant. tibial M extensor hailucis longus Tendon of post, tibial Tendon of flexor longus digitorum Tendo calcaneus (Achillis) caneo-navicular ligament {vide infra) , and so to its insertion, by numerous slips, into the tarsus and metatarsus, especially the tuberosity of the navicular. The tendon of the flexor hailucis longus cannot be felt. Having passed medially from the fibula, it crosses the lower end of the tibia in a separate furrow, then grooves the backof the talus, and passes under the sustentaculum tali on its way to its insertion. The arrangement of the structures at the medial ankle from above downward, and medio- laterally, is as follows (fig. 1177): — tibialis posterior, flexor digitorum longus, companion vein, posterior tibial artery, companion vein, tibial nerve, flexor hailucis longus. The tibiales pos- terior and anterior turn the sole mediaUy, antagonising the peronei. They also bear a large THE ANKLE 1463 share in maintaining the longitudinal arch of the foot. The flexors not only act upon the toes, but aid the calf muscles in straightening the foot upon the leg in walking or standing upon tip- toe; hence the value of educating them in cases of flat-foot. (D) Tendons on the lateral aspect. — The tendons of the two peronei, which arise from the fibula between the extensor digitorum longus and flexor hallucis longus, pass behind the lateral malleolus, the brevis being nearer to the bone (fig. 1177). They then pass forward over the lateral surface of the calcaneus, sepa- rated by the peroneal tubercle when present, and diverge. The brevis — the upper one — passes to the projection at the base of the fifth metatarsal; the longus, lying below the brevis on the calcaneus, winds round the lateral border of the foot, grooving the lateral border and under surface of the cuboid. Finally, crossing the sole obliquely forward and medially, it is inserted into the adjacent parts of the first cuneiform and the back part and under surface of the first metatarsal. While in connection with the under surface of the cuboid, this tendon is covered in by a sheath from the long plantar ligament, and often contains a sesamoid bone. The two peronei evert the foot, as is seen in talipes valgus and in fracture of the lower end of the fibula; the peroneus longus aids in the support of the arch of the foot (p. 1466), and, by keeping the great toe on the ground, is important in the third stage of walking, skating, etc. Annular ligaments and synovial membranes of tendons. — These strap-like bands of deep fascia, which serve to keep the above tendons in position, are three in number, viz.: — (A) Lateral. — This, the superior peroneal retinaculum, extends from the tip of the lateral malleolus to the lateral surface of the calcaneus. It keeps the two Fig. 1178. — Relations op Parts behind the Medial Malleolus. (Heath.) Tendo Achillis Tibialis posterior Flexor digitorum longus Cruciate Ugament 7^-i^ ' li'-f'CJ' ■ Posterior tibial artery Tibialis posterior Tibialis anterior Tibial nerve Fezor digitorum longus peronei in place, and surrounds them behind the fibula in one sheath with a single synovial sac, which extends upward into the leg for 3 . 7 cm. (1| in.), and sends two processes into the two sheaths in which the tendons lie on the calcaneus. Farther on, while in relation with the cuboid, the peroneus longus has a second synovial sheath. (B) Medial. — This, the laciniate ligament, crosses from the medial malleolus to the medial surface of the calcaneus. Beneath it are the following canals : — (1) For the tibialis posterior. This tendon-sheath is lined by a sj^novial membrane extending from a point 3.7 cm. (1| in.) above the malleolus to the navicular. (2) For the flexor digitorum longus. The synovial sheath of this tendon is separate from that of the closely contiguous tibialis posterior. It extends upward into the leg about as high as the sheath just given. It reaches down into the sole of the foot; but where the tendon subdivides to enter the thecse, each of these is lined by a separate synovial sheath. Next comes (3) a wide space for the posterior tibial vessels and nerve; and, lastly, (4) a canal, like the other two, with a separate synovial sheath, for the tendon of the flexor hallucis longus. The lower margin of this annular ligament gives an attachment to the abductor hallucis and blends with the plantar fascia. The medial calcaneal vessels and nerve perforate the ligament. \ 1464 CLINICAL AND TOPOGRAPHICAL ANATOMY (C) Anterior annular ligament. — This is a double structure. (1) Upper (transverse crural ligament), above the level of the ankle-joint, and tying the tendons down to the lower third of the leg, passes transversely between the ante- rior crest of the tibia and fibula. Here is one sheath only, with a synovial mem- brane for the tibialis anterior. (2) Lower, over the ankle-joint. This band, the cruciate ligament, is arranged like the letter -<, placed thus. It is attached by its root to the calcaneus, and by its bifurcations to the medial malleolus and plantar fascia. This arrangement of the branches of this ligament is not constant. In this, the lower annular ligament, there are usually three sheaths with separate synovial membranes — the most medial (the strongest in each) for the tibialis anterior, the next for the extensor halluois longus, and the third common to the extensor communis and peroneus tertius. The extensor digitorum brevis has a partial origin from this ligament. Points in tenotomy and guides to the tendons. — The tendo Achillis should be divided about 3.7 cm. (If in.) above its insertion, its narrowest point, which is about on a level with the medial malleolus. The knife should be introduced on the medial side and close to the tendon, so as to avoid the posterior tibial artery (fig. 1178). The tibialis anterior may be divided about 25 mm. (1 in.) above its insertion into the first cuneiform, a point which is below the level of its synovial sheath. The tendon has here the dorsalis pedis on its lateral side, but separated by the tendon of the extensor hallucis longus. The knife is introduced on this side. The tibialis posterior. — The usual rule for dividing this tendon is to take a spot 5 cm. (2 in.) above the medial malleolus, and as accurately as possible midway between the anterior and medial borders of the leg. This point will give the medial margin of the tibia, in close ap- position to which the tendon is lying, and is a point at which the tendon is rather farther from the artery than it is below, and is also above the commencement of its synovial sheath. A sharp-pointed knife is used first to open the sheath freely, and then a blunt-pointed one to divide the tendon. The flexor digitorum longus is usually cut at the same time. Owing to the risk of injury to the posterior tibial vessels, the difficulty of ensuring division of the tendons, the following open method is, nowadays, superior, being more certain, and ad- mitting of division of ligaments, e. g., talo-navicular and anterior part of deltoid (syndesmotomy of Parker), which are always contracted in advanced talipes equino-varus. A V-shaped flap with its apex over the first metatarsal bone, and its two limbs starting, the lower below the margin of the plantar fascia on a line with the medial malleolus, the upper from a point over the head of the talus, is turned backward. The plantar fascia is divided, the tibiaUs anterior is found, near its insertion, under the upper hp of the wound, the tibialis posterior and the flexor digitorum longus in the lower, the former close to the navicular. If necessary, the calcaneo- and talo-navicular and anterior part of the deltoid ligaments can be divided also. Peronei. — The peronei longus and brevis may be divided 5 cm. (2 in.) above the lateral malleolus, so as to be above the level of their synovial sheath. The knife should be inserted very close to the bone, so as to pass between the fibula and the tendons. Division below the ateral malleolus by a small flap is easier. THE FOOT Bony landmarks. — The following are of the greatest practical importance owing to the operations which are performed upon the foot. (A) Along the medial aspect of the foot are the following :■ — (1) Medial tuberosity of the calcaneus; (2) medial malleolus; (3) 2.5 cm. (1 in.) below the malleolus, the sustentaculum tali; (4) about 2.5 cm. (1 in.) in front of the medial malleolus, and a little lower, is the tuberosity of the navicular, the medial guide in Chopart's amputation, the gap between it and the susten- taculum being filled by the calcaneo-navicular ligament and the tendon of the tibialis posterior, in which there is often a sesamoid bone; (5) the first cuneiform; (6) the base of the first metatarsal; and (7) the head of the same bone, with its sesamoid bones below. (Holden). (B) Along the lateral aspect are : — (1) The lateral tuberosity of the calcaneus; (2) the lateral malleolus; (3) the peroneal tubercle of the calcaneus (when pres- ent), 2.5 cm. (1 in.) below the malleolus, with the long peroneal tendon below it, and the short one above; (4) the projection of the anterior end of the calcaneus, and the calcaneo-cuboid joint, midway between the tip of the lateral malleolus and the base of the fifth metatarsal bone; (5) the base of the fifth metatarsal bone; (6) the head of this bone. The greater process of the calcaneus and the muscular origin of the short extensor lie between the peroneus brevis and tertius. Levels of joints and lines of operations. — The line of the ankle-joint has been given at p. 1459. That of the talo-calcaneal joint — the limited lateral movements of the foot take place here and at the medio-tarsal joint — corresponds, on the lateral side, to a point a little in front of the lateral malleolus and midway between it and the peroneal tubercle; on the medial THE FOOT 1465 side, to one just above the sustentaculum tali. In Syme's amputation through the ankle-joint, the incision starts from the tip of the lateral malleolus, and is then carried, pointing a little back- ward toward the heel, across the sole to a point 1.2 em. (i in.) below the medial malleolus. The chief supply to the heel-flap is from the medial calcaneal. Care should be taken to divide the posterior tibial below its bifurcation and not to prick this vessel afterward. In Pirogoff's amputation the incision begins and ends at the same points, but is carried straight across the sole. In each amputation the extremities of the above incision are joined by one going directly across the ankle-joint, which lies about 1.2 cm. (5 in.) above the tip of the internal malleolus. In Chopart's medio-tarsal amputation, which passes between the talus and the navicular on the medial side, and the calcaneus and the cuboid on the lateral, the line of the joints to be opened would be one drawn across the dorsum from a point just behind the tuberosity of the navicular to a point corresponding to the calcaneo-cuboid joint, just midway between the tip of the lateral malleolus and the base of the fifth metatarsal bone. The convexity of the plantar flap should reach to a point 2.5 cm. (1 in.) behind the heads of the metatarsal bones. Owing to the tendency of the unbalanced action of the calf muscles to tilt up the calcaneus and thus thi'ow the scar down into the line of pressure, the powerful tibialis anterior tendon and those of the extensors should be carefully stitched into the tissues of the sole flap. In Lisfranc's, or Hey's, or the tarso -metatarsal amputation, the bases of the fifth and first metatarsals must be defined. The first of these can always be detected, even in a stout 'or swollen foot; on the medial side the joint between the first cuneiform and the first metatarsal Fig. 1179. — Vektical Section through the Cuneiform and Cuboid Bones. (One-half.) Dorsalis pedis vessels and nerve Extensor hallucis longus First cuneiform Tibialis anterior Second cuneiform I Third cuneiform , Extensor digitorum brevis , Dorsal aponeurosis I Cuboid I Peroneus tertius Abductor ballucus Medial plantar vessels and nerve Abductor hallucis Flexor hallucis longus Plantar fascia Flexor digitorum longus Abductor digiti quinti Lateral plantar vessels and nerve Tendon of peroneus longus Flexor digitorum brevis bone lies 3.7 cm. (IJ in.) in front of the navicular tuberosity. In opening the joint between the second metatarsal and the middle cuneiform, its position (the base of the former bone projecting upward on to a level 6 or 8 mm. (| or 5 in.) above the others), and the way in which it is locked in between its fellows and the cuneiform bones, must be remembered. The convexity of the plantar flap here reaches the heads of the metatarsal bones. In marking out the flaps for the amputation of the great toe, the large size of the head of the first metatarsal, and the importance of leaving this so as not to diminish its supporting power and the treading width of the foot, and thus of marking out flaps sufficiently long and large, must be borne in mind. The dorsal incision should begin 3.7 cm. (1| in.) above the web. The line of the joint is a httle distal to the centre of the ball of the toe (fig. 1181). The sesa- moid bones should be left, so as not to endanger the vitaUty of the flaps. In amputation of the other toes, the line of their metatarso-phalangeal joints lies a full inch above the web. Bursse and synovial membranes. — The synovial sheath of the extensor hal- lucis longus extends from the front of the ankle, over the instep, as far as the meta- tarsal bone of the great toe. There is generally a bursa over the instep, above, or it may be below, the tendon. There is often an irregular bursa between the tendons of the extensor digitorum longus and the projecting end of the talus over which the tendons play. There is much friction here. It is well to be aware that this bursa sometimes communicates with the joint of the head of the talus. (Holden.) There is a deep synovial bursa between the tendo Achillis and the cal- caneus. Numerous other bursie may appear over any of the bony points in the foot, especially when they are rendered over-prominent by morbid conditions. Synovial membranes. — In addition to that of the ankle-joint, there are six synovial membranes in the tarsus, viz.: — (1) Talo-calcaneal, peculiar to these i 1466 CLINICAL AND TOPOGRAPHICAL ANATOMY bones; (2) talo-calcaneo-navicular, common to these bones and the navicular; (3) between the calcaneus and the cuboid; (4) between the cuboid and the lateral two metatarsals; (5) between the first cuneiform and the first metatarsal; (6) a comphcated and extensive one, which branches out between the navicular and cuneiform bones; between the cuneiforms; between the third cuneiform and the cuboid ; between the second and third cuneiform and the second and third meta- tarsal bones; and between the second and third and the third and fourth meta- tarsal bones. Fig. 1180. — Superficial Nerves in the Sole of the Foot. (Ellis.) Abductor hallucis- Flexor digitorum brevis' Medial plantar nerva Medial plantar artery. Proper plantar digital nerve to medial side of hallux Abductor minimi digiti Lateral plantar artery Lateral plantar nerve Proper plantar digital branches of the lateral plantar Proper plantar digital branches of the medial plantar Dorsal artery. — The line of this is from the centre of the ankle-joint to the upper part of the first interosseous space. On its medial side is the tendon of the extensor hallucis longus ; on its lateral, the most medial tendon of the extensor digitorum longus. It is crossed by the most medial tendon of the extensor brevis. The origin of this muscle should be noted on the lateral and fore part of the calcaneus. Cutaneous nerves (fig. 1182). — The sites of these, numerous on the dorsum of the foot, are as follows: — The superficial peroneal (musculo -cutaneous) nerve, having perforated the fascia in the lower third of the leg, divides into two chief branches, medial and lateral, which supply all the toes save the lateral part of the little, and the adjacent sides of the first and second. The deep peroneal becomes cutaneous in the first space, and is distributed to the contiguous sides of the above- THE FOOT 1467 mentioned toes. The sural nerve runs with the small saphenous vein below the malleolus, and supphes all the lateral border of the foot and the lateral side of the little toe. The saphenous nerve, coursing with the great saphenous vein in front of the medial malleolus, supplies the medial border of the foot as far as the middle of the instep. The cutaneous nerves to the sole (from the medial calcaneal, medial, and lateral plantar) are shown in fig. 1180. Plantar arteries. — The line of the medial would be one drawn from the bifur- cation of the posterior tibial, or about midway between the tip of the medial mal- leolus and the medial border of the heel, to the middle of the plantar surface of the great toe. The course of the lateral plantar runs in a line drawn from the bifur- cation, first obhquely across the foot to a point a little medial to the medial side of the base of the fifth metatarsal, and thence obliquely across the foot till it reaches the first space and joins with a communicating branch from the dorsal artery. It thus crosses the foot twice. In the first part, it is more superficial, in the second Fig. 1181. — Longitudinal Section of Foot. (One-third.) (Braune.) Tendo AchiUis Posterior tibial vessels , Talus and nerve Kavicular First cuneiform Extensor hallucis longi Flexor hallucis longus Flexor hallucis brevis Lumbricalis Calcaneus Abductor digiti (juinti Lateral plantar vessels and nerve Quadratus plantse Flexor digitorum brevis Flexor digitorum communis Medial plantar nerve very deep ; it here forms the plantar arch, and is only separated from the bases of the metatarsals by the interossei. The anastomosing branches about the ankle-joint are shown in figs. 1170 and 1171. Tarsal bones. — The chief surgical points about these is the frequency with which they are diseased and their changes in taHpes. Frequency of disease. — This is explained, chiefly, by their delicate structure and the fact that on the aspect in which they are most exposed to injury the soft parts are scanty. Disease once started, often by slight injury, finds in the ter- minal circulation of the parts, and the frequent want of rest, other contributing causes. The numerous and complicated synovial membranes mentioned above explain the extension of the disease. The calcaneus is the only bone in which mischief is likely to remain limited. The presence of an epiphysis to this bone appearing about the age of ten and joining at puberty is to be remembered as a starting-point of disease here. Talipes. — To take one instance, a case of talipes equino-varus, of congenital origin and confirmed degree, the following are the chief structural changes which should have been obviated and now have to be met, given briefly. Calcaneus. — This is elevated posteriorly, and rotated so that its long axis is du"ected obliquely medially. Talus. — The inclination of the neck medially is much increased, and the whole bone protruded from the ankle-joint. According to some, the neck is increased in length. Navicular. — This is displaced medially so that it articulates with the medial side of the head of the talus, and its tuberosity may form a facet on the medial malleolus. Cuboid. — The dorsal surface of this is displaced downward, and bears much of the pressure in wall^ing. Tendons. — Those chiefly shortened are the tendo AchiUis and those of the tibials and flexor digitorum longus. The tendo AchiUis is displaced medially. Ligaments. — Those on the lateral side are stretched, those on the medial, especially the anterior part of the deltoid, the dorsal talo-navicular and the plantar calcaneo-navicular ligaments are shortened. The plantar fascia is also shortened, together with the abductor hallucis, which arises from it. i 1468 CLINICAL AND TOPOGRAPHICAL ANATOMY ■ ARCHES OF THE FOOT These are two — the longitudinal and the transverse. (A) Longitudinal arch (fig. 1181). — This is by far the most important. Ex- tent : From the heel to the heads of the metatarsal bones. The toes do not add much to the strength and elasticity of the foot. (Humphry.) They enlarge its area and adapt it to inequalities of the ground, are useful in climbing, and in giving an impulse to the step before the foot is taken from the ground, in the third stage of walking. Two pillars. — The late Professor Humphry laid stress on the important differences between these two: — (1) Posterior pillar: This consists of the calcaneus and hinder part of the talus, viz., only two bones in order to secure solidity, and to enable the calf-muscles to act directly upon the heel, without any of that loss of power which would be brought about by many moving joint-sur- faces. (2) Anterior pillar: Here there are many bones and joints to provide (a) elastic springiness, and (6) width. This anterior pillar may again be divided into two: (a) A medial pillar, very elastic, consisting of the talus, navicular, three cuneiforms, and three medial metatarsals. (6) A lateral, formed by the cuboids and two lateral metatarsals. This is stronger and less elastic, and tends to but- tress up the medial pillar. Keystone : This is represented by the summit of the trochlear surface of the talus. It differs from the keystones in ordinary arches in the following important particulars (Humphry) : (a) in not being wedge-shaped; (6) in not being so placed as to support and receive support from the two halves of the arch: in front the talus does fulfil this condition by fitting into the navicular; behind, it overlaps the calcaneus without at all supporting it; (c) this arch and the support of its keystone largely depend on ligaments and tendons; (d) it is a mobile keystone : to give it chances of shifting its pressure, and so obtaining rest, its equilibrium is not always maintained in one position. (B) Transverse arch (fig. 1179). — This is best marked about the centre of the foot, at the instep, along the tarso-metatarsal joints. This, as well as the longitu- dinal arch, yields in walking, and so gives elasticity and spring. Uses of the arches. — (1) They give combined elasticity and strength to the tread. Thus they give firmness, free quickness, and dignity, both in standing and walking, instead of what we see in their absence, viz., the lameness of an artificial limb, and the shufHing or hobbhng which goes with tight boots, deformed toes, flat-foot, bunions, corns, etc.; (2) they protect the plantar vessels, nerves, and muscles; (3) they add to man's height; (4) they make his gait a per- fect combination of plantigrade and digitigrade, as is seen in man's walking, when he uses first the heel, then all the foot, and then the toes. (Hiimphry.) Maintenance of the arch. — (1) Plantar fascia. — -This is (a) a binding tie between the pillars of the longitudinal arch; (6) it protects the structures beneath; (c) it is a self-regulating ligament and protection. Thus, having a quantity of muscular tissue attached to its upper and back part, is constantly responds by the contraction of this, to the amount of any pressure made upon the foot. (2) Plantar calcaneo-navicular ligament. — This is a thick tie-plate of fibro-cartil- aginous tissue, partly elastic, hence called the 'spring-ligament,' attached to the anterior margin of the sustentaculum tali and under surface of navicular. It is thickest at its medial side, where it blends with the anterior part of the deltoid ligament, and below, where the tibialis posterior, passing into the sole, is in contact with the ligament and gives much support to the head of the talus and the navicular, while it assists the power and spring of this ligament {vide infra). The dropping of the talus and navicular and their projection on the medial side in flat-foot are largely due to the giving way of the above ligament. (3) Calcaneo-cuboid ligaments, (o) Long; (b) short. — 'These ligaments are the main support of the lateral, firm, and less elastic part of the longitudinal arch. (4) Tibialis posterior. — The reason of this muscle having so many insertions below is to brace together the tarsal bones, and to prevent their separation when, in treading, the elastic anterior pillar tends to widen out. Of these numerous offsets, that to the navicular is the most important. Thus it strengthens the calcaneo-navicular ligament by blending with it, and thus supports the arch at a trying time. By coming into action when the heel is raised, this tendon helps the calcaneo-navicular ligament to support the head of the talus, and to main- tain the arch of the foot when the weight of the body is thrown forward on^to the instep. In other words, the tibialis posterior comes into play just when the heaviest of its duties is devolving upon this ligament, viz., when the heel is being raised, and the body-weight is being thrown over the instep on to the opposite foot. (5) Peroneus longus. — This raises the lateral pillar, and steadies the lateral side of the arch. Further, by its strong process attached to the first metatarsal bone, it keeps the great toe strapped down firmly against the ground; thus, keeping down the anterior pillar of the longitudinal arch, it aids the firmness of the tread. (Humphry.) (6) Tibialis anterior. — This braces up the keystone of the arch. Thus, by keeping up the first cuneiform, it maintains the navicular, and so indirectly the talus in situ. Fig. 1172 will remind the reader of the arrangement of the superficial lym- phatics of the lower extremity. These follow chiefly the saphenous veins, and enter the inguinal nodes, except those from the lateral aspect of the heel which THE LOWER LIMB 1469 drain into the popliteal lymph-nodes . The superficial lymphatics of the buttock enter the lateral, and those over the adductor muscles the most medial group of the inguinal glands. The deep lymphatics of the lower limb, comparatively few in number, follow the course of the deeper vessels. After passing through some four or five glands deeply placed about the popliteal vessels (these glands also receive the lymphatics along the small saphenous vein), the lymph is carried up by lymphatics along the femoral artery to the deep inguinal nodes; one very often occupies the femoral canal. Fig. 1182 shows the distribution of the superficial nerves on both aspects of the limb. Fig. 1182.- -DlSTRIBUTION OF CuTANEOUS NerVES ON THE POSTERIOR AND AnTEEIOB ASPECTS OF THE Inferior Extremity. Posterior branches of lumbar nerves Posterior branclies of sacral nerves Perforating cutaneous of fourth sacral Perineal branch of posterior cutaneous Branch of posterior cutaneous Obturator Branch of femoral nerve Twigs from saphenous Cutaneous branch of peroneal Superficial peroneal Deep peroneal Paralysis of the nerves of the lower extremity. — Ttie student sliould take this opportunity of considering from the surgical anatomy the results of paralysis of the nerve chiefly affected, viz., the great sciatic and its branches. Sciatic: The limb hangs flail-like, much in the position of one affected with advanced infantile paralysis. In addition to the results of paralysis of its two divisions, flexion at the knee will be lost, owing to paralysis of the hamstrings. Peroneal (external popliteal) nerve: The extensors and psronei being paralysed the foot drops, it cannot be dorsiflexed at the ankle nor abducted at the medio-tarsal joint. Adduction at the latter joint is impaired owing to paralysis of the tibialis anterior. The arch of the foot is largely lost owing to paralj'sis of the peroneus longus. Slight extension of the two distal phalanges of the four lateral toes is still possible by means of the interossei. Sensation is impaired over the distribu- tion of the medial sural cutaneous deep, and superficial peroneal nerves. Tibial (internal popliteal) nerve: Here the calf muscles, the flexors, and the muscles of the' sole of the foot are paralysed. The ankle cannot be plantar-flexed. i INDEX Bold-face type indicates the more complete descriptions Abdomen, 1142 clinical anatomy of, 1370 landmarks of, 1370 lymphatic nodes of, 730 lymphatics of, 730 morphology of, 1144 muscles acting on, 503 regions, 1142, 1370 Abdominal aorta, 690, 1382, 1408 branches, 591 aortic plexus of nerves, 1045 branches of vagus, 958 fossaj, 430 (inguinal) rings, 429, 430, 1371, 1394, 1396 portion of ureter, 1248 wall, lymphatics in^ 733 superficial veins m, 683 Abducens, 934 nucleus of, 826 Abduction, 321 Abductor acoessorius digiti quinti, 499 digiti quinti (foot), 454, 498 (hand), 404 hallucis, 496 longus, 482 ossis metatarsi quinti, 499 pollicis brevis, 406, 407 longus (extensor ossis metacarpi pollicis), 392, 393 Aberrant artery of aorta, 590 spinal ganglia, 965 Abnormalities (see individual organs). Aocessorius ad fiexorem digitorem profundum, 402 of gluteus minimus, 462 (ilio-costalis dorsi), 416 Accessory (spinal accessory) nerve, 958 Acervulus cerebri, 846 Acetabular artery, 608 foramen, 174 notch, 174 Acetabulum, 169, 173 Acoustic area, 814 (auditory) nerve, 949, 1096 nuclei of, 823 meatus (see "Auditory Meatus"), (medullary) strix, 814, 824 Acromial branches of posterior circumflex hu- meral artery, 573 of thoraco-acromial artery, 571 of transverse scapular artery, 565 (scapular) e.xtremity of clavicle, 141 Aoromio-clavicular joint, 251, 1363 Acromion angle, 144 process, 144 Acromio-thoracio axis, 671 Action of muscles (see corresponding muscle). Adam's apple, 1211 Addison's transpyloric line, 1153, 1370 Adduction, 321 Adductor brevis, 453, 471, 474 (Hunter's) canal, 468, 618, 1441 digiti secundi, 498 hallucis, 454, 496, 498 longus, 453, 471, 472, 1437 Adductor magnus, 453, 471, 474, 1437 (medial) group of thigh muscles, 453 minimus, 474 pollicis, 407, 408 tubercle of femur, 181 Adenoids, naso-pharyngeal, 1130, 1354 Adipose body, pararenal, 1243 capsule of kidney, 1242 folds of pleura, 1237 Aditus of larynx, 1222, 1223 Adminiculum lineae albse, 427 Adrenals (see "Suprarenal glands"). Aeby's division of bronchial branches, 1232 Agger nasi, 88, 1206 Aggregated follicles (Peyer's patches), 704 Air-cells, mastoid, 72 Air-sacs, 1232 Ala of central lobule of cerebellum, 806 cinerea (trigonum vagi), 814 nucleus of, 820 Alse of frontal bone, 60 nasi, 1201 Alar folds, 291 (lateral occipito-odontoid or check) liga- ments, 223 (lower lateral) nasal cartilages, greater, 1201 lesser, 1202 processes of ethmoid, 81 Alcock's canal, 441, 445, 1384 Alimentary tract, lymphatics of, 699, 733, 1168 Ali-sphenoid centre, 67, 119 AUantois, 13, 1253 Alopecia, 1293 Alveolar (dental) artery, inferior, 548 posterior superior, 549 anterior superior, 549 canals, 87 ducts, 1232 (dental) nerves, 938 inferior, 941 superior, 938 periosteum, 1119 point, 109 part of mandible, 96 maxilla, 87, 90 saccules (air-sacs), 1153 veins, 646 Alveoli (air-cells), 1232 Alveus, 877 of limbic lobe, 868, 869 Amastia, 1301 Amnion, 9, 10 Ampulla, of ductus (vas) deferens, 1257 lactiferous, 1302 phrenica, 1142 recti, 1176 of semicircular canals, 80 of tubs uterinse (Fallopian tubes), 1270 of Vater, 1188 Ampullae, membranous, 1095 of splenic arterioles, 1312 Ampullar branches of vestibular ganglion, 950 Anipullary crista, 1095 sulcus, 1095 Amputation at centre of the arm, 1416 Chopart's medio-tarsal, 1465 I 1472 INDEX Amputation of foot, 1465 of forearm, 1424 of great toe, 1465 of leg, 1459 Pirogoff's, 1465 Syme's, 1465 tarso-metatarsal (Hey's or Lisfranc's), 1465 through thigh, 1442 Amygdala (tonsil) of cerebellum, 807 Amygdaloid nucleus, 881 of lateral ventricle, 877 Amyloid tubercle of lateral ventricle, 877 Anal canal, 1177 surgical anatomy of, 1390 valves, 1177, 1390 Anapophysis, 38 Anastomosis of arteries (see corresponding artery). , Anastomotic branch of facial nerve, 944 (perforating) of middle meningeal arterj', 548 ulnar, of superficial radial nerve, 987 Anastomotica magna artery (genu suprema), 621 Anatomical neck of humerus, 147 Anatomy, definition of, 1 of fourth ventricle, 812 Anconeus, 374, 377, 379 internus, 402 Andersch, ganglion of, 951 Angle (s), acromion, 144 cephalo-auricular, 1084 of fissure of Rolando, 860 infrasternal, 139 of Louis, 139 lumbo-saoral, 43 of mandible, 86 of maxilla, 88 of occipital bone, 53 of parietal bone, 57, 1332 of rib, 127 sacro-vertebral, 39, 43 of scapula, 143 of sternum, 133, 139 subscapular, 145 Angular artery, 540 gyrus, 863 motion of joints, 214 process, lateral (zygomatic), 60 medial, 60 vein, 643 Angulus Ludovici, 139 Ankle, annular ligaments, 1463 bony landmarks of, 1459 clinical anatomy of, 1459 synovial membranes of tendons at, 1463 tendons at, 1460 Ankle-joint, 297 arterial supply, 300 ligaments of, 298 movements, 300 muscles acting upon, 301 nerve-supply, 299 synovial membrane of, 299 Annular ligaments of ankle, 1463 of superior radio-ulnar joint, 262 of trachea and bronchi, 1227 of wrist, 387 Annulus(i) fibrosi of heart, 518 fibrosus, 318 inguinalis abdominalis, 430 subcutaneous, 430 iridis major, 1054 minor, 1054 tendineus communis, 1067 of tympanic membrane, 1087 urethral, 1253 Ano-coccygeal nerves, 1018 Anomalous (muscle of nose), 335 Ano-rectal lymphatic nodes, 735 Ansa hypoglossi, 953, 974, 979 lenticularis, 880 subclavia (ansa Vieussenii), 1036 Antagonists (muscles), 322 Anthelix, 1082 Antibrachial cutaneous branch (external), dor- sal, of radial nerve, 985 cutaneous nerve, lateral, 987 (internal) medial, 984 interosseous nerve, dorsal, 986 fascia, 384 vein, median, 667 Anti-tragicus, 1084 Antitrago-helicine fissure, 1084 Antitragus, 1082 Antrum cardiacum, 1142 of Highmore (maxillary), 87, 90, 111, 1346 maxOlary, 77, 79, 1274 pyloric, of stomach, 1151 tympanic (mastoid), 72, 73, 78, 1092, 1336 Anus, 1177 clinical anatomy of, 1390 development of, 1179 lymphatics of, 735 sphincters of, 448 Aorta, 529, 586, 590 abdominal, 690, 1382, 1408 branches, 591 arch of, 530 ascending, 529 descending, 586 development, 633 relations of, 1369, 1382 semilunar valves of, 517 thoracic, 586, 1369 variations, 637, 638 Aortic arch, 530 intercostal arteries, 588 isthmus, 531 paraganglia, 1329 septum, 527 sinuses (of Valsalva), 518, 530 spindle, 531 Aortico-renal ganglion, 1043 Apertura pyriformis, 108, 112 Aperturae cutis, 1282 Apertures, anterior nasal (nares), 108, 1200 of larynx, 1222 palpebral, 1052 of pelvis, 175, 176 posterior nasal (choanae), 1206 superior thoracic, 138, 1365 Apex of arytsenoid cartilage, 124 of fibula, 190 of heart, 508 linguaj, 1106 of lung, 1230, 1233 of nose, 1200 of patella, 185 of prostate, 1264, 1389 of thyreoid lobes, 1315 of suprarenal gland, 1326 Apical dental (suspensory) ligament, 223 Aphasia, motor, 894 sensory, 894 Aponeuroses, 314, 317 Aponeurosis of epicranius (occipito-frontalis), 337 palmar, 387, 1430 pharyngeal, 1130 plantar, 492 Apophysis of femur, 184 Apparatus, lacrimal, 1078 olfactory, 1049 J INDEX 1473 Appendages of skin, 1290 cutaneous glands, 1296 hair (pili), 1290 mammary glands, 1299 nails (ungues), 1293 Appendices epiploicae, 1170 vesiculosi (hydatids of Morgagni), 1269 Appendicular artery, 598, 1378 skeleton, 139 Appendix epididymidis, 1257 testis (hydatid of Morgagni), 1257 ventricular, of larynx, 1223 vermiform, 1173, 1378 Aquaeductus cerebri (Sylvii), 834 vestibuli, 72, 80, 117 Aqueduct of Fallopius (facial canal), 72 Aqueous chambers, 1064 humor, 1052 Arachnoid granulations (Pacchionian bodies), 649, 919 membrane, 771, 917 cranial, 918 spinal, 919 vessels and nerves of, 920 Arantius, ventricle of, 813 Arbor vitK of cerebellum, 809 Arch of aorta, 530 branches of, 532 costal, 139 of cricoid cartilage, 1210 deep volar, 586, 639, 1426 venous, 671 dental, 1123 digital venous, 667 dorsal venous (foot), 684 jugular venous, 648 lateral lumbo-costal, 437 medial lumbo-costal, 437 parieto-occipital, 863 plantar, 627 pubic, 176 superciliary, 59, 108 superficial volar, 582, 639, 1425 venous, 671 tarsal, inferior, 554 superior, 554 venous, plantar, 687 of vertebrse, 30 zygomatic, 1332 Arches, of atlas, 32, 33 branchial, 17 of the foot, 1468 palatine, 1132 Architecture of heart, 518 Archoplasm, 5 Arciform process, 466 Arcs, reflex, 768 Arcuate (metatarsal) artery), 632 crest of arytajnoid cartilage, 1212 fibres of medulla oblongata, external, 800, 818 internal, 815, 817 ligament, external, 437 internal, 437 of symphysis pubis, 239 renal arteries, 1247 Arcus tendineus, 317, 440 fascise pelvis (white line), 440 Area(s) acustica, 814 association, of cerebral cortex, 894 auditory (cochlear), of cerebral cortex, 893 of Broca (area parolfactoria), 858, 865 cortical, of speech, 894 dangerous, of the leg, 1457 of scalp, 1333 gustatory, of cerebral cortex, 894 olfactory, of cerebral cortex, 893 Area(s), olfactory, of nasal cavity, 1049 plumiformis (of Retzius), 814 postrema of Retzius, 814 somsesthetic, of cerebral cortex, 893 surface, of telencephalon, 853 visual, of cerebral cortex, 893 Areas, cutaneous, of face, 1018 of lower extremity, 1024 of neck, 1019 of scalp, 1018 of trunk, 1020 of upper limb, 1022 of distribution of spinal nerves, 970 functional, of cerebral cortex, 893 Areola of mammary gland, 1300, 1304 secondary, 1304 Areolar glands (of Montgomery), 1304 Arm, centre of, as a surgical landmark, 1414 fasciaj of, 377 musculature of, 362, 374 veins of, 667 Arnold's bundle, 832, 889 ganglion, 963 nerve, 956 Arrectores pilorum, 1293 Arteria aberrans of aorta, 590 of superior intercostal, 568 centralis retinae, 553, 1065 princeps pollicis, 586 radialis indicis, 586 septi nasi, 541 Arterial supply of bones and joints (see corre- sponding bone or articulation), system, morphogenesis and variations of, 633 ArterioliE rectae of kidney, 1247 Artery (see also "Blood-vessels"). Artery (ies), 527 aberrant, 568, 590 accessory (small) meningeal, 548 pudendal, 610, 639 renal, 638 acetabular, 608 acromio-thoracic (thoraco-acromial), 571 angular, 540, 541 anterior central of medulla, 908 cerebral, 554, 562 ciliary, 553, 1065 circumflex humeral, 572 communicating, 555, 562 conjunctival, 553 deep temporal, 548 ethomidal, 554 inferior cerebellar, 561 intercostal, 588 interosseous, of forearm, 1423 mediastinal, 567 perforating, 620 peroneal, 626, 640, 1459 scrotal (or labial), 620 spinal, 561, 792, 638 superior alveolar (dental), 549 tibial, 629, 640, 1458 recurrent, 632 tympanic, 547 aorta, 529, 586, 637, 638 aortic intercostals, 588 appendicular, 598, 1378 arcuate (metatarsal), 632 articular, of knee-joint, 622, 1452 ascending cervical, 564 pharyngeal, 537 palatine, 540 of auricle (of ear), 1084 axillary, 569, 1412 azygos, of vagina, 610 basilar, 561 1474 INDEX Artery(ies), brachial, 573, 640, 1414 of brain, 555, 905 bronchial, 588, 638, 1234 buccal, 548 of bulb of urethra, 613 caroticotympanic, 552 central or ganglionic, 906 of pons, 908 of cerebellum, 907 of cerebral hemorrhage (Charcot), 562, 906 peduncles, 907 chorioid, 554, 908 ciliary, 553, 1065 circumflex (dorsal) scapular, 572 of the clitoris, 613 deep, 614 dorsal, 614 casliao, 593, 638 common carotid, 533 digital, 582 iliac, 603 interosseous, of forearm, 577 coronary, 519 cortical cerebral, 906 costo-cervical trunk, 568 cystic, 595 deep auricular, 547 cervical, 568 circumflex iliac, 616 lingual, 540 plantar (communicating), 633 deferential, 610 descending palatine, 549 dorsal of foot, line of, 1466 digital (foot), 633 (hand), 586 interosseous (metatarsal),^633 of forearm, 579 lingual, 539 metacarpal, 586 metatarsal (interosseous), 633 nasal, 554 perforating, of palm, 586 radial carpal, 585 thoracic (thoraco-dorsal), 572 ulnar carpal, 580 recurrent, 577 dorsalis hallucis, 633 pedis, 632 episcleral, 553 of external acoustic (auditory) meatus, 1086 carotid, 536, 1343 iliac, 614 maxillary (facial), 540, 638, 1343;] pudendal (pudic), 619 spermatic, 615 striate, 906 'I femoral, 616, 1441 common, 616 superficial, 616 fibular nutrient, 626 of the fraenum, 540 frontal, 554, 1343 gastro-duodenal, 594 genu suprema (anastomotica magna), 621, 640 gluteal, 608 hepatic, 594 of humerus, nutrient, 576 hypogastric (internal iliac), 605, 639 ilio-colic, 598 ilio-lumbar, 606 inferior alveolar (dental), 548 (deep) epigastric, 614, 639 gluteal, 609, 639, 1444 haimorrhoidal, 613 labial (coronary), 541 Artery(ies), inferior laryngeal, 564 lateral articular, 623 medial articular, 622 mesenteric, 602, 638 pancreatico-duodenal, 596 phrenic, 592, 638 quadrigeminate, 907 suprarenal, 598 thyreoid, 564 tympanic, 537 ulnar collateral, 576 vesical, 609 infraorbital, 549, 1075 innominate, 532, 1369 internal auditory, 561 carotid, 549 mammary, 566 maxillary, 645, 638 pudendal (pudic), 610,!639 spermatic, 598, 638, 1259 striate, 906 intercostals, 588, 638 interosseous recurrent, 580 intestinal, 596 jejunal and iliac, 598 lacrimal, 552 lateral circumflex, 620,^640 malleolar, 632 palpebral, 552 plantar, 627, 640 posterior malleolar, 626 sacral, 607 tarsal, 632 thoracic, 571 left colic, 603 common carotid, 533 iliac, 605 coronary, 520 gastric, 593 gastro-epiploic, 595 pulmonary, 529 subclavian, 556 superior suprarenal,*592,il326 lenticulo-optic, 562 lenticulo-striate, 562 of lig. teres uteri, 615 lingual, 539 long posterior ciliary ,""553, 1065 , lowest lumbar (ima), 603 lumbar, 593, 638 major palatine, 549 masseteric, 548 medial circumflex, 620, 640 malleolar, 632 palpebral, 554 plantar, 629 tarsal, 632 median, of forearm, 578, 639 of medulla oblongata, 908 meningeal, 917 middle or azygos, 623 cerebral, 555, 562 colic, 598 collateral, 576 hsemorrhoidal, 610 meningeal, 547, 1341 quadrigeminate, 907 sacral, 603 suprarenal, 598, 638 temporal, 545 vesical, 609 minor palatine, 649 musoulo-phrenic, 567 nutrient of femur, 621 of humerus, 576 of radius and ulna, 579 of tibia, 626, 1459 INDEX 1475 Artery (ies), obturator, 608, 639 occipital, 642, 638, 1343 oesophageal, 588 omphalo-mesenterio, 638 ophthalmic, 552, 638, 1074 ovarian, 602 parietal, 543 peduncular, 907 of penis, 613 deep, 614 dorsal, 614 perforating, of the profunda, 620 pericardiac (of aorta), 588 pericardio-phrenic, 567 perineal, 613, 639 peroneal, 626, 640, 1459 plantar digital, 628 metatarsal, 628 popUteal, 621, 640, 1452 posterior auricular, 543, 1343 central of medulla, 908 cerebral, 561 circumflex humeral, 573 communicating, 554 conjunctival, 554 deep temporal, 548 ethmoidal, 553 inferior cerebellar, 561 meningeal, 537 peroneal, 626 scapular, 565 scrotal (labial), 613 spinal, 561, 792 superior alveolar (dental), 549 tibial, 624, 640,1458 recurrent, 632 princeps cervicis, 543 poUicis, 586 profunda or deep femoral, 620, 640 (superior) profunda of arm, 576 axillaris, 640 proper digital, 582 heptaic, 595 of pterygoid canal (Vidian), 549 pulmonary, 528, 1234 of quadrigeminate bodies, 907 radial, 582, 1423 collateral, 576 recurrent, 583 at wrist, 584 radialis indicis, 586 renal, 598, 638 of retina, central, 1065 right cohc, 598 common iliac, 605 coronary, 519 gastric, 594 gastro-epiploic, 595 pulmonary, 529 subclavian, 557 superior suprarenal, 592 saphenous, 621 sciatic, 609, 640 short posterior ciliary, 553, 1066 sigmoid, 603 spheno-palatine, 549 spinal, 590 splenic, 595 stapedial, 638 sternocleidomastoid, 542 stylo-mastoid, 544 subclavian, 556, 638 subcostal, 588 subungual, 540 submental, 541 subscapular, 571 superficial cervical, 566 Artery(ies), superficial circumflex iliac, 618 ' epigastric, 618 temporal, 545, 1343 superior cerebellar, 561 epigastric, 567 gluteal, 608, 1444 hajmorrhoidal, 603 intercostal, 568 labial (coronary), 641 laryngeal, 538 lateral articular, 622 medial articular, 622 mesenteric, 696, 638 pancreatico-duodenal, 595 phrenic, 590 quadrigeminate, 907 thoracic, 570 thyreoid, 638, 638 tympanic, 548 ulnar collateral, 576 vesical, 609 supraorbital, 552, 1343 suprarenal, 1326 suprascapular (transverse scapular), 564 sural, 622 systemic, 529 temporal, 545, 548, 1343 testicular, 601 thoraco-aoromial, 571 of thymus, 567 thyroidea ima, 533 transverse cervical (transversa colli), 565. 638 '' ' facial, 545 scapular, 564, 638 ' of tympanic cavity, 1091 ulnar, 576, 1423 umbilical, 609 urethral, 613 uterine, 610 vaginal, 610 variations of, 637, 639 vertebral, 559, 638 of vertebral canal, 590 vesical, 609 Vidian, 549 volar interosseous of forearm, 677, 639 metacarpal, 586 radial carpal, 584 ulnar carpal, 580 recurrent, 577 zygomatico-orbital, 545 Arthrodial diarthroses, 212 Articular arteries of knee-joint, 622, 1452 branches of auriculo-temporal nerve, 941 of common peroneal (external popliteal) nerve, 1013 of deep peroneal (anterior tibial) nerve 1015 of genu suprema artery, 621 of obturator nerve, 1004 of popliteal artery, 623 of posterior circumflex humeral arterv 573 ^' of profunda artery, 621 of tibial (internal popliteal) nerve, 1010 of transverse scapular artery, 565 capsules of acromio-olavicular joint, 251 of articulation of atlas with occiput, 218 of atlanto-dental joint, 222 of capitular articulation, 241 of carpo-metacarpal joint of thumb, 273 of costo-transverse articulation, 243 of hip-joint, 277 of inferior radio-ulnar joint, 264 of knee-joint, 287 of lateral atlanto-epistrophic joint, 231 1476 INDEX Articular capsules of mandibular articulation, 215 of medial tarso-metatarsal articulation, 308 ^ , of metacarpo-phalangeal joint of thumb, 275 of shoulder-joint, 254 of sterno-costo-olavicular joint, 248 of tibio-fibular union, 295 of vertebral joints, 228 cartilage, 211 of shoulder-joint, 255 disc of aoromio-olavicular joint, 251 of inferior radio-ulnar joint, 264 of mandibular articulation, 216 of sterno-costo-clavicular joint, 249 furrows of skin, 1284 nerve, recurrent, of leg, 1013 process of vertebrae, 31 processes of vertebrae, ligaments conneotmg, 228 rete, of knee, 622 Articular tubercle of temporal bone, 71 veins of mandibular joint, 646 Articularis genu (subcrureus), 470 Articulation (s) , 2 1 1 acromio-clavicular, 250 ankle, 297 of anterior parts of tarsus, 303 arycorniculate, 1215 atlanto-epistrophic, 220, 221 of atlas with occiput, 218 of auditory ossicles, 1090 of bodies of vertebrse, 225 calcaneo-cuboid, 306 carpal, 268 carpo-metacarpal, 272 classification of, 212 constituents of, 211 costo-capitular, 241 costo-chondral, 245 costo-transverse, 243 costo-vertebral, 241 crico-arytaenoid, 1214 crico-thyreoid, 1213 cuboideo-navicular, 303 oubo-metatarsal, 308 ouneo-cuboid, 304 cuneo-navicular, 304 elbow, 258 front of thorax, 244 hip, 276, 1434 incudo-malleolar, 1090 incudo-stapedial, 1090 interchondral, 246 intercoccygeal, 238 intercuneiform, 304 intermetacarpal, 273 intermetatarsal, 309 interphalangeal, of fingers, 276 of toes, 310 intersternal, 244 knee, 284 mandibular, 215 of lower limb, 276 medio-carpal, 270 medio-tarsal (transverse tarsal) 305 metacarpo-phalangeal, 274 of thumb, 275 metatarso-phalangeal, 310 movements of, 213 occipito-epistrophic, 223 of ossicles of ear, 1090 of i)elvis, 234 radio-carpal (wrist-joint), 265 radio-ulnar, 261, 1419 sacro-coccygeal, 237 Articulation (s), sacro-vertebral, 232 shoulder, 253, 1413 of the skull, 215 between skull and vertebral column, 218 sterno-costal, 245 sterno-costo-clavicular, 248, 1363 synarthrosis, 212 talo-navicular, 305 tarsal, 301 tarso-metatarsal, 307 tibio-fibular, 295 transverse tarsal, 305 of the trunk, 224 of upper extremity, 248 of vertebral column, 225 Ary-oorniculate articulation (synchondrosis), 1215 Ary-epiglottic fold, 1221 muscle, 1220 Ary-membranosus muscle, 1220 Arytaenoid cartilages, 1211 Arytaenoideus obliquus, 1220 transversus, 1219 Ary-vocalis muscle of Ludwig, 1220 Ascending aorta, 529 cervical artery, 564 colon, 1173, 1379 lumbar veins, 662, 663 palatine artery, 541 pharyngeal artery, 537 Association areas of cerebral cortex, 894 frontal, 894 occipito-temporal, 894 parietal, 894 fibres of spinal cord, 789 system of cerebral hemisphere, 890 Asterion, 101, 1332 Asternal ribs, 127 Astragalus (talus), 192 Athelia, 1301 Atlanto-dental articular capsule, 222 articulation, 220 Atlanto-epistrophic articulation, 220 central, 221 lateral, 221 ligaments, anterior, 221 posterior, 221 Atlanto-mastoid muscle, 422 Atlanto-occipital articular capsule, 218 articulation, 218 ligaments, anterior, 218 posterior, 218 Atlas and epistropheus, joints between, 220 description, 32 development of, 46 with occiput, articulation of, 218 Atria of heart, 508, 511 of lungs, 1232 Atrial musculature, 518 Atrial plexus, 1041 Atrio-vetnricular bundle (of His), 517, 519, 627 orifice (ostium venosum) of left side, 514 of right side, 513 Atrium of heart, 612, 514 of middle nasal meatus, 1206 Attachments and origin of cranial nerves, 929 of spinal nerves, 964 topography of, 966 Attic of middle ear, 77 AttoUens aurem, 337 Attrahens aurem, 337 Auditory (cochlear) area of cerebral cortex, 893 artery, internal, 661 conduction paths, 900 INDEX 1477 Auditory foramen, 125 meatus, external, 75, 108, 1084, 1332 internal, 72, 117 (cochlear) nen^e, 949, 950 (Eustachian) tube, 1092 pharyngeal aperture of, 1130 veins, internal, 652, 657 Auerbach, plexus of, 1030, 1046, 1168 Auricle (pinna) of ear, 1082 cutaneous areas of, 1019 lymphatics of, 714 vessels and nerves, 1084 of heart, 508 Auricular artery, deep, 547 posterior, 543, 1343 branches, anterior, of auriculo-temporal nerve, 941 of great auricular nerve, 973 of occipital artery, 543 of posterior auricular artery, 544 of small occipital nerve, 977 of superficial temporal artery, 545 of vagus, 956 cartilage, 1084 fissure, 75, 108 lymph-nodes, anterior, 709 posterior, 709 muscles, 337 nerve, great, 978 posterior, 944 point, 101 sulcus, posterior, 1083 tubercle (tubercle of Darwin), 1083 veins, anterior, 646 posterior, 647 Auricularis anterior (attrahens aurem), 337 posterior (retrahens aurem), 337 superior (attoUens aurem), 337 Auriculo-frontalis muscle, 337 Auriculo-temporal nerve, 941 Axial set of bones, 27 skeleton, 27, 29 Axillary arch, 374 artery, 569 collateral circulation, 1412 parts, 569, 570 fascia, 370, 371 fossa, clinical anatomy of, 1411 lymphatic nodes, 719 (circumflex) nerve, 984 vein, 671 Axis (epistropheus), 33, 47 cceliac, 593 of eyeball, 1055 of heart, 509 of pelvis, 176 of scapula, 145 th}'reoid (thyreocervical trunk), 564 Axones, 762 motor (efferent), 764 sensory (afferent), 762 sheaths of, 766 of spinal cord, 777 terminations of, 762 Azygos artery of vagina, 610 (major) vein, 662 minor (hemiazygos) vein, 662 tertia (accessory hemiazygos) vein, 663 B Back of hand, 1433 clinical anatomy of, 1403 muscles (spinal), 410 Baillarger, stripes of, 879 Band, diagonal, of Broca, 866 ilio-tibial, 457, 458 Band, ilio-trochanteric, 280 moderator, of heart, 516 tendino-trochanteric, 280 Barba, 1290 Bars, hyoid, 119 mandibular, 119 metamorphosis of branchial or visceral, 119 thyreoid, 119 Barthohn, duct of, 1278, 1892 glands of, 1278, 1392 Basal ganglia, 878 vein, 657 Base of arytsenoid cartilage, 1211 of cranium, 103, 113 of encephalon, 794 of heart, 508 line, Reid's, 1341 of lungs, 1229, 1233 of nose, 1200 of prostate, 1264, 1389 of skull, external, 103 of suprarenal gland, 1325 of thyreoid lobes, 1315 Basi-bregmatic axis, 112 Basi-cranial axis, 112 Basi-facial axis, 112 Basi-hyal, 100, 119 Basilar artery, 561 groove, 54 plexus of veins, 651 sulcus of pons, 804 Basilic vein, 667 median (median cubital), 667 Basion, 108, 112 Basi-occipital, 119 Basi-pharyngeal canal, 63, 67 Basis (pes) pedunculi, 840 cranii, interna, 113 Basi-sphenoid centre, 67, 119 Basivertebral veins, 666 Bechterew's bundle, 784 nucleus of vestibular nerve, 823 • Bell, external respiratory nerve of, 982 Belly of muscle, 314 Bertin, bones of, 67 columns of, 1246 Biceps brachii, 374, 379, 382 relations, 1414 femoris, 453, 475 Bicipital groove, 148 muscles, 314 Bicuspid teeth, 1121 (mitral) valve, 515, 516 Bifurcation of trachea, 1225 Bile-duct, common, 1188, 1373 Bile-passages, 1186 Bipenniform muscles, 315 Birth, bones of skull at, 120 Biventer cervicis, 418 Biventral lobe of cerebellum, 807 Bladder (urinary), 1249 surgical anatomy of ,f 1390 Blandin, glands of, 1110 Blood-vascular system, 507 of small intestine, 1166 of spinal cord, 792 of stomach, 1155 Blood-vessels (see also "Arteries" and "Veins"). of abdominal wall, 1371 of brain, 905 of cerebellum, 907 ciliary, 1065 of conjunctiva, 1348 of ductus deferens, 1259 around elbow, 1418 of eyeball, 1065 1478 INDEX Blood-vessels of eyelids, 1078 of face, 1343 of Fallopian tube, 1270 of female external genitals, 1278 of heart, 519 of kidney, 1247 of large intestine, 1179 of larynx, 1224 of lips and cheeks, 1104 of liver, 1185 of lungs, 1234 of lymph-glands, 706 of mammary glands, 1305 of nose, 1203, 1208 of oesophagus, 1141 of orbit 1074 of ovary, 1269 of palate, 1106 of parathyreoids, 1319 of parotid, 1115 of penis, 1262 of pericardium, 523 of pharynx, 1138 of pleura, 1239 of prostate 1265 of rectum, 1391 retinal, 1065 of scalp, 1334 of scrotum, 1255 of skin, 1288 of spleen, 1312 of sublingual gland, 1117 of submaxillary gland, 1116 of suprarenal glands, 1326 of teeth, 1124 of testis and appendages, 1256 of thymus, 1322 of thyreoid gland, 1316 of tongue, 1111 of trachea and bronchi, 1228 of ureter, 1249 of urinary bladder, 1253 of uterus, 1274 of vagina, 1276 of vulva, 1192 Bochdalek, ganglion of, 939 Body(ies) of axis (epistropheus), 33 carotid, 1327 ciliary, 1060 coccygeal, 1329 of corpus callosum, 852 of epididymis, 1256 of femur," 178 of fornix, 869 of gall-bladder, 1187 geniculate, 834, 845 of hyoid bone, 99 inferior quadrigeminate, 839 of ischium, 171 (central portion) of lateral ventricles, 875 of Luys, 884 mammillary, 871 of nails, 1294 Nissl, 766 Pacchionian, 919 of pancreas, 1195 pararenal adipose, 1243 of penis, 1260 pineal, 845 pituitary, 848, 1352 of pubis, 172 of radius, 153 restiform, 810 of medulla oblongata, 800 of rib, 127 of scapula, 141 of sphenoid, 62 Body(ies) of sternum, 133 of stomach, 1151 superior quadrigeminate, 825, 841 • of sweat gland, 1297 of thymus, 1320 of tongue, 1106 of ulna, 157 of urinary bladder, 1250 of uterus, 1271 of vertebra, 30 vitreous, 1064 Wolffian, 1278 Bone(s), astragalus (talus), 191, 192 of Bertin (sphenoidal conchce), 67 calcaneus, 191, 195 capitate (os magnum), 159, 163 carpal, 159 clavicle, 139 cotyloid, 173 coxal (os innominatum), 169 cuboid, 191, 199 cuneiform, 161, 191, 197 epipteric, 68, 101 ethmoid, 81 of the face, 51 femur, 198 fibula, 189 fifth metacarpal, 167 fifth metatarsal, 203 first metacarpal, 165 first metatarsal, 201 of foot as a whole, 205 fourth metacarpal, 167 fourth metatarsal, 203 frontal, 59 greater multangular (trapezium), 159, 162 hamate (unciform), 159, 163 humerus, 146 hyoid, 99 incus, 79, 119 innominate, 169 inferior nasal concha, 84 interparietal (inca bone), 57 lacrimal, 85 lesser multangular (trapezoid), 159, 162 of limbs, homology of, 206 of the lower extremity, 169 lunate (semilunar), 159, 161 malar, 93 malleus, 79, 119 mandible, 95 maxilla, 87 metacarpal, 164 metatarsal, 200 of middle ear, 79 nasal, 86 navicular (scaphoid), 159, 160, 191, 196 occipital, 51 of orbit, 109 palate, 91 parietal, 57 patella, 184 phalanges, 167, 203 pisiform, 159, 162 pre-maxilla, 89 radius, 152 ribs, 126 scapula, 141 second metacarpal, 166 second metatarsal, 202 sesamoid, 168, 204, 275, 317 of the skull, 51 at birth, 120 morphology of, 117 sphenoid, 62 stapes, 80, 119 styloid, 168 INDEX 1479 Bone(s), suprasternal, 133 talus (astragalus), 191, 192 tarsal, 191 temporal, 68 at birth, 122 mastoid portion, 68, 71 petrous portion, 68, 72 squamous portion, 68, 70 tympanic portion, 69, 70, 75 third metacarpal, 166 third metatarsal, 202 of thorax, 126 tibia, 185 triquetral (cuneiform), 159, 161 turbinate, 67, 83, 84 of tympanum, 79 ulna, 155 of upper extremity, 139 vomer, 85 Wormian, 68 zygomatic, 93 Bony boundaries of perineum, 1383 landmarks of abdomen, 1370 of the ankle, 1459 of the buttocks, 1442 of elbow, 1417 of the foot, 1464 of forearm, 1419 of head, 1331 of the knee, 1447 of the leg, 1453 of the hip and thigh, 1434 ot thorax, 1363 of wrist and hand, 1424 sinuses of skull, 1335 Borders (see individual organs). Boundaries (see individual parts). Bowman's membrane, 1060 Brachia conjunctiva (superior cerebellar pe- duncles), 831, 840 Brachial artery, 573, 640, 1414 branches, 575 collateral circulation, 1414 (internal) cutaneous branch, posterior, of radial nerve, 985 cutaneous nerve, lateral, 985 medial, 983 fascia, 377 group of axillary Ivmphatic nodes, 719 plexus, 980 branches, 982 cords of, 981 relations of, 981, 1360 terminal branches of, 985 venae comitantes, 671 Brachialis, 374, 380, 382 surface markings of, 1415 Brachio-cephalic (innominate) veins, 641 Brachio-radialis (supinator radii longus), 387, 388 Brachium conjunctivum, 812 inferior, 834 superior, 834 pontis, 811 Brain (encephalon), 792 blood-supply of, 905 cerebral hemispheres, 850 cerebrum, 833 cerebellum, 804 diencephalon (inter-brain), 843 isthmus rhombencephali, 832 medulla oblongata, 799 meninges of, 908 mesencephalon (mid-brain), 833 pons (Varoli), 804 prosencephalon (fore-brain), 843 rhombencephalon, 799 Brain, telencephalon (end-brain), 847 topography of, 903, 1338 Branches (see corresponding vessel or nerve). Branchial arches, 17 bars, metamorphosis of, 119 grooves, 17 Branchiomerism, 16, 17 Breast, female (mammary gland), 1299 male, 1305 Bregma, 101, 112, 1332 Brim of pelvis, 175 Broad (lateral) ligaments of uterus (alse ves- pertilionis), 1267, 1393 Broca's area, 858, 865 convolution, 858 diagonal band, 866 Bronchi, 1226, 1231, 1408 Bronchial arteries, 588, 638, 1234 branches, Aeby's division of, 1232 of internal mammary artery, 567 (pulmonary) branches of vagus, 957 glands, 1231 lymphatic nodes, 725, 1225 tubes, branching of, 1231 veins, 664, 666, 1234 Bronchioles, 1232 Broncho-oesophageal muscle, 1141, 1228 Bronchus, eparterial, 1232 hyparterial, 1232 Brunner's glands, 1166 Bryant's triangle, 1436 Buccal branches of cervico-facial nerve, 945 artery, 548 nerve, long, 939 veins, 646 Buccinator, 334 (long buccal) nerve, 939 set of facial lymph-nodes, 711 Bulb(s) , artery of, 613 of hair, 1292 of internal jugular vein, 659 olfactory, 758, 865 of posterior cornu of lateral ventricle, 876 of urethra, 1262 Bulbar plexus, 1041 Bulbi vestibuh, 1277 Bulbo-cavernosus 443, 450 in female (sphincter vaginae), 451 Bulbo-urethral (Cowper's) glands, 1265 Bulbous corpuscles (end-bulbs of Krause), 1290 Bulbus aortae, 530 Bulla, ethmoidal, 84. Ill, 1205 Bundle, Arnold's, 832, 889 atrio-ventricular (of His), 517, 519, 527 commissural, 788 Helweg's (Bechterew's), 784 posterior longitudinal, 817 Tiirk's, 832, 890 of Vicq d'Azyr, 871 Burdach's column of spinal cord, 781 Bursa(Ee) anguli mandibuli, 1288 anserina, 474 of anterior ilio-femoral musculature, 456 thigh muscles, 471 of the arm, subcutaneous, 377 muscular, 379, 383 of back of leg, 486, 491 bicipito-radialis, 383 cubitalis interossea, 383 of dorsal arm muscles, 379 epicondyli medialis dorsalis, 379 of facialis musculature, 330 of foot, 500, 1465 of forearm and hand, 384, 395, 403 of front muscles of leg, 483 gluteofemorales, 462 1480 INDEX Bursa(ae), hyoid, 1217 iliaca subtendinea, 457 iliopeotinea, 456 of infra-hyoid muscles, 353 infrapatellaris profunda, 471 subcutanea, 466 intermetacarpophalangese, 395 intermetatarsophalangeae, 500 intratendinea olecrani, 379 ischiadiea musculi glutei maximi, 462 of ischio-pubo-femoral musculature, 464 of medial thigh muscles, 474 mucosEe, 313, 318 subcutaneous, 1288 subfascial, 318 submuscular, 318 subtendinous, 318 musculi abductoris pollicis longi, 395 anconei, 379 bicipitis femoris inferior, 476 superior, 476 gastrocnemiahs, 476 coraco-brachialis, 383 extensoris carpi radialis brevis, 395 ulnaris, 395 pollicis longi, 395 flexoris carpi radialis, 403 ulnaris, 403 gastroenemii lateralis, 486 medialis, 486 infraspinati, 370 latissimi dorsi, 370 obturatoris externi, 464 interni, 464 pectinei, 474 peetoralis majoris, 374 piriformis, 462 quadrati femoris, 464 recti femoris (inferior), 471 (superior), 471 sartorii propria, 471 semimembranosus, 476 sterno-hyoidei, 353 subscapularis, 370 supinatoris, 395 teretis majoris, 370 thyreo-hyoidei, 353 omentalis (lesser sac) 1146, 1372 of pectoral muscles, 374 pharyngeal, 1130 of posterior iho-femoral musculature, 476 praepatellaris subcutanea, 466 subfascialis, 466 subtendinea, 471 prepatellar, 1288, 1448 of shoulder musculature, 369 sinus tarsi, 483 subacromialis, 369 subcutanea acromialis, 365 caloanea, 477 digitorum dorsales, 384, 1288 epicondyli lateralis, 377 medialis, 377 infrapatellaris, 1288 malleoli medialis et lateralis, 477 metacarpo-phalangea dorsalis, 384, 1288 olecrani, 377, 384 prementalis, 330 prominentiiB laryngse, 330 sacralis, 1288 troohanterioa, 1288 tuberositatis tibiae, 477 submammary (retromammary), 1303 subtendinea musculi extensoris hallucis longi, 483 olecrani, 379 supracoracoidea, 370 Bursa(ae), suprapatellaris, 471 synovial, 313, 318 tendinis calcanei, 486 musculi tibialis anterioris, 483 of ventral arm muscles, 383 Bursa tendinum musculi extensoris digitorum communis, 395 of trapezius, 350 trochanterica musculi glutei maximi, 462 medii anterior, 462 posterior, 462 minimi, 462 subcutanea, 457 Buttocks, bony landmarks of, 1442 clinical anatomy of, 1442 nerves of, 1443 Caecum (caput coH), 1170 cupular, 1096 topography of, 1376 variations of, 1171 vestibular, 1096 Calamus scriptorius, 812 Calcaneal pillar, 205 Caleanean branches, lateral, of sural nerve, 1013 of peroneal artery, lateral, 626 of posterior tibial artery, medial, 626 nerves, medial, 1010 Caloaneo-cuboid articulation, 306 ligaments, 306, 307 Calcaneo-fibular ligament, 299 Calcaneo-metatarsal ligament 492, Calcaneo-navicular ligament, lateral, 302, 305 plantar (spring), 305 Calcaneo-plantar cutaneous nerves, 1010 Calcaneus (os calcis), 191, 195 Calcar avis (hippocampus minor), 864, 868 femorale, 184 Calcarine fissure, 864 Calcification of bones, 27 of teeth, 1126 Callosal convolutions, 868 Calloso-marginal fissure, 857, 859 Calyces of kidney, 1246 of ureter, 1248 Camper's fascia, 425 Canal(s), accessory palatine, 103 adductor (Hunter's), 468, 618, 1441 Alcock's, 441, 445 alveolar, 87 anal, 1177 basi-pharvngeal, 63 carotid, 73, 108 central, of spinal cord, 775 of cervix, 1272 ethmoidal, 61, 83, 110, 113, 126 facial (Fallopian), 72, 73, 77, 78 femoral (crural), 468 gubernacular, l06 of Huguier, 75, 77, 108 hyaloid, 1064 hypoglossal, 117 inferior dental, 96 infra-orbital, 87, 126 inguinal, 424, 430 clinical anatomy of, 1395 lateral semicircular, 78 mandibular (inferior dental), 96, 126 palatine, 92 of Petit, 1064 pharyngeal, 66, 92, 103 posterior palatine, 126 pterygoid (Vidian) canal, 103, 107, 108, 126 pterygo-palatine, 88, 92, 103 INDEX 1481 Canal (s), pyloric, 1152 sacral, 42 of Schlemm, 1059 semicircular, 80, 1092 zygomatico-facial, 126 zygomatico-orbital, 94 Canaliculi, carotico-tympanic, 74 Canaliculus coohlese (ductus perilvmphaticus), 73, 81, 108 innominatus, 65 mastoid, 73 tympanic, 73, 108 Canalis musculo-tubarius, 73, 77,'[108 facialis, hiatus of, 116 Canine fossa, 87 teeth, 1120 Caninus (levator anguli oris), 332 Capillaries, lymphatic, 697 Capilh, 1290 Capitate (os magnum) bone, 159, 163 Capitular (oosto-central) articulation, 241 ligaments of tibio-fibular union, 295 Capitulum of humerus, 150 Capsular ligament of elbow-joint, 258 (perirenal) branches of renal arteries, 598 Capsule, articular, acromio-clavicular, 251 atlanto-dental, 222 atlanto-epistrophic, 221 atlanto-occipital, 218 of capitular articulation, 241 carpo-metacarpal of thumb, 273 costo-transverse, 243 crico-thyreoid, 1213 of hip-joint, 277 of knee-joint, 287 of mandibular articulation, 215 of medial tarso-metatarsal joint, 308 of metacarpo-phalangeal joint of thumb, 275 of shoulder-joint, 254 of sterno-costo-clavicular joint, 248 of tibio-fibular union, 295 of vertebral joints, 228 external (telencephalon), 881, 888 Glisson's, 675, 1186 glomerular, 1246 internal (telencephalon), 878, 886 of kidney, 1242, 1303 of prostate, 1265, 1389 of suprarenal gland, 1326 Tenon's, 1073 surgical importance of, 1348 of thyreoid gland, 1316 Caput angulare (levator labii superioris alseque nasi), 332 infraorbitale (levator labii superioris), 332 zygomatioum (zygomaticus minor), 332 Cardia of stomach, 1151 Cardiac branches of vagus, 957 fossa of lungs, 1229 ganglion (of Wrisberg), 1041 nerve, inferior, 1037 middle, 1036 superior cervical, 1036 notch of left lung, 1229 portion of stomach, 1151, 1374 plexus, 1041 vein, anterior, 521 great, 520 middle, 520 small cardiac, 521 smallest cardiac, 521 Carina tracheae, 1225 urethral, 1275, 1278 Carotico-clinoid foramen, 65 Carotico-tympanic artery, 552 canaliculi, 74 Carotieo branches from tympanic plexus, 951, 961 Carotid arteries, common, 533 collateral circulation, 536, 1360 external, 533, 536, 1343 branches, 536 relations, 536 internal, 533, 549 variations, 637 canal, 73, 108 gland (body), 550, 1327 groove, 64 nerves, external, 1036 internal, 960, 1033 plexus of nerves, common, 1036 \\ external, 1036 internal, 1033 ridge, 73 sheath, 1362 _ triangle, inferior (tracheal), 1358 superior, 1358 (anterior) wall of tympanic cavity, 1054 Carpal arch (rete), volar, 581 artery, dorsal radial, 585 dorsal ulnar, 580 volar radial, 584 volar ulnar, 581 bones, ossification of, 164 head of adductor pollicis, 408 joints, 268, 269 (annular) ligaments of wrist, 1427 rete, dorsal, 579, 586 Carpo-metacarpal joints, 272 of the thumb, 273 Carpus, description of, 159, 270 ligaments, 384, 387 Cartilage (s), 211 alar, 1201, 1202 articular, of shoulder-joint, 255 arytenoid, 1211 auricular, 1084 corniculate (Santorini), 1212 costal, 130 cricoid, 1210 cuneiform (Wrisberg), 1213 epiglottic, 1212 interarytasnoid (procricoid), 1213, 1218 of larynx, 1209 lateral nasal, 1201 Meckel's, 98, 119 nasal, 120 periotic, 117 septal nasal, 1202 sesamoid nasal, 1202 laryngeal, 1213 sphenotic, 117 thyreoid, 1210 tracheal, 1227 varieties, 211 vomero-nasal, 1203 Cartilaginous plate (pelvic joints), ear-shaped, 235 CartUago triticea, 1217 Caruncle, lacrimal, 1052, 1055 sublingual, 1117 Carunculte hymenales (myrtiformes), 1275, 1392 Cauda equina, 772 helicis, 1084 Caudate branch of middle cerebral artery, 562 (Spigelian) lobe of liver, 1184 nucleus, 877, 879 process of liver, 1184 Cavernous nerves of clitoris, 1047 of penis, 1047 plexus of nasal conchse, 1208 of nerves, 1033 1482 INDEX Cavernous (spongy) portion of male urethra, 1264, 1388 sinus, 652, 691 Caves, Meckel's, 916 Cavity, body, 14 epidural, 911 glenoid, of scapula, 143 of larynx, 1220 lesser sigmoid, of ulna, 157 mediastinal, 1239 nasal, 1203 oral, 1100 of orbit, 1066 pelvic, 175 pericardial, 522 pleural, 1236 of radius, sigmoid, 154 subarachnoid, 918 subdural, 912 thoracic, 1235 of tooth, 1118 tympanic, 77, 1088 of ulna, greater sigmoid, 156 of uterus, 1271 Cavum conchas, 1082 pelvis subperitoneale, 448 Retzii, 1250, 1371 Cellifugal processes of neurone, 762 Cellipetal processes of neurone, 762 Cells, 4 chromaffin, 1323 ependymal, 768 ethmoidal, 83, 84, 111, 1207 Golgi, in cerebellum, 809 gustatory, 1050 olfactory, 1051 mastoid, 1092, 1336 of Purkinje, 809 stellate, 809 Cementum of teeth, 1119 Central (ganglionic) arteries of cerebrum, 906 of medulla oblongata, 908 branches of cerebral arteries, 562, 563 canal of spinal cord, 775 connections of cranial nerves, 818 of abducens, 934 of cochlear, 824 of facial nerve, 825, 946 of glosso-palatine, 825, 947 of glosso-phar\ns<"il, 820, 952 of hypoglossal, 820, '.).") 4 of masticator, 829, 94-_' of oculo-motor, 838, 933 of olfactory, 873, 929 of optic, 848, 931 of spinal accessory, 820, 959 of trigeminus, 826, 935 of trochlear, 837, 934 of vagus, 820, 958 of vestibular, 823, 950 gyrus, anterior (ascending frontal convolu- tion), 857 posterior (ascending parietal), 861 lobe or insula, 856 lobule of cerebellum, 806 nervous system, 751 point of perineum, 1385 sulcus (fissure of Rolando), 859, 1340 angle of, 860 inferior genu. 860 in foetus, 860 of insula, 857 superior genu, 860 tendon of perineum, 449 veins of retina, 659 Centres, association, of cerebral cortex, 894 Centrum semiovale, 886 Centrum (body) of vertebrse, 30 Cephalic index, 117 plexus, gangliated, 959 portion of sympathetic trunk, 1033 vein, 667, 671 Cephalo-auricular angle, 1084 Cerato-cricoid ligaments, 1213 muscle, 1218 Cerato-hyal center, 100 segment, 119 Cerebellar artery, anterior inferior, 561, 907 posterior inferior, 561, 907 superior, 561, 907 notches, 805, 915 peduncle, inferior, 810 superior, 812, 831 tract, direct, of Flechsig, 784 veins, 657 Cerebello-olivary fibres, 817 Cerebellum (hind brain), 804 ala of central lobule, 806 anterior medullary velum of, 812 arbor vitse of, 809 biventral lobe, 807 blood-vessels of, 907 brachium pontis, 811 conjunctivum, 812 central lobule of, 806 conduction paths of, 899 cortex of, 809 culmen of, 806 declive (clivus), 806 dentate nucleus of, 810 external features, 808 fissures, 805 flocculus, 807 peduncle of, 807 folium vermis (cacuminis), 806 fourth ventricle, anatomy of, 812 functions of, 832 gross divisions of, 805 hemispheres of, 805 inferior vermis, 808 internal structure of, 808 lingula of, 806 lobes and lobules, 805 montioulus, 806 nodule of inferior vermis, 808 notch of, 805 nuclei of, 809, 810 peduncles of, 810 posterior medullary velum, 808 pyramid of vermis, 808 sulci of, 805 superior vermis of, 806 tentorium of, 804 tonsil (amygdala) of, 807 tuber vermis, 808 uvula of vermis, 808 vallecula of, 807 veins of, 908 vermis of, 805, 807 Cerebral arteries, anterior, 554, 562 branches, 562 middle, 556, 562 posterior, 561, 562 commissure, anterior, 871 inferior, 842, 890 cortex, 879 cornu ammonis, 879 functional areas of, 893 structure of, 879 hemispheres, 850 caudate nucleus, 877 corpus striatum, 868, 879 cortex of, 852, 879, 893 gyri of, 852 INDEX 1483 Cerebral hemispheres, lateral ventricle, 873 lobes of, 853 central (insula), 856 frontal, 857 occipital, 863 parietal, 860 temporal, 854 rhinencephalon, 864 sulci of, 852 path for cranial nerves, 895 peduncles (crura), 833, 835 arteries of, 907 veins, 644, 657 central or deep (ganglionic), 655 great (of Galen), 657 inferior, 655 internal, 657 middle, 655 superior, 654 Cerebro-spinal fasciculus, lateral, 783 ventral, 788 fluid, 920, 1342 path, 895 Cerebrum, 833 mesencephalon (mid-brain), 833 prosencephalon (fore-brain), 843 diencephalon (inter-brain), 843 telencephalon (end-brain), 847 Cerumen, 1085, 1298 Ceruminous glands, 1085, 1297 Cervical artery, ascending, 564 deep, 668 superficial, 566 transverse, 565 branches of uterine artery, 610 chains of lymphatic nodes, deep, 714 enlargement of spinal cord, 772 fascia, external, 347 middle, 350 ganglion of sympathetic, inferior, 1036 middle, 1036 superior, 960, 1035 loop (ansa hypoglossi), 953, 974 muscle, 330 nerves, 971, 974 anterior primary divisions, 974 posterior primary divisions, 971 plexus, 974 ascending branches of, 977 deep branches of, 978 descending branches of, 978 posterior, of Cruveilhier, 971 superficial branches of, 977 supra-clavicular branches of, 978 transverse branch, 978 portion of external maxillary artery, 540 of internal carotid artery, 550 of sympathetic trunk, 1033 construction of, 1037 of vertebral artery, 559 ribs, 131, 1365 triangles, 1357 vein, deep, 661 veins, transverse, 672 vertebra;, description of, 31 development of, 47 Cervicalis ascendens, 416 Cervico-facial nerve, 945 Cervix of uterus, 1271 Chains of nerurones, 768 Chambers of the eye, 1064 Charcot's artery of cerebral hemorrhage, 562, 906 Check (alar) ligaments, 223 of eyeball, 1072 Cheek, 1103 Chiasma, optic, 848, 849 Choanaj (posterior nares), 107, 112, 1130, 1206, 1351 Chondro-cranium, 117 Chondro-humeralis (epitrochlearis), 374 Chondro-glossus, 346 Chopart's medio-tarsal amputation, 1465 Chorda tympani nerve, 826, 946, 948 Chorda tendinse, 515 Chords of Willis, 649 Chorio-capillaris, 1055 Chorioid, 1057, 1060 artery, 554, 908 branches of posterior cerebral artery, 563 fissure, 868 glomus, 876 plexus of fourth ventricle, 922 of lateral ventricle, 875, 877, 924 tela of fourth ventricle, 758, 812 of third ventricle, 923 vein, 657 Chorioidal arteries of medulla oblongata, 908 fissure, 1080 lamina, epithelial, 876, 924 membrane, 1052 Chorion, 10 Chromaffin bodies, 1329 cells, 1323 system, 1323 Chromatin, 5 Cilia, 1290 Ciliary arteries, anterior, 1065 long posterior, 1065 short posterior, 1065 body, 1060 ganglion, 961, 1076 branches, 961 roots, 932, 937, 961, 1033 glands (glands of Moll), 1078, 1297 muscle, 1057, 1060 nerves of eyeball, 1064, 1076 long, 937 short, 961, 1076 processes, 1057 veins, 658 Cingulum, 867, 890 of teeth, 1120, 1121 Circle of Willis (circulus arteriosus), 555 Circular sinus, 651 sulcus (limiting sulcus of Reil), 857 Circulation, collateral, of axillary artery, 1412 of brachial artery, 1414 of common carotid artery, 1360 iliac arteries, 1382 of external iliac artery, 1382 of femoral artery, 1441 of internal iliac artery, 1382 of popliteal artery, 1453 of subclavian artery, 1360 fcEtal, 695 pulmonary, 507 systemic, 507 Circulus arteriosus major, 1065 minor, 1065 tonsillaris, 952 Circumanal glands, 1297 Circumduction, 215 Circumferential cartilage, 211 Circumflex artery, lateral, 620, 640 medial, 620," 640 femora! veins, 690 humeral artery, anterior, 572 posterior, 573 iliac arterj', deep, 616 superficial, 618 vein, deep, 683 superficial, 684 nerve, 985 1484 INDEX Circumflex (dorsal) scapular artery, 572 veins, 671 Circumvallate papillae of tongue, 1106 Cisterna basalis, 918 cerebello-medullaris (cisterna magna), 919 chyli, 726 pontis, 918 subarachnoid, 918 superior, 919 Clarke's column of spinal cord, 776 Classification of articulations, 212 of muscles, 319 Claustrum, 880 Clava, 801 Clavicle, 139, 1357, 1410 ossification of, 141 structure of, 141 Clavicular branch of thoraco-aoromial artery, 571 Cleft, middle ear, 77 palate, 1106, 1352 Clinical and topographical anatomy, 1331 of abdomen, 1370 of back, 1403 of head, 1331 of lower extremity, 1434 of neck, 1354 of pelvis, 1382 of thorax, 1363 of upper extremity, 1409 Clinoid process, anterior, 65, 116 middle, 65, 116 posterior, 63, 116 Clitoris, 1277 artery of, 613 cavernous nerves of, 1047 deep artery of, 614 dorsal artery of, 614 vein of, 1018 lymphatics of, 745 Clivus, 117 Cloaca, 1179, 1253, 1278 Clunial (gluteal) branches, inferior, of poste- rior femoral cutaneous nerve, 1007 nerve, inferior medial (perforating cutan- eous), 1007 middle, 973 superior, 973 Coats of the eyeball, 1058 Coccygeal body, 1329 cornua, 43 foveola, 1284 ganglion, 1040 ligament, 911 nerves, 973 posterior primary division of, 973 rudimentary, 964 plexus, 1018 vertebras, 42 development of, 49 Coccygeus, 440, 448 Coccyx, 30, 42 muscles of, 448 Cochlea, 81, 1092 Cochlear area of cerebral cortex, 893 duct (membranous cochlea, or scala media), 1090 fenestra, 1089 nerve, 824 nuclei of, 824 Cochleariform process, 1089 Coeliac artery (axis), 593, 638 branches of vagus, 958 (semilunar) ganglia, 1043 lymphatic nodes, 730 plexus of nerves, 1043 Coelom, 14 Colic, artery, left, 603 middle', 598 right, 598 flexures, 1173, 1379 (basal) surface of spleen, 1310 veins, 677, 678 Collateral artery, inferior ulnar, 576 middle, 576 radial, 576 superior ulnar, 576 branch of intercostal arteries, 588 circulation of axillary artery, 1412 of brachial artery, 1414 of common carotid artery, 536, 1360 iliac arteries, 605, 1382 of external iliac artery, 1382 of femoral artery, 1441 of internal iliac artery, 1382 of popliteal artery, 1453 of subclavian artery, 1360 eminence, 868, 877 fissure, 864 trigone of lateral ventricle, 876 Collecting renal tubule, 1246 Colles' fascia, 445 fracture, 1420 CoUiouli, inferior, 834, 839 superior, 841 Colliculus of arytaenoid, 1212 facialis, 815 seminalis (verumontanum), 1263, 1389 Colloid of thvreoid gland, 1316 Colon, ascending, 1173, 1378 descending, 1174, 1379 iliac, 1174 pelvic, 1174, 1379 sigmoid, 1174, 1379 transverse, 1174, 1379 Colostrum, 1303 Column anterior of spinal cord, 786 Burdach's, 781 Clarke's, 776 GoU's, 781 lateral of spinal cord, 782. posterior of spinal cord, 780 vertebral, 29, 43 Columna rugarum, 1275 Columns, anterior, of fornix, 870 rectal (of Morgagni), 1177, 1390 renal (of Bertin), 1246 Comedo, 1298 Comma-shaped fasciculus, 782 Commissural branches of sympathetic, 1032 bundle, 788 fibres of white substance of spinal cord, 779 system of fibres, of telencephalon, 890 Commissure, 769 anterior cerebral, 848, 871, 890 grey, of spinal cord, 775 habenular, 872, 885, 890 hippocampal, 869, 890 inferior cerebral (Gudden's), 842, 850, 890 middle cerebral, 844 optic, 849 posterior, of cerebrum, 835, 890 of vulva, 1276 supramammillary, 871, '890 white, of spinal cord, 776 Common bile-duct (ductus choledochus), 1188 carotid artery, 533 branches, 536 collateral circulation, 536, 1360 in the neck, 533 relations, 533, 534, 1369 thoracic portion of left, 533 digital arteries, 582 veins (foot), 684 INDEX 1485 Common digital veins, volar, 671 facial vein, 644, 646 femoral artery, 616 iliac arteries, 603, 605 collateral circulation, 605 veins, 679 interosseous artery of forearm, 570 Communicans cervicalis, 974 fibularis, 1013 Communicating artery, anterior, 555, 562 posterior, 554 Comparative anatomy of large intestine, 1180 of lips and cheeks, 1104 of liver and gall-bladder, 1 192 of palate, 1106 of pancreas, 1197 of peritoneum, 1151 of salivary glands, 1117 of stomach, 1160 of teeth, 1127 of tongue, 1112 of tonsOs, 1138 Compartments under inguinal ligament, 1399 Complexus, 412, 417 Compound bones, 27 Compressor bulbi proprius, 450 hemisphserium bulbi, 451 venae dorsalis, 451 Conarium, 845 Concha, 1082 eminence of, 1083 Concha;, nasal, 83, 84, 1205 sphenoidal, 64, 67 Conchal (inferior tiarbinate) crest, 88, 92 Conduction paths, auditory, 900 involving cerebellum, 899 of nervous system, summary of, 895 methods of determining, 779 of olfactory apparatus, 902 of optic apparatus, 900 vestibular, 899 Condylar foramen (canal), 54 fossa, 54, 108 process of mandible, 96, 97 tubercle of mandible, 97 Condylarthroses, 213 Condyles, 29 of femur, 182 of femur and tibia, 1447 of mandible, 97 of occipital bone, 54, 108 third occipital, 56 of tibia, 185 Condyloid emissary veins, 652 Cone, elastic, of larynx, 1215 Conical papillte of tongue, 1106 Conjoined tendon of internal oblique and transversalis, 435 Conjugate diameter of pelvic inlet, 175 Conjunctiva, 1054, 1347 lymphatics of, 698, 712 ocular, 1054 palpebral, 1054 Conjunctival arteries, anterior, 553 posterior, 554 sac, 1054 semilunar fold of, 1055 veins, 658 Connecting fibro-cartilage, 211 Connections, central, of cranial nerves, 818 (for individual nerves, see "Central con- nections"), cortical, of thalamus, 883 of nuclei of corpus striatum, 880 Conoid ligament, 251 tubercle, 140 Constituents of articulations, 211 Constrictor laryngis, 1218 radicis penis, 450 vaginEe, 449 Constrictors of pharynx, 1137 Construction of nervous system, 762 Conus arteriosus, 516 meduUaris, 771 Convoluted renal tubules, 1246 Convolutions, cerebral, 852 Cooper's ligament, 1400 Coraco-acromial hgament, 252 Coraco-brachialis, 374, 379, 381 Coraco-clavicular union, 251 arterial supply, 251 ligaments, 251 movements, 252 nerve-supply, 251 (costo-coracoid) fascia, 371 Coraco-humeral ligament, 255 Coracoid (suprascapular or superior trans- verse) ligament, 253 process of scapula, 144 (conoid) tubercle, 140 Cord, oblique, 262 spermatic, 1259, 1387 spinal, 751, 771 clinical anatomy, 1408 external morphology of, 771 internal structure of, 775 Cords of brachial plexus, 917 ganghated, neurones of, 755 vocal (gee "Vocal folds"). Corium, 1286 Cornea, 1052, 1054, 1056, 1069, 1065 Comiculate cartilages (of Santorini), 1212 tubercle (of Santorini) of larynx, 1221 Corniculo-pharyngeal ligament, 1218 Cornu ammonis, 868, 879 Cornua of fascia lata, 467 of fossa ovalis (saphenous opening), 467 of hyoid bone, 99, 100 of lateral ventricles, 873, 874, 876 of sacrum, 40 of thyreoid cartilage, 1211 Cornucopise, 923 Corona cilaris, 1060 glandis, 1260 iridis, 1054 radiata, 887 ocoipito-thalamic (optic) radiation of, 888 Coronal suture, 57, 101, 1339 Coronary arteries, 519 ligaments of knee-joint, 290 of liver, 1184 plexuses of nerves, 1041 sinus, 521 valve (of Thebesius) of, 512 sulcus of heart, 510 (gastric) vein, 675 veins, 520 Coronoid fossa of humerus, 150 process of mandible, 97, 1351 of ulna, 156 Corpora albicantia, 844, 1269 cavernosa of clitoris, 1277 penis, 1260 mammillaria (albicantia), 844 quadrigemina, 834 quadrigemina-thalamus path, 786 Corpus adiposum buocse, 1103, 1104 callosum, 851 body of, 852 forceps major, 890 minor, 890 genu, 851 peduncle of, 866 radiation of, 851, 890 1486 INDEX Corpus callosum, rostral lamina of, 852 rostrum of, 852 spleuium of, 852 striffi of, 851 sulcus of, 867 cavernosum urethras (corpus spongiosum), 1261 Highmori, 1256 mammae, 1302 papillare of skin, 1286 spongiosum (cavernosum urethrae), 1261 striatum, 879 caudate nucleus of, 879 connections of nuclei of, 880 internal capsule of, 886 lenticular nucleus of, 879 trapezoideum, 824 Corpuscles, bulbous (of Krause), 1290 genital, 1290 colostrum, 1303 concentric (Hassal's) of thymus, 1321, 1322 Golgi-Mazzoni, 1290 lamellous (Vater-Paoinian), 1290 renal (Malpighian), 1246 Ruffini, 1290 salivary, 1132 splenic (Malpighian), 1311 tactile (Meissner), 1290 Corrugator cutis ani, 445 muscle, 336 Cortex, cerebellar, 809 cerebral, 879 functional areas of, 893 of kidney, 1246 of lens of eye, 1062 of suprarenal gland, 1326 of thymus, 1321 Corti, organ of, 1096 Cortical branches of cerebral arteries, 562, 563 (superficial) cerebral veins, 654 connections of thalamus, 883 Cortico-pontine fibres, 811 Costal arch, 139 branch, lateral, of internal mammary ar- tery, 567 cartilages, 130 Costal groove, 127 pleura, 1237 processes, 38 tuberosity of clavicle, 140 Costo-axUlary veins, 671 Costo-central (capitular) articulation, 241 ligaments, 241 Costo-cervical arterial trunk, 568 Costo-ohondral joints, 245 Costo-clavicular (rhomboid) ligament, 249 Costo-eoracoid fascia, 371 ligament, 371 Costo-coracoideus, 374 Costo-mediastinal sinus, 1238 Costo-transverse articulations, 243 arterial supply, 244 ligaments of, 243 middle (neck), 243 posterior (tubercular), 243 superior, 243 movements, 244 nerve-supply, 244 foramen, 32, 127 of atlas, 33 Costo-xiphoid ligament, 244, 245 Costo-vertebral articulations, 241 groove, 138 Cotunnius, nerve of, 962 Cotyloid bone, 173 fibro-cartilage, 281 fossa, 169 Cowper's (cremasteric) fascia, 426, 434, 1254 glands, 1265 Coxal bone (os innominatum), 169 ossification of, 174 Cranial arachnoid, 918 cavity, floor of, 112 relations of brain to walls of, 903 dura mater, 913 fossa, anterior, 113 middle, 116 posterior, 116 surgical anatomy of, 1342 nerves, 927 abducens, 934 central connections of, 818 cochlear, 950 facial, 943 glosso-palatine, 946 glosso-pharyngeal, 951 hypoglossal, 952 masticator, 942 oculo-motor, 931 olfactory, 929 optic, 930 paths of, cerebral, 895 short reflex, 898 spinal accessory, 958 superficial attachments of, 929 terminal, 929 trigeminus, 934 trochlear, 933 vagus, 954 vestibular, 949 pia mater, 922 subdural cavity, 917 venous lacunae, 649 sinuses, 649, 692, 916 Cranio-cerebral topography, 903, 1338 Cranio-mandibular musculature, 325, 338, 341 Cranium, 51 clinical anatomy of, 1333 measurements of, 117 remnants of cartilaginous, 124 Cremaster, 423, 434, 1254 external, 1259 internal, 1254, 1259 Cremasteric branches of internal spermatic arteries, 501 fascia (external spermatic, or Cowper's fascia), 426, 434, 1254 Crest(s), 29 arcuate, of arytaenoid cartilage, 1212 conchal, 88, 92 ethmoidal, 92 external occipital, 52 of fibula, 190 frontal, 60 of greater tuberosity of humerus, 148 of Uium, 169 incisor, 90 inferior turbinate, 92 internal occipital, 53 interosseous, of radius, 153 of ulna, 157 intertrochanteric, 178 lacrimal, posterior, 85 nasal, 90 neural, 754 obturator, 173 of scapula, 144 sphenoidal, 63 superior turbinate, 92 of tibia, anterior, 188 transverse, 72 Cribriform lamina, 119 plate of ethmoid, 81 INDEX 1487 Crico-arytaenoid articulation, 1214 ligament, 1214 Crico-arytaenoideus lateralis, 1219 posterior, 1218 Cricoid cartilage, 1210 Crico-pharyngeal ligament, 1218 Crico-thyreoid articulation, 1213 ligament, 1215 muscles, 1218 Crico-tracheal ligament, 1218 Crista, ampullary, 950, 1095 galli, 81, 113 supraventricularis, 516, 527 terminalis, 513 urethralis, 1263 vestibuli, 80 Crista} of matrix unguis, 1295 of skin, 1284 Crossed pyramidal tract, 783 Crown of tooth, 1117 Crucial anastomosis, 620 ligament of atlanto-epistrophic joint, 222 ligaments of knee-joint, 288 Cruciate ligament of leg (lower part of anterior annular ligament), 479 of fingers, 387 Crura of anthelix, 1083, of cerebrum, 833, 835 clitoridis, 1277 of diaphragm, 437 of fornix, 868 of greater alar nasal cartilages, 1202 of penis, 1261 of stapes, 80 Crural canal, 468 fascia, 477 nerve, anterior, 1001 interosseous 1010 Crureus, 468, 470 Cruro-pedal muscles, 486 Crus of helix, 1082, 1083 Cruveilhier, posterior cervical plexus of, 971 Cryptorohism, 1257 Crypts of iris, 1054 of Lieberktihn, 1166, 1177, 1390 of lingual tonsil, 1107 of palatine tonsil, 1132 Crystalline lens of eye, 1052, 1057, 1061 Cubital lymphatic node, superficial (supra- trochlear), 719 Cuboid, 191, 199 Cuboideo-navicular ligaments, 303 ' union, 303 Cubo-metatarsal joint, 309 ligaments, 309 Culmen of cerebellum, 806 Cuneiform bones, 159, 161, 191, 197 first (medial, 197 third (lateral,) 198 second or middle, 197 cartilages (of Wrisberg), 1213 tubercle (of Wrisberg) of larynx, 1221 Cuneo-cuboid articulation 304 Cuneo-lingual gyrus, anterior, 864 posterior, 864 Cuneo-navicular articulation, 304 Cuneus, 864 Cupola of pleura, 1237 Cupular CEecum, 1096 portion of epitympanic recess, 1090 Curvatures of spinal column, 43 of stomach, 1152, 1374 greater, 1152 lesser, 1152 Cusps of atrio-ventricular valves, 516 Cutaneous areas of face, 1018 of lower extremity, 1024 Cutaneous areas of neck, 1019 of pinna (auricle), 1019 of scalp, 1018 of trunk, 1020 of upper limb, 1022 branches of anterior ethmoidal artery, 554 of intercostal arteries, 589, 590 (communicans fibularis) of common pero- neal nerve, 1013 of deep circumflex iliac artery, 616 dorsal antibrachial (external) of radial nerve, 987 of ilio-hypogastric nerve, 995 lateral, of thoracic nerves, 995 of median nerve, 992 plantar, of medial plantar nerve, 1010 posterior brachial (internal), of radial nerve, 985 femoral cutaneous nerve, 1007 of sacral plexus, 1007 of superficial peroneal (musculo-cutane- ous) nerve, 1015 of superior epigastric artery, 567 (medial sural cutaneous or tibial com- municating) of tibial nerve, 1010 of ulnar nerve, 990 glands, 1296 glomiform, 1296 sebaceous, 1298 nerves, anterior of abdomen, 996 of femoral nerve, 1003 calcaneo-plantar, 1010 of foot, lateral dorsal, 1013 surface markings, 1466 intermediate dorsal, of leg, 1015 lateral, 1000 of abdomen, 995 sural, 1013 medial antibrachial (internal), 934 brachial, 983 dorsal, of leg, 1015 sural, 1010 posterior femoral (small sciatic), 1007 superficial cervical, 978 rete arteriosum, 1289 veins, 1289 Cuticle (epidermis), 1285 Cutis, 1285, 1286 Cymba conchse, 1082 Cystic artery, 595 duct, 1187 vein, 677 Cysto-colic ligament, 1379 Cytomorphosis, 7 Cytoplasm, 5 "Dangerous area" of leg, 1457 of scalp, 1333 Dartos, 1254, 1260 Darwin, tubercle of, 1083 Deciduous (milk) teeth, 1126 times of eruption, 1127 Declive of cerebellum, 806 Decussation, fountain, 842 of lemnisci, 815 of pyramids, 799, 815 of superior cerebellar peduncles (brachia conjunctiva), 840 Deferential artery, 610 plexus of nerves, 1047 Deiters' nucleus, 823 Deltoid branch of profunda artery, 576 of thoraco-acromial artery, 571 (internal lateral) ligament of ankle- joint, 298 surface markings, 1410 1488 INDEX Deltoideus, 365 Delto-peotoral lymphatic nodes, 719 Dendrites, 762 Dens (odontoid process), 33 Dental arches, 1123 branches, inferior, of inferior dental plexus, 941 superior, of superior dental plexus, 938 canal, inferior, 96, 126 nerves, 938, 941 inferior, 941 superior, 938 Dentary centre, 98 Dentate fascia, 868 gyrus, 868 nucleus of cerebellum, 810 sutures, 212 Dentine, 1118 Denticulate ligament, 920, 921 Depressor alfe nasi, 334 anguli oris, 333 labii inferioris, 332 septi nasi, 334 Derma (oorium), 1286 Descemet, membrane of, 1060 Descendens cervicalis (hypoglossi), 953, 974, 979 Descending aorta, 586 brandies of cervical plexus, 978 of lateral circumflex artery, 543 (princeps cervicis) of occipital artery, 543 of spheno-palatine (Meckel's) ganglion, 963 of transverse cervical artery, 565 colon, 1174, 1379 palatine artery, 549 Descent of the testis, 1257, 1387 Development of anus, 1179 of arteries, 633 of articulations (joints), 213 of bones, 27 (see also the individual bones) of brain, 754 of central sulcus (fissure of Rolando), 860 of oorium, 1290 of diaphragm, 120 of ear, 1096 of epidermis, 1286 of eye, lOSO of face, 18 of hairs, 1293 of heart, 523 of hypophysis cerebri, 848 of kidney, 1248 of large intestine, 1179 of larynx, 1225 of limbs, 20 of lips and cheeks, 1104 of liver, 1189 of lungs, 1235 of lymphatic system, 706 of lymph-nodes, 707 of mammary gland, 1306 of muscles, 316 of nails, 1296 of nerve fibres, 758 of nervous system, 754 of nose, 18, 1208 of oesophagus, 1141 of oral cavity, 1102 of palate, 1105 of palato-pharyngeal muscles, 1137 of pancreas, 1195 of parathyreoid glands, 1319 of pericardium, 527 of peritoneum, 1144 of pharynx, 1138 of reproductive organs, 1278 Development of salivary glands, 1117 of sebaceous glands, 1298 of skull, 117 of small intestine, 1168 of spleen, 1312 of stomach, 1157 of suprarenal glands, 1326 of sweat glands, 1297 of teeth, 1124 of thymus, 1322 of thyreoid gland, 1318 of tongue, 1112 of tonsils, 1133 of tympanum, 80 of urinary bladder, 1253 of veins, 690 of ventricles of brain, 758 of vermiform process, 1179 of vertebra3, 45 of viscera, 18 Diagonal sulcus, 858 band of Broca, 866 Diameters of the pelvis, 175, 177 Diaphragm, 425, 436, 1372 . crura, 437 and heart, recession of, 20 lymphatics, 725, 728 pelvic, 440, 1383 urogenital, 440, 1383 Diaphragraa pelvis (Meyer), 440 sella;, 848, 915 Diaphragmatic pleura, 1237 lymph nodes, 725, 736 pelvic fascia, 442, 447 plexuses of nerves, 1044 surface of heart, 509 of lung, 1229 of spleen, 1308 Diaphysis, 28 Diapophyses, 51 Diarthroses, 212 heteromorphic, 283 homomorphic, 212 Diencephalon (interbrain), 758, 843 Digastric fossa, 95 muscles, 314 triangle, 1357 Digastricus, 343, 344 Digestive system, 1099 abdomen, 1142 intestines, 1161 liver, 1180 mouth, 1100 oesophagus, 1138 pancreas, 1192 peritoneum, 1145 pharynx, 1129 stomach, 1151 Digital arteries, common (hand), 582 dorsal (foot), 633 plantar, 628 proper (hand), 582 branches, dorsal, of ulnar nerve, 990 of medial plantar nerve, 1011 volar, of ulnar nerve, 991 fossa of epididymis, 1255 of femur, 178 of fibula, 191 nerves, common plantar, 1011, 1013 common volar, of hand, 991 dorsal, of foot, 1013 of hand, 987, 990 proper plantar, 1011, 1013 volar, of hand, 992 veins (foot), dorsal, 684 plantar, common, 684 volar (hand), 671 INDEX 1489 Digital venous arch (hand), 667 Digitations, hippocampal, 877 Dilator naris anterior, 335 posterior, 335 pupilte, 1061 Dimples of skin, 1285 Diploe, veins of, 648 Direct cerebellar tract of Flechsig, 784 pyramidal tract, 788 Disc, articular, of the aoromio-clavicular joint, 251 of inferior radio-ulnar articulation, 264 of mandibular articulation, 216 of the sterno-costo-clavicular joint, 249 optic, 1055 Dislocation of mandible, 1345 metaoarpo-phalangeal, 1434 of patella, 1446 Diverticula, intestinal, 1170, 1379 Diverticulum, Meckel's, 1169 Dolichopellie pelvis, 177 Dorsalis hallucis artery, 633 pedis artery, 632 Dorso-epitrochlearis, 379 Dorsum of foot, muscles of, 492 of ilium, 165 of nose, 1200 of penis, 1260 sellte (epihippi), 63, 116 of tongue, 1106 Douglas' fold, 427 (recto-uterine or recto-vaginal) pouch, 1148, 1267 Duct(s), alveolar, 1232 of Bartholin, 1117 cochlear, 1096 common bile, 1188 cystic, 1187 efferent of testis, 1256 ejaculatory, 1257, 1263, 1387 endolymphatic, 1094 of epididymis, 1256 of gall-bladder, 1188, 1373 of Gartner, 1275 hepatic, 1187 of lacrimal gland, excretory, 1047 lactiferous, 1302 of mammary glands, 1302 MilUerian, 1257, 1267, 1279 naso-lacrimal, 1080, 1205, 1349 pancreatic (of Wirsung), 1194, 1375 accessory (of Santorini), 1195 papillary (of Bellini), 1246 paraurethral (of Skene), 1277 of parotid gland (Stenson's), 1115, 1343 right lymphatic, '728 of Rivinus, 1117 semicircular, 1094 of sublingual gland, 1117 of submaxillary gland (Wliarton's), 1116 of sweat glands, 1297 thoracic, 726 thyreo-glossal, 1318 utriculo-saccular, 1094 Wolffian, 1248, 1267, 1278 Ductless glands, 1306 aortic paraganglia, 1329 chromaffin system, ,1323 glomus caroticum, 1325 ooccygeum, 1329 parathyreoid glands, 1318 spleen," 1306 suprarenal glands, 1323 thymus, 1319 thyreoid gland, 1312 Ductuli aberrantes (of epididymis), 1257 Ductus arteriosus (Botalli), 528 Ductus oholedochus (common bile-duct), 1188 (vas) deferens, 1257, 1259, 1387 (canaliculi) lacrimales, 1079 perilymphaticus, 81 reuniens of membranous labyrinth, 1094 venosus, 675, 694 Duodenal fossa;, 1164 papQla;, 1164, 1195 veins, 677 Duodeno-jejunal flexTire, 1152, 1376 Duodenum, 1161, 1375 lymphatics of, 734 parts of, 1161 Dupuytren's fracture, 1455 Dura mater, 771, 910 blood-vessels of, 917 cranial, 913 filum of, 911 nerves of, 917 spinal, 911 surgical anatomy of, 1342 Ear, 1082 development of, 1096 internal, 1092 middle, 1086 muscles of, 337, 1084 ossicles of, 79, 1090 vessels and nerves, 1084, 1086, 1091, 1096 Ectoderm, 10 Ehrenritter, ganglion of, 951 Ejaculatory duct, 1257, 1263, 1387 Elastic cone of larynx, 1215 membrane of larynx (Lauth), 1215 Elbow, clinical anatomy of, 1417 Elbow-joint, 258 arterial anastomoses around, 1418 supply of, 261 ligaments of, 258 movements of, 201 muscles acting upon, 261 nerve-supply of, 261 synovial membrane of, 261 Elevations of skin, 1284 Eleventh thoracic vertebra, 39 Elliptical recess (fovea hemielliptica), 80 Embryonic disc, 9, 10, 11 Eminence of auricle, 1083 collateral, 868, 877 frontal, 59, 108 hypoglossal, 814 ilio-pectineal, 169 medial, of floor of fourth ventricle, 813 parietal, 57 pyramidal, of temporal bone, 77 Eminentia arcuata, 78, 116 Emissary veins, 647, 649, 652, 916 mastoid, 647 parietal, 649 of scalp, 1334 Enamel, 1118 _ Enarthrodial diarthroses, 213 Encephalon, 751, 792 blood-supply of, 905 divisions of, 796 Endocardium, 508 Endoderm, 10 Endognathion centre, 91 Endolymph, 1093 Endolymphatic duct, 1094 sac, 1094 Endometrium, 1274 Endomysium, 315 Endo-pelvic fascia (recto-vesical), 442, 447 1490 INDEX Endothoracic fascia, 1235 Enlargements of spinal cord, 772 Ensiform process (metasternum), 132, 134 Eparterial bronchus, 1232 Ependymal cells, 768, 846 Ephippial diarthroses, 212 Epicardium, 508 Epicondyles of femur, 183 of humerus, 151 Epicranial aponeurosis, 337 musculature, 336 Epicranio-temporalis, 337 Epicranius (occipito-frontalis), 336 Epidermis, (cuticle), 1285 Epididymal branches of int. spermatic ar- teries, 601 Epididymis, 1266, 1386 Epidural cavity, 911 Epigastric artery, inferior (deep), 614, 639 superficial, 618 superior, 567 lymphatic nodes, 732, 733 plexus, 1043 region, 1143 veins, inferior, 683 superficial, 684 superior, 666 Epiglottic cartilage, 1212 tubercle, 1212, 1222 vallecula, 1221 Epihyal segment of styloid process, 119 Epimysium, 316 Epiphyseal cartilages, 28 lines, 28 Epiphyses, 28 (see also individual bones). Epiphysis (pineal body), 758, 834, 845 Epiploic foramen (of Winslow), 1147 or omental branches of epiploic arteries, 595 Epipteric bones, 68, 101, 119 Episcleral arteries, 553 veins, 659 Epispadias, 1388 Epistropheus, description of, 33 Epithalamus, 845 Epithelial chorioid lamina, 924 Epithelium lentis, 1064 Epitrochleo-olecranonis (anconeus internus), 402 Epitym panic recess, 78 Eponychium, 1294, 1296 Epoophoron, 1269 Equator of eyeball, 1055 of lens of eye, 1062 Erector penis (or olitoridis), 451 spinas, 412, 414 Eruption of teeth, 1127 Ethmoid, 81 at birth, 124 cells, 83, 111, 1207 Ethmoidal artery, anterior, 554 posterior, 553 branches of anterior ethmoidal artery, 554 of posterior ethmoidal artery, 553 bulla. 111, 1205 canals, 61, 83, 110, 113, 126 (superior turbinate) crest, 92 fissure, 113 infundibulum, 1205 nerve, anterior, 936, 937 posterior, 937 notch, 61 process, 85 spine, 63, 113 veins, 659 Ethmo-turbinals, 119 Ethmo-vomerine region of skull, 117 Eustachian tube, 74, 1089, 1092 Eustachian tube, openings of, 1130, 1354 valve, 512 Excretory ducts of lacrimal gland, 1079 Exoccipital, 119 Exognathion centre, 91 Expiration, muscles which affect, 248 Extension (of muscles), 321 Extensor carpi radialis acoessorius, 391 brevis, 388, 389 intermedius, 391 longus, 387, 388 ulnaris, 388, 391 communis pollicis et indicis, 394 digiti annularis, 395 quinti proprius (extensor minimi digiti), 388, 391 digitorum brevis (foot), 454, 492 (hand), 395 communis, 388, 391 longus, 453, 480, 481 group of arm muscles, 377 hallucis brevis, 482, 492 longus, 453, 480, 482 indicis proprius, 392, 394 medii digiti, 395 ossis metacarpi pollicis (abductor pollicis longus), 393 pollicis brevis, 392, 394 longus, 392, 394 Extremity, lower, bones of, 169 clinical and topographical anatomy of, 1434 lymphatics of, 746 upper, bones of, 139 clinical and topographical anatomy of, 1409 lymphatics, 719, 1424 Extrinsic muscles of tongue, 345 Eye, 1051 blood-vessels of, 1031 clinical anatomy of, 1346 crystalline lens, 1052 development of, 1080 eyelids, 1053, 1076 general surface view, 1052 lymphatics of orbit, 715 nerves of, 1064, 1348 Eyeball, (bulbus ocuh), 1-055 blood-vessels of, 1065 equator of, 1055 hemispheres of, 1057 insertions of muscles, 1056 muscles of, 501, 1067 nerves of, 1064 poles of, 1055 Eyelashes (cilia), 1053, 1347 Eyelids, 1053, 1076 blood-vessels of, 1078 clinical anatomy, 1346 glands of, 1078 lymphatics of, 712, 1078 nerves of, 1078 structure of, 1077 Face, bones of, 51 clinical anatomy, 1342 cutaneous areas of, 1018 development of, 18 lymphatic vessels of, 712 muscles of, 324, 329, 501 veins of, 643 Facial (external maxillary) artery, 540, 1343 branches of great auricular nerve, 978 (Fallopian) canal, 72, 77, 78 lymph-nodes, 709, 711 INDEX 1491 Facial nerve, 943, 946, 1345 nucleus of, 825 paralysis of, 1345 portion of external maxillary artery, 540 vein, anterior, 643, 1343 common, 644, 646 posterior (temporo-maxillary), 644 transverse, 646 Facialis, musculature, 324, 329, 501 Falciform ligament of liver, 1185 margin of fascia lata, 467 process of great sacro-soiatic ligament, 236 Fallopian canal, 72, 77, 78 tubes, 1269 Fallopius, aqueduct of (facial canal), 72 Falx cerebelU, 915 cerebri, 914 inguinalis (conjoined tendon of internal ob- lique and transversalis), 436, 1396 Fascia(8B) antibrachial, 384 of arm, 377 axillary, 370, 371 brachial, 377 bulbi (Tenon's capsule), 1073, 1348 Camper's, 425 Colles', 425 coraco-clavicular (costo-coracoid), 371 cranio-mandibular, 339 cremasteric (Cowper's), 426, 434, 1254 cribrosa, 467 crural, 477 of deep musculature of shoulder girdle, 356 deep cervical, 1360 deep palmar, 387 dentate, 868 diaphragmatic pelvic, 442, 447 endo-pelvic (recto-vesical), 442, 447 endothoracica, 1235 external cervical, 347 spermatic, 1387 of foot, 491 of forearm and hand, 384 of hand, 1427 of head and neck, 329 hypothenar, 387 iliac, 455, 466 of ilio-femoral musculature, 455 ilio-peotineal, 455, 466 of infrahyoid musculature, 350 intercolumnar (external spermatic), 1304 interpterygoid, 339 of ischio-pubo-femoral musculature, 463 lata, 454, 457, 466, 1400, 1436 lateral pharyngeal, 339 of leg, 477 lingual, 346 lumbar, 436 lumbo-dorsal, 414, 428 masseteric, 339 middle cervical, 350 muscle, 313 of musculature of shoulder, 365 nuchae, 414 obturator, 439, 463 of orbit, 1071 palpebral, 1071 parietal (pelvic), 447 parotid, 339, 348, 1114 of pectoral muscles, 371 of pelvis, muscular, 443, 446, 447 subcutaneous, 445 penis, 1260 plantar, 1468 of posterior group of ilio-femoral muscles, 457 of prevertebral musculature, 355 prostatico-perineal, 447 Fascia (ae) psoas, 455 renal, 1242 of scalene musculature, 353 Scarpa's, 425, 445 of scrotum, 1385 semilunar, 382 Sibson's, 129, 356, 1237 of spinal musculature, 413 superficial, 313 permeal (Colles'), 446, 1385 of shoulder girdle, 347 of supra-hyoid musculature, 344 temporal, 339 thenar, 387 of thigh, 466 thoraco-abdominal musculature, 425 subcutaneous, 425 transversalis, 426 triangular, 430 of upper limb musculature, 363 of urogenital diaphragm, 445 of wrist, 1427 transversi of palmar aponeurosis, 387 Fas ci cuius (i), 769 anterior marginal, 786 comma-shaped, 782 cuneatus (Burdach's column), 781 gracilis (Goll's column), 781 inferior longitudinal, 892 intermediate, 784 lateral cerebro-spinal, 783 mammillo-mesen cephalic (tegmento-mam- millary or mammillo-peduncular), 871 mammilio-thalamic, 871, 883 medial longitudinal, 817, 842 oblique, 804 oooipito-frontal, 892 pedunculo-mammillary, 849 proprii, 769 proprius, dorsal, 782 lateral, 782 ventral, 786 retroflexus of Meynert, 841, 843, 872, 886 rubro-spinal, 786 spino-cerebellar, dorsal, 784 spino-olivary (Helweg's bundle), 784 sulco-marginal, 788 superficial ventro-lateral (spino-cerebellar), 784 superior longitudinal, 892 ■uncinate, 891 ventral cerebrospinal, 788 vestibulo-spinal, 786 Fasciola cinerea, 868 Fauces, isthmus of, 1100, 1130, 1131 Female, reproductive organs, 1265 clinical anatomy of, 1391 development of, 1278 external (vulva),- 1276 lymphatics of, 744, 1278 ovaries, 1238 tubffi uterinse (Fallopian tubes), 1269 uterus, 1271 vagina, 1274 vessels and nerves of, 1278 urethra, 1278 Femoral artery, 616, 1441 branches, 618 collateral circulation, 1441 common, 616 profunda or deep, 620, 640 superficial, 616 canal (crural canal), 468, 1400 cutaneous nerve, posterior (small sciatic), 1007 hernia, 1398 (anterior crural) nerve, 1001 1492 INDEX Femoral plexus of nerves, 1045 ring, 466, 1401 septum, 466 sheath, 1400 trigone (Scarpa's triangle), 467, 1438 vein, 690, 1441 tributaries, 690 Femoro-tibial muscle, 486 Femoro-popliteal vein, 685, 693 Femur, 178 clinical anatomy of, 1434, 1442 condyles of, 1447 ossification of, 184 trochanters of, 178 Fenestra cochleae (rotunda), 73, 1089 vestibuli (ovalis), 73, 1089 Ferrein, pyramid of, 1246 Fibras propriae, 890 Fibres, arcuate, 817 association, of telencephalon, 890, 893 of white substance of spinal cord, 779 of cerebellar cortex, 809 cerebello-olivary, 817 of cerebral cortex, 879 commissural system of, 890 external arcuate, of medulla oblongata, 800 interorural (intercolumnar fascia), 430 internal arcuate, 815 muscles, 315 nerve, 767 development of, 758 projection, of telencephalon, 886 sympathetic, 970, 1029 visceral afferent, 970 efferent, 970 Fibro-cartQages, cotyloid, 281 interosseous, 244 interpubic, 240 intervertebral, 225, 238 semilunar, 289 triangular (articular disc), 264 Fibula, description of, 189, 1454 ossification of, 191 Fibular branch of posterior tibial artery, 626 collateral ligament, 286 nutrient branch of peroneal artery, 626 Fibulo-calcaneus medialis, 491 Fibulo-tibialis, 486 Fifth ventricle (cavity of septum pellucidum), 872 Fila radicularia, 775', 964 Filaments, root, of spinal nerves, 775 of pons, lateral, 804 Filiform, papillae of tongue, 1106 Filum of dura mater, 911 terminale, 771, 721 Fimbria, 868, 877 ovarica, 127 Fimbriae of tubae uterinae (Fallopian tube), 1270 Fimbriate folds of tongue, 1107 Fimbrio-dentate sulcus, 868 Fingers, 4 muscles acting on, 505 Fissura prima, 866 serotina, 865 Fissure(s), anterior median, 772 antitrago-helicine, 1084 auricular, 75, 108 calcarine, 864 calloso-marginal, 857, 859 of cerebellum, 805 of cerebrum, 852 chorioid, 1080 collateral, 855, 864 ethmoidal, 113 external parieto-occipital, 862 Fissure(s), Glaserian, 71, 77 hippocampal or (chorioid), 868 horizontal (of cerebellum), 805 inferior orbital (spheno-maxillary), 102, 109, 126 lateral (Sylvian), 850, 855, 1340 of liver, 1183 longitudinal, of cerebrum, 850 of lung, 1230, 1234 oral, HOC parieto-occipital, 860, 864 petro-tympanic, 71, 77, 108, 126 portal, 1183 posterior median, of medulla oblongata, 801 postlimbic, 863 pterygo-maxillary, 102 pterygo-palatine, 102 retrotonsillar, of cerebellum, 807 of Rolando, 859, 1340 semilunar (of cerebellum), 805 spheno-maxillary, 102, 109 of spinal cord, 772 superior orbital (sphenoidal), 65, 109, 116' 125 of Sylvius, 850, 855 of telencephalon, 853 transverse, of cerebrum, 850 tympano-mastoid, 71, 75, 108 umbilical, of liver, 1183 Flechsig, direct cerebellar tract of, 784 secondary optic radiation of, 890 Flexion of muscles, 321 Plexor accessorius, 454, 495 longus digitorum, 491 carpi radialis, 396, 398 brevis (radio-carpeus), 403 ulnaris, 396, 398 brevis (ulno-earpeus), 402 digiti quinti brevis (foot), 454, 498, 499 (hand), 404 digitorum brevis, 454, 493 longus, 454, 486, 489 profundus, 401 Flexor digitorum profundus, 401 sublimis, 399 group of arm muscles, 379 haUucis brevis, 454, 496, 497 longus, 454, 486, 490 poUicis brevis, 407, 408 longus, 402 Flexure(s) of duodeno-jejunal, 1376 of duodenum, 1161 left cohe (splenic), 1174, 1379 of rectum, 1176 right colic (hepatic), 1173, 1379 Floating ribs, 127 Floccular fossa, 73 Flocculus of cerebellum, 807 peduncle of, 807 Floor of cranial cavitj', 112 of fourth ventricle, 813 pelvic, 1384 in female, 1394 Fluid, cerebro-spinal, 920 1342 Flumma pilorum, 1291 Fcetal circulation, 695 skull, general characters of, 120 Fold(s), adipose, of pleura, 1237 alar, 291 ary-epiglottic, 1221 of Douglas, 427 of duodenum, 1164 glosso-epiglottic, 1220 inferior palpebral, 1053 neural, 754 patellar, 290 recto-uterine, 1274 INDEX 1493 Fold(s), semilunar, of conjunctiva, 1055 of skm, 1284 sublingual, 1116 superior palpebral, 1053 transverse (Houston's), of rectum, 1177, 1390 of tympanic mucous membrane, 1089 ventricular, of larynx, 1222 vocal, 1223 Foliate papUlse of tongue, 1106 Folium vermis (cacuminis) of cerebellum, 806 Follicles, Graafian, 1269 of hair, 1292 lingual, 1107 lymph, 704 Fontana, spaces of, 1060 Fontanelle(s), sagittal, 59 of skull, 120 Foot, amputations of, 1465 arches of, 1468 arteries of, 627, 631 bones of, 191, 205, 1467 bony landmarks of, 1464 bursae of, 1465 clinical anatomy of, 1464 cutaneous nerves of, 1466 muscles acting on, at ankle-joint, 505 musculature of, 491 synovial membranes of, 1465 talipes, 1467 Foramen(ina), 29 acetabular, 174 apicis dentis, 1118 auditory, 125 ■ caecum, 61, 113, 1318 of ethmoid, 81 of medulla oblongata, 799 (Morgagni) of tongue, 1106 carotico-olinoid, 65 condylar, 54 costo-transverse, 127 of diaphragma sellae, 916 epiploic (foramen of Winslow), 1147 greater palatine, 106 hypoglossal, 54, 108, 125 incisive, 89 inferior dental, 96 infra-orbital, 87, 1345 intervertebral, 30 intraventricular (Monroi), 847, 874 jugular, 74, 108, 117, 125 laoerum, 63, 74, 108, 116 lesser palatine, 106 of Magendie, 813 magnum, 51, 56, 108, 117, 125 mandibular (inferior dental), 96 mastoid, 72, 108, 117 mental, 95 palatine, 106 of Monro, 847, 874 of nerves of skull, 125 of norma facialis, 108 obturator (thyreoid), 174 optic, 63, 64, 110, 116, 125 ovale, 66, 116, 125 of Pacchioni, 116 papillaria, 1246 parietal, 57 petro-sphenoidal, 125 . pharyngeal, 126 rotundum, 65, 103, 116, 125 sacral, 40 scapular, 142 of Scarpa, 89, 106, 126 spheno-palatine, 93, 103, 111, 126 spinosum, 65, 116 of Stenson, 89, 106 roramen(ina), sternal, 133 stylo-mastoid, 73, 108, 126 supra-orbital, 60 supratrochlear, 150 thyreoid (thyreoid cartilage), 1211 trigeminal, 125 venae cavae, 438 venarum minimarum (Thebesii), 514 vertebral, 31 Vesalii, 65, 116 zygomatioo-temporal, 126 Forceps major, 876 Forearm, clinical anatomj- of, 1419 common fractures of bones of, 1420 joints of, 1419 muscles of, 362 musculature of, 383 nerves of, 1423 synovial tendon sheaths of, 395, 403 vessels and nerves of, 1423 Fore-brain, 843 Formation, reticular, 816 Fornix, anterior pillars (columns) of, 870 body of, 869 conjunctival, 1054, 1347 fibres of, 869, 870, 871, 890 of Limbic lobe, 868 pharyngeal, 1130 posterior pillars (crura), 868 transverse, 869, 890 of vagina, 1275 Fossa (e), abdominal, 430 anterior cranial, 113 of anthelix, 1082 axillary, clinical anatomy of, 1411 canine, 87 cardiac, of lung, 1229 condylar, 54, 108 coronoid, 150 cotyloid, 169 digastric, 95 digital, of femur, 178 of fibula, 191 ductus venosi, 1183 duodenal, 1164 of femur, intercondyloid, 182 floocular, 73 of gall-bladder, 1183 glenoid, 29 of humerus, coronoid, 150 olecranon, 150 radial, 151 hypophyseos, 63, 116 iliac, 170 ileo-caecal, 1172 ileo-colic, 1172 ilio-pectineal, 467 incisive, 87 incisor, 95 infraspinous, 142 infra-temporal (zygomatic), 101, 1332 interpeduncular, 835 intersigmoid, 1175 ischio-rectal, 441, 445, 1384 jugular, 73, 108 lacrimal, 61, 109 mandibular, 108 mastoid, 72 middle cranial, 116 nasal, 108, 110 navicularis, 1264, 1277, 1392 olecranon, 150 ovalis (of heart), 512 (saphenous opening), 467, 1400, 1440 ovarica, 1268 paraduodenal (Landzert), 1164 pericardial, 1172, 1378 1494 INDEX Fossa(e), posterior cranial, 116 pterygoid, 66, 107 pterygo-palatine (spheno-maxillary), 102 radial, 151 rhomboidea, 802 of Rosenmueller, 1130 scaphoid, 54, 55, 66, 95, 107 of skull, surgical anatomy of, 1342 spheno-maxillary (pterygo-palatine), 102 subareuata, 73, 117 subscapular, 141 supraspinous, 141 supratonsillar, 1132 Sylvian, 854 temporal, 101 triangular, of auricle, 1082 of elbow, 1418 trochanteric or digital, 178 trochlear, 61 venee cavEe, 1183 vermiform, 53, 108, 117 zygomatic, 101, 1332 Fossula cochlearis, 72 petrosa, 73 vestibularis, 72 Fountain decussation (Forel), 842 Fourchette, 1276, 1392 Fourth ventricle, 812 anatomy of, 812 chorioid plexus of, 922 floor of, 813 roof of, 812 tela chorioidea of, 922 Fovea of arytaenoid cartilages, 1212 centralis, 1055 of femur, 178 hemielliptica, 80 hemisphserica, 80 inferior, of floor of fourth ventricle, 814 superior of, floor of fourth ventricle, 815 inguinalis, 430 pterygoidea, 97 sublingualis, 95 umbilical, 1284 Foveola palatina, 1104 Fracture or fractures of bones of the leg, 1454 doUes', 1420 common, of bones of forearm, 1420 Dupuytren's, 1455 of mandible, 1345 of olecranon, 1420 Pott's, 1454 Freckles, 1283 Frenulum of anterior medullary velum, 832 clitoridis, 1277 of ileo-caecal valve, 1172 of penis, 1260 of tongue, 1107, 1349 veli, 812, 835 Frenum (duodenal), 1164 Frequency of disease of tarsal bones, 1396 Frontal artery, 554, 1343 association area, 894 bone at birth, 123 description of, 59 branches of anterior ethmoidal artery, 554 of superficial temporal artery, 545 convolution, ascending, 851 crest, 60 eminences, 59, 108 gyrus, inferior, 858 middle, 858 superior, 857 lobe, 857 nerve, 936, 1075 notch, 60 operculum, 856 Frontal pole, 850 pontile path (Arnold's bundle), 832, 840, 889 process of maxilla, 87, 88 sinus, 59, 61, 1207, 1335 spine, (nasal), 60 sulcus, inferior, 858 middle, 858 superior, 858 suture, 59 vein, 644 Frontal vein, 644 diploic, 648 Frontalis, 337 Fronto-ethmoidal cells, 84 Fronto-marginal sulcus, 858 Fronto-nasal plate, 117 process, 119 Fronto-sphenoidal process, 95 Functional areas of cerebral cortex, 893 Functions of cerebellum, 832 of muscle groups, 500 Fundiform hgament of penis, 427 Fundus of gall-bladder, 1187 of stomach, 1151, 1374 uterus, 1271 Fungiform papillse of tongue, 1106 Funiculi of nerves, 769 spinal cord, 774, 780 Funiculus, anterior, 775, 786 cuneatus of medulla oblongata, 801 gracilis of medulla oblongata, 801 lateral, 775, 782 posterior, 774, 780 separans, 814 Furcal nerve, 998 Furrow, 29 Furrows, articular, of skin, 1284 Fusiform gyrus (occipito-temporal convolu- tion), 855, 864 muscles, 315 Galea aponeurotica (epicranial aponeurosis), 337 Galen, veins of, 923 Gall-bladder, 1187 clinical anatomy of, 1372 ducts of, 1187, 1188, 1372 Ganglion (ia), aberrant spinal, 965 of Andersch, 951 aortico-renal, 1043 basal, 878 of Bochdalek, 939 cardiac (ganglion of Wrisberg), 1041 ciliary, 961, 1033, 1076 ooccygeum impar, 1032, 1040 coeliac (semilunar), 1043 (neural) crest, 754 first thoracic, 1038 geniculate, 826, 947 inferior cervical, 1036 interpeduncular (von Gudden's), 843, 872, 885 jugular (superior), of glosso-pharyngeus, 957 of vagus, 954, 956 of glosso-pharyngeus, 951 middle cervical, 1036 nodosum (ganglion of trunk), 954, 956 otic (Arnold's), 963 petrosal, 951 phrenic, 1044 renal, 1044 of root of vagus, 956 roots of, 959 INDEX 1495 Ganglion (ia), second thoracic, 1038 semilunar (Gasserian), 826, 938, 1345 spheno-palatine (Meckel's), 962 spinal, 964 spiral, of cochlea, 950 splanchnic, 1039 submaxillary, 963 superior cervical, sympathetic, 960, 1035 jugular, or Ehrenritter's, 951 mesenteric, 1043, 1045 sympathetic, 959, 1032 of head, 959 of synovial sheaths, 1434 terminal, 930 of trunk of vagus, 956 of Valentine, 939 vestibular, 823, 950 of Wrisberg, cardiac, 498 Gangliated cephalic plexus, 959 nerve trunks (cords), 755, 1029, 1032 Ganglionic branches of middle meningeal artery, 548 Gartner, duct of, 1275 Gasserian (semilunar) ganglion, 826, 935, 1345 Gastric artery, left, 593 right, 594 branches of epiploic arteries, 595 of vagus, 958 lymphatic nodes, 730, 734 plexus of nerves, anterior, 958 inferior, 1045 posterior, 958 superior (coronary), 1045 surface of spleen, 1309 Gastrocnemius, 453, 484, 485 Gastro-duodenal artery, 594 Gastro-epiploic artery, left, 595 right, 595 vein, left, 675 right, 675 Gastro-hepatic ligament, 1150 Gastro-phrenic ligament, 1150 Gastro-splenic (gastro-lienal) ligament (omentum), 1150, 1310 Gastroptosis, 1160 Gemellus inferior, 464 superior, 464 Gemmules, 762 Genial tubercles, 95 Geniculate bodies, 834, 845 ganglion, 826, 949 Geniculo-tympanio branch of glosso-palatine, 951, 961 Genio-glossus, 346 Genio-hyoideus, 343, 344 Genio-pharyngeus, 346 Genital corpuscles, 1290 ridge, 1267, 1278 swellings, 1279 tubercle, 1279 Genitalia, female, external, 1276 clinical anatomy of, 1391 male, 1253 Genito-femoral (genito-crural) nerve, 1000, 1260 Genu of corpus callosum, 851 of facial canal, 78 inferior, of central sulcus (fissure of Rol- ando), 860 of internal capsule (telencephalon), 887 superior, of central sulcus (fissure of Rol- ando), 860 suprema artery, 621, 640 valgum, 1449 Germ laj'ers, 9 Gimbernat's hgament, 424, 429, 466, 1400 • Gingival branches, inferior, of inferior dental plexus, 941 superior, of superior dental plexus, 939 Ginglymi diarthroses, 213 Girdle, pelvic, 207 shoulder, 207 Glabella, 60, 101, 109, 1331 Gladiolus (mesosternum), 132 Gland(s), 1099 broncliial, 1231 Brunner's, 1166 bulbo-uretliral (Cowper's) 1265 carotid, 550, 1327 ceruminous, 1297 ciliary (of Moll), 1078, 1297 circumanal, 1297 ductless, 1306 of eyeUds, 1078 glomiform, 1296 greater vestibular (of Bartholin), 1278, 1392 Henle's 1078 I&ause's, 1078 lacrimal, 1079, 1348 lingual, 1108 lesser vestibular, 1278 of Lieberkuehn, 1166, 1177, 1390 of lips and cheeks, 1103 lymphatic, 704 intercolated, 706 mammary, 1299 of Montgomery, 1304 mucous, of larynx, 1224 nasal, 1208 of Nuhn or Blandin, 1110, olfactory, 1208 para-thyreoid, 1318, 1355 parotid, 348, 1113 accessory, 1114 preputial, 1298 prostate, 1264 salivary, 1113 sebaceous, 1298 of skin, 1296 of small intestine, 1166 of palate, 1104 sublingual, 1116 submaxillary, 1116, 1350 sudoriferous (sweat), 1296 suprarenal, 1323 accessory, 1326 tarsal (Meibomian), 1054, 1078 thymus, 1319 thyreoid, 1312 accessory, 1315 clinical anatomy of, 1355 tracheal, 1227 urethral (of Littrg), 1264 Zeiss's, 1078 Glandular branches of external maxiUarj', 541 of inferior thyreoid artery, 564 Glans clitoridis, 1277 of penis, 1260 Glaserian fissure, 71, 77 Gleno-humeral bands, 254 ligament, 255 Glenoid cavity of scapula, 143 fossa, 29 ligament, (lip) 255 of metacarpo-phalangeal joints, 294 lip of shoulder-joint, 255 of hip-joint (cotyloid fibro-cartilage), 281 Gliding motion of joints, 214 Glisson's capsule, 675, 1186 paUidus, 880 Glomerular capsule, 1246 layer of olfactory bulb, 866 Glomeruli of olfactory nerves, 929 1496 INDEX Glomiform glands, 1296 Glomus caroticum (carotid gland), 1327 choroideum, 876 cocoygeum, 1040, 1329 Glosso-epiglottic folds, 1220 ligament 1218 Glosso-hyal process, 99 Glosso-palatine arches, 1132 nerve, 826, 946 Glosso-palatinus (palato-glossus), lldo Glosso-pharyngeal nerves, 820, 951 Glottis, 1223 Gluteal arteries, 608, 1444 branches, 609 superior, 608 inferior, 609, 639 branches of internal pudendal artery, 613 of posterior femoral cutaneous nerve, 1007 line, anterior, 170 inferior, 166 posterior, 170 nerve, inferior, 1007 superior, 1007 tuberosity of femur, 178 veins, inferior 680 superior, 680 Gluteus maximus, 453, 457, 459 surface marking, 1443 medius, 453, 457, 461 minimus, 453, 457, 461 Golgi cells in cerebellum, 809 Golgi-Mazzoni corpuscles, 1290 GolUs column, 781 Gomphosis sutures, 212 Gonion, 112, 113 Gower's tract, 784 Graafian follicles, 1269 Gracilis, 453, 471, 472 Granular layer of cerebellar cortex, 809 Granulations, arachnoid, 649, 919 Great auricular nerve, 978 cardiac vein, 520 omentum, 1149 (anterior) palatine nerve, 963 prevertebral plexuses of nerves, 1010 (internal) saphenous vein, 684, 1456 splanchnic nerve, 1038 superficial petrosal nerve, 948 trochanter of femur, 178, 1435 Greater alar (lower lateral) nasal cartilages, 1201 curvature of stomach, 1152 multangular (trapezium) bone, 162 occipital nerve, 971 palatine foramina, 106 canals, 92 tuberosity of humerus, 147 , ,• n vestibular glands (glands of Bartholm), 1278, 1392 Grey commissure of spinal cord, 775 _ ■ rami communicantes of sympathetic sys- tem, 1030 substance, central, of niesencephalon, 836 of pons (nuclei pontis), 831 of nervous system, 768 of spinal cord, 775 Groove of atlas, 33 basilar, 54 bony, 29 carotid, 64 costal, 127 costo-vertebral, 138 of cuboid, peroneal, 199 infra-orbital, 87 intertubercular (bicipital), 148 lacrimal, 85, 87, 110 mylo-hyoid, 96 Groove, neural, 754 obturator, 172 occipital, 72 optic, 63, 113 for radial nerve (musoulo-spiral), 149 sacral, 41 sigmoid, 72 Grouping of muscles according to function, 500 Growth, prenatal, 22 of the organs, 25 of the parts, 24 of the systems, 25 Gubernacular canals, 106 Gubernaculum testis, 1257, 1387 Gudden's commissure (inferior cerebral com- missure), 842, 850, 890 Guftis, 1119 lymphatics of, 715 Gustatory area of cerebral cortex, 894 cells, 1051 organ, 1051 Gynecomastia, 1305 Gyrus (i) Andres Retzii, 868 ambiens, 865 angular, 863 anterior central, 857 cuneo-lingual, 843 orbital, 858 breves (precentral gyri), 857 of cerebellum, 804 of cerebrum, 852 cinguli (cingulum), 867 cunei, 864 cuneo-lingual, 864 deep annectant, 860 dentate, 868 epicallosus, 868 external orbital, 838 fornicatus, 867 cinguli (cingulum), 867 hippocampus, 868 isthmus of, 867 fusiform (occipito-temporal convolution), 855, 864 hippocampal, 868 inferior frontal, 858 temporal, 855 lateral occipital, 863 olfactory, 865 orbital, 859 lingual, 855, 864 longus, 857 marginal, 858 medial olfactory, 866 orbital, 858 middle frontal, 858 temporal, 855 orbital, 858 origin of, 853 ■ ^ in oci posterior central (ascending parietal), 86 J. orbital, 858 post-parietal, 863 profundi, 852 rectus, 858 semilunar, 865 , subcallosal (peduncle of corpus callosum). 866 submarginal, 858 superior frontal, 857 occipital, 863 parietal, 862 temporal, 854 supracallosal, 868 supramarginal, 863 transitivus, 852 transverse temporal, 855 • uncinatus, 868 INDEX 1497 H Habenulse, 846 Habenular commissure, 846, 872, 885, 890 nucleus, 872, 885 trigone, 835 Habenulo-peduncular tract, 873 Hajmolymph nodes, 708 Haemorrhoidal artery, inferior, 613, 1391 middle, 610, 1391 superior, 603, 1091 of middle sacral artery, 603 nerves, inferior, 1017 middle, 1017 superior, 1045 plexus of nerves, middle, 1045, 1046 superior, 1045 of veins, 683, 1391 Hairs (pili), 1290 development of, 1293 olfactory, 1050 Hamate (unciform) bone, 159, 163 Hamular process of sphenoid, 66, 106, 1351 Hamulus, 81, 163 Hand, bony points of, 1424 clinical anatomy of, 1424 fascia of, 1427 muscles acting on, at wrist, 504 musculature of, 363, 383, 403 skin-folds of, 1425 synovial membranes of, 1431 Hard palate, 1104 Hare-lip, 1352 Harmonic sutures, 212 Hassal's corpuscles of thymus, 1322 Head of axis, 33 of bone, 29 bony landmarks of, 1331 clinical and topographical anatomy of, 1331 deep lymphatic nodes of, 714 vessels of, 714 of epididymis, 1256 lymphatics of, 709 of muscle, 314 muscles acting on, 502 musculature of, 323 of pancreas, 1192 process, 11 sympathetic ganglia of, 959 Heart, 508 Heart, atria of, 511 development of, 623 foetal, 695 ventricles of, 516 lymphatics of, 701, 730, 522 muscle of, 518 nerves of, 522 relation to chest-wall, 523, 1368 vessels of, 519 Heister, valve of, 1187 Helicis major, 1084 minor, 1084 Helicotrema, 81 Helix, 1083 Helweg's (Bechterew's) bundle, 784 Hemiazygos vein (azygos minor), 662 accessory, 663 Hemispheres of cerebellum, 805 cerebral, 850 Henle, loop of, 1246 Henle's glands, 1078 Hepatic artery, 594 branches of superior epigastric artery, 567 of vagus, 958 duct, 1187 (right coUc) flexure, 1173, 1379 lymphatic nodes, 730, 736, 1186 Hepaticlymphatics, 1186 plexus of nerves, 1045 veins, 675 Hepato-oolic ligament, 1379 Hepato-duodenal ligament, 1150, 1185 Hernia, congenital, 1255, 1387, 1398 femoral, 1394 into the funicular process, 1255, 1398 infantile, 1398 inguinal, 1255, 1394, 1398 scrotal, 1255 surgical anatomy of, 1394 umbilical, adult, 1402 Hesselbach, ligament of, 430 triangle of, 1398 Hey's amputation, 1465 Hiatus, accessory, 116 aorticus of diaphragm, 437 canalis facialis, 73, 116 cesophageus, 437 sacralis, 40 semilunaris of middle nasal meatus, 1205 Highest nuchal line, 52 Highmore, antrum of, 87, 90, 111, 1206, 1346 Hilus of kidney, 1242 of lungs, 1229, 1230 of ovary, 1268 of spleen, 1309 of suprarenal glands, 1325 Hind-brain, 804 Hip, musculature of, 453, 454 Hip-joint, 276 arterial supply, 282 ligaments of, 277 lymphatics of, 750 movements of, 282 muscles acting upon, 283 nerve-supply, 282 relations, 282 surgical anatomy of, 1435 Hippocampal branch of posterior communi- cating artery, 554 commissure (psalterium or b'ra), 869, 890 digitations, 877 (ohorioid) fissure, 868 gyrus, 868 Hippocampus, 868 gyrus of, 868 major, 868, 877 minor (calcar avis), 864, 868, 876 Hirci, 1290 Homologies of parts in sexes, 1280 Homology of the bones of the limbs, 206 Horizontal fissure of cerebellum, 805 Horner's muscle, 336, 1078 Horns of spinal cord, 776 Houston's folds of rectum, 1177, 1390 Huguier, canal of, 75, 77, 108 Hum.eral artery, anterior circumflex, 572 posterior circumflex, 573 Humerus, description of, 146 clinical anatomy of, 1410, 1414 nutrient artery of, 576 ossification of, 161, 1416 tuberosities of, 147 Humor, aqueous, 1052, 1064 vitreous, of eye, 1052, 1064 Hunter's (adductor) canal, 468, 1441 Hyaloid canal (canal of Cloquet), 1064 membrane, 1064 Hydatid of Morgagni, 1257, 1269 Hymen, 1276, 1392 Hyo-epiglottic ligament, 1218 Hyo-glossal membrane, 346 Hj'o-glossus, 346 Hyoid bars, 119 bone, 99, 119 1498 INDEX Hyoid bone at birth, 124 cornua of, 99, 100 muscles acting on, 501 branch of lingual artery, 540 of superior thyreoid artery, 538 bursa, 1217 Hyo-mandibular muscles, 325 Hyo-temporal muscles, 325 Hyo-thyreoid ligament, 1217 membrane, 1217 Hyparterial bronchus, 1232 Hypertrichosis, 1290 Hypertrophy of nails, 1296 Hypochondriac region, 1143 Hypochordal bar, 51 Hypogastric (internal iliac) artery, 605, 638 branches, 606, 639 lymphatic nodes, 732 plexuses of nerves, 1045 region, 1143 (internal iliac) vein, 679 tributaries, 680 Hypoglossal eminence (trigonum hypoglossi), 814 foramen (canal), 54, 108, 117, 125 (cervical) loop, 974, 979 nerve, 952 central connections, 820, 954 nucleus of, 820 Hypomalar, 95 Hypophyseal fossa (sella turcica), 63 Hypophysis cerebri, 758, 847, 848, 1342 development of, 848 Hypospadias, 1280, 1388 Hypothalamic nucleus (body of Luys), 884 sulcus, (sulcus of Monro), 847 Hypothalamus, 881 optic portion of, 847 Hypothenar fascia, 387 Hypo-tympanic recess, 77 Ileo-csecal fossa, 1172 (colic) valve, 1172 region, 1376 Ileo-colic artery, 598 fossa, 1172 vein, 677 Ileum, 1165, 1376 Iliac arteries, collateral circulation, 605, 1382 common, 603, 605, 638 deep circumflex, 616 external, 614, 638 superficial circumflex, 618 branch of ilio-lumbar artery, 607 (nutrient) branch of obturator artery, 608 colon, 1174, 1379 fascia, 455, 466 fossa, 170 lymphatic nodes, common, 731 external, 732 plexus of nerves, 1045 spines, 169 vein, external, 683 internal (hypogastric), 679 veins, common, 679 Iliacus, 455 minor, 455 Ilio-cocoygeus, 440, 448 Ilio-costal region, 1407 Ilio-costalis cervicis (cervicalis asoendens), 416 dorsi (accessorius), 416 lumborum, 416 Ilio-femoral ligament, 278 musculature, 454 Ilio-hypogastric nerve, 998 Ilio-inguinal nerve, 1000 Ilio-lumbar artery, 606 ligament, 233 vein, 680 Iho-pectineal eminence, 169 fascia, 455, 466 fossa, 467 line, 173 Ilio-tibial band, 457, 458, 1436 Ilio-trochanteric band, 280 Ilium, 169 crest of, 169 tuberosity of, 171 Inca bone, (interparietal), 57 Incisive branch of inferior alveolar (dental) artery, 548 foramen, 89 fossa, 87 papilla, 1104 sutures, 106 Incisivus labii inferioris, 332 superioris, 332 Incisor crest, 90 fossa, 95 teeth, 1120 Incisura, 29 apiois cordis, 510 interarytsenoidea, 1222 Incisure, anterior, of auricle, 1082 antitragic, 1082 of Santorini, 1085 terminal (auricle), 1084 Incudo-maUeolar articulation, 1090. Incudo-stapedial articulation, 1090 Incus, 79, 119 ligaments of, 1091 Index, cephalic, 117 pelvic, 177 thoracic, 139 Induseum griseum, 868 Infra-clavicularis, 374 Infraglenoid tubercle of scapula, 143 Infrahyoid musculature, 327, 350 portion of external cervical fascia, 347 Infra-omental region of peritoneum, 1372 Infra-orbital artery, 549, 1075 branches of cervico-facial nerve, 945 , canal, 87, 103, 126 foramen, 87, 1345 groove, 87 nerve, 937, 939 plex-us, 937, 939, 945 process, 95 sulcus, 1284 vein, 646 Infraspinatus, 368 Infraspinous branches of posterior scapular artery, 566 of transverse scapular artery, 565 fossa, 142 Infra-temporal (zygomatic) fossa, 101, 1332 ridge, 65 Infratrochlear nerve, 936, 937 Infra-vomerine center, 71 Infundibula (ureter), 1248 Infundibular recess, 848 Infundibulo-pelvic ligament, 1267 Infundibulum of cerebrum, 848 of ethmoid, 83 in middle nasal meatus. 111, 1205 of tuba? uterinte (Fallopian tubes), 1270 Inguinal abdominal (internal abdominal) ring, 430, 1371, 1396 branches of femoral artery, 620 canal, 424, 430, 1371, 1395 hernia, 1255, 1394, 1398 INDEX 1499 Inguinal (Poupart's) ligament, 424, 429, 1371, 1399, 1438 reflected (triangular) fascia, 430, 1395 lymphatic nodes, 746 ring, subcutaneous (external abdominal), 429, 1371, 1394 (iliac) regions, 1143 Inion, 101, 1331 Inlet or brim (superior aperture) of pelvis, 175 Innominate artery, 532, 637, 1369 branches, 532 Innominate canal (canaliculus), 65 bone, 169 (brachio-cephalic) veins, 641, 691, 692 relations to thoracic wall, 1369 Inscriptio tendinea, 317, 430 Insertion of muscles, 314 (see also individual muscles) Inspiration, muscles which affect, 247 Insula (island of Reil), 856 Integument, 1281 Interarticular cartilage, 211 ligament (capitular articulation), 241 (sterno-costal joint), 245 menisci (semilunar ftbro-cartilages), 289 Interarytffinoid (procricoid) cartilage, 1213, 1218 Inter-brain, 843 Intercalated lymph-nodes, 706 Intercapitular veins (hand), 667 (foot), 684 Intercarpal ligaments, 269 Interchondral articulation, 246 arterial supply, 247 capsule of, 247 movements, 247 nerves, 247 Interclavicular ligament, 248 notch, 133 Intercoccygeal joints, 238 Intercondyloid fossa of femur, 182 eminence of tibia, 185 fossae of tibia, 185 tubercles, 185 Intercostal branches of internal mammary artery, 567 arteries, 588 superior, 568 branches of musculo-phrenic artery, 567 ligaments, external, 423, 432 lymphatics, 724, 728 muscles, function of, 422 nerves, thoracic, 995 spaces, 139 veins, 664 Intercostales externi, 423, 432 interni, 423, 433 Intercosto-brachial (interc osto- humeral) nerve, 995 Intercrural (intercolumnar) fibres of external obhque, 430, 1394 Intercuneiform articulation, 304 Interfascial (Tenon's) space, 715 Interfoveolar ligament, 430, 435 Interior of skull, 112 Interlobar fissure of lungs, 1230 Intermediate cell mass, 15 crus of diaphragm, 437 fasciculus (mixed lateral zone), 784 plex-us, 1041 Intermetacarpal articulations, 273 Intermetatarsal joints, 309 Intermuscular septa, 314 of foot, 492 of leg, 477 of thigh, 468 septum of arm, lateral, 377 Intermuscular septum of arm, medial, 377 Interossei dorsales (foot), 499 (hand), 410 plantares, 499 volares (hand), 409 Interosseous arteries of foot, 633 of forearm, 577, 579, 1423 artery, of forearm, common, 577 dorsal, 579 volar, 577, 639 crest of fibula, 190 of radius, 153 of tibia, 188 of ulna, 157 crural nerve, 1010 ligaments, anterior talo-calcaneal joint, 302 inferior, tibio-fibular articulation, 297 intercuneiform joints, 304 middle tarso-metatarsal joints, 308 of middle tibio-fibular union, 296 of pelvic, articulations, 235 of posterior talo-calcaneal joint, 301 superior, tibio-fibular joint, 295 membrane of forearm, 263, 264, 1420 muscles of foot, 454, 499 of hand, 409 nerve, posterior, 986 volar (anterior), 992 recurrent artery, 580 Interparietal bone, 119 sulcus (intraparietal), 861 Interpeduncular fossa, 835 nucleus (ganglion), 843, 885 Interphalangeal articulations of fingers, 276 of toes, 310 Interpterygoid fascia, 339 Interpubic fibro-cartilage, 240 Intersigmoid fossa, 1175 Interspinal muscles (interspinals), 412, 419 Interspinous ligaments, 231 Intersternal joints, 244 Intertragic notch, 1082 Intertransversarii, 412, 417 Intertransverse ligaments, 231 muscles, anterior and lateral, 356 dorsal, 412 Intertrochanteric crest, 178 Intertubercular (bicipital), groove, 148 Intervaginal space of optic nerve, 1073 Interventricular foramen (foramen of Monro), 847, 874 septum, 516 Intervertebral articulation, ligaments of, 225 fibro-cartilages, 225, 238 veins, 666 Intestinal arteries, 596 veins, 677 lymphatic trunk, 731 Intestines, clinical anatomy of, 1375 large, 1170, 1376 lymphatics of, 734 small, 1161, 1375 Intracranial portion of internal carotid artery, 550 of vertebral artery, 560 Intralabial muscles, 331 Intraparietal sulcus, 861 Intrinsic muscles of great toe, 495 of larynx, 1218 of httle toe, 498 of tongue, 1110 Introduction, 1 Intumescentia tympanica, 951 Involution of mammary gland, 1303 Iris, 1052, 1054, 1060, 1065. Ischial spine, 172 Ischio-bulbosus muscle, 451 1500 INDEX Ischio-capsular ligament, 278 Ischio-cavernosus (erector penis), 443, 451 Iseliio-femoralis, 461 Ischio-pubicus (Vlacovitoh), 450 Ischio-pubo-femoral musculature, 463 Ischio-rectal fossae, 441, 445, 1384 Ischium, 171 Island of Reil (insula or central lobe), 865 Isthmus, aortic, 531 of Fallopian tubes, 1290 of fauces, 1100, 1352 of gyrus fornicatus, 867 pharyngeal (faucium), 1100, 1130, 1131, 1352 of rhombeneophalon, 758, 832 of thymus, 1321 of thyreoid gland, 1313 of tuba auditiva (Eustachian tube), 1092 of uterus, 1271 Iter chordae anterius, 126 posterius, 78, 126 Jacobson, nerve of, 951, 961 organ of, 1057, 1204 Jejunal and Oiac branches of superior mesen- teric artery, 598 Jejuno-ileum, lymphatics of, 734 Jejunum, 1165, 1376 Joint-furrows, 1284 Joints (see "Articvdations"). Jugular foramen, 74, 108, 117, 125 fossa, 73, 108 ganglion (superior) of glosso-pharyngeal, 951 of vagus, 954, 956 nerve, 960, 1035 (interclavicular) notch, 133 process, 54, 108 vein, anterior, 648 line of, 1356 external, 646, 1359 internal, 659, 691 posterior external, 648 venous arch, 648 Jugum sphenoidale, 67 K Kidneys, 1241, 1379 clinical anatomy of, 1379 development of, 1247 lymphatics of, 701, 737, 1247 position and relations of, 1243, 1380 structure, 1246 surfaces of, 1243 variations and comparative, 1247 vessels and nerves of, 1247 Knee-joint, 284 anastomoses around, 1457 arterial supply, 291 bursae around, 1449 clinical anatomy of, 1449 ligaments of, 284 lymphatics of, 750 movements of, 292 muscles acting upon, 295 nerve-supply, 292 relations, 292 synovial membrane of, 290, 1448 Krause, end-bulbs of, 1290 glands of, 1078 Kronlein's method for topography of brain, 1340 Labia (see also "Lips"). of cervix uteri, 1272 majora, 1276, 1392 minora (nymphae), 1277, 1392 Labial arteries (of mouth), 541 (or scrotal) arteries, anterior, 620 posterior, 613 branches, inferior, of mental nerve, 941 superior, of maxillary nerve, 939 nerves, anterior, 1000 posterior, 1017 tubercle, 1102 veins (of mouth) 644 (of vulva), 683, 684 Labyrinth of ethmoid, 82 membranous, 1092 osseous, 80 Lacertus fibrosus (semilunar fascia), 382 Lacrimal apparatus, 1079 clinical anatomy of, 1346 artery, 552 bone, 85 at birth, 124 branch of dorsal nasal artery, 554 of middle meningeal artery, 548 canal, 1080 caruncle, 1052, 1055 crest, 85, 110 ductus (canaliculi), 1079 fossa, 61, 109 gland, 1079, 1348 groove, 85, 87, 110 nerve, 936, 1075 papilla, 1054 process, 85 puncta, 1079, 1349 sac, 1080, 1349 tubercle, 88 vein, 659 Lacrimo-ethmoidal cells, 84 Laciniate ligament (internal annular) of leg, 480 Lactiferous duct, 1254 sinus (ampulla), 1254 Lacuna(8e) laterales, 649 magna, 1264 of Morgagni (urethral), 1264 musculorum, 466 vasorum, 466 venous, of dura, 916 Lacunar (Gimbernat's) ligament, 424, 429, 466, 1400 Lalognosis, 894 Lambda, 101, 1331 Lambdoid suture, 57, 101 Lamellous corpuscles of (Vater, or Pacinian), 1290 Lamina(Ee), anterior elastic, of cornea, 1060 basal (vitreous), of chorioid, 1060 basilaris of membranous labyrinth, 1096 of cerebellum, medullary, 808 chorio-capillaris, 1060 cribriform, 119 cribrosa solera, 930, 1055, 1059, 1073 of temporal bone, 92 of cricoid cartilage, 1210 epithelial chorioid, 876, 924 fusca, 1059 mediastinales, 1237 medullary, of lenticular nucleus, 880 of thalamus, 882 papyracea (os planum), 83 posterior elastic, of cornea, 1060 quadrigemina, 833 rostal, of corpus callosum, 852 INDEX 1501 Lamina of septum pellucidum, 812 spiralis, 81 suprachoroidea, 1057, 1060 terminalis, (of brain), 848 (of isohio-rectal fossa), 1384 of thyreoid cartilage, 1210 tragi, 1084 of tuba auditiva, 1092 of vertebrEe, 30 Landmarks of abdomen, 1370 bony of the ankle, 1459 of the buttocks, 1442 of cranium and scalp, 1333 of elbow, 1417 of the foot, 1464 of forearm, 1419 of the knee, 1447 of neck, 1354 of the leg, 1453 of thigh and hip, 1434 of wrist and hand, 1424 Langerhans, islets of, 1195 Lanugo, 1290 Large intestine, 1170 anus, 1177 blood-vessels of, 1179 caecum or caput coli, 1170, 1377 clinical anatomy of, 1376 colon, 1173, 1378 development of, 1179 lymphatics of, 1179 nerves of, 1179 rectum, 1176 variations and comparative, 1130 vermiform process (appendix), 1173, 1378 Laryngeal artery, superior, 538 inferior, 564 nerve, inferior, 957 superior, 956 pharynx, 1134 prominence, 1211 veins, inferior, 659 superior, 659 ventricle, 1222 Larynx, 1209 cartilages of, 1209 cavity of, 1220 development of, 1225 joints of, 1213 lymphatics of, 719, 1224 muscles of, 326, 501, 1218 vessels and nerves of, 1224 vocal folds (cords), 1223 Latissimo-condjdoideus (dorso-epitrochlearis), 379 Latissimus dorsi, 368 clinical anatomy of, 1405 Law of developmental direction, 12 Laxator tympani muscle, 79 Left atrium of heart, 514 colic artery, 603 vein, 678 common carotid artery, 533 iliac artery, 605 coronary artery, 520 gastric artery, 593 gastro-epiploic artery, 595 vein, 677 innominate vein, 641 lower bronchial artery, 588 pulmonary artery, 529 veins, 529 subclavian artery, 556 upper bronchial artery, 588 ventricle of heart, 516, 517 Leg, bony landmarks of, 1453 clinical anatomy of, 1453 Leg, fasciae of, 497 nauscles acting on, 505 muscular compartments, 1453 musculature of, 453, 477 vessels of, 1456 Lemnisci, decussation of, 815 of medulla oblongata, 815 Lemniscus, 831, 839 lateral, 816, 831, 839 medial, 816, 831, 839 nucleus of, 824, 839 Lens, crystalline, 1052, 1057, 1062 Lens-capsule, 1057 Lenticular nucleus, 878, 879 process of incus, 79 papillte of tongue, 1106 Lenticulo-optic artery, 562 Lenticulo-striate arterjf, 562 Lesser alar (sesamoid) nasal cartilages, 1202 curvature of stomach, 1152 multangular (trapezoid) bone, 159, 162 (gastro-hepatio) omentum, 1150, 1185 palatine foramina, 106 sac of peritoneum, 1148 sigmoid cavity of ulna, 157 splanchnic nerve, 1039 tuberositj' of humerus, 147 Levator ani, 440, 448 claviculae, 359 cushion, 1130 epiglottidis, 347 labii superioris, 322 alaeque nasi, 332 menti, 334 palpebrae superioris, 1068 penis, 451 scapulffi 356, 359 of thyreoid gland, 1315 veli palatini, 1137 Levatores costarum, 423, 432 longi, 432 Levels, vertebral, 1409 Lieberkiihn, (crypts) glands of, 1166, 1177, 1390 Lienal plexTis of nerves, 1045 Lieno-renal ligament, 1310 Lieutaud, vesical trigone of, 1252 Ligament (s) (see also "Ligamentum"), 211 alar (occipito-dental or check), 223 of ankle-joint, 298, 1463 annular, at ankle, 1463 of finger, 387 ^ of superior radio-ulnar joint, 262 of trachea and bronchi, 1227 of wrist, 387 anterior, of ankle, 298 annular (wrist), 387 atlanto-epistrophic, 221 atlanto-occipital, 218 crucial, 288 longitudinal, 227 medio-carpal, 270 oblique (lateral occipito-atlantal), 219 sacro-coccygeal, 234 sacro-iliac, 234 of symphysis pubis, 239 talo-calcaneal, 302 talo-fibular, 299 apical dental (suspensory), 223 arcuate (subpubic), 239 connecting articular processes vertebrae, 228 Cooper's, 1400 of articulation of atlas with occiput, 218 of atlanto-epistrophic joint, 221 of auricle (of ear), 1084 uniting bodies of vertebrae, 225 broad (lateral), of uterus, 1267, 1393 1502 INDEX Ligament(s) of ealcaneo-cuboid joint, 306 calcaneo-fibular, 299 calcaneo-metatarsal, 492 of capitular (oosto-oentral) articulation, 241 capsular, of elbow-joint, 258 carpal (annular), 1427 of carpo-metacarpal joints, 272 of the carpus, dorsal, 384 transverse, 387 volar, 387 cerato-oricoid, 1213 check, of eyeball, 1072 coccygeal, 911 CoUes', 430 conoid, 251 coraco-acromial, 252 coraco-clavioular, 251 coraco-humeral, 255 corniculo-pharyngeal, 1218 coronary, of knee-joint, 290 of liver, 1184 costo-clavicular, (rhomboid), 249 of oosto-transverse articulation, 243 costo-xiphoid, 244,245 crioo-arytaenoid, 1214 crico-pharyngeal, 1218 crico-tracheal, 1218 crucial, of central atlanto-dental joint, 222 of knee-joint, 288 cruciate, of leg, 479 of fingers, 387 of cuboideo-navicular union, 303 of cubo-metatarsal joint, 308 of cuneo-ouboid articulation, 304 of cuneo-navicular articulation, 304 cysto-oolic, 1379 deltoid (of ankle-joint), 298 denticulate, 920, 921 dorsal intercarpal, 269 of elbow-joint, 258 external arcuate, 437 intercostal, 423, 432 lateral, of knee-joint, 286 falciform, of liver, 1185 fibular collateral, 286 of first row of carpal bones, 269 fundiform (superficial suspensory) of penis, 427 gastro-hepatic, 1150, 1185 gastro-phrenic, 1150 gastro-splenic, (gastro-lienal), 1150, 1310 Gimbernat's, 424, 429, 466 gleno-humeral, 255 glenoid (lip), 255 glosso-epiglottic, 1218 hepato-colic, 1379 hepato-duodenal, 1150, 1185 Hesselbach's, 430 of hip-joint, 277 hyo-epiglottic, 1218 hyo-thyreoid, 1217 ilio-lumbar, 238 ilio-femoral, 278 immediate, 225 of incus, 1091 inferior interosseous, (tibio-fibular), 297 of inferior radio-ulnar joint, 264 inferior sacro-iliac, 235 transverse, (spino-glenoid), 253 infundibulo-pelvic, 1267 inguinal (Poupart's), 424, 429, 1371, 1399, 1438 interarticular, 241, 245 interclavicular, 248 of intercuneiform joint, 304 interfoveolar, 430, 435 intermediate, 225 Ligarnent(s) of intermetacarpal joints, 273 of intermetatarsal joints, 309 internal arcuate, 437 lateral, of knee-joint, 286 of mandibular articulation, 215 interosseous, cubo-metatarsal joint, 309 anterior talo-calcaneal, 302 intercuneiform joints, 304 intermediate tarso-metatarsal joint, 308 metacarpal, 269 of pelvic articulations, 235 of posterior talo-calcaneal joint, 301 of interphalangeal joints, fingers, 276 of toes, 311 interspinous, 231 of intersternal joints, 244 intertransverse, 231, 238 of intervertebral articulation, 227 of knee-joint, 284 (internal annular) laciniate, of leg, 480 ischio-capsular, 278 lacunar (Gimbernat's) 424, 429, 466, 1400 of larynx, 1213 lateral, of ankle-joint, 299 calcaneo-navicular, 302, 305 hyo-thyreoid, 1217 malleolar, anterior, 296 posterior, 297 sacro-coccygeal (intertransverse), 238 of left vena cava, 521, 523 of liver, 1184 malleolar (of tympanum), 1091 of mandibular articulation, 215 , medial palpebral, 1052 median crico-thyreoid, 1215 hyo-thyreoid, 1217 of medio-carpal joint, 270 of metacarpo-phalangeal joints, 274,;_275 of metatarso-phalangeal joints, 310 of mid radio-ulnar union, 262 middle costo-transverse, 243 tibio-fibular (interosseous), 296 morphology of, 213 neck, 243 oblique, of mid radio-ulnar union, 262 popliteal (hgament of Winslow), 287 occipito-cervical, 223 uniting occiput and epistropheus,' 223 orbito-tarsal, 1071 of ossicles of ear, 1090 ovarian, 1269 patellar, 471 of pelvic articulations, 234 piso-hamate, 269 piso-metacarpal, 269 phreno-cohc or costo-colic, 1150, 1174, 1310, 1379 phrenico-lienal (lieno-renal) ,'1310 plantar, 1468 calcaneo-ouboid, 307 calcaneo-navicular, 302, 305 accessory, 310 long, 307 pulmonary, 1236 posterior, of ankle-joint, 298 annular (wrist), 384 atlanto-epistrophic, 221 atlanto-occipital, 218 costo-transverse, 243 crucial (of knee), 288 longitudinal, 227 (dorsal) medio-carpal,' 270 sacro-iliac, 234 of symphysis pubis, 239 of talo-calcaneal joint, 301 talo-fibular, 299 Poupart's, 424, 429,n371 INDEX 1503 Ligament (s), proper scapular, 252 pubo-prostatic (pubo-vesical), 1252 radial collateral, 261, 267 radiate of anterior costo-central or stellate, 242 of medio-carpal joint, 270 sterno-costal, 245 of radio-carpal joint, 266 of radio-ulnar joints, 261, 264 reflected inguinal (triangular fascia), 430 rhomboid (costo-clavioular), 249 round, of uterus, 1274 of liver, 1185 of sacro-coccygeal articulation, 238 sacro-lumbar, 232 saoro-spinous or small sacro-sciatic, 236 sacro-tuberous, 235 of sacro-vertebral articulations, 232 of second row of carpal bones, 270 of shoulder-joint, 254 between skull and vertebral column, 218 spheno-mandibular, 217 spino-glenoid (inferior transverse), 253 connecting spinous processes of vertebrae, 229 spiral, of cochlea, 1096 spring, 305 sterno-clavicular, 248 of sterno-costal joints, 245 of sterno-costo-clavicular articulation, 248 sterno-pericardial, 522 stylo-hyoid, 99 stylo-mandibular (stylo-maxillary), 217 superficial transverse, 387 superior costo-transverse, 243 interosseous, tibio-fibular joint, 295 sacro-iliac, 234 sterno-costal, 245 transverse (coracoid or suprascapular), 253 supraspinous, 230, 238 suspensory, of Cooper, 1303 of the eyeball, 1072, 1348 of lens of eye, 1057, 1064 of ovary, 1269 of penis, 427, 1260 of Treitz, 1164, 1376 of symphysis pubis, 238 talo-calcaneal, 302 of talo-navicular joint, 305 temporo-mandibular, 215 thyreo-epiglottic, 1215 thyreoid, 1314 tibial collateral, 286 tibio-fibular, 295 transverse, of central atlanto-epistrophic joint, 222 crural, 479 dorsal (medio-carpal joint), 270 - of heads of metatarsal bones, 309 of hip-joint, 280 humeral, 256 of knee-joint, 289 of pubis, 446 connecting transverse processes of vertebrae, 231 trapezoid, 251 triangular, of liver, 1185 tubercular (posterior costo-transverse), 243 ulnar collateral, 259, 266 umbilical, 1250, 1252 uniting laminae of vertebrae, 229 of urinary bladder, 1252 utero-sacral, 1274 vaginal, 317 vaginal (fingers), 387 ventricular of larynx, 1215 Ligament(s), vocal, 1215 volar accessory (glenoid), 274 intercarpal, 269 radio-carpal, 266 Ligamenta denticulata, 911 flava, 229 Ligamentous branch of ovarian artery ,"[ 602 Ligamentum (a) alaria (knee-joint), 291 ano-coccygeum, 449 arteriosum, 628, 531 breve, 399, 401 dentioulatum, 920, 921 epididymis, 1255 interfoveolare, 430 longum, 399, 401 rauoosum (knee-joint), 290 nuchas, 231, 414 patellae, 285, 1448 pectinatum iridis, 1060 sacro-iliaoa, anteriora, 177, 234 teres, 280 of liver, 675, 1185 (round ligament) of uterus, 1274 venosum of liver, 675, 1185 Winslowii, 287 Ligature of anterior tibial artery, 1458 of brachial artery, 1414 of common carotid artery, 1358 of femoral artery, 1441 in Hunter's canal, 1442 of popUteal artery, 1452 of posterior tibial artery, 1458 of third part of subclavian artery, 1359 of ulnar artery, 1423 Ligula (taenia ventriculi quarti), 813 Limbic lobe, 865, 866 Limbous sutures, 212 Limbs, cutaneous areas of,'1020, 1022,',1024 development of, 20 Limbus of cornea, 1025 fossae ovalis, 511 sphenoidalis, 63 of tympanic membrane, 1087 Limen of insula, 857, 865 nasi, 1204 Limiting sulcus of floor of fourth ventricle, 813 Line(s) (see also "Linea"). (striae) albicantes, 1283, 1384 bony, 29 of femur, intertrochanteric, 178 sph-al, 178 of fibula, oblique, 190 secondary obUque, 190 gluteal, 170 ilio-pectineal, 173 mylo-hyoid, 95 Nflaton's, 1436 oblique, of mandible, 95 of radius, 154 of thyreoid, 124 popliteal, 189 of scapula, oblique, 142 supra-condylar, of femur, 181 temporal (ridges), 57, 60, 1332 transpyloric (Addison's), 1153, 1370 trapezoid (oblique), 140 of ulna, oblique, 157 LLaea alba of abdomen, 427, 1370 viscera behind, 1373 aspera, 178 pectinea of femur, 181 semiciroularis, 427 semilunaris of abdomen, 1371 splendens, 921 suprema (highest nuchal line), 52 Lingual artery, 539 branches, 539 1504 INDEX Lingual (gustatory) branch of inferior alveolar (dental) artery, 548 of glosso-pharyngeal nerve, 952 of facial nerve, 944 ^ fascia, 346 follicles, 1107 ■' gyrus, 864 nerve, 940, 1350 papillae, 1160 plexus of nerves, 1036 tonsil, 1107 veins, 660 Lingula cerebelli (luigula vermis), 806, 831 of left lung, 1229 of mandible, 96 of sphenoid, 64 > of Wrisberg, 942 Lips, 1102, 1349 of Eustachian aperture, 1130 glenoid, 255 of ileo-c£ecal valve, 1172 lymphatics of, 713 variations and comparative, 1172 vocal, 1223 Lisfranc, amputation of, 1465 Lissauer, marginal zone of, 782 Little finger, muscles of, 404 Littr6, glands of (urethral), 1264 Liver, 1180 blood-vessels of, 1185 clinical anatomy of, 1373 development of, 1189 ductus oholedochus (common bile-duct), 1188 gall-bladder, 1187 ligaments of, 1184 lobes and fissures of, 1180 lymphatics of, 699, 736 topography of, 1373 Liver, surfaces and borders of, 1181 variations and comparative, 1190 Lobe(s), biventral, 807 central, 856 of cerebellum, 805 frontal, 857 inferior semilunar, of cerebellum, 807 limbic, 865, 866 of liver, 1183 of lungs, 1230 of mammary gland, 1302 occipital, 863 olfactory, 865 ■parietal, 860 of prostate, 1265 pyramidal, of thyreoid gland, 1314 quadrangular, 806 superior semilunar of cerebellum, 806 of telencephalon, 853 temporal, of cerebrum, 854 of thymus, 1320 of thyreoid gland, 1313 uvular, of cerebellum, 791 Lobule of auricle of ear, 1083 central, of cerebellum, 806 of cerebellum, 805 inferior parietal, 863 paracentral, 857, 863 quadrate, 863 splenic, 1312 superior parietal, 862 of testis, 1256 of thymus, 1321 of thyreoid gland, 1316 Lobulus epididymis (conus vasculosus), 1256 Locus caeruleus of floor of fourth ventricle, 815, 829 Loewenthal's tract, 786 Longissimus capitis (trachelo-mastoid), 416 cervicis (transversalis cervicis), 416 dorsi, 416 Longitudinal arch of foot, 1468 bundle, posterior, 817 fasciculus, inferior, 892 medial, 817, 842 nucleus of, 871 superior, 892 fissure of cerebrum, 850 ligament of intervertebral articulation, 227 (sagittal) sinuses, 649, 650 striEe of corpus callosum, 851, 892 of hippocampus, 871 vertebral veins, 665 Longitudinalis hnguse inferior medius, 347 Longus capitis (rectus capitis anterior major), 355 colli, 355 Loop, cervical (hypoglossal), 953, 979 Henle's, 1246 Louis, angle of, 139 Lower extremity, articulations of, 276 clinical anatomy of, 1434 cutaneous areas of, 1024 fasciie of, 454 lymphatics of, 746, 748 musculature of, 452 Lowest lumbar (lumbalis ima) artery, 603 Lumbar arteries, 593, 638 lowest (ima), 603 branch of ilio-lumbar artery, 607 enlargement of spinal cord, 772 fascia, 436 lymphatic nodes, 730 trunks, 730 muscle, 436 nerves, 973, 996 posterior primary divisions, 973 plexus, 998 branches of, 998 composition of nerves of, 998 situation of, 998 portion of sympathetic system, 1039 puncture (Quinclve), 1408 regions, 1143 ribs, 132 veins, 675 ascending, 662, 663 vertebrse, 37 description, 37 development of, 48 Lumbo-costal arch, lateral, 437 medial, 437 Lumbo-dorsal fascia, 414, 428 Lumbo-inguinal (crural) branch of genito- femoral nerve, 1000 Lumbo-sacral angle, 43 plexus, 996 trunk, 1005 Lumbricales (foot), 454, 495 (hand), 408, 409 Lunate (semilunar) bone, 159, 161 Lungs (pulmones), 1228 clinical anatomy of, 1367 development of, 1235 form of, 1228 lobes of, 1230 lymphatics of, 729, 1235 surfaces of, 1229 topography of, 1233, 1367 variations of, 1235 vessels and nerves of, 1234 Lunula of nails, 1295 of semilunar valves, 517 Luys, body of, 884 Lymph, movement of, 702 INDEX 1505 Lymphatic capillaries, 697, 698 duct, right (terminal collecting), 728 follicle, 70-1 nodes (glands) of abdomen and pelvis, 730 ano-rectal, 735 - anterior auricular, 709 mediastinal, 724 axillary, 719 bronchial, 725, 1226 buccinator, 711 coeliac, 730 common iliac, 731 deep cervical chain, 714 delto-pectoral, 719 development of, 707 diaphragmatic, 725, 736 epigastric, 732, 733 external iliac, 732 facial, 709, 711 gastric, 730, 734 of head and neck, 709, 714 hepatic, 730, 736 hypogastric, 732 inferior deep cervical, 714 inguinal, 746 internal mammary, 724 intercostal, 724 of larynx, 1224 of lower extremity, 746 lumbar, 730 mesenteric, 731 meso-colic, 734 occipital, 709 parietal, of thorax, 724 parotid, 709 of pelvis, 730 popliteal, 748 post-aortic, 731 posterior mediastinal, 725 auricular, 709 pre-aortic, 730 pulmonary, 725 sacral, 733 splenic, 730, 736 structure of, 704 subinguinal, 746 submaxillary, 709 submental, 711 superficial cubital (supratrochlear), 719,1 superior deep cervical, 714 supramaxillary, 711 of thorax, deep, 724 visceral, 724 umbilical, 733 of upper extremity, 719 system, 697 general anatomy of, 697 special anatomy of, 709 development of, 706 of eyeball, 1065 of orbit, 1076 vessels, 702, 705 of abdomen and pelvis, 733 of eyelids, 1078 of face, 712 of head, 712, 714 of hip-joint, 750 of knee-joint, 750 of lower extremity, 748 of neck, 712, 714 of CESophagus, 730, 1141 regeneration of, 707 structure of, 702 of thorax, deep, 725 superficial, 723 95 Lymphatic vessels of upper extremity, deep, 721 superficial, 721 Lymphatics of abdomen and pelvis, 730 in abdominal wall, 1372 of alimentary tract, 699, 733 of anus, 735 of auricle (of ear), 714, 1084 of brain, 714 capillaries, 697 of clitoris, 745 of conjunctiva, 698, 712 of diaphragm, 728 of digestive tract in head and neck, 715 ' of ductus deferens and seminal vesicles, 744 of duodenum, 734 of excretory organs, 737 of external auditory meatus, 714, 1086 of the eye, 715, 1065 of eyelids, 712 of Fallopian tube, 745, 1270 of female external genitals, 744, 1278 of gums, 715 of head and neck, 709 of heart, 522, 701, 730 of ileooEeoal region, 734 intercostal, 728 of jejuno-ileum, 734 of kidney, 737, 1247 of large intestine, 734, 1179 of larynx, 719, 1224 of lips, 713 of liver, 736, 1186 of lower extremity, 746, 1468 of lungs, 729, 1235 of mammary gland, 723, 1305 of nasal cavities, 717, 1208 of neck, 709 of nose, 712, 1203, 1208 of ovary, 745, 1269 of palate, 717 of pancreas, 736, 1195 of parotid gland, 1115 of penis, 744, 1262 offpharynx, 717, 1138 of pleura, 1239 of prostate, 739, 1265 of rectum and anus, 735 of reproductive organs, male, 742 of scalp, 712 of scrotum, 742, 1255, 1385 of shoulder-joint, 723 of skin, 698, 1289 of small intestine, 1168 of spleen, 736, 1312 of stomach, 734, 1156 of suprarenal glands, 738, 1326 of teeth, 1124 of testis, 744, 1256, 1387 of thoracic muscles, 723 of thorax, 723 of thj'reoid gland, 719, 1317 of thymus, 729, 1322 of tongue, 715, 1111 of tonsils, 1138 of trachea and bronchi, 699, 1228 of tubae (Fallopian tubes), 1270 of upper extremity, 719, 1424 of ureter, 738, 1249 of urethra, female, 742 male, 744 of urinary bladder, 739, 1253 of uterus, 745, 1274 of vagina, 745, 1276 of vulva, 744, 1278 Lymph-follicles, 704 Lymph-nodes, 704 1506 INDEX Lymphoglan dulse, 704 Lymphoid organs, 704 Lyra, hippocampal, 869 M Macewen's suprameatal triangle, 1337 Macula aoustica saoouli, 950, 1094 utriculi, 1093 lutea (yellow spot), 1055, 1057 Magendie, foramen of, 813 Major sublingual duct (of Bartholin), 1117 palatine artery, 549 Malar bone, 93 branches of maxUlary nerve, 938 of temporo-facial nerve, 945 tubercle, 95 tuberosity, 93 Male mammary gland, 1305 pelvis, 1382 reproductive organs, 1263, 1386 Malleolar artery, lateral, 632 medial, 632 posterior lateral artery, 626 folds of tympanic mucous membrane, 1089 ligaments, anterior lateral, 296 posterior lateral, 297 of ossicles of ear, 1091 prominence of tympanic membrane, 1087 recesses of tympanic mucous membrane, 1089 rete, lateral, 626, 632 medial, 626, 632 stria of tympanic membrane, 1087 Malleoli, clinical anatomy of, 1451 lateral, 191 medial, 189 Malleus, 79, 119 Malpighi, pyramids of, 1246 Malpighian corpuscle (renal), 1246 (splenic), 1311 Mammary artery, external, 1305 internal, 566, 1365 cutaneous branches of aortic intercostal arteries, 590 gland (mamma), 1299 clinical anatomy of, 1366 line (ridge), 1306 lymphatics of, 723, 1305 in male, 1305 vessels and nerves of, 1305 plexiis of nerves, internal, 1037 veins, internal, 666 venous plexus, 671 MammiUary bodies, 843, 871 process, 38 MammUlo-mesencephalic fasciculus, 871 Mammillo-thalamic fasciculus, 871, 883 Mandible (lower jaw), 95 age changes in, 99 at birth, 124 ossification of, 98 surgical anatomy of, 1345 Mandibular bars, 119 branches of cervico-faoial nerve, 946 (inferior dental) canal, 96, 126 foramen, 96 fossa, 108 nerve (third division of trigeminus), 939, 1345 (sigmoid) notch, 96, 97 portion of internal maxillary artery, 546 spine, 96 Manubrium of malleus, 79 sterni (presternum), 132, 133 Margin, falciform, of fascia lata, 467 of lungs, 1229, 1233 Marginal gyrus, 858 sinuses, 650 zone of Lissauer, 782 Marge aoutus of heart, 510 obtusus, 510 Marshall, obhque vein of, 521, 523 Massa intermedia, 844 Masseter muscle, 338, 341 Masseteric branch of external maxillary artery, 541 artery, 548 fascia, 339 nerve, 943 veins, 644, 646 Mastication, muscles of, 325 Masticator nerve, 829, 942 Mastoid antrum (see "Tympanic antrum"), branch of great auricular nerve, 978 of occipital artery, 543 of small occipital nerve, 977 of stylo-mastoid artery, 544 canaliculus, 73 cells, 72, 1092, 1336 foramen, 72, 108, 117 (supra-meatal) fossa, 72 notch (digastric fossa), 72 process, 72, 108 development of, 76 Mater, dura, 771 pia, 771 Maxilla, 86, 1346 at birth, 124 ossification of, 91 Maxillary artery, external, 540, 638, 1343 internal, 545, 638 nerve (second division of trigeminus), 937 plexus of nerves, external, 1036 internal, 1036 process of inferior turbinate, 85 of palate bone, 92 sinus (antrum of Highmore), 87, 90, 111, 1206, 1346 vein, internal, 646 Maxillo-ethmoidal cells, 84 Maxillo-turbinates, 119 Meatal branch of stylomastoid artery, 544 Meatus, external auditory (acoustic), 75, 108, 1084, 1332 internal auditory, 72, 117 naso-pharyngeus, 1206 of nose, 83, 111, 1205 Meckel's cartilage, 98, 119 caves, 916 diverticulum, 1169 ganglion, 962 Median antibrachial vein, 667, 668 artery of forearm, 578, 639 basilic (cubital) vein, 667, 669 cephalic vein, 668 crico-thyreoid ligament, 1215 cubital vein, 667 fissure of spinal cord, anterior, 772 hyo-thyreoid ligament, 1217 nerve, 991, 1423 results of paralysis of, 1424 sulcus of floor of fourth ventricle, 813 Mediastinal artery, anterior, 567 branches of aorta, 590 lymphatic nodes, anterior, 724 posterior, 725 pleura, 1237 septum, 1239 surface of lungs, 1229 veins, 664, 667 Mediastinum, 20, 1228, 1239 divisions, 1239 testis (corpus Highmori), 1256 INDEX 1507 Medio-oarpal joint, 270 arterial supply, 270 ligaments, 270 movements of, 271 muscles acting upon, 270 nerve-supply of, 270 Medulla of kidney, 1246 oblongata, 799 blood-vessels of, 908 central connections of cranial nerves in, 818 ventral aspect of, 799 of suprarenal gland, 1321 of thymus, 1326 Medullary cavity, 28 lamina of lenticular nucleus, 880 of thalamus, 882 laminae of cerebellum, 808 ray of kidney, 1246 sheaths, 759 strise, acoustic, 824 velum, anterior (superior), 812 posterior, 808 MeduUated fibres, 760, 767 Medullation of fasciculi of spinal cord, order of, 791 Meibomian glands, 1054, 1078 Meissner, tactile corpuscles of, 1290 plexus of, 1030, 1045 Membrana sacciformis, 265 Membrane (s). Bowman's, 1060 choroidal, 1052 of Descemet, 1060 elastic, of larynx, 1215 hyaloid, 1064 hyo-glossal, 346 hyo-thyreoid, 1217 interosseous, of forearm, 1420 of mid-radio-uLnar union, 263, 264 of middle tibio-fibular union, 295 pharyngeal, 1102 quadrangular of larynx, 1215 secondary tympanic, 1089, 1096 Shrapnell's, 1087 synovial, 211; (see also the individual ar- ticulations) Membrane, tectorial, 223 tympanic, 1086 vestibular (membrane of Reissner), 1096 Membranous ampullae, 1095 cochlea, 1095 cranium, 117 labyrinth, 1092 nasal septum, 511 semicircular canals, 1094 urethra, 1264, 1388 Meningeal artery, accessory (small), 548 arteries, 917 middle, 547 surgical anatomy of, 1341 posterior, 537 branches of anterior ethmoidal artery, 554 of maxillary nerve, middle (recurrent) 937 of occipital artery, 543 of ophthalmic nerve, recurrent, 935 of posterior ethmoidal artery, 553 of spinal nerve-trunks (recurrent), 970 of vagus, 956 of vertebral artery, 560 plexus of nerves, 1036 veins, 646, 917 Meninges, 908 arachnoid, 917 dura mater, 910 pia mater, 920 relation to spinal nerves, 965 Meningoceles, 1331 Menisci, interarticular, 289 Mental branch of inferior alveolar (dental) artery, 548 foramen, 95 muscle, 334 nerve, 941 protuberance, 95 spine, 95 tubercle, 95 Mentalis (levator menti), 334 Mento-labial sulci, 1284 Meridians of eyeball, 1055 Mesatipellio pelvis, 177 Mesencephalon, 758, 833 blood-vessels of, 907 external features of, 834 internal structure of, 836, 843 Mesencephalic root of masticator nerve, 836, 942 nucleus of, 829 Mesencephalo- or tecto-spinal tract, 786, 842 Mesenteric artery, inferior, 602, 638 superior, 596, 638 ganglion, superior, 1043, 1045 lymphatic nodes, 731 plexus of nerves, inferior, 1045 superior, 1045 vein, inferior, 678 superior, 677 Mesenteriolum, of appendix, 1173 Mesentery, 1165, 1376 development of, 19 Mesethmoid, 119 Meso-colic lymphatic nodes, 734 Meso-colon, 1174, 1175 Mesoderm, 10, 14 Mesognathion centre, 91 Meso-metrium, 1267 Meso-nephros (Wolffian body), 16, 1256, 1278 Meso-palatine suture, 89, 106 Meso-salpinx, 1267 Meso-scapula, 145 Meso-sternum, 132 Mesotendons, 318 Mesovarium, 1267 Metacarpal arteries, dorsal, 586 volar, 586 bones, 164 union of heads of, 274 head of adductor polUcis, 408 veins, dorsal, 667 volar, 671 Metacarpo-phalangeal joints, 274 of thumb, 275 Metacarpus, ossification of, 168 Metamerism, 15 of cranial musculature, 327 Metamorphosis of branchial (visceral) bars, 119 Metanephros, 1278 Metasternum, 132 Metatarsal artery, dorsal, 633 plantar, 628 bones, 200 union of heads of, 309 piUar, 205 veins, plantar, 687 Metatarso-phalangeal articulations, 310 Metatarsus, 200 Metathalamus (geniculate bodies), 845 Metopic suture, 69, 101 Meynert, fasciculus retroflexus, 843," 885 Micromastia, 1301 Mid-brain, 833 Middle alveolar canal, 87 (azygos) articular artery, 623 1508 INDEX Middle cardiac nerve, 1036 vein, 520 cerebral artery, 555, 562 vein, 655 clinoid process, 65 coat of eye, 1060 colic artery, 598 collateral (branch, of profunda) artery, 576 constrictor of pharynx, 1137 costo-transverse (neck or interosseous) liga- ment, 243 cranial fossa, 116 Middle ear, 77, 1086 ethmoidal cells. 111 hsemorrhoidal artery, 610 meatus of nose. 111 meningeal artery, 547, 1341 veins, 646 nasal conchae, 83 palatine foramina, 106 peduncle of cerebellum, 811 sacral artery, 603 vein, 679 suprarenal arteries, 598 temporal artery, 545 thalamic branch of posterior communicating artery, 554 thyreoid vein, 661 umbilical ligament, 1250 Mid-radio-ulnar union, 262 Milk, 1303 teeth, 1126 Minor palatine arteries, 549 sublingual ducts (of Rivini), 1117 Mitral cells of olfactory bulb, 866 (bicuspid) valve, 515, 516 Moderator band of heart, 516 Modiolus, 81 Molars, 1121 Molecular layer of cerebellar cortex, 809 Moll, glands of, 1078 Monro, foramen of, 847, 874 sulcus of, 847 Mons pubis (veneris), 1276 Montgomery, glands of, 1304 Monticulus of cerebellum, 806 Morgagni, columns of, 1177 hydatid of, 1257, 1269 lacunse of, 1264 sinus of, 1137 ventricle of, 1222 Morphogenesis, 7 (see also "Development") Morphological axis of scapula, 145 Morphology (see also "Comparative Anatomy") of alimentary canal, 1099 of joints, 213 of musculature of head and neck, 323 of pelvic outlet, 444 of skull, 117 of spinal cord, external, 771 of the testis, 1256 of the vertebrEe, serial, 50 Morula, 9 Motor aphasia, 894 area of speech, 894 roots (see individual nerves) TMouth, 1100 clinical anatomy of, 1349 muscles of, 332 Movements of joints, 214 (see also individual articulations) Mullerian duct, 1257, 1267, 1279 Multangular bone (trapezium) greater, 159, 162 (trapezoid) lesser, 159, 162 Multifidus, 412, 419 Multipenniform muscle, 315 Muscle(s) (see also "Musculature") abductor aocessorius digiti quinti (foot), 499 digiti quinti (foot), 454, 498 (hand), 404 hallucis, 454, 496 longus, 482 ossis metatarsi quinti, 499 poUicis brevis, 406, 407 longus (extensor ossi metaoarpi polli- cis), 392, 393 abnormal, of front of leg, 482 of back of leg, 491 of volar side of forearm and wrist, 392 accessorius ad flexorem digitorum profun- dum (forearm), 402 of gluteus minimus, 462 of spinal musculature, 416 accessory peroneal, 484 acting upon joints (see individual articula- tion) adductor brevis, 453, 471, 474 digiti secundi, 498 hallucis, 454, 496, 498 longus, 453, 471, 472, 1437 magnus, 453, 471, 474, 1437 minimus, 474 poUicis, 407, 408 anconeus, 374, 377, 379 internus, 402 of the angle of the mouth, 332 anomalus, 335 antagonists, 322 anterior and lateral intertransverse, 356 antitragus, 1084 articularis genu, 470 atlanto-mastoid, 422 attached to the tendons of flexor digitorum, longus, 495 attachments of bones (see individual bones) of auricle (of ear), 337, 1084 auricularis anterior (attrahens aurem), 337 posterior (retrahens aurem), 337 superior (attollens aurem), 337 auriculo-frontalis, 337 ary-epiglottic, 1220 ary-membranosus, 1220 arytaenoideus obliquus, 1220 transversus, 1218 ary-vocalis, of Ludwig, 1220 belly of, 314 biceps brachii, 374, 379, 382, 1414 biceps femoris, 453, 475 bicipital, 314 bipenniform, 315 biventer cervicis, 418 brachialis, 374, 380, 382 braohio-radialis (supinator radii longus), 387, 388 broncho-oesophageal, 1141, 1248 buccinator, 334 bulbo-cavernosus, 443, 450 in female, (sphincter vaginae), 450, 1278 oaninus, 332 caput angulare, 332 infraorbitale, 332 zygomaticum, 332 cerato-cricoid, 1218 cervical, 330 cervicalis ascendens, 416 chondro-humeralis (epitrochlearis), 374 chondro-glossus, 346 ciliaris Riolani, 1077 ciliary, 1057, 1060 classification of, 319 coooygeus, 440, 448 complexus, 412, 417 INDEX 1509 Musole(s), compressor bulbi proprius, 450 hemisphseriura bulbi, 451 venae dorsalis, 451 constrictor laryngis, 1218 radicis clitoridis, 451 penis, 450 vaginae, 449, 451 ooraco-brachialis, 374, 379, 381 corrugator, 336 cutis ani, 445 costo-coraooideus, 374 cremaster, 423, 434, 1254, 1259 crico-arytEenoideus lateralis, 1219 posterior, 1218 crico-thyreoid, 1218 crureus, 468, 470 cruro-pedal, 486 deltoideus, 364, 365, 1410 depressor alae nasi, 334 anguli oris, 333 labii inferioris, 332 septi nasi, 334 diaphragm, 425, 436 digastric variety of, 314 digastricus, 343, 344 dilator naris anterior, 335 posterior, 335 pupilte, 1061 divisions of, 316 of dorsum of foot, 492 epicranio-temporalis, 337 epicranius, 336 epitrochleo-olecranonis (anconeus internus), 402 erector spinas, 414 extensor carpi radialis accessorius, 391 brevis, 388, 399 intermedius, 391 longus, 387, 388 ulnaris, 388, 391 communis pollicis et indicis, 394 digiti annularis, 395 quinti proprius, 388, 391 digitorum brevis (foot), 454, 492 (hand), 395 communis, 388, 391 longus, 453, 480, 481 hallucis brevis, 482, 492 longus, 453, 480, 482 indicis proprius, 392, 394 medii digiti, 395 minimi digiti, 388, 391 ossis metacarpi pollicis, 392, 393 poDicis brevis, 392, 394 longus, 392, 394 erector penis (clitoridis), 443, 451 fascite, 313 femoro-tibial, 486 fibulo-calcaneus medialis, 491 fibulo-tibialis (peroneo-tibialis), 486 finer structure of, 315 flexor accessorius (digitorum longus), 491 (quadratus plantae), 495 carpi radialis, 396, 398 brevis (radio-carpeus), 403 ulnaris, 396, 398 brevis (ulno-carpeus), 402 digiti quinti brevis (foot), 454, 498, 499 (hand), 404 digitorum brevis (foot), 454, 493 longus (leg), 454, 486, 489 profundus, 401 sublimis, 399 hallucis brevis, 454, 496, 497 longus, 454, 486, 490 pollicis brevis, 407, 408 longus, 402 Muscle (s), of front of leg, 480 frontalis, 337 fusiform, 315 gastrocnemius, 453, 484, 485 gemellus inferior, 464 superior, 464 genio-glossus, 346 genio-hyoideus, 343, 345 genio-pharyngeus, 347 glosso-palatinus (palato-glossus), 1135 gluteus maximus, 443, 457, 459 medius, 457, 461 minimus, 457, 461 gracilis, 453, 471, 472 gross structure of, 314 grouped according to function, 500 head of, 314 helicis major, 1084 minor, 1084 Horner's, 336 hyo-glossus, 346 iliacus, 455 minor, 456 ilio-coccygeus, 440, 448 ilio-costalis cervicis (cervicalis ascendens), 416 dorsi (accessorius), 416 lumborum, 416 incisivus labii inferioris, 332 superioris, 332 incisure helicis (Santorini), 1084 inferior constrictor of pharynx, 1136 oblique, 1068 infra-clavicularis, 374 infraspinatus, 364, 368 insertion of, 314 intercostales externi, 423, 432 interni, 423, 433 internal cremaster, 1254, 1259 interossei dorsales (foot), 454, 499 (hand), 410 plantares, 454, 499 volares (hand), 409 interspinal, 412, 419 intertransversarii, 417 intralabial, 331 ischio-bulbosus, 451 ischio-cavernosus (erector penis or clitoris) 443, 451 isohio-femoraUs, 461 isohio-pubicus (Vlacovitch), 450 of larynx, 1218 latissimo-condyloideus (dorso-epitrochle- aris), 379 laxator tympani, 79 latissimus dorsi, 364, 368, 1405 levator anguli oris, 332 ani, 440, 448 clavioulae, 359 epiglottidis, 347 labii superioris, 332 alaeque nasi, 332 menti, 334 palpebrae superioris, 1068 scapulae, 356, 369 veli palatini, 1137 levatores costarum, 423, 432 longi, 432 of little finger, 404 longissimus capitis (trachelo-mastoid), 416 cervicis (transversalis cervicis), 416 dorsi, 416 longitudinalis superior and inferior, 1110 linguae inferior medius, 347 longus capitis, 355 colli, 355 lumbar, 436 1510 INDEX Muscle (s), lumbricales (foot), 454, 495 (hand), 408 masseter, 341 meatalis, 334 middle constrictor of pharynx, 1137 multifidus, 412, 419 multipenniform, 315 mylo-hyoideus, 343, 344 nasalis, 334 pars alaris (depressor alse nasi), 334 pars transversa (compressor naris), 334 nerves of, 318 nomenclature of, 319 number of, 315 obliquus abdominis externus, 423, 432 interaus, 423, 434 auriculae, 1084 capitis inferior, 412, 420 superior, 412, 420 obturator externus, 453, 463, 464 internus, 453, 463 occipitalis, 337 minor, 337 occipito-frontalis, 336 occipito-scapularis, 359 ocular, 1068 action, 1068 omo-hyoideus, 351 opponens digiti quinti (foot), 454, 498, 499 (hand), 404, 405 hallucis, 498 poUicis, 407, 408 oral, 331 orbicularis oculi, 336, 1077 oris, 331 of orbit, 324, 325,''1067 orbital (of Mueller), 1071 origin of, 314 of ossicles of ear, 1091 palmaris brevis, 404 longus, 396, 398 papillary, 515, 516, 517 pectineus, 453, 471, 472 pectoral group, 362, 370, 372 abnormal, 374 pectoralis major, 370, 372, 1411 minimus, 374 minor, 370, 373, 1411 pectoro-dorsalis (axillary arch), 374 periorbital, 335 peroneo-calcaneus internus, 491 peroneo-tibialis, 486 peroneus brevis, 453, 483 digiti quinti, 484 longus, 453, 483 tertius, 453, 480, 482 pharyngo-palatinus (palato-pharyngeus), 1136 of pharynx, 1134 physiology of, 320 piriformis, 467, 461 plantaris, 454, 484, 485 platysma, 330 pleuro-cesophageal, 1141 polygastric, 314 popliteus, 454, 486 procerus, 336 pronator quadratus, 402 teres, 395, 396 psoas major, 455 minor, 455, 456 pterygoideus externus, 342 internus, 342 pubo-cavernosus (levator penis), 452 pubo-coccygeus, 440, 448 pubo-peritonealis, 436 pubo-rectalis, 440, 448 Muscle (s), pubo-transversaUs, 436 pyramidalis, 424, 431 auriculae (Jungi), 1084 nasi, 336 quadrate, 332 quadratus femoris, 453, 463, 464 labii inferioris, 332 superioris, 332 lumborum, 425, 436 plantse (flexor accessorius), 454, 495 quadriceps femoris, 453, 468, 470 radio-carpeus, 403 recti, of eye, 1068 recto-cocoygeus, 449, 1177 recto-uterine, 1252 recto-vesical, 1252 rectus abdominis, 422, 424, 430 acessorius, 471 capitis anterior (minor), 356 major, 355 lateralis, 356 posterior major, 417, 419 minor, 412, 419 femoris, 468, 470, 1436 relation to the skin, 313 retrahens aurem, 337 rhomboideus major, 356, 358 minor, 356, 358 risorius, 333 rotatores, 412, 419 sacro-coccygeus anterior, 448 posterior, 448 sacro-spinalis (erector spinae), 412, 414 sartorius, 453, 468, 1436 scalenus anterior, 353 medius, 354 minimus, 355 posterius, 354 scansorius, 462 scapulo-clavicularis, 374 semimembranosus, 453, 475, 476 semispinalis capitis (complexus), 412, 417 cervicis, 419 dorsi, 419 semitendinosus, 453, 475, 476 serratus anterior, 356, 359 posterior inferior, 423, 431 superior, 423, 431 of shoulder musculature, 362, 365 of soft palate, 1134 of sole of foot, 493 soleus, 454, 484, 485 accessorius, 485, 491 sphincter ani, externus, 441, 449 internus, 1177 of bladder, 1253 pupdlae, 1061 urethrae (membranaceae), 449 urogenitalis, 442, 449 vagina;, 451, 1278 spinalis capitis (biventer cervicis), 418 cervicis, 412, 417 dorsi, 412, 417 splenius capitis, 414 cervicis, 414 accessorius, 414 stapedius, 1091 sternalis, 374 sterno-chondro-scapularis, 374 sterno-clavioularis, 374 sterno-cleido-mastoid, 347, 349 sterno-hyoideus, 351 sterno-thyroideus, 351 stylo-glossus, 346 stylo-hyoideus, 343, 344 stylo-pharyngeus, 1137 subanconeus, 378 INDEX 1511 Muscle (s), subclavius, 370, 373 subcostales, 423, 434 suborureus, 470 subcutaneous, 313 suboccipital, 328, 412, 419 subscapularis, 364, 369 minor, 369 superior constrictor of pharynx, 1137 obUque, 1068 tarsal (Mueller's), 1068 supinator (brevis), 392 radii longus, 388 supracostales, 432, 433 supraspinatus, 364, 368 synergists, 322 tail of, 314 tarsal, 1072, 1078 temporalis, 341 superficialis, 337 tensor capsularis artioulationis metacarpo- phalangei digiti quinti, 406 fascise dorsalis pedis, 482 lata; 457, 459, 1436 suralis, 476 lamina; posterioris vaginae musculi recti abdominis, 436 laminae posterioris vagina; musculi recti et fasciae transversalis abdominis, 436 ligamenti annularis anterior, 393 posterior, 393 tarsi (Horner's), 336 tympani, 1089, 1091 veil palatini, 1137 tenuissimus, 475 teres major, 364, 369 minor, 364, 367 of thigh, 453, 464 of the thumb, 406 thyreo-arytaenoideus (externus), 1219 internus (m. vooalis), 1220 obliquus, 1220 superior, 1220 thyreo-epiglottic, 1220 thyreo-hyoideus, 351 tibialis anterior, 453, 480, 1468 posterior, 453, 486, 490, 1468 secundus (tensor of capsule of anlde- _ joint), 491 tibio-astragalus anticus, 482 of tongue, 345, 346, 1110 trachelo-mastoid, 416 tragicus, 1084 transversalis cervicis, 416 transverso-spinal, 412, 419 transversus abdominis, 424, 435 auriculae, 1084 linguae, 1110 menti, 333 nuoh^, 337 perinei profundus, 442, 449, 1278 superficialis, 444, 452, 1278 thoracis (triangularis sterni), 424, 434 vaginae (Fiihrer), 449 trapezius, 347, 349, 1405 triangularis, (depressor anguli oris), 333 sterni, 424, 434 triceps brachii, 374, 377, 378, 1416 surae, 484 ulnaris digiti quinti, 392 ulno-carpeus, 402 unci-pisiformis, 403 unipenniform, 315 uvula;, 1137 variation in, 320 vastus intermedins (crureus), 468, 470 lateralis (vastus externus), 468, 470 medialis (vastus internus), 468, 470 Muscle(s), ventricular, of larynx, 1220 vertebro-ocoipital, 417 verticahs linguae, 1111 vessels of, 319 vocaUs, 1220 zygomaticus, 333 minor, 332 Muscular process of arytaenoid, 1211 veins (of orbit), 658 Musculature (see also "Muscles"), 313 of the arm, 362, 374, 377, 379 cranio-mandibular, 338, 341 epicranial, 336 of expiration, 248 external genital, 450 facialis, 324, 329, 380, 501 of forearm and hand, 362, 383, 387 of foot, 454, 492 functional groups, 600 of hand, 363, 403 of head, neck, and shoulder girdle, 323 of heart, 518 of the hip, 453, 454 of inspiration, 247 of leg, 453, 477, 480 of lower limb, 452 of mastication and swallowing, 325 of neck, 327 of pelvic outlet, 439, 448 prevertebral, 328, 355 of respiration, 503 of shoulder girdle, 327, 347, 363 spinal, 410, 412 of thigh, 453, 468 thoracic-abdominal, 422, 430 of the upper limb, 360 Musculi papillares, 515, 516, 517 pectinati (heart), 513 Musculo-cutaneous nerve, 987, 1014, 1459 results of paralysis, 1424 Musculo-phrenic artery, 567 Musculo-spiral groove, 149 (radial) nerve, 985 results of paralysis of, 1424 Musculus ciliaris Riolani, 1077 interfoveolaris, 435 uvulae, 1137 vocalis, 1220 Myelencephalon, 799 Mylo-hyoid branch of inferior alveolar (dental) artery, 548 nerve, 943 groove, 96 line 95 Mylo-'hyoideus, 343, 344 Myocardium, 508, 518 Myometrium, 1274 N Nail-bed, 1295 Nails (ungues), 1293 Nail-wall, 1294 Nares, 1200 posterior (choana;), 107, 112, 1206 Nasal aperture, anterior, 108 bones at birth, 124 description of, 86 branches of anterior ethmoidal artery, 554 nerve, 937 of infra-orbital artery, 549 of maxillary nerve, 939 of posterior ethmoidal artery, 553 of spheno-palatine artery, 549 (Meckel's) ganghon, 962 cartilages, 1201 cavity, 1203 1512 INDEX Nasal conchae (turbinate bones), 83, 84, 1205 crest, 90 fossa?, IDS, 110 glands, 1208 meatuses, 1205 muscles, 324, 334, 501 notch, 60, 87 pharynx, 1130 septum, cartilaginous, 1204, 1354 membranous, 1204 osseous. 111, 1354 sinuses, accessory, 1354 spine, anterior, 60, 87, 90, 112 posterior, 91 vein, external, 644 Nasalis, muscle, 334 pars transversa (compressor naris), 334 pars alaris (depressor alse nasi), 334 Nasion, 109, 1331 Naso-ciliary (nasal) nerve, 936 Naso-frontal vein, 658 Naso-lacrimal duct. 111, 1080, 1205, 1349 Naso-palatine nerve (of Cotunnius), 962 Naso-pharyngeal adenoids, 1130, 1354 meatus, 1206 Navicular (scaphoid) bone, 159, 160, 191, 196 Neck af axis, 33 cutaneous areas of, 1019 deep, lymphatic nodes of, 714 vessels of, 714 fascia; of, 347, 1360 of gall-bladder, 1187 landmarks, 1354 ligament, 243 lymphatics of, 709 musculature of, 323, 327 of penis, 1260 superficial lymph-nodes of, 709 surgical anatomy of, 1354 of teeth, 1117i triangles of, 1357 NiSlaton's line, 1436 Nephrotome, 16 Nerve (s), 769 in abdominal wall, 1372 accessory (spinal), 958, 1360 abducens, 934, 1075 accessory obturator, 1005 acoustic (auditory), 949,'?1096 to adductor magnus, 1009 ano-coccygeal, 1018 anterior crural, 1001 cutaneous of abdomen, 995 of thigh, 1003 ethmoidal, 936, 937 interosseus, 992 labial, 1000 palatine, 963 scrotal, 1000 superior alveolar (dental) ,'^938 tibial, 1015 of Arnold, 956 to artioularis genu (suborureus),^1003 of auricle of ear, 1084 auriculo-temporal, 941 axillary (circumflex), 984 to biceps femoris, 1009 bronchial (pulmonary), 957 buccinator (long buccal), 939 cardiac, 522 cavernous, of penis, 1047 of clitoris, 1047 cervical, 971, 974 cervico-faoial, 945 chorda tympani, 826, 946, 948 ciliary, of eyeball, 937, 1064, 1076 circumflex, 984 Nerve(s), coccygeal, 973 cochlear or auditory, 950 nucleus of, 624 common peroneal (external popliteal), 1013 plantar digital, 1011 communicans cervicalis, 974 fibularis, 1013 of conjunctiva, 1348 of Cotunnivis, 962 cranial, 927 nuclei in medulla oblongata, 818 of cranial dura mater, 917 cranio-spinal, 926 cutaneous, of face, 1345 of foot, 1466 of forearm, 1423 of lower extremity, distribution of, 1024, 1469 of thigh, 1025 perforating, 1007 deep peroneal (anterior tibial), 1015, 1466 radial (posterior interosseous), 985, 986 temporal, 943 descendens cervicalis, 953, 974 dorsal antibrachial interosseus, 986 digital, of foot, 1013 of hand, 986, 990 of ductus deferens, 1259 of penis (or clitoris), 1018 scapular (nerve to rhomboids), 982 thoracic, 984 of external acoustic (auditory) meatus, 1086 carotid, 1036 popliteal, 1013 to external pterygoid muscle, 943 external respiratory, of Bell, 982 superficial petrosal, 1036 of eyeball, 1064 of evelids, 1078 facial, 943, 1345 nucleus of, 825 of female external genitalia, 1278 femoral (anterior crural), ICJOl fibres, development of, 758 fifth cervical, 971 cranial (trigeminus), 934 first cervical, 971, 974 thoracic, 994 to flexor carpi radialis, 992 ulnaris, 990 digitorum longus, 1010 profundus, 990 sublimis, 992 hallucis longus, 1010 foramina of skull, 125 fourth cervical, 971, 975 frontal, 935, 1075 furcal, 998 geniculo-tympanic, 948 to genio-glossus, 954 to genio-hyoid, 954, 976 genito-femoral (genito-crural), 1000 glosso-palatine, 946 nucleus of, 825 glosso-pharyngeal, 951 nucleus of, 820 great auricular, 978 (anterior) palatine, 963 splanchnic, 1038 superficial petrosal, 948 greater occipital, 971 of heart, 522 to hyo-glossus, 954 hypoglossal, 952, 1111 nucleus of, 820 ilio-hypogastric, 998 ilio-inguinal, 1000 INDEX 1513 Nerve(s), inferior alveolar (dental), 941 cardiac, 957, 1037 clunial (gluteal), 1007 hsemorrhoidal, 1017 (or recurrent) laryngeal, 957 medial clunial (perforating cutaneous), 1007 vesical, 1017, 1047 infra-orbital, 937, 939, 1345 infratroohlear, 936, 937 intercosto-brachial (intercosto-humeral), 995 intermediate dorsal cutaneous, of leg, 1015 intermedius, 825 internal carotid, 960, 1033 pterygoid muscle, 939, 943 interosseous crural, 1010 ischiadicus, 1008 of Jacobson, 951, 961 jugular, 960, 1035 of kidney, 1247 lacrimal, 936, 1075 of large intestine, 1178 of larynx, 1225 last thoracic, 995 lateral anterior thoracic, 983 antibrachial cutaneous, 987 cutaneous, 1000 of abdomen, 995 brachial, 985 dorsal, 1013 sural, 1013 plantar, 1012 least splanchnic, ,1039 lesser internal cutaneous, 983 splanchnic, 1039 to levator scapula;, 979 lingual, 940,, 1111, 1350 of lips and cheeks, 1104 of liver, 1186 long ciliary', 937 (middle") subscapular, 984 thoracic, 982 to longus capitis, 979 colli, 979 of lower extremity, paralysis of, 1469 lower subscapular, 984 lumbar, 973, 995 of lumbar plexus, composition of, 998 of lungs, 1235 of lymphatic vessels, 702 ' of mammary gland, 1305 mandibular (third division of trigeminus), 939, 1345 masseteric, 943 masticator, 942 nucleus of, 829 maxillary, 937, 1076, 1345 medial anterior thoracic, 983 antibrachial (internal) cutaneous nerve, 984 brachial cutaneous, 983 calcaneal (calcaneo-plantar cutaneous), 1010 dorsal cutaneous, of leg, 1015 plantar, 1010 sural cutaneous, 1010 median, 991, 1415 mental, 941 middle cardiac, 1036 clunial, 973 hajmorrhoidal, 1017 a (recurrent) meningel, 937 (external) palatine, 948, 963 (long) subscapular, 984 superior alveolar (dental), 938 of muscles, 318 Nerve(s), musculo-cutaneous, 987, 1459 results of paralysis, 1424 musculo-spiral, 985 to mjdo-hyoid, 943 naso-ciliary (nasal), 936, 1076 naso-palatine, 962 of nose, 1203, 1208 obturator, 1003, 1440 accessory, 1005 to obturator internus, 1007 oculomotor, 835, 838, 931, 1075 nucleus of, 837 of oesophagus, 958, 1141 olfactory, 865, 929 to omo-hyoid, 953, 976 ophthalmic, 1075 optic, 848, 930, 1052, 1073 of orbit, 1075 of ovary, 1269 of palate, 1105 to palmaris longus, 992 of pancreas, 1195 of parotid gland, 1115 to peetineus, 1002 of penis, 1262 pericardiac, 957 perineal, 1017 peroneal, 1469 phrenic, 979 relations, 1360 to piriformis, 1007 of pleura, 1239 pneumogastrio (vagus), 954 to popliteus, 1010 posterior auricular, 944 belly of digastric, 944 brachial cutaneous, 985 ethmoidal, 937 femoral cutaneous (small sciatic), 1007 inferior nasal, 963 interosseus, 986 (small) palatine, 963 scrotal (labial) nerves, 1017 superior alveolar (dental), 938 thoracic, 982 to pronator teres, 992 proper plantar digital, 1011 volar digital, 992 of prostate, 1265 pudio (pudendal), 1017 to quadratus femoris, 1007 radial (musculo-spiral), 985, 1415 to rectus capitis anterior (minor), 979 lateralis, 979 femoris, 1003 recurrent articular, of leg, 1013 (inferior laryngeal), 957 to rhomboids, 982 roots, 769 rudimentary coccygeal, 964 sacral, 973, 1006 of sacral plex-us, composition of, 1006 saphenous, 1003, 1467 to sartorius, 1002 to scalene muscles, 978 sciatic (n. ischiadicus), 1008, 1443, 1469 of scrotum, 1255 to semimembranosus, 1009 to semitendinosus, 1009 seventh cranial (facial), 943, 1345 short subscapular, 984 of skin, 1289 of small intestine, 1168 occipital, 977 palatine, 948 sciatic, 1007 superficial petrosal, 951 1514 INDEX Nerve(s), smallest occipital, 971 to soleus, 1010 spheno-palatine, 938 spinal, 964 accessory, 958 nucleus of, 820 origin of, 1406 spinous (recurrent), 939 of spleen, 1312 to stapedius muscle, 944 to sterno-mastoid, 978 to sterno-thyreoid, 963 of stomach, 1156 to stylo-glossus, 954 to stylo-hyoid, 944 to subclavius, 983 sublingual, 941 gland, 1116 of submaxillary gland, 1117 suboccipital, 971 subscapular, 984 superficial cervical cutaneous, 978 peroneal (musculo-cutaneous), 1014, 1459, 1466 radial (radial), 986 superior alveolar, 938 cardiac,\957 cervical cardiac, 1036 clunial, 973 gluteal, 1007 hsemorrhoidal, 1045 laryngeal, 956 vesical, 1047 supra-acromial, 978 supraclavicular, 978 supra-orbital, 935, 1345 of suprarenal glands, 1326 suprascapular, 982 supratrochlear, 936 sural (external or short saphenous), 1013, 1467 of teeth, 1124 temporo-facial,r945 tenth cranial (vagus or pneumogastric), 954 terminalis, 929 thoracic, 971,' 994 intercostal, 995 thoraco-abdominal, 995 thoraco-dorsal (middle or long) subscapu- lar, 984 of thymus, 1322 to thyreo-hyoid, 953, 976 of thyreoid gland, 1318 tibial, 1009, 1469 communicating, 1010 to tongue, 1111 of trachea and bronchi, 1228 to trapezius, 979 trigeminus, 934 nuclei of, 826 trochlear, 835, 837, 933, 1075 nucleus of, 837 trunks, gangliated, 1029, 1032 of tubsE uterina3 (Fallopian tubes), 1270 tympanic, 961 of tympanic cavity, 1091 ulnar, 987, 1415 anastomotic, 987 collateral, 985 upper (short) subscapular, 984 of ureter, 1249 of urinary bladder, 1253 of uterus, 1274 of vagina, 1017, 1276 vagus or pneumogastric, 954 nucleus of, 820 Nerve(s), to vastus intermedius (crureus), 1003 lateralis, 1003 mediahs, 1003 vestibular, 949 nuclei, 823 Vidian, 962 volar digital, of hand, 992 (anterior) interosseous, 992 of Wrisberg, 946, 983 zygomatic, 938, 1076 zygomatico-facial (malar), 938 zygomatioo-temporal, 938 Nerve-foramina of the skull, 125 Nerve-supply of muscles (see "Nerves;" also corresponding muscles, articulations, etc.) Nerve-trunks, gangliated, 1029, 1032 mixed, 965 spinal, primary divisions of, 944, 967, 970 Nervous system, 751 central, 751, 770 construction of, 762 development of, 754 general summary of some of principal paths of the nervous system, 895 peripheral, 754, 924 sympathetic, 1026 Nervus intermedius, 825 Neural branches of spinal arteries, 590 crest, 754 folds, 754 groove, 10, 11, 754 plate, 11, 754 tube, 14, 754 Neuraxis, 762 Neurenteric canal, 11 Neurilemma, 761 Neuroblasts, 755 Neuro-central suture, 45 Neuro-fibrillfe, 765 Neuroglia, 759, 767 Neuroglia, 759, 767 Neuro-muscular spindle, 764 Neurone, 755, 762 chains, 768 structure of, 765 systems of spinal cord, 777 Neurones of cerebral path for cranial nerves, 895 of cerebro-spinal path, 895 Nipple of mammary gland, 1300, 1304 Nissl bodies, 766 Node(s), atrio-ventricular, 519 haemolymph, 708 lymph(atic) (see "Lymphatic nodes") Nodulus Arantii, 517 of cerebellum, 808 Nomenclature, anatomical, 1 of muscles, 319 Non-medullated fibres, 767 Norma basilaris, skull, 103 facialis of skull, 108 lateralis, skull, 101 occipitalis, skull, 101 verticalis, skull, 100 Nose, 1200 cartilages of, 1201 clinical anatomy of, 1352 development of, 1208 lymphatics of, 712 meatuses of, 1205 muscles of, 334 nostril (nares), 1200 olfactory area (region), 1050 sinuses connecting with, 1206 vessels and nerves, 1203, 1208 Notch, 29 acetabular, 174 INDEX 1515 Notch, cardiac, of left lung, 1229 of cerebellum, 805 ethmoidal, 61 frontal, 60 great scapular, 137 sciatic, 172 intertragic, 1082 jugular (interclavicular), 133 mandibular (sigmoid), 96, 97 mastoid, 72 nasal, 60, 87 pancreatic, 1194 posterior cerebellar, 915 preoccipital, 861 pterygoid, 66 radial (lesser sigmoid cavity) of ulna, 157 of Rivinus, 77 scapular, 142 semilunar (greater sigmoid cavity) of ulna, 156 small sciatic, 172 spheno-palatine, 91, 93 of spleen, 1311 supra-orbital, 60 temporal, 868 tentorial, 915 thyreoid, 1210, 1211 of tibia, popliteal, 185 tympanic, 77 ulnar (sigmoid cavity) of radius, 154 Notochord, 11 Notochordal region of skull, 117 Nuchal line, highest, 52 inferior, 52 superior, 52 Nuck, canal of, 1398 Nucleus(i), abducens nerve, 826 accessory olivary, 817 of the ala cinerea, 820 ambiguus, 822 amygdalae, 881 amygdaloid, of lateral ventricle, 877 arcuatus, 818 Bechterew's, 823 caudate, 877, 879 of cerebellum, 809 of cochlear nerve, 824 ■ of cranial nerves in meduUa oblongata, 818 Deiters's, 823 dentate, of cerebellum, 810 dorsal efferent, of cochlear nerve, 824 of vagus, 822 dorsalis (Clarke's column), 776 of Edinger and Westphal, 838 emboliformis of cerebellum, 810 of facial nerve, 825 fastigii (roof nucleus) of cerebellum, 810 funiculi cuneati (of Burdach's column), 801, 815 gracihs;(of GoU's column), 801, 815 globosus of cerebellum, 810 of glosso-palatine nerve, 825 of glosso-pharyngeus, 820 habenular, 872, 885 of hypoglossal nerve, 820 hypothalmio, 884 incertus of floor of fourth ventricle, 815 of inferior colliculus, 839 inferior olivary, of medulla oblongata, 817 intercalatus, 814 interpeduncular (Von Gudden), 843, 872, 885 of lateral lemniscus, 824, 839 of thalamus, 845 of lens of eye, 1062 lenticular, 878, 879 lentiformis, 857 Nucleus of masticator nerve, 829 of medial longitudinal fasciculus, 843, 871 medial thalamic, 845 of mesencephalic root of trigeminus nerve, 829 of oculomotor (or third) nerve, 837 pontis, 831 pulpy, 226 red, 840 respiratory, 822 salivatorius, 826, 947 of scapula, 139 Schwalbe's, 823 of solitary-tract, 820 of spinal accessory nerve, 820 tract, 826 spinahs, 823 Stilling's, 776 of superior colliculus, 842 superior olivary, 824 of termination, 770 of thalamus, 871, 882 trapezoidei, 824 of trigeminus nerve, 826 of trochlear (or fourth) nerve, 837 of vagus or pneumogastric, 820 vasomotor, 822 ventral cochlear, 824 vestibularis, 823 Number of muscles, 315 Nutrient arteries of femur, 621 of fibula, 626 of humerus, 576 of radius and ulna, 679 tibial, 626, 1459 branch of obturator artery, 608 of posterior circumflex humeral artery, 573 of transverse scapular artery, 565 Nymphaj (labia minora), 1277, 1392 O ObeUon, 101 Obex, 802, 813 Obhque diameter of pelvic inlet, 175 fasciculus, 804 head of adductor hallucis, 498 of adductor poUicis, 408 ligament (mid-radio-ulnar union), 262 line of clavicle, 140 of fibula, 190 of mandible, 95 of radius, 154 posterior, 154 of scapula, 142 of thyreoid cartilage, 1211 of ulna, 157 muscle of eye, inferior, 1068 superior, 1068 popliteal ligament (hgamentum Winslowii), 287 sinus of pericardium, 523 vein of left atrium (of Marshall), 521, 623, 691 Obliquus abdominis externus, 423, 432 internus, 423, 434 capitis inferior, 412, 420 superior, 412, 420 Oblong fovea of aryta;noid, 1212 Obturator artery, 608, 639 crest 173 externus, 453, 463, 464 fascia, 439, 463 (thyreoid) foramen, 174 groove, 172 internus, 453, 463 1516 INDEX Obturator nerve, 1003, 1440 accessory, 1005 vein, 680 Occipital artery, 542, 638, 1343 bone, 51 articulations of, 56 at birth, 121 ossification of, 56 branches of occipital artery, 543 of posterior auricular artery, 545 nerve, 944 of small occipital nerve, 977 condyle, third, 56 condyles, 108 crest, external, 52 internal, 53, 117 groove, 72 gyri, 863 lobe, 863 lymph-nodes, 709 nerve, greater, 971 small, 977 smallest, 971 point, 101, 112 pole, 850 pontile fibres, 840 portion of vertebral artery, 560 protuberance, external, 52, 101 internal, 53 sinus, 650 sulci, 862, 863 suture, 101 vein, 647 diploic, 648 Occipitalis, 337 minor, 337 Occipito-atlantal articulation, 218 ligaments, 219 Occipito-cervioal ligament, 223 Occipito-epistrophic articulation, 223 Occipito-frontal fasciculus, 892 Occipito-frontalis, 336 Ocoipito-mastoid suture, 101 Occipito-mesencephalic path (Flechsig's sec- ondary optic radiation), 890 Occipito-pontile path, 832 Occipito-scapularis, 359 Occipito-temporal association area, 894 convolution, 864 Oocipito-thalamic (optic) radiation, 888 Occiput and atlas, ligaments uniting, 218 Ocular conjunctiva, 1054 muscles, 325, 1067 Oculomotor nerves, 835, 838, 931 nucleus of, 837 sulcus, 835 Odontoid process (dens) of axis, 33 (Esophageal arteries, 588 branches of inferior thyreoid artery, 564 of left gastric artery, 594 of vagus, 958 plexuses, 954, 955 veins, 661, 664 (Esophagus, 1138 clinical anatomy of, 1369, 1408 development of, 1141 lymphatic vessels of, 730, 1141 variations and comparative, 1141 vessels and nerves of, 1141 Olecranon fossa of humerus, 150 process of ulna, 156 Olfacto-mammillary tract, 873 Olfacto-mesencephalic tract, 873 Olfactory apparatus, 1049 area of cerebral cortex, 893 (region) of nasal mucous membrane, 1049, 1352 Olfactory brain, 864 bulb, 758, 865, 1050 cells, 1050 conduction path, 902 glands, 1208 groove, 1206 gyrus, lateral, 865 medial, 866 layer of olfactory bulb, 866 lobe, 865 nerve, 865, 929 central connections, 929 organ, 1049, 1208 region of nasal cavity, 1208 strias (gyri), 865, 866 sulcus, 858 tract, 758, 865, 893 development of, 758 trigone (tubercle), 865 ventricle, 866 Olivary, nuclei, accessory, 817 inferior, 817 superior, 824 Olives of medulla oblongata, 800 Omental branches of epiploic arteries, 595 bursa (lesser sac), 1146, 1372 Omentum, great, 1149 lesser (gastro-hepatic), 1160, 1185 Omo-hyoideus, 351 Omphalo-mesenteric artery, 638 Opercula of insula, 856 Operculum proper, 854, 856 temporal, 854, 866 ■ Ophryon, 109, 112 Ophthalmic artery, 552, 638, 1074 branches, 552 division of trigeminus (fifth nerve), 936, 1075 veins, 658, 659, 1075 Ophthalmo-meningeal vein, 655 Opisthion, 107, 108 Opponens digiti quinti (foot), 454, 498, 499 (hand), 404, 405 hallucis, 498 pollicis, 407, 408 Optic-acoustic reflex path, 840, 842 Optic apparatus, conduction paths of, 900 chiasma, 847, 848, 849 cup, 1080 disc, 1055 foramen, 63, 64, 110, 116, 125 groove, 63, 116 nerve, 848, 930, 1052, 1073 sheaths of, 931, 1073 papilla of, 1055 portion of hypothalamus, 847 radiation, 888 Flechsig's secondary, 890 recess, 848 tracts, 849 vesicle, 758, 1080 Ora serrata, 1057 Oral cavity, 1100 development of, 1102 fissure, (rima oris), 1100 fossa, 1102 muscles, 331 orifice, muscles of, 501 pharynx, 1130 vestibule, 1100 Orbicular tubercle of incus, 79 Orbicularis ciliaris, 1060 ocuU, 336, 1097 oris, 331 Orbit, 108, 109, 1332, 1346 fascije of^ 107l lymphatic system of, 1076 muscles of, 325, 1067 INDEX 1517 Orbital branch of middle meningeal artery, 548 branches of maxillary nerve, 938 of spheno-palatine (Meckel's) ganglion, 963 fissure, inferior, 109, 126 superior, 65, 109, 116, 125 gyri, 858 muscle of Muller, 1071 periosteum, 1071 plates, 61 process of malar bone, 94 of palate bone, 91, 93 sulci, 858 wings of sphenoid, 64 Orbito-sphenoid centre, 67, 119 Organ (s), 4 of Giraldes, 1257 of Jacobson, 951, 961, 1051, 1204 lymphoid, 704 olfactory, 1049, 1208 reproductive, male, 1253 female, 1265 of special sense, 1049 spiral (organ of Corti), 1096 of taste, 1051 urinary, 1241 Orifice, atrio-ventricular, of heart, 513, 514 external urethral, 1264 of stomach, 1151, 1374 (os) of uterus, 1271 Origin of muscles, 314 (see also individual muscles) of spinal nerves, 964 Os calcis (calcaneus), 191, 195 centrale, 164, 208 innominatum, 169 Japonicum, 95 linguae, 99 planum, 83 trigonum, 194, 199 uteri, 1271 Vesalianum, 199 Osseous labyrinth, 80 part of tuba auditiva (Eustachian tube) , 1092 portion of external acoustic (auditory) meatus, 1085 Ossicles of ear, 79, 1090 articulations, 1090 ligaments, 1090 muscles, 1091 Ossification of bones, 27 (see also the in- dividual bones") Osteogenesis, 27 Osteology, 27 Ostium abdominale of tuba? uterinae (Fallo- pian tubes), 1270 venosum (atrio-ventrioular orifice), 513, 514 Otic (Arnold's) ganglion, 963 Otoconia (otoliths), 1095 Outlet (interior aperture) of pelvis, 176 Ovarian arteries, 602 branches, 602 branches of uterine artery, 610 ligaments, 1269 plexuses of nerves, 1045 veins, 674 Ovaries, 1268 clinical anatomy of, 1393 lymphatics of, 701, 745, 1269 vessels and nerves of, 1269 Ovula Nabothi, 1274 Ovum, segmentation of, 9 Pacchionian bodies (arachnoid granulations), 649, 919 Pacchionius, foramen ovale of, 116 Pacinian corpuscles, 1290 Palate, 1104 bone, 91 at birth, 124 development of, 1106 hard, 1104 lymphatics of, 717 muscles acting on, 502 soft, 326, 1104 surgical anatomy of, 1352 Palatine arches, 1132 branch of ascending pharyngeal artery, 537 artery, ascending, 541 descending, 549 major, 549 canals, 92, 103, 126 accessory, 103 foramina, 106 nerve, great (anterior), 963 middle (external), 948, 963 posterior (small), 948, 963 process of maxilla, 87, 88 tonsil, 1132 variations and comparative, 1106 vein, 644 superior, 646 Palato-ethmoidal cells, 84 Palm, muscles acting on, 504 Palmar aponeurosis, 387, 1430 arch, (see "Volar arch") cutaneous branch of median nerve, 992 of ulnar nerve, 990 fascia, deep, 387 Palmaris brevis, 404 longus, 398 Palpebra, inferior, 1053 superior, 1053 Palpebral aperture, 1052 arteries, lateral, 552 branches of infratrochlear nerve, 937 of maxillary nerve, inferior, 939 of ophthalmic artery, palpebral, 552 of supra-orbital artery, 553 conjunctiva, 1054, 1078 fascia, 1071 folds, 1053 ligament, medial, 1052, 1078 raphe, lateral, 1078 veins, 644, 658 Pampiniform plexus, 674, 1259 Pancreas, 1192 blood-supply of, 1195 development of, 1195 lymphatics of, 699, 736, 1195 topographic, 1375 variations and comparative, 1197 Pancreatic branches of splenic artery, 595 duct (canal of Wirsung), 1194, 1375 accessory (of Santorini), 1195 Pancreatico-duodenal artery, inferior, 596 superior, 595 vein, 675, 677 Panniculus adiposus, 313, 1287 carnosus, 313 Papilla, duodenal, 1164, 1195 hair, 1292 incisive, 1104 of kidney, 1246 lacrimal, 1054 (nipple) of mammary glands, 1300, 1304 optic, 1055 Papillae of skin, 1286 of tongue, 1106 Papillary ducts (of Bellini), 1246 muscles of heart, 515, 516, 517 process of liver, 1184 Paracentral lobule, 857, 858, 863 1518 INDEX Paradidymis (organ of Giraldes), 1257 Paraduodenal fossa, 1164 Paraganglia, 1323 aortic (lumbalia), 1329 Paralysis of deep radial (posterior interos- seous) nerve, results of, 1424 of facial nerve, 1345 of median nerve, results of, 1424 of musculo-cutaneous nerve, 1424 of nerves of lower extremity, 1469 of radial (musculo-spiral) nerve, 1424 of ulnar nerve, results of, 1424 Paramedial sulcus, 858 Parametrium, 1274 Paranasal sinuses, 1206 Parapophysis, 51 Pararenal adipose body, 1243 Parasinoidal sinuses, 919 Para-thyreoid glands, 1318 Paraurethral ducts, 1277 Parietal association area, 894 bones, 57 at birth, 123 branches of abdominal aorta, 592 of hypogastric artery, 606 (posterior temporal) of superficial tem- poral artery, 545 of thoracic aorta, 588 eminence, 57 emissary vein, 649 fascia of pelvis, 447 foramen, 57 lobe, 860 lobule, inferior, 863 (gyrus) superior, 862 lymphatic nodes of thorax, 724 peduncle of thalamus, 8 S3 pleura, 1237 Parieto-mastoid suture, 101 Parieto-ocoipital arch, 863 fissure, 860, 864 Parolfactory area (Broca's area), 858, 865 sulci, 865, 866 Paroophoron, 1269 Parotid branches of auriculo-temporal nerve, 941, 961 of superficial temporal artery, 545 fascia, 339, 348, 1114 gland, 348, 1113 accessory, 1114 duct (Stenson's), 1115, 1343 lymph-nodes, 709 veins, 644, 646 vessels and nerves, 1115 plexus (pes anserinus), 945 region, 1343 Pars alaris (depressor alee nasi), 334 ciliaris retinae, 1061 fixa of penis, 1260, 1264 flaccida (Shrapnell's membrane), 1087 glabra of Ups, 1104 intercartilaginea, 1223 intermedia of facial nerve, 946 (of Kobelt), 1278 intermembranacea, 1223 Ubera of penis, 1260, 1264 tensa, 1087 transversa (compressor naris), 334 villosa of lips, 1104 Parumbilical veins, 678 Patches, Peyer's, 704, 1166 Patella, 184 clinical anatomy of, 1444 Patellar fold (ligamentum mucosum), 290 ligament, 47l plexus, 1001 rete, 622 Paths, auditory conduction, 900 cerebral, for cranial nerves, 895 cerebro-spinal, 895 conduction, involving cerebellum, 899 of olfactory apparatus, 902 of optic apparatus, 900 summary of, 895 frontal pontile (Arnold's bundle), 832, 889 occipito-mesencephalic, 890 occipito-pontile, 832 optic, 900 optic-acoustic reflex, 840 short reflex, of cranial nerves, 898 spino-cerebral, 895 of spinal cord, short reflex, 895 temporal pontile (Turk's bundle), 832, 840, 890 vestibular, 899 Pecten of pubis, 173 Pectineo-femoral band, 278 Pectineus, 453, 471, 472 Pectoral (descending) branch of anterior circumflex humeral artery, 573 branch of thoraco-acromial artery, 571 group, of muscles, 362, 370 of axillary lymphatic nodes, 720 Pectoralis major, 372 surface markings, 1411 minor, 373 surface markings, 1410 minimus, 374 Pectoro-dorsalis (axillary arch), 374 Pedicles of axis, 34 of lumbar vertebrae, 37 of vertebrae, 30 Peduncles of cerebellum, 810, 831 of cerebrum, 833, 835 of corpus callosum, 866 of flocculus, 807 of superior olive, 825 of thalamus, 880, 883 Peduncular tract, transverse, 835 Pedunculi conarii, 846 Pelvic articulations, 234 ligaments of, 234 diaphragm, 440, 448, 1383 fasciae, 446 clinical anatomy of, 1385 floor in female, 1394 in male, 1383 girdle, 207 index, 177 inlet, diameters of, 175 measurements, 177 outlet, 176 muscles of, 439 colon, 1174, 1379 plexuses of nerves, 1046 portion of ureter, 1248 splanchnics, 1017, 1040, 1046 Pelvis, articulations of, 234 axis of, 176 description of, 175, 1382 differences according to sex, 177 inlet (superior aperature) of, 175 lymphatics of 730, 733 major (false), 175 measurements, 177 minor (true), 175 muscles acting on, 505 outlet (inferior aperature) , 176 renal, 1248 of ureter, 1247 visceral lymphatic vessels of, 733 Penis, 1260 artery of, 613 cavernous plexus of, 1047 INDEX 1519 Penis, deep artery of, 614 dorsal artery of, 614 nerves of, 1018 lymphatics of, 744, 1262 surgical anatomy of, 1388 vessels and nerves of, 1262 Perforated substance, anterior, 847, 866 posterior, 835, 844 Perforating branches of deep volar arch, 586 of lateral plantar artery, 628 of the profunda, 620 of internal mammary artery, 567 maxillary artery, 529 of peroneal artery, 626 veins, 690 Pericsecal fossa;, 1172, 1378 Pericardiac branches of aorta, 588 of internal mammary artery, 567 of phrenic nerve, 979 Pericardial branches of vagus, 956 cavity, 522 development of, 527 lymph-capillaries of, 702 pleura, 1237 Pericardio-phrenic artery, 567 Pericardium, 522 development, 20, 525 surgical anatomy, 1369 vessels of, 523 Perichondrium, 28 Pericranium, 1334 Perilymph, 1092 Perilymphatic space of membranous labyrinth, 1095 Perimetrium, 1274 Perimysium internum (endomysium), 315 externum (epimysium,) 316 Perineal artery, 613, 639 fascia, superficial, 445 nerve, 1017 Perineum, 1383 central tendon of, 449 muscles acting on, 503 surgical anatomy of, 1385 triangles of, 1383 Periorbita, 1071 Periorbital muscles, 335 Periosteal branches of supra-orbital artery, 553 Periosteum, 28 lymph-capOlaries of, 701 Periotic capsule, 69, 117 cartilages, 117 Peripheral, nervous system, 754, 924 cranio-spinal system, 926 sympathetic system, 926, 1026 Peritoneal branches of superior epigastri-c artery, 567 cavity, lymphatic capillaries of, 702 Peritoneum, 1141 clinical and topographical anatomy of, 1372 development of, 1144, 1151 of rectum, 1177 spaces of, 1372 sections, 1146 variations and comparative, 1151 vessels and nerves, 1151 Permanent teeth, times of eruption of, 1127 Peroneal artery, 626, 640, 1459 anterior (perforating), 626, 1459 posterior, 626 groove of cuboid, 199 muscles, accessory, 484 nerve, common (external popliteal), 1013 results of paralysis of, 1469 deep, (anterior tibial), 1015, 1466 Peroneal nerve, superficial (musculo-cutane- ous), 1014, 1459, 1466 retinacula, 480 vein, 688 Peronei muscles, tenotomy of, 1464 accessory, 484 Peroneo-caloaneus internus(of Macalister), 491 Peroneo-tibialis, 486 Peroneus brevis, 453, 483 digiti quinti, 484 longus, 453, 483, 1468 tertius, 453, 480, 482 Perpendicular plate (mesethmoid) of ethmoid, 82 Pes anserinus, 945 hippocampi, 877 pedunculi, 840 Petiole of epiglottic cartilage, 1212 Petit, canal of, 1064 triangle of, 434, 1406 Petrosal branch of middle meningeal artery, 548 ganglion, 951 nerve, external superficial, 1036 great superficial, 948 small superficial, 951 portion of internal carotid artery, 550 process, posterior, 63 sinuses,''652 Petro-mastoid, 119 Petro-sphenoidal foramen, 125 Petro-squamous sinus, 653 (squamo-mastoid) suture, 71 Petro-tympanic (Glaserian), fissure 71, 77, 108, 126 Petrous portion of temporal bone, 68, 72 Peyer's patches, 704, 1166 Phalanges of fingers, 167 ossification of, 168, 204 third, terminal, or ungual, 168, 204 of toes, 203 Pharyngeal aponeurosis, 1130 arterj', ascending, 537, 638 branches of ascending pharyngeal artery, 537 of inferior thyreoid artery, 564 of glosso-pharyngeal nerves, 951 of spheno-palatine (Meckel's) ganglion, 963 of vagus, 956 bursa, 1130 (pterygo-palatine) canal, 66, 92, 103 foramen, 126 hypophyseal remnants, 1352 sthmus (faucial), 1130, 1131 membrane, 1102 ostium of tuba auditiva, 1092 plexus of nerves, 956, 1036 of veins, 659 recess, 1130 tonsil, 1130, 1354 tubercle, 54, 108 veins, 659 Pharyngo-palatine arches, 1132 Pharyngo-palatinus (palato-pharjmgeus), 1136 Pharynx, 1128 development, 1138 laryngeal, 1134 lymphatics of, 717, 113S muscles of, 325, 502, 1134 nasal, 1130 oral, 1130 variations and comparative, 1138 vessels and nerves, 113S Philtrum, 1102, 1284 Phrenic arteries, inferior, 692, 638 1520 INDEX Phrenic arteries, superior, 590 branches of musculo-phrenic artery, 567 of superior epigastric artery, 567 ganglion, 1044 nerve, 979 relations of, 1360 (diaphragmatic) plexuses of nerves, 1044 veins, inferior, 675 superior, 667 Phrenico-oostal sinus, 1237 Phreno-colic ligament, 1150, 1174, 1310, 1379 Phrenicohenal (lienorenal) ligament, 1310 Physiology of muscles, 320, 323 Pia mater, 771, 920 cranial, 922 spinal, 921 Pigment of iris, 1061 retinal, 1062 of skin, 1286 Pillars of the foot, 205, 1468 of fornix, anterior, 870 posterior, 868 Pineal body, 845 Pinna (see Auricle) Piriformis, 453, 457, 461 Pirogoff's amputation, 1465 Pisiform bone, 159, 162 Pits, olfactory, 1050 rectal, 1390 Pituitary body, 848, 1342 Plane or arthrodial diarthroses, 212 Plantar aponeurosis, 492 arch, 627 arteries, lines of, 1467 artery, deep (communicating), 633 lateral, 627, 640 medial, 629 calcaneo-cuboid (short plantar) ligament, 307, 1468 calcaneo-navicular ligament, 1468 digital (collateral) arteries, 628 branches, proper, of medial plantar nerve, 1011 nerves, common, 1011, 1013 proper, 1011, 1013 veins, 684 fascia, 492, 1468 ligaments, 307, 1468 accessory, 310 metatarsal arteries, 628 veins, 687 nerve, lateral, 1009, 1012 medial, 1009, 1010 venous arch, 687 rete, 684 Plantaris, 454, 484, 485 Planum popliteum, 181 Plate, cribriform, of ethmoid, 81 fronto-nasal, 117 neural, 754 olfactory, 1050 orbital, 61 perpendicular, of ethmoid, 82 pterygoid, 66 tympanic, 108 Platypelhc pelvis, 177 Platysma, 330 Pleura, 1236 blood-vessels of, 1239 clinical anatomy of, 1368 development of, 20 lymphatics of, 701, 1239 nerves of, 1239 Pleural cavity, 1236 reflection, lines of, 1237 sinuses, 1237 vilh, 1237 Pleurapophysis, 51 Plexuses of nerves, abdominal aortic, 1045 anterior pulmonary, 957 atrial, 1041 of Auerbach, 757, 1030 brachial, 980 line of, 1360 bulbar, 1041 cardiac, 1041 cavernous, 1033 of penis (or clitoris), 1047 of cephalic ganglia, 960 cervical, 974 coccygeal, 1018 coeliac, 1043 common carotid, 1036 coronary, 1041 deferential, 1047 external carotid, 1036 maxillary (facial), 1036 femoral, 1045 gangliated cephalic, 959 hepatic, 1045 hypogastric, 1045 iliac, 1045 inferior dental, 941 gastric, 1045 mesenteric, 1045 infra-orbital, 937, 939, 945 internal carotid, 1033 mammary, 1037 maxillary 1036 intermediate, 1041 lingual, 1036 lumbar, 998 lumbo-sacral; 996 of Meissner, 757, 1030 meningeal, 1036 middle hajmorrhoidal, 1046 myentericus (plexus of Auerbach), 1045 cesophageal, 954, 955 ovarian, 1045 parotid, 945 patellar, 1001 pelvic, 1046 pharyngeal, 956, 1036 phrenic (diaphragmatic), 1044 popliteal, 1045 posterior cervical, of Cruveilhier, 971 oesophageal, 954 pulmonary, 954, 955, 957 pulmonary, 1043 prevertebral, 755, 1029, 1032, 1040 prostatic, 1047 pudendal, 1016 renal, 1044 sacral, 1006 spermatic, 1045, 1260 splenic (lienal), 1045 submucosus (plexus of Meissner), 1045 subsartorial, 1003 subtrapezial, 979 superior dental, 939 gastric (coronary), 1045 haemorrhoidal, 1045 mesenteric, 1045 thyreoid, 1036 thoracic aortic, 1038 suprarenal, 1044 tympanic, 951, 961, 1033, 1089 utero-vaginal, 1047 vertebral, 1037 vesical, 1047 of veins, anterior sacral, 679 basilar. 651 chorioid, of fourtli ventricle, 922 of lateral ventricle, 924 INDEX 1521 Plexuses choroid of third ventricle, 924 chorioidea, 875, 877 hsemorrhoidal, 683 of internal carotid, 653 mammary, 671 pampiniform, 674, 1259 pharyngeal, 659 pterygoid, 682 thyreoideus impar, 660 utero-vaginal, 683 vertebral, 664 vesical, 683 Plica(86) ciliares, 1057 ciroulares, 1165 epigastrioa, 430 fimbriata, 430 incudis, 1090 lacrimalis (Hasneri), 1080, 1205 longitudinalis duodeni, 1189 palatinsB transversa;, 1104, 1106 palmataa, 1272 salpingo-pharyngea, 1130 salpingo-palatina, 1130 semilunaris, 1053, 1170 triangularis, 1132, 1133 of tympanic membrane, 1087 umbilicalis lateratis, 430 ureterioa, 1252 Pneumogastrie nerve, 954 Point(s), alveolar, 109 auricular, 101 central, of perineum, 1385 occipital, 101 pre-auricular, 1332 Bolandic, 1340 subnasal, 109 Poles, of cerebral hemispheres, 850 of eyeball, 1055 of lens of eye, 1062 Polygastric muscles, 314 Polymastia, 1301 Polytheha, 1301 Pons (Varoli), 804 basilar sulcus of, 804 blood-vessels of, 90S brachia conjunctiva (superior cerebellar peduncles), 831 grey substance of, 831 internal structure of, 815, 829 lemniscus (fillet) in, 831 Pontile path, frontal, 832, 840, 889 temporal (Turk's bundle), 832, 890 Pontine branches of basilar artery, 561 sulci, 804 Popliteal artery, 621, 640, 1452 collateral circulation, 1453 ligament, oblique, 287 line, 189 lymphatic nodes, 748 nerve, external, 1013 internal, 1009 nerves, paralysis of, 1469 plexus of nerves, 1045 space, clinical anatomy of, 1451 vem, 688, 1452 accessory, 689 Pophteus, 454, 486 Pore, canal, 1051 of skin, 1285 sudoriferous, 1297 taste, 1051 Porta hepatis, 1183 Portal fissure of liver, 1183 vein, 528, 675 development, 694 tributaries, 675 veins, accessory, 678 Position of organs (see corresponding Or- gan) Post-aortic lymphatic nodes, 731 Post-auditory process, 122 Post-central branches of spinal arteries, 590 sulcus, inferior, 861, 862 superior, 861, 862 Post-glenoid process, 71 Post-limbic fissure, 863 Post-malar, 95 Post-nodular sulcus of cerebellum, 808 Post-parietal gyrus, 863 Post-scapula, 145 Post-sphenoid centre, 67 Pott's fracture, 1454 Pouch of Douglas, 1148, 1267, 1274 of Prussak, 1089 recto-uterine (recto-vaginal), 1148, 1267, 1274 recto-vesical, 1148 of Troltsch, 1089 Poupart's ligament, 424, 429, 1371, 1399, 1438 Precuneus (quadrate lobe), 863 Prjeputium clitoridis, 1277 penis, 1260 Praevesical space (cavum Retzii), 1250 Pre-aortic lymphatic nodes, 730 Pre-auricular point, 1332 Precentral sulcus, 807, 857 Preglenoid tubercle, 71 Pre-laminar branches of spinal arteries, 590 Premalar, 95 Premaxilla, 89, 91, 119 Premolars, 1121 Preoccipital notch, 861 Pre-palatine centre, 91 Prepatellar bursa, 1448 Prepuce, 1260 Pre-scapula, 145 Pre-sphenoid centre, 67, 119 Presternum, 132 Prevertebral musculature, 328, 355 plexuses, 755, 1029, 1032, 1040 Primary curvatures of spinal column, 43 divisions of spinal nerve-trunk, 967 anterior, 968 posterior, 967 Primitive groove, 10 node, 11 pit, 10 streak, 10 Princeps cervicis artery, 543 pollicis artery, 586 Procerus (pyramidalis nasi), 336 Process (es), accessory (of vertebra), 38 acromion, 144 alar, of ethmoid, 81 alveolar, 87, 90 anterior clinoid, 65, 116 arciform, 466 caudate, of liver, 1184 cihary, 1057 cochleariform, 1089 condylar, of mandible, 96 coracoid, of scapula, 144 coronoid of mandible, 96, 1351 ensiform, 132, 134 ethmoidal, 85 external auditory, 75 frontal, of maxilla, 87, 88 fronto-nasal, 119 fronto-sphenoidal, 95 glosso-hyal, 99 hamular, 66, 106 infra-orbital, 95 jugular, 54, 108 lacrimal, 85 1522 INDEX Process(es), lenticular, of incus, 79 mastoid, 72, 108 maxillary of inferior nasal concha, 84 of palate bone, 92 middle cHnoid, 65, 116 muscular, of arytEenoid cartilage, 1211 orbital, of malar bone, 94 of palate bone, 91, 93 palatine, 87, 88 posterior clinoid, 63, 116 petrosal, 63 post-glenoid, 71 pterygoid, 62, 66 pyramidal, of palate bone, 91, 92 sphenoidal, of palate bone, 91, 92 styloid, 70, 73, 75, 108 of fibula, 190 of radius, 155 of third metacarpal bone, 166 of ulna, 158 supracondylar, 149 temporal, of malar bone, 95 trochlear, 195 unciform, 163 uncinate, of ethmoid, 83 vaginal of sphenoid, 63, 66 of temporal, 75 vermiform, 1378 vocal, of arytenoid cartilage, 1212 xiphoid, 132, 134 zygomatic, 70, 87, 88 Processus cochleariformis, 77 Folii, 79 globulares, 119 gracilis, 79 marginalis, 95 tubarius, 66 uncinatus (of Winslow), 1194 vaginalis, 1387 Profunda (superior) artery, 576 axillaris artery, 640 (deep) femoral artery, 620, 640 branches, 620 vein, 690 Projection fibres of white substance of telen- cephalon, 886, 889 Prominence, laryngeal, 1211 Promontory in cochlea, 81, 1089 of temporal bone, 73 Pronation, 321 Pronator quadratus, 402 ridge of ulna, 157 teres, 395, 396 Proper digital arteries, 582 plantar digital nerves, 1011 scapular ligaments, 252 volar digital nerves of hand, 992 veins, 671 Prosencephalon (fore-brain), 843 external features of 843 internal structure of, 878 Prostate, 1264 lymphatics of, 700, 739 surgical anatomy of, 1389 vessels and nerves of, 1265 Prostatic branches of inferior vesical artery, 608 plexus of nerves, 1047 portion of urethra, 1263, 1265, 1388 Prostatic utriculus (sinus pocularis, uterus masoulinus), 1263 Prostatico-perineal fascia, 447 Protoplasm, 5 Protuberance, external occipital, 52 internal occipital, 52 mental, 95 Prussak, pouch of, 1089 Psalterium, hippocampal, 869 Psuedo-hermaphroditism, 1230 Psoas abscess, 1438 fascia, 455 major, 455 minor, 455 Pterion, 101, 1332 Pterygoid, accessory, 342 branches of internal maxillary artery, 548 (Vidian) canal, 103, 107, 108, 126 fossa, 66, 107 hamulus (of sphenoid), 66, 1351 muscles, 338, 342 notch, 66 plate, lateral 66 medial, 66 plexus of veins, 646 portion of internal maxillary artery, 546 processes, 62, 66 tubercle, 66 veins, 646 Pterygoideus externus, 338, 342 internus, 338, 342 Pterygo-maxillary fissure, 102 Pterygo-palatine (pharyngeal) canal, 88, 92, 103 fissure, 102 (spheno-m axillary) fossa, 102 portion of internal maxillary artery, 546 Pubes, 1290 Pubic arch, 176 branch of inferior epigastric artery, 615 of obturator artery, 608 Pubis, 172 symphysis, 238 tubercle (spine) of, 172 Pubo-capsular (pectineo-femoral) band, 278 Pubo-cavernosus (levator penis), 451 Pubo-coccygeus, 440, 448 Pubo-peritonealis, 436 Pubo-prostatic hgaments, middle, 1252 Pubo-rectalis, 440, 448 Pubo-transversalis, 436 Pubo-vesical ligaments, 1252 Pudendal (pudic) artery, 610, 639 accessory, 638 (superficial) external, 619 internal, 610, 639 nerve, 1017 long, 1007 vein, external, 684 internal, 681 plexus of nerves, 1016 of veins, 682, 683 Pulmonary artery, 528, 1234 circulation, 507 left, 529 relations, 1369 right, 529 variations, 637 branches of vagus, 957 ligament, 1236 lymphatic nodes, 725 (visceral) pleura, 1236 plexus, anterior, 957, 1043 posterior, 954, 955, 957, 1043 (semilunar) valves, 517 veins, 529, 1234 Pulp of tooth, 1118 Pulpa lienis, 1311 Pulpy nucleus of intervertebral fibro-cartU- ages, 226 Pulvinar of thalamus, 845, 889 Puncta lacrimalia, 1054, 1079, 1349 PupO, 1054 Purkinje cells, 809 fibres of heart, 516 INDEX 1523 Putamen, 880 Pyloric antrum of stomach, 1151 canal, 1152 portion of stomach, 1151 vein, 675 Pylorus, 1152, 1374 Pyramidal eminence of temporal bone, 77 fasciculi of pons, 830 fibres, 840, 889 lobe of thyreoid gland, 1314 process of palate bone, 91, 92 tract, anterior or direct, 788 crossed, 783 Pyramidalis, 424, 431 nasi, 336 Pyramids of Ferrein, 1246 of Malpighi (renal), 1246 of medulla oblongata, 783, 799 decussation of, 815 structure of, 815 of vermis, 808 vertebral, 43 Quadrangular lobe of cerebellum, 806 membrane of larynx, 1215 Quadrate lobe, of liver, 1184 muscles, 332 Quadratus femoris, 453, 463, 464 . labii inferioris (depressor labii inferioris), 332 superioris, 332 lumborum, 425, 436, 1407 plantae (flexor accessorius), 454, 495 Quadriceps femoris, 453, 468, 470 Quadrigeminate arteries, 907 body, inferior, 834, 839 superior, 825, 834, 841 Quadrigemino-pontile fibres, 841 R Radial artery, 582 in palm (deep volar arch), 586 at the wrist, 584 carpal artery, dorsal, 585 volar, 584 collateral ligament, 261, 267 fossa of humerus, 151 (musculo-spiral) nerve, 985 hne of, 1415, 1423 results of paralysis of, 1424 deep (posterior interosseous), 985 results of paralysis of, 1424 superficial (radial), 987 notch (lesser sigmoid cavity) of ulna, 157 recurrent artery, 583 vena) comitantes, 671 Radialis indicis artery, 586 Radiate (anterior costo-central or stellate) ligament, 242 sterno-oostal ligament, anterior, 245 Radiation of corpus eollosum, 851 Flechsig's secondary optic, 890 occipito-thalamic (optic), 888 Radicular veins, 792, 908 Radio-carpal or wrist-joint, 265 arterial supply of, 267 ligaments of, 266 movements of, 267 muscles acting upon, 268 nerve-supply, 267 relations of, 267 Radio-carpeus muscle, 403 Radio-ulnar joint, inferior, 263, 419 mid, 262 superior, 262, 1419 ligaments, 262, 264 Radius, 152 clinical anatomy of, 1419, 1422 Ramus(i) bronchial, 1231 colli (infra-mandibular branch), of cervico facial nerve, 946 communicantes, 969, 1030, 1037 of fissure of Sylvius, 856 of ischium, 172 isthmi faucium, 940 Knguales, 954 of mandible, 95 of pubis, 172 Ranvier, nodes of, 761, 767 Raphe of palate, 1104 lateral palpebral, 1078 scrotal, 1254 Receptaeulum (cisterna) chyli, 726 Recess(es), elUptical, 80 epitympanic, 78 hypo-tympanie, 78 infundibular, 848 optic, 848 pharyngeal, 1130 spheno-ethmoidal, 1206 spherical, 80 supra-pineal, 847 of tumpanic mucous membrane, 1089 Recessus ellipticus (fovea hemielliptioa), 80 sphajricus (fovea hemisphaerica), 80 Rectal branches of lateral sacral arteries, 608 (hsemorrhoidal) of middle sacral arteries, columns (of Morgagni), 1177, 1390 examination, 1391 pits, 1390 sinuses, 1177 stalk, 1391 triangle, 440, 1383 Recto-uterine folds, 1274 pouch (of Douglas), 1267, 1274 Recto-vaginal pouch of peritoneum, 1148 Recto-veslcal pouch of peritoneum, 1148 Rectum, 1176 clinical anatomy of, 1390 lymphatics of, 735 supports of, 1391 Rectus abdominis, 422, 424, 430 accessorius, 471 capitis anterior (minor), 356 lateralis, 356 major, 355 posterior major, 412, 419 minor, 412, 419 femoris, 468, 470, 1436 Recurrent artery, anterior tibial, 632 dorsal ulnar, 577 interosseous, 580 posterior tibial, 632 radial, 583 volar ulnar, 577 articular nerve of leg, 1013 branches of deep volar arch, 586 of lacrimal, 552 of spinal nerve-trunks, 970 of vagus nerve, 956 meningeal branch of maxillary nei-ve, 937 of ophthalmic nerve, 935 (inferior laryngeal) nerve, 957 Red nuclei, 840 References for articulations, 311 blood-vascular system ,''696 digestive system, 1197" ductless glands, 1329 lymphatic system, 750 morphogenesis, 25 musculature, 506 nervous system, 1047 1524 INDEX References for osteology, 209 respiratory system, 1240 skin and mammary glands, 1329 special sense organs, 1098 urogenital system, 1280 Reflected inguinal ligament (CoUes' ligament, triangular fascia), 1395 Reflex paths of cranial nerves, 898 of spinal cord, 895 optic acoustic, 840 Regeneration of lymphatics, 707 Region, ilio-costal, 1406 parotid, 1343 of skull, anterior, 108 inferior, 103 lateral, 101 posterior, 101 superior, 100 Regions of abdomen, 1142, 1370 Reil, island of (insula), 856 Reissner, membrane of, 1096 Relations of organs (see correspondmg organs) Renal arteries, 598, 638 accessory, 638 branches of lumbar arteries, 693 of vagus, 958 columns (of Bertin), 1246 (Malpighian) corpuscles, 1246 fascia, 1242 ganglia, 1044 pelvis, 1248 plexuses of nerves, 1044 pyramids (of Malpighi), 1246 surface of spleen, 1309 tubules, 1246 veins, 673 Reproductive organs, development of, 1278 female, 1265 male, 1253 lymphatics of, 742, 744 Respiration, 1199 musculature, 247, 248, 503 Respiratory nerve of Bell, external, 982 nucleus, 822 system, 1196 larynx, 1209 lungs, 1228 mediastinal septum, 1239 nose, 1200 pleura}, 1236 thoracic cavity, 1235 trachea and bronchi, 1225 region of nose, 1208, 1352 Restiform body, 800, 810 fibres of, 830 in pons, 830 Rate arteriosum, cutaneous, 1289 sub-papillary, 1289 articular of knee, 622 canalis hypoglossi, 650, 665 dorsal carpal, 579, 585 venous (foot), 684 (hand), 667 foraminis ovalis, 646 lateral malleolar, 626, 632 medial malleolar, 626, 632 patellar, 622 plantar venous, 684 testis, 1256 volar carpal, 579, 581 Retia venosa vertebrarum, 665 Reticular formation of medulla oblongati 816 layer of thalamus, 882 of pons, 816 of spinal cord, 776 Retina, 1051, 1057, 1061 Retinacula, 1287 mammaj, 1303 pateUse laterale, 471 mediale, 471 peroneal, 480 tendinum, 317 Retinal arteries, 1065 pigment layer, 1057 veins, 1065 Retractors of the lips, 332 Retrahens aurem, 337 Retro-pubic space (of Retzius), 1371 Retrotonsillar fissure of cerebellum, 807 Rhinencephalon, 864 Rhombencephalon, 758 isthmus of, 832 summary of principal structures in, 833 Rhomboid fossa, 802 ligament (costo-clavioular), 249 muscles, nerve to, 982 Rhomboideus major, 356, 358 minor, 356, 358 Ribs, 120 asternal or false, 127 bicipital, 132 cervical, 131, 1365 clinical anatomy of, 1363, 1404 eleventh, 130 first, 128 floating, 127 lumbar, 132 ossification of, 130 pecuUar, 128 second, 129 sternal (true), 127 tenth, 129 twelfth, 130 typical characters of, 127 variations of, 131 vertebral, 127 vertebro-chondral, 127 vertebro-sternal, 127 Ridge (s), carotid, 73 genital, 1267, 1278 nfra-temporal, 65 lateral supracondylar, 149 medial supracondylar, 149 pronator, of ulna, 157 transverse, of palate, 1104, 1106 temporal, 71 Right atrium (auricle) of heart, 512 branch of hepatic artery, 595 bronchial artery, 588 colic artery, 598 common iliac artery, 605 coronary artery, 519 branches, 519 gastric artery, 594 gastro-epiploic artery, 595 vein, 677 innominate vein, 641 lymphatic duct, 728 pulmonary artery, 529 veins, 529 superior intercostal vein, 664 terminal branch of hepatic artery, 589 collecting lymphatic duct, 728 ventricle of heart, 516 Rima glottidis, 1223 oris, 1100 palpebrarum, 1052 pudendi, 1276 vestibuli, 1222 . , ,. , , , , RinK(s), abdominal ingumal (mternal abdom- inal), 430, 1371, 1396 femoral, 466, 1401 INDEX 1525 Rings, subcutaneous inguinal (external abdom- inal), 429, 1371, 1394 tonsillar (Waldeyer's), 1133 Risorius, 333 Rivinus, notch of, 77 Rolandic angle, 860 points, 1340 Rolando, fissure of, 859, 1340 gelatinous substance of, 776 Root(s) of Arnold's or otic ganglion, 963 canal of tooth, 1118 ' of ciliary ganglion, long, 937 short, 932 filaments of spinal nerves, 775, 964 of hair, 1292 of lungs, 1229, 1230, 1234, 1408 of nails, 1294 of nose, 1200 of optic tracts, 849 of penis, 1260 of spheno-palatine (Meckel's) ganglion, 962 of spinal nerves, 771, 964 of teeth, 1117 of tongue, 1107 Rosenmtiller, fossa of, 1130 Rostral lamina of corpus calloum, 852 sulci, 858 Rostrum of corpus callosum, 852 of sphenoid, 63 Rotation, 215, 321 -Rotatores, breves, 412, 419 longi, 412, 419 Round ligament liver, 1185 of uterus, 1274 Rubro-spinal fasciculus, 786 Ruffini, corpuscles of, 1290 RugsB of vagina, 1275 Sac, conjunctival, 1054 endolymphatic, 1094 lacrimal, 1080, 1349 lesser, 1148 synovial, 313 Saccular branch of vestibular ganghon, 950 Saccule of membranous labyrinth, 1093 Sacculo-ampullar division of vestibular nerve, 950 Sacral arteries, lateral, 607 middle, 603 branches, lateral of middle sacral artery, 603 canal, 42 cornua, 40 foramina, 40 groove, 41 hiatus, 40 lymphatic nodes, 733 nerves, 973, 1006 plexus, 1006 composition of nerves of, 1006 of veins, anterior, 679 portion of sympathetic system, 1040 veins, lateral, 680 middle, 679 vertebrae, development of, 48 Sacro-coccygeal articulation, 237 ligament, anterior, 238 deep posterior, 238 superficial posterior, 238 Sacro-coccygeus, anterior, 448 posterior, 448 Sacro-iliac articulation, 234 ligaments, anterior, 234 inferior, 235 posterior, 234 superior, 234 Sacro-lumbar ligament, 232 Sacro-spinaUs (erector spinas), 412, 414, 1407 Sacro-spinous or small sacro-sciatic ligament, 236 Sacro-tuberous (great or posterior sacro-sciatic) ligament, 235 Sacro-vertebral angle, 39, 43 articulations, 232 Sacrum, description of, 30, 39 sex and racial differences of, 42 Sagittal fontaneUe, 59 sinus, inferior, 650 superior, 649 sulcus, 60 suture, 57, 101 Salivary corpuscles, 1132 glands, 1113 development of, 1117 variations and comparative, 1117 Salivatory nucleus, 826, 947 Santorini, cartilages of, 1212 duct of, 1195 incisures of, 1085 Saphenous artery, 621 nerve, 1003, 1467 external or short, 1010, 1013 opening (fossa ovaUs), 467, 1400, 1440 vein, accessory, 684 great (internal), 684, 1456 small (ex-ternal), 684, 1458 Sarcolemma, 315 Sartorius, 453^ 468, 1436 Scala media, 1096 tympani, 81, 1096 vestibuli, 81, 1096 Scalene musculature, 328, 353 tubercle, 129 Scalenus anterior, 353 medius, 354 minimus, 355 posterior, 354 Scalp, 1333 cutaneous areas of, 1018 lymphatics of, 712 Scansorius, 462 Soapha of auricle of ear, 1083 Scaphoid bone, 159, 160 fossa, 55, 66, 107 Scapula, 141 clinical anatomy of, 1406 Scapular artery, circumflex (dorsal), 572 posterior, 565 transverse (suprascapular), 564 • foramen, 142 nerve, dorsal, 982 notch, 142 veins, transverse, 648 Seapulo-clavicular union, 250 Scapulo-clavicularis, 374 Scarf-skin (epidermis), 1285 Scarpa, fascia of, 425, 445 foramina of, 89, 106, 126 triangle of, 467, 1438 Schindylesis sutures, 212 Schlemm, canal of, 1059 Schwalbe, nucleus of, 823 Sciatic artery, 609, 640 nerve (N. ischiadious), 1008, 1443 results of paralysis of, 1469 small, 1007 notch, great, 172 small, 172 Scleral sulcus, 1054 Sclera, 1052, 1056, 1058 Sclerotome, 15 Scrotal (or labial) arteries, anterior, 620 posterior, 613 1526 INDEX Scrotal nerves, anterior, 1000 posterior, 1017 veins, 684 Scrotum, 12ol lymphatics of, 698, 742, 1255 surgical anatomy of, 1385 vessels and nerves of, 1255 Scutum, 1089 Sebaceous glands, 1298 Sebum cutaneum, 1298 palpebrale, 1054 Secondary tympanic membrane, 1089, 1096 Sections of peritoneum, 1146 Segmentation of the ovum, 9 Sella turcica, 63, 113 Seraioanalis m. tensoris tympani, 74 Semicircular canals, 78, 80 ducts (membranous semicircular canals), 3094 Semilunar bone, 159, 161 fascia, 382 fibro-cartilages, 289 fissures of cerebellum, 805 fold of conjunctiva, 1055 of large intestine, 1170 ganglia, 1043 (Gasserian) ganglion, 826, 936, 1345 gyrus, 865 lobe, inferior, of cerebellum, 807 superior, of cerebellum, 806 notch (greater sigmoid cavity), 156 valves, aortic, 517 pulmonary, 517 Semimembranosus, 453, 475, 476 Seminal vesicles, 1257 Seminiferous tubules, 1256 SemispinaUs capitis (complexus), 412, 417 cervicis, 412, 419 dorsi, 412, 419 Semitendinosus, 453, 475, 476 Sense, organs of special, 1049 Sensory aphasia, 894 axones, 762 Sensory-motor area of cerebral cortex, 893 Septa, intermuscular, 314 of thigh, 468 Septal branches of spheno-palatine artery, 549 nasal cartilage, 1202 Septulse of mediastinum testis, 1256 Septum aortic, 527 of arm, intermuscular, 377 atriorum, 511 canalis musculotubarii, 73 femoral, 466 of foot, intermuscular, 492 of heart, membranous, 511, 527 interventricular, 516 of leg, intermuscular, 477 linguae, 346 mediastinal, 1239 nasal. 111, 1204, 1354 Septum pellucidum, 872 cavity of, 872 laminaj of, 872 of penis, 1261 posticum of Schwalbe (subarachnoid sep- tum), 919 sigmoid, 341 sphenoidal, 62 transversum, 20 Serial morphology of vertebrae, 50 Serrate sutures, 212 Serratus anterior (magnus), 356, 359 posterior inferior, 423, 431 superior, 423, 431 Sesamoid bones, 68, 205, 275, 317 cartilages of larynx, 1213 Sesamoid nasal cartilages, 1202 plate, plantar, 310 tibial and fibular, 209 ulnar and radial, 209 Seventh cervical vertebra?, 34 cranial nerve (facial), 943, 1345 Shaft of bones, 29 (see also the individual bones) of hair, 1292 Sheath (s), carotid, 1362 femoral, 1400 medullary, 759 of optic nerve, 931 of parotid gland, 1344 primitive, 761 of prostate, 1389 of rectus muscle, 427 of hair roots, 1292 synovial tendon, 317, 318, 403, 483, 484, 491 Shoulder, clinical anatomy of, 1409 musculature of, 323, 363, 503 Shoulder-blade (scapula), 141 Shoulder-girdle, 207 Shoulder-joint, 253 arterial supply, 257 clinical anatomy of, 1413 ligaments of, 254 lymphatics of, 723 movements of, 257 muscles acting upon, 258 nerve-supply of, 357 synovial membrane, 255, 1412 Shrapnell's membrane, 1087 Sibson's fascia, 129, 355, 1237 Sigmoid artery, 603 cavity of radius, 154 of ulna, greater, 156 lesser, 157 colon, 1174, 1379 groove, 72 notch, 96, 97 septum, 341 sinus, 652 vein, 678 Sinuses, accessory nasal, 1354 aortic (of Valsalva), 518 bony, of skull, 1335 cavernous, 652, 691 cervical, 17 circular, 651 connecting with nose, 1354 coronary, 521 costo-mediastinal, 1238 cranial venous, 649, 692, 916 of dura mater, 649 epididymidis (digital fossa), 1255 frontal, 59, 61, 1207, 1335 inferior petrosal, 652 sagittal (longitudinal), 650 interoavernosus, 651 of kidney, 1242 lactiferous, 1302 longitudinal vertebral, 665 mammarum, 1299 marginal, 650 v ■ o-r maxillaris (antrum of Highmore), 87, 90, 111, 1206, 1354 of Morgagni, 1137 _ oblique, of pericardium, 523 occipital, 650 paranasal, 1206 parasinoidal, 919 of pericardium, transverse, 523, 527 petro-squamous, 653 phrenico-costal, 1237 pleural, 1237 of portal vein, 675 INDEX 1527 Sinuses, rectal, 1177 sigmoid, 652 sphenoidal, 62, 1207, 1338 spheno-parietal, 653 straight, 650 superior petrosal, 652 sagittal (longitudinal), 649 tarsi, 195 transverse (lateral), 651 tympanic, 1089 uro-genital, 1279 of Valsalva, 518, 530 venarum, 513 venosus, of heart, 525 of sclera (Sohlemn), 1059 Sinusoids, 672, 675 Skeleton, 27 appendicular, 139 axial, 29 Skene, ducts of, 1277 Skin, 1281 appendages of, 129 cerium, 1286 development of, 1286, 1290 epidermis, 1285 lymphatics of, 698, 1289 muscle-fibres of, 1288 tela subcutanea (superficial fascia), 1287 vessels and nerves, 1288 Skin-folds of wrist and hand, 1425 Skull, appendicular elements of, 117 articulations of, 215 at birth, 120 bones of, 51 bony landmarks, 1331 sinuses of, 1335 fcetal, general characters, 120 interior of, 112 morphology of, 117 nerve-foramina of, 125 regions of, anterior (norma facialis), 108 inferior (norma basalis), 103 lateral (norma lateralis), 101 posterior (norma occipitalis), 101 superior (norma verticalis), 100 topography of, 1338 as a whole, 160 Small cardiac vein, 521 intestine, 1161, 1375 blood-supply, 1166 clinical anatomy of, 1375 development of, 1168 duodenum, 1161 ileum and jejunum, 1165 lymphatics of, 1168 nerves of, 1168 (accessory) meningeal artery, 548 occipital nerve, 977 palatine nerve, 948 (external) saphenous vein, 684, 1458 sciatic nerve, 1007 superficial petrosal nerve, 951 Smaller palatine canals, 92 Smallest cardiac vein, 521 occipital nerve, 971 Snuff-box space (tabati^re anatomique), 1433 Soft palate, 1104 muscles of, 326 Solar plex-us, 1043 Sole of foot, muscles of, 493 Soleus, 454, 484, 485 accessorius, 491 Solitary follicles, 704 glands of small intestine, 1166 tract, 820 Somresthetic (sensory-motor) area of cerebral cortex, 893 Somites, mesodermic, 14, 15 Space(s), Burns', 1356 of Fontana, 1060 intercostal, 139 interfascial (Tenon's), 715, 1073 popliteal, 1451 praevesical, 1250 snuff-box, 1433 subarachnoid, 771 subdural, 771 Special sense, organs of, 1049 Speech, cortical areas of, 894 Spermatic artery, external, 615 internal, 698, 638, 1259 branch, external, of genito-femoral nerve, 1000 cord, 1254, 1269, 1387 fascia, external, 1387 plexus of nerves, 1045 veins, 674, 1259 Spermatozoa, 1256 Spheno-ethmoidal branch of naso-ciliary (nasal) nerve, 937 cells, 84 recess, 1206 Sphenoid, 62 at birth, 122 Sphenoidal conchas (turbinate bones), 64, 67 at birth, 124 development of, 119 crest, 63 (superior orbital) fissure, 65, 109, 116, 126 process of palate bone, 91, 92 of septal cartilage, 1203 septum, 62 sinuses, 62, 1207 Spheno-mandibular ligament, 217 Spheno-maxillary fissure, 102, 109, 126 fossa, 102 Spheno-palatine artery, 549 nerve, 938 foramen, 93, 103, 111, 126 (Meckel's) ganglion, 962 branches, 962 roots, 962 notch, 91, 93 vein, 646 Spheno-parietal sinus, 653 Sphenotic cartilage, 117 Spherical recess, 80 Sphincter ani externus, 441, 449 internus, 1 177 tertius, 1177 internal, of urinary bladder, 1253, 1389 pupillae (iridis), 1061 urethras (in female), 449 membranaceae, 449 urogenitalis, 442, 449 vaginaj, 1276, 1278 Spigelian lobe of liver, 1184 Spinal accessory nerve, 958 nucleus of, 820 arachnoid, 919 artery, anterior, 561, 638, 792 posterior, 561, 792 branches of aortic intercostal arteries, 590 of deep cervical artery, 568 of Uio-lumbar artery, 607 of lateral sacral arteries, 60S of superior intercostal arteries, 568 of vertebral artery, 560 cord, 751, 771 blood supply of, 792 central canal of, 775 clinical anatomy of, 1408 external morphology of, 771 internal structure of, 775 1528 INDEX Spinal cord, meninges of, 908 summary of, 788 surface of, 772 systems of neurones in, 777 terminal ventricle, 775 dura mater, 911 ganglia, 964 aberrant, 965 neurones of, 755 musculature, 410 nerves, 964 aberrant ganglia, 965 areas of distribution of, 970 attachment of, 964 Cauda equina, 966 course of, 965 filia radicularia, 965 ganglion of, 964 origm of, 964 roots of, 964 topography of attachment of, 966, 1406 nerve-trunks, anterior primary divisions, 968 meningeal (recurrent) branch of, 970 posterior primary divisions, 967, 970 rami communicantes, 969 pia mater, 921 (inferior) portion of (spinal) accessory nerve, 958 tract, of trigeminus nerve, 828 veins, anterior, 665 posterior, 665 Spinalis capitis (biventer cerviois), 418 cervicis, 412, 417 dorsi, 412, 417 Spindle, aortic, 531 neuromuscular, 764 Spine (s), 29 anterior nasal, 87, 90, 112 ethmoidal, 63, 113 frontal (nasal), 60 of helix, 1084 of ilium, 169 ischial, 172 mandibular, 96 mental, 95 nasal (frontal), 60 posterior, 91 of pubis, 172 of scapula, 141, 144 of sphenoid, 65, 108 suprameatal, 72 of tibia (iatercondyloid eminence), 185 vertebral, 1403 Spino-cerebellar fasciculi, 784 path, 985 Spino-mesencephalic (spLno-tectal) tract, 786, 842 Spino-olivary fasciculus, 784 Spino-thalamic tract, 786 Spinous process of epistropheus, 34 of seventh cervical vertebra, 34 of vertebra:, 31 ligaments connecting, 229 Spiral canal of cochlea, 81 ganglion of cochlea, 950 ligament of cochlea, 1096 line of femur, 178 organ (organ of Corti), 1096 valve (of Heister), 1187 Splanchnic ganglion, 1039 nerve, great, 1038 least, 1039 lesser, 1039 pelvic, 1017, 1040, 1046 Spleen (lien), 1306 development, 1312 lymphatics, 736, 1312 Spleen, topography of, 1310, 1375 variations, 1310 vessels and nerves, 1312 Splenic artery, 595 branches of vagus, 958 (left colic) flexure, 1174, 1379 lobules, 1312 lymphatic nodes, 730, 736 (lienal) plexus of nerves, 1045 pulp, 1311 vein, 677 Splenium of corpus callosum, 852 Splenius, 412, 414 capitis, 414 cervicis, 414 accessorius, 414 Spongioblasts, 755 Spot, yellow, of fundus oculi, 1055 of larynx, 1223 Spring ligament, 305 Squamous portion of temporal bone, 68 sutures, 212 Stapedial fold, 1090 artery, 638 Stapedic branch of stylo-mastoid artery, 544 Stapedius, 1091 nerve to, 944 Stapes, 80, 119 Stellate cells of cerebellar cortex, 809 figures of lens of ej'e, 1063 ligament, 242 Stem of fissure of Sylvius, 855 Stenson's duct, 1115, 1343 foramina, 89, 106 Stephanion, 101 Sternal branches of internal mammary artery, 567 foramen, 133 synchondrosis, 133 Sternalis, 374 Sternebras, 132 Sterno-chondro-scapularis, 374 Sterno-clavicular joint, surgical anatomy of, 1363 ligaments, 248 Sterno-clavicularis, 374 Sterno-cleido-mastoid artery, 542 Sterno-cleido-mastoideus, 347, 349 Sterno-costal articulations, 245 ligaments, 245 surface of heart, 510 Sterno-oosto-clavicular articulation, 248 ligaments of, 248 movements of, 250 Sterno-hj'oideus, 3i51 Sterno-mastoid branch of superior thyreoid artery, 538 as a landmark, 1355 vein, 660 Sterno-pericardial ligaments, 522 Sterno-thyreoideus, 351 Sterno-xiphoid plane, 1370 Sternum, 132 abnormaUties of, 138 angle of, 133, 139 body of, 133 development of, 135 StUling's nucleus, 776 Stomach, 1151 blood-vessels of, 1151 clinical anatomy of, 1373 comparative, 1160 development of, 1157 lymphatics of, 734, 1156 nerves of, 1156 peristalsis of, 1159 position and relations, 1153 INDEX 1529 Stro/ight (collecting), renal tubule, 1167 sinus, 450 Stratum album medium, 842 profundum, 842 cinereum, 842 corneum, 1286 unguis, 1295 germinativum (Malpighii), 1286, 1295 granulosum, 1286 lemnisci, 825, 839, 842 lucidum, 1286 opticum (stratum album medium), 842 zonale, 839, 842, 845, 881 Streeter, nucleus incertus of, 815 Strias acustica(ae), 814 (linete) albicantes, 1283, 1304 intermediate olfactory, 865 Lancisii, 851, 871 lateral longitudinal, of corpus callosum, 851 longitudinal, of corpus callosum, 851, 892 of hippocampus 871 medial longitudinal, of corpus callosum, 851 medullares acustici, 824 (pineales) of thalami, 846, 872 olfactory, 865, 866 terminalis thalami (ttenia semicircularis), 845, 892 of thalamus, 873, 881, 892 transverse, of corpus callosum, 852 Striate arteries, external, 906 internal, 906 Stripes of Baillarger, 879 Structure of organs (see corresponding organ) Stylo-glossus, 346- Stylo-hyal portion of styloid process, 75, 119 Stylo-hyoid ligaments, 99 Stylo-hyoideus, 343, 344 Styloid bone, 168 process, 70, 73, 75, 77, 108 of fibula, 190 of radius, 155 of third metacarpal bone, 166 of ulna, 158 Stvlo-mandibular (stylo-maxillary) ligament, 217 Stylo-mastoid branch of posterior auricular artery, 544 foramen, 73, 108, 126 vein, 646 Stylo-pharyngeus, 1137 Subanconeus, 378 Sub-arachnoid cavity or space, 771, 919 cisternas, 918 Subcallosal gyrus (peduncle of corpus callo- sum), 866 sulcus, 866 Subclavian artery, 556 collateral circulation, 1360 left, 556 relations, 556, 558, 1369 right, 557 variations, 638 group of axillary lymphatic nodes, 719 sulcus, of lung, 1229 vein, 671 Subclavius, 373 Subcostal artery, 588 Subcostales, 423, 434 Subcrureus, 470 Subcutaneous dorsal veins of penis, 684 inguinal (external abdominal) ring, 429, 1371, 1394 muscles, 313 of hand, 404 Subdural cavity, 912, 917 space of spinal cord, 771 Subfascial bursse mucosae, 318 Subiculum of the promontory, 1089 Sublingual artery, 540 caruncle, 1116, 1117 fold, 1116 gland, 1116 ducts of, 1117 vessels and nerves, 1117 lymphatic nodes, 746 nerve, 941 vein, 660 Submammary (retromammary) bursa;, 1303 Submarginal gyrus, 858 Submaxillary ganglion, 963 roots, 963, 1036 gland, 1115, 1350 duct of (Wharton's) 1116 vessels and nerves, 1116 lymph-nodes, 709 portion of external cervical fascia, 347 (digastric) triangle, 1357 Submental artery, 541 set of facial lymph-nodes, 711 vein, 644 Submuscular bursa; mucosae, 318 Subnasal point, 109, 112 Suboccipital muscles, 412, 419 nerve, 971 Subparietal sulcus (postlimbic fissure), 863 Subphrenic area of peritoneum, 1372 Subsartorial plexus, 1003 Subscapular angle, 145 artery, 571 branches of posterior scapular artery, 566 of transverse scapular arterj', 565 fossa, 141 group of axillary lymphatic nodes, 720 nerves, 984 vein, 671 Subscapularis, 369 minor, 369 Substance, anterior perforated, 847, 866 central grey, of mesencephalon, 836 of medulla, 818 gelatinous, central, of spinal cord, 776 of Rolando, 776 grey, of pons, 831 of nervous system, 768 of spinal cord, 775 of telencephalon, 879 posterior perforated, 835, 844 white, nervous system, 768 of spinal cord, 775, 777 of telencephalon, 885 Substantia alba, 768 corticalis, 1293 grisea, 768, 818 medullaris, 1293 nigra, 836, 840 reticularis alba (Ai'noldi), 868 Subtendinous bursa; mucosse, 318 Subtrapezial plexus, 979 Sudoriferous glands (sweat-glands), 1296 pore, 1297 Sulco-marginal fasciculus, 788 Sulcus(i), 29 ampullary, 1095 antero-inferior, 807 antero-intermediate, 774 antero-lateral, 773 auricular, 1082 basilar, of pons, 804 breves, 857 central (fissure of Rolando), 859, 1340 of cerebellum, 805 of cerebrum, 852 cinguli (calloso-marginal fissure), 857, 858, 869 1530 INDEX Sulcus(i), circular, 857 coronarius, 510 of corpus callosum, 867 of crus of helix, 1084 cunei, 864 diagonal, 858 fimbrio-dentate, 868 of floor of fourth ventricle, 813 fronto-marginal, 858 of heart, 510, 511 hypothalamic, 847 inferior frontal, 858 postcentral, 861, 862 temporal, 855 infra-orbital, 1284 interparietal (intraparietal), 861 lateral occipital, 863 matricis unguis, 1294 median subcallosal, 866 mento-labial, 1284 middle frontal, 858 temporal, 855 of Monro, 847 oculomotor, 835 olfactory, 858 orbital, 858 parallel, 855 para-medial, 858 parolfactory, 865 pontine, 804 postcentral of cerebellum, 806, 861, 862 posterior median, 772 postero-inferior, 807 postero-intermediate, 773 postero-lateral, 773 post-nodular, 808 pre-auricularis, 177 precentral, 807, 857 rostral, 858 sagittal, 60 scleral, 1054 of skin, 1284 of spinal cord, 772 subclavian, of lung, 1229 subparietal, 863 superior frontal, 858 postcentral, 861, 862 temporal 855 supra-orbital, 1284 of telencephalon, 853 terminalis of tongue, 1106 of heart, 511 transverse occipital, 862, 863 temporal, 855 transversus, 69, 108 of anthelix, 1083 tympanicus, 75 Supercilia, 1290 Superciliary arch, 59, 108 Supination, 321 Supinator (brevis), 392 radii longus, 388 Supracallosal gyrus, 868 Supra-clavicular branches of cervical plexus, 978 nerves, 978 portion of brachial plexus, branches of, 982 Supra-condylar lines, 181 process, 149 ridge, lateral, 149 medial, 149 Supracostales, anterior, 433 posterior, 432 Supraglenoid tubercle of scapula, 144 Supra-hyoid musculature, 325, 344 Supramammillary commissure, 871, 890 Supra-mandibular branch of cervico-facial nerve, 946 Supramarginal gyrus, 863 Supra-maxillary set of facial lymph-nodes, 711 Supra-meatal fossa, 72 spine, 72 triangle, Macewen's, 1337 Supra-occipital, 119 Supra-omental region of peritoneum, 1372 Supra-orbital artery, 552, 1343 branches, 553 border, 60 nerve, 935 notch, 60 sulcus, 1284 vein, 644 Suprapineal recess, 847 Suprarenal artery, inferior, 598 middle, 598" superior, 592 glands, 1323, 1381 accessory (of Marchand), 1326 development, 1326 lymphatics, 701, 738 vessels and nerves of, 1326 plexuses of nerves, 1044 veins, 673 Suprascapular (transverse cervical) artery, 564 (coracoid or superior transverse) ligament, 253 nerve, 982 Supraspinatus, 368 Supraspinous branches of posterior scapular artery, 566 of transverse scapular artery, 565 fossa, 141 ligament, 230, 238 Suprasternal bones, 133 Supratonsilar fossa, 1132 Supratragic tubercle, 1082 Supratrochlear branch of frontal nerve, 936 foramen, 150 lymphatic node, 719 Sural branches of popliteal artery, 622 (ex-ternal or short saphenous) nerve, 1010, 1013, 1467 Surfaces of organs (see corresponding organ). Surgical anatomy of organs (see corresponding organ). Suspensorius duodeni, 1164, 1376 Suspensory ligament of Cooper, 1303 of the eyeball, 1072, 1348 of lens of eye, 1057, 1064 (apical dental) of occipito-epistrophic articulation, 223 of ovary, 1269 of penis, 427, 1260 of Treitz, 1164, 1376 Sustentaculum hepatis, 1174 lienis, 1174 tali, 195 Suture(s), 212 of anterior cranial fossa, 113 coronal, 57, 101, 1339 frontal, 59 incisive, 106 lambdoid, 57, 101, 1339 meso-palatine, 89, 106 metopic, 59, 101 neuro-central, 45 of norma facialis, 108 occipital, 101 occipito-mastoid, 101 parieto-mastoid, 101 petro-squamous, 71 INDEX 1531 Suture(s), sagittal, 57, 101, 1339 squamoso-parietal, 1339 transverse, 108 palatine, 106 of vertex of skull, 101 Swallowing, muscles of, 325 process of, 1137 Sweat-glands, 1296 Swellings, genital, 1279 Sylvian fossa, 854 point, 856 Sylvius, aqueduct of, 834 fissure of, 850, 855, 134,0 Syme's amputation, 1465 Sympathetic fibres, 970, 1029 nerves of orbit, 1076, 1348 relations of spinal cord, 789 system, 959, 1026 construction of, 1030 ganglia of, 959 origin of, 1029 prevertebral plexuses of, 1029 trunks, 1032, 1033 Symphysis of mandible, 95 pubis, 238 ligaments of, 238 Synapses, 762, 765 Synarthroses, 212 Synchondroses, 212 sternal, 133 Syncytium, 759 Syndesmoses (synarthroses), 212 tympano-stapedial, 1090 Synergists, 322 Synovial bursse, 313, 318 membrane, 211 (see also corresponding articulations) sheaths (vaginae mucosae tendinum), 378 tendon-sheaths, 317 of forearm muscles, 395, 403 of leg muscles, 483, 484, 491 System, association, of hemisphere, 890 blood-vascular, 507 chromaffin, 1333 digestive, 1099 of fibres, commissural, 890 lymphatic, 697 nervous, 751 central, 751, 770 peripheral, 754, 924 sympathetic, 1026 neurone, 777, 895 respiratory, 1199 urogenital, 1241 Systemic arteries, 529 circulation, 507 veins, 640 Tabatifere anatomique (of Cloquet), 1433 Table showing relations of cervical and thora- cic nerves to branches of brachial plex-us, 993 of lumbar and sacral nerves to branches of lumbar and sacral plexuses and to pudic nerve, 1016 of muscles of lower extremity to nerves of lumbar and sacral plexuses, 1016 of muscles of upper extremity to cervi- cal nerves, 993 of vertebral levels, 1409 of distribution of spinal nerves (Cow- ers'), 969 Tactile corpuscles (Meissner), 1290 Tsenia chorioidea, 844 fimbria, 868, 877 Taenia fornicis, 868 pontis, 855 semicircularis, 845, 873 thalami, 846, 872 Tail of caudate nucleus, 877 of epididymis, 1256 of muscle, 314 of pancreas, 1194 Talipes, 1467 Talo-calcaneal union, 301 Talo-fibular ligament, anterior, 299 posterior, 299 Talo-navicular articulation, 305 ligament, 306 Talus or astragalus, 191, 192 Tan, 1283 Tangential layer of fibres of cortex, 879 Tapetum of posterior cornu of lateral ventricle, 876 Tarsal arch, inferior, 554 superior, 554 arteries, medial, 632 bones, 191 clinical anatomy of, 1467 branches of dorsalis pedis artery, 632 elements, accessory, 199 (Meibomian) glands, 1054, 1298 joints, 301 transverse, 305 muscles, 1072, 1078 Tarso-metatarsal articulation, 308 Tarsus, 191 anterior articulations of, 303 of eyelids, 1053, 1077 Taste, organ of, 1051 Taste-buds, 1051 Taste-pores, 1051 Tectorial membrane, 223 Teeth, 1117 canine, 1120 deciduous or milk, 1126 incisor, 1119 molars, 1121 premolar or bicuspid, 1121 times of eruption, 1127 variations and comparative, 1127 vessels and nerves, 1124 Tegmen tympani, 77 Tegmento-mammUlary fasciculus, 871 Tegmentum of pons, 830 Tela chorioidea, 758 of fourth ventricle, 922 subcutanea (superficial fascia), 313, 1287 of the abdomen, 425 of the arm, 377 of the back, 413 of the forearm and hand, 384 of the foot, 491 of gluteal region, 457 of head and neck, 347 of leg, 477 of pectoral region, 371 of the perineum, 445 of shoulder, 365 of thigh, 466 of thoracic-abdominal musculature, 425 Telencephalon, 758, 847 gyri, fissures and sulci, 852 lobes, 853 central (insula), 856 frontal, 857 occipital, 863 parietal, 860 rhinencephalon, 864 temporal, 854 projection fibres of, 886 Telodendria of axones, 762 1532 INDEX Temporal artery, anterior deep, 54S middle, 545 posterior deep, 548 superficial, 545, 1343 bone, 68 at birth, 122 mastoid portion of, 68, 71 petrous portion of, 68, 72 squamous portion of, 68, 70 tympanic portion of, 69, 70, 75 branches, superficial, of auriculo-temporal nerve, 942 of maxillary nerve, 938 of temporo-facial nerve, 945 fascia, 339 fossa, 101 gyrus, inferior, 855 middle, 855 superior, 854 lines (ridges), 57, 60, 71, 1332 lobe of cerebrum, 854 operoula of, 854 nerves, deep, 943 notch, 868 pole, 850 pontile path (Ttirk's path), 832, 840, 890 process of malar bone, 95 sulcus, middle, 855 superior, 855 vein, deep, 646 diploic, 648 middle, 646 superficial, 646 wings of sphenoid, 65 Temporalis muscle, 338, 341 superficialis, 337 Temporo-facial nerve, 945 Temporo-malar branch of maxillary nerve, 938 . Tempo ro-maxillary (posterior facial) vein, 644 Tendino-trochanteric band, 280 Tendo Achillis, 485 ■ Tendon(s), 314, 317 at the ankle, 1460 conjoined, 435 of the conus, 518 popliteal,11451 of the quadriceps, 471 Tendon-sheaths, 317 of forearm muscles, 395, 403 of leg muscles, 483, 484, 491 Tenon's capsule, 1073, 1348 space, 715 Tensor capsularis articulationis metacarpo- phalangei digiti quinti, 406 of the capsule of the ankle-joint, 491 fasciae dorsalis pedis, 482 latffi, 457, 459 ,1436 suralis, 476 laminas posterioris vaginas musculi recti abdominis, 436 posterioris vaginae musculi recti et fasciae transversalis abdominis, 436 ligamenti annularis anterior, 393 posterior, 393 tarsi, (Horner's muscle), 336 tympani, 1089, 1091 vaginae femoris (tensor fasciae latae), 457, 459, 1436 veli palatini, 1137 Tentorial (recurrent meningeal) branch of ophthalmic nerve, 935 notch, 915 Tentorium cerebelli, 914 Tenuissimus, 475 Teres major, 369 minor, 369 Terminal branches (see corresponding artery or nerve) incisure (auricle), 1084 nerve, 929 stria, of thalamus, 873 sulcus, 1106 vein (of corpus striatum), 657 ventricle of spinal cord, 775 Testes, 1255, 1386 descent of, 1257, 1387 lymphatics of, 700, 744, 1256, 1387 Testicular arteries, 601 Tetrahedral-shaped spleen, 1310 Thalamencephalon, 844 Thalami, 758, 844 Thalamo-olivary tract, 817, 830 Thalamo-spinal tract, 786 Thalamus, 881 anterior tubercle (nucleus) of, 845, 882 cortical connections of, 883 medullary lamina of, 882 nuclei of, 871, 882, 883 peduncles of, 880, 883 pulvinar of, 882 stratum zonale, 881 stria terminahs of, 845, 881, 892 stria; meduUares, 872 Thebesius foramina of, 514 valvula of, 512 Theoa folhouli, 1292 Thenar fascia, 387 Thigh, bony landmarks of, 1434 fasciae of, 466 muscles, 453, 464 acting on, 505 muscular prominences of, 1436 Third occipital condyle, 56 part of axillary artery, 570 of subclavian artery, 558 ventricle of brain, 846 chorioid plexuses of, 924 Thoracic aorta, 586, 1369 aortic plexus, 1038 aperture, superior, 138 artery, dorsal, (thoraco-dorsal) , 572 lateral, 571 superior, 570 cavity, 1235 duct, 726 ganglia, 1038 intercostal nerves, 995 muscles, lymphatics, 923 nerves, 971, 994 lateral anterior, 983 medial anterior, 983 long, 982 posterior, 982 portion of left subclavian artery, 556 of sympathetic system, 1037 of thymus, 1321 vein, lateral, 671 vertebrae, description of, 30, 36 peculiar, 36 Thoracic-abdominal musculature, 422 fasciae of, 425 muscles of, 430 nerves, 995 Thoraco-acromial (acromio-thoracic axis), artery, 571 vein, 671 Thoraco-dorsal (middle or long) subscapular nerve, 984 Thoraco-epigastric vein, 671, 1372 Thorax, 126 articulations at front of, 244 bony landmarks, 1363 clinical anatomy of, 1363 INDEX 1533 Thorax, deep veins of, 665 lymphatics of, 723, 724, 725 movements of, 247 as a whole, 138 Thumb, muscles of, 406 acting on, 504 Thymic arteries, 567 veins, 661 Thymus, 1319 corpuscles of, 1321 cortex of, 1321 development of, 1322 lymphatics of, 729, 1322 medulla of, 1321 vessels (and nerves) of, 1322 Thyreo-arytsenoideus externus, 1219 internus (m. vocalis), 1220 obhquus, 1220 superior, 1220 Thyreocervical trunk (thyreoid axis), 564 Thyreo-epiglottic ligament, 1215 muscle, 1220 Thyreo-glossal duct, 1318 Thyreo-hyal centre, 100 segment, 119 Thyreo-hyoideus, 351 Thyreoid artery, inferior, 564 superior, 538, 638 bars, 119 cartilage, 1210 gland, 1312 accessory, 1315 clinical anatomy of, 1355 development of , 1318 lymphatics of, 699, 719, 1317 laminae, 1210 hgament, 1314 vessels, 1316 notch, inferior, 1211 superior, 1210 plexus of nerves, inferior, 1036 superior, 1Q36 tubercle, inferior, 1211 superior, 1211 veins, 660, 661, 1317 Thyreoidea ima artery, 533 vein, 661 Tibia, 185, 1454 condyles of femur and, 1447 epiphyses of, 1435 structures on head of, 1449 tuberosity of, and ligamentum patellaj, 1448 Tibial artery, anterior, 629, 640, 1458 posterior, 624, 640, 1458 collateral ligament, 286 communicating nerve, 1010 nerve (internal popliteal), 1009 paralysis of, 1469 anterior, 1015 posterior, 1009 nutrient artery, 626, 1459 recurrent artery, anterior, 632 posterior, 632 veins, anterior, 688 posterior, 688 Tibialis anterior, 453, 480, 1468 tenotomy, 1464 posterior, 454, 486, 490, 1468 secundus (tensor of capsule of ankle-joint), 491 Tibio-astragalus anticus, 482 Tibio-fibular ligaments, 295 union, 295 Tigroid masses, 766 Tissues, 4 Toes, muscles acting on, 506 Tomes' fibrils and sheath, 1118 Tongue, 1106 development of, 1112 glands of, 1108 lymphatics of, 715 muscles of, 325, 345, 346, 502, 1110 papillaj, 1106 surgical anatomy of, 1350 variations and comparative, 1112 vessels and nerves, 1111 Tonsil (amygdala) of cerebellum, 807 Tonsillar branch of external maxillary artery, 541 of ascending palatine, 541 of glosso-pharyngeal nerve, 952 fossEe, 1131, 1132 ring (Waldeyer's), 1133 TonsUs, lingual, 1107 lymphatics of, 1132 palatine, 1132, 1351 pharyngeal, 1130, 1354 variations and comparative, 1138 vessels of, 1132 Topography of attachment of spinal nerves, 966 of brain, general, 793, 1338 of organs (see corresponding organ) Torcular Herophili, 650 Torus tubarius, 1130 Trabecute (carnese) cordis, 516 lienis, 1311 Trabecular region of skull, 117 Trachea, 1225, 1408 lymphatics of, 699, 1228 vessels and nerves, of 1228 Tracheal branches of inferior thyreoid artery, 564 cartilages, 1227 glands, 1227 veins, 661 Trachelo-mastoid, 416 Tract, anterior or direct pyramidal, 788 crossed pyramidal, 7S3 direct cerebellar (Flechsig), 784 Gower's, 784 habenulo-peduncular, 873 Loewenthal's, 786 mesencephalo-(tecto-) spinal, 786, 842 olfacto-mammillary, 873 olfacto-mesencephalic, 873 olfactory, 758, 865, 893 optic, 849 solitary, 820 spinal, nucleus of, 826 of trigeminus nerve, 828 spino-mesencephalic (spino-teotal), 786, 842 spino-thalamic, 786 thalamo-olivary, 817, 830 thalamo-spinal, 786 transverse peduncular, 835 ventral vestibulo-spinal, 786 Tractus ilio-pubicus, 430 ilio-tibialis, 457, 458 spino-teotalis, 786 Tragi, 1290 Tragus, 1082 Trans-pyloric line (Addison), 1153, 1370 Transyersalis cervicis, 416 fascia, 426 Transverse arch of foot, 1468 carpal (anterior annular) ligaments, 1427 cervical (transversa coUi) artery, 565, 638 veins, 672 colon, 1174 crest, 72 crural ligament of leg (upper part of anterior annular ligament), 479 1534 INDEX Transverse diameter of pelvic inlet, 175 facial artery, 545 vein, 646 fissure of cerebrum, 850 (Houston's) folds of rectum, 1177, 1390 fornix, 869, 890 humeral ligament, 256 ligament of central atlanto-epistrophic, 222 of heads of metatarsal bones, 309 hip-joint, 280 inferior (spino-glenoid), 253 of knee-joint, 289 of pubis, 446 superior (coracoid, or suprascapular), 253 nasal branch of dorsal nasal artery, 554 palatine suture, 106 processes of atlas, 33 of vertebrte, 31 ligaments connecting, 231 scapular (suprascapular) artery, 664, 638 veins, 648 (lateral) sinus, 651, 1331 of pericardium, 523, 527 strise of corpus callosum, 851 sulci, 108 suture, 108 Transverso-spinal muscles, 412, 419 Transversus abdominis, 424, 435 group of lateral division of thoraco-abdomi- nal muscles, 434 menti, 333 nuchae (occipitalis minor), 337 •perinei profundus, 442, 449 superficialis, 444, 452 thoracis (triangularis sterni), 424, 434 vaginae (Fvihrer), 449 Trapezium, 159, 162 Trapezius, 347, 349 clinical anatomy, 1405 Trapezoid bone, 159, 162 ligament, 251 (obhque) line, 140 Treitz, suspensory ligament of, 1164, 1376 Triangle, Bryant's, 1436 Hesselbach's, 1398 inferior carotid (tracheal), 1358 Macewen's suprameatal, 1337 of neck, posterior, 1359 of Petit, 434, 1406 rectal, 440, 1383 Scarpa's 467, 1438 submaxillary (digastric), 1357 superior carotid, 1358 urogenital, 440, 1383, 1385 Triangles, cervical, 1357 of perineum, 1383 Triangular fascia, 430 fibro-cartilage, 264 fossa of auricle, 1082 fovea of aryta^noid, 1212 ligament, urogenital diaphragm, 442, 1384 (lateral) ligaments of liver, 1185 Triangularis (depressor anguli oris), 333 sterni, 424, 434 Tributaries of veins (see corresponding vein) Triceps brachii, 374, 377, 378 surface markings, 1416 surse, 484 Tricuspid valve, 515, 516 Trigeminal foramen, 125 impression, 73 Trigeminus nerve, 934 nuclei of, 826 spinal tract of, 828 Trigona fibrosa, 518 Trigone, collateral, of lateral ventricle, 876 femoral, Scarpa's triangle, 467, 1438 Trigone of lemniscus, 832, 835 of Lieutaud, 1252 olfactory, 865 urogenital, 442, 446, 1384 vesical (of Lieutaud), 1252 Trigonum lumbale (triangle of Petit), 434 Triquetral (cuneiform), bone, 159, 161 Trochanter, great, 178 third, 181 Trochanteric of digital fossa, 178 Trochanters of femur, 178 clinical anatoiny of, 1435 Trochlea, 318, 1068 of humerus, 150 of talus, 193 Trochlear branches of supra-orbital artery, 553 fossa, 61 nerve, 835, 837, 933 process, 195 Troltsch, pouches of, 1089 True ligaments of bladder and prostate, 1252 synchondroses, 212 Trunk, articulations of, 224 costo-cervical arterial, 568 cutaneous areas of, 1020 lumbo-sacral, 1005 lymphatic, intestinal, 731 lumbar, 730 sympathetic, gangliated, 1029, 1032 thyreocervical, 564 Tuba auditiva (Eustachian tube) 74, 1089, 1092, 1354 Tubae uteriuEe (Fallopian tubes), 1269 lymphatics of, 700, 745, 1270 vessels and nerves, 1270 Tubal branch of ovarian artery, 602 branches of uterine artery, 610 Tube, auditory, (Eustachian), 74, 1089, 1092, 1354 neural, 754 Tuber caloanei, 196 einereum, 847, 848 omentale, 1184 vermis, 808 Tubercle(s), 29 adductor, of femur, 181 amygdaloid, of lateral ventricle, 877 anterior of thalamus, 845, 882 articular, of temporal bone, 71 of atlas, 32 auricular (tubercle of Darwin), 1083 of calcaneus, anterior, 195 condylar, of mandible, 97 coracoid (conoid) of clavicle, 140 cornioulate, of larynx, 1221 cuneiform, of larynx, 1221 of epiglottis, 1212, 1222 of femur, cervical, 178 genial, 95 genital, 1279 inferior thyreoid, 1211 intervenosum (of Lower), 513 labial, 1102 lacrimal, 88 malar, 95 mental, 95 olfactory, 865 pharyngeal, 54, 108 preglenoid, 71 pterygoid, 66 (spine) of pubis, 172 for the quadratus, 178 of rib, 127 scalene, 129 of scapula, infraglenoid, 143 INDEX 1535 Tubercles, of scapula, supraglenoid, 144 superior thyreoid, 1211 supratragic, 1082 of thoracic vertebrse, 37 Tubercular (posterior costo-transverse) liga- ment, 243 Tuberculum aeustioum, 815 cuneatum, 801 intervenosum (of Lower), 513 jugulare, 54 sella;, 63, 116 Tuberosity, 29 of calcaneus, 196 of clavicle, costal, 140 of cuboid, 199 of femur, gluteal, 178 of fifth metatarsal bone, 203 of first metatarsal bone, 201 of humerus, greater, 147 lesser, 147 of ilium, 171 of ischium, 172 malar, 93 of maxilla, 87, 92, 106 of navicular (scaphoid), 161, 196 of radius, 152 of tibia, 185 of ulna, 156 ungual (of third phalanx), 168 Tubes, Fallopian, 1269 Tubules, renal, 1246 seminiferous, 1256 Tubuli recti, 1256 Tunica albuguiea of testis, 1256 of penis, 1260 of spleen, 1311 propria of corium, 1286 serosa of spleen, 1310 vaginalis communis (internal spermatic or infundibuliform fascia), 1254, 1259 propria, 1254 vasculosa (of testis), 1256 Turbinate bones (conchse) 83, 84, 1205 sphenoidal, 64, 67 Turk's bundle, 832, 890 Tympanic antrum, 72, 73, 78, 1092, 1336 artery, anterior, 547 inferior, 537 superior, 548 bone, at birth, 123 branch of petrosal ganglion, 951 of stylo-mastoid artery, 544 canaheulus, 73, 108 cavity, 77, 1088 vessels and nerves, 1091 walls of, 1088 membrane, 1086 secondary, 1089, 1096 mucous membrane, 1089 nerve, 961 notch, 77 ostium of tuba auditiva, 1092 plate, 108 plexus, 951, 961, 1033, 1089 portion of temporal bone, 69, 75 sinus, 1089 sulcus, 75 veins, 696 Tympano-hyal portion of styloid process, 75, 119 Tympano-mastoid (auricular) fissure, 71, 75, Tympano-petrosal branch of tympanic plexus, 961 Tympano-stapedial syndosmosis, 1090 Tympanum, 77 bones of, 79 development of, 80 U IHna, 155 clinical anatomy of, 1419, 1422 Ulnar anastomotic branch of superficial radial nerve, 987 arterj^ 576, 640, 1423 vena3 comitantes, 671 collateral artery, inferior, 576 superior, 576 nerve, 985 collateral ligament, 259, 266 nerve, 987 line of, 1415, 1423 results of paralysis, 1424 notch (sigmoid cavity) of radius, 154 recurrent artery, volar, 577 Ulno-carpeus, 492 Ultimobranchial bodies, 1318 Umbilical artery, 609 fissure of liver, 1183 fovea, 1284 hernia, 1402 hgaments, 1250, 1252 lymphatic nodes, 733 notch, 1182 plane, 1370 recess, 675 region, 1143 vein, 675, 680 Umbilicus, clinical anatomy of, 1371 Umbo of tympanic membrane, 1087 Unciform bone, 159 process, 163 Uncinate fasciculus, 891 process of ethmoid, 83 Unci-pisiformis, 403 Uncus, 868 Ungual phalanges, 168 process of third phalanx, 168 Ungues (nails), 1293 Union, coraco-clavicular, 251 cuboideo-navicular, 303 of heads of metacarpal bones, 274 of metatarsal bones, 309 of radius with ulna, 261 scapulo-clavicular, 250 talo-oalcaneal, 301 tibio-fibular, 295 Unipenniform muscle, 315 Urachal branch of superior vesical artery, 609 Urachus, 1250, 1252, 1253, 1398 Ureter, 1248 clinical anatomy of, 1381, 1394 lymphatics of, 738, 1249 portions of, 1248 vessels and nerves of, 1249 variations and development of, 1249 Ureteral branches of renal arteries, 598 of internal spermatic artery, 601 of ovarian arteries, 602 Ureteric branches of superior vesical artery, 609 Urethra, female, 1277, 1278 lymphatics of, 742 male, 1262, 1388 lymphatics of, 740 surgical anatomy of, 1389 Urethral annulus, 1253 artery, 613 bulb, artery of, 613 carina, 1276, 1278 glands (of Littr6), 1264 lacuna3 (of Morgagni), 1264 orifice of bladder, 1263 Urinary bladder, 1249 development of, 1253 1536 INDEX Urinary bladder, parts of, 1250 lymphatics of, 700, 739, 1249 vessels and nerves of, 1253 organs, 1241 bladder, 1249 kidneys, 1241 ureters, 1249 Urogenital diaphragm, 440, 449 sinus, 1279 system, 1241 triangle, 440, 1383, 1385 trigone (triangular ligament), 442, 1384 Uterine artery, 610 branch of ovarian artery, 602 veins, 683 Utero-sacral ligaments, 1274 Utero-vaginal plexus of nerves, 1047 of veins, 683 Uterus (womb), 1271 clinical anatomy of, 1393 lymphatics of, 700, 745, 1274 masculinus, 1263 vessels and nerves of, 1274 Utricle, 1093 Utricular branch of vestibular ganglion, 950 Utriculo-ampullar division of vestibular nerve, 950 Utriculo-sacoular duct, 1094 Utriculus, prostatic, 1263 Uvula of palate, 1104, 1106, 1137 of urinary bladder, 1252 of vermis, 808 Vagina, 1274, 1277 clinical anatomy of, 1392 lymphatics of, 745, 1276 vessels and nerves of, 1276 Vagina fibrosa tendinis, 317 musculi flexoris hallucis longi, 491 flexorum digitorum longi, 491 tibialis posterior, 491 tendinis musculi extensoris carpi ulnaris, 395 digiti quinti, 395 hallucis longi, 483 pollicis longi, 395 flexoris carpi radialis, 403 pollicis longi, 403 peronsei longi plantaris, 484 tibialis anterioris, 483 tendinum musculorum abductoris pollicis longi et extensoris pollicis brevis, 395 extensoris digitorum communis et ex- tensoris indicis, 395 longi, 483 . ' . . extensorum carpi radialium, 395 flexorum communium, 403 peroneorum communis, 484 VaginEE mucosa} tendinum, 318 tendinum digitales, 491 musculorum flexorum digitorum, 403 Vaginal artery, 610 ligaments, 317 of finger, 387 nerves, 1017 of sphenoid, 63, 66 of temporal bone, 76 Vagus (pneumogastric), 954 nucleus of, 820, 822 Valentine, ganglion of, 939 Vallate (circumvallate) papillis of tongue, 1106 Vallecula cerebelli, 807 epiglottic, 1107, 1221 Sylvii, 856 Valsalva, sinus of, 518, 530 Valve (s), anal, 1177, 1390 of aorta, semilunar, 517 atrio-ventricular, 515 bicuspid (mitral), 515 of fossa navicularis, 612 of Heister, 1187 (folds) of Houston, 1390 ileo-caical (colic), 1172 mitral, 515 pulmonary semilunar, 517 sinus coronarii, 512 (of Thebesius), 612 tricuspid, 515 of veins, 528 venfe cavaj (Eustachian), 512 Valvula foraminis ovalis, 512 Variability, 25 Variations of blood-vessels, 508 arteries, 637, 639 veins, 69 of organs (see corresponding organ) Vas aberrans, 640 (ductus) deferens, 1257 Vasa aberrantia hepatis, 1184 brevia, 696 vasorum, 628 Vascular coat of eye, 1060 Vaso-motor nuclei, 822 Vastus intermedins (crureus), 468, 470 lateralis (vastus externus), 468, 470 medialis (vastus internus), 468, 470 Vater, ampulla of, 1188 corpuscles of, 1290 Vein(s) (see also "Vena"), 528 of abdominal wall, superficial, 683 accessory cephalic, 667 hemiazygos (azygos tertia), 663 popliteal, 689 portal, 678 • saphenous, 684 angular, 643 anterior auricular, 646 bronchial, 666 cardiac, 521 external spinal, 792 facial, 643, 1343 jugular, 648, 693 mediastinal, 667 parotid, 644 tibial, 688 articular of mandible, 646 ascending lumbar, 662, 663 of auricle (of ear), 1084 axillary, 671 azygos (major), 662, 693 basal, 657 basilic, 667 basivertebral, 666 brachial vense comitantes, 671 of brain, 663 bronchial, 1234 buccal, 646 cardiac (coronary), 620 central (ganglionic), 666 of retina, 659 cephalic, 667, 671 accessory, 667 cerebellar, 657, 908 cerebral, 654 chorioid, 657 ciliary, 658 circumflex, 671 of cochlear canaliculus, 652, 658 common facial, 644, 646, 693 iliac, 699 volar digital, 671 INDEX 1537 Vein(s), condyloid emissary, 652 conjunctival, 658 coronary (gastric), 675 of corpus striatum, 657 cortical or superficial cerebral, 654 costo-axillary, 671 cutaneous, 1289 cystic, 677 deep (ganglionic), 655 cervical, 661 circumflex iliac, 683 of clitoris, 683 temporal, 646 of the diploe, 648 dorsal digital (foot), 684 of clitoris; 683 lingual, 660 metacarpal, 667 metatarsal, 684 of penis, 681 duodenal, 677 of the ear, 667 emissary, 647, 649, 652, 916, 1334 episcleral, 659 ethmoidal, 659 of external acoustic (auditory) meatus, 1086 iliac, 683 jugular, 646, 693 nasal, 644 pudendal, 684 femoral, 690 vena3 comitantes, 690 femoro-popliteal, 685, 693 frontal, 644 diploic, 648 great cerebral (of Galen), 657, 923 cardiac, 520 (internal) saphenous, 684, 693 hajmorrhoidal plexus of, 683 of head and neck, 642, 693 superficial, 643 deep, 648 of heart, 520 hemiazygos (azygos minor), 662 accessory, 663 hepatic, 675 hypogastric (internal iliac), 679 ileo-colic, 677 ilio-lumbar, 680 inferior alveolar (dental), 646 cerebellar, 657 cerebral, 655 epigastric, 683 gluteal (sciatic), 680 hemorrhoidal, 683 labial, 644 laryngeal, 659 mesenteric, 678 ophthalmic, 646, 659 palpebral, 644 phrenic, 675 thyreoid, 661 infra-orbital, 646 innominate (brachio-cephalic), 641, 691, 692 intercapitular (hand), 667 of foot, 684 intercostal, 664 internal auditorj', 652, 657 cerebral, 657 jugular, 659, 691, 693 mammary, 666 maxillary, 646 pudendal; 681 spinal, 792 intervertebral, 666 Intestinal, 677 labial (of mouth), 644 Vein(s), labial (of vulva), 683, 684 lacrimal, 659 lateral circumflex, 690 sacral, 680 thoracic, 671 left colic, 678 gastro-epiploio, 677 superior intercostal, 664 lingual, 660 of lower extremity, 683, 693 lumbar, 675 of Marshall, oblique, 521, 523 masseteric, 644, 645 mastoid emissary, 647, 652 medial perforating, 690 median antibrachial, 667, 668 basilic, 669 cephalic, 668 cubital, 667 of medulla, 908 of medulla oblongata, 657, 908 meningeal, 917 middle cardiac, 520 cerebral, 655 colic, 677 hajmorrhoidal, 683 meningeal, 646 sacral, 679 temporal, 646 morphogenesis and variations, 690 muscular (of orbit), 658 of nasal cavities, 657 naso-frontal, 658 oblique (of Marshall), of left atrium. 521, 623 obturator, 680 occipital, 647 oesophageal, 661, 662 ophthalmic, 658, 659, 1075 . ophthalmo-meningeal, 655 of orbit, 658 ovarian, 674 palatine, 644 palpebral, 658 pancreatic, 677 pancreatico-duodenal, 677 parietal emissary, 649 parumbilioal, 678 pericardiac, 666 of pharynx, 659 plantar, digital, 684 metatarsal, 687 of pons, 657, 908 popliteal, 688 portal, 528, 675 development of, 694 posterior auricular, 647 bronchial, 664 external jugular, 648 spinal, 792 facial (temporo-maxillary ) , 644 labial, 683 of left ventricle, 521 mediastinal, 664 parotid, 646 superior alveolar (dental), 646 tibial, 688 profunda or deep femoral, 690 proper volar digital (hand), 671 pterygoid plexiis of, 646 pulmonary, 529, 1235 pyloric, 675 radial vena; comitantes, 671 radicular, 792, 908 renal, 673, 693 right colic, 677 gastro-epiploic, 677 1538 INDEX Vein(s), right colic, superior intercostal, 664 sigmoid, 678 scrotal, 684 small cardiac, 521 (external) saphenous, 684, 693 smallest cardiac, 521 spermatic, 674, 1259 spheno-palatine, 646 spinal, 665 splenic, 677, 1312 sterno-mastoid, 660 stylo-mastoid, 646 subclavian, 671 subcutaneous dorsal of penis, 684 sublingual, 660 submental, 644 subscapular, 671 superficial, in abdominal wall, 683 circumflex iliac, 684 epigastric, 684 of lower extremity, 683 temporal, 646 of upper extremity, 667 superior cerebellar, 657 cerebral, 654 epigastric, 666 gluteal, 680 hsemorrhoidal, 683 labial, 644 laryngeal, 659 mesenteric, 677 ophthalmic, 658 palatine, 646 palpebral, 644 phrenic, 667 thyreoid, 660 supra-orbital, 644 suprarenal, 673 systemic, 640 temporal (of diploe), 648 temporo-maxillary (posterior facial), 644 terminal (of corpus striatum), 657 thoraoo-acromial, 671 thoraoo-epigastric, 671, 1372 of thorax, 662 thymic, 661 thyreoid, 660, 1317 thyreoidea ima, 661 tracheal, 661 transverse cervical, 672 facial, 646 scapular (suprascapular), 648 tympanic, 646 cavity, 1091 ulnar venae comitantes, 671 umbilical, 675, 680 of upper extremity, 667 development of, 692 uterine, 683 vermian, 908 vertebral, 661, 664 Vesalian, 646 volar metacarpal, 671 Velum, anterior (superior) medullary, 812 interpositum, 847, 923 of palate, 1104 posterior medullary, 808 Vena canaliculi cochleae, 652, 658 cava, inferior, 672 development of, 693 superior, 641 development, 690 centralis retinae, 1065 cerebri magna (Galeni), 657 comitans n. hypoglossi, 660 septi pellucidi, 657 Venae cava?, relation to thoracic wall, 1369 Venae cavffi comitantes, 528 vorticosa;, 659, 1057, 1065 Venous arch, digital (hand), 667 lacunae of dura, 916 plexuses, vertebral, 664 sinus of sclera, 1059 sinuses, cranial, 528, 649, 916 Ventricle(s) of Arantius, 813 of brain, development of, 758 fifth, 872 fourth, 812 of heart, left, 516, 517 right, 516 of larynx (ventricle of Morgagni), 1222 lateral, of cerebral hemisphere, 873 drainage of, 1341 olfactory, 866 terminal, of spinal cord, 775 third, of brain, 846 Verga's, 869 Ventricular appendix (laryngeal saccule), 1223 folds (false vocal cords), 1222 ligament of larynx, 1215 musculature, 518 muscle of larynx, 1220 Ventro-lateral fasciculus, superficial, 770 Verga's ventricle, 869 Vermiform process (appendix), 1173, 1378 fossa, 53, 117 Vermis of cerebellum, 805 furrowed bands of uvula of, 808 inferior, 807, 808 pyramid of, 808 superior, 806 tubes, 808 uvula of, 808 Vernix caseosa, 1299 Vertebra prominens, 35 structure of, 45 Vertebra(a3), 29 articulations of bodies of, 225 cervical, 30, 31 coccygeal, 30, 42 lumbar, 30, 39 ossification of, 45 thoracic (dorsal), 30, 36 Vertebral artery, 559, 638 articulations, 225 branches of lumbar arteries, 593 canal (spinal), 31 arteries of, 590 venous plexuses of, 664 column, 29 as a whole, 43 foramen, 31 groove, 43 levels, 1409 ligaments, 228 notches, 30 plexus of nerves, 1037 portion of vertebral artery, 560 spines, 1403 Vertebro-occipital muscle, 412, 417 Vertex of urinary bladder, 1250 Vesalian vein, 646 Vesahus, foramen of, 66, 116 Vesical arteries, inferior, 609 middle, 609 superior, 609 branch of obturator artery, 608 nerves, inferior, 1017, 1047 superior, 1047 plexus of nerves, 1047 of veins, 683 portion of ureter, 1249 vein, 661 Vesicle(s), brain, 755 INDEX 1539 Vesicles, optic, 758 of thyreoid gland, 1316 Vesicula; seminales, 1257, 1387 lymphatics, 744 Vessels (see "Blood-vessels," "arteries," "veins," "lymphatic vessels"). Vestibular branch of stylo-mastoid artery, 544 csecum, 1096 conduction paths, 899 fenestra, 73, 1089 ganglion (gangUon of Scarpa), 823, 950 glands, 1278 membrane (membrane of Reissner), 1096 nerve, 949 nuclei of, 823 slit, 1222 Vestibule (of temporal bone), 80 of larynx, 1221 of nose, 1204 oral, 1100 of vagina, 1277, 1392 Vestibulo-spinal fasciculus, 786 VibrisssB, 1204, 1290 Vicq d'Azyr, bundle of, 871 Vidian artery, 549 canal, 103, 107, 108, 126 nerve (n. canalis pterygoidei), 962 Villi, pleural, 1237 of small intestine, 1166 Vincula tendinum, 399, 401 Visceral bars, metamorphosis of, 119 lymphatic nodes of thorax, 724 vessels of abdomen, and pelvis, 733 Visual area of cerebral cortex, 893 Vitreous body or humor of eye, 1052, IO64 lamina of chorioid, 1026 Vocal folds (cords), false, 1222 true, 1223 ligaments, 1215 lip, 1223 muscle, 1220 process of arytenoid cartilage, 1212 Volar arch, deep, 586, 639, 1426 venous, 671 superficial, 682, 639, 1425 venous, 671 artery, superficial, 584 carpal rete (arch), 579, 581 digital veins, 671 interosseous artery of forearm, 577 (anterior) interosseous nerve, 992 ligament, accessory (or glenoid), 274 metacarpal arteries, 586 veins, 671 musculature, 363 perforating branches of radial artery, 586 radial carpal artery, 584 (anterior) radio-carpal ligament, 266 ulnar carpal artery, 580 Vomer, 85 Vomero-nasal organ (of Jaoobson), 1051, 1204 Vortices of hair, 1291 Vulva (external female genitalia), 1276 W Waldeyer's tonsillar ring, 1133 Wallerian degeneration, 780 Wharton's duct, 1116 White commissures of spinal cord, 776 ramus communicans, 1030 substance of nervous system, 768 of spinal cord, 775, 777 of telencephalon, 885 Whitlow, 1431 Willis, circle of (circulus arteriosus), 555 chords of, 649 Wings of sphenoid, 62 great or temporal, 65 small or orbital, 64 Winslow, foramen of, 1147 Wirsung, duct of, 1194 Wisdom teeth, 1122 Wolffian body, 1278 duct, 1248, 1267, 1278 Word-blindness, 895 Wormian bone, 68 Wrinkles of skin, 1284 Wrisberg, cardiac ganglion of, 1041 cartilages of, 1213 lingula of, 942 nerve of, 946, 983 Wrist, bony points of, 1424 clinical anatomy of, 1424 Wrist-joint, 265 Xiphoid branch of superior epigastric artery, 567 process, 132, 134 Yellovc spot (macula lutea), 1055 of larvnx, 1223 Yolk-sac, 10, 13 Zeiss's glands, 1078 Zinn, ligament of, 1067 Zona fasoiculata, 1326 glomerulosa, 1326 reticulata, 1326 Zone(s), marginal, of Lissauer, 782 mixed lateral, 784 Zonula oiliaris, 1064 Zonular spaces, 1064 Zygapophysis, 57 Zygomatic arch, 1332 bone (malar), 93 at birth, 124 branches of lacrimal artery, 552 (orbital or temporo-malar) of maxillary nerve, 938 (malar) of temporo-facial nerve, 945 fossa, 101, 1332 process, 70, 87, 88 Zygomatico-facial (malar) branch of maxillary nerve, 938 canals, 126 Zygomatioo-orbital artery, 545 canals, 94 Zygomatico-temporal (temporal) branch of maxillary nerve, 938 foramen, 126 Zygomaticus (zygomaticus major), 333 minor, 332 COLUMBIA UNIVERSITY LIBRARIES (hsLstx) QM 23 IV183 1914 C.1 Morris's human anatomy 2002191202 QM27j Hvunan anatomy UBz 1914 MAR 2 0 1944 '=i^' <> (^-^J^^<^ T)r '\