HX00014990 RECAP College of ^fjpsitians ani ^ursconsf ILibrarp Digitized by tine Internet Arcliive in 2010 witli funding from Open Knowledge Commons (for the Medical Heritage Library project) http://www.archive.org/details/humananatomyincl19191pier Ihe skeleton in relation to the contour of the body. HUMAN ANATOMY INCLUDING STRUCTURE AND DEVELOPMENT AND PRACTICAL CONSIDERATIONS THOMAS DWIGHT, M.D., LL.D. J. PLAYFAIR McMURRlCH, PH.D. N HARVARD PROFESSOR OF CARL A. HAMANN, M.D. GEORGE A. PIERSOL, M.D., SC.D. J. WILLIAM WHITE, M.D., PH.D., LL.D. JOHN RHEA BARTON PROFESSOR OF SURGERY IN THE UNIVERSITY OF PENNSYLVANIA WITH SEVENTEEN HUNDRED AND THIRTY-FOUR ILLUSTRATIONS. OF WHICH FIFTEEN HUNDRED AND TWENTY-TWO ARE ORIGINAL AND LARGELY FROM DISSECTIONS BY JOHN C. HEISLER, M.D. PROFESSOR OF ANATOMY IN THE MEDICO-CHI RURGICAL COLLEGE EDITED BY GEORGE A. PIERSOL VOL. I. SEVENTH EDITION PHILADELPHIA & LONDON J. B. LIPPINCOTT COMPANY Copyright, 1906, 1907, 1908, 191 1, 1913, 1916, 1918, 1919, by J. B. Lippincott Company. Entered at Stationers' Hall, London, England. All liiijhls Reserved. 61 ^'^ '^3 ELECTItOTTPED AND PRINTED BY J. B. LIPPINCOTT COMPANY, PillLADELrHIA, U. 3. A. PREFACE. The preparation of this work was undertaken \\ith three chief considerations in mind. i. The presentation of the essential facts of human anatomy, regarded in its broadest sense, by a descriptive text which, while concise, should be sufficiently com- prehensive to include all that is necessary for a thorough understanding not only of the gross appearances and relations of the various parts of the human body, but also of their structure and development. 2. Adequate emphasis and explanation of the many and varied relations of anatomical details to the conditions claiming the atten- tion of the physician and surgeon. 3. The elucidation of such text by illustrations that should portray actual dissections and preparations with fidelity and realism. To the first of these ends the co-operation of several American teachers of anatomy was enlisted, whose contributions have been welded into a homogeneous whole. Dr. Thomas Dwight has written the description of the skeleton, including the joints, and that of the gastro-pulmonary system and of the accessory organs of nutrition. Dr. Carl A. Hamann has contributed the account of the cerebro-spinal and sympathetic nerves. Dr. J. Playfair McMurrich has supplied the systematic description of the mus- cular and of the blood- and lymph-vascular system. Dr. George A. Piersol has written the introductory, histological and embryolog- ical paragraphs throughout the work and contributed the description of the central nervous S)'stem, including the deep relations of the cranial nerves, of the organs of special sense, of the carotid, coccygeal and aortic bodies, and of the uro-genital system. The second desideratum — adequate consideration of the practical applications of anatomy — has been ensured by the co-operation of Dr. J. William White, whose ripe experience, both as a surgeon and as a teacher of surgery, has enabled him to point out with unusual force the relations of anatomy to the requirements of the practitioner, and to associate for the benefit of the student anatomical facts with those conditions, resulting from injury or disease, that these facts elucidate. While no attempt has been made to cover the field of operative surgery, brief descriptions of operative methods have been given when they have seemed, necessary to complete the study of an anatomical region or of an important organ. Occasion- ally a relatively rare operation has been included because of the exceptional practical importance of the subject from an anatomical standpoint. The writer of the Practical Considerations has aimed at presenting, in connection with each organ or system, enough facts illustrative of the dependence of the diag- nostician and practitioner upon anatomical knowledge to awaken interest and to com- bat the tendency to regard anatomy as something to be memorized during student days and forgotten when examinations are over. E\-en when such facts do not seem at a first glance to come within the scope of a text-book of anatomy, it will be found that a careful comparison of this text with the descriptive portion of the book will show a real and practical relation between them — a relation which, once established vi PREFACE. in the minds of the student and the physician, will make it easier for the former to learn his anatomy and for the latter to remember and apply it. Dr. White desires to acknowledge fully his obligations to the e.xisting treatises on applied anatomy and to the various text-books and encyclopedias on surgery and medicine from which many valuable suggestions were gathered. To Drs. Gwilym G. Davis and T. Turner Thomas, his thanks are due for a careful search for possible errors, for friendly criticism, and for help in the selection of illustrations. The illustrations for the anatomy — a matter of fundamental importance in a work of this character — have received most conscientious attention. The determination to produce a series of original drawings that should faithfully record the dissections and preparations as they actually appear, and not as diagrammatic figures, has involved an expenditure of time and painstaking effort that only those having experience with similar tasks can appreciate. When it is stated that considerably more than two thousand original drawings have been made in the preparation of the figures illus- trating the work, some conception will be had of the magnitude of this feature. In the completion of this labor the editor has been most fortunate in having the assistance of Dr. John C. Heisler, to whose skill and tireless enthusiasm he is indebted for the admirable dissections from which most of the illustrations of the muscles, blood-vessels, nerves, perineum and inguinal region were drawn, as well as for many suggestions for and revision of the drawings themselves. Professor Gwilym G. Davis has also rendered valuable assistance in supplying the dissections for the drawings relating to the Practical Considerations, as well as in super\-islng that portion of the artist's work. In addition to the numerous dissections and preparations made especially for the illustrations, advantage has been taken of the rich collections in the museums of the Medical Department of the University of Pennsylvania, of the Harvard Medical School and of the Wistar Institute of Anatomy, which were kindly placed at the editor's service. Records of the dissections, in many cases life size, were made in water colors chiefly by Mr. Hermann Faber, whose renditions combine faithful drawing with artistic feeling to a degree unusual in such subjects. The records not made by the last-named artist are from the brush of Mr. Ludwig E. Faber. The translations of the colored records into black and white, from which the final blocks have been made, as well as the original drawings of the bones and of the organs, have been made by Mr. Erwin F. Faber. To the conscientious and tireless efforts of this artist are due the technical beauty that distinguish these illustrations. Mr. J. H. Emerton drew the joints, as well as some figures relating to the gastro-pulmonary system, from dissections and sections supplied by Professor Dwight. The numerous illustrations representing the histological and embryological de- tails throughout the work, and in addition the sections of the brain-stem under low magnification, are by Mr. Louis Schmidt. In all cases sketches with the camera lucida or projection lantern or photographs have been the basis of these drawings, the details being faithfully reproduced by close attention to the original specimens under the microscope. Notwithstanding the unusually generous allotment of drawings from original dissections and preparations, advantage has also been taken of a number of illus- trations which have appeared in special monographs or in foreign journals or works. With very few exceptions such borrowed illustrations have been redrawn and modi- fied to meet the present requirements, due acknowledgment in all cases being given. PREFACE. vif The editor gratefully acknowledges the many kindnesses shown by a number of his associates. Dr. William G. Spiller generously placed at his disposal a large collection of microscopical preparations of the central nervous system, from which drawings of selected sections were made. To Dr. George Fetterolf the editor is indebted for valuable assistance in preparing for and seeing through the press the section on the peripheral nervous system. The collaboration of Dr. Edward A, Shumway very materially facilitated the preparation of the description of the eye, which received only the editor's revision. Likewise, Dr. Ralph Butler, by placing in the editor's hands a painstaking review of the more recent literature on the ear and preliminary account of that organ, gready lightened the labor of writing the text. Further, Dr. Butler supplied the microscopical preparations from which several of the drawings were made. In addition to assuming the preparation of the index — a no insignificant undertaking in a work of this character — Dr. Ewing Taylor gave valu- able assistance in the final revision of the first hundred pages of the book. The editor is indebted to Dr. W. H. F. Addison for repeated favors in preparing special microscopical specimens. Dr. T. Turner Thomas kindly assisted in locating cross- references. This opportunity is taken to express full appreciation and thanks to the various authors and publishers, who so kindly have given permission to use illus- trations which have appeared elsewhere. Very earnest consideration of the question of nomenclature led to the conclusion, that the retention, for the most part, of the terms in use by English-speaking anatomists and surgeons would best contribute to the usefulness of the book. While these names, therefore, have been retained as the primary terminology, those adopted by the Basle Congress have been included, the BNA synonyms appear- ing in the special type reserved for that purpose. The constant aim of the editor has been to use the simplest anatomical terminology and preference has always been given to the anglicized names, rather than to the more formal designations. Although in many cases the modifications suggested by the new terminology have been followed with advantage, consistent use of the Basle nomenclature seems less in accord with the conceded directness of English scientific literature than the enthusi- astic advocates of such adoption have demonstrated. The editor desires to express his appreciation of the generous support given him by the publishers and of the unstinted facilities placed by them at his disposal throughout the preparation of the work. University of Pennsylvania, September, 1907. CONTENTS. VOL. I. INTRODUCTION. Relation of Anatomy to Biology . . Subdivisions of Anatomical Study General Plan of Vertebrate Construction Descriptive Terms THE ELEMENTS OF STRUCTURE. The Elementary Tissues 5 The Cells and Intercellular Sub- stances 5 The Embryonal Cell 5 Vital Manifestations 6 Metabolism 6 Growth 5 Reproduction 6 Irritability The Animal Cell Structure of the Cytoplasm . Structure of the Nucleus . . The Centrosome Division of Cells Mitotic Division Amitotic Division EARLY DEVELOPMENT. The Ovum The Spermatozoon Maturation of the Ovum Fertilization of the Ovum Segmentation of the Ovum The Blastoderm and the Blastodermic Layers : . . . Derivatives of the Blastodermic Layers. . The Primitive Streak and the Gastrula. . The Significance of the Primitive Streak. . The Fundamental Embryological Pro- cesses The Neural Canal The Notochord The Coelom The Somites The Fcetal Membranes The Amnion The Serosa The \'itelline Sac The Allantois and the Chorion The Human Fcetal Membranes 35 The Amnion and Allantois 35 The Chorion 41 The Amniotic Fluid 41 The Llmbilical Vesicle 42 The Deciduae 44 The Trophoblast 46 The Decidua Vera 46 The Decidua Placentalis 48 The Placenta 49 The Umbilical Cord 53 The After-Birth • 55 Development of Body-Form 56 The Stage of the Blastodermic Ves- icle 56 The Stage of the Embryo 56 The Visceral Arches and Fur- rows 59 The Development of the Face . . 62 The Stage of the Foetus 63 THE ELEMENTARY TISSUES. The Epithelial Tissues Squamous Epithelium Columnar Epithelium Modified Epithelium Specialized Epithelium Endothelium The Connective Tissues The Cells of Connective Tissue. . . . The Intercellular Constituents Fibrous Tissue Reticular Tissue Elastic Tissue Development of Connective Tissue Tendon Adipose Tissue Cartilage The Connective Tissues — Continued Hyaline Cartilage Elastic Cartilage Fibrous Cartilage Development of Cartilage . . . Bone Chemical Composition Physical Properties Structure of Bone Bone Marrow ' Red Marrow Vellow Marrow Development of Bone Endochondral Bone Membranous Bone Subperiosteal Bone THE SKELETON, INCLUDING THE JOINTS. The A.xial Skeleton 103 The Appendicular Skeleton 104 General Considerations of the Bones. .. . 104 General Considerations of the Joints , The Spinal Column The Thoracic Vertebrse 107 114 "5 CONTENTS. The Thoracic Vertebrae — Continued The Cervical Vertebrje ii6 The Lumbar \'ertebr2e 117 PecuHar Vertebras 119 Dimensions of Vertebra 122 Gradual Regional Changes 122 The Sacrum 124 The Coccyx 127 Development of the \'ertebrae 1 28 Variations of the \'ertebrae 131 Articulations of the \'ertebral Column . . 132 Ligaments Connecting the Bodies . . 132 Ligaments Connecting the Lamina; and the Processes 133 Articulations of the Occipital Bone, the Atlas and the Axis 135 The Spine as a Whole 138 Dimensions and Proportions 141 Movements of the Head 142 Movements of the Spine 142 Practical Considerations : The Spine.... 143 Curvature of the Spine 144 Sprains, Dislocations and Fractures . 144 Landmarks 146 The Thorax 149 The Ribs 149 The Costa! Cartilages 153 The .Sternum i55 Articulations of the Thorax 157 The Anterior Thoracic Articulations . 1 58 The Intersternal Joints 159 The Costo-Sternal Joints 160 The Interchondral Joints 160 The Costo-X'ertebral Articulations. . 160 The Thorax as a Whole 162 The Movements of the Thorax 165 Practical Considerations : The Thorax . . 167 Defor-mities 167 Fractures and Disease of the Ribs . . 169 Landmarks 17° The Skull 172 The Cranium 172 The Occipital Bone 172 The Temporal Bone 176 The Tympanic Cavity 1S3 The Sphenoid Bone 1S6 The Ethmoid Bone 191 The Frontal Bone 194 The Parietal Bone 197 The Bones of the Face 199 The Superior Maxilla 199 The Palate Bone 204 The Vomer 205 The Lachrymal Bone 207 The Inferior Turbinate Bone 20S The Nasal Bone 209 The Malar Bone 209 The Inferior Maxilla 211 The Temporo-Maxillary Articulation. . . . 214 The Hyoid Bone 216 The Skull as a Whole 216 The Exterior of the Cranium 218 The Interior of the Cranium 220 The Architecture of the Cranium . . . 220 The Face 222 The Orbit 222 The Nasal Cavity 223 The Accessory Pneumatic Cav- ities 226 The Architecture of the Face . . . 228 The Anthropology of the Skull 228 Practical Considerations : The Skull .... 235 The Cranium 235 Pract. Consid.: The Skull — Conthuu-d Malformations 235 The Wormian Bones 236 Diseases of the Cranial Bones . . 237 Fractures 238 Landmarks 240 The Face 242 Deformities and Fractures 243 Dislocation of the Jaw 246 Landmarks 246 The Bones of the Upper Extremity 24S The Shoulder-Girdle 248 The Scapula 248 Practical Considerations 253 Malformations 253 Fractures and Disease 254 Landmarks 255 Ligaments of the Scapula 256 The Clavicle 257 Practical Considerations 258 Malformations 259 Fractures and Disease 259 Landmarks 260 The Sterno-Clavicular Articulation . . 261 The Coraco-Clavicular Ligament . . . 262 Movements of the Clavicle and Scap- ula 262 Surface Anatomy of the Shoulder- Girdle 263 Practical Considerations 263 The Sterno-Clavicular Articula- tion 263 The Acromio-Clavicular Articu- lation 264 The Humerus 265 Practical Considerations 270 Malformations 270 Separation of the Epiphyses .... 271 Fractures and Disease 273 The Shoulder-Joint 274 Practical Considerations 278 Dislocations and Diseases 278 Landmarks 280 ■The Ulna 281 Practical Considerations 285 Malformations 2S5 F'ractures 286 Landmarks .. . 2S7 The Radius 287 Practical Considerations 293 Malformations 293 Fractures and Disease 294 Landmarks 296 The Radio-Ulnar Articulations 297 The Forearm as a Whole 299 The Elbow-Joint 301 Practical Considerations 305 Dislocations and Disease 305 Landmarks 308 The Bones of the Hand 309 The Carpal Bones 309 The Metacarpal Bones 314 The Phalanges 317 Practical Considerations 319 The Carpus 319 The Metacarpus 319 The Phalanges 320 Landmarks 320 Ligaments of Wrist and Metacarpus .... 320 Movements and Mechanics of Wrist and Carpo-Metacarpal Articu- lations 326 Surface Anatomy of Wrist and Hand 328 CONTENTS. Practical Considerations: The Wrist- Joint 329 Landmarks 330 Tlie Joints of the Carpus, Metacarpus ^ and Phalanges 330 The Bones of the Lower Extremity 332 The Pelvic Girdle 332 The Innominate Bone 332 Joints and Ligaments of the Pelvis. . 337 The SacroTliac Articulation. .. . 33S The Symphysis Pubis. 339 The Sacro-Sciatic Ligaments . . 339 The Pelvis as a Whole 341 Mechanics of the Pelvis 342 Surface Anatomy 345 Practical Considerations: The Pelvis . . 345 Malformations 345 Fractures and Disease 346 Landmarks 349 Joints of the Pelvis 350 The Femur 352 Surface Anatomy 360 Practical Considerations: 361 The Epiphyses 361 Fractures and Disease 363 Landmarks 366 The Hip-Joint 367 Practical Considerations 374 Outward or Posterior Luxations. .. . 375 Inward or Anterior Luxations 377 Congenital Luxation 3S0 Disease of the Hip-Joint 380 The Framework of the Leg 382 The Tibia 382 Practical Considerations 387 Separation of the Epiphyses 3S7 Fractures and Disease 389 Landmarks 390 PAGS The Fibula 391 Practical Considerations 393 Separation of Upper Epiphysis.... 393 Fractures and Disease 394 Landmarks 396 Connections of the Tibia and Fibula. . . . 396 The Bones of the Leg as one Apparatus 397 The Patella ' 398 The Ligamentum Patellss 400 The Knee-joint 400 Practical Considerations : The Knee- joint 409 Dislocations 409 Subluxation of Semilunar Cartilages 411 Disease of Knee-joint 412 The Patella 416 The Bones of the Foot 419 The Tarsal Bones 419 The Metatarsal Bones 42S The Phalanges 432 Practical Considerations : The Foot- Bones 436 Fracture, Dislocation and Disease. . 437 Landmarks 437 The Ankle-joint 43S The Articulations of the Foot 440 Intertarsal Joints 445 Tarso-Metatarsal Joints 446 Metatarso-Phalangeal Joints 447 Synovial Cavities 447 The Foot as a Whole 447 Surface Anatomy 449 Practical Considerations: The Ankle- Joint 450 Dislocations and Disease 450 Tarsal, Metatarsal and Phalangeal Joints 451 Landmarks 453 THE MUSCULAR SYSTEM. Muscular Tissue in general 454 Nonstriated or Involuntary Muscle. . 454 Structure 455 Development 457 Striated or Voluntary Muscle 457 General Structure 45S Structure of the Muscle-Fibre. . 459 Cardiac Muscle 462 Development of Striated Muscle. 465 Myomeres and their Modifica- tions 467 General Consideration of the Muscles. . . . 46S Attachments 468 Form 469 Fasciae 470 Tendon-Sheaths 470 Bursse 471 Classification 471 Nerve-Supply ' 473 The Branchiomeric Muscles 474 The Trigeminal Muscles 474 Muscles of Mastication 474 Submental Muscles 477 Trigeminal Palatal Muscle 479 Trigeminal Tympanic Muscle 479 The Facial Muscles 479 Hyoidean Muscles 4S0 Platysma Muscles 4S0 Superficial Layer 4S1 Deep Layer 486 Practical Considerations : Muscles and Fascise of Cranium 4S9 The Scalp., 4S9 The Face 492 Landmarks 494 The Vago- Accessory Muscles 495 Muscles of Palate and Pharynx 495 Muscles of Larynx .. Vol. 11 1824 Trapezius Muscles 499 The Metameric Muscles 502 The Axial Muscles 502 Orbital Muscles 502 Fascial of Orbit 504 Movements of Eyeball 505 Hypoglossal Muscles 506 The Trunk Muscles 507 The Dorsal Muscles 507 Transverso-Costal Tract 508 Transverso-Spinal Tract 511 The Ventral Muscles 515 Abdominal Muscles 515 Rectus Muscles 516 Obliquus Muscles 517 Ventral Aponeurosis 521 Inguinal Canal 523 Anterior Abdominal Wall . . 525 Hyposkeletal Muscles 526 Practical Considerations : The Abdo- men 526 The Loin 530 CONTENTS. Practical Considerations — Coa/inucd Landmarks a nd Topography o f Abdomen 531 Anatomy of Abdominal Incisions. . . 535 Examination of Abdomen 537 The Thoracic Muscles 538 Rectus Muscles 53S Obliquus Muscles 53S Hyposkeletal Muscles 542 Tl;e Cervical Muscles 542 The Deep Cervical Fascia 542 Rectus JIuscles 543 Obliquus Muscles 546 Triangles of the Neck 547 Hyposkeletal Muscles 548 Practical Considerations : The Neck.... 550 Cervical Fascia and its Spaces 551 Landmarks 554 The Diaphragm 556 The Pelvic and Perineal ^luscles 558 Pelvic Fascia 55S Obturator Fascia 559 Pelvic Muscles 559 Perineal Muscles 562 The Appendicular Muscles 566 The Muscles of the Upper Limb 56S Muscles e.xtending between A.xial Skele- ton and Pectoral Girdle 56S Pectoral Fascia 568 Prea.xial Muscles 56S Postaxial Muscles 571 The A.xilla 574 Muscles passing from Pelvic Girdle to Brachium 575 Preaxial Muscles 575 Postaxial Muscles 575 Practical Considerations : Muscles and Fascia of Axilla and Shoulder. . 579 Fracture of Clavicle 579 Dislocation of Shoulder- Joint 582 The Brachial Muscles 585 Preaxial Muscles 585 Postaxial Muscles 5S8 Practical Considerations : Muscles and Fascia of the Arm 5S9 Fractures of Humerus 590 The Antibrachial Muscles 591 Preaxial Muscles 592 Postaxial Muscles 598 Practical Considerations : The Forearm. 603 The Muscles of the Hand 606 Deep Fascia 606 PAGE The Muscles of the Hand — Co>i/i>iiicd Preaxial Muscles 607 Muscles of First Layer 607 Muscles of Second Layer 610 Muscle of Third Layer 610 Muscles of IV and Y Layers. . . . 611 Postaxial Muscie 613 Pract. Consid. : The Wrist and Hand.. . 613 Palmar Abscesses 616 Dislocation of Thumb 617 Surface Landmarks of Upper Extremity . 618 The Muscles of the Lower Limb 623 Muscles extending from Pelvic Girdle to Femur 623 Preaxial Muscles 623 Postaxial Muscles 630 The Femoral Muscles 633 Fascia Lata 633 Preaxial Muscles 636 Postaxial Muscles 639 Practical Considerations : Muscles and Fasciae 641 The Buttocks 641 The Hip and Thi.gh 642 Fractures of the Femur 644 The Knee 645 Bursae of Popliteal Region 646 The Crural Muscles 647 The Crural Fascia 647 Preaxial Muscles 648 Superficial Layer 649 IMiddle Layer 651 Deep Layer 654 Postaxial Muscles 655 The Muscles of the Foot 659 The Plantar Fascia 659 Preaxial Muscles 659 First Layer 660 Second Layer 662 Third Layer 662 Fourth and Fifth Layers 663 Postaxial Muscles 665 Practical Considerations : Muscles and Fasciae 665 The Leg 665 The Ankle and Foot 666 Club-Foot 667 Surface Landmarks of Lower Extremity 669 The Buttocks and Hip 669 The Thigh 670 The Knee 671 The Leg 671 The Ankle and Foot 672 THE VASCULAR SYSTEM. The Blood-\'.ascul,\r System. The Structure of Blood-Yessels 673 The Arteries 675 The Veins 677 The Capillaries 67S The Blood .' .' 680 General Characteristics 680 Blood-Crvstals 680 The Colored Blood-Cells '.'. 681 The Colorless Blood-Cells 684 The Blood-Plaques 685 Development of Blood-Yessels and Cells 686 The Heart 6S9 General Description 689 Position and Relations 6g2 Chambers of the Heart 693 Architecture of the Heart-Muscle.. . 700 Structure 702 Blood-Yessels and Lymphatics 703 Nerves 704 Development 705 Practical Considerations: The Heart.... 710 \'alvular Disease 711 Rupture and Wounds 713 The Pericardium 714 CONTENTS. Practical Considerations: The Pericar- dium 717 The General Plan of the Circulation .... 719 The Arteries 719 General Plan of Arterial System. .. . 720 The Pulmonary Aorta 722 The Systemic Aorta 723 The Aortic Arch 723 Practical Considerations: Aortic Arch and Thoracic Aorta 726 Surface Relations 726 Aneurisms 727 The Coronary Arteries 72S The Innominate Artery 729 Practical Considerations 729 The Common Carotid Arteries 730 Practical Considerations 731 The E.\ternal Carotid Artery 733 Practical Considerations 733 Branches of E.xternal Carotid Ar- tery 734 The Internal Carotid Artery 746 Practical Considerations 747 Branches of Internal Carotid Ar- tery 74S Anastomoses of Carotid System. .. . 753 The Subclavian Artery 753 Practical Considerations. 756 Branches of Subclavian Artery 758 The Axillary Artery ' 767 Practical Considerations 769 Branches of Axillary Artery 771 The Brachial Artery 773 Practical Considerations 775 Branches of Brachial Artery 777 The Ulnar Artery 778 Practical Considerations 7S0 Branches of Ulnar Artery 7S1 The Radial Artery 785 Practical Considerations 786 Branches of Radial Artery 787 The Thoracic Aorta 791 Branches of Thoracic Aorta 792 The Abdominal Aorta 794 Practical Considerations 796 The Visceral Branches 797 The Parietal Branches 805 The Common Iliac Arteries 807 Practical Considerations 807 The Internal Iliac Artery 808 Practical Considerations 810 Branches of Internal Iliac Artery. .. . 810 The External Iliac Artery 818 Practical Considerations 819 Branches of External Iliac Artery. . . 820 The Femoral Artery S21 Practical Considerations S24 Branches of Femoral Artery 826 Anastomoses of Femoral Artery . . . S31 The Popliteal Artery 831 Practical Considerations 832 Branches of Popliteal Artery S33 The Posterior Tibial Artery 835 Practical Considerations 836 Branches of Posterior Tibial Artery. 83S The Anterior Tibial Artery S42 Practical Considerations. 842 Branches of Anterior Tibial Artery, S44 The Dorsal Artery of the Foot S45 Development of the Arteries 846 The Veins 850 General Characteristics 850 Classification S52 The Pulmonary System _ S52 The Pulmonary Veins 852 The Cardinal System 854 The Cardiac Vems 854 The Superior Caval System 857 Vena Ca\-a Superior 857 Practical Considerations 85S The Innominate Veins 85S Practical Considerations 859 Tributaries of Innominate Veins .... 859 The Internal Jugular Vein S61 Practical Considerations 863 Tributaries of Internal Jugular Vein. S63 The Sinuses of the Dura Mater 867 Practical Considerations 869 The Diploic Veins 874 Practical Considerations 875 The Emissary Veins 875 Practical Considerations 876 The Cerebral Veins 877 Practical Considerations 87S The Ophthalmic Veins S79 Practical Considerations 8S0 The External Jugular Vein S80 Practical Considerations 881 Tributaries of External Jugular Vein 882 The Subclavian Vein 884 Practical Considerations 885 Veins of the Upper Limb 886 The Deep Veins 886 The Superficial Veins SS9 Practical Considerations 891 The Azygos System S93 The Azygos Vein S93 Tributaries 893 Practical Considerations 895 The Hemiazygos Vein 895 The Accessory Hemiazygos Vein. . 895 The Intercostal Veins 896 The Spinal Veins 897 Practical Considerations 898 The Veins of the Spinal Cord 898 The Inferior Caval System 898 Vena Cava Inferior 899 Practical Considerations 900 Tributaries of Inferior Cava. .. . got Practical Considerations . . . ■ 904 The Common Iliac Veins 905 The Internal Iliac Veins 905 Tributaries of Internal Iliac .... 905 The External Iliac Vein 909 Tributaries of External Iliac. . . . 909 The Veins of the Lower Limb 910 The Deep Veins 910 The Superficial Veins 914 Practical Considerations of Iliac Veins and Veins of Lower Limb 917 The Portal System 919 The Portal Vein 919 Tributaries of Portal Vein 920 Practical Considerations 925 Development of the Veins 926 The Fcetal Circulation 929 The Lymphatic System. General Consideration 931 Lymph-Spaces 931 Lymph-Capillaries 933 Lymph-Vessels 934 Lymph-Nodes 935 Structure of Lymphoid Tissue 936 Development of Lymphatic Vessels and Tissues 939 CONTENTS. PAGE The Thoracic Duct 941 Practical Considerations 944 The Right Lymphatic Duct 945 The Lymphatics of the Head 945 The Lymph-Nodes 945 The Lymph- Vessels 949 Practical Considerations 955 The Lymphatics of the Neck 957 The Lymph-Nodes 957 The Lymph-Vessels 95S Practical Considerations 959 The Lymphatics of the Upper Limb .... 961 The Lymph-Nodes 961 The Lymph- Vessels 963 Practical Considerations 965 PAGH The Lymphatics of the Thorax 966 The Lymph-Nodes 966 The Lymph-Vessels 968 Practical Considerations 971 The Lymphatics of the Abdomen 972 The Lymph-Nodes 972 The Lymph-Vessels 976 The Lymphatics of the Pelvis 983 The Lymph-Nodes 983 The Lymjjh -Vessels 984 Practical Considerations 990 The Lymphatics of the Lower Limb .... 991 The Lymph-Nodes 991 The Lymph-Vessels 993 Practical Considerations 994 VOLUME I. GENERAL CONSIDERATIONS THE CELL EARLY DEVELOPMENT THE ELEMENTARY TISSUES THE SKELETON THE BONES THE ARTICULATIONS THE MUSCULAR SYSTEM THE VASCULAR SYSTEM THE HEART THE ARTERIES THE VEINS THE LYMPHATICS HUMAN ANATOMY. Anatomy is that subdivision of morphology — the science of form as contrasted with that of function or physiology — which pertains to the form and the structure of organized beings, vegetal or animal. Phytotomy and Zootomy, the technical names for vegetal and animal anatomy respectively, both imply etymologically the dissocia- tion, or the cutting apart, necessary for the investigation of plants and animals. The study of organized bodies may be approached, evidently, from several stand- points. When the details of the structure of their various tissues and organs par- ticularly is investigated, such study constitutes General Anatomy or Histology, fre- quently also called Microscopical Anatomy, from the fact that the magnifying lens is used to assist in these examinations. The advantages of comparing the organization of various animals, representing widely different types as well as those closely related, are so manifest in arriving at a true estimate of the importance and significance of structural details, that Comparative Anatomy constitutes a department of biological science of far-reaching interest, not merely for the morphologist, but likewise for the student of human anatomy, since we are indebted to comparative anatomy for an intelligent conception of many details encountered in the human body. Devel- opmental Anatomy, or Embryology, also has been of great service in advancing our understanding of numerous problems connected with the adult organism by tracing the connection between the complex relations of the completed structures and their primitive condition, as shown by the sequence of the phases of development. These three departments of anatomical study — general, comparative, and developmental anatomy — represent the broader aspects of anatomical study in which the features of the human body are only incidents in the more extended contemplation of organized beings. The exceptional importance of an accurate knowledge of the body of man has directed to human anatomy, or aiitkropotomy , so much attention from various points of view that certain subdivisions of the subject are conveniently recognized ; thus, the systematic account of the human body is termed Descriptive Anatomy, while when the mutual relations and peculiarities of situation of the organs located in par- ticular parts of the body especially claim attention, such study is spoken of as Topo- graphical or Regional Anatomy. Consideration of the important group of anatomi- cal facts directly applicable to the diagnosis and the treatment of disease constitutes Applied Anatomy. General Plan of Construction. — Vertebrate animals, of which man rep- resents the most conspicuous development of the highest class, — fishes, amphibians, reptiles, birds, and mammals being the recognized subdivisions of the vertebrata, — possess certain characteristics in common which suffice to distinguish the numerous and \'aried members of the extended group. The fundamental anatomical feature of these animals is the possession of an axial coliitnn, or spine, which extends from the anterior or cephalic to the poste- rior or caudal pole and establishes an axis around which the various parts of the elongated body are grouped with more or less symmetry. While this body-axis is usually marked by a series of well-defined osseous segments constituting the ver- tebral column of the higher animals, among certain of the lower fishes, as the sharks or sturgeons, the axial rod is represented by cartilaginous pieces alone ; in fact, the tendency towards the production of a body-axis is so pronounced that the formation 2 HUMAN ANATOMY. of a primiti\"e axis, the notocliord , takes place among the early formatixe processes of the embryo. In addition to the fundamental longitudinal axis, \ertebrate animals exhibit a transverse cleavage into somatic or body-segments. While such segmentation is rep- resented in the maturer conditions by the series of vertebrae and the associated ribs, the tendency to this division of the body is most marked in the early embryo, in which the formation of body-segments, the somites, takes place as one of the primary developmental processes. Although these primary segments do not directly corre- spond to the permanent vertebrse, they are actively concerned in the formation of the latter as well as the segmental masses of the earliest muscular tissue. In man not only the skeleton, but likewise the muscular, vascular, and ner\-ous systems are affected by this segmentation, the effects of which, however are most evident in the structure of the walls of the thoracic portion of the body-cavity. Disregarding the many variations in the details of arrangement brought about by specialization and adaptation, the body of every vertebrate animal exhibits a fundamental plan of construction in which bilateral svmtnetry is a conspicuous fea- ture. Viewed in a transverse section passing through the trunk, the animal body Neural arch Neural tube Spinal Vertebral axis- Costal segment Parietal mesoblast ietal mesothelium \'isceral mesothelium ■ Entoblastic epithelium "Subepithelial mesoblast • Visceral mesoblast Diagrammatic plan of vertebrate body in trail section. {Modified /torn IViedersheim.) may be regarded as composed primarily of the axis, formed by the bodies of the vertebrse, and two tubular cavities of very unequal size enclosed by the tissues con- stituting the body-walls and invested externally by the integument (Fig. i). The smaller of these, the neural tube, is situated dorsally, and is formed by the series of the vertebral arches and associated ligaments ; it surrounds and protects the great cerebro-spinal axis composed of the spinal cord and the specialized cephalic extremity, the brain. The larger space, the visceral tube corresponding to the body- cavity, or cwlom, lies on the ventral side of the axis and contains the thoracic and abdominal viscera, including the more or less convoluted digestive-tube with its accessory glandular organs, the liver and the pancreas, and the appended respiratory tract, together with the genito-urinary organs and the vascular and lymphatic appa- ratus. The digestive-tube, which begins anteriorly at the oral orifice and opens posteriorly by the anus, is extended by two ventral evaginations giving rise to the respiratory tract and the liver, a dorsal glandular outgrowth representing the pan- creas. The sexual and urinary glands and their ducts primarily occupy the dorsal wall of the body cavity. The vascular system consists essentially of the ventrally placed contracting dilatation, the heart, divided into a venous and an arterial com- DESCRIPTIVE TERMS. partment, and the great arterial trunk, the aorta, the major part of which occupies the dorsal wall of the space. The elongated typical vertebrate body terminates anteriorly in the cephalic segment, posteriorly in the caudal appendage ; between these two poles extends the trunk, from which project the ventrally directed limbs, when these appendages exist. Just as the axial segments, represented by the bodies of the vertebras, take part, in conjunction with the neural arches, in the formation of the neural canal, so do these segments also aid in forming the supporting framework of the ventral body-cavity in connection with the series of ribs and the sternum. Descriptive Terms. — The three chief planes of the vertebrate body are the Sagittal, the transverse, and the frontal. The sagittal pla7ie, when central, passes through the long axis of the body vertically and bisects the ventral or anterior and the dorsal or posterior surfaces. The transverse pla7ie passes through the body at right angles to its long axis and to the sagittal plane. The frontal plane passes vertically but parallel to the anterior or ventral surface, being at right angles to both the sagittal and transverse planes (Fig. 2. ) The vertical position of the long axis in the human body is unique, since man. Fig. Fig. 3. : principal planes of human body. T, T, transverse; S, S, sagittal ; F, F, frontal. Human embr>'o showing primary relations of limbs. (7. a, preaxial surfaces; *, b, postaxial; s, s, somitic segments of trunk. of all animals, is capable of habitually maintaining the erect posture with full exten- sion of the supporting extremities. The lack of correspondence between the actual position of the chief axis of man and the horizontal fore-and-aft axis of vertebrates in general results in discrepancies when the three principal planes of the human body are compared with those of other animals. Thus, the sagittal plane alone retains the relation, as being at right angles to the plane of the support, in all verte- brates, although in man its greatest expansion is vertical. The transverse plane in man is parallel with the supporting surface, while it is, obviously, at right angles to the corresponding plane in the four-footed vertebrate ; likewise, the frontal plane in man is vertical, while it is horizontal in other animals. The various terms employed in describing the actual position of the numerous parts of the human body and their relations to surrounding stmctures have been adopted with regard to the erect attitude of man and the convenience of the student of human anatomy ; hence, in many cases, they must be recognized as having a limited specific and technical application and often not directly applicable to other 4 HUMAN ANATOMY. vertebrates. Superior and inferior, upper and lower, as indicating relations towards or away from the head-end of the body, are, probably, too convenient and useful as expressing the peculiar relations in man to be readily relinquished, although when directly applied to animals possessing a horizontal body-a.xis they refer entirely to relations with the plane of support, the additional terms cephalie and caudal being necessary to indicate relations with the head- and tail-pole. Likewise, "anterior" and "posterior," as referring respectively to the front and back surfaces of the human body, are more logically described as ventral and dorsal, with the advantage that these terms are directly applicable to all vertebrates. ' ' Outer' ' and "inner, " as e.xpressing relations with the sagittal plane, are now largely replaced by the more desirable terms lateral and mesial respectively, external and internal being reserved to indicate relations of depth. Cephalic and caudal, central and peripheral, prox- imal and distal, are all terms which have found e.xtensive use in human anatomy. Preaxial and postaxial, in addition to their general and obvious significance with reference to a.xes in common, have acquired a specific meaning with regard to the limbs, the appreciation of which requires consideration of the primary relations observed in the embryo. In the earliest stage the limbs appear as flattened buds which project from the side of the trunk and present a dorsal and ventral surface ; subsequently the limbs become folded against the body, the free ends being directed ventrally, while one border looks headward, the other tailward. If an axis corre- sponding to the transverse plane of the body be drawn through the length of the extremities, each limb will be divided into two regions, one of which lies in front of the axis, and is, therefore, preaxial, the other behind, or postaxial. On reference to Fig. 3 it is obvious that the preaxial border or surface of each limb is primarily directed towards the cephalic or head-end of the animal, and, conversely, that the postaxial faces the caudal or tail-end. These fundamental relations are of great im- portance in comparing the skeleton of the upper and lower extremities with a view of determining the morphological correspondence of the several component bones, since the primary relations become masked in consequence of the secondary dis- placements which the limbs undergo during their development. The terms hotnologue and analogue call for a passing notice, since an exact understanding of their significance is important. Structures or parts are homologous when they possess identical morphological values founded on a common origin ; thus, the arm of a man, the front leg of a dog, and the wing of a bat are homologues, because each represents the fore-limb of a vertebrate, although they differ in individual func- tion. On the other hand, the wing of a bat and that of a butterfly are analogous, since they are structures of functional similarity, although of wide morphological diversity. Homologue, therefore, implies structural identity, analogue implies functional similarity. Parts are said to be homotypes when they are serial homo- logues ; thus, the humerus and the femur are homotypes, being corresponding structures repeated in the same animal. Where parts possess both morphological and functional identity, as the wing of a bird and of a bat, they are analogous as well as homologous. THE ELEMENTS OF STRUCTURE. When critically examined, the various organs and parts going to make up the complex economy of the most highly specialized vertebrate — and, indeed, the same is true of all animals whose organization does not approach the extremely simple uni- cellular type — are found to be constituted by the various combinations of a very small number of elementary tissues ; these latter may be divided into four funda- mental groups : Epithelial tissues ; Connective tissues ; Muscular tissues ; Nervous tissues. Of these the nervous tissues are most specialized in their distribution, while the connective tissues are universally present, in one or another form contributing to the composition of every organ and part of the body. The tissues of the circulatory system, including the walls of the blood-vessels and lymph-channels and the corpus- cular elements of their contained fluids, the blood and the lymph, represent special- izations of the connective tissues of such importance that they are often conceded the dignity of being classed as independent tissues ; consideration of the develop- ment of the vascular tissues, however, shows their genetic relations to be so nearly identical with those of the great connective-tissue group that a separation from the latter seems undesirable. Each of the elementary tissues may be resol\-ed into its component morphologi- cal constituents, the cells and the intercellular substances. The first of these are the Fig. 4. Nucleus Vacuole Pseudopod A^ unicellular animal {amceba) ; B, Exoplasm nbrj'onal cell, — leucocyte. descendants of the embryonal elements derived from the division or segmentation of the parent cell, the ovum, and are highly endowed with vital activit}^ ; the intercellu- lar substances, on the other hand, represent secondary productions, comparatively inert, since they are formed through the more or less direct agency of the cells. The animal cell may exist in either the embryonal, matured, or metamorphosed condition. The embryonal cell, as represented by the early generations of the direct off- spring of the ovum, or b}' the lymphoid cells or colorless blood-corpuscles of the adult, consists of a small, irregularly round or oval mass of finely granular gelati- nous substance — the protoplasm — in which a smaller and often indistinct spherical body — the nucleus — lies embedded. In the embryonal condition, when the cell is without a limiting membrane, and composed almost entirely of active living matter, the outlines are frequently undergoing change, these variations in shape being known as amoeboid viovements , from their similarity to the changes observed in the oudine of an active amoeba, the representative of the simplest form of animal life, in which 5 6 HUMAN ANATOMY. the single cell constitutes the entire organism, and as such is capable of performing the functions essential for the life-cycle of the animal. As the embryonal cell advances in its life-history, the conditions to which it is subjected induce, with few exceptions, further specializations, since in all but the lowest forms division of labor is associated with a corresponding differentiation and adaptation to specific function. Vital manifestations of the cell include those complex physico-chemical phenomena which are exhibited during the life of the cellular constituents of the body in the performance of the functions necessary for fulfilment of their appointed life-work. These embrace metabolism, growth, reproduction, and irritability. Metabolism, the most distinctive characteristic of li\'ing matter, is that process by which protoplasm selects from the heterogeneous materials of food those partic- ular substances suitable for its nutrition and converts them into part of its own sub- stance. Metabolism is of two forms, — constructive and destructive. Constructive metabolism, or anabolism, is the process by which the cell converts the simpler com- pounds into organic substances of great chemical complexity ; destructive metabolism, or katabolism, on the contrary, is the process by which protoplasm breaks up the complex substances resulting from constructive metabolism into simpler compounds. Vegetal cells possess the power of constructive metabolism in a conspicuous degree, and from the simpler substances, such as water, carbon dioxide, and inorganic salts, prepare food-material for the nutritive and katabolic ])rocesses which especially dis- tinguish the animal cell, since the latter is dependent, directly or indirectly, upon the vegetal cell for the materials for its nutrition. G^o^vth, the natural sequel of the nutritive changes effected by metabolism, may be imrestricted and equal in all directions, resulting in the uniform expansion of the cell, as illustrated in the growth of the ovum in attaining its mature condition. Such unrestricted increase, however, is exceptional, since cells are usually more or less intimately related to other structural elements by which their increase is modi- fied so as to be limited to certain directions ; such limitation and influence result in unequal growth, a force of great potency in bringing about the differentiation and specialization of cells, and, secondarily, of entire parts and organs of the body. Familiar examples of the result of unequal growth are obser\'ed in the columnar elements of epithelium, the fibres of muscular tissue, and the neurones of the ner- vous system. Reproduction may be regarded as the culminating vital manifestation in the vegetative life-cycle of the cell, since by this process the parent element surrenders its individuality and continues its life in the existence of its offspring. \\'hile the details of the process by which new cells arise from pre-existing cells are reser\'ed for consideration in connection with the more extended discussion of the cell to follow (see page 9), it may here be stated that reproduction occurs by two methods, — the indirect or mitotic and the direct or amitotic. The first of these, invohing the complicated cycle of nuclear changes collectively known as mitosis or karyokinesis, is the usual method; the second and simpler process of direct division, or amitosis, is now recognized as exceptional and frequently associated with conditions of im- paired vital vigor. Irritability is that property of living matter by virtue of which the cell ex- hibits changes in its form and intimate constitution in response to external impres- sions. These latter may originate in mechanical, thermal, electrical, or chemical stimuli to which the protoplasm of even the lowest organisms responds, or they may be produced in consequence of the obscure and subtle changes occurring within the protoplasm of neighboring elements, as illustrated by the reaction of the neurones in response to the stimuli transmitted from other ner\'ous elements. THE ANIMAL CELL. Ever since the establishment of the Cell Doctrine, in 1838, by the announcement of the results of the epoch-making investigations of Schleiden and Schwann on "The Accordance of Structure and Growth of Animals and Plants," the critical examination of the cell has been a subject of continuous study. Notwithstanding the tireless enthu- STRUCTURE OF THE CELL. siasm with which these researches have been pursued by the most competent investi- gators and the great advance in our accurate knowledge concerning the intricate problems relating to the morphology and the physiology of the cell, much pertaining to the details of the structure and the life of the cell still remains uncertain, and must be left to the future achievements in cytology. The account here given of the mor- phology of the cell presents only those fundamental facts which at the present time may be accepted as established upon the evidence adduced by the most trustworthy observers. The more speculative and still unsetded and disputed problems of cy- tology, interesting as such theoretical considerations may be, lie beyond the purpose of these pages ; for such discussions the student is referred to the special works and monographs devoted to these subjects. An appreciation, however, of the salient facts of cytology as established by the histologists of the present generation is essen- tial not only for an intelligent conception of the structure of the morphological ele- ments, but likewise for the comprehension of the highly suggestive modern theories concerning inheritance, since, as will appear in a later section, the present views regarding these highly interesting problems are based upon definite anatomical ■details. Fig. 5- E.\oplasm Nuclear membrane Nucleolus Metaplastic inclu Centrosome surrounded by centrosphere Notwithstanding the great variations in the details of form and structure, cells -possess a common type of organization in which the presence of the cell-body or cyto- plasm and the nucleus is essential in fulfilling the modern conception of a cell. The latter may be defined, therefore, as a nucleated mass of protoplasm. The term protoplasm, as now generally employed by histologists, signifies the •organized substance composing the entire cell, and with this application includes both the cytoplasm and the nucleus. Structure of the Cytoplasm. — The cytoplasm, or the substance of the cell- body, by no means invariably presents the same appearance, since it may be regarded as established that the constituents of this portion of the cell are subject to changes in their condition and arrangement which produce corresponding morphological varia- tions ; thus, the cytoplasm may be devoid of definite structure and appear homoge- neous ; at other times it may be composed of aggregations of minute spherical masses and then be described as granular, or, where the minute spheres are larger and con- sist of fluid substances embedded within the surrounding denser material of the cell, as alveolar ; or, again, and most frequently, the cytoplasm contains a mesh-work of fibrils, more or less conspicuous, which arrangement gives rise to the reticular con- dition. The recognition of the fact established by recent advances in cytology, that the structure of cytoplasm is not to be regarded as immutable, but, on the contrary, ■as capable of undergoing changes which render it probable that a cell may appear 8 HUMAN ANATOMY. during one stage of its existence as granular and at a later period as reticular, has done much to bring into accord the conflicting and seemingly irreconcilable views regarding the structure of the cell championed by competent authorities. Whatever be the particular phase of structural arrangement exhibited by the cell, histologists are agreed that the cytoplasm consists of two substances, — an active and a. passive ; while both must be regarded as living, the vital manifestations of con- tractility are produced by the former. Since a more or less pronounced reticular arrangement of the active and passive constituents of cytoplasm is of wide occurrence in mature cells, this condition may serve as the basis for the description of the morphology of the typical cell. Critical examination of many cells, especially the more highly differentiated forms of glandular epithelium, shows the cytoplasm to contain a mesh-work com- posed of delicate fibrils and septa of the more active substance, the spojigioplasm ; although conspicuous after appropriate staining, the spongioplastic net-work may be seen in the unstained and living cell, thereby proving that such structural details are not artefacts due to the action of reagents upon the albuminous substances com- posing the protoplasm. The interstices of the mesh-work are filled with a clear homogeneous semifluid material to which the name of hyaloplasm has been applied. Embedded within the hyaloplasm, a variable amount of foreign substances is frequently present ; these Spermatogenic cells, showing variations in the condition and the arrangement ol tlie constituents of the cyto- plasm and the nucleus ; the centrosomes are seen within the cytoplasm close to the nucleus. A , from the guinea-pig X 1685 (Meves) ; B, from the salamander X 500 {Meves) ; C from the cat X 750 ^von Lenhossek). include particles of oil, pigment, secretory products, and other extraneous materials, which, while possibly of importance in fulfilling the purposes of the cell, are not among its essential morphological constituents. These substances, which are inert and take no part in the vital activity of the cell, are termed collectively mctaplasm. Cytoplasm consists, therefore, morphologically, of the spongioplasm and the hyaloplasm ; chemically, cytoplasm consists of certain organic compounds, salts and water. The organic compounds are grouped under the term proteins, which are complex combinations of carbon, hydrogen, nitrogen, and oxygen, with often a small percentage of sulphur. The proteins of the cytoplasm contain little or no phosphorus. .Structure of the Nucleus. — The nucleus, during the vegetative condition of the cell, or the "resting stage," as often less accurately called, appears as a more or less spherical body whose outline is sharply defined from the surrounding cyto- plasm by a definite envelope, the nuclear tneynbrane. Since the nucleus is the nutritive, as well as reproductive, organ of the cell, the fact that this part of the cell is relatively large in young and actively growing elements is readily explained. The nucleus consists of two parts, an irregular reticulum of nuclear Jidres and an intervening semifluid nuclear matrix, therein resembling the cytoplasm. Exam- ined under high magnification, after appropriate treatment with particular stains, such as haematoxylin, safranin, and other basic dyes, the nuclear fibres are shown to be composed of minute irregular masses of a deeply colored substance, appropriately STRUCTURE OF THE CELL. 9 called chromatin in recognition of its great affinity for certain stains ; the chromatin particles are supported upon or within delicate inconspicuous and almost colorless threads of Imiti. The latter, therefore, forms the supporting net-work of the nuclear fibrils in which the chromatin is so prominent by virtue of its capacity for staining. The forms of the individual masses of chromatin vary greatly, often being irregular, at other times thread-like or beaded in appearance. Not infrequently the chromatin presents spherical aggregations which appear as deeply stained nodules attached to the nuclear fibres ; these constitute the false nucleoli, or karyosomes, as distinguished from the true nucleolus which is frequently present within the karyoplasm. Chemi- cally, chromatin, the most essential part of the nucleus, contains niiclein, a com- pound rich in phosphorus. The matrix, or nuclear juice, which occupies the interstices of the net-work, possesses an exceedingly weak affinity for the staining reagents employed to color the chromatin, and usually appears clear and untinted. It is probably closely related to the achromatin and contains a substance described as paralinin. The nucleolus, or plasmosome, ordinarily appears as a small spherical body — sometimes multiple — lying among, but unattached to, the nuclear fibres ; its color in stained tissues varies, sometimes resembling that of the chromatin, although less deeply stained, but usually presenting a distinct difference of tint, since it responds readily to dyes which, like eosin or acid fuchsin, particularly affect the linin and cytoplasm. Concerning the e.xact nature, purpose, and function of the nucleolus much uncertainty still exists ; according to certain authorities, these bodies are to be regarded as storehouses of substances which are used in the formation of the chro- matin segments during division, while other cytologists attribute to the nucleolus a passive role, even regarding it as by-product which, at least in some cases, is cast out from the nucleus into the cytoplasm, where it degenerates and disappears. Since trustworthy observations may be cited in support of both of these conflicting views, definite conclusions regarding the e.xact nature of this constituent of the nucleus must be deferred. The nucleolus is credited with containing a peculiar substance known as pyrenin. The term amphipyrenin, as applied to the substance of the nuclear membrane, is of doubtful value. The Centrosome. — In addition to the parts already described, which are con- spicuous and readily seen, the more recent investigations into the structure of cells show the presence of a minute body, the cen- trosome, which plays an important role in Fig. 7. elements engaged in active change, as con- ,~^ '^ .^ spicuously. during division and, in a lesser f ; f " ' ''■ degree, during other phases of cellular activity. ' i j ' ; " ■ ; ""7"" Ordinarily the centrosome escapes attention '\_'a '' ..^ ..fW" because, on account 01 its mmute size and varia- '' 'i^ -i-sif- nj.? ble staining affinity, it is with difficulty distin- '"' ''- ' guished from the surrounding particles. Its d <^ usual position is within the cytoplasm, but the _ C _ ^^ <®> exact location of the centrosome seems to de- •■ ' :— c '' ,-~ ^^^-' pend upon the focus of greatest motor activity, ^^/ -^ since, as shown by Zinimermann, this little -^ ^^ /•*] body, or bodies, being often double, is always ,OT ,^, ' found in that part of the cell which is the seat vi/ l^ 1 ^ C" ' of greatest change ; thus, in a dividing ele- ' -* ^ ment, the centrosome lies immediately related ^.^ , „^ ^^ , , . "^ .u 1 ' . . , y, . , . Centrosomes (c, c) in human epithelium; to the actively changing nucleus, while within a, B, ceils from gastric glands; C, from duo- ■ 7> . J .^1 1- ... - 1 r .1 denal glands ; Z?, from tongue: /. leucocyte with ciliated epithelium it is removea from the nu- centrdome x 625. (a: iv7 zikmermank.) cleus and is found closely associated with the contractile filaments which probably produce the movements of the hair-like ap- pendages. In recognition of the intimate relations between this minute body and the active motor changes affecting the morphological constituents of the cell, the cen- trosome may be regarded physiologically as its dynamic centre ; the name kino- centrum has been suggested by Zimmerman as best expressing this probable function of the centrosome. This little body is frequently surrounded by a clear HUMAN ANATOMY. area or halo, the centrosphere or the altradioti sphere, within which it appears as a minate speck, frequently being double instead of single. In recapitulation, the chief constituents of the animal cell may be tabulated as follows : I Meshwork — Spons;ioplasm. Cytoplasm \ Ground-substance — Hyaloplasm, containing inclusions, Meta- (. plasm. {Linin fibrils. Chromatin (containing A'«- clein ) . I I Nuclear matri.x (containing /"rtra/;?;/;/). I Nucleus -j Xucleoliis (containing Pyrenin.) {, [, Nuclear membrane. DIVISION OF CELLS. Disregarding for the present, at least, the occurrence of direct fission as a means of producing new elements observed among the simplest forms of animal life, Diagram of mitosis, ^.resting stage, chromatin irregularly distributed in nuclear reticulum; a. centrosphere ■containing double centrosome; «, nucleolus. B, chromatin arranged as close spirem ; c, c, centrosomes surrounded by achromatic radial striations. C, stage of loose spirem. achromatic figure forming amphiaster {amp). Z>, chro- matin broken into chromosomes; nucleolus has disappeared, nuclear membrane fading; amphiaster consists of two asters (a. a) surrounding the separating centrosomes. connected by the spindle {s). E, longitudinal cleavage of the chromosomes which are arranged around the polar field ( p) occupied by the spindle. /■', migration of chromatic segments towards new nuclei, as established by centrosomes (c, c\\ .?/. equatorial plate formed by intermingling segjments. G, separating groups of daughter chromosomes {rf, rf) united by connecting threads {c t). H, daughter chromosomes (rf, d) becoming arranged around daughter centrosomes which have already divided ; C, C, beginning cleavage of cytoplasm across plane of equatorial spindle. /, completed daughter nuclei (Z?, D) ; cy-toplasm almost divided into two new cells. {Modified from Wilson). or as an exceptional method among effete and diseased cells of the higher types, the production of new generations of cells may be assumed as accomplished for all DIVISION OF CELLS. ii varieties of elements by a complicated series of changes, collectively known as kar- yokinesis, or mitosis, especially affecting the nucleus. As already pointed out, in addition to presiding over the nutritive and chemical changes, the nucleus is par- ticularly concerned in the process of reproduction ; further, of the several morpho- logical constituents of the nucleus, the chromatin displays the most active change, ^ince this substance is deeply concerned in transmitting the characteristics of the parent cell to the new elements. So essential is this substance for the perpetuation of the characteristics of each specific kind of cell that the entire complex mitotic cycle has for its primary purpose the insurance of the equal division of the chroma- tin of the mother cell between the two new nuclei, such impartial distribution of the chromatin taking place irrespective of any, or even very great, dissimilarity in the size of the daughter cells, the smaller receiving exactly one-half of the maternal chromatin. Mitotic Division. — The details of karyokinesis, or mitosis, sometimes also spoken of as indirect division, include a series of changes involving the centrosome, Fig. 9. ABC D H Chromatic figures in dividing- cells from epidermis of salamander embryo. X 960. A, resting stage ; B, close spireme ; C loose spireme; D, chromosomos (" wreath "), seen from surface; E, similar stage, seen in profile; F, longitudinal cleavage of chromosomes ; G, beginning migration of segments towards centrosomes ; //, separating groups of daughter segments ; /, daughter groups attracted towards poles of new nuclei, cytoplasm exhibits begin- ning cleavage. the nucleus, and the cytoplasm, which are conveniently grouped into four stages ; (i) the Prophases, or preparatory changes; (2) the Metaphase, during which the chromatin is equally divided ; (3) the Anaphases, in which redistribution of the chromatin is accomplished ; (4) the Telophases, during which the cytoplasm under- goes division and the daughter cells are completed. 12 HUMAN ANATOMY. In anticipation of the consideration of the details of mitosis, it should be pointed out that the process includes two distinct, but intimately associated and coinci- dent series of phenomena, the one involving the chromatin, the other the centro- somes and the linin. While as a matter of convenience these two sets of changes are described separately, it must be understood that they take place simultaneously and in coordination. The purpose of the changes affecting the chromatin is the accu- rate and equal division of this substance by the longitudinal cleavage of the chroma- tin segments ; the object of the activity of the centrosomes and the linin is to supply the requisite energy and to produce the guiding lines by which the chromatin segments are directed to the new nuclei, each daughter cell being insured in this manner one-half of the maternal chromatin. The Prophases, or preparatory stages, include a series of changes which involve the nuclear substances and the centrosomes and result in the formation of the kuryokinetic figure ; the latter consists of two parts, (i) the deeply staining chro- matin filaments, and (2) the achromatic figure, which colors but slightly if at all. The chromatin loses its reticular arrangement and, increasing in its staining affinities, becomes transformed into a closely con\'oluted thread or threads, constituting the " close skein ;" the filaments composing the latter soon shorten and thicken to form the "loose skein." The skein, or spij-eme, may consist of a single continuous fila- ment, or it may be formed of a number of separate threads. Sooner or later the skein breaks up transversely into a number of segments or chromosomes, which ap- pear as deeply staining curved or straight rods. A very important, as well as remark- able, fact regarding the chromosomes is their numerical constancy, since it may be regarded as established that every species of animal and plant possesses a fi.\ed and definite number of chromosomes which appear in its cells ; further, that in all the higher forms the number is even, in man being probably twenty-four. During these changes affecting the chromatin the nucleolus, or plasmosome, disappears, and, prob- ably, takes no active part in the karyokinesis ; the nuclear membrane likewise fades away during the prophases, the nuclear segments now lying unenclosed within the cell, in which the cytoplasm and the nuclear matri.x become continuous. Coincident with the foregoing changes, the centrosome, which by this time has already divided into two, is closely associated with phenomena which include the ap- pearance of a delicate radial striation within the cytoplasm around each centrosome, thereby producing an arrangement which results in the formation of two stars or asfcrs. The centrosomes early show a disposition to separate towards opposite poles of the cell, this migration resulting in a corresponding migration of the asters. In consequence of these changes, the retreating centrosomes become the foci of two systems of radial striation which meet and together form an achromatic figure known as the amphiaster, which consists of the two asters and the intervening spindle. Notwithstanding the observations which tend to question the universal importance of the centrosome as the initiator of dynamic change within the cell, as held by Van Beneden and Boveri, there seems to be little douljt that the centrosome plays an important role in establishing foci towards which the chromosomes of the new nuclei become attracted. The nuclear spindle, which originates as part of, or secondarily from the amphiaster, often occupies the periphery of the nucleus, whose limiting membrane by this time has probably disappeared. The delicate threads of linin composing the nuclear spindle lie within an area, the polar field, around which the chromosomes become grouped. The chromosomes, which meanwhile have arisen by transverse division of the chromatin threads composing the loose skein, appear often as V-shaped segments, the closed ends of the loops being directed towards the polar field which they encircle. Owing to this disposition, when seen from the broader surface, the chromosomes constitute a ring-like group, sometimes described as the mother ivrcath ; the same segments, when viewed in profile, ap])ear as a radiating group of- fibrils known as the mother star ; the apparent differences, therefore, be- tween these figures depend upon the point of view and not upon variations in the arrangement of the fibres. The Metaphase includes the most important detail of karyokinesis, — namely, the longitudinal cleavage of the chromosomes, whereby the number of the latter is MITOTIC DIVISION. 13 doubled and the chromatin is equally divided. This division is the first step towards the actual apportionment of the chromatin between the. new nuclei, each of which receives exactly one-half of the chromatin, irrespective of even marked inequality in the size of the daughter cells. Meanwhile the centrosomes have continued to separate towards the opposite poles of the cell, where, surrounded by their attraction spheres, each forms the centre of the astral striation that marks either pole of the amphiaster, the nuclear spindle being formed by the junction of the prolonged and opposing striae. The purpose of the achromatic figure is to guide the longitudinally divided chromosomes towards the new nuclei during the succeeding changes. The Anaphases accomplish the migration of the chromosomes, each pair of sister segments contributing a unit to each of the two groups of chromosomes that are passing towards the poles of the achromatic spindle ; in this manner each new nucleus receives not only one-half of the chromatin of the mother nucleus, but also the same number of chromosomes that originally e.xisted vtithin the mother cell, the numerical constancy of the particular species being thus maintained. Anticipating their passage towards the poles of the achromatic figure, the mi- g-rating chromatic segments, attracted by the linin threads, for a time form a com- pact group about the equator of the spindle known as the eguafoj'ial plate. As the receding segments pass towards their respective poles, the opposed ends of the sep- arating chromosomes are united by intervening achromatic threads, the connecting Jibres. Sometimes the latter exhibit a linear series of thickenings known as the €ell-plate or mid-body. The migration of the chromosomes establishes the essential features of the division of the nucleus, since the subsequent changes are only repe- titions, in inverse order, of the changes already noted. The Telophases, in addition to the final stages in the rearrangement of the chromatic segments of the new nuclei, including the appearance of the daughter wreath, the daughter skeins, the new nuclear membrane, and the nucleolus, witness the participation of the cytoplasm in the formation of the new cells. In these final stages of mitosis the cell-body becomes constricted and then divides into two, the plane of division passing through the equator of the nuclear spindle. Each of the resulting masses of cytoplasm invests a new nucleus and receives one-half of the achromatic figure consisting of a half-spindle and one of the asters with a centro- some. The new cell, now possessing all the constituents of the parent element, usually acquires the morphological characteristics of its ancestor and passes into a condition of comparative rest until called upon, in its turn, to enter upon the com- plicated cycle of mitosis. MITOTIC DIVISION. I. Prophases. A. Changes within the micleus : Chro7natic Jigure. Chromatin loses reticular arrangement, Close skein. Loose skein. Disappearance of nucleolus. Division of skein into chromosomes. Arrangement around polar field — mother wreath, Disappearance of nuclear membrane. B. Changes within the cytoplasm : Achromatic Jigure. Division of centrosome. Appearance of asters, Migration of centrosomes, Appearance of spindle, Formation of amphiaster. Appearance of nuclear spindle and polar field. II. Metaphase. Longitudinal cleavage of chromosomes. 14 HUMAN ANATOM\', III. Anaphases. Rearrangement of chromosomes into two groups, Migration of groups towards poles of amphiaster. Appearance of connecting fibres between receding groupB, Construction of daughter nuclei. IV. Telophases. Constriction of cell-body appears at right angles to spindle, Chromosomes rearranged in daughter nuclei to form skeins. Reappearance of nuclear membrane, Reappearance of nucleoli, Complete division of cell-body, Daughter nuclei assume vegetative condition, Achromatic striation usually disappears, Centrosomes, single or divided, lie beside new nuclei. i » AMITOTIC DIVISION. The occurrence of cell reproduction without the foregoing complex cycle of karyokinetic changes is known as amitotic or dited division. That this process does take place as an e.xceptional method in the reproduction of the simplest forms of ani- mal life, or in the multiplication of cells within pathological growths or tissues of a transient nature, as the fcetal envelopes, may Fig. io. be regarded as established beyond dispute. D .<*3"HR^ Tbe essential difference between amitotic and the usual method of division lies in the fact that, while in the latter the chromatin of the nucleus is equally divided and the number it-^ of chromosomes carefully maintained, in direct ^'^^ " division the nucleus remains passive and suffers cleavage of its total mass, but not of its indi- vidual components. Since the nucleus re- mains in the vegetati\-e condition, neither the chromatic nor achromatic figure is pro- duced, the activity of the centrosome, when exhibited, being possibl)- directly expended in effecting a division of the cytoplasm, and inci- dentally that of the nucleus. In many cases the amitotic division of the nucleus is not ac- companied by c!ea\age of the cvtoplasm, such processes resulting in the production of multi- While in general, it may be assumed that cells which undergo direct division are elements destined to suffer premature degeneration, the studies of Child ha\e shown that amitotic division is of much wider occurrence than formerly recognized; further, that due to changes of environmental conditions affecting the nutrition of the cell, as scarcity of oxygen or presence of ether, the mitotic cycle may be interrupted and replaced by amitotic division. The regular mitotic process may be restored upon removal of the abnormal environment ( Nathansohn). J Decidual cells showing amitotic nucleus {,A-D^ \ in £" an attempt at occurred. X 410. nuclear and aberrant nuclear forms. EARLY DEVELOPMENT. The human body with all its complex organism is the product of the differentia- tion and specialization of the cells resulting from the union of the parental sexual elements, — the ovum and the spermatozoon. The Ovum. — The maternal germ-cell is formed within the female sexual gland, the ovary, in which organ it passes through all stages of its development, from the immature differentiation of its early condition to the partially completed matura- tion of the egg as it is liberated from the ovary. The human ovum, in common with the ova of other mammals, is of minute size, being, as it is discharged from the ovary, about .25 millimetre in diameter. Ex- amined microscopically and after sectioning, the human ovum is seen to be enclosed within a distinct envelope, the zona pellucida, .014 millimetre in thickness, which in favorable preparations exhibits a radial striation, and hence is also named the zo7ia 7-adiata. This envelope at first was confounded with the proper limiting mem- brane of the cell, and for a time was erroneously regarded as corresponding to the KiG. II. -Corona radiata -Zona pellucida -Germinal vesicle (nu- cleus) containing germ- inal spot (nucleolus) -Zone rich in deutoplasm -Zone poor in deutoplasm fading into homogene- ous peripheral zone Human ovum from ripe Graafian follicle. X 170. {Nagel.) cell-wall. The nature of the zona pellucida is now generally conceded to be that of a protecting membrane, produced through the agency of cells surrounding the ovum. The substance of the ovum, the yolk, or vttelhis, consists of soft, semifluid pro- toplasm modified by the presence of innumerable yolk-granules, the representatives of the important stores of nutritive materials present in the bird's egg. Critically examined, the vitellus is resolvable into a reticulum of active protoplasm, or ooplasm, and the nutritive substance, or deutoplasm. At times the yolk is limited externally by a very delicate envelope, the vitellme membrane, which usually lies closely placed, or adherent, to the protecting zona radiata ; sometimes, however, it is separated from the latter by a perivitelline space. The vitelline membrane is probably absent in the unfertilized human ovum. A large spherical nucleus, the gertni7ial vesicle, approximately .037 millimetre in diameter, usually lies eccentrically within the yolk, surrounded by the distinct nuclear membrane. Within the germinal vesicle the constituents common to nuclei in 15 i6 HUMAN ANATOMY. Fig. 12. general are found, including the all-important chromatin fibrils, nuclear matrix, and nucleolus ; the latter, in the original terminology of the ovum, is designated as the germinal spot, and measures about .005 millimetre in diameter. In addition to these more easily distinguished components of the maternal cell, the centrosome must be accepted as a constant constituent of the fully formed, but unmatured, ovum, although its presence may escape detection. The Spermatozoon. — The male germ-cell, the spermatic filament, is produced by the specialization of epithelial elements lining the seminiferous tubules within the testicle. The human spermatozoon consists of three parts — the ovoid head, the cylindrical middle-piece, which includes the slightly-constricted neck and the connecting-piece, and the attenuated and greatly extended tail ; of these, the head and middle-piece are the most important, since these parts contain respectively the chromatin and the centrosome of the cells from which the spermatic filaments are derived. The centrosome is represented by two minute spherical bodies, the tieck-granulcs, which lie in the neck immediately beneath the head, at the e.xtremity of the axial fibre ; the latter extends throughout the spermatozoon from the head to the termi- nation of the tail, ending as an extremely attenuated thread, the terminal filament. The tail corresponds to a flagellum and serves the purposes of propulsion alone, taking no part in the important changes produced in the ovum by the entrance of the male element. Maturation of the Ovum. — Maturation, or ripening of the ovum, is that process by which the female element is prepared for the reception of the spermatozoon. It takes place, however, entirely independently of the influence of the male or of the probability of fertilization, every healthy ovum undergoing these changes before it becomes sexually ripe. About the time that the ovum is liberated from the ovary by the bursting of the Graafian follicle, as the sac which encloses the egg within the ovarian stroma is called, its nucleus engages in the complicated cycle already described as mitotic division. The nucleus migrates to the periphery of the ovum, loses its limiting membrane, and un- dergoes division, one pole of the nuclear spindle being located within the protrusion of protoplasm which has coincidently taken place. With the division of the nuclear chromatin, the protruded protoplasm becomes constricted and finally separated from the ovum ; the minute isolated mass thus formed, containing one-half of the maternal chromatin, is the first polar body. Almost imme- diately the mitotic cycle is repeated, and again results in the con- striction and final separation of a minute cell, the second polar body. These two isolated portions of the ovum remain visible for a long time as small, deeply stained cells lying within the perivitelline space beneath the zona pellucida. With each division of the egg-cell, one-half of the chromatin passes to the polar body, the matured ovum consequendy retaining but one-fourth of the original chromatin. While the latter is thus diminished at each division, the masses of chro- matin are reduced to one-half the normal quota of chromosomes, this reduction being effected just before the first polar division. The chromatin remaining within the ovum after the repeated division becomes collected within a new nucleus, which now takes a non-central position within the egg, and is henceforth known as the fie male pronucleus or egg-Jiucleus. After mat- uration the ovum is prepared for union with the spermatozoon, although in many cases the male sexual element has actually entered the ovum before the completion of the maturation cycle : should, however, impregnation not occur, the ovum passes along the oviduct into the uterus and is finally lost. The passage of the human egg "from the ovary to the uterus occupies, probably, about eight days, a period corresponding closely to the length of time that the ovum retains its capability of fertilization. The significance of the extrusion of the polar bodies — a process which occurs Diagram of human spermatozoon; o. neck- granules, representing the centrosome : h. axial fibre. X 1800. i^'SUves.) EARLY DEVELOPMENT. 17 with great constancy in almost all animals, and, indeed, is probably represented in the development of vegetal organisms as well — has been the subject of much dis- cussion and speculation. The most satisfactory explanation of the significance of maturation has been proposed by Van Beneden, Boveri, and others, based upon the comparison of the changes which take place in the development of the germ-cells of the two sexes. In order to appreciate the necessity and the meaning of maturation of the ovum, it will be of advantage to take a brief survey of the phenomena attending the devel- opment of the male sexual elements. The seminiferous tubules of the testicle are lined with epithelial cells, certain of which, known as the primary sperjnatocytes. Fig. 13. Semi-diagranimatic representation of the formation of the polar bodies, based upon observations of invertebrate ova {Ascatis and Physa). n, nucleus ; c, c, centrosomes ; j, nuclear spindle; p\ p" , first and second polar bodies ; ^, egg-nucleus. {After Kostanecki and Wierzejski.) increase in size and undergo division, the daughter cells constituting the secondary spermatocytes. Each of the latter, in turn, gives rise to a new generation, the sper- matids, from which the spermatozoa are directly formed, the chromatin of the sperma- tid being stored within the head, and the centrosome forming the neck-granules within the middle-piece. The spermatozoon, therefore, represents the third generation and corresponds to the mature ovum. Turning to the phenomena of maturation, a parallel process is presented, since the ovarian egg, or primary oocyte, divides into two cells, the seco7idary oocytes, represented by the ovum and the first polar body, each of which receives one-half of the chromatin, notwithstanding that one of the daughter cells, the first polar body, is disproportionately small ; the repetition of division effects a second distribution of »8 HUMAN ANATOMY. the chromatin, so that the mature egg, after the completion of maturation, represents the third generation, and is, therefore, morphologically equivalent to a spermatozoon. Attention has already been directed to the important fact that the cells of a given species contain a fixed, definite, and even number of chromosomes (page 12); hence, in their primary condition, each germ-cell contains the full complement of chromatin segments. Since, however, the new being arises from the elements derived from the segmentation of a cell to the nucleus of which both parents con- tribute an equal number of chromosomes, it follows that, unless some provision be made whereby the number of chromosomes in each germ-cell be reduced to one- Primordial germ-cell Fig. 14. Primordial germ-cell Spermalogon Maturation-period ng the genesis of the male and female germ-cells. {After Bov Oogonia Secondary oocytes {fgg and first polar body) Mature egg and polat bodies half the full number, the elements of the new being would be provided with double the number required to satisfy the normal complement for the particular species. In fact, such reduction of the chromosomes of the germ-cells does take place during the development of these elements, in consequence of which the ovum and the spermatozoon each contribute only one-half the number of chromosomes, the nor- mal quota being restored to the segmentation nucleus, and subsequently to the cells of the new being, by the sum of the contributions of both parents. Interpreted in the light of these considerations, maturation may be regarded as the means by which correspondence between the se.xual cells is secured, and, further, the polar bodies may be considered as abortive ova. Fertilization of the Ovum. — Impregnation, or fertilization of the ovum, includes the meeting of the male and female elements, the penetration into the sub- stance of the latter by the former, and the changes immediately induced by the presence of the spermatozoon within the egg. Coincidently with the rupture of the distended Graafian follicle, the surface of the ovary is embraced by the expanded fimbriated extremity of the oviduct, along the plications of which the liberated matured ovum is guided into the tube. It is highly probable that not an inconsiderable number of the ova discharged from the ovary fail to reach the oviduct and are lost in the abdominal cavity. Recent investigations have shown that both germ-cells contain particular acces- sory chromosomes, which are probably important factors in the determination of the se.x of the new being. The spermatozoa overcome the obstacles offered within the narrow channels by the mucus and the opposed ciliary currents of the uterine and tubal mucous membranes by virtue of their long actively vibrating tails, and advance at a rate estimated at from 1.5 to 2.5 millimetres per minute ; it is therefore probable that the seminal cells accomplish the journey from the mouth of the uterus to the ovum in from eight to ten hours. Spermatozoa retain their vitality and fertilizing pow- ers for many days within the normal female genital tract ; repeated observation on the human subject has shown that this period may extend throughout an entire FERTILIZATION OF THE OVUM. 19 menstrual cycle of twenty-eight days, — a possibility to be remembered when calcu- lating the probable termination of pregnancy. Of the many millions of spermatic elements deposited within the vagina, only Fig. 15. Fertilization of the ovum as illustrated by sections of the eggs of the mouse. (Sobotta.) All the figures are magnified 437 diameters except D-G, in which the amplification is 1310 diameters. A-C. prophases of formation of first polar body (p)\ z, zona pellucida; k, nuclear figure; m, head of spermatozoon. D-G. entrance of spermato- zoon (j) into ovum and subsequent changes. H-M, sequence of changes during the formation, approach, and blend- ing of the male (w) and female (y) pronuclei ; p.p^ polar bodies. an insignificant number ever reach the vicinity of the ovum. Notwithstanding that probably a number of spermatozoa penetrate the zona pellucida, normal fertili- zation in man and the higher animals is effected by a single seminal element. After 20 HUMAN ANATOMY. the entrance of the favored spermatozoon into the substance of tlie ovum, an eftec- tual barrier to the penetration of additional seminal cells is presented by the thick vitelline membrane which immediately forms. The point at which the spermatozoon is about to enter the egg is indicated by a conical elevation, the receptive eminence, into which the male germ-cell sinks, — the tail only partly entering the protoplasm of the egg and very soon disappearing. The position of the remains of the spermatozoon within the substance of the ovum is indicated by an ovoid body, the male pro7uicIcus, which contains the chro- matin and centrosome of the paternal germ-cell. The spcrm-mtcleus ■i.-nA 'Cne egg- nucleus, as the male and female pronuclei are now often designated, usually break up into their respective chromosomes without fusing into a single segmentation Early stages of sc^'iiiLi.tation as seen in ova of nu,..^, ,;.:;... ^j view. X 450. (Sobotta.) The external double contour represents the zona pellucida ; the cell marked w ith ^ , the polar body. A, fertilized ovum at stage of the pronuclei; ^, two segmentation spheres of equal size; C segmentation spheres of unequal size; Z>, three-cell stage resulting from division of larger sphere ; £, stage of four spheres; /", six; C, eight; /^.sixteen; /.twenty-five. nucleus. In this case the two groups of chromosomes unite in the first mitotic figfure, the segmentation spindle (Fig. 17 J. After the fusion of the pronuclei, and just as segmentation is beginning, the fertilized ovum presents a clear oval area which contains the two groups of chromo- somes contributed by the germ-cells of both parents ; on opposite sides of the chro- matin figure are the centrospheres, each containing a centrosome and surrounded by a marked polar striation within the substance of the egg. The centrosomes now pre-sent within the ovum are usually both derived from the substance of the cen- trosome of the spermatid, which entered the ovum as the neck -granules within the middle-piece of the fertilizing spermatozoon. The role of the latter, therefore, is two- fold,— to contribute the chromatin necessary to restore to the parent cell the normal SEGMENTATION OF THE OVUM. 2X complement of chromosomes, and to furnish the stimulus required to inaugurate the karyokinetic cycle of segmentation. Segmentation of the Ovum. — The union of the male and female pronuclei and the resulting formation of the segmentation nucleus is followed immediately by the division of the ovum into two new elements ; each of these gives rise to two additional cells, which, in turn, produce following generations of segmentation cells, or blastomeres. This process of repeated division of the fertilized ovum and its Early stages of segmentation as seen in sect o of ment of the chromosomes contributed by the n lie it of the fertilized ovum; p,p, polar bodies; ep, stage E^ F, the daughter cells arising from first cleavage, stage of this division. /, stage of three segmentation spheres (a 500 {Sobotla 1 D ho the rearrange- nd female /) pro ucle as preparator> to the fi st cleavage equatorial plate ; a, b, daughter groups of chromosomes. 11 (b) is larger and is preparing: to divide. H, later c) resulting from this division. descendants constitutes segmentation, — a process common to the development of all animals and plants above the very simplest. Study of the details of segmentation in the various classes of animals shows that a close relation exists between the character of the cleavage and that of the ovum with regard to the amount and distribution of the nutritive yolk, or deuto- plasm, present. In the human and mammalian ^^^ the nutritive yolk particles are compara- tively meagre and are uniformly distributed throughout the vitellus ; in such eggs there is no aggregation of the food particles, hence such ova are termed hoviolecithal or with a homogeneous yolk. In the eggs of birds, reptiles, and fishes, on the con- 22 HUMAN ANATOMY. trary, the deutoplasm, or nutritive material, is collected towards one pole of the egg, while the protoplasm, or formative material, is limited to the other ; eggs in which these conditions obtain possess a distinctly polar yolk, and hence are known as telolecithal ova. These aggregations of the protoplasm and the deutoplasm con- stitute respectively the formative and the iiutritive yolk, and correspond in position to the a?i!»ia/ and the vegetative poles of the egg. In an additional class of eggs, the centrolecithal, the yolk occupies the centre of the ovum, being covered by a peripheral zone of formative material ; since such ova belong alone to certain in- sects and are not found among vertebrates, they possess limited interest to students of mammalian forms. Comparison of the behavior of these various groups of ova during segmen- tation shows that only eggs poor in deutoplasm, as the alecithal mammalian and amphibian ova, undergo complete cleavage during segmentation, those of the bird, reptile, and fish undergoing cleavage only within the formative yolk. Ova, there- fore, are classified according to the completeness of their division into those exhibit- ing complete segmentation and those undergoing partial segmentation ; the former are known as koloblastic, the latter as meroblastic. The embryologist further recog- nizes an equal and an unequal complete segmentation according to the equality or inequality of the cells, or blaston'f.res, resulting from the division of the ovum. Since the segmentation spheres derived from the mammalian ^^'g may be regarded as practically of equal size, the egg of this class of animals, including the human o\um, is described as an homolecithal holoblastic ovum, undergoing equal segmenta- tion. It must be understood, however, that even in the segmentation of such ova Fig. 19. Ecloblast Entoblast Trophoblast Diagram of early mammalian blastodermic vesicle. Diagram of mammalian blastodermic vesicle ; inner consisting of trophoblast and inner cell-mass. cells differentiating into ectoblast and entoblast. (After (After i an Beneden.) Van Benedcn.) the blastomeres very early exhibit inequality in size and in rapidity of di\ision (Fig. 16 j, the effect of this differentiation being, that the more rapidly multiplying blas- tomeres are smaller than the more slowly dividing elements. It is of interest, in this connection, to note that the purest type of total equal segmentation is observed in the ovum of the lowest vertebrate, the amphioxus, — an animal whose development has shed much light on many obscure problems in the embryology of the higher forms, including mammals and even man. The meroblastic bird's egg, on the contrary, undergoes cleavage only within a limited circular field at its animal pole ; it is said, therefore, to undergo partial dis- forVij/ segmentation. In contrast to this, the centrolecithal ova exhibit partial super- ficial segmentation, the peripheral zone of formative material alone undergoing cleavage. The Blastoderm and the Blastodermic Layers. — The completion of segmentation in holoblastic ova results in the production of a mass of blastomeres, which is a solid sphere composed of mutually compressed segmentation cells ; to this sphere the older anatomists gave the name of the morula, or the mulberry mass. The solidity of the morula is temporary, since a cavity is soon developed within it. This cavity, often called the segmentation cavity, increases to such an extent that a THE BLASTODERMIC VESICLE. 23 hollow sac is formed, walled by a single layer of cells, at one point on the inner sur- face of which is attached a small mass of cells. The outer, covering layer of cells is known as the trophoblast ; the small group of cells attached to the inner surface of the trophoblast is known as the inner cell-mass (Fig. 18). Examined from the sur- face, this aggregation of inner cells appears as an opaque circular field, the embryonic area, due to the increased thickness and consequently diminished transparency of the wall of the blastodermic vesicle at the place of attachment of the included cells. In the purest type of the blastodermic vesicle, that seen in the amphioxus (Fig. 26, A), the sac consists of a single layer of blastomeres of almost uniform size ; the mammalian blastodermic vesicle, however, presents greater complexity, due to the unequal rate at which some of the segmentation cells divide and to the rapid increase in the size of the vesicle. The inner mass of germinal cells soon undergoes differentiation (Fig. 19) into two strata, — an outer layer, closely applied to the trophoblast, and an inner layer. These layers are respectively the ectoblast and the entoblast, — two of the three great primary blastodermic layers from which the embryo is differentiated. Coincidently with the formation of these germinal layers, the mammalian blas- todermic vesicle grows with great rapidity, increasing from a sphere of microscopic size to a vesicle of one or more millimetres in diameter. In consequence of this growth, the trophoblast undergoes great expansion, its cells becoming reduced to flattened elements, which, over the embryonic area, later disappear. In some ani- mals, as in the rabbit, the flattened trophoblast cells extend over the embryonic ectoblast and have been called the cells of Raiiber. In such cases, therefore, the ectoblast is overlaid within the embryonic area by the cells of Rauber, but at the margin of the area, the embryonic ectoblast is continuous with the trophoblast form- ing the outer layer of the wall of the blastodermic vesicle. With the subsequent expansion of the blastodermic vesicle, the cells of Rauber disappear from the surface of the embryonic ectoblast, which then lies upon the surface of the vesicle (Figs. 20, 21). Ftg. Fig. 20. Diagram of mammalian blastodermic vesicle ; the entoblast forms an almost complete inner layer. Diagra mesoblast layer. 1 of mammalian blastodermic vesicle ; th( ; just appearing as the third blastodermic The early blastodermic vesicle at first consists of only two primary layers, the ectoblast and the entoblast ; this stage of development is appropriately termed that of the bilaminar blastoderm (Fig. 20); a little later, a third layer, the mesoblast, makes its appearance between the outer and inner blastodermic sheets ; this stage is designated as that of the trilaminar blastoderm (Fig. 21). The early embryo, shortly after the formation of the blastodermic vesicle, con- sists of three layers of cells, — the ectoblast, the mesoblast, and the entoblast. The histological characters of the outer and inner of these primary layers differ, almost 24 HUMAN ANATOMY. from the first, from those of the mesoblast, their component elements being more compact in arrangement and early manifesting a tendency to acquire the character- istics of covering cells or epithelium. The mesoblastic elements, on the contrary, soon assume irregular forms and are loosely held together by intercellular substance, thus early foreshadowing the special features which distinguish the subsequently differentiated connective tissues. This early distinction becomes more marked as differentiation proceeds, the epithelial tissues possessing elements of comparatively regular form, separated by minute amounts of intercellular substance ; the latter in the connective tissues, on the con- trary, becomes conspicuous on account of its excessive quantity and the resulting profound modifications in the physical character of the tissue; the cells of the con- nective tissues rapidly assume the irregularly stellate or triangular form so charac- teristic in young tissues of this class. Since the three primary layers give rise to all the tissues of the organism, a brief synopsis presenting these genetic relations here finds an appropriate place. DERIVATIVES OF THE BLASTODERMIC LAYERS. From the ectoderm are derived — The epithelium of the outer surface of the body, including that of the conjunc- tiva and anterior surface of the cornea, the external auditory canal, to- gether with the epithelial appendages of the skin, as hair, nails, sebaceous and sweat-glands (including the involuntary muscle of the latter). The epithelium of the nasal tract, with its glands, as well as of the cavities communicating therewith. The epithelium of the mouth and of the salivary and other glands opening into the oral cavity. The enamel of the teeth. The tissues of the nervous system. The retina ; the crystalline Itns, and perhaps part of the vitreous humor. The epithelium of the membranous labyrinth. The epithelium of the pituitary and pineal bodies. From the mesoderm are derived — The connective tissues, including areolar tissue, tendon, cartilage, bone, den- tine of the teeth. The muscular tissues, e.xcept that of the sweat-glands and dilator pupillae. The tissues of the vascular and lymphatic systems, including their endothelium and circulating cells. The se.xual glands and their excretory passages, as far as the termination of the ejaculatory ducts and vagina. The kidney and ureter. From the entoderm are derived — The epithelium of the digestive tract, with that of all glandular appendages except those portions derived from ectodermic origin at the beginning (oral cavity) and termination of the tube. The epithelium of the respiratory tract. The epithelium of the urinary bladder and urethra. The epithelium of the thyroid and thvmus bodies, the modified primary epithe- lium of the latter giving rise to Hassall's corpuscles. The Primitive Streak and the Gastrula. — Examined from the surface during the formation of the primary layers, the mammalian blastodermic vesicle, as represented by that of the rabbit, presents a circular light-colored field, the einbn'onic area, which corresponds to the expansion of the original embryonic spot, the latter becoming larger with the e.xtension of the ectoblast and the entoblast differentiated from the inner cell mass. At first circular, the embryonic area later becomes oval or pyriform in outline (Figs. 22, 23), the larger end corresponding with the cephalic THE EMBRYONIC AREA. 25 pole of the future embryo. In consequence of the proliferation of the ectoblastic cells, the embryonic area becomes differentiated into a central field, the embryonic shield, and a peripheral zone, the area pellucida, which by transmitted lig-ht appear respectively dark and light, owing to the varying transparency of the thicker cen- tral and thinner peripheral portions of the germinal field. Fig. 22. Fig. 23. ->r Embryonic shield /\ a pellucida Wall of blastoder- Embn-onic area of rabbit of about six and one-' half days, seen from the surface by transmitted light. X 26. (Kottmann.) -Wall of blastodermic area of rabbit of about seven days, seen from the surface. X 26. {KolLmann.) Fig. 24. Coincidently with the assumption of the oval or pyriform outline, a linear thick- ening of ectoderm appears towards the smaller end of the embryonic area. This is Ihe primitive streak, which grows backward from a terminal thickening, the node of Hensen, that marks its anterior extremity. The primitive streak indicates the direc- tion of the longitudinal axis of the future em- bryo and is modelled by a shallow furrow, \h& primitive groove, due to the proliferation of the surrounding ectoderm. From the sides of the primitive streak cells are budded off to form the mesoderm, which grows between the outer and inner germ-layers until it, finally, surrounds the blastodermic vesicle. At first, the mesoblast e.xtends laterally and posteriorly and, later, grows forward as two lateral wings, that embrace the head-end of the embryonic area. While for a time attached only to the ectoderm, the primitive streak subsequently fuses with the entoderm, so that sections across the streak show all the germ-layers blended. The primitive streak is a transient organ and later entirely disappears ; it contributes, however, the rapidly growing mesoblastic tissue, which later becomes related to the anal region and the tail-bud. The Significance of the Primitive Streak and the mode of formation of the mesoblast are ve.xed problems in embryology. A brief note on this topic will suffice here. In amphioxus, the lowest vertebrate, the immediate result of segmentation is a hollow sphere, t\\Qblastu/a, filled with fluid, lined by a single layer of cells. Invagi- nation at one point of the wall of the blastula occurs, forming eventually a two-layered cup, the gastru/a, the outer layer of which is the ectoblast, and the inner one the ento- blast. The cavity within the entoblast is the archeniero?i or primitive gut. The open- ing into the archenteron is the blastopore. Cells given off from the entoblast, near the blastopore, form a third layer, the mesoblast. Typical gastrulation does not occur in the higher animals, although in the early human embryo a canal appears, known as the neurenteric cajial, the opening of which is often regarded as homologous with the blastopore. The primitive streak is regarded by some authorities, notably Hert- wig, as an elongated blastopore with lips fused. Since the primitive streak, the prod- uct of the outer germ-layer, is the principal primary source of the mesoblast, the latter may be regarded as indirectly derived from the ectoblast. A limited secondary and later production of mesoblast is attributed by some to the inner germ-layer. itra-embryonic part of blasto- dermic vesicle Embryonic area of rabbit of about eight days, seei from the surface. X 20. {A/ter Van Beneden. ) :6 HUMAN ANATOMY. THE FUNDAMENTAL EMBRYOLOGICAL PROCESSES. Shortly after the appearance of the primitive streak — a structure, it will be remembered, which is transient and only indirectly takes part in the formation of the embryo proper — a series of phenomena mark the earliest stages of the future new being. These changes are known as the fundamental embryological processes, and result in the formation of the neural canal, the notochord, and the somites. While described for convenience as separate processes, they progress to a great extent simultaneously. The Neural Canal. — The earliest indication of the embryo consists in the appearance of two slightly diverging folds (Fig. 27), enclosing the anterior end oi the primitive streak, which are produced by a local proliferation and thickening of the ectoblast. These are the medullary folds and mark the beginning of the formation of the neural canal, from which the great cerebro-spinal nervous axis, together with its outgrowths, the peripheral nerves, is derived. The medullary folds at first border a shallow and widely open furrow (Fig. 28), the medullary groove ; en BInstiila antl gastruLi stages in the development of amphioxus, drawn from the modtl;. of Halsclifk. X 260 A, blastula composed of single la\er of cells surrounding segmentation cavity ; ec. en, respectively ectoblastic and entoblastic areas, i?, beginning invagination of entoblastic area {en). C, completed gastrula; ,?(-, ^?i, ectoblast and entoblast ; tn, mesobtast cell ; d, blastopore, leading into archenteron. the latter becomes rapidly deeper and narrower as the medullary folds increase in height and gradually approach each other. The approximation of the folds (Fig. 29) and subsequent fusion take place earliest at some distance behind the cephalic end of the groove, at a point which later corresponds to the upper cer\-ical region of the spinal cord. After the closure of the groove and its conversion into the medullary canal (Fig. 32), the thickened and invaginated ectoblast forming the lining of the neural tube becomes separated from the outer layer of the embryo by the ingrowth of the THE NOTOCHORD. 27 mesoblast. The subsequent differentiation of the walls of the neural tube will be more fully considered in connection with the nervous system ; suffice it here to state that the cephalic portion expands into the brain vesicles, and subsequently becomes the brain with the contained ventricles, while the remainder of •^"^- ^7- the tube becomes the spinal cord, , ''" ' " "~"~~,^ enclosing the minute central canal. ' \^ The Notochord. — Coinci- \ dently with the formation of the med- ullary groove the entoblast opposite the bottom of that furrow exhibits proliferation and thickening ; the group, of cells thus differentiated be- comes separated from the general mass of • the inner layer and takes up a position immediately below the neural tube (Figs. 30, 31). This isolated column of entoblastic cells constitute 'the jioloc/iord, or chorda dorsalis, the earliest suggestion of the cardinal vertebrate axis around which the parts of the early embryo are symmetrically arranged. While for a time constituting the sole longitudinal axis of the embryo, extending from a point near the cephalic pole, which corresponds later Embryoni( - Medullary fold -Medullary groove -Primitive streak -Embryonic area of rabbit of about eight and one-half days, om the surface. X 24. ^KuUmann.) Fig. 28. Medullary fold Transverse section of rabbit embryo of about eight and one-half days. X 80. Future neural canal is represented by widely open groove. Amniotic sac Fig. 29. Closing neural canal Visceral mesoblast Entoblast Chorda Open gut-tube "Splanchnopleura Transverse section of rabbit embryo of about nine and one-quarter days. X 80. Neural canal is just closing. to the base of the skull, to the caudal extremity, the notochord is but a temporary structure, and subseauently is supplanted by the true vertebral column. It is 28 HUMAN ANATOMY. interesting to note, that in the connecting Hnk between the vertebrates and invertebrates, the amphioxus, the notochord remains as the permanent and sole spinal axis. The history of the notochord in man and mammals presents three stages : (a) it exists as an unbroken cord which extends uninterruptedly through the series of cartilaginous vertebrae ; (d) the notochord suffers segmentation in such manner that the breaks in its continuity correspond to the vertebral bodies, conspicuous proliferation and local increase' in its substance, on the contrary, marking the Fig. 30. f.^^ r^ ^^ Transverse sections through axis of early humai from entoblast. High magnification. (After Kollm. ating from entoblast ye) ; »i, mesoblast ; J, early bryo of about fifteen days, showing formation of notochord ) n, neural canal; ch, cells forming notochord difterenti- ite; d, sections of primitive aortae. position of the intervertebral disks in which the chordal tissue during the first mondis after birth is represented by a considerable mass of central spongy substance ; (/) atrophy of the remains of the notochord, resulting in the entire disappearance of the chordal tissue within the vertebrje and the reduction of the proliferated intervertebral cell-mass to the pulpy substance existing within the intervertebral disks. The cephalic end of the notochord in man corresponds in position to the dorsum sellae, and marks the division of the skull into two parts, that lying in front of Fig. 32. Transverse sect jural Visceral ItSody-cavity tube mesoblast i-quarter days. X So. Ne nali the termination of the notochord, the prechordal portion, and that containing the notochord, the chordal portion ; the latter is sometimes described as the vertebral segment of the skull. The Ccelom. — The downward growth of the neural ectoblast and the upward extension of the chordal entoblast effect a division of the mesoblast along the embryonic axis into two sheets (Fig. 28). These latter undergo further division in consequence of the formation of a cleft within their substance, as the result of which the mesoblast becomes split into two layers enclosing a space, the civlom, or primary body-cavity (Fig. 29). THE SOMITES. 29 The cleavage of the mesoblast, however, does not extend as far as the mid-line of the embryo, but ceases at some distance on either hand, thus leaving a tract of uncleft mesoblast on either side of the medullary groove and the chorda. The uncleft area constitutes the para.rm/ mesoblast (Fig. 32), which extends from the head towards the caudal pole and appears upon the dorsal surface of the embryo as two distinct ribbon-like tracts bordering the neural canal. Beyond the paraxial mesoblast, the cleft portions of the middle layer extend on either side as the lateral plates ; each lateral plate consists of two laminje, the one forming the. dorsal and the Fig. 34. Neural canal Chorda Intermediate cell- ry gut-tube etal mesoblast "Visceral mesoblast Transverse section of human embryo of about fifteen days, showing early differentiation of somite. X 210. {Kollmann.) Transverse section of human embryo of about twenty-one days, showing differentiation of somite. X 90. {Kollviann.) Fig. 35. Dorsal border of mjotome -Cutis plate Other the ventral boundary of the enclosed primary body-cavity ; in view of their subsequent relations to the formation of the body-walls and the digestive tube respectively, the dorsal mesoblastic lamina is appropriately named the parietal layer and the ventral lamina the visceral layer (Fig. 32). In the separation of these layers, which soon takes place in consequence of the dorsal and \-entral folding occurring during the formation of the amnion and the gut-tube, the parietal mesoderm adheres to the ectoblast, in conjunction with which it constitutes the soniatopleure (Fig. 29), the ecto-mesoblastic sheet of great importance in the production of the lateral and ventral body-walls. Siinilarly, the visceral mesoblast unites with the entoblast to form the splanchnoplcure (Fig. 29), the ento-mesoblastic layer from which the walls of the primary digestive canal are formed. The Somites. — The paraxial mesoblast at an earl}^ stage — about the twentieth day in man — exhibits indications of transverse division, in consequence of which this band-like area becomes differentiated into a series of small quadrilateral masses, the somites, or protovertebm. This segmentation of the embryonic mass appears earliest at some distance behind the cephalic end of the embryo, \jCohmann.) at a point which later corresponds to the beginning of the cervical region. The somites are seen to best advantage in the human embryo at about the twenty-eighth day (Fig. 71). The early somites, on transverse section, appear as irregular quadrilateral bodies, composed of mesoblast and covered externally by ectoblast, lying on either side of the neural canal and the notochord (Fig. 33). Each somite consists of a dorsomesial principal cell-mass, which is connected with the lateral plate by means of an intervening cell-aggregation, the intermediate cell-->nass (Fig. 33). Subsequently, Differentiation of myotome of human bryo of about twenty-one days. X 525. 30 HUMAN ANATOMY. the latter becomes separated from the remaining portion of the somite and is probably identified with the formation of the segmented excretory apparatus of the embryo, the Wolffian body, and hence is known as the ncphrotomc. The principal mass, including the greater part of the somite proper, consists ol an outer or peripheral zone of condensed mesoblast enclosing a core of looser struc- ture. The less dense mesoblastic tissue later breaks through the surrounding zone on the side directed towards the notochord and forms a fan-shaped mass of embrj'onic connective tissue which envelops the chorda and grows around the neural canal. The cell-mass derived from the core of the myotome constitutes the sclerotome, and directly contributes the tissue from which the permanent vertebra and the associated ligamentous and cartilaginous structures arise. The remaining denser part, the myotome, which collectively forms a compressed C-like mass, becomes differentiated into a lateral and a mesial stratum (Fig. 35). The lateral stratum, sometimes called the ciitisplale, co'nsists of several layers of closely packed elements. By some these cells are regarded as concerned in producing the connective tissue portion of the skin ; according to others they are in large part converted into myoblasts, which, with those of the mesial stratum, or vmscle-plate, give rise to the \oluntary muscles of the trunk. The genetic relations of the somite, therefore, may be expressed as follows : I Myotome — muscle segttient. Somite ., Sclerotome — axial segment. (_ 'Sephrotomer— excretory gland segment. The number of somites of the human embryo is about thirty-seven, comprising eight cervical, twelve tJioracic, fi\'e lumbar, five sacral, and from five to seven caudal segments. THE FCETAL MEMBRANES. The Amnion. — -With the exception of fishes and amphibians, — animals whose development takes place in water, — the young vertebrate embryo is early enveloped in a protecting membrane, the amnion. Animals possessing this structure, including reptiles, birds, and mammals, are classed, therefore, as amniota, in contrast to the anamnia, in which no such envelope is formed. An additional foetar appendage, the allantois, is always developed as a structure complemental to the amnion ; hence the am- niota possess both amnion and allantois. Since the development of the fcetal membranes in man presents certain deviations from the process as seen in other mammals, due to pecu- liarities affecting the early human embrvo, it is desirable - Cavitv of biastodemic ^? e-xamine briefly the forma- ■ Entobiiist vesicle tion oi these structures as ob- -Trophobiast Served in animals less highly specialized. Referring to the early mammalian embryo, in which the blastodermic layers are arranged as somatopleura and splanchnopleura on either side of the embryonic axis and the surrounding uncleft mesoderm, and extend as parallel sheets over the en- larging blastodermic vesicle, the first trace of the amnion appears as a duplicature of the somatopleura. The earliest indication of the process is seen slightly in front of the cephalic end of the embryo, the resulting head-fold being, however, soon fol- lowed by the appearance of the lateral and tail-folds. The rapid growth of these THE AMNION. Trophoblast 'Vitelline sac Diagram sh( ■ing formation of amniotic folds and of gut-tube ; trans- verse section of axis of embryo. duplicatures of somatopleura from all sides results in the encircling of the embryo within a wall which increases in height until the prominent edges of the folds meet and coalesce over the dorsal aspect of the enclosed embryo. The folds of the amnion first meet over the head-end, from which point the union extends tailward, where, however, fusion may be delayed for some time. The line along which the junction of the folds takes place is known as the amniotic suture. The amnion thus forms a closed sac completely in- Fig. 37. vesting the embryo and con- -j^S^. -jg^- jg''°sa taining a fluid, the liquor .^^ i^^ ^^^^^^v!'"^ r amnii ; at first closely sur- -^ ^^ N^r'^Sk^Mesobiastj rounding the embryo, the amniotic sac rapidly e.xpands until its dimensions allow the enclosed foetus to turn freely, practically supported by the amniotic fluid, which pos- sesses a specific gravity of 1003. It has long been known that in certain forms, conspicuously in the chick, the amnion executes rhythmi- cal contractions, at the rate of ten per minute, whereby the embryo is swayed from end to end of the sac. From the manner of its formation, as folds of the somatopleura (Figs. 37 and 38), it is evident that the amnion consists of an inner ectoblastic and an outer mesoblastic layer. The Serosa, or False Amnion. — Coincident with the fusion of the inner layers of the somatopleuric folds to form the closed sac of the amnion, the outer layers of the same folds unite to produce a second external en- \'elope, the serosa, or false am- nion. The serosa soon becomes separated from the amnion by an intervening space to form the primitive chorion ; the latter, therefore, consists of ectoblastex- ternallyand mesoblast internally, the reverse of the disposition of these layers in the amnion. The outer surface of the mammalian primitive chorion — the entire envelope formed of the serosa and the trophoblast -—is distinguished by prolifera- tion of the epithelial elements, which process results in the production of more or less con- spicuous projections or villi (Fig. 40), this villous condition being particularly well marked in man. The ectoblast of the primitive chorion takes no part in the formation of the boay of the embryo, but, on the other hand, assumes an important role in establishing the earliest connection between the embrvo and the maternal tissues and, later, participates in the formation of the placenta. The ectoblast of the Fig, Gut-tube Exoccelom Diagram showing formation of amniotic folds and i longitudinal section of embrvo. 32 HUMAN ANATOMY. primitive chorion is the direct derivative of the original ectodermal layer of the blastodermic vesicle beyond the embryonic region proper, a layer which, on account of this important nutritive function, has been called by Hubrecht the trophohlast. As already noted (Fig. 32), the cleft between the parietal and visceral layers of the mesoblast is the primary body-cavity or coelom ; with the separation of these layers following the dorsal and the ventral folding associated respecti\ely with the formation of the amniotic sac and the gut-tube, the intramesoblastic space becomes greatly expanded and extends between the amnion and primiti\e chorion. This large space is appropriated only to a limited extent by the future definite body- cavity, and hence is divisible into an embryonic and an extra-embryonic portion, or exoclvlom (Fig. 38), which are temporarily continuous. The Vitelline Sac. — While the somatopleura is engaged in producing the protecting amniotic sac, the splanchnopleura, composed of the entoblast and the adherent visceral layer of mesoblast, becomes approximated along the ventral sur- face of the embryo to define the primitive gut-tube by enclosing a part of the blastodermic vesicle ; the remaining, and far larger, portion of the latter cavity constitutes the vitelline sae, and corresponds to the yolk-sac of the lower forms. The constriction and separation of the gut-tube from the vitelline sac is accom- plished earliest at the Fig. 39. cephalic and caudal ends of the future alimentary canal, the interv'ening por- tion remaining for a time in widely open communi- cation with the yolk-sac. During the rapid diminu- tion of the latter the com- munication becomes re- duced to a narrow channel, the vitelline duct, which persists as a slender stalk terminating at its distal end in the remains of the yolk- sac. In animals other than mammal? in which a pla- centa is developed, the yolk-sac is the chief nutri- tive organ of the embryo ; the mesoblastic tissue of the vesicle becomes vascu- larized by the de\elopment of the blood-\'essels consti- tuting the vitelline circulation, of which the vitelline or omphalomcsentei-ic arteries and veins form the main trunks. The contents of the yolk-sac as such do not directly minister to the nutrition of the embryo, but only as materials absorbed by the vitelline blood-vessels. In man and other high mammals the nutritive function of the yolk is at best insignificant, the vitelline sac of these animals representing the more important organ of their humbler ancestors. In the lowest members of the mammalian group, the monotremata, in which the large ova are comparatively rich in deutoplasm, the vitelline circulation, is of great importance for nutrition, since it constitutes the sole means for this function until the immature animals are hatched and supplied with milk by the mother. In the kangaroo and opossum the yolk-sac at one point forms a disk-like organ, which, from the fact that it becomes provided with vascular villi that lie in contact with the uterine mucous membrane, is termed the vitelline placenta. The Allantois and the Chorion. — Coincidently with the formation of the amnion, another fcetal appendage, the allantois, makes its appearance as an out- Diagram showing X'ilelline duct , beginning allantois and THE VITELLINE SAC. 33 gro\vth from the caudal segment of the primar}- gut-tract. Although modified in man and certain mammals to such an extent that its typical form and relations are obscured, the allantois, when developed in a characteristic manner, as in the chick, assumes the appearance of a free vesicle connected with the embrj'O near its caudal pole by means of a narrow pedicle, the allantoic stalk. Since the allantois is an evagination from the primitive gut, its walls are formed by direct continuations of the primary layers enclosing the digestive canal, — namely, a lining of entoblastic cells, reinforced externally by a layer of visceral mesoblast. Beginning as a wide bay on the ventral wall of the hind-gut, the allantois elon- gates and appears as a pyriform sac projecting from the embryo behind the attach- ment of the still large vitelline stalk (Fig. 39). It rapidly grows into the exoccelom, and in mammals expands in all directions until it comes into contact with the inner surface of the primitive chorion, with which it fuses to constitute the true chorion. The latter, sometimes spoken of as the allayitoic chorion in contrast to the amniotic or primitive chorion; now becomes the most important envelope of the mammalian erabrj'o on account of the role that it is destined to play in establishing the respira- FiG. 40. ^^^^PtfBl^^^^^^h ^^Frimitive chorion Jt*^ _^^^2S!^&^fc^ ^^^8^^ __-- — ^-^ninion jt^r ^^^^ ^^^Hf^ ^^B " Amniotic sac ^^^^HB^^^^^^^^^ ^\*itelline sac Diagram showing villous condition of serosa, expanding allantois, and diminishing vitelline sac. tory and nutritive organ of the fcEtus, the placenta. After the fusion of the allantois with the primitive chorion to form the chorion, the villous projections upon the external surface of the latter become more highly developed, consisting of a core of mesoblastic tissue covered externally by the ectoblast. The primary purpose of the allantois, as a receptacle for the effete materials ex- creted by the Wolffian body of the early fcetus, is soon overshadowed by its function as a respiratory organ ; this occurs with the appearance of the rich vascular supply within the chorion following the invasion of its mesoblastic tissue by the blood-vessels constituting the allantoic circulation. The latter includes the two allantoic arteries. which are extensions from the aortic stem of the embryo and convev venous blood, and the two allantoic veins, which return the oxygenated blood to the embrj-o and become tributary to the great venous segment of the primitive heart. The vascu- larization of the chorion extends to the highly developed villi occupying its outer surface in many mammalian forms, especially man. The vascular villi of the chorion, bearing the terminal loops of the blood-vessels conveying the fcetal blood, are important structures on account of their intimate relations with the uterine mucous membrane (Fig. 41;, in conjunction with which .3 34 HUMAN ANATOMY. they form a respirative and nutritive apparatus. The intimacy between the uterine mucous membrane and the chorionic tufts presents all degrees of association, from simple apposition, as seen in the sow, where the feebly developed and almost uni- formly distributed vascular projections are received within corresponding depressions in the richly vascular uterine tissue, to the firm and complex attachment found in the highly developed human placenta. Fig. Villi of extraplacental chorion Gut-tube Mesoblast Entoblast — -Allantois Allantoic blood- Allantoic sac Maternal blood-spaces Decidua i:ilacentalis Diagram showing villous chorion, diffen nd vascularization of chorion. In contrast with the chorion of those animals in which the nutritive relations between the maternal tissues and the embryo are uniformly distributed are the local specializations seen in the chorion of those types in which a placental area is de- veloped. The animals in which the latter condition obtains are known as placentalia, of which three subgroups are recognized depending upon the multiple (cotyledons). Fig. 42. ;..^'Vr%k^ .,*«"' rti!^?^* ^S^.- \.>'- .>.i," •p Diagrams illiistnitiin; the various tvpes of development of the chorion. A. uniformly developed villi (hog, horse) ; if, multiple placenta? or cotyledons (cow, sheep); C zonular placenta (cat, dog); D, discoidal placenta (monkey, man). A-B comprise non-deciduate ; C-D, deciduate mammals. zonular, or discoidal form of the placenta, man and the apes representing the highest specialization of the last division. In its general plan of development, therefore, the placenta is formed of a fostal and a maternal portion, the former consisting of the vascular villi which are unusually well developed within a particular portion of the chorion, and the latter of the opposed uterine lining which becomes highly special- ized throughout a corresponding area and more or less intimately united with the THE HUMAN FCETAL MEMBRANES. 35 foetal structures. The mucous membrane of the entire uterine cavity, in many of the higher mammals, suffers profound change, and before the end of gestation becomes inseparably attached to the chorion even in its e.xtent beyond the placental area ; in such animals the fused uterine and chorionic tissue constitute the deciducB which, lined internally by the closely applied amnion, form the membranous envelope en- closing the foetus. After rupture consequent upon the expulsion of the foetus at the termination of pregnancy, the deciduje, including the specialized placental portion, are separated from the uterine wall and e.xpelled as the membranes and the placenta which are known collectively as the after-birth. The foregoing sketch of the general development of the foetal membranes in the higher mammals must be now supplemented by consideration of the peculiarities encountered in the development of these structures in man. THE HUMAN FCETAL MEMBRANES. The young human embryo is distinguished by the very early formation of the amniotic cavity, by the precocious development of the mesoblast and extra- embryonic ccelom, by the presence of the body-stalk and by the great thickening of the trophoblast. It must be remembered, in considering the formation of the human foetal membranes, that the earliest stages of development, to wit, fertilization, segmentation, the formation of the blastodermic vesicle, the earliest differentiation of the embryonic area and the formation of the amniotic cavity have not yet been observed on human specimens. Our knowledge of these processes is derived from a stud)' of some of the lower types ; beyond these very early stages, howe\"er, the conditions in the human embryo have been subject to direct study. The Human Amnion, Amniotic Cavity and Allantois. — The accompany- ing diagrams (Fig. 43) will serve to illustrate the process of formation of the foetal membranes in man. Of these five diagrams, A alone is purely hypothetical with reference to the human embryo. In diagram A the amniotic cavity is already indicated as a small cleft between the embryonic area below and a covering layer of cells above continuous with the trophoblast. This layer, the trophoblast, forms the outer covering of the entire vesicle. It is presumably already thickened at as early a stage as this diagram represents. Presumably also the surface of the trophoblast shows irregularities, for this tissue it is which comes into direct contact with the uterine mucous membrane and which, by its activities, forces its way into the maternal decidua. This latter process is known as h7iplantation, a process which supposedly is taking place, if not completed, at about the stage of this diagram. Whether the trophoblastic layer in man is originally a thin single sheet of cells, as for instance is the case in the rabbit, or whether it is from the beginning thickened, we do not know. Certainly the thickened condition appears at a very early stage. The embryonic area shows the embryonic ectoblast proper, which is of small e.xtent ; this ectoblast being so distinguished from the trophoblastic ectoblast. The ento- blast beneath is represented as already arranged in the form of a sac. Between the entoblast and ectoblast the mesoblast has made its appearance. It will be noted that in the diagram the entoblastic sac is much smaller than the outer trophoblastic vesicle. We do not know that this is really the condition when the entoblastic sac is first formed or only appears in conjunction with the great development of the e.xtra embryonic coelom in the mesoblast. It is certainly not unreasonable to suppose that the former case is the true one. The early appearance of the amniotic cavity is to be explained in this way. After the blastodermic vesicle has reached the stage when the inner cell mass is attached to one point on the inner surface of the trophoblast, the formation of a cavity occurs in the region of the inner mass. This cavity, at first very small, has below it the cells of the inner mass, which soon become arranged into the two primary germ layers of the embryonic area, ectoblast and entoblast, while above the cavity is a layer of cells continuous with the trophoblast. Such a method of formation of the amniotic cavity has been observed in some of the lower forms, for instance, in a lemur by Hubrecht, and since the eariiest human embryo accurately studied shows a completely closed amniotic cavity, while in HUMAN ANATOMY. a \er\' early stage of development it is a reasonable inference that in man such a process actually occurs. In diagram B the mesoblast has not only surrounded the entoblastic sac and the inner surface of the trophoblast. so enclosing the large extra-embryonic ccelom, but has invaded the layer of cells above the amniotic ca\ity, di\iding this layer into two parts, the inner part going to form the ectoblast of the amnion, the outer part being a continuation of the trophoblast of the chorion. There is here evidently a very great development of the extra-embr\-onic coelom. In explanation of this condition, it may be assumed that the entoblastic sac is at iirst much smaller than the trophoblastic covering of the \ esicle ; that the mesoblast, shortly after its appearance, Fig. 43. Diagrams illustrating development of human foetal membranes. Stage A is hypothetical ; others are based on stages which have been actually observed. Red represents trophoblast; purple, embn'onic ectoblast; gray, meso- blast ; blue, entoblast. ac, amniotic cavitv ; al. allantois : am. amnion ; *. body-stalk ; ch. chorion ; te. embryonic ectoblast; en, entoblast; g, gut-tube; »i, mesoblast ; p. placental area; /, trophoblast ; :■, yolk-sac ; :i, yolk-stalk. develops a coelom ; that the two layers of the mesoblast so formed grow separately around the vesicle ; the splanchnic layer around the entoblast, the somatic layer around the trophoblast, so enclosing between them as they grow, the considerable space which becomes, by this process, extra-embn,-onic bod}- cavity. This diagram corresponds roughly to the condition of Peters' embn,-o TFig. 44"). The trophoblast is greatlv thickened : its outer surface very irregular, showing lacunje or spaces filled with maternal blood. This early intimate contact of the fcetal tissue with the maternal blood permits nutrition of the young embr\-o from the maternal blood to be carried on through the trophoblast cells some time before the allantoic circulation and definite placenta are established- Hence the significance of this term trophoblast THE HUMAN FCETAL MEMBRANES. 37 In the next diagram, (Fig. 43), C, the e.xtra-embn-onic ccelom has invaded the sheet of mesoblast abo\'e the amniotic ca\-ity to such an extent that the chorion is completely separated from the amnion and the body of the embryo except at one point, the posterior end of the body, where a solid stalk of mesoblast connects the chorion and embrj^o. This solid band of mesoblast is called the body-stalk. It represents, therefore, a primary and permanent connection between the chorion and the body of the embrj^o. A small diverticulum from the entoblastic sac growing into the mesoblast of the body-stalk marks the beginning of the allantois. As the diagram shows, the amnion is at first a comparatively small membrane overlying the embr}-onic area. The ectoblast of the amnion is on the inner side facing the embn,-o, the mesoblast on the outer side. In the chorion these layers are placed inversely, the mesoblast on the inner side, the ectoblast (trophoblast) outside. The space betsveen amnion and chorion is seen to be a continuation of the extra-embryonic ccelom. In diagram D, the amnion has become considerably expanded in association with the growth of the body of the embrj-o and the accumulation of amniotic fluid. A constriction in the entoblastic sac has made its appearance, a constriction which separates the gut of the embryonic body from its appendage, the yolk-sac, the narrower connecting piece being known as the yolk-stalk, or sometimes as the vitello-intesthial duct. This constricted area is brought about by the rapid grow th of the body of the embryo. In the early condition the entoblastic sac is attached to the embryonic body practically along its entire ventral surface. The body region grows very rapidly, particularly the head end, which comes to project from the entoblastic sac to a marked e.xtent ; the tail end also projects somewhat. There is a corresponding growth of the gut within the body of the embr\'0. As a consequence of this process of e.xpansion of the body, the area of attachment of the entoblast external to the body becomes relatively much reduced in size, occupying only a small portion of the ventral surface of the body, and a progressively smaller portion as the body increases in bulk. In other words, the narrow area of the yolk-stalk makes its appearance. In the diagram (D, al) the allantois projects from the posterior end of the embr\-onic gut into the body-stalk. It will be noticed that the human allantois is never a free structure as it is in many of the lower types, where it grows from the body freely into the extra-embr\-onic ccelom and only later becomes connected with the chorion to form the placenta, but that in man it grows directly into the body- stalk, where, outside of the body of the embrj-o. it is an insignificant structure. Inside the body, part of the allantois persists as the bladder. The urachus, a fibrous cord which in the adult passes from the top of the bladder to the umbilicus, is also a remnant of the allantois. The thick irregular projections of the trophoblast have received a core of mesoblast tissue, so forming the early chorionic \"illi. These villi, at the point of attachment of the body-stalk, the area where the placenta is developing, are increasing in 'size, while the villi over the remainder of the chorion are diminishing in size. In diagram E. the amnion has become greatly e.xpanded. It lies closer to the inner surface of the chorion. In close association with this expansion of the amnion, and the accompanying growth of the body of the embryo, the structures which form the umbilical cord are so closely approximated that the area of the cord is clearly defined. These structures are the bodv-stalk containing the allantois and allantoic vessels, the yolk-stalk, and, bounding the other side of this area, the fold of the amnion from beneath the head. At first the bodv-stalk projects from beneath the e.xtreme posterior end of the bodv of the embr\-o, but as growth in this part of the body ad\-ances and the tail projects more and more, the body-stalk is brought to the ventral surface of the abdominal region in close proximit}- to the yolk-stalk. The allantoic blood-\-essels grow from the embryo through the body-stalk to the chorion, where they ramify in the chorionic \illi. At first there is an extension of the ccelom about the yolk-stalk in the umbilical cord, but the mesoblast tissues of the structures of the cord soon fuse together, obliterating this cavity. The area of attach- ment to the abdomen of the umbilical cord becomes relatively xexy much reduced in size and is know^n in the adult, after the separation of the cord, as the umbiliciis or navel. 38 HUMAN A5JAT0MY. The chorionic viUi at the point of attachment to the chorion of the body-stalk are enlarged. These villi constitute the fcetal portion of the placenta, the so-called chorion fro7idosiitn. They are imbedded in the maternal decidua, more specifically, the decidua basalis or placentalis. It must be remembered that the villi contain a core of mesoblast tissue in the stage represented by diagram E, although this meso- blastic core is not shown in the figure, and that the allantoic blood-vessels run in Caf> Fig. 44. nbran of B. Z., Bordering : tissue of uterine m over break in uieri side, described by Peters. ne; Ca., capillary in uterine ti> :osa; £.. embr>'o; ^.. gland of uterus : ,1/ . mesoblast ; ! surface; 7>., trophoblast ; f. £., epithelium of uterine i pregnant uterus c b, points of entran< Cap,, begii ded in' it an extremely young ,-esicle : B. L.. blood lacunae; 1 capsularis ; Comp., compact \tium ; T. M.^ covering tissue X 50 \Peters). this mesoblast: also that the villi are in reality considerably branched, not straight as in the diagram. The remainder of the chorion is acquiring a smooth surface and is commonly known as the chotion /crre. as a means of distinguishing the e.xtra- placental portion of this membrane. The yolk-sac, in man called the 7mibilical vesicle, at the e.xtremity of the yolk-stalk, is retained usually in the placental area just beneath the amnion. It is possible to find the yolk-sac in nearly every placenta THE HUMAN FCETAL MEMBRANES. 39 Reflected amnion- Medullary folds- Medullary groove- Neurenteric canaU by slightly stretching the umbilical cord at its insertion, when a fold appears containing no large vessels. This fold points to the position of the yolk-sac. To sum up, the chief peculi- arities of the human foetal mem- Fig. 45. branes are the following : 1. The amniotic cavity is Vitelline sac — ^ developed at a very early period apparently by a process of hollowing out in the region of the cells of the inner mass, and not by any folding process. The cells above this primi- tive amniotic cavity are later split into two portions by the entrance of the mesoblast and extra-embryonic ccelom ; the inner portion becomes the ectoblast of the amnion, the outer portion is merely a part of the the trophoblast of the chorion. 2. The mesoblast and extra- embryonic coelom are precociously developed at a very early period. 3. The body-stalk constitutes a primary and permanent connection between the em bryo and the chorion. 4. The allantois, which, ex- ternal to the body of the embryo, is an insignificant structure, grows into the body-stalk and therefore is never a free vesicle. 5. The trophoblast is very early greatly proliferated and very early in intimate contact with the maternal blood. Ectoblast- Mesoblast- Amnion Amniotic sac Gut-tube Cliorion. .., Chorionic villi' --I--' 'J-^.'-^' .'*-;' " ^^ '^ ' Dorsal surface of early liuman embryo, two millimetres in length. X 23. f^A/ter Spee.) The amnion has been divided and turned aside. ' Wall of vitelline' Longitudinal section of human embryo represented i Fig. 44, page 38, is a reproduction of the drawing of Peter's embryo and deserves special attention. The figure shows a small portion of the mucous mem- brane of the uterus in which is imbedded the embryonic or chorionic vesicle. 40 HUMAN ANATOMY. Between the points a, b in the figure Ues the area through which the embryonic growth has made its way into the mucous membrane of the uterus, and, in consequence, the uterine epithelium in this area has disappeared. Above this small area there lies a covering mass of tissue ( T. M. ) mainly composed of blood, the result evidently of hemorrhage following the breaking of the mucosa of the uterus in this region. The chorionic vesicle as a whole is quite large, especially in proportion to the embryonic area E, the surface of which is covered with a distinct columnar epithelium. Surrounding the chorionic vesicle there are two kinds of tissue, which make a very striking feature of the picture. First, there is the thickened and \ery irregular trophoblast, the cells of which appear dark, and which forms the outer covering of the wall of the embryonic vesicle itself. Then there are numerous large blood-spaces or Fig. 47. Umbilical or yolk-: Human embryo of about twenty da closed within the £ blood-lacunae lying among the irregular projections of the trophoblast. The maternal blood, therefore, in this very early condition bathes the trophoblast cells of the embryo, a relation very significant with reference to the nutrition of the embryo before the allantoic-placental circulation is established. The mesoderm ( J/ ) extends around the vesicle on the inner side of the trophoblast. In several places there are outgrowths of the mesoderm into the trophoblast, so indicating the beginnings of the villi of the chorion. It will be remembered that the cells of the trophoblast form the epithelial covering of the chorion. At several places in the figure the syncytial layer of the trophoblast Sj' can be distinguished. The proportionally large cavity within the vesicle is e.xtra-embryonic ccelom, a fact which can readily be verified by observing the relations of the mesoderm. The latter layer of tissue is seen to extend around the small yolk sac as the visceral layer of the mesoderm, while the layer of the mesoderm on the inner side of the trophoblast is of course the parietal layer, hence the cavity within these respective layers is the extra-embryonic ccelom, precociously developed for this early stage. There is a small amniotic cavity abo\'e the embryo. Between this cavity and the trophoblast the mesoderm extends as a solid sheet. There are one or two more points to be noted in the figure. In the areas THE HUMAN CHORION. 41 Fig 48 Extraplacental area {Chorion tizve) marked B. Z. , which are merely portions of the uterine mucosa lying against the trophoblast, the tissue is oedematous in character. This tissue is described by Peters as the bordering zone. In other portions of the mucous membrane there are seen parts of some of the uterine glands (g). In the region marked Cap., is seen the beginning of the decidua capsularis, growing in over the area- through which the embryonic vesicle broke into the surface of the uterus. This layer, decidua capsu- laris, is at this stage scarcely developed, only the beginning of it is apparent. This embryo, described by Peters, is one of the youngest which has been accu- rately studied. The inner dimensions of the vesicle, as given by Peters, are as follows: 1.6 by 0.8 by 0.9 mm. The youngest human embryo is that described by Bryce and Teacher, and is probably several days earlier than the one recorded by Peters. In a gen- eral way, it presents the relations of the amniotic and vitelline sacs already described. The Human Chorion. — The vascular chorionic villi, although becoming more complex by the addition of secondary branches, are for a time equally well developed over the external surface of the entire embryonic vesicle ; subsequently, from the end of the second month, a noticeable differentiation takes place, the villi included within the field that later corre- sponds to the placental area undergoing unusual growth and far outstripping those covering the remaining parts of the chorion. This inequality in the development of the villi led to the recognition of the chorion fro7idosum and the cko7'ioti lave, as the placental and non-placental portions of the chorion respectively are termed (Fig. 48). The vascular supply of the villi also shares in this differentiation, the vessels to those of the placental area becoming progres- sively more numerous, while, on the con- trary, those distributed to the remaining villi gradually atrophy as the chorion comes into intimate apposition with the uterine tissue. When well developed, the chorionic villi possess a distinctive appear- ance, the terminal twigs of the richly branched projections being clubbed and slightly flattened in form. Their recogni- tion in discharges from the vagina often affords valuable information as to the ex- istence of pregnancy. The Amniotic Fluid. — The amnion at first lies closely applied to the embryo, but soon becomes separated by the space which rapidly widens to accommodate the increasing volume of the contained liquor amnii. The accumulation of fluid within the amniotic sac, which in man takes place with greater rapidity than in other mam- mals, results in the obliteration of the cleft between the chorion and amnion until the latter envelope lies tightly pressed against the inner surface of the chorion. The union between the two envelopes, however, is never very intimate, as even after the expulsion of the membranes at birth the attenuated amnion may be stripped off from the chorion, although the latter is then inseparably fused with the remaining portions cf the deciduae. The amniotic fluid, slightly alkaline in reaction, is composed almost entirely of water ; of the one per cent, of solids found, albumin, urea, and grape-sugar are constituents. The quantity of liquor amnii is greatest during the sixth month of gestation, at which time it often reaches two litres. With the rapid increase in the general bulk of the fcetus during the later months of pregnancy, the available space for the amniotic fluid lessens, resulting in a necessary and marked decrease in the quantity of the liquid ; at birth, less than one litre of amniotic fluid is usually present. Sometimes, however, the amount of the liquor amnii may reach ten mills Placental ( Chorion /rondos. External surface of part of th the third month ; the lower portion highly developea villi of the placental area. 42 HUMAN ANATOMY litres, due to pathological conditions of the foetal envelopes : such excessive secre- tion constitutes hydnimnion. During the later months of pregnancy the foetus swal- lows the amniotic fluid, as shown by the presence of hairs, epithelial cells, etc., within the stomach. In view of the composition of the fluid, consisting almost en- tirely of water, it seems certain that the introduction of the liquor amnii does not serve the purposes of nutrition ; on the other hand, it is probable, as held by Preyer, that the unusual demands of the fcetal tissues for water may be met largely in this manner. The source of the amniotic fluid in man has been the subject of much discus- sion. The investigations of Mandl and of Biondi, however, have shown that probably the amniotic fluid is chiefly the result of excretory activity of the epithelium lining the amniotic sac. At first these epithelial cells are flat and plate-like, but dur- incr the later months of gestation they become taller and cuboidal and exhibit indi- cations of secretory phenomena. The early amniotic fluid resembles in appearance Fig. 49. Umbirical vesicle - Umbilical slalk Umbilical cord ^ Cut edge of _ --'V ~ nbryo of about thirty-three days, X 4- 1 and chorion have been cut and turned aside. and chemical composition a serous exudate; later, after the formation of the uro- genital openings, the liquor amnii becomes contaminated by the addition of a small amount of the fluid derived from the excretory organs of the foetus. During the later weeks of gestation the contents of the digestive tube are discharged into the amniotic sac as meconium. The Umbilical Vesicle. — The umbilical vesicle, as the yolk-sac in man is termed, presents a reversed growth-ratio to the amnion and body-stalk since it pro- gressively decreases as these latter appendages become more voluminous. The early human embryo is very imperfecdy differentiated from the large and conspicuous yolk-sac, with which its ventral surface widely communicates. With the advances made during the third week in the formation of the primitive gut, the connection between the latter and the vitelline sac becomes more definitely outlined in conse- quence of the beginning constriction which indicates the first suggestion of the later vitelline or umbilical duct (Fig. 47). By the end of the fourth week the connection THE UMBILICAL VESICLE. 43 between the umbilical sac and the embryo has become reduced to a contracted channel extending from the now rapidly closing ventral body-wall to the yolk-sac, which is still, however, of considerable size. The succeeding fifth (Fig. 50) and sixth weeks effect marked changes in the umbilical duct, now reduced to a narrow tube, which extends from the embryo to the chorion, where it ends in the greatly diminished vitelline sac. The lumen of the umbilical duct is conspicuous during the earliest months of gestation, but later disappears, the entoblastic epithelial lining remaining for a considerable time within the umbilical cord to mark the position of the former canal. * The chief factor in producing the elongation of the umbilical duct is the rapid expansion of the amnion ; with the increase in the amniotic sac the distance between this envelope and the embryo increases, until the amnion fills the entire space within Fig. 50. Umbilical vesicle, (yolk-sac) Chorionic sac of thirty-five day embryo laid open, showing embrj^o enclosed by amnion. X2. the chorion, against which it finally lies. In consequence of this expansion, the attachment between the embryo and the amnion around the ventral opening, which later corresponds to the umbilicus, becomes greatly elongated and narrowed. At this point the tissues of the embryonic body-wall and the amniotic layers are directly continuous. The tubular sheath of amnion thus formed encloses the tissue and structures which extend between the embryo and the chorion, as the constituents of the belly-stalk, together with the umbilical duct and the remains of the vitelline blood-vessels ; the delicate mesoblastic layer of the amnion fuses with the similar tissue of the allantois, the whole elongated pedicle constituting the iimbilical co7-d or funicidus. The latter originates, therefore, from the fusion of three chief com- ponents, the amr\iotic sheath, the belly-stalk, and the vitelline duct ; the belly-stalk. 44 HUMAN ANATOMY. as already noted, includes the allantois, with its blood-vessels, and diverticulum, while traces of the vitelline circulation are for a time visible within the atrophied walls of the umbilical duct. As gestation advances, the amnion and the chorion become closely related, but not inseparably united ; between these attenuated mem- branes lie the remains of the once voluminous yolk-sac, which at birth appears as an inconspicuous vesicle, from three to ten millimetres in diameter, situated usually several centimetres beyond the insertion of the umbilical cord. In cases in which the closure and the obliteration of the vitelline duct before birth are imperfectly effected, ft portion, or even the whole, of the intra-embryonic segment of the canal may persist as a pervious tube. Although in extreme cases of faulty closure a passage may lead from the digestive tube to the umbilicus, and later open upon the exterior of the body as a congenital umbilical anus, the retention of the lumen of the vitelline duct is usually much less extensive, being limited to the prox- imal end of the canal, where it is known as Meckel' s diverticulum. The latter is con- nected with the ileum at a point most frequently about 82 centimetres (thirty-two inches ) from the ileo-csecal valve. Such diverticula usually measure from five to 7.5 centimetres in length, and possess a lumen similar to that of the intestine with which they communicate. The foregoing envelopes, the amnion and the chorion, are the product of the embryo itself ; their especial purpose, in addition to affording protection for the deli- cate organism, is to aid in establishing close nutritive relations between the embryo and the maternal tissues, which, coincidently with the development of the fcetal envelopes, undergo profound modifications ; these changes must next be considered. The Deciduae. — The birth of the child is followed by the expulsion of the after-birth, consisting of the membranes and the placenta, which are separated from the uterine wall by the contractions of this powerful muscular organ. Close inspection of the inner surface of the uterus and of the opposed outer surface of the extruded after-birth shows that these surfaces are not smooth, but roughened, presenting evi- dences of forcible separation. The fact that the external layer of the expelled after- birth consists of the greater portion of the modified mucous membrane which is stripped off at the close of parturition suggested the name dcciduce for the mater- nal portion of the fcetal envelopes shed at birth. Since the deciduae are directly derived from the uterine mucous membrane, a brief sketch of the normal character of the last-named structure appropriately pre- cedes a description of the changes induced by pregnancy. The normal mucous membrane lining the body of the human uterus (Fig. 51) presents a smooth, soft, velvety surface, of a dull reddish color, and measures about one millimetre in thick- ness. The free inner surface is covered with columnar epithelium (said to be cili- ated ) which is continued directly into the uterine glands. The latter, somewhat sparingly distributed, are cylindrical, slightly spiral depressions, the simple or bifur- cated blind extremities of which extend into the deeper parts of the mucosa in close relation to the inner bundles of involuntary muscle ; all parts of the tubular uterine glands are lined by the columnar epithelium. The muscular bundles representing the muscularis mucosae are enormously hypertrophied and constitute the greater part of the inner more or less regularly disposed circular layer of the uterine muscle. The unusual development of the muscular tissue of the mucous membrane reduces the submucous tissue to such an insignificant structure that the submucosa is gener- ally regarded as wanting, the extremities of the uterine glands being described as reaching the muscular tunic. The glands lie embedded in the connective-tissue complex, rich in connective-tissue elements and lymphatic spaces, that forms the tunica propria of the mucosa. With the beginning of pregnancy the uterine mucous membrane undergoes marked hypertrophy, becoming much thicker, more vascular, and beset with nu- merous irregularities of its free surface caused by the elevations of the soft spongy component tissue. These changes take place during the descent of the fertilized ovum along the oviduct and indicate the active preparation of the uterus for the reception of the ovum. According to the classical description of the encapsulation of the ovum (Fig. 52) by the uterine mucous membrane, the embryonic vesicle becomes arrested within THE DECIDU^. 45 one of the depressions of the uterine lining, usually near the entrance of the ovi- duct, whereupon the adjacent mucosa undergoes rapid further hypertrophy, which results in the formation of an annular fold surrounding the product of concep- tion. This encircling wall of uterine tissue continues its rapid growth until the embryonic vesicle is entirely enclosed within a capsule of modified mucous mem- bi:ane, known as the decidiia reflexa, as distinguished from the dccidiia vera, the name applied to the general lining of the pregnant uterus. That portion of the uterine mucosa, however, which lies in close apposition to the embryonic vesicle, constituting the outer wall of the decidual sac, is termed the decidua serotina ; later it becomes the maternal part of the placenta. Fig. 51. Duct of gland Uterine mucous th part of muscular tissue. X 45- Our knowledge of the details regarding the encapsulation of the ovum has been materially advanced by the recent observations of Peters, who had the rare good fortune of carefully studying the details of the process at an earlier stage than any hitherto accurately investigated. The results of Peters' s observations lead to a somewhat modiiied conception of the early phases of the encapsulation of the ovum, as well as shed additional light on some of the ve.xed problems concerning the details of the formation of the placenta. According to these investigations, the embryonic vesicle, on reaching the uterine 46 HUMAN ANATOMY. Diagrams representing relations of the uterine mucous mi brane to the embryonic vesicle, or ovum, during the embedd of the latter, i. v, c, decidua serotina, vera, and reflexa, spectively ; o, ovum. cavity and becoming arrested at some fa\orable point, usually in the vicinity of the oviduct, brings about a degeneration of the uterine epithelium over the area of contact. The disappearance of the epithelial lining is followed by sinking and em- bedding of the embryonic vesicle within the softened mucous membrane, the process being accompanied by erosion of some of the uterine capillaries and consequent hemorrhage into the opening representing the path of the ovum. The e.xtravasated blood escapes at the point of entrance on the uterine surface and, later, forms a mushroom-shaped plug marking the Fig. 52. position of the embedded ovum. The latter thus comes into closer relations with the maternal tissues at an earlier period than was formerly recognized. The Trophoblast. — The ear- liest human embryonic vesicle that has been accurately studied, — that of Bryce and Teacher, — measuring only I millimetre in its greatest di- ameter, was already enclosed exter- nally by a conspicuous ectoblastic envelope, consisting of an outer and an inner cell-layer. This thick ectoblastic layer is evidently the proliferated trophoblast (page 31 ), a membrane so designated to indicate the important nutritive functions which it early assumes. Very early the trophoblast becomes honeycombed by the extension of the maternal vascular channels into the ectoblastic tissue (Fig. 53), which consequently is broken up into irregular epithelial trabecuhe separating the maternal blood-spaces. The inner surface of. the trophoblastic capsule presents numerous irregular depres- sions into which corresponding processes of the adjacent young mesoblast project ; this arrangement foreshadows the formation of the chorionic villi which soon become so conspicuous in the human embryonic vesicle. Coincidently with the invasion of the trophoblast by the vascular lacuna externally and the penetration of the Fig. 53. mesoblastic tissue internally, the pe- ripheral portions of the ectoblastic capsule undergo proliferation and extend more deeply into the sur- rounding maternal tissues. In con- sequence of the rapid growth of the embryonic vesicle, that part of the hypertrophied uterine mucosa which overlies the embedded embrvonic vesicle soon becomes elevated and projects into the uterine cavity, thus giving rise to the structure described as the decidua reflexa, or, preferably, the decidua capsiilaris. The Decidua Vera. — The changes which affect the uterine mu- cous membrane, the decidua vera, result in great thickening, so that the mucosa often measures nearlv a centimetre ; this thickening, however, is most marked in the immediate vicinity of the embedded ovum, throughout the greater part of the uterus the decidua attaining a much less conspicuous hypertrophy. Towards the cervix the mucosa is least affected, and at the internal orifice of the cervical canal presents its normal appearance. Examina- tion of the decidua shows that the normal constituents of the uterine mucosa undergo hypertrophy which results in enlargement of the uterine glands (Fig. 54), as well as in increase of the intervening connective-tissue stroma. The enlargement of the glands is not uniform, but is limited to the middle and terminal or deeper parts of Mesoblast Trophoblast THE DECIDUA VERA. 47 the tubular depressions ; the inner portions of the glands, directed towards the sur- face of the uterus, become elongated and lie embedded within a comparatively- dense matrix. In consequence of these changes, the decidua in the vicinity of the ovum, where the hypertrophy is most marked, presents in section two strata, an inner compact and an outer spongy layer. The ciliated columnar epithelium that normally clothes the free surface of the uterus, and perhaps also the uterine glands, gradually disappears, the degeneration beginning before the end of the first month. The integrity of the cells lining the uterine glands is maintained for a longer period, but the glandular epithelium likewise, after a time, suffers, losing its columnar character and changing to small cubical or flattened elements, which, after appear- ing as shrunken columns during the fourth and fifth months, finally disappear during the latter half of gestation. An important exception, however, is to be noted in the behavior of the epithelium lining the deeper portion, or the fundus, of the glands next the muscular tissue ; the epithelium situated in this position does not participate in the atrophic changes above described, but retains more or less per- FiG. 54. Enlarged gla: Enlarged gland Uterine muscle Section of mucous membrane hmng body of uterus (decidua vera) ; fourth month of pregnancy. {AJter Leopold.') fectly its normal condition to the close of pregnancy. After the expulsion of the decidual portion of the uterine mucous membrane, the epithelium remaining in the fundus of the glands becomes the centre of regeneration for the new lining of the uterus. The connective-tissue elements of the matri.x surrounding the glands, especially in the compact layer in the vicinity of the ovum, undergo active proliferation, in consequence of which large spherical elements, the decidual cells, are produced. The latter, from .030 to .040 millimetre in diameter, in places are so densely packed that they assume the appearance of epithelium ; although most typical and nu- merous in the compact layer, they are, nevertheless, present in the spongy stratum, in this situation being more elongated and lanceolate in form. The decidua vera retains this general character during the first half of preg- nancy ; from this time on, however, the increasing volume of the uterine contents subjects the decidua to undue pressure, in consequence of which the hypertrophied mucosa undergoes the atrophic changes characteristic of the so-called second stage. These include a gradual reduction in the thickness of the decidua vera from nearly 48 HUMAN ANATOMY. one centimetre to about two millimetres, the disappearance of the ducts and open- ings of the uterine glands, and the conversion of the compact layer into a dense homogeneous stratum, in which the tightly compressed glands later entirely disap- pear. The spongy layer, on the contrary, retains the dilated gland-lumina, which, however, in consequence of pressure, are converted into irregular spaces arranged with their longest dimensions parallel to the uterine surface. The clefts next the Fig. 55. Section through fcetal membranes and uterus at margin of the placenta ; sixth month of pregnancy. {After Leopold. muscular tissue are clothed with well-preserved epithelium ; the lining cells of those towards the compact layer, on the contrary, early atrophy and disappear. The Decidua Placentalis. — The decidua placentalis, or dea'diia scrotitia, being destined to contribute the maternal portion of the placenta, undergoes profound changes which particularly affect the blood-vessels of the mucosa. In addition to the initial general hypertrophy of the mucous membrane, which the placental decidua shares in common with other parts of the uterine lining, peculiar polynucleated ele- ments, the giant ce/h, make Pic rg. their appearance during the fifth month ; by the end of preg- nancy they are found in large numbers within the basal plate and the septa of the placenta, although they are not wanting within the remains of the spongy layer. The giant cells are par- ticularly numerous in the im- mediate vicinity of the large blood-vessels. The relations between the ingrowing foetal trophoblastic tissue and the ma- ternal structures early become so intimate within the placental area that especial modifications are instituted destined for the production of the vascular arrangement by which the maternal and fcetal blood-streams are brought into close relations. The proliferating trophoblastic tissue in\'ades the stroma of the mucous mem- brane and encroaches upon the capillaries until the latter in places become ruptured, allowing the escape of the maternal blood, which thus is brought into direct contact with the trophoblast. The erosion effected by the blood, on the one hand, and the encroachment of the fcetal mesoblast, on the other, gradually reduces the tropho- blastic stratum, which is broken up into narrow epithelial trabeculae separating the rapidly enlarging vascular lacunae, the primary representatives of the intervillous aggregations of syncytium {d)\ m, mesoblastic stroma of ' THE PLACENTA. 49 Fig maternal blood-spaces of the placenta. The active outgrowth of the mesoblastic tissue of the chorion into the trophoblastic envelope results in the production of the characteristic villous condition distinguishing the early human embryonic vesicle. When sectioned, the well-developed chorionic villi are seen to be composed of two portions, (^a) the central core of gelatinous connective tissue, containing nu- merous stellate cells and blood-vessels, repre- senting the fcEtal mesoblast, and (<^) the epi- thelial covering derived from the trophoblast. The investment of the villi consists of two layers, — an inner stratum, ne.xt the connective- tissue core, composed of low, distinctly out- lined polyhedral cells, the choriojiic epithe- lium, and an outer stratum, the syncytium, composed of an apparently continuous proto- plasmic layer, in which nuclei are visible, but definite cell boundaries are wanting. Irregu- larly distributed aggregations of nuclei, or cell-patches (Fig. 56), form slight elevations on the surface of the villi. The derivation of the outer layer, or syncytium, has been the subject of much discussion ; its close rela- tion to the maternal blood-spaces suggested a maternal origin to some investigators, while others regard it as a fcetal production. The ■observations of Peters on the very early human ovum, already mentioned, conclusively show the correctness of the latter view, and that the syncytium is formed by the transformation of the trophoblast next the vascular lacunae (Fig. 58) ; the syncytium, as well as the remaining parts of the villi of the chorion, therefore, is of fcetal origin. The epithelium covering the villi of the pla- cental area early evinces a tendency towards regression, and by the fourth month exists only as isolated patches ; during the later stages, and particularly on the larger villi, the layer of chorionic epithelium disappears, the syncytium remaining as the sole attenuated covering of the connective-tissue core of the villi. In certain parts of its extent, especially where it covers the chorion and the decidua serotina, , Isolated tuft of cfiorionic villi from placenta. Fig. 58. Chorionic mesoblast Mesoblastic core of foetal villus Trophoblast Syncytium Maternal blood-space bSS — Muscle Endothelium Maternal blood-vessel as well as upon some of the villi, the syncytium undergoes degeneration and is replaced by a peculiar layer of hyaline refracting material known as canalized fibrin. The Placenta. — The placenta constitutes, from the third month of intra- uterine life, the nutritive and respiratory organ of the fcetus. As seen at birth, it js of irregular discoidal form, concavo-convex in section, and measures from fourteen to eighteen centimetres in diameter and from three to four centimetres in thickness. 4 5° HUMAN ANATOMY. Its convex external or uterine surface is rough, owing to the separation from the deeper part of the lining of the uterus which has taken place at the termination of labor. This surface, moreover, presents a number of divisions, the cotyledons, de- fined by deep fissures. The inner or foetal surface is smooth, being covered by the amnion, and slightly concave. The weight of the fully developed placenta averages about 500 grammes. The position of the placenta is determined, evidently, by the point at which the ovum forms its attachment with the maternal tissues ; in the majority of cases this location is at the fundus of the uterus in the vicinity of the oviduct, right or left, the orifice of which becomes occluded by the expansion of the placental structures. Less frequently the placenta occupies the more dependent portions of the uterine wall and, in exceptional cases, its position is in the immediate vicinity of the internal mouth of the uterus ; in these latter cases the placenta may partially, or e\'en com- pletely, grow over the latter opening, thus constituting the grave condition known as placenta praevia. The general constitution of the placenta (Fig. 59), as consisting Fig. 59. Uterine blood \ esse] Decidua placentalis Umbilical \ esi Decidua capsul Interdecidual space Diagram illustrating the relations of the fuetu of the fcetal and the maternal portions, has already been sketched ; it now remains to consider briefly the arrangement of these structures. The^ fcetal portion of the placenta, the contribution of the chorion frondosum, soon becomes a mass of richly branching villi, the more robust main stalks of which are attached to the maternal tissue, while the smaller secondary ramifications are free, completely surrounded by the contents of the maternal blood-sinuses in which they float. In all cases the villous processes support the terminal loops of the foetal blood-vessels, the blood being conveyed to and from the placenta, along the umbil- ical cord, by the umbilical arteries and vein. Although coming into close relation, the syncytium and the meagre connective tissue surrounding the fcetal capillaries alone intervening, the blood-streams of the mother and of the child never actually mingle ; the delicate septum, however, allows the free interchange of gases necessary for the respiratory function as well as the passage of nutritive substances into the fcetal circulation. THE PLACENTA. 51 The ynaternal portion of the placenta is contributed by that portion of the uterine mucous membrane known as the decidua serotina ; its especial peculiarities consist in the intervillous blood-spaces, which may be regarded as derivations from the eroded maternal blood-vessels. As already described, the trophoblast and maternal tissues early come into close relation, and the capillary blood-vessels are opened by the invasion of the foetal tissue, which latter, in turn, is eroded and channelled out by the maternal blood which escapes upon the rupture of the blood \'essels of the mucosa. The extension of the blood-spaces thus originating constitutes the elaborate system of vascular lacunae, or hitervillous spaces, forming so conspicuous a part of the fully developed placenta. In'its earlier changes the decidua serotina closely resembles the decidua vera, presenting an inner compact and an outer spongy layer ; by the middle of preg- nancy, however, the previously enlarged glands have entirely disappeared in conse- quence of the atrophy induced by the increasing pressure caused by the augmenting volume of the uterine contents. When the placenta is detached from the uterus the Fig. 60. Stump of umbilical cord Villus ,^ ^^^J^ ,^Placental septum '^r^i?^^^^^ ^^'^^*^"^ serotina Sf^^i "^ \ ' Lme of separali oa m Uterus Basal- - 4^ i ^ }ft plate r^^.3':irm-«&"^'Co (.37 millimetre long) attached to the wall of the serosa by means of the belly-stalk. X 25. {A/ler Spet.) dermic vesicle, are completed, and the fundamental processes resulting in the differ- entiation of the medullary tube, the notochord, the somites, and the mesoblastic plates are begun. The early details of many of these processes have never been observed in man, but there is little reason to doubt that in its essential features the early human embryo closely follows the changes directly observed in other mammals. The Stage of the Embryo. — The stage of the embryo, from the second to the fifth week, is distin- ^"^- ^7- guished by the formation of organs essentially embry- onic and transient in char- acter, as the somites, the notochord, the Wolffian body, and the visceral arches. ' The earliest phase in the differentiation of the vertebrate body-form con- sists in the establishment of a dorsal tube by the appo- sition and fusion of the ectoblastic medullary folds, and a ventral tube by the approxi- mation and final union of the folds directly derived from the somatopleura. The dorsal, or animal, tube represents the early neural canal, and becomes the great cerebro-spinal nervous axis ; the ^-entral, or vegetative, tube, formed by the ventral extension and approximation of the somatopleura, constitutes the body-cavity, and encloses the prim.ary gut and the associated thoracic and abdominal viscera, and the vascular system. The primitive gut-tube originates by the delimitation of a part of Section of preceding enibryc Allantoit Umbilical sac vesicle and embryo. X 25. [Afte THE EARLY HUMAN EMBRYO. 57 the vitelline sac accomplished by the ventral approximation of the splanchnopleura, and for a time maintains a wide communication with the remains of the yolk-cavity. The early embryo, lying flatly expanded upon the blastodermic vesicle, becomes differentiated in form by the appearance of head- and tail-groo\'es, in consequence of which constriction the cephalic and the caudal poles of the body become defined and partially separated from the embryonal area ; the middle segment, however, em- bracing the widely open gut-tract, for a time remains closely blended with the vitel- line sac, of which, at first, the embryo appears as an appendage (Fig. 68, i and 2). HUMAN ANATOMY. Cephalic flexure Optic vesicle^ Maxillary process- Second visceral arch ^ Third visceral r process- Mandibul; of first visceral arch Caudal end ol -r embryo iL Lower limb-bud^ Upper limb-bud The more complete differentiation of the digestive tube and the ventral folding in of the body-walls change this relation, the rapidly decreasing umbilical vesicle soon becoming secondary to the embryo. At the close of the stage of the blastodermic vesicle — about the fifteenth day — the embryo possesses a general cylindrical body-form, the dilated cephalic pole being free, while the belly-stalk attaches the caudal segment to the chorion ; the amniotic sac invests the dorsal aspect, the large umbilical vesicle occupying the greater part of the ventral surface. Human Fig. 69. embryos of the fourteenth and fifteenth days ( Fig. 68, 3 and 4) are distinguished by a conspicu- ous fle.xure opposite the attach- ment of the utnbilical vesicle, the convexity being directed ven- trally, the deep corresponding concavity producing a marked change of profile in the dorsal outline. During these changes the expansion of the cerebral segments outlines the three pri- mary divisions of the cephalic portion of the neural tube, the anterior, the middle, and the posterior brain-vesicles. A little later a series of conspicuous bars, the visceral arches, appears as ob- liquely directed parallel ridges on either side of the head, immediately above the prominent heart-tube, which is now undergoing marked torsion. By the nineteenth day the dorsal concavity, which is peculiar to the human embryo, has entirely disap- peared, the profile of this part of the embryo presenting a gentle convexity ; the cephalic axis, however, exhibits a marked bend, the cephalic flexnre, in the vicinity of the middle cerebral vesi- cle, in consequence of which p,c yo the axis of the anterior cere- bral segment lies almost at right angles to that of the middle vesicle. The com- pletion of the third week finds the characteristic de- tails of the cephalic end of the embryo, the cerebral, the optic, and the otic vesi- cles, and the visceral arches and intervening furrows well advanced, with correspond- ing definition of the primitive heart and the umbilical stalk and vesicle. The limb-buds usually appear about this Lower limb-hud^ time, those of the upper ex- a- tremity Slighdy preceding Human embryo of about twenty-five days, drawn from the model of His. those of the lower. -^ 10. The period between the twenty-first and the twenty-third days witnesses remarkable changes in the general appearance of the embryo ; in addition to greater prominence of the visceral arches, the cerebral segments, and the limb-buds, the embryonic a.xis, which, with the exceptions already noted, up to this time is only slightly curved, now undergoes flexion to such extent that by the twenty-third day the overlapping cephalic and caudal ends of the embryo are in close apposition, the body-axis describing rather more than a complete circle (Fig. 69). Optic vesicle — \ Mandihularprocess \ m ^ of first visceral arch ,--* ' Cervical flexure •Second visceral arch Third visceral arch rth visceral arch Upper limb-bud THE MSCERAL ARCHES AND FURROWS. 59 From the twenty-third to the twenty-eighth day the excessive flexion gradually disappears, owing to the increased volume of the heart and the growth of the head, and by the end of the fourth week the embryo has acquired the most characteristic development of the embryonic stage (Fig. 71 ). The reduction in the curvature of the body-axis and the consequent separation of its poles and the raising of the head are accompanied by the appearance of four well-marked a.xial flexions, the cephalic, the cervical, the dorsal, and the sacral flexures (Fig. 71). The first of these, the cephalic, is an accentuation of the primary flexure, which is seen as early as the eighteenth day, and is indicated by the projection of the midbrain ; it corresponds in position to the future sella turcica. The second and very conspicuous bend, the cervical flexure, marks the caudal limit of the cephalic portion of the neural axis, and agrees in position with the subsequent upper cervical region. The dorsal and sacral flexures are less well defined, the former being situated opposite the upper limb-bud, where the cervical and dorsal series of somites join, the latter, near the lower limb-bud, corresponding with the junction of the lumbar and sacral somites. The cephalic segment at this stage presents numerous prominent details, the Fig. 71. Third \isceral arch First external \isceral farrow of firstc,^/ "^ST^^ Second visceral arch Dorsal flexure i.'pper limb -'•5^' // Human embr>'o of about twenty-eight days, dr; the model of Hi: secondary cerebral vesicles, the forebrain, the interbrain, the midbrain, the hind ■ brain, and the after-brain, the visceral arches and furrows, the optic and otic vesicles, the olfactory pits, and the primitive oral cavity all being conspicuous. The heart ap- pears as a large protrusion, occupying the upper half of the ventral body-wall, on ■\vhich the primary auricular and ventricular divisions are distinguishable. The somites form a conspicuous longitudinal series of paraxial quadrate areas, about thirty-seven in number ; they correspond to the inter^'ortebral muscles, and may be grouped to accord with the primary spinal nerves, being, therefore, distinguished as eight cer- vical, twelve dorsal, five lumbar, five sacral, and five or more coccygeal somites. THE VISCERAL ARCHES AND FURROWS. Since the visceral arches are best developed in the human embryo during the last half of the third week, a brief consideration of these structures in this place is appropriate. The visceral arches in mammalian embryos constitute a series of fiv^e parallel bars separated by intervening furrows, obliquely placed on the ventro-lateral aspect of the cephalic segment, occupying the region which later becomes the neck. They represent, in rudimentary development, the important branchial or gill- 6o HUMAN ANATOMY. apparatus of water-breathing vertebrates, in which the respiratory function is per- formed by means of the rich vascular fringes hning the clefts through which the water passes, thus permitting the exchange between the oxygen of the water and the carbon dioxide of the blood. Each arch is supplied by a blood-vessel, or aortic bow, which passes from the main ventral stem, the truncus arteriosus, through the substance of the visceral arch backward to unite with the similar bows to form the dorsal aortcB. In aquatic vertebrates the aortic bows supply an elaborate system of secondary branchial twigs, which form rich capillary plexuses within the gills ; in air-breathing vertebrates, however, in which these structures are only rudimen- tary, the main stems, the aortic bows, are alone represented. With the loss of func- tion which follows the acquisition of aerial respiration in the higher vertebrates, the number of visceral arches is reduced from six, or even seven, as seen in fishes, to five, the fifth arch in man, however, being so blended with the surrounding struc- tures that it is not visible externally as a distinct bar. In their condition of great- est perfection, as in fishes, each visceral arch contributes an osseous bar, which forms part of the branchial skeleton ; these bony bars are represented in man and mammals by cartilaginous rods, which temporarily occupy the upper arches, for the most part entirely disappearing. When viewed in frontal section (Fig. 73), the mammalian visceral arches are seen as mesodermic cylinders imperfectly separated by e.xternal and internal grooves, the visceral furroies and the pharyngeal pouches respectively ; this arrangement emphasizes another modification following loss of function, — namely, the conversion of the true visceral clefts of the lower forms into furrows, — since in man and mammals the Fjg. 72. fissures are closed by the occhiding mem- brane formed by the apposition of the ectoblast and the entoblast at the bottom of the outer and inner furrows. The First or Mandibular Arch early becomes differentiated into a short upper or maxillary process and a longer lower or mandibular process. The maxil- lary process, in conjunction with its fellow — tj-rmnarcn ^j ^^ opposite side and the frotifo-nasal Head of human embn-o of about twenty-one days, hrnrp^t: wViirVi HpspphHi; ts a median nro- seen from the side, showing visceral arches and external P'OCeSS wnicn QescenOS as 3. meaian prO visceral furrows. X 20. (A/ur His.) jcction from the head ( Fig. 75), contrib- utes the tissue from which the superior and lateral boundaries of the oral cavity and the nasal region are derived. The mandibular process joins with its mate in the mid-line and gives rise to the lower jaw and other tissues forming the inferior boundary of the primary oral cavity. The latter in its original condition appears as a widely open space leading into the primi- tive pharyngeal cavity ; later the septum is formed which divides the oral from the nasal cavity. The mandibular process contains a cartilaginous rod, which for a time represents the corresponding bony arch of the visceral skeleton of lower tvpes. The ventral and larger part of this rod, known as Meckel' s cartilage, entirely disap- pears, the lower jaw being developed independentlv around this bar of cartilage ; the upper end of the cartilaginous bar, however, persists and forms two of the ear- ossicles, the malleus and the incus. The Second or Hyoid Arch also contains a cartilaginous bar, from the ven- tral segment of which (known as the cartilage of Reicherf) is derived the smaller cornu of the hyoid bone ; the dorsal end of the bar, which is fused with the tem- poral bone, gives rise to the styloid process, the intervening portion of the cartilage persisting as the stylo-hyoid ligament. The cartilage of the second arch is also con- cerned in the formation of the stapes. The origin of this ear-ossicle is double, since the crura of the stapes are derived from the cartilage of the hyoid arch, while the base is contributed by the general cartilaginous capsule of the labyrinth. The char- acteristic form of the stapes is secondary and due to the perforation of the triangu- lar plate, the early representative of this bone, which thus acquires its characteristic stirrup-shape in consequence of the penetration of a minute blood-vessel, the perfo- rating stapedial artery, a branch of the internal carotid, which later disappears. '^. THE VISCERAL ARCHES. 6i The Third or First Branchial Arch contains a rudimentary cartilaginous bar from which part of the body and the greater cornu of the hyoid bone are derived. The fourth and fifth arches, or second and third branchial, enclose rudimentary cartilaginous bars which early fuse into plates ; these unite along their ventral borders and give rise to the thyroid cartilage of the larynx. The External Visceral Furrows (Fig. 73), the representatives of the true clefts of the lower types, appear with decreasing distinctness from the first towards the fourth ; the third and fourth early suffer modification, so that by the twenty-eighth day the first and second furrows alone are clearly defined. The First Visceral Furrow, the hyomandibular cleft, undergoes obliteration e.xcept at its dorsal part, which becomes converted into the external auditory meatus, the surrounding tissue giving rise to the walls of the canal and the external ear. The remaining clefts gradually disappear, becoming closed and covered in by the over- hanging corresponding arches ; this relation is particularly marked towards the Fig. 73. Optic vesicle Maxillary process Dorsal wall of primitiv oropharynx Primitive oesophagus Upper end of body-cavity Right umbilical Tuberculum impar tive aortae Upper half of human embryo of about eighteen days, drawn from His's models. X 45. A, dorsal wall of primitive oropharynx bounded by visceral arches, external and internal furrows. B, anterior wall of primitive oropharynx, seen from tjehind. 1-5, sections of aortic arches; I-IV, external visceral furrows. caudal end of the series, where the sinking in of the arches and the included furrows produces a depression or fossa — the sinus pmcervicalis of His — in the lower and lateral part of the future neck region. This recess subsequently entirely di_sappears_ on coalescence of the bordering parts ; sometimes, however, such union is defective, the imperfect closure resulting in a permanent fissure situated at the side of the neck, known as cervical fishda, by means of which communication is often established between the pharynx and the exterior of the body. Such communication must, however, be regarded as secondary, as originally the external furrows were sepa- rated from the primitive pharyngeal cavity by the delicate epithelial septum already mentioned as the occluding plate. Where entrance into the pharynx through the fistula is possible, it is probable that the septum has been destroyed as the result of absorption or of mechanical disturbance following the use of the probe. The Inner Visceral Furrows, or pharyngeal pouches, repeat the general arrangement of the external furrows. The first pharyngeal pouch becomes narrowed and elongated, and eventually forms the Eustachian tube : a secondary 62 HUMAN ANATOMY. Fronto-tiasal process nbr>-o of about twenty- dorsal expansion gives rise to the middle ear, while the occluding plate sepafating the outer and inner furrows supplies the tissue from which the tympanic membrane is formed. The second furrow in great part disappears, but its lower portion con- tributes the epithelium of the faucial tonsil and the supratonsillar fossa. The fossa of Rosenmiiller is a secondary depression and probably does not represent the original ' furrow. The third and fourth pouches give rise to ventral entoblastic outgrowths from which the epithelial portions of the thymus and of the thyroid body are developed respectivelv. The last-named organ has an additional unpaired origin from the ento- blast forming the ventral wall of the pharyn.x in the vicinity of the second visceral arch. The Development of the Face F"'G. 74- and the Oral Cavity. — The earliest suggestion of the primitive oral cavity is the depression, or stomodtriim, which ap- Laterai nasal process pears about the thirteenth day on the Mesial nasal process ^'^itral surface of the cephalic end of the Ma-viiiary process cmbryo immediately beneath the ex- Mandibuiar process panded anterior cerebral vesicle. The oral pit at first is separated from the ad- jacent expanded upper end of the head- gut by the delicate septum, the pharyn- i, geal membrane, composed of the opposed '■ ectoblast and the entoblast, which in this location are in contact without the inter- vention of mesoblastic tissue. With the rupture of the pharyngeal membrane, the deepened oral pit opens into the cephalic extremity of the head-gut, now known as the primitive pharynx. The formation of the face is closely associated with the growth and fusion of the upper visceral arches in conjunction with the surrounding parts of the ventral surface of the head. The first visceral arch, as already described, presents two divisions, the maxillary and the mandibular process. The latter grows ventrally and joins in the mid-line its fellow of the opposite side, to form, with the aid of the second visceral arches, the tissues from which the lower boundary and the floor of the mouth are derived. The upper and lateral boundaries of the primitive oral Fig. 75. cavity and the differentiation of the nasal region proceed from the modification and fusion of three masses, the two lateral paired maxillary processes of the first visceral arches and the mesial unpaired frojito-nasal process, which descends as a conspicuous projection from the ventral surface of the anterior part of the head. The maxillary processes grow towards the mid-line and, in conjunction with the descending fronto-nasal projection, form the lateral and superior boundary of the primitive oral cavity (Fig. 74). Very soon the development of the future nares is suggested by the appearance of slight depressions, the olfactory pits, one on each side of the fronto-nasal process ; these areas constitute part of the wall of the forebrain, a relation which foreshadows the future close association between the olfactory mucous membrane and the cortex of the olfactory lobe. During the fifth week the thickened margins of the fronto-nasal process undergo differentiation into the mesial nasal processes, while coincidently the lateral portions of the fronto-nasal projection grow downward as the lateral nasal processes, these newly developed projections constituting the inner and outer boundaries of the rapidly deepening nasal pits. The line of contact between the lateral nasal process and the maxillary process is marked by a superficial furrow, the naso-optic groove. Lateral nasal process Maxillary proces; First external vis ceral furro' Second visceral arch Third visceral arch' I embryo ot about thirty-four days. \ After His.) THE STAGE OF THE FCETUS. 63 Fig. 76. Dorsum of nose Anlage producing nasal tip al surface of llary process Portion of head of human t roof of primiti\e 1 Roof of oropharyr nbryo of about thirty-four days, showing -al cavity. X 10. (After His.) which leads from the nasal pit to the angle of the eye ; this furrow, however, merely indicates the position of the naso-lachrymal duct which develops independendy at the bottom of the primary groove. Reference to Figs. 74 and 75 emphasizes the fact that the nasal pits and the primitive oral cavity are for a time in widely open com- munication ; towards the close of the sixth week, however, the maxillary processes of the first arch have approached the mid-line to such an extent that the}' unite with the lateral margins of the fronto-nasal process as well as fuse with the lateral nasal processes above. Owing to this union of the three processes, the nasal pits become separated from the oral cavity, and with the appearance and completion of the palatal sep- tum the isolation of the nasal fossae from the mouth is ac- complished. The lateral nasal processes contribute the nasal ala;, while from the conjoined Naso-optic groove- mesial nasal process are devel- oped the nasal septum and the bridge of the nose in addition to the middle portion of the upper lip and the intermaxil- lary segment of the upper jaw, the superior maxillary part of the latter being a derivative of the maxillary process of the first arch. Arrested development and imperfect union between the maxillary processes and the fronto-nasal process result in the congenital defects known as harelip and cleft palate, the degree of the malformation depending upon the extent of the faulty union. The Stage of the Fcetus. — The fifth week marks the completion of the period of development during which the product of conception has acquired the characteristic features of its embryonal stage ; beginning with the second month and continuing until the close of gestation, the succeeding sfag-e of the fcetus is distin- guished by the gradual assumption of the external features which are peculiar to the young human form. In addition to the already mentioned changes affecting the visceral arches and frontal process in the development of the face, the fifth week witnesses the differentiation of the limbs into segments, the distal division of the upper extremity exhibiting indica- nt j^^- -^Kia^ tions of the future fingers, which thus anticipate the appear- kj^ KjjIP^i^— I ance of the toes. The liver is already conspicuous as a >•■■' > -'irjy^''m\ marked protuberance occupying the ventral aspect of the trunk immediately below the heart. The head by this time has acquired a relatively large size, the prominent cephalic flexure which marks the position of the midbrain being par- /^» ticularly conspicuous. At the end of the fifth week, or the ^ thirty-fifth day, the foetus measures about fourteen millimetres ' in its longest dimension. The sixth week finds the fcetus elongated with greater distinctness of the human form, the large size of the head, on which the cervical flexure is very evident, being highly characteristic when compared with corresponding stages of the lower mammals. The several constituents of the face become more perfectly formed, including the completion of the superior boundary of the oral cavity and its separation from the nasal pits by the septum resulting from the union of the fronto-nasal process with the maxillary processes ; the fusion of the latter with the lateral frontal processes now defines the external boundary of the nostrils of the still, however, broad and flattened nose, which lies immediately above the transverse cleft-like oral opening. The visceral arches are no longer visible as individual bars, having undergone com- plete fusion. The differentiation of the digits on both hands and feet has so far Fig. 77. Head of human embr>'0 of about seven weeks. X 5- {A/ter Ecker.) 64 HUMAN ANATOMY. progressed that fingers and toes are distinctly indicated, although the fingers only are imperfectly separated. The first suggestion of the external genitals appears about the end of the sixth week. At this time the foetus measures about nineteen millimetres. During the seventh and eighth weeks the foetal form of the body and the limbs attain greater perfection, the large head becoming raised from the trunk and the toes, as well as fingers, being now well formed, although the rudiments of the nails do not appear until some time during the third month. At the close of the second month the extra-embryonic protrusion of the intestine through the umbilicus into the umbilical cord reaches its greatest extent. The genito-urinary system is repre- sented by the fully developed Wolffian body, the vesical dilatation of the allantoic duct, the separation of the cloaca into rectum and genito-urinary passage, the indif- Vmbilical vesicle Umbilical stalk - Umbilical cord- ^rr^ Human embrj-o of about ihirty-fi\ tj da> s. ,-, 4. Amnion and chorion cut and turned aside. ferent sexual gland, and the undifferentiated external genitals, consisting of the geni- tal eminence and the associated genital folds and genital ridges. The external ear has assumed its characteristic form, and the eyelids appear as low folds encircling the conspicuous eye, in which the pigmentation of the ciliary region is visible. Although the face is well formed, the nose is still flat, the lips but slightly prominent, and the palate not completely closed. The rapid growth of the brain results in the dispro- portionate size of the head, which at this stage almost equals the trunk in bulk. It is to be noted that by the close of the second month the permanent organs are so far advanced that the subsequent growth of the fcetus is effected by the further de- \-elopment of parts already formed and not by the accession of new organs. The beginning of the second month marks the period of greatest relative growth ; at the end of this month the fcetus measures about thirty millimetres in its longest dimension. STAGE OF THE FCETUS. 65 The third month is characterized by greater perfection of the external forrn,- the rounded head is raised from the trunk so that a distinct neck appears, while the thorax and abdomen are less prominent ; the limbs, which are w^ell developed with completed differentiation of the fingers and toes, provided with imperfect nails, now assume the characteristic foetal attitude. . The eyelids become united by the tenth week, remaining closed until the end of the seventh month. The cloacal opening becomes differentiated during the ninth and tenth weeks into the genito-urinary and Fig. 79. Umbilical vesicle Human foetus of about eight weeks. X i'A- Amnion bas been cut and reflected, but still covers the umbilical vesicle and its stalk. the anal orifice, while during the eleventh and twelfth weeks the e.xternal genital organs acquire the distinguishing peculiarities of a definite sex. The greatest length of the foetus, measured in its natural position and excluding the limbs, at the end of the third month, is about eighty millimetres ; its weight approximates twenty grammes. The fourth month witnesses augmented growth in the foetus, which, how- ever, resembles in its general appearance the foetus of the preceding month. The 5 66 HUMAN ANATOMY. extra-fcEtal portion of the intestinal canal, which at an earlier period passes into the umbilical cord, duriiig the fourth month recedes within the abdomen. The differentiation of sex is still more sharply exhibited by the external organs : in the male the penis is acquiring a prepuce, and in the female the labia majora and the clitoris are becoming well developed. At the close of this period the fcetus measures approximately 150 millimetres and weighs about 120 grammes. During the fifth month the first foetal movements are usually observed. The heart and the liver are relativelv of large size. The decidua capsularis fuses with the decidua \era, thereby obliterating the remains of the uterine cavity. The meco- nmm within the intestinal canal shows traces of bile. The advent of the fine hair, the /aniigo, first upon the forehead and the eyebrows, and somewhat later upon the scalp and some other parts of the body, represents a conspicuous advance. Likewise adipose tissue appears in places within the subcutaneous layer. The approximate length, at the end of the fifth month, is twenty-three centimetres and the average weight about 320 grammes. The sixth month is characterized by complete investment of the body by lanugo and by the appearance of the vertiix caseosa, the protecting sebaceous secre- tion which coats the body of the foetus to prevent as far as possible maceration of the epidermis in the amniotic fluid. The latter now reaches the maximum quantity, being contained within the large sac of the amnion. The sixth month is distin- guished by the conspicuous increase both in the size and weight of the fcetus, and is known, therefore, as the period of greatest absolute growth. At the close of the sixth month the fcetus measures approximately thirty-four centimetres in its longest dimension and weighs about 980 grammes. The seventh month is marked by progressive changes in the various parts of the foetus, whereby the more advanced details become pronounced in the central nervous system and digestive tract. The length of the foetus at the close of the seventh month approximates forty centimetres and its weight about 1700 grammes. The eighth month is occupied by the continued growth and general develop- ment, as part of which the fcetus acquires greater plumpness than before and a brighter hue of the integument, now entirely covered with vernix caseosa. The lanugo begins to disappear, while the scalp is plentifully supplied with hair ; the nails have reached, or project beyond, the tips of the fingers. By the close of the eighth month the foetus has attained a length of about forty-six centimetres and a weight of about 2400 grammes. The ninth month witnesses the gradual assumption of the characteristics of the child at birth, among which are the rounder contours, the extensive, although not complete, disappearance of the lanugo, except from the face, where it largely persists throughout life, the completed descent of the testicles within the scrotum, the approximation of the labia majora, the permanent separation of the eyelids, with well-developed lashes, and the presence of dark greenish meconium within the in- testinal canal. The umbilicus has reached a position almost exactly in the middle of the body. The average length of the foetus at birth is about fifty centimetres, or twenty inches ; its average weight, while included between widely varying extremes, may be assumed as approximately 3100 grammes, or 6.8 pounds. The weight of the foetus at term is materially influenced by the age of the mother, women of about thirty-five years giving birth to the heaviest children. The weight and stature of the mother probably also affect the weight of the child. Repeated pregnancies exert a pronounced effect upon the foetus, since the weight of the child reaches the maximum with the fifth gestation. The purpose of the preceding pages is to present an outline of the general developmental processes leading to the differentiation and establishment of the defi- nite body-form of the human embryo : a more detailed account of the development of the various parts of the body is given in connection with the descriptions of the systems and the individual organs, to which the reader is referred. THE ELEMENTARY TISSUES. The various parts and organs of the complex body may be resolved, in their morphological constitution, into a few component or elementary tissues, of which there are four principal groups, — the epithelial, the contiective, the tnuscular, and the tiervous tissues. The first two of these may be discussed at this place ; the re- maining groups, the muscular and the nervous tissues, are considered most advan- tageously in connection with the muscular and nervous systems to which they are directly related and under which sections they will be found. THE EPITHELIAL TISSUES. The epithelial tissues include, primarily, the integumentary sheet of protecting cells covering the exterior of the body and the epithelium lining the digestive tube. Secondarily, they embrace the epithelial derivatives of the epidermis, such as the nails, hairs, and glands of the skin and its extensions, and the epithelial lining of the ducts and compartments of the glands formed as outgrowths from the primi- tive gut-tube, as well as the epithelium clothing the respiratory tract which originates as an evagination from the digestive canal. An apparent exception to the usual origin of the epithelial tissues from either the ectoblast or the entoblast is presented by the lining of the genito-urinary tract, since all the epithelium occurring in connection with these organs, as far as the bladder, is of mesoblastic origin, and hence genetically related closely with the e.xtensive mesoblastic group of tissues. It is to be noted in this connection that the epithelium of the bladder and of a part of the urethra is derived from outgrowths of the primary gut, and therefore is entoblastic in origin. The primary purpose of epithelium being protection of the more delicate vascular and nervous structures lying within the subjacent connective tissue of the integument or of the mucous membrane, the protecting cells are arranged as a con- tinuous sheet, the individual elements being united by a small amount of inter- cellular substance. Epithelium contains no blood-vessels, the necessary nutrition of the tissue being maintained bv the absorption of the nutritive juices which pass to the cells by way of the minute clefts within the intercellular substance. Likewise, the supply of nerve-fibres within epithelium ordinarily is scanty, although in certain localities possessing a high degree of sensibility, as the cornea or tactile surfaces, the termi- nations of the nerves may lie between the epithelial elements. The epithelial tissues are frequently separated from the subjacent connective tissue by a delicate basement membrane, or 7nembrana propria ; the latter, which may be regarded as a derivative or modification of the connective tissue, usually appears as a delicate subepithelial boundary, being particularly well marked beneath the epithelium of glands. According to the predominating form of the component cells, the epithelial tissues are best divided into two chief groups, — squamous and cobmi7iar, — with sub- divisions as shown in the following table : VARIETIES OF EPITHELIUM. I. — Squamous : a. Simple, — consisting' of a single layer. b. Stratified, — consisting of several layers. II. — Columnar : a. Simple, — consisting of a single layer. b. Stratified, — consisting of several layers. III. — Modified : a. Ciliated, b. Goblet, c. Pigmented. IV.— Specialized : a. Glandular epithelium, b. Neuro-epithelium. 67 68 HUMAN ANATOMY. Squamous epithelium, when occurring as a s/ng/c layer, is composed of flattened polyhedral nucleated plates which, when viewed from the surface, present a regular mosaic, sometimes described by the terms "pavement" or "tessellated." Such arrangement of the squamous type is unusual in the human body, the lining of the alveoli of the lungs, the posterior surface of the anterior capsule of the crystalline lens, the membranous labyrinth, and a few other localities being the chief places where a single layer of squamous cells occurs. The far more usual arrangement of such cells is several superimposed layers, this constituting the important group of stratified squamous epithelia. When Simple squamous epithelium from anterior capsule of crystalline lens. X 400. seen in section, the deepest cells are not scaly, but irregularly columnar, resting upon the basement membrane by slightly expanded bases. The surface of the un- derlying connective tissue supporting this variety of epithelium is beset with minute elevations or papillae, which serve as advantageous positions for the terminations of the blood-vessels, as well as specialized nerve-endings. Ounng to the more favored nutrition of the deepest stratum, the cells next the connecti\'e tissue exhibit the greatest vitality, and often are the exclusi\'e source of the new elements necessary Fig. S3. Isolated surface cells from epithe- lium lining the mouth. X 350. ri^ (^y Epithelial cells from epider- 5 showing mtercellular bridges. to replace the old and effete cells which are continually being removed at the free surface ; this loss is due not only to mechanical abrasion, but also to the displace- ment of the superficial elements by the new cells formed within the deeper layers. Passing from the basement membrane towards the free surface, the form of the cells undergoes a radical change. The columnar type belongs to the deepest layer alone ; the superimposed cells assume irregularly polyhedral forms and then gradu- ally expand in the direction parallel to the free surface to become, finally, converted into the large, thin scales so characteristic of the superficial layers of stratified epithelium. The position of the nucleus also varies with the situation of the cells, EPITHELIUM. 69 since within those next the basement membrane the relatively large nucleus — the nutritive organ of the cell — occupies the end nearest the subjacent connective tissue ; in the middle and superficial strata, the nucleus, comparatively small in size, is placed about the centre of the cell. The irregularly polyhedral cells of the deep or middle strata frequently are connected by delicate processes which bridge the intervening intercellular clefts ; when such elements are isolated, the delicate connecting threads are broken and the disassociated elements appear beset with minute spines, then constituting the prickle- cells. In certain localities, as in the urinary bladder, the columnar cells of the deepest layer rapidly assume the scaly character of the superficial strata ; such epithelium Fig. S4. Fig. 85. Fig Transitional epithelium from bladder of cliild. possesses relatively few laj-ers, and from the readiness with which the type of the cells changes, is often described as tiansitional epithelhmi ; the latter cannot be regarded as a distinct varietv, but only as a modification of the stratified scaly group. Coluninar epithelium, when occurring as a single layer of cells, constitutes the simple columnar varietv, which enjoys a much wider distribution than the cor- responding squamous group, the lining of the stomach and of the intestinal tube being important examples. When the single layer of such epithelial tissues is re- placed b}' several, as in the stratified columnar variety, the superficial cells alone Fig. 87. Ciliated epitlielial cells. A, from intes- tine of a mollusk [_cyclas) ; B, from nasal cavity of frog. X 750. i^Engelmann,) are typically columnar. The free ends of the columnar elements not infrequently present specializations in the form of a cuticular border or of cilia, while their ends which rest upon the basement membrane are pointed, forked, or club-shaped. The intervals thus formed by irregularities of contour are occupied by the cells of .the deeper stratum next the basement membrane. Each cell is provided with a nucleus, which is situated about midway between the ends of the superficial elements and nearer the base within the deeper ones. The surface cells often contain collections of mucous secretion which distend their bodies into conspicuous chalice forms known as goblet-cells, which occur in great profusion in the lining of the large intestine and the respiratory mucous membrane. 7° HUMAN ANATOMY. Fig. 89. Modified Epithelium. — The free surface of the epitheUum in many localities, as in the trachea, the inferior and middle nasal meatuses, and the uterus, is pro- vided with minute, hair-like vibratile processes, or cilia, which are produced by the specialization of the cytoplasm of the free end of the cell. The e.xact relations of the cilia to the cytoplasm are still matters of uncertainty, although the investigations of Engelmann and others on the ciliated epithelium of in\-ertebrates render it prob- able that the hair-like processes attached to the cells of higher animals are also connected with intracellular fibrillae, which appear as delicate striations within the superficial and more highly specialized parts of the cells. In man and the higher mammals ciliated epithelium is limited to the columnar variety. The e.\act number of individual cilia attached to the free surface of each cell varies, but there are usually between one and two dozen such appendages. Their length, likewise, differs with locality, those lining the epididymis being about ten times longer than those attached to the tracheal mucous membrane. When favorable conditions obtain, including a suffi- cient supply of moisture, o.xygen, and heat, ciliary motion may continue for many hours and even days. On surfaces clothed with columnar epithelium certain cells are distinguished by unusually clear cytoplasm and exceptional form and size ; these are intestine. X 500. the gobkt-cclls, the peculiar elliptical or chalice form of which results from the accumulation of the mucoid secretion elaborated within their protoplasm. When the distention becomes too great the cell ruptures in the direction of least resistance, and the secretion is poured out upon the surface of the mucous membrane as the lubricating mucus. The goblet-cells, therefore, may be regarded as unicellular glands, and represent the simplest phase in the specialization of glandular tissues. The protoplasm of epithelial cells often becomes invaded by particles of foreign substances ; thus, granules of fatty and proteid matters are very commonly encoun- tered, while the presence of granules of eleidin in certain cells of the epidermis char- acterizes the stratum granulosum. When the invading particles are colored, as when composed of melanin, the affected cells acquire a dark brown tint, and are then known as pigmented epithelium. E.xamples of such cells are seen in the retina and in the deeper cells of the epidermis in certain races. Specialized Epithelium. — Reference has already been made to goblet-cells as representing unicellular glands ; these may be regarded, therefore, as instances of a temporary specialization of epithelium into glandular tissue. When the epithelial elements become permanently modified to engage in the elaboration of secretory substances, they are recognized as glandular epithelium. The cells lining the ducts and the ultimate compartments of glands are modified extensions of the epithelial investment of the adjacent mucous membrane. Their form and condition depend upon the degree of speciali- zation, varying from columnar to spherical and polyhedral, on the one hand, and upon the nature and number of the secre- tion particles on the other. The cells lining parts of certain glands, as those clothing the ducts of the salivary glands, or the irregular portion of the uriniferous tubules, exhibit a more or less pronounced striation ; cells presenting this peculiarity are termed rod-epithelium. The highest, and often exceedingly complex, specializations affecting epithelial tissues are encountered in connection with the neurones supplying the organs of special sense. The epithelium in these localities is differentiated into two groups of elements, — the sustentacular and the perceptive; to the latter the name of neuro- epitheliuvi is applied. Conspicuous e.xamples of such specialization are the rod- and cone-cells of the retina and the hair-cells of Corti's organ in the internal ear. A more detailed description of the glandular tissues is given with the digestive tract ; that of the neuro-epithelia with the organs of special sense. Fig. 90. Pigmented epithelium from "human retina. X 435- ENDOTHELIAL TISSUES. 71 Mesothelial cells from omentum of dog. X 300. Intercellular cement-substance stained by argentic nitrate. ENDOTHELIUM. The modified mesoblastic, later connective-tissue, cells that line serous surfaces, including those of the pericardial, the pleural, and the peritoneal divisions of the body-cavity, together with those of the blood- and lymph-vessels and the lymphatic spaces throughout the bodv, constitute endothelnim. These spaces, in principle, are intramesoblastic clefts and the elements forming their lining are derivatives of the great connective-tissue layer. The endothelia, therefore, belong to the connective tissues and are properly regarded as modified elements of that class ; as Fig 91 a matter of convenience, however, they may be considered at this place in connection with the epithelial tis- sues. The most striking difference in situation between the endothelia and the epithelia is found in the fact that the former cover surfaces not com- municating with the atmosphere, while the epithelial tissues clothe mucous membranes all of which are directly or indirectly continuous with the integumentary surface. A further contrast between these tis- sues is presented in their genetic re- lations with the primary blastodermic layers, since the epithelia, with the exception of those lining certain parts of the genito-urinary tracts which are derived from the mesoblast, are the trans- formations and outgrowths from the ectoblast and the entoblast, while the endo- thelia are direct modifications of the mesoblastic cells. The young mesoblastic cells bordering the early body-cavity become differenti- ated into a delicate lining, the ynesothelmni, and later give rise to the characteristic plate-like elements which constitute the lining of the permanent serous sacs. The name mesothelium is sometimes retained to designate the permanent investment of the great serous cavities, as distinguished from the endothelium which clothes the vascular and other serous spaces. Seen in typical preparations, as ob- tained from the peritoneum after treatment with argentic nitrate and subsequent stain- ing with haematoxylin, the endothelial cells on surface view appear as irregularly polyg- onal areas mapped out by deeply tinted lines. The latter represent the silver- stained albuminous intercellular cement- substance which unites the flattened cells in a manner similar to that obser\'ed in simple squamous epithelium ; this superficial likeness is so marked that it has led to much confusion as to the proper classification of endothelium under the connective tissues. The lines of apposition are sinuous and less regular than bet^veen epithelial elements, in many cases appearing distinctly dentated. The exact form of the cells and the character of their contours, however, are not constant, since they probably depend largely upon the degree of tension to which the tissue has been subjected. Not infrequently the intercellular substance, at points where several endothelial cells are in apposition, shows irregular, deeply colored areas after silver staining ; Fig. Endothelial cells lining artery of dog, after silver staining. X 500. 72 HUMAN ANATOMY. these figures are described as stigmata or pseudostomata, and by some are interpreted as indications of the existence of openings leading from the serous cavity into the subjacent lymphatics. Critical e.xamination of these areas, however, leads to the conclusion that they are largely accidental, and due to dense local accumulations of the stained intercellular materials ; they are not, therefore, to be regarded as intercellu- lar ])assages. True orifices or sloinala, however, undoubtedly exist in certain serous membranes, as in the septum between the peritoneal cavity and the abdominal lymph-sac of the frog, and, possibly, the peritoneal surface of the diaphragm of mammals. The positions of these stomata are marked by a conspicuous modification in the form and arrangement of the surrounding endothelial plates, which exhibit a radial disposition about the centres occupied by the stomata. The immediate walls of the orifices are formed by smaller and more granular elements, xhe guard or ger- minating cells, the contraction and expansion of which probably modify the size of the openings. Although the ectoblast and the entoblast are the germ layers which furnish great tracts of epithelium in the adult body, yet the mesoblast, the middle germ layer, also supplies distinct epithelial tissues. As it has been already pointed out, the epidermis, the epithelial portion of the skin, with its derivatives, is a product of the ectoblast. The epithelial lining of the mouth cavity as far back as the region of the palatine arches, and the epithelium of the anus are also of ectoblastic origin, since they are formed as in-pocketings of the outer germ layer during early embryonic life. With the exception of these areas, the epithelium lining the entire digestive tube, and that of its accessory glands, notably the liver and the pancreas, is of entoblastic origin. The same thing is true of the epithelium of the respiratory tract, since this entire tract is an outgrowth from the primitive intestine. But in the case of the uro-genital system, the epithelium there found, or most of it, is derived directly from the. mesoblast. To be more specific, the Fallopian tubes (uterine tubes), uterus and vagina of the female, which have, of course, a distinct layer of epithelium on their inner surface, are formed from certain embryonic tubes known as the Miillerian ducts, which are derived from the mesoblast. The vas (ductus) deferens of the male is first represented in the embryo by a tube known as the Wolffian duct, which, with its epithelium, is also derived from the mesoblast. The sex-cells found in the sex -glands, which in the case of the male retain a distinct epithelial character, are apparently of mesoblastic origin. The ureter and part of the kidney are out- growths from the Wolffian duct and therefore mesoblastic, while the rest of the kidney not formed in this way is also of mesoblastic origin. Hence, it is evident that distinct lavers of epithelium are formed from all three germ layers, and that in this respect no peculiarity is attributable to any one of them. THE CONNECTIVE TISSUES. The important .group of connective substances, the most widely distributed of all tissues, is the direct product of the great mesoblastic tract ; the several members of this extended family are formed by the differentiation and specialization of the intercellular substance wrought, through the more or less direct agency of the meso- blastic cells. The variation in the physical characteristics of the connective tissues is due to the condition of their intercellular constituents. During the period of em- bryonal growth these latter are represented by gelatinous, plastic substances ; a little later by the still soft, although more definitely formed, growing connective tissue, which, in turn, soon gives place to the yielding, although strong, adult areolar tissue. Grouped as masses in which white fibrous tissue predominates, the intercellular substance presents the marked toughness and inextensibility of tendon ; where, on the contrary, large quantities of yellow elastic tissue are present, extensibility is conspicuous. Further conden- sation of the intercellular sub- F^'G- 93- stance produces the resistance encountered in hyaline carti- lage, intermediate degrees of condensation being presented by the fibrous and elastic varie- ties. In those cases in which the ground-substance becomes additionally impregnated with calcareous salts, the well-known hardness of bone or dentine is attained. Notwithstanding these variations in the density of the intercellular substance, the cel- lular elements have undergone but little change, the connective- tissue corpuscle, the tendon-cell, the cartilage- cell, and the bone- corpuscle being morphologically identical. The principal forms in which the connective substances occur may be grouped as follows : 1. Iin)nature connective tissue, as the jelly of Wharton in the umbilical cord and the tissues of embryos and of young animals. 2. Areolar tissue, forming the subcutaneous layer and filling intermuscular spaces, and holding in place the various organs. 3. Dense Jibro-elastic tissue, found in the fasciae, the sclera, the ligaments, etc. Where white fibrous tissue predominates and yellow elastic tissue is practically wanting, structures of the character of tendon or of the cornea are produced ; where, on the other hand, elastic tissue is in excess of fibrous tissue, highly extensible structures, as the ligamentum nuchae or the ligamenta subflava, result. 4. Cartilage, fibrous, elastic, and hyaline varieties. 5. Bone and dejitiiie, in which impregnation of lime salts contributes character- istic hardness. 6. Reticulated connective tissue, occurring as the supporting framework in the lymphatic tissues, and as the interstitial reticulum of many organs. 7. Adipose tissue. The Cells of Connective Tissue. — The cellular elements of the connective 73 nbryc ; cells from the umbilical cord. X 500. 74 HUMAN ANATOMY. tissues are usually described as of two kinds, — ihe Ji.ved or connective-tissue cells proper, and the migratory or it'andering cells. The latter, while frequently included among the elements of these tissues, are usually only migratory leucocytes which temporarily occupy the lymphatic clefts within the connective substance. Fig. 94. Fig. 95. Young: connective-tiss om subcutaneous tissue, of cat nbrjo. X 59°- Granule-cells (mast-cells) from submucous tissue of mouth. X 1000- ;', V, sections of blood-vessels. The typical conneclive-tissiie cell, in its younger condition, possesses a flattened, plate-like body from which branched processes extend. With the completed growth of the tissue, the expanded, often irregularly stellate, element contracts to the inconspicuous spindle cell commonly observed in adult areolar tissue. Granule-cells are addi- tional elements occasionally encountered in connective tissues. They are irregularly spherical in form and are dis- tinguished by conspicuous granules within their proto- plasm possessing a strong affinity for dahlia and other basic aniline stains. They include the plasma-cells of Waldever and the mast-cells of Ehrlich. Pigment-Cells. — The fixed cells sometimes contain accumulations of dark parti- cles within their cytoplasm, the elements then appearing as large, irregularlybranched pigment-cells ; these are con- spicuous in man within the choroid, the iris, and certain parts of the pia mater. The nucleus usually remains uninvaded, and hence appears as a lighter area within the dark brown, or almost black, cell-body. The Intercellular Constituents of the connective substances occur in three forms,— /?(^;-^«.f tissue, reticular tissue, and elastic tissue. Fibrous tissue consists morphologically of varying bundles of silky fibrils of Section of subcutaneous tissue, showing the usual constituents of areolar FIBROUS TISSUE. 75 such fineness that they possess no appreciable width. The fibrils are united by and embedded within a semifluid ground-substance , which may be present in such meagre amount that it suffices only to hold together the fibrillse, or, on the other hand, it may constitute a large part of the entire intercellular tissue, as in the matrix of hya- FlG. Fig. 98. -^^^ ,^- °' V^r Pigmented coiineclive-tissue cells from choroid. X 400. '^~^:^^^>X Surface view of portion of omentum. .■ 130. Fi brous and elastic tissue are arranged as a fenestrated membrane; the nuclei belong to the connective-tissue and the endothelial cells. line cartilage. Depending upon the dis- position of the bundles, fibrous tissue occurs in two principal varieties, — areolar and dense connective tissue. The fibrous tissue of the areolar group is arranged in delicate wavy bun- dles which are loosely and irregularly in- terwoven, as seen in the subcutaneous layer, the intervening clefts being largely occupied by the ground-substance. In the denser connective tissues the fibrous tissue is disposed with greater regularity, either as closely packed, parallel bundles, as in tendon and aponeuroses, or a^ intimately felted, less regularly arranged, bands forming extended sheets, as in fasciae, the cornea, and the dura mater. The ground- substance uniting the fibrillae of dense connective tissues often contains a system of definite interfascicular lynnph-spaces, Fig. 99. which, in suitably stained prepara- ^^^^ ^ stj^ tions, appear as irregularly stellate -^ •'-."-'■J*' '"..^ clefts that form, by union of their ^ , "t ramifications, a continuous net-work of channels for the conveyance of the tissue-juices throughout the dense connective substances ; in non-vascu- lar structures, as the cornea and the denser parts of bone, these systems of intercommunicating lymph-spaces serve to convey the nutritive sub- stances to the connective-tissue cells which lie within these clefts. Fibrous tissue yields gelatin on boiling in water, and is not digested by pan- creatin ; on the addition of acetic acid this tissue becomes swollen and trans- parent, the individual fibrillae being no longer visible. Reticular Tissue. — The in- vestigations of Mall ha\e emphasized the presence of a modified form of fibrous tissue in many localities, especially in organs rich in lymphoid cells. This variety of intercellular substance, known as reticular tissue or reticulum, consists of very fine fibrillae, either isolated or associated Cell-spaces of dense connectne tissue from cornea of calf; the surrounding ground substance has been stained with argen- tic nitrate. V 525 76 HUMAN ANATOMY. Connective-tissi occupy cell-spaces : figure. X 525 in preceding Fig. iui. as small bundles, which unite in all planes to form delicate net-works of great intri- cacy. In lymphatic tissues, where the reticulum reaches a typical development, the mesh-work contains the characteristic lymphoid elements and, in addition, supports the superimposed stellate connective-tissue cells which formerly were erroneously regarded as integral parts of the fibrillar Fig. 100. net-work. Reticular tissue, associated with fibrous and elastic tissue, is also present in many other organs, as the liver, kidney, and lung. This modifica- tion of fibrous tissue differs from the more robustly developed form in the absence of the ground-substance and not yield- ing gelatin upon boiling in water (Mall); ,;,■:'; like fibrous tissue, the reticulum resists pancreatic digestion. The development of fibrous tissue has been a subject of much discussion re- garding which authorities are still far from accord. Two distinct views are held at the present time ; according to the one, the fibres appear within the originally homogeneous intercellular matrix of the early embryonal connective tissue without the direct participation of the cells, the fibres being formed as the result of a process somewhat resembling coagulation. This conception of the formation of the fibres of connective tissue, known as the indirect mode, is held to account for the earliest production of the fibrils in embry- onic tissue. The other view, held by Flem- ming, Reinke, and others, attributes an actixe participation of the young connecti\e tissue cell, the peripheral zone of its protoplasm, known as e.x- oplasm, being directly transformed into fibrilke. In consideration of the careful observations of Hem- ming, it is now widely believed that the method of formation of the fibres of connecti\e tissue diredlv from the e.xoplasm of young con- nective tissue cells is the usual one. It is highly probable that the connective tissue cells are concerned in the production of the fibrous tissue, since these elements become much smaller as the formation of the fibrous tissue advances. Elastic tissue usually occurs as a net-work of highly refracting, homogeneous fibres lying among the bundles of fibrous tissue. The indi- vidual fibres are much thicker than pancreatic digesii< the fibrilL-e of fibrous tissue and, although differing in width, maintain a constant diameter until augmented by fusion with others. When disassociated, as in teased preparations, the elastic fibres assume a highly characteristic form, being wavy, bowed, or coiled. The proportion of elastic tissue in connective substances is, ordinarily, small ; in certain localities, however, as the ligamenta subflava of man, or especially the ligamentum nuchae of the lower mammals, almost the entire structure consists of bundles of robust fibres of elastic w%i{- Fibrous and reticular ELASTIC TISSUE. 77 tissue held together by a small amount of intervening fibrous tissue. In transverse section of such ligaments (Fig. 104), the individual elastic fibres appear as minute polygonal areas separated by the fibrous fibrills and the associated connective- tissue cells. Withiri the walls of the large blood-vessels the elastic tissue is arranged as membranous expansions containing numerous p,Q JQ2 openings oi varying size : these Jevesh-ated mem- branes, as they are called, are probabl)' formed by the junction and fusion of broad ribbon-like elastic fibres. Elastic tissue yields elastin upon Fig. 103. Reticular connective tissue from lymph- node. X 330. The cells lie upon the fibrous tissue at the points of intersection. Portions of isolated elastic fibres from ligamen- tuni nuchse of ox. X 375. boiling in water, and disappears upon being subjected to pancreatic digestion, thus differing from fibrous and reticular tissue ; by taking advantage of the especial affinity that elastic tissue possesses for certain stains, as orcein, a much wider and more generous distribution of elastic tissue has been established than was formerly appre- ciated. The development of elastic tissue has shared the uncertainty surrounding the mode of production of fibrous tissue, since here, as there, two opposed views have been held, — one of a cellular and one of an independent origin. Accord- v\g. 104. ing to the view of an independent origin, the older one, the elastic fibres first appear as rows of minute beads in the intercellular matri.x. These linearly dis- posed beads gradually fuse, thus produc- ing the primary elastic fibres. According to the view of an intracellular origin, the one less generally accepted, the elastic fibres are derived directly from the exoplasm of the young connective tissue cells, as in the case of the white fibrils. The density of connective substances depends upon the amount and arrange- ment of the fibrous tissue ; the extensibility is determined by the proportion of elastic tissue present. When the former occurs in well-defined bundles, felted together into interlacing lamellae, dense and resistant structures result, as fasciae, the cornea, etc. ; in such structures the cement- or ground-substance within the interfascic- ular clefts usually contains the lymph-spaces occupied by the connective-tissue cells. Tendon. — Tendon consists of dense connective tissue composed almost en- tirely of white fibrous tissue arranged in parallel bundles. The individual fibrillae Nucleu; necti' cell Transverse section of ligamentu 78 HUMAN ANATOMY. of the fibrous tissue, held together by cement-substance, are associated as compara- tively large primary bundles, which in turn are united by interfascicular fibrous Fig. 105. Fig. 106. 1 1 H^ ^ % Tendon-bund] Oblique view- Blood enclosing tertia Lougitudin.-.l ;^lUuii-j1 itiid'ii )i"m young subject; Tendon-bundles from tail of mouse, showing difiereni the tendon-cells are seen in protile between the bundles views of the cells. X 300. of fibrous tissue. < 300. substance and grouped into secondary bundles. The former, invested by a delicate areolar sheath and partially covered by plate-like cells, are held together by the septal extensions of the Fig. 107. general connective-tissue envelope which surrounds the entire tendon ; the larger septa support the interfascicular blood-ves- sels and the lymphatics. The flattened connec- ti\'e-tissue elements, here known as the tendon-cells, occur in rows within the clefts between the primary bundles, upon and between which the thin, plate-like bodies and wings of the tendon-cells e.xpand. Seen from the surface, these cells appear as nucleated quadrate bodies (Fig- 106) ; viewed in longitudi- nal profile, the tendon-cells present narrow rectangular areas, while, when seen in transverse section, the same elements appear as stellate bodies, the e.xtended limbs of which, often stretching in several planes, represent sections of the wing-plates. Examined in cross-section (Fig. 107), the cut ends of the primary tendon-bun- dles appear as light irregular polygonal areas, which, under high amplification, at \ section of a tendon, showing grouping of primary, 5 and tertiary bundles of tendon-tissue, y 85. ADIPOSE TISSUE. 79 times exhibit a delicate stippling due to the transversely sectioned fibrillse. The interfascicular clefts frequently are represented, in such preparations, by stellate figures in which the sections of the tendon-cells, lying upon the primary bundles, can be distinguished ; the remaining portion of the stellate cleft is occupied by the Fig. ioS. coagulated and stained interfascicular cement-substance. The larger divisions of the tendon, composed of the groups of secondary bundles, are separated by the septa prolonged inward from the general sheath investing the entire tendon. Ten- don is composed almost exclu- sively of fibrous tissue, elastic Fig. 109. fibres being practically absent. -^ Adipose Tissue. — The fatty material contained within the body is to a large extent en- closed within connective-tissue cells in various localities ; these modified elements are known as fat-cells, which, together with the areolar tissue connecting the cells and supporting the rich supply of blood-vessels, consti- tute the adipose tissue. The distribution of adipose tissue includes almost all parts of the body, although accumulations of fat are especially conspicuous in certain localities. Among the latter are the subcutaneous areolar tissue, the marrow of bones, the mesentery and the omentum, the areolar tissue surrounding the kidney, the vicinity of the joints, and the subpericardial tissue of the heart. On the other hand, in a' few situations, in- cluding the subcutaneous areolar tissue of the eyelids, the penis and the labia minora, the lungs, except near their roots, and the interior of the cranium, adipose Peripheral zone — ■ of protopl; enclosing on- ^' drop " Connective-tissue' Young fat-cells from subcutaneous 1 8o HUMAN ANATOMY. tissue does not occur even when developed to excess in other parts. As ordinarily seen, adipose tissue is of a light straw color and often presents a granular texture due to the groups of fat-cells within the supporting areolar tissue. Examined microscopically in localities where the fat-cells are not crowded, but occur in a single stratum and hence retain their individual form, adipose tissue is seen to be made up of relatively large, clear, spherical sacs held together by deli- cate areolar tissue. Unless treated with some stain, as osmic acid, Sudan III. or quinoline-blue, possessing an especial affinity for fat, the oily contents of the cells appear transparent and uncolored, and apparently occupy the entire cell-body. Critical study of the fat-cell, however, demonstrates the presence of an extremely thin enveloping layer of protoplasm, a local thickening on one side of the sac mark- ing the position of the displaced and compressed nucleus (Fig. 109). Fat-cells occur usually in groups, supported and held together by highly vas- cular connective tissue. In localities possessing, considerable masses of fat, as be- neath the scalp and the skin, the cells are grouped into lobules which appear as yellow granules to the unaided eye ; in such localities the typical spherical shape of the individual fat-cells is modified to a polyhedral form as the result of the mutual pressure of the closely packed vesicles. In connective-tissue elements about to become fat-cells, isolated minute oil- drops first appear within the protoplasm ; these increase in size, coalesce, and grad- ually encroach upon the cytoplasm until the latter is reduced to a thin, almost inappreciable, envelope, which invests the huge distending oil-drop. The nucleus, likewise, is displaced towards the periphery, where it appears in profile as an incon- spicuous crescent embedded within the protoplasmic zone. After the disappearance of the fatty matters, as during starxation, the majority of fat-cells are capable of resuming the usual appearance and properties of connective-tissue corpuscles ; cer- tain groups of cells, the fat-organs of Toldt, however, exhibit an especial tendency to form adipose tissue, and hence only under exceptional conditions part with their oily contents. CARTILAGE. Cartilage includes a class of connective tissue in which the intercellular substance undergoes increasing condensation until, as in the hyaline varietv, the intercellular matrix appears homogeneous, the constituent fibres being so closely blended that the fibrous structure is ordinarily no longer appreciable. Depending upon the differences presented by the intercellular matrix, three varieties of cartilage are recognized, — hyaline, elastic, und Jibroics. Considered in relation to the denser connective tissues, the description of fibrous cartilage, which differs but little from white fibrous tissue, should next follow ; since, however, the term "cartilage" is usually applied to the hyaline variety, the latter will first claim attention. Hyaline cartilage, or gristle (Fig. no), enjoys a wide distribution, forming the articular surfaces of the bones, the costal cartilages, the larger cartilages of the larynx and the cartilaginous plates of the trachea and bronchi, the cartilages of the nose and part of the Eustachian tube. In the embryo the entire skeleton, with the exception of part of the skull, is mapped out by primary hyaline cartilage. The apparently homogeneous matrix of hyaline cartilage, after appropriate treatment, is resolvable into bundles of fibrous tissue ; ordinarily, however, these are so closely united and blended by the cementing ground-substance that the presence of the component fibrils is not e\'ident. The cartilave-cells, as the connective-tissue elements which lie embedded within the hyaline matrix are called, are irregularly oval or spherical, nucleated bodies. They occupy more or less completely the interfascicular clefts, or lacuna, within which they are lodged. In adult tissue usually two or more cells share the same compartment, the group representing the descendants from the original occupant of the space. The matri.x immediately surrounding the lacunae is specialized as a layer of different density, and is often described as a capsule ; a further differentiation of the ground-substance is presented by the more recently formed matrix, which CARTILAGE. 8i often stains with greater intensity, thereby producing the appearances known as the cell-ai-eas. The lacunse of hyaline cartilage are homologous with the lymph- spaces of other dense forms of connective tissue ; although canals establishing com- munication between the adjacent lacunae are not demonstrable in the tissues of the higher vertebrates, it is not improbable that minute interfascicular passages exist which facilitate the access of nutritive fluids to the cells enclosed within the lacunse. The free surface of cartilage is covered by an envelope of dense connective tissue, the perichondrium ; the latter consists of an external fibrous layer of dense fibro-elastic tissue and an inner looser stratum or chondrogeiieiic layer, containing numerous connective-tissue cells. These are arranged in rows parallel to the sur- face of the cartilage and, during the growth of the tissue, gradually assume the characteristics of the cartilage-cells, being at first spindle-shaped and later ovoid and spherical. The young cartilage-cells thus formed become gradually separated by. more extensive tracts of the newly deposited intercellular matrix ; as the groups of cells originating from the division of the original occupant of the lacuna recede from the perichondrial surface, they lose their primary parallel dis- Fig iio position and become irregu- larly arranged and still further separated. Those portions of the ground-substance most re- mote from the perichondrium at times appear granular, this feature being intensified when, as in aged subjects, a deposition of calcareous matter takes place in these situations. In articular cartilage the su- perficial zone contains sparsely distributed groups of small cells arranged parallel to the free surface ; in the deeper strata these groups are replaced by elongated rows of larger ele- ments lying perpendicular to the articular surface. This columnar disposition of the car- tilage-cells is particularly evi- dent towards the underlying zone of calcified matrix. The blood-vessels of normal cartilage are usually limited to the periphery, within the perichondrium or the associated synovial membranes ; the nutrition of the cartilage is maintained by imbibition of the fluids through the matrix into lacunse, the existence of minute interfascicular canals being not impossible. In the thicker masses of the tissue, as in the cartilages of the ribs, nutrient canals exist in those portions most remote from the perichondrium ; these spaces contain a small amount of areolar tissue supporting the blood-vessels, which are, however, limited to the channels, the nutrition of the cartilage tissue being effected here, as at the periphery, by absorption through the matrix. Nerves have never been demonstrated within the cartilages, which fact explains the conspicuous insensibility of these tissues so well adapted to the friction, concus- sion, and compression incident to their function. Elastic cartilage, called 2X'so yellow elastic or reticular C2x\}\z%e. (Fig. iii), has a limited distribution, occurring principally in the cartilages of the external ear, part of the Eustachian tube, the epiglottis, the cartilages of Wrisberg and of San- torini, and part of the arytenoid cartilages of the larynx. In its physical properties this variety differs markedly from hyaline cartilage, as it is dull yellowish in color 6 ^^', Transverse section of peripheral portion of costal cartilage, X 250. 82 HUMAN ANATOMY. and pliable and tough in consistence, in contrast to the bluish opalescent tint and comparative brittleness of the hyaline variety. The characteristic feature of the structure of the elastic cartilage is the presence of elastic fibres within the intercellular matrix. The cell-nests are immediately sur- rounded by limited areas of hyaline intercellular substance corresponding to the matri.x of hyaline cartilage. The matri.x intervening between these homogeneous fields, however, is penetrated by delicate, often intricate, net-works of elastic fibres extending in all directions. The connective-tissue cells lie within the lacunae, in the hyaline areas, and closely resemble the elements of hyaline cartilage. Elastic carti- lage possesses a perichondrium of the usual description. Fibrous cartilage, ox Jibro-cartilage (Fig. 112), as the fibrous variety is usu- ally designated, is found in comparatively few localities, the marginal plates and the interarticular disks of certain joints, the symphyses, the intervertebral disks, sesamoid cartilages, and the lining of bony grooves for tendons being its chief representatives. Elastic net-work of intercellul.nr tissue Lacuna contain -^ ing cell ^si In its physical properties this tissue resembles both fibrous tissue and cartilage, pos- sessing the flexibility and toughness of the former combined with the firmness and elasticity of the latter. A proper perichondriun/ is wanting. In structure fibro-cartilage closely resembles dense fibrous tissue, since its prin- cipal constituent is the generallv parallel wa\-y bundles of fibrous connective tissue ; among the latter lie small, irregularly disposed oval or circular areas of hyaline matrix which surround the cartilage-cells, singly or in groups. The number of cells and the proportion of fibrous matrix differ in various localities. The development of cartilage proceeds from the mesoblast, the cells of which undergo proliferation and, forming compact groups, become the embryonal cartilage- cells ; at first the latter lie in close apposition, since the matrix is wanting. During the later stages, when the masses of embryonal cartilage map out the subsequent skeletal segments, the cells are separated by a small amount of homogeneous matrix formed throuq-h the influence of these elements. DEVELOPMENT OF CARTILAGE. 83 Cartilage grows in two ways : (a) by the expansion produced by the inier- stitial growth effected by the formation of new cells and the associated matrix, and (^b) by the addition of the new tissue developed by pcrichoyi- Fig 112 drial growth at the periphery of the cartilage from the chondro- ^ genetic layer. The latter mode continues throughout the period ^ of growth, and includes the di- , rect conversion of the connee- -Hsaiinearea tive-tissue cells of the perichon- ^ caniiage-ceiis drium intothecartilage elements, and the accompanying formation 1 „ ' ■" '' of new matrix. ' , The development of the ' elastic fibres within the elastic ^ ^ cartilage is secondary, the matrix during the early stages of growth Fibrous inter- being hyaline. The elastic tis- ^ sfance'^ ^"''' sue first appears in the form of ^ "^ minute granules, which later , "^' fuse and become the elastic '" <^ fibres ; this change first appears "^^ — Cartiiage-ceiis in the vicinity of the cartilage- , ^ cells, the elastic reticulum sub- v -- ' ^\ sequently invading the more re- '' mote portions of the matrix. In Section of fibrous cartilage from intervertebral disk. X 225. the development of the fibro- cartilage, the fibres appear coincidently with the limited pericellular areas of hyaline substance. Chemical Composition of the Connective Substances. Connective Tissue. — The fibrils of white fibrous connective tissue consist of a substance known as collagen. The interfibrillar ground-substance contains mainly nmcoid and the albuminous materials, serum globulin and serum albumin. Gelatin is the hydrate of collagen, and is obtained by boiling fibrous tissue with water, when the gelatin separates like a jelly on cooling. In the case of the yellow elastic fibres, clasthi is found in place of collagen. In reticular tissue 7-cticulin is found. The latter substance contains phosphorus. These substances, namely, collagen with its hydrate gelatin, elastin and perhaps reticulin, are among those known as albuminoids, which are closely related to the true albumins, yet differ in some important respects. The albuminoids, for the most part, contain less carbon and more oxygen than the albumins proper. Cartilage. — The fibres which are found in the matrix of fibro-cartilage and elastic cartilage are respectively composed of collagen and of elastin, just as they are in the corresponding connective tissues. According to His, the chemical composition of human cartilage is as follows : Costal cartilage. Articular cart.iage. Water 67.67 73,59 Solids 32.33 26.41 Organic matter 30.13 24.87 Mineral salts 2.20 1.54 In the mineral salts there is about 45 per cent, of sodium sulphate. A somewhat smaller percentage of potassium sulphate, and smaller amounts of the phosphates of sodium, calcium and magnesium, as well as of sodium chloride, are present. Adipose Tissue. — -The fats in the animal body are mainly the triglycerides of stearic, palmitic and oleic acid. There is found in man a comparatively large amount of olein. Small quantities of lecithin, cholesterin and free btty acids are also found in fat tissue. HUMAN ANATOMY. BONE OR OSSEOUS TISSUE. In the higher vertebrates, osseous tissue forms the bony framework, or skeleton, which gives attachment and support to the soft parts, affords protection to the more or less completely surrounded delicate organs, supplies the passive levers for the exercise of muscular action, insures stability, and maintains the definite form of the animal. In addition to contributing the individual bones composing the principal, and in man the only, framework, or entoskelcton, osseous tissue occurs in the lower ver- tebrates associated with the integument as an exoskeleton. Representatives of the latter are seen in the bony plates present in the skin of certain ganoid fishes, the dermal plates of crocodiles, the dorsal and ventral shields of turtles, or the dermal armor of the armadillo. Osseous tissue also e.xists within various organs in certain animals and then constitutes the splanchnoskelcton. E.xamples of the latter are furnished by the bony plates encountered in the sclerotic coat of the eyes of birds, in the diaphragmatic muscle of the camel, in the tongue of certain birds, in the heart of ruminants, in the nose, as the snout-bones of the hog, in the respiratory organs, as the laryngeal, tracheal, and bronchial bones of birds, and in the genital organs, as the penile bone of carnivorous and certain other mammals. True osseous tissue does not occur outside the vertebrates. Many invertebrate animals possess a skeletal framework, usually external but in some cases internal. Such a framework, however, consists of calcareous incrustations, hardened excre- tions or concretions composed principally of calcium carbonate and of silicious structures. These earthy or mineral hard parts of invertebrates are structureless deposits, so differing materially from the bone tissue of the higher vertebrates as well in structure as in chemical composition. Sometimes a deposit of calcareous material occurs in adult cartilage, a process entirely distinct from the formation of bone tissue. Familiar examples of such calcification are seen in the costal and some of the laryngeal cartilages. Chemical Composition. — Bone is a dense form of connective tissue, the matrix of which is impregnated with lime salts ; it consists, therefore, of two parts, an animal and an earthy portion, the former giving toughness and the latter hardness to the osseous tissue. The animal or organic part of bone may be removed by calcination, leaving the inorganic constituents undisturbed. If a bone be heated in a flame with free access of air, the animal matter at first becomes charred and the bone black ; continued combustion entirely removes the organic materials, the earthy portion alone remain- ing. After such treatment, while retaining its general form, the bone is fragile and easily crushed, and has suffered a loss of one-third of its weight, due to the destruc- tion and elimination of the animal constituents. The latter, evidently, constitute one-third and the mineral matters two-thirds of the bone. The inorganic constitu- ents include a large amount of calcium phosphate, much less calcium carbonate, with small proportions of calcium fluoride and chloride, and of the salts of magnesium and sodium. The animal portion of the bone, on the other hand, may be separated from the inorganic salts by the action of dilute hydrochloric acid, which dissolves out the earthly constitutents ; after such treatment the bone, although retaining perfectly its form and details, is tough and flexible, a decalcified rib or fibula being readily tied into a knot. The animal constituents of bone yield gelatin upon prolonged boiling in water, therein resembling fibrous connective tissue. The composition of bone, according to Berzelius, is as follows : Organic matter Gelatin and blood-vessels, 33-3° f Calcium phosphate, 5i-o4 I Calcium carbonate, 11.30 Inorganic matter -j Calcium fluoride, 2.00 Magnesium phosphate. 1.16 Sodium oxide and sodium chloride, 1.20 PHYSICAL PROPERTIES OF BONE. 85 Physical Properties. — Rauber has shown that a five-milhrnetre cube of com- pact bone of an ox when calcined will resist pressure up to 298 pounds ; when decal- cified up to 136 pounds ; under normal conditions up to 852 pounds, the pressure being applied in the line of the lamellae. It results from its composition that while bone is very hard and resistant to press- ure, it is also somewhat flexible, elastic, and capable of withstanding a tearing strain. It is remarkable that in many substances the power to resist a crushing strain is very different from that of resisting a tearing one. Thus, cast iron is more than five times as resistant to the former strain as to the latter, and wrought iron is nearly twice as resistant to the latter as to the former. Neither of these materials, therefore, is well fitted to resist both strains, since a much greater quantity must be used than would be needed were either material to be exposed only to the strain it is best able to with- stand. Bone, however, has the property of resisting both strains with approximately equal facility, its tearing limit being to its crushing- limit about as 3 is to 4. This has the advantage that strength need not be obtained by great increase of weight, con- sequently the plan of bone structure com- bines lightness and strength. Structure of Bone. — On sawing through a bone from which the marrow and other soft parts have been removed by ma- ceration and boiling, the osseous tissue is seen (Fig. 113) to be arranged as a pe- ripheral zone of compact bone enclosing a variable amount of spongy or cancellated bone. In the typical long bones, as the humerus or femur, the compact tissue al- most exclusively forms the tubular shaft enclosing the large marrow-cavity, the can- cellated tissue occupying the expanded extremities, where, with the exception of a narrow superficial stratum of compact bone, it constitutes the entire framework ; the clefts between the lamellae of the spongy bone are direct extensions of the general medullary cavity and are filled with mar- row-tissue. In the flat bones (Fig. 116), as those of the skull, the compact substance consists of an outer and inner plate, or tables, enclosing between them the cancel- lated tissue, or diploe, as this spongy bone is often termed. Short and irregular bones are made up of an inner mass of spongy bone covered by an external shell of compact substance which often presents local thickenings in order to insure additional strength where most needed. The cancellated bone consists of delicate bars and lamellae which unite to form an intricate reticulum of osseous tissue well calculated to insure considerable strength without undue weight ; in many positions, conspicuously in the neck of the femur (Fig. 374), the more robust lamellee are disposed in a definite manner with a view of meeting the greatest strains of pressure and of tension. Although composed of the same structural elements, compact and spongy bone differ in their histological details in consequence of the secondary' modifications which take place during the conversion of the spongy bone, the original form, into the compact substance. To obtain the classic picture of osseous tissue, in order to study its general arrangement in the most typical form, it is desirable to examine thin ground sections of the compact substance cut at right angles to the a.xis of a long bone which has been macerated and dried, and in which the spaces contain air. Section of upper end of humerus, showing the external layer of compact bone surrounding the med- ullary cavity below and the spongy bone above. 86 HUMAN ANATOMY. The compact bone in such preparations, when examined under low ampli- fication (Fig. ii4j, is seen to be composed of osseous layers arranged as three chief groups : (a) the circumferential lamella, which e.xtend parallel to the external and internal surfaces of the compact bone ; (^) the Haversiaii larnclla:, which are disposed concentrically and form conspicuous annular groups, the Haversian systems, enclosing the Haversian canals ; and (r) the interstitial or groiuid lamella, which constitute the intervening more or less irregularly arranged bony layers filling up the spaces between the Haversian systems and the peripheral strata. Fig. 114. 1 V Transver: e section of compact bone (metatarsal! ; the section 1 filled with air. X ;d, hence the la Each Haversian system consists of the concentrically disposed lamellae and the centrally situated channel, or Haversian canal, enclosing the ramifications of the medullary blood-vessels and associated marrow-tissue. Between the annularly arranged lamellae are seen small spindle-shaped or oval spaces, the lacuncE, about .02 millimetre long, .01 millimetre wide, and .006 millimetre thick, from which ex- tend minute radiating channels, the canaliculi, establishing communication between the adjacent lacunae of the same Haversian system. The lacunae and the canaliculi constitute an intercommunicating net-work of lymph-spaces similar to those encoun- STRUCTURE OF BONE. 87 tered in other forms of dense connective tissue. Since the lacunge are compressed oval cavities lying between the lamellae of the osseous matrix, when viewed in sec- tions which pass through the layers at right angles (Fig. 117), the lacunae present their narrower dimensions, appearing thus in profile as small lentiform spaces ; seen in sections, on the contrary, which pass parallel to the lamelte (Fig. 118J, the lacunae are broader and more circular, the spaces with the canaliculi forming the spider-like figures so conspicuous in longitudinal sections of dried bone. The characteristic arrangement of the lamellae of the Haversian systems is due to the secondary formation of the osseous tissue during the conversion of the older spongy bone into compact tissue, the circumference of the system corresponding to the Haversian space in which the subsequent development of the concentric lamellae Fig. 115. Longitudinal section of compact bone, ground and dried took place. It follows, from this relation, that Haversian systems exist only in com- pact bone, since the necessary secondary deposit does not occur during the gro-vth of the spongy or cancellous tissue. The lamellae of osseous tissue, when deprived of the mineral matters and exam- ined in thin fragments, often display the ultimate fibrous structure which they pos- sess, since they consist of delicate fibrils o\ fibrous tissue embedded within a ground- substance and associated into bundles which are arranged as crossing and interwoven layers. Within the Haversian lamellae the fibrous bundles cross generally at right angles, but in other locations they are less regularly and more acutely disposed. The perforating fibres of Sharpey (Fig. 119^ consist of bundles of fibrous tissue which penetrate the lamellae in a direction perpendicular or oblique to their 88 HUMAN ANATOMY. surface, and thus pin or bolt the layers together. These fibres are especially numer- ous in the superficial lamellje beneath the periosteum, to which membrane they owe their formation, and with which many seem to be directly continuous. They are Fig. ii6. 1 of frontal bone, sliowing tfie ab; readily found on the surfaces of the lamellae of decalcified bone which have been forcibly separated. Although usually consisting of bundles of fibrous tissue, it is probable that in some cases the perforating fibres are elastic in nature. They are sometimes imperfectly calcified and leave, therefore, on drying, tubular canals, which pierce the lamella from the ex- FiG. 117. terior of the bone. Since the perfo- rating fibres are associated genetically with the periosteum, they are never found in the secondary lamellae consti- tuting the Haversian systems. The Haversian canals are con- tinuations of the medullary cavity and serve the important purpose of con- veying the blood-vessels within the compact substance ; from these vessels the nutritive fluids pass into the peri- vascular lymph-spaces between the walls of the canal and the blood-ves- sels and thence, by way of the cana- liculi, which open into these lymph- spaces, into the adjacent lacunae, and so on into the surrounding portions of the compact substance, the nutrition of which is thus maintained. Although the average size of the canals is about .05 millimetre, those next the medullary cavity are larger, some measuring . i millimetre or more in diameter, and contain, in addi- Lacuna i profile THE BONE-CELLS. 89 nd canaliculi from dried bone cut parallel with the lameilse. X 300. tion to the blood-vessels, an extension of the marrow-tissue. The individual chan- nels are short, and communicate by oblique branches with adjacent canals (Fig. 115). The Haversian canals indirectly communicate with the external surface of the bone by means of the channels, or Volkmann' s canals, within the circumfer- ential lamellae, which open by minute orifices and receive vascular twigs from the periosteal blood-vessels (Fig. 122); the latter are thus brought into free anasto- mosis with the branches derived from the medullary vessels, the two constituting a freely communicating vascular net-work throughout the compact substance. The Bone-Cells. — The details of osseous tissue thus far considered per- Y\g. 118. tain to the structure of the passive in- tercellular constituents of a dense con- nective tissue ; in addition to these, as in other forms of connective substances, the more active elements are the con- nective-tissue cells, here known as the bo7ie-cells. As already pointed out, the lacunae and the canaliculi represent in- tercommunicating lymph-spaces, similar to those encountered in the cornea or other dense connective tissue ; as in the latter so also in the osseous tissue, the cellular elements occupy the lymph- spaces, the bone-cells lying within the lacuna. Since the classic pictures of bone are derived from ground sections of dried tissue, in such preparations the deli- cate bone-cells have shrunken and disappeared, and the lacunae contain, at best, only the indistinguishable remains of the cells mingled with debris produced during the preparation of the section ; the lacunae and the canaliculi in dried sections are filled with air, by reason of which condition they appear as the familiar dark, sharply defined, conspicuous spider- FiG. 119. like figures. In order to study the bone- cells, the tissue after fixation is de- calcified and stained, and mounted in an approved preserving medium ; in consequence of such treatment the air is displaced from the spaces within the bone, which now appear faintly outlined, the delicate ramifi- cations of the canaliculi in places being almost invisible. The bone- cells, after being stained in such decalcified preparations, appear as small lenticular or stellate bodies within the lacunae (Fig. 121), which they almost entirely fill. Each cell- body consists of granular cytoplasm from which delicate processes ex- tend for a variable distance into the canaliculi, in favorable localities the protoplasmic processes sent out by adjacent bone-cells sometimes meeting. The deeplv staining nucleus appears as a brilliant point within the stellate cell. The Periosteum. — The external surface of bones is closely in-\'ested, except where covered with cartilage, with a fibrous membrane, the periostevni, a structure of great importance during development and growth, and later for the nutrition and protection of the osseous tissue. During childhood an end of the irnmature bone may be broken of? and yet held in place by the periosteum. The adult peri- osteum consists of two layers, an outer fibrous and an \ax\cv fibro-elastic ; when covering young bones, however, in which growth is actively progressing, the peri- Semi-diagrammatic view of perforating fibres of Sharpey: iamellee of decalcified bone have been partially separated 90 HUMAN ANATOMY. osteum contains an additional stratum, the osteogeneiic layer, which lies closely asso- ciated with the exterior of the bone. After growth has ceased, the osteogenetic layer becomes reduced to an inconspicuous stratum included as par^t of the fibro- elastic constituent of the periosteum. The fibrous layer is composed of closely placed bundles of fibrous connective tissue, and serves to support larger blood-vessels which break up within the deeper parts of the periosteum into the minute twigs entering the canals opening onto the surface of the bone. Fig. 1 20. '■' cate with the lymph-channels within the bone. The osteogeneiic layer, conspicuous fei during the development and growth of the ^ osseous tissue, consists of delicate bundles of fibrous tissue and large numbers of ^.^ connective-tissue cells of an embryonal ■^ type. Those next the growing bone as- sume a low, irregular columnar form, and ''■'^v are disposed in rows upon the surface of Bone-cells lying within the lacuna. X 700. the developing osscous tissue ; since these cells are concerned in the production of the latter, they are appropriately termed osteoblasts. Later some of them become sur- rounded by the bony matrix, and are thus transformed into bone-cells. The osteo- genetic layer is rich in blood-vessels which, as the bone is formed, are continued into the primary marrow-cavities. The Marrow. — The spaces in the interior of bones, whether the large medullary cavities surrounded by the compact substance forming the shaft of the long bones or the irregular interstices between the trabeculae composing the cancel- THE RED BONE-MARROW. 9X lated tissue, are filled with bone-marrow. The latter also e.xtends within the larger Haversian canals. Although originally only of one variety within the bones of the early skeleton, the marrow in the adult consists of two kinds, the yellow and the red. Thus, within the shaft of the long bones it consists of a light yellowish tissue, presenting the char- acteristics of ordinary adipose tissue, while within the spaces of the cancellated tissue at the ends of the same bones the marrow appears of a dull red color. In addition to the ends of the long bones, the localities in which red marrow especially occurs are the bodies of the vertebrse, the ribs, the sternum, the diploe of the cranium, and the short bones. Red Marrow. — The ingrowth of the periosteal tissue and blood-vessels con- stitutes the primary marrow within the embryonal skeleton ; from this tissue the red marrow tilling the young bones is directly derived. The red marrow is, therefore, A ■) ^ ^ jj^B 1 i ^ '-"■' — ^-c-^ ^ Dense fibrous laye ■ J^""vV '- Periosteal blood essel passing iiit he bone r 4 f ''/% i "^ . - „ lacuna } "^ -4 ^ 1\ ■Marrow-tissue continu- ous with periosteum -Remains of osteogenetic layer k i Section of young periosteum and subjacent bone. X 275. the typical and first formed variety within the foetus and the young animal ; subse- quently, that situated w-ithin the shaft of the long bones becomes converted into yellow marrow by the replacement of the majority of the marrow elements by fat- cells. The red marrow (Fig. 123), when examined in section after fi.xation and staining, presents a delicate reticulum of connective tissue which supports the numerous medullary blood-vessels and the cellular elements. Next the bone the fibrous tissue forms a thin membrane, the endosieitm, lining the medullary cavity and the larger Haversian canals into which the marrow extends. This membrane is highly vascu- lar, its vessels joining those within the osseous canals on the one side and those of the marrow on the other. The delicate fibrous reticulum, in addition to the thin-walled blood-channels which it supports, contains within its meshes the several varieties of elements chai- 92 HUMAN ANATOMY. acteristic of the red marrow ; these are : (i) the marroiv-cells, (2) the coswophile cells, (3) \\-\Q giant cells, and (4) x!<-'iiii^t: fe and during the processes resulting in the removal of osseous tissue they are the osteoclasts which are actively engaged in effecting the absorption of the bony matrix. Ordinarily the giant cells occupy the central portions of the marrow ; when, however, they enter upon the role of bone-destroyers, they lie on the sur- face of the osseous trabeculae within the depressions known as Howship' s lacuntz (Fig. 128). The nucleated red blood-cells within the red marrow are concerned in the important function of renewing the colored ceils of the blood, the red marrow being the chief seat in which this process takes place after birth ; hence the red marrow is classed as a blood-forming organ. The nucleated red blood-cells exist within the marrow in two forms, an older and a younger. The genetically older cells, the normoblasts, are the descendants of the embryonal nucleated blood- cells on the one hand and the indirect parents of the younger blood-elements on the other. The normoblasts possess relatively large nuclei, with chromatin reticulum and cytoplasm tinged with haemoglobin ; they are frequently observed during mitosis, since they gave rise to the second generation of nucleated red blood-cells. The latter, the erythro- THE YELLOW BONE-MARROW. 93 blasts, are directly converted into the mature, non-nucleated red blood-disks on the disappearance of their nucleus. In addition to a larger amount of hjemoglobin in their cytoplasm, the erythroblasts differ from the normoblasts in the possession of a deeply staining nucleus, in which the chromatin no longer appears as a reticulum. It is usual to find isolated groups of fat-cells distributed within the red marrow, although the amount of adipose tissue is very meagre in localities farthest removed from the medulla of the long bones. The varieties of leucocytes usually seen in the blood are also encountered within the red marrow in consequence of the intimate relations between the latter tissue and the blood-stream conveyed by the medullary capillaries. Yellow Marrow. — Since the appearance of the yellow marrow is due to the preponderating accumulation of fat-cells which have replaced the typical elements of the marrow contained within the shaft of certain bones, the formation of this variety is secondary, and must be regarded as a regression. Examined in section, yellow marrow resembles ordinary adipose tissue, since it consists chiefly of the large oval fat-cells supported by a delicate reticulum of connective tissue. In localities in which the latter exists in considerable quantity, numerous lymphoid cells represent the remaining elements of the originally typical marrow-tissue. After prolonged fasting the yellow marrow loses much of its oily material and becomes converted into a gelatinous substance containing compara- tively few fat-cells ; upon the re-establishment of normal nutrition this tissue may again assume the usual appearance of yellow marrow. Blood-Vessels. — The generous blood-supply of bones is arranged as two sets of vessels, the periosteal and the medullary. The former constitutes an external net-work within the periosteum, from which, on the one hand, minute twigs enter the subjacent compact substance through channels (^Volkmann' s eanals) communi- cating with the Haversian canals, within which the}' anastomose with the branches derived from the medullary system ; additional vessels, on the other hand, pass to the cancellated tissue occupying the ends of the long bones. The medullary artery is often, as in the case of the long bones, a vessel of con- siderable size, which, accompanied by companion veins, traverses the compact sub- stance through the obliquely directed niedulla7y canal to gain tne central part of the marrow. On reaching this position the medullary artery usually divides into ascend- ing and descending branches, from which radiating twigs pass towards the periphery. The latter terminate in relatively narrow arterial capillaries, which, in turn, expand somewhat abruptly into the larger venous capillaries. Such arrangement results in diminished rapidity of the blood-stream, the blood slowly passing through the net^ work formed by the venous capillaries. The latter vessels, within the red marrow, possess thin walls and an imperfect endothelial lining in consequence of which the blood comes into close relation with the elements of the medullary tissue. During its sluggish course within the blood-spaces of the red marrow, the blood takes up the newly formed red cells, which thus gain entrance into the circulation to replace the effete corpuscles which are continually undergoing destruction within the spleen. It is probable that leucocytes also originate in the bone-marrow. After thus cominginto intimate relations with the marrow-tissue, the blood is collected by capillaries which form small veins. In addition to the companion veins accompanying the nutrient artery along the medullary canal, in many instances the larger veins pursue a course independent of the arteries and emerge from the can- cellous tissue by means of the canals piercing the compact substance at the ends of the bones. Although destitute of valves within the medulla, the veins possess an unusual number of such folds immediately after escaping from the bone. Lymphatics. — The definite lymphatic channels of the bones are principally associated with the blood-vessels of the periosteum and the marrow as perivascular channels, although it is probable that lymphatic spaces exist within the deeper layers of the periosteum, in close relation to the osseous tissue. The perivascular lym- phatics follow the blood-vessels into the Haversian canals, where, as well as on other surfaces upon which the canaliculi open, the system of intercommunicating juice- channels represented by the lacunae and the canaliculi is closely related with the lymphatic trunks. 94 HLMAX AXATOMV. Nerves. — The periosteum contains a considerable number of nerves, the ma- jority of which, however,, are destined for the supply of the underlying osseous tissue, since those distributed to the fibrous envelope of the bone are few. The periosteal nerves follow the larger blood-vessels, in the walls of which they chiefly terminate. Medullary nerves accompany the corresponding blood-vessels through the medullary canal, and within the marrow break up into tibrilloe to be, probably, distributed to the walls of the vascular branches along which they lie. Regarding the ultimate endings and arrangement of the sensory tibres little is known ; in view of the low degree of sensibility possessed by healthy bones and their periosteum, the number of such nerves present in osseous structures must be very small. Fig. 124. DEVELOPMENT OF BONE. The bones composing the human skeleton, with few e.xceptions, are preceded by masses of embryonal cartilage, which indicate, in a general way, the forms and relations of the subsequent osseous segments, although many details of the model- ling seen in the mature bones appear only after completed development and the pro- longed e.xercise of the powerful modifying influences e.xerted by the action of the attached muscles. Since the primary formation of such bones takes place within the cartilage, the process is appropriatelv termed endochondral development. Certain other bones, notably those forming the vault of the skull and almost all those of the face, are not preceded by cartilage, but, on the contrary, are produced within sheets of connective tis- sue : such bones are said, therefore, to arise by intra- 7nembranous dez'elopment. It will be seen, however, that the greater part of the bone formed by endochondral de- velopment undergoes absorption, the spongy substance within the ends of the long and the bodies of the irregu- lar bones representing the persistent contribution of this process of bone-production. E\'en in those cases in which the intracartilaginous mode is conspicuous, as in the de- \elopment of the humerus, femur, and other long bones, the important parts consisting of compact substance are the product of the periosteal connective tissue, and hence ge- netically resemble the intramembranous group. Although both methods of bone-formation in many instances proceed coincidently and are closely related, as a matter of con- venience thev may be described as independent processes. Endochondral Bone Development. — The pri- mary cartilage, formed by the proliferation and condensa- tion of the elements of the young mesoblastic tissue, grad- ually assumes the characteristics of embryonal cartilage, which by the end of the second month of intra-uterine life maps out the principal segments of the fcetal cartilaginous skeleton. These segments are invested by an immature form of perichondrium, ox primary periosteum, from which proceed the elements actively engaged in the production of the osseous tissue. The primary periosteum consists of a compact outer fibrous and a looser inner osteogenetic layer; the latter is rich in cells and delicate intercellular fibres. The initial changes appear within the cartilage at points known as centres of ossijicatio?!, which in the long bones are situated about the middle of the future shaft. These early changes (Fig. 125) involve both cells and matrix, which exhibit con- spicuous increase in size and amount respecti\'ely. As a further consequence of this activity, the cartilage-cells become larger and more vesicular, and encroach upon the intervening matrix, in which deposition of lime salts now takes place, as evidenced by the gritty resistance offered to the knife when carried through such ossific centres. On acquiring their maximum growth the cartilage-cells soon exhibit indications of impaired vitality, as suggested by their shrinking protoplasm and degenerating #'■ Clarified human fcetus of about three and one-half months, show- ing the partially ossified skeleton. Two-thirds natural size. DEVELOPMENT OF BONE. 95 nuclei. The enlarged spaces enclosing these cells are sometimes designated as the p7'imary aj'eola. Coincidently with these intracartilaginous changes, a thin peripheral layer of bone has been formed beneath the young periosteum ; from the latter bud-like processes of the osteogenetic layer grow inward from the periphery and invade the embryonal cartilage, by absorption of the cartilage-matrix gaining the centre of ossilicaiion and there effecting a destruction of the less resistant cells and inter- vening matrix. In consequence of the penetration of the periosteal processes and the accompanying absorption of the cartilage, a space, the primary marrow-cavity, now occupies the centre of ossification and contains the direct continuation of the osteogenetic layer. This tissue, xhz primary marrozv, which has thus gained access to the interior of the cartilage, contributes the cellular elements upon which a double r61e devolves, — to produce osseous tissue and to remove the embryonal cartilage. The cartilage-matri.x closing the Fig. 125. bryonal cartilage cells be- _ enlarged d regrouped Enlarged cartilage- cells at centre of fication enlarged cell-spaces next the pri- mary marrow-cavity suffers absorp- tion, whereby the cartilage-cells are liberated and the opened spaces are converted into the secondary ajxola;, and directly communicate with the growing medullary cavity. After the establishment of this communi- cation, the cartilage-cells escape from their former homes and undergo dis- integration, taking no part in the direct production 0/ the osseous tissue. Beyond the immediate limits of the primary marrow-cavity the car- tilage-cells, in turn, repeat the pre- paratory stages of increased size and impaired vitality already described, but in addition they often exhibit a conspicuous rearrangement, where- by they form columnar groups sepa- rated by intervening tracts of calci- fied matrix (Figs. 126, 129). This characteristic belt, or zone of calci- fication, surrounds the medullary cavity and marks the area in which the destruction of the cartilage ele- ments is progressing with greatest energy. In consequence of the columnar grouping of the enlarged cartilage-cells and the intervening septa of calcified matrix, an arrange- ment particularly well marked in the ends of the diaphysis of the long bones, a less and a more resistant portion of the cartilage are offered to the attacks of the marrow- tissue by the cell- and matrix-columns respectively ; as a result of this difference, the cells and the immediately surrounding partitions are first absorbed, while the intervening trabeculse of calcified cartilage-matrix remain for a time as irregular and indented processes, often deeply tinted in sections stained with haematoxylin, which extend beyond the last cartilage-cells into the medullary cavity. These trabeculae of calcified cartilage-matrix serve as supports for the marrow-cells assigned to pro- duce the true bone, since these elements, the osteoblasts, become arranged along these trabeculae, upon which, through the influence of the cells, the osseous tissue is formed. Simultaneously with the destructive phase attending the absorption of the car- tilage, the constrictive process is instituted by the osteoblasts by which the bone- tissue is formed. These specialized connective tissue elements, resting upon the ving centre of ossifi- 96 HUMAN ANATOMY. irregular trabecule of the calcified cartilage, bring about, through the influence of their protoplasm, the deposition of a layer of bone-matrix upon the surface of the Fig. 126. Young periosteum — ^- Cartilage-cells becoming larged and grouped Zone of calcificat Osteogenetic layer of perios- Central spongy b clpsing remains of carti- Longitudinal section of metatarsal bone of foetal sheep, showing stages of endochondral bone-development. X 40- trabecule;, which thus becomes enclosed within the new bone. After the latter has attained a' thickness of at least the diameter of the osteoblasts, some of the cells in closest apposition are gradually surrounded by the osseous matri.x (Fig. 127), until, ENDOCHONDRAL BONE. 97 Fig. 127. finally, they lie isolated within the newly formed bone as its cells ; the bone-cells are therefore imprisoned osteoblasts, which, in turn, are specialized connective-tissue elements. The bone-cells occupy minute lenticular spaces, the primary lacunts, at this immature stage the canaliculi being still unformed. The early bone-matri.\ is at first soft, since the deposition of the calcareous materials takes place subsequently. The increase in the thickness of the new bone is attended by the gradual disap- pearance of the enclosed remains of the calcified cartilage, the last traces of which, however, can be seen for some considerable time as irregular patches within the osseous trabeculae (Fig. 131), somewhat removed from the zone of calcification. The cartilage and the bone of the trabeculae stand, therefore, in inverse relations, since the stratum of bone is thinnest where the cartilage is thickest, and, con- versely, the calcified matrix disappears within the robust bony trabeculae. A number of the latter, together with the enclosed remains of the calcified cartilage, soon undergo absorption, with a corresponding enlargement of the intervening marrow-spaces. The remaining tra- beculae increase by the addition of new lamellae on the surface covered by the osteoblasts, and at some distance from the zone of calcification form a trabecular reticulum, the primary central spongy bone. In the case of the irregular bones, the central spongy bone is represented by the cancellated substance forming the internal frame- work ; in the long bones, on the contrary, the primary cancellated tissue undergoes further absorption within the middle of the shaft simul- taneously with its continued development at the ends of the diaphysis from the car- tilage. As the result of this absorption, a large space — the central marrow- cavity — is formed (Fig. 129), the growth of which keeps pace with the general expansion of the bone. The absorption of the young osseous tissue to which reference has been made is effected through the agency of large polymorphonucleated elements, the osteo- _ _ clasts. These are specialized marrow- cells whose particular role is the break- ing up and absorption of bone-matrix. They are relatively very large, their irregularly oval bodies measuring from .050 to .100 millimetre in length and from .030 to .040 millimetre in breadth. The osteoclasts (Fig. 128), singly or in groups, lie in close relation to the surface of the bone which they are at- tacking within depressions, or How- ship' slacuncB, produced in consequence of the erosion and absorption of the osseous matrix which they effect. When not engaged in the destruction of bone, these cells occupy the more central portions of the marrow-tissue, where, in the later stages, they are probably identical with the myeloplaxes or giant cells encountered in the red marrow. The only part of the central spongy bone which persists after the completed development and growth of the long bones is that constituting the cancellated tissue occupying their ends. It will be seen, therefore, in many cases, that the product of the endochondral bone-formation, the primary central osseous tissue, is to a large extent absorbed, and constitutes only a small part of the mature skeleton. The early marrow-cavity, as well as all its ramifications between the trabeculae, is filled with the young marrow-tissue ; the latter gives rise to the permanent red marrow 3 Portion of trabecula of spongy bone undergoing absorp- tion by osteoclast. X 500. 98 HUMAN ANATOMY. Fig. 129. in the limited situations where the central spongy bone persists, as in the vertebrze, the ribs, the sternum, and the ends of the long bones. The important fact may be here emphasized that the process sometimes spoken of as the " ossification of cartilage" is really a substitution of osseous tissue for car- tilage, and that even in the endochondral mode of formation cartilage is never directly converted into bojie. The ossification of the epiphyses (Fig. 130), which in the majority of cases does not begin until some time after birth, the cartilage capping the diaphysis mean- while retaining its embryonal character, repeats in the essential features the details already described in connection with endochondral bone-formation of the shaft. After the establishment of the primary marrow-cavity and the surrounding spongy bone, ossification extends in two directions, — towards the periphery and towards the adjacent end of the diaphysis. As this process continues, the layer of cartilage in- terposed between the central spongy bone and the free surface on the one hand, and between the central bone of the epiphysis and the diaphysis on the other, is gradually reduced until in places it entirely disappears. Over the areas which correspond to the later joint-surfaces the cartilage persists and be- comes the articular cartilage covering the free ends of the bone. With the final ab- sorption of the plates separating the epiphyses from the shaft the osseous tissue of the seg- ments becomes continuous, "bony union" being thus accomplished. Intramembranous Bone-Develop- ment.— The foregoing consideration of the formation of bone within cartilage renders it evident that the true osteogenetic elements are contributed by the periosteum when the latter membrane sends its processes into the ossific centre ; the distinction, therefore, be- tween endochondral and membranous bone is one of situation rather than of inherent difference, since in both the active agents in the production of the osseous tissue are the osteoblasts, and in essential features the pro- cesses are identical. Since in the produc- tion of membrane-bone the changes within pre-e.xisting cartilage do not come into ac- count, the development is less complicated and concerns primarily only a formative pro- cess. Although the development of all osseous tissue outside of cartilage may be grouped under the general heading of intramembranous, two phases of this mode of bone- formation must be recognized ; the one, the iyitramembranous. in the more literal sense, applying to the development of such bones as those of the vault of the skull and of the face, in which the osseous tissue is formed within the mesoblastic sheets, and the other, the subperiosteal, contributing with few exceptions to the production of every skeletal segment, in which the bone is deposited beneath rather than within the connective-tissue matrix. In consideration of its almost universal participation, the periosteal mode of development will be regarded as the representative of the intramembranous formation. Subperiosteal Bone. — The young periosteum, it will be recalled, consists of an outer and more compact fibrous and an inner looser osteogenetic layer. The latter, in addition to numerous blood-vessels, contains young connective-tissue ele- ments and delicate bundles of fibrous tissue. These cells, or osteoblasts, become more regularly and closely arranged along the fibrillae, about which is deposited the Longitudinal secti( I of phalanx of fcetus of fiv nlhs. X 23. SUBPERIOSTEAL BONE. 99 new bone-tissue, the osteoblasts becomino- enclosed uithJn th^ K^ .o c„„„i,„e ,.. .„e.ce,.. The „.e„„t ,Ji'S rsXSL'.TSrLTt™ Fig. 130. -Articular cartilage -Columns of car lage-cells - Spongy bone ot epiphysis - Marrow-tissue - Epiphyseal bone Marrow-tissue HUMAN ANATOMY. These cells cover the exterior of the trabeculae as they lie surrounded by the young marrow-tissue which extends from the osteogenetic layer of the periosteum into the intertrabecular spaces. The union of the young trabeculce results in the production of a subperiosteal net-work of osseous tissue, t)\Q peripheral spongv bone. The latter forms a shell surrounding the central endochondral bone, or, where the latter has already disappeared, the central marrow-cavity of the shaft. The two processes, central and peripheral bone-formation, progress simultaneously, so that the produc- tions of both lie side by side, often in the same microscopical field (Fig. 131). Fig. 131. ■Fibrous layer of periosteum ■Osteogenetic layer of peri- osteum Remains of car- tilage us of foetal sheep ng periosteal and central spongy bone. X l6o. The development of compact bone involves the partial absorption of the subperiosteal net-work of osseous trabeculae and the secondary deposition of new bone-tissue. The initial phase in the conversion of the peripheral spongy bone into compact substance is the partial absorption of the trabeculae by the osteoclasts of the primary marrow-tissue ; in consequence of this process the close reticulum of perios- teal bone is reduced to a delicate framework, in which the comparatively thin remains of the trabeculae separate the greatly enlarged primary marrow-cavities, which, now known as the Haversian, spaces, are of round or oval form. After the destructive work of the osteoclasts has progressed to the required extent, the osteoblastic elements of the young marrow contained within the Haver- INTRAMEMBRANOUS BONE. sian spaces institute a secondary formative process, by which new bone is deposited on the walls of the Haversian spaces. This process is continued until, layer after layer, almost the entire Haversian space is filled with the resulting concentrically disposed osseous lamellae ; the cavity remaining at the centre of the new bone per- sists as the Haversian canal, while the concentrically arranged layers are the lamellae of the Haversian system, the extent of the latter corresponding to the form and size of the Haversian space in which the secondary deposit of bone occurs. It is evident from the development of the compact substance that the interstitial or ground- lamellae of the adult tissue correspond to the remains of the trabeculae of the primary spongy bone ; these lamellae are, therefore, genetically older than those constituting the Haversian systems. The details of the formation of the Haversian lamellae, in- cluding the deposition of the matrix and the inclusion of the osteoblasts to form the bone-cells, are identical with those of the production of the trabeculae of -the earlier bone. Intramembranous Bone. — The development of certain bones, as those con- stituting the vault of the skull and the greater part of the skeleton of the face, differs in its earliest details from that of the subperiosteal bone, although the essen- tial features of the processes are identi- cal. The mode by which these mem- Fig. 132. brane-bones are formed may claim, therefore, a brief consideration. The early roof of the skull consists, except where developing muscle occurs, only of the integument, the dura mater, and an intervening connective-tissue layer in which the membranous bones are formed. The earliest evidences of ossification usually appear about the middle of the area corresponding to the later bone, delicate spicules of the new bone radiating from the ossific centre towards the periphery. As the tra- beculae increase in size and number they join to form a bony net- work (Fig. 132), close and robust at the centre and wide-meshed and delicate towards the margin where the reticulum fades into the connective tissue. With the con- tinued growth of the bony tissue the net-work becomes more and more compact until it forms an osseous plate, which gradually expands towards the limits of the area devoted to the future bone. For a time, however, until the completion of the earliest growth, the young bones are separated from their neighbors by an intervening tract of unossified connective tissue. Subsequent to the earlier stages of the formation of the tabular bones, the continued growth takes place beneath the periosteum in the manner already described for other bones. On examining microscopically the connective tissue in which the formation of membrane-bone has begun, this layer is seen to contain numerous osteogenetic fibres around and upon which are grouped many irregularly oval or stellate cells ; the latter correspond to the osteoblasts in other locations, since through the agency of these elements the osseous matrix is deposited upon the fibres. As the stratum of bony material increases some of the cells are enclosed to form the future bone-cor- puscles. Although the osteogenetic fibres correspond to delicate bundles of fibrous tissue, they are stiffer, straighter, and present less indication of fibrillar structure. Since the fibres forming the ends of the bony spicules generally spread out, they fre- quently unite and interlace with the fibres of adjacent spicules, thus early suggesting the production of the bony net-work which later appears. Growth of Bone. — It is evident, since the new bone is deposited beneath the periosteum, that the growth of the subperiosteal bone results in an increased diame- al bone of human foetus of three months, showing becular net-work of intramembranous bone. X 5- I02 HUMAN ANATOMY. ter of the shaft as well as in thickening of the osseous wall separating the medullary cavity from the surface. In order, therefore, to maintain the balance between the longitudinal growth of the medullary cavity, effected by the absorption of the endo- chondral bone, and its lateral expansion, the removal of the innermost portions of the subperiosteal bone soon becomes necessary. Absorption of the older internal trabeculce thus accompanies the deposition of new osseous tissue at the periphery ; by this combination of destructive and formative processes the thickness of the cylindrical wall of the compact substance of the diaphysis is kept within the proper limits and the increased diameter of the medullary cavity insured. Throughout the period of early growth the increase in length of the bone is due to the addition of new cartilage at the ends ; later, the cartilaginous increments, contributed by the chondrogenetic layer of the perichondrium, are supplemented by interstitial e.xpansion following the multiplication of the existing cartilage-cells. On attaining the maximum growth and the completion of epiphyseal ossification, a por- tion of the cartilage may persist to form the articular surfaces. After the cessation of peripheral growth and the completion of the investing layer of compact substance, the osteogenetic layer of the periosteum becomes more condensed and less rich in cellular elements, retaining, however, an intimate connection with the last-formed subjacent bone by means of the vascular processes of its tissue, which are in con- tinuity with the marrow-tissue within the intraosseous canals. In addition to being the most important structure for the nutrition of the bone, on account of the blood- vessels which it supports, the periosteum responds to demands for the production of new osseous tissue, whether for renewed growth or repair, and again becomes active as a bone-forming tissue, its elements assuming the role of osteoblasts in imitation of their predecessors. THE SKELETON: INCLUDING THE BONES AND THE JOINTS. Fig The skeleton forms the framework of the body. In the widest sense it includes, besides the bones, certain cartilages and the joints by which the different parts are held together. The skeleton of vertebrates is divided into the axial and the appendic- ular ;, the former constitutes the support- ing framework of the trunk and head ; the latter, that of the extremities. The Axial Skeleton. — The general plan of the a.xial skeleton of the trunk is as follows : a rod composed of many bony disks (the vertebral bodies) connected by fibro-cartilage separates two canals, a dorsal and a ventral. In most vertebrates the rod is in the main horizontal, with the dorsal canal above and the ventral below ; but in man the rod is practically vertical, with the dorsal canal behind and the ventral in front. The former is called the neural, because it encloses the central nervous system ; the latter, the visceral. The vertebral column has developed about the primary axis, the notochord. The neural canal is enclosed by a series of separate arches springing one from each vertebra. The skeletal parts of the anterior, or ventral, canal are less nu- merous ; they are the ribs, the costal carti- lages, and the breast bone. Above is the bony framework of the head, or the skull. This also is divided into a dorsal and a ven- tral portion by a bony element which is apparently a continuation of the bodies of the vertebrae, and, indeed, is actually de- veloped, in part, around the front of the notochord. The cephalic axis, however, is bent at an angle with the vertebral bodies, so that the neural arches, which here en- close the brain, are chiefly no longer be- hind but above. Below and in front of the brain-case is the face, which contains the beginning of the digestive tube, of which the jaws and teeth are special organs. In the head we do not find the separation of the parts enclosing the brain into a series of vertebrae, but they are clearly a continuation of the vertebral arches, the posterior, or occipital, division strongly suggesting a vertebra. The face is far more complicated, the vertebral plan being lost. In short, the axial skeleton consists of a 103 tinted portions constitute the axial skeleton ; the untinted, the appendicular skeleton. I04 HUMAN ANATOMY. central, manv-jointed rod bent forward near the top, with very perfect bony walls behind and above it, enclosing the central nervous system, and very imperfect bony and cartilaginous walls before and below it, enclosing the digestive apparatus and its associates, the circulatory, respiratorv, urinary, and reproductive organs. The Appendicular Skeleton has an entirely distinct origin ; it is the frame- work of the limbs. It consists of two girdles, a thoracic and a pelvic, to each of which is attached a series of segments, the terminal one of which e.xpands into five rays, — -fingers and toes. According to some anatomists, the true vertebrate plan is of seven terminal rays, but, the question being still undecided, the more usual sys- tem is followed. Each of these rays consists of three or four bones. Pro.ximal to this comes a series of short bones, — icrist and ankle ; still nearer, a pair of bones, — -fore- arm and leg ; then a single bone, — arm and thigh ; and lastly a bony arch, — the girdle. In man, the thoracic girdle, made up of collar-bone and shoulder-blade, lies external to the chest, while the pelvic girdle fuses on each side into one bone, meets its fellow in front, and unites with the bodies of certain vertebrte. Thus, besides bearing a limb, the pelvic girdle forms a part of the wall of the abdominal and the pelvic ca\-ities and would seem to belong to the a.xial skeleton, but embryology and comparative anatomy show that it does not. GENERAL CONSIDERATION OF THE BONES. The bones have the physiological function of bearing weight, of affording pro- tection, and especially, by the systems of levers composing the limbs, of effecting movements through the action of the muscles. They must, therefore, be capable of resisting pressure, accidental violence, and the strain caused by the pull of the muscles. The size of the bones must be such that besides serving the obvious needs of support and protection they may be sufficiently large to offer adequate surface for the origin and insertion of muscles, and the shape must be such as to allow this without undue weight. Shapes of Bones. — Bones are divided, according to their form, into lo7ig, flat, and irregular ; such classification, however, is of little value, since many bones might be variously placed. Long bones form the best-defined group. They consist of a shaft and two e-xtremities, each of which takes part in the formation of a joint, or, as in the case of the last phalanges, is terminal. Flat bones, where very thin, consist of a single plate ; where thicker, they con- sist of two plates separated by spongy substance called diploe. Irregular bones may be regarded as embracing all others. The group of the so-called short bones has no significance. Sesamoid Bones, with the exception of the patella, are not usually included in the description of the skeleton. With the above exception, they are small rounded bones developed, for the most part, in the capsules of joints, but sometimes in ten- dons. Usually one surface is cartilage-covered, and either enters into the formation of a joint or, separated by a bursa, plays on another bone, or on cartilage or liga- ment. Their function is to obviate friction, and, in some cases, to change the direc- tion of the pull of a muscle. The number of sesamoid bones is very variable ; but the usual idea that they are, so to speak, accidental, depending on the mechanics of a certain joint or tendon, must probably be abandoned. They are rather to be con- sidered as real parts of the skeleton,' all of which have their places in certain animals, but all of which either are not de\'eloped, or, if they do appear, are again lost in others. Thus, certain sesamoid bones of the fingers are very frequent in the foetus and very rare in the adult. Growth of Bones. — The microscopical details of bone-growth are given else- where (page 94). Suffice it to say here that each bone has certain so-called centres of ossification from which the formation of the new bone spreads. In the long bones there is one main centre in the shaft, or diaphysis, which appears in the first half of toetal life. Other centres appear, usually some time after birth, in the ends of the ' Thilenius : Morpholog. Arbeiten, Bd. vi., 1S96. MECHANICS OF BONE. 105 bones. There may be one or several in each end. The part formed around each of these secondary centres is called an epiphysis. Growth takes place chiefly in the cartilage between the epiphyses and the shaft. When, therefore, a joint is resected in childhood the surgeon tries to leave a part of the epiphysis in place. A curious relation exists between the course of the chief medullary artery of the shaft of a long bone and the behavior of the epiphyses. The epiphysis towards which the vessel is di- rected is the last to appear and the first to unite. (The fibula furnishes an exception. ) As a rule, also, the largest epiphyses appear first and unite last. In long bones with an epiphysis at one end only, the nutrient canal leads towards the opposite extremity. Mechanics of Bone. — A long bone has a hollow shaft containing maj-row, the wall being of compact bone. The hollowness of the shaft takes from the weight, and, moreover, conforms to the well-known law that a given quantity of matter is much stronger, both lengthwise and crosswise, when disposed as a hollow cylinder than as a solid one of equal length. The proportion of the central or medullary cavity is not the same in all bones. Perhaps, as an average, its diameter may be said to equal one-third of that of the bone. In the shaft this cavity is crossed by a few bony trabeculae, almost all of which are destroyed in maceration. Towards the ends, as the outer wall becomes thinner, large numbers of thin plates spring from its inner surface and incline towards one another in graceful curves, until at last the expanded end of the bone consists of spongy or cancellated tissue enclosed within a delicate wall of compact substance. The arrangement of these plates is distinctly pur- poseful, since it has been shown that they are so disposed as to correspond with the stress-lines an engineer would construct for the special purpose served by the end of the bone. None the less, it would be unwarranted to maintain that mathematical correctness is always to be found, or that there are not other modifying influences. The internal structure of all bones, excepting, perhaps, those of the skull, is of this nature, so that the following remarks apply to spongy bone in general. • The delicate cancellated structure is for the most part in thin plates. The sim- plest arrangement occurs in a short bone exposed to pressure only at two opposite surfaces ; in such cases the plates run between these surfaces with few and insignifi- cant cross-pieces. Where severe pressure may come in almost any direction, as in the case of the globular heads of the humerus and femur, the round-meshed pattern predominates, producing a very dense spongy structure which may be represented diagrammatically by drawing lines crossing at right angles and by enlarging every point of intersection. In the midst of this round-meshed type there is very fre- quently a central core with stronger plates and larger spaces. The vaidted system is found at the projecting ends of bones, and between the round-meshed cancellated substance and the shaft. Several special arrangements will be described in connec- tion with the bones in which they occur. An epiphysis, until it has fused, shows the mechanical structure of a separate bone. K process for the attachment of muscles or ligaments generally contains a very light internal structure, the surface of the shaft of the bone being rarely continued under it. The continuation of the fibres of attached tendons is not represented by internal plates of bone, although the oppo- site opinion has supporters. Certain of the bones of the cranium and the face are in parts hollowed out into mere shells bounding a cavity lined with mucous membrane continuous with that of the nose or the pharynx. The elasticity of bones is enhanced by curves. The long bones very usually present a double curve. It has been maintained that these curves form a spiral structure. There are striking instances of it, but the universality of the law is not proved ; although shocks are thus lessened, the passage of one curve to another is a weak point in the bone. The ends of the long bones are enlarged for articulation with their neighbors. The greater part of this enlargement forms the joint, the various shapes of which will be discussed later. Besides this, there are usually at the ends prominences foi muscles. The shaft generally bears ridges, which in some cases are made of dense bone and materially add to the strength of the bone. A ridge or prominence usually implies the insertion of a fibrous aponeurosis or a tendon. Muscular fibres, however, may spring from the periosteum over a flat surface. io6 HUMAN ANATOMY. Parts of Bones. — The following are some of the names applied to features pf bone : A process is a general term for a projection. A spine or spinous process is a sharp projection. A tuberosity is a large rounded one, a tubercle is a small one, either rounded or pointed. A crest is a prominent ridge. A head is an enlargement at the end of a bone, in part articular. A 7ieck is a constriction below a head. A condyle is a rounded articular eminence, generally a modification of a cylinder. A. fossa is a pit. A glenoid cavity is a shallow articular depression. A cotyloid cavity is a deep one. A sulcus is a furrow. K foramen is a hole, in the sense of a perforation. A sinus is the cavity of a hollow bone, equivalent to antrum. It is used also to designate certain grooves for veins in the cavity of the cranium. In addition to the cartilage-covered articular surfaces proper, the fresh bones show in some places a plate of cartilage quite like one for a joint; such plates ser\'e to lessen the friction of a tendon playing over the bone. In other places a look of pecul- iar smoothness is conferred by the presence of a bursa, although cartilage is wanting. Sex of Bones. — Female bones are characterized in general by: (a) a greater slenderness; (^) a smaller development of processes and ridges for muscular attach- ment'; if) and, most important of all, the small size of the articular surfaces. These guides usually suffice to determine the se.x of the chief bones; some, especially those of the pelvis, possess characteristic se.xual differences of form. Age of Bones. — At birth the long bones have cartilaginous ends in which, with one or two exceptions, the centres of ossification have not yet appeared. Many bones at this period still consist of several pieces which ultimately fuse. The shape and proportions are in some cases different from those of the adult. Sexual differ- ences cannot in most cases be determined. During the first years new centres of ossification appear, distinct pieces unite, and the proportions change from the type of the infant to that of the child. Towards puberty important further changes in proportion occur, and sexual differences develop. After puberty the bones present three stages, — adolescence, maturity, and senility. In the first the union of the epiphyses is going on ; after this has taken place the line of separation is visible for a time, but gradually disappears. Our knowledge of the time at which these changes occur enables us to determine the age of the skel- eton. The long period of maturity presents little that allows of a precise estimate of age. The separate bones of the vault of the cranium gradually fuse into one. The senile skeleton in its extreme stage is very striking. There is a general atrophy of the bones both within and without, those of the face becoming in parts of papery thinness ; not only the cavities within the cranial bones become larger, but also the spaces within the cancellous tissue inside the bones, due to the partial absorption of the spongy substance. The only bones, however, which show a distinct change of form are the jaws, and this is a secondary result of the loss of the teeth. In many cases, however, senile absorption and atrophy do not occur, except, perhaps, in the head ; it may be, therefore, absolutely impossible to distinguish a long bone of an old subject from one of an individual in early maturity. The periods at which the ?.ge of bones is most often a matter of medico-legal inquiry' are at the time of birth and in childhood and youth. The dates of the first appearance of ossification in the various bones are the criteria for the first. These are to be used, however, with great caution, since variation is considerable. The information to be derived from consideration of the general development of the body is perhaps of equal value. The same holds good for childhood and adolescence. The particular point on which the writer holds strong views, based on his own observations, differing from those generally accepted, is as to the time of union of the epiphyses at the end of ado- ' D wight ; American Journal of Anatomy, Vol. iv., 1904. GENERAL CONSIDERATION OF THE JOINTS. 107 lescence. He is convinced, as his statements will show, that this union occurs earlier than is generally taught. Relation of the Bones to the Figure. — While it may be said that power- ful muscles leave their imprint on the bones in strong, rough ridges, yet it is impos- sible to give a trustworthy description of the figure from the size and shape of the bones, since these are determined chiefly by prenatal influences. Very delicate, even puny, bodies may have large and strong bones, and great muscular develop- ment may coexist with a light framework. Variations. — Besides the great range of individual variation, without departure from the usual type, bones occasionally show greater peculiarities. These may occur through either e.xcess or defect of ossification. Structures which are normally car- tilaginous or fibrous may become replaced by bone, and abnormal foramina may occur in consequence, or to accommodate the aberrant course of blood-vessels or nerves. The most interesting of these variations are such as present an arrangement which is normal in some of the lower animals. Many variations may be plausibly accounted for as reversions, but others cannot be explained in this way according to any conceivable scheme of descent. By speaking of these variations as animal analogies we avoid theories and keep to scientific truth. Number of Bones. — The usual enumeration of the bones composing the human skeleton is misleading, for while it is customary in some parts, as the head, to count each bone, in others, like the sacrum and the hyoid, only the ultimate condition, after union of the component segments, is considered. In other cases, like the sternum, there may be grave doubt which course is the proper one to follow ; and finally, as in the coccyx, the number is variable. Bearing these impor- tant facts in mind, it may be stated that the human skeleton in middle life usually comprises, as conventionally reckoned, two hundred separate bones, excluding the sesamoids within the tendons of the short flexor of the thumb and of the great toe and the ear-ossicles, but including the patella and the hyoid bone. Of this number, seventy-four bones belong to the axial and one hundred and twenty-six to the appen- dicular skeleton. The skeleton is advantageously described in the following order : the spine, the thorax, the head, the shoulder-girdle and the arm, the pelvic girdle and the leg. The account of the bones of each region is succeeded by that of the joints and the ligaments holding them together, followed by a consideration of the region as a whole and of its relation to the. surface. The applications of anatomical details of the skeleton to the requirements of medicine and surgery are pointed out in appro- priate places. GENERAL CONSIDERATION OF THE JOINTS. A JOINT or articulation implies the union of two or more bones. Joints may be divided, according to their mobility, into three great classes : the fixed joint (Sjn- arikrosis), the half-joint {Amphiarthrosis) , and the true joint {Diarthrosis) . Fixed Joints. — These allow no motion in the mature condition, and are rep- resented by two subdivisions, the Suhire and the Syficho7idrosis. The suture is the direct union of two bones which at first may be separated by membrane or by fibrous tissue, but which eventually become firmly united. Several varieties of this form of union are recognized ; thus a serrated suture is one in which the edges are interlocked, as the teeth of two saws ; conspicuous examples are seen in the interparietal and the parieto-occipital junctures. Frequently one bone tends to overlap at one end of the suture and to be overlapped at the other. A squamous suture is one in which a scale-like bone very much overlaps another, as in the relation between the temporal and the parietal bone. An harmonic stdure is one in which two approximately plane surfaces are apposed, as in the case of the vertical plate of the palate and the maxillary bone. The term grooved suture is sometimes employed to designate a form of union in which one bone is received within the grooved sur- face of another, as the rostrum of the sphenoid and the vomer. Wortnian bodies are small, irregular ossifications which appear as bony islands in the course of a suture. Familiar examples of these are seen in the line of the parieto-occipital suture. io8 HUMAN ANATOMY. Sj'nchondrosis is the union of two bones by an intervening strip of cartilage, which usually ultimately becomes replaced by bone. Such is the union between the pieces of the body of the sternum and between certain bones of the base of the skull. The term is also applied to the union of the shaft and the epiphyses of long bones. Half-Joints, including Symphysis and Syndesmosis. From the stand-point of development, there is no fundamental difference between symphyses and the true joints. In both cases a small cavity appears withm the intervening niesoblastic tissue connecting the ends of the embryonal bones. This small cavity, in the case of the true joints, rapidly increases, and later is lined by the flattened mesoblastic cells investing the subsequently differentiated synovial membrane. When, on the con- trary, the bones are to become united by dense fibrous and fibro-cartilaginous tissue, as in the case of a symphysis, the interarticular space is always a mere cleft sur- rounded by the interlacing and robust bundles of the dense tissue forming the union in the mature joint. A symphysis implies great strength and very limited and indefinite motion, there being no arrangement of surfaces to determine its nature. The chief function of this form of union seems rather to be to break shocks. The central cavity is not always found. The symphysis pubis (^Fig. 361 j is a typical half-joint. Those con- necting the bodies of the vertebrae are usually so classed but it is not certain that they quite agree either in structure or development with the description A transi- FiG. 134. kn^n^ Diagra of suture, ^.serrated; 5, squamous ; C harmonic ; Z>, grooved. tional form leading from the symphysis to the true joint is one in which the limited synovial cavity, instead of being in the centre of a mass of libro-cartilage, lies between two cartilaginous surfaces, somewhat like that of a true joint, but so interlocked and surrounded by short, tense fibres as to preclude more than very slight motion. This arrangement is often seen in the articulation between the sacrum and ilium, some- times improperly called the sacro-iliac synchondrosis. Syndesmosis is to be included among the half-joints. It is the binding together of bones by fibres, either in bundles or qs a membrane, without any inter- vening cartilage ; an example of this arrangement is seen in the union effected by the interosseous ligament in the lower tibio-fibular articulation. True Joints. — These articulations develop in a similar manner to the half- joints, e.xcept that the opposed ends of the developing bones are of hyaline carti- lage, fibro-cartilage being present only at the sides, except in the case of a compound joint, where it forms the intervening plate. The tissue at the sides of the articular cleft differentiates into two layers, — the inner, which is the synovial membrane, consist- ing of a layer of cells continuous with the superficial layer of the cartilage-cells and secreting a viscid fluid, the synovia, which lubricates the joint ; and the outer part, which becomes a fibrous bag called the capsular ligmnent. The latter, in its simplest form, consists of only enough fibrous tissue to support the synovial membrane. The capsular ligament is strengthened by accessory /iffamcnts de\'eloping in or around it, the arrangement of which depends on the needs of the joint. During development. STRUCTURE OF JOINTS. 109 independent of the influence of motility or of muscular action, the articular ends of the bones assume definite shapes such as will allow the motion peculiar to that joint, and (barring the frequent want of perfect coaptation) no other. The common char- acteristics of true joints are articular surfaces covered by hyaline cartilage, so shaped as to determine the nature of the movement, enclosed by a capsule lined with a synovial membrane. The articular surfaces are not necessarily formed wholly of bone, since very often increased concavity is secured by the addition of a lip of fibro- cartilage to the margin of the bone ; in other cases ligaments coated with carti- lage complete a socket ; or again, disks of fibro-cartilage loosely attached to the periphery may project into a joint and partially subdivide it, following one bone in certain movements and the other in others. Compound joints result from the persistence and differentiation of a portion of the tissue uniting the ends of the embryonal bones into a partition which, in the complete compound joint, separates the two synovial cavities developed, one on either side of the septum. The tissue between the bones becomes a fibro-cartilagi- nous disk,' which partially or completely subdivides the cavity. In such a joint, when typical, there are two ends of bone covered with articular cartilage, separated Diagrams illustrating formation of joints. A, bones are united by young connective tissue; B, appearance o\ ioint-cavity; C, differentiation of joint-cavity and capsule; Z?, development of two joint-cavities separated by fibrous septum, resulting in a compound joint. by a fibro-cartilaginous disk or meniscus, and two distinct synovial membranes. The movements are, however, still determined to a considerable extent by the shape of the bones, so that these articulations may be classed as true joints. The fibro- cartilaginous meniscus may be replaced by a row of bones as in the wrist. Structure of True Joints. — The opposed ends of the bones, and sometimes other tissues, are coated with hyaline articular ca7-tilage, which gives a greater smoothness to the articulating surfaces than is found on the macerated bones. Though following in the main the bony contours, the cartilage does not do so accu- rately ; details are found on the cartilage that are obscure on the bones. It dimin- ishes the force of shocks. Although, as already stated, the shape of the articular ends determines the nature of the motion, it is important to recognize that, as in the case of saddle-joints, the opposed surfaces are not so accurately in apposition that irreg- ular movements cannot and do not occur. Failure to appreciate this fact has given rise to much difficulty in accounting for motions that undoubtedly take place, but which, according to the mathematical conception of the joint, are impossible. Further, the range of individual variation is great ; just as a man may have a long or a short head, so any of the articular ends of his bones may depart considerably from the average proportions. It is even possible in some of the smaller joints that ' Discus articularis. HUMAN ANATOMY. Fig the articular surface of a certain bone may be plane, convex, or concave in different persons. The capsule. — Every joint, with possibly some exceptions in the carpus and the tarsus, is enclosed by a capsule,^ or capsular ligament, which arises from the peri- osteum near the borders of the articular cartilage and surrounds the joint. This envelope consists of a membrane, often containing fat within its meshes, composed of two layers, the inner delicate synovial membrane and the external fibrous layer. The latter, while in some places very thin, is usually strengthened by the incorpora- tion of fibrous bands which, from their position, are known as lateral, anterior, or posterior ligaments. These bands are of strong, non-elastic fibrous tissue which under ordinary circumstances do not admit of stretching. The strength and security of the joint are often materially increased through thickenings of fasciae and expansion of tendons which blend with the underlying capsule. The capsule must be large enough to allow the characteristic movements of the joint ; consequently, when the bone is moved in any particular direction that side of the capsule is relaxed and thrown into folds. These folds are drawn out of the way either by small special muscles situated beneath those causing the chief movement or by fibres from the deeper surfaces of these latter muscles. In the joints of the arches of the vertebrae, there being no muscles inside the spinal canal, a dif- ferent arrangement exists for the inner side of the capsule, elastic tissue there taking the place of muscle. The relation of the insertion of the capsule to the line of the epiphysis is important. Although this point is fully con- sidered in the description of the individual joints, it may be here stated that, as a rule, in the long bones, the capsule arises very near the line of the epiphysis. The synovial membrane which lines the interior of the capsule and other portions of the joint, except the surfaces of the articular cartilages, consists of a delicate connective- tissue sheet, containing many branched and flattened connective-tissue cells. The latter, where numerous, as is the case except at points subjected to considerable pressure, are ar- ranged on the free surface of the synovial mem- brane as a more or less continuous layer, often spoken of as the endothelium of the synovial sac. Since in many places the layer of connective-tissue elements is imperfect and the component cells retain their stellate form, the cellular investment of the joint- cavity is at best endothelioid, suggesting, rather than constituting, an endothelium. The synovial membrane is in certain places pushed inward by accumulations of fat of definite shape between it and the capsule. It is also prolonged, as the syjwvial fringes,'^ into any space that might otherwise be left vacant in the various movements. They are alternately drawn in or thrust out, according to circumstances. Some- times pieces of them, or of fibro-cartilage, become detached in the joint, giving rise to much trouble. The cavity which is found when a joint is opened on the cadaver, with the tissues dead and relaxed, easily suggests a false impression. It is to be remembered that the synovial fluid normally is present in quantity little more than sufficient to lubricate the joint, and that in life all the parts are strongly pressed together so that no true cavity exists. This is well shown by frozen sections. Certain so-called intra-articular ligaments, as the ligamentum teres of the hip, or the crucial ligaments of the knee-joint, are found in the adult, roughly speaking, inside the joint. The sketch of development given above shows that they cannot be truly within the articular cavity. In fact, either they wander in from the capsule, carrying with them a reflection of synovial membrane, or they are the remnants of ^ Capsala articalaris. - Plicae svnoviales. Capsul Synovial membran Articular cartilage- Joint-cavit\ Reflection of sync- Epiphyseal bone Diagram showing the parts of a typical joint. BURS^. Ill the capsules separating two distinct joints which have broken down so as to make a common articular cavity. Such ligaments retain their synovial covering and really lie without the joint-cavity. Vessels and Nerves. — Important arterial anastomoses surround all the larger joints ; from the larger vessels small branches pass inward to the ends of the bones, to the periphery of the articular cartilages, and to the capsule. The margins of the cartilages are surrounded by vascular loops ; the articulating surfaces are, however, free from blood-vessels. The synovial membrane is usually well supplied with minute branches, a rich net-work being described at the bases of the synovial fringes. The veins form strong plexuses. Lvinphatics are found well developed directly beneath the inner surface of the synovial membrane ; while it is certain that they absorb from the joint, direct open- ings into the articular cavity have not been demonstrated. Nerves, presumably sensory and vasomotor, end in the tissues around the syno- vial membrane. In addition to the Pacinian bodies, which are sometimes very numerous, Krause has described special articular end-bulbs outside the synovial membrane surrounding the finger-joints in man. Fig. 137. Free surface of articular car tilage Synovial 1 .^-r'^^^^i ^ V> . ■ .ra^j^ Section through margin of joint, showing articular cartilage and capsule. X 135. •Union of carti- lage and syno- Bursae ' are sacs filled with fluid found in various places where friction occurs between different layers or structures. They are sometimes divided into synovial and mucous bursae. These varieties are distinct in typical instances, but, since the one passes insensibly into the other, it is doubtful whether this subdivision is war- ranted. Some bursae, especially those around the tendons of the fingers, have a true synovial lining reflected over the tendons, and are surrounded by strong fibrous sheaths known as the theccB synovialcs. ^ Other bursae are placed as capsules around a cartilage-coated facet over which a tendon plays. Both the vaginal and capsular varieties may be classed as synovial bursae. Representatives of the mucous bursae are those within the subcutaneous tissue where the skin is exposed to friction, as at the elbow and the knee. These bursas seem little more than exaggerations of the spaces between layers of areolar tissue. The same may be said of some of those among the muscles. The mucous bursa, are provided with more or less of a cellu- lar lining, but the latter is less perfect than in the synovial class. A bursa may be simple or composed of several cavities communicating more or less freely. They often communicate with joints. Their number is uncertain. Many, perhaps most, are present at birth, but new ones may appear in situations exposed in certain ^ Barsae synoviales. -Vagii 112 HUMAN ANATOMY. individuals to uncommon pressure or friction, and, under these circumstances, the ones usually present may be enormously enlarged. Modes of Fixation in Joints. — Ligaments, muscles, atmospheric pressure, and cohesion are the agents for fixation. Ligaments. — A capsular ligament, pure and simple, has little retaining strength. The accessory ligaments, on the contrary, have great influence. Their arrangement differs with the nature of the joint. Thus, a ball-and-socket joint has thickenings at such parts of the capsule as the particular needs of that joint require. A hinge-joint implies strong lateral ligaments ; a rotary joint, some kind of a retain- ing-band that shall not arrest motion. Sometimes certain ligaments are tense, or nearly so, in every position of the joint, as the lateral ligaments of a hinge-joint. Often a ligament is tense only when a joint is in a particular position, as the ilio- femoral ligament of the hip when the thigh is extended. A strong ligament like the one just mentioned is, when tense, the greatest protection against displace- ment. Muscles. — The action of the muscles is of great importance in maintaining the joints in position, in certain instances being the most efficient agency. The con- stant pull of the muscles keeps the more movable bone closely applied to the more fixed in all positions. Muscles which are nowhere in contact with the joint may exercise this function. The tendons of muscles sometimes act as ligaments, which differ from the ordinary ligamentous bands in that they may be made tense or relaxed by muscular action. Sometimes they are intimately connected with the capsule, at other times distinct from it. Some muscles, whose tendons cross several joints, exercise, by their tonicity, an influence on them all. Thus, the peroneus longus is essential to the maintenance of the transverse arch of the foot. Certain muscles passing over more than one joint exert a ligamentous action on one joint determined by the position of the other. This, however, is more properly dis- cussed in connection with the action of muscles. Atmospheric Pressure. — Much has been written about the action of this agency in holding joints in place. The atmosphere exerts a certain pressure on all bodies, animate or inanimate, and thus tends to compress them. The joints, as parts of the body, are subject to this general influence. It is by no means very effi- cacious. The shoulder-joint has a capsule long enough to allow very free motion, and consequently too long to hold the humerus in place. This is done chiefly by the muscles. When these are paralyzed the arm falls out of place, atmospheric pressure being inadequate to resist the weight. The most important action of atmospheric pressure is to keep the soft parts closely applied to the bones. Cohesion is the action of the viscid synovial fluid which tends to hold the surfaces together. It is very feeble, but probably has an appreciable influence in the smaller joints. Limitation of Motion. — The shape of the joint determines the nature of the movement ; its range depends in part on other factors, such as the tension of liga- ments or of the tendons of muscles and the resistance of the soft parts. Motion in True Joints. — It is easy to conceive that an upright rod on the highest point of rather less than half a sphere may Fig. 13S. slide to the periphery along an indefinite number of ROTATION^ Akig Hnes. This is angiila?- motion. The rod on reach- ■■■■■"' T ■■'-i^''' ingr the periphery, or at any point on the way, may ,.-• ; "•^'V travel round in a circle describing the surface of a giBcuM I oucriorv V^ cone. TMvsiVS, circumduction. Finally, without any /....• -uJ^^^^^^^^^^'^ Changes of Position of Parts of the Body. _. .,, .. ,.„ ... , — Assuming that the palms are looking forward, an- Uiagram lUustratine dinerent kinds of , . -^ , ,. ,* , P , motion. gular motion of a limb, or of a part 01 one, towards the median plane of the body is called additctioti ; the opposite movement, abductioJi. A motion bringing the distal end of a limb bone nearer to the head is called Jiexioji ; the opposite movement, extension. The move- ments of the ankle and the foot, however, present a difficulty, although the above VARIETIES OF TRUE JOINTS. 113 nomenclature is generally accepted, since the digital extensor muscles flex and the flexors extend. It is best with reference to the ankle-joint to speak of plantar flexion and dorsal flexion. Pronation in the arm is turning the front of a limb downward ; supination, the converse. Thus, when the palm rests upon a table the arm is pronated ; when the back of the hand rests upon the same support the arm is supinated. Reference to the skeleton during these movements will show that pro- nation is associated with crossing of the bones of the forearm, while during supina- tion they are parallel. These terms should not be applied to motions of the leg. Rotation is inward or outward, according as it is towards or away from the median line of the body. Varieties of True Joints. — The following are the chief kinds of true joints, the nature of the motion being determined by the articular surfaces : Arthrodia,' a gliding joint permitting merely a sliding between two nearly plane surfaces, as between the articular processes of the vertebrae. Enarthrosis,- a ball-and-socket joint permitting angular motion in any direc- tion, circumduction and rotation. The shoulder- and hip-joints are conspicuous examples. Condylarthrosis,^ an egg-shaped joiiit permitting angular motions more freely on the long axis than on the short one, circumductio7i but (theoretically, at least) no rotatio?i, as in the radio-carpal articulations. The imaginary axes for the angular motions lie in the convex bone. The Saddle-Joint/ is a modification of the above, the end of one bone being convex in one plane and concave in another, at right angles to the first, while the other bone is the converse ; thus in one plane one bone is the receiver and in the other the received. The articulation of the trapezium with the first metacarpel bone is an example. The motions in such joints are precisely the same as those of the preceding form. The two imaginary axes are, however, on opposite sides of the joint, each being at right angles to the convex plane of its own bone. It is clear that if the reciprocal curves of the two bones of a saddle-joint coincide, and that if they fit closely, rotation is out of the question ; but, in point of fact, that is not the case, for there is no very accurate agreement of the surfaces, and the contained curve is smaller than the containing, so that a certain amount of rotation is possible.* Ginglymus," a hinge-joint permitting motion only on a single axis approxi- mately transverse to the long axis of the bone, consequently the moving bone keeps in one plane. The ankle-joint is an example. The inclination of the transverse axis may vary, and one end of the joint be larger than the other. If the course of the revolving bone is that of a spiral around the transverse cylinder the articulation constiutes a screw-joint^ as the humero-ulnar articulation. Trochoides,' a pivot-joint permitting motion only on one axis coincident with at least a part of the long axis of the bone,- — namely, rotation, as in the atlanto-axial articulation. Should a part of the bone be so bent as to lie outside of the axis, as in the radius, this part undoubtedly changes position ; nevertheless, there is merely rotation, for the change of position is accidental, depending on the shape of the bone, not on the nature of the motion. Certain complicated joints may combine several of the above forms. *Ren^ du Bois-Reymond. Archiv fiir Anat. u. Phys., Phys. Abtheil., 1895. ^Arthrodia. "Enarthrosis. ^ Articulatio ellipsoidea. ■* .\rtlculatio sellaris. ^ Ginglymus. ^ Articulatio cochlearis. ^ Articulatio trochoidea. THE SPINAL COLUMN. The spinal column is the central part of the skeleton. It supports the head, bears the ribs, thus indirectly supporting the arms, and encloses the spinal cord. It gives origin to many muscles, some passing between different parts of the spine, others connecting it with the body. These purposes demand great strength and flexibility. The spine is composed of many pieces united by tough fibro-cartilagi- nous disks, by which the force of shocks is broken and the great range of move- ment is distributed among many joints. It is convex behind in the regions of the thorax and pelvis, so as to enlarge those cavities, and has forward convexities in the neck and loins. The numerous prominences which it presents serve for the support of the ribs, the attachment of muscles, and the interlocking of the various pieces. The spinal column is firmly fixed near the lower end between the bones of the pelvis. The bones composing this column are called vertebra:, of which in the adult there are thirty-three or thirty-four in all. They are divided into five groups. The Fig. 139. Transverse proci Superior articular proce I'erTii-facel for head of rit Sixth thoracii first seven are the cervical ; the next twelve, which bear ribs, are the thoracic ; the next five are the lumbar, making twenty-four above the pelvis. These are known as the presacral vertebrae. The remainder are in the adult united into two bones, the first five forming the sacrum, the last four or five the coccyx. As many as thirty-eight are seen in the young embryo, but some disappear or are fused. With the exception of the first two, the atlas and the axis, which require a separate description (page 1 19), the vertebrae above the sacruiu present the following features, which are common to all, but which are modified in the different regions : (i) a bodv^ or centrum ; (2) apedicle"^ springing from the back of the body on either side, supporting (3) the lamina,^ a plate which meets its fellow in the middle line to form an arcli bounding the spinal or vertebral foramen'' for the spinal cord. Each vertebra gives origin to se\'eral processes. — namely, (4) a sfiino2ts process,^ springing from the point of union of the larrinae : (5) a transverse process on each side, pro- jecting outward from the junction of the pedicle and lamina ; (6) two articulating ^ Corpus. 114 5.^ Processus transve THORACIC VERTEBRA. i'5 sixth thoracic vertebra from the side. piocesses^ on each side, one above and one below the lamina, forming true joints with the opposed processes of the neighboring vertebrae ; (7) a rib or costal element, which in the thoracic region is a separate bone, in the cervical region is a part of the vertebra, and in the lumbar region mingles with the trans- Fig. 140. verse process. The costal ele- • Pedicle ment is also represented in the sacrum. Thoracic Vertebrae. —A vertebra from the middle of the thoracic region is de- scribed first as intermediate in several respects to the others. The body is but a little broader transversely than from before backward. It is a little deeper behind than in front, thereby helping to form the curve of the spine. The upper and lower borders pro- ject a little anteriorly. The upper and lower surfaces, as in all the vertebrae, are rough where the intervertebral disks join them. The posterior surface is concave from side to side, and presents in the middle one or two foramina for the escape of the veins. At the back of the side of the body there is half an articular facet both above and below, which, with the intervening disk, forms an oval, shallow socket for the head of the rib belonging to the lower vertebra. The spinal foramen, en- closed by the arch, is circular. The pedicles, which are much deeper than thick, arise from the upper half of the body. The supe- rior border rises gradually to the articular process. The inferior bor- der is concave, forming the top of the7iotcli,' which, when the succeed- ing vertebra is in place, forms the top of the intervertebral foj-amen^ which is wholly behind the lower half of the body. The laminae are broad, each reaching to the level of those of the next vertebra. The spinous process is long, and points strongly downward, over- lapping the one below. It has a narrow under surface which is grooved, and two lateral ones meet- ing above in a ridge continued from the laminae. This arrangement of the laminae and spines completely closes the cavity of the spinal canal. The spinous processes are slightly enlarged at the end for the supraspinous liga- ment and muscles. The transverse processes are strong, having to support the ribs. They pro- ^ Processus articularis. - Incisura vertebralis. ■* Foramen intervertebrale. Superior artic lar process and facet Spinous process' Sixth thoracic vertebra from behind. Ii6 HUMAN ANATOMY. ject outward and backward, and enlarge at the tip, which anteriorly presents a con- cave articular surface for the tubercle of the rib, and is rough behind for muscles. The articular surfaces are in two pairs above and below, each pair facing in opposite directions, so that the lower ones of one vertebra meet the upper ones oi Inferior articular process Superior articular process Transverse foramen Transverse process ^Posterior limb of transverse Posterior tubercle Costal element \nterior tubercle Body Anterior limb of tr; Fourth cervical vertebra from above. the next. Each presents a smooth, rou'ghly oval articular surface. The superior ones face backward, a little outward, and a very little upward ; the inferior, con- versely, look forward, inward, and slightly downward. Fig. 143. Groove for spinal Superior articular process Anterior tubercle Posterior tubercle Fourth cervical vertebra f Cervical Vertebrae. — A typical cervical vertebra is much smaller than the thoracic. The body is decidedly longer from side to side than from before backward. The upper surface is raised at the sides so as to embrace the body ne.xt above, and has its front border rounded for the latter to descend over it ; for this pur- pose the lower anterior border is pro- longed downward. The height of the body is about the same before and be- hind. The spinal foramen is triangular, v/ith the greatest diameter transverse. The pedicles are short and light, and extend backward and outward from the body. The notches above and be- low them are about equal. The intervertebral foramen is opposite the intervertebral disk, and a part of the bodies of two vertebrae. Fourth cer\'ical vertebra from the LUMBAR VERTEBR/E. 117 The laminae are smooth and do not quite meet those of the next vertebra, unless the head be bent backward. The spinous process projects backward and a Httle downward. It is short and forked at the end, very often unevenly. The transverse processes are often described as double. The posterior limb, which is the true transverse process, projects outward and somewhat forward from the junction of the pedicle and lamina, and ends in a flattened, nearly vertical pro- jection, t\\& posterior transverse tiibeixle. The anterior limb, a vertical plate spring- ing from the side of the body and e.xtending outward, ends in the a?iterior traiisverse tiibercle. This limb is the shorter of the two and its tubercle the larger. The limbs are connected by a concave plate of bone, slanting slightly outward, which forms the floor of a gutter' in which the spinal nerve hes, and which represents the costal element. A round hole, the transverse foramen, for the vertebral artery and A-eins, lies internal to this plate ; the artery usually does not pass through the foramen of the seventh vertebra. Since the scalenus anticus muscle springs from the anterior Fig. 145. Spinous process Third lumbar vertebra from above. tubercles and the scalenus medius from the posterior ones, on leaving the spine the spinal nerves pass between these muscles. The articular processes are placed at the outer ends of the laminae ; the upper face upward and backward, the lower forward and downward. Lumbar Vertebrae. — A typical lumbar vertebra is very much larger than the others. The body is broad from side to side, the upper and lower borders projecting especially at the sides. The posterior surface is slightly concave and presents two large venous openings. The spinal foramen is three-sided, with a transverse diameter but slightly exceeding the antero-posterior. The pedicles are short and strong, diverging only slightly. They are very nearly on a level above with the top of the body, so that there is a small notch above and a large one below. The laminae are broad at the sides, but less so near the mid-line, so that in this Ii8 HUMAN ANATOMY. region there is a large opening into the spinal canal. A considerable part of the aich is lower than the body. The spinous process is a flat projection extending nearly straight backward, with two lateral surfaces and a superior, inferior, and posterior border. The last is rough and thickened below, with occasionally a tendency to become bifid. The transverse processes, which are solely for muscular attachments, and Fig. 146. Superior articul Third lumbar vertebra fi therefore not heavy, project outward and somewhat backward. They are thin, having an anterior and a posterior surface and a blunt end. The articular processes are large, very nearly vertical, and curved. The superior, facing somewhat backward but chiefly inward, are concave and embrace the inferior ones of the vertebra above, which are convex, and face in the opposite direction. Accessory process Inferior articular process Spinous process Lamina Third lumbar vertebra from behind and the side. The mammillary processes form on either side a rounded lateral projection on the posterior border of the superior articular process. Additional tubercles, the accessory processes, appear as inconspicuous elevations at the junction of the posterior border of the transverse with the superior articular processes. The details and the morphological significance of the mammillary and the accessory processes are discussed later (page 123). PECULIAR VERTEBRA. 119 The chief points of difference between typical vertebrae of the three presacral groups may be tabulated as follows : Cervical. Thoracic. Lumbar. Body. 1. Broad. 2. Upper surface with raised sides and rounded anterior bor- der. 3. No facets. Diameters nearly equal; concave behind. Plane. Costal semifacets. Broad. Plane. No facets. Spinal Foramen. Triangular, with great- est diameter trans- verse. Nearly circular. Triangular, with diam- eters nearly equal. Pedicles. Notches above and be- low nearly equal. Rising from top of body; great notch below. Small notch above, great one below. Lamina. Narrow, with spaces be- tween. Broad ; no spaces be- tween. Extending downward; large spaces be- tween. Trans\terse Pro- cesses. Double foramen at root ; two tubercles. Strong, with articular facet. Slender. Superior Articu- lar Surfaces. Nearly plane ; face up- ward and backward. Plane, vertical ; face Concave, vertical; nearly backward. face chiefly inward. PECULIAR VERTEBRA. Certain vertebrae differ more or less markedly from the type of their respective groups ; in some cases, as the upper two cervical vertebrae, these variations result in conspicuous modifications ; in others, as the lower thoracic, the peculiarities are less pronounced. Although the most noteworthy differences are here given, the reader Fig. 148. Posterior tubercle Posterior arch Lateral mass- Groove for vertebral artery Superior articular facet Transverse foramen Facet for odontoid process of Anterior tubercle , The atlas from above. is referred to the discussion of the gradual changes which occur in passing from one region to the other (page 122) for a more complete account of the modifications to be observed. The first and second cervical vertebrae, known as the atlas and axis, consti- tute a special apparatus for the security and movements of the head. The key to HUMAN ANATOMY. the arrangement is that the part which in the ordinary process of development should become the body of the atlas is instead fused with the body of the axis. The atlas, having no body, consists of two lateral masses, connected by a short anterior arch and a long posterior one. The lateral masses present the aiiicular facets on their lower and upper surfaces. The inferior look downward and slightly inward, and are very slightly concave from side to side. The superior facets are oval concavities the backs of which are strongly raised from the surface. Their long a.xis runs forward and inward, the outer wall being decidedly higher than the inner. The articular facet narrows at the middle, and is often marked by a trans- verse ridge at this point ; rarely it is divided into two parts. The articular surfaces of the two sides sometimes very nearly correspond with parts of the surface of a single imaginary sphere. Their\-ariation in all respects is great. Thus, Macalister ' finds in one hundred tiones that the distance between the front ends of the two facets varies from ten to twenty millimetres, being usually from fifteen to twenty millimetres, and that the hind ends are from thirty-two to fifty millimetres apart, the greater number being separated from thirty-five to forty millimetres. The angle formed by the intersec- FiG. 149. Posterior tubercle Fcslerior arch Transverse foramen Inferior -irticuHr facet Position of trans\erse ligament (dotted lines) Facet for odontoid process Anterior tubercle The atlas from below. tion of the prolonged a.xes of the articular facets ranges from thirty-two to sixty- three degrees. Each lateral mass presents a rough tubercle on the inner side between which passes the transverse ligament holding the odontoid process close against the anterior arch. The anterior arch is compressed from before backward. It presents the anterior tubercle in front in the median line, and behind has a slightly concave articular facet for the odontoid process. The posterior arch bounds the spinal canal behind. The transverse ligament, confining the odontoid process, bounds the spinal canal in front, and, being in place, the transverse diameter of the canal is the longer. The place of the spinous process is taken by the posterior tubercle. The transverse processes extend farther out than any in the cer\'ical region. Each ends in a single flattened knob with a surface slanting downward and forward. Bifurcation is rare. The transverse foraitien is at its base ; from the foramen a groove for the vertebral artery crosses the root of the- posterior arch and winds round behind the raised border of the articular surface. This groove is occasionally bridged over by a little arch of bone extending from the edge of the articular surface either to the trans- verse process or to the posterior arch. Variations. — The atlas may be fused with the occipital bone in various ways; this may occur by the pathological destruction of the joint, or the arch, or a • Journal of Anatomy and Physiolog:>-, vol. xxvii., 1893. THE AXIS. Superior artiLUlt facet ; from in front. part of it, may be fused with the skull around the foramen magnum. Such union may be partial or complete, and is usually associated with an imperfect development of the atlas, especially on one side. There is reason to regard such cases as con- genital. The transverse process and the paroccipital process of the occipital bone may be connected by bone. The axis ' differs less from the other cervical vertebrae ; seen from below it pre- sents no essential peculiarity. The body is very long even without the odontoid process (the separated body of the atlas) which surmounts it. The odo7ifoid,'' a cylindrical process lower behind than in front, ends above in a median ridge, Fig. 150, on either side of which is a rough, slant- ing surface for the origin of the check ligaments connecting it with the skull. It bears an oval articular facet in front, resting against one on the atlas, and a smaller facet behind at a lower level which forms part of a joint with the transverse ligament. The lamincs^ in- stead of being plates, are heavy and prismatic, each with a rather sharp upper edge, which, meeting its fellow, forms a ridge on the spine. The spinous process is heavy, projecting considerably beyond the third. It varies greatly in length and in degree of bifurcation. The transverse process is small ; the anterior tubercle is a mere point or altogether wanting. The transverse fora^neyi is replaced by a short canal, so curved that its upper opening looks almost outward. The superior articular surfaces are approxi- mately circular facets on the upper surface of the body instead of on the arch, as are all below ; they look upward and a little outward. Although nearly plane, they present a very slight antero-posterior convexity. The seventh cervical vertebra, called vertebra prominens on account of its long, knobbed spine, rather resembles the upper thoracics. The transverse foramen is smaller than those above it. Fig. 151. 3.nAxh^a7iterior tubercle cA\}i\^ transverse process is particu- larly small and near the body. The first thoracic ver- tebra has the sides of the upper surface somewhat raised at the roots of the pedicles. It has a complete facet for the head of the first rib and a half- facet at the lower border of the body. Sometimes the former is imperfect, being completed on the intervertebral disk. The facet on the transverse process is smaller and less con- cave than the ones following ; sometimes it is even convex. The ninth thoracic vertebra has no half-facet below. The tenth thoracic vertebra has a nearly complete facet above and none below. The eleventh thoracic vertebra has a complete facet on the body and none on the transverse process, which is small. The twelfth thoracic vertebra has a complete facet a little above the middle of the body. The transverse process is broken up into the three tubercles. The lower articular facets face outward. The spine is of the lumbar type. ' Epistropheus. - Dens. Odontoid process' Articular facet for transverse ligament, Spinous process Inferior articular process and facet The axis from the side. Transverse foramen HUMAN ANATOMY. The fifth lumbar vertebra is much higher in front than behind. The trans- verse process is broad at the base, springing in part from the body ; the spine is relatively small. DIMENSIONS OF VERTEBR/E. (The measurements are given in centimetres.) Height of Height of Height of Transverse Diameter. (Anderson.) Antero- Spread of Vertebrae. Front of Bodies. Front of Bodies. Back of Bodies. posterior Diameter. Transverse Processes. (Dwight.) ( Anderson .') (Anderson.) (Anderson.) (Dwight.) Twenty Thirty Thirty Fifty-three Twenty-eight Fourteen spines. spines. spines. spines. spines. spines. Cervical . . • 2 1-9 1-9 1-5 5-5 " .... 3 1.2 1.2 1-9 1-5 5-4 4 1.2 1.2 2.1 1-5 5-4 " .... 5 1.2 1.2 2-3 1.6 5-7 " .... 6 I.I I.I 2.5 1-7 5-9 " ... 7 1-3 1-3 2.7 1.8 7.2 Thoracic .... I 1-5 1.4 1-5 2.7 1-7 7.6 2 1-7 1.6 1-7 2.8 1-7 7-1 " . . . ■ 3 1-7 1-7 1.8 2.6 1-9 6.3 *' .... 4 1.7 1-7 1-9 2.6 2.2 6.3 *' .... 5 1-7 1-7 2.0 2-5 2.4 6.4 " .... 6 1.8 1.8 1-9 2.7 2-5 6.4 " . • . ■ 7 1.8 1.8 2.0 2.8 2.6 6-3 " ... 8 1.8 1.8 2.1 3-0 2.8 6.3 " .... 9 1-9 1-9 2.1 3-1 2.9 6.2 " ... lO 2.1 2.1 2.2 3-4 2-9 5-8 *' ... n 2.1 2.1 2-4 3-6 2.9 5.2 " .... 12 2-3 2.3 2-5 4.0 3-0 4.7 Lumbar .... I 2.4 2.4 2.6 4.2 2.9 7-3 " ... 2 2-5 2.5 2-7 4-4 3-1 8.0 " .... 3 2-5 2.6 2.7 4-7 3-6 9.0 " .... 4 2-5 2.6 2.6 4.8 3-3 8.5 ... 5 2.6 2.7 2.2 5-2 3-6 9-1 GRADUAL CHANGES FROM ONE REGION TO ANOTHER. Bodies. — The height of the bodies increases as we descend the spine, very gradually in each region but rather rapidly at the junction of two regions, as shown in the table. The first two lumbars, like those above them, are rather deeper behind than in front, but the reverse is true of the last two, and especially of the fifth, in which the difference is considerable. The breadth of the bodies increases to the first or second thoracic, then dwindles to the fourth or fifth, and then again increases to the sacrum. The elevation at the sides of the upper surfaces of the bodies of the cervical vertebrae diminishes in the lower part of that region ; in the seventh it is limited to near the root of the pedicle. The same condition is found in the first thoracic vertebra and to a slight extent in the ne.xt two. The downward prolonga- tion of the front of the body of a cervical vertebra is slight in the lower part of the neck. The first thoracic has an entire facet for the head of the first rib near the top of the body and a part of one at the lower border for a portion of the head of the second. As a rule, in the thoracic region the head of each rib rests in a facet on two vertebree and the intervening disk, the lower vertebra contributing more of the joint than the upper, and corresponding with the rib in name. Thus, the head of the fourth rib lies between the third and fourth thoracic vertebrae, and its tubercle rests on the transverse process of the fourth. Towards the lower part of the region the heads have a tendency to take a lower relative position on the column coinci- dently with the increase in size of the bodies. The head of the tenth rib usually rests wholly on the body of the tenth vertebra or on it and the disk above, conse- ' Journal of Anatomy and Physiolog>', vol. xvii., 1883. Anderson states that the vertical diameters of the front and back of the cervical vertebrae are generally the same ; hence, prob- ably, he thought it needless to give the posterior measurements. The close correspondence of his anterior measurements with those of the author is very striking. REGIONAL CHANGES. 123 quently the ninth vertebra has no half-facet below. The tenth has a nearly or quite complete facet at its upper border, the eleventh has a complete one rather below the top of the body, and the twelfth has a complete facet nearly half-way down. At the ninth or tenth the facet begins to leave the body and to travel backward onto the root of the pedicle. When the body is seen from above or below in certain parts of the thoracic region the front curve is flattened on the left by the pressure of the aorta. This com- pression usually is first seen at the top of the fifth thoracic, and is traceable down- ward for a few vertebrae, sometimes as far as the lumbar region. The depression gradually passes from the side to the front as it descends the spine. The Transverse Processes. — As shown by the table, the spread of the transverse processes increases greatly at the junction of the cervical and the thoracic regions, falls rapidly to the third thoracic, remains stationary to the tenth, falls to the last thoracic, the narrowest point, and then gains at once, reaching the maximum at the third lumbar. The anterior tubercles of the transverse processes of the cervical region increase to the sixth, which is the tuberxle of Chassaignac, who taught that the carotid artery can be compressed against it, the force being directed backward and a little inward. The anterior limb of the transverse process of the seventh ver- tebra is very short, and its tubercle is usually rudimentary. It is distinctly in series with the slight elevation of the socket for the head of the first rib often seen on the first thoracic vertebra. The piece of bone between the tubercles, forming the floor of the gutter for the spinal nerve, is much longer and more anteriorly placed in the seventh than in those above it. It is this piece connecting the two tubercles that is the true costal element in the neck. The so-called anterior limb of the transverse process with the tubercle on it is in line, not with the ribs but with the anterior tubercle called the processus costarius. The articular facet on the transverse process of the first thoracic is shallow, often convex, and faces a little downward. That of the second, at which point the processes slant more backward, is concave and some- what overhung above ; this is seen in the two or three following, after which the facets grow smaller, more shallow, and look upward as well as forward. As the eleventh rib has but a rudimentary tubercle and the twelfth none at all, there is no facet on the transverse process of the last two thoracic vertebrae. The latter process of the eleventh is small, and that of tho last broken up into three tubercles, (i) the superior or mammillary, rising from the posterior surface ; (2) the accessory or ittfe- rior, pointing downward ; (3) the exteryial, a knob, the smallest of the three. The latter two represent the transverse process of the upper thoracic vertebrae. All three tubercles are usually to be recognized on the eleventh thoracic, although the acces- sory tubercle is usually not seen higher up. The knobs for muscular attachment on the backs of the thoracic transverse processes are evidently in line with the mammil- lary tubercles, rudiments of which are found in a large part of the thoracic region. In the lumbar region they are found on the side of the superior articular processes, growing smaller in the lower vertebrae, and being lost in the fifth. The lumbar transverse processes increase in length to the third, which is the longest, unless it be equalled by the fifth. That >f the fourth is peculiar in being shorter and lighter than its n ighbors. It usually has a rather triangular outline, owing to the lower border approaching the upper near the tip, and also arises farther forward, — i.e., nearer the side of the pedicle than those above it. The fifth is much heavier and arises from the side of the body as well as from the pedicle, so that its ante- rior portion is evidently in series with the costal element developed in the sacrum, described in connection with that bone. The process which, in accordance with gen- eral usage, has been called the lumbar transverse process, is clearly in direct continua- tion with the line of the ribs. This is particularly striking in certain cases in which it is not easy to determine whether there is a thirteenth rib, or whether this process is to be considered as free in the first lumbar. The accessory tubercle, which can be inade out in the lumbar region, and is particularly large in the lower vertebrae, is in line with the ends of the transverse processes of the thorax. Thus the so-called lumbar transverse process represents at its root both a rib and the accessory and transverse tubercles, and beyond its root a rib only. This is especially marked in the broad process of the fifth lumbar, which springs from the side of the body 124 HUMAN ANATOMY. as well as from the pedicle. The homologies of the costal elements are shown in Fig. 158. The Spinous Processes. — These are short and bifid in the third, fourth, and fifth cervical vertebras ; longer and usually not forked in the sixth ; and longer, larger, and knobbed in the seventh. The type is that of the last mentioned in the upper thoracic, only the spine is a little longer, stronger, and more slanting. At about the fourth a sudden change occurs : the process becomes longer, sharper, and more descending. At about the tenth it shortens again, points more backward, and approaches the lumbar type, which is generally reached in the last thoracic. The spine of the last lumbar is usually much smaller than those above it. The Articular Processes. — The change from the cervical type to the thoracic is gradual, but that from the thoracic to the lumbar occurs suddenly at the junction of those regions. The inferior processes of the last thoracic face outward. Not infre- quently the change occurs a space higher, but rarely one lower. Occasionally the facets between the regions face in an intermediate direction. Sometimes the change is normal on one side and not on the other. Superior articular process erse process Lines of union between fused sacral vertebrae Notch for fifth sacral nen-e Apex The sacrum, anterior surface. THE SACRUM. This bone ' is composed of five fused and modified vertebrae, of which the three upper support the pelvis laterally. The vertebrae decrease very much in size from above downward, the lower being bent strongly forward. The first vertebra is com- paratively but little changed ; the last consists of little more than the body. The THE SACRUM. 125 essential modification, besides the fusion, is the occurrence of the lateral 7nasses,^ representing transverse processes and ribs, which, springing from the bodies and arches, are connected willi the innominate bones by joints and ligaments. The sacrum has an upper surface, or base, a lower, or apex, and a front, back, and two lateral surfaces. The base has above a rough space representing the end of the body of a vertebra to which the last lumbar disk is attached. It is raised a little from the bone and forms an acute projecting angle with the front surface, known as the promontory of the sacrum, an important landmark in midwifery. Behind the body of the first sacral vertebra is the triangular orifice of the sacral catial, the Articular process Fig. 153. Lamina Sacral t Rudii tary trans- pro- Gluteus maxtmus- Sacral canal The sacrum, posterior surface. transverse diameter of which is the greater. The articular process, springing from the side of the arch, is vertical, the concave facet facing backward and inward. The upper surface of the lateral mass, the ala, springs from the side of the body and the pedicle, expanding into a broad area, and is bounded in front by an ill-marked, rounded border which separates it from the anterior surface and curves forward ; behind by a shorter border curving backward, on which the auricular process rests ; and outside by an irregular convex border. The latter may often be subdivided into two parts : an anterior, running pretty nearly forward and backward and cor- responding to the top of the auricular surface, and a posterior, running backward ^ Partes laterales. 126 HUMAN ANATOMY. Rudimentarv transverse processes and inward. Thus the sacrum is broader before than behind. The apex is nothing but the under side of the body of the very small fifth sacral vertebra. The anterior surface is a triangular concavity formed by the bodies and lat- eral masses of the five sacral vertebrje. It has a double row of four openings, the anterior sacral foramina, one on each side of the ridges, representing the ossified disks connecting the bodies of the fused sacral vertebrae. The sacral nerves, like the other spinal nerves, divide into an anterior and a posterior division on leaving the spinal canal ; in the case of the sacral nerves, however, this takes place inside the bone, the anterior divisions escaping by these foramina. The bodies and the foramina grow smaller from above downward, and the latter are nearer together. A transverse depression across the body of the third vertebra usually marks a rather sudden change in the Fig. 154. curvature of the anterior Transverse process surface. The irregular outline of the lateral bor- ders may be divided into two parts : the upper, rather concave, ends be- low in a little point on a level with the third verte- bral body, and represents the e.xtent of the articu- lar surface. Below this the border slants down- ward and inward until opposite the lower part of the fifth sacral seg- ment, when it suddenly turns inward, forming a notch over the anterior division of the fifth sacral nerve, which emerges be- tween it and the coccyx. The posterior sur- face is coniposed of the fused latnincE and their modifications. The up- per borders of the first laminae slant downward, and below their junction is a well-marked spine} Below this the laminae of the sacral vertebrae are fused and the spines small. The laminee of the fifth sacral never join, and those of the fourth frequently do not, thus leaving the lower end of the canal uncovered. The laminae that do not meet end in tubercles each representing one-half of a spinous process. The lowest two project downward at the sides of the open canal, and are called the sacral corniia. Four posterior sacral foramina for the e.\it of the posterior divisions of the nerves appear on each side of the laminae. Outside of these are some irregu- lar tubercles representing the transverse processes,'' and internal to the first three foramina are tubercles in line with the articiilar processes.^ The lateral surface begins just outside of the transverse tubercles. It is broad above, but below the third vertebra is merely a line. The upper part is divided into two portions : the front one is the auricular surface, from a slight resemblance to an ear, which joins, by fibro-cartilage, the corresponding surface on the ilium. It is broader above than below, convex in front, indented behind, with ' Crista media. - Cristac laterales. ^ Cristae articulares. Fourth posterior sacral fora Sacral t The sacrum, lateral view. THE COCCYX. 127 slightly raised edges and a rough, irregular surface. The auricular surface is formed chiefly by the lateral mass of the first sacral (yeiiebra fulcralis , as having the most to do in supporting the pelvis), to a less extent by that of the second, and very little by that of the third. Behind this articular portion lies the rough ligamentous sur- face, which slants backward and inward, and affords origin for the posterior sacro- iliac ligaments. DifTerences depending upon Sex. — The female sacrum is relatively broadei than the male. The sacral index, or the ratio of the breadth to the length ( '°°^ "'^ "^ ) , is 112 for the white male and 116 for the female. Such a rule is, however, not abso- lute, there being many doubtful cases, but a narrow sacrum is almost invariably male. Another, and very reliable, guide, especially in conjunction with the first, is the curve. There are contradictory statements among authors, but the truth is, as originally shown by Ward, that the male sacrum is the more regularly curved, while the anterior surface of the female bone runs in nearly a straight line from the prom- ontory to the middle of the third piece and then suddenly changes its direction. Variations. — The sacrum often consists of six vertebrae. Such a one may be recognized even when the lower part is wanting, so that the vertebrae cannot be counted. If a line across the front, connecting the lowest points of the auricular surfaces, passes below the middle of the third sacral, the sacrum is of six pieces ; if above, of five.' Sacra consisting of only four vertebrae are rare. THE COCCYX. This bone is composed of four or five '^ flattened plates representing vertebral bodies. It is an elongated triangle with the apex below. The base, joined by fibro- cartilage to the apex of the sacrum, is dblique, the posterior border being higher than the front, so that the coccyx slants forward from the sacrum. The anterior surface of the coccyx is, moreover, very slightly concave. TYift first vertebra consists of a thin body, about twice as broad as long, from the back of which on each side the rudiment of an arch extends up'yard as a straight process, the coccygeal cornu, which Fig. 155. Surface for sacrum Transverse process* Transverse process Gluteus maximiis overlaps the back of the body of the last sacral vertebra and joins the sacral cornu. A short lateral projection from the side of the body represents the transverse process; perhaps the costal element also. On the upper border of this process, at its origin, is a notch, which usually forms a foramen with the sacrum for the anterior division oi the fifth sacral nerve. Very faint rudiments of these two pairs of processes are sometimes to be made out on the second vertebra, which is much smaller than the first, but also broad and flat. The succeeding ones are much smaller and ill-defined. Constrictions on the surfaces and notches on the edges mark the outlines of the • Bacarisse : Le sacrum suivant le sexe et suivant les races. Th^se, Paris, 1873. ' According to Steinbach, there are five in man and four or five in woman. t)ie Zahl der Caudalwirbel.beim Mensclien. Inaugural Dissertation, Berlin, 1899. 128 HUMAN ANATOMY. original pieces, which become less and less fiat and more and more rounded. It is rare to see more than four distinct segments, but very often the last is somewhat elongated and shows signs of subdivision. It is not uncommon for the first piece to remain separate, neither fusing with the sacrum nor the next coccygeal plate. STRUCTURE OF THE VERTEBR/E. The shell of compact bone forming the surface is everywhere very thin. The general plan of the internal spongy bone is one of vertical plates which in a frontal section ( Fig. 156, A) are bowed somewhat outward from the middle of the bone, and of transverse plates connecting them near together at the ends and farther apart in the Fig. 156. ng the arrangement of the bony Ian middle third where larger spaces occur. The strongest plates spring from the pedi- cles and diverge through the bone, joining, probably, for the most part the hori- zontal system. In the sacrum the same general plan prevails, but in addition there are series of plates, mainly horizontal, in the lateral parts ; those from the first sacral are the most important. DEVELOPMENT OF THE VERTEBRA. Presacral Vertebrae. — These vertebrae ossify from three cMef centres and at least five accessory ones. The median one of the three chief centres forms the greater part of the body ; while the other two, one appearing in each pedicle, form the postero-lateral part of the body, the arch, and the greater part of the processes. The oblique neuro-central sutures separate the regions of these centres. The lat- eral centres of the upper thoracic and the cervical vertebrae appear first. It is usually taught that they appear in the sixth or seventh week of foetal life, but Bade' with the Rontgen rays found no sign of them at eight weeks. The point is unset- tled. The first median centres to appear are those of the lower thoracic and the upper lumbar vertebrae. In this region and below it the median centres precede the lateral, ones ; in the upper part of the spine the growth is much more vigorous in the lateral centres. The median centres of the cervical vertebrae appear in order from below upward. The upper ones (judging from Rontgen-ray work and from transparent foetuses) sometimes have not appeared as late as the sixth month, although we have seen them towards the close of the third. At birth the upper and lower ends of the bodies are still cartilaginous, but the arches are well advanced in ossification, although bone does not cross the median line until some months later. The transverse processes of the thoracic vertebrae are farther advanced than those in other regions. The spines are still cartilaginous. The neuro-central suture is lost at from four to six years, disappearing first in the ' Arch, fiir Mikros. Anat.. Bd. Iv., iSgg. DEVELOPMENT OF THE VERTEBRA. 129 lumbar region. The tips of the spinous and transverse processes develop from cen- tres which appear about puberty and fuse about the eighteenth year. A thin epi- physeal disk, covering the upper and lower surfaces of each body, grows from a centre seen about the seventeenth year, and joins by the twentieth, the line of union per- sisting a year or two longer. The mammillary processes of the lumbar region arise from separate centres ; so do also the costal elements of the sixth and seventh cer- vicals, and sometimes tliat of the first lumbar. In cases in which this costal element of the seventh cervical remains free there is a cervical rib and no transverse fora- men ; exceptionally in these cases a foramen persists. According to Leboucq,' the development of the anterior limb of the transverse process of the cervical vertebrae is more complicated than is usually taught. There is a slight outward projection from the ventral side of the body rep- resenting the prominence for the head Fig. 157. of the rib to rest upon ; this grows out- ward and meets a growth from the transverse process that grows inward like a hook. This inward growth rep- resents what we commonly call the costal element of a cervical vertebra, but there may be also a separate ossi- fication representing an actual rib, — namely, a small piece of bone on the ventral aspect of the tip of the trans- verse process of the seventh cervical vertebra. When a separate ossifica- tion occurs in this region in the fifth or sixth vertebra, it is situated still more externally than in the seventh, and forms the fioor of the gutter be- tween the anterior and the posterior tubercles, which is the true costal ele- ment. It is probable that in certain cases of cervical ribs accompanied by a transverse foramen, the latter is en- closed by the hook-like process from the transverse process meeting the growth from the body of the vertebra, and that the rib coming from the separate ossification lies anteriorly to it and distinct from it. At birth the lumbar articular processes resemble the thoracic. The type changes in early childhood. The Sacrum. — Each sacral ver- tebra has the three primary centres of the others, the median ones appearing before the lateral of the same vertebra. Proba- bly the median centres of the first three appear first and then the lateral ones of the first vertebra ; data, however, are wanting for a definite statement. The time of the first appearance of ossification in the sacral vertebrae is very variable ; probably the earliest median centres appear about the beginning of the fourth month and the lateral ones some weeks later. In a skiagraph of a foetus estimated to be about three and a half months old the median centres of the upper three vertebrae and the lateral ones of the first are visible. This is, perhaps, earlier than the rule. Little progress in ossification of the last two sacrals takes place before birth. The lateral centres join the median, in the lower vertebrae, during the second year ; in the upper ones, three or four years later. In the upper three vertebrae a centre appears out- side the anterior sacral foramen, from which a part of the lateral mass is developed. Ossification of the vertebrae. A, cervical vertebra at birth ; centres for body (a), neural arches {^), and costal ele- ment (c). B, dorsal vertebra at two years; cartilaginous tips of transverse {a) and spinous {b) processes ; rf, centre for body. C, lumbar vertebra at two years ; position of ad- ditional later centres for various processes indicated (a, b, c) ; d, centre for body. ' M6moires couronn^s, etc., Acad. Royale des Sciences de Belgique, tome Iv., 1896. I30 HUMAN ANATOMY. This represents a costal element which fuses with the front of the pedicle. Those of the first two sacrals appear shortly before birth (Bade). The line of union can still be seen at seven years on the top of the first vertebra. The time at which the laminae Fig. 158. Illustrating homology of costal element (c. e.\. ^4, sixth cervical vertebra; .B, seventh c D, second lumbar ; £", fifth lumbar ; /", sacrum in transverse sectl( vical ; C, fifth thoracic; meet in the middle is uncertain ; the arch of the first vertebra is sometimes complete at seven, those below it being still open. The five distinct sacral vertebrae which are thus formed remain separate for some time, the bodies being separated by interver- FiG. 159. Superior and anterior surfaces of young sacrum of about five years. of about seventeen years. tebral disks. A thin plate appears in the upper and lower parts of these disks which fuses with the bodies before the latter unite. The union of the vertebrae begins below and proceeds upward in a very irregular manner. Probably union generally occurs first in the lateral masses, between the laminae VARIATIONS OF THE VERTEBRvE. 131 sooner than between the bodies. By the fifteenth year the lower three vertebrae are generally fused, the second joining them from eighteen to nineteen. The five pieces are united by the twentieth year. In some cases several of the sutures are still to be seen, but all may have disappeared. The union of the bodies, as shown by sections, in the case of the upper ones, may not be complete internally till a much later period. Two thin epiphyses appear on each side of the sacrum about the eighteenth year, one for the auricular surface and the other below it. The lines of union of these plates may be visible after twenty-one. The Coccyx. — Our data concerning the ossification of the coccyx are very un- satisfactory. Each segment has one centre, but the first may have two, one on each side, and, according to some, secondary centres for the cornua. Ossification begins in the first piece at about birth, and successively in the others, from above down- ward, until puberty. The lower three or four pieces fuse within two or three years after birth, and join the first at perhaps about twenty ; there is, however, great diversity, and frequently the first unites with the sacrum instead of with the others. The Atlas. — The adas is almost wholly formed from two centres which appear in the seventh week of fcetal life in the root of the posterior arches ; from these points ossification spreads most rapidly backward. In the course of the first year a centre is found in the middle of the anterior arch. The lateral masses meet behind in the fourth year and join the median anterior nucleus in the fifth. Sometimes the union of the posterior arches does not occur. The anterior nu- cleus may be absent, and the front arch may show a median suture or be represented by ligament or cartilage. In one in- stance the anterior arch was wholly wanting, the lateral masses being fastened to the odontoid by ligament^ (Fig. 161). The Axis. — The ossification of the axis begins by two lateral points appearing by the eleventh week. The median one, which does not come till the fifth month, is at first double, but the two points speedily fuse. At about the same time two nuclei appear side by side in the odontoid process, which join together before birth, leaving a space between them at the tip. This may be closed by the extension of ossification, or a centre may appear in it at the second year, which fuses by the twelfth. The piece thus formed has been held to represent the epiphyseal plate for the top of the atlas. The odontoid process joins the body at the periphery, the union beginning in the third year and being complete a year or two later ; a piece of car- tilage in the middle of the juncture is said to persist under the odontoid until old age. Very rarely the odontoid remains distinct.' The arches join the body in the third year, and usually meet behind at the same time ; the latter union, however, may be delayed. of absence of the anterior arch of the atlas. Variations of the Vertebrae. — The commonest 'and most interesting variations are those of number. These are ver>' frequent in the coccyx, since there are originally more elements than persist, and indeed we are not sure even of the normal number in this bone. Numerical varia- tions are also often obser\-ed in the sacral, less so in the lumbar, still less so in the thoracic, and extremely rarely in the cervical region. The number of \ertebrae above the sacrum (twentj"- four) is usually unchanged, but, owing to differences in development of the costal element, one region is not rarely increased or diminished at the expense of the next one. Thus the verj- com- mon condition of six lumbar vertebra is due to the «'ant of development of the costal element (the rib) of the last thoracic, and implies only eleven vertebrae in that region. Conversely, thir- teen thoracics imply an undue development of the costal element of the first lumbar, and con- sequently only four lumbar vertebrae. Often the costal element of the last cervical is free and over-de\'eloped, making a cer\'ical rib. But even if this be large enough to reach the sternum, which is exceedingly rare, the number of cer\-ical vertebrae is usually considered unchanged. Other changes are due to variations in de\'elopment of the costal element in the last lumbar and the first sacral. Transitional forms are here very frequently met with. The last lumbar Dwight : Journal of Anatomy and Physiology', vol. xxi., 18 132 HUMAN ANATOMY. may, by an excessive growth of these elements, become sacrahzed, articulating more or less per- fectly with the ilium, and, conversely, the first sacral may have almost freed itself from those below it. Thus we may find a partially sacralized \ertebra, which may be either the twent>-fifth or the twenty-fourth, ft often happens, particularly in the latter case, that a vertebra appears to be a first sacral on superficial examination, which is found to have little or nothing to do in form- ing the articular surface, in which case it is not a true sacral, for the first sacral is the fitlcralis which has the largest surface for the joint with the ilium. A false promontory may coexist with the normal one. This is probably most frequent ■ when the twenty-fourth \ertebra is partly sacralized. Any of the preceding peculiarities may be unilateral, so that sometimes a vertebra may seem from one side to belong surely to one region, and equally surely to the other region when seen from the opposite side. There is, however, another set of variations in which the number of presacral vertebrae is increased or diminished. There may be, for instance, one thoracic or one lumbar vertebra too many or too tew, without any compensatory change in the next region. In these cases, more- over, the terminal vertebra of the region may be very nearly typical ones, and sometimes even the size of the vertebra v\ill be modified so as to give the region its approximate relative length. Similar changes may be found in the neck, but they are exceedingly rare. Variations of either kind are likely to have an effect on the column as a whole ; thus, ii there be a large cervical rib the last thoracic rib is likely to be small, or if the first rib is rudi- mentary the last is apt to be large. It follov\-s that the thorax seems to be in certain cases moved upward or downward ; this change may occur on one side only. Rosenberg's theory, formerly much in vogue, is that there are opposite tendencies at the Kwo ends of the spine. At the upper there is a tendency tor the cervical region to encroach on the thoracic, and at the lower for each of the regions to encroach on the one above it. Such changes he considers progressive. On the other hand, the opposite movement by which the thorax encroaches on the neck or loins is considered reversive. Rosenberg has described a spine which he considers archaic, in which there are two extra presacral vertebrse and fifteen pairs of ribs, the first being cer\'ical. There are two spines in the Warren Museum with a simi- lar number of presacrals in which the last is sacralized on one side. As to the way in which anomalies of the lower part of the spine come about, Rosenberg ' thinks he has shown that in the course of development the sacrum is composed of vertebrse placed farther back than the perm:inent ones, and that the ilium enters into connection with vertebrae more and more ante- rior. As new ones join it above former ones become detached from it below. If it does not make the usual progress the spine is archaic, having too many presacrals ; if it goes too far the spine is of the future. Rosenberg's theory has been overthrown by Bardeen,' who has shown that the original position of the ilium is opposite the superior part of the lumbar region and that it travels tailwards. Having joined a vertebra at the fifth week, it never leaves it. At this early time the thoracic vertebrae are differentiated. The author^ and Fischel* believe that numerical variation is the result of an error in segmentation. A want of development of the bodies, which may be only half the normal height, is found almost exclusively in the lumbar region. We have seen (apparently congenital) fusion of the lumbar bodies while all the arches were present, but three of them crowded together. The separation of the pedicles of the fifth lumbar from the body is a very rare anomaly among whites, but not among American aborigines. ARTICULATIONS OF THE VERTEBRAL COLUMN. The ligaments connecting the segments of the spine may be divided, according to the parts of the vertebrae which they unite, into two groups : 1. Those connecting the Bodies of the Vertebrse ; 2. Those connecting the Laminae and the Processes. LIGAMENTS CONNECTING THE BODIES. Intervertebral Disks'* (Figs. 162, 163). — These form a series of fibro-carti- lages interposed between the bodies of the vertebrae, forming about one-fourth of the movable part of the spine and adding greatly to its strength. They are de\'eloped, like the bodies, around the notochord, persisting parts of this structure forming a central core to each disk. The outer part of the disks consists of oblique layers of fibres, slanting alternately in opposite directions, some almost horizontal, which hold the vertebral bodies firmly together ; the centre of the disks is occupied by a space containing fluid in the meshes of a yellowish pulp.* This central core is strongly compressed, so as practically to be a resistant ball within the more yielding fibro- cartilaginous socket. The proportion of the disks to the vertebral bodies varies in the different parts of the spine. They are absolutely largest in the lumbar region, but relatively in the cervical. For many reasons it is difficult to reckon the per- ' Morph. Jahrbuch, Bd. i. and xxvii. * Anatomische Hefte, No. 95, 15106. 'Anat. Anzeiger, Bd. xxv., 1904, and Atnerican Journal of Anatomy, vol. iv., 1905. ' Dwight : Memoirs Boston Society of Nat. Hist., vol. v., 1901. ^Flbrocartllaeioes intervertebrales. ''Nucleus pulposus. LIGAMENTS OF THE SPINE. 133 Posterior at- laiito-axial ligament Body of first Ihorac c vertebra centage very accurately, and there is much variation. The following proportions are, therefore, only approximate. The disks form in the cervical region forty per cent., in the thoracic, twenty per cent., and in the lumbar, thirty-three per cent, of the length of the spine. Anterior and Posterior Fig. 162. Common Ligaments. The odontoid proces of a Trans erse 1 gament bodies are connected by short fibres surrounding the disks, and by long bands which are only partially separable from the general envelope. The an- terior common ligament^ (Figs. 163, 165) begins at the a.xis and extends to the sacrum. It consists of shorter and longer fibres blending with the peri- osteum and springing from the edges of the vertebrse and from the disks, to end at similar points on the next vertebra, or on the second, third, fourth, or fifth. The borders are not sharply defined. The posterior common ligament' ( Fig. 164) is a much more distinct struc- ture. It arises from the back of the body of the axis, re- ceiving fibres from the occipito- axial ligament, and runs to the sacrum. It also is attached to the disks and the edges of the bodies, but possesses a dis- tinct margin, which, except in the neck, expands laterally into a series of points at the intervertebral disks. It stands well out from the middle of the bodies, bridging over the veins of the larger ones. LIGAMENTS CONNECT- ING THE LAMINA AND THE PROCESSES. The articular processes (Fig. 165) are coated with hyaline articular cartilage and surrounded by loose capsules, with which, especially in the fhorax, the ligamenta subflava are inseparably connected, pre- venting by their tension the occurrence of folds. The ligamenta subflava' (Fig. 163) are elastic membranes of considerable strength connecting the laminse from the axis to the sacrum. They are particularly developed in the lumbar region. As just mentioned, they encroach on the side of the capsules towards the canal. They also extend a short distance under the spinous processes. The supraspinous ligament (Figs. 162, 163) extends as a well-marked cord - Lig- longitudinale posterius. ^ Ligg. flava. , of upper haU of spine. 134 HUMAN ANATOMY. along the tips of the spines from the last cervical to the sacrum. The interspinous ligaments are membranes connecting the spinous processes between the tips and the laminffi, extending from the ligamenta subflava to the supraspinous ligament. Fig 163 First lumbar vertebra posterior common ligamei t rV' 'fO^' Inter\-ertebral d W Anterior common ligame I Fifth lumbar verteb; First sacral vertebra- Median section of lower half of spine. The ligamentum nuchae (Fig. 166) represents in the neck a modification of the two last-mentioned ligaments. It is a vertical curtain reaching from the e.xter- LIGAMENTS OF THE SPINE. 135 nal occipital protuberance to the spine of the seventh cervical, separating the muscles of the two sides. The free border is continuous with the supraspinous ligament, but, instead of touching the cervical spines, it lies in the superficial layer of muscles, and is rein- forced below by radiating fibres from each of the spinous processes of the cervical region. It is inseparably blended with the origin of the trapezii and with the fasciae between the muscular layers, especially with that covering the semispinalis and the short suboccipital muscles. In the region of the axis it is a thick median membrane ; in the lower cervical region it is of little importance. In man it contains but a small proportion of elas- tic fibres, in marked contrast to what is found in many quadrupeds in which the structure con- sists principally of elastic tissue, since in these animals the ligamentum nuchae forms an important organ for the support of the head at the end of the horizontal vertebral axis. The intertransverse ligaments (Fig. 162) are trifling collections of fibres between the transverse processes, although occasionally distinct round cords in the thoracic region. Fig. 165. Anterior occipito-atlantal ligament Mastoid process Posterior surface of bodies of vertebrae shown after removal of arches by cutting through the pedicles. Lateral occipito-atlantal ligament Anterior tubercle of atlas' Atlanto-axial ligament and joint Anterior common ligament- Anterior ligaments of upper end of spine. ARTICULATIONS OF THE OCCIPITAL BONE, THE ATLAS, AND THE AXIS. The arrangement here differs in some points considerably from that of the rest of the spine in order to provide for the security and the free movement of the head. The ligaments effecting this union consist of three groups : I. Those connecting the Atlas and the Axis, including the Anterior Atlanto-Axial ; Transverse ; Posterior Atlanto-Axial ; Two Capsular. 136 HUMAN ANATOMY. 2. Those connecting the Occipital Bone and the Atlas, including the Anterior Occipito-Atlantal ; Posterior Occipito-Atlantal ; • Accessory Occipito-Atlantal ; Two Capsular. 3. Those connecting the Occipital Bone and the Axis, including the Lateral Odontoid or Check ; Middle Odontoid ; Occipito-A.xial. The important peculiarities are the odontoid and the transverse ligaments. The odontoid, or check ligaments' ( Fig. 168), are two strong, symmetrical bundles of fibres extending from the slanting surface on each side of the top of the odontoid process outward and a little upward to a roughness on the inner side of each occipital condyle. Some fibres pass directly across from one condyle to the Ligamentum nucha Trapezius muscle Ligamentum nuchae Posterior occipito-atlantal Posterior atlanto-axial ligament Ligaments of back of neck. Other. These are occasionally collected into a distinct round, glistening bundle. The space above the odontoid process, between it and the basilar process, is oc- cupied by a mass of dense fibrous tissue reaching to the anterior occipito-atloid ligament, in the midst of which is a more or less distinct median band connecting these parts, the middle odontoid ligament.' A supra-odontoid bursa may be developed in this tissue. ' The transverse ligament* (Figs. 167, 168) of the atlas is a strong band passing between the tubercles on the inner side of each lateral mass of the atlas. It does not run straight, but curves backward around the odontoid, from which it is separated by a bursa. A band from the middle of the transverse ligament passes upward to the cerebral side of the basilar process, and another downward to the body of the axis, so that the whole structure is called the cruciform ligament.* ' Trolard : Journ. de I'Anat. et de la Physiol., 1S97. ' LisB. alaria. - Lie. apicis dentis. ^ Lis. trans/ersnia atlantis. -"Lie cniciatum atlaotis. OCCIPITO-SPINAL LIGAMENTS. 137 Another bursa lies between the odontoid and the anterior arch of the atlas. The transverse ligament and the two check ligaments are in series with the interarticular ligaments of the heads of the ribs. The other ligaments of this region are in the main simple membranes connect- FiG. 167. Upper end of occipito-axial ligament Lateral odontoid ligament ^^^^.Occipito-atlantal joint Cruciform ligament Atlamo-axial joint Front of foramen magn Lateral odontoid ligament Back of occiput and arches removed ; occipito-axial ligament cut and turned down. ing neighboring parts. The anterior occipito-atlantal ligament ' (Fig. 165) extends between the front of the foramen tnagnum and the anterior arch of the atlas ; the anterior atlanto-axial (Fig. 165; is in serial continuation with it. A distinct rounded, raised band, the accessory occipito-atlantal, passes in the median line from the under side of the occiput to the front tubercle of the atlas (Fig. 165), and thence to the body of the axis, where it joins the anterior common ligament of the spine. The occipito-axial ligament' ( appa- ratus liganientosus) (Fig. 167) descends in- side the spinal canal from the basilar process to the body of the axis, where it joins the posterior common ligament and completely conceals the odontoid process and its special ligaments. The posterior occipito-atlantaP and the posterior atlanto-axial ligaments* lie in the region of the arches (Fig. 166). The former e.xtends between the posterior border of the foramen magnum and the arch of the atlas ; the latter between the arch of the atlas and that of the axis. These are in series with the ligamenta subflava, but differ from them in being non-elastic. In the former of these membranes there is an opening just behind the facets on the atlas for the condyles, bridged over by a band, for the entrance of the vertebral artery. ■ anterior. -Membrana tectoria. ^Membrana atlantooccipitalis posterior. ^ Membrana Posterior surface of odontoid process shown by removal of middle of transverse ligament; basilar process is thrown strongly upward. 138 HUMAN ANATOMY. Synovial joints, the shapes of which are described with the bones, exist be- tween the occipital bone and the atlas and between the atlas and the axis. The capsule of the upper joint is very thick, especially behind, where it is continuous with the posterior occipito-atloid ligament. The capsule surrounding the articular surfaces of the atlas and axis is strengthened posteriorly by a bundle running upward and outward from the axis. Fig. 169. Posterior tubercle of atlas rtebral arter>' cut obliquely Posterior burs.-i- Section of odontoid process ^S-^ -Anterior bursa Transverse ligament Anterior tubercle of atlas Transverse section of spine passing through atlas and odontoid process. THE SPINE AS A WHOLE. Anterior Aspect (Fig. 170). — The bodies enlarge, in the main, regularly from above downward. This progression is interrupted only by a slight decrease from the first to the fourth thoracic. In the cervical region the origin of the costal elements from the sides of the bodies gives the latter a false appearance of breadth. The middle of the thoracic region is particularly prominent in front, owing in part to the aortic depression on the left. A slight curve to the right in this region is generally seen ; it is probably attributable to this cause. Posterior Aspect (Fig. 170). — A deep gutter extends on each side of the spinous processes, bounded externally in the neck and loins by the articular pro- cesses and in the back by the transverse. In the latter region the spines which are subcutaneous are often deflected from the median line, and may be arranged in zig- zag. The laminae completely close the spinal canal in the convex thoracic and sacral regions, while it is left open in the neck and loins, except during extension of the former. Lateral Aspect (Fig. 171 ). — The profile view shows best of all the increase in the importance of the bodies from above downward, and coincidently with this the gradual moving backward of the intervertebral foramina. These increase greatly in size from the lower part of the thoracic region. The Curves. — The curve of the spine is necessarily an arbitrary one, since it varies not only in individuals and according to age, sex, and occupation, but also with position and the time of day, being longer when lying than standing, and after a night's rest than after a day's work. The difference occasioned by position occurs especially in youth, when it may amount to half an inch or more. It is of little consequence after middle age. Bearing these variations in mind, the following guide to the curve, suggested by Humphry, may be accepted : a line dropped from the middle of the odontoid process passes through the middle of the body of the second thoracic, that of the twelfth thoracic, and the anterior inferior angle of the fifth lumbar. Henle divides the spine into four quarters ; and although this method has the defect of using the unreliable pelvic section, it very often proves remarkably correct. Thus, if we continue Humphry's line to the level of the tip of the coccyx, the middle point is opposite the eleventh thoracic, the end of the first quarter oppo- site the lower border of the third thoracic, and that of the third quarter opposite the lower edge of the fourth lumbar. The development of the curves can hardly be said to have begun at birth. At THE SPINE AS A WHOLE. Fig. 170. 139 r' i •M' ' (. c^ Coccyx Anterior and posterior views of adult spi HUMAN ANATOMY. Fig. 17 rVf:^ -I Thoracic ift" <"*■* a- I. Coccygeal Lateral view of adult spine. that age the infant's spine presents in front one general concavity, slightly interrupted by the promontory of the sacrum. The liga- mentous spine, containing little bone, is ex- ceedingly flexible in any direction : the atlas can be made to touch the sacrum. It is more accurate to say that the general axis of the spine is a curved one than that any per- manent or fixed curve exists. The cerx'ical curve appears as the infant grows strong enough to hold up its head ; it is never, properly speaking, consolidated (Syming- ton), since it is always obliterated by a change in the position of the head. The lumbar curve appears at from one to two years when the child begins to walk. The mechanism of its production is explained as follows. When an infant lies on its back the thighs are flexed and fall apart. If these be held together and pressed forcibly down, the lumbar region will spring upward, owing to the shortness of the ilio-femoral ligaments, which bend the pelvis and, indirectly, the spine. The psoas muscles, moreover, act directly on the spine. When the child first stands, the body is inclined forward ; when the muscles of the back straighten it, the lumbar curve is produced by the same mech- anism, since it is immaterial whether the legs are extended on the trunk or the trunk on the legs. How or when these curves be- come consolidated is very difficult to deter- mine. The influence of differences in thick- ness of the front and back of the various bodies and disks is inappreciable in the neck ; in the lower part of the back and in the first, and perhaps the second, lumbar vertebrae the height is greater behind. In the loins the fifth vertebra is much thicker in front and, above it, the fourth and third in a less degree. The intervertebral disks are also much thicker in front. How soon actual difference in the diameters of the vertebrae appears is un- certain. A child of about three shows little of it, except in the last lumbar, and, accord- ing to Symington's plates, there is not much more difference at five or even thirteen years. It is certain that throughout the period of growth the curves can be nearly or quite effaced. The restraining influences are the gradually developing differences in the verte- bree and the disks, the effect of the sternum and the ribs on the thoracic region, the pull of the elastic ligaments of the arches, and perhaps, above all, muscular tonicity. In the latter part of middle age the curves of the back and loins become consolidated ; this is, however, distinctly a degenerative process. LENGTH OF PRESACRAL REGIONS. 141 Dimensions and Proportions. — The length and the proportions of the dif- ferent presacral regions (including the intervertebral disks), measured along the an- terior surface of the spine, have, in fifty males and twenty-three female bodies, been found by us as stated below. We give for comparison Ravenel's^ and Aeby's" propor- tions combined. The former measured eleven and the latter eight spines of each sex. Cunningham's' proportions, from six male and five female spines, are also added. In the proportions, one hundred represents the total presacral length along the curves. ACTUAL LENGTH OF PRESACRAL REGIONS OF SPINE. Male. Female. Centimetres. (Inches.) Centimetres. (Inches.) Neck 13.3 ( 5-25) 12.1 ( 4.75) Back 28.7 (11.31) 26.5 (10.44) Loins . . . _i9^9 ( 7-82) 18.7 ( 7-38) 61.9 (24.38) 57.3 (22.57) PROPORTIONS OF PRESACRAL REGIONS OF SPINE. Male. Female. (Dwight.) (R. &A.) (Cunningham.) (Dwight.) (r! & A.) (Cunningham.) Neck ... - 21.5 21.7 21.8 21.2 21.7 21.6 Back .... 46.3 46.7 46.5 46.1 46.5 45.8 Loins .... 32.2 31-4 3i-7 32-7 . 32-4 32.8 100. o 99-8 100. o 100. o 100.6 100.2 Thus, while it is true that the lumbar region is relatively longer in woman, the difference is trifling. ABSOLUTE AND RELATIVE LENGTH OF PRESACRAL REGIONS DURING GROWTH. At birth At birth ... At birth One month One month Three months Six months Six months Ten months One year, boy One year, boy One year and one month, boy One and a half years, girl . . One and a half years, boy . Two years, boy Two years, boy Three years, girl Four years, girl Four and a half years, boy . Five years, boy Five years, boy Si.x years, boy Nine years, girl Eleven years, boy Thirteen years, girl .... Fifteen years, boy Sixteen years, girl Sixteen years, girl Seventeen years, girl .... Ravenel. Ravenel. Ravenel. Chipault.* Chipault. Ravenel. Aeby. Aeby. Dwight. Chipault. Chipault. Chipault. Chipault. Chipault. Ravenel. Aeby. Dwight. Aeby. Chipault. Symington.' Ravenel. Symington. Ravenel. Aeby. Symington. Dwight. Aeby. Aeby. Dwight. Absolute Length. (In Millimetres.) Neck. Back. Loins. Total 50 40 40 40 42 50 52.5 53-5 61 60 69 67 62 68 70 79-5 78 79-9 81 85 91 95 120 100 107.5 "3 93 100 95 80 80 100 103 107 125 121 129 118 130 132 140 153-5 162 162 174 170 180 175 195 218.7 220 265 221.8 229.5 250 103-3 102.8 104 ■ 135 106 150 153-5 151 152.5 161 193 190 185 165 166 _ 208 215-5 221.5 263 253 281 264 261 279 300 331 341 345-2 357-8 354 395' 361 430 463-2 451 568 472-8 489.5 524 Relative Length. (Total = 100.) Neck. Back. Loins 25-9 21 21.6 24.2 25-3 24 24-3 24.1 23.2 23-7 24-5 25.2 23-7 24-3 23-3 24 22.9 23.1 22.6 22.5 20.3 22.2 19.8 19-7 21.5 21. 1 21. 1 2r.9 21.5 48.2 52.6 51-3 48.4 •47.5 48.6 47.5 47.8 45-9 44-8 49-7 47-4 46.7 46.4 47-5 46.9 48.9 48 45-6 48-5 45-4 47-2 48-7 46.6 46.9 46.9 47-7 259 26.3 27 27.4 26.6 27.9 27.8 27-5 29.2 28.5 29.6 30 26.6 28.3 30 29.6 29.6 29.9 28.5 29.4 34-2 29-3 34-9 33-1 29.1 32.2 31-9 3I-I 30-7 ' Zeitschrift fur Anat. und Entwicklng., 1876. ' Cunningham : Memoirs, 1886. 5 The Anatomy of the Child. ' Arch, fiir Anat. und Entwicklng., 1879. ■* Revue d'Orthop^die, 1895. 142 HUMAN ANATOMY. It appears from the above that in the adult the neck is a little more than one- fifth of the movable part of the spine and the loins a little less than one-third. In the young embryo these proportions are reversed, but by the time of birth these two parts are nearly equal. Movements of the Head. — Those between the occiput and atlas are almost wholly limited \.o flexion and extension,. o\ which the latter is much the greater. This is in part due to the reception of the posterior pointed extremities of the articu- lar processes of the atlas into the inner parts of the posterior condyloid fossae. The anterior occipito-atlantal ligament and the odontoid ligaments are tense in extreme extension. Inflexion the tip of the odontoid is very close to, if it does not touch, the basilar process. The range of both these motions is much increased by the participation of the cervical region. There may be a little lateral motion between the atlas and head, and there is some slight rotation. The great variation of the shape of the articular facets makes it clear that both the nature and extent of the motions must vary considerably. The joint between the atlas and axis is devoted almost wholly to rotation. The transverse ligament keeps the odontoid in place, and the very strong odontoid liga- ments check rotation alternately. The head is highest when directed straight forward, but the joints are in more perfect adaptation if one condyle be a little anterior to the other, and if the atlas be slightly rotated on the axis. This position, though entail- ing a slight loss of height, is the one naturally chosen as that of greatest stability. Movements of the Spine. — The very extensive range of motion of the whole spine is the sum of many small movements occurring at the intervertebral disks. The whole column is a flexible rod, but this conception is modified by the following peculiarities : ( i ) the motion is not equally distributed, owing to the vary- ing distances between the disks and the differences of thickness of the disks them- selves ; (2) the bodies, which form the essential part of the rod, are not circular, so that motion is easier in one direction than in another ; (3) the rod is not straight but curved ; (4) the kind of motion is influenced by the articular processes, and varies in the different regions. Other modifying circumstances exist, but these suf- fice to show that, while certain general principles may be laid down, an accurate analysis of the spinal movements is absolutely impossible. The incompressible semifluid centre of each disk has been compared to a ball on which the rest of the disk plays. This would, therefore, be a universal joint were there no restraining apparatus. The motions are flexion and extension, — i.e., angular movements on a transverse axis ; lateral motion, — i.e., the same on an antero-posterior a.xis, and rotation on a vertical axis. It is unlikelv that any single one of these motions ever occurs without some mingling of another. Flexion and extension are greatest in the neck and loins. Extension is more free than flexion in the neck, where it is limited by the locking of the laminae, which, when the head is thrown as far back as possible, gives great rigidity to the neck. In the loins and in the region of th? last two thoracic vertebrae flexion is the more exten- sive. Before the spine is consolidated, slight flexion is possible throughout the back, but e.xtension is very quickly checked by the locking of the laminae and spines. Lateral motion is greatest in the neck, considerable in the back and least in the loins. Such motion is always associated with rotation, which is most free in the neck, considerable in the back, and very slight, at most, in the loins. It is to be remembered that motions both in the antero-posterior and in the transverse plane are checked by the tension of the ligaments on the side of the body of the vertebrs opposite to the direction of the motion, and also by the resistance to compression of that side of the intervertebral disk towards which the motion occurs. The liga- menta subflava, being elastic, tend continually to bring the bones back into position from the innumerable slight displacements to which they are subject. That this replacement is effected by a purely physical property of the tissue instead of by muscular action implies a great saving of energy. The amount of all motions, and of rotation in particular, decreases throughout life and varies much in individuals. According to Keen, the rotary motion between the atlas and the axis amounts to twenty-five degrees, that in the rest of the neck to forty-five degrees, and that of the thoracic and lumbar regions to about thirty degrees on each side. PRACTICAL CONSIDERATIONS: THE SPINE. 143 PRACTICAL CONSIDERATIONS. While the number of vertebrae in the neck is almost invariable in man (and indeed in all the mammalia except the sloth and the sea-cow), the length of the cervical region varies greatly in individuals. As it is apparently shortened during full inspiration and lengthened during full expiration, so an actual change in its length is associated with the types of thorax that correspond to these conditions. The long neck is therefore found in persons with chests that are flat above the mammae, with wide upper intercostal spaces and narrow lower ones, and with lack of prominence of the sternum. These conditions are often associated with phthisical tendencies. The short neck is found in persons with chests of the reverse type. Its theoretical association with apoplectic tendencies is very doubtful. The remaining variations both in the length and in the shape of the vertebral column are closely connected with corresponding variations in its curves. The normal curves of the spine are four : the cervical, thoracic, lumbar, and pelvic (or sacro-coccygeal). The cervical and lumbar are concave backward, the thoracic and pelvic convex backward (Fig. 171). These curves are produced and kept up partly by the twenty-three intervertebral disks. They are altered by disease. An additional curve not uncommon in absolutely healthy persons consists in a slight deflection of the thoracic spine to the right ; this asymmetry is usually ascribed to the greater use of the right arm, but it is due to the position of the heart and the aorta. All the vertebral bodies are composed of cancellous tissue, which is more spongy in direct proportion to the size of the vertebrae, and therefore is least so in the neck and most spongy in the lumbar region. This corresponds with the greater succu- lence and elasticity of the lower intervertebral disks and aids in minimizing the effect of jars and shocks such as are received in alighting from a height upon the feet, the lower portion of the column of course receiving the greater weight. If in such falls the calcaneum or tibia is broken, the spine usually escapes injury. If the lower extremity remains intact, the safety of the spine depends largely upon the elasticity given by its curves and by the disks. The fact that the bodies have to bear the chief strain of such shocks and of extreme flexion and e.xtension, the most usual forms of spinal injury, serves, together with their comparative vascularity, to make them the seat of tuberculous infection when it invades the spine. Their spongy texture, once they are softened by inflam- mation, leads to their ready disintegration under the superincumbent weight. In the neck and in the loins the process may at first merely cause a straightening of the column, the normal curves being concave backward. In the thoracic region — the most common situation — it soon produces kyphosis, an exaggerated backward curve, the sharp projection of the spinous processes of the affected vertebrae causing it to be known as "angular curvature." The abscesses which result from caries of the vertebrae are governed as to their position and course by the fasciae and muscles that surround them. They will, therefore, be described later (page 643). The suspension of the whole body from the chin and occiput separates the indi- vidual vertebrae so that they are held together mainly by their ligaments. This obviously relieves or removes the pressure of the superincumbent weight on the bodies of diseased vertebrae. The relief of pressure in cases of thoracic caries is continued by the use of appliances which transfer the weight of the head and shoulders to the pelvis. The simplest of these is the plaster jacket. For cervical caries, the weight of the head is transferred to the trunk beneath the level of disease by means of an apparatus extending from above the head to a band (of leather or plaster) encircling the chest. In cases of kyphosis corrected by the method of ' ' forcible straightening' ' it is obvious that a gap proportionate to the amount of bone which has previously been destroyed must be left between the bodies of the diseased vertebrae. The ultimate integrity of the spinal column will depend upon the e.xtent and character of the ankylosis which takes place between the separated vertebrae. It is asserted (Calot) that such consolidation does occur between the bodies in moderately severe cases, and between the laminae, transverse processes, and spines in the more serious 144 HUMAN ANATOMY. ones. It has been shown (WuUstein) that injury to the dura and cord and even fracture of the arches and processes are possible concomitants of forcible rectifica- tion of kyphosis. If the curve forward of the lumbar spine is exaggerated, constituting /ordosis, it is usually compensatory, and is acquired in an effort to maintain the erect position, as in cases of high caries, great obesity, pregnancy, ascites, abdominal tumors, etc. Scoliosis or lateral curvatur,c commonly results from faulty positions in young, undeveloped persons with weak muscles, as school-girls, who sit or stand in such atti- tudes that the muscles are relieved and the strain is borne by insensitive structures, like ligaments and fasciae. This results in a deflection of one part of the column — generally the thoracic — to one side, usually the right, and the formation of a compen- satory curve below, and occasionally of one above also. The bodies of the affected vertebrae are at the same time rotated, partly by the action of the slips of the longis- simus dorsi which are attached to the ribs near the angles and to the tips of the trans- verse processes (Fig. 520), so that in advanced cases the tips of the spinous pro- cesses of the affected segments turn towards the concavity of the curves, while the transverse processes of the vertebne involved tend to lie in an antero-posterior plane and can. often be felt projecting backward. A further e.Kplanation of the causes of the rotation may be found in the behavior of a straight flexible rod under similar conditions. Torsion results from any motion in which all particles of a straight flexible rod do not move in parallel columns. Therefore, if it be bent in two planes at the same time torsion must inevitably occur. The vertebral column being bent in the antero-posterior plane by a series of gentle curves, lateral bending must, therefore, inevitably lead to torsion, since it means bending in two planes. A little consideration of the relations of the spine to the ribs, scapula, and pelvis will show that lateral flexion and rotation cannot take place without causing (a ) sep- aration of the ribs on the convex side; (3) change in the costal angles, making the ribs more horizontal on the convex and more oblique on the opposite side ; (c) undue prominence of their angles on the convex side, the scapula being carried upon them so that it also is more prominent ; {d ) diminution of the ilio-costal space on the concave side ; (^) elevation of the shoulder on the convex side ; (/) flatten- ing of the chest in front on the convex and undue prominence of the chest on the opposite side ; (g) projection of the ilium on the concave side. Lateral curvature with these secondary deformities may also be produced by unequal length of the lower limbs, one-sided muscular atrophy, hypertrophy, or spasm, sacro-iliac disease, empyema, and asymmetry of either the pelvis or the head. The latter factor is especially interesting from an anatomical stand-point. From what has been said (page 142) of the position of greatest stability of the joints be- tween the head and the atlas and the latter and the axis, it is evident that the position of greatest ease is with the head slightly turned to one side, the condyles of the occiput not being in their best contact with the superior articular surfaces of the atlas when the head is held straight, but rather when the head is slightly twisted (Dwight). The effects of this are far-reaching. First, there is an instinctive effort to get the eyes on the same plane in looking forward, which is presumably the primary cause of the asymmetry of the face that is usually found. It is also easier to support the weight in standing chiefly on one leg, hence the other side of the pelvis is allowed to fall so that the lumbar region slants awav from the supporting leg. This must be corrected by a lateral motion of the spine above it, and as this is not pure but mixed with rotation, there occurs a twist in the spine : one shoulder is higher than the other as well as farther forward. In healthy persons such positions, if not maintained too long, do little harm ; but there is likely to be some spinal asymmetry in all, and there is the danger that it may become pronounced and fixed in the weak. Sprains of the spine are most common in the cervical and lumbar regions : in the former because of the greater mobility of the articulation with the cranium, and in both because of their own mobility, the greatest degree of bending in an antero- posterior direction being possible in those two segments of the spine. The thoracic and pelvic curves are primary, form part of the walls of the thorax and pelvis, PRACTICAL CONSIDERATIONS : THE SPINE. 145 appear early, and are chiefly due to the shape of the vertebral bodies. The cervical and lumbar curves are secondary, develop after birth, and depend mainly on the shape of the disks. Greater mobility would naturally be expected under the latter circumstances. The close articulation between the separate vertebrae throughout the whole column, while it renders a slight degree of sprain not uncommon, tends at the same time to diffuse forces applied to the spine and to concentrate them within certain areas. These areas are the points at which-fixed and movable portions of the spine join each other, as in the neighborhood of the atlan to-axial, the cervico- thoracic, and the thoracico-lumbar regions. If the force is sufficient to cause an injury of greater severity than a sprain it is apt to be a dislocation or a fracture with dislocation at one or other of these localities. The latter accident is usually caused by extreme flexion of the spine, and of the three points mentioned is most often found in the segment including the lower two thoracic and the upper one or two lumbar vertebra. This is due to the fact that ( I ) this segment has to bear almost as much weight as the lumbar spine, and yet its vertebrae are smaller and weaker. (2) The transverse processes are short, while the longer ones below, together with the crest of the ilium and the ribs above, give a powerful leverage to the muscles that move the region in question. (3) It is the region at which the most concave part of the thoracico-lumbar curve is found, making the "hollow of the back" and corresponding to the "waist" where the circumference of the trunk is smallest. (4) Its nearness to the middle of the column enables a greater length of leverage to be brought to bear against it than against any other part. (5) The different segments of the spine above it are com- paratively fixed (Humphry). These anatomical facts account for the frequency and severity of the injury known as " fracture-dislocation" in this region as a result of extreme flexion. A view of the vertebral column from behind .(Fig. 170) serves well to illustrate some of these points. ■Pure dislocations are rare, but are more frequent in the upper than in the lower part of the spine, because the bodies of the cervical vertebrae are small, and the interlocking of the articular processes is less firm than it is lower in the column. The vertebra most commonly dislocated is the fifth cervical, which might be expected from the fact that in the neck flexion and extension are freest between the third and sixth vertebrae. The dislocation is usually anterior, — that is, the articular process of one vertebra slips forward and falls down on the pedicle of the vertebra below, resting in the intervertebral notch, — this accident being rendered easy by the com- paratively horizontal position of the articular processes in the cervical region. Such dislocation is practically impossible in the thoracic or lumbar region without fracture, while fracture is comparatively rare in the cervical region. The lumen of the spinal canal may be but little, if at all, invaded. As to reduction, experiments show (Walton) that no moderate amount of exten- sion in a direct line would raise the displaced articular processes in the least degree. It was, however, found easy to unlock these processes by retro-lateral flexion, bend- ing the head towards the side to which the face was already turned, an inappreciable amount of force being necessary. Rotation into place completed the reduction. All pure dislocations are really subluxations, as without extensive fracture of the processes and great laceration of ligaments a complete separation of the articu- lar surfaces of two adjoining vertebrae is practically impossible. Pure fracture, not the result of a gunshot wound, is rare. If from flexion, the fracture involves the body ; if from direct violence, usually the laminae. These facts require no explanation. Dislocations and fractures of the upper two cervical vertebrae are especially serious on account of the proximity of the medulla and of their position above the roots of the phrenic nerve and of the nerves supplying the external muscles of respiration. If the accident is from overflexion, it may be a dislocation between the occiput and the atlas, as it is there that the movements of flexion and extension of the head take place. If it arises from extreme rotation, and especially if there is rupture of the check ligaments, it may be a dislocation of the atlas from the axis, as it is there that the rotary movements of the head occur. " A dumb person expresses ' yes' at the 146 HUMAN ANATOMY. occipito-atloid joint and 'no' at the atlo-axoid" (Owen). Painless nodding and rotation of the head aid, therefore, in the exclusion of the occipito-atlantal and atlanto-axial regions in obscure cases of high caries. The axis is more spongy than the atlas, and is weakest about one centimetre below the neck of the odontoid process, and this is one of the most frequent seats of fracture. In fracture-dislocations, which constitute from seventy to eighty per cent, of se- vere spinal injuries, the thoracico-lumbar region suffers most commonly for the reasons above stated. The almost vertical direction of the articular processes of the thoracic vertebrae causes them, when flexion is extreme, as when a weight has fallen on the back, to be frequently fractured, which, together with the accompanying crushing of the vertebral body and rupture of the supra- and interspinous ligaments and the ligamenta subflava, permits the immediate sliding forward of the vertebrae above the crushed one and the compression of the cord — often its practical severance — ■ between the anterior edge of the posterior arch of the upper vertebra and the poste- rior edge of the body of the lower one. (For the resulting symptoms, see section on Nervous System, page 1053.) It may be mentioned here that the spinal nerves do not arise from the cord opposite the vertebrae after which they are named. Their regions of origin may briefly be stated as follows : ( I ) Occiput to si.xth cervical spine, — eight cervical nerves. (2) Seventh cervical to fourth thoracic spine, — upper six thoracic nerves. (3) Fifth to tenth thoracic spine, — lower six thoracic nerves. (4) Eleventh and twelfth thoracic spines, — five lumbar nerves. (5) First lumbar spine, — five sacral nerves. Landmarks. — To fix the limits of the spine in the lix'ing, draw a horizontal line from the anterior nasal spine, to the lower edge of the external occipital pro- tuberance and another backward from the top of the symphysis pubis. Seen from the side, the top of the spine is in a line connecting the front of the lobe of each ear, passing behind the neck of the lower jaw. Frozen sections show that the front of the vertebral bodies is much nearer the centre of the body than one is prepared to expect. A vertical transverse, or frontal, plane through the thorax at its greatest breadth strikes the angle of the jaw, the front of the cervical convexity of the spine, and cuts the body of the fourth lumbar (Langer). The relations of the spine anteriorly are considered with the parts in front of it. The parts felt from the surface are the spinous processes and some few of the trans- verse ones. The line of the spines is a good example of the general rule that prominences on the skeleton lie in hollows in the flesh ; a deep furrow between the muscular masses marks their position. Palpation of the norma! spine with the soft parts in place gives the following information. The spine of the second cervical can be felt by deep pressure a little below the occiput. The short spines of the succeeding vertebrae are made out with great difficulty. The fifth is longer than those just above it. The sixth, is much longer and nearly as long as that of the seventh. The name vertebra prominens conferred on the seventh is misleading, for the spine of the first thoracic is the most prominent in this region. The third, fourth, and fifth cervical spines recede from the surface by reason of the forward curve of the cervical segment and on account of their shortness. This permits of free extension of the head and neck. The liga- mentum nuchae also prevents them from being felt distinctly. The sixth and seventh cervical and first thoracic are easily felt. The remainder, lying in the groove caused by the prominence of the erector spinae muscles, can usually be palpated without much difficulty. The relative sizes vary so much that it is not safe to identify any spine in this way. If the whole series from the second cannot be counted, it is best to start from the fourth lumbar, which is on a level with the highest points of the ilia. Vertebrae can also be identified from the lower ribs by the relations of the heads to the bodies. The relations of the spinous processes to the body vary. Thus, in the cervical region the first five spines pass nearly straight backward. The sixth and seventh, like the upper two or three thoracic spines, descend a little, so that the tip is opposite LANDMARKS OF THE SPINE. Fig. 172. U7 Anterior boundary of foramen magnum Superior laryngeal opening Cricoid cartilage Thyroid gland Upper border of manubrium Left innominate vein Innominate artery Ascending portion of aortic arch Upper border of body of sternum Section of right lung Right auricular appendage Right auricle Lower border of body of sternum Diaphragm Lower end of ensiform cartilage Stomach Pancreas Duodenum Transverse colon Sigmoid flexure Bladder. Symphysis pubis Medulla Posterior boundary of foramen magnum Odontoid process of axis Division of trachea Right pulmonary artery Left auricle End of abdominal aorta Left common iliac vein Coccyx Seminal vesicles Prostate Median section of the body of a man aged twenty-one years. {After Braune.) 148 HUMAN ANATOMY. to the body next below it. With the fourth or fifth thoracic they point much more strongly downward, so as to be opposite the disk below the succeeding body. This continues to the tenth, where they are opposite the body below. In the loins the spines have a considerable posterior surface, which is opposite the disk and the upper part of the body below it. The tips of the spines are not always in a straight line, but sometimes describe a zigzag. The transverse process of the atlas can be felt below the tip of the mastoid process, moving with the head when the latter is turned. The transverse processes below this are felt with great difficulty through the muscles of the side of the neck. Those of the back and loins are too thickly covered to be felt. The laminae are also thickly covered with muscles, so that the operation of laminectomy necessarily involves a deep wound, and in the thoracic region this difficulty is increased by the backward projection of the ribs. As landmarks the spines of the vertebrae, on account of their accessibility, have great value. These spines have the following relations. The fourth cervical spine corresponds to (i) the opening of the laryn.x ; (2) the bifurcation of the carotid artery, and hence the point of origin of both the e.xternal and internal carotid arteries. The sixth cervical indicates the level of the carotid tubercle (transverse process of the sixth vertebra) and the entrance of the vertebral artery into the bony canal. The seventh cervical spine is a guide to (i) the lower border of the cricoid cartilage ; the lower opening of the larynx and the beginning of the trachea ; (2) the lower end of the pharynx and the upper opening of the oesophagus ; (3) the crossing of the omo-hyoid over the common carotid ; (4) the le\-el of the apex of the lung and to the summit of the arch of the subclavian artery. The fourth thoracic spine corresponds to the level at which the aorta reaches the spinal column, the trachea bifurcates, and posteriorly the apex of the lower lobe of the lung is found. It is on the same level as the root of the spine of the scapula. The seventh thoracic lies on a level with the inferior angle of the scapula. The eighth thoracic indicates the lower level of the heart and that of the central tendon of the diaphragm and the level at which the inferior vena cava passes through the diaphragm. The ninth tho- racic marks the level at which the upper edge of the spleen is found in health, and at which also the oesophagus pierces the diaphragm. The tenth thoracic corresponds to the lower edge of the lung, the spot at which the liver comes to the surface poste- riorly. The spines of the third to the ninth thoracic correspond to the heads of the fourth to the tenth ribs respectively. The eleventh thoracic is a guide to the normal situation of the lower border of the spleen and to the upper part of the kidney. The t'u'cl/th thoracic marks the lower limit of the pleura, the passage of the aorta through the diaphragm, and the situation of the pyloric end of the stomach, and is on a level with the head of the last rib. The Ji}'st lumbar spine is on the line of the renal arteries and the pelvis of the kidney. The second lumbar spine corre- sponds to ( I ) the termination of the duodenum and the commencement of the jejunum ; (2) the opening of the ductus communis choledochus into the intestine ; (3) the lower border of the kidney ; (4) the lower border of the pancreas ; (5) the upper end of the root of the mesentery ; (6) the point of origin of the superior mesenteric artery ; (7) the commencement of the thoracic duct ; (8) the commence- ment of the vena porta ; (9 ) the termination of the spinal cord and the origin of the Cauda equina; (10) the upper end of the receptaculum chyli. The third lumbar corresponds to the level of the umbilicus and the origin of the inferior mesenteric artery ; the fourth lumbar spine marks the point of bifurcation of the abdominal aorta into the two common iliac arteries, and lies on a level with the highest part of the ilium ; and, finally, the fifth lumbar spine is a little below the beginning of the inferior \-ena cava. Direct cocainization of the spinal cord has recently been employed in surgery in operations on the lower abdomen, pelvis, and lower extremities. The injection into the subarachnoid space surrounding the cord is made through the space between the fourth and fifth lumbar vertebrae. To find this space, draw a line connecting the highest points of the crest of the ilium posteriorly. This will pass through the spine of the fourth lumbar vertebra. The point for injection is one centimetre below and one centimetre to the outer side of the point at which the transverse line crosses the vertebral spine in the median line. THE THORAX. The thorax is that part of the body-cavity separated by the diaphragm from the abdomen below, but without complete separation from the neck above. Its bony walls are formed behind by the thoracic vertebrse, at the sides by the ribs, and in front by their continuations, the costal cartilages, and the sternum. The bony thorax, anterior view. THE RIBS. The ribs, arranged as twelve pairs, are flat bars of bone, curved and twisted, which are attached behind to the spine and continued in front by the costal cartilages ; they form the greater part of the bony walls of the thorax. The first seven pairs, 149 I50 HUMAN ANATOMY. exceptionally eight, reach the sternum through their cartilages ; hence they are called sternal ribs,' as distinguished from the remaining fi\'e pairs of asternal ribs.' Each cartilage of the next three joins that of the rib above it. The last two pairs have the cartilages ending free, and are termed floating ribs. Their complicated curves are best understood by studying them in place. Each rib (with certain exceptions to be detailed later) has an articular surface, the head, at the posterior end ; followed by a narrower neck, succeeded by an articular facet on the tubercle which rests on the transverse process of the vertebra. The first rib has an upper and a lower surface, an outer and an inner border ; the second faces in a direction intermediate to this and the following, which have an outer and an inner surface, an upper and a lower border. They are placed obliquely, the front end being lower than the hind one. The outline of the ribs is irregular, so that their declination is not due wholly to their position, but in part also to their shape. Thus, one in the middle of the series slants a little downward as far as the tubercle, then declines more sharply to a roughness near the tubercle known as the a7igk\ and thence more gradually to the end. The main curve of such a rib is backward, outward, and downward as far as the angle, which marks a rather sudden change of direction, the course changing to one forward, slightly outward, and downward, until, as it reaches the front of the chest, it runs forward, downward, and inward. The external surface is vertical at the back and side and slants slightly upward in front. Bearing the declination of the rib in mind, it is evident that to accomplish this the rib must be twisted on itself, otherwise the upper edge would project in front. Fig. 174. Articular facets for bodies of verteb Right fifth rib from behind. The head ' is an enlargement at the posterior end and on the outer surface, — 7.e., the one farthest from the cavity of the chest. It has an articular siuface at the end facing inward and backward, divided into an itpper and a loieer facet, each for the body of a vertebra, by a transverse ridge, whence a ligament passes to the inter- vertebral disk. The lower facet is the larger, and is generally concave ; the upper is nearly plane. The head increases in size to the ninth rib and then lessens. The neck* is compressed from before backward, smooth in front and rough for ligaments behind. The upper aspect has a sharp border, the crcst,^ for the superior costo-transverse ligament. The neck grows slightly longer in descending the series to the same level. The crest on the top of the neck is most developed in the sixth, seventh, and eighth ribs. The tubercle ^ is an elevation beyond the neck on the posterior surface of the rib, bearing internally a round articular surface facing backward and, in rnost cases, downward, to rest on the transverse process ; beyond the articular facet is a rough knob for the external costo-transverse ligament. The shaft ' is smooth inside, the surface being continuous with that of the neck. The subcostal groove^ for the intercostal vein is best marked in the middle ribs, begin- ning at the tubercle and running forward, growing fainter, along three-quarters of the rib, just under cover of the lower border. The outer surface is rather irregular. The angle ^ at which the shaft changes its direction is marked by a rough line on the posterior surface, some distance beyond the tubercle, receiving muscles from the system of the erector spinae. The angle, which is not found in the first rib, is 1 Costac vcrae. = Costae spuriae. ^Capitulum. * Collum. ^Crista colli. "Tubercnlum. 'Corpus costae. 'Sulcus costalis. *■' Angulu THE RIBS. 151 very near (one centimetre beyondj the tubercle in tlie second ; it gradually recedes from the tubercle, being in the ninth and tenth about five centimetres distant. The angle is a little nearer in the eleventh, and is wanting in the last. The twist is greatest from the sixth to the ninth rib. Several of the upper ribs present near Fig. 175. Right fifth lib: A^ under surface; B, post the middle a rough impression for a point of the serratus magnus. The upper border of the shaft is thick and rounded behind, but thin near the front. The lower •border is sharp where it overhangs the subcostal groove ; less so 'in front. The anterior end of each rib is cupped to receive the costal cartilage. 152 HUiMAN ANATOMY. The ribs increase in length from the first to the seventh or eighth, after which they decrease to the last, which is usually the shortest. The length of the last rib is, however, very uncertain, varying from one centimetre to perhaps fifteen centime- tres or more. It often is longer than the first. The curve is comparatively regular in the first rib, after which the difference between the two ends becomes more marked, the curve being very pronounced behind and less so in front. The curve is much less throughout in the lower ribs ; in fact, it decreases continually. The first rib is the broadest of all at the anterior end. There is a general, but not regular, increase from the second to the seventh rib, and a subsequent decrease. The fourth rib is relatively broad, the fifth narrow.' Exceptional Ribs. — Certain of the ribs — the first, second, tenth, eleventh, and twelfth — present peculiarities which claim mention. Fig. 176. - Second digitation of serratus magnum -1 hiui digitation of serraijis magntts First and second ribs of right side, upper surface. The first rib is flat, not twisted, with an outer and an inner border. The head is small and has but one facet, resting as it does on the first thoracic vertebra. The neck is small and flat like the body. The tubercle is very prominent. The scalene hibercle is a very small but, from its relations, important elevation on the inner margin of the upper surface, at about the middle, for the insertion of the scalenus anticus. It separates two grooves crossing the bone for the subclavian artery and vein. The posterior one for the artery is the more marked. There is a rough, impression behind the latter near the outer border for the scalenus medius. There is no subcostal groove. The second rib is intermediate in shape between the first and the rest. The roughness for the serratus magnus is very marked about the middle of the shaft. ' Anderson : Journal of Anatomy and Physiologj', vol. xviii., 1884. EXCEPTIONAL RIBS. 153 The tenth rib has usually only a single articular facet on the head ; it may or may not have a facet on the tubercle. The eleventh rib has a single articular facet on the head ; the tubercle is rudi- mentary and non-articular ; the angle and the subcostal groove are slightly marked. Tlie twelfth rib has also a single articular facet on the head ; the tubercle is at most a faint roughness ; the angle and the subcostal groove are wanting. Development. — The first centre for the shaft appears in the ninth week of fcetal life, and spreads so rapidly that by the end of the fourth month the perma- nent proportion of bone has been formed. At an uncertain period, probably before puberty, a centre appears for the head and another, except in the last two or three ribs, for the tubercle ; these unite presumably by the twentieth year. Variations. — The num- ber of ribs is often increased or Fig. 177. diminished by one, generally by Tenth rib. a change at the end of a re- gion, as explained in varia- tions of the spine (page 131). Cei'vical ribs occur by the cos- tal element of the seventh cer- vical becoming free. In the lowest and most common grade it consists of a head, a neck, a tubercle, and a rudimentary shaft one or two centimetres long, ending free. In the next grade it is. longer, and its end, perhaps continued in cartilage, rests on the first rib. Some- times it fuses with the first rib, which then becomes bicipital, as is normal in certain whales. In the third grade, which is very uncommon, it resembles a small first rib, reaching the ster- num. A cervical rib has been seen more than once with the transverse foramen persisting. The explanation of this condition is given under ossification of the vertebrae. When a cervical rib reaches the sternum, the next rib is usually attached to the side of the manubrium by a broad cartilage, fusing with that of the cervical rib. The rib of the eighth vertebra has been seen to end like an ordinary second rib. It is also very rare to have only twelve pairs of ribs, of which the first is cervical. There may be thirteen ribs by the addition of the costal element of the first lumbar. This may be so small as to present no rib-like feature, or it may resemble an ordinary twelfth rib. In cases of an extra rib from this source the twelfth rib is usually uncom- monly long. Very rarely the first true thoracic rib is imperfect, being continued in ligament to the sternum, joining the shaft of the second rib, or even ending free. A bicipital rib may occur also by the fusion of the first thoracic with the second be- yond the tubercles. The resulting plate later subdivides, to be continued by two normal costal cartilages. Ribs sometimes divide, generally near the front. The parts formed by such cleavage are continued by costal cartilages which usually re- unite, so that a foramen is formed which is bounded laterally or externally by bone, mesially by cartilage. This occurs most commonly in the third and fourth ribs, espe- cially in the latter. THE COSTAL CARTILAGES. The costal cartilages " continue the ribs, the first seven going directly to the ster- num, the next three each to the one above it, and the last two ending free. They grow longer from the first to the seventh, sometimes to the eighth. The last two ^ Cartilagines costales. Vertebral ends of tenth, elev nd twelfth ribs of right side from 154 HUMAN ANATOMY. cartilages are short and pointed. There is occasionally a projection downward from the fifth, at its most dependent point, which articulates with the sixth, visually there is a similar projection on the latter for the seventh. The eighth, ninth, and Fig. 17S. Interclavicular notch Surfaces of sternum with coossified ensifortn cartilage tenth cartilasjes have usually their chief connection with the one above, not through their ends, but through sim'ilar facets. As to direction : the first cartilage descends the second is horizontal, the third rises very slightly, and the fourth is the first to tall and then rise. This change of direction occurs in each to the ninth or tenth carti- THE STERNUM. 155 lage, the falling portion becoming always relatively shorter and the rising longer. The'last two cartilages continue the line of their ribs, having no rising portion. It is not uncommon to find eight cartilages joining the sternum. Tredgold found this condition in ten per cent, of white men. It is very much more frequent in negroes and in other dark Fig. 179. races.' It is said to occur more often on the right side. THE STERNUM. The adult sternum consists of three flat m*edian <:ar"ia; plates, the two former being bone, the last largely car- tilage,— namely, the presternum or viaiiubriiim, the mesosternum, gladiolus, or body, and the metaster7iimi or ensiform cartilage. The manubrium^ is broad in mammals having clavicles, to which it gives support at the upper angles. , In man it is irregularly quadrilateral, with the angles cut off, broad above, narrower below, the greatest breadth equalling or exceeding the length. It is con- cave behind, but in front it is conve.x from side to side and slightly concave from above down. The upper border is concave in the middle, forming the bottom of the interclavicular notch."^ On each side of this, in the place of a corner, is a concavity for the sternal end of the clavicle. This depression^ is more on the top than on the side of the sternum, and usually encroaches more on the back of the bone. It is concave from within outward and may, or may not, be slightly con- cave from before backward. The facet is coated with articular cartilage. Just below the joint, the side of the manubrium projects outward to meet the cartilage of the first rib. This is the widest part of the first piece, the border then slanting inward to the lower angle, which also is cut off by a notch for the second costal cartilage, which is received between it and the body. The lower border, separated from the meso- sternum by fibro-cartilage, projects a little forward into a transverse ridge, always to be felt in life, which in- dicates the level of the second costal cartilage. The oblong body, or gladiolus, ° ossifying origi- nally in four pieces, one above another, varies con- siderably in shape. It is generally slightly concave behind and nearly plane in front, but it may be convex or even concave. The greatest breadth is below the middle, whence the borders slant inward to the lower end, the narrowest part, where it joins the ensiform cartilage. The sides of the body present alternately smooth concavities opposite the spaces between the costal cartilages and articular facets for the latter. To understand the position of these articular facets, we must recall the composition of the mesosternum as consisting of four pieces. . The second cartilage reaches the junction of the manubrium and the body ; the third. Right side of stemum. that of the first and second pieces of the body ; the fourth, that of the second and third pieces ; the fifth, that of the third and fourth pieces. The two remaining sternal ribs send their cartilages to this fourth piece of the body ; the sixth to the side, and the seventh to the lower angle, or even the ' Journal of Anatomy and Physiology, vol. xx.xi, 1S97. Lamb : Nature, 1SS8. " Maanbrium sterni. ^Incisura jucularis. ■* Incisura clavicularis. ^ Corpus sterni. 156 HUMAN ANATOMY. lower edge. The first and second pieces of the body are about equal in length ; the third is shorter, and the fourth still more so ; hence the fifth, sixth, and seventh cartilages end very close together, especially the two last. The ensiform cartilage,' or xiphoid process, more or less bony in middle life, is a fiat plate with a rounded end, not rarely bifid. It is fastened to the lower end of the body in such a way that their posterior surfaces are continuous, but that the ensiform, being thinner, is overlapped by the ends of the seventh cartilages ; its front is therefore at a deeper level than that of the body. The size and shape of the ensiform cartilage are very uncertain ; usually the tip projects somewhat forward. Differences due to Sex. — The body of the male sternum is both absolutely and relatively longer than that of the female. This is in accordance with the greater development of the male thorax. The following table gives the actual size, accord- ing to the writer^ and to Strauch.' Centimetre Manubrium 5.37 Body 11.04 Total 16.41 Women. Centimetres. 4-94 9- '9 14-13 16.063 Women. Centimetre 5-056 9-059 14- 115 Hyrtl gave a rule for determining the sex, that the manubrium of the female exceeds half the length of the body, while the latter in the male is at least twice as long as the manubrium. A study of 342 sterna, of which 222 were male and 120 female, confirmed Hyrtl's 't-a*^ <>^*ai ^^^^' ^'-"^ ^^^ mean ; since, however, approximately forty •e ' ' ^\ P^"^ cent, of the cases were exceptions, it is clearly ^^ worthless to determine the se.x in any given case. Probably the law would be correct if we had to do only with well-formed sterna, but the body varies greatly. It is easy to recognize a typical male or female sternum. The former has a long, regular body, the lower pieces of which are well developed, sepa- rating the lower cartilages of the true ribs. The latter has a shorter and relatively broader body, the lower parts of which are poorly developed, so that the carti- lages are near together, and the seventh ones of the two sides almost, or quite, meet below the body in fiont of the base of the ensiform. Variations. — The very rare cases of fissure of the sternum, and the not uncommon ones of perfora- tion in the median line, represent different degrees of arrest of development. The lower half of the sternum is sometimes imperfectly developed. We have de- scribed a case in a negress in which there was but little and irregular ossification below the fourth costal carti- lage. A very rare anomaly is that of the manubrium being prolonged to the insertion of the third costal cartilages, as occurs usually in the gibbons and occa- sionally in other anthropoid apes. The st/pras/erna/ bones, very rarely seen in the adult, are a pair of rounded bones compressed later- ally, about the size of peas, placed on the top of the manubrium at the posterior border just internal to the sterno-clavicular joint. They are presumably the tops of the lateral cartilaginous strips forming the sternum, in which they are normally lost. They are regarded as representing the episterrium of lower vertebrates. sternum, showing foramen due tc perfect union of lateral parts 'Journal of Anatomy and Physiology, vol. xxiv., 1S90. ^ Processus xiphoideus. ' Inaug. Disser., Dorpat, iSSi. DEVELOPMENT OF THE STERNUM. 157 Fig. iSi. B Development and Subsequent Changes. — The cartilaginous bars repre- senting the ribs in the early embryo end in front in a strip connecting them from the first to the ninth, which approaches its fellow above and recedes from it below. The union of these two strips, which begins above, forms the future sternum as far as the ensiform cartilage. Thus at this early stage there are nine sternal ribs. While the mesosternum is forming by the union of the lower part, a portion of the ninth strip separates itself from the rest to fuse with its fellow for the ensiform cartilage, and the remainder of the ninth joins the eighth, which, as a rule, itself later recedes from the sternum. The original cartilaginous strips having fused, points of ossification first appear in the manubrium about the sixth month of foetal life. There is one chief one and a varying number of small ones variously disposed. Sometimes it ossifies in a larger upper and a smaller lower piece. In the latter months, before birth, several points appear in the mesosternum. The first piece generally has a single centre, those below two in pairs. At birth one usually finds ossification begun in the first three pieces of the body. The centre for the last piece of the body begins to ossify at a very variable time. We have seen bone in it at thirteen days and have found none at seven years. Perhaps three years is not far from the average. The centre, or cen- tres, for this last piece of the body are placed in its upper part. Its cartilage is directly continuous with that of the ensiform, the line of demarcation being determined by the difference in thickness, the ensiform being thinner and continuing the plane of the posterior surface. Thus, the lower part of the last piece may continue cartilaginous for a con- siderable time. A centre in the ensiform is sometimes seen at three, but may not come for several years later. The four pieces of the meso- sternum join one another from be- low upward, the union being com- pleted on the posterior surface first. The process is extremely variable. The only points regarding which we are certain are that it is more rapid than is usually stated and that the body is almost always in one piece at twenty. The fourth piece of the body joins the third at about eight, the third joins the second at about fifteen, and the second unites with the first usually at eighteen or nineteen. We once saw all four pieces distinct at eighteen, but in one or two instances only have we found the body incomplete after twenty. The amount of bone in the ensiform at twenty is still small. The adult condition, except that the ensiform gradually becomes wholly bone, may persist to extreme old age. The ensiform often joins the body after middle age, rarely before thirty. The union of the manubrium and the body is rare, and appears to be the result of a con- stitutional tendency rather than of age, as in our observations we have repeatedly found it under fifty, and have seen all three pieces united at twenty-five. The different pieces are more apt to fuse in man than in woman. ^1f Ossification of the sternum. A, at sixth foetal r for manubrium. B, at birth; a, for manubrium ; ments of body. C, at about ten years ; a , manubr ments of body ; e, ensiform cartilage. onth ; a, centre 5, c. dy for seg- jm ; b, c, (f, seg- ARTICULATIONS OF THE THORAX. The joints uniting the bones taking part in the formation of the bony thorax constitute two general groups, the Anterior and the Posterior Thoi-acic Articula- tiotis. The former include the joints between the pieces of the sternum, those be- tween the sternum and the costal cartilages, and those between the costal cartilages ; the latter, or the costo-vertebral articulations, include those between the vertebrae and the ribs. 158 HUMAN ANATOMY. THE ANTERIOR THORACIC ARTICULATIONS. These include three sets : I. The Intersternal Joints, or those uniting the segments of the sternum Anterior intersternal j^^ ] 1 lament Chondro-sternal ligament ^SvWCosto-xiphoid ligament Interchondral ligament 2. The Costo-Sternal Joints, or those uniting the ribs by means of their cartilaginous extensions with the sternum ; 3. The Interchondral Joints, or those uniting certain of the costal cartilages with one another. INTERSTITIAL ARTICULATIONS. 159 THE INTERSTERNAL JOINTS. While the manubrium and the four pieces of the body, or sternebrae, are still separate ossifications in a common strip of cartilage, the structure is greatly strength- FiG. 1S3. MANUBRIUM Chondro-stemal joint Interchondral joint ENSIFORM CARTILAGE ■Interchondral ligamtsit Longitudinal section througii sternum and costal cartilages. ened by the thick periosteum, reinforced by the radiating bands from the costal joints and longitudinal fibres before and behind. When the body has become one piece it is separated from the manubrium by the persisting cartilaginous strip. The i6o HUMA\ ANATOiMY. streiK^theiMiig bands require no fuurther desoriptiionL A cavity b <^teii femnd in the cartilage making' a tvpical lialf-ji>int- At what tinBe it appears is urnkmowinL Stwne- tim€s it is so developed tfaat tbe joint e piacsicallly a tree one, with articiilar carti- lage : rhr? ejcceptioiiKtl anrat^jement s more ODamnon in vcwncai than in men. beii^ especiaHv adapted tO' the ietnale type <^ resfHtaticMi. The cartil^e pei^stxi^ b^nsreen bodv and ensifonna is strei^thened in a aimillar manner. A cavity rarely occurs in the caiitilage, vhich, on the coQtiaiy, ctften ondei^^oes osstiication. THE COSTO-STERXAL JOIXTSl r The first costal cartilag;e joins directly, without intenuptiion. the latesal escpan- sion of the stenium ; the foMowing^ costal cartilages articulate at the points already mentioned br sj"iio^"ial joints. Tbose that come between different steraehraB — that is, from the second to the fifth — olteni have the joint subdivided by a band mto an upper and a lower halL ThB k uBnal in the joint of the second cartilage ; jwogies- siv^v rare as we descend. The sixth and seventh caitulages frequently have no true jmnt.'' Each of these joints is eadosed by a capenle, the front and badk: fibres of which radiate over die stermniim. THE ESTERCHOXDRAL JOEVTS. The seventh, ^^th, nimrh, and tenth costal cartilages have each an articnlatioD bf a true jrant on the projections above described with the one above it^ There is a connection b^ween the fifth and sixth cartilages ; usoally on the r^;fat, very frequently on the l^L^ Ths is, as a rule, also a tine jmnt, but the cartilages may be merdy bonnd together by bands of fibres The joint on the r%;ht side e almost always a tnie one. The ends of the eighth, ninth, and tenth cartilages are joined by fibrous bEsoe to the cartilage above. The costo-xiphoid ligament is a band extendii^ from either side ol the base of the ensifoon to the lower border and, perfaa^is, the frtrnt viaI capsule and are separated by an imiaraartiada.r UgawKid^ a band rannii^ from die ri^e on the head of die rib to die postetioir part of die inter- vertebral dkk. In die foetus b^oire term it extends across the faadk of die disk to die head of the opposite rib. The front of the capsules is strengthened by the amlerm- aubxxrtetral ligmmiemi,'' which is a series of ratfiatii^ fibres from die head to both veitebne and the interven- ii^ disk, not clearly separable into three bands. These stdlmle Kgmmiemts (F%. 1S4) are least developed in the tqiper part of the thorax. The stroi^^ist ooDectioa of fibres is to die lower vertefata. The joint of the first and last two ribs e not sob- dBvided ; that of the tenth is uncertain. StrcM^ fibaes pass from the head of die first rib to die sevendi cervical vertdxa. Few or no fibres frooi the last rib teach die body of die deventh thocadc. The lower fibres are made tense when the rib is raised arid the upper when it k depressed. The Costo-Transverse Joints. — The articnlar amiiaces of the tubsdes, 'HbEgrove: Journal of Anatnmf and Fbisiolog;, voL xxvS., 1S93. -Faacett: AnaL .^me^er. Bd. x«. Baidfddien : Biid. COSTO-TRANSVERSE ARTICULATIONS. i6i convex vertically, are received into the hollows on the facets of the transverse pro- cesses. The cavities are deepest in the upper part of the thoracic region, but the facet on the first transverse process is nearly plane. In the lower part of the region Fig 184 Posterior costo-trans- verse ligament Upper part of stellate Lower part of same Ligaments uniting ribs with spine, from before. these cavities are smaller and less concave, allowing freer motion. There is none for the twelfth rib, and but a poor one, if any, for the eleventh. There are three costo-transverse ligaments : the posterior^ the middle^ and the superior. The pos- FiG. 1S5. Transverse process Posterior costo- Lamina of vertebra above of vertebra below transverse ligament Middle costo- transverse liga- ment Middle costo-trans- ligament Intervertebral disk Transverse section through terior^ are strong bands running outward from the tips of the transverse processes to the rough part of the tubercle beyond the joint. The fuiddle'' are strong short tibres connecting the front of the trans\'erse process and the back of the neck of the ^ Lig. costotransversariam posterins. - Lig. colli costae. l62 HUMAN ANATOMY. rib between the head and the tubercle. Those for the last two ribs are small, that for the twelfth springing from the accessory tubercle. The superior costo-transverse ligaments ' are thin bands, passing downward and a litde inward from the under side of the transverse processes to the crest on the upper edge of the neck o^ the rib below. Those of the first and last two ribs are of little account. This band becomes tense when the rib is depressed and carried inward ; the inner fibres are tense when the rib is raised. The outer fibres fuse with the front surface of the posterior inter- costal aponeurosis. Weaker and inconstant bands of the same general direction are described behind these. The fibres of the aponeurosis are particularly strong between the last two ribs. A special band of the same series runs from the transverse process of the first lumbar upward and outward to the last rib. The movements of the ribs are described with those of the thorax (page 165J. THE THORAX AS A WHOLE. The thora.x is a cage with movable walls capable of expansion. In shape it is an irregular truncated cone, much deeper behind than in front and broader from side to side than from before backward. The thoracic vertebrae form the posterior VII thoracic rib Intertransverse ligament Ligaments uniting ribs with spine, from behind. boundary ; the sternum, including the verv beginning of the ensiform cartilage, the anterior. The inlet, or upper boundary, is an imaginary plane slanting downward and forward from the top of the first thoracic \'ertebra to that of the sternum, and bounded laterally by the inner borders of the first rib. The inferior boundary, made by the diaphragm, does not exist in the skeleton. SufSce it to say that the dome- like disposition of the diaphragm makes the abdomen much larger and the thorax much smaller than one would expect from the skeleton alone. The thorax of the living presents a fairlv well-defined posterior surface, while the lateral ones pass in- sensibly into the anterior : the upper part is hidden bv the shoulder-girdle and arm. The line of the angles of the ribs marks the limits of the back and sides. The inside of the thora.x is heart-shaped in horizontal section. The spine projects into it behind, and the ribs recede from this on either side. As the bodies of the vertebra are larger in the lower part, the projection into the thorax is greater ; but as the area of the section is much larger, the effect is less striking. The distance from front to THE THORAX AS A WHOLE. 163 back in the median line is least at the top. It increases at once, owing to the back- ward bend of the spine and the forward slant of the sternum, reaching the maxi- mum at about the middle of the thorax. It decreases slightly below, owing to the forward sweep of the spine, but the position of the lower end of the sternum is so uncertain that this is very variable. The breadth of the thorax increases very rapidly, reaching nearly the maximum where the third rib crosses the axillary line. Below this it increases a little, being greatest where the fifth rib crosses the same The bony thorax, lateral line. It then continues very nearly the same with some slight diminution below. The greatest length of the thoracic framework is in the axillary line, the lowest point being the cartilage of the tenth or eleventh rib, which in the male may nearly reach the crest of the ilium. The downward slant of the ribs and the rise of most of the cartilages make the study of horizontal sections at first very confusing. The relations at certain levels must be somewhat conventional, for the variations are very great, depending on figure, age, health, position, and the stage of the respiratory movements. Two levels must be taken as standards, subject to these corrections. 164 HUMAN ANATOMY. The top of the sternum is on a level with the disk between the second and third thoracic vertebrse ; the junction of manubrium and body of sternum is on a level Fig. 18S. Fig. 189. •0 a \ a 0' ^ ; section at level of < {Braun, ighth thoracic vertebra. Transverse section through thorax at level of third thoracic vertebra. {Braitne.) with the top of the fifth thoracic vertebra. Less accurate, but still useful, is a third level : the lower end of the body of the sternum is opposite the ninth thoracic vertebra. Accompanying diagrams, Fig. 190. taken from Braune, show the varia- Q ) tions of size, form, and relations at different levels (Figs. 188 to 191). The breadth of the intercostal spaces is very different in diverse parts. Between the tubercles and angles it is pretty nearly the same throughout, but the last two spaces are a little broader. The first two spaces are much the broader at the sides and in front. They are broad near the sternum as far down as the fifth cartilage. At the sides the ribs are very close together, from the fourth to the ninth often almost in contact. The lowest spaces are again broader. The Thorax in Infancy and Childhood. — At birth the thorax is relatively insignificant. The sternum is small and undeveloped in the lower part. The ribs are more horizontal. The top of the sternum is opposite the body Fig. 191. of the first thoracic vertebra. In 7 ■ ^ the course of the first year it lies am^ * ^^ opposite the upper part of the second, and at five or si.x has reached its definite level opposite the disk between the second and third thoracic vertebrse. The lower part of the sternum is undeveloped, and the ribs do not fall so low at the sides. The want of breadth is very striking, while in the adult, throughout the chest below the level of the second costal cartilage, the antero-posterior diameter is to the transverse as i to 2}4, or as I to 3 ; at birth it is as 2 to 3. We have found it at probably three vears as i to 2 ; at five or six the thorax has nearly reached its permanent ^ ^ <=i7 ^' /' iverse section at level of eleventh vertebra (6, 7) are sections of costal cartilages. Shaded areas (BrauM.) shape Differences due to Sex. — The whole structure is lighter in women, but the MOVEMENTS OF THE THORAX. 165 chief differences in the proportions appear below the third rib. The manubrium is as large, relatively to the height, in one sex as the other, although the mesosternum in women, especially its lower part, is less developed ; hence the ends of the car- tilages of the lower sternal ribs are crowded together, and those of the seventh often meet below the sternum, in front of the ensiform, thus practically lengthening the body. The effect of this is that the relations of the viscera to the walls are not so different in the sexes as one would expect'.' The floating ribs are small in women and do not approach the pelvis so closely as in the male. The antero-posterior diameter of the female chest is to the transverse as i to 2^ (subject to variation), thus more resembling the proportions of the child. THE MOVEMENTS OF THE THORAX. The motions permitted by the following joints are to be considered separately, although their interdependence is to be remembered. First, the joints of the verte- bral ends of the ribs, the costo-central and the costo-transverse being taken together ; second, those between the manubrium and gladiolus ; third, the costo-sternal and interchondral joints ; fourth, as modifying these, flexion and extension of the spine ; and fifth, the elasticity of the ribs and cartilages. Motions in the Costo-Vertebral Joints. — These vary greatly in different parts of the column. The first rib moves as a hinge on a fixed axis running out- ward, backward, and a little upward through the joint on the body of the verte- bra and that on the transverse process. If this axis were strictly transverse, the rising of the front of the rib would increase only the antero-posterior diameter of the thorax, as the motion occurs in a plane at right angles to the axis. Since, however, the axis is oblique, a plane at right angles to it extends forward and outward, and motion in it thus increases also the transverse diameter of the chest. The shape of the first rib is such that this transverse increase amounts to httle or nothing, but this principle comes into play with the longer ribs. The joint of the second rib is prac- tically similar, except that the outer end of the axis at the tubercle is farther back, so that the plane of motion slants more outward and the lateral expansion g-ained by raising the second rib is more marked independently of the greater length of that rib. With the third rib, usually, an important modification begins ; the outer end of the axis is not fixed, for the tubercle slides on the transverse process. The changes in the facets on the transverse processes have been described ; it appears that, as we descend the spine, they are so placed and so shaped as to allow this movement more and more freely. Thus, in the middle of the thoracic region the outer end of the axis of rotation is so movable that the motion is to be decomposed into two, — namely, one on the axis already described through the head and the tubercle, and another on an antero-posterior axis passing through the head of the rib and the joint between its costal cartilage and the sternum. At the eighth rib of the dissected spine a new motion appears, which becomes much more extensive in the succeeding ones. The ligaments connecting the tubercle and neck to the transverse process are less tense, and it is possible to move the tubercle a little forward from its socket ; in the lower joints the rib can be moved upward, down- ward, forward and backward, and circumducted. These motions are particu- larly free at the last two thoracic vertebrae. Motion backward is checked by contact with the transverse process ; forward, by the posterior and middle costo- transverse ligaments ; upward motion of the last two ribs by the particularly strong bands of fascial origin described with the ligaments ; downward motion by the in- tercostal structures. An important deduction from this is that the last ribs can be pulled downward and backward, so as to fix the posterior costal origin of the diaphragm. Motions in the Intersternal Joints. — The joint between the manubrium and the body of the sternum admits of motion on a transverse axis, which is free in the young, but much restricted or abolished in the old. At rest, the two parts form a slight angle open behind. This is effaced by the forward motion of the body on ' Henke : Arch, fur Anat. u. Phys., Anat. Abtheil, 1883. i66 HUMAN ANATOMY. the manubrium, but in no case is an entering angle formed in front. A slight twisting may also occur in this joint in the young. .In these motions the second costal cartilages follow the manubrium. The motions at the inconstant joint between the sternal body and the ensiform process are necessarily indefinite ; they appear to consist chiefly of a drawing in of the ensiform. Motions in the Costo-Sternal and the Interchondral Joints. — On the dissected preparation the second cartilage can be moved up and down, forward and backward, and circumducted ; these motions, however, are very slight. In the succeeding joints the same motions are more and more free as we descend. The lower cartilages of the true ribs from the fifth to the seventh, or to the eighth, inclu- sive, should the latter meet the sternum, move in a somewhat similar manner, but nearly as in one piece. The motion on an antero-posterior axis is most free. The joints between the costal cartilages are very lax, and the surfaces are so placed that the lower one slides forward on the upper. The advantage of these joints is that the lower ribs and the thorax give and receive support, while greater freedom of motion is possible than would be the case were they of one piece. Flexion and extension of the spine modify these motions. The more the spine is flexed the more the upper ribs in particular are depressed, and the more it is extended the more they are raised, independendy of any motion in the joints. Thus, when the chest is fully inflated the spine is always strongly extended. The elasticity of the ribs and cartilages, particularly of the latter, exercises an important, but indefinite, influence on all motions which does not admit of accurate analysis. Even the ribs (except in the old) are not rigid bars, and, especially in forced inspiration, there is a pull upon them increasing their convexity. Moreover, the walls of the chest adapt themselves to the surface of the lungs and to abnormal contents of the thorax, so that certain conditions are marked by particular forms of thorax. It follows from the above that the nature of the respiratory movements cannot be deduced solely from the movements of each set of joints considered separately. The soft parts connecting them alone modify greatly the freedom of motion. Braune has shown that the motion of the ribs is much limited by the sternum, and that if the gladiolus be divided into its original pieces and the cartilage above it cut through, the thorax can be more fully inflated. Beyond question in forced inspiration the sternum is raised, thus increasing the antero-posterior diameter ; since the ribs at the same time swing upward and outward, the transverse diameter is likewise increased. Surface Anatomy. — The sternum is always to be felt in the middle line. The suprasternal notch is filled up to a large extent by the interclavicular ligament. The angle between the manubrium and the body varies considerably, but it is always easily recognized by a cross-ridge. The ensiform cartilage is at a deeper level and overhung on each side by the costal arch. The front of the chest on each side is covered by the pectoralis major, making it hard to feel the ribs, except at the borders of the sternum. At the side they are easily felt to near the top of the axilla, where the third can be recognized. The upper ribs are concealed by thick muscles, especially between the spine and the angles. The scapula covers them from the second to the seventh, with considerable variations. The first rib cannot be felt except where its cartilage joins the sternum. To count the ribs, begin with the second at the junction of the manubrium and body of the sternum. There is no possibility of error, for the rare cases of .the manubrium reaching to the third cartilage may be disregarded ; feel the third and fourth cartilages below it, and then carry the finger downward and out- ward across the chest. The twelfth rib may be too small to be made out. It is not safe to begin counting from below, for the error of mistaking the eleventh rib for the twelfth has led to opening the pleural cavity in an operation in the lumbar region. The nipple is said to be usually over the fourth intercostal space some two centimetres external to the cartilage, but it is very variable, especially in women, and should never be used as a starting-point for counting the ribs. The width of the intercostal spaces at different parts is of obvious importance, but has been described elsewhere (page 164). PRACTICAL CONSIDERATIONS : THE THORAX. 167 PRACTICAL CONSIDERATIONS. The bony and cartilaginous thorax is made up of the ribs, sternum, costal car- tilages, and thoracic vertebrae, and varies in shape as a result of several influences. The slightly larger circumference of the right side of the chest as compared with the left side is probably due to the greater use of the right upper limb, and may be accepted as physiological. Increased circumference of the left side, therefore (in a right-handed person), should indicate careful examination of the spine (for lateral curvature) and of the thoracic viscera. \vi pigeon-breast the sternum protrudes together with the costal cartilages, while the line of the costo-chondral junction becomes a deep groove. The sides of the chest are flattened, and a transverse section would be almost triangular in shape. There are three modes of production of this very common deformity : 1. In rickety children it is favored by the softening of the bones and cartilages, which are thus of diminished resiliency, the actual exciting cause being often some form of respiratory obstruction, — e.g., enlarged pharyngeal and faucial tonsils, bronchitis, nasal obstructions, etc. In ordinary breathing, on inspiration, air enters the chest freely to prevent the production of a vacuum, and at the end of the act the external atmospheric pressure is balanced by the pressure within. If an impedi- ment to the free ingress of air exists, the external pressure during at least part of the act is in excess, and in young children, particularly rickety children, this is followed by the bending inward along the weakest part of the thorax (the costo- chondral line) and the relative projection of the sternum. 2. The lowest five costal cartilages form an especially weak portion of the chest- wall. They are the most distant from the fulcrum (the spine) on which the ribs move in respiration, and hence the expansive forces act with the greatest disadvan- tage of leverage (Humphry). At the same time the diaphragm, during its contrac- tion, tends to draw them inward. If, however, its central arch cannot descend during inspiration on account of an engorged liver, enlarged abdominal lymphatics, persistent flatulence, etc. (as in a poorly nourished child), it becomes the fixed point, and the lateral walls are pulled in and the sternum correspondingly protruded. 3. Some cases of "pigeon-breast" are seen at, or soon after birth in otherwise healthy children. It is probable that these are cases of arrest of development. The so-called "keeled chest " (in which the antero-posterior diameter is increased at the expense of the transverse diameter) is characteristic of the quadrupedal class of mammals, and is necessitated by, and correlated with, the backward and forward swing of the anterior limbs in walking.^ In the foetus the antero-posterior diameter is relatively greater than in the adult. Attention has already been called (page 164) to the varying ratio between the antero-posterior and transverse diameters of the chest, the transverse diameter in the adult exceeding the anterior in the proportion of 2.5 to i. If this change stops short of full completion, a greater or less degree of relative prominence of the ster- num results. The " bellows chest "Ms found among mammals almost exclusively in the bats, the anthropoid apes, and man, that have in common simply the disuse of the anterior limbs as a means of support. In them the chief movements of these limbs tend to pull the sternum towards the vertebral column. The exaggeration of this type results in the so-called "flat chest," which is, however, within proper limits, the type of vigor, as it results from the full contraction of normal muscles. Emphysema produces a rotund configuration of the chest-walls, affecting chiefly the upper portion, throwing out the ribs, effacing the intercostal spaces, and making the thorax "barrel-shaped." Old age, owing to an increased bowing of the thoracic spine under the weight of the head and shoulders and to a slipping forward of the shoulder-girdle with its mass of muscles, often causes a depression of the sternum and its approximation to the spine, — a common form of flat chest. ' Woods Hutchinson : Journal of the American Medical Association, vol. xxix., 1897. ' Ibid. i68 HUMAN ANATOMY. The pulmonary capacity is but roughly indicated by the circumference of the chest, as the vertical diameter is also obviously an important determining factor. Chest measurements, to be of value, should therefore be supplemented by investiga- tion into the amount of air which can be inhaled and exhaled. The resulting information is often of great value as a basis for prognosis and for advice as to exer- cise and hygiene, especially in persons with a predisposition to pulmonary disease. In the infant the thorax is relatively smaller than in the adult. In the female the upper portion of the thorax is less compressed from before backward and is more capacious than in the male. The upper aperture is larger and the range of movement between the upper ribs and the sternum and vertebrae is greater. These circumstances account both for the fulness of the upper portion of the chest in the female and for the character of the respirator}' movement, which is known as thoracic ; while that of the male, in which the lower ribs and abdominal walls move more freely, is known as the abdominal type of respiration. The sternum may be entirely wanting, or may be divided into two portions by a fissure down the middle, the result of developmental failure, which, when it exposes the thoracic cavity and the heart, is known as ectopia cordis. Its subcutaneous position makes it the subject of slight but frequent traumatisms, which often serve to localize the bone lesions of syphilis, tuberculosis, and other infections ; and this fact, in conjunction with its cancellous structure, accounts for the frequency with which it is the seat of gummatous periostitis and tuberculous caries. There are sometimes little circular defects in the body of the sternum, through which an abscess may pass from the mediastinum outward, or infections from without may find their way within the thorax. They are congenital defects due to a failure of the two halves of the body of the sternum to unite. The seven depressions on each side of the sternum for the reception of the cartilages of the seven true ribs are so shaped that the upper and anterior edges of each notch are more prominent and larger than the lower and posterior edges. This accounts for the rarity of luxation forward of these cartilages and their ribs by the forces which so constantly pull the ribs upward and forward, as the action of the scaleni and intercostals in violent inspiratory efforts, that of the pectorals in swinging by the hands or on parallel bars, etc. Backward dislocation at the chondro-sternal junction is even rarer ; but this is because, owing to the elastic curves of the ribs, the sternum and the anterior extremities of the ribs move backward together on the application of direct force to the front of the chest. As it is thus movable, and is supported on the ends of elastic levers or springs, the sternum is rarely fractured. When the fracture is the result of indirect violence, it is often associated with injuries to the spine, as the extreme extension or extreme fle.xion, which is the common cause of a sternal fracture, must necessarily put a severe strain on the thoracic spine. In extension the sternum is fixed between the sterno-mastoids and sterno- hyoids and thyroids above and the recti and diaphragm below. In flexion the force may be transmitted through the chin. In either case the most common seat of fracture is at or about on a line with the second costal cartilage, because (a) the bone there is narrowest (Fig. 173), and {b') at that le\-el lies the junction between the manubrium and body. As the various portions of the bone are not united until about twenty years of age, fracture is almost unknown before that time. Moreover, during that period the symphj-sis between the manubrium and the body is so shaped that, together with the natural curve forward of the bone, it increases the elasticity of the sternum and enables it to resist both direct violence and tensile strain. The projection' at the union between the manubrium and body {angidiis Ludovici) is sometimes exceptionally prominent, and when this is noticed for the first time after an accident or an illness, may give rise to the erroneous diagnosis of fracture or of bone disease. This angle is increased in phthisis, owing to the reces- sion of the manubrium ; it is increased in emphysema, as the second ribs carry for- ward the lower border of the manubrium. The greater thickness and strength of the layer of fibrous tissue that covers ^ Angulus sterni. PRACTICAL CONSIDERATIONS : THE THORAX. 169 the posterior surface of the sternum, as compared with that on the anterior surface, account for the rarity with which effusions of blood or collections of purulent fluid find their way to the anterior mediastinum. The ribs, in addition to the already described classification into stejjial, astertial, and Jioating, are sometimes designated as 2ipper and lower. It may be well to mention that the term " upper" includes the first six ribs, which have convex lower borders, give origin to the pectoralis major (an elevator of the ribs), and move upward in inspiration ; while the term "lower" applies to the last si.x ribs, which have concave lower borders, give origin to the diaphragm (a depressor of the ribs), and move downward in inspiration. The obliquity of the ribs adds greatly to their range of movement in respiration. The most oblique rib, the longest, and the most movable — the seventh — is a part of the wall of that portion of the thorax that contains the largest amount of pulmo- nary tissue. The most fixed and most nearly horizontal of the ribs (and the shortest of the sternal ribs) — the first — is a part of the wall where the least lung tissue is to be found. The ribs below the eighth have less and less relation to the lungs, and become both shorter and more horizontal. They have increased mobility as regards their anterior ends, but lessened rotation on a line drawn between their two extrem- ities, the movement most important in respiration. These facts have relation to the distribution of acute and chronic disease in the lungs : the acute affecting particularly the area of greatest movement and vas- cularity, the bases ; the chronic, the area of lessened mobility and expansion, the apices. The involuntary partial immobilization of the chest-wall after injury and in inflammatory affections of the pleura is of some diagnostic value, as is also the permanent restriction of its movements following the contraction of old adhesions, as after a pleurisy, or pleuro-pneumonia, or fibroid phthisis. The obliquity of the ribs serves also the purpose of securing the necessary expansion of the chest with the least possible motion in the joints between the ribs and the spine and between the cartilages and the sternum. They are thus but little liable to strain, and, in spite of their unceasing movement during life, are very rarely the seat of either dislocation or disease. At the articulation of the ribs with the spine the provision for preventing the ascent of the ribs during the action of the inspiratory muscles (similar to that at the costo-sternal junction) is seen in the fact that the articulating surface of the upper vertebra entering into the joint stands out more boldly than that of the lower one. The participation of the intervertebral disks in the costo-vertebral articulation gives greater safety to those joints and adds to the elasticity of the whole thorax by furnishing a resilient buffer which takes up and distributes forces directed against the chest-wall. Variation in the development of the costal element of the seventh cervical vertebra (page 129) may result in the production of a cervical rib. This, growing beyond its ordinary limits, sometimes reaches half-way to the sternum, running parallel to the first rib, with which its anterior end is sometimes joined. Occasion- ally a process grows up from the first rib to meet it. This, or the cervical rib itself, may raise the subclavian artery and give rise to a mistaken diagnosis of aneurism, or may be thought to indicate chronic (tuberculous or syphilitic) infection of bone, and lead to unnecessary operation or treatment. As a result of rickets, changes often take place at the chondro-costal junctions, causing beaded ribs when a few bones only are afiected, or the "rickety rosary" when the enlargements are bilateral and numerous. The ribs most frequently broken are the sixth, seventh, and eighth ; the first and second are protected by the clavicle ; the lower two by their small size and great mobility. The most common form of muscular action causing fracture is coughing ; sneezing and lifting heavy weights have had the same effect. The lower ribs are most frequently broken in this way. When the first rib is broken, a character- istic symptom is said to be pain behind the upper part of the sternum on lifting with the hand on the injured side. This may be due to the fact that the first thoracic nerve lies for about two inches in contact with the under surface of the first lyo HUMAN ANATOMY. rib, and ends at or near the region mentioned, pain being often referred to the peripheral ends of sensory nerves. In fractures by indirect violence (when the sternum and spine are forced together), the theoretical point of fracture would be at or about the summit of the arch ; but practically it is often found very near the point at which the force is apt to be received, — i.e., an inch or two outside of the sternal extremity. Unless the force has been great, there is but little displacement in fracture of a rib, owing to the splinting of the bone between the two sets of intercostal muscles above and below it. Shortening is absent, unless an extensive crush of the whole side of the chest has occurred, because the two ends of the bone are fixed, and because of the unbroken bones above and below the fractured one. The complica- tions are those obviously due to the pro.ximity of the pleura and lung on the inner surface of the fracture, the common results of wounds of those structures being various degrees of haemothorax, or pneumothorax, or sometimes (by valvular action) emphysema of the cellular tissue of the trunk (.page 1865J. Broken ribs always unite with a considerable amount of ensheathing or pro- visional callus, due to the motion which to some degree must be present between the fragments during the process of union. Rupture of an intercostal artery (unless associated with a wound of the pleura) is not usually a serious complication ; but occasionally it is necessary to arrest hemorrhage from this vessel. It lies between the inner and outer intercostal muscles in the groove running along the lower part of the inner surface of each rib. The collateral branch runs near the upper surface of the ribs. Midway between the ribs is, therefore, the safest place to introduce a trocar or to make an incision in opening the chest. The intercostal spaces are wider in the antero-lateral parts of the chest than they are more posteriorly, especially in the neighborhood of the seventh rib ; they are narrowest in close proximity to the sternum and spine. They can be widened by bending the body to the opposite side. For paracentesis of the thorax the centre of the sixth or seventh space should be selected in the mid-axillary line. The lower spaces are in too close pro.ximity to the diaphragm, especially on the right side. More anteriorly it is also in danger ; farther posteriorly the intercostal artery ( which runs more horizontally than the ribs) crosses the space obliquely, and behind the angles the ribs are covered by the thick muscles of the back. The ribs are frequently subject to infectious disease. Syphilis and tubercu- losis often produce periostitis or caries, and they are more often the seat of post- typhoidal osteitis than any other bones of the skeleton. This is due to their subcutaneous position exposing them to frequent traumatisms and to the similar effects produced by the numerous strains through muscular action in coughing and sneezing and in lifting or straining. Pus is very apt to travel along the loose connective tissue between the two planes of intercostal muscles, and it is therefore unusual to find suppurative disease confined to one rib, or even to the immediate vicinity of its point of origin. No instance of traumatic separation of the epiphysis of either the head or the tuberosity of a rib has been recorded. The internal mammary artery runs from above downward beneath the cartilages about half an inch from the sternum. Landmarks. — The oblique elevations formed by the ribs can usually be seen extending downward from the axillary region. The upper ribs are covered by the great pectoral, but beneath its lower border the ribs from the sixth to the tenth can often be seen. The lower border of the great pectoral follows the direction of the fifth costal cartilage. The curved arch of the costal cartilages is frequently plainly visible, and is accentuated during forced expiration and when a superincumbent weight is held up by the trunk and arms. In short persons the arch is commonly flatter than in tall ones. In counting the ribs it is well to begin with the second, which is easily identified by its relation to the ridge between the manubrium and body of the sternum. The nipple is usually over the fourth intercostal space, somewhat less than 2.5 PRACTICAL CONSIDERATIONS: THE THORAX. 171 centimetres (one inch) external to the costo-chondral junction, or about ten centi- metres (four inches) from the middle line. Its position is variable, and is much lower in fat persons, especially females. In emphysema the nipple may remain stationary, while the upper ribs ascend, and it may be opposite the fifth, sixth, seventh, or even the eighth rib. In phthisis with a shallow depressed chest it may be opposite the fourth rib. A line drawn horizontally from the nipple around the chest is on a level with the sixth intercostal space at the mid-axillary line. A horizontal line around the trunk on the level of the angle of the scapula (the arms hanging down) would traverse the sternum between the fourth and fifth ribs, the fifth rib at the nipple line, and the ninth rib at the vertebral column (Treves). The sternum is subcutaneous in the groove between the pectoral muscles. Near the upper third the ridge between the manubrium and body may be seen or felt. It is on a level with the second costal cartilage. This cartilage projects for- ward more than the others. As the origins of the pectoral muscles diverge the sternal groove becomes broader. It ends at the lower portion of the body of the sternum in a slight projection usually seen and easily felt. This marks the upper limit of the " infrasternal depression" {epigastric fossa, scrobiculus cordis), the floor of which is over the ensiform process, and which is bounded laterally by the seventh costal cartilages and inferiorly by the upper ends of the recti muscles. In many abdominal diseases, and sometimes after laparotomies, the obliteration of this depression (by the occurrence of tympany) is an important clinical symptom. When the arm is raised, the highest visible digitation of the serratus corre- sponds to the fifth rib ; the largest is that attached to the sixth rib. During expiration the upper end of the sternum is on a level with the second dorsal intervertebral disk ; the line between the manubrium and body is on a level with the fifth thoracic vertebra ; the junction of the sternal body and the ensiform process is opposite the lower part of the ninth thoracic vertebra. The eleventh and twelfth ribs can be felt as blunt bony proiections directed downward and outward just outside the erector spinae muscles. ■ (The relations of the various thoracic viscera to the chest-wall will be con- sidered in connection with the anatomy of the former. ) THE SKULL The head consists of the cranium and the face. The former is the brain-case ; the latter is chiefly concerned in forming the jaws. The head also contains the terminal organs of four special senses. That of hearing is entirely inside one of the cranial bones, while the organs of sight and of smell lie in cavities formed partly by cranial and partly by facial bones. The special organ of taste, a part of the surface of the tongue, is in the mouth, bounded wholly by facial bones. Thus, while the cranial bones have a share in forming the face, no facial bone has an}' part in forming the brain-case. The latter is an egg-shaped cavity which communicates by a large opening — the foramen magnum — with the spinal canal, through which the spinal cord passes down from the brain. The brain-case has many smaller openings in the base, through which nerves escape both to the face and to a large part of the body and blood-vessels pass for the nutrition of the brain and its membranes and the walls of the skull. As the bones of the head can be separated in a young subject, it is customary to describe every bone by itself. It is too often forgotten that this knowledge is merely a means to an end, — namely, the understanding of the skull as a whole. In the following account this end is kept constantly in view. THE CRANIUM. The cranial cavity is formed by eight bones : the occipital, the sphenoid, the two temporals, the etk?noid, ihe/rotital, and the Iwo parietals. The cranium consists of the vault and the base. The vault is formed by \.he parietals, the greater part of the frontal, and a part of the sphenoid, of the temporals, and of the occipital. The base of the cranium is divided into three fossae extending across the skull. The posterior fossa is the lowest ; it opens by the foramen magnum into the spinal canal, and contains the cerebellum, the medulla, and the pons. The middle one is narrow at the centre and expands laterally into the temporal regions. The anterior is the highest, lying above the orbits and the nose. The anterior fossa transmits the olfactory nerves, the middle the optic, the posterior the auditory and the glosso- pharyngeal, the nerve of taste. THE OCCIPITAL BONE. The occipital bone' is divided for description into an anterior part, the basilar; two lateral ones, the condylar ; and a posterior one, the tabular or squamous poHion. These correspond to the basi-occipital, the exoccipital, and the supra-occipital of comparative anatomy. They all develop from separate centres and bound the foiamen magnum,'' a nearly circular opening, transmitting the spinal cord with its enveloping membranes. The spinal accessory nerves and the vertebral arteries ascend within the latter from the cavity of the spine to that of the cranium. The basilar portion ' bounding the foramen magnum in front is originally rough anteriorly, but shortly after puberty it coossifles with the bodv of the sphenoid. Its superior surface is smooth and concave and supports the medulla oblongata. Just internal to the edges is a ver\' shallow groove for the inferior petrosal sinus. The inferior surface is smooth for about one centimetre in front of the foramen magnum, and rough in front of this for the rectus capitis anticus major and minor. In the mid- dle line at the junction of the rough and smooth surfaces is the pharyngeal tubercle,* Very rarely this aspect presents a depression, the pharyngeal fossa. Sometimes there is a facet near the edge of the foramen for the anterior arch of the atlas. Also, there may be a tubercle on the posterior part of the basilar portion against which the odontoid process may rest, called the third condyle. Laterally, the basilar portion ^ Os occipitale. ^ Foramen occipitale magaum. -^ Pars basilaris. ^Tnbercnlnm pharyngeom. 172 THE OCCIPITAL BONE. is separated by a suture, the pefro-occipital, containing cartilage, from the petrous portion of the temporal. Each condylar portion ' (exocdpitai') presents on the inferior surface an oval articular swelling, the condyle, which rests in the hollow on the atlas. They are placed on each side of the front half of the foramen magnum. The hind ends reach almost precisely to the middle of the aperture, and anteriorly they extend to the line of the anterior border, their long axes converging in front. The articular surface, which is convex in the line of the long axis, faces downward and outward. The curve it presents varies greatly. In some cases it is nearly regular, in others the front and back halves almost meet at an angle. There is usually a constriction of the articular surface at the middle, where it may be crossed by a groove or a ridge. On the thick inner border of each condyle is a tubercle for the odontoid ligament. Behind the. condyle is a fossa, into which usually opens the inconstant posterior condyloid fora- men,'' transmitting a vein. In front of the base of the condyle at its outer border is the constant atitei'ior condyloid forajne^i,^ the termination of a canal, from five to ten millimetres long, which pierces the bone above the condyle and transmits the hypo- FiG. 192. Highest curved line' Superior curved line Inferior curved line E^.ternal occipital protuberance Occipitahs Sterno-niastoideus Jugular process Jugular notch Pharyngeal tubercle d>IoKi foramen, probe \ptt anUc minor consti ictor ipit antic major Occipital bone, external surface, from below. glossal nerve and, usually, a branch from the ascending pharyngeal artery and vein or veins. It is sometimes divided into two. The bone projects outward from the condyle as the jugular process,^ which is enlarged at its outer end where it coossities with the petrous portion of the temporal. This enlargement, moreover, extends downward as i\\Q paroccipital p>-ocess, which shows its greatest development in odd- toed ungulates. In man it is usually very small, but it may be large and, very rarely, join the atlas. The concave front of the jugular process and the bone extending forward on its inner side form the jugular notch,^ which bounds the posterior lacer- ated foramen '' behind and internally. This is completed by the temporal bone. A very small point, the anterior jugular process, marks the front of the foramen. A little behind this a larger though very delicate spine, the inti'ajugular process, reaches across, marking off a small anterior part of the jugular foramen for the passage of the ninth, tenth, and eleventh nerves from the larger one behind for the lateral sinus. Sometimes the front of the jugular process is a smooth surface bounded below by a ridge to which is attached the rectus capitis lateralis, and above by a short border marking off a fossa on the upper surface of the bone ; occasionally - Canalis coodyloideus. Caoalis bypoglo: 1 jugularis. " Incisara jugalar: 174 HUMAN ANATOMY. the latter ridge is wanting, the groove of the lateral sinus curving over the jugular process. The upper surface of the lateral portion of the process shows on its inner side the entrance of the anterior condyloid foramen, which is really a short canal. Above and anterior to this is a slight swelling, the jugular tubercle. The upper surface of the jugular process is marked by the termination of the groove of the lateral sinus, which curves round an upward projection of the process. In some cases, as just mentioned, the groove is depressed into a deep hollow. The inner opening of the posterior condyloid foramen, when present, is connected with the lateral sinus. The squamous portion ' forms the lower and back part of the skull. Below it contributes the posterior boundary of the foramen magnum and joins the e.xoccipitals. The lateral borders meet above at a sharp angle. These borders may be subdivided into a lower part, which ascends nearly vertically in articulation with the mastoid part of the temporal, and into a higher part, very serrated and joining the parietal. A slight angle lies on either side at the junction of these two divisions. Fig. 193. Internal occipital protuber- Jugular process' Jugular iiotLh'^ riroove for lateral sinus Jugular tubercle condyloid foramen, probe Occipital bone, internal surface, from before. The posterior surface is marked by a prominence, somewhat below the middle, tha, external oceipital protuberanee,- to which is attached the ligamentum nuchse. This tuberosity varies greatly in de\elopment. From it the superior curved line^ extends laterally to the above-mentioned angle. To this line are attached a series of muscles which form the contour of the back of the neck, chiefly the trapezius and part of the sterno-cleido-mastoid. A short and varying distance abo\e the supe- rior ridge is often seen the so-called highest curved line.^ It is usually very faint, and may curve down to the external occipital protuberance, or pass abo\ e it. The epicranial aponeurosis and part of the occipitalis spring from this line. The surface of the bone above the level of the protuberance is smooth ; below it is rather rough and irregular. The torus occipitalis transversus is an occasional prominence in- volving the protuberance and extending laterally along the superior cur\ed line. It sometimes involves the space between that line and the highest one. The upper border of the swelling may have a median concavity. In the mid-line a slight ridge, ^ Squamosa occipitalis, - Protuberantta occipitalis externa, ■* Linea nnchae superior, ^ Linea nucbae saprema. DEVELOPMENT OF THE OCCIPITAL BONE. 175 Superior median fissure the external occipital crest, ^ runs from the protuberance to the foramen magnum. Above the middle of this crest the infej-ior curved line'' leaves it to extend outward and downward to the border of the bone. The inner part of this line is rough, the outer indistinct. Below this line there is usually a depression on either side of the crest. The internal surface of the squamous portion is divided into four depressions or fosses ; the upper two lodge the occipital lobes of the cerebrum and the lower two the lateral lobes of the cerebellum. Below the middle is the internal occipital pro- tuberance^^ approximately opposite to the outer. A ridge runs from the apex of the bone to the protuberance, and is continued as the internal occipital crest* to the foramen magnum. Very often the second part of this ridge divides shortly after its origin, so as to enclose a depression, the vermian fossa, so called because it is below the middle lobe, or vermis, of the cerebellum. A ridge runs transversely from the protuberance to the lateral angle of the bone. The superior vertical ridge may be grooved for the superior longitudinal sinus and the transverse ridge for the lateral sinus. More efrequently the longitudinal sinus lies to one side of the vertical ridge and is continued into one of the lateral ones, much larger than its fellow, and usually the right, which lies above the transverse ridge, and shows in Fig. 194. the bone no communication with the smaller, which lies in or above the other ridge. There are many variations in this arrangement, of which the rarest is a symmetrical course and division of the supe- rior groove. A single or a bifur- cated groove is sometimes found on the internal crest. Development. — Four cen- tres appearin the cartilage around the foramen magnum about the eighth week of fcetal life : one for the basilar, one for each exoccipi- tal, and one (or more probably a pair that speedily fuse) for the lower part of the squamous por- tion, \.\\& supra-occipital. A week or so later two nuclei appear in the membrane above the latter, from which a strip of bone de- velops which soon joins it. From this upper ossification, the stcpe- rior occipital, is developed all the upper part of the squamous por- tion, including the external occipital protuberance and the superior curved line." Occasionally still another nucleus appears on each side, anterior and external to the preceding, which probably accounts for certain separate ossifications often found in the lambdoidal suture. The squamous part shows a median cleft above, which quickly disappears, two lateral ones between the ossifications, which persist till birth, and a notch at the posterior border of the foramen magnum. The squa- mous portion joins the exoccipitals in the course of the second or third year. The latter begin to unite with the basilar a year or so later. None of these sutures, es- peciallv the latter, is completely closed before the seventh year, or even later. The front parts of the condyles are formed from the basilar, which joins the ex- occipitals at the anterior condyloid foramina. Separate ossifications, large Wofmian bones,'' are found in the suture between the squamous portion and the parietals. Sometimes there is a large median triangular one which is interpreted as the result of a want of union of the usual superior centre of the squamous portion, and said to 'Consult Stieda : Anatomische Hefte, iv., 1S92, and Debi^rre : Journ. de I'Anat. et de la Phys., 1895. "Exoccipital Posterior condyloid foramen at birth, from before. 1 onchae medians. "L. inferior. '^Protub. occip. interna. ''Crista occipitalis interna. *'Ossa saturarun 176 HUMAN ANATOMY. be the homologue of the interparietal bone. This interpretation is inconsistent with the history of ossification. Kerkring has described an occasional triangular minute piece of bone which appears during the fifth month in the notch at the back of the foramen magnum, and is fused before birth. We have specimens which imply that it is, or may be, originally double. Improved methods of investigation will prob- ably show that this' bone is not uncommon. The cerebral side of the basilar is fused with the sphenoid by seventeen ; the lower side unites later, probably before twenty. THE TEMPORAL BONE. The plan of the organ of hearing must be known to understand the temporal bone.' The external ear, besides the auricle, consists of a cartilaginous and bony tube, the external aitditorv meatus,^ \e&Am^ to the membrane of the tympanum which closes it. The middle ear, the cavity of the tympanum, is a space internal to the Fig. 195. squamous portion Supramastoid crest , Occipitalis Spina suprameatum- Splenius capitu ~v Squamo-mastoid sutu*-' - ■■ Auricularis posteriO' Tympa Masseter Anterior root of zygoma Glenoid fos=ia APEX OF PETROUS PORTION Glasenan fissure Trachflo MASTOID PORTION t-maatoid fissure Mastoid process External auditory meat TYMPANIC PORTION \'aginal process Slyln-glossus Stylohyoid Styloid process Right temporal brfno. external aspect. membrane, opening through the Eustachian tube into the throat, and communicating behind with cavities in the bone. It is lined with mucous membrane and is crossed by a chain of small bones, the ear ossicles, the embryological importance of which is explained elsewhere. The internal ear is a complicated system of cavities in the substance of the bone containing the organ of hearing connected with the brain by the auditory nerve, which leaves the bone through a canal, the internal auditory meatus. Development shows that the bone consists of the following three parts. TO The petro-mastoid, the petrous part of which is first found surrounding the special apparatus of the organ of hearing, constituting the internal ear, while the mastoid process is a much later outgrowth. (2) The tympanic portion, which nt birth is a ring, incomplete above, encloses the membrane of the tympanum as a frame holds a glass. This ring grows out later into a cylinder, still open above, which forms the external auditory meatus. Not all its growth, however, is outward, since a part ' Os tcmporalc. - Meatus acusticus exterous. THE TEMPORAL BONE. 177 expands forward and deeper than the original ring, making the front part of the tympanic plate, bounding the cavity of the tympanum and the Eustachian tube externally. The tympanic cavity, or the middle ear, lies between the petro-mastoid and the tympanic portion, the roof and floor being developed from the former. (3) The sq7i,amous portion is external and above. It forms a part of the side of the skull, the roof of the external meatus where the tympanic portion is deficient, the articulating surface for the jaw, and a part of the mastoid process. There is also the long, s\end&\- styloid process, which is a part of the hyoid bar of the second visceral arch of the embryo. It begins as an ossification of a distinct piece of cartilage, but joins the petro-mastoid. The following description is that of the adult bone. The Squamous Portion.' — Most of this is a thin vertical layer forming part of the wall of the skull, joined below by a horizontal one which forms a small part of the base of the skull, the articulating surface for the jaw, and the roof of the external Fig. 196. Eminentia articularis Eustachian tube Glenoid fossa. Postglenoid tubercle Fissure of Glaser Tympanic plate. External auditory, meatus' Carotid canal Semicircular canal Facial canal Groove for lateral sinus Horizontal section through right temporal bone, seen from below. auditory meatus. The edge of the vertical part is convex except below. The upper and posterior borders overlap the parietal bone by a broad bevelled surface. The anterior border joins the great wing of the sphenoid, overlapping above and over- lapped below, where it passes into the horizontal part. The posterior angle of the vertical portion sends downward the postauditory process, from which the upper part of the mastoid, including some of the mastoid cells, is developed. The sqiiamo- 7nastoid suture, separating this from the mastoid portion, is usually lost in the second year. When it persists, it shows that the anterior portion of the mastoid down to the lower border of the external meatus, or even lower, is formed from the squamosal, its surface is smoother than that of the mastoid proper. A small, particularly smooth, but inconstant patch situated on the level of the upper part of the meatus, one centimetre or more behind it, marks the position of the antrum. The thick- ness of the bone at this place, which is that of note-paper in the infant reaches 178 HUMAN ANATOMY. six millimetres in the adult. A small, sharp prominence, the spina sitprameatutn, 13 found just behind the upper part of the meatus. It is an important landmark in the surgery of the region. Just posterior to it is usually a minute venous foramen. The inner side of the squamous portion, besides the large bevelled articular surface, presents a smooth one, forming part of the wall and floor of the cranial cavity. This is separated from the petrous portion by the pctro-sqiiamous suture, which is closed early. Two grooves for branches of the middle meningeal artery diverge from its lower border, one running upward and the other backward. The front of the hori- zontal part forming the floor is rough and thick, joining the great wing of the sphenoid. The sygoinatic p)-ocess^ projects forward from the outer surface of the squamosal to complete the zygomatic arch with the malar, which it joins by a serrated end. The free part has an external and an internal surface, a rounded bor- der below and a sharp edge above. The latter, which receives the insertion of the temporal fascia, can be followed back to the origin of the process. The zygoma has two roots. The posterior root passes directly backward above the auditory Fig. 197. squamous portion Zygoma Groove for meningeal arterv PETROUS PORTION for lateral si MASTOID PORTION Aqua?ductus cochleae Right temporal bone, interna] aspect. meatus, crosses the squamous portion above the postauditory process, and, curving slightly upward, is lost at the notch between the squamous and mastoid portions. Its hind part is the supramastoid crest, which joins the inferior temporal ridge on the parietal. The anterior root bends sharply inward. It is grooved above for the passage of the fibres of the temporal muscle. Its lower surface forms a semi-cylin- drical transverse elevation, the eminent ia articn/aris,'' the front part of the articular cavity of the lower jaw. Near its outer end is a tubercle for the external lateral ligament. Just in front of the auditory meatus, on the under side of the bone, is the smaller postglenoid tubercle, sometimes described as a third root. The glenoid fossa^ is a deep hollow on the under side of the squamous portion, with its greatest diameter nearly transverse, but passing somewhat forward and outward, bounded externally by the posterior root of the zygoma ; behind, by the fissure of Glascr,* which separates it from the tympanic portion ; and extends forward and inward to meet the inner end of the eminentia articularis. Both glenoid fossa and articular eminence are covered with cartilage. The bone separating the glenoid fossa from ' Processus Zfgomaticus. -Tuberculum articularc. ^ Fossa maodibularjs. * Fissura petrotj-mpanica. THE TEMPORAL BONE. 179 the interior of the cranium is very thin. Behind the glenoid fossa the horizontal part of the squamosal forms the roof of the e.xternal auditory meatus. The Tympanic Portion.' — The tympanic portion of the temporal bone appears as a trumpet-shaped layer of bone, forming all but the roof of the external auditory meatus. Its edge is thin in front, thick below, and very thin behind, where it curls up before the mastoid to meet the postauricular process of the squamosal. It is separated from the mastoid by the minute tympano-viastoid fissure. The ante- rior part of the tympanic portion, called the iympayiic plate, runs obliquely forward, concealing the petrosal. It is separated from the glenoid fossa and from the thick anterior edge of the squamosal by the fissure of Glaser, which opens into the tvm- panic cavity. The outer end of the fissure is closed ; the inner part is double, since a thin piece of the petrous, the tegmen tympani, bends down between the squamous and tympanic portions. The lower edge of the tympanic plate ends free. A part covering the base of the styloid process is the vaginal process,'' which sometimes splits to enclose it. „ SQUAMOUS PORTION Eustachian tube Glenoid fossa- Tegmen tympani Glaserian fi TYMPANIC PORTION Styloid process- Stylo-mastoid foramen Mastoid process- Digastric gTOOV ^^f» iZ^-fr- Aquaeductus cochlea; -^^^^^^^S'^^^^^t^ V PETRO-MASTOID PORTION -Jugular fossa ■Joinmg occipital Occipital J Right temporal bone from below. The Petro-Mastoid Portion.' — This part of the temporal bone may for convenience of description be subdivided into the mastoid and the petrous. The mastoid subdivision forms a part of the wall of the skull behind the tympanic. It is prolonged downward into a nipple-shaped process, the outside of which is rough and slightly prominent. On its lower surface, under cover of the apex, is the digastric groove* for the origin of the posterior belly of the digastric muscle. Just internal to this, at the very edge of the bone, is the much smaller occipital groove for the occipital artery. The ridge between the two may be developed into a para- tnastoid process. The greater part of the internal surface is occupied by a broad and A&&^ groove' running obliquely downward, forward, and inward for the lateral sinus on its way to the jugular foramen. The direction of this groove is very uncertain. Sometimes it descends gradually ; at others it turns far forward and descends nearly vertically. In the latter case it approaches closer than otherwise to the outer wall of the skull, but the distance in all cases is very variable (Figs. 199, 200). It may be only a few millimetres. As it descends it reaches the inner side of the antrum and the mastoid cells. It is separated from the antrum by a plate some six - Vagina processus styloideus. ^ Pars petf' astotdea. ^ locisura mastoidea. ^Sulcus sigmoldeoaL i8o HUMAN ANATOMY. millimetres thick in early childhood, and from the antrum or upper mastoid cells by a very thin one in adult life.' Behind the groove a small, smoolti surface forms a part of the cerebellar fossa. Fig. 199. A B Carotid canal Tympanic cavity Jugular fossa Groove for lateral sinus Mastoid canal Tympanic cavity Groove for lateral Horizontal sections through a right temporal bone with slight development of the mastoid cells. A, just above the fioor of the external auditorj- meatus ; B, near the roof of the same canal. Fig. 200. A small canal, the mastoid for ayneyi,'^ transmitting a vein, runs from the sinus to the outside of the bone, \vhich it sometimes reaches as far back as the suture between ^Clarke: Journal of Anatomy and Physiology, vol. xxvii, 1893. -Forameo mastoideum. THE TEMPORAL BONE. Bottom of right internal auditory meatu the temporal and the occipital. The interior of the mastoid process contains spaces, the mastoid cells, to be described later. The size and shape of the masto'd process are very variable. The rough upper border of the mastoid subdivision forms an entering angle with the squamosal, into which tits a sharp point from the lower bor- der of the parietal, which rests on it above. Behind and below the Fig 2ui mastoid joins the occipital bone. ^?%^-~- The petrous subdivision is -«?"?*^$^^ ^ an elongated pyramid running for- "^ ward and inward, presenting four „ . , r ^1-1 11 J Facial canal surfaces (besides the base covered ^Area crihrosa by the mastoid), four borders, and superior Ti r .1 Crista faki — an apex, llie surfaces are the supe- formis -cm wall of in- rior, posterior, inferior, and anterior. Tractus spi _ vvt'i'fr'ibrosa"^ The superior surface slants '''^"^ ' media forward and downward in the floor — Foramen singu- of the middle cerebral fossa. It has the following features. Above the apex there is a depression ' for the Gasserian ganglion. Just e.xternal to this the bone is excessively thin and often deficient, so as to leave the end of the carotid canal uncovered. Behind the middle of the pyramid is an elevation, nearly at right angles to its long axis, caused by the superior semicircular canal. External to this the surface is made of a very thin plate of bone, the tegmen tympani, which, extending outward from the petrous, forms the roof of the tympanum and of its continuation, the Eustachian tube. Externally, this plate bends down into the Glaserian fissure, so that its edge may appear between the squamosal and tympanic portions (Fig. 198). At the inner border of the tegmen tympani near Fig. 202. its front is a groove leading to a little rent in the bone, the hiatus Fallopii," through which passes the great su- perficial petrosal nerve. A minute opening, more external, transmits the smaller superficial petrosal nerve. In youth the outer side of the teg- men is bounded by the petro-squa- viciis suture. The posterior surface forms a part of the posterior cranial fossa. The chief feature is the internal auditory meatus,^ a nearly round canal with a slight groove leadinf' to it from the front. Its shorter posterior wall is about five milli- metres long. The canal is closed by a plate of bone, the lamina cribrosa (Fig. 201), which is divided by the falciform crest into a smaller fossa above and a larger one below. The former has an opening by which the facial nerve enters its canal, the aqueduct of Fallopius. Branches of the auditory nerve pass through minute openings in both fossee. About one centi- metre behind the meatus is a little cleft, the aqucsductiis vestibuli,* entering the bone obliquely from below. Higher and nearer to the meatus is a minute depression, the remnant of the floccular fossa,^ which is large in some animals and in the infant. It receives a fold of the dura. The inferior surface of the petrous presents in front a large rough surface for • Impressio tegmenti. -Hiatus canalis facialis. ^Meatus acusticus interous. ' Apertura externa aquacductus vcstibuli. ^ Fossa subarcuata. Petro-squamous suture Internal audi- tory meatus Internal Tympanic cavity Tympanic ring Styloid process l82 HUMAN ANATOMY. the origin of the levator palati and tensor tympani muscles. External to the back of this is the round orifice of the carotid canal^ ; back of this, and more internal, is the jugular fossa. This presents two e.xtreme types, entirely different, with inter- mediate forms. It may be a large thimble-shaped hollow, the edge of which bounds the venous part of the jugular foramen internally, forming a large reservoir for the blood of the lateral sinus as it leaves the skull. On the other hand, it may be a small flat surface. A minute, but very constant, foratiitti in the ridge bet^veen it and the carotid canal transmits the tympanic branch of the glosso-pharyngeal nerve. A mmnte foramen, usually found in the jugular fossa, transmits the auricular branch of the vagus. The aquizdudus cochlea ends at a small triangular opening " in front of the jugular fossa, close to the inner edge. Behind the fossa is a small surface where the temporal bone is united to the occipital, first by cartilage and then by bone. The stjlo- mastoid foramen, the orifice of the facial canal for the facial nerve, is near the outer edge of this surface. The stylo-mastoid branch of the posterior auricular artery enters it. Fig. 203. SQUAMOUS PORTION Groove for meningeal artery for lesser superficial pe- trosal ner\'e Hiatus Fallopii I )epression for Gasse rian ganglion Iiustachian tube I'.irotid canal APEX OF PETROUS Carotid canal (lower end) Zygomatic tubercle Styloid process. Right temporal bone from before. The anterior surface of the petrous is nearly all hidden by the tympanic plate. It forms the inner wall of the cavity of the tympanum and of the bony part of the Eustachian tube, which leaves the bone in the entering angle between this surface of the petrous and the tympanic. The features of this surface are treated in the section on the ear. The processus cochleariformis,'' attached like a shelf to this outer wall, divides the canal for the tensor tympani muscle from the Eustachian tube below it. The front of this plate can be seen at the entering angle, where the bony tube ends. The small portion of the outer surface of the petrous which is visible is in front of this point, and rests against the inner edge of the great wing of the sphenoid. The superior internal border of the petrous is a prominent ridge in the base of the skull, separating the middle and the posterior fossae. The tentorium is attached to it. The superior petrosal sinus runs along it in a shallow groove within the attached border of the tentorium. Near the front a groove by which the fifth nerve reaches the Gasserian ganglion crosses this border. The inferior internal border articulates anteriorly with the basilar process of ^ Canalls caroticus. - Apertura externa aquaeductas cochleae. •''Septum caaalis musculotubarit. THE TEMPORAL BONE. 183 the occipital bone, and is separated posteriorly from the occipital by the jugular foramen. A little spine on the edge of the thimble-shaped fossa, or on the plane surface that may take its place, the intrajugular process, joins the corresponding process of the occipital either directly or by ligament, so as to divide the foramen into two parts, the posterior for the vein, the anterior for nerves. In front of the foramen a small groove on the cerebral edge of this border marks the position of the inferior petrosal sinus. The superior and the inferior external borders are concealed by the other elements of the temporal, except near the front, where they bound the surface which touches the sphenoid. The apex of the petrous is mostly occupied by the opening of the carotid canal. The styloid process is a part of the hyoid bar (from the second branchial arch), which joins the temporal under cover of the vaginal process. It is thick at its origin, but presently becomes thinner and ends in a sharp point. It is usually about an inch long, but varies greatly. It runs downward, forward, and inward, and is con- tinued as the stylo-hyoid ligament to the lesser horn of the hyoid. Three muscles, the stylo-glossus, stylo-hyoid, and stylo-pharyngeus, diverge from it to the tongue, the hyoid bone, and the pharyn.x. An ill-defined process of the cervical fascia, the stylo-maxillary ligament, passes from it to the back of the ramus of the lower jaw. CAVITIES AND PASSAGES WITHIN THE TEMPORAL BONE. ' The Cavity of the Tympanum.' — The tympanic cavity is a narrow cleft about five millimetres broad at the top, narrowing to a mere line below. It measures about fifteen millimetres vertically and from be- ' Fig. fore backward. It is bounded internally by the petrous ; above by a projection from it, the tegmen tympani ; below by the jugular fossa, or, if this be very small, by the bone external to it ; externally by the tym- panic portion of the bone and the membrane, except at the top, where the squamosal is ex- ternal to it. The part above the level of the membrane is the sicpra- tympa7iic space, the atiic, or the epityyiipanum. This is separated from the cranial cavity by a very thin plate, which is sometimes imperfect. In front, the cavity of the tympanum narrows to the Eusta- chian tube. It opens behind through the antrum, which serves as a vestibule, into the mastoid cells. The antrum is a cavity of irregular size and shape, compressed somewhat from side to side, with an antero-posterior diameter of from ten to fifteen millimetres, situated behind the epitympanum in the backward projection of the squamosal, which forms the superficial part of what appears to be the mastoid, and contains some of the so-called mastoid cells. The communication with the tympanum is a narrow one, and a certain number of cells open into the latter independently. The antrum and the cells nearest it are lined with mucous membrane continued from the middle ear. The inside of the mastoid varies greatly. Sometimes it con- ' The detailed description of this space is given in connection with the ear. ferior end) Sagittal section through right temporal bone, seen from outer side. i84 HUMAN ANATOMY. tains large pneumatic cavities, sometimes diploe instead of air-cells, and, again, it may be almost solid ; the latter condition is, however, probably always pathological. According to Zuckerkandl's ' in\'estigations of 250 temporal bones, the mastoid is entirely pneumatic in 36.8 per cent, and wholly diploetic in 20 per cent. The re- maining 43.2 per cent, were mixed, the diploe being at the point of the mastoid and the cells above. Neither size nor shape indicates its internal structure. The relation of the cells to the lateral sinus has been already mentioned. The Facial Canal. — The course of the canal '' for the facial nerve is important. It runs outward from the superior fossa of the internal auditory meatus for some three millimetres, until joined by the canal from the hiatus Fallopii. It then makes a sharp turn ( the genii) backward, passing internal to the attic of the tympanum just below the external semicircular canal, which almost always projects a little farther outward. It then curves backward to descend to the stylo-mastoid foramen, passing just above the fenestra ovalis. The descending portion is rarely strictly vertical. Below the genu the facial canal may make a bend either outward or inward, but its general line of descent usually inclines outward, sometimes very strongly. Rarely the descent is tortuous. The lower part may incline forward. The genu is opposite a point on the surface above the e.xternal meatus, and the subsequent course of the canal can be indicated in general by a line following the posterior border of the auditory opening. An instrument introduced straight into the front of the mastoid will pass behind the facial canal." The diameter of the latter is about one and one- half millimetres. Just before its lower end a very minute canal, transmitting the chorda tympani nerve, runs upward and forward from it to the cavity of the t)^mpa- num. From the front of the cavity this nerve escapes by the minute canal of Huguier^ which opens near the inner end of the fissure of Glaser, passing between the tym- panic plate and the tegmen tympani. The facial canal has several other minute openings. There are also minute canals for Jacobson' s nerve from the glosso- pharyngeal, leading to the tympanum, and for Arnold' s branch of the vagus, which enters the jugular fossa and leaves by the fissure between the mastoid and tympanic portions. The carotid canal ' is close to the front of the tympanum and just before the cochlea of the internal ear. The internal auditory meatus is almost behind the canal. and the Eustachian tube lies to the outer side of its horizontal portion. The temporal bone is porous in structure, except about the internal ear, where it is very dense. A transverse section, either vertical or horizontal, through the external and internal meatus (the middle and internal ears) shows how nearly the entire bone is pierced (Fig. 202). The carotid canal and the jugular fossa, when deep, are further sources of weakness. The fossa sometimes opens into the middle ear by a small rent. Articulations. — The temporal bone joins the occipital by the petro-mastoid portion. These two bones form the entire posterior fossa of the skull, except at the extreme front, in the middle, where it extends along the back of the sphenoid, and at the side, where a small portion of the lateral sinus is made by the posterior inferior angle of the parietal. This latter bone articulates with the squamous and the top of the mastoid. The great wing of the sphenoid fits into the angle between the squamous and petrous portions, articulating at the side of the skull with the front of the foramen. These two bones — the sphenoid and the temporal — form the entire middle fossa. The malar bone joins the zygoma, completing the arch. The lower jaw articulates with the glenoid fossa by a true joint. Development. — The squamous portion is ossified in membrane from one centre, appearing near the end of the second month of foetal life. In the course of the third month a centre appears in the lower part of the future tympanic ring. The ossification of the petro-mastoid portion comes from several nuclei, the number of which probably varies. The process begins towards the end of the fifth month abo\it the membranous labyrinth. The opisthotic nucleus lies> at the inner side of the tympanic cavity and spreads to the lower part of the bone. 'Y\\z prootic is near the superior semicircular canal. The cpiotic, arising near the posterior canal, ' Monatsschrift fiir Ohrenheilkunde, Bd. xiii, JS79. 'Joyce : Journal of Anatomy and Physiology, vol. xxxiv., 1900. -Caoalis facKiHs. ''Canalis caroticus. DEVELOPMENT OF THE TEMPORAL BONE. JS5 C Stai Tympanic Malleus \ fe^ien tympani In Inner wall Glaserian fissure ot t\mpanum Temporal bone at about birth, outer aspect. spreads into the mastoid portion. This one is sometimes double. There is also a separate nucleus for'the tegmen, but this is not constant. When present, it seems to be the last to fuse with the others, which become one by the end of the Fig. 205. si.xth month. The carotid artery passes ^ s^''^"-""^ portion at first along the base of the skull in a _ .'"'^ '^ "^>;i groove which is made into a canal by the opisthotic. The separated petrous portion, when ossification has made some progress, shows a very promi- nent superior semicircular canal, and a deep cavity under it, extending back- ward from the inner surface. This is the floccular fossa, \\-hich, howe\-er, is completely hidden by the dura. The viastoid process becomes fairly distinct in the course of the second year. It develops greatly about the time of puberty, when it becomes pneumatic. This may occur much earlier. J. J. Clarke has seen it wholly pneumatic several times before the tenth year ; once at three and a half.' The squamosal joins the petrous in the course of the first year. At birth the tympanic por- FiG.. 206. tion consists solely of the im- Petro-squamous suture perfect ring Open above. This enlarges trumpet-like from the edges, the front one forming the tympanic plate. The growth is of unequal rapidity, so that the lower part is left behind, presenting a deep notch the outer edges of which meet by the end of the second year, leaving a foramen below, which usually closes two or three years later, but exceptionally persists. The tympanic plate fuses almost at once with the petrous, but the Glaserian fissure remains ; the groove showing the line of union of the tj'mpanic and mastoid processes generally disappears in the second year, but occasionally persists through life. Kircher^ found it present on both sides in five per cent, of 300 skulls. The styloid process consists of two parts. The first joins the petrous at about birth. The second, which represents all but the base, is an ossification of the stylo-hyoid ligament, and does not join till puberty or later. In very early fcetal life the chief vein returning the blood from the brain passes through the membrane that is to become the squamosal. This open- ing— the foramen jugulare spiirium — is later of less importance, and is finally closed. In the skull, at birth, a pin-hole representing it may be found at the postglenoid tubercle. later. Temporal bi T>Tnpanic ring mpanic portion of temporal bone in the second } It is sometimes seen ^ Journal of Anatomy and Physiology-, vol. xxvii., 1895. ^ Archiv fiir Ohrenheilkunde, Bd. xiv., 1879. HUMAN ANATOMY. THE SPHENOID BONE. In the adult this bone ' consists of a cubical body^ from the sides of which arise the great wings, from its front the lesser wings, and from below the pterygoid pro- cesses. Both development and comparative anatomy show that these parts represent several bones. The body consists of two parts, a posterior and an anterior. The posterior, the basisphcnoid, is the centre of the middle fossa of the base of the skull ; from its sides spread the great wings, or alisphenoids. These with the temporal bones complete the middle fossa. The anterior part, the prcsphcnoid, inseparably connected with the basisphenoid, is in both the middle and the anterior fossae. The lesser wings, the orbito-sphenoids, spread out from the presphenoid and cover the apices of the orbits. 'Xha pterygoid processes consist each of two plates, the inner of which represents a separate bone of the face, the outer being an expansion from the alisphenoid. Two bones called the cornua sphenoidalia, or sphenoidal turbitiates, of independent origin, ultimately form a part of the body of the sphenoid. Fig. 208. Sphenoidal turbinate Sphenoidal foramen Hamular process Pterygoid notch Internal pterygoid plate The sphenoid bone from before. The Body. — It is necessary to describe the basisphenoid And the presphenoid together, since they form the roughly cubical body. The superior surface con- tains the dee^) pituitary fossa,'' or sella turcica, in which hangs the pituitary body from the brain. Behind it is the dorsum sella, a raised plate continuous with the surface of the basilar process of the occipital and which completes the posterior fossa. Its outer angles are knobs pointing both forward and backward, the posterior clinoid processes, to which the tentorium is fastened. Beneath these, on either side of the dorsum, is a groove for the sixth nerve. In front of the sella is the olivary eminence^ (of the presphenoid), which is usually an oval swelling, though it may be plane or concave. At its sides grooves, often very poorly marked, lead to the optic foramina. The posterior edge of this eminence is sometimes grooved for a vein and sometimes sharp. Its lateral ends may become tubercles, the middle clinoid processes. The olivary eminence is in most cases bounded in front by a transverse elevation con- necting the lesser wings, of which, indeed, it is a part, forming, when present, the separation of the anterior and middle fosste. The front border presents in the median line a triangular point, the ethmoidal spine. At each lateral surface of the body is the carotid groove ' for the internal carotid artery. It is well marked only at the posterior edge, where the artery enters ' Os sphenoidale. - Fossa hypophyseos. ^ Tuberculum sellae. * Sulcus carotlcus. THE SPHENOID BONE. 1S7 it from the apex of the petrosal. It is here bounded internally by a little tubercle, the petrosal process, at the base of the dorsum, and externally by a very delicate plate, the lingula, which sometimes projects considerably ; these two processes touch either side of the end of the carotid canal in the petrous. The rest of the side of the body is hollowed for the cavertioics sinus, in which the carotid artery runs. It is covered below by the origin of the great wing. The posterior surface of the body is rough up to puberty for the cartilage that binds it to the basilar process of the occipital ; later these parts coossify, and thereafter the posterior surface is made artificially by the saw. The anterior surface presents in the middle a sharp ridge, the sphenoidal crest, ' to join the vertical plate of the ethmoid. Just at the sides of this the bone is smooth and aids in forming the wall of the nasal fossa. In each lateral half is an opening, the sphe7widal foramen,'^ into the cavity of the bone. The inferior surface presents in the middle a longitudinal swelling, thick behind, narrow and sharp in front, the rostrum, fitting into the vomer and usually joining the lower edge of the crest without interruption. It may stop short of it. On either side of the rostrum there is a smooth triangular surface made of delicate plate, which extends up onto the front, forming the smooth surface beside the crest, and bound- FiG 209 Foramen rotundum Carotid groo\ Scaphoid fos=;a' Pterygoid fossa- External pterj'goid plate Hamular process The sphenoid bone from behind. ing a large part of the hole into the antrum. These are the bones of Berlin, or sphe7ioidal spongy boties, of which more is to be said under Development (page 191). The body of the sphenoid is hollow, enclosing two cavities, the sphenoidal sinuses, separated by a septum, which runs obliquely backward from the crest, so that one sinus is usually much larger than the other. These sinuses have irregular ridges partially subdividing them. They are lined by mucous membrane and open into the nasal cavity by the sphenoidal foramina. The opening is reduced when the ethmoid is in place. The great \vings ' have each a cerebral or superior surface forming a large part of the middle fossa, an exterjial surface looking outward into the temporal and downward into the zygomatic fossa, and an orbital surface forming most of the outer wall of that cavity. The superior surface is smooth and concave ; springing from the side of the basisphenoid, it spreads upward and outward and also backward to fill the gap between the petrous and squamosal parts of the temporal. By the side of the body there is a short canal running forward to open on the front of the bone into the spheno-maxillary fossa ; this is the foramen rotundimi for the superior max- illary division of the fifth nerve. A little further back and more internal is a pin- ^ Crista sphenoidMis. " Apertura sinas spheaoidalls. ^ Alae mafinae. i88 HUMAN ANATOMY. hole, the foramen of Vesalius, for a minute vein. Farther back and outward near the angle is the foramen ovale, transmitting the mandibular division oi the fifth cranial nerve to the base of the skull, and admitting the small meningeal branch of the internal ma.xillary artery. Just beyond this, in the extreme angle, so as some- times to be com])leted by the temporal, is the foramen spinosum, admitting the middle meningeal artery to supply the bone and the dura. The external surface is divided into a larger, superior, vertical part, looking towards the temporal fossa, and one looking into the zygomatic fossa. These are separated by the infratem- poral crest, which near the front points downward as a strong prominence, the infra- temporal spine. The inferior surface contains the foramen ovale and the foramen spinosum. Just behind the latter, at the posterior angle, is the spine of the sphenoid, pointing downward, grooved at the inner side by the chorda tympani nerve. The external surface has an anterior border where it meets the orbital surface, which joins the malar. The superior border slants upward, overlapping the frontal and parietal bones. The posterior border is about vertical as far down as the infra- temporal crest, and bevelled, especially above, to be overlapped by the squamous part of the temporal. The lower part of this border runs backward and somewhat overlaps the squamosal. The posterior border of this surface, from the spine to the Articulates with frontal Fig. 2IO. Ethmoidal crest Oi tc foramen Foramen spinosum Post, clinoid process The sphenoid bone from above. body, is slightly rough for the petrous, making with it a groove on the under side for the cartilaginous Eustachian tube. The smooth orbital surface, facing inward and forward, is quadrilateral, broader in front than behind. Almost the whole of it is in the outer wall of the orbit, of which it forms the greater part ; but a small portion, narrow behind and expanding in front, looks into the spheno-maxillary fissure, which bounds this surface below. It joins the malar in front. On the top of the bone there is a rough triangular region in the angle formed by the meeting of the external and orbital surfaces, on which the frontal bone rests. This is above the front half of the orbital plate. The remainder of the upper and the whole of the posterior border of the latter bound the sphenoidal fssurc.^ This cleft is an elongated aper- ture, directed obliquely outward and upward between the great and lesser wings of the sphenoid, completed externally by the frontal. It opens anteriorly into the orbit and transmits the third, the fourth, the ophthalmic division of the fifth and sixth cranial nerves, and the ophthalmic \-eins. There is a small projection near the middle of the hind border for a ligament crossing the fissure and for the outer head of the external rectus. The lesser wings," forming the back part of the anterior fossa and of the roof of the orbit, arise by two roots. The superior is a plate covering the presphenoid ; the inferior is a strong process from the side of the body. With the latter they ^ Fissura orbitaTis superior. - Alae parvae. THE SPHENOID BONE. 189 spur of Sphenoid bone, showing abnormal de\elop>ment of middle clinoid processes, especially on the left side. Re- duced one-half. enclose a canal, commonly called the optic foramen, ' for the optic ner\-e, \\hich is accompanied by the ophthalmic artery. The length of the canal measured along the inferior root is about five millimetres. The length of the roof is greater, per- haps nearly twice as much, but it is variable from the uncertain development of that part of the bone ; definite dimensions are, therefore, wanting. The vertical diameter, some five millimetres, of the opening into the orbit is a little greater than the transverse. The small wing o\'er- hangs the front of the middle fossa Fig. 211. bounding the sphenoidal fissure above, and ends laterally in a sharp point. The anterior clinoid process is a sharp pro- jection backward above the inferior root and towards the posterior clinoid. Sometimes it reaches the latter ; some- times it is connected by a spur with the middle clinoid process, then bridging the carotid groove and making a carotico- clinoid foramen (Fig. 211). The an- terior border of the lesser wings is rough at its inner part and smooth at the outer, where it joins the posterior edge of the horizontal plate of the frontal. The posterior border is smooth, form- ing most of the boundary of the anterior and middle cranial fossae. The pterygoid processes ' are downward projections which, articulating with the palate bone, form the back of the framework of the upper jaw. Each consists of two plates, an inner and an outer, united in front, diverging behind to form the pterygoid fossa, and separating below on either side of the pteiygoid notch. The inner springs from the body, the outer from the great wing. The inner pterygoid plate ^ is the longer. It is nearly vertical, ending in the slender hamular process'' which points outward, bounding a deep little notch through which the tendon of the tensor palati plays. At the inner side of its origin the internal plate presents a scale-like cur\'ed projection, the vaginal Fig. 212. process, above which is an antero-poste- rior groove below the body of the sphe- noid, in which the lateral expansion of the base of the vomer is received. Just external to the vaginal process is an- other small groove, the pterygo-palati)ie , which the palate bone converts into a canal leading back from the spheno- maxillar)- fossa. The outer pterygoid plate ^ is broader and flares outward. The anterior surface of the root is nearly smooth, forming the back wall of the spheno-maxillary fossa. It has the openings of two canals : the upper and outer is that of the foramen rotundum ; the lower and inner, which is smaller, is the Vidian canal, transmitting the nerve and vessels of that name. There is a vertical ridge between the two, and a slight groove below the latter, forming with the palate bone the beginning of the poste- rior palatine canal which runs from the spheno-maxillary fossa through the hard palate, transmitting a descending palatine nerve and vessels. The lower anterior edges of both plates are rough to articulate with that bone. The outer surface of the external plate is irregular for the origin of the external pterygoid muscle. The inner wall of the inner plate is smooth. It bounds laterally the back of the nasal cavity. The posterior borders of both plates are sharp, excepting that the inner is formed by the union of two lines which enclose the scaphoid fossa where the tensor palati arises. Rather less than half way down the internal plate presents a premi- - Processus pterygiidei. ■^ Lamina medialis proc. pteryg. * Hamulus pterygoidei. ^ Lamina lateralis Oroc. pteryg. I go HUMAN ANATOMY. Fig. 213. Hxt. pterj'goid plate int. pterygoid plate nence bounding a groove below, which supports the Eustachian tube. The posterior border of the outer plate is irregularly scalloped. Near the top a transverse ridge crosses its inner surface ; if well marked, this forms the top of the pterygoid fossa. It may be barely discernible (Waldeyer '). Just above the scaphoid fossa is the hind end of the Vidian canal opening into the middle lacerated foramen opposite the apex of the petrous. The development of the pterygoid plates varies greatly. The upper part of the outer may be prolonged to the spine of the sphenoid, just outside of the foramen ovale, with a perforation at this point, so that some of the branches of the third division of the fifth cranial nerve may pass on either side of it. This occurs by the ossification of a band of fibrous tissue, connecting the back of the plate with the spine, and thus forming the foramen ptcrygo- spinosum of Civinini (Fig. 212). This is always behind the fora- men ovale, or internal to it. Just outside of the foramen is found, very rarely, a little canal on the under side of the great wing, transmitting a branch of the mandibular division of the fifth nerve, the porus crotaphit- ico-huccinaioriiis of Hyrtl. Articulations. — Much has been already said incident- ally on this point in the fore- going description. The sphenoid bone joins the occipital behind. The great wings send the spine into the entering angle between the squamous and petrous portions of the temporal. These two bones — the sphenoid and the temporal — form the entire middle fossa of the skull. The middle lacerated foramen is just behind the carotid groove at the side of the body and in front of the end of the petrous. At the side of the skull the great wings join the squamous behind, the parietal and the frontal above, and the malar in front. The ethmoid covers the front of the body of the sphenoid, its vertical plate joining the crest. The vomer covers the rostrum below. The palate bone fills up the pterygoid notch, com- Fig. 214. pleting the fossa, and by its sphenoidal process touches the edge of the body. The frontal bone joins the lesser wings. Development. — The presphcnoid and basisphenoid each ossify from a pair of nuclei, those of the former appearing at the end of the second month of fcetal life and the latter a little later. At about the eighth week a nu- cleus is to be seen in each of the greater wings near the body and extends outward, involving also the external pterygoid plate. The internal pterygoid plate has a nucleus of its own, which is present in the fourth month and joins the outer a month later. Two little gran- ules appear in the fourth month for the lingula and a neighboring piece of the bone. The orbUo-sphenoids have each two centres, — one on either side of the optic foramen. It would seem that the inner may in some cases take the place of those for the presphenoid. In any case the presphenoid and the lesser wings unite before birth. In the seventh or eighth month the presphenoid and basisphenoid unite, but at birth they are still separated by cartilage on their lower surface. At birth the bone con- ' Sitzungsber. Acad. Wissen., Berlin, 1893. ving (orbito-sphenoid) Foramen rotundum Great wing falisphenoid) Basisphenoid Lingula noid bone at about birth, seen from behind. THE ETHMOID BONE. 191 Crista galli sists of the basisphenoid, the presphenoid, and the lesser wings in one piece, and a lateral one on each side,— namely, the greater wing and the pterygoids. The dorsum sella; has a separate epiphysis which appears after birth. In the first year the lesser wings spread across the top of the presphenoid, joining the jugum sphenoidale, so that it does not show in the anterior fossa. The external pterygoid plate is an out- growth of the great wing. The comua sphenoidalia, bones of Berti7i, or sphenoidal turbbiate bones, are two thin plates which appear before birth at the front of the presphenoid. They cover both the front and its inferior surface at the sides of the rostrum. At five years they are still free, but have approacned their permanent shape of hollow cones. The hollowing out of the body of the sphenoid now begins, and at the same time the upper part of these bones is absorbed, so that the foramina become notches. These bones are ultimately joined to the sphenoid, the ethmoid, and the palate. Though usually reckoned as parts of the sphenoid, there is reason to believe that they are generally fused earlier with the ethmoid. The basisphenoid begins to coossify with the occipital at about the fifteenth year. The process is first completed above. THE ETHMOID BONE. The ethmoid^ consists of a median plate forming a part of the nasal septum, of the cribiform plate joining it at the top on either side and forming the roof of the nasal cavity, and of two lateral masses attached to the lateral border of each cribriform plate, and touching the vertical plate very slightly just below its junction with the front of the cribriform plate. These lateral masses are roughly cubical, interposed between the cavities of the nose and of the orbit. They consist of Fig. a series of delicate plates forming the walls of air-spaces or cells, which are mostly completed by neighboring bones. The vertical or median plate 2 projects near the front into the cranial cavity as the C7'ista galli, thicker in front than behind, with an oblique upper border run- ning sinuously downward and backward. Its greatest elevation is about one centimetre. The front part is occasionally hollow, Mid. turbinate - forming a part of the frontal sinus. It gives attachment to the falx cerebri, a fold of dura separating the hemispheres of the brain. A little plate, a/a,' facing downward and forward, arises from the front on either side, articulating with the frontal. Just before the crista galli is a pin-hole, the forameti ccecum, usually formed by both ethmoid and frontal, but which may be in either. It is said to transmit a vein in early life, but is closed later. The part of the vertical plate below the horizontal one is five-sided. The upper border runs along the base of the skull ; one in front of it slants downward and forward under the nasal spine of the frontal, sometimes reaching the nasal bones ; another descends nearly vertically along the crest of the sphenoid. Of the two inferior borders, the posterior runs downward and forward along the greater part of the vomer, while the anterior, running downward and backward to meet it, is free in the skeleton, but in life is attached to the triangular cartilage which forms a large part of the septum. The sides, covered with mucous membrane, are smooth except at the upper part, where there are vertical grooves for the olfactory nerves. This plate usually slants to one side. The horizontal or cribriform plate * forms the floor of a narrow groove on either side of the crista galli and, farther back, in the middle of the anterior fossa of ^ Os ethmoidale. ^ Lamina perpendicutarls. ^ Processus alaris. ^ Lamina cribrosa. Uncinate prOLCSS The ethmoid bone, outer aspect from the right side. 192 HUMAN ANATOMY. the skull. The greatest breadth of the groove is about five millimetres. It nar- rows in front to a point, and thus allows the lateral masses to touch the mediaii plate. It supports the olfactory lobe of the brain, and is perforated by holes for the passage of the olfactory nerves. These are arranged rather vaguely in three rows. There are many in front and few behind. Many of the larger ones, which are near the septum or at the outer side, are small perforated pits. At the front a longi- tudinal Jissiire, close to the crista galli, transmits the nasal branch of the fifth nerve. The lateral masses ' are two collections of bony plates imperfectly bounding cavities. They are roughly six-sided, the greatest diameter being antero-posterior. The outer surface presents a vaguely quadrilateral plate, the os pla7mm,' forming a large part of the inner wall of the orbit. In its upper border are two notches, which become the anterior and posterior ethmoidal foramina when the frontal bone is in place. The former transmits the nasal branch of the fifth nerve from the orbit to the cranial cavity. The os planum is bounded behind by the body of the sphenoid ; below by the palate bone and superior ma.xilla, the former of which usually, and the latter always, complete some eth- moidal cells which appear along the lower border. There is ' a large mass of open cells in front of the / ; / OS planum. Those nearest to it are completed by the lachrymal and the more anterior ones by the Median or perpendicular plate of ethmoid bone in place. The ri^ht lateral mass of the ethmoid has been removed. nasal process of the superior maxilla. Posteriorly, the lateral mass rests against the body of the sphenoid, the posterior cells being separated from those of the sphenoid by the cornua sphenoidalia. The open cells on the upper surface of the lateral mass are closed by the imperfect cells on the under side of the horizontal plate of the frontal beside the ethmoidal notch. The few cells that open anteriorly are contin- uous with the lateral ones, and are closed by the nasal process of the upper jaw. The numerous spaces within the ethmoid are, for the most part, completed by the neighboring bones, after which they are named. There are some beneath the os planum, however, entirely within the ethmoid. The ethmoidal cells' are divided into anterior and posterior, of which the former open into the nose below the middle turbinate bone and the latter above it. The size and shape of the ethmodial cells are very irregiilar ; sometimes the middle turbinate is hollowed into one, some- * Labyrinthas etbmoidalis. ■ Lamina papyracca. ''Cellulae ethinoidalcs. THE ETHMOID BONE. 193 Fig. 217. Median plate The ethmoid bone from above. times they swell out into the cavities of other bones, notably into the frontal sinus. The internal surface of the lateral mass, forming the outer wall of the nasal cavity, cannot be seen on the entire bone. It is best studied on the bisected skull ; but to study the whole bone, further cutting is necessary, since this sur- face is made of a series of con- voluted plates, some of which conceal others. At least two of these — the superior and the mid- dle tii7'binate bones ' — are evident. They are curled with their con- vexities towards the median plane, so as to overhang two antero-posterior passages, the superior and the middle meatus of the nasal fossa. According to Zuckerkandl, there are three ethmoidal turbinate bones in more than eighty per cent, and sometimes four. When only two are seen, it is owing either to the absence of the second or to its slight development, so that it is hidden by the upper. It is certain that only two are evident in most cases, and we shall follow the usual method of so describing the bone.'^ The inferior ethmoidal (middle) tur- binate is much the larger, very prominent, and joins the ascending process of the superior ma.xilla at the crista ethmoidalis or superior turbinate crest. Its general course is backward and downward, to end in a point at the posterior border of the bone. The free edge is so much curled under as to be hidden. The superior iurbiiiate is much smaller, occupying the postero- superior angle. It appears to separate from the turbinate below it at about the middle of this sur- face. The superior meatus, which it overhangs, is therefore small. As above implied, an additional ethmoidal turbinate may appear from beneath it, and still another small one may -very exceptionally be found above it at the e.xtreme upper posterior angle. At the point at which the middle turbi- nate bone joins the nasal process of the ma.xilla there is often a slight elevation, the agger nasi, which is supposed to be the an- terior end of another turbinate which passes under the preceding. When the mid- dle turbinate is removed, a curved projecting plate, the uncinate process,^ is" seen on the lateral mass, curving downward and backward. It is some two or three millimetres broad and, extending beneath the rest of the bone, joins the inferior turbinate. The uncinate process, together with the agger, is held to represent the ^ There are practically three turbinate bones, the upper t\^-o of which are parts of the ethmoid and the lowest a separate bone. These are called superior, middle, and inferior ; hence we speak of the inferior ethmoidal turbinate as the middle one. ^ Concha nasalis superior et media. ^ Processus, uncinatus. Fig. 2x8. Superior Posterior ethmoidal' Middle turbinate plate and lateral 194 HUMAN ANATOMY. Uncinate p: 'id bone, inner aspect from left side, part of the i having been removed. liddle turbinate 7iaso-tin-binal bone of many mammals. Behind this is a globular swelling, the bulla, ^ formed by a plate springing from the os planum, covering cells, which also is held to represent a turbinate. Between the uncinate process and the bulla is a deep groove, the in/itndibiilitm' curving downward and backward, the opening into which from the nasal fossa is known as the hiatus semilunaris. The upper end of the infundibulum opens into Fig. 219. the frontal sinus in about half the cases, ' ending blindly in the others ; it is bounded externally to a varying extent by the lachrymal. A number of anterior ethmoidal cells generally open into this portion. The upper part of the infundibu- lum has an opening on its outer side into the antrum. Articulations. — These have already been described incidentally. Briefly recapitulated, however, the articula- tions of the ethmoid are with the frontal, the sphenoid, the palatals, the vomer, the inferior turbinates, the lachrymals, and the nasals. Development. — The ethmoid is very small at first and backward in its development. About the middle of fcetal life ossification appears in the os planum and the middle turbinate bone. A centre (two, according to Poirier) for the vertical plate occurs in the first year, from which ossification extends into the crista galli. The cribriform ossifies chiefly (perhaps wholly) from the lateral masses. The date of the union of the three pieces is rather uncertain ; it takes place, probably, at about the sixth year. The cells appear first as depressions during foetal life. According to the more generally accepted view, their growth is by absorption of bone. It is hard to believe that this is not, at least, a factor ; Poirier, however, holds that they are due to the course of ossification. THE FRONTAL BONE. This bone,* which forms the front of the vault of the skull, most of the floor of its anterior fossa, and bounds the greater part of the orbits and the ethmoidal cells above, is developed into two symmetrical halves which unite in the second year. It is convenient to divide the bone thus formed into a vertical and a horizontal portion, although this division rests on no scientific basis. The vertical portion,^ convex anteriorly, presents on either side, below its middle, the frontal emitieJice,^ which represents the chief centre of ossification f either half. Very prominent in infancy, it diminishes during growth, and is hardly ■ to be made out in most adult skulls. The lower border of the vertical portion grows downward in front between the orbits. At the sides of this projection are the ititernal angular processes of the orbits. In the middle-line a faint zigzag line marks the remnant of the inter/rontal suture. Above this is a smooth, rather prominent surface, called the glabella, external to which are the superciliary ridges,'' or emi- nences, which extend outward, somewhat above the inner ends of the orbits. The development of these varies greatly. On either side of the nasal projection is the orbital arch, extending outward from the internal angular process. At about the 'H. A. Lothrop : Annals of Surgery, vol. x.wiii., 1898. 'Bulla ethmoidalis. ^ lofuodibnlum ethmoidale. ^Os frontale. ^Squama frontalis. 'Tutier frootalc. ^ Arc THE FRONTAL BONE. 195 inner third of the arch is the supraorbital notch ' for the nerve and the artery of the same name. The outer edge of the notch is more prominent than the inner. Very often this is replaced by a foramen, which may be four or five millimetres above the edge of the bone. The arch ends externally in the extei-nal angular process,"^ which joins the malar and is very prominent. From it springs the teriiporal crest,^ which, curving upward and backward, separates the anterior surface of the bone from the lateral one, which is a part of the temporal fossa. This crest generally, before leaving the bone, divides into two lines, of which one is much more distinct than the other. The vertical part of the bone has a slight point above in the middle and a very jagged posterior border interlocking with the parietal. The latter is slightly overlapped above and overlaps below. The bevelled, though jagged, articular sur- face broadens below to meet a triangular rough space on the inferior surface. At the lower lateral edge the bone is covered by the top of the great wing of the sphenoid. Temporalis ' mporal I rest 1 ■ mporal -urface External angular process Supra-orbital foramen Corrugator supercilii Orbicularis palpebrar Nasal spine The frontal bone from before. The horizontal portion * shows in the middle of its lower aspect a rough surface extending onto the front, called the nasal process, which articulates anteriorly with the nasal bones and laterally with the ascending processes of the upper jaw. In the middle projects a thin plate, the nasal spine, behind and between the nasal bones. On either side of this there is often found a small smooth surface forming a small part of the roof of the nasal cavity. Behind this lies the median ethmoidal notch,'' on either side of which is an irregular space reaching to the inner edge of the orbit, made of imperfect cells, completing the ethmoidal ones. In front of these a cavity extends directly up, hollowing out the bone into the frontal sinus, which may extend outward and backward over the orbits. A partition separates the sinuses of the two sides, which are rarely symmetrical. The sinus opens into the middle meatus either directly, under the front of the middle turbinate, or through the infundibulum. When the ethmoid is in place, the cribriform plate and the crista galli fill up the ethmoidal notch ; the ethmoidal cells are then closed, and the ethmoidal foramina raorbita'.is. " Processus zygomatirus ^ Linea temporalis. * Pars orbitalis. -' lacisura ethmoidalls. 196 HUMAN ANATOMY. and canals are formed. External to this lies the orbital plati\ the front of which is overhung by the supraorbital arch. It is slightly concave from side to side. Just under cover of the external angle is an ill-marked depression ' for the lachrymal gland. Near the internal angular process there may be a small fossa ' for the cartilaginous pulley for the superior oblique muscle. More frequently there is a minute tubercle. The inner border of the orbital surface runs nearly straight backward. Its sharp edge articulates from before backward with the ascending process of the maxilla, the lachrymal, and the ethmoid. The outer edge runs obliquely inward. External to it, behind the angular process which joins the malar, is a rough triangular surface articulating with the great wing of the sphenoid. The posterior border of the orbital plate is short and serrated to join the small wings of the sphenoid. The internal surface of the frontal presents \.\\e frontal crest below in the for longitudinal Meningeal grooves External angular process Supra-orbital fora Frontal crest Foramen cascum Nasal spine Nasal process The frontal bone from behind. median line. It is a slight ridge, to which the falx is attached. A narrow groove runs along it, starting at the foramen arciim, a hole either in this bone or between it and the ethmoid. This groove is for the superior longitudinal sinus. After a short distance the crest disappears, but the groove broadens and extends to the top of the bone. There are a few grooves for branches of the middle meningeal artery at the side and some small Pacchionian depressions.^ Below, on either side of the notch, are the orbital plates, which slant strongly downward and inward, so as to leave the ethmoid in a dee]) gutter. Their upper surfaces are very irregular with so called digital impressions for the opposed cerebral convolutions. It is now evident how the frontal, tlie ethmoid, and the lesser wings of the sphenoid form the anterior fossa of the skull. ' See Parietal Bone (page 198). ^ Fossa Blandulae lacrlmalis. - Fovea trochlcaris. THE PARIETAL BONE. 197 Articulations. — The frontal articulates with the nasal, superior maxillary, lachrymal, malar, ethmoid, sphenoid, and parietal bones. Development and Changes. — The only important centres are the two sym- metrical ones appearing in the membrane at the frontal eminences towards the end of the second month of foetal life. There is a separate point for the nasal spine and one near each angular process of the orbit. These smaller ones are fused in the seventh month of foetal life. There is a centre for the posterior angle (Gegenbaurj, which also unites before birth. The median {metopic) suture usually closes towards the end of the second year, and a year or two later is hardly to be recognized, except by the rudiment at the lower end. Occasionally the suture persists ; in that case it remains in extreme old age after the others have vanished. Not very rarely in the foetus or infant a dilatation of the fissure, metopic fontanelle, is found near the upper part of its lower third. There are a few cases of traces of this in the adult.' The frontal sinuses appear about the seventh year and increase up to adult life. Later they are said to grow again, since in the latter part of life the inner table of the skull follows the shrinking brain. As their size is dependent chiefly on the behavior of the inner table, we can infer little about it from the shape of the fore- head, unless the superciliary eminences are very prominent. THE PARIETAL BONE. The two parietal bones " complete the vault of the skull. Each is a thin quadri- lateral bone with an inner and an outer table separated by diploe. Near the middle Nvvv Fig. 222. Parietal foramen Post. sup. angle Ant. sup. angle Anterior inferior angle Right parietal bone, outer surface. on the convex external surface \=, the parietal emi7ie7ice ,'^ where ossification begins. It is very prominent in childhood, but, as a rule, is not very evident in the adult. Crossing this surface below the middle are two curved lines * continuous with those 'Schwalbe : Zeitschrift fiir Morph. und Anthrop., Bd. iii., 1901. - Ossa parietalia. ^ Tuber parietale. ^ Linae temporales igS HUMAN ANATOMY. into which the temporal crest of the frontal divides. The superior crosses the bone, ending at its posterior border. The iiifenor turns down towards the posterior part so as to reach the lower border to become continuous with the supramastoid crest of the temporal. In the middle of their course the lines are about two centi- metres apart. The space between them is a little smoother than the surface above and below. It is uncommon to be able to trace both lines throughout. The inferior is usuallv the better marked. Sometimes a part of each is suppressed. The identity of a single line is shown by its termination. Near the upper posterior angle is a minute pin-hole, the parietal foramen,^ which transmits a vein. This foramen is very often wanting, and, when visible, may be closed. In very rare cases it is a large hole, which may e\en. admit a finger. It is occasionally double. The internal surface is smooth and glistening, as is the case throughout the inside of the cranium. It is marked by tree-like grooves for the branches of the middle meningeal artery. Fig. 22^. Am. sup. angl \'lf<^ ' ~ ^ w v3» T^'*\ r.roove for longiludl- ^J i\\ ^ Post. sup. angle Grooves for middle — .^ _ ^ meningeal art er> ■, ^ — ^_ —-^■^i Anterior inf. angle Right parietal bone, One of these starts close to the anterior lower angle, being at first very deep and sometimes a canal for a short distance. Its situation is exceedingly constant. One or two other branches appear in the posterior half of the lower border. The superior longitudinal sinus rests in a groove ■ completed by both bones along the upper border. This groove is rarely symmetrical, being generally largest on the right. At the posterior inferior angle there is a small surface completing the groove ' of the lateral sinus at the point at which it turns from the occipital into the temporal bone. Pacchi- onian depressions are small pits of varying size and number, found in the upper part of the inner surface, and most commonly near the groove for the longitudinal sinus, which contain the Pacchionian bodies of the arachnoid. The largest might receive the tip of the little finger. The anterior, superior, and posterior borders are all jagged. The anterior border meets the frontal, overlapping it below, overlapped above. The superior border meets that of its fellow. The serrations are most developed in the middle. I parietale. - Sulcus sagittal'! Sulcus transvei THE SUPERIOR MAXILLA. 199 the end of the suture behind the parietal foramina being nearly straight. The pos- terior border interlocks with the squamous portion of the occipital by a very irregular line of suture. The inferior border, concave in the middle, is bevelled on its outer surface, except behind. It is covered anteriorly by the top of the great wing of the sphenoid, and along the concavity by the squamous part of the temporal. The pos- terior portion presents a point at the back of the concavity which fits into an angle between the squamous and mastoid parts of the temporal. Behind this it is thick and jagged for the top of the mastoid portion. The anterior superior corner is about a right angle. The inferior one is somewhat drawn out. The superior posterior corner is rounded. The inferior is cut off. Parietal impressions is the term applied to depressions which are observed very e.xceptionally on the outer surface of the parietal bones above the parietal emi- nences and near the upper border. They are usually large, — i.e., some seven centi- metres long by five or six centimetres broad. Some sections have shown that they involve only the outer surface of the bone. A thinning above the sagittal suture has also been observed, and even one over the lambdoidal suture. These latter are generally considered atrophic changes occurring in old age. The same explanation is offered for the parietal impressions proper, and very possibly with justice ; still, the case is reported by Shepherd ' of an old woman who remembered having them all her life, and who declared that her father had them likewise. This would point to their being occasionally both congenital and hereditary. The late Professor Sir George Humphry " observed them in the orang-outang. Articulations. — Each parietal articulates with its mate, the occipital, temporal, sphenoid, and frontal bones. Development. — A single centre appears in the membrane at the end of the second fcetal month. According to Toldt {Lotos, 1882), this is double, consisting of an upper and a lower part, which soon fuse. The centre becomes very prominent, and bone-rays extend from it, making the bone very rough till after birth. The fontanelles at the four corners of the bone are discussed in describing the skull as a whole (page 231 J. The radiating lines of bone leave an interval near the back of the upper border of the bone, called the sagittal foyitanelle, which closes during the latter part of foetal life. According to Broca, this can be seen at birth once in four times. The parietal foramen is left as this fissure closes. Its occasional great size is accounted for by irregularities in the process. Very rarely a suture divides the parietal into an upper and a lower portion. THE FACE. The face consists of the orbits, the nose, and the jaws. Portions of the sphe- noid and the ethmoid form a considerable part of it, as has been described. The facial bones are two superior maxillce, two malar, two nasal, two lachrymal, two palate, two inferior turbinates, the vomer, the inferior maxilla, and the hyoid. The future nasal septian, extending in the median plane from the base of the skull to the upper jaw, is very early developed in cartilage. Ossification progresses from superficial centres on either side. These form the vertical plate of the ethmoid and the vomer ; but a considerable part, the triangular cartilage, remains cartilaginous. THE SUPERIOR MAXILLA. The superior maxilla^ is a very irregular bone, which with its fellow forms the front of the upper part of the face, the floor of the orbit, much of the outer waU and floor of the nasal cavity, much of the hard palate, and supports all the upper teeth. It has a body, and malar, iiasal, alveolar, and palatal processes. The general shape of the body ' is that of a four-sided pyramid ; the base looking towards the nasal cavity, one surface forming the floor of the orbit and the other two the front and back of the bone. These three surfaces meet at the apex, which is the malar process.^ 'Journal of Anatomy and Physiology, vol. x.xvii., 1893. ''Ibid, vol. viii., 1874. Maxilla. ^Corpus maxillae. '' Processus zygomaticus. HUMAN ANATOMY. This is a rough triangular surface articulating with the malar, often perforated, and sending downward a smooth ridge separating the anterior and posterior surfaces ; the former is in the front of the face, the latter in the zygomatic fossa. The lower border of both is the alveolar process} which is simply a curved row of tooth sockets made of very light plates of bone, which are absorbed after the loss of the teeth. The palatal process'^ joins the inner side of the body like a shelf and supports the anterior part of the alveolar process. The 7iasal process^ rises from the anterior inner part to meet the frontal bone. In certain parts of the description it is con- venient to disregard these subdivisions. The anterior surface of the bone forms the lower and outer boundary of the nasal opening, which is finished above by the nasal bone. On the entire skull this aperture resembles an ace of hearts inverted. The lower boundary of the opening is slightly raised and smooth. On the side it is sharp. The pointed anterior nasal spine projects forward where the two bones meet below the opening.* There is a slight depression — the incisor or myrtiform fossa — over the lateral incisor tooth. External to this is a ridge caused by the socket of the canine tooth. Farther outward is a well-marked hollow, the ca7iine fossa. Above Fig. 224. Lachrymal groove Lachrymal notch. Orbital surface Infra-orbital groove »^Ss^=%!s-T> — T,^ ll-^ ■ — -Nasal crest Anterior nasal spine- itcj*- it -^*(™'"" - ^^=^' '^ ^ Palatal process Anterior palatine canal Alveolar procesi inferior turbinate rests on the inner surface of the maxilla, and the vomer on the crest made by the union of the palate processes. Development and Changes. — There are certainly four chief centres, all of which appear at about the end of the sixth week of fcetal life. Three of them fuse very rapidly. There is one on either side of the infra-orbital groove, a malar and an orbito-facial, and below and internally 2l palati7it\ The fourth, the intermaxillary, stays distinct longer. It comprises the front of the palate as far back as the anterior palatine canal, and represents a very constant separate ossification in vertebrates, the premaxilla, in front of the maxilla, except in certain mammals in which it is between them. It bears the incisor teeth, and at the third fcetal month fuses with the maxilla. As the intermaxillary grows, the suture in the roof of the mouth per- sists for a time. It is very plain at birth and often for a year or two later. Some- times it is seen in the adult. At first the posterior suture is very close to the incisors, but as it grows the intermaxillary forms a large part of the palate. If detached, it is seen notched behind, so as to form the inner wall of the upper part of ' Virchow's Archiv, Bd. Ixiii. THE SUPERIOR MAXILLA. 203 Stenson's canal. The suture is rarely seen above and never in front, being concealed by the plate forming the front of the bone. Albrecht ' asserts that each intermaxil- lary is double. In support of this is the fact that in cleft palate the fissure does not always come between the incisor teeth and the canine, but an incisor may be found on its outer side. In reply to this it has been pointed out that three incisors on each side occasionally occur, and that, as anomalies are likely to be found in groups, this is merely an irregular arrangement. Moreover, in cases in which the cleft has but one incisor on each side of it, it is well argued that the original position of the tooth-sacs has no certain relation to the bones (Th. Kolliker^). In sup- port of Albrecht is the occasional presence of a line subdividing the lower surface of the premaxilla ; but, on the other hand, it is not certain that this is really a suture, and there seems no evidence that the premaxilla has two centres of ossifi- cation. While there is much that is plausible in Albrecht' s views, they cannot be considered as established. Sir William Turner' thus concludes an excellent discussion of the question : " What is yet wanted, however, to give completeness to the evidence of the division of the interma.xillary bone into an inner and an outer part is the discovery that the intermaxillary bone normally rises from two distinct centres of ossification, one for the inner, the other for the outer part. Of this we have at present no evidence. Fig. 22-. Lachr>'mal groove Inferior surface of upper jaw at about birth. ^rr-^— ^-Antrum Ant. palatine canal Palatal process Mesial surface of upper jaw at about birth. But, in connection with this matter, we ought not to forget that it is quite recently that the embryological evidence of the origin of the intermaxillary part of the human upper jaw from a centre distinct from that of the superior maxilla has been completed. And yet for nearly a century, on such minor evidence as was advanced by Goethe, — viz., the suture on the hard palate extending through to the nasal surface, — anatomists have believed and taught that the human upper jaw represented both the superior and intermaxillary bones in any other mammal. Where a question in human embryology hinges upon an examination of parts in a very early stage of development, we often have to wait for many years before an appropriate specimen falls into the hands of a competent observer. The upper and lower sides of the bone are at first very near together. The tooth-sacs are directly below the orbit. In the latter part of fcetal life the antrum appears as a slight pouch growing in from the nasal side. As the bone grows, the antrum remains for some time on the inner side of the infra-orbital canal. The outer part of the bone, especially towards the malar, is filled with diploe, which subse- quently is absorbed as the sinus extends outward. By the end of the second year the cavity has extended above the first permanent molar ; by the twelfth or thirteenth year, when the second molar has appeared, the antrum approaches, though it has not yet reached, its definite shape. During the first dentition it is separated by the uncut teeth from the front of the bone. ' Sur las quatres os intermaxillaires, Soc. d'Antropol. de Bruxelles, 1S83. Die morpho- logische Bedeutung der Kiefer-, Lippen-, und Gesichtsspalten, Langenbeck's Archiv, Bd. xxi. ^ Ueber das Os intermaxillare des Menschen. Nova Acta der Leopold. Carol. Akad. der Naturforschen, Bd. xliii,, 1882. ' Journal of Anatomy and Physiology, vol. xix., 1895. 20^. HUMAN ANATOMY. Orbital surface Fig. 228. Orbital process After the loss of the teeth from old aa^e or otherwise the alveolar process is absorbed. Senile atrophy is particularly marked in this bone. THE PALATE BONE. This' consists of a horizontal and a vertical plate and three processes, the /_r- ramidal, the orbital, and the sphenoidal. The horizontal plate" is quadrilateral. It completes with its fellow the hard palate, filling the space left vacant be- tween the back parts of the superior ma.xillae. Its superior surface is smooth like the rest of the floor of the nares, and the lower rough, but less so than that of the superior max- illa. The anterior border hts the back of the palatal process of the maxilla ; the inner border is rough to meet its fellow, and' raised into a nasal crest meeting the back of the lower edge of the vomer. This is prolonged behind to form with the other the posterior nasal spine. The postgrior border is smooth and concave from side to side. The outer border joins the vertical plate.' This is very thin, with an outer and an inner sur- face. It is surmounted by two processes, between which is a deep notch which forms three-quarters or more of the spheno-palatine foramen * when the bone is in position, so that both processes touch the body of the sphenoid. The outer surface presents near the top a smooth vertical surface forming part of the ptery go-maxillary Fig. 229. For ethmoid Orbital process Spheno-maxillary fossa Spheno-palaline notch ERTICAL PLATE For ext. pteryg. plate Pterygoid fossa HORIZONTAL PLATE For int. pterygoid plate' Right palate bone from behind TUBEROSITY Sup. turbinate crest Sphenoidal process Middle nasal meatus — Inf. turbinate crest Inferior meatus .Tuberosity Posterior nasal spine Nasal crest Inner aspect of right palate bone in place. Part of inferior turbinate removed. fissure. This narrows below into a groove which makes the posterior palatine canal when applied to the corresponding groove in the maxilla. In front of this the surface is at first rough where it rests against that bone, and more anteriorly smooth where it closes the lower part of the opening of the antrum by an irregulal - Pars horizontalis. Pars perpendlcula I sphenopaiatinun THE PALATE BONE. 205 Oibital surface prolongation. The inner surface, looking towards the nasal cavity, is free and smooth. It is crossed below the middle by a ridge, the inferior turbinate cresf^ for the posterior attachment of the inferior turbinate bone. Nearly on a level with the base of the notch is another ridge faintly marked behind it ; this is the superior turbinate crest' for the middle turbinate bone of the ethmoid. A small part of the top of the vertical plate looks into the superior meatus. The pyramidal process, or tuberosity, is the only solid part of the bone. It projects backward and some- what outward from the lower part of the vertical plate. A smooth, hollowed, triangular surface fits into the space left between the pterygoid plates, completing the floor of the pterygoid fossa ; on one side of this is a groove for the front of the internal pterygoid plate and on the other a rough surface for that of the outer. Thus, through the palate bone, the pterygoids support the back of the upper jaw. The outer side of the process rests against the tuberosity of the maxilla in front of the tip of the external pterygoid plate. The orbital process, is the anterior of the two processes above the vertical plate, the larger and higher, so called because it forms a small part of the floor of the orbit near its apex on the inner side. This little surface, on the outer side of the process, is triangular, one edge articulating with the upper jaw and one with the os planum, the hind edge being free. Another smooth surface looks outward and backward towards the spheno-maxillary fossa. It is separated from the preceding surface by an angle. Three other surfaces rest F'g, against other bones. An antero-inferior one joins the maxilla, sometimes helping to close the antrum ; an anterior one touches the ethmoid, bounding part of a cell ; and a small one, just at the top of the notch, touches the sphenoidal spongy bone. The posterior or sphenoidal process has a narrow upper surface, which, joining the sphenoidal spongy bone near the base of the internal ptery- goid plate, completes the pterygo-palatine canal. This surface reaches the edge of the vomer. The internal surface, slant- ing a little downward, is free, looking into the nasal fossa. The outer surface is di- vided by a vertical ridge into an anterior part, free and smooth, looking into the spheno-maxillary fossa, and a scale-like pos- terior portion which rests against the external pterygoid plate. The Spheno-Maxillary Fossa. — When the palate bone is applied to the sphenoid and the maxilla, the spheno-palatine foramen forms a window between the nasal chamber and a little hollow, the spheno-maxillary fossa, just below and behind the apex of the orbit. The posterior wall of this space, formed by the smooth sur- face of the sphenoid above the pterygoid plates, is pierced by the for-amen rotundum and the Vidian canal. Below, it narrows funnel-like into x\\& posterior palatine canal. Articulations. — The palate bone articulates with its fellow, the superior max- illary, sphenoid, ethmoid, vomer, and inferior turbinate bones. Development. — Ossification begins from a single centre appearing in mem- brane near the end of the second foetal month at about the junction of the vertical and horizontal plates. It is very delicate throughout foetal life, but the posterior free edge of the palate is very early much denser. Originally the horizontal plate is larger than the vertical one ; at birth they are about equal. THE VOMER. The vomer' is a thin, irregularly quadrilateral plate, forming the back and lower part of the nasal septum. The superior border expands laterally into two wings, or ales, which articulate with the under surface of the body of the sphenoid, and enclose a medium groove for the rostrum.' Laterally, the wings fit under the vaginal pro ^ Crista turbinalis. - Crista ethmoidaiis. ^ Vomer. Riglit palate bone, outer aspect. 2o6 HUMAN ANATOMY. cesses of the sphenoid. The posterior border is free. Thick above, just under the alae, it soon narrows and runs downward and forward. The injerior border fits — SUPERIOR BOR Naso-palatine groove Vomer in place, from left side. Fig. 232. Groove for rostrum of sphenoid between the nasal crests of the palatals and ma.xilhE, and anteriorly changes its direc- tion so as to rise over the higher incisor crests as far as the anterior palatine canal. The anterior border is the longest. Its upper part articulates with the back of Fig. 233. the vertical plate of the ethmoid, the lower part with the triangular cartilage of the nasal septum. The latter is received into a groove which may extend behind the vertical plate. The sides of the vomer are covered with mucous membrane. They present a few irregularities, the most important of which is a groove on either side, nearer the front than the back, for the naso-palatine nerve ; and, just anterior to this, a thickening which is normally insignificant, but occasionally is developed to one side or the other, forming a spur which may nearly close the passage. Articulations. — The vomer articulates with the sphenoid, ethmoid, palate, and superior ma.xillary bones and the median triangular cartilage. Development. — It is to be remembered that, although the vomer becomes through ossification one of the separate bones of the face, at an early period it is but a portion of the septal car- tilage without any hint of demarcation. A single centre appears before the close of the second foetal month in the membrane at the under border of the cartilage, which then forms the septum. This grows upward on either side of the cartilage until the bone is complete. The young bone shows very clearly its formation in two plates ; but in the adult this appears only in the groove between the wings and in the lower part of the front border, which still receives the triangular cartilage. Grooved ant. border for septal cartilage THE LACHRYMAL BONE. 207 THE LACHRYMAL BONE. The lachrymal bone ' is an exceedingly thin osseous plate, filling the vacancy in the inner wall of the orbit between the orbital plate of the ethmoid and the ascending process of the superior ma.xilla. It is quadrilateral, the long diameter being vertical, and presents an outer surface directed towards the orbit and an inner surface towards the nasal fossa. The latter rests, in part, against the turbinate process of the eth- moid, which more or less overlaps it. It closes the infundibulum and several anterior Fig. 234. Lachrvmal crest Nasal process of sup. Orbital surface -^Lachr>'mal groove ^^^i—T 7^ Hamular process Right lachrymal bone in place, outer aspect. Fig. 235. ethmoidal cells. The lower and anterior portion of this surface forms a part of the wall of the middle nasal meatus. The outer surface is subdivided by a vertical ridge, ^ marking off a smaller anterior part, which forms the lachrymal groove ;''' and, joining the corresponding groove of the superior ma.xillary, complete the lachrymal canal. The posterior part of the orbital surface is plane. The ham,ular process * is a small tongue of bone curving forward from the lower part of the dividing ridge to form the posterior border of the canal at the floor of the orbit. The descending process is a downward prolongation of the grooved portion, forming part of the wall of the canal, and meeting the lachrymal process of the inferior turbinate. The bone also articulates with the frontal by its upper surface, and with the front of the os planum by its pos- terior border. Articulations. — The lachrymal articulates with the eth- moid, frontal, superior maxillary, and inferior turbinate bones. Development. — Ossification is from a single centre said to appear in the eighth foetal week, although the variations imply extra ones. Macalister' enumerates six separate ossicles which may occur about the bone. It varies greatly in size ; it may be wanting, though rarely, and sometimes is very large. A considerable development of the hamular portion, which may be separate, represents the condition of prosimians and platyrhine apes.' It may be subdivided or perforated.' ^ Proc. Royal Society, 1SS4. ' Gegenbaur : Morph. Jahrbuch, Bd. vii. ' Le Double : Essai sur la Morphogenie et les Variations du Lacrymal, 1900 ; and Zabel : Varietaten und Vollstandiges Fehlen des Tranenbeins beim Menschen, Anat. Hefte. Bd. xv., Heft I, 1900. ^ Os lacrimale. -Crista lacrimalis. ^Sulcus lacrimalis. * Hamulus lacrimalis. Right lachrymal bona, inner aspect. Upper part completes anterior ethmoidal cells, lower looks into middle nasal meatus. 2o8 HUMAN ANATOMY, THE INFERIOR TURBINATE BONE. This is an elongated curved bone ' placed in the lateral wall of the nasal cavity below the superior and middle turbinates, which are parts of the ethmoid. The inner convex surface is pitted and grooved by the cavernous tissue beneath the mucous membrane. This condition is continued round the free lower border a little way up the outer side. The rest turbinate bone in place, inner aspect. Fig of the outer surface, overhanging the inferior nasal meatus, is nearly smooth. The ends of the bone are pointed. They are connected below by the regular cur^-e of the inferior border. The upper border is thin and irregular. It articulates in front with the inferior turbinate crest of the max- illa. Behind this rises the /ac/i>iy)>/a/ process' — the highest — to meet the lachrymal bone. Posterior to this the viaxillaiy process ' bends outward and downward. It does not, how- ever, usually hook over the upper edge of the plate bounding the entrance of the an- trum, but meets it edge to edge, consider- ably reducing the opening. Still farther back is the ethmoidal process^ meeting the uncinate process ; and, finally, the border rests on the inferior turbinate ridge of the palate bone. Articulations. — The inferior turbinate articulates ^\•ith the superior ma.xillary, ethmoid, palate, and lachrymal bones. Development. — Ossification proceeds from a single center which appears about the middle of foetal life. Maxillary process Right inferior turbinate bone, outer aspect. > Concha inferior. - Proc. la * Proc. ethmoidall* THE NASAL AND MALAR BONE. 209 Fig. 2^8. Right nasal bone, ouler and inner aspects. THE NASAL BONE. The two nasal bones' bound the anterior nasal opening aJDOve. Each one is a four-sided plate with an outer and an inner surface. The upper end is thick and jagged, articulating with the frontal above and also behind. The anterior border, which articulates with its fellow, is thick above and thin below. When the two bones are in place, the united upper portions of these borders form posteriorly the nasal crest, which articulates with the nasal spine of the frontal, and sometimes with the vertical plate of the eth- moid below it. The pos- terior border joins the as- cending process of the maxilla. The thin lower border, slanting downward and outward, has one or two indentations. The outer surface is broader below than above. It is depressed in the upper third, and has there a foramen for a vein. The extreme upper part of the inner surface is rough to join the frontal. Below this it is smooth where it forms the front of the nasal chamber ; the lower part of the inner surface sometimes seems hollowed out. A vertical groove for the nasal nerve ends near the notch in the lower border. Articulations. — The nasal bone articulates with the frontal, ethmoid, superior maxilla, and the opposite nasal. Development. — Ossification spreads from a centre appearing about the eighth week of fcetal life. At first the bone is broad and short. Occasionally a little Wormian bone is found in the median line between the nasals and the frontal. The two bones sometimes coossify, after the fashion of apes. Either a vertical or a trans- verse suture may be found. THE MALAR BONE. This bone^ forms the prominence of the cheek, the outer border of the orbit, most of the wall separating the orbit from the temporal fossa, and completes the zygomatic arch. For simplicity of description it is best to consider it a diamond- shaped bone, with an outer and an inner surface, four angles, four borders, and one important process, the orbital, which is neither an angle nor a border. The outer surface presents a slight prominence, the tuberosity,^ a little below the middle. The surface is nearly smooth, except that near the lower border there is often a certain roughness extending onto the zygomatic process for the origin of the masseter muscle. The greater part of the inner surface is smooth, looking towards the temporal and zygomatic fossa ; but a rough space under the front angle joins the malar process of the maxilla. It sometimes helps to close the antrum, in which case a part of it is smooth, being lined with mucous membrane. The superior angle, or frontal pi'ocess,^ joins by a rough surface the external angular process of the frontal. The posterior angle, or zygomatic process,'' more prominent below than above, joins the zygomatic process of the temporal, passing below it. The anterior and the inferior angks have no special names. The postero-superior, or temporal boj-der, is at first vertical, becoming horizontal towards the hind end. Near the beginning there is a posterior projection, t\\& marginal process, which varies considerably. The postero-inferior, or masseteric border, slightly irregular, is free, forming the lo\^-er edge of the front of the zygoma. The antero-inferior, or maxillary border, is slighdy concave. Itarticu- ^ Ossa nasalia. - Os zj-gomaticum. •* Tuberositas malaris. ■* Processus frontosphenoidalis. Processus temporalis. 2IO HUMAN ANATOMY. lates with the front of the malar process of the maxilla, bounding externally the rough surface of the inner side of the malar. The antero-superior, or orbital border, is smooth and concave, forming the external and most of the inferior boundary of the orbit. The orbital plate, or process, which forms the front of the outer wall of the orbit, projects inward from this border, joining the bone at nearly a right angle. Fig. 239. Tuberosity alar bone, outer aspect. Temporal canal It is narrow in front and broad behind, where its anterior surface looks towards the orbit and its posterior towards the temporal fossa. Its projecting edge is jagged throughout, and in front meets the superior maxilla. Behind that it joins the outer border of the great wing of the sphenoid, and above articulates with the frontal. Be- tween the part meeting the maxilla and that meeting the great wing there is usually a short, smooth surface bound- ing the end of the spheno- maxillary fissure, which lies between these bones in the lower outer angle of the orbit. Two foramina on the orbital surface lead to minute canals. The lower, the malar, ^ opens on the outer surface of the bone ; the upper, the tem- poral,- opens on the back of the orbital process. They transmit branches from the superior maxillary division of the fifth nerve. They vary greatly. In all mammals the pri- mary function of the malar is to unite the maxilla and the temporal bone. Its union Only in primates does it join the sphe- Orbital process Maxillary surface Right with the frontal is a further development noid and separate the orbit from the temporal fossa. Articulations. — The malar bone articulates with the frontal, superior maxillary, temporal, and sphenoid bones. Development and Variations. — There are three centres of ossification — an 1 zysomatictttemporate. THE INFERIOR MAXILLA. anterior, a posterior, and an inferior — appearing towards the end of the second foetal month. They fuse in the course of the third. Sometimes, but very rarely in the white races, the bone is divided by a fissure — as in some apes — into an upper and a lower part. This is said to be relatively common (seven per cent. ) in the Japanese. A division into three has been seen. The roughness for the masseter sometimes gives a deceptive appearance of a separate piece to this portion. On the other hand, an occasional slight horizontal cleft in the zygomatic process is probably a remnant of a division. THE INFERIOR MAXILLA. The inferior maxilla,' mandible, or lower jaw develops in two symmetrical halves, which soon fuse. The bone, as a whole, consists of a central part — the body — forming the chin and supporting the teeth, and two ra^ni projecting upward from the back on either side and articulating with the glenoid fossa of the temporal. The body is convex in front and concave behind. The line of junction of the original halves is the symphysis, marked by a slight line. There is a forward pro- jection of the lower border of the chin which is a human characteristic. A short Fig. 241. Coronoid process External pterygoid CONDYLE Sigmoid notch Neck fossa Levator tnenti BODY External oblique lin Platys Inferior maxillary bone, outer aspect. Mental foramen Depressor arig-uli oris distance from the median line at the lower border is the viental tubercle"^ bounding this projection laterally. The alveolar process, above the body, is of the same nature as that of the upper jaw. A slight depression, the incisor fossa, is found below the teeth of that name on the front of the bone. The mental foramen for the terminal branches of the inferior dental nerve and artery is rather below the middle of the bone under the second bicuspid, sometimes just before it. The external obliqzie line^ starting from the mental tubercle, passes below the mental foramen into the front edge of the ramus. Sometimes it seems to spring from the lower border under the molar teeth, and sometimes both these origins may be present at once. On the lower border of the bone, rather to its inner side, there is a rough oval behind each mental tubercle for the anterior belly of the digastric muscle. The inner side of the body is in the main smooth. The superior and inferior genial tubercles^ are two pairs of small, sharp spines near the lower part of the inner side of the symphysis for the genio-glossi and genio-hyoid muscles respectively. The internal obliqzie line begins at first very indistinctly near the genial tubercles, and is lost on the inner side of the ramus. It is particularly prominent under the molars, and gives attach- ^ Maadibula. - Tuberculum mentale. HUMAN ANATOMY. ment to the mylo-hyoid, which forms the muscular partition separating the oral cavity from the superficial region under the chin. There is a faint hollow, the sub- lingual fossa, above it, below the incisors, for the sublingual gland lying beneath the mucous membrane, and a deeper one, the submaxillary fossa, for the submaxillary gland below the line near the junction of the body and ramus. The ramus, which joins the body at an angle of from iio° to 120° in the adult, is a four-sided plate with an outer and an inner surface. The point of union of the posterior and inferior borders is called the angle, and is generally turned out- ward with a lip, which helps to form the under part of the masseteric fossa, on its outer side, for that muscle. When well marked, it represents the fossa which is so striking in the carnivora and some other orders. The fossa is not always present, the muscle being then inserted into a roughness. At the front of this space the lower border of the bone is often grooved by the facial artery crossing it. A projec- tion, known as the lemurine process, may e.xtend from the angle either backward or downward, but is not often large. The lower border of the ramus, where it joins the body, often presents a concavity, which is sometimes very marked, giving a peculiar'outline ; it is named the antegonium by Harrison Allen. There is a rough- FiG. 242. Sigmoid notch 'goid Fossa for sublin- gual gland. Sup. genial tuber. (genio-gloss„s). Inf. genial tuber. i.gcnio-hyoid) Submaxillary gland Inferior maxillary bone, inner aspect. ness on the inner side of the ramus at the angle for the internal pterygoid. About on a line with the free edge of the alveolar process is the lowest point of the inferior dental foramen,^ an opening into the inferior dental canal for the nerve and artery to the teeth ; the foramen is guarded in front by a sharp point, the lingula. A faint groove is continued from this opening below the internal oblique line for the mylo- hyoid vessels and nerve. The front border of the ramus is thick below and narrow above, where it becomes the coroJioid process," pointing upward and outward, into which the temporal muscle is inserted. The outer border of the thick part is made by the e.xternal oblique line, which is continued into the thin edge above ; the inner border is continued from the inner edge of the alveolar process, or sometimes from the internal oblique line. It ends on the inner surface of the coronoid process. The posterior border of the ramus slants upward, backward, and a little outward. It is rough at the angle and smooth above, where it widens to form the back of the head or condyle.^ This presents an articular surface convex from before backward and higher at the middle than at the ends. The longest diameter is not quite trans- verse, for the a.xes, if prolonged, would meet near the front of the foramen magnum. There is a pretty distinct tubercle at the outer and inner ends. The condyle has THE INFERIOR MAXILLA. 213 the appearance of being set rather on the front of the neck,' which is merely a constriction below the head ; the articular surface, however, extends at least as far down behind as in front. There is.a depression for a part of the insertion of the external pterygoid on the front of the neck internal to the sigmoid notch,' which is the deep depression separating the coronoid process from the condyle. The dental canal' sweeps downward and forward with a slight curve, and then runs Fig. 243. Coronoid process Section through body of lower jaw, anterior surface. horizontally nearer the lower than the upper border of the body of the jaw.* It lies at first against the inner wall, but soon is nearer the outer. This relation then varies, but towards the anterior end of its course it is against the inner wall. It divides under the second bicuspid into the mental canal, some five millimetres long, running to the mental foramen, and into the incisive canal, much smaller, for the vessels and nerves of the front teeth, which, after dividing, is lost in the cancellated tissue under the lateral incisor. Structure. — The jaw is of very tough bone, especially at the symphysis, where it is almost solid. On section the body shows very thick walls below, before, and behind. The alveolar processes, on the contrary, are made of very light plates that are ab-- sorbed rapidly after the loss of the teeth. Development and Growth. — The two halves of the inferior maxilla are formed separately, each from six centres. They are at first connected by ligament. Even before birth the union seems very close, but they become coossified only in the course of the first year. The centres appear from the sixth to the eighth week of foetal life in the membrane of Meckel's cartilage, except as otherwise mentioned. They fuse during the third month. The centres are : ( i ) the dentary, which is a line of ossific deposit forming the lower border and the front of the alveolar process ; (2) one in the distal end of Meckel's carti- lage, for the region of the symphysis ; (3) one for the coronoid ; (4) one appearing in cartilage, not that of Meckel, for the condyle and top of the ramus ; (5) one for the angle ; (6) the splenial, for the inner alveolar plate, extending back to include the lingula. This one appears some three weeks later than the others. Still another minute one is said to help to form the mental foramen (Rambaud et Renault). All these, except that for the condyle, which ynites at fifteen, fuse shortly after their appearance. The mandible, being at first nothing but a hollow bar to hold tooth-sacs, is very shallow. The ramus is small, .the head bent back- ward and the angle very large. At birth it is about 140°. With the loss of teeth, from whatever cause, the alveolar process atrophies. In old age the bone is very small and of light structure, and the angle enlarges considerably, so as to mimic the infantile form. *Fawcett : Journal of Anatomy and Physiology, vol. xxix., 1895. ^ Collum mandibulae. ^ Incisura maiidibulae. ^ Canalis mandibulae. Right haif of low at about birth, 214 HUMAN ANATOMY. Interarticular fibro-cartilagi Fig. 246. Zygoma, THE TEMPORO-MANDIBULAR ARTICULATION. This is a compound joint, the elements of .which are the socket, the condyle, and the meniscus, an intra-articular disk of fibro-cartilage, dividing the cavity into an upper and a lower part, both being enclosed by one capsular membrane. The socket includes the glenoid fossa and the articular eminence of the temporal bone. The articu- lar coating of the socket, which is continued onto the front of the articular eminence, is not true cartilage (Langer), though resem- bling it to the naked eye. The socket is bounded behind by the fissure of Glaser. The tympanic plate behind it is covered by areolar tissue and a part of the parotid gland, which extend to the back of the head of the jaw and make the socket much narrower and deeper than it seems on the dry bone. The interarticular fibro-caj-tilage^ is oblong trans- versely v.ith rounded angles. It rests more on the front of the condyle than on the top. It is concave both above and below, being moulded on the eminentia articularis and on the condyle. It may be merely one millimetre thick in the middle, and is said to be some- times perforated. The thick posterior border fits into the highest part of the socket. The capsule, lax and weak, is attached to the borders of the articular surfaces and to the edges of the interarticular fibro-cartilage. The external lateral ligament"- is a com- paratively strong collection of fibres, strengthening the capsule externally. The fibres run downward and back- FiG. 247. 1 ligament External late Styloid process Stylo-mandihi lar ligament ward from the tubercle on the zygoma, at the outer end of the articular eminence, to the outer side of the neck as far as the hind border. The effect of this insertion is to place the trans- verse axis of rotation of the jaw, not in the head of the mandible, but in the neck. The capsule receives at the front and inner side two bands of fibrous tissue continuous with the dura mater, which passes through the fora- men ovale around the third di- vision of the fifth ner\e.' The spheno-mandibular ligament,* formerly improperly called the internal lateral, is a weak fibrous structure originally developed around a part of Meckel's car- tilage. It runs from the spine of the sphenoid to the lingula without connection with the joint. The capsule is far too loose to hold the jaw firmly in place, hence it is supplemented by the powerful muscles of mastication. One of these, the external pterygoid, is inserted into both the head of the lower jaw and the meniscus, which it draws forward, being incorpo- 'Fawcett : Journal of Anatomy and Physiology, vol. x.wii., 1S93. ^ Discus articularis. - Lig. temporomandibulare. * Lig. sphenomandibulare. THE ARTICULATION OF THE MANDIBLE. 215 Capsule The tempo; rated with the front of the capsule. The stylo-tnaxillary Iiga7ne7it is a bundle of fibres of the cervical fascia running from the styloid process to the angle of the jaw. Movements. — These occur on both sides of the meniscus, which slides for- ward and backward on the articular eminence. They may be divided into those of opening and closing the mouth and of grinding the teeth. In the former, as the mouth begins to open, the meniscus and the head of the jaw move forward, the condyle at the same time- advancing on the former as the lower jaw turns on a transverse axis pass- ing through the neck in both halves of the jaw. This continues as the mouth opens wider, the meniscus descending onto the articular eminence, and probably, when the movement is extreme, rising a little on the other side. This has been graphically demonstrated on the living by an apparatus bearing luminous points at the sym- physis, the condyle, and the angle of the jaw, which were photographed as the mouth opened to various widths.' It was shown that the for- ward movement of the meniscus occurs even in a very slight opening of the mouth. The angle of the jaw moves forward at the very beginning of the act, but soon passes backward. The point on it describes some very complex curves. Grinding movements , in which the mouth is not opened, must occur chiefly between the skull and the meniscus ; just what occurs below the latter is uncertain. The lower jaw can be thrust for- ward evenly, as the meniscus of each side de- scends onto the articular eminence ; but in ordinary motions it seems to advance on one side and perhaps to recede on the other. Spee ^ has shown that the opposed crowns of the molars (and apparently of the premolars also) fall on the arc of a cir- cle that touches the front of the condyle, drawn, when projected on a plane, from a centre on the crest of the lachrymal bone. This allows the teeth of the lower jaw to slide on those of the upper, which the joint would not allow were the line between the teeth a straight one. To this ma}' be added that the inferior incisors rest against the lingual surfaces of the superior, and that the tendency of the edges of the former to make a transverse arch, increased by the wearing away of the outer corners of the lower lateral incisors, implies an alternate rising and falling of either side of the jaw in grinding movements with the mouth closed, though the axis, in the main antero-posterior, can- not be a fi.xed one. It must be remembered in this connection and in the mechanics of the jaw throughout that the range of variations is great, and that there is frequently a want of symmetry in the joints. This want of precise working is in- creased by the laxity of the ligaments and the num- ber of muscles acting on various parts of the jaw. Development. — The tympanic portion of the temporal being at birth nothing but the ring, it is evident that the joint belongs solely to the squamous portion, and is always bounded by the fissure of Glaser. At this age the glenoid fossa is nearly flat and the eminentia articularis but slightly raised. Even after birth the joint below the meniscus is very slight, so that but little motion can occur in it, while the meniscus ' Luce : Boston Medical and Surgical Journal, July 4, 1889. ' Arch, fiir Anat. und P'.iys., Anat. Abtheil., 1S90. Fig 2l6 HUMAN ANATOMY. — Great cornu itself can play freely on the flat glenoid. The socket gradually deepens, and as- sumes something like its definite shape apparently in the course of the third year. THE HYOID BONE. This is a U-shaped bone ' not in contact with any other, situated below the jaw and above the laryn.x, with which its physiological relation is intimate. It gives origin to a la ge part of the muscular fibres forming the tongue. It consists of a central body, elongated transversely, and of a pair of greater and lesser horns. The convex anterior surface of the body looks forward and upward ; the posterior surface, which is deeply hollowed, faces in the opposite direction. The front surface is divided by a median and a transverse ridge into four spaces, of which the upper are the larger. The greater cornua extend with a curve backward and a little upward. They are broadest at their front, and Fig. 250. as they pass backward are somewhat twisted, so that the upper surface comes to look outward. Each ends in a small knob. They are connected with the body sometimes by fibro-cartilage, occasionally by a synovial joint. The lesser cornua, slender processes some five millimetres long, are the bony ter- minations of the stylo-hyoid ligaments. There is usually a synovial joint be- tween them and the body, which they join at the ends of the upper border. They may be connected by ligament, and are not very rarely wanting, which simply means that ossification has not occurred at the lower ends of the stylo-hyoid ligaments. The outline of the body and greater horns is easily felt from the surface, and the whole bone can be grasped and moved from side to side. Development. — As embryology shows, the basihvoid, or body, is connected with the second visceral arch through the stylo-hyoid ligaments, the lower ends of which become the lesser horns, or cet-ato-liyoids, and with the third arch by the greater horns, the thyro-hyoids. The bone ossifies in cartilage, two nuclei appearing (according to Sutton ) in the fourth fcetal month, one on each side of the median line, and speedily fusing. A nucleus appears in each greater horn in the fifth month. Statements as to the time of appearance of ossification in the lesser horns vary from a few months after birth to the end of adolescence. The latter is probably nearer the truth. The greater horns rarely coossify with the body before forty-five, but after that age not infrequently. Indeed, in old age they are generally joined. The lesser horns are rarely consolidated before advanced age. The hyoid bone f: THE SKULL AS A WHOLE. In connection with the description of the skull as a whole, which is not intended to recapitulate the points already mentioned, but to discuss the general features, especially those resulting from the apposition of the distinct parts, let it be remem- bered that the skull is an egg-shaped structure, and that the face is placed under its anterior and middle fossze. The Cranial Sutures. — There are three antero-posterior sutures, a median and a lateral one on each side, and two transverse ones. The median antero- posterior suture is the sagittal;" it lies between the parietal bones, and is jagged, except at the posterior part, which is usually straight. Occasionally the vietopic suture" persists between the original halves of the frontal bone. It is rarely in direct continuation with the sagittal. The coronal suture^ crosses the top of the head, sep- arating the frontal from the parietals. It ends at the top of the great wing of the ' Os hyoide - Sutura sagittalis. S. frontalis. THE SKULL AS A WHOLE. 217 sphenoid below. Its termination is at a vague region where several sutures approach one another, called the pterion. In the lower races occasionally, but rarely in the higher, the lower end of the coronal is continuous with the suture between the squa- mosal and the great wing, in which case two sutures cross each other at right angles, and the pterion is a definite point, an ape-like feature. If the lower corner of the parietal bone is carried downward, and the suture between the great wing and the lower border of the frontal falls considerably, the general plan is that of an H, the cross-piece being the suture between the parietal and the sphenoid ; but the H is not often very clear. A separate bone, the €pipte7'ic, is occasionally found in this Fig. 251. Supra-orbital fora Exter. angular process. Infra-orbital fora Middle turbinate Nasal sept Inferior turbinate Anterior nasal spine Styloid process Corrugaior superctlu ■Orbicularis palpebraru Tendo oculi Orbicularis palpebrarum ■Levator labii superioris aldFgite nasi -Levator labii superioris Zygomaticus major Zygomaticus minor ■Masseter evator anguli oris .Compressor naris ■Depressor ala; nasi Buccinator Mental foramen. labii inferioris Dtp} essor anguli oris Platy stna region. (See under Growth and Age of the Skull.) The Imnbdoidal sutu7'€'^ starts from the top of the mastoid on each side to run upward and backward to a point separating the occipital from the parietals, the interlocking teeth being very long. What is practically a continuation of this suture runs downward between the oc- cipital and the mastoid. Wormian bones are often found, and sometimes in great numbers, in the lambdoidal suture. Sometimes there is a very large triangular one occupying the place of the upper part of the occipital. Such a one may be sub- divided. We incline to consider it a Wormian bone rather than a representative of the interparietal ^ Sntura lambdoldca. 2l8 HUMAN ANATOMY. The lateral antero-posterior suture begins at the root of the nose and runs through the orbit to the side of the head, ending at the lambdoidal. Its various parts are named from the adjacent bones. Thus, it begins with the fronto-riasa/, to continue between the frontal and the following bones : the superior ma.xilla, the lachrymal, the os planum of the ethmoid, the body, the lesser and greater wings of the sphenoid, the malar, and in the temporal fossa the great wing of the sphenoid again. Then behind the coronal it runs between the parietal above and the sphenoid and temporal below. Fig. 252. Inferior temporal line Coronal suture Sup. temporal 1 I fj i-Ext angu- ^^■yr J lar process .'* /. — Great wltig of SI henoid ^^-A- — Lachrymal \ \ -, Nasal Styloid process The skull from the side. THE EXTERIOR OF THE CRANIUM. Superior Aspect.' — This is oval and broader behind than in front, showing the coronal, sagittal, and the top of the lambdoidal sature. On either side is the parietal emineiicc, and in front the smaller frontal ones. The superior, and perhaps a little of the inferior, curved lines appear laterally. It is rarely quite symmetrical. Posterior Aspect.' — This is circular in outline, or sometimes five-sided, having an inferior, two lateral ( nearly vertical), and two oblique superior borders. Below the middle is the external occipital protubcraiice, which is beneath the most posterior point of the skull. Lateral Aspect.'' — This shows nothing of the face that has not been mentioned. The zvgomatic arch is prominent, bridging over a deep hollow. The part of the hollow above the arch is the temporal fossa, deepest in front, and nearly filled by the temporal muscle. The inner wall is formed by the squamosal and the great wing of the sphenoid ; the front one chiefly by the orbital plate of the malar. The infra- temporal crest on the great wing separates the temporal fossa from the zygo?natic fossa below. (The latter fossa is described with the face, page 227.) The two temporal ' Norma verticalis. - Norma occipitalis. ^ Norma lateralis. THE EXTERIOR OF THE CRANIUM. 219 lines are to be seen in whole or in part. Tlie inferior always ends in the supra- mastoid ridge. The mastoid process varies much in development. Anterior Aspect.' — The cranial portion of the skull is seen only above the orbits and the root of the nose. Much of its lower part is occupied by the frontal sinuses. Inferior Aspect." — (The lower jaw is supposed to be removed.) This aspect may be divided into three regions by two cross-lines, one being at the roots of the pterygoid plates and one at the front edge of the foramen magnum. Passing from behind forward, near the posterior surface, are seen the external occipital pro- Postenor nasal Posterior palatine canal Foramen ovaTe Eminentia articularis Middle lacerated foramen Foramen spino- sum Glenoid fossa Fissure of Glaser Condyle Ii ferior curved line External occipital protuberance Superior curved lii Ease of skull from below, the lower jaw removed. fuberance and the sziperior and itife?-ior curved lines. In front of the latter the occipital bone is convex to the outer side of the foramen magnum. A line con- necting the backs of the condyles halves the foramen magnum. The mastoid pro- cesses appear laterally. Internal to them are the digastric grooves, and just internal to these the occipital grooves, nearly or quite in the suture. Between the mastoid and styloid processes is the stylo-mastoid foramen. The region between the two above-mentioned lines includes the guttural fossa in the middle for the pharynx ; on each side of this are openings for great vessels and nerves, and, externally, the joint of the jaw. The basilar process in front of the foramen magnum forms the ^ Norma frontalis 220 HUiMAN ANATOMY. roof of the pharynx. On either side of it is a rent separating it from the temporal bone. The Back of this rent is the Jugular forameti ; then comes the y?j\y//;-t' proper ; and, at the ape.x of the petrous portion, the middle lacerated foramen, which in hfe is filled with cartilage, as is also the fissure. Outside, in the petrous bone, is the carotid opening, internal to the tympanic plate, which is separated by the fissure of Glaser from the glenoid fossa. The outer border of the petrous forms a gutter with the great wing of the sphenoid for the cartilaginous part of the Eustachiaii tube. Just outside of this is the foramen spinosum, often in the suture between the sphenoid and temporal, and before it the foramen ovale. In the front part of the base outside of the pterygoid is that part of the great wing which looks downward, overhanging ihe zygomatic fossa. THE INTERIOR OF THE CRANIUM. The vault' of the cranium has the groove for the superior lotigiiudinal simis in the middle, with Pacchionian depressions on each side of it. The grooves for the middle meningeal artery cover the parietal region. The base of the cranium is divided into three foss;e, — the anterior, the middle, and the poster ior. The anterior fossa' is bounded behind by the line in front of the olivary emi- nence and by the edge of the lesser wings of the sphenoid. It has a deep hollow over the nasal cavity, the floor of the depression being the cribriform plate of the ethmoid. In the median line are the crista galli and the foramen caecum. The lateral part of the anterior fossa slants downward, inward, and backward, and is quite smooth in the middle behind the hollow. The middle fossa ^ is limited in the centre to the sella turcica, but expands at the sides. It is separated from the posterior fossa by the dorsum sella and the superior border of the petrous. The middle fossa has the olivary eminence and the optic foramina in front of the sella turcica, at each side of which is the groove for the internal carotid artery and the cavernous sinus. The clinoid processes tend to meet above its sides, and sometimes do so, especially when the middle clinoid is developed. On the anterior border of the fossa, near the middle, is the sphenoidal fissure opening into the orbit. Just behind its inner end is the foramen rotundum ; farther back and outward are the foramen ovale and foramen spinosum, from which latter start the grooves of the middle meningeal artery ; more internal lies the middle lacerated foramen. The depression for the Gasserian ganglion is seen at the apex of the anterior surface of the petrous portion of the temporal bone ; the ganglion is very conveniently placed for its ophthalmic, superior ma.xillary, and mandibular branches to reach the sphenoidal fissure, the foramen rotundum, and the foramen ovale re- spectively. The posterior fossa* is much the larger. In the middle is tk^e foramen mag- num, with the basilar groove before it. The impression for the superior petrosal sinus is at the top of the petrous. The inferior petrosal sinus lies on the suture between the petrous bone and basilar process. The intcryial auditory meatus, the jugular foramen, and the anterior condyloid foramen are very nearly in a \'ertical line. The impressions for the lateral sinuses run outward from the internal occipital protuberance until they suddenly turn downward, making a deep groove in the tem- poral bone. The course of the second portion of the sinus is straight downward and inward, the highest point of the sinus corresponding with the supramastoid crest above the middle of the mastoid process. This point is sometimes so near to the surface that the bone is translucent. In its descent the sinus may for a time keep near the surface, or leave it at once. There is much variation in many respects ; sometimes the downward turn of the sinus is less sharp. The claim that anything can be predicated of this from the shape of the head is extremely uncertain. Just before reaching the jugular foramen the sinus once more changes its direction, running forward and upward. THE ARCHITECTURE OF THE CRANIUM. The curved vault of the skull is well adapted to break shocks, but the base is much weaker ; not only is the bone thin in many places, but it is interrupted by ^ Calvaria. - Fossa cranii anterior. ^ F. craoii media. 4 F. cranii posterior. THE ARCHITECTURE OF THE CRANIUM. 221 many openings. The whole of the anterior fossa is very thin ; so is the sella turcica, being just over the sphenoidal sinus. A chain of openings crosses the middle fossa on either side. The temporal bone is practically crossed by the external and internal meatuses and the middle ear, besides containing other cavities. Thus the petrous is brittle, although the bone is very dense. A rim of comparatively firm bone extends around two-thirds of the skull, starting on each side from the occipital protuberance, which may be even two centimetres in thickness, along the line of the lateral sinus to the supramastoid ridge ; it follows the line of origin of the zygoma, Torcular Herophili Base of skull £ and ends in the infratemporal crest on the great wing of the sphenoid. A median ridge strengthens the skull in both the frontal and occipital regions. The average thickness of the vault is about four millimetres. It is thick through- out the frontal region and at the parietal eminences, a thin area lying behind and below the latter. The Pacchionian depressions may almost perforate the skull. It is very thin in the squamous part of the temporal ; less so in the superior occipital fossae. If the base of a skull be held to the light and examined from within, the 222 HUMAN ANATOMY. translucency of the following parts will be very evident : the roofs of the orbits, one or two uncertain points in the great wing of the sphenoid, one in the lower part of the squamous portion just outside of the petro-squamous suture corresponding to the glenoid fossa, the beginning of the basilar process, a varying portion of the descending part of the groove for the lateral sinus, and nearly the whole of the floor of the cerebellar fossa. A litde rim of firm bone surrounds the foramen magnum except in front. THE FACE. This consists essentially of the framework of the jaws and of the orbital and nasal cavities, as well as of certain accessory regions, the zygomatic and spheno- maxillary fossa. Apart from features in the bones already described, the front view shows the outline of the orbits, of the nasal opening, of the prominence of the cheek, and of a vacant space left between the upper jaw and the ramus of the lower. The foramina for the escape of the terminal branches of the three divisions of the fifth nerve are very nearly in a vertical line, only the mental foramen is usually a little lateral. The side view shows the zygomatic fossa below the arch and within the ramus. The Orbit. — Although the base is quadrilateral, the orbital cavity is conical rather than pyramidal, since its section a litde behind the base is almost circular. The upper margin of the entrance is formed by the frontal bone, which slants down- ward to the very prominent external angular process, which affords great protection to the eye. The suture with the malar can easily be felt in life,owing to the greater projection of the upper bone. The outer border and the inner half of the lower are made by the malar, which has a sharp orbital edge throughout. This is continued by an ascending sharp edge of the superior ma.xillary into the front border of the lachrymal canal, at the top of which it becomes indistinct. This is to be considered the inner boundary ; but there is difficulty in accurately determining this border, for if the upper border be followed down at the inner side, it will be seen to run to the posterior edge of the lachrymal groove made by the ridge in the lachrymal bone. In some skulls this is much the more evident border. The upper part of the inner border is the only one that cannot easily be felt in life. The roof di the orbit is arched from side to side and from before backward. It is overhung by the border, especially at the outer angle, where it lodges the lachrymal gland. The inner ivall, composed of part of the ascending process of the maxilla, the lachrymal, the os planum of the eth- moid, and part of the body of the sphenoid, is nearly vertical in front, but farther back slants inward. The inner wall is frequently quite convex in the middle ; if this condition is marked, it is probably pathological. There is an approach to an angle between this surface and the upper. The two ethmoidal foramina are found above the OS planum. The inner wall curves gradually into the inferior surface, formed by the maxilla, and presenting the infra-orbital groove and canal. The outer wall slants strongly inward, its lower border being internal to the upper. It is formed bv the malar bone in front and the great wing of the sphenoid behind. The back part of the upper angle of the outer wall is occupied by the sphenoidal fissure, which opens into the middle fossa of the skull, and the lower angle by the spheno-maxillary fissure, separating the wing of the sphenoid from the maxilla ; the outer end of this fissure, closed by the malar bone, opens into the zygomatic fossa. The optic fora- men is at the posterior point of junction of the roof and the inner wall. The apex of the orbit is at the inner end of the sphenoidal fissure. The axes of the orbits, if prolonged, cross each other at the back of the sella turcica at an angle of from 42° to 44°. The orbital axis is, therefore, very differ- ent from the visual axis, which is antero-posterior. The former, moreover, runs downward from the apex to the base, making an angle of from 15° to 20° with the horizontal plane. The dimensions of the adult orbit vary with different observers and, no doubt, in different localities. The depth is from forty to forty-five millimetres, the breadth at the base is about forty millimetres, and the height about thirty-five millimetres in males. In females the dimensions are rather less. The roof is thin and separates the orbit from the cranial cavity, except in THE NASAL CAVITY. 223 front, at the inner side, where the frontal sinus intervenes. This sinus extends downward, mesially, almost to the top of the lachrymal groove. The inner and lower walls, separating the orbit from the nasal cavity and the antrum respectively, are very thin and offer little resistance to a tumor or a foreign body. The great wing of the sphenoid in the outer wall is thick, except just at the edge of the sphenoidal fissure ; it separates the orbit from the middle cranial fossa. The outer wall just behind the anterior border is thin, where it cuts off union with the temporal fossa. The Nasal Cavity. — -The nasal cavity of each side has an anterior and a pos- terior opening, a roof, a floor, an outer wall, and an inner, the septum, which, when Fig. 255. Crista gall: Partition sepa- rating frontal sinus from orbit Sup. turbinate Floor of nasal fossae Front section of skull through pla Inferior meatus nunication betwe the cartilage is present, completely separates it from its fellow. The anterior common opening of the two cavities is shaped like an inverted ace of hearts, bounded above by the border of the nasal bones and elsewhere by the superior maxillae. In the middle of the floor of the opening is the aiiterior nasal spine, resembling closely the bow of a boat. The anterior edge where the two bones meet is the cutwater, and above is a triangular surface, the deck, bounded by a sharp line, which runs outward, forming the lower border of the opening. In the adult this line is usually continuous with the lateral border of the opening, but in infants' skulls the line passes from the side onto the anterior surface of the maxillary bone. Another line a little behind this, starting inside the nose at the front of the inferior turbinate crest, runs close to the line from the spine. Though these lines are usually 224 HUMAN ANATOMY. fused in the adult, forming a rather dull inferior border continuous with the lateral sharp one, thev may remain distinct and enclose a well-marked fossa on the face just below the nasal opening ; this is the fossa pmnasalis, rarely seen in other than low races. Variations in the arrangement of these lines may occur, and according to Zuckerkandl,' the line from the border of the nose may not always form the anterior border of the fossa. The combined nasal openings, though in the main triangular, may be roughly quadrilateral. More or less asymmetry is the rule. The nasal bones and the nasal spine may point sideways, but not necessarily to the same side. The spine points to the side on which the opening is the wider ; the broader aperture usually does not descend so low as the narrower one. The tip of the nose is more often turned to the right. In life the shape of the nose depends quite as much on the soft parts as on the bones. The posterior openings of the nares, the choantz, are remarkably symmet- rical ; bounded above by the wings of the vomer, which conceal the body of the sphenoid, on the sides by the internal pterygoid plates, internally by the vomer, and below by the horizontal plate of the palate, each is much higher than broad. The index of the choanae, showing the proportion of the breadth to the height ('°°hei'°M''"')' '^ ^° ^°^ "■"^" ^""^ ^"^ ^°'' "'omen, showing relatively lower openings in the latter (Escat). Measuring the combined breadth frorii one pterygoid process to the other at the hard palate on Fig. 256. ten adult skulls irrespective of sex, Probe in infundibuium vve found the average breadth 27.7 centimetres and the average height 28.4 centimetres. The extremes were 24 and 31 centimetres for the breadth and 25 and 31 for the height." The inclination of the posterior border of the vomer is in a general direct ratio to the degree of prognathism,' or the forward projection of the face. Each nasal chamber (Figs. 255, 256) is very narrow, and much higher in the middle than at either orifice. The front part, the vestibule, extends under the bridge of the nose. The roof is extremely narrow except at the posterior end. It is composed of the nasal bones, thin below, thick above ; of a small part of the frontal, a thin plate separating it from the frontal sinus ; the very thin cribriform plate, easily broken ; the vertical anterior surface of the sphenoid, pierced by an opening into the sinus ; and, finally, the wing of the vomer. The floor is a smooth gutter, formed by the palatal processes of the maxillae and palate bones. The lower border of the anterior nasal opening is higher than the floor, so that an instrument has to be tilted over it. The anterior palatine canal opens through the floor near the front on either side of the septum. The floor, except at the posterior part, is of strong bone, and is smooth all over. The median icall is derived from a plate of cartilage, developed at a \erv early period, from which the vertical plate of the ethmoid and the vomer are also formed. A large quadrilateral space is left vacant in the macerated skeleton, which in life is filled by the unossified portion of the original plate, known as the triangular cartilage. Apparently the process of ossification is excessive along the line of union between the ethmoid and the vomer, since the adult septum is usually bent to one side in its anterior two-thirds, thus making one nasal cavity much smaller Portion of anterior section of preceding skull, seen from be- hind. The arrows occupy the opening from the antrum into the hiatus semilunaris. ' Normale und pathologische Anatomie der Nasenhohle, 2te Auflage, Vienna, 1893. ' The development of the nasal cavity is described with that of the head. ' Escat : Cavity Naso-Pbarjngiene, Paris, 1894. THE NASAL CAVITY. 225 than the other. A ridge is often found at or near the junction of these two bones on the prominent side, thereby still further reducing the smaller cavity. This ridge may be developed into a shelf, called a spur, which may even touch the opposite wall. The outer wall is the most instructive, as giving the most light on the con- struction of the region. In front is the smooth-walled vestibule, formed by the inner side of the nasal and the ascending process of the maxilla, extending upward under the frontal sinus. The swelling known as the agger may be found near the top of its outer wall. The inferior turbinate is much the largest, reaching forward almost to the opening in the bone. The large inferior meatus which it overhangs is higher in front than behind. The middle turbinate, over the middle ?neatus, does not extend nearly so far forward. The litde superior turbinate with the limited superior meatus below it is still farther back, reaching only half-way along the Fig. 257. Spheno-ethmoidal recess Extension of sphenoidal ! Pituitary fossa / Spfienoidal siiiu Crista galli Frontal sinus Spheno-pa latin Hamular process Palatal plate of sup maxilla Inner aspect of outer wall of right nasal fossa. middle turbinate. The three turbinates end behind very nearly in a vertical line, the middle sometimes projecting farthest. The lines of attachment of the turbinates all slant downward and backward, but the inclination of the middle one is greatest. The variations in number of the turbinates and the structures concealed by the middle one have been described with the ethmoid. The spheno-ethmoidal recess is a lateral expansion of the cavity behind the superior turbinate and the front of the body of the sphenoid. The posterior portion of the outer wall of the nasal chamber, formed by the palate bone and the internal pterygoid plate, is smooth. The outer wall slants inward, so that the roof of the nasal cavity is narrower than the floor, and has the following openings: in the superior meatus that of the posterior ethmoidal cells ; farther back is the spheno-palatine forameji communicating with the spheno- maxillary fossa. The middle meatus receives the opening of the fro7!tal sinus either directly under the front of the middle turbinate or through the infundibulum., 15 226 HUMAN ANATOMY. These arrangements are about equally common. It receives also the openings of the anterior ethmoidal cells, the aperture of the antrum into the infundibulum, and a larger opening from the antrum behind the infundibulum. The lacluymal canal opens into the inferior meatus under the fore part of the turbinate. External to the outer wall are the orbit, the antrum, and farther back the spheno-ma,\illary fossa with the posterior palatine canal below it. The Accessory Pneumatic Cavities. — These include the fro7ital sinuses, the maxillarv antra, the ethmoidal cells, and the sphenoidal sinuses. They have alreadv been described with the separate bones, but may be here further briefly con- sidered in their mutual relations to the nasal fossae and the skull. All of these spaces open into the nasal chambers above the inferior meatus, — the sphenoidal cells into the roof, the posterior ethmoidal cells into the superior meatus, the anterior eth- moidals, the antra, and the frontal sinuses into the middle meatus. Fig. 25S. Infratemporal crest Spheno-palatine foramen Glenoid fossa Mastoid pr<.itc>3 External auditory meatus Styloid process Zygoma Inner wall of zygomatic fossa (external ptery- goid plate I Spheno-maxillary fossa seen through ptery maxillary fissure Lateral 1 of skull with zygomatic arch removed. The sphenoidal sinuses (Fig. 257) are almost invariably unequal, the sep- tum being much to one side. The large openings in the front of the body of the sphenoid are much reduced when the cornua sphenoidalia are in place. The open- ings of the posterior ethmoidal cells are small and irregular. The anterior cells make a part of the floor of the frontal sinuses. They open either into the infundibulum or under the middle turbinate. The frontal sinuses (Figs. 255, 257), when exposed from the front, have a vaguely triangular outline. One side is against the septum, separating it from its fellow, which is rarely symmetrical. The upper border runs from the top of this downward and outward. The lower border bends downward at the inner end, where the cavity runs down to the nose at the inner angle of the orbit. The innei part extends back for a van,Mng distance over the orbit. In about half the cases the cavity opens directly into the middle meatus; in the rest it opens into the top of THE SPHENO-MAXILLARY FOSSA. 227 the canal in the ethmoid, known as the infiindibulu77i. In the former cases one of the cells of the ethmoid is particularly liable to make a projection — x\\& frontal bulla — into the floor of the sinus. The antrum (Fig. 255) is a four-sided pyramid with an irregular base towards the nasal cavity (Merkel). The apex is at the malar. In addition to the base, an orbital, an anterior, and a posterior surface are recognized. Owing to the irregularity of the base there is a groove instead of an angle below, above the alveolar process. (This relation is described with the upper jaw.) The large in- ternal aperture in the superior maxilla is divided into two when the other bones are in place. Both are near the top ; the anterior opens into the infundibulum, the pos- terior into the middle meatus. Partial septa project into the antral cavity. An important projection is that of the infra-orbital canal. The zygomatic fossa (Fig. 258) is the space internal to the lower jaw, sepa- rated from the temporal fossa by an imaginary plane at the level of the upper border of the zygoma. It is open below and behind. The front wall is made by Fig. 259. Orbital surface of great- wing of sphenoid Frontal process of malar- Cut surface of zygoma. Tympanic plate of temporal Mastoid process. Optic foramen Sphenoidal fissure Sphenoidal sinus Foramen rotundum Vidian canal Posterior wall of spheno- llary fossa Hamular process of internal pterygoid plate Zygomatic surface of external pterygoid plate Portion of right half of skull, showing posterior wall of spheno-maxillary fossa. The superior maxilla, ethmoid, and part of malar have been removed. the maxilla, what little roof there is bv that part of the great wing of the sphenoid internal to the infratemporal crest, and the inner wall by the external pterygoid plate. It has two important fissures, — the spkeno-niaxilla?y , horizontal, admitting to the orbit, between the sphenoid and maxilla ; the other, the pterygo-maxil- lary, vertical, between the maxillary bone and the front of the united pterygoid plates. The spheno-maxillary fossa (Fig. 259) is a small cavity below and behind the ape.x of the orbit at the point of junction of the spheno-maxillary and the pterygo-ma.xillary fissures. The posterior wall is formed by the sphenoid above the roots of the pterygoid plates. The transverse and antero-posterior diameters of the fossa are about fifteen millimetres. It contains the spheno-palatine or Meckel's ganglion. The foramen rotiindtan opens into it behind, transmitting the superior maxillary division of the trifacial nerve. More internal and lower on the posterior wall is the orifice of the Vidian canal, transmitting the great superficial and deep petrosal nerves and accompanying blood-vessels. Still nearer the median line is 228 HUMAN ANATOMY. the minute pkrygo-palatiyic canal, formed by the pahite and sphenoid bones. The sphe7io-palatine foramen opens through the inner wall into the nasal cavity. The fossa opens below into the posterior palatine canal. The Roof of the Mouth. — This comprises the hard palate and the inner aspect of the alveolar process. The proportions, as stated elsewhere (page 229), vary ; as a rule, the broad palate is less vaulted than the narrow one. The oral roof presents the orifices of three canals, — the anterior^ and the two posterior palatine. The first is situated in the mid-line in front, the others at the outer posterior angles. The palatine grooves for the anterior palatine nerves and accom- panying blood-vessels extend forward from the posterior palatine foramina. Be- hind, but close to, the latter are the orifices of the accessory palatine canals. The inner side of the alveolar process is rough except opposite the second and third molar teeth, and the same is true of that part of the palate made by the superior maxillae. An occasional swelling, the torus palatimts, is in the mid-line at the junction of the superior maxillae. Internal to the first molar is a ridge with the groove outside of it at the lateral border of the maxilla. The line separating the superior maxillse from the horizontal plates of the palate bones has a forward curve in the middle in nearly three-quarters of the cases. It is about straight in some twenty per cent, and curved backward in the rest. The fissures are not always symmetrical." The Architecture of the Face. — With the exception of the lower jaw, the structure of the face is extremely light. It is subject to no strain save through that bone, and to some extent through the action of the tongue on the palate ; it has, however, to be protected against occasional violence. There are certain strong and strengthening regions. The hard palate is strong throughout, except at the hind part, and especially strong back of the incisors. Some strength is gained by a thickening just outside of the nasal opening above the canine teeth, running up into the ridge in front of the lachrymal groove. The root of the nose is also very thick. The face is considerably strengthened through the malar bone and its con- nections, especially with the robust external angular process. A little support is probably given to the back of the jaw through the pterygoids. ANTHROPOLOGY OF THE SKULL. There are certain terms and measurements which should be known, especially as some of them come into practical use in the surgery of the skull. Points on the Surface of the Skull. — (.See also Fig. 265, page 241.) Alveolar point, the lowest point in the mid-line of the upper alveolar process. Astcrioti, the l^wer end of the lambdoidai suture ; three sutures diverge from it like rays. AuriLiilar point, tlie centre of the external auditory meatus. Basion, the anterior point of the margin of the foramen magnum. Bregma, the anterior end of the sagittal suture. Dacryon, tlie point of contact of the frontal, maxillary, and lachrymal bones. Glabella, the region above the nose between the superciliary eminences. Glenoid point, the centre of the glenoid fossa. Gonioti. the outer side of the angle of the lower jaw. Inion, the external occipital protuberance. Lambda, the posterior end of the sagittal suture. Malar point, the most prominent point of that bone. Mental point, the most anterior point of the symiihysis of the lower jaw. Nasion, the point of contact of the frontal bone with both nasals. Obelion, the sagittal suture in the region of the parietal foramina. Occipital point, the most posterior point in the mid-line. (It is above the protuberance.') Ophryon, the point of intersection of the median line with a line connecting the tops of the orbits. Of>istliion. the posterior point of the margin of the foramen magnum. Pierian, the region where the frontal, the great wing of the sphenoid, the parietal, and the temporal bones almost meet. ( As, in fact, they very rarely do meet, the term is a vague one.) • For the description of this canal, see under Superior Maxilla (page 201). ' Stieda : Arch, fiir Anthropol., 1893. ANTHROPOLOGY OF THE SKULL. ■ 229 Stephanion, the region where the curved lines on the temporal bone cross the coronal suture. Subnasal point, in the median line at the root of the anterior nasal spine. Indices. — The cephalic index is the ratio of the breadth to the length of the skull /iooxJ^radth\ .pj^g length is taken from the glabella to the occipital point, and the breadth is the greatest transverse diameter abo\-e the supramastoid ridge. _ A high index means a short skull ; a low index, a long one. A skull with an index above So is brachycephalic ; from 75 to 80, viesaticephatic ; below 75, dolichocephalic. The index of height is the ratio of the line from basion to bregma to the length /loox height \ ^ gj.yjj ^^,jj[^ ^j^ index above 75 is hypsicephalic ; from 70 to 75, orthocephalic ; \ length / below 70, platycephalic. The facial index is the ratio of the length to the breadth of the face ( '° breadt'h ) " "^^^ length is from the nasion to the mental point, and the breadth is the greatest at the zygomatic arches. A high index means a long face. A head with a facial index above 90 is leptoprosopic ; one with a lower one, cliama:prosopic. In the absence of the lower jaw the index of the upper face may be taken, which is almost equally valuable. The only difference is that the length is taken from the nasion to the alveolar point, and that an index above 50 is leptoprosopic, and one below it chaniczprosopic. The nasal index is the ratio of the length of the nose to the breadth ( ""farg^dth^ ) ' "^^^ length is measured ift a straight line from the fronto-nasal suture to the anterior nasal spine. A skull is hptorhine when the index is below 48 ; when from 48 to 53, viesorhine ; and when above 53, platyrhine. The orbital index is the ratio of the height of the base to the breadth, thus ( ""breadTif ) ' The breadth is a horizontal from the outer border to the point of contact of the frontal with the maxilla and lachrymal. A large index means a high orbit. An orbit with an index below 84 is microsenie ; with one from 84 to 89, viesoseme ; with one above 89, megaseme. An index of 70 is low for a Caucasian, and one of 106 vePi- high. The a\'erage for English skulls is said to be 88. The index depends considerably on the extent to which the upper border overhangs. The palatal index is the ratio of the breadth to the length. The former is taken from the socket of the second molar of one side to that of the other ; the latter is from the alveolar process in the middle line to the posterior nasal spine ( '°° 1 nTh — ) ' Prognathism denotes the forward projection of the face. This was formerly expressed by what is known as Camper'' s facial angle, which was measured on the arc bet\x'een two lines meeting at the nasal spine, one starting from the auricular point, the other from the most promi- nent part of the forehead in the middle line (avoiding the projecting nose). This has fallen into disuse owing to inherent defects, and perhaps in part to the discordant directions given for drawing the lines. Flower' s gnathic index: is the ratio of the line from the basion to the alveolar point to the line from the basion. to the nasion ( '°° '■ ^^' a\eoar ine\ ^ skull is ^ V basi-nasal hne / orthognathous with an index below 98 ; viesogtiathous with one from 98 to 103 ; prognathous with one above 103. Shape of the Skull. — Extreme forms occur in Caucasians. The long, narrow skull, with often a slight prominence along the sagittal suture, the scaphoid form, is due to the early closure of the sagittal suture, and the short, round skull to that of the transverse ones. In support of this theory is the fact that the metopic or median frontal suture is never found in narrow, but only in broad skulls. The high, sugar-loaf, acrocephalic skull shows obliteration of all three sutures on the top of the vault. The great backward occipital projection sometimes seen is usually asso- ciated with many Wormian bones in the lambdoidal suture. The long type of skull is naturally associated with the long, narrow face, and the round head with the broad face ; but the connection is not absolute. The tv\'0 types of face deser\'e a short consideration. The narrow face has the high orbit, the narrow nose, with the aperture pointed above, and a long, narrow palate. The outline of the range of teeth in one jaw to a great extent determines that of the other ; but, in addition to the smaller curve, the lower jaw in this form is rather delicate, is particularly likely to show the constriction in front of the masseter, and has a more obtuse angle. The sho7-t and broad face has wide, low orbits, a broad and almost quadrilateral opening of the nose, and a wide pair of jaws, the lower with an approxi- mately square angle. If, as is most probably the case, the head is orthognathous, the edges of the teeth tend to form part of an antero-posterior curve, which is particularly marked in the region of the molars. It is to be noted, however, that some, or any, of these features may be found in a face of the opposite t\-pe. Dimensions of the Skull. — The actual length of the various diameters is of much less importance than their relations to one another in the science of craniology ; they may, however, be important in medico-legal questions. With the exception of the height, tliey vary within wide limits, even among Caucasians. In the following table the means of both sexes are from Broca : Males. Females. Mean. Millimetres. Millimetres. Length 182 174 Breadth 145 135 Height 132 125 230 HUMAN ANATOMY. Cranial Capacity. — This may vary in all races from looo to 1800 cubic centimetres. Welcker gives the following means and e.xtremes for white races : ' Males 1450 Females 1300 1790 1550 1220 1090 A skull with a capacity exceeding 1450 cubic centimetres is megacephalic ; one with a capacity from 1350 to 1450, mesocephalic ; one below 1350, microcephalic. Manouvrier has devised a formula for calculating the weight of the brain from the cranial capacity, as follows : weight in grammes is to capacity in cubic centimetres as i to 0.S7. Asymmetry. — The whole head is almost always asymmetrical. The left side of the cranium, as shown by halters' models, is larger, especially in the frontal region. The right side of the head is usually the higher. The cause of this is probably to be found in habitual position. The spine is not held symmetrically, but the atlas inclines to the left ; the head, when held most hrmly, does not rest evenly on both condyles, but on one, usually the left. The position of the head, thus taken, is not enough to compensate for the obliquity of the base ; but certain changes take place in the relations of the component parts. Thus a face which seems Fig. 260. Anterior fontanelle The skull at birth, from before. tolerably symmetrical when resting on the left condyle only becomes quite uneven if placed upon both. The right orbit is usually the higher, the right side of the jaw is the stronger, and its teeth are set in a smaller curve. The tip of the nose turns to the right. Moreover, the face lacks symmetr>' in another direction : the right upper jaw and the malar bone are more promi- nent than the left. More striking differences, depending on these, are seen during life, which are ascribed to the effect of gravity on soft parts habitually held unevenly, the right side being the higher. The right eye is the higher and, apparently, the larger, the lids being farther apart ; while the cleft is narrow on the left and the eye nearer the nose. The left nostril is the larger ; the left fold of the cheek is less marked. In a certain proportion of persons all these peculiarities are reversed, and some of them may be transposed u-ithout the others. Growth and Age of the Skull. — By the si.xth month of fcetal life the skull, though smaller, is in much the same condition as at birth, except that then the occipital region is relatively larger. The most striking points are the insignificance of the face and the flatness of the inferior surface. In the cranium the frontal region is relatively small. The vault, which is developed in mem- brane, presents marked prominences at the parietal and frontal eminences, and a smaller one at ' Extreme cases occasionally pass these limits. There is in the Warren Museum the skull of a Highlander with a capacity of 1990 cubic centimetres, and one of a tall man, presumably an American, who could read and write, though his intelligence was defective, with a capacity of 1225 cubic centimetres. Turner has noted the skull of a female Australian of 930 cubic centi- metres' capacitj'. GROWTH OF THE SKULL. 231 the external occipital protuberance, from which radiating lines in the bone mark the process of development. The bones of the vault are exceedingly thin. Each is separate, the external periosteum and the dura uniting at the edges, thus limiting the spread of an effusion under the former to one bone. Six places where there are considerable membranous intervals between the developing bones are called fontanelles. They are situated at the four angles of the parietal bones, so that two are median and two are on either side. The median ones, by far the most prominent, are the anterior and posterior fontanelles. The anterior fontane lie, an important landmark in mid- wifery, is a diamond-shaped space between the rounded angles of the parietals and frontals, some thirty-five millimetres long by twenty-five millimetres broad. This one continues to grow after birth, and is not closed till some time in the first half of the second year, or even later. The posterior f07itanelle is situated at the apex of the squamous portion of the occipital, extending between the parietals. At an early stage, owing to the median fissure in the occipital, it is diamond-shaped, but later it is triangular. The space is more or less filled up in the last two months before birth, but it may not be truly closed for a month or two after. The anterior lateral fontanelle is a small unimportant space at the lower anterior angle of the parietal, above the great wing of the sphenoid, and extending around it. It usually closes at from two to three months after birth. The part between the sphenoid and squamosal is likely to persist the longest. According to Sutton,' in early foetal life the orbito-sphenoid bone reaches the lateral Fig. 261. lateral fontanelle The skull at birth, lateral aspect. wall of the skull at this point, and a piece of cartilage belonging to it is found in this fontanelle. It becomes bone in the course of the first year, and may unite with either sphenoid, temporal, frontal, or parietal, or persist as the epipteric bone. It most often joins the parietal. The pos- terior lateral fontanelle, under the corresponding angle of the parietal, extends down between the temporal and the occipital. It is larger than the preceding, and may be \'ery distinct for a month or more after birth. Its complete closure is said never to occur before the twelfth rnonth, and, perhaps, usually not till the second year.^ The sagittal fontanelle (see Ossification of Parietal) may be present at the seventh month of fcetal life, or later. The oblique fissure at the line of junction of the two parts of the squamous portion of the occipital persists till after birth, and must not be mistaken for an effect of violence. The mastoid process does not exist at birth. The tympanic bone is a mere frame for the ear-drum. The base of the cranium is very flat. The condyles are barely prominent, and the basilar process rises but sli.ghtly. In the first year the outer surface of the bones of the vault becomes smooth. The bones gain in thickness, and in the second year the diploe appears. At the same time the jagged points develop in the sutures, and at the end of that year the metopic suture between the frontals closes. ' Journal of Anatomy and Phvsiologv, vol. xviii., 1SS4. ''■ Adachi : Ueber die'Seitenfontanelie'n, Zeitschrift fiir Morph. und Anthrop., Bd. ii., Heft 2. 232 HUMAN ANATOMY. The/ace, while helping to form the orbit and nasal cavities, is essentially for the jaws, and the jaws for the teeth. The greatest change in the head after birth is the downward growth of the face. According to Froriep, in the infant the face is to the cranium as i to 8 ; at two years as I to 6 ; at five, as i to 4 ; at ten, as i to 3 ; in the grown woman as i to 2.5 ; in the man as I to 2. On contrasting the front view in the infant and adult, counting as "face" all below a line at the top of the orbits and as " cranium" all above it, it will be seen that in the infant the cranium forms about one-half and in the adult much less. The lower border of the nasal opening is at birth but very little below the orbit. A line connecting the lowest points of the malar bones passes at this age midway between the nasal opening and the border of the alveolar process. At birth the nasal aperture is relatively broad ; its lower border is not sharply marked off from the face A line from the nasal spine runs outward to end inside the cavity, and the crest from the outer border is still rudimentary, ending shortly on the front of the face, so that at the outer angle there is no distinct separation between face and nasal cavity.' The nasal cavity is shallow, the posterior nares very small. The vomer slants strongly forward. Tne lower jaw is small and the angle of the ramus very obtuse. The alveolar processes are rudi- mentary. The breadth of the skull at its widest equals or exceeds the combined height of the Posterior fontanelle Interparietal sutu Anterior fontanel! The skull at birth, Irom above. cranium and face in the infant ; in the adult it is but three-quarters of it. The breadth of the face is to its height as 10 to 4 at birth, and about as 9 to 8 in the adult. Merkel tli\'ides the growth of the head into two periods, with an intervening one of rest. The first ends with the seventh year, and is followed by inactivity till puberty, when the second period begins. The _firs/ period may be subdivided into three stages. In the Jzrsi stage, reach- ing to the end of the first year, the growth is general, but the face gains on the cranium. At six months the basilar process rises more sharply, which, with the downward growth of the face, has an important effect on the shape of the naso-pharynx. The lower part of the nasal cavity gains particularly. The posterior opening doubles its size in the fir.st six months, to remain stationary till the end of the second year. Intlie second s/age, to the end of the fifth year, the vault grows more than the base, assuming a more rounded and finished appearance. The face still gains relatively, but grows more in breadth than in height. In the third stage, corresponding roughly to the seventh year, the base grows more and the vault less. The face lengthens considerably, the growth in the nasal chambers being chiefly in the lower part. The head, though small, has lost the infantile aspect. The forameii magnum and the petrous portion of the temporal have reached their full size, and the orbit very nearly. The parietal and frontal eminences are still very prominent. The mastoid is rudimentary. This condition lasts till puberty, when the ' Macalister : Journal of Anatomy and Physiology, vol. xxxii., 1898. GROWTH OF THE SKULL. 233 second period begins. This is marked by growth in all directions, the gradual rounding off of the eminences of the vault, the progress of the mastoid, the strengthening of ridges, the greater curving of the zygomatic arches, and the increase of the face. This last is due chiefly to the advance of the nose, the gain of the superciliary eminences, and the increase of the lower jaw. The rise of the basilar process increases and the occipital condyles stand out more from the bases at the front edges. These processes are nearly finished in the female by nineteen and in the male one or two years later, though, especially in the latter, they require several years more for their absolute completion. The thickness of the vault is very nearly reached by puberty. At seven the frontal sinus is only as large as a pea. Its development is not completed before the twentieth year. There is no means of knowing whether or not it then entirely ceases. The orbit bears nearly the same proportion to the cranium at all ages ; but at birth it equals about one-half of the height of the face, and in the adult rather less than one-third. At birth the axis of the orbit is horizontal.' While sometimes the transverse diameter of the base of the orbit is much the larger, this does not seem to be always so. As the face grows the vertical diameter increa.ses rapidly, so that, according to Merkel, at five the base lacks only two or three millimetres of the adult height, which it gains in the next two years. The full breadth is probably not attained before puberty. The changes in the nasal cavity are important as an essential element in the growth of the face. At birth the line of the hard palate, if prolonged back, would strike near the junction of the basilar process and sphenoid ; at three it strikes near the middle of the basilar ; at six, the front edge of the foramen magnum, which is nearly or quite the condition of the adult. The measurements of the \ertical diameter of the choanse are important from their significance with regard to both the nose and the pharynx. At birth the height is from five to six millimetres (seven millimetres is exceptional) and the breadth of each opening very little greater. At from six months to a year both diameters have doubled, their proportions remaining unchanged. There is little change before the end of the second year, when the height increases more rapidly. Thus they change from circular to oblong openings. It is not till after puberty that the height exceeds the distance between the internal pterygoid plates. HEIGHT OF POSTERIOR NARES. Authority. Age. Se.x. Millimetres. Disse 4 male 16 Disse 5 female 11 Escat 5 15 Escat 8 18 Dwight 7 or 8 20 Dwight 7 or 8 21 Dwight ID female 22 Dwight II 22 Dwight 14 female 22 Escat 14 20 Dwight 15 male 23 Dwight 16^ female 23 Dwight 17 female ig Dwight 18 male 29 Dwight . . 19 male 24 Escat . . 15 to 18 (9 cases) 25 The Closure of the Sutures. — The occipital bone unites with the basisphenoid at the cerebral aspect about seventeen and on the outside of the skull some three years later. The lower end of the suture between the occipital and the mastoid process is one of the first to close. We have seen it lost in a skull of fourteen, of which the other bones were almost falling apart. No doubt this was exceptionally early. The closure of the great sutures of the vault ' ( to which the term is usually applied) begins on the inside of the skull, probably before thirty, at the lower ends of the coronal and at the back of the sagittal, and spreads irregularly. The process is generally far advanced before it appears on the outside. The closure of the sutures on one side of the head does not necessarily follow the same course on the other. It has usually begun on the outside by forty, although the sutures are still distinct. They probably are nearly or quite obliterated on the "inside by fifty-five. The apex of the lambdoidal suture is one of the last points to persist internally. It is impossible to state with accuracy the time at which the sutures disappear on the oiitside, as this may never occur, and the process throughout is utterly irregular. All may be gone \'ery early or all may be distinct at an advanced age. When the mefopic suture fails to close in early childhood it is one of the very last to disappear. It is unsafe from the sutures alone to draw any conclusions as to the age of a skull. The weight of the skull in both sexes is greatest from twenty to forty-live.^ The changes in old age are essentially atrophic. The most striking is the absorption of the alveolar processes ; this, however, may occur prematurely from the loss of teeth. The angle of the lower jaw becomes much more obtuse. The thin parts of the face and of the base ' Dwight : The Closure of the Cranial Sutures as a Sign of Age, Boston Medical and Sur- gical Journal, 1890. Parsons : Anthrop. Institute G. Brit, and Ireland, vol. xxx, 1905. '' Gurriere and Massetti : Rivista speriment. di Freniatria e de Med. legale, 1895. 234 HUMAN ANATOMY. of the skull become still thinner and mav be quite absorbed. The thinning of the vault is less marked. Occasionally, in e.xtreme age, symmetrical depressions appear in the upper parts of the parietals behind the vertex. In the latter part of life the frontal sinuses enlarge, as the inner table follows the shrinking brain. In some rare cases the skull grows heavier in old age, owing to an increase in thickness of the inner table. Differences due to Sex.— There is no marked sexual difference in skulls up to puberty. These characteristics appear during the last stage of growth. They may be summed up by saving that the female skull differs less than the male from that of childhood. The parietal and frontal eminences are more prominent ; the superciliary prominences and glabella less marked ; the zygomata, mastoid, occipital protuberance, and muscular ridges less developed. The whole structure is lighter. The face is smaller in proportion to the cranium, owing to the lighter jaws. The lower jaw alone is also relatively lighter to the cranium.' The frontal and occipital regions are less developed than the parietal. Two points are of especial value, — namely, in the female skull the change of direction from the forehead to the top of the head is more sudden, suggesting a definite angle, while in man the passage is imperceptible ; and, secondly in man a wedge-shaped growth above the front of the condyle is more developed, so as to throv, the face higher up. There is no trouble in recognizing a typical skull of either sex ; but in many cases the decision is difficult, and sometimes impossible. Surface Anatomy. — It is convenient for many reasons to settle on what shall be called the normal level of the skull. This should be parallel with the a.xis of the eye when looking at the horizon. It is e.xpressed by a plane passing through the points above the middle of each external auditory meatus and the lowest points of the anterior border of each orbit. A simple method is to regard the upper border of the zygoma as horizontal, but this is not sufficiently accurate with skulls of low races. The following parts are easily explored by the finger : the whole of the vault as far as the superior occipital line, the occipital protuberance behind, and- the supe- rior temporal ridges at the sides. Often the bregma and sometimes the chief sutures can be made out. The possibility of parietal depressions is to be remembered in cases of injury ; also that they may be expected to be symmetrical. The superciliary eminences and the upper borders of the orbits are easily explored. The prominence of the former is likely to imply a large frontal sinus ; but the conyerse is not true, for, especially in the latter part of life, there may be a large sinus with no external indication. The sinus always e.xtends downward to the inner side of the orbit, but its expansion outward and backward is very uncertain. The external angular process protects the outer side of the eye, and one or both temporal ridges can be followed from it. The suture between the process and the malar is easily felt through the skin. A line connecting the most prominent points of the zygomatic arches indicates the depth of the orbits. The zygoma is easily followed backward to the auricle. By pressing the latter forward, the supramastoid crest can be made out. Just below this is the spina supra- meatum, close to the cartilaginous meatus. The outside of the mastoid is easily e.xplored. The course of the lateral sinus is in a curved line with the convexity upward from the external occipital protuberance to the upper part of the mastoid, only the lower part of the sinus touching a straight line between those points. According to Birmingham, the descending part follows roughly the line of the attachment of the ear. There is, however, great variation in its course as to the sharpness of its descent and its relation to the surface of the mastoid. It may be exceedingly close, or in no particular relation to it (Figs. 199, 200, and de- scription of the temporal bone, page 179). The antrum leading to the mastoid cells is just back of the upper part of the meatus, often under a small, smooth surface. The antrum of Highmore in the superior maxilla extends upward to the floor of the orbit, outward into the malar prominence, dowmward to just above the line of reflection of the mucous membrane from the lips to the alveolar process, and inward to the line of attachment of the ala of the nose, which is above the canine eminence and marks the separation of the antrum from the nasal cavity. The variations of the upper end of the infundibulum are of interest. In the cases (about one-half) in which it drains the frontal sinus it is easy for fluid from the latter to run through the infundibulum both into the nasal ca\-ity through the hiatus semilunaris and into the antrum through the opening in its outer side. If the ' Gurriere and Massetti : Rivista speriment. di Freniatria e de Med. legale, 1S95. PRACTICAL CONSIDERATIONS : THE SKULL. 235 infundibulum ends blindly, there is less likelihood of inflammation spreading from the frontal sinus to the antrum. The nasal bones and their junction with the nasal cartilages are easily recognized. The ramus and body of the lower jaw are to be examined from the outside. The head and coronoid process are felt more easily if the mouth be opened. PRACTICAL CONSIDERATIONS. The Cranium. — In the development of the cranium, pro\'ision is made for its continuous enlargement, so that it may accommodate the rapidly growing brain. Accordingly, the first rudiment is a membranous capsule, at the base of which carti- lage is soon formed, giving support to the overlying portions. Then several centres of ossification appear in various portions of the membrane and grow quickly, so as to protect the cerebral mass, the membrane remaining between these centres still permitting the growth and expansion of the contents. Finally, the separate bones become united, first at their edges, then at their angles, to make the complete unyielding bony cranium. Arrest of these processes at various stages produces the equally various forms of malformation, only a few of which need be mentioned here. It is to be observed that, as a rule, they affect that part of the cranium that is of membranous origin, the base (developed from cartilage) being much more rarely involved. Turner (quoted by Allen) states that this is because the areas of the different bones are less precisely defined, and because the process of ossification is more liable to disturbance in mem- brane than in cartilage. In some cases the whole calvaria may be lacking and represented only by a membrane. Fissures extending from the margins of the bones towards the centres may exist, especially in the frontal and parietal bones, and may be mistaken for fractures. Other irregular gaps filled with membrane may be found, and are gen- erally situated at or near the natural foramina for vessels. The ossification of the bones may be so incomplete as to constitute what is called aplasia cranii congenita. a condition in infants due, usually, to maternal cachexia, and characterized by the absence of bone either in localized patches or at points scattered over the entire calvaria. The non-closure of the sutures, or defective development, may be followed by protrusion of the dura mater, either with or without part of the brain, constituting a ■meningocele if the protrusion consists only of the membranes and cerebro-spinal fluid ; an e7icephaloceIe if it contains brain ; or a hydrencephalocele if the contained brain is distended by an excess of ventricular fluid. These protrusions, in the order of frequency, occur (a) in the occipital region ; {b) at the fronto-nasal junction ; {c) in the course of the sagittal, lambdoidal, and other sutures ; {d) at the anterior or lateral fontanelles, and at the base of the cranium, entering the orbit, nose, or mouth through normal or abnormal openings. In hydrocephalus there are practically always atrophy and thinning of the cranium. ' ' The deformities of hydrocephalus are largely determined by the con- dition of the sutures at the time of the occurrence of the disease. Fixation at the line of the sagittal suture causes bulging at the forehead and the occiput. Fixation at both the lambdoidal and the sagittal sutures causes vertical bulging at the line of the coronal suture and enormous increase of the ascending portion of the frontal bone. Should the intracranial pressure announce itself prior to the closure of anv of the sutures of the vertex, the several bones composing it become widely separated and the fontanelles enormously increased in size" (Allen). In microcephalus there is diminution in the size of the cranium and of its cavity, due to premature ossification of the sutures. The subjects of microcephalus are usually idiotic. The operation of "linear craniotomy," by which a strip of bone is excised on either side of the median line of the cranium, was intended to permit of the expansion of the brain in such cases. It has not established itself in surgical favor. The arrested growth of the skull is thought to be due to the arrested development of the brain, and not vice versa. The skulls of idiots, even when not markedl}' microcephalic, approximate in many ways to those of the lower animals, 236 HUMAN ANATOMY. and form a distinct type characterized by the proportionate largeness of the facial bones, the contraction of the brain-case, especially in front and above, the upward slant of the occipital bone between the foramen magnum and the occipital crest, the projection backward of the frontal bone between the parietals at the situation of the anterior fontanelle, and by many minor peculiarities. In spite of these, however, thej' are easily referred to the human species by the descent of the cranial cavity below the level of the glenoid fossa, the number of the nasal bones, the shape of the jaws, the number and direction of the teeth, etc. Cretinism is said to be associated with initial deformities of the base pertaining to errors of development and trophic changes in the bones arising from cartilage, especially the basilar process of the occipital and the body of the sphenoid. Accessory to these deviations, and in a measure dependent upon them, are the modified facial proportions and dental irregularity of cretins. The Wormiati bones, "detached centres of ossification in the marginal area of growing membrane bones, which they aid in occupying intervening spaces among the bones themselves," have been depressed in injuries of the skull, and have resembled fragments of bone pressing against the meninges. The edge of such a bone has been mistaken for a line of fracture. The most frequent cause of the formation of Wormian bones is the stretching of the membranous envelope of the cranial cavity which occurs in hvdrocephalus, assistance in the completion of the cranial cavity being supplied by Wormian bones, which may form in numbers, espe- cially along the sagittal, lambdoidal, and squamous sutures. The fact that in development the cranial bones touch first and unite first at the points nearest their centres of ossification explains the formation and situation of the fontanelles. The four sides of each parietal bone, for example, become united to the four surrounding bones earlier in the middle than at the four angles. At the latter, therefore, there remain spaces covered with membrane. The anterior fontanelle, at the junction with the frontal of the antero-superior angles of the parietal, is the largest, and is not closed for from one to two years after birth. In rickets its closure is much retarded. Its condition, as to fulness or the reverse, gives a valuable indication in many of the diseases of children. In a state of health, the opening, while still membranous, is level with the cranial bones or is very slightly depressed. Systemic exhaustion, malnutrition, diseases associated with depletion of the vascular system, gastric catarrh, chronic diarrhoea, and maras- mus, or simple atrophy, all produce a marked depression of the fontanelle, which in the great majority of cases indicates feeding and stimulation. A bruit de souffle of greater or less intensity, and svnchronous with the pulse, is often heard over the anterior fontanelle, and was at one time thought to be charac- teristic of rickets and of hydrocephalus, but has little diagnostic significance. The thickness of the skull varies in individuals, in the various portions of the skull, and often even in the two halves of the same skull. Humphry obser\-es that, as he has often found the skull to be thick in idiots, and the several bones to be thickest when the skull is small. — i.e., when the brain is small, — " the term ' thick-headed,' as a svnonvm for ' stupid,' derives some confirma- tion from anatomy." Anderson says, however, that the weight of the brain does not seem to have any relation to the thickness of the skull, although this does not affect the truth of the statement that as the brain diminishes with age the skull is apt to thicken, the addition of bone taking place on the interior and giving rise to the irregular surface with close dural adhesions often met with in operations upon the cranium in old persons. The middle cerebral fossa, the centre of the squamous portion of the temporal, and the middle of the inferior occipital fossae are the thinnest parts of the skull, varying from 1.75 millimetres to .85 of a millimetre, and in exceptional skulls meas- uring only . 2 millimetre in thickness. This has an important bearing on the location of fractures (page 239). At the parietal eminence, the posterior superior angle of the parietal, the superior angle of the occipital, and especially at the frontal eminences and the occipital protuberance areas of thickening are found ; at the latter point the skull may measure fifteen millimetres in thickness (Anderson). The average thick- ness of the remaining parts of the calvaria is from five to 7.5 millimetres. PRACTICAL CONSIDERATIONS : THE SKULL. 237 In trephining these general facts should be remembered, as should the occa- sional want of parallelism between the inner and outer tables. The shape of the skull is influenced by race and by disease. The racial pecu- liarities have sometimes a medico-legal significance, but cannot be described here. (See also page 229.) Pathological asymmetry is caused in many ways. In rickets the head is enlarged, and this enlargement seems greater than it really is on account of the retarded growth of the facial bones. All the fontanelles are larger than usual and close later. The anterior fontanelle is sometimes patent at the end of the third or fourth year. In craniotabes the rhachitic softening of the bones favors absorption under pressure. Consequently the regions most affected by the thinning of the bones are the occipital and the posterior half of the parietal, which are between two forces, — the expanding and growing brain within and the supporting surface, as the pillow, without. Various peculiar shapes may result. The changes in hydrocephalic and microcephalic skulls have already been described. Syphilis in the young affects especially the fronto-parietal region, producing thickening or nodes of those bones in the vicinity of the anterior fontanelle. This site is probably determined by the vascularity accompanying growth, as this is the last portion of the cranium to become bony. Such nodes are, therefore, analogous to the rings or collars that form in the long bones of syphilitic children near the epiphyses ; the immobility of the cranial bones, however, causes the exudate to harden rather than to take on inflammatorv action. The bulging of the forehead in some hereditary syphilitics is due to the catarrh of the frontal sinuses which often accompanies the Schneiderian catarrh, that produces first the so-called "snuftles"' and later caries of the nasal bones, with the characteristic flattening of the nose. In adults syphilis of the cranium usually causes necrosis, spreading from the external to the internal table. Necrosis from whatever cause is more apt to affect the external table, which is more exposed to injury and less richly supplied with blood. The calvaria is far more frequently attacked by disease than the base, doubt- less from its greater liability to traumatism. The bones of the cranium are supplied with blood by arteries entering from the pericranium on one side and from the dura mater on the other. The dural supply is the larger ; hence the foramina on the inside of the cranium are larger and more numerous than those on the exterior, and hence also traumatic detachment of the pericranium over considerable areas may not result in necrosis. When detached from disease, the latter (as in syphilis"), even when originating externally, is apt to spread along the vessels, and thus cause necrosis by finally affecting the dural supply. The meningeal blood-vessels running on the exterior surface of the dura — the remnant of the primitive membranous cranium (Humphry) — and sending branches to the cranium are not very strong, and consequently do not offer much resistance to the separation of the dura from the skull ; neither do their branches furnish e very large quantity of blood, surgically considered. It follows that a traumatic separation of the dura is not in itself a lesion followed by serious consequences, unless the separation takes place at or about the situation of the main trunks. Hence, when an extradural clot is suspected to be the cause of gra\'e symptoms, it is usually sought for first over the anterior inferior angle of the parietal bone, — z.e. , about three centimetres (approximately one inch and a quarter) behind the external angular process on a level with the upper border of the orbit. This will make accessible the region of the main trunk and the anterior branch of the middle meningeal. This latter branch at this point runs through a bony canal on the inner surface of the cranium, and is therefore frequently torn when fracture occurs in this region. An opening on the same level, but just below the parietal eminence, will permit the posterior branch to be reached. The venous channels (emissary veins) connecting the sinuses within and the superficial veins without the cranium sometimes convey infective disease, such as erysipelas or cellulitis of the scalp, and thus bring about a septic meningitis or sinus thrombosis. 2r,8 HUMAN ANATOMY. The time-honored custom of bhstering or leeching behind the ear in intra- cranial inflammations rests on the fact that the largest emissary vein is the mastoid, traversing the mastoid foramen and connecting the lateral sinus with an occipital vein or with the posterior auricular. (For further discussion of these channels of communication, see the section on the \'enous System. ) While the spinal dura mater has no intimate connection with the inner surfaces of the vertebrse (being separated from the arches by adipose tissue and from the bodies by the posterior ligament), the dura mater of the cranium becomes closely attached to the bones, especially at the base, where it adheres tightly to the man> ridges and prominences and to the edges of the foramina which transmit the nerves and vessels. To the sides and summit of the skull the dura is less closely attached ; hence in fractures at the base the dura is generally torn, and the risk both of serious hemorrhage and of infection is thereby increased, while in fracture of the caharia it much oftener escapes. Fractures of the Cranium. — That fractures in this region are not vastly more frequent is due to various factors ; among them are the rounded shape of the calvaria, causing blows to glance ofi : the Fig. 26^. division of the separate bones into inner and outer tables, with the coniparati\ely spongy diploe intervening; and the curved thicken- ings which, like buttresses, strengthen the skull e.xternally, and extend on each side through the supra-orbital ridge and the upper border of the temporal fossa to the mastoid process and thence to the occipital tuberosity. From this latter point on the inner surface other ridges, like the groining of a roof, run forward in the median line to the frontal bone, downward to the foramen magnum, and laterally, on either side of the groove for the lateral sinus, e.xtend to the mastoid. In very young persons the dome of the skull is made up of three dis- tinct arches composed of the occipital, the frontal, and the parietal bones. In child- hood the centre (the most prominent portion) of each of these bones is, on account of early ossification, thicker than the rest, while the edges are connected by mem- brane and are comparativelv movable. These mechanical conditions, together with the elasticitv of the individual bones in young persons, make fractures of the skull in them comparatively rare. In the adult the membranous layer between the sutures becomes thinner or disap- pears and the bones denser and less elastic ; they are, therefore, more easily fractured. The two tables may be broken separately, although this is rare. In almost all cases in which fracture is complete the inner table suffers more than the outer. This is because (a) it is more brittle : (6) the fibres on the side of greatest strain suffer most (as in "green-stick" fracture) ; (<-) the material carried inward from without is greater at the level of the inner table than at the point of application of the external force. Agnew explains this diagrammatically as follows : Section of frontal bone, natural size, showing rela- tion of external and internal tables of compact bone to intervening diploe. C G E AB represents a section of the arch of the skull. CD and EF represent the lines of a vertical force applied about G. The effect is to flatten the curve so that it is as HI, while at the same time the vertical lines diverge ( JK and LMl and the particles of bone in the external table tend to be forced together at N and separated or burst apart at O. PRACTICAL CONSIDERATIONS : THE SKULL. 239 Force applied to the vertex would tend to drive apart the lower borders of the parietal bones, but the bases of the great arch formed by these bones are overlapped by the squamous portions of the temporal, and thus this outward thrust is prevented. If the force be applied to the frontal bone, as it overlaps the parietals at the middle of the coronal suture, it is transmitted to them and is resisted by the same mechanism. The occipital bone and the bones at the sides of the skull (beneath the level of the ridges that have been described) break more easily, as they are thinner, the diploe is less developed, and the two tables are more closely united ( Humphry) ; but from their situation they are less exposed to injury, and are protected by a thicker covering of soft parts. Fractures of the base are usually due to indirect violence. Thev may result from foreign bodies thrust through the nose, orbit, or pharynx ; or from a blow upon the nose acting through the bony septum to produce fracture of the cribriform plate of the ethmoid ; or through a blow or fall upon the point of the chin, driving the condyles of the inferior maxilla into the cranium. As a rule, however, the force Fig. 264. traverses the vault or, more rarely, the spinal column (as in falls upon the feet or buttocks). Fractures of the base are very frequent for several reasons. The large expanse of bone forming the vault is contracted at the base into three comparatively narrow por- tions, which descend in successively lower planes from before backward, but which all have relatively thin floors, on which the force received at a distant portion of the cra- nium is ultimately expended. This impact reaches the base by the shortest route, so that a blow of sufficient violence upon the frontal bone will fracture the orbital plates in the anterior cerebral fossa; upon the vertex, the petrous portion of the temporal and the floor of the middle fossa ; and upon the occiput, the floor of the posterior or cerebellar fossa. Furthermore, the base is provided with a series of well-marked ridges which aid in the transmission of force and which fade away into the vault. Base of skull from above, showing lines of fractures. The anterior ridges are gathered into the lesser wing of the sphenoid and end at the sides of the anterior clinoid process. The middle group, collected into the petrous portion of the temporal bone, passes to the centre of the base of the skull and terminates at the foramen lacerum medium. , The ridges of the posterior group, meeting at the torcular Herophili, continue to the foramen magnum, at the posterior limit of which they divide and pass for- ward to meet again in the basilar process, and end in the posterior clinoid process. The region of the sella turcica is therefore the centre of resistance to the transmis- sion of forces from the vault to the base. This is well surrounded by fluid, and the vibrations which are concentrated here may thus become lost in the fluid without injuring the brain-substance. The region of the middle fossa suffers, however, most frequently because : i. It is connected (by the fronto-sphenoidal and petro-occipital sutures) with both the other fossse, and hence often participates in their injuries. 2. It is intrinsically one of the weakest parts of the skull, on account of the presence of the foramina lacera, the carotid grooves, the hollows for the pituitary body, the depression for the sphe- noidal sinus, the petro-sphenoidal suture, and the thin walls of the tj'mpanum, of the e.xternal auditory canal, and of the temporal fossa. Moreover, just in front of this region the descending pterygoid processes and the lower jaw reinforce the 240 HUMAN ANATOMY. cranium proper, while behind it are the thickening of the basilar process and the posterior clinoid plate (Humphry) (Fig. 254). The differential symptoms of fracture through the floors of these fossae are determined by their anatomical relations. They are as follows : 1. Anterior Cerebral Fossa. — (a) Epistaxis when the Schneiderian membrane and the dura and arachnoid are torn. It should not be forgotten that the blood may come from the mucous membrane alone, {b) Loss of smell from injury to the olfactory bulbs resting on the cribriform plate, {c) Subconjunctival ecchymosis. The blood is usually derived from the meningeal vessels over the orbital plates, but in bad cases may come from the ophthalmic artery, ophthalmic vein, or cavern- ous sinus. If the body of the sphenoid is fractured, the blood may find its way through the sphenoidal sinuses into the pharyn.x and stomach, and then be vomited, giving rise to a mistaken diagnosis of gastric injury. 2. Middle Cerebral Fbtsa. — (a) Hemorrhage from the ear. This may be merely from a torn tympanic membrane, (b) Escape of cerebro-spinal fluid from the ear. This indicates that the petrous portion of the temporal is broken, the dura mater and the arachnoid torn, and the membrana tympani ruptured. If the latter escapes injury, the fluid may trickle into the throat through the Eustachian tube, (r) In rare and very severe cases the lateral sinus has been opened or the internal carotid torn, (d) There may be deafness or facial paralysis, or both. 3. Posterior or Cerebellar Fossa. — {a) Hemorrhage into the pharynx if the basilar process is involved and the pharyngeal mucous membrane torn, {b) Ecchy- mosis at the nape of the neck and about the mastoid. Of course the characteristic symptoms of any two or even of all three of these injuries may be commingled if the fracture is extensive enough. Just as fractures would be more frequent were it not for the mechanism that has been described, so concussion or laceration of the brain would occur far oftener were it not for certain factors, among which are the different strata of \'arying density intervening between the brain and the outer surface of the scalp. The soft diploe and the dense inner "vitreous" table both tend to diminish shock to the brain, the former by arresting vibrations and the latter by lateralizing them. The eminences on the inner surface of the skull project into the spaces between the great divisions of the brain, where, in places, there is more subarachnoid fluid than else- where ; such elevations are intimately connected at their edges and terminal points with the strong expansions of the dura mater, — the falx and the tentorium, — which still further take up and distribute the final vibrations. ' ' Thus there is every facility for causing jarring impulses to deviate from the direct line and take a circumferential route, in which they are gradually weakened and rendered harmless" (Humphry). The conditions tending to minimize the effects of violence inflicted upon the skull are thus summarized by Jacobson : "(i) The density and mobility of the scalp. (2) The dome-like shape of the skull. This, like an egg-shell, is calculated to bear hard blows and also to allow them to glide off. (3) Before middle life the number of bones tends to break up the force of a blow. (4) The sutures interrupt the transmission of violence. (5) The internal membrane (remains of foetal peri- osteum) acts in early life as a linear buffer. (6) The elasticity of the outer 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 pres- ence of ribs or groins, — e.g., (a) from the crista galli to the internal occipital pro- tuberance ; (b) from the root of the nose to the z)'goma ; (c) the temporal ridge from orbit to mastoid ; (d) from mastoid to mastoid ; (e) from t1ie external occipital protuberance to the foramen magnum. (9) Buttresses, — e.g., malar and zygomatic ' processes, and the greater wing of the sphenoid. (10) The mobility of the head upon the spine." Landmarks. — The prominence of the occiput, of the parietal region, or of the frontal eminence indicates in a general way the de\elopment of the corresponding portions of the brain. The terms used to designate particular points on the skull have already been described (page 228); additional attention may here be paid to those of especial importance as landmarks. PRACTICAL CONSIDERATIONS : THE SKULL. , 241 The inion or external occipital protuberance, which approximately corresponds to the point of convergence of five sinuses (the superior longitudinal, the two lateral, the straight, and the occipital), is easily felt in the mid-line behind. The superior curved lines which run outward from this point indicate the muscular origin of the occipito-frontalis, and hence are often the lower limit of effusions beneath the aponeurosis. These ridges indicate approximately the course of the lateral sinuses, which are on a line drawn from the inion to the superior border of the mastoid apophysis, — i.e., to a point about 2.5 centimetres, or one inch, behind the external auditory meatus. The asterion or junction of the squamous and lambdoid sutures is 12.5 milli- metres, or half an inch, above and 18.5 millimetres, or three-quarters of an inch, behind the upper level of the posterior border of the mastoid. A line from the asterion to the inion is therefore also the line of the lateral sinus. The /ambda, the junction of the lambdoid and sagittal sutures, lies in the median line posteriorly about seventy millimetres, or two and three-quarters inches, above the inion. In early life the posterior fontanelle is found at that point. Fig. 265. Bregma Biauricular line Stephanioni Inferior stephanion Glabella, Nasion Malar point, Alveolar point Mental point Lateral aspect of the skull, showing the points. (See also description on page 228.) The breg7na, the junction of the coronal and sagittal sutures (and in childhood of the frontal suture), marks the position of the anterior fontanelle, and is found a little anterior to the centre of the shortest line that can be drawn over the vertex between the two external auditory meatuses. The pterion is the point of junction of the temporal, sphenoid, frontal, and parietal bones. It is from thirty to thirty-eight millimetres, or one and a quarter to one and a half inches, above the zygoma, and the same distance behind the external angular process of the frontal. It represents the position of the trunk and of the large anterior branch of the middle meningeal artery. The zygoma can easily be traced from its anterior to its posterior extremity. The tempo>-al ridges can often be felt as two curved lines, the upper one mark- ing the attachment of the temporal fascia and the lower one that of the muscle. They indicate the upper boundary of the temporal fossa^ and often limit the spread of effusions or the growth of tumors. i5 242 HUMAN ANATOMY. The course of the longitudinal sinus is indicated by a line drawn from the nasion (the junction of the nasal and frontal bones j to the inion. The lateral sinus is irregular in its course (page 234). According to Macewen, it may be fairly indicated by the two following lines : ' ' The first from the asterion to the superior margin of the external osseous meatus, of which line the posterior two- thirds correspond to the upper part of the sigmoid groove, which is also the more superficial. The second line from the parieto-squamo-mastoid junction to the tip of the mastoid process corresponds in its upper two-thirds to the vertical part of the sigmoid groove. The knee of the sigmoid — its most anterior convexity — is variable in its position, but is generally on a level with the upper part of th'e external osseous meatus. The sigmoid groove is situated at a variable distance from the external auditory meatus, the tympanum, and the exterior of the skull. The distance between the external osseous meatus and the sigmoid groove varies from one or two to thirteen millimetres." The frequency with which infective thrombosis of the lateral sinuses occurs as a complication of middle ear disease renders the topographical anatomy of these sinuses and the associated region of the skull of great practical importance. The suprameatal triangle is formed by the posterior root of the zygoma running somewhat horizontally above, the portion of the descending plate of the squamous which forms the arch of the osseous part of the external auditory meatus below, and a base line uniting the two, dropped from the former on a level with the posterior border of the external auditory meatus. At this point there is usually a depression in the bone, though occasionally there is a slight- prominence as if the antrum had bulged at that point. The apex of this triangular depressed area points forward (Macewen). The mastoid antrum may be reached through this triangle. (The relations of this antrum, the facial canal, and the lateral sinus to one another, to the temporo-sphenoidal lobe, and to the surface of the skull will be considered in connection with the general subject of Cranio- Cerebral Topography, page I 214.) The size and extent of the frontal sinuses vary, as described on page 234. The communication of these sinuses with the nose accounts for the frontal headache in ozaena, and the fact that a patient with a compound fracture opening up the sinuses can blow out a flame held close by. The frontal sinuses may be occu- pied by bony or other tumors ; emphysema may result from fracture of the sinus wall ; insects may gain access to these cavities and give rise to infection or to epistaxis ; infective inflammations of the nose and naso-pharynx may involve the sinuses. The sphenoidal sinuses are less important surgically, but these points should be remembered : ( i ) 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 cer- tain cases of oztena ; (3) here and in the frontal sinuses very dense exostoses are sometimes formed (Jacobson). The Face. — The nasal bones are so joined together as to form a strong arch resting upon the nasal processes of the superior maxillary bones. They are sel- dom dislocated, because this line of union is one in which there is an alternation in the bevelling of the sutures (similar to that between the frontal and parietal bones). Thus the lower portion of the nasal bones overlaps the maxillary, while nearer the root of the nose the latter is external. The line between the bones and the nasal cartilages can easily be felt. The skin is very tightly attached to the cartilages. The upper or frontal portion of these bones is very strong, and will resist a great degree of force without fracture. The lower portion is most frequently broken, usually within a half-inch of the lower margin. The resulting deformity is usually lateral, but if the perpendicular plate of the ethmoid is broken the nose will be depressed. The thinness and close .application of the mucous membrane to the bones render these fractures almost invariably com- pound. Emphysema of the cellular tissue of the face and forehead may follow such an injury. The vascularity of the bones leads to very rapid union, and it is therefore PRACTICAL CONSIDERATIONS : THE FACE. 243 important to secure early reposition of the fragments. The relation of the perpen- dicular plate of the ethmoid through the crista galli to the olfactory bulbs and the base of the brain should be remembered in severe injuries to the bones of the nose. By reason of this relation suspension or destruction of the sense of smell has re- sulted ; and even septic meningitis and death have followed accidents in which the prominent early symptom was fracture of the nasal bones. The malar bones, binding together the maxillae and the cranium, are very strong, and seldom broken unless by severe force directly applied. Fracture of the body is apt to run into the orbit, producing a subconjunctival ecchymosis near the outer canthus, and there may also be a loss of sensation in some of the teeth, the gums, the ala of the nose, and a part of the cheek, on account of injury to, or pressure upon, the infra-orbital branch of the fifth nerve. The zygomatic process is most subject to fracture ; that part of the arch which is on the temporal side of the suture is much weaker and most apt to %\\'!i Supraspinatu Trapez v Smooth Sui — j^ face for tra (^ pezius ^ Coraco acromi-il ligament Biceps and coracq- hi achiahs *''°'-^ Right scapula from behind. clavicular edge is rudimentary, so that it is three-sided ; or the metacromial tubercle is at the ape.x of a very obtuse angle, so that it is curved and narrow. There are also intermediate forms. ^ The inclination of the acromion to the horizon is on an average not far from 45°, with a variation of probably 15° either way. This may or may not depend on a corresponding variation of slant in the spine. All the details determining the outline of the scapula vary greatly. The hind border may be convex, or the infraspinous portion concave. The bone lying with the dorsum up should rest on the coracoid and the upper and lower angles, with the vertebral edge rising from the table ; but this may be almost straight, or even bend the other way so as to change the usual points of support. The length from the upper to the lower angle ranges from 13.2 centimetres ' Macalister: Journal of Anatomy and Physiology, vol. xxvii., 1893. 252 HUMAN ANATOMY. or less up to 20. i centimetres. The scapular indrx is the ratio of the breadth, measured along the base of the spine, to the length ('°°ie,/th )' •''• ""^"S^^ irom 55 to S2. The following means have been given for Caucasians : ISroca, 65.9 ; Flower and Garson, 65.2 ; D wight, 63.5. A high inde.x means a broad scapula, which is one of a low t>-pe. The infj-aspinoiis index- is the ratio of the breadth to the length of the infraspinous fossa, measured from the lower angle to the starting-point of the spine — '-. ; — --r). This ranges from 72.3 to 100.2, with a .nfraspinous length/ ° ' -^ mean of about 87. Although high indices imply a broad scapula, this method is of small value, as very diverse shapes may have similar indices. It is not possible to predicate anything of the figure during life from the shape of this bone. The most that can be said is that a long arm requires the leverage furnished by a long scapula. Differences due to Sex. — The chief point is the size. From the study of eighty-four male and thirtv-nine female bones it appears that of 123 bones, twenty- si.x measure less than fifteen centimetres in length, of which only three were male ;. also that seventy-six measure si.xteen centimetres or more, of which only five were Serratus magnus Process for teres majot Serratus magnus Right scapula from before. female. There was no single instance of a bone measuring less than fourteen centi- metres being male, nor of one measuring seventeen centimetres being female. In doubtful cases the glenoid cavity is very valuable. In woman it is not" only smaller, but relatively narrower. \'ery few male sockets are less than 3.6 centimetres in length, and very few female as long. The typical female scapula is very delicate ; PRACTICAL CONSIDERATIONS : THE SCAPULA. 253 the lower angle is sharp, the process on the front border small ; the hind border straight up to the spine, then slanting forward in another straight line ; the upper border descends sharply ; the coracoid is slight, with the end compressed instead of knobbed ; the acromion is curved and narrow. An expert should be reasonably sure of the sex four times in five. Doubtful bones are almost always male ; so are those of pecuHar shape, with the exception of concave vertebral borders. The scapular index has no sexual significance.' Structure. — The strong parts are seen when the bone is held to the light. The head, neck, coracoid, acromion, and most of the spine are strong. So also are the front border, the lower angle, and, to a less extent, the hind border, which is strongest above the spine. Most of the body is very thin. A section through the socket, along the origin of the spine, shows the bony plates so disposed as to resist pressure in that line. Development. — There is one chief centre for the scapula proper and one for the coracoid, besides an indefinite number of accessory ones. The first appears about the eighth week (Rambaud et Renault) at the neck, and forms nearly the Fig. 272. Ossification of scapula. A , at eiglith fcetal month ; i?, towards end of first year ; C, from fourteen to fifteen years ; D, from seventeen to eighteen years ; £, about twenty years, a, chief centre ; d, for coracoid process ; c, for acro- mion ; rf, for inferior angle ; e, additional for acromion ; /, for vertebral border. whole bone, including the spine and the root of the acromion and the dorsal part of the root of the coracoid. The coracoid centre appears in the first year ; it forms also the top of the glenoid cavity, and fuses with the first at fourteen or fifteen, beginning to unite at the ventral surface. At the earlier age the acromion is carti- lage beyond a line drawn from the back of the clavicular facet to the front of the metacromion. At about fifteen many little nuclei appear in the acromion. The anterior tubercle is formed from a single nucleus ; the others coalesce into two groups, — one in the centre, the other at the outer margin. At about eighteen the latter joins the body and the other two fuse. A year later the mass so formed also joins the body. Sometimes this remains connected by fibro-cartilage ; very rarely several pieces persist. A scale-like epiphysis appears at the conoid tubercle of the coracoid about fifteen, and soon fuses. About seventeen or eighteen a nucleus appears in the strip of cartilage along the posterior border and one at the lower angle. Both are generally fused by twenty, but the lower is one of the last to fuse in the skeleton, and the line of union may remain for years. PRACTICAL CONSIDERATIONS. The scapula is rarely absent and rarely malformed. The outer part of the acromion may exist as a distinct bone, as may, but less frequently, the coracoid. Many cases of so-called fracture of the acromion and others of supposed traumatic separation of the acromial epiphysis are probably cases of persistent epiphysis. The centre for the inferior angle sometimes remains distinct, being united to the body ' Dwight : The Range and Significance of Variation in the Human Skeleton, Proc. Mass. Med. Soc, i8q4. 254 HUMAN ANATOMY. Lines ot fracture of the scapula by a synchondrosis. The possibihty of its detachment by excessive action of the latissimus dorsi lias been mentioned, but no case of traimiatic separation has been recorded. Fracture is rare, in spite of the thinness of much of the bone, because ot its mobility, the adaptation of its curves to the underlying thoracic surface, the elasticity and compressibility of that surface, the thickness of the muscles that cover the scapula and of those that lie beneath it, the fragility of the clavicle (which by frac- turing often saves the scapula), and the great range of Fig. 273. movement and corresponding weakness of the shoulder- joint, which, in like manner, by undergoing luxation, prevents the force of the traumatism from reaching the scapula. Fracture of the body and of the inferior angle from indirect violence has been reported in a few cases. The arms were fixed, and strong traction was being exer- cised in more than one case. It seems probable that the bone breaks between the opposing forces of the rhomboids and trapezius on the one hand, and the teres muscles, the subscapularis, anci the infraspinatus on the other. The most common fracture is that of the body, usually running transversely or obliquely through the subspinous fossa. The attachments of the subscapu- laris beneath and of the infraspinatus above usually prevent any marked displacement. There is pain on lifting the arm to a horizontal position, because, in order that the deltoid may be able to do this, the acromion must become a fixed point, and that necessitates the contraction of the rhomboids and other muscles whose function it is, aided by the leverage afforded by the pro- longation of the scapula downward, to fix the blade of the scapula when the deltoid is in action. Superficial ecchymosis is rare on account of the dense infraspinous fascia which prevents the effused blood from reaching the surface. Fracture of the acromion is attended with slight flattening of the tip of the shoulder, the weight of the arm, acting through the deltoid, dragging the frag- ment downward. There may be the usual symptoms of preternatural mobility, crepitus, etc. Fracture of the coracoid is rare. Before the age of seventeen it may be an epiphyseal separation. Displacement is not common, as the downward pull of the pectoralis minor, short head of the biceps, and coraco-brachialis (page 590) is effectually resisted by the coraco-acromial and coraco-clavicular ligaments. Crepitus and preternatural mobility may possibly be recognized by sinking the fingers into the interval between the deltoid and pectoral muscles. The coracoid will be found just beneath the inner deltoid margin. Fractures of the neck of the scapula include, in surgical language, those which begin at the suprascapular notch and run to the axillary border of the bone detach- ing the glenoid cavity and the coracoid process. There is no instance of fracture of the anatomical neck, — the constricted part supporting the glenoid cavity. Th^ fragment, with the arm, will drop downward, away from the acromion. This puts the deltoid on the stretch and causes flattening of the shoulder. There will be a depression beneath the edge of the acromion. The arm will be increased in length. These symptoms (which will occur only if the coraco-acromial and coraco-clavicular ligaments are torn) are also found in subglenoid luxation of the humerus (page 583); but in the fracture, the presence of crepitus, the downward displacement of the coracoid, the ready disappearance of the deformity on pushing the head of the humerus upward, its prompt reappearance when the arm is allowed to hang by the side, and the ease with which the hand may be placed on the opposite shoulder serve clearly to denote the character of the accident. Excisio7i of the scapula itself is not uncommonly indicated on account of malig- PRACTICAL CONSIDERATIONS : THE SCAPULA. 255 nant neoplasm, subperiosteal and central sarcomata especially. The main danger of the operation is hemorrhage. The subclavian should, therefore, be controlled. The dorsalis scapulae, crossing the axillary border of the scapula at a point on a level with the centre of the vertical axis of the deltoid (Treves), and the subscapular run- ning along the lower border of the subscapularis muscle to reach the inferior angle, are the largest vessels that require division, but the suprascapular, posterior scapular, and branches of the acromio-thoracic artery will also be cut. Infectious diseases giving rise to caries and necrosis and to suppuration are rare. When they affect the supraspinous region the pus is directed forward by the fascia covering the supraspinatus, which encloses that muscle in an osseo- fibrous compartment. In the infraspinous region the still denser infraspinous fascia con- ducts the pus in the same direction ; hence abscesses originating in scapular dis- ease are likely to point near the axilla and in the neighborhood of the insertions of the scapular muscles into the humerus. On the under surface of the scapula, between the ridges which give origin to the tendinous fibres that intersect the subscapularis muscle, the periosteum is loose and easily separated. Suppuration following caries of this aspect of the bone may, therefore, cause extensive detachment of the perios- teum, and it has been found necessary to trephine the thin portion of the blade of the scapula to give vent to such a purulent collection. Landmarks. — The greatest breadth of the scapula is in a line from the glenoid margin to the vertebral border ; the greatest length in a line from the superior to the inferior angle. The general outlines ot the scapula can easily be felt. The bony points most readily recognized by touch are the acromion, the coracoid, the spiae, the vertebral edge, and the»inferior angle. The edge of the acromion is an important landmark. Measurement from it to the suprasternal notch is the easiest way of determining shortening in fracture of the clavicle. If this measurement is less than on the sound side, and the clavicle itself is unchanged in length, it indicates a dislocation of the acromial end of the latter. Undue prominence of the edge of the acromion is seen in luxation of the humerus (page 582) and in fracture of the neck of the scapula. In these conditions the fingers may be pressed beneath the acromion, as they can in old cases of deltoid paresis or paralysis with atrophy of that muscle, when the weight of the arm drags the humerus downward and increases the space between the greater tuberosity and the acromial edge. The coracoid process may be felt through the inner deltoid fibres, below the inner portion of the outer third of the clavicle, by thrusting the fingers into the space between the pectoral and deltoid. In fracture it may be depressed, as it is in fracture of the scapular neck. The axillary artery can be felt just to the inner side of the coracoid as it passes over the second rib. The spine is least prominent in muscular and most conspicuous in feeble and emaciated persons. This is also true of the inferior angle, which in weak, and especially in phthisical, subjects is not held tightly to the chest, but projects in a wing-like manner (scapulce alatae). This is partly due to general muscular weak- ness, in which the latissimus dorsi and serratus magnus participate, and partly to the shape of the thorax and the direction of the clavicles. The flatter and shallower the chest the more oblique in direction and the lower are the collar-bones, carrying with them downward and forward the upper and anterior portions of the scapulae, and by that much tending to make the lower and posterior portions more promi- nent. The length of the arm is usually measured from the junction of the spine of the scapula and the acromion — the acromial angle — to the external condyle of the humerus. The vertebral edge of the scapula lies just at the side of the spinal gutter. When the arm hangs at the side of the body, this edge is parallel with the line of the spinous processes. It can be made prominent (for palpation) by carrying the hand of the patient over the opposite shoulder. The superior angle is made accessible by the same position. The axillary border of the scapula and the inferior angle are best examined with the elbow flexed and the forearm carried behind the 256 HUMAN ANATOMY. back. With the arm at the side, the superior angle is about on the level of the upper edge of the second rib ; the inferior angle is opposite the seventh intercostal space (and hence is a guide in selecting a space for the various operations for em- pyema, page 1S67); the inner end of the spine is opposite the spinous process of the third dorsal vertebra. With the shoulders drawn forcibly backward, the vertebral borders of the scapulae can be made almost to touch at the level of the spines, and are not more than from two to three inches apart at the angles. With the hands clasped on the verte.\, the inferior angles are from si.xteen to seventeen inches apart. By crossing the arms on the front of the chest, and leaning forward, the scapulje are also widely separated, and this position is therefore selected for auscultation and percussion. The mobility of the scapula lessens the functional disability in ankylosis of the shoulder-joint. LIGAMENTS OF THE SCAPULA. Two ligaments — the trans\erse and the coraco-acromial — pass from one part of the scapula to another. The transverse or suprascapular ligament ' (Fig. 289) is a little band on the upper border, just behind the root of the coracoid, making a bridge over the supra- scapular notch, under which the suprascapular ner\'e passes. It may be replaced by bone. The coraco-acromial ligament" (Fig. 274) is a triangular structure, broad at its base, along the outer border of the coracoid process, and narrowing to its insertion into the inner side of the end of the acromion just in front of the acromio- clavicular joint. The borders are strong, converging bands with * weak space between, the front one being the stronger and overlapping the other when they Capsule of shoulder joint Tendon of biceps Coraco-acromial ligament V >*' ' Fig. 274. Acromio-clavicular joint Coracoid process Coraco-clavicular ligament meet. The course of the fibres in the weaker part is variable ; sometimes they diverge from near the front of the coracoid to the posterior band, sometimes they are in the main parallel with the latter, sometimes a band passes from this membrane to the front of the clavicle. The weak portion of this ligament is pierced by the pectoralis minor, when, as often happens, this muscle is inserted into the capsule of the shoulder or the upper end of the humerus. This ligament is really part of the apparatus of the shoulder-joint, forming a roof over the capsule, from which it is separated by a bursa. Before dissection the hind border of the ligament is not very ^ Lig. traDsversum scapulae superius. * Lig. corpcnacromlale. THE CLAVICLE. 257 distinct, since the bursa appears to connect it with the capsule below and a thin fascia with the clavicle abo\e. The spino-glenoid ligament' is an occasional little band at the great scapular notch, running from the anterior border of the spine to the posterior edge of the glenoid cavity, crossing the suprascapular vessels and nerve. THE CLAVICLE. The function of the clavicle,' or collar-bone, which extends from the top of the sternum to the acromion, is to give support to the shoulder-joint in the wide and varied movements of the arm. It is found in mammals that climb, fly, dig, or swim with movements requiring an outward and backward sweep of the arm. It is absent in those that use the fore-limb simply for progression with movements nearly restricted to one plane. It is present, but imperfectly developed, in some carnivora Fig. 275. ACROMIAL END Right clavicle, superior and posterior surfaces. STERNAL END Pectoralis major whose arms serve, in part, for prehension. In man it has a doubly curved shaft, a thick inner end, and a flattened outer one. The shaft is convex in front through the two inner thirds and concave in the outer one. The former portion has a superior, an inferior, an anterior, and a pos- terior surface ; but in the outer third the two latter surfaces narrow into borders. The superior surface is smooth, except for a slight unevenness at the inner end, Fig. 276. Acromial facet Pectoralis major Sternal facet Trapezoid ridge Conoid tubercle Right clavicle, anterior and inferior surfaces. giving origin to the clavicular head of the sterno-cleido-mastoid. The inferior sur- face has near the inner end an oval roughness, which may or may not be raised, for the rhomboid ligament from the cartilage of the first rib. Beyond this is a longi- tudinal groove, more marked near the outer end, for the insertion of the subclavius muscle. Outside of the middle, near the hind border (sometimes on the hind surface) , is the nutrient foramen, directed outward. The anterior surface narrows continu- ally from within outward. The inner two-thirds are rough for the pectoralis major ; ^ Lifi. transversum scapulae inferjus. - Clavicula. 17 258 HUMAN ANATOMY. external to this the rough concave edge gives origin to the dehoid. The beginning of this is often marked by a minute tubercle, which, when exceptionally large, is the deltoid tubercle. The posterior surface is smooth, and narrows graduall)' till it reaches the outer end, the beginning of which is marked by a tubercle on the under surface. The borders are very ill marked. The sharpest is that separating the anterior from the inferior surface. That between the anterior and superior ones is fairly well marked near the inner end ; but it soon grows indistinct, so that often at the middle of the bone the front surface seems to twist into the upper, and the anterior inferior border becomes the front border of the outer end. Of the posterior borders, the upper, though rounded, is distinct along the middle of the bone ; the lower is very- vague, but usually is well defined in the outer part ; when it is not, the posterior surface seems to twist into the lower. The inner or sternal extremity' is club-shaped, drawn out downward and somewhat backward. Its inner surface, coated with articular cartilage, is of very variable shape. It is approximately oval, with the long axis slanting downward and backward, and is rough and generally concave, but not always so. The front edge of the inner surface forms an acute angle with the anterior border of the bone, and the hind one an obtuse angle. The outer or acromial extremity - is flattened above and below and curved forward. At the very front of this end is Fig. 277. an articular surface joining the scapula. It ^ is oval, with the long axis horizontal, and usually faces downward as well as outward. There is generally behind this a rough space for ligament at the end, which gradually slants into the hind border. The conoid tubercle ' is at the posterior border of the lower surface of the outer extremity just at its junction with the shaft. The trapezoid ridge extends from it forward and outward , ... J o , K„ , .i„i„.,„ across the bone. Its anterior portion is ire; «. r, cartilaginous ends. .S, at about eighteen -t^i-^u 1 j-j years ; majus. ®Tub. 266 HUMAN ANATOMY. Fig. 281. Lesser tuberosity Sitpraspifiatus Stihscapidaris Brachio-radiali Tendon common to exten. carp, rad. brev.y ex- ten, communis digiiorum, ex- ten, min. digi'ii, exten. carpi ul- External bicipital or pecto- ral ridge common lalor ra- dii teres, flex, carpi radialis, palmaris lon- giis, Jiex. sub- lim. dig., flex, carpi ulnaris 1 condyle Capit.'num Truchk-a Right humerus from before. The outline figure shows the areas of muscular attachment. THE HUMERUS. Fig. 282. 367 In/rasp inatus Teres minor External head of triceps Deltoid ■Brachialis aniicu •Brachio-r^dialis Olecranon fossa External condyle Right humerus from behind. The outline figure shows the areas of muscular attachment. 268 HUMAN ANATOMY. The lower extremity is broad from side to side, with an articular surface below, and two lateral projections, the condyles. The inner condyle,^ much the larger, is sharp and prominent, giving rise with a part of the supracondylar ridge to the flexor pronator mus- cles. It is faintly groo\ed behind bv the ulnar nerve, and the lower part of the front often presents a smooth surface. The outer condyle'' is a slightly raised knob. The articular surface, most of which is at a lower level than the condyles, consists of two parts, — an inner pulley-like surface, the troehlca, for the ulna, and an outer convexity, the capitelliim, for the radius. The trochlea ' is bounded internally by a sharp border, forming about three-quarters of a circle, and projecting below the rest of the bone as well as before and behind it. It is bounded externally by a ridge, which is prominent behind where the trochlea forms the whole of the articular surface, but is faint in front where it separates the trochlea from the capitellum. Above the joint this ridge is continuous with the an- terior border of the shaft. The trochlea is convex from before backward. A section through the middle forms almost a complete circle, being broken only above, where a thin plate con- nects it with the shaft. It is concavo-convex from side to side, the convexity being greatest at the inner bor- der. There is a depression above the trochlea both before and behind ; the former, the eoronoid fossa, is small and receives the eoronoid process of the ulna in fle.xion ; the posterior depression, triangular and much the larger, is the olecranon fossa^ recei\'ing that process in extension. The bone separating these fossae — the plate just alluded to — is so thin as to be translucent. It may be perforated by the supratrochlear foratneji, most frequently found in savage tribes. The joint be- tween the humerus and ulna is commonly called a hinge-joint, but there are serious modifications. First, the axis of the trochlea is not at right angles to that of the shaft, but slants downward and inward ; next, the borders of the trochlea are not at right angles to its axis, but are so placed as to transform it into a spiral or screw -joint ; finallv, these borders are not parallel to each other, but the inner slants downward and inward so that the transverse diameter of the joint is greater below than at the top, either before or behind. The capitellum,'' on which the concave head of the tadius plavs, is situated on the front of the outer part of the lower end. It is not far from being a por- tion of a sphere, since it is convex and nearly equally so in all directions, but the arc from above downward is the longest. A groove runs between it and the outer ridge of the trochlea ; the outer border is straight ; the posterior runs from it obliquely backward and inward. Longitudinal section of humerus. The Capitellum is placed SO much to the front as to be ,...: elation of compact and ^^^^^.j^, ^^ ^^^^^ invisible from behind ; hence the articu- lar surface is much more extensive on the front than the back. The radial fossa, a small depression above the capitellum, receives the edge of the head of the radius in extreme flexion. The supracondylar process is a small bony spur occurring in probably two or three per cent. , which arises from the front of the bone a little anterior to the ' Epicoadylus medialis. - Epicond^'lus lateralis. ^Trocblca. ^ Capitulum. 1^ '-r '' spong>' bone. THE HUMERUS. 269 internal supracondylar ridge. It is usually connected by a fibrous band to the tip of the inner condyle, thus representing the supracondylar foramen found very generally among mammals. The median nerve and generally either the brachial or the ulnar artery pass through it. The process, without any completing ligament, has been seen hooking over the nerve alone. We have once seen a bony foramen. The so-called torsion of the humerus is a very complicated problem arising from the theory of the changes necessary to account for the adult condition of the humerus and femur, assuming them to have been originally symmetrical. The practical point is that the horizontal axis subdividing the articular surface of the head of the humerus, imagined on the same plane as the transverse a.xis of the elbow, forms an angle with the latter. This angle varies consider- ably ; according to Gegenbaur, it is 12° for the adult European. In the lower races it is greater, and still greater in the lower animals. (This is what Continental anatomists call the supple- mental angle, as they assume that the twisting has approached iSo°, and that thus the true angle is i6S°. We give this as the simplest. ) The angle is greater in the foetus. Gegenbaur gixes it as 59° at from three to four months, and as 34° at from three to nine months, after birth. This change probably occurs in the epiphyses. It is certain that the shaft of the developing humerus does not actually twist, for the borders are straight, as are all the long nerves with the single exception of the musculo-spiral. No spiral fibres have been found in the bone. Structure. — The walls of the shaft are of compact bone enclosing a cavity. At the upper end the head is made of round-meshed tissue of considerable density ; the greater tuberosity is of lighter structure ; both are enclosed by thin bone. The line of union of the upper epiphysis is seen on section after it has disappeared from the surface. Transverse sections at the lower end show a system of strong plates passing obliquely from the front to the back above the inner condyle. Differences due to Sex. — The chief guides are the greater delicacy of the female bone, and especially the smaller size of the head. It is generally thought that the female humerus presents a sharper angle between the axis of the shaft and the transverse a.xis of the trochlea than does the male, but Berteau.x's' measurements make the difference too slight to be significant, — 79° for man and 78° for woman. Development. — The primary centre for the shaft appears towards the end of the second fcetal month, and before birth bone has reached to the extremities, which are formed by the union of several centres. There are two or three for the upper, a chief one for the head coming soon after birth and sometimes earlier. It is Ossification of humerus. A, just before birth ; B, in the first year; C. at three years; C, sections of ends ol preceding ; D, at five years ; E, at about thirteen years ; E\ sections of ends of preceding; F, at about sixteen ; F\ sections of -ends of preceding, a, centre for shaft'; *, for head ; c, for capitellum and part of trochlea ; d, for greater tuberosity ; e, for head and tuberosities in transverse section ; f, for internal condyle ; j-, for inner part of trochlea. present at birth in 22.5 per cent, of foetuses weighing seven pounds and over (Spen- cer^). It is almost always present by the end of the third month after birth. In the third year ossification begins in the greater tuberosity, and another point may appear somewhat later in the lesser one. At five all the centres for this end have ' Le Humerus et le Femur, Paris, 1891. ^ Journal of Anatomy and Physiology, vol. xxv., 1S91. 270 HUMAN ANATOMY. become one, making a cap for the top of the shaft, which latter extends into the head. The largest centre for the lower end is that for the capitellum, which is seen by the end of the first half-year. It forms also a part of the outer side of the trochlea. A centre for the tip of the inner condyle is evident by the fifth year. One or more minute points of ossification for the trochlea appear in- the tenth year, and one for the tip of the external condyle in the fourteenth. Although all these epiphyses are originally in the same strip of cartilage, they do not unite into one piece of bone. The capitellum is joined by the ossification for the trochlea, and joins the shaft at from fourteen to fifteen. We are not sure whether the insignificant centre for the outer condyle, which fuses at about the same time, joins the epiphysis or the shaft. Rambaud and Renault seem to believe the latter. The centre for the internal condyle remains separate after the rest are fused and joins the shaft at about eighteen. The upper end joins at about nineteen, the line of union being lost at twenty or twenty-one. It is usually lost earlier in the female. Surface Anatomy. — The external and internal condyles are the only points that are truly subcutaneous. The outer is easily recognized under normal conditions, but is quickly obscured by swelling. The internal is so prominent that it can always be recognized, unless the joint has been utterly broken to pieces. The fact that the inner condyle joins the shaft after the rest of the lower end exposes it to the danger of being broken off before the union has occurred, or while it is still weak. The upper end of the humerus is everywhere covered by muscle, but much of its outline can be explored. The amount of its forward projection varies much ; but it always projects outward bevond the acromion. The lesser tuberosity and the bicipital groove can be recognized on rotating the bone, but indistinctly. The groove is filled by the tendon and still further obscured by the capsule and muscles. The surgical neck is best felt in the axilla, whence, the arm being extended, the head can be examined, though imperfectly. PRACTICAL CONSIDERATIONS. The humerus occasionally fails to develop, either alone or together with the other bones of the extremity. The bone of one arm may be shorter and thicker than the normal bone. Lengthening beyond normal Fig. 285. limits is much rarer. The shallowness of the glenoid cavity obviates the necessity for projecting the head of the bone from the shaft, as in the femur ; the "neck" is, therefore, merely a very narrow and superficially shallow constriction of an inward prolongation of the shaft between the tuberosities below and the joint surface above. Both its shortness and its shallow-ness render it far less liable to fracture than the femoral neck. When, in old age, absorption and fatty degeneration of the cancellous tissue have occurred, fracture does take place, as a result usually of falls upon the shoulder. It is often accompanied by impaction, the head being driven into the broad surface of cancellated tissue on the upper end of the lower fragment (Fig. 285). This results in a lessening of the bulk of the upper end, or subacromial portion, of the humerus, and thus in a little flattening of the deltoid and a little increased promi- nence of the acromion. If impaction does not occur, and the capsule of the joint is completely torn through its entire circumference, necrosis of the upper fragment must follow. Usually, through untorn periosteum and through portions of capsule reflected from the inner side of the shaft below the anatomical neck to the edge of the articular cartilage on the head, the blood-supplv is maintained so that necrosis is prevented and union results. There is no direct blood-supply to the head of the humerus corresponding to that received by the femoral head through the ligamentum teres. The displacement m W PRACTICAL CONSIDERATIONS : THE HUMERUS. 271 is apt to be slight, tlie muscles inserted into the bicipital groove and acting on the lower fragment being antagonized by those inserted into the greater tuberosity. That tuberosity may be torn off as a rare accident. The displacement — theoreti- cally— will depend upon the action of the muscles inserted into that portion of the bone (page 590). The large upper epiphysis of the humerus (made up of centres for the head and the tuberosities which begin to coalesce about the sixth year) is fully formed by the age of puberty. It includes then the two tuberosities, the upper fourth of the bicipi- tal groove, all of the head, the anatomical neck, and a little of the shaft just below it. A line nearly horizontal and crossing the bone beneath the great tuberosity, and therefore considerably below the anatomical neck, represents the epiphyseal line at the twentieth year, when the epiphysis and shaft become united. It is within a half inch of the so-called surgical neck (Fig. 286). The lower surface of the epiphysis is concave and the upper surface of the diaphysis convex or conical (Fig. 287). Fig. 286. Fig. 287. Upper end of humerus, showing cupping of epiphysis to receive the pointed end of diaphysis. The traumatic separation of this epiphysis is a not infrequent accident of child- hood and adolescence. It is commonly caused by forcible traction of the arm upward and outward. In such cases three anatomical factors probably enter into the production of the lesion. ( i ) The partial fixation of the epiphysis by the sub- scapularis, supra- and infraspinatus, and the upper fibres of the teres minor. Even on the dead subject, rotation outward with abduction will most readily produce the disjunction. (2) The ease with which the periosteum, strongly attached to the epiphysis but very loosely to the diaphysis, may be separated from the latter. This is illustrated by the fact that in cases of detachment the teres minor, though inserted below the epiphyseal line, is apt to retain its connection with the periosteum covering the epiphysis. (3) The powerful muscles resisting abduction and inserted into the diaphysis just below the epiphyseal line. There may be only separation with little or no displacement ; but if displace- ment occurs, the muscles just alluded to (the latissimus, pectoral, and teres) tend to 272 HUMAN ANATOMY. draw the diaphyseal fragment strongly towards the chest-wall, so that its upper end may be found beneath the coracoid process. The shape of the opposing surfaces of the epiphysis and diaphysis lessens both the frequency and the amount of the dis- placement. The two surfaces usually remain in contact at some point: (i) on account of that shape ; (2j because the humerus on the epiphyseal line is broader than at any other part of its upper end. The deformity will be recurred to in connection with that of the conditions which it most closely resembles, — fracture of the surgical neck and dislocation of the humerus, — which (on account of the importance of muscular action in their production and in their treatment) will be considered after the muscles have been described. It might be expected that, as the chief growth of the humerus takes place from its upper epiphysis, arrest of growth and development should be a usual sequel. The upper epiphysis from the tenth year to adult life will, according to \'ogt, add from seven to ten centimetres to the length of the humerus, the lower epiphysis during the same time adding but one-tiflh as much. The activity of the upper epiphysis is shown by the frequency of conical stump after amputation through the upper end of the humerus.' Despite these facts, in comparatively few cases of disjunction is atrophy or arrest of growth reported as a result. It has been sup- posed, too. that necrosis of the epiphysis should follow this injury on account of deficient blood-supply to the head ; but, through the tuberosities, through the connection of the reflected capsule to the articular cartilage, and through portions of untorn periosteum, the blood-supply is ample. Firm bony union is therefore the usual result in well-treated cases. This is favored by the fact, already alluded to, that the opposing surfaces are nearly always in contact at some point. The portion of the shaft just beneath the head and tuberosities is known as the "surgical neck" because it is so often the seat of fracture. It contains, as will be seen on examining a longitudinal section of the humerus (Fig. 283), a considerable quantity of cancellous tissue, the absorption of which in old persons leaves the bone weak at that point. The factors already described as favoring epiphyseal separation are operative in this case (page 271). The upper curve of the bone, beginning on this level, ends inferiorly at about the lower margin of the deltoid tubercle. Its convexity is forward and outward. The lower cur\'e is concave forward. Both curves may be markedly increased in rickets. The middle of the bone is not only the point of union of these curves, but is also the smallest and hardest and least elastic portion of the shaft ; hence it is most frequently broken, though fractures of the shaft at various levels below and above this point are not uncommon. The deltoid tubercle, when unusually developed, should not be taken for an exostosis. The region is, however, a fre- quent seat of bony outgrowths on account of the insertion and origin, respectively, of the coraco-brachialis and deltoid, and the brachialis anticus and internal head of the triceps. The close attachment of the periosteum to the shaft which is thus necessi- tated favors the development of osteo-periostitis, and thus of osteophytes as a consequence of repeated muscular strains. Other favorite seats of e.xostoses are near the insertion of the pectoralis major, the latissimus dorsi, and the third head of the triceps. Tumors of a more serious variety, especially the sarcomata, attack the hu- merus. The central sarcomata are found in the upper extremity chiefly at the upper end of the humerus and at the lower ends of the radius and ulna. It may be interesting to note that those are the extremities towards which the respective nutrient arteries are not directed, and therefore, in accordance with the general rule, the extremities at which bony union of the epiphyses and diaphyses takes place latest. The close attachment of the periosteurn at the middle of the shaft has been said to account for the fact that non-union after fracture occurs in this region more fre- quently than in the shaft of any other long bone of the skeleton. This has also been attributed to interference with the nutrient artery (which enters the bone near its ' Owen, Lejars, and others, quoted by Poland. PRACTICAL CONSIDERATIONS : THE HUMERUS. 273 middle) and to imperfect immobilization of the humerus, the elbow being fixed by splints, any motion of the hand or forearm under those circumstances being trans- formed into motion of the upper end of the lower fragment. These may be factors, but the chief reason for non-union is the entanglement of muscular and tendinous fibres of the brachialis anticus and of the triceps between the bony fragments (page 59°)- Descending the shaft it is not difficult to see why a fracture just above the con- dyles ("at the base of the condyles," "supracondylar") should often be met with. The olecranon fossa, the coronoid fossa, the shallower fossa for the radius just above the external condyle, all contribute to weaken the bone at this point. Moreover, in falls upon the elbow (the common cause of this fracture) the tip of the olecranon is frequently driven directly into its fossa and against the very thin lamina at its base, starting a fracture which extends laterally through the supracondylar and supra- trochlear ridges to the border of the bone. If this transverse line of fracture is associated with one running perpendicularly Fig. 2S8. into the joint, it constitutes the so-called " T-fracture" ("inter- condylar' ' ) ; it is produced in the same manner, but usually by a greater degree of force. In the so-called "extension" and "flexion" fractures in this region the same mechanism is probably present, though it is easy to imagine the same result (if the capsule and ligaments of the elbow-joint remain intact) without the agency of the olecranon. It should be noted that the external supracondylar ridge, the strongest and most prominent, springs from the external condyle, ascends in the line of the shaft, and terminates in the head, so that it is well adapted to receive and distribute force applied through the radius, as in falls on the hand, or in pushing or striking strongly. The external is smaller than the internal condyle because the extensors and supinators arising from it are less powerful muscles than the flexors and pronators connected with the former. This makes it less prominent ; but in spite of these protective conditions it is at least as frequently broken, es- pecially from indirect violence, because of its direct connection with the hand through the radius and capitellum. On account of the dense triceps fascia covering it, and its connection with the ligaments of the elbow-joint, the displacement is slight. The line of fracture usually passes through the radial fossa and enters the joint through the depression between the capitellum and the trochlear ridge. The internal condyle is more often broken by direct violence, or by the wedge-like action of the olecranon starting a fracture which runs through the thin bone of the olecranon and coronoid fossse, and through the trochlear depression. The displacement is usually upward, is the result of the force causing the break, and is but little influenced by anatomical factors. The brachialis anticus may elevate the fragment, but the ulna remains attached and prevents much displacemefit. Either epicondyle may be broken. The line of the lower epiphysis runs obliquely across the bone from just above the external epicondyle to a point just below the internal epicondyle. In infancy both epicondyles (as well as the trochlea and capitellum) enter into the epiphysis ; but at the thirteenth year the internal epicondyle is quite distinct, and the trochlea, capitellum, and external epicondyle are welded into the lower epiphysis proper, which by the fourteenth to the fifteenth year (Dwight), sixteenth year (Treves and Stimson), seventeenth year (Poland), is firmly united to the diaphysis. After the thirteenth year, there- fore, separation of the epiphysis will probably leave the internal epicondyle attached to the diaphysis. "The point of junction of the trochlear and capitellar portions of the lower epiphysis at the middle of the trochlear groove at the sixteenth year Lines of fractures of the humerus, a, through anatomical neck; b, through tuberosities ; c, through surgical neck ; d, through shaft ; e, T-frac- ture involving condyles. 274 HUMAN ANATOMY. is the narrowest portion of the bone, and much more Hkely to be broken across, detaching one or other portion of bone rather than the whole epiphysis separating at this age" (Poland). As the synovial membrane is attached on the inner side about five millimetres (three-si.xteenths of an inch) below the internal epicondyle, fracture of the latter does not necessarily extend into the joint-cavity. On the outer side it is attached up to the level of the external epicondyle, so that the joint is likely to be involved in traumatic separation of that process. As the capsule of the joint is attached at a higher le\'el than the epiphysis in front, behind, and laterally, the displacement in epiphyseal separations is within the capsule, and therefore likely to be limited. The close relationship of the synovial membrane gives rise, however, to extensive effusion, which affects both diagnosis and treatment. The union to the diaphysis at about the fifteenth year leaves the further growth of the bone dependent upon the upper epiphysis (page 272 ) ; hence injuries involving the epiphysis, or e.xcision of the elbow in which the epiphyseal limits are overstepped, will not be followed by arrest of growth if the patient is more than fifteen years of Epiphysitis, on account of the synovial and capsular relations above described, is apt to involve the elbow-joint, and to result in considerable stiffness. The anatomical deformity and diagnosis of ejsiphyseal separation will be con- sidered in connection with the subjects of supracondylar fracture and luxation of the elbow (page 590 j. About two inches above the inner condyle there is often found (one per cent, of recent skeletons, Turner ) a hook-like process projecting downward and converted into a foramen by a ligamentous band. When it is present the median nerve usually passes through it, which demonstrates that " it is the homologue and rudi- ment of the supracondyloid foramen of the lower animals" (Darwin). The process can sometimes be recognized by the sense of touch. The intercondylar foramen, which is occasionally present in man, occurs, but not constantly, in various anthro- poid apes, and, though it weakens the bone somewhat, is chieflv interesting because it is found in much greater frequency in skeletons of ancient times, and thus illus- trates Darwin's assertion that "ancient races more frequently present structures which resemble those of the lower animals than do modern." THE SHOULDER-JOINT. The ligaments of this articulation are ; Capsular; Glenoid Accessory ligaments : Coraco-Humeral ; Gleno- Humeral. This is a very simple instance of the ball-and-socket joint, the only irregularity being the position of the humeral head somewhat on one side instead of at the top of the bone, so that the a.xis of rotation does not correspond with the a.xis of the shaft. The shallow socket of the glenoid cavity, lined with articular cartilage, is deepened by the glenoid ligament' (Figs. 290, 292), a fibro-cartilaginous band attached by its base to the border of the cavity and ending in a sharp edge. It is thus triangular on section (Fig. 291), the breadth of the base being five millimetres and the height at its greatest about one centimetre. This ligament is composed chiefly of fibres running around the socket. It is directly continuous with the fibres of the long head of the biceps from the insertion of the latter into the top of the socket. The capsular ligament' (Fig. 289) is so la.x that in the dissected joint the head of the humerus falls away from the socket. In life it is kept in place chiefly by the tonicity of the surrounding muscles. The course of the fibres is in the main longitudinal, but they are indistinct. The capsule arises above from the edge of the ' Labrum glenoidale. -Capsula artirularls. THE SHOULDER-JOINT. 275 glenoid cavity and the bone just around it, from the outer surface of the glenoid ligament as far as its edge, excepting at the top, where it does not encroach on the ligament, and at the inner side, where its origin is uncertain. It may arise there as Fig. 2S9. Coraco-acromial ligament Right shoulder-joint from before. described, but very often it arises at some distance from the border of the joint from the anterior surface of the scapula. In exceptional cases this distance may be half an inch, perhaps more. The inferior attachment of the capsular ligament is to the Fig. 290. Acromio-clavicular joint Tendon of biceps Head of humerus Glenoid ligament Glenoid cavity Spine of scapula Right shoulder-joint, capsule opened and humerus everted. groove round the head, close to the latter above and externally, but a little way from it below and internally. This applies to the attachment as seen from within 276 HUMAN ANATOMY. the opened joint ; on the outside, the fibres can be traced for a considerable distance from the joint before they are lost in the periosteum. P'ibres going to the tuberosi- ties blend with the tendons of insertion of the muscles of the scapular group, the supra- and infraspinati, the teres minor, and the subscapularis, which materially strengthen the capsule. The latter is thinnest behind. Certain accessory ligaments strengthen the capsule. The most important is the coraco- humeral (Fig. 289), which, arising from the outer edge of the horizontal portion of the coracoid where a bursa separates it from the capsule, soon fuses with the latter and runs, without very distinct borders, to both tuberosities, crossing the bicipital groove. A few transverse fibres (the transverse humeral ligament ) bridge in the bicipital groove below the capsule proper. Three gleno-humeral bands { P'ig. 290) are described on the inside of the capsule, of which the most important is the Tendon of subscapularis and capsule Fig. 291. Lesser tuberosity idon of biceps in bicipital groove Glenoid ligament Glenoid cavit Glenoid ligament Greater tuberosity Subdeltoid bursa of infraspinatus capsule 1 section through the right shoulder-joint from above. superior. This band springs from near the top of the inner border of the glenoid cavity and is inserted into the lesser tuberosity. In a part of its course it makes a prominent fold of the synovial membrane along the inner border of the tendon of the long head of the biceps. This ligament has been described as a deep part of the coraco-humeral. The middle ligament is ill-defined. The inferior, running from the lower end of the glenoid socket to the inner side of the neck of the humerus, may be seen both from without and within the capsule. It is made tense when the arm is abducted, and materially strengthens the joint. The capsule usuallv presents an opening on the inner side in the upper part, by which the bursa below the tendon of the subscapularis communicates with the joint. The cases in which the capsule THE SHOULDER-JOINT. 277 arises internally at quite a distance from the glenoid cavity are probably due to a very free opening into a large bursa. The tendon of the long head of the biceps lies within the capsule from its origin at the top of the glenoid till it leaves the cap- sule in the bicipital groove. The tendon does not lie free within the joint, but is covered by a reflection of the synovial membrane as it lies curved over the head of the humerus. On the young fcetus it is attached to the inside of the capsule by a synovial fold. The sytiovial membrane of this joint is remarkably free from synovial fringes. The bursae about the joint are numerous. The largest is the subacromial or subdeltoid bursa (Figs. 291, 292), situated between the top of the capsule, the coraco-acromial ligament, and the acromion, and extending downward under the deltoid. The subcoracoid bursa separates that process and the beginning of the Fig. 292. Co aco clavicular ligament Subdeltoid bur; Frontal frozen section through the right shoulder-joint coraco-humeral ligament from the capsule. Other bursae are often found between the capsule and the muscles inserted into the tuberosities ; that under the subscapu- laris is constant. Of the others, the one most frequently found is under the infra- spinatus ; it also may open into the joint. Movements. — When the arm is hanging close to the side adduction is almost wanting, since, apart from the interference of the body, the humerus is arrested at once by the lower border of the glenoid cavity. Backward movement is not free, for the arm soon impinges on the overhanging acromion. Abductio7i has a range of some 90° before the tenseness of the lower part of the capsule stops it. 278 HL.MAX ANATOMY. (Unless the arm is raised somewhat forward, it is stopped still sooner by the acromion. ) Forward movement is about equal to abduction, and is checked in the same way. When the arm is at a right angle with the body, the range of motion in a horizontal plane is about 90°. The degree of rotation in the shoulder is very variable. It is greatest when the arm is partially abducted, when in a dis- sected joint it may appro.xiniate 135°. When raised to a right angle it is about 90°, and in the hanging arm, if not closely adducted, nearly the same. Circum- duction is free. Probably none of the important joints is so dependent on others as that of the shoulder. The scapula takes part in practically all the movements, not waiting till the range of movement at the shoulder is exhausted, but sharing in it from the start. The acromion and coraco-acromial ligament make an extra socket under certain cir- cumstances, as when the body is supported by the arms, the subacromial bursa act- ing as a synovial membrane. The long head of the biceps is a great assistance to the stability of the joint, the muscle pulling the bones firmly together and making them rigid under circumstances of strain. It has the further advantage over a liga- ment that its tension can vary without change of position. PRACTICAL CONSIDERATIONS. The extremely wide range of motion of the humerus upon the scapula in the human species is associated, for mechanical reasons, with many anatomical conditions of interest to the surgeon. The most important of these conditions in relation to displacement are: (i) The shallowness of the glenoid cavity. (2) The relatively large size of the humeral head, only one-third of which is in contact with the glenoid surface when the arm is by the side of the body. (3) The thinness and the great laxity of the capsule, which, if fully distended, would accommodate a bulk twice as large as the head of the humerus. This laxity (to permit of free elevation of the arm ) is greater at the inferior portion of the joint. The primary office of the cap- sular ligament in this joint is not to maintain apposition, but to limit movement. (4) The maintenance of the contact between the articular surfaces by muscular action, aided by atmospheric pressure, and not by the ligamentous or capsular at- tachments. (5) The length of the humerus, aftording a very long leverage ; and the exposed position of the shoulder. All these circumstances favor dislocation, and render this joint more frequently the subject of that accident than any other joint in the body. The usual position in which luxation occurs is that of abduction and advancement of the arm, as in falls on the hand. It is to be noted that this attitude brings the most prominent part of the lower edge of the head of the bone against the thinnest and weakest part of the capsule. Moreover, the greatest diameter of the head of the humerus is involved, adding to the pressure against the capsule (Fig. 293). As such accidents happen suddenly, the muscles are usually taken off their guard, and hence that source of protection to the joint is lacking. As opposed to these factors, and as tending to prevent displacement, should be mentioned : ( i ) The exceptional relation of the biceps tendon to the joint, strength- ening the capsule at its upper portion, preventing the humerus from being too strongly pressed against the acromion by the powerful deltoid and the other elevators of the arm ; steadying the head of the bone through its connection in the bicipital groove, in which way ' ' it serves the purpose of a ligament, with the advan- tage of being available in all positions of the joint, and without restricting the range of mo\'ement in any direction" (Humphry). (2) The arrangement of the glenoid cup, the inner and lower edges of which are more prominent than the outer and upper, resisting somewhat the tendency of the powerful axillary muscles, and of blows on the shoulder, to displace the humerus inward, and of falls with the arm in abduction, to displace it downward. (3) The glenoid ligament deepening the articular cavity, and aided in this by the insertions of the long head of the biceps above and the scapular head of the triceps below. (4) The resistance offered by the strong coraco-acromial ligament to any upward displacement. If it were not for PRACTICAL CONSIDERATIONS : THE SHOULDER-JOINT. 279 these provisions, luxations of the shoulder would be even more frequent than they are. The head of the bone may leave the joint-cavity at other points than the in- ferior. If the force is so applied as to drive the head of the bone against the cap- sule at the anterior portion, a direct subcoracoid luxation may result ; if against the posterior portion, a subspinous. The latter is very rare, and the former is also rare as a primary luxation. The further mechanism of luxations, their deformities and anatomical diagnosis, will be considered after the muscles, which are such important factors in producing and modifying them, have been described (page 582). Disease of the shoulder-joint may be of any variety. In spite of the frequent strains to which the joint is subjected and its wide range of movement, the diseases produced by traumatism are not exceptionally frequent. This is probably because of (i) its ample covering of muscles protecting it from the effects of cold and damp. (2) The mpbility of the scapular segment of the shoulder-girdle lessening greatly the effect of traumatisms. (3) The laxity of its capsular and synovial elements, which, though it favors lu.xation, permits a moderate effusion to occur without harm- ful tension. (4) The influence of the weight of the upper extremity in the usual position of the body in resisting by gravity the destructive pressure of joint surfaces against each other, caused by muscular spasm after injury or during disease. (5) The Spine of scapula Fig. 295. Supraspinatus Reflection of capsule /A /el/-' Reflection of capsule Infraspinatus Head of scapula Teres minor Section through right shoulder-joint with arm in abduction. ease with which the joint may be immobilized without irksome confinement of the patient. These circumstances, especially the latter, account also for the facts that tuber- culous disease of the joint and epiphysitis involving the joint are not so common as in other joints, and that the results are exceptionally good, operative interference being required with comparative rarity. Synovial distention causes a uniform rounded swelling of the shoulder, but it can best be recognized by the touch in the bicipital groove, where one synovial diverticulum runs, and in the axilla, where part of the capsule is exposed beyond the margin of the subscapular muscle. The diverticula beneath the tendons of that muscle and (more rarely) of the infraspinatus are usually involved, pain when the arm is rotated being a resultant symptom. The subdeltoid bursa does not usually communicate with the joint. It may be the subject of independent disease. When it is inflamed the position of ease will be one which relaxes the deltoid (abduction of the arm), and rotation or pressure upward will be painless. In disease of the subacromial bursa, abduc- tion and upward pressure are painful because the sac is then pinched between 28o HUMAN ANATOMY. the head of the bone and the under surface of the acromion and coraco-acromial ligament. When suppuration occurs, pus may find its way out from the joint, (i) By following the bicipital tendon and opening on the arm below the anterior border of the axilla. (2) By following the subscapular tendon, getting between that muscle and the body of the scapula, and opening beneath and behind the a.xilla. (3) By penetrating the capsule beneath the deltoid, when the dense deltoid and infraspinous fascia prevent it from going backward and direct it to the anterior aspect of the arm. Tre\es mentions a c;ise in which it followed the course of the musculo-spiral nerve and appeared on the outer side of the elbow. Landmarks. — The edge of the acromion and the tip of the coracoid can readily be felt, though the coraco-acromial ligament completing the important arch above the joint is beneath the deltoid, and therefore cannot be so distinctly pal- pated, but can usually be recognized by touch. An incision through the centre of this ligament would open the shoulder-joint where the bicipital tendon enters its groove. The head of the bone, when pressed upward against this arch, com- municates motion to the outer fragment in cases of fractured clavicle, and this is often the easiest way in that lesion of eliciting crepitus and preternatural mobility. In cases of paresis or paralysis of the deltoid, the resultant atrophy may leave the whole arch palpable, or even visible, in some instances the bone dropping from one to several inches. The lower margin of the glenoid cup and the head of the humerus may be felt in the a.xilla when the arm is abducted (Fig. 293). The greater tuberosity may be felt through the deltoid, directly beneath the acromion, the arm hanging at the side. It faces in the direction of the external condyle. Together with the lesser tuberosity it produces the normal roundness of the deltoid. The head of the bone cannot be felt externally. It faces in the general direction of the internal condyle. Two-thirds of it, when the arm is by the side, is in front of a vertical line drawn from the anterior border of the acromion process. ■ It is also altogether external to the coracoid process. The lesser tuberosity faces forward. Between it and the greater tuberosity, when the arm is hanging loosely and is supine, the lower part of the bicipital groove may be felt in thin subjects. This also faces directly forward, and is on a line drawn through the middle of the biceps and its lower tendon. The upper part of the humeral shaft cannot be felt. The circumfle.x nerve winds around it a little above the middle of the deltoid. The deltoid tubercle may be recognized at the middle of the arm. From there downward the bone is more superficial externally, and the outer supracondylar ridge may be traced down to the condyle. The less prominent internal ridge can be felt onlv for a short distance above the elbow. The middle of the humerus, indicated by the insertion of the deltoid on the outer side, is also on a level with that of the coraco-brachialis on the inner and with the upper portion of the brachialis amicus on the anterior surface, with the origin of the nutrient and inferior profunda arteries, with the exit through the deep fascia of the nerve of \Vrisberg and the entrance of the basilic vein, with the passage of the median nerve across the brachial artery, and with the departure of the ulnar nerve from its proximit\- to the vessel. Posteriorly, the middle of the bone is covered by the triceps. Just below the middle the musculo-spiral nerve and the superior profunda wind around in the groove below the deltoid insertion, and the inner head of the triceps arises from the bone. At the junction of the middle and lower thirds the brachial artery from the inner side and the musculo-spiral ner\e from the outer side tend to approach the front of the bone. The landmarks at the lower extremity will be considered in relation to the elbow-joint and the bones of the forearm. The surface anatomy and the relations of the soft parts to the humerus will be recurred to after those structures have been described. THE ULNA. 281 THE FOREARM. The skeleton of the forearm consists of two bones, — an inner, the tihia, and an outer, the radius. The former is large above and small below ; the latter, the con- verse. The ulna plays around the trochlea in flexion and extension, carrying the radius with it. The radius plays on the ulna in pronation and supination, carrying with it the hand. These bones are connected by an interosseous membrane, which gives origin to muscles, adds to the security of the framework, and yet implies a great savmg in weight. THE ULNA. The ulna consists of a shaft and two extremities. The upper extremity is devoted to the joint with the humerus, and laterally to that with the head of the radius. The former articular surface is the greater sig- moid cavity hollowed out of the continuous surfaces of the olecranon process behind and above and the coronoid process in front. The olecranon,' a cubical piece of bone projecting upward in continuation with the shaft, presents this articular surface in front (to be described later), and a superior, a posterior, and two lateral surfaces. The superior surface is pointed in front, with the Doint or beak external to the middle. A slight groove just back of the edge serves for the attachment of the capsular ligament. Behind this are two parts of different texture, the posterior of which is for the insertion of the triceps. The posterior surface is triangular, bounded above by the irregular edge of the top, and laterally by two lines which meet below to make the posterior border of the shaft. It is subcutaneous, and is covered by a bursa (Fig. 294). The outer sutface is bounded in front by the sharp edge of the sigmoid cavity, along which is the groove for the capsule. Behind this is a hollow for the anconeus. The i^mer sutface has in front the inner border of the sigmoid, less sharp than the outer, the capsular groove, and farther back a rough elevation. The coronoid process '^ rises from the anterior surface of the front of the shaft. It has an upper, articular surface, an anterior, and two lateral ones. The front surface rises to a point nearer the outer side. The capsular groove runs along the border ; and below this, bounded by two lines meeting below, is a rough region for the brachialis anticus. Within the angle formed by the meeting of these two lines is a rough rounded space, the tuberosity of the ulna, from the edge of which arises the oblique ligament. The brachialis anticus is inserted into the lower part of this sur- face and the tuberosity. The inner surface is bounded above by the sharp project- ing border of the sigmoid cavity, at the edge of which is a rough prominence from which certain fibres of the flexor sublimis digitorum take origin. The outer surface presents the lesser sigmoid cavity. The greater sigmoid cavity' occupies the anterior surface of the olecranon and the superior one of the coronoid process. There is a constriction in the middle of both borders, but deeper in the outer, where the two processes meet, and the articu- lar surface on the dry bone seems often to be interrupted in a line between them. The sigmoid cavity, concave from above downward, is broader in the upper half than the lower. It is surrounded, except where it is joined by the lesser sigmoid cavity, by an ill-marked groo\'e for the capsular ligament. The articular surface is subdivided by a rounded ridge, running from the point of the olecranon to that of the coronoid, into a larger inner and a smaller outer portion. The course of this ridge is generally somewhat inward as well as downward. This and the cross-line divide the articular surface into four spaces. Of the upper, the inner is concave and the outer convex from side to side. Of the lower, the inner is concave in the same direction and the curve of the outer is uncertain ; probably, as a rule, slightly concave, it may be plane or a little convex. The lesser sigmoid cavity,* for the head of the radius, is a concavity on the outer side of the coronoid process, separated from the greater by a ridge, which does not interrupt the cartilage coating both. It generally is an oblong quadrilateral area forming about one-sixth of the circumference of a cylinder, with parallel borders ; ' Olecranon. ^ Processus coronoideus. ^ In 282 HUMAN ANATOMV Fig 294 Flex, subh digitormi Aponeurosis of txt. carpi uinarr fiex. profundus dlgitorum and flex, carpi ulna} Posterior border Fig. 295. Tip of olecranon ■ Coronoid process Tuberosity- Upper end of right ulna, posterior aspect. Brachialis anlicus Supinator brevis Flex, profund. digitorum Flex, sublim. dig. (coronoid liead) Pronat. ladii letes (lesser head) Flex, long.pollicis (accessory headj Nutrient canal - Interosseous border \\\i ||il | Pronator quadralus d:„;,. ..1 ***- -ji>loid process R.ght ulna, inner aspect. The outline figure shows the areas of muscular attachment. THE ULNA. Fig. 296. 283 Groove for ext. carp, ulnar. Styloid process Ayiconeus- - Ext. carpi ulnaris- Suphiator brevis Ext. assis met pollicts Ext. long, poinds Right ulna, outer aspect. The outline figure shows the areas of muscular attachment. 284 HUMAN ANATOMY. but sometimes the front border is short and the inferior runs obliquely backward, making it almost triangular. The shaft,' which presents three borders and three surfaces, steadily diminishes from abo\'e downward. In the upper part the bone curves slightly backward and outward (i.e., towards the radius), then inward through the greater part of its e.xtent, till at the lower quarter it again bends outward and, at the same time, for- ward. The posterior border'' is formed by the union of the two lines bounding the subcutaneous surface at the back of the olecranon. Following Fin. 597. the curves just described, it runs to the back of the styloid process, being very distinct in the first two-thirds, where it gives origin to the aponeurosis of the fle.xor carpi ulnaris. The anterior border^ springing from the junction of the front and inner sides of the coronoid, runs down to end just above the front of the styloid process. Its last quarter, which is rough to give origin to the pronator quadratus, has a backward slant. The outer or in- terosseous border^ is very sharp in the middle two-fourths of the shaft, where it gives origin to that membrane. It begins above by the union of two lines, which, starting from the front and back of the lesser sigmoid cavity, bound a triangular depression. The posterior of these lines, sharp and raised, is the supinator ridge. The depression which gi\'es origin to the supinator brevis receives the bicipital tuberosity of the radius in pronation. The border becomes indistinct below and is lost as it approaches the head of the ulna. The anterior surface is usually concave through- out, though the upper part may be convex. In the third quarter a line often appears which slants downward into the front border, giving origin to the upper fibres of the pronator quadratus. Below this line, when present, there is a depression occupied by that muscle. Abo\'e this arises the flexor profundus digitorum. The nutrient foramen running upward is a little above the mid- dle. The in7ier surface, concave at the side of the upper ex- tremity and convex below, gives further origin in its upper two- tliirds to the last-named muscle. The posterior surface has several features which are to be recognized onlv on a well-marked bone, and are very variable. The oblique line starts from the supinator ridge, or from the hind edge of the lesser sigmoid cav- ity, and runs downward to the posterior border at the end of the first third. It gives origin to a part of the supinator brevis, and helps to mark ofT a three-sided depression running onto the olecranon for the anconeus. It is sometimes the apparent continuation of the supinator ridge, as in Fig. 296. The region '^ I below this is subdivided by a veitical ridge of uncertain beginning and end. Sometimes it springs from the interosseous border, and it is usually lost below in the hind one. The extensor carpi ulnaris springs from the surface internal to it, which is some- times a deep gutter. External to the vertical ridge are areas for the extensor ossis metacarpi pollicis, extensor longus pol- licis, and e.xtensor indicis from above downward in the order named. The lower extremity of the ulna consists of the head and ^^^"^"■"^ . the styloid process. The head' is a rounded enlargement pro- Longitudinal section ..-'.^, , , . .,'^ , of ulna. jectmg forward and outward, jiresentrng an articular surface on the outer side, which passes onto the front and the back, making at least two-thirds of a circle, around which the radius swings. A ridge marks the upper border of this surface, which overhangs the lower. The latter is rounded, so that the lateral articular surface continues without real interruption into the inferior, which is separated from the wrist-joitit by the triangular fibro-cartilage. The under side of the articular surface is somewhat kidney-shaped, the concavity looking towards the styloid process, from which it is separated by a groove for the ' Corpus ulnae. - Margo dorsalis. ^ Marfio volaris. ^Crista ioterossea, •' Capitulum. PRACTICAL CONSIDERATIONS: THE ULNA. 285 attachment of the fibro-cartilage. The styloid process is a short, slender process running down from what may be called the posterior internal angle of the lower end. There is a distinct groove between the styloid process and the head on the posterior aspect, and sometimes a faint one in front, transmitting respectively the tendons of the extensor and the flexor carpi ulnaris. Structure. — There is much solid bone in the shaft, and altogether the ulna is a strong-walled bone. Many plates near together from the anterior surface pass upward under the coronoid process to the middle of the greater sigmoid notch. The best-marked system of plates in the coronoid is in the main parallel to these. The greater sigmoid notch is bounded by compact substance. Sagittal sections show plates radiating from it, some of which form arches near the top of the olecranon with others from the posterior surface. The head is composed of spongy tissue within thin walls. Development. — The centre for the shaft appears in the eighth week, from which practically all the bone except the lower end is developed. At about five, Fig. 298. Ossification of ulna. A, at birth ; B, at five years ; C, at ten years ; D, at about sixteen years, a, centre for shaft ; d, c, cartilaginous epiphyses ; d, centre for lower epiphysis ; Cy for upper epiphysis. one appears for the head and styloid process ; and at about ten, one for the top of the olecranon. This fuses at about sixteen ; the lower end joins the shaft at eighteen. PRACTICAL CONSIDERATIONS. The ulna may be absent, or may be more or less defective in size or shape. Such deformities are not common. Fracture of the olecranon at its junction with the shaft, where it is narrowed, is frequent. The degree of displacement is largely determined, as in the parallel case of the patella, by the amount of laceration of the enveloping fibrous structure (Fig. 585). If this is great, the triceps strongly elevates the fractured process. Occasionally the mere tip of the olecranon, or even a thin portion of the superficies only, may be separated either by muscular action or by direct violence. The epiphyseal line is above the constriction that marks the union of the olec- ranon with the shaft. The epiphysis is small and includes the upper part of the olecranon with the insertion of the triceps, a part only of the attachment of the pos- terior ligament, and a very small portion of the posterior triangular subcutaneous surface. The epiphyseal line runs from the upper part of the sigmoid cavity in front downward and backward. The epiphysis enters but little into the elbow-joint ; it is largely within the limits of strong periosteal and tendinous and ligamentous €xpansions, is of small size, and before the fourteenth or fifteenth year is on a 286 HUMAN ANATOMY, Fig. plane anterior to the epicondj^es. For these anatomical reasons, neither muscular action (triceps) nor falls on the elbow are so producti\e of separation of this epiph- ysis in children as of fracture of the olecranon in adults. It is, in fact, one of the rarest of epiphyseal disjunctions. The symptoms are very- similar to those of fractured olecranon. The coronoid process is rarely broken except in cases of dislocation of the forearm backward from falls upon the hand. The mechanism is obvious. The force is applied through the medium of the oblique fibres of the interosseous membrane. The line of fracture is nearer the tip than the base of the process. The insertion of the brachialis anticus tendon in the latter region prevents much displacement of the fragment, and the attachment of the capsule of the joint to its edge insures a sufficient vascular supply for pur- poses of repair. Great proneness to recurrence after re- duction in a case of backward dislocation of the forearm should lead to a suspicion of the existence of this fracture. Fracture of the shaft of the ulna alone may occur at any point, and is usually the result of direct violence, as when the arm is raised to protect the head from a blow, or in a fall upon the ulnar side of the forearm. In the lat- ter case, when the ulnar fracture is in the upper third, it is not infrequently associated with forward dislocation of the head of the radius (Fig. 300). The subcutaneous position of the ulna renders fracture frequently compound. This accounts for the greater fre- quency of non-union in this bone as compared with the radius. In fracture at the lower third the lower fragment is drawn towards the radius by the pronator quadratus. "■"j Fractures associated with those of the radial shaft will be considered in relation to the effect of muscular action upon them (page 604). The lower epiphysis of the ulna comprises the articular surfaces on the radial and inferior aspects and the styloid process. It is concave superiorly to fit the rounded lower end of the diaphysis. The level of the epiphyseal line is about one- sixteenth of an inch above the level of that of the radius. This epiphysis is strongly Lines of frnctu noid. olecranon, a processes of ulna. i of upper third of held to the lower epiphysis of the radius by the inferior radio-ulnar ligaments and also by the triangular fibro-cartilage extending from the root of the styloid process to the concave margin of the radius. For that reason, and because of its indirect relation to the hand, the uncomplicated separation of this epiphysis is of great THE RADIUS. 287 rarity. Even in cases of separation of the lower epiphysis of the radius, or of Colles's fracture, the strain reaches the tip of the ulnar styloid through the internal lateral ligament and produces fracture of that process, or of the ulnar diaphysis at its smallest point (about three-quarters of an inch above the lower end), rather than separation of the epiphysis. As the growth of the ulna depends almost exclusively upon the lower epiphy- sis, injuries stopping short of recognizable disjunction have been followed in a number of cases by failure of development, resulting in lateral displacement (adduc- tionj of the hand. Landmarks. — The olecranon can always easily be felt at the back of the elbow. It is somewhat nearer the internal than the external condyle. With the forearm at right angles to the arm, the tip of the olecranon and the two cond3'les Fig. 301. are on the same plane as the back of the upper arm. In extreme extension it is about one-sixteenth of an inch or less above a straight transverse line joining the two condyles ; in full flexion it is anterior to them. In front the tip of the coronoid process can be felt with difficulty in non-muscular subjects. The shaft is subcutaneous through its entire length. The styloid process is a half-inch nearer the forearm than the styloid process of the radius. It is most distinct in full supination, and is found at the inner and posterior aspect of the wrist. In full pronation the head of the ulna becomes prominent posteriorly. THE RADIUS. The radius includes a shaft and t\vo extremities. The upper extremity consists of a head and neck. The head ' is a circular enlargement with a shallow depression on top to articulate with the capitellum, and ^Capitulum. 288 HUMAN ANATOMY. Bursal surface- Bicipital surfa Fig. 302. -Interosseous border Suiiivator brrvis Biceps tendo\ Supinator b'evisA * Flex, sitdiimis. digitorum Flex. long, pollici. Pronator quadi at. Brachio-radialts—l ^ Ext. ossis met polUcii Ext. brevis pollicis iVulnar surface ^Semilunar surface Styloid process ^JELj/^^ ^"^ SLiphoid surface ,. . , Th^ nmiine fieure shows the areas of muscular attachment. Right radius, inner asnect. The outline ngure snuw THE RADIUS. 289 a smooth margin to turn in the socket formed by the lesser sigmoid cavity and the orbicular ligament, which completes it. The term "circular" is not used with mathematical precision, for slight variations from it are the rule. The most common one is an increase of the antero-posterior diameter. The depression on top is not symmetrical, for there is almost invariably a greater thickness of the rim in front, extending more to the inner than to the outer side. The smooth margin has a downward projection internally. The plane of the upper surface is not always at right angles to the a.xis of the neck, but often looks a little outward. The neck is a smooth constricted portion some two centimetres in length and approximately cylindrical. The shaft ' immediately bends outward below the neck, and has a slight forward curve at the lower end, where it broadens considerabl)-. The bicipital tuberosity ■ is a large prominence at the inner and front aspect of the shaft, just below the neck. Its posterior border, which is rough and projecting, slants forward and receives the biceps tendon. In front of this the tuberosity is smooth for a bursa, lying beneath the tendon, which, in pronation, is rolled around it. The shaft is described as having three surfaces separated by three borders ; there is convenience in retaining the plan, although only one border is always distinct and one is almost imaginary. The distinct border is the internal or interosseous^^ which, starting from the bicipital tuberosity, soon becomes sharp for the interosseous membrane, and runs to the lower quarter of the bone, where it divides into two descending lines to the front and back of the articular facet on the inner side of the lower end. The anterior border'' which is generally distinct above, starts from the front of the tuberosity and runs downward and outward to about the middle of the bone. This part is known as the oblique line of the radius, which gives origin to a part of the flexor sublimis digitorum, and separates the insertion of the supinator brevis from the origin of the flexor longus poUicis. The border is thence poorly marked till, slanting forward tc the beginning of the lower fourth, it becomes a distinct ridge running to the 'front of the styloid process and receives the insertion of the pronator quadratus. It broadens at the end into a triangular tubercle for the insertion of the brachio-radialis. The posterior border is important only as helping to define the posterior and outer sur- faces ; it is usually to be seen in the middle third of the bone, and has neither a definite beginning nor end. The anterior surface, limited above by the oblique line, is slightly concave, and gives origin to the flexor longus pollicis as far down as the last quarter, which is slightly hoUow'ed for the pronator quadratus and sometimes separated from the upper part by an oblique ridge. The nutrient foramen is seen above the middle, running upward. The outer surface, which is convex, presents about the middle a 7-oughness for the insertion of the pronator radii teres. The posterior surface has a concavity in the middle third, internal to the posterior bordei, and is convex both above and below. The lower extremity bends slightly forward, ending in front in a prominent ridge to which the capsule is attached. The outer side is prolonged downward as the styloid process, ending in a blunt point. It usually shows grooves for the tendons of the extensors of the metacarpal bone and first phalanx of the thumb, which pass over it. The external lateral ligament of the wrist arises from it. The posterior surface has a groove at its edge for the capsule, and above this is furrowed for the passage- of certain tendons. Next to the styloid process is a broad depression, sometimes faintly divided into two, for the extensores carpi radialis longior et brevior ; internal to this is a marked ridge, the tube?-cle, slanting downward and outward, with a narrow, deep gutter beyond it for the tendon of the long extensor of the thumb. A very slight border separates this internallv from a broad, shallow groove for the tendons of the extensor communis and that of the index-finger. At the extreme limit of the posterior surface is sometimes a minute furrow for a part of the tendon of the extensor of the little finger, which passes over the radio-ulnar joint. The inner side of the lower end is occupied by a concave articular area, the sigmoid cavity ' of the radius, which receives the head of the ulna and much resembles the lesser sigmoid cavity of that bone. The lower surface is articular for the scaph- oid and semilunar bones of the wrist. It is in the main triangular, the base being the inner side. It is overhung both before and behind, and is continued onto the ^Corpus. - Tuberositas radii, ^Crista interossea. ^ .Margo volaris. 19 290 HUMAN ANATOMY. Fig. 303. Supinator brevis\ V " /■biceps Pronator radii te Brachio-radiali Bursal surface Tuberosity Biceps tendon Semilunar surface Scaphoid surface Sl^ loid process Right radius from before. The outline figure shows the areas of muscular attachment. ' THE RADIUS. 291 Fig. 304. Posterior borde Interosseous border - Biceps Ext. ossh tnet. pollicis- Ext. brevis poUicis- Supinator breviS — Pronator radii tere^ W'lA \ Ext. OSS. Viet. poll. \Ext. brev.poU. ~Ext. carp. rad. long, etbrev. Ext. com. dig. and ext. indicis • Ext. long. poll. Styloid process Right radius from behind. The outline figure shows the areas of muscular attachment. 292 HUMAN ANATOMY. inner side of the styloid. A faint ridge from before backward, beginning at a slight notch, marks ofT an inner square surface for the semilunar and an outer triangular one for the scaphoid. The surface looks slightly forward, thus causing the forward rising of the hand from the forearm. In man the ulna is evidently the more important bone at the elbow and the radius at the wrist. In mammals below primates they are often more or less fused and the upper end of the radius relatively larger than in man. It often occupies the front of the elbow-joint, being anterior instead of external to the upper end of the ulna. Structure. — The radius, like the ulna, is thick-walled through the greater part of the shaft. The tuberosity is composed internally chiefly of longitudinal Fig. 305. styloid proces; Sigmoid cavity Ext. OSS. met. poll. I Ext. brcii. poll. Ext. carp. rail. long. / \'!_5\ Ext. cnmniums dig. Ext. carp. rad. brev. I E.vt. long, pollicis and ext. indie Tubercle Lower end of right radius. Fig. 306 A. Longitudinal sections of rad frontal plane, showing arrangement of trabecula? in lower end of bone. plates. A frontal section of the lower end of the radius shows the walls splitting up into longitudinal plates, which run to the lower end, connected by a system of liafhter transverse ones. PRACTICAL CONSIDERATIONS : THE RADIUS. 293 Development. — The centre for the shaft appears at the end of the second month, and forms the whole bone, except the lower end and the head. The nucleus for the former appears at the end of the second year and that for the head at the Fig. 307. Ossification of radius. Ay at birth ; S, at two years ; C, at five years ; Z?, between eighteen and nineteen years, a, centre for shaft ; d, for lower epiphysis ; c, for upper epiphysis. end of the fifth. The latter unites at about fifteen, the lower at eighteen or nineteen. A scale-like epiphysis for the bicipital tuberosity is said to appear towards eighteen and to fuse very promptly. PRACTICAL CONSIDERATIONS. The radius may be absent or more or less defective, and in either case there is apt to be corresponding absence or deficiency in the hand (Humphry). As might be expected, injuries of the upper end in the adult are extremely rare. Except at one point (just below the external condyle posteriorly), the head is far from the surface and deeply buried beneath the thick supinators and the long and short radial extensors of the carpus. Even at that point, more prominent bony processes — the external condyle and the olecranon — receive the brunt of the injury in cases of falls or blows. The upper epiphysis does not become fully ossified until the fifteenth year, and is united to the diaphysis at the beginning of the sixteenth year. It is, therefore, among the last of the epiphyses of the long bones to ossify and the first to join its diaphysis. The violence which separates it from the shaft is often direct. In cases of indirect violence the force is applied usually as a combined pull and twist on the forearm of a very young child. As the epiphysis is altogether intra-articular (the synovial membrane lining the whole inner surface of the orbicular ligament), swelling is early and marked. As there is direct communication with the larger synovial cavities of the elbow, the whole joint will participate in the effusion. Although no ligaments or tendons are attached to the epiphysis, the orbicular ligament hugs it closely and holds it in place. If any displacement occurs, the upper part of the diaphysis may go either forward or backward. On movements of pronation and supination, the epiphysis can be felt immovable just below the external condyle. An injury known as "elbow-sprain," or "pulled elbow," and described as a "subluxation of the orbicular ligament" and as a "subluxation of the head of the radius," should be mentioned here because, although it has been known for more than two hundred years, has well-defined and constant symptoms, occurs in one 294 HUMAN ANATOMY. per cent, of all surgical cases in children under si.\ years of age, and is believed to depend on a distinct anatomical lesion, the e.xact nature of that lesion is still un- known. It is usually caused by traction on the forearm. The most plausible of many theories are : ( i ) that it is due to the head of the radius slipping out from beneath the orbicular ligament, which is pinched between it and the capitellum (Fig. 311) ; and (2) that it is a partial epiphyseal separation. The differential diagnosis is said to depend chiefly on the facts that in the " sublu.xation" the head of the radius will rotate with the shaft, and that all the symptoms disappear rapidly after forced supination has removed the functional disability. There seems nothing absolutely inconsistent with these symptoms in the view that a slight epiphyseal separation has occurred, the upper end of the diaphysis being displaced forward, but carrying with it the radial head. This theory is strongly favored by the fact that very few cases have occurred in children over five years of age. Ossification of the radial head begins towards the end of the fifth year. It should be remembered that the epiphy- sis includes only the upper part of the head, the lower portion and the neck being ossified from the shaft. The upper end of the diaphysis is therefore appro.ximately of the same size and shape as the head, and may easily have been mistaken for it in many of the cases. The problem pre- FiG. 308. sented is so purely an anatomical one ■■' ^ that, in spite of the prevalent differences of opinion, it seems proper to make this brief presentation of it. Fractures of the head are uncom- mon. Fractures between the head and the lower end will be considered in refer- ence to the effect of muscular action upon them ( page 604). In the neighborhood of the tubercle \(| I . 11 1 the thickness of the bone, the ridges that run up towards the head and down towards the outer edge, and the ample covering of muscles render fracture com- paratively uncommon. A little lower the union of the two secondary curves near the point of greatest curvature in the primary curve of the whole shaft renders the bone more vulnerable. Still lower the effects of indirect violence through falls upon the hand, the union near the lower end of the compact tissue of the shaft with the cancellous tissue of the expanded lower extremity, the compara- tively superficial position of the bone, and the projection of the anterior articular lip, into which the anterior carpo-radial ligament is inserted, all very markedly favor fracture. Accordingly, we find that, on account of these anatomical conditions, of one hundred fractures of the radius, approximately, three will be in the upper third, six in the middle third, and ninety-one in the lower third, the large majority of these latter being within from 2.5 to 5 centimetres (one to two inches) of the wrist- joint. Fractures of the lower end of the radius are almost always produced by a cross-breaking strain caused by falls on the hand, and exerted through the strong anterior common ligament. The broad attachment of this ligament to almost the whole anterior lip of the radius brings the strain equally on the bone through its entire width. The fracture is, therefore, usually irregularly transverse. In addition to the force transmitted by means of the ligament, there is an approximately vertical force, due to the weight of the body, which thrusts the sharp lower end of the shaft into the lower fragment, made up chiefly of spongy tissue, with merely a thin shell of com- pact tissue holding it together. This vertical force transmitted through the forearm Lines of fracture of neck and of lower end of radiu (Colles's fracture). A, dorsal ; J?, lateral aspect. PRACTICAL CONSIDERATIONS : THE RADIUS. 295 Fig. 309. and hand not only thus impales the lower fragment on the upper, but necessarily carries the former to a higher level. In addition, the ulno-carpal fasciculus of the common ligament drags on the lower end of the ulna, and either causes fracture of the styloid process, into the side and base of which it is attached, or causes the lower end of the ulna to project unduly on the antero-internal aspect of the wrist. The stripping up of the periosteum, the laceration of the tendon sheaths that are so closely applied to the bone, — especially the flexor tendons by the jagged edge of the upper fragment, — and the consequent effusion are the chief remaining anatomical factors in producing the character- istic deformity of this most common of all fractures. The lower fragment is found on the dorsum of the wrist. The lower end of the upper fragment is found anteriorly beneath the pronator quadratus or under the fle.Yor ten- dons (Fig. 586). The styloid process of the radius is on a higher level than that of the ulna ; in dislocation of the wrist this is not the case. The hand is carried towards the radial side (Fig. 309). In cases with but very trifling displacement it is still possible to recognize the absence of the projection of the anterior articular lip of the bone on the front of the wrist, and some slight elevation of the dorsum. The angle between the axis of the forearm and the ground is said (Chiene) to determine whether in such a fall the line of force passes upward in front of the axis of the forearm and the radius is broken, or extends up the forearm itself, resulting in a sprain of the wrist or a dislocation of the bones of the forearm backward at the elbow. The forward sloping of the carpal surface of the radius causes the posterior edge of the bone to receive the greater part of the force ; hence the lower fragment is rotated backward on a transverse axis, and hence the disappearance of the prominence of the anterior articular lip. The carpal surface of the radius also slopes down- ward and outward ; hence the radial edge of the lower fragment receives (through the ball of the thumb) a greater part of the shock than the ulnar edge, which is, moreover, firmly attached by the triangular ligament. This favors the upward displacement of the radial styloid and the radial displacement of the hand. There are almost always some crushing and distortion of the lower spongy fragment, even when it is not materially displaced. Anterior displacement of this fragment may occur when the force is applied in the reverse direction, — i.e., v/ith the hand in forced palmar flexion. The infre- quency of falls on the back of the hand explains the rarity of this accident, but the greater weakness of the posterior ligament and the absence of any projecting articular lip to increase the leverage exerted through the ligament also contribute to make the accident showLTh^^d carried fowLrds'S uncommon. radial side. The later results of these fractures are much influ- enced by the close proximity of the flexor and extensor tendons to the region of injury, as, even when the sheaths escape laceration origi- nally, they are liable to become adherent during the process of repair. The lower epiphysis of the radius is osseous about the end of the tenth year and is united to the shaft in the nineteenth or twentieth year. The epiphyseal line is almost transverse (Fig. 310), and extends from about nineteen millimetres (three- fourths of an inch) above the apex of the styloid process to six millimetres (one- fourth of an inch) above the lower edge of the sigmoid cavity. The epiphysis is 296 HUMAN ANATOMY. Fig. thinnest in the centre (five miUimetres), the line at that point crossing the bone about three milHmetres below the tip of the prominent middle thecal tubercle. The need for an accurate conception of this epiphysis is emphasized by the facts : (i) that it is more often separated than any other in the body, with the possible e.xception of the lower epiphysis of the femur ; (2) that its line has more than once been figured and described as a line of fracture on the basis of skia- graphs. The cause of separation is almost always a fall on the pronated hand. The carpal bones are carried against the posterior border of the radial epiphysis, the pro- nator quadratus and other muscles fi.x the lower ends of the diaphyses of the radius and ulna, and the epiphysis is forced backward. The anterior carpal ligament and the tendons on the palmar surface of the wrist are put on the stretch and aid in the displacement. The supinator longus is directly attached to the epiphysis and aids in maintaining the deformity. The synovial membrane of the wrist-joint does not reach the level of the epi- physeal line of either the radius or the ulna. That joint is, therefore, not frequently invol\-ed. The thinness of the centre of the epiphysis would lead to the expectation that fracture would often complicate the separation. This is not the case, however. Poland says that the epiphysis is more solid than the lower end of the bone of the adult (which has, of course, become cancellous in structure), and that it thus escapes the fracture, comminution, and impaction which are so frequent in later life. The radius is often the subject of rickets, and of both syphilitic and tuberculous epiphysitis, especially at its lower end, on account of the exceptional frequency of falls upon the hand and strains of the epiphyseal joint. Subperiosteal sarcomata are rare. Central sarcomata almost invariably attack the lower end of the bone (page 366). Landmarks. — The head of the bone may be felt at the bottom of the dimple or depression just below the e-xternal condyle and to the outer side of the olecranon. It lies be- tween the outer border of the anconeus and the muscular swell of the supinator longus and radial extensors of the car- pus. It is covered by the external lateral and orbicular liga- ments. It can readily be felt to move when the forearm is pronated and supinated. Its presence in that position demon- strates that dislocation of the radius or of both bones of the forearm backward — the common dislocation at the elbow — Its free rotation negatives the existence of a non-impacted Lower end of left rad showing epiphyseal 1 dorsal aspect. has not occurred, fracture of the radius The upper edge of the head lies immediately below the elbow-joint. In full supination the tubercle can be indistinctly felt a little below the lower edge of the head. The upper half of the radial shaft cannot be felt, as it lies beneath the bellies of the extensors and the supinator brevis. The lower half is almost subcutaneous and can readily be palpated through or between the tendons and muscles. The expanded lower extremity is partly subcutaneous (at the base of the styloid exter- nally) and is readily felt. The styloid itself, the prominent tubercle at the radial side of the groove for the extensor longus pollicis (middle thecal tubercle), and the sharp tubercle at the base of the styloid can easily be recognized. The latter is the inferior termination of the pronator crest of the diaphysis, marks the ex- ternal termination of the epiphyseal line, and is on a level with the lower and outer part of the pronator quadratus muscle. The posterior end of the middle thecal tubercle is three millimetres above the epiphyseal line on the posterior aspect of the bone. The styloid process of the radius is lower— z'.^. , nearer the hand — than the styloid process of the ulna. RADIO-ULNAR ARTICULATIONS. 297 JOINTS AND LIGAMENTS BETWEEN RADIUS AND ULNA. These include, — 1. Superior Radio-Ulnar Articulation : Orbicular Ligament ; Capsular Ligament. 2. Inferior Radio-UInar Articulation : Triangular Cartilage ; Capsular Ligament. 3. Ligaments uniting the Shafts : Interosseous Membrane ; Oblique Ligament. The superior radio-ulnar joint' (Figs. 311, 312) is between the circum- ference of the head of the radius and the lesser sigmoid cavity of the ulna extended into a circle by the orbicular ligament. The articular ends of the bones are coated Fig. 311. External condyh Tuberosity of radius- Internal condyle Coronoid process Oblique ligament Superior radio-ulnar articulation, anterior aspect. The capsule of the elbow has been removed. with cartilage requiring no particular description. The orbicular ligament' (Fig. 311) surrounds the head of the radius, springing from the two ends of the lesser sig- moid cavity and from the lines running down from them. This band embraces the head tightly, but is separated from it by the cavity of the joint, and is lined with ^ Artie, radioulnaris prosimalis. - Lig. annulare radii. 298 HUMAN ANATOMY. synovial membrane. It narrows below so as to fold under the projecting head, and is attached, chiefly through fibres from the lower border of the lesser sigmoid cavity, to the inner side of the neck. It is connected above with the capsular ligament of the elbow-joint. That the fibres to the neck limit rotation is easily shown by dividing all bands connecting the bones, e.xcepting the orbicular ligament ; for were it not so, the radius could then be turned continuously, which is not the case. It is doubtful, however, whether these fibres become tense by any movement which can occur in the undissected joint. The inferior radio-ulnar joint' is, when seen from the front, an L-shaped cavity, the vertical part being between the head of the ulna and the hollow on the radius, and the horizontal limb between the ulna and the triangular cartilage,' which is attached by its base to the border between the inner and lower ends of the radius in such a manner that its distal surface is in the same plane as the lower end of the radius. The ape.x of the cartilage is attached by a ligament some three millimetres long to the groove between the head and the styloid process of the ulna and to the inner surface and anterior edge of the latter. Strong bands, inseparable from the ligaments of the wrist, run along its border to the front and back of the articular surface of the radius. The fibro-cartilage is very flexible Fig. 312. Front of capsul Radial nerve Coronoid process Inner side of greater-^ J' sigmoid cavity \\ S Horizontal section through right elbow-joint from above. The trochlea of h Orbicular ligament and adapts itself to the surfaces of the lower end of the ulna and of the first row of the carpus. Its inner end, however, is not as broad as the lower end of the ulna. It is in some cases perforated. The membrana sacciformis is the synovial mem- brane of this joint, lining the capsule between the ulna and the triangular cartilage, between the ulna and radius, and extending a little above the level of the top of the apposed articular surfaces of these bones. The capsule enveloping it is delicate, but strengthened in front and behind by ill-marked bands passing between the bones ; these are sometimes described as distinct anterior and posterior ligaments. The connection between the lower ends of the bones is much strengthened by the pronator quadratus. The ligaments between the shafts are the interosseous membrane and the oblique ligament. The interosseous membrane ' fFig. 315), composed of fibres running downward and inward, closes, except above, the opening between the bones. Beginning from one to two centimetres below the tubercle of the radius on the anterior surface of the interosseous ridge, and lower from the sharp edge, it connects the two ridges as far as the lower joint, following the posterior division of the inter- osseous ridge of the radius. The upper fibres are nearly transverse. Some long fibres, particularly on the posterior surface, run from ulna to radius. There are ^ Artie, radloulaarls distalis. " DiscuS' articularls. ^Membrana iaterossea intcrbrachii. THE FOREARM AS A WHOLE. 299 several small openings for the passage of vessels and nerves. Pressure transmitted upward from the hand through the radius would tend to stretch the greater number of the fibres, and thus distribute the strain through both bones. While the radius Fig. 313. Capsule of wrist-joint Styloid process of radiuS' Capsule of inferior radio-ulnar joint Ligament of triangular cartilage Triangular cartilage Styloid process of ulna Lower end of right radius in supination. can hardly be enough displaced to bring this about, it is conceivable that the bones might bend sufficiently to make this action effective. The oblique ligament' (Fig. 311), an inconstant little band, runs downward and outward, partly closing the space above the membrane, from the tubercle of the Fig. 314. Capsule of inferior radio-ulnar joint Ligament of triangular cartilage. Styloid process of ul tyloid process of radius Triangular cartilage Capsule of wrist-joint Lower end of right radius in pronation. ulna to the beginning of the oblique line of the radius. It has been plausibly sug- gested that it represents a part of the flexor longus poUicis muscle. THE FOREARM AS A WHOLE, AND ITS INTRINSIC MOVEMENTS. The two bones and the ligaments form an apparatus capable of being moved as a whole on either the arm or the hand, and of greatly changing its own shape by the movements of the radius on the ulna. As these latter are theoretically inde- pendent of the position of the forearm with regard to the arm, it is best to consider them here. The movement of the radius is a very simple one of rotation on an axis coincid- ing with that of the neck of the bone, and then, owing to the outward bend of the shaft, passing down between the bones and finally through the head of the ulna. The amount of rotation probably rarely exceeds 160°. Rotation is limited chiefly by the anterior and posterior radio-ulnar ligaments, the former being very tense at the end of supination and the latter at the end of pronation. The oblique ligament limits forced supination. As above stated, it is unlikely that the fibres of the orbicular ligament to the radius become tense during life. The fact that the lower end of the radius swings round the ulna in no way changes the character of the movement. If the radius were throughout in continuation of the axis of the neck, and the ulna enlarged below to support it, rotation on the axis of the neck would not change the position of the bone. The departure of the greater part of the radius from that line necessitates the swinging round of the lower end, but does not affect the nature of the movement. The changes of relative position of the bones during rotation are very important. It must be remembered that when the ulna is held so that the front of the middle of the shaft is horizontal, the head of the radius is in a plane above that of the main ^ Chorda obllqua. 300 HUMAN ANATOMY. axis of the ulna. When the radius is brought into semipronation (so that the thumb will point upward ) the bones are most nearly parallel and at the greatest possible distance from each other, and the membrane is approximately tense (Fig. 315). The forearm is broadest at about the middle. The membrane is at the bottom of a moderate hollow seen from either the front or the back. In extreme supination the anterior hollow is effaced and the posterior deepened. The radius approaches the ulna, especially above the middle. In extreme pronation the front hollow is much deepened and the hind one lost. The bones are much nearer together than in any other position. The radius crosses the ulna, and is above and internal to it at the wrist. Should the capsule be opened from below without disturbing the triangular car- tilage in a specimen from which the hand has been disarticulated, in supination the front of the under side of the head of the ulna will be exposed ; in forced pronation Fig. 315. Interosseous membrane, — Oblique ligament -Interosseous membrane Position of the bones of the forearm in pronation and supination. almost the whole under end will appear (Figs. 313, 314). As the radius passes behind the head, the ligament of the triangular cartilage is relaxed and the band at the back of the joint is made tense. This ligament becomes tense before com- plete supination and is somewhat relaxed when supination is extreme. The motion above described is the only one between the radius and ulna ; nevertheless, in certain movements of twisting the hand and arm the ulna plays a part to be considered later (page 304). Surface Anatomy of the Radius and Ulna. — The position of both bones can be felt in a bodv that is not verv muscular, though comparatix'ely little of them is subcutaneous. The triangular space of the back of the olecranon, and the pos- terior border of the ulna starting from it and running to the styloid process, can all be traced with the finger. When the arm is straight, the top of the olecranon is a little above the level of the internal condyle and behind it ; when the arm is bent at a right angle, the top of the olecranon is in the same vertical plane as the back of THE ELBOW-JOINT. 301 the humerus ; and when it is strongly flexed, the top of the olecranon corresponds to the vertical plane of the internal condyle. The head of the radius and the furrow above it opening into the joint are easily felt at the outside and behind. In the lower third of the forearm the bones can easily be felt. The ulna here is posterior and best felt at the back. In supination the styloid process is distinct. It is hidden by the soft parts in pronation, and the head is exposed. The forward sweep of the lower end of the ridius is evident. The inferior expansion can be felt both before and behind ; the styloid process is examined best from the outer side. It extends nearly one centimetre lower than that of the ulna. The inequalities on the back can be felt vaguely ; the most evident is the ridge bounding the groove for the long extensor of the thumb. THE ELBOW JOINT.' This is a considerably modified hinge-joint, the axis of rotation being oblique to the long axis of both the humerus and the ulna, and the course of the latter at the joint being also a spiral one. It is to be understood that the radius follows the ulna, which is the directing bone of the forearm in the motions of the elbow. The Articular Surfaces. — These have been described with the bones ; it remains only to give here a summary. The motions between the forearm and the humerus depend essentially on the trochlea and on the surfaces of the greater sigmoid cavity. This is a modified hinge-joint. As has been shown, the transverse axis of Fig. 316. ^Brachialis anticus Coronoid process Subcutaneous bursa Sagittal section of right elbow-joint through the trochlea. the trochlea is not at right angles to the shaft, and it may be added that the same is true of the sigmoid cavity and the axis of the ulna. The effect of this will be noticed later. Again, as already pointed out, the trochlea is not onh' oblique, but is so shaped that the ulna in turning on it describes a spiral line. It has also been shown that the trochlea is not equally broad throughout, and that there are curious differ- ences of curve in the sigmoid cavity. Finally, the lateral ligaments are not quite tense, especially when the joint is half flexed. It follows from these facts that the motion is a very complicated one, and that a certain lateral motion of the ulna on ^Articulatio cubitJ. 302 HUMAN ANATOMY. the humerus is possible. The head of the radius plays on the capitellum, but it follows the ulna. The capsular ligament' surrounding the joint is very weak behind, stronger in front, and very strong at the sides, which last-named parts are usually called the lateral ligaments. The anterior fibres arise from the humerus above the coronoid and radial fossae, and from the front of the bases of both condyles. Behind, they arise from about the middle of the olecranon fossa, which is onF)- partly within the capsule. Transverse fibres bridge it, passing between the highest points of the borders of the trochlea. Below this the posterior fibres arise beyond these borders, so that the trochlea is included in the joint. At the sides the fibres forming the so-called lateral ligaments radiate from points below the tips of the condyles. A little of the external and a large part of the internal condyle are not enclosed. The FiG. 317. Band stn capsule engtheningfrontof.^A/ \V%\ il \\\ 3 VlVj/^' -^ Fibres of orbicular ligament Thin part of capsule Bursa for tendon of biceps Internal condyle of humerus Cut tendon of biceps Oblique ligament Capsule of right elbow-joint from before. capsule is inserted below, posteriorly, into the little groove described with the bone at the border of the olecranon. The radiating fibres from the external condyle are inserted into the surface of the orbicular ligament, behind, outside, and in front. They are covered by tendinous fibres of the muscles from the condyle, which are almost inseparable from them, and which greatly strengthen the joint. The fibres radiating from the tip of the inner condyle, or the internal lateral ligament,^ are in two layers. The posterior, the deeper, is attached to the side of the olecranon ; the anterior is a strong band passing to the side of the coronoid process, which sends fibres backward, overlapping the deeper" layer. The anterior fibres go to the orbicular ligament and to the coronoid process near its edge. The front part of the capsule is strengthened by delicate oblique fibres from the front of the internal con- dyle, passing downward and outward. Masses of fat, incorporated in the capsule both before and behind, project into the joint, carrying the synovial membrane before ^Capsula articularis. -Lig. coUaterale n1aar& THE ELBOW-JOINT. 303 them. There is a thick pad of fat, which, when large, may bear well-marked synovial folds at the notch on the inner side of the ulna where the olecranon joins the coronoid. Movements. — These are of two orders : that of flexion and extension, and those which occur in twisting the forearm. For practical purposes the former may be reduced to those of the ulna, which the radius is forced to follow. The move- ments of the ulna are not far from turning on an oblique axis, which cuts the long axis of the humerus at an angle of approximately 80° externally. When the forearm is fully e.xtended, it therefore forms externally an obtuse angle with the humerus. Were the long axis of the ulna perpendicular to the axis of the joint, the forearm in flexion would cross the humerus, as indeed is often erroneously stated ; in fact, however, the long axis of the ulna also forms an angle of about 80° with the axis of the joint, and, as these angles equal each other, in fle.xion the forearm is parallel with the humerus. A simple demonstration of this is gained by cutting out a copy of Fig. 320.' On folding it at the line of the joint (a 3) the two parts will lie one on Fig. 318. Olecranon fossa Internal condyle* Posterior part of capsule External part of capsulp con- cealing orbicular ligament Right elbow-joint, poste the other. If then another model be made with the axis of the lower piece at right angles to the joint, it will show that the lower piece crosses the upper. When extension is complete, the tip of the olecranon can go no farther into the fossa on the back of the humerus, and the front of the capsule is tense. In complete flexion of the dissected arm, the tip of the coronoid is in contact with the humerus in front ; but in life the motion may be checked by the soft parts before it has reached its limit. Morris has shown that there is much variation in the range of movement, depending on differences in the upper end of the ulna. The lateral ligaments of a theoretically perfect hinge-joint should always be tense ; in the elbow they are not quite tense in semiflexion. Moreover, the imaginary axis does not remain fixed throughout the motion. Motions of the Forearm on the Humerus in twisting the Hand. — The articulation between the concave head of the radius and the convex capitellum of the humerus is practically a ball-and-socket joint ; the radius may glide on the humerus, following the ulna, or it may rotate on a fixed axis, as described above. It is easily shown, however, that the swinging of the lower end of the radius round ' Potter : Journal of Anatomy and Physiology, vol. xxix., 1895. 304 HUMAN ANATOMY. a motionless ulna is not what actually occurs in life. Let the reader grasp lightly his right wrist with his left thumb and forefinger, so that they nearly meet at the styloid process of the radius, and, pressing the right elbow to the side for steadiness, Fig. 319. Deeper layer of internal lateral ligament Right elbow-joint, inner aspect Fig. 320. pronate the right arm. The lower end of the radius will occupy the place at the base of the left thumb previously occupied by the ulna, which will have travelled outward along the left forefinger. It is very doubtful whether in this experiment all motion at the shoulder is eliminated ; nevertheless, the ulna undoubtedly changes its place, and with equal certainty it does not " rotate." To prove this, let the arm of a subject be held in a vice above the elbow, which should be semiflexed, and, the forearm being supine, let a long pin pointing outward be fixed into the outer side of the radius above the wrist, and another pointing inward into a corre- sponding point of the ulna. On pronating the hand, the pin in the radius will describe a large curve and that in the ulna will make no evident movement. On close inspection, aided by placing some object close to the head of the pin in the uina, it will appear that, though the bone has not rotated, the pin-head has changed its place : it has moved down- ward and outward. If the hand be now disarticulated, and two pins bearing brushes dipped in paint be placed in the end of the head of the ulna and in the lower surface of the radius, pointing downward so as to continue the line of the shafts of these bones, on twisting the forearm, each of these brushes will describe a curve on a sheet of paper held against them ; that in the radius making a large curve upward and inward, and the ulnar pin a small one downward and out- ward. The relative size of these curves may be varied greatly bv the operator. What has occurred is this : besides the rotation of the radius, there has been a lateral movement between the ulna and humerus combined with a slight extension. This mo\ement is less when the arm is nearly straight than when flexed, for in the latter position the lateral parts of the Diagram showing the equal angles of the long a.\es of the bones with the axis of the joint. PRACTICAL CONSIDERATIONS : THE ELBOW-JOINT. 305 capsule are least tense. It is probably assisted by a want of perfect adaptation between the articular surfaces. These e.xperiments on the dead body do not quite fulfil the conditions of the living, because we have no evidence that then the muscles can produce quite the same movement ; moreover, Cathcart has shown that in anky- losis of the shoulder-joint this motion is greatly impaired, thus proving that in life a small amount of motion at that joint is an essential part of free twisting of the hand. Experiments by Hultkrantz on the living subject tend to show that the slight motion of the ulna is in the opposite direction to that described. There is probably much individual variation.' PRACTICAL CONSIDERATIONS. The Elbow-Joint. — This joint is dependent for its strength more upon the shape of the bones that enter into it than upon the ligaments or muscles. As the elbow ceased to be useful for support, but became of the utmost importance for prehension, the radius became movable instead of fixed, and the strength of the joint came to depend in much larger proportion upon the ulna. Force applied in the line of the long axis of the limb, as in hanging by the hands (the weight being transferred from the wrist and the radius to the ulna and the elbow, largely by means of the triangular and orbicular ligaments, with very slight help from the oblique ligament), is resisted in the order of effectiveness (a) by the hook of the olecranon over the trochlea ; (d) by the lateral ligaments ; (c) by the biceps, triceps, and brachialis anticus, aided by the flexors, extensors, prona- tors, and supinators. The lower part of the lesser sigmoid cavity of the ulna under- hangs the inner edge of the radial head, and aids in preventing the radius from being drawn away from the ulna. Force applied in the same line, but in the opposite direction, as in falls upon the hands (the thrust being transferred from the radius to the ulna by means of the oblique fibres of the interosseous membrane), is resisted almost exclusively by the coronoid process, aided perhaps by the surface of contact between the radial head and the capitellum, which is diminished in full extension. As the dislocation usually occurs with the forearm hyperextended, the lateral ligaments, particularly the inner one, are often stretched and torn ; the brachialis anticus is drawn tightly over the humerus and is sometimes ruptured. The coronoid process is not infrequently broken. Antero-posterior dislocations are the most frequent, because of {a) the lesser antero-posterior diameter of the joint as compared with the lateral diameter ; (^) the varying efficiency of the hold of the ulnar processes — the coronoid and olecranon — on the humerus in different positions of the elbow ; {c) the weakness of the anterior and posterior ligaments, and the absence of effective muscular support. Backward dislocation of both bones is far more frequent than forward, be- cause : (i) The capsular ligament is weakest posteriorly. (2) The coronoid, which resists backward displacement, is smaller, less curved, and received in a shallower fossa than the olecranon, which prevents luxation forward. (3) It is in its relation of least effectiveness when the joint is in full extension. (4) Falls upon the hand with the forearm extended greatly outnumber all other causes of dislocation of the elbow. (5) In full extension the already slight surface of contact between the radius and humerus is diminished and the posterior articular edge of the radial head projects ■ behind the capitellum. (6) The ulna and radius are apt to be dislocated together rather than separately because of the strong ligaments which hold them to each other — the triangular ligaments below, the interosseous membrane, and the orbicular and oblique ligaments above — and because of the absence of any such intimate connection of either bone with the humerus. It is this ligamentous connection with the ulna which enables the radius, in spite of the shallowness of the articular cup upon its head, to resist the powerful forward pull of the biceps. ' Heiberg : Ueber die Drehung der Hand, 1884, contains an exhaustive bibliography. Heiberg : Journal of Anatomy and Physiology, vol. xix., 1S85. Cathcart: ibid. Dwight : ibid. Hultkrantz : Das Ellenbogen Gelenk und seine Mechanik, Jena, 1897, contains the later bibliography. 3o6 HUMAN ANATOMY. Lateral dislocations of the separate bones are infrequent for the same reason ; of both bones because of the great relative width of the joint, its irregular undulating transverse outline, the prominences of the border of the trochlea and of the capi- tellum, the strength of the lateral ligaments, and the presence of tlie flexor and extensor muscular masses arising from the condyles. Inward dislocation is the rarest on account of the greater projection of the inner border of the trochlea. When either bone is dislocated separately, it is most apt to be the radius, and in the forward direction on account of the slightness of its humeral connection, its mobility, its direct relation with the hand and wrist, and the effect of muscular action (biceps) upon its upper extremity. The orbicular ligament offers the chief, if not the only resistance to this forward pull of the biceps. Therefore, if this is torn, recurrence of the luxation is common, unless the arm is kept in the acutely flexed position. When the ulna is dislocated alone, it is almost always backward for reasons already mentioned. In the common backward dislocation of both bones, the tip of the coronoid may rest upon the posterior surface of the trochlea, or may ascend to the level of the olecranon fossa, which, however, it is pre\-ented from actually entering by the pres- ence of the soft parts and by the tension of the structures on the front of the joint. The most easily recognized symptom of this displacement is the change in the rela- tion of the tips of the condyles and the olecranon, the latter occupying a much higher position in extension, or lying much more posteriorly in flexion (page 287, Fig. 301). In making this measurement it is important to be sure that the line uniting the tips of the condyles, and in full extension in the normal arm, crossing the olec- ranon about one-sixteenth of an inch below its tip, is a straight line at right angles to the long axis of the humerus. Any upward or downward curve given to this line destroys its diagnostic significance. The large majority of cases of dislocation of the elbow occur in young males, usually below the age of twenty. Kronlein has called attention to the fact that at this age fractures of the clavicle are also common and luxation of the shoulder is rarely met with, while after twenty both clavicular fracture and elbow dislocation are comparativelv rare and shoulder dislocation is common. He concludes that in childhood fracture of the clavicle is the equi\alent of dislocation of the shoulder by direct violence, and dislocation of the elbow is the equivalent of the shoulder dis- location from indirect violence. The anatomical explanation may be that the disproportion between the head of the humerus and the glenoid cavity (page 278 ) is less marked in childhood, the articular surfaces are therefore not so easily separated, and force applied to the point of the shoulder is more apt to reach and be expended upon the clavicle. As to the elbow, the shallowness in children of the fossae which receive the processes and a corresponding want of prominence in the latter, together with the ease with which the elbow-joint in childhood may be hyperextended (which is not the case in adult life), are possible explanations of the frequency of this dislocation in young persons. Congenital dislocations occur. In some instances they have been associated with deficiency of the capitellum, and have then been accompanied by such elonga- tion of the radial neck as to place the head of that bone on a level with the tip of the olecranon. This affords an illustration of the general law, which may be mentioned here, that the rate of growth of epiphyses is inversely as the pressure upon them. Other examples are to be seen in the overgrowth of the cranial bones in hydrocephalus, when their edges are separated by the pressure of the ventricular fluid : in the pro- jection of the vomer and intermaxillary bones beyond the level of the alveolar arch in some cases of cleft palate : in the bony outgrowths that fill up the glenoid cavity or the acetabulum in unreduced luxations of the humerus or femur ; and in many other similar conditions. Disease of the elbow-joint is most often tuberculous, but may be of any variety. In spite of the constant exposure of the joint to traumatism, it is not attacked by disease with exceptional frequency. This is probably partly due to the firm inter- PRACTICAL CONSIDERATIONS : THE ELBOW-JOINT. 307 locking of its bony constituents, preserving its ginglymoid character and preventing the injurious effect of side strains, partly to the similar protective efiect of its strong- lateral ligaments, and somewhat to the laxity of its capsule, permitting of moderate distention without undue tension. It is easily and often spontaneously immobilized in the early stages of disease ; it then bears no weight and is but little exposed to harmful increase of intra-articular pressure from muscular spasm ; and finally, as its fixation does not, as in the joints of the lower extremity, interfere greatly with moderate out-door exercise, the general resistant power is not so easily lowered. Svyelling first shows itself posteriorly on either side of the olecranon process, and extends to the fossa over the head of the radius. In these directions the capsule is thinnest and most lax and the synovial cavity is nearest the skin. As distention continues there may be a bulging beneath the anconeus to the outer side of the olecranon, or on the front of the elbow beneath the brachialis anticus and extending towards the outer side, as it is limited internally by the thickening of the capsule constituting the internal lateral ligament. Pus is apt to follow the same lines of least resistance, and discharge upon the back of the arm on either side of the triceps, but especially on the outer side on account of the attachment of the dense intermuscular fascia above the internal con- dyle ; over the head of the radius beneath the external condyle ; or in front to the outer side of the tendon of the biceps, a position determined by the resistance of the bicipital aponeurosis on the inner side. The radio-ulnar joint, which is part of the articulation, is often involved, affecting the motions of pronation and supination. The upper radial epiphysis and most of the lower humeral epiphysis are within the limits of the capsule, and may either be the starting-point of joint disease or become secondarily involved. The position of semiflexion which gives the greatest ease, and is therefore voluntarily assumed, is that which affords most room for synovial distention and relaxes the muscles most immediately in relation with the joint. Distention of the joint is easily distinguished from disease of the neighboring bursse. The bursa over the olecranon, when enlarged, constitutes a single rounded superficial prominence ; that beneath the triceps tendon, while it causes swelling on either side of that structure, does not extend to or obliterate the fossa over the head of the radius, nor does it cause a ''puffiness between the inner condyle and the olecranon process when the arm is bent at a right angle" (Harwell). The bursae beneath the brachialis anticus and between the tubercle of the radius and the biceps tendon, if enlarged, cause a \'ague fulness over those regions, but none of the charac- teristic appearances of synovitis. Chronic enlargement of the latter bursa, in a case of Agnew, caused pressure paralysis of the muscles supplied by the median and posterior interosseous nerves. The obliquity of the line of the elbow-joint (page 268) should be remembered in the treatment of fractures involving the articulation. In obscure injuries about the joint the position of acute fle.xion, with the hand upon the front of the chest, is the one least likely to be followed by serious ankylosis, as in that position the full functional value of this obliquity is more apt to be preserved than when the forearm is at a right angle. The position is also the one in which it is easiest to retain in place many fractures in the region of the elbow. Especially in fractures of the lower end of the humerus, if the fragments are at once replaced, the coronoid process in front and the njuscular and tendinous structures behind hold them firmly and prevent recurrence of deformity. If the fracture is intercondylar, or T-shaped, the acutely fle.xed position not only holds the condyles in position, but tends to prevent by pressure the involvement of the joint line by callus, which later would prove obstructive. If either the coronoid or olecranon fossa, or both, be involved, it is more important to prevent the filling up of the former than of the latter, as full flexion is of far greater functional importance than full extension. If the condyles — espe- cially the inner — be split off, the position relaxes the muscles that cause displacement. It is also, of course, the most useful position of the limb in case ankylosis does occur. In excision of the elbow-joint the following anatomical points should be remem- bered : (i) The lines of the various epiphyses. (2) The position of the ulnar nerve 3o8 HUMAN ANATOMY. in the groove between the internal condyle and olecranon. (3) The close relation of the posterior interosseous nerve to the head of the radius. {4) The post-operative value (in extending the forearm) of the outer aponeurotic e.xpansion of the triceps and 01 the anconeus muscle. These should be carefully protected from injury. Landmarks. — The following points may be mentioned in addition to those which may be found under the Humerus, Radius, and Ulna : A line from one condyle to the other will be at right angles with the humeral axis, but will be oblique in relation to the axis of the forearm. The line of the radio-humeral articulation is horizontal. The line of the humero- ulnar articulation is oblique downward and inward ; the tip of the internal condyle is therefore from a quarter to a half inch farther above the articular line than is the tip of the external condyle. The internal condyle points backward rather than inward. The length of the articulation line is about two-thirds of the length of a line joining the tips of the condvles. In semiflexion the external condyle is easily seen ; in acute flexion it disappears, and the rounded capitellum of the humerus, with the outer edge of the triceps stretched over it, can be seen and felt. The Inferior Radio-Ulnar Joint. — This articulation has been dislocated in a few instances, in most of which, the cause having been extreme pronation of the wrist, the lower end of the ulna was carried backward, projecting on the back of the wrist and pointing outward, — i.e., towards the middle finger. The backward dis- placement probably involves the tearing of the triangular fibro-cartilage and a rup- ture of the posterior radio-ulnar ligament. The de\-iation of the ulna to the radial side may be due to the action of the pronator quadratus. The shallowness of the sigmoid cavity on the radius favors recurrence after reduction. But little is known of this injury. THE CARPUS. 309 THE HAND. The hand is composed of the carpus or wrist, consisting of eight small bones arranged in two rows, which is succeeded by five rays of four segments each, — • namely, a metacarpal bone and three phalanges, excepting the thumb, in which one phalanx is wanting. THE CARPUS. There are eight carpal bones arranged in two rows of four each. The first row includes, named from the radial towards the ulnar side, the scaphoid, the semilunar, the cuneiform, and the pisiform ; the second row, the trapezium, the trapezoid, the OS magnum, and the imci/orm. Exceptionall}', several other bones may occur, due to the persistence of centres laid down in early fcetal life, which normally fuse with other centres or disappear. Thus there is much in favor of the view that the plan of the carpus is more complicated. This point is further considered in the dis- cussion of variations (page 313). The pisiform of the first row, whatever may be its morphological significance, is in man practically nothing but a sesamoid bone in the tendon of the fiexor carpi ulnaris, resting on the palmar surface of the cunei- form, and having no share in the mechanics of the wrist excepting as giving attach- ment to a part of the anterior annular ligament. The first row, therefore, consists really of the three first-mentioned bones, which are joined into one flexible piece by interosseous ligaments. The upper end of this combination bears an egg-shaped articular surface for the wrist-joint, to which all three bones contribute. Its lower side has a concavo-convex outline, the concavity receiving the inner two bones and the convexity bearing the outer two of the second row. The latter consists of four bones connected by ligaments : the trapezium, for the thumb ; the trapezoid and OS magnum, for the next two fingers ; and the unciform, for the ring and little fingers. The dorsal side of the carpus is slightly convex and the palmar deeply concave, forming by its middle the floor of a deep canal, bridged by the anterior annular ligament, which runs between bony elevations on each side of the carpus. To shorten the description, it may be said that little depressions for ligaments can be seen on well-marked bones near their edges on the dorsal and palmar aspects, especially the former. The scaphoid [os naviculare] , or boat-shaped bone, is the largest and most external of the first row. It is a flattened elongated disk placed with the long axis running outward and downward. It receives its name from being convex on the upper and outer side for the radius and concave on the opposite side for the head the OS magnum. Nearly corresponding with the long axis is the long and very Fig. 321. For trapes ;ium ^^For trapezoid .rvnfi^^^^^^ ' \^^ Tuberosity— ft^^ . ^-^SSj*^'^^^4w ^^^%r -Dorsal surface External ^^m surface ^fey ^ft ) ^y 1 For radius Right scaphoid, dors al aspect. Fig. 322. Palmar surface Right scaphoid, inner aspect. uberoslty narrow dorsal surface. The palmar surface is broader, runs more downward, and the outer end rises into the tuberosity of the scaphoid, from which part of the anterior annular ligament springs. The convex proximal surface for the radius is wholly articular ; the inner edge is straight, the dorsal and palmar converge externally ; it tends to encroach on the dorsal surface. Internally there are two surfaces, both 3IO HUMAN ANATOMY. articular : the upper, very narrow, articulates at its lower border with the semilunar and gives attachment above to the fibro-cartilaginous ligament connecting these bones ; the lower is an elongated cavity embracing part of the top and the outer side of the head of the os magnum. The outer surface, continuous with the dorsum, is a small groove for the lateral ligament of the wrist. The distal surface, forming the convexity of the medio-carpal joint, articulates with the trapezium and trapezoid. It is convex in all directions. The scaphoid articulates withyfi'^' bones, — the radius, semilunar, trapezium, trapezoid, and os magnum. The semilunar [os lunatum] receives its name from its outline when seen from the side, the pro.ximal surface being convex and the distal deeply concave. The dorsal surface is quadrilateral. Its proximal and inner borders are longer than the Fig. 323. Fig. 324. For cuneiform Kc^r unciform Dorsa For scaplioid Riglit semilunar, outer aspect. Rigfit semilunar, inner aspect. Others, so as to make it kite-shaped, the long axis running distally outward. The two shorter surfaces meet at an overhanging point. The palmar surface is of the same general shape. Its larger distal portion is smooth as for a bursa. 'Wxq proxi- mal surface is convex and articular, chiefly for the radius ; but, extending under the triangular cartilage, broadest at the scaphoid edge, it narrows internally. The con- cave distal surface is divided by a ridge into a larger part for the os magnum and an inner for the edge of the unciform. An outer surface articulates with the scaphoid and an inner with the cuneiform. Both are semilunar, but the outer is the more slender. Both are nearly plane and practically wholly articular, there being but a slight roughness for the interosseous ligaments at the pro.ximal end near the dorsum. The semilunar articulates with five bones, — the radius, scaphoid, cuneiform, os magnum, and unciform. The cuneiform [os triquetrum] , or pyramidal is of such form that the latter name is the more fitting. The base is the articular surface for the semilunar ; the apex is at the inner side of the wrist. The base is plane and articular except where the interosseous ligament joins it. The dorsal surface is narrow and not clearly Fig. 325. For pisiform For semilunar Palmar surface'' For triangular cartilage Right cuneiform, palmar aspect. Fig. 326. Non-articular Right cuneiform, distal aspect. separated from the proximal on the macerated bone. The proximal surface is a triangle with the base inward, and has near the base a smaller triangle of articular surface for the triangular cartilage. The inner half of 'Cn^ palmar surface is occupied by a round facet for the pisiform. The distal surface is a very complexly curved articular facet for the unciform. It suggests a saddle-joint that has been spirally twisted. A transverse section of this surface is concavo-convex from without inward. THE CARPUS. 3" A vertical section near the outer end is concave, near the inner convex. It is prac- tically a screw surface. A small part of the inner side is non-articular. The mner surface is the apex of the pyramid, a small knob for the lateral ligament. The cuneiform articulates with three bones, — the semilunar, pisiform, and unciform. The pisiform [os pisiforme] is a small rounded bone, rough everywhere except where the greater part of one surface is occupied by a round, slightly concave articu- lar facet which joins the palmar aspect of the cuneiform. The facet is at the proxi- Fig. 327- Fig. 328. 1 Rougli surface for an- terior annular lig- ament and flexor carpi ulnaris IP' — )m. -For cuneiform Right pisiform , dorsal aspect. Right pisiform, palm ar aspect. mal part of the dorsal surface, the bone projecting from it downward, forward, and inward, lying in a plane anterior to that of the outer carpal bones. The pisiform articulates with only one bone, — the cuneiform. The trapezium [os multangulum majus] is distinguished by an isolated facet on the distal surface for the metacarpal bone of the thumb. This surface is that of a typical saddle-joint, concave from side to side where the borders are most raised ; convex from before backward ; broadest transversely. The proxhnal sujface is a four-sided concavity for the scaphoid, separated by a ridge from the inner surface. The inner surface is subdivided : the proximal portion, much the larger, is an articular concavity for the trapezoid ; the distal portion is rough except for a facet at the dorsum for a part of the side of the second metacarpal. The outer surface is concave, receiving the lateral ligament. The dorsal suyface is elongated from side to side, slightly hollowed in the middle, with a variously developed tubercle on Fig: 329. Fig. 330. For first metacarpal For second , metacarpal r trape Right trapezium, palmar aspect. I flexor carpi radialis For scaphoid Ridge For scaph< Right trape: For trapez proximal and i either side. On the palmar surface is a deep groove for the tendon of the flexor carpi radialis. Just beside this is a prominent ridge at the junction with the external surface for a part of the outer insertion of the palmar annular ligament. The trape- zium articulates with/tjwr bones, — the scaphoid, trapezoid, and first and second meta- carpals. The trapezoid [os multangulum minus] is best recognized by the do7-sal surface, which is pointed distally where it projects into the second metacarpal. The outer convex border against the trapezium is much longer than the inner against the os magnum. The proximal border runs obliquely forward and inward. The small palmar surface is irregularly quadrilateral. The proximal surface is a quadrilateral, nearly plane, facet for the scaphoid, longer from dorsum to palm than transversely. The distal surface, entering the base of the second metacarpal, is divided by a ridge into two facets, concave from dorsum to palm, of which the inner is the longer. The hiternal surface, in the main concave, articulates with the body of the os mag- num, but has a non-articular surface near the dorsum for an interosseous ligarnent. The outer surface is mostly articular and slighdy convex, joining the trapezium ; 312 HUMAN ANATOMY. distally and towards the palm there is a rough surface for ligaments. The styloid process of the third metacarpal often reaches the dorsal aspect of the trapezoid For trapezium For magnum Right trapezoid, inner aspect. Right trapezoid, outer and distal aspect. between the os magnum and the second metacarpal. The trapezoid articulates with four bones, — the scaphoid, trapezium, os magnum, and second metacarpal. The OS magnum [os capitatum] is the largest bone of the carpus, and possesses a head, neck, and body. The head is a rounded articular eminence at the pro.ximal end, playing in a socket formed by the scaphoid, semilunar, and unciform. The con- vex articular surface extends much farther on the dorsal side than on the palmar. A faint line above often separates the part resting on the scaphoid from that resting on the semilunar. The former extends down the outer side of the head. The inner side of the head is a sharply cut plane surface articulating with the unciform. The neck is a constriction, best marked on the dorsal aspect, generally seen on all sides except the inner. The distal surface, broader on the dorsal end, faces a little out- ward. It is wholly articular, bearing the third metatarsal bone. A groove in the place of the outer angle receives the edge of the second metatarsal. A smaller surface for the fourth exists at the inner angle just below the dorsum. The dorsal Fig. 334. Dorsal surface Neck For scaphoid Right OS magnum, outer aspect. surface shows the head, and distally to it a sharp, slightly concave inner border, a shorter outer one, and a distal one slanting downward and inward, so that the outer angle is obtuse and the inner would be acute, but that the point of the angle is replaced bv a small border touching the fourth metacarpal. The palmar surface is narrow and prominent below the neck. The inner surface is rough for a ligament near the palmar border ; above, it has a narrow articular surface for the unciform, continuous with that on the head. The outer surface has,a small articulation with the trapezoid, which exceptionally is continuous with the facet on the head. The OS magnum articulates with seven bones', — the scaphoid, semilunar, trapezoid, unci- form, and second, third, and fourth metacarpals. The unciform [os haraatum] is distinguished by a prominent hook projecting from the inner side of the palmar surface for a part of the annular ligament. The dorsal surface is nearly or quite triangular. It presents an oblique proximal border, a nearly straight, but often conve.x, outer one, and a distal one tending to meet the inner end of the proximal border. Should they meet, the surface is triangular ; but more often there is a very short inner border separating them, which is either straight THE CARPUS. 313 or concave. The palmar surface, of about the same shape as the dorsal, presents externally a deep groove, a part of the canal for the flexor tendons, overhung inter- nally by the unciform process, which has a broad outer and inner surface, the former conca\'e and smooth, the latter convex. The free border of the hook presents a curved outline from the inner side. The rounded edge between the proximal and outer surfaces rests against the semilunar. The proximal siaface is a spirally twisted, oblong facet corresponding to the adjacent side of the cuneiform, with a prominent convexity at the proximal end. The oiiter surface, rough at the distal and palmar angles for an interosseous ligament, is elsewhere articular for the os Fig. 335. Fig. For magnum Right unciform, inner and pro.ximal aspect. Right unciform, outer and distal aspect. magnum. The distal surface, wholly articular, bears the fourth and fifth metacarpals, a ridge marking the interspace between them. The surface is, in the main, convex from side to side and concave from dorsum to palm. Often, however, the part for the fourth finger is concave from side to side and convex in the other direction. The distal surface may meet the proximal at a sharp border, or a very narrow rough surface may intervene. The unciform articulates with five bones, — the semilunar, cuneiform, os magnum, and fourth and fifth metacarpals. Development and Variations. — In early fcetal life centres appear for the above-described carpal bones, and also for many others, which disappear, or are fused with the usual ones, long before the appearance of bone. Additional carpals depend either on the persistence and subsequent ossification of centres that normally are lost or on the separate development of two or more that should fuse. The number of carpal elements is put by Pfitzner^ at thirty-three. He arranges the constant and possible bones in five rows : (i) an antibrachial row, consisting of an ossification in or on the triangular cartilage, representing the os intermedium, and a little apparent outgrowth from the pisiform ; (2) a proximal row, consisting of the normal bones and certain subdivisions of the scaphoid and cuneiform ; (3) a central row, composed entirely of occasional bones ; (4) a distal row, composed of the four normal bones plus a minute metastyloid ; (5) a carpo-7netacarpal row, composed entirely of occasional bones. The most common anomaly is the appearance of a styloid bone, which is the separated styloid process of the third metacarpal. The metastyloid of the fourth row is a minute bone representing the very tip of the styloid. Very rarely the scaphoid is divided into a radial and an ulnar part. The os centrale is the persistence of still another piece, which normally either joins the scaphoid in the third month of fcetal life or disappears. It apparently is composed of a dorsal and a palmar element, of which the latter is the more subject to degeneration. The os magnum contains two elements exceedingly rarely found distinct, the siibcapi- tatum on the distal end of the palmar surface and the subcapitatum secmidarium forming the inner distal angle of the dorsum. The hook of the unciform may be separate. Fusion may occur between bones normally distinct. The semilunar may fuse with the cuneiform, especially in negroes. Ossification occurs from one centre for each bone ; but according to some authorities, the unciform and the scaphoid have two centres. The former and the os ' Zeitschrift fvir Morphologic und Anthropol., Bd. ii., 1900. 314 HUMAN ANATOMY. magnum are the first to ossify, the process beginning in the latter part of the first year. The order of its appearance in the other bones is very uncertain. Those of the first row, excepting the pisiform, contain bone by the end of the first five or six Fig. 337. Ossification of bones of hand. A, at binh : B, latter half of first year ; C. at three years ; B. at eight years ; E. at twelve years, a. centres for shafts of metacarpals and phalanges; *. magnum ; f, unciform: rf, cuneiform-, ft^(sc

loid notch Obturator ex ternus Adductor m-agnus^ ischial ramus Right innominate bone, outer aspect. of the socket and above the sciatic notch, is smooth ; the posterior is rough. The latter presents anteriorly the rough and pitted auricular su7-face ^ corresponding to that of the sacrum. A narrow depression, the pre-artic7ilar groove, bounds this on the smooth surface, receiving the fibres of the anterior sacro-iliac ligament. Behind the auricular surface is a rough area of a different character with an elevation at or below the middle of the preceding surface. This area serves for the attachment of the strong posterior sacro-iliac ligaments. Still farther back the bone has a smoother finish where it gives origin to the erector spinse. The ilium has several large ^ Fossa iliaca - Etninentia iliopcctlnea. '' Facias auricularis. 334 HUMAN ANATOMY, nutrient foramina ; one on the inside of the lower hind part of the iHac fossa runs forward, one or two on the outside near the anterior inferior spine run backward, and one near the middle of the second curved hne runs downward. The Pubis. — The pubis' (os pedinis) has a tiat squarish body, which, meeting its fellow at the symphysis, forms the front wall of the pelvis, and two rami, the superior joining the ilium and the inferior joining the ischium. The median end of the body ^ is wholly taken up by a rough oval area, the symphysis pubis, bearing the libro-cartilage of the joint. The spine* of the pubis is a pointed tubercle, projecting Internal lip -^^^^ Transversalis Qtt^dratus tumborum Cotnptcs I < Attachment of Isck fopvard from the front of the upper border of the bone some two centimetres from the symphysis, to which Poupart's ligament is attached. A ridge runs from this obliquely backward and inward to the posterior end of the top of the symphysis, which, together with the rough surface internal to it, constitutes the crest. The term angle is applied to the line of junction of this surface with the symphysis. The superior ramus * is prismatic, having an antero-superior, an inferior, and a posterior side. It enlarges as it runs outward to form a part of the socket. The ilio-pectineal ^ Os pubis. - Corpus ossis pubis. ■'Tuberculum pubicum. * Ramus superior. THE INNOMINATE BONE. 335 liyie starts from the spine and runs obliquely backward and outward to the iUum. The triangular antero-superior side of the ramus, narrow at the inner end, broad at the outer, concave from side to side, convex from before backward, is bounded behind by the ilio-pectineal line, in front by the obturator crest, ' which runs from the Fig. 354. Ilio-pectineal eminence Conjoined tendon- Gimbemat b ligamem'" Poupart's ligament '^ Conjoined tendon / / Rectus abdominis Pyramidalis Region of symphysis pubis from above. Spine to the inner border of the acetabular notch, and externally by a swelling at the upper inner part of the socket, — the ilio-pectineal emuience. The posterior side, broad at the inner end and narrow at the outer, is quite smooth. The inferior border is marked by the broad obturator groove'' above the foramen, passing from behind for- mic. 355. Epiphj"seal lamina on ilium. ■ Epiphyseal lamina on ischium Innominate bone at about fifteen years. ward and inward for the obturator vessels and nen'e. The inferior ramus,- flat and thin, rough in front, smooth behind, extends backward and outward to join the ramus of the ischium. ' It is constricted just above the point of union. The inner edge, forming part of the pubic arch, is somewhat everted. ^ Crista obtnratoria. - Snlcns obturatorms, '^Ramas inferior. 336 HUMAN ANATOMY. The Ischium. — The ischium,' the thickest and most solid part of the bone, consists of a hodv, chiefly concerned with the acetabulum, a hiberosity, and a vacuus. The body, continuous above with the ilium, forms the front of the great sciatic notch ' below which is the sharp spine of the ischium pointing backward and inward for the lesser sacro-sciatic ligament. The tuberosity ■' is a great thickening of the back of the lower end of the body of the ischium which bears the weight in sitting. It is broad above and behind, narrowing in front as it passes into the ramus. It extends but little onto the inner side of the bone, which otherwise is smooth. Its inner lip receives the great sacro-sciatic ligament and its falciform prolongation. A smooth surface (in life coated with cartilage) passes from the inside of the back of the bone just below the spine and above the tuberosity, forming the lesser sciatic tiotch,* occupied by the tendon of the obturator internus. In front of this, under the ace- tabulum and above the tu- berosity, is a groove for a part of the obturator ex- ternus. The upper part of the tuberosity is divided into an upper and front area for the origin of the semimem- branosus, and one behind and below it for the semi- tendinosus and biceps. Be- low these, extending onto the ramus, is a surface for the adductor magnus. The ramus'^ is a strip of bone running forward to meet the inferior ramus of the pubis. The lower edge, forming the margin of the subpubic arch, is twisted outward and rough. The border towards the foramen is relatively, sharp. The line of junction of the rami of the ischium and pubes can be distin- guished by the greater breadth of the former. The acetabulum, the socket for the hip, is a deep hemispherical cavity with a raised border, imperfect be- low. The imaginary a.xis of the cavity runs upward, inward, and backward. It is formed by all three bones, the ischium contributing the most and the pubes the least. The lines of union are sometimes seen on the smooth posterior surface in the adult. The cavity is only in part articular. In shape this portion may be com- pared to a horseshoe beaten concave and fitted into the cavity with the two ends pointing downward, enclosing a non-articular cavity at a somewhat deeper level, which extends more than half-way up the back of the socket. The bone at the bottom of the cavity is very thin. The articular strip is broadest above and behind the middle and narrowest in front. Of the two ends of this articular strip the posterior is the more prominent, overhanging a groove leading into the non- articular hollow from below. The front one has no corresponding projection. The border of the acetabulum is formed by the convexity of this horseshoe-shaped strip, and consequently is wanting below. The interruption is the cotyloid notch.^ The Pubes Oblique sagittal secti( JOINTS AXD LIGAMENTS OF THE PELVIS. 337 border rises from the surface of the bone distinctly below and to a less degree behind and abo\'e. The thyroid or obturator foramen ' is a large oval opening, with the laro-er end above and the long axis running downward and outward, bounded by the pubis and ischium. A little tubercle, seen best from the inner side, marks the upper limit of the ischium. Abo\-e is the obturator groove under the ramus of the pubis. It is closed by a membrane, e.xcept under the groove. Structure. — The innominate bone is, as a whole, ver\' strong. The two thin places are in the middle of the ilium and of the cotyloid cavit}-. It is very thick round the joint wherever pressure may be transmitted through the head of the femur. Sections show radiating trabeculae from the socket connected by concentric lines. The bone is verj' thick in a line from the socket to the outer e.xpansion of the ihac crest, which runs nearly \-ertically in the upright position. It is very strong also at and behind the auricular surface. Development. — ^A centre for the Uium appears early in the third fcetal month above the acetabulum and spreads quickly through the upper part of the bone. One for the ischium appears below the socket, usually before the end of the same month. One for the pubis comes decidedly later in the iliac ramus. It is said to appear from the fourth to the fifth month, but it may not be present till the sixth. At birth there is stiU much cartilage around and between the bony e.xpan- sions from these centres. The rami of the pubis and ischium unite at about eight years or earlier, but the suture may be visible on the inside at eighteen. Ossifica- tion commences by several centres in the Y-shaped cartilage separating the bones in Fig. 357. Ossification of innominate bone. A, at third foetal month ; B, at birth ; C, during first year; D, at six years ; £■, at about fifteen years, a. chief centre for ilium; b, chief centre for ischium ; c, for pubis'; d, for tuberosity of ischium ; e, for iliac crest ; /', for anterior inferior spine. the socket at an uncertain date, probably before ten years. One of these centres, much larger than the rest, the os acetabtdi, persists at the front of the cavity be- tween the pubis and Uium till perhaps fifteen, when union has made much progress between the various parts of the acetabulum. The lines of junction may be seen on the inside at seventeen or eighteen, that between the pubis and ischium persisting longest. Secondarj- centres come about puberty" for the crest of the Uium, the an- terior inferior Uiac spine, the sj-mphysis pubis, and the ischial tuberosity-. They are fused at tn-enty, excepting, perhaps, that for the crest of the ilium,' the' union of which may be delayed ; the suture marking its presence is one of the last in the body to disappear. JOINTS AND LIGAMENTS OF THE PELVIS. These may be divided into (i) those connecting the Uium with the sacrum and last lumbar vertebra, (2) those connecting the pubic bones at the symphysis, and (3} the ligaments forming the lateral walls, — the sacro-sciatic Ugaments and the obtu- rator membrane. ^Foramen obtaratnm. 338 HUMAN ANATOMY. THE SACRO-ILIAC ARTICULATION. The sacro-iliac articulation, often improperly called the sacro-iliac synchondrosis, partakes of the nature of both a true and a half-joint. The opposed surfaces of the sacrum and ilium vary greatly in shape. The sacrum is broader in front than behind, so that the line of the joint slants inward as well as backward ; but occasion- Fic. 358. Posterior sacro-iliac 1 Sacro-iliac joint Fig. 359. Ilio lumbal ligament Anterior sacro-iliac ligament Horizontal section through right sacro-iliac joint. ally in some part it is a little broader behind than in front. Often there is an out- ward swelling between the borders, so that, a part of the sacrum is received into a hollow in the ilium, and a transverse cut of the joint shows a sinuous line. Perhaps quite as often the ilium projects into the sacrum. In any case, as a rule, there is a certain amount of interlocking. The opposed surfaces are covered with cartilage. The layer on the sacrum, from one to two millimetres thick, is at least twice as thick as the other, and, though generally reckoned fibro-cartilage, has much the appear- ance of hyaline. The two are sepa- rated by a synovial cavity, which is enclosed by the sacroiliac liga- ments. The size of this cavity is very uncertain. It may extend backward beyond the auricular surfaces, occupying on the ilium a part of the space usually serving for the origin of the posterior sacro-iliac ligaments, or it may be encroached upon by fibres. Some- times, before old age, the joint is replaced by bone. The fibres around the joint are severally named according to position. The posterior sacro- iliac ligament f Fig. 358 ) is very important. It comprises many layers of strong fibres, filling up the depths of the cleft between the sacrum and the overhanging ilium, extending from the rough area on the latter behind the auricular surface to the back of the lateral masses of the sacrum, nearly or quite to the pos- terior sacral foramina below the three upper sacral vertebrae. Those of both sides nd f the last lumbar THE SYMPHYSIS PUBIS. 339 resist any tendency of the weight of the body to force the sacrum forward. A rather distinct superficial band, the oblique sacro-iliac ligament' (Fig. 362), passes from the posterior superior iliac spine to the second and third sacral vertebrse. Anterior and superior fibres are spread about the joint, and require no special description. Some of them go to the pre-auricular sulcus of the ilium. The ilio-lumbar ligament" (Fig. 359) is a triangular band of strong fibres diverging from the apex and the front surface of the transverse process of the last lumbar vertebra to the top of the crest of the ilium opposite to it and to the an- terior surface, where it mingles with the anterior sacro-iliac fibres. A more or less distinct bundle of diverging fibres to the top of the sacrum near the joint with the ilium is the sacro-lumbar ligament (Fig. 359). THE SYMPHYSIS PUBIS. The symphysis pubis is generally a typical half -joint, the fibro-cartilage coating the opposed pubic surfaces being very dense and the central cavity small. In section it appears as a linear cleft nearer the back than the front. Sometimes, however, especially in women, a part of the surface^ is"coated with hyaline cartilage. The total breadth of the soft parts (greater in woman than in man) rarely exceeds five millimetres. The cartilages are ensheathed in fibres, the deeper parts of which Fig. 361. Superior Synovial pubic ligament ca\ity Fibro-cartilage The symphysis pubis, anterior surface. Inferior pubic ligament Frontal section through the symphysis pubis. are inseparable from them : those above and behind are of little consequence. The anterior ones are in several layers, being in part composed of fibres from the aponeurosis of the external oblique and of fibres of origin of the rectus. They are in the main transverse, but those from the obliques run downward and inward, sometimes making a distinct decussation. The inferior or subpubic fibres are col- lected into a dense transverse band, bounding by the lower side the pubic arch and being joined by the upper to the fibro-cartilage. THE SACRO-SCIATIC LIGAMENTS. These are two layers of fibres passing from the sides of the sacrum to the ischium and forming a partial wall for the pelvis at the sacro-sciatic notch, where the bony walls are wanting. The great or posterior sacro-sciatic ligament-^ (Fig. 362) is external to the lesser, which it conceals to a large extent. It arises from the outer surface of the pelvis, beginning at the inferior posterior spine of the ilium, where its fibres mingle with those of the posterior sacro-iliacs, then from the posterior edge of the border of the three lower pieces of the sacrum and from one or two of the coccyx. From this broad origin it narrows as it passes forward, and at the same time twists so that the outer surface becomes the inferior as it is inserted into the under side of the tuberosity of the ischium. As it reaches the tuberosity the fibres at its inner ^ Lie. sacroiliacom postcrius longuni. - Lig. iliolu Lig. sacrotubcrosun 340 HUMAN ANATOMY. Posterior superior spine of tlium Supraspinous ligament Sacro-coccygeal ligament Tip of '//? \\\ Great sacro-sciatic Lesser sacro-sciatic ligament Spine of ischium Origin of biceps- -Tuberosity of ischium External surface of the sacro-sciatic ligaments. Fig. 363. I- lith lumbar vertebr: Obturator canal Ohturalor membrane Falciform process of great sacro-sciat ligameiil Auricular surface articular surface Internal surface of the sacro-sciatic ligaments, showing the falciform continuation of the great. THE PELVIS AS A WHOLE. 341 border become raised from the rest and are inserted into the inner border of the ramus of the ischium, from which they rise in a fold, the falcifor}?i ligatnent, within the pelvis, continuous with the obturator fascia. The ligament at its insertion into the tuberosity is continuous with the fibres of origin of the biceps. The lesser or anterior sacro-sciatic ligament ' (Fig. 363), much the smaller, is situated internally to the great, springing from the edge of the sacrum below- the junction with the ilium and from the side of the upper part of the coccy-x, being more or less continuous with the interior surface of the great. It narrows to its insertion into the spine of the ischium. The great sacro-sciatic foramen' (Fig. 362) is bounded above by the ilium, in front by the ilium and the ischium, behind by the great ligament, and below by the lesser. It transmits the pyriformis muscle, the gluteal, sciatic, and internal pudic vessels and nerves, and the nerves to the obturator internus and quadratus femoris. The lesser sacro-sciatic foramen^ (Fig- 362) is bounded in front by the body of the ischium, above by the lesser ligament, and below and behind by the oblique border of the great. Through it pass the obturator internus muscle, the internal pudic vessels and nerve, and the nerve to the obturator internus. The obturator membrane* (Fig. 363) is attached to the margin of the fora- men of that name, which it completely closes, except for a small space at the top of the groove under the ramus of the pubis. Sometimes there are perforations. The attachment at the inner side is directly to the sharp edge of the rami of the pubis and ischium. At the outer border it passes into the periosteum lining the pelvis. THE PELVIS AS A WHOLE. The promontory of the sacrum and the ilio-pectineal line separate the true pelvis'" below from \\\& false^ above. The latter is bounded by the lower lumbar vertebrse Fig. 364. and by the flaring ilia. The true pelvis is bounded by the sacrum and coccyx behind, by the bodies and symphysis of the pubis in front, and by the sacro-sciatic ligaments, - Foram. ischiadic Foram. isch. * Membrana obturatoria. '' Pelv 342 HUMAN ANATOMY. the ischia, part of the ilia, and the pubic rami and obturator membrane at the sides and front. The plane just described as separating; the true and false pelvis is the plane of the inlet^ of the latter. Its greatest individual variations are due to the greater or less projection forward of the sacral promontory. The outlet" \iacula (Fig. 390). There are generally three chief ones : a superior^ starting from the superior cer\ical tubercle and running along the upper border, or backward across the neck to the head of the femur ; a middle, from near the inferior cervical tubercle along the front of the lower border of the netk ; and an i)iferior, from near the lesser trochanter along the lower side. Any of these may be more or less free from the neck. ' Journal of Anatomy and Physiology, vol. xvii., 1883. THE HIP-JOINT. 373 The retinacula ' probably strengthen the union of the head and neck before the union of the epiphyses. Movements. — As a ball-and-socket joint, the hip permits motion on an indefi- nite number of a.xes. If the ball were on the end of a straight rod, we could assume that flexion and extension occur on a transverse axis and adduction and abduction on an antero-posterior one, but the inclination of the shaft of the femur and that of the neck in two directions complicates the problem, so that accurate analysis of the Fic;. ,^89 Crest of ilium Head of femur Obturator membran Symphysis The Inner wall of the hip-joint socket has been cut away, exposing the head and round ligament without disturbing the capsule. movements is practically impossible. Rotation is motion on a vertical axis which is generally assumed to pass through the head and the intercondylar notch. This must, of course, vary with the shape of the bone. Although the angular motions in the four conventional planes are far from simple, they may be assumed to be so for practical purposes. Flexion is stopped in life by the contact of the thigh and the trunk before the limits of the motion are reached. Extension is limited by the ' Fawcett : Journal of Anatomy and Physiology, vol. xxx., 1896. 374 HUMAiN ANATOMY. resistance of the strong ilio-femoral ligament, excepting the outer band. Abduction is limited, the thigh being extended, by the pubo-iemoral ligament and perhaps by the inner limb of the ilio-femoral. Fig. 390. Round ligament Posterit intertroclia ridge Capsule When the thigh is flexed, the latter is certainly relaxed, and the strain comes on the pubo-femoral and a part of the capsule behind it, — a very weak re- gion. Adduction with a straight thigh is limited by the outer limb of the ilio-femoral, the top of the capsule, and Morris's band from the rectus tendon to the vastus externus, if it be present. After moderate flexion is passed, the ilio-femoral is relaxed. Outward rotatio7i, the thigh being straight, is checked by the ilio-femoral, especially by its inner band. As the thigh is flexed the inner band is re- laxed and the outer is at first tense, but both are relaxed as flexion reaches about 45°. Morris's band now be- comes tense, and as flexion becomes extreme the round ligament is tense also, unless the thigh be abducted, when it is completely relaxed. In- ward rotatio}i is checked by the ischio- femoral ligament in any position. The most important part of the capsule is the ilio-femoral band, which is extremely strong and prevents over- extension. It is an essential element in maintaining the upright position. The round ligament has probably no mechanical function, though it can be made tense by flexing, and at the same time either adducting the femur or rotating it outward. It is too weak to be of any real use as a restraint. Probably its chief usefulness is to carry vessels to the head of the femur in childhood. PRACTICAL CONSIDERATIONS. The greater security of the hip-joint, as compared with the shoulder-joint, is due to the depth of the acetabular cavity : to its reinforcement by the cotyloid fibro- cartilage ; to the attachments of the ilio-psoas, gluteus minimus, and vastus externus to the capsule ; but chiefly to the thickenings of the capsule itself, which are described as the ilio-, ischio-, and pubo-femoral ligaments. The greatest pressure upon the capsule in all ordinary positions is in an upward and outward direction, or upon the anterior surface of the capsule, as when, under the influence of the powerful extensors, the pelvis and trunk tend to roll backward upon the thighs in the erect posture. The tension and pressure are, of course, greatest near the pelvic attachment of the capsule where the head will impinge upon it with the most advantage as to leverage. The capsule is especially fitted to resist this pressure. If two lines be drawn, one from the anterior inferior iliac spine to the inner border of the femur near the lesser trochanter, the other from the anterior part of the groove for the external obturator {i.e., the upper part of the tuberosity of the ischium) to the digital fossa, all the ligament outside and above these lines is very thick and strong ; whereas, all to the inner side and below, except along the narrow pubo-femoral band, is very thin and weak, so that the head of the bone can be PRACTICAL CONSIDERATIONS : THE HIP-JOINT. 375 Diagram indicating strong and weak portions of c joint. [AI/i's.) seen through it (Morris). Fig. 391 represents this diagrammatically. In addition, the greater elevation and thickness of the upper and outer rim of the acetabulum, and the pressure against the trochanter exerted by the ilio-tibial band of the fascia lata (Allisj in adduction of the thigh (which means an outward movement of the upper extremity of the femur), should be mentioned among the factors that resist displacement. The ligamen- tum teres is of little value, as its bony attachment to the femoral head is easily separated by a force less than that required to rupture the ligament. A line drawn from the anterior spine to the tuber ischii will approxi- mately bisect the acetabulum and will divide each half of the pelvis into two planes, the pubo-ischiatic, inner or anterior, and the ilio-ischi- atic, outer or posterior (Fig. 392). When the head of the femur escapes from the acetabulum it must lie on the surface of one or other of these planes. All dislocations are, there- fore, either (i) outward — i.e., pos- terior— or (2) inward — i.e., anterior. I. Outward or Posterior Ltixations. — Traumatisms in which the force is expended upon the region of the hip result, as a rule, in children in epiphyseal sep- aration (page 361), in old persons in fracture of the neck of the femur (page 363). In 173 cases of dislocation of the hip, 138 were between fifteen and forty-five years of age. In practically all positions of the hip in which luxation is probable the force acts through some form of leverage which brings the short arm of the lever — always the head and neck of the femur — against a weak portion of the cap- sule. If it does this with the aid of a bony fulcrum, the power is ex- erted to the greatest possible ad- vantage. Thus, in hyperextension of the thigh, the acetabular rim acts as a fulcrum, but the head of the bone is brought against the anterior part of the capsule, — the ilio-femoral ligament, — which is usually stronger than the bone itself. Hyperfiexion is arrested by the contact of the soft parts of the front of the thigh with the abdomen ; hyperadduction by the contact of the shaft with the pubes. Hyperabduction, however, brings the greater trochanter against the prominent outer lip of the ace- tabulum, while the head is carried downward against the thin inner and lower part of the capsule ; the ilio-femoral and ischio-femoral liga- ments are relaxed, and the weak pubo-femoral ligament offers but little resistance ; the head, being opposite the shallowest part of the acetabulum, projects half its bulk out of that ca\ity ; the weight — i.e., the resistance of the capsule — is \ery close to the fulcrum, greatly increasing the power of the leverage. Fig. 392. Diagra: 376 HUMAN ANATOMY. The ilio-femoral ligament may, in cases in which the thigh is adducted and rotated inward at the time of application of the force, take the place of the acetabu- lar rim as a fulcrum. In that position it is wound round the neck of the femur, and Luxation of the head of the femur onto the dorsum of the ilii Fig. when the fle.xed leg is used as a crank the head may be made to burst through the lower and posterior part of the capsule. Allis ' has shown that these conditions, easily demonstrated e-xperimentally, are reproduced in many forms of accident. It is obvious that they are all favorable to a downward diiilocation, and this, as is the case with the humeral head, is the direc- tion primarily taken in the vast majority of these luxa- tions. If the thigh has been rotated inward, either in ad- duction or abduction, the head of the bone will pass outward and backward and rest behind the acetabulum on some part of the outer or posterior plane of the pelvis. If it lies upon the ilium, a little above the acetabulum, it constitutes the " iliac" dis- location,— "above the obtu- rator tendon ;" if upon the ischium, on a level with or a little below the acetabulum, it is the " ischiatic" or "sci- atic" dislocation, — " below the obturator tendon." This obturator internus tendon sometimes interposes an ob- stacle to the upward passage of the head, but its impor- tance in this respect has been exaggerated. The degree of flexion of the limb at the time of the accident is more likely to determine the level at which the head rests. ' Reduction of Dislocations of the Hip, Philadelphia, 1896. niiiate bone in PRACTICAL CONSIDERATIONS : THE HIP-JOINT. 377 In both positions the ilio-femoral ligament, which is almost invariably intact, has now become the fulcrum. As the short arm of the lever — the head and neck — has moved outward, the long arm — the shaft of the femur — must move inward ; hence adduction is present in all cases of outward luxation in which the Y-ligament is not lacerated, and is persistent because the head lying in contact with the outer wall of the pelvis cannot be moved inward. Rotation inward, which is also present and persistent, is due to the same tension upon the Y-ligament. This explains the usual position of the limb with the line of the femur crossing that of the opposite thigh a little above the knee and the great toe resting upon the instep of Fig- 395- the sound foot. Flexion of the thigh is maintained partly by the tension on I J the ilio-psoas. t ;; The muscles have a very minor A ;J part in the production or maintenance ^^ -^' of the characteristic deformity. The ^ ^ ? e.xternal rotators, the glutei and the pectineus, are often lacerated. There is shortening, and the trochanter is above the level of Nelaton's line. |i In the rare cases in which the Y- ' - ligament — or its outer limb — is torn, | -^ outward luxation with neither adduc- tion nor inversion becomes possible. 2. In'djard or Anterior Luxations. — These always occur with the thigh in abduction, and are favored by out- ward rotation, which carries the head towards the lower anterior part of the capsule. If it passes upward and rests on the body of the pubis, it constitutes the "pubic" luxation (Figs. 395, 396) ; if downward, it is in or opposite the thyroid foramen, and is often called an "obturator" or "thyroid" lu.xa- tion (Figs. 397, 398). The ilio-femoral ligament again becomes the fulcrum ; the short arm of the lever has been carried inward, necessitating a corre- sponding outward movement of the long arm ; hence abduction is present. The exaggerated rotation outward is maintained by the tension of the liga- ment ; hence the eversion of the limb. Neither abduction nor eversion can be overcome, because the head is held firmly against the pubo-ischiatic pelvic plane. The gracilis, pectineus, and ad- ductors are apt to be torn ; the stretch- ing of the ilio-psoas, the glutei, and the muscles inserted into the greater trochanter aids in maintaining both the flexion and the eversion. The ilio-tibial band of fascia will be found relaxed ; the trochanteric prominence disappears as the trochanter approaches the mid-line and is in a measure sunk in the socket. There will be shortening on measurement from the anterior superior spine to the condyle ; the head of the femur will be unduly prominent in the pubic variety. With the patient in dorsal decubitus, it will be evident that the acetabula are situated on a horizontal plane about midwav between the pubes and the sacrum. From this level the pelvis slopes upward to the symphysis and downward to the Luxation of the head of the femur onto the pubb 378 HUMAN ANATOMY. sacro-iliac junction. It is obvious that no anterior dislocation can be below the bi- acetabular line and no posterior dislocation can be above it. As the femur is about equal in length to the tibia and tarsus, if the head is in the socket the foot will be on the acetabular level when the thigh is vertical and the knee flexed. If the head is dislocated anteriorly, the foot will be on a higher level ; if posteriorly, the foot will be lower, and may even touch the surface on which the patient lies. There will be corresponding changes in the level of the knees (AUis). The femoral vessels are not often injured in hip lu.xations, because they lie above the joint and lu.xations are always primarily downward ; and because, as the head approaches them in the inward variety only, and as for the production of that variety abduction is necessary, the muscles beneath them — the pectineus and ilio- psoas— are put upon the stretcli and the vessels are lifted out of harm's way. The relations of the sciatic nerve to these injuries are of great importance. The nerve is in close relation to the hamstring muscles, especially to the biceps. These structures are made tense Fk;. 396. and are stretched across the neck of the femur pos- teriorly by flexion of the thigh on the pelvis, espe- cially if the leg is also extended on the thigh, so that the origin and inser- tion of the hamstring mus- cles are separated. If, in a dislocation, the head of the femur originally lies on the anterior plane of the pelvis, and either by the force producing the dis- placement (as is commonly the case), by the action of muscles, or during efforts at reduction is made to pass to the posterior plane, it must traverse the narrow space between the sciatic nerve and hamstrings and the edge of the acetabu- lum. The nerve is thus \'ery apt to be bruised and stretched and separated somewhat from the biceps tendon. Later, if replace- ment by " circumduction" is attempted, the head mav pass beneath the nerve, which will then be tightly stretched over the front of the neck, will prevent full extension of the thigh, and will cause continued pain and disability. Other com- plications associated with the nerve may occur, and have been fully demonstrated by AUis, whose excellent experimental and clinical work forms the basis for the fore- going summary of the anatomy of hip luxations. In reduction of posterior dislocations by the method of circumduction the thigh, which is already flexed, adducted, and inverted by the agencies above described, is still inrther /^exed and adducted and lifted upward to relax the ilio-psoas and to bring the head of the bone near the margin of the acetabulum ; it is then abducted, tightening the inner band of the ligament, and everted, tightening the outer band and converting the femoral attachment of the whole ligament (but chiefly of its outer limb) into a fulcrum around which, as a centre, ^-the abduction andeversiofi being continued into circumduction, — the head of the bone sweeps, skirting the lower edge of the acetabulum, and finally, by extension of the thigh, re-entering PRACTICAL CONSIDERATIONS : THE HIP-JOINT. 379 that cavity at the point where it emerged. The whole movement is made up of the successive steps of flexion, adduction, abduction, eversion, and extension. In reduction of anterior dislocations some of the steps of the procedure are reversed, ^/.f., the movement consists of fle.xion, abduction, adduction, inversion, and e-xtension, in the order mentioned. The inner limb of the ligament is then of chief importance as a fulcrum. The objection to this method in both cases is the danger to the sciatic nerve, already pointed out, and also to the femoral vessels. Allis's methods of reduction are intended to avoid this danger. He endeavors to cause the head to retrace accurately the path by which it left the socket. In a posterior dislocation the head has usually left the Fig. 397. acetabulum in a down- ward direction, has fallen below the socket, and has passed outward around the edge of the acetabu- lum to its new position ; the limb has then fallen into partial extension by its own weight. Thus there are three steps, which, naming them in their reverse order, are : 3, extension ; 2, motion outward ; i, motion downward. The steps of his method are accord- ingly' : I, flexion ; 2, ro- tation of the head inward (by carrying the leg out), placing it where it was immediately after leaving the acetabulum ; 3, lifting — to bring the head to the le\-el of the socket — and extension (using the ilio-femoral ligament, which then be- comes tense, as a ful- crum, and aided by the upward pressure of the thumbs of an assistant), carrying the head up- ward into the socket. In the reduction of anterior dislocations the anatomical and mechani- cal principles involved are the same. In those dislocations the head has left the socket by tearing the capsule on its inner margin, and has passed inward to the pubo-ischiatic plane ; the Hmb representing the other end of an inflexible lever must move in the opposite direction, or outward ; and as it falls a little downward by its own weight, the head rises slightly. To restore it, reversing these steps, flex to a perpendicular, lowering the head somewhat ; make traction on the limb, drawing the head outward ; and then, the head being fixed by the hands of an assistant, adduct and extend the thigh, causing the head to enter the socket. By these methods reduction of dislocation complicated with fracture of the Luxation of the head of the femur into the obturator foramen. 38o HUMAN ANATOMY. femur becomes possible because of the firm connection between (a) the base of the neck and the acetabulum through the unruptured portion of the capsule, and (d). the two fragments through the attachment of muscles along the linea aspera. These connections enable the limb to be used for traction, although the fracture quite precludes the employment of circumduction and rotation. Allis summarizes the principles of his method by saying that the cardinal rule applicable to every form of dislocation of the hip is : draw the head in the direction of the socket ; apply a fulcrum at the upper part of the lever ; pry the head into the socket. The old view that the opening in the capsule was often a slit which required enlargement before the head could be replaced has been shown (Allis and Morris) to be fallacious. The inelastic character of the capsular fibres, the globular shape of the femoral head, and the suddenness of application of the force (preventing stretching) make the rent in every Fig. 398. case as large as the head ; it is not infrequently larger. If, however, it is situated near the femoral attachment of the capsule, it may leave a cuff of the latter hanging from its pelvic ori- gin over the acetabulum, and offering a serious, if not insuperable, obstacle to reduction. Congenital dislocation of the hip rnay be unilateral or bilateral, and while occasionally the result of intra- uterine traumatism, is usually due to an arrest of development of the ace- tabulum. The head rests on the dor- sum ilii, either directly upon the bone or on the gluteus minimus. The cap- sule is stretched and thickened to bear the weight of the trunk. The tro- chanters can be seen through the glutei ; they are above N^laton's line ; there is usually lumbar lordosis to compensate for the displacement pos- teriorly of the centre of gravity. The perineum is. widened. Disease of the hip-joint is fre- quent and grave. It may begin in the epiphysis for the head, in the synovial membrane, or, much more rarely, in the articular cartilage. It may be of any variety, but tuberculous disease outnumbers all others. Both the frequency and the gravity of disease of the hip-joint are due to : i, the e.xceptional exposure of the joint to strains or traumatism on account of its im- portance in carrying the weight of the trunk and in progression ; 2, the intra- capsular situation of the 'upper femoral epiphysis; 3, the relation of the joint to some of the most powerful muscles of the body, so that great intra-articular pressure is easily set up and with difficulty overcome ; 4, its enclosure by dense, unyielding fibrous structures that increase tension after disease has begun ; 5, the thinness of the non-articular plate of bone that separates it from the pelvis, and the presence up to puberty of the Y-shaped cartilage which divides the acetabulum into three bony segments (Fig. 353) ; 6, its deep situation, rendering the early symptoms in many cases inconspicuous ; 7, the deprivation of fresh air and exercise, and often of sunlight, involved in the immobilization of the joint. The disease is attended by certain symptoms having a definite anatomical basis : I. Swelling, which is most easily demonstrated (a) at the lower anterior portion of the joint just internal to the ilio-femoral ligament, where the capsule is thin and the PRACTICAL CONSIDERATIONS : THE HIP-JOINT. 381 joint is nearest the surface ; and (b) at the lower posterior part of the capsule, which is also thin. 2. Tenderness over these points, — i.e., beneath the middle of Pou- part's ligament and behind the trochanter. 3. Alteration in position, the femur being flexed, abducted, and everted. This puts the joint in the position of greatest comfort, which is that of its greatest capacity. In extension the head of the bone presses against the upper anterior portion of the capsule, and the Y-ligament is drawn as a dense band across the front of the joint. Flexion relaxes the superior or main portion of the Y-ligament and the ilio-psoas muscle ; abduction, the outer limb of the ligament and the ilio-tibial band of fascia lata ; eversion, the inner limb. Flexion is, in its effect on tension, the most effective of these motions ; eversion the least. The joint will now hold a larger quantity of fluid than when the limb is in extension. 4. At this stage, to bring the limb parallel with its fellow, to overcome the shortening caused by abduction, and to relieve strain, as the thigh cannot be moved on the pelvis, the lumbar spine is curved with the convexity towards the diseased side and the pelvis is tilted downward on that side. This is the stage of apparent lengthening. The real position of the limb in abduction is shown by straightening the pelvis so that a line drawn between the two anterior superior spines is at right angles to the longitudinal mid-line of the body. 5. With the same object of securing parallelism, — i.e., of reducing strain upon the mus- cular and fibrous structures which are holding the limb in its abnormal position, — the deformity caused by flexion (maintained by the ilio-psoas, which is in such close relation to the front of the capsule) is met by an arching forward — lordosis — of the lumbar spine. The real position of the limb in flexion is shown by raising the thigh of the affected side until the lumbar curve is effaced and the lumbar spines touch the surface on which the patient lies. 6. Pain in the knee is often marked. It is due to the association of the nerve-supply to the two joints, both being innervated from the same spinal segments, as they both receive twigs from the anterior crural, obturator, sciatic, and sacral plexus. 7. Rigidity of the joint is due to fixation by (a) the muscles inserted into and passing over the cap- sule ; (b) all the muscles moving the lower limb on the pelvis. Rotation is the most valuable movement for diagnostic purposes because it is least likely to be interfered with by extra-articular disease. For example, in abscess beneath the gluteus, or in enlargement of the subgluteal bursa, flexion of the thigh is interfered with ; in psoas or iliac abscess extension is limited ; in superficial disease of the upper end of the shaft, or in suppuration of the bursa over the trochanter, adhe- sions of the soft parts may limit both flexion and extension. 8. Muscular wasting is often a very early symptom, and is then due to reflex atrophy from the associa- tion— emphasized long ago by Hilton — of the nerves supplying a joint with those of the muscles moving that joint ; in this instance both joint and muscles are supplied by the anterior crural, the sciatic, the sasral plexus, the obturator, etc. Later, atrophy of muscles may be due to disuse. The glutei and the thigh muscles are those most obviously affected. The atrophy of the former aids in producing the characteristic obliteration of the gluteo-femoral crease. 9. After softening of the capsule and diminution of tension have occurred, the adductors draw the limb inward. The lumbar spine is now curved so that the concavity is towards the diseased side, thereby drawing up the pelvis on that side so as to relieve strain and secure parallelism of the limb. This is the stage of apparent shortening. The real position of the limb in adduction is shown by bringing the interspinous line to a right angle with the longitudinal axis of the body. The adductors are supplied almost exclusively by the obturator nerve, which enters largelv into the supply of the articulation, and act to great advantage when the capsular and ligamentous resistance has partly disappeared. As the shaft and lower end of the femur move inward, the head is necessarily brought more forcibly against the outer fibres of the capsule near its pelvic attachment, and when they soften is partially projected from the acetabulum, against the upper and outer rim of which it rests. 10. During this stage the trochanter on the diseased side is often found to be nearer the middle line of the body than the other trochanter. The cause of this is either absorption of the head and neck of the femur or deepening of the acetabulum with sinking in of the head, and the diagnosis between these may be made by rectal examina- 382 HUMAN ANATOMY. tion, which sometimes shows thickening over the inner surface of the acetabuhim in the latter case and not in the former (Cheyne). In dislocation from disease, unless there has been separation of the head or great absorption of the neck, the tro- chanter will be farther away from the middle line on the affected side than on the sound one. This will serve to distinguish shortening of the limb due to this cause from shortening due to acetabular deepening. Abscesses developing within the joint may pass outward through the thin posterior part of the capsule, and under the gluteal muscles, to a point beneath the greater trochanter ; they may make their ''e.xit through the cotyloid notch and point in Scarpa's triangle ; they frequently pass out anteriorly, and are found beneath the tensor vaginae femoris at the outer aspect of the thigh ; they may perforate the acetabulum and point within the pelvis. A finger in the rectum may then detect fluctuation through the structures that separate the abscess from the rectal wall, — viz. , the anal fascia, the levator ani, the obturator fascia and obturator internus, and the periosteum of the inner surface of the innominate bone. After perforation of the acetabulum, an abscess may extend upward and point above Poupart's ligament on the inner side of the vessels. Excision of the hip may be done either by means of an anterior incision passing between the tensor vaginae and sartorius muscles superficially and the glutei and rectus more deeply, or by a posterior incision in the line of the limb and just back of the greater trochanter, the muscles attached to which being divided as close to the bone as possible. THE FRAMEWORK OF THE LEG. This is formed by the tibia and the fibula and the intcroiseous membrane ( Fig. 411). The bones are so closely united as to constitute one apparatus, but as they are separable it is necessary to describe them apart. The tibia, very much the larger, is the only one concerned in forming the knee-joint, and bears almost the whole weight. It forms the upper and inner side of the mortise known as the ankle-joint. The fibula, placed e.xternally and posteriorly, is a slender bone. The upper end has a true joint with the tibia, the lower is more closely fastened to it. The interosseous membrane is at the bottom of a hollow between the bones. The arrangement favors lightness, as it gives increased size for the origin of muscles. The joints of the fibula, as well as its elasticity, serve to break shocks. THE TIBIA. The tibia consists of a shaft, an upper and a lower extremity. The upper extremity, or head, composed of an outer and an inticr tubcrositv, is very large, expanding laterally from the shaft. The outline of the upper surface is transversely oval, the inner end being«the broader. It is chiefly occupied by two articular surfaces for the condyles of the femur, separated at the middle by a promi- nence, the spine, '^ with a triangular non-articular surface before and behind it. The former of these is rough, the latter smooth and grooved. The spine itself is com- posed of two lateral parts connected behind, of which the inner is the longer from before backward, rising from the condylar surfaces. The crucial ligaments of the knee-joint are attached to the non-articular surfaces before and behind it. The i}i7ier condylar facet is concave ; it has an oval outline and is longer from before backward than transversely. It rises as a ridge on the side of the spine. The outer facet is more nearly circular, being shorter than the inner. It is slightly depressed in the middle. The posterior half is usually a little convex from before backward, and is often prolonged onto the posterior surface of the bone. The convexity is much greater when the semilunar cartilage is intact. The front half may be plane, convex, or concave in the same direction. This facet rises to a point on the outer side of the spine. The tuberosities ' overhang the back of the tibia. They are separated behind by the popliteal notch^ continuous with the groove from the top. Under the back of the outer tuberosity is a small articular facet for the head of the fibula, looking downward and a little backward and outward. Its outline is uncer- tain, being either round or quadrilateral. It may be curved in any direction, and ' Emiacatia iutercondyloidea. " Condj'lus lateralis ct medialis. ^ Fossa intercondyloidea posterior. THE TIBIA. ^83 its inclination varies much. In some cases it nearly or quite reaches the superior articular surface. Laterally, this tuberosity is rough for the ligaments of the knee- joint. The same may be said of the side of the inner tuberosity, which towards the back has a broad horizontal groove running along it for the tendon of the semi- membranosus. The hibercle^ of the tibia is a triangular prominence on the front of the upper end. Its lower part is rough for the tendon of the extensor quadriceps, and its upper smooth for a bursa between this tendon and the bone. The top of the tubercle is about an inch below the top of the bone ; it is lost below in the ridge of the front of the shaft. The shaft * has three borders and three surfaces. The anterior border, the crest'' begins at the outer side of the tubercle, curves as it descends, at first a little inward, then a little the other way through the middle of the shaft, where it is very sharp, and, finally, at the lower third, becoming much less prominent, it sweeps to the front of the in7ier ??ialleolus. The inner border, the least marked of the three, begins under the inner tuberosity near the back and goes to the back of the inner malleolus. It is most distinct in the middle. The outer border, or i7iterosseous ridge,* begins below the facet for the head of the fibula, runs downward and somewhat backward past the middle of the shaft, and then, inclining forward, divides some two or three inches above the lower end into two lines enclosing a space on the outer side of the lower end, to which the fibula is bound by ligaments. The anterior of these divisions is the more evident continuation of the ridge. The internal surface is subcutaneous : generally convex above and concave below ; the outer, bounded behind by the in- terosseous ridge, is at first external, but in the lower third twists to the front. The posterior, in its upper and lower parts, faces also somewhat outward. It is crossed in the upper third by the oblique line,^ which, running downward and inward from the back of the fibular facet to the inner border, marks off a triangular space above it which is occupied by the popliteus muscle. A vertical line, generally very faint, running down for some distance from the oblique line partially divides this sur- face into an inner broader and an outer narrower part : the former for the flexor of the toes, the latter for the tibialis posticus. The mdrient foramen, the largest in the body, is on this surface at the junction of the first and second thirds external to the oblique line ; it runs down into the bone. The shaft is triangular on section in the upper and middle thirds, being narrower and sharper in front in the middle one. In the lower third the section becomes quadrilateral as the shaft broadens and the anterior border sinks and turns inward. The lower extremity is thickest transversely. The internal malleolus'' is a thick projection downward and inward from the whole of the inner side, to form one boundary of the ankle. Its lower end is thick, reaching farthest down in front, with a depression at the back for the lateral ligament of the ankle. The surface looking towards the joint is articular ; it slants a little away from the median line of the bone. The outer side of the lower end of the shaft is slightly concave, with a tubercle both before and behind. The articular cartilage of the lower end is pro- longed some two or three millimetres onto this outer side. Both in front and behind, but especially in front, the bone presents a swelling, separated by a depression from the lower border, above which the capsule is inserted. On the posterior surface a broad groove for the tendons of the tibialis posticus and the flexor longus digitorum runs obliquely downward and inward onto and along the hind border of the mal- leolus. A faint groove for the flexor* longus hallucis is sometimes seen near the outer end of the posterior surface. The lower side forms the top of the ankle- joint and is wholly articular. It is broader before than behind, as the sides converge towards the back. It is concave from before backward. There is a slight antero- posterior elevation in the middle, fitting into a depression on the top of the as- tragalus. Variations. — The transverse axes of the knee- and ankle-joints are rarely parallel. The shaft of the tibia is so twisted as to make the foot point outward. The angle between the two axes varies from o to 48°, but is usually between 5° and 20°. The backward inclination of the top of the tibia varies considerably. When excessive; it seems to imply an aptitude for the squatting position, as among the natives of India, but no inability to assume the upright position. A continuation ^ Tuberositas tibiae. - Corpus tibiae. ^ Crista anterior. ^ Crista tnterossea. ^ Linea poplitea. "^ Malleolus medialis. 384 HUMAN ANATOMY. Fig. 399. Spine Ext. condylar surface y-^-. I"'- condylar surface For ligamentum , patella \ "i y PatelicB extensor quadriceps) GtaciHs Sar tortus Semit endinosus For ast^agalui^^j((r Internal malleolus Right tibia from before. The outline figure shows the areas of muscular attachment THE TIBIA. 385 Fig. 400. Int. condylar surface Internal tuberosity y Groove for semimemdranosits- Popliteal notch Ext. condylar surface External tuberosity Sentimembranostis- Soleus (tibial head)- Flex. lo7ig. digitorum— I (tibial head) I — Tibialis poshcu > Oblique line Nutrient foramen -Poster or surface \ 'I w\ , "' Groove for tibial, post, andjlex. long-, digit. _ Internal malleolu ^Posterior division of interosseous border -Tibio- fibular ligament ^Groove for^?^^. long, hall ' astragalus Right tibia from behind. The outline figure shows the areas of muscular attachment. 386 HUMAN ANATOMY. of the lower articular cartilage onto the front of the tibia, allowing extreme dorsal flexion of the ankle, is often associated with this. The thickness of the tibia is Fig. 401. Spine Ext. fibro-cartilage ^ Post, crucial ligament Ext. condylar surfac Ext. fibro-cartila^i Anterior crucial ligame _Jj_Int. condylar surface t Int. fibro-cartilage 1 ursal surface \ttachment of tendon patellae Upper end of right tibia from abo\'e and before. very \ariable. The very thin, platycnemic, form is most common in savage races, and is therefore associated with the pilastered femur. It is found not rarely among Fig. 4u2. Fig. 403. Frontal section of upper if tibia. whites, but the shape of the accompanying femur is uncertain. The tibial index i "^"^""'^^ lameterxioo j j^ ^-^^ ratio of the transverse to the antero-posterior diameter. ^ antero-Dosterior diameter / r PRACTICAL CONSIDERATIONS : THE TIBIA. 387 According to French statistics, this in whites is from 70 to 80 ; in savage races it is much lower. The method of reckoning it at the level of the nutrient foramen is likely to be superseded by one choosing the middle of the bone. Structure. — The shaft has strong walls in the middle, being especially thick under the crest. At both ends the walls become thin. The head contains a large amount of cancellated tissue with comparatively thin walls. The architectural arrange- ment of the trabeculae at the ends is very clear. A frontal section of the upper end shows successive vertical plates springing from the sides to support the expanding tuberosities, with an irregular system in the middle. Sagittal sections show plates from the walls meeting each other in arches. A somewhat similar pattern is seen at the lower end. In a frontal section there are several transverse plates, of which the strongest marks the border of the epiphysis. Several of these from the outer side turn down to join the lower surface at the origin of the malleolus, where there is a distinct thickening of the crust. There is sometimes an imperfect bony canal for the nutrient artery for a short distance after its entrance into the cancellated tissue. Development. — There are only three centres of ossification : one for the shaft, appearing in the seventh or eighth fcetal week ; one for the upper end, appear- ing usually in the last month of fcetal life ; and one in the lower, appearing in the second half-year.' These epiphyses correspond to what has been described as the Fig. 404. Ossification of tibia and fibula. A , at eighth fcetal month ; B, at birth ; C, at two and one-half years ; £>,at four years ; £, at about fifteen years, a, centre for shafts ; d, for upper epiphysis of tibia ; c, for lower epiphysis of fibula ; d, for lower epiphysis of tibia ; e, for upper epiphysis of fibula ; y, for tubercle of tibia. ends of the bone. The upper extends farthest down on the front, including the tubercle, which may have a separate nucleus. According to Rambaud and Renault, this is of usual occurrence, appearing at from eight to fourteen years and quickly joining the epiphysis. The lower end joins the shaft at about eighteen and the upper at nineteen or twenty. PRACTICAL CONSIDERATIONS. The upper epiphysis of the tibia is separated only by traumatism of marked severity because of : (i) its great width; (2) its irregularly cupped surface; (3) the downward projection in which the tibial tubercle is developed, or to which the latter becomes united when it arises from a separate centre ; (4) the protection afforded it (a) on the outer side by the head of the fibula (which is connected exclusively with this epiphysis), the anterior and posterior upper tibio-fibular liga- ments, and indirectly lay the external lateral ligament ; (6) on the inner side by the internal lateral ligament, and (c) on both sides by the fibres of insertion of the ' Fagerlund : loc. cit. HUMAN ANATOMY. vasti and semimembranosus and of their fascial expansions ; (5) the toughness of the periosteum uniting it with the diaphysis ; and (6) the fact that while there is no possibility of its displacement by muscular action, it does not project enough to be exposed to the effects of direct violence. The possibility of disjunction of this epiphysis complicating an injury to the knee continues up to the twentieth year at least ; in injuries to the elbow epiphyseal separation may be excluded after the eighteenth year. Three-fourths of the recorded cases have occurred in males, as might be expected on account of their more frequent exposure to serious injury. The epiphysis has been displaced forward, and outward and forward. It has never been displaced backward, partly, at least, on account of the tongue-like process con- necting it with the tibial tubercle. Its inward displacement would necessitate the separation of the head of the libula or the laceration of the Fig. 405. superior tibio-fibular ligaments. The attachment of the syno- \ial membrane of the knee-joint does not descend to the level I if this epiphysis ; hence that articulation is often not involved in these injuries. They should not, when severe, be mistaken for dislocation, or, when slight, for sprains of the knee. They may be distinguished from the former by the age of the patient and the unimpaired mobility of the knee, and from the latter by the situation of the pain or tenderness. Dislocation of the knee is \ery rare in children. Good union has taken place in some cases ; arrest of growth has followed in others, as might be expected from the fact that the chief increase in length of the tibia takes place from this epiphysis. The tubercle of the tibia has been detached in some recorded instances, mostly males : nine from violent action of the quadriceps in powerful young men, eight of whom were between si.xteen and eighteen years of age, the age of the remaining male not having been mentioned (Poland). This separation should be carefully distinguished from frac- ture of the patella. In disjunction the latter bone is drawn upward, the patient is unable to extend the leg, and the swell- ing following laceration of the subligamentous bursa may simu- late swelling of the knee-joint. The latter may be involved directly — as the synovial membrane is in close proximity to the tubercle — or indirectly, through the occasional, though rare, communication with the subligamentous bursa. Fracture of the patella, however, does not occur in children and is very rare in adolescence. In patella fracture the fragments of bone are brought together, so that crepitus may be felt only by pushing the two fragments towards each other; the groove between them can almost always be recognized. In disjunction of the tubercle crepitus can be elicited only by pulling the fragment downward ; the outline of the patella is normal, and can usually be made out. The X-rays would be conclusi\'e. Bony union should be expected. The shaft of the tibia gradually decreases in size to about the junction of the middle and lower thirds, and then expands again to the ankle. At its smallest point — on an average about ten centimetres (four inches") above its lower end — it has to bear a greater weight on a smaller area than any other bone (Humphry). At this level meet the two independent vertical columns into which, according to Fayel and Duret, the spongy tissue of the tibia is divided (one occupying the upper two-thirds, the other the lower third of the bone), and hence these authorities assert that this spot represents the minimum of resistance (Treves). In some tibiae it is at or near the junction of an ill-defined long upper curve, in which the crest terminates, and a short lower curve. On transverse section the tibia is seen to be cylindrical in its lower third and three-sided above. As it has been demon- strated that if two homogeneous solids present on section equal areas, the one Epiphyseal lines of tibia. PRACTICAL CONSIDERATIONS : THE TIBIA. 389 triangular and the other circular, the former has the greater power of resistance (Tillaux), the shape of the tibia in this region is thought to be an additional source of weakness. For all these reasons it is the most frequent seat of fracture from indirect vio- lence. As in such cases the breaking strain is usually continued for a moment after the tibia gives way, the weak fibula is apt to be broken also. The line of fracture usually runs from its level on the crest upward and backward, and under the action of the calf muscles and the weight of the body the sharp lower end of the upper fragment frequently protrudes, making the fracture compound. Fracture at about the same level from direct violenci is also very common on account of the exposed position of the bone, and all fractures are apt to be com- pound as a result of the large proportionate area of the bone which is subcutaneous. Fracture of the shaft at the upper end involving the knee-joint is rare, and is usually from either direct violence or a fall from a considerable height, — "com- pression fracture." Fracture of the lower end of the shaft invoh'ing the ankle-joint is a not infrequent complication of Pott's fracture. Fig. 406. Separation of the lower epiphysis is near-ly three times as fre- quent as that of the upper. It is caused usually by a considerable degree of violence, and in fifty per cent, of recorded cases has been associated with fracture of the lower end of the fibula or separation of the fibular epiphysis, in which case the displacement is often outward ; usually it is backward. It may be mistaken for dislocation of the ankle. In patients from eleven to seventeen years of age disjunction of the epiph- ysis is more frequent than dislocation ; as the malleolus and the foot go backward. with the epiphysis, the inner malleolus preserves its normal relation to the foot, but not to the leg or outer ankle. In dislocation the reverse is the case. The ankle-joint usually escapes, as both anteriorly and pos- teriorly the synovial membrane is below the epiphyseal line. The synovial pouch of the lower tibio-fibular joint that extends upward between these two bones is in close relation to that line, but is sepa- rated by the periosteum which is continuous over the epiphysis, and thus also escapes injury. Arrest of growth is not common, but has occurred, and severe ankle sprains in the young should be treated with especial care on ,, ,1 account of the possibility of involvement of the epiphyseal joint and // L later disease or deformity. Disease of the tibia, if infectious, is most common in the neigh- borhood of its two epiphyses and at the junction of the middle and lower thirds. The region is a favorable one for " juxta-epiphyseal sprain," in which the violence is expended on the spongy tissue of the diaphysis near the epiphyseal line. " Many of the pains called 'growing pains' are due to juxta-epiphyseal sprain or injury. Such a sprain is often nothing Isut the first degree of an epiphyseal separation, in the same way that an articular sprain is nothing but the first degree of dislocation" (Poland). The usual causes — strain, traumatism, cold, etc.— influence the localization of tuberculous disease in or near the epiphyses. If recognized early, and if the infected focus is removed by operation, the knee- and ankle-joints will usually escape. In the later stages the products of liquefaction may find their way from the upper epiphyseal line to the knee-joint, either directly through the intervening half-inch of bone or by way of the tibio-fibular joint, — which is in close relation to the epiphysis (Fig. 425), — and then to the subpopliteus bursa, which always communicates with the knee-joint and often with both ; or they may gain the surface of the tibia and extend upward beneath the periosteum. If the lower epiphysis is involved a similar direct or indirect infection of the ankle-joint may occur, the tibio-fibular synovial pouch being sometimes first involved. 390 HUMAN ANATOMY. Post-typhoidal periostitis and osteitis of the tibia are exceedingly common, and affect particularly the subcutaneous area of the bone near the lower third, where there are no muscular attachments. They are probably due, therefore, to slight traumatisms. This same area is peculiarly subject not only to this form of infection and, as has been said, to fracture, but also to tuberculosis (when the epiphyses are spared), to syphilitic nodes and gummata, to softening and deformity from rickets, and to sepsis spreading inward from cutaneous inflammations and ulcers. It is probably so vulnerable by reason of its exposure to frequent slight injury and to strain disproportionate to its size and strength {vide supra), and because of its dependent position and it§ distance from the main source of the blood-supply of the bone (the nutrient artery entering it at its upper third), both of which circumstances favor passive hyperEemia and the localization of infection. Sarcoma, in accordance with the general rule already mentioned (page 366), affects chiefly the upper third of the tibia. Landrnarks.— On the inner side of the knee the internal tuberosity of the tibia is in close relation in extension with the internal condyle of the femur, the two making a uniform rounded prominence. The interval between them can be felt but not seen. If the leg is flexed and the ankle rested upon the opposite knee, the tibial tuberosity becomes visible and lies in advance of the inner condyle. The prominence of the outer tuberosity is distinctly to be seen and felt on the antero- external aspect of the limb about 2.5 centimetres (one inch) below the joint-line. It represents the lowest level of the synovial membrane. Into it is inserted, about half-way between the tip of the patella and the head of the fibula, the important ilio-tibial band of fascia to which illusion has been made in reference to fracture of the neck of the femur and dislocation of the hip (page 377). The posterior edge of the head of the tibia is not accessible to direct examina- tion, and this is true of the external and posterior surfaces throughout. The internal border can be traced from the tuberosity to the malleolus. The antero-internal surface, which is subcutaneous throughout, can be seen and felt. The anterior border or crest constitutes the prominence of the "shin." It is sharp in the upper two-thirds and fades into the shaft at the summit of the lower third. In well-marked tibiie it presents a distinct double curve, the upper part of which has its concavity outward. The tubercle is easily felt and seen. It should be in line with the ligamentum patellse and a point on the front of the ankle mid- way between the malleoli. It is about on a level with the head of the fibula. The inner malleolus is twelve millimetres (half an inch) above and in front of the outer malleolus, but on the same plane posteriorly. Its lower border is rounded. The notch for the internal lateral ligament can be felt. Its tip is twelve millimetres below the joint-line. Its sharp posterior border forms the inner boundary of the groove for the tibialis posticus tendon. THE FIBULA. The fibula is a long, slender bone with a knob-like upper end and a pointed lower one. The upper extremity, called the head,^ has a rounded or vaguely quadri- lateral articular surface above, looking upward, a little inward and forward, to meet the corresponding one on the tibia. The styloid process,' a short prominence, juts upward from its outer posterior angle. The outer part of the head is rough. An ill-marked neck below it is indistinguishable from the shaft. The shaft ' is best described as having four borders, separating four sides, though one of the borders joins another near the lower end. The borders, proceeding in regular order round the bone from the front, are ( i ) the antero-external, ( 2 ) the postero-e.xternal, (3 ) the postero-internal, sometimes called the oblique ridge, and (4) the antero-internal or interosseous. The antero-external border begins faintly on the front of the shaft, a little below the neck, and becomes very prominent as it descends, twisting slightly outward. In the last quarter it splits into two lines which run to the front and back of the outer malleolus, enclosing a triangular subcutaneous space. The postero-external border begins on the outer side of the neck below the styloid ' Capitnlam fibalae. -Apex capituli fibulae. ^Corpus fibulae. THE FIBULA. 391 Fig. 407. Stylcid process Fig. 40S. styloid process Right fibula from before. Right fibula from behind. The outline figures show the areas of muscular attachment. 392 HUMAN ANATOMY. Anterior surface Antero-internal border 1 Antero-external border — , Internal surface; -Posterior surface Tibialis' posticus -Postero-extemal border -Postero-iiiternal borde Inferior interosseous ligament tw^|i0s cubrideum. THE ASTRAGALUS. 423 part of which is coated with cartilage. The external surface of the bone is deeply notched. The internal surface is mosdy rough, but presents at about the middle an articular facet for the external cuneiform, broad above, narrow below, and not usu- ally reaching the plantar surface. Commonly another smaller facet for the scaphoid is found behind this one, from which it is separated sometimes completely, but more often merely by a ridge, which makes no real interruption. The anterior surface, articular for the bases of two metatarsals, has an inner, an upper, and a lower border, the two latter meeting at a rounded angle externally. A faint vertical ridge, nearer the inner than the outer border, usually divides this facet into an inner oblong and an outer triangular part for the fourth and filth bones. The curves of these articu- lations vary greatly : sometimes both parts are concave from above downward ; sometimes both are practically plane. The posterior surface, entirely articular, is the complement of the front of the os calcis. The cuboid articulates with the calcaneum, the external cuneiform, the fourth and fifth metatarsal bones, often with the scaphoid, and at times with the astragalus. Development. — There is but one centre, appearing at about birth ; in our experience, more often after than before. For Secondary Cuboid, see Scaphoid. ASTRAGALUS. I'ery irregular bone devoted almost THE The astragalus, ' or talus, is a very irregular bone devoted almost wholly to articular surfaces. It is enclosed above by the socket of the leg bones. Its main part, or body, rests on the calcaneum, and presents in front a constricted neck bearing a rounded head, projecting forward and inward into the hollow on the back of the scaphoid. The upper surface presents a pulley-like articular facet covering the greater part of the bone, convex from before backward, slightly concave transversely, decidedly broader in front than behind. The cartilage covering it is continued down on either side to meet the articular surfaces of the malleoli. The inner border Fig. 436. Interos- groove Internal tubercl External tubercl Groove for tendon of flex. long. hall. Right astragalus from above. e for flex, long hall. External tubercle Right astragalus from below. of the upper articular surface is distinct, but generally not sharp ; the outer, which reaches higher, is better defined in the region just anterior to its middle, but behind on the dry bone it seems rounded. A very well-marked bone shows (what is very striking in the freshly opened joint) that this blunted edge is really a narrow tri- angular area belonging to the superior surface, broadest behind, made apparently by the pressure of the posterior tibio-fibular ligament from the external malleolus to 424 HUMAN ANATOMY. the back of the tibia. A much smaller similar surface is found at the front, made by the corresponding anterior ligament. The direction of the anterior border of the articular surface is \ery uncertain. It usually projects forward at the outer end, the rest being either transverse, posteriorly concave, or oblique. Just anterior to it is a deep trans\'erse hollow on the upper surface of the neck, which receives the edge of the tibia in extreme dorsal flexion of the foot. The posterior border of the articular surface is also of uncertain shape. Its inner end is usually somewhat farther back than the outer. Behind it two rough tubercles project backward, slanting down to Fig. 437. Type of calcaneo-astragaloid joint with a posterior sharp edge. Between them is a deep groove for the tendon of the flexor longus hallucis, running obliquelv downward and inward. The outer tubercle, which is much the larger, is sometimes separated by a suture from the rest of the bone, and is then known as the os trigo7mm. The inner tubercle may be barely distinguishable. This region behind the superior articular facet is sometimes de- scribed as the posterior surface of the bone. The external surface of the body shows the triangular facet for the outer malleolus, concave from above downward, Fig. 438. Synovial not cartilag Caica T>'pe of calcaneo-astragaloid jo For internal calcaneo phoid ligament For suslenlaculu Astragalus J not only divided but has front porti( with the lower end projecting outward, plane or convex from before backward. This is bounded before and behind by a rough strip, with a hollow at the upper ends for the front and back bundles of the external ligament of the ankle. The internal surface has at the top a narrow cuned facet for the inner malleolus, with a concave lower border, deepest in front and pointed behind. A part of the internal lateral ligament is inserted into a hollow below it. The inferior surface of the body presents a four-sided facet, concave in the line of its long axis, which is oblique, corresponding to that of the greater surface on the top of the calcaneum. In front of and parallel to this is a deep groove for the interosseous ligament, expanding at the outer end into a triangular hollow on the under side of the neck. This is a THE SCAPHOID. 425 constricted portion, much broader transversely than vertically, connecting the head with the body. It often presents a groove along the upper and inner aspect near the articular surface of the head for the insertion of the ligament passing to the scaphoid. The head, which points forward and inward, is articular in front and below. The anterior surface, which fits into the hollow on the back of the scaph- oid, is vaguely oval, with its long axis running downward and inward. The upper edge, parallel with this, is nearly straight. The articular surface of the head ex- tends onto the under side, reaching to the deep groove separating the neck from the posterior facet for the calcaneum. On a fresh bone the cartilage shows the following facets, which are less well marked on a macerated one : a facet on the front of the head to fit into the scaphoid ; one on the lower and inner side to rest on the anterior articular facet of the top of the calcaneum ; one partly between these, which in the dried bones would be free, appearing between the sustentaculum and the scaphoid, but in life resting on the inferior calcaneo-scaphoid ligament, which is partly covered with cartilage and elsewhere with synovial membrane, forming a part of the socket. The cartilage on this surface is distinguished by its thinness. These facets are modified according to the arrangement of those on the calcaneum. If there be but one long anterior facet on both sustentaculum and on the end of the body of the calcaneum, the facet on the head for the anterior facet of the calcaneum reaches that for the concavity of the scaphoid in front, leaving internally a triangular interval between the two, occupied by the facet for the liga- ment (Fig. 437). In the other extreme (Fig. 438), where the anterior facet on the calcaneum does not reach beyond the sustentaculum, the area of the head rest- ing against the ligament completely separates the two others and plays on that part of the calcaneum where the anterior articular cartilage should be. Finally, when the anterior facet on the calcaneum is divided into two, the corresponding facet may be completely subdivided by an interruption of the cartilage, or in less marked forms there may be merely a ridge breaking the surface into two, but without sepa- ration ; such a ridge is often found even when the opposed articular surface is not divided. The lines, however, on the head of the astragalus do not strictly correspond to the boundaries of these surfaces. The astragalus articulates with four bones, — the tibia, fibula, calcaneum, and scaphoid. Development. — The nucleus probably appears at about the seventh month of fcetal life. When the os trigonum occurs, that implies another centre for the ex- ternal tubercle and the part of the articular surface under it. The deviation of the axis of the neck from that of the long axis of the bone varies considerably among individuals, but, nevertheless, changes during develop- ment. In the adult the angle varies from o to 24°, the mean of forty-three bones being 12.32°. In the foetus (presumably at term) the angle ranges from 17.5° to 45.5°, the mean of twenty-two bones being 35.76°.' THE SCAPHOID. The scaphoid,' or Clavicular, may be compared to a disk, concave behind where it fits onto the head of the astragalus, convex in front where it rests on the three cuneiform bones. It is thinner at the outer end, where it touches the cuboid, than at the inner, where it presents the tuberosity. The superior, or dorsal, surface is long transversely. Its posterior border is regularly concave, the anterior slightly scalloped, presenting two small points projecting forward on either side of the mid- dle cuneiform. When in position the highest point on the scaphoid is behind that bone. The greater part of the dorsal surface slants downward on the inner side of the foot. The inferior, or plantar, surface is rough, and in the main transversely concave. The iuberosity at the inner border for the attachment of a part of the tibi- alis posticus muscle is a knob formed by the junction of the dorsal and plantar sur- faces, and projecting downward chiefly into the sole of the foot. The end of the knob is sometimes distinct from the scaphoid, and is known as the tibiale externum. ' C. L. Scudder : Congenital Talipes Equino-Varus, Boston Med. and Surg. Journ., vol. ii., 1887. Parker and Shattock : The Pathology and Etiology of Congenital Club-Foot, London, 426 HUMAN ANATOMY. Its identity is quite evident in cases in which, though fused, it projects as a hook. It may be represented by the sesamoid bone in the tendon of the tibialis posticus. Near the outer end of the plantar surface there is almost always a slight projection by the side of the cuboid which may be very much developed, extending to near the notch in front of the sustentaculum of the calcaneum, in which case it is known as the secondary cuboid. The external surface is narrow and rough, resting against the cuboid, with which it articulates in about half the cases lay a facet near the dor- sum, which rarely extends far towards the sole.' The posterior surface is con- cave, in the main o\'al and completely articular. Usually the regularity of the lower border is interrupted near the outer part by the external knob of the plantar surface. If this be much developed the shape of the posterior surface is changed from oval into quadrilateral, but it is always articular throughout. The anterior surface is slightly convex and entirely articular, e.xcept when the process just men- tioned is so large as to appear below it. The articular surface is divided into three Fig. 439. Dorsal surface Fig. 440. Dorsal surface Right scaphoid fn For head of astragalus 1 behind, proximal aspect. form d from in front. facets, in the main triangular, corresponding to the outline of the bases of the three cuneiform bones. The character of these facets is not constant : the inner is usually conve.x and the outer concave. The scaphoid articulates with the astragalus, the three cuneiform bones, often with the cuboid, and exceptionally it touches or joins the calcaneum. The secotidary cuboid, above alluded to, has but once been seen isolated, although we have met with one foot in which it seemed possible that it might have been distinct earlier. It is fused with either the cuboid or the scaphoid, but apparently much more frequentlv with the latter, in which it occupies the position above described, lying at the weak part of the inferior calcaneo-scaphoid ligament. Development. — It is generally held that ossification begins in the fourth or fifth year, but, according to Gegenbaur, it begins in the first. The tibiale externum exists as a separate cartilage at the second month of foetal life. Usually this fuses with the rest, but it may have a centre of its own. THE THREE CUNEIFORM BONES. These wedge-shaped bones, placed between the scaphoid and the three inner metatarsals, and abutting externally on the cuboid, form an important part of the transverse arch of the foot. The thin edge of the internal cuneiform, which is much the largest, points up, that of the others down. The middle cuneiform is the smallest and shortest, so that the second metatarsal bone lies in a mortise between the inner and outer. THE INTERNAL CUNEIFORM. The internal cuneiform,^ besides the proximal and distal surfaces, has an internal, an external, and an inferior. The posterior, or proximal surface, rounded below and pointed above, is slightly concave and wholly articular. The anterior, or distal, surface, also articular, is kidney-shaped, with the notch in the outer border. The inner surface has a small ridge in its distal half, pointing upward, which is the 'Pfitzner: Morph. Arbeiten, Bd. vi., 1896. THE CUNEIFORM BONES. 427 highest part of the bone, but almost the whole of this surface is on the inner side of the foot. Its outer border runs obliquely forward and outward with a sinuous course till it reaches the end of the middle cuneiform, when it turns forward. It has a short concave posterior border for the scaphoid and a long, nearly straight one for the first metatarsal bone. It passes without a sharp boundary into the lower surface. It is crossed by a faint groove, which exceptionally is deep, running obliquely downward and forward to a smooth swelling for a bursa under the tendon Fig. 441. Fig. 442. Mid. cuneiform Scaphoid. Right internal ( liform, outer aspect of the tibialis anticus just before its insertion. The inferior surface, rough and round, has a tubercle near the pro.ximal end for a part of the tibialis posticus. The external surface is mostly rough, with a smooth articular strip for the middle cuneiform following its upper and posterior border. The internal cuneiform articu- lates with the scaphoid, middle cuneiform, and first and second metatarsal bones. Development. — A centre appears in the third year. Very e.xceptionally it is double, and the bone is divided by a suture into two, — a dorsal and a plantar. THE MIDDLE CUNEIFORM. The middle cuneiform ' has a sharp ridge below and an oblong surface above. The latter, or superior surface, is very little longer than broad. The lateral borders of this surface have an outward inclination. The inner of them corresponds to the proximal part of the outer border of the first cuneiform. The outer border, for its proximal two-thirds, rests against the external cuneiform, beyond which there is a small space between the bones. The proximal side of this surface is a little convex and the distal about straight. The posterior surface, wholly articular, Fig. 443. r aspect ; B, outer aspect. is slightly concave. It is triangular, with the dorsal border rounded, the outer concave, and the inner straight or slighdy convex. The anterior surface, ar- ticular for the second metatarsal, is narrower. It has a slight convexity in the upper part in a vertical plane. The internal surface has an articular facet corresponding to that on the internal cuneiform and a rough depression for an interosseous liga- ment. The external surface has a facet along the hind border, broader above than below, and rarely a small one at the front lower angle, both for the external ^ Os cuneiforme secundum. 428 HUMAN ANATOMY. cuneiform. The middle cuneiform articulates with the scaphoid, the internal and external cuneiforms, and the second metatarsal. Development. — One centre appears in the fourth year. THE EXTERNAL CUNEIFORM. The e.xternal cuneiform,' seen from above, is much longer than broad, with a very oblique pro.ximal border slanting outward and backward, an anterior border running less obliquely in the same direction, an inner one close against the middle bone in its proximal third or one-half, then receding from it and extending onto the outer side of the second metatarsal, and an outer border first running forward and outward against the cuboid, and then forward not quite against it, but o\erlapping the fourth metatarsal. The ridge constituting the inferior surface does not quite reach the proximal end. The posterior surface, wholly articular, is oblong, with the long axis vertical, and often a little convex. The anterior surface, articular for the third metatarsal, is triangular and about plane. Its inner border rises higher than the outer. The internal surface articulates with the second cuneiform bone by Fig. 444. one or two corresponding facets, as the case may be, and has, in addition, a facet for the outer side of the base of the second metatarsal at the front upper angle, and often extending down the border ; or the middle portion may be wanting. In the middle of the surface is a roughness for the interosseous ligament. The external surface is chiefly rough, giving origin to an interosseous ligament for the cuboid ; at the upper proximal angle is a large facet for the same bone, and at the distal upper angle there may or may not be a small one for the side of the fourth meta- tarsal. The external cuneiform articulates with the scaphoid, the middle cuneiform, the cuboid, and the second, third, and fourth metatarsals. Development. — Ossification begins in the first year. The Intercuneiform Bone. — On the dorsum there is a little pit which we have called the intercuneiform fossa, situated between the proximal portions of the internal and middle cuneiform bones, usually more at the expense of the latter than of the former. We have at least twice seen a separate ossicle, the intercuneiform bone' in this fossa. The better specimen was wedge-shaped, its length exceeding one centimetre. It clearly was more intimately related to the middle than to the internal cuneiform. Pfitzner has since seen it fused with the former. THE METATARSAL BONES. Of these five bones' the first is very much the largest, although the shortest. The second is the longest, and the others of about equal length. The first metatarsal bone has a concave base corresponding to the facet on the internal cuneiform, which is prolonged down into a point (tuberosity) rather to the outer side, on the external aspect of which the peroneus longus is inserted into a round impression. On the inner side of the base is a small prominettce for the tibialis anticus. A smooth facet for the second metatarsal is often found on the outer side. A groove for the capsular ligament more or less perfectly encircles the 'Anat. Anzeiger, Bd. x.\., 1902. ^ Os cuneiforme tercium. ^Ossa metatarsalia 1-V. THE METATARSAL BONES. 429 base. The strong shaft has three sides : an iyiteryial^ looking also upward, in the main convex ; an external, concave and nearly vertical ; and an inferior, or p2a7ita?\ Phalangeal surface Internal surface Inferior surface Impression of peroneus longus Tuberosity Internal cuneiform Right first metatarsal. A, proximal aspect; B, plantar aspect; C, dorsal aspect. also concave. The borders bounding the outer surface are the most distinct. One or two nutrient foramina enter this surface, running distally. The enlarged and Fig. 446. Lateral ligament Ext. cuneiform Third metatarsal Third metatarsal Ext. cuneiform External cuneiform Right second metatarsal. A, proximal aspect ; By outer aspect ; C. i rounded distal end, the head, is articular except at the sides, where it is flattened. The facet extends farther onto the plantar aspect, where it expands laterally. It 430 HUMAN ANATOMY. has there a median elevation, with a groove on either side for a sesamoid bone. There is a rough surface for ligaments on each side of the head. Fig. 447. Middle cuneiform. Fourth metatarsal Right third metatarsal. .-I, pr Second melata External cunt al aspect ; B, outer aspect ; C, inner aspect The four outer metatarsal bones are distinguished by their bases. That of the second is concave at the end, and fits the middle cuneiform ; on the inner side a small facet at the top meets the outside of the first cuneiform ; on the older side there are two, an upper and a lower, with a deep cut between each, resting Fig. 448. Third metatarsal External cuneiform Fifth metatarsal Cuboid Right fourth metatarsal. A. proximal aspect ; B, outer aspect ; C. inner aspect. on both the outer cuneiform and the third metatarsal. The occasional facet for the first metatarsal is on the shaft rather than on the end. It is often wanting on the THE METATARSAL BONES. 431 second when present on the first, implying the presence of a bursa rather than of a joint. The base of the third metatarsal fits the outer cuneiform, and is nearly plane. The posterior upper border, seen from the dorsum, is oblique, running Fig. 449. Fourth metatarsal Right fifth metatarsal. A, distal aspect ; B, dorsal aspect ; C, plantar aspect. outward and backward. The inner surface has two facets for the second, and the outer surface one at the top for the fourth metatarsal. The base of the fourth metatarsal is also oblique. It has an oblong facet for the cuboid, and a single internal one at the top for the third. Fig. 450. which is separated from the proximal end by a rough space for the insertion of an interosseous ligament from the tarsus. There is externally a triangular facet at the upper angle for the fifth. This last facet is bounded in front by a deep groove which receives the edge of the facet on the fifth. The fifth metatarsal has an even more oblique base, the inner two-thirds of which bear a facet for the cuboid. The outer part is prolonged as the hiberosity beyond the edge of the foot, overhanging the joint. The inner side has a facet for the fourth metatarsal bone. The shafts of the metatarsal bones are flattened lat- erally, but theoretically three-sided, like the first. The second has an external surface looking directly outward ; a superior one at the base, which twists so as to become in- ternal. This is separated from the former in the distal two- thirds of the shaft by a sharp ridge. The third side is internal at the base, but soon becomes inferior. The shaft of the third differs only slightly, the external surface looking some- what upward and there being more of a ridge below. In the fourth it seems as if the proximal part of the shaft had been bent outward on its axis, so that the outer side looks more upward and . the other two are less twisted. In the fifth this process has gone farther ; the originally outer side is now the upper, separated by one border from the inner and by another from the inferior. This last border, now external, represents the one that was the inferior of the third metatarsal. The nutrient foranii7ia of the four outer metatarsals are in the external surfaces, running upward. They are not very constant. Right fifth metatarsal, aspect. 432 HUMAN ANATOMY. Fig. 451. Os intermetatarseum The heads of the metatarsal bones are compressed, like the shafts, from side to side, and have each a pair of lateral tubercles at the dorsal aspect of the end of the shaft, separated by a groove from the articular surface. Lateral ligaments are attached both to the tubercles and the grooves. The ar- ticular surface is oblong, extending well onto the plantar side, where it ends in two lateral prolongations, of which the outer is the more prominent. A line connecting their ends would be oblique to the shaft, especially in the outer toes. Fusion of the outer cuneiform with its metatarsal occurs occasionally at the plantar aspect. It is probably con- genital. Pfitzner has seen it at seventeen and we at nineteen. Development. — Centres for the shafts of the meta- tarsals appear towards the end of the third month of foetal life. A pro.ximal epiphysis for the first and distal ones for the others appear in the third year, fusing at about seven- teen. Occasionally the metatarsals, especially the first, have an epiphysis at each end. Os Intermetatarseum. — This is an occasional wedge-shaped bone found on the dorsal aspect of the foot, between the internal cuneiform and the first and second metatarsals. It may articulate with all three, or with any of them, or be attached to them by connective tissue. More often it is connected by bone with one of the three neighbors, especially with the internal cuneiform, of which it mav seem to be a pro- cess (Fig. 451). It is found in some form once in ten feet (Pfitzner). Intermetatarsal bone fused \ right internal cuneiform Fig. 452. THE PHALANGES. There are two for the great toe and three for each of the others. Although of very different proportions, they present the features which have been described for those of the hand, especially the shape of the articular sur- faces. The first phalanx of the great toe is about as long as that of the thumb and nearly twice as broad. There is a tubercle for muscular insertion at each side of the pal- mar aspect of the base. The terminal phalanx of the great toe is also very massive. The first, or proximal, pha- langes of the other toes diminish in length from within out- ward. Those of the second row are so short as to be almost cubical, although they are broader than thick. The terminal, or distal, phalanges are very rudimentary. Pfitzner" has shown that in about one-third of the cases the terminal phalan.x of the little toe is fused with the middle one, even before birth. Presumably they never were distinct in the embryo. As he has found this condition in Egyptian mummies, certain \-ery pessimistic views as to the degener- ation in store for the human foot are probably unwarranted. Sesamoid Bones. — Those of the first metatarso- pha- langeal joint are large and constant ; those of the same joint in the other toes very rare. The least uncommon are those of the fifth toe, of which the inner sesamoid is found in 5.5 per cent, and the outer in 6.2 per cent. A sesamoid of the interphalangeal joint of the great toe is found in 50.6 per cent. (Pfitzner^). Development. — The first nucleus to appear is that of the distal phalanx of the great toe at the end of the third foetal month. Those of the other distal phalanges, except the fifth, come some two weeks later. The bones of the pro.ximal row seem to ossify rather later than the ' Arch, fiir Anat. und Entwick., 1890. ' Morph. Arbeiten, Bd. i. Third distal or ungual, phalanx Second, or middle, phalanx First or proximal, phalanx Phalanges of right second toe, plantar surface. THE PHALANGES. 433 distal ones, but this order is not constant. According to Bade,' the middle phalanges have begun to ossify in the eighteenth week of foetal life, but we have found bone wanting considerably later. The process of ossification in the fourth and tifth toes is decidedly later than at the inner side of the foot. It does not begin in the middle phalanx of the fifth till near term, and we have sometimes seen no sign of it in the Fig. 453. Ossification of bones of the foot. A. during sixth fcetai month: S, at eighth fcetal month; C at birth; D, during first year ; £, between three and four years ; F, at about fifteen \ears. a, for shaft of metatarsals ; *, for cal- caneum ■ c, for proximal phalanges; d, for distal phalanges ; e, for astragalus ;/, for middle phalanges; g-, for cuboid: A. for external cuneiform ; i, for heads of metatarsal bones and base of first proximal phalanx ; j\ for base of first distal phaianx ; k, for internal cuneiform ; /. for base of first metatarsal. fifth, and even in the fourth at birth. Proximal epiphyses appear from the fourth to the si.xth year, and fuse at about sixteen. The terminal phalanges have distal caps like those of the hand. The fifth toe, according to Pfitzner, has the following pecu- liarities : the proximal epiphysis of the second phalanx and the centre for the shaft of the terminal one are wanting, the proximal epiphysis of the latter being greatly exaggerated. ' Arch, fiir Mik. Anat., Bd. Iv., 1900. 28 434 HUMAN ANATOMY. Fig. 454- I ostero inferior surface of calcaneum Groove for tendon of. flexor longus halhicis Sustentaculum lal Scaphoid ^^ Tibialis postic. External cuneilorm Middle cuneiform Internal cuneiform Tibialis anticus First metatarsal. Sesamoid boni Abductor and Hexor brevis hallucis Adductores obliguus et transversus Flexor longits hallu Bones of right foot, plantar aspect. BONES OF THE FOOT. 435 Fig. 455. Ttndo Achilhs Bursal surface Lateral articular surface for fibul Groove ior peroneus long Groove iox peron. Extensor brevis digits Groove for peroneus /on^. Groove iorjiexor iotigus halluc Superior articular surface of astragalus Peroneus tert. Fourth dorsal interosse. Extensor brevis digitorum Extensor longus digitorum External cuiieifornr Middle cuneiform Internal cuneiform First metatarsal First dorsal inter Extefisor brevis hallucis Extensor longus hallucis Bones of right foot, dorsal aspect. 436 HUMAN ANATOMY, PRACTICAL CONSIDERATIONS. The union of the foot with the leg at a right angle, while necessitated by the erect attitude of man, makes it essential that the bones of the foot shall be so shaped and united that they may aflord a basis for both support and propulsion, all pre- hensile function being sacrificed to those ends. Accordingly, we find the tarsus proportionately much larger, both it and the metatarsus stronger, and the pha- langes much smaller and less mobile than the corresponding parts of the hand. The strength of the foot and its comparative freedom from injury, in spite of its con- stant exposure to traumatisms of various grades of severity, are due to the arrange- ment of its component bones into the form of an arch, which is well adapted not only to sustain weight and to provide leverage for motion, but also to resist and distribute e.xcessive force received, as in falls upon the feet. The posterior pillar of the arch, composed of the os calcis and the hinder portion of the astragalus, has but one joint — the calcaneo-astragaloid — with a very limited range of motion. The action of the calf muscles upon the heel is thus applied to the elevation of the hinder pillar with the least possible expenditure of force, as there are no unnecessary movements between their point of insertion and the ankle-joint. The anterior pillar beginning at the top of the astragalus — the summit of the arch — may be said to include practically most of the foot anterior to the ankle and to separate naturally into ( i ) a larger and stronger inner division consisting of the neck and head of the astragalus, the scaphoid, the three cuneiforms, and the three inner metatarsals ; and ( 2 ) a weaker and smaller outer division composed of the cuboid and the remaining metatarsals. The anterior pillar thus secures in the wide surface of the distal extremities of the metatarsal bones a broad basis of support ; its inner division carries most of the weight, and is enabled to do this by the thickness and strength of the metatarsal bone of the great toe and by the parallelism of the latter with the great toe ; its outer division bears less weight, but supports the inner division laterally and broadens the surface in contact with the ground. The normal foot thus rests directly upon the os calcis and the anterior e.xtremities of the metatarsals, the outer side of the foot aiding more in preserving balance than in carrying weight. An imperfect transverse arch — including the scaphoid, cuboid, and cuneiforms — adds to the elasticity of the foot and aids the main arch in affording a pressure-free area for the plantar vessels and nerves. Both arches depend for their integrity not only upon the shape of the bones-, but also upon the fasciae, ligaments and tendons, and to some extent upon the small plantar muscles. Still another transverse arch is formed by the bases of the metatarsal bones, and a third, but less distinct one, by their heads. Perhaps the most accurate conception of the foot mechanically is as a semi-dome (Ellis), the whole dome being completed in well-shaped feet when the inner borders are approximated. The epiphysis of the os calcis occupies the posterior rounded extremity of the bone, and has inserted into it the tendo Achillis. No positive clinical evidence of separation exists, but it is probable that the X-rays will show that in young persons lesions heretofore supposed to be fractures of the os calcis from muscular action are actually epiphyseal disjunctions. The epiphyses of the remaining bones of the foot have but little surgical interest. The first metatarsal, like that of the thumb, has its epiphysis at the proximal end, and to that extent resembles a phalanx. The other four metatarsals have their epiph- yses at the distal ends. All the phalangeal epiphyses are at the proximal ends. In the metatarso-phalangeal joints the synovial membrane is in close relation to the epiphyseal lines ; in the phalangeal joints it is not. A knowledge of these facts may occasionally be useful in cases of disease or injury limited to a particular bone. Fract2ire of the bones of the tarsus is rare, e.xcept as a result of crushing injuries or of falls from considerable heights. If the bones of the anterior pillar are broken, it is usually by direct violence, as the numerous joints and ligaments of this region render it so elastic, and so diffuse forces applied, as in jumps or falls, as effectually to PRACTICAL CONSIDERATIONS : THE FOOT BONES. 437 prevent fracture. The bones of the posterior pillar are broken in both ways. In falls the astragalus is apt to break about its neck, — the weakest portion ; or if the foot is strongly dorsiflexed, the anterior articular edge of the tibia may act as a wedge and split it across. The os calcis may be broken between the astragalus and the ground, — compression fracture ; or it may be broken behind the insertion of the inferior calcaneo-scaphoid ligament, the anterior arch being flattened by the fall, but the ligament resisting rupture. A few cases of fracture of the sustentaculum tali have been reported, the foot having been in forcible inversion, the lesser process (susten- taculum) being broken off against the edge of the astragalus. In each case this was followed by eversion and sinking of the inner border of the foot (valgus), the support given by the internal articulating surface to the astragalus having been removed. Of the metatarsal bones, the first, although the strongest, is most frequently broken because it carries so large a proportion of the body weight and because it receives an undue share of the violence in falls associated with eversion of the foot. The fifth comes next in frequency because of its exposed position on the outer side of the foot and the added violence in cases of inversion. Dislocation of separate bones, especially of the astragalus, is rare. It is always the result of the application of considerable crushing force, is usually associated with other injuries, and is influenced but little by anatomical factors. Disease of the bones of the foot, and especially tuberculous disease of the tarsus, is common because of : (i) the frequency of traumatism ; (2) the exposure to cold and damp and the scanty protection afforded by the superjacent tissues; (3) the remoteness from the centre of circulation and the dependent position of the part, both favoring congestions ; (4) the preponderance of cancellous tissue in the bones ; and (5) the difficulty in securing perfect rest, especially after minor injuries, which are those most often followed by tuberculous osteitis. It affects most frequently those bones that bear most of the weight of the body, — the os calcis, the head of the astragalus, and the base of the first metatarsal. It is more likely to remain localized when situated in the os calcis or in the hinder part of the astragalus ; in the anterior portions of the tarsus the number and complexity of the synovial cavities (often intercommunicating) tend to prolong and to spread the disease. In disease of the tarsal bones — excepting the astragalus, to which no muscle is attached — the tendon sheaths in the vicinity may be involved by direct extension from the periosteum. Any metatarsal bone may be involved in cases of ' ' perforating ulcer, ' ' the situa- tion of the latter being determined usually by the degree of pressure upon the sole in cases in which anaesthesia is already present ; hence the frequency with which the first metatarsal is involved in this disease. Excision of the separate bones has frequently been performed, especially of the astragalus and os calcis. Landmarks. — On the inner side of the foot can be felt : («) the ridge between the inner and posterior surfaces of the os calcis ; ((5) the tubercle of the os calcis ; (^) the sustentaculum tali, one inch directly below the tip of the malleolus ; (^) from one- half to three-quarters of an inch in front of the latter the head of the astragalus, very noticeable in flat-foot ; {e) from one-half to three-quarters of an inch more anterior the prominent tuberosity of the scaphoid, the space between it and the sustentaculum being filled by the inferior calcaneo-scaphoid ligament and the tibialis posticus tendon ; from the tuberosity the tendon may be traced to the back of the inner malleolus ; (/) the internal cuneiform ; (^) the base (one and a half inches in front of the scaphoid tuberosity), the shaft, and the expanded head of the first metatarsal ; (^) the base of the first phalanx with the internal sesamoid bones just beneath ; (z) the phalanges. On the outer side are to be felt : {a) the ridge between the outer and posterior surfaces of the os calcis ; {b') the external tubercle of the os calcis ; (<:) the peroneal tubercle, three-quarters of an inch below and a little in front of the tip of the e.xternal malleolus, lying between the long and short peroneal tendons ; {d') the external surfaces of the os calcis and (when the foot is inverted) the edge of its anterior extremity, lying just above the cuboid ; ( Section of right foot throng 1 tit i t lioum^ support b\ first and fourth. terminal phalanx of the same toe. These dislocations are nearly always upward. Dislocation of the proximal phalanx of the great toe may be as difficult to reduce as is that of the thumb. Morris thinks that the sesamoid bones may act as the anterior ligament does in the latter case, — i.e., being more firmly attached to the phalanx than to the metatarsal bone, they may be torn away with the former, and by their interposition prevent reduction. The painful affection known as metatarsalgia has been thought (Morton) to be due to the position of the fifth metatarso-phalangeal joint, so much posterior to the fourth that the base of the first phalanx of the little toe is opposite the head and neck of the fourth metatarsal. As the fourth and fifth metatarsal bones have greater mobility than their fellows, it was supposed that this relation afforded opportunity for PRACTICAL CONSIDERATIONS : THE FOOT-JOINTS. 453 accidental compression of the branches of the external plantar nerve. R. Jones thinks that it is often a communicating branch between the fourth division of the internal plantar and the external plantar that is compressed between the bone and the ground as it passes beneath the head of the fourth metatarsal. A transverse section of the foot through the heads of the metatarsals shows that the first and fourth bear the most pressure (Fig. 467). The situation of the plantar digital nerves, superficial to and not between the bones, and the collapse of the transverse arch in most cases of metatarsalgia, broadening the inter\'als between the bones, but increasing pressure on the structures beneath them, support the latter view. Flat-foot is so closely associated in its anatomical deformities with talipes valgus that it will be considered in relation with the latter, which, with the other varieties of club-foot, can best be understood after the muscles and fasciee of the leg and foot have been described. Disease of the tarsal joints, like that of the bones, is most frequently tuberculous in character, and is more apt to remain localized when it is situated in the posterior pillar of the main arch, — i.e., in the posterior half of the calcaneo-astragaloid joint. If in front of the interosseous ligament dividing that articulation, or if in either of the mid-tarsal joints (with which it communicates), or in any of the remaining four synovial cavities, it is apt to extend much beyond its original limits. The circum- stances that favor the origin (page 437) and influence unfavorably the course of bone disease in this region apply in the main to disease of the joints. In whichever tissue — bony or synovial — it originates, it is apt to spread to the other. The astragalo- scaphoid joint, on account of its superficial position and its range of motion (which is greater than that of any of the joints below the ankle), is most apt to be affected. The situation of the swelling and tenderness will usually differentiate it from ankle- joint disease (page 451 ). Probably on account of the diffuse infection of the abundant cancellous tissue of the tarsal bones (either primary or secondary to joint disease), remote tuberculous infection — phthisis — follows or accompanies disease of the ankle and tarsus more frequently than it does disease of any other part except possibly the wrist (Cheyne). Gout affects peculiarly the metatarso-phalangeal joint of the great toe. In 516 cases of gout, 341 were of one or both of the great toes alone and 373 of the great toe with some other part (Scudamore). This is due to (a) the abundance in that region of dense fibrous tissue of little vascularity ; {h) its remoteness from the heart, the force of the circulation being at its minimum ; {t) the large share of the body weight which it sustains, as the anterior extremity of the main arch of the foot ; {d') the frequency of traumatism ; (i?) the constant exposure to cold and damp ; (_/) its dependent position. LandmarkSo — The ankle-joint {g.v.) lies about half an inch above the tip of the inner malleolus. Syme's amputation is done through this joint, the incision being made from the tip of one malleolus to the tip of the other, and at right angles to the long axis of the foot. The mid-tarsal joint (through which Chopart's amputation is done) runs out- ward from a point just back of the scaphoid tuberosity, and passes directly over the dorsum of the foot to a point a little In advance of the middle of a line between the tip of the external malleolus and the tuberosity of the fifth metatarsal. Tne tarso-metatarsal joint begins at a point about one and a half inches in front of the tubercle of the scaphoid, — i.e., just back of the base of the first metatarsal, -r- passes at first directly outward, then passes irregularly around the three sides of the mortise between the internal and external cuneiforms in which the base of the second metatarsal rests, and then slopes slightly backward to its easily recognized termination on the outer side of the foot, just behind the base of the fifth metatarsal. Hey's amputation begins and ends at the two extremities of this joint-line, but the projection of the internal cuneiform is sawn across. In Lisfranc's amputation the joint-line is followed throughout. The metatarso-phalangeal joints lie an inch behind the interdigital web. THE MUSCULAR SYSTEM. Muscular Tissue in General. — Contractility, although exhibited to some degree by all living protoplasm, is possessed especially by muscular tissue, the sum of "the contractions of such tissue being expressed in motion, the most conspicuous characteristic of all the higher forms of animal life. Muscular tissue represents a high specialization in which contraction takes place along definite lines corresponding to the long axes of the component cells, in contrast to the uncertain contractility occurring within other elements. The simplest form of contractile tissue, as seen in some of the low invertebrates, is represented by elements of which the superficial part is related to the integument, the deeper being differentiated into contractile fibres. Although such musculo-epithe- lial cells may form an almost complete contractile layer, the muscular fibres do not exist as an independent tissue, 'f he differentiation of certain cells into definite mus- cular tissue, however, soon appears in the members of the zoological scale, although the existence of a distinct muscular system is deferred until an adequate nervous system is developed. In the higher animals muscular tissue appears in two chief varieties, the striated and non-striated, depending upon the respective histological characteristics of their constituent elements. The former makes up the muscles controlled by the will, and is, therefore, also termed voluntarv muscle ; the latter, which constitutes the contrac- tile tissue within the walls of the hollow viscera, blood-vessels and other tubes, acts independently of volition, and is spoken of as involuntary muscle. The last named is sometimes also designated vegetative muscle, since the organs in which it is present are largely concerned in the nutritive processes ; the term animal may be applied in contrast to voluntary muscle. The association of the striated muscle with response to volition and, on the contrary, of the non-striated variety with involuntary action must be accepted with certain reservations, since in some animals the development of marked striation never takes place within the fibres of voluntary muscle. There is, indeed, not a little evidence going to show that the structural differences which exist between the striated and non-striated musculature are correlated with their physio- logical activities, and that no fundamental distinction can be drawn between them on purely morphological grounds. Muscles which in one group of animals possess the characteristics of striated muscle-tissue may, in another group, be represented by non-striated fibres (the muscles of the oesophagus, for instance), and it seems probable that the greater portion of the voluntary cranial musculature is serially equivalent to the involuntary musculature of the trunk. The non-striated or involuntary muscle represents a tissue less highly specialized than the striped, the latter exhibiting to a conspicuous degree histological differentia- tion. Constituting, in a way, a separate and intermediate group stands heart muscle, which, while beyond the control of the will, presents striated fibres ; the latter occupy histologically a place between the fibre-cell of the involuntary and the elongated striated fibre of the voluntary muscle. It is desirable, therefore, to consider the sim- pler type of contractile tissue before examining the more complex voluntary muscle. NON-STRIATED OR INVOLUNTARY MUSCLE. This, the less highly differentiated variety of muscular tissue, occurs in the form of bundles and thin sheets principally within the walls of the organs and vessels, although enjoying a wide distribution, seldom presenting robust masses, and being entirely unconnected with the skeleton. Even when present in considerable amount, this tissue is usually inconspicuous, presenting a faint yellowish tint. The distribution of non-striped muscle includes : i. The digestive tract, — the muscularis mucosje from the oesophagus to the anus and delicate bundles within the 454 NON-STRIATED OR INVOLUNTARY MUSCLE. 455 mucosa and villi ; the muscular tunic from the lower half of the oesophagus to the anus ; in the large excretory ducts of the liver, pancreas, and some salivary glands, as well as in the gall-bladder. 2. The respiratory tract, — in the posterior part of the trachea, encircling bundles in the bronchial tubes as far as their terminal divisions. 3. The urinary tract, — in the capsule and pelvis of the kidney, ureter, bladder, and urethra. 4. T\\& 7Hale ge7ie)-ative organs, — in the epididymis, vas deferens, seminal vesicles, prostate body, Cowper's glands, and cavernous and spongy bodies of the penis. 5. 'Wi^ female generative organs, — in the oviducts, uterus, and vagina ; in the broad and round ligaments ; in the erectile tissue of the external genitals and of the nipple. 6. The vascular system, — in the coats of the arteries, veins, and larger lymphatics. 7. The lymphatic glands, — in the capsule and trabeculae of the spleen ; sometimes in the trabeculse of the larger lymph-nodes. 8. The eye, — in the iris and ciliary body ; in the eyelids. 9. The iiitegument, — in the sweat- and some sebaceous glands, as the minute erector muscles of the hair-follicles and in the skin covering the scrotum and parts of the external genitals. Structure. — Non-striated, unstriped, pale or involuntary muscle consists of an aggregation of structural units known as the fibre-cells. These are deli- cate spindle, often prismatic, elements which terminate in oblique surfaces at either end for contact with adjacent cells. They vary greatly in size, measuring from .050- .225 mm. in length and .003-. 008 mm. in width. The muscle-cells found in the skin and blood-vessels are short (.015- .020 mm.) and broad; those in the in- testinal wall are more elongated (.215— ^ .220 mm.) and delicate. The largest } elements are encountered in the gravid / uterus, in which they attain a length of j .500 mm. and a breadth of .030 mm. Occasionally the cells are bifurcated at the ends, especially among the lower ver- tebrates. c Fig. 470. I niuscle-cells, showing nucleus and "■^hly magnified. {Levkossek.) oluntary muscle in transverse section, showing the fibre-cells cut crosswise. X 400. More recent critical examinations of the fibre-cells have demonstrated the existence of greater structural complexity than was formerly recognized.' According to these later views, each fibre-cell consists of a protoplasmic mass in which lie embedded the nucleus and the co?tfractile fibrillce. The former is appropriately '_An exhaustive review of the literature and various opinions concerning the structure ot unstriped muscle is given by M. Heidenhain : Ergebnisse der Anatomie und Entwick., Bd. x., I goo. 456 HUMAN ANATOMY. Fig. 471. described as rod-shaped, being cylindrical with rounded ends. Its position is fre- quendy eccentric with regard to the a.xis of the cell, as well as often somewhat nearer one pole than the other. The nuclei of these muscle-cells are rich in chromatin, which usually presents a reticular arrangement. Under the influence of contraction, the nuclei present more or less variation from their typical rod form. Centrosomes (Fig. 469) may be distinguished in favorable preparations Iving within the cy- toplasm close to the nucleus (Zim- mermann, Lenhossek). The contractile Jibrillcs rep- resent differentiated anisotropic threads within the cell- body, in their property of double refraction resembling the fibrillje of striped muscle. They are most conspicu- ous at the periphery of the fibre- cell, where they lie closely related to the condensed boundary zone (Heidenhain) which forms the e.xterior of the fibre and fulfils the purpose of a limiting membrane or sarcolemma, although no such definite structure encloses the muscle-cell as in the case of the striated fibre. The demonstration of contractile fibrillje within the muscle- cells of the higher vertebrates is unsatisfactory on account of the small size of the elements ; in the large cells of the amphibia, especially in the huge elements of the amphiuma, their presence is readily established. Although lying usually within the periphery of the fibre-cell, the existence of a conspicuous axial fibre is seen in certain cases, as in the large isolated muscle-cells within the mesentery of newts. The individual elements of unstriped muscle are held together by delicate mem- branous expansions of connective tissue prolonged from the more robust septa investing and uniting the bundles and fasciculi of the fibre- cells. On cross-section (Fig. 470), these inter- cellular membranous partitions appear as delicate lines between the transversely cut cells, which were formerly interpreted as tracts of cement- substance uniting the muscular elements. The appearances of intercellular bridges, described by several authors (Barfuth, de Bruyne, Werner, Bohemann, Apathy) as connecting the adjacent cells, depend probably upon the shrinkage of the latter due to the action of reagents (Stohr, Heidenhain ). The blood-vessels supplying involuntary muscle are guided in their distribution by the septa of interfascicular connective tissue in which the larger twigs run. The latter give of! minute branches which terminate in capillaries that ex- tend between the primary bundles of the muscle- cells. The blood-supply of non-striated muscle is meagre when compared with that of the striped muscles. The lymphatics occur closely associated with the muscular tissue in localities in which the latter exists in considerable quantity, as in the wall of the stomach and intestine, the interfascicular connective tissue containing plexuses of lymph-channels. The nerves supplying involuntary muscle are intimately related to the sympa- thetic system. The larger trunks form plexuses, in close association with microscopic Fig. 472. ■ r-^-^ i;<; Portion of injected intestinal wall, showing arrangement of blood-vessels supplying invol- untar>' muscle ; upper longitudinally, lower transversely cut. >, 50. STRIATED OR VOLUNTARY MUSCLE. 457 ganglia, from which delicate twigs pass between the bundles of muscle-cells. The mode of their ultimate termination is described in connection with nerve-endings (page 1015). Development. — All muscular tissue in the higher types, with the exception of that found within the swea.t-glands and the iris,' may be regarded practically as a derivation of the mesoblast. Reference to Fig. 34 (page 29) recalls the division of the mesoblast into the parietal and visceral layers, the latter, in conjunction with the entoblast, constituting the splanchno-pleuric folds by the union of which the gut-tube is formed. The subsequent differentiation of the visceral mesoblast contributes the layers of the wall of the digestive canal outside the epithelial structures derived from the entoblast ; in typical parts of the tube these layers are the submucous, muscular, and serous coats. The muscular tunic consists of the unstriped involuntary variety, the component fibre-cells representing specialized mesoblastic elements. Fig. 473. Differentiating muscular tissue' Young connective tissue Epithelium lining gut Section of developing intestinal wall sh The details of the development of the muscular tissue include condensation of the young mesoblast produced by conspicuous proliferation and increase in the cells, followed by their gradual elongation and conversion into spindle elements. These are at first short, but become extended as the tissue assumes its fully developed character. In localities in which the involuntary muscle occurs in sparingly dis- tributed bundles and net-works the mesoblastic elements gradually assume the form of spindle-cells which for a time are inconspicuous and difficult to distinguish from ordinary young connective tissue. The formation of the muscular tissue within the walls of blood-vessels is closely identified with the intramesodermic origin of the vascular channels, the entire walls of which tubes are contributions of the middle germinal layer. STRIATED OR VOLUNTARY MUSCLE. The striped muscular tissue constitutes the conspicuous masses known as the "muscles" or " fiesh" attached to the bony framework of the body. These organs are also termed the skeletal muscles, and supply the active agents in moving the passive levers represented by the bones in producing the movements of the animal. The muscles are usually elongated in form, and consist of aggregations of bundles of the ultimate contractile elements, the fibres, grouped into fasciculi ; upon the size of the latter depends the texture of the muscles, coarse or fine, as distinguished in the dissecting-room. In localities in which the fasciculi are of large size, as in the gluteus ' Szili : Archiv fiir Ophthalmol., Bd. liii., 1902. 458 HUMAN ANATOMY. ^^.-^ r>= maximus, the muscles are conspicuous on account of their coarse texture ; a fine- grained muscle, on the contrary, is composed of small fasciculi. In addition to variations in the thickness of the fasciculi, the latter differ greatly in length irrespec- tive of the extent of the entire muscle, since the length -of the fasciculi depends largely upon the arrangement of the ten- riG. 474- dons. A long muscle may be '^^ '"• composed of short fasciculi, since the latter may be attached to ten- dons which cover its opposite I) sides or extend within its sub- ■ ' stance as septa. In such cases, .^1 as in the rectus femoris or the ^■\ deltoid, the short fasciculi run i-/, obliquely, thereby producing a pennate arrangement which often •' characterizes muscles of great ' strength. When, on the con- ■ ..'■}. trary, the tendons are limited to ' '^ the ends of a muscle, the fascic- '■ i uli are relatively long and may extend its entire length. The sartorius contains fasciculi, as well as fibres, of conspicuous e.\- jvi/ tent, some bundles stretching 'rf' the entire distance between the ,''■ tendons. General Structure of Striated Muscle. — The histo- logical unit of voluntary muscular tissue is the transversely striated or striped imisde- fibre, which ving the represents a highly specialized single cell. The fibres are the contractile elements by the shortening of which the length of the entire muscle is decreased and the force e.xerted. The fibres are cylindrical, or prismatic with rounded angles, in form, and vary from .oi-. i mm. in diameter ; no constant relation exists between the thickness of the fiisres and the size of the muscle of which they are the components, and, indeed, their diameter varies even within the same muscle. In general the limb muscles are composed of large fibres, those of the mature male sub- ject usually exceeding the corresponding fibres of the female. TJhe length of the muscle-fibres is likewise subject to great variation. As a rule, the fibres composing a muscle are of limited length, generally not exceeding from 4-5 cm. ; in exceptional instances, however, as in the sartorius, they mav attain a length of over 12 cm. and a width of from 1-5 mm. (Felix). The fibres are usually somewhat spindle-shaped, being slightly larger in the middle than at the ends, which are usually more or less pointed ; blunted or club-shaped and, more rarely, branched ex- tremities are not uncommon. Branched and anastomosing fibres occur in certain localities, as in the tongue, facial and ocular muscles. The individual fibres, each invested in its own sheath, or sarco/emma, are grouped into small primary bundles, the component fibres of which are held together by a meagre amount of connective tissue, the endomysium. The latter is continuous with the perimysium investing the primary bundles. These are associated into uncertain groups, the secondary bundles, which are united and enclosed by extensions and subdivisions of the general connective-tissue envelope of the entire muscle, the epimysium. In muscles Several primary muscle-bundles in transverse secti( arrangement of component fibres. ,\ i Fig. 475. STRIATED OR VOLUNTARY MUSCLE. 459 possessing a fine grain the secondary bundles correspond with the fasciculi, but in muscles of coarse texture each fasciculus includes a number of secondary bundles between which the ramifications of the epimysium extend. The characteristic picture presented in transverse sections of muscles (Fig. 474) illustrates the relation of the fibres to the larger groupings of the muscular elements. Structure of the Muscle-Fibre. — Each fibre corresponds to a greatly elongated multinucleated muscle-cell, and consists of a sheath, or sarcolemma, and the contained sarcous substance. The sarcolemma forms a complete investment of the fibre and alone comes into contact with the surrounding connective tissue by which the muscle-fibres are attached either to one another or to the tendinous structures upon which they exert their pull. The sarcolemma is a transparent, homogeneous, elastic membrane which so closely invests the contained sarcous substance as to be almost invisible under ordinary conditions. Being of greater toughness than the muscle-substance, it often withstands mechanical disturbance, as teasing, while the latter becomes broken ; where such breaks occur the sarcous substance sometimes contracts within the sarco- lemma, which at the points of fracture then becomes visible as a delicate tubular sheath stretching across the space separating the broken ends of the more friable. Fig. 476. B : B! II W ' ^ p^ ™ ii In In ini PHi ffWi I iijgi Diagran^s illustrating; structure of striated muscle-fibre. A, usual view; B, correct view, showing sustentacuiar septa continued across fibre from sarcolemma; C septa shown after vanadium-haematoxylin staining. .2', interme- diate disk {Zwischenschcibe) ; /, light band ; i?. transverse disk {Querscheibe) ; il/, median disk {Mittelscheibe) ; .S, sarcolemma. {After lil. Hcidcnkain.) sarcous substance (Fig. 475). In teased preparations the sarcolemma is sometimes also seen projecting beyond the sarcous substance, as a coat sleeve covers the stump of an arm. The sarcous or muscular substance within the sarcolemma in turn consists of two parts, the less differentiated passive sarcoplasm and the highly specialized contractile fibrillte in which the active changes take place resulting in the contraction of the muscle-fibre. Since the highly characteristic appearance of cross-striation which distinguishes the fibres of voluntary muscle, as well as supplies the reason for its designation as striped or striated, depends upon the arrangement of the contractile fibrillae, the details of the latter first claim attention. The cross-striation consists of alternate dark and light bands which extend the entire width of the fibre and depend upon the differentiation of the contractile fibrillae into segments of greater or less density. Close lateral approximation of the more dense and deeply staining segments in the fibrillae, lying side by side within the sarco- lemma, produces the dark band ; the similar relation of the less dense and non-staining segments produces the impression of the light band. If it were possible to isolate the individual contractile fibrillae, each would present the details shown in the accompany- ing diagram (Fig. 476). The dark, broad transverse disk (^Q) of doubly refracting, 460 HUMAN ANATOMY. or anisotropic, substance is succeeded at either end by the light band (JJ) of singly refracting, or isotropic, substance. The light band is subdivided by a delicate line, the interttiediate disk (if ), also known as Krause s tnettibrane. The sequence which by repetition makes up the contractile fibrilla consists, therefore, of Z +/+ Q +y +Z. .Under fa\orable conditions for examination the transverse disk exhibits less density midway between its ends ; this zone is traversed by a delicate line {M), the median disk (Hensen, Merkel) or middle membrane (M. Heidenhain). The interpretation of these appearances, shown as usually seen under moderate amplification in the accompanying photograph (Fig. 477), has been the subject of much laborious investigation and vexed discussion ; even at the present time authorities are far from accord as to the significance of the observed details in their relations to the architecture of the muscle-fibre. It is beyond the purpose of these pages to review the various theories concerning the ultimate structure of striped muscle ; ' suffice it to point out that, apart from the conclusions of those observers who from time to time have contended that the appearances are entirely optical and do not correspond to actual structural details, two chief Fig. 477. views regarding the architecture of the muscle-fibre have been held. According to the one, championed by Krause, the intermediate zone is regarded as the expression of a membranous septum which stretches entirely across the mus- cle-fibre as an inward extension of the sarcolemma and thus subdi- vides the fibre into a number of minute compartments, or contrac- tile disks, by the longitudinal ap- position of which the entire fibre is built up. The other view, early accepted by Kolliker, regards the fibre as made up of fibrilla ex- tending the length of the fibre, the transverse cleavage into disks being secondary and artificial. The fibrillar theory as advanced by Rol- let has received wide acceptance and deserves brief mention. Ac- cording to this authority, the con- tractile fibrillfe are to be conceived as forming anisotropic rods consisting of alternating thicker and thinner segments (Fig. 478), the former corresponding in position with the broad, dark, transverse disk, the latter with the lighter band, since the meagre amount of doubly refracting substance in this zone is masked by the large quantity of isotropic sarcoplasm. Rollet recognized the intermediate disk as consisting, not of a continuous membrane, but as an interrupted line representing a row of minute beads which exi.st as local accumulations on the thinner segments of the fibrillse. Rollet' s conception of the fibre, therefore, included the sarcolemma containing the sarcoplasm in which the con- tractile fibrillae were embedded. More recent investigations with the aid of improved differential stains have led to a modification of the fibrillar view in so far that the intermediate disk is to be regarded as a structure that is attached to the sarcolemma and extends between the fibrilte. M. Heidenhain believes the median disk to be an additional membrane that likewise meets the sarcolemma at the periphery of the fibre. The later conception of muscle architecture in no wise questions the existence of the fibrillae as the con- tractile elements of the fibre, but regards them as held in place by the lateral braces ' An exhaustive review of the literature and various opinions re.a;ardin.s; the structure of striped muscle is given by M. Heidenhain: Ergebnisse der Anatomie und Entwick., Bd. ix., 1S99. Photograph of striated muscle, showing th under moderately high magnificatio STRIATED OR VOLUNTARY MUSCLE. 461 represented by the intermediate and median bands. The foregoing diagram (Fig. 476J, modified from Heidenhain, indicates the relations of the several bands to be seen in muscle when examined under the most favorable conditions. That various reagents produce marked changes in the details of the muscle-picture admits of no question ; this has been graphically represented by the last-quoted author. ^ The fact that the intermediate disk is attached to the sarcolemma is shown by the constrictions or scalloped margin in the outline of the fibre during contraction, the constrictions corresponding in position to the attachment of the membranes of Krause. The striped muscle of certain insects exhibits an additional band, the accessory disk, sub- dividing the light zone i^J). The distribution of the contractile fibrillee throughout the fibre is not uniform, since the fibrillae are grouped into bundles, the fiiuscle-columns or sarcostyles. This arrangement is well shown in suitably prepared transverse sections of muscular tissue (Fig. 479), in which the individual fibres are seen to be made up of minute stippled areas separated by clear lines. These areas are known as Cohnheim' s fields, ^^xiA represent the transversely cut groups of contractile fibrillae. The clear lines indicate the distribution of the sarcoplasm ; in addition to forming the net-work dividing_ Cohnheim's fields, the sarcoplasm separates the groups of individual fibrillae, each muscle-column being entirely surrounded by the less highly differentiated substance. Fig. 47S. Fig. 479. ^^ Diagram muscle-fibre appearances illustratii and relati( of tissue. Muscle-fibres of lizard in trans\erse section, sho' fields of Cohnheim and muscle nuclei. X 650. When seen in longitudinal section, the sarcoplasm between the groups of fibrillae appears as lines extending the entire length of the fibre, to which an inconspicuous longitudinal striation is thus imparted. The muscle-fibre has already been spoken of as a multinucleated cell. The nuclei resulting from the division of the nucleus of the embryonal cell remain within the sarcoplasm and are termed muscle-nuclei. Their position in mammalian muscle is usually immediately beneath the sarcolemma ; in certain fibres, however, as those composing the semitendinosus of the rabbit (Fig. 480), and of uncertain distribution in man, the nuclei lie more deeply embedded within the sarcoplasm, therein agreeing in location with the position occupied by the nuclei in the muscular tissue of many of the lower vertebrates (Fig. 479). Variations in the color and contractility of muscular tissue have been described by Ranvier and Krause, Klein, Griitzner, and others. While the skeletal muscles are usually of a pale tint and contract energetically when stimulated, particular mus- cles of certain animals, as the semitendinosus and the soleus in the rabbit, possess a deeper color and contract more slowly and prolongedly under stimulation. Such red niicscles, as they haye been named, are composed of fibres which are thinner than common and possess a relatively larger amount of sarcoplasm, in which the muscle- nuclei are embedded not only immediately beneath the sarcolemma, but also in the ' M. Heidenhain : Anatom. Anzeiger, Bd. xx., Nos. 2 and 3, 1901. 462 HUMAN ANATOMY. deeper parts of the fibre (Fig. 480). The longitudinal striation is also unusually con- spicuous, due to the exceptional amount of interfibrillar sarcoplasm. Although not present in mammals generally in sufificient quantity to affect the appearance of entire muscles, the peculiar "red" fibres are found in many localities intermingled with the more usual pale variety. Klein has described such fibres in the diajjhragm, and, according to the investigations of Griitzner and of J. SchafTer, it is probable that they are found in all muscular tissue upon which devolves prolonged effort. These fibres are, therefore, present in the heart, the eye muscles, and the muscles of respiration and of mastication. The red fibres must be regarded as representing a less complete differentiation of the muscle-cell and as possessing consequently a larger proportion of reserve protoplasm ; they are better able to withstand the fatigue of contractions than those in which the specialization of a larger part of the cytoplasm has occurred. The pale fibres gain in rapidity of contract'on at the e.xpense of early exhaustion. Attachment of the muscular fibres, whether to other fibres or to tendons, is accomplished by the union of the sarcolemma with the connective or tendinous tissue Fig. 4S0. Fig. 4S1. /• r^" -' \ :' ' ' •' ^ n Portion of the soleus niu 1 I ll i il 1 l i i tn verse scLtioii The more coirsi.l> sih)[_1lJ ti!-r '\n red muscle, the> also contain nuclei within the ; cous substance. X 160. and never by direct fusion of the connective tissue with the sarcous substance, the latter remaining completely invested by its sheath. On joining a muscle (Fig. 481), the tendon-tissue subdivides into small bundles which receive and surround the pointed ends of the muscle-fibres, the fibrous tissue becoming attached to the sarcolemma, while the areolar tissue between the tendon-bundles blends with that separating the muscle-fibres. Cardiac Muscle. — The striped muscle of the heart, in atldition to the pecu- liarity of being beyond the control of the will, although striated, presents certain modifications in the form and arrangement of its fibres which call for special con- sideration. According to the views formerly held, the histological unit of the myo- cardium was the branched fibre-cell (Fig. 482), by the apposition of which the sheets of muscular tissue were formed. The fibre-cell was regarded as a short branched fibre, devoid of a sarcolemma and possessing a nucleus surrounded by a considerable area of undifferential sarcoplasm. Studies of the histogenesis of cardiac muscle show that the contractile tissue arises as a continuous network, or syncytium, without cell boundaries, but provided with nuclei. The subsequent appearance of the transverse STRIATED OR VOLUNTARY MUSCLE. 463 lines, or intercalated discs, has been interpreted as expressing a later differentiation into fibre-cells, the cross-lines being regarded as indicating the limits of the compo- nent fibres. According to Jordan, ' how- FiG 4S2. ever, the intercalated discs are neither cell boundaries (Zimmermann) nor growth- ,|\ . f"^ P~s^ zones (Heidenhain), but must be inter- preted in terms of the ultimate fibrillae, not of the whole fibre, and are due to Fig. 483 (i) >,4 ' Muscle hbres of human lieait \ 375. Diagram showing the form and arrangement of the intercalated discs. (M . Heidenhain.) accumulations of anisotropic substance, associated in some 'way with contraction. The heart muscle possesses a large amount of sarcoplasm, as evidenced by the con- FiG. 484. Capillary blood-vessel Undifferentiated sarcopla v**""^ Fibres of cardiac muscle in transverse section. X 375- siderable accumulation surrounding the nucleus, as well as the thicker strata separat- ing the muscle-columns. ' Anatomical Record, vol. v, No. 11, 1911. 464 HUMAN ANATOMY. Fig. 4S5. ■(X - The blood-vessels of striped muscle are very numerous to insure adequate nutrition to a tissue of great functional activity. The larger arteries and accompany- ing veins penetrate the muscle along- the septal extensions of the epimysium and divide into smaller branches which run between the fasciculi. These vessels undergo further subdivision into twigs which pass between the finer bundles of muscle-tibres and ultimately break up into the capillaries enclosing the indi- vidual fibres. The capillary vessels of voluntary muscle form a characteristic net-work consisting of nar- row rectangular meshes (Fig. 485), the longer sides of which correspond to the direction of the muscle-fibres between which they run ; the shorter sides of the meshes are formed by the capillaries which extend across or may encircle the individual fibres. The capillaries supplying muscles subjected to prolonged and powerful contractions often exhibit local dilatations, which may serve for temporary reservoirs for the blood during contraction. The closeness of the capil- lary net-work is determined by the size of the muscle-fibres, muscles composed of fine fibres possessing the smallest vascular meshes. The relation of the blood-vessels to cardiac muscle is unusually intimate, the capillaries not only enclosing the muscle-fibres with a rich net- work, but lying within depressions on the surface of the fibres, or even in channels surrounded by the muscular tissue (Meigs). The lymphatics of striated muscular tissue are represented by the interfascicular clefts, which extend within the connective tissue between the muscle-fibres, and the more definite channels within the septa. The larger lymph-vessels formed by the confluence of those lying between the fasciculi pass to the sheath of the muscle and tendon and carry off the lymph from the muscular tissue. The nerves supplying striped muscle include both motor and sensory fibres. The former terminate in specialized arborizations, the motor nerve-endings, which Injected voluntary muscle, showing arr ment of interfascicular vessels and capill; X50. Fig. 486. Ectoblast. Lateral plate of myotome — - Medial plate of myotome. Parietal mesoblast of. somatopleura Wolffian body Parietal mesoblast V-"**'^i2^>^^^^*"^^^'*^^^ ^^'" Body-cavity Body-cavity Transverse section of rabbit embr>'o, showing differentiation of myotomes, X 90. are usually regarded as lying beneath the sarcolemma upon the sarcous substance. The sensory fibres are connected with the neuro-muscular end organs or muscle- spindles, from which the afferent nerves proceed centrally. The detailed description STRIATED OR VOLUNTARY MUSCLE. 465 of both varieties of terminations in striped muscle will be found under nerve-endings (page 1014). Development of Striped Muscle. — The early appearance of a series of quadrilateral segmental areas, the somites, within the tract of the paraxial mesoblast on each side of the neural tube has been described (page 29). Likewise the sub- sequent breaking up of each somite into the centrally situated sclerotome and the peripheral myotome (Fig. 34). The latter soon becomes a compressed C-shaped mass, in which the more compact lateral part is usually described as the cutis-plaie and the medial portion as the muscle-plate. The histological characters of these parts of the myotome differ, the cutis-plate consisting of several layers of closely packed cells resembling epithelial elements, while the muscle-plate is composed of more loosely disposed spindle-cells, between which lie irregularly round cells, many of Fig. 487. Fig. 488. Frontal section of rabbit embryo, showing myotomes. X loo. Frontal section of two myotomes of rabbit embryo, showing developing muscle. X I3°- which are actively engaged in division. The less differentiated round cells, or myoblasts, become elongated and transformed into the spindle-cells, the elements which are direcdy converted into the young muscle-fibres. The spindle-cells, at first mononuclear, rapidly increase in length, the round or oval nucleus at the same time undergoing division. In consequence the elongated muscle-cells become multinuclear. The cytoplasm of the cells early exhibits clifferentiation into a peripheral and a central zone. During the second foetal month the former manifests a disposition to become fibrillar, while the central zone for a time remains undifferentiated and contains the muscle-nuclei. On cross-section the young muscle-fibres at this stage appear as stippled rings enclosing an indifferent core surrounding the nuclei, the stippling being due to the partially differentiated fibrills. The latter appear first as marginal groups, but later form a continuous peripheral zone. This gradually widens and, by the close of the sixth fcetal month, the fibres composing the muscles of the upper extremity 466 HUMAN ANATOMY. have become fibrillar throughout their entire thickness ; those of the lower ex- tremity acquire a similar condition a month later. With the deeper e.xtension of the fibrillae the characteristic cross-striation appears, the nuclei migrating to the periphery of the fibre as the less differentiated cytoplasm becomes invaded. The sarcolemma appears by the time the entire fibre has become fibrillar. The sarcoplasm surrounding the nuclei of the mature fibre represents the remains of the less highly differentiated cytoplasm of the original muscle-cell ; that, however, separating the muscle-columns must be regarded Fig. 4S9. as the product of a secondary dif- ferentiation. The designation ' ' cutis-plate, ' ' applied to the compact outer epi- thelioid portion of the myotome, expresses the relation to the in- tegument which has been widely accepted, since this part of the myotome is generally regarded as concerned in the formation of the connective-tissue portion of the skin. This fate of the ' ' cutis- plate" was long age denied by Balfour, who held that both layers of the myotome are concerned in the formation of muscular tissue. Kaestner ' arrived at similar conclusions, and more recently Bardeen '' has shown that . in the pig practically the entire epithelial lamella is converted into muscle. According to this investigator, while some of the epithelial elements of the skin-plate degenerate, the greater number undergo mitosis and give rise to myoblasts which, in turn, become the spindle-cells from which the muscle-fibres are developed. The outer margin of the epithelial lamella is sharply defined by a limiting membrane formed by the adja- cent cells ; a somewhat similar but less pronounced boundary guards the inner con- tour of the lamella. The external limiting membrane persists until the conversion of the epithelioid elements into myoblasts and spindle-cells has been well established, by which time the mesoblastic tissue surrounding the myotomes has grown in betiveen the latter and the adjacent ectoblast ; it is from this source, therefore, and not from the "cutis-plate," that the connective-tissue layer of the integument is derived. The masses of embryonal muscle, or myomeres, derived from the somites are early separated by the ingrowth of intersegmental septa of connective tissue which Developing voluntan- 1 ; ?ti]l unslriated. X 525. Fig. 490. fi^^''/' Developing muscle-fibres in which striatif ; just appearing. X 375- later support the intersegmental blood-vessels and nerv'es and, in the thoracic region, the costal elements, and, by the ingrowth of a connective-tissue partition, each one is further divided into a dorsal and a ventral portion, from which, in a general way, the muscles associated with the spine and the antero-lateral body-walls are derived respectively. In this primitive condition the trunk musculature is represented by a series of ' Archiv fiir Anat. u. Phys., Suppl. Bd., icSgo. ' Johns Hopkins Ho.spital Reports, vol ix., 1900. STRIATED OR VOLUNTARY MUSCLE. 467 bands, the myomeres (Fig. 493), which consist of a dorsal and a ventral portion, and which succeed one another regularly and segmentally throughout the entire length of the trunk. The muscle-fibres of which each myomere is composed extend from the intersegmental septum in front to that behind, having thus a regular antero- posterior direction. In the lower vertebrates this condition persists with but little modification throughout life, producing the flake-like arrangement of the muscles characteristic of the fishes. In the higher vertebrates, however, numerous secondary modifications supervene, whereby the myomeres are broken up into individual mus- cles, their original segmental arrangement becoming at the same time greatly ob- scured, although it still persists in those regions in which the muscles are intimately associated with segmental skeletal structures such as the vertebrse and ribs. These changes are of several kinds, and, as a. rule, several varieties of modi- fication cooperate in the differentiation of a muscle. Some of the more important are as follow : 1. An end-to-end fusion of several myomeres or portions of myomeres takes place, producing a muscle-sheet or band which extends uninterruptedly through sev- eral primary segments. Such a modification gives rise to muscles supplied by a number of segmental nerves ; just as many, indeed, as there are myomeres partici- pating in the formation of the muscle. Examples of muscles formed in this way are to be seen in the musculature of the abdominal walls, the oblique muscles, the trans- versalis, and the rectus, for instance, being all polymeric muscles, as are also many of the longitudinal muscles x)i the back. Not infrequently the origin of these mus- cles by the fusion of portions of successive myomeres is shown, independently of their nerve-supply, by the persistence in their course of some of the intermuscular septa, these forming transverse tendinous bands traversing the muscle in a horizontal direction.- Such tendinous inscriptions {inscriptiones tefidiriea:), as they are termed, occur normally in the rectus abdominis, and are also frequently found in the internal oblique, the sterno-hyoid, and the sterno-thyroid muscles. 2. A longitudinal division of the myomeres into a number of distinct and origi- nally parallel portions may occur. Examples of this modification combined with the end-to-end fusion of the portions so formed from successive myomeres are very abundant. Thus, the rectus abdominis is the result of the splitting off of the ventral portion of a number of successive myomeres, whose remaining portions are largely represented in the oblique and transverse abdominal muscles. So, too, in the neck, the difrerentiation of the sterno-hyoid and omo-hyoid is due to the same process, and it has also acted in the differentiation of the various muscles of the transverso- costal group of the dorsal musculature. 3. A tangential splitting of the myomeres is again an occurrence of great fre- quency, producing superposed muscles, and is clearly shown in the dorsal muscula- ture and in the ventro-lateral muscles of the thoracic and abdominal walls. It does not necessarily involve all portions of a myomere when this has already divided longitudinally, but may be confined to only certain of the parts so formed. Thus, while it affects the ventro-lateral abdominal muscles, it does not affect the rectus abdominis, this muscle representing the entire thickness of the ventral borders of a number of successive myomeres. 4. Associated with the change just described there is frequently a modification in the direction of the fibres in one or more of the superposed muscles. Primarily the fibres of each myomere have a cephalo-caudal direction, — a condition which is still retained in the rectus abdominis, for instance. In the ventro-lateral abdominal and thoracic muscles, however, the original direction of the fibres has been greatly altered, those of the superficial layer being directed in general downward and inward, those of the middle layer to a considerable extent downward and outward, while those of the deepest layer are directed almost or quite transversely, — that is to say, in a direction which is 90° different from that taken by the fibres of the myomere. 5. An exceedingly interesting modification is that which results from the migra- tion of some of the myomeres over their successors, so that a muscle formed from certain of the cervical myomeres, for example, may in the adult condition be super- posed upon muscles derived from the thoracic segments. In such cases of migration 468 HUMAN ANATOMY. the segmental nerve, or at least those fibres of it which originally supplied the por- tions of the myomeres in question, retains its connection and is consequently drawn out far beyond its usual territory, a ready explanation being thus afforded for the extended course of the long thoracic, long subscapular, and phrenic nerves. The muscles supplied by these nerves, as well as the pectoralis major and minor muscles, are all derived from cervical myomeres, their adult position being due to the process of migration, of whose existence they form convincing examples. 6. Finally, portions of one or several successive myomeres may undergo degen- eration, becoming converted into connective tissue, which may have the form of fascia, aponeurosis, or tendon. Examples of this degeneration are to be found in practically all muscles, since the tendons by which they make their bony attachments have resulted from its action. In the lower vertebrates and in the foetus tendons and aponeuroses are much less developed than in the higher forms or in the adult, being represented by muscular tissue which later becomes con\erted into tendon or aponeurosis. The intermuscular septa between the muscles of the limbs seem to have arisen in this way, and occasionally relatively large aponeurotic sheets have so arisen, as in the case of the aponeurosis which unites the two posterior serratus muscles. Of especial interest in this connection are the degenerations into liga- ments of muscle-tissue primarily occurring in the neighborhood of many of the joints, the accessory ligaments being in many cases formed in this manner. Thus, the external lateral ligament of the knee-joint, the ligamentum teres of the hip-joint, and even the great sacro-sciatic ligament owe their origin to this process, and many other of the ligaments may also be referred to it. As a result of these various modifications and their combinations the individual muscles of the adult body, together with the aponeurotic sheets which are frequently associated with them, are formed. GENERAL CONSIDERATION OF THE VOLUNTARY MUSCLES. The voluntary or striated muscles constitute a very considerable portion of the entire mass of the body, their weight in an average adult male having been esti- mated at about 43.4 per cent, of the total body weight ( Vierordt). Each muscle is a distinct organ composed of a number of contractile fibres united into bundles or fasciculi surrounded by a delicate sheath of connective tissue, the perirnysium, in which blood-vessels and ner\es ramify to the various fasciculi, and which, at the surface of the muscle, is continuous with the fascia which encloses the entire organ. At each extremity of the muscle the contractile tissue is united with dense connective tissue, the general structure of which resembles that of the muscle, its fibres being arranged in distinct bundles separated and enclosed by looser tissue comparable to the perimysium. By means of these tendons, as they may generi- cally be termed, the attachment of the muscle to portions of the skeleton or other structures is effected. The extent to which the tendon is developed varies greatly in different muscles, in some being hardly noticeable, so that the mu.scle-tissue appears to be directly attached to the bone (Fig. 496), at other times forming a long rounded or flattened band (Fig. 576), to which the term tendon is usually applied, or again forming a broad, flat expansion, termed an aponeurosis (Fig. 525). Both the tendons and aponeuroses are to be regarded as representing portions of the original muscle converted into connective tissue, and, indeed, comparative anatomy shows that many of the ligaments and aponeuroses of the body, even although they may not seem to be directly related to neighboring muscles, are really to be regarded as muscles which have undergone a tendinous degeneration. Attachments. — The great majority of the voluntary muscles are attached at either end to portions of the skeleton, passing over one or more joints, in which they effect movement by their contraction. Occasionally, however, a muscle may be attached at one of its extremities, in part or entirely, to fascia, as, for instance, the gluteus maximus and the tensor fasciae latae, or both of its attachments may be to fascia, as is the case with some of the muscles of expression and with the muscles of the palate and the intrinsic musculature of the tongue. Others, again, may have their attachments to tendons of other muscles, — e.g., the flexor accessorius pedis GENERAL CONSIDERATION OF THE VOLUNTARY MUSCLES. 469 and the lumbricales, — while others may pass between portions of the skeleton and special organs upon which they act, as is exemplified by the muscles of the eyeball. Whatever may be the nature of the structure to which the attachment is made, it is convenient for purposes of description to regard one of the points of attachment of each muscle as the fixed point from which it acts in contraction, and to speak of this as its origin, and to regard the other as the point upon which it acts, speaking of it as the insertion. It must be understood, however, that this distinction between the two attachments is somewhat arbitrary, since what is usually the fixed point may under certain circumstances become the movable one. For instance, in the case of a muscle passing frpm the pelvis to a leg bone, if the body be erect, the contraction of the muscle will cause an inclination of the trunk on the hip-joint, the attachment to the leg bone being then the fixed point and that to the pelvis the movable one. In other positions of the body, however, the contraction of the muscle will produce a movement of the leg, the fixed and movable points being exactly reversed. Since, however, the movement of the leg may be regarded as the more usual result of the contraction of the muscle, the pelvic attachment is arbitrarily regarded as the origin and the attachment to the femur or tibia the insertion of the muscle in question. Fig. 491. septa of insertion Tendon of insertion. Diagrams showing semi-pinnate (A) and pinnate {B) arrangement of muscle-fibres, which pass from tendo origin above to that of insertion below. C, compound pinnate arrangement, as in central division of deltoid mu: (After Poirier.) Form. — The muscles assume various forms, dependent to some extent upon the structures to which they are attached. Some are thin sheets with almost parallel fibres, others are more or less band-like, while others may have considerable thick- ness, and be quadrate, triangular, or spindle-shaped. Surrounding certain of the orifices of the body are what are termed orbicular or sphincter muscles (Figs. 495, 499), consisting of a muscular sheet whose fibres have a crescentic course around either side of the orifice, the lips of which will tend to be drawn together by the con- traction of the muscle. Where the surfaces for attachment are considerable, the fibres composing a muscle have a more or less parallel course ; but where a comparatively small area is all that is available for the attachment of a strong muscle, as is the case with many of the limb muscles, it is clear that such an arrangement cannot obtain. The muscle- fibres then converge from either one or both sides to be inserted one above the other into the tendon, forming what is termed a semipinnate (e. g. , many of the muscles of the leg. Fig. 609), or pinnate \\\\mz\& (e. g. , interossei dorsales. Fig. 590.) This convergence may take place towards either one or both tendons of attachment, and occasionally these may spread out over opposite surfaces of the muscle to form apo- neurotic sheets which overlap, so that the muscle-fibres pass obliquely from the sur- face of one tendon to that of the other (e.g., gastrocnemius, semitendinosus, Fig. 635). Finally, in some of the broader muscles (e.g., deltoid and subscapularis) the muscle-fibres may arise from and converge to a series of tendinous bands which 470 HUMAN ANATOMY. alternate with one another, the muscle having thus a compoioid pinnate arrangement (Fig. 491, C). As a rule, the tendons occur in connection with the e.xtremities of the muscle, but occasionally one or more tendinous intersections may occur in the course of the muscle, which thus becomes divided into two or more bellies. This condition may be the result of the end-to-end union of the tendons of attachment of two primarily distinct muscles {e.g., digastric. Fig. 497) or to the persistence of some of the dividing lines which separate the x-arious embryonic segments of which a muscle may be composed {e.g., rectus abdominis, Fig. 523) ; or it riiay be due to a sec- ondary attachment formed by a muscle in its course, it being bound down to a neighboring bone by a band of fascia {e.g., omo-hyoid). Certain muscles present the peculiarity of possessing two or more separate heads of origin, attached to different bones and uniting to form a common tendon of insertion. In certain cases {e.g., biceps femoris, pronator radii teres) this condition indicates the union of two primarily distinct muscles which had a common insertion, or which were, at all events, originally inserted close together, but in other cases it has resulted from a separation of an original muscle into two portions. The ana- tomical nomenclature is not quite consistent as regards such muscles, since it describes the biceps femoris as a two-headed muscle, although its two heads are fundamentally distinct organs ; while, on the other hand, it usually regards the psoas and iliacus and the gastrocnemius and soleus as distinct muscles, notwith- standing their common insertion. Fasciae. — Connecting the various muscles and uniting them into groups, and also surrounding the entire musculature of the body and separating it from the deeper layers of the integument, are sheets of connective tissue known as fascia. These sheets are by no means isolated portions of connective tissue, but are rather to be regarded as parts of the general interstitial connective-tissue net-work which traverses all parts of the body, thickened to form more or less definite sheets stand- ing in relation to the neighboring organs. The density of the sheets varies greatly ; in some regions they are imperfectly developed and may contain considerable amounts of fat, while in others they form dense, glistening sheets resembling the expansions of tendons mentioned above, and termed, like these, aponeuroses. It is convenient to recognize two principal layers of fascise, the superficial and the deep. The superficial fascia immediately underlies the skin of the entire body, and is sometimes considered a portion of it and termed the panniculus adiposus, since, except in the eyelids, penis, scrotum, and labia minora, it contains considerable quan- tities of fat. It is connected with the subjacent deep fascia by a more or less e.xten- sively developed layer of areolar tissue, which, however, is lacking in certain regions, such, for instance, as the face, the palmar surface of the hand, and the plantar surface of the foot, where the superficial and deep fasciae are intimately united. The deep fascia, on the other hand, immediately covers and invests the muscles, and in the intervals between them becomes continuous with the periosteal connec- tive tissue enclosing the bones. Those lamellze of the fascia which dip down between the muscles of the limbs — the intermuscular septa — are frequently of con- siderable firmness and serve for the origin of fibres of the neighboring muscles, and occasionally muscles {e.g. , soleus, levator ani) take their origin in part directly from portions of the deep fascia, which then becomes thickened along the line of the origin to form strong bands, termed arcus tendinei, attached at either extremity to neighboring bones. Certain portions of the deep fascia, and especially of the intermuscular septa, represent portions of the muscular system which have undergone tendinous degen- eration, and are represented by muscular tissue in the lower vertebrates. Indeed, the relative amount of aponeurotic and tendinous tissue, as compared with the mus- cular, is very much greater in the higher than in the lower forms, and is appre- ciably greater in the human embryo than in the adult, indicating a transformation of one tissue into the other during the life of the individual. Tendon-Sheaths. — Where tendons run in grooves of bones, bands of dense connective tissue extend across between the lips of the grooves, being continuous GENERAL CONSIDERATION OF THE VOLUNTARY MUSCLES. 471 there with the periosteum, and convert the grooves into canals within which the ten- dons are enclosed, although capable of free movement to and fro. These connective- tissue bands are the tendon-sheaths, and the canals which they assist in forming may contain one or more tendons. Each sheath is lined on its deeper surface by a synovial membrane similar to those occurring in the joints, and at either extremity of the sheath this membrane is reflected upon the tendon which it encloses, so that the tendon is contained within a double-walled cylinder whose cavity is filled with a fluid serving to diminish friction during the movements of the tendon (Fig. 492). It is customary to distinguish the synovial portion of a tendon-sheath as the serous or synovial sheath ( vagina mucosa ) from the fibrous sheath {vagina fibrosa) with which it is always closely con- "^ nected. Strands of connective tissue pass at intervals across the synovial cavity of the sheath from the floor of the groove on the bone and transmit blood-vessels to the tendon ; these strands constitute what are termed viti- cida tendinum, or, from their general similarity to the mesentery, niesotendons. In some cases a tendon-sheath may serve to a cer- tain e.xtent as a pulley, affording a smooth surface o^'er 'which the tendon changes its direction, as in the case of the extensor tendons of the hand when this is partly extended. A special development of this condition is to be seen in the tendinous loop {troclilea muscularis) over which the tendon of the superior oblique muscle of the eyeball is reflected (Fig. 516). Bursae. — The intervals between the various muscles and between these or their tendons and the bone are occupied by loose areolar tissue. In situations in which a muscle or tendon in its movements comes in contact with a bony prominence, or in which two tendons glide upon each other, the spaces of the areolar tissue enlarge and become filled by a fluid resembling that of the synovial cavities, the result being the formation of what is termed a bursa, whose purpose is to diminish the friction between the muscle or tendon and the bone. Examples of such bursae are to be found abun- dantly in connection with the muscles of the limbs, and some of those which occur in the vicinity of joints frequently fuse with the adjacent synovial cavities ; the bursa of the subscapularis, situated between that muscle and the neck of the scapula, for instance, uniting with the synovial cavity of the shoulder-joint, and the bursa supra- patellaris, between the tendon of the quadriceps femoris and the femur, fusing with the cavity of the knee-joint. Bursae are also developed in the areolar tissue intervening between the superficial and deep fascise in situations in which the integument rests directly upon a bone, as, for instance, over the olecranon process, and is frequently subjected to pressure in that region. Such bursae are termed sitbaitaneous bursts to distinguish them from those developed in connection with the muscles. Classification of the Muscles. — The muscles may be classified according to three plans : they may be arranged according to their topographical relations, according to their physiological significance, or, finally, upon a morphological basis, their embryological or developmental significance forming the guide for their arrange- ment in groups. In the following pages the last-named plan will be followed as far as possible. Embryologically the skeletal muscles are formed, for the most part, from a series of segmentally arranged masses of mesoblast — the mesoblastic somites — which appear at an early stage of development on either side of the notochord and later extend ventrally towards the mid- ventral line (page 465). That portion of the musculature which has such an origin may be regarded as consisting primarily of a series of plates arranged segmentally along each side of the body, each plate corresponding to and being supplied by one of the segmental nerves and by those fibres of it which arise from the cells of the anterior horn of the spinal cord or their homologues in other portions of the central nervous system. A diagrammatic representation of this mus- culature in its primary condition is shown in Fig. 493, and from this it will be per- ceived that the series of muscle-plates extends throughout the entire trunk and neck 472 HUMAN ANATOMY. Fig. 493- regions of the body and to a certain extent into the head region, there being, how- ever, in this last region a considerable area in which the muscle-plates are unrepre- sented. Throughout this area of the head region muscles occur which arise in relation to the branchial arches and, accordingly, in a much more ventral position than the mesodermic somites. Furthermore, these muscles are supplied by branches from the mi.xed cranial nerves, arising from cells situated in a portion of the medulla oblongata which is comparable to the lateral horn of the spinal cord and con- stituting" what are termed lateral motor roots, in contradistinction to the median or anterior motor roots which supply the muscles derived from the mesodermic somites. There are thus two sharply defined systems of musculature : the one, primarily confined to the cranial region, is supplied by lateral motor nerves, and from its rela- tion to the branchial arches maybe X.&x'nxaAxiv^ branchiomcric musculature ; the other, supplied by anterior motor nerves, is arranged primarily in a series of segmental (metameric) plates, and may be termed the metameric mtts- culatitrc. These two systems constitute. the first divisions in the morphological classifica- tion of the musculature. The further subdivision of the branchio- meric muscles is most conveniently made with reference to the various cranial nerves by which they are supplied. For the metameric musculature a more complicated subdivision is both necessary and con\enient, and in the first place it may be divided into the axial and the appet!dic7-go-spinosus bears to the spheno-mandibular ligament seems to indicate that it represents the musculature of that portion of the mandibular arch which has become transformed into the ligament, and that usually it is represented by the connective tissue enclosing the ligament. (*) THE SUBMEXTx\L MUSCLES. I. Mylo-hyoideus. 2. Digastricus (Anterior Belly). This group of trigeminal muscles contains but two representatives, the mylo- hyoid and the anterior belly of the digastric. This latter muscle, as ordinarily described, consists of two distinct muscles united at their attachment to the hyoid bone, the anterior of the two muscles belonging to the trigeminal group, while the posterior is a member of the facial group. It will be convenient to describe the muscle as a whole, even although it belongs only in part to the group under con- sideration. I. Mylo-Hyoideus (Fig. 497). Attachments. — The mylo-hyoid a?-ises from practically the entire length of the mylo-hyoid ridge of the mandible, from which the fibres pass inward and slightly backward to be inserted for the most part into a median fibrous raphe common to the two muscles of opposite sides, the posterior fibres, however, being attached to the upper border of the body of the hyoid bone. The two muscles, taken together, form a muscular floor for the mouth, the diaphragma oris, upon which the tongue may be said to rest. Nerve-Supply. — By the mylo-hyoid from the inferior dental branch of the mandibular division of the trigeminus. Action. — To draw the hyoid bone upward and at the same time to raise the floor of the mouth, pressing the tongue against the palate. Relations. — The superficial surface of the mylo-hyoid is in relation with the anterior belly of the digastric and with the facial artery. The subma.xillar)^ gland curves around its posterior free margin and is thus in relation with both its surfaces, the submaxillary duct running forward upon its deeper surface. This latter surface is also in relation ^\■ith the genio-hyoid, genio-glossal, hyo-glossal, and stylo-glossal muscles, with the sublingual gland, and with the lingual branch of the trigeminus and the hypoglossal ner\'e. 2. Digastricus (Figs. 497, 502). Attachments. — The digastric, as its name indicates, consists of two bellies which are united by a strong cylindrical tendon. The anterior bellv, which alone belongs to the trigeminal group of muscles, arises from the digastric fossa of the mandible, and is directed downward, backward, and slighdy outward to become con- 478 HUMAN ANATOMY. tinuous with the intermediate tendon. This is bound down to the greater horn and body of the hyoid bone by a pulley-like band of the cervical fascia and to a certain extent by the stylo-hyoid muscle, which divides near its insertion into the hyoid into two slips, between which the tendon of the digastric passes. The posterior belly ( Fig. 502 ) takes its origin from the mastoid groove of the temporal bone, and passes downward and forward to become connected with the intermediate tendon, Nerve-Supply. — The anterior belly is supplied by the mylo-hyoid nerve from the inferior dental branch of the mandibular division of the trigeminus, the posterior belly by the digastric branch of the facial. Action. — The digastric either raises the hyoid bone or depresses the jaw, Fig. 497. Genio-hyoid (mjio-hyoid removed) F.iscial loop binding tiiulons to liyoid bone Thyro-hyoid membraii Stylo-glossus- Internal pterygoid- Thyro-h Thyroid carlilaK" Stylo-pharyngeu Crico-thyroid— 7 , Digastric, i posterior belly il_LTlivroid gland tracbea lias been ramidalisnasi Lev, labii sup. alseque n Compressor r Dilatores naris Depressor alse nasi Orbicularis oris Depiessor ang-uli oris Depressor labii inferioris Le\ator menti Superficial dissection of head, siiowing' platysma muscles. 4. Auricularis Superior (Fig. 499). Attachments. — The superior auricular {attollens aurem) is a triangular muscle which arises from the lateral portion of the galea aponeurotica or from the temporal fascia and converges to be inserted into the upper part of the cartilage of the auricle. Nerve-Supply. — By fibres from the rami temporales of the facial nerve. Action. — To draw the auricle upward. 5. Auricularis Anterior (Fig. 499). Attachments. — The anterior auricular (attrahefis aureni) is frequently con- tinuous with the preceding muscle, lying immediately anterior to it. It arises from the lateral part of the galea aponeurotica or from the temporal fascia and is inserted into the upper anterior part of the auricular cartilage or into the fascia immediately anterior to the cartilage. 484 HUMAN ANATOMY. Nerve-Supply. — By fibres from the rami temporales of the facial ner^'e. . Action. — To draw the auricle upward and forward. Internal palpebral ligament Tensor tarsi Fig. 500. Orbicularis palpebrarum a' 6. Orbicularis Palpebrarum (Figs. 499, 500). The orbicularis palpebrarum (m. orbicularis oculi) is an elliptical sheet whose fibres have their origin in the neighborhood of the inner angle of the eye and curve thence, some upward and outward and some downward and outward, around the rima palpebralis to terminate in the neighborhood of the external angle. The course of the fibres lies partly in the substance of the upper and lower eyelids and partly over the bones surrounding the margin of the orbit. In accordance with these relations, it is customarv to regard the muscle as consisting of two main portions, the pars palpe- bralis and the pars orbitalis. The internal palpebral ligament (ligamentum palpebrale mediale). Where the fibres of the orbicularis arise at the inner angle of the eye there is a dense band of fibrous tissue which is attached at one extremity to the frontal process of the maxilla. Thence it is directed outward across the outer surface of the lachrymal sac and bifur- cates to be inserted into the inner border of each tarsal plate. Just before its bifur- cation the ligament gives off from its posterior surface a bundle which is reflected inward over the lachrymal sac and passes behind this to be attached to the crest of the lachrymal bone. This ligament, which is also known as the tendo oculi, ma)' be regarded as the tendon of origin of the fibres of the orbicularis oculi. At the outer angle of the eye there is a certain amount of decussation of the fibres of the muscle to form a raphe palpebralis lateralis, but there is no distinct formation of a fibrous band comparable to the inter- nal ligament. iPars Palpebralis. — The palpe- bral portion of the muscle arises partly from the internal palpebral ligament and partly from the crest of the lachrymal bone. The fibres which take origin from the ligament arch outward in the upper and lower eyelids to terminate in the lateral palpebral raphe, forming a thin, pale sheet in the subcutaneous tissue of the eyelid. Its marginal fibres, sometimes more or less distinct from the others, form what has been termed Xhe pars ciliaris or muscle of Riolan. The fibres which arise from the posterior lachrymal crest are usually reg-arded as forming either a distinct muscle, which has been termed the te7isor tarsi or Horner' s muscle, or else as a separate part of the orbicularis, the pars lacrimalis. It is directed horizontally outward behind the lachrymal sac, resting upon the posterior surface of the reflected bundle of the internal palpebral ligament. Towards its outer end it bifurcates, sending a slip to each eyelid partly to be inserted into the tarsal plates and partly to fuse with the rest of the pars palpebralis. Pars Orbitalis. — The orbital portion of the muscle is usually of a deeper color and somewhat thicker than the palpebral, and the fibres towards its periphery tend to scatter themselves among the adjacent platysma muscles and to make num.erous connections with these. Some bundles from the lateral and lower parts of the muscle which extend downward and forward upon the cheek have been regarded as a dis- t'nct muscle, the malaris. The main muscle arises from the internal palpebral ligament, the frontal process of the maxilla, and the inner portions of the upper and lower margins of the orbit. The fibres arch outward to the lateral palpebral raphe, a portion of those arising from the maxilla inserting into the integument of the eyebrow and forming what has been termed the corrugator supercilii (Fig. 499). Nerve-Supply. — By the rami temporales and zygomatici of the facial nerve. Orbicularis palpeb; surface and reflected I portion or tensor tarsi. r tarsal plate ^Orbicularis palpebrarum T has been dissected from its deeper d with eyelids, showing lachrj mal THE FACIAL MUSCLES. 485 Action. — The principal action of the orbicularis palpebrarum is to approximate the upper and lower eyelids, closing the palpebral fissure. In addition, the attach- ment of the orbital portion to the skin draws the eyebrow downward and the skin of the cheek upward to form a fold around the margin of the orbit, giving increased protection to the eyeball. The corrugator supercilii draws the eyebrow downward and inward, producing vertical wrinkles of the integument over the glabella and giving a thoughtful expression. The pars lacrimalis draws the tarsal plates inward and backward and so tenses the internal palpebral ligament, causing it to compress the lachrymal sac. 7. Zygomaticus Major (Figs. 499, 502). Attachments. — The zygomaticus major (m. zygomaticus) is a slender muscle which arises above from the outer surface of the zygomatic bone, near its articulation with the zygomatic process of the temporal, and passes obliquely downward and for- ward towards the angle of the mouth. Its fibres interlace with those of the depressor and levator anguli oris, and terminate by blending with the orbicularis oris and by inserting into the subcutaneous tissue of the lips. Nerve-Supply. — By fibres from the zygomatic branch of the facial nerve. Action. — To draw upward and outward the angles of the mouth, as in smiling and laughing. Variations. — A slender muscle is very frequently found arising from the zygomatic bone anterior to the zygomaticus and passing downward to be inserted into the upper lip. It has been termed the zygomaticus minor, and appears to be a separation of a portion of the zygo- matic muscle. 8. Levator Labii Superioris Al^que Nasi (Figs. 499, 501). Attachments. — This muscle takes its origin from the outer surface of the frontal process of the maxilla, and descends along the angle which marks the junction of the nose and the cheek to be inserted into the integument of the upper lip and into the posterior part of the ala nasi. Nerve-Supply. — From the rami zygomatici of the facial nerve. Action. — The principal action of this muscle is to raise the upper lip, although its insertion into the ala nasi enables it to assist in the dilatation of the nostrils. Variations. — This muscle is subject to considerable variation in its development, and frequently comes into continuity with neighboring muscles, especially «'ith the zygomaticus minor, when this is present, and with the levator labii superioris proprius. Indeed, these two muscles are often associated with it to form what is termed the qjiadraius labii superioris, of which the levator labii superioris alasque nasi forms the caput annulare, the levator labii superi- oris proprius the caput infraorbitale, and the zygomaticus minor the caput zygomaticus. Since, however, the levator labii superioris proprius belongs to the deep layer of the platysma muscles, and therefore to a different group than the other heads of the quadratus, it seems preferable to regard all the heads as distinct muscles. 9. Depressor Labii Inferioris (Figs. 498, 499). Attachments. — The depressor of the lower lips (m. quadratus labii inferioris) arises from the body of the mandible beneath the canine and premolar teeth, its origin being covered by the depressor anguli oris. It forms a thin quadrate sheet which is directed upward and forward and is inserted in the skin of the lower lip, its fibres mingling also with those of the orbicularis oris. Nerve-Supply. — From the supramandibular branch of the facial nerve. Action. — To draw down the lower lip. 10. Levator Menti (Fig. 498). Attachments. — The levator menti (m. mentalis) arises from the body of the mandible below the incisor teeth, and its fibres descend, diverging as they go, to be inserted into the integument above the point of the chin. Nerve-Supply. — From the supramandibular branch of the facial nerve. 486 HUMAN ANATOMY. Action. — To draw up-nard the skin of the chin, thereby causing protrusion of the lower lip, as in pouting. When its action is combined with contraction of the depressors oi the angles oi the month, it gives an expression of haughtiness or con- tempt, and has thence been termed the ?n. superbus. When slightly contracted, it gives an expression oi firmness or decision. Belonging to the superficial layer of the platysma musculature are a number of additional more or less rudimentarj- muscles attached at both extremities to various parts of the cartilage of the concha. These muscles will be considered in connection with the description of the ear (page 1499). (6) THE MUSCLES OF THE DEEP L.WER. I. Orbicularis Oris (Figs. 499. 501, 503). Attachments. — The orbictilaris oris is a rather strong elliptical muscle whose fibres occupv the thickness of both the upper and lower lips between the skin and the mucous membrane of the mouth. For the most part the fibres comjxising the muscle are foraard prolongations of the buccinator, but mingled with these there are fibres from all the muscles which are inserted in the x-icinit)- of the mouth, such as the rvgomaticus, levator anguli oris, levator labii supierioris, depressor anguli oris, depressor labii inferioris, and risorius. It possesses, however, some slight attachment to skeletal structures by three groups of fibres which have frequently been regarded as distinct muscles. These groujjs are : ( i j the incisivi labii superioris, a series of bundles of fibres which arise from the incisive fossze of the maxillae and pass downward and outward to mingle with the other fibres of the orbicularis at the angles of the mouth ; ( 2 ) the iruisivi labii inferioris. which arise from the alveolar border of the mandible beneath the canine teeth and unite with the orbicularis at the angles of the mouth : and (3) the depressor septi, composed of the uppermost fibres of the orbicularis, which bend up- ward from either side in the median line and are inserted into the margin of the septal cartilage of the nose- Nerve-Supply. — From the rami buccales and supramandibular branch of the facial ner\e. Action. — The main action of the orbicularis oris is to bring the lips together, closing the mouth, and if its action be continued, it will press the lips against the teeth. Its more peripheral fibres, aided by Fig. 501. the incisive bundles, wUl tend to pro- P}-ramidalis nasi tTude the lipS. 2. N.\s.\Lis (Fig. 501). Attachments. — The nasalis forms a thin sheet which arises from the maxilla in close association with the incisive bundles of the upper lip. The more medial fibres, the pars alaris (depressor ala nasi ) , are inseiied into the alar cartilage of the nose, while the more lateral ones, the pars trans- versa (compressor narium), often re- cei\-ing slips from the adjacent levator labii superioris alaeque nasi and the levator anguli oris, extend forward over the ala of the nose to terminate Ufjon its dorsal surface in a thin aponeurosis which unites it to the muscle of the opposite side. Nerve-Supply. — From the zygomatic and buccal rami of the facial ner\'e. Action. — The more median fibres draw the alar cartilage downward and in- ward, while the more lateral ones slighdy depress the tip of the nose and at the same time compress the nostril. ^Dilalores naris Muscles of the nose. THE FACIAL MUSCLES. 487 Variations, — Fibres from the nasalis sometimes pass upward upon the nasal bones and may enter into the formation of the pyramidalis nasi (page 482). Frequently the pars alaris and pars transversa are recognized as distinct muscles, the former being termed the depressor ala: nasi or mvrliformis, while the lattfer is named the compressor narium. Uncertain and at best feeble muscular slips on the outer margin of the nostrils are sometimes described as distinct muscles, the dilatores naris anterior et posterior. 3. Levator Labii Superioris (Fig. 499). Attachments. — The elevator of the upper Hp (m. levator labii superioris pro- prius) arises above from the infraorbital margin of the maxilla and e.xtends almost vertically downward over the infraorbital vessels and nerve to join with the orbicu- laris oris and also to be inserted into the skin of the upper lip between the insertions of the levator labii superioris alseque nasi and the levator anguli oris. Nerve-Supply. — From the zygomatic branches of the facial nerve. Action. — To raise the upper lip. Acting in conjunction with the levator labii superioris alaeque nasi, it plays an important part in the expression of grief. 4. Levator Anguli Oris (Figs. 499, 502). Attachments. — The elevator of the angle of the mouth (m. caninus ) arises from the canine fossa of the maxilla by a rather broad origin, from which its fibres con- verge to be ijiserted into the skin at the angle of the mouth, partly mingling with the fibres of the depressor anguli oris. Nerve-Supply. — From the zygomatic branches of the facial nerve. Action. — To raise the angfle of the mouth. 5. RisoRius (Fig. 499). Attachments. — The risorius is a triangular sheet of muscle which arises from the outer surface of the parotido-masseteric fascia and from the integument of the cheek and passes forward towards the angle of the mouth, where it unites with the depressor anguli and orbicularis oris. Nerve-Supply. — From the rami buccales of the facial nerve. Action. — To draw the angle of the mouth outward. Its contraction imparts a tense and strained expression to the face which is termed the risus sardonicus. Variation. — The risorius is frequently absent, and may be represented only by some scattered muscular bands. Its intimate association with the depressor anguli oris indicates its derivation from that muscle. 6. Depressor Anguli Oris (Figs. 498, 499). Attachments. — The depressor of the angle of the mouth (m. triangularis) takes its origin from the outer surface of the body of the mandible and from the skin and passes upward to the angle of the mouth, where its fibres are inserted into the skin and also mingle with those of the caninus, risorius, and orbicuraris oris. Nerve-Supply. — From the supramarginal branch of the facial nerve. Action. — To draw the angle of the mouth downward and slightly outward, giving an expression of sorrow. Variations. — A bundle of fibres not infrequently arises from the anterior border of the depressor anguli oris near its origin and passes obliquely downward and inward towards the median line beneath the chin, either losing itself in the superficial fascia of that region or uniting with its fellow of the opposite side. This slip has been regarded as a distinct muscle and termed the transversiis menti. It seems exceedingly probable that both this bundle and the risorius are derivatives of the depressor, and this muscle, notwithstanding its position super- ficial to both the depressor labii inferioris and the platysma, is really a portion of the deeper layer of the platysma musculature, its present position having iDeen acquired by a migration from the region of the upper lip. 488 HUMAN ANATOMY. 7. Buccinator (Fig. 502). Bucco-Pharyngeal Fascia. — The buccinator .alone of the platysma group of muscles is covered by a distinct layer of fascia which forms the anterior part of .the fascia buccopharyngea and is a dense, resistant sheet of connective tissue intimately Fig. 502. Corrugator superciHi Orbtc. palp., palpebral part dalis nasi Orbic. palp., orbital part . Lev, labii sup. al. nasi (cut) _\,^ Levator labii superioris (cut) pressor narium Levator anguli oris Zygomatic us w Tensor palati ^ Levator palati Styloid process Hamular process Digastric, posterior bell Superior constrii Stylo-gl, Pteo'go-mandihular ligament Stylo-phyarjngeus Stylo.hyoid Mandible (cut) Hyo-glossus Greater hyoid cornu Middle constrictor Oral, pharyngeal, and styloid groups of Jt^ — Depressor labii Levator menti ; part of mandible has been removed to show deeper structures. adherent to the outer surface of the muscle. Anteriorly the fascia thins out to disap- pear in the tissue of the lips ; above it is attached to the aheolar portion of the maxilla and to the internal pterygoid plate of the sphenoid, and thence is continued backward over the superior con- FiG. 503. stricter muscle of the pharynx to meet with its fellow of the opposite side behind the phar- ynx ; below it is attached to the '■' posterior part of the mylo-hyoid ridge of the mandible. Along a line which descends vertically from the tip of the hamulus of the sphenoid to the posterior extremity of the mylo-hyoid ridge of the mandible the fascia is greatly thickened, forming the ptervgo-niandibiilar liga- 7ne7if, from which fibres of the buccinator arise anteriorly, while posteriorly it gives origin to a portion of the superior constric- tor of the pharynx. Attachments. — The buc- cinator forms a thick quadrilateral muscle lying immediately exterior to the mucous membrane of the cheek. Its line of origin is horseshoe-shaped, extending above along the alveolar border and tuberosity of the maxilla and thence upon the hamulus L.evator anguli oris anguli oris PRACTICAL CONSIDERATIONS : THE SCALP. 489 of the internal pterygoid plate of the sphenoid. It then descends upon the anterior border of the pterygo-mandibular raphe, whence it passes forward along the body of the mandible, above the mylo-hyoid ridge, as far as the premolar teeth. F"rom this e.xtensive origin its fibres are directed forward to become continuous with those of the orbicularis oris, also inserting to a certain extent into the integument of the lips. Nerve-Supply. — From the buccal branch of the facial nerve. Action. — The buccinator draws the angle of the mouth laterally, pressing the lips against the teeth. When the cheeks are distended the muscle serves to com- press the contents of the mouth, and plays an important part in mastication in pre- venting the accumulation of the food between the cheek and the jaws, forcing it back between the teeth. Relations. — Superficially with the bucco-pharyngeal fascia, which is separated from the anterior part of the masseter and from the zygomaticus and risorius by an extensive pad of fat, — the buccal fat-pad. This is prolonged backward into the zygo- matic fossa between the temporal and pterygoid muscles, and is traversed by the facial vessels and the buccal branches of the trigeminal and facial nerves. The buccinator is pierced from without inward by the parotid duct and by the buccal branch of the trigeminal nerve on its way towards its distribution to the mucous membrane of the cheek. PRACTICAL CONSIDERATIONS : MUSCLES AND FASCIA OF THE CRANIUM. The Scalp. — The Occipito- Frontal Region. — The layers of the scalp from within outward are : I. The pericraniu7n — as the periosteum covering this part of the skull is termed — closely invests the underlying bones and is firmly attached at the sutures through which, so long as these remain ununited, it is continuous ( intersutural mem- brane) with the outer layer of the dura, — the endosteum of the cranium. A similar Fig 504 ■S perficial fascia Portion of frontal section of liead hardened and more constant continuity exists through the foramina. As the dura is the chief source of blood-supply of the cranial bones, they rarely necrose after accidents which strip the pericranium from their surface (page 237). Subpericranial effusions of blood, or collections of pus, are limited and outlined by the lines of the sutures. "CephalhEematomata" in this situation correspond in shape to that of one bone ; they are commonly congenital, constituting a form of caput succedaneum, following head presentations, and are then apt to be found over a parietal bone, since that region is most exposed to pressure during child-birth. Tillaux suggests that in early life they may be encouraged by the softness and vascularity of the cranial bones and the 490 HUMAN ANATOMY. laxity of the pericranium, and that their greater frequency in male children may depend upon the larger size of the head in the male foetus. The close association of the bloody effusion with the pericranium — an osteogenetic membrane — sometimes results in the development of bone at the periphery of the swelling. The hard ridge which is usually present at this situation may give rise, through contrast with the relatively depressed centre, to the mistaken diagnosis of fracture of the skull. Occasionally a collection of blood beneath the pericranium communicates with the diploic sinuses, when it will probably be situated to one side of the cranium ; or with the superior longitudinal sinus, when it will be in the mid-line. No traumatic history may be obtainable. The swelling will be soft, reducible, of varying tension, and may receive from the brain a feeble pulsatile impulse. The importance of the emissary veins in transmitting extracranial infection to the venous channels of the dura may be mentioned here, but can better be under- stood after the venous system has been described (page 876). 2. The subaponeurotic connective tissue betv\een the pericranium and the apo- neurosis of the occipito-frontalis. This is so loose, thin, and elastic that the union between these layers is not a close one. The motion of the "scalp" upon the skull is a motion of the parts above upon the parts beneath this layer. Movable growths will, therefore, be found to occupy the former region and immovable swellings will probably have deeper attachments. Effusions of blood, suppuration, or infective cellulitis occurring in the subaponeurotic space may extend widely, and may be limited only by the attachments of the musculo-fibrous layer. They may reach, there- fore, posteriorly to the superior curved line of the occipital bone, anteriorly to a little above the eyebrows, and laterally to a level somewhat above the zygoma. Exten- sive h;ematomata are uncommon, as the vessels in this cellular tissue are few and small. If they are large, they suggest fracture of the skull with laceration of a branch of the middle meningeal artery or of a venous sinus. They may, however, by reason of a hard border and soft centre, be mistaken for depressed fracture when the skull itself is uninjured. Suppuration and cellulitis are often serious on account of the tendency to spread, the possible extension to the meninges, and the difficulty in applying antisepsis, in securing drainage, or, later, in obtaining the rest necessary for rapid healing. In abscess the diffusion of the pus is favored by the density and the vitality of the super- jacent layers, which, in consequence of the former property, do not soften and permit pointing, and, because of the latter, do not slough and thus give exit to the pus, which therefore may extend in the line of least resistance, — i.e., along the loose subapo- neurotic layer. Wounds involving either the muscle or its aponeurosis, if transverse to the direction of their fibres, gape widely. Their healing will be hastened by firm bandaging of the whole cranium so as to control and limit the movements of the scalp. 3. The occipito-frontalis muscle and aponeurosis ; 4, the supcrjicial fascia ; 5, the skin. These three layers are so intimately blended that from the practical stand-point they may be considered together. The thin aponeurosis is tied to the skin (which is here thicker than anywhere else in the body) by dense, inelastic, perpendicular and oblique fibres of connective tissue, enclosing little shot-like masses of fat. This area is very vascular, almost all the vessels of the scalp being found in it adherent to the cellular-tissue walls of the fat-containing compartments. As a result of these anatomical conditions it is found that (i) suppuration is very limited in extent ; (2) superficial infections (such as ervsipelatous dermatitis) are accom- panied by but little swelling ; (3) incised wounds do not gape ; (4) lacerated and contused wounds are not followed by sloughing, which is also rare as a result of continuous pressure, as from bandages ; (5) hemorrhage after wounds is abundant and is persistent because of the adherence of the vessel-walls to the subcutaneous layer of fascia, which pre\ents both their retraction and contraction : (6) collections of blood after contusions mav, like the deeper ones already described, become very firm at the periphery, — in this case from an excess of fibrinous exudate and from the presence of particles of displaced fat, — while the inelastic fibres of cellular tissue (from among which the fat particles have been driven out by the force of the blow) remain depressed in the centre ; these appearances have not infrequently led to a PRACTICAL CONSIDERATIONS : THE SCALP. 491 mistaken diagnosis of fracture of the skull ; (j) lipomata are rare, as in the only layer in which fat is found its abnormal growth is resisted by the density of the surrounding connective tissue. Baldness affects especially the area of the scalp which directly overlies the occipito-frontal aponeurosis. It is attributed (Elliott) largely to the lack of muscular fibres in this region, so that the skin is not " exercised" and the lymph-current is made to depend chiefly on gravity. The density of the superficial fascia connecting the skin and the aponeurosis allies it with that of the palmar and plantar regions, in both of which similarly dense fascia is found and hair is absent. Dermoids are common over the anterior fontanelle and the occipital protuber- ance because the early contact of the skin and dura mater continues longest in these regions. "Should the skin be imperfectly separated, or a portion remain persist- ently adherent to the dura mater, it would act precisely as a tumor germ and give rise to a dermoid cyst" (Sutton). Wens are also common on account of the presence of large numbers of seba- ceous glands. In removing such growths, if the dissection is carried close to the sac, the subaponeurotic layer will not be opened and all danger, even in case of infection, will be minimized. So-called "horns" are found here with relative frequency by reason of the number of sebaceous glands. Emphysema of the scalp may occur as a complication of fractures involving the pharyn.x, the frontal sinuses, or the ethmoid or nasal bones. The air infiltrates either the subaponeurotic or subcutaneous cellular tissue. Pneicmatocele of the frontal region is very rare, but has occurred in a few cases as a result of a communication between the nasal cavity and bony defects in the anterior wall of the frontal sinuses. The swelling is soft, elastic, and resonant, and is made more tense by forced expiration, less so by pressure. The entrance and escape of air may be heard on auscultation. The air is always beneath the pericranium. Syphilis, tuberculosis, carcinoma, and sarcoma may affect the scalp primarily, and are mentioned in the order of frequency of occurrence. Cirsoid aneurism is especially frequent upon the scalp. The Temporal Regio?i. — Here the skin is thinner and less intimately adherent to the subcutaneous fascia than in the occipito-frontal region ; that fascia also is somewhat less closely connected to the aponeurosis beneath. Hemorrhage between these layers is therefore more easily controlled by the usual process of picking up and tying the vessel, the walls of which will be found freer from attachments to the bundles of fascia. The fascia over the temporal muscle itself is of such strength and thickness that abscesses beneath it rarely point above the zygoma, but are directed into the pterygo- ma.xillary region and thence into the pharyn.x or into the neck, or along the anterior temporal muscular fibres to the coronoid process and thence into the mouth. Abscesses above it have no special anatomical peculiarities. The fat in the temporal fossa is abundant, and is found in the subcutaneous fascia, between the two layers of the temporal fascia, and directly upon the muscle itself. The disappearance of this fat in diseases attended by emaciation causes the characteristic unnatural prominence of the zygoma and apparent deepening of the temporal fossae. The temporal muscle should be considered with the pterygoids in their relation to fracture of the ramus and coronoid process (pages 245, 493), to dislocation of the inferior maxilla (pages 246, 493), and to resection of that bone. The pericranium of this region is thinner and more adherent than that of the occipito-frontal region, and the subpericranial connective tissue is absent ; hence subperiosteal abscess or hsematoma is practically unknown. The region may be invaded by tumors originating in the orbit and spreading through the spheno-maxillary fissure or through the thin orbital process of the malar bone. Trephining and other operations in this region are so closely related to intra- cranial diseases and middle-ear disease that they will be considered in that relation (page 1509). 492 HUMAN ANATOMY, The Mastoid Region. — For the same reasons the practical anatomy of the soft parts covering the remaining region of the skull — the mastoid — will be taken up later (page 1508). The Face. — The skin of the forehead and cheeks is thin and vascular and the cellular tissue beneath is loose. Therefore wounds bleed freely but unite rapidly ; sloughing is rare ; cellulitis tends to spread ; oedema is common ; superficial infections (favored by the constant exposure of the region) are attended by much redness and swelling and little pain ; if they result in abscess, it is not apt to attain a large size, as the delicacy of the skin permits of early pointing. On the other hand, necrotic processes (as in cancrum oris) once established in the loose cellular tissue aud fat of the cheeks, run a rapid and destructive course, and may be followed by great dis- figurement and by limitation of the motions of the inferior maxilla. Abscesses beneath the buccinator aponeurosis, like fatty growths in the same situation, project towards the cavity of the mouth ; they should be opened through the mucous membrane. Fig. 505. \ i ^^' ) Upper cut edge of masseter Temporal-^ External pterygoid , ,,. hiteriial pten-goid Masseter (cut)' Parotid gland partly fragment of fracture .Anterior fragment igastric, anterior belly ■lo-hyoid Hyo-glossi: Body of hyoid bone Dissection of fractu showing displacement produced b>- Over the lower third of the nose the skin is closely adherent, as it is over the chin, where it is also very dense. Infections in those regions are therefore exception- ally painful (page 246). The vascularity and mobility of the skin of the forehead and of the cheeks make it especially useful in plastic operations upon the region of the nose and mouth. On account of the rich blood-supply, naevi are common on all parts of the face, as, by reason of the numerous sweat and sebaceous glands, are acneiform eruptions. Lupus and malignant pustule are frequent and grave forms of local infection ; rodent ulcer (epithelioma) is common ; while on the forehead the early syphilitic roseola or papule (corona veneris) and about the lips and nose the later tubercular syphilide are often seen. Lipomata, in spite of the considerable quantity of fat in the subcutaneous tissue, are very rare. The mass of fat between the buccinator and masseter muscles — PRACTICAL CONSIDERATIONS : THE F'ACE. 493 Fig. 506. Upper joint-cavity Dissection showing relations when mandible rests within glenoid fossa ; outer part of capsular ligament has been cut away, exposing upper and lower joint-cavities. " boule de Bichat," "sucking cushion" — is believed to receive and distribute the increased atmospheric pressure which follows the establishment of a partial vacuum in the mouth during sucking. It thus aids in preventing the buccinator from being carried in between the alveoli. It is relatively smaller in adults than in infants and in the latter does not much diminish in size, even in the presence of emaciation, when the general subcutaneous fat has largely disappeared (Ranke). Sutton says, "The sucking cushions sometimes enlarge in adults and simulate more serious species of tu- mors, and it is curious that in some of the recorded cases the enlargement has been as- sociated with the impaction of a salivary calculus in the duct of the parotid gland. ' ' The importance of avoid- ing conspicuous scars on the face leads the surgeon to make his incisions, whenever possi- ble, either in or parallel with the lines of the natural furrows due to the insertion of some of the facial muscles into the skin itself, or in the shadow of overhanging parts, as beneath the upper brow or the lower edge of the inferior maxilla. For a reason not understood, but possibly associated with the difficulty in securing rest, combined with the large vascular sup- ply, cicatricial overgrowth and true keloid are both relatively common after wounds of the face. In fracture of the inferior maxilla the irregularity in the horizontal planes of the two fragments (the anterior being the lower) is due to (a) the weight of the chin and opposite side of the jaw ; (i) the action on the an- terior fragment of the di- gastric and other depressors of the chin ; and (c) the effect of the posterior fibres of the temporal, the internal pterygoid, and the super- ficial fibres of the masseter in elevating the posterior fragment (Fig. 505). In fracture of the ramus there is little displacement, as the bone lies between the two muscular planes of the masseter and internal ptery- goid and is .splinted by them. In fracture of the neck of the condyle the upper fragment is drawn upward and forward by the external pterygoid ; the re- mainder of the jaw is some- what elevated by the masseter, temporal, and internal pterygoid. The difficulty in approximation of the fragments may result in excess of callus, which greatly interferes with the subsequent movements of the temporo-maxillary articulation. The rnechanism of dislocation of the lower jaw has already been described (page Fig, Dissection showing relations when mandible is depressed and carried forward upon articular eminence; capsular ligament is stretched in con- sequence. 494 HUMAN ANATOMY. 246), but can now be better understood. It should be remembered that the muscles of mastication are exceptionally irritable and are all supplied by the motor branch of the mandibular division of the fifth nerve. When the mouth is opened very widely, as in yawning, or in an effort to take an unusually large bite, the deep posterior ver- tical fibres of the masseter (which are the only ones attached to the ramus and aiding m closing the mouth that do not run forward as well as upward) are carried behind the centre of motion, so that their contraction tends still further to open the mouth or to keep it open. Refle.x contraction from overstretching is e.xcited in the general group, and the e.xternal pterygoid acting with most advantage in that position, draws the condyle into the 'zygomatic fossa, where it is held by the masseter and internal pterygoid. ' ' Noisy movement' ' of the temporo-maxillary joint is often due to weakness of the muscles of mastication, permitting the joint surfaces to fall apart as the result of the slight lengthening of the ligaments produced in time by the weight of the jaw. Paralysis and spasm of the facial and masticatory muscles will be considered in relation to the nerves supplying them (pages 1255, 1248). The most frequent congenital defect of the muscles of the face is in connection with harelip, in which deformity Fig. 50S. the portion of the orbicularis oris corresponding to the cleft is absent. Dermoids are not infre- quently found at the angles of the orbit, in the cheeks near the corner of the mouth, in the naso-labial furrows, at the root of the nose, and in the mid-line of the chin. Reference to the embryology of the face will show that these are localities in which epiblastic inclusion is likely to occur. Marked congenital asym- metry of the face may occur from failure of developmental processes. Landmarks. — Just within the mid-point of a line drawn from the mastoid process to the external occipital protuberance the occipital artery can be felt as, with the great occipital nerve, it enters the scalp on its way to the vertex. The superficial temporal artery can be felt, and often can be seen where it runs over the base of the zygoma in front of the ear. Its vein and the auriculo-temporal nerve are just behind it. The dix'ision of the artery into its anterior and posterior branches takes place about 5 cm. (2 in.) above the zygoma. These branches are easily palpable on the firm underlying structures, and thus afford testimony as to the presence or absence of arterial degeneration. In old persons they are often tortuous and plainly visible, especililly the anterior branch where it crosses the anterior por- tion of the temporal muscle. The region is a frequent seat of cirsoid aneurism. At the junction of the middle with the inner third of the supra-orbital bony margin the supra-orbital notch may be felt. From this point the supra-orbital nerve and artery pass almost directly upward, crossing the orbital margin. Between that point and the root of the nose the frontal artery and supratrochlear nerve ascend and the frontal vein descends. The movement of the condyle of the inferior maxilla up to the summit of the eminentia articularis when the mouth is open and the external pterygoid contracts, and its return into the glenoid cavity when that muscle is relaxed and the mouth is closed, can plainly be felt. ndyle having THE VAGO-ACCESSORY MUSCLES. 495 The relation of many of the bony points to the overlying soft parts has been described (page 246). The shape of most of the muscles cannot be separately distinguished. Com- parison of a skull with a partially dissected head will show, however, that over the vault of the cranium from the supra-orbital ridges to the nucha the general shape of the skull determines the surface form during life, the flattened muscles and aponeu- rosis closely conforming to it. In the temporal regions, in spite of the deep bony fossa, the triangular muscle and the accompanying fat (page 491) make the surface in vigorous, well-nourished persons slightly convex. The outlines of the muscle can be seen when it is in contraction, especially the portion anterior to the hairy scalp. On the face the characteristics that distinguish the individual are due largely to the presence of muscles and of subcutaneous fat. The edge of the orbit and the naso-frontal junction are covered and given rounded outlines by the orbicularis palpebrarum and the pyramidalis nasi. The muscles running from the malar bone and ma.xilla to the upper lip aid the buccinator and the fat of the cheek in filling up the great hollows beneath the malar prominences. The orbicularis oris gives shape and expression to the mouth. The masseter fills out the posterior portion of the cheek and becomes visible in outline when in firm contraction, especially the vertical anterior border, just in front of which the facial artery crosses the inferior maxilla. As nearly all the facial muscles have fibres of insertion into the facial integument, their influence upon expression and upon the creases and folds that become perma- nent as "wrinkles," "crows' feet," etc., is apparent. III. THE VAGO-ACCESSORY MUSCLES. The muscles supplied by the glosso-pharyngeal, vagus, and spinal accessory nerves may be grouped together both on account of their relations in the adult and on account of the intimate relations which exist between the three nerves. The glosso-pharyngeal and vagus correspond to the posterior branchial arches, the glosso- pharyngeal to that represented in the adult by the greater cornu of the hyoid bone and the vagus to those represented by the laryngeal cartilages. Consequently we find the muscles supplied by these nerves to be those associated with the pharynx and larynx, one of the muscles of the soft palate, the levator palati, being also included in the group. The pharyngeal muscles, for the most part, are supplied from the pharyngeal plexus, into which fibres from both the glosso-pharyngeal and vagus nerves enter. The laryngeal muscles, however, are supplied by branches coming directly from the stem of the vagus nerve. The spinal accessory nerve stands in such intimate relations with the vagus that its nucleus of origin may well be regarded as an extension of that of the vagus, and by the union of a portion of its fibres with those of the vagus to form a common trunk opportunity is afforded for its fibres to participate in the formation of the pharyngeal plexus, and there is evidence pointing to the origin of the fibres of the inferior laryngeal nerve, which supplies the majority of the laryngeal muscles, from the spinal accessory nucleus. In addition, however, to its participation in the supply of the pharyngeal and, possibly, the laryngeal muscles, the spinal accessory also innervates the trapezius and sterno-mastoid muscles, and these, on account of their relations, must constitute a subgroup distinct from the other vago-accessory muscles. (a) THE MUSCLES OF THE PALATE AND PHARYNX. 1. Stylo-pharyngeus. 5. PalatOTpharyngeus. 2. Levator palati. 6. Constrictor pharyngis superior. 3. Azygos uvulse. 7. Constrictor pharyngis medius. 4. Palato-glossus. 8. Constrictor pharyngis inferior. I. Stylo-Pharyngeus (Figs. 502, 509). Attachments. — The stylo-pharyngeus arises from the inner surface of the styloid process near its base. It is directed downward, the glosso-pharyngeal nerve 49f> HUMAN ANATOMY. covering its outer surface, passes between the middle and superior constrictors of the pharynx, and, being joined by fibres from the palato-pharyngeus, is inserted into the posterior border of the thyroid cartilage and the posterior wall of the pharynx. Nerve-Supply. — By a branch of the glosso-pharyngeal ner\-e. Action. — To draw upward the posterior wall of the pharynx and the thyroid cartilage. 2. Levator Pal.vti (Fig. 509). Attachments. — The elevator of the soft palate (m. levator veil palatini) arises from the under surface of the apex of the petrous portion of the temporal bone and from the cartilaginous portion of the Eustachian tube. It descends obliquely dovvn- FiG. 509. Eustachian tube Levator palati .S I (-1 )r orifiL^ of larynx Pobtenor criLO arjlenoid Muscles of palate and pharynx 1 from behind ; phao'nx laid open. ward and forward, and, broadening out, enters the substance of the soft palate, into the aponeurosis of which it is inserted. Nerve-Supply. — From the pharyngeal ple.xus by fibres which probably have their origin in the anterior part of the nucleus of the spinal accessory nerve. Action. — To ele\ate the soft palate. 3. AzvGOS UvuL^ (Fig. 509). Attachments. — The azygos uvulae (m. uvulae), so named on the supposition that it was an unpaired muscle, consists of two narrow slips which arise from the THE VAGO-ACCESSORY MUSCLES. 497 aponeurosis of the soft palate and from the posterior nasal spine. They pass back- ward and downward, almost parallel with each other, into the uvula to be itiserted into its aponeurosis. Nerve-Supply. — From the pharyngeal plexus. Action. — To raise the uvula. 4. Palato-Glossus (Fig. 1339). Attachments. — The palato-glossus (in. glossopalatinus) is a thin sheet which a7'ises from the under surface of the aponeurosis of the soft palate and descends in the anterior pillar of the fauces (arcus glossopalatinus) to be inserted into the sides of the tongue, mingling with the fibres of the stylo-glossus. Nerve-Supply. — From the pharyngeal plexus, probably by fibres from the anterior part of the nucleus of the spinal accessory nerve. Action. — To raise the back part of the tongue and at the same time to narrow the fauces by causing an approximation of the anterior pillars. Acting from below, it will depress the soft palate. 5. Palato-Pharyngeus (Fig. 509). Attachments. — The palato-pharyngeus (m. pharyngopalatinus) arises from the aponeurosis of the soft palate, from the posterior border of the hard palate, and also from the lower portion of the cartilage of the Eustachian tube. It passes downward and backward in the posterior pillar of the fauces (arcus pharyngopalatinus), internal to the superior and middle constrictors of the pharynx, and is inserted into the pos- terior border of the thyroid cartilage and into the posterior wall of the pharynx. That portion of the muscle which arises from the cartilage of the Eustachian tube is often regarded as a distinct muscle which has been termed the salpitigo-pharyngeiis. Nerve-Supply. — From the pharyngeal plexus, probably by fibres from the anterior part of the nucleus of the spinal accessory nerve. Action. — It draws the pharynx and thyroid cartilage upward and at the same time approximates the two posterior pillars of the fauces. Acting from below, it will depress the soft palate. 6. Constrictor Pharyngis Superior (Figs. 501, 510). Attachments. — The superior constrictor of the pharynx forms a thin quadri- lateral sheet whose origin is closely associated with part of that of the buccinator, there being usually some interchange of fibres between the two muscles. It arises from the lower part of the posterior border of the internal pterygoid plate and from its hamulus, from the posterior border of the pterygo-mandibular ligament, and is thence continued upon the internal oblique line of the mandible, the mucous mem- brane of the mouth, and the side of the tongue. The uppermost fibres pass in a curve backward and upward and are inserted into the pharyngeal tubercle of the occipital bone, while the remainder unite with the muscle of the opposite side in a median raphe on the posterior wall of the pharynx. Nerve-Supply. — From the pharyngeal plexus by fibres which probably arise from the anterior portion of the nucleus of the spinal accessory nerve. Action. — To compress the pharynx. Relations. — Between the uppermost fibres of the muscle and the base of the skull is an interval in which may be seen the levator palati and the Eustachian tube. This interval has been termed the sinus of Morgagni, and is closed by a sheet of connective tissue termed the fascia pharyngobasilaris, which is an upward prolonga- tion to the base of the skull of the pharyngeal portion of the bucco-pharyngeal fascia (page 488). Externally the superior constrictor is in relation above with the internal carotid artery, the vagus nerve, and the cervical sympathetic, and below with the upper part of the middle constrictor and the stylo-pharyngeus. Internally it is lined by mucous membrane throughout the greater part of its extent, being in relation, how- ever, witii the tonsil and the palato-pharyngeus muscle. 498 HUMAN ANATOMY. Variations. — A considerable amount of independence may e.\ist between the bundles of fibres coming from different portions of the line of origin, and the muscle has consequently been described as consisting of various portions to which the terms pterygo-pharyngeus, bucco- pharyngeus, mylo-pharyngeiis. and g losso-pharyngeus have been applied. Not infrequently a bundle of fibres is to be found arising from the basilar portion of the occipital bone or even from the inferior surface of the petrous portion of the temporal or the spine of the sphenoid, and passing downward to be inserted along with the phar>ngo-palatinus. A bundle which passes from the cartilaginous portion of the Eustachian tube to be inserted with the palato-phar^-ngeus has been termed the salpingo-pharyngeus. lateral expan- Muscles of phan^Tix from behind ; portii Longitudinal muscle of cesophagus r constrictor has been i 7. Constrictor Ph.\rvngis Medivs (Fig. 510). Attachments. — The middle constrictor of the pharynx is a fan-shaped sheet which arises from the stylo-hyoid jisjament and both cornua of the hyoid bone. The fibres pass backward to be inserted into the pharyngeal raphe, the upper fibres THE VAGO-ACCESSORY MUSCLES. 499 overlapping the lower part of the superior constrictor and extending in some cases almost to the occipital bone, while the lower fibres are overlapped by the inferior constrictor. Nerve-Supply. — From the pharyngeal plexus, probably by fibres from the anterior portion of the spinal accessory nucleus. It is said to be supplied also by the glosso-pharyngeal nerve. Action. — To compress the pharynx. Variations. — As in the case of the superior constrictor, the fibres from different parts of the origin may have considerable independence. Thus the fibres from the greater cornu of the hyoid have been recognized as a muscle, the ceralo-pharytigeus, distinct from the remainder, to which the term chondro-phaiytigeus has been applied. 8. Constrictor Pharyngis Inferior (Figs. 501, 510). Attachments. — Like the middle constrictor, the inferior is also a fan-shaped sheet and arises from the outer surface of the thyroid and cricoid cartilages of the larynx. The fibres radiate backward to Ije inserted into the pharyngeal raphe, the upper ones overlapping the lower part of the middle constrictor, while the lower ones mingle with the musculature of the oesophagus. Nerve-Supply. — From the pharyngeal ple.xus, probably through fibres from the anterior part of the nucleus of the spinal accessory. It is said to receive also fibres from the vagus through both the superior and inferior laryngeal nerves. Action. — To compress the pharynx. The three constrictors of the pharynx play important parts in the final acts of deglutition, forcing the food towards the oesophagus. They are also important agents in producing modulations of the voice, since the pharynx may be regarded as forming a resonator, alterations of whose form will naturally result in modifications of voice. Variations.— The portions of the muscle arising from each of the two laryngeal cartilages may be more or less distinct and have been termed the thyro-pharyngeus and crico-pharyngms. (d) THE MUSCLES OF THE LARYNX. The muscles of the larynx will be considered in connection with the description of that organ (page 1824). (c) THE TRAPEZIUS MUSCLES. I. Sterno-cleido-mastoideus. 2. Trapezius. , This group includes but two muscles, the trapezius and sterno-cleido-mastoid, which extend from the skull to the pectoral girdle. Both are in reality compound muscles, formed by the fusion of fibres derived from the branchiomeres supplied by the spinal accessory with portions of the myotomes supplied by the second, third, and fourth cervical nerves. Strictly speaking, therefore, they belong only partially to the series of branchiomeric muscles, but the union of the elements derived from the two sources is so intimate that any attempt to distinguish them in a brief descrip- tion of the muscles would tend to confusion. I. Sterno-Cleido-Mastoideus (Fig. 541). Attachments. — The sterno-mastoid is attached below by two heads to the sternum and the clavicle. The sternal head arises by a strong rounded tendon from the anterior surface of the manubrium sterni, while the clavicular head is more band- like, and takes origin from the upper surface of the sternal end of the clavicle. The two heads are directed upward and backward, the clavicular head gradually passing beneath the sternal one, and the two, eventually fusing, are inserted into the mastoid process of the temporal bone and into the outer part of the superior nuchal line. 500 ^ HUMAN ANATOMY. Nerve-Supply. — The external branch of the spinal accessory and the second and third cervical nerves. Action. — The two muscles of opposite sides, acting together, will draw the head forward, thus bending the neck. Acting singly, each muscle will tend to draw the head, towards its own side and at the same time to rotate it towards the opposite side. Relations. — Superficially the muscle is covered by the platysma, and is crossed obliquely by the external jugular vein and in varying directions by the superficial branches of the cervical plexus. It covers, Fig. 511. above, the upper part of the posterior belly of the digastric, the splenius capitis, the levator scapulae and the scaleni, and below it crosses the omo-hyoid and covers the lower attach- ments of the sterno-hyoid and sterno-thyroid. It also covers the common carotid artery and the lower portions of the e.xternal and internal carotids, the facial and -internal jugular A-eins, the cervical plexus, and the lateral lobe of the thyroid gland. pi'a! Variations.— Considerable variation exists in the amount of fusion of the two heads, their complete distinctness being of so frequent occurrence as to be regarded as normal by some authors. But, in ad- dition to these two portions, the muscle presents fre- quently a separation into other parts, and compara- tive anatomy reveals a primary constitution of the muscle from at least five distinct portions, any one or more of which may appear as distinct bundles ■'■ — S ' .^~i^'iU\4iV^\ ' (F"ig- 51 0- These portions are arranged in two ■^^^ ■ jf' v^liii|»~__Cleido-occipi- layers, the superficial one consisting of a superficial ^^J:-^' f'j ^^SHP tal, lower stemo-mastoid , a stcrno-occipital, and a cleido- \ '" ^^^ fj'"'' '^"■'""l occipital portion, while the deep one is formed by downward ^ j^.^p ^temo-mastoid and a cleido-mastoid portion, Quadricipital type of stemo-mastoid, showing the the names apiilied indicating the attachments of the components of the muscle. (After Mavbrac.) various bundles Occasionally the lower portion of the muscle is traversed by a tendinous intersection, a peculiarity of interest in connection with the formation of the muscle by the fusion of portions derived from different myotomes. 2. Trapezius (Figs. 512, 559). Attachments. — The trapezius is the most superficial muscle upon the dorsal surface of the body, and is a triangular sheet whose base corresponds with the mid- dorsal line. The two muscles of opposite sides being thus jilaced base to base, form a rhomboidal sheet which covers the nape of the neck and the upper part of the back and shoulders, resembling somewhat a monk's cowl, whence the name cucullaris sometimes applied to the muscle. It arises above from the superior nuchal line and the external occipital pro- tuberance, and thence along the ligamentum nuchae and the spinous processes of the seventh cervical and all the thoracic vertebrae, together with the supraspinous ligaments. The upper fibres pass downward and outward, the middle ones directly outward, and the lower ones upward and outward, and are hiserted, the upper ones into the outer third of the posterior border of the clavicle, the middle ones into the inner border and upper surface of the acromion process and the upper border of the spine of the scapula, and the lower ones into a tubercle at the base of the scapular spine. Throughout the greater part of its length the origin of the muscle is by short tendinous fibres intermingled with muscle-tissue, but from about the middle of the ligamentum nuchae to the spinous process of the second thoracic vertebra it is entirely tendinous. Furthermore, throughout the upper half of this portion' of the origin the tendinous fibres gradually increase in length and throughout its low-er half they again diminish, so that there is formed by the two muscles of opposite sides, in this region, THE VAGO-ACCESSORY MUSCLES. 501 a well-marked oval or rhomboidal tendinous area, which has been termed the oval aponeurosis. In their course to their insertion the lower fibres pass over the smooth surface at the base of the spine of the scapula, and sometimes a bursa mucosa is developed between the bone and the muscle. Nerve-Supply. — From the external branch of the spinal accessory and from the third and fourth cervical. nerves. .1 ' _ Action. — Acting from above, the upper fibres draw upward the point of the shoulder, while, acting from below, they draw the head backward. The middle and lower fibres draw the scapula towards the Fig. 512. mid-dorsal line and at the same time rotate it so as to raise the point of the shoulder. Variations.— Like the sterno-mastoid, the trapezius is a comjpound muscle consisting of three distinct portions. That portion of the muscle which inserts into the tuberosity of the Fig. 513. Rhomboideus major Superfinil disseetion of back showing trapezius and adjacent muscles Cleido-occipitalis cervicalis Dorso-scapularis ^.,^;=>-<^ superior Tuberosity of spine reiHmous slip to raspinous fascia ;o-scapularis inferior Components of hu (St ■ scapular spine represents what is termed in the lower mammals the dorso-scapularis inferior, while the portion which inserts into the spine and acromion process represents the dorso-scap- ularis superior. The clavicular portion, on the other hand, is in the lower forms associated with the cleido-occipitahs element of the sterno-cleido^mastoid, and may therefore be termed the cleido-occipitalis cervicalis. Indications of this triple constitution are to be seen in a more or less distinct separation of the clavicular portion of the muscle from the rest and, less frequently, by a separation of the lower from the middle portion (Fig. 513). Occasionally, too, bundles pass from the anterior border of the clavicular portion to join the cleido-occipitalis portion of the sterno-cleido-mastoid, indicating the common origin of the two muscles. Variations likewise occur in the extent of the spinal attachment of the trapezius, owing to the reduction of one or other of its parts, and it may be remarked that this attachment usually e.xtends lower in the muscle of the right side than in that of the left. Of especial interest from the comparative stand-point is the occasional existence of a bundle of fibres which lies beneath the cervical portion of the trapezius, and is attached at one extremity to the outer end of the clavicle or to the acromion process and above to the transverse processes of some of the upper cervical vertebras, usually the atlas and axis. It is apparently the equivalent of the omo-transversarius of the lower mammals, a muscle which is closely associated with the members of the trapezius group. 502 HUMAN ANATOMY. THE METAMERIC MUSCLES. THE AXIAL MUSCLES. As has been pointed out. the history of the anterior two groups of myotomes, suppUed b)' cranial ner\es, differs somewhat from that of the remaining ones, and it is convenient, therefore, to consider the muscles derived from these myotomes separately from the rest. I. THE ORBITAL MUSCLES. 1. Levator palpebrtt superioris. 2. Rectus superior. 3. Rectus intefnus. 7. Obliquus inferior. 4. Rectus inferior. 5. Rectus externus. 6. Obliquus superior. The most anterior of the persistent myotomes are three in number, supplied by the oculo-motor, trochlear, and abducent nerves. They give rise to the muscles situated in the orbit. I. Lev.\tor P.\lpebr,e Superioris (Fig. 516). Attachments. — The levator palpebrse superioris is a rather slender muscle which lies in the greater portion of its course immediately beneath the periosteal lining of the roof of the orbit. It arises at the back of the orbit, a short distance above the upper margin of Fig. 514. the optic foramen, and is directed forward, broad- ening as it goes, to be />/- seriedhy a broad aponeu- rosis principally into the upper border of the tarsal plate of the upper eye- lid, the uppermost fibres mingling somewhat with those of the palpebral portion of the orbicularis oculi. The aponeurosis by which the levator inserts into the tarsal plate is largely composed of non- striated muscular fibres, which constitute what has been termed the orbiio- palpcbral muscle. This is triangular in shape, with the truncated apex united to the levator and with the base attached to the external palpebral raphe, the tarsal plate of the upper eyelid, and the internal palpebral ligament. Nerve-Supply. — From the oculo-motor nerve. Action. — To draw the upper eyelid upward and backward. Relations. — Immediately above the levator palpebrse superioris, between it and the periosteum of the roof of the orbit, are the trochlear and frontal nerves and the supra-orbital vessels. Below it rests upon the medial half of the rectus superior. Ocular muscles seen from above after removal of roof of orbit ; upper eyelid has been cut and reflected for\vard. THE AXIAL MUSCLES. 5<^3 2. Rectus Superior (Fig. 514). Attachments. — The superior rectus arises from the upper portion of a fibrous ring termed the annulus of Zinn (annuhis tendineus communis), which surrounds the optic foramen and is formed by a thickening of the orbital periosteum in that region. Thence the muscle is directed forward over the eyeball and is inserted into the sclera a little above the upper margin of the cornea. Nerve-Supply. — From the oculo-motor nerve. Action. — To rotate the eyeball so that the pupil is directed upward and at the same time somewhat inward. 3. Rectus Internus (Fig. 514). Attachments.— The internal rectus (m. rectus medialis) arises from the inner portion of the annulus tendineus communis and passes forward along the inner wall of the orbit to be inserted into the sclera a short distance behind the inner margin of the cornea. Nerve-Supply. — From the oculo-motor nerve. Action. — To rotate the eyeball so that the pupil is directed inward. Fig. 515. Superior rectus Levator palpeb Sphenoidal fissure External rect Optic nerve (cut) Spheno-maxillary fi supenoris Superior oblique Troctilea, tendo oblique in place _Internal rectus Inferior' rectus Right orbit i from before, showing stumps of ocular muscles attached to ring of origin. 4. Rectus Inferior (Fig. 516). Attachments. — The inferior rectus arises from the lower portion of the com- mon tendinous ring, its line of origin being continuous with that of the rectus internus. It is inserted into the sclera a short distance below the inferior margin of the cornea. Nerve-Supply. — From the oculo-motor nerve. Action. — To rotate the eyeball so that the pupil is directed downward and at the same time somewhat outward. 5. Rectus Externus (Fig. 514). Attachments. — The e.xternal rectus (m. rectus lateralis) arises by two heads, one of which is attached to the lower and outer portion of the common tendinous ring and to the spine on the lower border of the sphenoidal fissure, and the other to the upper and outer part of the common tendinous ring. It passes along the outer wall of the orbit and is inserted into the sclera a little behind the outer border of the cornea. Nerve-Supply. — From the abducens or sixth nerve. Action. — To rotate the eyeball so that the pupil is directed outward. Relations. — Between the two heads of the external rectus there pass the oculo- motor, nasal, and abducent nerves and the ophthalmic vein. 504 HUMAN ANATOMY. 6. Obliquus Superior (Figs. 514, 516). Attachments. — The superior oblique muscle of the eyeball arises a little in front of the inner part of the optic foramen and passes forward along the upper and inner wall of the orbit to terminate in a round tendon which passes through a ten- dinous loop, the trochlea, attached to the fovea trochlearis of the frontal bone. Thence it is reflected outward, downward, and backward, and, passing beneath the superior rectus, is inserted into the sclera beneath the outer margin of that muscle and at about the equator of the eyeball. Nerve-Supply. — From the trochlearis or fourth nerve. Action. — To rotate the eyeball so that the pupil is directed inward and downward. Fig. 516. Levator palpebrse superioris — Superior oblique Superior rectus. External rectus (ci Internal rectus Opt Stump of external rect Insertion of levator palpebrse superioris into upper tarsal plate .Inferior oblique Inferior rectus 7. Obliquus Inferior (Fig. 516). Attachments. — The inferior oblique muscle arises near the margin of the orbit from a small depression on the orbital surface of the ma.xilla. It is directed out- ward, backward, and upward, and, passing between the inferior rectus and the floor of the orbit, is inserted into the sclera a little behind the equator of the eyeball and under cover of the external rectus. Nerve-Supply. — From the oculo-motor nerve. Action. — To rotate the eyeball so that the pupil is directed upward and outward. Fasciae of the Orbit. — The muscles, nerves, and vessels of the orbit are em- bedded in a mass of loose areolar tissue which, abundantly intermingled with a soft fat, completely fills the orbital cavity. Around the vessels, ner\es, and muscles this areolar tissue condenses to form their sheaths, and a special condensation, the capsule of Teno7i {{asxxz. biilbi), surrounds the posterior four-fifths of the eyeball, forming a socket for it. The inner surface of this capsule is smooth and is united to the outer surface of the sclera only by lax and slender bands of fibres which traverse a distinct lymph-space termed \}i\^ space of Tenon ( spatiiim intcrfasciale), which inter- venes between the capsule and the eyeball, thus facilitating the movements of the latter in the socket. Posteriorly the capsule is continuous with the sheath of the optic nerve and anteriorly it joins with the conjunctiva anterior to the line of insertion of the rectus muscles into the sclera. The tendons of the rectus muscles conse- quently perforate the capsule, which is prolonged backward upon the tendons for a short distance, — in the case of the superior oblique as far as the trochlea, — and then becomes continuous with the areolar sheaths of the muscles which are intimately THE AXIAL MUSCLES. 505 adherent to the muscle-tissue and constitute the fascise musculares. These fasciae are somewhat thicker in their anterior portions than more posteriorly, and give ofE pro- longations to neighboring parts. From the fascia of the rectus superior a prolonga- tion passes to join the tendon of the levator palpebrse superioris, and one from the rectus inferior passes to the lower border of the tarsal plate of the lower eyelid, these two recti thus acquiring a certain amount of action upon the eyelids. From the lateral surface of the fascia of the external rectus a rather strong prolongation is given of! which attaches to the orbital surface of the zygomatic arch, forming what has been termed the external check ligament of the eyeball, while from the medial surface of the fascia of the internal rectus a similar, although somewhat laxer, prolon- gation passes to the crest of the lachrymal bone and the reflected portion of the internal palpebral ligament. The Movements of the Eyeball. — The four recti muscles of the eyeball may be regarded as forming a cone whose apex is at the annulus tendineus communis Fig. 5 [7 Levator palpebral superioris Fat Superior rectus Capsule of Te Superior oblique (cut) Fat Optic nerve \^ Septum orbitale i,\ / Upper fornix of conjunctiva Upper tarsal plate Lower tarsal plate Space of Tenon Inferior rectus Inferior oblique Space of Tenon Septum orbitale Diagrammatic sagittal section through orbit, showing relations of fascia to muscles, eyeball, and orbital wall. and the base at the insertions of the muscles into the sclera. The line joining the insertions of the muscles is not, however, a circle, but rather a spiral, the insertion of the internal rectus being nearest to and that of the rectus superior farthest from the edge of the cornea. The axis of the cone does not correspond in direction with the antero-posterior axis of the eyeball, but, owing to the divergence of the axes of the two orbits, is inclined to it from within outward at an angle of about 20°. It follows from this that during the contraction of either the superior or infe- rior rectus the axis of rotation of the eyeball will not coincide with its transverse axis, but will be inclined to it (Fig. 518), and consequently the action of either of these muscles in directing the pupil upward or downward will be complicated by a certain amount of oblique movement, in the one case inward and in the other case outward. In producing purely upward or downward movements of the pupil the rectus muscles are associated with the oblique ones, the coordination of the inferior oblique with the superior rectus producing a purely upward rotation, while that of the superior oblique with the inferior rectus produces a purely downward movement. 5o6 HUMAN ANATOMY. Fig. 518. It has been demonstrated also that the obHque movements of the eyeball are by no means due to the action of the superior and inferior oblique muscles acting alone, but that in every such movement there is a coordination of two of the recti muscles with one of the obliques. Thus, in rotations which direct the pupil upward and inward the superior and internal recti cooperate with the inferior oblique, and in the downward and outward movements the inferior and external recti cooperate with the superior oblique. A purely outward or inward rotation can be produced by the action of the external or internal rectus, as the case may be. But it is to be noted that the movements of the eyeball are always bilateral, and that the in- ward rotation of the one eye is generally as- sociated with the outward rotation of the other, the combined movements thus re- quiring the cooperation of different muscles. In all movements of the eyeballs there is, accordingly, a coordination of various orbital muscles, and when the combined oblique movements are performed this co- ordination becomes somewhat complicated. The direction of both pupils upward and to the right requires the coordination in the right eye of the inferior oblique and the su- perior and external recti and in the left eye of the inferior oblique and the superior and internal recti. niagramshowingaction of ocular muscles. S,S\, O'Qi, sagittal and transverse axes of eyeball; di- rection of pull of muscles is indicated by lines ; dotted lines indicate axes around which superior and inferior recti and oblique muscles rotate eye- ball : vertical axis (O) corresponds to axis of rota- tion of internal and external recti. {Landois.) Variations.— But few variations have been observed in the orbital muscles. Absence of tlie levator palpebra superioris has been noted, and a slip from this muscle, termed the Unsor trochlecT, sometimes passes to the trochlea. II. THE HYPOGLOSSAL MUSCLES. 1. Genio-glossus. 2. Hvo-glossus. Stylo-glossus. Lingualis. It is well known that the hypoglossal ner\-e represents the anterior roots of three spinal nerves which have secondarily been taken up into and consolidated with the cranial region. Corresponding to these three nerves are three myotomes which combine to give rise to muscles connected with the tongue. I. Genio-Glossus (Fig. 1339). The genio-glossus is described with the tongue (page 1578). 2. Hvo-Glossus (Fig. 1339). The hyo-glossus is described with the tongue (page 157S). Variations. — The fibres which arise from the lesser cornu of the hyoid bone are frequently separate from the rest of the muscle and have been described as the chondt'O-glossus, and the fibres arising; from the body of the hyoid are frequently separated by a distinct interval from those arising from the greater cornu, the former constituting a muscle which has been termed the basio-giossus and the latter the cerato-glossiis. A bundle of fibres, forming what has been termed the iriticeo-ghssus, sometimes arises from the cartilage triticea, situated in the lateral hyo-thyroid ligament, and passes upward and forward to insert along with the posterior fibres of the hyo-glossus. THE TRUNK MUSCLES. 507 3. Stylo-Glossus (Fig. 1339). The stylo-glossus is described with the tongue (page 1579). Variations. — The stylo-glossus is occasionally absent, and may in such cases be replaced by a mylo-glossus, which arises from the inner surface of the angle of the mandible or from the stylo-mandibular ligament and is inserted into the sides and under surface of the tongue. This muscle is usually present in the form of some small bundles of fibres having the attach- ments described. 4. LiNGUALIS (Fig. 1340). The hngualis is described with the tongue (page 1579). III. THE TRUNK MUSCLES. THE DORSAL MUSCLES. In employing the term dorsal to indicate a group of muscles it must be clearly understood that the group does not include all the muscles which, in the adult con- dition, are found upon the dorsal surface of the body. The term, so far as it has a topographic significance, refers to a phylogenelic stage in which the muscles it is intended to designate were the only dorsal muscles, and, as here employed, it indi- cates only those muscles which are derived from the dorsal portions of the embryonic myotomes and are supplied by the posterior divisions (dorsal rami) of the spinal nerves. An examination of the muscles of the back readily shows that they consist of two distinct sets. There is a superficial set, consisting of broad and flat muscles, which are, with few exceptions, attached to the skeleton of the fore-limb, and a deeper set, consisting of elongated and relatively thick muscles, whose attachments are confined to portions of the axial skeleton. The muscles of the former set, which may con\'eniently be designated the spino-humeral muscles, are all supplied by branches from the ventral rami of the spinal nerves ; they have reached their present position, in which they almost completely cover in the true dorsal muscles, by a secondary migration from the more ventral portions of the trunk, and prop- erly belong to the system of limb muscles, in connection with which they will be ■described. The true a.xial dorsal muscles are all included in the deeper set. Viewed from the surface, they appear to form elongated columns of muscle-tissue, extending con- tinuously, more or less parallel with the spinal column, over considerable stretches of the back ; but when the more superficial portions of the columns are removed, it will be seen that the deeper portions are associated with the individual vertebrae, their fibres possessing a more or less distinct segmental arrangement. The columns, indeed, are to be regarded as formed by the' fusion of a number of originally inde- pendent muscle-segments, deiived from the dorsal portions of a corresponding number of myotomes, a mode of formation also indicated by the fact that the columns are supplied by nerves from a greater or less number of successive spinal nerves, from just as many, indeed, as there are myotomes entering into their composition. Comparative anatomy demonstrates that the dorsal musculature may, further- more, be regarded as consisting of two parallel portions or tracts, a median and a lateral. The former portion, which includes the majority of the dorsal muscles, is composed of those muscles which fundamentally arise from the transverse processes of the vertebrse and are inserted into the spinous processes, and may therefore be termed the trayisverso-spinal portion ; while the more lateral tract consists of mus- cles which, taking their origin primarily from the transverse processes, are inserted into the ribs or their homologues, and may accordingly be termed the transverso- costal portion. A certain amount of overlapping of the median tract bv the lateral one occurs in man ; indeed, in the lumbar region the two tracts fuse to a certain extent to form the sacro-spinalis ; but throughout the thoracic and cervical regions they are fairly distinct. 5o8 HUMAN ANATOMY. Psoas magnus t'ertebra Subperitoneal tissue Fascia Pfiritoneura The deep fascia of the back invests all the muscles of the dorsal group, separating them from the spino-humeral group. Above, the fascia is not especially strong, and in the cervical and upper thoracic regions forms what is termed the fascia nuchje, which lies beneath the trapezius and rhomboid muscles. In the lower thoracic and lumbar regions, however, the fascia becomes considerably thickened, especially that portion which invests the sacro-spinalis (verfebral aponeurosis), form- ing a strong rhomboidal sheet e-xtending from about the level of the si,\th thoracic vertebra to the tip of the sacrum, its anterior borders giving attachment to various muscles, while the posterior ones are attached to the posterior portions of the iliac crests, where it becomes contin- FiG. 519. uous with the fascia lata covering the gluteal muscles. This dense layer is termed the fascia lumbo-dorsalis ( F'ig. 559), and is generally regarded as consisting of two lateral por- tions which are practically united in the mid-dorsal line by their common attachment to the spi- nous processes of the vertebrae and the supraspinous ligaments. Each of these lateral portions is again considered as consisting of two layers which together invest the sacro-spinalis ( Fig. 519), the posterior layer being that which has already been described, while the anterior layer is attached medially to the tips of the transverse processes of the lumbar \'ertebrae, abo\'e to the lower border of the twelfth rib, and below to the crest of the ilium. It passes outward beneath the sacro-spinalis, separating it from the quadratus lumborum, and at the outer border of the former muscle it fuses with the posterior layer to form a strong aponeurotic band, from which the latissimus dorsi and the internal oblique and trans- verse abdominal muscles take partial origin, and which is continued ventrally over the inner surface of the transversus abdominis as xh^/aseia transversaiis. .Transversalis fascia Transversaiis muscle Internal oblique External oblique Triangle of Petit uadratus lumborum Lumbar spine Ant la\tr of lunibo-dorsal fascia Superficial fascia Posterior la\er of lumbo-dorsal fascia Sacro-spinalis showing formation and relations of lumbo-dorsal fascia to muscles of body-wall. (a) THE TRANSVER.SO-COSTAL TRACT. Sacro-spinalis. Ilio-costalis. 3. Longissimus. 4. Splenius. I. S.\cro-Spinalis (Fig. 520). Attachments. — The sacro-spinalis, sometimes termed the erector spi7ice, forms a large muscular mass occupying the lumbar portion of the vertebral groove. It takes its origin from the under surface of the lumbo-dorsal fascia, the crest of the ilium, the posterior surface of the sacrum, and the spines of the lumbar ver- tebrae. Anteriorly it divides into three separate muscles, two of which, the ilio- costalis and the longissimus, belong to the transverso-costal group, while the third, the spinalis, is a member of the transverso-spinal series. Nerve-Supply. — The posterior divisions of the lumbar nerves. 2. Ilio-Cost.\lis (Fig. 520). Attachments. — The ilio-costalis, also termed the sacro-lumbalis, is the most lateral of the three muscles into which the sacro-spinalis divides, and is the forward continuation of the portion of that muscle which arises from the crest of the ilium. The muscle is continued upward in the vertebral groo\e immediately internal to the angles of the ribs as far as the fourth cervical vertebra, receiving, however, acces- sions from the ribs as it passes over them. The fibres which arise from the iliac THE TRUNK MUSCLES. 509 Fig. 520. Obliquus supern 1 — Rectus capitis postn Rectus capitis posticus majo .Obliquus inferior Semispinalis capitis (complexus and biventer) Dissection of muscles of back, showing transverso-costal and transverso-spinal tracts. 5IO HUMAN ANATOMY. crest are mainly inserted into the lower six or seven ribs, and form what is termed the ilio-costalis lumborum. With the remainder of the iliac fibres' bundles arising from the lower five, six, or seven ribs associate themselves to form the ilio-costalis dorsi. also termed the accessorius, which inserts into the upper five or six ribs ; and, finally, the uppermost portion of the muscle, the ilio-costalis ceroids or cervicalis ascendens, is formed by the union of bundles arising from the upper six or seven ribs, and is in- serted into the posterior tubercles of the transverse processes of the fourth, fifth, and sixth cervical vertebrse. Nerve-Supply. — From the posterior divisions of the spinal nerves from the lower cervical to the first lumbar. Action. — The various portions of the ilio-costalis tend to bend the spinal column backward in the lower cervical, thoracic, and lunsbar regions, and also to draw it somewhat to one side. They may likewise have some action in drawing down the ribs, assisting in forced expiration. 3. LoNGissiMUS (Fig. 520). Attachments. —The longissimus represents the upward prolongation of that portion of the sacro-spinalis which arises from the dorso-lumbar fascia and the lumbar vertebrae. It is continued upward immediately medial to the ilio-costalis to be inserted into the mastoid process of the temporal bone, but, like the ilio-costalis, it receives in its course accessory bundles and also gives off bundles which are inserted into the skeletal parts over which it passes. The fibres which represent the direct continuation of the sacro-spinalis are con- tinued as far upward as the first thoracic vertebra, and are reinforced by short acces- sory bundles from the transverse processes of the lower six thoracic \-ertebrEe to form what is termed the longissimus dorsi. The fibres of this portion of the muscle are inserted along two lines, the medial of which passes along the accessorv processes of the lumbar vertebrae and the transverse processes of all the thoracic vertebrae, while the lateral line passes along the transverse processes of the lumbar vertebrae and the angles of the ribs as far forward as the second. From the transverse processes of the upper six thoracic vertebrae bundles arise which unite to form the longissimus cervicis or transversa/is eervieis, which continues the line of the longissimus to an insertio7i into the posterior tubercles of the transverse processes of the second to the sixth cervical vertebrae ; and, finally, the longissimus capitis or traehelo-mastoid is formed by bundles arising from the transverse processes of the three upper thoracic vertebrae and the articular processes of the three lower cervical, and passes upward to be inserted into the mastoid process of the temporal bone. Nerve-Supply. — From the posterior divisions of the spinal nerves from the" third cer\'ical to the second sacral. Action. — The thoracic and cervical portions of the longissimus will draw the spinal column backward and to one side ; the longissimus capitis will have a similar action on the head. 4. Splexius (Fig. 520). Attachments. — The splenius forms a flat muscle which arises from the spinous processes of the upper four or six thoracic and the seventh cervical \ertebrae and from the lower half of the ligamentum nuchae. It passes upward and slightly laterally and divides into two portions, the lower of which, curving around the outer edge of the upper portion, passes to an insertion in the posterior tubercles of the upper three cer\'ical vertebrae, forming the splenius eervicis. The upper portion, . which is termed the spleiiius capitis, continues upward, and is inserted by a short tendon into the posterior border of the mastoid process of the temporal bone and into the outer part of the superior nuchal line. Nerve-Supply. — From the posterior divisions of the second to the eighth cer- vical ner\-es. Action. — The splenius cervicis will draw the upper cervical vertebrae backward and will rotate the atlas towards the side of the muscle in action. The action of I. Spinalis. 6. 2. Semispinalis. 7- 3- Multitidus. 8. 4- Rotatores. 9- 5- Interspinales. lO. THE TRUNK MUSCLES. 511 the splenius capitis upon the head will be similar ; the simultaneous action of the two muscles of opposite sides will bend the head backward, each muscle neutralizing the rotatory effect of the other. (b) THE TRANSVERSO-SPINAL TRACT. Intertransversales. Rectus capitis posticus major. Rectus capitis posticus minor. Obliquus capitis superior. Obliquus capitis inferior. I. Spinalis (Fig. 520). Attachments. — The spinalis in its lower portion is the continuation of the deeper and innermost fibres of the sacro-spinalis, and, like the longissimus, with which it is partly associated, it is regarded as consisting of a thoracic, a cervical, and a cranial portion. The spinalis dorsi arises from the spinous processes of the upper two lumbar and the lower two or three thoracic vertebrse by tendons common to it and the longissimus dorsi. It forms a thin, flat muscle which passes upward, inserting as it goes into the spinous processes of the thoracic vertebree from the second to the eighth or ninth, but one vertebra intervening between its uppermost tendon of origin and its lowermost tendon of insertion. The spinalis cervicis arises from the spinous processes of the upper two or four thoracic and the lower two cervical vertebrae, and ascends alongside the spinous processes of the cervical ver- tebrae to be i7iserted into those of the second, third, and fourth vertebrae. The spinalis capitis consists of bundles arising from the spinous processes of the upper thoracic and last cervical vertebrae, and passes upward to be inserted with the semi- spinalis capitis. Nerve-Supply. — From the posterior divisions of the spinal nerves from the third cer\'ical to the last thoracic. Action. — To extend the spinal column. 2. Semispinalis (Fig. 520). Attachments. — The, semispinalis forms the superficial layer of the muscles lying in the groove between the spinous and transverse processes of the vertebrae. Three portions may be recognized in it. The semispinalis dorsi arises from the trans- verse processes of the lower six or seven thoracic vertebrae ; its fibres are directed obliquely upward and medially and are inserted into the spinous processes of the fi\'e or six upper thoracic and last two cervical vertebrae. The semispinalis cervicis arises from the transverse processes of the five or six upper thoracic vertebrae and is insei'ted into the spinous processes of the second, third, fourth, fifth, and sometimes the sixth cervical vertebrae. This portion of the muscle is almost concealed beneath the upper- most portion, the semispinalis capitis, which arises from the transverse processes of the upper six thoracic vertebrae and the articular and transverse processes of the lower three or four cervical vertebrae. The fibres are directed almost vertically upward, and are joined by the spinalis capitis to form a broad muscle-sheet which is inserted into the under surface of the squamous portion of the occipital bone between the superior, and inferior nuchal lines. An intermediate tendinous intersection usually divides the semispinalis capitis into an upper and a lower portion, and is much more distinct in the more medial bundles than in the lateral ones. Frequently these more medial bundles are sep- arated somewhat from the others, and they have been considered a distinct muscle and termed the biventer, the lateral portion of the muscle being named the complexus. Nerve-Supply. — From the posterior divisions of the spinal nerves from the second cervical to the last thoracic. Action. — The semispinalis dorsi and cervicis extend the vertebral column and rotate it somewhat towards the opposite side. The semispinalis capitis draws the head backward and also rotates it slightly towards the opposite side. 512 HUMAN ANATOMY. 3. MuLTiFiDus (Figs. 520, 521). Attachments.— The multiCrtus (midtifidus spina) constitutes the middle layer ot the muscles occupying the groove between the transverse and spinous processes Fir.. 521. Levatores costarum Levatores costai Interspinales. Deep muscles of back. of the vertebrae, and is covered, in the thoracic and cervical regions, by the semi- spinalis. It takes its origiii from the dorsal surface of the sacrum' and from the trans- THE TRUNK MUSCLES. 513 verse or articulating processes of all the vertebrae as far up as the fourth cervical. The fibres from each vertebra pass over from two to four of the succeeding vertebrae and are inseficd into the spinous processes of the third to the fifth, the entire insertion of the muscle extending from the spinous process of the last lumbar vertebra to that of the axis. Nerve-Supply. — From the posterior divisions of the spinal nerves from the third cervical to the last lumbar. Action. — To bend the spinal column backward and rotate it towards the op- posite side. 4. ROTATORES (Fig. 521). Attachments. — The rotatores {rotatores dorsi) form the deepest layer of the muscles occupying the spino-transverse groove. They form a series of small muscles hardly distinguishable from the bundles of the multifidus, beneath which they lie. They are to be found along the entire length of the spinal column from the sacrum to the axis, arising from the transverse process of one vertebra and passing, some of the fibres to the base of the spinous process of the next succeeding vertebra {?vtatores breves) and the rest to a corresponding point of the second vertebra above (rotatores longi) . Nerve-Supply. — From the posterior divisions of the spinal nerves from the third cervical to the last lumbar. Action. — To bend the spinal column backward and rotate it towards the op- posite side. 5. Interspinales (Fig. 521). Attachments. — The interspinales are relatively small muscles which pass be- tween the spinous processes of succeeding vertebrae. They are usually absent throughout the greater portion of the thoracic region, occurring only in connection with the first and the last two spines, but they are exceptionally well developed in the lumbar region and are usually paired in the cervical region, where they stop at the axis. Nerve-Supply. — From the posterior divisions of the spinal nerves from the third cervical to the fifth lumbar. Action. — Acting together to bend the cervical and lumbar portions of the spinal column backward. 6. Intertransversales (Fig. 521). Attachments. — The name intertransversales (mm. intertransversarii) has beer; applied to a series of small muscles occurring in the cervical and lumbar regions and extending between the transverse or mammillary processes of successive vertebrae. In each of the regions named two sets of intertransversales are recognized, but it seems probable that only one of the sets in such region belongs to the dorsal group of muscles. This set will alone be considered here, the other (anterior) one being described with the ventral muscles of the regions in which it occurs. The intertransversarii posteriores occur only in the cervical region and extend between the posterior tubercles of the transverse processes of succeeding vertebrae. The intertransversarii mediales occur only in the lumbar region and extend between the mammillary processes of successive vertebrae. Nerve-Supply. — Probably by fibres belonging to the posterior divisions of the cervical and lumbar nerves, but it is at present insufficiently determined. Action. — To bend the cervical and lumbar portions of the vertebral column laterally. 7. Rectus Capitis Posticus Major (Fig. 522). Attachments. — The greater straight muscle (m. rectus capitis posterior major) arises from the apex of the spinous process of the axis and passes upward and out- ward, broadening as it goes, to be inserted into the middle portion of the inferioi nuchal Hne. 514 HUMAN ANATOMY. Nerve-Supply. — By a branch from the posterior division of the suboccipital nerve. Action. — To draw the head backward and to rotate it towards the same side. 8. Rectus C.\pitis Posticus Minor (Fig. 522). Attachments. — The lesser straight muscle ( ra. rectus capitis posterior minor) arises from the posterior tubercle of the atlas and passes upward, broadening as it goes, to be iiisoifd into the inner portion of the inferior nuchal line. Nerve-Supply. — By a branch from the posterior division of the suboccipital nerve. Action. — To draw the head backward. Fig. 522. Rectus capitis posticus Rectus capitis posticus major Obliquus superior' Suboccipital triangli Obliquus infer Posterior tubercle of atlas Transverse process of atlas Supraspinous ligament Deep dissection of neck, showing suboccipital group of muscles. 9. Obliquus Capitis Superior (Fig. 522). Attachments. — The superior oblique muscle of the head arises from the trans- verse process of the atlas and passes upward to be inserted into the squamous portion of the occipital immediately above the outer part of the inferior nuchal line. Nerve-Supply. — By a branch from the posterior division of the suboccipital ner\e. Action. — -To draw the head backward and slightly laterally. 10. Obliquus Capitis Inferior (Fig. 522). Attachments. — The inferior oblique muscle of the head arises from the tip of the spinous process of the a.xis and is directed outward and upward to be inserted into the transverse process of the atlas. Nerve-Supply. — By a branch from the posterior division of the suboccipital nerve. Action. — To rotate the axis towards the same side. THE VENTRAL MUSCLES. 515 The Sacro-Coccygeus Posterior. — The reduction of the caudal vertebrae in man, indicated by the condition of the coccygeal vertebrae, has brought about a reduction of the terminal portion of the dorsal axial musculature, it being, as a rule, represented only by the ligaments upon the dorsal surface of the coccyx. Quite frequently, however, muscular fibres occur inter- mingled with the connective tissue, and occasionally a distinct muscle, the sacro-coccygeus posterior, may be found, extending from the last sacral vertebra or even from the greater sacro- sciatic ligament to the coccyx. THE VENTRAL MUSCLES. The ventral trunk musculature includes all those a.xial muscles which are supplied from the anterior divisions (ventral rami) of the spinal nerves. As already indicated (page 473), it is divisible into three subgroups : a group of more median muscles, char- acterized by their fibres retaining more or less perfectly a longitudinal direction and constituting the rectus group ; a more lateral group, in which the fibres possess a distinctly oblique or transverse direction, and may consequently be termed the obliquus group ; and, finally, Sl hyposkeletal gt'oup, whose fibres have a longitudinal direction, and which is situated anterior or ventral to the spinal column. Instead of considering the various muscles belonging to each of these groups in succession, it seems more convenient to combine a topographic classification with the morphological one, and to describe the various groups as they occur in the neck, thoracic, abdominal, and perineal regions. It must be understood, however, that the delimitations of these regions are somewhat arbitrarily chosen, and that there is, so far as the muscles are concerned, a considerable amount of overlapping of certain regions, portions of myotomes which strictly belong to the thoracic region, for instance, being found within the limits of what is recognized as the abdominal region. In many cases these overlapping myotomes have united with myotomes of the lower region to form a continuous muscle, and it is consequently impossible to refer them to their proper topographic position without doing violence to the individuality of the muscles which they help to form ; but when they remain practically distinct from the muscles of their adopted region, they will be referred to the region from which they have come. It will be convenient to consider first the muscles of the abdominal region, there- after taking up in succession those of the thoracic and cervical regions, those of the perineal region being left until the last. THE ABDOMINAL MUSCLES. The Superficial Fascia of the Abdomen. — The superficial fascia of the abdomen is usually described as consisting of two layers. These, however, are well marked only over the anterior and especially the lower part of the abdominal wall, losing their distinctness laterally and above, where they pass over into the superficial fasciae of the back and thorax. The superficial layer (Camper s fascia) usually con- tains a considerable amount of fat, except at the umbilicus, and may occasionally reach a great thickness owing to the development of that tissue. The deeper layer immediately underlies the fatty layer, and is a connective-tissue membrane of vary- ing density, containing a considerable amount of yellow elastic tissue. It is con- nected to the deep abdominal fascia which covers the muscles of the abdominal wall by loose areolar tissue, except along the median line, where it is firmly adherent along the linea alba and around the umbilicus. A short distance above the sym- physis pubis it gives off a band which is largely composed of elastic tissue and is inserted below into the fascia of the penis, forming the suspensory ligament of that organ (Fig. 528). In the inguinal region the deep layer of the superficial fascia is especially well defined, forming what has been termed the fascia of Scarpa. Laterally it passes down over Poupart's ligament to unite with the fascia lata of the thigh, the super- ficial vessels and lymph-nodes of this region lying between it and the superficial layer. More medially it is continued down over the spermatic cord, becoming con- tinuous below partly with the deep layer of the superficial fascia of the perineum {fascia of CoHes) and partly, after fusing with the superficial layer, which loses its fat, with the dartos of the scrotum. .Si6 HUMAN ANATOMY. (<0 THE RFXTUS MUSCLES. I. Rectus abdominis. 2. Pyramidalis. I. Rectus Abdominis (Fig. 523). Attachments. - The rectus abdominis forms a flat but strong muscle which traverses the entire length of the ventral abdominal wall immediately lateral to the linea alba. It arises from the anterior surface of the xiphoid process of the sternum and from the cartilages of the fifth, sixth, and seventh ribs, and is inserted by a strong tendon into the crest and symphysis of the pubis. Fig. 523. Pectoralis major Rectus, cut and turned Posterior slieath of rectus. External oblique Semilunar fold Transversalis fascia Deep epigastric artery Rectus, stump Saphenous opening Sheath of rectus, turned ( Anterior superior ilii idalis External abdominal ring _Cribriform fascia closing saphenous oliening _,Spermatic cord The fibres are directed longitudinally, and are interrupted along three and occasionally four transverse lines by tendinous intersections of the muscle. One of these inscriptiones tendinea: occurs about the level of the umbilicus, another, often affecting only the medial portion of the muscle, corresponds approximately to the lower margin of the thorax, and the third lies about midway between the two. The fourth, when present, frequently is limited to the lateral portion of the muscle, and occurs about midway between the level of the umbilicus and the crest of the pubis. THE VENTRAL MUSCLES. 517 Nerve-Supply. — From the anterior divisions of the thoracic nerves from the fifth to the twelfth. Action. — The recti act as flexors of the thorax upon the pelvis or, acting from above, they flex the pelvis on the thorax. They also aid in the compression of the abdominal viscera in defecation and parturition and in strong expiratory efforts. Variations The origin of the rectus sometimes ascends to the fourth or third rib or even higher. The tendinous inscriptions are probably the persistent representatives of the connective- tissue partitions between certain of the myotomes of which the muscle is composed. They are subject to a certain amount of variation in number, five or si.x occasionally occurring, while, on the otlier hand, they may be reduced to two. 2. PVRAMIDALIS (Fig. 523). Attachments. — The pyramidalis is a somewhat variable muscle which aj'ises below from the upper surface of the body of the pubis and from the symphysis and is inse7-ted above into the linea alba, somewhere between the umbilicus and the sym- physis. Nerve-Supply. — From the anterior divisions of the eleventh and twelfth thoracic nerves. Action. — To tense the linea alba. Variations. — The extent to which the muscle is developed varies greatly, its insertion some- times extending well up towards the umbilicus, while, on the other hand, it is not infrequently absent. This latter condition has been estimated to occur in over 16 per cent, of cases. {b) THE OBLIQUUS MUSCLES. 1. Obliquus externus. 4. Transversalis. 2. Obliquus internus. 5. Ouadratus lumborum. 3. Cremaster. 6. Intertransversales laterales. 1. Obliquus Externus (Fig. 524). Attachments. — The external oblique forms a muscular sheet in the lateral portions of the anterior abdominal wall. It arises by seven or eight fleshy digitations from the corresponding number of lower ribs, the upper digitations alternating with digitations of the serratus magnus, while the lower three alternate with those of the latissimus dorsi. The fibres from the lowest ribs pass vertically downward to be in- serted into the crest of the ilium ; the remainder are directed mainly downward and forward and, above, directly forward to join a broad aponeurotic sheet which con- tributes to the formation of the ventral abdominal aponeurosis. Nerve-Supply. — From the anterior divisions of the eighth to the twelfth thoracic nerves and from the ilio-hypogastric and ilio-inguinal nerves. Action. — Since the external oblique is a curved sheet which passes from the lateral portions of the abdominal wall towards the mid-ventral line, contraction of its fibres will tend to compress the abdominal contents and so assist in micturition, defe- cation, parturition, and expiration, its action in the last-named process being increased by the power which it possesses of drawing the lower ribs downward. Furthermore, according as it acts from below or above, it will fle.x 'the thora.x and spinal column upon the pelvis or the pelvis upon the spinal column, at the same time producing a slight rotation of the thorax to the opposite side and the pelvis to the same side. When the two muscles of opposite sides act together, the rotatory action of each will be neutralized. By the most lateral fibres a lateral flexion of the thorax or pelvis will be produced. 2. Obliquus Internus (Fig. 525). Attachments. — The internal oblique muscle lies immediately beneath the ex- ternal one. It arises from the outer half of Poupart's ligament, from the whole length of the middle lip of the crest of the ilium, and from the lumbo-dorsal fascia. From this extended origin its fibres spread out in a fan-shaped manner, the more posterior ones passing upward and slightly forward to be inserted into the 5i8 HUMAN ANATOMY. lower three ribs, while of the rest the more anterior ones pass forward and upward, those from the neighborhood of the anterior superior iliac spine directly forward, and those from Poupart's ligament forward and downward, all joining in a flat aponeu- rosis which unites with the anterior abdominal aponeurosis at the linea semilunaris. In its lowermost portion the aponeurosis unites with that of the transversalis to form what is termed the conjoined tendon, and by this it is attached to the crest of the pubis. Fig. 524. Serratus ma^us Latissimus di Pectoralis major Line of subcostal arch ea transversa :nca semilunaris nibilicus Anterior superior iliac spine — Suspensory- ligament of penis Poupart's ligament Dissection of lateral body-wall, showing external oblique and adjoining muscles. Nerve-Supply. — From the anterior divisions of the eighth to the twelfth thoracic nerves and from the ilio-hypogastric and IHo-inguinal nerves. Action. — The internal oblique acts very similarly to the external in compressing the abdominal contents, in drawing the lower ribs downward, and in flexing the thorax or pelvis laterally. It will also flex the thorax and vertebral column upon the pelvis or the pelvis upon the vertebral column, but in these actions the accompanying rotation will be in a direction contrary to that caused by the external oblique, the thorax being rotated to the same side and the pelvis to the opposite side. It may be remarked that the rotatory action of the external oblique of the one side and the internal oblique of the other will be in the same direction. Variations. — The internal oblique may be crossed by one or more tendinous intersections which have probably the same significance as those of the rectus abdominis. THE VENTRAL MUSCLES. 519 3. Cremaster (Figs. 525, 1671). Attachments. — The cremaster muscle consists of a series of somewhat scat- tered loops of muscle-tissue derived from the lower part of the internal oblique and to a slight extent from the transversalis. It is attached laterally to Poupart's liga- ment and medially to the anterior layer of the sheath of the rectus. The loops de- scend through the inguinal canal along with the spermatic cord, the muscle being Fig. 525. Serratus magnus. Latissimus dorsi- Edge of cut external oblique Posterior aponeurosis of internal- oblique Iliac crest. Fascia lata Cut edge of fascia lata Gluteus maximus Pectoralis major Internal obliqi Edge of cut aponeurosis of externa] oblique Anterior aponeurosis of interna] oblique Anterior superior iliac spine Conjoined tendon Suspensory ligament Cremaster fibres of lateral bod\ wall showing internal oblique muscle. well developed only in the male, and spread out in the tunica vaginalis communis of the testis and spermatic cord. The loops are united by connective tissue which forms part of the cremasteric fascia. Nerve-Supply. — By the genital branch of the genito-crural nerve. Action. — To draw the testis upward towards the external abdominal ring. 4. Transversalis (Fig. 526). Attachments. — The transversalis (m. transversus abdominis) is the deepest layer of muscle on the lateral abdominal wall and immediately underlies the internal oblique. It arises from the cartilages of the lower six ribs, from the lumbo-dorsal 520 HUMAN ANATOMY. fascia, the inner lip of the crest of the ihum, and the outer one-third of Poupart's ligament. Its fibres pass horizontally inward to join the ventral abdominal aponeu- rosis along the linea semilunaris ; the lower ones, however, bending somewhat down- ward, pass into an aponeurosis which unites with that of the internal oblique to form the conjoined tendon attached to the crest of the pubis. Nerve-Supply. — From the anterior divisions of the seventh to the twelfth thoracic ner\'es and from the ilio-hypogastric and ilio-inguinal nerves. Action. — To compress the contents of the abdomen. Fig. 526. Pectoralis major Edge of cut external oblique Edge of cut internal oblique Lumbo-dorsal fascia Cut edge of fascia lata Gluteus maximus Tensor fascise latje Edge of aponeurosis of external oblique Edge of aponeurosis of internal oblique Aponeurosis of transversalis Rectus, covered by sheath Conjoined tendon Cremaster fibres ction of lateral body The fascia transversalis is a thin layer of connective tissue which lines the inner (deeper) surface of the transversalis muscle. Posteriorly it is continuous with the strong aponeurotic band formed by the fusion of the superficial and deep layers of the lumbo-dorsal fascia, anteriorly it combines with the deeper layer of the ventral ebdominal aponeurosis to form the posterior layer of the sheath of the rectus muscle, and above it unites with the fascia covering the lower surface of the diaphragm. Below its lateral portion is attached to the crest of the ilium and the outer part of Poupart's ligament where it becomes continuous with the iliac fascia, but more medially it is continued downward beneath Poupart's ligament to form the anterior wall of the sheath of the femoral vessels, the portion of it immediately above the vessels being THE VENTRAL MUSCLES. thickened somewhat to form the deep c7-ural arch (Fig. 1496). More medially still it is attached to the free edge of Gimbernat's ligament and to the upper surface of the superior ramus and body of the pubis. A little over i cm. above Poupart's ligament, and about half-way between the anterior superior iliac spine and the symphysis pubis, the transversalis fascia is per- forated by the spermatic cord in the male and by the ligamentum teres of the uterus in the female. The fascia is continued downward and forward over the cord or ligament to form a somewhat funnel-like investment for it termed the infiindibuHform fascia, the inner margin of the funnel marking the position of the internal abdominal ring. 5. OUADRATUS LUMBORUM (Fig. 527). Attachments. — The quadratus lumborum is a flat quadrilateral muscle which lies towards the back part of the ab- dominal wall, e.xtending between the Fig. 527. crest of the ilium and the lower bor- der of the twelfth rib. It consists of two layers of fibres which frequently are distinguishable from each other only with difficulty. The anterior layer, which arises from the trans- verse processes of the lower four lum- bar vertebree and from the posterior part of the iliac crest, is inserted into the lower border of the twelfth rib ; the posterior layer (Fig. 527) arises from the crest of the ilium and is in- serted into the lower border of the twelfth rib and into the transverse processes of the upper four lumbar vertebrae. Nerve-Supply. — By branches from the lumbar ple.xus. Action. — To draw downward the last rib and to bend the lumbar por- tion of the spinal column laterally. Relations. — The quadratus lum- borum rests behind upon the deep layer of the fascia lumbo-dorsalis (Fig. 5 1 9 ), which separates it from the spino- sacral muscle. Its anterior surface is in relation to the kidney and the as- cending or descending colon, is crossed by the lumbar arteries, and is covered towards its inner margin by the psoas major. Quadratus lun 1 muscle of right side 6. Intertransversales Laterales (Fig. 521). Attachments. — The lateral intertransversales are aseries of small quadrilateral muscles which extend between successive transverse processes of the lumbar vertebrae. Nerve-Supply. — Probably from the anterior rami of the lumbar nerves. Action. — To bend laterally the lumbar portion of the spinal column. The Ventral Abdominal Aponeurosis (Fig. 528). — The broad aponeurotic sheets into which the oblique and transverse muscles of the abdomen are continued at their anterior (medial) edges unite more or less intimately with one another and with the fascia transversalis to form the ventral abdotnifial apo7ie2irosis. Laterally the various layers of which this aponeurosis is composed are to a certain extent discerni- ble, since the lines along which the fibres of the three muscles pass into the apo- neurosis do not coincide, that of the external oblique extending from the outer border of the rectus muscle above obliquely downward and laterally to the anterior superior spine of the ilium, while those of the internal oblique and transversus follow essen- 522 HUMAN ANATOMY. tially the outer border of the rectus, except below, where they He a Httle lateral to that muscle. More medially, however, the layers become intimately associated and can only be separated artificially. At the outer border of the rectus muscle the aponeurosis di\-ides into two layers (Fig. 529, A) which pass one in front and the other behind the rectus, thus forming a sheath for it ( vagina rausculi recti). The line of the division is indicated on the surface of the abdomen by a slight groove, and constitutes what is termed the /tnea semi- lunaris. When they reach the mesial border of the rectus the two layers unite and become continuous in the middle line with the aponeurosis of the opposite side to form a strong fibrous band which e.xtends from the front of the .xiphoid process of the sternum above to the Fig, 52S. symphysis pubis be- low, and is termed the linea alba. In its upper part this band is fairly broad, but below the umbilicus, which is situated in the band, it suddenly narrows to a thin line which becomes con- tinuous below with the superior pubic liga- ment, behind the in- sertion of the recti, by a triangular e.xpansion which occasionally contains muscle-fibres and is termed the ad- niinicuium lineae albae. 'Y\'\& posterior layer of the aponeurosis, which forms the poste- rior wall of the sheath of the rectus, is fairly thick above, but a lit- tle below the level of the umbilicus it sud- denl}- becomes very much thinner along an arched line, the con- cavity of which is downward, and may sometimes be represented by a distinct fold. This margin is termed the line or fold of Douglas (linea semicircularis) (Fig. 523). Uncovered, fibres of exter- nal oblique >uspensor>' lij^ament oi penis ,:J Superficial dissection of abdomen, sbowi al aponeurosis. \'arious suggestions have been made in explanation of this sudden change in the thickness of the posterior layer of the sheath of the rectus. It has been supposed that it was connected with the passage of the inferior epigastric arter\- into the substance of the muscle (Henle), a somewhat inadequate cause even if the point of passage of the arten,' through the sheath cor- responded with the semicircular line. The thinness of the portion of the sheath below the line has been explained on the ground that it represents the portion v\ith which the urinarj- bladder was in contact in fretal life (Gegenbaur), and also by the view that the strain exerted on this portion of the sheath is less than that placed upon the upper part, since the latter is acted on by fibres of the oblique and transverse muscles wliich have bony attachments drawn upward during inspiration, while the lower part is in relation to the less active fibres attached to the inguinal ligament (Solger). Finally, it may be stated that the immediate cause for the sudden change in thickness has been assigned to the development of the processus vaginalis peritonsei, the pouch of peritoneum which in the embryo descends into the genital swelling and gives rise in the male to the tunica vaginalis testis. The formation of this peritoneal pouch is held to prevent the lower portions of the posterior layer of the abdominal aponeurosis which are derived from the aponeuroses of the internal oblique and transversalis from passing behind the rectus muscle, the posterior wall of its sheath being formed only by the fascia transversalis (Eisler). THE VENTRAL MUSCLES. 523 In the lowei' part of the anterior abdominal wall the lowermost fibres of the abdominal aponeurosis — those extending between the anterior superior spine of the ilium and the pubic spine — form a strong ligamentous band, the ligament of Pou- part (ligamentum inguinale) (Figs. 524, 530J, the outer portion of which gives rise to some of the fibres of the internal oblique and transversalis muscles, while the fascia lata of the thigh is attached to it below. Near its medial end some of its fibres pass inward to be attached to the ilio-pectineal line of the pubis, forming a horizontal trian- gTjlar sheet whose free concave lateral border forms the medial boundary of \h.& femo- ral ring (annulus femoralisj through which the femoral hernias make their exit from the. pelvis. This reflection (Fig. 531) is the ligament of Gimbernat (ligamentum lacunare). Furthermore, a sheet of fibres, variable in its development and termed the triayigular fascia (ligamentum inguinale reflexum), or ligament of Colles (Fig. 1485), is reflected upward and medially from the inner portions of Poupart's and Gimbernat' s ligaments in front of the lower medial portions of the aponeuroses of the internal oblique and transversalis muscles to the anterior layer of the sheath of the rectus. The Inguinal Canal. — At an early stage in the development of the foetus an outpouching of the lower part of the abdominal wall occurs on each side to form the genital swellings, which later become the scrotum in the male and the labia majora Fig. 529. Transversalis muscle Transversalis fascia Peri- Division of aponeurosis of i toneum / Posterior sheath temal oblique - Rectus - External obliq Internal oblique Aponeurosis of internal obliq -mea j / Anterior sheath of rectus Superficial fascia Aponeurosis of external oblique Transversalis muscle Internal oblique Transversalis fasi / Peritoneum Superfi Aponeurosis of external oblique Diagrams showing constitution of sheath of rectus muscle. Anterior sheath of rectus upper three-fourths ; B, in lower fourth. in the female. The points at which the outpouchings occur are those at which the lower ends of a ligament descending from the primitive kidneys (mesonephri) are attached to the abdominal wall, and these ligaments, consequently, are carried through the length of the outpouching beneath its peritoneal lining to attach to the walls of the scrotum or the labia. In the female the ligaments become in part the round ligaments of the uterus, but in the male the relations of the outpouchings become more complicated. Owing to the descent into them of the testes (page 2040), the ligaments are drawn completely into the pouch, forming the gubernacula of the testes, while the vasa deferentia and the vessels and nerves of the testes are also carried into the pouch, uniting to form the spermatic cord. There are, consequently, pass- ing from the abdominal cavity into each pouch, in the female the round ligaments of the uterus and in the male the spermatic cord. At first, and in the male for a considerable time after birth, the communication of the pouch with the abdominal cavity is widely open ; but later, in the upper part of the pouch in the male and throughout its entire length in the female, the lumen becomes reduced, and finally is completely obliterated by the union of its walls to the sper- matic cord or the round ligament, its lower portion persisting in the male as the space which exists between the visceral and parietal layers of the tunica vaginalis testis. 524 HUMAN ANATOMY. As a result of these processes the lower portion of the abdominal wall is traversed on either side by the spermatic cord or by the ligamentum teres of the uterus, and it is customary to regard the space occupied by the one or the other of these structures as a canal, which is termed the inguinal canal. It should be understood, however, that an actual space surrounding the cord or ligament does not exist, the walls of the canal being united to the structure contained within it. Nevertheless, the union is by no means a strong one, the region of the abdominal wall traversed by the ligamentum teres or especially by the spermatic cord being relatively weak and not infrequently the seat of an inguinal hernia. The inguinal canal is somewhat over 3 cm. ( i "^ in. ) in length and is situated immediately above Poupart's ligament, which it crosses oblicjucly from above down- ward, medially, and forward. Its upper or inner end is about midway between the anterior superior spine of the ilium and the spine of the pubis, and lies about 12 mm. {% in. ) above the line of Poupart's hgament. It is marked by a more or less distinct depression on the posterior surface of the abdominal wall surrounding the sperrrjatic cord or round ligament, termed the internal abdominal ring (annulus inguinalis Fig. 530. Anterior superior iliac spine Poupart's ligament — Falciform process Iliac portion of fascia lata. * Saphenous openin; Femoral artery Femoral Internal saphenous vein of external obliqu External abdominal ring External pillar Internal pillar Pubic portion of fascia lata Spermatic cord Dissection of right inguinal region, showing external abdo and saphe abdominis). The depression (Fig. 532) is due to the transversalis fascia being pro- longed downward over the spermatic cord as a funnel-like sheath, the infjiiidihu/i- form fascia. The lower or medial end of the canal corresponds to the external abdominal ring (annulus inguinalis subcutancus) (Figs. 523, 530), and lies just lateral to and a little above the spine of the pubis and is surrounded by the lower medial portion of the aponeurosis of the e.xternal oblique. The fibres of the aponeu- rosis which bound this ring are somewhat thickened, forming what are termed the pillars (crura) of the ring, the uppermost of which, the internal pillar (cms superior), consists of fibres passing to the symphysis pubis ; the lower one, the external pillar (crus inferior), is formed by the fibres passing to the pubic spine, and corresponds to the medial end of Poupart's ligament. Stretching across between the two crura are numerous obliquely arching i7itercohim7iar fibres (fibrae intercrurales) which extend laterally almost as far out as the anterior superior spine of the ilium. From the margins of the e.xternal ring an attenuated prolongation of the aponeurosis of the external oblique is continued downward over the spermatic cord as a thin membrane known as the intercolnmnar or external spermatic fascia. THE VENTRAL MUSCLES. 525 Owing to the oblique direction of the canal, that portion of the aponeurosis of the external oblique which is strengthened by the intercolumnar fibres, together with a portion of the internal oblique, forms its anterior wall, while its posterior wall is formed by the aponeurosis of the transversalis, together with the more medial lower portion of that of the internal oblique, these two layers of fascia uniting in this region to form what is termed the conjoined tendon, which is attached below to the body and superior ramus of the pubis, and medially is especially thickened to form a band, the falx inguinalis, firmly attached along its medial border to the tendon of the rectus. More laterally, where it forms the medial boundary of the internal abdominal ring, it is also thickened (Fig. 531), forming the ligament of Hesselbach (ligamentum inter- foveolare). Between these two thickenings the abdominal wall is weaker (Fig. 1493) and may give way to internal pressure, permitting a hernia, which comes to the sur- face at the external abdominal ring without having traversed the inguinal canal, and is therefore spoken of as a direct hernia, in contradistinction to the more usual oblique hernia which enters the canal at the internal abdominal ring. Fig. 531. Deep epigastric artery. Interfoveolar or Hesselbach's ligament- Weak Conjoined tendon- Muscular fibre; Lower end of Poupart's ligame Urach! Bladd — Poupart's ligament '^^}^ Transversalis muscle Spermatic vessels E.xternal iliac artery External iliac vein Deep epigastric artery (cut) V'as deferens Femoral ring bernat's ligament will show mg relatK al abdonimal ring 5 of conjoined tendon and its expansions A small fasciculus of muscle-tissue is sometimes found close to the medial border of the internal abdominal ring. It is the m. interfoveolaris (Fig. 531), and arises from the superior ramus of the pubis, passing almost directly upward to spread out on the posterior surface of the transversalis. It is generally regarded as an aberrant portion of the transversalis muscle. The Posterior Surface of the Anterior Abdominal ^A^a^. — Throughout its entire extent, with the exception of a small area in the median line below, the posterior surface of the anterior abdominal wall is lined by peritoneum. In the exceptional area the peritoneum is kept from actual contact with the wall by a band of fibrous tissue, the urachus, which extends from the apex of the urinary bladder to the umbilicus and supports the peritoneum somewhat in the manner of a ridge-pole of a tent, so that between it and the abdominal wall there is an interval occupied only by loose areolar tissue and termed the prevesical space of Retzius (page 1906). Laterally from the urachus a fibrous cord, the lateral ligament of the umbilicus, may be seen on each side, passing from the side of the bladder to the umbilicus and representing the obliterated hypogastric arteries of the fcetus ; while still more laterally there may be seen coming from the external iliac artery the inferior or deep epigas- tric artery, which, passing immediately to the inner side of the internal alsdominal ring and posterior to the interfoveolar ligament (Fig. 532), extends upward and inward to penetrate the posterior layer of the sheath of the rectus a short distance below the level of the umbilicus. Both these structures produce a slight ridging or fold of the peritoneum, that formed by the obliterated hypogastric artery being termed the plica umbilicalis lateralis, while the other is the plica epigastrica. These two folds, together with the urachus, mark off the lower portion of the abdominal wall 526 HUMAN ANATOMY. into three areas or foveae (Fig. 532). The median of these fovece lies between the urachus and the lateral umbilical fold and forms the supravesical fossa, ha\ing for its floor the rectus muscle. Between the lateral umbilical and the epigastric folds is the iniu:r inguinal fossa, ha\ing for its floor the conjoined tendon, and being therefore the region in which direct inguinal hernias arise ; and lateral to the epi- Outer edge of rectus Peritoneal surface- Plica epigastric; Hesselbach's triang! External iliac arter\- External iliac vei Plica hypogastric; Median umbilical ligament Posterior surface of anterior abdominal wall of formalin subject. gastric fold is the outer itiguinal fossa, in whose floor is found the internal abdominal ring, just to the outer side of the deep epigastric artery. The triangular area bounded by Poupart's ligament below, the lateral edge of the rectus muscle medially, and the plica epigastrica laterally has been termed the triangle of Hcsselbaeh. It is almost identical with the middle inguinal fossa, and defines a Uttle more precisely the seat of the direct hernias. (c) THE HYPOSKELET.\L MUSCLES. It seems probable that the psoas major and the psoas minor muscles are, in part at least, assignable to the group of abdominal hyposkeletal muscles. The close association of the psoas major with the iliacus and its attachment to the femur make it convenient, however, to defer their description until later (page 623). PRACTICAL CONSIDERATIONS. THE ABDOMEN. The abdominal cavity is bounded above by the diaphragm ; below bv the floor of the pelvis : laterally by the diaphragm, the lower ribs, the abdominal muscles, and the lateral expansions of the ilia ; posteriorly bv the diaphragm, the tenth, eleventh, and twelfth ribs, the lumbar muscles and vertebrse, the posterior portions of the ilia, and the ischial, sacral, coccygeal, and pubic bones ; and inferiorly by the le\atores ani and coccygei muscles. It should be noted that the roof, the floor, and much of the remaining parietes of the abdomen are made up of muscular tissue which, by contraction or by relaxation or stretching, can alter the size of the cavity, affect the relations of the contained \iscera, and vary the compression to which they are subject. The tonicity of the muscular walls brings about a normal intra-abdominal pressure which ser\-es in health to retain in position and to give support to the viscera This pressure is increased in inspiration and by straining, lifting, or coughing. I. then, by increasing the outward pressure of the \-iscera upon the internal sur- face of the parietes, favors the production of hernia, the protrusion of the intestine PRACTICAL CONSIDERATIONS : THE ABDOMEN. 527 through a wound, the stretching of scars, and some forms of dystocia and of uterine displacement. The pelvic cavity — " a recess leading downward and backward from the abdomi- nal cavity proper" (Cunningham) — is divided from the latter by an imaginary plane extending from the promontory of the sacrum to the upper edge of the pubes. It will be considered separately. The general shape of the abdominal cavity is described on page 16 15 as are also the regions into which, for convenience, the abdomen proper may be divided by cer- ' tain arbitrary lines (page 1615). The structures and organs underlying the spaces thus marked out are approxi- mately as follows ; Right Hypochondriac. Greater part of right lobe of liver, hepatic fle.xure of colon, and part of right kidney. Right Lumbar. Ascending colon, part of right kidney, and sometimes part of ileum. Epigastric Greater part or whole of left lobe and part of right lobe of liver, with gall-bladder, part of stomach, including both ori- fices, first and major portion of the second parts of duo- denum, duodeno-jejunal flex- ure, pancreas, upper or inner end of spleen, parts of kid- neys, and suprarenal bodies. Umbilical. Greater part of transverse colon, lower portion of second and much of third part of duo- denum, some convolutions of jejunum and ileum, with por- tions of mesentery and greater omentum, part of right, often of left, and sometimes of both kidneys, and part of both ureters. Left Hypochondriac. Part of stomach, portion of spleen, tail of pancreas, splenic flexure of colon, part of left kidney, and sometimes part of left lobe of liver. Left Lumbar. Descending colon, part of jejunum, and sometimes part of left kidney. Right Iliac Csecum with vermiform ap- pendix and termination of ileum. Hypogastric Convolutions of ileum, blad- der in children, and when dis- tended in adults also, uterus when in the gravid state, and, behind, sigmoid flexure. Sigmoid colon, convolutions of jejunum and ileum. The contents of the various regions and the structures intersected by the different planes — if the arbitrary lines are continued into planes — vary considerably within normal limits and greatly in the presence of disease. The shape and size of the abdomen are also extremely variable. In the normal adult male it is irregularly cylindrical, with a central bulging, an antero-posterior flattening, and a greater width near the pelvis than near the ribs. In the adult female the larger relative size of the lower abdomen is due to the greater development of the pelvis, and usually to flabbiness of abdominal muscles and accumulation of fat from want of e.xercise,.and to compression of the upper segment by corsets ; it is increased by the stretching of repeated pregnancies. In infancy and childhood the abdomen is prominent on account of the undeveloped condition of the pelvis, the pelvic viscera being then practically within the abdomen, and is broader above than below by reason of the relatively great bulk of the liver. In obesity the weight of the intra-abdominal and subcutaneous fat carries the lower part of the abdominal wall downward by gravity, stretches it, and produces a pendulous abdomen. This condition is also favored by ascites, pregnancy, etc. In 528 HUMAN ANATOMY. emaciation the whole anterior abdominal wall becomes concave {scaphoid), especially the upper portion bounded by the ensiform cartilage and the subcostal angle, — the scrobiculus cordis (page 171), — which, with the patient supine, may appear to rest directly upon the vertebral column, with walls more nearly vertical than horizontal. Congenital deformities of the abdominal wall usually consist in a failure of the ventral plates to unite in the middle line, producing various degrees of umbilical hernia {q.v.) or leaving the contents of the abdomen uncovered over a considerable area. Contusions of the anterior abdominal wall, bounded laterally by the outer free border of the external oblique, — i.e., by a line just e.xternal to a vertical line dropped from the lowest part of the ninth rib, — are of importance in relation to the effect upon the organs contained within the abdomen. As the skin over the abdomen and the abdominal muscles receive their nerve-supply from the lowest six intercostal nerves and the branches of the anterior division of the first lumbar, the contraction of the muscles upon the approach of danger, if not voluntary, may be reflexly hastened at the moment of external application of force, and a protecting elastic barrier may thus be interposed between the latter and the abdominal contents. The rigidity caused by the contact of a cold hand with the abdominal surface, preventing palpation of the viscera beneath, affords a familiar illustration of the close relation between skin and muscles. The relation of the nerve-supply of the muscles and that of the underlying viscera explains the rigidity of the belly so usually seen in injury or disease of abdominal organs (page 1683 J. Finally the relation of the cuta- neous and muscular branches of the intercostal ner\'es is \\c\\ shown by the sudden inspiratory effort caused by a dash of cold water on the lower thoracic or abdominal region, six of these ner\es supplying the intercostal muscles as well as the antero- lateral surface of the chest and belly. The injurious effect of contusions is diminished by the presence of a thick layer of subcutaneous fat or by the interposition of a fleshy omentum. If the abdominal muscles are relaxed, serious injury to the viscera may be done without obvious damage to the parietes. Absence of ecchymosis or other visible sign of injury should therefore not lead to an absolutely favorable prognosis until after the lapse of suffi- cient time to permit of the development of visceral symptoms. Wounds. — The thinness and loose attachment of the skin of the abdomen favor the occurrence of cellulitis as a result of infection from superficial wounds. The superficial layer of the superficial fascia contains the greater part of the subcutaneous fat and covers the superficial blood-vessels. The thickness of the abdominal wall depends chiefly upon the thickness of this fatty layer, which may be of several inches. An abdominal wound may therefore be of considerable depth and yet be attended by little or no bleeding and be practically ' ' superficial. ' ' The deeper layer of the super- ficial fascia (page 515) is firmer, is elastic, and in its lower part is the vestige of the "tunica abdominalis," well developed in the horse and some other quadrupeds for reinforcement of the abdominal muscles, on which the weight of the viscera comes more direcdy than in man. It is attached in the middle line to the deeper struc- tures and to the iliac crest, and below Poupart's ligament blends with the fascia lata of the thigh. It is not attached over the space between the pubic spine and symphysis, but, being carried downward over the spermatic cord, becomes continuous with the dartos layer of the scrotum and with the fascia of Colles. Cellulitis superficial to this layer may therefore spread in all directions, but beneath it is likely to be at least tempo- rarily arrested at the lines of attachment indicated. General emphysema, effusions of blood, and collections of pus have for a time similar limitations. They are apt to be guided by this fascia into the space between the spine and the symphysis and to descend into the scrotum and towards the perineum, where the lateral attachments of CoUes's fascia to the margins of the pubic arch and posteriorly to the base of the triangular ligament prevent their spreading in those directions. More usually the extravasa- tion— blood, pus, or urine — gains this subfascial space below, as from rupture of the urethra anterior (inferior) to the triangular ligament (page 1932;, and ascends to the abdomen bv the same route, being prevented from crossing the mid-line or descend- ing to the thighs by the attachments of the deep layer of the superficial fascia that ha\'e been described. PRACTICAL CONSIDERATIONS: THE ABDOMEN. 529 Wovmds involving- the -muscular layers of the abdominal wall may gape widely, but the differing directions of the fibres of the extonal oblique, inteiaal obEqne, and traDS\'ersali3 tend to limit this just as they lessen the after-risk ok ventral hernia and favor cert^r. rhvsfr'.T^irsI a73. as the emptying of the bladder, the bowds, or the uterus. Thii iif tr -- z- : : i;rt :don is taken advantage of in gaining access to the abdominal canr.- ;r. 5 ; — r ; ' -r^-.i r.s (page 535). Infection in rht ^-.T-il ;;::-:. Yora/ar ^^ar-fx usually spreads rapidly on account of the abundance : . fr t. '^r tissue- The cdlulids or resulting abscess for collection of Wooc r . - ' . semilunar line in front, by the costo- chondral arch abc T ! , i the crest of the ilium bdow, and by the edge of the err;: - r ...c :-_ . _ -nsr words, by the attachments of the muscles between -■-'-::':. -'r.^y spread (Treves;. Beneath the a: 1 :~:-il -.vail, pracricaUy making a portion of it. Kes a layer of loose connective tii; i : — : ".r rj.bperitcmeal or subserous areolar tissue — which connects the peritoneum wirh ... ; ~ i-:r:e3. ""Extraperitoneal connective tissue'' has been sug-- gested (Ecdes) as s. '; t :: r r .-. ^~. ? f- r it. Infection of this tissue, whether from without. as in the case of -. ; i.'. i; r ; y txtenaon from some .._" .- ;. rrr.se the abdominal cavity has been op>ened. The s;.":r.'::~.; a.-. i la.-.it.'s :: ir.fec- tion will be as above enumerated. \Voun, V-, K', divisions of fifth cranial neri'e ; GA, great auricular; GO, SO, greater and smaller occipital ; SC, superficial cervical ; St, CI, Ac, sternal, clavicular, and acromial branches of supraclavicular {Scl) ; Ci, circumflex ; MS, musculo-spiral ; IH, intercosto-humeral ; LIC, IC, lesser internal and internal cutaneous ; EC, external cutaneous ; IH, ilio-hypogastric ; //, ilio- inguinal ; 7"i2, last thoracic ; GC, genito-crural ; EC, external cutaneous ; MC, middle cutaneous ; IC, internal cutaneous ; P, pudic ; ^.J, small sciatic ; O, obturator ; C, T, L, and S, cervical, thoracic, lumbar, and spinal nerves. 536 HUMAN ANATOMY. separated on the same line. No effort has been made, therefore, to show the latter muscle in the diagram. Incisions Nos. i, 2, and 3 are through the linea alba, No. 2 being carried around the umbilicus to the left to avoid the parumbilical vein and the round liga- ment of the liver. The chief advantage is the accessibility to the whole cavity afforded by prolonging the incision. The slight vascularity of the median raphe and the thinness of the abdominal wall, while operative advantages, tend to favor the later production of hernia. Incision No. 4 combines the disadvantages of the incisions through the linea alba with the added interference with the nerve-supply to the rectus. Incision No. 5 (McBurney) is described later (page 1685). It represents merely the separation of the aponeurotic fibres of the external oblique ; the deeper wound separates the internal oblique and transversalis fibres transversely. It may be noted that its inward extension (Weir), even if it in\olves division instead of retraction of the rectus (page 1685), would equally avoid nerve-trunks, but might involve ligation of the deep epi- gastric. The resulting scar in the rectus \yould, however, merely add in effect another linea transversa and would not impair the efhciency of that muscle. Incision No. 6 (Eads) separates the same structures, but affords a bet- ter opportunity for approach to many appendicular abscesses without going through the peritoneal cavitv (page 1685)": " The incision for inguinal colos- tomy (page 1688) may be made on the same lines as those just described. Incision No. 7, after division of the external oblique, permits the sepa- ration of the fibres of the internal ob- lique and of the upper abdominal in- tercostal nerves, which, like the others, run beneath that muscle, and is used to gain access to the gall-bladder region. Incision No. 8 also respects the internal oblique fibres and the seventh and eighth intercostal nerves and, when used for gastrostomy, permits the development of a valvular or sphincteric action about the orifice (page 1633). Incision No. g — the \'ertical incision through the rectus recommended for gas- trostomy (Howse) — must divide the terminal branches of the intercostal nerves, and consequently that portion of the muscle distal to the line of division will be weakened or paralyzed and unable to contribute to the formation of a sphincter fEads). The incision for lumbar colostomy is described later (page i688j. The re- maining incisions through the loin may be more appropriately considered in relation to the approach to the kidneys or ureters (page 1894). Anatomical Relations bearing on the Exa>nination of the Abdomen. — Harris has suggested utilizing the fi.xed and circuitous route of the colon (Fig. 1383) to subdi- vide the abdominal cavity by taking the inner or mesial laj^ers of the longitudinal mesocolons and the inferior layer of the transverse mesocolon as the dividing lines. We would thus obtain four regions, — namely, (i) the central region surrounded by mesocolon, (2) the superior region lying abo\'e the transverse mesocolon, (3) the right postero-lateral and (4) the left postero-lateral regions lying external to and behind the longitudinal mesocolons. Tumors of special viscera begin, as a rule, in the region normally occupied by PRACTICAL CONSIDERATIOx\S : THE ABDOMEN. 537 those organs, and often, when they overlap its boundaries, displace the colon in definite directions. The course of the colon being made apparent by inflating it with air, it may therefore be said that : 1. Growth in the central region would include tumors of the omentum, mesen- tery, small intestine, and peritoneum, many retroperitoneal tumors, and such growths afiecting the female generative apparatus as rise from the pelvis into the abdomen. In the latter case the caecum and sigmoid would be displaced upward and outward. 2. Tumors beginning in the superior region would include those of the liver, gall-bladder, stomach, lesser omentum, spleen, and pancreas. Harris calls attention to the fact that pancreatic cysts have usually been mistaken for ovarian cysts, although the former almost always displace the transverse colon downward. They also, being retroperitoneal, carry it forward, while tumors of the spleen, although they cause downward displacement of the colon, especially of the splenic fle.xure, override it and hug the anterior abdominal wall. Enlargement of the gall-bladder similarly tends to depress and to overlap the right half of the transverse colon. 3 and 4. In the postero-lateral or external regions the most common tumors are those of the kidneys ; but as they are all retroperitoneal, they tend to carry the ascending or descending colon forward as well as inward. There are, of course, exceptions to these relations, — as, for example, in the case of a movable kidney, which may be displaced so as to carry the inner layer of the mesocolon forward and inward and so have the colon lying to the outer side, — but they are rare, and the anatomical relations described are of distinct diagnostic value. Bowlby has formulated the anatomical reasons for first exploring the right lower half of the abdomen in cases of intestinal obstruction of doubtful origin. He says that here are to be found : (» the appendix ; (b') intestinal diverticula perhaps attached to the umbilicus or to the neighboring mesentery ; (c) a common site for volvulus, — that is, the caecum ; (' artery Dissection of anterior thoracic wall from behind, showing triangularis sterni and intercostal muscles. Action. — To draw downward the anterior portions of the ribs and so assist in expiration. Relations. — The internal mammary vessels pass downward upon the anterior surface of the muscle, separating it from the fibres of the internal intercostals. 4. Lev.\tores Cost.\rum (Fig. 521). Attachments. — The levatores costarum form a series of thin triangular mus- cles which arise from the transverse processes of the seventh cervical and all the thoracic vertebrae except the twelfth. They are directed downward and laterally to be inserted Into the posterior surface of the next succeeding rib (levatores eostarian breves) between the tubercle and the angle, some of the fibres of the lower mus- cles passing over a rib to be inserted into the next but one below {levatores costarum longi). THE THORACIC MUSCLES. 541 Nerve-Supply. — From the anterior divisions of the eighth cervical and the first to the eleventh thoracic nerves. Action. — To assist in drawing the ribs upward. Acting from the ribs, they will assist in bending the spinal column backward and laterally towards the same side and in rotating it towards the opposite side. 5. Serratus Posticus Superior (Fig. 539). Attachments. — The superior posterior serratus is a quadrangular, flat muscle which arises by a flat tendon from the lower part of the ligamentum nuchse and from the spinous processes of the seventh cervical and upper two or three thoracic ver- FiG. 539- Splenius capitis et Levator anguh scapulas Serratus posticus sup Trapezius--r (cut) Vertebral aponeurosis Trachelo-mastoid Internal pter>'goid omplexus Bi\ enter cervicis Scalenus medius -\ II cervical spinous process .Complexus Scalenus posticus Dorsal, cervical. Longissimus dorsi nd thoracic muscles. tebrae. Its fibres are directed downward and laterally to be inserted into the outer surface of the second to the fifth ribs, lateral to their angles. Nerve-Supply. — From the anterior divisions of the first to the fourth thoracic nerves. Action. — To raise the ribs to which it is attached and accordingly assist in inspiration. 6. Serratus Posticus Inferior (Fig. 559). Attachments. — The inferior posterior serratus arises by a broad but thin tendon from the posterior layer of the lumbo-dorsal fascia from about the level of the second lumbar to that of the tenth or eleventh thoracic vertebra. Its fibres are 542 HUMAN ANATOMY. directed upward and laterally and are inserted into the outer surfaces of the lower four ribs. Nerve-Supply. — From the anterior divisions of the ninth to the twelfth thoracic nerves. Action. — To draw the ribs to which it is attached downward and outward. The muscle contracts during inspiration and assists in this act by counteracting the tendency which the costal part of the diaphragm has to expend a portion of its con- traction in drawing the lower ribs upward and inward. Variations. — Variations in the extent of their origin are not uncommon in both the posterior serrati. Stretching; betueen them tliere is an aponeurosis, termed the vertebral aponeurosis. which represents the degenerated portion of a large muscle-sheet present in the lower mam- malia, of which the two posterior .serrati are the persistent upper and lower portions. (r) THE HVPOSKELETAL Ml"SCLE.S. The hyposkeletal group of muscles is practically unrepresented in the thoracic region. THE CERVICAL MUSCLES. The Deep Cervical Fascia. — The deep cervical fascia (fascia colli) is a well-marked sheet of connective tissue which lies beneath the platysma and forms a complete investment for the neck region, giving off from its deeper surface numer- ous thin lamellae which surround the various structures of the neck region. Pos- FiG. 540. Slerno-h Thyro-hyoid Omo-hyoid' ytenoideus Infer! Carolid shealh Prevertebral layer Platysma Sterno-mastoid Longus colli Scalenus anticus Scalenus medius Scalenus posticus Trachelo-niastoid Levator anguli scapulae Splenius colli Multifidus spin^e Seinispiualis ce: Trapeziu Splenius ca Pharyn.v RiglU carotid artery Rii^lit internal jugular Section across neck at 1 teriorly the fascia is attached to the ligamentum nuchae and, traced laterally, it is found to divide into two layers which enclose the trapezius and, uniting again at its outer border, are continued forward over the posterior triangle of the neck to the lateral border of the sterno-cleido-mastoid, where it again di\'ides into two layers to enclose that muscle. The two layers again unite at the medial border of the muscle and are continued over the anterior triangle of the neck to the median line, where the fascia becomes continuous with that of the opposite side. This is the superficial layer of the deep cervical fascia. Above it is attached to the superior nuchal line and the mastoid process, whence it is continued along THE CERVICAL MUSCLES. 543 the gi eater cornu and body of the hyoid bone, to which it is firmly attached, and where it becomes continuous above with the deep fascia of the submental region. This fascia covers in the anterior belly of the digastric, the mylo-hyoid, and the submaxillary gland, and is attached above to the lower border of the mandible, where it becomes continuous with the parotideo-masseteric fascia. Below the cervical fascia ends over the anterior surface of the cla\'icle, and, more medially, in the interval between the lower portions of the two sterno-cleido- mastdid muscles, it splits into two lamellae, enclosing what is termed the spatium siiprasternale or space of Burns. Both the lamellae pass down to be attached to the upper part of the manubrium sterni, so that the suprasternal space is completely closed. It contains some fatly tissue, usually some lymphatic nodes, and the lower portions of the anterior jugular veins ; a diverticulum from it- is prolonged laterally behind the insertion of the sterno-cleido-mastoid along each vein as it passes towards its point of union with the subclavian vein. From the under surface of this superficial layer a deeper or middle layer is given off at the sides of the neck, and, passing forward, assists in the formation of the sheath for the carotid artery and internal jugular vein, and then divides to enclose the omo-hyoideus and the other depressors of the hyoid bone, a special thickening of it extending downward from the intermediate tendon of the omo-hyoid to the clavicle. Above, the middle layer is attached to the greater cornu and body of the hyoid bone along with the superficial layer, but below it is continued down into the thorax in front of the oesophagus and trachea and becomes lost upon the upper part of the pericardium. A third or deep layer of the cervical fascia, also termed the preve^'tebral fascia, is given off from the under surface of the superficial layer about on the line of the transverse processes of the vertebrae. It passes almost directly inward over the scalene and hyposkeletal muscles of the neck, enclosing the cervical portion of the sympathetic trunk and contributing to the formation of the carotid sheath. It unites with the corresponding layer of the opposite side over the bodies of the vertebrae. This fascia is continued downward into the thorax in front of the verte- bral column and above it extends to the base of the skull. Towards the median line in its upper part it is separated from the pharyngeal portion of the fascia bucco-pharyngea by some loose areolar tissue which occupies the so-called retro- pharyngeal space. This is continued downward in the loose tissue surrounding the oesophagus, but is bounded laterally by the union of the pharyngeal and prevertebral fasciae. The carotid sheath is formed by the union of portions from the middle and deep layers of the cervical fascia. It forms an investment for the common carotid artery, the internal jugular vein, and the vagus nerve. (a) THE RECTUS MUSCLES. 1. Sterno-hyoideus. 3. Sterno-thyroideus. 2. Omo-hyoideus. 4. Thyro-hyoideus. 5. Genio-hyoideus. I. Sterno-Hyoideus (Fig. 541). Attachments. — The sterno-hyoid is a flat band-like muscle situated in the front of the neck close to the median line. It arises from the posterior surface of the sternal end of the clavicle and from the manubrium sterni and passes upward to be inserted into the lower border of the body of the hyoid bone. A mucous bursa, more constant in the male than in the female, usually occurs beneath the upper part of the muscle, resting upon the hyo-thvroid membrane near the median line and immediateh' below the hyoid bone. Nerve-Supply. — From the first, second, and third cervical ner\'es, through the ansa hypoglossi. Action. — To draw the hyoid bone downward. 544 HUMAN ANATOMY. Variations. — The sterno-hyoid may arise entirely from the clavicle or it may extend its origin to the cartilage of the first rib. It is often divided transversely by a tendinous band which may occur either in its lower part on a line with the intermediate tendon of the omo-hyoid or, more rarely, in its upper part on a level with the insertion of the sterno-thyroid. 2. Omo-Hyoideus (Fig. 541). Attachments. — The omo-hyoid is a long, flat muscle consisting of two bellies united by an intermediate tendon. The mfcrior belly arises from the lateral portion of the superior border and the superior transverse ligament of the scapula, and is directed forward, medially, and slightly upward to terminate in the intermediate tendon. This lies behind the clavicular portion of the sterno-cleido-mastoid, and is enclosed by the middle layer of the deep cervical fascia, a specially thickened portion of which binds it down to the posterior surface of the clavicle and to the first rib. The superior belly arises at the medial end of the intermediate tendon and passes upward and slightly medially to be inserted into the lower border of the hyoid bone, lateral to the sterno-hyoid. Fig. 541. Styloid proi Stylo-glossus- Stylo-pharyngeui Stylo h\ Digastric, postenor belly Rectus capitis anticus major. Spl, Sterno-cleido mastoid. Orbicularis oris Digastric, anterior belly Mylo-hyoid Hsoid bone Inferior pharyngeal constrictor lh\ro hyoid Muscles of the neck; larynx has been dr. Nerve-Supply. — From the first, second, and third cervical nerves, through the ansa hypoglossi. Action. — To draw downward the hyoid bone. Acting from above, it will assist slightly in drawing the scapula upward. This muscle may also act as a tensor of the cervical fascia, thereby preventing undue pressure on the great vessels of the neck. Relations. — At its attachment to the scapula the inferior belly is covered by the trapezius and the muscle is crossed in the middle part of its course by the sterno-cleido-mastoid. The inferior belly is in relation posteriorly with the scalene muscles and the roots of the brachial ple.xus and sometimes with the third portion of the subclavian artery, the transversalis colli and suprascapular arteries, and the supra- scapular nerve. The superior belly crosses the common carotid artery and the internal jugular vein at the level of the cricoid cartilage. THE CERVICAL MUSCLES. 545 Variations. — The omo-hyoid and the sterno-hyoid are derived from a muscular sheet which, in the louer vertebrates, invests the anterior portion of the neck region, lying beneath the platysma. This sheet is represented in man by the two muscles and the middle layer of the deep cervical fascia. The omo-hyoid or one or other of its bellies may be absent, or, on the other hand, an accessory omo-hyoid may be developed. The superior belly not infre- quently fuses more or less completely with the .stemo-hyoid and the inferior belly has some- times a clavicular origin. Occasionally the band which binds the intermediate tendon to the clavicle remains muscular, and, uniting at the tendon with the superior belly, produces what has been termed the cleido-hyoideus. 3. Sterno-Thyroideus (Fig. 541). Attachments. — The sterno-thyroid is a band-like muscle which lies immedi- ately beneath the sterno-hyoid. It arises from the posterior surface of the manu- brium sterni and from the cartilages of the first and second ribs, and passes upward to be insei'ted into the oblique line of the thyroid cartilage. Nerve-Supply. — From the first, second, and third cervical nerves, through the ansa hypoglossi. Action. — To draw the laryn.x downward. Relations. — Superficially the sterno-thyroid is covered by the sterno-hyoid. Deeply it is in relation with the inferior constrictor of the pharyn.x, the crico- thyroid muscle, the cricoid cartilage, the lobes of the thyroid gland, the inferior thyroid veins, the trachea, and the common carotid artery, and it crosses the- left innominate vein. Variations. — The lower portion of the muscle is often crossed by a tendinous intersection, and frequently some of its fibres are continued directly into the thyro-hyoid muscle. The two muscles of opposite sides are frequently united in the median line, sometimes throughout the greater portion of their length, at other times merely by scattered bundles. 4. Thyro-Hyoideus (Fig. 541). Attachments. — The thyro-hyoid lies beneath the upper portion of the omo- hyoid. It arises below from the oblique line of the thyroid cartilage and is inserted above into the lateral portion of the body and into the greater cornu of the hyoid bone. Nerve-Stipply. — From the first and second cervical nerves, by fibres which run with the hypoglossal nerve. Action. — To draw down the hyoid bone, or, if that be fi.xed, to draw the larynx upward. Relations. — As the muscle passes across the hyo- thyroid membrane it covers the superior laryngeal nerve and artery. A bursa, the b. musculi thyro-hyoidei, is interposed between the muscle and the upper part of the hyo-thyroid membrane. Variations.— The thyro-hyoid is often practically continuous with the sterno-thyroid. A bundle of fibres is sometimes to be found passing either from the lower border of the hyoid or from the thvroid cartilage to the lobe, isthmus, or pyramid of the thyroid gland. It is termed the levator 'glandule thyroideis, under which name are also comprised fibres which are exten- sions of the inferior constrictor of the pharynx to the thyroid gland. 5. Genio-Hyoideus (Fig. 497). Attachments. — The genio-hyoid is the superior portion of the rectus group of muscles. It is a rather narrow band which arises from the lower genial tubercle of the mandible and extends backward and downward to be inserted into the anterior surface of the body of the hyoid bone. It is situated close to the median line, under cover of the mylo-hyoid and immediately beneath the lower border of the genio-glossus. Nerve-Supply. — From the first and second cervical nerves, by fibres which accompany the hypoglossal. Action. — If' the hyoid bone be fixed, the genio-hyoid depresses the mandible ; if the mandible be fixed, it draws the hyoid bone forward and upward. 35 546 HUMAN ANATOMY. {6) THE OBLIQUUS MUSCLES. 1. Scalenus anticus. 3. Scalenus posticus. 2. Scalenus medius. 4. Rectus capitis lateralis. 5. Intertransversales anteriores. I. Scalenus Anticus (Fig. 542). Attachments. — The anterior scalene (m. scalenus anterior) arises by four tendinous slips from the anterior tubercles of the transverse processes of the third to the sixth cervical vertebrae. The four slips unite to form a rather flat muscle which extends downward and forward to be iiisoicd into the scalene tubercle on the upper surface of the first rib. Fig. 542. Sterno-mastoid, stump ■Rectus capitis aiuicus major Subscapularis Serratus magnus middle port' Levator anguli scapula?. Scalenus antic Scalenus medius Scalenus post Rhomboid Dissection of right side of neck, showing Serratus magnus, upper portion d adjacent muscles. Nerve-Supply. — By branches from the fourth, fifth and sixth cervical nerves. Action. — To bend the neck forward and to the same side and to rotate it to the opposite side. If the cervical vertebrae be fixed, it will then raise the first rib, assisting in inspiration. Relations. — The anterior scalenus lies in front of the roots of the brachial plexus, and near its insertion it passes over the second portion of the subclavian artery and under the subclavian vein. The phrenic ner\'e rests upon its anterior surface during its course down the neck. 2. Scalenus Medius (Figs. 541, 542). Attachments. — The middle scalene is situated behind the scalenus anterior. It arises by si.x or seven tendinous slips from the transverse processes of the lower six or of all the cervical vertebrae and extends downward and outward to be inserted THE CERVICAL MUSCLES. 547 into the upper surface of the first rib, behind the groove for the subclavian artery. Some fibres of the muscle may extend across the first intercostal space to be inserted into the outer surface of the second rib. Nerve-Supply. — By branches from the anterior divisions of the cervical nerves. Action. — To bend the neck laterally, or, if the cervical vertebrae be fixed, to raise the first rib, assisting in inspiration. Relations. — As the middle scalene passes downward to its insertion it diverges from the scalenus anterior, so that a triangular interval exists between the two muscles through which the subclavian artery and the brachial plexus pass, these structures lying in front of the insertion of the scalenus medius. 3. Scalenus Posticus (Fig. 542). Attachments. — The posterior scalene (m. scalenus posterior) lies immediately behind the scalenus medius and anterior to the ilio-costalis cervicis. It arises by two or three tendinous slips from the transverse processes of the lower two or three cervical vertebrae and passes downward and laterally to be mserted into the outer surface of the second rib. Nerve-Supply. — From the anterior divisions of the lower three cervical nerves. Action. — To bend the neck laterally, or, if the cervical vertebrae be fixed, to raise the second rib. Variations of the Scalene Muscles. — There is not a little variation in the extent of the upper attachments of the scalene muscles, the origins being increased or, more usually, dimin- ished in number. A certain amount of fusion may also occur, especially between the medius and posterior, so that it is not always possible to distinguish these two muscles. Occasionally the subclavian artery perforates the lower portion of the anterior scalene, and the portion so separated may form a distinct muscle, the scale?ius minimus, which lies in the interval between the anterior and middle scalenus, and is attached above to the transverse processes of the sixth or the sixth and seventh cervical vertebras and below to the upper surface of the first rib and to the dome of the pleura. A muscle occasionally occurs between the upper part of the pectoralis major and the upper external intercostals, from both of which it is separated by a lamella of areolar tissue. It is termed the supracostalis, and takes its origin from the first rib and sometimes also from the fascia which covers the anterior scalene, and passes downward to be inserted into the outer surface of the third and fourth ribs, sometimes attaching also to the second rib and sometimes descending as low as the fifth. It has been regarded as an aberrant portion of the pectoralis major or rectus abdominis, but it seems to be more probably a portion of the obliquus muscu- lature and is apparently related to the scaleni. 4. Rectus Capitis Lateralis. Attachments. — The rectus capitis lateralis is a short, flat muscle which arises from the transverse process of the atlas and is inserted into the inferior surface of the jugular process of the occipital bone. Nerve-Supply. — From the suboccipital nerve. Action. — To bend the head laterally. 5. Intertransversales Anteriores. Attachments. — The anterior intertransversales are a series of small muscles which pass between the anterior tubercles of the transverse processes of the cervical vertebrae. Nerve-Supply. — From the anterior divisions of the cervical nerves. Action. — To bend the head laterally. The Triangles of the Neck. — The sterno-cleido-mastoid muscle, on account of its position somewhat superficial to the remaining muscles of the neck, serves to divide that region into two triangular areas which are of considerable importance from the stand-point of topographic anatomy. 548 HUMAN ANATOMY. 543- Digastric, posterior belly Stylo-hjoid (cut) One of these triangles, the posterior, is bounded by the lateral border of the upper part of the trapezius behind and by the lateral border of the sterno- cleido-mastoid in front, and has for its base the upper border of the clavicle between the insertion of these two muscles. The anterior triangle is reversed with respect to the posterior one, having its apex downward and its base above. Its lateral boundary is the medial border of the sterno-cleido-mastoid, its medial boundary is the median line of the neck, and its base is formed by the lower border of the mandible and a line Fig. 54.S. extending horizontally backward from the an- gle of the mandible to the mastoid process. Each of these two triangles is again di- visible into subordinate triangles by the mus- cles which cross them. Thus the posterior tri- angle is divided by the inferior belly of the omo- hyoid, which crosses it obliquely, into an upper or occipital triangle and a lower or subclavian triangle, while the an- terior triangle is divisi- ble into three triangles by the superior belly of the omo-hyoid and the posterior belly of the digastric. The lowest of these triangles, termed the miiscnlarox inferior carotid triangle, has its. base along the median line and its apex directed laterally, its sides being formed by the sterno-cleido- mastoid below and the superior belly of the omo-hyoid above. The superior carotid triangle has its base along the upper part of the sterno-cleido-mastoid and its apex directed medially ; its sides are formed by the superior belly of the omo-hyoid below and the posterior belly of the digastric above. Finally, the submaxillary or digastric triangle is the basal portion of the original anterior triangle, and is bounded below by the two bellies of the digastric muscle and above by the line of the lower border of the mandible and its continuation posteriorly to the sterno-mastoid muscle. Omo-hyoid, anterior belly no-hyoid, posterior belly Triangles of neck. (f) THE HYPOSKELETAL MUSCLES. ■ I. Longus colli. 2. Rectus capitis anticus major. 3. Rectus capitis anticus minor. I. Longus Coi.m (Fig. 544). Attachments. — The longus colli forms an elongated triangular band whose base is towards the median line and the wide-angled apex directed laterally. It may be regarded as consisting of three portions. The medial portion consists of fibres which arise from the bodies of the upper three thoracic and lower two cervical vertebrae, forming a muscular band which is inserted into the bodies of the three or four upper cervical vertebrae, the slip to the atlas being inserted into its anterior tubercle. From the lower part of the medial portion slips are given off which con- stitute the iyiferior oblique portion, and are inserted into the transverse processes of the fifth and sixth, and sometimes also of the fourth and seventh, cervical vertebrae. THE CERVICAL MUSCLES. 549 And, finally, the superior oblique portion is formed by slips arising from the trans- verse processes of the sixth to the third cervical vertebrae and joining the upper part of the medial portion. Nerve-Supply. — From the anterior divisions of the second, third, and fourth cervical nerves. Action. — To bend the neck ventrally and laterally. Fig. 544. — Antenoi tubercle of atlas Longus colli, superior oblique portion Rectus capitis anticus major- Longus colli, median port] VII cervical vertebra I thoracic vertebra Deep dissection of neck, sho prevertebral muscles. 2. Rectus Capitis Anticus Major (Fig. 544). Attachments. — The rectus capitis anticus major (m. longus capitis) partly covers the upper part of the longus colli. It arises by four tendinous slips from the transverse processes of the third to the sixth cer\'ical vertebree, and passes directly upward to be inserted into the basilar portion of the occipital bone, lateral to the pharyngeal tubercle. Nerve-Supply. — From the anterior divisions of the second, third, and fourth cervical nerves. Action. — To flex the head and rotate it slightly towards the opposite side. 550 HUMAN ANATOMY. 3. Rectus Capitis Anticus Minor. Attachments. — The rectus capitis anticus minor (m. rectus capitis anterior) is a sliort, flat muscle vvliich arises from the anterior surface of the lateral mass of the atlas and is directed obliquely upward and medially to be hiserted into the basilar portion of the occipital bone, immediately behind the insertion of the longus capitis. Nerve-Supply. — By the first cervical (suboccipital) nerve. Action. — To fle.x the head. PRACTICAL CONSIDERATIONS ; THE NECK. The skin of the front and sides of the neck is thin and movable. The platysma myoides is closely connected to it by the thin superficial fascia. The edges of wounds transverse to the fibres of that muscle are therefore often inverted. In the region of the nape of the neck the skin is thicker and much more closely adherent to the deep fascia; it is poorly supplied with blood ; hair-follicles and sebaceous glands are numerous ; it is frequently exposed to minor traumatisms and to changes of surface heat, and is often at a lower temperature than the parts immediately above, which are covered with hair, or than those directly below, which are protected by clothing; the nerve-supply is abundant. For these reasons furun- cles and carbuncles are of common occurrence and are apt to be e.xceptionally painful. The subcutaneous ecchymosis which follows fracture through the posterior cerebral fossa first appears anterior to the tip of the mastoid and spreads upward and back- ward on a cur\ed line ; the blood is prevented from reaching the surface more directly by the cervical fascia, and therefore goes laterally in the intermuscular spaces, being directed towards the mastoid tip by the posterior auricular artery. In the submaxillary region the looseness of the skin makes it available for plastic operations on the cheeks and mouth. In the submental region the accu- mulation of subcutaneous adipose tissue seen in stout persons gives rise to the so-called " double chin." In both the latter regions (covered by the beard in men) furuncles and sebaceous cysts are common. The surgical relations of the fascia of the neck can best be understood by refer- ence to a horizontal section at the level of the seventh cervical vertebra (Fig. 545). The superficial layer {a, a' ) will then be seen to envelop the entire neck. Pos- teriorly it is attached between the external occipital protuberance and the seventh cervical spinous process to the ligamentum nuchre ; anteriorly it is interlaced with the same layer of fascia from the other side of the neck ; superiorly between the external occipital protuberance and the middle of the chin it is attached on each side to the superior curved line of the occipital bone, the mastoid, the zygoma, and the lower jaw ; inferiorly between the seventh spine and the suprasternal notch it is attached on each side to the spine of the scapula, the acromion, the clavicle, and the upper edge of the sternum. After splitting to enclose the trapezius and covering in the posterior triangle, this fascia divides again at the hinder border of the sterno- cleido-mastoid. The superficial layer continues over the surface of that muscle, covers in the anterior triangle, and blends with its fellow of the opposite side. From its under surface, after reaching the sterno-mastoid, the deeper layer gives off from behind forward {b) a process — pre\-ertebral fascia — which begins near the posterior border of the sterno-mastoid, passes in front of the scalenus anticus, the phrenic nerve, the sympathetic nerve, and the longus colli muscle, and behind the great vessels, the pneumogastric nerve, and the cesophagus to the front of the base of the skull and the bodies of the cervical vertebrae. In the mid-line this descends behind the gullet into the thorax. At the sides of the neck it helps to form the pos- terior wall of the carotid sheath, spreads out over the scalene muscles, and passes down in front of the subclavian vessels and the brachial plexus, until it dips beneath the clavicle. It is then applied closely to the under surface of the costo-coracoid membrane and splits to become the sheath of the axillary vessels. A second process (<■), leaving the sterno-mastoid more anteriorly, aids in forming the anterior wall of the carotid sheath, and joins the preceding layer just internal to the vessels. It is PRACTICAL CONSIDERATIONS : THE NECK. 551 usually described as part of (d) a process— tracheal— which leaves the sterno-mastoid nearer its anterior border, and, running behind the sterno-hyoid and sterno-thyroid muscles, descends in front of the trachea and the thyroid gland to become connected with the fibrous layer of the pericardium. The adhesion of the deep fascia to the blood-vessels, by preventing contraction and collapse of their walls, favors hemorrhage and increases the risk of the entrance of air into divided veins. Tracing the layers of fascia vertically and from the surface inward, it will be useful to remember that the superficial layer {a, Fig. 546) passes to the top of the sternum (sending a slip to be attached to its posterior border) and to the clavicle. The second layer {b) descends behind the depressors and in front of the thyroid gland and trachea to merge into the pericardium, and farther out to form a sheath for the omo-hyoid and for the subclavian vein, and is lost in the sheath of the subclavius. Fig. 545. Fusion of superficial layer in mid-line CEsophagu Carotid arter> Internal jugular Vertebral vessels. Trap. Space Extern, jugular Spinal nerves, cut obliquely Fascia covering \ posterior triangle Li^amentum nuchae enth cervical vertebra. This relation of the omo-hyoid is of value in enabling that muscle, when the hyoid is fi.xed, to increase the tension of this layer of fascia, and thus hold open and prevent atmospheric pressure upon the walls of the vessels — especially the veins — and the soft parts (including the pulmonary apices) at the base of the neck. Hilton uses this function of'the muscle — which connects it with the act of respiration — to illustrate the precision of the nerve-supply to muscles generally. The omo-hyoid arises in close proximity to the suprascapular notch, and therefore to the supra- scapular nerve. Yet it never receives a filament from that nerve, but is supplied by the cervical nerves to bring it in relation to the movements of the other neck muscles, is connected with the hypoglossal to associate it with the movements of the tongue, and with the pneumogastric to enable it to act as above described during forced respiration, when the rush of air into the thorax might otherwise cause harmful increase of atmospheric pressure in the lower cervical or supraclavicular region. The pretracheal layer is found between the depressors and the trachea passing down to its pericardial insertion. Hilton thus explains this insertion : ' ' The peri- cardium is most intimately blended with the diaphragm, distinctly identified with it, and capable of being acted upon by it at all times. It is also attached above to the deep cervical fascia. It is thus kept tense by the action of the respiratory muscles in the neck attached to the cervical fascia above and the diaphragm attached to it 552 HUMAN ANATOMY. below ; or, in other words, these two muscular forces are acting on the interposed pericardium in opposite directions, and so render it tense and resisting. And the special object, no doubt, of this piece of anatomy is that during a full inspiration, when the lungs are distended with air and the right side of the heart gorged with blood from a suspension of re^iration, the heart should not be encroached upon by the surrounding lungs." The prevertebral layer (r. Fig. 546 ) lying between the cesophagus and spine passes in the mid-line directly into the posterior mediastinum; laterally — beyond the scalenus anticus — it aids in forming the sheath of the subclavian vessels and accom- panies them into the axilla. Another way of elucidating the practical effect of the somewhat complex dis- tribution of the cervical fascia is to regard the three chief layers — superficial, middle, and deep — as dividing the neck into four anatomical spaces (Tillaux). 1. Subcutaneous (Space i, Fig. 545) : between the skin and the superficial layer. The most important structure in this space is the external jugular vein, which perforates the fascia just above the middle of the clavicle. 2. Intra-aponeurotic (Space 2, Fig. 546) : between the superficial and mid- dle (sterno-clavicular) layers. This Fig. 546. space does not exist in fact at the summit of the neck where the two layers are one, but at the base its / depth is equal to the thickness of the sternum. It may be continuous with the space left at the top of the sternum between the two leaflets of i the superficial layer attached to the j anterior and posterior borders of the sternum, — Griiber's "suprasternal I intra-aponeurotic space," " Burns' s ] space." It contains fat and lym- i phatic glands, the sternal head of \ the sterno-mastoid, and the anterior \ jugular veins. It is not infrequently the seat of abscess. 3. Visceral (Space 3 ^ 3fl + 3(^, 1 Fig. 545): between the pretracheal I and prevertebral layers. This in- cludes all the principal structures of the, neck. As it communicates di- rectly with the thorax and axilla, in longitudinal .- ^ 1 • ^i. j- suppuration may travel in those di- rections. It is divided into minor spaces (3rt and ^d) by a layer of fascia coming from the under surface of the sterno- mastoid muscle and by the bucco-pharyngeal fascia, a thin layer that comes of! from the prevertebral fascia where it leaves the carotid sheath, and which lines the constrictors of the pharynx, leaving between it and the layer applied to the spinal column a small but easily distended space — retropharyngeal — in which infection from pharyngeal lesions occasionally occurs. 4. Retro visceral (Space 4, Fig. 546): the space between the prevertebral fascia and spinal column, including the longus colli and rectus capitis anticus, the sympa- thetic nerve, etc. It is obvious in a general way that all infections beneath the middle layer of fascia are more likely to be serious than those superficial to it. But to summarize in a little more detail the practical relations of the cervical fascia, we may conclude that superficial to the outer layer (a. Fig. 545) there might occur from traumatism a wound of the external jugular, or from infection a spread- ing cellulitis. The space is the seat of superficial phlegmons, which tend to spread under the skin only (Space i. Fig. 545), and, in the absence of tension, are unat- tended by throbbing pain or marked constitutional symptoms. Left innominate vein Aortic arch Diagram showing PRACTICAL CONSIDERATIONS : THE NECK. 553 The space between c and b (2,l>, Fig. 545) is occupied only by the great vessels and the pneumogastric. Infection there — i.e., within the sheath — may mean de- scending thrombosis from original infection of a cerebral sinus, or may have spread directly through the sheath from infected tracts of cellular tissue outside. Behind b, Fig. 545 (retrovisceral space), suppuration is not uncommon as a result of verte- bral disease. Direct infection through the pharyngeal wall usually involves the retropharyngeal space. In either case dysphagia and dyspncea are usual for obvious reasons. Between b and c. Fig. 546 (pretracheal' and prevertebral layers), abscess would spread most readily along the line of the trachea and in front of the vessels into the superior mediastinum. In the intra-aponeurotic space (Space 2, Fig. 546) an abscess would probabl)'- point superficially, as the fascia in front of it is very thin. If it were influenced by gravity, however, it would follow the hyoid depressors and their intermuscular spaces to the root of the neck, and might enter the superior mediastinum. Two additional and important spaces are formed by extensions or reduplications of the cervical fascia. That portion of the superficial layer above the level of the angle of the inferior maxilla, and passing from that bone to the zygoma, constitutes the parotid fascia, which on the surface is continuous with that over the masseter, while beneath it becomes thickened to constitute the stylo-maxillary ligament, sep- arating the parotid and submaxillary glands and resisting overaction of the external pterygoid muscle. As the outer fascial investment of the gland is dense and resistant, and as internal to this Fig. 547. ligament the inner layer is thinner and weaker than elsewhere, — a positive gap existing between the styloid process and the pterygoid muscle,— suppuration within the gland may result in extension to the retropharyngeal I -^ \ -Myio-hyoid muscle region. It may follow the external carotid downward to the chest, or, as the fascial investment is also incomplete above, may extend upward to the base of the skull, or even into the skull. It sometimes follows the branches ~/' of the third division of the fifth nerve through the fora- / / Outer layer of fascia men ovale into the cranium. / inner layer of fascia The second space alluded to is formed by ^that por- Submaxillary gland tion of the superficial layer between the jaw and the „anc°ibirsh"y'in'g^^^^^^ hyoid bone and in front of the stylo-mandibular ligament, vicai fascia. As it passes forward from the latter structure it splits and envelops the submaxillary gland, and becomes firmly attached below to the hyoid and above to the lower jaw externally and the under surface of the mylo-hyoid muscle internally (Fig. 547). Infection — " Ludwig's angina," "submaxillary phlegmon," "deep cervical phlegm.on" — in this space, which contains the salivary gland and its attendant lymphatics, is rendered exceptionally grave by the density of these fascial layers. The infecting organisms — usually streptococci — may gain access through a lesion of the floor of the mouth near the frenum, or from an alveo- lar abscess, or by way of the digastric muscle from a focus of disease in the middle ear. Once established, they, with their secondary products, are forced along the lines of least resistance — by the side of the mylo-hyoid usually — towards the base of the tongue, involving the cellular tissue about the glottis and along the vessels that perforate the fascia, causing infective venous thrombosis and involving the deeper planes of connective tissue. Under the latter circumstances, if tension is not promptly relieved, large vessels- may be opened by the necrotic process. Jacobson long ago called attention to the interesting fact that communications between ab- scesses and deep vessels have usually taken place beneath the cervical fascia and the fascia lata, two of the strongest fasciae of the body. Tumors of the neck may originate in any of the diverse structures of that region. It may be mentioned here that their situation above or beneatli the cervical fascia is an important factor in determining their mobility, and hence the probable ease or difficulty of their removal. In the latter situation associated pressure- symptoms are common. 554 HUMAN ANATOMY. Lipoma is frequent ; fibroma and enchondroma are occasionally seen in the region of the ligamentum nuchse ; primary carcinoma is rare. Congenital cysts — " hydroceles" — of the neck are found beneath the deep fascia, usuaHy in the anterior triangle and below the level of the hyoid. They may arise from dilatation of the lymphatic vessels, or, as Sutton suggests, they may originate, as do the cervical air-sacs in some monkeys, especially the chimpanzees, by the formation of diverticula from the laryngeal mucous membrane. In any event, they ramify in the various intermuscular spaces, and their complete removal is therefore very difficult. Branchial cysts and dermoids are not infrequent. They should be studied in connection with the embryology of the region. Congenital tumor of the sterno-mastoid is a condition resulting from either rup- ture of muscular fibres or bruising of the muscle against the under surface of the symphysis during delivery. It may be a cause of torticollis. Torticollis — "wry-neck" — maybe due to spasm of the sterno-mastoid either alone or associated with a similar condition of the trapezius, especially the clavicular portion, and often of the scaleni or the complexus. Later there is apt to be second- ary contraction of the deep fascia and of the posterior cervical muscles. Tenotomy of the muscle for the relief of this affection is performed at a level just above its sternal and clavicular insertion. The subcutaneous method has been largely dis- carded in favor of division through an open wound. By the former plan, not only were the anterior, and sometimes also the external, jugular veins endangered, but the cervical space described as "visceral" was occasionally opened, and, if infection occurred, with fatal results from septic cellulitis or pleurisy. Section of the spinal accessory nerve may be resorted to when the spasm is limited to the sterno-mastoid and trapezius, or of the posterior primary divisions of the first, second, and third cervical nerves when the posterior muscles are involved. Landmarks. — Athough but few organs belong e.xclusively to the neck, a great many structures of much diversity, and connecting the trunk and head, pass through it. The " landmarks" will therefore be found in relation to different systems, — vas- cular, nervous, etc. , — those given here referring chiefly to the muscles and their effect upon surface form. The mid-line posteriorly has already been described in its relation to the spines of the cervical vertebrae (pages 146-148). On the sides of the neck the platysma, when in action, produces inconspicuous wrinkling of the skin. Its fibres are in a line from the chin to the shoulder. The sterno-mastoid, running obliquely from the skull to the sternum and clavicle, divides each lateral half of the neck into two triangles. The anterior of these is bounded above by the lower border of the inferior maxilla and a line extending from the angle of that bone to the mastoid process ; anteriorly by a straight line between the middle of the chin and the sternum ; posteriorly by the anterior border of the sterno-mas- toid. Its apex is at the middle of the upper edge of the manubrium. The posterior triangle is bounded posteriorly by the anterior edge of the trapezius, the hinder edge of the sterno-mastoid in front, and the middle of the clavicle below. Its apex is just behind the mastoid process. It will be seen that by this — the usual — description those structures lying imme- diately beneath the sterno-mastoid would be excluded from both triangles. It is cus- tomary, however, to include the common carotid and internal jugular vein in the anterior triangle, although they are both under cover of the anterior edge of the sterno-mastoid. The anterior triangfe is divided into three — the superior carotid, the inferior carotid, and the submaxillary — by the digastric muscle and the anterior belly of the omo-hyoid. The posterior belly of the omo-hyoid divides the posterior triangle into a lower or subclavian and an upper or occipital triangle. The structures included within these various triangles will be described in connection with the vessels, nerves, etc. The dividing line between the two main triangles — the sterno-mastoid — can be both seen and felt if, with the mouth closed, the chin is depressed and the skull is rotated towards the opposite shoulder. The thick, prominent, rounded anterior bor- PRACTICAL CONSIDERATIONS : THE NECK. 555 der can then be made out from mastoid to sternum, but is more accentuated below, where the sternal head is salient and sharply defined. This thin posterior border may be felt vaguely at the upper part, but cannot be seen. At about the lower third it becomes visible and is continued into the broader and flatter clavicular head. The middle of the muscle is seen throughout most of its length as a fleshy, rounded elevation. Over it, and usually plainly visible, is the external jugular vein, running between the platysma and the deep fascia in a line from the angle of the jaw to the centre of the clavicle. In rest the anterior border is still visible. The position of the muscle on the side towards which the head is turned is indicated by a slight furrow in the skin. The muscles partly overlapped by the sterno-mastoid are, from above downward, the splenius, levator scapulae, digastric, omo-hyoid, sterno-thyroid, and sterno-hyoid. Fig. 548. External jugul; Trapezius' Acromio-clavicular joint Acromion process \- Greater / tuberosity / of humerus"^^ — Coracoid_ process Submaxillary gJana Digastric, anterior belly H>oid bone Thyroid cartilage Cricoid cartilage praclavicular fossa Suprasternal notch {jugular fossa) Omo-hyoid, posterior belly Supraclavicular fossa cular fossa Surface markings of neck, from living subject. The interval between the sternal and clavicular heads of the muscle is indicated by a slight depression, — the lesser supraclavicular fossa, — and is bounded below by the upper edge of the inner third of the clavicle. Beneath it, about on a line with the sternal end of the clavicle, lie on the right side the bifurcation of the innominate artery and on the left the common carotid artery. Between the outer edge of the clavicular head of the sterno-mastoid and the base of the anterior edge of the trapezius is a broad, flat depression, — the supracla- vicular fossa, — which is made very evident by shrugging the shoulders, and across which the posterior belly of the omo-hyoid runs and can often be seen and felt in thin persons, especially during inspiration or when the head is turned towards the opposite side (Fig. 548). The line of the muscle is from the suprascapular notch, slightly ascending to the anterior margin of the sterno-mastoid at a level with the cricoid cartilage and then rapidly ascending to the body of the hyoid. Below its 556 HUMAN ANATOMY. posterior belly run the brachial plexus, which can often be felt and sometimes seen, and, near the clavicle, the subclavian artery. Farther out the anterior border of the trapezius may be seen passing from the occiput to its insertion at the outer end of the middle third of the clavicle. The triangular interval between it and the posterior border of the sterno-mastoid is filled — from below upward — by the scalenus medius, the levator anguli scapulae, and the splenius, but none of them is recognizable through the deep fascia. In the mid-line behind, in addition to the bony points already given (pages 146—148), the line of origin of the trapezii can be seen as a slight elongated de- pression. None of the deeper muscles can be seen or felt upon the surface. In the mid-line in front the hyoid bone and its cornua can be felt in the angle between the under surface of the chin and the front of the neck. From the hyoid bone on either side the anterior bellies of the digastric run up towards the symphysis and with the subcutaneous fat give convexity to the submental region. Farther out on this level the submaxillary salivary glands can be felt and often seen. The thyro-hyoid depression, the prominence of the thyroid cartilage { pomiim Adami'), the crico-thyroid space, the cricoid cartilage, and sometimes the upper rings of the trachea may be felt from above downward. The relations of these parts to important vascular and nervous structures will be considered later. The sterno-thvroid and sterno-hyoid muscles, while not visible, co\'er over and obscure the outlines of the trachea, as does also the thyroid isthmus. The thyroid lobes may be felt on each side of the larynx. The average distance from the cricoid to the upper edge of the manubrium is about one and a half inches when the head is erect. In full extension three-quarters of an inch additional can be gained. The trachea recedes as it approaches the sternum, so that it is fully an inch and a half behind the upper border of the latter. In this position between the two sternal heads of the sterno-mastoid is the deep, V-shaped suprasternal notch (fossa jugularis), the depth of which is noticeably affected by forced respiration, being much increased in obstructive dyspnoea. All the surface appearances above described differ in different indi\'iduals, and vary in the same person in accord with many conditions, as the amount of subcu- taneous fat, the muscular vigor and development, the pulmonary capacity, the state of repose or of violent exertion, etc. This should be remembered in looking for landmarks in this region, which is in that respect one of the most variable of the body, and most unlike that of the cranium, which perhaps typifies the other extreme of unchangeability. DlAPHR.\GMA (Fig. 549). The diaphragm is a dome-shaped muscular sheet which separates the thoracic and abdominal cavities. Notwithstanding its position in the adult, it is a deri\ative of the cervical myotomes. It represents the upper portion of a structure which is termed in embryology the septum transversum (page i70i),a connective-tissue partition which extends between the ventral and lateral walls of the body and the heart, and serves to convey venous trunks to that organ. Like the heart, when first formed it lies far forward in the uppermost part of the cervical region, but later it descends with the heart until it reaches its final position. As it passes the third and fourth cervical myotomes in its descent, it receives from them some muscle-tissue which eventually forms all the muscle-tissue of the diaphragm, that structure, so far as it is to be regarded as a muscle, being a derivative of the cer\'ical myotomes named. The diaphragm is a muscular sheet composed of fibres radiating from the lower border of the thorax and from the upper lumbar vertebree towards a central tendi- nous area, termed the centrum tcndinciim. According to their origin, the muscle- fibres mav be grouped into three portions. The sternal portion consists of, usually, two bands which arise from the posterior surface of the xiphoid process of the stermmi and are separated from one another by a narrow interval filled with con- nective tissue. Laterally they are separated by a similar interval, through which the superior epigastric artery enters the sheath of the rectus abdominis, from the THE CERVICAL MUSCLES. 557 costal portion, the fibres of which take their origin from the cartilages of the lower six ribs, interdigitating with the origins of the transversalis abdominis. In conti- nuity with the costal part is the lumbar part, whose fibres take oi'igin (i) from two tendinous arches, the internal and external arcuate ligaments, which pass over the upper portions of the psoas ( arciis lumbocostalis medialis) and the quadratus lum- borum muscles (arcus lumbocostalis lateralis) respectively, stretching between the twelfth rib and the transverse process of the first lumbar vertebra, and (2) by two downward prolongations, the C7'u)'a, from the anterior and lateral surfaces of the upper three or four lumbar vertebrse. The right crus usually extends somewhat farther downward than the left, whose attachment does not pass below the second or third vertebra. Each crus has been divided into three portions, medial, intermediate, and lateral, which are not, how- ever, always clearly recognizable, although indicated by the passage of certain struc- tures from the thorax to the abdomen. Thus, between the medial and intermediate Fig. 549. Interval between sternal and costal portions Inferior vena ca^a. Lower end of sternum Right greater splanchnic nerve, XII rib. Aorta Thoracic duct XII nb External arcuate ligament Quadratus lumbor 1 Internal arcuate ligament Left crus Psoas magnus Diaphragm, viewed from below and the left. crura the greater splanchnic nerve and the azygos (or hemiazygos) veins pass, while between the intermediate and lateral crura is the sympathetic trunk. The two crura, as they pass upward, leave between them an opening, the hiatus aorticus, which is bridged over by a tendinous band (media?! arcuate ligarnent^ and gives passage to the aorta and thoracic duct. Just behind the posterior margin of the centrum tendineum the crural fibres diverge to surround in a sphincter-like manner the hiatus cesophageus, through which pass the oesophagus and the vagus nerves and oesophageal branches from the gastric artery and veins. The centrum te^idineiim, into which the fibres of the three portions insert, is situated somewhat nearer the anterior than the posterior margin of the diaphragm, so that the fibres of the sternal muscular portion are considerably shorter than the others. It has a trefoil shape, possessing a central and two lateral lobes, the right one of these being perforated by a somewhat quadrate foramen, the foramen veins cavcB {foramen qtiadratuni) , which transmits the vena cava inferior. The centrum tendineum forms the centre of the dome of the diaphragm, and from its borders the muscular fibres slope downward towards their insertion, the slope of the crural fibres being much steeper than those of the other portions. 558 HUMAN ANATOMY. The dome does not, however, form a simple cur\'e, but is divided by a median depression, which traverses it from before backward, into two secondary lateral domes which are unequally developed, that of the right side extending upward as far as the level of the junction of the fourth costal cartilage and rib, while that of the left reaches only to the fifth costo-cartilaginous junction. Nerve-Suppiy. — From the third, fourth, and sometimes the fifth cervical nerves, by the phrenic nerves. Action. — To increase the vertical diameter of the thorax, a contraction of the muscle-fibres depressing the summit of the dome. Relations. — The upper surface of the diaphragm forms the floor of the thoracic cavitv and is in contact with the pleurae and pericardium, the latter being adherent to the centrum tendineum. Below, the diaphragm is largely invested by peritoneum, and is in relation with the liver, stomach, spleen, kidneys, suprarenal bodies, duodenum, pancreas, inferior vena cava, and the branches of the cceliac artery. Variations. — Occasionally the diaphragm is incomplete in its posterior portion, a condition which permits the formation of congenital diaphragmatic hernias. Embr\ ologically the pos- terior portion of the diaphragm is the last to form, and in this fact is probably to be found an explanation of the location of this imperfection and also of tlie course of the phrenic nerves anterior to the roots of the lungs to reach the earlier formed anterior portion of the diaphragm. Fibres which arise from the crura and pass to neighboring structures are frequently present. Among the more constant of these are fibres which arise from the inner borders of both cnira and pass to the lower portion of the cesophagus, mingled with dense connective-tissue fibres, and others which pass from one crus or the other into the niesenten,- of tlie upper part of the jejunum. Probably the suspensory muscle of the duodenum, or muscle of Trcilz, which passes from the left crus to tlie terminal portion of the duodenum, belongs to this latter group of fibres, although it has been stated to be formed by non-striated muscle-fibres. THE PELVIC AND PERINEAL MUSCLES. The ventral portions of the myotomes succeeding the first lumbar and from that as far down as the third (or second) sacral are almost entirely unrepresented in the trunk, being devoted to the formation of the musculature of the lower limb. Below Fig. 550. xtenial iliac vessels Obturator interim'. — Alcock's caml Pelvic fascia Obturator fascia ..Anal fascia Ischio-rectal fossa Seminal vesicle E.vternal sphincter Internal sphincter Rectum Diagrammatic frontal section through pelvis, showing relations of fascial lay Fascia endopelv ■^ Pelvic fascia Recto-vesical layer vail and floor. the point mentioned, however, the ventral musculature again appears in the trunk in the pelvic, the perineal, and occasionally the coccygeal region. Owing to the conditions under which it appears, it is not possible to refer the muscles derived from it to the various subdivisions into which the ventral musculature of other regions is divisible, and they will therefore be considered in sequence without any attempt at classification other than regional. The Pelvic Fascia. — The pelvic fascia is attached above to the promontory of the sacrum and the ilio-pectineal line (linea terminalis) of the pelvis, where it THE PELVIC AND PERINEAL MUSCLES. 559 becomes continuous with the ihac fascia. It descends over the surface of the pyri- formis and laterally over the upper portion of the obturator internus and the pelvic surface of the pelvic diaphragm. In the upper part of its course over the pehic dia- phragm it is crossed by a curved thickening, the arcus tendineus, which is attached behind to the spine of the ischium and passes in front upon the sides of the prostate gland or, in the female, upon the bladder, and is continued thence to the anterior pelvic wall to be attached on either side of the symphysis pubis, a little above its lower border, as a lateral pubo-prostatic (^pubo-vesical) ligament. Along this tendi- nous arch the pelvic fascia gives of? a layer which passes inward to the peh-ic viscera, and is termed the fascia endopelvina. In its anterior portion this forms an in\-estment of the prostate in the male and of the base of the bladder in the female, and its under surface in this region is in contact with, and indeed may be regarded as being fused with, the superior layer of the triangular ligament (page 563). That portion of the layer which intervenes between the prostate (or bladder) and the posterior surface of the body of the pubis forms what is termed the tnedian pubo-prostatic {pubo-vesical ) ligament. The continuation of the pelvic fascia passes downward over the surface of the peh'ic diaphragm, and is termed the superior fascia of that structure (fascia dia- phragmatis pelvis superior). The Obturator Fascia. — From the line along which the pelvic fascia leaves the surface of the obturator internus muscle to pass upon the pelvic diaphragm a sheet of fascia is continued downward over the surface of the obturator internus muscle to be attached below to the tuberosity and ramus of the ischium and the ramus inferior of the pubis. This is the obtia'ator fascia. Along its upper border, nearly corresponding with the arcus tendineus of the pelvic fascia, but lying abo\-e this thickening and ending anteriorly farther from the median line, is a similar curved thickening extending from the spine ot the ischium, or in some cases from the ilio-pectineal line behind to the posterior surface of the body of the os pubis in front. From this thickening the greater portion of the levator ani muscle arises ; it is consequently termed the arcus tendineus m. levatoris ani, or more briefly the white line. From the line a thin layer of fascia is continued inward upon the under surface of the le\'ator ani, forming what is termed the anal fascia (fascia diaphragmatis pelvis inferior). This latter fascia forms the inner and the obturator fascia the outer wall of the ischio-rectal fossa. Near its lower border the obturator fascia splits into tsvo layers to form a canal, the canal of Alcock, along which the pudic vessels and ner\^e pass towards the perineum. In the above description the term peh^ic fascia is applied to the layer of fascia which lines the entire true pelvic cavity, — that is to say, the funnel-shaped cavit>' included between the pel- vic brim and floor. This conception, employed bv the German authors, differs somewhat from that usually held by English anatomists, in that the latter restrict the term to that portion of the fascia extending from the ilio-pectineal line to the white line, the continuation down- ward over the pehic diaphragm being termed the recto-z'esical fascia, from which extensions pass to the bladder, prostate gland, and rectum. The term recto-vesical has also been restricted to the portion of the sheet which extends between the rectum and the bladder and encloses the seminal vesicles (Cunningham), and if the term is to be employed at all, this application of it seems to be the preferable one. Confusion has also existed in the application of the term "white line," since it has been made to include both the arcus tendineus proper and the thickened band from which the leva- tor ani takes its origin (arcus tendineus ni. levatoris ani). These two bands are, hou'e\er, quite distinct, especially anteriorly, as a careful inspection of the subject will demonstrate, and it seems preferable to restrict the term "white line" to that from which the levator ani arises, naming that at which the fascia endopelvina begins the arcus tendineus. {a) THE PELVIC MUSCLES. I. Levator ani. 2. Coccygeus. 3. Pyriformis. The floor of the pelvis is formed by two muscles which constitute an almost complete partition, the pelvic diaphragtn, separating the pelvic from the perineal region. The more anterior and larger of these muscles is the le\ator ani, the coccy- 56o HUAiAN ANATOMY. geus lying along its posterior margin. Above the upper margin of the latter, and forming the posterior wall of the pelvis, is the pyriformis. Slight intervals occupied by connective tissue usually exist between the coccygeus and the other two muscles, presenting opportunities for pelvic hernias. I. Levator Ani (Fig. 551). Attachments. — The levator ani cir/ses from the posterior surface of the body of the OS pubis in front, from the spine of the ischium behind, and in the interval between these two points from a thickening of the ujaper border of the obturator fascia, the white line. From this long line of origin the fibres converge downward and medially to be inserted into the sides and tip of the coccyx, into a tendinous raphe extending in the median line between the tip of the coccy.x and the anus, and into the sides of the lower part of the rectum. The fibres from the most anterior portion of the origin pass almost directly backward and downward to reach the sides of the rectum, and between them and the corresponding fibres of the muscle of the opposite side is a Fig. 551. Pyriformis -(^' Coccygeus White line^ \ Levator ani obturator inter- ■ered by pelvic fascia Muscular floor of pelvis, viewed from above space, occupied in the male by the lower part of the prostate gland and in the female by the base of the bladder and lower part of the vagina, the fascia endopelvina in this region coming into contact with the upper surface of the superior layer of the triangular ligament of the perineum. Nerve-Supply. — The posterior portion of the muscle is supplied by a special branch from the third and fourth sacral nerves, the anterior portion by twigs from the inferior hemorrhoidal branches of the pudic nerve. Action. — To bend the coccyx forward and to raise the pelvic floor and viscera. Variations. — The levator ani is always a well-developed muscle, although the extent of its attachment to the sides of the coccyx varies inversely to the attachment of the coccygeus to that bone. There is usually to be found a dividing line extending across the muscle on a level with the junction of the superior ramus of the pubis with the iliuiu and separating those fibres which are inserted into the coccyx and the posterior portion of the fibrous raphe from those which pass to the anterior part of the raphe and the rectum. Each of the portions so separated is sup- plied by a separate nerve, and this, combined with the results of comparative anatomy, seems to show that the posterior portion of the levator is really a muscle quite distinct from the ante- rior portion. It has been termed the m. ilio-coccygeus. Furthermore, it seems probable that THE PELVIC AND PERINEAL MUSCLES. 561 the anterior portion is composed of two morphologically distinct muscles, one of which arises from the pubis and anterior part of the white line and is inserted into the median fibrous raphe, whence it is termed the m. pubo-coccygeus ; while the other, situated beneath, — i.e., superficial to the pubo-coccygeus, — consists of those fibres which arise from the pubis and are inserted into the rectum, and is termed the m. pubo-rectalis. It may be added that in the lower mammals the muscles corresponding to the ilio-coc- cygeus and pubo-coccygeus are inserted into the caudal vertebrae and act as lateral flexors of the tail. 2. COCCYGEUS (Figs. 55I, 603). Attachments. — The coccygeus, which forms the posterior and lesser portion of the diaphragma pelvis, lies immediately behind the levator ani. It arises from the spine of the ischium and is inserted into the sides of the sacrum and coccyx. Nerve-Supply. — From the third and fourth sacral nerves. Action. — To assist the levator ani in raising the pelvic floor. It also flexes the coccyx laterally. Variations. — Occasionally the insertion of the coccygeus is confined to the sides of the sacrum, in which cases its coccygeal area is occupied by fibres of the levator ani. The muscle is sometimes termed the ischio-coccygens, and is represented in the lower mammals by a muscle attached to the caudal vertebrae and acting as a lateral flexor of the tail. The Sacro- Coccygeus Anterior. — Occasionally muscular fibres are to be found arising from the ventral surface of tlie sacrum and inserting into the coccy.x. They form what is termed the sacro-coccygeus anterior or curvator coccygis, and apparently belong to the hyposkeletal group of muscles. 3. Pyriformis (Figs. 551, 552, 602.) Attachments. — The pyriformis (m. piriformis) arises from the ventral surface of the sacrum, between the first, second, third, and fourth sacral foramina. It passes laterally through the great sciatic fora- men, receivingabundle of fibres from the upper margin of the foramen, and is inserted into the summit of the great trochanter, its tendon shortly before its inser- tion becoming closely united with that of the obturator internus. Nerve - Supply. — By branches from the sacral plexus from the first and second sacral nerves. Action. — To ro- tate the thigh outward and to draw it slightly outward and back- ward. Relations. — By its anterior surface, while within the pelvis, the pyriformis is in relation to the sacral plexus, the anterior branches of the internal iliac vessels, and the rectum. It lies immediately above the upper border of the coccygeus muscle. Outside the pelvis it is usually separated from the capsule of the hip-joint by the gluteus minimus and is covered by the gluteus medius. Above the upper border of the muscle at its exit from the greater sciatic foramen are the gluteal vessels and the superior gluteal nerve, while below its lower border, between this and the superior gemellus, are the sciatic and internal pudic vessels and the pudic, sciatic, small sciatic, and inferior gluteal nerves. A bursa, the bursa m. pyriformis, inter- venes between the tendon of the muscle and the summit of the great trochanter. 36 Greater sacro- sciatic foramen Durbum of ilium Greater sacro- SLiatic foramen P\riformis Obturator internus Capsule of hip-joint Deep dissectif internal and external obturator 562 HUMAN ANATOMY. Variations. — The pyriformis is occasionally absent, and it may be more or less fused with the gluteus minimus or medius. Frequently it is divided into two or more portions by being perforated by the sciatic nerve. From the comparative stand-point the pyriformis is to be regarded, in part at all events, as a portion of the musculature extending between the axial skeleton and the pelvic girdle or limb, and is represented in the lower vertebrates by the caudo-femoralis. 1. Sphincter ani e.xternus. 2. Transversus perinaei superficialis. 3. Ischio-cavernosus. (b) THE PERINEAL MUSCLES. 4. Bulbo-cavernosus. 5. Transversus perinaei profundus. 6. Compressor urethrse. In the early stages of development, while the urogenital ducts and the digest- ive tract open into a common terminal cavity, the cloaca, muscle-fibres derived from the second, third, and fourth sacral myotomes arrange themselves in a flat layer around the external aperture of the cavity, forming what is termed the sphincter cloaca. Later, with the division of the cloaca into a urogenital and a rectal portion and the resulting formation of the perineum, this primary sphincter becomes divided into two portions, one of which forms a sphincter ani, while the more anterior portion gives rise to the muscles of the perineum. The fibres of this latter portion undergo various modifications in accordance with the changes which Fig. 553- I vV. Pentoneui Urach Supravesical space. Symphysis pubi Suspensory ligament of penis Triangular ligpment, sup. layer Deep perineal interspaci Triangular ligam't,iuf. layer. Ureth Penis, corpus cavernosu II \\ \ Superfici: f Colles's fascia Diagrammatic sagittal section, showing relations of fascial layers of perineum. take place in the urogenital sinus, and a horizontal separation of the original sphincter into two layers also occurs, whereby the perineal muscles are arranged in two layers separated by the superior fascia of the urogenital trigone. The muscles formed during these changes retain the original sheet-like form of the sphincter cloacae and are for the most part pale in color, resembling not a little in their general character the platysma muscles of the face. They show a considerable amount of difference in their development in different individuals, numerous acces- sory muscles having been described by various authors, some of which will be referred to in the succeeding descriptions. The Superficial Perineal Fascia. — The superficial perineal fascia, being continuous anteriorlv with the superficial fascia of the lower portion of the anterior abdominal wall, is, like this, composed of two layers. The more superficial layer usually contains a certain amount of fat, and, as in the abdomen, is really the pan- niculus adiposus of the skin. The deeper layer, which has been termed the fascia of Co/les, forms a continuous membrane which is attached at the sides to the rami of the pubes and ischia and in front becomes continuous with the dartos of the THE PELVIC AND PERINEAL MUSCLES. 563 scrotum (or fascia of the labia majora) and on either side of this with the corre- sponding layer of the abdomen. Behind it unites with the posterior border of the trigonum urogenitale on a line extending between the two ischial tuberosities, and thence is continued backward, forming a single sheet with the superficial la)'er, to unite with the superficial fascia of the gluteal region. This posterior portion of the superficial perineal fascia may conveniently be termed the circumanal fascia. By the union of the deep layer of the superficial fascia with the triangular liga- ment behind, an almost completely enclosed space is formed between the two struc- tures ; it is open only anteriorly where it communicates with the areolar spaces between the superficial and deep layers of the abdominal fasciae. This space is the superficial perineal interspace , and contains the bulb and spongy portion of the urethra, the corpora cavernosa, and certain of the perineal muscles. The Trigonum Urogenitale. — The trigonum urogenitale, more usually called the triangular ligament of the perineum, is formed by the deep fascia of the peri- neum, and, like the superficial fascia, is composed of two layers, the supei'ior and inferior (fasciae trigoni urogenitalis superior et inferior). At the sides both layers are attached to the rami of the pubes and ischia, in front to either edge of the lower border of the pubis, and behind they unite with each other and with the deep layer of the superficial fascia along a line extending transversely across the perineum between the tuberosities of the ischia. Between the two layers there is a completely closed space, the deep perineal interspace, in which are to be found the membranous portion of the urethra, the bulbo-urethral glands, the pudic vessels and nerves, and, in front, the subpubic or arcuate ligament of the pubis. At their lateral insertions the layers of the trigone are continuous with the obturator fascia, and the superior layer is fused above with the portion of the fascia endopelvina which invests the lower surface of the prostate gland (or the base of the bladder). The trigone is perforated by the urethra and, in the female, by the vagina, and anteriorly the dorsal vein of the penis passes through it immediately behind the subpubic ligament of the pubis, the fibres of the trigone immediately behind the opening for the vein being thickened to form a transverse band known as the trans- verse ligament of the pelvis. I. Sphincter Ani Externus (Fig. 554). Attachments. — The external sphincter of the anus consists of a group of fibres which surround the terminal portion of the rectum, the superficial fibres standing in close relationship with the integument. Its fibres arise posteriorly from the coccy.x and from the raphe extending from that bone to the anus, and, passing forward around the anus, are inserted into the superficial fascia and the central tendon of the perineum, and may in some cases be continued forward to join with the fibres of the superficial transverse perineal and bulbo-cavernosus muscles. The central tendon of the perineum is situated in the median line about 2.5 cm. in front of the anus, and is the point of union of five muscles, — namely, the external sphincter ani, the two superficial transversi perinei, and the bulbo-cavernosi. Nerve-Supply. — From the fourth sacral nerve and the inferior hemorrhoidal branches of the pudic. Action. — To close the anal aperture. It also serves to fix the central tendon of the perineum during the contraction of the bulbo-cavernosi. Variations. — The common embryological origin of the external sphincter ani and the perineal muscles is indicated by the extension forward of the fibres of the former to join the bulbo-caver- nosus, and occasionally a fasciculus of it extends as far forward as the base of the scrotum, forming what has been termed the retractor scroti. The longitudinal muscle-fibres of the lower portion of the rectum pass below into a sheet of connective tissue, which divides into three more or less distinct layers e.xtending to the integument. The outer two of these layers traverse the substance of the e.xternal sphincter ani, a portion of the outermost one being continued backward to the region of the coccyx on each side of the median line as a moderately strong band known as the ano-coccygeal ligament. By these layers of fibrous tissue the external sphincter is divided, .sometimes quite distinctly, into three portions which fiave been regarded as distinct muscles. One of these lies imme- diately beneath the skin surrounding the anus, and has consequently been termed the sphincter 564 HUMAN ANATOMY. suirii/aiieiis. The sphincter superficialis is that portion of the muscle which lies above and to the outer side of the sphincter subcutaneus, while more deeply still, and forming a ring-like mass of fibres closely encircling the rectal wall, is the sphincter profundus. It is frotn the sphincter subcutaneus that the retractor scroti, when present, is derived, and fibres from the sphincter superficialis are frequently prolonged in front of the anus to various insertions, as, for instance, to the tuber ischii, tlie lower layer of the trigonum urogenitale, or even the sheath of the corpora cavernosa. This layering of the external sphincter is probably a relic of the separa- tion of the sphincter cloacae into two layers, the subcutaneous and superficial sphincters repre- senting a portion of the superficial layer, while the deeper one is responsible for the sphincter profundus. 2. Transversus Perin.«i Superficialis (Fig. 554). Attachments. — The superficial transverse perineal muscle is an exceedingly variable sheet of muscle-fibres situated in the posterior portion of the superficial perineal interspace. In its typical form it may be described as a band of fibres which Fig. 554. Trans. perirse!_l superficial Triangular liga- t. int. layer Tendinous I centre \nils >l)tnrator fascia Gluteus maximus (cut) Greater sacro-sciatic ligament arises from the medial surface of the ischial tubenosity and passes directly medially to be inserted into the central tendon of the perineum. Nerve-Supply. — From the perineal branches of the pudic nerve. Action.^ To assist in fi.xing the central tendon of the perineum during the contraction of the bulbo-cavernosi. Variations. — The muscle may occasionally be entirely absent. It frequently receives fibres from the anterior ( pubo-rectal ) portion of the levator am and from the external sphincter ani and makes connections with the bulbo-cavernosi. 3. Ischio-C.wernosus (Fig. 554"). Attachments. — The ischio-cavernosus, also named the erector penis (erector c/itoridis), represents the lateral portion of the sphincter cloacae. The two muscles occupy the lateral parts of the superficial perineal interspace, each arisino- from the base of the tuberosity of the ischium, enclosing the base of the cms penis ( clito- ridis) as in a sheath, and passing forward to be inserted into the corpus cavernosum. The muscle in the female differs from that of the male only in size. Nerve-Supply. — From the perineal branches of the pudic nerve THE PELVIC AND PERINEAL MUSCLES. 565 Action. — To compress the corpus cavernosum and thus assist in producing or maintaining erection of the penis (or clitoris). 4. Bulbo-Cavernosus (Fig. 554). Attachments. — The bulbo-cavernosus differs somewhat in its relations in the two sexes. In the male, in which it is also termed the accelerator uriniz, the two muscles of opposite sides are united in a median fibrous raphe which e.xtends forv\'ard from the central tendon of the perineum over the bulb and corpus spongiosum. Arising from this raphe, the fibres are directed laterally and forward over the bulb and corpus spongiosum and are inserted into the under surface of the inferior layer of the urogenital trigone and into the fibrous sheath of the corpus cavernosum, some of the more anterior fibres being continued dorsally to insert into the fascia covering the dorsum of the penis and forming what has been termed the 7ttuscle of Houston, or compressor vena dor salis penis. In the female, in which the muscle has been termed the sphincter vagintz (Fig. 1732), the two muscles of opposite sides are widely separated from each other by the vagina, which they surround. They arise from the central tendon of the perineum, pass forward, investing the bulbi vestibuli, and are lost in the fascia covering the corpora cavernosa and the dorsal surface of the clitoris. Nerve-Supply. — From the perineal branches of the pudic ner\'e. Action. — To compress the bulb and corpus spongiosum and so tend to expel any fluid contained in the urethra. The fibres which pass to the dorsum of the penis (or clitoris j may aid slightly in the erection of that organ, either directly or by compressing the dorsal vein. Variations.— The posterior portion of the muscle, that surrounding the bulb, is unrepre- sented in the female and is frequently distinctly separable from the anterior part in the male ; it has been termed the compressor bulbi. The deeper fibres of this part of the muscle are sep- arated from the more superficial ones by a thin layer of areolar tissue, and have been regarded as forming a distinct muscle, the compressor hemisphericum bulbi, which closely surrounds the bulb, the two muscles of either side interlacing above the bulb so as to form practically a single muscle very variable in its development. Finally, fibres may arise from the ischial tulDerosities in common with those of the transversi superficiales and pass forward and medially to unite with the bulbo-cavemosi forming what have been termed the iscfiio-biilbosi. 5. Transversus Perin^i Profundus (Fig. 1629). Attachments. — The deep transverse perineal muscle is situated in the poste- rior part of the deep perineal interspace. It arises from the medial surface of the inferior ramus of the ischium and passes transversely inward to the median line, where it partly unites with its fellow of the opposite side and partly inserts into the central tendon of the perineum. Nerve-Supply. — From the perineal branches of the pudic ner\'e. Action. — To assist in fixing the central tendon of the perineum. 6. Compressor Urethra (Fig. 1629). Attachments. — The compressor or constrictor of the urethra (m. sphincter urethrae membranaceae) in the male is a thin sheet of muscle-tissue situated in the deep perineal interspace anterior to the deep transversus perinaei. It arises from the inner surface of the inferioi- ramus of the pubis and is inserted by passing medially to sur- round the membranous portion of the urethra, its anterior fibres forming a median raphe with those of the opposite side. The posterior fibres of the muscle enclose the bulbo-urethral gland. In the female the fibres are inserted vato the walls of the vagina as it tra\'erses the deep perineal interspace. Nerve-Supply. — From the perineal branches of the pudic nerve. Action. — To constrict the membranous urethra and, in the female, also to flatten the wall of the vagina. The m. ischio-piibicus is a small muscle situated at the side of the deep perineal interspace. It arises from the inferior rami of the ischium and pubis and passes anteriorly to be attached to the arcuate ligament of the pubis. It is frequently wanting. 566 HUMAN ANATOMY. THE APPENDICULAR MUSCLES. The limbs make their appearance as two pairs of flat buds (Fig. 69), the upper pair being situated in the lower cervical and the lower pair in the lower lumbar and upper sacral regions. Into the buds processes e.\tend from the myotomes of the regions concerned and apparently give rise to the more pro.ximal muscles of the limb, but that they are the source of all the limb musculature is as yet undetermined. The greater mass of this musculature develops from a blastema which occupies the interior of the limb-bud and which cannot at first be distinguished from that which gives rise to the limb skeleton, and whether it represents a condensation of tissue whose fundamental derivation is the myotomes or is a derivative of the ventral mesoderm has not yet been definitely decided. However that may be, the limb musculature stands in relation to the anterior divisions of definite spinal nerves, that of the upper limb being supplied by the lower five cervical and the first thoracic nerves and that of the lower limb by the lower four lumbar and upper three sacral nerves, and, furthermore, there is a distribution of these nerves to the muscles which may well be regarded as segmental. It is also worthy of note that in those regions of the trunk in which the limbs develop the ventral musculature is either very much reduced or, as in the lower limb, practically wanting. An examination of the limb muscles shows that they may be regarded as being arranged in a ventral or pre-axial group and a dorsal or post-axial group, and in harmony with this arrangement the nerve-fibres which pass to the muscles arrange themselves in ventral or pre-axial and dorsal or post-axial groups. In the fore-limb the dorsal group is represented by the posterior fasciculus or cord of the brachial plexus, while the ventral one is distributed between the lateral and medial fasciculi. In the lower limb the correct relationships of the two groups of muscles and their nerves are less readily perceivable, owing to the forward rotation which the limb has undergone in order to bring its axis into a plane parallel with that of the sagittal plane of the body, a rotation which brings it about that in the adult, e.xcepl in the more proximal portion of the limb, the pre-axial musculature is on the posterior and the post-axial on the anterior surface. The pre-axial nerve-fibres are distributed mainly by the obturator and greater sciatic (internal popliteal) nerves, while the post-axial ones pass to their destinations by way of the anterior crural and greater sciatic (external popliteal) ; and in this connection it is interesting to note that the fibres of the external popliteal or peroneal, if traced to their e.xit from the spinal foramina, will be found to lie dorsal to those of the internal popliteal or tibial, not- withstanding that the former are supplied to the anterior and the latter to the pos- terior muscles of the leg. In this arrangement into pre-axial and post-axial groups there is, accordingly, to be found a clue to the proper understanding of the relations of the nerves to the muscles of the limbs, and a further examination of the two groups will reveal indica- tions of a segmental distribution of the nerves and muscles in each. This arrange- ment may be most satisfactorily understood by means of a diagram (Fig. 555) showing the arrangement of the muscles and nerves in what may be regarded as its fundamental condition. The limb-bud may be regarded as a flat plate whose surfaces are directed dorsally and ventrally. Into the upper portion of this plate the upper- most of the spinal nerves which are associated with it is prolonged, its post-axial and pre-axial fibres passing respectively to either side of its frontal plane, and the succeeding nerves are similarly prolonged into it in succession from above downward. The nerves, however, which lie along the upper and in the lower limb also along the lower borders of the bud are not prolonged into it quite so far as the others, the free edge of the plate being, as it were, rounded oE, so that it is only the more cen- tral (or upper) nerves of the series that reach that portion of the bud from which the foot (or hand) and digits will be developed. It follows from this arrangement that in the adult each spinal nerve concerned supplies a portion of both the pre-axial and post-axial groups of muscles, and, THE APPENDICULAR MUSCLES. 567 Mesoblastic limb-core Post-axial furthermore, that the muscle-fibres in succession from one border of the limb to the other are supplied by successive nerves, those supplied by the uppermost and, in the pelvic limb at least, the lowermost nerves extending only to the neighborhood of the knee (or elbow) or even a shorter distance into the limb. Thus, in the fore- limb one may expect to find the more lateral muscles of the shoulder and arm suppHed by fibres from the uppermost nerves of the brachial plexus, those lying towards the middle of the shoulder and brachial regions and in the lateral portion of the antibrachium and hand regions by the middle nerves, and those along the medial portion of the limb by the lower ones. In the lower limb, however, owing to the rotation which it has undergone, the arrangement is to a certain extent reversed, and although in the more proximal muscles the fibres are supplied by suc- cessive nerves from above downward, lower down the fibres from the upper nerves are Fig. 555. to be found along the inner side of the leg and those from the lower nerves along the outer side. If, then, an originally segmental ar- rangement of the muscle-fibres of the limbs is to be recognized, the segments must run parallel to the long axis of the limb, and this arrangement has permitted their free consolidation to form the various muscles found in the adult, very few indeed of which are supplied by a single nerve, and represent, accordingly, portions of a sin- gle primitive segment. Furthermore, the adaptation of the muscles to act effectively on the various joints of the limbs has brought about a transverse division of the segments, and has also led to a complete degeneration of the portions of some of the segments in one part of the limb while they are retained in another. Thus, for example, in the pre-a.xial musculature of the brachial region no trace is to be found of the segments supplied by the eighth cer\'ical and first dorsal nerves, although the eighth cervical is represented in the post-axial musculature and both in the pre-axial musculature of the forearm. On account of the occurrence of both fusion and degeneration, little trace of an original segmental arrangement of the muscle-fibres is to be found in the adult limb muscles, and their classification according to the segments from which they may be derived is not feasible. Comparative anatomy, however, shows that primarily the limb muscles were arranged with relation to the various joints of the limb, each muscle, as a rule, passing over but a single joint, and in this relation may be found a basis for classification. In man the original relations have been modified in many cases by an alteration in one of the original points of attachment of a muscle so that it passes over two joints, or by the end-to-end union of originally distinct muscles so that the same result is brought about. Making allowance for these modifications, however, the muscles of the upper limb may be classified into ( i ) those passing from the axial skeleton to the pectoral girdle, (2) those passing from the girdle to the brachium or arm, (3) those passing from the brachium to the antibrachium or fore- arm, (4) those passing from the antibrachium to the carpus, and (5) the digital mus- cles. Similarly in the lower limb, in which, however, owing to the firm articulation of the pelvis to the sacrum, the first group of muscles is practically unrepresented, or at least may be placed with those of the second group extending from the pelvic girdle to the femur. With this grouping there may be combined a recognition of the pre-axial and post-axial musculature, these terms being used in the lower limb as well as in the upper to indicate the relationships which obtained before the rotation of the limb. Diagram of pre- i LitPio \entral muscles Body-cavity nd post-axial groups of limb-muscles. {KoUmann.) 568 HUMAN ANATOMY. THE MUSCLES OF THE UPPER LIMB. THE MUSCLES EXTENDING BETWEEN THE AXIAL SKELETON AND THE PECTORAL GIRDLE. (<7) THE PRE-AXL-\L MUSCLES. I. Pectoralis major. 2. Pectoralis minor. 3. Subclavius. The Pectoral Fascia. — The superficial pectoral fascia is continuous above with the superficial cervical and below with the superficial abdominal fasciae, and covers the entire anterior wall of the thorax. It usually contains a considerable amount of fat and has embedded in it the mammary gland. The deep fascia is attached above to the clavicle, and forms a thin membrane closely adherent to the surface of the pectoralis major, at the lower border of which Fig. 556. External anterior thoracic Cephalic Branch of acromio-thoracic arten Distal stump of. pectoralis major Cut edge of dee pectoral fascia Pectoralis minor enclosed clavi-pectoral fascia _ Pectoralis major, cut edge of clavicular portion Pectoralis major, cut edge of sterno-costal portion it becomes continuous with the axillary fascia. Medially it is attached to the ventral surface of the sternum and laterally it is continuous with the fascia covering the deltoid. Beneath the deep fascia there arises from the clavicle a second sheet of fascia (clavi-pectoral fascia) (Fig. 556) which encloses the subclavius muscle and is then continued downward to the upper border of the pectoralis minor. There it divides into two sheets which enclose the muscle and at its lower margin unite to form a single sheet which becomes continuous with the axillary fascia close to the lower bf^-rder of the pectoralis major. The portion of this fascia which intervenes between the clavicle and the subclavius muscle and the upper border of the pectoralis minor is termed the coraco-clavicular fascia or costo-coracoid membrane. It is prolonged laterally along the upper border of the pectoralis minor, over the upper portion of the axillary vessels, to the coracoid process, its outer portion being thickened to form THE PECTORAL MUSCLES. 569 a band, the costo-coracoid ligwment (Fig. 560), which passes obhquely downward and laterally from the clavicle to the coracoid process. The coraco-clavicular fascia occasionally contains muscle-fibres (the m. coraco-clavicidaris) , and is usually perfo- rated by the cephalic vein on its way to join the a.xillary, by the thoraco-acromial artery, and by the external anterior thoracic nerve. I. Pectoralis Major (Fig. 557). Attachments. — The pectoralis major is a strong fan-shaped muscle situated on the anterior thoracic wall. It is composed of three portions : (i) thenars cla- vicularis, which arises from the inner half of the anterior border of the clavicle ; (2) \h& pars sterno-costalis, which arises from the anterior surface of the sternum and the upper six costal cartilages ; and (3) t\\e portio abdomi7ialis, which arises from Fig. 557. Pectoralis major, clavicular portion Pectoralis major, sterno- costal porti* Serratus magnus Latissimus dorsi . Pectoralis major, abdominal portion Dissection of tho wall, showing pectoralis major. the upper part of the anterior layer of the sheath of the rectus abdominis. From these origins the fibres are directed laterally to be inserted into the external bicipital ridge which extends downward from the greater tuberosity of the humerus, the lower fibres of the sterno-costal and the abdominal portions of the muscle passing behind those of the clavicular and upper portions, so that the tendon of insertion is U-shaped in section, consisting of two layers separated above but continuous below. A bursa is usually interposed between the posterior surface of the tendon and the anterior surface of the long head of the biceps humeri. Nerve-Supply. — From the external and internal anterior thoracic nerves by fibres from the lower four cervical and the first thoracic nerves. 570 HUMAN ANATOMY. Action. — When the arm is abducted to a position at right angles to the body, the pectoralis major will draw the arm forward and at the same time will adduct it. As the arm approaches the vertical position, the adductor action becomes more pronounced and the flexor action less so, and a slight amount of internal rotation appears. When the arm is raised above the level of the shoulder and fixed, the muscle will assist in drawing the trunk upward, as in climbing, and it will also assist in raising the ribs in forced inspiration. Variations. — In the lower mammals the pectoralis major is represented by a number of distinctly separate portions, a condition which may be indicated in man by a more than usual distinctness of the three portions of the muscle and by the occurrence of accessory slips. The sterno-costal and abdominal portions may be greatly reduced or even absent. The m. sternalis is present in something over 4 per cent, of all cases examined. It is very variable in its development, and consists of fibres which arise anywhere from the third to the seventh costal cartilage, or even from the sheath of the rectus, and extends upward to be attached to the anterior surface of the sternum, the clavicle, or the tendon of the sterno-cleido-mastoid. Usually the fibres are directed vertically, but sometimes they may have a more or less oblique course. The muscle has been variously regarded as a portion of the platysma, a downward pro- longation of the sterno-cleido-mastoid, an upward prolongation of the rectus abdominis, and as a displaced portion of the pectoralis major. The fact that in the majority of cases it is sup- plied by branches from the anterior thoracic nerves indicates clearly its usual derivation from the pectoralis, but it is asserted that in certain cases it received its nerve-supply from the third and fourth intercostal nerves, in which cases it is more probably to be regarded as representing a thoracic portion of the rectus trunk muscles. The chondro-epityochlearis is a slip derived from the pectoralis major which takes its origin from the lower costal cartilages or the abdominal portion of the pectoralis and is inserted into the brachial fascia or the medial epicondyle of the humerus. 2. Pectoralis Minor (Fig. 560). Attachments. — The pectoralis minor lies beneath the pectoralis major. It arises from the outer surface of the third, fourth, and fifth ribs and from the fascia covering the intervening intercostal muscles, and passes obliquely upward and later- ally to be inserted into the coracoid process of the scapula. Nerve-Supply. — By branches of the external and internal anterior thoracic nerves from the seventh and eighth cervical and first thoracic nerves. Action. — To draw the lateral angle of the scapula downward and forward ; if the scapula be fixed, to raise the ribs to which it is attached. Relations. — The pectoralis minor is completely covered by the pectoralis major. It covers the outer surface of the upper ribs and their intercostal spaces, and near its insertion it passes over the middle portion of the axillary vessels and the cords of the brachial ple.xus. 3. SuBCLAVius (Fig. 560). Attachments. — The subclavius is an almost cylindrical muscle attached at one extremity to the anterior surface of the first costal cartilage and at the other to the under surface of about the middle third of the clavicle. Nerve-Supply. — By a special nerve from the brachial plexus from the fifth and si.xth cervical nerves. Action. — To draw the outer end of the clavicle downward and forward. Variations. — The subclavius seems to be the persistent representative of a group of muscles more perfectly developed in the lower mammals and especially in those in which the clavicle is more or less rudimentary. Muscle-bands, which represent portions of the group normally degenerated, are occasionally found in man, and on account of their variable relations have been described under various names. They may all be grouped, however, under three terms, the sterno-chondro-scapularis, the scapii/o-c/avini/aris, and the sterno-claviciilaris (Le Double). In the mammals which lack a clavicle — in many Ungulates, for example— a strong muscle-band passes transversely across the upper part of the thorax from the sternum and first costal cartilage to the scapula. This is the sterno-chondro-scapularis, and it occasionally occurs ;n tnan as a band arising from the points named, or from either one of them, or from the first rib, and inserting into the coracoid process of the scapula. In those mammals which possess a rudimentary clavicle, such as the Rodents, only the terminations of the sterno-chondro-scapular persist, each inserting into the clavicle, and forming THE SCAPULAR MUSCLES. 571 the scapulo-clavicularis and the sterno-clavicularis. Each of these may occur as an anomaly in man, the sterno-clavicularis appearing under various forms, and passing either above, behind, or in front of the clavicle. It should be stated, however, that there is a possibility that some of the varieties of the sterno-clavicularis may really represent persisting portions of the muscular sheet which has given rise to the middle layer of the cervical fascia and to the sterno-hyoid and the omo-hyoid (page 545). In the lower mammals a thin muscular sheet invests a greater or less portion of the trunk in intimate association with the integument, resembling in this respect the platysma. It is termed the panniculus carnosus, and in man is normally unrepresented. Occasional traces of it are found, however, and of these the most frequent is the muscle of the axillary arch, a somewhat variable band of muscle-tissue which passes across the anterior portion of the a.xillary cavity from the lateral border of the latissimus dorsi to the tendon of the pectoralis major. It presents considerable variation in its insertion, being connected sometimes with the biceps, the coraco-brachialis, the pectoralis minor, or the chondro-epitrochlearis, or being united with slips from the abdominal portion of the pectoralis major, or being inserted into the coracoid process of the scapula. It is suppUed by branches from the anterior thoracic nerves. (*) THE POST-AXIAL MUSCLES. 1. Serratus magnus. 3. Rhomboideus minor. 2. Levator anguli scapulae. 4. Rhomboideus major. 5. Latissimus dorsi. I. Serratus Magnus (Fig. 558). Attachments. — The serratus magnus (m. serratus anterior) forms a large muscular sheet covering the lateral waA. of the thorax. It arises by nine or ten fleshy digitations from the outer surfaces of the eight or nine upper ribs, the second rib giving attachment to two slips. Its fibres may be regarded as arranged in three groups : the uppermost group consists of fibres from the first and second ribs and is inserted into the ventral surface of the medial angle of the scapula ; the middle group, from the second and third ribs, is inserted into the ventral surface of the vertebral border of the scapula ; while the remaining fibres, constituting the strongest portion of the muscle, converge to the inferior angle of the same bone. Nerve-Supply. — By the long thoracic nerve from the fifth, sixth, and seventh cervical nerves. Action. — It serves to keep the scapula closely applied against the thoracic wall and draws it laterally. Since the portion inserted into the inferior angle is the strongest, a rotation of the scapula is produced whereby its lateral angle is raised. By this action the serratus . plays an important part in the elevation (abduction) of the arm, since, in the first place, by fixing the scapula it allows the deltoid to expend all its action on the humerus instead of wasting part of it in tilting the acromion downward, and, in the second place, after the deltoid has completed its action and has raised the arm through about 90°, the further elevation through another right angle is accomplished by a rotation of the scapula resulting from the action of the serratus magnus and trapezius. Variations. — Absence of a portion or the whole of the muscle has been observed. Its origin may extend as low as the tenth rib, and it may receive slips from the transverse processes of the cervical vertebrae and from the levator scapulas. 2. Levator Anguli Scapula (Fig- 559)- Attachments. — This (m. levator scapulae) is an elongated muscle on the lateral surface of the neck. It arises from the transverse processes of the upper four cer- vical vertebrae and passes downward, forward, and laterally to be inserted into the medial angle and outer surface of the vertebral border of the scapula as far down as the base of the spine. Nerve-Supply. — By the dorsal scapular nerve from the fifth cervical nerve. Action. — To draw upward the medial angle of the scapula, producing a rota- tion of the bone contrary to that effected by the serratus anterior. If the scapula be fixed, the action is to bend the cervical portion of the spinal column laterally, rotating it slightly to the opposite side. 572 HUMAN ANATOMY. Variations.— The origin may e.xtend to the transverse processes of all the cervical ver- tebra; and may be continued upon the mastoid process above and upon the upper ribs below. Slips may occur connecting the levator with various neighboring muscles, the most mterestmg of these connections being that with the serratus magnus, since comparative anatomy shows that the levator was primarily continuous with that muscle. . „ . A separated portion of the outer part of the muscle is occasionally inserted into the outer end of the clavicle, forming what is termed the levator ctavkulic. 3. Rhomboideus Minor (Fig. 559). Attachments. — The rhomboideus minor is a band-like muscle which arises from the lower part of the ligamentum nucha; and from the spinous process of the Fig. 558. Serratus posticus superior Levator anguli scapula Sup«»riftr angle of scapula '^npraspinatus Corannd j Fendon of supraspiualus Acromion ^,b!^ process— ^^^^jp. Lesser, tuberosity of humerus Scalenus posticus Scalenus medius Subscapularis Serratus mag- nus, upper, middle, and lower por- tions Latissimus dorsi, cut edg< Dissection of thoracic wall, showing serratus magnus; clavicle has been removed and scapula drawn outward. last cervical vertebra and passes laterally and downward to be inserted into the ver- tebral border of the scapula at the base of the spine. Nerve-Supply.— By the dorsal scapular nerve from the fifth cervical nerve. Action.— To draw the scapula upward and medially, at the same time rotating it s6 that the lateral angle is moved downward. 4. Rhomboideus Major (Fig. 559)- Attachments. — The rhomboideus major immediately succeeds the rhom- boideus minor, and is a quadrilateral sheet which arises from the spinous processes of the four upper thoracic vertebrae and from the intervening interspinous liga- THE SCAPULAR MUSCLES. Fig 539. 573 Stemo cleido-mastoideits Supraspinatus Infraspinatus . ^fSSr' Rhomboideus major Rhomboldeus major Vertebral aponeurosis Serratus magiius JM t Gluteus medius — ^ Gluteus maximus- Superficial muscles of the back. 574 HUMAN ANATOMY. merits. It is directed downward and laterally and is inserted into the lower two- thirds of the vertebral border of the scapula. Nerve-Supply. — By the dorsal scapular nerve from the fifth cervical nerve. Action. — To draw the scapula upward and medially, at the same time rotating it so that the lateral angle is moved downward. Variations of the Rhomboidei. — The rhomboidei are sometimes entirely wanting, and the origins of both muscles may be extended beyond the usual limits. The octipito-scaputaris is a muscle occasionally present which is intimately associated in its derivation with the rhomboids. It arises from the inner part of the superior nuchal line and passes downward between the trapezius and splenius to join the rhomboideus minor, inserting with it into the vertebral border of the scapula. 5. Latissimus Dorsi (Fig. 559). Attachments. — The latissimus dorsi is a large triangular muscle which arises from the spinous processes of the last si.x thoracic vertebrae and the intervening interspinous ligaments beneath the origin of the trapezius, from the lumbo-dorsal fascia, from the posterior portion of the crest of the ilium, and by fleshy digitations from the outer surfaces of the lower three or four ribs. Its fibres pass upward and laterally over the inferior angle of the scapula, from which an additional slip is usu- ally added to the muscle. It then curves around the lower border of the teres major and is inserted, ventrally to that muscle, into the crest of the inner tuberosity of the humerus. A mucous bursa {biosa m. latissimi dorsi) lies between the tendons of insertion of the latissimus dorsi and teres major. Nerve-Supply. — By the long subscapular nerve from the seventh and eighth cervical nerves. Action. — To draw the humerus downward, backward, and inward, at the same time rotating it inward, the action being that of the arm in swimming. If the. humerus be fixed, as in climbing, it draws the pelvis and lower portion of the trunk upward and forward. Variations. — The latissimus dorsi, like the serratus anterior and pectorales, is a muscle which has migrated extensively from the region of its first formation, the lower cervical region, and this migration can be witnessed in the ontogeny of the nniscle. Consequently variations may be e.xpected and do occur in the extent of the origin of the muscle, whose descent and backward migration to the vertebral column may be interrupted at various stages. A great amount of variation of this nature is seen in its attachment to the crest of the ilium. In some cases this attachment extends so far forward as to meet the posterior extremity of the attachment of the external oblique of the abdomen, but usually this does not occur, and a tri- angular interval, known as the triangle of Petit, occurs between the borders of the two muscles and above the crest of the ilium. The floor of the triangle is formed by the internal obliquus abdominis, and. since the abdominal wall is here thinner than elsewhere, the triangle may occa- sionally be the seat of a lumbar hernia. Closely allied to the latissimus dorsi is a muscle, the m. dorso-epitrochlearis. which occurs in 18 or 20 per cent, of cases. It takes its origin from the body or tendon of insertion of the latissimus and passes to the brachial fascia or to the medial epicondyle of the humerus. It has been regarded as an aberrant portion of the pectoralis group of muscles, but its supply by the musculo-spiral nerve places it among the post-axial muscles. The Axillary Fascia. — The a.xillary fascia is a firm sheet which e.xtends across from the lower border of the pectoralis major to that of the latissimus dorsi and teres major, forming the floor of the axilla. Laterally it passes over into the deep fascia of the arm, medially into the fascia covering the serratus magnus, and near the border of the pectoralis major it has inserted into it the downward continu- ation of the fascia which encloses the pectoralis minor (Fig. 556). It is pierced by numerous lymphatic vessels, and along its medial edge is considerablv thickened to form a curved band, whose concavity is directed laterally, and which stretches across between the tendons of the pectoralis major and the latissimus, forming what is termed the axillary arch. Muscle-fibres are occasionally found in this arch (page 571). The axilla is a pyramidal space intervening between the upper part of the brachium and the lateral wall of the thorax. Its apex is directed upward and the THE SHOULDER MUSCLES. 575 base, which is formed by the axillary fascia, downward. Its ventral wall is formed by the pectoralis major and pectoralis minor, its dorsal wall by the latissimus dorsi, teres major, and subscapularis, and its medial wall by the serratus magnus. In the angle formed by the junction laterally of its ventral and dorsal walls lies the m. coraco- brachialis, and in the groove between that muscle and the posterior wall are the axillary vessels and the cords of the brachial plexus. The cavity of the axilla con- tains a considerable amount of fat and a variable number of lymphatic nodes ; it is traversed by the thoracic branches of the axillary vessels and by the intercosto- humeral nerve, and the long thoracic nerve passes downward along its medial wall to the serratus magnus. THE MUSCLES PASSING FROM THE PECTORAL GIRDLE TO THE BRACHIUM. Prk-Axial. Post-Axial. I. Coraco-brachialis. i. Supraspinatus. 4. Teres major. 2. Infraspinatus. 5. Subscapularis. 3. Teres minor. 6. Deltoideus. {a) THE PRE-AXIAL MUSCLES. I. Coraco-Brachialis (Figs. 560, 570). Attachments. — The coraco-brachialis arises from the tip of the coracoid pro- cess of the scapula by a tendon common to it and the short head of the biceps. It extends downward along the humerus and is inserted at about the middle of its medial border. Nerve-Supply. — By the musculo-cutaneous nerve from the seventh cervical nerve. Action. — To draw the upper arm forward. Relations. — It is crossed ventrally by the pectoralis major, and dorsally it is in relation with the tendons of the latissimus dorsi, the teres major, and the subscapu- laris, from the last of which its tendon is separated by a mucous bursa i^bursa m. coraco-b7'achialis) . Laterally the muscle is in contact with the short head of the biceps. It is usually pierced by the musculo-cutaneous nerve, and is in relation medially with the axillary artery and the median and ulnar nerves. Variations. — Comparative anatomy shows that the coraco-brachialis is primarily an ex- tensive muscle consisting of three portions, of which only the middle one and a part of the inferior are normally present in man. The variations which occur usually consist in the appearance of one or other of the missing portions. Thus the upper portion is sometimes represented by a coraco-brachialis superior, which arises from the coracoid process and passes laterally to be inserted into the lesser tuberosity of the humerus or into the capsule of the shoulder-joint, while the lower portion may be more completely represented by the insertion of the muscle extending as far down as the medial epicondyle of the humerus. {b) THE POST-AXIAL MUSCLES. I. Supraspinatus (Fig. 561). Attachments. — The supraspinatus occupies the supraspinous fossa of the scapula, arising from the inner two-thirds of this and from the supraspinous fascia. Its fibres pass laterally and converge to a tendon which is inserted into the upper facet upon the greater tuberosity of the humerus and into the capsule of the shoulder- joint. Nerve-Supply. — By the suprascapular nerve from the fifth and sixth cervical nerves. Action. — To abduct the arm. The supraspino7is fascia is the layer of connective tissue which covers the supraspinatus muscle. It is attached to the superior border of the scapula above, to the vertebral border medially, to the spine below, and gradually fades out laterally. 576 HUMAN ANATOMY. 2. Infraspinatus (Figs. 561, 572). Attachments. — The infraspinatus occupies the infraspinous fossa of the scapula and arises from the entire extent of the fossa, with the e.xception of a portion towards the axillary border of the bone. It also arises from the infraspinous fascia which covers it. The fibres pass laterally and converge to a strong tendon, which is frequently separated from the capsule of the shoulder-joint by a small bursa (bursa Fig. 560. Clavicle Axillary vein Axillar>' artery [ Brachial plexus 1 1 ^- Deltoid. Long head of biceps. Short head of biceps. Insertion of oectoralis major. Subclavius Costo-coracoid ligament -Pectoralis minor -Serratus magnu m. infraspinati) and is ins€7-ted into the middle facet of the greater tuberositv of the humerus. Nerve-Supply. — By the suprascapular nerve from the fifth and sixth cer\'ical nerves. Action. — -When the arm is hanging vertically, it is the chief outward rotator of the humerus. When the arm is abducted to a horizontal position, the muscle draws it backward. Variations. — The upper portion of the muscle is sometimes distinctly separated from the rest, and has been termed the infraspiuaius viinoy. On tlie other hand, the separation which usually exists between the infraspinatus and the teres minor may be entirely wantino;. The infraspmons fascia is a strong fascia which covers the infraspinatus and the teres minor, giving origin to some of the fibres of both muscles. It is attached above to the spine of the scapula, medially to its vertebral border, and fades out laterally into the brachial fascia. 3. Teres Minor (Fig. 561). Attachments. — -The teres minor arises from the upper two-thirds of the dorsal surface of the scapula, close to its axillary border, and from the infraspinous fascia. THE SHOULDER MUSCLES. 577 It passes laterally along the lower border of the infraspinatus to be inserted into the capsule of the shoulder-joint and into the lower facet of the greater tuberosity of the humerus. Nerve-Supply. — By the circumflex nerve from the fifth and sixth cervical nerves. Action. — When the arm is vertical, it rotates the humerus outward ; when it is horizontal, it draws it backward. Spine of- scapula Sectional surface of Greater tuberosity -Quadrilateral space 1 endon of latissimus dorsl Triangular space \ Long (middle) head of triceps Outer head of triceps A "^^ Posterior scapular muscles and part of triceps ; outer part of j nion has been removed. 4. Teres Major (Figs. 561, 572). Attachments. — The teres major arises from the dorsal surface of the scapula, along the lower third of its axillary border, and passes laterally to be hisei'ted into the crest of the lesser tuberosity of the humerus immediately dorsal to the insertion of the latissimus dorsi. Nerve-Supply. — By the lower subscapular nerve from the fifth and sixth cervi- cal nerves. Action. — To draw the arm backward and medially, at the same time rotating it inward. Relations. — The teres major is in relation below with the latissimus dorsi, which bends around its under surface so as to lie ventral to it at its insertion. Above it is in relation with the teres minor at its origin, but separates from it as it passes later- 37 578 HUMAN ANATOMY. ally, so that a triangular interval, the base of which is the humerus, lies between the two muscles. This interval is crossed by the long head of the triceps, which overlies the dorsal surface of the teres major, and is thus divided into a more medial triangular space, occupied by the dorsal scapular artery, and a more lateral quad- rangular space, through which the posterior circumflex vessels and the circumflex nerve pass. Variations. — Considerable variation occurs in the size of the teres major, an increase in the size of that muscle being associated with a diminution of that of the latissimus dorsi, and vice versa. The teres major is, indeed, to be regarded as fundamentally a portion of the latissimus. 5. SUBSCAPULARIS (Fig. 558). Attachments. — The subscapularis is a powerful muscle occupying the ventral (costal) surface of the scapula. It arises from nearly the whole of that surface, with the exception of a small portion near the neck of the bone, some fibres also taking origin from the subscapular fascia. The fibres pass laterally, converging to a strong tendon which is inserted into the lesser tuberosity of the humerus and to a certain extent into the capsule of the shoulder -joint. Nerve-Supply. — By the upper and lower subscapular nerves from the fifth and sixth cervical nerves. Action. — When the arm is vertical, the subscapularis acts as a powerful inward rotator of the humerus ; when the arm is abducted to a right angle with the body, the muscle serves to draw it forward. Relations. — The subscapularis forms a considerable portion of the dorsal wall of the axilla, and is in relation, by its ventral surface, with the axillary vessels and the cords of the brachial plexus, and laterally with the coraco-brachialis and short head of the biceps. Its lower border is in contact with the teres major and with the dorsal scapular vessels and the circumflex nerve. Dorsally it is in contact with the long head of the triceps, and is separated from the neck of the scapula by the large subscapular bursa (bursa m. subscapularis) which frequently is continuous with the synovial cavity of the shoulder-joint. Variations. — The subscapularis differentiates in the embryo from the same sheet which gives rise to the teres major and the latissimus dorsi. It is occasionally divided into two or more fasciculi, and sometimes there is separated from its lower portion a small muscle, termed the subscapularis minor, which arises from the axillary border of the scapula and is inserted into the crest of the lesser tubercle of the humerus and sometimes into the capsule of the shoulder- joint. The subscap2(lar fascia is a firm sheet of connective tissue which covers the ventral surface of the subscapularis. It is attached above, medially, and below to the border of the scapula and fades out laterally into the brachial fascia. 6. Deltoideus (Fig. 562). Attachments. — The deltoid is a large triangular muscle which covers the shoulder as with a pad. It arises from the ventral border of the outer third of the clavicle and from the acromion process and lower border of the spine of the scapula. Its fibres pass downward, and converge to be inserted into the deltoid tubercle of the humerus. Where the muscle passes over the greater tuberosity of the humerus a mucous bursa (bursa subdeltoidea ) is interposed between it and that prominence. Nerve-Supply. — By the circumflex nerve from the fifth and sixth cervical nerves. Action. — To abduct the arm to a position at right angles to the body. Fur- ther abduction is accomplished bv a rotation of the scapula by the contraction of the trapezius and the serratus anterior, whereby the lateral angle of the bone is tilted upward. Relations. — The deltoid is in relation by its deep surface with the coracoid process and the capsule of the shoulder-joint and with the various muscles attached to or in the neighborhood of these structures. The cephalic vein passes upward along its anterior border. PRACTICAL CONSIDERATIONS : AXILLA AND SHOULDER. 579 Variations. — The portion of the deltoid which arises from the clavicle is subject to con- siderable variation, either being gready reduced in size or even entirely suppressed, or else being more extensively developed than usual, so that it is in contact or even fused with the clavicular portion of the pectoralis major. It may also be distinctly separated from the remain- der of the muscle, and not infrequently a separation of the acromial and spinal portions may also occur, so that the muscle becomes three-headed. Spine of scapul Acroni Deltoid, spinal port Deltoid, acromial porti Sterno-cleido-mastoid Pectoralis major Deltoid, clavicula portion Deltoid muscle viewed from side. Accessory bundles of fibres are occasionally found arising from the fascia infraspinata or from some point along the a.xillary border of the scapula, and either insert with the deltoid {?«. basio-deltoideus) or join with the upper part of the muscle, being condnued onward as tendinous fibres w'hich pass to the acromion process and lateral extremity of the clavicle {ni. costo-deltoidetis) . These fibres represent a portion of the deltoid which in the anthropoid apes arises from the borders of the scapula and in some of the lower mammals forms a distinct muscle. PRACTICAL CONSIDERATIONS: THE MUSCLES AND FASCIA OF THE AXILLA AND SHOULDER. The practical relations of the fascia descending to the superior borders of the clavicle and scapula have been sufficiently described (page 551). Fi'adure of the Clavicle. — The action of the muscles which mo\-e the arm and shoulder and of those attached to the clavicle (page 259) should be considered with reference to the common form of displacement in cases of fracture of the latter bone. The acromial fragment, as it moves with the shoulder, is the more markedly affected. It is carried dowmcaj-d by gravity acting on the upper extremity and aided by the two pectoral muscles and the latissimus dorsi. It is drawn inward by 58o HUMAN ANATOMY. the sternal fibres of the pectoraUs major and by all the muscles passing from the trunk to the humerus and scapula. It is rotated on a vertical a.xis so that its inner end points backward and its outer end forward. The cause of the rotation is the action of the two pectorals upon the shoulder and the contraction of the serratus, which ( the support of the clavicle having been removed) draws the scapula (and with it the point of the shoulder ) inward and forward instead of more directly for- ward, and so causes an anterior projection of the acromial end of the outer fragment. Theoretically the inner fragment is displaced upward by the clavicular fibres of the sterno-mastoid, but this action is so strongly resisted by the costo-clavicular (rhomboid) ligament and by the upper and inner fibres of the pectoralis major, as well as by the subclavius, that it is not often productive of much deformity (Fig. 563). The rationale of the good effect of recumbency with the head slightly elevated is evident. The weight of the upper extremity ceases to drag the outer fragment downward. The vertebral border of the scapula is pressed closely to the thorax by the weight of the trunk. Its outer border, therefore, cannot be drawn forward by the pectorals and serratus, but tends to fall backward and outward, correcting both the rotation and the inward Fig. 563. displacement. The slight ele- vation of the head rela.xes the sterno-cleido-mastoid and re- moves whatever influence it may have in raising the outer end of the inner fragment. Fractures within the limits of the rhomboid ligament at the inner end or within those of the conoid and trapezoid ligaments at the outer end are attended by but little displace- ment. Fractures of the scapula have already been dealt with (page 254). Muscular action influences them but little be- yond what has been mentioned. The fascia beneath and connected with the clavicle is cie. of much surgical importance. The superficial fascia of the The processes which pass from it to the skin ), by their involvement and contraction in Dissection of fracture of middle of cla thora.x splits to enclose the breast. (Cooper's " ligamenta suspensoria' carcinoma, produce the characteristic adhesion and dimpling of the skin. The deep pectoral fascia splits to form the sheath of the pectoralis major muscie. Carcinoma of the mamma will usually be found adherent to this layer on the anterior surface of the muscle. Such adhesion can best be demonstrated by attempting to move the tumor and breast in the direction of the pectoral fibres. Motion trans- verse to that line may, even in cases in which the tumor and muscle are inseparably connected, appear to be free, because the muscle itself is moved on the subjacent structures. Beneath the deep pectoral fascia an additional sheet, the clavi-pectoral fascia, extends as a continuation downward of the sheath of the subclavius, the two layers of which begin above at the two lips of the subclavian groove on the inferior surface of the clavicle and unite into one layer at the lower edge of the subclavius. This layer is continuous towards the sternum with the deep fascia covering in the first and second intercostal spaces ; externally it is attached to the coracoid process ; inferiorly, after splitting to enclose the pectoralis minor muscle, it blends with the axillary fascia. The portion of the clavi-pectoral fascia abo\'e the upper border of the pectoralis minor is known as the costo-coracoid membrane. It, together with the subclavius PRACTICAL CONSIDERATIONS : AXILLA AND SHOULDER. 581 muscle (which it invests), forms the floor of the so-called superficial infraclavicular triangle, the roof. of which is made by the clavicular fibres of the great pectoral, the base by the anterior fibres of the deltoid, the upper side by the sternal half of the clavicle, and the lower side by a line parallel to the uppermost sternal fibres of the great pectoral. Its apex is at the sterno-clavicular angle of junction. The floor of this space is pierced by the external anterior thoracic nerve, the acromio-thoracic vessels, and the cephalic vein (Fig. 556). Fat containing a few lymphatic glands, often involved in carcinoma of the breast, is found there. It is closed in above by the clavicle, but is continuous below with the space between the two pectoral muscles down to the level where the superficial layer of the deep fascia and the clavi-pectoral fascia (which has invested the pectoralis minor and continued downward as a single layer againj unite at the lower border of the pectoralis major to form the axillary fascia. Effusions of blood or collections of pus occupying this space between the two muscles are therefore prevented from passing upward by the clavicle, forward by the pectoralis major, and backward by the clavi-pectoral fascia and pectoralis minor. Fig. 564. Humeral branch of acromio-thoraci Pectoralis minor Deltoid ^^ " c artery \ Ceph: Pectoralis major distal stump ^_^ __ tO^^"^ Cut edge of — st- superficial pec total fascia Cut edge of superficial la> er of clavi pectoral fascia Teres major covered by Dissection of tho wall ; pectoralis minor has been piriU 'ing deep layer of clavi-pectoral Consequently they are apt to approach the surface near the anterior axillary margin or in the groove between the great pectoral and deltoid, — i.e., at either the lower border of the sternal portion of that muscle or the upper border of its clavicular fibres. Beneath the costo-coracoid membrane is a region described as the deep infra- clavicular triangle. Although continuous with the axilla, this space is conveniently studied as a separate region on account of the important structures which it contains and the frequency with which it is invaded by disease. Its floor is formed by the first and second ribs and the intercostal, serratus magnus, and subscapularis muscles. Its apex is at the angle made by the line of the upper border of the small pectoral and that of the clavicle at the coracoid process, those two lines constituting its sides. The base is towards the sternum at the line where the costo-coracoid membrane is fused with the deep fascia over the upper intercostal spaces. Through this triangle pass the axillary, superior thoracic, and acromio-thoracic vessels, the cephalic vein, the external and internal anterior thoracic and long thoracic nerves, and the brachial plexus. It contains fat, with numerous lymphatic glands and vessels. It is obvious .S82 HUMAN ANATOMY. that it is continuous above with the neck and inferiorly with the axilla. The latter space is shut in below by the continuation of the axillary fascia from the lower bor- der of the pectoralis major backward to the latissimus dorsi, outward to the deep fascia of the arm, and inward to the deep fascia of the thorax. Abscess or effusion of blood, as its progress in all these directions is resisted, may therefore point in the neck, following the vessels and the trunks of the plexus up from the axilla through the deep infraclavicular triangle, to make its appearance above .the clavicle. The skin over the fascia at the base of the axilla is thin and richly supplied with hair-follicles and with sebaceous and sudoriparous glands ; hence superficial infections are frequent and secondary glandular abscesses are common. The con- nective tissue of the axillary space is loose and abundant, permitting of free motion of the arm, but also favoring the occurrence of large collections of blood or of pus. Fig. 565. Fig. 566. ■ Acromion, process Shoulder of subject in atinn has been produced, deforniitv. in preceding subcoracoid The fascia over the scapular muscles — supraspinous and infraspinous fascia — has already been described in reference to caries, necrosis, and abscess (pages 255. 279)- Dislocation of the Shoulder-Joint. — The circumstances that fa\or or resist dislo- cation of the shoulder-joint have been enumerated (pages 27S, 279), but the ana- tomical symptoms of that lesion may now be considered with especial reference to the muscles invoUed. Shoulder dislocation is either subglenoid or subcoracoid in the vast majority of cases, the former being almost invariably the primary form, for reasons previously given (page 278). A luxation, subglenoid primarilv, usually becomes subcoracoid from the con- tinuance of the force producing it, aided strongly by the pectoralis major ; hence the subcoracoid is the most common. The subcla\-icular, in which the head passes farther inward and lies on the second and third ribs beneath the pectoralis major, PRACTICAL CONSIDERATIONS: AXILLA AND SHOULDER. 583 and the supracoracoid, in which, owing to fracture of the coracoid or the acromion, the head is displaced upward, are so uncommon that they need merelybe mentioned here. The backward (subspinous) luxation is resisted so strongly by the subscapu- laris, and especially bythe long head of the triceps, that it also is a surgical rarity. In the subglenoid and subcoracoid varieties (Figs. 565, 566) it will be found : I. That the normal curve of the shoulder is replaced by a straight line, because of (a) the absence of the head of the bone and the tuberosities beneath the deltoid ; {d) the stretching of that muscle. 2. For the same reasons it will be found that (a) a ruler applied to the outer side of the arm will touch both the acromion and the external condyle at the same time (Hamilton) ; and {d) the edge of the acromion is unnaturally prominent, while beneath it is a palpable depression instead of the nor- mal resistance of the tuberosities. 3. The elbow is abducted because of the tension of the deltoid. 4. The forearm is flexed on account of the tension of the biceps. 5. The vertical measurement of the axilla is increased (Callaway), because of (a) F"^' 567 the presence of the head or upper por- ^^,. \^^ tion of the shaft in the line of meas- '' ^ urement ; and (d) the lowering of the axillary folds (Bryant), the insertions of the pectoralis major and latissimus dorsi being, of course, carried down- ward with the humerus. 6. The elbow cannot be made to touch the chest-wall while the hand is placed on the oppo- site shoulder (Dugas), because the head of the bone is held in contact with that wall by the tense muscles and overlying structures, and its lower extremity — the other end of a straight, inflexible axis — cannot be made at the same time to touch at a second point the curve represented by the wall of the thorax. 7. There is rigidity because of the ten- sion or spasm of the muscles moving the humerus, especially of the sub- scapularis, the deltoid, the supra- and infraspinatus, the biceps, and the coraco- brachialis. 8. In the subcoracoid luxa- tion the prominence of the head may be felt beneath the coracoid or outer third of the clavicle where it lies, the anatom- ical neck resting on the anterior border of the glenoid cavity. There is a little real lengthening, — i.e., the distance between the glenoid, surface and the lower end of the humerus must be increased, — but this may be converted into apparent short- ening by abduction, which approximates the tip of the acromion and the external condyle. 9. In the subglenoid variety the head- may be felt low in the axilla, the anterior wall of which is widened. It rests on the upper part of the outer border of the scapula just below the glenoid cavity. Lengthening is apt to be marked, and, when the arm is adducted somewhat, may exceed an inch. The stretching and "hollow tension" of the deltoid and, therefore, the abduction of the arm are marked. 10. There is usually (a) pain from direct pressure upon or from stretch- ing of the brachial plexus, and frequently {/>) cedema from similar involvement of the axillary vessels. In all lu.xations, but especially in the subglenoid and subspinous, the circumflex nerve is apt to be injured ; hence obstinate paresis or paralysis of the deltoid is a not infrequent sequel. In all methods of reduction of shoulder luxations the humerus is used as a lever, and in all it is desirable to secure fixation of the scapula by means of (a) the Superficial dissection of preceding subcoracoid luxation, showing muscles after removal of skin and fasciae. 584 HUMAN ANATOMY. weight of the trunk in the supine and recumbent position ; {b) pressure on the acromion and clavicle ; (c) the use of a folded sheet placed high in the axilla, so that it presses upon the axillary border in front and the dorsum posteriorly when the two ends are carried across the body and made taut ; or (a? ) by dragging on the opposite arm, "which, by making tense the trapezius of the opposite side, pro- vokes contraction of the muscle on the injured side" (Makins). The use of the heel or foot in the axilla as a fulcrum while manual extension is made — the long arm of the lever, the shaft of the humerus, being carried inward so as to move the short arm, the head, outward — requires no anatomical explanation. Kocher's method (applicable especially to subcoracoid luxation) is more com- plex in its mode of action. There is some difference of opinion as to its exact mechanism, but it is safe to say that in its various stages it acts approximately as follows. I. The elbow is flexed, rela.xing the biceps, and the arm is pressed closely to the side, making tense the untorn posterior portion of the capsule extending between the posterior lip of the glenoid fossa and the under and back part of the neck of the humerus. This Fig. 56S. ci, Coracoid process Long head of biceps Supraspinatus Infraspinatus Teres minor. ajor (cut) portion of the capsule and the tendons of the posterior scapu- lar muscles are drawn tightly across the glenoid fossa. 2. The arm is rotated outward until the forearm is parallel with the transverse a.xis of the bodv, the hand pointing di- rectly outward. This rolls the head of the bone outward on the tense portion of the cap- sule, which is partly wound, as it were, upon the neck, and at the same time relaxes the scapular tendons and removes them from the fossa. 3. The elbow is raised until the arm is parallel with the antero- posterior axis of the body. This relaxes the anterior fibres of the deltoid, the coraco- brachialis, and the upper por- tion of the capsule, and perhaps widens the space between the margins of the rent, although no obstacle to reduction is usu- ally met with there. The lower portion of the capsule is still tense. 4. Rotation inward on this portion as a fulcrum now moves the articular face of the head towards the comparatively free glenoid cavity and relaxes the subscapularis ; as the elbow is then lowered in adduction the lower capsular segment relaxes and the head re-enters through the rent by which it originally emerged. These details can be worked out satisfactorily in experimental luxations on the cadaver, and have apparently been demonstrated as to the main points by Farabceuf, Helferich, and others. Recurrent or "habitual dislocation" — i.e., dislocation occurring from trifling causes, such as abduction of the arm — may be a remote result of the rupture or for- cible separation of the tendons of the supra- and infraspinatus muscles from the cap- sule of the joint, with rupture of the capsule at its upper portion, and the formation of a free communication between the joint-cavity and that of the subcoracoid bursa (Jossel, quoted by Stimson). It is, however, usually due to the injury to the capsule and to the weakness of the shoulder muscles resulting from the original accident. Bursa. — -The large subacromial bursa and the subdeltoid bursa have been de- scribed in relation to their possible enlargements (page 279). The subscapular bursa Deeper dissection of preceding : displacement of head of hum Libcoracoid luxat THE BRACHIAL MUSCLES. 585 and the bursa beneath the infraspinatus often communicate with the shoulder-joint, and disease of the latter may spread to them. An infraserratus bursa has been described (Terrillon), situated between the infe- rior scapular angle and the chest-wall. Its enlargement gives rise to friction-like crepitation or creaking, which has been mistaken for fracture of ribs or scapula or for an arthritis of the shoulder. Nancrede says that this symptom is due to (a) an exostosis on the ribs or scapula which has caused such atrophy of the subscapular and serratus magnus muscles as to allow the two bony surfaces to come in contact ; or (^) a localized projection of the ribs due, for example, to a post-pleuritic con- traction of the chest, and with the same muscular atrophy ; or (c) a primary atrophy of the muscles, as in ankylosis of the scapulo-humeral joint, which will admit of the normal scapula and ribs becoming apposed. This latter condition especially causes increased movements of the scapula over the thoracic wall and favors the development of this bursa. THE BRACHIAL MUSCLES. Pre-Axial. Biceps Brachialis anticus. POST-AXIAL. 1. Triceps. 2. Anconeus. Superficial fasc Deep fascia The brachial group includes those muscles which act primarily upon the fore- arm and form the muscular substance of the arm. Some of them, however, take origin in whole or in part from the pectoral girdle and thus have some effect on the movements which occur about the shoulder-joint, although their principal action is upon the forearm. The Brachial Fascia. — The deep layer of the fascia of the arm forms a com- plete investment of the muscles of the brachial region. Above it passes over into the thin fascia covering the deltoid muscle, and me- ^ ^ ,• • ^^5- . ' . Cephalic vein Biceps dially It becomes continu- ous with the axillary fascia, while below it is continuous with the fascia of the fore- arm, adhering firmly to the periosteum covering the subcutaneous portions of the humerus and the ole- cranon process, and being reinforced by tendinous prolongations from the bi- ceps and triceps muscles. From its lateral and medial surfaces it sends sheet-like prolongations in- ward to be attached to the humerus. These sheets, termed the intermuscular septa, are of considerable strength and give attach- ment to adjacent muscles. They pass to the humerus between the lateral and medial borders of the triceps and the remaining muscles of the arm, and it is to be noted that, while the medial or inner septum marks the boundary between the pre-axial and post-axial muscles, this is not the case with the lateral or external septum. In the lower part of their extent the septa are attached to the supra- condylar ridges of the humerus and terminate at the cond3des, a number of post-axial muscles of the forearm arising from the outer condyle anterior to the external septum. A number of subcutaneous bursse occur between the integument and the bra- chial fascia in those regions in which the fascia is adherent to the subjacent perios- teum covering so-called subcutaneous portions of the skeleton. Thus there is a External intermuscular septum Triceps, outer head Triceps Tendon of triceps third. 586 HUMAN ANATOMY. bursa acromialis over the acromion process of the scapula, a bursa olecraiii over the olecranon process of the ulna, and a bursa may occur over each condyle of the humerus. {a) THE PRE-.\XIAL MUSCLES. I. Biceps (Figs. 560, 570). Attachments. — The biceps (m. biceps brachii), as its name indicates, takes oris;in by two heads. The long head arises from the upper border of the glenoid cavity of the scapula by a slender round tendon, which traverses the cavity of the shoulder-joint invested by the synovium and then bends downward into the bicipital groove ( Intertubercular sulcus ) of the humerus, accompanied by a prolongation of the joint capsule (vagina mucosa intertubercularis ) , and then, becoming muscular, unites with the short head, which arises from the tip of the coracoid process of the scapula in common with the coraco-brachialis. By the union of the two heads a strong muscle is formed which descends in front of the humerus and a short distance above the elbow-joint passes over into a flat tendon, which is continued downward to be inserted into the tuberosity of the radius, a mucous bursa (bursa bicipitoradialis) being interposed between the anterior surface of the tuberosity and the tendon. Some of the fibres of the muscle, instead of passing into the tendon, are continued into a flat tendinous expansion, the semilunar ox bicipital fascia ( lacertus fibrosus), which passes downward and medially to become lost in the fascia of the forearm. Nerve-Supply. — By the musculo-cutaneous nerve from the fifth and sixth cervical nerves. Action. — To flex the forearm on the brachium, and when the forearm is in pro- nation to supinate it. It will also act to a slight extent in movements of the arm at the shoulder-joint, assisting the coraco-brachialis in drawing the arm forward. Relations. — The biceps is crossed on its ventral surface by the tendon of the pectoralis major and is covered above by the lateral portion of the deltoid. Deeply it is in relation with the humerus, the brachialis amicus, and the supinator. Upon its inner side lie the coraco-brachialis abo\'e and below, in the groove between it and the triceps (sulcus bicipitalis medialis), the brachial vessels, and the median nerve. Variations. — The biceps presents numerous variations. Its long head is occasionally want- ing, but more frequently additional heads occur. Of these the most frequent, occurrino: in some- thing over 10 per cent, of cases, is a head which arises from the medial surface of the humerus, between the insertions of the deltoid and coraco-brachialis. Other heads may arise from the external tuberosity of the humerus or from the outer border of that bone, between the deltoid and brachio-radial muscles. 2. Br.\chi.\lis Anticus (Fig. 571). Attachments. — The brachialis anticus (m. brachialis) occupies the anterior sur- face of the lower part of the humerus and is for the most part covered by the biceps. It arises froin the intermuscular septa and the anterior surface of the humerus imme- diately below the insertion of the deltoid, which it partly surrounds. It passes downward, and the fibres converge to a short tendon which is inserted into the anterior surface of the coronoid process of the ulna. Nerve-Supply. — The main mass of the muscle is supplied by branches from the musculo-cutaneous nerve. The fibres which arise from the lateral intermuscular septuin and are covered by the brachio-radialis are supplied bv a branch from the musculo-spiral nerve. The nerve-fibres come in both cases from the fifth and sixth cer\ical nerves. Action. — To flex the foreann. Variations. — The ner\e-supply shows the brachialis anticus to be a composite muscle the major portion of which is derived from the pre-axial muscle-sheet, while the lateral portion of it comes from the post-axial sheet. In correspondence with this derivation of the muscle, its lateral portion is occasionally separate from the rest and may terminate below on the fascia of the forearm or on the radius. A longitudinal separation of the pre-axial portion of the muscle may also occur, and it seems probable that the most frequently occurring third head of the biceps (see above) is a derivative of this portion of the brachialis. The epitrochleo-ancotieus is a small, usually quadrangxilar muscle which is present in about 25 per cent, of cases. It arises from the posterior surface of the inner condyle of the humerus THE BRACHIAL MUSCLES. 587 and passes downward and laterally to be inserted into the external surface of the olecranon process of the ulna. Notwithstanding its position upon the posterior surface of the arm, it is a Fig. 570. m. Biceps< [ Long head — LmA V \ I Pectoralis minor Fig. 571. Tendon of sertion of pec- toralis maji Brachialis anticus Tendon of insertion of biceps Brachio-radialis Head of_^ radius \| ?%k Bicipital Jy- tuberosity of radius — Insertion of biceps — Bicipital fascia Muscles of anterior surface of ai Brachialis anticus and supinator, seen from in front. derivative of the pre-axial muscle-sheet and is suppHed by the ulnar ner\'e, whose main stem, as It passes down between the olecranon and the inner condvle, is covered by the muscle. When absent, the muscle is represented by a strong fibrous band. 588 HUMAN ANATOMY. {*) THE POST-AXIAL MUSCLES. I. Triceps (Figs. 570, 572). The triceps (m. triceps brachii) is a strong muscle whichi occu- The scapular or Attachments pies the entire dorsal surface of the arm. It arises by three heads Fig. 572. Supraspinatus Spine of scapula Head of humerus covered by psular ligament Tendon of insertion of teres A\ilHr\ border ot "^^A scapula Inferior angle ol scapula Teres major/' Serratus magi long head takes its origin by a tendon from the infra- glenoid tuberosity of the scapula ; the inner or medial head, from the posterior (dorsal) surface of the humerus and from both intermuscular septa below and medial to the groo\'e for the musculo-spiral nen-e ; and the outer or lateral head, from the external intermuscular septum and the posterior surface of the humerus above and lateral to the groove for the musculo-spiral nerve. The three heads unite to form a strong, broad tendon which IS inserted into the olecranon process of the ulna. The common tendon of insertion begins as a broad aponeurosis upon the anterior surface of the long head, the fibres of which are attached to the upper border and the upper part of the posterior sur- face of the aponeurosis. The fibres of the lateral head are attached to the lateral border of the aponeurosis, while those of the medial head, which is much stronger than the lateral one, pass to its anterior surface. Nerve-Supply. — By the musculo-spiral nerve minor cui away, from the sixth, seventh, and eighth cervical nerves. Action. — To extend the forearm on the upper arm and to draw the entire arm backward. Variations. — The triceps occasionaljy possesses an additional head arising either from the coracoid process of the scapula or from the capsule of the shoulder-joint. d posterior scapular mus- of infraspinatus and teres PRACTICAL CONSIDERATIONS : MUSCLES AND FASCIA. 589 2. Anconeus (Fig. 581). Attachments. — The anconeus is a short muscle which arises from the posterior surface of the external condyle of the humerus. Its fibres diverge to form a triangu- lar sheet which is insef'ted into the upper part of the posterior surface of the ulna and into the outer surface of the olecranon process. Nerve-Supply. — By the musculo-spiral nerve from the seventh and eighth cervical nerves. Action. — To assist the triceps in extending the arm. PRACTICAL CONSIDERATIONS : MUSCLES AND FASCIA OF THE ARM. The deep fascia of the arm, continuous above with that over the deltoid and with the clavi-pectoral fascia, closely embraces all the muscular structures and resists the outward passage of subfascial collections of blood or pus, which therefore, under the influence of gravity, tend for a time to follow the intermuscular spaces downward. CEdema and swelling above the elbow are thus not uncommon as a result of disease or injury at a higher level. Blood or pus may reach the surface by following the structures that pierce the fascia, — viz., the basilic vein and the internal and external cutaneous nerves. The ecchymosis after fracture sometimes takes this course. The intermuscular septa (page 585) divide the space enclosed by the brachial aponeurosis into an anterior and a posterior compartment extending from the level of the deltoid and coraco-brachialis insertions to that of the two condyles. They, too, have some eftect in limiting effusions, but the latter, especially if due to infection, can readily pass from one space to the other by following the musculo-spiral nen,'e or the superior profunda artery through the outer septum, or the ulnar nerve, inferior profunda artery, or anastomotica magna through the inner septum. In selecting a method of amputation through the arm it should be remembered that above the middle most of the muscles that it would be necessary to divide are free to retract, — i.e., the deltoid, the long head of the triceps, the coraco-brachialis, and the biceps. Below the middle the biceps is the only muscle unattached. In the former situation, therefore, the circular method is apt to lead to a "conical stump' ' from the too free retraction of the flaps and from the activity of the upper humeral epiphysis (page 272). In amputation just above the elbow the circular method is applicable, but the incision should be a little lower at the antero-internal aspect of the limb to allow for the greater retraction in the bicipital region. Inward dislocation of the tendon of the long head of the biceps muscle has probably occurred from direct violence as an uncomplicated lesion in a few cases. The symptoms are said to be (White) : [a) the recognition of the bicipital groove empty ; {b) inward rotation due to the pressure of the tendon on the lesser tuberosity and on the tendon of the subscapularis ; (c) adduction of the humeral head, leaving a slight depression beneath the tip of the acromion ; (if) obvious tension along the inner edge of the biceps muscle when the forearm is extended ; (if) diminution in the vertical circumference of the shoulder ; and if) shortening of the distance between the acromion and external condyle ; both of the last two symptoms are due to the elevation of the humeral head under the influence of the deltoid, the suf.raspinatus, and the clavicular fibres of the pectoralis major, that of the biceps tendon being with- drawn. These and other symptoms of this lesion (although it is extremely rare) should be studied in connection with the anatomy of the muscles involved, as an aid in elucidating their action.' Rupture of the biceps tendon has always been causedby violent muscular action, and is usually accompanied either by the sudden appearance of a more or less firm tumor on the front of the arm or by complete relaxation and flabbiness of the whole muscle. The symptoms mentioned as characteristic of dislocation of the tendon have pot been noted in any recorded case of rupture, with the exception of those due to the elevation of the head of the humerus. ' J. William White : American Journal of the Medical Sciences, January, 18S4. 590 HUMAN ANATOMY. Fractures of the humerus are much influenced by muscular action, although the controhing force in the production of the deformity is often that which causes the fracture. In fracture of the tuberosities the theoretical displacement is upward and back- ward for the greater tuberosity under the action of the supra- and infraspinatus and teres minor, and forward and inward for the lesser tuberosity, which is supposed to be drawn in that direction by the subscapularis. The injury is extremely rare ; the clinical signs are obscure. Increased breadth of the shoulder, localized tender- ness and disability, occurring after the application of direct force or after violent action of the shoulder muscles, would be suggestive ; recognition of a preternaturally mobile or displaced fragment would be conclusive ; but the X-rays will usually»be essential. In fracture of the surgical neck of the humerus — i.e., between the tuberosities and the insertions of the axillary muscles — and in separation of the upper epiphysis the fragments are similarly influenced by muscular action. The upper fragment is held in place, is a little elevated, and is obliquely tilted by the supra- and infraspinatus, subscapularis, and teres minor. 573- Fig. The upper end of the lower fragment is drawn towards the chest-wall by the pectoralis major, latissimus dorsi, and teres major. Their action may be aided by that of the deltoid, which may fi.x the middle of the bone so that it acts as a fulcrum, or may actually abduct the elbow. The biceps, triceps, and coraco-brachialis and del- toid draw the lower fragment upward, causing shortening (Fig. 573)- Epiphyseal disjunc/ion may be suspected if (a) the patient is a child or an adolescent ; {b) the anterior projection of the upper end of the lower frag- ment is at an unusually high level, — i.e., about that of the coracoid ; (e) the crepitus is muffled ; (d ) the shortening is slight (page 272). The ap- plication of the tests mentioned above (page 583) will distin- guish this lesion from luxation of the shoulder, which, moreover, is very rare before adult life (page 306). In fracture of the shaft of the humerus between the insertions of the axillary muscles and that of the deltoid the upper fragment is drawn inward by the former muscles ; the lower fragment is drawn upward by the biceps, triceps, and coraco- brachialis, and upward and outward by the deltoid (Fig. 573). In fracture just below the deltoid insertion that muscle acts to such ad\antage in abducting the upper fragment as to counteract the pull of the axillary muscles in the contrary direction. The relation of the fragments will therefore chiefly depend upon the direction of the line of fracture ; the shortening, under the influence of the biceps, triceps, and coraco-brachialis, will depend on its degree of obliquity. In this fracture it is sometimes necessary to dress the arm in abduction to overcome the deltoid con- traction. In fracture just above the condyles (page 273) the line of fracture is usually oblique from above downward and forward (Fig. 288). The short lower fragment will be drav\n upward by the biceps and triceps and backward by the latter muscle. 1 neck ot humerus. THE ANTIBRACHIAL MUSCLES. 591 The lower end of the upper fragment will then arrest flexion of the forearm by contact, or may puncture the brachialis anticus, the bicipital fascia, and even the skin. The diagnosis of this fracture from luxation of the elbow (Fig. 575) can be made by (a) the recognition of the relations of the three bony points, — the tips of the two condyles and of the olecranon (page 306) ; (6) the presence of crepitus ; (c) the disappearance of the deformity on extension and counterextension, and, usually, its reappearance when extension is discontinued ; and {d ) the greater freedom of exten- sion of the forearm on the arm in fracture ; flexion may be limited, as above men- tioned, by the contact of the upper fragment with the forearm at the bend of the elbow and other points ; (e) the arm is shortened in fracture ; the forearm in dislocation. In separations of the lower humeral epiphysis (page 273) (a) the patient is a child or an adolescent ; ((5) there is muffled crepitus ; (c) the lower end of the upper Fig 574 Fig. 575- Posterior luxation of elbow of right fragment has greater breadth and is more rounded than in fracture ; (d) the line of separation is nearer the end of the bone, and the anterior projection of the diaph- ysis is on a level with the fold of the elbow ; in fracture it is usually above it (Poland). Condylar fractures have been described (page 273), but it may be mentioned here that the elevation of the internal condyle, if not corrected, causes the line of the joint to incline inward instead of outward. If union takes place in that malposition, the so-called "gun-stock deformity," or "cubitus varus" (in which the "carrying angle" of the forearm with the arm is obliterated or changed to a similar angle opening inward) results. The bursae about the elbow h&ve been described (page 307). THE ANTIBRACHIAL MUSCLES. The muscles which belong to this group act primarily upon the bones of the forearm or of the carpus and constitute the muscular substance of the forearm. Some of them, however, have undergone a secondary extension into the hand and act as 592 HUMAN ANATOMY. flexors or extensors of the digits, this extension being due in some cases to the differentiation of the fascia of the hand into tendons continuous with those of the an- tibrachial muscles, in other cases to end-union of antibrachial and hand muscles. It will be convenient, however, to regard the long flexors and extensors of the digits, formed in this way, as antibrachial muscles. Comparatively studied, an arrangement of the antibrachial muscles in distinct layers is clearly perceivable, three layers being found in the pre-axial and two in the post-axial muscles. In both cases the superficial layer takes its origin from the humerus, while the remaining layers are attached above to the bones of the forearm. Secondary adaptations have in some cases interfered with the distinctness of the layers, but the primary conditions will be taken as the basis for the classification of the muscles. The antibrachial fascia completely invests the muscles of the forearm and is the downward continuation of the brachial fascia. It is especially strong upon the dorsal surface of the forearm, where it is attached to the olecranon process and the entire length of the posterior border of the ulna, and anteriorly it is strengthened in its upper part by the fibres of the semilunar fascia of the biceps. At the wrist it is attached to the bones of the forearm and carpus, and becomes thickened by trans- verse fibres to form the dorsal and volar carpal ligaments. The atiterior a?i?iidar Ugatnent (ligamentura carpi volare) lies on the anterior sur- face of the wrist, covering the flexor muscles in that region (Fig. 577). Laterally and medially it is connected with the dorsal ligament. This, the posterior- annular ligament ( liKaraentum carpi dorsale), is a stronger trans%erse band on the posterior surface of the wrist, and is attached laterally to the outer surface and to the styloid process of the radius, and passes inward and slightly downward to the styloid process of the ulna and to the pisiform and cuneiform bones, making attachments to the ridges on the posterior surface of the radius and ulna an^l thus converting the six intervening groo\'es into canals which lodge the tendons of the long extensor muscles (Fig. 579). Beginning at the radial side, the first canal transmits the tendons of the extensor ossis metacarpi pollicis and the extensor brevis pollicis ; the second, the tendons of the two extensores carpi radiales ; the third, that of the extensor longus pollicis ; the fourth, those of the extensor communis digitorum and the e.xtensor indicis ; the fifth, that of the extensor minimi digiti ; and the sixth, that of the extensor carpi ulnaris. Each of the canals is lined by an independent synovial membrane. (<7) THE PRE-AXIAL MUSCLES. (aa) The Superficial Layer. 1. Pronator radii teres. 3. Palmaris longus. 2. Flexor carpi radialis. 4. Flexor carpi ulnaris. 5. Flexor sublimis digitorum. I. Pronator Radii Teres (Fig. 576). Attachments. — This muscle (m. pronator teres), thick and band-like, arises by two heads ( a ) from the inner condyle of the humerus, the adjacent intermuscular septa, and the deep fascia, and (b^ from the medial border of the coronoid process of the ulna. It passes downward and laterally and is inserted into about the middle of the outer surface of the radius. The median nerve passes downward between the two heads. Nerve-Supply. — By the median nerve from the sixth cervical nerve. Action. — To pronate and fle.x the forearm. Variations. — The pronator teres is formed by a combination of portions from the super- ficial and deep layers of the forearm musculature, the condylar head representing the superficial portion and the coronoid head the deep one. In the lower mammals the pronator quadratus frequently extends well up towards the elbow-joint, and the coronoid head of the pronator teres represents the uppermost portion of this muscle, its lower portion persisting as the pro- nator quadratus. Not infrequently the coronoid portion of the muscle is completely separate from the condylar head, or it may be rudimentary or represented only by a connective-tissue THE ANTIBRACHIAL MUSCLES. 593 band. The entire muscle is some- times incompletely separated from the neighboring muscles of the su- periicial layer, receiving accessory heads from the palmaris longus or the flexor sublimis digitorum. 2. Flexor Carpi Radialis (Fig- 576). Attachments. — The flexor carpi radialis arises from the inner condyle of the humerus, by a tendon common to it and the neighboring muscles of the super- ficial layer, from the adjoining intermuscular septa and the deep fascia. It passes downward and slightly laterally and is ins£7ied into the bases of the second and third metacarpal bones. Nerve-Supply. — By the median ner\-e from the sixth cer- vical ner\^e. Action. — To flex the hand and to assist in pronating the forearm. Relations. — In its course down the forearm the flexor carpi radialis passes obliquely across the flexor sublimis digitorum and the lower part of the flexor longus poUicis. At the wrist it passes through a special sheath within the superficial part of the anterior annular ligament, and just before its insertion it is crossed by the tendon of the flexor longus pol- licis. A bursa (bursa m. flexoris carpi radialis) is interposed be- tween the tendon and the base of the second metacarpal bone. Laterally the muscle is in contact abo\'e with the pronator radii teres and below with the brachio- radialis, from which it is sepa- rated near the wrist by the radial artery. 3. Palmaris Loxgus (Fig. 576). Attachments. — The pal- maris longus' arises with the neighboring superficial muscles by the common tendon from the inner condyle of the humerus, from the adjoining intermuscular septa, and from the deep fascia. It forms a short spindle-shaped belly which is continued into a Fig. 576. Brachialis anticus Biceps Brachio-radial Extensor carpi radialis longior Styloid process- Extensor ossis / metacar])' polllLii f' /r//j Fltxor carpi ulnaris Palmaris brevis Palmar fascia Superficial dissection of forearm and palm, anterior surface; portion of antibrachial fascia covering origin of superficial muscles has been left in place. 3S 594 HUMAN ANATOMY. Fig. 577- Tendon oi bicep: Extensor carpi radialis longior Superficial Lumbricales Lunibricales |il;i ""^ L '^ '■■^ Dissection of muscles of forearm and hand, anterior surface ; most superficial muscles liave been removed long, slender tendon that passes in front of the an- terior annular ligament of the wrist, and is I'n- serted into the palmar fascia. Nerve-Supply. — By the median ner\-e from the sixth cer\ical ner\e. Action. — To tense the palmar fascia andtle.x the hand. Variations. — The pal- niaris longus is a ver>' vari- able muscle. It is not in- frequently absent, and may present various modifica- tions in its structure, being sometimes entirely tendi- nous, or entirely fleshy, or tendinous above and fleshy below. It is occasionally double. 4. Flexor Carpi Ul- XARis (Fig. 576). Attachments. — The flexor carpi ulnaris arises from the medial condyle of the humerus in common with the neighboring superficial muscles, from the inter- muscular septa and deep fascia, and also from the posterior surface of the olecranon process, and from the upper part of the posterior border of the ulna by means of an aponeurosis common to it and the flexor pro- fundus digitorum and the e.xtensor carpi ul- naris. It descends along the ulnar border of the forearm and is inserted into the pisiform bone, its tendon being contin- ued on to be attached to the hook of the unciform and, often, to the base of the fifth metacarpal bone. Nerve-Supply. — By the ulnar nerve from the eighth cervical and first thoracic nerves. Action. — To flex and adduct the hand. THE ANTIBRACHIAL MUSCLES. 595 Relations. — By its deep surface this muscle is in relation with the subliniis and profundus digitorum and with the ulnar vessels and nerve. The ulnar nerve and posterior recurrent ulnar artery pass beneath a tendinous band which stretches across between the. two heads of the muscle, and towards the wrist the ulnar artery comes to lie along the lateral border of the tendon. A mucous bursa (bursa m. flexoris carpi ulnaris ) is frequently to be found between the tendon and the upper part of the pisiform bone. Variations. — The flexor carpi ulnaris frequently passes distally to be inserted into the base of the fifth metacarpal. The conversion of the ulnar head into connective tissue has been observed. 5. Flexor Sublimis Digitorum (Fig. 577)- Attachments. — The superficial fie.xor (m. flexor digitorum sublimis) arises from the inner condyle of the humerus in common with the neighboring superficial mus- cles, from an oblique line on the anterior surface of the radius, and from the tendi- nous arch extending between these two bony points and beneath which the median nerve and ulnar artery pass. The fibres arising from these origins form four bellies, prolonged below into as many tendons, which at the wrist pass beneath the ante- rior annular ligament and then diverge towards the bases of, the second, third, fourth, and fifth fingers and enter the corresponding digital sheaths. Here each tendon divides over the surface of the first phalanx into two slips, which pass one on either side of the subjacent tendon of the fle.xor profundus digitorum and partially unite beneath it to be inserted into the base of the second phalanx. Slight tendinous' bands, vinada tendinum, pass between the tendons of the profundus and the terminal portions of those of the sublimis. Nerve-Supply. — By the median nerve from the se\enth and eighth cervical and first thoracic nerves. Action. — Primarily to fle.x the second phalanx of the four medial digits, but a continuation of its action will flex the first phalanges of the same digits and eventually the hand. Relations. — Superficially the flexor sublimis is covered by the remaining muscles of the superficial layer ; deeply it is in relation with the flexor profundus digitorum, the flexor longus pollicis, the ulnar vessels, and the median nerve. Variations. — Occasionally the portion of the muscle which gives rise to the tendon of the fifth digit appears to be wanting, the tendon arising from the palmar fascia, the anterior annular ligament, or the flexor profundus. An explanation of this anomaly is found in the developmental history of the muscle. In the lower vertebrates the superficial flexor inserts into the palmar fascia, v\hich gives origin to a set of superficial digital muscles whose relations are similar to those of the digital portions of the sublimis tendons. In the mammalia these digital muscles de- generate into tendinous bands, with which the tendon of the antibrachial portion of the muscle becomes continuous. The origin of the tendon for the fifth digit from the palmar aponeurosis or transverse carpal ligament is, therefore, a persistence of a phyletic stage, as is also its origin from the flexor profundus, since in the lower mammals the antibrachial portions of the two muscles are united to form a single mass (page 597). {bb) The Middle Layer. I. Flexor profundus digitorum. 2. Flexor longus polHcis. I. Flexor Profundus Digitorum (Fig. 578). Attachments. — The deep flexor (m. flexor digitorum profundus) arises from the anterior and outer surfaces of the ulna and from the inner half of the interosseous membrane. Its fibres are directed downward, and at about the middle of the fore- arm are continued into four tendons, which pass beneath the anterior annular liga- ment along with the tendons of the flexor sublimis to enter the digital sheaths of the second, third, fourth, and fifth fingers. Opposite the first phalangeal joint each tendon passes between the two slips of the corresponding tendon of the flexor sub- limis and is inserted into the base of the terminal phalanx. Nerve-Supply. — The lateral half of the muscle is supplied by branches from the anterior interosseous branch of the median nerve and the medial half by the 596 HU.MAN ANATOMY. Fig. 578. Brachialis anticus Insertion of pronator radii teres— r Fle..„. brevis pollicis Adductor pollicis, oblique portion. Dissection of muscles of forearm and hand, anterior surface; superficial muscles have been removed. ulnar ; the fibres come from the seventh and eighth cer- vical and the first thoracic nerves. Action. — The primary action of the fle.xor pro- fundus is to flex the ter- minal phalanges of the second, third, fourth, and fifth fingers, but, continu- ing its action, it also flexes the remaining phalanges of those digits and finally the hand. Relations. — In the arm the muscle is covered by the flexor sublimis digi- torum and the flexor carpi ulnaris, and has resting upon its anterior surface the ulnar vessels and the median and ulnar nerves. Posteriorly it is in relation to the pronator quadratus and the wrist-joint. In the hand its tendons are cov- ered by those of the flexor sublimis and by the lum- brical muscles ; they rest upon the adductor pollicis and interosseous muscles and cross the deep palmar arch. Variations. — The flexor profundus frequently receives additional slips from the flexor sublimis and may be united to the flexor longus pollicis. A slip which has been termed the ntifssorius ad ftexorem projuiidinn digitorum not in- frequently occurs, arising from the coronoid process of the ulna and joining with one of the tendons of the profundus. The significance of the varia- tions of the profundus will be considered in connection with those of the flexor longus pol- licis. 2. Flexor Longus Pol- licis (Fig. 57S). Attachments. — The long flexor of the thumb (m. flexor pollicis Ion<;us) lies to the lateral side of the flexor profundus digi- torum and arises from the anterior surface of the ra- dius and the adjacent half THE ANTIBRACHIAL MUSCLES. 597 of the interosseous membrane. It usually possesses also an origin by means of a slender slip from the coronoid process of the ulna or the medial epicondyle of the humerus. The muscle-fibres pass into a strong tendon at the middle of the forearm, and this passes downward beneath the lateral part of the annular ligament and extends along the \-olar surface of the thumb to be mserted into the base of its ter- minal phalanx. Nerve-Supply. — By the anterior interosseous nerve from the eighth cervical and first thoracic ner\'es. Action. — To flex the terminal phalanx of the thumb ; continuing its action, it will also flex the proximal phalanx and assist in the flexion of the hand. Relations. — In the forearm it is covered by the flexor sublimis digitorum, the flexor carpi radialis, and the brachio-radialis, and has resting upon it the radial ves- sels. Deeply it is in relation with the pronator quadratus and the wrist-joint. In the hand its tendon is covered by the opponens poUicis and the flexor brevis poUicis, and it rests upon the adductor pollicis. Variations. — The head from the coronoid process or medial epicondyle of the humerus is sometimes absent and the muscle is frequently connected with the flexor profundus digitorum or even fused with it. Occasionally there arises from the lower part of the anterior and external surfaces of the radius a muscle which has been termed \}n(t flexor carpi radialis breins. Its insertion varies some- what, being sometimes on one of the carpal bones, at other times on either the second, third, or fourth metacarpals, and at others, again, into the transverse carpal ligament. Although asso- ciated by name with the flexor carpi radialis, it is more probably a derivative of the deeper layer of the flexor musculature and is supplied by the volar interosseous branch of the median nerve. The majorit}- of the variations of the flexor longus pollicis and flexor profundus digitorum find an explanation in the historical development of the muscles. In the lowest group of the mammalia, the monotremata, the two muscles are fused with each other and also with the flexor sublimis to form a common long flexor, from the tendon of which the tendons of the flexor sublimis arise. In slightly higher forms this common fle.xor can be seen to be composed of five portions, which, from their points of origin and relations, may be termed the condylo-ulnaris, condylo-radialis, centralis, ulnaris, and radialis, and as the scale is ascended one finds at first a part of the condylo-ulnaris and later the whole of that portion separating from the common mass and joining the tendons of the sublimis. In still higher forms the centralis and condylo-radialis portions follow the example of the condylo-ulnaris, the flexor sublimis digitorum in man being composed of these portions of the common mass. The ulnaris and radialis portions remain, as a rule, united and, after the separation of the superficial portions is completed, constitute the flexor profundus. In man and a few other forms the radialis separates from the ulnaris to form the flexor longus pollicis. The connections which occur between the sublimis, profundus, and flexor longus pollicis are consequently to be regarded as relics of the historical development of the muscles, as the incomplete separation of a common fle.xor mass. In the lower terrestrial vertebrata the superficial and deeper layers, corresponding practi- cally to the sublimis and profundus (plus the fle.xor longus pollicis), are distinct, their fusion in the monotremes being a secondan,- condition, which forms the starting-point for the differentia- tion of the mammalian arrangement of the muscles. In these lower forms both layers insert into the palmar aponeurosis, the extension of the deeper layer to the digits being due to the separation of the layer of the aponeurosis to which the deeper muscle-layer is attached and its differentiation into tendons. It may be added that in the lower vertebrates the palmaris longus is not represented as a separate muscle, and it is to be regarded as a portion of the superficial sheet which has retained its original relations to the palmar aponeurosis, its occasional absence being ascribed to its sharing the history of the flexor sublimis and being incorporated in that muscle. {cc) The Deep L.wer. I. Pronator quadratus. I. Prox.-\tor Ouadr.\tus (Fig. 588). Attachments. — The pronator quadratus is a flat quadrangular sheet extending across between the lower portions of the radius and ulna. It arises from the volar surface of the ulna and passes laterally and slightly distally to be inse>ied into the lateral and anterior surfaces of the lower end of the radius. Nerve-Supply. — By the anterior interosseous branch of the median nerve from the seventh and eighth cer\'ical and the first thoracic neri'es. Action. — To pronate the forearm. 598 HUMAN ANATOMY. Variations. — The pronator quadratu.s usually occupies about the lower fourth of the fore- arm, but it may be considerably reduced or, on the contrary, may e.xtend as high as the middle of the forearm or even higher. It represents the lower portion of a muscle-sheet which e.xtends in some of the lower mammals almost the entire length of the forearm, the upper portion of this sheet being represented, as already pointed out, by the coronoid head of the pronator teres. {6) THE POST-AXIAL MUSCLES. The post-axial muscles of the forearm may be regarded as consisting of two layers, the more superficial of which arises from the external condyle of the humerus, while the deeper one is attached to the bones of the forearm. As was the case with the pre-axial muscles, constituents of both layers have extended into the hand to act as extensors of the digits. (aa) The Superficial L.wer. 1. Brachio-radialis. 4. Extensor communis digitorum. 2. E.xtensor carpi radialis longior. 5. Extensor minimi digiti. 3. Extensor carpi radialis brevior. 6. Extensor carpi ulnaris. I. Br.\chio-R.\dialis (Fig. 576). Attachments. — The brachio-radialis, sometimes termed the supinator longiis, arises from the external condylar ridge of the humerus and from the lateral inter- muscular septum. Its fibres form a strong muscle which, at about the middle of the forearm, passes into a tendon which is inserted into the base of the styloid process of the radius. Nerve-Supply. — By the musculo-spiral nerve from the fifth and sixth cervical ner\es. Action. — To flex the forearm. If the arm be in a position of complete prona- tion, it will produce a slight amount of supination. Relations. — In its upper part it is in contact medially with the brachialis anti- cus, a portion of whose lateral border it covers, and with the radial ner\e. Below it rests upon the upper portion of the extensor carpi radialis longior, the supinator, the pronator teres, the flexor sublimis digitorum, and the radial artery and nerve. It is crossed near its insertion by the tendons of the abductor longus pollicis and e.xtensor brevis pollicis. Variations. — The brachio-radialis is sometimes wanting. It may be inserted a consider- able distance above the base of the styloid process of the radius, a condition characteristic of the lower mammals, or it may pass as far down as the carpal bones or even to the base of the third metacarpal. 2. Extensor C.\rpi R.\dl\l:s Longior (Figs. 576, 579). Attachments. — The longer of the radial carpal extensors ( m. extensor carpi radialis lonsjus ) lies immediately posterior to the brachio-radialis. It arises from the lower third of the external supracondylar ridge of the humerus, the external inter- muscular septum, and the extensor tendon common to it and the neighboring super- ficial muscles. About the middle of the foicarm it is continued into a tendon which passes beneath the posterior annular ligameiii. m the second compartment, along with the extensor carpi radialis brevior, and is inserted into the base of the second meta- carpal. Nerve-Supply. — By the deep di\ision of the musculo-spiral nerve from the sixth and se\enth cervical nerves. Action. — ^To e.xtend and slightly abduct the hand. Variations. — The extensor carpi radialis longior is occasionally fused with the extensor carpi radialis brevior. It may send tendinous slips to the first and third metacarpals and to the trapezium. 3. Extensor C.^rpi R,\dialis Brevior (Fig. 579). Attachments. — The shorter radial carpal e.xtensor (m. extensor carpi radialis brevis ) is fused with the neighboring superficial extensors where it arises from the THE ANTIBRACHIAL MUSCLES. 599 external condyle of the hu- merus, from the adjacent in- termuscular septa, and from the deep fascia of the fore- arm. Its fibres converge at about the middle of the fore- arm into a flat tendon, which passes with the long e.xten- sor carpi radialis beneath the posterior annular ligament in the second compartment and is inserted into the base of the third metacarpal, a . bursa (bursa m. extensoiis carpi radialis) being inter- posed between the tendon and the bone. Nerve-Supply. — By the posterior interosseous branch of the musculo-spiral nerve from the sixth and seventh cervical nerves. Action. — To extend the hand. Variations. — It may be fused to a greater or less e.xtent with the extensor carpi radialis lon- gior and may be inserted into the bases of both the second and third metacarpals. 4. Extensor Communis DiGiTORUM (Fig. 579). Attachments. — The common extensor of the fingers (m. extensor digitorum communis) arises in com- mon with the neighboring superficial extensors from the external condyle of the humerus, from the septa be- tween it and the adjoining muscles, and from the deep fascia of the forearm. At about the middle of the forearm its fibres go over into four tendons, which pass through the fourth compart- ment beneath the posterior annular ligament and diverge to be inserted into the bases of the middle and terminal pha- langes of the second, third, fourth, and fifth fingers. Just before they pass over the metacarpo-phalangeal joints of their digits the four ten- dons are usually united by Fig. 579. Biachio-radialis ^External condyle _Extensor carpi radialis longior Flexor carpi ulnan'^. E-Ytensor carpi ulnarib. Extensor minimi digit f '' _^ Extensor communis digitorum Extensor ossis ,. '%^ metacarpi pollic ^ M Extensor brevis ' " pollicis Extensor longus pollicis Posterior annular ligament Tendon of extensor j^.^ ( carpi radialis longicT i k^fj Tendon of extenso pi radialis brevior U '3 6oo HUMAN ANATOMY. Fig. 580. Olecranon process Flexor carpi ulnaris Extensor carpi radialis longtor External condyle -Extensor pollicis brevis -Extensor longus pollicis -Extensor alls brev carpi radi ior tendor ■Extensor alls long carpi radi ior tendon < ■' VI i /[Xryv Extensor brevis three obliquely transverse ten- dinous bands (juncturae ten- dinum), the one between the index and median digits being, however, frequently wanting. As each tendon passes upon the dorsum of the first phalanx of its digit it spreads out into a membranous expansion, which receives the insertions of the interosseous and lumbrical muscles and then divides into three more or less well-defined slips. The median slip passes to the base of the second pha- lanx, while the lateral ones, passing over the first interpha- langeal joint, unite over the dorsum of the second phalanx and are inserted into the base of the third or distal phalanx. Nerve-Supply. — By the posterior interosseous branch of the musculo-spiral nerve from the sixth, seventh, and eighth cervical nerves. Action. — To extend the phalanges of the second, third, fourth, and fifth fingers and, continuing its action, to extend the hand. Variations. — The principal variations of the common e.xtensor consist in the absence of one or other of the tendons, usually that to the fifth digit and more rarely that to the second, or else in the occurrence of additional tendons, due to the division of one or more of those typically occurring, cer- tain of the digits then receiving two or even three tendons. Oc- casionally an additional tendon is present which passes to the thumb to unite with the tendon of its long extensor. 5. E.XTENSOR Minimi Dig- iTi (Fig. 579). Attachments. — The ex- tensor of the little finger (m. extensor digiti quinti pioprius) arises in common with the preceding muscle from the lat- eral epicondyle of the humerus and from the antibrachial fas- cia. Its tendon passes beneath the posterior annular ligament in the fifth compartment and fuses over the fifth metacarpal THE ANTIBRACHIAL MUSCLES. 60 1 with the tendon of the extensor communis digitorum which passes to the httle finger. Nerve-Supply. — By the posterior interosseous branch of the musculo-spiral nerve from the si.xth, seventh, and eighth nerves. Action. — To extend the lit- tle finger. Variations. — This muscle is some- times absent, probably remaining in- corporated in the extensor communis. Its tendon occasionally sends a slip to the fourth finger. 6. Extensor Carpi Ulnaris (Figs. 577, 579). Attachments. — The exten- sor carpi ulnaris arises in common with the adjacent superficial ex- tensors from the external condyle of the humerus, from the deep fascia, and, usually, from the apo- neurosis attached to the posterior border of the ulna common to this muscle, the flexor profundus digitorum, and the flexor carpi ul- naris. Its tendon passes through the sixth compartment beneath the posterior annular ligament and is inserted into the base of the fifth metacarpal bone. Nerve-Supply. — By the posterior interosseous branch of the musculo-spiral nerve from the sixth, seventh, and eighth cervical nerves. Action. — To extend and ad- duct the hand. Fig. 5S1. Brichialis anticus Olecranon — fii^ process |AJ, condyle Head of radius Ulna \ — , showing deep muscle: nitv of elbow. Variations. — A fibrous band is often given off from the tendon of the Dissection muscle to be inserted somewhere over the fifth metacarpal into the sheath of the tendon of the extensor of the little finger ; it has been termed the m. ulnaris quinti digiti. {bb) The Deep Layer. 1. Supinator. 3. Extensor brevis pollicis. 2. Extensor ossis metacarpi pollicis. 4. Extensor longus pollicis. 5. E.xtensox indicis. I. Supinator (Figs. 580, 581). Attachments. — The supinator, also termed the supinator radii brevis, is a flat triangular muscle which arises partly from the outer condyle of the humerus and the orbicular ligament of the elbow-joint, and partly from the upper part of the lateral border of the ulna and the smooth surface beneath the lesser sigmoid cavity of that bone. Its fibres pass obliquely downward and outward, diverging as they go, and are inserted into the posterior, lateral, and anterior surfaces of the radius, curving around that bone. The insertion extends downward to about the middle of the radius. 6o2 HUMAN ANATO.MY. Nerve-Supply. — By the posterior interosseous branch of the musculo-spiral nerve from the sixth cervical nerve. Action. — To supinate the forearm. Variations. — The posterior interosseous nerve perforates the supinator and occasionally marks the line of separation of the muscle into two portions, which correspond to the epicon- dylar and ulnar portions of the muscle. The muscle is indeed a composite one, a portion of it being derived from the superficial e.xtensor layer and the rest of it from the deep layer. Brachio-radialis Flexor sublimis digitorum 2. Extensor Ossis Metacarpi Pollicis (Fig. 580). Attachments. — The extensor of the metacarpal bone of the thumb (m. abduc- tor pollicis lons;usj arises from the middle third of the posterior surfaces of the ulna, the interosseous membrane, and the radius. It passes down- ward and laterally, and its ten- don passes through the first compartment beneath the pos- terior annular ligament to be inserted into the outer side of the base of the first metacarpal bone. Nerve-Supply. — By the posterior interosseous branch of the musculo-spiral nerve from the sixth, seventh, and eighth cervical nerves. Action. — To abduct and slightly extend the thumb and, continuing its action, to abduct the hand. Relations. — It is covered by the muscles of the superficial layer and is crossed obliquely by the dorsal interosseous artery. Below it crosses obliquely the tendons of the extensores carpi radiales and the radial artery. digitorum Variations. — It may be par- tially or wholly fused with the e.x- tensor brevis pollicis. Occasionally it possesses two tendons, one of which may be inserted into the dor- sal carpal ligament, the abductor brevis pollicis, or the trapezium. Extensor Brevis Polli- cis (Fig. 580). Attachments. — The short lowing f , , , extensor of the thumb ( m. exten- sor pollicis brevis), also termed the extensor prinii internodii pollieis, hes along the medial border of the extensor ossis metacarpi polHcis. It arises from the interosseous membrane and the pos- terior surface of the radius, partly under cover of the extensor longus pollicis, and its tendon, after passing with that of the abductor through the first compartment of the posterior annular ligament, is inserted into the base of the first phalanx of the thumb. Nerve-Supply. — -By the posterior interosseous branch of the musculo-spiral nerve from the sixth, seventh, and eighth cervical nerves. Action. ^To abduct the thumb and extend its first phalanx. PRACTICAL CONSIDERATIONS: THE FOREARM. 603 Relations.— The relations of the muscle are essentially the same as those of the extensor ossis metacarpi poUicis. Variations.— The extensor brevis and the metacarpal extensor of the thumb are differen- tiations of a common muscle and show indications of this in their partial or complete fusion The tendon of the extensor brevis is sometimes continued onward to the terminal phalanx of the thumb or may send a slip to the base of the second metacarpal. 4. Extensor Longus Pollicis (Fig. 580). Attachments. — The long extensor of the thumb (m. extensor pollicis longus), also known as the extensor secundi internodii pollicis, is an elongated fusiform mus- cle lying along the medial border of the extensor brevis pollicis, which it partly covers. It arises from the interosseous membrane and posterior surface of the ulna ; its tendon passes downward in the third compartment beneath the posterior annular ligament and, crossing over the tendons of the extensores carpi radiales, is inserted into the base of the terminal phalanx of the thumb. Nerve-Supply. — By the posterior interosseous branch of the musculo-spiral nerve from the sixth, seventh, and eighth cervical nerves. Action. — To extend the terminal phalanx of the thumb and, continuing its action, to extend and at the same time slighdy adduct the thumb. 5. Extensor Indicis (Fig. 580). Attachments. — The extensor of the index-finger (m. extensor indicis proprius) lies along the medial border of the extensor longus pollicis. It arises from the in- terosseous membrane and the dorsal surface of the ulna. Its tendon passes, along with the tendons of the extensor communis digitorum, through the fourth compart- ment beneath the posterior annular ligament, and eventually is inserted with the tendon of the common extensor which passes to the index-finger. Nerve-Supply. — By the posterior interosseous branch of the musculo-spiral nerve from the seventh and eighth cervical nerves. Action. — To e.xtend the inde.x-iinger. Variations. — The e.xtensor indicis may be wanting, or its tendon may send slips to the third and fourth digits. Occasionally a muscle arises from the ulna, below the origin of the e.x- tensor indicis, and passes to the third or fourth finger, forming what has been termed the extensor digiti niedii (vet annularis) proprius. This muscle represents an additional portion of the deep extensor layer which normally disappears. PRACTICAL CONSIDERATIONS : THE FOREARM, The fascia descending from the arm to the forearm should be studied anteriorly with relation to the expansion known as the bicipital aponeurosis (Fig. 570), — one of the " two inferior tendons of the biceps" of the older anatomists, — which becomes continuous with the deep fascia of the forearm, and thus, through the origin from its under surface of fibres of many of the superficial muscles of that region, associates their action with that of the biceps itself. Partly for this reason injuries and diseases affecting the bicipital region are sometimes associated with a certain w'eakness of grasp and feebleness of wrist flexion. The facts that only this aponeurotic expansion separates the median basilic vein from the brachial artery, and that in persons of poor muscular development it is often so thin as scarcely to constitute a recognizable layer, were of practical importance when phlebotomy of the median basilic was fre- quent. Arterio-venous aneurism from accidental puncture of the artery was then quite common. Posteriorly the outer aponeurotic expansion of the triceps, running over the anconeus to become continuous with thel deep fascia of the forearm, is of im.portance in its relation to the power of extension of the forearm after excision of the elbow (page 308). _ The fascia of the forearm, besides giving origin to many fibres of the subjacent muscles, as has been noted above, envelops the forearm completely, being continu- 6o4 HUMAN ANATOMY. Palmaris longi Flexor carpi radial Pronator radii teres Radial artery Radial neni longus pollicis Median nerve irtery Flexor s ous at the wrist with the anterior and posterior annular ligaments. The septa which run in from it to be attached to the sides of the ulna and radius di\ide the forearm, with the aid of the interosseous membrane, into two musculo-aponeurotic spaces, an antero-e.xternal and a posterior (Fig. 583). The former contains numerous muscles and the main vessels and nerves, the latter is almost entirely muscular. The interpenetration of these main septa and of the intermuscular fascia by nervo-vascular structures renders them of slight importance in limiting the spread of infectious disease or of collections of blood or pus. But in the not infrequent cases of incised wounds severing the muscles and tendons of this region it may systematize the search for and reunion of the divided structures if the somewhat artificial topog- raphy, as described by Tillaux, is borne in mind. The antero-external compart- ment is thus regarded as including four spaces. i. That between the skin and the first muscular laver, — the palmaris, fle.xor carpi ulnaris, pronator radii teres, etc., — and containing the internal cutaneous and musculo-cutaneous nerves, the perforating branches of the radial and ulnar nerves, the superficial veins, and sometimes the ulnar artery when there is a high bifurcation of the brachial. 2. That between the first muscular layer and the fle.xor sublimis. with the brachio-radialis and short supinator externally. This contains Fig. 5S3. the radial ner\e, artery, and veins. 3. That be- tween the flexor sublimis and the flexor profundus and flexor longus pollicis. This contains the median ner\e and the ulnar nerve and vessels. 4. That be- tween the last-named mus- cles and the interosseous membrane, containing the anterior interosseous ves- sels and the interosseous ner\-e. In the posterior com- partment are to be found, in addition to the exten- sors and the anconeus, only the posterior inter- osseous vessels and nerve (Fig- 5^3)- Fractures of the neck of the radius (between the head and the tuberosity") are ver}- rare, as it is covered and protected from direct violence bv the long and short supinators and the long and short radial extensors. Angular displacement forward is thought to be caused by the action of the biceps on the upper end of the lower fragment. The upper frag- ment is rotated outward by the supinator brevis. Fracture of the radius below its tubercle and above the insertion of the pronator radii teres ( a little above the middle of the outer side of the bone ) is followed by supination and flexion of the upper frag- ment by tl>e biceps and supinator bre\-is. The lower fragment is pronated and drawn towards the ulna by the pronators. It is well to treat cases of this fracture with the forearm in moderate supination, so as to approximate the fragments and preserve the axis of the bone and the future usefulness of the supinators. In fracture of the radius below the insertion of the pronator radii teres the upper fragment is flexed by the biceps, so that its lower end can sometimes be seen and felt on the front of the forearm just above the middle, and is sometimes pronated by the pronator radii teres ; the lower fragment is drawn towards the ulna by the pronator quadratus, aided bv the action of the brachio-radialis on the styloid process (Fig. 584). In the usual position in which such fractures are treated, the flexion of the elbow Extensor carpi rad brev. Supinator' Extensor Post, inteross jiid nerve Interosseous membrane Extensor ossis nieta^ Extensor carpi arpi pollicis Extensor longus pollicis of right forearm. PRACTICAL CONSIDERATIONS : THE FOREARM. 605 Fig and the mid-position between pronation and supination sufficiently relax the biceps and the pronator radii teres. The weight of the hand in adduction overcomes the pull of the brachio-radialis and pronator quadratus. Fracture of both bones, from either direct or indirect violence, usually takes place below the middle of the fore- arm, as there the muscular masses which protect the upper half of the radius from direct violence have largely been replaced by tendons, the ulna is slender and weak, and the opposing forces rep- resented by the biceps and brachialis anticus above and the weight or force applied through the hand e.xpend themselves. Thus Malgaigne (quoted by Agnew) reports a case in which both bones were broken by muscular action alone while the patient was carrying weight in the form of a shovelful of dirt. When the resulting deform- ity is due chiefly to the con- traction of muscles, it is apt to consist in flexion of both upper fragments by the bi- ceps and brachialis anticus, supination of the upper frag- ment of the radius by the biceps and supinator brevis, and approximation of the two lower fragments by the pronator quadratus. Much overlapping and shortening are usually prevented by the untorn fibres of the interosseous membrane. During the period of repair the mid-position — between pronation and supination — preserves the parallelism of the two bones, maintains the interosseous space at almost its greatest Fig. 586. tion of fracture c the two pronato Dissection of fracture of ole- cranon process of left ulna ; joint opened from behind. E^t carpi radlahs long Lower fragment Ext carpi radialls brev. / / Brachio-radialis / / / / Ext longus poinds width, relaxes (in conjunction with the fle.xion of the elbow) the muscles involved so far as is possible, and by the weight of the hand dropping to the ulnar side over- comes the resist- ance of others, espe- cially of the brachio- radialis. The large pro- portion of the re- turn current of blood that is carried by the superficial veins of the forearm makes it especially impor- tant that the splints used should be so broad that the bandage does not unduly com- Radlal arterj ^ — .. r tendons Lower end of upper fragment Ext. brevis and ext. ossis met. poll., cut and turned forward Dissection of Colles's fracture of radius, showing relation of tendons and radial artery. 6o6 HUMAN ANATOMY. press the soft tissues ; while the ease with which both veins and arteries may be obstructed at the bend of the elbow should lead to careful avoidance of pressure in that region from the upper end of the palmar splint. The preservation of the interosseous space is favored by the omission of -the primary roller bandage and by the avoidance of direct pressure upon the soft parts by the bandage used to retain the splints. THE MUSCLES OF THE HAND. The Deep Fascia of the Hand. — The deep fascia of the palmar surface of the hand is usually regarded as being represented by the palmar aponeurosis, a firm sheet of connective tissue which occupies the palm of the hand and lies imme- FiG. 5S7. Thenar with lati palmar fascia Hypothenar Palmar fascia, central portion Palmar fascia, lateral portic Superficial transverse ligament Digital arteries' Superficial dissection of hand, showing palmar fascia. diately beneath the skin. This structure represents, however, the superficial layer of a thick aponeurosis which occurs in the lower vertebrates, receiving the insertion of the antibrachial flexors and giving origin to the digital flexors. From the proxi- mal portion of this aponeurosis there is formed, however, the anterior annular liga- ment, and this may be considered as a portion of the palmar aponeurosis. The latter (Fig. 587), often called the pa/inar fascia, is a fan-shaped sheet whose apex is directed proximally, receiving the insertion of the palmaris longus and being to a certain extent continuous with the anterior annular ligament. It reaches THE MUSCLES OF THE HAND. 607 its greatest breadth over the distal portions of the metacarpals, and is continued onward as four more or less distinct bands, which are inserted into the integument at the bases of the second, third, fourth, and fifth fingers. A little below the lower edge of the aponeurosis transverse bands of fascia (fasciculi transversi) stretch across between the same fingers, lying immediately beneath the skin and being connected to a greater or less extent with one another. These bands constitute the superficial transverse metacarpal liga7nent beneath the webs of the fingers. The anterior annular ligament (ligamentum carpi transversum ) (Fig. 578) is a strong band which stretches across from the trapezium and scaphoid bones of the carpus on the radial side to the pisiform and unciform bones on the ulnar side, forming a bridge across the groove on the anterior surface of the carpus which trans- mits the tendons of the long flexors and of the flexor carpi radialis and the median nerve. The canal so formed is divided by a partition into a small radial compart- ment through which the fle.xor carpi radialis passes, and a large ulnar one which gives passage to the other structures mentioned. The tendons are enclosed within synovial sacs which e.xtend downward to about the middle of the palm and upward to a short distance above the upper edge of the ligament. The sac which surrounds the flexor longus pollicis is usually separate from that which surrounds the remaining tendons of the ulnar compartment ; occasionally the portion surrounding the tendons of the index-finger is also -separate. Towards either side of the palmar surface of the hand the palmar fascia forms a thin covering for thenar and hypothenar eminences formed by the superficial muscles of the thumb and the little finger respectively. Upon the dorsal surface the fascia is thin, and is continued downward from the lower border of the posterior annular ligament over the extensor tendons to the fingers, where it unites with the aponeu- roses of the tendons. (a) THE PRE-AXIAL MUSCLES. The pre-axial muscles of the hand are to be regarded, from the comparative stand-point, as being arranged in five layers. Although these layers become con- fused to a certain extent in the human hand, it will, nevertheless, aid in the proper understanding of their relations to group them according to the primary layers from which they are derived. {aa) The Muscles of the First Layer. 1. Palmaris brevis. 4. Fle.xor brevis pollicis. 2. Abductor pollicis. 5. Abductor minimi digiti. 3. Opponens pollicis. 6. Opponens minimi digiti. 7. Flexor brevis minimi digiti. The most superficial layer of the palmar muscles in the lower vertebrates takes its origin from the palmar aponeurosis. The greater portion of the layer, as has already been pointed out, becomes converted in the mammalia into the palmar por- tions of the tendons of the flexor sublimis digitorum, and it is only towards either margin of the hand that it persists as muscles, which show indications of their primary relations in their origin from the palmar aponeurosis or the anterior annular ligament. I.' Palmaris Brevis (Fig. 576). Attachments. — The palmaris brevis is a thin quadrangular sheet which lies immediately beneath the skin of the hypothenar eminence. It arises from the proximal portion of the ulnar border of the palmar aponeurosis and is itiserted into the skin of the ulnar border of the hand. Nerve-Supply. — By the superficial division of the ulnar nerve from the first thoracic nerve. Action. — To wrinkle the skin upon the ulnar border of the hand, deepening the hollow of the hand. Variations — The muscle may be greatly reduced in size and is occasionally wanting. 6o8 HUMAN ANATOMY. 2. Abductor Pollicis (Fig. 577). Attachments. — The abductor of the thumb (m. abductor pollieis brevis) is the most superhcial muscle of the thenar eminence. It arises from the anterior annular ligament and from the scaphoid bone or the trapezium and passes distally to be in- serted along with the flexor brevis pollicis into the radial side of the base ot the first phalanx of the thumb and into the sheath of the tendon of the extensor longus pollicis. Nerve-Supply. — By the median nerve from the sixth and seventh cervical nerves. Action. — To flex and abduct the thumb. Variations — The portion of the muscle arising frona the carpus is sometimes sejiarate from that taking origin from the transverse carpal ligament. Slips are occasionally sent to the abduc- tor from the extensores carpi radiales, the e,xtensor ossis metacarpi pollicis, the opponens pol- licis, and the fie.xor brevis pollicis. 3. Opponens Pollicis (Figs. 578, 588). Attachments. — -The opponens pollicis is almost completely covered by the abductor pollicis. It arises from the anterior annular ligament and from the trape- zium, and is inserted into the whole length of the radial border of the first metacarpal. Nerve-Supply. — By the median nerve from the sixth and se\enth cervical nerves. Action. — To fle.x and adduct the thumb, opposing it to the other fingers. 4. Flexor Brevis Pollicis (Figs. 578, 588). Attachments. — The flexor brevis pollicis lies along the lower (ulnar) border of the opponens pollicis. It arises from the lower border of the anterior annular ligament and is inserted, along with the abductor pollicis, into the radial side of the base of the first phalanx of the thumb. The muscle above described is usually regarded by English anatomists as representing the outer or radial head of the flexor brevis, a second inner or ulnar head being included as part of that muscle. Concerning the inner head three views are held : (a) no inner head is recognized, the small slip arising from the ulnar side of the base of the first metacarpal bone and passing downward to be inserted with the adductor pollicis into the base of the first phalanx, which by many English anatomists is regarded as a small inner head of the flexor brevis, being described as an additional (first) palmar interosseus (page 612) ; [b) the small slip ju.st noted-is the inner or ulnar head of the flexor brevis ; (r) the small slip and all the fibres described as forming the adductor obliquus (page 610) are regarded as the inner head of the flexor brevis. The first view, adopted by German anatomists, is here followed. Nerve-Supply. -By the median nerve from the sixth and seventh cervical nerves. Action. — To flex the first phalanx of the thumb. Variations. — The muscle is sometimes intimately connected with the abductor pollicis and opponens pollicis. 5. Abductor Minimi Digiti (Fig. 577). Attachments. — The abductor of the little finger (m. abductor digiti quinti) occupies the ulnar border of the hand. It arises from the anterior annular ligament and from the pisiform bone and is inserted into the ulnar side of the base of the first phalanx of the little finger. Nerve-Supply.— By the deep division of the ulnar nerve from the eighth cer- vical and first thf)racic nerves. Action. — To abduct the fifth finger. 6. Opponens Minimi Digiti (Fig. 578). Attachments. — This muscle (m. opponens diyiti quinti ) is almost completely covered by the abductor and short flexor of the little finger. It arises from the anterior annular ligament and the uncinate process of the unciform bone and is in- serted into the whole of the ulnar border of the fifth metacarpal bone. THE MUSCLES OF THE HAND. 609 Nerve-Supply.— By the deep division of the ulnar nerve from the eighth cer- vical and first thoracic nerves. Action.— To flex and at the same time adduct the fifth metacarpal. 7. Flexor Brevis Minimi Digit: (Figs. 577, 578). Attachments.— The short flexor of the littie finger (m. flexor brevis digiti quinti) lies along the lateral (radial) border of the abductor minimi digiti. It arises Radius- Anterior interosseous artery _ Pronator quadratus Flexor brevis pollicis First palmar interosseus Flexor lonffus pollicis tendon L.^^ carpi ulnaris tendon Cut edge of anterior annular ligament Pisiform bone Adductor pollicis, oblique porti( Third palmar interosseus Fourth palmar interosseus Fourth dorsal interosseus Deep dissection of wrist and hand, showing pronator quadratus and short muscles of thumb. from the anterior annular ligament and the uncinate process of the uncinate bone and is inserted into the ulnar side of the base of the first phalanx of the little finger. Nerve-Supply. — By the deep division of the ulnar nerve from the eighth cer- vical and first thoracic nerves. Action. — To flex and slightly abduct the first phalanx of the little finger. Variations. — The flexor brevis and opponens minimi digiti are often united by muscle- bundles and may even be completely fused. 6io HUMAN ANATOMY. {b6) The Muscles of the Second Layer. In the lower vertebrates the second layer also arises from the palmar aponeu- rosis, but from its deeper layers. These, as has been stated (page 597 1, differentiate into the palmar portions of the tendons of the fie.xor profundus digitorum, and in the mammalia the muscles retain their primary origin and arise from those tendons forming the lumbrical muscles. I. LuMBRic.\LES (Fig. 578). Attachments. — The lumbricals are four slender, band-like muscles, situated in the palm of the hand. Counting from the radial side of the hand, the /irsi and secofid lumbricals arise from the radial side of the fie.xor profundus tendons to the inde.x and middle fingers respectively, while the f/iirc/ one arises from the adjacent sides of the tendons to the middle and ring fingers, and the fourth from those of the tendons to the ring and litde fingers. The muscles pass distally into slender tendons which are continued to the radial side of the first phalanges of the second, third, fourth, and fifth fingers, and are inserted into the membranous expansions of the tendons of the extensor communis digitorum to those fingers. Nerve-Supply. — The first and second lumbi-icals are supplied by the median nerve from the sixth and seventh cervical nerves ; the third and fourth by the deep division of the ulnar nerve from the eighth cerxical and first thoracic nerves. Action. — To fle.x the first phalanges of the second, third, fourth, and fifth fingers. At the same time, by their traction upon the extensor tendons, they will tend to keep the second and third phalanges extended. Variations. — \'anations in the arrangement of the lumbricals, and especially of the third and fourth, are not uncommon. The tendon of each of these muscles may bifurcate and be in- serted into the adjacent sides of the third and fourth or fourth and fifth fingers, and more rarely the sole insertions may be into the ulnar sides of the first phalanges of the middle and ring fingers. The third lumbrical is frequently supplied wholly or in part from the median nerve. (ri-) The Muscle of the Third Layer. In the lower vertebrates the third layer consists of muscles which arise from the carpal and metacarpal bones and pass to each of the digits. In the mammalia they become greatly reduced in number, frequently persisting, howe^■er, in connection with the thumb, inde.x, and little fingers, but in man they are represented onlv by an adductor pollicis. I. -Adductor Pollicis (Figs. 578, 588). Attachments. — The adductor pollicis is a flat triangular muscle which rests ypon the metacarpal bones and the interosseous muscles. It may be regarded as consisting of two portions. The poit/o obliqna (often described as a distinct muscle, the adductor obliquus pollicis) arises from the trapezium, trapezoid, and os magnum and from the bases of the second and third metacarpals. Its fibres are directed dis- tally and radially, and are inserted bv a tendon, in which a sesamoid bone is usually developed, into the ulnar side of the base of the first phalan.x of the thumb. It also sends off a slip which passes beneath the tendon of the flexor longus pollicis to be inserted into the radial side of the base of the first phalanx of the thumb along with the fle.xor brevis pollicis. The portio transversa ( often described as the adductor transzrrsus po/licis) arises from the lower two-thirds of the \-olar surface of the third metacarpal, and its fibres pass almost directly radially to be inserted into the ulnar side of the base of the first phalanx of the thumb. Nerve-Supply. — By the deep division of the ulnar nerve from the eighth cervical and first thoracic nerves. Action. — To adduct the thumb. Relations. — -The adductor pollicis is covered by the tendons of the flexor profundus digitorum for the second and. third fingers and by the first and second lumbricals. It conceals the interosseous muscles of the two radial intermetacarpal intervals and also the radial artery and the arteria princeps pollicis. The deep palmar arch passes between the two portions of the muscle, near their origins. THE MUSCLES OF THE HAND. 6ii Pisiform bone {dd) The Muscles of the Fourth and Fifth Layers. I. Interossei volares. * 2. Interossei dorsales. In the lower vertebrates the musculature of the fourth palmar layer consists of a pair of muscles for each digit, arising from the carpal and metacarpal bones and inserting into either side of the base of the first phalanx. The fifth layer lies dorsal to these, and consists of four muscular bands, which extend slightly obliquely across the four inter- metacarpal spaces. Fig. 5S9. In the mammalia /' a shifting of the in- sertion of one of the muscles of the pairs belonging to the first and fifth digits takes place, so that they are attached to the radial and ulnar sides re- spectively of the ad- jacent second and fourth digits, uniting with the correspond- ing members of the pairs belonging to those digits. With the compound mus- cles so formed the first and fourth inter- metacarpal muscles unite to form the first and fourth dorsal in- terossei, these two muscles being com- posed, accordingly, by the fusion of three primary muscles. The second and third intermetacarpal muscles unitewith the radial and ulnar mem- bers respectively of the pair belonging to the third digit, and form with these the second and third dor- sal interossei. The remaining members of the pairs belonging to the first, second, fourth, ' and fifth digits persist as independent muscles, forming what are term.ed the volar interossei, whose arrange- ment is consequently complementary to that of the dorsal interossei. The intermetacarpal muscles occupy the most dorsal position of all the palmar muscles, and it is probably owing to their participation in the formation of the dorsal interossei that these possess an almost dorsal position in the hand. They are clearly, however, of palmar origin and are supplied by pre-axial nerves. Fourth dorsal iruerosseus > Tliird dorsal interosseus Deep dissection of hand, show 6l2 HUMAN ANATOMY. I. Interossei Volares (Fig. 589). Attachments. — The volar or palmar interossei are four slender muscles situated in the intervals between the metacarpal bones and resting upon the in- terossei dorsales. TheyiVrf and second muscles, counting from the radial side, arise from the ulnar side of the bases of the first and second metacarpals, and are ifiserted into the ulnar side of the base of the first phalan.x and, in the case of the second muscle, also into the membranous expansion of the long extensor tendon of the Fig. 590. xtensor carpi radialis longior tendon Extensor carpi radialis brevior Second dorsal interosseus Third dorsal interosseus Fouith dorsal interossexis Extensor communis digitorum tendons ^. N First \ ... dorsal,,.- \ ,, .\ terosseus \, , ' Dissection of back of hand, showing d' terossei and insertion of extensor tendons. corresponding digit. The third ■3x\A fourth muscles arise from the radial side of the fourth and fifth metacarpals, and are inserted similarly to the second muscle, but into the radial sides of the fourth and fifth digits. Only three palmar interossei are usually described by English anatomists, the muscle in- cluded in the series by the German school as the first interosseus (;«. interosseus primus votaris) being regarded as the small ulnar head of the flexor brevis poUicis (page 608). The inclusion of this muscle in the series of palmar interossei is warranted by its morphological relations. Nerve-Supply. — By the deep division of the ulnar nerve from the eighth cervical and first thoracic nerves. Action. — To draw the first, second, fourth, and fifth digits towards the middle finger and to flex the first phalanx of the same digits. PRACTICAL CONSIDERATIONS : WRIST AND HAND. 613 Variations. — The first volar interosseus is the most slender of the series and is covered by the oblique portion of the adductor pollicis, with which it may be practically incorporated. Occasionally it is so reduced in size as to appear to be wanting. 2. Interossei Dorsales (Fig. 590). Attachments. — The dorsal interossei are also four in number and lie in the intervals between the metacarpal bones, dorsal to the volar interossei. Each is a bipinnate muscle arising from the adjacent surfaces of the metacarpals which bound the interspace in which the muscle lies. The Jirsf and secotid muscles, counting from the radial side, are inserted into the radial side of the base of the first phalanx and into the membranous expansion of the extensor tendons of the second and third fingers, while the third and fourth are inserted similarly into the ulnar sides of the third and fourth fingers. Nerve-Supply. — By the deep division of the ulnar nerve from the eighth cervical and first thoracic nerves. Action. — The first and fourth muscles draw the second and fourth fingers away from the third, while the second and third draw the third finger radially or ulnarly, as the case may be. All the muscles flex the first phalanx of the digits to which they are attached. Variations. — Occasionally the second dorsal interosseus is inserted into the base of the first phalanx of the index-finger, upon its ulnar side. {b) THE POST-AXIAL MUSCLE. Normally no post-axial muscles exist in the human hand. Occasionally, however, an ex- tensor brevis digitorutii manus is more or less perfectly developed. It arises from the dorsum of the carpus, or sometimes from the lower end of the radius and ulna, and passes distally into a varj'ing number of tendons. Most frequently the muscle is small and gives rise to but a single tendon, which joins with the tendon of the extensor digitorum communis of either the second or third digit. Sometimes two tendons occur, passing to the second and third digits, and more rarely three have been observed, passing to the second, third, and fourth fingers. In a single case a fourth tendon was observed which terminated upon the dorsal surface of the fifth metacarpal. PRACTICAL CONSIDERATIONS. The Wrist and Hand. — The skin of the wrist and of the back of the hand is thin and freely movable and contains numerous hair-follicles and sebaceous glands. These structures are absent in the palm and on the palmar and lateral surfaces of the fingers, as well as on the dorsal surface of the terminal phalanges. Sudoriparous glands are, on the contrary, relatively more numerous in the palms of the hands than on any other part of the body surface. These anatomical conditions and the existence of the subungual and periungual spaces and irregularities render the sterilization of the hands for surgical purposes very difficult. The absence of hair-follicles and of sebaceous glands explains the freedom of the palm from the superficial furuncular infections that are so common on the dorsum. In the palm the subcutaneous connective tissue, like that in the plantar region and in the scalp between the skin and aponeurosis, is very dense. This similarity has already been alluded to (page 491) in relation to the absence of hair-follicles in the two former regions and the frequency of baldness in the latter. On the dorsal surface the subcutaneous tissue is -loose. As a result, in whitlow, in palmar abscess, in hemorrhagic extravasation, in oedema or cellulitis, the swelling is apt to be much more marked on the dorsum and may be misleading as to the real seat of the trouble. Abscesses immediately beneath the palmar fascia will sometimes point in a metacarpal space on the dorsum. The thickness and close adhesion of the skin to the dense fascia beneath', while admirably protecting the vessels and nerves of the palm and enabling it to withstand pressure and friction, greatly increase the pain in cutaneous or subcutaneous infections. On account of this same adhesion, superficial wounds of the palm do not gape, and heal readily if non-infected and kept at rest. 6i4 HUMAN ANATOMY. Ext. carp, ulnaris annular ligament — Extens.-carp. rad. g. et brev. Ext. brevis pollicis Ext. ossis metacarpi pollicis xt. longus pollicis " It must be noted that the front of the hand, and especially the palm, is singu- larly free from surface veins. Indeed, the great bulk of the blood from the hand is returned by the superficial veins on the dorsum of the fingers and hand" (Treves). The annular ligaments at the wrist are of importance in their relation to the tendons and their sheaths. The tendon-sheaths (Fig. 591) which pass through the six compartments in or under the posterior ligament behave as follows. i. That for the short extensors and the extensor of the metacarpal bone of the thumb runs from the joint between the first metacarpal' and the trapezium to a point almost an inch above the styloid process of the radius. 2. That for the long and short radial extensors of the carpus runs Fig. 5QI. from the insertions of those muscles to a point a half inch above the ligament. 3. That for the extensor longus pol- licis runs from the insertion to the upper border of the Ijgament. 4. That for the extensor indicis extends from the upper border of the met- acarpus, and that for the ex- tensor communis from the middle of the metacarpus, both to the upper border of the ligament. 5. That for the extensor minimi digiti runs from the middle of the metacarpus ; and 6, that for the ulnar extensor of the car- pus from the insertion, both to the upper border of the ligament. Infective disease of the dorsum of the wrist and hand is rare as compared with the palmar surface. The dense connective-tissue fibres of the palm run vertically down- ward to the palmar fascia and tendon-sheaths, and thus convey infection directly to the deeper parts. This layer is often described as the su- perficial palmar fascia. The subcutaneous connective-tis- V sue fibres on the dorsum run horizontally, and infective in- "- flammation is therefore more Dissection of dorsum ui hand, .1.,:;,,,, .uuikiaiiy distended sheaths of ^'l^ely to remain Superficial extensor tendons. (Warren). If, howcver, it does penetrate and gains access to the tendon-sheaths, the natural anatomical limitations are those indicated above. Teno-synovitis from strain, from gout, or from rheumatism is especially frequent in these sheaths, on account of their exposure to wet and cold, and also because the muscles connected with them are relatively weak and are less often used than those on the palmar surface of the forearm. They are thus more liable to strain from unaccustomed exertion. Ganglion of the simple (non-tuberculous) variety is also frequent here, probably for the same reasons. PRACTICAL CONSIDERATIONS : WRIST AND HAND. 615 Bursa surrounding ten-, don of flexor longub polHcis One of the most common and most serious of the sequelae of fracture of the lower end of the radius is stiffness of the wrist and fingers from adhesions of these extensor tendons and their sheaths to the bone, to each other, and to the surrounding structures. It is important to remember, as Treves has pointed out, that ' ' the tendons do not lie free within the sac, but are bound to it by folds of synovial membrane in much the same way as the bowel is bound to the abdominal parietes by its mesen- tery (Fig. 492). These folds may be ruptured in severe sprains, when the nutrient vessels for the tendon, which are contained in them, may be torn. Rupture is fol- lowed by effusion into the sac. These folds are almost absent within the digital sheaths, the slight ligamenta ^ longa and brevia, near the insertion of the tendons, being the sole representatives. Sy- novial sacs are lined by endothelium, and have e.xtremely free com- munication with the lymphatic vessels of the part. Hence the free absorption of in- fective matter from such cavities. ' ' The arrangement of the synovial sheaths beneath the anterior annular ligament is of great practical im- portance (Fig. 592). There are two sacs, one for the tendons of the superficial and the deep flexors ; one for the long flexor of the thumb. They extend upward to about two finger-breadths above the annular ligament. Downward, that for the thumb extends to the insertion of the tendon in the terminal phalanx ; the divertic- ula for the index, mid- dle, and ring fingers end about the mid- dle of the metacarpal bones ; that for the lit- tle finger accompanies the tendon of the deep flexor to its insertion in the last phalanx. The synovial sheaths for the digital portions of the flexors for the index, middle, and ring fingers extend upward only to about the necks of the corresponding metacarpal bones. They are thus separated by an interval of from half an inch to an inch from the synovial sac, extending up under the annular ligament to the forearm (Fig. 592). It results from this that infections (felons, wounds, etc. ) of the thumb or little finger are especially apt to extend upward above the wrist and involve the forearm. Compound ga7iglio7i (tuberculous teno-synovitis) frequently affects the common synovial sac of the flexor tendons and not infrequently that of the longus poUicis. Dieital sheaths of long fle: tendons Dissection of pal: g artificially distended sheaths 6i6 HUMAN ANATOMY. The two sacs occasionally communicate with each other. On account of the density of the annular ligament, the distention has a central constriction and expansions in the palm and above the wrist, — " hour-glass shape." These tendons also are often involved in fractures of the lower end of the radius, although, on account of the fact that the extensors are in closer relation to that bone than is the deep flexor, and that the other flexors — excepting the longus poUicis — -are still farther separated from it, limitation of their motion is neither so frequent nor so marked. In the palm of the hand the thenar and hypothenar eminences are covered in by their fasciae, which separate them from the central space of the palm through which the flexor tendons run, and over which is spread the fan-shaped, deep palmar fascia, beginning at the tendon of the palmaris longus above, and spreading out to be divided below into the slips for the fingers (Fig. 587). Transverse fibres unite and strengthen these slips, which send fibres also to the sheaths of the flexor tendons and to the skin. It may be noted here that progressive muscular atrophy usually begins in the hand muscles, affecting first those of the thenar, then those of the hypothenar emi- nence, and next the interossei. When the latter are greatly wasted the hand assumes the appearance of a bird's claw, — the main en griff e (Duchenne). Dupiiytren s contraction affects chiefly the digital prolongations of the palmar fascia, although it extends secondarily to the bundles of fibres uniting the skin and the aponeurosis. It begins usually as a dense thickening of the fascia near the line of the metacarpo-phalangeal articulation. It extends in both directions, the concomitant shortening slowly drawing down first the distal and then the intermediate phalanx. The skin becomes closely adherent to the contracted fascia. The condition is seen oftenest in hands subjected to frequent slight traumatism, as in laborers, or in those of gouty or rheumatic persons past middle age. Beneath the flexor tendons, and above the interossei, the metacarpal bones, and the radial arch, lies another layer of fascia (interosseous) which resists but feebly the passage of pus towards the dorsum of the hand. It is connected with the thenar and hypothenar fascife. Several varieties of palmar abscess have been described (Tillaux) in accord- ance with the original site of the infection, the spread of which will be determined by the above-mentioned anatomical considerations. («) Infection just beneath the thick epidermis causes a superficial pustule or abscess (subepidermic) which, if promptly and freely opened, gives rise to no difficulty. {b) Infection beneath the skin (subdermic) is attended by more pain, and, if neglected, may penetrate the aponeurosis ; but it is separated by that structure from the syno\ial sheaths and cavities ; it may be widelv opened with no reference to the latter or to vessels ; it is accompanied by little or no swelling on the dorsum ; it has no tendency to extend up to the wrist ; movements of the fingers are not very painful, (c) Subdermic infec- tion beginning in the spaces just above the interdigital clefts (i.e., between the digital slips of the palmar fascia) may extend by continuity of connecti\e tissue very rapidly to the dorsum of the hand, which may then appear to be the chief seat of the infection ; the symptoms are relatively mild, as the toxic exudate is not under great pressure. {d) Subaponeurotic infection — true palmar abscess — is excessively painful, extends rapidly to the dorsum by perforating the interosseous fascia, and often to the front of the wrist and forearm by following up the flexor tendons ; move- ments of the fingers are painful ; the dorso-palmar diameter of the hand is vastly increased ; the constitutional symptoms are often marked. Such abscess may also point just above the interdigital webs or near the ulnar or radial borders of the hand. Early incision is imperative and, if made over the line of a metacarpal bone and limited in an upward direction by a transverse line correspond- ing to that of the web of the fully extended thumb (to avoid the digital vessels and palmar arches), may be made freely. Above the wrist the region of safety is just to the ulnar side of the palmaris longus. Onthe fingers the skin resembles in its characteristics that of the hand. On the palmar surface of the first and second phalanges the skin and the subcutaneous fat are connected with the dense fibrous sheath of the flexor tendons by vertical connective- tissue fibres, and at the level of the joints — where the sheaths are lax and thinner — PRACTICAL CONSIDERATIONS : WRIST AND HAND. 617 Tendon of flex, longus poll. Adductor poll., obi. portion Dissection of metacarpo-phalangeal dislocation of thumb. by vessels which penetrate the sheath to supply the tendons. Over the last phalanx the fibro-fatty subcutaneous layer — the ' ' pulp' ' of the finger — lies directly upon the periosteum. Infection of the dorsum of a finger often originates near or about the root of a nail (onychia) and may invoke the matrix of the latter. It is not under much pressure, and is therefore not usually serious, although through the Fig. 593. veins and lymphatics it may e.xceptionally e.xtend rapidly up the arm. Infection of the palmar surface of a finger ( panaritium, paronychia, whitlow, felon) is of two chief varieties : {a) subcutaneous^ in which the symptoms are at first limited to the seat of infection and are superficial, although, as it is a true cellulitis, they may e.x- tend to the dorsum or towards the palm ; and (b) thecal, with more severe pain, greater lim- itation of . flexion, and more rapid extension upward. If the felon involves the distal portion of the finger, the close relation of the ' ' pulp' ' and the periosteum ol the last phalanx makes necrosis of that bone frequent, although its upper part usually escapes because (a) it is an epiphysis ; (/5) the insertion of the tendon of the deep flexor probably keeps up its blood-supply (Treves). The absence of the tendon-sheath over the body and tip of the last phalanx pre- vents the conversion of the subcutaneous into the thecal variety, unless the infection extends upward as far as the base of the phalanx. Elsewhere the thecal \'ariety often results from extension from a subcutaneous focus by the vertical connective-tissue fibres and the vessels already mentioned. The interphaiangeal joints are often affected because it is opposite them that (a) the tendon-sheaths are thinnest and • Fig. 594. {b) the vessels enter. In infection of the tendon-sheaths of the index, middle, and ring fingers the upward extension is arrested, at least for a time, about opposite the necks of the metacarpal bones. If the thumb or little finger is involved, the infection is likely to spread to a higher level (page 615). The so-called ' ' subcuticular' ' felon is a superficial pustule, while the ' ' subperiosteal' ' felon may either result from e.xtension of the foregoing varieties or may be origi- nally an infective osteo-periostitis or osteo-myelitis. In relation to amputation of the finger it may be noted that the insertion of the flexor sublimis tendon into the sides of the second phalanx renders amputation at the metacarpo-phalangeal joint often more satisfactory in its results than one done through the first phalanx or first interphaiangeal joint. Dislocation of the first phalanx of the thumb upon the dorsum of its metacarpal bone requires special mention on account of the difficulty of reduction. It has been Dissection showing position of bones in dislocation of thumb. 6i8 HUMAN ANATOMY. attributed (a) to the gripping of the neck of the metacarpal bone between the flexor brevis pollicis and the oblique portion of the adductor pollicis (these often being considered as the two heads of the flexor brevis pollicis) ; (6) to a similar entanglement of the head and neck in the slit in the capsule ; (c) to the winding of the tendon of the flexor longus pollicis around the neck of the bone ; and (d) to the interposition of the gleno-sesamoid plate. Of these theories the last tivo seem to oi?er the most satisfactory- explanation of the difficulties met with in attempts at replacement. The Surface Landmarks of the Upper Extremity. — The axilla (page 574) is very distinctly bounded anteriorly by the lower border of the pectoralis major, which runs in the line of the tifth rib from the si.xth costal cartilage to the -external bicipital ridge ; posteriorly by the lower edge of the latissiums dorsi and teres major, extend- ing to the bicipital groove. The shape of the axillarj' fossa varies with the position of the arm, becoming deeper when the arm is raised at a right angle to the trunk or when the great pectoral and latissimus are contracted. With the arm still farther elevated, the depth of the space decreases as traction on those muscles approximates the axillary borders and the humeral head enters and partly obliterates the cavity. With the arm close to the thorax, the third rib may be reached by the exploring finger. The concavity of the space is lessened or effaced by glandular tumors, effu- sions of blood, or collections of pus (page 582). In opening an a.xillary abscess it should be remembered that the inner or thoracic wall is the direction of safety so far as the great vessels are concerned. In the region of the shoulder the rounded surface is produced by the thick deltoid muscle spread over the greater tuberosity of the humerus. It is fuller anteri- orly than posteriorly, partly on account of the presence of the lesser tuberosity in the former position, but chiefly because the hinder portion of the muscle is thinner than the fore part and because of its close attachment to the infraspinatus fascia and muscle. The greatest width of the shoulders does not correspond to the points at which the deltoid muscles overlap the head of the humerus, but is at the level of the lower border of the anterior axillary fold, — i.e.. on the level of the point at which the various bundles of deltoid fibres are gathered together to pass to their insertion (Thomson). The bony points in this region have been described (pages 270, 279, 280). The anterior border of the deltoid presents a rounded eminence bounded internally above by the infracla\icular fossa (z'lde infra) and below by the closely applied outer margin of the pectoralis major. In the shallow groove between these two muscles the cephalic vein and a branch of the acromio-thoracic artery are to be found. Just external to the groove under the inner fibres of the dtltoid is the cora- coid process (page 255). The infraclavicular fossa is the triangular inter\'al bounded by the outer fibres of the pectoralis major internally, the inner fibres of the deltoid externally, and the clavicle abo\'e. The surface depression known by this name may be much larger than this intermuscular interval, and may almost correspond in extent to the roof of the superficial infraclavicular triangle (page 581). It is not very marked in muscular subjects. It is effaced — owing to tension of fascia and muscles — in sub- coracoid lu.xation of the humerus, or in fracture of the clavicle with marked displace- ment of the fragments. It mav be converted into a rounded elevation by glandular growths extending upward from the a.xilla, or by the head of the humerus in intra- coracoid (infraclavicular) luxation. At the bottom of this fossa, just within the cora- coid process, — i.e.. not far from the middle of the clavicle, — the first portion of the a.xillary artery may be compressed against the second rib by pressure directed back- ward and a little inward, the patient being supine. The posterior border of the deltoid above is tendinous, is closely attached to the infraspinatus muscle beneath it, and is scarcely discernible. Below it is thicker and presents a well-marked rounded eminence which inclines from behind forward to meet the anterior border at the middle of the outer side of the arm, where a distinct depression indicates the insertion of the deltoid (Fig. 595). This depression is a valu- able practical landmark for the reasons that : ( i ) It corresponds to the middle of the shaft of the humerus, where the two curves of the bone unite and where the cylin- drical joins the prismatic part of the shaft, which is there smallest, hardest, and least elastic (page 272), and hence is most frequently broken. ( 2) It indicates the region PRACTICAL CONSIDERATIONS : SURFACE LANDMARKS. 619 of insertion of the deltoid and coraco-brachialis, and embraces part of the origin of the brachialis anticus and internal head of the triceps, and is therefore, and on account of the intimate attachment of the periosteum (page 272), a not uncommon seat of exostoses. (3) The region is — by reason of the close relation of these mus- cles to the bone — a frequent seat of ununited fracture (page 273). (4) The nutrient artery enters the bone and the superior profunda artery and musculo-spiral nerve wind around its posterior surface at that le\'el, at which also the lesser internal cuta- neous nerve and the basilic vein penetrate the deep fascia, the median nerve crosses the brachial artery, and the ulnar nerve leaves it. On the outer surface of the arm below the insertion of the deltoid can be seen the shallow furrow (Fig. 596) 'between the outer head of the triceps and the brachio- radialis which indicates the position of the external intermuscular septum and of the external supracondyloid ridge (page 273) . On the posterior surface of the arm the three heads of the triceps can be seen when the forearm is strongly extended (Fig. 596). The outer head makes a distinct prominence just beneath the posterior border of the deltoid ; the inner head is less distinct ; the long head comes into view where it descends from between the two teres muscles, and lower in the arm — where it has become tendinous — is indi- cated by a broad, shallow depression ending at the olecranon. The long and outer heads cover the musculo-spiral nerve and superior profunda artery from just beneath the posterior axillary fold to the point where they perforate the external septum. On the anterior and inner surfaces of the arm the rounded swell of the biceps and the external and internal bicipital furrows are the most important landmarks. Fig. 595, Tendon of pal longus Transverse furrows Antero-median surface of right Pectoralis major odelling on living subject. The elevation of the biceps shades off superiorly into the narrower and less distinct prominence of the coraco-brachialis where it comes into view below and beneath the anterior axillary fold. Inferiorly it narrows externally and merges into the biceps tendon, easily seen passing into the forearm in the deep interval between the rounded supinator and extensor mass on the radial side and the pronator and flexor mass on the ulnar side (Fig. 595). Internally the broader flat slip of bicipital fascia — the inner tendon — may be seen with its sharp upper edge when the forearm is semi- flexed and the biceps is in strong action. The outer bicipital furrow indicates the posi- tion of the subcutaneous cephalic vein. The inner and deeper furrow marks the line of the basilic vein (subcutaneous in its lower half, then subfascial), of the median nerve and the brachial vessels, and in its upper half of the ulnar nerve. To the outer side of the outer furrow from above downward lie the deltoid, the outer head of the triceps, the outer portion of the brachialis anticus and the brachio-radialis, and the common extensor mass (Fig. 596). To the inner side of the inner furrow are seen the coraco-brachialis, the long head and then the inner head of the triceps, the brachialis anticus, and the pronato-flexor mass. At the bend of the elbow anteriorly the subcutaneous veins are often visible. Their arrangement is sufficiently described and figured elsewhere (page 892, Fig. 764). The bicipital fascia passes between the median basilic vein and brachial artery, and, by springing from the inner edge of the biceps tendon, makes that edge 620 HUMAN ANATOMY. less distinct to both sight and touch than the outer edge. Just within the inner edge is the brachial artery and farther in the median nerve. The fold of the elbow is a transverse crease in the skin, seen in fle,\ion, convex downward, and running from the tip of one condyle to the tip of the other. It lies above the line of the elbow-joint. In dislocation of the radius and ulna backward the lower end of the humerus is below this crease ; in fracture of the humerus above the condyles the lower end of the upper fragment is either on a line with or above the crease. This relation will not be demonstrable in the presence of much swelling, as this fold is then obliterated. On the front of the forearm, below the apex of the triangular space resulting from the convergence of the two muscular masses descending from the condylar regions, there are no salient surface landmarks, and none of great practical importance until the wrist is reached. Many of those of that region and of the hand have been de- scribed (pages 228, 229, 230, 320). It should, however, be noted that, instead of being flattened from before backward and widest from side to side as when in the supine position, the forearm when the hand is pronated becomes rounded and its antero-posterior slightly exceeds its lateral thickness (Thomson). This is due to the fact that the tendons of the supinator and extensor masses are held in grooves in the lower end of the radius by the posterior annular ligament, and are thus car- ried towards the ulna when the radius mo\es in that direction. Fig. 596. Outer head of triceps Erachialis amicus External bicipital furrow Brachio-radiali! Common extensor Extensor longus pollicis Triceps Ulnar styloid process Internal condyle Posterior surface of arm shown in preceding figure. Of the two transverse furrows on the flexor surface of the wrist the lower is the more marked. It is almost three-quarters of an inch below the summit of the upward curve of the wrist-joint, is on the line of the intercarpal joint and of the upper border of the anterior annular ligament, and is about a half-inch above the carpo-metacarpal joint. At the wrist the palmaris tendon — when present — is made prominent by extending the digits, slightly flexing the wrist, and closely approximating the thenar and hypothenar eminences. To its radial side from within outward lie the median nerve, the tendon of the flexor carpi radialis, and the radial artery. To its ulnar side lie first the rounded elevation made by the flexor sublimis tendons, then the ulnar artery, and then the fle.xor carpi ulnaris tendon, made easily palpable, although not very prominent, by strong flexion of the wrist and little finger. On the postero-lateral aspect of the forearm may be seen : 1. The elevation of the anconeus, triangular in shape, to the radial side of the posterior subcutaneous surface of the olecranon and separated from the common extensor mass by a well-defined depression. This muscle and the e.xpansion of the triceps tendon that covers it are of great value in the movement of extension of the forearm after excision of the elbow. 2. The curved border of the ulna (subcutaneous in supination), at the bottom of the ulnar furrow, between the flexor carpi ulnaris and the common extensor group, is easily accessible for examination through its whole length (page 289). 3. The very important depression just below the external condyle and exter- nal to the olecranon has been described (page 296). PRACTICAL CONSIDERATIONS : SURFACE LANDMARKS. 621 4. The oblique elevation beginning at the lower third of the forearm in the interval left by the divergence of the supinator and the common extensor muscles, and running downward and outward, to be lost on the posterior surface of the thumb, represents the extensors of the thumb crossing over the tendons of the extensores carpi radialis longior and brevior to their points of insertion (Fig. 582). 5. The bony points to be seen and felt at the elbow and wrist have been de- scribed in their practical relations in connection with the bones and joints (pages 287, 296, 308, 320, 330J. The tendon most easily identified on the dorsum of the wrist is that of the extensor longus poUicis when the thumb is strongly extended and abducted. It is the posterior or inner boundary of the hollow at the base of the thumb (vide infra), and its groo\'e in the lower end of the radius is about the middle of the posterior surface and just to the ulnar side of the prominent middle thecal tubercle, — a useful landmark (page 296). The tendon, just before it reaches the radius, corresponds approximately to the scapho-semilunar joint. The surface markings of the palm of the hand are often valuable landmarks. The most important are : (i) The triangle called the " hollow of the hand," the "cup of the palm," etc., the base of which corresponds to the three elevations oppo- site the interdigital clefts, ^formed by protrusion of fat between the flexor tendons and the digital slips of the palmar fascia and by the distal extremities of the lumbri- cales, — and seen best when the metacarpo-phalangeal joints are extended and the interphalangeal joints are flexed. The sides of the triangle are formed by the thenar and hypothenar eminences. Over this palmar hollow the intimate connection of the skin and fascia is of practical importance (page 613). (2) The chief cutaneous creases (Fig. 597) are four in number : (a) from just above the apex of the palmar triangle to the radial side of the hand above the base of the index-finger ; {b) from the lower end of a to a point a little above the middle of the ulnar border of the palm, Avhich it does not quite reach ; {c) from about the junction of the lower fourth with the upper three-fourths of the ulnar border of the palm to a point a little above the cleft between the index and middle fingers ; (fi?) from b to c, often extending upward towards the wrist and downward towards the base of the middle finger. a and d are longitudinal, the former being caused by adduction of the first meta- carpal, the latter by adduction of the fifth metacarpal bone, both movements being towards the mid-line of the hand ; b and c are transverse, and are produced chiefly by flexion {b) of the first and second {c) of the three inner metacarpo-phalangeal joints. a represents the inner border of the thenar eminence and therefore, approxi- mately, of the outer group of the short muscles of the thumb and the inner margin of the fascia intervening between them and the palmar space through which run the flexor tendons. It intersects the deep palmar arch at about the highest point where it crosses the metacarpal bone of the middle finger. b, at the centre of the palm, where it is intersected by d, crosses the same metacarpal bone a line or two below, — i.e., nearer the fingers than the superficial palmar arch, which runs about on a cur\'ed line from the lower border of the thumb, when it is at right angles to the hand, to the pisiform bone. The deep palmar arch is from a quarter to a half an inch nearer the wrist. c represents the upper limits of the syno\'ial sheaths of the flexor tendons of the index, middle, and ring fingers, is a little above the division of the palmar fascia into the digital slips and the bifurcation of the digital arteries, crosses the necks of the three inner metacarpal bones, and is as much above the corresponding meta- carpo-phalangeal joints as they are above the webs of the fingers. d, at its upper portion, irregularly outlines the outer border of the hypoth- enar eminence, — i.e., of the short muscles of the little finger and of the fascia sepa- rating them from the central space of the palm, — but it is the most irregular and unimportant of these creases. The transverse folds on the palmar surfaces of the fingers correspond, the highest to the web of the fingers, — i.e. , from one-half to three- quarters of an inch below the metacarpo-phalangeal joint, — the middle to the proxi- mal interphalangeal joint, and the lowest to a line a little above the distal interpha- langeal joint. On the thumb the line of the radial side of the index-finger, if continued upward, almost coincides with the higher of the creases, which crosses the 622 HUMAN ANATOMY. metacarpo-phalangeal joint obliquely. The lower crease corresponds to the inter- phalangeal joint. The papillary ridges of the skin covering the terminal phalanges assume varied curves and form patterns, — immutable and characteristic in the indi- vidual,— impressions of which have been used of late years for purposes of identifica- tion of criminals. On the dorsum of the hand the hollow at the base of the thumb (the so-called " snui?-box" j is bounded externally (radially) by the tendon of the e.xtensor of the arkiugs of right pain metacarpal bone of the thumb and the short extensor, and internally by the tendon of the long extensor (Fig. 582). The radial artery, a large vein, — cephalic \'ein of the thumb (Treves), — and the inner division of the radial nerve cross this space. Beneath it are the scaphoid and trapezium and the articulation between the latter and the first metacarpal bone. The abductor indicis muscle makes a distinct fusiform prominence when the thumb is adducted. The tendons of the common extensor and of the extensor of the little finger and the slip connecting them may be seen. It should be remembered that the "knuckles" are at each joint, the distal extremities of the proximal bones entering into the articulation. THE MUSCLES OF THE LOWER LLMB. 623 THE MUSCLES OF THE LOWER LIMB. In describing the muscles of the lower limb a classification similar to that which was employed for the upper limb muscles will be followed. Owing, however, to the firm articulation of the innominate bones to the sacrum, the muscles extending between the axial skeleton and the pelvic girdle are greatly reduced, and those (such as the psoas) which might be included in this group are continued to the femur, and for present purposes are more conveniently grouped with the muscles extending from the girdle to the femur. There is also, in the lower limb, a greater number of muscles passing over two joints ; indeed, many of the muscles which are inserted into the upper portions of the leg bones take their origin from the pelvic girdle. Most of these seem to be, primarily, members of the femoral group of muscles and will be so classified in the succeeding pages, but one (the gracilis), at least, appears to belong to the group extending from the girdle to the femur. THE MUSCLES EXTENDING FROM THE PELVIC GIRDLE TO THE FEMUR. I. Psoas magnus. 6. Adductor brevis. 2. Iliacus. 7. Adductor magnus. 3- Pectineus. 8. Ouadratus femoris. 4- Gracilis. 9. Obturator externus. 5- Adductor longus. ID. Obturator internus. II. Gemelli. I. Psoas Magnus (Fig. 598). Attachments. — This muscle (m. psoas major) arises from the sides of the bodies of the twelfth thoracic and all the lumbar vertebra and from the transverse processes of the lumbar vertebrae. Its fibres pass directly downward and slightly forward over the superior ramus of the pubis and are mseried by a tendon, in com- mon with the iliacus, into the lesser trochanter of the femur. Nerve-Supply. — By branches from the lumbar plexus from the second, third, and fourth lumbar nerves. Action. — To bend the spinal column laterally and to fle.x the body and pelvis upon the femur. Acting from above, it flexes the thigh and rotates it outward. Relations. — The psoas magnus lies along the side of the lumbar vertebrae, resting upon their transverse processes and the medial portion of the quadratus lumborum. Extending as high as the last thoracic vertebra, it passes beneath the internal arcuate ligament, or medial lumbo-costal arch, of the diaphragm, and below it passes beneath Poupart's ligament to reach the thigh. In its abdominal portion it is in relation ventrally with the peritoneum, on the right side with the ascending colon and duodenum, and on the left side with the descending colon and pancreas. The inner border of the kidney overlaps the lateral portion of the muscle, and the ureter and spermatic (or ovarian) arteries descend obliquely along it. The inferior vena cava lies in front of the right muscle. The nerves formed by the lumbar plexus perforate the muscle, and the genito-crural nerve passes down on its anterior surface. In the pelvis the external iliac vessels lie along its medial border, and it is crossed, just before it passes beneath Poupart's ligament, by the vas deferens. In the thigh it forms a portion of the floor of the femoral or Scarpa's triangle, and lies between the iliacus and pectineus muscles, behind the femoral vessels. As the ten- don which is common to it and the iliacus passes o^'er the hip-joint it rests upon a rather large bursa (bursa iliopectinea) ; just above the insertion a second bursa (bursa iliaca subtendinea) intervenes between the tendon and the femur. 624 HUMAN ANATOMY. External arcuate ligament' — ^Internal arcuate ligament The psoas magnus appears to be formed by the union of a hyposkeletal trunk muscle with a femoral muscle, the remaining portions of which are represented by the iliacus and pectineus. It is interesting to note in this connection that in those mammalia in which the quadratus lum- borum is weirdeveloped the psoas magnus is correspondingly weak, and vice versa. The psoas parvus or Fig sq8. »«/«or (Fig. 59S) is along, flat muscle which lies upon the ventral surface of the psoas magnus, represent- ing a separated portion of it, and is present in some- thing over 50 per cent, of cases. It arises from the bodies of the last thoracic and first lumbar vertebrae and is inserted into about the middle of the ilio-pec- tineal line (linea termina- lis) of the pelvis. 2. Iliacus (Fig. 598). Attachments. — The iliacus arises from about the upper half of the anterior surface of the ilium. Its fibres con\erge downward to form a common tendon with the psoas major, which is inserted into the lesser trochanter of the femur. Nerve -Supply. — By the anterior crural nerve from the second, third, and fourth lum- bar nerves. Action. — To fle.x the thigh and rotate it slightly inward ; when the thigh is fixed, to fle.x the pelvis and trunk upon the femur. Relations. — The iliacus covers the pos- terior wall of the false pelvis, and upon the right side has resting upon it the caecum and on the left side the sigmoid colon. It is crossed obliquely by the e.xternal cutaneous and the anterior crural nerves ; its inner border is covered by the psoas magnus. It passes beneath Poupart's ligament external to the psoas magnus, its relations in the thigh being identical with those of that muscle. Variations. — The iliacus and psoas magnus are not infrequently extensively united, and the two muscles, together with the psoas parvus, when this is present, are frequently spoken of as the m. ilio-psoas. The fibres of the iliacus which arise from the posterior superior spine of the ilium are often separated from the rest of the muscle to form an iliacus minor, which is inserted into the capsule of the hip-joint or into the anterior intertrochanteric line. The Iliac Fascia. — This fascia is a strong sheet of connective tissue which covers the entire ilio-psoas. Above it is attached to the internal arcuate ligament of Deep dissection of posterior bod\ nd iliac fossa of right side. THE MUSCLES OF THE LOWER LIMB. 625 the diaphragm, and thence descends over the anterior surface of the psoas. On reach- ing the level of the crest of the ilium, it is prolonged outward along that structure, where it is in connection with the lower edge of the transversalis fascia. It descends thence over the anterior surface of the psoas and iliacus, at the inner border of the former muscle passing over into the pelvic fascia. Below it is attached in its lateral two-thirds to Poupart's ligament, more medially it remains in contact with the ilio- psoas and passes down into the thigh behind the femoral vessels, separating these structures from the muscle and the anterior crural nerve and forming the posterior wall of the sheath for the femoral vessel. It thus divides the space beneath Pou- part's ligament (Fig. 599) into a muscular compartment (lacuna musculorum) which contains the ilio-psoas muscle and the anterior crural and external cutaneous nerves, and a vascular compartment (lacuna vasorumj which contains the femoral artery and vein and the crural branch of the genito-crural nerve, its innermost portion, between the femoral vein and the free edge of Gimbernat's ligament, transmitting only a few loosely arranged lymphatic vessels and forming what is termed the femoral ring (annulus femoralis). This ring (Fig. 599), which is covered over by a portion of the transversalis fascia, known as the septum crurale or femorale, is the upper end of a space, occu- FiG. 599. Anterior superior iliac spine- Iliac fascia attached to Poupart's ligament Aponeurosis of external oblique Iliacus muscle Anterior crural External abdoi Gimbernat's ligament Femoral ring Iliac fascia continued as^. posterior wall of femo- ral sheath Pudic branch of obturator' Obturator membrane Obturator nerve Artery Vein Dissection showing structures contained within the muscular and vascular compartments formed by attachments of iliac fascia. pied by loose areolar tissue and lymphatic vessels, which extends a short distance downward along the inner side of the femoral vein, forming what is termed the femoral canal. Owing to the nature of its contents and to its upper end being closed only by the relatively thin septum femorale, this canal may allow of the escape of a portion of the intestine from the abdominal cavity downward into the thigh, producing a femoral hernia. Medially the portion of the iliac fascia which forms the posterior wall of the sheath for the femoral vessels is continued over the anterior surface of the pectineus muscle (Fig. 1496), this portion of it being sometimes termed the pectineal or ilio- pectineal fascia. Above it is attached to the ilio-pectineal eminence and below becomes continuous with the deep layer of the fascia lata. 3. Pectineus (Fig. 600). Attachments. — The pectineus a^-ises from the anterior surface of the superior ramus and ilio-pectineal line of the pubis and passes downward and laterally to be inserted into the pectineal line of the femur, a bursa intervening between it and the bone. 626 HUMAN ANATOMY. Fig. 600. Aponeu- Tosis of external oblique Nerve-Supply. — From the anterior crural nerve by the second and third lumbar nerves. Action. — To adduct and flex the thigh and rotate it sHghtly outward. Variations. — The fibres which in- nervate the pectineus sometimes pass to it wholly or partly by the obturator nerve. 4. Gracilis (Fig. 600). Attachments. — The gra- cilis is a long band-like muscle which arises from the anterior surface of the body and inferior ramus of the pubic bone. It de- scends along the inner surface of the thigh, passes behind the inner condyle of the femur, and then, bending slightly forward, is J7t- serted into the inner surface of the tibia near the tuberosity, just above the semitendinosus and be- hind and beneath the expanded tendon of the sartorius. Nerve-Supply. — By the anterior division of the obturator nerve from the second, third, and fourth lumbar nerves. Action. — To adduct the leg and flex the thigh. It will also assist in rotating the leg inward, especially if the thigh be flexed. 5. Adductor Longus (Fig. 600). Attachments. — The ad- ductor longus arises from the an- terior surface of the body and superior ramus of the pubis and passes downward and laterally to be inserted into about the middle third of the inner lip of the linea aspera of the femur. Nerve-Supply. — By the anterior division of the obturator nerve from the second and third lumbar ner\'es. Action. — To adduct, flex, and outwardly rotate the thigh. 6. Adductor Brevis (Fig. 601). Attachments. — The ad- ductor brevis arises from the body Muscles of right thigh, antero-median aspect. ^^^ inferior ramUS of the pubic bone, below and partly external to the origin of the adductor longus. It passes laterally and obliquely downward to be inserted into the upper third of the medial lip of the linea aspera of the femur. Tendo patelb THE MUSCLES OF THE LOWER LLMB. Fig. 6oi. 627 Vi Dorsum of ilii riiiteus mininuis Greater trochanter Quadratus fcmoris, insertion Obturator e\tcrnus Perforating arteries Vastus externus Fourth perforating artery Internal condyle, / ^Jl --r-^-^^ External condyle Deep dissection of posterior surface of right thigh. 028 HUMAN ANATOMY. Nerve-Supply. — By the anterior ramus of the obturator nerve from the third and fdurth kmibar nerves. Action. — To adduct, flex, and outwardly rotate the thigh. 7. Adductor Magnus (Fig. 601). Attachments. — The adductor magnus arises from the inferior rami of the pubis and ischium, as far laterally as the base of the tuber ischii. Its anterior fibres are directed laterally and downward to be mserted into nearly the whole length of the inner lip of the linea aspera by a series of tendinous arches which give passage to the perforating branches of the profunda fenioris artery on their way to the back of the thigh. Its posterior fibres converge downward to a strong tendon which is inserted into the adductor tubercle on the inner condyle of the femur. Nerve-Supply. — By the posterior division of the obturator nerve from the third and fourth lumbar nerves. Action. — To adduct the thigh. Relations. — ^The adductor muscles, together with the gracilis, occupy the medial surface of the thigh, intervening between the extensor and flexor muscles. The adductor brevis and adductor longus enter into the formation of the floor of Scarpa's triangle (page 639), and from the apex of the latter the femoral vessels are Greater sacro-sciatic foramen Greater sacrosciatic ligament Lesser sacro-sciatic ligament Lesser sacro-sciatic foramen Gemellus superior Obturator intern us Gemellus inferior Deep dissection of ripht buttock, shi Crest of ilium j/flHf Gluteus m Pyriformi^ ttached to greater trochanter of femur. continued downward upon the longus and magnus close to their insertion, and, together with the internal saphenous nerve, are bridged over by an aponeurotic membrane which passes from the longus and magnus to the surface of the \'astus internus. By this membrane the space occupied by the \essels and nerve is con- verted into a closed passage-way termed Hunter s canal (canalis adductorius) (Fig. 606), the lower end of which corresponds to the interval (hiatus tendineus) between the tendons of the anterior and posterior portions of the adductor magnus. The perforating branches of the deep femoral artery pierce the adductor magnus near its insertion, the first one passing above and the second below the adductor brevis, or both perforate that muscle also, while the third passes through the magnus a little above the hiatus tendineus. THE MUSCLES OF THE LOWER LIMB. 629 Variations. — A separation of any of the adductor muscles into distinct portions may occur, and indeed the upper part of the anterior portion of the magnus is usually quite separate from, the rest of the muscle and has been termed the adductor minimus. The posterior fibres of the magnus frequently receive their nerve-supply through the great sciatic nerve. 8. OuADRATUS Femoris (Figs. 602, 608). Attachments. — The quadratus femoris arises from the lateral border of the tuber ischii and passes almost directly outward to be inserted into the femur along the linea quadrati, which e.xtends a short distance downward from about the middle of the intertrochanteric line. Nerve-Supply. — By a special nerve from the fourth and fifth lumbar and first sacral nerves. Action. — To rotate the thigh outward. * Relations. — The quadratus femoris is concealed by the lower portion of the gluteus ma.ximus, and its posterior surface is crossed by the great and small sciatic nerves. Beneath it lie the obturator externus and the termination of the internal Fig. 603. V lumbar vertebra Obturator foramen Dissection of right posti Greater sacro-sciatic foramen Spine of iscliium "occygeus \ ."^Lesser sacro-sciatic foramen NvGreater sacro-sciatic ligament Obturator internus Tuber ischii pyriformis and obturator internu circumfle.x artery. Its upper border is in contact with the gemellus inferior and its lower border with the adductor magnus. Variations. — The muscle is not infrequently apparently absent, being fused with the adductor magnus. 9. Obturator Externus (Figs. 552, 601). Attachments. — The obturator externus, a thick triangular muscle, arises from the anterior surface of the lower half of the obturator membrane and from the rami of the pubis and ischium which bound the lower half of the obturator foramen. The fibres are directed outward, and converge to a rounded tendon which is inserted into the floor of the digital fossa of the femur. Nerve-Supply. — By the posterior division of the obturator nerve from the third and fourth lumbar nerves. Action. — To rotate the thigh outward. 10. Obturator Internus (Figs. 602, 603). Attachments. — The obturator internus arises from (i) the inner surface of the rami of the pubis and ischium which bound the obturator foramen, (2) from the 630 HUMAN ANATOMY. smooth surface of bone immediately behind the foramen, corresponding to the acetabulum externally, and (3) from the whole of the inner surface of the obturator membrane. Its fibres, passing downward and backward, converge to a strong tendon, which gains the lesser sacro-sciatic foramen, and there, bending around the margin of the foramen, a bursa (bursa m. obturatoris interni ) intervening between the tendon and the bone, passes outward through the foramen to be mserted into a facet on the inner surface of the greater trochanter of the femur just above the digital fossa. Nerve-Supply. — By a special nerve from the first, second, and third sacral nerves. Action. — To rotate the thigh outward. II. Gemelli (Fig. 602). Attachments.— The gemelli are two slender muscles which lie one on either side of the tcntlon of the obturator internus. The gemellus superior ai-ises from the spine of the ischium and the gemellus inferior from the upper part of the tuber ischii. Both muscles are inserted into the inner surface of the greater trochanter of the femur along with the obturator internus. Nerve -Supply. — -The superior gemellus by the nerve to the internal obturator from the fifth lumbar and first and second sacral nerves ; the inferior by the nerve to the quadratus femoris from the fourth and fifth lumbar and the first sacral nerves. Action. — To assist in rotating the thigh outward. Variations. — One or other of the gemelli, usually the superior, is occasionally wanting. This is very probably due to fusion with adjacent muscles, the gemellus superior with the pyriformis and the inferior with the quadratus femoris. (b) THE POST-AXIAL MUSCLES. 1. Gluteus ma.ximus. 3. Gluteus medius. 2. Tensor fasciae lat£e. 4. Gluteus minimus. I. Gluteus Maximus (Figs. 604, 607). Attachments. — The gluteus ma.ximus is an exceedingly thick, coarse muscle which forms the principal mass of the buttock. It arises from the lateral surface of the posterior portion of the ilium, behind the superior gluteal line, from the pos- terior surface of the sacrum and coccy.x, and from the posterior sacro-iliac and greater sacro-sciatic ligaments. The fibres pass laterally and downward, the upper ones curving over the lateral surface of the greater trochanter of the femur and the lower ones over the tuberosity of the ischium, and are i7iserted by a broad tendon partly into the ilio-tibial band of the fascia lata and partly into the gluteal tuberosity of the femur. Nerve-Supply. — By the inferior gluteal nerve from the fifth lumbar and first and second sacral nerves. Action. — To draw the thigh backward and rotate it slightly outward. Acting from below, it extends the trunk. Relations. — The gluteus maximus is covered by the upper posterior portion of the fascia lata. It covers the gluteus medius, pyriformis, obturator internus, gemelli, quadratus femoris and the origin of the hamstring muscles, and also the gluteal, sciatic, and pudic vessels and nerves. It is separated from the lateral surface of the trochanter major by a large bursa ('bursa trochanterica m. glutaei maximi), two or three additional small bursse (bursae glutaeofemorales ) separating the lower portion of the muscle from the shaft of the femur. A bursa is also frequently present beneath the muscle where it passes over the ischial tuberosity (bursa ischiadica m. glutaei maximi). Variations. — The lower border of the gluteus maximus is occasionally separated from the rest of the muscle, forming what may be termed the coccygeo-femora/is, and it occasionally receives a slip from the ischial tuberosity, which has been named the ischio-femoralis. THE MUSCLES OF THE LOWER LIMB. 631 Fig 2. Tensor Fascia Lat^ (Figs. 600, 604). Attachments. — The tensor fascije latae, also termed the tensor vagina fe7no- ris, is a flat muscle which arises from the crest of the ilium, immediately behind the anterior superior spine, and passes downward and slightly backward to be itiserted into the upper portion of the ilio-tibial band of the fascia lata. Nerve-Supply. — By the superior gluteal nerve from the fourth and fifth lumbar and first sacral nerves. Action. — To tense the fascia lata and at the same time to flex the thigh and rotate it slightly inward. 3. Gluteus Medius (Figs. 604, 609). Attachments. — The gluteus medius arises from the outer surface of the ilium, between the superior and middle gluteal lines. Its fibres pass downward, converging to a tendon which is inserted into the lateral surface of the great trochanter 01 the femur near its summit. Nerve-Supply. — By the superior gluteal nerve from the fourth and fifth lumbar and first sacral nerves. Action. — ^To abduct the thigh and by its stronger anterior fibres to rotate it inward. Acting from below, to flex the pelvis laterally. Relations. — The an- terior portion of the mus- cle is covered by the fascia lata and the tensor fasciae latae, the posterior portion by the gluteus maximus. Beneath it are the gluteus minimus and the superior gluteal vessels and nerve, its tendon passing over that of the pyriformis near its insertion. A bursa (bursa trochanterica m. glutaei medii anterior) is interposed between the . long head' Biceps, short head- "ighl thigh, lateral aspect. 632 HUMAN ANATOMY. Fig. 605. Gluteus maximusr Im^^S1\ ' lute us niedius covered by fascia lata \nterior superior spine of ilii I tnsor fasciae lata? —^Fascia lata, cut edges .' I y }) — Symphysis pubis Ilio-tibial band L . ./ Lateral surface of right thigh invested by fascia lata. THE FEMORAL MUSCLES. 633 tendon of the muscle and the upper part of the great trochanter, and another (bursa trochanterica m. glutaei medii posterior) is usually present between the tendon and that of the pyriformis. 4. Gluteus Minimus (Figs. 601, 602). Attachments. — The gluteus minimus is the most deeply situated of the gluteal muscles. It arises from the lateral surface of the ilium, between the middle and inferior gluteal lines, and passes downward and laterally to a strong tendon which is inserted into the anterior surface of the great trochanter of the femur. Nerve-Supply. — By the superior gluteal nerve from the fourth and fifth lumbar and first sacral nerves. Action. — To abduct the thigh and, acting from below, to flex the pelvis laterally. Relations. — Superficially it is covered by the gluteus medius and crossed by the superior gluteal vessels and nerve. Deeply it rests upon the capsule of the hip- joint. A bursa (buisa trochanterica m. glutaei minimi) is interposed between the tendon and the great trochanter. Variations. — The anterior portion of the muscle is sometimes distinctly separated from the rest, forming a muscle frequently present in the lower mammals and termed the scansorius. THE FEMORAL MUSCLES. Many of the muscles which belong to this group extend the entire length of the thigh, taking their origin, in whole or in part, from the pelvis. The Fascia Lata (Fig. 605). — This, the deep fascia of the thigh, is a Fig. 606. Rectus femoris Vastus internus Crureus Internal intermuscular septum Sartonus Internal saphenous nerve Femoral vessels Internal saphenous vein .Adductor longus Hunter's canal Gracilis Vastus extern us External intermuscular septi Biceps, 1 Adductor magnus head Greater sciatic nerve Semitendii across right thigh through Hunter's canal, seen from below. Strong kyer which completely encloses the muscles of the thigh and covers the glu- teal region. Its upper attachment, beginning from behind, is to the coccyx and sacrum ; thence forward along the entire length of the crest of the ilium and me- 634 HUMAN ANATOMY. dially along Poupart's ligament to the body of the pubis ; thence it passes backward and downward along the inferior rami of the pubis and ischium to the ischial tuberos- ity, where it passes upon Fig. 607. the greater sacro-sciatic ligament and so back to the starting-point. Below it is attached to the bor- ders of the patella and be- comes continuous with the fascia of the leg. The fascia lata varies considerably in thickness in different regions. Over the gluteal region itisthin, but over the great tro- chanter of the femur it becomes greatly thick- ened, and this thickening is continued downward upon the lateral surface of the thigh (Fig. 605) as far as the external tuber- osity of the tibia, forming what is termed the ilio- tibial band ( tractus ilio- tibialis). This receives at its upper part the inser- tions of the tensor fasciae lat£e and part of the glu- teus ma.ximus, and from the posterior edge of its upper portion a much smaller and feebler band can be traced backward at first across and then below the lower portion of the gluteus maximus to the ischial tuberosity ; it pro- duces the gluteal sida' Anterior tibial Extensor longus digitorum, Musculo-cutaneous Extensor longus halluci Peroneus longu; Peroneus brev Fibul: em. intermuscular sept Flexor longus hall Peroneal v Deep fascial septum. Gastrocnemius, outer head amicus Interosseous membrane Tibialis posticus longus digitorum Internal saphenous vein Posterior tibial vessels Internal saphenous r Posterior tibial nerve Tendon of plantaris Gastrocnemius, inner head Superficial fascia right leg at junction of upper and middle thirds, viewed from belo one in front of and one behind the muscles, to be attached to the fibula. These are the anterior and posterior intermuscular septa ; they serve for the origin of portions of the adjacent muscles. In regions in which the crural fascia is adherent to subjacent bony structures a number of subcutaneous bursa occur between the deep fascia and the integument. Thus, over the patella there is usually to be found a bursa (bursa prepatellaris sub- cutanea) ; occasionally one (bursa prepatellaris subfascialis ) occurs between the patella and the fascia. Another (bursa infrapatellaris subcutanea ) frequently lies over the ligamentum patellae, and immediately below it the bursa subcutanea tuberositatis tibiae. Again, over each malleolus a bursa often exists (bursae malleoli lateralis et medialis) ; finally, a bursa frequently occurs over the tendo Achillis at its insertion into the tuberosity of the calcaneum (bursa subcutanea tendinis calcanei). (ff) THE PRE-AXIAL MUSCLES. As is the case with the antibrachial pre-axial muscles, those of the crus are primarily arranged in three lavers, the most superficial sheet being attached above to the condyles'of the femur, for the most part to the outer one. A further simi- larity to the arrangement in the forearm is to be found in the continuation of the muscles of the middle laver into the foot, to act as flexors of the digits. THE CRURAL MUSCLES. 649 (aa) The Superficial Layer. I. Gastrocnemius. 2. Soleus. 3. Plantaris. The main mass of the calf of the leg is formed by two muscles, the gastroc- nemius and the soleus, which unite below in a common tendon, the /etido Achillis (tendo calcaneus), inserted into the posterior surface of the tuberosity of the calca- neum, a bursa (bursa tendinis calcanei ) intervening between the tendon and the upper part of the tuberosity. Since the gastrocnemius arises by two heads, these two muscles together are sometimes spoken of as the triceps sura. Gastrocnemius (Fig. 618). Attachments. — The gastrocnemius takes origin by two heads. The outer head arises from the posterior surface of the femur, just above the lateral condyle, by a short, strong tendon which sometimes contains a sesamoid cartilage ; the inner head aiises also by a short tendon just above the medial condyle of the femur. Above, the two heads are separated from each other by a groove, but below they unite to form a thick belly, the fibres of which pass over into a broad, fiat tendon inserted below with the tendo Achillis. Nerve-Supply. — By the internal popliteal (tibial) division of the greater sciatic nerve from the first and second sacral nerves. Action. — To extend the foot and to assist in flexing the knee-joint. Relations. — The gastrocnemius is in relation by its posterior surface with the short saphenous vein and nerve. On its deep surface it is in contact with the plantaris and soleus muscles (Fig. 617), and in its upper part with the capsule of the knee-joint, the popliteus, and the popliteal vessels and nerves. A bursa (bursa m. gastrocnemii medialis) intervenes between the inner head and the capsule of the knee-joint, with the synovial cavity of which it is frequently continuous; the bursa m. gastrocnemii lateralis frequently presents similar relations to the outer head. Variations. — Absence of the entire muscle or of the outer head has been obsen'ed, but the most frequent anomaly is the occurrence of a third head which arises from some portion of the popliteal surface of the femur. 2. Soleus (Fig. 619). Attachments. — The soleus is a broad, flat muscle which arises from the head and upper posterior portion of the fibula, from the oblique line of the tibia, and from a tendinous arch which passes across between the tibial and fibular origins. Its fibres pass downward to a broad tendon which joins with the tendo Achillis below. Nerve-Supply. — By the internal popliteal (tibial) division of the greater sciatic nerve from the first and second sacral nerves. Action. — To extend the foot. 3. Plantaris (Fig. 619). Attachments. — The plantaris is a small spindle-shaped muscle which passes over into a long, slender tendon extending downward between the gastrocnemius and soleus. The muscle arises from the femur, just above the outer condyle, internal to the lateral head of the gastrocnemius, and from the adjacent part of the posterior ligament of the knee-joint. The tendon traverses almost the entire length of the leg and IS mserted either into the tuberosity of the calcaneum along with, but to the inner side of, the tendo Achillis, sending also some fibres to tlie internal annular liga- ment, or into the tendo Achillis itself. Nerve-Supply. — By the internal popliteal (tibial) division of the greater sciatic nerve from the fifth lumbar and first sacral nerves. 650 HUMAN ANATOMY. Fig. 61S. Fig. 619. condyle i; lA Gastrocnemius, 1 — Sim inner head Gastrocnemius,^ Tendo Achillis-. Superficial dissection of posterior sur- face of right leg, showing muscles undis- turbed. Muscles of posterior surface of r'gh' leg; gastrocnemius has been removed, ex- posing plantaris and soleus. THE CRURAL MUSCLES. 651 Action. — To assist in extending the foot and to tense the crural fascia at the ankle-joint. Variations. — The plantaris is absent in about 7 per cent, of cases. Its insertion may be into the calcaneum, the tendo Achillis, the crural fascia, or even into the plantar aponeurosis. (bb) The Middle Layer. I. Flexor longus digitorum. 2. Flexor longus hallucis. I. Flexor Longus Digitorum (Figs. 620, 628). Attachments. — The long flexor of the toes (m. flexor digitorum longus) arises from almost the whole of the posterior surface of the tibia below the oblique line and from the deep surface of the deep layer of the crural fascia. Its fibres converge in a bipinnate manner to a tendon which passes laterally to the tendon of the tibialis anticus beneath the internal annular ligament, and so reaches the plantar region of the foot. There it is directed somewhat laterally, receiving the insertion of the flexor accessorius, and divides into four tendons which, passing through the divided ten- dons of the flexor brevis, are inserted into the base of the third or distal phalanx of the second, third, fourth, and fifth toes. Nerve-Supply. — By the posterior tibial nerve from the fifth lumbar and first sacral nerves. Action. — To flex the second, third, fourth, and fifth toes ; continuing its action, to extend the foot and to cause slight inversion of the sole. Relations. — In the leg (Fig. 617) the flexor longus is covered by the soleus and has resting upon it the lower portions of the posterior tibial vessels and nerve. It rests upon the tibialis posticus, crossing it obliquely in the lower part of the leg. In the foot its tendons are covered by the flexor brevis digitorum, and pass between the two terminal slips of the tendons of that muscle over the first phalanges. Its tendon is also covered by the abductor hallucis, and crosses obliquely the tendon of the flexor longus hallucis and the oblique portion of the adductor hallucis. The lumbricales take their origin from its tendons, and it receives the insertion of the flexor accessorius. Variations. — A flexor digitorum longus accessorius is occasionally found arising indepen- dently from the tibia or from the fibula and joining the tendon of the long flexor below, or else imiting with the flexor accessorius. 2. Flexor Longus Hallucis (Figs. 620, 628). Attachments. — The long flexor of the great toe (m. flexor hallucis longus) arises from the posterior surface of the fibula, from the posterior intermuscular septum, and from the deep surface of the deep layer of the crural fascia. Its fibres converge bipinnately to a tendon which passes beneath the internal annular ligament, pos- terior to the posterior tibial vessels and nerve, and so enters the plantar surface of the foot. There it passes beneath the tendon of the flexor longus digitorum, to which it sends a slip, and continues distally to be inserted into the base of the distal phalanx of the great toe, passing between the flexor brevis hallucis and the first plantar interosseous. Nerve-Supply. — By the posterior tibial nerve from the fourth and fifth lumbar and first sacral nerves. Action. — To flex the hallux and extend and slightly supinate the foot. Variations.— -The principal variations of the flexor longus hallucis concern its union with the tendon of the flexor longus digitorum. The passage of a slip between the two tendons is constant, but its distribution to the tendons of the flexor'digitorum varies considerably. Usually it separates into two slips which pass to the tendons for the second and third toes, but it may also pass to the tendons for the second, third, and fourth toes, to that of the second alone, or even to all the tendons of the flexor longus digitorum. It may also completely replace the tendon usually passing from the flexor longus digitorum to the second digit. 652 HUMAN ANATOMY. These variations of the flexor longus hallucis are explicable on the basis that its history, t^ether with that of the flexor longus digitorum, has been very similar to that of the flexor Fig. 620. lernal condyle of femur Tendon of semimembranosus-^ Popliteus Plantaris, cut Head of fibula Peroneus longus Soleus, cut Tibialis posticus Flexor longus hallucis Tendon of peroneus longus Peroneus brevis Tibia and posterior inferii fibular ligament -^_Tendo Achillis, stump Internal lateral ligament Inner tubercle of os calcis Outer tubercle of os calcis Flexor brevis digitorum, stump Abductor minimi digiti Flexor accessorius brevis minimi digiti Interosseus - Tendons of flexor brevis digitonim Deeper dissection of right leg, showing flexors passing into foot. sublimis digitorum and flexor longus poll ids of the ^re/irm. In other words these m^^^^^^^ reoresent a laver of muscle-tissue which primarily arose from the bones of the 'eg ana v, as in sirted into the deeper layers of the plantar aponeurosis. Later tendons differentiated from the THE CRURAL MUSCLES. 653 plantar aponeurosis and the muscles were continued to the digits. The separation of the flexor hallucis from the rest of the muscle took place later, and even yet is somewhat incomplete, the Internal condyle Internal lateral ligament' Tendon of popliteus Head of fibula Anterior tibial artery Fibula /V -* — P r neus longus — r bialis posticus Internal lateral ligament. Tibialis anticus, Abductor hallucis. stump Insertion of tibialis posticus Insertion of tibialis anticus Tendon of fiexor longus hall Peroneus longus Fibula Posterior inf. tibio-fibular ligament Tendo Achillis, stump Inner tubercle of os calcis Outer tubercle of os calcis Flexor brevis digitorum, stump ■Flexor longus digitorum tendon Flexor accessorius Abductor minimi digiti Deep dissection of right leg; flexors have been turned aside to expose tibialis posticus. connections between its tendon and that of the flexor longus digitorum being indications of its developmental history. 654 HUMAN ANATOMY. (fr) The Deep Layer. I. Tibialis posticus. 2. Flexor accessorius. 3. Popliteus. I. Tibialis Posticus (Fig. 621). Attachments. — The posterior tibial (m. tibialis posterior) arises from the pos- terior surface of the interosseous membrane and from the adjacent surface of both the tibia and fibula. Its fibres pass into a tendon, situated along- its inner border, which passes obliquely downward and inward beneath the fle.xor longus digitorum. It is continued onward beneath the most central portion of the internal annular liga- ment to the plantar surface of the foot, where it is inserted into the tuberosity of the scaphoid bone, sending prolongations to all the other tarsal bones, except the astra- galus, and to the bases of the second, third, and fourth metatarsals. Nerve-Supply. — By the posterior tibial nerve from the fourth and fifth lumbar and first sacral nerves. Action. — To extend the foot and to slightly invert the sole. Relations. — The posterior tibial is the deepest muscle upon the posterior sur- face of the leg. It is covered by the soleus and by the flexor longus digitorum, and has resting upon it the upper portion of the posterior tibial and peroneal vessels (Fig. 617). The anterior tibial vessels pass through the interosseous membrane immedi- ately above the origin of the muscle. A bursa sometimes intervenes between its tendon and the tuberosity of Fig. 622. the scaphoid bone, and the tendon usually contains a ses- amoid cartilage or bone where it passes over the head of the astragalus. Variations. — A portion of the muscle is sometimes inserted into tlie internal annular ligament. A muscle, which has been called the peronco-tibialis, not in- frequently extends across between the fibula and tibia, immediately beneath the tibio-fibular articula- tion and above the anterior tibial vessels as they pass towards the front of tlie leg. It is usually ru- dimentary, but may form a well- marked triangular sheet. Vastus extemus ndyle Cut edge of capsular liganieut Long external lateral ligament ). — Short external lateral ligament Interosseous membran Deep dissectiun of leg, sliowing popliteus muscle 2. Flexor Accessorius (Fig. 628). Attachments. — The ac- cessorv fle.xor of the toes (m. quadratus plantae) arises by two heads from the medial and inferior surfaces of the calcaneum and, passing distally, is inserted into the tendon of the flexor longus digitorum. Nerve-Supply. — By the external plantar nerve from the first and second sacral nerves. Action. — By acting on the long flexor tendons, to flex the second, third, fourth, and fifth toes, and to counteract the oblique pull o' the long flexor. The flexor accessorius, although apparently located entirely in the foot, is, nevertheless, a crural muscle, since the tendon of the flexor longus digitorum, into which it is inserted, repre- sents, as has already been pointed out, a portion of the plantar aponeurosis. Into this many of the muscles of the leg were primarily inserted, and the accessorius represents the most distal portion of the original deep sheet of the crural musculature. THE CRURAL MUSCLES. 655 3. POPLITEUS (Fig. 622). Attachments. — The popliteus arises by a narrow tendon from the outer con- dyle of the femur and by a sUp from the posterior Hgament of the knee-joint. It passes inward and downward to be inserted into the posterior surface of the tibia above the obhque line. Nerve-Supply. — By the internal popliteal (tibial) division of the greater sciatic nerve from the fifth lumbar and first sacral nerves. Action. — To flex the leg and rotate it inward. Relations. — On its posterior surface it is covered by the plantaris and gas- trocnemius, and it is crossed by the popliteal vessels and internal popliteal nerve. By its deep surface it is in relation to the capsule of the knee-joint, a bursa (bursa m. poplitei) intervening. Variations. — The most frequent anomaly in connection with the popliteus is the occurrence of a second head, which arises from the sesamoid cartilage of the lateral head of the gastroc- nemius.- The occurrence of this head is frequently associated with the absence of the plantaris. («) THE POST-AXIAL MUSCLES. 1. Tibialis anticus. 4. Extensor longus hallucis. 2. Extensor longus digitorum. 5. Peroneus longus. 3. Peroneus tertius. 6. Peroneus brevis. Tibialis Anticus (Fig. 623). Attachments. — The anterior tibial muscle (m. tibialis anterior) arises from the outer tuberosity and surface of the tibia and also from the interosseous membrane and the crural fascia. Its fibres extend downward to a strong tendon which passes through the inner compartment of the anterior annular ligament and is inserted into the inner surface of the internal cuneiform and the base of the first metatarsal bone. Nerve-Supply. — By the anterior tibial nerve from the fourth and fifth lumbar and first sacral nerves. Action. — To flex the foot ; to draw up the inner border and hence invert the sole. Relations. — The anterior tibial rests upon the lateral surface of the tibia and upon the interosseous membrane, and is in contact externally with the extensor longus digitorum, the extensor longus hallucis, and the anterior tibial vessels and nerve (Fig. 617). A bursa (bursa subtendinea m. tibialis anterioris) intervenes between its tendon and the medial cuneiform bone. Variations. — Not infrequently a bundle is detached from the muscle to be inserted into the anterior annular ligament, into the dorsal fascia of the foot, or, in some cases, into the astragalus. It forms what has been termed the tibio-fascialis anterior or tibio-astragalus. 2. Extensor Longus Digitorum (Fig. 623). Attachments. — The long extensor of the toes (m. extensor digitorum longus) arises from the external condyle of the tibia, the upper part of the fibula, the in- terosseous membrane, the intermuscular septum, and the crural fascia. Its fibres pass downward and terminate at about the middle of the leg in a tendon which passes through the outer compartment of the anterior annular ligament and divides into four tendons which pass to the second, third, fourth, and fifth toes. Over the metatarso- phalangeal joint of its digit each tendon spreads out into a membranous expansion which covers the dorsum of the first phalanx and receives the insertions of the inter- ossei and lumbricales, and, in the case of the second, third, and fourth toes, those of the extensor brevis digitorum. Distally each membranous expansion divides into three slips, of which the middle one is insei-ted into the second phalanx and the lateral ones into the third phalanx of its digit. Nerve-Supply.— From the anterior tibial nerve from the fourth and fifth lum- bar and first sacral nerves. Action. — ^To extend the second, third, fourth, and fifth toes and to flex the foot. 656 HUMAN ANATOMY. bercle of tibia Relations. — By its deep surface and medially the muscle is in relation with the extensor longus hallucis, medially with the tibialis anticus, the anterior tibial ves- sels and nerve, and deeply with the "^" ^■^' deep peroneal nerve above and the ankle-joint below. Laterally it is in contact with the peroneus longus above, with the peroneus tertius be- low, and with the musculo-cutaneous nerve, which passes down\\ard be- tween it and the peroneus longus (Fig. 617). Variations. — Considerable variation occurs in the arrangement of the terminal tendons, one of the most usual departures from the typical condition being a duplica- tion of the tendon to one or more of the toes, the additional tendon either passing to the same digit as its fellow or to an adjacent one. Occasionally a slip passes from the innermost tendon to that of the extensor longus hallucis, and slips may pass from any of the tendons to the meta- tarsal bones. 3. Peroneus Tertius (Fig. 623). Attachments. — The peroneus tertius lu/st's from the lower part of the anterior surface of the fibula and from the interosseous membrane, the intermuscular septum, and the crural fascia. At about the level of the ankle its fibres pass over into a ten- don which continues through the lateral compartment of the anterior annular ligament, together with the tendon of the extensor longus digi- torum, and is inserted into the base of the fifth metatarsal bone. Nerve-Supply. — By the ante- rior tibial nerve from the fourth and fifth lumbar and first sacral nerves. Action. — To flex and evert the foot. Variations. — The peroneus tertius is quite frequently absent, and is usually more or less closely united with the extensor longus digitorum above. Its tendon some- times splits into two portions, the additional one passing either to the fifth toe or to the fourth metatarsal. Notwithstanding its name, which has reference to its origin from the fibula, the peroneus tertius has morphologically nothing to do with the other peroneal muscles, but is a separated portion of the extensor longus digitorum, whose connec- tions with the metatarsals are interesting in this regard. Superficial dissection of anterior surface of right leg, sfiowing muscles uiulisturbed. 4. E.xTENSOR Longus Hallucis (Fig. 624). Attachments. — The long or proper extensor of the great toe (m. extensor hallucis longus) arises from the inner surface of the fibula and from the interosseous membrane. THE CRURAL MUSCLES. 657 Fig Outer tubi itv of tibia Head of fibula Tubercle of tibia Calf muscles Its fibres are collected into a tendon which passes through the middle compartment of the anterior annular ligament and is continued distally to the great toe. Over the metatarso-phalangeal joint it spreads out into a mem- branous expansion which receives a tendon of the extensor bre\ds digitorum and is then continued dis- tally to be inserted into the first and second phalanges. Nerve-Supply. — By the anterior tibial nerve from the fourth and fifth lumbar and first sacral nerves. Action. — To extend the great toe and flex the foot. Relations. — The ex- tensor longus hallucis is co\'- ered in its upper part by the tibialis anticus and the extensor longus digitorum. Near the ankle it crosses obliquely over the anterior tibial artery and passes upon the foot between the ten- dons of the extensor longus digitorum and the tibiahs anticus, internal to the ar- teria dorsalis pedis. Variations. — The muscle is occasionally united at its origin with the extensor longus digitorum, and, in addition to the connections which may ex- ist between its tendon and that of the long extensor, it may also be connected with one of the tendons of the extensor brevis digitorum. A small muscle is some- times to be found passing down- ward alongside of the extensor brevis hallucis to be inserted into the base of the first meta- tarsal. It may be termed the abductor longus lialtucis, and takes its origin either from the fibula close to the origin of the extensor longus hallucis, or from that muscle, or from the extensor longus digitorum or the tibialis anticus. What has been termed an extensor brevis hallucis is fre- quently represented by a slip from the extensor longus hal- lucis, the extensor longus digi- torum, or even from the tibialis anticus inserting into the base of the first phalanx of the hallux. Anterior cut edgi Peroneus bre\ is tendon Base of *ifth met-^tirsus Abductor minimi digiti' Muscles of anterior surface of right leg ; extensor loi been drawn aside to expose extensor longu 5. Peroneus Longus (Figs. 625, 629). Attachments. — The peroneus longus arises from the upper part of the lateral surface of the fibula and from the intermuscular septa and crural fascia. 42 Its fibn 658 HUMAN ANATOMY. Head of fibula Tubercle of tibi: extend obliquely downward to a tendon which passes behind the outer malleolus and then runs forward in a groove on the Fig. 625. calcaneuni, in which it is held by fibrous bands (retinacula mm. pero- naeorum). On the cuboid it again changes its direction, passing upon the plantar surface of the foot in a groove upon that bone which is cov- ered in by the long plantar liga- ment, and then, running obliquely across the foot, it is inserted into the internal cuneiform and the base of the first metatarsal bone. In front of the tuberosity of the cuboid the tendon usually contains a sesamoid cartilage. Nerve-Supply. — By the mus- culo-cutaneous ner\e from the fourth and fifth lumbar and first sacral nerves. Action. — -To extend the foot and evert the sole. Relations. — The peroneus lon- gus occupies the lateral surface of the leg (Fig. 617). It is in contact pos- teriorly with the soleus and internally with the extensor longus digitorum, being separated from these muscles by the intermuscular septa. The musculo- cutaneous nerve passes through the substance of the upper part of the mus- cle and is continued downward between the peroneus longus and the extensor longus digitorum. In the foot the ten- don of the peroneus longus is deeply placed, resting directly upon the plan- tar surfaces of the cuboid, the external cuneiform, and the bases of the second and third metatarsal bones. Peroneus Brevis (Fig. 624). Attachments. — The peroneus bre\is lies beneath the peroneus lon- gus and arises from the lower portion of the lateral surface of the fibula and from the intermuscular septa. Its fibres join a tendon which passes behind the external malleolus and then dis- tally, along with the ten- don of the peroneus lon- gus, beneath the fibrous bands or retinacula to be inserted into the tuberos- ity of the fifth metatarsal bone. Nerve-Supply. — By the musculo - cutaneous nerve from the fourth and fifth lumbar and first sacral nerves. Superficial dissection of right leg, antero-lateral ; showing peroneal muscles. THE MUSCLES OF THE FOOT. 659 Action. — To extend and evert the foot. Variations. — A slip is very frequently given off from the tendon of the short peroneus which is inserted either into the tendon of the extensor longus digitorum passing to the fifth toe or direcdy into that digit. In some cases the slip arises from the belly of the muscle, from that of the peroneus longus, or even from the fibula directly, and represents what has been termed the peroneus guintus. A peroneus giiartus, where distinctness from the quintus seems doubtful, sometimes occurs as a muscle arising from the lower part of the fibula and inserting into the calcaneum or the tuber- osity of the cuboid. THE MUSCLES OF THE FOOT. The plantar fascia or aponeurosis (Fig. 626) is a dense sheet of connective tissue lying immediately beneath the skin of the plantar surface of the foot and covering the pre-axial mus- cles. It is attached behind to the tuberosity of the cal- caneum, and extends dis- tally in a fan-like manner to be attached by five processes to the skin over the meta- tarso-phalangeal joints of the digits. The aponeuro- sis is much thicker in its middle portion than at the sides, where it. is continued dorsally over the sides of the foot to become continu- ous with the fascia of the dor- sum of the foot and with the crural fascia. Between its cutaneous insertions trans- verse bands of fibres stretch across to form the super- ficial transverse metatarsal ligament (fasciculi trans- versi) ; from its deep sur- face strong sheets are given off which pass to the sheaths of the flexor tendons. Ex- pansions are also given off from its deep surface which invest the flexor brevis digi- torum and, on either side, the abductor hallucis and abductor minimi digiti. Between the aponeu- rosis and the integument over the inferior surface of the tuberosity of the calca- neum a bursa (bursa subcu' tanea calcanea) is constantly present. The dorsal surface of Fig. 626. al dissection of sole of right foot (subject lying on bell> ) show ing plantar fascia the foot is covered by the fascia dorsalis pedis, a rather thin sheet continuous with the crural fascia above. It covers the long extensor tendons. {a) THE PRE-AXIAL MUSCLES. Like the pre-axial muscles of the hand, those of the foot may be regarded as derived from five primary layers, which have undergone a considerable amount of modification, including some fusion. 66o HUMAN ANATOMY. (aa) The Muscles of the First Layer. 1. Fle.xor brevis digitorum. 3. Abductor hallucis. 2. Flexor brevis hallucis. 4. Abductor minimi digiti. I. Flexor Brevis Digitorum (Fig. 627). Attachments. — The short fle.xor of the toes (m. flexor digitorum brevis) arises from the inner process of the calcaneal tuberosity and from the plantar aponeurosis. It extends distally, beneath the aponeurosis, as a thick quadrangular muscle, the fibres of which are collected Fig. 627. Flexor brevis fifth tOeS. d.gitl over the metatarsal bones into four tendons which pass to the second, third, fourth, and fifth toes. Over the first phalanx of the toe each tendon di\ides into two ter- minal slips, betiveen which the corresponding tendon of the flexor longus digitorum passes and which are zw- setted into the second pha- lanx. Nerve-Supply. — By the internal plantar nerve from the fourth and fifth lumbar and first sacral ner\es. Action. — To ffex the second, third, fourth, and ngus digitorum Superficial muscles of sole of right foot. Variations. — The most fre- quent variation in this muscle is the absence of the tendon to the fifth toe. an absence which occurs in somewhat over 21 per cent, of cases examined. Some- times the tendon is replaced by a slip or muscle which arises from the tendon of the flexor longus digitorum. The flexor brevis repre- sents the middle portion of the superficial flexor layer, and cor- responds, accordingly, to the terminal portions of the ten- dons of the flexor sublimis of the hand. Its origin is primarily from the plantar aponeurosis, and hence the occasional origin of the portion for the fifth toe becomes intelligible, since the tendon of the flexor longus is a differentiation of the deeper layer of the aponeurosis. 2. Flexor Brevis Hallucis (Fig. 628). Attachments. — The short flexor of the great toe (m. flexor hallucis brevis) arises from the plantar surface of the internal cuneiform bone and the adjacent liga- mentous structures. Its fibres pass distally to a tendon which contains a sesamoid bone, and is hiscrted into the inner surface of the base of the first phalan.x of the g^eat toe. Nerve -Supply. — By the internal plantar nerve from the fourth lumbar nerve. Action. — To flex the great toe. THE MUSCLES OF THE FOOT. 66i Variations.— The flexor brevis hallucis is frequently intimately fused with the abductor * a' portion of the deeper fibres of the flexor brevis hallucis is frequently inserted into the whole length of the first metatarsal. Occasionally these fibres are quite distmct from the rest of the muscle, forming what has been termed an opponens hallucis. In the description of the muscle given above, account has been taken only of what is usually described as the inner portion, the flexor brevis pollicis being usually regarded as consistmg of two bellies the second of which is inserted into the lateral side of the base of the first phalanx of the' threat toe. The relations of this outer belly and its nerve-supply, however, indi- cate that it belongs to an entirely difterent layer than the medial belly. It will, therefore, be considered later in connection with the interossei (page 663). Fig 628 Os calcis, inner tubercle Abductor hallucis calcaneal origin Internal annular ligament Flexor brevis digitorum, origin Flexor longus hallucis tendon Tibialis posticus tendon Flexor longus digitorum tend Abductor hallucis, part of origin Abductor hallucis, cut Flexor longus hallucis tendon Flexor brevis digit' Flexor longus digitorum First plantar interosseus Flexor brevis hallucis Long and accessorj^ fle of right sole, exposed by al of superficial muscles. 3. Abductor Hallucis (Fig. 627). Attachments. — The abductor hallucis extends along the inner border of the foot, arising from the inner tubercle and surface of the calcaneuni and from the plantar aponeurosis and being inserted, along with the flexor brevis hallucis, into the inner side of the base of the first phalanx of the great toe. Nerve-Supply. — By the internal plantar nerve from the fourth and fifth lumbar and first sacral nerves. Action. — To abduct and flex the hallux. 662 HUMAN ANATOMY. Abductor Minimi Digiti (Fig. 627). Attachments. — The abductor of the little toe (m. abductor digiti quinti) is situated along the outer border of the foot. It arises from the under surface of the calcaneum and from the plantar aponeurosis, and e.\tends distally and laterally to be i?iserted partly into the tuberosity of the fifth metatarsal bone and partly into the lateral side of the base of the first phalan.x of the little toe. Nerve-Supply. — By the external plantar nerve from the first and second sacral ner\'es. Action. — To abduct and fle.x the little toe. Variations — A portion of the abductor digiti quinti frequently separates from the rest of the muscle to form a fusiform belly which has been termed the abductor ossis metaiarsi quinti. It arises from the lateral part of the inferior surface of the os calcis and is inserted, either inde- pendently or in common with the abductor, into the tuberosity of the fifth metatarsal. {bb) The Ml'scles of the Second Layer. I. LUMBRICALES (Fig. 628). Attachments. — The lumbricales are four spindle-shaped muscles which arise from the adjacent borders of the tendons of the fle.xor longus digitorum and from the inner border of its first tendon. They pass distally to the inner surfaces of the first phalanges of the second, third, fourth, and fifth digits, where they are inserted into the membranous expansions of the tendons of the e.\tensor longus digitorum. Nerve-Supply. — The first or first and second muscles, counting from the tibial side, are supplied by the internal plantar nerve ; the remaining three or two are sup- plied from the external plantar from the fourth and fifth lumbar and first sacral ner\'es. Action. — To fle.x and draw medially the second, third, fourth, and fifth toes. Variations. — Absence of one or other of the lumbricales has been noted, the fourth and third being those most frequently lacking ; these same muscles are frequently bifid at their insertions. Small bursas may intervene between the tendons and the first phalanges. The significance of the lumbricales is similar to that of the corresponding muscles of the hand. They arise primarily from the deeper layers of the plantar aponeurosis, and when these differentiate into the tendons of the flexor longus digitorum they come to arise from those structures. (fc) The Muscles of the Third Layer. I. Adductor Hallucis (Fig. 629). Attachments. — The adductor hallucis consists of two portions, often described as two distinct muscles, united only at their insertions. The oblique portion (caput obliquum), or adductor obliqtius, arises from the bases of the second, third, and fourth metatarsals and from the long plantar ligament and passes distally and inward along the interval between the first and second metatarsals, its fibres converging to a strong tendon which unites with that of the transverse portion (caput transversum), or adductor transversus. This extends almost transversely, under cover of the three medial tendons of the long and short flexors and the lumbricales, over the heads of the fourth, third, and second metatarsals. It arises from the capsules of the four lateral metatarso-phalangeal joints and passes medially to join the tendon of the oblique portion. The common tendon so formed unites with the tendon of the first plantar interosseous and is inserted into the sesamoid bone of that tendon and into the lateral surface of the base of the first phalanx of the great toe. Nerve-Supply. — By the deep branch of the external plantar nerve from the fifth lumbar and first and second sacral nerves. Action. — To flex and adduct the hallux. Variations — Some variation occurs in the extent of the origin of both portions of the adductor hallucis. The oblique portion may be limited to the long plantar ligament, or may receive an accessory slip from the shaft of the second metatarsal, while the origin of the trans- verse portion from the fifth metatarso-phalangeal joint may be lacking. It is to be noted that in the fretus the two portions of the adductor are not separated by a wide interval as in the adult, but lie in contact with each other. THE MUSCLES OF THE FOOT. 663 A small muscular slip has occasionally been observed passing from the long plantar liga- ment to the lateral surface of the base of the first phalanx of the second toe. It appears to represent an adductor secundi digiti. Fig. 629. Os calcis. inner tubercle Flexor brevis digitorum- Flexor longus hallucis tendon Flexor longus digitorum tend> Flexor accessorius, inner head Tibialis posticus tendon Os calcis, outer tubercle Abductor minimi digiti Flexor accessorius, outer head ■ I . — ^ — Peroneus longus tendon I Ai-, Long plantar ligament Abductor ossis metatarsi quinti (part of abductor minimi digiti) Abductor hallucis cut Flexor brevis hallucii. First plantar interosseus Adductor hallucis, oblique portion Tendon of flexor longus digitorum Tendon of flexor bre\ is digitorum Flexor longus hallucis tendon Abductor minimi digiti Adductor hallucis, transverse portion nMim \ , \ I' .^ ir- Deep dissection of sole of right foot showing bhort flexors of great and little toes and adductor muscles. {dd) The Muscles of the Fourth and Fifth Layers. I. Interossei plantares. 2. Interossei dorsales. 3. Flexor brevis minihii digiti. As in the hand, the fourth and fifth layers of the pre-axial musculature become united to form the dorsal interossei, portions of the fourth layer remaining distinct to form the plantar interossei. The arrangements in the hand and foot differ, however, in this respect, that in the foot the lateral muscle derived from the fourth layer forms a large, well-developed structure termed the flexor brevis minimi digiti. I. Interossei Plantares (Fig. 630). Attachments. — The plantar interossei are four spindle-shaped muscles. The first is very much stronger than the others, and is often described as the outer head of the flexor brevis hallucis (page 661). It arises, in common with the i^e.xor brevis 664 HUMAN ANATOMY. Long plantar ligament Insertion of peroneus long hallucis, from the inner cuneiform bones and the adjacent ligamentous structures. It extends distally along the lateral surface of the first metatarsal bone and passes over into a strong tendon, which contains a sesamoid bone, and is inserted into the outer surface of the base of the first phalan.x; of the great toe, along with the adductor hallucis. The remaining three muscles are much smaller and arise in succession from the medial surfaces of the third, fourth, and fifth metatarsals, and, passing distally, are inserted by slender ten- FiG. 630. dons into the membranous expansions of the long ex- tensor tendonsof the third, fourth, and fifth toes, on the medial sides of their first phalanges. Nerve-Supply. — By the external plantar nerve from the first and second sacral ner\es. Action. — To flex the first, third, fourth, and fifth toes and to draw the last three medially. Variations. — As above stated, the first plantar inter- osseus is usually described as a second head of the flexor brevis hallucis. It is some- times more or less insepara- ble from the oblique portion ^^^^^ of the adductor hallucis. Adductor i' ' '^ Wwjm. i^^^BB^^m \ obliq ^^ ^ ^ ^^^ ^ 2. InTEROSSEI DORSALES (Figs. 623, 630). Attachments. — The dorsal interossei are also four in number. They arise from the adjacent sides of each pair of met- atarsals and pass distally in the interspaces between these bones. The fibres of each muscle converge to a narro\\' tendon which is inserted into the mem- branous expansions of the extensor tendons over the first phalanges of the sec- ond, third, and fourth toes. The first and second mus- cles insert into the opposite sides of the second toe and the third and fourth into the lateral sides of the third and fourth toes. Nerve-Supply. — By the external plantar nerve from the first and second sacral nerves. Action. — To flex the second, third, and fourth toes ; the first also draws the second toe medially and the rest the second, third, and fourth toes laterally. 3. Flexor Brevis Minimi Digiti (Fig. 629). Attachments. — The short flexor of the little toe (m. flexor digiti quinti brevis), which really represents a fifth plantar interosseus, arises from the base of the fifth Tendonsof fit or brevis hallu and first plant;ii interosseus n fleeted, with ;iti- ductor and ad- ductor tendons, showing the two sesamoid bones J \ Deep dissection of sole of right foot, showing interosseous ! PRACTICAL CONSIDERATIONS : THE LEG. 665 metatarsal and passes distally along the outer side of the fourth plantar interosseus to be inserted by a tendon into the outer surface of the base of the first phalanx of the fifth toe and also into the distal portion of the fifth metatarsal. Nerve-Supply. — From the external plantar ner\re from the second sacral ner\-e. Action. — To flex the fifth toe and draw it lateralward. Variations. — The portion of the flexor brevis minimi digiti which passes to the fifth meta- tarsal is frequently more or less distinct from the rest of the muscle, and has then been termed the opponens giiinti digiti. {6) THE POST-AXIAL MUSCLES. I. Extensor Brevis Digitorum (Fig. 624). Attachments. — The short extensor of the toes (m. extensor digitorum brevis) arises from the lateral and superior surfaces of the calcaneum. It passes distally beneath the tendons of the extensor longus digitorum and divides into four portions, the outer three of which soon become tendinous and are inserted by fusing with the tendons of the extensor longus to the second, third, and fourth toes over the first phalanges of those toes; the innermost tendon is inserted into the base of the first phalanx of the great toe. Nerve-Supply. — By the anterior tibial nerve from the fourth and fifth lumbar and first sacral nerves. Action. — To extend and draw laterally the first, second, third, and fourth toes. Variations. — Occasionally one or other of the tendons of the extensor brevis may be doubled, this condition being most frequent in the tender, -io the second toe ; sometimes a fifth tendon passes to the little toe. The innermost tendon is nearly always much stronger than the others ; the fibres which insert into it are occasionally separate from the remainder of the muscle, then forming the extensor brevis hallucis. PRACTICAL CONSIDERATIONS: MUSCLES AND FASCIA OF THE LEG, ANKLE, AND FOOT. I. The Leg. — The skin over the leg is everywhere more adherent to the un- derlying fascia than it is in the thigh. Its inability at certain places, as over the spine and antero-internal surface of the tibia, to glide away when force is applied pardy accounts for the frequency with which bruising or laceration, superficial ulceration, or even periostitis or caries follows injuries to the "shin." The deep fascia blends with the periosteum at ihe head and inner and anterior borders of the dbia, at the head of the fibula, and at the two malleoli. It is thicker and denser above and anteriorly than below and posteriorly. The two septa (Figs. 627, 623) that run inward from it on the outer side of the leg and are attached to the anterior and external borders of the fibula constitute an osseo-aponeurotic space that contains the peroneal muscles and that may, for a time, limit the spread of infection or of suppuration. The peronei, in their compartment, and, farther in, the bones and interosseous membrane, separate the anterior group of muscles — the tibialis anticus, extensor communis, etc. — from the posterior group. The fascia over the anterior group embraces them so closely, that when it is wounded or torn the muscle-fibres protrude and approximation of the edges of the fascial wound may be difficult. In the anterior compartment the muscles are intimately adherent to its fibrous walls, as is the case in the forearm, but not in the arm or thigh (Tillaux). In the posterior compartment, on the contrary, a loose layer of connecdve tissue intervenes between the gastrocnemius and the deep fascia, and permits the greater degree of motion between the muscle and the aponeurosis necessitated by the greater range of motion in plantar, as compared with dorsal, flexion of the foot. The difference will be noted in dealing with wounds involving these regions, or in some operations, as amputation of the leg. The septum, anteriorly, at the upper third of the leg, between the tibialis anticus and extensor longus digitorum, is of variable density, gives no indication of its pres- 666 HUMAN ANATOMY. ence on either the skin or fascial surface, and although described as a guide to the anterior tibial arterj- {q.v.), is untrustworthy on account of the difficulty of recog- nizing it (Treves). Posteriorly the deep layer of fascia that holds down the deep muscles to the tibia and libula and runs transversely beneath the soleus and gastrocnemius, is weaker above, where it is covered and reinforced by the latter Fig. 631. muscles, and stronger below, where it loses their sup- port. It is continued downward and separates the tendo AchUlis from the deeper structures. In ap- proaching the vessels behind the malleolus, one finds, therefore, two layers of deep fascia. Growths originating in the head of the tibia or occupying the interosseous space are much influenced by the resistance of the deep fascia, which, as is the case with the fascia lata, may for a time determine their shape and direction and alter their surface ap- pearance and their apparent density. Cellulitis and abscess are for a while confined beneath the fascia, but, like the coloring matter of the blood after fracture, may soon find their way to the surface by following the vessels that perforate it. Some fibres of the gastrocnemius or, more fre- quently, the tendo Achillis at its weakest point, on a level with the internal malleolus, may be ruptured during strong effort, as in raising the body on the toes while bearing a weight. Sometimes, however, this accident follows comparatively trifling e.xertion. 2. The Ankle and Foot. — The skin around the ankle and upon the dorsum of the foot is thin and la.x. The absence of a fatty or muscular layer between it and the subjacent bones and the distance of the region from the centre of circulation make gangrene from relatively slight contusion, or from the pressure of splints or dressings, more common here than elsewhere. Over the sole, especially at those places which normally bear the weight of the body, — the heel, the ball of the great toe. the line of the heads of the metatarsal bones (page 452), and the outer side of the foot, — the skin is much denser. It often contains callosities which cause pain by pressure and are usually the result of friction between the sole and an ill-fitting shoe. Its close connection with the underlying plantar fascia is similar to that between the skin of the palm and the palmar fascia, and between the skin of the scalp and the occipito-frontalis aponeurosis, in all of which regions the integument is exceptionally thick and dense, and in the former two hairless (page 491 ). Under the heel the thick skin and the pad of subcutaneous fascia containing fat are especially valuable in lessening the force of falls upon that part of the foot, where there is no elastic arch composed of a number of bones and joints to take up and distribute the force, as do both the transverse arch and the anterior pillar of the main arch (page 436). This tissue, vertical and scanty in the sole, is loose and abundant on the dorsum and around the tendo Achillis, in which latter region it contains some fat. Its la.xity over the dorsum, while it somewhat protects the instep from the effects of direct violence, adds greatly to the ease with which swelling or oedema may occur in cellulitis or, on account of the dependent position of the part and its remoteness from the heart, in anasarca. The deep fascia at the ankle is thickened on the dorsum and sides to form the annular ligaments, the chief function of which is to hold in place the tendons that move the foot and toes. Anteriorly this is done by two bands, beneath the upper of which the tendon of the tibialis anticus runs, while the lower covers in the tendon of the same muscle and those of the extensor proprius poUicis and of the extensor com- Dissection of fracture of left tibia. showing eltect of muscular action on fragments. PRACTICAL CONSIDERATIONS : ANKLE AND FOOT. 667 munis and peroneus tertius, the last two running in one sheath. Internally — i.e., between the heel and the internal malleolus — the tendons of the fle.xor longus pol- licis, the fle.xor longus digitorum, and the tibialis posticus run beneath the internal annular ligament, the last named being the deepest and in the closest pro.ximity to the ankle-joint, disease of which may originate in the tendon. The relation of the flexor longus pollicis tendon to the posterior ligament is intimate, and is believed to be of advantage in resisting posterior luxation of the astragalus (page 450 j. The peroneus longus tendon is thought to be more frequently displaced than any other tendon in the body. When this accident happens, the tendon slips from its groove behind the external malleolus and over the thin posterior border of the latter to its anterior face. This dislocation is favored by (a) the length and slender- ness of the tendon ; (^) the shallowness of the groove in which it runs ; (c) the relative weakness of the single slip of the external annular ligament that covers the tendon; (if) the fact that it changes its direction twice between the lower third of the leg and its insertion, — i.e. , once at the malleolus and once at the margin of the cuboid. Disease of the sheaths of the tendons about the ankle-joint is not rare, is apt to be tuberculous, and is favored by the frequent strains and the exposure to cold and wet to which they are subjected, and by their dependent position and remoteness from the heart. Their relation to disease of the tarsal bones should be remembered (page 437). The appro.ximately vertical .direction of the swelling in the early stages is some- times of use in differentiating teno-synovitis from ankle-joint disease (page 451). The involvement of the tendon-sheaths in sprain of the ankle-joint (page 450) adds to the duration of the disability produced by that accident. On the sole of the foot the dense plantar fascia is of importance in relation to infection or suppuration beneath it. Of its three divisions (page 659), the central one is much the strongesf. With the intermuscular septa that run from its lateral bor- ders into the sole and separate the flexor brevis digitorum from the abductor minimi digiti externally and from the abductor hallucis internally, it makes a compartment . the floor of which is rarely penetrated by inflammatory or purulent effusions. An abscess beginning in the mid-region of the sole beneath the plantar fascia may pass forward betvveen the digital slips or upward through the interosseous spaces, or along the tendon-sheaths to the ankle. More rarely apertures in the plantar fascia permit suppuration to spread through it to the subcutaneous region of the sole. The abscess cavity then consists of two portions connected by a narrow neck, abces en bouton de chemise (Tillaux). The lateral progress of such an abscess — through the intermuscular septa above described — is easier than penetration of the strong central leaflet of the plantar fascia. It will be noted that the three compartments into which the sole is then divided are analogous to the thenar, hypothenar, and central divisions of the palm. Con- traction of the plantar fascia, which aids in maintaining the curve of the arch of the foot, as a string would that of its bow, increases that arch, is often associated with the different forms of talipes, and is thought to be one of the common causes of a subvariety, — -pes cavus. Relaxation or elongation of the plantar fascia favors depres- sion of the normal arch, and hence contributes to the development of the condition known as "flat-foot" (^pes planus^ {vide ififra). Club- Foot. — The mechanics of the normal foot have already been sufificiently described (pages 436, 447). Of the deformities, either congenital or acquired, which are grouped under the name club-foot, it is necessary to describe, from the anatomical stand-point, only the chief varieties. I. Talipes eqicino-varus , when congenital, is believed to result from retention of the foetal position, — i.e., from defective development. The inward rotation of the fle.xed and crossed limbs in utero, which in the later periods of foetal life removes the pressure from the fibular side of the legs and the dorsum of the feet and puts the latter in the position of extreme fle.xion with the soles — instead of the tops — of the feet against the uterine walls (Berg), does not take place. This is the commonest of all the forms of club-foot. When it is acquired, it may be due to paralysis of those muscles that oppose the adduction and extension pf the foot, — i.e., chiefly of 668 HUMAN ANATOMY. the extensor longus digitorum and the peronei. The muscles that draw up the heel, — the gastrocnemius and soleus, — the muscles that elevate the inner border of the foot and adduct it, — the tibalis anticus and posticus and the flexor longus digitorum, — are not resisted ; or, if the case is congenital, are assisted by the position of the foot, which is therefore found with (a J the heel elevated ; (b) the inner edge of the sole drawn upward ; (c) its axis turned inward ; {d) the sole shortened, partly through contraction of the plantar fascia. In marked cases the calcaneum will be almost vertical, as will the astragalus, which will also be rotated forward so that its head may have two articular facets, one of them projecting on the dorsum; the scaphoid is atrophied and is close to the inner malleolus; the cuneiform bones accompany it, and the cuboid becomes the chief point of support of the weight of the body. Corresponding changes occur in the metatarsal bones and phalanges, which may be at right angles to the line of the inner side of the leg. Pure talipes varus, in which the elevation of the heel is absent, is very rare. The other varieties of club-foot are seldom congenital. 2. Talipes Valffus. — The foot is abducted and the outer border elevated by the peronei, the inner side being correspondingly depressed and the arch of the foot flattened out. 3. Talipes Eqninus. — The heel is drawn up by the gastrocnemius and soleus ; the patient walks on the balls of the toes ; the os qalcis and the astragalus are changed in position as in equino-\arus. The astragalo-scaphoid and calcaneo- cuboid joints are much Hexed, so that the scaphoid may even be in contact with the OS calcis. 4. Talipes Calcaneus. — The extensor longus digitorum and the extensor pro- prius pollicis raise the toes and with them the foot, so that the anterior portion of the OS calcis is elevated and the astragalus is rotated backward until its articular sur- face points in that direction. The patient walks on the heel. Flat-foot results from weakness or relaxation of plantar muscles, fascise, and ligaments, especially the inferior calcaneo-scaphoid (page 445). When, in persons who stand much of their time,, or in those with defective ankles originally, this liga- ment yields, the head of the astragalus is carried downward and inward by the body weight, which, owing to the width of the pelvis, the obliquity of the femur, and the curve of the tibia, is transmitted to the astragalus somewhat from without inward. This is associated with abduction of the foot, resisted by the internal lateral and calcaneo-astragaloid ligaments. This sinking of the astragalus and increased promi- nence of the internal malleolus may be seen in many normal feet when the weight of the body is thrown on one foot (page 449). In well-marked cases of flat-foot the tibialis posticus fails to resist this change effectually, the peronei add to the abduction or shortening, the arch of the sole of the foot entirely disappears or may even become a rounded downward curve, the deltoid ligament stretches, as do the long and short plantar ligaments, and the head of the astragalus, the scaphoid tubercle, and the sustentaculum tali (page 449) become unduly prominent and may be the main points of support. Two bursae about the foot are of enough importance to demand attention. The retrocalcaneal bursa lies between the os calcis and the tendo Achillis, the depressions at the sides of which are effaced when the bursa is distended. The cor- responding obliteration of the anterior depressions just beneath the malleoli (page 451), which occurs in ankle-joint disease, does not take place. Flexion or extension of the foot or contraction of the calf muscles is painful. Bunions. — There mav be normally a bursa over the metatarso-phalangeal joint of the great toe, or an " adventitious" bursa — formed by dilatation of lymph-spaces, condensation of connective tissue, and localized effusion — may de\elop there, as a result of pressure and friction from badly fitting shoes. The great toe is_ forced out- ward, the internal lateral ligament of the articulation is elongated, the joint is made unduly prominent, the head of the first metatarsal bone sometimes enlarges, and the cartilage over its inner surface not uncommonly atrophies and disappears, leaving a communication between the bursal sac and the synovial cavity of the joint. Flat- foot and all degrees of valgus tend to produce a similar condition by exposing the SURFACE LANDMARKS : THE LOWER EXTREMITY. 669 inner border of the foot — and thus the first metatarso-phalangeal joint — to excessive pressure. Adventitious bursse are found over the external malleolus, — "tailor's bursa," — over the cuboid in equino-varus, and at other points exposed to pressure in the different forms of club-foot. SURFACE LANDMARKS OF THE LOWER EXTREMITY. I. The Buttocks and Hip. — The iliac furrow (page 349) indicating the line of the crest of the ilium, with the external oblique above and the gluteus medius below, passes forward to the anterior Fig. 632. superior spme, and is more or less effaced posteriorly where the crest is covered by the flat tendon of the erec- tor spinae. The posterior superior spine is always indicated by a surface depression. In women the continuous layer of fat passing from the loin to the but- tock blends the surface forms of these regions into one uniform curve (Thom- son), and there is no such marked defi- nition of them as is seen in the male. The rounded prominence of the buttock (Fig. 632) is due partly to subcutaneous fat, partly to the thick muscular mass of the gluteus maximus, especially developed in man by reason of his assumption of the upright po- sition. It is more prominent posteri- orly, becomes flattened as it passes outward, and ends in a distinct de- pression (Fig. 632) at the tendinous insertion of that muscle just behind and below the greater trochanter. Al- though the trochanter is on a plane external to that of the iliac crest, the hollow between it and the ilium is so obliterated by the gluteus medius and minimus muscles that it ordinarily does not appear as a surface prominence. It§ upper border — on a level with the centre of the acetabulum — is indistinct on account of the presence of the glu- teus medius tendon which passes over it to be inserted into the outer surface of the trochanter. In front the muscular eminences where the region of the buttock passes into that of the hip are due to the glu- teus medius above and more anteriorly to the tensor facise latse (Fig. 632), which shows as a broad elevation just behind a vertical line drawn through the anterior superior spine and just below the forepart of the iliac crest. It can be best seen if the thigh is in abduction and inward rotation. As the skin of the buttock is made tense when the thigh is flexed on the pelvis, the fold of the nates (gluteo-femoral crease), due to creasing or drawing in of the skin, is formed when the thigh is extended. It begins just below the level of the 670 HUMAN ANATOMY. tuberosity of the ischium, runs horizontally outward, and crosses the middle of the lower edge of the gluteus maximus, part of which — the inner — is therefore above it and part — the outer — below it. In flexion of the hip the gluteus maximus is flattened and the skin stretched over it, and hence this fold is more or less completely effaced. As flexion is an almost constant early symptom of hip-joint disease (page 381), and is usually associated with atrophy of the muscles moving the joint, the obliteration of the gluteo-femoral crease, characteristic of this disease, can readily be understood. In women, on account of the thickness of the supragluteal layer of fat, the gluteo- femoral crease is longer and deeper than in men. The various bony points of this region have been described (pages 345, 349), as have the different lines and measurements employed in the diagnosis of fractures of the neck of the femur and of dislocation (pages 362, 364, 367). 2. The Thigh. — (a) Anterior crural region. The hip passes insensibly in front and below into the region of the thigh. The inguinal furrow, a valuable land- mark, separates the surface of the abdomen from that of the thigh (page 1774). It indicates the line of Poupart's ligament, which may be felt, in the absence of much subcutaneous fat, from the iliac spine to the pubic spine, more easily over its inner half, and still more easily if the thigh is in extension, abduction, and outward rotation. The ligament is relaxed by flexion, adduction, and inward rotation of the thigh, and with it, to some extent, the deep fasciae of the thigh and abdomen ; therefore that position is the one most favorable to reduction of either inguinal or femoral hernia by taxis (pages 1770, 1774). Below this a second furrow — " Holden's line" — is sometimes seen with the thigh in slight flexion, beginning at the scroto-femoral angle and becoming less distinct until it is lost at or over the supratrochanteric space. It runs across the front of the cap- sule of the hip-joint and is lost in the presence of synovitis of that joint. It is often indistinct, and in some subjects cannot be made out at all (Treves). On the line of this furrow, and just external to a vertical line drawn through the middle of Poupart's ligament, the head of the femur can sometimes be made palpable by extension and rotation of the thigh, but this is rarely possible in fat or muscular persons. The depression or flattening of Scarpa's triangle (page 639) can usually be seen. The tendon of origin of the adductor longus — made prominent by abduction — and the upper portion of the sartorius, emphasized by flexion and outward rotation of the thigh with the knee bent, mark its inner and outer borders respectively. The sar- torius, continued downward, becomes flattened and is lost in the rounded fulness on the inner side of the knee. Just internal to a line bisecting the triangle the femoral artery may be felt and its pulsations sometimes seen. A very trifling depression is occasionally present near the inner angle at the base of the triangle, and then indi- cates the position of the saphenous opening (page 635), the centre of which is from one to one and a half inches below and the same distance external to the pubic spine, which is on a transverse line drawn through the upper margin of the greater trochan- ter. From the apex of the, triangle the shallow groove, extending towards the inner side of the knee, marks the course of the sartorius and the interval between the quad- riceps extensor and the adductors. To the outer side of the triangle the rectus can be seen, showing below the anterior superior spine in the interval between the sartorius and the tensor fasciae latae ; it runs down the front of the thigh, giving it its convex fulness, and narrowing to its ending in the flattened quadriceps tendon, the edges of which stand out when the leg is strongly extended on the thigh. The obliteration of Scarpa's triangle, in full extension of the thigh, is due to the thrusting forward of the overlying tissues by the neck and the upper end of the shaft of the femur. To the inner side of Scarpa's triangle, below and posteriorly to the adductor longus, the other adductors and the gracilis give the rounded outline to the inner side of the upper thigh. Near the knee, when the leg is flexed, the tendon of insertion of the adductor magnus can be plainly felt between the sartorius and vastus internus. The latter muscle stands out along the lower half of the thigh and is still more promi- nent near the knee, where it becomes superficial between the rectus and the sartorius. On the outer side the vastus externus gives the thigh its broad, slightly convex surface, down the centre of which there is sometimes a slight vertical groove indi- SURFACE LANDMARKS: THE LOWER EXTREMITY. 671 Fig. 633. Poupart's ligament -Scarpa's A eating the position of the iho-tibial band of fascia between the insertions of the tensor fasciae latae and gluteus maximus and the external tibial tuberosi'ty. More pos- teriorly a distinct longitudinal depression corresponds to the external intermuscular septum, between the vastus externus and the short head of the biceps. At the lower third of the thigh this groove indicates the line of nearest approach of the shaft of the femur to the surface. Elsewhere it is usually so covered by muscular masses that it is not to be felt, even indistinctl}^. The corresponding internal septum— between the vastus internus and the adductors and pecti- neus — produces no surface marking. {b) Posterior crural regio?i. The ham- strings, descending from beneath the lower edge of the gluteus maximus, cannot at first be separately identified. Lower, a very slight depression may mark the interval between the semimembranosus and the semitendino- sus, and the biceps tendon becomes a salient rounded cord. When the limbs are straight with the knees together there should be but a slight interval between the thighs, and that only where the sartorius muscles curve back to lie along the inner surface of the limb. In women, owing to the greater quantity of sub- cutaneous fat, the thighs may be in contact all the way down (Thomson). 3. The Knee. — On the anterior sur- face the quadriceps tendon and the ligamen- tum patellae are made more prominent by strong extension of the leg, and on each side of the ligament the little eminence made bv the protrusion of the soft subpatellar fat becomes visible. The angle made by the axes of the tendon and ligament should be noted (page 418). The oudine of the patella is easily felt and can usually be seen. Above it is a slight depression. At its sides are two concavities — the inner of which is a little more marked, as the inner border of the patella is the more prominent — which in fat persons may disappear, as they do, together with the su- prapatellar depression, in synovitis of the knee-joint (page 413). Both anteriorly and laterally the landmarks have been sufficiently described (pages 367, 390). Posteriorly the popliteal space — the ham — is slightly convex during extension of the leg and deeply concave when it is flexed. The boundaries, the relations of the ham- string tendons, of the ilio-tibial band externally and of the sartorius tendon internally have been described (pages 409, 646). At the lower portion of the space the con- verging fleshy bellies of the gastrocnemius may be felt. 4. The Leg. — The landmarks relating to the tibia (page 390) and fibula (page 396) have been described. Between these bones the belly of the tibialis anticus causes a distinct prominence, to the fibular side of which is the narrower and less-marked elevation due to the extensor longus digitorum. Below the middle third of the leg these muscles are tendinous, but by dorsal flexion of the foot and of the toes (exten- Tubercle of tibia ght leg, showing f subject. 672 HUMAN ANATOMY. sion) they can be made to stand out with the tendon of the extensor proprius hallucis between them ; to the outer side of the extensor longus digitorum tendOn a slight groove indicates the interval between that muscle and the peroneus tertius. The latter — as a muscle peculiar to man and probably developing as a result of his assump- tion of the erect posture — is not invariably present. Above, between the extensor longus digitorum and the soleus, the peroneus longus makes alongitudintil elevation shading off below — where the fleshy fibres become tendinous — into the flatter pero- neus brevis. Posteriorly the swell of the calf is formed by the gastrocnemius, and its surface markings are due to the peculiar arrangement of the fleshy and tendinous portions of that muscle. When the calf muscles are in action, as in standing on the toes, it will be seen that the inner head is the larger and descends somewhat lower than the outer head ; and the lateral borders of the soleus will be seen coming to the surface beyond the lower part of the gastrocnemius and the tendo Achillis and showing as curved eminences, of which the outer is the longer. 5. The Ankle and Foot. — The bony landmarks have been described (pages 390, 396, 437, 449, 453;. At the front of the ankle the extensor tendons are easily recognized. The largest and most internal is that of the tibialis amicus ; then, in order, the extensor proprius hallucis, extensor longus digitorum, and — when present — the peroneus ter- tius. Beneath the tendons of the long extensor and just below the external mal- leolus, the fleshy belly of the short extensor of the toes, filling the space between the OS calcis and astragalus, can easily be felt as a soft swelling over the outer part of the tarsal region, and is distinctly visible when in action. On either side of the tendi- nous elevation, on a level with the line of the ankle-joint and in front of each malleolus, is a little depression. This is effaced when the capsule is distended by effusion (page 451). The two fleshy masses on the inner and outer border of the foot are due respectively to the abductor and flexor brevis hallucis and the ab- ductor and flexor bre\'is minimi digiti. The dorsal interossei project upward slightly between the metatarsal bones. The lines on the dorsum of the foot corresponding to the various joints have been described (page 453). Behind the ankle and at the sides of the tendo Achillis — between it and the pos- terior surfaces of the malleoli — are two concavities, of which the outer is the deeper. In it the tendons of the peroneus longus and brevis may be felt, the latter the nearer to the fibula. In the inner concavity lie, in order from the malleolus backward, the tendons of the tibialis posticus, the flexor longus digitorum, and the flexor longus pollicis. On the sole of the foot the abductors of the great and little toes show somewhat on the surface, but the chief outlines are determined by the arch of the foot, the strong plantar fascia, and the thick integument. The digital creases have but little practical value. As the foot, taken as a whole, acts as a lever, and as the calf muscles are attached to the heel, — the short end of such a lever, — it follows that the develop- ment of these muscles will stand in some relation to the length or projection of the heel. As a short lever will require the application of a greater force to produce the same result than will a long lever, we find the most marked muscular develop- ment of the calf associated with a short foot and a short heel, while a long foot and a long heel are the usual concomitants of a poorly developed calf (Thomson). The athletic feats of some runners with poorly developed calves may sometimes be explained by observing the unusual length and projection of the heel. THE VASCULAR SYSTEM. The vascular system is composed of the organs immediately concerned in the circulation throughout the body of the fluids which convey to the tissues the nutritive substances and oxygen necessary for their metabolism and carry from them to the excretory organs the waste products formed during metabolism. The system is usually regarded as being composed of two portions, the one con- sisting of organs in which circulates the red fluid which we term blood, while the organs of the other contain a colorless or white fluid known as lymph or chyle ; the former of these subsystems is the blood-vascular system and the latter is the lyinphatic system. It must be recognized, however, that the two systems communicate, and that the lymphatic system develops as an outgrowth from the blood-vascular system ; so that while it proves convenient for descriptive purposes to regard the two systems as distinct, nevertheless, they are intimately associated both anatomically and embryo- logically. THE BLOOD-VASCULAR SYSTEM. The blood-vascular system consists of ( i ) a system of canals known as blood- vessels, traversing practically all parts of the body, and (2) of a contractile organ, the heart, by whose pulsations the blood is forced through the vessels. The vessels are again divisible into ( i ) vessels which carry the blood from the heart to the tissues and are known as arteries, (2) exceedingly fine vessels which form a net-work in the tissues and are termed capillaries, and (3) vessels which return the blood from the tissues to the heart and are known as veins. THE STRUCTURE OF BLOOD-VESSELS. Although passing into one another insensibly and without sharp demarcation, where typically represented the arteries, capillaries, and veins present such character- istic histological pictures that they are readily distinguished from one another. All blood-vessels, including the heart, possess an endothelial lining which may constitute a distinct inner coat, the tunica inthna, or, as in the capillaries, even the entire wall of the vessel. Usually, however, the intima consists of the endothelium reinforced by a variable amount of fibro-elastic tissue in which the elastica predomi- nates. Except within the walls of capillaries, external to the intima lies a thick middle coat, the tunica media, which typically is composed of intermingled lamellae of involuntary muscle and elastica and fine fibrillse of fibrous tissue. Outside the media follows the tu?iica externa or adventitia, which, although usually thinner than the middle coat, is of exceptional strength and toughness — characteristics conferred by its fibro-elastic tissue and upon which the integrity of a ligature often depends. It should be noted that the endothelial tube is the fundamental and primary structure in all cases, the other coats being secondary and variable according to the size and character that the vessel attains. The customary division into the three coats is more or less artificial and in the larger vessels is often uncertain. The recognition of an inner endothelial and an outer musculo-elastic coat often more closely corresponds to the actual arrangement of the tissues than the conventional subdivision into three tunics. The endothelial lining of the arteries consists of elongated spindle-shaped plates united by narrow sinuous lines of cement substance which, after silver-staining, map out the irregular contours of the cells with diagrammatic clearness (Fig. 634). At the junction of the plates, occasional accumulations of the cement substance mark minute intercellular areas, the stigmata, that indicate points of less accurate apposi- tion. Within the veins, the endothelial plates are shorter and broader than in the arteries, approaching somewhat irregular polygons in outline. The demarcation of 43 673 674 HUMAN ANATOMY. the endothelium into distinct cells is less evident in the capillaries than in the larger vessels, in some cases a continuous syncytial sheet replacing the definitely outlined plates. The presence of a relatively small oval nucleus is readily demonstrated by suitable stains. The involuntary muscle varies in amount, from the imperfect single layer of muscle-cells found in the arterioles, to the robust muscular coat of many lamellae in the larger arteries. It is relatively best developed in arteries of medium size, where the muscle occurs in distinct broad or sheet-like bundles between the strands of elastic tissue. The component fibre-cells are short and often branched and, for the most part, circularly disposed. The distribution of the muscular tissue is much less regular and constant in the veins than in the arteries, since in many it is scanty, in some entirely wanting, and in a few veins excessive, occurring in both circular and longitudinal layers. The striated muscle found in the large vessels communicating with the heart resembles that of the cardiac wall from which it is derived. Connective-tissue is represented in the arteries and veins by both fibrous and elastic tissue. The former is present as delicate or coarser bundles of fibrillae that extend between the other components of the vascular wall. Fig. 634. 1 of aiteriole after silver-staining ; X 200. B, endotlielial ( more highly magnified. X 500. The elastic tissue is very conspicuous in all arteries save the smallest, and in many veins. It presents all variations in amount and arrangement from loose net- works of delicate fibres in the smaller vessels to robust plates and. membranes in the largest arteries. Within the intima of the latter, the elastica often occurs as sheets broken by pits and perforations, which are, therefore, known as fenestrated mem- branes. Nutrient blood-vessels are present within the walls of all the larger vessels, down to those of i mm. in diameter, and provide nourishment for the tissues com- posing the tubes. These vasa Z'asorum, as they are called, are usually branches from some neighboring artery, their favorite situation being the external coat within which they ramify, breaking up into capillaries that, in the larger vessels, invade the adja- cent media. The blood from the vascular wall is collected by small veins that accom- pany the nutrient arteries, or, as in the case of the veins, empty directly into the venous trunk in whose walls they course. Lymphatics are represented by spaces both within the muscular tissue and beneath the endothelium. In certain situations, conspicuously in the brain and the retina, the blood-vessels are enclosed within lymph-channels, the perivasciilar lymph- shcaths, that occupy the adventitia. The nerves distributed to the walls of blood-vessels, especially to the arteries, are numerous and include both sympathetic and spinal fibres. The former are des- STRUCTURE OF BLOOD-VESSELS 675 tined particularly for the muscular tissue and, therefore, are directed to the media, althouo-h vessels in which muscle is wanting, as in certain veins and the capillaries, are not without nerves. From the plexus that surrounds the vessel, notably rich about the arteries, nerve-iibrilla; penetrate the media and end among the muscle- fibres in the manner usual in such tissue (page 1015). Special sensor>- nerve- endino-s have been described in both the external and internal tunics. The Arteries. — Since the arrangement of the component tissues is most typical in arteries of medium size (from 4-6 mm. in diameter; , the radial artery may appropriately serve for description. Seen in cross-section (Fig. 635), after the usual methods of preservation and staining, the intima presents a plicated contour as it follows the foldings of the internal elastic membrane that appears as a conspicuous corrugated light band marking the outer boundars' of the inner tunic. The lining endothelial cells are so thin that in profile their presence is indicated chiefly by the slightly projecting nuclei. Between the endothelium and the elastic membrane the Fig. 635. Involuntar>" muscle Transverse section of artery of medium size. X 150. intima includes a thin layer of fibrous and elastic fibrillae. The media, thick and conspicuous, consists of circularly disposed flat bundles of involuntary muscle sepa- rated by membranous plates of elastic tissue, that in the section appear light and unstained. After the action of selective dves, as orcein, the elastica is very con- spicuous (Fig. 636). Delicate fibrillae of fibrous tissue course among the musculo- elastic strands. Beneath the outer coat, the elastica becomes condensed into a more or less distinct external elastic membrane that marks the outer boundary^ of the media. The adventitia varies in thickness, in the medium-sized arteries being relatively better developed than in the larger ones. It consists of bundles of fibrous tissue intermingled with elastic fibres of varying thickness. The adventitia contains the vasa vasorum and chief lymph-channels of the vascular wall. Followed towards the capillaries, the coats of the artery' gradually diminish in thickness, the endothelium resting directly upon the internal elastic membrane so long as the latter persists, and afterwards upon the rapidly attenuating media. The elastica becomes progressively reduced until it entirely disappears from the middle 676 HUMAN ANATOMY. coat, which then becomes a purely muscular tunic and, before the capillary is reached, is reduced to a single layer of muscle-cells. In the precapillary arterioles the muscle no longer forms a continuous layer, but is represented by groups of fibre-cells that Fig. 636. External elast Transverse section of artery of mediun stained to show elastic tissue. X '• partially wrap around the vessel, and at last are replaced by isolated elements. After the disappearance of the muscle-cells, the blood-vessel has become a true capillary. The adventitia shares in the general reduction and gradually diminishes in thickness until, in the smallest arteries, it consists of only a few fibro-elastic strands outside the muscle-cells. In the large arteries, on the other hand, the intima and media chiefly undergo augmentation. Although the inner coat greatly thickens and contains a large amount of fibrous tissue and elastica, a conspicuous internal elastic membrane, as seen in the smaller vessels, is lacking, since the elastic plates and membranes are now so abundant that the local accumulation is no longer striking, the boundary between the inner and middle coats being, therefore, less ^'°- ^■37- sharply defined. The character of the thickened media also changes, the muscular tissue be- ing relatively reduced and over- shadowed by the excessive de- velopment of the fibro-elastic tissue, which is arranged in reg- ularly disposed lamellae separa- ting the muscle-bundles and conferring a more compact and denser character to the wall of the vessel. The adventitia, while relatively thinner than in arteries of medium size, is also increased and consists of robust fibres and plates of elastica, many of which are longitudinally disposed and irreg- ular, although strong, bundles of fibrous tissue. E.xceptionally, longitudinal strands of muscle appear in the outer coat next the media. In the roots of the aorta and lar coat is reduced to STRUCTURE OF BLOOD-VESSELS. 677 A distinct internal .-^gs I "™* pulmonary artery, the media consists chiefly of striated muscle which resembles that of the myocardium with which it is continuous, both vessels having been derived from a common trunk, the bulbus arteriosus, the anterior segment of the primary heart-tube. The Veins. The walls of the veins are always thinner than those of corre- sponding arteries and are more flaccid and less contractile in consequence of the smaller amount of elastic and muscular tissue that they contain. In veins of medium size (from 4-8 mm. in diameter), the inhma consists of the linino- endothelium, the cells of which are relatively broad and short,^ a thin layer of fibrous connective tissue and net-works of fine elastic fibres, elastic membrane is seldom pres- ent, at most a condensation of F'^. 638. elastic fibrillee marking the outer limit of the inner coat. In some veins, as the cephalic, basilic, femoral, long saphenous, and pop- liteal, bundles of smooth muscle occur within the intima. In ad- dition to the circularly disposed thin sheets of muscular and fibro- elastic tissue, the media contains fibro-elastic plates, sometimes mingled with a few bundles of muscle-cells, that extend longi- tudinally. In certain veins, as in the saphenous, deep femoral, and popliteal, the longitudinal fibres may constitute a zone beneath the intima to the exclusion of the inus- cular tissue. The adventitia is often thicker than the media, and consists of interlacing fibres and net-works of fibro-elastic strands, the general direction of which is lengthwise. In many veins, par- ticularly in those of the lower ex- tremity, the outer coat contains bundles of longitudinally disposed muscle-cells. The valves with which many veins are provided consist of paired crescentic folds (Fig. 641) of the intima, covered on both sides with endothelium, containing a small amount of fibro-elastic tis- sue. The attached border of the leaflets ends in narrow prolonga- tions that extend beyond the free margin of the valve. Between the leaflets of the valve and the wall of the vein lie the pocket-like si- nuses, which the blood distends when the valve is closed. In the structure of their walls, the large veins present many deviations frorn the typical arrangement. While the intima is only exceptionally increased, as in the hepatic part of the inferior vena cava and the beginning of the portal vein, the media is often markedly thickened. This increase is chiefly due to augmentation of the elastic and fibrous tissue, the mus- cle remaining comparatively scanty. * The splenic and portal veins, however, are particularly ■ rich in muscular tissue ; on the other hand, the media may be almost wanting, as in the greater part of the inferior vena cava and the larger hepatic veins. ; section of abdominal aorta. X 90. 678 HUMAN ANATOMY. Lack of muscle within the media is often compensated by an unusual develop- ment of such tissue in the adventitia; in some large veins, as in the hepatic portion of the inferior cava, su- FiG. 639. -^'#=^ "^a^iSsiias^* Transverse section of pulmonary artery 1 showing striated muscle, xr perior mesenteric, or external iliac, the in- ner half or two-thirds of the outer coat is occupied by robust bundles of longitudi- nally arranged muscle. In some cases, how- ever, as in the renal and portal veins, the longitudinal muscle in- vades the entire thick- ness of the adventitia, or, as in the supra- renal vein, the muscle of the outer tunic may include both circular and longitudinal layers. The walls of the small veins ( less than .4 mm. in diameter) consist of only endo- thelium and connective tissue. The latter rep- resents a relatively ro- bust adventitia and a feebly developed me- dia, muscle-fibres being wanting. Traced tow- ards the capillaries, the connective tissue gradually diminishes until the endothelial coat alone remains. In passing into veins of medium size, at first the muscle-cells are short and scattered and only partly encircle the tube. Far- ther along the elastica appears in the form of delicate fibres and net-works that increase in size and density as the muscu- lar tissue becomes more pro- nounced. It is worthy of mention that certain veins, no- tably those of the brain and pia mater, the dural sinuses, and the blood-spaces of cavernous tissue, are usually entirely devoid of muscle, although in the walls of some of the larger cerebral veins, small strands of such tissue occur. The Capillaries. — The most favorable arrangement for efficient nutrition is mani- ^^ festly one insuring the passage of the blood-stream at a re- duced rate of speed in inti- mate relations with the tissue-elements. These requirements are met in the capil- laries whose collectively increased cal'bre and thin walls favor slowing of the biood- Fi(j 640 _^T:¥a.^ (l(v f r .4^^ w Trans\erse sectu STRUCTURE OF BLOOD-VESSELS. 679 Fig. 641. stream and the passage of the plasma and oxygen into the surrounding tissues. The walls of the capillaries consist of only the lining plates, the entire vessel being in fact a delicate endothelial tube. The cells composing the latter are elongated lanceolate plates, possessing oval nuclei, united by nar- row lines of cement substance. Although the transition from the arterioles is gradual, the final disappearance of the muscle-cells marks the beginning of the true capillaries ; the passage of the latter into the veins is less certain, since muscular tissue is wanting in those of small size. In the smallest capillaries two endothelial plates may suffice to encircle the entire lumen ; in the larger three or four cells may be required to complete the vessel. Preformed openings (sto- mata) in the walls of the capillaries do not exist, the passage of the leucocytes and, under certain conditions, also of the red blood-cells (diapedesis) and of small particles of foreign substances, being effected between the endothelial plates. In some capillaries, as in those of the choroid, liver, or renal glomeruli, the usual demarcation of the wall into distinct cells is wanting, the individual endothelial plates being replaced by a continuous nucleated sheet or syncytial layer. Where the capillaries course within fibrous tissue, not uncommonly the vessel is accompanied by delicate strands of connective tissue (^adventitia capillaris) that suggest an e.xternal sheath. The capillaries are usually arranged as net-works, of which the channels are of fairly constant size within the tissue to which they are distributed. During life it is prob- able that none are too small to permit the passage of the red blood-cells, while many admit two or even three such elements abreast. Their usual diameter varies between .008 and .020 mm. The capillary net-works in various parts of the body differ in the form and closeness of their meshes, since these details are influenced by the arrange- ment of the component elements and by the function of the structures supplied. Thus, in muscles, tendons, and nerves the meshes are elongated and narrow; in glands, the lungs, and adipose tissue they are irregularly polygonal; in the liver-lobules converg- ingly or radially disposed; while in the subepithelial papillae of the mucous membranes and the skin the capillaries commonly form loops. In general, it may be assumed that Portion of fem- oral vein, opened to show bicuspid Fig. 642. rising from arteriole and ending in small i I omentum. X : the greater the functional activity of an organ, the closer is its capillar}- net-work. Organs actively engaged in excretion, as the kidneys, or the elimination of substances 68o HUMAN ANATOMY. from the blood, as the lungs or liver, as well as those producing substances directly entering the circulation (organs of internal secretion), as the thyroid gland, are pro- vided with exceptionally rich and close net-works. The mesh-works within the walls of the pulmonary alveoli are of remarkable closeness and are often narrower than the capillaries surrounding them. Under the name, sinusoids, Minot' has grouped the circulation occurring in certain organs, as the liver, in which the capillaries are formed by the invasion and subdivision of the large original blood-channel by the tissue-cords. The resulting sinusoids differ from ordinary capillaries, therefore, in connecting afferent and efferent vessels of the same nature, both being either venous or arterial. Capillaries, on the contrary, form communications between arteries and veins. In consequence of the invagination of the original vessel, its endothelium bears an unusually intimate rela- tion to the tissue-trabeculee, little or no connective tissue intervening. F. T. Lewis ' has shown that the Wolffian body and the developing heart also present examples of sinusoidal formation, and suggests the significance of sinusoids as representing a primitive type of circulation. THE BLOOD. The fluid circulating within all parts of the blood-vascular system consists of a clear, almost - colorless plasma or liquor sangjiinis in which are suspended vast numbers of small free corpuscular elements, the blood-cells. The latter are of two chief kinds, the colored cells, or erythrocytes, and the colorless or leucocytes. The characteristic appearance of the blood is due to the presence of hemoglobin con- tained within the erythrocytes which, while individually only faintly tinted, collect- ively impart the familiar hue as well as a certain degree of opacity. That the characteristic pigment is limited to the cells is shown by the lack of color and the transparency of the plasma when examined under the microscope, although to the unaided eye the blood appears uniformly red and somewhat opaque. The most im- portant property of hemoglobin is its great affinity for oxygen which, taken up from the air during respiration and combined as o.xy hemoglobin, is carried by the red cells to all parts of the body. When rich in oxygen (containing about twenty vol- umes) the blood possesses the bright scarlet hue characteristic of arterial blood; after losing approximately one-half of its oxygen and acquiring about an equal volume of carbon dioxide during its intimate relations with the tissues, the blood returned by the veins is dark purplish-blue in color. If the hemoglobin escapes from the eryth- rocytes into the plasma, the latter becomes deeply tinged and the blood loses its opacity and becomes transparent or "laked." This discharge is known as hemolysis. The specific gravity of normal blood is about 1055 ; its reaction is alkaline and due chiefly to the presence of sodium carbonate. Immediately after withdrawal from the body the blood possesses a characteristic odor that probably depends upon cer- tain volatile fatty acids. When fresh it is slippery to the feel, but after exposure to air becomes sticky. L'pon standing it undergoes coagulation, whereby the cor- puscles become entangled among the innumerable delicate filaments of fibrin, a pro- teid substance that appears in the plasma after withdrawal of the blood from the body. As the result of this entanglement the corpuscles are collected into a dark- colored, jellv-like mass, the blood-clot or crassamentiim, that separates from the sur- rounding clear straw-colored scrum. The latter possesses an alkaline reaction and a specific gravity of 1028. The serum closely resembles the liquor sanguinis, con- taining about ten per cent, of solid substances, of which about three-fourths are pro- teids — serum-albumin, serum-globulin, and fibrin-ferment, the latter replacing the fibrinoijen present in the plasma before coagulation occurs. Blood-Crystals. — The chief constituent of the red cells, the hemoglobin, prob- ably exists within the corpuscles as an amorphous mass in combination with other substances (Hoppe-Seyler) from which it must be freed by solution before crystal- lization can occur. After laking, the coloiing matter of the blood, in the form of oxyhemoglobin, separates into microscopic crystals that belong to the rhombic sys- tem, usually appearing as elongated rhombic or rectangular plates (Fig. 643). ' Proceedings Boston Soc. Nat. History, vol. xxix, 1900. ' Anatomischer Anzeiger, Bd. xxv., 1904. THE BLOOD. esi Fig. 643 Crystals of t When unusually large or superimposed they exhibit the characteristic crimson hue, but when single and small the hemoglobin crystals are colorless or of a faint greenish- yellow tint. On mixing dried blood with a few grains of sodium chloride and a small quantity of acetic acid and heating until bubbles appear, minute brown crystals are formed in large numbers. These are known as Teichmann s or hemin crystals and re- present one of the products derived from the reduction of hemoglobin. Being yielded by blood from various sources, they are indica- tive only of the presence of blood and are valueless in differentiating the blood of man from that of other animals. In blood-clots of long standing minute hematoidm aystals often appear as yellowish-red plates. This substance is likewise a reduction-product of hemoglobin. The Colored Blood-Cells.— The ma- ture colored blood -cells, erythrocytes, or red corpuscles, of man and other mammals (ex- cept those of the camel family, which are elliptical in outline) are small, biconcave, circular, nonnucleated discs, with smooth contour and rounded edges. When viewed by transmitted light, the individual "red" cells possess a pale greenish-yellow tint, and only when they are collected in masses or superimposed in several layers is the distinc- tive blood-color evident. The peculiar form of the corpuscle — biconcave in the centre and biconvex at the periphery — renders accurate focussing of all parts of its broader surface in one plane impossible ; hence under the high amplification necessary for their satisfactory e.xamination, the entire cells are never sharply defined and, according to focal adjustment, appear either as light rings enclosing dark centres or vice versa. Viewed in profile, the thicker conve.x marginal areas are connected by the thinner concave centre, the corpuscle presenting a general figure somewhat resembling a dumb-bell. After fresh blood has been distributed as a thin layer and allowed to remain unshaken for some time, the red cells exhibit a peculiar tendency to become arranged in columns, with their broad surfaces in contact, similar to piles or rouleaus of coin (Fig. 646). Agitation dis- perses the corpuscles, which, however, may resume their /^■v ■ former grouping when again undisturbed. The columns " \ ^ ^ , may join one another until a net-work of rouleaus is formed. If the stratum of blood be thin, the red cells usually later separate, but they may retain their columnar grouping. The long-accepted biconcave discoidal form of the mam- malian erythrocytes has been questioned by Dekhuyzen ' and, more recently, by Weidenreich ^ and by F. T. Lewis,' who be- lieve that the normal form of the red blood-cells is cup-shaped, similar to a sphere more or less deeply indented, thus reviving the conception held by Leeuwenhoek nearly two centuries ago. Although such cupped corpuscles are familiar, they are generally regarded as changed cells resulting from modification of the density of the plasma. The posi- tive testimony of so careful an observer as Lewis as to the occurrence of the cup-shaped red cells within the circulation during life entitle these views to consideration.* ' Anatomischer Anzeiger, Bd. xv., 1899. ' Archiv. f. mikros. Anatom , Bd. Ixi., 1902. ' Journal of Medical Research, voh x., 1904. * A critical review concerning the form and structure of the red cells is given by Weiden- reich in Lrgebnisse d. Anat. u. Entuick., Bd. xiii., 1904. Fig. 644. 682 HUMAN ANATOMY. Dresbach ' has recorded the presence of elliptical red cells in the blood of an apparently healthy mulatto. 1 he oval corpuscles, which measured .010 mm. by .004 mm., were approxi- mately constant in size, slightly biconcave, and constituted ninety per cent, of all the red cells. They were observed over a period of four months, during which time the number of erythro- cytes and leucocytes and the amount of hemoglobin were normal. Dresbach con- cludes that the oval form was not an arti- fact, but probably due to developmental variation. The average diameter of the red blood-cells of man is .0078 mm. C^tVt ^"Oi some corpuscles meas- uring as little as .0045 mm. and others as much as .0095 mm. Their average thickness is about .0018 mm. It is probable that the average diam- eter is uninfluenced by se.x and is constant for all races, although ac- jrding to Gram, the size of the cor- juscles is somewhat greater in the ihabitants of northern countries. The number of red cells normally contained in one cubic millimeter of blood is appro.ximately 5,000,000 in the male and something less (4,500,- 000) in the female. The number of Fig. 645. 9)0> corpuscles is practically the same whether the blood be taken from the arteries, capillaries, or veins, but is lower in the blood from the vessels of the lower extremity than of the upper, probably owing to the greater proportion of plasma in the more dependent parts of the body. Within the first day after birth, the number of erythrocytes is normally very high; in ad- vanced old age it is usually diminished. In general, the red blood-cells of mammals are small and their size, which greatly varies in different orders, bears no relation to that of the animal. The corpuscles of man, which are among the largest and exceeded by only those of the elephant (.0094 mm.) and the two-toed sloth (.0091 mm.), are approximated by those of the guinea-pig (.0075 mm.), dog (.0073 mm. ), rab- Fig. 646. bit (.0069 mm.), and cat (.0065 mm.). Those of many familiar mammals are distinctly smaller, as the hog (.006 mm.), horse (.0056 mm.), sheep (.005 mm.) and goat {.004 mm.). The smallest mammalian corpuscles are those of the musk-deer, with a diameter of .0025 mm. It is obvious that a positive differentiation of human blood from that of some of the do- mestic animals, based on the measurement of the red cells, is uncertain and often impossible. The application of the "biological" test has placed a much more reliable and even specific means in the hands of the medico-legal expert. This test depends upon the fact, demonstrated by Bordet, Uhlenmuth, and others, tliat the blood-serum of an animal that has been repeat- edly injected with small quantities of human blood will produce a distinct cloudy precipitate or turbidity when added to a dilute solution of human blood, but will yield no result when added to similar solutions of blood from other animals. An important advantage of this test is that even when the blood is putrid, contaminated, or derived from old dried clots, the char- acteristic changes occur. Certain exceptional disturbing conditions, such as the presence of • Science, March 18, '904, and March 24, 1905. r -:■ r. 625. THE BLOOD. 683 monkey's blood, human lachrj-mal or nasal secretion, being eliminated, a positi\e reaction with the serum-test is strong evidence of the presence of human blood. The nonnucleated condition of the mature erj-throcytes is the distinguishing characteristic of mammalian blood as contrasted with the colored corpuscles of other \ertebrates, since even in the exceptional oval red cell of the camel family the nucleus is wanting. The mammalian red corpuscles, however, must be regarded as a secondarj- de\iation from the fundamental type represented by the o\al nucleated er}throcyte of the other vertebrates, the nucleated embrj-onic red cell losing its nucleus as maturity is acquired. In general, the oval nucleated red cells are laro-er than the mammalian nonnucleated discs. The largest erythrocytes are found in the tailed amphibians; those of the amphiuma, the largest known, attain the gigantic length of .oSo mm., and are appro.ximately ten times as large as the human red blood-cell. The structure of the red blood-cell has long been and still is a subject of dis- cussion, two opposed views finding ardent supporters. According to the one, held by Schaefer,' Weidenreich, and others, the erythrocyte consists of a membranous e.xternal envelope inclosing the colored fluid contents. On the other hand, Rollett and many others regard the corpuscle as composed of an insoluble flexible spongy stroma of great delicacy, occupied by the coloring matter or hemoglobin. Although no definite envelope is present, in the sense of a distinct cell-membrane, it is highly probable that a peripheral condensation of the stroma exists. The fact that the Fig. 647. Nucleated amphibian red blood-cells ; A, from newt ; B, from amphi fragments into which the red blood-cells may be broken up after certain treatment, as by heating, retain the appearance and structure identical with the larger original cell, is strong evidence that the hemoglobin has not escaped and, therefore, does not exist in a fluid condition within the cell, notwithstanding the ingenious but scarcely convincing explanations of the phenomena advanced by the supporters of the vesicular structure of these cells. Further, the evidence afforded bv those parts of the corpuscles that remain after abstraction of the hemoglobin by water, ether, and other reagents, points to the existence of a distinct stroma, the thicker edges of which appear in profile as outlines of the "ghosts" that then represent the former colored cells. The erythrocytes are extremely sensitive to a wide range of reagents and conditions and, therefore, require great care in their collection and examination if distortions are to be avoided. Exposure to even a current of air often suffices to produce conspicuous changes in the red blood- cells. Alterations in form may be grouped into those resulting from the action of solutions of lower and of higher density than that of the normal plasma. The latter is convenientlv sub- stituted by an .85 per cent, solution of sodium chloride. If the proportion of salt be grad- ually reduced, the corpuscles show evidences of swelling, at first b)- losing their concavity on one side and later, as the density of the reagent approached that of water, assuming the spherical form and parting with the hemoglobin and becoming colorless. On the other hand, ' Anatomischer Anzeiger, Bd. xxvi., 1905. 684 HUMAN ANATOMY. when subjected to saline solutions stronger than the "normal," the exterior of the corpuscles becomes irregular and beset with knob-like projections or spines. When the concentration of the medium is increased, the " crenation ' gives place to marked shrinkage and distortion, until the cells lose all resemblance to their normal form. Upon treatment with water, aqueous dilutions of acetic acid, ether, and other reagents, the erythrocytes are promptly decolorized by the extraction of the hemoglobin. An interesting modification of the phenomenon may be produced by solutions of tannic acid or potassium bichromate of varying strength. When the reaction is vigorous, the decomposed hemoglobin is caught within the cell and appears as a mass somewhat resembling a nucleus. When the reaction is feeble, as with very weak solutions, the hemoglobin is less suddenly precipitated, and appears as a minute projection attached to one part of the exterior of the decolorized corpuscle. Alkaline solutions effect the complete destruction of the red cells. Among the reagents employed in histological investigations, osmic acid (i per cent.) deserves especial confidence as preserving the form of the red corpuscles. Fixation by heat, so commonly used in the prepara- tion of blood specimens for clinical examinations, produces alterations and often marked changes in the red cells, and, therefore, is unsuitable for histological study of these elements. Attenua- tion of the central parts of the cells produces appearances that have been mistaken for a nucle- ated condition of the erythrocytes. Upon cautious application of. heat, with precautions against evaporation and drying, the corpuscles extrude portions of their substance which, after separation, resemble miniature red cells. The Colorless Blood-cells. — It may at once be emphasized that the colorless cells observed within the blood are only incident- ,. ally related to the red cells and, further, that ?-^^*!' they, in part at least, primarily circulate within ^vil;;^' the lymph-vascular system, from which they are poured into the blood. When examined in fresh and unstained preparations, the colorless cells or leuco- cytes appear as pale nucleated elements which, by their pearly tint and refracting properties, are readily distinguished from the much more numerous surrounding erythro- cytes. Their shape is very variable, but when first withdrawn from the body is usually Varieties of colorless blood-cells seen in :.-.-.-.^..1.^.-l.. ...^V.^..;.,..! ^^ ^,.^1 WTU^^ ^1 A normal human blood; a. small lymphocytes; irregularly sphencal Or oval. When placed *, large lymphocyte or mononuclear leucocyte; qu a warmed slide and maintained at the c, transitional leucocyte; a, polymorphonuclear f i i i r i n leucocytes; f, eosinophiie ;/, red cells. X 900. temperature ol the body, many 01 these cells soon exhibit amoeboid ??iotio>i, whereby are produced not only alterations in their form, but often also changes in their actual position. A nucleus is always present, but may be obscured in the contracted spherical condition of the cell by the overlying granular cytoplasm. In the expanded con- dition, as when the cell is undergoing amoeboid change, the nucleus is very evi- dent and the cytoplasm often differentiated into a homogeneous peripheral zone (exop/astn) and a central granular area {cndoplasm) surrounding the nucleus. A distinct cell-wall is absent, although it is probable that a slight peripheral condensa- tion serves to outline the corpuscle. That such condensation does not constitute a definite envelope is shown by the readiness with which foreign particles may be taken into the bodv of the cell. Although the size of the colorless corpuscles varies with the type of the cell, as presentlv described, in general the diameter of these elements is larger than that of the erythrocytes, and is commonly from .010-.012 mm. Their number is much less than that of the red corpuscles, the usual ratio between the white and red cells being about 1 : 600. Even within physiological limits this ratio varies considerably, from 5000 to 10,000, with an average of 7500, white cells being normally found in one cubic millimeter of blood. Critical examination of the colorless cells, after fixation and staining, has shown that among the elements collectively designated as the "white cells" or "leucocytes," five varieties are usually present in normal blood. .Since the recognition of these forms is sometimes of practical THE BLOOD. 685 importance, a brief resum^ of their cliaracteristics, based on the descriptions of EhrHch and of Da Costa,' may appropriately here find place. It should be noted that the differentiation of these cells is founded upon not only their morphological characters, but also the behavior of the granules embedded within their cyto- plasm when subjected to certain combination stains. A generation ago Ehrlich divided the aniline dyes into three groups — acid, basic, and neutral. The first includes such dyes as acid fuchsin, orange G or eosin, in which the coloring principle acts or exists as an acid and exhibits an especial affinity for the cytoplasm. The second group, the basic stains, includes dyes, as hematoxylin, methylene-blue, methyl-violet, methyl-green or thionin, in which the coloring prin- ciple exists chemically as a base in combination with a colorless acid and particularly affects the chromadn ; hence, such are nuclear stains. Neutral dyes, produced by mixture of solutions of an acid and a basic stain, have a selective affinity for certain so-called neutrophilic granules. Assuming that the blood-film has been fixed by heat and tinged with Ehrlich's "triacid Stain" (a combination of solutions of acid fuchsin, orange G, and methyl-green) the following varieties of colorless cells are distinguishable in normal blood : 1. Small Lymphocytes. — These are non-granular cells, with an average diameter of .0075 mm. or about that of the erythrocytes, distinguished by a large deeply staining nucleus that occupies almost the entire cell. The meagre cytoplasm is reduced to a narrow peripheral zone, so inconspicuous that it may be overlooked. The small lymphocytes, which constitute from 20-30 per cent, of all the white corpuscles, are the most common derivative from the lymphoid tissues. 2. Large Lymphocytes, or Mononuclear Leucocytes. — These elements, about .012 mm. in diameter, possess a relatively small round or oval nucleus, which is usually eccentrically placed and so poor in chromatin that it stains faintly. The cytoplasm is non-granular and comparatively large in amount. 3. Transitional Leucocytes.— Assuming that the lymphocytes and leucocytes are related and not distinct elements, the transitional forms represent the developmental stage linking the large lymphocytes with the mature leucocytes. Their distinguishing feature is the indented or kidney-shaped nucleus which usually occupies an eccentric posidon within the non-granular cytoplasm. The latter, as well as the diameter of the transitional forms, corresponds with that of the large mononuclear leucocyte. 4. Polymorphonuclear Leucocytes. — These represent by far the most common type of white cells, of which they constitute about 70 per cent. Their diameter is approximately .oio mm., hence they are somewhat smaller than the transitional forms, but larger than the red cells. Their cytoplasm is relatively large in amount and contains fine neutrophilic granules. On account of the great diversity of the forms that they assume, the nuclei are very conspicuous features of this type of leucocyte. At first sight the nuclei appear multiple; closer e.xamination, however, shows the seemingly distinct nuclei to be connected by delicate processes, so that, although exceptionally two or more isolated nuclei exist and the cells are truly polynuclear| their actual condition is appropriately designated as polymorphonuclear. 5. Eosinophiles.— Leucocytes of this type are conspicuously distinguished by the coarse, highly refractive granules within the cytoplasm that display an especial affinity for acid dyes^ particularly for eosin. These resemble the polymorphonuclear leucocytes in size (.010 mm.) and in the character of their nuclei, the latter, however, in general being less distorted and commonly eccentrically placed. The eosinophiles are prone to rupture, after which the pale nucleus lies in the midst of a swarm of brightly tinged oranules. Although other types of colorless cells, as myelocytes and mast cells, are of clinical interest they do not occur m normal blood and, hence, need not be here discussed. An occasional addi- tional type of leucocyte, the basophile cells, is rarely present in normal blood. These elements resemble the polymorphonuclear leucocytes, but are distinguished from the latter by the presence withm the cytoplasm of closely packed fine granules that possess a strong affinitvfor basic dyes. In the foregoing grouping the varieties of white cells are regarded as different stages of elements genetically related and derived from the same sources— a view supported by the early development of the leucocytes. It should be mentioned, however, that Ehrlich and manv other hematologists consider the lymphocytes and the leucocytes as entirely distinct elements, believing the former to be derived from lymphoid tissues and the leucocvtes exclusively from bone-marrow. Accordingly, the large lymphocytes and the large mononuclear leucocvtes are of different nature, although, as universally admitted, their assumed differentiation is at best uncertain. The presence ot all forms of white cells m the circulation of the embryo long before the appearance of bone- marrow (Ebner) seems conclusive evidence that the origin of the leucocytes is not limited to the marrow, tissue. The Blood Plaques. — In addition to the erythrocytes and leucocvtes, the blood of man and other mammals regularly contains small bodies, the blood plaques 'Clinical Hematology. Phila., 1901. 686 HUMAN ANATOMY. or thrombocytes. As they are extraordinarily sensitive to exposure, even to entire disappearance, special precautions are necessary to insure their presence in an unal- tered condition in preparations examined. If blood be drawn directly into and mixed with a drop of .85 per cent, salt solution, or, still better, into one of weak osmic acid solution, the blood plaques appear as round or oval discs, from .002-.004 mm. in diameter, usually somewhat less than one-third of the size of the red cells. From these they further differ in being colorless and devoid of hemoglobin and in staining readily in very dilute solutions of methyl-violet. The blood plaques appear faintly granular and contain masses of chromatic substance representing a nucleus. They seem to be minute cells and are capable of undergoing amceboid movement. They possess the ability of rapidly throwing .out processes and adhering together on coming into contact with foreign bodies. Their assumed role, that of arresting hemorrhage by assisting in the formation of a coagulum, suggested the name, thrombocytes, given them by Dekhuygen. Notwithstanding the attention bestowed upon them, the source of the plaques is still undetermined. This has been variously attributed to disintegration of the leucocytes, Fig. 649. to extrusion from the red cells, or from the megakaryocytes, or to destruction of the en- dothelial lining of the vessels. None of these assumptions can be regarded as established, or even probable, in view of their constant ■^ -■' presence and large normal quota — an average ^ of 300,000 plaques in one cubic millimeter of blood. r"\ Granules. — In addition to the corpus- *■»—'" cles and the plaques, extremely minute gran- (O* fj ules occur in varying numbers in normal e human blood. The nature of these particles '^.-' differs. Some are undoubtedly finely divided fat; others, described by H. F. Miiller under ® the name, hcnwconia, are of uncertain compo- ^, , . , ,, J sition, but not fatty; while a certain propor- Human blood, showing red cells and ,. . i i i i ■ i r i i* • - blood plaques. X 625. tion IS probably derived from the disintegration of endothelial and blood-cells. The destruc- tion of the latter is accountable for the minute particles of pigment that are constant, if not numerous, constituents of the circulation. DEVELOPMENT OF THE BLOOD-VESSELS AND CORPUSCLES. The earliest blood-vessels appear within the extra-embryonic mesoblast covering the vitelline sac and, therefore, beyond the limits of the embryo proper and entirely independent of the heart and axial trunks. In the lower mammals, the formation of the primary vessels takes place towards the periphery of a limited field, known as the vascular area, that encircles only a portion of the vitelline sac; in man the limited proportions of the latter enable the net-work of developing blood-channels to extend completely over the vesicle, so that the vascular area becomes coextensive with the yolk sac. Although the initial stages in the formation of the primary blood-vessels have never been observed in man, since the vessels were already present over the vitelline sac in the youngest embryo so far examined, it is probable that the development of the human vascular tissues is essentially the same as that seen in other mammals. In the rabbit, the first indications of the developing blood-vessels are cords or groups of spherical cells that appear within the deeper, later splanchnic, layer of the mesoblast covering the vitelline sac. These tracts become larger in consequence not only of proliferation, but also of separation of the component cells. The meso- blastic elements surrounding the tracts soon become disposed as enclosing, walls, within which the separated cells, now suspended in a clear fluid that has meanwhile appeared, represent the earliest blood-cells. The channels thus established unite into a net-work of primary blood-vessels that at first occupies the periphery of the vascular area, but later extends towards the DEVELOPMENT OF BLOOD-VESSELS AND CORPUSCLES. 687 Fig 650 embryo and, after the appearance of the large converging trunks, the vitelline veins and arteries, joins the intra-embryonic trunks that coincidehtly have been formed. Although the generally accepted current views relating to the independent origin of the primary blood-vessels within the vascular area have not escaped challenge, it may be regarded as established that the development of subsequent blood-vessels proceeds from the cells constituting the walls of pre-existing channels. The walls of the growing capillaries consist of delicate endothelial plates from which pointed sprouts grow into the surrounding tissue (Fig. 651;. These outgrowths, direct pro- longations of the cytoplasm of the endothelial cells, are at first solid, but later become hollowed out by the gradual extension of the lumen of the capillary. Vascular loops are often formed by the meeting and fusion of the outgrowths proceeding in opposite directions, the communication being established by the final disappearance of the sep- tum in consequence of the extension of the lumen of the parent vessels. At first rep- resented by only a single layer of endothelial cells, the walls of the larger blood-vessels become rein- forced by the additional layers derived from the surrounding mesoblast. Development of the Erythrocytes. — The first, and for a time the only, blood-cells present within the embryo are the primary nucleated erythro- cytes derived probably directly from the mesoblastic elements within the angioblastic areas in which the earliest vessels appear. These cells, the primary eryihro- blasts, separated by the colorless plasma which appears between them, undergo mitotic division, producing nucleated elements that, in turn, give rise to the primary erythrocytes. These are spherical, nucleated, and larger (about .012 mm. in diam- eter) than the adult red cells. At first their cytoplasm is color- less and slightly granular, but soon becomes homogeneous and tinged with hemoglobin. After the earlier fcetal months, during which prolifera- tion of the blood-cells occurs in all parts of the circulation, the corpuscles engaged in division withdraw to localities in which the blood-current is sluggish and, therefore, favorable for mitosis. Such localities are particularly the liver, spleen, and bone-marrow, the large capillaries and tissues of which afford tem- porary resting places during proliferation. From the primary blood-cells arise megal- oblasts and normoblasts , from which latter the definite erythrocytes are derived. These changes begin during the second foetal month, more and more nonnucleated discoidal red cells appearing as gestation advances, so that at birth almost all the nucleated erythrocytes have disappeared from the circulation. Since the red cells possess only a limited vitality, their constantly occurring death requires the production of new corpuscles. Preceding the development of the spleen and bone-marrow, the liver is the principal centre of blood-formation. Later the splenic and marrow tissues share this function, while after birth the red bone- marrow is the chief seat in which the continual additions of new erythrocytes necessary Surface view of vascular area of chick embryo with twelve pomites (29 hours) ; net-work of developing blood-vessels, most distinct in periphery of area, is connected with vitelline veins from embryo by faint channels ; cephalic segment of neural tube shows brain-vesicles and eye-buds ; caudal segment still widely open. X 16. 688 HUMAN ANATOMY. to maintain the normal quota are made. The production of the new red cells within the marrow proceeds from slightly colored elements, the erythroblasts, that by division give rise to normoblasts and nucleated erythrocytes, which latter, upon the distribu- tion of hemoglobin and the Fig. 651. disappearance of their nuclei, are transformed into the usual red cells, and as such enter the circulation. The disappearance of the nucleus of the normoblasts has long been a subject of discus- sion and speculation. Accord- ing to the older view — still, however, accepted by many — the nucleus is e.xtruded from the erythrocyte and under- goes disintegration, thus, in the opinion of some, supply- ing the source of the blood plaques. According to the more recent views, held by Developing blood-vessels in embr>'onal subcutaneous tissue ; Neumann, Kolliker, Pappen- a. larger capinary; t. young capillaries i c. solid protoplasmic , . T „] pknpr indothers outgrowths forming new vessels. X 300. iieiiu, ibraei, i:-uiier, auuoiiiers, the disappearance of the nu- cleus is due to its solution and absorption within the erythrocyte. Under normal conditions the immature nucleated red cells do not occur in the circulation. After severe hemorrhage or in other conditions requiring unusual activity of the blood- forming processes, they may be present in large numbers until the normal quota of erythrocytes has been once more established. In view of the constant presence of normoblasts and nucleated erythrocytes within the splenic pulp, the spleen has been regarded as a possible, although under usual conditions limited, source of the red blood-cells. When, however, the necessity for rapidly augmenting the number of red cells arises, the spleen may assume the role of an active blood-producing tissue. Since such cells are found also in the thymus, this body probably may be included among the blood-forming organs of early life. There is no satisfactory evidence that the erythrocytes are derived from the colorless cells or from the blood plaques. Development of the Colorless Cells. — Immediately succeeding the appear- ance of the primary red cells, the latter are the chief elements within the circulation. In the early weeks, however, colorless cells appear and henceforth are the com- panions of the erythrocytes. As already noted, the white cells are elements that primarily belong to the lymphatic Fig. 652. system, from which they are poured into the blood chan- nels. Genetically, the red and white cells are unrelated. .^^ Concerning the origin of the first colorless cells un- « «fc ® 'i certainty exists, although it is generally assumed that ® % they arise from mesoblastic cells and, therefore, to that ® ^^^ ' extent, share with the erythrocytes a common source. @ © ^ According to Maximow,' the progenitors of the white ~~ . '^'^^^ cells are lymphohlasts, deri\-ed from the primitive blood- ®_ Jv^ cells, the hemoblasts ; the latter are, therefore, the source \^) of both the red and white cells, including the various -> forms of the colorless corpuscles. The conclusion of Beard, 2 that the first Ivmphocytes to appear within the ^ Nucleated embryonal eryihro- , , . 'i . , . r c\-tes; two dn-idnig cells exhibit embryo owe their production to the metamorphosis of mitotic figures, x 600. the entoblastic epithelium of the primary thymus, and that the subsequent migration of the lymphocytes so derived establishes foci from which are developed the various masses of lymphoid tissue occurring throughout the •Archivf. mikros. Anatom., Bd. Ixxiii., 1909. •Anatom. Anzeiger, Bd. xviii., 1900. THE HEART. Megakaryocyte body, has been challenged by Hammar and by Maximow,' who found lymphocytes in the blood and connective tissues before they appear within the thymus. It is probable that the early lymphocytes also originate from mesenchymal cells outside the vessels, which they later enter, aided by their migratory powers. Their subsequent multiplication is effected by division, for the most part mitotic, of the pre-existing cells. This proliferation occurs chiefly within the lymphoid tissue throughout the body, the lymph-nodules, spleen and bone-marrow being the most important local- ities. ' The germ-centres of the lymph-nodules (page 936) are seats of especial activity for the formadon of the types of colorless cell known as -the mononuclear lymphocyte, although whether the proliferating cells originate within the germ- centres, or only complete their division in these situations after being carried from other points (Stohr), is still unsetded. From the developmental standpoint, the sharp separation of the colorless blood- cells into lymphocytes and leucocytes, as insisted upon by Ehrlich and his supporters, based on the assumption that the leucocytes originate exclusively within bone-marrow, is not well founded in view of the presence of all the typical forms of white cells, in- cluding the polymorphonuclear leucocytes, shordy after the first appearance of the white corpuscles and long before the advent of the earliest bone- • Fig. 653. marrow (Ebner). For the pres- ent, at least, it seems most reason- able to regard the various forms of the white cells as constituting a genetic sequence in which the lymphocyte, leucocyte, and eosin- ophile represent different stages in the development of elements hav- ing a common origin. In addition to the red blood- cells in various stages of develop- ment and the different types of leucocytes, peculiar huge elements early appear in the embryonic blood-forming organs, and after birth in bone-marrow. These giant cells, or megakaryocytes (Howell), are distinguished by their large, irregularly lobulated but single nucleus from the osteo- clasts, since the nuclei of the latter are usually oval and multiple. The megakaryo- cytes are often observed containing within their substance the remains of both white and red cells; they are, therefore, regarded as phagocytes upon which devolves the removal of effete blood-corpuscles. Their origin is uncertain, by some (Howell, van der Stricht, Heidenhain) being referred to the leucocytes, and by others (Kblliker, Kuborn) to the endothelium of the vessels, while Ebner regards those within the bone- marrow as probably derived from fi.xed connective-tissue cells of the reticulum. Nei- ther form of these giant marrow-cells is normally found within the post-natal circulation. Section of embryonal bone-marrow, showing nucleated erythrocytes, leucocytes and mega- karyocyte. X 625. THE HEART. General Description. — The heart is a hollow, muscular organ of a somewhat conical shape, situated in the lower part of the thoracic cavity, behind the lower two- thirds of the sternum. It is enclosed within a double-walled serous sac, the pericar- dhim, and has a somewhat oblique position in the thorax, its base (basis cordis) looking upward, dorsally, and to the right, while its apex (apex cordis) points downward, ven- trally, and to the left. In consequence of this obliquity about two-thirds of the organ lies to the left and one-third to the right of the median plane of the body. • Archiv f. mikros. Anatom., Bd. Ixxxiv., 1909. 44 690 HUMAN ANATOMY. It may be regarded as possessing two surfaces, which are not, however, distinctly separated, but pass into each other with rounded edges, especially upon the left side. One of these surfaces looks forward and somewhat upward, and is separated by the peri- cardium and some loose areolar tissue from contact with the sternum and the lower costal cartilages, the thin anterior edges of the lungs and pleura; also inter\'ening to a considerable extent; this is the ajitero-superior surface (facies sternocostalis), and for convenience it may be more briefly termed the anterior surface. The other, the postero-infcrior or posterior surface (facies diaphragmatica), rests directly upon the upper surface of the diaphragm. At about one-third of the distance from the base to the apex a deep circular groove, more distinct upon the posterior surface, surrounds the heart, separating an Fig. 654. Superior vena cava Systemic aorta (aorta) Line of reflection of pericardium Ductus arteriosus Right auricle Auriculo-ventricular groove Anterior inter\-entricu- lar groove Anterior aspect of heart hardened in situ ; probe 1 of pericardii upper thin-walled auricular portion of the organ from a lower thick-walled ventricular one : this groo\'e is termed the auriculo-ventricular groove (sulcus coi'onarius), and contains the proximal portions of the coronary vessels which supply the heart's sub- stance. Extending towards the apex from this groove, two other shallower grooves are to be observed, one situated towards the right side of the anterior surface and the other upon the posterior surface. These grooves, which also lodge portions of the coronary vessels, are the anterior and posterior interventriadar grooves (sulci longi- tudinales), and mark the line of separation of the ventricular portion of the heart into two chambers known as the right and left ventricles. From the base of the right ven- tricle a large blood-vessel, \\\(t pulmonary aorta or pulmonary artery, arises, while from the base of the left ventricle, and almost immediately posterior to the root of the pul- monary aorta, the systemic aorta takes its origin. The orifices by which each of these THE HEART. 691 great vessels communicates with its ventricle are guarded by special valves known as the semilunar valves. The auricular portion of the heart rests upon the posterior part of the base of the ventricular portion, and is best viewed from the posterior surface (Fig. 655), since it is almost completely hidden anteriorly by the two aortse. Like the ventricular portion, it is composed of two separate chambers, which are not, however, very apparent on surface view. These chambers are the right and left aicricles, and com- municate with the corresponding ventricles by auriculo-ventricular orifices guarded by special auriculo-ventricular valves. From the lateral part of the anterior sur- face of each auricle a process, the auf icular appendix, arises. These appendices are Fig. 655. Left common carotid arterj' Left subclavian artery Innominate artery Vestigial fold Sup. left pulm vein Left auricular appendix Inf. left pulm vein Coronary Left ventricle Azygos vein Superior vena cava right ^pulmonary Inferior vena cava Right ventricle Apex Posterior aspect of heart hardened of reflection of pericardium. slightly flattened prolongations of the auricles, and bend forward around the bases of the aortse, which they slightly overlap in front ; they are the only portions of the auricles visible upon the anterior surface of the heart. Upon its superior surface the right auricle receives the termination of a large venous trunk, the vena cava superior, which returns to the heart blood from the head, neck, upper extremities, and walls of the thorax ; while upon its posterior surface is the opening of another large vessel, the vena cava infe7-ior, which returns blood from the abdominal and pelvic walls and viscera and from the lower limbs. The left auricle receives upon its surface the four pulmonary veins arranged in pairs, one pair situated towards the left portion of the auricle and the other towards the right. 692 HUMAN ANATOMY. Position. — The heart may vary considerably in position without being regarded as abnormal, but what may be considered its typical position with reference to the anterior thoracic wall may be stated about as follows : The apex is situated behind the fifth intercostal space, about 8 cm. (3i/( in.) from the median line, this position being median to and slightly below the junction of the fifth costal cartilage with its rib. The level of the base may be approximately indicated by a line drawn from a point slighdy above the upper border of the third costal cartilage of the left side, about 4.5 cm. ( i^-i in.) from the median line of the sternum, to a point upon the upper border of the third costal cartilage of the right side, about 3 cm. (\y^ in.) from the middle line. If now the left end of the base-line be united to the apex point by a line which is slightly convex towards the left, and a line, markedly convex towards the right, be drawn from the right end of the base-line to the junction of the seventh costal cartilage of the right side with the sternum and thence to the apex point, a heart-area will be en- FiG. 656. closed which corresponds to the out- line of the organ as seen from in front. Considerable importance at- taches to the location of the auriculo- ventricular and aortic orifices with reference to the anterior thoracic wall. The right atiriculo-ventrieidar ori- Jlee in a typical heart lies on a level with the attachment of the fifth costal cartilages to the sternum, almost be- hind the median line of that bone and opposite the fourth intercostal space, while the left auriculo-ventricular orifice is opposite the sternal end of the left third intercostal space. In other words these openings lie along a line which corresponds with the auriculo-ventricular groove, and this may be represented by a line drawn from the upper border of the junc- tion of the seventh costal cartilage of the right side with the sternum to the sternal end of the third left costal cartilage. The right orifice is lo- cated upon the line where it is inter- sected by a line joining the sternal jkj'' ^<0cr ends of the fifth costal cartilages, ^ while the left one is situated at its upper end. The systemic and pulmonary aortic orifices are situated at about the level of the attachment of the third costal cartilages to the sternum, the pulmon- ary orifice being behind the sternal end of the third left cartilage, while the aortic orifice is behind the left half of the sternum, a little below and to the right of the pul- monary one, the two orifices overlapping for about one-quarter of their diameters. It is to be noted, however, that the pulmonary aorta is directed upward and to the left, while the systemic aorta inclines decidedly towards the right in the first part of its course; and since the sounds caused by the valves which guard the orifices are carried in the direction of the blood-stream, auscultation of the pulmonary semilunar valves may be practised over the sternal end of the second left intercostal space, while that of the systemic valves is best performed over the sternal end of the second right space. Similarly the close proximity of the areas of the left auriculo-ventricular and systemic aortic orifices, as projected upon the thoracic wall, might lead to confusion, Position of heart and valv wall. A, aortic vaKe ; P. \ cuspid valve ; M, mitral val ■s in relatioi live of pulmonary aona THE CHAMBERS OF THE HEART. 693 were it not that the course of the blood passing through the two orifices is in opposite directions, and the auscultation of the auriculo-ventricular orifice is consequently satisfactorily performed towards the apex of the heart. Considerable variation from the position of the heart indicated above may be found. Thus, the apex may be situated behind the fifth costal cartilage, or more rarely the si.\th, and the pul- monary aortic orifice may occur as high up as the second intercostal space, or as low as the level of the fourth costal cartilage. The heart naturally has its position altered somewhat during its contraction and during the respiratory acts, and the position of the body will also have some effect in modifying its location. Resting, as it does, upon the diaphragm, the heart will alter its position somewhat with altera- tions of that muscle ; and since in the child the diaphragm is somewhat higher and in the aged somewhat lower than in the middle period of life, corresponding changes according to age will be found in the position of the heart. It may be noted, furthermore, that the position of the heart as determined in the cadaver will, as a rule, be slightly higher than in the living body, owing to post-mortem tissue changes which allow the diaphragm to assume a more vaulted form than is usual in life. Relations. — As regards its relations the heart is completely enclosed within the pericardium, with which alone surrounding organs come into contact. In what fol- lows it is really the relations of the pericardium that will be described, although of necessity these relations are indirectly those of the heart and will be spoken of as such. Anteriorly the greater part of the heart is covered by the anterior- borders of the lungs and pleurae, which separate it from contact with the anterior thoracic wall. As a rule, the anterior borders of the pleurae are in contact from the level of the second costal cartilage to that of the fourth, but below the latter level they separate, the border of the left pleura diverging from the median line more rapidly than that of the right. In consequence, throughout an irregularly triangular area (Fig. 1580), whose vertical diameter extends from the level of the fourth to that of the sixth costal cartilages, the heart is uncovered by the pleurae and lies directly behind the thoracic wall. This area forms what is termed by clinicians the area of absohde diil- ness. Laterally the heart is in relation with the lungs, the phrenic nerves passing downward on either side between the pericardium and the pleura. Posteriorly the relations are again with the lungs and with the oesophagus and the thoracic aorta. Inferiorly the heart rests directly upon the diaphragm, beneath which is the stomach. Size and Weight. — There is considerable individual variation in the size of the heart, and marked discrepancies exist in the observations that have been re- corded. It may be said that in the adult the heart, on an average, will possess a length of from 12-15 cm. (43^-6 in.), a greatest breadth of from 9— 11 cm. (31^-41^ in.) and a thickness of from 5-8 cm, (2-31^ in.). Its weight has been given at from 266-346 gm. (9^-12^ oz. ) for males and from 230-340 gm. (8^-12 oz. ) for females, the average of a series of observations by different authors giving 312 gm. (11 oz.) for the male and 274 gm, (93/j; oz. ) for the female. The proportion of heart to the weight of the entire body, according to an average drawn from several observers, is i : 169 in the male and i : 162 in the female. It must be remembered, however, that the weight of the heart increases with age up to about the seventieth year, probably a slight diminution taking place after that period. THE CHAMBERS OF THE HEART. It has already been noted that the heart is composed of four chambers, a right and left auricle and a right and left ventricle. As the heart lies in position, litde of the auricles, with the exception of the auricular appendices, can be seen, since they have in front of them the roots of the aortae. In the ventricular portion the greater part of the anterior surface is formed by the right ventricle, a small portion only of the left ventricle showing to the left and at the apex, the whole of which is form.ed by the left ventricle. The four chambers will now be considered in succession, begin- ning with the auricles. The Right Auricle.— The right auricle ratrium dextrtim) is a relatively thin- walled chamber having in cross-section a roughly triangular form, the various sur- 694 HUMAN ANATOMY. faces, however, passing into one another almost insensibly without forming distmct angles. Viewed externally, the roof of the chamber is directed upward, backward, and somewhat to the right, and near its junction with what may be termed the poste- rior wall receives the superior vena cava. The posterior wall, also smooth and rounded, receives, near its junction with the median wall, the inferior vena cava, and below and to the left of this, in the posterior auriculo-ventricular groove, is the ter- minal portion of a vein which winds around the heart from the left and is termed the coronarv sinus. The antero-lateral wall is prolonged into a somewhat triangular diverticulum with crenulated edges, which winds anteriorly around the proximal por- tion of the systemic aorta and is known as the right auricular appendix (auricula dextra). The median wall is not visible on surface view, and is formed by a rather thin muscular partition, the auricular septum (septum atriorum), which is common to both auricles ; and the floor, also invisible from the exterior, corresponds to the base of the right \entricle, and is perforated by an oval aperture, the right auriculo-ven- tricular orifice, which places the cavity of the auricle in communication with that of the right ventricle. Fig. 657. Systemic aorta lmonar>- aorta or artery Right pull nar>' arter>' Sup. pul Right auricular appendage Eustachian valve Dep Interior of right auricle exposed after recei\ ing lhcbt:^iau \cins val of part of heart wall. d by Thebesian valv When the interior of the right auricle is examined (Figs. 657, 661 ),_ the surface is found to be for the most part smooth, being lined throughout by a delicate shining membrane covered by flattened cells and termed the endocardium. The general smoothness of the surface is, however, interrupted here and there by minute depressions (foramina venarum minimarum) into some of which open the orifices of Thebesian veins that traverse the walls of the heart. The ca\-ity of the auricular appendix is crossed by a net-work of anastomosing fibro-muscular trabeculae, the musculi pectinati, which are ever^-^vhere lined upon their free surfaces by endocardium and give to the appendix a sonriewhat spongy texture. In the roof of the auricle is seen' the circular orifice of the superior vena cava, unguarded by valves and having a diameter of from 18-22 mm., and on the posterior wall is the somewhat oblique opening of the inferior vena cava, somewhat larger than that of the supenor one, measuring from 27-36 mm. in diameter. The lower and lateral margins of this orifice are guarded bv a crescentic fold, the Eustachian valve (valvula venae cavae inferioris), which tends to direct the blood entering by the vein upward and medially, and is the remains of a structure of considerable importance during fcEtal life (page THE CHAMBERS OF THE HEART. 695 Pulmonary aorta 708). Between the superior and inferior venae cavae there may sometimes be seen a more or less marked prominence of the posterior wall, the tubercle of Lower (tuberculum intervenosum), the remains of a structure also of importance in the foetal circulation. Below and somewhat median to the opening of the inferior vena cava is the circular orifice of the coronary' sinus, measuring about 12 mm. in diameter, and guarded, like the inferior caval orifice, by a crescentic valve which surrounds its lateral margin and is termed the Thebesian valve (valvula sinus coronarii). The median wall, in addition to a number of Thebesian orifices, presents at about its centre an oval depression, the fossa ovalis, whose superior and anterior borders are surrounded by a thickening or slight fold termed the amndus ovalis (limbus fossae ovalis). The fo.ssa ovalis indicates the position of what was in foetal life the foramen ovale, through which the blood entering the right auricle from the inferior vena cava passed directly into the left auricle and so joined at once the sy.stemic circulation (page 929). This foramen traversed the auricular septum obliquely, the septum really consisting of two folds, one of which projected backward from the anterior wall of the auricular portion of the heart, and the other forward from the posterior wall, the plane of the latter fold lying slightly to the left of that of the former one. After birth these two folds increase in size so that their free margins overlap and event- ually fuse, closing the foramen, and the original free edge of the ante- Fig. 6.s8. rior fold becomes the annulus of Vieussens, while the floor of the fossa ovalis is formed by the pos- terior fold. It occasionally happens that the foramen ovale fails to close after birth, remaining sufficiently open to permit of serious disturb- ances of the circulation which are usually, although not always, early fatal. Very frequenth-, however, the fusion of the overlapping sur- faces of the two folds is not quite complete, and a small, oblique, slit- like opening persists between the two auricles. In such cases during the contraction of the auricles the pressure of the blood on the over- lapping walls of the slit brings them into close apposition and effectually closes the slit, so that no disturbances of the circula- tion result from its presence. This slit-like opening has been found to be present in somewhat over 30 per cent, of the adult hearts e.xamined. The Left Auricle. — The left auricle (atrium sinistrum) has the same general external form as the right one, and, as in the latter, its antero-lateral wall is prolonged into an auricular appendix which curves forward around the left side of the proximal portion of the pulmonary aorta. Upon its posterior surface the auricle receives the four pulmonary veins arranged in pairs, one of which is situated nearer the medial and the other towards the lateral edge of the surface, and passing obUquely over this surface towards the coronary sinus is a small vein, known as the oblique vein of the left auricle (vena obliqua atrii sinistri [Marshalli] ), which represents the proximal end of the left vena cava superior present during early embryonic life (page 927). Viewed from the interior, the walls of the left auricle, like those of the right one, are everywhere lined by a smooth, shining endocardium ; in the appendi.x the spongy structure due to the existence of anastomosing 7misculi pccti?iaii also occurs, and occasional depressions of the surface mark the openings of ve7i(S Thebesii, which are, however, much less abundant than in the right auricle. The openings of the pul- monary veins on the posterior wall are circular, and each measures from 14—15 mm. in diameter ; they are unguarded by valves, although a slight horizontal fold sepa- rates the portion of the auricular cavity into which the left veins open from the entrance into the auricular appendix. Upon the median wall, over the area occupied by the fossa ovalis of the right auricle, a slight depression is frequently to be observed, and immediately anterior to it there is usually a small crescentic fold, the seinilunar fold, whose concavity is Heart of foetus just before birth ; wall of right auricle has been cut away, showing foramen ovale. 696 HUMAN ANATOMY. directed forward, and which represents the free edge of the posterior segment or fold of the auricular septum (,page 708). In the floor is situated the large circular auriculo-ventricular orifice by which the cavity of the auricle communicates with that of the left ventricle. The Ventricles. — The two ventricles present many features in common and may be described together, such differences as e.xist between them being pointed out as the description proceeds. Each has a form which may be likened to a three-sided pyramid whose base is directed upward and the apex downward. The edges of the left ventricle are, however, somewhat more rounded than those of the right, so that its form approaches more nearly that of a cone ; and, furthermore, it is somewhat Fig. 659. Superiorvena cava Systemic aorta Left pulmonary artery Superior left pulmonary Left auricular append Part of posterior leaflet of mitral valve Anterior (aortic) leaflet of mitral valve Coronary sinus, cut Interior of Ilti am i^ le and ventricle, seen from behind ; posterior wall of heart has been partially removed by frontal section. longer than the right, its apex alone forming the apex of the heart. The surfaces presented by each ventricle may be termed anterolateral, posterior, and median, but in using these terms the heart is to be regarded as placed so that its long axis is ver- tical ; hi siht the antero-lateral surfaces look largely upward and the posterior sur- faces downward. The median wall is a partition, the interveyitricular sepUun (septum ventricuiorum), common to the two ventricles, and completely separates their cavities. Throughout the greater part of its extent this septum is muscular, but towards its upper border it becomes fibrous {pars membrajiaced) and is continuous with the septum of the auricles ; the position of its edges is indicated upon the external sur- face of the heart by the anterior and posterior interventricular grooves. The bases of THE CHAMBERS OF THE HEART. 697 the ventricles are directed upward, backward, and to the right, and each is perforated by two orifices. One of these in each ventricle is the auriculo-ventricular orifice, while the other, in the case of the right ventricle, is the opening of the pulmonary aorta, and is placed in front and a little to the left of the auriculo-ventricular orifice upon the summit of a slight conical elevation of the base of the ventricle, termed the conus arteriosus or infundihdum. The second orifice of the left ventricle is the opening of the systemic aorta, and is situated in front and a little to the right of the corresponding auriculo-ventricular orifice, immediately adjoining it. Compared with those of the auricles, the walls of both ventricles are very thick, that of the left especially so, being from two and a half to three times as thick as the right one. Unlike the auricles in another way, the inner surfaces of the ventricles. Pulmonary aorta (pulmonary artery) Left coronary artery Inferior vena cav Eustachian valv Pectinate muscles Thebesian valve guarding opening of coronary sinus Posterior leaflet of tricuspid valve Membranous part of interventricu- lar septum -Medial leaflet of tricuspid valve Septal papillary muscl Posterior papillary muscle, cut Posterior portion of heart, hardened in situ and sectioned parallel to posterior surface ; viewed from before. instead of being even, are very irregular, being everywhere covered by muscular ridges or columns, over and around which the endocardium is folded. These mus- cular elevations are usually regarded as consisting of three varieties : ( i ) ridges which are attached throughout their entire length to the wall of the ventricle, upon which they stand out like bas-reliefs ; (2) columns which are attached at either e.xtremity to the wall of the ventricle, but are free from it throughout the interv^ening portion of their length ; and (3) columns which are attached only by one extremity to the ventricular wall and by their other extremity give attachment to slender ten- dons, chordcB tendijietE. which pass to the edges of the valves guarding the auriculo- ventricular orifices. To the columns belonging to the first and second of these groups the term columnce carnece is applied, while those of the third group are known 698 HUMAN ANATOMY. as the musculi papillarcs. Quite frequently in the right ventricle and more rarely in the left, a muscular band occurs, which passes across the cavity from one wall to the other near the apex ; such a structure constitutes what has been termed a moderator band. Here and there between the columnae carneae of both ventricles minute orifices of the Thebesian vessels occur. Around the orifices situated at the bases of the ventricles the muscular sub- stance of the heart's walls passes over into dense fibrous tissue, of which the portion Fig. 661. Systemic aorta Right auricular appendage Anterior leaflet of tricuspid valve Margin of tricuspid Chordae tendineae Anterior papillary muscl Anterior wall of heart hardened in situ and sectioned parallel to posterior surface, viewed from behind ; oniy very- small part of left ventricle is seen ; probe passes from pulmonary aorta (artery) into right ventricle. surrounding the auriculo-ventricular orifices serves to connect the auricles and ven- tricles. If the auricles and the pro.ximal portions of the aortte be removed, the fibrous tissue will be seen to form four rings (annuli fibrosi), one corresponding to each of the basal orifices of the ventricles; and, furthermore, three of the rings — those .surrounding the two auriculo-ventricular orifices and that of the systemic aorta — will be seen to be directly in contact, while the fourth — that surrounding the pul- monary aortic orifice — is separate from the others, although connected with the right auriculo-ventricular ring by a narrow fibrous band which descends in the posterior THE CHAMBERS OF THE HEART. 699 wall of the conus arteriosus. The ring surrounding the left auriculo-ventricular orifice is somewhat thicker than that of the right, and is fused with the systemic aortic ring throughout about the medial third of its circumference, whereas the correspond- ing fusion of the right ring is of much less extent. In the angle formed by the junction of the right auriculo-ventricular ring at the side with the systemic aortic ring in front a special thickening of the fibrous tissue occurs, so that it becomes of almost cartilaginous consistency, and a similar, although smaller, thickening also occurs in the angle formed by the junction of the anterior walls of the left auriculo- ventricular and systemic aortic rings. These thickenings form what are termed the right and left atiriculo-ventricidar nodes (trigona fibrosa), and they are of interest as being occasionally the seat of a calcareous deposit or of a fatty infiltration, a condi- tion which may be shared by fibre-like prolongations of the nodes (y?/a coronaria) which extend into adjacent portions of the auriculo-ventricular rings. The Auriculo- Ventricular Valves. — Attached by its base to each auriculo- ventricular fibrous ring, and projecting downward into the cavity of the correspond- ing ventricle, is a valve having the general form of a membranous cone, whose walls are of thin but strong fibrous tissue covered on both sides by the endocardium. Each cone, however, is divided by deep incisions into triangular segments, of which there are three in the valve of the right ^'entricle, whence it is usually termed the tricuspid valve, while two incisions divide the left valve into two segments and procure for it the name of the bicuspid or mit?-al valve, the latter term being suggested by its resemblance to a bishop's mitre. Of the three segments of the tricuspid valve, one (cuspis anterior), larger than the others and also known as the infundibular cusp is attached to the anterior border of the auriculo-ventricular orifice ; a second one (cuspis posterior) is attached to the posterior border ; while the third or septal (cuspis medialis) occupies the interval between the medial edges of the other two, and is attached to that portion of the auriculo-ventricular fibrous ring which is united to the right auriculo-ventricular node and to the upper part of the ventricular septum. In the mitral valve one segment (cuspis posterior) is -attached to the posterior border of the auriculo-ventricular fibrous ring, while the other (cuspis anterior) or aortic cusp is situated anteriorly, and depends from that portion of the ring which is united to the ring surrounding the systemic aortic orifice, and consequently appears to be a downward prolongation from the posterior border of that orifice. It is to be noted that the depths of the incisions separating the seg- ments of both valves vary considerably, and additional incisions may occur, resulting in the formation of additional segments. Not infrequently a small accessory segment occupies the apex of one or more of the incisions. These vah'es, while permitting the free passage of blood from the auricles into the ventricles, prevent its passage in the reverse direction during the contraction of the ventricles ; for the pressure of the blood within the ventricles forces the segments up- ward so that they completely occlude the auriculo-ventricular orifices, the chordae tendineae which are attached to them, and which are rendered taut by the contraction of the papillary muscles, preventing them from being forced back into the auricles. The musculi papillares of each ventricle are arranged in two groups, one consisting of small papillae, situated near the upper portion of the ventricle behind the segments of the valves, and the other, composed of larger conical muscles, situated nearer the apex. The chordae tendineae which arise from the upper group are short, and are attached to the ventricular surface of the \'al\'e near its base ; those which arise from the lower group are much larger, and are attached to the edges of the valve and to its ventricular surface near its free edge. The papillary muscles belonging to this lower group tend to be arranged in sets -corresponding in position with the incisions which separate the segments of the vah'es, and there are, accordingly, three sets in the right ventricle and two in the left ; but this arrangement is not quite definite, and there is also considerable variation in the number of papillary muscles in each set, only one being present in some cases and several in others. However that may be, the chordae tendineae arising from the apices of the muscles of each set diverge as they pass upward and are attached to both the adjacent segments of the \'al\'e. When distinct accessory segments occur, they also receive the insertion of some of the chordae tendineae. 700 HU-MAN ANATOMY. The Semilunar Valves. — Although really belonging to the pulmonary and systemic aortse, it is convenient to consider these valves along with the heart, since they prevent the regurgitation of the blood contained in the aortae into the ventricles at the completion of their contraction. The segments guarding these valves are three in number in each aorta and are attached to the fibrous ring of the aortic orifices. Each segment is a crescentic pouch-like structure, whose cavity is directed away from the heart, so that any ten- dency for the blood to return from the aortae into the ventricles will result in the fill- ing of the pouches so that the three are brought into apposition and effectually close the orifice. Their efficiency is increased by ( i ) the occurrence at the middle of the free edge of each segment of a small fibro-cartilaginous nodule, the nodule of Am7i- tius, which fills the small gap which might otherwise be left at the point of meeting of the free edges of all three segments ; and by (2) the aorta being pouched out behind each segment to form a small pocket, a sinus of Valsalva, greater opportunity being thus allowed for the blood to enter the cavities of the valves and so force their free edges together. The segments of the semilunar valves of the systemic aorta (valvulae semihmares aortae) are somewhat stronger than those of the pulmonary aorta (valvulae semiiu- FlG. 662. Post, leaflet of pulm. valve Left coronary artery, behind left posterior leaflet Valves of heart Right posterior leaflet of i\ aortic valve Medial cusp Y^ — Posterior cusp Fibrous rin^ surrounding tricuspid valve removal of auricles and greater part of aortae. nares a. pulmonalis), and are arranged, if considered with reference to the planes of the body, the heart being /« situ, so that one is situated anteriorly and the other two right and left posteriorly. In the pulmonary aorta one valve segment will be posterior and the others right and left anteriorly. If, however, the heart be held so that its ventricular septum lies in the sagittal plane, then the valve segments differ by 60° from the relative position given above, those of the pulmonary artery being arranged so that one lies anteriorly and the other two right and left posteriorly, while in the systemic aorta one is posterior and the other two right and left anter- iorly, an arrangement to be expected from the manner of development of the valves (page 7101. The Architecture of the Heart Muscle. — The musculature of the walls of the auricles is relatively \ery thin, and it is diflicult to distinguish any definite arrangement of its fibres in layers. Groups of fibers can, however, be distin- guished, and of these certain are confined to each auricle, while others are common to the two. Of the fasciculi proper to each auricle two principal groups can be recognized. I. Annular fasciculi, which surround the orifices of the veins entering the auricles, and represent the continuation of the circular muscle layer of the veins into the auricular walls. THE CHAMBERS OF THE HEART. 701 Fig. 663. Anterior cusp of aortic valv Portion of left ventricle, showing position (-)-) of auriculo-ventricular muscle bundle in membran- ous part of interventricular septum. \Riizer,) 2. Ansiform fasciculi, which take their origin from the auriculo-ventricular fibrous ring anteriorly and extend over the auricle to insert into the fibrous ring posteriorly. These bundles are situated as a rule more deeply than the annular fasciculi and produce the pectinate mus- cles of the auricular appendage, as well as certain columnar elevations, covered by endocardium, which occur upon the inner surfaces of the walls of the auricles. The fasciculi common to both auri- cles are developed only in the neighbor- hood of the auriculo-ventricular groove, ,and constitute thin superficial bands, which run parallel to the groove. The anterior fasciculus is broader and more highly developed than the posterior one. The auriculo-ventricular fibrous ring- forms an almost complete separation be- tween the musculature of the auricles and that of the ventricles, the only direct con- nection between the two being formed by a slender auriculo-ventricular fasci- culus. This takes its origin in the pos- terior wall of the right auricle close to the auricular septum (His, Jr.) and passes downward towards the upper border of the muscular portion of the ventricular septum (Fig. 663). Here it bends forward and runs across the septum in the line of junction of its membranous and muscular portions, and is lost anteriorly in the musculature of the ventricles. The existence of this auriculo-ventricular fasciculus is of considerable importance in connection with transmission of the contraction wave from the auricles to the ventricles, the application of a clamp to the bundle having been shown to produce heart-block (Erlanger). It can readily be perceived that the muscle-fibres of which the walls of the ventricles are composed are arranged in more or less definite layers, and that the direction of the fibres in the deeper layers is different from that of the more super- ficial ones. The descriptions of the various layers and of their relations to one another vary greatly in different authors; in that given here the results obtained by MacCallum, by the application Fig, 664. of more suitable methods than were available to the earlier ob- servers, will be followed. The fibres of the ventricles can start only from the fibrous rings surrounding the ventricu- lar orifices or else from the sum- mits of the musculi papillares, to which a certain amount of fixa- tion is afforded by the chordae tendinese and their attachment to the auriculo-ventricular valves. It will be convenient to regard the fibrous rings as the principal points of origin, and the most superficial layer of the muscula- ture may be said to arise from them and from the tendinous band which descends upon the posterior surface of the conus arteriosus towards the right auriculo-ventricular ring. Those fibres which take their origin from this ten- dinous band and the right ring wind in a left-handed spiral over the surface of the half of tendon of c of superficial muscle layers originating ventricular rings and in posterior 5 arteriosus. {MacCallum.) 702 HUMAN ANATOMY. Left auriculo- ventricular orifice Tendon of con us arteriosus Right auriculo- ventricular orifice ventricles, and when they reach the apex, they bend upon themselves and pass deeply and upward to terminate in the papillary muscles of the left ventricle. Those fibres which arise from the left auriculo-ventricular fibrous ring cross the posterior in- terventricular groove and, pass- '^'^ ^^5 ing beneath the fibres from the right ring, encircle the right ven- tricle and finally terminate in the papillary muscles of that ven- tricle. On the removal of these superficial fibres a deeper set is seen, which seem to form two muscular cones, each surround- ing one of the ventricles. In the adult heart it is difificult to perceive the true relations of the two cones, but in the hearts of young individuals up to two or three years of age it has been anterior fQ^j^j \\^^i both" the cones are formed by the curving of a con- tinuous sheet of fibres in an S-shaped manner. This dcc/> sheet of fibres takes its origin principally from the right auriculo-ventricular fibrous ring and from the ten- dinous band of the conus arteriosus, and encircles the right ventricle, lying beneath the superficial layer. When it reaches the posterior border of the ventricular sep- tum, it passes forward in that structure, and then encircles the left ventricle, termi- nating finally in the papillary muscles of that ventricle. The deep fibres which arise from the left fibrous ring are entirely confined to the left ventricle, forming a circular band surrounding its basal portion. Structure. — The heart muscle, the viyocardimn, is both covered and lined with serous membrane, the epicardiu??i, as the \isceral laver of the pericardium is often called, investing it externally and the endocardium, continuous with the intima of the large blood-vessels, clothing all parts of its elaborately modelled inner surface. The epicardium corresponds in its general structure with other parts of the pericardium, consisting, as do other serous membranes, of a single layer of endothelial cells that covers its free surface and rests upon a stratum of fibro-elastic connective tissue. The elastic fibrillse are very fine and numerous and, immediately beneath the endothelium, form a dense net-work. When not separated from the muscle by subserous fat, as it con- spicuously is in the in- ^'^ 666 terventricular and auric- ulo-ventricular grooves, the epicardium is inti- mately attached to the subjacent muscular tis- sue. The numerous branches of the coron- Deepei dxy vessels, as well as the ner\-e trunks and the microscopic ganglia connected with the car- diac plexuses, lie be- h. neath the epicardium or within its deepest layer. The endocardium follows all the irregular- ities of the interior of the heart, lining everv recess and covering the free surfaces of the valves, tendinous cords and papillarv muscles. It consists of the endothelium and the underlying connective tissue. The latter is differentiated by the distribution %..ser — r^ v\ ^ ^^ ^ VESSELS OF THE HEART. 703 Fibro- elastic tissue of of the elastica into two strata, a thin subendothehal layer practically free from elastic fibres and a broad layer in which the elastica predominates. The deepest stratum of the endocardium is continuous with the endomysium that penetrates between the fibres of the heart muscle. The valves consist of duplicatures of the endocardium, in their thicker parts strengthened by an intermediate middle layer of fibro-elastic tissue prolonged from the fibrous rings of attachment. Towards the free margins of the valves all three layers are blended and reduced to a thin fibrous stratum covered by endothelium. In the auriculo-ventricular leaflets, the fibro-elastic tissue of the chordje tendineje is continuous with the middle layer, while meagre peripheral bundles of muscle may be present beneath the endocardium. Al- though thinner than the auriculo- Fig. 667. ventricular, the pulmonary and aortic L, semilunar valves possess essentially the / ^ same structure, the endocardial layer, "^ however, being thickened to produce the noduli Aurantii. In addition to the structural de- tails of the fibres composing the myo- cardium already described in connec- tion with the general histology of muscle (page 462), it may be noted that in the immediate vicinity of their nuclei the fibres of the heart-muscle constantly contain accumulations of undifferentiated sarcoplasm in which lie groups of highly refracting brown- ish granules that, under moderate magnification, appear as pigment at the poles of the nuclei. The muscle- fibres, branching into net-works with long narrow meshes, are held together by delicate lamellae of connective tis- sue, the endomysium, which, together with the more robust septa that as the perimysium invest the muscular bun- dles, support the blood-vessels. The relation of the capillaries to the muscle- substance is unusually intimate, the capillary loops often modelling the sur- face of the fibres, lying in deep grooves almost completely enclosed by the sur- rounding sarcous tissue (Meigs). Al- though much less constant and typical than in the ventricular myocardium of many of the lower animals, as the sheep, goat, and o.x, the imperfectly differentiated fibres, known as fibres of Purkinje, are represented in the human heart-muscle by subendocardial filjres. There is reason to believe that these fibres are related to the co-ordinating auriculo-ventricular bundle of His (page 701.) The Blood-Vessels and Lymphatics of the Heart. — The heart receives its blood-supply through the two coronary arteries which arise from the svstemic aorta immediately above its origin, the return flow being by the coronary veins which open into the right auricle by the coronary sinus. Both these sets of vessels will be described later (page 728), but it may be pointed out here that the branches of the coronary artery upon the surface of the heart are, as a rule, all end-arteries, — that is, arteries which form no direct anastomoses with their neighbors. Practically no blood can be carried directly, therefore, by the left coronary artery into the territory Longitudinal section of leaflet of tricuspid valve. /.. 20. 704 HUMAN ANATOMY. supplied by the right one, or fice versa, and sudden occlusion of either of the arteries will produce serious disturbances or, in some cases, complete arrest of the contrac- tions of the heart. Since, however, the capillaries of the heart's substance, into which each artery is continued, form a continuous net-work, a passage-way for the blood of one artery into the territory normally supplied by the other may be formed by their enlargement, opportunity for which may be afforded in cases in which the occlusion of an artery has been very gradual in its development. There is, however, another way by which the tissue of the heart may receive nutrition in cases of gradual occlusion of the coronary- arteries, namely, through the Thebesian orifices in the walls of the auricles and ventricles. These openings communicate by means of capillaries with the coronar\' vessels, and it has been shown experimentally that the heart can be effectively nourished by blood passing from the chambers of the heart through the Thebesian vessels and back into the coronary veins. The lymphatic vessels of the heart form a net-work beneath the visceral layer of the pericardium, and a second less distinct net-work has also been described as occurring beneath the endocardium. These net-works communicate with two sets of principal vessels which lie in the anterior and posterior portions of the auriculo-ven- tricular groove. The anterior set passes from the right to the left, and, on reaching the pulmonary aorta, passes around its left surface to reach the systemic aorta, upon which it ascends to terminate in a lymphatic node situated to the left of the trachea. The posterior set opens in part into the anterior one and in part ascends along the right side of the pulmonary aorta to terminate in one of the nodes situated beneath the bifurcation of the trachea. The Nerves of the Heart. — The nerves of the heart are derived from the cardiac plexuses and, passing downward along the aortae, are distributed partly to the auricles and partly accompany the coronary arteries along the auriculo-ventricular groo\'e, where they form the coronary plexus, from which branches are distributed to the ventricles. Over the surfaces of the auricles and ventricles the branches form a fine plexus situated beneath the visceral layer of the pericardium, and from this ple.xus branches pass into the substance of the heart to terminate upon the muscle- fibres. Some ner\'e-tibres are also distributed to the pericardium and endocardium, and these are regarded as being afferent in function, as are also certain fibres which terminate in the connective tissue of the heart's walls. Scattered in the superficial plexuses there are numerous ganglion-cells, some- times occurring singly and sometimes collected into small ganglia. They tend to be especially numerous around the orifices of the great veins opening into the auricles, in the coronary plexuses, and over the upper portions of the ventricles. It has been asserted that ganglion-cells also occur embedded in the walls of the ventricles, but at present this requires confirmation. Much has yet to be learned concerning the qualities of the various nerve-fibres which pass to the heart in man, but it is presumable that they resemble in general tliose which have been deter- mined experimentally for those of the lower mammals. In the latter it has been shown that the cardiac plexuses contain both afferent and efferent nerve-fibres. The cardiac plexuses are formed by branches from the pneuniogastric and sympathetic nen,es. and among the fibres from the former nerve are some which, when stimulated, cause a cessation of the heart's contractions, whence they are termed the inhibitory nerves. Stimulation of sympathetic fibres, which, in the dog, for example, pass to the cardiac plexus from the first thoracic ganglion of the ganglionated cord, produces an increase in either the rapidity or the intensity of the heart-beat, and these fibres are consequently termed the accelerator or augmoitor fibres. Both the inhibitor)- and augmentor fibres are efferent, — i.e., they carry impulses from the nerve-centres out to the heart ; m addi- tion, the existence of afferent fibres has been determined among the pneuniogastric constituents of the plexuses. These are the depressor fibres, so called because their stimulation produces a marked fall in the blood-pressure, not on account of any action upon the heart-beat, since they lead the stimulus away from the heart, but by acting reflexly upon the inte.stinal vessels so as to produce their dilatation and, by thus lessening the peripheral resistance against which the heart must contend, lessen the work which the organ has to do. Whether the various efferent fibres pass directly to the muscular tissue of the heart or ter- ^ m;nate upon cardiac ganglion-cells which transmit the impulse to the muscle-fibres is a point which remains to be determined, although, from analogy with what is known as to the relation of the cerebro-spinal fibres to other portions of the involuntan,- muscular tissue, it would seem probable that the pneumogastric efferent fibres terminate prirharily upon the cardiac ganglion- cells. THE PRIMITIVE HEART. 705 DEVELOPMENT OF THE HEART. In the mammals in which the earliest stages in the development of the heart have been observed, this organ arises as two separate tubes that are formed by folding of the visceral mesoblast near the margin of the embryonic area. This folding occurs while the embryo is still spread out upon the surface of the yolk-sac and produces on each side an elevation, a heart-tube, that projects into the primitive body-cavity (Fig. 668). Each heart-fold differentiates into a thicker outer or myocardial layer, which gives rise to a portion of the cardiac muscle, and a very thin inner endocardial layer, from which the serous lining of the heart is derived. The latter consists of a single stratum of mesoblastic cells surrounded by the muscle-layer, but separated by a distinct space, as a shrunken cast lies within its mould. With the beginning constriction of the gut-tube from the vitelline sac and the associated approximation of the splanchnopleura of the two sides, the heart-tubes, at first widely apart, gradually approach the mid-line until they meet beneath the ventral surface of the primitive pharynx, in advance of the yolk-sac. Upon coming into contact, the cavities of the two heart-tubes for a brief period remain separated by the partition formed by the opposed portions of the myocardial layers. Very soon, how- ever, solution of this septum occurs and the two sacs become a single heart. The endothelial tubes are last to fuse, retaining their independence after the myocardial walls have blended. Upon fusion of the endothelial layers the conversion of the double tubes into a single heart is complete. Fig. 668. The early venous trunks — the body-stems (cardinals and jugulars) within the em- bryo and the viteUine and allantoic ( later umbilical ) veins from the e.xtra embryonic vas- cular net-works — converge to- wards a common sac, the sinus ve7iosus, which joins the caudal end of the cylindrical primitive heart. The slightly tapering cephalic extremity of the latter becomes the triuicus arteriosus, from which two trunks, the ventral aortee, are prolonged forward beneath the primitive pharynx, giving of! the aortic bows that traverse in pairs the series of visceral arches. The primitive heart consists, therefore, of a cylinder, somewhat contracted at its anterior end, that occupies the ventral mid-line in the later cervical region. The blood poured into the sinus venosus by the veins enters its posterior extremity and escapes anteriorly through the truncus arteriosus. Although for a brief period the heart-tube retains its median position and straight cylindrical form, its increasing length soon causes it to become bent upon itself and to assume the S-like contour shown in Fig. 672 A, from an embryo of 2. 15 mm. in length, in which the venous end of the tube lies below and to the left and the arterial trunk above and to the right. The intermediate portion of the tube, extending at first downward and then obliquely upward and towards the left, is the primitive ventricle, the early sigmoid heart-tube already suggesting the recognition of an arterial, ventricular, and venous segment. During the further development of the heart a rearrangement of these three divisions takes place, since the venous segment, orginally below, gradually acquires a pbsition above and behind, while the primitive ventricle comes to lie in front and ^below (Fig. 672). With the completion of this rotation, a deep external groove appears between the ventricular and venous chamber, now the priinitive auricle, that indicates the position of a contracted passage, the aiiricnlar canal (Fig. 672, C ), as the common auriculo-ventricular opening is termed. Coineidently with the upward migration of the venous segment,- a lateral outpouching of the auricular chamber appears on each side of the truncus arteriosus. These expansions, the primary au- 45 Myocardial layer Endocardial lay 7o6 HUMAN ANATOMY. ricular appendages, rapidly increase, until they form the most conspicuous part of the young heart (Fig. 673, C), embracing the upper part of the truncus arteriosus and overlying the ventricle. Meanwhile the ventricular segment has assumed the most dependent and ventral position, for a time appearing as a transversely expanding sac (Fig. 672, B) that in form recalls a greatly dilated stomach, the truncus arteriosus joining the " pylorus," and the contracted auricular canal suggesting the oesophagus. Soon, however, the higher right end of the ventricular segment sinks to the level and gains the ventral plane of the left end, the ventricle in consequence losing in width but gaining in height. A shallow longitudinal crescentic furrow, the later intervejitrieit/ar groove, now appears on the surface of the ventricle and suggests the subdi\'ision of this seg- ment into right and left Fic;. 669. chambers, at the same time indicating the posi- tion of the growing inter- nal partition that leads to this separation. Sections of the young heart ( Fig. 670 ) show the venous and ventricular segments as widely com- municating portions of the sigmoid tube, the walls of which are composed of the myocardial and endothe- lial layers. In somewhat older embryos (Fig. 671), the communication between these divisions of the heart- tube exhibits a slight con- traction, marking the posi- tion of the later auricular canal, which becomes a nar- row tran.s^■erse cleft that connects the primitive ven- tricle with the auricular chamber. The myocar- dial layer of the heart- wall, particularly in the \entricle, also shows the beginning of the trabeculae that invaginate the endo- thelial lining and event- ually lead to the conspicu- ous modelling of the interior of the adult heart. Frontal sections of the young human heart (Fig. 674, A) show the commencing separation of the ventricular and auricular chambers into right and left halves. This division is effected by the formation of a vertical partition consisting of an upper auricular, a middle valvular, and a lower ventricular part, supplemented by the aortic septum that appears in the truncus arteriosus and subdivides the latter into the pulmonary and systemic aortae. The subdixision of the auricle, which anticipates that of the ventricle, begins in the fourth week with the downward e.xtension of a crescentic fold, the aiirictilar sep- tum, or septutn prhniim, that gradually grows from the postero-superior wall of the auricle tow^ards the auricular canal and fuses with the partition that, as the septum intermedium, is formed within the canal by local thickening of its anterior and pos- terior lips. In this manner not only the common auricular chamber, but also the transversely elongated auriculo-ventricular opening, is separated into a right and a -rrr~ Left umbil- Reconstruction of upper part of human embryo of third week (3.2 mm.), showing relation of heart and blood-vessels. X 50* {Drawn from His model.) DEVELOPMENT OF THE HEART. 707 Neural canal left half. The interauricular partition, however, is not complete, since an opening appears in its upper part even before it has finished its downward growth and union with the vah-ular septum. This opening enlarges and remains as \h& foramen ovale that persists until birth as a direct passage for the blood from the right into the left auricle during the continuance of the fcetal circulation (page 929). The subdivision of the ventricular chamber, which commences a little later than that of the auricle, is accomplished chiefly by the formation of the vetitricular septum. The latter grows from the postero-inferior wall of the ventricle as a cres- centic projection that continues inward, a thickening of the ventricular wall corre- sponding in position with the external interventricular groove. The partition thus formed extends towards the auriculo-ventricular opening, where it meets and fuses with the septum intermedium, in this manner insuring the communication of the right and left auricles with the corresponding ventricles through the intervening respective portions of the valvular opening. The isolation of the two ventricles from each other, however, is not at first com- plete, owing to the ventricular partition being imperfect above and in front. This deficiency is overcome by the down- ward extension of the aortic septum Fig. 670. within the bulbus arteriosus (as the somewhat dilated lower end of the trun- cus arteriosus is now appropriately called) until it meets and fuses with the ventricular partition, thus completing the separation of the cardiac chambers into a right and left heart. The part of the ventricular partition contributed by the aortic septum always remains thin and constitutes the pars membran- acea of the adult organ. Coincidently with the foregoing changes, the auricles undergo impor- tant modifications in their relations with the blood-vessels opening into them. During the development of the auricles, the oval sinus venosus, into which is conveyed the blood returned by the vi- telline, allantoic (umbilical) and body- veins, elongates transversely into a crescentic sac, the convexity of which is in contact -.vith the back of the auricles, its opening into the latter having shifted so that it is in relation with only the right half of the auricular chamber. With the expanded body and right horn of the venous crescent communicate the vessels that later are represented by the superior and inferior venae cavae, while the elongated and smaller left horn receives the left duct of Cuvier that becomes the coronary sinus. For a time the opening of the sinus venosus, or sinus reiiniens ( His), into the heart occupies the posterior wall of the right half of the auricle. It is guarded by the venous valve, consisting of a right and left leaflet, that is prolonged forward along the roof of the auricle as a crescentic ridge, the septum spiii'ium (Fig. 674, A). With the continued appropriation of the venous sinus by the expanding auricle, the single aperture of the sinus disappears as the sac becomes part of the auricular chamber, thereupon the two venae cavae and the coronary sinus open directly into the right auricle by an independent orifice. That of the superior cava lies in the upper posterior part of the auricle, that of the inferior cava being lower and more lateral, with the smaller orifice of the coronary sinus slightly below. The septum spurium, the greater part of the left, and the upper part of the right segment of the arching fold that originally surrounds the opening of the sinus venosus disappear during the appropriation of the venous sac by the auricle. The lower part of the right leaflet, Myocardial layer Primitive ventricle Transverse section of early rabbit em- bryo passing through young- heart, showing venous segment behind and arterial in front. X 75- 7o8 HUMAN ANATOMY. on the contrary, persists and differentiates into the larger Eustachian valve, that guards the lower margin of the inferior vena cava and directs its blood-stream towards the foramen ovale, and the smaller Thebesian valve, that protects the orifice of the coronary sinus. As above noted, the separation of the two auricles is incomplete on account of the existence of the foramen ovale within the interauricular partition. From the roof and anterior wall of the right auricle an additional and relati\ely thick crescentic ridge, the septum secundum, arches around the foramen ovale of which it forms the anterior or ventral boundary. It lies close to and parallel with the auricular septum and fuses below with the lower part of the left segment of the venous valve to form the limbus Vieussenii that later limits the fossa ovalis, marking the former position of the foramen ovale. The latter, therefore, is included between two partially overlapping crescentic margins, that contributed by the septum auriculum lying behind and to the left, and that by the septum secundum in front and to the right, a narrow sagittal cleft intervening so that the surfaces of Fig. 671. the lunate borders are not in contact. Since the division of the heart into a right and left side is inseparably con- nected with the development of the lungs and the consequent necessity for a distinct pulmonary circulation, pro\is- ion for the return of the blood from the lungs to the heart is made by the early formation of the pulmonary veiris. These arise in pairs, one pair for each lung; close to the heart each pair unites into a single right or left stem that, in turn, joins with its fellow of the oppo- site side to form one short common trunk. For a time none of these ves- sels communicate with the heart, but later the common single pulmonary vein opens into the left auricle close to the septum. With the subsequent growth and expansion of the auricles an appro- priation occurs on the left side similar to that affecting the sinus venosus on the right, in consequence of which the short common pulmonary vein is first drawn into the heart, to be followed ne.xt by the two secondar}- and, finally, by the four primary pulmonary veins, all of which then open by separate orifices into the enlarging left auricle. The fre- quent variations in the number of the pulmonary veins and in their relations to the heart are usually to be referred to arrest or modification of this fcetal appropriation. The differentiation of a right and left auriculo-venfricular valve proceeds from the subdivision of the auricular canal by the septum intermedium. The latter is formed by the approximation and union of the median cushion-like projections upon the ventral and dorsal walls of the common auriculo-ventricular opening. The unob- literated lateral portions of the latter are triangular in outline and guarded by pro- liferations of the endocardium. Those of the lower margins of the \-alves elongate and project into the \-entric!es on the right side, giving rise to two leaflets, and on the left to a single flap. An additional prolongation from the partition contributes a septal leaflet on each side. In this manner the complement of flaps for the tricuspid and bicuspid (mitral) valves is early provided. The close relation between the leaf- lets and the attached restraining bands, the chordse tendineee, results from the secondary union of the immature flaps with the trabeculae of the spongy myocardium of the young heart. The loose muscular walls undergo partial consolidation, so that Truncus arteri( Transverse section of somewhat older em- bryo, showing differentiation into auricles, ventricle and truncus arteriosus. X 75. DEVELOPMENT OF THE HEART. 709 the outer strata of the ventricular muscle become compact while the inner layers for a time retain their characteristic trabeculae. Those attached to the valves undergo thickening and consolidation and become the papillary muscles; a few persist as ties FiG. 672. Reconstructions of developing hearts; A, from human embryo of about 14 days { (4.2 mm.) ; C, of 23 davs (4.3 mm.) ; fa, truncus arteriosus : pv, primitive ventricl* right and left auricular appendages ; avc, auriculo-ventricular canal. X 20. {Drawi Fig. 673. pv . long) ; B, of 21 days :; sv, sMius venosus ; aa^a'a\ from His models. ) Reconstructions of developing hearts; A, from human embryo of 25 days (5 mm. greatest length); ^.endo- thelial heart from same ; C, of 35 days (13.7 mm.); ra, /a, right and left auricles represented by large auricular appendages; » t/, /z/, right and left ventricles; /a, truncus arteriosus; f, endothelial tube; ac, auriculo-ventricular canal ; ag, interventricular groove. X 20. {Drawn from His models.) Fig. 674. embryo of 30 days (i' eart opened on right side showing Reconstructions of developing hearts; A, posterior half of heart of hu from in front ; B, same from embryo of 35 days (Cin preceding figure); C, same imperfect septa ; ai', auricular septum ; 2/5, ventricular septum; .yi', septum spur valve; jz', septum intermedium; rw, /z/, right and left ventricles ; /a, left auricle; rai/, /at/, right and left auriculo- ventricular valves ;_/b, foramen ovale, occupied in A and B by arrow; sse, septum secundum; Ivv^ left leaflet of venous valve; sc^ ic, superior and inferior vena cava; cs, coronary sinus; Idc, left duct of Cuvier; aos, aortic septum in truncus arteriosus. X 20. {Drawn from His models.) . or moderator bands; while the majority retain their freedom to a lesser degree and, as the columnae carnese, produce the conspicuous modelling of the interior of the ven- tricles. The muscular tissue, which at first extended to and even within the valve- 7IO HUMAN ANATOMY. leaflets, subsequently undergoes partial atrophy and disappears from the flaps and adjoining parts of the attached bands, the latter thereby being converted into the fibrous chordae tendineae. Even before the longitudinal subdivision of the bulbus arteriosus occurs, the junction of this tube with the primarj' \ entricle is marked by four cushion-like thick- enings that project from the interior of the bulb. These elevations, which consist of immature connective tissue covered by endothelium; furnish the leaflets of the aortic and pulmonarj- se/uilunar valves. The formation of the aortic septum within the bulbus arteriosus begins some distance above the vahe and immediately below the origin of the right and left pulmonaiy arteries. From this point the partition gradu- ally grows downward imtil it encounters the elongated lateral pair of the original four valve-cushions, of which one lies in front, one behind, and two at the sides of the bulb. With the completion of the division of the bulbus arteriosus into the systemic and pulmonary aortae, the septum clea\-es the two lateral cushions, each of the resulting valves being guarded by three leaflets so disposed that the original and undivided flap of the pulmonary artery lies in front, and that of the aorta behind. The partial rotation that later places the aortic valve behind and to the left of the pulmonary brings about the disposition obser\ed in the adult (page 700), in which the single leaflet of the aortic semilunar valve lies in front and that within the pulmonarv- artery is behind. At first comparatively thick, the leaflets suffer partial absorption, whereby they are converted into the membranous cusps that bound crescentic pouches, the sinuses of A'alsaha, which lie between the leaflets and the wall of the \essels. PRACTICAL CONSIDERATIONS : THE HEART. It is possible here only to indicate with great brevit)- certain changes in the position of the heart which should be studied in connection with its relations. The apex beat, normally to be found about one inch below and two inches to the sternal side of the left nipple, is due to the recoil of the left ventricle as it empties its contents into the aorta, to the lengthening of that vessel as the blood enters it, to the consequent straightening of the arch ( carr\-ing the heart forward ) , and to the absence of any interposed lung-tissue over the ' 'area of absolute dulness. ' ' The apex beat (and usually the heart itself) is (^) raised in cases of ascites, tympanites, large abdominal tumors, and atrophic pulmonarj' conditions ; ((5) de- pressed in aortic aneurism, mediastinal growths, pulmonarv' emphysema, pleural effusion, and hypertrophy or dilatation of the left \'entricle ; (r) displaced laterally to the right by left pleural eftusion, s]ilenic tumors, hypertrophy of the right \entri- cle, to the left by hepatic tumors, right pleural effusion, hypertrophy of the left ven- tricle. The heart may be drawn to either side by contracting pleural adhesions. As the area of absolute dulness^" superficial cardiac area"" — corresponds to that portion of the cardiac substance which is not separated by pulmonarv- tissue from the thoracic wall, it follows that its extent varies inxersely with the size or expansion of the lungs. In emphysema the area of cardiac dulness may quite disappear ; in the later stages of fibroid phthisis it may be much larger than normal. In relation to the anatomy of the valves and ca\ities of the heart, the sounds produced by the passage of blood through them should be considered in connection with at least a few of the modifications caused bv the chief pathological changes that affect that organ. It may be said here, for the sake of clearness, that x\v^ first sound occurs during the contraction of the ventricles, when the auriculo-ventricular open- ings should be closed by the mitral and tricuspid valves and the aortic and pul- monary orifices should be open, and that it is due to ( artery ^^ Diagram Ascending aorta ^ Ventral aortas . showing derivation of arteries in man by modifications in precedii External carotids ng plan ; left fourth aortic bow becomes aortic arch. It will be seen, therefore, that the arterial system consists of two fundamental portions, a branchial and a dorsal ao?-tic portion. A classification of the vessels of the adult according to such a plan would, however, result in considerable confusion, since, owing to the secondary modifications which have occurred, it would necessi- tate the separation into different groups of arteries which are closely related, and, 46 722 HUMAN ANATOMY, conversely, would associate quite distinct \-essels. It will be more convenient, there- fore, to employ a topographic classification, according to which two main subdivi- sions of the system — that of the pul)nona>y aorta and that of the systemic aorta — may be recognized, the systemic subdivision being again divided into the aortic arch, the thoracic, and the abdomiiial portions THE PULMONARY AORTA. The pulmonar}- aorta, most frequently termed the pulmonary artery ( a. piil- monalis) takes its origin from the summit of the conus arteriosus of the right ventricle. It is from 4.5-5 cm. (about 2 in ) in length, and is directed upward, backward, and slightly towards the left, and beneath the arch of the aorta it di\-ides into the right and left pulmonary arteries (Fig. 679). Fig. 679. Left coronary artery Right coronary vessels nd great vessels, viewed from before ; part of superior vena ( have been removed to show right pulmonar>' artery. Relations. — Throughout the greater portion of its length the pulmonary aorta is in\ested by that part of the visceral layer of the pericardium which surrounds it and the basal portion of the systemic aorta. At its origin it is partly overlapped in front by the tip of the right auricular appendi.x, and posteriorly it is in relation with the base of the systemic aorta and the pro.ximal portion of the right coronary artery. More distallv it lies to the left of the systemic aorta and rests upon the anterior sur- face of the left auricle. Branches. — The right pulmonary artery ( ramus dexter) has an almost transverse course from its origin towards the base of the right lung. It passes outward above the right auricle, behind the ascending portion of the systemic aorta and the superior vena cava and in front of the right bronchus. At the root of the king it divides into three branches which are distributed to the three lobes of the lung. The left pulmonary artery (ramus sinister) is somewhat shorter than the right, and passes outward in front of the descending portion of the aortic arch and the left bronchus to the root THE AORTIC ARCH. 723 of the left lung, where it divides into two branches to be distributed to the lobes of the lung. From the upper border of the artery a short cj-lindrical cord passes to the under surface of the transverse portion of the aortic arch, a little beyond the point at which the left subclavian artery arises from its upper conve.\ surface. This cord is the remains of a communication between the pulmonary and systemic aortse which exists in foetal life, when the lungs are not functional, and is termed the ductus arteriosus. It represents the outer portion of the vessel of the sixth branchial arch of the left side, and its lumen usually becomes occluded during the first few months after birth, so that, as a rule, the cord is solid in the adult. Variations. — The majority of the variations that have been observed in the pulmonary aorta are associated with serious malformations o'f the heart which usually result in early death, ■ and are consequently to be classed as pathological rather than as merely anomalous conditions. A precocious division of the main stem of the pulmonary aorta occasionally occur.s, absence of the right pulmonary artery has been observed, and an accessory coronary artery has been noted arising from the pulmonary aorta. Failure of the ductus arteriosus to undergo complete occlusion is a not infrequent occur- rence, and is often associated with a persistence of the foramen ovale. The ductus has also been observed to arise directly from the right ventricle. THE SYSTEMIC AORTA. The systemic aorta, or, as it is more commonly and more simply termed, the aorta, is the main arterial stem for the supply of the tissues of the body. It arises from the base of the left ventricle and curves in an arch-hke manner to the left side of the vertebral coluriin, along which it runs to the level of the fourth lumbar vertebra. There it gives off a pair of large common iliac arteries, and is continued onward, much reduced in size, along the ventral surface of the sacrum and coccy.x, being termed in this portion of its course the middle sacral artery. It may be regarded, for the purpose of description, as being composed of three portions : (i) the aortic arch, which extends from the heart to the left side of the body of the fourth thoracic vertebra ; (2) the thoracic aorta, extending from the lower end of the aortic arch to the diaphragm ; and (3) the abdominal aorta, extend- ing from the diaphragm to the fourth lumbar vertebra. The middle sacral artery may most conveniently be treated as a branch of the abdominal aorta. THE AORTIC ARCH. The aortic arch arises from the base of the left ventricle (Figs. 679, 690), and in the first or ascending portioji (aorta aseendens) of its course is directed upward and somewhat forward and to the right. It then curves to the left and backward as the transverse portion (arctis aortae), and finally bends downward as the descending portion along the left side of the body of the fourth thoracic vertebra, to become continuous with the thoracic aorta. At its origin the aortic arch presents three rounded swellings, one anterior and the other two postero-lateral, marking the position of the sinuses of Valsalva '(sinus aortae). The diameter of the ascending portion is about 2.7 cm. and that of the descending portion about 2 cm. , the diminution appearing rather suddenly below the origin of the left subclavian artery and forming what has been termed the aortic isthmus. Where the ascending portion passes over into the transverse an enlargement of the diameter occurs which is especially well marked in older individuals, and is presuma- bly due to the impact of the blood forced out of the ventricle by its contractions. At about the junction of its transverse and descending portions the arch has attached to its under surface the fibrous cord which represents the foetal ductus arteriosus. Relations. — The ascending portion of the arch is enclosed throughout almost its entire length (about 5 cm. , or 2 in. ) in the sheath, formed by the visceral layer of the pericardium, which it shares with the pulmonary aorta. At its origin it lies behind and somewhat to the left of that vessel, but higher up crosses it obliquely, so that it comes to lie upon its right side ; to the right and left it is in , relation with the corresponding auricles, and anteriorly its upper portion is separ- ated froin contact with the sternum by a more or less abundant fatty tissue in which are the remains of the thymus gland. Posteriorly it is in relation with the anterior surface of the auricles. 724 HUMAN ANATOMY. The transverse portion is crossed on its anterior surface by the left phrenic, cardiac, and pneumogastric nerves, arranged in that order from right to left, the pneuniogastric crossing it on a level with the origin of the left subclavian artery. Fig. 6So. Pericardial sac Ascending portion Bronchial lymph-node Pleural sac Transverse portion Left pneumogastric Left recurrent laryngeal nerve Descending portion Right phrenic nerve Superior vena cava Bronchial lymph-node furcation of trachea ght pneumogastric nerve Oesophagus Thoracic duct Part of cross-sectic 1 of body at level of fourth thoracic vertebra, viewed from above ; upper part of aortic arch has been removed. More posteriorly the anterior surface is in contact with the left pleura. Behind it is in relation from right to left with the superior vena cava, the trachea, the oesoph- agus, and the body of the fourth thoracic vertebra, and below it are the right pul- monary artery, the left recurrent laryngeal nerve, and the left bronchus, the arch crossing this last structure obliquely from abo\-e downward and outward. The descending portion of the arch has in front of it a portion of the left pleura and the root of the left lung. Behind, it rests upon the fourth thoracic ver- tebra: to the right of it are the oesophagus and the thoracic duct and also the body of the fourth thoracic vertebra, and to the left are the left pleura and lung. Branches. — Just above its origin the aortic arch gi\'es off ( I ) the right and left coronary arteries, and from the upper or convex surface of the trans\-erse portion there arise in succession, from right to left, (2) the innom- inate or brachio-cephalic, (3) the left common carotid, and (4) the left S7ibclaviati arteiy. Variations. — Owing to the com- plexity of the changes by which the primary arrangement of tfie branchial arch vessels is transformed into the adult arrangement (Figs. 681, 6S2), and owing also to the possibility of some of tlie normal changes remaining uncompleted, the variations which oc- cur in connection with the arch of the aorta are rather numerous. They may be convenienth' classed in five groups. Group I.— In the normal development (Fig. 6S2) the'distal portion of the_ right aortic arch degenerates as far up as the right subcla\'ian artery, indications of it persisting as a more or less rudimentary I'as aberrant arising from the thoracic aorta. This degeneration may not occur, both the right and left aortic arches persisting in their entirety (Fig. 683); and, since in Diagram sh arrangement o stems and serie bow VA, DA, ventral ng prmiary on^itudinal f si.\ aortic arteriosus ; d dorsal aortae; A, unpaired do aorta; /-/*/, aortic bow which Fis rudimenlan*. Diagram showing normal derivations in man of primary vessels by modification of pre- ceding plan ; W. aorta; .-f^, aortic arch ; /, innominate artery ; CC, common carotids: EC. IC, exter- nal and internal carotids ; .S. sub- clavian artery ; /*, pulmonary art- ery; Z?.^, ductus arteriosus. THE AORTIC ARCH. 725 such cases the descending aorta usually retains its normal position to the left of the spinal column, a condition is produced in whicli the aortic arch appears to be split lengthwise into two portions, one of which, the left arch, passes in front of the trachea and cesophagus and gives origin to the left common carotid and the left subcla\ian arteries, while the other passes Fig. 683. Fig. 6S4. Developmental Group I, giving rise to anomaly shown in next figure. RAA.LAA, right and left aortic arches ; RS, LS, subclavian arteries ; A, aorta ; /*, pulmonary artery. Left c carotid Left subclavian Pulmonary artery Double aortic arch through which trache and cesophagus pass. {Hommel). behind the structures named and gives origin to a right common carotid and a right subclavian (Fig. 684). The relative diameters of the two portions of the aortic arch so formed may vary con- siderably, that passing in front of the trachea (the true left arch) being sometimes larger and at other times smaller than the other one. In the latter case an obliteration of the distal portion of the left arch may occur, and the left common carotid and left subclavian arteries will then appear to arise close to the innominate stem, from a common trunk, the aortic arch passing to the left behind the trachea. Group II. — A more frequent anomaly is the complete persistence of the distal portion of the right aortic arch (Fig. 685) associated with the disappearance of a greater or less portion of Fig. 685. Right common carotid _ Right vertebral - Developmental variations 01 Group H, giving rise to anomaly shown in next figure. A, aorta; P, pulmonan,- artery ; RS. LS, right and left subclavian arteries ; R V, right vertebral artery. Fig. 686. (Esophagus ^/^ ^ Left common carotid ^TlT" /| Left vertebral » If J 57 ^^3- Left Origin of right subclavian artery from descending aorta. its proximal part, the result being the apparent origin of the right subclavian artery from the descending aorta, whence it passes to the right behind.the trachea and oesophagus. Variations of this condition, depending upon the location and e.xtent of the disappearing portion of the right arch, may modify the relations of the right vertebral and subclavian arteries. Thus, in some 726 HUMAN ANATOMY. KiG. 687, cases the vertebral may arise as in the normal arrangement from the subclavian, or it may, as it were, exchange positions with the subclavian, arising from the descending aorta, while the sub- clavian arises, in common with the right common carotid, from an innominate stem ; or the vertebral may arise with the right common carotid from the innominate stem, the subclavian alone coming from the descending aorta ( Fig. 686) . Group III. — A third group of anomalies depends upon the complete persistence of the right aortic arch, associated with the disappearance of the distal portion of the left one (Fig. 6S7). In such cases the result is a complete reversal of the aortic arch and its branches, unaccompanied, however, b)' a reversal of any of the other organs of the body, and thus differing from a true situs inversus viscerum. The arch is directed from left to right, and gives rise to an innominate stem, from which the left common carotid and left subclavian arteries arise, a right common carotid and a right subclavian, the descend- ing aorta lying upon the right side of the vertebral column. Variations of these anomalies concern principally the rela- tions of the ductus arteriosus or the cord which represents it. It may unite with the descending aorta, in which case it is the persistent right si.xth branchial vessel, or it may be formed, as usual, from the left si.xth branchial vessel, com- municating distally with the left subclavian, this artery, in cases where the ductus remains patent, appearing to arise by two roots, one from the innominate stem and one from the pulmonary aorta. Group IV. — In the fourth group there is a complete persistence of the right aortic arch associated with a dis- appearance of the proximal portion of the left arch (Fig. 688), the resulting arrangement being the reverse of that seen in cases belonging to the second group. The left sub- clavian artery appears to arise from the descending aorta, which lies upon the right side of the vertebral column, and passes to the left behind the trachea and cesophagus. yaria- tions in the relations of the ductus arteriosus, similar to those mentioned as occurring in the third group, may be found. Group v.— A fifth group includes those cases in which the arch itself is normal, but in which there are variations m the vessels that arise from it. These variations may be either a diminution or an increase of the normal number' of vessels or an abnormal arrangement of a normal number. The diminu- tion and altered arrangement of the vessels depend upon a shifting of more or fewer of them, so that, for example, the left common carotid and left subclavian arteries may arise from a common left innominate stem, all the vessels may arise from a common stem, the two conmion carotids may have a com- mon origin, while the two subclavians arise independently, or, what is the most frequent of these variations, the left com- mon carotid may arise from the innominate stem and pass upward and to the left obliquely across the front of the trachea. An increase in the number of vessels may be brought about by the independent origin from the arch of both the right common carotid and the right subclavian, the innominate being absent. In other cases, vessels which normally do not come into relation with the arch may take origin from it, this being most frequently the case with the vertebral arteries and Developmental variations less frequently with the internal mammaries ; and, finally, an of Group IV. ^, aorta; p. additonal branch to the thyroid gland, the art. thyroidea ima, PigS°"and ''leFt'"*' iubdavfali occasionally takes origin from the arch. arteries. Developmental variations of Group III. A^ aorta; P, pulmonary artery; RAA, right aortic arch; /? .4, duc- tus arteriosus ; RS, LS, right and left subclavian arteries. Fig. 688. Practical Considerations. — The Aortic Arch and Thoracic Aorta. — Surface Relations. — The ascending aorta begins beneath the sternum just to the right of the inner end of the third left costal cartilage. It ascends obliquely and towards the upper border of the second right costal cartilage. The second (trans- verse') part passes backward and to the left, crossing the mid-line about an inch from the suprasternal notch, the lower (concave) border corresponding in level with the ridge between the manubrium and the gladiolus, the upper (convex) border to the level of the third thoracic spinous process, to the middle of the manubrium, and the middle of the first costal cartilage. This border is about one inch below the supra- sternal notch. The surface relations of this portion vary with the development of PRACTICAL CONSIDERATIONS: THE AORTIC ARCH. 727 the thorax. In persons with small chests the upper border may almost reach the level of the top of the manubrium, while in those with large chests it may be no hio-her than the junction of the first and second pieces of the sternum (angjilus Ludovici). The transverse portion reaches the left side of the vertebral column at a level just above the fourth thoracic spine. The third (descending) portion and the thoracic aorta lie at first a little to the left of the body of the fourth thoracic vertebra and gradually incline to the mid-line, passing through the diaphragm at the level of the twelfth thoracic vertebra. Aneurisms of the aorta are more frequent than are those of any other vessel, on account of the great strains to which the aorta is subject. They may most con- veniently be considered here by following the anatomical subdivisions of the vessel, premising, however, that the symptoms thus described frequently commingle and overlap. A. The ascending portion is more subject to aneurism than are the remaining portions, because it receives the first and most vigorous impulse of the heart's stroke, and because it is within — enclosed by— the pericardium, and its walls are not rein- forced by blending with the fibrous pericardial layer, as is the case in the second and third portions. Aneurism most frequendy involves the region of the anterior sinus of Valsalva, where regurgitation of blood chiefly takes place ; or, if higher, the anterior wall of the aorta in the vicinity of the normal dilatation, probably due to the impact of the blood-current leaving the heart. The symptoms are : i . Venous con- gestion, causing (a) lividity of the face from pressure on the descending cava, the left innominate, and the internal jugular veins ; {b") dizziness and headache from the same cause ; (c) swelling and cedema of the right arm from pressure on the sub- clavian vein ; (fi?) swelling and oedema of the ayiterior thoracic wallirom pressure on the internal mammary, azygos, or hemiazygos veins. 2. Dyspnma with altered breath sounds over the right chest, from pressure on the root of the right lung. 3. Dys- phonia or aphonia, with croupy or stridulous respiration, from pressure on the right recurrent laryngeal nerve ; sometimes from venous congestion due to pressure on the internal jugular and innominate acting through the superior thyroid and inferior thyroid veins on the corresponding laryngeal veins. 4. Swelling or tumor, often first seen at or about the sternal end of the third right intercostal space. 5. Dis- placement of the heart, occasionally occurring when the aneurism involves especially the concave side of the vessel and pushes the heart downward and to the left. 6. Ascites and cedema of the legs ayid feet from compression of the ascending cava when the aneurism occupies the same situation. 7. Pain in the sternum, the ribs, or the spine from direct pressure ; encircling the upper part of the chest from pressure on the intercostal nerves ; running down the side of the thorax and the inner surface of the arm from pressure on fibres distributed by the intercosto-humeral nerve. B. Aneurism of the transverse portion may cause : i. Dyspnoea and dysphonia or aphonia from direct pressure on the trachea or bronchi, or from involvement of the left recurrent laryngeal nerve in its course around the arch. 2. Dilatation of the pupil followed by contraction from, first, irritation and then paralysis of the sympathetic. 3. hianition from pressure on the thoracic duct. 4. Swelling, begin- ning in the mid-line, then extending to the right (only four left-sided cases out of thirty-five aneurisms, Browne, quoted by Osier), and sometimes simulating innomi- nate or common carotid aneurism. 5. Ve7ious congestion of the head, neck, left arm, etc. , often more marked on the left side from the greater exposure to pressure of the left innominate vein. 6. Weakness or absence of radial or temporal pulse — espe- cially on the left side — due to pressure on or involvement of the innominate, left sub- clavian, or left carotid artery. C. Aneurism of the descending portion of the arch and of the thoracic aorta may cause : i. Dysphagia, which is common and apt to appear earlier on account of the more direct relation with the oesophagus. 2. Great pain in the spine, some- times followed by paralysis, from erosion of the vertebrae and compression of the cord. 3. Swelling in the left scapular region or at the vertebral ends of the middle ribs on the left side. 4. Bronchiectasis, with cough and expectoration, from press- ure on the left bronchus, or asthmatic attacks from involvement of the left pulmo- nary plexus. 728 HUMAN ANATOMY. THE CORONARY ARTERIES. The coronary arteries, which supply the heart, are two in number, and arise from the right and left prominences at the base of the aorta which mark the corresponding sinuses of Valsalva. The left coronary artery (a. coronaria sinistra) lies at its origin (Fig. 679) behind the base of the pulmonary aorta, and passes forward between that vessel and the left auricular appendix to reach the anterior interventricular groove, in which it divides into two branches. The larger of these (ramus descendens anterior) descends in the groove to the apex of the heart, giving of? branches which supply the anterior surface of both ventricles, while the smaller one (ramus circumflexus) passes backward in the left portion of the auriculo-ventricular groove and gives off branches to the left auricle and ventricle. Branches to the left auricle also arise from the main stem of the artery, as well as twigs to the walls of the aortae. Fig. 6S9. Left pulmonary artery Superior left pulmonary vein Inferior left pulmonary vein Termination of left coronary vein Circumflex branch of left coronary artery Left ventricle Superior vena cava Superior right pulmonary i Right pulmonary artery Inferior right pulmonary v Inferior vena cava Coronary sinus Right coronary vein Right coronary artery Posterior descending branch of right coronary artery Middle cardiac vein Right ventricle Postero-inferior surface of injected heart, \-ie\ved from below and behind. The right coronary artery (a. coronaria dextra) passes outward from its origin in the right portion of the auriculo-ventricular groove, in which it lies, until it reaches the posterior interventricular groove, down which it ( ramus descendens posterior) is continued towards the apex of the heart (Fig. 689). In its course it gives oS num- erous branches, which are distributed to the right auricle and ventricle and to the portion of the left ventricle which adjoins the posterior interventricular groove. Usually a large branch, the marginal artery, descends along the right border of the heart (Fig. 679) and gives branches to both surfaces of the right ventricle. The peculiarities of the ultimate distribution of these arteries have been described in connection with the heart (page 703). Variations. — The two coronary arteries may arise by a common stem ; one of them may be wanting, or supernumerary vessels may occur. THE INNOMINATE ARTERY. 729 THE INNOMINATE ARTERY. The innominate artery (a. anonyma) (Figs. 679, 690), also known as the brachio-cephalic, is the first as well as the largest of the three vessels which arise from the arch of the aorta. It passes directly upward to the level of the right sterno-clavicular articulation, where it divides into the right common carotid and the right subclavian, but gives rise to no other branches. Relations. — Anteriorly it is separated from the sternum and from the origins of the right sterno-hyoid and sterno-thyroid muscles by the left innominate vein and by some fatty tissue which contains the remains of the thymus gland. Posteriorly it is in relation with the trachea and the sympathetic cardiac nerves ; on the right it is in contact with the right pleura and on the left of it is the left common carotid artery. Variations.— The variations of the innominate artery have already been discussed in connection with the variations of the aortic arch, since the vessel represents the pro.ximal portion of the right arch. It shows considerable variation in length, measuring between 2.8 and 4.5 cm., although occasionally reaching a length of 5 or even 7 cm. Occasionally it is absent, the right common carotid and the right subclavian. arteries arising directly from the aortic arch. ^ Although the innominate artery does not, as a rule, give origin to any branches e.Kcept the two terminal ones, yet in about 10 per cent, of cases there arises from it a vessel which is termed the arteria thyroidea ima. This takes its origin usually from near the base of the innominate, upon its medial surface, and passes directly upward upon the anterior surface of the trachea to terminate in branches which are distributed to the isthmus and the lower portions of the lobes of the thyroid body. The presence of this thyroidea ima is frequently associated with a more or less e.xtensive redirction of the size of one or other of the mferior thyroid arteries, and, indeed, these arteries may be entirely supplanted by it. it is somewhat variable in its origin, for, instead of arising from tlie innominate, it may be given off by the aortic arch, by the right common carotid, by either the right or left subclavian, or, in rare cases, by one of the branches of the subclavians. Practical Considerations. — The line of the innominate artery is from the middle of the manubrium to the right sterno-clavicular joint. Its point of bifurca- tion would be crossed by a line dravvn backward, just above the clavicle, through the interval between the sternal and clavicular portions of the sterno-mastoid muscle. Aneurism of the innominate artery, often associated with aneurism of the aortic arch, causes pressure-symptoms easily explained by the chief relations of the vessel. They may be summarized as follows : i. Vascular, (a) arterial, weakness or irregu- larity of the right radical pulse or of the right carotid or temporal pulse from inter- ruption of the direct blood-current ; {b') venous, duskiness of the face and neck, especially of the right side, cedema of the eyelids, protrusion of the eyeballs, lividity of the lips, from pressure on the left innominate, deep jugular, and transverse veins lying between the vessel and the thoracic wall ; cedema of the right arm from subclavian pressure. 2. Nervous, cough and hoarseness or aphonia from involve- ment of the right recurrent laryngeal : dilatation or contraction of the pupil from pressure on the sympathetic ; hiccough from irritation of the phrenic ; pain, particu- larly severe on the right side of the neck and head, the same side of the chest, and down the right arm from pressure on the branches of the cervical and brachial plexuses. In addition, dyspncea and dysphagia from compression of the trachea and oesophagus, and the appearance of a swelling at and above the right sterno- clavicular articulation, often obliterating the suprasternal depression, are character- istic symptoms. In endeavoring to differentiate these aneurisms from those of the arch of the aorta it may be well to remember that the position of the innominate is above, to the right, and, in a way, cervico-thoracic, while that of the arch is on a lower level, is median or to the left, and is wholly thoracic. Ligation. — Two skin incisions, each three inches in length, are made along the anterior edge of the sterno-mastoid muscle and the upper, border of the inner third of the clavicle, uniting at an acute angle near the right-sterno-clavicular articulation. The sternal portion and the greater part of the clavicular portion of the sterno-mas- 730 HUMAN ANATOMY. toid muscle are divided just above their origin. The anterior jugular vein runs behind the sternal head, and is to be avoided or tied. The thyroid plexus of veins may appear in the wound, and should be tied or drawn out of the' way. The sterno-hyoid and sterno-thyroid muscles are divided close to the sternum. The deep cervical fascia is divided in the line of the superficial wound. The common carotid artery should be found, its sheath opened, and the vessel traced down to the innomi- nate bifurcation. The internal jugular vein may be much engorged and should be drawn outward. The innominate \ein may protrude into the wound. Osteoplastic resection of the manubrium ( Bardenheuer j, or a median longitudinal division of that bone (Woolsey) with retraction of the edges, will facilitate the exposure of the vessel. The most important relations are to the outer side,^viz. , the vagus, the pleura, and the right innominate vein. The left common carotid and trachea lie to the inner side. The needle should be passed from without inward. The ligature should be placed as high as possible, to leave room between it and the aorta for the formation of a satisfactory clot. It is well to ligate the common carotid and the vertebral at the same time, to lessen the risk of secondary hemorrhage on the distal side of the ligature. The collateral circulation is carried on from the proximal or cardiac side of the ligature by [a^ the first aortic intercostal \ (b) the upper aortic intercostals ; (c~) the inferior phrenic branch of the abdominal aorta (within the diaphragm); (d) the deep epigastric (within the rectus sheath); (<*) the ^■ertebrals and internal carotids of the left side (within the cranium — circle of Willis); and (/) the branches of the left external carotid ; anastomosing respectively with (a) the superior intercostal of the subclavian ; (b) the intercostals of the internal mammary and the thoracic branches of the axillary ; (r) the musculo-phrenic branch of the internal mammary ; (yd ) the superior epigastric branch of the internal mammary ; (r) the vessels in the right half of the circle of Willis ; and ( f ) the branches of the right external carotid, all receiving their blood-supplv from beyond — or to the distal side of — the ligature. THE COMMON CAROTID ARTERIES. The right common carotid artery arises from the innominate and the left one from the arch of the aorta (Fig. 690). Both pass directly upward in the neck, along the side of the trachea and larynx, and terminate opposite the upper border of the thyroid cartilage by dividing into the external and internal carotid arteries, their course being represented by a line drawn from a point midway between the angle of the jaw and the mastoid process to the sterno-clavicular articulation. Throughout its course neither of the common carotids gives off any branches, and they consequently have an almost uniform calibre, except towards their point of division, where they present a dilatation frequentlv continued into the internal carotid and usually becoming hiore marked with ad\-ancing age. Relations. — The left common carotid lies in the thoracic cavity during the first part of its course, and in this respect differs from the right artery-, whose origin from the brachio-cephalic is at the level of the sterno-cla\icular articulation. This thoracic portion of the left common carotid is usually about 3 cm. (114 in.) in length, and is crossed obliquely in front, near its root, by the left innominate (brachio-cephalic) vein and by the cardiac branches of the pneumogastric ner\e. It is separated from the sternum and the origin of the sterno-thyroid muscle by some fatty tissue which contains the remains of the thymus gland, and posteriorly it is in relation with the trachea below and higher up with the left recurrent laryngeal nerve. Below, to its right side and a short distance away, is the innominate artery ; above it is in close relation with the trachea, while to its left and somewhat posteriorly are the left subclavian artery and the left pneumogastric nerve. Throughout their cervical portions the relations of both arteries are iden- tical. Each is enclosed within a fibrous sheath formed by the deep cervical fascia (page 550), the sheath also containing the internal jugular \-ein and the pneumo- gastric nerve, the vein Iving lateral to the artery and the nerve between the two vessels, but in a plane slightly posterior to them. Extending downward for a vari- able distance upon the anterior surface of the sheath is the descending hypoglossal THE COMMON CAROTID ARTERIES. 731 nerve, and overlapping it to a certain extent is the sterno-cleido-mastoid muscle and, below, the sterno-hyoid and sterno-thyroid. At about the level of the cricoid cartilage of the larynx the artery is crossed obliquely by the omo-hyoid muscle, and higher up 'by the middle and superior thyroid, the lingual and sometimes the facial veins, and the sterno-mastoid branch of the superior thyroid artery. Posteriorly the sheath rests upon the prevertebral fascia covering the longus colli and the rectus capitis anticus major muscles, and is in relation with the ganglionated cord of the sympathetic nervous system and its superior and middle cardiac branches. Lower down, opposite the sixth cervical vertebra, the branches of the Fig. 690. Vertebral arteries Infenor thj roid arterj* Transverse cervical artery Mesial surface of lung Right coronary artery \ 3^.-^/^;;^^ %: Dissection showing aortic arch and its branches ; lungs have been pulled aside. inferior thyroid artery pass behind it. Medially are the trachea and the cesophagus, together with the recurrent laryngeal nerve, the lobe of the thyroid gland, and, above, the larynx and the pharynx. Variations. — The variations of the common carotid arteries have been sufficiently discussed in connection with the anomalies of the aortic arch (page 724). Practical Considerations. — A7ie2iris->n of the common carotid artery is not very frequent. It most commonly occurs near the bifurcation {a) because of the slight dilatation normally existing there ; {F) because there the vessel is more super- 732 HUMAN ANATOMY. ficial, — i.e., least supported by overlying muscle ; and {c) because of the increased resistance to the blood-current at that point. It is seen oftener in the right carotid than in the left. Pressure-symptoms : pain in the side of the neck, face, and head in the distribution of the superficial cervical ple.xus of nerves ; duskiness or mottling of the skin from pressure on the sympathetic ; dyspncea and coiigli from lateral deflection of the laryn.x and trachea ; defective vision, vertigo, or stupor from press- ure on the internal jugular ; hoarseness or aphonia from implication of the recurrent laryngeal nerve ; dysphagia from direct pressure on the oesophagus, or — possibly, together with irregular heart action, vomiting, or asthmatic respiration — from press- ure on the pneumogastric. Digital compression may be used in a case of stab wound or in the treatment of aneurism («) by making pressure backward and outward beneath the anterior edge of the sterno-mastoid muscle at the level of the cricoid cartilage, so as to flatten out the artery against the transverse process of the si.xth cervical vertebra (carotid tubercle ) about two and a half inches above the clavicle. As the vertebral artery at this level enters its canal in the foramina of the transverse processes, it will probably escape pressure. The internal jugular vein is usually displaced laterally. The common carotid artery may also be effectually compressed in cases of wound ((^) by grasping the anterior edge of the sterno-mastoid and the artery together between the thumb and fingers, or (c) bv placing the thumb beneath the artery and the anterior edge of the muscle, and the fingers along its posterior edge. In all three of these methods it is necessary to fle.x the head and turn it a little towards the affected side so as fully to rela.x the sterno-mastoid. Ligation. — -It may be necessary to tie the common carotid in cases of (a) aneu- rism, including certain pulsating tumors of the orbit or scalp or within the cranium ; iyb) hemorrhage from wound of the neck, or from pharyngeal wound or ulceration ; or (f) for the prevention of bleeding during some operations. Whenever ligation of the e.xternal carotid satisfactorily meets the indications, it is better to tie that vessel {q.v.), as the cerebral circulation is not thereby interfered with. The lower portions of the common carotids on both sides of the neck are deeply seated ; they are covered by three planes of muscles ( the sterno-mastoid, sterno- hyoid, and sterno-thyroid) ; the inferior thyroid artery and recurrent laryngeal nerve run behind them on each side, and on the left side the internal jugular \ein usually passes from without inward in front of the artery, which is also in close relation to the thoracic duct, the innominate artery, and the left innominate vein. Two operations for ligation of the common carotid may be described : i. The place of election for the application of a ligature is just above the omo-hyoid muscle, where the artery has become more superficial and is co\'ered only by the skin, the platysma, the fasciae, and the anterior edge of the sterno-mastoid. The skin incision — three inches in length — is made in the line of the vessel, the centre being placed opposite the anterior arch of the cricoid cartilage. It divides also the platysma. The deep fascia is divided, and the anterior edge of the sterno-mastoid is exposed and followed downward to the angle between it and the upper edge of the omo- hyoid muscle. The former muscle is then drawn outward, the latter downward, the descendens hypoglossi nerve avoided, the sterno-mastoid branch of the superior thyroid artery and the superior — and sometimes the middle — thyroid vein held aside or tied, and the sheath opened over the carotid compartment, — /.*'., well to the inner side, — so as to avoid injury to the larger internal jugular \'ein, which some- times— as in cases of embarrassed respiration— bulges o\'er the artery so as com- pletely to obscure it. The needle should be passed from without inward to avoid injury to the vein, care, of course, being taken not to include the \agus. 2. Below the omo-hyoid muscle the skin incision — three inches in length — still follows the anterior border of the sterno-mastoid, beginning now a little below the lower border of the cricoid cartilage and ending just above the sterno-clavicular articulation. A second incision along the upper border of the cla\icle is often advis- able. The sterno-mastoid is drawn outward and the outer edge of the sterno-hyoid muscle exposed, and that muscle, with the sterno-thyroid, drawn downward and inward. Frequently the sternal portion of the sterno-mastoid, and occasionally the sterno-hyoid and sterno-thyroid muscles also, will require division if the ligature has THE EXTERNAL CAROTID ARTERY. 733 to be placed as near the root of the neck as possible. The internal jugular vein — especially on the left side— the inferior thyroid artery-, and the recurrent laryngeal nerve must be avoided. The needle is passed from without inward. The collateral circulation is carried on from the proximal or cardiac side through (a) the branches of the external carotid on the opposite side, (b) the inferior thy- roid, (c) the profunda cen'icis (from the superior intercostal and thus from the sub- clavian), ((3?) the internal carotid and the \'essels of the opposite segment of the circle of Willis, and {e) the vertebral, by anastomosing respectively with {a) the external carotid branches, [b) the superior thyroid, {c) the princeps cervicis (from the occipital j, and (d ) and ( erior Thyroid Artery. — The superior thyroid artery (a. thy- roidea superior ) ( Fig. 692 ) arises from the anterior surface of the external carotid, a short distance above its origin, and is at first directed almost horizontally anteriorly, but soon turns downward and, passing over the superior laryngeal nerve and beneath the omo-hyoid and thyro-hyoid muscles, breaks up into a number of branches which enter the substance of the thyroid gland. It possesses always a calibre of consider- able size, but varies directly according to the size of the gland, and in\-ersely according to the amount of blood' reaching the gland from other sources. It anas- tomoses abundandy with its fellow of the opposite side and with the inferior th\Toid branch of the subclavian. Branches — From its horizontal portion are gi\en off — (a) An infrahyoid branch ( ramus hyoideus), which passes along the lower border of the hyoid bone, supplving the muscles inserting into that bone. (16) A sterno-mastoid branch (ramus stemocleidomastoideus). always small and occasionally wanting, which passes downward and backward across the sheath enclosing the coiimon carotid to enter the substance of the stenio-cleido-mastoid muscle. ((-) A superior laryngeal branch (a larjngea superior), which passes forward and downward beneath the thyro-liyoid muscle and, piercing the thyro-hyoid membrane along with the superior larjTigeal nerve, is distributed to the intrinsic muscles and mucous membrane of the larynx. From its descending portion it gives off — (d) The crico-thyroid branch (ramus cricothyroideus). usually of small .size, which pa.sses horizontally forward over the crico-thyroid membrane and anastomoses with its fellow of the opposite side, giving oft' branches which perforate the membrane aid are distributed to the muscles and mucous membrane of the lower part of the larynx. Variations. — The superior thyroid may give origin to both the ascending pharyngeal and the ascending palatine. The crico-thyroid not infrequently arises from the superior laryngeal, and may appear to be the main stem of that artery, and Ihe superior laryngeal may arise directly from the external carotid. THE LINGUAL ARTERY. 735 Practical Considerations. — The superior thyroid artery or one of its branches is frequently divided in cut-throat wounds. The sterno-mastoid branch may have to be tied in the operation of Hgation of the common carotid at the place of election and the crico-thyroid branch during the performance of laryngotomy. Ligation. — The skin incision, two inches in length, with its centre opposite the thyro-hyoid space, is made along the carotid line. After the superior thyroid veins have been dealt with and the external carotid has been recognized, the vessel may most easily be found in the sulcus between the upper border of the thyroid cartilage Fig. 691. Posterior branch oftemporal Anterior branch oftemporal Middle temporal artery — Transverse facial artery- Superficial temporal artery Great occipital Trapezius Internal carotid Eatery Transverse Posterior scapul; Supra-orbital artery (shown the muscles> Frontal artery Nasal artery Angular artery Lateral nasal artery Buccinator Inferior labial artery Masseteric branch Facial arterj- Superficial dissection, showing; arteries of neck, face and sca-lp. and the great vessels, where for a short distance it is superficial and runs almost horizontally. The needle should be passed from above downward with the point directed some- what towards the mid-line. The close proximity posteriorly of the superior laryngeal nerve should be remembered. 2. The Lingual Artery. — The Hngual artery fa. lingualis) (Fig. 692) usually arises from the anterior surface of the external carotid, between the origins of the superior thyroid and the facial, although it is sometimes given, off from a trunk 736 HUMAN ANATOMY. common to it and one or other of these arteries, especially the facial. In the first part of its course it passes forward and slightly upward and inward towards the tip of the lesser cornu of the hyoid bone, and is crossed by the posterior belly of the digastric and the stylo-hyoid muscles and by the hypoglossal nerve. On reaching the pos- terior border of the hyo-glossus, it passes beneath that muscle and is continued almost directly forward beneath the mucous membrane covering the under surface of the tongue and between the genio-hyo-glossus and the inferior lingualis muscles. In this terminal portion it has a sinuous course, and is frequently termed the ranine artery ( a. profunda linguae) ; it gives branches to the adjacent muscular substance and mucous membrane of the tongue, and near its termination anastomoses with its fellow of the opposite side. Branches. — (<;) The suprahyoid branch (ramus hyoideus), given off from tlie first portion, passes horizontally forward over the hyoid bone, sending branches to the muscles which are inserted into that bone from below. (d) The dorsal lingual branch (rami dorsales linguae), from the second portion, arises under cover of the posterior border of the hyo-glossus and, passing upward medial to the stylo- glossus, brea'KS up into branches which are distributed to the mucous membrane of the dorsum of the tongue, as far back as the epiglottis, and also to the tonsil. Occasionally a branch unites with a corresponding one from the artery of the opposite side, inmiediately in front of the fora- men cscum, and is continued forward in the median line, immediately beneath the mucous membrane of the dorsum of the tongue, as far as the tip. (c) The sublingual branch (a. sublingualis) is given ofY near the anterior border of the hyo- glossus muscle and runs forward in the same plane as the ranine artery, but on a lower level, resting upon the mylo-hyoid muscle and lying between the genio-hyoid laterally and the genio- hyo-glossus medially. It is accompanied by the submaxillary ( Wharton's) duct, which lies upon its medial side, and it terminates in the sublingual gland, also sending branches to the neighbor- ing muscles and to the alveolar border of the mandible. Anastomoses. — The various branches, of the lingual artery anastomose exten- sivel)- with their fellows of the opposite side. The anastomoses of the two aa. dor- sales linguae take place, however, only through exceedingly tine twigs, so that the tongue may be divided longitudinally in the median line without any great loss of blood, except towards the tip, where a larger anastomosis of the ranine arteries occurs. In addition to these contra-lateral anastomoses, the lingual also anastomoses through its suprahyoid branch with the infrahyoid of the superior thyroid artery, through its sublingual branch with the submental branch of the facial, and through the a. dorsalis linguae with the various tonsillar arteries. Variations. — The lingual artery sometimes arises from a common trunk with the facial, and it has been observed to terminate at the root of the tongue, being replaced in the rest of its course by branches from the internal maxillary or by the submental branch of the facial. The sublingual branches are not infrequently lacking, being replaced by branches of the submental, and, in addition to its normal branches, the main artery may give rise to a superior laryngeal and an accessory superior thyroid branch. Practical Considerations. — The lingual artery is tied most frequently as a preliminary to excision of the whole or part of the tongue, but one or both arteries may be ligated to stop bleeding following wound or malignant ulceration of that organ, or in an effort to arrest growth by cutting off blood-supply, as in cases of cancer of the tongue or of macroglossia. Ligation. — The artery is for con\'enience divided into three portions, the yfrj'/ between its origin — about opposite the greater cornu of the hyoid— and the posterior edge of the hyo-glossus muscle, lying upon the middle constrictor of the pharynx ; the second beneath the hyo-glossus muscle, lying upon the genio-glossus ; the third, {ranine) from the anterior border of the hyo-glossus along the under surface of the tongue to its termination. The place of election is in the second part. The skin incision, two inches in length, cur\-ed, with the concavity upward, begins a half- inch below and external to the mandibular symphysis and ends a little below and internal to the point where the facial arterv crosses the lower edge of the inferior maxilla ; its centre is just above the greater cornu of the hyoid. If the incision is carried too far backward, THE FACIAL ARTERY. 737 the facial vein may be cut. The remainder of the operation may be described as if it were done in four stages, i. That portion of the deep fascia constituting the anterior layer of the capsule of the submaxillary gland is divided in the line of the incision, the lower edge of the gland exposed, and the gland itself cleared and ele- vated over the lower jaw, with due care to avoid injury to the facial artery which passes through its substance and the facial vein which runs upon its surface. 2. The thin posterior leaf of the capsule of the gland being divided, the white, shining aponeurotic loop attaching the digastric tendon to the greater cornu of the hyoid will be seen. The tendon near the bone or the digastric aponeurosis should be fixed by a blunt hook or tenaculum and drawn downward and towards the surface. 3. After the division of the posterior layer of the capsule of the submaxillary gland, the posterior edge of the mylo-hyoid muscle, the fibres running upward and slightly backward, can be recognized at the anterior angle of the wound and should be clearly defined. 4. The hypoglossal nerve separates from the artery at the poste- rior border of the hyo-glossus muscle, where the vessel disappears to run between that muscle and the middle constrictor. The nerve, accompanied by the ranine vein, runs almost horizontally across the surface of the hyo-glossus, and in its turn disappears under the edge of the mylo-hyoid muscle. It will have been brought into view when the submaxillary gland has been raised, the posterior layer of its capsule divided, and a littie fatty connective tissue picked away. In the irregular triangle formed by the nerve above, the mylo-hyoid anteriorly, and the posterior belly and tendon of the digastric posteriorly, the lingual artery runs beneath the hyo-glossus muscle and near the apex of the triangle — /. e. , near the hyoid bone. The nerve and vein, which are on a slightly higher level — a few millimetres — having been raised and the fibres of the hyo-glossus divided parallel with the hyoid and just above it, the artery will be brought into view. In ligation of the lingual for carcinoma of the tongue, the state of the salivary gland, which varies in size, in density, and in the closeness of its attachments, is the main element of uncertainty (Treves). 3. The Facial Artery. — The facial artery (a. maxillaris externa) (Fig. 691) arises usually a short distance above the lingual, from the anterior surface of the external carotid. It passes at first forward and slightly upward, lying beneath the posterior belly of the digastric and the stylo-hyoid muscles and the hypoglossal nerve, and is then continued almost horizontally forward in a groove in the submaxillary gland. When it reaches the level of the anterior border of the masseter muscle, it assumes a vertical direction and passes over the ramus of the mandible, and is then continued in a sinuous course obliquely across the face towards the naso-labial angle, resting upon the buccinator and levator anguli oris muscles, and being crossed by the risorius and zygomatic muscles and by some branches of the facial nerve. Arrived at the naso-labial angle, it again takes an almost vertical course, passing upward beneath (or sometimes over) the levator labii superioris and the levator labii superioris alseque nasi towards the inner angle of the orbit, where it terminates by anastomosing with the nasal branch of the ophthalmic artery. This terminal vertical portion of the vessel is usually termed the angular aj'tery (a. angularis). Branches.— The branches of the facial artery (Figs. 691, 693) may be arranged in two groups according to their origin from the cervical or facial portions of the artery. From the cervical portion arise: {a) The ascending palatine branch (a. palatina ascen- dens), a small arterj- which passes upward between the stylo-glossus and stylo-pharyngeus mus- cles, to which it sends branches, and then comes to lie upon the outer surface of the superior constrictor of the pharynx. It terminates by sending branches to the soft palate, the tonsil, and the Eustachian tube. (5) The tonsillar branch (ramus tonsillaris) is another small branch which passes verti- cally upward. It arises close to the ascending palatine and, passing over the stylo-glossus muscle, pierces the superior constrictor of the pharynx to be distributed to the tonsil. (c) The glandular branches (rami glandulares), two or three in number, are distributed to the submaxillary gland. (a?) The submental branch (a, submentalis) arises just before the artery bends upward over the mandible, and continues onward in the horizontal course followed by the facial, 47 738 HUMAN ANATOMY. through the submaxillary gland. It passes forward upon the niylo-h\oid muscle, close to its origin, until it reaches the insertion of the anterior belly of the digastric, when it passes upward upon the ramus of the mandible to supply the depressor labii inierioris and to anastomose with the mental branches of the inferior dental artery and with the inferior labial branches of the facial. It sends branches to the muscles in its vicinit\- and also to the integument, and branches perforate the mylo-hyoid muscle to anastomose with the sublingual branches of the lingual. From the facial portion, {c) The masseteric branches arise from the posterior surface of the artery — and are directed upward to supply the masseter muscle and to anastomose with branches of the internal ma.xillary and transverse facial arteries. {/ } The inferior labial branch ^a. labialis inferior) passes forward along the outer surface of the horizontal ramus of the mandible, supplying the depressor anguli oris, the depressor labii inferioris, and the integument, and anastomosing with the mental branches of the inferior dental and submental arteries. (g) The inferior coronary artery passes forward in the substance of the lower lip between the mucous membrane and orbicularis oris, supplying the latter, and terminates by anastomosing with its fellow of the opposite side. (/i ) The superior coronary artery (a. labialis superior) has the same course and relations in the upper lip that the inferior coronary has in the lower one. It anastomoses with its fellow- of the opposite side, and near its termination usually sends a small branch upward to the septum of the nose, the a. septi narium. (/) The lateral nasal takes its origin just as the artery reaches the naso-labial angle ; it passes forward over the ala of the nose, supplying its muscles and integument. (j) The angular artery (a. angularis) is the terminal portion of the facial arter>' beyond the naso-labial angle. It passes directly upward in the angle between the nose and the cheek, and gives branches to the adjacent muscles, the lachrymal sac, and the orbicularis palpebrarum, anastomosing with the nasal branch of the ophthalmic artery and with the infra-orbital branch of the internal ma.xillarj-. Anastomoses. — The facial artery, by means of its facial branches and the sub- mental arteries, makes abundant anastomoses with its fellow of the opposite side. In addition, it is connected with other branches of the external carotid; with the dorsalis linguae and submental branches of the lingual by its tonsillar and inferior labial branches respectively; with the descending palatine, infra-orbital branches, and mental branches of the internal ma.xillary by its tonsillar, angular, and inferior labial branches; and with the transverse facial branch of the superficial temporal by its masseteric branches. Finally, it is connected with the ophthalmic branch of the internal carotid by the angular artery. Variations. — The facial artery may arise by a trunk common to it and the lingual, or it may arise above the le\el of the angle of the jaw. Quite frequently it does not extend upon the face beyond the angle of the mouth, being replaced in the upper part of its course by branches from the transverse facial or internal maxillary arten,-. The ascending palatine branch frequently arises directly from the external carotid, or it may take its origin from the ascending pharyngeal or from the occipital, and the tonsillar is frequently a branch of it. The submental branch may be greatly reduced in size or even absent, being replaced in whole or in part by the sublingual, these two arteries being inversely proportionate to each other so fai as their development is concerned. Practical Considerations. — The facial artery may require ligation on account of division of one of its branches, as the coronary, but whene\er direct ligation of the wounded vessel is possible, it is preferable on account of the very free anastomosis between the branches of opposite sides, leading usually, after ligation of the main trunk, to recurrence of the hemorrhage. In bleeding after tonsillotomy (page i6oS), either the tonsillar branch of the facial or the main vessel (where it runs between the posterior belly of the digastric and the stylo-glossus muscles) may be invohed ; but as the blood may also be furnished by the ascending pharyngeal, ligation of the e.xternal carotid itself rather than of the facial would be more likely to be efficient. Ligation. — (a) The cervical portion of the vessel may be reached through an incision like that for the lingual, placed a little higher, and not extending so far anteriorly. When the subma.xillary gland is drawn upward, the artery will be drawn with it and made prominent. This portion may also be reached near its origin by uncovering the external carotid iq-v.) and identifying the vessel where it runs THE INTERNAL MAXILLARY ARTERY. 739 between the posterior belly of the digastric above and the hypoglossal nerve below. {b) The facial portion is easily exposed where it crosses the mandible at the ante- rior border of the masseter, either by a vertical cut parallel with that muscle and the artery or by a horizontal cut crossing the vessel and placed under the inferior margin of the jaw so as to leave the scar in an inconspicuous position. Beneath the skin and the superficial fascia the platysma and deep fascia are the only structures that require division. The vein lies in the groove between the artery and the edge of the masseter. 4. The Internal Maxillary Artery. — The internal maxillary (a. maxillaris interna) (Fig. 692) is a large branch which arises from the anterior surface of the Fig. 692. Small meningeal branch Middle meningeal Tympanic btanch Superficial temporal Stylo-mastoid Meningeal branch Posterior auricular Scalenus mediui,' Tendinous origin of scalenus mediu: Deeper dissect external carotid, opposite the neck of the mandible. It passes forward with a flexuous course, lying at first between the neck of the mandible and the spleno-mandibular ligament, and then passing either between the two pterygoid muscles, in which case it crosses the inferior dental and lingual nerves, or else over the external surface of the e.xternal pterygoid, between that muscle and the temporal. It then passes between the two heads of the external pterygoid, in the one case passing from below upward and in the other from without inward, and enters the spheno-maxillary fossa, in which it is directed upward and inward towards the spheno-palatine foramen, which it traverses under the name of the spheno-palatine artery. Branches. — For convenience in description it is customary to regard the internal maxillary artery as consisting of three portions. Its first, or niaudibiilar portion, is that which Hes inter- 740 HUMAN ANATOMY. nal to the neck of the mandible ; the second, or pterygoid portion, is that which traverses the zygomatic fossa, and is in relation with the pterygoid muscles ; and the third, or spheno-tnaxil- lary portion, extends from where it passes between the two heads of the external pterygoid mus- cle to Its entrance into the spheno-palatine foramen. Of the sixteen named branches arising from the internal maxillary artery, five arise from llie first portion, five from the second, and six from the third. From the first or mandibular portion arise (i) the deep auricular, (2) the tympatiic, (3) the middle metiingeal, (4J the small meningeal, and (5) tlie inferior dental ax\mranches, and perforates the anterior wall of the external auditory meatus to supply llie skin lining that passage and the outer surface of the tympanic membrane. \ (b') The tympanic (a. tympanica anterior), also a small branch, passes upward, giving off branches to the temporo-mandibular articulation, and enters the Glaserian fissure. Thence it traverses the iter chorda anterius along with the chorda tympani, and reaches the middle ear, to whose mucous membrane it is distributed, anastomosing with the tympanic branches of the stylo- mastoid arter)-. (c) The middle meningeal (a. meningea media) is the largest of all the branches. It as- cends vertically towards the base of the skull and enters the cranium by the foramen spinosum, and, after passing outward and upward for a sliort distance upon the great wing of the sphenoid, divides into an anterior and a posterior terminal branch, which ramify over the surface of the dura and supply nearly the whole of its lateral and superior surfaces, making abundant anasto- moses with the \essel of the opposite side. The anterior branch, the larger of the two terminal branches, passes obliquely forward o\er the greater wing of the sphenoid, crosses the anterior inferior angle of the parietal, and then ascends along the anterior border of that bone almost to the superior longitudinal sinus, sending off numerous branches. The posterior branch passes backward and upward over the squamous portion of the temporal bone, and then over the pos- terior part of the parietal bone, giving off numerous branches which pass upward as far as the superior longitudinal sinus and backward as far as the lateral sinus. In addition to these ter- minal branches, the main stem within the cranium also gives origin to (aa) s. petrosal branch (a. petrosus superficialis) which enters the hiatus Fallopii and anastomoses with the terminal por- tion of the stylo-mastoid arteries ; to ybb) Gasserian branches, minute twigs which pass to the Gasserian ganglion and the fifth nerxe ; to (cc\ a tympanic btanch (a. tympanica superior) which descends tlirough the petro-squamous suture to the mucous membrane of the middle ear and the mastoid cells ; and, finally, to (dd ) an orbital branch, a small vessel that pa.sses into the orbit through the outermost portion of the sphenoidal fissure and anastomoses with the lachrjmal branch of the ophthalmic. (d ) The small meningeal I r. meningeus accessorius) is an inconstant branch, sometimes arising from the middle meningeal. It passes upward along the mandibular division of the fifth nerve, and enters the cranium through the foramen ovale to be distributed to the Gasserian ganglion and the dura mater in its neighborhood. (e) The inferior dental (a, alveolaris inferior) is given off from the lower surface of the arterj- and descends along uith the inferior dental nerve to the mandibular foramen. Before reaching the foramen it gives off (aa) a lingual branch, which accompanies the lingual nerve to the tongue, and (bb) a mylo-hyoid branch (ramus mylohyoideus'l, accompanying the mylo-hyoid nerve to the muscle of that name. Entering the mandibular foramen, it traverses the man- dibular canal, giving oft branches to the roots of the lower teeth as it passes them, and finally emerges at the mental foramen as ( cc) the mental artery (a. mentalis), supplying the neighboring muscles and integument and anastomosing with the .submental and inferior labial branches of the facial. Just before issuing from the mental foramen it gives off (dd ) an incisive branch vv hich distributes twigs to the incisor teeth. From the second, or pterygoid portion, arise branches distributed chiefly to the adjacent muscles ; they are ( n the masseteric. {2') the deep temporal, (3 and 4) the internal and exter- nal pterygoid, and (5) the i^/^rcf?/ artery. (/) The masseteric branch (a. massetcrica) passes with the corresponding nerve through the sigmoid notch of the mandible to enter the deep surface of the masseter. ig) The deep temporal branches are two in number, the anterior and the posterior. The posterior branch (a. temporalis profunda posterior") arises close to or in common with the mas- seteric, while the anterior one (a. temporalis profunda anterior) is given off near the termination of the pterv-goid portion of the arterv-. They both pass upward between the temporal muscle and the bone, supplying the muscle and anastomosing with the middle temporal branch of the temporal arten,-, (h and /) The internal and external pterygoid branches (rami ptervgoidei ) are short and variable in number. They pass directly into the muscles of the same names. THE INTERNAL MAXILLARY ARTERY. 741 (7) The buccal branch (a. buccinatoria) passes downward and forward with the buccal nerve along the anterior border of the tendon of the temporal muscle, and supplies the bucci- nator muscle and the mucous membrane of the mouth. From the third or spheno-maxillary portion arise (i) the alveolar, (2) the infraorbital^ (3) the descending palaliiie, (4) the Vidian, (5) \ki^ptery go-palatine, and (6) the spheno- palatine. {k) The alveolar branch (a. alveolaris superior posterior) descends upon the tuberosity of the maxilla, giving off branches which penetrate small foramina in that bone and are distributed to the molar and premolar teeth and the gums of the upper jaw and to the mucous membrane lining the antrum of Highmore. The main stem terminates upon the tuberosity of the maxilla by breaking up into a plexus with which branches from the buccal artery unite. Fig, 693. Anterior temporal v Posterior temporal Middle temporal Transverse facial Great meninj^eal Superficial temporal -.^ Small meningeal A Tympanic Internal maxillary Inferior dental artery Mylo-hyoid artery Posterior auricular Inferior dental nerve Sterno-mastoid artery Occipital artery Tonsillar artery Ascending palatine Hypoglossal nerve Facial artery Internal carotid External carotid •— — Superior thyroid ■ Common carotid Stemo-mastoid arterj-— — — Coronoid process of mandible with insertion of tem- poral muscle Buccinator perior coro- nary artery Inferior coro- nary artery Inferior labia! artery Mental branch of facial emerging from mental for- Submental artery Genio-hyoid muscle ~ Lingual artery ^--.Hyoglossusmu! cle, cut ~^ Mylo-hyoid mu cle of left side Superior laryn- geal artery — -~ Thyro-hyoid muscle External carotid, internal maxillary and inferior dental arteries ; condyle and outer table of mandible have been removed. (/) The infraorbital artery (a. infraorbitalis) frequently arises in common with the alveolar. It passes forward and upward through the spheno-maxillary fossa and the spheno-maxillar> .foramen to traverse the infraorbital groove and canal along with the infraorbital nerve. In this part of its course it gives off i^aa) 07'bital branches, distributed to the adipose tissue of the orbit and to the neighboring muscles of the eye, arid {bb') anterior dental bra?tches (aa. alveolares superiores anteriores) which pass down the anterior wall of the antrum of Highmore, along with the anterior and middle superior dental nerves, to supply the mucous membrane lining the antrum and the canine and incisor teeth of the upper jaw. The main stem emerges upon the face at the infraorbital foramen and divides into (cc) palpebral, (dd) nasal, and (ee) labial branches, whose distribution is indicated by their names, and which anastomose with the nasal and lachrymal branches of the ophthalmic artery, the transverse facial branch of the superficial temporal, and the superior coronary and angular branches of the facial. (?«) The descending palatine artery (a. palatina descendens) accompanies the anterior ptila- tine nerve from the spheno-palatine ganglion through the posterior palatine canal, and, on its 742 HUMAN ANATO.MV. emergence from the posterior palatine foramen, divides into an anterior and a posterior branch. The former passes forward beneath the mucous membrane of the hard palate, which it supplies, and at the anterior palatine foramen anastomoses with the spheno-palatine artery ; the latter passes backward to supply the soft palate and the tonsil, anastomosing with the ascending palatine branch of the facial. (/;) The Vidian artery (a. canalis pterygoidei ) is a small branch which passes backward along the \'idian ner\e through the \'idian canal, and sends branches to the roof of the pharyn.x and to the Eustachian tube. (o) The pterygo-palatine artery (a. palatina major) is also a somewhat slender branch. It passes backward through the pterjgo-palatine foramen along with the pharjmgeal nerve from the spheno-palatine ganglion, and supplies the roof of the pharynx, the Eustachian tube, and the mucous membrane lining the sphenoidal cells. ip) The spheno-palatine artery (a. sphenopalatina) is the terminal branch of the internal maxillary. It passes into the nasal cavity through the spheno-palatine foramen along with the spheno-palatine nerve from the splieno-palatine ganglion. Shortly after traversing the foramen it divides into an internal and an external branch. The internal branch, sometimes termed the naso-palatine, passes transversely across the roof of the nasal cavity to reach the septum, upon which it passes downward and forward, giving off numerous branches which anastomose to form a rich net-work beneath the mucous membrane of the septum. It finally reaches the anterior palatine foramen, where it anastomoses with the anterior branch of the descending palatine. Throughout its course it is accompanied by the naso-palatine ner\-e. The external branch ramifies downward and forward oxer the lateral wall of the nasal fossa, forming a rich plexus beneath the mucous membrane lining the meatuses and the turbinate bones. It will be observed that all the branches arising from the first and third portions of the internal maxillary arten,' traverse bony canals or foramina, while those of the second portion do not, but are distributed directly to muscles. Anastomoses. — The communications of the internal ma.xillarv artery are with the branches of the artery of the opposite side, with other branches of the artery of the .same side, with other branches of the external carotid, and with branches of the internal carotid. The most abundant anastomoses with the artery of the opposite side are made through the branches of the middle meningeal; the alveolar branch anastomoses with the dental branches of the infraorbital of the same side and with the buccal artery, and the anterior branch of the descending palatine makes a large anastomosis with the naso-palatine branch of the spheno-palatine at the anterior palatine foramen. The other branches of the external carotid w ith which anastomoses are made are the facial, the temporal, and the posterior auricular; the facial com- municates by means of its submental and inferior labial branches with the mental branch of the inferior dental, by its superior coronary and angular branches with the terminal branches of the infraorbital, by its superior coronary with branches of the naso-palatine, and by its ascending palatine with branches of the descending palatine. The deep temporal arteries anastomose with branches of the superficial temporal and the infraorbital with the transverse facial branch of the same artery; while the posterior auricular communicates by means of its stylo-mastoid branch with the tympanic branch and with the petrosal branch of the middle meningeal. Of the anastomoses with the internal carotid arteries the most important are those between the orbital branch of the middle meningeal and the lachrymal artery, between the terminal branches of the infraorbital and the terminal branches of the ophthalmic, and between the spheno-palatine branches and the ethmoidal arteries. Variations. — In the earlv stages of development the main portion of the intemal maxillarj- is represented by a stem which arises from the internal carotid (Tandler). This is known as the a. stapedia (Fig. 694, Ast) , since it traverses the middle ear, passing through the foramen of the -Stapes (sf); it makes its exit from the middle ear by the Glaserian fissure and divides into two stems, one of which ( Rs^ passes through the forameri spinosum ( fsp ) and is distributed to the supraorbital region, while the other divides into two branches which, from their distribution, are termed the infraorbital (Ri^ and the mandibular (inferior dental) [Rm'). A branch {Ras) arises later from the external carotid which anastomoses with the lower stem where it divides into the two branches just mentioned, and the main stem of the .stapedius disappears, except in its distal portion, which persists as the tympanic branch of the internal maxillan,-, which fre- quently arises in the adult from the middle meningeal instead of directly from the internal max- illa r\-. By these changes, as mav be seen from the accompanying diagrams, the adult intemal maxillary is formed, the supraorbital branch becoming the middle meningeal { Min\ and the mandibular branch the inferior dental, while the infraorbital branch (Ri^ becomes the main stem of the artery from wliich the remaining branches gradually de\ elop. THE OCCIPITAL ARTERY. 743 In correspondence with this history, a persistence of the stapedial artery is occasionally found ; but the majority of the usual variations of the internal maxillary are due to the second- ary anastomoses which its branches make with other vessels. Thus, by an enlargement of the anastomoses between the middle meningeal and the branches of the ophthalmic artery, that vessel or some of its branches, notably Fig. 694. Diagrams illustrating development of internal max- illary artery ; ^, early stage; .5, later stage; C, common carotid; Ce, Ci, external and internal carotid. For ex- planation of other letters, see text. ( Tandler.) the lachrymal, may come to arise from the middle meningeal (page 749). And, similarly, by the anastomoses with the facial or transverse facial arteries, the terminal branches of the infraorbital may be transferred to those vessels, the infraorbital itself stopping in the middle of the infraorbital groove. 5. The Ascending Pharyn- geal Artery. — The ascending pharyngeal artery (a. pharyngea ascendens) (Fig. 695) differs from all the other branches of the e.xternal carotid by its vertical course. It is a comparatively small stem which arises close to or immediately at the origin of the external carotid and passes upward, at first between that vessel and the internal carotid, and later between the internal carotid and the internal jugular vein. Branches.— ( a ) A prevertebral branch which supplies the prevertebral muscles of the neck and anastomoses with the ascending cervical branch of the inferior thyroid artery. {b) Pharyngeal branches (rami pharyngei), two or three in number, which supply the con- strictor muscles and the mucous membrane of the pharynx. (r) Meningeal Branches.— A number of small twigs, into which the artery breaks up as it approaches the base of the skull, pass through the jugular and anterior condyloid foramina to supply the dura mater of the posterior fossa of the skull, and through the cartilage of the middle lacerated foramen to supply the dura of the middle fossa. Variations.— The ascending pharyngeal frequently gives origin to the ascending palatine and more rarely to the superior laryngeal artery. It is very variable in its origin, not infre- quently being given off from one or other of the neighboring branches of the external carotid. 6. The Sterno- Mastoid Artery. — The sterno-mastoid artery (a. sterno- cleidomastoidea) arises from the posterior surface of the external carotid, near its origin, and passes downward and backward to enter the sterno-cleido-mastoid muscle along with the spinal accessory ner\'e. It is a comparatively small vessel and is not infre- quently absent, being replaced by branches passing to the muscle from other arteries. When it is present, the hypoglossal nerve bends around to it to pass forward to the lingual muscles. 7. The Occipital Artery. — The occipital artery (a. occipitalis) (Figs. 691, 692) arises from the posterior surface of the carotid, opposite or a little below the facial. It passes upward and backward, and is at first partly covered by the posterior belly of the digastric and the stylo-hyoid muscles, the parotid gland, and the temporo- maxillary vein. It crosses in succession, from before backward, the hypoglossal nerve, which, when the sterno-mastoid artery is wanting, winds around it to pass for- ward to the tongue, the pneumogastric nerve, the internal jugular vein, and the spinal accessory nerve. It then passes more deeply, lying in a groove on the posterior sur- face of the mastoid process and beneath the origin of the posterior belly of the digastric, the sterno-cleido-mastoid, and the splenius capitis. Emerging from beneath these muscles, it reappears in the upper part of the occipital triangle, and then ascends in a tortuous course over the back of the skull, sometimes perforating the trapezius near its origin, and breaks up into numerous branches which anastomose with branches from the artery of the opposite side and with those of the posterior auricular and superficial temporal. In this last part of its course it is superficial, lying beneath 744 HUMAN ANATOMY. the integument upon the aponeurosis of the occipito-frontalis. The artery pierces the deeper structures, accompanied by the great occipital nerve, a short distance lateral to and a little below the external occipital protuberance. Branches. — In addition to its terminal branches, the occipital arterj- gives oft : (a) A superior sterno-mastoid branch which supplies the upper part of the sterno-cleido- mastoid. (d) Posterior meningeal branches, one or more slender vessels which pass upward along the internal jugular vein and, entering the skull by the jugular foramen, are supplied to the dura mater of the posterior fossa. (c } An auricular branch (ramus auricularis) which passes upward over the mastoid process to supply the jjinna ot the ear. (d ) A mastoid branch (ramus mastoideus) which enters the skull by the mastoid foramen and supplies tlie mucous membrane hning the mastoid cells, the diploe, and the dura mater. (e) An arteria princeps cervicis (ramus descendens) which arises from the artery, just as it passes out from beneath the splenius and descends the neck, supplying the adjacent muscles and anastomosing with the superficial cervical branch of the transversalis colli and with the pro- funda cervicis from the superior intercostal. (y ) Muscular branches (rami rausculares) wliich are given off all along the course of the artery to the neighboring muscles. Anastomoses. — The occipital artery makes comparatively large and abundant anastomoses in the scalp with the stylo-mastoid and temporal arteries, and also, by means of its art. princeps cervicis, with branches of the transversalis colli and superior profunda arteries, which arise from the subclavian. These latter anastomoses are of considerable importance in the development of a collateral circulation after ligation of either the common carotid or the subclavian arteries. Variations. — The occipital artery occasionally passes superficial to the sterno-cleido-mas- toid muscle instead of beneath it, and it not infrequently gi\es origin to the ascending pharyn- geal artery or to the stylo-mastoid. Practical Considerations. — The occipital artery is rarely formally ligated. The cervical portion may be reached through an incision along the anterior border of the sterno-mastoid, beginning midway betw'een the ramus of the mandible and the lobe of the ear and extending downward two and a half inches. The deep fascia at the upper angle of the wound (parotid fascia) is spared on account of the risk of salivary fistula. At the lower angle it is divided, the parotid and sterno-mastoid are separated, and the digastric and stylo-hyoid muscles recognized and drawn upward. The occipital artery, near its origin, will then be seen crossing the internal carotid artery and internal jugular vein and in contact with the curve of the hypo- glossal nerve where it turns to cross the neck. The artery may be ligated close behind the ner\'e, the needle being passed from without inward to avoid the jugular vein. The occipital portion is approached through an almost horizontal incision two inches in length, beginning at the tip of the mastoid apophysis and extending back- ward and a little upward. The outer fibres of the sterno-mastoid and its aponeu- rotic expansion, the splenius, and often the complexus, must then be divided and the pulsation of the arterv sought for in the space between the mastoid and the transverse process of the atlas, whence the vessel may be traced outward. If it is isolated near to the mastoid, great care must be taken not to injure the important mastoid venous tributaries of the occipital vein which in this region connect it with the lateral sinus. S. The Posterior Auricular Artery. — The posterior auricular artery (a. auricularis posterior) (Fig. 693) arises from the external carotid after it has passed beneath the posterior belly of the digastric. It passes upward and backward, cov- ered at first by the parotid gland, which it supplies, and divides in the angle between the pinna and the mastoid process into terminal branches, some of which supply the pinna, while others anastomose with branches from the occipital and superficial temporal. THE SUPERFICIAL TEMPORAL ARTERY. 745 Branches. — In addition to branches to the parotid gland and to neighboring muscles, it gives rise to the stylo-mastoid artery (a. stylomastoidea). This vessel enters the stylo-mastoid foramen and traverses the facial canal (aqueduct of Fallopius) as far as the point at which the hiatus Fallopii passes off from it. During its course through the canal it gives oR branches to the mucous membrane lining the mastoid cells, to the stapedius muscle, and to the mucous membrane of the middle ear, those twigs which pass to the inner surface of the tympanic mem- brane anastomosing with the tympanic branch of the internal ma.xillary. Arrived at the hiatus Fallopii, the artery accompanies the great superficial petrosal nerve through that canal and enters the cranium, supplying the dura mater and anastomosing with branches of the middle meningeal arterj'. Variations.— The stylo-mastoid artery may arise from the occipital or its place may be taken by the petrosal branch of the middle meningeal, with which the stylo-mastoid normally anastomoses. 9. The Superficial Temporal Artery. — The superficial temporal artery (a. temporalis superficialis) (Fig. 693) is the continuation of the external carotid after it has given oS the internal maxillary. At its origin it is embedded in the substance of the parotid gland, and is directed upward over the root of the zygoma and imme- diately in front of the pinna. After ascending a short distance, usually about 2 cm., upon the aponeurosis covering the temporal muscle, it divides into an anterior and a posterior branch, which, diverging and branching repeatedly, pass upward over the temporal and occipito-frontal aponeuroses almost to the verte.x of the skull, anasto- mosing with the supra-orbital branches of the ophthalmic branch of the internal carotid, with the posterior auricular and occipital branches of the external carotid, and with the artery of the opposite side. Branches. — {a) Parotid branches (rami parotide!), small branches to the parotid gland. {6) Articular branches to the temporo-mandibular articulation. (f ) Muscular branches to the masseter muscle. (d) The anterior auricular branches (rami auriculares' anteriores) supply the outer surface of the pinna and the outer portion of tlie external auditory meatus. (e) The transverse facial artery (a. transversa faciei) arises just below the main stem of the artery, crosses the zjrgoma, and is directed forward parallel with the zygoma and between it and the parotid duct. It gives off branches to neighboring muscles and to the integument of the cheek, and anastomoses with the masseteric branches of the facial and with the buccal, alveolar, and infra-orbital branches of the internal maxillary. {/) The middle deep temporal (a. temporalis media) arises just above the zygoma, and after perforating the temporal aponeurosis and muscle, it ascends upon the surface of the skull to anastomose with the deep temporal branches of the internal maxillary artery. (^) The orbital branch (a. zygomaticoorbitalis) runs forward along the upper border of the zygoma, suppl3-ing the orbicularis palpebrarum and also sending branches into the cavity of the orbit. Anastomoses. — The superficial temporal artery makes extensive anastomoses in the scalp with its fellow of the opposite side, with the occipital and posterior auricu- lar branches of the external carotid, and with the supra-orbital branch of the oph- thalmic. By means of the transverse facial it makes anastomoses with the facial and internal maxillary arteries. Variations. — The principal variations of the superficial temporal are its division into the terminal branches below the level of the zi,'gomatic arch and the absence of its posterior ter- minal branch ; in the latter case the area of distribution of the posterior branch is supplied by the posterior auricular or the occipital artery. Practical Considerations. — The superficial temporal artery may require ligation on account of wound of the vessel, or of one of its branches, or in cases of aneurism. It or one of its chief subdivisions used frequently to be selected for the now rare operation of arteriotomy. The vessel never becomes very superficial imme- diately after emerging from beneath the upper part of the parotid. In the first por- tion of its track of ascent its pulsations are difficult to perceive. In the presence of the least swelling of the region they become incapable of serving as a guide for the incision (Farabeuf). 746 HUMAN ANATOMY. Ligation. — The skin, superhcial fascia, and some fibres of the attrahens aurem muscle are divided fox- an inch on a vertical line between the tragus and the condyle of the mandible, a little nearer the latter. The artery will be found closely bound by connective-tissue bands to the temporal aponeurosis. THE INTERNAL CAROTID ARTERY. The internal carotid (Figs. 693, 695) is the second terminal branch of the coni- mon carotid, from w^hich it arises on a level with the upper border of the thyroid Branch of left middle meningeal artery' Posterior cerebral Left vertebral artery Right vertebral artery- Middlfc cerebral artery 'Anterior cerebral artery -Anterior clinoid process -Middle fossa of skull :arotid, cav. portion Sup. maxilla, malar process carotid, petrous portior Internal maxillary artery — -Eustachian tube Transverse process of atlas Sup. constictorof pharynx ■^IjE^'r Int. carotid, cervical portion -Ascending pharyngeal ■Sljlo-glossus -Stylo-pharyngeus ■Kxtemal carotid artery iStylo-hyoid muscle, cut I-ingual Superior thyroid artery Thyrohyoid muscle Thyroid cartilage Prani-h to II. intercostal ;.[■ n. aortic intercostal Deep dissection, showing i al carotid, vertebral and superior intercostal ; cartilage. In they?r^/ or cejincal portion of its course it lies upon the outer side of the external carotid, but, as it passes upward, it comes to lie behind and then internal to that vessel, from which it is separated by the stylo-hyoid, digastric, and stylo- pharyngeus muscles. It passes almost vertically up the neck to the entrance to the carotid canal, resting posteriorly on the prevertebral fascia covering the rectus capitis THE INTERNAL CAROTID ARTERY. 747 anticus major, and having upon its median side the wall of the pharynx and laterally the internal jugular vein, between which and the artery, and on a plane slightly pos- terior to both, is the pneumogastric nerve. It is also in relation in the upper part of this cervical portion of its course with the glosso-pharyngeal ner\-e, which lies at first behind it, but crosses its e.xternal surface lower down as it bends forward towards the tongue, and with the superior sympathetic ganglion, whose cardiac branch descends along its internal surface, while the pharyngeal branches cross it and the carotid branch ascends with the artery to the carotid canal, in which it breaks up to form the carotid plexus. In the second or petrosal portion of its course the internal carotid traverses the carotid canal, to whose direction it conforms, passing at first vertically upward and then bending so as to run for^vard and inward to enter the cranial ca\ity at the foramen lacerum medium. It then enters upon the third or intracranial portion of its course, ascending at first towards the posterior clinoid process, but soon bending forivard and entering the outer wall of the cavernous sinus. In this it passes forward, accompanied by the sixth nerve (abducens), and at the level of the anterior clinoid process bends upward, pierces the dura mater, and quickly divides into its terminal branches. Branches.^Throughout its cer\dcal portion the internal carotid normally gives off no branches, in its petrosal portion, in addition to some small twigs to the peri- osteum lining the carotid canal, it gives origin to (i ) a tympayiic branch. In its intracranial portion, in addition to small branches to the walls of the ca^-ernous sinus and the related cranial nerves, to the Gasserian ganglion, and to the pituitary body, 'Caexe:'ax\s,& {11) anterior meningeal bra7iches, (3) \h^ ophthalmic, {i^') posterior coni7nu- nicati?ig, (5) anterior clioroid arteries. And, finally, its terminal branches, (6) the middle and (7) the anterior cerebral arteries. Variations. — In its cer\-ical portion the internal carotid occasionally takes a somewhat sinuous course, and, especially in its upper part, may be thrown into a pronounced horseshoe- shaped curve. It may gi\e rise to branches which normally spring from the external carotid, as, for example, the ascending pharyngeal and the lingual, and accessor)- branches may arise from its intracranial portion. Practical Considerations. — The internal carotid artery, on account of its deeper position, is not so often wounded as the external carotid. It has been punc- tured through the pharynx and has been wounded in tonsillotomy (page 160S ). Aneurism of the internal carotid is not common. When it involves the petrosal or intracranial portion of the vessel it causes symptoms referrible to those regions and better dealt with after the venous system has been described (page 873). In its cer\'ical portion it shows a tendency to become tortuous in elderly persons, owing doubtless to its fixity above, where it enters the carotid canal, and to the rela- tive lack of fixation below (Taylor). As the artery is crossed externally by the dense layers of the deep cen/ical fascia, and by the stylo-hyoid, stvlo-glossus, stvlo-pharsmgeus, and digastric mus- cles, the progress of a swelling in this direction is strongly resisted. Internally the middle constrictor and mucous membrane of the pharynx ofter far less obstruction to the extension of the aneurism, and in many of the recorded cases a pulsating pha- ryngeal protrusion has been the chief svmptom. The eftects of pressure on surround- ing structures, the internal jugular vein, and the pneumogastric and sympathetic nerves, for example, are not unlike those observed in other carotid aneurisms. The direct interference with cerebral circulation is greater in aneurism of the internal carotid, and vertigo, headache, drowsiness, etc. , are apt to be more conspicuous as early symptoms. Ligation. — The vessel mav be reached close to its origin and tied through the same incision as that used in ligating the external carotid (page 733). The stemo- mastoid muscle is drawn outward, the digastric muscle and hypoglossal ner\'e (which are usually seen) upward, and the external carotid arterv' inward. The tivo vessels should be carefully distinguished. The needle should be passed from with- 748 HUMAN ANATOMY. out inward, avoiding the internal jugular vein, the pneumogastric and sympathetic nerves, and the ascending pharyngeal and external carotid arteries. The collateral circulation is carried on through the \-ertebrals and the vessels of the circle of Willis and is freely re-established. I. The Tympanic Artery. — The tympanic artery franius caroticotympani- cus) is a small vessel which arises from the petrosal portion of the internal carotid. It passes through a foramen in the wall of the carotid canal to supply the mucous membrane of the middle ear, anastomosing with the tympanic branches of the stylo- mastoid and internal maxillarv arteries. Fig. 696. Frontal artery Nasal artery Anterior ethmoidal branch Supraorbital artery Superior oblique Superior rectus Internal carotid artery. Posterior clinoid process. Nasal artery Supraorbital artery Lachrj nial artery Lachrymal gland Temporal branch Arteria centralis r< Lonji posterior Middle fossa of skull Branches of right ophthaln emoval of roof of orbit. 2. The Anterior Meningeal Arteries. — The anterior meningeal arteries are a number of small branches which arise from the intracranial portion of the inter- nal carotid and are supplied to the neighboring dura mater, anastomosing ^^ ith the branches of the anterior ramus of the middle meningeal artery. 3. The Ophthalmic Artery. — The ophthalmic artery (a. ophthalmica) ( Figs. 696, 697) arises from the internal carotid immediately after it has issued from the roof of the cavernous sinus. It passes fonvard beneath the optic nerve and traverses the optic foramen with that structure. In the orbit it ascends to the outer side of the optic nerve and, crossing over it, passes in a sinuous course towards the inner wall THE OPHTHALMIC ARTERY. 749 of the orbit, along which it runs between the superior oblique and internal rectus muscles to the inner angle, where it terminates by dividing into palpebral, frontal, and nasal branches. Branches. — ((z) The arteria centralis retinae arises from the ophthalmic while that vessel is still below the optic nerve. It runs forward along the under surface of the nerve to a point about 15 mm. from the posterior surface of the eye, where it passes into the substance of the nerve and continues its course forward in the centre of that structure. Arrived at the retina, the artery divides into two main branches, one ascending and the other descending, and these, branching repeatedly, form an arterial net- work upon the .surface of the retina. The finer branches of the net-work e.xtend deeply into the substance of the retina, although none reach the layer of visual cells. They pass over directly into the corresponding veins .without making connections with any of the other arteries supplied to the eyeball. Just after its entrance into the eyeball, however, the main stem of the artery anastomoses with the short ciliary vessels. {b) The ciliary arteries, which are distributed to the choroid coat, the ciliary processes, and the iris, are somewhat variable in their number and origin. Two sets are distinguishable, and are named from their relative position the posterior and anterior ciliary arteries. {aa) "Wi^ posterior ciliary arteries (aa. ciliares posteriores) arise from the ophthalmic artery as it crosses over the optic nerve, either as two trunks which pass forward, tlie one on the inner and the other on the outer side of the optic nerve, or else as a variable number of small vessels. Eventually the vessels break up into from ten to twenty branches, which surround the distal portion of the optic nerve, and, piercing the sclerotic, are distributed to the choroid coat of the eye. Two of the vessels, lying one on either side of the optic nerve, are usually stronger than the others, pierce the sclerotic some distance nearer the equator of the eyeball, and are termed the long posterior ciliary arteries (aa. ciliares posteriores longae). They pass forward between the sclerotic and choroid coats, send branches to the ciliary muscle, and divide at the peripheral border of the iris into two stems, which, passing around the iris, unite with their fellows of the opposite side and with branches of the anterior ciliary arteries to form the circulus arteriosus iridis, from which branches radiate to the iris and the ciliary processes. {bb) The anterior ciliary arteries (aa. ciliares anteriores) usually take their origin from the muscular branches of the ophthalmic and accompany the tendons of the recti muscles (two arteries being associated with each muscle, e,\cept in the case of the external rectus, where there is only one) to the sclerotic, where they send off perforating branches which, after piercing the sclerotic, unite with the long ciliaries to form the arterial circle of the iris. The main stems are continued onward towards the margin of the cornea, where they divide and anastomose to form a narrow net-work surrounding that portion of the eyeball and also give branches to the conjunctiva. An anterior ciliary vessel is frequently contributed by the lachrymal artery. (r) The lachiymal artery (a lacrimalis) arises from the ophthalmic as it passes upward over the external surface of the optic nerve and passes forward and outViJard, in company with the lachrymal ner\'e, along the upper border of the external rectus muscle. It traverses the substance ,of the lachrymal gland, to which it gives branches, and terminates in small branches to the eye- lids. In its course it gives off a number of small twigs to the external rectus muscle ; a me?iin- geal branch, which passes back into the cranium through the sphenoidal fissure and anasto- moses with the middle meningeal ; and a malar branch, which passes to the temporal fossa through a small canal in the malar bone and anastomoses with the anterior deep temporal and the transverse facial arteries. ( d ) The muscular branches ( rami musculares) are somewhat irregular in their number and origin. Usually there are two principal stems and a variable number of small twigs, but occa- sionally the two principal stems arise by a common trunk. When the two are distinct, the /«- ferior one arises close to the lachrymal, and is distributed to the inferior and internal recti and the inferior oblique muscles ; while the superior, smaller and less constant, ari.ses after the oph- thalmic has crossed over the optic nerve, and is distributed to the superior and external muscles of the orbit. In addition to branches to the muscles, these arteries also give origin to the anterior ciliary arteries described above. {e) The supraorbital artery (a. .supraorbitalis) arises as the ophthalmic passes over the optic nerve. It is at first directed upward, and then passes forward between the periosteum of the roof of the orbit and the levator palpebra; superioris, and, making its exit from the orbit through the supraorbital notch or foramen, terminates in branches which ascend over the frontal bone towards the vertex of the skull, supplying the integument and periosteum and anastomosing with the superficial temporal artery. In its course through the orbit it gives off periosteal, diploic, and muscular twigs, and, after its exit from the supraorbital notch, a palpebral branch to the upper eyelid. (/) The ethmoidal arteries are two in number, and arise from the ophthalmic as it passes along the inner wall of the orbit. The posterior ethmoidal (a. ethmoidalis posterior) , which is the 750 HUMAN ANATOMY. smaller and less constant of the two, passes through the posterior ethmoidal foramen and is distributed to the mucous membrane lining the posterior ethmoidal cells and the upper poste- rior part of the nasal septum, where it anastomoses with the spheno-palatine branch of the internal maxillary. It sometimes arises from the supraorbital artery. The anterior ethmoidal (a. ethmoidalis anterior) passes through the anterior ethmoidal foramen along with the nasal ner\e, and, entering the cranium, passes forward over the cribriform plate of the ethmoid to the nasal slit at the side of the crista galli. Through this slit it enters the nasal ca\ity and passes downward in a groove upon the under surface of the nasal bone, supplying the iiasal m.ucous membrane. While within the cranium it gives off a small meningeal branch to the dura mater of the anterior portion of the cranium, and it also sends branches to the mucous membrane lining the anterior and middle ethmoidal cells and the frontal sinuses. <~^) The palpebral branches (aa. palpebrales mediales) are two in number, and are distrib- uted to the upper and lower eyelids respectively. They arise opposite the pulley of the superior oblique muscle and descend towards the inner canthus of the eye. Each artery then bends out- ward towards the outer canthus along the free border of the lid, between the tarsal cartilage and the orbicularis muscle, forming the palpebral arches (arms tarseits superior et inferior). Fig. 697. Lacrimal arter\' Posterior ethmoidal Ophthalmic artery Optic nerve Imenial carotid artery Posterior clinoid Int. carotid arter\ cavernous portio Supraorbital artery Frontal artery- Nasal artery- Superior and in- ferior palpebral arteries Arteria centralis retin Long posterior ciliary artery Short posterior ciliary arteries / Internal maxillary artery Branches of ophthalmic artery, seen from side after removal of lateral orbital wall. from which branches pass upward or downward, as the case may be, to supply the orbicularis, the Meibomian glands, and the integument of the lid. As they approach the outer canthus, the arches anastomose with the palpebral branches of the lachrymal artery. (h) The frontal branch (a. frontalis) is usually .small, and is distributed to the integument over the glabella and to the pyramidalis nasi and frontalis muscles. It also sends some twigs to the eyelids. (z) The nasal artery (a. dorsalis nasi) is the true terminal branch of the ophthalmic. It passes downward in the angle formed by the nose and the lower eyelid and becomes directly continuous with the angular portion of the facial artery. In its course it gives branches to the walls of the lachrymal sac and to the integument of the root of the nose. Anastomoses. — The principal communications of the ophthalmic artery are with the superficial temporal, internal ma.xillary, and facial branches of the external carotid. With the first of these it communicates extensively by means of the supra- orbital branch and less importantly throus^h the anastomosis of the malar branch of the lachrj-mal with the trans\'erse facial artery. It makes a very important anasto- THE POSTERIOR COMMUNICATTNG ARTERY. 75» mosis with the middle meningeal branch of the internal maxillary through the lachry- mal branch, and communicates also with the spheno-palatine artery by means of the ethmoidal branches. The anastomosii of the nasal branch with the angular ar- tery from the facial is also a large one, the two vessels being practically continuous. Variations. — In addition to the varia- tions in the number and origins of its branches, the ophthalmic artery also presents variations in its course, in that, instead of pass- ing to the inner wall of the orbit above the op- tic nerve, it sometimes passes below that structure. The most striking variation which it presents, howe\'er, is associated with the development of the branch of the lachrymal artery, which passes back through the sphe- noidal fissure to anastomose with the middle meningeal (Fig. 69S). Occasionally this branch becomes exceptionally large and forms the main stem of the lachrj'mal artery, the connection of that vessel with the ophthalmic vanishing, so that it seems to be a branch of the middle meningeal. A further step in this process which sometimes occurs results in the origin of the entire ophthalmic system of ves- sels from the middle meningeal arterv- Fig 698. Supraorbital eningeal rtery ; lachrymal coming 4. The Posterior Communicating Artery. — The posterior communicating artery (a. communicans posterior) (Fig. 702) arises from the posterior surface of the Parietal arterv Fig. 699. h of ascending frontal artery of Rolando / / Precentral sulcus Ascending frontal artery Branches of anterior ( bral artery from mesial surface Calcarine branches of posteri- or cerebral Branches of anterior cerebral artery Fxternal 1 ital artery .Inferior frontal artery Middle cerebral arter> Parieto temporal i rtery Pons Left \ ertebral arter\ Middle cerebellar pedu Right \ ertebral artery Lateial surface of brain, showing cortical branches of middle cerebral artery ; those of anterior and posterior cerebral arteries are seen curving over supero-mesial border of cerebral hemisphere. internal carotid, opposite the sella turcica. It is directed backward beneath the optic tract and the inner border of the cms cerebri, and terminates posteriorly by 752 HUMAN ANATOMY. opening directh- into the posterior cerebral artery. In its course it gives off twigs to the tuber cinereum, the corpora albicantia, and the crus cerebri. 5. The Anterior Choroid Artery. — The anterior choroid artery ( a. choroi- dea) (Fig. 702) arises from the posterior surface of the internal carotid, slighdy distal to the posterior communicating arten,-. It is directed ouUvard and backward at first, and then, curving upward between the brain-stem and the temporal lobe it gives branches to the hippocampus major. It is then continued upward and for- ward as the artery- of the choroid ple.xus of the lateral ^•entricle, and anastomoses at the foramen of Monro with the arterj- of the choroid ple.xus of the third \ entricle, which comes from the superior cerebellar branch of the basilar arterv'. 6. The Middle Cerebral Artery. — The middle cerebral arterj- (a. cerebri media) (Figs. 699, 702) is one of the terminal branches of the internal carotid. It passes at first outward to the low er end of the Sylvian fissure, and is then directed backward and upward, lying at first deeply in the fissure close to the surface of the Fig. 700. Middle iDterOd] fronul artery Interna] carotid artery External oibital Middle cerebral artery a temporal branch of middle cerebral Posterior cxtnuQumcating artery Anterior choroid Posterior cerebtal arterj* Mesial surface of cerebral hemisphere, showing cortical blanches of anterior and posterior cerebral arteries. island of Reil, but gradually becoming more superficial until at the posterior ex- tremity of the horizontal limb of the fissure it reaches the surface and divides into branches which ramif)- over the lateral surface of the cerebral hemisphere. Branches. — In its course outward to enter the Sylvian fissure it gi\es off a number of small central branches which penetrate the substance of the cerebral hemisphere at the anterior per- forated space, and, as the striate arteries, supply the corpus striatum. These antero-lateral ganglionic branches, as they are often called, are arranged as two groups : (a) the internal striate arteries, which pass upward through the lenticular nucleus (globus pallidus) and the internal capsule and end in the caudate nucleus, supplying the anterior part of the structures traversed ; [h^ the external striate arteries, which after traversing the putamen and the internal capsule terminate in either the caudate nucleus or the optic thalamus. One of the former ( lenticulo-striate^ vessels, which passes around the outer border of the lenticular nucleus before traversing its substance, is larger than the others and, since it frequently ruptures, is known as the artfry of cerebral hemorrhage. WTiile in the Sylvian fissure the middle cerebral arter>' gives oflf numerous branches to the cortex of the island of Reil and continues into the conical bi-anches, which are distributed to the lateral surface of the hemisphere and are usually four in THE SUBCLAMAN ARTERY. 753 number, {a) The inferior frontal is distributed to the inferior frontal convolutions, (b) the ascending frontal passes to the lower portion of the ascending frontal convolution, (c) the parietal supphes the whole of the ascending parietal convolution and the neighboring portions of the inferior parietal, and (d) the parieto-temporal passes to all the convolutions around the posterior limb of the fissure of Sylvius. 7. The Anterior Cerebral Artery. — The anterior cerebral artery (a. cerebri anterior) (Fig. 700) is the smaller of the terminal branches of the internal carotid. It passes fonvard above the optic chiasma to the anterior end of the great longitudi- nal fissure, and, bending upward around the rostrum of the corpus callosum, is con- tinued backward along the medial surface of the cerebral hemisphere to the posterior portion of the parietal lobe. At its entrance into the great longitudinal fissure it is connected ■i\ith its fellow of the opposite side by a short trans%-erse \'essel term.ed the anterior communicating artery (Fig. 702). Branches. — Immediately after it has crossed the optic chiasma the anterior cerebral artery gives off a number of small central branches (antero-mesial ganglionic) , which penetrate the base of the brain and are distributed to the lamina cinerea, the rostrum of the corpus callosum, the septum lucidum, and the tip of the caudate nucleus. Throughout its course in the great longitudinal fissure it gives branches to the corpus callosum and also cortical Branches to the medial and lateral surfaces of the cerebral hemisphere. These branches are {a) the orbital, which vary in number and are distributed to the orbital surface of the frontal lobe, also sup- plying the olfactory bulb ; {b') the anterior internal frontal, which supplies the anterior and lower part of the marginal convolution and sends branches to the lateral surface of the hemis- phere supplying the superior and middle frontal convolutions ; {c\ the middle internal frontal, which is distributed to the middle and posterior parts of the marginal convolution and to the adjacent' portions of the superior and ascending frontal and ascending parietal convolutions; and {d) the posterior internal frontal or quadrate, which, in addition to sending branches to the corpus callosum, supplies the quadrate lobe and the upper part of the superior parietal convo- lution. These branches anastomose upon the inferior and lateral surfaces of the hemisphere with the branches of the middle cerebral artery, the main stem of the arter)- anastomosing posteriorly with branches of the posterior cerebral. Anastomoses of the Carotid System. — Although the majoritv^ of the anastomoses of the branches of the carotid arteries are with one another, yet there is a sufficient amount of communication with other vessels to allow of the establishment of a collateral circulation after ligation of the common carotid of one side. The con- nections which are available for the circulation in such a case are as follows. ( i ) There is abundant communication between the branches of the right and left external carotids across the median line ; (2) the anterior communicating artery forms an important communication between the internal carotids of opposite sides ; (3) anastomoses exist between the ascending cervical branch of the inferior thyroid, the superficial cenical branch of the transversalis colli, and the deep cervical branch of the superior intercostal, on the one hand, all of these being branches of the sub- clavian artery, and the a. princeps cer\-icis, a branch of the occipital artery ; (4) abundant communications exist between the terminal branches of the inferior thyroid from the subcla\'ian and the superior thyroid from the external carotid ; and, finally, (5) by means of the posterior communicating artery- the internal carotid may receive blood from the posterior cerebral artery, which, through the basilar and vertebral arteries, belongs to the subclavian system. THE SUBCLAVIAN ARTERY. In the primary arrangement of the branchial blood-vessels, while there are t\vo aortic arches (Fig. 678), the two subclavian arteries arise symmetrically from these arches as lateral segmental branches corresponding to the seventh cer\-ical segment. With the disappearance of the lower portion of the right arch, however, an apparent lack of symmetry in their origin super^-enes, the \-essel of the right side arising from the innominate stem, while that of the left side springs directly from the persist- ing aortic arch. As a matter of fact, however, the proximal portion of the right aortic arch is represented by the innominate stem, together with a small portion of the proximal end of the right subclavian artery, so that the original morphological sym- 754 HUMAN ANATOMY. metry is retained ; but, since a portion of the original right aortic arch is included in the adult right subclavian, this vessel is a little more than equivalent to its fellow of the opposite side. Furthermore, since the innominate stem ascends directly upward from its origin, a topographical asymmetry of the two vessels results. The origin of the 7-ight subclavian is opposite the right sterno-clavicular articula- tion, and from that point the artery ascends upward and outward in a gentle curve over the dome of the pleura to the inner border of the scalenus anticus. The origin of the left S2tbclavian is from the termination of the transverse portion of the aortic arch, and is consequently much deeper in the thorax (Fig. 690). From its origin it ascends at first almost vertically and then curves outward and slightly forward to reach the inner border of the scalenus anticus. From this point onward the course of the two arteries is the same. Passing behind the anterior scalene muscle, each artery continues its course outward across the root of the neck, curving downward to the outer border of the first rib, at which point it becomes known as the axillary artery. Fig. 701. Descending branches of cervical plex Subclavian artery Subclavian vein In consequence of the difference in origin, the right subclavian artery is usually approximately 7.5 cm. (3 in.) in length, or about one inch shorter than the left. In its course across the root of the neck the height which the subclavian artery may reach varies considerably in different individuals ; in some it never rises above the clavicle, while in others its highest point may be from 2. 5-3 cm. ( i-i }4 in. ) above that bone. Most frequently it reaches a point about 1.5 cm. (S/g in. ) above the clavicle, this highest point being reached as it passes beneath the scalenus muscle. As it commences its downward course towards the first rib, the artery undergoes a more or less pronounced diminution in diameter, which persists for a distance of from 0.5-1 cm., and is followed by an enlargement to about its original size, what has been termed an arterial isthmus and spindle thus resulting (page 720). Relations. — For convenience in description, the subclavian artery is usually regarded as consisting of three portions. The first portion extends from its origin to the inner edge of the scalenus anticus, the second portion lies behind that muscle, THE SUBCLAVIAN ARTERY. 755 while the third portion extends from the outer border of the scalenus to the con- ventional termination of the artery at the lower border of the first rib. On account of the difference in their origins, the relations of the first portions of the right and left vessels differ somewhat. The first portion of the right subclavian artery lies behind the clavicular portion of the sterno-cleido-mastoid, and is crossed in front by the internal jugular and vertebral veins and by the right pneumogastric, phrenic, and superior sympa- thetic cardiac ner\-es. Behind, it is in relation with the trans\'erse process of the seventh cervical \-ertebra, with the inferior cervical sympathetic ganglion, and with the right recurrent laryngeal nerve, which winds around its under surface from in front. Below, it is in contact with the dome of the right pleura. " The first portion of the left subclavian artery, at its origin, is deeply seated in the thoracic ca\-ity and ascends almost vertically through the superior mediastinum. Behind, and somewhat medial to it, are the oesophagus, the thoracic duct, and the longus colli muscle, and at its emergence from the thora.x the lower cervical sympa- thetic ganglion. Medial, or internal to it, are the trachea and the left recurrent laryn- geal ner\'e, and lateral to it, on its left side, are the left pleura and lung, which also overlap it in front. Near its origin it is crossed by the left innominate (brachio-ceph- alic)-vein, and, shortly before it passes over into the second portion, it is crossed by the internal jugular, vertebral, and subclavian \'eins, as well as by the phrenic nen-e and the thoracic duct, the latter arching o\'er it to reach its termination in the subclavian vein. The left pneumogastric and cardiac sympathetic nerves descend into the thorax in front of it, the pneumogastric, before passing over the aortic arch, coming into contact with the anterior surface of the vessel. As it emerges from the thorax the subclavian lies behind the clavicular portion of the sterno-cleido-mastoid. In the neck it rests below upon the dome of the left pleura. The second portion of the subclavian artery, the relations of which and of the succeeding portion of the vessel are the same on both sides, zVz front is co\'ered by the scalenus anticus muscle, anterior to which and on a slightly lower plane is the subclavian vein. Behind and above it are the trunks of the brachial plexus, which separate it from the scalenus medius, and belozc it is in contact with the pleura. The third portion of the subclavian artery lies in the supraclavicular fossa, and is co\'ered only by the skin, the platysma, and that part of the deep cervical fascia which contains the e.xternal jugular vein and the supraclavicular branches of the cervical ple.xus, and encloses a quantit}' of fatty tissue, in which the suprascapular artery passes outward. Behind, it is in contact with the scalenus medius and the brachial ple.xus, and above it are the brachial plexus and the posterior belly of the omo-hyoid. Below, it rests upon the first rib, at the lower border of which the \'essel becomes the axillary artery. Branches. — Considerable variation exists in the arrangement of the branches of the subclavian, but in what is probably the most frequent arrangement the branches are as follows : From the first portion arise (i) the vertebral, (2) the internal mammary. (3) the superior intercostal, and (4) the thyroid axis ; from the second portion no branches are given off ; from the third portion (5) the transverse cervical. Variations. — The variations in the origin of the subclavian artery have already been consid- ered in describing the variations of the aortic arch (page 725). Other anomalies occur in its relation to the scalenus anticus, in front of which it sometimes passes, and it may also traxerse the substance of the muscle obliquely. More rarely the artery divides at the inner border of the muscle, the two branches so formed continuing onward through the axilla and down the arm to become the radial and ulnar arteries. Numerous supernumeran,- branches may arise from the subclavian. These may be either (i) accessory to the branches normally arising from the arter)% such as an accessor}' vertebral, an accessory internal mammary, or an accessory inferior thyroid ; (2) they may be branches, such as the long thoracic, dorsal scapular, subscapular, and the anterior and posterior circum- fle.xes, which normally arise from the axillary artery, but have secondarily shifted to the sub- clavian as the result of the enlargement of anastomoses which they make with branches of that \'essel ; or (3I they ma}- be branches to neighboring organs, such as a bronchial or a pericar- dial branch, or occasionally the thyroidea ima (page 729). 756 HUMAX ANATOMY. Practical Considerations. — The subclavian arterv mav require ligation, on account of stab wounds, as a preliminary to the removal of growths — axillary or scapular — or to an interscapulo-thoracic amputation, or in cases of axillar)- or sub- clavian aneurism, or, together with the common carotid artery, in aortic or innominate aneurism. On the surface of the neck the subclavian artery is represented by a curve, convex upward, beginning at the sterno-clavicular articulation and ending beneath the middle of the clavicle, its highest point being on an average about five-eighths of an inch above that bone. The vein is lower, is in front of the artery ( separated from it by the scalenus anticus muscle), and is usually nearly or quite under cover of the clavicle. Aneurism, of the subcla\ian is more frequent on the right side, probably because of the greater use and consequent greater exposure to strain of the right upper extremity. It may affect any portion of the vessel, but the third portion — e.xternal to the scaleni, where it is least supported by surrounding muscles — is most com- monly involved either primarih- or by extension of an aneurismal dilatation upward from the axillary or downward from the arch of the subcla\'ian. The thoracic portion of the left subclavian is ne\"er the primary seat of aneurism. The symptoms are : ia) pain or numbness and loss of poiccr in the arm-^and hand from pressure on the brachial plexus ; {b) s'lcelling and adema of the arm and hand from pressure on the subcla\ian \-ein ; (r) hiccough or iircgulai-. jerky res- piration from pressure on the phrenic nerve ; {d) vetiigo, scnnnolence, defective vision, from compression of the internal jugular :' ((?) tianor, usualh' appearing in the posterior inferior cer\ical triangle, with its long diameter approximately parallel with the clavicle, and extending upward and outward ; exceptionally it grows down- ward, but this is rare on account of the resistance ofiered by the claxicle. the first rib, and the structures tilling the costo-clavicular space. Digital compression of the first and second portions of the ai-tery is practically impossible. The third portion may be imperfectly occluded by making strong pressure directly backward just above the clavicle, a little external to its middle, so that the arterv may be flattened out or narrowed against the scalenus medius muscle and the seventh cer\ical transverse process. Much more effectual pressure may be made at the same point, especially if the tip of the shoulder can be lowered so as to carry the claxicle downward and make the upper surface of the first rib more accessible, in a direction downward, backward, and inward, — i.e., in a line nearly or quite perpendicular to the plane of that surface. The \essel is thus compressed against it, and is not pushed off of it. It will be useful to recall that the outer border of the scalenus anticus and the posterior border of the stemo-mastoid — the latter palpable and often visible — are approximately on the same line, immediately outside of which is the third portion of the vessel. The scalene tubercle — the elevation or roughening on the upper surface of the first rib between the shallow depression for the subclavian vein and the deeper groo\-e for the subclavian artery ^gi\-es attach- ment to the scalenus anticus and, when recognized, serves as a valuable guide to the vessel. Ligation. — The first portion — between the origin of the vessel and the inner side of the scalenus anticus- — has been ligated with uniformly fatal results. On the left side it is so situated as to depth, origin of branches — the vertebral, internal mammary, thyroid axis, and superior intercostal — and contiguity of important structures — the heart, the aorta, the pleura, the innominate vein, the thoracic duct, the pneumogastric, cardiac, recurrent laryngeal and phrenic nerves — that its ligation has only once been accomplished (Rodgers). On the right side the operative procedure is some- what less difificult, but many of the relations are identical (vide supra), and the procedure is still so formidable that its description is included in some works on operati\e surgery only because the ligation ' ' affords good practice on the dead subject " ( Jacobson ) . The steps of the operation are the same as those in ligation of the innominate (page 729) until the carotid sheath is reached and opened. The internal jugular vein and pneumogastric nerve should be drawn aside (inward, Agnew : outward, Barwell) and the subclavian recognized, springing from the bifurcation of the innom- PRACTICAL CONSIDERATIONS: SUBCLAVIAN ARTERY. 757 inate at an acute angle with the carotid and deeper by the full diameter of the latter. The needle should be passed from below upward, while the pleura is gently depressed with the finger. The second portion — behind the scalenus anticus — has in a few cases been suc- cessfully ligated for aneurism external to it, but the operation does not require special description. It is identical with that for tying the third portion, with the addition of more extensive division of the clavicular portion of the sterno-mastoid and a partial division of the scalenus anticus, having due regard to the position of the phrenic nerve on the inner part of the anterior surface of that muscle. The third portio7i — from the outer edge of the scalenus anticus to the lower border of the first rib — has been frequently and successfully ligated. Three methods may be described : 1. By the first and usual one it is approached by a transverse incision, parallel with the clavicle and extending along the base of the posterior cen,'-ical triangle from the middle of the clavicular head of the sterno-mastoid to the anterior border of the trapezius. This is best made by drawing the skin down and incising it directly upon the bone, in this way easily avoiding the external jugular vein. The platysma muscle and the supraclavicular nerves are divided at the same time. On releasing the skin the wound will be placed about a half-inch above the clavicle. The shoulder is then well depressed so as to lower this bone and increase the supraclavicular space. The deep fascia, which, as it is attached to the superior border of the clavicle, is not pulled down with the skin and platysma, is then divided, the external jugular vein drawn aside or tied and cut, the loose cellular tissue, and possibly the omo-hyoid aponeurosis, scratched through or cut, and one or the other of four landmarks iden- tified : (a) the tense outer edge of the anterior scalene muscle or {b) the scalene tubercle at the insertion of that muscle Into the first rib, the artery lying just outside these on the rib; (f) the first rib itself traced inward with the finger from the outer angle of the wound until the artery is reached ; (d) the lowest cord of the brachial ple.xus, lying immediately abo\-e, or sometimes slightly overlapping the artery. The cord has been mistaken for the vessel, but compression between the finger and the rib does not flatten it out, as in the case of the artery, and, of course, does not arrest the radial pulse. The tubercle is often poorly developed, and has a less close relation to the vessel when the latter rises high above the cla\-icle. The process of cervical fascia reaching from the posterior border of the scalen-us to the sheath of the artery may be so tense as to. obscure to both sight and touch the line of the outer edge of the muscle The artery is cautiously denuded, care being taken to avoid injury to the pleura or to the subclavian vein. The transverse cervical artery is usually abo\'e and the suprascapular artery below the line of incision. The phrenic nerve has been known to pass directly over the third portion of the subclavian (Agnew), and the possibility of the presence of this rare anomaly should be remembered. The needle, the tip kept between the artery and the rib, is passed from abo\'e down- ward, and from behind forward and a little inward. In the case of a high arch of the subcla\'ian the third portion is nearly vertical, and it would then be more correct to speak of passing the needle from without inward. 2. The middle of the clavicle for two or more inches, or the whole cla^'icle, may be resected subperiosteally, as in interscapulo-thoracic amputations, and the ap- proach to the artery greatly facilitated. 3. By strongly elevating — instead of depressing — the shoulder and clavicle, using the arm as a tractor, the artery may be exposed by an incision just below and parallel with the middle of the clavicle. A portion of the outer edge of the pec- toralis major and some of the inner deltoid fibres wall usuall)' have to be di\'ided, although it may be possible to gain sufficient room 'bv drawing the margin of the former muscle inward and that of the latter outward. The cephalic vein dipping in through this intermuscular depression (Mohrenheim's fossa) to join the axillary vein must be avoided. The artery is found lying between the vein internally and the close bundle of the cords of the brachial plexus externally. The point at which the vessel is tied is said to be identical with that at which it is ligated through the usual incision (Dawbarn). 758 HUMAN ANATOMY. The collateral circulation after ligation of the third portion of the subclavian artery is carried on from the proximal or cardiac side of the ligature by ( a ) the suprascapular and posterior scapular ; {b) the aortic intercostals, the superior inter- costals, and the internal mammary ; and (c) numerous subdivisions of subclavian branches running through the axilla, anastomosing respectively with (a) the sub- scapular, and the acromio-thoracic ; (i5), the subscapular, long thoracic, infrascap- ular, and dorsalis scapuke ; (c) the axillary trunk or its branches. I. The Vertebral Artery. — The vertebral artery (a. vertebralis) (Figs. '695, 704), the first and largest branch of the subclavian artery, is destined chiefly for the supply of the spinal cord and the brain, joining with the internal carotid arteries to form the remarkable intracranial anastomotic circle of Willis. In view of its peculiar course, the vertebral artery may be conveniently divided into four parts. The first portion arises from the upper surface of the first part of the sub- clavian artery, opposite the interval between the longus colli and scalenus anticus, and courses upward and somewhat backward, between these muscles and in front of the transverse process of the seventh cervical vertebra, to the foramen in the transverse process of the sixth cervical vertebra, which it enters. The artery is surrounded by a plexus of sympathetic nerve-fibres, and in front is crossed by the inferior thyroid artery and covered by the vertebral and internal jugular veins. The second portion includes the ascent of the artery through the foramina in the transverse process of the upper six cervical vertebra, surrounded by plexiform net- works of sympathetic nerve-fibers and of veins, and lying in front of the trunks of the cervical nerves. As the artery traverses the foramen in the axis it abandons its previous almost vertical course and passes upward and outward to reach the foramen in the atlas. As it emerges from this opening, passing between the suboccipital nerve and the rectus capitis lateralis muscle, its third portion begins, bending hori- zontally to the outer side and back of the superior articular surface of the atlas to enter the suboccipital triangle (Fig. 522) where it rests in the vertebral groove upon the posterior arch of the atlas, being separated from the bone, however, by the suboccipital nerve. The artery then perforates the lower border of the posterior occipito-atlantoid ligament and enters the spinal canal. The fourth portion of the artery pierces the spinal dura mater, passes between the roots of the hypoglossal nerve and the dentate ligament and enters the cranial cavity by traversing the fora- men magnum. Passing forward along the medulla oblongata and gradually inclin- ing towards the mid-ventral line, at the posterior border of the pons the \'ertebral artery unites with its fellow of the opposite side to form the basilar artery (a. basi- laris), which extends forward along the median line of the pons to the anterior border of that structure, where it terminates by dividing into the two posterior cerebral arteries. Branches. — In its course up the neck the vertebral artery gives off, opposite each inter- vertebral space which it passes, lateral and medial branches which rei^resent the original seg- mental arteries by the anastomoses of whose branches the vertebral was formed (page 721). (a) The lateral or muscular branches pass to the muscles of the neck and fnrni anasto- moses with the ascending and deep cervical branches of the subclavian and with the arteria princeps cervicis of the occipital. (b) The medial or spinal branches (rami spinale-s) pass through the intervertebralforaniina into the spinal canal, accompanying the spinal nerves, and are distributed to the bodies of the vertebrte and to the membranes and substance of the spinal cord. Each branch gives off an ascending; and a descending ramus upon the posterior surface of the spinal cord, and these, anastomosing with each other and with twigs from the spinal branches of the intercostal, lum- bar, and lateral sacral arteries below and with the posterior spinal branches of the upper part of the vertebral, assist in the formation of the posterior spinal arteries, which run the entire length of the spinal cord upon its posterior surface on each side of the median line. Ante- riorly the spinal branches of the vertebral unite with the anterior spinal artery, reinforcing that vessel. (r) The posterior meningeal artery (ramus meninKeus') arises from the \'ertebral, just after it has pierced the dura mater, and supplies the portion of that membrane which lines the pos- terior portion of the posterior fossa of the skull. THE VERTEBRAL ARTERY. 759 (a?) The posterior spinal artery (a. spinalis posterior) is a slender vessel which anasto- moses below with the posterior ascending ramus of the uppermost spinal branch from the cervical portion of the vertebral and forms the uppermost part of the posterior spinal arter)'. (e) The anterior spinal artery (a. spinalis anterior), much larger than the preceding, arises from the inner surface of the vertebral, a short distance before the latter unites with its fellow to form the basilar. It passes downward and towards the ventral median line, and unites with its fellow to form a single median longitudinal stem which extends the entire length of the spinal cord along the line of the anterior median fissure, receiving reinforcing branches from the various spinal branches of the vertebral, intercostal, lumbar, and lateral sacral arteries. (/) The posterior inferior cerebellar artery (a. cerebelli inferior posterior) arises at about the same level as the preceding vessel, but from the outer surface of the vertebral. It passes upward over the sides of the medulla oblongata to supply the lower surface of the cerebellum, Fig 702. Internal carotid artery Pituitary body Anterior choroid Posterior eating arter> Corpora Posterior cerebral Superior cerebellar Anterior cerebral artery A pontine arter) Auditory arterj Inferior surface of brain, showing internal carotid, vertebral and basilar arteries and circle of Willis; apex of left temporal lobe has been removed to expose ganglionic arteries. giving branches to the medulla and to the choroid plexus of the fourth ventricle and anasto- mosing with the superior cerebellar artery. From the basilar artery, (Fig. 702) the anterior median continuation of the vertebrals. ( g) Numerous transverse arteries are given off and pass outward over the pons to supply that structure and the adjacent portions of the brain. (A) The internal auditory arteries (aa. auditivae internae), one on each side, are additionally given off, and accompany the auditory nerve through the internal auditory meatus to supph' the internal ear. {i) The anterior inferior cerebellar arteries (aa. cerebelli inferiores anteriores), pass out- ward on either .side over the surface of the pons to the lower surface of the anterior portion of the cerebellum, supplying that structure and anastomosing with the superior cerebellar arteries. (7') The superior cerebellar arteries (aa. cerebelli superiores). These arise from the basilar, immediately behind its division into the posterior cerebral arteries. They pass outward and backward over the pons and the crura cerebri, immediately behind the roots of the oculo-motor 76o HUMAN AiNATOMY. nerves, and, curving upward in the tentorial fissure almost parallel with the trochlear nerves, are distributed to the upper surface of the cerebellum and anastomose with the inferior cere- bellar arteries. (i) The posterior cerebral arteries (aa. cerebri posteriores) (Fig. 702) are the terminal branches of the basilar. From its origin at the anterior border of the pons each artery passes outward and slightly forward, curving around the crus cerebri, immediately in front of the root of the oculomotor nerve, which separates it from the superior cerebellar artery. It then passes upon the inferior surface of the cerebral hemisphere, where it breaks up into cortical branches which ramify over the surface of the temporal and occipital lobes, anastomosing with one another and with the branches of the anterior and middle cerebrals. The cortical branches (Fig. 700) include the antctior temporal, which supplies the anterior parts of the uncinate and occipito-temporal convolutions; \\\v. posterior temporal, distributed to the posterior part of the uncinate and the occipito-temporal convolutions and the adjoining gyrus lingnalis : the calca- fine, the continuation of the posterior cerebral along the calcarine fissure, which passes to the cuneus and the gyrus lingualis, and winds to the outer surface ; and \\\c parieto-oceipita/, which follows the parieto-occipital fissure to the cuneus and the quadrate lobe. Immediately at their origin the posterior cerebrals give rise to a number of small central branches [postero-mcsia/ and postcro-lateral gangliotiic) which dip down into the substance of the posterior perforated .space to supply the optic thalannis and the adjacent parts of the brain-stem, and somewhat more laterally each gives off a posterior ehoroidal branch, which passes forw-ard in the transverse fissure to the choroid ple.xus of the third \entricle. Near wliere-it passes in front of the oculo-motor nerve, each posterior cerebral receives the posterior communicating artery which passes back to it from the internal carotid, and more laterally it gives off some small branches which are distributed to the corpora quadrigemina and the posterior part of the optic thalamus. Variations. — The vertebral artery may arise from a trunk common to it and one of the other branches of the subclavian, and sometimes it arises directly from the arch of the aorta or, on the right side, from the innominate artery or. the common carotid. It may traverse a foramen in the trans\-erse process of the seventh cervical vertebra, or the lowest vertebrarterial foramen through which it passes may be the fifth, fourth, third, or even the second. Very rarely the two vertebrals fail to unite to form a single median basilar, that arterj- being thus represented by two longitudinal trunks united by transverse anastomoses. Occasionally the basilar divides into two longitudinal stems which reiinite farther forward, and its formation by the fusion of two parallel vessels is frequently indicated by the presence in its interior of a more or less perfect median .sagittal partition. The vertebral may give origin to an inferior thyroid artery or to the deep cer\ical, and oc- casionally, in its upper part, to a branch which anastomoses with the occipital. One of the pos- terior inferior cerebellar arteries may be wanting, as is also not infrequently the case with one of the anterior inferior cerebellars, or these latter vessels may arise from the posterior cerebral. Occasionally the pro.ximal portion of one or other of the posterior cerebral arteries is reduced to a mere thread, the blood reaching the terminal portions of the \-essel from the internal carotid, through the posterior communicating artery. The Circle of Willis. — The circle or, as it is more properly called, the polygon of Willis (circulus arteriosus) is a continuous anastomosis at the base of the braiii (Fig. 702) between branches of the internal 'carotids and subcla\ians (\erte- brals). It surrounds the posterior perforated space and the flonr of the thalamen- cephalon. Posteriorly it is formed by the proximal portions of the posterior cerebral arteries, at the sides by the posterior communicating and internal carotid arteries behind, and by the pro.\imal portions of the anterior cerebrals in front, and it is completed anteriorly by the anterior communicating artery which unites the two anterior cerebrals. By means of these connections free communication is established at the base of the brain between the two internal carotids and also between these vessels and the vertebrals. It may be noted that a further communication between these sets of vessels exists upon the lateral surfaces of the cerebral hemispheres where branches of the posterior cerebral arteries anastomose with branches of both the middle and anterior cerebrals. In marked contrast to this abundant- anastomosis of the larger vessels upon the surface of the cerebrum is the lack of direct communication between the small vessels which penetrate its substance. These are all terminal or end-arteries, — that is, vessels which have no communication with others except through the general capil- lary net-work, which offers but little opportunity for the establishment of an efficient collateral circulation in the case of occlusion of one of the arteries. PRACTICAL CONSIDERATIONS: VERTEBRAL ARTERY. 761 Practical Considerations. — The vertebral artery may require ligation on account of wounds, or of traumatic aneurism of the vessel itself, or (in addition to the ligation of other vessels) in aortic or innominate aneurism, or to prevent or arrest secondary hemorrhage after ligation of the innominate. Aneimsm — except from wound — is excessively rare, the vessel being well sup- ported, first between the scalenus anticus and the longus colli muscles and then in the bony canal in the transverse processes. Only one case of spontaneous aneurism of the cervical portion of the artery has been reported ( Hufschmidt). Traumatic aneurism is more frequent, but, on account of the vessel's depth, is rare. Paralysis of some of the tongue muscles has been attributed to pressure on the hypoglossal nerve by a vertebral aneurism and severe occipital headache to pressure on the suboccipital nerve. Digital compression of the \'ertebral is possible below Chassaignac's carotid tubercle (q.v.), — i.e., below the level of the cricoid cartilage, if pressure is made in the line of the great vessels. Alternating pressure above and below this level is of great diagnostic value in distinguishing the source of the bleeding, or of the supply of blood to a pulsating tumor, after a deep wound of the neck. Pressure along the line of the common carotid below the tubercle — i.e., for from two to two ana a half inches above the clavicle — will usually arrest such bleeding and puistaion, no matter whether the vertebral or either of the carotids is in\-olved. Pressure above the tubercle will affect only the carotids and their branches, but — except in the presence of an anomaly — will leave unchanged a flow of blood or an aneurismal pulsation proceeding from the vertebral. Furthermore, as in one of the not infrequent vertebral variations {vide sjipra), the artery may not enter its vertebrarterial foramen until it reaches the fifth, fourth, third, or even the second transverse process, and as, in such a case, it would be effectually compressed when pressure was applied higher than the carotid tubercle, it would be well always to supplement the above test by the method of "lateral compression" (Rouge), — i.e., by pressing together between the thumb and fingers the anterior portion of the relaxed sterno-mastoid muscle and the carotid sheath and its contents. This avoids all risk of coincident compression of the verte- bral, and if it arrests the temporal pulse without affecting materially the bleeding or the pulsation on account of which the examination is made, it greatly increases the probability that the latter are of vertebral origin (Matas). The importance of making the diagnosis is shown by the fact that in sixteen out of thirty-six cases of injuries to the vertebral artery the common carotid had been ligated, aggravating the hemor- rhage by increasing the strain on the vertebral circulation and, of course, also increas- ing the risk from shock, and later from cerebral complications (Matas). Ligation of the vertebral has been effected through variously placed incisions : I. Low in the neck, one of three inches in length along the posterior border of the sterno-mastoid and with its lower end at the cla\icle, with division of some of the clav- icular fibres of that muscle and of the deep fascia, will permit the recognition of the carotid tubercle, the displacement inward of the sterno-mastoid and internal jugular vein, the definition of the space between the scalenus anticus and the longus colli, and the identification of the artery by its pulsation. The vertebral vein lies in front of the artery. The pleura,, the inferior thyroid \'essels, the phrenic nerve, and on the left side the thoracic duct must be avoided. The fibres of the cervical sympathetic will be almost necessarily disturbed, and may be included in the ligature. Contrac- tion of the corresponding pupil, through the then unopposed action of the oculo- motor, will indicate that the vessel has been secured; it will be only temporary. 2. For a ligation in continuity, as for wound or aneurism in the suboccipital region, the artery may be much more easily reached through an incision identical with that used for ligating the common carotid above the omo-hyoid (page 732). When the carotid sheath is well exposed it is drawn outward with its contents. Chassaignac's tubercle is felt (on the cricoid level or one centimetre above it) and the longus colli fibres below, overlying the artery, are seen. A transverse division of that muscle exposes the vertebral artery in a much safer region than below and at a less depth (Dawbarn). The collateral circulation is very freely re-established through the vessels of the circle of Willis. 702 HUMAN ANATOMY. '^^c,. 703. I. chondro-stemalarticulatioD -Internal mammary artery I. ant. perf. arterj* of left side —Anterior intercostal arteries of 1.. III.. IV. and V. intcrspacel --Superiur epigastric artery Rectus abdominis ^niiluDat fold of Douglas Anterior superior spine of iliin Deep epigastric artery Superficial circumflex Iliac artery Superficial epigastric artery .Superficial external pudic arterj Deep external pudic artery Dorsalis penis arteries Internal mammar>' and deep epigastric arteries. THE INTERNAL MAMMARY ARTERY. 763 2. The Internal Mammary Artery. — The internal mammary artery (a. inam- maria interna ) (Figs. 692, 703) arises from the lower surface of the subclavian, usually a few, millimetres lateral to the origin of the vertebral. It is at first directed downward, inward and slightly forward to reach the posterior surface of the first costal cartilage, about half-an-inch lateral to the border of the sternum, and is thence continued vertically downward upon the inner surface of the anterior thoracic wall to the sixth intercostal space, opposite which it terminates by dividing into the musculo-phrenic and superior epigastric arteries. In the upper part of its course the artery rests upon the dome of the pleura, crosses the posterior surface of the subclavian vein, and is crossed obliquely from above downward and inward by the phrenic nerve. In the thora.K it is in con- tact behind with the parietal layer of the pleura as far down as the third costal carti- lage, and below that with the triangularis sterni muscle. Anteriorly it rests upon the posterior surfaces of the upper five costal cartilages, and, in the intercostal spaces, upon the anterior portions of the internal intercostal muscles. Branches.— The internal mammar)' gives off the following branches ; ( i ) the superior phrenic, or conies nervi phrenici., (2) the mediastinal branches. (3) the anterior intercostals, {4) the ««&r/'o/- /(v/c^rfi/wo- branches and the two terminal branches, (5) the musculo-phrenic, and (6) the superior epigastric. (a) The superior phrenic artery or comes nervi phrenici (a. pericardiacophrenica) arises from the upper part of the internal mammary, and is a long, slender branch which accompanies the phrenic nerve to the diaphragm, where it anastomoses with the inferior phrenic and musculo- phrenic vessels. In its course it gives off numerous small branches to the pleura and peri- cardium, which anastomose with the mediastinal branches and the bronchial \essels from the thoracic aorta. (b) The mediastinal branches (aa. mediastinales anteriores) are a number of small vessels which are distributed to the sternum, the remains of the thymus gland, the pericardium, and the adipose tissue of the anterior mediastinum. ((-) The anterior intercostal arteries (rami intercostales) arise from the internal mammary opposite each of tlie five upper intercostal spaces, and are two in number for each space. They pass outward and slightly downward upon the posterior surface of the intercostal muscles, one along the upper border of each of the intercostal spaces concerned and the other along its lower border, and after having pierced the internal intercostal muscles, they terminate by becoming continuous with the upper and lower divisions respectively of the intercostal branches of the superior intercostal artery and of the three uppermost aortic intercostals. These branches really represent ventral prolongations of the aortic intercostal arteries from which arose the upward and downward branches whose anastomosis resulted in the formation of the internal mammary (compare page 848). (rf) The anterior perforating branches (rami perforantes) arise from the internal mam- mary, one opposite each intercostal space that it crosses, and represent the ventral ends of the original aortic intercostal. They pierce the internal intercostal muscles, the anterior intercostal membrane, and the pectoralis major, to supply branches to the sternum and to the integument. The arteries of the third and fourth intercostal spaces are larger than the others and send branches to the mammar\' gland. [e) The musculo-phrenic artery (a. musculophrenica) is the lateral terminal branch of the internal mammary. It arises opposite the anterior end of the sixth intercostal space and passes downward and outward along the attachments of the diaphragm to the seventh and eighth costal cartilages, and then, piercing the diaphragm, is continued onward upon the under surface of that muscle to the level of the tenth or eleventh rib. where it terminates by anastomosing with the inferior phrenic arteries and with the ascending branch of the deep circumflex iliac. In addition to branches to the diaphragm, it gives off two anterior intercostal branches opposite each of the intercostal spaces that it crosses as far down as the ninth ; these branches have the same arrangement and significance as the anterior intercostal branches of the internal mammary. (/) The superior epigastric artery (a epigastrica superior) is the medial terminal branch of the internal mammary. It continues tlie course of that artery downward, and passes through the diaphragm in the interval between its costal and sternal origins and enters the sheath of the rectus abdominis. Lower down it passes into the substance of that muscle, where it termi- nates by anastomosing with branches of the deep epigastric .artery. Anastomoses. — By means of its terminal branches the internal mammary makes a double anastomosis in the anterior abdominal walls with branches from the iliac vessels, — namely, with the deep epigastric and deep circumflex iliac branches of 764 HUMAN ANATOMY. the external iliac, and thus connects the superior and inferior portions of the aortic system of vessels. In addition, by means of the anterior intercostals, it makes extensive connections with the thoracic aorta through the aortic intercostals. Variations. — The internal mammary may arise from the second or even the third portion of the subclavian, or it may take its origin from the thyroid axis or from the superior intercostal. In its course down the anterior thoracic wall it varies considerably in its relation to the lateral border of the sternum, its distance from it varying in different cases from 5-20 mm. Of the supernumerary branches to which it may give rise, one of the most important is the lateral internal mainviary (ramus costalis lateralis). This arises from the internal mammary above the first rib, or in some cases directly from the subclavian, and descends upon the inner surfaces of the upper four or si.x ribs and the intervening intercostal spaces, parallel with the internal mammary, but some distance lateral to it. It gives off branches in each intercostal space, which anastomose ventrally with the anterior intercostal branches of the internal mammary and dorsally with the aortic intercostals. Practical Considerations. — The internal mammary is not infrequently involved in stab wounds of the chest, and this accident may be suspected if after such a wound there are threatening symptoms of internal hemorrhage with no evidence of injury to the lung itself. The bleeding may take place into the pleural cavity, causing the characteristic symptoms of hiemothora.x (page 1866). Co»iprcssio7i.—^\n emergencies the bleeding may sometimes be arrested by pushing through the wound into the intrathoracic space or pleural cavity a pouch of antiseptic gauze, packing it with other strips of gauze so as to distend the portion within the ribs, and then making traction upon it so as to compress the wounded vessel against the costal cartilages and the chest-wall. This same method is applicable in some cases of intercostal hemorrhage when it is not possible or desirable to approach the vessel directly in its groove on the under and inner border of the rib by incision or by resection of a portion of the rib. Ligation. — In some cases it may be necessary to ligate the vessel in its con- tinuity, although its free anastomoses make it very desirable to find and tie it on both sides of the wound. It may be reached through an incision parallel with the sternum and a half-inch from its margin or through a transverse incision extending outward along an intercostal space. In either event, the skin, superficial fascia, sternal fibres of the great pectoral muscle, the external intercostal aponeurosis ( connecting the external intercostal muscle with the sternum), and the internal intercostal muscle must be divided. The artery with its accompanying veins will be found in loose cellular tissue lying, in the first two spaces, upon the endothoracic fascia, which sepa- rates it from the pleura ; in the lower spaces the vessel rests upon the triangularis sterni muscle. Below the third or fourth space resection of a cartilage will usually be necessary for the purpose of gaining room, and at any level is often resorted to to permit direct access to the bleeding ends. 3. The Superior Intercostal Artery. — The superior intercostal artery rtruncus costocervicalis) (Fig. 695 J arises from the upper posterior surface of the subclavian artery, usually about opposite the origin of the internal mammary, but quite frequently, and especially upon the right side, under cover of the scalenus anticus. It passes at first upward and medially, and then curves backward and downward over the dome of the pleura to reach the anterior surface of the neck of the first rib, where it di\ides into two terminal branches which pass laterally in the first and second intercostal spaces. As it enters the thorax, the superior intercostal lies be- tween the first thoracic sympathetic ganglion and the first thoracic spinal nerve. Branches. — The superior intercostal gives rise to (i) the deep eervical artery, and to two terminal branches, (2) the first ^wA (3) the second intereostal arteries. {a) The deep cervical artery (a. cervicalis profunda) arises just as the superior intercostal reaches the upper border of the neck of the first rib, although occasionally it takes origin directly from the subclavian. It is directed upward and backward, passing between the last cervical and first thoracic nerves and beneath the transverse process of the last cervical verte- bra, and ascends the neck between the complexus and the semispinalis colli, to which it sends branches. It anastomoses with branches of the ascending cervical, vertebral, and princeps cer- vicis arteries, and gives off a spinal branch which passes along the eighth cervical nerve to the THE THYROID AXIS. 765 spinal canal, where it anastomoses upon the surface of the spinal cord with the spinal branches of the vertebral and of the intercostal arteries. In all its relations the deep cervical is comparable to a posterior branch of an intercostal artery, and is to be regarded as the posterior branch of the seventh cervical segmental artery, which is the subclavian. (6) The first intercostal artery passes outward and forward in the first intercostal space, and resembles in its course and distribution an aortic intercostal (page 792). {c) The second intercostal artery arises at the bifurcation of the superior intercostal and passes downward over the neck of the second rib to the second intercostal space, in which it Fig. 704. .J S Common carotid Suprascapular Biceps, long head Anterior circuniHL Biceps, short het 1 Axillary irter> Posteno Subscapular Dorsalis scapulae Latissimus dorsi Serratus magnus Deep dissection exposing subclavian and axillary arteries and their branches. courses similarly to an aortic intercostal (page 792). It usually receives an anastomosing branch from the third intercostal arter>' or else directly from the thoracic aorta, and may be replaced by it. Variations. — The superior intercostal may arise from the vertebral artery and may termi- nate in the first intercostal alone, the second arising from the third or from the thoracic aorta. Anastomoses occur between the first and second intercostals and the arteria aberrans (page 792), when that vessel is present. 4. The Thyroid Axis. — The thyroid a.xis (truncus thyreoceiTicalis) (Fig. 704) arises from the upper border of the subclavian, usually just medial to the medial border of the scalenus anticus. It ascends vertically upward for from 2-10 mm., 766 HUMAN ANATOMY. and terminates by dividing into three branches; {i) the inferior thyroid, (2) the superficial cervical, and (3) the suprascapular. (a) The inferior thyroid artery (a. thyreoidca inferior) (Fig. 692) is the largest of the branches which arise from the thyroid a.xis. It passes at first \erti- cally upward to about the level of the transverse process of the si.xth cervical vertebra, and then bends medially. It passes behind the common carotid artery, the internal jugular vein, and the pneumogastric nerve, either behind or in front of the recurrent laryngeal nerve and in front of the vertebral artery, and finally breaks up into branches which supply the lower part of the thyroid gland and anastomose with their fellows of the opposite side and with the superior thyroid artery. Branches. — In addition to these terminal branches, the inferior thyroid gives origin to the following arteries ; I aa ) Muscular branches to the scalenus anticus and the inferior constrictor of the pharyn.x. (bb) The ascending cervical artery (a cervicalis ascendens) frequently arises directly from the thyroid axis and passes vertically upward, parallel to the plirenic nerve, in the interval be- tween the scalenus anticus and the rectus capitis anticus major. It supplies the deep muscles of the neck, sends branches through the spinal foramina which accompany the spinal branches of the vertebral artery, and anastomoses with the vertebral, the occipital, the ascending pharyn- geal, and the deep cervical arteries. {cc) The inferior laryngeal artery (a. laryngea inferior") passes upward in the groove be- trt-een the trachea and cesophagus in company with the recurrent laryngeal nerve. It passes beneath the lower border of the inferior constrictor of the pharyn.x and enters the larynx, to whose mucous membrane and muscles it is distributed. It anastomoses with the superior laryngeal branch of the superior thyroid. Finally, it gives off small branches to the pharyn.x, cesophagus, and trachea, one of those to the last-named structure extending down upon its lateral surface to anastomose below with the bronchial arteries. The anastomoses which the inferior thyroid makes by its thyroid branches with the supe- rior thyroid and by its ascending cervical branch with the occipital constitute important connec- tions between the subclavian and carotid systems and play an important part in the establish- ment of the collateral circulation after ligation of the common carotid artery. Variations. — The thyroid axis occasionally arises under cover of or even lateral to the scalenus anticus, and it may be entirely wanting, its branches arising directly from the subcla- vian. The inferior thyroid may be absent on one side or on both, and its size varies inversely to the development of its fellow of the opposite side or to that of the superior thyroid arteries. Practical Considerations. — The inferior thyroid may be tied for a wound or during the operation of thyroidectomy. It has been frequently tied, in conjunction with the superior thyroid, in various forms of goitre, but the procedure has been abandoned. It may be reached through the incision for tying the carotid below the omo-hyoid (page 732). The sterno-mastoid and the carotid sheath and its contents are drawn outward. The carotid tubercle being found, the inferior thyroid should be sought for at a slightly lower level, — opposite the body of the si.xth cervical ver- tebra or about the level of the onio-hyoid crossing, — coming out from behind the sheath of the great vessels and running in front of the vertebral artery obliquely upward and inward towards the gland. It should be remembered that before enter- ing the gland it lies for a short distance close to its posterior surface, and that the recurrent laryngeal nerve is in intimate relation to this part of the vessel or to its terminal branches. It should therefore be tied in the fissure between the oesophagus and the great vessels, as close to the carotid sheath — i.e., as far from the inferior angle of the gland — as possible, to avoid inclusion of this nerve. The middle cer- vical ganglion of the sympathetic, the phrenic and the descendens hypoglossi nerves, and, on the left side, the thoracic duct should be carefully avoided. (//) The superficial cervical artery (a. cen'icalis superficialis) (Fig. 705) passes almost directly laterally from the thyroid a.xis, passing in front of the scalenus anticus and ,then across the lower part of the posterior triangle of the neck at a level of about 25 cm. above the clavicle. Arrived at the anterior border of the trapezius, it passes beneath that muscle and breaks up into ascending and descending branches which supply the trapezius, the levator angulv scapulae, the rhomboidei, and the THE AXILLARY ARTERY. 767 splenii. The ascending branches anastomose with the deep and ascending cervical arteries, and with the princeps cervicis of the occipital and the descending branches with the suprascapular and transverse cervical. (c) The suprascapular artery (a. transversa scapulae) (Fig. 704), like the superficial cervical, passes almost directly laterally across the lower part of the pos- terior triangle of the neck. It lies, however, on a somewhat lower level than, and anterior to, the superficial cervical, lying usually behind the clavicle, in front of the subclavian artery, and resting below upon the subclavian vein. It is continued later- ally beneath the trapezius, to which it sends branches, and, having reached the upper border of the scapula, it passes over the transverse ligament of that bone, or occasionally through the suprascapular notch, into the supraspinous fossa. Here it gives branches to the supraspinatus muscle, and, winding around the lateral border of the spine, passes through the scapular notch into the infraspinous fossa, where it breaks up into branches supplying the infraspinatus muscle ancl anastomos- ing abundantly and widely with the branches of the dorsal scapular artery. 5. The Transverse CervicaL — The transverse cervical (a. transversa colli) is the only branch which arises from the third portion of the subclavian. It also is directed laterally, parallel with the superficial cervical and suprascapular arteries, about midway between them, but on a much deeper level. It rests upon the anterior surface of the scalenus medius muscle, and upon the trunks of the brachial ple.xus, and, passing beneath the posterior belly of the omo-hyoid, reaches the lower portion of the levator anguli scapuke, beneath which it terminates by dividing into ascending and posterior scapular branches. Branches. — In addition to the two terminal branches, the transverse cervical gives off branches to the trapezius, the supraspinatus, and the levator anguli scapulae muscles. (a) The ascending terminal branch (ramus ascendens) passes upward to supply the splenius muscles, and forms anastomoses with the superficial cervical. (d) The posterior scapular artery (ramus descendens) descends along the entire length of the vertebral border of the scapula beneath the rhomboid muscles. It supplies these muscles and the serratus posticus superior, and sends branches laterally upon both the dorsal and ventral surfaces of the scapula, supplying the infraspinatus and subscapular muscles and anastomosing with the dorsal scapular and subscapular arteries Anastomoses. — The anastomoses which the suprascapular and transverse cer- vical arteries make with the branches of the subscapular artery from the a.xillary are of considerable importance in the establishment of the collateral circulation from the arm after ligation of the third portion of the subclavian. Additional paths which may be employed for the same purpose are afforded by the anastomoses which occur between the thoracic branches of the axillary artery and the intercostal branches of the superior intercostal, and more especially the perforating branches of the internal mammary. Variations. — Very frequendy indeed the anastomosis which exists between the ascending branch of the transverse and the superficial cervical develops to such an extent that it forms the principal channel by which the blood reaches the posterior scapular from the subclavian, and in such cases the main stem of the transverse cervical disappears, the posterior scapular then becoming a terminal branch of the superficial cervical. This arrangement (Fig. 705) is of such frequent occurrence that it is regarded as the normal one by many authors. When this is done, the name, transverse cervical, is applied to the main stem' of the superficial cervical, the latter term being retained for and limited to the ascending branch of the original arter},'. When this arrangement obtains, there is no branch from the third portion of the subclavian artery. THE AXILLARY ARTERY. The axillary artery (a. axillaris) (Figs. 704, 705) is the continuation of the subclavian through the axillary space. It begins at the lower border of the first rib, at the apex of the axillary space, and passes downward along the outer wall of the space to the lower border of the teres major, where it becomes the brachial artery. When the arm is abducted to a position at right angles to the axis of the trunk, the artery has an almost straight course, which may be repre- sented by a line drawn from the middle of the clavicle to a point midway between 768 HUMAN ANAT(JMY. the two condyles of the humerus. When, hovvevei', tin- arm lianj^s vertically, the V(;ssel is sliirhtly curved, the convexity ot the curve hxjkinj,^ ujnvard and outward. Relations. — For convenience in description it is cust(jmary to rej.(ard the axil- lary artery as consisting of three portions, the first of which is above the uijper border of the pectoralis minor, the second behind that muscle, and the third below its lower border. The first portion of the artery is covered anteriorly by the clavicular portion of the jjectoralis major, by the costo-coracoid membrane which separates it from the cephalic vein and the branches of the acromif)-thoracic artery, and by the subclavius muscle. The artery is enclosed along with its accompanying vein and the cords of Fig. 705. Pectoralis major, cut and everted, Deltoid Bleeps, long head Superficial cervicai Posterior Deltoid, scapular Tra[>eziu! Axillary artery, third itortlon Biceps, sliort head. Coraco-brachialis ^ Serratus tnagnus Subclavian and axillary aiieries, pectoralis minor still in place. the brachial plexus in a downward prolongation of the cervical fascia known as the axilla}-)' sheath, and rests behind upon the upper serration of the serratus magnus and u[)on the first intercostal space. The internal anterior thoracic and the posterior thoracic nerves cross it obliquely behind, the latter nerve intervening between it and the serratus magnus. Above, at the outer side, are the cords of the brachial plexus and the external anterior thoracic nerve, and below and to the inner side is the axillary vein, between which and the artery is the internal anterior thoracic nerve. In its second portion the artery is covered anteriorly by both the pectoralis major and the pectoralis minor. Posteriorly it lies in contact with the posterior cord of the brachial plexus, and is separated by a quantity of areolar and fatty tissue from PRACTICAL CONSIDERATIONS: AXILLARY ARTERY. 769 the aiiturior surface of the subscapularis muscle. External to it is the outer cord of the bracliial ]j)e,\(is, and internally the inner cord, which separates it from the axillary vein. In its third portion the artery is covered in its upper half by the lower part of the pectoralis major, but in its lower half only by the integument and the superficial and deep fasciae. The inner head of the median nerve passes obliquely across its anterior surface. Posteriorly it is in relation with the subscapularis, latissimus dorsi, and teres major, in that order from above downward, a considerable amount of areolar tissue, in which run the circumflex and musculo-spiral nerves, intervening^, however, between the artery andthe muscles. To the outer .side are the median and musculo- cutaneous nerves and the coraco-brachialis muscle, while internally are the internal cutaneous and ulnar nerves and the axillary vein. Branches. — .Much variation occurs in the arrangement of the branches of the axillary artery. It is customary to recognize seven branches, but one or more of them is frequently absent as a distinct branch arising directly from the artery. These branches are arranged as follows : from the first part are given off ( ij the superior thoracic and ( 1) the acromial thoracic ; from the second part ('3; the long thoracic and ( \) the alar thoracic ; and from the third part ( '^j the subscapular. (6) the anterior circumflex, and ( -j ) \.\\(: posterior circumflex. Variations. — As stated in the description of the variations of the subclavian, the axillary artery may be represented by two parallel vessels which arise from the first portion of the sub- clavian and are continued below into the radial and ulnar arteries. The more frequent varia- tions, however, concern the occurrence of additional branches from the axillary, and of these there may be mentioned the occurrence of the superior profunda, normally a branch of the brachial, but not infrequently arising from the axillary in common with the subscapular. Practical Considerations. — The axillary artery niay require to be ligated on account of wounds, of rupture, of high aneurism of the brachial, or, rarely, in distal ligation for subclavian aneurism. Wounds of the axillary are not uncommon when the vulnerating body — a knife- blade, a bullet, etc. — is directed from within outward, the artery in all positions of the arm maintaining a much closer relation to the outer, or humeral, wall of the axilla than to the inner, or thoracic, wall, which is therefore known as the wall of safety. It is always well in such cases to expose the artery and to tie both ends, as the exact source of the bleeding is often necessarily in doubt anri the free anastomosis of its branches is likely to lead to secondary hemorrhage from the wound if the vessel is tied in continuity. Rupture of the axillary artery has occurred in a considerable number of cases as an accident due to the movements employed in attempted reduction of old dislocations of the shoulder. The preponderance of arterial as compared with venous rupture Ttwenty-six out of twenty-eight cases, Stimson ; or forty out of forty-four, Korte) is striking, the greater thinness of the vein and its attachment to the costo-coracoid membrane — circumstances that would seem to favor its rupture — being more than counterbalanced by the greater frequency and extent of atheromatous degeneration and consequent loss of elasticity in the artery, and possibly by the greater liability of the latter to undergo tension during the movements of abduction, ele\-ation, and circumduction Twhich are those chiefly associated with the accident in question), and — as the outermost or rather uppermost vessel — to contract adhesion to the displaced humeral head. Aruurism of the axillary is comparatively frequent, as might be expected from the number, variety, and range of the movements of the shoulder-joint, during which the vessel is subjected to strains and to a variety of flexures. It is more common on the right side on account of the more general use of the right arm, and affects oftenest the third pordon of the vessel, or that least supported by surrounding stnictures and most subjected to changes in tension and position and to certain injuries, as those which occur during luxation of the shoulder or during elTorts at reduction (vide supra). On account of the looseness of the tissue in which it lies, such an aneurism rapidly attains a large size and, by reason of the minor traumatisms inflicted during the shoulder movements, is especially prone to inflammation. 770 HUMAN ANATOMY. The symptoms are {a) s'lCt'l/ing showing immediately below the clavicle (in Mohrenheim's fossa) and pushing that bone upward if the first portion is involved, or pushing the pectoral muscles forward if the aneurism is lower, or appearing as a pulsating tumor in the axilla if the third portion is involved ; (b)a-dema of the arm and hand from pressure on the axillary vein ; {c) pain down the arm, in the shoulder and neck, and down the side of the chest, and feebleness and limitation of shoulder and arm movements from, first, spasm, then paresis of the associated muscles, all due to pressure on the brachial plexus and its branches. Digital compression of the axillary artery is only effectively possible in the lower part of the third portion, where, with the fingers beneath the anterior axillary fold, Fig. 706. Pectoralis turned back First intercostal space Subclavian vein Pectoralis major, cut Second rib showing relations of axillao' artery in first part of its course. the vessel, if the effort is made with due care and gentleness, may be flattened against the humerus just within the edge of the coraco-brachialis and biceps. Ligation of the Jirst poriioti maybe effected in two ways: i. \\\t\\ the arm abducted to a right angle, an incision three inches -long, slightly con\ex downward, and w^ith its centre about an inch below the middle of the clavicle, is made through the skin, superficial fascia, and platysma. The cephalic vein and the descending branch of the acromial thoracic artery will be seen, just beneath the fascia, in the groove between the deltoid and greater pectoral muscles. The outer cla\'icular fibres of the pectoralis major are then divided close to the clavicle ; the interpectoral and axillary fascia and some loose connective tissue are broken up ; the upper border of the pectoralis minor is identified and traced to the coracoid process ; the costo-cora- coid membrane is cautiously cut through by a vertical incision close to the coracoid ; the artery is then sought for, lying between the brachial plexus of nerves externally and AXILLARY ARTERY: BRANCHES. 771 the vein internally. The internal anterior thoracic nerve is sometimes seen coming out between the vein and the artery. The arm should be brought to the side to relieve tension on the vessels, especially the vein, which in that position will be least prominent. The needle should be passed from within and below outward and upward. 2. With the arm abducted, so as to make evident the fissure between the sternal and clavicular portions of the pectoralis major, an oblique incision is made over this space and will usually begin about a half-inch from the sterno-clavicular joint. The muscular interspace having been exposed, its sides are separated, not directly back- ward, but backward and upward towards the clavicle. The arm is brought to the side to relax the pectoral fibres. The pectoralis minor and the space between it and the clavicle are reached^ and if the latter is too contracted, the muscle may be divided close to the coracoid process. The artery is then exposed and secured as in the method above given. The second portioji is not formally ligated, but may have a ligature applied when- ever, as in the last-mentioned method, the lesser pectoral has been divided. Ligation of the third portion of the subclavian artery is, on account of its ease of performance, almost invariably preferred to any of these operations. The third portion of the axillary is that almost always selected for ligation of that vessel, for a similar reason. - ■■ The line of the vessel, the arm being at right angles to the trunk, is from the junction of the anterior and middle thirds of the summit of the axilla to the middle of the bend of the arm at the elbow. This line will be found to follow the inner margin of the coraco-brachialis muscle, the prominence of which may be seen just internal to the swell of the biceps where it emerges from beneath the anterior axillary fold. An incision is made on this line through the skin and superficial and deep fasciae, and the fibres of the coraco-brachialis margin are exposed and cleared. Internally to them lies the vessel, the median and musculo-cutaneous nerves external to it, and the inter- nal cutaneous nerve and axillary vein on its inner side. The needle should be passed from within outward. The collateral circulation is established after ligation of the first portion above the origin of the acromial thoracic precisely as after ligation of the third portion of the subclavian (page 757). After ligation of the third portion above the origin of the subscapular the anastomoses take place between {a) the intercostals, long thoracic, posterior scapular, and suprascapular, and (^) the acromial thoracic, on the cardiac side of the ligature ; and {a) the subscapular, and (1^) the posterior circumflex on the distal side. When the vessel has been tied between the origins of the subscapular and the two circumflex arteries — probably the point of election (Taylor) — the anastomoses occur between the branches of the axillary and those of the thyroid axis, — i.e., the suprascapular and acromial thoracic above and the posterior circumflex below. Still lower, — i.e., below, the circumflex arteries — the collateral circulation is established just as after ligation of the brachial above the superior profunda {^q.v.'). 1. The Superior Thoracic Artery. — The superior or short thoracic (a. thoracalis suprema) (Fig. 704) arises just after the axillary has emerged from beneath the subclavius muscle, and is directed downward and forward to the first intercostal space, the muscles of which it supplies. Not infrequently it gives off a branch which supplies the muscles of the second intercostal space also. Its branches anastomose with those of the internal mammary and acromial thoracic, and occasionally its place is taken by a branch from the latter vessel. 2. The Acromial Thoracic Artery. — The acromial thoracic (a. thoraco- acromialis) (Fig. 705) is a very constant branch which arises from the front of the axillary artery, a short distance below the superior thoracic. It is directed forward for a short distance, but soon divides into thoracic, clavicular, and acromio-humeral branches. Branches. — {a) The thoracic branches (rami pectorales) pass downward and forward to the side of the thorax, supplying the muscles of the second and third, and sometimes of the fourth and fifth intercostal spaces, and also giving branches to the pectoraUs major and the pectoralis minor. It anastomoses with the intercostal arteries and the superior and long thoracics. 772 HUMAN ANATOMY. (6) The clavicular branch, which is the smallest of the three, passes upward to supply the subcla\ius muscle, and anastomoses with the suprascapular artery. (c) The acromio-humeral branch passes upward and outward across the costo-coracoid membrane and over the coracoid process of the scapula, and then divides into an acromia/ and a A««/d'?-a/ branch. The former (ramus acromialis) passes upward towards the acromial process to supply the deltoid muscle, while the latter (ramus deltoideus) turns downward in the groove between the deltoid and the clavicular portion of the pectoralis major, acconipanjing the cephalic vein. It sends branches to the two adjacent muscles and to the integument, and anastomoses with the anterior circumflex arterj-. 3. The Long Thoracic Artery.— The long thoracic (a. thoracica lateralis) (Fig. 704) is a somewhat inconstant branch, whose place is very frequently taken by the thoracic branch of the acromial thoracic or by a branch from the subscapular. It passes downward and forward upon the serratus magnus, sending branches to that muscle, the pectoralis minor, and the muscles of the third, fourth, and fifth intercostal Fig. 707. Deltoid, everted Triceps ^I'i'M. tm-umflexait. -"riceps, scapular head Spine of scapula DoRal scapular artery 5 of posterior aspect of shoulder. spaces. It also sends branches to the mammary gland (rami mammarii externi), whence it has been termed the external maniniary artery. It anastomoses with the thoracic branch of the acromial thoracic, with the subscapular and the intercostals, and with the perforating branches of the internal mammary. 4. The Alar Thoracic Artery. — The alar thoracic (Fig. 704) is a very incon- stant small branch which passes to the fascia and lymphatic glands of the a.xillary space. Its place may be taken by branches from the subscapular, the long thoracic, or the thoracic branch of the acromial thoracic. 5. The Subscapular Artery. — The subscapular (a. subscapularis) (Fig. 704) is the largest branch of the axillary and arises just as that artery crosses the lower border of the subscapularis muscle. It passes downward and inward, accom- panied by the long subscapular nerve, along the lower border of the subscapular muscle as far as the lower angle of the scapula, and distributes branches through- out its course to the subscapularis and teres major and to the latissimus dorsi. It also gives off — THE BRACHIAL ARTERY. 773 (a) Thoracic branches (rami thoracodorsalee) , which supply the serratus magnus and the muscles of some of the intercostal spaces, and net far from its origin it gives off — (b) The dorsal scapular (a. circumflex scapulae). This vessel, of large size, winds around the axillary border of the scapula in the triangular space bounded by the teres major, the teres minor, and the long head of the triceps, and is distributed to the infraspinatus and the teres minor. The subscapular artery anastomoses through its thoracic branches with the intercostals and with the long thoracic, and through the dorsal scapular with the suprascapular and posterior scapular arteries. Variations. — The subscapular arter>' varies somewhat in its origin. Occasionally it springs from the second portion of the axillary, and may also arise from the brachial; Quite frequently it arises from a trunk common to it and one or other or both circumflex arteries, and the supe- rior profunda brachii, normally a branch of the bracnial artery, may also arise from this common trunk. The subscapular has been observed to give rise to an aberrant artery which passes down the arm and either unites with the brachial or else becomes the ulnar, or may even extend to the neighborhood of the wrist, where it unites with a branch of the anterior interosseous artery ■ to form the radial. 6. The Anterior Circumflex Artery. — The anterior circumfle.x (a. circiim- flexa humeri anterior) (Fig. 704) is the smallest of the three branches of the third portion of the a.xillary, and arises either directly from the artery or from a common trunk with the posterior circumfle.x ; more rarely it arises from the subscapular. It passes outward beneath the coraco-brachialis and the heads of the biceps, and winds around the surgical neck of the humerus, lying close to the bone. Opposite the bicipital groove it gives off a branch which ascends along the groove to be distributed to the capsule of the shoulder-joint, and it also sends branches to the coraco- brachialis and biceps. It terminates by anastomosing with the posterior circumflex and with the humeral branch of the acromial thoracic. 7. The Posterior Circumflex Artery. — The posterior circumflex (a. cir- cumfle-xa humeri posterior) (Fig. 704) arises from the axillary, almost opposite the anterior circumflex, or from a common trunk with that vessel or with the subscap- ular. More rarely it may arise from the upper part of the brachial artery. It passes backward and outward through the quadrilateral space bounded by the subscapularis above, the teres major below, the long head of the triceps internally, and the humerus externally, and winds around the posterior surface of that bone at the level of its surgical neck. Passing under the deltoid muscle externally, it divides into a number of branches, most, of which pass into the muscle to supply it, while some pass to the shoulder-joint. It anastomoses with the acromial branch of the acromial thoracic, with the anterior circumflex, and with the superior profunda branch of the brachial. THE BRACHIAL ARTERY. The brachial artery (a, brachialis) (Figs. 708, 709)13 the continuation of the axillary down the arm. It begins at the lower border of the teres major and termi- nates a little below the bend of ■ the elbow by dividing into the radial and ulnar arteries. In the upper part of its course the vessel lies along the inner side of the arm, but as it passes downward it inclines somewhat outward, so that in ' its lower part it is on the anterior surface of the brachium. Its course may be indicated by a line drawn from the junction of the outer and middle thirds of the folds of the axilla to a point midway between the condyles of the humerus. Relations. — Aiiterioj-ly the brachial artery is covered throughout the greater part of its course by only the deep and superficial fasciee and the integument. About the middle of its length it is crossed obliquely, from without inward, bv the median nerve, and at the bend of the elbow it passes beneath the aponeurotic slip, the so-called bicipital fascia (laeertus fibrosus) from the tendon of the biceps, and is separated by it from the median basilic vein. Posterioi'Iv it rests in succession, from above downward, upon the long head of the triceps, the inner head of the triceps, the insertion of the coraco-brachialis, and the brachialis anticus. The musculo-spiral nerve and the superior profunda artery pass downward and inward between the vessel and the long head of the triceps. Externally to it, above, is the median nerve 774 HUMAN ANATOMY. and the coraco-brachialis muscle, and, lower down, the biceps and its tendon. Inteynally it is in relation, above, with the ulnar, internal cutaneous, and lesser internal cutaneous nerves, and, in its lower third, with the median nerve. The basilic vein is somewhat superficial to it and to its inner side. Two venae comites accompany the artery, lying respectively upon its inner and outer sides, and cross branches pass between the two. It is also accompanied by two lymphatic vessels which ha\-e in their course three or four lymphatic nodes, usually of small size. Branches. — The brachial artery gives of? muscular branches to the biceps, coraco-brachialis, brachialis anticus, triceps, and pronator radii teres, and a small Fig. 708. Deltoid Cephalic ve Humeral brancli of acromial tlioracic arte Pectorali^ maj Axillary Outer head of median n Inner liead of medi Axillary artery Brachial artery r profunda artery Median nerve Brachial arter>' In relatit rmtruni artery for the humerus (a. nutriciae humeri) arises either directly from the brachial or from one of its muscular branches or from the inferior profunda. It enters the nutrient foramen upon the inner surface of the shaft of the humerus. In addition, there arise from the brachial (i) the superior profunda, (2) the mferior profunda, and (3) the anastomotica magna. Variations. — The variations which the brachial arter>' presents are both numerous and important, in that they affect materially the origin of the two terminal branches, the radial and ulnar. In cases in which there is a well-developed supracondyloid process on the humerus (page 268), the brachial arten,- accompanies the median nerve behind it, and only passes upon the an- terior surface of the arm after it has passed it. In such cases there cjenerally arises from the upper part of the brachial, or even from the axillarv, a vessel which descends upon the anterior .■surface of tlie arm, lying superficially and sending branches to the biceps and brachialis anticus THE BRACHIAL ARTERY: BRANCHES. 775 muscles. - This has been variously termed the vas aberrans^ the a. brachialis stiperficialis, or the a. radialis superficialis, and it appears to be normally present, but much reduced in size and included among the muscular branches. The majority of the modifications of the brachial artery are due to an extraordinary devel- opment of the superficial brachial. Thus it may enlarge and become continuous below with the radial artery, giving rise to a condition usually termed a " high" origin of the radial ; more Fig. 709. Humeral branch of acromial thoracic artery - Pectoralis minor stuinp^ Biceps and coraco-brachialis, stump Axillary artery Anterior circumflex artery Tendon of long head of biceps Teres major and lati; Superior profunda artery Tendon of biceps [dorsi Origin of superficial flexors Anterior ulnar recurrent artery Posterior ulnar recurrent artery - Radial artery Brachial artery and its branches. rarely it may unite with the ulnar artery, producing a *' high" origin for that vessel ; occasion- ally it gives rise to both the radial and ulnar, the true brachial being continuous below with the common interosseous ; or, finally, it may unite with the lower part of the brachial artery proper, the portion of the latter tietween the origin and anastomosis of the superficial brachial disap- pearing, so that what is termed a brachial artery is formed, which passes behind instead of in front of the median nerve. 776 HUMAN ANATOMY. Comparative anatomy and embryology both indicate that the occurrence of a well-devel- oped superficial brachial, continuous below with tlie radial, is the primary condition, and that the origin of the radial as a terminal branch of the brachial proper is a secondary condition, due to an anastomosis between the lower part of the original superficial stem and the brachial and to the subsequent diminution or partial obliteration of the former above this anastomosis (Fig. 74S E). Another branch, normally present but usually insignificant, which may reach an extraor- dinary development, is the a. plica cubiti siiperjicialis. It arises from the lower portion of the brachial and, passing inward and downward beneath the tendon of the biceps, is distributed to the fie.xor carpi radialis and the palmaris longus. When abnormally developed, it forms what has been termed the accessory ulnar arlery, and passes down the forearm, immediately beneath the deep fascia and between the two muscles just mentioned, and terminates by anasto- mosing with the ulnar, or in some cases replaces it and enters into the formation of the palmar arches. Supernumerary branches accessory to the branches usually present may also occur, and, in addition, the brachial may give rise, in its upper part, to the subscapular and the posterior circumflex, normally branches of the axillary ; in its lower part, to the radial recurrent; and, at its bifurcation, to the interosseous artery or to the median, which is usually a branch of the interosseous. Practical Considerations. — Spontaneous aneurism of the brachial artery is rare, and is usually associated with marked arterio-sclerosis or with cardiac disease. Wounds and traumatic aneurism are common, though lessened in frequency by the protected position of the upper two-thirds of the artery on the inner side of the arm. Aneurism has, however, followed a stab-wound from the outer side, which, after passing through the biceps, involved the vessel. Arterio-venous aneurism just above the bend of the elbow was formerly often met with as a result of the accidental wounding of the artery during phlebotomy of the median basilic vein, parallel with the vessel at that .point and separated from it only by the lacertus fibrosus. The line of the artery is from the junction of the anterior and middle thirds of the a.xilla to the middle of the bend of the elbow when the arm is abducted and the forearm e.xtended and supinated. The artery in the upper two-thirds of its course may be compressed against the inner side of the humerus by pressure directed outward and a very little backward along the internal border of the coraco-brachialis and biceps. This muscular border may be visible, or maybe recognized by picking it up between the thumb and finger. The artery may be overlapped by this inner edge of the biceps, especially in mus- cular subjects. At the middle of the arm, over the insertion of the coraco-brachialis into the flat surface above the beginning of the internal supracondyloid ridge, it may most easily be subjected to compression. In the lower third the pressure must be directed backward, as the huinerus — separated from it by the brachialis anticus muscle — then lies behind it. Ligation of the vessel at its tipper third is effected through an incision made along the inner border of the muscular ridge of the coraco-brachialis muscle, the fibres of which may with ad^■antage be exposed and identified. Nothing lies between the artery and the muscle except the median nerve. The basilic vein is to the inner side of the vessel and may, before the incision is made, be identified and a\'oided by compression of the a.xillary vein above. The ulnar nerve also lies to the inner side. The needle may be passed in either direction. In ligation at the middle of the arm, the limb should be abducted with the elbow slightly fie.xed, and should be supported by an assistant. If the arm is allowed to rest upon a flat surface, the triceps is pushed upward and may be mistaken for the biceps, and the dissection may bring into view the inferior profunda artery and the ulnar nerve instead of the brachial and the median ( Heath j. It is well to see and identify the innermost fibres of the biceps. After they are displaced outward, the median nerve (beginning to bear to the inner side) should be separated from the vessel, the sheath opened, the vente comites (the inner of which is usually the larger) drawn aside, and the needle passed from the ner\e. Jacobson calls attention to the fact that this usually easy ligation may be difficult when the artery is concealed by the median ner\'e at the point at which it is sought, and when its calibre is small' and its beat feeble as the result of hemorrhage. The median nerve (from transmitted pulsation), the inferior profunda artery, and even the basilic vein have been mistaken for the brachial. THE BRACHIAL ARTERY; BRANCHES. 777 In ligation at the lower tlm-d — abo\'e the bend of the elbow — the inner edge of the biceps tendon should be distinctly recognized, and the position of the superficial Acins, especially the median basilic, should be made apparent by com- pression above. The incision should lie just within the edge of the tendon and should be parallel with it, running therefore obliquely from within outward. It will usually be just outside of the median basilic vein. Its centre is about on a level with the transverse fold of the bend of the elbow. The fibres of the bicipital fascia are di\-ided in the line of the skin incision, — i.e., diagonally, as they run downward and inward. The needle may be passed from within outward so as to avoid the median nerve, which, however, is here some distance to the inner side. In all ligations of the brachial, its frequent variations {z'ide supra) should be remembered, and the possibility of the presence of a " vas aberrans' ' or an " accessory ulnar' ' should be borne in mind, as should the occasional occurrence of a muscular slip crossing tlie vessel and derived from the pectoralis major or from one of the humeral muscles. The collateral cbxidatioti is carried on after ligation above the superior profunda between the ascending or recurrent branches of that vessel and the circumflex ( espe- cially the posterior) and subscapular arteries. After ligation below the origin of the inferior profunda, the circulation is carried on through the anastomosis between the branches of the profunda from above and those of the anastomotic and the recurrents from the radial, ulnar, and posterior interosseous from below. After ligation below the anastomotic, the branches of that vessel, as well as those of the profundae, carry the blood to the recurrents. 1. The Superior Profunda Artery. — -The superior profunda (a. profunda brachii) (Fig. 709 ) arises from the upper part of the brachial, on its posterior surface, and is directed downward and outward, between the inner and long heads of the triceps, to reach the posterior surface of the humerus. Accompanied by the musculo- spiral nerve, it curves around to the outer surface of the bone, lying in the musculo- spiral groove, and having arrived at the external supracondylar ridge, it pierces the external intermuscular septum and continues downward between the brachialis anticus and the supinator longus, to terminate by anastomosing in front of the external condyle with the radial recurrent artery. Branches. — In its course the superior profunda gives off a number of branches, among which may be mentioned : (a) A deltoid branch (ramus deltoideus), which passes transversely outward to the inser- tion of the deltoid, and then bends upward in the substance of that muscle. {b) Muscular branches to the triceps. (c) A median collateral branch (a, collateralis media), which passes downward in the sub- stance of the inner head of the triceps to the olecranon process, where it anastomoses with the posterior ulnar recurrent, the posterior interosseous recurrent, and the anastomotica magna. ( d ) An articular branch, which is given off from the lower portion of the artery, just before it pierces the external intermuscular septum, and is distributed to the elbow-joint. ( e ) Cutaneous branches, which accompany the external cutaneous branches of the mus- culo-spiral nerve. Variations. — The superior profunda occasionallv arises from the axillar>- artery' either directly or in common with the posterior circumflex. That portion of its main stem which traverses the musculo-spiral groove beyond the point where the medial collateral branch is given off is sometimes termed the radial collatei-al. the profunda being regarded as dividing, after a short course, into the two collateral branches. The deltoid artery not infrequently arises directly from the brachial artery or else from the inferior profunda. 2. The Inferior Profunda Artery. — The inferior profunda (a. collateralis ulnaris superior ) ( Fig. 709) arises from the inner surface of the brachial, at about the middle of its course. It passes downward and backward, accompanying the ulnar nerve, through the internal intermuscular septum, and then downward" along the anterior surface of the inner head of the triceps to the back of the internal condyle, where it terminates by anastomosing with the anastomotica magna and the posterio' ulnar recurrent. It gives branches to the triceps and to the brachialis anticus. 778 HUMAN ANATOMY. 3. The Anastomotica Magna. — The anastomotica magna (a. collateralis ulnaris inferior) (Fig. 709) arises from tlie inner surface of tlie bracliial artery, about 4 cm. (I ^'8 in.) above its termination. It passes inward over the brachialis amicus and beneath the median nerve, and, piercing the internal intermuscular septum, winds around the inner border of the humerus and passes transversely across its posterior surface, just above the olecranal fossa. It anastomoses with the posterior ulnar recur- rent and with both the superior and inferior profunda arteries, and also, by means of a branch given off before it pierces the intermuscular septum, with the anterior ulnar recurrent. Anastomoses around the Elbow. — The brachial artery forms rich anasto- moses around the elbow-joint with both the radial and ulnar arteries by means of its superior and inferior profunda branches and the anastomotica magna, abundant opportunity being thus afforded for a collateral circulation to the forearm after ligation of the brachial. Thus, the superior profunda anastomoses in front of the e.xternal condyle of the humerus with the radial recurrent, and its medial collateral branch anastomoses in the neighborhood of the olecranon process with the posterior inter- osseous and the posterior ulnar recurrents. The inferior profunda also anastomoses with the posterior ulnar recurrent behind the internal condyle, while the anastomotica magna makes connections in front of the internal condyle with the anterior ulnar recurrent; and posteriorly, with the posterior ulnar and the posterior interosseous recurrents. THE ULNAR ARTERY. The ulnar artery (a. ulnaris) ( Figs. 710, 712) is the larger of the two terminal branches of the brachial. It arises just below the bend of the elbow and passes at first distally and inward, in a gentle curve, beneath the muscles which arise from the internal condyle of the humerus, and at the junction of the upper and middle thirds of the forearm assumes a more vertical direction. Arrived at the wrist, it passes over the anterior annular ligament to the radial side of the pisiform bone and then passes across the palmar surface of the hand, forming the superficial palmar arch ( arcus volaris superficialis), whose conve.xity looks distally, and terminates opposite the second intermetacarpal space by anastomosing with the superficial volar branch of the radial. For convenience in description, the ulnar artery may be regarded as consisting of three parts : ( i ") an antibrachial portion extending from the origin of the vessel to the upper border of the anterior annular ligament, ( 2) a carpal portion resting upon the annular ligament, and (3) a palmar portion in the hand. The course of the lower two-thirds of the antibrachial portion may be represented by a line drawn from the front of the internal condyle of the humerus to a point immediately to the radial side of the pisiform bone, while the course of the upper third may be indicated by a line drawn from the middle of the bend of the elbow to meet the first line at the junction of its upper and middle thirds. The superficial palmar arch is on a level with the thumb when the digit is abducted to a. position at right angles to the a.xis of the hand. Relations. — The antibrachial portion of the ulnar in its upper third is cov- ered by the pronator radii teres, the flexor carpi radialis, the palmaris longus. and the flexor sublimis digitorum, and is crossed obliquely by the median nerve. Behind, it rests upon the tendons of the brachialis anticus and upon the flexor profundus digi- torum. In its lower two-thirds it is overlapped above by the flexor carpi ulnaris, but below it lies entirely to the radial side of the tendon of that muscle, and is covered onlv bv the skin and fasciae. It rests upon the flexor profundus digitorum, and to its radial side is the tendon of the flexor sublimis digitorum, while to its ulnar side it is in close relation with the ulnar nerve, as well as with the tendon of the flexor carpi ulnaris. In its carpal portion it rests upon the anterior surface of the anterior annular ligament, immediatelv to the radial side of the pisiform bone, and is covered by an e.xpansion from the tendon of the flexor carpi ulnaris. The palmar portion, in the upper part of its course, is covered by the palmaris brevis and rests upon the flexor brevis minimi digiti. The superficial palmar arch, as it passes radialwards, is crossed successively by the palmar branch of the ulnar THE ULNAR ARTERY. 779 Musculo- spiral Radial recurrent artery nerve, the palmar fascia, and the palmar branch of the median nerve. It rests upon the digital branches of the ulnar nerve, the long flexor tendons, and the digital branches of the median nerve. Branches. — From its antibrachial portion the ulnar artery gives rise to numerous muscular branches supplying the muscles of the forearm, and, in addition, to ( I ) the anterior ulnar recurrent, (2) the pos- I''G- 7i°- terior ulnar recurrent, (3) the common inter os- seous, (4) a nutrient branch, (5) the poster- ior ulnar carpal, and (6) the anterior ulnar carpal. From the carpal Superfi^ portion arise no branches of considera- ble size. From the palmar portion arise (7) the superior and (8) the in- ferior deep palmar branches and (9) the digital branches, and, in addition, muscular branches to superficial Brachial muscles of the palm and cutaneous branches. Va r i a t i o n s . — From the developmental stand- point the ulnar artery (page 848), although earUer in its appearance than the radial, is, nevertheless, preceded as the principal artery of the forearm by two others. In the most primitive con- dition the brachial is con- tinued down the forearm, resting upon the interos- seous membrane and giving rise at the base of the hand to a leash of digital branches. Later there de- velops from the brachial a second artery, which passes ^^j, distally in a plane superfi- cial to the original vessel, accompanying the median nerve through the interval between the flexor sublimis digitorum and the fle.xor profundus digitorum. This median artery, near the wrist anastomoses with the original one, and the latter then begins to diminish in size and separates from the median above the point of its anastomosis, forming the anterior interosseous arter}-. In this condition it is the median artery which gives origin to the digital branches. Finally, the ulnar arises as another distinct branch from the brachial and gradually supplants the median, which now appears as a branch of the interosseous kno«'n as the a. comes ner\-i median!. As is frequently the case where the development passes through a series of well-marked stages, its arrest may occur at any one of these, and consequently an anomaly may occur in which the ulnar artery is represented only by some muscular branches, its place being taken by Inferior profunda artery Origin of superficial flexors Median nerve Brachial artery Tendon of biceps Brachialis anticus Origin of superficial flexors Ant. ulnar recurrent artery Post, ulnar recurrent artery non interosseous arter>' Ulnar arterj- Flexor profui Flexor sublimis digitorum Palmaris longus tendon Anterior carpal artery Posterior carpal artery Flexor carpi ulnaris Radial and ulnar arteries : superficial dissection. ySo HUMAN ANATOMY. a persistent median or interosseous artery, — a condition of which indications are to be seen in the participation of the interosseous or median artery in the formation of the superficial palmar arch (page 785). An interesting condition in which indications are clearly retained of all the stages which the forearm arteries pass through in their evolution is shown in Fig. 711. An artery which is the superficial brachial, and which arose from the axillary, descends the arm parallel to the brachial proper and terminates by becoming the radial. A distinct ulnar has developed and the anterior interosseous has acquired its typical • arrangement, but there is a well-developed median artery which sends a strong branch across to the radial and termi- nates by anastomosing with the superficial palmar branch of the ulnar to form the superficial palmar arch. Another variation may occur in the form of a "high origin" of the ulnar artery, a condi- tion which results from the anastomosis of the superficial brachial artery (page 774) with the ulnar. In such cases the ulnar frequently passes down the forearm in a much more superficial position than usual, passing over, instead of under, Fig. 711. the muscles arising from the interna! condyle. Such a superficial course may also be followed when the arterj' has a normal origin, and occasionally it passes to the ulnar border of the forearm be- tween the palmaris longus and the fle.xor sublimis digitorum. Practical Considerations. — The ul- nar artery may be ligated for wound or for aneurism — of which it is rarely the subject — either ( i ) about the middle of the forearm or (2) just above the wrist. I. With the forearm supinated, an in- cision on the line indicated {vide supra) through the skin and the thin deep fascia should e.xpose either a white line — the ten- dinous edge of the flexor carpi ulnaris — which is not always present (Treves), or a yellow (fatty) interspace (Farabeuf) between that muscle and the fle.xor sublimis digitorum. It is best marked at the lower part of the wound. If more than one white line should be present, the one sought for would be nearer the ulnar margin of the limb. At the bottom of the interspace thus identified, which runs oblique- ly inward towards the ulna, the artery will be found lying on the fle.xor profundus digitorum, with the ulnar ner\'e to its inner side. It is often overlapped by the inner deep edge of the fle.xor sublimis, so that that muscle must be lifted up and drawn outward before the vessel can be fully exposed. In sepa- rating the muscles care must be taken not to go beyond the vessel and nerve — pushing them to the radial side — and open up the in- terspace between the flexor carpi ulnaris and the flexor profundus. The space between the flexor sublimis and the palmaris longus lies to the outer side of the proper space, but is much- more shallow and even less well marked. 2. Forcibly extend the hand so as to bring into prominence the fleshy swell of the flexor sublimis muscle and tendons, just to the ulnar side of the palmaris longus (page 620). The incision, beginning abotit one inch above the flexure of the wrist, should be made in the groove to the inner side of this prominence, and is immedi- ately in line with the pisiform bone. After the deep fascia is divided the tendon of the flexor carpi ulnaris is seen and, after it is relaxed by flexion of the wrist, is drawn a little inward, when the artery will be found still lying upon the flexor profundus and bound to it by a definite layer of fascia, which must be carefully di\'ided (Treves). The ulnar nerve lies in close pro.ximity to the vessel on the ulnar side.' Variation of arteries of left arm. showii retention of developmental conditions. THE ULNAR ARTERY. 781 The venae comites of the ulnar are closely attached to it, but may be included in the ligature without danger, as the other venous channels of the forearm are amply sufficient to carry on the circulation. The collateral circulation is maintained by means of the free anastomosis between the branches of the radial and ulnar, those of the interosseous vessels, and those of the carpal and palmar arches. 1. The Anterior Ulnar Recurrent Artery. — -The anterior ulnar recurrent (a. recurrens ulnaris anterior; (Fig. 71 2 J arises from the upper part of the ulnar artery, frequently in common with the posterior recurrent. It is usually a rather slender branch, and is directed upward in the groove between the brachialis anticus and the pronator radii teres towards the internal condyle, over which it terminates in branches which anastomose with the inferior profunda and anastomotica magna of the brachial. It gives of! branches to the neighboring muscles and a branch to the anterior inner portion of the capsular ligament of the elbow-joint. 2. The Posterior Ulnar Recurrent Artery. — The posterior ulnar recurrent (a. recurrens ulnaris posterior) (Fig. 712) arises either immediately below the anterior recurrent or by a common trunk with it. It is usually considerably larger than the anterior recurrent, and passes at first almost horizontally inward and backward be- tween the flexor sublimis and the fle.xor profundus digitorum, and then bends upward along the side of the ulnar nerve between the two heads of the flexor carpi ulnaris. It terminates upon the posterior surface of the internal condyle of the humerus in branches which anastomose with the posterior branch of the inferior profunda and with the anastomotica. magna of the brachial. It gives branches to the adjacent muscles, to the skin, and to the posterior in- ternal portion of the capsule of the elbow-joint. 3. The Common Interosseous Artery. — The common interosseous (a. interossea communis) (Fig. 710) arises from the outer and back part of the ulnar artery, a short distance below the posterior ulnar recurrent. It is a short, stout trunk which passes downward and outward and, having reached the upper border of the interosseous ligament, divides into the anterior and posterior interosseous arteries. Variations. — In cases in \\;hich a superficial brachial artery (page 774) exists, the true brachial may be directly continuous below with the common interosseous, the radial and ulnar arteries arising by the bifurcation of the superficial brachial. Such cases form what are usually termed " high" origins of the common interosseous ; and, since the superficial brachial may arise from the axillary, owing to the anastomosis with it of the aberrant branch of that artery, the common interosseous may also appear to arise from the axillary. In cases of high origin of the radial the common interosseous may arise from that vessel and give origin to the recurrent ulnar branches, and it may also give rise to these branches when it has a normal origin. When it has a high origin, it may give off both the radial and ulnar recurrent branches. a. The Anterior Interosseous Artery. — The anterior interosseous (a. inter- ossea volaris) (Fig. 712) descends from the point of bifurcation of the common inter- osseous artery, along the anterior surface of the interosseous membrane, between the adjacent edges of the fle.xor profundus digitorum and the fle.xor longus pollicis, and divides at the upper border of the pronator quadratus into an anterior and a pos- terior terminal branch (Fig. 715). Branches. — In addition to muscular branches to the adjacent muscles and to the ex- tensor muscles of the thumb, — the latter perforating the interosseous membrane to reach their destinations, — the anterior interosseous artery gives off a number of more or less important branches. (aa) The median artery (a. comes nen'i mediani) arises from the anterior surface of the ante- rior interosseous, immediately .below the origin of that vessel. It passes forward to join the median ner\'e, which it accompanies down the arm, and in whose substance it is frequently embedded. It continues its course with the ner\'e beneath the anterior annular ligament, and, when well developed, may terminate by anastomosing directly with the superficial palmar arch. {bb') A nutrient branch is usually given off to the radius and occasionally also to the ulna. 782 HUMAN ANATOMY. («■) The anterior terminal branch passes either over or beneath the pronator quadratus, and terminates usually by anastomosing with branches of the anterior radial and ulnar carpal and with the palmar recurrent arteries. Occasionally it anastomoses directly with the super- ficial palmar arch. (dd ) The posterior terminal branch is larger than the anterior. It perforates the inter- osseous membrane, anastomoses with tlie posterior interrosseous artery, and terminates in branches which anastomose with the posterior radial and ulnar carpals to form the dorsal carpal net- work. Variations.— The anterior interosseous artery may arise from the radial, and it may form anastomoses below with the radial or with both the radial and ulnar. The relations which it sometimes possesses witli tlie superficial palmar arch will be considered later, The median artery is occasionally of considerable size and frequently arises from the common interosseous. Its relations to the superficial palmar arch will also be considered later (page 7S5). b. The Posterior Interosseous Artery. — The posterior interosseous (a. inter- ossea (lorsalis) (Fig. 715) [jasses backward between the radius and ulna, above the concave upper margin of the interrosseous memlarane. It thus reaches the posterior portion of the forearm and turns abruptly downward between the superficial and deep layers of the extensor muscles, and breaks up at the wrist into branches which anas- tomose with the posterior radial and ulnar carpals and with the posterior terminal branch of the anterior interosseous, assisting in the formation of the dorsal carpal net-work. Just as it reaches the posterior surface of the forearm it gives off a posterior interosseous recurrent branch (a. interossea recurrens), which ascends between the anconeus and the supinator brevis to the posterior surface of the external condyle of the humerus, where it anastomoses with the superior profunda and the anastomotica magna. In its course down the arm the posterior interosseous gives branches to the e.xtensor muscles, and, through the dorsal carpal net-work, it takes part in the supply of the articulations of the wrist and carpus. 4. The Ulnar Nutrient Artery. — The nutrient branch for the ulna arises from the upper third of the ulnar artery or from one of its muscular branches, or from the anterior interosseous. It enters the nutrient foramen situated upon the anterior surface of the bone, near its outer border. 5. The Posterior Ulnar Carpal Artery. — The posterior ulnar carpal (ramus carpeus dorsalis) (Fig. 715) is small. It arises from the inner surface of the ulnar artery, just above the pisiform bone, and winds inward beneath the tendon of the flexor carpi ulnaris to the back of the carpus, where it anastomoses with the posterior radial carpal and the posterior interosseous to form the dorsal carpal net-work. 6. The Anterior Ulnar Carpal Artery. — The anterior ulnar carpal (ramus carpeus volaris) (Fig. 712) is also small. It arises from the ulnar artery, just above the upper border of the anterior annular ligament, and passes outward upon the car- pal ligaments and beneath the long fle.xor tendons to anastomose with the anterior radial carpal and anterior interosseous to form the anterior carpal net-work. 7 and S. The Deep Palmar Arteries. — The deep palmar branches (rami volares profundi) (Fig. 712) are gi\en off from the ulnar artery, just after it has entered the palm. The superior branch arises just after the ulnar artery has passed the pisiform bone, and passes dorsally in the interval between the flexor brevis minimi digiti and the abductor minimi digiti. It then perforates the opponens minimi digiti, and terminates bv inosculating with the deep palmar arch. The inferior branch arises just as the ulnar artery is bending to pass trans- versely across the palm. It passes dorsally between the flexor brevis minimi digiti and the long flexor tendon for the little finger, and terminates by inosculating with the deep palmar arch, near the superior branch. Frequently one or other of these branches, more usually the superior one, is lacking, and only one communication between the ulnar and the deep palmar arch exists. In their passage dorsally, both arteries give off branches to the adjacent muscles. THE ULNAR ARTERY. 783 Fig. 712. Musculo-spiral nerve Superficial branch of superior profunda- Tendon of biceps- Radial nerve, cut Posterior interosseous Supinator brevis Radial recurrent artery Poster Radial artery'"^ )r interosseous artery Pronator radii teres Extensor carpi radialis longior Brachio-radialis ' Radial artery. Princeps poUicis. Branch to superficial palmar arch Radialis indicis Flexor longus pollici Anterior radial carpal artery Brachial artery Inferior profunda artery Origin of superficial flexors Inner condyle Brachialis anticus Anterior ulnar recurrent artery Posterior ulnar recurrent artery Ulnar artery Common interosseous artery Ulnar portion of flexor profundus Ulnar artery Anterior interosseous artery Anterior interosseous nerve Pronator quadratus Anterior ulnar carpal artery Wrist joint Pisiform bone Deep branch of ulnar artery Ulnar artery Deep palmar arch Palmar interosseous arteries Digital arteries Deep arteries of right forearm and hand ; flexor surface. 7S4 HUMAN ANATOMY. g. The Digital Arteries. — The diy;ital branches (aa. digitales volares com- munes) arise from the portion of the uhiar artery which passes transversely across the pahii of the hand and is termed the superficial palmar arch (arcus volaris superficialis). They are four in number; the first of the four, starting from the ulnar border of the hand, passes obliquely downward and inward across the hypoth- enar muscles and continues distally along the ulnar border of the little finger. The Radial artery Superficial volar artery Abductor poll Opponens pollicis Flexor brevis pollicis Flexor loiigus pollicis tendon Princeps pollicis Superficial palmar arch and its branches. remaining three pass downward in the second, third, and fourth intermetacarpal spaces resting upon the lumbrical muscles, and, just before reaching the clefts of the fingers, each receives the corresponding palmar interosseous artery and then divides into two branches, the collateral digital branches (aa. digitales volares propriae), which extend distally upon the adjacent sides of the neighboring digits. These col- lateral branches make numerous transverse anastomoses with one another, especially in the neighborhood of the interphalangeal joints, and terminate in fine branches which supply the bulb of the finger and the bed of the nail. Variations. — -The variations of the digital arteries depend principally (i) upon their pro- portional development with regard to the palmar interosseous vessels from the deep palmar arch, and (2) upon variations in the mode of formation of the superficial palmar arch. The palmar interosseous branches of the radial anastomose with the digitals just before the division of the latter into their collateral branches, and if the interossea; are strongly devel- oped, the digitals are apt to be of small calibre, and may be so much reduced in size that the collaterals of one or more of them may be regarded as continuations of the corresponding palmar interosseae. Conversely, although normally the supply for the radial side of the index- finger and the thumb is from the deep palmar arch, yet occasionally it is derived from the superficial arch, the princeps pollicis and the radialis indicis, the branches from the deep palmar arch, being much reduced in size. THE RADIAL ARTERY. 7S5 The variations in the formation of the superficial palmar arch are frequent and numerous, and may be grouped in two classes : (, i ) those in which additional branches from the forearm participate in the formation of the arch or replace the radial in its composition, and (2) those in which there is no true arch, the arteries which should participate in its formation, and in some cases additional ones also, failing to anastomose and each giving rise independent!)- to a certain number of digital branches. To the first of these classes belong the cases in which the median or anterior interosseous arterj- anastomoses directly with the arch formed by the superficial volar and the ulnar, and also those in which the superficial volar fails to reach the ulnar, the arch being formed by the union of the latter vessel with the median or the anterior interosseous. And, finally, the arch may be formed by the ulnar artery alone, no direct communication taking place between it and the arteries mentioned. In the second class of cases — that in which there is no true arch — the ulnar and the super- ficial volar, on reaching the palm, divide in a somewhat fan-like manner to give rise to the digital branches. The superficial volar may contribute the fourth digital, as well as the \-essels to the Fig. 714. of palmar arteries replacing superficial arch. ( /asckfschznski). thumb and radial side of the index (Fig. 714, A ), or it may be limited to the latter vessels, all four normal digitals being deri\-ed from the ulnar. With the absence of the arch there may be associated an extra development of the median arten,-, which continues distally into the palm as the fourth digital vessel, the remaining digitals and the radialis indicis and princeps poUicis being supplied by the ulnar and radial respectively ( C). Or, finally, ^\•ith the extra development of the median there is associated an absence, more or less complete, of the superficial volar, the median giving off the branches to the radial digit as well as the fourth digital {£ ) . THE RADIAL ARTERY. The radial artery (a. radialis) (Figs. 710, 712) is the smaller of the two terminal branches of the brachial, whose course it continues downward through the forearm. It arises at the bend of the elbow and passes down the outer border of the forearm to the level of the styloid process of the radius, where it bends outward, cur\'ing around the external lateral ligament of the wrist. It then extends do\^■nward o\'er the pos- terior surface of the trapezium until it reaches the inter\-al between the first and second metacarpal bones, and here it again changes its direction and passes forward into the palmar surface of the hand, across which it is continued inward o\'er the anterior sur- faces of the second, third, and fourth metacarpals, forming what is termed the deep palmar arch (arcus volaris profundus). It terminates opposite the proximal part of the fourth metacarpal interspace by anastomosing with the deep palmar branch of the ulnar. In accordance with its position with reference to the bony axis of the forearm and hand, the radial artery may be regarded as consisting of three parts. In its first or antibrachial portion it is preaxial in position, in the second or carpal portio7i it is postaxial, and in the third or palmar poHioji it is again preaxial. Relations. — In its antibrachial portion the' course of the artery may be indi- cated by a line drawn from a point midway bet\\'een the two condyles of the humerus to a point about i cm. internal to the styloid process of the radius. In its upper half it is overlapped in front by the inner border of the brachio-radialis (supinator longus) muscle, but lower down it is covered only by the deep and superficial fasciae 50 786 HUMAN ANATOMY. and the skin. Posteriorly it rests successively, from above downward, upon the tendon of the biceps, the supinator bre\is, the pronator radii teres, the radial portion of the flexor sublimis digitorum, the flexor longus pollicis, the outer border of the pronator quadratus, and the anterior surface of the lower end of the radius. Inter- nally it is in contact with the pronator radii teres in its upper third, and throughout the rest of its course with the outer border of the flexor carpi radialis. Externally it is in relation throughout its entire length with the brachio-radialis, and in the middle third of its course it is in contact with the radial nerve. Two venae comites accom- pany the arter\-, lying to its inner and outer sides. In its carpal portion the radial artery rests at first upon the external lateral ligament of the wrist and then upon the posterior surface of the trapezium. It passes beneath, successively, the tendons of the extensor ossis metacarpi pollicis, the e.xten- sor brevis pollicis, and the extensor longus pollicis, being covered in the interval between the last two and to the ulnar side of the extensor longus pollicis only by the skin and fascia, in which are some branches of the radial ner\e and tributaries of the radial vein. In its palmar portion, as it passes forward through the proximal portion of the first intennetacar])al space, the arterj' lies between the two heads of the first dorsal interosseous muscle. It then bends inward beneath the oblique head of the adductor pollicis, and, either penetrating that muscle or passing bet\veen it and the transverse head of the same muscle, is continued ulnarward beneath the tendons of the long flexors, resting upon the bases of the metacarpal bones and upon the interosseous muscles. Branches. — From its antibrachial portion the radial artery- gives off numer- ous muscular branches to the muscles on the radial side of the forearm, and, in addition, gives origin to (i) the radial recu7rc7it, (2) the aiiterior radial carpal, and (3) the superjjcial volar. From its carpal portion it gives rise to (4) the posterior radial carpal, (5) the iorsalis pollicis. and ( 6 ) the dorsalis i?idicis. From its palmar portion its branches are (7) the princeps pollicis, (8) the palmar interosseous (of which there are three), and (9) the recurrent carpals. Variations. — The high origin of the radial has already been considered in discussing the variations of the brachial arten,- (page 774). It is the last of the forearm arteries to be devel- oped in the comparative series, and its relations with the arterial supply to the hand is due to secondarv' anastomoses which it makes with \essels originally present, whereby it has come to give origin to many branches formed before its appearance. Thus the dorsalis indicis and the dorsalis pollicis are primarily digital branches from the dorsal interosseous artery of the first intermetacarpal space, and this arten,- arose from the posterior carpal arch and has become a portion of the radial by the anastomosis of that artery «ith the arch. Siniilarh- the portion of the radial which passes forward between the first and second metacarpals to join the deep palmar arch is primarily the first posterior perforating vessel, which has secondarily become the deep palmar apparent continuation of the radial, and has brought that vessel into direct con- tinuity' with the arch and given it tlie branches which originall)' arose from that \essel. The secondarv- anastomoses of the original radial with pre-existing \essels have, however, become well established, and variations of the radial, other than its high origin, are rather uncommon. It has been observed to terminate in an anastomosis with an enlarged posterior carpal arch, or in the lower part of the foreami by anastomosis with the anterior interosseous arter>-. Its absence below the point where the radial recurrent is given off has also been ob- ser\ed, its territory- in such cases being supplied by the interosseous. Occasionally it passes to the dorsal surface of the arm much higher up than usual, and in such cases the superficial volar branch also arises at a much higher level than usual and passes downward along the line usually occupied by the radial arten,-. It is an exceedingly slender ves- sel, and, being felt at the place where the pulse is usually examined, may give rise to erroneous conclusions as to the qualit\' of that phenomenon. Practical Considerations. — The radial arter)\ like the ulnar, is the subject of idiopathic aneurism only with great raritv, but a stab-wound may result in a trau- matic aneurism, or may necessitate immediate ligation for control of hemorrhage. The vessel may be tied in any part of its course. I. At the upper third of its antibrachial portion it is reached through an incision made on the line described {vide supra), which, after the deep fascia is opened up, should disclose the interspace between the brachio-radialis and the pronator radii THE RADIAL ARTERY. 787 teres. This is often indicated by a yellowish (cellulo-fatty) line. The fibres of the former muscle are almost parallel with the long axis of the forearm and overlie the artery ; those of the latter are oblique and lie close to the inner side of the vessel. The nerve is so far external that it is not likely to be seen. The artery, with its venae comites, lies on the supinator brevis. 2. At the middle of the forearm the incision is made on the same line. The same relations exist, except that there the nerve is usually very near to the outer side of the artery, which now lies on the tendon of insertion of the pronator radii teres. As the brachio-radialis is not very wide at this part (especially if the artery is sought for at the lower end of the middle third), it is very easy to expose the outer instead of the inner border of the muscle, in which case the muscle is apt to be drawn inward, and when the depths of the wound are opened up the radial nerve is reached. This is the common error of beginners. The tendon of the brachio-radialis, as a rule, first makes its appearance at the outer border of the muscle, so that if this tendinous edge is exposed the operator will know that he has laid bare the wrong side of the muscle. The inner border of the latter remains muscular, until it ends somewhat abruptly in the tendon (Treves). 3. At the lo~wer third the incision should be m.ade midway between the tendon of the brachio-radialis and that of the flexor carpi radialis, the latter of which may be made prominent by strongly extending the hand. The vessel is very superficial, and is disclosed as soon as the thin fascia is ' divided. The nerve has left the vessel altogether (at a level of from three inches above the wrist to the middle of the forearm) and has passed under the brachio-radialis tendon to the dorsum of the hand. 4. In the triangular fossa between the lower end of the radius and the root of the thumb {tabatiere atiatomiqiie), bounded externally by the tendon of the extensor longus poUicis, internally by the tendons of the extensor brevis poUicis and the extensor ossis metacarpi pollicis, and superiorly by the inferior margin of the posterior annular ligament (Fig. 716), the radial artery may occasionally require ligation on account of wound or of aneurism. An incision one inch and a half long should be made obliquely across the fossa, observing to avoid one of the chief radicles of the radial vein, which lies in the superficial fascia immediately in the course of the wound. After opening the fascia, and displacing some loose adipose tissue, the artery will be reached at the bottom of the depression between the tendons of the thumb. It is desirable to avoid opening the sheaths of the tendons or the joint between the scaph- oid and trapezium ; these bones together with the base of the first metacarpal form the floor of the space. The collateral circulation after ligation of the radial is carried on as after ligation of the ulnar, q.v. Wounds of a palmar or carpal arch are apt to be troublesome on account of the occasional difficulty in finding and securing both ends of the divided vessel, and because of the very free anastomosis between the palmar and carpal arches and the interosseous vessels, which leads to recurrent hemorrhage, even after ligation of both radial and ulnar. Compression over the wound, firm bandaging from the finger-tips to the axilla, and elevation of the limb, are, for these reasons, the methods usually first employed, and if applied thoroughly will generally be effectual. Ligation of the brachial is indicated when these have failed, on account of the necessity for getting above the interosseous anastomotic supply (vide szcpra). I. The Radial Recurrent Artery. — The radial recurrent (a. recurrens radialis] (Fig. 712) arises from the outer surface of the radial, shortly below its origin. It is at first directed downward upon the surface of the supinator brevis, but quickly bends upward towards the external condyle of the humerus, passing between the radial and posterior interosseous nerves and lying beneath the supinator longus. It gives numerous branches to the supinator longus and brevis and to the extensor carpi radialis longior and the extensor carpi radialis brevior, and terminates at the external condyle by anastomosing with the superior profunda from the brachial artery. HUMAN ANATO.MY. Olecranon process Interosseous recurrent arler>' Extensor carpi Extensor longus polli 2. The Anterior Radial Carpal Artery. — The anterior radial carpal (ramus carpea volarisj (^Fig. 712 j is usually a small branch which arises from near the lower end of the antibrachial portion ^"■'•''''' of the radial. It passes inward beneath the flexor tendons at about the lower border of the pronator quadratus, and breaks up into a number of small branches which anastomose \\ith branches from the anterior ulnar carpal, the anterior inter- osseous, and the recurrent car- pals to form an anterior carpal net-work. From this net -work branches pass to the wrist and to the carpal articulations. 3. The Superficial Vo- lar Artery.— The su[)erficial volar ( ramus volaris supertici- alis) (Fig. 713) arises usually just where the radial bends out- ward and backward to reach the posterior surface of the wrist. It is usually rather slender, although variable in size, and is directed downward, passing either o\er, through, or beneath the adductor poUicis, supplying that and the other muscles of the thenar eminence, and terminates usually bv anastomosing with the superficial palmar branch of the ulnar to form the superficial palmar arch. Variations. — The superficial volar is somewliat variable both as to size, origin, and mode of termina- tion. It occasionally arises high up upon the radial, and in such cases that vessel passes to the posterior surface of the arm at a much higher level than usual. Not infrequently it takes no part in the formation of the superficial palmar arch, and may terminate in the muscles of the thenar eminence, the digital branches being all given off by the superficial palmar branch of the ulnar ; or, on the contrary-, appear- ing as a well-developed stem, it may divide distally into from one to four digital arteries, the remain- ing ones arising directly from the superficial palmar branch of the ulnar or partly from that and partly from the median arteni- (page yS^.). 4. The Posterior Ra- dial Carpal Artery. — The posterior radial carpal (ramus carpeus dorsalis ) (Fig. 715) is a small branch which is gi\'en off from the radial just as that vessel passes beneath the tendon of the extensor ossis metacarpi pollicis. It passes horizontally inward beneath Posterior ulnar carpal artery Dorsal interosseous arteries Arteries of extensor surface of forearm and hand. THE RADIAL ARTERY. 789 the tendons of the extensor carpi radiaUs longior and the extensor carpi radiaHs brevior, and anastomoses, either directly or by means of a number of small branches, with the posterior ulnar carpal, forming ■&. posterior carpal arch or net-work. Branches. — From the posterior carpal arch or net-work a longitudinal stem passes distally in each of the three inner intermetacarpal spaces. These are the dorsal interosseous arteries (aa. metacarpeae dorsales). At the upper extremity of its intermetacarpal space each interosseous artery receives the corresponding perforating branch from the palmar interosseous artery, and when it reaches the interval between the bases of the proximal phalanges, it divides into two branches, which run forward upon the inner and outer surfaces respectively of the proximal phalanges of the adjacent digits and terminate in small branches upon these phalanges. A slender branch, which arises either directly from the dorsal carpal arch or from the in- terosseous artery of the fourth intermetacarpal space, passes along the inner border of the metacar- pal and proximal phalanx of the little finger. It terminates upon the proximal phalanx of its digit. Variations. — Considerable variation occurs m the size of the dorsal interosseous arteries. That which traverses the fourth intermetacarpal space is sometimes wanting, while that of the second space is sometimes of considerable size and may arise directly from the radial artery. Occasionally each artery undergoes a sudden increase of calibre at the point where it is joined by the perforating branch from the deep palmar arch, and may appear to be the continuation of the perforating branch. Where it divides into its two terminal branches, each interosseous gives off an inferior perforating branch, which passes forward to communicate with the corresponding palmar digital artery ; but these perforating branches are frequently wanting, with the exception of that given off from the artery of the second intermetacarpal space. 5. The Dorsalis PoUicis Artery. — The dorsalis pollicis (Fig. 715) is a slender artery which arises from the radial just before it passes beneath the tendon of the extensor longus pollicis. It passes distally along the dorsal surface of the first metacarpal and terminates upon the dorsum of the first phalanx of the thumb. 6. The Dorsalis Indicis Artery. — The dorsalis indicis (Fig. 715) arises from the radial just as it passes between the two heads of the first dorsal interosseous muscle to enter the palm of the hand. It passes distally along the radial border of the second metacarpal, resting upon the first dorsal interosseous muscle, and terminates Extensor carpi radiahb longior Lower extremity of radi Radial artery Extensor ossis metacarpi pollicis Extensor brevis pollicis Dissection showing relation of radial artery to extensor tendo upon the first phalanx of the index-finger. It frequently gives off a small branch which passes along the inner border of the metacarpal and first phalanx of the thumb. Variations. — Tlie dorsalis indicis, together with the carpal portion of the radial distal to the point at which the posterior radial carpal is given off, represents the dorsal interosseous artery of the first intermetacarpal space. The branch to the inner border of the thumb repre- sents one of the terminal branches of that artery, and frequently arises directly from the radial opposite the main stem of the dorsalis indicis. 7. The Princeps Pollicis Artery. — The a. princeps pollicis (Fig. 717) arises from the radial just as it emerges from between the two heads of the first dorsal inter- osseous muscle and is bending horizontally inward to form the deep palmar arch. The artery passes directly distally, resting upon the palmar surface of the first dorsal inter- osseous muscle and being covered by the adductor pollicis. While still beneath the 790 HUMAN ANATOMY. caput obliquum of the adductor, the vessel frequently divides into two branches, one of which is continued distally along the radial border of the index-hnger, forming what has been termed the a. radialis indicis (a. volaris indicis radialis), while the other extends along the first metacarpal and, passing between the two heads of the adductor, divides beneath the tendon of the flexor longus pollicis into two branches, which pass distally along the palmar surface of the thumb, one along the inner and the other along the outer border, anastomosing with the branches of the dorsalis polHcis. Variations. — The a. princeps pollicis is in reality the palmar interosseous artery of the first intermetacarpal space, and. when developed as described, corresponds in the arrangement of its branches with the dorsalis indicis, too:ether with the dorsalis pollicis. Frequently, however, the branch to the radial border of the index-finger is lacking, or, on the other hand, it may be well developed and arise directly from the deep palmar arch, or sometimes both it and the princeps pollicis are derived from the superficial palmar arch (page 784). 8. The Palmar Interosseous Arteries, — The palmar interosseous arteries (aa raetacarpeae volares ) are three in number, and arise from the deep palmar arch as Fig. 717- Anterior carpal branch Superficial volar Posterior carpal branch Metacarpal Dorsales poll Radial artery Princeps pollicis Radialis indicis Dorsalis indicis Branch from radialis in dicis fo.- superficial arch Ulnar artery Anterior carpal branch Posterior carpal br: Posterior carpal br; Poste arpal : Deep branch of ulnar A periorating branch of deep palmar arcli "Superficial palmar arch ^" sal interosseous arteries -Palmar interosseous arteries Digital arter Semidiagrammatic reconstruction of right hand, viewed from palm, showing relations of arteries to surface and to bones; vessels on dorsal surface are represented in outline. it crosses the second, third, and fourth intermetacarpal spaces. Each artery passes distally in its intermetacarpal space, resting upon the interosseous muscles, and THE THORACIC AORTA. 791 nates by anastomosing with the corresponding digital artery from the superficial palmar arch just before the digital divides into its two terminal branches. Immediately at its origin each palmar interosseous gives off a perforating branch (ramus perforans) which passes dorsally between the adjacent metacarpals to communicate directly with the corresponding dorsal interosseous artery. Variations. — The palmar interosseous arteries vary considerabI\- in size, according: as the digital branclies from the superficial palmar arch are well or poorly developed (page 7S4). When the ulnar palmar digital is small, an extra branch may arise from the deep palmar arch, passing along the ulnar border of the little finger. 9. The Palmar Recurrent Arteries. — The palmar recurrent arteries (Fig. 717) are two or three small branches which arise from the concave surface of the deep palmar arch and pass pro.ximally over the carpus to anastomose with the terminal branches of the anterior interosseous and of the anterior radial and ulnar carpal arteries. By the anastomosis of these \-arious arteries there is formed upon the anterior surface of the carpus a net-work, the rete carpale volare, from which branches are distributed to the wrist and to the carpal articulations. The Collateral Circulation in the Forearm. — The brachial artery, after being ligated, will convey blood to the forearm arteries by means of its superior and mferior profunda branches and by the anastomotica magna, which form a rich anas- tomosis at the elbow-joint with the radial recurrent, the anterior and posterior ulnar recurrent, and the posterior interosseous recurrent. The collateral circulation in the parts supplied by the ulnar and radial arteries, after ligation of one or other of these vessels, will be carried on by means of the direct anastomoses between the two arteries in the superficial and deep palmar arches and also by way of the anterior and posterior carpal net-v.^orks. To the former of these net-works the radial artery sends contributions from its posterior carpal branch and the ulnar from its posterior carpal and anterior and posterior interosseous branches, while to the latter the radial sends its anterior carpal branch and the ulnar its anterior carpal and anterior interosseous branches. THE THORACIC AORTA. • The thoracic aorta (aorta thoracalis ) (Fig. 718) is the continuation of the descending limb of the aortic arch, and begins upon the left side of the body of the fourth thoracic vertebra. It passes downward through the thorax in the posterior mediastinum and terminates below at the diaphragm, behind which it passes to become continuous with the abdominal aorta. In the upper part of its course it lies a little to the left of the median line, but it tends slightly to the right as it descends, and eventually occupies the median line just before it reaches the diaphragm. Relations. — Anteriorly it is in relation with the left bronchus and the root of the left lung in its upper part, and it is crossed very obliquely by the oesophagus, which separates it from the pericardium and the posterior surface of the left auricle of the heart. Posteriorly it rests upon the bodies of the eight lower thoracic ver- tebrae, or rather throughout the greater part of its extent upon the anterior common ligament of the thoracic vertebrae, and at about the level of the fifth vertebra has passing obliquely "pward behmd it the thoracic duct and, at the level of the eighth vertebra, the vena hemi-azygos. Upon the right side are, above, the oesophagus and lower down the right pleura. The thoracic duct passes upward upon its right side and slightly behind it as far as the fifth thoracic vertebra, and the \'ena azygos also lies upon its right side, but on a plane slightly posterior to it. On the left side are the left lung and pleura above, and below, the' cesophagus, while the vena hemi-azygos also lies upon its left side, but on a somewhat posterior plane. Branches. — The branches which arise from the thoracic aorta may be divided into two groups, according as they are distributed to the thoracic \'iscera or to the parietes. The visceral branches are (i) the bronchial, (2') the (Esophageal, and (3) the mediastinal. The parietal branches are (4) the aortic intercostal arteries, and (5) the diaphragmatic branches. 792 , HUMAN AXATO.MY. Variations. — The passage of the thoracic aorta down the right side of the vertebral column in the upper part of its course and the origin from it of the riglit subclavian artery have already been discussed in connection with the variations of the aortic arch (page 724). It was there pointed out that both these abnormalities depend upon the more or less perfect persistence of the louer portion of the right primitive aortic arch. Not infrequently a modification of this condi- tion is to be seen in the existence of a small branch arising from the upper part of the thoracic aorta and passing obliquely upward and to the right behind the tesophagtis. This is the arteria aberrans, and it is to be regarded as a persistence in a rudimentary condition of the distal jior- tion of the right primitive aortic arch. It is regarded by some authors as a normal branch of the thoracic aorta, but it is somewhat inconstant in its occurrence. Occasionalh- it anastomoses with the first or second intercostal branches of the superior intercostal artery (page 765). 1. The Bronchial Arteries. — The bronchial arteries (aa. Iminchiaks) (Fig. 71S) are somewhat variable in ninnber; while three are usually described, they may be reduced to two or increased to four. They arise from the upper portion of the thoracic aorta and pass to the right and left bronchi, and are continued along these to supply the tissue of the lungs. The right bronchial artery, which verj- frequently arises from the first right aortic intercostal, passes to the right in front of the oesophagus and applies itself to the posterior surface of the right bronchus, along which it passes to the lung. In its course it gives off minute branches to the oesophagus, bronchus, and pericardium, and to the lymphatic nodes in its neigh- borhood. The left bronchial arteries, which are usually two in number, apply them- selves at once to the posterior surface of the left bronchus as it passes in front of the aorta and are continued along this to the lung. They gi\e off small branches to the oesophagus and to neighboring lymphatic nodes. The upper of the two vessels fre- quently arises by a common stem with the right bronchial, and may be the only one that is present. 2. The CEsophageal Arteries. — The oesophageal branches (aa. cesophageae) (Fig. 718) of the thoracic aorta are also variable in number, forming a series of four or sometimes fi\e or six small vessels which arise in succession from abo\e downward from the anterior surface of the aorta. After a short but somewhat tortuous course, they reach the oesophagus, in the wall of which they branch to form a net-work which recei\-es branches from the bronchial arteries, from the inferior thyroid above and the gastric artery below. 3. The Mediastinal Arteries. — The mediastinal arteries (rami pericardiac!) are a number of small \'essels which arise from the anterior surface of the thoracic aorta and are distributed to the mediastinal lymph-nodes and the posterior surface of the pericardium. 4. The Aortic Intercostal Arteries. — The aortic intercostals (aa. inter- costales) (Fig. 718) supplying the tissues of the lower intercostal spaces, are usually nine in number on each side, while a tenth, sometimes termed the subcostal artery, runs along the lower border of the last rib, supplying the upper part of the abdom- inal wall. The arteries arise in pairs from the posterior surface of the thoracic aorta and pass outward o\'er the bodies of the vertebrae to the intercostal spaces, those of the right side being, for the most part, somewhat longer than those of the left, ow'ing to the position of the thoracic aorta to the left of the vertebral column through- out the greater portion of its length. Arrived at the intercostal space, each artei y passes obliquely outward and upward across the space towards the angle of the rib next abo\'e, resting upon the internal intercostal fascia, and covered by pleura. It then pierces the intercostal fascia and, as far as the angle of the rib, nms between the fascia and the external intercostal muscle. On reaching the angle of the rib the artery passes beneath the internal intercostal muscle and is continued around the thoracic wall in the subcostal groove of the rib, and between the two intercostal muscles, to terminate usually by inosculating in front with the upper of the two anterior inter- costal arteries given off by the internal mammary or the musoulo-phrenio to each intercostal space. The arteries which pass to the tenth and eleventh intercostal spaces continue onward beyond the extremities of their corresponding ribs, and, passing between the oblique muscles of the abdomen, anastomose with the deep epigastric artery. The same arrangement occurs in the case of each of the tenth aortic intercostal (subcostal) arteries. These, however, throughout that portion of THE THORACIC AORTA. 793 their course in which they are in relation to the twelfth ribs, rest upon the quadratus lumborum muscles, beneath the transversalis fascia, and at the outer border of that muscle pass beneath the fibres of the transversalis abdominis, and, more laterally, perforating the internal oblique, come to lie between that muscle and the external oblique. Relations. — In the first portion of their course, while passing over the bodies of the vertebrje, the right aortic intercostals are crossed by the thoracic duct and by the vena azygos, and the upper ones are also crossed by the cesophagus. Those of the left side are crossed by the vena hemiazygos, and both sets are covered by the pleura. Opposite the heads of the ribs they are crossed by the ganglionated cord of the sympathetic nervous system, the lower ones also by the splanchnic ner\'es, and in their course through the intercostal spaces they are in relation to the inter- costal veins and nerves, each artery lying below its corresponding vein and above the nerve, but on a plane slightly posterior to both. The arteries of the upper spaces lie at first below the corresponding nerves, but as they approach the lower borders of their ribs they cross the ner\-es obliquely, and throughout the greater part of their course possess the relation described. Branches. — Each artery gives off small branches to the bodies of the vertebrse and to the pleura, and throughout its course through the intercostal space numerous. {a) Muscular branches, which supply the intercostal muscles, the serratus magnus, and the pectorales major and minor, anastomosing with the thoracic branches from the a.\illar>' arten-. The vessels of the lower spaces and the subcostal also supply the upper portions of the abdominal muscles, the subcostal anastomosing with branches of the uppermost lumbar artery and with the ascending branch of the superficial circumflex iliac ; the lower vessels also give off numerous branches to the diaphragm which anastomose with the phrenic arteries from the abdominal aorta. Some of the muscular branches which arise from the vessels of the third, fourth, and fifth spaces send branches to the mammary gland, assisting the perforating branches of the internal mammary and the long thoracic branch of the a.xillary in the supply of that structure. These intercostal mammary branches (rami mammarii laterales) may become greatly enlarged during lactation, and may give rise to considerable hemorrhage in the operation for removal of the gland. In addition, each aortic intercostal gives off a dorsal, a lateral cutaneous, and a collateral branch. (b) The dorsal branch (ramus posterior) arises from each artery, just as it enters its inter- costal space, and passes directly backward, in company with the posterior division of the corresponding spinal nerve, between the necks of the adjacent ribs and internal to the superior costo-transverse ligament. Having reached the \'ertebral groove, it divides into a spina/ and a 7nuscidar branch. The former (ramus spinalis) passes through the inter\-ertebral foramen in company with the root of the spinal nerve, and, within the spinal canal, gives off branches to the body of the vertebra and its neural arches and to the dura mater, and also branches which pass to the spinal cord and anastomose with the anterior and posterior spinal arteries. The muscular brmich (ramus muscularis) continues posteriorly in the direction of the main stem of the vessel and divides into an external and an internal branch which pass bet\veen the principal masses of the dorsal musculature, supplying these and terminating in branches to the integu- ment of the back. (c) The lateral cutaneous branch (ramus cutaneus lateralis) arises at about the axillan,- line and perforates the external intercostal muscle in company with the lateral cutaneous branch of the corresponding intercostal nerve. It is distributed with the ner\-e to the integument of the lateral portions of the thorax, also supplying the serratus magnus and the pectoral muscles and anastomosing with the perforating branches of the internal mammary and with the thoracic branches of the axillar)- artery. (rf) The collateral branch arises as the intercostal approaches the angle of its rib. It passes obliquely outu-ard and downward to the upper border of the rib next below, along which it runs to terminate by anastomosing with the lower of the two anterior intercostal branches given off by the internal mamman,- or the musculo-phrenic to each intercostal space. The collateral branches of the three lower intercostals are small and inconstant and,- when present, terminate in the abdominal wall. • Variations.— The intercostal arteries of the first and second spaces usuallv arise from the superior mtercostal branch of the subclavian, but occasionallv the artery- of the second space, and more rarely that of the first, may arise from the thoracic aorta. Or, converselv, the arteries of the third and fourth intercostal spaces, as well as those of the first and second, mav arise from the superior intercostal, the aortic intercostals being cortespondingly reduced in niimber. 794 HUMAN ANATOMY. Occasionally the second intercostal is formed by a branch from the first aortic intercostal which runs upward to the second space over the neck of the third rib, and a similar condition may be met with in the lower arteries, two or more intercostal spaces being supplied from a common stem. Finally, the right and left arteries of one or all of the pairs may arise from a common stem, springing from the posterior median line of the aorta. Practical considerations of the thoracic aorta are discussed with those of the aoitic arch on page 726. THE ABDOMINAL AORTA. The abdominal aorta is the continuation below the diaphragm of the thoracic aorta. It may be said to begin, therefore, at the lo\\er border of the twelfth thoracic vertebra, and passes downward upon the bodies of the four upper lumbar \ertebrae lying almost in the median line. It is usually described as terminating opposite the fourth lumbar vertebra by dividing into the right and left common iliac arteries, although it is really continued onward beyond that point as a relati\ely feeble vessel which is termed the middle sacral aiiery. It seems ad\isable, however, to adhere to the classic definitions of the artery, and to regard the middle sacral, for purposes of descrii)tion, as one of its branches. Relations. — Posteriorly, the abdominal aorta rests upon the anterior com- mon ligament of the four upper lumbar vertebrae and crosses the left lumbar \eins. Anteriorly, in its uppermost part, it is in\-ested by the sympathetic solar plexus, from which branches pass downward along the \-essel, forming the aortic plexus. A little lower it is crossed by the splenic vein, the pancreas, the left renal vein, and the third portion of the duodenum, and still lower it is in relation with the coils of the small intestine, from which, however, it is separated by the peritoneum. Upon a more anterior plane there are, abo\e, the left lobe of the li\er, and the stomach and transverse colon. To the right, it 'is in contact, in its upper part, with the thoracic duct and the receptaculum chyli, which lie partly covered by it, and with the right crus of the diaphragan, which separates it from the inferior \ena cava ; lower down it is in direct contact with the vena cava. To the left, is the left crus of the diaphragm and the fourth portion of the duodenum above, while below it is separated by the peritoneum from coils of the small intestine, and has running alongside the left spermatic (ovarian) arter)- and vein, and still more laterally the left ureter. Branches. — The branches of the abdominal aorta, like those of the thoracic, may be di\ided into two sets, visceral and parietal. The visceral branches are ( i j the caliac axis, (2) the superior inesaiteric, and (3) the inferior mesenteric artery. These are median unpaired branches which arise from the anterior surface of the aorta; in addition, there are a number of paired visceral branches: (4) the inferior phrenic, (5) the suprarenal, (6) the renal, and (7) the spermatic or ovarian arteries. The parietal branches are (8) the /?/w3^;- arteries, of which there are four pairs, (9) the middle sacral, and (10) the common iliac artenes. With the excep- tion of the middle sacral, the parietal branches are all paired. Considered in the order of their origin from the aorta, the branches are ar- ranged thus: (i) The inferior phrenics, (2) the cceliac axis, (3) the suprarenals, (4) the superior mesenteric, (5) the first pair of lumbar arteries, (6) the renals, (7) the spermatics or ovarians, (8) the second pair of lumbar s, (9) the inferior mesenteric, (10 and 11) the third dind fourth pairs of lumbars, (12) the middle sacral, and (13) the comment iliacs. Variations of the abdominal aorta are not common. In cases in which the aortic arch bends to the right, the abdominal aorta may lie somewhat to the right of the median line, and it has been observed to pass downward upon the right of the inferior vena cava. A'ariations also occur in the level at which the aorta bifurcates into the common iliacs. In the majority of cases the bifurcation is opposite the middle of the fourth lumbar vertebra, but it is not infrequently lower, taking place opposite the lower half of that vertebra, opposite the succeeding interver- tebral disc, or, in rare cases, opposite the upper portion of the fifth \ertebra. Bifurcation at a higher level than usual is less frequent, but it has been obser\'ed as high as opposite the inter- vertebral disc between the third and fourth vertebrae, and, in very rare cases, the arterj- has been 'ound to divide as high as the second lumbar vertebra. THE ABDOMINAL AORTA 795 Fig. 71S. \'ertebral artery Common carotid artery Superior intercostal artery Subclavian artery Innominate artery I. aortic intercostal artery Riglit bronchus II. and III. aortic mtercostal arteries Right and left coronary arteries Leaflets of aortic semilun IV. -VII- aortic intercostal arteries Thoracic duct Subcostal artery Part of right crus of diaphragm I. lumbar artery CJuadratus lumborum Superior mesenteric artery Suprarenal artery Renal artery Inferior mesenteric arter\' Psoas magnus / t! muscle — ■/- Trachea Left common carotid arterj' Scalenus anticus muscle Vertebral artery Sectional surface of I. rib Superior intercostal artery I. and II. aortic intercostal Left bronchus arteries Aorta Upper left bronchial artery CEsophagus left bronchial artery III , IV. and V. aortic intercostals A pericardial branch VI. -X. aortic intercostal arteries An oesophageal branch Inferior phrenic arteries ■Subcostal arterv tmbar artery Lumbar fascia— middle layer Suprarenal arterj- II. lumbar artery Spermatic arteries III. lumbar artery Origin of quadratus lumborum IV. lumbar artery Middle sacral artery Left common iliac artery Interna! iliac artery Ilio-lumbar arter>- Posteriortrunk of int. iliac Anterior trunk of int. Ilia* External iliac artery ''-'^-^^^^^Ir.^^.^TS^^--^^^ 796 HUMAN ANATOMY. Although the abdomhial aortic stem is very constant in its relations, considerable variation occurs in the origin of its branches. Most of these will be considered in connection v\ ith the description of the branches concerned, but it may be noted here that verj- frequently a number of small branches, terminating in the neighbormg organs or connective tissue and lymph-nodes, arise from the abdominal aorta, in addition to the branches which have already been named. These small branches are rather inconstant, and may arise from either the anterior surface of the aorta, in which case they are unpaired vessels, or in pairs from its sides. Their e.xistence seems to indicate the occurrence of a primitively strictly segmental arrange- ment of the branches of the abdominal aorta, and a type-condition has been siipposed to occur in which the aorta gives off, opposite each segmental interval that it passes, three pairs of ves- sels, which arrange themselves in three distinct sets P[C5 -jg. (Fig. 719). One set arises from the anterior surface of the aorta, and is usually reduced, either by fusion or by the degeneration of one or other of each pair, to a single unpaired vessel for each segment ; a second set arises from the sides of the aorta and, like the first set, is distributed to the abdominal viscera; and a third set arises from the posterior surface of the aorta and is dis- tributed to the abdominal parietes. Of the unpaired set of vessels, only three persist until adult life, becoming the coeliac axis and the sup- erior and inferior mesenteric arteries, the position oc- cupied by these vessels in the adult being due to a downward migration which they undergo, the coeliac axis representing the ventral \isceral branch of the fourth thoracic or possibly a higher segment, the sup- erior mesenteric that of the seventh thoracic, and the inferior mesenteric that of the twelfth thoracic. The paired visceral branches are developed mainly in con- „. u ■ r J . , - nection with the embrvonic kidney, and on the replace- Diaeram showiriEr fundamental arranfi:e- ^ r ^i ■ u ^i. j 1^ i\ • -. .- ..1 ment of branches of abdominal aorta. A, main ment of this by the adult organ the majority of them body-trunk (aorta) : .s, somatic branch to body- disappear, the suprarenal, renal, and spermatic arteries wall's: Cpaired visceral branches: />, unpaired and certain inconstant branches which are lost in the visceral branch ; £. peritoneum. neighboring connective tissue representing them in the adult. Of the parietal paired set, the four pairs of lumbar arteries correspond to the four upper lumbar segments, while the common iliacs are the branches of the fifth lumbar .segment. The lumbar arteries are evidently serially homolo- ' gous with the thoracic intercostals and present many similarities to the lower members of that series, but the common iliacs are peculiar in that they give rise to branches which pass to the pelvic viscera, a condition which may be explained by the fact that the paired visceral branches of the third lumbar segment unite with them and are represented by the hypogastric artery and its branches. Practical Considerations. — The abdominal aorta is the subject of aneurism much more rarely than is the thoracic aorta, because of the relati\'ely less powerful cardiac impulse which reaches it. The sac is most often situated in the neighbor- hood of the cceliac a.xis because {a) in this region the artery has lost the support afforded by the tendinous arch of the diaphragm, which produces a constriction in its walls at each ventricular systole ; {F) it rather suddenly contracts about one and a half inches below this level (after having given ofT a number of large branches), so that the intervening portion is somewhat fusiform or pouched (Agnew) ; (r) the pressure on this aortic segment is increased by the sudden alteration in the direction of the blood-current caused by the presence of these branches (the inferior phrenics, the coeliac a.xis, the suprarenals, superior mesenteric, etc.); and (' and its branches. condition which results from this arrangement is that described above, the main stem of the internal iliac appearing to divide into two divisions, from the anterior of which the hypogastric axis arises. The second type is that in which the three large vessels arise independently from the hypo gastric, the resulting adult condition closely resembling that produced from the first t\'pe, except that the hypogastric axis seems to arise from the internal pudic, the separation of the anterior division into its two terminal branches occurring high up. The third type is that in which the gluteal and sciatic arteries arise by a common trunk from the hypogastric, the pudic remaining distinct. In the adult, in such cases, the anterior division gives rise to the hypogastric axis and the internal pudic, the sciatic arising from the posterior division. Finally, in the fourth type, which is of rare occurrence, all three large vessels arise froni a common stem, in which case there will be no apparent separation of the adult internal iliac into an anterior and a posterior division. 8io HUMAN ANATOMY. The variations of the smaller branches, which are quite numerous, will be considered in connection with their description, it may be pointed out, however, that, since the superior vesical artery is the persistent portion ot the original hypogastric artery and primarily the direct continuation of the hypogastric a.xis, some of the visceral branches which normally arise from the axis may take their origin from the superior vesical. Furthermore, vessels which embryologically arise from one or other of the great branches of the hypogastric may, on account of the variations in the origin of these, come to arise from the hypogastric axis. Practical Considerations. — The internal iliac artery is almost never the seat of aneurism. It has been ligated for hemorrhage, for gluteal and sciatic aneurism, and in the treatment of inoperable pelvic grow'ths. It may be approached intraperi- toneally by the same incision and the same general procedure as employed in ligation of the common iliac (q.v.). The vein lies behind and to the inner side, and Fig. 725. Diagram illustrating four types of arrangement of branches from hypogastric (internal iliac) artery ; c/. ei, tt\ common, external and internal iliac artery ; i7, ilio-lumbar; /j, lateral sacral ; g-, gluteal; i, sciatic : tp^ internal pudic ; Aa, hypogastric axis. by reason of its size and its close proximity to the vessel must be very carefully dealt . with. The needle should be passed from within outward. The relation of the ureter, which crosses the vessel obliquely from without inward and downward, and of the hypogastric plexus should be borne in mind. In the extraperitoneal method the incision and procedure are just as in extra- peritoneal ligation of the external iliac (page 819), except that the separation of the peritoneum from the iliac fascia must be carried to a higher level. The collateral circulation is carried on chiefly through (a) the inferior mesen- teric ; {b) the circumflex iliac ; {c) the middle sacral ; (d ) the deep femoral ; (^) the obturator and internal pudic of the opposite side, all of which carry blood from above the ligature into (a) the hemorrhoidal branches of the internal iliac ; {b') the ilio- lumbar ; (r) the lateral sacral ; {^d) the sciatic and gluteal ; and (<') the corresponding vessels of the other side {i. e., the side of the ligature). I. The Ilio-Lumbar Artery. — The ilio-lumbar artery (a. ilio-lumbalis) (Fig. 724) is most frequently given off from the main stem of the internal iliac, shortly above its separation into the anterior and posterior divisions. Not infre- quently, however, it is a branch of the posterior di\ision. It passes upward and outward towards the brim of the pehis, crossing in front of the lumbo-sacral ner.-e and behind the external iliac artery, beyond which it passes beneath the psoas muscle. On reaching the crest of the ilium it di\'ides into two Branches.— ((7) The lumbar branch (ramus liimbalis'l is directed upward and backward be- neath the psoas and supplies that muscle and the quadratus lumbonnn. It sends a spinal branch {ramus spinalis) through the intervertebral foramen between the last lumbar and fir.st sacral vertebrae, and anastomoses with branches of the last lumbar artery. (b) The iliac branch (ramus iliacus) passes outward beneath the psoas and ramifies upon the surface of the iliacus muscle, supplying it and usually giving off a nutrient branch to the ilium. 2. The Lateral Sacral Arteries. — The lateral sacral arteries (aa. sacrales laterales) (Fig. 724") are usuallv two in number, and arise from the posterior division of the internal iliac. The superior one passes downward and inward to the first anterior sacral foramen, and passes through it to supply the spinal membranes and anastomose THE INTERNAL ILIAC ARTERY. 8ii with the other spinal arteries. The inferior artery passes at first inward and then downward upon the surface of the sacrum, parallel to the middle sacral artery, with which it anastomoses at the tip of the coccyx and also, by delicate transverse branches, opposite each sacral vertebra. Opposite each anterior sacral foramen that it passes — i.e., opposite the second, third, and fourth — it gives off a branch (ramus spinalis) which enters the foramen and behaves like the spinal branch of the superior artery. In its downward course the inferior lateral sacral lies to the outer side of the sacral portion of the sympathetic cord and crosses the slips of origin of the pyriformis muscle. Variations. — \'erj- frequently the two lateral sacral arteries arise by a common stem, and occasionally the branch which enters the second anterior sacral foramen arises independently. In all probability the longitudinal stem of the inferior artery is to be regarded as having been formed by the direct anastomosis of ascending and descending twigs from the lateral branches of the middle sacral, each of which is serially homologous with the lumbar and intercostal arte- ries. The process is similar to v\'hat has occurred in the formation of the vertebral artery (page 721). 3. The Gluteal Artery. — The gluteal artery (a. glutaea superior) (Fig. 727) is the continuation of the posterior division of the internal iliac. It is the largest of all the branches of that vessel, and passes backward between the lumbo-sacral cord and the first sacral nerve to the upper border of the great sacro-sciatic foramen. It passes through the foramen, in company with the superior gluteal nerve, above the pyriformis muscle, and soon after making its exit from the pelvis divides into a superficial and a deep branch. Branches. — (a) The superficial branch (ramus superior) soon divides into a number of branches which enter the upper portion of the gluteus maximus, some supplying that muscle, while others traverse it to supply the skin over the upper part of the gluteal region. One branch, larger than the others, passes outward along the upper border of the origin of the gluteus medius almost to the anterior superior spine of the ilium, anastomosing with branches of the external circumflex iliac artery. (b) The deep branch (ramus inferior) soon divides into two branches, (aa) The superior branch passes outward along the upper border of the gluteus minimus almost to the anterior inferior spine of the ilium, where, under cover of the tensor vaginas femoris, it anastomoses with the descending branch of the e.xternal circumflex iliac ; it sends branches to both the glu- teus medius and minimus, {bb) The in/ei-ior branch passes outward and downward, over the surface of the gluteus medius, towards the greater trochanter of the femur, and gives branches to both the gluteus medius and minimus and to the hip-joint. 4. The Superior Vesical Artery. — The superior vesical artery (a. umbilicalis) (Fig. 724) represents the original main stem of the foetal hypogastric artery, and consequently takes its origin from the hypogastric a.xis and is continuous anteriorly with the fibrous cord which represents the obliterated hypogastric artery (Fig. 728). It passes forward, beneath the peritoneum, towards the urinary bladder, and as it approaches that structure gives off branches to it (aa. vesicales superiores) which ramify over its surface and sides and supply its upper and middle portions. They anasto- mose below with branches of the prostatic and inferior vesical arteries. Variations. — Not infrequently an accessory branch arising from the superior vesical is dis- tributed to the middle and lower portions of the bladder, forming what has been termed the middle vesical artery ( Fig. 724) . 5. The Inferior Vesical Artery. — The inferior vesical artery (a. vesicalis inferior) (Fig. 724) may arise from the hypogastric axis, from the anterior division of the internal iliac below the a.xis, from the middle hemorrhoidal, or quite frequently from the prostatic. It descends towards the lower portion of the bladder, supplying the base and neck of that structure, and also sending branches to the prostate gland and the seminal vesicles in the male. It anastomoses with branches of the prostatic and superior vesical arteries. Variations. — The inferior vesical is usually a rather slender branch, and may be replaced by vesical branches from the prostatic or by branches of the superior vesical. 8l2 HUMAN ANATOMY. 6a. The Prostatic Artery. — The prostatic artery arises either from the hypo- gastric axis, or, more usuallv, from a trunk common to it and the inferior vesical or the middle hemorrhoidal. It passes downward, forward, and inward to the lateral surface of the prostate gland, and sends branches into the interior of that structure and also to the base of the bladder, anastomosing with branches of the inferior vesical artery. (lb. The Vaginal Artery. — The vaginal artery (a. vaginalis) (Fig. 726), the homologue of the prostatic artery, arises either from the hypogastric axis, more usually from a trunk common to it and the inferior vesical or middle hemorrhoidal, or from the anterior division of the internal iliac, below the hypogastric axis. It passes down- , ward and inward towards the lower part of the sides of the vagina, where it di^•ides into numerous branches which ramify over the anterior and posterior surfaces of that organ, anastomosing with the corresponding branches of the artery of the other side. It also anastomoses above with the cervical branches of the uterine artery and below with the perineal branches of the internal pudic. By these anastomoses there is usually formed along the median line of both the anterior and posterior surfaces of the vagina a more or less regular vessel which is known as the asygos artery of the vagina. Fig. 726. flex iliac artery Round ligament External iliac artery Dorsal artery of Variations. — The vaginal artery occasionally arises from a common trunk with the uterine. Frequently, as a result of its precocious division, it is represented by two or more vessels. 7(7. The Vesiculo-Deferential Artery. — The vesiculo-deferential artery Ta. deferentialis ) usually arises from the hypogastric axis, but sometimes from the proximal part of the superior vesical or from the anterior division of the internal iliac, below the hypogastric axis. It passes downward, forward, and inward, and, crossing the ureter, gives a branch to the vas deferens and then breaks up into a number of small branches which are distributed to the vesicula seminalis. The deferential branch, on reaching the vas, divides into an ascending and a descending branch. The former passes upward along the vas to the internal abdoininal ring and thence through the inguinal canal to the neighborhood of the epididymis, anastomosing with branches of the spermatic artery. The descending branch accompanies the vas to the prostate. •]b. The Uterine Artery. — The uterine artery (a. uterina) (Fig. 726) corres- ponds to the vesiculo-deferential and has a similar origin. It passes at first downward and inward upon the surface of the levator ani, and then inward in a tortuous course THE INTERNAL ILIAC ARTERY. 813 along the base of the broad ligament towards the neck of the uterus. Just before reaching the uterus, usually about 2 cm. ( ^4 in. ) from it, the artery crosses in front of the ureter and then bends upward between the two layers of the broad ligament along the side of the uterus. Arrived at the junction of the Fallopian tube with the uterus, it bends outward along the lower border of the tube, and then, passing beneath the hilum of the ovary, terminates by inosculating with the ovarian artery. In its course between the layers of. the broad ligament the artery is accompanied by the large uterine veins, which almost conceal it, and both artery and veins are enclosed in a rather dense sheath of areolar tissue. During pregnancy the artery becomes much enlarged, and its course, as well as that of its branches, becomes exceedingly sinuous and even spiral. Branches. — (a) As the uterine arter>- crosses the renal duct, a ureteral branch is supphed to the ureter. On reaching the sides of the uterus, it gives off — (d) One or several cervical branches. These pass to the cervi.x and divide into numerous branches which supply that portion of the uterus and the upper part of the vagina. They are relatively long and tortuous, and anastomose belovv- with the branches of the vaginal arteries. Throughout the rest of its course along the sides of the uterus it gives off numerous — {c) Uterine branches, which, although tortuous, yet differ from the cervical branches in being rather short. They pass to both the anterior and posterior surfaces of the uterus and supply its body and fundus, and it is to be remarked that both these branches and tlie cervical ones diminish rapidly in calibre as they branch upon the surface of the uterus, so that at the middle line of the organ only exceedingly minute twigs are to be found. From the portion of the artery that runs outward along the lower border of the Fallopian tube — (d) Tubal branches (rami tubarii) are given off. One of these, much stronger than the others, arises just before the uterine inosculates with the ovarian artery, and passes outward along the tube to its fimbriated extremity, sending branches to it through its entire course., (e) Ovarian branches (rami ovarii) to the ovary are finally .given off from the uterine artery in the vicinity of its anastomosis with the ovarian. 8. The Middle Hemorrhoidal Artery. — The middle hemorrhoidal artery (a. haemorrhoidalis media) (Fig. 726) is somewhat variable both in its origin and in its size. It arises either from the anterior division of the internal iliac, below the hypogastric artery, or, as frequently happens, from the inferior vesical or occasionally from the internal pudic. It passes along the lateral surface of the middle portion of the rectum, giving off branches which, in addition to aiding in supplying the vagina and communicating with the vaginal arteries, anastomose above with the superior hemorrhoidal from the inferior mesenteric and below with the inferior hemorrhoidal from the internal pudic. 9. The Obturator Artery. — The obturator artery (a. obturatoria) (Fig. 724) arises from the anterior division of the internal iliac, below the hypogastric axis. It passes forward along the lateral wall of the pelvis, resting upon the pelvic fascia which covers the upper portion of the internal obturator muscle, and having the obturator nerve immediately above it and the vein below. Just before reaching the anterior wall of the pelvis it is crossed by the vas deferens in the male, as it passes downward from the internal abdominal ring, and then it pierces the pelvic fascia and makes its exit from the pelvic cavity through the obturator canal, on emerging from which it divides into two terminal branches, an internal and an external. Branches. — Ulthin the pelvis the obturator artery gives off several small branches, of which the more important are — ( a ) An iliac branch, which is given off near the origin of the obturator and passes up to the iliac fossa, supplying the ilio-psoas muscle, giving nutrient branches to the ilium and anasto- mosing with the iliac branch of the ilio-lumbar artery. {b) Muscular branches, which are distributed to the obturator intemus and the levator ani. (c) Vesical branches, which pass to the bladder beneath the false lateral ligament and anastomose with branches from the superior vesical ; and {d) A pubic branch (ramus pubicus) which arises just before the artery enters the obtu- rator canal and ascends upon the posterior surface of the os pubis to anastomose above with the pubic branch of the deep epigastric artery. Outside the pelvis the obturator artery divides into an external and an internal branch. 8i4 HUMAN ANATOMY. (e) The external branch passes around the external border cf the obturator foramen, beneath the external obturator muscle, and terminates by anastomosing u ith the internal branch and with the internal circumflex from tlie deep femoral. Near its origin it gi\es oR — ( aa ) An iniei-nal branch, which passes downward on the posterior surface of the obturator membrane, under cover of the internal obturator muscle, to the tuberosity of the ischium, and it also gives rise to — {bb) An acetabular branch (ramus acetabuli), which passes through the cotyloid notch and supplies the fatty tissue occupying the bottom of the acetabulum. (f) The internal branch runs around the inner border of the obturator foramen, beneath the external obturator muscle, and terminates by anastomosing with the external branch. Variations. — The obturator artery \aries greatly in its origin, and these variations may be divided into two groups, according as the origin is from the internal or the external iliac system of arteries. While the origin of the vessel from the anterior division of the internal iliac is the most frequent, yet, when compared with all the variations taken together, it occurs in some- what less than 50 ]5er cent, of cases. Of other origins from the system of the internal iliac there may be mentioned those from the main stem of the iliac before its division, from its posterior division, and from the gluteal artery. Furthermore, its origin may occur from either the sciatic or the internal pudic artery, although such cases are rare. JMore frequent and of greater importance from the practical stand-point is the origin from the external iliac system, which occurs in about 30 per cent, of cases. In the immense majority of such cases — in almost twenty-nine out of every thirty — the origin is from the deep epigastric artery, being in the remaining cases from the external iliac distal to the deep e]>igas- tric or from the upper part of the common femoral artery. Undoubtedly the primar\- relations of the obturator artery are with the internal iliac system of vessels, and the origin from the ex- ternal iliac system is to be regarded as due to the secondary enlargement of an anastomosis nor- mally present and the diminution or inhibition of the original stem of the obturator. Possibilities for such a process are furnished by the normal anastomosis between the pubic branches of the obturator and the external circumflex, and all gradations may be found between the normal ar- rangement and the complete replacement of the original intrapelvic portion of the obturator by the pubic anastomosis. The origin of the obturator from the deep epigastric artery ( Fig. 728) becomes of importance from the fact that, in order to reach its point of exit from the pelvis, the obturator canal, the vessel must come into intimate relations with the crural ring, and mav thus add an important complication to the operation for the relief of femoral hernia (page 1775). There are three possi- ble courses for the vessel in relation to the ring : ( i ) it may pass inward from its origin over the upper border of the ring and then curve downward and inv\ard along the free border of Gim- bernat's ligament to reach the obturator canal ; (2) it may bend downward abruptly at its origin and pass in an almost direct course to the obturator canal, passing over the inner surface of the external iliac vein, and therefore down the outer border of the crural ring ; or (3) it may pass directly across the ring. As regards the relative frequency of each of these courses it is mteresting to note that, according to observations made by Jastschinski, the course along the outer border of the ring is much the most frequent, occurring in 60 per cent, of cases, and being more frequent in females than in males. The course across the ring occurs in about 22.5 per cent, of cases, and is again more frequent in females than in males ; while the course along the free edge of Gimbernat's ligament occurs in only 17.5 per cent, of cases, and is more common in males than in females. The difTerences in the two sexes are associated with the differences in the form of the pelvis and of the obturator foramen. Practical Considerations. — The gluteal and sciatic arteries have not uncom- monly been affected by aneurism which has shown itself as a pulsating compressible tumor in the gluteal region, often with a bruit, and usually causing pain over the nates, extending down the posterior aspect of the thigh— from pressure on the sciatic nerve — and causing lameness. The gluteal aneurism is situated somewhat farther back in the buttock than the sciatic, which is apt to be farther forward and downward, near the gluteo-femoral crease (Agnew). Either of these vessels or the internal pudic may require ligature on account of stab-wounds. Serious hemorrhage from a wound in the upper part of the gluteus ma.ximus, i.e., a little below a line from the posterior superior iliac spine to the top of the great trochanter, is likely to proceed from the gluteal artery. Lower, nearei to the fold of the buttock, it mav come from the sciatic. The gluteal may be tied through an incision made along the line just mentioned, from the posterior superior spine to the trochanter. With the thigh in inward rotation, the junction of the middle with the upper third of that line indicates about the point where the gluteal artery comes out through the sciatic notch. The fibres of the gluteus ma.ximus are sepa- rated, the muscle is rela.xed by full extension of the thigh, and the upper bony margfin THE INTERNAL ILIAC ARTERY. 815 of the sciatic notch is felt for with the finger through the interspace between the pyri- formis and the gluteus medius. The artery may be found as it turns over the bony tip of the sacro-sciatic foramen towards the dorsum ilii. The sciatic artery may be reached through the same incision, the finger then being carried below the pyriformis muscle, when the spine of the ischium and the sharp edge of the sacro-sciatic ligament will serve as landmarks. The point of emergence of both the sciatic and internal pudic arteries is indicated with sufficient accuracy by the junction of the lower and middle thirds of a line drawn from the tuberosity of the ischium to the posterior superior spine of the ilium. The incision employed should follow the direction of the fibres of the greater gluteal muscle. 10. The Sciatic Artery. — The sciatic artery (a. glutaea inferior) (Fig. 727) is one of the two terminal branches of the anterior division of the internal iliac. It lies at first internal and posterior to the internal pudic artery, and is directed downward and backward towards the lower part of the great sacro-sciatic foramen, passing usu- ally below the fourth sacral nerve. It makes its exit from the pelvis through the great sacro-sciatic foramen, below the pyriformis muscle, and bends downward beneath the gluteus ma.ximus. It crosses the internal pudic artery at about the level of the spine of the ischium, and in the rest of its course lies to the inner side of the great sciatic nerve. It descends upon the gemelli, the internal obturator, and the quad- ratus femoris, and, after giving ofi its principal branches, is continued down the leg as a slender vessel, the comes nervi ischiadici. Branches. — Within the pelvis the sciatic artery gives off some small and inconstant branches to the internal obturator and pyriformis muscles and to the trunks of the sacral pelvis. Outside the pelvis it gives rise to several larger branches. {a) The coccygeal branch passes inward and pierces the great sacro-sciatic ligament and the gluteus ma.ximus near its origin, terminating in the tissues over the lower part of the sacrum and coccyx. {b) Muscular branches, variable in number, pass to the neighboring muscles, some of them being continued beneath the quadratus femoris to reach the capsule of the hip-joint. One branch somewhat larger than the rest can frequently be seen entering tha deep surface of the gluteus maximus in company with the inferior gluteal nerve ; it supplies the muscle and forms anastomoses with the gluteal artery. {c) An anastomotic branch passes transversely outward, usually beneath the great sciatic nerve, towards the greater trochanter of the femur. It gives twigs to the gemelli muscles, and in the neighborhood of the trochanter anastomoses with the terminal branch of the internal cir- cumflex, with the transverse branch of the e.xternal circumflex, and, below, with the first per- forating artery, completing what is termed the crucial anastomosis. ( d ) Cutaneous branches, variable in number, wind around the lower border of the gluteus maximus in company with branches of the small sciatic nerve, and supply the integument over the lower part of the gluteal region. {e) The a. comes nervi ischiadici is the continuation of the sciatic artery. It is a long, slender branch which passes downward upon or in the substance of the great sciatic nerve, sup- plying it and anastomosing with the perforating branches of the profunda femoris. Variations. — The occasional origin of the sciatic from the gluteal artery or from the hypogastric axis has already been described in connection with the variations of the internal iliac (page 808). Occasionally it has a double origin from both the gluteal and the anterior division of the internal iliac, or it may be double, owing to the existence of stems from each of these vessels which pursue independent courses. In addition to its normal branches, it may give origin to the lateral sacral, the inferior vesical, and the uterine or the middle hemorrhoidal. Especial interest attaches to the comes nervi ischiadici, which occasionally traverses the entire length of the thigh to unite below with the popliteal artery. It represents the original main stem of the sciatic artery, of which the popliteal was primarily the continuation, the connection of that arterj' with the femoral, and the subsequent diminution of the sciatic being secondary arrangements (page S24). 11. The Internal Pudic Artery. — The internal pudic artery (a. pudenda interna) (Fig. 727) is the other terminal branch of the anterior division of the internal iliac. It is directed downward in front of the sciatic artery to the lower portion of the great sacro-sciatic foramen, where it makes its e.xit from the pelvis, passing between 8i6 HUMAN ANATOMY. Fig. 727. Superior gluteal artery. Coccygeal arteir Internal pudic artery Gluteus medii Muscular branch of sup. gluteal Lower ramus of deep branch t'yriforniis (of sup. gluteau Tendon of obturator internus Articular branch from ascending branch of internal cirrumfiex Articular branch of sciatic artery Anastomotic branch From external circumflex Superior perforating artery From external circumflex Middle perforating artery Inferior perforating artery Biceps — short head Biceps— long head Superior external articular artery External sural artery Inferior external articular artery Arteries of gluteal region and posterior surface of right thij THE INTERNAL ILIAC ARTERY. 817 the pyriformis and coccygeus muscles. It then bends forward, under cover of the gluteus maximus, and, curving beneath the spine of the ischium, passes through the lesser sacro-sciatic notch to enter the ischio-rectal fossa. Its course is then forward along the lateral wall of the fossa, lying with its accompanying vein and the pudic nerve in a fibrous canal known as Alcock' s canal, formed by a splitting of the obtu- rator fascia near its lower border. At the anterior portion of the ischio-rectal fossa the artery perforates the triangular ligament of the perineum and passes forward between the two layers composing that structure, finally perforating the superficial layer and becoming the dorsal artery of the penis (or clitoris). Branches. — In the pelvic and gluteal portions of its course the internal pudic, as a rule, gives off only slender muscular branches to the neighboring muscles. In its ischio-rectal por- tion its branches are more important. (a) The inferior hemorrhoidal arteries (aa. haemorrhoidales inferiores), usually two in num- ber, but frequently only one, which early divides into two 'or three stems, arise from the internal pudic, just after it has traversed the lesser sacro-sciatic foramen. They perforate the inner wall of Alcock' s canal and pass through the fat-tissue which occupies the ischio-rectal fossa towards the lower part of the rectum. They give branches to the ischio-rectal fat-tissue, to the sphincter and levator ani, to the gluteus maximus, to the skin over the ischio-rectal and anal regions, and to the lower part of the rectum, anastomosing above with the middle hemorrhoidal branches of the internal iliac. {b) The superficial perineal artery (a. perinei) arises just before the internal pudic enters the space between the layers of the triangular ligament of the perineum. It is at first directed almost vertically downward, but quickly bending around the posterior border of the superficial transverse muscle of the perineum, near its origin from the ischial tuberosity, it is directed for- ward and inward in the interval between the ischio-cavernosus and bulbo-cavernosus muscles. In this portion of its course it is covered only by the superficial perineal fascia and the integu- ment, and passes forward to be distributed to the posterior 'portion of the scrotum in the male and to the labia majora in the female. In its course it gives off numerous cutaneous branches as well as branches to the neighboring muscles. One of these latter, usually somewhat larger than the rest, passes inward towards the median line, beneath the superficial transverse muscle of the perineum, which it supplies, as also the bulbo-cavernosus and external sphincter ani. This is what has been termed the ira?isverse artery of the perineum. It anastomoses at the central point of the perineum with its fellow of the opposite side, with other branches from the superficial perineal artery anteriorly and with branches of the inferior hemorrhoidals posteriorly. In its perineal portion also the internal pudic gives oft" important branches. (c) The artery to the bulb (a. buibi urethrae or a. buibi vestibuli) arises from the internal pudic a short distance after it has entered the deep perineal interspace. It is a relatively large vessel in the male, and passes almost horizontally inward towards the median line. Before reaching this, however, it perforates the superficial layer of the triangular ligament, enters the substance of the bulbus urethrae about 15 mm. in front of its posterior extremity, and is distributed to that structure and to the posterior third of the corpus spongiosum and urethra. In the female it is of a lesser calibre than in the male, and is distributed to the bulbus vestibuli. (rf) The urethral artery (a. urethralis) arises usually some distance anteriorly to the artery of the bulb, and, like it, is directed medially, and penetrates the superficial layer of the tri- angular ligament to enter the substance of the corpus spongiosum. It reaches the corpus spongiosum just behind the symphysis pubis, where the two corpora cavernosa come together to form the penis, and is continued forward in the spongiosum to the glans. It is a somewhat inconstant branch, and is quite small in the female. (e) The artery of the corpus cavemosum (a. profunda penis s. clitoridis) arises from the internal pudic, just posterior to the lower border of the symphysis pubis, and is directed outward towards the bone. It penetrates the superficial layer of the triangular ligament close to its attachment to the pubic ramus, and enters the corpus cavemosum at about the junction of its middle and posterior thirds. It passes to the centre of the corpus and there divides into a posterior branch which supplies blood to the posterior third of that structure, and an anterior one which distributes to its anterior two-thirds. It is much smaller in the female than in the male. (/) The dorsal artery of the penis or clitoris (a. dorsalis penis s. clitoridis) is the continua- tion of the main stem of the internal pudic beyond the origin of the artery to the corpus cav- emosum. It penetrates the superficial layer of the triangular ligament near its apex, and passes upward in the suspensory ligament of the penis or clitoris to the dorsal surface of that organ, along which it passes, lying to the side of the median line and separated from its fellow of the opposite side by the single median dorsal vein. Laterally to it is situated the dorsal nerve of 52 8i8 HUMAN ANATOMY. the penis (or clitoris), and still more laterally the deep external pudic branch of the common femoral arter\'. On reaching the glans, it forms an anastomotic circle around the base of that structure, uniting with its fellow of the opposite side. Throughout its course it gi\es branches to the corpus cavernosum and the integument of the penis or the prepuce of the clitoris. Variations. — The occasional origin from the internal pudic of the inferior vesical, middle hemorrhoidal, and uterine arteries has already been noted. The internal pudic, instead of passing out of the pelvis by the great sacro-sciatic foramen, may be directed forward upon the floor of the pelvis and pass out beneath the pubic symphysis to become the dorsal artery of the penis. More frequently this course is taken by an accessory internal pudic w hich arises from the pudic in cases where this vessel appears to arise from the hypogastric a.xis, a condition which results in the early division of the common stem from which the sciatic and internal pudic arteries normally arise. The artery of the bulb may arise opposite the ischial tuberosity and pass obliquely forward and medially across the ischio-rectal fossa, and in some cases it passes at first directly across towards the anus and then bends forward to reach the bulb. The dorsal artery of the penis or clitoris occasionally unites with its fellow of the opposite side to form a single median artery, or the two arteries of opposite sides may be united by trans- verse anastomoses. Sometimes a third vessel arises either directly from the anterior division of the internal iliac or from the obturator, even when this vessel takes its origin from the deep epigastric. Anastomoses of the Internal Iliac. — The internal iliac makes anastomoses with branches of the abdominal aorta and of the e.xternal iliac, and with its fellow of the opposite side, and it is through these connections that the collateral circulatioa may be established. Of branches communicating with the abdominal aortic system there are the hemorrhoidal branches which anastomose with the superior hemorrhoidal from the inferior mesenteric, the uterine which anastomoses with the ovarian, and the lateral sacrals which anastomose with the middle sacral. Communications with the system of the e.xternal iliac are through the sciatic with branches of the profunda femoris, through the ilio-lumbar and gluteal with the external and internal circumfle.x iliacs, and through the obturator with the deep epigastric through the pubic branches. The anastomoses across the middle line occur between the vesical, prostatic (vaginal), obturator, and internal pudic branches. THE EXTERNAL ILIAC ARTERY. The external iliac artery (a. iliaca externa) (Figs. 724, 728) extends from the bifurcation of the common iliac, opposite the sacro-iliac articulation, to a point beneath Poupart's ligament midway between the anterior superior spine of the ilium and the symphysis pubis. It there becomes the femoral artery. In the adult the external iliac is usually larger than the internal and is directed more nearly in the line of the common iliac, downward, forward, and outward along the brim of the true pelvis. Relations. — Anteriorly, the artery is covered by peritoneum and is enclosed, together with the vein, in a moderately dense sheath deri\ed from the subperitoneal tissue and termed Abernethy s fascia. By the peritoneum it is separated on the right side from the terminal portion of the ileuin and sometimes from the vermiform appendix, and on the left from the sigmoid colon. Near its origin it is crossed by the ovarian vessels in the female and sometimes by the ureter ; near its lower end it is crossed obliquely by the genital branch of the genito-crural ner\e and by the deep epigastric vein. Some Ivmph-nodes are also found resting upon its anterior surface. Postcriorlv, it rests upon the iliac fascia, which separates it from the psoas muscle ; medially, it is crossed near its lower end by the vas deferens in the male and the round ligament of the uterus in the female, and is accompanied throughout its course by the external iliac vein, which lies, however, on a slightly posterior plane. Laterally, it is in relation to the genito-crural ner\-e. Branches. — In addition to some small twigs to the psoas muscle and to the neighboring Ivmphatic glands, the external ihac gives origin to (i) the deep epigastric and ( 2 ) the deep circumfle.x iliac arteries. Variations. — The external iliac varies considerably in length, according to the level at which the abdominal aorta and the common iliac bifurcate. Independently of this, however, and especially in aged individuals, it is frequently longer than is necessar)- to reach in a direct THE EXTERNAL ILIAC ARTERY. 819 line from the common iliac to beneath Poupart's ligament, and in such cases it makes a more or less pronounced bend which may dip below the brim of the pelvis. In the embryo it is a comparatively small vessel, the main supply of the lower limb being through the sciatic, which is continuous below with the popliteal (page 823). Occasionally this condition is retained, the artery then terminating by becoming the deep instead of the common femoral. In addition to the usual branches it may give off the obturator (page S14), or an accessory deep epigastric or deep circumflex iliac. Or branches usually arising from the common femoral, such as the superficial external pudic or even the profunda femoris, may arise from it. Practical Considerations. — The external iliac artery is occasionally tlie seat of aneurism, and such tumors have been mistaken for malignant growths or for abscess. A swelling with expansile pulsation and bruit can usually be found in the line of the vessel near the brim of the pelvis, and the patient will be unable to extend freely the thigh or the trunk, and will lean forward in walking or standing to relieve the ilio-psoas from pressure. There is apt to be pain in the groin and down the front of the thigh from pressure on the anterior crural nerve, or on the crural branch of the genito-crural. It may be imperfectly compressed just abo\'e its termination at the middle of Poupart's ligament, but, as is the case with the common and internal iliacs, the circulation through it is better controlled by pressure on the abdominal aorta. The line of the vessel extends from a point half-way between the pubic symphysis and the anterior superior spinous process to a point a little below and to the left of the umbilicus. The course of the external iliac corresponds to the lower third of this line, the upper two-thirds representing the line of the common iliac. Ligation of the vessel has been done for aneurism of the common femoral, for hemorrhage, and as a palliative in malignant growths or in elephantiasis of the extremity. Like the other iliacs, it may be approached by either: (i) the intraperitoneal; or (2) the extraperitoneal route. 1. The incision should be made in the semilunar line, and will thus cross the line of the vessel obliquely. Its lower end should reach Poupart's ligament. Its length will vary (with the thickness of the abdominal wall) from three inches to four inches. The superficial circumfle.x ilii and the deep epigastric arteries may require ligation. The intestines are displaced upward. At the left side the sigmoid flexure, and on the right the termination of the ileum, may be found in close relation to the vessel. On both sides the spermatic vessels cross it, and their distention (analogous to that of the mesenteric vessels spoken of in connection with ligation of the left common iliac) (page 808), when deprived of their peritoneal support, has been noted (Makins). The peritoneum over the vessel — on the left side possibly a part of the sigmoid mesocolon — is divided parallel with the long axis of the artery, and the needle is passed from the vein. 2. Ligation by the extraperitoneal method — still preferred by many surgeons in the case of this vessel — is done through an incision parallel with Poupart's ligament, but slightly convex downward, beginning one inch above the anterior superior spinous process of the ilium and ending at the outer pillar of the external abdominal ring. After dividing the abdominal muscles and the transversalis fascia, the separation of the peritoneum from the iliac fascia is begun near the outer extremity of the wound, where the subperitoneal areolar tissue is more abundant and the connection of the peritoneum and the fascia less intimate. After the detachment has been effected (chiefly by means of a finger), the vessel is exposed with the vein lying behind it above and to the inner side near Poupart's ligament, and the anterior crural nerve some distance to the outer side. The needle should be passed from within outward. The collateral circulationis carried on from above the ligature by (a) the lumbar; (b) the obturator; (c) the sciatic; (rf) the gluteal; {e) the internal pudic; and (_/) the internal mammary and lower intercostals anastomosing respectively with (a) the deep circumflex iliac; (1^) the internal circumflex; (c) the perforating (profunda); (rf) the external circumflex; (f ) the external pudic (femoral); and {/) the deep epigastric from below. S20 HUMAN ANATOMY. I. The Deep Epigastric Artery. — The deep epigastric artery (a. epigastrica inferior) (Fig. 728) arises from tlie anterior surface of tlie external iliac, a short distance above where it passes beneath Poupart's ligament. Immediately after its origin it bends downward and medially to pass the lower border of the internal abdominal ring, being crossed in this situation by the vas deferens in the male and the round ligament of the uterus in the female. It then curves upward and medially along the medial border of the internal abdominal ring and ascends along the outer border of Hesselbach's triangle (page 526), of which it forms the lateral boundary. Throughout this portion of its course it lies between the peritoneum and the trans- versalis fascia, but at about the level of the fold of Douglas, in the posterior surface of the sheath of the rectus abdominis, it pierces the fascia and ascends between the muscle and the posterior layer of its sheath, eventually entering the substance of the muscle, w here it terminates by anastomosing \\ith the superior epigastric branch of the internal mammary artery. Branches. — Throughout its course the deep epigastric arterj- gives off a number of branches. ( <; ) The cremasteric branch ( a. spermatica externa in the male, a. ligamenti teretis in the female) is gi\en off a short distance beyond the origin of the deep epigastric and accompanies Fig. 72S. Anterior superior spine of i!i abdominis, rned downwartl th part of ab- External iliac artery- External iliac vein Upper part of left broad ligament passing over ex- ternal iliac artery as the in- fundibulo-pelvic ligament Common iliac artery Common iliac vein Edge of ovary Round ligament of Cut edge of broad ligament Portion ot lelt half pelvis of female subject viewed from above and right side, showing obturator arter>- arising from deep epigastric. the Spermatic cord or round ligament of the uterus through the inguinal canal. In the male it supplies the cremaster muscle and the spermatic cord, anastomosing with the spermatic and deferential arteries, and in the female, in which it is small, it supplies the lower part of the round ligament and terminates in the labia majora by anastomosing with branches of the super- ficial perineal arter3\ (d) The pubic branch ( ramus pubicus) arises a short distance beyond the cremasteric and, passing either above or below the femoral ring, passes downward and inward upon the posterior surface of the os pubis, where it may anastomose with the pubic branch of the obturator. It is by the anastomosis and enlargement of this arter>- and the pubic branch of the obturator that the latter vessel comes to arise so frequently from the deep epigastric (page 814). And even when the obturator has its normal origin, the anastomosis may render the pubic branch of the deep epigastric of considerable importance in the operation for the relief of femoral hernia. (r) Muscular branches, variable in number, are given off, for the most part, from the outer side of the artery and supply the muscles of the abdominal walls. They anastomose with branches of the lower intercostal and lumbar arteries. id) Cutaneous branches, also variable in number, pierce the rectus and the anterior wall of its sheath and supply the skin of the abdomen near the median line. THE FEMORAL ARTERY. 821 Variations.— The deep epigastric may arise from the e.xternal iliac higher up than usual, — as high, indeed, as a point 6 cm. {2}i in.) above Poupart's ligament. In such cases it pa-sses downward and forward upon the anterior surface of the e.xternal iliac to reach the abdominal wall. It may also arise below its usual position, — that is to say, from the coinmon femoral artery, — and it may be given off from a trunk common to it and the deep circumflex iliac. In addition to being frequently the origin of the obturator (page S14), it may be given off from that artery as a result of the enlargement of the anastomosis of the pubic branches of the two arteries and the subsequent degeneration of the proximal portion of the deep epigastric. Occasionally it gives origin to the dorsal artery of the penis or clitoris, an arrangement which also results from its relation to the obturator, from which this artery sometimes arises. 2. The Deep Circumflex Iliac Artery. — The deep circumflex iliac artery (a. circumflexa ilium profunda) (Fig. 728) arises from the outer surface of the external iliac, a little below the deep epigastric. It passes outward along the lower border of Poupart's ligament, enclosed in a sheath formed by the iliac fascia, and opposite the anterior superior spine of the ilium, or it may be a little beyond it, divides into an ascending and a horizontal branch. Branches. — In its course it gives branches to the muscles of the abdominal wall and, at the anterior superior spine of the ilium, to the upper part of the sartorius and to the tensor vaginas femoris. (a) The ascending branch pierces the transversalis muscle and ascends directly upward between that muscle and the internal oblique. It sends branches to both these muscles, as well as to the external oblique and the integument, and terminates by anastomosing with the lumbar arteries and with the tenth aortic intercostal (subcostal). {6) The horizontal branch continues the course of the main stem. It lies at first a little below the crest of the ilium, but later ascends and perforates the transversalis muscle, passing onward upon the crest of the ilium between that muscle and the internal oblique. It gives ofT branches which supply the abdominal muscles and anastomose with the lumbar arteries, and terminates by anastomosing with the lumbar branches of the ilio-lumbar. Variations. — The deep circumfle.x iliac artery may arise from a common stem ■.vith the deep epigastric or from the upper part of the common femoral artery. Not infrequently it gives rise to a branch, shortly after its origin, which passes upward upon the anterior abdominal wall, un- derneath the transversalis fascia, parallel and lateral to the deep epigastric. This lateral epi- gastric artery, as it has been termed, is occasionally of considerable size, in which case the ascending branch of the circumflex iliac may be more or less reduced. It may ascend to the level of the umbilicus or even above that point, sending branches to the muscles of the abdom- inal wall. Anastomoses of the External Iliac. — Opportunities for the development of a collateral circulation after ligation of the external iliac artery are afi^orded by the anastomoses of its deep epigastric branch with the superior epigastric branch of the internal mammary, with the lower aortic intercostals, and with the lumbar arteries. The deep circumfle.x iliac also makes connections with the lumbar arteries by its ascending and lateral epigastric branches, and, furthermore, anastomoses with the ilio-lumbar and gluteal branches of the internal iliac. Another connection with the internal iliac system is made by the anastomoses of the pubic branches of the deep epigastric and obturator arteries. Anastomoses between branches of the internal iliac and the femoral arteries are also of importance in this connection, but will be described in connection with the femoral artery (page 831). THE FEMORAL ARTERY. The femoral artery (a. femoralis) ' (Figs. 729, 732) is the continuation of the external iliac below Poupart's ligament. Its course is almost vertically downward, with a slight inclination inward and backward, and may be indicated by a line drawn from a point in Poupart's ligament midway between the symphysis pubis and the anterior superior spine of the ilium to the adductor tubercle upon the inner condyle of the femur, when the thigh is fle.xed upon the pelvis and rotated outward. It ter- minates at about the junction of the middle and lower thirds of the thigh, where it passes through the adductor magnus muscle, close to the inner surface of the femur, to become the popliteal artery'. 822 HUMAN ANATOMY. Fig. 729. Sartorius. stump — Anterior crural nerve Superficial circumtiex iliac Rectus femoris, stump Iliacus Ascending branch of external circumtlex' Deep femoral artery External circumflex arterj- Transverse branch of external circumflex Rectus femoris, cut Vastus externus Superficial epigastric Femora] artery Deep external pudic ■Superficial ex- ternal pudic Femoral vein -Adductor longus Aponeurotic roof of Hunters canal Adductor magnus Anastomotica magna — superficial branch Inner hamstring muscles ■Vastus internus From anastomotica magna Tendon of sartorius Anastomotica magna of front of thigh; superficial dissection. THE FEMORAL ARTERY. 823 Relations. — ^^In its uppermost part, for a distance of about 3 cm. (ij^ in.), the femoral artery, together with the accompanying vein, is enclosed within a sheath formed by a prolongation of the transversalis and iliac fasciee below Poupart' s liga- ment. TYasfemoi-al sheath is funnel-shaped and is divided by partitions into three compartments, the most lateral of which contains the artery, the middle one the femoral vein, while the medial one forms what is termed the femoral or crural canal (page 625). Below, the walls of the sheath gradually pass over into the con- nective tissue which invests the vessels. In the upper half of its course the femoral artery lies in Scarpa's triangle (page 639)1 while in its .lower half it is contained within a space known as Hunter' s cajial, situated between the adductor magnus and vastus medialis muscles and covered in by the sartorius. In Scarpa's triangle the relations of the artery are as follows. Anteriorly, it is covered by the integument, the superficial fascia, and the fascia lata, the inner margin of the attenuated portion of the latter fascia, which is known as the cribriform fascia, overlapping it at about the junction of its upper and middle thirds. Superficial to the fascia lata are some of the superficial inguinal lymphatic nodes and the superfi- cial circumflex iliac vein, while deeper and resting upon the upper part of the artery is the crural branch of the genito-crural nerve, and towards the apex of the triangle the internal cutaneous nerve. Posteriorly , the artery rests upon the tendon of the ilio- psoas muscle, which separates it from the capsule of the hip-joint, and lower down it lies upon the pectineus muscle. Throughout the lower part of the triangle it is sep- arated from the adductor longus muscle by the femoral vein and by the deep femoral artery and vein. Medially, it is in relation abo\'e with the femoral vein and below with the adductor longus; late^-ally, with the ilio-psoas muscle and the leash of nerves formed from the anterior crural nerve. In Hunter's canal the artery lies beneath the sartorius muscle and is crossed obliquely from without inward by the long saphenous nerve. Posteriorly it rests upon the adductor longus and the adductor magnus, and also upon the femoral vein which, below, comes to lie somewhat laterally as well as posterior to it and is firmly united to the artery by dense connective tissue. To the inner side of the artery is the ad- ductor longus above and the adductor magnus below, while to its outer side, and ■ partly overlapping it, is the vastus internus. Branches. — In Scarpa's triangle the femoral artery gives off (i) the super- ficial epigastric, (2) the superficial circunifiex iliac, (3) the siiperficial external ptidic, (4) the deep extej-nal pudic, (5) the profiu7ida fie9notis, and (6) muscular branches. In Hunter's canal it gives off additional muscular branches and, just before perforating the adductor muscle, (7) the anastomotica magna. The profunda femoris so much surpasses in size the other branches of the femoral that the latter artery is frequently regarded as bifurcating at the point where th-s vessel arises. The pordon of the artery above the bifurcation is then termed the common feni07-al, while its continuation through Scarpa's triangle and Hunter's canal is known as the supetficial fiemoral. Variations. — A comparative study of the arteries of the thigh reveals the fact that the exist- ence of a well-developed femoral artery forming the main blood-channel for the leg is a condi- tion characteristic of the mammalia. In the lower vertebrate groups the sciatic is the principal artery of the thigh, e.xtending throughout the whole length of its flexor surface and becoming continuous below with the popliteal artery, the femoral arterj' being comparatively insignificant and terminating as the profunda femoris. The peculiar course of the mammalian femoral, start- ing, as it does, as an artery of the extensor surface of the limb and later perforating the adductor magnus to become continuous with the popliteal upon the flexor surface, is to be regarded, therefore, as a secondary arrangement, and its history is somewhat as follows. While the sciatic is still the principal vessel of the thigh and retains its connection with the popliteal below, a branch is given off from the femoral which accompanies the long saphenous nerve through Hunter's canal and down the inner surface of the crus, having in this lower por- tion of its course a superficial position corresponding with that of the nen-e. Near the lower part of Hunter's canal this vessel, which is known as the saphenous artery, gives off a branch which perforates the adductor magnus and unites with the sciatic, producing an arrangement which, in various degrees of development, may be regarded as characteristic of the mammalia as a group. In man, however, the process goes a step further in that, correlatively with an enlargement of the anastomosis between the saphenous and the sciatic, there is a diminution of the main stem of the latter vessel, so that eventually it becomes reduced to the slender a. comes 824 HUMAN ANATOMY. nerz'i ischiadici which loses, as a rule, its continuity with the popliteal. That artery now appears to be the continuation of the saphenous (femoral), since there occurs a degeneration of the saphenous below the point where the anastomosing branch is given off. These changes are shown diagrammatically in Fig. 748, (page 849) from which it willbe seen that the femoraf artery below the origin of the profunda is the upper part of the original a. saphena, the continuation of that vessel down the crus being represented only by the superficial branch of the anastomotica magna. The principal variations which are shown by the femoral artery are associated with these changes which it has passed through in its development, and represent a cessation of the devel- opment at one stage or other of its progress. Thus, as already pointed out (page 815), the comes nervi ischiadici may remain the principal vessel of the thigh, the femoral terminating in the profunda femoris. Or the development may proceed to the formation of the a. saphena, which may ari.se either immediately above the profunda femoris, in such case the superficial femoral being wanting and the comes nervi ischiadici still well developed, or else from the lower part of the femoral, just before it pierces the adductor muscle. From this point the vessel, when fully develoi)ed, is continued onward with the long saphenous nerve between the adductor rrmgnus and the vastus medialis, and below the knee-joint perforates the crural fascia and is continiied superficially down the inner side of the crus, accompanying the long saphenous nerve and vein to the internal malleolus, where it makes connections with the posterior tibial artery and may sometimes persist as a branch of that vessel. In addition to these anomalies, the femoral artery frequently gives off branches which nor- mally arise from other vessels. Thus it may give rise to the deep epigastric or the deep cir- cumfle.x iliac, normally branches of the e.xternal iliac, or to the e.xternal or internal circumflex, normally branches of the profunda femoris. It has also been observed to give origin to the ilio- lumbar artery. Practical Considerations. — The femoral artery is more often wounded than the brachial on account of the position of its upper half — in Scarpa's triangle — ^on the anterior surface of the limb, and of its relatively more intimate relation to the bone at its lower end. In the latter region it has been opened by spicules of necrotic bone. Ne.xt to the popliteal, it is more frequently the subject of aneurism than any other e.xternal arterial trunk. On account of the close relation of the l\-niphatic glands in and near the groin, the vessel has been opened by ulceration and sloughing in bubo or in carcinoma, and has been involved in sarcomatous growths. The same relation has caused the aneurism to be mistaken for a glandular abscess, an error which has occurred oftener in connection with this A'essel than with any other. Compression of the femoral artery has yielded very satisfactory results in the treatment of popliteal aneurism. The pressure is best applied in a direction backward and outward just below the inferior edge of Poupart's ligament where the vessel can be flattened against the brim of the pelvis — the upper margin of the acetabulum — just outside the ilio-pectineal eminence, only a very thin portion of the ilio-psoas muscle intervening. A little lower, a more fleshy portion of that muscle separates it from the head of the femur, and yet lower the artery has back of it the still less resistant mass of the pectineus and adductor bre\'is muscles, and more force will be required to obliterate its lumen. At the ape.x of Scarpa's triangle the pressure must be directed backward and somewhat more outward, and a little lower still more directly outward, the artery at these places being compressed against the femur, the vastus internus intervening. E.xtreme fle.xion of the thigh upon the trunk will occlude the femoral, and has been used successfully in the cure of popliteal aneurism and for the temporary arrest of hemorrhage. Ligation of the vessel may be done : i. Between Poupart's ligament and the origin of the profunda — the common femoral {vide supra). 2. At the ape.x of Scarpa's triangle. 3. In Hunter's canal. T. The common femoral is rarely ligated e.xcept as a preliminary to some forms of hip-joint amputations, or for the relief of hemorrhage. In aneurism of the upper portion of the superficial femoral the external iliac is ordinarily preferred because of (a) the possibility of a high origin of the profunda. The common femoral is normally only about one and a half inches in length. If its bifurcation occurs above the usual level — the most common variation — the ligature would be in dangerously close pro.ximity to so large a trunk. (/') The presence of a number of smaller branches — the deep epigastric and deep circumflex iliac coming off immediately above Poupart's ligament, the superficial epigastric, circumflex iliac, and external pudic, the deep e.xternal pudic, and occasionally one of the circumflex arteries (especially the internal), THE FEMORAL ARTERY. 825 arising from the femoral. . This circumstance hkewise interferes with the firmness anci security of the clot formation after ligature, {c) The fact that ligature of the common femoral cuts off the chief blood-supply to the lower limb also militates against its selection and leads to the choice of the superficial femoral whenever pos- sible, so as to permit the profunda and its branches to maintain a sufficient vascular current. The incision should be begun on the abdomen a little above Poupart's ligament, midway between the anterior superior spine and the symphysis pubis, and e.xtend downward to about two inches below the ligament in the line of the vessel — vide supra. The structures to be avoided in approaching the artery are the glands and veins that lie in the fat over the cribriform fascia, the superficial epigastric artery and, when the sheath is exposed, the crural branch of the genito-crural nerve lying upon it near its outer side. The vein is in close contact with the inner side of the artery. The needle should be passed from within outward. The collateral circulation will be carried on from above the ligature by (^a) the internal pudic (from the internal iliac) ; (b) the gluteal and sciatic (from the same vessel); (c) the deep cir- cumffe.x iliac, from the Fig. 730. external iliac ; (rf)theob- / ^ turator, and (d?) the comes nervi ischiadici, anasto- mosing respectively with («) the superficial and deep external pudic : {b) the circumflex and per- forating arteries ; {c) the e.xternal circumflex ; (d) the internal circumflex ; and (e) the perforating, all from either the common, superficial, or deep fem- oral. 2. At the apex of Scarpa's triangle an inci- sion with its centre at the apex of the triangle is made on the line of the vessel, the thigh being ab- ducted and rotated out- ward, the hip a little flexed, the knee well flexed, and the leg resting on its outer surface. Be- fore reaching the deep fascia, the long saphenous ' vein or the external super- ficial femoral vein, may be met with and should be avoided. After opening the deep fascia the fibres of the inner edge of the sartorius should be exposed, and may be recognized by their oblique course. That muscle should be displaced outward, the vascular groove containing the vessel and some fatty areolar tissue identified, and the sheath exposed. The internal cutaneous branch of the anterior crural nerve in front, and the nerve to the vastus internus and the long saphenous nerve externally, should be avoided, and the sheath opened. The needle should be passed from without inward to avoid the vein, which here lies behind and to the outer side of the artery. 3. To reach the vessel in Hunter's canal, the limb being in the position above described, an incision is made on the line of the vessel extending from the apex of the triangle to about three inches above the internal condyle. The long saphenous vein should be avoided. The deep fascia is opened, and the outer edge of the sartorius identified. The only structure that could be mistaken for it is the vastus internus, ; triangle, showing 826 HUMAN ANATO.MY. Fig. -Adductor longus muse I -Femoral vein -Internal ciilaneo s nerv -Internal sapheno IS ner\ -Femoral artery Roof of Hunter- canal — Internal saphei the fibres of which run obHquely outward instead of inward. The sartorius is displaced inward and the thigh more strongly abducted, when the tension on the adductor fibres — the adductor magnus and the lower edge of the adductor longus — will clearly define the lower — inner — border of Hunter's canal. The aponeurotic roof of the canal stretch- ing across to the vastus internus is pierced by the in- ternal saphenous nerve, which may be a useful guide. This aponeurosis is di- vided and the ^•essel exposed. The vein lies behind and somewhat to the outer side. The needle should be passed from without inward. The collateral ciirulatjoii after liga- tion of the superficial femoral is carried on from above by (a) the perforating and terminal branches of the profunda ; and i^b) the descending branch of the exter- nal circumflex anas- tomosing respectively with {a) the superior articular and muscular branches of the popliteal ; and (b) the anastomotica magna and superior articular from below. 1. The Superficial Epigastric Artery. — The superficial epigastric artery (a. epigastrica supertjcialis) (Fig. 729) arises from the anterior surface of the femoral, about I cm. below Poupart's ligament. It is directed at first forward, but, after per- forating the fascia lata or sometimes the cribriform fascia, it bends upward over Poupart's ligament and ascends between the superficial and deep layers of the super- ficial abdominal fascia to the neighborhood of the umbilicus. It gives branches to adjacent inguinal lymphatic nodes and to the integument, anastomosing with the cutaneous branches of the deep epigastric artery. 2. The Superficial Circumflex Iliac Artery. — The superficial circumflex iliac artery (a. cncumtlexa iliitm siiperticialis ) (Fig. 729) arises from the anterior surface of the femoral, a little below the superficial epigastric, or from a common trunk with that artery. It perforates the fascia lata or the cribriform fascia and is then directed laterally more or less parallel with Poupart's ligament, extending almost as far as the anterior superior spine of the ilium. It gives branches to the adjacent inguinal lym- phatic nodes and to the sartorius muscle, and anastomoses with the cutaneous branches of the deep circumflex iliac. 3. The Superficial External Pudic Artery. — The superficial external pudic artery (a. pudenda externa supcrficialis) (Fig. 729) arises from the inner surface of the femoral artery and is directed inward and slightly upward towards the spine of the pubis. It pierces the cribriform fascia and, crossing over the spermatic cord or round ligament, sends branches to the integument above the pubes. It is then continued along the dorsal surface of the penis or clitoris, lateral and external to the dorsal artery of that organ, with which it anastomoses at the glans. It supplies branches to the integument of the penis and to the preputium clitoridis, and also gives branches to the scrotum or labium majus. 1 showing femoral and disappearing THE FEiMORAL ARTERY. 827 Fig. 732. Stump of sartorius Superficial circumflex iliac artery Rectus tendon Femoral artery Ascending branch of external circumflex anery Deep femoral artery Transverse branches of external circumflex artery Descending- branch of external circumflex artery Vastus externus Tendon of quadriceps extensor, cut Superficial epigastric artery- — Superficial ext. pudic artery Deep external pudic artery Femoral vein Pectineus — Penis—sectional surface Buttock Adductor longus .Semitendinosus Gracilis ■Adductor magnus Anastomotica magna -Anastomotica magna- superficial branch ■Popliteal artery Semimembranosus Inferior internal articu'ar artery Arteries of front of thigh ; deeper dissection. 828 , HUMAN ANATOMY. 4. The Deep External Pudic Artery. — The deep external pudic artery (a. pudenda externa profuiidaj (Fig. 732J arises from the inner surface of the femoral, either a little below the superficial external pudic or in common with that vessel. It passes medially beneath the fascia lata across the femoral vein and the pectineus and adductor longus muscles. It then pierces the fascia lata close to the ramus of the pubis and is distributed to the sides of the scrotum or labium majus, anastomosing with branches of the superficial external pudic and of the superficial perineal branch of the internal pudic. 5. The Deep Femoral Artery. — The deep femoral artery (a. profunda femoris) (Fig. 733) arises from the outer surface of the femoral, usually about 4 cm. belo.w Poupart's ligament, and at first is directed downward parallel to the femoral and to the outer side of that vessel. It then bends medially and passes obliquely behind the femoral artery and vein, and on arriving at the upper border of the adductor longus, passes behind that vessel and is continued downward between it and the adductor magnus, rapidly diminishing in size. Finally it perforates the adductor magnus and terminates in branches to the lower portions of the hamstring muscles. Relations. — .At first the profunda lies alongside the femoral and is, like it, su- perficial, having in front of it only the fascise and integument, together with some branches of the anterior crural nerve. Later it lies behind the femoral artery and the femoral and profunda veins, and still later the adductor longus and the adductor magnus. Posteriorly it rests at first upon the ilio-psoas and then successively upon the pectineus, the adductor brevis, and the adductor magnus. Branches. — The profunda femoris gives origin to the following branches : ( i ) the exlcrnal circumflex, (2) \\\^ internal circumflex, (3) the three /f)ybrn/'/«^ arteries. The terminal por- tion of the profunda, after it has pierced the adductor magnus, is sometimes spoken of as tlie fourth perforating artery. {a) The external circumflex artery (a. circumflexa femoris lateralis) is the largest of the branches of the profunda and arises from it a short distance beyond its origin. It is directed horizontally outward across Scarpa's triangle, resting upon tlie ilio-psoas muscle and passing between the superficial and deep branches of the anterior crural nerve. It then passes beneath the sartorius and rectus muscles and terminates by dividing into an a.scending, a transverse, and a descending branch. The ascending branch passes upward and outward to beneath the tensor vaginje femoris, running along the anterior trochanteric line of the femur, and terminates by anas- tomosing with the gluteal and the deep circumflex iliac arteries. It sends twigs to the neigh- boring muscles and to the hip-joint. The transverse branch is small and runs directly outward to below the greater trochanter, passing between the rectus and the cnireus muscles and through the substance of the vastus lateralis. It unites with branches of the sciatic, internal circumflex, and first perforating arteries to form the crucial anastomosis. The descending branch runs downward beneath the rectus muscle, along with the nerve, to the vastus lateralis, and usually extends to the neighborhood of the knee-joint, where it anastomoses with the superior external branch of the popliteus and assists in the formation of the circumpatellar anastomosis. It gi\-es branches to the rectus, crureus, and vastus lateralis. (b) The internal circumflex artery (a. circumflexa femoris medialis) arises from the inner surface of the profunda, very nearly opposite the external circumflex. It passes over the surface of the ilio-psoas and beneath the pectineus to reach the anterior surface of the neck of the femur. It then crosses the upper portion of the adductor brevis and adductor magnus and passes along the lower border of the obturator externus and, finally, upon the anterior surface of the quadratus femoris, where it divides into its terminal branches. {aa) The ascending branch (ramus ascendens) passes upward towards the digital fossa of the femur, sending branches to the capsule of the hip-joint and anastomosing with the sciatic and external circumflex arteries. (bb) The descending branch (ramus descendens) passes downward and curves around the lower border of the C|uadratus femoris to terminate in the upper portion of the hamstring mus- cles. This branch anastomoses with the sciatic, external circumflex, and first perforating ves- sels to form the crucial anastomosis. In addition, the internal circumflex in its course sends muscular branches to the adjacent muscles and also an articular branch (ramus acetabuli) to the hip-joint. (f) The three perforating branches arise in succession from the profunda and pass back- ward, curving around the inner surface of the femur. They perforate the adductor muscles close to the bone, and supply the hamstring muscles and the vastus externus, anastomosing with one another and with neighboring vessels. THE FEMORAL ARTERY. 829 {aa) The first or superior perforating artery (a. perforans prima) is generally the largest of the three, and arises just as the profunda passes behind the adductor longus. it either passes through the adductor brevis or between that muscle and the pectineus and pierces the adductor Fig. 733. Superficial < Femoral arter> Tendon of rectus Tensor vaginae femoris Ascending branch of external c; Profunda femi External circum Transverse branches of Vastus extern First perforating artery- Adductor brevib Second perforating artery Vastus internus Third perforating artery- Adductor Ion Fourth perforating artery. Deep branch of anastomotica magna Adductor magnus Gracilis Superficial epigastric artery Psoas muscle Pectineus — Spermatic cord Obturator artery Adductor longus Adductor brevis Corpus spongiosum of penis Obturator externus Internal circumflex arterj' Adductor magnus Femoral artery Semimembranosus Superficial branch of anastomotica magna Deep femoral artery and its branches, magnus, and then divides into an ascending and a descending branch, the latter of which anasto- moses with the ascending branch of the second perforating, while the former assists in the for- mation of the crucial anastomosis. 830 HUiMAN ANATOMY. {bd) The second or middle perforating artery (a. perforans secunda) arises a little below the first and, after piercing the adductor bre\ is and the adductor magnus, divides into an ascending and a descending branch which anastomose respectively with the descending branch of the first and the ascending branch of the third perforating. A nutrient artery to the femur is usually given off from this vessel, although frequently it comes from the third perforating. (cc) The third or inferior perforating artery ^a. perforans tenia 1 arises usually on a level with the lower border of the adductor brevis. It pierces the adductor magnus and terminates, like the other perforating arteries, by dividing into an ascending and a descending branch. The ascending branch anastomoses with the descending branch of the second perforating, while the descending one anastomoses with branches from the terminal portion of the profunda. The nutrient artery to the femur is frequently given off by this branch. Variations. — The variations of the profunda and its branches are somew hat numerous, and to a very considerable e.xtent are largely associated with one another. In other words, there may be more or less dissociation of the various vessels of the profunda complex, one or other of them having an independent origin from the femoral, and, indeed, this process may occur to such an e.xtent that a profunda femoris as a definite vessel can hardh' be said to exist. The point of origin of the profunda from the femoral is stated to be usually about 4 cm. distant from Poupart's ligament, but the figure must be taken as a general a\erage from which there may be wide departures. Thus, in 430 limbs Quain found that the distance from Poupart's ligament of the origin of the profunda was between 2.5 and 5.1 cm. in 6S per cent., and of this number it was between 2.5 and 3 8 cm. in 42.6 per cent. It was distant less than 2.5 cm. in 24.6 per cent, of the limbs and more than 5.1 cm. in only 7.4 per cent. (Juain's figures are as follows : Origin at Poupart's ligament 7 cases. 0-1.3 cm. below Poupart's ligament 13 cases. 1.3-2.5 cm. below Poupart's ligament 86 cases. 2.5-3. 8 '^"1- below Poupart's ligament 183 cases. 3.S-5.icm. below Poupart's ligament . 109 cases. 5.1-6.3 cm. below Poupart's ligament 19 cases. 6.3-7.6 cm. below Poupart's ligament 12 cases. II 6 cm. below Poupart's ligament i case. Essentially similar results have been obtained by Srb and other observers, and it seems evident from the statistics that the origin of the profunda is more apt to be above than below the point taken as the avera.ge. One or other of the circumflex arteries may arise independently from the femoral, this con- dition occurring somewhat more frequently in the case of the internal circumflex than in that of the outer one, and the point of origin of the inde- pendent vessel may be either above or below that of the profunda. When it is the internal circum- flex which is the independent vessel, its origin is most frequently above that of the profunda; or per- haps it would be more correct to say that with an independent internal circumflex the origin of the profunda is apt to be somewhat below the typical point. With a high origin of the profunda, the external circumflex may be represented by two vessels, one of which arises from the profunda, while the accessory one springs from the femoral lower down. Occasionally both circumflexes may arise independently from the femoral, the profunda in such cases having usually a low origin, and one or other of the perforatin.g arteries may arise from the circumflexes. An extreme case of this nature, representing an almost complete dissociation of the profunda, has been described by Ruge, ( Fig. 734) in which the superior perforating arises from the internal circumflex and the middle one from the external circumflex, what may be termed the pro- funda arisin.g 9.7 cm. below Poupart's ligament and giving off only the inferior perforating. The internal circumflex may be very much reduced in size or even absent, its territory being suppHed by branches from the obturator artery. Occasionally, although rarely, one or other of the perforating branches arises directly from the femoral, and a similar origin has also been obser\-ed for the descending branch of tlie external circumflex. 6. The Muscular Branches. — The muscular branches frami musculares ) of the femoral artery are rather numerous and are distributed to all the muscles upon the front of the thigh. They are variable in number and position and do not call for any- special description. Fig. 734. Superficial perforating' Inferior perforating (profunda femoris) Diagram showing almost complete dissociation of profunda femoris. {Ruge). THE POPLITEAL ARTERY. 831 7. The Anastomotica Magna. — The anastomotica magna (a. genu suprema) (Fio-. 733) arises from the femoral, just before it passes through the adductor magnus. It passes" downward a short distance in front of the adductor magnus and divides into two branches, a superficial and a deep. Branches. — (a) The superficial branch (ramus saphenus) follows the course of the long saphenous nerve and, perforating with it the crural fascia, is supplied to the integument over the inner side of the knee and the upper portion of the leg. It anastomoses with the inferior in- ternal articular branch of the popliteal, then entering into the formation of the circumpatellar anastomosis. (6) The deep branch (ramus musculo-articularis) enters the substance of the vastus intemus and passes downward to take part in the formation of the circumpatellar ple.xus, also sending branches to the capsule of the knee-joint. Variations.— The anastomotica rnagna is occasionally given off from the upper portion of the popliteal artery. Occasionally it is continued some distance down the leg with the long saphe- nous nerve, representing in such cases more perfectly the original saphenous artery (page S49) ; or this vessel may be indicated by a series of anastomoses which accompany the nerve and vein and begin with the superficial branch of the anastomotica. Anastomoses of the Femoral Artery. — In the case of obliteration of the external iliac artery, blood may reach the femoral by means of the anastomoses of the iliac arteries already noted (page 821), and, in addition, byway of the anastomoses between the superficial and deep epigastrics and between the superficial circumflex iliac artery and the deep \'essel of the same name and the gluteal. The anastomoses between the external and internal pudics would also assist. If the obliteration of the femoral artery be above the origin of the profunda femoris, a collateral circulation may be established by the union of the branches of that vessel with the sciatic in the crucial anastomosis and also b}' the communication exist- ■ ing between the external circumflex and the gluteal and the deep circumflex iliac. If the obliteration be below the origin of the profunda, circulation will be main- tained through the anastomoses around the knee-joint, in which the descending branch of the external circumflex and the terminal portion of the profunda, on the one hand, and the anastomotica magna, on the other, participate. THE POPLITEAL ARTERY. The popliteal artery (a. poplitea) (Fig. 736) is the continuation of the femoral, and extends from the point where the latter pierces the adductor magnus to the lower border of the popliteus muscle, where it divides into the anterior and posterior tibial arteries. Its course is at first downward and slightly outv.'ard, but it soon becomes almost vertical, corresponding practically with the long axis of the popliteal space. Relations. — Anteriorly^ the popliteal artery is in relation to the posterior sur- face of the lower part of the femur, from which it is separated, howe\'er, by a layer of adipose tissue. Lower down it rests upon the posterior ligament of the knee-joint, and still lower upon the fascia covering the posterior surface of the popliteus muscle. Posteriorly, it is somewhat overlapped in the upper part of its course by the border of the semimembranosus, and below by the inner head of the gastrocnemius. In its pas- sage through the popliteal space, however, it is co\'ered only by the integument and fasciae, beneath which is a considerable amount of fatty tissue. About the middle of its course it is crossed obliquely from without inward by the internal popliteal ner\e, and throughout its entire length it has resting upon and firmly adherent to it the popliteal vein, which lies, however, slightly to its outer side abo\'e and to its inner side below. Internally, it is in relation from above downward with the semimembranosus, the internal condyle of the femur, the internal popliteal ner\'e, and the inner head of the gastrocnemius, and externally with the internal popliteal nen'e, the external condyle of the femur, the outer head of the gastrocnemius, and the plantaris. Branches. — The branches which arise from the popliteal artery are all small and may be arranged in three groups : (i) musadar, (2) articular, (3) cutaneous. Variations. — The popliteal artery occasionally divides into the tibial arteries above the upper border of the popliteus muscle, and more rarely the division is delayed until the artery has reached a point almost half-way down the leg. 832 HUMAN ANATOMY. FiG. imembranobus Practical Considerations. — The popliteal artery is rarely wounded because of its protected position on the posterior aspect of the limb and in the hollow of the ham. Its upper portion is overlapped by the outer border of the semimembranosus muscle, and its lower portion by the inner head of the gastrocnemius ; the inter- mediate portion, covered only by skin, fascia, and areolo-fatty tissue, is ^•ery deeply placed and is not more than an inch in length. It may be torn in luxation of the knee, or wounded in fracture of the lower end of the femur, or during certain opera- tions, as osteotomy of the femur for genu valgum. Laceration or wound of this vessel is more dangerous than a corresponding injury to the brachial at the bend of the elbow, because of the greater pro.ximity — in the case of the popliteal — of the branches on which the chief anastomotic supply depends ; and because of the unyielding character of the walls of the space in which the effused blood is confined. Aneurism of the popliteal arterj' comes next in frequency to aneurism of the thoracic aorta. This is due {a) to the frequent minor strains occurring during flexion and extension of the knee. If extreme, the former mo^■ement bends the artery at such an acute angle that the flow- of blood through it is arrested and the pressure above this point greatly increased ; and the latter may so stretch the \essel longi- tudinally that if its elasticity is at all diminished by ather- omatous changes the inner and middle coats are thinned or ruptured. (^) The lack of muscular sup- port which the artery — sur- rounded by loose cellular tissue^recei^es also favors the development of aneur- ism, (f ) The arter}' is said to be unusually liable to ath- eromatous degeneration, (rf) It divides a short dis- tance below into two vessels, thus increasing the blood-pressure above the bifurcation, (e) Its course is cur\ed (like that of the aortic arch), and hence the pressure 'is irregularly distributed. (_/) The ten- dinous opening in the adductor magnus, through \\hich the vessel runs, con- stricts it slightly at each pulse-beat and tends — as in the case of the abdominal aorta below the hiatus aorticus — to produce a little dilatation below that level. As both these vessels have been said to be especially weak in these regions, it may be possible that some trifling but oft-repeated interference with the vasa vasorum favors degenerative changes by slightly diminishing the blood-supply to the \essel walls. Aneurism may occur suddenly, with a sensation resembling that produced by a blow with a whip. It may develop slowly, and, if it takes a fonvard direction, with symptoms simulating rheumatism on account of the pressure upon the posterior ligament of the knee-joint — i.e., dull pain, stifTness, semi-flexion of the knee, inability to extend the joint freely. If it develops in the opposite direction, the absence of resistance causes the early appearance of a characteristic pulsating tumor with bruit and the usual signs of aneurism. It should not be confused with an enlarged bursa <^page 647), the subject of transmitted pulsation, or with tumor or abscess overlying THE POPLITEAL ARTERY. 833 the artery and similarly influenced. Ultimately there is apt to be oedema of the leg from interference with the venous circulation, or erosion of the posterior lower sur- face of the femur, or great pain with weakness of the leg from pressure on the inter- nal popliteal nerve, or even moist gangrene if the aneurism has leaked or burst and the venous current has been cut ofi by the pressure of the effused blood confined for a time within narrow limits and under great pressure by the fascia of the region (page 646). Compression of the popliteal may. be effected directly at its upper end by pres- sure forward, so that it is flattened out against the femur, only a little fatty connective tissue intervening. It is almost impossible, however, to avoid including the thick- walled vein which is nearer the surface and very closely attached to the artery. Compression is therefore almost in\-ariably applied to the common femoral (page 824). On account of the shortness of the popliteal^-and the consequent proximity of a ligature to the diseased portion, if the vessel itself is tied — the superficial femoral at the point of election — the ape:i of Scarpa's triangle — is usually selected for liga- tion when that becomes necessary. Ligation of the popliteal artery is effected at either : (i) its upper, or (2) its lower third, the depth of the middle portion and the density of the lateral fascial border of the space in which it lies rendering it unsuitable for operation. 1. The patient being prone with the leg extended, an incision is made along the external border of the semimembranosus muscle, beginning at the junction of the middle and lower thirds of the thigh. The skin and fascia and some fatty tissue having been divided, the muscle is drawn inward, and the vessel will be found with the internal popliteal nerve external to it and much more superficial, and the vein external and behind it, — i.e., nearer the surface of the popliteal space — and closely adherent. The needle is passed from without inward. 2. An incision is made beginning opposite the line of the articulation a little external to the middle of the popliteal space, the inner head of the gastrocnemius being slightly larger than the outer head. The external saphenous vein lying in the superficial fascia is drawn to one side, the fascia is divided, and the two heads of the gastrocnemius are exposed and separated with the finger, the knee being a litde flex'ed so as to relax them. At the bottom of the interval between them will be found the nerve and vein lying to the inner side of the artery and somewhat superficial to it. The needle is passed from within outward. The collateral circulatioti is carried on from above the ligature by means of (a) the superior articulars ; (<5) the anastomotica magna ; {c) the descending branch of the external circumflex and the terminal portion of the profunda anastomosing respectively with (a) the inferior articulars ; {b) the tibial recurrent ; and (<:) the superior fibular and branches of the popliteal. The rete patellae takes part in this anastomosis. 1. The Muscular Branches. — These (Fig. 736) are arranged in two groups, and are supplied to the muscles which bound the popliteal space. The siiperior group consists of a variable number of small vessels which pass to the biceps, semimembra- nosus, and semitendinosus, while the inferior group is composed of some small branches which pass to the popliteus muscle, and two larger vessels, the largest of all the vessels which arise from the popliteal, which pass respectively to the inner and outer heads of the gastrocnemius, and are termed the sural arteries (aa. surales). They arise just as the popHteal is passing beneath the inner head of the gastrocnemius. 2. The Articular Branches. — These (Fig. 736) are five in nurnber, four being arranged in pairs, two above and two below, while the fifth is unpaired or azygos. The paired branches wind around the femur and the capsule of the knee- joint towards the front, where they anastomose with one another and with adjacent vessels to form a rich circumpatellar anastomosis. They give off branches to the capsule of the knee-joint and also to the neighboring muscles. (a and b") The internal and external superior articular branches faa. genu superior medialis et lateralis) arise opposite each other and pass transversely abo\-e the corresponding heads of the gastrocnemius. The external one then passes beneath the biceps and winds around the femur 53 834 HU.MAX ANATOMY. above its external condyle, embedded in the substance of the vastus externus, dividing finally into branches which take part in the formation of the circumpatellar anastomoses. The termi- nation of the internal branch is similar, and its course is beneath the semimembranosus and through the tendon of the adductor magnus into the substance of the \astus internus. (c) The internal inferior articular branch (a. genu inferior niedialis) arises about opposite or a Httle above tlie Hne of the tibio-femoral articulation and courses downward and inward over the surface of the po]iHteal muscle, beneath the inner head of the gastrocnemius. It passes beneath the internal lateral ligament of the knee-joint and winds around the tuberosity of the tibia to join the circumpatellar anastomosis. (d j The external inferior articular branch (a. genu inferior lateralis) arises a little lower down than its fellow and passes almost transversely outward, at first beneath the external head of the gastrocnemius and the plantaris, and winds around the outer tuberosity of the tibia, beneath the long internal lateral ligament of the knee-joint, to join the circumpatellar anastomosis. (e) The azygos articular branch i a. genu media ) is the smallest of all the articular branches. It arises either from the anterior surface of the popliteal or from the external superior articular branch, and pierces the posterior ligament of the knee-joint to be distributed to the crucial, mucous, and alar ligaments. The circumpatellar anastomosis (rete patellae) (Fig. 732) is a rich net-work of vessels which occurs in the superhcial fascia surrounding- the patella, and from which branches are sent to the patella, the capsule of the knee-joint, and the neighboring muscles. The following vessels take part in its formation. From above, the anasto- motica magna from the femoral rnd the descending branch of the external circumfle.x; from the sides, the internal and external superior and the internal and external inferior articular branches of the popliteal and the muscular branches of the same artery ; and from below, the anterior tibial recurrent. 3. The Cutaneous Branches. — These are variable in origin and number and are distributed to the integument covering the popliteal space and the tipper part of the calf of the leg. One of them occasionally attains a considerable size and is termed the posterior saphenous artery. It accompanies the short saphenous vein down the back of the cms, sending off branches to the adjacent integument. The Collateral Circulation of the Popliteal Artery. — The passage of blood to the leg after ligation of the popliteal artery is effected by means of the rich anastomosis which exists around the knee-joint, and in w hich the branches of' the popliteal take part. In addition to these, however, it also receives from above the anastomotica magna, the descending branch of the external circumflex, and the terminal portion of the profunda artery, while there pass to it from below the superior fibular and the anterior and posterior tibial recurrent arteries. THE POSTERIOR TIBIAL ARTERY. The posterior tibial artery- (a. tibialis posterior) (Fig. 736) is the direct con- tinuation of the popliteal down the posterior surface of the leg. It begins at the bifurcation of the popliteal at the lower border of the popliteus muscle and passes almost vertically downward, under cover of the more superficial muscles of the calf, to the groove between the inner malleolus and the os calcis, where, opposite the tip of the malleolus, it terminates by dividing into the internal and external plantar arteries. Its course may be indicated by a line drawn from the centre of the popli- teal space to a point midway between the inner malleolus and the os calcis. Relations. — Antcriorlw the artery rests in succession, from above downward, upon the tibialis posticus, the flexor longus digitorum, the posterior surface of the lower part of the tibia, and the internal lateral ligament of the ankle-joint. It is closely bound down to the muscles upon which it rests by the layer of the deep fascia which covers them, the thickness and density of this fascia increasing towards the lower part of the leg. Posteriorly, it is covered by the soleus and gastrocnemius throughout the greater part of its course, but in the lower third of the leg it is super- ficial, being covered only by the skin and fascice, except just before its termination, where it lies beneath the internal annular ligament and the origin of the abductor hallucis. A short distance below its commencement it is crossed obliquely, from within outward, by- the posterior tibial nerve. Internally , it is in relation with the posterior tibial nerve for a short distance above, and in the malleolar groove it has THE POSTERIOR TIBIAL ARTERY. Fig. 736. 835 Semitendinosus Superior internal articular artery Gastrocnemius — Inferior internal articular Internal lateral ligament Posterior tibial artery Popliteal artery Superior external articular artery Azygos articular artery Sural branches —Inferior external articular Plantaris Gastrocnemius— outer head Tendon of popliteus - Anterior tibial artery Peronealartery Soleus, turned aside Flexor longus hallucis tendon Flexor longus hallucis Anterior peroneal artery Communicating branch Tendon of peroneus longus Peroneus brevis Flexor longus hallucis Tendo Achillis External calcanean (posterior peroneal) branches — -Internal calcanean branch Plantar fascia and flexor bre^ digilorum Tendon of flexor longus digitorum Arteries of posterior surface of right leg. 836 HUMAN AxNATOMY. internally and in front of it the tendon of the flexor longus digitorum, and internal to that the tendon of the tibialis posticus. Exteryially, the posterior tibial nerve accom- panies it throughout the greater portion of its course, and at the ankle-joint the nerve lies external and posterior to the artery, between it and the tendon of the flexor longus hallucis. The artery is accompanied throughout its course by two \enae comites which lie respectively to its outer and inner side. Branches. — In addition to numerous viuscular branches which are distributed to the neighboring muscles, and cutaneous branches to the inner and posterior sur- faces of the leg, the posterior tibial gives origin to ( i ) a nidriait branch to the tibia, (2) the peroneal artery, (3) a communicating branch, (4) an internal malleolar branch, (5) an intetnal calcaneal and the two terminal branches, (6) the internal, and (7) \}ci' of the flexor surface of the leg and the direct continuation of the popliteal, developmentally the posterior tibial is a secondary vessel, the original main vessel being the peroneal. The historj- of the posterior tibial seems to have been somewhat as follows. The saphenous artery, whose origin has been mentioned in connection with the variations of tlie femoral arterj- (page 823), in the lower part of the leg winds around to the posterior surface and passes behind the internal malleolus, where it termi- nates by dividing into the plantar arteries. From the upper part of the peroneal artery a branch arises which passes down the tibial side of the leg, beneath the superficial flexor muscles, and at the internal malleolus anastomoses with the saphenous. This vessel is the posterior tibial, and, its calibre enlarging, exceeds that of the peroneal, which thus sinks to the rank of a branch of the artery to which it gave birth. A- reason for this increase of calibre in the posterior tibial is to be found in the degeneration of the saphenous artery (page 849), whereby the tibial be- comes the channel of supply for the plantar arteries, which seem to be its continuation. The majority of the principal variations of the posterior tibial are readily explained in the light of such a history. Thus there may be no posterior tibial, or it may be represented by a small vessel whose distribution is confined to the upper part of the leg. In such a case, as the saphenous artery degenerates, anastomoses between it and the terminal portion of the pero- neal may enlarge so that the plantar arteries come to take their origin from that vessel. Or, again, the development of the posterior tibial may proceed normally, but the lower portion of the saphenous may not degenerate completely, but persists, as has been observed, as a branch of the tibial, passing upward upon the leg in company with the long saphenous nerve. Other variations of the posterior tibial which have been observed, however, cannot appar- ently be explained as resulting from modifications of the normal course of development, but are rather to be regarded as progressive variations due to the enlargement of what are usually more or less insignificant anastomoses. Of this nature is the origin from the posterior tibial, at about the middle of the leg, of a branch which pierces the interosseous membrane and divides into an ascending and a descending branch, which together represent the anterior tibial arterj'. Or, again, the posterior tibial has been observed to perforate the lower part of the interosseous membrane and to be continued down the dorsum of the foot as the dorsalis pedis artery, the plantar arteries arising from the peroneal. Occasionally, also, the posterior tibial may terminate by inosculating with the peroneal, probably by the enlargement of the communicating branch, the peroneal in this case also giving rise to the plantar arteries. The high and low origins of the posterior tibial have already been mentioned in connection with the variations of the popliteal (page 831). Practical Considerations. — The posterior tibial artery on account of its deep position beneath the large superficial calf muscles is rarely wounded and, by reason of the support which it receives in its upper two-thirds from those muscles and the deeper muscular layer on which it lies, and in its lower third from the dense fascia covering it, it is seldom the subject of aneurism. E.xcept for a short portion of its course immediately above the ankle, it is separated from the tibia by the deep calf muscles, and is therefore not often involved in fractures of that bone. The bifurcation of the popliteal is not infrequentlv the region at which an em- bolus carried down from the popliteal is arrested, and such a clot mav block both the tibial arteries. Their free anastomosis prevents gangrene if only one of them is occluded ; but if both are involved, and especially if the succeeding additions to the clot invade the anterior tibial recurrent — interfering with anastomosis from above — gangrene almost certainly follows. Compression of the posterior tibial is scarcely possible abo\'e its lower third. Above the ankle and behind the inner malleolus it may be flattened against the tibia by pressure directed outward and a little forward. Ligation of the posterior tibial mav be done at any part of its course, but in its upper third is an operation of some difficulty. THE POSTERIOR TIBIAL ARTERY. 837 Venag comites I. The artery is best approached irom the inner side of the leg. The leg being flexed, the Hmb is laid on its outer side, and an incision three and a "half or four inches in length is made along the inner margin of the tibia, beginning two ^'g. 737, and a half inches from the upper end of , that bone. The skin being divided, care must be exercised in opening the superficial fascia not to injure the internal saphenous vein or nerve, both of which lie directly in the track of the wound. These structures being dis- placed, the deep fascia must be slit up to the full extent of the incision. It should also be cut transversely, so as to allow a freer access to the intermus- cular parts. The next step consists in detaching the origin of the soleus muscle from the tibia. It is at this stage of the operation that one of two errors is often committed, — the inter- muscular space between the inner head of the gastrocnemius and the soleus muscle is opened, or all the muscular tissue is separated from the bone, the tibialis posticus muscle be- ing raised along with the soleus. The first mistake leads the operator above the vessel and the second leads him underneath. There is, however, a guide which will afford important assistance. If the soleus has been properly detached and raised, its under surface will present a white, shining sheet of tendinous material, beneath Fig 7^S which will be seen a layer of fascia (inter- muscular) covering the tibialis posticus muscle. If search is now made externally and towards the middle of the leg, the artery will be found covered by the inter- muscular fascia, the nerve lying to its outer side. After the vessel has been separated from the investing con- nective tissue and the accompanying veins, the needle must be passed from without inward (Agnew). 2. At the middle third the artery is reached through an incision parallel with the inner edge of the tibia and a half inch from its border. Avoiding the saphenous vein and nerve the superficial fascia and the deep fascia (with its fibres running transversely)' are Dissection of back of right leg, showing relations of pos- terior tibial vessels and nerve,- gastrocnemius and soleus muscles have been cut and drawn aside. 'Post, tibial artery ■Post, tibial nerve ■Tendo Achillis Flex. long, hallucis Vena comites / ner side of right ankle, showing relation of tendons, vessels as they pass between calcanium and internal malleolus. 838 HUiMAN ANATOMY. divided in the line of the skin wuund, the inner margin of the soleus displaced outward, and the vessel, with its vente comites, exposed, the posterior tibial nerve lying to its outer side. A little lower — i.e., in the lower third of the leg — the incision should be made midway between the inner edge of the tibia and the inner edge of the tendo Achillis, and the artery will be found lying on the fibres of the flexor longus digitorum, the tendon to the inner side, and the nerve external. - 3. To ligate the vessel at the inside of the ankle the incision should be semi- lunar in shape, parallel with the margin of the inner malleolus, and about half-way between it and the margin of the tendo Achillis. After dividing the deep fascia — internal annular ligament — the artery will be found, with its accompanying veins, lying between the flexor longus digitorum and tibialis posticus tendons on the inside — each in a separate synovial sheath and the latter near the malleolus — and the ner\e and flexor longus pollicis tendon on the outside. The sheaths of these tendons should not be opened. The collateral circulation is carried on from above the ligature by (t?) the anterior and posterior peroneal arteries and their muscular and communicating branches ; {b) the external malleolar branch of the anterior tibial; {c) the internal malleolar (anterior tibial); {d) the dorsalis pedis. Anastomosing respectively with (' gives off an anterior per- forating branch, which passes dorsally to communicate with the corresponding dorsal interos- seous arten,-, and then divides into two plantar digital branches, which pass onward upon the adjacent sides of neighboring digits. THE POSTERIOR TIBIAL ARTERY. The ^//^ plantar interosseous artery is considerably larger than the others, and arises from the inner end of the plantar arch, opposite the communicating branch which passes between the plantar arch and the dorsalis pedis. It runs forward at first along the first intermetatarsal space and then upon the first metatarsal bone, and gives off a digital branch which passes to the inner surface of the great toe and continues on towards the metatarso-phalangeal joint of that digit. Before reaching this, however, it gives off an anterior perforating branch and then divides into two plantar digital branches, which supply respectively the inner side of the second and the outer side of the great toe. Since the communicating branch which traverses the first intermetatarsal space is some- times regarded as the terminal portion of the dorsalis pedis artery, and the fifth plantar inter- osseous artery seems to be, upon such a view, the branch of the communicating vessel, the fifth plantar has been de- scribed as a branch of Fig. 740. the dorsalis pedis ar- tery, under the name of the a. pj-inceps hallucis. There can be no doubt, however, that both the communicating and the princeps are equiv- alent to the other pos- terior perforating and plantar interosseous arteries. Variations. — The external plantar artery may be quite small, in which case the plantar arch seems to be a continuation from the anterior tibial artery through the posterior perforating branch of the first intermetatar- sal space. The arch is occasionally double, owmg to its division at its origin into two stems which reunite opposite the first inter- metatarsal space. The first plantar interosse- ous may arise by a common stem with the second, and, con- versely, one or more of the plantar digital branches may have an independent origin from the arch. Anastomoses of the Posterior Tibial Artery. — A collateral circulation for the posterior tibial after interruption of that \'essel below the origin of the peroneal may readily be estabHshed through the anastomoses which its branches form with those of the peroneal and those of the anterior tibial. The anasto- moses with the peroneal are between the ffommunicating branches of the two arteries, between the anterior peroneal and the external plantar, and between the posterior peroneal and tlie internal calcaneal. With the anterior tibial artery there is communication through the malleolar branches of the two arteries, through the anastomotic branch of the e.xternal plantar and the tarsal and metatarsal branches of the dorsalis pedis, and through the union of anterior and posterior perforating branches of the plantar arch and the plantar interosseous arteries with the dorsalis pedis and dorsal interosseae. Arteries of plantar surface of right foot ; deeper dissectio 842 HUMAN ANATOMY. THE ANTERIOR TIBIAL ARTERY. The anterior tibial artery (a. tibialis anterior j (Figs. 742, 743) is the other terminal branch of the popliteal. It begins at the lower border of the popliteus muscle, and is at first directed forward, passing between the tibia and fibula and the two uppermost slips of origin of the tibialis posticus, above the upper border of the interosseous membrane. It then bends downward and traverses the entire length of the crus to the front of the ankle-joint, wliere it becomes the dorsalis pedis artery. Its course may be represented by a line drawn from the head of the hbula to a point half-way between the two malleoli. Relations. — In its course down the leg the anterior tibial artery rests posteriorly upon the interosseous membrane, to which it is more or less firmly united by fibrous bands ; in the lower quarter of its course it rests upon the front of the tibia. Anteriorly ^ in the upper two-thirds of its course, it is overlapped by the tibialis anticus, lying along the deep edge of the connective-tissue partition which separates that muscle from the ex- tensor longus digitorum and the e.xtensor proprius hallucis. Lower, howe\er, it is superficial, and just above the ankle-joint it is crossed obliquely, from without inward, by the tendon of the extensor proprius hallucis, and then passes beneath the anterior annular ligament. Internally to it is the tibialis anticus, and at the ankle-joint the ten- don of the extensor proprius hallucis ; externally it has in its upper third the extensor longus digitorum, in its middle third the extensor proprius hallucis, and at the ankle the inner tendon of the extensor longus digitorum. The anterior tibial nerve lies to the outer side of the artery in its upper and lower thirds ; in the middle third of the leg it is usuallv in front of the vessel. Variations. — The anterior tibial arten,-, as it occurs in man, appears to be the result of a union of two originally distinct vessels, both of wfiich arise from the primitive peroneal arterj- and pass to the front of the leg. The up- FiG. 741. Ext. longrus digitorum Ant. tibial neri-e Ant. tibial artery C\iinpanion vein permost of these forms the greater portion of the artery, while the lower one, which is represented by the anterior peroneal arter)', forms only the lower part of the anterior tibial and its continuation upon the dorsum of the foot, the dorsalis pedis. In case of faikire in the union of these two vessels, the anterior tibial may appear to terminate in muscular branches a short distance above the ankle- joint, the dorsalis pedis being the continuation of the aur terior peroneal. This ar- rangement is not infrequent ; more rarely the upper portion of the vessel is greatly re- duced, being represented only by a small stem w hich gives oft the posterior and anterior recurrent branches as well as branches to the popliteus mu.scle, the front of of the leg, in such cases, being sometimes supplied by an in- dependent perforating branch from the posterior tibial. Practical Consid- erations.— The anterior tibial artery is more often wounded than the pos- terior tibial because of its more exposed position on the front of the limb and its close relation to the tibia. It is not infrequently lacerated by the sharp edge of a fragment in fracture of that bone. It is THE ANTERIOR TIBIAL ARTERY. Tendo patella; Inferior internal articuliir 3 843 rarely the subject of aneurism. Ligation may be done at ( i) the upper; (2) the middle; or (3) the lower third. The line of the artery is from a point midway between the exter- nal tibial tuberosity and the head of the fibula to Fig. 7J2 the middle of theanteri- or intermalleolar space. I. When through an incision made at this line the deep fascia is reached and divided, the interspace in which the artery lies should be sought for. It is that between the tibi- alis anticus and the extensor longus digi- torum, is the only in- termuscular interstice in the upper anterior tibial region, is about an inch or an inch and a quarter external to the tibial crest, and a half to three-quarters of an inch mternal to the septum which di- vides the extensor lon- gus from the peroneus longus. This septum is often marked by a white line visible before the deep fascia is di- vided ; or it may be recognized by slipping a director outward be- neath the aponeurosis until its point is firmly arrested. The inter- space containing the anterior tibial artery will then be internal to this and can be felt as a line of lessened resist- ance when the fore- finger is pressed length- wise along the muscles (Treves). On the other hand, the apon- eurotic partition be- tween the extensor and the peroneus — external to the inter- space sought for — resists and vibrates under the point of the director or the fore- finger (Farabeuf). At Internal malleolar artery Doi^ mterosseous Dorsalis pedis Communicating artery Dorealis hallucis perforating arteries Tendons of extensor longus dlgitorum Arteries of front the bottom of the interspace the artery will be found lying upon the interosseous membrane to the outer side of the tibia and with the nerve external to it. 844 HUMAN ANATOMY. 2. At the middle of the hmb the same interspace is found — usually more easily, as there is often some yellowish-white fatty tissue lying between the muscles and seen as a line on the surface of the deep fascia — and is opened. The artery which still lies on the interosseous membrane will be found in the deeper space thus disclosed between the e.xtensor proprius pollicis and the tibialis anticus. 3. At the lower third an incision on the same line will expose the vessel lying usually in the innermost of the two interstices found at that part of the limb, viz., that between the tibialis anticus and the extensor proprius pollicis. Occasionally it will be found to the outer side of the tendon of the extensor proprius — the second tendon from the tibia — in the space between that muscle and the extensor longus digitorum. The vessel lies on the front of the tibia, with the nen-e external. The collateral ciradation is carried on from above the ligature by (a) the pero- neals ; and (F) the posterior tibial, anastomosing respectively with {a) the external malleolar, the branches of the dorsalis pedis and the plantar ; and {b) the internal malleolar from below, assisted by the many small anastomotic vessels piercing the interosseous membrane and derived from the two tibials. Branches. — In addition to nimierous muscular branches which supply the adjacent muscles, the anterior tibial artery gives off the following : 1. The superior fibular branch (ramus fibularis) is a small vessel which arises from the anterior tibial immediately below its origin ; occasionally it arises by a com- mon trunk with the posterior tibial recurrent or else from the lower part of the popliteal. It passes upward behind the neck of the fibula, traversing the substance of the soleus, and sends branches to that muscle and to the peroneus longus, and anastomoses with the external inferior articular branch of the popliteal. 2. The posterior recurrent tibial artery (a. reeurrens tibialis posterior) arises while the anterior tibial is still upon the posterior surface of the leg. It passes upward between the popliteal muscle and the posterior ligament of the knee-joint, both of which it supplies, and terminates by anastomosing with the external and internal inferior articular branches of the popliteal. 3. The anterior recurrent tibial artery fa. reeurrens tibialis anterior ) is given off just after the anterior tibial has reached the front of the leg. It runs upward in the substance of the tibialis anticus and over the outer tuberosity of the tibia, and terminates by taking part in the formation of the circumpatellar anastomosis. It gives branches to the tibialis anticus, the extensor longus digitorum, the capsule of the knee-joint, and the adjacent integument. This artery is of importance in the establishment of a collateral circulation after ligation of the popliteal artery (page 834), on account of its anastomoses with the descending branch of the external circumflex artery and with the anastomotica magna. 4. The internal malleolar artery (a. malleolaris anterior medialis) arises from the inner surface of the anterior tibial, a little above the ankle. It passes inward beneath the tibialis anticus, over the surface of the inner malleolus, and terminates by anastomosing with the malleolar branch of the posterior tibial, the internal plantar, and the internal calcaneal arteries. 5. The external malleolar artery (a. malleolaris anterior lateralis) arises from the outer surface of the anterior tibial, usually a little below the internal malleolar. It is directed outward and downward beneath the extensor longus digitorum and the peroneus tertius, over the surface of the external malleolus, and anastomoses with branches from the anterior and posterior peroneal arteries. Anastomoses of the Anterior Tibial Artery. — Collateral circulation is readily established, in cases of interruption of the anterior tibial artery, by means of its abundant anastomoses with branches of the posterior tibial. Thus there are rich anastomoses between the internal malleolar branch of the anterior tibial and the malleolar branch of the posterior tibial, and between the external malleolar branch of the anterior tibial and the anterior and posterior peroneal branches. Further, since the dorsalis pedis artery is the continuation of the anterior tibial, it will assist mate- rially in the collateral circulation by the anastomoses of its tarsal and metatarsal branches with the plantar and peroneal arteries and by its connections with the plantar arch. THE DORSAL ARTERY. 845 Ant. tibial artery Ant. tibial nerve Dorsalis pedis artery — Peroneus brevis ^Peroneus loiigus THE DORSAL ARTERY OF THE FOOT. The dorsal artery of the foot (a. dorsalis pedis) (Fig. 743 J is the continuation of the anterior tibial beyond the ankle-joint. It extends to the pro.ximal portion of the first intermetatarsal space, where it receives the large fourth perforating branch of the plantar arch, and is thence continued forward along the intermetatarsal space as the a. dorsalis hallucis. Relations. — The dorsalis pedis is covered in the proximal portion of its course by the anterior annular ligament, and is crossed just before it reaches the intermetatarsal space by the tendon of the e.xtensor brevis digitorum which passes to the great toe. It rests successively upon the anterior ligament of "^' ''•*3' the ankle-joint, the head of the astragalus, the astragalo-scaphoid liga- ment, the dorsal surface of the scaphoid bone, the dorsal scapho-cuneiform ligament, and the in- tercuneiform ligaments which extend between the middle and internal cuneiform bones. Ex- tej'nally it is separated from the innermost ten- don of the extensor lon- gus digitorum and from the e.xtensor brevis digi- torum by the inner termi- nal branch of the anterior tibial nerve, and inter- nally it is in relation with the tendon of the e.xten- sor hallucis proprius. Branches. — In addition to numerous cu- taneous branches to the skin of the dorsum of the foot and musc2ilar branches to the e.xtensor brevis digitorum, the dorsalis pedis gives rise to the following vessels. 1. The internal tarsal branches (aa. tarseae mediales) are one or more small vessels which pass over the outer border of the foot, supplying the integument and the tarsal articulations and anastomosing with the internal malleolai ' and internal plantar arteries. 2. The external tarsal branch (a. tarsea lateralis) arises opposite the head of the astragalus and passes outward and forward over the scaphoid and cuboid bones, under cover of the extensor brevis digitorum. It gives branches to that muscle, to the skin, and to the tarsal articulations, and anastomoses with the external malleolus and anterior peroneal arteries above, with the external plantar laterally, and with the metatarsal below. 3. The metatarsal branch (a. arcuata) arises over the internal cuneiform bone and is directed at first laterally forward and then laterally over the bases of the four outer metatarsal bones and beneath the tendons of the extensor longias and extenso! cLion bho%Mn§; relations of \essels and nerves in vicinity of left portion of anterioi annular ligament still in place. 846 HUMAN ANATOMY. brevis digitorum. It thus forms an arch upon the dorsal surface of the foot corres- ponding in position with the plantar arch below. It anastomoses laterally with the external tarsal and with the external plantar, and opposite each of the intermetatarsal spaces which it passes — the second, third and fourth — gives off a dorsal interosse- ous artery (a. metatarsea dorsalis). Each of these passes forward along its intermetatarsal space, and, immediately beyond its origin, gives off ^ posterior perforating branch which communicates directly with the corresponding posterior perforating branch of the plantar arch. At the distal end of its intermetatarsal space each artery gives off an anterior perforating branch which unites with the similar branch of the corresponding plantar interosseous, and then di\ides into tii'o dorsal digital branches ( aa. digitales dorsales) which pass along the adjacent surfaces of two neighboring digits and anastomose with one another and with the plantar digital branches. 4. The dorsal interosseous branch of the first intermetatarsal space appears to be the continuation of the dorsalis pedis, and is usuallv termed the a. dorsalis hallucis. Its course is exactly similar to that of each of the other dorsal interosseous arteries, except that, in addition to the anterior dorsal perforating and terminal dorsal digital branches, it gives off, not far from its origin, a third digital branch which passes forward along the outer surface of the great toe. The posterior communicating artery which should arise from this vessel is represented by the large branch by which the dorsalis pedis communicates with the plantar arch. Variations. — The origin of the dorsalis pedis from the peroneal by means of the anterior peroneal branch has already been noted in connection with the variations of the anterior tibial artery-. Another origin which has been observed is from the external plantar artery, which sends upward through the astragalo-calcaneal canal a large branch which is continued distally upon the dorsum of the foot and gives ofT the tarsal and metatarsal branches. This \essel is represented in the adult by a small branch which arises from the external tarsal arter)- and pur- sues the course indicated to anastomose with the external plantar ; it appears to be much more highly developed in the embrjo than in the adult ( Leboucq). Other variations in the dorsalis pedis and its branches depend upon a correlation which exists between the de\elopment of the dorsal and plantar system of vessels. If, for e.xample, the plantar interosseae are well developed, they will, through the anterior perforating branches, furnish the main blood-supply for the dorsal digital branches, and the dorsal interosseous ves- sels, as well as the metatarsal, may be much reduced. Or the plantar arch, through the pos- terior perforating branches, may be the main supply for the dorsal interosseous vessels, and the dorsalis pedis itself may be diminished in size or may even terminate in a net-work of small vessels over the dorsal surface of the tarsus. DEVELOPMENT OF THE ARTERIES. In the preceding pages some of the more important facts regarding the development of the arteries ha\-e been mentioned in connection with the anomalies in whose production they are concerned ; these facts may now be briefly restated in a more connected manner. At an early stage of development, while the heart lies far forward beneath the pharyngeal region and its ventricle is still undi\-ided, the blood leaves it by a single vessel which passes forward along the mid-ventral line of the phan,-nx and divides to form two ventral longitudinal stems, from each of which six lateral branchial vessels arise, the fifth vessel of each stem, counting from before backward, being quite rudimentaPi' and closely associated with the fourth. These branchial vessels pass dorsally in the branchial arches to the dorsal surface of the pharynx, where those of each side unite to form a longitudinal stem which passes backward, and at about the level of the eighth cer\'ical vertebra unites with its fellow of the opposite side to form a single longitudinal tnmk, the dorsal aorta (Fig. 677). This is continued backward to the posterior extremity of the trunk, lying immediately ventral to the vertebral column. From the anterior ends of the ventral and dorsal longitudinal stems branches pass forward into the cranial region; and from the dorsal longitudinal stems and the dorsal aorta lateral and ventral branches are given off in regular segmental succession. The modifications undergone by the branchial arch vessels in the course of development may first be traced and then the arrangement and modifica- tions of the segmental branches will be considered. The first modification of the branchial arch vessels consists in the disappearance of the two anterior ones on either side, and then follow a number of changes which may be briefly stated as follows. ( I ) The portions of the dorsal longitudinal stems intervening between the third and fourth branchial vessels disappear ; (2) the fifth branchial vessels disappear ; (3) the sixth loses its connection with the dorsal longitudinal stem on the right side ; (4) the proximal portion of DEVELOPMEiNT OF THE ARTERIES. 847 Fig. 744. Diagrams illustrating primary arrangement (A) and second- ary modifications (£) in branchial arch vessels. TA, truncus arteriosus; /-F/, aortic bows; FA, DA, ventral and dorsal aortas; A, aorta; AA, aortic arch; /, innominate artery; CC, CE, CI, common, external and internal carotids; .5", subclavian ; P, pulmonary artery ; rfa. ductus arteriosus. the ventral longitudinal stem divides in the frontal plane into two portions, one of which is con- nected with the si.xth branchial vessels, while the other retains the remaining ones ; and (5) the posterior portion of the right dorsal longitudinal stem disappears, so that the dorsal aorta is formed only by the left stem (Fig. 678). As the result of these changes the anterior portion of the ventral longitudinal stem becomes the external carotid artery ; the anterior portion of the dorsal longitudinal stem the internal carotid ; the third branchial vessel becomes the connection between the two carotids ; the fourth branchial vessel of the left side, together with the left dorsal longi- tudinal stem, becomes the arch of the aorta ; the right fourth branchial vessel and the persisting portion of the right dorsal longitudinal stem become the proximal portion of the right subclav- ian artery ; the sixth branchial vessels become the pulmonary arteries, the persisting connection of the left one with the aortic arch being the ductus arteriosus ; the proximal portion of the ventral longitudinal trunk which re- mains connected with the sixth vessels becomes the pulmonary aorta, while the other portion becomes the prox- imal part of the aortic arch. These changes are shown diagrammatically in Fig. 744, A and B. From the forward prolongations of the carotid arteries the vessels which supply the cranial structures are de- veloped, and lateral branches also pass from the carotids to the .structures which are formed from the branchial arches. Of these branches the superior thyroid, lingual, and facial arteries are probably from the beginning connected with the external carotid, but the greater part of the internal maxillary takes its origin from the internal carotid and only secondarily becomes con- nected with the external one (page 743). From the dorsal longitudinal stems, posterior to the point at which the sixth branchial vessels join them, branches pass off laterally to each of the cervical segments, the most anterior pair accompanying the hypoglossal nerve and passing to the occipital segments with which the nerve is associated. Later, as the heart recedes towards its final position in the thorax, carrying with it the dorsal longitudinal .stems, the majority of the cervical lateral branches separate from the stems and are represented in the adult by the segmental muscular and spinal branches which arise from the vertebral artery. The seventh branches, however, retain their connection with the longitudinal stems and become the subclavian arteries of the adult. Throughout the entire length of the dorsal aorta segmental branches are distributed not only to the body-wall, but also to the viscera, and in each seg- ment two typical sets of visceral branches may be distinguished, — a pair of lateral branches which pass laterally beneath the peritoneum to the paired viscera, and a single median branch which passes ventrally in the mesentery and is supplied to the digestive tract and its derivatives (Fig. 745). The lateral branches to the body-wall persist in the adult as the inter- costal lumbar and lateral sacral branches, the fifth lumbar branches entering into the formation of the iliac arteries. The visceral branches belonging to both sets, however, undergo much modification, some disappearing and others fusing, so that little trace of their primary segmental arrangement is to be recognized in the adult. Representatives of the paired visceral branches are to be found in the bronchial, suprarenal, renal, and spermatic (ovarian) arteries, and in the foetus the umbilical arteries represent the paired branches of the third lumbar segment. At an early stage, however, these vessels make connections with branches of the iliac arteries and Fig. 745. Diagram showing fundamental arran.gement of branches from aorta {A) ; B, lateral branches to body-wall; C, paired visceral, D, unpaired visceral branch ; E, peritoneum. HUMAN AXATO.MV. Fig 746. then lose their original connections with the aorta, so that they seem in the fcctus to arise from the iliac vessels, and these latter, although primarily somatic in their distribution, give off a number of visceral branches. Of the unpaired visceral branches representatives are to be found in the thoracic region in the oesophageal and mediastinal vessels and in the abdomen m the cceliac axis and the superior and inferior mesenteric arteries, the superior mesenteric representing the omphalo-mesenteric or vitelline arteries of the embryo which primarily arise by several roots, only the lov\-est of which persists to form the adult vessel. According to the general plan of the embryonic arterial system thus outlined, the only ves- sels which have primarily a longitudinal course are the dorsal and ventral longitudinal stems, the dorsal aorta, and its prolongation, the a. sacra media. In the adult^ howe\er, several other longitudinal vessels e.xist, such, for instance, as the \ertebrals, the internal mammaries, and the superficial and deep epigastrics. All these vessels are secondary formations due to the end-to- end anastomoses of upwardly and downwardly directed branches of the lateral segmental ves- sels. The internal mammaries and the epigas- trics (Fig. 746) are formed in this manner from branches of the intercostal arteries, with which they remain connected to a greater or less ex- tent , the vertebrals are formed from branches of the lateral cer\ical vessels, and become inde- pendent stems by the separation of these vessels from the dorsal longitudinal stems, as already described. The arteries of the limbs are formed, as already stated, by the lateral somatic branches of the seventh cervical and fifth lumbar segments respectively, but in both limbs a series of changes is necessary before the adult arrangement is acquired. In the arm the subclavian artery at first extends as a single main stem as far as the carpus, where it terminates by dividing into digital branches for the fingers (Fig. 747, j4i. Throughout its course in the forearm it lies between the two bones, resting on the interos- seous membrane, in the position occupied by the adult anterior interosseous artery ; from the upper part of this portion of its course a branch is given off which takes a more super- ficial course, accompanying the median ner\'e. This median artery gradually becomes larger, while the anterior interosseous undergoes a cor- responding retrogression, and eventually the median, by fusing with the lower portion of the interosseous forms the main channel for the digi- tal branches and becomes the principal artery of the foreami (Fig. 747, B). A further stage is marked by the development of the ulnar arter>- as a branch from the brachial, and this, extending down the ulnar side of the forearm, unites with the median to form a carpal arch from which the digital branches arise ( C). Later there develops high up upon the brachial a superficial brachial arterv', which, after traversin,g the brachium, passes down the radial side of the forearm and near the wrist passes to the posterior surface, dividing over the carpus into branches for the dorsum of the thumb and index-finger. After the appearance of the ulnar artery a retrogression of the median begins, whereby it becomes the a. comes nervi mediani of the adult ; a branch, the superficial volar, arises from the lower part of the superficial brachial and passes downward into the palm to unite with the palmar arch already present ( D) ; and, finally, a branch arising from the lower part of the brachial anastomoses with the superficial brachial just below the bend of the elbow and together with the antibrachial part of the superficial brachial, forms the radial arterv". The upper part of the superficial brachial then degenerates until it is normally represented in the adult by a small branch of the brachial which passes to the biceps muscle ( E) . In the leg the changes are equally complicated. Primarily it is the sciatic artery which forms the main stem, extending the entire length of the posterior surface of the limb into the plantar surface of the foot, where it divides into the digital branches (Fig. 74S, A). The ex- ternal iliac at this stage is a relatively slender vessel which e.xtends but a short distance down the thigh and terminates in what is later the profunda femoris. In a later stage there arises from Trunk-arteries of embryo of six weeks, showing origin of internal mammary (/»il and epigastric arteries (j^. superficial, rff, deep) ; a, aorta ; z/, vertebral ; ci, common iliac, continuing as large hypogastric (Al; external iliac, giving off deep epigastric and femoral, is still small. X 5. (Mat/.) DEVELOPMENT OF THE ARTERIES. 849 the external iliac a vessel {saph) which accompanies the internal saphenous nerve down the leg and, entering the foot, takes from the original main stem its digital branches (B). From this saphenous artery a branch is given off which pierces the substance of the adductor magnus mus- FiG. 747. Diagrams illustrafing development of arteries of upper limb ; *, brachial ; i. interosseous ; d, digital ; m, median; «, ulnar; sb, superficial brachial ; r, radial. Fig. 74S. /— ! /^ '^^lllWi Diagrams illustrating development of arteries of lower limb ; s, sciatic ; rf, digital ; y, femoral ; saph, saphenous ; pop, popliteal ; per, peroneal ; pt, at, posterior and anterior tibial. cle and anastomoses with the sciatic arterj' just above the upper end of the popliteal space (C). whereupon the portion of the sciatic arter>' immediately above tne anastomosis degenerates and 54 850 HUMAN ANATOMY. the vessel becomes reduced to the slender a. comes ner\i ischiadic! of the adult. Its lower por- tions, which become the popliteal and peroneal arteries, now seem to be the continuation of the femoral (i.e., the saphenous). From the lower part of the popliteal a branch arises which anastomoses with the saphenous and, together with the lower part of that arterj', forms the posterior tibial, the upper part of the saphenous then disappearing except in so far as it is represented by one of the branches of the anastomotica magna. The anterior tibial is a late formation resulting from the fusion of an upper and lower branch from the peroneal which perforate the interosseous membrane ( C), the con- nection of the lower branch with the peroneal degenerating after the anastomosis, except in so far as it persists as the anterior peroneal arten,' (D). THE VEINS. The veins are those vessels which receive the blood from the capillary net-work and return it to the heart. Compared with the arteries, they present many difTerences, both of structure (page 677) and arrangement. Their walls are much thinner, so that the color of the blood which they contain shows through, and they are readily compressible to the extent of a complete obliteration of their lumen and are also exceedingly dilatable. Notwithstanding their thinness, they are less easily ruptured by over-distention than are the arteries and are capable of undergoing a remarkable elongation, those of an adult withstanding an extension to at least 50 per cent, more than their original length without losing their elasticit)- — a property which explains the more direct course taken by the veins as compared with the arteries in mobile portions of the body {e.g., the facial vein as compared with the artery). Indeed, it seems that the veins when in place in the body are always stretched to a considerable extent, the cephalic vein, ior example, contracting when removed from the body to 40 per cent, of its length in the extended arm (Bardeleben). The most striking structural peculiarity of the veins, however, is the occurrence in them of semilunar valves, arranged usually in pairs, with their ca\ities directed towards the heart. These valves resemble in their general form the semilunar valves of the systemic and pulmonary aortse, and, as in those vessels, the veins are somewhat enlarged immediately above the attachment of each pair, so that the blood may readily flow behind the valves, force their free margins together and so occlude the vessel. These valves play an important part in directing the flow of blood in the veins towards the heart, since, in the event of any pressure, such as that exerted by a contracting muscle, acting on the vein, they will prevent a backward flow of blood tow-ards the capillaries. Valves do not occur in veins of less than i mm. in diameter and are also lacking in many of the larger trunks, such as the superior and inferior vente cavae, the pulmonary and the portal veins. In general the)' are more numerous in the \eins of the limbs than in those of the trunk and in the deep than in the superficial vessels. Their number in any vessel in which they normally occur is subject to con- siderable \'ariation in different individuals and even on opposite sides of the body in the same subject. It seems probable that this variation is brought about by a degeneration of a greater or less number of the pairs originally present, since in the majority of the veins the number of valves diminishes with age (Bardeleben), and even in adult bodies evidence of degeneration may be seen in the insufficiency of some of the valves or even in their perforation. It is possible, therefore, that the arrangement of the valves in the adult is a secondary rondition, derived from one in which the valves were much more numerous and v ere situated at regular intervals along the vessels. In favor of this view it has been found ("Bardeleben) that in certain veins the valves in the adult are separated bv intervals either of a definite length or of a multiple of this, the length of the intervals stand'ng in relation to the length of the part or, in general, to the height of the individua' m which the vein occurs. Thus, in a man measuring 160 mm. in height, the valves of the right long saphenous vein were separated by interv'als which were all approximately multiples of 6.85 mm. in length, while the intervals separating the valves of the right cephalic vein were approximately multiples of 5.2 mm.: and in a male child Si cm. in height, the valves of the right long saphenous vein were separated by intervals of 3 mm. or some multiple of this. THE VEINS. 851 A more readily appreciable relation of the valves is that which they bear to the branches which open into the vein, a pair of valves being found immediately distal to the entrance of each collateral vein ; and, furthermore, a pair, or at least a single valve, very generally occurs at the termination of a vein, where it enters either a larger stem or the heart. These terminal valves are present in certain veins which other- wise are quite destitute of valves, as, for instance, in the internal jugular, the internal ma.xillary, and the vertebral veins. It has already been noted that valves are entirely wanting in certain veins. Among these are the sinuses of the cranium, the cerebral, ophthahnic, periosteal, pulmonarj', bronchial, portal, renal, uterine, ovarian, and innominate ( brachio-cephalic ) veins, and the superior and inferior venEe cavae. Furthermore, they are usually absent in the internal iliac and facial veins, although occasionally they occur in both. In their position and arrangement also the veins differ noticeably from the arteries. While veins are usually to be found accompanying the arteries, enclosed with them in a common fibrous sheath, additional veins of considerable size are abundant immediately beneath the skin — a condition which is almost entirely foreign to the arteries. Furthermore, although in a general way a vein may pursue the same course as an artery, it may lie at some little distance from the latter and fail to follow its course exactly. This is true, for instance, of the facial and the lingual veins and also of the subclavian vein, which is separated from the corresponding artery by the scalenus anticus muscle ; this likewise applies to the veins at the root of the neck which accompany in a general way the branches of the subclavian artery, but open into the innominate vein instead of the subcla\'ian. In many cases the veins which accom- pany arteries are double, one lying on either side of the artery and forming what are generically known as venae comites (venae comitantes ). The causes which determine this double condition are obscure. The arrangement is not found in the larger venous trunks, occurring, for instance, in the leg only below the knee and in the arm only as far up as the middle of the brachium ; size alone, however, does not seem to be the determining factor, since the internal mammary and epigastric veins are double, while the intercostal and lumbar veins, almost of the same size as the former, are single. Nor does the quality of the tissue in which the veins occur determine their duplication, for those which are embedded within the muscles of the tongue are doubled, while those within the heart musculature are single ; again, while, as a rule, the veins which occur in fibrous tissue — as, for instance, the menin- geal veins — are double, yet those of the skin are single. Finally, it may be noted that there are exceptions to the rule that the veins which occur in the cavities of the body are single, since a duplication is found in the spermatic veins and also in those of the gall-bladder. Not only doubling of many of the veins occurs, but a prevailing tendency exists towards extensive anastomoses far surpassing that displayed by any of the arteries. Even in the cases of the larger proximal trunks communications exist, those between the pulmonary and bronchial veins and that between the superior and inferior venae cavae by way of the azygos being examples. In the smaller vessels the anastomoses are often so numerous as to result in the formation of plexuses. Venae comites are united by frequent cross-connections, sometimes so numerous as to present the ap- pearance of a plexus surrounding the artery. Complicated venous plexuses also accompany the various ducts of the body, as, for example, the parotid ducts, the ureters, and the vasa deferentia. In addition, extensive venous plexuses occur in various regions of the body, as in the neighborhood of its orifices, in the terminal phalanges of the fingers and toes, in the diploe of the skull, in the spinal canal, in the pelvis, and in connection with the genito-urinary organs. Since the larger trunks usually arise at several points both from these and from the wider-meshed plexuses occurring elsewhere, opportunity is thus afforded for the return of the blood to the heart by different paths — an arrangement explaining the frequent ineffi- ciency of a ligation of even large trunks to prevent venous hemorrhage. Special mention should be made of one set of the venous channels — namely, the sinuses of the dura mater — which establish communication between the cerebral and ophthalmic veins and the internal jugular. They are channels contained within 852 HUMAN ANATOMY. the dura mater, lined by an endothelium similar to and continuous with that of the extracranial veins, but lack any extensive development of elastic fibres in their walls, which are formed by the dura. They possess no valves, although in certain of them, as in the superior longitudinal and cavernous sinuses, the lumen is traversed by irregular trabeculge of fibrous tissue. These are especially well developed and almost tendinous in character in the superior longitudinal sinus, while in the cavernous sinus they are softer, and from them and from the walls of the sinus fringe-like prolongations, .5-2 mm. in length, project freely into the lumen. Connected with certain of these sinuses and developed from certain of the smaller veins which open into them are so-called blood-lakes (lacunae) — cavities or plexuses in the dura mater, lined with endothelium, and connecting either directly or by means of a short canal with an adjacent sinus. They are usually situated more or less sym- metrically with reference to the sinus with which they are connected, and some are very constant in occurrence. Thus, a certain number usually occur on either side of the superior longitudinal sinus (page 1199), others in the tentorium cerebelli con- necting with the lateral sinus, others in the middle fossa of the skull along the course of the meningeal veins, and others in the vicinity of the straight sinus. They occasion- ally reach a considerable size, bulging outward the dura which encloses them and excavating by absorption irregular depressions upon the inner surface of the skull. Occasionally this absorption of the cranial bones proceeds so far that bulging of the outer table of the skull over a lake takes place, and, in the case of those occurring along the course of the superior longitudinal sinus. Pacchionian bodies developed from the subjacent arachnoid tissue may invade them, pushing before them the attenuated floors of the lakes. Classification of the Veins. — Theoretically a description of the veins should start with the peripheral vessels and proceed towards the great trunks, following the course of the blood. Such a method would prove, however, somewhat confusing, largely on account of the numerous anastomoses that occur ; it is preferable, therefore, to base a classification primarily upon the great trunks and to consider their afferents topographically, according to the areas which they drain. From the'embryological stand-point, there are primarily four great systems of veins : ( i ) the cardinal system, represented by the vena ca\a superior and its tributa- ries ; (2) x}n^ inferior c aval system; (3) \\\e portal system ; and (4) xhe puhnonary system. Owing to subsequent changes, it is necessary to recognize in the cardinal system three sub-systems : (i) that of the cardiac veins ; (2) that of the superior vena cava and its tributaries, except (3) the azygos veins. In all, then, six great systems of veins may be recognized in the adult. They are as follows : 1. The pulmonary system. 2. The cardiac system. ^ 3. The superior caval system. - The cardinal system. 4. The azygos system. ) 5. The inferior caval system. 6. The portal system. In the descriptions which follow the veins are considered on the basis of this classification. THE PULMONARY SYSTEM. The Pulmonary Veins. The pulmonary veins f venae pulmonales) ("Figs. 749, 750) are four in number, two passing from the hilum of each lung to the posterior surface of the left auricle of the heart. Each vein is formed at the hilum of its lung by the union of a number of smaller vessels which take origin ultimately from the capillary net-work formed by the branches of the pulmonary artery and to a certain extent from that formed by the bronchial arteries. The arrangement of the afferent branches in the substance of the lungs is described in connection with the anatomy of these organs (page 1854), and it will be sufficient to note here that they correspond in number to the branches of the pulmonary artery and of the bronchi, and pursue a course more or less independent of these, which lie side by side. Converging and uniting as they pass towards the hilum, the branches from the superior lobe of each lung unite to form the superior THE PULMONARY VEINS. 853 pulmonary vein of that side, those from the inferior lobe unite to form the in- ferior pulmonary vein, while those from the middle lobe of the right lung unite to form a single trunk which usually opens into the right superior vein, although it occasionally opens independently into the left auricle, forming what is then termed the tniddle pulmonary vein. Each of the four pulmonary veins has a length of about 15 mm., and for about one-third of its course is partially invested by the visceral layer of the pericardium (page 715). The right superior vein is usually slightly the largest of the four, while the left superior is the smallest, the right and left inferior veins being about the same size. No valves occur either throughout the course or at the orifices of the pulmonary veins. Relations. — The superior pulmonary veins have a course which is obliquely downward and inward. In their extrapericardial portion they lie anterior to and below the pulmonary arteries, and are separated by them from the bronchi; the Fig. 7iJ9- Left . carotid artery ^.^ — Left subclavian arte ^ — Left internal jugul; ^ — Left subclavian vei: , Aorti s\stem c ^r"- R pul onar> art ^^^y^ Pulnionar> aorta Injected heart and great vessels, viewed from before ; parts of superior v have been removed to show right pulmonary artery. I cava and aorta vein of the right side is crossed from above downward by the phrenic nerve and by the vena cava superior. In its intrapericardial portion the right superior vein lies behind the terminal portion of the superior vena cava and the left one behind the pulmonary aorta (pulmonary artery), while posteriorly each is in relation with its corresponding inferior vein. The inferior veins are more horizontal in position, but are directed forward as well as inward. They lie in a plane considerably posterior to that of the corresponding superior veins and are situated internally to and behind an anterior descending branch of each bronchus. Anastomoses. — In addition to serving for the return flow of the blood carried to the lungs by the pulmonary arteries, the pulmonary veins also receive a certain amount of the blood carried by the bronchial arteries. Communications bet«'een 854 HUMAN ANATOMY. the bronchial and pulmonary veins in the region of the smaller bronchi are abundant, and, in addition, the main stems of the pulmonary veins recei\e at the hilum of the lung one or more branches from the larger bronchial veins. They also receive com- munications from the venous ple.xus which surrounds the thoracic aorta in the pos- terior mediastinum, and occasionally also a \ein from the pericardium. There is thus a certain commingling of venous blood with the arterialized blood which forms the principal contents of the pulmonary veins. Variations. — At one stage in the development of the embryo the veins from each lung converge to a single short trunk before opening into the portion of the atrium \\ hich corresponds to the lelt auricle. As the development of the heart proceeds, this trunk is gradually taken up into the auricle, until the two stems which unite to form it open independently into that structure. An inhibition of this process occasionally obtains, so that but a single vein, repre- senting the original terminal trunk, opens into the auricle from one lung or from both. On the other hand, the taking up of the pulnionarj- \ein into the wall of the auricle may proceed further than usual, or, to state it perhaps more correctly, the union of the various stenis emerging from the hilum of the lung may be pardy delayed until they have reached the original terminal tnmk, so that when this is taken up into the auricle an additional vein will open independently into the latter. This extra vein is most frequently that from the middle lobe of the right lung, but three distinct veins have also been observed upon the left side. THE CARDINAL SYSTEM. The cardinal system of veins is so named because its main trunks are the repre- sentatives of the cardinal veins of the embryo. These \eins are four in number, disposed symmetrically in pairs, two returning the blood from the head, neck, and upper e.xtremities, while the other two return that from the thoracic and abdominal walls, from the thoracic viscera, and from the lower extremities. Just before they reach the heart, the superior and inferior or posterior cardinal veins of each side unite (Fig. 776) to form trunks known as the dticts of Cuvicr, the two ducts opening independently into the primitive right auricle. By a series of changes, which are described more fully in the section on the development of the veins (page 927), the left superior cardinal becomes connected with the right at the base of the neck, the stem so formed constituting what is termed the superior vena cava. The portion of the left superior cardinal between the connecting \-essel and the heart becomes greatly reduced in size, indeed, almost completely degenerates ; the left duct of Cuvier, however, persisting as the coronary sinus, which receives the coronary veins returning the blood from the heart's walls. On the development of the vena cava inferior the veins of the lower extremity make connection with it, separating from the inferior cardinals; these latter become considerably reduced in size, especially in the abdominal region, a cross-connection develops betvveen the left and right veins, and the former severs its connection with the left ductus Cuvieri, the final result being the formation of the venae azygos and hemi-azygos of the adult. There are, then, developed from the cardinal veins of the embryo three sub- systems of veins : (\) that of the cardiac veins ; ( 2 ) that of the superior vena cava, which includes the jugular and subclavian groups of veins, the original superior cardinals being represented bv the internal jugular veins : and (3) the azygos sub- system. These will be considered in the order in which they have been named. THE CARDIAC VEINS. The Coronary Sinus. The coronary sinus (sinus coroiiarius) (Fig. 750) is a short venous trunk about 3 cm. (a little over an inch) in length, which occupies the right half of that portion of the posterior auriculo-ventricular groove which lies between the left auricle and ventricle. At its right end it opens into the right auricle, its orifice (Fig. 657) being situated upon the posterior surface of the auricle, below that of the inferior vena cava, and being guarded by the Thebesian valve (valvula sinus coronariD. At its left end it receives the great coronapy- vein, from whose proximal portion it is not always clearly distinguish- able upon superficial examination. A close inspection usually reveals, however, either a constriction or a slight dilatation at the union of the two vessels, and on THE CARDIAC VEINS. 855 laying them open a distinct valve, of either one or two cusps, but usually insuffi- cient, will be found at their line of junction. This valve is known as the valve of Vieusseyis. Furthermore, the walls of the sinus differ from those of the vein in pos- sessing a complete layer of muscular fibres, both oblique and circular, continuous with the musculature of the auricle. In addition to the great coronary vein, the coronary sinus also receives the posterior vein of the left ventricle and the middle cardiac vein, which open into it from below, and the oblique vein of the left auricle, which passes to it from above. Variations. — The coronary sinus, as already stated, represents the left ductus Cuvieri of the embryo. It varies somewhat in length, reaching in extreme cases a length of 5.4 cm. It has been observed to be obliterated at its entrance into the right auricle, the great coronary vein then opening into the left innominate (brachio-cephalic) vein, and, in addition to the veins already noted as emptying into it, it frequently receives the marginal vein of the left ventricle. I. The Left Coronary Vein. — The great cardiac or left coronary vein (v. cor- dis magna) (Fig. 749) begins upon the anterior surface of the heart at the ape.x, where it anastomoses with the veins of the posterior surface, and ascends the anterior Fig. 750. Superior vena cava Superior right pulmonary vein Left pulmonary artery ^ y jx___ l^ ^T Right pulmonary artery nor right pulmonary vein Superior left pulmonary vein Inferior left pulmonary Circumflex branch of left coronary artery Left ventricle Coronary sinus Posterior descending branch of right coronary artery Right ventricle Posterior-inferior aspect of injected heart, showing blood-vessels. interventricular groove in company with the left coronary artery, to the anterior auriculo- ventricular groove, in which it passes to the left and, curving around the left border of the heart to the posterior surface, terminates by opening into the left end of the coronary sinus. In the vertical portion of its course it receives veins from the anterior surface of both ventricles, and in its course in the auriculo-ventricular groove, throughout which it is embedded in the fat which usually occupies the groove, it receives a number of small veins from the surfaces of both the left auricle and ventricle. Among those from the ventricle there is especially to be mentioned, as larger and more constant than the rest, the vena marginalis sinistra, which ascends along the left border of the heart and empties into the great coronary vein shortly before its opening into the sinus. 856 HUMAN ANATOMY. 2. The Posterior Cardiac Vein. — The posterior cardiac vein (v. posterior ventriculi sinistrij ascends along- the posterior surface of the left \'entricle, lying about midway between the left border of the heart and the posterior interventricular groove and receiving collateral branches from the walls of the ventricle. It opens above into the coronary sinus near the point of entrance of the great coronary vein and occasionally unites with that vessel. 3. The Middle Cardiac Vein. — The middle cardiac vein (v. cordis media) (Fig. 750J occupies the posterior interventricular groove, accompanying the right coronary artery. It arises in the vicinity of the ape.x of the heart and ascends, receiving collateral branches from the posterior surfaces of both ventricles, to open into the coronary sinus near its termination. This, ne.xt to the great coronary vein, is the largest vein of the heart, and occasionally opens independently into the right auricle close to the entrance of the coronary sinus. 4. The Right Coronary Vein. — The small cardiac or right coronary vein (v. cordis parvaj (Fig. 750) occupies, when present, the right half of the posterior auriculo-ventricular groove and opens 'into the coronary sinus just before its termi- nation. Occasionally it opens into the middle cardiac vein, or directly into the right auricle, and is not infrequently lacking as a distinct vessel, the tributaries which empty into it from the posterior surface of the right auricle and the upper part of the posterior surface of the right \entricle then opening directly into the auricle. One of the largest and most constant of these tributaries ascends along the right border of the right ventricle and is termed the right marginal vein or vein of Galen. 5. The Oblique Vein of the Left Auricle. — The oblique vein of the left auricle (v. obli(|iia atrii sinistri), also known as Marshall' s vein, is a small vein of variable development which descends obliquely over the posterior surface of the left auricle and opens below into the coronary sinus. Above, it is continuous with a fibrous cord contained within the vestigial fold of the pericardium (page 716), the cord and vein together representing the lower part of an original left superior vena cava. The degree of development of the vein varies greatly, and occasionally the fibrous cord retains its original lumen, so that a more or less developed left superior vena cava is really present. This anomaly may, however, be more conveniently considered in connection with those of the superior caval system of veins (page 859). In addition to these principal veins of the heart there is a varying number of others which open direcdy into the right auricle and are situated upon the anterior surface of the right ventricle, whence they have been termed the anterior cardiac veins (vv. cordis anteriores). They are all comparatively short vessels and usually accompany descending branches of the right coronary artery. Owing to the fre- quency with which it opens directly into the auricle, the \'ein of Galen is usually regarded as one of this group of veins. Finally, the Thebesian veins (vv. cordis minimae) form part of the cardiac venous system. These are minute veins, imbedded in the substance of the heart walls, and communicating with the heart cavities by means of the Thebesian foramina (page 716 ), which occur most abundantly upon the walls of the right auricle, though also upon those of the left auricle, and, less abundantly, upon those of the ventricles. At their other ends these veins communicate in the heart's substance with the radicles of the other cardiac veins, and, in cases of stenosis of the coronary arteries, may consequently contribute to some extent to the nutrition of the heart musculature, carrying blood to it directlv from the heart cavities. Valves of the Cardiac Veins. — The Thebesian valve, which guards the right auricle, may be considered as the ostial valve of that vessel, which throughout its course is destitute of valves. So, too, throughout the extent of the cardiac veins valves are entirely lacking, but certain of those which open into the coronary sinus are provided with ostial valves. That of the great coronary vein is the valve of Vieussens, and others are usually present at the mouths of the middle \-ein and the posterior vein of the left ventricle, and less constantly at the mouths of the marginal and the small coronary veins. These valves may be either single or paired and are frequently insufficient. No valves are present either throughout the course or at the orifice of the oblique vein of the left auricle. THE SUPERIOR CAVAL SYSTEM. 857 Variations. — The principal variations which occur in connection with the cardiac veins have been noted in the description of the vessels, and it need only be added that the oblique vein of the left auricle is not infrequently entirely lacking, except in so far as it is represented by a fibrous cord, that absence of the great coronary vein has been observed, and that the middle vein occasionally opens directly into the right auricle. THE SUPERIOR CAVAL SYSTEM. The Vena Cava Superior. The superior or descending vena cava (Figs. 749, 751) is the main venous trunk which delivers to the heart the blood returning from the head, neck, upper limbs, and thorax. It measures 7-8 cm. (3 in. ) in length, and has a diameter at its termination of about 2. 2 cm. (a little less than i in. ). It is situated throughout its entire course in the thoracic cavity, lying in the superior mediastinum, and is formed immediately Fig. 751. Left internal jugular vein '-)calen s anticus muscle Left inferior thyroid vetn I. rib Left innominate vein ■Superior intercostal vein I. left posterior intercostal ■^Internal mammary vein Line of pericardial refiectio R. and L. pull ary n ■Adi^ of left bronchus Pulmonary artery 4* Left pulmonary vein ■Bronchus Left ; ricular appendix Diaphragm, thoracic surface "Hie) Dissection sliowi; ^nominate veins and superior \-ena cava in position; lungs have been pulled aside. below the lower border of the first costal cartilage of the right side by the union of the right and left innominate (brachio-cephalic) veins. Its course is downward and slightly backward, with a curvature corresponding to the first portion of the arch- of the aorta, with which it is in relation. Below, it opens into the upper posterior portion of the right auricle on a level with the third costal cartilage of the right side. Relations. — The lower portion of the superior vena cava is invested by the peri- cardium to an extent varying from a few to 40 mm. , on an average, perhaps to about one-third its length. The upper extrapericardial portion is in relation anteriorly b5S HUMAN ANATOM\. with the thymus gland or the fatty tissue which replaces it, and is overlapped by the right pleura and lung. Behind, it crosses the origin of the right bronchus and the structures at the root of the right lung, from which it is separated by numerous lymphatic nodes ; to the right it is in contact with the pleura covering the inner suHace of the right lung and with the right phrenic ner\e ; and to the left it lies alongside the ascending portion of the aortic arch. In its lower intrapericardial portion it has to the left the systemic aorta: anteriorly, the right auricle; posteriorly, the right pulmonary artery, the right superior pul- monary \ein, and the right bronchus, while upon the right it is free. The vena ca\'a superior contains no vah'es. Tributaries. — In addition to the right and left innominate veins, by the union of which it is formed, the vena cava superior receives the \ena azygos major and small veins from the mediastinum and pericardium. Variations. — Cases liave been recorded in which the vena cava superior received the right internal mammary or the right superior intercostal vein which normally open into the right innominate vein. It may also receive the vena tliyreoidea ima, a vein only occasionally present and draining the territory supplied by the art. thyreoidea ima. A more remarkable and rarer variation is the union with the superior vena cava of a com- paratively large vein which issues from the right lung. A similar condition has been obser\-ed in connection with the innominate veins, and its probable significance will be considered in connection with tlie variations of those vessels. Practical Considerations. — The superior vena cava would be involved in a stab-wound passing through either the first or the second intercostal space on the right side, close to the sternum. The vessel is subject to compression in aneurism of the ascending aorta (q.v.), producing venous congestion in the veins of the neck and of the upper extremities. The Innominate Veins. The innominate or brachio-cephalic vems (vv. anonymae) (Fig. 751) are two in number, a right and a left. They are situated in the upper portion of the thoracic cavity, being formed by the union of the internal jugular and subclavian veins, and terminate by uniting opposite the first costal cartilage of the right side to form the vena cava superior. The union of the internal jugular and subclaxian vein takes place on each side opposite the sternal end of the clavicle ; but, since the vena cava superior lies entirely to the right of the median line of the bodv, the left innominate vein has a much greater distance to traverse in order to reach its point of termination than has the right one, and consequently it will be necessary to describe each vein separately. The right innominate vein has a length of 2-4 cm. (3/j-ii-X in.) and an almost vertical course, opening directly downward into the vena ca\a superior. It lies behind the inner end of the right clavicle, from which it is separated by the lower portions of the sterno-hyoid and sterno-thyroid muscles, and a little lower it is behind the first right costal cartilage. To the right it is in relation with the inner surface of the right pleura and with the right phrenic ner\'e, to the left with the brachio- cephalic artery and right pneumogastric nerve, and behind with the pleura. The left innominate vein has a length almost double that of the right, meas- uring 5-9 cm. C2-3I2 in. ) from its origin behind the sternal end of the left clavicle to its union with the right vein to form the vena cava. Its course is transverse from left to right and at the same time slightly downward, and it e.xtends completely across the uppermost part of the thoracic cavity, resting below upon the aortic arch, and passing in front of the left subclavian and common carotid arteries, the trachea, the brachio-cephalic artery, and the pneumogastric ner\'e. It is separated from the manubrium sterni by the insertion of the sterno-hyoid and sterno-thyroid muscles and by the fatty tissue representing the thymus gland, and, being on a level with or slightly above the upper border of the manubrium, it can usually be felt in the supra- sternal fossa. Neither of the innominate veins possesses valves. The left is of somewhat greater diameter than the right, owing to the greater number of tributaries which it receives. THE SUPERIOR CAVAL SYSTEM. 859 Variations. — As pointed out in the account of the development of the great veins (page 926), there is at one stage a symmetrical arrangement of the vessels which open into the right auricle from above ; in other words, the left internal jugular is continued directly downward from the point where the left subclavian vein opens into it to the auricle, this downward continuation being usually termed the left superior vena cava. Later a cross-connection, the left innominate vein, forms between the right and left jugulars at the root of tlie neck, and the left superior vena cava then normally undergoes degeneration, traces of it only persisting as the oblique vein of the left auricle and the coronary sinus. Occasionally this normal progress of events fails to occur, the result being the complete absence or imperfect development of the left innominate vein together with a persistence of the left superior vena cava ; or else, even with the perfect development of the left innominate, there may be a failure of the left superior vena cava to degen- . Pjg --j erate. Various gradations between the embryonic and adult conditions may occur, and the anne.xed diagram ( Fig. 752 ) shows the nature of the anomaly. It may be noted that with the persist- ence of the left superior vena cava there is frequently a retention of the communica- ^ tion with it of the left cardinal vein, which normally be- comes the V. hemi-azygos, —a condition which will be more especially considered in con- I nection with the anomalies of the azygos veins ( page 893 ) . Practical Consid- erations.— The left in- nominate vein, running horizontally just below the upper border of the ma- • nubrium, lies immediately above the aortic arch. When the latter is unusually high, and occasionally in children, the vein — especially if engorged — may project above the level of the suprasternal notch and may be endangered during a thyroidectomy, the removal of a tumor, or a low tracheotomy. ior aspect of heart and great vessels, showing persistence of left superior vena cava; (semidiagrammatic). Tributaries. — In addition to the subclavian and internal jugular veins, by whose union they are formed, each innominate vein receives (i) the deep cervical, (2) the vertebral, (3) the internal mammary, and (4) the inferior thyroid \&.ns of its side. The left innominate vein receives in addition (5) the superior phre^iic, (6) the thymic, (7) the pericardial, (8) the anterior mediastinal, and (9) the left superior intercostal vein. Of these the left superior intercostal vein will be described with the other intercostals. I. The Deep Cervical Vein. — The deep cervical vein (v. cervicalis profunda) takes its origin in a plexus situated in the occipital triangle and having also con- nected with it the vertebral and occipital veins. It passes down the neck, lying be- tween the semispinalis cervicis and the splenius cervicis, and in the upper part of its course accompanies the deep branch of the art. princeps cervicis. Lower down it accompanies the deep cervical branch of the superior intercostal artery and bends slightly outward and forward, passes between the transverse process of the seventh cervical vertebra and the first rib, and opens into the innominate vein either behind the vertebral vein or by a common trunk with that vessel. Tributaries. — In its course down the neck it receives numerous tributaries from the deeper cervical muscles, and opposite each intervertebral foramen which it passes it makes connections with the vertebral vein and the veins of the spinal canal. The most important of its tributaries is, however, the occipital vein, which arises in a plexus covering the occipital portion of the skull and commvmicating with branches of the pos- terior auricular and temporal veins. It passes downward with the occipital artery, pierces the 86o HUMAN ANATOMY. traoezius muscle near its origin from the superior nucha! line, and enters the suboccipital tri- angle where it opens into the deep cervical vein. Occasionally, however, it either unites with the posterior auricular vein or opens directly into the e.xternal jugular below the posterior auricular. The mastoid emissary vein (page S76) usually opens into one of its branches. 2. The Vertebral Vein. — The vertebral \ein (v. veitebralis ) accompanies the artery of the same name through all but the cranial portion of its course, and is usually a single trunk, although frequently it is double or occasionally even ple.xiform throughout more or less of its course. It arises in the suboccipital triangle from a ple.xus of small veins with which the occipital and deep cervical veins also communi- cate, and passes downward through the foramina in the transverse processes of the six (occasionally seven or five or even only four) upper cervical vertebrte. At its exit from the foramen of the sixth vertebra it is continued obliquely forward and down- ward behind the inferior thyroid artery and the internal jugular vein, and, passing usually in front of, but occasionally behind, the subclavian artery, opens into the innominate vein near its origin. The opening into the innominate is guarded by a pair of valves. Throughout its course the vein is connected to the periosteum, lining each of the vertebrarterial canals it traverses, by 'fibrous bands, and in its terminal portion it is adherent to the deep cervical fascia, so that its walls do not collapse even when it is emptied of blood. Tributaries. — Like the vertebral artery, the vein receives tributaries from the deep mus- cles of the neck and, at each intervertebral foramen which it passes, communicating branches from the plexuses in the spinal canal on the one hand, and from the posterior spinal plexus and the deep cervical vein on the other. In its terminal portion, after it has issued from the fora- men in the transverse process of the sixth cervical vertebra, it receives the ascending cervical vein, which arises in the plexus upon the anterior surfaces of the bodies of the upper cervical vertebrae, and accompanies the ascending cervical artery down the neck. Very frequently it also receives, shortly before its termination, the deep cervical vein. 3. The Internal Mammary Vein. — The internal -mammary xe\n (v. mamma- ria interna) is formed by the union of the venge coniites of the musculo-phrenic and superior epigastric arteries, and throughout the greater part of its course is double, one stem lying along the outer and the other along the inner side of the artery in its course along the inner surface of the anterior thoracic wall. Opposite the second or third intercostal space the two stems unite, the single vein so formed lying to the inner side of the artery and opening above into the innominate vein of the same side. Numerous valves occur in the course of the vein. Tributaries. — The tributaries of the internal mammary veins correspond in general with the branches of the internal mammary artery, with the exception of the superior phrenic, medi- astinal, pericardial, and thymic branches, which usually open independently into the left innom- inate vein. Its sternal branches form plexuses upon both surfaces of the sternum, and so form communication with the vein of the opposite side, and the anterior intercostal branches unite with the posterior intercostals (page 896). The perforating branches assist in riturning the blood from the pectoral muscles, those of the first and second intercostal spaces being larger than the rest in the female, and serving to return a considerable portion of the blood from the mammary gland. By means of the superior epigastric branches the internal mammary makes connection with the subcutaneous veins of the abdomen, and. since these are also connected with the epigastric and circumflex iliac branches of the iliac veins, an anastomosis is formed between the superior and inferior caval systems of veins. 4. The Inferior Thyroid Veins. — The inferior thyroid veins fvv. thyreoideae inferiores) have their origin in a venous ple.xus (plexus thyreoideus irapar ) which covers the anterior surface and sides of the trachea immediately below the isthmus of the thyroid gland, the vessels which form the plexus issuing from the substance of the thy- roid gland, or in some cases being downward prolongations of the branches of origin of the superior thyroid veins. From the plexus two or soinetimes three veins descend the neck, following paths quite distinct from those of the inferior thvroid arteries, and open below into the innominate veins, their orifices being guarded by vah-es. When three veins are present, the odd one occupies a median position and is known THE SUPERIOR CAVAL SYSTEM. 86i as the vena thyreoidea ima, corresponding to the artery of the same name, which, however, need not be present with it. It opens usually into the left innominate vein, but occasionally is prolonged inward to terminate in the superior vena cava. Tributaries. — The plexus thyreoideus itnpar receives communications from the superior thyroid veins and also has opening into it the inferior laryngeal veins (vv. laryngeae inferlores) which descend from the larynx. The inferior thyroid veins receive directly branches from the trachea (vv. tracheales) and from the cesophagus (vv. oesophageae). •Practical Considerations. — An incision across the inferior thyroid vein, whose walls, being imbedded in inflamed tissue, could not collapse, has caused sudden death by the entrance of air. Parise, in attempting to seize the divided inferior thyroid vein during tracheotomy, lifted the superficial wall only, thus per- mitting air to enter the vein with a fatal result (Allen). 5. The Superior Phrenic Vein. — The superior phrenic vein (v. phrenica superior) has its origin upon the upper surface of the diaphragm and ascends through the thorax, lying between the pericardium and pleura and accompanying the phrenic nerve and the superior phrenic artery, of which it is a companion vein. Usually the veins of both sides are double. They open above into the left innominate vein, fre- quently uniting with the thymic, pericardial, and mediastinal veins before their termi- nation. They are provided with valves both at their orifice and along their course. 6. The Thymic Veins. — The thymic veins (vv. thymicae) are rather insig- nificant in the adult and are usually two or three in number. They arise in the adipose tissue which replaces the thymus gland and empty above into the left innomi- nate vein, frequently uniting with the superior phrenic veins. In the child they are of considerable size in correlation with the development of the thymus gland. 7. The Pericardial Veins. — The pericardial veins (vv. pericardiacae) var^^ considerably in number. They are all small, and empty in part into the left innomi- nate vein and in part into the azygos and interna! mammary veins. 8. The Anterior Mediastinal Veins. — The anterior mediastinal veins (vv. mediastinales anteriores), like the preceding, are variable in number and small. They arise in the anterior mediastinum and open above into the left innominate vein. The Internal Jugular Vein. The internal jugular vein (v. jugularis interna) (Figs. 753, 760) is the principal venous trunk of the neck. It is the continuation of the lateral sinus at the jugular foramen, and descends the neck in company with the internal and common carotid arteries to a point a little external to the sterno-clavicular articulation, where it unites with the subclavian to form the innominate vein. At its origin it rests upon the anterior sloping surface of the jugular process of the occipital bone, and usually presents at this point a distinct bulbous enlargement (bulbus venae jugularis superior) measuring about 1.5 cm. in diameter. Below the bulbus superior, at its exit from the jugular foramen, the diameter of the vein averages about 9 mm. , although subject to consider- able variation, and usually differing on the two sides, since the lateral sinuses, of which the veins are the continuations, differ on the two sides, that of the right being in the majority of cases the larger. As it descends the neck the vein gradually increases in size as it receives its various tributaries, and just before its union with the subclavian vein it presents a more or less pronounced spindle-shaped enlargement (bulbus venae jugularis inferior). This dilatation is usually much more distinct in the right vein than in the left, and at its upper end is provided with a pair of valves or else with a single one, the cavities of the valves being directed downward as if to prevent an upward flow of blood. Even when a pair is present they are insufficient, but they may nevertheless play an important part in preventing the blood from flowing into the innominate through the subclavian vein and from producing, during the systole of the auricle, a back pressure in the cerebral veins which are in connection with the internal jugular. Since the right innominate is much more nearly in a line with the vena cava superior than is the left, the greater development of the inferior bulb in the right internal jugular can be readily understood. HUMAN ANATOMY. Relations. — In the upper part of its course the internal jugular rests upon the rectus capitis lateralis and the transverse processes of the upper cervical vertebrae. To its inner side and somewhat in front of it is the internal carotid artery, the glosso- pharyngeal, pneumogastric, spinal accessory, and hypoglossal nerves separating the two vessels above. The external branch of the spinal accessory crosses it obliquely either in front or behind, and somewhat lower it is crossed anteriorly by the stylo- hyoid muscle and the posterior belly of the digastric and also by the occipital and posterior auricular arteries. To its inner side is the wall of the pharynx, with which it is not, however, directly in contact. Throughout the neck it lies beneath the sterno-cleido-mastoid muscle, imme- diately to the outer side of the common carotid artery, being enclosed in a common Superficial letnporal vein ^ Fig. 753. Posterior auricular vein External auditory Mastoid Occipital Right innominate I. rib Internal mammary vein Superior vena cava Inferior thyroid v Dissection showing; deep veins of neck and head. sheath with it, as is also the pneumogastric nerve, which lies behind and between the two vessels. Below the omohyoid muscle the vein tends to separate from the artery,, passing somewhat more anteriorly. In this part of its course it, or, to be more pre- cise, the inferior bulb, is situated immediately behind the space which separates the two heads of the sterno-cleido-mastoid. Behind, it rests upon the inner border of the scalenus anticus, crosses the subclavian artery, and has the pneumogastric and phrenic nerves passing downward on either side. Variations. — Variations of the internal jus:ular vein are not numerous. It may be noted, however, that in its course down the neck it occasionally overlaps the carotid artery to a con- siderable extent, — a condition which is especially marked in the region of the inferior bulb when this is well developed. THE SUPERIOR CA\AL SYSTEM. 863 The left internal jugular has been observed much reduced in size, there being a compen- satory enlargement of the corresponding external jugular, and it may be doubled throughout a greater or less portion of its course, although always single at either extremity. In addition to the normal tributaries described below, it may receive the temporo-maxillary vein, the verte- bral, superior laryngeal, or left superior intercostal, a bronchial vein, the suprascapular, or the transverse cervical vein. Practical Considerations. — The internal jugular vein — the largest of the superficially placed veins of the body — may be involved in cut-throat or other wounds of the neck. Like the carotid, it usually escapes in attempts at suicide on account of the usual position assumed — with the chin elevated and the head thrown back so that the muscles are rendered tense and prominent and the vessels are protected. If the wound is above the thyroid cartilage they are still safer on account of their inclination backward, and such a wound may reach the spinal column without injuring them. In wounds below the thyroid if the air passages are opened in attempted suicide, the sudden exit of air from the lungs, accompanied by collapse of the chest, may, it has been suggested, result in the dropping of the arm carrying the weapon before the wound has reached the level of the vessels, although they are here more vulnerable than they are above. The internal jugular, the other veins of the neck, and the subclavian and axillary veins, are greatly influenced by respiration, emptying during inspiration, distending during expiration — the "respiratory wave," or "venous pulse." Their attachments to the fascia keep them from entirely collapsing. This is especially noticeable in the internal jugular. After the carotid sheath has been opened the vein will vary in appearance from a distended thin-walled tube perhaps half an inch in diameter, (expiration), to a flaccid, ribbon-like structure with walls apparently in contact (inspiration). During inspiration air may thus be readily drawn into one of these veins if it has been wounded, and if the wound is dry, or if pressure is not immediately applied to the vein on the cardiac side of the wound. If the air is in large quantity it may cause instant death when it reaches the right auricle by over- distension and paralysis of the right side of the heart ; or sometimes less rapidly by asphyxia following air embolism of the pulmonary veins. The internal jugular vein may be infected secondarily to infective intracranial sinus thrombosis, especially of the sigmoid. Phlebitis or thrombosis of the internal jugular is attended by pain and tenderness along the course of the vein, and later by the development of a cord-like mass to the inner side of the sterno-mastoid muscle and the outer side of the carotid artery. This may involve the whole length of the vein but is apt to be confined to the upper third. When an infected thrombus in the sigmoid sinus has undergone such extensive disintegration that it is unlikely to be entirely removed by operative obliteration of the upper two-thirds of the sinus, or when in a thrombosed internal jugular, giving the sensation of a hard cord-like struc- ture, its upper part becomes soft from disintegration of the thrombus and this disin- tegration descends, ligation of the vessel below this point usually becomes necessary (Macewen). The ligation shuts off the main channel between the sigmoid sinus and the lungs, although the latter may still be infected by way of the occipital sinus and condylar veins and the subclavian vein. The vessel is approached by the same incision as that made for ligation of a caro- tid. The vascular sheath is opened well to the outer side so that the carotid com- partment may, if possible, be left intact. The vein should be tied in two places and divided between the ligatures. After occlusion of the vein either by ligature or bv pressure from a growth, the blood from the corresponding side of the head passes by a transverse vein to the internal jugular of the opposite side. Tributaries. — In addition to the lateral and the inferior petrosal sinuses, which will be described with the other cranial sinuses, the internal jugular receives the following tributaries : (i) the pharyn_g;eal, (2) the facial, (3) the lingual, (4) the superior thyroid, and (5) the viiddle thyroid vems. I. The Pharyngeal Veins. — The pharyngeal veins (\y. pharyngeae) are small vessels, varying in number, which open, either independently or after having united to a single stem, either directly into the internal jugular or indirectly by way of the 864 HUMAN ANATOMY. lingual or superior thyroid vein. They take their origin from a venous plexus (plexus pharyngeus) which covers the outer surface of the pharynx, lying between the constrictor muscles and the pharyngeal portion of the bucco-pharyngeal fascia. In addition to branches from the pharyngeal wall, this plexus also receives tributaries from the anterior recti and longus colli muscles, and from the soft palate, the tonsillar plexus and the Eustachian tube, and has opening into it branches from a plexus which surrounds the internal carotid artery in its course through the carotid canal, communi- cating above with the cavernous sinus. It also receives the veins ( vv. canalis pterygoidei) which accompany the Vidian artery through its canal, and communicates with the pterygoid, oesophageal, and vertebral plexuses. 2. The Facial Vein. — The facial vein (v. facialis anterior) (Fig. 754) is formed at about the inner extremity of the eyebrow by the union of the frontal and supraorbital veins. From its point of origin it skirts around the inner border of the orbit and is then directed obliquely downward and backward across the face, crosses over the anterior inferior angle of the masseter muscle and the ramus of the mandible a short distance in front of the angle, and is thence continued onward across the posterior part of the submaxillary and the upper part of the superior carotid triangles to open into the internal jugular at about the level of the hyoid bone. It follows in a general way the course of the corresponding artery, lying posterior to it, but the path across the face is much more direct than that followed by the artery. That portion of the vein which extends from the junction of the frontal and supra- orbital arteries to the lower border of the orbit is usually termed the angular vein, and branches arise from this which pass backward into the orbit to communicate with the ophthalmic vein. Just below the ramus of the mandible it usually receives a large communicating branch from the external jugular, and the portion which in- tervenes between this communication and the internal jugular is termed the common facial vein (v. facialis communis). Both the facial and the angular veins are usually described as being destitute of valves ; these structures do occur, however, but they are always insufScient and form no bar to the passage of blood in an inverse direc- tion— i.e., from the facial and angular backward into the ophthalmic veins. Relations. — The angular vein rests upon the nasal process of the maxillary vein internal to the lachrymal sac. In its upper portion the facial vein lies under cover of the orbicularis palpebrarum, and it also passes beneath the zygomatic muscles, but is superficial to the other muscles of the face. In its inframandibular or cervical portion it lies beneath the platysma in a groove in the submaxillary gland. Variations.— The upper portion of the facial vein may begreatly reduced in size. Below, it frequently unites with the lingual vein to form a linguo-facial trunk, which may also be joined by the superior thyroid. Instead of opening into the internal jugular, it occasionally passes across the sterno-cleido-mastoid muscle to unite with the external or anterior jugular. Practical Considerations. — Allen has called attention to the fact that the venous supply of the face differs in some important particulars from that of the trunk and limbs. In the last-named localities, both deep and superficial currents flow in the same direction towards the heart. The facial trunk, however, is not formed by primal venules, as is commonly the case, but by branches communicating with the frontal and supraorbital veins, and by a transverse branch found at the bridge of the nose. The two most important communications with the cavernous sinus are through the ophthalmic vein, which receives tributaries from the angular vein, and the deep facial vein, which empties into the pterygoid plexus, which in its turn communicates with the cavernous sinus by veins passing through the foramen ovale. The veins corresponding to the deep parts of the face, other than those mentioned, also seek an outlet in the same direction, so that much of the superficial blood of the upper part and side of the face passes inward to the brain-case and to the interior of the facial region, while the remaining portion flows downward to join the jugular veins. The facial vein at its lower end receives a large communicating branch from the external jugular, and therefore at or below that point carries a considerable volume of blood, making wounds of the vein dangerous. THE SUPERIOR CAVAL SYSTEM. 865 The facia! vein is said to be less flaccid than most superficial veins, and there- fore to remain more patent after section ; it possesses either imperfectly developed or rudimentary valves, or none at all. As a consequence of these facts, septic dis- ease— malignant pustule, furuncle, carbuncle, cancrum oris — involving the face or forehead, is e.xceptionally dangerous, as the infection may spread by way of the ophthalmic vein or the pterygoid plexus to the cavernous sinus and result in a fatal thrombosis or meningitis. The relations existing between the venous blood of the face and that of the brain-case are rendered evident by the fact that the state of the circulation of the external nose is sometimes an index of the condition of the vessels of the brain. Moreover, in cases of orbital or intracranial tumors, the ophthalmic, angular, and facial veins become congested, dilated, and tortuous from pressure-interference with the venous current. The line of the facial vein is from the canthus of the eye to a point on the mandible at the anterior border of the masseter muscle and just behind the facial artery. This line is straight instead of tortuous, as is the case with that of the latter vessel. Tributaries. — The tributaries of the facial vein are (a) Xhs. frontal and (b) the supraorbital, by the union of which it is formed. In addition it receives in its course across the face (f) the palpebral, [d) the lateral nasals, (e) the superior labial, (f) the inferior labial, {g) the deep facial, (h) tlie masseteric, and (i ) the anterior parotid veins. In its cervical portion it has open- ing into it (j ) the inferior or descending palatine, and (k) the stibmental veins. [a) The frontal veins (vv. frontales) descend over the forehead on either side of the median line, lying immediately beneath the skin upon the frontalis muscle. The branches from which they take origin communicate at the sides and vertex of the skull with tributaries of the occip- ital and temporal veins, and also through small foramina in the frontal bone with the superior longitudinal sinus. The two veins are connected by numerous Cross-branches, and not infre- quently unite more or less completely to form a single median stem which bifurcates below. Each vein terminates at the inner angle of the orbit by uniting with the corresponding supraor- bital vein to form the angular. At the root of the nose the two veins are usually united by a distinct cross-branch, the nasal arch, which receives from below the dorsal nasal veins. {b) The supraorbital vein (v. supraorbitalis) is a relatively large trunk which runs trans- versely above the superior margin of the orbit and consequently is quite distinct from the artery of the same name. It arises at the external angle of the orbit, where it communicates with affluents of the temporal veins, and passes inward beneath the orbicularis palpebrarum, and, piercing that muscle just above the inner angle of the orbit, unites with the frontal vein to form the angular. It receives numerous small branches from neighboring regions and from the diploic vein of the frontal bone, and at the supraorbital notch it communicates with the ophthalmic system of veins. (c) The palpebral veins (vv. palpebrales superiores et inferiores) are small vessels which take .heir origin from the venous plexus of the eyelids and open into the angular vein. The palpe- bral plexus also communicates laterally with the affluents of the temporal veins. {d ) The lateral nasal veins (vv. nasales externae) arise in a rich plexus which occupies the alas and tip of the nose and with which the dorsal nasal vein communicates and also branches from the extensive pituitary plexus, these latter branches emerging along the line of junction of the nasal bones and cartilage. The veins extend upward and backward and open into the lower part of the angular vein. {e) The superior labial or coronary vein (v. labialis superior) takes its origin in a plexus in the substance of the upper lip with which branches from the septum and alse of the nose com- municate. The course of the vein is independent of that of the artery of the same name, passing backward and somewhat upward to the naso-labial groove, and opening into the facial vein about opposite the ala of the nose. {f) The inferior labial vein (v. labialis inferior) arises from a venous plexus in the lower lip and passes downward and outward to open into the facial just after it has crossed the ramus of the mandible. Usually a second vein, the inferior coronary , also arises from the inferior labial plexus and passes almost horizontally outward to open into the facial a litde below the angle of the mouth. [g) The deep facial vein, also termed the anterior internal maxillary , takes its origin from the pterygoid plexus (page SS2) over the tuberosity of the maxilla, through which it receives branches from a net-work lying beneath the mucous membrane lining the antrum of Highmore. It passes forward and downward between the buccinator and masseter muscles, and opens into the outer surface of the facial where that vein passes beneath the zygomatic muscle. 55 866 HUMAN ANATOMY. (Ii) The masseteric veins ( vv. massetericae) are several small veins which return the blood from the masseteric and buccinator muscles, opening into the outer surface of the facial vein. (/ ) The anterior parotid veins (vv. parotideae anteriores) consist of several small veins which issue from the anterior border of the parotid gland and from the socia parotidis. They follow- the parotid duct, around which they form a net-work, and open into the outer surface of the facial vein. (j) The inferior or descending palatine vein (v. palatina") accompanies the ascending palatine or tonsillar branch of the facial artery. It takes its origin in the tonsillar plexus and descends upon the side of the pharjn.x to open into the facial after it has crossed the ramus of the maiidible. Fig. 754. Superficial Middle temporal nd neck ; external jugular li< riiich has been partly removt: {k) The submental vein (v. submentalis) accompanies the arterj- of the same nacie. It rests upon the superficial surface of the mylo-hyoid muscle and passes backward and outward in the submaxillary triangle, beneath the platjsma, to open into the cervical portion of the facial. It communicates with the sublingual vein by several branches which perforate the mylo-hyoid muscle, and, in addition to cutaneous and muscular branches, also receives tributaries from the submaxillary- gland, these latter vessels, however, frequently opening directly into the facial as it traverses the groove upon the gland. THE SUPERIOR CAVAL SYSTEM. 867 3. The Lingual Vein. — The lingual vein (v. lingualisj is a short trunk which either opens directly into the internal jugular or unites with the facial vein to form a hnguo-facial trunk. It is formed by the union of two vessels, the deep lingual veins, which are the venae comites of the lingual artery, and the sublingual. The deep lingual veins are of small calibre and accompany the lingual artery throughout its entire course, numerous cross-connections between them involving the artery as in a plexus. Shortly before opening into the lingual stem the two veins unite, and into the vessel so formed the companion veins of the dorsal artery of the tongue (w. dorsales linguae) open, these vessels communicating with the tonsillar plexus and the superior laryngeal vein. The sublingual vein, also termed the rajiine, has its origin on the under sur- face of the tip of the tongue, beneath the mucous membrane. It passes backward, at first in company with the subma.xillary duct, and, after receiving communicating branches from the deep lingual and the submental veins, it passes to the outer side of the hyoglossus muscle and continues backward in company with the hypoglossal nerve, whence it has been termed the v. comitans n. hypoglossi. All the branches of the lingual vein are provided with valves. Variations. — Considerable variation exists in tiie extent to which the lingual vein is de- veloped, both its constituent tributaries as well as the dorsales lingua sometimes opening inde- pendently into the internal jugular. It may open into either the e.xternal or anterior jugular instead of the internal, and the deep Unguals may open into the pharyngeal vein. Occasionally, by the enlargement of the connection normally occurring, the submental vein becomes a tribu- tary of the sublingual. 4. The Superior Thyroid Vein. — The superior thyroid vein (v. thyreoidea superior) accompanies the artery of the same name. It arises in the upper portion of the plexus which encloses the thyroid gland, communicating through it with its fellow of the opposite side and with the middle and inferior thyroid veins. It is directed up- ward and backward, and opens either directly into the internal jugular or more usually into the lingual or the linguo-facial trunk. Tributaries. — The following are received by the superior thyroid vein, (a) The superior laryngeal vein (v. laryngea superior), which arises in the pharyngo-laryngeal recess from a plexus which receives the blood from the aryepiglottidean fold and the laryngeal musculature and com- municates with- the vv. dorsales linguae above and also with the lower portion of the pharyngeal plexus. It passes upward and backward in company with the corresponding nerve and artery and opens into the superior thyroid vein or occasionally into the linguo-facial trunk or the anterior jugular, (b) The crico-thyroid vein is a slender vessel which accompanies the artery of the same name. (<:) The sterno-mastoid vein (v. sternocleidomastoidea ) receives blood from the sterno-cleido-mastoid muscle and is associated with the artery of the same name. 5. The Middle Thyroid Vein. — The middle thyroid vein is not always present and may be regarded as accessory to the superior thyroid. It issues from the thyroid plexus, opposite the lower part of the lateral lobe of the gland, and passes downward and outward, independently of any artery, to open into the internal jugular at the junction of its middle and lower thirds. The Sinuses of the Dura Mater. The sinuses of the dura mater (sinus durae matris) form a series of channels, frequently of considerable size, occupying clefts in the substance of the dura mater. They receive the cerebral, meningeal, and diploic veins and, in addition, communicate with the extracranial veins by numerous connecting veins known as emissary veins, the largest and most important of which are the ophthalmic veins. They are drained mainly by the internal jugular. A statement of their general structure and a brief description of the blood-lakes associated with them have already been given (page 85 1). I. The Lateral Sinus. — The lateral sinus (sinus transversus) (Figs. 756, 757) has its origin opposite the internal occipital protuberance, at which point there is a meeting of five sinuses, the two lateral, the superior longitudinal, the straight, and 868 HUMAN ANATOMY. the occipital. From this meeting-point, which is termed the torciilar Hcrophili fcon- Qucns sinuum), each lateral sinus passes outward over the squamous portion of the occipital bone along the line of the attachment of the tentorium cerebelli, and, passing over the posterior inferior angle of the parietal, is continued inward upon the inner surface of the mastoid portion of the temporal and the jugular process of the occipital to reach the jugular foramen, where it opens into the internal jugular vein. As it passes upon the mastoid portion of the temporal, it leaves the line of attachment of the ten- torium cerebelli, passing somewhat downward as well as inward, and follows the line of junction of the petrous and mastoid portions of the bone in a somewhat S-shaped course, whence this portion of it is frequentlv termed the sigmoid sinus. A difference in size is usually noticeable in the sinuses of the opposite sides, that of the right being usually the larger, and this difference is due to the mode in which the various sinuses meet at the torcular Herophili. Most frequently the superior longitudinal sinus communicates mainly with the right lateral, while the Fig. 755- Superior longitudinal sinu Fibro-aponeurotic layers of scalp Parietal layer of dura Superior worm Inferior worm Frontal section of head, viewed from behind, showing relations of dura mater to sinuses and to cerebral hemispheres and cerebellum. Straight sinus opens principally into the left, the greater amount of blood carried by the superior longitudinal, as compared with that transmitted by the straight, resulting in the larger size of the right lateral sinus. Indeed, in some cases the right lateral sinus is practically the direct continuation of the superior longitudinal and the left lateral of the straight, the two laterals being connected only by a short and relatively small connecting arm, which represents the torcular Herophili. Throughout that portion of their courses in which the lateral sinuses lie in the line of attachment of the tentorium cerebelli they are triangular in cro.ss-section fFig. 755), but in their mastoid (sigmoid) portion they are semi-circular ; the right sinus has a diameter of from 9-12 mm., while the left \aries from 3-5 mm. At the jugular foramen each sinus makes a sudden bend and opens either directly into the summit of the superior jugular bulb, or else at a varying distance downward upon the anterior surface of the bulb, the upper extremity of which then forms a dome-shaped structure projecting upward into the jugular foramen. THE SUPERIOR CAVAL SYSTEM. 869 Tributaries. — The lateral sinuses, in addition to the sinuses which communicate with them at the torcular Herophili, receive the following tributaries, most of which will be described in greater detail later: (a) the posterior inferior cerebral veins, which pass backward from the temporo-sphenoidal regions of the cerebral hemispheres ; (6) some of the inferior cerebellar veins ; (c) the superior petrosal sinus, this latter communicating with it just where it leaves the line of attachment of the tentorium cerebelli. Into the sigmoid portion there open {d ) the internal au- ditory veins (vv. auditivaeinternae), which issue from the internal auditory meatus ; {e) the mastoid emissary vein (page 876) ; and (/) some of the veins of the medulla oblongata and pons. Variations. — Considerable variation exists in the relative sizes of the right and left lateral sinuses, in accordance as the superior longitudinal sinus opens more or less directly into one or the other. As stated, the tendency is for the superior longitudinal to open into the right lateral ; quite often, however, it opens into the left, and occasionally it may communicate equally with both. In 100 crania, Riidinger found that the right lateral sinus was the larger in 70 cases, the left in 27, and the two were equal in size in only 3 cases. The horizontal portion of the left sinus has been observed to be lacking or reduced to an exceedingly fine channel, and one or both of the sinuses have been observed to pass through a greatly enlarged mastoid foramen to open into the posterior auricular vein, the sigmoid sinus being represented only by a very small channel. In a considerable number of cases a small sinus, known as the petro-squaniosal sinus, opens into the lateral just as it bends downward and inward upon the mastoid portion of the temporal. This sinus passes downward over the anterior surface of the petrous portion of the temporal, along the line of its junction with the squamous portion, and occasionally passes through a foramen — the foramen jugulare spurium — which opens to the exterior just behind the articular eminence of the zygomatic process. The sinus represents the original terminal portion of the lateral sinus, the sigmoid portion of that sinus being a secondary formation, and opened after its exit from the foramen jugulare spurium into the internal jugular, although its connection in the adult is with the temporal vein. Practical Considerations. — By reason of its proximity to the middle ear, mastoid antrum and cells, the sigmoid portion of the lateral sinus is more often the subject of thrombosis than any other sinus (page 1509). This may arise in the following six ways, mentioned in the order of frequency, the first outnumbering all the others : (i) Extension from chronic purulent inflammation of the middle ear ; (2) extension of acute inflammatory disease from the mouth, pharynx, and tonsils into the middle ear, antrum, and cells ; (3) extension of thrombosis from other sinuses, especially the so closely associated superior petrosal ; (4) trauma, such as fracture of the base extending through the middle ear to the sinus ; (5) pressure of tumors or discharge associated with them ; (6) infection from septic wounds of the head, neck, or mastoid region (Macewen). The anatomical symptoms of thrombosis of this sinus may be due to (a) obstruc- tive distension of the superficial veins communicating with the sinus, chiefly the mastoid vein {q-v.) ; (b) mastoid inflammation Tosteitis) resulting from contiguity and from the venous connection ; (e) phlebitis of the veins communicating with the sinus, especially the internal jugular (page 863), condyloid (page 876), and, occasion- ally, the mastoid. The subject of sigmoid sinus thrombosis is further considered in relation to the mastoid (page 1508). The knee (genu) of the sigmoid portion of the lateral sinus extends further inward and forward- on the right side than on the left, and this fact, together with the larger size of the right lateral sinus as compared with the left, aids in explaining the greater frequency of sinus thrombosis, septic meningitis, and cerebral abscess as sequelae of otitis media on the right side (page 1509). The infection is carried by the veins which connect the mastoid cells and antrum with the genu of the sigmoid sinus. On the surface the top of the curve represented by the horizontal and descending (sigmoid) portion of the lateral sinus should correspond to a point (asteric) 2.5 cm. above and 3.8 cm. (ij^ in.) behind the centre of the auditory meatus. This is about the infero-posterior parietal angle. The superior limit of the horizontal portion of the sinus is represented by a line from this asteric point to 3.8 cm. (i J^ in.) above the inion. The superior and anterior boundary of the sigmoid portion is indicated by a line from the same point curving downward and forward along the skin groove at the auriculo-mastoid junction to a little below the level of the external 870 HUMAN ANATOMY. auditory meatus. Here the sinus turns inward and forward to reach the jugular foramen and has no further close relation to the lateral cranial wall. A cur\ed line drawn 12 mm. (J4 in.) below the horizontal and behind the vertical portions of the curved line last described represents approximately the interior and posterior boundary of the sinus. The width thus indicated — a half inch — varies ; it is usually greater in the descending part of the sinus. So, too, the space intervening between the genu and the posterior wall of the external auditorv meatus may vary from 2-12 mm. The direction of the sinuses is also indicated (Macewen) by a line from the upper edge of the external meatus to the asterion, and by one from the tip of the mastoid to the parieto-squamo-mastoid junction, the latter corresponding to the midportion of the sinus, or that most often in\olved in middle-ear disease. The region of danger in trephining is enclosed (Birmingham) by two lines, one from a point 3.3 cm. (i}( in.) above and 3.8 cm. (ij^ in.) behind the centre of the external auditory meatus to a point 12 mm. (i^ in.) above the inion ; the other from a point 3.8 cm. (i}4 in.) behind the meatus and on the same level to a point 12 mm. {}2 in.) below the inion. The sinus almost ne\'er o\erpasses these limits in either a downward or an upward direction, and hence the trephine or chisel may be safely applied either below or above these lines. Fracture of the base of the skull may extend into the lateral sinus, in which case the blood may pass outward into the tympanum and thence by way of the Eusta- chian tube to the pharynx, or — if the tympanic membrane is torn — may find exit, mingled with cerebro-spinal fluid, at the external auditory meatus (page 1505). For further remarks on the practical relations of this important sinus, see page 1508. 2. The Superior Longitudinal Sinus. — The superior longitudinal sinus (sinus sagittalis superior) (Fig. 756) is an unpaired sinus which lies along the line of attachment of the falx cerebri to the cranial vault. It begins blindly anteriorly by a small vein-like portion which Hes in the foramen caecum between the frontal and ethmoidal bones, but soon becomes a true sinus which passes upward and backward in the median line of the frontal bone, beneath the sagittal suture of the parietals, and down the median line of the .squamous portion of the occipital to terminate at the internal occipital protuberance by opening into the torcular Herophili, or, usually, more or less directly into the right lateral sinus. The sinus is triangular in section and increases gradually in size from before back- ward, measuring about 1.5 mm. in diameter at the level of the apex of the crista galli and 1 1 mm. at its termination. Its lumen is usually traversed by numerous irregular bands of connective tissue known as chorda: IMllisii, and frequently, espe- cially in aged persons. Pacchionian bodies, which are numerous along its course, project into it (Fig. 1039). Tributaries. — In the fcetus and in early childhood the superior longitudinal sinus coniniuni- cates with the veins of the nasal cavity through the foramen caecum, but this connection is dissolved in the adult. In addition, it communicates with the neighboring blood-lakes and through these with the meningeal veins, and receives {a) branches from the adjacent portions of the dura mater ; (A 1 the superior cerebral veins, from ten to fifteen in number (page 877) ; and (r) diploic veins, some of which traverse the parietal bone and constitute emissary vefns, the most noticeable of these being one which traverses the parietal foramen (page 876). Variations. — The superior longitudinal sinus varies considerably in size and is occasionally exceedingly small, the tributaries which normally open into it passing downward in the fal.x to open into the inferior longitudinal sinus. It has been observed to divide into two trunks throughout a portion of its course, and also to divide at the apex of the occipital bone into two trunks which followed the lines of the lanibdoid suture to open into the lateral sinuses. Usually, as stated, the sinus communicates more or less directly with the right lateral sinus, but occasion- ally it may bend to the left of the internal occipital protuberance and open into the left lateral. Practical Considerations. — The superior longitudinal sinus may become infected (a) from the scalp through the diploic veins : { b') from foci of cerebral or meningeal disease through the contiguous blood-lakes or through the cerebral \'eins ; (f) in childhood from the nose through the veins traversing the foramen caecum. THE SUPERIOR CAVAL SYSTEM. 871 When the latter veins are patent epistaxis may be a symptom of cerebral hyperaemia (as in congestive headaches) and may relieve it. In children epistaxis, in infants cedema of the scalp over the anterior fontanelle, and in adults oedema over the parie- tal and occipital regions are common symptoms of thrombosis of this sinus, and are easily understood in view of its venous tributaries. Nffivi in the scalp in the mid-line sometimes communicate directly with the sinus by veins passing between the parietals or directly through them near the medial edge. Traumatic or inflammatory thrombosis may follow a depressed fracture of the cranial vault if the fragment invades the lumen of the sinus and obstructs or arrests the flow of blood. A noninfective form of thrombosis is sometimes observed in connection with this sinus. It has received the name of marasmic thrombosis, as it has usually been associated with weakness and debility. The construction of all the sinuses predisposes them to thrombosis. Their rio-idity, their width, the trabecute which occasionally cross them, the peculiar manner in which they are prevented from being too rapidly depleted during inspira- FiG. 756. Head has been sectio terminal portit left of mid-sagittal plane and brain re»ioved, showing dural septa in position ; some superior cerebral veins are seen upon the surface of falx cerebri. tion when the lowering of pressure takes place in the great cervical veins (page 878), and, in the case of the longitudinal sinus, the direction in which the blood from the cerebral veins enters at an obtuse or right angle against the current, all tend to retard the flow of blood and favor coagulation. When to these conditions is added a deficient supply of possibly defective blood, as in exhaustion or depletion from pro- fuse diarrhoea, marasmic thrombosis is apt to occur (Macewen). The line of the sinus begins at the root of the nose and runs in the mid-line to the external occipital protuberance. Rarely there are found in the mid-line of the vertex small reducible swellings to which are feebly transmitted the brain pulsations. They are subpericranial, contain venous blood, and connect with the longitudinal sinus through apertures in the skull, either congenital, the result of bone disease or atrophy, or due to accident. 3. The Inferior Longitudinal Sinus. — The inferior longitudinal sinus (sinus sagittalis inferior') (Fig. 756) is an unpaired sinus which lies in the inferior or free edge of the falx cerebri. It begins at about the middle of the border of the falx and passes 872 HUMAN ANATOMY. backward, gradually increasing in size, to the junction of the falx with the tentorium cerebelli, where it opens into the straight sinus. It receives small tributaries from the falx and sometimes also from the corpus callosum. 4. The Straight Sinus. — The straight sinus (sinus rectus) (Fig. 756), also unpaired, lies along the line of junction of the falx cerebri with the tentorium cerebelli. It is formed at the anterior border of the tentorium by the junction of the inferior longi- tudinal sinus and the great cerebral vein {vena Galeni) (page 877), and is directed backward to open into the torcular Herophili or more usually into the left lateral sinus. In addition to the two trunks by whose union it is formed, it receives a number of small branches from the tentorium, branches from the posterior portion of the medial surfaces of the cerebral hemispheres, and sometimes a median superior cere- bellar vein. 5. The Occipital Sinus. — The occipital sinus (sinus occipitalis) (Fig. 757) is an unpaired, or in some cases a paired, sinus which descends from the torcular Herophili along the line of attachment of the falx cerebelli to the posterior border of the foramen magnum. There it divides into two trunks, the marginal sinuses, which pass forward along the margin of the foramen magnum, one on one side and one on the other, to open into the bulbus superior of the corresponding interna! jugular vein. The occipital sinus receives as tributaries branches from the falx cerebelli and the adjacent portions of the dura, and also some veins from the inferior surface of the cerebellum. At the posterior border of the foramen magnum, where it bifurcates to form the marginal sinuses, it makes connection with the veins of the posterior spinal plexus. Variations. — The occipital sinus is occasionally wanting, and frequently extends only as far as the posterior border of the foramen magnum, the marginal sinuses being undeveloped. It may open above into either the right or left lateral sinus, or into the straight sinus a short distance before its termination. 6. The Cavernous Sinus. — The cavernous sinus (sinus cavernosus) (Fig. 757) is a paired sinus of considerable size w hich extends along the sides of the body of the sphenoid bone from the sphenoidal fissure in front to the apex of the petrous portion of the temporal. It measures about 2 cm. in length and has a diameter of about i cm. and is almost quadrilateral in cross-section. Its external diameter does not, however, represent the actual capacity of its lumen, since this is greatly reduced in size ( i ) by being tra\ersed by numerous trabeculae from which fringe-like prolongations hang freely into the blood-current, a section of the sinus having very much the appearance of a section of the corpus cavernosum penisj whence the name bestowed upon it by Winslow ; and (2) by the fact that the internal carotid arterj' and the abducent (sixth) ner\'e traverse it, -while certain other of the cranial ner\es are embedded in its outer wall. These nerves are tfie oculomotor, the pathetic, and the ophthalmic and maxillary divisions of the trigeminus, which lie in that order from abo\'e downward. Tributaries. — At the sphenoidal fissure the cavernous sinus receives the ophthalmic vein and, farther back, occasionally the basilar vein, both of which are described later on (page 877). In addition, it receives veins from the neighboring portions of the dura mater, and has connecting with it the spheno-parietal and the intercavernous sinuses. These latter are transverse sinuses which pass across between the two cavernous sinuses, the one (sinus intercavemosus anterior) passing in front of the sella turcica and the other (sinus intercavemosus posterior) behind that cavitN', and they receive branches from the dura mater and from the pituitar\- body. The two sinuses, together with the portion of the cavernous sinus between their terminations on each side, form what is usually termed the circular sinus (sinus circularis). Besides the vessels which are trulv tributaries, the cavernous sinus also has connected with it certain vessels which are emissan,' in function, leading blood away from it. The two petrosal sinuses in which it terminates are of this nature. In addition, veins pass from its under surface ( i ) through the foramen ovale, along with the mandibular division of the trigeminal ner\-e, to communicate with the pterygoid plexus; (2) through the fibrous tissue which closes the foramen lacerum medium ; (3) through the foramen of Vesalius, when this exists ; and (4) occasionally through the foramen rotundum with the maxillary division of the trigeminal nerve. THE SUPERIOR CAVAL SYSTEM. 873 Where the internal carotid enters the cavernous sinus at the internal orifice of the carotid canal the sinus projects downward around the artery in a funnel-shaped manner, and Jrom it there arises a close net-work of veins, the carotid plexus or carotid sinus, which completely invests the artery throughout its course through the carotid canal, at the lower opening of which it is continued into one or two veins which open into the internal jugular. Practical Considerations. — The cavernous sinus, though less frequently affected with thrombosis than any other large sinus, may become infected from foci apparently far removed, through the extra-orbital communications of the opiuhalmic veins (pages 879, 880). Thus, carbuncle of the face, cancrum oris, alveolo-dental periostitis, ulceration of the Schneiderian mucous membrane, empyema of the maxillary antrum, abscess of the frontal sinus, osteomyelitis of Fig. 757. Eyeball Superior ophthalmic vein Inferior ophthalmic vein Optic nerve Ophthalmic vein Cavernous sinus- Lateral sinus- Occipital sinus- Lateral sinuF :ular sinus Cavernous sinu Basilar sin Inferior Foramen magnum Tentorium cerebelli Inferior cerebral vein Inferior longitudinal section Lateral sinus Torcular Herophili Dural sinuses at base of skull ; falx cerebri and left half of tentorium ha the frontal diploic tissue, may each be followed bv cavernous sinus thrombosis. In the presence of thrombosis, there are two groups of pressure symptoms (a) venous, causing exophthalmos, oedema of the eyelids and of the corresponding side of the root of the nose, and some chemosis ; (d) nervous, causing ptosis, strabismus, variations in the pupil, pain, etc. _ Arterio-venous aneurism between this sinus and the internal carotid, in addition to similar symptoms of venous obstruction (page 863), often likewise causes paralyses in the distribution of the third, the fourth, and the ophthalmic division of the fifth cranial nerves, which lie in the dura mater on the outer wall of the sinus, and of the sixth nerve, which is in close relation to the internal carotid. The bulk of the blood of the contents of the anterior and lower portions of the skull empties into the cavernous sinus ; that of the remaining portion,— including the greater part of the cerebrum, the cerebellum, the pons, and the cerebral peduncles 874 HUMAN ANATOMY. — chiefly into the tributaries of the lateral sinus. The two sinuses through the superior petrosal sinus and other venous channels, have free anastomotic connection which eftectually tends to equalize or distribute blood-pressure. The communication between the two cavernous sinuses through the basilar sinus — or plexus — and the circular sinus, is an important portion of the mechanism by which the pressure of venous blood within the skull is equalized. This same com- munication may, however, in a case of anterio- venous aneurism {vide supra) bring about involvement of the orbit on the other side, the blood from the aneurism entering the opposite sinus by way of these intercommunicating sinuses, or infection may follow the same channel. 7. The Spheno-Parietal Sinus. — The spheno-parietal sinus (sinus spheno- parietalisj, also known from its position as the sinus ala; parvce, arises at the outer extremity of the lesser wing of the sphenoid from one of the meningeal veins and passes horizontally inward, under cover of the posterior border of the lesser wing, to reach the ca\ ernous sinus near its anterior extremity. It receives dural, diploic, and some of the anterior cerebral \eins. 8. The Superior Petrosal Sinus. — The superior petrosal sinus (sinus petrosus superior) is the smaller of the two sinuses into which the cavernous divides at the ape.x of the petrous portion of the temporal. It passes outward and backward along the superior border of the petrous bone and opens into the lateral sinus just at the point where it lea\es the line of attachment of the tentorium cerebelli to become the sigmoid sinus. The superior petrosal sinuses receive some small tympanic veins and some branches from the cerebellimi and cerebrum. 9. The Inferior Petrosal Sinus. — The inferior petrosal sinus (sinus petrosus inferior) is the larger terminal branch of the ca^ ernous sinus, and extends from the posterior extremity of that sinus, at the apex of the petrous portion of the temporal bone, along the petro-occipital suture to the jugojlar foramen, where it opens into the superior bulb of the jugular vein, or, frequently, into the vein below the bulb. In addition to small branches from the neighboring portions of the dura and from the cerebellum, pons, and medulla oblongata, the inferior petrosal sinus receives some internal auditory veins and an anterior condyioid vein which arises from a plexus surrounding the hypoglossal nerve in its course through the anterior condyloid foramen. In its anterior portion the sinus is also in communication with the basilar sinus. ID. The Basilar Sinus. — The basilar sinus (plexus basilaris), also termed the transverse sinus, is usually a plexus of sinuses rather than a single, distinct sinus. It occupies the dura mater which covers the basilar process of the occipital bone and communicates with the inferior petrosal and posterior intercavernous sinuses in front, and behind, at the anterior border of the foramen magnum, with the anterior spinal plexus. It receives branches from the medulla oblongata and from the diploe. Practical Considerations. — Fracture of the base of the skull through the posterior (cerebellar) fossa may invohe the basilar plexus of sinuses and be followed by an intracranial hemorrhage which slowly oozes through the line of fracture and, following the lines of vessels or nerves, ultimately causes swelling and ecchymosis of the skin of the neck ; the latter is apt to show first anterior to the tip of the mastoid, to which region the blood is conducted bv the cellular tissue around the auricular artery. It spreads thence upward and backward in a curved line. The Diploic Veins. The spaces of the diploe are traversed by a rich plexus of veins, characterized by the thinness of their walls and opening by numerous small communicating branches either into the veins of the scalp, the middle meningeal veins, or the cranial sinuses. Some larger, although rather inconstant, stems also arise from the plexus and form what are termed the diploic veins. Of these, four are usually- recognized (Fig. 758). THE SUPERIOR CAVAL SYSTEM. 875 1. The anterior diploic vein (v. diploica frontalis) descends in the diploe of the frontal bone and at the level of the supra-orbital notch opens either into the supra-orbital or ophthalmic vein. It communicates v\ith the anterior temporal diploic vein and also with the frontal veins and the superior longitudinal sinus. 2. The anterior temporal diploic vein (v. diploica temporalis anterior) passes downward and forward in the diploe of the anterior portion of the parietal bone and opens either into a deep temporal vein or into the spheno-parietal sinus. 3. The posterior temporal diploic vein (v. diploica temporalis posterior) passes downward in the diploe of the posterior part of the parietal bone and usually opens into the mastoid emissary vein, thus communicating with the lateral sinus. It also communicates with the posterior auric- ular vein and may open into it. 4. The occipital diploic vein (v. diploica occipitalis) passes downward in the squamous portion of the occipital bone, not far from the median line, and opens either into the occipital vein or into the occipital emissary vein, by which it communicates with the torcular Herophili or the lateral sinus. Fig. 758. Outer table of skull has been removed spaces of diplofi. Practical Considerations. — The diploic veins being incapable of effective contraction, bleed very freely and persistently, and are sometimes a source of embarrassment during operations on the skull. Through their communications with the veins of the scalp on the one hand, and with the endo-cranial sinuses and meningeal veins on the other, they may, as in some cases of compound fracture, convey infection from the surface to the diploe, causing osteomyelitis and necrosis, or within the cranium, causing septic meningitis or sinus thrombosis. Pyjemia has followed an infective phlebitis of the diploic veins themselves. Diploic infection introduced from without — pyogenic — or through the blood — tuberculous — is apt to spread rapidly within the diploic tissue itself, as well as to the underlying structures. The Emissary Veins. The term e^nissary vein is applied to those branches which place the sinuses of the dura mater in communication with veins external to the cranial ca\'ity. Using the term in its broadest sense, the emissary veins are very numerous, since both the diploic and the meningeal veins might be regarded as such, as well as the carotid 876 HUMAN ANATOMY. plexus (page 873) and the ophthalmic vein {.page 879), all these making connections with the sinuses, on the one hand, and with extracranial veins, on the other. It is customary, however, to limit the term to certain veins which, for the most part, traverse special foramina in the cranial walls, a few, however, passing through foramina whose principal content is one of the cranial nerves. 1. The parietal emissary vein (emissarium parietale), rather variable in size, traverses the cor-, respondingly variable parietal foramen, placing the superior longitudinal sinus in communication with the \euis of the scalp. 2. The occipital emissary vein (emissarium occipitale) traverses the occipital protuberance and places the torcular Herophili or one or the other of the lateral sinuses in communication with the occipital veins. Its size is variable ; it usually receives the occipital diploic vein, and may perforate only the external or the internal table of the occipital bone, representing in such cases the terminal portion of the diploic vein rather than a true emissary. 3. The mastoid emissary vein ^ emissarium mastoideum) passes through the mastoid foramen and places the lateral sinus m communication with either the occipital or the posterior auricular veins, it is occasionally wanting, and, on the other hand, may be so large as to appear to be the continuation of the lateral sinus, the terminal portion of that vessel between the mastoid and jugular foramina being greatly reduced in size. 4. The posterior condyloid emissary vein (emissarium condyloideum) is very inconstant, and when present traverses the posterior condyloid foramen, extending between the lateral sinus near its termination and the vertebral \eins. 5. The anterior condyloid emissary vein (retecanalis hypoglossi ) is a net-work which sur- rounds the hypoglossal nerve in its course through the anterior condyloid foramen. From the plexus two veins arise, one of which passes to the inferior petrosal sinus and the other to the vertebral veins. 6. The emissaries of the foramen ovale ( reie foraminis ovalis ) are formed by two veins which communicate above with the cavernous sinus and pass to the foramen ovale, where they form a plexus surrounding the mandibular division of the trigeminal nerve and communicate v\ ith the pterygoid plexus of veins. Occasionally, also, a similar plexus accompanies the maxillarj- division of the trigeminus through the foramen rotundum. 7. The emissary vein of the foramen of Vesalius is, like the foramen, inconstant, occurring only about once in three cases. It extends between the cavernous sinus and the pterygoid plexus of veins. 8. Finally, a variable number of small veins pass through the connective tissue which closes the foramen lacerum medium and place the cavernous sinus in coninninication with the pterygoid ple.xus. Practical Considerations. — The relations of the emissary veins explain many cases of spread of extra-cranial infection to the meninges and the sinuses. If there were no emissary veins, injuries and diseases of the scalp and skull would lose half their seriousness (Treves). Infected wounds of the scalp, cellulitis or erysipelas involving that structure, osteomyelitis, or necrosis of the cranial bones may through the emissary veins result in serious intra- cranial disease. The largest of these veins is usually the mastoid, the communication between the lateral sinus and the occipital or posterior auricular vein (vide supra). This relation and the considerable quan- tity of blood carried by the mastoid vein are thought to explain the supposed effect of leeches or blisters applied behind the ear in cerebral hypersemia or inflammation, especially as nearly all the blood of the brain leaves it through the lateral sinuses. They also explain the extensive oedema behind the ear and around the mastoid region often seen in lateral sinus thrombosis. Pus has formed in the cerebellar fossa outside of the sigmoid sinus, made its exit through the mastoid foramen and appeared as an occipito-cervical abscess (Erichsen). The escape of pus by the mastoid foramen indicates extradural pus in the cerebellar fossa about the sigmoid groove, with the probability that sigmoid sinus thrombosis exists, especially if the mastoid vein is itself thrombosed (Macewen). In suppurative sigmoid sinus disease the posterior condyloid vein may convey infection to the cellular tissue in the upper part of the posterior cer\ical triangle, causing abscess beneath the deep fascia ; or, as a result of cerebellar pachymen- ingitis, there may be phlebitis of this vein, with marked tenderness in the same region. The emissary veins are important agents in the equalization of intra-cranial pressure. THE SUPERIOR CAVAL SYSTEM. 877 The Cerebral Veins. The cerebral veins (vv. cerebri) convey the blood carried to the brain by the cerebral arteries to the sinuses of the dura mater. They differ from most of the other veins in that they contain no valves, their walls are very thin and destitute of muscle-tissue, and their arrangement does not usually follow that of the arteries. 1. The Superior Cerebral Veins. — The superior cerebral veins (vv. cerebri superiores) are from eight to twelve in number, draining the upper, lateral and medial surfaces of the cerebral hemispheres. They follow, for the most part, the sulci of the hemispheres, although connected across the gyri by numerous anastomoses, and they open above into the superior longitudinal sinus. The various veins show a tendency to increase in size from before backward, and while the anterior ones have a course almost at right angles to the superior longitudinal sinus, the more posterior ones are directed forward as well as upward and open obliquely into the sinus and in a direc- tion contrary to the flow of the blood contained within it. 2. The Middle Cerebral Vein. — The middle cerebral vein (v. cerebri media ), also termed the superficial Syl'^'ian vein, lies superficially along the line of the Sylvian fissure and opens below into either the cavernous or the spheno-parietal sinus. It receives affluents from the surface of the brain on either side of the fissure and through these anastomoses with both the superior and inferior cerebral veins. One of these affluents which lies appro.ximately along the line of the fissure of Rolando is ilsually of large size and communicates directly with one of the superior cerebral veins, the two forming what is known as the great ariastomotic vein of Trolard, uniting the superior longitudinal sinus with the median cerebral vein. 3. The Inferior Cerebral Veins. — The inferior cerebral veins (vv. cerebri inferiores) are a number of small veins which occupy the inferior surfaces of the hemi- spheres. They are somewhat irregular in their arrangement, those of the frontal lobes anastomosing with the superior cerebrals and opening into the anterior portion of the superior longitudinal sinus, while those of the temporo-sphenoidal region anastomose with the middle cerebral and open into the spheno-parietal, cavernous and superior petrosal sinuses and into the basilar vein. 4. The Great Cerebral Vein. — The great cerebral vein (v. cerebri magna), also known as the great vein of Galen, is a short stem about i cm. in length which is formed beneath the splenium of the corpus callosum in the neighborhood of the pineal body, by the union of the two internal cerebral veins. It passes backward and upward, curving around the posterior extremity of the corpus callosum, and terminates (Fig. 756) by opening into the anterior end of the straight sinus. Tributaries. — The great cerebral vein is formed by the union of the two (a) internal cerebral veins (vv. cerebri internse), also known as the small veins of Galen. These are situated, one on either side of the median line, in the velum interpositum, which forms the roof of the third ventricle. Each is formed at the foramen of Monro b>' the union of three veins, the choroid vein, the vein of the septum lucidum, and the vein of the corpus striatum. The choroid vein (v. chori- oidea) seems to be the direct continuation of the internal cerebral vein. It begins at the junc- tion of the body and descending horn of the lateral ventricle, passes forward along the floor of the ventricle in the outer edge of the choroid plexus, and opens at the foramen of Monro into the internal cerebral vein of its side. The vein of the septum lucidum (v. septi pellucidi) passes backward along the outer (ventricular) surface of the septum lucidum, returning the blood from the head of the caudate nucleus and neighboring parts, and the vein of the corpus striatum (v. terminalis), which drains the lenticular nucleus and to a certain extent the caudate nucleus also, passes backward in the groove between the corpus striatum and the optic thalamus (stria termi- nalis). (b) The posterior vein of the corpus callosum passes backward from about the middle of the superior surface of the corpus callosum and, bending around the splenium, empties into the great cerebral vein or into the internal cerebral vein near its termination. It receives blood from the corpus callosum and from the median surface of the hemisphere. {c) The basilar vein (v. basalis) is a large paired vein which arises at the anterior per- forated space by the junction of the deep Sylvian vein with the anterior vein of the corpus cal- losum. It passes backward over the optic tract of its side and then curves upward around the cms cerebri to reach the dorsal surface of the brain-stem, where it opens into either the great or the internal cerebral vein. Occasionally the terminal portion which bends upward around the 878 HUMAN ANATOMY. crus is lacking, the vein then emptying into the cavernous sinus. The deep Sylvian vein, which is its main stem of origin, begins in a number of vessels which ramify over the surface of the insula (island of Reil) and passes downward and forward at the bottom of the Sylvian fissure to become continuous with the basilar at the anterior perforated space. Occasionally it unites with the lower portion of the middle cerebral vein or opens with it into the spheno-parietal sinus. The anterior vein of the corpus callosum corresponds to the anterior cerebellar artery, sometimes termed the anterior central vein ; it arises on the anterior part of the upper surface of the corpus callosum and bends downward around the genu to unite with the deep Sylvian vein at the anterior perforated space. The basilar vein drains all the central part of the base of the brain, and, in addition to the two veins which are regarded as its stems of origin, it receives branches from the optic tract, the olfactory bulb, the anterior perforated space, the tuber cinereum, the corpora mammillaria, and the posterior perforated space, and it furthermore receives a vein from the superior vermis of the cerebellutn. The veins of the anterior perforated space are from ten to fifteen in number and have their origin in the nuclei of the corpus striatum and in the internal capsule, while those of the posterior perforated space drain the optic thalami. Practical Considerations. — The free communication of the thin-walled valveless cerebral \eins w ith one another is one of the agents for the equalization of intracranial venous pressure. An anastomotic trunk unites the middle cerebral vein with the posterior cerebral, thus permitting the passage of venous blood by means of the anterior basilar vein into the sinuses about the foramen magnum. Relief from excessive intracranial blood-pressure may, in addition, be effected by the escape of blood from within the cranium (a) in the occipital region through the internal jugular and mastoid vein ; (d) in the frontal region through the ophthalmic vein and the vein traversing the foramen ovale ; (c) in the basal region through the petrosal sinuses and the posterior condyloid vein ; and (d) at the vertex through the diploic veins and the venules penetrating the outer table of the cranium to join those of the scalp (Allen). The avoidance of sudden depletion of the intracranial venous channels through the inspiratory emptying of the large extracranial veins is admirably provided for and the mechanism should be understood, as it has practical relation to many phe- nomena of cerebral anjemia and hyperaemia, to shock and syncope and concussion, to sinus thrombosis, and to many other intracranial conditions. The chief factors in equalizing the flow in the sinuses — and thus practically throughout the brain — may be briefly summarized as follows : (a) The oblique entrance into the longitudinal sinus of its tributaries — the larger middle and posterior cerebral veins — pouring their blood into it against the stream ; (fi) the division of the sinus at the Torcular Herophili into two trunks diverging at right angles ; (c) the course of the blood-current in the lateral sinus — first horizontal, with a convexity outward ; then — in the first part of the sigmoid — vertical ; then horizontal, with a convexity downward, and then a quick upward and outward turn, with narrowing of its calibre before entering the jugular fossa ; (d) the widening of the upper part of this fossa — which is above the outlet of the sig- moid— and the narrowing of its exit (Macewen). Were it not for these and other subsidiary anatomical arrangements contributing to the same end, the effect of a deep inspiration on the cervical veins (page 863) would be so to aspirate the venous channels of the brain as to cause faintness or momentary unconsciousness. The cerebral veins are so delicate that in operations upon the brain it is often better to arrest bleeding by gauze-pressure than to attempt to seize and tie separate vessels. 5. The Cerebellar Veins. — The cerebellar veins form a net-work over the surface of the cerebellum, the course of the larger stems being, for the most part, at right angles to that of the folise. The superior cerebellar veins (vv. cerebelli superiores) open in part laterally into the lateral and superior petrosal sinuses, while others pass medially and unite to form a superior median cerebellar vein, which passes forward and downward along the superior vermis and opens either into the great cerebral vein or the terminal portion of the basilar vein. THE SUPERIOR CAVAL SYSTEM. 879 The inferior cerebellar veins (vv. cerebelli inferiores), somewhat larger than the superior, pass in part forward and outward to open into tlie lateral or superior petrosal sinuses, and in part backward to unite with the occipital sinus. The Ophthalmic Veins. The ophthalmic veins take their origin from the contents of the orbit and pass from before backward, uniting to form two principal trunks, a large superior and a smaller inferior ophthalmic vein, which open at the sphenoidal fissure into the anterior extremity of the cavernous sinus. At the margin of the orbit both veins form important connections with the angular vein, and, since no valves occur in any of the branches of the ophthalmic veins, they form important emissaries connecting the cavernous sinus with the facial \'ein. 1. The Superior Ophthalmic Vein. — The superior ophthalmic vein (v. oph- thalmica superior) (Fig. 757) is formed at the inner angle of the orbit by the fusion of usually two vessels which come from the supra-orbital and angular veins and pass respectively above and below the pulley of the superior oblique muscle of the eye and unite a short distance posterior to that structure. The anterior portion of the superior ophthalmic vein so formed is sometimes termed the v. yiaso- frontalis, and in its further course it is directed somewhat tortuously, at first obliquely backward and outward, passing across the optic nerve and beneath the superior rectus muscle, and then more directly backward to the sphenoidal fissure. Tributaries. — The superior ophthalmic receives numerous tributaries from both the eyeball and the other contents of the orbit, most of the branches from the latter sources corresponding to branches of the ophthalmic artery. Thus it receives (a) the anterior and (i) the posterior ethmoidal veins (vv. ethmoidales anterior et posterior) which return blood from the sphenoidal sinus and the superior meatus and turbinate bone of the nose, communicating with the other veins of the nasal cavity and entering the orbit by the ethmoidal foramina ; {c) the lachrymal vein (v. lacrimalis), a vein of considerable size arising in the lachrymal gland and accompanying the artery of the same name ; and (rf) muscular veins (vv. musculares) which return the blood from the levator palpebrae superioris, the superior and internal recti, and the superior oblique, the veins from the other muscles of the orbit usually opening into the inferior ophthalmic vein. From the eyeball it receives {e) the two superior venae vorticosae. These veins return the blood from the choroid coat, the ciliary body, and the iris, and are four in number, each having its origin from a rich plexus which occupies one of the four quadrants of the choroid, the prin- cipal stems of the plexus radiating from all directions towards the central point of its quadrant. Here they unite to form a single trunk which pierces the sclera obliquely at about the equator of the eyeball, the veins from the two superior quadrants emptying into the superior ophthalmic, while the two from the inferior quadrants connect with the inferior ophthalmic. Occasionally five or six venje vorticosa exist, and they open sometimes into the muscular veins instead of direcdy into the ophthalmic stems. (/) The anterior ciliary veins (vv, ciliares anteriores) are very slender veins which leave the eyeball at the points where the recti muscles are inserted into the sclerotic ; two or three veins are associated with each muscle-tendon and open into the muscular veins, [g) The posterior ciliary veins (vv. ciliares posteriores) accompany the poste- rior or short ciliary arteries. The territory supplied by the arteries is, however, drained by the vena; vorticosa;, and the posterior ciliary veins, which are very small, take their origin only from the posterior portion of the sclerotic and from the sheath of the optic nerve, (h) The vena cen- tralis retins is a single stem which accompanies the corresponding artery through the centre of the optic nerve, and has its origin in branches which ramify over the surface of the retina. The vein leaves the optic nerve usually before the artery and opens either into the superior ophthalmic vein or, more frequently, directly into the cavernous sinus. 2. The Inferior Ophthalmic Vein. — The inferior ophthalmic vein (v. oph- thalmica inferior) (Fig. 757) takes its origin from a net-work of small veins situated on the inner portion of the floor of the orbit near its border. This plexus communi- cates with the facial vein and is continued backward towards the fundus of the orbit, more frequently as a coarse net-work than as a definite stem. The vein, when \t exists, or the net-work, anastomoses with branches of the superior ophthalmic. Tributaries. — {a) Muscular branches from the inferior and external recti and the inferior oblique muscles and [b) the inferior venae vorticosae from the lower half of the eyeball. It opens posteriorly either directly into the cavernous sinus or else unites with the superior ophthalmic vein. 8So HUMAN ANATOMY. Anastomoses of the Ophthalmic Veins. — The ophthalmic veins are throughout destitute of valves and open posteriorly into the cavernous sinus, and, since they also communicate with peripheral veins, they may well be regarded as emissary channels through which the blood may flow either from the cavernous sinus to the peripheral veins or in the reverse direction, as may be determined by the relative pressure within and without the cranium. The principal connec- tions which the veins make are ( i ) with the facial vein, which is itself practically devoid of valves, through their branches of origin ; ( 2 ) with the veins of the nasal cavity through the eth- moidal branches ; and (3) with the pterygoid plexus by means of a branch of the inferior ophthal- mic which passes downward througli the spheno-maxillary fissure. Practical Considerations. — The communication between the superior ophthalmic vein — the largest channel in the adult between the vessels of the venous system of the head and face and the sinuses of the dura mater — and the facial vein, while adding to the danger of intracranial complications as a result of infectious disease situated upon the face (page 873), afiords relief to intraocular tension in cases of pressure upon the cavernous sinus, as from an inflammatory exudate or an intra- orbital or intracranial growth. Such relief delays the appearance of " choked disc" (page 1471), due to the distension of the tributaries of the vein, especially the poste- rior 'ciliary veins and the vena centralis retinae. In arterio-venous aneurism of the cavernous sinus and internal carotid artery — due to basal cranial fracture, a bullet- or stab-wound, or to idiopathic vascular degeneration — the ophthalmic veins are usually compressed and may transmit pulsation from the sinus to the dilated veins of the eyelids and of the frontal region. The conjunctivEe are congested. Exoph- thalmos (page 1439), bruit and thrill are not uncommonly present as a result of involvement of the intraorbital veins. Nervous symptoms — noise in the head, intracranial or frontal pain and paralyses — are rarely absent. These symptoms may be simulated by those caused by traumatic aneurism of an orbital artery or by the direct pressure of an internal carotid aneurism on the ophthalmic vein as it empties into the sinus. The External Jugul.\r Vein. The external jugular vein (v. jugtilaris externa) (Fig. 759), notwithstanding its usual connection with the subclavian, is closely related both in its development and topographical relations with the internal jugular, and may be most conveniently con- sidered here. It is formed in the neighborhood of the angle of the mandible by the union of the temporo-maxillary and posterior auricular veins, and couises downward immediately below the platysma, crossing the sterno-cleido-mastoid muscle obliquely. In the lower part of the neck it pierces the superficial layer of the deep cervical fascia, sometimes above and sometimes below the posterior belly of the omo-hyoid, and opens into the subclavian vein near its junction with the internal jugular. A short distance below its origin it gives off a large branch which passes forward and downward to communicate with the facial vein. At its entrance into the subclavian it is provided with a pair of vaKes, and usually a second pair occurs at about the middle of the neck. A third pair is occasionally present in the interv'al between the other two, and all of them are insufficient. The superficial layer of the deep cervical fascia is intimately adherent to the walls of the vein at the point where the latter perforates it, and sometiines the fascia is especially thickened immediately below and to the inner side of the vein. This attachinent of the fascia prevents any collapse of the walls of the lower part of the vein, if for any reason there is a deficiency in the amount of blood it contains, and predisposes, therefore, to the entrance of air in case the vein is severed. Variations. — Considerable differences of opinion exist as to the definition of the external jugular vein. Some authors describe it as formed by the union of the posterior auricular and occipital veins, the communicating branch described above as occurring between it and the facial being then regarded as the main stem of the temporo-maxillary ; others, again, regard it as formed by the union of the temporal and maxillary veins, the temporo-maxillary then con- sthuting its upper portion. The vein is subject to considerable variation in size, an inverse correlation existing between it and the anterior jugular. It may even be entirely wanting or, on the other hand, it may be double throughout a portion of its course. It occasionally divides below, one branch passing, as usual, to the subclavian, while the other, passing over the clavicular attachment of the sterno- cleido-mastoid, opens into either the anterior or the internal jugular. THE SUPERIOR CAVAL SYSTEM. 88i In connection with the abundant \'ariation shown in the size of the external jugular it is interesting to note that in the majorirs' of mammals it is the most important vein of the neck, surpassing the internal jugular in size. It is, houever, of later de\-elopment than the latter] and its later importance is due largely to the union with it of the facial vein or of the linguo-facial trunk. In man, however, a new connection of the facial with the internal jugular occurs, whereby the importance of the external jugular becomes reduced, and its \-ariation in size is largely dependent upon the extent to which the original direct connection of the facial with it is retained. Fig. 759. 1 of head and neck ; external juj muscle, which has been partly"" jlar lies beneath platysma Practical Considerations. — The line of the external jugular vein is from the angle of the jaw to the centre of the clavicle. Backward pressure made about an inch above the latter point will cause the vein to become visible- through- out its length. For that reason it was at one time selected for phlebotomy in congestions or inflammations about the face and neck. The vein is in the superficial fascia and therefore courses over the stemo-mastoid muscle. In all operations on the side of the neck its size and its course should be borne in mind. 882 HUMAN ANATOMY. Tributaries. — The tributaries of the external jugular are (i) the temporo- maxillary, (2) the posterior auricular, (3) the posterior exterfial jugular, (4) the suprascapular, and (5) the anterior jugular vein. It may also receive the occipital vein CP^Re 859)- I. The Temporo-Maxillary Vein. — The temporo-maxillary vein (v. facialis posterior J (Fig. 753; is formed in the substance of the parotid gland by the union of the temporal and internal maxillary veins. It passes directly downward, and at about the angle of the jaw unites with the posterior auricular vein to form the external jugular. The temporal vein accompanies the temporal artery and is formed just above the zygoma by the union of the superficial and middle temporal veins. The super- ficial temporal vein (v. temporalis siiperticialis) (Fig. 759) is formed by the union of an anterior and a posterior branch, which take their origin in a plexus covering the greater portion of the skull-cap and communicate anteriorly with branches of the frontal vein and posteriorly w ith the posterior auricular and occipital veins. The middle temporal (v. temporalis media) arises from a plexus which lies upon the outer surface of the temporal muscle, beneath the temporal fascia and above the zygoma. Branches of the plexus pierce the temporal fascia near the external angle of the eye and communicate with branches of the facial and lachrj-mal ner\-es, while other branches pass deeply into the substance of the temporal muscle and anastomose with the deep temporal veins. The middle temporal, from its origin in the plexus, passes backward parallel with the upper border of the z\goma, perforates the teinporal fascia, and joins with the superficial temporal \ein. Tributaries. — The temporal vein receives the following tributaries, (a) The anterior auricular veins (w. auriculares anteriorcs) are four or five small vessels which come from the anterior surface of the pinna, (b^ The posterior parotid veins (vv parotideae posteriores), small branches which drain the parotid glanil communicating with tlie anterior parotid branches of the facial, (c ) The articular veins (vv. articulares mandibulae), several in number, arise in a rich ple.xus which surrounds the svTiovial membrane of the temporo-mandibular articulation. This plexus receives tympanic branches (vv tympanicae), which accompany the tympanic arterj- through the Glaserian fissure, and communicates anteriorly with the pterygoid plexus. {d) The transverse facial vein (v. transversa faciei) which accompanies the artery of the same nan-.e. The internal maxillary vein (v. ma.xillaris interna) (Fig. 760) appears sometimes as a distinct vessel accompanying the internal ma.xillary artery and receiving as tributaries veins corresponding to the arterial branches. In other cases it is represented by a plexus of veins, frequendy e.xceedingly dense, occupying the pterygoid fossa and communicating anteriorly with the facial vein and posteriorly with the temporo-maxillary. This pterygoid plexus (plexus ptengoideus) (Fig. 760) is embedded in the adipose tissue which occupies the pterygoid fossa and consists of two portions, one situated upon the outer surface of the external pterygoid muscle and the other between the two pterygoids, this latter plexus being somewhat more extensive than the other, with which it is united by branches passing through, above, and beneath the e.xternal pterygoid muscle. It is also continued forward as a fine plexus surrounding the infra-orbital nerve, and that portion which rests upon the tuberosity of the maxilla is occasionally more or less distinct from the remainder, and has been termed the plexus alveolaiis. The pterA'goid plexus communicates with the facial vein through the deep facial or anterior internal maxillary \'ein, with the phar\'ngeal plexus, and with the articular plexus of the temporo-mandibular articulation. It further receives the emissai^' veins from the cavernous plexus which traverse the foramen o\ale, the fora- men of \^esalius, and the foramen lacerum medium, and also a branch from the inferior ophthalmic vein which passes through the spheno-maxillary fissure. Tributaries. — The tributaries of the internal maxillary- vein or the ptery-goid plexus may be described as follows. ((7) The spheno-palatine vein has its origin in the rich venous plexus which underlies the mucous membrane of the nasal cavity and with which the ethmoidal veins also communicate. It traverses the spheno-palatine foramen with the arter\- of the same name, and is joined by the Vidian, pteiygo-pa/atiiie, and superior palatine veins, all small vessels whose origin is indicated THE SUPERIOR CAVAL SYSTEM. 883 by their names. It then passes between the two heads of the e.xternal pterygoid muscle and opens into the pterygoid ple.xus or into the internal ma.xillary vein. (b) The superior dental veins open into the infra-orbital and alveolar portions of the ple.xus. (c) Muscular veins from the masseter, buccal, and pterygoid muscles. {d) The deep temporal veins (vv. temporales profundae) descend from the substance of the temporal muscle, where they anastomose with the superficial temporals, between the muscle and the bone. [e) The middle meningeal veins (vv. meningeae mediae) accompany the main stem and branches of the middle meningeal artery as vense comites and return the blood from the dura mater lining the sides and vertex of the cranium. Lying in the substance of the dura mater, these veins Fig. 760. Veins of head ; part of ndible and aKsociated muscles have been to expose pterygoid plexus. resemble the sinuses of the dura in their stmcture, and they communicate with the blood-lakes of the dura, with the superior longitudinal, spheno-parietal and petro-squamosal sinuses, and with the superficial Sylvian vein. They open below into the deeper portion of the pterygoid plexus. {/) The inferior dental vein follows the course of the inferior dental artery, opening above into the more superficial portion of the plexus. 2. The Posterior Ataricular Vein. — The posterior auricular vein (v. auricularis posterior) arises from a plexus situated over the mastoid portion of the temporal bone and communicating with branches of the occipital and temporal yeins. It descends S84 HUMAN ANATOMY. behind the pinna, occasionally receiving the mastoid emissary vein, and terminates near the angle of the jaw by uniting with the temporo-maxillary to form the external jugular. 3. The Posterior External Jugular Vein. — 'Ihe posterior external jugular vein arises from the integument and muscles of the upper and back part of the neck, just below the occipital region, and descends obliquel)- behind the sterno-cleido-mastoid muscle to open into the external jugular just after it has crossed the muscle. 4. The Suprascapular Vein. — The suprascapular vein (v. transversa scapulae) is really a double vein, being represented by two vessels provided with valves which accompany the suprascapular artery as its \enEe comites. They arise upon the upper part of the dorsal surface of the scapula, pass o\'er the trans\erse ligament of that bone, and are continued inward, pai'allel with the clavicle and behind it, to open into the external jugular near its termination or else directly into the subcla\'ian. Just before their termination the two venae comites unite to a single stem. The suprascapular vein is usually joined either at or near its termination by the transverse cervical veins which form the venae comites of the trans\'ersalis colli artery. These veins may also open, however, directly into the subclavian. 5. The Anterior Jugular Vein. — The anterior jugular \ ein (v. jugularis anterior) ( Fig, 753 ) arises beneath the chin, upon the inylo-hyoid muscle, by branches Avhich come from the integument and superficial muscles of that region, communicating with the submental branches of the facial. The vein passes almost vertically down the neck resting upon the sterno-hyoid muscle a short distance lateral from the median line, until it meets the anterior (inner) border of the sterno-cleido-mastoid near its sternal attachment. There it makes an abrupt bend, passing almost horizontally outward beneath the muscle to open into the external jugular immediately above its termination. The anterior jugular receives a communicating branch, occasionally of con- siderable size, from the facial subcutaneous veins, and tributaries from the median region of the neck also open into it ; it may also receive small branches from the larynx and thyroid gland. It contains no valves. At its origin it is superficial to the deep cervical fascia, but below the hyoid bone it is embedded in the superficial layer of that fascia, and below lies in the spatium suprasternale (space of Burns) formed by the splitting of the fascia into two lamellae. In this space there occurs a trans\'erse anastomosis between the two veins, forming what is termed the arcus venosus juRuli, and into this a jiumber of small branches from neighboring structures open. The horizontal portion of the vein eventually pierces the posterior layer of the space to reach the external jugular. Variations. — The anterior jiigiilar varies considerably in size, inversely to the external jugular. Occasionally the two, veins of opposite sides unite throughout the vertical portion of their course to form a single stem, which pa.sses down the median line of the neck and has con- sequently been termed the v. mediana colli. The communicating branch from the facial vein, which passes downward along the anterior border of the sterno-cleido-mastoid, is sometimes quite large, functioning as the direct continua- tion of the facial, which may thus pour its blood mainly, if not entirely, into the anterior jugular. Below, while the anterior jugular usually opens into the external jugiilar, yet it sometimes opens directly into the subcla\ian, and occasionally it receives near its termination an exicrnal thoracic vein, which ascends from the region of the mammary gland over the clavicle, posterior to the attachment of the sterno-cleido-mastoid. The Subcl.\vi.\n Vein. The subclavian vein (v. subclavia) (Fig. 753) is the terminal portion of the \enous sy.stem of the upper extremity. It begins at the anterior border of the first rib, where it is directly continuous with the axillary vein, and passes almost horizontally inward, anterior to the scalenus anticus muscle and behind the cla\'icle, to the junction of that bone with the sternum, where it unites with the internal jugular to form the innominate vein. Its course is \-ery similar to that of the subclavian artery, but it is more horizontal and somewhat anterior to the artery, from which it is separated by the scalenus anticus. It is provided with a pair of \-alves at its junction with the internal jugular and with another pair at its junction with the axillary vein. In the first portion of its course it is in relation anteriorly with the subclavius muscle, and its anterior wall is united to THE SUPERIOR CAVAL SYSTEM. 885 the fascia which encloses that muscle ; near its termination it is united to the middle layer of the deep cervical fascia, behind which it lies. As a result of these connections the vein does not collapse when empty, and, furthermore, its lumen is enlarged by movements, such as those of inspiration or the raising of the arm, which affect the fascia. With the exception of the external jugular and occasionally the anterior jugular, the subclavian vein receives, as a rule, no tributaries, the veins which correspond to the branches of the subclavian artery opening either into the innominate or the external jugular. Occasionally, however, it receives the supra- scapular and the superior intercostal vein (page 896), and the acromial thoracic vein may open into it near its beginning. Fr 761 Descending branches of cervical plexus Cla\ (cuTar ponu stenio I lumed forvard Subclavian artery ^ Z- Subclavian vein Anterior scalene muscle Phrenic nerve Internal jugular vein Sternal portion of sterno-mastoid carotid artery Sterno hyoid muscle Variations. — Occasionally the course of the subclavian vein has the form of a cur\-e which rises above the level of the clavicle and may even bring the vein to lie above the arterv-. It may pass with the artery behind the scalenus anticus, the arterj- and vein may exchange places with reference to that muscle, or the vein may divide to form a ring encircling the muscle. Rarely it passes between the subclavius muscle and the clavicle. Practical Considerations. — The subclavian vein occupies the acute inner angle between the clavicle and the first rib, and therefore — and on account of its slight resistance — in periosteal or osseous growths from those bones is especially likely to suffer compression. The interposed subclavius muscle usually protects it, as it does the artery and the brachial plexus, from injury in case of fracture (page 259). The vein barely rises above the clavicle, and therefore usually escapes in stab- wounds involving the supraclavicular fossa, while the artery which arches an inch to an inch and a half above that line suffers much oftener. The connection of the anterior wall of the vein with the fascia of the subclavius muscle, causing an increase in its calibre during forced inspiration or an elevation of the arm ivide supra), should be remembered in case of wound of this vessel during 886 HUMAN ANATOMY. operation, as elevation of the cla\icle may then be followed by the entrance of air into the vein (Henle). Obstruction of the subclavian at the point of junction with the internal jugular results in compression of the orifice of the thoracic duct. THE VEINS OF THE UPPER EXTREMITY. Instead of following distally the various branches which return the blood from the upper limb it will be more convenient to begin with the peripheral branches and trace the vessels pro.ximally towards the subclavian. The veins of the upper e.xtremity may be divided into a superficial and a deep set. The latter follow in general the course of the arteries, of which they are, as a rule, the venje comites. They anastomose frequently with the superficial veins and are more richly supplied with valves than are the latter. THE DEEP VEINS. The Deep Veins of the Hand. The deep veins of the hand are all relatively small and are of less importance than the superficial ones in returning the blood. Each of the palmar arterial arches is accompanied by venae comites, and into those of the superficial arch (arcus volaris venosus superficialis) the superficial digital veins (vv. digitales volares com- munes) open, while those of the deep arch (arcus volaris venosus profundus) receive the veins (vv. metacarpeae volares) which accompany the aa. princeps pollicis, radialis indicis, and interossei palmares. Upon the dorsum of the hand even more than on its volar surface the chief part is played by the superficial \'eins. Three or four pairs of dorsal interosseous veins occur, however, accompanying the corresponding arteries and opening event- ually ]5artly into the radial veins and partly, through the veins corresponding to the posterior carpal net-work, into the superficial \eins of the dorsum of the wrist (rete venosum dorsale manus). As in the case of the arteries, the deep veins of the dorsal and volar surfaces of the hand are connected by perforating veins, and both make numerous connections with the superficial veins. The Deep Veins dr the Forearm. The deep veins of the forearm are the venae comites which accompany the radial and ulnar arteries and their branches. The radial veins (vv. radiales) are the upward continuation of the veins of the deep palmar arch and are relatively slender. The ulnar veins (vv. ulnares) are larger and are formed by the union of the ulnar ends of the venae comites of both the superficial and deep palmar arches. Usually they have a large communication from the superficial veins of the dorsum of the hand, and receive near the elbow the veins which accompany the interosseous artery and its branches, and also a strong communicating branch, the deep median vein, from the superficial median (page 890). Both the ulnar and radial veins are well supplied with valves, and they unite at the elbow to form the brachial veins. The Brachial Veins. The brachial veins (vv. hrachiales) (Fig. 762) are the companion veins of the brachial artery and receive tributaries corresponding to the branches of the artery. They are formed at about the elbow-joint bv the union of the radial and ulnar veins, and extend upward, one on either side of the brachial artery, to the lower border of the pectoralis major muscle, at about which level they unite to form a single trunk, termed the axillary vein. As is usual with vente comites, the two brachial veins are united by numerous anastomoses and occasionally unite through portions of their course, especially above, to form a single trunk. At the elbow one of the veins frequently lies in front of the artery and sometimes the two veins pursue a spiral course around it. In addition to the tributaries which accompany the branches of the brachial artery, the brachial veins, or rather the inner one of the two, receive near their termination the basilic vein (page 890). VEINS OF THE UPPER EXTREMITY. The Axillary Vein. The a.xillary vein (v. axillaris) (Fig. 762) is formed by the union of the two brachial veins, usually at about the lower border of the pectoralis major. It lies along the inner side of the axillary artery, and at the lower border of the first rib passes directly into the subclavian vein. In the lower part of its course it is separated from the artery by the ulnar nerve and the inner head of the median ; above, it is more nearly in contact with it. The axillary vein possesses a pair of valves, usually situated at the level of the lower border of the subscapularis muscle. Its walls are intimately connected with the fascia of the axillary space, so that, as in the case of the subclavian, its lumen remains patent even when empty of blood, and con- sequently air may possibly enter in cases where the vein is wounded. Tributaries . — These correspond in general with the branches of the artery, except that the axillary vein receives the cephalic, which is un- represented by an artery, and, furthermore, the acromial thoracic, which corresponds to the artery of the same name, instead of opening into the axil- lary, connects with the cephalic. Of especial importance among the tributaries is the long thoracic vein (\. thorac- alis lateralis) which brings to the axillary the blood from the lateral walls of the thorax. Its branches of origin are the Fig. 762. Superficial and veins of anterior surface of riglit forearm axillary vein and its tributaries. are the venae comites of the branches of the thoracic arteries, and they return the blood from the 88« HUMAN ANATOMY. pectoral and serratus magnus muscles and in part from the intercostals. They are abundantly supplied with \alves, and unite to a single stem which presents variations in its connections with the axillary \ ein similar to those described for the corresponding artery. By means of the costo-axillary veins (vv. costo-axillares ), which pass from the middle portions of the upper six or seven intercostal spaces, it forms anastomoses with the intercostal veins which open into the azygos system. These costo-axillary veins open either directly into the long thoracic or into the thoraco-epigastric vein (v. thoraco-epigastrica), a more or less definite stem which extends upward along the lateral walls of the thorax, subcutaneously, to open into the long thoracic near its termination. It receives numerous tributaries from the rich subcutaneous venous net-work which occurs upon the anterior and lateral walls of the thorax (vv. cutaneae pectoris;, and communicates directly below with epi- gastric branches from the femoral vein, thus forming an important communication between the superior and inferior ca\al systems. It also recei\es the \'eins coming from the region of the mammary gland, where the pectoral cutaneous veins form a net-work surrounding the nipple, the plexus venosus mammillae. The deeper veins of the gland open in part directly into the long thoracic, whence this has been termed the external mammary vein, and partly into the internal mammary by branches which accompany the perforating branches of the internal mammary artery (page S6o ). Practical Considerations. — When the axillary vein is formed by the junc- tion of the two brachial veins with the basilic vein, the union occurs usually at the inferior border of the subscapularis muscle. The vein is then somewhat shorter than the artery. Occasionally the coalescence of these tributaries does not take place until a level just beneath the lower border of the cla\'icle has been reached. When this is the case, operations in the axilla will in\-olve the ligation of many com- municating transverse veins crossing the artery to join the \'ense comites lying upon either side of it. Phlebitis of the veins of the upper extremity is but seldom transmitted to the axillary vein, rarely to the subcla\ian, and ne\er to the internal jugular or innomi- nate (Allen). This immunity is supposed to be due to disproportionately greater size of a main venous trunk as compared with its tributaries ; any of the radicles of the veins of the hand, forearm, and arm — whose calibres are nearly equal — readily transmitting .infection. Phlebitis of the axillary vein may, through the costo-axillary branches of the long thoracic vein, extend to within the thorax and result in a septic pleurisy. Accidental wounds of the axillary vein — especially of its upper portion — are dangerous on account of its size, its nearness to the thorax — so that it markedly shows the respiratory wave — and its attachment to the costo-coracoid membrane, preventing its collapse, favoring hemorrhage, or, when it is empty, permitting the entrance of air. It lies within and a little below the artery, which it overlaps, particularly towards its upper and lower portions, and w^hen it is distended during expiration. As it is straighter than the artery, the curve of the latter carries it a little awav from the \-ein at the middle portion. Abduction of the arm brings the \cin to a higher level and often almost in front of the artery so as partly to hide it. It will therefore be found with this relationship in many operations upon the axilla, and it is on account of it — i.e. , its more superficial position — and of its larger size that the \-ein is more frequently wounded than is the artery. On the other hand, the axillary artery is oftener ruptured, as in the manipulations for the reduction of old luxations of the shoulder, probably, as such luxations are more frequent in old persons, on account of the greater loss of elasticity of its thicker walls, and possibly on account of greater traction upon it by reason of its deeper and more external position f page 769). The close relation of the vein to the deep chain of axillary glands makes it the chief source of danger in operations for the removal of the breast and cleaning out the axilla in cases of mammary cancer, especially if the axillary nodes are already notably involved. It is well, therefore, to expose the vein at an early stage of the operation. If the walls have been invaded by the disease, or if extirpation of the cancerous mass is impossible without resection of the vein, the latter operation may VEINS OF THE UPPER EXTREMITY. 889 be performed. The resulting swelling and oedema of the upper limb are minimized by the consecutive enlargement of the cephalic vein. Such swelling and cedema are common symptoms of pressure upon the a.xillary vein by cancerous lymph-nodes in the later stages of mammary cancer (page 770J. Suture of the waif of the vein in cases of accidental and of operative wound has been successfully performed. THE SUPERFICIAL VEINS. The Superficial Veins of the Hand. 63) form the principal superficial They begin in a ple.xus upon the Fig. 763. E.xternal condyl The veins upon the dorsal surface (Fig. channels for the return of blood from the hand, dorsum of the first phalanges, surrounding the nail, and are continued over the suc- ceeding phalanges as a coarser ple.xus in which longitudinal trunks (vv. digitales dorsales propriaej can be more or less distincdy perceived. At about the middle of the dorsum of the proximal phalanges transverse arches (arcus venosi digitalesj, one for each digit, connect the various dorsal digital veins ; each arch is conca\'e proximally, and at either end unites with the extremities of the neighboring arches to form four dorsal metacarpal veins ( \T. metacarpeae dorsales ) which pass upward along the lines of the intermeta- carpal spaces. Just before joining with its neighbors each digital arch receives intercapitular veins (\y. intercapitu- lares) which ascend in the web of the fingers from the volar surface and assist in the passage of the blood of the superficial volar \'eins into those of the dorsal surface. The four dorsal metacarpal veins are abundantly connected by anastomosing branches which pass obliquely from one vein to the other, a net-work (rete venosum dorsale manus) with elongated meshes being thus formed. The veins of the first and fourth intermetacarpal spaces, as a rule, however, retain a greater amount of individuality than the other two, and have consequently received special names, that of the first interspace being sometimes termed the vena cephalica poUicis, while that of the fourth interspace is the vena salvatella. The dorsal net-work is drained by two \'eins \\hich pass up the forearm, the cephalic and basilic veins. The superficial veins of the volar surface of the hand are small and for the most part open into the dorsal veins. They arise as a plexus in the balls of the fingers and pass along the volar surfaces of the digits as a plexus in which longitudi- nal trunks (w. digitales volares propriae) can be distinguished. From the plexus of each finger branches wind around the sides c f the digits to open into the dorsal digital veins, and at the roots of the fingers important connections in a similar direction are made by the intercapitular veins (see above). Superficial veins of right hand and forearm ; posterior surface. 890 HUMAN ANATOMY. The superficial veins of the palm of the hand are situated superficially to the palmar aponeurosis. They are for the most part small, and form a net-work which is open o\'er the central part of the palm, but much closer over the thenar and hypothenar eminences. These lateral portions communicate with the dorsal net-work as well as the net-work of the anterior surface of the forearm, into which the central portion opens. The B.\silic \'ein. The basilic vein (v. basilica) (Fig. 762) takes its origin from the ulnar side of the dorsal net-work of the hand, and is sometimes described as the direct continuation of the dorsal metacarpal vein of the fourth interspace. It passes obliquely upward and inward, winding around the border of the hand towards the anterior surface of the fore- arm, up which it ascends. Beyond the bend of the elbow it continues its way upward along the inner border of the biceps muscle as far as the upper third of the brachium, at which level it pierces the fascia of the arm, and after a usually short subfascial course terminates by opening into the internal brachial \ein. The basilic is the largest of all the superficial veins of the arm, and is provided with from ten to fifteen pairs of valves. It receives tributaries from the superficial ple.xus of the thenar eminence and from the anterior and posterior surfaces of the forearm. Near the elbow it receives from the cephalic vein the median vein, the connecting stem being termed the vicdian basilic vein, and it also communicates with the cephalic higher up by branches which pass across the biceps muscle, and with the brachial veins by small branches which pierce the brachial fascia. Variations. — The basilic is little subject to variation except in regard to its termination, which is frequently in the axillary and sometimes in the subclavian ; in both these cases the sub- fascial portion of its course is considerably longer than usual. Occasionally it is accompanied throughout its course by an accessory basilic. The portion of the vein extending from its origin to the bend of the elbow is frequently spoken of as the superficial ulnar vein, the term basilic being limited to the brachial portion of the vein as described above. The Ceph.\lic Vein. The cephalic vein (v. cephalica) (Fig. 762) takes its origin from the radial portion of the dorsal net-work of the hand, and especially from the dorsal metacarpal vein of the first interspace. It passes upward, inclining fonvard o\'er the surface of the brachio-radialis muscle, and so reaches the anterior surface of the forearm. Arrived at the bend of the elbow, it ascends along the groove which marks the outer border of the biceps muscle and then in the groove between the deltoid and the pectoralis major, and at the upper border of the latter muscle it passes between it and the clavicle, per- forates the costo-coracoid membrane, and, crossing in front of the a.xillary arter)', empties into the axillary vein. It is provided with from twelve to fifteen pairs of valves, of which from four to seven occur in its antibrachial portion, seven in its brachial portion, and one at its union with the a.xillarv. Tributaries. — The cephalic vein recei\es numerous branches from the super- ficial- net-work of the posterior surface of the forearm and, indeed, plays a much more important part in the drainage of this region than does the antibrachial portion of the basilic. (}uite frequently it is accompanied in its course up the forearm by an accessory cephalic vein (v cephalica accessoria ), which arises in the posterior super- ficial net-work and opens into the main cephalic vein at the bend of the elbow. It also receives branches from the superficial net-work of the anterior surface of the forearm and, a short distance below the bend of the elbow, gives off a strong branch, the median vein (v mediana cubiti), which passes obliquely upward and inward to open into the basilic, giving off in its course a communicating branch to one or other of the deep veins of the forearm. In its brachial portion it is connected with the basilic by branches which pass across the biceps muscle, and just before opening into the axillary it receives the acromial thoracic vein (v. thoracoacromialis), w-hich corresponds to the artery of the same name. VEINS OF THE UPPER EXTREMITY. 891 Variations. — Unlike the basilic, the cephalic vein frequently presents variations which affect principally its brachial portion. One of the most important of these is the complete absence of this portion of the vein, the antibrachial portion emptying its blood into the basilic by means of the median vein. In other cases it is only the uppermost part of the brachial portion that is lacking, the lower part in such cases either making connection with the brachial veins or else conveying its blood downward to the median vein, by which it passes to the basilic. Another interesting anomal}' consists in the occurrence of a branch which is given off just as the vein dips downward to pierce the costo-coracoid membrane. It is termed the jugulo- cephalic vei?i, and passes up over the clavicle to open above into the external jugular near its communication with the subclavian. These variations find an explanation in the changes undergone by the superficial veins of the arm during their development, both the absence of the brachial portion of the vein and the occurrence of a jugulo-cephalic being the persistence of conditions normally passed through in development. It would seem that three, or perhaps better four, stages are to be recognized in the development of the superficial veins of the arm. In the first stage the basilic vein forms the only great superficial trunk, extending up the inner side of the arm from the wrist to the axilla and opening into the axillary vein abo\'e. Later, however, this condition is modified by the de- velopment of the antibrachial portion of the cephalic, which increases in size at the expense of the antibrachial portion of the basilic until it becomes the most important \-ein of the forearm. At the bend of the elbow this vein receives a short transverse branch formed by the union of an ascending and descending limb, and then bends obliquely inward to join the brachial portion of the basilic. Higher up in the groove between the pectoralis major and deltoid muscles is a small deltoid vein, which is unconnected with the veins already described. Such a stage as this gives a clue to the variations in which the brachial portion of the cephalic is either absent or only partially developed. The ascending limb of the transverse branch of the elbow, and this branch itself, together represent what will later be the lower part of the brachial portion of the cephalic, while the deltoid vein represents its upper part ; the descending limb of the trans- verse branch represents the accessory cephalic vein, and the oblique portion of the antibrachial cephalic, between the transverse branch and the basilic, represents the median \-ein. Indeed, relics of this condition are to be seen even in the normal arrangement, for while the antibrachial portion of the cephalic usually e.xceeds in size the corresponding portion of the basilic, the con- ditions are' reversed in the brachial portions of the two veins, the antibrachial portion of the cephalic and the brachial portion. of the basilic (connected by the median) forming the main channel for the return of blood from the superficial portions of the arm. A third stage is brought about by the completion of the cephalic vein by the union of the ascending limb of the transverse branch with the deltoid, the vein so formed being continued up over the clavicle to open into the external jugular ; and, finally, the fourth or adult stage is pro- duced from this by the degeneration of that portion of the cephalic which corresponds to what is termed the jugulo-cephalic. The antibrachial portion of the cephalic is frequently termed the superficial radial vein, the accessory cephalic being then the accessory superficial radial. Furthermore, it is to be noted that quite frequently one or more strong longitudinal stems are developed in the superficial net- work of the anterior surface of the forearm, and to one of these the term median vein has been applied. This condition has generally been accepted by the English and French anatomists as typical, and their description of the origin of the basilic and cephalic veins is as follows. The median vein when it reaches the bend of the elbow divides into two divergent stems (Fig. 764) which are termed the median basilic and median cephalic veins. The median basilic, which corresponds with what has been termed above the median vein, unites with the superficial ulnar to form the basilic vein, while the median cephalic, which represents the fcetal transverse branch of the elbow, similarly unites with the superficial radial to form the cephalic. Such an arrange- ment is undoubtedly of frequent occurrence ; but since the median vein, as understood in such a description, is so variable and so manifestly a secondary' formation, and since the arrangement taken above as typical is not only also of frequent occurrence, but furthermore follows more closely the embryonic relations of the various vessels, it has been given the preference. Pr.'Vctic.\l Considerations. — The Veins of the Upper Extremity. The Deep Veins. — The venae comites of the radial artery have been said, when distended, to alter, by pressure, the character of the pulse. The numerous short anastomotic branches which unite the venae comites of the brachial artery cross in front of that vessel and may have to be tied as a preliminary to ligation of the artery. The Superficial Veins. — The Hand. — The veins of the dorsal surface are subcutaneous, prominent, and, in order that the circulation may not be inter- rupted during prehension, are much larger than those of the palmar surface. Like the other superficial veins of the upper extremity, they are scantily supplied with valves and are therefore easily distended by the effects of gravity or by any constric- tion of the limb above. The Forearm. — -The large size of the superficial veins in the forearm, their sub- cutaneous position, the small number of valves they contain, and the fact that most HUMAN ANATOMY. Basilic vein Accessory basilic v Brachial artery Median neI^•e Brachial vein of the venous blood of the limb is returned by them, make circular constriction of the arm or forearm — as in cases of poorly applied splints — especially dangerous. Swelling and oedema distal to the constriction are sure to result speedily and, if the pressure is continued, to be followed bv ulceration or gangrene. On the e.xtensor surface of the forearm the superficial veins are less conspicuous than on the flexor, and between the olecranon and the level of the pronator teres insertion are almost completely lacking. This is the surface most exposed to trau- matism, and along it main arteries and nerve-trunks are also absent. The Elbow. — The vein ^ven ofT by the median vein when it reaches the bend of the elbow, and known by the English and French anatomists (vide supra) as the median basilic, is of the greatest practical importance among the veins at the bend of the elbow. The M-like figure made by the superficial ulnar and superficial radial in uniting respectively with the median basilic and median cephalic to form the basilic and cephalic veins is by ' ■*■ no means constant, but is present in only from one-half to two-thirds of all cases (Treves). Even, however, if the basilic and cephalic \eins do not originate in this way, the median vein (if from the cephalic), the median basilic ( if from the median) , will be found begin- ning a short distance below the elbow, to the outer side of the biceps tendons, and crossing the tendon, the brachial artery, the brachial veins, and the median nerve, from all of which it is separated b)- the bicipital aponeurosis, the inner of the two lower biceps tendons of the old anatomists. The vein may, however, run either more transversely or more \ertically and so have different relations to the artery and nerve ; it is usually the largest of the anticubital veins, but may be smaller than the median cephalic, which is commonly the second in size, followed by the median, ulnar, and radial, in the order mentioned. For reasons explained above, abnormalities and even absence of the cephalic and radial veins are more frequent than those of the basilic. For this reason, and on account of its large size, the greater quantity of blood it carries — as it is above the entrance of the deep median vein, and thus receives blood from the deep veins of the forearm — its superficial position, its prominence, and its relati\-e fixation to the bicipital fascia by cellular tissue, the median basilic is the vein selected for either intravenous transfusion or phlebotomy. In opening the vein, certain dangers are to be avoided : ( i ) Wound of the brachial artery, if it results in a direct communication between the vein and artery, will cause an aneu- rismal varix ; if it results in the formation of an intervening sac in the perivascular connective tissue, through which the blood from the artery flows before entering the vein, it will cause a varicose aneurism. (2) A septic wound may cause a lymphan- gitis from infection of the lymph-vessels accompanying the vein, and may result in axilary abscess. (3) Unnecessary damage to the filaments of the internal cuta- Superfic of region of elbow, showing THE AZYGOS SYSTEM. 893 neoos nenre (Tljing' in feomt of the vein) may give rise to ciurooic tratiinatic neuritis (Tilla«ix), while imJHjrjr of the etitaneous branches of the musculo-cutaneous nen.'e (iim closer relatioe to the median cephaJic vein), or entanglement of those branches im the cicatrix, may, by reflex irntatioa acting throug'h the motor fibres, cause tonic spasna of the biceps and brachialis anticus, "bent arm" (Hilton;. The Arm. — ^The cephalic vein and its anomalies should be studied in relation tf} ligation of the axiliar}' arterj^ (?-^'- h ths first portion of which it crosses T sepa- rated frO'm it far the clavi-pectoral fascia;, on its way to reach the axiilary \€isl. It may be remembered that the basikc vein pierces the brachial aponeurosis a litde bdlow the middle of the arm and ceases to be superficial THE AZYGOS SYSTEM. The principal trunks of the azygos system of veins are persistent portions of the embryonic caidinal veins which drained the thoracic and abdominal waUs, as well as the paiired v^cera of the abdomen, and united above with the jugular trunks to form the Cnvieoasi dnicts (page 926)'. On the development of the inferior vena 'sa^'a their importajace diminished greatly, and in the adult they serve principally to ooiBect the Hood froni the intercostal spaces. The reduction of the lower part of the left jogular vein (j>age 927) brought about further modifications of the left cardinal, its original comnectiom with the left jugular being dissolved and a new one formed with the right cardinal This latter vein fo'rms what is termed the azygos vein of the adult, whffle what persists off the Irft one is known as the hemiazygos and accesso^ry heoniazj'^os. The Aztgos Vees. The az>'gos vein > v, si-^i.,-S) f Fig. 765), sometimes called the azygos major, b-^iias inninediately below the diaphragm, where it is direcdy continuous with the right ascending- lumbar vein, formed by the anastomosis of branches of the lumbar veins and ooimecting below with the ilio-Inmbar or common iliac. The arv'gos vein passes up- waird into the thoracic ca«ty, traversing the diaphragm either by the cleft between the medial and intermediate portions of the right cms or else by the aortic opening. It then contiimes its way upward in the posterior mediastinum, resting upon the ante- rior sorfaces ol the bodies of the thoracic vertebra a litde to the right of the middle line, passiiiig: over the right intercostal arteries and having the thoracic aorta and the thoracic dwct immediately to the left of it. When it reaches the level of the fourth \'ertd>ja it bends forward and somewhat to the right, and, curving over the right foronchnis and the right pulmonary artery, it descends slighdy to open into the pos- terior surface of the superior vena ca^-a, just above the level at which that vessel becomes invested by the pericardium. The terminal portion of the vein from the fouBTth vertebra onward is sometinies termed the azygos arch. The azygos vein im a considerable proportion (22 per cent., Gruber) of cases is entirely destntute of I'alves, and when present they rarely exceed four in number, are, apparently, never esacdy paired, and are usually insufficient. They occur more fre- quently in the arch than im the vetical portion of the vein. Xribatanes. — The azygos veim at its origin has usually some small connections with the vena ca^'a inferior, but its principal tributaries are the right intercostal veins. Im addition it receives branches fmom the oesophagus ( tt. oesophageae) , from the are- olar tissue and lymph-modes of the posterior mediastinum and from a plexus which surrouuads the thoraac aorta, from the posterior surface of the pericardium, and from the substamce of the r%ht lumg, these last bronchial veins ('tt. bronchioles posteri- ores )' tssuing from the hilum of the lung' and opening into the azygos at the beginning of its arch. They amastonaose with the pulmonary veins both along the course of the smaller bronchi and also outside the iung-, and they receive some smaller bronchial veins (tt. bronefaiales anterioresj situated upon the anterior surface of the bronchi The azygjos vein furthermore receives the hemiazygos vein ; this and the intercostal veins will be described bdow. Variatrnos- — SiDce the cardinal Teins, from which the azygos and hemiazj'giDS are formed, are primarily symmetrica], it may happan, |nst as was the case v' veins, another gives rise to the portal and umbilical veins, while the third is represented by what are termed the cardinal veins. It is to these last that attention may first be directed. The Cardinal Veins. — The cardinal veins ( Fig. 776) are two longitudinal stems which extend the entire length of the body, one on either side of the median line, receiving throughout their course lateral somatic and visceral branches Fig. 776. in more or less perfect segmental succession. From each vein a branch passes medially towards the heart, and the portion of the longitudinal vein anterior to this cross-branch is termed the anterior cardinal or priiiiiiive jugular, while that behind it is known as Xhe posterior cardinal. The cross-branch, which is usually described as formed by the union of the anterior and pos- terior cardinals, is termed the duct of Cuvier. The anterior cardinals take their origin from veins which ramify over the surface of the brain and receive at first both the ophthalmic and facial veins. The cerebral veins later condense to form the superior and inferior longitudinal, the straight, and the lateral sinuses, with the last of which the ophthalmic veins unite, their intra- cranial portions becoming the cavernous and inferior petrosal sinuses. The facial veins, how- ever, sever their connection with the cerebral veins and unite with other superficial veins to form tlie external jugular — a \-essel which in some mammalia reaches a high degree of devel- opment, almost or entirely replacing the internal jugular, which represents the main stem of the cardinal. In man the original condition, in which the external jugular is of subordinate Segmental 1 1 Venous sinus of heai ~1\^ Duct of Cuvier \'nW Vitelline vein Diagram showing primary symmetrical arrangement of venous system. DEVELOPMENT OF THE VEINS. 927 importance, is more nearly retained, but indications of a transference of blood from the intracranial portions of the internal jugular system to the external vessel are to be seen in the emissary veins. At first each internal ju^lar opens independently into the right auricle through the corresponding duct of Cuvier (Fig. 777, A), but later a communicating branch e.xtending obliquely across from the left to the right vein is developed (Fig. 777, £), and thereafter the Fig. 777. Anterior cardinal I (internal jugular) T Cuvierian duct Primary inf. Posterior cardinal 1 — n — Internal jugular I H — External jugular ^Jil^ISubclavian Diagrams illustrating development of superior vena cava; /4, primary symmetrical arrangement ; .ff, establishment of transverse connection ; C, atrophy on left side and persistence on right side of superior vena cava. lower portion of the left vein degenerates until it is represented only by the small oblique vein of the left auricle, opening into the coronary sinus, which is the persisting left ductus Cuvieri (Fig. 777, C). The oblique connecting branch becomes the left innominate vein of adult anatomy, and the portion of the right anterior cardinal below the point where it is joined by the innominate, together with the right ductus Cuvieri, becomes the superior vena cava. The Inferior Vena Cava. — The posterior cardinals persist in part as the azygos veins, but their history is so intimately associated with that of the inferior vena cava that an account of the development of the latter may first be presented. In the early stages of development the only portion of the inferior vena cava which exists is the portion which intervenes between the entrance of the hepatic veins and the right auricle, this portion representing the terminal part of the ductus Fig. 77S. Posterior cardinal Diagrams illustrating developmental changes leading to formation of inferior caval and azygos veins. venosus (page 705). Branches which pass to the posterior cardinal veins from the mesentery anastomose longitudinally to form on each side of the bod\- a venous stem which has a course parallel to that of the cardinals, with which it unites below (Fig. 77S, //). This is the subcarditial vein, the two vessels of opposite sides of the body being united with one another and with the cardinals by a strong cross-branch which joins the cardinals opposite the point of entrance into 928 HUMAN ANATOMY. Fig. 779. those of the renal veins. The portion of the right subcardinal which Hes anterior to the cross- branch then enlarges and unites with the existing portion of the inferior vena cava, and the lower portion of the right cardinal, together with the portion of the cross-branch which intervenes between it and the right subcardinal, also enlarges, and these three elements eventually come into line with one another and with the terminal portion of the ductus venosus to form the inferior vena cava. The lower portions of both subcardinals now degenerate, and the upper portion of the left vein, diminishing in size, becomes the left suprarenal vein. A cros.s-branch forms between the two posterior cardinals at the level of the conmion iliac veins, and the lower part of the left cardinal then disappears (Fig. 77S, C), a small portion below the original renal cross-branch alone persisting to form the terminal part of the left spermatic (ovarian) vein, which thus comes to open into the left renal vein, since the terminal portion of that vessel represents the original renal cross-branch. As a result of this degeneration the left common iliac vein comes to open into the lower part of the right posterior cardinal by way of the iliac cross-branch. The Azygos Veins. — While these changes have been taking place the anterior portions of the posterior cardinals have undergone degeneration immediately anterior to the renal cross- branch (Fig. 778), so that they form independent vessels, receiving the intercostal veins and terminating above in tlie ductus Cuvieri. They now constitute the azygos veins, and, on the degeneration of the lower part of the left anterior cardinal, the left azjgos develops connection with the right by one or two transverse branches and then separates from the cordnary sinus, the adult condi- tion of the hemiazygos vein being thus acquired. The Portal Vein. — Passing along the umbilical cord to the body of the embryo are tv\o fi/r/Zhie or omphalo-nieienleric veins, which ha\e their origin in the yolk- sac, and the umbilical vein, which brings back the blood from the placenta. When it reaches the umbilicus, the umbilical vein divides into two stems which pass upward upon the inner surface of the anterior abdominal wall and unite above with the corresponding vitelline veins to open into the ductus Cuvieri. The vitel- line veins pass from the umbilicus to the intestine and ascend along it, receiving tributaries from it ; abo\e, they traverse the liver, breaking up into a net-work in its substance, and are then continued on to unite with the umbilicals (Fig. 779, A). By the enlargement of certain portions of the hepatic net-work a well-marked venous stem is formed, extending from the point where the left vitelline vein enters the liver to the junction of the common stem formed by the right vitelline and umbilical veins with the duct of Cuvier. This new stem is the ductus vcnosus\¥\%%. 779, i.' and C), and it later forms a connection with the left umbilical vein and becomes the continuation of that vessel as the result of the degeneration of the upper part of the umbilical {D). li> the meantime three cross-connections have developed between the two vitelline veins (Fig. 779, A, B, C), two of them passing ventral to the intestine and one dorsal to it, the intestine thus becoming surrounded by two venous rings. The right half of the lower ring and the left half of the upper one now degenerate (D), and the persisting portions, which terminate partly in the hepatic net-work and partly in the ductus venosus, become the portal vein. The upper portion of the right umbilical vein has in the meantime made a connection with the upper ring of the vitelline, and the part above the connection then degenerates, the lower part becoming much reduced in size and persisting as a small parumbilical vein in the anterior abdominal wall. This arrangement persists until birth, the placental blood passing by way of the left umbilical vein partly to the ductus veiiosus and thence by the inferior vena cava to the heart and partly through the hepatic net-work byway of the communication between the left umbilical and vitelline veins. At birth the placental supply of blood is of course cut off, the ductus g transforniat velopmeiit of liver-' , In, right and left um IV, /z/, right and left vitelline veins; rf?-. ductus portal vein. (Hockstetter.) THE FCETAL CIRCULATION. 929 venosus degenerates to a solid cord up to the point where the hepatic veins, developed from the hepatic net-work, unite with it. The umbilical vein al.so degenerates to form the round ligament of the liver, which frequently presents more or less distinct evidences of its original lumen. The Veins of the Limbs. — The details of the development of the limb veins are not as yet thoroughly known. The superficial veins are the finst to form, the basilic vein of the arm and the long saphenous of the leg being the primary vessels and the axillary and .subclavian and the iliac veins their respective continuations. The remaining superficial veins and the deep veins are later formations. The Pulmonary Veins. — The pulmonary veins make their exit from the lungs as four vessels, two belonging to each lung, but as they approach the heart they unite first in pairs and then to form a single trunk which opens into the right auricle. Later a considerable portion of the original veins is taken up into the wall of the auricle, the absorption eventually extending beyond the point of the union of the original veins in pairs, so that in the adult all four vein.s open independently into the auricle. THE FCETAL CIRCULATION. The primary or vitelline circulation of the mammaHan embryo, formed by the ramifications of the vitelline arteries and veins over the yolk-sac (umbilical vesicle), must be regarded as an inheritance from ancestors in whom the yolk provided the nutrition for the developing animal. While in birds and reptiles the vitelline veins are important channels for the conveyance of the nutritive materials taken up from the yolk, in mammals in this respect they are of little consequence, thus affording an e.xample of structures that, although no longer useful, recur in the development. The vitelline circulation is soon followed by a second, the allantoic circulation, which in man and the higher mammals provides the vessels connecting the fcetus with the placenta — the organ whereby respiration and nutrition are secured to the fcetus during the greater part of its sojourn within the uterus. The blood is carried from the foetus to the placenta by the hypogastric arteries and their prolongations, the two umbilical arteries. After passing through the vascular tufts of the chorionic villi that constitute the essential structures of the fcetal part of the placenta, the foetal blood, renewed in oxygen and laden with nutritive material derived from the maternal circulation, is carried by venous tributaries that unite into the single runbilical vein. The latter vessel accompanies the umbilical arteries within the umbilical cord as far as the umbilicus, from which point it then passes along the free margin of the crescentic peritoneal fold, the falciform ligament, to the under surface of the liver to join the portal vein and pour its stream of freshly oxygenated blood into the current of venous blood returned from the digestive tract to the liver. For a short time the rapidly growing liver is capable of transmitting all the blood brought to it by the vitelline (later portal) and the umbilical veins, and this blood is returned to the heart after making the circuit of the vessels of the liver. Soon, however, the latter organ can no longer accommodate the entire volume of blood conveyed to it by the portal and umbilical veins, and the necessary relief is afforded by the development of a short vessel, the ductus venosus, or ductus Ara7itii, that extends from the portal vein to the inferior vena cava and thus establishes a by-pass for the greater part of the o.xygenated blood returned from the placenta. On reaching the inferior cava, this pure blood is mingled with the venous blood being returned from the lower half of the body and the abdominal viscera, the mixed stream so formed being poured into the right auricle. On entering the heart the current is directed by the Eustachian valve towards the foramen ovale in the auricular septum and enters the left auricle. After receiving the meagre additions returned by the pulmonary veins from the uninflated lungs, the blood passes through the left auriculo-ventricular opening into the left ventricle. Contraction of this chamber forces the blood into the systemic aorta and thence to all parts of the body. After traversing the vessels of the head, neck, upper extremities, and thorax, the venous blood from these parts is returned to the heart by the superior vena cava, but on entering the right auricle does not mingle to any extent with the current returned by the inferior cava, but passes through the auriculo-ventricular orifice into the right ventricle. With contraction of the ventricles the blood is propelled into 59 93° HUMAN ANATOMY. the pulmonary artery and towards the lungs. Being uninflated these organs can appropriate only a small part of the entire volume of blood brought by the pulmonary artery, hence the necessity of a second by-pass, the ductus arteriosus, or diictus Botalli, that extends from the beginning of the left pulmonary artery to the adjacent aorta and represents the still per\ious distal portion of the last aortic arch on the left side (page 847). By means Fig. 7S0. Qf (j^g. ductus arteriosus, the venous blood returned from the head and upper extremities is poured into the great descending trunk, the aorta, and carried to the abdominal viscera and the lower extremities. On reaching the bifurcation of the common iliac arteries, the blood- stream divides, that part going into the internal iliacs being of much greater importance, so far as the general nutri- tion of the foetus is concerned, since it is carried by the continuations of these \essels — the hypogastrics and umbilical arteries — to the placenta, to be once more purified and again returned to the foetus by the umbilical vein. From the foregoing sketch of the fcetal circulation it is evident that, with the exception of the umbilical vein, no vessel within the foetus conveys strictly arterial or fully oxygenated blood, since on entering the inferior cava the pure blood is mixed with the \enous returning from the lower half of the body. It is further evident that the blood distributed to the head and upper extremities is less contaminated than that passing to the lower half of the body from branches of the aorta given off after junction with the venous stream conveyed by the ductus arteriosus. It may be borne in mind that the umbilical vein and the ductus venosus carry arterial blood and the pulmonary artery and the ductus arteriosus purely venous blood, the aorta distributing mixed. Upon the assumption of the respiratory function at birth, the three anatomical structures peculiar to the fcetal circulation — the ductus venosus, the foramen ovale, and the ductus arteri- osus— become useless and soon undergo occlusion and atrophy, the two former ducts being represented by the fibrous cords seen on the posterior surface of the liver and terminal part of the aortic arch respectively. Closure of the foramen ovale proceeds more slowly, a week or more being usually consumed in effecting obliteration of the opening ; indeed, in a large proportion of individuals complete closure never occurs (page 695). shortly before birth : iws. P, placenta; UA. PV. portal Diagram of foetal circulatic course of blood is indicated by ar UV, umbilical arteries and ve ductus venosus ; IVC, inferior vein; HV, hepatic veins; RV. LV. right ventricle: PA. pulmonary artery; DA. ductus arteri osus; SVC. superior vena cava ; AA, abdominal aorta; HA, hypogastric arteries (internal iliac) ; EIA. ex- ternal iliac arteries ; I.intestme; L, lungs; K. kidney. THE LYMPHATIC SYSTEM. The lymphatic system is a system of vessels which occur abundantly in almost all portions of the body and converge and anastomose to form two or more main trunks, which open into the subclavian veins just before they are joined by the internal jugular. The vessels contain a fluid termed lymph, usually colorless, and containing numerous corpuscles known as lymphocytes. Since the latter usually come under obser\'ation as they circulate within the blood-vessels, the detailed account of the lymphocytes is given in connection with blood-corpuscles (page 684). In those vessels which have their origin in the wall of the small intestine, however, the contained fluid has, especially during digestion, a more or less milky appearance, owing to the lymphocytes being loaded with particles of fat which they have taken up from the intestinal contents. On this account, these vessels are usually spoken of as ladeals, although it must be recognized that they are merely portions of the general lymphatic system. In certain respects the vessels of the system strongly resemble the veins, closely associated with which the)' take their origin embryologically and into which they finally pour their contents iit the adult. They arise from a capillary net-work, their walls have a structure closely resembling that of the veins, they are abundantly supplied with valves, and it may be said that the fluid which they contain flows from the tissues towards the heart. With these similarities there are combined, however, marked differences. One of the most important of these consists in the fact that the capillaries are closed and do not communicate with any centrifugal set of vessels, as the venous capillaries do with the arterial ; and another important difference is to be found in the frequent occurrence upon the lymphatic vessels of character- istic enlargements, the lymphatic nodes or so-called glands (lymphoglandulae), quite different from anything occurring in connection with the veins. Lymph-Spaces. — Throughout practically all regions of the body spaces of varying size, occupied by a clear, more or less watery fluid, exist, and to these the term lymph-spaces has been applied (Fig. 781). It was long believed that they were directly continuous with the lymphatic capillaries, that the latter, indeed, opened out from them, the spaces forming the origins of the capillaries. There is, however, a growing tendency to dispute this view and to regard the lymphatic capillaries as being quite independent of the spaces, — the entire lymphatic system, in fact, being a closed system, except for its communications with the subclavian veins. Since, however, the lymphatic capillaries form net-works in the tissues which bound these spaces, interchange of their contents with those of the capillaries is by no means difficult, the lymphocytes, even, passing on occasion through the walls of the capillaries into the spaces and returning again to the interior of the capillaries. If a colored fluid be injected into the portal vein it will pass through the walls of the venous capillaries and invade the spaces of the interlobular hepatic connective tissue, and later it will flow away by the hepatic lymph-capillaries. By varying the extent of the injection it will be found that the lymphatic vessels will be injected when the lymph-spaces are completely filled, but will not be when the spaces are only partially injected (Mall), so that it may be concluded that the extravasation from the portal capillaries is primarily into the hepatic lymph-spaces and thence makes its way into the lymph-capillaries. The spaces vary greatly in size, existing in certain tissues even between the individual cells. They are more evident, however, in the connecti\'e tissues, reaching a considerable size in areolar tissue, where they form a continuous net-work, and, since the blood-vessels are usually surrounded by a greater or less amount of con- nective tissue, lymph-spaces are quite distinct along their courses, forming what are known as the perivascular lymph-spaces (Fig. 782). In other regions of the body somewhat extensive spaces occur which have been regarded as belonging to the 931 932 HUMAN ANATOMY. category' of lymph-spaces, and among these there may be mentioned the subarachnoid and subdural spaces of the meninges, Tenon's space in the orbit, and even the Fig. 781. Perivascular lymph-space ph-vessel Deeply stained ground substance I of central tendon of rabbit"? diaplira^jn irregular tracts ; lymph-space: I Willi siUer nitrate; lymphatic vessels are sho 1 within stained ground substance. X 120. "^ spaces occupied by the aqueous and vitreous humors of the eye, as well as the smaller spaces of that organ. So, too, the spaces surrounding that enclosed by the membranous labyrinth of Fig. 7S2. the ear ha\e been regarded Bl/7) 3s lymph-spaces, as is ' ' . indicated by their names. ' "sV . Finally, it may be ^ mentioned that the syn- ^,^_ ovial cavities of the artic- ulations and the greater serous cavities of the body enclosed by the pleura, pericardium, and perito- neum ha\e been regarded as being in direct com- munication with the lym- phatic capillaries; but this view is also in all proba- bility erroneous. Notwithstanding the independence of these spaces from the lymphatic capillaries, it must be recognized that some of them at least play im- poi'tant roles from the physiological standpoint, in serving as middle-men between the tissues and the lymphatics, and, furthermore, those of the eyeball, by their communication with neighboring spaces, permit of a iding retinal blood-vessels. X 230. THE LYMPHATIC SYSTEM. 933 capillary net-works witl belong to superficial net-work, larger to deeper. rapid compensation for variations in the intraocular tension. From the anatomical standpoint, however, they are not to be regarded as actually parts of the lymphatic system, and the mention that they here receive is merely a tribute to their historical importance in the problem of the origin of the lymphatic capillaries. The Capillaries. — The lymphatic capillaries (Fig. 783J, which are arranged in the form of net-works of very different degrees of fineness and complexity, closely resemble in structure the blood - capillaries, their Fig. 7S3. walls consisting of a single layer of endothelial plates, which, however, are usually larger and less regularly disposed than those lining the blood - channels. They differ from those of the blood - vascular system not only in their ultimate branches being closed, but also in their general appearance. Thus, they are of much greater calibre, their diameter varying from .030-. 060 mm. , while that of the blood-capillaries may be as little as .008 mm. ; they do .not present the regularity of size and gradual increase or diminution of calibre noticeable in the blood-capillaries, but larger and smaller stems are indefinitely interspersed, and spindle-shaped or Fig. 784. nodular enlargements may occur at irregular intervals throughout the net-work. And, finally, as a result of these peculiarities, the meshes of the net-work are of very varying size and form. The arrangement assumed by a net-work depends largely upon the tissue and organ in which it occurs. In the integument, for in- stance, the lymph-capillaries arrange themselves in two more or less distinct layers, a more superficial one, composed of smaller capillaries, and a deeper, coarser one, — numer- ous communications necessarily existing between the two. Both net- works are confined to the dermis, the more superficial one lying close to its epidermal surface, while the deeper one is situated in its deeper layers, the distance between the two varying according to the develop- ment of the dermis in different portions of the body and in different individuals. From the superficial layer loops or single capillaries project upward into the dermal papillse, and special portions of the net-work surround each hair-follicle and sudoriparous gland. * Das Saugadersystem. Leipzig, 1861. Transverse section ot small lymph-vessel 934 HUMAN ANATOMY. Fig. 7S5. The mucous membranes have essentially the same arrangement, the net-work with- in the small intestine, for instance, being arranged in two more or less distinct layers, one of which lies in the submucosa and sends loops or blindly ending processes into the villi, while the other is situated in the muscular coat. What may be regarded as a third net- work, lying beneath the serous or connective-tissue investment, is formed by the anas- tomosis of the stems arising from the deeper net-works and it is from this last net-work that the efferent stems arise. In most other organs lined by mucous membrane a similar arrangement occurs, although in the uterus, bladder, and ureters the submucous net-work seems to be wanting, the muscular set alone being demonstrable. Through- out the serous membranes the net-works possess naturally a layered arrangement, but in the more massive organs, such as the liver and pancreas, they are arranged with reference to the constituent lobules, each being invested by an interlobular net-work. Considerable variation exists in the closeness of the net-work in difierent organs, and, indeed, in different parts of the same organ, but everywhere the lymph- capillaries are exceedingly thin-walled and possess no valves. As has been pointed out, the view formerly prevailed that the capillaries communicated directly with the great serous cavities of the body, with the spaces of the connective tissues, and even with the pericellular spaces which occur in the more compact tissues, all these being regarded as radicles of the lymphatic vessels. It is now believed, however, that such is not the case, but that the net-works, which are everywhere continuous, are completely closed except for their communications with the efferent vessels. The Lymph-Vessels. — The lymph-vessels, which issue from the capillary net-works and convey the lymph ultimately to the subclavian veins, have an arrangement closely resembling that of the veins, and, indeed, the larger ones are usually situated alongside and accompany the course of blood-vessels. Just as it is possible over the surface of the body and limbs to distinguish between superficial and deep veins, so there can be recognized a sitperjicial set of Ivmphatic vessels (vasa lymphatica superficialia), situated superficially to the fascia which encloses the musculature, and a deep set (vasa lymphatica profunda), the vessels of which lie beneath the fascia ; numerous communications, however, exist between the two sets. Just as the veins unite to form larger trunks as they pass from the capillaries toward their termi- nation, so, too, the lymphatics ; but the latter present two peculiarities which distinguish them ' from the veins. They do not anastomose as abun- dantly as the latter and there is not the same proportional increase in the size of a lymphatic vessel formed by the junction of others as in the veins, so that, while the lymphatics at their origin from the capillary net-works may have the same calibre as the corresponding veins, yet their terminal trunks are of much smaller diameter. As a rule, several lymphatic \-essels arise from the capillary net-work of any organ or region of the body, and, since the net-work is to be regarded as practically continuous over large areas, it would appear that the flow of lymph from any circumscribed area might take place through widely separated stems and be carried along very different paths. And such, to a certain extent, is the case ; but it has been found bv experiment and by the obser\ation of pathological conditions that for each organ or region there is a more or less definite lymphatic path, each vessel or group of vessels tending to drain a somewhat definite area of the net-work, a fact of considerable importance from the diagnostic standpoint. shaded part of figure shows ai drained by right lymphatic duct; ly phatics of remaining territory receiv by thoracic duct. THE LYMPHATIC SYSTEM. 935 All the lymphatic vessels terminate directly or indirectly in one of two main trunks, which, as already stated, open respectively into the right and left subclavian veins. The left trunk, the thoracic duct (ductus thoracicus), is much larger than the rio-ht, beginning in the abdominal region and traversing the entire length of the thorax to reach its destination. It receives all the lymph returned from the lower limbs, the peh-ic walls and viscera, the abdominal walls and viscera, the lower part of the right half and the whole of the left half of the thoracic wall, the left half of the thoracic viscera, the left side of the neck and head, and the left arm. The other trunk, the right lymphatic duct (ductus lymphaticus dexter), is very short, and, indeed, is frequently wanting, the vessels which typically unite to form it opening independently into the vein. It receives the lymph from the upper part of the right side of the thoracic wall, from the right half of the thoracic viscera and the upper surface of the liver, the right side of the neck and head, and from the right arm (Fig. 785J. In structure the larger lymphatic vessels are similar to the veins, but, as a rule, their walls are thinner than those of veins of corresponding cahbre and their valves are more numerous. The walls of the most robust trunks, particularly those of the thoracic duct, consist of three coats. From within outward these are : (a) the intima, composed of the endothelial lining and the fibro-elastic subendothelial layer ; {b) the media, made up of involuntary muscle interspersed with fibro-elastic tissue ; and (c) the adventitia, consisting of fibro-elastic tissue and, frequently, of longitudinal bundles of in\-oluntary muscle. (Fig. 784.) The Lymphatic Nodes. — Scattered along the course of the lymphatic vessels are to be found in various regions of the body elliptical flattened nodules (Fig. 796") of varying size, some- times singly but more V\g. 786. frequently in chains or groups ( plexus lym- phatici) of from three to six or even ten to fifteen. These are the lymphatic nodes (lyni' phoglandulae). As it approaches a node, a lymph - vessel divides into a number of stems, the vasa afferentia, which enter the sub- stance of the node and communicate with a capillary net-work in its interior, from which a somewhat smaller number of vessels, the iiasa efferentia, arise (Fig. 786). These, leaving the node, the surface of which fre- quently presents a slight depression, the hilum, at their point of emergence, unite to form the continuation of the vessel. The lymph conveyed by any of the vessels traverses one or more nodes before emptying into the thoracic or right lymphatic duct, and in those cases in which a plexus occurs in a lymph-path a number of nodes must be traversed. The passage through the intranodular net -work produces a greater or less retardation of the flow of the fluid and affords opportunity for the accumulation of Ivmphocytes. Moreover, since these possess a phagocytic function, in cases of infection of any part of the body the nodes along the Ivmph-paths leading from it become more or less engorged with lymphocytes and enlarged, and in case the lymphocytes are unable to contend successfully with the infective material, the nodes may serve as Cortical follicle ph-node 936 HUMAN ANATOMY. foci for its distribution to other parts of the system. The nodes therefore, serving as traps for the infective material, possess a high degree of importance from the surgical standpoint, an accurate knowledge of their location and of the lymph-paths along which each group is situated being of great value. In addition to the ordinary lymph-nodes there occur in various regions of the body, especially in the prevertebral regions of the abdomen, structures which resemble lymph-nodes in their form and size, but differ from them in color. In general the lymph-nodes are of a pale pinkish color, although those in the vicinity of the lungs are usually blackish, from the deposition in them of dust particles from the lungs, and those in connection with tiie vessels arising from the small intestine are milky white during digestion. The structures in question, however, are of a deep red color, owing to the presence of abundant blood-vessels in their cortical portion. These bodies hav^e been termed the hemolymph nodes, but their exact nature and function have not yet been definitely ascertained. By some they are regarded as special structures, quite different from the lymph-nodes, perhaps partaking somewhat of the character of the spleen ; while others regard them as ordinary lymph-nodes with an especially rich blood supply, transitional forms between them and the usual lymph-nodes being believed to exist. Whether or not direct communication exists between the cortical blood-vessels and the medullary lymphatics within these hemolvmph nodes is also a question concerning which differences of opinion e.xist. Structure of Lymphoid Tissue. — Wherever found, whether as diffuse masses, simple nodules, or as the larger and more complex lymph-nodes, lymphoid or adenoid tissue is composed of two chief con- FiG. 7S7. stituents, the supporting reticulum and the Ivmphoid cells contained within the meshes of the framework. The rdiculuvi varies in the thickness of the component fibres and the size of its meshes, but in the denser types of lymphoid tissue, as seen in the periphery of the solitary nodules and in the cortical follicles and medullary cords of the lymph-nodes, it is so masked bv the innumerable over- Iving cells that only after removal of the latter can the supporting framework be satisfactorily demon- strated. The reticulum, the nature of which is still a subject of discus- sion, may be regarded as modified fibrous connective tissue, upon the trabeculae of which, particularly at the points of junction, flattened con- nective tissue cells are closely applied as a more or less complete invest- ment. In certain localities where of exceptional delicacy, the. reticulum may be formed almost entirely by the anastomosing processes of stellate connective-tissue elements. The cells composing lymphoid tissue, exceedingly numerous and closely packed, present the general characteristics that distinguish the lymphocytes, being small elements with comparatively large nuclei, which exhibit a strong affinity for nuclear (basic) stains. The simple lymph-nodules, of varv'ing size but seldom more than 2 mm. in diameter, are irregularly spherical or elliptical masses of lymphoid tissue in which a denser peripheral zone encloses and blends with a core of less compact texture. Within the looser and therefore lighter central area, lymphoid cells in various stages of mitotic division are frequently seen, such foci, known as germ-centres, indicating Ml '^A -Submucous laye Simple lymph-nodule from large intestine. X 120. THE LYMPHATIC SYSTEM. 937 the birthplaces of new lymphocytes. Although the limits of the lymph-nodules are commonly imperfectly defined by a condensation of the surrounding connective tissue, a distinct capsule is usually wanting. Definite lymph-channels are found neither Fig. 7SS. upon the surface nor within the simple nodules ; the latter are provided, however, with a generous net-work of capillary .^-^ - ;,. blood-vessels (Fig. 792). f|j?i J .i%; Intermediate in their comple.xity of ■" arrangement, between the simple nodules on the one hand and the typical lymph- ' ■ , , '^ nodes on the other, stand such structures - ' ', . '" 'f as Peyer' s patches and the faucial and ' ; pharyngeal tonsils, in which groups of ,; simple nodules are blended into a single organ, the component follicles only partly ;-&':'; - .}!- retaining their individuality. -Av'"'^ ? The lymph-nodes interposed along "'";-",■ :..■-- the lymphatic vessels, usually embedded within fatty tissue, represent still higher differentiation as distinct organs. In form and size they vary from minute bodies resembling millet-seeds to flattened oval or bean-shaped organs, that may measure almost an inch in their longest diameter. They are invested by a distinct fibrous capsule, in which elastic fibres constantly and unstriped muscle occasionally are present. From the deeper surface of this envelope numerous radially directed trabeculae penetrate the outer zone, or cortex, which is thus subdivided into a series of pyramidal compartments. On reaching the inner limits of the cortical zone, the trabecule are less regularly disposed and more freely united, thereby breaking up the deeper parts, or medulla, of the node into uncertain cylindrical compartments. The spaces thus imperfectly defined by the trabeculae are ot lymph-n( of germ-c Lymph s n Capsule Trabecula Cort cal follicles Hilum \ asa eiferentia MeduHar> cords Section of small lymph-node through hilum. X 25. incompletely filled by masses of compact lymphoid tissue, the general form and arrangement of which correspond to the compartments in which they lie. The masses contained within the peripheral spaces are spherical or pyriform and constitute 938 HUMAN ANATOMY. Fig Lymph-s Lvmph-s PorUon of peripheo of hmph node showing relatu and hmphoid ti='-'"' c%^ between trabecula the cortical nodules; those within the communicating central compartments form a net-work of irregular cylinders, the wcditllary cords, which are contmuous with one another and with the deeper part of the cortical nodules (Fig. 789). The intervals between the tracts of lymphoid tissue and the trabecular frame-work constitute a system of freely intercom- municating channels, the Ivmpli - sinuses, through which passes the lymph brought to the node by the afferent lymphatic vessels. The latter pierce the capsule on the convex surface of the node and empty into the sinuses that surround the outer and lateral surfaces of the cortical nodules. After tra\ersing the periph- eral sinuses, the lymph passes into the irregular channels of the medulla and towards the point at which the efferent lymph- vessels leave the nodule. The position of this exit is usually indicated by a more or less pronounced indentation, known as the liiliii?!, on the surface of the node opposite the entrance of the _ ^ afferent lymph-vessels. "^ '^ ' The lymph-sinuses, there- fore, are bounded on one side by the capsule or the trabeculse and on the other by the masses of dense lymphoid tissue. The lumen of these channels, however, is not free, but occupied by a delicate wide-meshed reticulum consisting of fine strands of connective tissue where most marked, or of the processes of stellate cells where very delicate (Ebner ). The sinuses are lined by an imperfect layer of flattened piate-like cells, that represent the endothelium of the adjoining lymphatic vessels and also cover the more robust trabeculse cross- ing the channels. The reticulum occupying the sinuses is continu- ous with the closer and more delicate net-work within the adja- cent dense lymphoid tissue. Although both the afferent and efferent lymphatics are pro\ided with valves, the lymph-channels Portion of medulla ot Ivmph-node, showing details of lymph-sinus and medullary cords. X 250- THE LYMPHATIC SYSTEM. 939 of small lymph-nod supply. njected to within the node are destitute of such folds. The passage of the lymph through the nodes is retarded by the reticulum within the sinuses, thus favoring the entrance ol the young lymphocytes from the surrounding lymphoid tissue into the sluggishly circulating fluid. Germ-centres, the particular foci for the production of the lympho- cytes, usually are present within the cortical nodules, but are not found within medullary cords. The blood-vessels for the nutrition of the lymph-nodes are numerous. Entering at the hilum , they divide into arterioles which follow the trabeculae, giving off smaller branches that pene- trate the medullary F"'G- 792- cords and the cortical nodules and break up into rich capillar)' net- works for the supply of the denser lym- phoid tissue. Both medullated and non-medullated nerves enter the node at the hilum in company with the blood-vessels. They are chiefly sympa- thetic fibres destined for the involuntary muscle of the vessels and of the capsule. The distribution of the medullated fibres is uncertain. According to Tonkoff, fibrillae are traceable into the lymphatic tissue of the medulla. Development. — The origin of the first lymph-cclls, the lymphocytes, is uncer- tain, these elements appearing outside the vessels as derivatives from the mesoblast (page 688). After the establishment of the lymphoid tissue new cells are continually being formed within the various lymph-nodes and nodules. The development of the lymphatic vessels has generally been believed to proceed from the veins by a process of budding (Ranvier), similar to that followed in the extension of the blood-vessels; and certain recent investigators, — Sabin,' who studied the development of the lymphatics in pig embryos, and F. T. Lewis, ^ who worked with rabbit embryos, — while differing as to details of the development ■of the definitive lymphatic stems, agree as regards their origin in this manner. Sabin, by employing a method of injection, found that the first traces of a lymphatic system appear in pig embryos, 14.5 mm. in length, as two small out- growths, which develop, one on each side, at the junction of the subclavian and jugular veins ; from these, by a process of endothelial budding, vessels gradually grow towards the skin, radiating and anastomosing in all directions to form a subcutaneous net-work, which gradually e.xtends throughout the anterior half of the body. Later two additional outgrowths develop at the junction of the femoral and post-cardinal veins, and give rise to a subcutaneous net-work throughout the posterior half of the body, the two sets of net-works thus formed eventually uniting. Lewis's studies of serial sections of rabbit embryos gave somewhat different result? and indicated that Sabin' s method of studv did not suffice to reveal the actual origin of the lymphatics. He found the first of these vessels along the course of the internal jugular vein as a series of spaces, each of which he supposed to represent an independent outgrowth from the vein. These spaces eventually fused to form a single lymph-channel accompanying each vein, and other channels were found to arise in a similar manner in connection with the subcardinal, mesenteric, and azygos ^ Amer. Tour, of Anatomy, vol. i., 1902. ''■ Amer. jour, of Anatomy, vol. v., 1905. 940 HUMAN ANATOMY. veins. The various channels finally unite to form a continuous system which acquires new openings with the venous system near the termination of the subclavian veins, the condition found in the adult being thus established. More recently Huntington and McClure,' working with cat embryos, have also found the earliest traces of the lymphatic system in a series of spaces which appear in the tissue surrounding the intima of the anterior cardinal veins, but they found that these spaces have at first no connection with the veins, nor are they outgrowths from them. The anterior cardinal vein of each side is early divided longitudinally into two portions by the passage through it of the cervical nerves, and the dorso- lateral portion of the vein later undergoes retrogression, the ventro-medial portion persisting as the internal jugular. As the dorso-lateral portion shrinks, the lymphatic spaces along its course rapidly enlarge, fuse together, and form a large lymphatic, stem, which subsequently makes con- nection with the subcla\ian vein, and thus forms the primary Ivmphatic trunk of the body (^'ig- 793)- Later, spaces develop along the course of the anterior cardinal veins below the point where the subclavians open into them, but it is noticeable that those occur- ring in association with the left vein, which undergoes retrogres- sion, develop more rapidly than those accompanying the same portion of the right \ein and form the thoracic duct ( Fig. 794), this structure thus belonging essen- tially to the left half of the body, since the principal persistent veins occur on the right side. Similar spaces appear in the peri-intimal tissue of other veins, and in all cases those associated with retro- gressive veins are the most rapidly de\eloped. While most of the principal lymphatic trunks unite with the thoracic duct, yet they may also form temporary or even permanent communications with other \eins than the subclavian, certain of the adult anomalies being results of these connections. From these observations it seems that the lymphatics arise from spaces which are primarily independent of, although associated with, the \eins, and that, while this mode of origin of the lymphatics applies to those following the primitive s)stemic veins, yet the more peripheral portions of the system are developed by a process of budding from the main stems, just as is the case with the smaller branches of the blood-vessels. By this budding process the system gradually extends throughout the body, invading the various tissues, the in\'asion, however, failing to afTect certain of the tissues, such as cartilage and the central ner\'ous system. The development of the lymph-nodes has been recently studied by Kling" and by Sabin.'' According to the latter investigator, the lymph-nodes may be regarded as formed by two fundamental parts — the lymphoid element, consisting of lympho- cytes in a reticulum surrounding the terminal artery and its capillaries within the ' Amer. Jour, of Anatomy, vol. vi., 1907. ' Archiv f. mikros. Anat., Bd. 63, 1904. ^ Amer. Jour, of Anatomy, vol. v., 1905. * Amer. Jour, of Anatomy, vol. v., 1905. Developing lymphatics in rabbit embryo of n X 9. Lymphatic vessels are heavily shaded ; veins ; Ex. J,, internal and external jugular veins; Pt-.C, A.r.il/.. external mammary; .-Jz., azygos; FC/., inferior v G".. gastric; S.Af., superior mesenteric; K, \itelline ; Si dinal ; R.A.y renal aiiastomosis of subcardinals ; Pr.Fi., fibular; c.d., connecting branch ; y4«. T'., anterior tibial; c J. ^1 J, (S, position of corresponding cervical nerves. {F. 1 THE THORACIC DUCT. 941 cords and germ-centres respectively, and the sinus-element, represented by channels resulting from the multiplication of the lymph-vessels. The former, or vascular factor, is constant and present in the simplest nodule ; the sinus-element, on the contrary, varies, sometimes (as in the usual type of node} being developed from numbers of closely packed lymph-ducts and, therefore, of lymphatic origin, and at other times (as in the hemolymph nodes) being venous channels occu- pied by blood. By the sub- sequent intergrowth of the lymphoid element and the greatly multiplied lymph- capillaries, the intervening bridges of connective tissue are reduced in thickness until finally only the reticulum remains and the lymphoid tissue is ultimately brought into intimate relation with the surrounding sinus. In certain nodes the sinus retains its character as a direct out- growth from the veins and becomes filled with erythro- cytes. Such nodes assume the peculiarities of hemolymph nodes, in which the blood- sinuses replace those that convey lymph. As Sabin has emphasized, the follicle is the anatomical as well as the vascular unit, the simplest nodule consisting of a single follicle. The latter may be without a sinus, or surrounded by one which is either a lym- phatic or a venous channel. Fig. 794. In describing the various lymphatic vessels and nodes it will be convenient to consider first the great terminal trunks of the system, the thoracic and right lymphatic ducts, and then discuss the remaining portions of the system from the topographical standpoint. Attention will be directed primarily to the nodes of each region, the course of the lymph-paths from each organ and their relations to the nodes being subsequently considered. Developing lymphatics in rabbit Lymphatic vessels are heavily shadec of lettering see preceding figure ; in chial : ^., radial ; .S^., subscapular; iliolumbar. {F. T. Lewis.*) imbrjo of 21 mm. (17 days); X 6. ; veins are light; for significance addition, Ce., cephalic ; i>>., bra- Sci., sciatic ; />., femoral ; //., THE THORACIC DUCT. The thoracic duct (ductus thoracicus) (Fig. 795) extends from the lower border of the second lumbar vertebra, through the entire length of the thora.x, to open into the left subclavian vein close to the point where it is joined by the left internal jugular. Its entire length is from 43-46 cm. (17-18 in.). The duct lies at first in *Amer. Jour, of Anatomy, vol. v., 1905. 942 HUMAN ANATOMY. front of the first and second lumbar vertebrae, and passes upward through the aortic opening of the diaphragm. In the thorax its course, although slightiy sinuous, in Fig. 795. Internal jugular vein Trachea. — \'ertebral vein Right lymphatic duct Subclavian vein 1. rib Right innominate vein' Right lumbar lymph trunk Crest of ilium Left common carotid arter>' Left innominate vein Thoracic duct Left subclavian vein Scalenus anticus Left subcla\ian artery Thyroid axis l.rib \'ertebral artery Thoracic duct Intercostal arteries Receptaculum chyli Intestinal lymph trunk Left lumbar lymph trunk Dissection of posterior body-wall, seen from in front, showing thoracic duct and right lymphatic duct; veins have been laterally displaced to expose terminations of thoracic duct. general is at first almost directly upward, a litde to the right of the median line of the bodies of the thoracic vertebrae ; at the level of from the sixth to the fourth THE THORACIC DUCT. 943 vertebrse, however, it begins to incline slightly towards the left, and, finally, at about the lower border of the seventh cervical vertebra it changes its direction somewhat abruptl)', passing upward, forward and to the left, and then downward and forward, thus forming an arch whose convexity is directed upward and whose extremity opens into the subclavian vein. The thoracic duct is formed by the union of the right and left lumbar trunks (trunci lumbales) which drain the lumbar nodes. The left trunk, shortly before its union with the right, is usually joined by an unpaired intestinal trunk (truncus intes- tinalis) that drains the coeliac and mesenteric nodes. Just above its commencement the thoracic duct usually, although not always, presents a pyriform enlargement, the receptaculum chyli ( cisterna chyli), which extends upward as far as the level of the eleventh thoracic vertebra, and" measures from 5-7.5 cm. (2-3 in.) in length and from 6-8 mm. in diameter. Above the eleventh thoracic vertebra the duct gradually diminishes in calibre until about the middle of its course, where it again_ enlarges. The thoracic duct possesses few valves in comparison with other lymphatic vessels, those which do occur being frequently insufficient. Its entrance into the subclavian vein, however, is guarded by two well-developed leaflets, which pre\-ent the passage of blood into the duct. Relations. — In its abdominal portion the thoracic duct lies almost in the median line in front of the bodies of the first two lumbar and twelfth thoracic vertebra, and between the crura of the diaphragm, or under cover of the right crus. Anteriorly, it is in relation with the right side of the abdominal aorta, with the greater azygos vein to the right. In its thoracic portion it lies at first within the posterior mediastinum, but above, it enters the superior mediastinum. In the former it lies anterior to the bodies of the eleventh to the fifth thoracic vertebrae, and has in front of it, from below upward, the pericardium, the oesophagus, and the arch of the aorta. The thoracic aorta lies to the left of it, and to the right are the right pleura and the greater azygos vein. The lower right intercostal arteries pass between it and the bodies of the vertebra, as does also the terminal portion of the hemiazygos vein. In the superior mediastinum it rests upon the lower part of the left longus colli muscle, being separated by it from the bodies of the upper three thoracic \'ertebrae. Anteriorly, it is in relation with the origin of the left subclavian artery and with the vertebral vein ; to the left is the left pleura and to the right are the oesophagus and the left recurrent laryngeal nerve. Its arch is in relation below with the apex of the left lung and with the left sub- clavian artery ; to the left and posterior to it is the vertebral vein and to the right and anteriorly are the left common carotid artery, the left internal jugular vein, and the left pneumogastric nerve. Tributaries. — In addition to the right and left lumbar and the intestinal trunks by whose union it is formed, the thoracic duct receives on either side ( i ) near its origin, a descending tru?ik which drains the posterior nodes of the lower six or seven intercostal spaces ; (2) an ascending stem from the upper lumbar nodes which trav- erses the crus of the diaphragm and joins the duct at about the level of the ninth or tenth thoracic vertebrae ; (3) the efferent vessels from the upper posterior intercostal nodes, which sometimes unite to form a single ascending stem opening into the upper part of the duct ; (4) the efferent vessels of the posterior mediastinal nodes ; (5) the left jngular trunk ; and, occasionally, (6) the left subclavian and (7) the left broncho- mediastinal trunks, these last three uniting with the duct just before it opens into the subclavian vein. Variations. — The thoracic duct is subject to numerous variations, so much so that certain authors have regarded as typical arrangements which others have considered to be abnormal. Its origin is frequently opposite the body of the first lumbar vertebra or even opposite the last thoracic ; and rarely it is below the lower border of the second lumbar. Instead of being formed by the union of only two trunks, three are frequently found participating in its origin, the odd one being the intestinal trunk which usually opens into the left lumbar trunk. Occasionally all three trunks are represented by a number of smaller stems which anastomose with one another as well as with the descending stems from the posterior intercostal nodes, the plexus so formed communicating by a number of efferents 944 HUMAN ANATO.MY. with the receptaculum chyli. It must be remembered that embrj-ologically what are usually termed the origins of the thoracic duct are in reality its prolongations, that is to say, outgrowths from it, so that possibilities for variation in these stems are abundant. In another respect the embryological history of the duct probably throws light upon its anomalies. In the rabbit the spaces formed along the course of the left posterior cardinal vein frequently unite to form two more or less distinct, parallel stems, which together represent the thoracic duct (Fig. 794). Whether this condition also exists in man is unknown, but if it does then an explanation is afiforded for one of the most frequent anomalies of the duct, namely, its division in its lower part into two parallel stems which unite again after a longer or shorter inde- pendent course. This condition is so frequent that it has been regarded as typical by some authors ; usually the union of the tuo stems occurs at about the level of the sexenth thoracic vertebra, but occasionally they remain separate throughout the entire length of the ihorax and may be connected by trans\erse anastomoses. Another group of anomalies, probably ha\ing a quite different embryological basis, includes cases in which there are either two distinct thoracic ducts, or else a single one \\hich branches in its upper part, one of the two stems in either case passing to the left subcla\ ian vein and the other to the right. This condition is due to the fact that the lymphatic system is symmetrical in its embryological origin, a trunk arising in connection with the right azygos vein as well as with the left. Ordinarily the left trunk, developing more rapidly than the right, becomes the thoracic duct, while the right outgrowth remains short and forms the right lymphatic duct. Conditions might occur, however, in which the right trunk would undergo a more extensive de\elopment and either unite \\ ith the left trunk or grow downward to form a second thoracic duct, thus producing the conditions under discussion. A further modification along the same line would lead to the development of the thoracic duct from the right trunk, the left giving rise only to a short lymphatic duct, an exact reversal of the normal arrangement being thus produced. Several such cases have been recorded, and it is interesting to note that they frequently accompany abnormalities of the aortic arch, such as the origin of the right subclavian from the descending portion ; the anom.aly also occurs, however, independently of any variation in the blood-vessels. Considerable variation exists in the level to which the arch of the thoracic duct rises in the neck, and it is stated that it may lie anywhere between the levels of the fifth cervical and first thoracic vertebrae. Likewise, variations in the mode of termination of the thoracic duct are often observed. It may open into the subclavian vein at some distance from the junction of the internal jugular, or, occasionally, into its posterior surface, and not infrequently it divides near its termination into two or more stems (Fig. 795). which may open into the internal or the external jugular or into the azygos or vertebral veins as well as into the subclavian. The connection with the azygos \em is probably of frequent occurrence. Practical Considerations. — The thoracic duct may be obstrvded by {a) aneurism of the arch of the aorta ; (3) enlarged mediastinal nodes (tuberculous, lymphadenomatous, or carcinomatous) ; {c) mediastinal neoplasms — especially if in the anterior mediastinum; id') exophthalmic goitre ( very rarely ) : (f) thrombosis of the left innominate vein or of the subcla\ian at its junction with the internal jugular ; (y) tricuspid incompetence (through backward pressure) ; {g) cardiac hyper- trophy ; (//) dense pancreatic growths (Agnew) ; (/) thrombosis (tuberculous) of the duct itself ; (/ ) filarial disease (obstruction by the parent worms) ; (k) cicatri- cial contraction or adhesion involving the duct ; (/) disease (tuberculous, carcino- matous) of the walls of the duct. The duct mav be injured (a) during operations — as for growths or enlarged glands — or by stab or bullet wounds (usually in its cer\ical portion) ; or (b) by grave trauma, as fracture dislocation of the spine (usually in the thoracic or abdomi- nal portion), or violent compression of the thorax ; or (f) by muscular effort or during a paroxysm of vomiting (Busey\, or whooping-cough (W'ilhelm). The fact that the duct as a rule extends upward but little if at all above the level of the junction of the internal jugular and subclavian renders operati\'e injury of it rare, but as it occasionally is found higher, and may even extend to 5.5 cm. (2^ in.) above the upper border of the sternum, its possible presence and its tela tions and variations (v?de supra) should not be forgotten during extensive operations at the base of the neck on the left side. The results of obstruction of the thoracic duct are (a) increased pressure and dilatation of the vessels behind the obstruction; (b) the establishment of collateral circulation and entrance of lymph into the general circulation; or — if such collateral circulation is not established — (f) leakage by transudation into the surrounding tissues, into the pleural cavity (rare), or into the peritoneal cavity ; or (d) rupture of the duct or its tributaries. The stomata of the thin-walled THE LYMPHATICS OF THE HEAD. 945 lymphatic vessels ofEer little obstacle to free transudation, which, when it follows obstruction, may be compared to the hematemesis seen in hepatic cirrhosis (Rolleston). The symptoms of obstruction are neither so constant nor so marked as they would be if it were not that (a) the lymphatic system is not, like the veins, a series of closed vessels, but is practically continuous with the interstices of the tissues ; and that {b) it communicates with the venous system, the duct itself with the azygos vein in the posterior mediastinum, and the smaller lymphatics with venules elsewhere — certainly, for example, in the inguinal region, and probably in other parts of the body (Leaf). The effects of obstruction are most often noticeable when the interference with the flow of lymph takes place near the termination of the duct on the outer side of the internal jugular vein, near its junction with the subclavian. This is probably due to {a) the frequency of tumor or of injury in this situation ; (b) the consolida- tion of the lymph-vessels here into a single trunk ; (c) the greater difficulty in estab- lishing a compensatory collateral circulation between the parts of the duct above and below the obstruction than if the latter were lower down- (Rolleston). Chylous ascites may be due either to obstruction with transudation of chyle from distended lacteals into the peritoneal cavity, or to wound or rupture of the thoracic duct, or of the larger lymph-vessels, or of varicose lymph-vessels, or of lymphangiomata. Chylous pleural effusions may similarly result, or an effusion fol- lowing wound or rupture may be partly thoracic and partly abdominal, as in a case in. which, after extreme compression of the chest, death followed in three weeks, and the thoracic duct was found ruptured where it traversed the hiatus aorticus (Bellamy). When the receptaculum chyli is involved, the thoracic duct above may be quite healthy, and 'lymph may pass into it by anastomotic channels' and no chylous ascites be produced. Carcinoma of the aortic or mesenteric nodes may cause enough dilatation of the lymphatics to bring about chylous ascites. THE RIGHT LYMPHATIC DUCT. The right lymphatic duct (ductus lymphaticus dexter) (Fig. 795) opens into the right subclavian vein and is a very short stem, rarely having a length of more than from 10-12 mm. It is formed by the union of the right jugular and subclavian lymphatic trunks, the right broncho-mediastinal trunk rarely contributing to its formation, but having usually an independent opening into the subclavian vein. Very frequently no right lymphatic duct exists, the jugular and subclavian trunks, as well as the broncho-mediastinal, opening independently into the vein. THE LYMPHATICS OF THE HEAD. The Lymph-Nodes. The lymphatic nodes of the head are arranged in groups, which, for the most part, are situated along the line of junction of the head and neck regions, that is to say, along a line extending from the external occipital protuberance to the temporo- mandibular articulation and thence along the rami of the mandible. A few small nodes also occur upon the cheeks, -■nd others which lie upon the surfaces of the hyo-glossus and genio-hyo-glossus muscles and upon the upper part of the posterior surface of the pharynx may be regarded as belonging to the head region. Including these, the various groups recognizable in the region are (i) the occipital, (2) the posterior auricular, (3) \hft antej'ior auricular, (4) Xh^ parotid, (5) ^& submaxillary, (6) the submental, (7) the /«««/, (8) the lingual, and (9) the retropharyngeal %ro\x\i's,. The occipital nodes (lymphoglandulae occipitales) are from one to three in num- ber and are situated at the base of the occipital triangle, immediately lateral to the border of the trapezius muscle and resting upon the upper part of the semispinalis capitis (Fig. 796). Their affe^-ents come from the occipital portion of the scalp and their efferents pass to the upper nodes of the superior deep cervical group. The posterior auricular or mastoid nodes (lymphoglandulae auriculares posteriores) are usually two in number and are of small size ; they rest upon the mastoid portion of the insertion of the sterno-cleido-mastoid muscle (Fig. 796). 60 946 HUMAN ANATOMY. Their affere7its are from tlie temporal region of the scalp, from the posterior surface of the pinna and of the external auditory meatus. Their effere7its pass to the upper nodes of the superior deep cervical group. The anterior auricular nodes O.vmphoglandulae auriculares anteriores) vary from one to three in number and are situated immediately in front of the tragus, beneath the parotid fascia. Their afferents come from the anterior surface of the pinna and of the external auditory meatus, from the integument of the temporal region, and from the outer portions of the eyelids. Their cffcrents pass to the superior deep cervical nodes. The parotid nodes (lymphoglandulae parotideae) are situated in the substance of the parotid gland (Figs. 796, 801). They are quite numerous and vary greatly in size. They Fig. 796. receive afferents from the same regions as the anterior auricular nodes, and the lower nodes of the group also receive stems from the soft palate. Their efferents pass to the superior deep cervical nodes. The submaxillary nodes (lymphoglaiidiilae siibmaxillaresj are from three to eight or more in number, forming a chain along the lower border of the horizontal ramus of the mandible, as far forward as the attachment of the ante- rior belly of the digastric muscle (Fig. 796). One node which rests upon the facial artery just before it passes over the ramus of the mandible is larger than the rest, and this, together with two others, which are some- what smaller and lie one on either side of the larger node, are the most constant represen- tatives of the group, the remaining nodes being usually still smaller and varying both in number and position. Occasionally a small node occurs imbedded in the substance of the submaxillary gland. These nodes receive, as afferents, vessels from the submental and facial nodes and also direcdy from the territory drained by the latter, namely, the upper lip, the outer surface of the nose and the cheek, from the inner portions of the evelids, from the lower lip, the gums of both jaws, and from the anterior part of the tongue. Their efferents descend upon the surface of the submaxillary gland to open into the superior deep cervical nodes, especially into those situated in the neighborhood of the bifurcation of the common carotid artery. The submental nodes are two or sometimes three in number, and are situated in the triangular space included between the anterior bellies of the two digastric muscles, each of the two principal nodes resting upon the inner border of one of the Superficial lymphatic vessels and nodes of head and neck ; semidiagrammatic. THE LYMPHATICS OF THE HEAD. 947 Fig, muscles (Figs. 796, 797). They receive afferents from the integument of the chin, from the lower lip, and from the floor of the mouth ; their effererits pass partly to the subma.\illary nodes and partly to a node of the superior deep cervical group situated on the internal jugular vein a little above the level at which it is crossed by the omo-hyoid muscle. The facial nodes (lymphoglandulae faciales profundae) consist of sev- eral small groups (Fig. 798). One of these is composed of two or three nodes situated upon the outer surface of the horizontal ramus of the mandible, in front of the anterior border of the masseter muscle ; these may be termed the mandibular nodes. A second group is to be found resting upon the surface of the buccinator muscle, and its nodes are therefore termed the buccinator nodes. They are three or four in number and are situated in the interval between the facial vein and artery, or posterior to the vein, almost opposite the angle of the mouth and either beneath or slightly below the Fig. 798. zygomaticus major. A third group is formed by the maxillary nodes, which are somewhat scattered, one or two occurring in the groove formed by the junction of the nose and cheek, while another rests upon the malar bone near the lower border of the orbit. These maxillary nodes are nor- mally quite small and may readily be overlooked. The afferents for the various groups of facial nodes take their origin in the upper lip, in the integument and mucous membrane of the nose and cheek, and probably also in the eyelids, the conjunctiva, and the lachrymal gland. Their efferents pass to the submaxillary nodes. The lingual nodes (lymphoglandulae linguales) are a number of small enlarge- ments situated upon the vessels which drain the lymphatic capillaries of the tongue. They do not possess any very definite grouping and are to be found upon both * Archiv f. Anat. u. Physiol., 1898. t Beitrage zur klin. Chirurgie, Bd. 39. Facial lymph-nodes. (Tiende/.f) 948 HUMAN ANATOMY. surfaces of the hyo-glossus muscle and in the interval between the two genio-hyo- glossi. From the surgical standpoint they are of comparatively little importance, and have been termed "intercalated nodes," to distinguish them from the true terminal nodes of the lingual lymphatics (page 954), in which enlargement occurs in cases of cancerous or Fig. 799. Keuui'luirviigeal hnipli- other infection of the tongue. The retro-phar- yngeal nodes are for the most part small, appearing as slight en- largements of the lym- phatics which drain the posterior surface of the pharynx. In addition to these "intercalated nodes, ' ' however, one or two much larger nodes occur at the junc- tion of the lateral and posterior surfaces of the pharynx, about on a level with the anterior arch of the atlas. They are imbedded in the bucco-pharyngeal fas- cia and rest upon the lateral portions of the rectus capitis anticus major. AJferents come to them from the upper part of the pharynx and from the mucous membrane of the nose, and their efferents pass to the upper deep cervical nodes (Fig. 799). The Lvmph.\tic Vessels. The Scalp. — The lymphatics of the scalp form a rich net-work, which is espe- cially dense in the neighborhood of the \-ertex, the meshes becoming more elongated as the vessels pass away from the median line. From the frontal region some ten to twelve vessels pass downward and backward to terminate in the parotid nodes ; from the parietal and temporal regions from six to ten vessels pass downward, some in front of the external auditory meatus to terminate in the anterior auricular and paro- tid nodes, and some behind the meatus to reach the posterior auricular nodes ; and from the occipital region the more posterior vessels pass downward, partly to the occipital and partly to the superior deep cervical nodes, while the more anterior five or six converge to form a single large trunk which descends along the posterior border of the sterno-cleido-mastoid muscle and terminates in the inferior deep cervical nodes. The Brain and the Meninges. — No lymphatic vessels have as yet been cer- tainly demonstrated either in the central nervous system or in the meninges, although they have been described as accompanying the middle meningeal artery in the dura mater and the middle cerebral artery in the pia (Poirier). Lymph-spaces, how- ever, some of them of considerable size, are abundantly present. Of these there may be mentioned, first, \.\\^ pericellular spaces which surround the individual cells of the brain and spinal cord, both the actual nerve-cells and the neuroglia-cells, those accompanying the latter extending along their processes to communicate with an epicereKral space believed to exist between the surface of the brain and the pia (His), and also with spaces which occur along the course of the cerebral blood-vessels. Of this second group of spaces, the perivascular spaces, two sets have been described, one occurring in the adventitia surrounding the vessels and the other between the adventitia and the brain substance, and, accompanying the blood-vessels into the pia, * Archiv f. klin. Chirurgie, Bd. 41, 1900. THE LYMPHATICS OF THE HEAD. 949 they communicate with the subarachnoid spaces. The third group of spaces is formed by the subdural and subarachnoid spaces, but no special description need here be given of these, since they are more properly described (page 1197) as portions of the meninges than as parts of the lymphatic system. By some authors an epidural space, situated between the dura and the skull, is also recognized. Lymph-spaces have been described as occurring in the substance of both the dura and the pia, forming in the latter a rather close net-work with which the perivascular spaces communicate. The spaces of both membranes communicate with the subdural space, and those of the dura are said also to communicate with the epidural space. Practically nothing is yet known concerning the lymphatics of the spinal cord. The Eye and Orbit. — No lymphatic vessels have as yet been described as occurring in the orbital tissues, nor do they occur in the eyeball. But, on the other hand, numerous lymph-spaces occur in connection with the latter structure, one of the most important of these being the space of Tenon (spatium interfasdale), with which the remaining spaces communicate more or less directly (Fig. 800). A description of this space has already been given (page 504), but it may be recalled that, in the first place, the space is continued, by means of the supravaginal lymph- Conjunctival sac Space of Tenon Diagram showing relation of space of Tenon to intracranial lymph-spaces. path surrounding the optic nerve, along the latter to the apex of the orbit, where it communicates with the subdural space of the cranium, injection of that space resulting in the injection of the space of Tenon (Schwalbe), and, secondly, that the sheaths of the anterior portions of the orbital muscles are formed by reflections of the capsule of Tenon,, so that no obstacles exist in the way of the passage of lymph from the muscles into the space. The cavities occupied by the vitreous and aqueous humors have also been re- garded as lymph-spaces, and pericellular spaces in the cornea, which come into rela- tion with the lymphatic vessels of the conjunctiva at the corneal margin, are readily demonstrable. In the tissue of the sclerotic spaces also occur, communicating on the one hand with the space of Tenon and on the other with suprachoroid spaces which are abundantly present in the lamina fusca of the choroid coat and, by means of spaces accompanying the vense vorticosae, communicate with the space of Tenon. In the eyelids, conjunctiva, and lachrymal apparatus true lymphatic vessels occur. In the eyelids three net-works have been distinguished, one of which is subcutaneous, the second lies immediately external to the tarsal plate, and the third is subconjunctival. Communicating branches pass between adjacent plexuses, especially between the 950 HUMAN ANATOMY. subcutaneous and praetarsal ones, and all three are united at the palpebral margins in a rather finely meshed plexus. Efferents pass both toward the inner and the outer angle of the orbit, and the former pass downward, obliquely across the cheek, in company with the facial vein, to terminate in the submaxillary nodes, possibly making connections with some of the facial nodes on their way (Fig. 798). The outer ones pass partly to the anterior auricular and partly to the upper parotid nodes. In the conjunctiva two net-works occur, one situated in the superficial and the other in the deeper layers of the conjunctival dermis. Communicating stems pass between the net-works, which are much finer in the neighborhood of the corneal margin than more peripherally. They come into relation with the pericellular lymph-spaces of the cornea, and their efferents pass toward the outer and inner angles of the orbit, to accompany the palpebral efferents to the submaxillary, posterior auricular, and parotid nodes. Of the lymphatic vessels of the lachrymal gland but little is known, but in ma- lignant diseases of the gland enlargement of some of the facial and anterior auricular nodes has been observed, and it is probable that vessels from the gland accompany the palpebral and conjunctival efferents. The vessels from the nasal duct probably partly accompany branches of the facial vein to the facial nodes, while those from its lower portion pass with the efferents from the nasal mucous membrane to the retro- pharyngeal and superior deep cervical nodes. The Ear. — No true lymphatics have yet been observed in the tissues of the inter7ia/ ear, but the space which intervenes between the osseous wall of the ear cavity and the membranous ear has been regarded as a lymph-space, and on that account has been termed the Fig. 801. perily7nphatic space. It com- municates with the subdural space of the cranium by the aqueductus cochleae and by the prolongations of it which accom- pany the ductus endolymphaticus and the auditory nerve. In the middle ear spaces have been observed in the con- nective tissue lining the bony walls, as well as in that of the tympanic membrane. In addi- tion a feebly developed net- work has been described as occurring beneath the epithelium lining the inner (tympanic) surface of the tympanic membrane, efferents from it accompanying the tym- panic artery and terminating in the parotid nodes. Much more extensively developed are the lymphatic vessels of the external car. Beneath the epithelium covering the outer (meatal) surface of the tympanic membrane there is a very fine net-work, whose effer- ents accompany the blood-vessels, radiating toward the periphery of the membrane, and eventually open partly into the posterior and partly into the anterior auricular nodes. A net-work also occurs throughout the entire extent of the external auditory meatus, its efferents having the same destination as those of the pinna. The vessels of the last named portion of the ear form a rich net-work extending throughout the whole e.xtent of the organ, and from it stems pass in three principal *Anatom. Anzeiger, Bd. xv., 1S99. cle of new-born THE LYMPHATICS OF THE HEAD. 951 directions ; it must be recognized, however, that this classification of the stems into three groups does not imply a corresponding division of the net-work into distinct areas, since there is a considerable overlapping of the areas drained by the various stems, and, indeed, stems from the same region may pass in some cases with one of the group, and in others with another. From the outer (anterior) surface the stems pass mainly to the anterior auricular nodes, a few bending backward over the helix and terminating in the posterior auricular nodes. From the upper part of the posterior surface (Fig. 801 j the stems pass mainly to the posterior auricular nodes, some, however, continuing past them to terminate in the external jugular nodes. From the lower part of the pinna, including the lobule, a number of stems pass to the parotid nodes. The Nasal Region. — The lymphatic vessels of the integument of the nose (Fig. 802) form numerous anastomoses with those of the mucous membrane, especially with those of the middle and inferior meatuses, and those of the one side of the nose are also continuous with those of the other side. Some of the vessels which drain the upper portion of the nasal integument Fig. S02. pass almost directly backward to the parotid nodes, but the principal path, followed by vessels from all parts of the nasal integument, is downwards and backwards across the cheek, in com- pany with the facial blood - vessels. In their course some of them traverse some of the facial nodes, which appear as if intercalated in their course, but the ma- jority pass directly to the submaxillary nodes. A rich lym- phatic net-work lies beneath the mucous membrane of the • nasal cavities, and from it vessels pass in two directions. Those of the anterior and lower portions of the fossa pass forward and, partly at the external nares and partly by passing between the nasal bones and the cartilages, communicate with the superficial nasal lymphatics. The majority of the vessels, however, take a backward course, terminating in different node groups. Some join the vessels draining the palate and tonsils to pass to the superior deep cervical nodes and especially to that one which is situated in the angle formed by the union of the facial and internal jugular veins, while the rest unite to form from two to four stems which pass over the lateral surface of the pharynx and terminate in the retropharyngeal nodes. The lymphatics of the sinuses which open into the nasal cavities follow, in part at least, the same courses as those of the nasal mucous membrane, their principal termination being in the larger retropharyngeal nodes. The Cheeks, Lips, Gums, and Teeth. — The lymphatics from the more posterior portions of the cheeks empty into the parotid nodes ; those from the more anterior portions pass to the submaxillary nodes, and the deepei ones communicate with the facial nodes. * Beitrage f. klin. Chirurgie, Bd. xxv., 1S99. 952 HUMAN ANATOMY. The vessels from the submucous tissues of the hps pass mainly to the submaxil- lary nodes, two or three stems passing from the lower lip and one or two from the upper. Those of the louder lip pass downward and outward toward the facial artery and follow its course into the submaxillary region, while those from the upper lip are directed at first almost horizontally outward toward the facial vein, whose course they follow toward their termination. No anastomoses occur between the submucous vessels of the two sides in either lip. The subcutaneous vessels of the Jipper lip (Fig. 803) have a course similar to that of the corresponding submucous stems, with which they may unite, and they terminate principally in the submaxillary nodes, although communication may also be made with one of the lower parotid nodes. The subcutaneous vessels of the lower lip are from two to four in number, and pass principally to the submental nodes, from which efferents pass to the sub- FiG. S03. maxillary and superior , deep cervical nodes. A noteworthy peculiarity of these lower lip \-essels, which is in marked con- trast with what obtains in the submucous stems, is that those of the right and left hahes of the lip anastomose, so that an injection may pass from the vessels of the right half into the left sub- mental and submaxillary nodes. The lymphatics of the lo'urr giiiiis form a very rich net-work from which from fourteen to seventeen stems arise. These empty into a single large collecting stem on either side, which passes outward over the outer surface of the mandible and, opposite the last molar tooth, dips down- ward to terminate in the submaxillary nodes. Whether or not the pulp of the teeth contains lymphatic capillaries is a disputed question. All attempts to inject them ha^'e failed, but it has been maintained that their existence has been demonstrated by histological methods. Enlargement of the submaxillary nodes has been observed to follow dental lesions, but this may be due to the involvement of the tissues of the gums rather than to that of the tooth pulp. The Tongue. — Tiie lymphatics of the tongue (Fig. 804) are divisible into two groups according as they arise in the submucous tissue or in the musculature. The submucous vessels take their origin from an exceedingly rich net-work which extends throughout the entire surface of the tongue. It is especially close toward the tip, the meshes becoming larger posteriorly, and that portion of it which lies posterior to the circumvallate papillae is independent of that of the more anterior portions of the tongue. The vessels of the muscular portion of the organ are much less extensively developed and the efferent stems which pass from them early unite with those of the submucous net-work. These latter are quite numerous and for purposes of description may be arranged in four groups. * Internat. Monatsschrift f. Anat. u. Physiol., 1900. ubcutaiieous hmpha i of lips nd superior deep i (Dorendorf.*) THE LYMPHATICS OF THE HEAD. 953 Fig. S04. The first or apical group (Fig. 805) consists of from two to four stems which arise from the net-work at the tip of the tongue and pass downward and backward, half of them lying on one side of the frenum and half on the other side. They follow at first the anterior border of the genio-hyo-glossus muscle and then pass upon the outer surface of that muscle and are continued downward and backward, either e.xternal or internal to the hyo-glossus, until they reach the greater cornu of the hyoid bone, just below the attachment of the stylo-hyoid. They then cross obliquely over the outer surface of the greater cornu, and are continued down the neck along the outer border of the omo-hyoid muscle to open into one of the inferior deep cervical nodes situated upon the jugular vein just above the point where it is crossed by the omo-hyoid muscle. Sometimes an additional apical stem passes down the frenum in company with those just described, but continues on downward to perforate the mylo-hyoid muscle and terminate in one of the submental nodes. A second or lateral g7-oup consists of a number of vessels which emerge from the net-work along the borders of the tongue (Fig. 804). There are from eight to twelve stems in this group on either side, and all are at first directed almost verti- cally downwards, a few, three or four, passing later- ally to the sublingual gland and the rest medial to it. The former continue their downward course, perforate the mylo-hyoid muscle, and terminate in the submaxil- lary nodes, while the others take a course obliquely downward and backward, and, passing some upon the median and others upon the lateral surface of the hyo-glossus muscle, terminate in the superior deep cervical nodes and especially in one situated a little above the level of the bifurcation of the common carotid artery. This node, on account of its relations to these lingual stems, has been termed the principal node of the tongue (Fig. 805). A third or basal group takes its origin from the dense portion of the submucous net-work which surrounds the circumvallate papillae and the foramen ceecum. Four stems issue from the net-work in the neighborhood of the median line, and two on each side more laterally. The median stems pass at first directly backward and then bend outward in the glosso-epiglottidean folds, two on either side, and join the lateral stems beneath the tonsils. The lateral stems, which drain the regions of the lateral circum- vallate papillse, the foliate papillae, and the glandular region of the tongue, are directed backward towards the lower border of the tonsil, and, after being joined in that situation by the median stems, they pass deeply to terminate in the superior deep cer\'ical nodes. Finally, a fourth or median group arises from the net-work of the median portion of the tongue, anterior to the circumvallate papillae. These stems are five or six in number, and pass at first directly downward through the substance of the tongue and through the inter\'al which separates the two genio-hyo-glossal muscles. One or two of them then continue in their downward course and pass, in some cases phatics of dorsum and margins of tongue. {Kiittner*) * Beitrage f. klin. Chimrgie, Bd. xxi., 1S95. 954 HUMAN ANATOMY. to the right and in some to the left, between the genio-hyo-glossus and the genio- hyoid muscles, perforate the mylo-hyoid, and terminate in the submaxillary nodes. The remaining three or four stems pass backward along the mylo-hyoid muscle and, emerging at its posterior border, pass to the superior deep cervical nodes. From this account it will be seen that four different groups of nodes stand in relation to the lymphatics of the tongue. ( i ) The submental nodes receive a stem from the tip ; (2j the subma.xillary nodes receive stems from the marginal and cen- tral regions ; (3) the superior deep cervical nodes receive stems from the marginal, central, and basal regions ; and (4) the inferior deep cervical nodes receive a stem from the apical region. Fig. S05. In addition it may be mentioned that many of the stems have upon their course one or more of the small ' ' inter- calated ' ' lingual nodes ( page 948 ). Special importance, however, attaches to that supe- rior deep cervical node already mentioned as occurring at about the level of the bifurcation of the common carotid artery, on account of the numerous aflerents it receives from the tongue. The lymphatics of the floor of the mouth have essentialh- the same terminations as those of the tongue. The stems which arise from its anterior half pass with the stems from the tip of the tongue to the inferior deep cer\'ical nodes, while from its entire surface stems pass to the subma.xillary and superior deep cervical nodes. The Palate, Pharynx, and Tonsils. — The lymphatics of the hard palate form a tine n^t-work in the superficial portions of the mucous membrane and are continuous laterally with those of the upper gum. They empty into se\eral stems which pass backward in the median line of the palate and at about the level of the last molar teeth bend outward to the right and left, and, passing in front of the anterior pillars of the fauces, pierce the superior constrictor of the pharyn.x to terminate in those superior deep cervical nodes which are situated on the internal jugular vein above the level at which it is crossed by the posterior belly of the digastric muscle. The net-work of the soft palate is exceedingly close and especially so in the uvula, which in a successful injection of the lymphatics may treble its volume, be- coming exceedingly turgid (Sappey). Stems emerging from the net-work pass toward both surfaces of the palate, those Iving below the upper surface passing back- ward and outward to join the stems from the nasal mucous membrane just below the orifice of the Eustachian tube, whence their course is similar to that of the nasal stems. Some of them pass upward and backward to perforate the superior con- strictor of the pharyn,x and terminate in the lateral retropharv-ngeal nodes, while others descend beneath the mucous membrane covering the posterior pillars of the fauces and, after perforating the superior constrictor, terminate in the upper nodes of the superior deep cer\-ical group. Lymphatics of tongue. (i*(>j ' Gazette hebdomadaire, 1902. THE LYMPHATICS OF THE HEAD. 955 The lymphatics of the tonsil, which resemble those of the soft palate in their abundance, pass with the stems from the basal region of the tongue to the superior deep cervical nodes. Those of the pharynx are also abundant, especially above (Fig. 799). The stems which arise from the roof and upper part pass principally to the retro- pharyngeal nodes, although some reach the superior deep cervical nodes directly by following the course of the ganglionated cord. The stems which have their origin in the lower part of the pharyngeal net-work pass downward toward the larynx and unite with its vessels to be distributed to the superior deep cervical nodes as far down as opposite the level of the second or third tracheal ring. Practical Considerations. — The Lymph-Nodes of the Head. — The lymphatics of the scalp pass from the plexus of fine radicles on the vertex into the suboccipital (occipital), mastoid (postauricular), parotid (preauricular), and superficial cervical nodes, and a few — from the frontal region — into the submaxillary node, into one or the other of which infection may be carried from any portion of the scalp. The suboccipital 7iodes — one to three on each side — lie on a line drawn from the junction of the upper and middle thirds of the ear to the inion and about two inches external to that point. They are often enlarged as a result of wounds or irritation of the occipital and postauricular portion of the scalp and — especially in neglected children — as a conseovence of eczema affecting the skin back of the ear. The close relation of the node ' o the great occipital ner\'e, on which it usually lies, gives rise to marked tenderness on pressure, the nerve being compressed bet\veen the node and the bone. The source of infection of these nodes may be intracranial — e.g. , suppurative meningitis of the cerebellar fossa (Macewen). T\v& posterior auricular or mastoid node, found directly over the mastoid insertion of the sterno-cleido-mastoid, is likewise usually infected from the same scalp region. It may also be involved alone or together with the suboccipital and deep cervical nodes in localized tuberculous mastoiditis or even in tuberculous otitis media. The parotid nodes, lying both in and upon the gland, receive lymph from and consequently may be infected by lesions of the scalp, the outer portion of the lids, the orbit, the cheeks, the nasal fossse, the naso-pharyn.x, the external auditory meatus, the tympanum, or the temporo-mandibular joint. Chronic enlargement of these nodes, especially of the deeper ones in the substance of the gland and beneath the parotid capsule, may lead to a mistaken diagnosis of parotid tumor. Suppura- tive inflammation of these deeper nodes gives rise to a true parotid abscess, which, on account of the resistance of the strong parotid fascia, will be under great tension. Sloughing of the parotid tissue may occur. There will be shooting pains in the head, neck, and ear, from pressure on the branches of the trigeminus accompanying the facial, or on the auriculo-temporal and great auricular nerves. The contiguity of the temporo-mandibular joint — into which the abscess may open — makes movement of the lower jaw painful. The relative weakness of the capsule anteriorly and on its inner aspect causes the pus to travel fonvard towards the cheek, or inward towards the pharyn.x, following sometimes the pharyngeal process of the parotid and giving rise to a retropharyngeal abscess. Gravity and the cervical process of the parotid may conduct the pus into the neck. The lymphatics of the face empty, the superficial set — accompanying the facial vein-— into the parotid and subma.xillary nodes ; the deep set, with some of those of the orbit, palate, nasal fossae, and upper jaw, are said to end in the internal maxil- lary nodes situated at the sides of the pharynx anteriorly. According to Leaf, these are only exceptionally present. Their involvement in infections spreading from the above regions may give rise to ' ' latero-pharyngeal abscess, ' ' causing a swelling externally behind the angle of the mandible, and an inward projection of the phar\-n- geal wall posterior to the tonsil. The proximity of the internal carotid should be remembered, and the fact that an aneurism of that vessel has been opened under the impression that it was an abscess of this \-ariety (page 747). Some lymphatics from the chin and the mid-portion of the lower lip empty into the suprahyoid (submental) nodes lying on the mylo-hyoid between the two anterior bellies of the digastrics. Enlargement of these nodes may be distinguished 956 HUMAN ANATOMY. from a bursal tumor (thyro-hyoid) by the fact that tlie former is above, the latter below, the hyoid bone. Enlargement of a submaxillary node, as of a parotid node, may, particularly if it lies within the sheath of the gland, be mistaken for a growth of the gland itself. The latter — as compared with the parotid — is, howe\er, much less closely and firmly enveloped by its capsule, is more superficial, and is not in near relation to such important structures. On the other hand, the wide area which drains into the sub- ma.xillary nodes — the middle of the forehead and of the face, the inner portions of the lids, the mouth, pharyn.x, anterior portion of the tongue, gums and teeth of the lower jaw — renders them especially liable to pyogenic or tuberculous or syphilitic infection, or to secondary involvement in carcinoma of any of these regions — espe- cially of the tongue or lower lip. In e.xamining for enlargement of these nodes, the chin should be lowered so as to rela.x the depressors of the lower jaw and the deep cervical fascia and permit of more accurate palpation of the region. When these submaxillary nodes require removal for infectious or malignant disease, the salivary gland is often involved and must be removed with them. On account of its accessi- bility and the la.xity of its capsular connections, enucleation of this gland is easily accomplished. The relation of the facial artery lying close to the upper part of its deep aspect — which it grooves — before crossing the jaw in front of the masseter muscle should be remembered. The efferent vessels from all these nodes — suboccipital mastoid, parotid, and submaxillary — enter into the superficial cervical nodes, the efferent vessels from which, in their turn, enter the deep cer\-ical nodes (page 957). Extracranial lesions of an irritati\'e kind will thus first show themselves in enlargement of the first mentioned groups ; if the irritation is continued, the superficial cervical nodes will enlarge ; and if it persists and is sufficiently severe, the deep cervical will also participate in the enlargement ( Macewen). As the intracranial lymph-paths, having their origin in the cerebral pia mater and the choroid ple.xuses of the ventricles, pass out of the skull in company with the internal carotid and vertebral arteries and, lower, the internal jugular vein and empty into the deep cervical nodes, these latter are, theoretically, first affected by intracranial irritation. As they lie beneath the cer\'ical fascia, their enlargement may not be early noticed. These \ariations in the seat of glandular swelling cannot, however, be relied upon as a basis for a positive differential diagnosis between intracranial and more superficial (extracranial) sources of irritation or infection. THE LYMPH.\TICS OF THE NECK. The Lymph-Nodes. The principal group of nodes in the neck region is that which is situated along the course of the internal jugular vein, forming the jugular plexus ( plexus jugularis). It consists of a variable, but usually large, number of nodes and is interposed in the pathway followed by the entire lymphatic system of the head and neck. It is prac- ticallv a continuous chain of nodes, e.xtending the entire length of the neck, but for convenience in description it is convenient to regard the nodes as forming two sub- groups which are named the superior and infeiior deep cervical nodes. In addition to these some smaller groups occur more superficially, forming what are termed the superficial cervical nodes, so that altogether there are three main groups of nodes in the cervical region. The superficial cervical nodes (lymphoglandulae cervicales superficiales) may conveniently be divided into two subgroups, both of which are composed of rather small and somewhat inconstant nodes. The external jugjilar nodes, as their name indicates, are situated along the course of the external jugular vein, and consequently rest upon the outer surface of the sterno-cleido-mastoid muscle. They occur a little below the lower extremity of the parotid gland (Fig. 796), and are usuall)- two or three in number, one or tw'O additional nodes sometimes being present at a somewhat lower level. They receive afferents from the pinna of the ear and from the parotid region, and their efferents pass over the anterior border of the sterno-cleido-mastoid to open into the superior deep cervical nodes. THE LYMPHATICS OF THE NECK. 957 The second subgroup is that of the a7iterior cervi and inconstant and are situated beneath the depressor muscles of the hyoid bone, resting upon the anterior surface of the larynx and on the anterior and lateral surfaces of the trachea. Those which rest upon the trachea are some- what more constant than the others, but like them they are usually small and are therefore likely to be overlooked in normal conditions. The more lateral members of the series, from three to six in number, are arranged in a chain which follows the course of the recurrent (inferior) laryngeal nerve and are some- times spoken of as the remrrential nodes. The anterior cervical nodes receive afferents from the larynx and trachea, and their ef^erents pass to the lower superior deep cervical nodes. The superior deep cervical nodes (lymphoslandulae cervicales pro- fundae superiores) vary from ten to sixteen in number, and extend along the course of the internal jugular vein from the tip of the mastoid process to the level at which the vein is crossed by the omo-hyoid muscle. They lie either directly upon the vein or slightly posterior Fig. S07. cal nodes, which are both variable Fig. S06. Digastric muscle ^ stump Anterior cer\- of larynx. (Most.*) d lymphatic Sterno mastoid muscle, cut Deep cervical lymph-nodes. the more posterior nodes are the efferent stems *Anatom. Anzeiger, Bd. xv. beneath the sterno-cleido- mastoid muscle, and are all united by numerous connecting stems so that they form a \'eritable plexus. Some of the nodes are exceedingly constant in position, one, especially, which receives numerous afferents from the lingual region and has therefore been termed the principal node of the tongue, occurring at about the level of the bifurcation of the common carotid artery, and a second is situated just above the omo-hyoid muscle. The afferents of the group are very numerous, and may be divided into two classes according as they take their origin in nodes belonging to other groups or come directly from the lymphatic net-works. Belonging to the first class and terminating in for the posterior auricular and 958 HUMAN ANATOMY. occipital nodes, while in the more anterior nodes efferents from the retropharyn- geal, parotid, submaxillary, submental, and superficial cer\ical nodes terminate. Belonging to the second class and terminating in the more posterior nodes are (i) a vessel which descends direcd)' from the occipital region of the scalp ; (2) some stems from the posterior surface of the pinna ; and (3) stems from the upper part of the back of the neck. To the more anterior nodes pass ( i ) the majority of the stems descending from the tongue ; (2) stems from the nasal mucous membrane, the palate, and the upper portions of the pharjmx ; (3) stems from the cervical portion of the oesophagus ; (4) the majority of the stems from the larynx and those which come from the cervical portion of the trachea, and (5) the stems from the thyroid gland. The effe7'ents from the lower nodes of the plexus pass partly to the inferior deep cervical nodes, and partly unite with the efferents of these to form the jugular trunk, which is described below. The inferior deep cervical nodes (lymphoglandulae cer\icales profundae inferiores), also termed the supraclavicular nodes, occupy the supraclavicular triangle of the neck, resting upon the scalene muscles and upon the trunks of the brachial plexus. They are fewer in number and, as a rule, smaller than the superior deep cer\'ical nodes. In addition to the afferents from the superior nodes they receive (i) a stem which passes directly downward from the occipital region of the scalp along the posterior border of the sterno-cleido-mastoid muscle ; (2) vessels from the integument and muscles of the lower portion of the neck ; (3) vessels from the integument of the upper portion of the pectoral region ; (4) occasionally some vessels from the arm which follow the course of the cephalic vein ; (5) some eiTerents from the brachial groups of the axillary nodes ; and (6) vessels which pass to the lower nodes of the left, rarely the right, side from the liver, ascending in the suspensory ligament of that organ, piercing the diaphragm, and following the course of the internal mammarv' vessels upward through the thorax. Their efferents unite with some of those from the superior deep cer\-ical nodes to form a single stem, the jugular trunk ( truncus jiigularis ), which on the left side opens into the arch of the thoracic duct and on the right unites with the subclavian trunk to form the right lymphatic duct. Both the right and the left trunks, how- ever, frequendy open direcdy into the subclavian \'ein. The Lymphatic Vessels. The Integument and Muscles of the Neck. — The lymphatic stems arising from the subcutaneous and muscular net-works of the neck open into the posterior nodes of the superior deep cer\-ical chain. The Larynx and Trachea. — The lymphatic net-work of the lar\-nx is very well developed over the greater portion of the mucous membrane and is especially rich in the regions of the false vocal cords and the \entricles. Over the true vocal cords, however, it is very feebly developed, and the entire net-work may therefore be regarded as consisting of two portions, one of which is situated above the le\'el of the true cords and the other below them. The two portions are not, it is true, perfectly distinct, since they are connected by the feeble net-work of the true cords ; but it has not been found possible to force an injection from one portion into the other and, furthermore, each portion gives rise to a special set of efferent stems. The stems which arise from the upper net-work are from three to six in numbf-r on each side, and make their exit from the larynx through the lateral portions of the thyro-hyoid membrane, in close proximity to the superior laryngeal artery (Fig. 806). They then pass outward to the anterior nodes of the superior deep cer\ical chain, some opening into the nodes situated in the neighborhood of the bifurcation of the common carotid artery, while others, bending downward, terminate in lower nodes. The stems from the lower net-work pass in two directions ; a few small ones perforate the crico-thyroid membrane near the median line, while the rest are directed posteriorlv and make their exit below the lower border of the cricoid cartilage. The anterior stems pass partly to an anterior cer\'ical node situated usually in the median THE LYMPHATICS OF THE NECK. 959 line behveen the two crico-thyroid muscles, another descends over the isthmus of the thyroid gland to terminate in one of the nodes which rest upon the anterior surface of the trachea, while one or two pass outward along the upper border of the lobes of the thyroid gland and then descend to terminate in one of the superior deep cervical nodes situated about opposite the middle of the sterno-cleido- mastoid muscle. The posterior stems, which are from three to six in number, after making their exit from the larynx, follow the course of the recurrent laryngeal nerves and terminate in the recurrential nodes situated in the course of those nerves, some of the stems frequently anastomosing to form a plexus which descends along the vagus nerve and may be followed, in some cases, to the inferior deep cervical nodes. The net-work of the trachea is formed of delicate and slender vessels arranged so as to form elongated meshes, and the stems which arise from it emerge from the lateral surfaces of the trachea, passing between the tracheal cartilages. Those from the upper part of the trachea pass to the recurrential nodes, while the lower ones pass to the bronchial nodes situated in the neighborhood of the bifurcation of the trachea. The Thyroid Gland. — The lymphatic stems from the thyroid gland pass for the most part to the superior deep cervical nodes, following the course of the superior thyroid artery, some of them, however, passing at first directly upward and coming into relation with an anterior cervical node situated upon the crico-thyroid membrane. Those which arise from the lower border of the isthmus and from the neighboring portions of the lobes are directed downward, and terminate in the anterior cervical nodes which are situated upon the anterior surface of the trachea and in the recurrential nodes. The CEsophagus. — The cervical portion of the oesophagus will be considered together with its thoracic portion (page 971). Practical Considerations. — The Lymph-Nodes of the Neck. — i. 'Wi^ super- ficial cervical nodes — not invariably present — are found over the sterno-mastoid, along the external jugular vein, between the deep fascia and the platysma, and may be enlarged in various affections of the external ear and of the skin of the face and neck, or consecutively to infections of the suboccipital (occipital), mastoid (post- auricular), parotid (preauricular), or submaxillary nodes. Those found posteriorly near the anterior border of the trapezius muscle enlarge early in the secondary' stage of syphilis and, on account of their accessibility for palpation, are then of diagnostic value. 2. The deep cervical nodes are divisible, for convenience, into two groups : («) an upper group, situated about and above the bifurcation of the common carotid artery and the upper part of the internal jugular vein, some of which lie partly beneath the posterior edge of the sterno-mastoid and partly projecting into the posterior cer\'ical triangle ; (3) a lower group, found near the lower portions of the internal jugular, external jugular, subclavian, and transverse cervical veins, and lying almost com- pletely beneath the sterno-mastoid. At the root of the neck this group is continuous e.xternally with the subclavian and axillary, and internally with the mediastinal nodes. All these deep cervical nodes lie in or beneath the deep fascia and receive the efferent vessels from the superficial nodes (and thus from their tributaries mentioned above) as well as all other lymphatics of the head and neck — retropharyngeal, suprahyoid, etc. — that do not directl}^ communicate with the superficial group. The deep cervical nodes are accordingly found to be inflamed or enlarged consecutively to a great variety of conditions, — e.g., eczema, wounds or ulcers of any portion of the scalp or face, dental caries, alveolo-dental abscess, pharyngeal or buccal or tonsillar inflammation or ulceration, fissures or ulcers or carcinoma of the tongue, otitis (external or medial), rhinitis, hordeolum, labial herpes or chancre or epithelioma. They may also be enlarged — though with great rarity — from primary carcinoma and — less rarely — from lympho-sarcoma or from Hodgkin's disease. Furthermore, various intracranial conditions may be followed by involve- ment of the cervical nodes, both superficial and deep. In most cases the infection comes from the same side of the head, face, or neck, as the enlarged glands, but occasionall}' the original lesion is on the opposite side. 96o HUMAN ANATOMY. Swellings of this deep chain of glands — especially of those beneath the sterno- mastoid — may be present without being distinctly palpable, and are apt, in any case severe enough to come to operation, to involve many more nodes than were previously suspected. One node of the upper group lies behind the posterior belly of the digastric in the angle between the internal jugular and facial veins. Leaf has suggested that it be called the " jugulo-digastric" node. In some affections of the tonsir and of the base of the tongue, it enlarges and projects in front of the anterior border of the sterno-mastoid, its contents being about half an inch below and somewhat internal to the angle of the jaw. Other glands of this group, which are very constant in position, lie over the insertion of the splenius capitis under cover of the upper end of the sterno-mastoid and surround the spinal accessory nerve before it perforates the latter muscle. En- largement of these glands would compress the nerve against the transverse process of the atlas (Leaf). The retropharyngeal nodes lie in the space of that name (page 552), about opposite the axis, on the rectus capitis anticus major and to the inner side of the glosso-pharyngeal nerve where it curves around the lower border of the stylo- pharyngeus. They communicate with the upper group of the deep nodes. They may be enlarged from infection through the overlying mucosa, as they are in close relation to the buccal portion of the pharyn.x, which, on account of its many crypts or recesses, the large amount of adenoid tissue present, its relatively direct exposure to mechanical injury and to the current of inspired air (drying it, reducing its temperature, and possibly conveying microbic irritants), is especially susceptible to inflammation. They may also enlarge as a result of caries of the bodies of the cervical vertebrae. In either case, there may be pharyngeal and tonsillar pain, ear- ache, and other evidence of glosso-pharyngeal irritation. If suppuration occurs, a fluctuating swelling appears which pushes the posterior wall of the pharynx forward ( the retropharyngeal connective tissue being lax to permit of the free movement of the pharyn.x during deglutition), depresses the soft palate, and causes dysphagia ; or, if lower, causes dysphonia and dyspnoea by obstructing the laryngeal opening. Such an abscess may gravitate along the oesophagus into the mediastinum and may even reach the diaphragm ; or it may extend laterally behind the parotid and great vessels to the side of the neck, or, reaching the cords of the brachial plexus, may be conducted by them to the posterior cervical triangle or down into the axilla. Such an abscess should not be left to spontaneous evacuation, on account of the danger of its extension in these directions, or — if the abscess should suddenly burst into the pharynx — of suffocation or of septic pneumonia if the pus entered the air-passages. It may be opened through the mouth, in the mid-line of the pharyn.x (the head being bent over so that the pus would not run toward the glottis), or externally by an incision along the posterior margin of the sterno-mastoid, the great vessels being pushed forward as the wound is deepened. The lower group of deep cervical nodes enlarge most frequently consecutively to infection or disease of the upper group. They also receive the lymphatics from the supraspinous fossa which follow the suprascapular artery, and those from the upper part of the deltoid. Those that lie at the very base of the neck, in the sub- clavian triangle, or on the omo-hyoid muscle, are not uncommonly affected in the latter stages of mammary carcinoma (page 2035). They are continuous with the axillary nodes, while those to their inner side — lying on the levator anguli scapulae and scalenus medius just external to the internal jugular vein — are also often involved in the upward extension of cancer. Both sets communicate with the mediastinal nodes. On the left side they are in close proximity to the thoracic duct. The branches of the cervical plexus pass among the nodes of this deep cervical group. In cases of chronic inflammation and enlargenient of these nodes they will usually be found adherent to the internal jugular vein, which is in close relation to most of them. As the majority of them lie beneath the sterno-cleido-mastoid, that muscle will often have to be divided either partially or completely in operations for their removal. Certain cysts, in most cases congenital, usually, subcutaneous but with deep prolongations into the intermuscular spaces, are found in the neck, and are believed THE LYMPHATICS OF THE UPPER EXTREMITY. 961 to be of lymphatic origin, because (a) they are often associated, and sometimes anatomically connected with other congenital defects of the lymphatic system, such as macroglossia (cavernous lymphangioma of the tongue) and macrocheilia (labial lymphangioma) ; and (d) they are in communication with the lymphatic trunks (RoUeston). THE LYMPHATICS OF THE UPPER EXTREMITY. The Lymphatic Nodes. The lymphatic nodes of the arm are for the most part confined to its upper portions, the principal group occurring in the axilla and consisting of a considerable number of nodes united by connecting stems to form a plexus axillaris. A few scattered nodes also occur in the brachial region and some are occasionally to be found in the antibrachium, but they are entirely lacking in the hand. An especial interest attaches to the axillary nodes on account of the extensive area from which they receive afferents, for, in addition to almost the entire lymphatic drainage of the arm, they also receive the vessels from the anterior and lateral thoracic walls, from the mammary gland, and from the scapular region. The brachial and antibrachial nodes, on the other hand, are rather to be regarded as "intercalated" nodes inter- posed in the course of certain of the lymphatic vessels ; some of them lie superficial to the deep fascia, while others are situated more deeply along the course of the principal blood-vessels, and, consequently, it is convenient to divide them into two sets according as they are superficial or deep. The superficial brachial nodes (lymphoglandiilae cubitales superCciales) are arranged in two principal groups. One of these rests upon the brachial fascia imme- diately over the internal condyle of the hunjerus, and may be termed the epih-ochlear group (Fig. 809). It consists of from one to four nodes, of which one, the lowest of the group, is especially constant and is termed the epitrochlear node. The remaining nodes, if present, are situated along the course of the basilic vein, one frequently lying almost in the median line of the arm a short distance above the bend of the elbow. The afferents of the epitrochlear nodes are the superficial vessels of the forearm and hand, especially those which pass upward along the ulnar border of the forearm ; their ejfereyits pass upward along the basilic vein and join the deep vessels where the basilic vein dips down to join the brachial. A second group, which may be termed the delto-pector-al group, consists of from one to four nodes situated along the course of the cephalic vein, in the groove between the deltoid muscle and the clavicular portion of the pectoralis major (Fig. 809). They are not always distinguishable and are usually quite small. They are interposed in the course of the delto-pectoral lymphatic stem which passes upward in the groove and opens into the subclavicular group of axillary nodes or occasionally into the inferior deep cervical nodes. The deep brachial nodes sometimes include some small nodes occurring on the lymphatic stems which accompany the ulnar and radial blood-vessels, but these nodes are relatively inconstant. Of more frequent occurrence is a group of two or three small nodes (lymphoglandulae cubitales profundae) which occur upon the stems accompanying the brachial artery and are situated at about the middle part of its course. Their ajfcrents are the deep lymphatics of the forearm and their effere>its pass upward to terminate in the humeral nodes of the axillary group. The axillary nodes, which are embedded in the areolar tissue occupying the axillary space, vary in number from sixteen to thirty-six. Some of them are usually of considerable size, especially in those cases in which their number approaches the lower limit mentioned, for it is a general rule that the size of the nodes in any group is inversely proportional to their number ; but it seems probable that in addition to those which may be observed macroscopically, exceedingly small ones, approaching micro- scopic size, also occur, and that these, under pathological conditions or after removal of the larger ones, may increase in size and form additional or new foci of infection. Although united by connecting stems to form a plexus, the axillary nodes may be divided, according to their position and the source from which their afferents come, into a number of more or less distinct subgroups (Figs. 808, 814), and of 61 962 HUMAN ANATOMY. these, four are terminals for lymphatic stems coming from the arm and the thoracic walls, while two others form relays between these terminal nodes and the subclavian trunk by which the lymph from the entire axillary plexus is conveyed to the right lymphatic duct or to the arch of the thoracic duct. 1. The brachial subgroup is composed of a number of usually large nodes, arranged in a chain along the axillary vein, for the most part along its inner surface, although a node is to be found behind it, between it and the subscapular muscle. The ajfcrents of this group come from the arm and include almost the entire set of collecting stems from that region, only one of them, that which accompanies the cephalic vein, passing to another group. Their cfferents pass partly to the intermediate subgroup of the axillary plexus, partly to the subclavicular subgroup, and partly to the lower nodes of the inferior deep cervical group. 2. The anterior pectoral subgroup is composed of two or three usually small nodes situated over the second and third intercostal spaces, beneath the lower Fig. 808. Brachial plexus Subclavian artery. Intermediate nod Subclavicular iicd Mammary gland Brachial nodes Subscapular nodes Anterior pectoral nodes Inferior pectoral nodes Axillary lymph-nodes, new-born child. {Ochnet .*) border of the pectoralis major muscle and anterior to the long thoracic artery. They receive affei'CJits from the integument of the anterior surface of the thorax, from the pectoral muscles, and from the mammary gland. Their efferents pass partly to the intermediate and partly to the subclavicular subgroup of the axillar nodes. 3. The inferior pectoral subgroup is composed of two or three small riodes, situated either upon or posterior to the long thoracic artery over the fourth and fifth intercostal spaces or even higher. They receive their afferents mainly from the integument of the lateral wall of the thorax and from the subjacent muscles, and their efferents pass to the nodes of the intermediate subgroup. 4. The subscapular subgroup (lymphoglandxilac subscapulares) consists of a chain of six or more nodes situated along the course of the subscapular artery, and, in addition, includes two or three nodes which rest upon the dorsal surface of the scapula in the groove between the teres major and minor muscles. The afferents * Archiv f. klin. Cliirurgie, Bd. l.xiv., 1901. THE LYMPHATICS OF THE UPPER EXTREMITY. 963 come from the integument and muscles of the lower part of the neck, from the dorsal surface of the thorax, and from the scapular region ; the efferents pass mainly to the nodes of the intermediate subgroup. 5. The intermediate subgroup consists of a number of rather large nodes imbedded in the adipose tissue which occupies the interval between the lateral wall of the thorax and the upper part of the long thoracic vein as it bends outward to open into the terminal part of the axillary vein. It receives affcrents from all the terminal subgroups of the axillary plexus, and its efferents pass to the nodes of the subclavicular subgroup. 6. The subclavicular subgroup consists of from six to twelve nodes situated near the apex of the axillary space, partly beneath the pectoralis minor and partly above the upper border of that muscle. They constitute the final link in the axillary chain, since they receive as afferents, either directly or indirectly through the intermediate nodes, the efferents from all the other subgroups. Their efferents unite to form a trunk of considerable size, the subclavian trunk (truncus subc.aviu'j), which, from its origin opposite the first intercostal space, passes almost vertically upward over the subclavian vein to open into it near its junction with tKv- •='xi;ernal jugular, or else to unite with the jugular trunk on the right side or ^o open into the arch of the thoracic duct on the left side. In addition to this principal termination one or more of the subclavicular efferents usually pass to one of the lower nodes of the inferior deep cervical group. The independent termination of the subclavian trunk in the subclavian vein is probably the most frequent arrangement, but the exact position of its junction with the vein is variable. Most frequently it empties at the angle formed tjy the junction of the subclavian and internal jugular veins, but it may terminate upon the superior surface of the subclavian vein some distance ( i cm. ) away from the angle, and quite frequently it opens upon the anterior surface of the vein, or, in rarer instances, upon its posterior surface. Not unfrequently two or even more subclavian trunks occur, and in such cases one may unite with the jugular trunk, or, if on the left side, open into the arch of the thoracic duct, while the other terminates directly in the vein. Fig, The Lymphatic Vessels. The lymphatic vessels of the upper limb are divisible into two groups according as they lie superficial to or beneath the deep fascia. The superficial vessels, which are far more numerous than the deep ones, have their origin in the subcutaneous net-work which occurs throughout the entire extent of the limb, but is especially developed upon the palmar surface of the hand and upon the fingers (Fig. 810). The net-work of each digit tends toward its sides and at its base unites with those of the adjacent digits to form a number of stems which pass upward upon the dorsal surface of the hand, for the most part over the intermetacarpal spaces, althouafh abun- dant anasto- moses occur betwQen the vessels of neighboring spaces so that _ Epitrochlear node an open dorsal net-work is formed. The stems which arise from the net-works of the inner border of the little finger and of the outer border of the inde.x also pass upward upon the dorsum of the hand, lying respectively toward its inner and outer borders, and the net- work of the thumb is drained by vessels vi'hich pass upward on its dorsal surface. From the central portion of the palmar net-work some small stems pass deeply, penetrating the palmar aponeurosis to join the deep lymphatic vessels, but its remaining portions radiate in all directions to join the stems of the dorsal net-work. Thus, the distal portions of the net-work converge Superficial lymphatic vessels of upper limb: semidiagrammatic. (Based on figures of Sappey.) 964 HUMAN ANATOMY toward the webs of the fingers and pass dorsally to join the stems which pass upward over the intermetacarpal spaces ; the inner portions pass over into a number of small stems which cur\e around the inner border of the hand to join the stems coming from the little finger ; the outer portions similarly empty into the stems coming from the outer surface of the index finger and from the thumb ; while the proximal portions give rise to a number of stems which pass upward along the anterior surface of the forearm. The arrangement, indeed, is very similar to that followed by the veins. At the wrist, then, there are a considerable number (about thirty, more or less) of longitudinal stems which are arranged in two groups, one of which is dorsal and the other ventral (Figs. 810, 811). The former consists of the stems which drain the digital net-works and the distal and lateral portions of the palmar net-work, while the latter is formed of stems arising from the proximal portion of the palmar net-work. As they ascend the arm these stems receive afterents from the sub- FiG. Sio. Lymphatics of hand : Fig. Sio, pain of fingers into larger stems (*. c), which : nicate (Fig. Sjo, 6) with deeper lympliatic _ [I, dorsal surface. Superficial digital net-works (a) empty at bases tributary to trunks on forearm (d) ; superficial palmar vessels commu- (Sapfiej.*) cutaneous net-work of the forearm, and at the same time anastomose with one another, so that their number diminishes gradually as they ascend, until, at about the middle of the brachium, they are reduced almost to half the original number. As they approach the elbow (Fig. 8og), the stems of the dorsal group divide into two sets, which curve forward, one around the outer border and the other around the inner border of the forearm, so that above the elbow all the principal stems are situated upon the anterior (ventral) surface of the arm, an arrangement which again recalls that presented by the veins. Just abo^■e the bend of the elbow one or two of the inner stems pass into the epitrochlear nodes (Fig. 809), whose efferents pierce the brachial fascia to empty into the deep brachial lymphatics, but the majority of the remaining stems pass directly upward along the anterior surface of the brachium to terminate above in the brachial nodes of the axillary plexus. The most external stem follows, however, a different course (Fig. 809), accompanying the cephalic vein along the groove between the deltoid and pectoralis major muscles ; after traversing the delto-pectoral ■Description at iconographie des vaisseau.\ lymphatiques, 1874. THE LYMPHATICS OF THE UPPER EXTREMITY. 965 nodes it perforates the costo-coracoid membrane and terminates in one of the subclavicular nodes or, more rarely, follows the course of the jugulo-cephalic vein over the clavicle and terminates in one of the lower inferior deep cervical nodes. From the net-work of the posterior surface of the brachium a number of small stems arise and pass obliquely upward, those lying towards the outer border of the arm curving around it to join the outer main stems, while the inner ones partly join the inner main stems and partly terminate in the subscapular nodes along with the vessels from the posterior surface of the shoulder. The deep lymphatics of the arm are much less numerous than the super- ficial ones and follow the courses of the main blood-vessels, usually corresponding in number with the venee comites. They occur in company with the radial, ulnar, anterior and posterior interosseous, and brachial vessels. The radial lymphatics are formed by the union of two stems, one of which follows the course of the main stem of the artery from the deep palmar arch, while the other accompanies the superficial volar artery from the superficial arch. They come together, usually a short distance above the wrist-joint, to form two stems which pass upward along the artery and may traverse one or two small and inconstant nodes. They terminate by uniting with the ulnar stems to form the brachial lymphatics. The ulnar lymphatics are also formed by the union of two stems, which accompany the deep and superficial branches of the ulnar artery. They accompany the ulnar artery up the forearm, occasionally traversing one or two small nodes, and, near their union with the radial stems below the bend of the elbow, they receive the stems which accompany the anterior and posterior interosseous arteries. The brachial lymphatics are two in number and are formed by the union of the radial and ulnar stems. They accompany the brachial artery, traversing three or four nodes in their course and receiving the ef^erents of the epitrochlear nodes, or, these failing, the inner stems of the forearm. They terminate in the brachial nodes of the a.xillary plexus, especially in one which usually lies between the axillary vein and the subscapular muscle. Practical Considerations. — The Lymph-Nodes of the Axilla and Upper Extremity. — The palm has relatively few large lymphatics (as it has few superficial nerves and blood-vessels) ; hence wounds of the fingers or of the dorsum of the hand, where the lymphatics are of larger size, are more commonly followed by lymphangitis than are wounds of the palm. Nodes are occasionally found along the course of the arteries of the forearm and arm, but are inconstant and not of great practical importance. One or two beneath the deep fascia on the flexor surface of the elbow and on a level with the internal condyle or an inch or two above it, are less variable and are sometimes palpably enlarged in syphilis at the time of the early general adenopathy. The axillary nodes will be almost sufficiently described in relation to the subject of mammary cancer (page 2035). Further reference to them will be found in the description of the axilla (page 581). These nodes may be the primary seat of lympho-sarcoma, may be the subject of tuberculous or syphilitic enlargement, and are constantly infected after septic wounds of the hand, forearm, or arm, and less frequently from wounds in the remaining areas which drain into them, viz. , the cervical region over the trapezius muscle, the dorsal region, the lumbar region as far down as the level of the iliac crest, the abdominal region above the umbilicus, and the front and sides of the thoracic region. Their progressive enlargement widens the a.xilla, renders it more shallow by pushing its floor downward, makes the anterior fold prominent, and increases the space between the outer border of the scapula and the thoracic wall. Axillary abscess commonly originates in these nodes, consecutively to sepsis elsewhere, as in the regions mentioned, or after shoulder-joint suppuration, or mammary infection, or caries of an upper rib. Such an abscess will produce rapidly the same phenomena as those caused by a growth. It may make its way behind the clavicle into the supra- clavicular fossa by following the cords of the brachial plexus, or may gravitate down the arm along the course of the vessels. It cannot come directly forward on account of the pectoral muscles and clavi-pectoral fascia, or downward on account of the 966 HUMAN ANATOMY. axillary fascia, or backward by reason of the attachment of the serratus magnus to the scapula, or outward or inward because of the upper limb and the wall of the thorax. It should be opened half way between the anterior and posterior folds near the inner or thoracic wall. Intercostal node Internal THE LYMPHAiTCS OF THE THORAX. The Lymph-Nodes. Certain of the nodes which have been described as belonging to the axillary plexus, namely, uLose forming the anterior and inferior pectoral subgroups, might well be considered as belonging to the thoracic set, since their afterents drain the anterior and lateral w^alls of the thorax. On account of their situation, however, as well as their intimate connection by efterents with the intermediate and subclavicular axillary nodes, they are more conveniently classed with the axillary set. The remaining thoracic nodes may be divided into two sets according as they occur in connection with the thoracic walls, parietal nodes, or with the viscera, visceral nodes. Of the parietal nodes there are two principal groups. The sternal or internal mammary nodes (lymphoglandulae sternaies ) form two chains which extend upwards upon the inner surface of the anterior thoracic wall, along the course of the internal mammary blood-vessels ( Fig. 812). They vary in number from four to ten, l-iG. bi2. ^^^ ^j-g situate^] at; the ante- rior or sternal ends of three or more of the upper inter- costal spaces, resting upon the internal intercostal mus- cles and being covered, so far as the lower members of the group are concerned, by slips of the triangularis sterni. Their afferents come from the anterior diaphragmatic nodes, from the upper por- tions of the rectus abdominis, from the anterior portions of the intercostal muscles, from the integument over the ster- num and costal cartilages, and, to a certain extent, from the mammary glands. Since the nodes are arranged in the form of a chain, the effer- ents from the lower members of the series are afferents for the higher ones ; the terminal efterents usually unite to form a single stem which joins the efferents of the anterior mediastinal and bronchial nodes to form the broncho-mediastinal trunk Cpage 96S). The intercostal nodes (lymphoglandulae intercostales) are situated along the courses of the intercostal arteries, the principal and most constant members of the series being situated towards the posterior extremities of the intercostal spaces. Some nodes which occur in the lateral portions of the spaces are inconstant and always small ; they are usuallv situated, when present, at the point where the intercostai arteries give off their lateral perforating branches. The ajfereyits of the intercostal nodes drain the posterior portions of the inter- costal spaces. The efferents of the lower members of the series unite to form a stem which passes downward and terminates in the receptaculum chyli, while those from Lymph-nodes of anterior thoracic wall, viewed fn (Based upon figure of Poirier and Cuneo ^ Poirier et Charpy : Traite d'anatoniie humaine. Tome ii., 1902. THE LYMPHATICS OF THE THORAX. 967 the nodes of the upper spaces are directed more or less medially to open into the thoracic duct. The visceral nodes of the thorax may be arranged in three main groups, one consisting of the nodes situated in the anterior mediastinum, a second of those situated in the posterior mediastinum, and a third of those which occur in the neighborhood of the bifurcation of the trachea and along the bronchi. The anterior mediastinal nodes ( Ij mphoglaiidulae mediastinales anteriores) are arranged in two groups, one of which occurs in the lower and the other in the upper part of the mediastinum. The nodes of the lower group, termed the diaphrag- matic nodes, are from three to four in number, and are situated upon the anterior part of the upper surface of the diaphragm, immediately behind the xiphoid process of the sternum ; their afferents come from the diaphragm and from the upper surface of the liver, and their efferents pass to the lower deep cervical nodes, following the course of the internal mammary vessels. The upper group, that of the cardiac yiodes, is composed of from eight to ten nodes situated upon the anterior surfaces of the arch of the aorta and the left innominate vein. They receive ajfereyits from the anterior surface of the pericardium and thymus gland and from the sternal and bronchial nodes. Their efferents pass upward and unite with those from the bronchial nodes to form the broncho-mediastinal truuk (page 968). The posterior mediastinal nodes (lymphoglandulae mediastinales posteriores), eight to twelve in number, are situated along the thoracic aorta in the posterior mediastinum. Their afferents come from the oesophagus, the posterior surface of the pericardium, and the upper surface of the liver, while their efferents open mainly into the thoracic duct, a few passing to the bronchial nodes. Two or three small nodes which may be regarded as belonging to this group occur upon the convex surface of the diaphragm in the neighborhood of the opening for the inferior vena cava. They receive afferejtts from the diaphragmatic net-work and also from the superficial net-work of the upper surface of the liver. The bronchial nodes (lymphoglandulae bronchiales) on account of their number and size are the most im- t- c r 1 1 • Fig. S13. portant of the thoracic fs»Si- nodes, and for the con- ill^^sx venience of description they may be regarded as forming three subgroups (Fig. 813). One of these is formed by the tracheal nodes ( lymphoglandulae tracheales), seven to ten in number and situated on either side of the lower part of the trachea. Those upon the right side are as a rule more numerous and larger than those on the left side, varying from the size of a pea to that of a bean in the normal condition. A second subgroup is that of the bronchial 7iodes proper, from ten to twelve in number and situated in the angle formed by the two bronchi. They are „ . , , , . . , , , ■( Tracheal and bronchial lymph-n for the most part large, those beneath the right bronchus being usually larger and more numerous than * Clinique m^dicale, Tome iv. 968 HUMAN ANATOMY. those below the left one. The third subgroup is formed by the pulmonary nodes, usually of small size and situated in the hilus of the lungs, between the larger divisions of the bronchi. The afferents of the bronchial nodes are (i) from the lungs, (2) from the lower part of the trachea and from the bronchi, (3) from the heart, and (4) from the posterior mediastinal nodes. Their cfferents may either pass as a number of stems to the thoracic duct or directly to the subclavian vein on the right side, but more frequently they unite to form a single stem, with which the stems coming from the sternal and anterior mediastinal nodes unite to form a single broncho-mediastinal trunk (truncus bronchomediastinalis), which passes upward toward the confluence of the internal jugular and subclavian veins. It either opens independently into the subclavian vein, which is the most usual arrangement, or else, on the right side, it unites with the subclavian and jugular trunks to form the right lymphatic duct or, on the left side, it unites with the subcla\ian trunk to open into the arch of the thoracic duct, into which it may also open directly. The Lymphatic Vessels. The cutaneous lymphatics of the thorax form a rich net-work extending throughout the subcutaneous tissue and being continuous abo\e with the subcutaneous net-work of the cervical region and below with that of the abdomen. From the net-work of the anterior surface a considerable number of stems arise, which pass outward, the upper ones almost horizontally and the lower ones obliquely upward and outward, to terminate in the anterior pectoral nodes of the axillary plexus (Fig. 814). These stems form the principal path of the anterior thoracic drainage, but, in addition, some stems which arise from the upper portion of the net-work pass upward over the clavicle and terminate in some of the lower inferior deep cervical nodes, and from the portions of the net-work near the median line short stems perforate the intercostal spaces and terminate in the sternal nodes. Further- more, it is to be noted that the net-works of either side are continuous across the median line over the surface of the sternum, and there may consequently be a certain amount of crossing in the lymph flow, that coming from the more median portions of the net-work of the right half of the anterior thoracic wall, for instance, terminating in the left axillary nodes. These decussating paths are, however, of comparatively litde importance except in cases of stoppage of the normal flow to the axillary nodes of the same side, and in such cases a collateral drainage may also be established for the lower portion of the thoracic w alls through the abdominal lymphatics to the inguinal nodes. Upon the lateral portions of the thorax the net-work gives rise to some half dozen stems which pass upwards to terminate in the inferior pectoral nodes of the axillary plexus, and from the net-work of the posterior thoracic wall about ten or twelve main stems arise which converge laterally to terminate in the subscapular group of the axillary plexus. As was the case in the anterior net-work, so in the posterior net-work some stems from the upper portions of the dorsal net-work pass to the lower inferior deep cer\'ical nodes, and below more or less anastomosis occurs between the net-works of the thoracic and abdominal (lumbar) regions. The Mammary Gland. — The lymphatics of the mammary gland arise in the deeper portions of the mammary tissue from sack-like enlargements situated in the connective tissue between the various lobules of the gland. The majority of the stems follow in general the course of the ducts and, passing toward the surface, communicate with an exceedingly fine subareolar net-work, which is a special development of the general subcutaneous net-work of the anterior thoracic wall. PVom the subareolar net-work two or more stems arise and form the principal paths for the mammary lymph, but accessory paths are also furnished by stems which arise from the sack-like enlargements and pass toward the periphery of the gland, avoiding the subareolar net-work. The stems which arise from the subareolar net-work pass at first almost directly outwards until they reach the lower border of the pectoralis major. They then ascend along the lower edge of this muscle for a short distance, and eventually bend THE LYMPHATICS OF THE THORAX. 969 around it, perforate the axillary fascia, and terminate in the anterior pectoral nodes of the axillary plexus. Occasionally one finds along the course of one or other of the stems a small intercalated node, and one or two small nodes, the pa7-amammillary 7iodes, may occur a short distance below the lower border of the gland on one of the efferents which passes to the lower principal stem. The accessory paths of the mammary lymph are principally two in number, (l) In about ten per cent, of cases examined a stem issued from the deep surface of the gland, perforated the pectoralis major, and passed upward between that muscle and the pectoralis minor to terminate in the subclavicular nodes. (2) A varying number of small stems leave the medial portion of the periphery of the gland and perforate the sternal border of the pectoralis major and the intercostal muscles, to terminate in the sternal nodes. It may be noted that the obstacle to the flow of lymph presented by enlarged a.xillary nodes in severe affections of the mammary gland may lead to the development of accessory or collateral paths other than those mentioned above. Thus, since the subareolar net-work is Delto-pectoral nod Subscapular node Anterior pectoral node Vessel passing to anterior pectoral node Inferior pectoral nod Subclavian node Intermediate node Subareolar plexus over mammary gland Lymphatic nd and axillary node (Po, ltd Cufteo.*) continuous with the general anterior thoracic subcutaneous net-work, and the latter is continuous across the median line, affection of the gland of one side may cause enlargement of the axillary nodes of the opposite side, and, furthermore, since the thoracic subcutaneous net-work is continuous with that of the abdomen, there is a possibility for the establishinent of a collateral path leading to the inguinal nodes. Furthermore, it is to be remembered that, although the anterior pectoral nodes are the terrhination of the principal mammary stems, yet the connection between these and other axillary nodes, especially those of the intermediate and subclavicular subgroups, is so intimate that practically all the axillary nodes may be involved, or are at least open to suspicion, in cases of mammary carcinoma. The intercostal lymphatics are arranged in two sets corresponding to the two intercostal muscles (Sappev). The'vessels from each internal intercostal unite to form a single stem which passes forward along the lower border of the rib forming the upper boundary of its space. The stems of the upper spaces open independently into the sternal nodes, while those from the lower spaces unite to form a common ascending stem which terminates in the lowest node of the sternal chain; *Poirier et Charpy : Traits d'anatomie humaine, Tome ii., 1902. 970 HUiMAN ANATOMY. The vessels from the external intercostals are somewhat larger than those from the interna! muscles and have a backward direction, terminating in the intercostal nodes. It is upon these stems that the lateral intercostal nodes are situated when present. Anastomoses occur between the two sets of vessels, and the internal set also receives communicating stems from the parietal layer of the pleura, while the external one receives branches from the muscles which cover the thoracic wall, although the principal path for these leads to the axillary nodes. The Diaphragm. — The lymphatics of the diaphragm form rich net-works upon both its surfaces, that upon the peritoneal surface being especially well developed, and numerous vessels traverse the substance of both the muscular tissue and the centrum tendineum, uniting the net-work of the abdominal with that of the thoracic surface. Upon the thoracic surface the net-work is e.xceedingly fine and close-meshed in the region of the centrum tendineum, being most distinct in the regions of the lateral leaflets. From this net-work branches pass outward parallel to the muscular fibres to unite with a series of anastomosing stems whose general direction is forward. Branches coming from the more peripheral portions of the diaphragm also empty into these stems, which carry the lymph forward to the diaphragmatic nodes, whence it passes to the anterior mediastinal nodes. From the net-works of the lateral leaflets of the central tendon collecting stems are also directed backward and medially towards the aortic opening, which they tra\erse to terminate in the upper coeliac nodes. It is to be observed that the nodes of the thoracic surface are for the most part situated anteriorly, while the coeliac nodes, which may be regarded as the principal nodes of the inferior surface, are located -posteriorly. Both sets of nodes, however, receive lymph from both surfaces of the diaphragm by means of the perforating branches which connect the upper and the lower net-works. The lower net-work is, furthermore, connected with the lymphatics of the more lateral portions of the peritoneum and also with those of the liver (page 980), while the upper net-work makes connections with the lymphatic \essels of the pleura. These communications, when considered in connection with the existence of the perforating branches, explain the occurrence of pleuritis as a sequence of subphrenic abscess or of the latter as a sequence of thoracic empyema. The Heart. — The lym] hatics of the heart are arranged in two principal net- works, one of which lies immediately beneath the endocardium, while the other is upon the outer surface of the organ immediately beneath the \isceral layer of the pericardium. The endocardial net-work communicates with the superficial one by branches which tra^■erse the heart musculature, and the flow of lymph from the endocardial net-work takes place only through these communicating branches; The superficial net-work extends over the whole surface of the heart, the \essels of which it is formed being well supplied with valves and arranged so as to form characteristic 'quadrate or rhomboidal meshes. From the net-work longitudinal stems pass up- ward towards the base of the heart, corresponding in a general way to the cardiac veins. Upon the anterior surface three stems are to be found passing upward along the anterior interventricular groove, parallel to the anterior cardiac vein, and, on arriving at the auriculo-ventricular groove, they unite to form a single trunk. With this another stem unites which has its origin in the net-work of the posterior surface of the heart and ascends along the posterior interventricular groove, parallel with the posterior cardiac vein. On reaching the auriculo-ventricular groo\e it bends round to the left and, encircling the base of the left ventricle, unites with the anterior \-essels. The conjoined trunk so formed passes upward along the pos- terior surface of the pulmonary aorta, perforates the parietal layer of the pericardium, and terminates in one of the bronchial nodes. From the net-work over the right side of the right ventricle another longitudinal stem arises and passes upward parallel to the right marginal vein, and, on reaching the auriculo-\entricular groove, winds around to the right and so reaches the anterior surface of the heart. It then ascends parallel with the anterior trunk, along the pos- terior surface of the pulmonarv aorta, and also terminates in one of the bronchial nodes. The Lungs. — The Ivmphatics of the lungs may be regarded as consisting of two sets, deep and superficial. The deep set is composed of a number of stems which accompany the branches of the pulmonary arteries and veins and of others THE LYMPHATICS OF THE THORAX. 971 which are associated more especially with the bronchi. The bronchial vessels take their origin from a net-work contained in the walls of the bronchi, and are traceable along the entire length of each bronchus and its branches until the terminal bronchi are reached ; here the net-work disappears and no indications of it are to be found in the walls of the atria or alveoli. In the larger bronchi the net-work is double- one portion of it occurring immediately beneath the mucous membrane and the other external to the cartilaginous rings, but in the finer bronchi only one layer is present and from this branches pass to the stems which accompany the arteries and veins. All the stems belonging to this deep set of lymphatics pass to the hUus of the lung and there open into the pulmonary nodes. The superficial set consists of a net-work situated upon the surface of the lung, immediately beneath the visceral layer of the pleura. The vessels composing it are well supplied with valves and have communicating with them branches from the visceral layer of the pleura and valved branches which have their origin in the interlobular and intralobular connective tissue. No communication has been observed between the superficial and deep pulmonary net-works, the stems from the superficial net-work alone passing directly to the hilus of the lung to terminate in the pulmonar)' nodes. Lymphatic vessels have been demonstrated in the parietal layer of the pleura. Those upon its costal surface communicate with the intercostal vessels ; those upon the diaphragmatic surface with the diaphragmatic net-work ; and those upon the mediastinal surface with the posterior mediastinal nodes. The CEsophagus. — The lymphatics of the oesophagus are arranged in two net- works, one of which is submucous, while the other is situated in the muscular coat. The stems which drain the net-works of the cervical portion of the oesophagus pass to the superior deep cervical and the recurrential nodes, while those draining the thoracic portions of the net-works pass to the posterior mediastinal nodes. Finally, the stems originating in the net-works of the terminal portion pass to the upper nodes of the coeliac group. Practical Considerations. — The Lymph- Nodes of the Thorax and Medias- timun. Ante7-ior Mediastinum. — The nodes in close relation to the internal mammary artery are of practical importance on account of their relations (a) to the diaphragm ; ((^) to the anterior e.xtremities of the intercostal spaces ; ('ri, development of, 1190 hippocampal, 11 51 Hair-cells (auditory-) inner, 1520 outer, 1520 Hair-foUicle, 1392 blood-vessels of, 1394 nerv-es of, 1394 Hairs, 1389 arrangement of, 1391 development of, 1401 growth of, 1402 structure of, 1391 whorls of, 1 39 1 Hair-shaft, 1391 Hamular process of inner pterygoid plate, i i Hamulus of bony cochlea. 15 14 Hand, 309 deep fascia of, 606 landmarks of, 320 h-mphatics of. 964 muscles of, 606 pract. consid., 613 surface anatomy of, 328 Harelip, 1589 Hassall, corpuscles of, 1799 Haversian canals of bone, 88 system of bone, 86 Head, movements of, 142 Heart, annuli fibrosi of, 698 annulus ovalis, 693 of Vieussens, 695 architecture of walls, 700 auricles of, 693 blood-vessels of, 703 canal auricular of, 705 chambers of, 693 chordae tendinea of, 697 columnse cameae of, 697 development of, 705 endocardium of, 702 epicardium of, 702 fasciculus auriculo-ventricular, 701 foramen ovale of, 695 fossa ovalis of, 695 general description of, 689 His's bundle, 701 HTnphatics, 703 muscle of, 462 muscles, pectinate of, 695 nerve-endings in, 1015 nerves of. 704 position of, 692 practical considerations, 710 relations of, 693 septum, aortic, 707 auricular of, 694 intermediiun, 706 interventricular of, 696 primum, 706 secundum, 708 spurium, 707 Thebesian veins of, 694 tubercle of Lower, 695 valves. Eustachian, 694 auriculo-ventricular, 699 mitral, 699 position of, 692 structure of, 703 Thebesian, 695 tricuspid. 699 vein, oblique of, 695 ventricles of, 696 THib VOLUME CONTAINS PAGES 1 TO 995. INDEX. Hsidenhain, demilunes of, 1534 Helicotrema, 15 14 Helix, 1484 Hemispheres, association fibres of, 11S2 of cerebellum, 1082 cerebral, 1133 commissural fibres of, 11 84 lobes of, 1139 projection fibres of, 1186 white centre of, 11 82 Henle, glands of, 1445 loop of, 1 88 1 Hensen, node of, 25 Herbst, corpuscles of, 1019 Hernia, abdominal, 1759 diaphragmatic, 1778 femoral, 1773 funicular, 1768 infantile, 1767 inguinal, 1763 direct, 1770 indirect, 1766 internal (intra-abdominal retroperito- neal), 1779 interparietal, 1768 labial, 1769 lumbar, 1777 obturator, 1777 perineal, 1778 sciatic, 1778 scrotal, 1769 umbilical, 177S acquired, 1776 congenital, 1775 ventral, 1776 Hesselbach, ligament of, 525 triangle of, 526 Hiatus, aortic, of diaphragm, 557 Fallopii, 181 oesophageal, of diaphragm, 557 semilunaris, of nasal cavity, 194 of nose, 141 1 Highmore, antrum of, 1422 Hind-brain, 1061 Hip, landmarks of, 669 muscles and fascia of, pract. consid., 642 Hip-joint, 367 movements of, 373 pract. consid., 374 synovial membrane of, 372 Hippocampus, 1165 His's bundle, of heart, 701 Histogenesis of neuroglia, loio of neurones, ion Homologue, 4 Horner, muscle of, 484 Howship, lacunas of, 97 Humerus, 265 development of, 269 pract. consid., 270 sexual differences, 260 structure of, 269 surface anatomy, 270 Humor, aqueous, 1476 Hunter's canal, 628 Hyaloid canal, 1474 Hyaloplasm, 8 Hydatid of Morgagni, 2002 Hydramnion, 42 Hymen, 2016 Hyoid bone, 216 development of, 216 Hyomandibular cleft, 61 Hypogastric lymphatic plexus, 984 Hypophysis, 1S06 Hypospadias, 1927 Hypothalamus, 11 27 Hypothenar eminence, 607 Ileo-cascal fossae, 1666 valve, 1 66 1 Ilio-femoral ligament, 369 liio-pectineal line, 334 Ilio-tibial band, 634 Ilium, 332 Implantation, 35 Impregnation, 18 Incisor teeth, 1543 Incus, 1497 Inferior caval system of veins, 898 Inf undibulum, 1 1 2 9 of nasal cavitj', 194 of nose, 141 1 Inguinal canal, 523 lymphatic plexus, 991 Inion, 228 Innominate bone, 332 structure of, 337 Insula, 1 149 Intersigmoid fossa, 1671 Intervertebral disks, 132 Intestine or intestines, development and growth of, 1 67 1 glands of, 1637 large, 1657 appendices epiploicae, 1660 blood-vessels of, 1660 glands of Lieberkuhn of, 1657 lymphatics of, 1660 lymphatic tissue of, 1658 nerves of, 1660 peritoneum of, 1670 pract. consid., 1680 structure of, 1657 tcenia coli of, 1660 lymph-nodules of, 1640 small 1633 blood-vessels of, 1642 glands of Lieberkuhn of, 1637 lymphatics of, 1 643 nerves of, 1643 Peyer's patches of, 1640 pract. consid., 1652 structure of, 1634 valvulffi conniventes of, 1636 villi of, 1635 solitary nodules of, 1640 Involuntar}' muscle, 1015 Iris, 1459 pract. consid., 1461 structure of, 1460 Irritability, 6 Ischio-rectal fossa, 1678 Ischium, 336 Islands of Langerhans, 1735 of Reil, 1 149 Isthmus of fauces, 1569 rhombencephali, 1061 Jacobson's nerve, 1264 organ, 1417 development of, 143 a Jejuno-ileum, 1649 blood-vessels of, 1652 lymphatics of, 1652 mesentery of, 1650 THIS VOLUME CONTAINS PAGES 1 TO 996. INDEX. Jejuno-ileum, nerves of, 1652 topography of, 1650 Joint or joints, of ankle, 438 calcaneo-astragaloid, posterior, 445 calcaneo-cuboid, 446 calcaneo-scapho-astragaloid, anterior, 445 capsule of, no of carpus, metacarpus and phalanges, pract. consid., 330 costo-central, 160 costo-stemal, 160 motions in, 166 costo-transverse, 160 costo-vertebral, motions in, 165 crico-arytenoid, 1S16 crico-thyroid, 181 5 of ear ossicles, 1498 elbow, 301 fixed, 107 general considerations, 107 half, 108 of hip, 367 interchondral, 160 intersternal. 15Q of knee, 400 limitation of motion, 112 metatarso-phalangeal, 447 modes of fixation, 112 of pelvis, 337 of pelvis, pract. consid, 330 radio-ulnar, 297 inferior, pract. consid., 30S saddle, 113 scapho-cubo-cuneiform, 446 of shoulder, 274 synovial membrane of, no tarso-metatarsal, 446 of tarsus, metatarsus and phalanges, pract. consid., 45 true, 108 motion in, 112 structure of, 109 varieties of, 113 vessels and nerves of, i-i i Jugular ganglion, of glosso-pharyngeal, 1263 of vagus, 1267 ' plexus, lymphatics, 956 Karyokinesis, 11 Karyosomes, g Kidnev or kidneys, 1869 architecture of, 1875 blood-vessels of, 1884 capsule of, 1S69 cortex of, 1876 development of, 1937 ducts of, 1894 fixation of, 1871 glomeruli of, 1876 hilum of, 1869 labyrinth of. 1876 lobule of. 187s loop of Henle of. 1881 h-mphatics of, 1S85 Tilalpighian body of, 1879 medulla of, 1876 medullary rays of, 1876 movable. 1888 nerves of, 18S6 papillae of. 1875 papillary dvicts of, 1882 pelvis of, 1894 Kidney or kidneys, position of, 1870 pract. consid., 18S7 pyramids of, 1876 relations of, 1873 sinus of, 1874 structure of, 1877 supporting tissue of, 1883 surfaces of, 1S69 tubule, collecting of, 1882 connecting of, 1882 distal convoluted of. 1882 proximal convoluted of, 1880 spiral of, 1880 uriniferous of, 1877 Knee, landmarks of, 671 muscles and fasciae of, pract. consid , 645 Knee-joint, 400 burSEE of, 406 capsule of, 400 landmarks of, 416 movements of, 40 S pract. consid., 409 semilunar cartilage of, 402 synovial membrane of, 405 Krause, end-bulbs of, 1016 glands of, 1445 Kupffer, cells of, 1717 Labia major, 2021 minora, 2022 nerves of, 2024 vessels of, 2023 Labyrinth, membranous, 1514 blood-vessels of, 1522 canalis reuniens of, 151 5 cochlea of, 151 7 ductus endolymphaticus of, IS14 endolymph of, 15 14 maculas acusticas of, 151 6 saccule of, 1 5 1 5 semicircular canals cf, 1515 utricle of, 15 14 osseous, 1511 cochlea of, 1513 semicircular canals of, 1512 vestibule of, 1511 Lachrymal apparatus. 1477 pract. consid., 1479 bone, 207 articulations of, 207 development of, 207 canaliculi, 1478 caruncle, 1443 gland, 1477 lake. 1443 papillce, 1478 puncta, 1478 sac, 1478 Lactation, 2029 Lacteals, 1643 Lacunas, of bone, 86 of cartilage, 80 of Howship, 97 Lambda, 228 Lamina cinerea (terminalis), 1130 fusca, 1450 suprachoroidea, 1456 Landmarks, of abdomen, 531 of ankle and foot, 672 of bones of foot, 437 of buttocks and hip, 669 of clavicle, 260 of elbow-joint, 308 THIS VOLUME CONTAINS PAGES 1 TO 995. INDEX. 1013 Landmarks, of face, 246 of femur, 366 of fibula, 396 of hand, 320 of joints of foot, 453 of knee, 671 of knee-joint, 416 of leg, 671 of lower extremity, 669 of male perineum, igi8 of neck, 554 of pelvis, 349 of radius, 296 of scapula, 255 of shoulder-joint, 280 of skull, 240 of spine, 146 of surface of thorax, 1868 of thigh, 670 of thorax, 170 of tibia, 390 of ulna, 287 of upper extremity, 618 of wrist-joint, 330 Langerhans, islands of, 1735 Lanugo, 66 Laryngo-pharynx, 1598 Larynx, 1S13 age changes of, 1828 arytenoid cartilages of, 181 6 corniculs laryngis, 181 7 cricoid cartilage of, 1S13 cuneiform cartilages of, 181 7 development of, 1862 elastic sheath of, 181 7 epiglottis, 1816 form of, 1 81 8 lymphatics of, 958 mucous membrane of, 1823 muscles of, 1824 nerves of, 1827 ossification of, 181 8 position and relations of, 182S pract. consid., 1828 region, glottic of, 1820 infraglottic of, 1823 supraglottic of, 1818 sexual differences of, 182S thyroid cartilage of, 1814 ventricle (sinus) of, 1822 vessels of, 1826 vocal cords, false of, 1820 true of, 1820 ligaments of, 1818 Leg, bones of, as one apparatus, 397 surface anatomy, 397 framework of, 382 landmarks of, 671 lymphatics, deep of, 994 superficial of, 993 muscles and fasciae of, pract. consid., 665 Lens, crystalline, 147 1 development of, 1481 pract. consid., 1473 suspensory apparatus of, 1475 Leptorhines, 1404 Leucocytes, 684 development of, 688 varieties of, 685 Lieberkuhn, glands of, 1637 Lieno-phrenic fold, 1785 Ligament or ligaments, 112 alar, of knee-joint, 405 Ligament or ligaments, anterior annular, of ankle, 647 of wrist, 325 arcuate, external, 557 internal, 557 atlanto-axial, anterior, 137 atlanto-axial, posterior, 137 of auricle, i486 broad, of uterus, 2004 ■ broad, vesicular appendages of, 2002 check, of orbit, 1438 of CoUes, 523 common anterior and posterior, of spine, coraco-acromial, 256 coraco-clavicular, 262 conoid part, 262 trapezoid part, 262 coronary, of liver, 1721 costo-clavicular or rhomboid, 262 cotjdoid, of hip-joint, 367 crucial, of knee-joint, 404 cruciform, of axis, 136 deltoid (lat. int.) of ankle-joint, 439 denticulate, of spinal cord, 1023 dorsal, of foot, 442 duodeno-hepatic, 1644 of epiglottis, 1 81 7 external check, of eyeball, 505 falciform, 1745 gastro-phrenic, 1747 of GimlDernat, 523 of Hesselbach, 525 ilio-femoral, 369 ilio-lumbar, 339 interarticular of ribs, 160 interclavicular, 262 interosseous, of foot, 441 interspinous, 134 inteitransverse, 135 ischio-femoral, 370 of lamina and processes of vertebrs, 133 lieno-renal, 1747 of liver, 1721 metacarpal, superficial transverse, 607 nuchffi, 134 occipito-atlantal, accessory, 137 anterior, 137 posterior, 137 occipito-axial, 137 odontoid, or check, 136 orbicular, of radius, 297 of ovary, 1987 palpebral, 1441 internal, 484 patellae, 400 pectinate of iris, 1452 of pelvis, 337 of pericardium, 716 plantar, 444 posterior annular, of wrist, 325 of Poupart, 523 pterygo-mandibular, 488 radio-ulnar, 297 round, of hip-joint, 370 of liver, 1721 of uterus, 2005 sacro-iliac, posterior, 338 sacro-sciatic, 339 great or posterior, 339 lesser or anterior, 341 of scapula, 256 of shoulder-joint, 274 THIS VOLUME CONTAINS PAGES 1 TO 995. IOI4 INDEX. Ligament or ligaments, spino-glenoid, 257 stylo-inandibular, 475 subflava, 133 suprascapular or transverse, 256 supraspinous, 133 suspensory, of lens, 1475 of orbit, 1438 of ovary, 1986 thyro-arytenoid, inferior, 1818 superior, 1S17 thyro-hyoid, 181 5 transverse, of atlas, 136 triangular, of liver, 1721 of perineum, 563 of vertebral bodies, 132 of Winslow, of knee-joint, 401 of wrist and metacarpus, 320 Limb, lower, muscles of, 623 Limbic lobe, 1 150 Linea alba, 522 semilunaris, of abdomen, 532 transversa, of abdomen, 532 Linin, 9 Lips, 1538 lymphatics of, 951 muscles of, 1540 nerves of, 1542 pract. consid., 1590 vessels of, 1542 - Liquor amnii, 31 pericardii, 714 Littre, glands of, 1925 Liver, 1705 bile-capillaries of, 1715 biliary apparatus, 17 18 blood-vessels of, 1709 borders of, 1707 caudate lobe of, 1709 cells of Kupffer, 1717 common bile-duct, 1720 cj'Stic duct of, 1720 development and growth of, 1723 fissure of ductus venosus of, 1707 fossa for gall-bladder of, 1708 gall-bladder of, 17 19 Glisson's capsule of, 1708 hepatic arter)' of, 1 7 1 1 ducts of, I 718 veins of, i 710 impression, cesophageal of, 1708 renal of, 1709 intralobular connective tissue of, 1 7 1 7 bile-ducts of, 1 7 1 7 veins of. 17 10 ligaments of, 1721 coronary, 1721 falciform, 1721 round, 1721 triangular, 1721 lobes of, 1706 lobular blood-vessels of, 17 13 lobules of, 1712 lymphatics of, 1 7 1 1 nerves of, 1 7 1 1 non-peritoneal area of, 1707 peritoneal relations of, 1721 portal (transverse) fissure of, 1708 vein of, 1709 position of, 1722 pract. consid., 1726 quadrate lobe of, 1709 size of, 1706 Spigelian lobe of, 1707 Liver, structure of, 17 12 sublobular veins of, 17 10 surfaces of, 1707 tuber omentale of, 1709 umbilical fissure of, 1708 notch of, 1707 weight of, 1706 Liver-cells, 17 14 Lobe or lobes, cerebral, 1135 frontal, 1139 of hemispheres, 1139 limbic, 1 1 50 occipital, 1145 olfactory, 1151 parietal, 11 43 temporal, 1147 Lobule of auricle, 1484 Loin, pract. consid., 530 Lordosis, 144 Lumbar plexus, lymphatic, 973 Lumbo-sacral cord, 133 1 Lung or lungs, 1843 air-sacs of, 1850 alveoli of, 1850 atria of, 1850 blood-vessels of, 1853 borders of, 1S43 development of, 1861 external appearance of, 1846 fissures of, 1845 ligament broad of, 1858 lobes of, 1845 lobule of, 1849 nerves of, 1855 physical characteristics of, 1846 pract. consid., 1864 relations to chest-walls, changes in, i853 to thoracic walls, 1855 roots of, 1838 diniensions of, 1S40 nerves of, 1839 relations of, 1840 structure of, 185 1 surfaces of, 1843 vessels of, 1839 Lunula, of nail, 1395 Luschka, foramina of, 11 00 gland of, 1 810 Lutein cells, 1990 Luys, nucleus of, 1128 Lymphatic or lymphatics, of abdomen, 972 of abdominal walls, 976 of arm, deep, 965 superficial, 963 of bile-duct, 98 1 of bladder, 985 of bone, 93 of brain, 948 of brain and meninges, 948 broncho-mediastinal trunk, 968 capillaries, 933 of cervical skin and muscles. 95S of cheeks, 951 of diaphragm, 970 duct, right, 945 of ear, 950 of eye and orbit, 949 of eyelids, 1445 of Fallopian tubes, 988 of gall-bladder, 981 of glands, 1536 of gums. 951 of hand, 964 THIS VOLUME CONTAINS PAGES 1 TO 996. INDEX. 1015 Lymphatic or lymphatics, of the head, 945 of heart, 970 hemolymph nodes, 936 intercostal, 969 of intestine, large, 978 small, 977 jugular trunk, 958 of kidney, 982 lacteals, 931 of larynx, 958 of leg, deep, 994 superficial, 993 of lips, 951 of liver, 9S0 of lower extremity, 991 mammary gland, 968 of meninges, 948 of muscle, non-striated, 456 of nasal fossa, 1426 region, 951 nodes, 935 of nose, 1407 of oesophagus, 971 of palate, 954 of pancreas, 979 of pelvis, 983 of pericardium, 716 of perineum, 987 of pharynx, 954 of prostate gland, 985 of rectum, 1680 of reproductive organs, external, fe- male, 987 external, male, gS6 internal, female, 988 internal, male, 987 of retina, 146S of scalp, 948 of seminal vesicles, 98S of skin, 1388 of small intestine, 1 643 of spleen, 982 of stomach, 976 of striated muscle, 464 subclavian trunk, 963 of suprarenal body, 983 system, 931 of teeth, 951 of testis, 987 thoracic duct, 941 pract. consid., 944 of thorax, 966 cutaneous, 968 of thyroid gland, 959 of tongue, 952 of tonsils, 954 of trachea, 958 of upper extremity, 961 of ureter, 982 of urethra, 986 of uterus, 989 of vagina, 989 of vas deferens, 98S vessels, development of, 939 Ljrmph-corpuscles, 931 Lymph-nodes of abdomen, pract. consid., 990 abdominal, visceral, 974 ano-rectal, 976 anterior auricular, 946 appendicular, 975 of arm, pract. consid., 965 of axilla, pract. consid., 965 axillary, 961 Lymph-nodes, brachial, deep, 961 superficial, 961 bronchial, 967 buccinator, 947 cervical, deep, inferior, 958 superior, 957 of Cloquet, 992 coeliac, 973 delto-pectoral, 961 development of, 940 epigastric, 972 epitrochlear, 961 facial, 947 gastric, 974 of head, pract. consid., 955 hepatic, 975 hypogastric, 984 iliac, circumflex, 972 internal, 984 inguinal, 991 intercostal, 966 of intestine, 1640 jugular plexus, 956 of leg, pract. consid., 994 lingual, 947 mammary, internal, 966 mandibular, 947 mastoid, 945 maxillary, 947 mediastinal, anterior, 967 posterior, 967 mesenteric, 975 mesocolic, 976 of neck, 956 pract. consid., 959 occipital, 945 pancreatico-splenic, 975 parotid, 946 pectoral, 962 of pelvis, pract. consid., 990 popliteal, 992 posterior auricular, 945 retro-pharyngeal, 948 of Rosenmtiller, 992 sternal, 966 structure of, 937 submaxillary, 946 submental, 946 subscapular, 962 stiperficial cervical, 956 thorax, pract. consid., 971 tibial, anterior, 993 tracheal nodes, 967 umbilical, 972 Lymph-nodules, 936 Lymphocytes, 931 varieties of, 685 Lymphoid structures of pharynx, 1599 tissue, structure of, 936 Lymph-spaces, 931 Lymph-vessels, 934 Lyra, 11 58 Macula lutea. 1466 Macule acusticffi, 1516 Magendie, foramen of, iioo Malar bone, 209 articulations of, 210 Malleus, 1497 Malpighian bodies of spleen, 1784 Mammary glands, 2027 development of, 2032 lymphatics, 968 THIS VOLUME CONTAINS PAGES 1 TO 9S5. ioi6 INDEX. Mammary glands, nerves of, 2032 pract. consid., 2033 structure of. 2029 variations of, 2033 vessels of, 2031 Mandible, 2 1 1 Manubrium of sternum, 155 Marrow of bone, go Mast-cells of .connective tissue, 74 Mastoid cells, 1504 pract. consid., 1508 process, pract. consid., 1508 Maturation of ovum, 16 Maxilla, inferior, 211 development of, 213 structure of, 213 superior, 199 antrum of, 201 articulations of, 202 development of, 202 Maxillary sinus, 1422 Meatus, auditory, internal, 181 inferior, of nose, 141 2 middle, of nose, 141 1 superior, of nose, 141 1 Meckel, diverticulum of, 44 Mediastinum, anterior, 1833 middle, 1833 posterior, 1833 pract. consid., 1S33 superior, 1833 Medulla oblongata, 1063 central gray matter of, 1073 development of, 1 1 c i internal structure of. 1068 Medullary folds, 26 groove, 26 sheath, looi velum, inferior, 1099 superior, loqg MeduUated fibres, 1003 Megakaryocytes, 68q Meibomian (tarsal) glands, 1444 Meissner, corpuscles of, 10 17 plexus of, 1 643 Membrane or membranes. Bowman's, 1451 of Bruch, 1456 cloacal, 1939 costo-coracoid, 568 crico-thyroid, 1815 of Demours, 1452 Descemet's, 1452 fenestrated, 77 foetal, 30 human, 35 hyaloid, 1474 interosseous, of tibia and fibula, 396 mucous, 1528 obturator, 341 olfactory (Schneiderian), 1414 pharyngeal, 1694 pleuro-pericardial, 1700 pleuro-peritoneal, 1700 of Reissner, 151 7 of Ruysch, 1456 of spinal cord, 1022 synovial, of joint, no tectoria, 1521 thyro-hyoid, 18 15 of tympanum, 1494 vitelline, 15 vitrea, 1456 Meninges of brain, pract. consid., 1208 lymphatics of, 948 Menstruation, 2012 Merkel, tactile cells of, 1016 Mesencephalon, 1105 development of, 1 1 1 7 internal structure of, 1109 Mesenteries, 1741 Mesenterium commune, 1697 Mesentery, anterior, 1744 of appendix, 1665 of jejuno-ileum, 1650 of large intestine, 1670 permanent, 1752 posterior, part ist, 1746 part 2nd, 1 7 51 part 3rd, 1753 priniitive, 1697 Meso-appendix, 1665 Mesocolon, 1670 development of, 1704 Mesoblast, 23 lateral plates of, 29 paraxial, 29 parietal layer, 29 visceral layer, 29 Mesogastrium, 1697 Mesognathism, 229 Mesometrium, 2005 Mesonephros, 1935 Mesorarium, 2040 Mesorchium, 2040 Mesorhines, 1404 Mesosalpinx, 1996 Mesotendons, 471 Mesothelium, 71 Mesovarivim, 1987 Metabolism, 6 Metacarpal bones, 314 Metacarpo-phalangeal articulations, 327 Metacarpus, pract. consid., 319 Metanephros (kidney), 1937 Metaphase of mitosis, 12 Metaplasm, 8 Metatarsal bones, 42S Metathalamus, 11 26 Meynert, commissure of, 1115 Mid-brain, 1061 Milk, 2030 Milk-ridge, 2032 Mitosis, 1 1 anaphases of, 13 metaphase of, 12 prophases of, 12 telophases of, 13 Molar teeth, 1546 Moll, glands of, 1444 Monorchism, 1950 Monroe, foramen of, 1131 Mons pubis, 2021 veneris, 2021 Montgomery, glands of, 2028 Morgagni, columns of, 1674 hydatid of, 2002 sinus of, 497 valves of, 1674 Morula, 22 Mouth, 1538 floor of, pract. consid., 1593 formation of, 1694 pract. consid., 1589 roof of, 228 pract. consid., 1592 THIS VOLUME CONTAINS PAGES 1 TO 995, INDEX. 1017 Mouth, vestibule of, 153S Mucoid, 83 Mucous membranes, 152S structure of, 152S Mullerian duct, 2038 Muscle or muscles, abdominal, 515 abductor hallucis, 661 minimi digiti, 60S minimi, of foot, 662 poUicis, 60S adductor brevis, 626 hallucis, 662 longus, 626. magnus, 628 polUcis, 610 anconeus, 589 of ankle, pract. consid., 666 antibrachial, 591 post-axial, 598 pre-axial, 592 of anus, 1675 appendicular, 566 of arm, pract. consid., 5S9 arytenoid, 1S26 of auricle, 14S6 aiu-icularis anterior, 4S3 posterior, 4 S3 superior, 4S3 axial, 502 of axiUa and shoulder, pract. consid., 579 azygos uvulae, 496 biceps, 586 femoris, 636 brachial, 5S5 post-axial, 588 pre-axial, 5S6 brachialis anticus, 586 brachio-radialis, 598 branchiomeric, 474 buccinator, 4S8 bulbo-cavemosus, 565 of buttocks, pract. consid., 641 cardiac, 462 cer\'ical, 542 chpndro-glcssus, 1578 ciliary, 1458 coccygeus, 561, 1676 compound pinnate, 469 compressor urethrEe, 565 constrictor inferior of phar^Tix, 1606 middle of pharynx, 1605 pharyngis inferior, 499 medius, 4q8 superior, 497 superior of pharynx, 1604 coraco-brachialis, 575 of cranium, pract. consid., 4S9 cremaster, 519 crico-arytenoid lateral, 1825 posterior, 1825 crico-thyroid, 1S24 crural, 647 post -axial, 655 pre-axial, 64S cr^ireus, 640 dartos, 1963 deltoideus, 578 depressor anguli oris, 487 labii inferioris, 485 diaphragma, 556 digastricus, 477 dilator pupillas, i4'^c iluscle or muscles, dorsal, of trunk, 507 of Eustachian tube, 1503 extensor brevis digitorum, 665 poUicis, 602 carpi radialis brevior, 598 longior, 598 ulnaris, 601 communis digitorum, 599 indicis, 603 longus digitorum, 655 longus hallucis, 656 pollicis, 603 minimi digiti, 600 ossis metacarpi pollicis, 602 of face, pract. consid., 492 facial, 479 femoral, 633 post-axial, 638 pre-axial, 636 flexor accessorius, 654 brevis digitorum, of foot, 660 hallucis, 660 minimi digiti, 609 digiti of foot, 664 pollicis, 60S carpi radialis, 593 radialis brevis, 597 vilnaris, 594 longus digitorum, 651 hallucis, 651 pollicis, 596 profundus digitorum, 595 sublimis digitorum, 595 of foot, 659 post-axial, 665 pract. consid., 666 pre-axial, 659 gastrocnemius, 649 gemelli, 630 genio-glossus, 15 78 genio-hyoid, 157S genio-hyoideus, 545 gluteus maximus, 630 medius, 631 minimus, 633 gracilis, 626 of hand, 606 pre-axial, 607 of hip and thigh, pract. consid., 642 hypoglossal, 506 hyo-glossus, 1578 hyoidean, 4S0 variations of, 480 iliacus, 624 ilio-costalis, 508 infraspinatus, 576 intercostales extemi, 538 interni. 539 interossei dorsales of foot, 664 of hand, 613 plantares, 663 v'olares, 612 interspinales, 513 intertransversales, 513 anteriores, 547 laterales, 521 intratympanic, 1499 involuntary, arrectores pilorum, 1394 ner\-e-endings of, 1015 ischio-cavemosus. 564 of knee, pract. consid., 645 of larynx, 1824 latissimus dorsi, 574 THIS VOLUME CONTAINS PAGES 1 TO 986. toi8 INDEX. Muscle or muscles, of leg, pract. consid., 665 levator anguli oris, 48 7 scapulae, 571 ani, 560, 1675 , labii superioris, 487 labii superioris alaeque nasi, 485 menti (superbus), 485 palati, 496, 1571 palpebrae superioris, 502 levatores costarum, 540 lingualis, 1579 of lips, 1540 longissimus, 510 longus colli, 54S of lower limb, 623 lumbricales, of hand, 610 of foot, 662 masseter, 474 of mastication, 474 variations of, 477 metameric, 502 multifidus, 512 mylo-hyoideus, 477 nasalis, 486 non-striated, blood-vessels of, 456 development of, 457 (involuntary), 454 lymphatics of, 456 nerves of, 456 structure of, 455 obliquus capitis inferior, 514 superior, 514 externus, 517 inferior, 504 internus, 517 superior, 504 obturator externus, 629 internus, 629 occipito-frontalis, 482 omo-hyoideus, 544 opponens minimi digiti, 608 poUicis, 608 orbicularis oris, 4S6 palpebrarum, 484 orbital, 502 of palate and pharynx, 495 palato-glossus, 497, 1579 palato-pharyngeus, 497, 1371 palmaris brevis, 607 longus, 503 pectinate, of heart, 695 pectineus, 625 pectoralis major, 569 minor, 570 pelvic, 559 perineal, 562 peroneus brevis, 658 longus, 657 tertius, 656 of pharynx, 1604 pinnate, 469 plantaris, 649 platvsma, 481 popliteus, 655 pronator quadratus, 597 radii teres, 592 psoas magnus, 623 parvus (minor), 624 pterygoideus externus, 476 internus, 476 pyloric sphincter, 1626 pyramidalis, 517 Muscle CT muscles, pyriformis, 561 quadratus femoris, 629 lumborum, 521 quadriceps femoris, 639 of rectum, 1675 rectus abdominis, 516 capitis anticus major, 549 capitis anticus minor, 550 lateralis, 547 posticus major, 513 posticus minor, 514 externus, 503 femoris, 639 inferior, 503 internus, 503 superior, 503 rhoiiiboideus major, 572 minor, 572 risorius, 487 rotatores, of back, 513 sacro-spinalis, 508 salpingo-pharyngeus, 1606 sartorius, 638 scalene, variations of, 547 scalenus anticus, 546 medius, 546 posticus, 547 of scalp, pract. consid., 489 seminiembranosus, 43 8 semi-pinnate, 469 semif;pinalis, 511 semitendinosus, 638 serracus magnus, 571 posticus inferior, 541 posticus superior, 541 of soft palate, 1570 soleus, 649 sphincter ani, external, 1676 externus, 563 internal, 1677 pupillse, 1460 vesical, external, 1925 internal, 1925 spinalis, 511 splenius, 510 stapedius, 4S0, 1499 sternalis, 570 sterno-cleido-mastoideus, 499 sterno-hyoideus, 543 stemo-thyroideus, 545 striated, attachments of, 468 blood-vessels of, 464 burSce of, 471 classification of, 471 development of, 465 form of, 469 general considerations of, 468 lymphatics of, 464 nerves of, 464 nerve-supply, general, 473 structure, general of, 458 variations, 461 (voluntary), 457 stylo-glossus, 1579 stylo-hyoideus, 480 stvlo-pharyngeus, 495, 1606 siibclavius, 570 subcostal, 539 subcrureus, 640 submiintal, 477 subscapularis, 578 supinator, 601 supraspinatus, 5J5 THIS VOLUME CONTAINS PAGES 1 TO 995. INDEX. 1019 Muscle or muscles, temporalis, 475 tensor fasciae latse, 631 palati, 47g, 1570 tympani, 479, 1499 teres major, 577 minor, 576 thoracic, 538 thyro-arytenoid, 1825 thyro-hyoideus, 545 tibialis anticus, 655 posticus, 654 of tongue, 1577 trachealis, 1835 transversalis, 519 transverso-costal tract, 508 transverso-spinal tract, 511 transversus perinei profundus, 565 superficialis, 564 of tongue, 1579 trapezius, 500 triangularis sterni, 540 triceps, 588 trigeminal, 474 palatal, 479 tympanic, 479 of trunk, 507 of upper limb, 568 vago-accessory, 495 vastus externus, 640 internus, 640 ventral, of trunk, 515 voluntary, motor nerve-endings of, zygomaticus major, 485 minor, 485 Muscle-fibre, structure of, 459 Muscular system, 454 tissue, general, 454 Myelin, looi Myelocytes, of bone-marrow, 92 Myelopiaxes, of bone-marrow, 92 Myometrium, 2008 Myotome, 30 Myxoedema, 1794 Naboth, ovules of, 2008 Nail, structure of, 1395 Nail-bed, 1396 Nail-plate, 1395 Nails, 1394 development of, 1403 Nares, anterior, 1404 posterior, 1413 Nasal bone, 209 articulations of, 209 development of, 209 cavities, pract. consid., 1417 cavity, 223 hiatus semilunaris of, 194 infundibulum of, 194 meatus inferior of, 225 middle of, 225 superior of, 225 chamber, 224 fossa, blood-vessels of, 1425 floor of, 1 4 13 lymphatics of, 1426 nerves of, 1426 roof of, 141 2 fossas, 1409 index, 1404 mucous membrane, 1413 septum, 223, 1410 triangular cartilage of, 224 Nasion, 228 Nasmyth, membrane of, 1550 Naso-lachrymal duct, 1479 Naso-optic groove, 62 Naso-pharynx, 1598 Navel, 37 Neck, landmarks of, 554- pract. consid., 550 triangles of, 547 Nephrotome, 30 Nerve or nerves, abdominal, of vagus, 1272 abducent, 1249 development of, 1379 aortic (sympathetic), 1364 auditory, 1256 development of, 1379 of auricle, 1487 auricular, great, 1286 posterior, of facial, 1254 of vagus, 1268 auriculo-temporal, of mandibular, 1244 of bone, 94 buccal, of mandibular, 1243 calcanean, internal, 1344 cervical, anterior divisions of, 1285 cardiac inferior, of vagus, 1270 superior, of vagus, 1270 first, posterior division of, 1281 posterior divisions of, 1281 second, posterior division of, 1281 superficial, 1287 third, posterior division of, 12S1 cervico-facial, of facial, 1254 chorda tympani, of facial, 1253 ciliary, long, of nasal, 1234 circumflex, 1307 pract. consid., 1308 of clitoris, 2025 coccygeal, posterior division of, 1284 of cochlea, membranous, 1521 cochlear, of auditory, 1256 of cornea, 1452 cranial, 12 19 crural, anterior (femoral), 1327 cutaneous internal, of anterior , crural, 1328 middle, of anterior crural, 1327 perforating, of pudendal plexus, 1347 dental, inferior, of mandibular, 1245 superior anterior, of maxillary, 1239 middle, of maxillary, 1239 posterior, of maxillary, 1238 descendens hypoglossi, 1277 development of, 1375 digastric, of facial, 1234 digital of median, 130 1 dorsal of clitoris, 13 51 of penis, 13 51 of epididymis, 194S of external auditory canal, 1490 external cutaneous, of lumbar plexus, 1324 of eyelids, 1446 facial, 1250, 1 2 51 development of, 1378 genu of, 1251 pract. consid., 1255 of Fallopian tube, 1999 frontal, 1234 THIS VOLUME CONTAINS PAGES 1 TO 995. I020 INDEX. Nerve or nerves, ganglionic, of nasal, 1234 genito-crural, 1322 of glands, 1536 glosso-pharyngeal, 1260 development of, 1379 gluteal, inferior, 1333 superior, 1333 of heart, 704 hemorrhoidal, inferior, 1350 hypoglossal, 1275 development of, 1380 pract. consid., 1277 ilio-hypogastric, 1320 ilio-inguinal, 13 21 infratrochlear. 1235 intercostal, 1314 intercosto-humeral, 13 17 intermedius of Wrisberg, of facial, 1250 internal cutaneous, 1303 cutaneous lesser, 1303 interosseous anterior of median, 1300 of kidney, 18S6 of labia, 2024 labial, superior, of maxillary, 1240 lachrymal, 1233 laryngeal, external, of superior laryn- geal, 1270 inferior (recurrent) of vagus, 1270 internal, of superior laryngeal, 1270 superior, of vagus, 1270 of lai'ynx, 1S27 lingual, of glosso-pharyngeal, 1264 of hypoglossal, 1277 of mandibular, 1244 of lips, 1542 of liver, 1 7 1 1 lumbar, posterior divisions of, 1282 of lungs, 1855 of mammary glands, 2032 mandibular, (maxillar)- inferior), 1242 masseteric, of mandibular, 1242 maxillary (superior), 1237 median, 1298 branches of, 1300 pract. consid., 1301 meningeal, of hypoglossal, 1277 of vagus, 1268 mental, of inferior dental, 1246 of muscle, non-striated, 456 muscular of glosso-pharyngeal, 1264 musculo-cutaneous, of arm, 1298 of leg, 1338 musculo-spiral, 1308 branches of, 1309 pract. consid., 13 14 mylo-hyoid, of inferior dental, 1245 nasal, 1234, 1235 anterior, 1235 external, 1235 fossa, 1426 internal (septal), 1235 lateral, of maxillary, 1240 septum, 141 o superior posterior, of spheno-pala- tine ganglion, 1241 naso-palatine, of spheno-palatine gan- glion, 1 241 of nose, 1407 obturator, 1324 accessory, 1326 occipital, small, 1286 Nerve or nerves, oculomotor, 1225 development of, 1377 oesophageal, of vagus, 1272 of ccsophagus, 1613 olfactory, 1220 development of, 1376 pract. consid., 1222 ophthalmic, 1233 optic, 1223 development of, 1482 pract. consid., 1470 orbital, of spheno-palatine ganglion, 1241 of ovary, 1993 of palate, 1573 palatine, of spheno-palatine ganglion, 1241 palmar cutaneous of median, 1301 palpebral, inferior, of maxillary, 1240 of pancreas, 1737 of parotid gland, 1583 of penis, 197 1 pericardial of vagus, 1272 of pericardium, 716 perineal, 1350 peripheral, development of, loii peroneal, communicating, of externa) popliteal, 1335 petrosal, deep, small, 1264 superficial, external, of facial, 1253 great, of facial, 1252 small, 1264 pharyngeal of glosso-pharyngeal, 1264 of vagus, 1269 of pharynx, 1606 phrenic, 1290 plantar external, 1345 internal, 1344 of pleuras, 1861 popliteal, external (peroneal), 1335 internal (tibial), 1339 posterior interosseous, 1311 of prostate gland, 1978 pterygoid, external, of mandibular, 1243 internal, of mandibular, 1242 pterygo-palatine (pharyngeal), of spheno-palatine ganglion, 1242 pudic, 1349 pulmonary, anterior, of vagus, 1272 posterior, of vagus, 1272 (sympathetic), 1364 radial, 1313 of rectum, 1680 recurrent, of mandibular, 1242 of maxillary, 1237 respiratory, external of Bell, 1295 sacral, posterior divisions of, 1282 sacro-coccygeal, 1352 posterior, 1283 saphenous, internal (long), of anterioj crural, 1329 short (external), 1342 scapular, posterior, 1295 sciatic, great, 1335 small, 1348 of scrotum, 1964 of skin, 1389 of small intestine, 1643 somatic, 1218 of spermatic ducts, 1959 spheno-palatine, of maxillary. 1237 THIS VOLUME CONTAINS PAGES 1 TO 986. INDEX. Nerve or nerves, spinal, 1278 spinal-accessory, 1274 pract. consid., 1275 splanchnic, (s\Tnpathetic), 1364 of spleen, 17S7 stapedial, of facial, 1253 of stomach, 1628 of striated muscle, 464 stylo-hyoid, of facial, 1254 of sublingual gland, 1585 of submaxillary gland, 15S5 subscapular, 1306 supraorbital, 1234 of suprarenal bodies, 1803 suprascapular, 1295 supratrochlear, 1234 sural, of external popliteal, 1335 of sweat glands, 1400 of taste-buds, 1435 temporal, deep, of mandibular, 1243 superficial, of auriculo-temporal 1244 temporo-facial, of facial, 1254 temporo-malar (orbital), of maxillary 1238 of testis, 1948 thoracic, 13 14 anterior, external, 1297 internal, 1303 branches of, 13 17 cardiac, of vagus, 1272 first, 13 15 lower, 1315 posterior divisions of, 1282 posterior (long), 1295 pract. consid., 1296 pract. consid., 13 18 second, 13 17 third, 13 1 7 twelfth (subcostal) 13 17 upper, 13 1 5 of thyroid body, 1793 of thymus body. 1800 thyro-hyoid, of hypoglossal, 1277 tibial, anterior, 1336 communicating, 1342 posterior, 1342 recurrent, 133^ of tongue, 1580 tonsillar of glosso-phar3-ngeal, 1264 of trachea, 1836 trigeminal, 1230 development of, 1378 divisions of, 1232 pract. consid., 1248 trochlear, 1228 development of, 1377 tympanic, of glosso-pharvngeal, 1264 to tympanic plexus, of facial, 1252 ulnar, 1303 branches of, 1305 pract. consid., 1306 of ureter, 1898 of urethra, 1927 of urinary bladder, igio of uterus, 2010 of vagina, 2018 vagus, 1265 and spinal accessory, development of, 1380 ganglia of, 1267 pract. consid., 1272 vestibular, of auditor}', 1256 Nerve or rier\'es, visceral, 1218 Nerve-cells, 99S ■ bipolar, 999 multipolar, 1000 luiipolar, 999 Nerve-endings, motor, 1014 of cardiac muscle, 1015 of involuntary muscle, 10 15 of voluntary muscle, 1014 senson,', 10 15 encapsulated, 10 1 6 free. 10 15 genital corpuscles, 1017 Golgi-.Mazzoni corpuscles, 1019 Krause's end-bulbs, 1016 Meissner's corpuscles, 1017 Merkel's tactile cells, 1016 neuromuscular endings, 1019 neurotendinous endings, 1020 Ruffini's corpuscles, 1017 Vater-Pacinian corpuscles, loiS Nerve-fibres, 1000 arcuate. 107 1 axis-cylinder of, looi cerebello-ohvary, 1072 cerebello-thalarnic, 11 14 cortico-bulbar, 1115 cortico-pontine, 1115 cortico-spinal, 1 1 1 5 medullary sheath of, 1001 medullated, 1003 neurilemma of, looi nonmedullated, 1003 rubro-thalamic, 11 14 of sympathetic system, 1356 Nerve -terminations, 1014 Nerve-trunks, 1006 endoneurium of, 1006 epineurium of, 1006 funiculi of, 1006 perineurium of. 1006 Nervous system, 996 central, 1021 peripheral, 12 18 S3-mpathetic, 1353 development of, 10 13 tissues, 997 development of, 1009 Neurilemma, looi Neuroblasts. loio Neuro-epithelium, 70 Neuroglia. 1003 ependymal layer of, 1004 glia-fibres of, "1004 of gray matter, of spinal cord, 105? histogenesis of, 10 10 spider cells of, 1004 Neurokeratin. looi Neuromuscular endings, IC19 Neurone or neurones, 996 axones of, 997 dendrites of, 997 histogenesis of, ion Neurotendinous endings, 1020 Nictitating membrane, 1443 Nipple, 2028 Nodose, ganghon of vagus, 1268 Nodules of Arantius, 700 Nonmedullated fibres, 1003 Normoblasts, 92 Nose, 1404 blood-vessels of, 1407 cartilages of, 1404 THIS VOLUME CONTAINS PAGES 1 TO 996. I022 INDEX. Nose, development of, 1429 hiatus semilunaris of, 1411 inferior meatus of, 141 2 infundibulum of, 141 1 lateral cartilages of, 1405 lymphatics of, 1407 middle meatus of, 14" nerves of, 1407 olfactory region of, 1413 pract. consid., 1407 respiratory region of, 141 5 superior meatus of, 141 1 vestibule of, 1409 Mostrils, 1404 Notochord, 27 Nuck, canal of, 2006 Nuclem, g Nucleolus, 9 Nucleus or nuclei, abducent, 1249 acoustic, 1257 ambiguus, 1074 amygdaloid, 11 72 arcuate, 1076 caudate, 11 69 cuneate, 1069 facial, 1 2 51 dentate, of cerebellum, 1088 emboliformis (embolus) of cerebellum 1085 facial, 1 2 51 fastisiii, of cerebellum, lobg globosus, of cerebellum, 1089 gracile, io6g internal, of cerebellum, lobS of lateral fillet, 1258 lenticular, 1169 mammillaris, 1129 olivary, 107 1 olivary, superior, 1257 red, 1 1 14 structure of, 8 trapezoideus, 1257 vago-glosso-pharyngeal, 1073 vestibular, of reception, 1 2 59 Nuhn, glands of, 157 7 Nutrition, accessory organs of, 1781 Nympha;, 2022 Obelion, 228 Obex. 1096 Occipital bone, 172 lobe, 1 145 protuberance, external, 174 internal, 175 Odontoblasts, 1558 CEsophagus, i6oq course and relations of, 1609 Ivmphatics of, g7i nerves of, 161 3 pract. consid., 1613 structure of, 1611 vessels of, 161 2 Olecranon, of ulna, 281 Olfactory bulb, 1151 cells, 1 41 4 hairs, 141 5 lobe, 1 1 51 membrane, 141 4 pits, 62 region of nose, 1413 stria, 1 1 53 tract, 1 1 52 trigone, 1 1 53 Olivary eminence, 1066 nuclei, 107 1 accessory, 1072 nucleus, inferior, 1072 Omental sac, 1703 Omentum, duodeno-hepatic, 1740 gastro-colic, 1747 gastro-hepatic (lestier), 1745 gastro-splenic, 1747 greater, 1747 greater, structure of, 1749 Oocyte, primary, 17 secondary, 17 Ooplasm, IS Opercula insulcB, 1137 Ophryon, 228 Opisthion, 228 Optic commissure, 1223 entrance or papilla, 1462 recess, 1 132 thalami, 11 18 tracts, 1223 Ora serrata, 1467 Oral cavity, development of, 62 glands, development of, 1 589 Orbit, 222 axes of, 222 fasciae of, 504 lymphatics of, 94g^ pract. consid., 1438 Organ or organs, accessory, of nutrition, 1781 of Corti, I 519 genital, external female, 2021 Jacobson's, 14 17 reproductive female, 1985 male, 1941 of respiration, 18 13 of sense, 1381 of taste, 1433 urinary, 1869 Oro-pharynx, I5g8 Orthognathism, 229 Os intermetatarseum, 432 magnum, 312 Osseovis tissue, 84 Ossicles auditory, 1496 articulations of, 1498 incus, 1497 malleus, 1497 movements of, i 500 stapes, 1498 of ear, development of, 1525 Ossification, centres of, 94 of epiphyses, 98 Osteoblasts, 95 Ostium maxillare, 1422 Otic ganglion, 1246 Ova or ovum, 15 centrolecithal, 22 fertilization of, 18 holoblastic, 22 homolecithal, 21 human, 1990 maturation of, 16 meroblastic, 22 primordial, 1993 segmentation of, 21 stage of. 56 telolecithal, 22 zona pelKicida of. 1989 Ovarv or ovaries, 1085 cortex of, 1987 THIS VOLUME CONTAINS PAGES 1 TO 995. INDEX. ro23 Ovary or ovaries, descent of, 204.3 developmeat of. 1993 fixation of, 1986 Graafian follicles of, 1988 Viil'im of, 19S5 ligament of, 1987 medulla of, 19S8 nerves of, 1993 position of, 1986 pract. consid., 1993 surfaces of, 1985 suspensorv" ligament of, 19S6 structure of, 1987 vessels of, 1992 Oviduct, 1996 Pacchionian bodies, 1205 depressions, 19S Palate, 1567 bone, 204 articulations of, 203 development of, 205 hard, 1567 h-mphatics of, 954 nerves of, 1573 pract. consid., 1392 soft, 1568 muscles of, 1570 vessels of, 1572 Pallium, development of, 1189 Palmar aponeurosis, 606 fascia, 606 Pancreas, 1732 body of, 1733 development of, 1737 ducts of, 1736 ■ head of, 1732 interalveolar eeU-areas of, 1735 islands of Langerhans of, 1735 l\-mphatics of, 979 nerves of, 1737 pract. consid., 173S relations to peritoneum, of, 1736 structure of, 1734 vessels of, 1736 Panniculus adiposus, 13 84 Papilla or papillse, c-ircnm vallate, 1575 dental, 155S of duodenum, 1720 filiform, 1575 fungiform, 1575 lachr\-Tnal, 1478 optic, 1462 renal, 1S75 Paradid\-mis, 1930 Parametrium, 2005 Parathyroid bodies, 1793 structure of, 1795 Parietal bone, 197 articulations of, 199 impressions, 199 lobe, 1 143 Paroophoron, 2002 Parotid duct, 13S3 gland, 1 58 2 nerves of, 1383 relations of, 15S2 structure of, 1386 vessels of, 1583 Parovarium, 2000 Patella, 398 development of, 400 m^ovements of, 409 Patella, pract. consid., 416 Peduncle, cerebellar, inferior, 1067 cerebral, 1107 Pelvic girdle, ^^^2 Pelvis, 332 development of. 344 diameters of, 342 diaphragm of, 539 index of, 343 joints of, 337 pract. consid., 350 of kidney, 1894 landmarks of. 349 ligaments of, 337 UTnphatics of, 9S3 position of, 342 pract. consid.. 343 sexual differences. 343 surt"ace anatomy of. 345 white lines of, 559 as a whole, 341 Penis, 1963 corpora cavernosa of, 1966 corpus spongiosum of, 1967 crura of, 1967 glans of, 1968 nen,-es of, 197 1 pract. consid., 1972 prepuce of, 1966 structure of, 1968 vessels of, 1970 Pericsecal fosss, 1666 Pericardiiom. 714 blood-vessels of, 716 hgaments of, 716 Ijtnphatics of, 716 nerves of, 716 pract. consid., 716 Perichondrium, 81 Pericranium. 489 Peril\"mph of internal ear, 13 14 Perimetrium, 2009 Perimysium. 45S Perineal body, 2046 Perineum, female. 2046 Umiphatics of, 987 male. 19 15 landmarks of, igi8 triangular ligament of, 363 Perineiuium, 1006 Periosteum, 89 alveolar. 1333 Peritoneum, 1740 cavity, lesser of, 1749 development of, 1702 of large intestine, 1670 parietal, anterior. 1742 folds of. 1742 fossje of, 1742 pract. consid., 1754 Perivascular lymph-spaces, 931 Pes anserinus, 1252 hippocampi, 1163 Petit, triangle of. 374 Petro-mastoid portion of temporal bone, 179 Petrous ganglion, of glosso-pharvngeal, 1264 subdivision, of petro-mastoid bone, 181 Peyer's patches, 1641 Phalanges of foot, 432 of hand, 317 THIS VOLUME CONTAINS PAGES 1 TO 995. INDEX. Phalanges of hand, development of, 318 peculiarities, 318 pract. consid., 320 variations of, 319 Pharyngeal pouches, 1695 Pharynx, 1596 development of, 1603 growth of, 1603 laryngo-, 1598 lymphatics of, 954 lymphoid structures of, 1599 muscles of, 1604 naso-, 1598 nerves of, 1606 oro-, 1598 pract. consid., 1606 primitive, 1694 relations of, 1601 sinus pyriformis of, 1598 vessels of, 1606 Philtrum of lips, 1540 Pia mater, of brain, 1202 of spinal cord, 1022 Pigment-cells of connective tissue, 74 Pillars of fauces, 1569 Pineal body, 11 24 Pinna, 1484 Pisiform bone, 311 Pituitary body, anterior lobe of, 1806 development of, 1808 (hypophysis), 11 29 Placenta, 49 basal plate of, 51 cotyledons of, 50 discoidal, 34 fcetal portion, 50 giant cells of, 51 intervillous spaces of, 51 marginal sinus of, 53 maternal portion, 51 multiple, 34 septa of, 51 vitelline, 32 zonular, 33 Placentalia, 34 Plane, frontal, 3 sagittal, 3 transverse, 3 Plasma-cells of connective tissue, 74 Plasmosome, 9 Plates, tarsal, 1444 Platyrhines, 1404 Pleura or pleurae, 1858 blood-vessels of, i860 nerves of, 1861 outlines of, 1859 pract. consid., 1864 relations to chest-walls, changes in, 1863 of to surface, 1859 structure of, i860 Plexus or plexuses, aortic, 1373 of Auerbach, 1 643 brachial, 1292 branches, infraclavicular of, 1297 supraclavicular of, 1295 constitution and plan of, 1293 pract. consid.; 1294 cardiac, 1367 carotid (sympathetic). 1360 cavernous, of penis, 1374 (sympathetic), 13 61 cervical, 1285 branches of, 1285 Plexus or plexuses, cervical, branches, communicating of, 1289 deep, of, 1289 descending of, 1288 muscular of, 1289 superficial of, 1286 supraacromial of, 1289 supraclavicular of, 1288 suprasternal of, 1288 pract. consid., 1292 coccygeal, 1352 cceliac, 1370 lymphatic, 973 coronary, 1368 gastric, 1370 hemorrhoidal, 1374 hepatic, 1370 hypogastric, 1373 lymphatic, 984 iliac, lymphatic, 983 inguinal, lymphatic, 991 lumbar, 13 19 lymphatic, 973 muscular branches of, 1320 of Meissner, 1643 mesenteric inferior, 1373 superior, 1372 oesophageal, 1272 ovarian, 13 71 pampiniform, i960 parotid, 1252 pelvic, 1374 phrenic, 13 71 pract. consid., 1330 prostatic, 1374 pudendal, 1345 branches, muscular of, 1346 visceral of, 1346 pulmonary, anterior, 1272 posterior, 1272 renal, 13 71 sacral, 133 1 branches, articular of, 1334 collateral of, 1332 muscular of, 1333 terminal of, 1334 lymphatic, 984 posterior, 1282 pract. consid., 1352 solar, 1368 spermatic, 1371 splenic, 1370 suprarenal, 13 71 of sympathetic nerves, 1367 tympanic, 1264 utero-vaginal, 1374 vesical, 1374 Plica fimbriata, 1573 semilunaris, of eye, 1443 sublingualis, 1573 Polar body, first, 16 second, 16 Pons Varolii, 1077 development of, 11 03 internal structure of, 107S Pontine flexure, 1062 nucleus, 1078 Portal system of veins, 919 Postaxial, 4 Pouch of Douglas, 1743 pharyngeal, 61 recto-uterine '1743 recto- vesical, 1743 THIS VOLUME CONTAINS PAGES 1 TO 995. INDEX. 1025 Poupart, ligament of, 523 Preaxial, 4 Pregnancy, 2012 Prepuce of penis, 1966 Primitive streak, 24 significance of, 25 Process or processes, ciliary, 1457 fronto-nasal, 62 mandibular, 62 maxillary, 62 nasal, mesial, 62 lateral, 62 styloid, of petrous oone, 1S3 uncinate of ethmoid, 193 Processus cochleariformis, 182 vaginalis, 2041 Proctodasum, 1695 Prognathism, 229 Pronephros, 1934 Pronucleus, female, 16 male, 20 Prophases of mitosis, 12 Prosencephalon, 1059 Prostate gland, 1975 development of, 1979 lymphatics of, 9S5 nerves of, 19 78 pract. consid., 1979 relations of, 1976 structure of, 1977 vessels of, 1978 Proteins, 8 Protoplasm, 7 Proto vertebrae, 29 Psalterium, 11 58 Pseudostomata, 72 Pterion, 228 Pterygoid plate, inner, 189 outer, 189 processes of sphenoid bone, 1S9 Pubes, 334 Pulmonary system of veins, S52 Pulp of teeth, 1554 Pulvinar, 1 1 19 Puncta, lachrymal, 147S Pupil, I45y Purkinje cells of cerebellum, 1090 Putamen, 11 70 Pyramid, 1065 Pyramidal tract, in medulla, 1075 Pyramids, decussation of, 1064 renal, 1876 Pyrenin, 9 Radius, 287 development of, 293 landmarks of, 296 pract. consid., 293 structure of, 292 surface anatomy, 300 Rami communicantes of sympathetic system, 1356 Ranvier, nodes of, looi Rauber, cells of, 23 Recto-uterine pouch, 1743 Recto-vesical pouch, 1743 Rectum, 1672 blood-vessels of, 1679 growth of, 16S0 lymphatics of, 1680 muscles and fascias of, 1675 nerves of, 1680 peritoneal relations of, 1679 Rectum, pract. consid., i68g structure of, 1674 valves of, 1674 Reduction division, iS Reil, island of, 1149 limiting sulcus of, 1139 Reissner's fibre, 1030 membrane, of cochlea, 1517 Remak, fibres of, 1003 Renal duct, 1S94 Reproduction, 6 Reproductive organs, development of, 2037 external, female, lymphatics of, 987 male, lymphatics of, 986 female, 1985 internal, female, lymphatics of, 988 male, lymphatics of, 987 ■ male, 1941 Respiration, organs of, 1S13 Respiratory region of nose, 141 5 tract, development of, 1861 Restiform body, 1067 Rete Malpighi, 1386 Reticular tissue, 75 Reticulin, 83 Retina, 1462 blood-vessels of, 1467 development of, 1482 lymphatics of, 1468 pars optica of, 1462 pract. consid., 1468 structure of, 1463 Retro-colic fossa, 1667 Retzius, prevesical space of, 525 space of, 1906 veins of, 924 Rhinencephalon, 11 51 development of, 1193 Rhombencephalon, derivatives of, 1063 Ribs, 149 asternal, 150 exceptional, 152 floating, 150 pract. consid., 169 sternal, 150 variations of, 153 Right lymphatic duct, 945 Rima glottidis, 1820 Ring, abdominal, external, 524 internal, 524 femoral (crural), 1773 Riolan, muscle of, 484 Rivinus, ducts of, 1585 notch of, 1493 Rolando, fissure of, 113 7 funiculus of, 1067 Rosenmtiller, fossa of, 1598 lymph-nodes of, 992 organ of, 2000 Rostrum, of corpus callosum, 11 56 of sphenoid bone, 187 RuiBni, corpuscles of, 1017 Ruysch, membrane of, 1456 Sac, conjunctival, 1443 lachrymal, 1478 vitelline, 32 Saccule, 151 5 structure of, 151 6 Sacral lymphatic plexus, 984 Sacro-iliac articulation, 33S ■ THIS VOLUME CONTAINS PAGES 1 TO 995. ro26 INDEX. Sacro-sciatic ligaments, 339 Sacrom, 124 development of, 129 sexual differences of, 127 variations of, 127 Salivary glands, 1582 structure of, 1585 Santorini, cartilages of, 181 7 duct of, 1736 Saphenous opening, 635 Sarcolemma, 459 Sarcous (muscular) substance, 459 Scalatympani, 1514 vestibuli, 1514 Scalp, Ij-mphatics of, 94S muscles and fasciae, pract. consid., 4S9 Scaphoid, 309 bone of foot, 425 development of, 426 Scapula, 24S development of, 253 landmarks of, 255 ligaments of, 256 pract. consid., 253 sexual differences, 252 structure of, 253 Scapulo-clavicular articulation, 262 Scarpa, canals of, 201 fascia of, 515 ganglion of, 1259 triangle of, 639 Schlerrmi, canal of, 1452 Schwann, sheath of, looi Sclera, 1449 development of, 14S2 pract. consid., 1453 structure of, 1450 Sclerotome, 30 Scoliosis, 144 Scrotum, 1961 dartos muscle of, 1963 nerves of, 1964 pract. consid., 1964 raphe of, 1962 tunica vaginalis of, 1963 vessels of, 1964 Segmentation, 21 complete, 22 equal. 22 partial, 22 Sella turcica, 1S6 Semilimar bone, 310 cartilages of knee-joint, 402 valves. 700 Seminal vesicles, 1956 hTnphatics of, 9S8 pract. consid., 1959 relations of, 1957 structure of, 1958 vessels of, 1958 Seminiferous tubules, 1942 Sense, organs .of, 1381 Septum or septa, aortic, 707 auricular, 694 crurale (femorale"), 625 intermedium, 706 intermuscular. 470 interventricular, 696 lucidum, 1 1 59 median, posterior, of spinal cord, 1027 nasal, 1410 cartilage of, 1405 placental, 51 Septum or septa, primum, 706 secundum, 708 spiu"iuiTi, 707 transversum, 1701 Serosa, 31 Sertoli, cells of, 1943 Sesamoid bones, 104 of foot, 432 of hand, 318 Sharpey's fibres of bone, 87 Shoulder, muscles and fascia of, consid., 579 Shoulder-girdle, 24S surface anatomy of, 263 Shoulder-joint, 274 bursae of, 277 dislocation of, 5S2 landmarks of, 280 ligaments of, 274 movements of, 277 pract. consid., 278 Shrapnell's membrane, 1494 Sigmoid cavitj-, greater, of ulna, 281 lesser, of ulna, 281 flexure, 1669 peritoneal relations of, 1671 pract. consid., 1685 Sinus or sinuses, basilar, 874 pract. consid., 874 cavernous, 872 pract. consid., 873 circular, 872 confluence of, 868 of dura mater, 867 frontal, 1423; 226 (bony) development of, 1432 pract. consid., 1427 intercavernous, 872 lactiferus, 2030 lateral, 867 pract. consid., 869 longitudinal, inferior, 871 superior, 870 pract. consid., 870 marginal, 87 2 of placenta, 53 maxillary. 1422; 20 (bony) development of, 1431 pract. consid., 1428 of Morgagni. 497 occipital, 872 palatal, 1425 petrosal, inferior, 874 superior, 874 pocularis, 1922 pracervicalis. 61 pvriformis of pharynx, 1598 renal, 1874 reuniens, 707 sigmoid. 86S sphenoidal, 1425 pract. consid., 1428 spheno-parietal, 874 straight, 872 uro-genital, 1939 of Valsalva, 700 venosus, 705 Skeleton, 103 appendicular, 104 axial, 103 Skene, tubes of, 1924 Skin, blood-vessels of, 1387 development of, 1400 pract THIS VOLUME CONTAINS PAGES 1 TO 995. INDEX. 1027 Skin, end-bulbs of Krause, 1389 end-organs of Ruffini, 1389 genital corpuscles, 13S9 Golgi-mazzoni corpuscles, 13 89 lymphatics of, 1388 Meissner's corpuscles, 1389 nerves of, 13 89 pigmentation of, 1387 stratum corneum of, 1387 germinativum of, 1385 granulosum of, 13S6 lucidum of, 1386 structure of, 1382 Vater-Pacinian corpuscles, 1389 Skull, 172 alveolar point of, 228 anthropology of, 228 asymmetry, 230 auricular point of, 228 capacity of, 230 changes in old age, 233 chordal portion, 28 dimensions of, 229 fontanelles of, 231 glenoid point of, 228 growth and age of, 230 index, cephalic of, 229 facial of, 229 of height of, 229 nasal of, 229 orbital of, 229 palatal of, 229 landmarks of, 240 malar point of, 228 mental point of, 228 occipital point of, 2 28 pract. consid., 235 prechordal portion, 28 sexual differences, 234 shape of, 229 subnasal point of, 229 surface anatomy, 234 weight of, 233 as whole, 216 Smegma, 1966 Solitary nodules of Intestine, 1640 Somatopleura, 29 Somites, 29 Space or spaces, of Burns, 543 of Fontana, 1452 perforated, anterior, 1153 posterior, 1107 quadrangular, of m. teres major, 578 of Retzius, 1906 subarachnoid, of spinal cord, 1022 subdural, of spinal cord, 1022 sublingual, 1581 of Tenon, 1437 triangular, of m. teres major, 578 Spermatic cord, 1960 constituents of, i960 pampiniform plexus of, i960 pract. consid., 1961 ducts, 1953 nerves of, 1959 structure of, 1956 vessels of, 1958 filaments, 1946 Spermatids, 1944 Spermatocytes, primary, 1944 secondary, 1944 Spermatogenesis, 1944 Spermatogones, 1944 Spermatozoa, 1946 Spennatozoon, 16 Sperm-nucleus, 20 Spheno-ethmoidal recess, 141 1 Sphenoid bone, 186 articulations of, 190 development of, 190 great wings of, 187 lesser wings of, 188 pterygoid processes of, 189 Sphenoidal sinus, 1425 Spheno-palatine ganglion, 1240 Spigelius, lobe of, 1707 Spinal column, 114 Spinal cord, 1021 anterior horn, nerve-cells of, 1030 arachnoid of, 1022 blood-vessels of, 1047 Cauda equina of, 1025 central canal of, 1030 columns of, 1027 anterior, 1027 lateral, 1027 posterior, 1027 commissure, grajr of, 102S white, anterior of, 1028 conus medullaris, 102 1 denticulate ligaments of, 1023 development of, 1049 dura mater of, 1022 enlargement, cervical, of, 1026 lumbar of, 1026 fibre-tracts of white matter, 1038 fissure, median anterior of, 1027 form of, 1026 gray matter of, 1028 nerve-fibres of, 1036 neuroglia of, 1035 ground-bundle, anterior, 1046 lateral, 1045 horn, anterior of, 1029 lateral of, 1029 posterior of, 1029 membranes of, 1022 microscopical structure of, 1030 nerve-cells, grouping of, 1032 pia mater of, 1022 posterior horn, nerve-cells of, 1033 pract. consid., 1051 root-line, ventral of, 1027 segments of, 1024 septum, median posterior of, 1027 substantia gelatinosa Rolandi of, 1029 sulcus postero-lateral of, 1027 tract, anterior pj^ramidal (direct). 1046 of Burdach, 1039 direct cerebellar, 1044 of GoU, 1039 of Gower, 1044 lateral (crossed pyramidal), 1043 of Lissauer, 1042 white matter of, 1036 ganglia, 1279 nerves, 1278 constitution of, 12 78 divisions, primary, anterior, of, 1284 posterior, of, 1279 number of, 1279 size of, 1279 . typical, 1284 131 THIS VOLUME CONTAINS PAGES 1 TO 995. I028 INDEX. Spinal nerves, ventral (motor) roots of, 1279 Spine, 114 articulations of, 132 aspect, anterior of, 138 lateral of, 13S posterior of, 138 curves of, 138 dimensions and proportions of, 141 landmarks of, 146 lateral curvature of, 144 ligaments of, 132 movements of, 142 practical considerations, 143 sprains of, 144 as whole, 138 Splanchnopleura, 29 Splanchnoskeleton, 84 Spleen, 1781 development and growth of, 17S7 lymphatics of, 982 movable, 1788 nerves of, 1787 nodules (Malphighian bodies) of, 1784 peritoneal relations of, 1785 pract. consid., 1787 pulp of, 1783 structure of, 1783 surface anatomy of, 1787 basal, 1782 gastric, 1782 phrenic, 1781 renal, 1782 suspensory ligament of, 1786 vessels of, 1786 Spleens, accessory, 17S7 Splenium, of corpus callosum, 11 56 Spongioblasts loio Spongioplasm, 8 Sprains, of spine, 144 Squamous portion of temporal bone, 177 Stapes, 1498 Stenson, canals of, 201 duct, 1583 Stephanion, 229 Stemo-clavicular articulation, 261 pract. consid., 263 Sternum, 155 development of, 157 pract. consid., 168 sexual differences of 156 variations of, 1 56 Stigmata, 72 Stilling, canal of, 1474 Stomach, 161 7 blood-vessels of, 1627 curvature greater of, 161 7 curvature lesser of, 161 7 fundus of, 1 61 8 glands of, 1623 growth of, 1629 lymphatics of, 976, 1628 nerves of, 1628 peritoneal relations of, 161 9 position and relations of, 1619 pract. consid., 1629 pylorus. 1 61 8 shape of, 161 8 structure of, 1621 variations of, 1629 weight and dimensions of, 1619 Stomata, 72 Stomodfcum, 1694 Strabismus, 1440 Stratum zonale, of thalamus, 11 23 Stria medullaris, 11 19 Striae, acoustic, 1096 Structtire, elements of, 5 Styloid process of ulna, 285 Sublingual ducts, 1585 gland, 1585 nerves of, 1585 structure of, 1587 vessels of, 1585 space, 1 58 1 Submaxillary duct, 1584 ganglion, 1247 gland, 1583 nerves of, 1585 structure of, 15S7 vessels of, 1585 Subpatellar fat, 405 Subperiosteal bone, 98 Sub-peritoneal tissue, 1742 Substantia nigra, nog Sulci, development of, 1190 fissures, cerebral, 113 5 Sulcus hypothalamicus, 11 19 Suprarenal bodies, 1801 accessory, 1S05 development of, 1804 growth of, 1804 nerves of, 1S03 pract. consid., 1806 relations of, 1801 structure of, 1802 vessels of, 1S03 body, lymphatics of, 983 Suture or sutures, 107 amniotic, 31 coronal, 216 cranial, 216 closure of, 233 lambdoidal, 217 sagittal, 216 Sylvian aqueduct, 1108 gray matter, 1109 Sylvius, fissure of, 1136 Sympathetic nerves, plexuses of, 1367 Sympathetic system, 1353 aortic nerves, 1364 association cords of, 1357 constitution of, 1355 ganglia of, 1356 gangliated cord of, 1355 gangliated cord, cervico-cephalic portion, 1358 lumbar portion, 1366 sacral portion, 1367 thoracic portion, 1364 nerve-fibres of, 1356 plexus, aortic, 1372 cardiac, 1367 carotid, 1360 cavernous, 1361 cavernous, of penis, 1374 coeliac, 1370 gastric, 1370 hemorrhoidal, 1374 hepatic, 1370 hypogastric, 1374 mesenteric, inferior, 1373 superior, 1372 ovarian, 1372 pelvic, 1374 phrenic, 1371 prostatic, 1374 THIS VOLUME CONTAINS PAGES 1 TO 995. INDEX. 1029 Sympathetic system, plexus, renal, 1371 solar, 1368 spermatic, 1372 splenic, 1370 suprarenal, 13 71 utero-vaginal, 1374 vesical, 1374 plexuses of, 1356 pract. consid., 1375 pulmonary nerves, 1364 rami communicantes of, 1356 splanchnic afferent fibres of, 1357 efferent fibres of, 1357 nerves, 1364 Symphysis, 108 pubis, 339 Synarthrosis, 107 Synchondrosis, loS Syncytium of chorion, 49 Syndesmosis, loS System, gastro-pulmonary, 1527 muscular, 454 nervous, 996 uro-genital, 1869 Tsnia chorioidea, 11 64 coli, 1660 fornicis, 1 163 semicircularis, 11 62 thalami, 11 19 Tapetum, 11 57 Tarsal bones, 419 plates, 1444 Tarsus, 419 Taste, organ of, 1433 ■ Taste-buds, 1433 development of, 1436 nerves of, 1435 structure of, 1434 Teeth, 1542 alveolar periosteum, 1553 bicuspids (premolars), 1545 canines, 1544 milk, 1545 cementum of, 1552 dentine of, 1550 development of, 1556 enamel of, 1548 homologies of, 1566 implantation and relations of, 1554 incisors, 1 543 milk, 1544 lymphatics of, 951 milk, eruption of, 1564 (temporary), 1542 molars, 1546 milk, 1547 neck of, 1542 permanent, 1542 development of. 1564 eruption of, 1565 relations of, 1554 pract. consid., 1591 pulp of, 1 554 pulp-cavity of, 1542 temporary, relations of, 1556 variations of, 1566 Tegmen tympani, 1496 Tegmentum, 1112 Tela chorioidea, 1097 subcutanea, 1384 Telencephalon, 1 1 3 2 Telophases of mitosis, 13 Temporal bone, 176 articulations of, 184 cavities and passages, 183 development of, 184 portion, petro-mastoid, 179 squamous, 177 tympanic, 179 lobe, 1 1 47 Temporo-mandibular articulation, 214 Tendo oculi, 484 Tendon, 77, 468 conjoined, 518 Tendon-cells, 78 Tendon-sheaths, 470 Tenon, capsule of, 504 space of, 1437 Tentorium cerebelli, 1199 Terms, descriptive, 3 Testis or testes, 1941 appendages of, 1949 architecture of, 1942 descent of, 2040 lymphatics of, 987 mediastinum of, 1942 nerves of, 1948 pract. consid., 1950 structure of, 1942 tubules seminiferous of, 1942 tunica albuginea of, 1942 vessels of, 1948 Thalamic radiation, 1122 Thalamus, 11 18 connections of, 1 1 2 1 structure of, 11 20 Thebesian valve, 695 veins, 694 Theca foUiculi, of hair, 1392 Thenar eminence, 607 Thigh, landmarks of, 670 muscles and fasciae of, pract. consid. 642 Third ventricle, 1131 choroid plexus of, 1131 Thorax, 149 articulations of, 157 in infancy and childhood, 164 landmarks of, 170 lymphatics of, 966 movements of, 165 pract. consid., 167 sexual differences, 164 subdivisions of, 1832 surface anatomy, 166 landmarks of, 1868 as whole, 162 Thumb, articulation of, 326 Thymus body, 1796 changes of, 1797 development of, 1800 nerves of, 1800 shape and relations of, 1796 structure of, 179S vessels of, 1799 weight of, 1797 Thyroid bodies, accessory, 1793 Thyroid body, 1789 development of, 1793 nerves of, 1793 pract. consid., 1794 shape and relations of, 1789 structure of. 1791 vessels of, 1792 cartilage, 1814 THIS VOLUME CONTAINS PAGES 1 TO 995. I030 INDEX. Thyroid cartilage, development of, 1S15 growth of, 181 5 gland, lymphatics of, 959 Tibia, 382 development of, 387 landmarks of, 390 pract. consid., 387 structure of, 387 variations of, 3 S3 Tibio-fibular articulation, inferior, 396 superior, 396 Tissue or tissues, adipose, 79 connective, 73 elastic, 76 elementary, 67 epithelial, 67 fibrous, 74 muscular, general, 454 nervous, 997 osseous, 84 reticular, 75 Tongue, 1573 foramen csecum of, 1574 frenum of, 1573 glands of, 1575 growth and changes of, 15S0 lymphatics of, 952 muscles of, 1577 nerves of, 1580 papillae, circumvallate of, 1575 filiform of, 1575 fungiform of, 1575 pract. consid., 1594 vessels of, i 580 Tonsil or tonsils (amvgdala), of cerebellum, 1086 faucial, 1600 faucial, relations of, 1602 lingual, 1575 lymphatics of, 954 pharyngeal, 1601 pract. consid., 1608 tubal, 1 503 Tooth-sac, 1562 Tooth-structure, 1548 Topography, of abdomen, 531 cranio-cerebral, 12 14 Trachea, 1834 bifurcation of, 1837 carina of, 1837 growth of, 1837 lymphatics of, 958 nerves of, 1836 pract. consid., 1840 relations of, 1836 structure of, 1835 vessels of, 1836 Tract or tracts, (fibre) rubro-spinal, 1 114 habenulo-peduncular, 11 24 mammillo-thalamic, 1121 of mesial fillet, 1076 olfactory, 11 52 thalamocipetal, lower, 11 22 Tragus, 1484 Trapezium, 311 Trapezoid bone, 311 Treitz, muscle of, 558 Triangle of Hesselbach, 526 rectal, 191 6 uro-genital, 19 16 Triangles of neck, 547 Trigone of bladder, urinary, 1904 Trigonum acustici, 1097 habenulae, 1123 hypoglossi, 1097 lemnisci, 1108 urogenitale, 563 vagi, 1097 Trochanter, greater, of femur, 352 lesser, of femur, 353 Trochlea of humerus, 268 of orbit, 504 Trochoides, 113 Trophoblast, 46 Truncus bronchomediastinalis, lymphatic, 968 subclavius, lymphatic, 963 Tube, Eustachian, 1501 Tuber cinereum, 11 29 Tubercle of Lower, 695 Tuberculum acusticum, 1097 olfactorium, 1 1 53 Tubes, Fallopian, 1996 Tunica vaginalis of scrotum, 1963 Turbinate bone, inferior, 208 articulations of, 208 development of, 20S middle, of ethmoid, 193 superior, of ethmoid, 193 Tympanic portion of temporal bone, 179 Tympanum, 1492 attic of, I 500 cavity of, 183 contents of, 1496 membrane of, 1494 pract. consid., 1505 mucous membrane of, 1500 oval window of, 1495 pract. consid:, 1504 promonotory of, 1495 pyramid of, 1496 round window of, 1495 secondary membrane of, 149S tegmen of, 1496 Tyson, glands of, 1966 Ulna, 281 development of, 285 landmarks of, 287 pract. consid., 285 structure of, 285 surface anatomy, 300 Umbilical cord, 53 allantoic duct of, 54 amniotic sheath of, 54 blood-vessels of, 54 furcate insertion of, 55 jelly of Wharton of, 54 marginal insertion of, 55 velamentous insertion of, 55 fissure of liver, 1708 hernia, 1775 notch of liver, 1707 vesicle, 42 Umbilicus, 37 Unciform bone, 312 Uncus, 1 1 54 Upper limb, muscles of, 568 Urachus, 525 Ureter or ureters, 1895 female, 1896 lymphatics of, 982 nerves of, 1898 pract. consid., 1898 THIS VOLUME CONTAINS PAGES 1 TO 986. INDEX. 1031 Ureter or ureters, structure of, 1896 Ureteral sheath, 1897 Urethra, 1922 crest of, 1922 development of, 1938 female, 1924 structure of, 1926 fossa, navicular of, 1924 glands of, 1925 lymphatics of, 986 male, pract. consid., 1927 structure of, 1924 meatus of, 1924 nerves of, 1927 orifice of, external, 1924 internal, 1904 portion, membranous of, 1923 prostatic of, 1922 spongy of, 1923 vessels of, 1926 Urethral bulb, 1968 crest, 1922 Urinary organs, 1869 development of, 1934 Uriniferous tubule, 1S77 Urogenital cleft, 2021 sphincter, 2049 system, 1869 Utero-sacral folds, 1743 Utero- vesical pouch, 1943 Uterus, 2003 attachments of, 2004 body of, 2003 broad ligament of, 2004 cavity of, 2003 cervical canal of, 2003 cervix of, 2003 changes of menstruation, 2012 of pregnancy, 2012 development of, 2010 fundus of, 2003 glands of, 2007 lymphatics of, 989 nerves of, 2010 OS, external of, 2003 peritoneal relations of, 2004 position of. 2007 pract. consid., 2012 relations of, 2007 round ligament of, 2005 structure of, 2007 variations of, 2012 vessels of, 2009 Utricle, 1514 prostatic, 1922 structure of, 1 516 Uveal tract, 1454 Uvula, 1569 Vagina, 2016 development of, 2019 fornix, anterior of, 2016 posterior of, 2016 lymphatics of, 989 nerves of, 201 8 pract. consid., 2019 relations of, 2016 structure of, 2017 variations of, 2019 vessels of, 2018 vestibule of, 2022 Vaginal process of inner pterygoid plate, Vallecula of cerebellum, 1083 Valsalva, sinus of, 700 Valve or valves, aortic, 700 auriculo-ventricular, of heart, 699 Eustachian, 694 of Hasner, 1479 ileo-CEecal, 1661 mitral, 699 of Morgagni, 1674 pulmonary, 700 of pulmonary artery, 700 rectal (Houston's), 1674 semilunar, 700 Thebesian, 695 tricuspid, 699 Valvulse conniventes, 1636 Vasa aberrantia of epididymis, 195c Vas deferens, 1954 ampulla of, 1955 lymphatics of, 988 Vasa vasorum, 674 Vater, ampulla of, 1 7 2 1 Vater-Pacinian corpuscles, 1018 Vein or veins, allantoic, ^;^ circulation, 929 angular, of facial, 864 auditory, internal, 869 auricular, anterior, 882 posterior, 8S3 axillary, 88 7 pract. consid., 888 azygos, 893 arch, 893 development of, 928 major, S93 minor, 895 superior. 895 pract. consid., 895 system, 893 basilar, 877 basilic, 890 median, 891 basivertebral, 897 brachial, 886 brachio-cephalic, 858 bronchial, 893 cardiac, 854 anterior, 8 56 great, 85 5 middle, 856 posterior, 856 small, 856 valves of, 856 cardinal, 926 posterior, 854 superior, 854 system of, 854 centralis retinje, 879 cephalic, Sgo accessory, 890 median, 891 cerebellar, inferior, 879 superior, 87S median, 878 cerebral, 877 great, 877 inferior, 877 posterior, 869 internal, 877 middle, 877 pract. consid., 878 superior, 877 cervical, ascending, of vertebral, S60 THIS VOLUME CONTAINS PAGES 1 TO 995. T032 INDEX. Vein or veins, cen'ical, deep, 859 luiddle, SS4 chordae Willissi, 870 choroid, 877 ciliarj', anterior, 879 posterior, S79 circulation, total, 929 circumflex, iliac, deep, 910 superficial, 917 of leg, 914 classification of, 852 clitoris, 909 colic, middle, 921 right. 921 condyloid, anterior, S74 confluence of the sinuses, 868 coronary, of facial, 865 inferior, of facial, 865 left, 8^5 right. 8 56 of corpus callosum. anterior, S78 posterior, 87 7 cavemosum, 907 striatum, 877 co.'"to-axillar>", 896 crico-thyroid, of superior thyroid, 867 cystic. 923 deep dorsal of penis (clitoris), 909 of forearm. 886 of hand. 886 dental, inferior. 883 superior. S83 development of, 926 diploic. S74 anterior, S75 occipital. 87 5 pract. consid.. 875 temporal, anterior, 875 posterior. 875 dorsal, of foot, 910 interosseous, 886 ductus Arantii, 929 arteriosus, 930 Botalli, 930 venosus, 929 emissaries of foramen lacerum medium, 876 emissary", 875 condyloid, anterior, 876 posterior. 876 of foramen ovale. S76 of Vesalius, 876 mastoid. S76 occipital, 876 parietal. S76 pract, consid., 876 epigastric, deep. 909 superficial, 017 superior, of internal mamman.", 860 ethmoidal. S79 facial, 864 common. 864 deep, S65 pract, consid., 864 transverse. 8S2 femoral, deep. 914 pract, consid,, 918 foetal circulation, 929 of foot. deep. 910 superficial. 914 foramen lacerum medium, 876 frontal, of facial, 865 of Galen, 856 Vein or veins, gastric, 923 short, 921 gastro-epiploic, left, 921 right, 921 gluteal, 905 hemiazygos, 895 accessor^■, 89 5 hemorrhoidal, inferior, 907 middle, 908 plexus, 90S superior, 922 hepatic, 902 pract. consid,, 904 hepatica communis, 900 Ueo-colic, 921 ihac, common, 905 pract. consid., 917 external, 909 pract. consid., 918 internal, 905 pract. consid,, 918 ilio-lumbar, 906 inferior cava, pract, consid., 900 caval system, 898 innominate, S58 development of, 859 pract. consid,, 859 intercapitular of hand, 889 intercostal, 896 anterior, of internal mammar}" 860 superior, 896 accesson.- left, 896 intervertebral, 898 jugular, anterior, 8S4 external, 880 posterior, 884 pract, consid,, 8Sx internal, 861 bulbs of, 861 prac. consid,. 863 labial, inferior, of facial, 863 superior, 865 lacunae of dural sinuses, 85 2 larjTigeal, inferior. 86 1 superior, of superior thyroid, 867 of leg, deep, 911 pract, consid., 918 of hmbs, development of, 929 lingual, deep, of facial, 867 of facial, 867 lumbar, 901 ascending. 901 mammary, external, 888 internal, 860 marginal, right, 856 marginalis sinistra, 8^5 of MarshaU, S56 masseteric, of facial. 866 mastoid emissar\". 869 maxillary', internal. 882 internal, anterior, of facial, 865 median, 890 deep. 886 mediastinal, anterior. 86 1 medulli-spinal. 808 meningeal, middle. 8S3 mesenteric, inferior, 922 superior. 921 metacarpal, dorsal. 8S0 nasal, lateral, of facial, 865 obUque. of heart. 695 of left auricle, 856 obturator, 907 This VOLUME CONTAINS PAGES 1 TO 995. INDEX. ^033 Vein or veins, occipital, S59 ophthalmic, anastomoses of, 880 inferior, S79 pract. consid., S80 superior, 879 ovarian, 903 palatine, ascending, of faciai, 866 inferior, of facial^ 866 palmar arches, 886 superficial, 890 palpebral, of facial, 865 pampiniform plexus, 903 pancreatic, 921 pancreatico-duodenal, 921 parotid, anterior, of facial, 866 posterior, SS2 parumbiUcal, 923 perforating, of internal mammary, 860 pericardial, 861 perineal, superficial, 907 peroneal, 911 pharyngeal, 863 plexus, 864 phrenic, inferior, 901 superior, 861 plantar, 910 external, 910 plexus, alveolar, 882 external, spinal, 897 hemorrhoidal, venous, 908 internal, spinal, 89 7 pterygoid, S82 sacral, 905 of Santorini, 909 venosus mammilla, 888 popliteal, 911 pract. consid., 918 portal, 919 accessory, 923 collateral circulation of, 923 development of, 928 of liver, 1709 system, 919 pract. consid., 925 pterygoid, plexus, 882 pudendal plexus, 909 pudic, external, 916 internal, 907 pulmonary, 8 52 anastomoses of, S53 pyloric, 923 radiaL 886 superficial, 891 accessory, 891 lenal, 902 pract. consid., 904 of Retzius, 924 sacral, anterior, plexus, 905 lateral, ■;o6 middle. 905 saphenous, accessory, 916 long, 9r6 short, 915 sciatic, 906 of septum lucidum, 877 sigmoid, 922 sinus, basilar, S74 pract. consid., 874 cavernous, 872 pract. consid., 873 circular, 872 coronary, 854 of dura mater, 867 Vein or veins, sinus, dural. blood-lakes of, 852 structure 01, 85 1 intercavernous, 87 2 lateral, 867 pract. consid., 869 longitudinal, inferior. 87 1 superior, 870 pract. consid., 27c marginal, S72 occipital, 872 petrosal, inferior, 874 superior, 874 spheno-parietal, 874 straight, 872 small, of Galen, S77 intestine, 921 spermatic, .903 pract. consid., 904 spheno-palatine, 882 spinal, 897 cord, 898 pract. consid., S98 splenic, 921 stemo-naastoid, of superior thyroid 867 structure of, 677 subclavian, 884 pract. consid., 883 :. 882 :ar\-, 8S2 ial, 890 th:ri;:-rri;.=-:-:. ?53 th-.-;i:. v;: thyr:id,inieri:r, i:: pract. consid., 861 iaid