DUPLICATE HX00017434 mr *' "r^l-^ 0 -^ M'v*V ' ■^irA'^"^t< ''-/y ■-^P» •r •-? Human Anatomy Digitized by the Internet Archive in 2010 with funding from Open Knowledge Commons (for the Medical Heritage Library project) http://www.archive.org/details/humananatomyincl19161pier The skeleton in reiatioii lo the contour of the body. HUMAN ANATOMY INCLUDING STRUCTURE AND DEVELOPMENT AND PRACTICAL CONSIDERATIONS BY THOMAS DWIGHT, M.D., LL.D. J. PLAYFAIR McMURRICH, PH.D. PARKMAN PROFESSOR OF ANATOMY IN HARVARD PROFESSOR OF ANATOMY IN THE UNIVERSITY OF UNIVERSITY MICHIGAN CARL A. HAMANN, M.D. GEORGE A. PIERSOL, M.D., SO.D. PROFESSOR OF ANATOMY IN WESTERN RESERVE PROFESSOR OF ANATOMY IN THE UNIVERSITY OF UNIVERSITY PENNSYLVANIA AND 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-CHIRURGICAL COLLEGE EDITED BY GEORGE A. PIERSOL VOL. I. FIFTH EDITION PHILADELPHIA & LONDON J. B. LIPPINCOTT COMPANY yn 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 oblii^^ations to the existing 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 helj) 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 supervising 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. vii 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, greatly 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. The Thoracic X'ertebra? — Covtimicd The Cervical Vertebr:e 1 16 The Lumbar Vertebr:e 1 17 PecuHar Vertebrae 119 Dimensions of Vertebrie 122 Gradual Regional Changes 122 The Sacrum 1 24 The Coccyx 127 Development of the X'ertebrcC 128 \'ariations of the X'ertebra; 131 Articulations of the X'ertebral Column . . 132 Ligaments Connecting the Bodies . . 132 Ligaments Connecting the Laminae 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 I44 Sprains, Dislocations and Fractures ; 144 Landmarks 146 The Thorax I49 The Ribs 149 The Costal Cartilages 153 The Sternum i55 Articulations of the Thorax 157 The Anterior Thoracic Articulations. 158 The Intersternal Joints 159 The Costo-Sternal Joints 160 The Interchondral Joints 160 The Costo-\'ertebral Articulations. . 160 The Thorax as a Whole. 162 The Movements of the Thorax 165 Practical Considerations : The Thorax . . 167 Deformities 167 Fractures and Disease of the Ribs . . 169 L andmarks 170 The Skull 172 The Cranium 172 The Qccipital Bone 172 The Temporal Bone 176 The Tympanic Cavity 183 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 208 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 F"ace 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 — Coniiiined 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 248 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 Slioulder- 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 285 Fractures 286 Landmarks 287 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. XI PAGE Practical Considerations: The Wrist- Joint.. 329 Landmarks . .^ 330 The Joints of the Carpus, Metacarpus and Phalanges' .<■, 630 The Bones of the Lower Extremity 332 The Pelvic Girdle 332 The Innominate Bone ._. . . 332 Joints and Ligaments of the Pelvis. . 337 The Sacro-Iliac Articulation. . . . 338 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 380 Disease of the Hip-Joint 380 The Framework of the Leg 382 The Tibia 382 Practical Considerations 387 Separation of the Epiphyses 387 Fractures and Disease 389 Landmarks 390 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 Patellae 400 The Knee-joint 400 Practical Considerations : The Knee- joint 409 Dislocations 409 Subluxation of Semilunar Cartilages 411 Disease of Knee-Juint 412 The Patella 416 The Bones of the Foot 419 The Tarsal Bones 419 The Metatarsal Bones 428 The Phalanges 432 Practical Considerations : The Foot- Bones 436 Fracture, Dislocation and Disease. . 437 Landmarks 437 The Ankle-joint 438 The Articulations of the Foot 440 Intertarsal Joints .' 445 Tarso-jMetatarsal Joints 446 Metatarso-Phalangeal Joints 447 Synovial Cavities 447 The Foot as a Whole 447 Stirf ace 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 Developinent 457 Striated or Voluntary Muscle 457 General Structure 458 Structure of the I\Iuscle-Fibre. . 459 Cardiac Muscle ^ 462 Development of Striated Muscle. 465 Myomeres and their Modifica- tions 467 GenerarConsideration of the Muscles. . . . 46S Attachments 468 Form .-;'. .'-. 469 Fasciae 470 Tendon-Sheaths 470 Bursae 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 480 Platysma Muscles 480 Superficial Layer. 481 Deep Layer 486 Practical Considerations : Muscles and Fasciae of Cranium 489 The Scalp 489 The Face 492 Landmarks 494 The Vago-Accessory Muscles 495 Muscles of Palate and Pharynx 495 Muscles of Larynx . . Vol. U 1824 Trapezius Muscles 499 The Metameric Muscles 502 The Axial Muscles 502 Orbital Muscles 502 Fasciae 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 xu CONTENTS. PAGE Practical Considerations — Continued Landmarks a nd Topography o f Abdomen 531 Anatomy of Abdominal Incisions. . . 535 Examination of Abdomen 537 The Thoracic Muscles 538 Rectus Muscles 538 Obliquus Muscles 538 Hyposkeletal Muscles 542 The Cervical Muscles 542 The Deep Cervical Fascia 542 Rectus l\iuscles 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 Muscles 558 Pel vie Fascia 558 Obturator Fascia 559 Pelvic Muscles 559 Perineal Muscles 562 The Appendicular Muscles 566 The Muscles of the Upper Limb 568 Muscles extending between Axial Skele- ton and Pectoral Girdle 568 Pectoral Fascia 568 Preaxial Muscles 568 Postaxial Muscles 571 The Axilla 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 588 Practical Considerations : Muscles and Fascia of the Arm 589 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 — Continued Preaxial Muscles 607 Muscles of First Layer 607 Muscles of Second Layer 610 Muscle of Third Layer 610 Muscles of IV and V Layers. ... 611 Postaxial Muscle 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 Thigh 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 Middle 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- Vascular System. The Structure of Blood- Vessels 673 The Arteries 675 The Veins 677 The Capillaries 678 The Blood 680 General Characteristics 680 Blood-Crystals 6S0 The Colored Blood-Cells 681 The Colorless Blood-Cells 684 The Blood-Plaques 685 Development of Blood-Vessels and Cells 686 The Heart 689 General Description 689 Position and Relations 692 Chambers of the Heart 693 Architecture of the Heart-Muscle. . . 700 Structure 702 Blood-Vessels and Lymphatics 703 Nerves 704 Development 705 Practical Considerations: The Heart. .. . 710 Valvular Disease 711 Rupture and Wounds 713 The Pericardium 714 CONTENTS. xui PAGE 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 728 The Innominate Artery 729 Practical Considerations 729 The Common Carotid Arteries 730 Practical Considerations 731 The External Carotid Artery 733 Practical Considerations 733 Branches of External Carotid Ar- tery 734 The Internal Carotid Artery 746 Practical Considerations 747 Branches of Internal Carotid Ar- tery 748 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 780 Branches of Ulnar Artery 781 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 y 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 821 Practical Considerations 824 Branches of Femoral Artery 826 Anastomoses of Femoral Artery ... 831 The Popliteal Artery 831 Practical Considerations 832 Branches of Popliteal Artery 833 The Posterior Tibial Artery 835 Practical Considerations 836 Branches of Posterior Tibial Artery. 8'8 The Anterior Tibial Artery 842 Practical Considerations 842 Branches of Anterior Tibial Artery, 844 The Dorsal Artery of the Foot 845 Development of the Arteries 846 The Veins 850 General Characteristics 850 Classification 852 PAGE The Pulmonary System 852 The Pulmonary Veins 852 The Cardinal System 854 The Cardiac Veins 854 The Superior Caval System 857 Vena Cava Superior 857 Practical Considerations 858 The Innominate Veins 858 Practical Considerations 859 Tributaries of Innominate Veins .... 859 The Internal Jugular Vein 861 Practical Considerations 863 Tributaries of Internal Jugular Vein. 863 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 878 The Ophthalmic Veins 879 Practical Considerations 880 The External Jugular Vein 880 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 889 Practical Considerations 891 The Azygos System 893 The Azygos Vein 893 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 .... 901 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 Foetal 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 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 Anatoiny 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 anthropotomy, 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 Anatmny. 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 sufifice to distinguish the numerous and varied members of the extended group. The fundamental anatomical feature of these animals is the possession of an axial column, 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 lir.MAN ANATOMY. of a jirimitivc axis, the )iotocJioyd, takes ])lace ainon^ the vwv\\ fonnatixe processes of the embryo. Ill addition to the fuiulaniental longitudinal axis. \ertel)rate animals exhibit a transxerse cleaxage into somatic or l)ody-segments. While such segmentation is rep- resented in the maturer conditions by the series of \ertebne 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 i)rocesses. Although these primary segments do not directly corre- spond to the permanent vertebne, 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 nervous 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 \ertebrate animal exhibits a fundamental \)h\\\ of construction in which bilateral syinnutrv is a conspicuous fea- ture. Viewed in a transverse section passing through the trunk, the animal body Fig. I. Neural arch Neural tube Spinal cord Vertebral axis- Costal segment Parietal mesoblast Parietal mesoblast Aorta •Parietal mesothelium ■N'isceral mesothelium • Entoblastic epithelium 'Subepithelial mesoblast \'iscerai mesoblast Diagrammatic plan of vertebrate body in transverse section. {Modified from Wiedersheim.') may be regarded as composed primarily of the axis, formed by the bodies of the vertebrae, 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 coelom, 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 oritice and opens posteriorly by the anus, is extended by two ^•entral 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, dixided into a venous and an arterial com- DESCRIPTIVE TERMS. 3 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 tru7ik, from which project the ventrally directed limbs, when these appendages exist. Just as the axial segments, represented by the bodies of the vertebrae, 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 plane, when central, passes through the long axis of the body vertically and bisects the ventral or anterior and the dorsal or posterior surfaces. The trayisverse plane passes through the body at right angles to its long axis and to the sagittal plane. ^\\& fro7ital 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. 2. Fig. 3. Three principal planes of human body. T, T, transverse ; S, S, sagittal ; F, F, frontal. Human embryo showing primary relations of limbs, c, a, preaxial surfaces ; b, 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 structures 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 haA'ing a limited specific and technical application and often not directly applicable to other 4 HUMAN ANATOMY. vertebrates. Superior and inferior^ upper and h7cer, as indicating relations towards or away from the head-end of the body, are, probably, too convenient and useful as expressin^;^ the peculiar relations in man to be readily relinquished, although when directly ap|)lied to animals possessing^ a horizontal body-axis they refer entirely to relations with the plane of support, the additional terms cephalic 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 expressing relations with the sagittal plane, are now largely replaced by the more desirable terms lateral and mesial respectively, external and internal being reser\'ed to indicate relations of depth. Cephalic and caudal, central and peripheral, prox- imal and distal, are all terms which have found extensive use in human anatomy. Preaxial and postaxial, in addition to their general and obvious significance with reference to axes 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 ; subsecpiently the limbs become folded against the body, the free ends being directed ventrally, while one border looks headward, the other taihvard. 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 homolo^ue and analoo^ue 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. Homolcgue, therefore, implies structural identity, analogue implies functional similarity. Parts are said to be homotypes A\hen 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 maybe 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 resolved into its component morphologi- cal constituents, the cells and the intercellular substances. The first of these are the ,^N Fig. 4. Nucleus Vacuole Pseudopod Vegetal food inclusions Exoplasm A^ unicellular animal {amceba) ; B. embryonal cell, — leucocyte. Endoplasm descendants of the embryonal elements derived from the division or segmentation of the parent cell, the ovum, and are highly endowed with vital activity ; 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 olT- spring of the ovum, or by 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 — \h^ 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 amceboid movements, from their similarity to the changes observed in the outline of an active amoeba, the representative of the simplest form of. animal life, in which 6 HUMAN ANATOMY. the single cell constitutes the entire organism, and as such is capable of i)erf()rniing the functions essential for the life-c\-cle of the animal. As the embryonal cell achances in its life-history, the conditions to which it is subjected induce, with few excejnions, further specializations, since in all but the lowest forms division of labor is associated with a corresponding differentiation and adaptation to sj)ecihc function. Vital manifestations t)f 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 distinctixe characteristic of living 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 anabo/ism, is the process by which the cell con\erts the simpler com- pounds into organic substances of great chemical complexity; destructive metabo/isui, or kafabolisni, 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. Growth, the natural sequel of the nutritive changes effected by metabolism, mav be unrestricted 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 laiequa/ grozvth, 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 observed 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. While the details of the process by which new cells arise from pre-existing cells are reserved 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 ox mitotic and the direct or amitotic. The first 'of these, involving the complicated cycle of nuclear changes toUectively 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 \'ital 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 low-est 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 nervous 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. 7 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 unsettled 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. Exoplasm Endoplasm Nuclear membrane Nucleolus Centrosome surrounded by centrosphere Cytoplasm Karyosoine Linin threads Chromatin Spongioplasm Hyaloplasm Metaplastic inclusions Diagram of cell-structure. In the upper part of the figure the granular condition of the cytoplasm is represented ; in the lower and left, the reticular condition. 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. Wliatever be the particular phase of structural arrangement exhibited by the cell, histologists are agreed that the cytoi)lasm consists of two substances, — an active and \.\ passiir : while both must be regarded as living, the \ital 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 sponi^ioplasm ; although conspicuous after aj)proj:)riate 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 hyaloj)lasm, a variable amount of foreign substances is frequently present ; these Fig. 6. A />' Spermatogenic cells, showing variations in the condition and the arrangement ol the 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 {Aleves) ; B, from the salamander X 500 (Meves) ; C, from the cat X 750 (von Lenliossek). 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 metaplasm. 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 njulear viembrane. 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 fibres 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 liniyi. 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 karyoso7)ies, as distinguished from the true nucleolus which is frequently present within the karyoplasm. Chemi- cally, chromatin, the most essential part of the nucleus, contains miclein, 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 paraliniji. The nucleolus, or plasmosorne, 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 exact 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 exact nature of this constituent of the nucleus must be deferred. The nucleolus is credited with containing a peculiar substance known as pyrenin. The term amphipyreyiin, as applied to the substance of the nuclear rnembrane, 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 . . ■ • ^ . . ,y degree, during other phases of cellular activity. • 1 \ ' ' ^ ^^ -^ ^ ' Ordinarily the centrosome escapes attention ^'X"^J Jfiidi -^^ '^ because, on account of its mmute size and varia- :• . < u-; *^ 'jf ble staining affinity, it is with difficulty distin- "' ' ' -^ - guished from the surrounding particles. Its D M^ 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 Zimmermann, this little _^ •' f^, body, or bodies, being often double, is always /^j ,^ '^Jii ^ found in that part of the cell which is the seat 4-'' t# -%f''^%^ of greatest change; thus, in a dividing ele- "^^ ' V "^ ment, the centrosome lies immediately related r»„f.^=^^»= i. .\ ■ %. " -,%. v ' - 1 1 • 1 • 1 • 1 • Lentrosomes (t, c) in human epithelium ; to the actively changing nucleus, while within a, B, cells from gastric glands; C, from duo- •T , 1 VI !• -^ • It ii. ._ denal glands; Z*, from tongue ; /, leucocyte with Ciliated epithelium it is remOVea from the nu- centrolome X 625. {K. W. zimmermann.) 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 V lO HUMAN ANATOMY. area or halo, the centrosphere or the attraction sphere, w ithin wliich it appears as a minute speck, frequently being double instead of single. In recapitulation, the chief constituents of the animal cell may be tabulated as follows : I Meshwork — Spottji^iop/asm. Cyt()pl;isiii -J Gniwnd-^uh^Xiiwcit—Hya/op/asm, containin.^: inclusions, Meta- \ plas))t. iLinin fibrils. Chrouiatiii (containinjf Nu- cleiu). I I Nuclear matri.K (containing /"flTrt//';//;/). I Nucleus \ \u(-/eo/us (conUuning /yreni/i.) I L Nuclear tneiiibranc. 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. Ay resting: stage, chromatin irregularly distributed in nuclear reticulum ; a, centrosphere containing double centrosome; n, 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 la. a) surrounding the separating centrosomes, connected bv the spindle (s). A", longitudinal cleavage of the chromosomes which are arranged around the polar field { p) occupied by the spindle, j^, migration of chromatic segments towards new nuclei, as established by centrosomes (c. c) ; <"/!, equatorial plate formed bv intermingling segments. G. separating groups of daughter chromosomes {d. d) united bv connecting threads (c t). H. daughter chromosomes id. d) becoming arranged around daughter centrosomes which have alreadv divided ; C. C. beginning cleavage of cytoplasm across plane of equatorial spindle. /, completed daughter nuclei '(/?, £>) ; c\loplasm almost divided into two new cells. {Modified fiom Wilson'). or as an exceptional method among ef?ete 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- yoki?iesis, 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, since 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 i7idirect division, include a series of changes involving the centrosome, C E W^^: H "^ \ Chromatic figures in dividing cells from epidermis of salamander embryo. X 960. A, resting stage; B close spireme ; C loose spireme; Z>, chromosomos (" wreath "), seen from surface; E, similar stage, seen in profile; /=", longitudinal cleavage oi chromosomes ; G, beginning migration of segments towards centrosomes ; H, 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 coordinatic)n. The purpose of the changes allfectiiig the chromatin is the accu- rate and equal division of this substance l)y the longitudinal clea\ age of the chroma- tin segments ; the object of the activity of the centrosonies 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 invoKe the nuclear substances and the centrosonies and result in the formation of the katyokinctic fji^urc ; 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 conxoluted thread or threads, constituting the " close skein ;" the filaments composing the latter soon shorten and thicken to form the "loose skein." The skein, or spireme, 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 7iumerical constancy, since it may be regarded as established that every species of animal and plant possesses a fixed 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 matrix 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 asters. The centrosonies 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 centrosonies become the foci of two systems of radial striation which meet and together form an achromatic figure known as the amphiastcr, 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 doubt 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 icreath ; the same segments, when viewed in profile, appear 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 tiie 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 existed within 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- grating chromatic segments, attracted by the linin threads, for a time form a com- pact group about the equator of the spindle known as the equatorial 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 fibres. Sometimes the latter exhibit a linear series of thickenings known as the cell-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 compara*-'ve rest until called upon, in its turn, to enter upon the com- plicated cycle of mitosis. MITOTIC DIVISION. lo Prophases. A. Changes within the nucleus : Chromatic figure. 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 figiire. 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, M HIMAX ANATO>n'. III. Anaphases. Rcarnini^emcnt of chroiiiosonics into two sjroups, Migration of groups towards j)oles of anijihiaster. Appearance of connecting fibres between receding groups, 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. AMITOTIC DIVISION. The occurrence of cell reproduction without the foregoing complex cycle of karyokinetic changes is known as amitotic or direct division. That this process does take place as an exceptional 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 foetal envelopes, may KiG. lo. be regarded as established beyond dispute. The essential dift'erence 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 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 vegetative condition, neither the chromatic nor achromatic figure is pro- duced, the activity of the centrosome, when exhibited, being possibly 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 cleavage of the cytoplasm, such processes resulting in the production of multi- In general, it may be assumed that cells which undergo direct division are elements destined to suffer premature degeneration, since such cells subserve special purposes and are not capable of perpetuating their kind by normal reproduction. Flemming has pointed out the fact that those leuco- cytes which arise by amitotic di\-ision. and therefore deviate from the usual mode of origin of these elements, arc cells which are doomed to early death; this form of cell-division among the higher forms must be regarded, probably, as a secondary process. C^ ®^:| Decidual cells showing amitotic division of nucleus {A-D) ; in K an attempt at mitosis has 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 ovuvi, 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 pelhicida, .014 millimetre in thickness, which in favorable preparations exhibits a radial striation, and hence is also named the zona radiata. 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 Fig. II. Corona radiata -Zona pellucida -Germinal vesiiie (nu- cleus) containuig 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 i7o. {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 vitellus, 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 vitelline mem,brane, 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, t\\e germi7ial 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. —b TaiH jjeneral are found, including the all-imj)ortant 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 unmatiux>d, ovum, although its jiresence 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 viiddlc-piccc, 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 neck-grannies, which lie in the neck immediately beneath the head, at the extremity 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 ser\es 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 ^%' oocyte (ovarian egg) Secondary oocytes (ff^K ond first polar body) Maturr efcf; and polar bodies Diagram illustrating the genesis of the male and female germ-cells. (After Boveri.) 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 sexual 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. Coincidendy 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 sex 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 ^\ r-x w ■**^'-2.-i».«=^'' B rvvJ R ■rxf «> G ^ ■ '^^ J K M Fertili7ation 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 ; n, nuclear figure; m, head of spermatozoon. D-G, entrance of spermato- zoon (s) into ovum and subsequent changes. H-M, sequence of changes during the formation, approach, and blend- ing of the male {m) and female (f) 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 the ovum, an effec- tual barrier to the penetration of additional seminal cells is i)resented by the thick vitelline membrane which immediately forms. The ])oint at which the spermatozoon is about to enter the e^^g is indicated by a conical elewation, the 7cccptive cmiticncc, into which the male germ-cell sinks, — the tail only partly entering the protoplasm of the egg and very soon disai)pearing. The position of the remains of the spermatozoon within the substance of the ovum is indicated by an ovoid body, the male pronucleus, which contains the chro- matin and centrosome of the paternal germ-cell. ^\\(t speriu-nucleus 7i.x\A \\\^ egg- nucleus, as the male and female pronuclei are now often designated, usually break up into their respecti\e chromosomes without fusing into a single segmentation Fig. i6. 3 O M Early stages of segmentation as seen in ova of n. . :. ., e view. X 450. {Sobolta.) The external double contour represents the zona pellucida; the cell marked wiih ^ , the polar body. A, fertilized ovum at stage of the pronuclei; 7^, 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; .F, six; G, eight ; //■, sixteen; /, twenty-five. nucleus. In this case the two groups of chromosomes unite in the first mitotic figure, the segmentation spindle (Fig. 17). After the fusion of the pronuclei, and just as segmentation is beginning, the fertihzed 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 Q%^. The centrosomes now present within the ovum are usually both derixed 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. 21 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 G H Early stages of segmentation as seen in sections of ova of mouse. X 500. (Sobotta.) A^-D show the rearrange- ment of the chromosomes contributed by the male (ni) and female (_/") pronuclei as preparatory to the first cleavage of the fertilized ovum; p,p, polar bodies; o of about fifteen days, showing formation of notochord from entoblast. High magnification. (After A'ollmanti.\ n, neural canal; c/i, cells forming notochord diflerenti- atiiig from entoblast {e) ; m, mesoblast ; s, early somite ; d, sections of primitive aortae. position of the intervertebral disks in which the chordal tissue during the first months after birth is represented by a considerable mass of central spongy substance ; (c) atrophy of the remains of the notochord, resulting in the entire disappearance of the chordal tissue within the vertebrae 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. Paraxial mesoblast / Ectoblast Amniotic cavitv Somatopleura Body-cavity Splanchno- Open Ento- Chorda Neural Visceral Bodv-cavity pleura gut blast tube mesoblast Transverse section of rabbit embryo of about nine and one-quarter days. X 80. Neural canal is now closed. the termination of the notochord, the prechordal portiofi, and that containing the notochord, the chordal poi'tion ; 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 ccelom, or primary body-cavity (Fig. 29). THE SOMITES. 29 The cleavage of the mesoblast, however, does not extend as far as the mid-Hne 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 \h& paraxial 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 laminae, the one forming the dorsal and the Fig. 33. Fig Neural canal -Somite -Chorda Intermediate cell- mass Primary gut-tube Parietal mesoblast Visceral mesoblast Transverse section of human embryo of about fifteen days, showing early difTerentiation of somite. X 210. (Kollmann.) Neural canal nt — ^^- tV" I Gut-tube -Coelom Transverse section of human embryo of about twenty-one days, showing differentiation of somite. X 90. {Kolbnann.) \ W7 Muscle- plate Fig. 35. — Dorsal border of m>otome -Cutis-plate other tjie 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 ventral 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 somatopleura (Fig. 29), the ecto-mesoblastic sheet of great importance in the production of the lateral and ventral body- walls. Similarly, the visceral mesoblast unites with the entoblast to form the splanchnopleura (Fig. 29), the ento-mesoblastic layer from which the walls of the primary digestive canal are formed. The Somites. — The paraxial mesoblast at an early 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 " -'^ J '? somites, or protovertebrce. This segmentation of the embryonic mass appears earliest at some Differentiation of myotome of human J. 1 1 • 1 1 11- embr\o of about twenty-one days. X 525- distance behind the cephalic end of the embryo, {Koiimann.) 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-mass (Fig. 33). Subsequently, Sclero- tome 30 HUMAN ANATOMY. the latter becomes separated from the remaining portion of the somite and is probably itlentiticd with the formation of the sej^niented excretory apparatus of the embryo, the Wolttian body, and hence is known as the ncphrotomc. The principal mass, includint;^ the ijreater part of the somite proper, consists of an outer or peripheral zone of condensed mesoblast enclosinj; 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 embryonic connective tissue which envelops the chorda and grows around the neural canal. The cell-mass derived from the core of the myotome constitutes the scUrotovic, and directly contributes the tissue from which the permanent vertebrae and the associated ligamentous and cartilaginous structures arise. The remaining denser j)art, 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 cutis-plaic, consists of se\'eral 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 vuisde-plate, give rise to the voluntary muscles of the trunk. The genetic relations of the somite, therefore, may be expressed as follows : SO.MITE I Myotome — imiscle sef(inent. -j Sclerotome — axial se^inejit. (. Nephrotome — excretory gland segment. Fig. 36. Embrvoiiic area Embryonic ectoblast Mesoblast Entoblast The number of somites of the human embryo is about thirty-seven, comprising eight cervical, twelve thoracic, fi\'e lumbar, fixe sacral, and from ti\e to se\en caudal segments. THE FCETAL MEMBRANES. The Amnion. — With the excejition 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 fcetal appendage, the allantoiSj is always de\eloped as a structure complemental to the amnion ; hence the am- niota possess both amnion and allantois. Since the dc\elopment of the foetal membranes in man presents certain deviations from the process as seen in other mammals, due to pecu- liarities affecting the early human embryo, it is desirable to examine briefly the forma- tion of these structures as ob- 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 2ind tail-folds. The rapid growth of these Cavity of blastodermic Entoblast vesicle Trophoblast Diagram of mammalian blastodermic vesicle. THE AMNION. 31 Ectoblast ) > Amnion •MesoblastJ Exoccelom pen gut-tube Splanchnopleura 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- taining a fluid, the liqtior amnii ; at first closely sur- rounding the embryo, the amniotic sac rapidly expands 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 Fig. 38. Serosa -Amnion Trophoblast Vitelline sac Entoblast Diagram showing formation of amniotic folds and of gut-tube; trans- verse section of axis of embryo. Amniotic sac Gut-tube produce a second external en- velope, 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 body of the embryo, but, on the other hand, assumes an important role in establishing the earliest connection between the embryo and the maternal tissues and, later, participates in the formation of the placenta. The ectoblast of the Diagram showing formation of amniotic folds and vitelline sac; longitudinal section of embryo. HUMAN ANATOMY. Amniotic sac Gut-tube primiti\c chorion is the direct cieri\ative of the original ectodermal layer of the blastodermic vesicle beyond the embryonic re.^ion proper, a layer which, on account of this important nutritive function, has been called by Hubrecht the troplwblast. As already noted (Fij;. 32), the cleft between the parietal and \isceral layers of the mesoblast is the primary body-ca\ity or ccelom ; with the separation of these layers foUowinjy the dorsal and the ventral folding associated respectively with the formation of the amniotic sac and the gut-tube, the intramesoblastic space becomes greatly exi)anded and extends between the amnion and primitive chorion. This large space is approjjriated only to a limited extent by the future definite body- cavity, and hence is divisible into an emJ:»ryonic and an extra-embryonic portion, or exoctelom (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 sac, 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 -Primitive chorion ^f j^e future alimentary canal, the intervening 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 I)ersists as a slender stalk terminating at its distal end in the remains of the yolk- sac. In animals other than mammals in which a pla- centa is de\eloped, the yolk-sac is the chief nutri- tive organ of the embryo ; the mesoblastic tissue of the vesicle becomes vascu- larized l)y the de\elopment of the blood-vessels consti- tuting the \itelline circulation, of which the vitelline or omphaloinesefiteric 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 arnnion, another foetal appendage, the allantois, makes its appearance as an out- CiL-Ioni Allantois Diagram showing completed \ itelline duct rosa, beginning allantois and THE VITELLINE SAC. 33 growth from the caudal segment of the primary 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 embryo 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 chorio7i. The latter, sometimes spoken of as the allantoic chorion in contrast to the amniotic or primitive chorion, now becomes the most important envelope of the mammalian embryo on account of the role that it is destined to play in establishing the respira- FiG. 40. Primitive chorion Amnion Amniotic sac Allantois ■^Vitelline sac Diagram showing villous condition of serosa, expanding allantois, and diminishing vitelline sac. tory and nutritive organ of the foetus, 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 foetus, 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 allayitoic arteries^ which are extensions from the aortic stem of the embryo and convey venous blood, and the two allantoic veins, which return the oxygenated blood to the embryo 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 foetal blood, are important structures on account of their intimate relations with the uterine mucous membrane (Fig. 41 J, in conjunction with which 3 34 HUMAN ANATOMY. they form a respirative and nutriti\c apparatus. The intimacy between the uterine mucous membrane and the chorionic tufts presents all degrees of association, from simple apposition, as seen in the sqw, 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 Ectoblast Amniotic meso- blast Subchorionic space Vitelline sac Space between am- nion and chorion — AUantois -Allantoic blood- vessels —Allantoic sac Villi of placental chorion Mesoblast Entoblast "Maternal blood-spaces 'Decidua placentalis Diagram showing villous chorion, difTerenlialion of placental area, and 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 2iS placental ia, of which three subgroups are recognized depending upon the multiple ( cotyledons j, Fig. 42. K c D \, 2'-.L '<&f.^ "vWJ-~"' \^^■ ^^^-t^l^' Diagrams illustratmg the various types of development of the chorion. A, uniformly developed villi (hog, horse) ; .S, multiple placentae 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 t^. foetal 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 extent 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 fcetus. After rupture consequent upon the expulsion of the foetus at the termination of pregnancy, the deciduae, including the specialized placental portion, are separated from the uterine wall and expelled as the inembranes 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 coelom, 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 study of some of the lower types ; beyond these very early stages, however, 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 implantation, 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 extent ; 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 extra 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 earliest human embryo accurately studied shows a completely closed amniotic cavity, while in 36 HUMAN ANATOMY. a very 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 cavity, dividing this layer into two parts, the inner jxirt going to form the ectoblast of the amnion, the outer part being a continuation of the trophoblast of the chorion. There is here e\idently a very great development of the extra-eml)ryonic coelom. In explanation of this condition, it may be assumed that the entoblastic sac is at first much smaller than the trophoblastic covering of the vesicle ; that the mesoblast, shortly after its appearance, Fig. 43. Diagrams illustrating development of human foetal membranes. Stage .-f is hypothetical ; others are based on stages which have been actually observed. Red represents trophoblast; purjjle, embryonic ectoblast; gray, meso- blast; blue, entoblast. ar, amniotic cavity; a/, allantois ; am, amnion; b, body-stalk; ch, chorion; ee. embryonic ectoblast; en, entoblast; g, gut-tube; >/?, mesoblast ; /, placental area; /, trophoblast ; z/, yolk-sac ; z/j, 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-embryonic body cavity. This diagram corresponds roughly to the condition of Peters' embryo (Fig. 44). The trophoblast is greatly thickened ; its outer surface very irregular, showing lacunae or spaces filled with maternal blood. This early intimate contact of the foetal tissue with the maternal blood permits nutrition of the young embryo 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 extra-embryonic coelom has invaded the sheet of mesoblast above the amniotic cavity 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 embryo. 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 embryo. 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 embryonic area. The ectoblast of the amnion is on the inner side facing the embryo, 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 between 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 embryo 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-intestinal duct. This constricted area is brought about by the rapid growth 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 extent ; the tail end also projects somewhat. There is a corresponding growth of the gut within the body of the embryo. As a consequence of this process of expansion 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 (/?, al) the allantois projects from the posterior end of the embryonic 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-embryonic coelom 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 embryo, 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 villi. 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 expanded. 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 body-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 body-stalk projects from _ beneath the extreme posterior end of the body of the embryo, but as growth in this part of the body advances and the tail projects more and more, the body-stalk is brought to the ventral surface of the abdominal region in close proximity to the yolk-stalk. The allantoic blood-vessels grow from the embryo through the body-stalk to the chorion, where they ramify in the chorionic villi. At first there is an extension of the coelom 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 very much reduced m size and is known in the adult, after the separation of the cord, as the umbilicus or navel. 38 HIMAX ANATOMY. The chorionic villi at the pt)int of attachment to the chorion of the body-stalk are enlarged. These villi constitute the fcetal portion of the placenta, the so-called chorion frondosum. They are imbedded in the maternal decidua, more specihcally, the decidua (uxsalis ox piacentalis. It must be remembered that the villi contain a core of mesoblast tissu.; in the stage represented by diagram R, although this meso- blastic core is not shown in the figure, and that the allantoic blood-vessels run in Com p. f Ca I Fig. 44. B. z. : M. B. L. B.L. Section of mucous membrane, decidua. of a pregnant uterus containing imbedded in it an extremely young D ■"#" embryonic vesicle, described by Peters, a, b. points of entrance of embr^ onic vesicle ; B. L.. blood lacunae ; B. /C., Bordering zone; Ca., capillary in uterine tissue; Caf>.. beginning of decidua capsularis ; Comp , compact tissue of uterine mucosa; E., embryo; ^., gland of uterus : .1/ , mesoblast ; Sv.. svnc\-tium ; T. M., covering tissue over break in uterine surface; 7>-., trophoblast ; C/. .£., epithelium of uterine mucosa. ' X ^o {Peters). this mesoblast: also that the villi are in reality considerably branched, not straight as m the diagram. The remainder of the chorion is acquiring a smooth surface and is commonly known as the choyion Iczve, as a means of distinguishing the extra- placental portion of this membrane. The yolk-sac, in man called the unibili.cal vesicle, at the extremity 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 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. up, the chief peculi- FiG. 45. mem- \X-,. To sum up, the chief arities of the human foetal branes are the following : 1. The amniotic cavity is 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 coelom ; 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 embryo 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. Fig. 46 Ectoblast. Vitelline sac Amnion Amniotic sac Gut-tube Vitelline sac- Reflected amnion- Medullary folds- Medullary groove- Neurenteric canal- Primitive streak- Belly-stalk- Chorion Chorionic villi .;"r=-~ ■ ■ J ~^ "~ "' Dorsal surface of early human embryo, two millimetres in length. X 23. {After Spec.) The amnion has been divided and turned aside. Wall of vitelline sac Belly-stalk Primitive streak Chorion Longitudinal section of human embryo represented in preceding figure. X 23. {After Spee. 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 ])()ints a, h in the figure hes the area throu^li which the embryonic growth has made its way into the mucous membrane of the uterus, and, in consequence, the uterine epithehimi in this area has disapjK-ared. Above this small area there lies a co\ ering mass of tissue ( T. M. ) mainly composed of blood, the result evidently of hemorrhage ft)llo\ving 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. P'irst, there is the thickened and very 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 Amnion Umbilical or yolk-sac. .S : ^ Body-stalk- Chorion Human embryo of about twenty days, enclosed within the amnion. X 30. blood-lacunse 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 (v^/) 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 laver of the trophoblast Sy can be distinguished. The proportionally large cavity within the vesicle is extra-embryonic coelom, 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 above 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 IcEve) 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 frondosum and the chorion Iceve, as the placental and non-placental portions of the chorion respectively are termed (Fig. 48 J. 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 aninii. 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 tighdy 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 deciduse. The amniotic fluid, slighdy 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 foetus 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 .4 Placental area // {Chorion frondosum) \^^'L^^ ',' ^*i External surface of part of the human chorion of the third month ; the lower portion is covered with the highly developed villi of the placental area. 42 HUMAN ANATOMY. litres, due to pathological conditions of the ftetal envelopes ; such excessive secre- tion constitutes hydramnioti. 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. While it has been impossible to determine accurately the extent to which the mother participates in the formation of this fluid, it may be accepted as established that the maternal tissues are the principal contributors ; it is also probable that the foetus likewise aids in the production of the liquor amnii ; the latter, therefore, orig- inates from a double source, — maternal and foetal. The early amniotic fluid resembles Fig. 49. Umbilical vesicle- Umbilical stalk Inner surface ^i»iSf of chorion ^^ V Umbilical cord — Cut edge of amnion- Masses of chorionic villi- Human embryo of about thirty-three days. X 4. Amnion and chorion have been cut and turned aside. in appearance and chemical composition a serous exudate ; later, after the formation of the urogenital openings, the liquor amnii becomes contaminated, as well as aug- mented, by the addition 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 imperfectly 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. Amnion Umbilical vesicle, (yolk-sac) Inner surface of chorion Chorionic villi of outer surface Chorionic sac of thirty-five day embryo laid open, showing embr>-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 tanbilical cord or funiculus. The latter originates, therefore, from the fusion of three chief com- ponents, the amniotic sheath, the belly-stalk, and the vitelline duct ; the belly-stalk. 44 HUMAN ANATOMY. as already noted, includes the allantt)is, 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, a 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 lunbilicus, 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 MeckcV s diverticulum. The latter is con- nected with the ileum at a point most frequently about 82 centimetres (thirty-two inches) from the ileo-ceecal 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 de\'elopment of the fcetal envelopes, undergo profound modifications ; these changes must next be considered. The Deciduae. — The birth of the child is fcllowed 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 decidual for the mater- nal portion of the foetal 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- brane, known as the decidzia refiexa, as distinguished from the decidua 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 decid^ia serotina ; later it becomes the maternal part of the placenta. Fig. 51. Duct of gland Spiral portion of gland Process of muscular ^ tissue extending be- ^ tween the glands Muscular tissue Uterine blood- vessel Uter ne mucous membrane h part of muscular t ssue Y 40 Our knowledge of the details regarding the encapsulation of the ovum ha= 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 modified conception of the early phases of the encapsulation of the ovum, as well as shed additional light on some of the vexed problems concerning the details of the formation of the placenta. According to these investigations, the embiyonic vesicle, on reaching the uterine 46 HUMAN ANATOMY. Diagrams representing relations of the uterine mucous mem- brane to the embryonic vesicle, or ovum, during the emhedding of the latter. .?, v, c, decidua serotina, vera, and retlexa, re- spectively ; o, ovum. cavity and becoming arrested at some favorable point, usuallv in tlie vicinity of the oviduct, brings about a degeneration of the uterine epithehum over the area of contact. The disappearance of the epithehal Hning 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 extravasated 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 x^fc ^^ ^^P^^ j'^^"'^\. ""* i^ii earlier jxriod than was formerly \ ^ M I --.„^^ recognized. \» m L. — ga "f IfJ iff in> TheTrophoblast. — Theear- \ » ml _-- ^^ licst human embrvonic vesicle that \^L ^^/ s^^^MBISlB^^==~3 ^'^^ been accurately studied, — that \if^f ^^^^^mpT^tm^^^^ 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 tro[)hoblastic, 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. Coincidentlv 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 embryonic 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 nearly 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 Dia-i and matci 11.11 blood-vessels. ( Peters. ) :73g~Uterine muscle ittachment between fcEtal trophoblast by maternal 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 coinpact 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 Free surface Enlarged gland Blood-vessel Enlarged gland Uterine muscle Section of mucous membrane lining body of uterus (decidua vera) ; fourth month of pregnancy. {After Leopold.') fectly its normal condition to the close of pregnancy. After the expulsion of the decidual portion of the uterine mucous membrane, the epitheliui^i 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 matrix 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. Blood-space Enlarged lumen — k; of glands Amnion Choi ion Decidua reflexa Blood-space of compact layer Spongy layer Muscle '.■2c-< Section through ftetal membranes and uterus at margin of the placenta; sixth month of pregnancy. {After Leopold.) muscular tissue are clothed with well-preserved e[)ithelium ; the lining cells of those towards the compact layer, on the contrary, early atrophy and disappear. The Decidua Placentalis. — The decidua placentalis, ox decidua serotina, being destined to contribute the maternal portion of the jjlacenta, 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 giayit cells, make Fig. 56. 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 foetal blood-streams are brought into close relations. The proliferating trophoblastic tissue invades 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 foetal 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 Sections of chorionic villi from placenta. X 170. a, b, small branches of umbilical artery and vein; r, capillary vessels; c, cell- aggregations of syncytium (d ) \ m, mesoblastic stroma of villi. THE PLACENTA. 49 Fig. 57. Main stalk 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 foetal mesoblast, and (<5) the epi- thelial covering derived from the trophoblast. The investment of the villi consists of two layers, — an inner stratum, next the connective- tissue core, composed of low, distinctly out- lined polyhedral cells, the chorionic epiihe- liu7n, and an outer stratum, the syncytitim, 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 foetal 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 chorionic villi from placenta. X3S. Fig. 58. Chorionic mesoblast Mesoblastic core of fcetal villus Trophoblast Syncytium Maternal blood-space Muscle Endothelium Maternal blood-vessel Diagram showmg formation of placenta {Petets ) 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 canalised 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 is 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 50 HUMAN AXATOMV. Its con\ex t^xternal or uterine surface is roui^h, 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 fcetal 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 even 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 Uterine blood-vessels Fig. 59. Maternal blood-spaces Foetal villi Decidua placentalis Umbilical vesicle Decidua capsular! Amnion Chorion Decidua vera Interdecidual space Amniotic sac ' Diagfram illustrating the relations of the foetus, the membranes, and the uterus during the early months of pregnancy. of the fcetal and the maternal portions, has already been sketched ; it now remains to consider briefly the arrangement of these structures. T\\Q 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 foetal 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 foetal circulation. THE PLACENTA. 51 The 7naternal 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-vessels of the mucosa. The extension of the blood-spaces thus originating constitutes the elaborate system of vascular lacunae, or intervillous 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 Villus Chorion Villus '%■■ Placenta. .^Placental septum Decidua serotina ( ,.-'' ,Line of separation ..Uterus Spiral branches of uterine artery Inner limit of muscle Arteries Section of placenta and uterus at the seventh month. {Ecker.) line of separation passes through the junction of the former spongy and compact layers ; according to Webster, however, the separation occurs in the compact layer. The condensed decidual tissue closing in the vascular lacuna, on the one hand, and covering the surface of separation, on the other, constitutes the basal plate. The latter is continued deeply within the placenta by connective-tissue portions, the septa placentcB, which extend between the groups of chorionic villi, forming the cotyledons visible on the outer surface of the placenta as irregular lobules separated by deep furrows. These septa do not reach as far as the chorion except at the margin of the placenta, where they form a thin membranous sheet beneath the chorion, the subcho- rionic occluding plate of Waldeyer. Large, round, multinucleated elements, the giant cells, measuring from .04 to .08 millimetre in diameter, are present within the tissue of the maternal placenta, especially within the basal plate and the septa. At the margin the placental tissue becomes directly continuous with the fcetal mem- branes, the chorion and the decidua being closely united. The numerous branches of the arteries supplying the uterus pierce the muscular tunic and gain the basal plate ; here the arterial vessels lose their muscular coat and 52 HUMAN ANATOMY penetrate the placental septa as spirally tlirecteci channels of enlartjed calibre bounded by endothelial walls. After a shorter or longer coiu'se within the septa, the arterial Fig. 6i. -= — Stalk of \illus Intervillous blood-spaces Section of larger villus Intervillous blood-spaces Maternal blood-vesseT Maternal blood-space Maternal blood-vessel ^fr- — Basal plate Torn surface at line of separation Section of human placenta at end of pre^ancy. X 12. The foetal blood-vessels have been injected ; the maternal blood-spaces appear as clear areas surrounding the sections of the foetal villi. trunks open directly into the intervillous or intraplacental blood-spaces which are limited by the chorion and the villi on the one side and by the septa and basal plate THE UMBILICAL CORD. 53 on the other. Maternal capillaries are wanting within the placenta, since they have become early replaced by the intervillous lacunae. The maternal blood is carried away from these spaces by wide venous channels which pass directly from the lacunae through the placental septa into the basal plate, where they form net-works from which proceed the larger venous trunks. At the edge of the placenta the anastomosing cav- ernous spaces form an annular series of intercommunicating venous channels known collectively as the marginal si7ius , into which empty numerous placental veins, on the one hand, and from which, on the other, pass tributaries to the larger veins of the uterus. Fig. 62. Umbilical vein Umbilical arteries Corrosion preparation of human placenta, showing general grouping of fcetal vessels into lobules. The Umbilical Cord. — The umbilical cord, or funiciclics lunbiHcaHs, which connects the body of the foetus with the placenta, thereby conveying the foetal blood to and from the respiratory and nutritive apparatus, is formed in consequence of the fusion of three originally distinct structures, — the belly-stalk, the vitelline stalk, and the amnion. The first of these, in addition to forming the early attach- ment of the foetus to the chorion, supports the rudimentary allantoic canal and the allantoic, later umbilical, blood-vessels. The vitelline stalk encloses the diminish- ing vitelline duct and the remains of the vitelline blood-vessels, while surrounding these stalks the amniotic sheath gradually becomes more closely applied. These 54 HUMAN ANATOMY. Fig. 63. Umbilical vein Remains of allantoic duct three constituents of tlie cord lie embedded within the delicate stroma formed by the gelatinous connective tissue, theyV//)' of W'hartoi, surrounded e.xternally by the common amniotic investment. The details of the cord must necessarily vary with the period of gestation, since the component structures undergo marked changes. On section of the funic- ulus at the end of pregnancy, the following features may usually be distinguished : (i) The amniotic sheath, which is closely united with the underlying connective tissue, except for a short distance beyond the umbilical opening, at which point the amnion may be separated as a distinct layer. (2) The yVV/v of Wharton forms the common ground-substance in which the remaining constituents of the cord lie embedded. This tissue corresponds to the mucoid type, and contains a generous distribution of stellate connective-tissue cells which form a reticulum by their anastomosing i:)rocesses. (3) The nnibilical blood-vessels — two arteries and one vein — are the most con- spicuous components of the cord, since their size increases with the demands made by the growing foetus. The markedly tortuous umbilical arteries usually entwine the single umbilical vein and slightly increase in lumen in their progress towards the placenta, in the immediate vicinity of which an anastomosis very constantly is to be found. Seldom in man, but always in certain mammals, as the mouse, the umbilical artery is single. According to His, even the youngest human cords possess only a single umbilical vein, except in the immediate vi- cinity of the placenta ; again, on entering the body of the foetus the single vessel is represented by two umbilical veins which, for a time, course within the abdominal wall. The right vein, however, soon un- dergoes atrophy, while the left takes part in the formation of the hepatic circulation. Valves have been described within the um- bilical vein. The latter shares with the pulmonary vein the distinction of conveying blood which has been oxygenated by respi- ratory function. (4) The allayitoic duct, as a distinct canal, is usually obliterated by the third month of fcetal life ; at birth, however, atrophic remains, consisting of a narrow column of epithelial cells situated between the umbilical blood-vessels, are seen in sections of the cord taken from the \icinity of the navel. The stalk of the vitelline sac, or umbilical vesicle, enclosing the vitelline duct and supporting the vitelline, or omphalomesenteric, blood-vessels, is still present during the second month ; at this period it lies within the extension of the coelom, which is continued into the young cord. With the early disappearance of this space the vitelline stalk and the associated structures disappear, and by the end of gesta- tion usually all traces of these structures have vanished from the cord. The most conspicuous details of the umbilical cord at birth, therefore, are the three umbilical vessels, embedded within the gelatinous connective tissue and invested by the sheath of amnion. The human umbilical cord is conspicuous on account of its exceptional length, which averages from fiftv to sixty centimetres, while measuring only about twelve millimetres in thickness. The extremes of length include a wide range, varying from twelve to 160 centimetres (four and three-quarters to sixty-three inches). The cord almost constantly exhibits a torsion, the spirals passing from left to right when traced towards the placenta. In addition to the general twisting of the cord, which begins towards the close of the second month, the umbilical arteries display even more marked spiral windings, usually enclosing the somewhat less twisted umbilical vein. The cause of this conspicuous torsion is probably to be sought in the spiral growth of the umbilical blood-vessels, the twisting of the cord, as well as the revolutions of the foetus, being secondary. Remains of vitelline duct and vessels Umbilical artery Transverse section of umbilical cord of third month. X 12. THE AFTER-BIRTH. 55 Artery Artery Vein Transverse section ot umbilical cord at end of pregnancy, taken from placental end; the umbilical blood-vessels are em- bedded within the embryonal connective tissue. X lo. While the attachment of the cord usually is situated near the middle of the placenta, it is seldom exactly central ; the insertion is subject to great variation, however, the eccentricity sometimes being so great that the cord is fixed to the periphery of the placenta, such disposition constituting insertio marginalis. Among the more exceptional variations in the arrangement of the cord are the cleft and the extraplacental attachment known respectively as insertio furcata and insertio vela- mentosa. In the former condition, where the cord divides before reaching the pla- centa, each limb conveys one of the umbilical arteries and a branch of the umbilical vein. When the insertion of the cord is into the chorion entirely p^ g outside the placental .area, in ex- ceptional cases being as far re- moved as the opposite pole of the membranous capsule, the umbilical vessels course within the non-vil- lous portions of the chorion until they reach the foetal placenta. In addition to the true knots, which often occur and are due to the excursions of the foetus, the um- bilical cord sometimes presents nodular thickenings and irregular constrictions, as well as projections formed by loops and varicosities of the blood-vessels. The After-Birth.— The ex- pulsion of the child through the rupture in the enveloping mem- branes, which is produced by the powerful contractions of the uterine muscle at the close of pregnancy, is followed, after a short interval, by the separa- tion and expulsion of the ' ' after-birth ;' ' under this term are included the placenta and the enveloping membranes. The latter, as will be understood from the fore- going consideration of the encapsulation of the fcetus, consist of three chief constit- uents,— the remains of the decidua vera, the chorion, and the amnion ; the reflexa undergoes complete absorption. Since the decidua represents the shed portion of the modified uterine mucosa, the outer surface of the after-birth appears rough and studded with shreds of uterine tissue ; the inner surface of the decidua is so closely fused with the adjacent cho- FiG. 65. rion by means of delicate connective tissue that only '--"- ^^-5 a limited and uncertain ^-s-zr^ separation is possible. The ^ , , _ amnion, on the other hand, • ~ ^ although attached to the chorion by bands of connec- tive tissue, may be peeled off the chorion with relative ease, since the union be- tween the two membranes is never firm. The inner ectoblastic surface of the amnion in contact with the fcetus is smooth and bathed in the liquor amnii. The external and unshed portion of the modified uterine mucosa contains the incon- spicuous remains of the epithelium lining the fundus of the glands : these elements are of the utmost importance for the regeneration of the glandular and epithelial tissues of the new uterine mucous membrane, since the reparation of these struc- tures, which is effected within a few weeks after labor, begins in the proliferation of the deeper glandular epithelium, which remains throughout pregnancy as the latent source of subsequent repair. Amnion Chorion Decidua Remains of uterine glands Uterine muscle ^^->.£r^ Section through foetal membranes and uterus at end of pregnancy. {After Leopold.) .St' HUMAN AXATO>n' DEVELOPMENT OF THE GENERAL l^ODV-FORM. In considering the evolution of the external form of the human i)n)duct of con- ception, it is convenient to recognize the three developmental epochs suggested by His, — the stage of the o\um. the stage of the cnibrvo, and the stage of the foetus. The Stage of the Blastodermic Vesicle. — This stage, or the sfa(^c of the oz-ii»i, embraces the first Xwo weeks of intra-utcrine life, during which the initial phases of de\'elopment, including fertilization, segmentation, and the formation of the blasto- FiG. 66. Embn-o with amnion ''^ -Villous chorion Ectoblast Mesoblast Belly-stalk Umbilical vesi- cle; blood- islands appear- ing Early human embryonic vesicle ol about thirteen days laid open, showing the young embryo (.37 millimetre long) attached to the wall of the serosa by means of the belly-stalk. X 25. (After Spee.) 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- ^"^'- 67- 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 appro.xi- 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 ventral, or vegetative, tube, formed by the ventral extension and approximation of the somatopleura, constitutes the body-cavity, and encloses the primary gut and the associated thoracic and abdominal viscera, and the vascular system. The primitive gut-tube originates by the delimitation of a part of Mesoblast ..... ^ .-.-,. ..^,... ---Belly-stalk Allantoic duct Cmbilical sac Section of preceding embryonic vesicle and embryo. X 25. {After Spee.) 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-grooves, in consequence of T^ 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). .8 HUMAN ANATOMY. Cephalic flexure Optic vesicle Maxillary process Mandibular proces: of first visceral arch Caudal end of embryo Umbilical cord ia section Lower limb-bud Human embryo of about twenty-three days, drawn from the model of His. ,\ 10. Second visceral arch Third visceral arch Fourth visceral arch 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 uinlMlical 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 eml)ryos of the fourteenth and fifteenth days (Fig. 68, 3 and 4) are distinguished by a conspicu- ous tle.xure opposite the attach- ment of the umbilical 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- marv 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 Jlexure, in the vicinity of the middle cerebral vesi- cle, in consequence of which the axis of the anterior cere- bral segment lies almost at right angles to that of the niiddle 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 time, those of the upper ex- tremity slightlv preceding those of the lower. The period between the twentv-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 axis, which, with the exceptions already noted, up to this time is only slighdy 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). Fig. 70. Otic vesicle / Cephalic flexure Optic vesicle Mandibular process of first visceral arch Olfactory pit Umbilical cord- Cervical flexure •Second visceral arch Third visceral arch Fourth visceral arch Heart •Upper limb-bud Lower limb-bud' # .X Human embryo of about twenty-five days, drawn from the model of His. X 10. THE VISCERAL 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 axial 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. Cervical flexure Otic vesicl Maxillary process of first visceral arch Cephalic flexure Third visceral arch First external visceral furrow Second visceral arch Mandibular process of first visceral arch Dorsal flexure \ — J| Upper limb Heart Lower limb Sacral flexure Human embryo of about twenty-eight days, drawn from the model of His. X lo. 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 which 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 intervertebral 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 five 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 h'ning 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 sui)i)lied by a blood-\essel, or aortic bow, which passes from the main \entral stem, the truncus arteriosus, through the substance of the visceral arch backward to unite with the similar bows to form the dorsal aortcE. In aquatic vertebrates the aortic bows sujiply an elaborate system of secondarv 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 external and internal grooves, the visceral furrows 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 Fig. 72. Second arch Third arch Fourth arch . -^Fifth arch Head of human embryo of about twenty-one days, seen from the side, showing visceral arches and external visceral furrows. X 20. (After His.) fissures are closed by the occluding 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 of the opposite side and the fronto-nasal process, which descends as a median pro- jection 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 types. 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 Reichert) is derived the smaller cornu of the hyoid bone ; the dorpal 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, \\\& perfo- rating stapedial ay'tery, 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 hyomandihdm' cleft, undergoes obliteration except 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. Tuberculum impar 4 ;| I ^ -4 Primitive larynx IV -HPT"'""" Sl ^ ^^^~~^ — 1 — Primitive aortae Jyis^ ' — Neural tube Optic vesicle Maxillary process Dorsal wall of primitive oropharynx Primitive oesophagus Upper end of body-cavity Right umbilical vein 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 behind. 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 prcEcervicalis of His — in the lower and lateral part of the future neck region. This recess subsequently entirely disappears 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 fistula, 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 potiches, 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 HIMAX ANATOMY. Fronto-nasal process Mesial nasal process Maxillary process Mandibular process Head of human embr>-o of about twenty-seven days showing boundaries ot primitive oral cavity. X 7 {^/ter His.) dorsal expansic^n tjives rise to the middle ear, while the oceludinin plate separating the outer and inner furrows supplies the tissue from which the tympanic membrane is formed. The second furrow in ^reat \y.\vX. disa[)j)ears, 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 docs 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 pharynx in the \icinity of the second \isceral arch. The Development of the Face y^o.-^x- and the Oral Cavity. — The earliest suggestion of the primitive oral cavity is the depression, or stomodwum, which ap- Laterai nasal process pears about the thirteenth day on the ventral surface of the cephalic end of the embryo immediately beneath the ex- panded anterior cerebral vesicle. The oral pit at first is separated from the ad- jacent expanded uj^per end of the head- gut by the delicate septum, the pharyn- 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 maiidibnlar 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 Y\c,. 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 fronto-7iasal 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 foreshadow^s the future close association between the olfactory mucous membrane and the corte.x of the olfactory lobe. During the fifth week the thickened margins of the fronto-nasal process undergo differentiation into the juesial tiasal 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 process First external vis- ceral furro Second visceral arch Third visceral arch Head of human embrvo ot about thirty-four days. '{After His.) X5- THE STAGE OF THE FGETUS. 63 Fig. 76. Aniage producing nasal tip Nasal groove Naso-optic groove' Oral surface of maxillary process Dorsum of nose •Lateral nasal pro- cess Mesial nasal pro- cess Maxillary process of first arch Roof of oropharynx Portion of head of human embry-o of about thirty-four days, showing roof of primitive oral 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 independently 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 they 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 alae, while from the conjoined 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 Foetus. — 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 stage of the foetiis 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- tions of the future fingers, which thus anticipate the appear- ance of the toes. The liver is already conspicuous as a 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 foetus 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. 7 Head of human embryo of about seven weeks. X 5. {After Ecker.) 64 HUMAN ANATOMY. progressed tliat tinkers and toes are distinctly intlicatcd, altlunij^h the tinkers only- are imperfectlv separated. The first snti^gestion of the external ijenitals appears about the end of the sixth week. At this time the foetus measures about nineteen millimetres. During the seventh and eighth weeks the ftetal 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 hails 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 dex'elojied Wolffian body, the vesical dilatation of the allantoic duct, the separation of the cloaca into rectum and genito-urinary passage, the indif- FiG. 78. Umbilical vesicle - Umbilical stalk - Inner surface of- amnioii Umbilical cord- •1l9f^. ^y- Human embryo of about thirty-five days. X 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 fiat, 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 foetus is efTected by the further de- velopment of parts already formed and not by the accession of new organs. The beginning of the second month marks the period of s;reatest relative growth; at the end of this month the foetus measures about thirty millimetres in its longest dimension. STAGE OF THE FCETUS. 65 The third month is characterized by greater perfection of the external form, 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 well developed wath 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 difierentiated during the ninth and tenth weeks into the genito-urinary and Fig. 79. Umbilical cord ■ Umbilical stalk Allantoic vessels Umbilical vesicle . Human foetus of about eight weeks. X 3^- Amnion has been cut and reflected, but still covers the umbilical vesicle and its stalk. the anal orifice, while during the eleventh and tAvelfth weeks the external 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 rnonth 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-foetal portion oi the intestinal canal, which at an earlier period passes into the umbilical cord, duriiiij the fourth month recedes within the al)domen. The differentiation of sex is still more sharply exhibited by the external organs : in the male the penis is acquirin«j[' a prepuce, and in the female the labia majora and the clitoris are becoming;- well developed. At the close of this period the fcttus measures approximately 15b millimetres and weiijlis about 120 grammes. Durint^ the fifth month the first foetal movements are usually observed. The heart and the liver are relatively of large size. The decidua capsularis fuses with the decidua vera, thereby obliterating the remains of the uterine cavity. The meco- nium within the intestinal canal shows traces of bile. The advent of the fine hair, the /a/N/i^o, first upon the forehead and the eyebrows, and somewhat later upon the scalp and some other parts of the body, represents a conspicuous achance. 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 ajjpearance of the vernzx 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 fiuid. The latter now reaches the maximum quantity, being contained within the large sac of the amnion. The sixth month is distin- guished bv the conspicuous increase both in the size and weight of the foetus, and is known, therefore, as the period of greatest absolute gro'ccth. At the close of the sixth month the foetus 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 plunii)ness 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 a\erage weight, while included between widely varying extremes, may be assumed as approximately 3100 grammes, or 6.8 pounds. The weight of the fcetus 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 testation. 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 connective, the muscular, and the nervous 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 extensive 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 by 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 membrana 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 columnar, — with sub- divisions as shown in the following table : VARIETIES OF EPITHELIUM. I. — Squamous : a. Simple, — consistin2: of a single layer. b. Stratified, — consisting of several laj'crs. 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 single 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 stnitijicd s<^ua)U0HS epithelia. When Fig. 8i. Fig. 8o. V / Simple squamous epithelium from anterior capsule of crystalline lens. X 400- Section of stratified squamous epithelium from anterior surface of cornea. >' 500. 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. Owing to the more favored nutrition of the deepest stratum, the cells next the connective tissue exhibit the greatest vitality, and often are the exclusive source of the new elements necessary Fig. S2. Fig. 83. :■•"'> ^, Isolated surface cells from epithe- lium lining the mouth. X 350. Epithelial cells from epider- mis, showing intercellular bridges. X675. 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 Xh^ 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. 84. Fig. 85. Fig. 86. i§,^^^^ Transitional epithelium from bladder of child. X 300. Simple columnar epi- „^ .^ , , .^, ,. thelium from intestinal Stratihed columnar epithehum mucosa. X 750. f™'" ^'^^ deferens. X 500- possesses relatively few layers, and from the readiness with which the type of the cells changes, is often described as transitio7ial epithelhmi ; the latter cannot be regarded as a distinct variety, but only as a modification of the stratified scaly group. Columnar epithelium, when occurring as a single layer of cells, constitutes the simple columnar variety, 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 by several, as in the stratified columnar variety, the superficial cells alone Fig. 87. si!« Tihated border J^Goblet- * cells Stratified ciliated columnar epithelium from trachea of child. X 550. Fig. 88. B Ciliated epithelial cells. A, from intes- tine of a mollusk (cyclas) ; B, from nasal cavity of frog. X 750. {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. 70 HUMAN ANATOMY. Fig. 89. Goblet-cells irom epilheliuni lining large intestine. X 500. Modified Epithelium. — The free surface of the epithehuni in many locahties, 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 in\estigations 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 hbrilke, which apjiear as delicate striations within the superficial and more highly specialized i)arts of the cells. In man and the higher mammals ciliated epithelium is limited to the columnar variety. The exact numlier 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 sufifi- cient supply of moisture, oxygen, 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 the goblet-ceils, 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 rui)tures 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. Examples 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 polvhedral, 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 netiro- epithelium is applied. Conspicuous examples 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 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 body, constitute endothelium. 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 mesothelium, and later give rise to the characteristic plate-like elements which constitute the Fig. 92. 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 hsematoxylin, 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 observed 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 between 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 infrequendy the intercellular substance, at points where several endothelial cells are in apposition, shows irregular, deeply colored areas after silver staining ; Endothelial cells lining artery of dog, after silver staining. X 500. 72 HUMAN ANATOMY. these figures are described as stig^mata ox pseudostomata, and by some are interpreted as indications of the existence of openings leading from the serous cavity into the subjacent lymphatics. Critical examination 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 passages. True orifices or stomata, however, undoubtedly exist in certain serous membranes, as in the septum between the peritoneal cavity and the abdominal lymjjh-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, the i^uard or ger- 7ninatinp^ 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 atlult lK)dy, 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 lixer 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 Wolf^an 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 layers 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. Fig. 93. 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-« 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. Immature 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. De7ise fibro-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 nuchse or the ligamenta subflava, result. 4. Cartilage, fibrous, elastic, and hyaline varieties. 5. Bone and dentine, 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 Embryonal connective-tissue cells from the umbilical cord. X 500. 74 HUMAN ANATOMY. tissues are usually described as of two kinds. — ihi; Jixcd or connective-tissue cells proper, and the migratory or xvandcring cells. The latter, while frequently inclutled 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-tissue cells from subcutaneous tissue of cat embryo. X 590. '^^Mm Granule-cells (mast-cells) from submucous tissue of mouth. X 1000 7', V, sections'of blood-vessels. Fig. 96. Connective- tissue cell (Fixed cell) The typical connective-tissue 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. Gramile-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 afifinity for dahlia and other basic aniline stains. They include the plasma-cells of Waldeyer 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, irregularly branched pii>;ment-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, ccll-bodv. The Intercellular Constituents of the connective substances occur in three forms, — -fibrous tiss?/e, reticular tisstie, and elastic tisstie. Fibrous tissue consists morphologically of varying bundles of silky fibrils of Section of subcutaneous tissue, showing the usual constituents of areolar tissue. X 300. FIBROUS TISSUE. 7.5 such fineness that they possess no appreciable width. The fibrils are united by and embedded within a semifluid groimd-siibstance , which may be present in such meagre amount that it suffices only to hold together the fibrillae, or, on the other hand, it may constitute a large part of the entire intercellular tissue, as in the matrix of hya- l^IG. 97. Fig. 98. 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. Pigmented connective-tissue cells from choroid. X 400- 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 as 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 lymph-spaces, Fig. 99. which, in suitably stained prepara- _^-^_ ., ..^.j^-'^^^^ tions, appear as irregularly stellate clefts that form, by union of their 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 have 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 connective tissue from cornea of calf the surrounding ground-substance has been stained with argen tic nitrate. X 525. 76 HUMAN ANATOMY. Fig. loo. Connective-tissue cells from cornea of calf which occupy cell-spaces similar to those shown in preceding figure, y 525. 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 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 connectixe 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 active participation of the young connective tissue cell, the peripheral zone of its protoplasm, known as ex- oplasm, being directly transformed into fibrillae. In consideration of the careful observations of Flem- ming, it is now widely believed that the method of formation of the fibres of connectixe tissue directly 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 the fibrillae 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 Fibrous and reticular connective tissue from human liver after pancreatic digestion. / 230. 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 fibrillae and the associated connective- tissue cells. Within the walls of the large blood-vessels the elastic tissue is arranged as membranous expansions containing numerous Fig. 102. openings of varying size : \\\^s^ fenestrated mem- branes, as they are called, are probably formed by the junction and fusion of broad ribbon-like elastic fibres. Elastic tissue yields elastin upon Fig. 103. -^ J Reticular connective tissue from lymph- node. X 350. The cells lie upon the fibrous tissue at the points of intersection. Portions of isolated elastic fibres from ligamen. turn nuchae 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 afhnity 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- ^''^- ^°4- ing to the view of an independent origin, the older one, the elastic fibres first appear as rows of minute beads in the intercellular matrix. These linearly dis- posed beads gradually fuse, thus produc- ing the primary elastic fibres. According to the view of an intracellnlar 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 Elastic fibres in section Interfibrillar connective tissue ^^ ^^ , Nucleus of con =^-r;^^'^_, nective-tissue ^"^^A-J^'-O^ -) ^ cell '^t '^ <#■ "^ "" -^ Transverse section of ligamentum nuchas of ox. X 45°- 78 IIIMAN ANATOMY. of the ribrous tissue, held together by cement-substance, are associated as compara- tively lar^-e primary bundles, which in turn are united by interfascicular fibrous Fig. 105. Fig. iu6. Tendon-bundle Profile view Oblique view- Surface view Blood-vessel within septa enclosing tertiary bundles Longitudinal section ot tendon irom young subject; Tendon-bundles from tail of mouse, showing difiereni the tendon-cells are seen in profile between the bundles views of the cells. X 3°0' of fibrous tissue. X 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- tive-tissue elements, here known as the tendoji-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 expand. Seen from the surface, these cells appear as nucleated quadrate bodies v'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 extended 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 Primary bundle Transverse section of a tendon, showing grouping of primary, secondary, and tertiary bundles of tendon-tissue. X S5. ADIPOSE TISSUE. 79 times exhibit a delicate stippling due to the transversely sectioned fibrillae. 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. io8. J /•^.'^r Adipose tissue from omentum. X i6o. The fat-cells are arranged as groups between the bundles of connecli\e tissue. 109. 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 I^'g. 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 protoplasm enclosing oil- drop Young fat-cell- Connective-tissue cells Young fat-cells from subcutaneous tissue. X 550. 8o HUMAN ANATOMY. tissue does not occur even when developed to excess in other parts. As ordinarily seen, adipose tissue is of a lij;ht 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 starvation, 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 variety, 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, zwdjibroiis. 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 evident. The cartilage-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 lacunce, 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 matrix 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. ■r=z. — Perichondrium Voung cartilage- cells Group of older cells. /CP ^^> '^ Cartilage-cells often stains with greater intensity, thereby producing the appearances known as the cell-areas. The lacunae of hyahne 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 lacunae. The free surface of cartilage is covered by an envelope of dense connective tissue, the perichondrmni ; the latter consists of an external fibrous layer of dense fibro-elastic tissue and an inner looser stratum or chondrogenetic 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 lacunae, 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, hmited 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 a\so yellow elastic or reticular czv\.\\z.ge (Fig. in), 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 $?j/x ^ a, (^^ ^^^w^ ~c^ - Lacuna contain- ing nest of cells ^2^- ^'A [^' "Empty lacuna surrounded by hyaline matrix •>/ 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 matrix of hyaline cartilage. The matrix 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 hvaline areas, and closely resemble the elements of hyaline cartilage. Elastic carti- lage possesses a perichondrium of the usual description. Fibrous cartilage, or fihro-cartilage (Fig. 1 12), 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. Fig. III. ;:' -^^'t. {*Si.> -jSvWV- 4 ,'^'^■'' Hyaline areas- Elastic net-work - of intercellular tissue V'. Lacuna contain- V.,^. ; i — . /^ /"'■'^ - v'' "i' ''^ £&. ^wf' ^mM .Section of elastic cartilage from the epiglottis. X 450. ing cell In its physical properties this tissue resembles both fibrous tissue and cartilage, pos- sessing the flexibility and toughness of the former combined w'ith the firmness and elasticity of the latter. A proper perichondriuni is wanting. In structure fibro-cartilage closely resembles dense fibrous tissue, since its prin- cipal constituent is the generally parallel wavy 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 dif?er 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 through the influence of these elements. DEVELOPMENT OF CARTILAGE. 83 Cartilage grows in two ways : (a) by the expansion produced by the inter- stitial growth effected by the formation of new cells and the associated matrix, and (<^) by the addition of the new tissue developed by perichon- Pig. 112. drial gj^owth 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 COnneC- ' -Hyaline area ,, . , . , surrounding tive-tissue cells 01 the perichon- cartiiage-ceiis driumintothecartilage elements, ^ and the accompanying formation ^ of new matrix. The development of the elastic fibres within the elastic V cartilage is secondary, the matrix \ during the early stages of growth J' - -Fibrous inter- being hyaline. The elastic tis- ' ^ttn^'f '''^' sue first appears in the form of minute granules, which later fuse and become the elastic ' *" ^ fibres ; this change first appears V 7 — Cartiiage-ceiis in the vicinity of the cartilage- ' ^ cells, the elastic reticulum sub- ' v.-.- x ^, . - . . \> sequently invading the more re- ^-^v-x^NiV-^ ^ . „ '^^V^s^s^.-^^^v^i 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 mucoid 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, elastin is found in place of collagen. In reticular tissue reticulin 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 cartilage. Water 67.67 73.59 Solids 32.33 26.41 Organic matter ' 30-i3 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 com.paratively large amount of olein. Small quantities of lecithin, cholesterin and free iatty acids are also found in fat tissue. 84 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 entoskcleto7i, osseous tissue occurs in the lower ver- tebrates associated with the integument as an exoskelcton. 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 exists within various organs in certain animals and then constitutes the splanchnoskeleton. Examples 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 : Organ'ic matter Gelatin and blood-vessels, 33.30 f Calcium phosphate, 5i-04 I Calcium carbonate, 11.30 Inorganic matter -j Calcium fluoride, 2.00 Magnesium phosphate, 1.16 Sodium oxide and sodium chloride, 1.20 lOO.CX) PHYSICAL PROPERTIES OF BONE. 85 Fig. 1T3. Physical Properties. — Rauber has shown that a five-milHmetre 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 ca7icellated 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 lamellae 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 axis 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 anipH- fication (Fig. 114), is seen to be composed of osseous layers arranged as three chief groups : {a) the circumferential lamellce, which extend parallel to the external and internal surfaces of the compact bone ; {_b) the Haversian lamelhc, which are disposed concentrically and form conspicuous annular groups, the Haversian systems, enclosing the Haversian canals ; and (r) the interstitial or (ground lainelhr, which constitute the intervening more or less irregularly arranged bony layers tilling up the spaces between the Haversian systems and the peripheral strata. Fig. 114. ■:>^;:)fe» -Extertial ciriutnfeten- tial lamella: Haversian canal sur- rounded by Havel - sian laniellaj )^^*^ '•3P-^¥" "V^. ty^- ■Internal circumferen- tial lamellae Transverse section of compact bone (metatarsal) ; the section has been ground and dried, hence the lacuna; are filled with air. X 85. Each Haversian system consists of the concentrically disposed lamellae and the centrally situated channel, or Haversian cajial, enclosing the ramifications of the medullary blood-vessels and associated marrow-tissue. Between the annularly arranged lamellce 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 canalic7ili, 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 lacunae 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 lacuna present their narrower dimensions, appearing thus in profile as small lentiform spaces ; seen in sections, on the contrary, which pass parallel to the lamellae (Fig. 118), 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. Circumferential lamellae Interstitial lamellae Haversian canal Obliquely cut Haver- sian canal Longitudinal section of compact bone, ground and dried. X 85. 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 growth 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 oi fibrosis tissiie 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 hiyers together. These fibres are especially numer- ous in the superficial lamellae beneath the periosteum, to which membrane they owe their formation, and with which many seem to be directly continuous. They are Fig. Section of frontal bone, showing the absence of Haversian systems. Y 20. 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- 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 Portion of adjacent Haversian svstems cut transversely. X 250. ■ THE BONE-CELLS. 89 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 Volkviann' 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- Fig. 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 bone-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 lacunae. 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- Lacunae and canaliculi from dried bone cut parallel with the lamellae. X 300. 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 deeply staining nucleus appears as a brilliant point within the stellate cell. The Periosteum. — The external surface of bones is closely invested, except where covered with cartilage, with a fibrous membrane, the periosteum, 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 immature 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 inner fibro-elastic ; when covering young bones, however, in which growth is actively progressing, the peri- Semi-diagrammatic view of perforating fibres of Sharper ; the lamellae of decalcified bone have been partially' separated. 90 HUMAN ANATOMY. osteum contains an additional stratum, the osieogeticlic layer, vviiich lies closely asso- ciated with the exterior of the bone. After growth has ceased, the osteogenetic layer l^ecomes reduced to an inconspicuous stratum included as part of the fibro- elastic constituent of the periosteum. The fibro2(s 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. I 20. •'^-^:r'^:<^2^2^r**^ 'fr',^, -^^^^^rntx^*^'- Lacuna Fig. 121. ^V:^^ Oblique section of decalcified tibia, showing fibrous character of lamella; and groups of Sharpey's fibres. X 420. 'WxQ fibro-clastic layer consists of a rich felt-work of elastic fibres, often arranged as several distinct strata ; the elastic tissue is separated from the surface of the bone by a layer of fibrous tissue comparatively rich in flat, plate-like connective-tissue cells, the remains of the elements of the osteogenetic layer. The inner surface of the periosteum is intimately attached to the osseous tissue by means of delicate processes of connective tissue which accompany the blood-vessels into the nutrient canals ; this relation persists from the continuity of the formative tissue of the young periosteum with the early marrow-tissue. Between the fibrous bundles next the bone numerous cleft-like lymph-spaces exist ; these are imperfectly lined by the endothe- lioid connective-tissue cells and communi- cate with the lymph-channels within the bone. The osteoge7ietic layer, conspicuous 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 are disposed in rows upon the surface of the developing osseous 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- .1 Bone-cells Ivins' within the lacunae. THE RED BONE-MARROW. 9i lated tissue, are filled with bone-marrow. The latter also extends 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 vertebrae, 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 filling the young bones is directly derived. The red marrow is, therefore, Fig. 122. Last formed lamella of bone Periosteal blood vessel passing iiiti the bone Dense fibrous layer Marrow-tissue continu- ous with periosteum Bone-cell within ■. — —^ .~'- i?,- .1 '-■«;.' s.*-^ui — i-_i — l^; , :' ■■ ly''i^'pV Remains of osteogenetic 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 within 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 fixation 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 endosteion, 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 marroxc-ccUs, (2) the cosinophile cells, (3) \.\\^ i^iant cells, and (4) the nucleated red blood-cells. The marrow-cells, or myelocytes, resemble the large lymphocytes of the blood, but mav differ from the latter in their slightly larger size and in the possession of a relatively large round or oval nucleus which contains comparatively little chromatin; the j^resence of neutrophile granules within the cvtoplasm of the marrow- cells affords an additional differential characteristic when compared with the large lymphocytes in which these granules are absent. The eosinophile cells occur in considerable numbers within the red marrow, and appear in varying stages of growth, as evidenced by their round mononuclear, the indented transitional and segmented polymorphonuclear condition ; the cells con- taining the latter form of nucleus are most abundant and represent, probably, the mature elements. The giant cells, or myehplaxes, are huge elements of irregular oval form, and contain simple or polymorphous nuclei. They represent specialized myelocytes, Fig. \2x. Marrow-cells Voung red blood-c Giant eel Blood-vessel Blood-vessel Connective-tissue reticulum '^i^^s^fc^S®^- Section of red marrow Irom epiphysis of jouiig femur, y 300. 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 How ship' s lacioia (Fig. 128). The nucleated red blood-cells within the red marrow are concerned in the important function of renewing the colored cells 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-formitisr or^^an. 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 haemoglobin 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, th.^ 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 canals') communi- cating with the Haversian canals, within which they 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 7?iedullaty canal to gain the 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 coming into 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 HUMAN ANATOMY. Nerves. — The periosteum contains a considerable number of nerves, the ma- jority of which, however, are destined for the supply of the underlyins^'^ 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 fibrilLe to be, probably, distributed to the walls of the vascular branches along which they lie. Regarding the ultimate endings and arrangement of the sensory fibres 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 exceptions, 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 exercise of the powerful modifying influences exerted by the action of the attached muscles. Since the primary formation of such bones takes place within the cartilage, the process is appropriately termed endochondral developmeyit. 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- viem6ra7ious development. 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. Even in those cases in which the intracartilaginous mode is conspicuous, as in the de- velopment 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 they 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 fatal cartilaginous skeleton. These segments are invested by an immature form of perichondrium, ox primary periostejan, 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 osteogejietic layer; the latter is rich in cells and delicate intercellular fibres. The initial changes appear within the cartilage at points known as centres of ossification, which in the long bones are situated about the middle of the future shaft. These early changes CFig. 125) involve both cells and matrix, which exhibit con- spicuous increase in size and amount respectively. 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 foetus of about three and one-half months, show- ing the partially ossified skeleton. Two-thirds natural size. DEVELOPMENT OF BONE. 95 -Embryonal cartilage nuclei. The enlarged spaces enclosing these cells are sometimes designated as the primary areolce. 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 ossification 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 7?iarrow-cavity, now occupies the centre of ossification and contains the direct continuation of the osteogenetic layer. This tissue, the priynary marrow, which has thus gained access to the interior of the cartilage, contributes the cellular elements upon which a double idle devolves, — to produce osseous tissue and to remove the embryonal cartilage. The cartilage-matrix closing the enlarged cell-spaces next the pri- Fig. 125. mary marrow-cavity suffers absorp- tion, whereby the cartilage-cells are liberated and the opened spaces are converted into the sccojidary areolcB, 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 of 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 trabecule, 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 constructive process is instituted by the osteoblasts by which the bone- tissue is formed. These specialized connective tissue elements, resting upon the Cartilage-cells be- coming enlarged and regrouped Enlarged cartilage- cells at centre of ossification Periosteum Section of tarsal bone of foetal sheep, showing centre of ossifi- cation. X 50. 96 HUMAN ANATOMY. irregular trabecuK-e 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. Em Young periosteum Cartilage-cells becoming en- larged and grouped «! ,y ■- ^-^ — ^— a-- ;?-.=^^~ -^'=:. '; I,', //.-J I' Zone of calcification Osteogenetic layer of perios- teum Central spongy bone en- closing remains of carti- lage Longitudinal section of metatarsal bone of foetal sheep, showing stages of endochondral bone-development. X 4°- trabeculae, 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 matrix (Fig. 127), until, ENDOCHONDRAL BONE. 97 Osteoblasts Bone-cell Section of a portion of osseous tra- becula and fcetal marrow. X 375. 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 lacunce, at this immature stage the canaliculi being still unformed. The early bone-matrix 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. Fig. 127. 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 bo7ie. 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- FiG. 128. (,gl]g 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' s lacuna, produced in consequence of the erosion and absorption of the osseous matrix which they ef?ect. 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 7 Osteoclast Osteobiasts Portion of trabecula of spongy bone undergoing absorp- tion by osteoclast. X 500. 98 HUMAN ANATOMY. Fig. 129. in the limited situations where tlie central spon_y;y bone persists, as in the vertcbrse, the ribs, the sternum, and the ends of the long bones. The important fact may be here emjjhasized 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 cartilao;c is never directly converted into bone. The ossification 0/ the epiphyses (Fig. 130J, 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 marrows-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-existing 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 intramembranotis. 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 fibrill^e, about which is deposited the Embryonal cartilage Zone of calci- fication Endochondral spongy bone Periosteum Subperiosteal bone Young mar- row Endochondral spongy bone Zone of calci- fication Embryonal cartilage Longitudinal section of phalanx of foetus of five months. X 23- SUBPERIOSTEAL BONE. 99 new bone-tissue, the osteoblasts becoming enclosed within the homogeneous matrix to constitute the bone-cells. The osseous trabecula thus begins to increase not only Fig. 130. Articular cartilage Columns of carti- lage-cells Spongy bone o! epiphysis ;■'. .- 1^:^~'- — Marrow-tissue - Epiphyseal bone -^\Si.< Remains of carti- lage separating bone of epiphysis and diapliysis ■ Diaphyseal bone • Marrow-tissue Longitudinal section including epiphysis and upper end of diaphysis of long bone of cat, just before osseous union of the head and shaft takes place. X 50. in length, by the addition of the last-formed matrix upon the supporting fibres, but also in width, by the deposition of new layers of osseous material by the osteoblasts. loo I UMAX ANATOMY. These cells cover the exterior of the trabecuhe as they lie surrounclecl by the young marrow-tissue which extends from the osteogenetic layer of the periosteum into the intertrabecular spaces. The union of the young trabecuke results in the production of a subperiosteal net-work of osseous tissue, [.he pcripfirral spongy bone. The l.itter 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 tield (Fig. 131). Ftg. t.^i. Fibrous layer of periosteum Osteogenetic layer of peri- osteum Osteoblasts St formed bone trabecula Bone trabecula Osteoblasts niary mar- ow Bone trabecula Remains of car- tilage Portion of developing humerus of fietal sheep, showing periosteal and central spongy bone. X i6o. 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. lOI \ 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 f layer in which the membranous bones / are formed. The earliest evidences of i 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- quendy 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- Parietal bone of human foetus of three months, trabecular net-work of intramembranous bone. showing X5. I02 HUMAN ANATOMY. ter of the shaft as well as in thickening of the osseous wall separating the medullary cavitv 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 trabecuke 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 lengtli of the lione 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 e.xisting cartilage-cells. On attaining the ma.ximum 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 element;? 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 appeyidic- tilar ; 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 axial 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 vertebree, 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 The tinted portions constitute the axial skeleton ; untinted, the appendicular skeleton. the I04 HUMAN ANATOMY. central, many-jointed rod bent forward near tlie top, with \ery perfect bony walls behind and abo\e 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, respiratory, urinary, and reproductive organs. The Appendicular Skeleton has an entirely distinct origin ; it is the frame- work of the limbs. It consists of two s^hdhs, a thoracic and a pelvic, to each of which is attached a series of segments, the terminal one of which expands into five rays,^'///i,'^fi/>/n's/s iuu\ Svfidrs/uos/s. I ram the stand-pomt ot development, there is no fundamental ilifference between symphyses and the true joints. In both cases a small ca\ity appears withm the intervenmg mesol^lastic 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 subsequendy differentiated synovial membrane. When, on the con- trary, the bones are to become united by dense tibrous and fibro-cartilaginous tissue, as in the case of a svmphysis, 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) 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 9gree either in structure or development with the description. A transi- FiG. 134. Ui.-i^jrams III' various forms of suture. W, serrated; .ff, squamous ; C harmonic ; /?, 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 fibro-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 imjiroperly 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 as 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, except that the opposed ends of the developing bones are of hyaline carti- lage, fibro-cartilage being present only at the sides, e.xcept 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 mewbrane, 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 ligament. The latter, in its simplest form, consists of only enough fibrous tissue to support the synovial membrane. The capsular ligament is strengthened by accessory liframents developing in or around it, the arrangement of which depends on the needs of the joint. During development, STRUCTURE OF JOINTS. [09 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 viembrane. 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. Compozmd 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;^, appearance of joint-cavity; C, differentiation of joint-cavity and capsule; D, 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 cartilage, 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 1 Discus articularis. HUMAN ANATOMY. 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 synovial fringes C' 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 sufificient 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 w-ander in from the capsule, carrying with them a reflection of synovial membrane, or they are the remnants of ' Capsala articularis . - Plicae synoviales. Capsule Synovial membrane Articular cartilage Joint-cavity Reflection of syno- vial membrane 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. Lymphatics 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 Blood-\essel -— — ---.^^/%. t V brane Marrow-cavitj Synovial mem- Union of carti- lage and syno- vial membrane Section through margin of joint, showing articular cartilage and capsule. X 135. 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 hning reflected over the tendons, and are surrounded by strong fibrous sheaths known as the thec(Z syfioviales. ^ Other burs^ 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 bursae 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 bursat 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 * Bursae synoviales. -Vaginae mucosae tendinum. 112 II I'M AN ANATOMY. individuals to uncommon pressure or fiiclion, 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 tixation. 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 fi.xed 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. 138. slide to the periphery along an indefinite number of ROTATION^ /n/v^j lines. This is angular motion. The rod on reach- .- - ~ -'^''' ^'^S ^^ periphery, or at any point on the way, may .-■ ■'^°^ travel round in a circle describing the surface of a ciP*^"*^ i "i^cr/oft, ■% cone. This is ciraimdiidioii. Finally, without any / ,,.,,^y : \ ^^^.-^ axis. This is rotation. ^"'^:^^^^^;-^ ■ rp^:-:^^^^^^^^^ Changes of Position of Parts of the Body. .' .„ ,.j , — Assuming that the palms are looking forward, an- Diagram Illustrating different kinds of , . ^ . .. F , P 1 motion. gular motiou of a limb, or of a part oi one, towards the median plane of the body is called adductioyi ; the opposite movement, abductioyi. A motion bringing the distal end of a limb bone nearer to the head is called flexion ; the opposite movement, exteiision. 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 ; supinatio7i, 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 Lg. 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 joi7it permitting merely a sliding between two nearly plane surfaces, as between the articular processes of the vertebrae. Enarthrosis/ a ball-aiid-socket joint permitting angular motion in any direc- tion, circumduction and rotation. The shoulder- and hip-joints are conspicuous examples. Condylarthrosis,'^ an egg-shaped joint permitting a?ig2clar motions more freely on the long axis than on the short one, circianduction but (theoretically, at least) no rotation, 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-joiyit 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, 7'otatioji, 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. ^Rene du Bois-Reymond. Archiv fiir Anat. u. Phys., Phys. Abtheil., 1895. 1 Arthrodia. - Enarthrosis. ^ Articulatio ellipsoidea. ■* Articulatio 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 l)y 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 veriebnr, of which in the adult there are thirty-three or thirty-four in all. They are divided into five groups. The Fio. 139. Spinous process Facet for tubercle- of rib Transverse process Superior articular process Demi-facet for head of rib Sixth thoracic vertebra from above. 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 vertebra;. 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 119), the vertebrae above the sacrum present the following features, which are common to all, but which are modified in the different regions : (i) a body^ or centrum ; (2) a. pedicle'^ springing from the back of the body on either side, supporting (3) the lamina^^ a plate wh'ch meets its fellow in the middle line to form an arch bounding the spinal or vertebral foramen^ for the spinal cord. Each vertebra gives origin to several processes. — namely, (4) a spinous process,^ springing from the point of union of the laminae ; CsJ a transverse 'pj-ocess on each side, pro- jecting outward from the junction of the pedicle and lamina ; (6) two articulating ' Corpus. - Radix arcus vertebrae. H4 • Arcus. ■• Foramen vertcbrale. ' Processus spinosus.'' Processus transversus. THORACIC VERTEBRA. H5 pjocesses^ 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 Fig. 140. Pedicle Superior articular process and facet Articular facet on transverse process Superior demi-facet for rib region mingles with the trans- verse process. The costal ele- 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- FiG. 141. Body Spinous process Sixth thoracic vertebra from the side. Superior articu- lar process and facet 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 th.Q 7iotch,' which, w^hen the succeed- ing vertebra is in place, forms the top of the intervertebral foramen^ 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 abo\'e 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. Spinous proces: Sixth thoracic vertebra from behind. ii6 HUMAN ANATOMY. ject outward and backward, and cnlarj^e 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 of Fig. 142. Spinous process Inferior articular process Superior articular process Transverse foramen Transverse process Posterior limb of transverse process Posterior tubercle .tal element Anterior tubercle Bo(i\ Anterior limb of transverse process Fourth cervical vertebra from above. the next. Each presents a smooth, roughly oval articular surface. The superior ones face backward, a litde outward, and a very little upward ; the inferior, con- versely, look forward, inward, and slightly downward. Groove for spinal nerve Fig. 143- Superior articular process Anterior tubercle Posterior tubercle Fourth cervical vertebra from in front. Fig. 144. Superior articular process and facet 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 next 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. Inferior articular pro- cess and facet Intervertebral notch Groove for spinal nerve Fourth cer\'ical vertebra from the side. LUMBAR VERTEBRA. 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 little 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, Xh^ posterior transverse tubeixle. The anterior limb, a vertical plate spring- ing from the side of the body and extending outward, ends in the miterior transverse tubercle. This limb is the shorter of the two and its tubercle the larger. The limbs are connected by a concave plate or bone, slanting slightly outward, which forms the floor of a gutter ^ in which the spinal nerve lies, and which represents the costal element. A round hole, the tra^isverse foramen, for the vertebral artery and veins, 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 Superior arti ular fa et Mamniillary proces 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 ^ Sulcus D. spinalis. Ii8 HUMAN ANATOMY. rcijion there is a large openiny; into the spinal canal. A considerable part of the arch is lower than the body. The spinous process is a flat projection e.xtending 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 articular process. Mammillary process Transverse process Inferior articular process and facet Third lumbar vertebra from the side. 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. Superior articular process and facet MTmmillary process 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. The chief points of difference between typical vertebrae of groups may be tabulated as follows : 119 the three presacral Body. Spinal Foramen. Pedicles. Lamina. Cervical. Thoracic 1. Broad. Diameters nearly equal; concave behind. 2. Upper surface with Plane, raised sides and rounded anterior bor- der. 3. No facets. Triangular, with great- est diameter trans- verse. Costal semifacets. Nearly circular. Notches above and be- Rising from top of body; low nearly equal. great notch below. Narrow, with-spaces be- tween. Broad ; no spaces be- tween. Transverse Pro- Double foramen at root ; Strong, with articular CESSES. two tubercles. facet. Superior Articu- Nearly plane ; faceup- Plane, vertical ; face lar Surfaces. ward and backward. nearly backward. Lumbar. Broad. Plane. No facets. Triangular, with diam- eters nearly equal. Small notch above, great one below. Extending downward ; large spaces be- tween. Slender. Concave, vertical ; 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 Transverse pro cess Transverse foramen Facet for odontoid process of axis Anterior arch 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 I20 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, havintj no body, consists of two lateral masses, connected by a short anterior areh and a long posterior one. The lateral masses present the articular facets on their lower and upper surfaces. The inferior look downward and slightly inward, and are verv slightly concave from side to side. The superior facets are oval concavities the backs of which are strongly raised from the surface. Their long axis 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. Theirvariation in all respects is great. Thus, Macalister ' finds in one hundred bones 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 Posterior arch Transverse foramen Anterior arch Inferior articular facet Position of transverse ligament (dotted lines) Facet for odontoid process Anterior tubercle The atlas from below. tion of the prolonged axes of the articular facets ranges from thirtv-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 attterior areh 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 cervical region. Each ends in a single flattened knob with a surface slanting downward and forward. Bifurcation is rare. The transverse foramen 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 Physiology-, vol. xxvii., 1893. THE AXIS. 121 Fig. 150. Superior articular Articular facet on front of odontoid process The axis from in front. Inferior articu- lar facet 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 \'ertebr3e ; 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 odontoid,'^ a cylindrical process lower behind than in front, ends above in a median ridge, 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 laniincE^ 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 spmoiis 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 trayisverse foramen 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 verteb7'a prominens on account of its long, knobbed spine, rather resembles the upper thoracics. The transverse foramen is smaller than those above it, Fig. 151. znd th.& anterior tubercle o{ th.^ 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. Superior articular facet- Spinous process Inferior articular process and facet The axis from the side. Transverse foramen 122 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 Antero- Spread of Vertebrae. Front of Bodies. Front of Bodies. Back of Bodies. Diameter. (.Anderson.) 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 i.S 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 " II 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 ii 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 especiall)^ 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 next 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 vertebrae 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 Physiology-, vol. xvii., 18S3. Anderson states that the vertical diameters of the front and back of the cerx'ical 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 tubercle 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 t7'tie 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 X^cvo. 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 the last broken up into three tubercles, (i) the superior or viatnniillary, rising from the posterior surface ; (2) the accessory or infe- rior^ pointing downward ; (3) the external, 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 sid^ 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 of the fourth is peculiar in being shorter and lighter than its neighbors. 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 iJiade 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 bitid in the third, fourth, and fifth cer\ical \ ertebne ; 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 })rocesses 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. Fig Superior articular process Transverse process Lines of union between fused sacral vertebrae Iliacus \nterior sacral foramina fytifotmis Notch for fifth sacral ner\e Apex The sacrum, anterior surface. THE SACRUM. This bone ' is composed of five fused and modified vertebra, 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 \'ertebra is com- paratively but little changed ; the last consists of litde more than the body. The ' Os sacrum. THE SACRUM. 125 essential modification, besides the fusion, is the occurrence of the lateral masses,^ representing transverse processes and ribs, which, springing from the bodies and arches, are connected with the innominate bones by joints and hgaments. 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 canal, the Articular process Fig. 153. Lamina Sacral canal Transverse process ol first sacral vertebra Gluteus maximus Sacral comu 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 ij^ard The upper surface of the lateral mass, the «/«, springs from the side of the body and the pedicle, expanding into a broad area, and is bounded m front by an ill-marked, rounded border which separates it from the anterior surface and curves forw^ard ; 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 1 Partes laterales. 126 HL'MAN ANATOMY. Articular process Rudimentary transverse processes and inward. Thus the sacrmn is broader before than behintl. 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 vertebrae. It has a double row of four openings, the anterior saeral foramina, one on each side of the ridges, representing the ossitied disks connecting the bodies of the fused sacral vertebra.-. 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 {)lace 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 ¥\G. 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 extent 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 composed of the fused lamince 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 lamince 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 cornua. Four posterior sacral foramina for the exit 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 articular 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 latcrales. ' Cristac articularcs. Auricular (articular) surface Fourth posterior : forainei Sacral cornu 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 {vertebra fidcralis, 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 broader 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 oblique, 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. T\\^ 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 cor^iu, which Fig. 155. Surface for sacrum Transverse process- Coccygeus Levator ani. Cornu Transverse process Gluteus maximus Sphincter ani The COCCYX. 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 of 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 at suivant les races. These, Paris, 1873. ^ According to Steinbach, there are five in man and four or five in woman. Die Zahl der Caudalwirbel beim Vlenschen. Inaugural Dissertation, BerHn, iSgq. 128 Hl'MAN ANATOMY. original pieces, which become less and less flat 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 ne.xt 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 Fic;. 156. Frontal {Aj and sagittal (B) sections of body of lumbar vertebra, showing the arrangement of the bony lamelte. Natural size. 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. DEVELOP.MEXT OF THE VERTEBRAE. Presacral Vertebrae. — These vertebrae ossify from three c/n'e/ cefiires 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-ceyitral sulures separate the regions of these centres. The lat- eral centres of the upper thoracic and the cervical vertebra appear first. It is usually taught that they appear in the sixth or seventh week of foetal life, but Bade * w'ith 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-rav 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, fur Mikros. Anat., Bd. Iv,, 1899. I 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 that 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- FiG. 157. resenting the prominence for the head 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 floor 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. ' M^moires couronnes, etc., Acad. Royale des Sciences de Belgique, tome Iv., 1896. 9 Ossification of the vertebrae. A, cervical vertebra at birth ; centres for body (a), neural arches (6), and costal ele- ment (c). B, dorsal vertebra at two years; cartilaginous tips of transverse (a) and spinous (6) processes; rf, centre for body. C, lumbar vertebra at two years ; position of ad- ditional later centres for various processes indicated (a, 6, c) ; d, centre for body. I30 HUMAN ANATOMY. Tliis represents a costal tlcniint which fuses with the front of tlie 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 laminie Fu;. 15.S. Costal elonienl lllustraliiig homology of costal flt-ment (c. - com- mon condition of six lumbar vertebrae is due to the want 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-developed, making a cervical rib. But even if this be large enough to reach the sternum, which is exceedingly rare, the number of cervical vertebrae is usually considered unchanged. Other changes are due to variations in development of the costal element in the last lumbar and the first sacral. Transitional forms are here ver\' frequently met with. The last lumbar ' Dwight : Journal of Anatomy and Physiolog>', vol. xxi., 1887. 132 HUMAN ANATOMY. may, by an excessive g^rowth of these elements, become sacralized, articulatinj; more or less per- fectly with the ilium, and, conversely, the first sacral may have almost freetl itself from those below it. Thus we may hnd a partially sacralized vertebra, which may be either the twenty-tifth or the twenty-fourth. It often happens, particularly in the latter case, that a vertebra appears to be a first sacral on superficial e.xamination, 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 fuUralis 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 vertebra 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 few, without any compensatory change in the next region. In these cases, more- over, the terminal vertebrce of the region may be very nearly typical ones, and sometimes even the size of the vertebrae will 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- mentar\' the last is apt to be large. It follows 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 two ends of the spine. At the upper there is a tendency lor 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 firogressive. 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 vertebra and fifteen f)airs of ribs, the first being cer\ical. There are two spines in the Warren Museum with a simi- ar 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 \ertebrae placed farther back than the permanent 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 theorj' 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 vertebras 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 almo.st 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 \ERTEBRAL 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 X'ertebr^e ; 2. Those connecting the Lamina; 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 vertebrse, forming about one-fourth of the movable part of the spine and adding greatly to its strength. They are developed, 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 \ertebral 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, 1906. 'Anat. Anzeiger, Bd. xxv. . 1904, and American Journal of Anatomy, vol. iv. , 1905. ' Dwight : Memoirs Boston Society of Nat. Hist., vol. v., 1901. ^Fibrocartilagiaes intervertebrales. '^ Nucleus pulpo^uj. LIGAMENTS OF THE SPINE. 133 centag-e 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. Fig. 162. Odontoid process of axis Transverse ligament Anterior arch of atlas Posterior at- lanto-axial ligament Interspinous ligament Seventh cei^i- cal spine Intervertebral foramen Anterior and Posterior Common Ligaments. — The 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 conimo7i ligament^ (Figs. 163, 165) begins at the axis and extends to the sacrum. It consists of shorter and longer fibres blending with the peri- osteum and springing from the edges of the vertebrae 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. Tha 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 thorax, 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 laminae 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 anterius. " Lig. longitudinale posterius. ' Ligg. flava. Ligamentum subfiavum Supraspinous ligament Tenth tho- racic ver- tebra Median section of upper half of spine. 134 HUMAN ANATOMY. alony the tips of the spines from the last cervical to the sacrum. The interspmous ligaments are membranes connecting the spinous processes between the tips and the laminae, extendinj; from the ligamenta subtlava to. the supraspinous ligament. Fig. 163. Tenth thoracic vertebra Ligamentutn subflavum Intervertebral foramen First lumbar vertebra Posterior common ligament Intervertebral disk Anterior common ligament Fifth lumbar vertebra First sacral vertebra Supraspinous ligament Fifth lumbar spine 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 exter- LIGAMENTS OF THE SPINE. 135 Fig Inten'ertebra! disk Cut surface of pedicle 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- Axial. The important peculiarities are the odontoid and the transverse ligaments. The odontoid, or check ligaments ' ( Fig. i68j, 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 Fig. 166. Ligamentum nuch* Trapezius muscle Ligamentum nuchse Posterior occipito-atlantal ligament 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. ' Ligg. alaria. - Li|b apicis dt-ntis. ■* Lig. transversum atlaatis. ' Lig cruciatum atlaatis. 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- Upper end of occipito-axial ligament Lateral odontoid ligament Occipito-atlantal joint Cruciform ligament Atlanto-axial joint Occipito-axial ligament, fused with dura, turned down A the Fig. 168. Front of foramen magnum Lateral odontoid ligament Bursa on back of odontoid 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 magnum and the anterior arch of the atlas ; the anterior atlanto-axial (Fig. 165) is in serial continuation with it. distinct rounded, raised band, the accessory occipito-atlantal, passes in 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 ligame7itosus) (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-atlantal' and the posterior atlanto-axial ligaments* lie in the region of the arches (Fig. 166). The former extends between the posterior border of the foramen magnum and the arch of the atlas ; the latter iDctween the arch of the adas 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. ^ Membrana atlantooccipitalis poscerior. * Membrana Atlas Transverse lig:a- ment, cut Articular facet of axis Posterior surface of odontoid process shown by removal of middle of transverse ligament; basilar process is thrown strongly upward. ^ Membrana atlantooccipitalis anterior atlantoepistrophica. - Membrana tectoria. 138 HUMAN ANATOMY. Synovial joints, the shapes of which are tiescrihetl witli 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: ^^ articular surfaces of the atlas and axis is strengthened posteriorly by a bundle running upward and outward from tlie axis. Fig. 169. Posterior tubercle of atlas pinal cord Posterior bursa- Transverse process ot atlas X'crtebral artery cut obliciuely Dura Apparatus liganicntosus X'ertebral artery cut in transverse foramen Section of odontoid process ^^^I-^ 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. Anterior I. Cervical Posterior 139 I. Thoracic /^r^nz-tfj Sacrum «^> ■^ // Coccyx Anterior and posterior views of adult spine. 140 HUMAN ANATOMY. Fig. ^^^^ m -I. Thoracic H .#^r W ■I. Lumbar (t -l-MHIWl ^M ^: M^ I Sacral Ml 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 a.xis of the spine is a curved one than that any per- manent or fi.xed curve e.xists. The cervical 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 ])roduction 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 inapprecij^ble 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, e.xcept in the last lumbar, and, accord- ing to Symington's plates, there is not much more difference at fi\e 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- brae 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) I2.I ( 4.75) Back 28.7 (11-31) 26.5 (10.44) Loins 19.9 ( 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 31-7 32-7 32-4 32.8 loo.o 99-8 100. o loo.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 Six 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 93 50 193 40 100 50 190 40 95 50 i«5 40 80 45 165 42 80 44 166 50 100 58 208 52.5 103 60 215-5 53-5 107 61 221.5 61 125 77 263 60 121 72 253 69 129 »3 281 67 118 79 264 62 130 69 261 68 132 79 279 70 140 90 300 79-5 153-5 98 331 7« 162 lOI 341 79-9 162 103.3 345-2 81 174 102.8 357-8 80 170 104 354 80 180 135 395 80 175 106 361 8.S 195 150 430 91 218.7 153-5 463.2 95 220 136 451 120 265 i«3 568 100 221.8 151 472.8 107.5 229.5 152.5 489-5 113 250 161 524 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 21.9 21-5 48.2 52.6 51-3 48.4 48.1 48.1 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 25-9 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 31-I 30.7 ^ Zeitschrift ftir Anat. und Entwicklng., 1876. ^ Cunningham : Memoirs, 1886. * 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 httle 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 to flexion and extension, of 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 adas into the inner parts of the posterior condyloid fossa-. The anterior occipito-atlantal ligament and the odontoid ligaments are tense in extreme e.xtension. \nJiexion 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 viotion between the adas 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 devotetl almost wholly to rotation. The transverse ligament keeps the odontoid in place, and the \ery 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 adas be slighUy 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 certaiA 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 y?k'.vz-, vol. x.xiv., 1S90. ^ Inaug. Disser., Dorpat, iSSi. ' Processus xipboideus. Sternum, showing foramen due to im perfect union of lateral parts. DEVELOPMENT OF THE STERNUM. 157 A Fig. 181. 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. ^ ^-3 t? Ossification of the sternum, yi, at sixth foetal month ; a, centre for manubrium. B, at birth ; a, for manubrium ; b, c, d, for seg- ments of body. C, at about ten years ; a, manubrium ; b, c, d, seg- ments of body ; e, ensiform cartilage. 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 Thoracic Articula- tions. 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 ARTICl'LATIONS. These include three sets : I. The Intersternal Joints, or tliosc uniting the segments of the sternum Fig. 182. SlL'rtu)clavicular joint Anterior intersternal liRanieiil Chondro-stenial ligament f^^Costo-xiphoid ligament Interchondral ligament The sternum and costal cartilages from before. 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. 183. First rib . MANUBRIUM rf Interarticular ligament Chondro-sternal joint Interchondral joint -ENSIFORM CARTILAGE Interchondral ligament Longitudinal section through 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 cartilagmous strip. The i6o HUMAN ANATOMY. streiii^^thening bands require no further description. A cavity is often found in the cartilage, making a typical half-joint. At what time it appears is unknown. Some- times it is so developed that the joint is practically a true one, with articular carti- lage : this exceptional arrangement is more common in women than in men, being especially adapted to the female type of respiration. The cartilage persisting between bodv and cnsiform is strengthened in a similar manner. A cavity rarely occurs in the cartilage, which, on the contrary, often undergoes ossification. THK COSTO-STERNAL JOINTS. The first costal cartilage joins directly, without interruption, the lateral expan- sion of the sternum ; the following costal cartilages articulate at the points already mentioned by synovial joints. Those that come between different sternebrae — that is, from the second to the fifth — often have the joint subdivided by a band into an upper and a lower half. This is usual in the joint of the second cartilage ; progres- sivelv rare as we descend. The sixth and seventh cartilages frequently have no true joint.' Each of these joints is enclosed by a capsule, the front and back fibres of which radiate over the sternum. THE IXTERCHONDRAL JOINTS. The seventh, eighth, ninth, and tenth costal cartilages have each an articulation by a true joint on the projections above described with the one above it. There is a connection between the fifth and sixth cartilages ; usually on the right, very frequently on the left.'^ This is, as a rule, also a true joint, but the cartilages may be merely bound together by bands of fibres. The joint on the right side is almost aUvavs a true one. ' The ends of the eighth, ninth, and tenth cartilages are joined by fibrous tissue to the cartilage above. The costo-xiphoid ligament is a band extending from either side of the base of the ensiforni to the lower border and, perhaps, the front of the seventh cartilage near its end. THE COSTO-VERTEBRAL ARTICULATIONS. The joints between the ribs and the spine are in two series : an inner, or Costo- Central, between the heads of the ribs and the bodies of the vertebrae ; an outer, or Costo- Transverse, between the tubercles and the transverse processes. The Costo-Central Joints. — The head of the rib is received in a hollow articular fossa formed by a part of two bodies and the disk between them. Although as a whole concave, it may in a typical case be further analyzed. The lower half of the socket is convex from above downward, fitting into the hollow at the lower part of the joint of the rib ; the upper part is about plane, looking downward and out- ward, with the ujiper border considerably overhanging the joint. These two facets ha\'e each a syno\ial capsule and are separated by an i7iter articular ligament;^ a band running from the ridge on the head of the rib to the posterior part of the inter- vertebral disk. In the foetus before term it extends across the back of the disk to the head of the opposite rib. The front of the capsules is strengthened by the anterior costo-vcrtebral ligament,'' which is a series of radiating fibres from the head tr both vertebrae and the interven- ing disk, not clearly separable into three bands. These stellate ligaments (Fig. 184) are least developed in the upper part of the thorax. The strongest collection of fibres is to the lower vertebra. The joint of the first and last two ribs is not sub- divided ; that of the tenth is uncertain. Strong fibres pass from the head of the first rib to the seventh cervical vertebra. Few or no fibres from the last rib reach the body of the eleventh thoracic. The lower fibres are made tense when the rib is raised and the upper when it is depressed. The Costo-Transverse Joints. — The articular surfaces of the tubercles, 'MusgTove: Journal of Anatomy and Physiology, vol. xxvii., 1893. ^ Fawcett : Anat. Anzeiger, Bd. xv. Bardeleben : ibid. •'Lig. capituli costae intcrarticulare. ^ Lig. cipituli costae radiatum. I 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. I VII rib Superior costo-trans- verse ligament VIII rib Posterior costo-trans- verse ligament IX rib Intervertebral foramen Upper part of stellate ligament Lower part of same Body of ninth thoracic vertebra 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:- \h& posterior, the middle, and the superior. T\\^ pos- FiG. 185 Lamina of vertebra above Transverse process of vertebra below Middle costo- transverse liga- .ment Posterior costo- transverse ligament Costo-transverse joint Rib Middle costo-trans- verse ligament Costo-vertebral joint Interarticular liga- ment Intervertebral disk Transverse section through intervertebral disk and ribs. terior^ are strong bands running outward from the tips of the transverse processes to the rough part of the tubercle beyond the joint. The middle '' are strong short fibres connecting the front of the transverse process and the back of the neck of the ^ Lig. costotransver sarium posterius. - Lig. colli costac. l62 HUMAN ANATOMY. rib between the head and ilic tubercle. Those for the last two ribs are small, that for the twelfth sprinjj^ing from the accessory tubercle. The superior costo-transvcrse ligaments ' are thin bands, passing downward and a little inw ard from the under side of the transverse processes to the crest on the upper edge of the neck of the rib below. Those of the first and last two ribs are of little account. This band becomes tense when the rib is depressetl and carried inward ; the inner fibres are tense when the rib is raised. The outer fibres fuse with the front surface of the j)osterior 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 thora.x (page 165). THE THORAX AS A WHOLE. The thorax 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 l^efore backward. The thoracic vertebrae form the posterior Fig. 186. Tubercle Lamina of V'll thoracic vertebra Middle costo-lransverse ligament Posterior costotransverse ligament Superior costo-transverse ligament Ligameiitum subflavum Intertransverse ligament VII thoracic rib VIII rib IX rib Ligaments uniting ribs with spine, from behind. boundary ; the sternum, including the very beginning of the ensiform cartilage, the anterior. The inlet, or upper boundary, is an imaginary plane slanting dovvnward and forward from the top of the first thoracic vertebra 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. Suffice 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 fairly well-defined posterior surface, while the lateral ones pass in- sensibly into the anterior ; the upper part is hidden by 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 thorax 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 eflfect is less striking, the distance from front to ' Lig. custutransversarium anterius. THE THORAX AS A WHOLE. i6' 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 Fig. 187. The bony thorax, lateral view. Ime. 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 vertebrae ; the junction of manubrium and body of sternum is on a level KiG. 18S. Fig. 1 89. ^ 'Q Si ^ ^s 0= a Transverse section through thorax at level of third thoracic vertebra, {/{ratine.) Transverse section at level of fourth thoracic vertebra. {Braittte.) Kit".. 190. CD 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, taken from Braune, show the varia- 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,butthelasttwo 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 0 Transverse section at level of eighth thoracic vertebra. (Brai4ne.) Fig. 191. 7 ^ '0 ^ '0 ^ cr^ V the sternum is opposite the body of the first thoracic vertebra. In the course of the first year it lies opposite the upper part of the second, and at five or six has reached its definite level opposite the disk between the second and third thoracic vertebrae. 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 1^, or as I to 3 ; at birth it is as 2 to 3. We have found it at probably three years as i to 2 ; at five or six the thorax has nearly reached its permanent shape. Differences due to Sex. — The whole structure is lighter in women, but the I / Transverse section at level of eleventh vertebra. Shaded areas (6, 7) are sections of costal cartilages. (Braune.) 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 io 2'^4. (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 little 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 gained 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 1 Henke : Arch, fiir 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 manul)rium. The motions at the inconstant joint between the sternal hotly and the ensiforni i)rocess are necessarily indefinite ; they apj)ear to consist chieriy of a ilrawing in i-f the ensiforni. 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 nearlv as in one piece. The motion on an antero-poslerior a.xis 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 dne 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, independently 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, e.xercises 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. Moreoxer, 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 shoVn 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 antcro-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 carrv 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 centmietres 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. \w 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 " ' is 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 makmg 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 Init roiiglily 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 respiratory 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 w^ay 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 rarelv 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 flexion, 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 level 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 symphysis 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 {angulus Liidovici) 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 ster^ial, asternal, and floating, are sometimes designated as zipper 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 six 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 Httle 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 affected, 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 frequendy 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 liftmg 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 I70 HUMAN ANATOMY. rib, and ends at or near the region mentioned, pain l)eing 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 tiie 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 proximity 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 1865). 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-a.xillary line. The lower spaces are in too close j)roximity 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 abo\-e 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 (Ti'eves). 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 anaton-y 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 forminiu^ 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 any 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 meinbranes 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 ethmoid, \.\\c frontal, and the Uvo parietals. The cranium consists of the vault and the base. The vault is formed by xha 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 exj^ands 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, \\\^ condylar : and a posterior one, the tabttlar or squamous portio7i. These correspond to the basi-occipital, the exoccipital, and the supra-occipital of comparative anatomy. They all develop from separate centres and bound the fotamen magnum,' a nearly circular opening, transmitting the spinal cord with its enveloping membranes. The spinal accessory nerves and the \crtebral 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 coossifies with the body of the sphenoid. Its superior surface is smooth and concave and supports the medulla oblongata. Just internal to the edges is a very 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 \\\^ pharyngeal tubercle,'' Very rarely this aspect presents a depression, \\\ft pharyyigeal fossa. Sometimes there is a facet near the edge of the foramen for the anterior arch of the adas. 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 occipirale macnum. '' Pars basilaris. ''Tuberculum pbaryngeum. 172 THE OCCIPITAL BONE. 173 is separated by a suture, the petro-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- 77ie7i,'^ transmitting a vein. In front of the base of the condyle at its outer border is the constant anterior condyloid foramen ^^ 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 cur\'ed line-^ Condyle Jugular process Jugular notch Pharyngeal tubercle External occipital protuberance apezius Complexus Occipitalts Sterno-tnastoideus Rect. capit. post. minor Splenius Rect. capit. post. tnajor Obliguus superior y~~~Posterior condyloid fora- men Rect. capit. lateralis Anterior condyloid foramen, probe in canal Rect. capit. antic, minor Superior constrictor Rect. capit. 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 coossifies with the petrous portion of the temporal. This enlargement, moreover, extends downward as the paroccipital process, 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 a^tterior jugular process, marks the front of the foramen. A little behind this a larger though very delicate spine, the intrajugular 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 ^ Pars lateralis. ^ Canalis condyloideus. ^ Canalis hypoglossi. * Processus jugularis. ° Incisura jngnlaris. " Foramen jugulare. 174 HUMAN ANATOMY. the latter ridge is wanting, the groove of tlie 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 exoccipitals. 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. Y\G. 193. Superior occipita fossa Groove for right lateral sinus Inferior occipital fossa Itittiiial occipital protuber- .uKe Groove for left lateral sinus Jugular process Jugular notch Groove for lateral sinus Jugular tubercle Anterior condyloid foramen, probe in canal Occipital bone, internal surface, from before. The posterior surface is marked by a prominence, somewhat below the middle, \\\kt external oeeipital protuberance,'^ to which is attached the ligamentum nuchcE. This tuberosity varies greatly in development. 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 above 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 above it. Thej 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- volvmg the protuberance and extending laterally along the superior curved 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, - Protuberantia occipitalis externa. * Linea nuchae superior. < Linea nuchae suprema. DEVELOPMENT OF THE OCCIPITAL BONE. 175 the external occipital crest, ^ runs from the protuberance to the foramen magnum. Above the middle of this crest the inferior 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 f OSS CB ; 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 i^iternal 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 inte7nal 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 frequently 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 Fig. 194. Superior median fissure superior oc- cipital Squamous por- tion Fissure be- tween upper and lower portions Supra-occipital Exoccipital transverse ridge, and shows in 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 appearinthe cartilage around the foramen magnum about the eighth week of foetal 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, the sup7^a-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 stipe- rior occipital, is developed all the upper part of the squamous por- tion, including the external occipital protuberance and the superior curved linc^" 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- pecially 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 Wormian 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 s Consult Stieda : Anatomische Hefte, iv., 1892, and Debierre : Journ. de I'Anat. et de la Phys., 1895. 1 Linia nuchae mediana. -L. nuchae inferior. ^Protub. occip. interna. ' Crista occipitalis interna. * Ossa suturanim. Basi-occipital Posterior condyloid foramen Occipital bone at birth, from before. 176 HUMAN ANATOM^'. be the homologuc of the interparietal Ooiie. Tliis interpretation is uiconsistent with the history of ossification. Kerkrin^ 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 cerel:)ral side of the basilar is fused with the sphenoid by seventeen ; the lower side unites later, probably before twenty. THE TEMPORAL RONE. 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 auditory meatus,'^ leading to the membrane of the tympanum which closes it. The middle ear, the eavity of the tympanum, is a space internal to the Fig. 195. squamous portion Supramastoid crest Occipitalts Spitia suprameatutii' Spieniiis capiti Squamo-niastoid suture Sterno-mastoid- Mastoid foramen Auricularis posterior Trachelo mastoid MASTOID PORTION Tympano-mastoid fissure Mastoid process External auditory meatus TYMPANIC PORTION Vaginal process Zygoma Masseter Anterior root of zygoma Glenoid f )ssa APEX OF PETROUS PORTION Glaserian fissure StyJo-glossus Stylo-hyoid Styloid process Right temporal bone, 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 77iter7ial auditory meatus. -^ Development shows that the bone consists of the following three parts ( i ) The petro-mastoid th^ 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 tymf>anic portion^ which at birth is a ring, incomplete above, encloses the membrane of the tvmpanum 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 temporale. - Meatus acuscicus exterous THE TEMPORAL BONE. % 1/7 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 petrt-mastoid and the tympanic portion, the roof and floor being developed from the former. (3) The squamous pG7'tion is external and above. It forms a-.part of the side of the skull, the roof of the external meatus where the tympanic plortion is deficient, the articulating surface for the jaw, and a part of the mastoid process. Thtre is also the long, s\&\\<\&x styloid process, which is a part of the hyoid bar of the seco id visceral arch of the embryo. It begins as an ossification of a distinct piect of car ilage, 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 Zygoma Glenoid fossa. Postglenoid tubercle Fissure of Glaser Tympanic plate External auditory meatus Eustachian tube Carotid canal Cochlea emicircular canal Groove for Horizontal section through right temporal bone, seen from Antrum lateral sinus below . ^m auditory meatus. The edge of the vertical part is convex ex):ept below The upper and posterior borders overlap the parietal bone by a broad bevelled ;• rface. The anterior border joins the great wing of the sphenoid, overlapping ab e and over- lapped below, where it passes into the horizontal part. The posterir ^ angle cf the vertical portion sends downward the postauditory process, from which ; le upper part of the mastoid, including some of the mastoid cells, is ' developed. The squamo- mastoid 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 so-iamos; 1. Its surface is smoother than that of the mastoid proper ^ ^■-lall, p- smooth, but inconstant patch situate-' on the b el of th r '' one centimetre or more behind it, : : arks the position 0: ness of the bone at this place, ■ hich is that of note-pap.. r !• ,-J fl- 1 Pars squamosa. 12 lyS HUMAN ANATOMY. six millimetres in the adult. A small, sharp prominence, the spina supranieahim , is found just behind the u|'i)er part of the meatus. It is an important landmark in the surgery of the region. Just jjosterior tt) it is usually a minute venous foramen. The inner side of the squamous portion, besides the large beVelled articular surface, prest nts a smooth one, forming part of the wall and Hoor of the cranial cavity. This is separated from the petrous portion by the petrosquamous suture, which is closed early. Two grooves for branches of the middle ni'-ningeal artery diverge from its lower border, one running upward and the other backward. Tne front of the hori- zontal part forming the Hoor is rough and thick, joining the great wing of the sphenoid. The zvt^oinalic process^ projects forward from the outer surface of tin 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 Fk;. 197. squamous portion Zygoma Groove for nicniiigeal artery Aquteductus ves- tibuli Groove for lateral sinus MASTOID PORTION Aqua-ductus cochlea? Right temporal bone, internal 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 supmmastoic/ 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 articular is, '^ the front part of the articular cavity of the lower jaw. Near its outer end is a tubercle for the external lateral ligament. Ju:5t in front iA rhe 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 Glaser,'' 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 zygoma tlcus. -Tuberculum articulate. ^ Fossa niaadibularis. * Fissura pctrotj-mpanica. THE TEMPORAL BONE. 179 the interior of the cranium is very thin. Behind the glenoid fossa the horizontal part ot the squamosal forms the roof of the external 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-mastoid fissure. The ante- rior part of the tympanic portion, called the tympajiic 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 ,G laser, which opens into the tym- panic cavity. The outer end of the fissure is closed ; the inner part is double, since a thin piece of the petrous, the teg7nen 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 vagi?ml process,'' which sometimes splits to enclose it. ^ • Fig. 198. SQUAMOUS PORTION Zygoma Articular eminence Glenoid fossa ■ Tegmen tympani Glaserian fissure' TYMPANIC PORTION Styloid process' Stylo-mastoid foramen Mastoid process' Digastric groove Eustac hian tube Carotid canal Aquaeductus cochleae PETRO-MASTOID PORTION ■Jugular fossa Joining occipital Occipital groove 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 z. para- mastoid process. The greater part of the internal surface is occupied by a broad and '^.'to.^ groove,^ running obliquely downward, forward, and inward for tln^ lateral sinus on its way to the jugular foramen. The direction of this groove-i? ' rtam. Sometimes it descends !,Tadually ; ?t ...lers it t'u^us far forward and u>-oc<.,. .^ nearly vertically. In the latter case it approaches closfcr than ot lerwise \o the outer" wall of the skull, but the distance in all cases is ver}^ variajle (Figs. 199, _2ot>). It may be onb, 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 scimeisix ' Pars tjmpa'iica. - Vagina processus styloifie' 13. ^ Pars oetrosa ec mastoi'ica. *^Jiici'-.u!ii masl->ii1i-a . ",S. ileus sii'iiniii'ou; HUMAN ANATOMY. millimetres thick in early childhood, and from the antrum or upper mastoid cells by a very tliin one in adult life.' Behind the groove a small, smooth surface forms a part of the cerebellar fossa. Fig. 199. A B Carotid canal Tympanic cavity Jugular fossa I'acial canal External auditory meatus Groove for lateral sinus Mastoid canal Tympanic cavity Facial canal External auditory meatus Groove for lateral sinus Horizontal sections through a right temporal bone with slight development of the mastoid cells. A, just above the floor of the external auditory meatus ; B, near the roof of the same canal. Fig. 200. — Facial canal External auditory meatus Groove for lateral f Similar sections of a right temporn, bone with considerable development of the mastoid cells and consequent remo\ al of the lateral smus from the surface. i^onsequent A small canal the mastoid foramen,-^ transmitting a vein, runs from the sinus to the outside of the bone, which it sometimes reaches as far back as the suture beUveen ' Clarke : Journal of Anatomy and Physiology, vol. x.xvii, 1893. "Foramen niastoideum. THE TEMPORAL BONE. isi Facial canal ^j^-L "Area cribrosa superior Cut wall of in- ternal meatus \rea cribrosa media Foramen singu- lare Bottom of right internal auditorj- meatus. X 5. 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 mastoid process are very variable. The rough upper border of the mastoid subdivision forms an entering angle with the squamosal, into which fits a sharp point from the lower bor- der of the parietal, which rests on it above. Behind and below the Fig. 201. mastoid joins the occipital bone. The petrous subdivision is an elongated pyramid running for- ward and inward, presenting four surfaces (besides the base covered by the mastoid), four borders, and an apex. The surfaces are the supe- rior, posterior, inferior, and anterior. The superior surface slants forward and downward in the floor of the middle cerebral fossa. It has the following features. Above the apex there is a depressioJi ^ for the Gasserian ganglion. Just external 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 elevatioji, 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 tympajii, 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 FaUopii," through which passes the great su perficial petrosal nerve. A minut' opening, more external, transmit the smaller superficial petrosal nerve. In youth the outer side of the teg- men is bounded by the petro-sqna- mcus suture. The posterior surface forms a part of the posterior cranial fossa. The chief feature is the inte7-nal auditory meatus,^ a nearly round canal with a slight groove leading 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 Ia77ii7ia cribrosa (Fig. 201), which is divided by the falcifor77i C7'est into a smaller fossa above and a larger one below. The former has an opening by which the facial nerve enters its canal, the aqjceduct of Fallopius^ Branches of the auditory nerve pass through minute openings in both fossa^. About one centi- metre behind the meatus is a little cleft, the aqucediictus vestibtdi,^ entering the bone obliquely from below. Higher and nearer to the meatus is a minute depression, the remnant of xhe: Jiocciilar 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 Mmpressio tegmenti. -Hiatu^ canalis facialis. >= Meatus acusticus internus. ^ Apertura externa aquaeductus vestibuli. Fossa subarcuata. Petro-squamous suture Tegmen tympani Epitympanic space Facial canal Squamous por- tion External audi- tory canal Tympanic ring Styloid process Frontal section through temporal bone, showing the cavities o£ the outer, middle, and inner ear and the four sides of the petrous. [S. HUMAN ANATOMY til' , 1 of the levator palati and tensor tympani muscles. External to the back of t. IS is the round orifice of the carotid canal^ ; back of this, and more internal, is the ujrular fossa. This presents two extreme types, entirely different, with inter- mediate forms. It may be a lari^e thimble-shaped hollow, the edge of which bounds the venous part t)f the jugular foramen internally, forming a large reservoir for the bloocl of the lateral sinus as it leaves the skull. On the other hand, it may be a smai flat surface. A minute, but very constant, yb;v7wr;/ in the ridge between it and the carotid canal transmits the tympanic branch of the glos.so-phar)ngeal nerve. A minute foramen, usually ft)und in the jugular fossa, transmits the auricular branch of thv \agns. The aqiucductus cochlea- ends at a small triangular o])(.iiing" 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 antl then by bone. The sty! '-mastoid foramen, the orifice of the facial canal for the facial nerve, is near the outer edge of this surface. The stylo-niastoid branch of the posterior auricular artery enters it. Fig. 203. SQUAMOUS PORTION Zypoina Zygomatic tubercle Groove for meningeal artery Foramen for lesser superficial pe- "j trosal nerve Hiatus Fallopii Depression for Gasserian ganglion Eustachian tube Carotid canal APEX OF PETROUS Carotid canal (lower end) Tympanic plate -p-'. Vaginal process Styloid process Right temporal bone from before. The anterior surface of the petrous is nearly all hidden by the tympanic plate. It forms tlu- inner wall of the cavity of the tympanum and of the bony jjart of the Eustachian tube, which leaves the bone in the entering angle between this surface of the petrous and tlie tympanic. The features of this surface are treated in the section on the ear. 'Wxa processus cochleariforviis'' attached like a shelf to this outer wall, dixides 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 fossce. 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 j^rocess of Canalis caroticus. - Apertura externa aquaeductus cochleae. ■" Septum canalis musculotubarii. THE TEMPORAL BONE. 183 the occipital bone, and is separated posteriorly from the occipital by the jugular foraynen. 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 pharynx. 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. Canal for tensor tympani 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. 204. fore backward. it is bounded internally by the petrous ; above by a projection from it, the tegineyi 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 supra- tympanic space ^ the attic, or the epitynipaman. 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 antrimi 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 F^^ith the ear. Carotid canal (inferior end)' Sagittal section through right temporal bone, seen from outer side. ^ HUMAN ANATOMY. \..ns laru^c pneumatic cavities, sometimes diploe instead of air-cells, and, agfain, it may be almost solid ; the latter condition is, however, probably always pathological. According to Zuckerkandl's' investigatii)ns of 250 temporal bones, the mastoid is entirely pneumatic in 36.8 per cent, and wholly diploetic in 20 per cent. The re- nr lining 4-^.2 per cent, were mixed, the dii)loe being at the point of the mastoid and t! : cells above. Neither size nor shape indicates its internal structure. The relation ..f the cells to the lateral sinus has l)een alreaily 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 sharj) turn (the i^eriu) backward, passing internal to the attic of the tympanum just below the external semicircular canal, which almost always projects a litde farther outward. It then curves backwartl 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 .1 point on the surface above the external 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- i.ilf millimetres. Just before its lower end a very minute canal, transmitting the chorda tynv ini nerve, runs upward and forward from it to the cavity of the tympa- num. Fror,. the front of the cavity this nerve escapes by the minute canal of Huguier, which opens near the inner end of the fissure of (ilaser, passing between the tym- panic plate and the tegmen tympani. The facial canal has several other minute openings. There are also minute canals for Jacob s o n' s 7iervc 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 •ochl'ja of the internal ear. The internal auditory meatus is almost behind the canal, md the Eustachian tube lies to the outer side of its horizontal portion. ['he temporal bone is porous in structure, except about the internal ear, where it is \erv dense. A trans\'erse section, either vertical or horizontal, through the ' Kternal 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 bv a small rent. t rticulations. — The temporal bone joins the occipital by the petro-mastoid portif^ 1. These two bones form the entire posterior fossa of the skull, except at the extrci If front, in the middle, where it extends along the back of the sphenoid, md a.i the side, where a small jiortion of the lateral sinus is made by the posterior inferior angle of the jxirietal. This latter bone articulates with the squamous and the tup of the mastoid. The great wing of the sphenoid fits into the angle between the seuamous 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 middl -'. fossa. The m.ilar bone joins the zygoma, completing the arch. The lower jaw articulates with the nrlenoid fossa by a true joint. Development. — The sqjiamotts 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 centi apjjcars in the lower part of the future tympanic ring. The ossification of the petro-rrastoid portion comes from several nuclei, the number of w'.ich probably varies. The process begins towards the end of the fifth month aboiil jthe membranous labyrinth. The opisthotic nurjeus lies at the inner side of the ry npanic cavity and spreads lo the lower part of the bone. The prootic is near the siii.-rior semicircular canal. The cpiotic, arising near the posterior canal, ' Monatsschrift fiir Ohrenheilkunde, Bd. xiii, 1S79. ^ Joyce : Journal of Anatomy and Physiology, vol. xxxiv., 1900. ~ Canalis facialis. '* Caoalis caroticus. DEVELOPMENT OF THE TEMPORAL BONE. 185 Fig. 205. '^ ^uamous portion Tj-mpanic rin Tegmen tympani in Inner wall Glaserian fissure of tympanum Temporal bone at about birth, outer aspect. Fig. 206. 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 sixth month. The carotid artery passes at first along the base of the skull in a 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 Jloccular fossa, which, however, is completely hidden by the dura. The mastoid 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 tyriipanic por- tio7i consists solely of the im- 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 tympanic 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 earlv foetal 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 sp2irium — 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. It is later. ' Journal of Anatomy and Physiology-, vol. xxvii.,'1893. ^ Archiv fiir Ohrenheilkunde, Bd. xiv., 1S79. Petro-squamous suture Position of superior semicircular canal Posterior semicir- cular canal Floccular fossa Carotid canal Internal auditory canal Temporal bone at about birth, from above and within. Tympanic ring Tegmen tympani in Glaserian fissure Tympanic portion of temporal bone in the second year. sometimes seen c 8t> HUMAN ANATOMY. THE SPHENOID BONE. (a the adult this bone' consists of a cubical body, from the sides of which arise the H'cat wings, from its front the lesser wi?igs, and from below the pterygoid pro- esses Both development and comparative anatomy show that these parts represent ^ever.il bones. The body consists of two parts, a posterior and an anterior. The postcMor the bashphenoid, is the centre of the middle fossa of the base of the skull ; from Its sides spread the irreat wings, or alisphenoids. These with the temporal bone'^ complete the middle fossa. The anterior part, the /./r.0//f«^/a', inseparably connL. ted with the basisphenoid, is in both the middle and the anterior fossa;. The lesser 7iWgs, the orbito-sphenoids, spread out from the presphenoid and cover the ipices of the orbits. 'W^a pter\goid 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 turbinates, of independent origin, ultimately form a part of the body of the sphenoid. optic foramen Fig. 208. Sphenoidal turbinate Sphenoidal foramen •,jU\Oft Infratemporal^ — i--*- — ». Extenial ptery guid plate Foramen ro- luiiflum Hamular process Pterygoid notch Internal pterygoid plate The sphenoid bone from before. The Body. — It is necessary to describe the basisp/ienoid 7md ihc presp //en old together, since thev form the roughly cubical body. The superior surface con- tains the deep pif/a'tary /ossa,'- or sella turcica, in which hangs the pituitary body from the brain. Behind it is the dorsum seller, 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 thf dorsum, is a groove for the si.xth nerve. In front of the sella is the olivary eviiyience' (of the presphenoid), which is usually an oval swelling, though it may be plane or conca\e. At its sides grooves, often very poorly marked, lead to the optic foramina. Tho [.Qsterior 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 fossae. The front border presents in the median line a triangular point, tlie ethmoidal spine. A t each lateral surface of the body is the carotid groove ' for the internal ' irotit artery. Tr is well marked ' "^'^ at the posterici edge, where the artery enter.- "> ■\. vj. ipliyseov. 'Tuli n .•. ■(.•llae. * Sulcus laroticns. THE SPHENOID BONE. 187 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 cavernous 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 sphenoidal fora7nen,'^ 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- FlG. 209. Posterior clinoid process Optic foramen Foramen rotundum Carotid groove Scaphoid fossa^ Pterygoid fossa External pterygoid plate Hamular process The sphenoid bone from behind. ing a large part of the hole into the antrum. These are the bo7ies of Berlin, or sphe7ioidal spongy bones, 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 hned 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 wings '' have each a cerebral or supeinor surface forming a large part of the middle fossa, an external 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 7-otu?idum for the superior max- illary division of the fifth nerve. A litde further back and more internal is a pin- ' Crista sphenoidalis. - Apertura sinus sphenoidalis. ' Alae magnae. L^s HUMAN ANATOMY. hole, t le foramen of \ \salius, for a minute vein. Farther back and outward near the ;r ^le is the foramen ovale, transmitting^ the niancHbuhir division of the hftli crani.i. nerve to the base of the skull, and atlmittinij^ the small meningeal branch of the internal maxillary artery. Just beytmtl this, in the e.xtreme ang^le, so as some- times lo be completed by the temporal, is the foramen spinosnin, atlmittinL; the mitliil' meningeal artery to supply the bone and the dura. The external surface is di\iMed into a larg^er, superior, vertical part, looking towards the temjioral fossa, and t'tie looking into the zygomatic fossa. These are separated by the infratem- poral res/, which near the front points downward as a strong prominence, the infra- tempcral spine. /JTTie inferior surface contains the foramen ovale and the foramen spinoMun. 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 ncr\en'The ••xternal surface has an anterior border vv'here it meets the orbital surfiTOTrw-hich joins the malar, "^he superior border slants upward, overlapping the frontal and parietal bones. i^ 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. 2Iu. Ethmoidal crest Liiijiula^ Petrosal process Dorsum selke I'ost. cliiiold process The sphenoid hone from ahove. e- \ rame ) rotun- lum Foramen ovale Foramen spinosum bodv, is slightly rough for the petrous, making with it a groove on the under side for the cartilaginous ^t^it^chian 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, narroA- behind and expanding in front, looks into the spheno-maxillary fi.ssure, whicli boiinfis 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 fissured This cleft is an elongated aper- ture, 'iirected obliquely outward and upward between the great and lesser wings of th' sphenoid, completed externally by jiie -frontal. It opens anteriorly into the orl-' and transmits the third, the fourth, the ophthalmic division of the fifth and s.:;tl . ranial nerves, and tlie ophthalmic veins. There is a small projection near the iiiidf', of the hind border for a ligament crossing the fis.sure and for the outer head of the external rectus. 1 he 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 ' Fis-ijra orbitalis superior. - Alae parvae. THE SPHENOID BONE. 189 enclose a canal, commonly called lh& optic foramen,^ for the optic nerve, which 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. /^Jhe small wing over- hangs the front of the middle fossa Pig. 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 pterygoid 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 curved projection, the vaginal Sphenoid bone, showing abnormal development of middle clinoid processes, especially on the left side. Re- duced one-half. Fig. Spheno-maxillary fossa 212. Foramen ovale 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 pterygopalatine , which the palate bone converts into a canal leading back from the spheno- maxillary 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 cafial, 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 jalajx-arisesr- Rather less than half way down the internal plate presents a promi- ^ Foramen opticum. - Processus pterygoidei. ^ Lamina medialis proc. pteryg. ' Hamulus pterygoidei. ^ Lamina lateralis: »roc. pteryg. Portion of sphenoid bone, showing the foramen pterygo- spinosum. .-/ HIM AX AXATOMV Fig. 213. Great wing (alisphcnoid ) Small wing ( orbito-sphenoid ) Foramen \ Kiian Presphenoid | Hxl. pterygoid plate rolundvini canal Int. pterygoid plate Sphenoid bone at about birth, seen from before. rt;nct.' bounding a groove below, which supports the Eustachian tube. The posterior V>rdor of the outer plate is irregularly scalloped. Near the top a transverse ridge crc '-es its inner surface ; if well marked, this forms the top of the pterygoid fossa. It m..v be barely discernible (Waldeyer 'j. Just above the scaphoid fossa is the hind --nd of the Vidian canal opening into the middle lacerated foramen opposite the apex C)f the petrous. The development of the pterygoid plates varies greatly. The upper part of the outer mav 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 pterygo- spinosiim of Civinini (Fig. 212), This is always behind the fora- \rvl I / / ^^2^7:^im nien ovale, or internal to it. v.- w^nt to a jioint, and thus allows the lateral masses to touch the median plate. It supports the olfactory lobe of the brain, and is perforated by holes for the pass.ige of thr olfactory nerves. These are arranged rather vaguely in three rcnvs. Fhere 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 /on^i- tudinal Jissiirc, close to the crista galli, transmits the nasal branch of the fifth nerve. The lateral masses ' are two collections of bony plates imperfectly bounding t avities. Thev are roughly si.x-sided, the greatest diameter being antero-posterior. rhe outer surface presents a vaguely quadrilateral plate, the os planum ^'^ forming a larg'j part of the inner wall of the orbit. In its upjx-r border are two notches, which become the anterior and posterior ethmoidal fora}nina when the frontal bone is in place. The former transmits the nasal branch of the fifth ner\e from the orbit to the cranial cavity. The os planum is bounded behind by the body of the sphenoid ; below by the [lalate bone and sujjerior maxilla, 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 ' -> planum. Those nearest to it are completed by the lachrymal and the more anterior ones bv the Median or perpendicular plate of ethmoid bone in place. The right lateral mass of the ethmoid has been removed. nasal process of the superior ma.xilla. 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 massj are closed by the imperfect cells on the under side of the horizontal plate of th« fronti'l beside the ethmoidal notch. The few cells that open anteriorly are contin-.j UOU5 with the lateral ones, and arc closed by the nasal process of the upper jaw. Tht nun rous spaces within the ethmoid are, for the most part, completed by the] neighborii g^ bones, after which they are named. There are some beneath the osi 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] tirbiii,'' jone and the latter above it. The size and shape of the ethmodial cells] ar \ri irregular ; sometimes the middle turbinate is hollowed into one, sonie-| .ntlius ethtnoidalis. - Lamina papyracea. "^ Cellulae ethmoidales. THE ETHMOID BONE. 193 Median plate Infundibulum Crista galli Anterior ethmoidal cells 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 Fig. 217. conceal others. At least two of these — the superior and the mid- dle turbinate 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 maxilla at the crista ethmoidalis or superior hirbinate 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 turbinate 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 extreme upper posterior angle. At the point at which the middle turbi- nate bone joins the nasal process of the maxilla 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 laicinate 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 two 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. T3 Fig. 218. Superior surface Alar process of crista galli Posterior ethmoida cells Posterior ethmoidal cells Middle turbinate Sup. meatus Median plate The ethmoid bone from behind, showing median plate and lateral masses. 194 HUMAN ANATOMY. naso-turbitial bone of many mammals. Behind tliis is a globular swelling, the bu/Ia,' 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 infundibulum,'' curving downward and backward, the opening into which from the nasal fossa is known as the hiatus semilunaris. The upper end of the infundihulum opens into Fig. 219. Prcibe in infundibulum Crista galli Sup. turbinate Sup. meatus Uncinate process Bulla The ethmoid bone, inner aspect from left side, part of the middle turbinate having been removed. the frontal sinus in about half the ca.ses, "' 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 foetal 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 vear, 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 fcetal life. According to the more generally accepted \iew, 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 \ault 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 -Awdi a horizontal \yox\\ox\, although this division rests on no scientific basis. The vertical portion,^ convex anteriorly, presents on either side, below its middle, the frontal eminejice,^ which represents the chief centre of ossification f either half. Very prominent in infancy, it diminishes during growth, and is hardl>- to be made out in most adult skulls. The lower border of the \ertical portion ', vol. xxviii., 1S98. ' Bulla ethmoidalis. saperciliares. Infundibalum cCbmuidale. ^Os frontalt. ' Squama frontalis. 'Tuber frontale. ' Arr THE FRONTAL BONE. 195 inner third of the arch is the supraorbital yiotch ^ 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 foKamen, which may be four or five milHmetres above the edge of the bone. The arch ends externally in the external angular process ^^ which joins the inaJar and is very prominent. From it springs the temporal 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. Fig. 220. Temporalis Fxternal angular process Supra-orbital foramen Corrugator supercilii Orbicularis palpebrarum 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 bdnes 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 fro7ital 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 infundibuium. When the ethmoid is in place, the cribriforrn plate and the crista galli fill up the ethmoidal notch ; the ethmoidal cells are then closed, and the ethmoidal foramina ' Incisara supraorbitaUs. " Processus zygomatirus. ^ tinea temporalis. ^ Pars orbitalis. ^ Incisura ethmoidalJs. 196 HIMAN ANATOMY. and canals are formed. External to this lies the orbital plate, the front of which is overhung- by the supraorbital arch. It is slightly concave from side to side. Just untler cover of the external angle is an ill-marked dcpressioti ' 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 fre(juently 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 the frontal crest below in the ^Groove for longitudinal ^y^ sinus External angula Supra-orbital foramen Frontal sinus rest Foramen caecum Xasal spine Nasal process The frontal bone from behind. median line. It is a slight ridge, to which the falx is attached. A narrow q-roove runs along it, starting at the foramen ca-citm, a liole either in this bone or between it and the ethmoid. This gromc-is for the superior longitudinal sinus. After a short distance the crest disappears, but the groo\e broadens and extends to the top of the bone. There are a few groo\'es 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 deep gutter. Their upper surfaces are very irregular with so called digital impressions for the opposed cerebral convolutions. It is now e\ident how the frontal, the ethmoid, and the lesser wings of the sphenoid form the anterior fossa of the skull. ■'See Parietal Bone (page 198). J-\ v^ ' Ko4sa glandulae lacrimalis. " Fovea trochleari*. «V J- 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 (Gegenbaur), which also unites before birth. The median (jnetopic) 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, nietopic fontajielle, 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 Fig. 222. Parietal foramen Post. sup. angle Ant. sup, angle Posterior inferior angle Anterior inferior angle Mastoid Right parietal bone, outer surface. Sphenoid on the convex external surface \% \hft parietal eminence ^^ where ossification begms. 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 li?ies^ continuous with those ^Schwalbe : Zeitschrift fiir Morph. und Anthrop., Bd. iii., 1901. ^ Ossa parietalia. ^ Tuber parietale. * Linae temporales 198 HUMAN ANATOMY. into which the temporal crest of the frontal divides. The superior crosses the bone, ending at its posterior border. The inferior 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 even admit a finger. It is occasionally double. The internal surface is smooth and glistening, as is the case throught)Ut the inside of the cranium. It is marked by tree-like ^;t>(?z'd'.y for the branches of the middle meningeal artery. Fig. Groove for longitudi- nal sinus Post. sup. angle Ant. sup. angle Grooves for middle meningeal artery Anterior inf. angle Posterior inferior angle Right parietal bone, inner surface. 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 depressioyis 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, ' Foramen parietale. - Sulcus satfittaPs. 'Sulcus transversus. 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 a^iterior superior corner is about a right angle. The inferior one is somewhat drawn out. The superior posterior coryier is rounded. The inferior is cut ofi. Parietal impressions is the term applied to depressions which are observed very exceptionally 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 foetal 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). The radiating lines of bone leave an interval near the back of the upper border of the bone, called the sagittal fontanelle, which closes during the latter part of fcetal 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 septum, 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 wall and floor of the nasal cavity, much of the hard palate, and supports all the upper teeth. It has a body, and malar, nasal, 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. "" 1 Journal of Anatomy and Physiology, vol. xxvii., 1893. 2 Ibid, vol. viii., 1874. ^Maxilla. ^Corpus maxillae, -' processus zygomaticus. 200 HIM AN ANAT()M\'. This is a roii<,^h triani::iilar surface articulatinjL; w ith the malar, often perforated, andj sending downward a smooth ridj^e separatini^ 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 aj^erture resembles an ace of hearts inverted. The lower boundary of the opening is slighdy raised and smooth. On the side it is sharp. The pointetl anterior nasal spine projects fcjrward where the two bones meet below the opening.* There is a slight depression — the incisor or vivrtifortn 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 canine fossa. Above Lachrymal groove Lachrymal notch Orbital surface Infra-orbital groovf Nasal process Orbicularis palpebrarum lab. sup. alcrq. nasi is palpebrarum tal foramen Posterior dental canal Zygomatic surface. Masst'ter Malar process sup. fossa sor crest Lev. ang. oris Compres. naris Incisor fossa Depres. alee nasi Alveolar process Right superior maxillary bone, outer surface. this, about fi\e millimetres below the edge of the orbit, is the infra-orbital foramen, transmitting the nerve and artery of the same name. This surface is bounded above and externally by the malar process. The zygomatic surface is in the main convex, except for a smooth concavity behind the malar j)r()C('ss. The lower posterior portion, the tuberosity," is rough, and presents at its upper part two or three minute /^^/if-r/^r doital foramina^' hy which those nerves enter canals in the bone. The smooth superior or orbital surface, slanting a little downward and outward, is triangular. The posterior border is free, forming the lower limit of the spheno-maxillary fissure, and running obliquely forward to the malar process. The anterior border passes outward and backward to the same. The inner border is in the main antero-posterior. The hind end slants outward, articulating with the little triangular orbital surface of the palatal. Anterior to this, the border joins the os planum of the ethmoid ; and anterior to the latter, at the base of the nasal process, lies a semicircular indentation, the lachry- vial notch'' the posterior border of which touches the lachrymal bone. The deep infra- orbital groove" runs more than half across the orbital surface from behind, and then * For a more detailed account, see the section on the Nasal Cavity. ^Processus alveolaris. -Processus palatinus. ''Processus frontalis. 'Tuber maxillare. ''Foramina alveolaria. " Incisura lacrimalis. '" Sulcus infraort)italis. THE SUPERIOR MAXILLA. 201 becomes a canal, opening at the corresponding foramen in front. Occasionally a suture marks the course of the canal. The internal wall of the body presents on the separate bone a very large opening into the antrum, or maxillary sinus, which is much reduced when the other bones are in place. In front of this opening the wall is smooth and concave, forming a part of the lachrymal groove. Near the level of the top of the body there is the rough horizontal inferior hirbinate crest for articulation with that bone. The wall at the back of this surface has a vertical groove, which, when the palate bone is in place, forms part of t\\Q. posterior palatine canal, opening near the back of the hard palate and transmitting the descending palatine artery and the anterior palatine nerve. The malar and the alveolar processes have been incidentally described. The nasal or ascending process rises at the inner side of the orbit. It is thin below, with an outer surface towards the face and an inner towards the nose. The top is thick and rough, joining the frontal. The lachrymal groove'^ for the tear-sac and the nasal duct begins on its outer surface and passes down behind it, making a deep notch at the front of the orbital plate. The lower part of the process extends down as far as the inferior turbinate crest, forming, with the lachrymal, the inner side of the groove. The point of junction of the front border of the groove with the orbital plate is usually marked by the lachrymal tubejxle. The inner side shows above at the pos- terior border some cellular spaces completing the anterior ethmoidal cells, bounded below by a ridge, the crista ethmoidalis, which articulates with the front of the middle turbinate bone. Below it the bone is concave, forming part of the vestibule of the nose ; above it is plane and marked with vascular grooves. The palatal process projects inward from the anterior two-thirds of the body and joins the alveolar process in front. It is very smooth above, the mucous mem- brane being lightly attached to it. It is slightly concave from side to side, and has a raised edge in front. It is also raised along the median line to form the nasal cresf- with its fellow. The front of this ridge, called the incisor crest, suddenly rises to a higher level and juts out below the nose as the anterior nasal spi7ie. The vomer rests on the ridge, except at the front, where its place is taken by the triangular cartilage. The under surface of the palatal process, horizontal behind, slants down- \Yard in front to the incisor teeth. It is rough for the firm support of the mucous membrane. The median surface of the palate is rough to join with its fellow. A little behind the incisors it shows a groove in the lower part, which becomes a canal in the upper, and opens into the floor of the nasal fossa of either side. Thus there are two canals above and one below, like a Y placed transversely. These are the cayials of Stenson, which transmit an artery connecting the vessels of the nose and mouth. Their common orifice is called the anterior palatine canal. '^ Into this open two minute canals, the left anterior to the right, made by the junction of the bones. These are the ca7ials of Scarpa, and transmit the naso-palatine nerves. They are by no means always to be found. The canals of Stenson represent the anterior palatine canal of lower animals, which in them is generally double throughout. In man the whole opening is usually closed by mucous .membrane. The back of the palate process joins the horizontal plate of the palate bone, which completes the palate behind. The antrum or maxillary sinus* is a large cavity within the body, the shape of which it follows in the main, although with many variations of size. The large opening on its inner wall is much diminished when the palate, the ethmoid, and the inferior turbinate are in place. It lies near the anterior end of the lateral wall of the middle nasal meatus, covered by the middle turbinate. A small part of the roof of the antrum is often formed by the palate bone, and sometimes the cavity extends into the malar. The inner and most of the posterior and outer walls are generally very thin, as is also the roof, except around the infra-orbital canal, which projects into the antrum. The development outward towards the malar bone varies much, as does the downward and forward growth towards the alveolar process. The lower border of the antrum is usually a trifle below the level of the floor of the nares. According to C. Reschreiter,^ this is a male characteristic. Be that as it may, it certainly is in 5 Zur Morphologie des Sinus Maxillaris, Stuttgart, 1878. 1 Sulcus lacrimalis. - Crista nasalis. ^ Foramen incisivura. * Sinus maxillaris. 202 HUMAN ANATOMY. accord with the larger size of. the sinuses in man. The internal surface is largely] smooth. Bony ridges springing from \arious parts tend to subcHvide the cavity. They sometimes form little pockets above the teeth. According to Oruber,' itj may in rare cases be completely subdivided into a smaller posterior chamber and a] larger front one, both of which open into the nasal cavity. The lowest part of the antrum is indented by the roots of the molars and of the second bicuspid, at leas| verv frequently. The first and second molars always indent it, but the bicuspid anc the wisdom-tooth may not. (For further details, see Teeth, page 1556.) Articulations. — All the bones of the face, except the lower jaw and the hyoid^ touch the superior maxilla. It has been described as the key to the architecture of the face. The palate bone both completes the palate and lies between this bone and the ptervgoids, closing the posterior part of the opening into the antrum. The malar, joining the process of that name, makes the prominence of the cheek ant helps to bound the orbit. The nasals complete the anterior nasal aperture. The lachrvmals and ethmoid touch the inner side of the orbital plate, and the ethmoid the inner surface of the nasal process. The frontal rests on the nasal process, the Fig. 225. Nasal Ethmoidal crest Middle meatus Inferior turbinate crest Inferior meatus Incisor crest Anterior nasal spine Anterior palatine canal Alveolar process Completes ethmoidal cells Posterior palatine canal Nasal crest Palatal process Tuberosity Right superior maxillary bone, inner surface. 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 foetal life. Three of them fuse very rapidly. There is one on either side of the infra-orbital groove, a 7nalar and an orbito-facial, and below and internally ^palatine. 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 w'hich it is between them. It bears the incisor teeth, and at the third foetal 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. KoUiker^). 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 intermaxillary 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. 226. Alveolar process Fig. 227. Lachrymal groove Inferior surface of upper jaw at about birth. 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 foetal 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 les quatres os intermaxillaires, Soc. d'Antropol. de Bruxelles, 1883. 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. 204 HUMAN ANATOMY. Orbital surface Sphenoidal process Outer surface Fig. 228. Orbital process Inf. turbinate crest Nasal crest Post, nasal- spine Spheno-maxillary fossa Spheno-palatine notch VERTICAL PLATE For ext. ptervK. plate Pterygoid fossa HORIZONTAL PLATE For int. pterygoid plate Right palate bone from behind. TUBEROSITY After the loss of tlie teeth from old a^e or otherwise the alveolar process is absorbed. Senile atrophy is particularly marked in this bone. THE PALATE BONE. This' C(insists of a horizonfal and a vertical folate and three processes, the /r- ramidal, the orbital, and the sphenoidal. The horizontal plate' is cjuadrilateral. It completes with its fellow the hard palate, filling the space left vacant be- tween the back parts of the superior nia.xilke. 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 ma.x- 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 posterior 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 \ertical surface forming part of \h^ pterygo-maxillary Fig. 229. For ethmoid Orbital process To complete ethmoidal cells Spheno-palatine foramen Sup. turbinate crest Sphenoidal process Middle npsal meatus Inf. turbinate crest Inferior meatus Tuberosity Ant. part of inf turbinate 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 ma.xilla. In front of this the surface is at first rough where it rests against that bone, and more anteriorly smooth Avhere it closes the lower part of the opening of the antrum by an irregular ^ Os palatinum. " Pars horizontalis. ' Pars perpendicularis. ■* Foramen sphenopalatinum. THE PALATE BONE. 205 Orbital surface Spheno-ma prolongation. The inner surface, looking towards the nasal cavity, is free and smooth. It is crossed below the middle by a ridge, the inferior turbiyiate crest^ 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 Fig. 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-palathie foramen forms a window between the nasal chamber and a litde hollow, the spheno-viaxillary 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 th^foraineti rotiindum and the Vidian canal. Below, it narrows funnel-like into the posterior palati?ie ca^ial. 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 alee, 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 ethmoidalis. ' Vomer. Tuberosity Right 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 inferior border fits Fig. 231. SUPERIOR BORDER Naso-palatine groove Vomer in place, from left side. Fig. \'onier. superior surface. between the nasal crests of the palatals and maxilke, 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 Aiae 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 ner\'e ; 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 maxillary 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 wmgs and in the lower part of the front border, which still receives the triangular cartilage. Groove for rostrum of sphenoid Ant. border for ethmoid Grooved ant. border for septal cartilage Vomer from before and above. 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 maxilla. It is quadrilateral, the long diameter beino- 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. Orbital surface Lachrvmal crest Nasal process of sup. max. Lachrymal groove 4[ Hamul; 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 maxillary, complete the lachrymal canal. The posterior part of the orbital surface is plane. The hamzdar 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 desceyiding 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, 1S84. ''Gegenbaur: Morpfi. Jahrbuch, Bd. vii. ' Le Double : Essai sur la Morphogenie et les Variations du Lacr>'mal, 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 bone, inner aspect. Upper part completes anterior ethmoidal cells, lower looks into middle nasal meatus. 208 HUMAN ANATOMY. THE infp:rior turbinate bone. \ This is an elongatcil curved Ixmic ' 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 Right inferior turbinate bone in place, inner aspect. Fig. 237. 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 curve 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 lachrymal process '^ — the highest — to meet the lachrymal bone. Posterior to this the viaxillary process'' bends outward and downward. It does not, how- e\er, 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 with the superior maxillary, ethmoid, palate, and lachrymal bones. Development. — Ossification proceeds from a single center which appears about the middle of foetal life. ' Concha iaferior. - Proc. lacrimalis. ^ Proc. maxiilaris. * Proc. ethiiioidalis. Maxillary process Right inferior turbinate bone, outer aspect. THE NASAL AND MALAR BONE. 209 Crest Groove for nasal nerve Right nasal bone, outer and inner aspects. THE NASAL BONE. The two nasal bones ^ bound the anterior nasal opening above. 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 Fig. 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 foetal 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 otder surface presents a slight prominence, the tuberosity,^ a little below the m.iddle. 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 m.asseter muscle. The greater part of the in7ier surface is smooth, looking towards the temporal and zygomatic fossae ; 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, ox frontal process," 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 border, is at first vertical, becoming horizontal towards the hind end. Near the beginning there is a posterior projection, the inarginal process, which varies considerably. The postero-inferior, or masseteric border, slightly irregular, is free, forming the lower edge of the front of the zygoma. The antero-inferior, or maxillary border, is slighdy concave. It articu- ^ Ossa nasalia. - Os zygomaticum. ^Tuberositas malaris. * Processus frontosphenoidalis. = Processus temporalis. 14 210 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-su])erior, 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. V\<^. 239. Malar canal Tuberosity Right malar bone, outer aspect. 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- FiG. 240. ing the end of the spheno- Frontai process 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 te7n- 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- Temporal canal Malar canal Maxillary surface Orbital process Temporo-zygo- niatic surface Right malar bone, inner aspect. 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 ' Foramen zygumaticofaciale. -'Furamen zygomaticotemporale. THE INFERIOR MAXILLA. 211 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 rami 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 sy7nphysis, 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 Temporal Sigmoid notch Neck Masseter, External oblique line Platysma Inferior maxillary bone, outer aspect. Mental foramen Depressor anguli oris Incisor fossa Levator menti SYMPHYSIS Mental tubercle Depressor labii inf. distance from the median line at the lower border is the mental 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 me^ital 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 oblique 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 superiot 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 oblique 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- Mandibula. - Tuberculum mentale. ^ Linea obliqua. * Spinae mentales. ° Linea mylohyoidea. 212 HUMAN ANATOMY. inent to the mylo-hyoid, which forms the muscular partition separating the oral cavity from the superficial region under the chin. There is a faint IidUovv, 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 i io° 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 extend 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 oudine ; it is named the antegonium by Harrison Allen. There is a rough- Fit;. 242. Coronoid process Sigmoid notch Superior constrictor Alveolar border Condyle Kxt. pterygoid Neck Fossa for sublin- gual gland Sup. genial tuber. (zenio-glossiis) Inf. genial tuber.'. (genio-hyoid) Inferior dental foramen Int. pterygoid Digastric Mylo-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 i?iferior dental canal for the ner\e and artery to the teeth ; the foramen is guarded in front by a sharp point, the lingnla. 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 abo\e, where it becomes the coronoid process,"^ painting upward and outward, into which the temporal muscle is inserted. The outer border of the thick part is made by the external 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 axes, if j)rolonged, would meet near the front of the foramen magnum. There is a pretty distinct tubercle at the outer and inner ends. The condyle has ' Foramen mandibulare. " Processus coronoideus. ^ Capitulum mandibulae. \ 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 canaP sweeps downward and forward with a slight curv^e, and then runs Fig. 243. Inner surface -Dental canal Section through body of lower jaw, anterior surface. Fig. 244. Alveolar process Coronoid process %- Condyle Symphysis Dental canal Right inferior maxilla at about birth, inner aspect. Fig, Condyle 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 unites 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., 1S95. ' CoUum mandibulae. - Incisura mandibulae. ^ Canalis mandibulae. Right half of lower jaw at about birth, from above. 214 HUMAN ANATOMY. Interarticular fibrocartilaKf Fig. 246. Zygoma, cut surface External pterygoid The temporo-niaiulihular articulation ; the joint opened. 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 tibro-cartilage, dividing the cavity into an upper and a lower part, both being enclosed by one capsular niembrane. 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 Jibro- cartilage'' 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 exter?ial lateral ligament" is a com- paratively strong collection of fibres, strengthening the capsule externally. The fibres run downward and back- 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 nerve.' The spheno-mandibidar 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., 1893. ' Discus articularis. " Lig. temporomandibulare. * Lig. sphenomandibulare. Fig. 247. External lateral ligament Ext. auditon,- meatus Styloid process Stylo-niandihu- lar ligament Hyoid bone The temporo-mandibular articulation, outer aspect. THE ARTICULATION OF THE MANDIBLE. 215 Fig. 248. ■Capsule The temporo-mandibular articulation from behind. rated with the front of the capsule. The stylo-maxillary ligament 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 viovements , 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 may 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 fixed 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 1 Luce : Boston Medical and Surgical Journal, July 4, 1889. » Arch, fiir Anat. und P'.iys., Anat. Abtheil., 1890. Fig. Capsule Interarticular fibro-cartilage Ext. lateral ligament Condyle of jaw Transverse section of right temporo-man- dibular articulation from behind. 2l6 HUMAN ANATOMY. Fig. 250. Great coriiu 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 larynx, with which its physiological relation is intimate. It gives origin to a large part of the muscular fibres forming the tongue. It consists of a central bod\\ 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 ujjper are the larger. The greater eorniia extend with a curve backward and a little upward. They are broadest at their front, and 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 coryiua, 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 basihyoid, or body, is connected with the second visceral arch through the stylo-hyoid ligaments, the lower ends of which become the lesser horns, or eej-ato-hyoids, 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 foetal 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. Small cornu The hyoid bom- from in front. 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 fossae. 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 metopic suture'' persists between the original halves of the frontal bone. It is rarely in direct continuation with the sagittal. The coro7ial 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 hj-oideum. - Sutura sagittalis. ' S. frontalis. ^ S. coronalis. 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 epipteric, is occasionally found in this Fig. 251. Supra-orbital foramen Frontal Exter. angular process .esser wing of sphenoid Optic foramen Great wing of sphenoid. Lachrymal grroove Ethmoid' Malar- Superior maxillary. Infra-orbital foramen Middle turbinate Nasal septum Inferior turbinate Anterior nasal spine Styloid process 'orrugator superciHi Orbicularis palpebrarum Tendo oculi Orbicularis palpebrarum ■Levator labii superio'-H aleeque nasi ■Levator labii superioris Zygoviaticus major Zygomaticus minor Masseter evator anguli oris Compressor naris ■Depressor altz nasi Buccinator Mental foramen Leratoi tnenti Depressor labii inferioris Depi essor anguli oris Platysma The skull from in front. region. (See under Growth and Age of the Skull.) The lambdoidal s^iha-e^ 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 ^ Sutura lambdoidea. 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 /ronto-7iasal, to continue between the frontal and the following bones : the superior maxilla, 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 line LambdoidaLvi 1 suture '(^ O \.. External — -^ XiVK/ '^ occipital ^v!lt^'*^ protuberance ^**^ "N Mastoid process External auditorj meatu St>loid process Ext. angu- lar process Great wing of sjihenoid Mental foramen 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 eminence, 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 protiiberafice, which is beneath the most posterior point of the skull. Lateral Aspect.' — This shows nothing of the face that has not been mentioned. The zygomatic 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 zygomatic fossa below. (The latter fossa is described with the face, page 227. ) The two tetnporal ' Korma verticalis. - Norma occipitalis. '' Norma lateralis. THE EXTERIOR OF THE CRANIUM. 219 lines are to be seen in whole or in part. The 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- FiG. 253. Anterior palatine canal Posterior nasal spine Posterior palatine canal Hamular process Great wing of sphenoid Carotid canal Styloid process Jugular fossa- Stylo-mastoid' foramen Mastoid process Digastric fossa. Occipital groove Parietal bone^ Posterior condyloid foramei Posterior nares •Vomer Foramen ovaie Eminentia articularis Middle lacerated foramen Foramen spino- sum Glenoid fossa Fissure of Glaser Condyle Inferior curved line External occipital protuberance Superior curved line Base of skull from below, the lower jaw removed. tuberance and the superior and inferior curved lines. In front of the latter the occipital bone is convex to the outer side of the foramen magnum A Ime 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 mternal 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 giMural 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. - Norma basalis. 220 HUMAN 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 \hQ Jugu/ar /oramc?i ; then comes the yii\i/^;r proper ; and, at the apex of the petrous portion, the middU lacerated foramoi, 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 Eustachian 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 the zygomatic fossa. THE INTERIOR OF THE CRANIUM. The vault' of the cranium has the groove for the superior longitudinal sinus in the middle, with Pacchionian depressions on each side of it. 'X\\it grooves for the middle meningeal artery cover the parietal region. The base of the cranium is divided into three fosstX, — the anterior, the middle, and the. postet ior. The anterior fossa' is bounded behind bv 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 ca\-ity, the floor of the depression being the cribriform plate of the ethmoid. In the median line are the crista galli and the foramen ciecum. 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 sellce and the superior border of the petrous. The middle fossa has the olivary eniineyice 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 gafiglion 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 maxillary, 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 the foramen mag- num, w'ith 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 internal auditory meatus, the Jugular foramen, and the anterior condyloid foramen are \'ery nearly in a vertical 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. cranii 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, Ethmoidal spine Crista o-^lli Fig. 254. Foramen caecum Frontal sinus Olivary emi- nence Cribriform plate Optic foramen Lateral sinus Torcular Herophih Sella turcica Sphenoidal fissure (con- cealed) Foramen ro- tundum Foramen spi- nosum Inf. petrosal sinus Sup. petrosal sinus Lateral sinus Post, condy- loid foramen Base of skull from above. 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 tlie 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 little 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 fossce. 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 me?ital 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 little 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 itiner 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 of 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 i?ifier wall, composed of part of the ascending process of the ma.xilla, 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 by 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 galli Partition sepa- rating frontal sinus from orbit Sup. turbinate Lower part of infundibulum Nasal septum Antrum Antrum Inferior turbinate Floor of nasal fossae Inferior meatus Front section of skull through plane of outer border of orbits. Arrows pass through communication between antrum and middle meatus. 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' maxillffi. In the middle of the floor of the opening is the anterior 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 Hne 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, forniin|n;- a rather dull inferior border continuous with the lateral sharp one, thev mav remain distinct and enclose a well-niarketl fossa on the face just below the nasal openiui;- ; this is \\\c fossa pturuasa/is, 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 choance, 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 /iooxbi^dth|^ is 60 for men and 64 for women, showing relatively lower openings in the latter ( Escat). Measuring the combined breadth from one pterygoid process to the other at the hard palate on Fig. 256. ten adult skulls irrespective of sex, Piobe in infundibuium wc 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 wall is derived from a plate of cartilage, developed at a verv 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 iriano^ular 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 Inferior turbinate Portion of anterior section of preceding skull, seen from be- hind. The arrows occupy the opening from the antrum into the iiiatus semilunaris. ' Xormale und pathologische Anatomic der Nasenhohle, 2te Auflao:e, \'ienna, 1895. - The development of the nasal ca\ity is described with that of the head. ' Escat : Cavite Naso-Pharjngiene, 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 iniddle nieattis, does not extend nearly so far forward. The little 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 sinus Crista galli Pituitary fossa enoidal sinus Spheno-palatine foramen Inf. meatus Anterior palatine canal 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 wath the ethmoid. The sphe^w-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 t]\e postej'ior ethmoidal cells ; farther back is the sphenopalatiyie foramen communicating with the spheno- maxillary fossa. The middle meatus receives the opening of x}a& frontal sinus either directly under the front of the middle turbinate or through the infundibtdum.. 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 infuntiibulum, and a larger opening from the antrum behind the infundibulum. The lachrymal canal opens into the inferior meatus untlcr the fore part of the turbinate. External to the outer wall are the orbit, the antrum, and farther back the spheno-maxillary fossa with the posterior palatine canal below it. The Accessory Pneumatic Cavities. — These include \.\\q frontal sinuses, the maxillary antra, the ethmoidal cells, and the sphenoidal sinuses. They have already 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. 258. Infratemporal crest Spheno-maxillary fissure Spheno-palatine foramen Glenoid fossa Mastoid process External auditory meatus Styloid process Zygoma , Inner wall of zygomatic fossa (external ptery- goid plate) / Spheno-maxillary fossa seen through ptervgo- maxillary fissure Posterior dental canal Hamular process Lateral view of skull with zygomatic arch removed. The sphenoidal sinuses frig. 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 inner part extends back for a varying 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 infundibulum. In the former cases one of the cells of the ethmoid is particularly liable to make a projection — the 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 v/hen 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 — #j wing of sphenoid A',!,,, Frontal process of malar /(fi/j I Cut surface of zygoma Y', Tympanic plate of. temporal Mastoid process, Optic foramen Sphenoidal fissure Sphenoidal sinus Foramen rotundum Vidian canal Probe in pterygo-palatine canal Posterior wall of spheno- maxillary fossa Palate bone -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 ma.xilla, what little roof there is by 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 spheno-maxillary, 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 t^ig. 259) is a small cavity below and behind the apex of the orbit at the point of junction of the spheno-maxillary and the pterygo-maxillary 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 fora^nen rotundum 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 ■ Hr.MAN ANATOMY. the minute ptcrvi^o-palaiinv ca/ia/, formed by the palate and sphenoid bones. The sphcno-palatine foranicn opens throui,di the inner wall into the nasal cavity. The fossa opens below into the posiirior pa/atinc 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 anijles. 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 palatinus, 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 maxilke 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 liackward in the rest. The fissures are not always svmmetrical.' 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 considcrablv strengthened through the malar bone and its con- nections, especially with the robust external angular process. A little support is probably gi\en to the back of the jaw through the pterygoids. ANTHROPOLOGY OF THE SKULL. There are certain terms and measurements wliich should be known, especially as some of them come into practical list in the surijery 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. Asterion, the lower end of the lanibdoidal suture ; three sutures diverge from it like rays. Auricular point, the centre of the external auditory meatus. Basion, the anterior point of the margin of the foramen magnum. Breguia, the anterior end of the sagittal suture. Dacryon, the 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. Gonion. 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, llie most prominent point of that bone. Mental poijtt, the most anterior jjoint of the symphysis of the lower jaw. Nasion, the jwint of contact f)f the frontal bone with both nasals. Ohelion. the sagittal suture in the region of tiic jiarietal foramina. Occipital point, the most posterior point in the mid-line. (It is abo\-e the protuberance.) Ophryon. the point of intersection of the median line with a line connecting the tops of thej orbits. Ofiisthion. the posterior point of the margin of the foramen magnum. Pterion, the region where the frontal, the great wing of the sphenoid, the parietal, anc the temporal bones almost meet. (As, in fact, "they ver>-" rarely do meet, the term is a vague one. I 1 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 ('°° len^T '^ )• ^^^ length is taken from the glabella to the occipital point, and the breadth is the greatest transverse diameter above the supramastoid ridge. A high index means a short skull ; a low index, a long one. A skull with an index above 80 is brachycephalic ; from 75 to 80, mesaticephalic ; below 75, dolichocephalic. The index of height is the ratio of the line from basion to bregma to the length (^°°iengt^h^ ^)- ^ ^'^^^^ ^^^* ^" index above 75 is hypsicephalic ; from 70 to 75, orthocephalic ; below 70, platycephalic. The facial index is the ratio of the length to the breadth of the face ('-^^^^5^)- The 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, chamczprosopic. In the absence of the lower jaw the inde.x 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 chamceprosopic. The nasal index is the ratio of the length of the nose to the breadth (' J°° >^ length \ ^^^ \ breadth / length is measured in a straight line from the fronto-nasal suture to the anterior nasal spine. A skull is leptorhine when the index is below 48 ; when from 48 to 53, niesorhine ; and when above 53, platyrhine. The orbital index is the ratio of the height of the base to the breadth, thus / 1°° >^ height \ ' \ breadth / 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, niesoseine ; with one above 89, megasenie. An index of 70 is low for a Caucasian, and one of 106 ver>' high. The average 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 ( "^^^-l — E^5 — \. 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 between 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 / 1°° •;' basi-alveolar line \ ^ gj.^jj j^ < basi-nasal line / orthognathous with an index below 98 ; mesognathous with one from 98 to 103 ; prognathous with one above 103. Shape of the Skull. — E.xtreme 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 inetopic 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 m.any 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 two types of face desene 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 short 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 oj'thognathoiis, 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 type. 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, they varv^ 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 i35 Height 132 125 230 HUMAN ANATOMY. Cranial Capacity. — This may vary in all races from looo to 1800 cubic centimetres. Welcker Lri\ ts the tollowing means and extremes for white races : ' Meuii. Maximum. Minimum. Cu. cm. Cu. cm. Cu. cm. Males i45'-> I79*J 1220 Females i3<>J i55^ i^>9" A skull with a capacity exceeding 1450 cubic centimetres is incgaccplialic ; one with a capacity from 1350 to 1450, mcsocephalic ; 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 0.87. Asymmetry. — The whole head is almost always asymmetrical. The left side of the cranium, as .shown by hatters' 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 positi(jn 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 fontanclle .Anterior lateral 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, arid its teeth are set in a smaller curve. The tip of the nose turns to the right. Moreover, the face lacks symmetry 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 without the others. Growth and Age of the Skull. — By the sixth month of foetal 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' capacity. 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 fonta?ie 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 fontatielle 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 fonianelle 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. Anterior lateral fontanelle Posterior 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 fo7itanelle, under the corresponding angle of the parietal, extends down between the temporal and the occipital. It is larger than the preceding, and may be ver>^ distinct for a month or more after birth. Its complete closure is said never to occur before the twelfth month, and, perhaps, usually not till the second year.^ The sagittal fontanelle (see Ossification of Parietal ) may be present at the seventh month of foetal 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 slightly. In the first year the outer surface of the bones of the vault becomes smooth. The bones gam 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 Physiology, vol. xviii. , 1884. =" Adachi : Ueber die Seitenfontanellen, Zeitschrift fur Morph. und Anthrop. Bd. ii.,Heft2. 232 HUMAN ANATOMY. The/ace, while helpinj; to fi»rm the orbit and nasal cavities, is essentially for the jaws, ami the jaws for the teeth. The i^reatest change in tiie head after birth is tiie downward j^rowth of the face. Accordini^ to Kroriep, in the infant the face is to tiie cranium as i to S ; at two years as I to 6 ; at live, as i to 4 ; at ten, as 1 to 3 ; in tlu- j^^rown woman as i to 2.5 ; in the man as I to 2. On contrasting the front view in tiie 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 Iwrder of the nasal opening is at birth but very little below the orbit. A line connecting the lowest jioints of tiie malar liones passes at tiiis age midway between the nasal opening and the border of the alveolar process. At birth the nasal aperture is relatively broad ; its lower iiorder is nt)t sharply marked off from the face A line from the nasal spine runs outward to end inside the cavity, and tiie crest from tiie outer border is still rudimentary, ending shortly on the front of the face, so tliat at the outer angle there is no distinct separation between face and nasal cavity.' The nasal cavity is shallow, tiie posterior nares very small. The vomer slants strongly forward. The lower jaw is small and tiie angle of the ramus ver\- obtuse. The alveolar processes aie rudi- mentary. The breadth of the skull at its widest eijuals or exceeds the combined height of the Fig. 262. Posterior fontanelle Interparietal suture Anterior fontanelle- The skull at birth, from 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. Merkei divides the growth of the head into two periods, with an interv-ening one of rest. The first ends witii the seventh year, and is followed by inactivity till puberty, when the second period begins. The yirsi period mny be subdivided into three stages. In the first stage, reach- ing to the end of the first year, the growth is general, but the face gains on the cranium. At si.\ months the basilar process rises more siiar|:)ly, which, with the downward growth of the face, has an important effect on the siiape of the naso-phar>n.x. The lower part of the nasal cavity gains particularly. The posterior opening doubles its size in the first six months, to remain stationary till the end of the second year. In the second stage, 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 foramen magnum and the petrous portion of the temporal have reached their full size, and the orbit \ery 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 increases 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 vertical 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. Sex. 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 10 female 22 Dwight -. II 22 Dwight 14 female 22 Escat 14 20 Dwight ...>.. 15 male 23 Dwight i6>^ female 23 Dwight 17 female 19 Dwight 18 male 29 Dwight 19 male 24 Escat i5toi8 (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 earlv. The closure of the great sutures of the vault 1 ( 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 outside, as this may never occur, and the process throughout is utterly irregular. All may be gone very early or all may be distinct at an advanced age. When the metopic 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-five.'^ 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 1 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. 2 Gurriere and Massetti : Rivista speriment. di Freniatria e de Med. legale, 1895. 234 HUMAN ANATOMY. of the skull become still thinner and may be (|uite absorbed. The thinning of the vault is less marked. Occasionally, in extreme age, symmetrical depressions appear in tiie upper parts of the parietals behind the verte.x. 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 dilTerence in skulls uj) to puberty. The.se characteristics api)ear during the last stage of growth. They may be summed up by saying 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 zvgomata, mastoid, (jccipital protuberance, and nuiscular 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 throw the face higher up. There is no trout)le 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 axis of the eye when looking at the horizon. It is expressed 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 protubef-ance 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 converse is not true, for, especially in the latter part of life, there may be a large sinus with no external indication. The sinus always extends 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 explored. 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, downward 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 cavity 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, 1895. 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, provision 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 C7'a7iii co7igenita, 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 encephalocele 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 ; (J)) at the fronto-nasal junction ; (/■) 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 fine 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 any 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 markedly microcephalic, approximate in many ways to those of the lower animals, 236 HUMAN ANATOMY. and form a distinct type characterized by the ]M-o])()rtionate largeness of the facial bones, the contraction of the brain-case, especially in front and al)ove, the upward slant of the occipital bone between the foramen maj^nuun and the occipital crest, the projection backward of the frontal bone between the parietals at the situation of tlu anterior fontanelle, and by many minor peculiarities. In spite of these, however, they are easily referred to the human species by the descent of the cranial cavity below the level of the glenoid fossa, the number of tin 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 sj^henoid. Accessory to these deviations, and in a measure dependent upon them, are the modified facial proportions and dental irregularity of cretins. The Wormian hones, "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 hydrocephalus, assistance in the completion of the cranial cavity being supplied I)y 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 indicaticm 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 brnit de souffle of greater or less intensity, and synchronous 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 observes 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 synonym 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 fossse 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 inflammatory 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 " snufBes" 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 of?er much resistance to the separation of the dura from the skull ; neither do their branches furnish a 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 grave symptoms, it is usually sought for first over the anterior inferior angle of the parietal bone, — i.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. 238 HUMAN ANATOMY The time-honored custom of bHsterinii: or leeching^ behind the ear in intra- cranial intiammations rests on the fact tliat the larj^est emissary vein is tlie mastoid, traversinij the mastoid foramen and connectini^ the lateral sinus with an occipital vein or with the posterior auricular. ( P\)r further discussion of these channels of communication, see the section on the Venous System. ) While the spinal dura mater has no intimate connection with the inner surfaces of the vertebrre (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 calvaria 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 off ; the division of the separate bones into inner and outer tables, with the comparatively spongy diploe intervening; and the curved thicken- ings which, like buttresses, strengthen the skull externally, 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, extend 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, w^hile the edges are connected by mem- brane and are comparatively movable. These mechanical conditions, together with the elasticity 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 ; (b) the fibres on the side of greatest strain suffer most (as in "green-stick" fracture) ; (c) 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 LM ) 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 Fig. 264. 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. They 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 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. 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 hmit 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 frequendy because : i. It is connected (by the fronto-sphenoidal and petro-occipital sutures) with both the other foss«, 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 tympanum, of the external auditory canal, and of the temporal fossa. Moreover, just in front of this region the descending pterygoid processes and the lower jaw reinforce the Base of skull from above, showing lines of fractures. 240 HUMAN ANATOMY. cranium proper, while behind it are the thickeninij of the basilar process and the posterior clinoid plate (Humphry) (Fig. 254). The differential symptoms of fracture through the floors of these fossce are determined by their anatomical relations. They are as follows : 1. Anterior Cerebral /'ossa. — (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. ( d) 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 pharynx and stomach, and then be vomited, giving rise to a mistaken diagnosis of gastric injury. 2. Middle Cerebral Fossa. — («) Hemorrhage from the ear. This may be merely from a torn tvmpanic 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 P2ustachian tube. {c) 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. (3) 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 varying 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 jioints 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 \'iolence 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 zygoma ; (c) the temporal ridge from orbit to mastoid ; (d) from mastoid to mastoid ; (e) from the 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 development 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. 1 PRACTICAL CONSIDERATIONS: THE SKULL. 241 The inio7i 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 asterioyi 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 lambda, 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 Stephanion Inferior stephan Obelion Malar point Alveolar point Mental point Auricular point Gonion Lateral aspect of the skull, showing the various points. (See also description on page 228.) The bregma, 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 temporal 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. 16 242 HUMAN ANATOMY. The course of the longitudinal sinus is indicated by a Hue drawn from the nasion (the junction of the nasal and frontal bones) to the inion. The lateral sinus is irregular in its course (page 234). According to Macevven, 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 le\el with the upper part of the 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 1214.) 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 oziena, 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 ozaena ; (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 maxillse 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 give way. The deformity may usually easily be recognized by touch. The fragments are always driven inward, and sometimes become entangled in the fibres of the tem- poral muscles. The attachment of the strong temporal fascia to the upper edge of the zygoma, and of the masseter muscles to its lower edge, prevents displacement upward or downward. The siiperior maxilla, on account of its very various and complicated relations (being associated with nine other bones), has considerable surgical importance. Its position in the same vertical plane as the forehead (instead of in advance of it, as in the lower animals) indicates the limitation of its function to mastication, the need for its use in prehension having disappeared. Many of its diseases (infections, tumors, etc. ) originate in the teeth or teeth-sockets, and may be avoided by early atten- tion to these structures. Others arise by reason of the contiguity of the maxillary antrum to the inferior turbinated bone, the mucous membrane of which is often the subject of chronic catarrh. Injuries of the superior maxilla causing fracture must, as a rule, be direct and of considerable violence. The line of fracture may involve the antrum, the nose through the nasal process, the orbit through the orbital process, or the mouth through the alveolar or palatine process. It may also run into the zygomatic or the spheno- maxillary fossa. The force may be transmitted from the malar bone, or from the lower jaw through the teeth. The maxilla is very vascular, and hence recovery from even serious or crushing injuries is apt to be rapid and thorough. Like the nasal bones, it has attached to it no muscles that can cause or perpetuate deformity, and therefore, unless it is comminuted, its fragments will retain their position when once replaced. It is frequently affected by " phosphorus necrosis," the osteitis causing the ne- crosis being probably due to the direct toxic action of the phosphorus fumes gaining access through carious teeth. This theory is not undisputed. Tumors involving the alveolar border show first in the mouth. Tumors of the body usually occupy the antrum (maxillary sinus). They are apt to grow in every direction except towards the malar bone, where they meet with the greatest resist- ance. They accordingly produce prominence of the eye from pushing upward the floor of the orbit, bulging of the cheek from pushing outward the thin anterior wall, and depression of the roof of the mouth from pressure upon the palatal plate. After the anterior the most yielding wall of the antrum is the orbital. Abscess of the antrum gives rise to the same symptoms when it attains a large size. The relations of the molar teeth to the floor of the antrum and of the infra- orbital nerve to its roof account for the toothache and facial neuralgia that so often accompany antral disease. It is said to be a fact that cystic distention does not involve the lachrymal duct, while solid tumors may cause overflowing of the tears (Warren-Heath). The chief defor^nity associated with the superior maxilla is cleft palate, which results from a failure 0I the palatal plates to unite in the median line. The cleft in the hard palate is always median, but when it reaches the alveolus it follows the line of the suture between the preraaxillary bone (os incisivum) and the superior 244 HUMAN ANATOMY. maxilla, endiny;^, therefore, opposite the space between the lateral incisor and the canine. In single harelip, which is often associated with cleft palate, and due to faulty union of the fronto-nasal and maxillary processes (page 60 j, the gap is found at the same point, never in the middle line. Sometimes the premaxillary bone, which carries the two upper central incisors, is left attached to the nose. This con- dition is usually associated with double harelip. Cleft palate may involve only the soft palate and not the hard, but the reverse is almost never true. Occasionally the identity of the premaxilla is established pathologically. Instances of exfoliation of this bone carrying the two incisor teeth have been recorded, not only in children but even in adults. Excision of the superior maxilla involves { the bone ha\ing been exposed by a suitable incision through the soft parts) the disjunction of {a) its connection with the malar bone ; (^) its nasal process from the nasal, lachrymal, and frontal bones ; (f) its orbital plate from the ethmoid, malar, lachrymal, and palate bones ; ((/) its posterior connection with the pterygoid processes and palate bone ; and {e) its articulation with its fellow through the palatal plates and its connection with the soft palate. These indications are met, as a rule, by sawing through the malar bone just beyond its articulation with the maxilla (so that advantage may be taken of the proximity of the spheno-maxillary fissure), dividing the nasal process a little below the junction with the nasal bones, sawing through the hard j^alate ( from the nose downward) at or beyond the median line, dividing the orbital plate with a fine chisel (or leaving it to be brought away at the last step), and, finally, wrenching the bone away from its attachment to the pterygoid processes (and the orbit) by means of a pair of lion-forceps. The hinder wall, in contact with the palate bone, is very thin, and may give way and remain behind at this stage. This is most likely to happen when it is most undesirable, — i.e., when the operation is performed for malignant disease. The inferior maxilla, the only bone of the skull which is movable upon the others, is especially dense, so that it may be strong enough to withstand the \ery considerable force which its muscles exert upon it in mastication. It is, therefore, not easily divided in operations. The alveolar processes are thicker and stronger than those of the upper jaw, and more force is, therefore, usually required to extract a tooth ; hence damage to the bone through rough or unskilful effort at extraction is more frequent in the lower than in the upper jaw. The last molar, or wisdom tooth, is often a cause of trouble, owing to the limited space it occupies near the angle between the ramus and the body of the jaw. The smaller that angle the greater the difficulty in cutting this tooth, which may be compelled to carry before it a portion of the gum closely applied to the base of the coronoid process, causing inflammation or ulceration, or, through irritation of the sensorv branches of the fifth nerve, may even produce trismus, since the motor supply of the muscles of mastica- tion is derived from the same nerve-trunk. It is thus much oftener the source of, trouble in the white races than in negroes, in whom the angle between the ascending and horizontal portions of the bone is more obtuse. Congenital deformities of the lower jaw are very rare. When they do occur, as in a case reported by Humphry, they show that the jaw consists essentially of two! portions, the alveolus and the remainder of the jaw. In that case the jaw in adult life preserved the proportions of infancy so far as the body was concerned, but the i teeth and alveolus had attained normal dimensions. The division, as Allen has' emphasized, is an important one to remember for the following reasons : the alveolus j is developed with the teeth ; it is an outgrowth from the jaw for a specific temporary! purpose. John Hunter declared that the "alveolar processes of both jaws should rather be considered as belonging to the teeth than as parts of the jaws." Hence I all diseases of the alveolus are to be considered as dental in their significance. Epulis, or fibroma of the gums, is essentially an alveolar disease. A tooth in any] portion of the jaw other than the alveolus is a foreign body. If it is lodged beneath ; the alveolus, it may give rise to chronic abscess, or may, through long-continued irritation, cause one of the various forms of odontomata. Cystic disease about thej angle of the jaw is often e.xcited by a misplaced third molar. PRACTICAL CONSIDERATIONS: THE FACE. 245 The inferior maxilla has no epiphysis, and, as might therefore be expected, the ends of the bone at and near the articular surfaces are usually exempt from disease, in marked contrast to the long bones, in which those regions especially suffer. The inferior maxilla is not a very vascular bone ; the mucous membrane of the gum is in close contact with it ; it occupies a peculiarly exposed position, and is subject to frequent minor traumatisms ; it is readily infected through carious teeth or tooth-sockets. Such a tooth or an open socket communicates direcdy with the cancellous tissue of the bone, thus probably permitting in the lower, as in the upper jaw the direct contact of the toxic agent in phosphorus necrosis. Similar conditions are found in no other bones of the skeleton. As a result of the conditions just enumerated, osteitis and necrosis are common, are associated with much pain, and are often very slow in their progress. The excessive pain, dysphagia, dribbling of saliva, and occasional aphasia and marked nervous symptoms are thought to be due to reflex irritation associated with compression of the inferior dental nerve in the dental canal by the products of inflammation. Such irritation of a cranial nerve confined within a bony canal is rare, and associates the above symptoms with those occasioned by pressure from similar causes on the other branches of the fifth pair and on the seventh. Fracture of the lower jaw may occur at any point. The whole bone is to a great extent protected from fracture by its horse- shoe shape, which gives it some of the ^^*^- '^^^• properties of a spring, by its density of struc- ture, by its great mobility, and by the buffer- like interarticular cartilages that protect its attached extremities (Treves). The neck of the condyloid process and the coronoid process are so deeply situated and so sheltered in the temporal fossa by the zygomatic arches that they are seldom broken. The ramus is protected (though to a Mandible, showing lines of fractures. less extent) by the masseter externally and the internal pterygoid internally, and is not often fractured. The angle and the symphysis are thickened, and thus resist fracture. About three centimetres (approximately one and a quarter inches) laterally to the symphysis the bone is weakened by the presence of the mental foramen and the large socket for the canine tooth. It is most often broken there or thereabouts either by direct or by indirect violence. Most fractures of the body of the bone are compound on account of the firm adhesion of the gum, which is usually torn ;• hence necrosis and non-union following infection from the mouth-fluids are not un- common results. (For the displacement accompanying this fracture see section on Muscles, page 493.) The deformity, in so far as it is produced by anatomical forces, is apt to consist of depression of the anterior and larger fragment by the digastric, the genio-hyo-glossus, and the genio-hyoid, and elevation of the posterior and smaller fragment by the temporal, the masseter, and the internal pterygoid. The dental nerve, while escaping injury at the time of the accident, may later be compressed by callus, and, if irritated, may, by reason of its anatomical associa- tions with the regions in front of the pinna or in the external auditory meatus, give rise to " faceache" or to "earache." If paralyzed, and the patient puts a cup to his lips, he feels with his lower lip only half of it ; in paralysis of the fifth nerve itself it seems to him exactly as though it were broken (Owen). The capsule of the temporo-maxillary joint is thinnest anteriorly and strongest externally ; hence suppuration is most likelv to extend in a forward direction. The strong external lateral ligament arising from the lower edge of the zygoma and running backward and downward seems to prevent the condyle being pressed back- ward against the bony meatus and the middle ear (Fig. 247). As Treves observes, if it were not for this provision, blows upon the chin would be far more dangerous than they are. In spite of its great mobility and its frequent use, the joint is rarely the subject 246 m'MAN ANATOMY. of acute disease, the intra-articiilar cartilati;;e being so ariany^ed (paije 214) that it acts as an elastic butler presentinu^ one surface upon which the hini^e-hke, and another upon which the shchng, movement of the jaw may take j)hicc. Suppurative disease of the middle ear may extend to the joint (Barker). Rheumatoid arthritis is perhaps the most common disease of the joint, and may be localized there in subjects otherwise j^rcdisposed by the frequent e.xj:)osure of the joint to cold and wet. The so-called "subluxation," sometimes, perhaps, depending' upon relaxation of the liijaments, is more prt)bably in the majority of cases due to rheumatic or gouty changes in the joint. Dishnaticyn of the ja'a' (discussed in connection with the action of the associ- ated muscles, page 493) occurs only when the mouth is widely open, as in yawning, so that the condyle passes beyond its proper limits, over the summit of the ridge, and is lodged in front. " When the mouth is widely opened the condyles, together with the interarticular fibro-cartilage, glide forward. The fibro-cartilage extends as far as the anterior edge of the eminentia articularis, which is coated with cartilage to receive it. The condyle never reaches quite so far as the summit of that emi- nence. All parts of the capsule save the anterior are rendered tense. The coronoid process is much depressed. Now, if the external pterygoid muscle (the muscle mainly answerable for the luxation) contract \igorously, the condyle is soon drawn over the eminence into the zygomatic fossa, the interarticular cartilage remaining behind. On reaching its new position it is immediately drawn up by the temporal, internal pterygoid, and masseter muscles, and is thereby more or less fixed. A specimen in the Musee Dupuytren shows that the fixity of the luxated jaw may sometimes depend upon the catching of the apex of the coronoid process against the malar bone" (Treves). Excision of the inferior maxilla, since it is concerned chiefly with the soft parts, will be considered in connection with the Muscles (page 493). Landmarks. — The supra-orbital ridges mark the boundary between the face and the cranium. The supra-orbital notch can be felt at the junction of the inner and middle thirds of the supra-orbital margin. A line from that point to the interval between the two bicuspid teeth in both jaws crosses the infra-orbital and the mental foramina (Holden). The attachment of the nasal cartilages to the superior maxillae and to the nasal bones can easily be felt. The connective tissue between the skin and the cartilages is very scanty. This is a source of difficulty in some of the plastic operations on the nose, and is also a cause of the severe pain felt in cellulitis and in furuncles of that region. The great vascularity of the part and the fact that ' ' the edge of the nostril is a free border and the circulation therefore is terminal" (Treves) favor congestion and engorgement, while the close connection of the skin and cartilage resists the swelling ; hence the nerve-pressure and the excessive pain. The malar prominence, the concavity of the superior maxilla representing the anterior wall of the antrum, its malar process, corrcs[)onding to the apex of that cavity, the incisor fossa, and the canine fossa can easily be recognized either through the cheek or, more readily, through the gums with a finger in the mouth. The zygoma can be both seen and felt, the lower border more distinctly than the ui:>per on account of the attachment to the latter of the dense temporal fascia. Wasting diseases cause an apparent increase in the prominence of the zygoma. The condyle of the inferior maxilla can be outlined and its motions observed (Fig. 246) just in advance of the ear. A line drawn from the angle to the condyle indicates the posterior border of the ramus. In making incisions in this region for inflammatory or suppurative conditions this line is to be remembered. Posterior to it important blood-vessels may be injured ; anterior to it deep punctures may be made with safety, the only structure of consequence endangered being branches of the facial nerve. From the angle of the jaw forward the outline of the inferior maxilla can be seen and felt both externally and within the mouth. The alignment of the teeth is usually disturbed in fracture, and is often the most easily recognized symptom. With a finger between the cheek and the teeth, the anterior border of the coronoid PRACTICAL CONSIDERATIONS: THE FACE. 247 Fig. process may readily be defined. In dislocation this is unnaturally prominent. Be- tween its base and the last molar tooth there is often a space through which liquid food or other fluids can be conveyed by a tube to the pharynx in cases in which fracture- dressing, or trismus, or ankylosis renders the lower jaw immovable. Along the lower border externally, just in advance of the anterior edge of the masseter, the groove for the facial artery may be felt, and in the rniddle line the ridge which indicates the thickening at the symphysis. On the inner surface of the jaw may be recognized the genial tubercles, some- times in two distinct pairs, indicating the attachments of the genio-hyo- glossi and genio-hyoidei. The sub- lingual fossae may be located, and just external to them, and at their lower border, the faint beginning of the mylo-hyoid ridge, which runs upward and backward, becoming more evident opposite the last two molars. Above this line the bone is cov- ered by the mucous membrane of the mouth ; hence diseases of this portion find their expression in the oral cavity, while those of the lower portion of the bone are more apt to involve the soft parts and glands of the neck fFig. 267). The fossae for the submaxillary glands cannot be felt through the mouth, but, as they lie below the ridge, while the sublingual fossae lie above it, the well-known clinical relations of the former glands to the neck and of the latter to the mouth are explained. The familiar change in the shape of the lower jaw in edentulous old persons is due to absorption of the alveolar process. (Most of the landmarks of the face are of more importance in relation to the soft parts, the nerves, and the contents of the cavities of the orbit, nose, and mouth than in connection with the bones themselves. They will, therefore, be further con- sidered in those connections.) Inner surface of lower jaw, showing various areas. THE UPPER EXTREMITY. The Shoulder-Girdle. — This consists of the clavicle and scapula. The latter is far the most important morphologically, representing, as it does, both the scapula and the coracoid of the lower classes of vertebrates ; while the clavicle is inconstant in mammals, and seems to be no part of the primitive shoulder-girdle. The scapula bears the socket for the humerus. It h?s no bony attachment to the trunk save through the clavicle, wliich, interposed between it and the sternum, is connected with both by joints. THE SCAPULA. Physiologically, the essential part of the scapula is the socket for the shoulder ; a part of this is made by the coracoid clement, which in man is an insignificant pro- cess of the shoulder-blade. The secondary functions of the bone are to give origin to some muscles and to afford leverage to others for their action on the arm. In most mammals the scapula may be considered a rod running upward from the joint, from which three plates expand, one towards the head, one towards the tail, and one outward. In man the second of these plates points downward and is excessively developed. It is more convenient in man to speak of one main plate, the body of the scapula, with the spine springing from the dorsal surface. The body is triangular, with two surfaces, — a ventral one towards the ribs and a free dorsal one. — three borders, and three angles. The posterior or vertebral border,' sometimes called \S\Qbasc, is the longest. It, is nearly vertical from the lower angle to a triangular space on the dorsum, oppo- site the origin of the spine, above this it, as a rule, slants forward, but at a very varying angle. The upper border- slants downward and forward to \h^ supra- scapular notch ' at the base of the coracoid process. This notch, transmitting the suprascapular nerve, is sometimes imperceptible, but usually is well marked and sometimes very deep. It is bridged by a ligament, which may be replaced by bone, transforming the notch into a foramen. The anterior or axillary border* is the only thick one. Just below the glenoid cavity it begins as a triangular roughness for the long head of the triceps. This is continued as a line which ends on the dorsal surface near the lower angle, a little above an unnamed process curving for- ward and inward from which a part of the teres major arises. This is the analogue of a process much developed in some small monkeys. It is sometimes very large, the increase of size being in no relation to that of the bone nor of the muscle. Above this on the anterior border there is a deep groove for a part of the sub- scapularis muscle just internal to the anterior edge proper. Below the process the border runs downward and backward to the inferior angle. ^ This angle is some- times very sharp, sometimes quite the reverse. The same, in a less degree, may be said of the upper angle,* usually sharp, sometimes squarely truncated. The anterior angle " is the glenoid cavity. This, with the base of the coracoid process, is called the head of the scapula, the neck being a constricted region behind it, reaching to the suprascapular notch. The glenoid cavity* is an oval, slightly •hollowed, cartilage-covered surface expanding from a narrower base. The long axis is vertical and the broad end below. There is often an indentation at the upper part of the inner margin. The edge is a little raised where it bears the gleyioid ligament, which deepens the cavity for the reception of the head of the humerus. The top of the edge forms the supraglenoid tubercle, whence starts the long head of the biceps. The coracoid process springs from the top of the head just behind the glenoid ca\ity and a little to the inner side. The first part, or root, which is compressed from side to side, rises inclining somewhat inward. The second, the free projecting portion, irregularly cylindrical, runs forward, rather outward and downward, to end in a knob near the inner side of the shoulder-joint. The upper and inner surface is ' Margo rertebralis. - .M. superior. ^ Incisura scapulae. ^ M. axillaris. ^ Angulos inferior. ''A. medialis. ' A. lateralis. ^ Cavitas glenoidalis. 248 THE SCAPULA. 249 rough and convex, the under and outer smooth and concave. A rounded promi- nence, the conoid tubercle, for the conoid hgament, is situated on the top of the first part and rather to the inner side, just above the angle formed by the two parts. A ridge from behind this, running outward and forward, separates the two parts dis- tinctly. The trapezoid ridge for the trapezoid ligament runs forward from the conoid tubercle along the inner side. The outer side of the upper aspect has a ridge for Fig. 268. acromion process Supraglenoid tubercle Conoid tubercle Root of spine Superior border SUPERIOR ANGLE Long head of it iceps CORACOID PROCESS Biceps and coraco- brachialis ANTERIOR SURFACE Subscapularis) POSTERIOR SURFACE INFERIOR ANGLE Right scapula from before. the coraco-acromial ligament. The short head of the biceps and the coraco- brachialis arise from a roughness at the tip of the process, and the pectoralis minor inserts into one at its inner side. The anterior surface, or venter/ is concave, forming the subscapular fossa, the deepest hollow being along the origin of the spine. At the very top the bone often takes a turn outward. The serratus magnus is attached to rough surfaces inside the upper and lower angles and to a narrow line connecting them just beside ^ Facies costalis. 250 HUMAN ANATOMY. the \-ertebral border. These surfaces are separated from the rest of the fossa by well-marked lines, which, with some four ridges running forward and upward from the spinal border, give origin to tendinous septa from which the subscapulars springs. This muscle arises also from the deep groove inside the axillary border. The posterior surface.' or dorsimi, is divided by the spine into a supraspinous and an infraspinous fossa. The former gives origin to the supraspinatus. Near the back it is often strengthened by a vertical swelling. The infraspinous fossa is chiefly occupied by the infrasj)inatus, but two other areas are marked off by two lines : one, running forward and upward, separates the dorsal side of the lower angle and of the unnamed process on the axillary border ; from this space springs the teres major. The second line leaves the axillary border near the glenoid ca\ity and, diverging slightly, strikes the former line near the front, bounding a narrow region for the teres minor, which is crossed high up by a groove for the dorsal scapular artery. Fig. 269. Anterior tubercle acromion Coraco-acromial ligament Short head of biceps CORACOIO PROCESS Long head of biceps Suprascapular n Upper part of vertebral bordci Metacroinial tubercle SUPERIOR ANGLE I Right scapula from above. The spine - is a triangular plate arising from a small triangular surface at the pos- terior border, running outward and somewhat upward. Its attached border stops at the neck before reaching the glenoid cavity. The spine forms an acute angle with the floor of the supraspinous fossa, and an obtuse one with that of the infraspinous. Its front border is rounded and curves forward, and forms the posterior boundary of the great scapular notch connecting the supra- and infraspinous fossae. The free border is narrow beyond the triangular area, but soon broadens, presenting an upper and a lower lip. The descending fibres of the trapezius are inserted into the whole length of the former, and of its continuation into the acromion. The lower lip often begins with a tubercle for the ascending and horizontal fibres, a little beyond which it narrows again. It gives origin to the deltoid muscle, which also is continued along the acromion. The acromion^ is a broad, flat expansion overhanging the shoulder-joint and articulating with the clavicle by an elongated facet slanting slightly upward. A ' Facies dorsaris. - Spina scapulae. ^ Acromion. THE SCAPULA. 251 short predavicular border in front of this, receiving the outer end of the coraco- acromial hgament, runs forward and outward to the anterior tubercle. From this the outer border runs backward to the metacromial tubercle, whence the posterior border runs into the hind edge of the spine. The 02iter border has three or four irregularities above for the tendinous septa of the deltoid, and is smooth at its lower edge for the same muscle. The lower lip of the spine runs directly into the hind border of the acromion, but often splits so as to enclose a narrow space continued into the back of the process, from which the deltoid springs. The acromion varies much in shape ; according to this description it is quadrate ; often, however, the pre- FiG. 270. SUPERIOR ANGLE Levator anguli scapula Supi aspinatus Tt apezius. Rhomboideiis L minor j Smooth sur face for tra pezius VERTEBRAL BORDER Coraco acromial ligament coRAcoiD PROCESS Bleeps and coraco- brachialis ACROMION ?^?^^S^^Si^x:^ — Anterior K^^^gj^'ja tubercle Deltoid Metacromial tubercle Triceps long head Groove for dorsal artery INFERIOR ANGLE Tei es major -Occasional origin of latissimus dorsi Right scapula from behind. clavicular edge is rudimentary, so that it is three-sided ; or the metacromial tubercle is at the apex of a v&xy obtuse angle, so that it is curved and narrow. There are also intermediate forms.' The inclination of the acromion to the horizoii 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 determinino; the outline of the scapula vary greatly. The hmd 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 rismg trom the table ; but this may be almost straight, or even bend the other way so as to change the usual points of support. 'The le^igth from the upper to the lower angle ranges from 13.2 centunetres 1 Macalister : Journal of Anatomy and Physiology, vol. xxvii., 1893. 252 HUMAN ANATOMY. or less up to 20.1 centimetres. The scapu/ar iHcirx is the ratio of the breadth, measured alonjj the base of the spine, to the length ( -"° i^.,/ih' )• It ranges from 55 to 82. The following means have been given for Caucasians: Hroca, 65.9; Flower and Garson. 65.2; Dwight, 63.5. A high inde.x means a broad scapula, which is one of a low type. The in/raspinoiis indc.v 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 (i„fras^ni3iiTleiiKih )• ^^'^ ranges from 72.3 to 100.2, with a mean of about 87. Although high inrlices imply a broad scapula, this method is of small value, as ver>' diverse shapes may have similar indices. It is not jwssible to j^redicate 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 thirty-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-si.\ measure si.xteen centimetres or more, of which only five were Fig. 271. SUPERIOR ANGLE — Scrralus magnus NECK Glenoid cavity Triceps (long head) ■^^-^ Subscap ula ris AXILLARY BORDER VERTEBRAL BORDER Ridges for tendi- nous attach- ments Process for teres major — ' ^ Serratus magnus Right scapula from before. INFERIOR ANGLE 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. Very few male sockets are less than 3.6 centimetres in length, and very few female as long. The typical female scapula is \ery delicatt 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 peculiar 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 eighth foetal month ; B, towards end of first year ; C, from fourteen to fifteen years ; Z>, from seventeen to eighteen years ; E, about twenty years, a, chief centre ; b, for coracoid process ; c, for acro- mion ; d, 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. Sec, i8q4. 254 HUMAN ANATOMY. KiG. 273. Lines of fracture of the scapula. by a synchondrosis. The possibihty of its detachment by excessi\e action of the latissimus doisi has been mentioned, but no case of traumatic separation has been recorded. Fracture is rare, in spite of the thinness of much of the bone, because ot its mobihtv, the adajjtation of its cin\ es 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 movement and corresponding weakness of the shoulder- joint, which, in like manner, by undergoing luxation, pre\ents the force of the traumatism from reaching the scapula. Fracture of the liody 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, and 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 infrasi)inatus 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 j)ro- longation of the scapula downyvard, 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 ef?used 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 bv sinking the fingers into the interval between the deltoid and pectoral muscles. The coracoid will be found just beneath tlie 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. The 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 Mill occur only if the coraco-acromial and coraco-cla\icular 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. Excision 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 scapulse, 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- teurri, 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 of the scapula can easily be felt. The bony points most readily recognized by touch are the acromion, the coracoid, the spine, 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 (scapula; alatae). This is pardy 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 scapulse, 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 HLMAN 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 1867); 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 thescapuke 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 vertex, the inferior angles are from sixteen to seventeen inches apart. By crossing the arms on the front of the chest, and leaning forward, the scapula:? are also widely separated, and this position is therefore selected for auscultation and percussion. The mol>ility of the scapula lessens the functional tlisability in ankylosis of the shoulder-joint. LIGAMENTS OF THE SCAPULA. Two ligaments — the transverse 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 nerve 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 a weak space between, the front one being the stronger and overlapping the other when they Capsule of shoulder-joint Humerus Tendon of biceps Coraco-acromial ligament -Vv Coracoid process Coraco-clavicular ligament Fig. 274. Acromio-clavicular joint Clavicle Ligaments about the right shoulder from above. 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. transrersum scapulae superius. - Lig. corpcracroroiale. THE CLAVICLE. 257 distinct, since the bursa appears to connect it with the capsule below and a thin fascia with the clavicle above. 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 chmb, 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. Trapezius 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 Sterno-hvoid 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 ; ^ Lig. transversum scapulae inferius. - Clavicula. 17 258 HUMAN ANATOMY. external to this the rough concave edge gives origin to the deltoid. The beginning of this is often marked by a minute tubercle, which, when exceptionally large, is the dtltoid tubercle. The posterior surface is smooth, and narrows gradually 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 detined 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 abo\ e 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 cotioid 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 Ossificalioii ot claviL-le. .^, at birll; ; u, chief cen- arrn teres l— Tendon common lo pronator ra- dii teres, flex, carpi radialis. palmaris lon- gus, flex, sub- lim. dig., flex, carpi ulnaris > Anterior border External hmi'f supra- lililW'] condylar //*M' /' ridge ' "*'' t'"' RadiaV fossa External condyle Internal supracondylar ridge '"oronoid fossa Internal condyle Common tendon for flexor muscles ' Capitellum Trochlea Rin-. The lower extremity is broad from side to side, with an articular surface below, and two lateral i)rojections, the condyles. The inner condyle, "^ much the larger, is sharp and prominent, giving rise with a part Fig. 2S3. ,,f the supracondylar ritl|L;e to the flexor pronator mus- ^ • , ;; :-> cles. It is faintly grooved l)ehind by the ulnar nerve, w;'' ' ' ■; '-hMt^jx 'I'l^^l the lower part of the front often i^resents a smooth ■ '■% surface. The outer condyle' \'^ a •>\v^\\\y raised knob. k: - 1 he articular surface, most of which is at a lower level fel" than the condyles, consists of two parts, — an inner ^v^'v' pulley-like surface, the trochlea, for the ulna, and an outer convexity, the capitcllnm, 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-con\ex 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 coronoid fossa, is small and receives the coronoid process of the ulna in flexion ; the posterior depression, triangular and much the larger, is the olecranon fossa, receiving that process in extension. The bone separating these fossae — the plate just alluded to — is so thin as to be translucent. It mav be perforated by the supratrochlear firanien, 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 ; finally, 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 concaxe head of the radius plays, 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 b' 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 axis 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 180°, and that thus the true angle is 168°. We give this as the simplest. ) The angle is greater in the foetus. Gegenbaur gives 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 axis of the trochlea than does the male, but Berteaux'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 fostal 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 OsMfication of humerus. A, just before birth ; B, in the first year; C at three vears ; C', sections of ends of preceding- D at five vears ; ^, at about thirteen vears ; £', sections of ends of preceding; i=^, at about sixteen ; F , sections of ends of preceding, a, centre for shaft ; b, for head ; c. for capitellum and part of trochlea ; d. for greater tuberosity ; e, for head and tuberosities in transverse section ; /. for internal condyle ; g, for inner part ot 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 1 Le Humerus et le Femur, Paris, 1891. 2 Journal of Anatomy and Physiology, vol. xxv., 1891. 270 HUMAN ANATOMY. become one, makinc: a cap for the top of the shaft, wliich latter extends into the head. The largest centre tor 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. Althou,c,di all these epiphyses are orisfinallv in the same strip of cartilacje. 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 insip^nificant 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 condvle 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 ofT 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 beyond 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 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 shallowness 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-supply 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 Fig Head Shaft Fracture of anatomical neck of humerus, showing impaction. 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. 287. Fig. 286. Upper end of humerus, showing epiphyseal line. A, on surface; £, in section. Upper end of humerus, showing cupping 01 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 ni.iy 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 ; (2) because the humerus on the epiphyseal line is broader than at any other jKirt of its upper end. Tile 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 i 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 de\elopment shoukl be a usual sequel. The upper epiphysis from the tenth year to adult life will, according to Vogt, add from seven to ten centimetres to the length of the humerus, the lower epiphysis during the same time adding but one-iifth 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 retiected cajwule 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 curve 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 exostoses 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 niav 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 periosteum 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 Fig. 2S8. 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 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 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 fossffi, 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 displacement. Either epicondyle may be broken. The line of the lower epiphysis runs obHquely 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 18 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 Hkcly to be broken across, detaching one or other jjortion 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-sixteenths 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 level 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 excision 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 age. 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 epiphyseal separation will be con- sidered in connection with the subjects of supracondylar fracture and luxation of the elbow (page 590;. 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 frecjuency 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 axis of rotation does not correspond with the axis of the shaft. The shallow socket of the glenoid ca\ity, lined with articular cartilage, is deepened by the glenoid ligament' (Figs. 290, 292), a fibro-cartilaginous band attached by its base to the l)order 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 lax 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 artiiularis. 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. 289, Coraco-acromial ligament Bursa Trapezoid ligament Clavicle Capsule Long- head of biceps Humerus Conoid ligament Suprascapular 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 Acromion Tendon of biceps Head of humerus reflected Glenoid ligament Glenoid cavity Spine of scapula igament Superior gleno-humeral ligament -Anterior border 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 HLMAN ANATOMY the opened joint ; on the outside, the hbrcs can be traced for a considerable distance from tlie joint Ixfore they are lost in the periosteum. Fibres li^oin^ to the tuljerosi- 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 l.Uter 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, witht)ut very tlistinct borders, to both tuberosities, crossing the bicipital groove. A few transverse hbres (the transverse humeral ligament) bridge in the bicipital groove below the capsule proper. Thvi^Q gle?io-liumeral bands ( Fig. 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 Tendon of biceps in bicipital groove Glenoid ligament Glenoid cavity Glenoid ligament Greater tuberosity Subdeltoid bursa Tendon of infraspinatus nd capsu4e Horizontal frozen section through the right shoulder-joint from above. superior. This band springs from near the top of the inner border of the glenoid cavitv and is inserted into the lesser tuberositv. 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 7niddle 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 Usually presents an opening on the inner side in the upper part, bv 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 foetus it is attached to the inside of the capsule by a synovial fold. The synovial ^netnbrane of this joint is remarkably free from synovial fringes. • The bursae about the joint are numerous. The largest is the sxib acromial 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. Clavicle Coraco-clavicular ligament Capsule, Subdeltoid bun Deltoid muscle 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. Abduction has a range of some 90° before the tenseness of the lower part of the capsule stops it. 278 HUMAN 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 approximate 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 jKirt in practically all the mo\ements, not waiting till the range of movement at the shoulder is exhausted, but sliaring in it from the start. The acromion and coraco-acromial ligament make an e.xtra 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 la.xity 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, affording 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 movement 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 mobility 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 luxation, 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. 293. Supraspinatus Reflection of capsule Deltoid ReflectL 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 commuYiicate 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 hone and the under surface of the acromion and coraco-acromial hgament. 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 axilia. (2) By following the subscapular tendon, getting between that muscle and the body of the scapula, and opening beneath and behind the axilla. (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. Treves mentions a case in which it followed the course of the musculo-spiral nerve and appeared on the outer side of the elbow. Landmarks. — The cdi^e of the acromion and the tij) of the coracoid can readily be felt, though the coraco-acromial ligament comi^leting 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 dropj)ing from one to several inches. The lower margin of the glenoid cup and the head of the humerus may be felt in the axilla 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 circumflex 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 jjrominent internal ridge can be felt only 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 anticus 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 Wrisberg 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 proximity 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 nerve 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 ulna, 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 saving 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 coro7ioid 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 point 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. T\\& posterior surface is triangular, bounded above by the irregular edge of the top, and laterally by two lines which mxcet below to make the posterior border of the shaft. It is subcutaneous, and is covered by a bursa (Fig. 294). The outer surface 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 inner surface 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 siirface 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 groove 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, slighdy 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. ^ Incisura semilunaris ^ Incisura radialis. 282 HUMAN ANATOMV Tricep. Subcutaneous surface Flex, sublim digitorunt Fig. 294. Aponeurosis of ext. carpi ulnar is, , , fiex. profundus [''' dtgilorum and flex, carpi ulnar: Fig. 295. Lesser sigmoid cavity Anconeus \[ »— 4- Posterior border Tip of olecranon Greater sigmoid cavity Upper end of right ulna, posterior aspect. m^ -Anterior border Nutrient canal- Brachialis anticus Supinator brevis — ''llFlex. sublim. dig. (coronoid head) Pronat. radii teres f( lesser head) Flex. long, pollicis (accessory head) / Flex, prof una.. digiioruni Interosseotis border — v\. mm ii Vjulf, Pronator quadratui Articular facet- for radius . — .:>tyIoid process Right uln.-i, mner aspect The outline figure shows the areas of muscular attachment THE ULNA. Fig. 296. 283 Olecranon tip Greater sigmoid cavity nterosseous border Vertical ridge Groove for exi. carp, ulnar. Styloid process Triceps Anconeiis-l- Ext. carpi ulnaris— Supinator brevis Ext. ossij Viet, pollicis Ext. long, pollicis — Ext. indicis Right ulna, outer aspect. The outline figure shows the areas of muscular attachmeut. 284 HUMAN ANATOMY Fig. 297. ■m ■^i: but sometimes the front border is short and the inferior runs obHquely backward, making it ahiiost triangukir. The shaft,' which presents three borders and three surfaces, steadily (Hniinishes from abo\e downward. In the uj^per i:)art the bone curves sHghtly backward and outward (i.e., towards the radius), then inward through the greater part of its extent, till at the lower quarter it again bends outward and, at the same time, for- ward. 'Wx^ posterior border"^ is formed by the union of the two lines bounding the subcutaneous surface at the back of the olecranon. Following the curves just described, it runs to the back of the styloicl process, being very distinct in the first two-thirds, where it gi\es origin to the aponeurosis of the flexor carpi ulnaris. The ayitcrior 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 rais-ed, is the supinator ridge. The depression which gives 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. Above this arises the flexor profundus digitorum. The nutrient foramen running upward is a little above the mid- dle. The in7irr surface, concave at the side of the upper ex- tremity and convex below, gives further origin in its upper two- thirds to the last-named muscle. The posterior surface has several features which are to be recognized only 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 off 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 below this is subdivided by a vertical 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 «arpi 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 extensor 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- jecting forward and outward, presenting 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-joint 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. ■* Margo volaris. * Crista interossea. -' Capitulum. Longitudinal section of ulna. PRACTICAL CONSIDERATIONS: THE ULNA. 28 = 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, Ossification of ulna. A, at birth ; B, at five years; C, at ten years ; £), at about sixteen years, a, centre for shaft ; d, c, cartilaginous epiphyses ; d, centre for lower epiphysis ; e, 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 hmits of strong periosteal and tendinous and ligamentous expansions, is of small size, and before the fourteenth or fifteenth year is on a 286 HUMAN ANATOMY. Fig. plane anterior to the epicondyles. For these anatomical reasons, neither muscular action (triceps) nor falls on the elbow are so productive 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 e.xcept 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 oblicjue fibres of the interosseous membrane. The line of fracture is nearer the tip than the base of the process. The insertion of the brachialis amicus 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. 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 fracture of coro- noid, olecranon, and styloid processes of ulna. Fig. 300. Fracture of upperthird of ulna, with dislocation of radius forward. 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 stvloid 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 CoUes'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- tion) 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 condyles Fig. 301. Posterior view of elbow, showing relative position of condyles and olecranon. A, in extension ; £, in flexion. 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 difificulty 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 two 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 AXATUMV Fig. 302. Neck- Bursa! surface- Bicipital surfaco- ~'rHr'- \i '■>'^ \M W? ] -'•-S"-i)itiaioy l>i rvis I/'' if Biceps tendon- J^. btevis- ■/ \ -Interosseous border Stdpinator bt cvis- Flex, sublimis- digiioyum Flex. long;, poinds - Ext. ossis met pollicii ■Ext. brevis pollicis R^^' K:. Pronator quadrctus. Brachio-radialis—l . ,?( Ulnar surface Semilunar surface Styloid process Scaphoid surface Right radius, inner aspect. The outline figure shows the areas of muscular attachment. 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 axis 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 considerably. 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 almjst 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 obliqiie 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 pollicis. The border is thence poorly marked till, slanting forward to 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 hollowed 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 roughness for the insertion of the pronator radii teres. The posterior surface has a concavity in the middle third, internal to the posterior border, 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 faindy divided into two, for the extensores carpi radialis longior et brevior ; internal to this is a marked ridge, the tubercle, 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 internally 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. * Incisura ulnaris. 19 290 HUMAN ANATOMY. Fig. 303. Head '^ ,^ Necic Supinator brevis( V ' /Biceps Pronator radii teres^ Flex, suhliiiiis digiloruni ~Flex. long, pollicis Brachio-radialis Pronator quadratus Oblique line m ' • Nutrient foramen Interosseous border Anterior border- f^l \i!s,l^ ^»!j; ■«^«"\ VAV^/ij* Sigmoid ^cavity lor ulna Groove for ext. OS. met. pol. Groove for ext.' brevis pol. Semilunar surface Scaphoid surface Styloid process Right radius from before. The outline figure shows the areas of muscular attachment. THE RADIUS. 291 Head Tuberosity . Fig, 304. Posterior border. Interosseous border- Biceps - Ext. OSS-is met. pollicts— Supinator brevis — Pronator radii tez-e^ Ext. brevis i>orucis~ \m\ Sigmoid cavity , Tubercle ) Ext. OSS. met. poll. \ Ext. brev. poll. -Ext. carp. rad. long-, et brev, Ext. com. dig. and ,«^ ext. indicis \ Styloid process Ext. long. poll. 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 of? an inner square surface for the semilunar and an outer triangular one for the scaphoid. The surface looks slightly forward, thus causing the forwartl 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 i)rimates 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. Scaphoid surface Semilunar surface Styloid process Ext. OSS. met. poll. 1 Ext. brev. poll. / Sijtnioid cavity Ext. carp. rad. long. J X_3 \ Ext. communis dig. Ext. carp. rad. brev. I Ext. long, pollicis and ext. indicts Tubercle Lower end of right radius. Fig. 306 B. Fig. 306^. a' ttWi Longitudinal sections of radius ; B in frontal plane, showing arrangement of trabeculae 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 lighter 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 Ossification of radius. A, at birth ; B, at two years ; C, at five years ; D, between eighteen and nineteen years, a, centre for shaft ; b, 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 — reeeive 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 jjinched between it and the capitellum ( Fig. 311); and (2) that it is a jjartial 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 disai^ility. There seems nothing absolutely inconsistent with these symptoms in the view that a slight eiDiphyseal separation has occurred, the upper end of the diaphysis being dis[)laccd 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 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 bv 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 radius (CoUes's fracture). /J, dorsal; ^, 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 flexor 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., with 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 uncommon. 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 Fracture of lower end of radius, showing liand carried towards the radial side. 296 HUMAN ANATOMY. thinnest in the centre (five milhmetrcs), the line at that point crossing the bone about three inilHmctres below the tip of tlic prominent midclle thecal tubercle. The need for an accurate conception of this epiphysis is enij)hasized by the facts: (I) that it is more often separated than any other in the l)ody, with the possible exception of the lower ej)iphysis 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 j)ronated hand. The carpal bones are carried against the posterior border of the radial epiphysis, the pro- nator quadratus and other muscles fix 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 j)ut 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 involved. 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 in\ariably 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 external 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 Fig. 310. Lower end of left radius, showing epiphyseal line, 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 — i.e., 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 ; 2. Inferior Radio-Ulnar Articulation : Triangular Cartilage ; 3. Ligaments uniting the Shafts : Interosseous Membrane ; Oblique Ligament. Capsular Ligament. Capsular 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 condyle Orbicular ligament surrounding head of radius Tuberosity of Internal condyle Coronoid process Oblique ligament Radius 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 proximalis. " Lig. annulare radii. 298 HUMAN ANATOMY syno\'ial membrane. It narrows below so as to fold under the projectinj,^ head, and is attached, chiefly through tibres from the lower border of the lesser sigmoid ca\ity. to the inner side of the neck. It is connected above with the capsular ligament of the elbow-jtjint. That the fibres to the neck limit rotation is easily shown by dividing all bands connecting the bones, excepting the orl)icular 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 moxement which can occur in the imdissectcd 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 antl 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 apex 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 Front of capsule Fig. 312. Median nerve Radial nen-e Coronoid process Inner side of greater sigmoid cavity Ulnar nerve igament Horizontal section through right elbow-joint from above. The trochlea of humerus has been removed. 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 syno\ial 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 ayitcrior and posterior ligameyits. 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 ' (Fig. 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, radioulnaris distalis. - Discus articularis. ^ Membrana intcrossea intcrbrachii. THE FOREARM AS A WHOLE. 299 several small openings for the passage of vessels and nerves. Pressure transmitted upward fsom 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 Head of ulna 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 Head of ulna Ligament of triangular cartilage Styloid process of ulna \ Fig. 314. Capsule of inferior radio-ulnar joint Styloid 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 obliqua. 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 tl-fce greatest possible distance from each other, and the membrane is approximately tense (F"ig. 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 from hollow is much deepenetl and the hind one lost. The bones are much nearer together than in any other position. The radius crosses the ulna, and is abo\e 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. Pronation. Supination. Interosseous membrane^ Head of ulna ir\i -oblique liRament -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 abo\e 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 body that is not very muscular, though comparatively 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 lovyer end of the radius 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. Triceps- — Brachialis anticus Capsule Trochlea Bursa Subcutaneous bursa Olecranon Coronoid process Ulna 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 only 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 cubiti. 302 HUMAN ANATOMY. the humerus is possible. The head of the radius plays on the capitellum, hut 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 lii^anic?its. The anterior fibres arise from the humerus above the coronoid and radial fossc^e, and from the front of the bases of both condyles. Behind, they arise from about the middle of the olecranon fossa, which is only 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 j^oints 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. nil I. Band strengthening front of ^, / \ A- capsule i / '^ \ \ ' . Fibres of orbicular ligament 'feC';;.^^ ^-» ' • V ^ ^' Thin part of capsule Bursa for tendon of biceps Radius Internal condyle of humerus Cut tendon of biceps Oblique ligament Ulna Capsule of right elbow-jomt 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 interyial 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. collaterale ulnars 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 extended, 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 flexion 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 d) the two parts will lie one on Fig. 318. Olecranon fossa Internal condyle Posterior part of capsule Radius External part of capsule, con- cealing orbicular ligament Ulna Bursa Right elbow-joint, posterior and outer aspect. 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 lip^htly 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. Interosseous membrane Ulna Tendon of biceps Superficial layer of inter, lat. ligament Olecranon Deeper layer of internal lateral lijjament 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 ulna, 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 tw^isting 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 by 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 movement 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 axes 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 experiments 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 elTective 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., 1885. 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 the 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 troclilea. 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 mobilitv, its direct relation with the hand and wrist, and the etiect 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 prevented 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 comparatively rare and shoulder dislocation is common. He concludes that in childhood fracture of the clavicle is the equivalent of dislocation of the shoulder by direct violence, and dislocation of the elbow is the equixalent 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 cla\'icle. 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 accompanieil 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 fluici : 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 effect 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. Swelling 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 bursae. 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 " pufhness between the inner condyle and the olecranon process when the arm is bent at a right angle" (Barwell). The bursse beneath the brachialis anticus and between the tubercle of the radius and the biceps tendon, if enlarged, cause a vague 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 flexion, 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 muscular and tendinous structures behind hold them firmly and prevent recurrence of deformity. If the fracture is intercondylar, or T-shaped, the acutely flexed 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 expansion of the triceps and of the anconeus muscle. These should be carefully protected from injury. Landmarks. — The following points may be mentioned in addition to those which may l)e found under the Humerus, Radius, and Ulna : A line from one condyle to the other will be at right angles w ith 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 condyles. 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 deviation 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 magmun, and the -unciform. Exceptionally, several other bones may occur, due to the persistence of centres laid down in early foetal 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 flexor 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 trapezium Fig. 322. Tuberosity For trapezoid For radius Right scaphoid, dorsal aspect. Tuberosity Palmar surface Right scaphoid, inner aspect. 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 HTMAN ANATOMY. articular : the upper, very narrow, articulates at its lower bortler with the semilunar antl 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 trapeztjid. It is convex in all directions. The scaphoitl articulates with five bones, — the radius, semilunar, traj)ezium, trajjczoid, and os magnum. The semilunar [os liinatiim] receixes its name from its outline when seen from the side, the proximal surface being convex and the distal deeply concave. The dorsal siirface is quadrilateral. Its proximal and inner borders are lunger than the Fig. 323. Concavity for magnum Fig. 324. For cuneiform For unciform Dorsal For radius For magnum For scaphoid Riglil semilunar, outer aspect. Palmar Right 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. T\\q proxi- mal surface is con\-ex 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 ijiner 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 proximal 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 unciform For pisiform-«|j — ,\l^. ^ Mi'" Palmar surfac For semilunar For triangular cartilage Right cuneiform, palmar aspect. Fig. 326. For unciform Dorsal surface For semilunar 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 the 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. 311 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 inner 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. Rough surface for an- terior annular lig- ament and flexor carpi ulnaris For cuneiform Right pisiform, dorsal aspect. Right pisiform, palmar 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 proximal surface 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 02iter surface is concave, receiving the lateral ligament. T\\& dorsal szuf ace \% ^Xow^'aX^A 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 For trapezoid Ridge Groove for flexor carpi radialis For scaphoid Right trapezium, palmar aspect. Ridge For scaphoid Right trapezium, proximal and inner aspect. For second metacarpal For trapezoid either side. On the palmar stirface 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/^z^r bones,— the scaphoid, trapezoid, and first and second meta- carpals. The trapezoid [os multangulum minus] is best recognized by the dorsal 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. T\i(t 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 internal sxLrf ace, in the main concave, articulates with the body of theos mag- num, but has a non-articular surface near the dorsum for an interosseous ligament. The outer surface is mostly articular and slightly convex, joining the trapezium ; 312 HUMAN ANATOMY. distally and towards the palm there is a rougli surface for Hg^aineiits. The styloid process of the third metacarpal often reaches the dorsal aspect of the trapezoid Fig. 331. Dorsal surface Fig. 332. For trapezium For niaginim Right trapezoid, inner aspect. Right trapezoid, outer and distal aspect. between the os maijnum 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 botly. 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 donsal 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. Ill- For unciform Neck Right OS magnum, inner aspect. Fig. 334. Dorsal surface Neck For scaphoid Head For semilunar 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 by 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 otiter surface has a small articulation with the trapezoid, which exceptionally is continuous with the facet on the head. The OS magnum articulates with seve^i bones, — the scaphoid, semilunar, trapezoid, unci- form, and second, third, and fourth metacarpals. The unciform [os hamatura] 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 convex, 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 iinciform process, which has a broad outer and inner surface, the former concave and smooth, the latter convex. The free border of the hook presents a curved oudine from the inner side. The rounded edge between the proximal and outer surfaces rests against the semilunar. The proximal surface is a spirally twisted, oblong facet corresponding to the adjacent side of the cuneiform, with a prominent convexity at the proximal end. The outer surface, rough at the distal and palmar angles for an interosseous ligament, is elsewhere articular for the os Fig. 335- For cuneiform ^^^^^ITjI metacarpal For fourth metacarpal '^'^^^Wfr~ Inner border For fifth metacarpal Fig. 336. -Hook Right unciform, inner and proximal aspect. For magnum Hook 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 foetal 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 a7itibrachial row, consisting of an ossification in or on the triangular cartilage, representing the os intermediiiin, 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 cajpo-nietacarpal 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 foetal life or disappears. It apparently is composed of a dorsa! 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- latum on the distal end of the palmar surface and the subcapitatum secundariiim 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 fiir Morphologic und Anthropol., Bd. ii., 1900. 314 HUMAN ANATOMY magnum are the first to ossify, the process beginnintj 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 t'iG. 337- Ossification of bones of hand. A, at birth: B, latter half of first year; Cat three years; D, at eif.ht years; £, at twelve years, a, centres for shafts of metacarpals and phalanges; f>, magnum; c, unciform; li, cuneiform; f, base of first metacarpal ; /, heads of metacarpals ; g-, bases of proximal phalanges ; h, bases of distal phalanges ; »', scaphoid ; j, trapezium ; k, trapezoid ; /, semilunar ; ni, bases of middle phalanges ; n, pisiform. years. These are followed by the trapezium and the trapezoid, so that by the eighth year the process has begun in all the carpals save the pisiform, in which it begins about the twelfth year. THE METACARPAL BONES. The metacarpal bone of the thumb ' in many respects resembles a phalan.x and calls for a separate description; the others have the following jjoints in common. They possess a shaft ^ and two extremities, of which the proximal is the dase and the distal the head^^ Each base^ has an articular surface at the end to join the carpus and one on the side or sides that come into contact with the other metacarpal bones, with a depression for an interosseous ligament beyond it. The bases themselves are cubical and rough both above and below. The shaft narrows in front of the base, and has a tfiedian dorsal rid^e, which soon divides into two lines running to either Side of the head, thus bounding a long, flat dorsal surface occupying more than half the bone. A palmar rid^e runs nearly the whole length of the shaft, dividing very near the head into two faint lines to either side of it. Thus, near the base the shaft may be called cylindrical, with a ridge above and below, while farther forward it has a dorsal and two lateral sides. This description applies most closely to the bone of the index, and becomes less and less accurate as we proceed to the little ^ Os metacarpale I. - Corpus. '' Capitulum. '' Basis. THE METACARPAL BONES. 315 finger. The distal end or head has a rounded articular surface projecting to the pahiiar side, while it does not rise above the level of the dorsum. Both on the palmar and dorsal aspects, but especially on the former, its angles are produced backward, and the whole surface encroaches a litde more on the palmar side, where it is de- cidedly broader than on the back.. A tubercle exists on each side where the diverging Fig. 338. CARPUS Ext. carpi ulnaris Styloid process -j, Ext. carpi rad. long. Ext. carpi rad. brev. THIRD PHALANX Bones of right hand, dorsal aspect. lines of the dorsum end, with a depression below it on the side of the head. The lat- eral ligaments spring from both tubercle and depression. The mitrierit foramina excepting that of the first metatarsal, are recurrent, runnmg towards the proxmial end. Peculiarities of the Different Metacarpals.— The first metacarpal is shortest, the second longest, from which the remainmg ones decrease m lengtn from without inward. The chief distinguishing marks are on the bases. 3i6 HUMAN ANATOMY. The first metacarpal, sliurtcr than tlie otliers, has a nearly Hat dorsal surface bounded by two definite borders, of which the outer is tlie sliarper. The pa/mar surface of the shaft is overhung by the ends. It is thickest and most convex towards the inner side. These two points are the best guides to determine the side the bone belongs to. The difference is striking in a transverse section. The base is broad Fig. 339. For radius OS MAGNUM Tuberosity Abdiictoi polite ti TRAPEZOID Adductor obliquity Opponens poll TRAPEZIUM Ext. OS. met. poll. Flex, carpi rod. Opponens poll. Abductor and flexor brevis pollicts Adductores obliquus et /■/// transversus /// For triangular cartilage PISIFORM Abductor minimi digiti CUNEIFORM UNCIFORM I IK ifdriii \>'!o>:k%^, flex .brevis iiul oppon. min. dig. I It x. carpi ulnar is Opponens niin. dig. :. Palmar inlet ossei Abductor and flex, brevis min. digiti Flex, sublim. digit Flex, profund. digit Bones of right hand, palmar aspect. and runs to a point on the palmar aspect rather nearer the inner side. A groove for the capsule surrounds the joint, and on the outer side is a tubercle for the tendon of the extensor of the bone. The articular proximal end is convex from side to side and concave from above downward, forming a typical saddle-joint with the trapezium. The head is also broader from side to side. The articular surface is carried only a THE PHALANGES. 317 little way onto the dorsum, but bends strongly forward, ending in two lateral pro- longations with a notch between them, on each of which a sesamoid bone plays. The outer of these is the more prominent. The nutrient foramen runs towards the distal end. The second metacarpal has a base which is triangular when seen from the end, and forked to straddle the point of the trapezoid. On the outer side is a small square facet near the dorsum for the trapezium ; on the inner side there is a narrow oblique surface for the os magnum, and in front of it one showing a tendency to subdivide, articulating with the next bone. The third metacarpal has an oblong proximal surface, broadest on the dor- sum, where a tubercle, the styloid process, projects towards the trapezoid. We have found the third metacarpal touching this bone in forty per cent, of 100 specimens, and sometimes this occurred when the styloid process was not particularly developed. Externally there is a facet like the lower part of the inner one of the second, and internally a double one to meet the next. The fourth metacarpal has a nearly square upper surface articulating with the unciform, and therefore of uncertain nature, — sometimes convex, sometimes concave. At the outer dorsal angle of this surface is a small distinct facet for a joint with the OS magnum. On the outer side are two facets for the third, and on the inner a long one, concave from dorsum to palm, for the fifth. The fifth metacarpal has a base generally broader than deep, concave from side to side and convex from above downward. A single facet on the outer side has a convexity to meet the concavity on the fourth. The inner side has, of course, no facet, but a tubercle. The dorsal ridge on this bone is twisted, starting from the inner side. Development. — Each bone has two centres, a primary one for the shaft, appearing early in the third month of foetal life, and one for an end, appearing in the third year. The secondary centre is for the distal end in the four inner metacarpals and in the proximal of the first,— that is, at the end towards which the nutrient artery does not run. They fuse at about eighteen. Rarely smaller epiphyses appear at the other ends also, as in mammals generally. A centre for the styloid process of the third is sometimes seen, and it may become distinct, as an extra carpal bone, or it may fuse with one of the adjoining ones. THE PHALANGES. Features of Each Bone. — The phalanges ^ of the first and second row differ (except in size) only in the proximal ends. The dorsum of the shaft is rounded from side to side ; the palmar surface is flat with raised edges for the sheaths which bind down the tendons very closely. It is considerably overhung by the distal and somewhat by the proximal end. The nutrient foramen, when present, runs distally. T\i& proximal end oi thefrst row is a concave articular surface, broadest trans- versely. A groove runs round the end, except on the palmar surface, for the cap- sule and for fibres from the extensor tendons of the fingers on the dorsum. Two very slight inequalities in front mark the attachment of the glenoid ligament. There is a rough tubercle on each side, just below the groove for the partial insertion of the interosseous muscles. The distal end in both the first and second rows has an articular surface which curves over two condylar promi7ie7ices, separated by a median furrow, onto the palmar aspect. This surface is seen on the dorsum only as a small curved median facet which broadens as it passes over the end and continues to expand to its termination. The lateral borders of the joint are well defined. A depression with an overhanging tubercle is on each side of this end ; both depression and tubercle give attachment to the lateral ligament. Th^ proximal ends of the second and third rows are essentially the same. They differ from that of the first row because, while the latter fits onto the single rounded end of a metacarpal, those of the two distal rows fit onto double condylar ends. Thus the proximal articular surface presents a median elevation, separating two hollows, continued into a projecting point on the surface front and back. In the phalanges of the second row the dorsal point is the larger ; in the last row the points ^ Phalanges digitorum manus. 3i8 HUMAN ANATOMY. are about equal. In the last row the palmar point is at a lower level than the rough- ness that succeeds it. There is a transverse ridge in 'both on the dorsal aspect for extensor tendons ; the flexor tendons are inserted on the palmar side to a slight ridge on the second phalanx and to a roughness spreading considerably on the shaft of the terminal one. T\\(t pha/aui^cs oi the third rocu are much smaller and flatter than the preceding. The dorsum of the diminutive shaft is convex from side to side and its palmar aspect plane where not encroached upon by roughnesses. The free end is sharp and rounded, with points at each end j)rojecting backward. The dorsal distal border bears a narrow semilunar roughness ; a much broader one on the palmar side sup- ports the pulp of the end of the finger, giving firm attachment to the connective tissue. Peculiarities of Individual Phalanges. — Every phalanx of the first row is longer than any of the second row. The first and second phalanges of the middle finger are longer than the corresponding ones of the ring finger, which in turn sur- pass those of the index. Those of the little finger are the smallest. The terminal phalanges are of very nearly the same length. The phalanges of the first row have the following jieculiarities. That of the index-fino;er has a \cry large external tubercle at the dorsum ; the hollow at the base is deeper than that of any other ; the base is relatively strong compared with the shaft, which is flatter than any other. The phalanx of the middle finger is strong in all its parts ; there is a large external tubercle, often divided into a dorsal and a palmar part ; at the distal end the ulnar condyle is more prominent. The phalanx of the ring finger has the base relatively small and the condyles relatively large, so that the borders are nearly parallel ; the dorsum is more convex transversely than that of the third, and much more so than that of the index ; it is also narrower. The phalanx of the little finger is weak, narrowing rapidly so as to appear pointed ; there is a tubercle at the inner and dorsal side of the base, and the radial condyle is the more projecting. One cannot, therefore, determine to which side the phalanx of the ring finger belongs. In the second row the phalanx of the middle finger is always stronger than that of the ring finger, and the latter than that of the index. According to Pfitzncr,' the distal ends are the more characteristic. In the second finger the radial condyle is the more prominent ; this is also true in the third, but to a less degree ; the ulnar condyle is the larger in the fourth, and still more so in the fifth. The distal or terminal phalanges can be distinguished more surely by strength than by length ; the third is the strongest ; then comes the fourth ; next the second, which is more or less pointed ; and last the fifth, which is relatively weak. These characteristics are to be used with great caution in drawing differential deductions. Development. — The phalanges have each a centre for the shaft and one for the proximal end. The former appears in the latter half of the third month of foetal life at about the same time in the terminal and proximal rows. Probably the termi- nal row shows ossification somewhat earlier than the other (Bade). The centres for the second phalanges appear after a distinct interval about the middle of the fourth month. In both the first and second rows the centre appears nearer the proximal end. It is said that in all the rows ossification begins in the middle finger, next in the index, and later in the ring and little fingers ; there is, however, con- siderable variation. The centre for the second phalanx of the little finger is dis- tinctly later than the others. Ossification begins in the epiphyses in the third year or later. They are fused by eighteen. In addition to the proximal epiphyses, the terminal phalanges have each a distal cap-like ossification of perichondrial origin, which (juickly joins the shaft. Sesamoid bones • occur in the mctacarpo-phalangeal joints. In the foetus of the fourth month they are very numerous, but many disappear by fusion or other- wise during development. A pair is constant in the joint of the thumb. They are two bones of variable size, in general rather larger than a small pea, lying on the palmar side of the head of the first metacarpal. The tendon of the long flexor passes. 'Schwalbe's Morpholog. Arbeiten, Bd. i. and ii., 1893. -Ossa sesamoidea. PRACTICAL CONSIDERATIONS : THE HAND BONES. 319 between them. They each have one cartilage-covered surface against the bone and are otherwise surrounded by fibrous tissue. A small one on the radial side of the joint of the index-finger occurs in rather less than half the cases, and one on the ulnar side of the little finger in rather more than four-fifths. Pfitzner^ gives the following table of percentages showing the frequency of the various sesamoid bones, combining his work and that of Thilenius : Fourth-month fcetus . . Fourteen to ninety years Number of Hands. 30 1323 Thumb. Rad. Uln. 100 100 99.9 100 Index. R. 46 47.8 23 O.I Middle. 30 1-5 L. 15 Ring. R. 23 L. 30 O.I Little. Rad. Uln. 15 63 2.3 82.4 Variations in the number of the fingers are generally regarded as malforma- tions. The most common occurrence is an extra finger, the identification of which is not certain. It seems often as if we should content ourselves with saying that there is an extra finger, but that no particular one has been repeated. Sometimes the thumb has three phalanges. Occasionally any of the terminal phalanges is doubled. A very uncommon condition is that of seven or eight fingers and no thumb. The dissection of such a case revealed the absence of the radius and of the radial side of the wrist, the skeleton of the forearm consisting of two ulnae, and that of the hand of the ulnar sides of two opposite ones fused together. PRACTICAL CONSIDERATIONS. The Carpus. — Of the carpal bones the scaphoid and semilunar are most fre- quently broken, on account of their more direct relation to the line of transmission of force in falls upon the hand. The diagnosis is difficult, and has been made oftenest by the help of a skiagraph. There is but little displacement. The other bones of the carpus, on account of their shortness, irregular and rounded shape, and compact union by strong ligaments which yet permit slight movements be- tween the bones, usually escape injury except in cases of crush of the whole hand. They are, however, not infrequently the seat of tuberculous disease, as might be expected from their great liability to traumatism of all grades. Their synovial re- lations (Fig. 342) favor the spread of such disease from one bone to the remainder, and render conservative treatment unsatisfactory. The result, too, is affected by the close proximity of the flexor and extensor tendons, which become involved in the tuberculous process or bound down by adhesions. The Metacarpus. — The first metacarpal bone, which is morphologically a phalanx, is, like all the phalanges, developed from an epiphysis situated at its proximal end. But one case of disjunction has been recognized during life. It re- sembled a dislocation at the carpo-metacarpal joint, but the seat of abnormal move- ment was below the level of the lower edge of the trapezium. In the remaining metacarpal bones the epiphysis is situated at the distal extremity. Falls upon or striking with the closed fist tend to produce forward displace- ment. As the metacarpal bones of the index-, middle, and ring fingers are the longer, their epiphyses are more likely to be separated in this manner. A fall on the extended fingers and metacarpo-phalangeal region may cause backward displace- ment, though this is rarer. The diagnosis from dislocation of the proximal phalanges is not easy. It is aided by the recognition of "muffled crepitus" (Poland) and by the great tendency of the deformity to recur, due partly to the small articular areas of the separated bones and pardy to the action of the flexors and the interossei. Skiagraphy will usually establish the diagnosis. Fracture of the metacarpal bones is usually the result of a blow with the clenched fist. The metacarpals of the thumb and litde finger are therefore rarely broken. On account of the mode of application of the force, the seat of fracture is ' Zeitschrift fiir Morph. und Anthropol., Bd. ii., 1901. 320 HUMAN ANATOMY. apt to be near the distal end, although the thinnest and weakest parts of the bones are just above the middle and they sometimes break there. The proximal fragment is held firmly by its ligamentous attachments and is less movable than the phalangeal portion ; its distal end may project on the dorsum. The knuckle of the aflfected finger sinks and partially disappears. The lumbricales and the interossei aid in producing this deformity, and may cause the pro.ximal end of the distal fragment to become prominent on the dorsum of the hand. In examining for these fractures it should be remembered that the metacarpal bones of the index- and middle fingers are bound tightly to the carpus and possess but little power of independent movement. The others are more movable. In the treatment of the.se fractures the normal palmar concavity of the metacarpal bones should never be forgotten. The Phalanges. — Epiphyseal separation of the phalanges is extremely rare. The epiphyses are all at the upper ends of the bones. The diagnosis from severe sprain or from fracture will usually be made by the X-rays. It is now thought that not a few of the cases of necrosis of the proximal end of a phalanx following acute inflam- mation or whitlow are the result of epiphyseal sprain or disjunction. Of course, necrosis is often the sequel of the spread of infection from the superficial structures of the hand to the closely applied fibro-cellular tissue over the terminal phalanges. Fractures occur most frequently in the proximal and most rarely in the ter- minal phalanges. The relation of the tendons on the dorsal and palmar surfaces usually prevents any marked displacement. Occasionally an anterior angular de- formity of the proximal phalanx is seen after fracture. It is believed to be favored by the action of the interossei. The frequency with which both tuberculous and syphilitic inflammations affect the phalanges is probably due to their exposure to slight injury. They are, how- ever, not often the subject of post-typhoidal infection. The cause of whitlow has already been mentioned, and will be recurred to. The reason for the over- growth of the bony structures of the hand in acromegaly and in hypertrophic pul- monary osteo-arthropathy is not known. In the latter case it has been suggested that the enlargement of the terminal phalanges, like the " clubbing" of the fingers in phthisical patients, may be due to an osteogenetic stimulus derived from the pres- ence in the circulation of the secondary products of the pulmonary infection. This would be analogous to the increased rapidity of growth observed in adolescents during convalescence from typhoid. Landmarks. — On the inner side of the hand, below the wrist, the pisiform bone can be felt, and when grasped firmly can be given slight lateral movement. Lower and more externally the hook of the unciform can be made out. On the outer side the tuberosity of the scaphoid just below and internal to the radial sty- loid and still lower the ridge of the trapezium may both be felt. With the hand in full flexion, the dorsal prominence of the scaphoid and semilunar and the curved line of their articulation with the radius may be felt ; the anterior and posterior lips of the articular surface of the latter bone can be palpated and the groove or depression beneath them recognized. The projection of the os magnum on the back of the hand, and occasionally of the base of the third metacarpal at its articu- lation with the OS magnum, may easily be felt. When an unusual prominence of these bones exists, and is first noticed after a fall or strain, it sometimes leads to a mis- taken diagnosis of exostosis or of ganglion. The metacarpal bones, their concavity, their expanded anterior extremities form- ing the knuckles, the shape and size of the shafts and ends of the phalanges, and of their articulations with the metacarpus and with each other, can all readily be made out through or between the oveHying tendons. The surface markings of the hand and of its joints will be considered later (page 621.) LIGAMENTS OF THE WRIST AND METACARPUS. The ligaments and joints of the wrist include three articulations, the radio- carpal, the intracarpal, and the carpo-ynetacarpal , which often recei\e detailed separate description. The simpler and in many ways more desirable conception of these joints is to regard them as parts of a common articulation consisting of a LIGAMENTS OF THE WRIST AND METACARPUS. 321 general capsular ligament enclosing synovial cavities separated by an interarticular fibro-osseous septum composed of the bones of the first row and their interosseous ligaments. Preparatory to the common description which follows, it is necessary to consider the ligaments and relations of the groups of bones which take part in' the formation of the subdivisions of the general articulation. The pisiform being practically a sesamoid bone, the upper end of the carpus is an egg-shaped articular surface made chiefly by the convexities of the scaphoid and semilunar and to a small extent by the cuneiform (Fig. 340). These three bones are united into one apparatus by two strong interosseous ligaments situated just below the proximal ends of the bones, covered by synovial membrane and corn- Radius Triangular cartilage Semilunar Dorsal ligament of first row Interosseous carpo-metacarpal ^ ligament Dorsal ligament of second row Dorsal intermetacarpal ligaments Dorsal aspect of right wrist. The joint of ulna is opened and the shaft displaced forward and inward to show under side of head. The radio-carpal, intracarpal, and carpo-metacarpal joints are shown by removing the dorsal ligaments and flexing the hand. pleting the articular surface. They completely shut of? the radio-carpal from the in- tracarpal joint. The latter is concavo-convex, the concave part being formed by the cuneiform, the semilunar, and the hollow surface of the scaphoid ; the convexity by the lower surface of the latter bone, which articulates with the trapezium and trape- zoid. The concavity amounts to a socket, of which the side formed by the scaphoid is nearly at right angles to the base, while the inner, formed by the cuneiform, is oblique. The scaphoid is attached to the semilunar much less tightly than is the cuneiform, so that considerable motion occurs between them. The scaphoid, besides sliding in various directions on the semilunar, can turn on an approximately trans verse axis through its proximal part, which permits of flexion and extension, to some degree independent of the rest of the first row. Its lower end may also move 322 lU.MAX ANATOMY somewhat oiitwartl and inward, so as to broaden or narrow tlie socket. The cHstal row of carpal bones presents a prominence made by the os magnum and the unci- form, which are held firmly toj^cther so as to move nearly as one, fitting into the socket presented by the hrst row. The outer side of this prominence is quite straight, making an entering angle with the trapezoid, receiving the ridge between the concavity and convexity of the scaphoid. At this point near the palmar surface the OS magnum receives a ligament from the scaphoid, which may occasionally deserve to be called interosseous. The pisiform has a capsular ligament enclosing the joint between it and the cuneiform. The four bones of the second row are joined by three interosseous ligaments: one Fig. 341. I'lna Interosseous membrane Radius I Inferior dorsal radio-ulnar. ligament (relaxed) Dorsal transverse ligament Dorsal carpo-metacarpal ligaments Scapho-metacarpal band Dorsal aspect of right wrist. between the trapezium and trapezoid, near the palm ; one between the trapezoid and OS magnum; near the dorsum ; and one between the os magnum and unciform, much the strongest, connecting the palmar halves of the bones at the distal end. None of these interrupt the communication of the syno\ial cavity of the intracarpal joint and those at the bases of the metacarpals. The scaphoid, semilunar, and cuneiform have very properly been compared to an intra-articular fibro-cartilage or meniscus, subdividing a joint. No muscle of the forearm is inserted into them. (The fle.xor carpi ulnaris, which has the pisiform as a sesamoid bone in its tendon, has its real termination in the fifth metacarpal. ) Hence this series is never directly moved, but changes position under the pressure of the distal row, which is pulled against it by the muscles moving it. It plays an important part in the movements of the joint. LIGAMENTS OF THE WRIST AND METACARPUS. 323 The bases of the metacarpals, except the thumb, articulate with one another by the lateral facets, and just below these joints are held together by strong interosseous ligaments connecting the rough depressions below the bases. The fibres of the Fig. 342. Radio-caipal joint Ititracarpal joint (between scaphoid and os magn Joint between trapezium and first metacarpal Ulna Inferior radio-ulnar joint iangular fibro-cartilage . — iinracarpal joint ' (between cuneiform and unciform) — Carpo-metacarpal joint Carpal synovial sacs seen in longitudinal section. interosseous ligament from the trapezium to the trapezoid are inseparable from some from the trapezium to the second metatarsal. A common description will best serve for the ligaments connecting the forearm, the first row, the second row, and the bases of the metacarpals (Figs. 340, 341). The simplest conception is of a capsule passing from the forearm to the metacarpus and attached to the intervening bones. It is much strengthened by neighboring 324 HUMAN ANATOMY. tendons and their sheaths. It is stionij at the sides ; weak in front and behind. The stronger bands are ine.xtrical^ly blended with the rest ; that on tlie outside, the external lateral ligament,^ runs from tlie radial stjloid process to the outer side of the scaphoid, thence to the trapezium, and is continuous \vith the capsule of the carpo-metacarpal joint of the thumb. The internal lateral ligament"^ runs from the styloid process of the ulna to the side of the cuneiform, and to the pisiform, thence to the narrow internal edge of the imciform, and finally to the fifth metacarpal. The dorsal part of the capsule is the weakest, but is much strengthened by the e.xtensor tendons. A continuous layer passes from the radius and ulna to the first row, thence to the second, and thence to the metacarpals. The general direction of the fibres of Fig. 343. Radius Interosseous membrane I'lna *''/■/ "^^K — ' — "-t^^JfT— Ant inferior radio-ulnar iffament .^^^^y^"* ;^J-St^ loid process ( /jil — Pisiform ligament Ridge 0 Anterior carpal ligament Pisiform Int lateral ligament iciforni ^t -^Tendon of ext. carpi '^' ulnaris Outer end of ant. annular ligament Inner end of ant. annular ligament Anterior aspect of right wrist-joint. \ portion of the anterior annular ligament has been removed and the canal for the flexor carpi radialis opened. the pro.ximal part is transverse, inclining inward from the styloid process of the radius and the scaphoid to the cuneiform. This constitutes the dorsal transverse ligament, which serves to hold the head of the 6s magnum and the adjoining part of the unci- form in the socket made by the concavity of the first row. It has no definite borders. Tolerably distinct bands pass to the bases of the four inner metacarpals ; those to the second and third are tense and the others lax. Various accessory bands are often found. The ayiterior part of the capsule in the hollow of the wrist is stronger : it is reinforced by oblique bands converging downward. Many of these fibres are attached to the narrow palmar prominence of the os magnum. Pretty distinct bundles go to the bases of the metacarpals. Very small disks project into both the radio-carpal and the intracarpal joints from the dorsum, which are hardly seen except ^ Lig. coUaterale carpi radiale. " Lig. collaterale carpi ulnare. LIGAMENTS OF THE WRIST AND METACARPUS. 325 in frozen sections. Their broader bases are attached to the capsule, and the free sharp edges end in the joint fitting- in between the bones. 'Wx^ pisiform has a special joint on the palmar side of the cuneiform, with a lax capsule. This is strength- FiG. 344. Palmar fascia Muscles of little finger Anterior annular ligament Palmar carpal ligaments Tendon of flex, carpi rad. Scaphoid Cuneiform Unciform Os magnum Dorsal carpal ligaments Transverse section through right wrist from above. The flexor tendons have been removed from the canal beneath the annular ligament. Fig. 345- Radius Intra-articular disk Semilunar Intra-articular disk Os magnum • I ened internally by a bundle from the cuneiform run- ning from the dorsal to the palmar side. Two well- marked bands pass down- ward from it on the latter aspect ; the one to the base of the fifth metacarpal is really the end tendon of the fiexor carpi ulnaris, the other passes obliquely to the proximal edge of the unciform process. The Anterior An- nular Ligament. — This is an extremely strong structure, bridging the hollow of the wrist, and enclosing a canal through which pass the tendons of the long flexors of the thumb and fingers and the median nerve. It springs internally from the process of the unciform and from the pisiform, the latter part being fused with the band from it to the unciform. It is attached externally to the ridge on the trapezium, and by a deeper process to the tuberosity of the scaphoid and to the inner side of the front surface of the trapezium, thus splitting to allow the passage of the tendon of the flexor carpi radialis through a special canal in the groove of the trapezium. Frozen sections through the wrist, passing through the pisiform (Fig. 344) (but not those through the unciform), show deep fibres from the annular liga- ment passing down under the canal and blending with the front of the capsular ligament of the wrist. The proximal and distal borders of the ligament are somewhat artificial, as it is connected with the fascia of the forearm and with the palmar fascia, besides receiving fibres from the flexor carpi ulnaris. This anterior annular ligament holds the sides of the wrist firmly together and prevents them from spreading when pressure is applied from above. Its fibres mingle with the origins of mus- cles of the thumb and of the little finger. The posterior annular ligament is but a thickening of the fascia of the back of the forearm, and has no place among the true ligaments. The Carpo-Metacarpal Articulations. — Those of the four inner fingers have been partially described. They connect with the general articular cavity of the wrist. A band from the adjacent edges of the os magnum and unciform to those of the third and fourth metacarpals (Fig. 340) does not completely interrupt the continuity of this cavity, as it does not reach the dorsal surface. The carpus and metacarpus are connected on both front and back by bands which can be fairly distinguished from the capsule. Trans- verse bands run also on both surfaces from the base of one metacarpal to the next. The opposed sides of the bases are partly covered with articular cartilage, m Third metacarpal f^ Frozen section through right middle finger, the hand being straight. \26 HUMAN ANATOMY. Radius Disk Semilunar Os magnum Third metacarpal Same as Fig. 345, the hand being flexed. as has been described. Interossi'ous metacarpal ligaments connect their sides distally from this. These complete the capsules, which are imperfect only on the carpal side. The articulation of the thumb ( Fij^. 342) differs from the others in being complete in itself. It is a saddle-shaped joint. The hand lying supine, the long axis of the joint slants down- ward and inward. In this direction the trapezium is con- cave ; at right angles to it con- vex. The joint is surrounded by a capsule, which is strongest on the dorsal and palmar sides, where the direction of the fibres is longitudinal ; it is weak at the outer anterior end, where it is strengthened by the tendon of the extensor of the metacarpal bone. The motions are flexion, extension, adduction, abduc- tion, and circumduction. Ro- tation in the flexed position may be possible from the im- perfect adaptation of the ar- ticular surfaces, but can hardly be of practical importance. Flexion is limited by the locking of the palmar projection of the metacarpal against the tra{)ezium ; the other angular motions by the tension of the ligaments. Movements and Mechanics of the Wrist and Carpo-Metacarpal Articulations. — It is convenient in studying these movements to imagine that the metacarpus follows the motions of the second row of carpal bones. This is true of the index- and middle fingers, but not of the others. The motions of the wrist in the widest sense are flexion, extension, adduction, abduction, and circumduction. The joint is a compound one, egg-shaped above, the scaphoid, semilunar, and cuneiform acting as a meniscus. The motions are best studied by removing the skin and tendons on the dorsal aspect and inserting long pins into the radius, semi- lunar, and OS magnum, and, for some purposes, the scaphoid. The Rontgen rays have been useful chiefly as corroboratory evidence. In Fig. 347. /lexiofi the motion begins in the upper joint, where it is most extensive ; as it goes on the lower takes part. In extefision, starting with the arm straight, more than half occurs in the lower joint. Adduction (ulnar flexion) (Fig. 348, B), owing to the lesser prominence of the ulna, is more free than abduction. The meniscus glides towards the radial side, and in so doing assumes the relation to the radius that it has in extension. The scaphoid touches the radius only by one end, so that its long axis approaches the direction of that of the forearm, and the semilunar leaves the triangular cartilage. The curve of the meniscus broadens, increasing the distance between the ends of the cuneiform and the scaphoid. A small part of the motion occurs in the mid-carpal joint. The unciform, moving with the os magnum, comes nearer to the semilunar. The space Radius Semilunar Third metacarpal Os magnum Same as Fig. 345, the hand being overextended. LIGAMENTS OF THE WRIST AND METACARPUS. 327 between the neck of the os magnum and the scaphoid enlarges. In abduction (radial flexion) (Fig. 348, A) the second row of the carpus has a larger share in the motion than in adduction. The meniscus moves to the ulnar side and is flexed, while its ends approach each other, narrowing the arch. The lower end of the scaphoid is crowded against the os magnum and the proximal end of the unciform recedes from the semilunar. Lateral motions do not occur when the wrist is either strongly flexed or extended. The screw surfaces of the cuneiform and unciform are important factors in the combination of antero-posterior and lateral motions ; but the os mag- num and unciform, which move together, do not twist in the socket formed by the first row if the latter be fixed. Circumduction is a combination of the preceding motions. Though the meniscus moves as a whole, the scaphoid is less closely attached to the semilunar than is the cuneiform. Fig. 348. Reduced tracings from skiagraphs, showing Ihe position of the carpal bones. A , in radial flexion ; i?, in ulnar flexion.' Flexion is limited by the tension of the dorsal ligaments ; extension in the upper joint chiefly by the lateral ligaments, in the lower by the locking of the bones of the meniscus against those of the first row. The anterior fibres of the capsule probably assist. Lateral motion is checked in the upper joint by the side liga- ments ; in the lower joint it is limited chiefly by the shape of the bones. The number of joints between the carpal bones divide the force of shocks transmitted through the hand. The motions of the carpo-metacarpal joints of the fingers are almost wanting, except for the ring and little fingers. In both these the motion is essentially flexion, most marked in the latter, and, owing to the dorsal convexity of the carpus, tending to oppose the little finger to the thumb. The metacarpo-phalangeal articulations are surrounded by a rather loose capsule, which is inserted into both bones pretty close to the articular cartilage. It is weakest on the dorsum, where it is supported by the extensor tendons. It ' In tracings from X-ray photographs it is in places very difficult satisfactorily to outline the separate bones, partly because the contours of both surfaces as well as of thick processes are shown, and partly because some bones lie in front of others, owing to the palmar concavity of the wrist. The greatest difficulty is with the respective outlines of the trapezium and trapezoid In the above figures the outline of the latter is indicated in dotted lines. This confusion is of little practical importance, since the drawings are to illustrate the changes of position between the first row and the forearm on one side and the second row on the other. 328 HUMAN ANATOMY. Fig Glenoid cart Insertion of ext. commun. digitorum Outer side of right forefinger. The metacarpo- phalangeal joint is opened. springs from little hollows on the sides of the heads of the metacarpals. Longi- tudinal fibres are distinct at the sides, if sought for from within the joint. The cap- sule is strengthened on the palmar surface by fibrous or fibro-cartilaginous plates, — ih^ glenoid cartilages, — which form the beginnings of the floor of the canals for the flexor tendons (Fig. 350). These plates are firmly fastened to the bases of the phalanges, whose motions they follow, and loosely to the metacarpals. In the thumb the glenoid plate amounts to little or nothing, as the palmar aspect of the joint is chiefly covered by the two sesamoid bones, which are firmly held near together by transverse fibres. When sesamoids are present in the other joints, they are lost in the fibrous tissue at the sides of these plates. The glenoid cartilages of the four inner fingers are attached to one another by a series of bands of little strength, —the transverse ??ietacarpal ligament (Fig. 351 ). The articular surface of the metacarpal is in the main convex and that of the phalan.x concave. They do not make a true ball-and- socket joint, for the long axis of the latter is transverse and at right angles to that of the former, which, moreover, is much broader at its palmar than at its dorsal end. As the glenoid disks are parts of the floors of the canals for the tendons diverging from the mid- dle of the wrist, those of the second and fifth fingers are not scjuarely placed, but incline to the middle of the hand. Movements. — When the finger is straight, it can be moved laterally, a little backward, and flexed, as well as circumducted. It can, on the dead hand, be slightly rotated ; but this motion does not occur in life. When it is fully flexed, ■lateral motion is impossible owing to the tenseness of the capsule, which has occurred in two ways, — partly from the fact that in flexion the phalanx rests on the broadest, instead 9f the narrowest, part of the head, and because, the depressions for the origins of the strongest lateral parts being near the dorsum, Fig. 350. these are stretched when the phalanx has tra\elled round the palmar prominence of the head. The interphalangeal ar- ticulations differ from the pre- ceding by the peculiarities of the articular ends and the greater relative strength of the lateral parts of the capsules. The gle- noid cartilages are small. There is no lateral motion. They are the purest hinge-joints in the body. Tfie Surface Anatomy of the Wrist and Hand. — The joint between the forearm and the carpus can be approxi- mately indicated by a line either on the back or the front, but more accurately on the former, starting from the head of the ulna, running nearly transversely, but with a slight upward bend, to near the radial styloid, and then sweeping downward to its tip. The first row of carpal bones can be made prominent on the back by flexing the wrist. The hollow Transverse metacarpal ligament 11. A IV. V. Metacarpals Phalanges Palmar aspect of right metacarpophalangeal joints fle.xor tendons opened. Glenoid cartilages Sheaths for PRACTICAL CONSIDERATIONS: THE WRIST-JOINT. 329 process can Metacarpals on the dorsum of the os magnum is distinct, and some indication of the mid-carpal joint may be felt near it. " Slightly external to the middle of the hand is a promi- nence, sometimes indistinct, but often very well marked, formed by the styloid process on the base of the third metacarpal bone at its articulation with the os magnum" (Thane and Godlee). On the palmar side the pisiform can be felt just at the beginning of the hypothenar eminence. When the hand is flexed and the muscles relaxed, it is easily moved from side to side. The unciform be indistinctly felt below it. The tubercle of the scaphoid Fig. 351. is felt with difficulty below and internal to the radial styloid, and at the beginning of the thenar eminence (the ridge on the trapezium) more clearly. The position of the annular ligament may be de- duced from these points, and it may be felt by pressure on the hand. It is a general rule for the joints between the meta- carpals and the phalanges, as well as for those between the latter, that the more distal moves on the proximal, and that, therefore, the promi- nence of the knuckle in flexion is made by the head of the metacarpal. All the meta- carpo-phalangeal joints can be made out from the dorsum. The sesamoid bones of the thumb are felt with difficulty. The web of the fingers lies about thirteen millimetres distal to the palmar aspect of the metacarpo-phalangeal joints. That of the index-finger is about midway between the transverse furrow reaching the radial side of the hand and the first crease on the finger ; those of the other fingers are in the same relation to the second furrow and the respective creases. The interdigital joints are slightly distal to the upper line of the complicated creases of the first joints and to the single line of the creases of the second row. Sheath for flexor tendons opened Transverse metacarpal ligament Palmar aspect of right metacarpo-phalangeal joints. Sheath for flexor tendons on one finger opened ; on adjacent finger still closed. PRACTICAL CONSIDERATIONS. The Wrist-Joint. — The radio-carpal has the greatest amount of motion of the three rows of joints that intervene between the metacarpus and the forearm. Its strength is not derived from the shallow concavity on the lower end of the radius, or from the ligaments which, taken together, compose the capsule, but rather from the tough fibrous tissues forming the sheaths of the large number of tendons that pass over the anterior and posterior aspects of the joint and are closely united to the bones. It escapes frequent injury, also, because of the numerous bones that enter into the carpus, which by their gliding motion one upon the other diffuse force received through falls upon the hand ; because of the same effect produced by the movement of the mid-carpal joint (intracarpal of Dwight), which takes up part of the force in overextension of the hand before it reaches the wrist ; and because of the absence of any long rigid lever on the distal side of the joint. Dislocation backward is by fai the most common, on account of the frequency of falls upon the hand. The diagnosis from Colles's fracture is made by observing that in dislocation : (i) the anterior swelling is nearer the ball of the thumb ; (2) the posterior swelling is mqre sharply defined at its upper edge ; (3) the styloid process of the radius is nearer the hand than that of the ulna ; (4) the distance from 330 HL'MAN ANATOMY. it to the head of the metacarpal bone of the iiidex-tinger is sliortened ; (5) the antero-posterior diameter of the wrist is increased ; (6) the flexion and immobihty of the wrist are greater. In dislocation fonvard the posterior swelling (the sharp l)order of the radius and ulna) approaches the hand ; the rounded prominence of the carpus is on the front of the wrist ; the antero-posterior diameter is increased and the stylo-meta- carpal measurement is lessened. Outward (radial) dislocation of the wrist is resisted by the contact of the scaphoid with the styloid process of the radius and by the internal lateral ligament. Inward dislocation would theoretically be easier, as there is no bony obstacle, and as adduction may be effected to a greater extent than abduction, and with greater power, on account of the leverage afforded by the projection of the cuneiform and pisiform bones on the inner side of the wrist. It is for this reason that the hand commonly assumes the position of adduction and the little finger becomes inclined towards the ulna when, from disease or other cause, the muscles lose the influence of volition and exercise an uncontrolled sway over the part (Humphry). Disloca- tion in either lateral direction is, however, very rare. Spontaneous subluxation forward is a condition thought to be associated with hard manual labor in which the strong anterior ligament becomes stretched and the radial side of the carpus is displaced forward and upward. This is followed, in accordance with a general law of growth (page 104), by an overgrowth of the posterior portion of the lower end of the radius, from which the normal opposing pressure of the carpus has been removed. The lower end of the ulna becomes unduly prominent. Disease of the wrist-joint is frequently tuberculous, but may be se[)tic or rheu- matic or gonorrhoeal in its origin. As the joint-cavity does not include the epiphyseal lines of either the radius or ulna, the synovial membrane being attached to the margins of the epiphyses, disease and injury of the latter do not of necessity involve the joint. The circumstances already detailed that protect the joint from dislocation also protect it from sprains and lessen the frequency of traumatic synovitis and of the sequelae of traumatism. Disease of any variety once established is apt to extend to the various syno\'ial pouches of the carpus on account of their proximity, to involve the flexor and ex- tensor tendon sheaths for the same reason, and to result, in accordance with its character, in either extensive disorganization or much limitation of motion. The flexors and extensors on the front and back of the wrist act with about equal force, and therefore but little displacement occurs. The swelling usuallv shows itself first on the dorsum through the thinner pos- terior ligament, the joint being nearer the surface on that aspect. Landmarks. — The line of the wrist-joint is convex upward. A straight line drawn between the two styloid processes is oblique downward and outward. It unites the two extremities of the arc which represents the line of the joint. The highest point of that arc is a half-inch above the interstyloid line. If a knife were introduced horizontallv below the tip of the stvloid process of the ulna, it would open the wrist-joint : below the styloid of the radius, it would Strike the scaphoid. The remaining landmarks are described on page 621. The Joints of the Carpus, Metacarpus, and Phalanges. — As the inter- mediate ligaments uniting the separate bones of each row of the carpus are all trans- verse, and do not pass from one row to another, the mid-carpal (intracarpal ) joint permits of considerable motion in both flexion and extension. It undergoes disloca- tion with extreme rarity, and usually only as a result of a degree of force sufificient to stretch or tear tendons and ligaments. Dislocation of the second row of the carpus fonvard is prevented by the manner in which the concave surfaces' of the trapezium and trapezoid rest upon the posterior convex facet of the scaphoid, as well as by the undulating manner in which the side of the unciform is disposed with regard to the side of the cuneiform. Displacement (^fl;r-^7£'ar^ is prevented by the manner in jvhich the round head of the OS magnum and the convex posterior and upper surface of the unciform are let into PRACTICAL CONSIDERATIONS : THE CARPAL JOINTS. 331 the hollow formed in the anterior and inferior surfaces of the bones of the first row (Humphry). The joints between the individual bones of the carpus allow of but little motion, and much force is needed to produce displacement of those bones. In the order of frequency the os magnum, semilunar, scaphoid, pisiform, trapezium, trapezoid, and unciform have been reported as separately dislocated. It is interesting to note in relation to the order of frequency that the middle finger is the longest, and is the one most exposed to injury and to force applied to the fingers ; its metacarpal bone is the longest ; it articulates directly with the strongest carpal bone, — the os magnum, — and it, in its turn, with the semilunar, which unites with the scaphoid in connecting the hand with the forearm. In reported cases the pisiform was thought to be dislocated secondarily after the rupture of the tendon of the flexor carpi ulnaris below the bone. The other separate carpal luxations have but little anatomical interest. Disease of the mid-carpal joint is usually tuberculous, and is apt to begin in or extend to the os magnum because — i. It is the bone most exposed to traumatism {vide supra), receiving the effects of injury to three metacarpal bones. 2. The joint participates in the movements of flexion and extension of the wrist, which are partly limited by the portion of the oblique fibres (both radial and ulnar) of the anterior annular ligament (page 325) and by some of the radial fibres of the weak posterior ligament, which are attached to the os magnum. 3. The slight rotation permitted in the mid-carpal joint is around a vertical axis drawn through the head of the os mag- num. A very slight enlargement of the bone would tend to pinch and bruise the synovial membrane between it and the trapezoid, those two being more closely bound together than any of the other bones. It has been noticed (Mundell) that the point of greatest tenderness in these cases of carpal tuberculosis was in a line between the index- and middle fingers, corresponding to the junction of the os magnum and the trapezoid. Harwell says that in tuberculosis of the wrist-joint the point of special tenderness is on the outer side of the extensor indicis tendon. This is on the same line, and, in cases in which the carpus has become involved, would correspond to the same point of junction. Dislocations of the metacarpal bones from the carpus usually involve single bones, are incomplete, and are in the backward direction. The wavy, irregular out- line of the distal edge of the carpus, the dovetailing of the metacarpals and carpals by means of the alternating convexities and concavities, and the strength of the interosseous and transverse metacarpal ligaments sufficiently explain the infrequency of dislocation of the metacarpus as a whole. Dislocations of the metacarpo-phalangeal and interphalangeal joints amount to "nearly thirty per cent, of all dislocations" (Stimson). Backward displacement of the proximal phalanx of the thumb is the most frequent and the most important. The cause is usually exaggerated extension of the phalanx, which carries its proximal end up onto the dorsum of the metacarpal bone above the articular surface. The relation to the muscles of the thumb is so important that the luxation will be described in that connection (page 617). Dislocations between the phalanges usually occur at tne first phalangeal joint, and in the backward direction, as the cause is commoniv a fall upon the palmar surface of the finger in extension. THE LOWER EXTREMITY. The Pelvic Girdle. — This consists of the two innominate bones, which join each other in front, and the sacrum behind. While the thoracic girdle is adapted to freedom of motion, the pelvic is fitted for strength and support. The study of the innominate bone should be preceded by a general idea of the pelvis. A plane between the promontory of the sacrum and the top of the pubes divides the pelvis into xhe false pc/vis above, formed chiefly by the ilia, and the tnie pelvis below. The latter presents the sacrum and coccyx behiiul, the arch of the pubes in front and below, and the tuberosity of the ischium at the side. Beliind this is the sacro-sciatic notch, much reduced by ligaments. On the sides are the hip- joints, and towards the front the obturator or thyroid foramen. THE INNOMINATE BONE. This' consists originally of the ilium, pubis, and ischium, each of which forms a part of the hip-joint, but which fuse so completely that the lines of union are noc usually to be seen in the adult. The ilium forms the upper and posterior part of the bone, the pubis the front, and the ischium the inferior. The two latter enclose the obturator foramen. The Ilium. — The ilium," a plate of bone forming the side c)f the false pelvis and a part of the true, may be said to have four borders. The superior border, or crest,'' very much the longest, is convex upward and outward. It connects two tubercles, the anterior and posterior superior spines of the ilium, of which the former is a knob overhanging the concave anterior border and giving attachment to Pou- part's ligament and the sartorius, while the latter is less prominent. The crest has a double lateral curve, the front half being convex externally and the posterior inter- nally. It is thicker at the ends than in the middle, and presents also a thickening near the middle of each curve, projecting on the convex side. There is an external lip, from the whole length of which s[)rings the fascia lata of the thigh, an internal lip, and an intermediate space. The anterior border is short, rounded, and con- cave, descending to the anterior inferior spine, a knob a little above the bf)rder of the acetabulum giving origin to the straight head of the rectus fcmoris and a part of the ilio-femoral band of the capsule of the hip-joint. The posterior border, very short and also concave, ends in the posterior inferior spine, an ill-marked angle at the bottom of the surface that joins the sacrum. The inferior border consists anteriorly of an attached part, which meets the other bones in the acetabulum, and behind this of a free concave part, which bounds the upper part of the great sacro- sciatic 7iotck.* The ilium might also be described as consisting t)f an expanded por- tion, narrowing below to a stem, which joins the other bones in the acetabulum. Its upper part follows the curves of the crest. The lateral or outer surface is crossed by the three curved or gluteal lines, convex above and behind, all ending at or near the sciatic notch. The superior, much the strongest, arises from the crest at the middle of its second curve and ends a little in front of the posterior inferior spine, marking off a raised rough surface behind its upper two-thirds. The middle begins at the crest, one or two inches from the anterior superior spine, and ends near the top of the notch. The inferior, the faintest, starts a little above the anterior inferior spine and is lost near the front of the notch. The three gluteal muscles, maximus, medius, and minimus, arise respectively behind these three lines in the order given. A slight groove for the reflected tendon of the rectus femoris, starting at the anterior inferior spine, runs backward above the acetabulum. The ventral or inner surface is divided into an upper posterior and a lower anterif>r part by the ilio-peetineal line'' in front, and a rough border con- tinuing it. The former is a line beginning on the pubis and continued across the ' O.s coxae. - (ts ilium. ' Crista iliaca. * Incisara ischiadica major. ' Linea arcuata. THE INNOMINATE BONE. 333 ilium to the sacrum, separating the true pelvis below from the false above. All of the ilium above this line, except a small part posteriorly, is a smooth, shallow con- cavity, the iliac fossa, ^ which contains the ihac muscle. It ends in front in a groove between the anterior inferior spine of the ilium and the ilio-pecti7ieal eminerice,' a swelling above the inner part of the acetabulum made by both the ilium and the pubis at their point of meeting. The bone is very thin at the middle of the fossa. The lower half of the inner surface of the ilium may be subdivided into two very dissimilar parts. The front one, forming the wall of the true pelvis, opposite a part Middle gluteal line External lip Laiissitnus dot si Superior gluteal line Obhguus externus Obliquus internus Post. sup. spine POSTERIOR BORDER — Gemellus supet lot Spxne of ischium LESSER SAORO-SCIATIC NOTCH Gemellus inferior TUBEROSITY Semitendinosus and biceps Sem.imem.br anostts Qiiadratus femorts Reflected tendon of rectus Articular surface Nonarticular surface SUPERIOR RAMUS Pectineus Obturator crest SPINE Adductor longus INFERIOR RAMUS Gracilis Adductor brevis Cotyloid notch Obturator externus SCHIAL RAMUS Adductor magnus ' 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 stirface'' corresponding to that of the sacrum. A narrow depression, xkio. pre-articular 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 spinae. The ilium has several large Fossa iliaca - Bminentia iliopectinea. ■* 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 inferif)r spine run backward, and one near the middle of the second curved line runs dt)wnward. The Pubis. — The i)ubis' (os pcctinis) has a flat 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 o\'al area, the syjnphysis pubis, bearing the fibro-cartilage of the joint. The spine '^ of the pubis is a pointed tubercle, projecting I'^"^"'- 353- CREST OF ILIUM Internal 1 Transversa/is Qi'adratus lumoorum ILIAC '"^ PpSSA Post. sup. spine Post. inf. spine Ant. inf. spin Groove for ilio-psoas — -,~» Psoas parvus Uio-pectineal eminence I SPINE OF PUBIS Levator ani >A\X LESSER SACRO-SCIATIC NOTCH Levator ani RAMUS OF ISCHIUM TUBERO! ITY OF ISCHIUM Obturator internus Compressor urrthrir Attachment of crus penis Ischio-cavernosus Transver sus perinei Right innominate bone, inner aspect. forward from the front of the upper border of the bone some two centimetres Trom 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 atigle 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. ^Tubercnlum pubicum. * Ramus superior. THE INNOMINATE BONE. 335 line starts from the spine and runs obliquely backward and outward to the ilium. 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 Conjoined tendon Gimbemat's ligament Poupart's ligament Ilio-pectineal eminence Conjoined tendon / / Rectus abdominis Pyramidalis Obturator crest Spine of pubis 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 eminence. 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- FiG. 355. Epiphyseal lamina on ilium Os acetabuli nodules Epiphyseal lamina on ischium Innominate bone at about fifteen years. ward and inward for the obturator vessels and nerve. 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. 1 Crista obturatoria. - Snlcus obturatorius. ^ Ramus inferior. 336 HUMAN ANATOMY. Iliac crest The Ischium. — Tlie ischium ' the thickest and most sojid jxirt of the bone, consists of a body, chietiy concerned with the acetal)ulum, a tuberosity, and a ramus. The body, continuous above with the ihum, forms the front of tlie i^reat sciatic uotch,"^ below which is the sharp spine of the iscliium 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 7iotch,' occuj)ied by the tendon of Fig. .^s6. 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 e.x- 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 axis 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 strij) 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 mterruption is the cotyloid notch.^ The ' Os ischiL '-'incisura ischiadica major. ' Tuber ischii. ^ Incis. isch. minor. ' Ramus inferior. '' Incisura acetabuli. Pubes Ischium Oblique sagittal section of right innominate bone passing through bottom of acetabulum ; inner surface. JOINTS AND LIGAMENTS OF THE PELVIS. 337 border rises from the surface of the bone distinctly below and to a less degree behind and above. The thyroid or obturator foramen ^ is a large oval opening, with the larger 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. Above is the obturator groove under the ramus of the pubis. It is closed by a membrane, except under the groove. Structure. — The innominate bone is, as a whole, very strong. The two thin places are in the middle of the ilium and of the cotyloid cavity. 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 very thick in a line from the socket to the outer expansion of the iliac crest, which runs nearly vertically in the upright position. It is very strong also at and behind the auricular surface. Development. — A centre for the ilium 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 still much cartilage around and between the bony expan- 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; Z), at six vears ; E, at about fifteen years, a, chief centre for ilium; b, chief centre for ischium ; c, for pubis; of, for tuberosity of ischium ; e, for iliac crest ; f, 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 acetabuli, persists at the front of the cavity be- tween the pubis and ilium 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. Secondary centres come about puberty for the crest of the ilium, the an- terior inferior iliac spine, the symphysis pubis, and the ischial tuberosity. They are fused at twenty, 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 ilium 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 ligaments and the obtu- rator membrane. ^ Foramen obturatntn. 22 338 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 j^-reatly 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- FiG. 358. Posterior sacro-iliac ligameii Sacro-iliac joii 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- FiG. 359. ^__^^^ Ilio-lumbar ligament 4- Fifth lumbar rated by a synovial cavity, which is enclosed by the sacro-iliac liga- ments. The size of this cavity is very uncertain. It may e.xtend 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'ig. 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 ,(( vertebra romontory of sacrum Sacro-lumbar ligament Sacro-iliac — ligament T t'/^ Anterior view of the sacro-iliac joint and of the last lumbar ver- tebra. 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 ligfament ^ (Fig- 362), passes from the posterior superior iliac spine to the second and third sacral vertebrae. 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 surfaces 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. 360. Fig. 361. Superior Synovial pubic ligament cavity 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 stibpubic 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 Liu. sacroiliacum posterius longum. "Lig. iliolumbale. ^' Lig. sacrotuberosum. 340 HUMAN ANATOMY. Fig. 362. Posterior superior spine of ilium Oblique sacro-iliac ligameiu Supraspinous ligament Sacro-coccyg-eal ligament Tip of Great sacro-sciatic foramen Lesser sacro-sciatic ligament Spine of ischium Lesser sacro-sciatic foramen Origin of biceps Tuberositj of ischium External surface of the sacro-sciatic ligaments. Fig. 363. Fifth lumbar vertebra Obturator canal __ Symphysis pubis Obturator membrane Auricular surface — Non-articular surface Lesser sacro-sciatic ligament Falciform process of great sacro-sciati ligament 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, \hQ falciform ligament, 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 coccyx, 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 thefalse^ above. The latter is bounded by the lower lumbar vertebrae The pelvis from behind. 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, * Lig. sacrospinosum. ' Pelvis major. ' Foram. ischiadicum majus. ^ Foram. isch. minus. * Membrana obturatoria. ^ Pelvis minor. 342 HUMAN ANATOMY. the ischia, part of the iha, and the jnibic rami and obturator membrane at the sides and front. The plane just described as separatinj^ 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'' is bounded behind by the coccyx, from the sides of which the ijrcat sacro-sciatic litjaments pass to the ischial tuberosities, thence by the rami of the ischia and pubes, forming^ the pubic arch, and by the subpubic ligament below the symj^hysis. It is evident that these planes converge in front and that the axis of the pelvis (an imaginary line in the centre, perpendicular to an indefinite number of intermediate planesj must be a curved one. The Position of the Pelvis. — The plane of the inlet of the pelvis is inclined to the horizon al)out 60° when the body is upright. This inclination varies accord- ing to the figure and to the individual peculiarities of the pelvis itself. Hermann von Meyer's conjugata vera, a line from the top of the symphysis to the line usually Fig. 365. Male pelvis from belore. found in the third sacral vertebra, runs at about 30° with the horizon. This is a more trustworthy angle than that of the plane of the inlet ; but even this is not constant. It is better to try to determine the proper position of every pelvis for itself than to attempt to make all conform to one angle, which for these reasons is impossible. The two borders of the cotyloid notch should be put in the same level, which will bring the anterior superior spines of the ilia into the same vertical plane as the spines of the pubes. The tip of the coccyx should be at about the level of the top of the symphysis ; owing to the many variations of the former, however, its position must be uncertain. The height of the promontory above the symphysis is about 9.5 centimetres i/^Yx inches) in man and about 10.5 centimetres (4^ inches) in woman. The diameters of the true pelvis of woman are of great practical importance in midwifery. The standards are the antero-posterior, the transverse, and the oblique (the latter from the sacro-iliac joint to the acetabulum of the opposite side) measured at the inlet, the outlet, and at an intermediate plane. ' Apertura pelvis superior. - Apertura pelvis inferior. THE PELVIS AS A WHOLE. 343 DIAMETERS OF THE TRUE PELVIS. Male. Female. Inlet. Cm. (Inches). Cavity. Cm. (Inches). Outlet. Cm. (Inches). Inlet. Cm. (Inches). Cavity. Cm. (Inches). Outlet. Cm. (Inches). Antero-posterior Transverse . . . Oblique .... 10.25 (4) 12.75 (5) 12.00 (43^) 11-5 (4>^) 12.0 (434:) 11-5 (4>^) 8.25(33^) 10.25 (4) 10.25 (4) 13-25 (5X) 12.75 (5) 12.75 (5) 12.75 (5) 13-25 (5^) ii-5(4>^) 12.0(4^) ii-5(4>^) The index of the pelvis, of interest in anthropology, is the proportion of the antero-posterior diameter to the transverse at the pelvic inlet, the latter being 100. This index is 80 for European males and 78 for females (Verneau). In the lower races it is considerably higher, implying a narrower pelvis. Pelves with indices below 90 are platypellic, with indices from 90 to 95 mesatipellic, and above 95 dolichopellic. Another index to show the relative depth of the pelvis is the proportion of the breadth between the most distant points of the iliac crests to the height from the top of the crest to the tuberosity of the ischium, the latter being ioo. According to Fig. ^66. Female pelvis from before. It is lower Topinard, this index is 126.6 for male and 136.9 for female Europeans, in the lower races, showing that in them the pelvis is relatively deeper. Differences due to Sex. — The sexual differences of the pelvis are far more marked than those of any other part of the skeleton. The male pelvis is deeper and narrower, the female shorter and broader. It is to be noted that the greater breadth of the female applies essentially to the true pelvis. At the inlet this is both relatively and absolutely broader in woman. The male promontory is more projecting. The most characteristic feature is the pubic arch, which is of a much greater angle in woman. According to Verneau, it is from 38° to 77° in the male, with an average of 6q° ; and from 56° to 104° in the female, with an average of 74°. The symphy- sis is shorter in woman, and the borders of the arch probably more everted. The 344 HUMAN ANATOMY. greater lightness of the female skeleton shows particularly in this part of the pelvis. It is owing to the greater divergence of the rami that the front of the obturator fora- men is straighter in the female, making it more triangular antl less oval than in the male. The spines of the ischia are farther apart in woman. According to Verneau,' those in man are rarely more than 10.7 centimetres (4^/( inches) apart, and often less than 9 centimetres (3^ inches) ; while in woman they are often more than 10.7 centimetres apart, and never less than 9 centimetres. He states also that in man the spines of the ischia are sometimes internal to the posterior inferior spines of the ilia, but that they are always external to them in woman. The sacro-sciatic notch is usually wider and less deep in the female. There is much irregularity in regard to the false pelvis. The anterior superior spines of the ilia are farther apart in woman. It does not follow that the same is true of the most lateral points of the crests of the ilia. In powerful male bodies they are farther apart than in female ones. The vertical depth of the false as well as of the true pelvis is greater in the male. As has been stated elsewhere, the male sacrum is the more regularly curved. Development. — The pelvis of the foetus and infant is strikingly small, and continues relatively so for some years. The peculiarity of its shape is largely due to the sacrum. Even at birth there is but a very rudimentary promontory, and the sacrum is straight or nearly so. Consequently the pelvis is funnel-shaped, being largest above. The height is greater in proportion to the breadth than later. It has been shown by Fehling ' and Thompson * that the se.x of the pelvis may be recognized by the usual signs as early as the fourth month of foetal life. In the foetus the transverse diameter of the inlet exceeds the conjugate, especially in the female. The average subpubic angle of the foetus is 50° in males and about 68° in females. In the latter the ischial spines are farther apart and the sacro-sciatic notches wider. Although after birth the promontory becomes stronger, it has a tendency to be double partly above and partly below the first sacral. This is cor- rected at a very indefinite time in early childhood. Of the details of the changes by which the great difference between the sexes is brought about we know very little. Waldeyer* states that the external measurements of the female pelvis surpass those of the male from the eleventh to the fifteenth year, but particularly from the four- teenth to the sixteenth. The growth of the male pelvis is more regular. Mechanics of the Pelvis. — The mechanical function of the human pelvis, apart from protecting the viscera, is chiefly to support the spine, whether sitting or standing. The interruptions of the bony girdle at the symphysis and the sacro-iliac joints add to the strength of the structure and break shocks. There is, however, a real motion at the sacro-iliac joints which, slight under ordinary circumstances, is of importance in childbirth. The weight of the body transmitted through the spine may theoretically be said to tend to force the sacrum down between the innomipate bones and also to carry the promontory downward and forward into the pelvis, the sacrum rotating on a transverse axis passing through the second piece at the sacral canal. Motion in the former direction does not occur, but in the latter it may to a slight degree.^ With the body lying on the back, if the legs are strongly flexed and pressed against the abdomen, the pelvis rotates on the sacrum, the symphysis rises, and the antero-posterior diameter of the inlet is lessened ; if the legs be strongly extended by being brought down over the edge of the table, this diameter is in- creased, the difference between the extremes being one centimetre. At the end of pregnancy these joints, as well as that of the symphysis, are loosened so as to admit of more motion, which is no doubt of real value. Assuming, as at first, the pelvis to be the fixed part, the tendency to displacement of the sacrum in either of these directions is resisted by the posterior sacro-iliac ligaments. The sacrum is not really a keystone, for the anterior surface is broader than the posterior, except in some few sections. ^ Le bassin dans les sexes et dans les race, Paris, 1870. ' Arch, fiir Gynakol., Bd. x., 1876. ' Journal of Anatomy and Physiology, vol. xxxiii., 1899. * Das Becken, Bonn, 1899. * G. Klein : Zeitschrift fiir Geburtshiilfe und Gynakol., Bd. xxi., 1891. PRACTICAL CONSIDERATIONS : THE PELVIS. 345 The weight in standing is transmitted to the thigh bones, in sitting to the tuberosities of the ischia ; in both cases the parts of the pelvis running to the pubes act as ' ' ties' ' to prevent the spreading of the arch. The circumference of the acetabulum is of strong bone to resist pressure from the joint, and in the erect position a strong part runs from the socket directly upward to the crest of the ilium. The thinness of the bottom of the acetabulum in all ages and the meeting there in childhood of the three bones make it a weak place. Surface Anatomy. — The anterior superior spine of the ilium is easily felt, but care must be taken not to mistake for it a swelling of the crest an inch or more behind it. To make sure of this spine as a point for measurements, the finger should be carried over it from the crest and then back again till it is arrested by the overhanging spine. The anterior inferior spine cannot be felt. The outer lip of the crest of the ilium can easily be followed to the posterior superior spine, which is marked by a dimple, and is on a level with the middle of the sacro-sciatic joint. The tuberosity of the ischium is readily felt, but it is too thickly covered for details to be recognized. A line drawn from the posterior superior spine to the outer part of the tuberosity of the ischium will cross the inferior spine of the ilium and the spine of the ischium. A line from the same point to the top of the greater trochanter will pass very close to the highest point of the great sacro-sciatic notch. The sym- physis of the pubes and most of the borders of the pubic arch can be felt. The spine of the pubes can be recognized, but usually not without some difficulty. It may be necessary to feel for it beneath the skin by invaginating the scrotum or labium. In woman it is nearly 2.5 centimetres from the median line ; in man some- what less. PRACTICAL CONSIDERATIONS. Failure of development in the separate bones of the pelvis produces certain well-known deformities. In the sacrum, the arch of the upper sacral vertebra, which is formed later than the others and varies notably in thickness, is frequently incomplete, which results in the very common occurrence of spina bifida at this region (page 105 1). When the pelvic girdle is incomplete anteriorly, there is an interval of several inches between the pubic bones, and all the bones of the pelvis are changed some- what in shape and direction. The defect may be associated with exstrophy of the bladder, epispadias in the male, split clitoris in the female, double inguinal hernia, ectopia of the testicles, and sometimes ventral hernia from separation of the recti muscles. Deformities of the pelvis have even more interest to the obstetrician than to the surgeon. The usual differences between the male and female pelves are some- times absent, constituting an abnormality, though perhaps stopping short of actual deformity. The so-called masculine pelvis, for example, is characterized by a diminution in the breadth of the pubic arch and an increase in the pubic angle. The female pelvis, as compared with that of the male, is lighter, less compact, more expanded, shorter in vertical depth, broader at the inlet, witha greater angle in its pubic arch, a lesser curve in the sacrum, and a greater separation between the ischial spines, and is thus more perfectly adapted to the purposes of parturition. The chief deformities due to faulty development may be at least enumerated here on account of their importance in this relation. In the simple flat pelvis the antero-posterior diameter is contracted by the advancement of the sacrum in a down- ward and forward direction between the iliac bones. The equally contracted pelvis resembles a miniature normal female pelvis with other peculiarities that approxi- mate it to the infantile type. The funnel-shaped pelvis is contracted transversely at the outlet in both the antero-posterior and transverse diarneters, the cavity is deeper, the sacrum is narrow and less curved. These peculiarities are found in very early life, and hence this is also known as Xki^ frntau pelvis. The obliqtiely con- tracted pelvis is due to imperfect development of the ala on one side of the sacrum, which is associated with many secondary deformities, among them a lack of curva- ture of the innominate bone on the affected side. The transversely contracted pelvis in which both sacral alae are undeveloped is rarest of all contracted pelves. The 346 HUMAN ANATOMY. functional importance of these peUic contractions should be studied in connection with the mechanism of labor. The pelvis may be deformed as a result of morbid conditions in other parts of the skeleton. A lateral curvature of the lumbar spine to the left may thus be ac- companied not only by the usual compensatory dorsal curve to the ri^ht, but by a curve in the latter direction in the sacrum, the upper margin of which will be higher on the right side than on the left. E\en the corresponding rotation will take place, and the ala on the concave side will be rotated forward, as are the transverse pro- cesses of the dorsal vertebrit. Irregularity in the lengths of the lower limbs may produce a similar curve in the sacrum. In both cases the whole pehis will be tilted laterally, the iliac crest being higher on the convex side of the sacrum. It has been suggested that this continu- ation of a spinal curvature into the sacrum is sometimes a cause, and not a result, of the obliquely contracted pelvis described above, with which it is often associated, but which is regarded as congenital in its origin. Humphry, after describing the ring of the pelvis as heart-sha{)ed, and calling attention to the wide arch with a flattened or depressed centre of the upper or posterior half, and the greater curve with flattening at the ilio-pectineal regions of the lower or anterior half, says, "It results from this configuration of the pel- vic ring that it is weakest at five points, — viz., at or a little external to both sacro- iliac synchondroses, at the symphysis pubis, and midway between the latter and the acetabula. Hence fractures, whether from falls, blows, or foreign bodies pass- ing over the pelvis, are most frequent at these points." In studying the clinical effects of traumatism applied to the pelvis, it is helpful, however, to consider it with reference to its various functions, — i.e., (a) as inter- posed between the vertebral column and the lower extremities as a weight-carrier ; (d) as a means of providing for the motions of the trunk upon the lower limbs and of affording advantageous points of attachment for the muscles which effect that motion ; (c) as a bony protection or receptacle for the abdominal and pelvic \'iscera. I. If it is viewed as a bony ring between the spine and the thigh bones, intended to transmit the weight of the head and trunk from the former to the latter, the pelvis may be regarded as made up of two main arches, — one which is in use when standing, the other when sitting. The sacrum is the point of union of both these arches, — one, the femoro-sacral (Morris), extending from the acetabulum through the strong thickened mass of bone indicated on the inner surface by the upper third of the ilio-pectineal line to the sacrum through the sacro-iliac joint ; the other, the ischio-sacral, extending from the tuber ischii through the strong bony mass at the posterior edge of the acetabulum to the same point. These are the essential weight-carrying portions of the pelvis. Although Cunningham says that, as the sacrum narrows towards its dorsal sur- face, and is really suspended from the iliac bones by the posterior sacro-iliac liga- ments, it cannot be considered as the keystone of an arch, vet the union between the sacrum and the ilia is so close by virtue of these powerful ligaments, of those upon the anterior aspect, and of the reciprocal irregularities of the sacro-iliac articu- lar surfaces, that the objection, though technically correct, is clinically a theoretical one only. In describing the mechanics of the remaining or accessory portions of the pelvis, regarded as a weight-carrier, Morris calls attention to the fact that when much strength is essential in an arch, it is often prolonged into a ring so as to form a counterarch, — i.e., the ends of the arch are tied together to prevent them from starting outward. A portion of any weight to be carried by the arch is thus con- veyed to the centre of the counterarch, and borne in what is called the sine of the arch. In the pelvis "the body and horizontal rami of the pubes form the tie or counterarch of the femoro-sacral, and the united rami of the pubes and ischium the tie of the ischio-sacral arch." The ties of both arches are united in front at the symphysis pubis, which, like the sacrum, is common to both arches. It can now be understood how and why a fall upon the feet, or a crush either antero-posterior or lateral in direction, though such dissimilar accidents, are so apt to PRACTICAL CONSIDERATIONS : THE PELVIS. 347 produce fracture of the horizontal or the descending ramus of the pubes, the ramus of the ischium, or of the ilia external to the sacro-iliac junction. If the accident has been a fall upon the feet, the injury will probably be confined to the acetabulum or to the pubes. In young subjects the acetabulum may be sep- arated into its three anatomical components (Fig. 355), or a portion of the rim may be broken off, or in rare cases the head of the femur may be driven through into the pelvic cavity. If the traumatism has been a crush in the antero-posterior direction, the pubes will probably first fracture ; if the force is continued, the protection afforded by the *' tie arch" having been withdrawn, the pressure comes upon the main arches, which tend to open out. A portion of one of these arches may then give way, and a sec- ond fracture may occur through the ilium into the sacro-sciatic notch, or vertically through the sacrum itself. More commonly, however, the anterior sacro-sciatic ligaments give way and a certain amount of disjunction of that joint occurs. Even if the crushing force is applied laterally, it is usual to find the pubes again fractured from indirect violence. If the application of the force is continued, the strain comes upon the posterior sacro-iliac ligaments, which may rupture, ^''*^- 367- but are more likely to with- stand the violence, which then may result in the tearing away of a portion of the bone into which the ligament is inserted. The pubic fracture is dis- coverable by the usual means. The vertical fracture of the ilium or the disjunction of the sacro-iliac synchondrosis an- teriorly should be suspected if there is pain in the region supplied by the superior glu- teal, the lumbo-sacral, the upper sacral nerves, or the obturator, — i.e., in the sacral region, the buttock, the back or inner part of the thigh, or the knee, — on account of the relation of these nerves to the anterior surface of the joint. Marked ecchymosis, swelling, and tenderness over the sacro-iliac regions pos- teriorly indicate tearing of the posterior ligaments or the fracture by arracheinent that has been described. In all these cases the gravity of the injury depends upon the presence or absence of visceral complications. If a double vertical fracture exists, extending through the rami of the pubes and ischium in front and through the ilium near the sacro- ihac junction posteriorly, it is obvious that there will be one large fragment of the pelvis more or less movable, to which the femur on that side is connected. This condition may be associated with upward displacement of the fragment, carrying the femur with it, and it may give rise to a mistaken diagnosis of fracture of the neck of the femur. It should be remembered, as Tillaux has pointed out, that in the pelvic lesion the relation of the greater trochanter to the anterior superior iliac spine is normal, and the real length of the Hmb on the affected side is the same as that on the sound side. 2. Other fractures, as those through the lateral expansions of the ilia, and epiphyseal separations involving the pelvis, have relation more especially to its function as affording a means of moving the trunk upon the lower limbs. The epiphyses chiefly separated are those of (a) the iliac crest, (<5) the anterior superior spine, (f) the posterior superior spine, and ( of the coccyx and a little of the anterior curve can be felt, as well as the small sacro-sciatic ligaments leading to the ischial spines. Laterally, the tuberosities of the ischium, the smooth bone forming the wall of the pelvis, and the structures back of the acetabulum (page 1693) can be palpated. Through the vagina the configuration of the subpubic arch can be felt, aLso the pelvic wall to either side. If the promontory of the sacrum can be touched, it indicates deformity accompanied by diminution of the antero-posterior pelvic diameter. With the hand in the rectum, the brim of the pelvis, the arch of the pubes, the sacral promontory, the curve of the sacrum and coccyx, the spines of the ischium, and the margins of the sacro-ischiatic foramina can be palpated. The Joints of the Pelvis. — The sacro-liunbar joint has a wider range of movement than any of the joints between the contiguous dorsal or lumbar verte- brae. This is due to the greater thickness of the inter\'ertebral substance, permit- ting flexion and extension, and to the fact that the inferior articulating processes point more antero-posteriorly than those of the other lumbar vertebrae, thus admit- ting of more rotation on a vertical axis. In spite of this, on account of the strength of the ligaments of the joint, and more particularly for the reasons that tend to localize the effect of traumatism some- what higher in the spine (page 145), sprain and disease of the sacro-lumbar articu- lation are both uncommon. Overextension of the joint is brought about if with the body prone the shoul- ders are raised while the hips are fixed. Pain thus produced suggests lumbar or sacro-lumbar disease, as in sacro-iliac disease this movement is often painless. The sacro-coccygeal joint is not infrequently strained by falls upon the buttocks, and occasionally the coccy.x is displaced forward. The joint is sometimes the subject of disease. The symptoms are very similar in all these conditions. The attachment of the gluteus maximus makes a change from a sitting to a standing posture or the reverse movement painful ; it also causes pain if long steps are taken or if running is attempted, and this is aggravated by the action of the hamstring muscles through the medium of the great sacro-sciatic ligament. As the fixed point of the e.xternal sphincter is at the tip of the coccy.x, and as the levator ani is inserted into the sides of the tip, defecation is associated with movement in this joint, and therefore with pain. The latter is often disproportionate to the apparent severity of the injury or disease, and there may be also great tenderness to the touch posteriorly, with no swell- ing or local heat. As these cases chiefly occur in women, Hilton thinks that they are truly " hysterical," and calls attention to the intimate structural communication between the many sacral nerves spread over the posterior surface of the sacrum and coccyx and the anterior sacral nerves, which join with the hypogastric plexus of the sympathetic within the pelvis and thence proceed to the uterus and ovaries. The motion of the sacro- coccygeal joint is of great importance in its relation to obstetrics. Ankylosis occurs, as a rule, between the thirtieth and fortieth years, but the joint between the first and second sacral vertebra- usuallv remains unaffected, and leaves the capacity for antero-posterior expansion during labor practically un- impaired. The Sacro- Iliac Joint. — Injury to and disjunction of this joint have been suffi- ciently described under Fractures of the Pelvis (page 347). Disease of the joint, on account of its strength and immobility, is rare. It is usually tuberculous in character, and is often secondary to suppuration beneath the ilio-psoas from disease of the spine, ilium, or hip. Pain is felt on standing, walking, or sitting, as the sacrum in all these positions bears the weight of all the super- incumbent structures, and on account of its shape (page 346) transmits it to the sacro-iliac synchondrosis. The pain is increased by coughing, straining, or twisting the loins, — i.e., by whatever calls into action the muscles attached to the ilium. Through the relation of the superior gluteal nerve to the front of this joint, pain is often felt in the buttock, and there is wasting of the deep gluteal muscles. The PRACTICAL CONSIDERATIONS : THE PELVIC JOINTS. 351 relation of the lumbo-sacral cord, the upper sacral nerves, and the obturator has already been mentioned (page 347). The body is inclined to the sound side, so that when sitting the pressure on the diseased structures may be lessened, and when standing separation of the joint sur- faces may be secured by the weight of the lower limb. The length of the latter is apparently increased on account of a downward rotation of the innominate bone on the affected side, but measurements from the anterior spines to the malleoli will be the same. Tenderness on direct pressure may be elicited just below the posterior iliac spine ; on indirect pressure by squeezing the ilia together or by separating them so as to put the anterior ligaments on the stretch. Pus may find its way backward and appear at or near the joint line. It more often passes forward on account of the greater thinness of the anterior ligament. It may then enter the sheath of the ilio-psoas and be conducted to the anterior surface of the thigh ; it may follow the obturator vessels through the obturator canal and point on the inner aspect of the thigh ; it may be guided by the sciatic nerve and the lumbo-sacral cord to the region behind the greater trochanter ; it may descend between the obturator fascia and the anal fascia into the ischio-rectal fossa and appear at the side of the anus ; or, finally, it may ulcerate into the rectum and be dis- charged per anum. The symphysis pubis, as the centre of the counterarch of the pelvis (page 346), is subject to manifold strains and injuries ; but, as the union between the two innomi- nate bones at that point is really by a strong, solid, fibro-cartilaginous band, and is without a synovial cavity, and as it is greatly strengthened by the decussation of the fibres of the anterior and inferior ligaments, its separation by traumatism is very rare, and is in effect a fracture. The anterior ligament is much stronger than the posterior to resist the down- ward and forward pull of the adductors and the weight of the abdominal walls and viscera. Its strength accounts for the fact that fracture of the horizontal rami is more common than disjunction of the symphysis in cases in which compressing force has been applied to the pelvis laterally. In cases of disease when the bond of union is weakened, the function of the counterarch readily explains the weakness and powerlessness in standing or sitting. The symphysis is of great importance in its relation to obstetric mechanics and measurements. The plane of greatest pelvic expansion extends from the junction of the second and third sacral vertebra posteriorly to the middle of the symphysis ; the plane of least pelvic diameter from the sacro-coccygeal articulation to the lower third of the symphysis. There is thought to be a trifling separation of the symphysis during pregnancy and labor, but this is counteracted by the decussation of the aponeurotic fibres of the oblique muscles at the linea alba. On account of this decussation these muscles tend, when in vigorous action, as in parturition, to draw the pubic bones together. The symphysis, however, although comparatively unyielding, is in almost the same horizontal plane with the coccyx, the most movable bone that enters into the formation of the pelvis, and with the obturator foramina and the lower part of the great sacro-sciatic foramina. This is in accord with the fact that in no horizontal plane does the pelvis form a complete bony and unyielding ring, but everywhere the resisting bony portion has opposite to it one or more soft and yielding segments, as, for example, the hypogastric region of the abdomen is opposite the fixed and immovable sacrum (Morris). In obstructed labor in which the delivery of a living child may be made possible by a moderate increase in the pelvic oudet, the operation of symphysiotomy is often performed. The aponeurosis of the recti is incised, the retro-pubic structures sepa- rated by a finger, and a probe-pointed bistoury passed down and made to cut for- ward and upward. The incision may with advantage be made in the reverse direc- tion, as the symphysis is wider at its upper than at its lower margin, and is wider anteriorly than posteriorly. The subpubic Hgament and the deep perineal fascia should then be detached from the pubic arch close to the bone, so as to avoid tear- ing the structures that penetrate the fascia — the vagina, the urethra, the dorsal vein of the clitoris, and other venous channels — when the pubes are separated. 352 HUMAN ANATOMY. The motion which permits of separation takes place in the sacro-iUac joints, and the pubic bones move downwara as well as outward, addinjj;^ materially to the amount of pelvic space g^ained. With a separation of seven centimetres (two and three-fourths inches), which is possible under gentle pressure without laceration of the sacro-iliac ligaments, the gain in the conjugate diameter is 1.5 centimetres (three-fifths of an inch). The projection of. the anterior parietal boss into the pubic interspace as the bones recede from each other adds to the space gained, so that by opening the pubic joint to the extent of 6.5 centimetres (two and three-fifths inches) the increase in the conjugate diameter amounts in effect to about two centimetres (three-fourths of an inch) (Cameron). THE FEMUR. The femur, a typical long bone, has a shaft and two extretnities. The lower end rests on the tibia, pretty nearly in a horizontal plane ; from this the shaft slants outward, forming an angle of about 10° with a vertical line. The upper extremity consists of a head, a neck, and tu'o trochanters. These last are on the shaft at the junction with the neck, which runs upward and inward, forming with it an angle of about 125° on the average. The head is a rounded swelling, representing rather more than half a sphere, capping the end of the neck. It is not put on symmetrically, but covers more of the upper side of the neck than of the lower, and probably, as a rule, more of the front than of the back. Occasionally it is prolonged onto the upper anterior aspect of the neck. It is smooth and co\ered with articular cartilage e.xcept at a depression for the ligamentum teres, l^elow and posterior to the axis of the head. Brockway,' having examined 300 fertiurs, found this depression oval in 43 per cent. , with the long axis running downward and somewhat backward, triangular in 35 per cent., and circular in 22 per cent. In 84 per cent, he found vascular foramina, which are larger in the young and not necessarily pervious in the old. In a few cases he found a persistence of the foetal condition, — namely, a groove descending nearly to the border of the articular surface. The neck* extends upward and inward, and usually forward. Being compressed from before backward, it has a front and a back surface with thick upper and lower borders. The lower rises more steeply from the shaft than the upper, so that the neck is much broader at the base than where it joins the head. The lower border is the longer, and the posterior surface is longer than the anterior. The neck is smooth below and behind, rather rough in front and above. The upper border has numer- ous nutrient foramina. The lower border, springing from the inner aspect of the shaft, often presents a rounded ridge running to the lesser trochanter. The neck is bounded behind by an elevation connecting the trochanters, the posterior intertro- chanteric ridged The spiral line,^ also called the anterior intertrochanteric ridge^ bounds the greater part of the front. It starts at the little sjtperior cervical tubercle, at the junction of the top of the neckVith the greater trochanter, runs downward and inward to the level of the lesser trochanter, where it sometimes presents a smaller inferior cervical tiibercle, and then, descending more rapidly, twists round the shaft to join the inner lip of the linea aspera. Thus a small part of the neck between this line and the lesser trochanter has no boundary. We have found the average length of the neck on thirty-eight male bones and twenty-six female ones respectively 4.3 centimetres and 4 centimetres. . Bertaux gives 46.6 millimetres and 43.1 millimetres respectively. The greater trochanter' is a large process projecting upward and outward from the top of the shaft and turning inward to overhang the back of the neck. Seen from the outside its outline is roughly square, but the upper border generally rises towards the back so as to form a point. The anterior surface presents d. depressed area for the insertion of the gluteus minimus. The outer side is crossed by a ridge running downward and forward, to and in front of which is attached the gluteus medius. The upper border receives at the front end the tendons of the obturator internus and gemelli, and a little farther back that of the pyriformis. The hollow ^ Proceedings of the Association of American Anatomists, 1S96. ^ Caput femoris. -Fovea capitis femoris. ^Collum femoris. -^Crista intertrochanterica. *"' Linca intertrochanterica. ' Trochanter major. 1 THE FEMUR. 353 •between the neck and the overhanging trochanter is the trochanteric or digital fossa. ' There is usually a round recess at its anterior end for the tendon of the obturator extern us. The lesser trochanter = is a rounded knob at the inner side of the posterior -aspect of the shaft at its junction with the neck. The posterior side is triangular. It is at the junction of three lines : the posterior intertrochanteric ridge, a line run- ning down to the linea aspera, and an inconstant ridge on the neck. It receives on its end the tendon of the ilio-psoas, and below some of the iliac fibres of that muscle Fig. 369. Fossa for round ligament SntiATER TROCHANTER Tubercle for quadratus femoris Third trochanter. Gluteal ridge Upper extremity of left femur from behind. That part of the spiral line above the level of the lesser trochanter (the so- called anterior intertrochanteric ridge) is generally a very distinct rough line. It may be so faint as to be hardly distinguishable, and extremely rarely a hollow may be found in its place. The posterior intertrochanteric ridge is a thick swell- mg, broader above than below. Near its junction with the greater trochanter it has a slightly rounded prominence, or occasionally a vertical line, liriea quadrati, for the quadratus femoris. The shaft '^ is very strong, and convex in front, except below the neck, where it as slightly concave. In the middle it would be nearly cylindrical were it not for the Fossa trcfchanterica, ^ Trochanter minor. ^ Corpus femoris. 354 HUMAN ANATOMY. Fig, 370. Superior cervical tubercle Fossa for round liganienl OBEATER TBOCMANTt Psoas Vastus i tit emus Adductor tubercle EXTERNAL CONDYLE INTERNAL CONDYLE Right femur from before. Tiic du.u.c ugure shows the areas of muscular attachment. THE FEMUR. Fig. 371. 355 Fossa for round ligament — Psoas and iliacus Pectiyiens Adductor brevis Adductor longus Vastus internus Adductor magnus Gastrocttemius (inner head) GREATER TROCHANTER Linea quadrati Gluteal ridge Outer lip of linea aspera Ext. supracondylar ridge Adductor tubercle Depression for gastrocnemius rMTERNAL TUBEROSITY Depression for gastrocnemius EXTERNAL TUBEROSITY Popliteal groove Intercondylar notch Right femur from behind. The outline figure shows the areas of muscular attachment. 356 HUMAN ANATOMY. prominence of the linea aspera at the back. The surface on either side of this Hne may be plane, concave, or convex, perhaj)s more often concave. The shaft expands slightly above, where it is roughly four-sided with rounded borders. A ridge, which is very variously developed, often runs from the lower side of the neck, separating the anterior and internal svnfaces. When strong, it emphasizes the concavity of the former. The lower third of the shaft broadens. The linea aspera' is a prominent longitudinal ridge along the back of the middle thirtl of the bune, strengthening the concavity and gixing attachment to many muscles. It has two more or less well-defined borders or lips. It is formed from abo\e by the union of three lines : the spiral, a faint intermediate line coming down from the lesser trochanter, and a third external one coming from the back of the greater trochanter. The upper part of the last is called the gluteal ridge, as it receives fibres of the gluteus maximus. This part may be considerably elevated, especially in muscular subjects, into a rough knob, the spurious third trochanter. The true third trochanter, which is sometimes seen at this point, is a smooth rounded eminence, the analogue of the third trochanter extensively found among mammals and particularly developed in the odd-toed ungulata. This is sometimes best developed on delicate female femurs with no rough muscular ridges. Of course the two forms may coexist. A rough elongated depression, \\\it fossa hypotrochanterica , also receiving fibres of the gluteus, is sometimes found outside the gluteal ridge. The linea aspera divides somewhat below the middle of the bone into two supra- condylar ridges, which bound a triangular space' as they pass down to the tops of the condyles. The outer ridge is at first much the sharper, but it becomes indis- tinct an inch or more above the condyle. The inner is but slightly raised ; it is interrupted above its middle for the passage of the femoral vessels into the popliteal space. It ends in the sharp adductor tubercle above the inner border of the condyle. At its termination the shaft has four surfaces : a posterior one nearly plane, a front one slightly convex, a distinct outer one, and an oblique inner one, passing insensibly backward and inward from the anterior surface. There are usually two Jiutrient foramina, both directed upward, the larger between the lines converging to the linea aspera, the other near the middle of the bone, a little to the inside of that line. The lower extremity, articulating with the tibia below and the patella in front, presents two backward prolongations, the condyles, along which the tibia travels in flexion. These are compressed from side to side, and separated by the intercondylar fossa J^ which is beneath the back part of the shaft. The inner condyle^ is the lower when the shaft is \ertical, but in life both are in the same plane. The outer" is longer from before backward ; it lies in an antero-j^osterior plane, while the inner extends backward and inward. The lateral outline of each has been well com- pared to a watch-spring partly uncoiled. Each bears a tuberosity near the posterior end of the lateral side, very nearly in continuation with the supracondylar ridges for the so-called lateral ligaments of the knee. A depression on each side for the head of the gastrocnemius is found above and behind the tuberosities. The ex- ternal condyle bears a deep oblique groove for the tendon of the popliteus at the back of the outer surface. The articular surface for the knee not only covers the lower and posterior aspects of the condyles, but is prolonged upward on the front for the support of the patella, as a groove which is shown by horizontal sections to be concave in the middle and convex at either side. The upper boundary slants upward and outward, the shaft just above it presenting a slight depression. Its outer border is a promi- nent ridge resisting outward dislocation of the knee-pan. The patellar surface is continuous with the articular facets of the condyles, being marked off only by certain lines, which, though distinct on the fresh cartilage, are often obscure on the dried bone, representing the separation of these joints. In some animals the separation is complete. The outer line, usually concave posteriorly, runs obliquely inward to just in front of the intercondylar notch. The inner, less clear and generally straight, begins much farther forward and runs obliquely backward to the inner side of the front of the notch. The outer in particular marks a distinct change of level. Be- hind these lines the articular surfaces extend along the lower and posterior sides of the condyles even onto the upper aspect, so as to allow extreme flexion of the knee. ' Linea aspera. - Planum popliteum. ^ Fossa intercondyloidca. ''Condylus medialis. "Condylus lateralis. THE FEMUR. 357 Frontal sections through the back part of the condyles show that the inner is nearly symmetrical in its convexity from side to side, while the inferior surface of the outer Fig. 372. Outer head of gastrocnemius External lateral ligament External tibial facei Popliteal grot \ e Patellar facet Lower end of right femur, outer aspect. slants upward and inward. The length of the articular surface of the inner condyle from the back to the line marking of^ the patellar facet is considerably greater (perhaps two centimetres ) than that of the outer. Fig. 373. Patellar surface External tuberosit> Limit of patellar surface Internal tuberosity Lower end of right femur from below. Structure. — Transverse sections in series through the whole length of the femur are very instructive. They show the great strength of the shaft, the thick- ness of its walls, the smallness of the central canal, and the addition made by the linea aspera ; likewise that the shaft becomes four-sided both above and below, and that in the latter region the greater diameter is transverse. Coincident with these changes are a great diminution of the thickness of the walls and a great increase of the spongy tissue. The weakness of the walls just above the knee is very striking. The architecture of the condyles is well exhibited, consisting of vertical plates run- 358 HUMAN ANATOMY. ning in the main forward and backward, crossed by transverse ones, in part diverging from the solid bone at tlie bottom of the intercondylar notch. Such sections show also the prominence of the outer border of the patellar surface and the curve of that articulation. At the upper end they disjilay the ])r()minence of the lesser trochanter, the series of strong plates crossing it, which at a higher level are seen diverging from a single plate, Bigelow's true neck^ {MevkeVs ca/ciu/cfnora/e^), to which we shall return. The greater trochanter, quite free from all pressure, is very light and the head very dense. Frontal sections of the head and neck (Fig. 374) show the series of plates given off successively from both the inner and outer walls forming Gothic Fig. 374. Fic. 375- Oblique section of right femur paiallel to lower border of neck, through upper end <>f lesser tro- chanter. Frontal section through upper end of femur, showing " arrangement of pressure and tension lamellae. arches at the top of the bone. The under side of the neck is thick and gives off A series of plates, near together, running obliquely up into the head in the line of the greatest pressure,- especially when the shaft is oblique, as in life. A less distinct series of long arches springs from the outer side, curving across, and acting as "ties." The head is of the round-meshed pattern, fitted to resist pressure in any direction, often presenting an almost solid core at the middle, and generally showing the curved line of union of the epiphysis of the head. The true neck of the femur is a plate, or a series of plates, springing from a thick spur of bone, which leaves the hind wall of the neck to run outward towards the greater trochanter. This is best ' The Hip. Philadelphia, 1S69 ; also Boston Medical and Surgical Journal, 1875. ' X'irchow's Archiv, Bd. 1., 1870. THE FEMUR. 359 seen in sections parallel with the lower wall of the neck (Fig. 375) ; it appears also in transverse ones. When strongly developed it can be shown as a real septum by- gouging away the spongy tissue of the posterior intertrochanteric ridge beneath which it passes. Sexual and Individual Variations. — Apart from general lightness of struc- ture, the female femur presents distinctly smaller articulations than the male. The average diameter of the head of thirty-eight male bones is 4.8 centimetres, and of twenty-six female ones 4.15 centimetres. In only two of the male bones is the diameter less than 4.5 centimetres, and in only two of the female is it greater. Both of the latter are long ones. In women the size of the head increases with the length, but in men a short femur is about as likely to have a large head as a long one. The breadth of the articular surface of the knee is less conclusive ; the averages are 8.3 centimetres and 7.4 centimetres, but there is much overlapping. The peculiarity of outline in the typical female femur is very characteristic when well marked : the shaft narrows gradually from the condyles till at or above the middle the nar- rowest part is reached, above which there is a much less evident expansion. The typical male bone narrows much more suddenly above the condyles, so that the stouter shaft soon reaches a tolerably uniform thickness. The inclination of the shaft is somewhat greater in woman. The angle with a vertical line in the above series is 9.3° in man and 10.6° in woman. (According to Bertaux, it is 8.75° and ii°.) It is naturally greater in shorter femurs, and consequently is of very doubtful value as a sexual characteristic, especially in view of the great individual variation. The angle of the 7ieck with the shaft is of minor significance. In the writer's series it ranges from 110° to 144°, the average for men being 125.1° and that for women 125.6°. In the male bones there is little connection between the length of the femur and the size of the angle ; in women long bones have a large angle and short bones a small one. The average angle of the longer half of the male bones is 126.5° and that of the' shorter 123.6°, while the longer and shorter halves of the female series give 129.2° and 121.9° respectively. A long neck gen- erally has a high angle and a short neck a low one.^ Thus it appears that there are great variations in the angle of the shaft and that of the neck. The same is true of almost every detail. 'Y\\^ forward i7iclinatio7i of the neck is in two-thirds of the cases from 5° to 20°, and usually from 12.° to 14°. Its extreme is 37°. Very rarely this angle is negative, — that is, the neck slants backward. An extreme negative angle of 25° has been observed, but this is extraordinary.^ The curve and outline of the shaft vary much. An extreme form is the pilastered femur, very convex, with a prominent linea aspera, generally stout, implying strength. An opposite form is nearly straight, has a low linea aspera, and is flattened before and behind in the upper part of the shaft. In extreme forms the depression in the front of the top of the shaft is increased and bounded internally by a sharp ridge running up to the under side of the neck, which usually has a low angle. Though apparently weaker, this form is sometimes found in very powerful men. The index of the shaft is the proportion of the thickness to the breadth, the latter being 100. Thus (—breadth '°°)- '^^^^ ^^ ^^^^" ^^ ^^^"^ *^^ middle of the shaft where the linea aspera is most prominent. It is said to be greater on the right than on the left and in men than in women. Bertaux found the average in adults 104.4, ^rid in a series of young femurs 112. i. The index of the neck is the proportion of the thickness to the height. Thus \ "^ h^^^hf ^°°)- '^^^ average is 133.05. It is a trifle higher in women, but the difference in unimportant. A strong convexity of the shaft outward as well as forward suggests a patho- logical condition. Development and Changes. — The shaft begins to ossify not later than the seventh week of foetal life. A centre appears in the lower end during the last month of pregnancy. It is rarely wanting at birth, but the precise time of its appearance as well as its size are too variable to make it a very valuable guide to the age of the ^ H. H. Hirsch : Anatomische Hefte, Bd. xxxvii., 1899. 2 Mikulicz : Arch, fur Anat. und Phys., 1878. r^6o HUMAN ANATOMY. fcEtus or infant. Its growtli sconis to be slight during the first three weeks after birth. The neclc grows as a part of the shaft and recei\ cs three epiphyses, — one for each trochanter and one for the head, which fits over it Hke a cap. The hitter appears in tlie second half of the first year,' and is pretty conclusive evidence that the age of six months at least has been reached. The epiphysis for the greater trochanter comes in the third year (sometimes some years later), and that for the lesser at a time variously stated as from eight to fourteen years. It is probable that Fig. 376. Ossification of femur. v4,at eighth foetal month; />', at birth; C, during first year; £>,at eight years; /;, at about fifteen years, a, centre for shaft; 6, lower epiphysis; 'c, for head; d, for greater trochanter; e, for lesser trochanter. the former is much nearer the mark. The head unites with the shaft at about eighteen, the trochanters somewhat later ; probably there are great variations ; but all these superior epiphyses should be joined by nineteen, and at twenty the line of union is indistinct or lost. An epiphysis for the third trochanter has been seen. The lower epiphysis is joined by twenty, and often sooner. At birth the angle of the neck may be i6o°, but is often less ; it diminishes under the pressure of the weight as the child walks, and by the time of puberty has probably assumed about its permanent angle. There is no reason to believe that the angle diminishes in old age. Surface Anatomy. — The greater trochanter can be explored when the muscles about it are relaxed. The lesser trochanter, though deep, can be felt from behind. A large third trochanter can be recognized, and must not be mistaken for a tumor. Owing to the individual variations of the neck and the pelvis, the relations of the trochanter must vary. According to Langer, a horizontal line at the top of the greater trochanter divides the head, touches the top of the symphysis, and about divides the nates. This is particularly true of broad pelves, and therefore of women. We have found from measurements of ii8 males and 37 females that the trochanter is I.I centimetres, on the ave.age, higher than the symphysis in the male and three millimetres in the female. Topinard gives as provisional distances in the male the following : the anterior superior spine of the ilium is six centimetres above the head of the femur, the latter two centimetres above the greater trochanter (practically agreeing with Langer), and the greater trod inter two centimetres above the pubes. The head of the femur lies under a crease beneath the proper fold of the groin, and can sometimes be distinguished at the inner side of the sartorius. Nelaton's line is drawn from the anterior superior spine of the ilium to the most prominent point of the tuberosity of the ischium. It should just touch the top of the greater trochanter. The shaft is too thickly covered to be examined in detail, except near the knee. The sides of both condyles are easily examined ; the lateral tubercles and the adductor ^ Fagerlund : Wiener Med. Presse, 1S90. PRACTICAL CONSIDERATIONS: THE FEMUR. r.oi tubercle can be felt. The latter marks the line of union of the lower epiphysis with the shaft. When the knee is flexed, the patellar surface, its borders, and part of the articular surface of the condyles can be felt. PRACTICAL CONSIDERATIONS. Before the age of four the upper epiphysis is not distinct, and traumatism is apt to result in separation of the upper cartilaginous end of the bone, — i.e., a fracture through some part of the cartilaginous neck. Later three epiphyses may be affected by injury, — viz., those for the head and the two trochanters. Fig. 377- / mi Section through hip-joint, showing epiphyses of head and great^er trochanter of femur. The epiphysis for the head is shaped like a hollow hemisphere set upon the convex upper end of the neck. The epiphyseal line slopes downward and inward, and is entirely within the synovial memb.a'ne. Separation by 'indirect violence occurs as a result of extreme extension of the thigh, as in falls backward with the limb fixed, or as when a child carried in the arms of a nurse throws itself violently backward. The force is thus in effect applied at the lower end of the femur, which acts as the long arm of a lever. When it is carried far backward the ilio-femoral ligament is put upon the stretch, and its point of insertion becomes the fulcrum. The resistance (or weight) is at the point where the forward movement of the short arm of the lever — the neck and head — 362 HUMAN ANATOMY. is resisted, perhaps slig^htly, by the hgamentuiu teres, hut chiilly \yy the anterior margin of the acetahuhnn. Se]>arati()n is f(»lh)\\ecl l)y shortening. This nia\- he recoj^ni/rd by Nelaton's hne (Fig. 378), by the base hne of the " ilio-fenioral triangle" ( Bryant's; (I'ig. 379), or by Robson's Hne, which is a Hne dropped verticaUy from the anterior spine to meet a trans\erse Hne drawn forward and inward from the tip of the greater tro- chanter across the front of the thigh, the patient being in dorsal decubitus. Eversion, from the weight of the limb, is usually present. The toughness of the periosteum and the strength of the cartilaginous bond between the neck and head in childhood may make the epiphyseal Hne stronger than the thin neck beneath it, and fracture of the neck may therefore occur even in young children or adolescents. The symptoms are very similar to those of epi- physeal sejiaration. The crepitus may be rough instead of " muffled." The X-rays will sometimes differentiate the two conditions. In a case of injury to the hip in a young person, it is, however, probable that epiphyseal disjunction will result rather than fracture of the neck; but in youth, on account of the presence of the epiphyseal Fig. 378. Fig. 379. Showing Nelaton's line. Showing Bryant's triangle. joint and the weakness of the neck, both of these lesions are more frequent than dislocation. Either of them will convert the normal obliciuity of the neck to a position more nearly horizontal, causing prominence and ascent of the trochanter, and bringing about at once the condition known as co.xa vara, which will probably increase later, as whenever the angle of the neck with the shaft is diminished the strain upon the former is increased. Thus, either epiphyseal separation, fracture! of the neck, or slight rhachitis in early childhood may result in coxa vara at the period of adolescence, when the softening incident to rapid growth is taking place, the body weight is increasing, — often disproportionately, — and laborious occupations] are frequently begun. The epiphysis for the g7-eatcr trochatifcr wmics at about the nineteenth year. It] is easily dislocated, almost always from direct violence, and usually between the thirteenth and eighteenth years, because that is the period of greatest exposure to] traumatism, and because at the latter date the epiphysis is joined to the shaft. The line of junction with the shaft is on the level of the tubercle for the quadratus on the posterior edge of the greater trochanter (Fig. 383). It is therefore below the level of j the capsule of the hip-joint and of the insertions of the glutei, obturators, pyriformis, PRACTICAL CONSIDERATIONS: THE FEMUR. 363 Fig. 380. / and gemelli. Disjunction from indirect violence — through the action of these muscles — is rare, on account of : (i) The prolongation downward and outward of the fibres of the capsular ligament which extend below the epiphyseal line. (2) The attachment above that line of some of the aponeurotic fibres of origin of the vastus externus. (3) The toughness of the periosteum. For these same reasons, when disjunction does occur, there is usually but little displacement. If it exists, and is marked, the epiphysis is drawn into approxi- ,mately the same position as that occupied by the head of the bone in a dislocation onto the dorsum of the ilium. The age of the patient (epiphyseal separation being impossible after nineteen and dislocation rare before that age) and the failure of the displaced epiphysis to move with rotation of the femur are aids to diagnosis. The absence of rotation and of shortening of the limb distinguishes this lesion from "extracapsular" fracture of the neck. About fifty per cent, of the recorded cases have died of py- aemia. This is probably because : ( i ) The greater trochanter is an apophysis rather than an epiphysis, and is in contact at its base with cancellous tissue of a lighter and more spongy character than that adjoining the true terminal epiphyses of the long bones. (2) The violence causing the injury is direct and thus associated with much bruising and crushing of that tissue. (3) The disjunction is attended by extensive detachment of the periosteum from the vascular upper end of the bone, as the periosteum over the tro- chanter is very thin and the dense tendinous fibres are almost di- rectly attached to the osseous tissue itself (Poland). The epiphysis for the lesser trochanter can be separated usu- ally only between the thirteenth year and the nineteenth, when it joins the shaft. But one case has been recorded. It was then torn ofi in a boy of fourteen, as the result of the strain on the ilio- psoas in a fall backward on the feet. Death from pyaemia followed. Fracture of the neck of the feimir is common (especially in old age), in spite of its depth and its thick covering of soft parts, because : (i) In falls upon the feet or hip it receives and transmits much of the weight of the body, which, in the former case at least, reaches it in a direction which causes a cross-strain favorable to fracture. (2) It is a comparatively fixed portion of a very long lever into the upper end of which many powerful muscles are inserted. (3) It is of itself lengthened and thus made more vul- nerable,— as compared, for example, with the neck of the hu- merus,— so as to increase the leverage of these muscles, the degree of mobility of the hip-joint, and the basis of support for the trunk. (4) Its mechanical weakness increases in old age (a) from the absorption of cancellous tissue which occurs everywhere in the skeleton, but begins and proceeds most quickly (according to Humphry) in the femoral neck ; {b) from a corresponding thin- ning of the compact tissue, including that part of the cortex which unites the lesser trochanter and the under and anterior part of the head, the line of greatest press- ure in the erect position. (5) The angle between the neck and the shaft is believed by many surgeons gradually to decrease, though this change is not in- variable and is denied by some excellent authorities. It is true, however, that the angle is smaller the less the stature ; that it is thus smaller in women, and that in- them, after the age of fifty, these fractures are two and a half times more common than in men. When the age of the patient is advanced, and the violence is slight and indirect, the femoral neck breaks more frequently near its junction with the head, because there it is thinnest and weakest. Such fractures are entirely intracapsular. In j'ounger persons, and especially if the violence is severe and is received directly upon the hip, the fracture is more apt to involve the base or wider portion of the neck, and is likely to be partly intra- and partly extracapsular. If it is Lines of fracture of femur. 364 HI "MAX ANAIOMN. Fic. .vSi. Showing elevation of tip of trochanter and shorttning of baje of Bryant's triangle in fracture of neck of femur; <;, base on sound side; b, on fractured side. entii-fly belnw the line of Ciii)siil.ir attachment lioth in front and behind, it cannot be a fracture of the neck, as it would then be below the anterior intertrochanteric line, and would involve the extreme upper «nd of the shaft. Posteriorly, it is possible for a jiartial fracture of the neck to be e.xtracapsular, as the insertion of the capsule is from twelve to seven- teen millimetres ( one-half to two- thirds of an inch ) above the base of the neck. Impaction of fracture at the narrow part of the neck is not very common. When it occurs, SDme spicula of the compact cortex of the neck are dri\en into the ex- panded cancellated structure of the head. Impaction of fracture at the base is common, because the spongy tro- chanter is easily thrust upon and sometimes split by the small and relatively compact cervi.x. In most fractures of the neck there will be found : (I) Eversion, due chiefly to {a) the weight of the limb, which tends normally to roll outward ; but also to a certain extent to {b) the action of the ilio- psoas and other external rotators ; (c) the greater comminution or crushing of the posterior wall of the neck, which is weaker than the anterior wall. (2) A fulness over the upper portion of Scarpa's triangle, due to efTusion into the hip-joint or to forward projection of the fragments against the front of the capsule. This is likely to occur because the neck is normally convex forward, the lesser trochanter, marking the inner and lower boundary of the neck, being on a plane posterior to the head ; and because of the greater destruction of the posterior portion of the neck. (3) Relaxation of the ilio-tibial band of the fascia lata (page 367). (4) Approximation of the trochanter to (a ) the anterior superior spine, as shown by shortening, best determined by the length of the horizontal side or base of the ilio-femoral triangle ; and to (b) the mid- line of the body, as shown by Morris's line. Nelaton's line shows the former, but in- \olves more disturbance of the patient. Chiene demonstrates shortening by placing the edge of a straight flexible piece of metal on the two anterior spines and that of an- other on the tips of the tw-o trochanters. Parallelism negatives the idea of fracture. Morris measures from the symphysis pubis to the external trochanteric surfaces. The distance is lessened on the side of fracture. These points can easily be understood by reference to P'igs. 381 and 382. Emphasis is placed on these measurements because it is perhaps more important in this than in any other fracture to avoid vigorous efforts to elicit crepitus. The blood-sup])ly of the proximal fragment — the head — will reaclr it only through the reflected portions of the capsule, untorn strips of periosteum, and the ligamentum teres, that through the cervix being cut off. It is, therefore, scanty and Fig. Morris's measurements to show the trochanter of the injured side nearer the mediati hne in fracture of neck of femur. PRACTICAL CONSIDERATIONS: THE FEMUR. 365 Fig. 383. may be insufficient to furnish reparative material. Any movement that might tear the remaining connections between the fragments is, therefore, most undesirable. The great length of the lower fragment, and the leverage thus exerted as a result of any motion of the inferior extremity, together with the action of the powerful muscles running from the pelvis to the thigh, make it especially difficult to keep the frac- tured surfaces in close apposition, particularly if the small part of the neck is involved. Impaction, even if very slight, may thus be a favorable circumstance, and should not be broken up by rough handling. Intracapsular fractures, in spite of the scanty blood-supply, the presence of synovial fluid, which is perhaps the most important unfavorable factor, and the mo- bility of the lower fragment, do unite, but rather as an excep- tion. As a rule, fractures at the base of the neck unite. Fracture of the shaft is most common at the middle, at the point of greatest convexity of the forward curve, in spite of the fact that here the bone is denser and its compact outer wall thicker. At the upper third fracture is usually due to indirect violence, at the lower third to direct violence. In the former case it is apt to be oblique, in the latter transverse. These lesions, as well as those of the lower end, just above the condyles, will be considered in their relation to the muscles that influence them (page 644). The lower epiphysis of the femur, the only one whose ossi- fication begins before birth, — " with the exception of the occa- sional early appearance of the osseous nucleus in the upper epiphysis of the tibia" (Poland), — is the last to join its diaphy- sis, union occurring about the twentieth year. It has a cup- shaped upper surface, which is higher externally. Its internal level is just beneath the adductor tubercle. The epiphysis includes all the articular surfaces of the lower end of the femur. In the majority of the cases of disjunction of this epiphy- sis the cause has been hyperextension of the tibia on the femur, often combined with some twisting and traction upon the leg, as when a boy hanging behind a cab has his foot caught be- tween the spokes of a wheel. In twenty-seven out of sixty- eight cases the lesion was caused in this way. The ligaments of the knee-joint are so powerful (as they must be for security, on account of the shape of the bones that enter into it) that when the leg is brought into overextension tremendous leverage is exerted on this epiphysis through the crucial ligaments, the external and internal lateral ligaments, and the popliteus muscle, aided by the gastrocnemius. Al- though the latter is attached partly above the epiphyseal line, the periosteum is torn off the lower end of the diaphysis down to the extremely dense layer at the cartilaginous junction. The muscle then becomes an important factor in carrying the epiphysis forward — the usual displacement — and, aided by the popHteus, in rotating its posterior upper edge downward. The mechanism has been compared to that of fractures of the radius in falls upon the hand, the posterior hgament of the knee-joint bringing a cross-strain upon the epiphysis similar to that conveyed to the radius by the anterior ligament of the wrist. The diaphysis projects into the popliteal space or through the skin, and has caused grave injuries to vessels and nerves. Amputation has been required in a large proportion of these cases, on account of these injuries or because of the de- tachment of the periosteum and the suppuration that often follows it. The joint is rarely involved, because the ligaments uniting the bones of the leg to the epiphysis are more powerful than the cartilaginous connections of the latter with the diaphysis. As might be expected, the chief growth of the femur taking place from this Showing; epiphyses of femur. 366 HIMAN ANATOMY. epiphysis, a number of cases of arrest of growth have been reported. The disjunc- tion has been mistaken for a dislocation of the knee or a supracondylar fracture of the femur, but the undisturbed relations of the condyles and the head of the tibia and the freedi)m of motion in the knee-joint serve to distinguish it from the luxation, while the fracture is rare in children, ami presents (.lilTerential signs that will be mentioned later (page 644). Fractures between the condyles (intercondylar), when T-shaped, as they often are, are thought to be secondary to the main or supracondylar fracture, — i.e., the shaft breaks above the condyles and the force continuing splits them apart. The line of the latter fracture is nearly vertical and follows the intercondylar notch, already weakened by numerous foramina for vessels. The proximity of the popliteal vessels has resulted in grave complications from pressure or from rupture. Either condyle may be split off separately. The joint is necessarily involved in all these fractures, and rapid distention may make the diagnosis difficult. The X-rays should, of course, be employed in such cases, and indeed in all doubtful fractures of the femur. Osteotomy for genu valgum may be done through an incision on the outer side of the thigh — the region of safety — about two inches above the external condyle. The ilio-tibial band of fascia is cut ; the incision passes in front of the biceps ; when about two-thirds of the shaft has been divided by the osteotome, the remainder will fracture easily, as the outer part of the bone is here thicker than the inner. The operation has the advantages of remoteness from the epiphyseal line, from important blood-vessels, and from the synovial membrane of the knee. The bone is divided at a narrow part. Disease. — Infective disease of the upper end of the femur usually involves the hip-joint, even when it begins in the diaphysis, the epiphyseal line being intra- articular. In spite of the protective covering of muscles surrountling the shaft, it is not infrequently the subject of inflammation, probably as a result of the great strains and numerous traumatisms to which it is subjected, and of the physiological activity necessitated by its rapid growth, which between birth and maturity is proportionately nearly twice as much as that of the leg and more than twice as much as that of the whole body. Thus, post-typhoidal osteitis attacks the femur in about twenty-five per cent, of the cases in which the lower extremitv is involved, and more frequently than any other bone except the tibia and ribs, although the superficial bones of the skeleton are involved by this disease three and a half times more frequently than the deep bones. At the lower end of the femur, disease resulting in necrosis, especially of the posterior aspect, often requires amputation, as, owing to the thinness of the perios- teum in that region, there is scarcely any attempt at the formation of an involucrum (Rose). Exostoses of the femur are not uncommon, especially in horsemen, in the neigh- borhood of the tendon of the adductor longus — i.e., at the upper end of the femur — and occasionally in that of the adductor magnus at the lower end, — "rider's bones. ' ' The great comparative frequency with which sarcomata attack the femur is in accord with the general rule that they are more frequendy found on long bones than on short ones, on the lower limb than on the upper, and on bones near the trunk than on those remote from it. As they are also more malignant the nearer they approach the trunk, these tumors, like those of the humerus, are clinically more serious than those of the distal portions of the extremity. Both central and sub- periosteal sarcomata, but especially the former, have a predilection for the ends of the bones ; but whereas they affect chiefly the upper end of the humerus and the lower ends of the radius and ulna, in the inferior extremity they are most often found at the lower end of the femur and the upper ends of the tibia and fibula, — that is, at the ends towards which the nutrient arteries are not directed, and at which epiphyso-diaphyscal union takes place latest (page 272). Landmarks. — In very thin persons the head of the femur can sometimes be felt immediately below Poupart's ligament and just external to its middle. THE HIP-JOINT. 367 The greater trochanter is almost subcutaneous, being covered by the aponeu- rotic insertion of the upper fibres of the gluteus maximus. It is from 7.5 to 10 cen- timetres (three to four inches) below the crest of the ilium. In the erect position it is slightly anterior to and farther from the mid-line than the mid-point of the crest. It is visible in thin persons, and assumes abnormal prominence when there has been wasting- of the gluteal muscles, as the gluteus medius and minimus nor- mally efface the hollows between it and the ilium. In fat or muscular persons the fascial attachments to the trochanter cause a visible depression. Its upper border is on a level with the centre of the acetabulum (so that Nelaton's line passes over those two points), is nineteen millimetres (three-quarters of an inch) lower than the top of the femoral head, and is almost on a level with the pubes. The depression immediately beneath it corresponds to the tendinous lower portion of the gluteus maximus close to its insertion. The gap between it and the iliac crest is bridged over by the upper portion of that part of the fascia lata known as the ilio-tibial band. Relaxation of this band in fracture of the femoral neck can be both felt and seen (AUis). The three gluteal bursae interposed between the trochanter and the gluteal muscles may become enlarged, especially that beneath the gluteus maximus, and obscure the outlines of the trochanter. This condition is sometimes mistaken for hip-joint disease, as the thigh is usually adducted and flexed on the pelvis, because abduction and extension bring into action the gluteal muscles, and thus cause painful pressure on the bursa. Inflammation of that bursa is almost always the result of a blow upon the trochanter ; the joint movements are free, there is no referred pain in the knee, and forcing the head of the femur against the acetabulum by pressure upon the knee is painless, as is pressure over the capsule of the joint below Pou- part's ligament. In subcutaneous osteotomy of the neck of the femur the incision for admission of the saw is made about one inch in front and one inch above the top of the trochanter. The saw cut runs parallel with Poupart's ligament and is about 2.5 centimetres (one inch) below it. The lesser trochanter cannot be felt. The shaft of the femur is deeply situated and cannot be closely approached for palpation, except at the outer side of the lower third in the space between the biceps and vastus externus. The most prominent part of the inner rounded surface of the knee is the tuberosity on the inner condyle of the femur. Above it is the adductor tubercle marking the tendinous insertion of the great adductor and just above the inner end of the epiphyseal line. The external condyle is subcutaneous. The remaining landmarks in this region will be considered in relation to the knee-joint and the soft parts (page 671). THE HIP-JOINT. This is a ball-and-socket joint. The socket is formed by the acetabulum with the assistance of the transverse and cotyloid ligamejits. The articular facet which bears the articular cartilage has been described. The notch at the lower part of the periphery of the acetabulum is bridged over by the transverse ligament^ (Fig. 384), a collection of interlacing fibres, which thus completes the margin of the socket. An opening is left below it through which vessels and nerves pass ; from its sides the round ligament^ arises. Some fibres of the transverse ligament mingle with those of the latter. The cotyloid ligament^ (Fig. 384) is a fibro-cartilaginous rim, which deepens the socket overlapping the head of the femur until the cavity embraces more than half a sphere. It is attached to the edge of the acetabulum,^ and, where this is wanting, to the transverse ligament. The cotyloid ligament is about five millimetres broad at the attached base, and narrows to a sharp border, so as to be triangular on section. The distance from the base to the free edge is very nearly one centimetre at the top of the joint, where it is greatest. The non-articular space at the bottom of the joint is filled with fat and by the round ligament nearly up to ^ Lig. transversum acetabuli. ^ Lig. teres femoris. ^Labrum glenoidale. ^6S Hl"MAN ANATOMY. the level of the articular surface. These structures are C()\ere(l by syno\ ial meni- brane. The head of the femur is covered by articular cartilage, except at the de- pression for the insertion of the round ligament. The bones are connected by the capside and the nnnid ligament. The capsule' (Figs. 385, 3.S6) is a fibrous envelope enclosing the joint, strengthencti l>y certain Ijands, which are inseparable parts of its substance, though they have names of their own. The capsule is attached to the c(jtyloid ligament and to the periphery of the acetabulum just outside of the origin of the latter. In this respect there is much uncertainty ; the capsule always rises from the free edge of the transverse ligament, and, as a rule, elsewhere outside the base of the cotyloid ; but it may in parts arise from its edge. This applies to the capsule examined from within ; externally the fibres extend a considerable distance from the border of the joint. They almost conceal the opening at the notch below ; above, they partly bridge over the reflected tendon of the rectus and partly join its deeper fibres. The cap- Fk;. 3S4. Articular surface. Fat in acetabular fossa Tuberosity of ischium Anterior inferior spine of ilium Cotyloid ligament Stump of round ligament Transverse ligament Capsule reflected Socket of right hip-joint. The capsule has been divided near its origin and reflected. •sule extends to the base of the anterior inferior sjiine of the ilium and some distance on the obturator crest. The attachment to the femur, seen from without, runs from the top of the greater trochanter, just above the superior cervical tubercle, down the spiral line to the level of the top of the lesser trochanter, where the line of insertion turns in for about two centimetres, when it passes upward along the back of the neck, less than half-way from the head to the posterior intertrochanteric line, till, reaching the top of the neck, it gradually passes outward to the starting-point- Thus the capsule stops about a finger' s-breadth short of the lesser trochanter, in- cludes less than half the hind side of the neck, and stops short of the digital fossa and of the inner side of the top of the greater trochanter. Posteriorly,*it is not truly inserted into the neck, but simply "crosses it, its position being determined by the line of reflection of the synovial membrane. The general direction of the fibres is longitudinal ; but the posterior fibres, when the femur is strongly extended, .assume .the joxxn of a twisted band running from the back of the socket out-ward ' Capsula articularis. THE HIP-JOINT. 369 and upward across the back of the neck to the top of the greater trochanter (Fig. 387). Moreover, beneath the longitudinal layer there is a sling of circular fibres, the zona orbicularis , starting from the anterior inferior spine of the ilium and pass- ing behind the neck to return to the same point. It lies near the head of the femur, completely concealed by the longitudinal fibres. It is isolated only by a rather artificial dissection. The capsule varies much in thickness in different places ; thus, it is very weak behind and very strong in front. It is strengthened by three collections of accessory Fig Ilio-femoral ligament Right hip-joint, anterior aspect. fibres. Much the most important is the ilio-femoral ligament ^ (Fig. 385), a thick triangular expansion, intimately fused with the capsule, arising by its ape^rom the lower part of the anterior inferior spine of the ilium and from the bone below and behind it above the lip of the acetabulum, and extending by its base from the superior cervical tubercle to the level of the lesser trochanter. The borders of this are often particularly strong, and are spoken of as the oziter and imier limbs of the ligament. A weak space is sometimes seen between them near the insertion, whence it has been called by Bigelow the Y-ligament from a resemblance to an inverted Y. ^ Lig. iliofemorale. 24 370 HUMAN ANATOMY. Striking examples of this arc generally artificial productions. The beginning of the ilio-femoral ligament covers the outer part of the head. The capsule is much thinner over the inner part of the head, and is covered by the bursa under the ilio- psoas, which often communicates with the joint. The pubo-femoral liga- ment' (Fig. 385) is a slender band of fibres, thickening the under side of the capsule, extending from the lowest point of the capsular insertion on the spiral line to the outer end of the obturator crest. It is rarely very evident. The ischio-femoral ligament' (Fig. 3S7 ) is a strong but ill-defined bundle at the back of the joint, extending frt)m the ischial origin of the capsule to the top of the digital fossa. The capsule is further supportetl by muscles and by bands of fibrous tissue, generally expansions from tendons or fasciae. Morris describes a band on the upper Fig. 386. Cotyloid ligameni Capsule. Fat in acetabular fossa ■ •'. ' Round ligament i — ^Obturator membrane Frontal section through right hip-joint. The femur has been allowed to fall from the socket. anterior aspect, passing between the reflected tendon of the rectus and the highest origm of the vastus externus, which is sometimes very strong, but. in our opinion, mconstant. The relation of the ilio-psoas has been mentioned. Fibres are received at the upper outer part from the gluteus minimus. The obturator internus and the gemelh are close against it behind, and the obturator externus behind and below. We have seen a tendmous band beneath the tendon of the obturator internus quite distinct from the capsule internally and fused with it externally. It mav have been a reduplication of that muscle or an extra ischio-femoral ligament =* f 1; J^"^ ^°""^ ligament {ligamenhim teres) (Figs. 384, 389) is a weak band othbrous tissue, containing vessels and nerves, surrounded by synovial membrane, lying under the fat in the deep non-articular hollow of the socket, connecting the ■"• Journal of Anatomy and Physiology-, vol. viii., 1874. ' Lig. pubocapsolare "Lig. iscbiocapsulare. THE HIP-JOINT. 371 rim of the acetabulum with the head of the femur. The origin is from each edge of the notch and from the deeper fibres of the transverse hgament, the insertion into the deepest part and upper edge of the depression in the femoral head. A fresh specimen, especially from a child, shows the lower half of the depression becoming gradually shallower and forming a groove in which the upper part of the band rests, which, covered with the synovial membrane, completes the spheri- cal shape of the head. Vessels run along the round ligament, which in infancy Reflected tendon of rectus Back of capsule Tuberosity of ischium Rig-ht hip-joint, posterior aspect. and early childhood nourish the head, but in the adult they often do not enter the bone. This ligament is sometimes wanting. According to Moser,^ this defect is only in the old, and is to be looked upon as a degenerative change. Comparative anatomy teaches that it is the analogue of a part of the capsule. It is remarkable that it is wanting in certain species closely allied to others possessing it. Besides the two extremes of complete freedom within the joint and of total absence, the ligamentum teres of animals is also found in an imperfectly developed condition as a fold along * Schwalbe's Morpholog. Arbeiten, Bd. ii., 1893. This paper gives the literature. 372 HUMAN ANATOMY. the side of the cavity between the notch in the acetabulum and the liead of the bone. Many of the statements of its absence require confirmation by more observations. Thus, amone:' the anthropoid apes it seems to be generally present in all but the ourang. In this animal, though usually wanting, it has been found in a rudimentary condition. Meckel declared that it was absent in the gibbon, but we believe no other observer has had a similar experience. It is very strongly developed in the ostrich, but is wanting in the rhea ( the American ostrich ) and probably in the casso- wary. Sutton' considers it as the tendon of the pectineus muscle which has become separated through skeletal moditications. Sutton relies a good deal on the condition in the horse for support in his argument. He fountl it consisting of two bands, — one within the joint, apparently the usual ligament, and another passing out of the cavity to the linea alba at its junction with the pubes, which he calls the pubo- femoral portion. The pectineus muscle arises in part from this latter portion. Sutton gives a table telling the story of the structure according to his theory. In sphenodon (a lizard) the tendon of the ambiens, representing the pectineus, passes Fig. 38S. Cotyloid ligament Bursa beneath ilio-psoas Round ligament . 'i' -Front of capsule Spine of ischium Capsule a tached to neck of femur Cotyloid ligament Tendon of obturator externus Horizontal section through right hip-joint. into the joint to the head of the femur : in the ostrich the ligament is continuous with the tendon by means of connective tissue ; in the horse the two parts are distinct ; and in man the external part is wanting. The structure is evidently a very variable one. The synovial membrane (Figs. 386, 388) lines the capsule, covers the cotyloid and transverse ligaments, surrounds the ligamcntum teres, and covers the fat in the fossa of the acetabulum. It is reflected from the femoral attachment of the capsule onto the neck, which it invests to the border of the articular cartilage. This reflected part presents certain folds caused by fibres from the capsule running up along the neck, called retinacula (Fig. 390). There are generally three chief ones : a superior, starting from the superior cervical 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 neck ; and an iyiferior, 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 axes. 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 Fjg. 389. Crest of ilium Head of femur Tuberosity of ischium Obturator membrane Symphysis pubis 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 HUMAN ANATOMY. resistance of the stroiij^ ilio-femoral liijaincnt, excepting the outer band. Abduction is limited, the thigh being e.xtended, by the pubo-temoral Hgament and perhaps by the inner Hnib of the iho-femoral. Kiu. 390. Round ligament Retinaculum Posterior intertrochanteric ridge Capsule When the thigh is flexed, the latter is certainly relaxed, and the strain comes on the piibo- femoral and a part of the capsule behind it, — a very weak re- gion. Adduciion with a straight thigh is limited by the outer limb of the ilio-fcmoral, 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-iemoral is relaxed. Old-ward rotation, 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 rotation 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. Right femur seen from inner side, showing reflection of synovial membrane onto the neck. 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-icmoral 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 seen through it (Morris). Fig. 391 represents this diagram matically. 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 (AUis) in adduction of the thigh (which means an outward movement of the upper extremity of the femur) , should be mentioned among the factors that Fig. 391. 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 Lux-ations. — 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 w^ere 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 — Diagram indicating strong and weak portions of capsule of hip- joint. {Allis.) Fig 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 usuallystronger than the bone itself. Hyperflexion 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 ofTers but little resistance ; the head, being opposite the shallowest part of the acetabulum, projects half its bulk out of that cavity ; the weight — i.e., the resistance of the capsule — is very close to the fulcrum, greatly increasing the power of the leverage. Diagram showing dividing line (X, V) between outer and inner pelvic planes. (Allis.) 376 HUMAN ANATOMY. The ilio-femoral ligament may, in cases in which the thigh is adducted and rotated inward at the time of api)licatit)n 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 KiG. 393- Luxation of the head of the femur onto the dorsum of the ilium. Fig. 394. 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 experimentally, are reproduced in many forms of accident. It is obvious that they are all favorable to a downward dislocation, and this, as is the case with the humeral head, is the direc- tion primarily taken in the vast majority of these lu.xa- 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 abo\'e 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. Relation of tlic bt_a( iif tlie ft inur to the innominate bone in dorsal luxation. PRACTICAL CONSIDERATIONS : THE HIP-JOINT. 377 In both positions the iHo-femoral Hgament, 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 ; v 1 the ilio-psoas. | The muscles have a very minor part in the production or maintenance of the characteristic deformity. The external rotators, the glutei and the pectineus, are often lacerated. There is shortening, and the trochanter is above the level of Nelaton's line. In the rare cases in which the Y- ligament — or its outer limb — is torn, ; j outward luxation with neither adduc- tion nor inversion becomes possible. 2. hiward 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' ' luxa- 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 midway between the pubes and the sacrum. From this level the pelvis slopes upward to the symphysis and downward to the K~"> Luxation of the head of the femur onto the pubis. 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 (A 11 is). The femoral vessels are not often injured in hip luxations, because they lie above the joint and luxations 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 stretch 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 tenst Fig. 396. and are stretched across the neck of the femur j)os- 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 very apt to be bruised and stretched and separated somewhat from the biceps tendon. Later, if rej)lace- 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 Allis, 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 further y^^.r^'fl' 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 Jts outer hmb) into a fulcrum around which, as a centre, — the abduction and eversion 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 Relation of the head of the femur to the innominate bone in pubic luxation. PRACTICAL CONSIDERATIONS: THE HIP-JOINT. 379 4 X \ 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, — i.e., the movement consists of flexion, abduction, adduction, inversion, and extension, 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. AUis'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 level 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 limb 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. 380 HUMAN ANATOMY. Fic;. 39S. femur becomes possible because of the tinii connection between (a) the base of the neck and the acetabuhnn throup^h the unruptured portion of the capsule, and {d) the two frai^ments through the attachment of muscles alonj; 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 tlislocation of the hip is : draw the head in the direction of the socket ; ai:)ply 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 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 cut^ 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 may 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 Nelaton'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 gra\'e. It mav 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 : r, 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 Relation of the head of the femur to the innominate bone in obturator luxation. . PRACTICAL CONSIDERATIONS : THE HIP-JOINT. 381 joint is nearest the surface ; and (<5) 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 («) the muscles inserted into and passing over the cap- sule ; {b~) all the muscles moving the lower hmb 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 sacral 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 hmb 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 largely 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 thickeninj^ over the inner surface of the acetabulum in the latter case and not in the former (Cheyne). In dislocation from disease, unless there has been separati<«i 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 tlK- 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 pointbeneath the greater trochanter ; they may make their exit through the cot\loid notch and point in Scarpa's triangle ; they frequently pass out anteriorly, and are found beneath the tensor vaginee 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 vaginie 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 Jibtda and the interosseous 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 externally 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 inner tuberosity, 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 condvles of the femur, separated at the middle by a promi- nence, the spitie,^ with a triangular non-articular surface before and behind it. The former of these is rough, the latter smooth and grooved. The spi7ie itself is com- posed of two lateral parts connected behind, of which the inner is the longer from before backward, rising from the condylar siwfaces. The crucial ligaments of the knee-joint are attached to the non-articular surfaces before and behind it. The iyiner 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 otiter 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 ik\^ 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 litde backward and outward. Its outline is uncer- tain, being either round or quadrilateral. It may be curved in any direction, and ' HmiaenCia iutercondylnidea. - Condjlus lateralis et medialis. ''Fossa intercondyloidea posterior. I THE TIBIA. .383 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 tubercle^ 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 inner malleolus. The inrier 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 iiiterosseous 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 hnes 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 nutrient 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 inter?ial 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 litde 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 interossea. ^ Linea poplitea. ° Malleolus medialis. 384 HUMAN ANATOMY. Fio. 399. Spine Ext. condylar surface y-^ ^^ '"'• condylar surface Tubercle - P.ursal surface For ligamentum patellae \ Anterior border or crest External or inter f » , osseous border > * n||' Biceps Ext. long.- digiioriim Tibialis anticiisl -=i^'» "i*,?^ ..^.^.;-]-^^. 'li: m — Internal border Tendon patella (extensor - quadriceps) -Gracilis ^Sartorius -Semilendinosus ^■"■^ '"' ' — ~ ii>^^ 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" Groove for semimembranosus- 'm Popliteal notch Spine / Ext. condylar surface External tuberosity -Articular surface for fibula Pophteiis- Setnitnembf-anosus Popliteus- Soleus (tibial head) — Flex Jong, digitorum- Soleus (tibial head) - Tibialis posticus > Oblique line Nutrient foramen Posterior surface -External (interosseous) border .Posterior division of interosseous border ■Tibio-fibular ligament tGroove lor fiex. long, hall Groove for tibial, post, and Jiex. long, digit _ Internal malleolus __ -For astragaius Right tibia from behind. The outline figure shows the areas of muscular attachment. ^.S 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 Exl. fibro-cartilage /\ Post, crucial ligament Int. fibro-carlilagc Ext. condylar surface- \\ Ext. fibro-cartilage' Anterior crucial ligament Int. condylar surface Int. fibro-cartilage 'Uirsal surface Mtachment of tendon patellae Upper end of right tibia from above and before. very variable. The very thin, platycnemic, form is most common in sqvage races, and is therefore associated with the pilastered femur. It is found not rarely amonfy Fig. 402. Fig. 403. Frontal section of upper end of tibia. Frontal section of lower end of tibia. whites, but the shape of the accompanying femur is uncertain. The tibial index /transverse diameter X 100 \ • .^ .• r \ , ... (antero-posterior diameter) ^^ ^"^ ^^^lo of the transvcrse to the antcro-posterior diameter. PRACTICAL CONSIDERATIONS : THE TIBIA. 38.7 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 foetal week ; one for the upper end, appear- ing usually in the last month of foetal life ; and one in the lower, appearing in the second half-year.^ These epiphyses correspond to what has been described as the n g— J 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 ; 5, for upper epiphysis of tibia ; c, for lower epiphysis of fibula ; d, for lower epiphysis of tibia ; e, for upper epiphysis of fibula ; _/, 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 by the external lateral ligameiht ; (d) on the inner side by the internal lateral ligament, and (c) on both sides by the fibres of insertion of the ^ Fagerlund : loc. cit. 388 HUMAN ANATOMY. Fig. 405. vasti and semimembranosus and t)f 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 heacl of the fibula or the laceration of the superior tibio-fibular liganunts. The attachment of the syno- \ ial meml)rane of the knee-joint does not descend to the level of this epii:)hysis ; hence that articulation is often not involved in these injuries. They sh(~)uld not, when sex'ere, 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 very 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 ten recorded instances, all males : nine from violent action of the quadriceps in powerful young men, eight of whom were between sixteen and eighteen years of age, the age of the remaining two 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 conclusive. Bonv 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 Fig. 406. w Ji 1 % 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 violence 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 involving the ankle-joint is a not infrequent complication of Pott's fracture. Separation of the lower epiphysis is nearly 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 account of the possibility of involvement of the epiphyseal joint and 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 but 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. Lines of fracture of tibia and fibula. 390 HLMAN ANATOMY. Post-typhoidal periostitis aiul 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 antl 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 expt)sure to frecjuent slight injury and to strain disproportionate to its size and strength i^vide supra), and because of its dependent position and its 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 hypera^mia and the localization of infection. Sarcoma, in accordance with the general rule already mentioned (page 366), affects chietlv the upjjer third of the tibia. Landmarks,— 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 tlie 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 tibiae 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 patelke 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-marketl 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-external, (3 ) the postero-internal, sometimes called the ob/iqjte 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 si'de of the neck below the styloid ' Capitulam fibulae. '-'.Apex capituli tibulac. ' Corpus fibulae. THE FIBULA. 391 Biceps Peroneus brevis Fig. 407. Styloid process Facet for tibia External malleolub Interosseous border Fig. 408. -Styloid process Head Postero-internal border For tibia Articular surface for astragalus Tibialis { posticus -Posterior surface Postero- external border External surface Biceps 'Soleus ) Flex. long, hallucis "eronejis longus ) Peroneus brevis Groove for tendons External malleolus • Right fibula from before. Right fibula from behind. The outline figures show the areas of muscular attachment. 392 HUMAN ANATOMY, Fig. 409. -Styloid process Tibial facet i\m"'' Anterior surface Antero-internal border- Antero-external border — Internal surface' -Posterior surface Tibialis' posticus .Postero-external border -Costero-interiial border iSoleus I jF/rx. ions' halliicis Inferior interosseous ligament Facet for astragalus ( -lossa ~Ext. lateral ligament Right fibula, inner aspect. The outline figure shows the areas of muscular attachment. PRACTICAL CONSIDERATIONS: THE FIBULA. 393 process. It is strongest at and below the middle of the bone. It twists backward and is lost at the back of the malleolus. The postero-internal border begins at the inner side of the back of the head. It is very strong at about the middle. It ends in the last quarter by joining the interosseous ridge. The latter, or antero-internal border, begins poorly marked at the inner side of the neck, soon becomes sharp, and descends rather straighter than the others to some three inches above the lower end, where it divides into two lines which, ending at the borders of the articular facet for the astragalus, enclose a rough space for ligaments. The interosseous membrane, being attached to this ridge, separates the front of the bone from the back. The a7iterior surface, between this and the antero-external border, is very narrow. It forms a part of a hollow, of which the membrane is the floor, from which certain extensor muscles arise. The external surface, between the antero-external and the postero-external borders, is a characteristic one, presenting for more than the lower half a shallow groove for the peroneus longus and brevis, which sweeps down to the back of the malleolus behind the subcutaneous space enclosed by the splitting of the antero-external border. 'Wi^ posterior surface is bounded by the postero- external border and by the postero-internal till that border joins the interosseous ridge, which bounds the surface in its lower part. . It faces backward above and inward below. The nutrient foramen, running downward, enters it rather above the middle, usually near the postero-internal border. A roughness on the outer part of this surface is for the origin of the soleus. The internal surface, relatively broad in the greater part of its course, looks inward to the hollow between the two bones. It ends in the last quarter where the oblique ridge joins the interosseous one. The lower extremity of the fibula is pointed, forming the outer malleolus,^ which projects downward and a little outward. Its outer surface is a continuation of the subcutaneous triangle, and the greatest prominence near its back is in line with the posterior of the borders of the space. Most of the internal surface is occupied by a triangular articular facet for the astragalus, the upper part of which is nearly vertical, while the lower slants outward. Below and behind this, on the inner side of the greatest projection, is a deep hollow for part of the external lateral ligament. The malleolus is broader behind than in front, presenting a groove in continuation of the external surface for the peroneal tendons. Development. — The centre for the shaft appears in the eighth foetal week ; that for the head of the bone, which, according to the usual order of long bones, should develop next, does not come till after that of the malleolus. The latter ap- pears in the second year, the former two or three years later. The lower epiphysis is probably fused with the shaft by eighteen or nineteen and the upper by twenty. PRACTICAL CONSIDERATIONS. The upper epiphysis has a flat lower surface and is about on a level with the most prominent part of the tibial tubercle. It includes, therefore, all that portion of the head of the fibula into which the biceps tendon and external lateral ligament are inserted. Its line of cartilage at and after the thirteenth year is in close relation with the synovial membrane of the tibio-fibular joint. Its disjunction is favored by its situation on the most exposed aspect of the limb, its subcutaneous position, and the insertion into it of the biceps muscle. The attachment of the external lateral ligament also enables a powerful strain to be brought upon it in over-adduction of the leg. In spite of these favorable circumstances, the protection afforded by the slight overhang of the external tuberosity of the tibia and the fixation given by the strong anterior and posterior upper tibio-iibular ligaments make separation of this epiphysis a very rare occurrence. Boyd says that several cases are known in which it has been pulled off by violent contraction of the biceps in an effort to prevent falling. It is then felt as an easily recognizable fragment the space between which and the diaphysis is increased upon extension of the leg. Fracture of the shaft of the fibula in its upper two-thirds occurs from direct violence and as a secondary result of fracture of the tibia. In spite of the slender- ness of the bone and its position on the outer aspect of the leg, fracture is not very frequent because of (a) its elasticity, which is marked ; (<^) its protective covering 1 Malleolus lateralis. 394 HI "MAN ANATOMY. of muscles and fascia ; and ( r ) its backward curvature, which carries it to a plaiu posterior to that of the tibia, which thus jjrotects it both internally and anteriorly from direct violence. . , . , . i • n »i Fractures about the middle of the lower third of the shaft, and especia ly those about 7.. centimetres (three inches) from the ankle, are so commonly produced by leverac'e that whatever their exact level, most of them may be grouped as instances of Pott's fracture. althouKh an effort has been made to draw between them distinc- tions that are ordinarily academic rather than practical. These fractures usually result from over-abduction of the foot. When that occurs suddenly, the wei^^ht of the body being upon the limb, the tension hrst comes upon the deltoid ligament. This may stretch slighUy or some ot its hbres may be torn or there mav be a small detachment from its malleolar origin. As a rule, such a case ends in a more or less severe sprain. If the ligament ruptures or the tip ot the malleolus is torn off, or the malleolus itself is fractured, the abduction of the foot continues, and the astragalus is subluxated and carried against the inner surface of the external malleolus, the hbula is thus converted into a lever of the hrst order. The force is api)lied at its lower end ; the fulcrum consists ot the stout tibio-hbular lieaments which are often stronger than the bone itself and which are rarely com- pletely ruptured, though often stretched and lacerated ; the weight or resistance is in the body of the bone, which is prevented from moving inward by the articulation of its upper end with the tibia. As soon, therefore, as its limit of elasticity is ex- ceeded, it breaks at a weak (if not its weakest) point, and the upper end ot the lever—/ e of the lower fragment— is forced in the direction opposite to that ot the lower end,— /.r., the malleolus (Fig. 410). The impact of the astragalus and the pull of the ligaments may cause, in addition to the fracture of the tip of the malleolus, fracture of the anterior' or of the outer articular edge of the tibia. If the tibio- fibular ligaments rupture, the fibula becomes a lever of the second order, the fulcrum shifting to its upper end. The dislocation of the astragalus outward will be more marked. ' The bone may break at any point, but the fracture is still likely to be within the limits of the lower third. Rose and Carless have adopted the following useful classification based on the injury to the inner side of the foot or to the tibia itself. It divides these fractures into four groups, the term Pott's fracture being correctly applied, according to these authors, to the first two only. i. The internal lateral ligament is torn through; the intact internal malleolus can be felt projecting beneath the skin (Fig. 410, A). 2. The malleolus is torn off and a distinct sulcus can be felt between it and the lower end of the tibial shaft (Fig. 410, B). 3. The interosseous tibio-fibular ligament is ruptured (or the flake of bone at the tibial attachment is torn off) ; the subluxation outward is very marked ; either the inner malleolus or the deltoid ligament yields, — "Dupuytren's fracture" (Fig. 410, C). 4. The tibia fractures transversely just above the base of the malleolus : the lower end of the upper fragment may be mis- taken for the tip of the malleolus (Fig. 410, D^. The less frequent accident of forcible over-inversion of the foot, if the external lateral ligament holds, produces by the same mechanism a similar series of occur- rences. The tip of the external malleolus is dragged violendy inward, the tibio- fibular ligaments act again as a fulcrum, and the bone is apt to break at about the same level, — i.e., from 5 to 7.5 centimetres (two to three inches) above the joint, — the upper end of the lower fragment being carried outward instead of inward. In these cases there is a subluxation of the astragalus inward which not infrequently results in a fracture of the inner malleolus. In all these forms of fracture the lacera- tion of ligamentous structures loosening the connection of the foot to the leg, the upward pull of the calf muscles, and the'weight of the foot itself combine to produce a subluxation of the foot backward which is often overlooked. The cardinal symptoms of the common form of Pott's fracture are eversion of the foot, prominence of the inner malleolus, shortening of the distance from the front of the ankle to the web of the great toe, increased width between the malleoli, and tenderness over (a) the space between the tibia and the external malleolus anteriorly, i,e., over the strained or torn tibio-fibular ligaments ; (b) over the base or tip or anterior border of the internal malleolus, — i.e., over a ruptured internal lateral PRACTICAL CONSIDERATIONS: THE FIBULA. 395 ligament or a fracture of the malleolus ; and (c) over the fibula from two to four inches above the tip of the malleolus, — i.e., over the fibular fracture. The lower epiphysis of the fibula is an exception to the rule that the epiphyses of long bones appear first at the end from which the nutrient artery is directed, and to the more important rule that the chief growth of the long bones takes place at the end where the epiphysis is last united to the shaft ; in the other long bones this is also the ^ni. y^ Ant. super, tibio- fibular ligaments Interosseous membrane / Antero-intemal surface Anterior border- CONNECTIONS OF THE TIBIA AND FIBULA. These are the superior and inferior joints and the interosseous membrane. The Superior Tibio-Fibular Articu- lation ' (Fig. 411}. — The cartilage-covered ar- ticular surfaces already described vary greatly both in direction and in the nature of their curves. Perhaps the more ordinary arrange- ment is for the tibial facet to be concave in a horizontal and convex in a vertical plane ; but the converse may occur, and there are many intermediate forms. The synovial sac extends upward behind and may communicate with the knee-joint. The capsule is very strong, except below, and especially so at the outer side where the long external lateral ligament of the knee is incorporated with it. The anterior and pos- terior superior tibio-fibular ligavients ^ are strong fibres, strengthening the capsule and passing outward and slightly downward from the tibia to the fibula. The interosseus membrane^ (Fig- 4^0 extends from the head of the fibula down along the interosseous ridges of both bones till these split. Its fibres run in the main downward and outward, but in the upper part many run downward and inward. There is a large opening at the top abo\e the membrane or through it. The Inferior Tibio-Fibular Articulation * (Fig. 411 ). — This joint is essen- Ant. infer, tibio-fibular ligament Tibio-fibular ligaments from before. ' Articulatiu tiliiolibularis. tibiotibulare. Ligg. capituli fibulae anterius et posterius ''Memb interossea cruris. 'Syndesmosis THE BONES OF THE LEG AS ONE APPARATUS. 397 tially ligamentous, though the articular cartilage of the ankle-joint extends for a few millimetres onto the opposed sides of each bone. The inferior ligaments are the interosseous, the anterior ^.nd posterior, and the transverse. The interosseous ligament is a thickened continuation of the mem- brane, consisting of short fibres connecting the rough surfaces bounded by the spUt- ting of the interosseous ridges. The anterior and posterior ligaments^ (Fig. 411, 412) are strong bands situ- ated respectively on the front and the back of the tibia and running downward and outward to the fibula. The anterior deepens the socket but slightly, while the posterior, reaching nearly half-way down to the malleolus, makes a considerable addition to the back of the joint. The transverse ligament (Fig. 412) containing Fig. 412. Ant. tibio-fibular ligament Capsule reflected Ant. lateral ligament Middle lateral ligament Deltoid ligament Outer malleolus Transverse ligament - Pad of fat /'''^C::^ \ Capsule Post, external lateral ligamenl Post, tibio-fibular ligament Socket of right ankle-joint from below. probably elastic fibres, runs obliquely from the back of the lower border of the tibia to the tip of the outer malleolus. It projects into the joint, the capsule form- ing a pouch between it and the posterior tibio-fibular ligament. It is closely con- nected at the fibula with the posterior fibulo-astragaloid ligament. The two have the appearance of diverging bundles of the same structure. The synovial cavity is prolonged some three millimetres upward between the bones. The back part of the crack between the bones is concealed by a pad of fat (Fig. 412) covered by synovial membrane projecting into the joint. It advances or recedes between the bones according to changes of position. Movements, — The motions between the tibia and the fibula are slight and not very definite; The head of the fibula may play a little forward and backward, and the bone may rotate on its long axis. These motions are resisted alternately by the anterior and posterior ligaments at both ends. THE BONES OF THE LEG AS ONE APPARATUS. Surface Anatomy. — The upper part of this support consists of the head of the tibia with that of the fibula well back on the outer side. The framework nar- rows to the junction of the middle and lower thirds, where the tibia is nearly at its smallest and seems to bend towards the fibula. Below this it broadens for the socket of the ankle. The fibula in the lower third is close to the tibia and no longer so much behind it, which is due in part to the subsidence of the crest of the tibia. The difference of relations is shown by sections at three levels (Fig. 413). The whole apparatus is described as having three borders and three surfaces. As the details have been given with the bones, the chief features only are here enumerated. The anterior border is the crest of the tibia ; the posterior and iyiternal border is the posterior border of the same bone ; between them is the subcutaneous internal surface. T\i^ posterior and external border is the postero-external border of the fibula. Thus there remain an antero-external and a posterior surface, each of which is formed in ' Ligg. malleoli lateralis anterius et posterius. 398 HUMAN ANATOMY. part by the interosseous membrane. The anlcro-extcnia/ S2ayair presents the fol- lowing features : ( i ; a large surface of the tibia, looking outward as far as the lower third and then forward ; (2) the interosseous membrane ; (3) a narrow' sur- face of the fibula, bounding externally the fossa of the front of the leg, shallow above, deep and narrow below ; (4) the antero-external border of the hbula, split- ting below to enclose the subcutaneous surface above the outer malleolus ; (5) the grooved surface of the fibula occupied by the peronei. The posterior surface presents, continuing in the same course : ( i ) the posterior surface of the fibula,' looking backward above, inward below ; (2) the postero-in- ternal border, ending in the "interosseous ridge ; in the upper two-thirds this over- hangs a deep hollow ; (3) the internal surface, which ends below with the preceding border ; (4) the interosseous membrane ; (5) the posterior surface of the tibia. The interosseous membrane is at the bottom of a much deeper gutter than in front, which also becomes very narrow below. The outward twist of the ankle has been mentioned, and it has been shown that this depends on the twist of the tibia. It is to be noticed that while the antero- external, the postero-external, and the postero-internal borders of the fibula run as if Oblique line Postero-int. border' .■\nterior border Internal border Antero-ext. border O^X Postero-int. border Postero-ext. border .Anterior border Anterior border Anteroexl. border Internal border Postero-ext. border .■\iiterr A.\ border y Postero-ext. border Sections across the bones of right leg, showing their relations at difEerent levels; seen from above. A, near head of fibula ; B, near the middle ; C, a little above the ankle. the lower end of that bone had been twisted outward, the same is not true of the borders and surfaces of the tibia. On the contrary, the crest, with the surface on each side of it, slants in the lower half of the leg downward and inward. It is as if thes6 borders of both bones had been twisted away from the median line of the leg, one to each side, and that the interosseous ridge had stayed straight. There seems to be no relation between the degree of forward bend of the neck of the femur and the outward twist of the socket of the ankle. Probably both have an influence on the direction of the foot, but it depends chiefly on the latter. It is un- warranted, therefore, to expect all children to turn out the toes alike. The whole of the front and sides of the head of the tibia is easily felt, but it is thickly covered behind. The top of the tuberosities is clear on either side, and in front the whole of the tubercle can be explored when the tendon is relaxed. The head of the fibula is distinct far back on the outer side. Descending the leg, it is easy to follow the sharp crest of the tibia into the lower third, and the internal subcutaneous surface down to the malleolus. The external surface, where it becomes anterior above the ankle, is plain in spite of the tendons crossing it. The shaft of the fibula is so covered with muscles that little more than its general position is to be made out above the triangular subcutaneous surface over the outer malleolus, which latter is also easily explored. The relations of the malleoli are considered with the foot (page 449). THE PATELLA. The knee-pan, the largest sesamoid bone, is triangular or shield-shaped. The anterior surface is covered by the tendinous fibres of the quadriceps, which re- place the periosteum and mark the surface with longitudinal lines. Jagged spines from the ossification of the tendon are often found at the top. The transverse 1 In the transverse sections (Fig. 413) this surface is exceptionally small. THE PATELLA. 399 diameter is usually rather larger than the vertical, especially in strong, and conse- quently in male, bones. The base^ is above with a slightly curved outline, and the apex"' below, usually somewhat internal to the middle. The outer lower border is more oblique than the Fig. 414. Tendon of quadriceps extensor Ligamentum patellae Ligamentum patellae Right patella, anterior and posterior surfaces. inner. The posterior surface is divided into an upper articular part and a much smaller non-articular one below, in which the bone is thinner at the expense of the Fig. 415 Prepatellar' bursa Alar ligament \ — Cavity of joint Lateral part of capsule Cavity of joint Posterior crucial ligament Horizontal frozen section through right knee-joint. posterior surface and is covered by the fibres of the ligamentum patellae. The upper part, covered with articular cartilage and forming a part of the knee-joint, is Basis patellae. ^ Apex patellae. ^ Facies articularis. 400 HUMAN ANATOMY. much broader transversely llian vertically. The outer three-fifths or so, which plays on the external condyle, is concave transversely and the inner two-tifths con- ve.x. The convexity begins with a vertical prominence which marks the greatest thickness of the bone and appears to divide the hind surface into two parts, as a horizontal section shows, the surface receding from it on either side. Neverthe- less, the whole inner part is convex, as describetl. Vertically, both sides are slightly concave. A close examination of a fresh specimen shows, what rarely is to be seen on the dry bone, that the articular surface is to be further subtlixided. A narrow vertical facet is seen along the inner side, constituting a surface which rests on the edge of the inner condyle in extreme Hexion. The rest of the articular surface is divided into three horizontal zones, one above another, by two transverse lines. The top of the bone is very thick, most of it being occupied by the insertion of the rectus. The capsule of the knee-joint is inserted all around the articular surface some two or three millimetres from its edge, so that a little of the border is enclosed in the joint. Several nutrient foramina are found on the anterior surface. Development. — The patella appears as a cartilaginous point in the course of the third ftetal month. Ossification begins by the deposit of several granules some time between two and five years. ' These soon unite into a central mass, from which ossification spreads, more rapidly, however, in the deeper parts. The bone is not fully formed till after puberty, perhaps not before eighteen. THE LIGAMENTUM PATELL.^i:. This name is applied to the tendon of the quadriceps extensor muscle, in which the patella is a sesamoid bone (Fig. 416). It is a strong, flattened, fibrous band some two inches long. Just below the knee-pan it is at least one and one-quarter inches broad, but at its insertion into the front of the upper part of the tuberosity of the tibia its breadth is not over one inch. The line of insertion is oblique, the outer end being the lower. Just above the insertion a synovial bursa lies between the tendon and the bone. A mass of fat above the bursa separates the tendon from the capsule. The tendon is fused at the sides with fibrous expansions from the quadriceps. THE KNEE-JOINT. This is a compound joint between the femur and the tibia, the patella being a sesamoid bone in the tendon of the extensor of the leg, incorporated in the front of the capsule. The patella is in relation to the femur only, and sometimes it is con- venient to consider the knee-joint as the sum of three distinct ones, — namely, that between femur and patella, and one for each condyle with the tibia. The joint is enclosed by a capsule partially subdivided in many ways. Fibro-cartilaginous disks, the semilunar cartilages on the top of the tibia, tend to subdivide the joint below each condyle into an upper and a lower half. The crucial ligaments nearly cut of^ communication between the parts of the joint under each condyle. The mucous ligament assists in this, and with the alar ligaments tends to isolate the patella. Discussion of the knee-joint calls for the description of the following component structures : The Capsule and its Accessories. The Semilunar Cartilages and their Accessories. The Crucial Ligaments. The Subpatellar Fat with the Ligamentum Mucosum and the Ligamenta Alaria. The Synovial Membrane. Certain Bursse. The capsule (Fig. 416) arises from the femur, mingling with the periosteum, a litde above the anterior articular surface ; from the sides of the condyles as high as the level of the lateral tuberosities ; from the back one centimetre beyond the highest point that the cartilage reaches on the top of the condyles ;■ and from a slighdy lower level above the intercondyloid notch. It is attached in front around the articular surface of the knee-pan and inferiorly to the tibia all around, but a THE KNEE-JOINT. 401 little below the top ; for the articular cartilage is continued over the border onto the sides. It is lower at the back of the outer tuberosity, where the joint sometimes joins that of the head of the fibula. It is attached to the periphery of the semi- lunar cartilages. This, which is the capsule proper, is very much strengthened by surrounding structures. On each side a strong fibrous layer passes from the con- dyles to the patella {^ailerons de la rotule of French authors) (Fig. 418). Super- ficial to this, and not adherent to it, come the aponeurotic fibres of the vasti, and still more superficially the fascia lata. They fuse with the capsule at the sides of Fig. 416. Tendon of quadriceps extensor Capsule External lateral ligament — |-. Tendon ot biceps Internal lateral ligament Ligamentum patellae Sartorius turned back Fibula Interosseous Tibia membrane Right knee-joint from before. the patella, but extend over the latter in two tolerably distinct layers. Both heads of the gastrocnemius and the plantaris are to a great extent incorporated with the capsule behind (Fig. 417). The tendon of the semimembranosus, which has its chief insertion in the groove in the inner side of the tibia where it is covered by the more superficial lateral fibres of the capsule, sends across the back of the capsule : strong transverse diverging fibres, known as the ligament of Winslow, some of which are directly continuous with the outer head of the gastrocnemius (Fig. 417). Some longitudinal fibres near the back of the inner side, only artificially separable 26 402 HUMAN ANATOMY. from the rest, liavc l)ec'n calktl the internal lateral ligament' (I-Ik- 4i6j. The long external lateral ligament' (Fig. 41S), though connected with the capsule by areolar tissue on its deep surface, is truly a distinct Hganient. It arises from the external tuberosity of the femur and runs as a flattened cord downward and some- what backward to the outer surface of the head of the fibula, almost, or quite, splitting the tendon of the biceps, which is inserted external to it, overlajipiiig the ligament in front and behind. A shorter band placed more posteriorly and insepa- rable from the capsule can often be traced to the styloid process. The tendon of the Fig. 417. Femur 1 Fibres to capsule from tendon of adductor nia^nus Int. head of ijastrocneniius Bursa opening into joint Tendon of semimembranosus Posterior ligament of VVinslow External head of gastrocnemius plantaris condyle Bursa opening into joint Popliteus tendon External lateral ligament Tendon of biceps perior tibio-fibular ligament Tibia Interosseous Fibula membrane Right knee-joint from behind. popliteus entering the joint from behind is incorporated with the capsule beneath the long external lateral ligament, as described with the bursae. The semilunar cartilages (Figs. 419, 420) are two crescentic disks of fibro- cartilage lying each on top of one of the tuberosities of the tibia, with their thick outer borders at the periphery attached to the capsule and their thin edges free, so as partially to divide the joint into an upper and a lower part. The pointed ends {cortuia) are fastened near the middle line of the joint. Those of the external cartilage* are attached to the front and back of the fibular facet of the spine of the tibia and to the inner border of the raised articular facet before and behind it. The ' Lig. collaterale tibiale. ' Lig. coIlaCerale fibulare. ^Meniscus lateralis. THE KNEE-JOINT. 403 posterior horn, moreover, joins the posterior crucial hgament. There is not more than one centimetre between the two horns, so that this cartilage is almost circular. The internal cartilage ^ is C-shaped. The anterior horn, thin and fibrous, is in- serted into the rough surface near the anterior border at no very definite point. Sometimes it runs into the transverse ligament without any fixed ending ; some- times the extreme point is free. The posterior horn is attached to the back of the tibial facet of the spine and to the edge of the articular facet behind it. The Fig. 418. Extensor tendon Subrectal bursa Inner head of gastrocnemius Popliteus tendon and opening into joint Long external lateral ligament Tendon of biceps Head of fibula Superficial band to patella Ligamentum patellae Anterior tibio-fibular ligament Right knee-joint, external aspect. The extensor tendon is drawn forward and upward. distance between the horns is about three centimetres. The anterior horn of the internal cartilage may not come into contact with the femur. The vertical diameter of the cartilages at the periphery is from six to eight millimetres. The breadth varies in different joints, ranging from one to nearly two centimetres.^ The broadest part is near the back of the internal one, but the external is, on the whole, the broader. It is said sometimes to completely divide that half of the joint. The free border is very thin and may present fine prolongations with scalloped edges. ^ For various statistics, consult Higgins : Journal of Anatomy and Physiology, vol. xxix., 1895. ^ Meniscus medialis. 404 HUMAN ANATOMY. The lower surfaces of the disks ad.ipt themselves to the top of the tibia, the outer cartilage concealing the convexity at the back of the tuberosity. The uppet surfaces form cups to receive the femoral condyles. At the sides of the spine, where the cartilages are wanting, the cups are completed by the upward slope of the tuber- osities. The coronary ligaments ( Fig. 420) are parts of the caj)sule connecting the periphery of the semilunar cartilages with the tibia. They are of little strength and allow more or less motion. Those of the external cartilage are mtjre than two cen- timetres long at the front and 1.3 centimetres at the back, while those of the internal are from four to five millimetres. Thus the external cartilage can move very freely on the tibia, both from the length of these ligaments and from the appro.ximation of its horns, while the internal can move but little. This has an important influence t'lG. 419. Shaft of femur ■ Bursa beneath extensoi tendon MVt~ Capsule Patel! Alar ligament - Internal semilunar cartilage- Posterior crucial ligament- Bursa of tendon of semimembranosus Alar ligament iilV*^ .Anterior crucial ligament External semilunar cartilage \i i'^^ '- ' ^"'^^-^-^—-^it^-fr Tendon of popli |i**V(i. ^V'''^'*'"''. , Ilife^T ~^' ^^^'"'^ reflected Anterior wall of right knee-joint seen from behind, the lower end of the femur having been removed. on the mechanics of the joint. The popliteus muscle is attached to the outer, which is significant in the same connection. The transverse ligament' (Fig. 420) is a band, usually ill-defined and often quite wanting, which connects the cartilages at the front of the knee, running from the convexity of the outer to near the anterior cornu of the inner and sonietimcs into it. It is closely attached to the capsule in front. The crucial ligaments-' (Figs. 419, 420; are two broad, thick bands, the strong- est in the joint. The anterior arises from the depression in front of the spine of the tibia, close to the external semilunar cartilage, and runs upward, backward, and outward to the back of the inner side of the outer condyle. The posterior, the stronger, arises from the back of the groove at the posterior aspect of the top of the bone, and from its outer border, leaving the floor of the groove and the transverse piece of the spine of the tibia free and covered by synovial membrane. It is also closely connected with the external semilunar cartilage. It runs forward, upward, and a little inward to the front of the outer side of the inner condyle and of the ' Lig traasrersam eeao. - LigamcDta cmciata genu. THE KNEE-JOINT. 405 intercondylar notch. The fibres from the external semilunar cartilage run along it in a varying- position, but usually as a well-defined bundle. When the joint is straight the surface of the anterior ligament looks approximately forward and up- ward, its line of insertion being about vertical ; when it is fully flexed the outer edge is brought forward so that the ligament is somewhat twisted on itself and the upper part looks inward, the line of insertion slanting slightly downward and back- ward. In the former position the posterior crucial has the anterior surface looking outward, forward, and downward, the line of insertion being horizontal, with the front external. With the knee flexed the ligament is closely applied to the internal condyle. The Subpatellar Fat, the Ligamentum Mucosum, and the Ligamenta Alaria (Figs. 419, 423). — If the joint be opened by dividing the capsule just above Fig. 420. Patellar surface Capsule reflected External condyle Ant. crucial ligament Ext. semilunar cartilage Transverse ligament Coronary ligament Edge of superior surface of tibia Capsule reflected Post crucial ligament Internal condyle Internal semilunar cartilage Coronary ligament Bursa beneath ligamentum patellae Tuberosity of tibia Right knee-joint, opened and the knee flexed. Seen from before. the patella, or, better, by splitting the patella and turning one-half to either side, a large mass of fat is seen inside the capsule, below the patella and above the front and top of the tibia, covered by the synovial membrane. This mass has a definite shape, though, of course, subject to change by pressure. It is perhaps best described as pyramidal, the base being towards the surface between the knee-pan and the tibia. When the knee is straight it fills the patellar surface of the femur and laterally passes under the condyles, filling the space between them and the tibia. It reaches to the semilunar cartilages. Towards the joint it has two free angles, a larger one below entering between the bones as just described and a smaller one above. The lateral halves, including the synovial covering, are called the alar ligaments ^ (Figs. 419, 423). From the middle of this mass below the patella runs a collection of fat with areolar and elastic tissue, invested by synovial membrane, to the top of the inter- condylar notch. This is the ligamentum mucosum,' of litde strength and not absolute constancy, which acts as a guy, preventing the mass of fat from falling away from the femur. There are also collections of fat about the crucial ligaments and at the back of the joint between the posterior crucial and the capsule. The synovial membrane lines the capsule in a general way, buc is separated ^ Plicne alares. ' Plica synovialis patellae. 4o6 HUMAN ANATOMY. from it by the masses of fat just described. It surrounds the lower halves of the crucial ligaments with the fat in a common envelope, so that there is in nature no interval between them. There is but a small chink between the upper halves, though each has its separate sheath. The back of the posterior crucial is partly un- covered by synovial membrane. Synovial fringes formed by the membrane and more or less underlying tissue project from the folds of the alar ligaments, from the ligamentum mucosum, and from near the borders of the patella. Bursae. — ( i ) The most important is a large one under the extensor tendons, just above the capsule, with which it usually communicates. It probably in most cases develops independently of the capsule, which then lies in front of its lowest Fig. 421. Posterior surface of femur Gastrocnemius Back of capsule Internal condyle Post, crucial ligament Int. semilunar cartilage Tibia Gastrocnemius Insertion of anterior cruiialligament External condyle Ext. semilunar cartilage .Tendon of popliteus Ji Tendon of biceps Fibula Frontal frozen section of right knee-joint passing through condyles and behind shaft of femur. The superior tibio-fibular joint is opened. Seen from behind. part, a communication forming subsequently. Such a communication almost always exists in the adult, less frequently in the infant. The opening may be small and well defined or so large that the cavities of the joint and bursa give no sign of subdivision. This carries the cavity of the joint any part of three finger-breadths above the knee-pan. It is possible that sometimes there is a communication from the beginning. (2) Prepatellar burs(s are found on the front of the patella at different depths. Directly below the skin is the superficial fascia, often lamel- lated and adherent to the layer beneath it. According to Bize,' (a) a bursa is present in this superficial layer, usually over the lower half of the patella, in eighty- eight per cent, of knees examined. The next layer is an aponeurotic one continu- ous with the fascia lata, beneath which {b) a bursa is found in ninety-five per cent., most commonly at the inner inferior part. A still deeper (c) bursa occurs beneath * Journal de I'Anat. et de la Phys., 1896. THE KNEE-JOINT. 407 the fibrous layers from the tendon of the quadriceps over the lower part of the bone in eighty per cent. (3) A large and constant bursa lies on the smooth anterior surface of the tubercle of the tibia beneath the ligamentum, patellae, which is inserted into the lower part. It extends upward to about the level of the top of the tibia, from which it is separated by the fat below the knee. It practically never communi- cates with the knee-joint. As the tendon before it is inserted obliquely, descend- ing lower on the outer side, the shape of the bursa is roughly triangular. The greatest diameter is the transverse one at the top, the outer border is not quite so long, and the inner about half the length of the outer. The breadth is from 3 to 4 centimetres, the outer border from 2.5 to 4, and the inner from 1.5 to 2.5 centi- metres. (4) A subcutaneous bursa is often found over the tuberosity of the tibia Fig. 422. Posterior crucial ligament Anterior crucial ligament Capsule Internal semilunar cartilage Fascia lata Fascia lata Externa! semilunar I cartilage Capsule Frontal section through middle of right knee-joint. Seen from behind. and (5) another over the ligament of the patella. At the back of the knee there are several bursee. (6) The largest is that beneath the inner head of the gastrocne- mius (Fig. 426), which later in life often connects with the joint. _ It is usually prolonged between the gastrocnemius and the tendon of the semimembranosus. (7) A bursa is commonly found between the long lateral ligament and the tendon of the popliteus as it passes beneath it, and another between the ligament and the tendon of the biceps. The relations of the tendon of the poplitetis muscle are so important as to re- quire a separate description. The muscular belly is usually separated from the back of the tibia, near the top, by a prolongation of the capsule between the tibia and the back of the external semilunar cartilage, which is described by some as a bursa com- municating with the joint. According to either view, there is a deficiency of the coronary ligament at this point. The muscle is connected beyond this with the outer side of "the external semilunar cartilage. Passing above this, it becomes a part 4o8 HUMAN ANATOMY. of the capsule, and on reaching its insertion it makes a more or less prominent pro- jection into the joint. There niav or may not be a projection of the capsule like a bursa at the point where the two are fused. On its way the tendon often sends some fibres to the posterior crucial ligament. Movements. — The motions between the femur and the patella w ill be consid- ered after those between the thigh and the leg. The knee cannot be a hinge-joint, for in such the moving part is always at the same distance from the axis of rotation, which is out of the question in the knee, owing to the shape of the condyles. The fact that these are neither of equal length nor parallel complicates the problem. The joints are further subdivided by the semilunar cartilages, which make a slight socket for each condyle. This socket is more or less movable and also compressible and elastic, so that it may change its shape to accommodate itself to the form of P'iG. 423. Tendon of extensor quadriceps Capsule Post, crucial ligament ternal condyle ^ — Alar ligament Capsule Ligamentum mucosum External condyle Alar ligament Ligamentum patellae Tubercle of tibia Patella removed from rijcht knee, which is strongly flexed to show alar ligaments and ligamentum mucosum. A probe is passed beneath the latter. different parts of the condyle. The external semilunar cartilage, having its horns securely attached near together and having a long coronary ligament, can swing backward and forward pretty freely as a whole. The internal cartilage is more closely fastened to the tibia, excepting the anterior horn, which has no constant arrangement. Not only can the semilunar cartilages change shape, but, as Braune has shown, the cartilage of the joint is capable of compression. For all these reasons accurate mathematical statements are impossible. In extensio7i of the leg on the thigh, beginning with the knee flexed, the tibia travels along the irregular curve of the condyles, carrying the semilunar cartilages with it. There is practically no movement between the internal cartilage and the tibia, unless at the end, and probably little beneath the external. The external tuberosity of the tibia reaches the front of the shorter condyle before the internal tuberosity has completed its course. The last part of the advance of the latter is accompanied by an outward rotation of the tibia on a vertical axis passing through about the middle of the outer condyle, so that while the inner tuberosity still swings PRACTICAL CONSIDERATIONS: THE KNEE-JOINT. 409 forward, the outer part of the external swings back. This motion occurs below the external semilunar cartilage. Flexion begins with a corresponding inverse rotation of tlie tibia. While the knee is straight the tibia is firmly fixed, so that in rotation of the limb at the hip the bones move as one. The long lateral ligament and that part of the capsule called the internal ligament are placed so far back that they are relaxed in flexion but become tense in extension. Both the crucial ligaments are always nearly tense, especially the posterior. The anterior is quite tense in exten- sion, the posterior in flexion. The latter prevents forward displacement of the femur on the tibia when, as in alighting from a leap, the whole weight is carried for- ward by the irnpetus, the knee being flexed. Another rotation on a vertical axis through the middle of the joint may occur when the knee is flexed. The motion is between the femur and the internal semilunar cartilage, and both above and below the external one. This motion is chiefly passive, — i.e., imparted by another person twisting the leg when the muscles are relaxed. It probably, however, can be exe- cuted actively to some extent. It is very slight in less than semiflexion of the knee, and diminishes as flexion becomes more extreme. The precise angle at which it is greatest seems uncertain. Rotation of the tibia outward, tending to untwist the crucial ligaments, is resisted by neither, but by the internal lateral ligament. Rota- tion iyiward is resisted by both crucials, especially the anterior, and by the external lateral. The posterior ligament is made tense in life in positions in which it would otherwise be lax by the action of the semimembranosus. It is tense in extension. The front part of the capsule is tense in flexion and relaxed in extension, but its condi- tion in the latter state is considerably modified by the degree of contraction of the quadriceps extensor. Movements of the Patella. — The patella in the upright position, when the muscles are relaxed, has the lower part of the articular surface resting against the top of that of the femur. When the muscle is contracted the former is drawn entirely above the latter. As flexion begins the lower zone of the articular surface fits into the groove on the femur, the two upper and the internal strip not being in contact with it. In semiflexion the knee-pan has passed below the patellar surface of the femur, and the middle zone rests on the front of the outer condyle and on a small part of the inner. As flexion becomes extreme the patella follows the outer condyle, resting on its under side by its superior zone, the convex portion is in the notch, and only the strip along the inner edge is in contact with the outer side of the internal condyle. In the latter part of the movement the mucous ligament becomes tense, and through it, and still more by atmospheric pressure, the alar ligaments are brought close in to fill the chink between the femur and the tibia. PRACTICAL CONSIDERATIONS. The Knee-joint. — The anatomical conditions which should render the knee- joint peculiarly subject to dislocation are as follows : i. Its situation between the longest bones of the skeleton and its consequent exposure to tremendous leverage. 2. Its similar exposure to frequent strain and traumatism. 3. The extensive and varied character of its movements. 4. The absence of bony prominences, which could effectively strengthen the joint, upon either the articular surface of the lower end of the femur or the shallow upper surface of the tibial tuberosities. The ability of the joint to resist dislocation, which is of very rare occurrence, lies in (a) the strength of the ligaments, especially the crucial ; (<^) the expansions of the quadriceps tendon on the front of the joint ; (<:) the reinforcement of the posterior ligament by the semimembranosus tendon ; (^d) the similar relation of the internal lateral ligament to the semimembranosus, and of the external lateral to the tendons of the biceps and popliteus ; {e') the power thus conferred upon strong muscles to meet and modify or resist sudden strains by varying the tension of the capsule and even of the ligaments ; (/) the deepening of the tibial cup by the semi- lunar cartilages, and the adaptation of the latter to the varying positions of the bones so that the contact between and pressure upon the joint-surfaces are as extensive and as uniform as the shape of the condyles will permit. Dislocations of the knee may be antero-posterior or lateral in direction. The 4IO HUMAN ANATOMY. former usually and the latter invariably are incomplete, owing to the large superficial areas of the joint-surfaces. In the great majority of cases dislocations of the knee are due to indirect violence acting through the femur as a lever, — as, for example, in falls forward, the foot and leg being fixed. The weight of the trunk carrying the upper end of the thigh forward, brings tlie lower end with great power — the fulcrum and the resistance, or weight, being so close to each other — against the posterior ligament, a rupture of which permits the movement to continue and results in an anterior dislocation of the knee, which is, regarded from an etiological stand point, a displacement of the femur backward. If the fall is in the opposite direction, the femur may be displaced anteriorly, — i.e., posterior dislocation of the knee may occur. Occasionally the anterior disloca- tion has followed the fall of a weight upon the front of the femur. The application of force to the front of the leg when the knee was Hexed has produced a posterior dislocation, the effect of the biceps, popliteus, and semimembranosus in reinforcing the posterior ligament being minimized in that position. Lateral dislocations are caused by adduction or abduction of the leg, the thigh being fixed, or by falls sideways when the foot and leg are fixed. The great width Vastus iiiternus / Tendon of adductor magnus Tibia/ ^---^^^\ Internal condyle / •-- Tendon of sartorius Inner aspect of right knee-joint, showing expansion of quadriceps tendon. of the joint and the slight resistance offered by the interposition of the tibial spine between the femoral condyles render them rarer than antero-posterior luxations. Forward dislocation is more common, possibly because of the greater laxity of the capsule in front, and is more apt to be complete than the backward. The knee is extended ; the tibial tubercle prominent ; the antero-posterior diameter increased ; the anterior margin of the tibial tuberosities palpable in front ; the rounded condyles may be felt, but less distinctly posteriorly ; the popliteal concavity is obliterated ; the aponeurotic expansion of the quadriceps is loose and lies in folds about the upper border of the patella. The femoral vessels and nerves may be bruised, compressed, or lacerated. In backward dislocation also the knee is in extension and the antero-posterior diameter increased. The displaced bony prominences may be recognized by palpa- tion. This dislocation is even less apt to be complete than the forward variety ; but if it is, the vessels and nerves are oftener injured, as shown by the more frequent occurrence of gangrene. This is probably due to the sharpness and prominence of the backward projection of the upper edge of the tibial tuberosities, as compared with the rounded depressed notch between the femoral condyles which receives the vessels in forward dislocation. In lateral dislocation, in accordance with the direction of the displacement, PRACTICAL CONSIDERATIONS: THE KNEE-JOINT. 411 one or other condyle becomes prominent, as does, on the opposite aspect of the limb, the head of the fibula or the inner tuberosity of the tibia. The patella, owing to the shortness and strength of its ligament, is carried with the tibia. The lateral diameter of the joint is increased. The foot is apt to be rotated in the direction of the luxation owing to the tension of the biceps in the outward and of the popliteus and inner hamstrings in the inward variety. Dislocations by rotation have also occurred. Fig. 425. Internal semilunar cartilage Crucial ligaments External semilunar cartilage Cavity of knee-joint Superior tibio-fibular articulation Tibia Fibula Frontal section through knee-joint, showing articulating surfaces and epiphyseal lines. In the various forms of luxation the crucial, the lateral, and the posterior liga- ments and the biceps and gastrocnemias muscles suffer most severely ; the popliteus and semimembranosus less so. They are often compound, and may for that reason necessitate amputation. The injury to the ligaments leaves the jomt weak ana insecure for a long time. ■ a a S7ibluxation of the semilunar cartilages occurs usually when the leg is hxed, the knee slightly flexed, and the femur rotated upon the tibia, because the move- ments of flexion and extension take place between the femur and these cartilages, which, therefore, follow the motion of the tibia ; whereas in rotation— the move- 412 HUMAN ANATOMY. monts then occurring between the tibia and the cartilages — one of them is fixed between the corresi)ondini^ condyle and the til)ia which rotates beneath it ; the remaininij^ cartilage, especially it the rotation is marked, may lie dragged or squeezed so that it is nipped between the tibia and femur. Thus the contraction of the biceps which effects outward rotation of the leg brings more closely together the external tuberosity of the tibia and the external condyle, and the outer cartilage is held tirmly between them. This increases slightly the distance between the internal condyle and the head of the tibia, leaving the internal cartilage freer to move into an abnormal position. When the popliteus, semitendinosus, and semimembranosus contract to rotate the leg inward, they, in like manner, fix the internal cartilage and allow of increased mobility of the external cartilage. Subluxation of the inner cartilage is the more frequent because (i) outward rotation of the leg is far more common than inward rotation ; (2) the muscle chietiy concerned in effecting inward rotation, — the popliteus, — when it contracts, steadies and supports the external cartilage by pressure against its outer margin ( Morris j ; no corresponding support is given the internal cartilage during outward rotation , (3) the anterior crucial ligament is attached somewhat in front of, and often directly' to the inner cornu of the external cartilage, tending to limit its forward motion. It is altogether behind the internal cartilage ; (4) the external cartilage has a strong attachment to the femur through the ligament of Wrisberg posteriorly. The displacement is forward in the majority of cases. The symptoms are pain, from the pressure on the cartilage itself, increased by reflex spasm of the muscles moving the joint, and followed by a synovitis. The edge of the cartilage may often be felt. Disease of the knee-joint is of great frequency on account of its exposure to (a) direct violence and to cold and wet, by reason of its superficial position, and (^) to strains and wrenches through the leverage of the femur and tibia. The factors competent to resist luxation are not able to protect it from minor injuries. It is a favorite seat, therefore, of traumatic synovitis, and — on account also of its complexity, its large size, and the difificulty in keeping it at absolute rest — disease, if acute, is apt to be severe and threatening ; if subacute, tends to become chronic or to recur. All the above reasons, combined with its inclusion of the lower femoral epijjhysis and its close relation to the upper tibial epiphysis, — the seats of the chief growth of the lower limb, — make it also one of the joints most commonly subject to tuberculous disease, while gout, rheumatism, and syphilitic and gonococcic infection are often localized in it. Most of the chronic diseases due to infection, as well as those directly following traumatism, begin in the synovial membrane because of the large superficial expanse of that membrane. The intra-articular effusion — whether "simple," from hyper- c'emia, or inflammatory, from infection — causes the knee to assume the position of moderate flexion because ( i ) its capacity is then greater than in full extension or full flexion, and maximum capacity is equivalent to minimum pressure ; (2) flexion relaxes the densest and most resistant ligaments, — the posterior and the lateral (as they are attached behind the centre of the bone) and (if moderate) the posterior crucial. It is resisted only by the ligamentum patellae, which is in less close rela- tion to the joint (being separated by the pad of fat on which it lies), and by the thinner and more extensible anterior portion of the capsule ; (3) the joint is inner- vated in accordance with the general law that the same nerves which supply the interior of an articulation supply also both the muscles moving it and the skin over the insertion of those muscles (Hilton). The knee-joint is acted on by ten muscles, four of which are extensors and six flexors. The latter are not only numericallv in excess, but are also the more powerful and 1:he more favorably situated for acting upon the joint. Therefore, when the articular twigs of the obturator, sciatic, and anterior crural nerves are irritated by disease, and both the anterior and posterior groups of muscles contract reflexly, the flexors predominate. The principle is of wide-spread application, and should be considered in reference to the position of most joints, at least in the early stages of disease. Later in knee-joint disease the softening and elongation of the ligaments permit the pull of the flexors to produce posterior displacement of the bones of the leg PRACTICAL CONSIDERATIONS: THE KNEE-JOINT. 413 upon the thigh. This is aided in dorsal decubitus by gravitation, which also favors the outward rotation of the leg that commonly occurs at the same time. The swelling of synovitis/, whether acute or chronic, is limited, until the capsule gives way, by the attachments of the synovial membrane, — that is, it extends upward beneath the rectus for from two to three finger-breadths or from four to five centi- metres (one and a half to two inches) above the summit of the patella ; laterally, it reaches the same level under the vastus internus, but is not quite so high on the other side, under the vastus externus. Downward, it descends to nearly the middle of the ligamentum patellae, attaining the same level on the inner side, but stopping Fig. 426. Tendon of extensor quadriceps Suprapatellar bursa — Cavity of joint External condyle— ^ -Patella External lateral ligament — Tendon of popliteus Popliteal bursa — Head of fibula -Prepatellar bursa External semilunar cartilage Ligamentum patellae Subpatellar bursa Tubercle of tibia Tibia Right knee-joint. The joint-cavity and several bur. t. li iv . I...n di.tended with injection mass before dissection. {Spaltthulz.) just above the head of the fibula on the outer side. The patella is separated from the trochlea of the femur— " floated up." In testing for this symptom, it is impor- tant to grasp the anterior muscles of the thigh firmly and draw them towards the knee so as to relax the pull of the quadriceps, which is occasionally great enough to hold the patella in contact with the femur, even in the presence of considerable effusion (Fig. 426). ,,-«•• j r The condition is usually unmistakable, but may have to be differentiated from periarticular abscess or haematoma. In the latter cases the swelling will not be uniform ; the inner depression at the side of the patella may be obliterated, and not 414 HUMAN ANATOMY. Fig. 427. the outer, ov vice versa ; fluctuation cannot be obtained in every direction, — i.e., from side to side under the patella or obliquely ; the patella will lie directly upon the femur. The diagnosis from l)ursal enlargements will be considered in relation to those structures. Syphilitic disease of the gummatous type is apt to bey;in in the subcutaneous tissue without the joint, which it involves secondarily. In its earlier stages the swelling would therefore be periarticular, and recognizable by the foregoing symp- toms. Later, as it extends in. both directions, there will usually be ulceration of the skin. The knee is more often the seat of the so-called loose bodies than is any other joint. They are sometimes the result of osteo-arthritis (which affects the knee by preference), causing thickening and fibrinous or calcareous change in some of the syno- vial fringes ; or they may be produced in those fringes from embryonic remnants, and are then composed of hyaline cartilage or fibro-cartilage ; or they may result from the organization of inflammatory lymph after an acute arthritis ; or they may be portions of an interarticular or articular cartilage de- tached by violence, although this is rare. In a case of suppurative arthritis the incisions for drainage should be made on either side of the patella and a little below its middle, and should be placed towards •the posterior aspect of the lateral pouches of the syno\ial membrane. Genu valgum — " knock-knee" — in young children may be directly due to rickets, or may follow Charcot's disease, in- fantile paralysis, or any sprain or dislocation of the knee that leaves the internal lateral ligament weak or defective. In children and adolescents without these antecedents its essential cause is still a matter of dispute. There can be no doubt, however, that in the great majority of cases the production of the deformity is fa\'ored by static modi- fications of certain anatomical conditions which are probably the cause and not the result of the diaphyseal overgrowth of femur and tibia (Mikulicz), of the contrac- tion of the biceps and tensor vaginae femoris (Duchenne), of the elongation of the in- ternal lateral ligament (Stromeyer), and of the atrophy of the external condyle (Oilier) which are found in most cases of this de- formity, and each of which has been given etiological importance. The angle between the femoral and tibial axes (corresponding to that between the arm and forearm) opens outward at the knee. It results not, as in the upper extremity, from an outward obliquity of the lower segment of the limb, but from the inward slant of the thighs from the pelvis to the knees, the tibiae (like the humerus) being parallel to the longitudinal axis of the body and to each other. That the line of the knee-joint may be horizontal, the internal condyle of the femur is longer than the external. In a normal person standing erect in the military attitude of "atten- tion" the weight of the trunk is transmitted downward from the head of the femur in a vertical line which passes through the external condyle (Fig. 427). The erect position must therefore be maintained, not merely through the approximation of the Line of pressure between hip and knee. PRACTICAL CONSIDERATIONS : THE KNEE-JOINT. 415 Fig. 428. bones, as would be the case if the axis of the whole lower limb were a perpendicular running through the acetabulum and the centre of the ankle-joint, but by the help of muscular and ligamentous structures. The tendency (which is so common a factor in the production of deformities) to assume an attitude which will transfer strain from a tired muscle to the neighboring ligaments operates here to cause stretching and elongation of the internal lateral ligament, as the "attitude of rest" with the feet separated and everted is the one usually adopted. The evil effects are, of course, favored by much standing, and are most marked in young persons of feeble physique whose weight has increased dis- proportionately to their muscular strength. The outer side of the knee shows the changes due to increased pressure and to long-continued approximation of musculo- tendinous points of origin and insertion, — i.e., atrophy of the outer condyle and outer tuberosity ; contraction and shortening of the ilio-tibial band of fascia, of the external lateral ligament, of the tendon of the biceps, and of the tensor vaginae femoris. The inner side shows the effects of removal of normal pressure from grow- ing bones and of chronic strain of fibrous and periosteal tissue, — i.e., overgrowth of the femoral diaphysis just above the inner end of the epiphyseal line and of the tibial diaphysis just below the corresponding level ; lengthening of the internal lateral ligament ; bony outgrowth at its tibial insertion from chronic periostitis. The tibia is apt to be rotated outward, possibly through the action of the short- ened biceps. Talipes valgus i^q.v- ) may be either a cause or a result of genu valgum. The disappearance of the deformity when the knees are flexed is probably due to the outward rotation of the femur that ac- companies flexion, and not, as is generally stated, to the fact that the antero-posterior diameter of the condyles is unaffected by the disease. The clinical symptoms and results and the treatment by apparatus cannot be described here. In Macewe7i' s osteotomy the femur is divided from the inner side of the thigh at a point twelve millimetres (half an inch) above the adductor tubercle and in a line at right angles to the long axis of the femur. Osteotomy may also be done from the outside of the thigh and at the same level. These opera- tions are usually safe, but the popliteal artery, the anastomotica magna, the external peroneal nerve, and other important struc- tures have been accidentally divided. Genu varum — " bow-leg" — is almost always rhachitic in its origin. A child with rickets and having lumbar lordosis of the spine stands with its thighs slighdy flexed, either as a secondary result of the shortening of the ilio-femoral ligaments produced by backward rotation of the pelvis (to compensate for the for- ward rotation of the sacrum) or more simply as an easy method of relaxing the weak ilio-psoas muscles and preserving the centre of gravity. As the thighs flex the knees separate, the femurs rotate outward on their own axes, the hne of gravity falls to the inside of the centre of the knee-joint (Fig. 428), the pressure is greatest on the inner condyle and tuberosity, the stram conies upon the external lateral ligament, and the outward bowing begins and is continued by the leverage of the body weight. Genu r^«^r7;a/z^^2—" back-knee"— is a deformity in which, as a result of intra- uterine malposition, or of congenital paralysis of the flexors and pophteus, or of pressure brought upon the posterior and crucial ligaments in walking in a case of partial paralysis of the quadriceps,— the limb being swung forward, the heel coming to the ground in full extension, and the weight of the body reaching the joint in front of its centre of gravity,— the knee is bent backward and the whole limb presents a long curve with its concavity forward. j -r 1, In excision of the knee the lines of the epiphysis should be remembered 1 the patient is under twenty or twenty-one years of age (page 365), the relation of the femoral vessels to the posterior ligament, the situation and extent of the synovial Showing the form of the bones in bow-legs. 4i6 HUMAN ANATOMY. pouches (which in infectious cases arc usually in\olved), the direction of the articular line (with which the saw cut should be jjarallel), and sometimes the possibility of infection of the neighboring bursa-. Landmarks. — The synovial membrane rises from four to five centimetres (one and a half to two inches) above the upper border of the patella ; it is higher on the inner than on the outer side of the thigh ; its upper limit descends in flexion of the knee. The bony points have been described in connection with the femur and tibia (pages 367, 390) ; the bursie will be described later. The Patella, — Com^inila/ abscnct' of the patella on one or both sides has been noted in a number of instances, and has in some cases been observed in several members of the same family. The functional disability was slight or altogether unnoticeable. Fracture by muscular action is more common in this bone than in any bone of the skeleton. It occurs usually with the leg in partial flexion upon the knee. In this position fracture is favored because (i) the ligamentum patellae is then taut and fixes the lower edge of the bone ; (2) the patella is in contact only through the upper third of its convex under surface with the most prominent part of the articu- lar surface of the condyles (Fig. 429); and (3) at this time the quadriceps extensor Fig. 429. Rectus muscle Patella Subpatellar tissue Tendo patellie Femur Showing position of patella in relation to condyles of femur w ith knee partially flexed. Tibia has the greatest advantage of le\erage upon the patella, as when the knee is fully bent the muscle gets its leverage for the beginning of extension through the projec- tion of the front of the condyles, and the patella lies on the pad of fat between the femur and tibia (Fig. 430), and when the knee is almost or quite extended, the patella — or three-fourths of it — occupies the depression of the trochlea, or even that just above it. As a result of the cross-strain brought to bear in the partially flexed position the bone usually breaks trans\'ersely a littlebelow its mid-line, — i.e., through the area unsupported by the femur beneath (Fig. 429). Occasionally it gives way at a higher level. The accident may happen as the result of a fall, but the fall is more apt to follow than to precede the fracture. In ordinary falls upon the knee the force is received upon the tubercle of the tibia, not upon the patella. Direct violence often causes an irregular, comminuted, or stellate fracture. Fracture never occurs in children and is extremely rare before adult life. When the bone is broken the fragments are immediately separated by the action of the quadriceps upon the upper one. The degree of their separation will de- pend upon the amount of laceration of the lateral aponeurotic expansions of the conjoined tendon. Unless that fibrous structure is torn, no great separation of the fragmeats can occur, as it is inserted into the borders and front of the patella, PRACTICAL CONSIDERATIONS : THE PATELLA. 417 which is thus embedded, as it were, in a hood spread out over the front of the joint and extending to the lateral ligaments and to the oblique lines running up from the tubercle to the tuberosities (Fig. 424). The force causing the fracture in cases of direct violence, or atmospheric pressure on the front of the knee if the fracture was from muscular action, drives in between the fragments, as they separate, in the shape of shreds or of an irregular fringe, portions of that part of the rectus tendon which was inserted into the longitudinal grooves or striae on the anterior surface of the bone. These offer an obstacle to bony union. As the synovial membrane of the knee-joint lies in contact with, and is attached to, the under surface of the patella, it will usually be lacerated, — i.e., the knee-joint will be opened and the fragments surrounded by bloody synovial fluid. The synovial membrane is re- flected from the patella some distance above the apex of the bone ; hence a fracture may occur at that level without involvement of the joint. The pad of fat on which Fig. 430. Patella Subpatellar tissue Showing position of patella in relation to condyles of femur with knee flexed at right angle the tip of the bone rests, and over which the membrane is reflected, may aid in saving the joint from injury. . The common failure to get bony union by non-operative methods is thus seen to be due to (i) separation of the fragments by the quadriceps, (2) the interposition of portions of the capsule, (3) the presence of blood-clot and synovial fluid, and is supposed to be further favored by (4) the sesamoid character of the bone inclining it to unite by fibrous rather than by bony tissue. It has been asserted, however (Wirth), that the patella is a detached portion of the upper tibial epiphysis and not a true sesamoid bone. . As non-union is common on account of the above anatomical conditions, oper- ative measures are often resorted to. In the open operations used in old united fractures the fragments are drilled obliquely from a half-inch above and below the line of fracture to just above the cartilaginous under surface, so that the wire used to hold them together does not lie in the joint. 27 4i8 HUMAN ANATOMY. To approximate the fragments elevation of the limb sometimes suffices, but occasionally partial section of the lateral expansions of the ijuadriceps, of the rectus tendon, and of the muscle itself will be required as successive steps. In the best of the operations used in recent fractures, and which do not widely open the joint, a silk or silver ligature is carried through an incision at the lower border of the patella behind that bone and between it and the trochlear groove in the femur, is brought out through an incision at the upper border, rcthreadcd on a needle with an eye near the point, brought down in front of the patella. — beneath the skin, — and tied or twisted so as to hold the fragments together. The blood-clot and synovial exudate are squeezed out through the two incisions ; the entangled capsular fibres are removed by attrition of the fractured surfaces against each other. These operations are, of course, not applicable to old fractures in which shortening of the muscle has taken place and approximation and forcible rub- bing together of the fragments are impossible. Operations for recent fracture by open arthrotomy permit the direct removal of the fringe of interposed tendinous and capsular fibres and the repair by suture of the rents in the capsule and in the lateral expansions of the quadriceps. The patellar fragments may also be sutured, but this is not always necessary. Dislocation of the patella usually occurs from muscular action and as a conse- quence of sudden contraction of the quadriceps. The displacement is commonly in the outward direction because the long axis of the quadriceps muscle and tendon is inclined to that of the ligamentum patella in such a way that the bone is situated at the ape.x of an obtuse angle which opens outward. When the quadriceps contracts the tendency is to straighten this angle. — i.e., to carry the patella outward, — and this, aided by the greater strength of the vastus externus as compared with that of the inner vastus, is more than suf- ficient to overcome the resistance offered by the greater prominence of the external condyle, as well as the relatively more extensive insertion of the vastus internus into the inner margin of the patella. The bone may even, as in one recorded case, be carried entirely past the condyle, so as to lie behind the centre of motion of the knee when the joint is bent, thus causing the quadriceps extensor to act as a flexor of the leg on the thigh. The external articular facet on the under surface of the patella is larger than the internal. The patella is in relation, therefore, chiefly with the external condyle, and even if dislocation occurs from direct violence, it is more likely to be driven in that direction (Humphry). If it has once passed beyond the edge of the outer condyle — a "complete" luxation necessarily attended by laceration of the capsule — it is less likely to be replaced than if it had gone in the opposite direction, because of ia) the resistance offered by the prominence of the condyle itself and (<5) the greater comparative strength of the vastus externus. Outward luxation is not very rare in cases of genu valgum, and, per contra, in congenital cases of patella luxation and in unreduced traumatic luxations genu valgum has followed (Makins). The patella may be displaced inward by direct force. It is sometimes turned on edge by a force insufficient to dislocate it completely, and is held in that position by the tension of the soft parts attached to it and by the pressure of the over- lying fascia, "like a stick on end under a tightly stretched sheet" (.Stimson). In flexion of the knee the patella lies deeply in the depression between the condyles and the quadriceps tendon is on the stretch. The bone is therefore somewhat removed from danger of direct violence, and is steadied and fixed by the quadri- ceps muscle. In extension the patella rests on the trochlear surface of the femur only by its lower margin ; it is more prominent and thus more exposed to force directly applied ; the quadriceps is relaxed, leaving the bone freely movable. For these reasons extension is the position in which dislocation most commonly occurs. THE TARSAL BONES. 419 THE FOOT. The framework of the foot consists of the tarsus, metatarsus, z.nA phalanges, which differ in their proportionate size from the corresponding divisions of the hand. Thus, in the latter the carpal region is the shortest and that of the phalanges the longest, equalling almost precisely the other two ; in the foot, on the. contrary, the region of the phalanges is the shortest and that of the tarsus makes about half the entire length. The tarsus differs also in its arrangement more than the carpus from the primitive type. The tarsal bones may be considered as divided into two lateral divisions : an outer series of two bones bearing the two outer toes, and an inner series of five bearing the three inner toes, so placed that the proximal bone of the inner part rests on top of the proximal of the outer. The outer side of the skeleton of the foot rises but little from the ground, while the inner is highly arched. THE TARSAL BONES. The tarsal bones are the calcaneum, or os calcis, the heel-bone ; the cuboid, which with it forms the outer division ; the astragalus, or talus, which joins the leg ; the scaphoid, placed between the astragalus and the three cuneiform, which bear the three inner jnetatarsals. THE CALCANEUM. The calcaneum ^ is a narrow elongated bone forming the heel, supporting the astragalus, and joining the cuboid in front. It has six surfaces. The inferior sur- face presents at the back a swelling subdivided into the internal and exterrial plan- tar tubercles, of which the former is much the larger, forming the posterior pier, of the foot. These tubercles are continuous at the posterior border, in front of which a deep notch divides them. Each appears on its side of the bone. In front of these the lower surface, convex from side to side, is marked by longitudinal grooves. Near the front is the anterior tubercle, a small swelling, from which and from a depression near it arise calcaneo-cuboid ligaments. The posterior surface is roughly oval with the small end up. The tendo Achillis is attached to a roughness occupying its lower half, above which the bone slants forward and is smooth for a bursa between it and the tendon. The lower part of the posterior surface is con- tinuous with the plantar tubercles. The internal surface is smooth and concave ; for the internal tubercle projects strongly inward, while in front and above there is a shelf-like process, the sustentacuhmi tali, to support the head of the astragalus, slanting downward and forward. Beneath this is a slight groove for the tendon of the long flexor of the great toe. Lower down near the front border a depression for a ligament to the cuboid runs down in front of the anterior tubercle. The ex- ternal surface is the longest. It presents about its middle a vague tubercle for the middle bundle of the outer lateral ligament of the ankle, and nearer the front a larger one, the pero?ieal spine. When well marked this is a ridge, covered with cartilage, slanting downward and forward, separating two grooves for the tendons of the peroneus longus and brevis. The outer posterior plantar tubercle projects somewhat on this side. Rather more than the anterior two-thirds of the superior surface are devoted chiefly to the joints with the astragalus ; the posterior portion is convex from side to side and concave from before backward. There are two articular facets : th^ posterior facet, the larger, a vaguely four-sided swelling, occu- pies the middle of this surface. Its long axis runs forward, downward, and out- ward. It is convex in this direction. The upper inner end is the broader, and near it the facet is very often concave at right angles to the long axis, but in the main it is about plane in that direction and may be even slightly convex. The anterior facet, long and narrow, concave from before backward, runs forward and outward, nearly parallel to the long axis of the former. It begins internally on the top of the sustentaculum and ends at the most anterior point of the bone. In about half the cases this surface is subdivided into two, and, as a rule, when it is not there is a ^ Calcaneus. 420 HUMAN ANATOMY. A F>G. 431. CUBOID SCAPHOID .V .tL' ' ,-pe of calcaneo-astragaloid joint when anterior facet on calcaneum is not only divided but has frotit portion rudimentary. 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 curved 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 pardy 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 foetal 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 navicular, 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 tuberosity at the inner border for the attachment of a part of the tibi- ahs 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. >i-, 1887. Parker and Shattock : The Pathology and Etiology of Congenital Club-Foot, London, r884. ° Os naviculare pedis. 4^6 HUMAN ANATOMY. Its identity is quite evident in cases in uliich, though fused, it projects as a hook. It may be represented by the sesamoid bone in the tendon of the tibiahs posticus. Near the outer end of the phmtar surface there is ahnost always a shght 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 by a facet near the dor- sum, which rarely extends far towards the sole.' The posterior surface is con- cave, in the main oval 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, except when the process just men- tioned is so large as to appear below it. The articular surface is divided into three Fig. 440. Dorsal surface For lioaii 01 astragalus Right scaphoid from behitid, proximal aspect. External Middle Internal Tuberosity cuneiform cuneiform cuneiform Right scaphoid 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 convex 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 secondary cuboid, above aUuded 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 frequently 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 fcetal life. Usually this fuses with the rest, but it mav 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 concaxe 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. ■ Os cuneiformc primum. 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 Mid. cuneiform Scaphoid Fig. 441. Fig. 442. Dorsal Dorsal Right internal cuneiform, outer aspect. Right internal cuneiform, inner aspect. of the tibialis anticus just before its insertion. The inferior surface, rough and round, has a tubercle near the proximal 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 exceptionally 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. Scaphoid Right middle cuneiform. ^4, inner aspect ; .5, outer aspect. is slightly concave. It is triangular, with the dorsal border rounded, the outer concave, and the inner straight or slightly 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 external cuneiform,' seen from above, is much longer than broad, with a very oblique proximal border slanting outward and backward, an anterior border running less oblicjuuly 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 overlapping 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. Cuboid Fourth metatarsal Third metatarsal Right external cuiieiforin. /I, inner aspect ; ^, outer aspect. 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. Phtzner 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 prominence 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 tertium. ^Ossa metatarsalia I'V. THE METATARSAL BONES. 429 base. The strong shaft has three sides : an internal, looking also upward, in the main convex ; an external, concave and nearly vertical ; and an inferior, or plantar, Fig. 445. B Grooves for sesamoid bones Phalangeal surface Head Internal surface Inferior surface Tibialis anticus 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 Lateral ligament Ext. cuneiform Third metatarsal Mid. cuneiform Third metatarsal Ext. cuneiform Plantar External cuneiform Right second metatarsal. ^, proximal aspect ; 5, outer aspect ; C, inner aspect. 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 hgaments on each side of the head. Middle cuneiform External cuneiform Plantar Second metatarsal Fourth metatarsal External cuneiform Right third metatarsal. ^4, proximal aspect ; ^, 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 mner side a small facet at the top meets the outside of the first cuneiform ; on the oufer side there are two, an upper and a lower, with a deep cut between each, resting Fig. 448. Plantar Cuboid Third metatarsa External cuneiform Fifth metatarsal Cuboid Right fourth metatarsal. A. proximal aspect ; S. outer aspect ; C. inner aspect Ligament 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 Dorsal Tuberosity Cuboid Plantar Fourth metatarsal. Cuboid Tuberosity Fourth metatarsal Cuboid Fig. 450. Right fifth metatarsal. A, distal aspect ; B, dorsal aspect ; C, plantar aspect. outward and backward. The m?ier 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, 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 tuberosity 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 foramina of the four outer metatarsals are in the external surfaces, running upward. They are not very constant. Fifth metatarsal Cuboid Right fifth metatarsal, inner aspect. 43- HUMAN ANATOMY. Fig. 451. Os interinetatarseum 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 t«) 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, ha\e 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 may seem to be a pro- cess (Fig. 451). It is found in some form once in ten feet (Pfitzner). Intermetatarsal bone fused with right internal cuneiform. Third, distal or ungual, phalanx 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 phalanx 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 very 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 proximal row seem to ossify rather later than the * Arch, fiir Anat. und Entwick., 1890. * Morph. Arbeiten, Bd. i. 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 fifth 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 Ossification of bones of the foot. A, during sixth fcetal month ; B, at eighth foetal month ; C, at birth ; £), during first year ; E, between three and four years ; E, at about fifteen years, a, for shaft of metatarsals ; d, for cal- caneum • c, for proximal phalanges ; d, for distal phalanges ; e, for astragalus ;/, for middle phalanges ; £■, for cuboid ; «,for external cuneiform; z, for heads of metatarsal bones and base of first proximal phalanx ; 7, for base of first distal phalanx; A, for internal cuneiform ; /, for base of first metatarsal. fifth, and even in the fourth at birth. Proximal epiphyses appear from the fourth to the sixth 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., igcxi. 28 434 HUMAN ANATOMY. Fir.. 454. Abduclot hallucis. Internal tuberoi>it> Flexor brevis digiti>t um Groove for tetidon of flexor longus hallucis Sustentaculum tal Astragalus ^ Scaphoid Tibialis posticus External cuneiform Middle cuneiform. Internal cuneiform Tibialis anticus Peroneus longus First metatarsal- Sesamoid bones Abductor and flexor brevis hallucis Adductores obliquus et transversus Flexor longus halluci Postero-inferior surface of calcaneum \bductor minimi digiti ICxternal tuberosity Abductor ossis metatarsi quinti Inferior surface of calcaneum Flexor brevis hallucis Cuboid ridge Groove iox peroneus longus Abductor ossis met at at si quinti Flexor brevis minimi digiti . Ahduclor obliquus hallucis ■ Third plantar interosseus ■Second plantar interosseus FiJst plantar interosseus Abductor and flexor brevis minimi digiti yf — Third plantar interosseus Second plantar interosseus First plantar interosseus Flexor brevis digitorum Flexor longus digitorum Bones of right foot, plantar aspect. BONES OF THE FOOT. 435 Fig. 455. Tendo Achillis Bursal surface Calcaneum Lateral articular surface for fibula Groove for peroneus longus Groove for peroneus brevis Extensor brevis digitorum Groove ior peroneus longus Peroneus brevis Peroneus tertius-M Fourth dorsal interosseus Extensor brevis digitorum Extensor longus digitorum- Groove ior flexor longus hallucis Superior articular surface of astragalus Lateral articular surface for tibia Cuboid Scaphoid External cuneiform Middle cuneiform Internal cuneiform First metatarsal First dorsal interosseus Extensor 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 afford 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 excessive 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 di\'ision 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 extremities 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 \'essels 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. Fracture of the bones of the tarsus is rare, except 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 T 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. Excisio7i 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 : (' sal *;^"^''V metatarsal Third metatarsal TFourth metatarsal if ^?'\ Fifth metatarsal I- Oblique section through the right foot. ligaments it is our object to avoid pedantic attention to useless details. We shall consider first the interosseous ligaments, then the dorsal, and lastly the plantar ones. THE INTEROSSEOUS LIGAMENTS. The astragalo-calcaneal (Fig. 457) is a thick layer of fibres filling the groove between the two adjacent articular surfaces of each bone. At the outer part, where the groove widens, it tends to divide into two layers. A considerable quantity of fat is found in its meshes. Each side of it is lined by the synovial mem- brane of the joints which it separates. An occasional superficial band — the external astragalo-calcaneal (Fig. 457) — may be continuous with this ligament. The calcaneo-cubo-scaphoid (Fig. 460) (seen by removing the astragalus and the synovial membrane covering it) is a series of short, strong fibres, collected into bundles, joining the front of the calcaneum with the outer border of the scaph- oid, and by a weaker division with the inner side of the cuboid. It forms the outer part of the capsule for the head of the astragalus, reaching to the dorsum. This capsule is completed by the superior and inferior calcaneo-scaphoid ligaments. 442 HUMAN ANATOMY. The cubo-scaphoid (V\^. 45S) passes crosswise between these bones, close to the last liirament. Its size varies, being in inverse ratio to the articular facet between the bones it unites. ^ The cubo-cuneiform (Fig. 458) is a strong band connectnig the non-articuiar surfaces of the cuboid and the outer cuneiform at their distal ends from the plantar to the dorsal border. The intercuneiform (Fig. 458) are strong ligaments connectmg the distal non-articular surfaces of these bones. That from the inner side of the middle cuneiform does not completely separate the joints before and behind it. The arrangement between the middle and outer cuneiforms is variable in this respect. The interosseous tarso-metatarsal ligaments (Fig. 458) are an inner and an outer, with an occasional middle one. The i/nirr, a strong band arising from the outer side of the internal cuneiform where it overlaps the second metatarsal, runs obliquely outward and forward, most of its fibres going to that bone, but a few to the Fig. 459. Astragalus Astragalo-calcaneal ligament Articular surface for cuboid Articular surfaces for astragalus Sustentaculum The inner part of the right astragalus has been removed. outer side of the first metatarsal. The oii/er interosseous ligament arises from the adjacent sides of the external cuneiform and the cuboid, mingling with the fibres of the ligament already described as passing between them, and runs forward to the inner side of the base of the fourth metatarsal, to the rough surface pro.ximal to the facet, and to the plantar half of the outer side of the third. The middle interosseous ligament is inconstant and small. It runs from the outer cuneiform to the second metatarsal. The interosseous intermetatarsal ligaments (Fig. 458) are strong bands, best seen on section, between the bases of the four outer bones. The few fibres between the bases of the first and second do not deserve the name. The distal intermetatarsal ligament is not an interosseous one, properly speaking, but is mentioned here as it is an important piece of the general framework. It is a fibrous band connecting the glenoid cartilages at the metacarpo-phalangeal joints precisely as in the hand, except that it goes to the great toe as well as to the others. THE DORSAL LIGAMENTS. The dorsal ligaments of the tarsus are a number of bands of varying degrees of distinctness, all of which, in part at least, assist in forming the capsules of tfie various joints, although they may extend farther. The superior astragalo-scaphoid (Fig. 460) might be divided into an inner part, composed of fibres running from the inner side of the former bone to the inner and dorsal aspect of the latter, and into a dorsal part, running from the margin of the head of the astragalus forward, with an inclination either inward or outward. THE DORSAL LIGAMENTS. 443 A series of well-marked but not strong ligaments radiate forward and outward from the scaphoid (Fig. 460): three dorsal scapho-cuneiform and one scapho- cuboid ligament. The dorsal calcaneo-cuboid ligament (Fig. 460) is a thin band of little note. The interosseous calcaneo-cubo-scaphoid reaches the dorsum by the part going to the scaphoid. The ligament just mentioned is sometimes continuous with it at its origin, and the two have been called by French anatomists the Y-ligament, to which much consequence has been ascribed. The interosseous ligament is the important one. Fig. 460. Dorsal tarso-metatarsal— ijil ligaments Dorsal scapho-cuneiform ligaments Astragalo-seaphoid ligament Scaphoid Calcaneo-cubo-scaphoid ligament Inferior calcaneo scaphoid ligament Fibro-cartilage Sustentaculum Interosseous astragalo- calcaneal ligament Dorsal intermetatarsai ligament Peroneus tertius Superior scapho- cuboid ligament — Dorsal calcaneo-cuboid ligament Peroneus brevis Astragalo-calcaneal ligament Calcaneum Upper aspect of the right tarsus, the astragalus having been removed. The dorsal tarso-metatarsal ligaments (Fig. 460) are simple for the first metatarsal, being bands running from the internal cuneiform. For the others they are more irregular, and there is an interlacing with transverse dorsal ligaments between the metatarsals connecting the outer four bones and the second to the 444 HUMAN ANATOMY. internal cuneiform. The bands over the cuboid and the two outer metatarsals are closely interwoven with the tendon of the peroneus tertius when that muscle is present. These ligaments constitute an interrupted series of bands converging for- ward from either side of the foot. The dorsal ligaments arc weak, and need the help of the extensor muscles of the toes to resist the strain of the strong muscles of the sole. THE PLANTAR LIGAMENTS. The plantar ligaments are of three kinds : (a) those passing from one bone to the next, and therefore nothing but thickenings of the capsule ; (d) those passing Fig. 461. Inlcrnietatarsal ligament elatarsal nieiit Tendon of peroneus longus Short plantar ligament Long plantar ligament Peroneal spine Tendon of tibialis amicus rni ligament igament Calcaneum Tendo Achillis Right tarsus, inferior aspect. from one bone to one or se\eral distant ones ; (c) and those continuous with the tendon of the tibialis posticus, which is very strong and has a far-reaching action. THE CALCANEO-ASTRAGALOID JOINT. 445 The plantar calcaneo-cuboid ligaments are the long and the short. The former, known as the long plantar ligament (Fig. 461), arises from the perios- teum of the under side of the calcaneum in front of the posterior tubercles, and runs forward as a flat band, at first some two centimetres broad, to the whole length of the ridge of the cuboid, except its inner end. It passes beyond this to the bases of the outer three metatarsals in a somewhat broken and weak layer of fibres forming a bridge over the groove for the tendon of the peroneus longus. The short plantar ligament (Fig. 461) is in part hidden by the longer, but is seen at its inner side. It arises from the anterior tubercle of the calcaneum and the bone in front of it and goes to the under side of the cuboid, between the posterior border and the ridge. The inner fibres run obliquely forward and inward. The inferior calcaneo-scaphoid ligament (Fig. 460) fills the gap on the plantar side of the foot between the sustentaculum and the scaphoid. It is more or less divisible into two parts, which have a common origin from the anterior border of the sustentaculum. The inner and stronger part runs obliquely forward and inward to the lower border of the scaphoid near the tuberosity. The outer part runs more nearly straight forward to the outer part of the same border. There is generally a small interspace between them. The upper surface of the inner portion of the ligament is covered by a coating of articular cartilage completing the joint for the head of the astragalus. This cartilage is usually wanting at the anterior outer angle of the space between the bones. Beneath and to the inner side of the ligament runs the tendon of the tibialis posticus. On the inner side of the foot this ligament is continuous with a part of the superior astragalo-scaphoid and with the termination of the deltoid ligament. The inferior scapho-cuboid ligament (Fig. 461) is an insignificant group of fibres. The inferior scapho-cuneiform ligaments (Fig. 461) are three distinct bands, of which the inner is the broadest, the others being more cord-like, diverging from the under side of the scaphoid to the three cuneiform bones. They are all continuous with the fibres of the tendon of the tibialis posticus. On the plantar side there is a very irregular arrangement of fibres passing from the tarsus to the metatarsus and a considerable system of oblique fibres running- inward and forward from the cuboid and the fifth metatarsal to the external cunei- form and to the bases of several metatarsal bones. The joints of the phalanges are on the same plan as in the hand and require no further description. The sesamoid bones at the tarso-metatarsal joint of the great toe are very large and connected by the glenoid ligament. THE POSTERIOR CALCANEO-ASTRAGALOID JOINT. This joint (Fig. 460) is separated from the anterior by the interosseous ligament, which is continuous with the capsule that completely surrounds the articulation. This capsule is in most parts weak, but is strengthened behind by the posterior astragalo-calcaneal ligament. THE ANTERIOR CALCANEO-SCAPHO-ASTRAGALOID JOINT. This articulation (Fig. 460) may be called a ball-and-socket joint, although the head of the astragalus is not a part of the surface of a sphere. The articular surfaces have been described with the bones. The socket is made by the anterior articular facet or facets of the calcaneum, by the posterior facet of the scaphoid, by the inter- osseous ligament joining these externally, and by the inferior calcaneo-scaphoid liga- ment, with its cartilaginous plate, which fuses on the inner side with the superior calcaneo-scaphoid and the deltoid ligament, all of which make a capsule around the head, completed by the interosseous astragalo-calcaneal ligament. A fold of syno- vial membrane,' variously developed, which may contain fibrous tissue, is generally found on the floor of this socket, extending back from the interruption of the anterior facet on the calcaneum, or from a corresponding place when it is simple, to the inferior ^ E. Barclay Smith : Journal of Anatomy and Physiology, vol. xxx., 1896. 446 HUMAN ANATOMY. border of the head of the astra.u^alus. The tendon of the tibiahs posticus directly beneath and internal to the joint adds to its security. The motions of the two subastragaloid joints must, of course, be considered tog^ether. They are resolved into turning on an oblique axis running through the interosseous ligament, somewhat internal to its middle, downward with something of a backward and inward inclination. Rotating on this, the posterior concave articular surface of the astragalus twists with a screw motion on the opposed surface of the calcaneum. As the back of the astragalus moves upward and outward, the head passes downward and inward in the socket. This movement is stopped by the front of the posterior articular surface of the astragalus catching in the hollow at the front of the convex surface of the calcaneum that it plays on. This is a most efficient device for locking the joint. The opposite motion is stopped by the inner posterior tubercle of the astragalus striking the back of the sustentaculum tali. In the anterior joint there is also to be considered the motion between the head of the astragalus and the scaphoid. The strong interosseous and inferior calcaneo-scaphoid ligaments do not allow much displacement of the scaphoid, but it seems that it can travel for a short distance up or down and in or out, and can therefore be slightly circum- ducted ; the chief motion, however, is one of rotation on the above-mentioned axis through the astragalus. Variations in the slant of the posterior articular surface of the OS calcis must, of course, modify the position of the axis. THE CALCANEO-CUBOID JOINT. The calcaneo-cuboid joint (Fig. 458), surrounded by a capsule the inner side of which is formed by the interosseous calcaneo-cubo-scaphoid ligament, is a modi- fication of the saddle-joint. Apart from some indefinite gliding, the nature and amount of which vary in different feet, the chief motion is rotation on an approxi- mately antero-posterior axis running through the joint. It might, perhaps, be more accurately defined as a screw motion. This movement, however, is very limited. Rotation of the cuboid in a direction that would raise its outer border is checked by the interosseous and dorsal ligaments at its inner side. Rotation in the opposite direction, if not sooner arrested by the ligamenfs, is effectually checked by the plantar tubercle of the cuboid catching on the overhanging lip of the articular surface of the OS calcis, thus locking the joint. THE SCAPHO-CUBO-CUNEIFORM JOINT. This articulation is a synovial cavity bounded behind by the scaphoid, extending forward to varying distances between the different bones. Thus, between the first and second cuneiforms it communicates with the joint of the second metatarsal, it is usually bounded by the interosseous ligament between the second and third meta- tarsals, and finally by that between the latter with the cuboid. The motions are very slight in each joint and of no great importance when combined. There is next to no motion of the internal cuneiform of the scaphoid and very little of the second. The external moves more freely, sliding slightly up and down. The interosseous ligaments resist the undue spreading of the transverse arch of the foot. THE TARSO-METATARSAL JOINTS. That of the first metatarsal bone (Fig. 458) is an independent joint with its own capsule, the interosseous ligament between the internal cuneiform and the second metatarsal shutting it off. The front of the cuneiform is convex from side to side and about plane from above down. Rarely it is subdivided into an upper and a lower compartment. It may be prolonged onto the side of the second metatarsal. An articular facet coated with cartilage is common on the outer side of the first meta- tarsal, but that on the second is indistinct or wanting. It seems that this, is simply a bursa in most cases just beyond the joint, but they sometimes communicate. Lat- eral motion with this metatarsal is the most free, and there is a certain sliding up and down. THE METATARSAL JOINTS. 447 The second tarso-metatarsal joint opens at the inner side into the great tarsal joint, and usually with that of the external cuneiform and third metatarsal. The motions of these joints are slight and indefinite. Fig. 462. The fourth and fifth tarso-metatarsal Head of first metatarsal joints, between the cuboid and the two outer metatarsal bones, are nearly or quite separated ^ . . r 1 T 1 i'. 1- Synovial-] from the preceding by the interosseous hga- cavity ment from between the outer cuneiform and the cuboid to the third and fourth metatarsals ; i„,^^„^i internal- v,>\\;21i^&\'''i''*''"''X*C T5" t l practically they form a distinct joint. The sesamoid bone %^^g^^'^sesamo[d bone motion is much more free than in the others. ^inn*l*^!l hi w?!''^^^*^ rru ( ,.U ,- ^ ^ U 1 4-1 ^u- J longus hallucis Glenoid ligament Ihe fourth metatarsal bone plays on the third 1 c ^j-..!^..!-^ 1- ^ Transverse section through head of first meta- by a facet distal to the interosseous ligament tarsal bone. just mentioned. The fifth plays still more freely both on the fourth and on the cuboid. The motion is of a nature to permit the drawing of the outer side of the foot downward and inward so as to. deepen the hollow of the sole. It also allows the outer metatarsals to be displaced dorsally when the transverse arch is flattened. THE METATARSO-PHALANGEAL JOINTS. These articulations in the foot are similar to the corresponding ones of the hand, the capsule including the £- /enozd a.nd lateral ligaments ; the latter arise from both the tubercles and the depressions on the heads of the metatarsals. That of the great toe is large and distinguished by the large size of the sesamoid bones, which are interposed between the head of the metatarsal and the ground. As in the hand, there is no glenoid ligament in this joint. The tra7isverse metatarsal ligament differs from that of the hand in connecting all the toes. The motions correspond to those of the hand, but the range of dorsal extension is greater. Lateral motion is possible only when the toes are nearly straight. The structure and motions of the interphalangeal joints are as in the hand. SYNOVIAL CAVITIES. The following synovial cavities are found (Figs. 458, 463). (i) That of the ankle-joint proper ; (2) the posterior calca7ieo-astragaloid ; (3) the anterior calcaneo- astragaloid completed by the scaphoid ; (4) the calcaneo-cuboid ; (5) the scapho- cuneiform cuboid, the great tarsal cavity which communicates with the joints at the bases of the second and third metatarsals by a passage at the inner side of the middle cuneiform and sometimes by one on its outer side. This may also open into the preceding synovial cavity ; (6) the joint between the internal cuneiform and the first metatarsal ; (7) that of the cuboid and the outer two metatarsals. The arrangement of the synovial sacs about the bases of the second and third metatarsals is variable. THE FOOT AS A WHOLE. The foot is a vault which may be considered as composed of an indefinite number of arches diverging from the internal tuberosity of the calcaneum and ending in front at the heads of the metatarsals. The highest arch is that in the line of the great toe, a fact in some degree due to the sesamoid bones which are between the head of the first metatarsal and the ground. The arch at the outer side of the foot is the lowest. It is clear from this conception that transverse sections of the foot rnust also show an arched structure the details of which must vary with the line of section. The shape of the three cuneiforms is an essential element in this construction. _ This vault is, however, not rigid, but elastic and capable of considerable modification of shape under varying pressure. In the motions of the foot the essential joints below the ankle are the subastraga- loid and those between the astragalus and the scaphoid and the calcaneum and the cuboid. 448 HUMAN ANATOMY. Tlie bones in front of the astragalus and os calcis move very nuich as a unit, althouiih there niav be some plav between the scaphoid and cuboid and between the latter and the fifth "metatarsal, the astragalus, having no muscle inserted into it, is acted on in the ankle-joint by the other bones, as is the hrst row of the carpus, its motions depending on the pressure it receives. When the foot is in extreme dorsal flexion all the joints of the tarsus are locked and no motion is possible, btartmg Fig. 463. Tibia Astragalus Calcaneo- aslragaloid igameiit Internal sesamoid hone Sustentaculum Inferior calcaneo-scaphoid ligament Longitudinal section through right foot in axis of first metatarsal bone. from a position of moderate flexion, the motions (excepting those of simple flexion and extension which occur in the ankle) are combinations of adduction and abduction, inversion and eversion. Adduction is generally combined with inversion, and these two motions are more extensive than the opposite ones. They practically never occur pure. Inversion and eversion occur chiefly in the joints below the astragalus, but in part in the mid-tarsal joint. Adduction and abduction are perhaps about equally divided between the two ; but if the calcaneum be held by one hand and the Fig. 464. Middle cuneiform External cuneiform Fig. 465. Middle cuneiform External cuneiform Cuboid /< --^ Fifth " ')* tarsal Interosseous ligament Transverse section through cuneiform bones of right foot, seen from behind. Interosseous ligaments Oblique section through cuneiform bones of right foot, seen from behind. front of the foot moved by the other, it is clear that the mid-tarsal joint allows much more abduction and adduction than eversion and inversion, which therefore occur chiefly between the calcaneum and astragalus. In the ordinary position of supporting the body it appears that the essential arch is through the calcaneum, the cuboid, the external cuneiform, joined to the latter by a firm interosseous ligament, and the third metatarsal.' This can be proved by * H. v. Meyer : Der men.schliche Fuss. THE FOOT AS A WHOLE. 449 Fig. 466. removing the first and fifth metatarsals with their phalanges and the first cuneiform bone, without impairing the stability of the foot. The fourth metatarsal may next be taken away without trouble. If the second with its cuneiform be detached with care, the arch is still reasonably firm. It is possible to preserve the arch after taking out the astragalus, and then removing the scaphoid. Although the arch still stands, it will bear little weight, the third cuneiform being inadequately supported behind ; but with the scaphoid and astragalus retained the arch is a good one. The arches depend very much for their stability on the action of the peroneus longus and the tibialis posticus, which pull against each other from opposite sides. The former is efficient in maintaining the transverse arch, the latter in maintaining both the trans- verse and the antero-posterior. To these should be added the plantar fascia and the muscles to the toes arising from the calcaneum. When in life the weight is equally divided between the feet, the part in contact with the ground is the heel, the outer border of the foot, the region of the heads of the metatarsals, and, separated from the rest, the balls of the toes, which bear no weight. The outer border also, as a rule, is doing no work and often does not even touch the ground, It is easy to pass a thin spatula under the head of the fifth metatarsal, and usually not hard to pass it under that of the first, thus showing that in this position they are not essential parts of the arch. When the whole or nearly the whole weight is transferred to one foot the following changes occur. The head of the astragalus turns inward, at the same time sinking under the weight of the body so as to make a prominence at the inner side of the foot. The internal malleolus follows this movement. The outer malleolus advances, but does not descend. Thus the relation of the front part of the foot to the posterior is one of abduction and e\-ersion.^ The weight-bearing region changes both its shape and position. The line at the outer part of the heel is the only part that remains stationary. The surface of pressure (Fig. 466) is broader at the heel and still more so at the heads of the metatarsals. The connecting strip moves inward, but becomes no broader ; sometimes it even narrows. The chief agent in resisting this change, which is greater after fatigue, is the tibialis posticus, which opposes the inner turn of the head of the astragalus which precedes its descent. When this is inadequate, the change of position is exaggerated and the foot breaks down. As the heel is raised, under normal conditions, the weight is transmitted through the astragalus chiefly to the bones and soft parts forming the socket for its head, the calcaneum receiving httle of it. The strain comes chiefly on the ligaments securing the scaphoid, for that bone is most directly in the line of pressure, which it transmits through the front of the tarsus to the heads of the metatarsals, chiefly to the first ; but in this last respect individuals vary. Usu- ally the region of the heads of the metatarsals narrows, the weight being borne chiefly at the inner side, but in some cases by all the heads. When the weight is borne by the toes, the foot being inverted and abducted, the locking by the catching of the plantar tubercle of the cuboid in the os calcis is an important factor of stability. Surface Anatomy. — The malleoli are easily felt, the inner being square, the outer longer and more pointed ; the latter is the lower and the more posterior. The ankle-joint is, therefore, more easily opened from the inner side. The front lower border of the tibia is hard to examine on account of the extensor tendons ; the line of the joint is from one to two centimetres above the tip of the inner malleolus, run- ning transversely. The general features of the os calcis can be made out. The sus- tentaculum is distinct and the peroneal spine can be recognized. Along the inner side, the head of the astragalus can be felt at the dorsum where it enters the hollow of the scaphoid. The tubercle of the latter is lower down and farther forward. The Surface of pressure on sole of foot as seen through a ^lass plate supporting the body. ^ Lovett : New York Medical Journal, 1S96. 29 450 HUMAN ANATOMY. first cuneiform and the joint l)cliintl and before it, the first metatarsal and i)erhaps the inner sesamoid come in order. A very moderate swelHny obscures most of these points. On the outer side the joint between the calcaneum and the cuboid can be found. A little in front of this is the tuberosity of the fifth metatarsal, the only dis- tinct landmark on the outer side. The general dorsal outline of the tarsal bones is to be recognized, but only under favorable circumstances. The dorsal surfaces of the metatarsals are distinct. The joint between the astragalus and calcaneum behind and the scaphoid and cuboid in front is sinuous : convex forward at the inner part and tending to concavity at the outer, the two ends of the line being nearly in the same transverse plane. The tarso-metatarsal joint is very oblique, running from within outward and backward. It is repeatedly irregular, the chief interruption of the direction being at the mortise of the second metatarsal between the inner and outer cuneiforms. The joints of the first phalanges with the metatarsal bones are about 2.5 centimetres behind the web of the toes. PRACTICAL CONSIDERATIONS. The Ankle-joint.— Uncomplicated dislocations, inward or outward, are almost unknown because of (a) the close lateral approximation of the malleoli, which are lield to the sides of the astragalus by the strong inferior tibio-fibular ligaments ; (d) the further support of the lateral ligaments, especially the inner ; and, (c) to a very minor extent, the wavy outline of the upper surface of the astragalus, which slightly resists sidewise movements. Lateral dislocations are accordingly almost always associated with fracture of one or other of the bones of the leg, and have been sufificiently described in that connection (page 395 ). They are incomplete. In addition to the inward or out- ward movement of the astragalus it undergoes a partial rotation on an antero-po.sterior axis, so that its til)ial surface points obliquely upward in a direction opposite to that of the displacement. Reduction is easy and the after-treatment is that appropriate to the fracture. >5ar>tzt'ar^ dislocations of the astragalus — i.e., of the foot ( which are etiologically forward dislocations of the tibia ) — are resisted by (a ) the shape of the upper articular surface of the astragalus, which is about one-fourth narrower behind than in front ; (^) the corresponding shape of the irregular arch in which the astragalus rests ; (r) the outward slope from behind forward of the lateral facets of the astragalus ; {d) the lower level of the posterior as compared with the anterior articular edge of the tibia ; and (>'■ Section of right foot through heads ol metatarsal bones, showing support by 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 difificult 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 relatrion 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 ner-\-es, superficial to and not between the bones, and the collapse of the transverse arch in most cases of metatarsalgia, broadening the intervals 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 fasciae 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 ; (<5) its remoteness from the heart, the force of the circulation being at its minimum ; {c) 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 ; ( ■fJT / '' '"' ' resent differentiated anisotropic threads within the cell-body, in their jjroperty of double refraction resembling the hbrillie of stri])ed muscle. They are most cons])icu- ous at the periphery of the fibre- cell, where they lie closely related to the condensed boundary zone ( Heidenhain) which forms the exterior 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 fibrillae 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 anij^hibia, 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 (Pig. 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, Boheniann, 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 off 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. \ / o5', V r^-^: t Portion of injected intestinal wall, showing arrangement of blood-vessels supplying invol- untar>- muscle ; upper longitudinally, lower transversely cut. X 50. STRIATED OR VOLUNTARY MUSCLE. 457 ganglia, from which deUcate 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 sweat-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. Mesothelium of serous coat Differentiating muscular tissue Young connective tissue Epithelium lining gut tube Section of developing intestinal wall, showing earliest differentiation of involuntary muscular tissue from splanchnic mesoblast. X 200. 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 " flesh' ' 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, th&Jibres, grouped mtofasciciili ; upon the size of the latter depends the texture of the muscles, coarse or fine, as distinguished in the dissecting-room. In locahties in which the fascicuH are of large size, as in the gluteus 1 Szili : Archiv fiir Ophthalmol., Bd. liii., 1902. 458 HUMAN ANATOMY. maximus, the muscles are conspicuous on account of their coarse texture ; a fine- jj^raincd nuiscle, 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 len- 474- < ■>- 13\ Perimysium. K. ■r> Muscle-fibres^ ^?.' tiG. 474- dons. A long muscle may be comj)Osed of short fasciculi, since the latter may be attached to ten- dons which cover its opposite sides or extend within its sub- stance as septa. In such cases, as in the rectus femoris or the deltoid, the short fasciculi run 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- uli are relatively long and may extend its entire length. The sartorius contains fasciculi, as well as fibres, of conspicuous ex- tent, some bundles stretching 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 luuscle-Jibre, which 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 exerted. 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 fibres 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. The 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 may attain a length of over 1 2 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 sarcolemma, are grouped into small primary bimdles, the component fibres of which are held together by a meagre amount of connective tissue, the endomxsiion. The latter is continuous with the perimysium investing the primary bundles. These are associated into uncertain groups, the secondary biaidles, which are united and enclosed by extensions and subdivisions of the general connective-tissue envelope of the entire muscle, the epimysiiim. In muscles Several primary muscle-bundles in ti,iii~\. i ~c section, showing the arrangement of componeiu nbres. x 40. Fig J- Sarcolemma Portion of muscle-fibre, showing sarcolemma bridging break in sarcous substance. X 370. STRIATED OR VOLUNTARY MUSCLE. 459 possessing a fine grain the secondary bundles correspond with the fascicuH, 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 sarcole77ima^ 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 Q ■ ■H Fig. 476. £ ^■t^ ■t-U' 1 in ii ii 'mm ■a wm'- :■ Wl Ws 1 ■ ■' c -M in^ 'iii' ~n~.j U- - • • - -•« ' ' ' ■ •- u Diagrams 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-hsematoxylin staining. .?, interme- diate disk (Zwischenscheibe) ; /, light band ; Q, transverse disk {Querscheibe) ; M, median disk {Mtttelscheibe) ; 5, sarcolemma. {After M. Heidenhain.) 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 sarcoplasni and the highly specialized contractile fibrillce 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 dift'erentiation of the contractile fibrillae into segments of greater or less density. Close lateral approximation of the more dense and deeply staining segments in the fibrilte, 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 anisoiropic, substance is succceilcd at cither eiul by the h.^ht l)aiul ( // ) of singly refracting, or isotropic, substance. The Hght band is subdivided by a delicate line, the intermediate disk ( Z ), also known as A'rause s membrane. The sequence which by repetition makes uj) the contractile hbrilla consists, therefore, of Z +/+ Q -\-J-\-Z. Under favorable conditions for examination the transverse disk exhibits less density midway between its ends ; this zone is traversed by a delicate line (J/), the median disk (Hensen, Merkel ) or middle membrane ( .M. Heidenhain ). The interpretation of these appearances, shown as usually seen under moderate amplification in the accom|)anying photograph (Fig. 477), has been the subject of much laborious investigation and \exed 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. \ievvs 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- \ides the fibre into a number of minute compai tments, or co)itrac- ti/e 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 fibrillce ex- tending the length of the fibre, the transverse cleavage into disks being secondary and artificial. The fibrillar theory as ad\ anced by Rol- Ict has received wide acceptance and deserves brief mention. Ac- cording to this authority, the con- tractile fibrillae 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 exist as local accumulations on the thinner segments of the fibrillae. 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 fibrillae. 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 regarding the structure of striped muscle is given by M. Heidenhain: Ergebnisse der Anatomic und Entwick., Bd. ix.. 1899. Photograph of striated muscle, showing the usual appearance under moderately high magnification. 700. STRIATED OR \'OLUNTARY MUSCLE. 461 represented by the intermediate and median bands. The foregoing diagram (Fig. 476), 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 {/). The distribution of the contractile fibrillae throughout the fibre .is not uniform, since the fibrillae are grouped into bundles, the viusde-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 Cohnheiin s fields, and 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. . 4 4 i I Sarcolemma Fig. 479. Muscle- nuclei Endom\sium Diagram illustrating Rollet's view of structure of muscle-fibre and relations of assumed details to usual appearances of tissue. Nuclei of interfibrillar tissue Muscle-fibres of lizard m transverse section, showing 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 muscles, as they have 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 (Fitj. 4.S0). The ioncfitudinal striation is also unusually con- sjiicuous, due to the exceptional amount of interhbrillar sarcoplasni. Althouj^h not present in mammals generally in sufficient quantity to affect the appearance of entire muscles, the peculiar "red" fibres are found in many localities intermingled with thr more usual pale variety. Klein has described such fibres in the diaphragm, and according to the investigations of Griitzner and of J. Schaffer, it is probable that the\ are found in all muscular tissue upon which devolves prolonged effort. These fibres are, therefore, present in the heart, the eye muscles, antl 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 contraction at the expense 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. c - -■ ''^ Portion of the soleus muscle of the rabbit in trans- Section ot Iciulon, showiiij; terniinulion of muscle- verse section. The more coarsely stippled fibres are of fibres. X 200. " red" muscle; they also contain nuclei within the sar- cous substance. X 160. and never by direct fusion of the connective tissue with the sarcous substance, the latter remaining completely invested b}' 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 addition 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 Fig. 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- ever, the intercalated discs are neither cell boundaries (Zimmermann) nor growth- zones (Heidenhain), but must be inter- preted in terms of the ultimate fibrillae, not of the whole fibre, and are due to Muscle-fibres of human heart. Fig. 483. It ! •■*■ ^ 375- If-H 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 "m Mi 1. Undifferentiated sarcoplasm Nucleus 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. Fu;. 4S5. The blood-vessels of sirii)rcl nuisclc are very luinicrous to insure adequate nutrition to a tissue of ^reat functional activity. The larij^er arteries and accompany- injj veins penetrate the muscle aloni; the septal extensions of the epiniysiuni and divide into smaller Imuiches which run between the fascicuH. These vessels undergo further subdivision into twit,fs which pass between the finer bundles of muscle-fibres and ultimately break up into the capillaries enclosin<; the indi- vidual fibres. The capillary vessels of voluntary muscle form a characteristic net-work consisting of nar- row rectans^ular meshes (Fig. 485), the longer sides of which correspond to the direction of ■- / £"!:■::»=- Wolffian body ^ 0'' rt^ Parietal mesoblast V» ,<*./•?•' ^^^'■^Umbilical vein Body-cavity Transverse section of rabbit embryo, 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 7miscle- 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-plate 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 Neural canal Wall of neural tube Neural canal Frontal section of rabbit embryo, showing myotomes. X loo. Intersegmental blood-vessel Ectoblast Lateral plate Developing muscle-filDres Intersegmental septum Wall of neural tube Developing muscle-fibres Intersegmental blood-vessel Frontal section of two myotomes of rabbit embryo, showing developing muscle. X 130- 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 directly 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 differentiation into a peripheral^ and a central zone. During the second foetal month the former manifests a disposidon to become fibrillar, while the central zone for a time remains undifferendated 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 foetal month, the fibres composing the muscles of the upper extremity .30 466 HUMAN ANATOMY. have become fibrillar throii};h(nit their intire thickness ; those of the lower ex- tremity acquire a similar coiulitioii a month later. With the deeper extension of the hbrilUe the characteristic cross-striation appears, the nuclei migrating to the periphery of the fibre as the less diflferentiatecl 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 difierentiated cytoplasm of the original muscle-cell ; that, however, separating the muscle-columns must be regarded Fk;. 4Hg. as the ])rocluct of a secondary dif- ferentiation. The designation "cutis-plate," _. :>s ■**^ apjiiied to the compact outer epi- '*■-'* ' ■ ' thelioid |)()rtion of the myotome, vK*^"' ' exj)resses the relation to the in- '^^ tegument which has been wideh rmw*' accejjted, since this part of the '*/ myotome is generally regarded as ■^^ _ '"'^'l] concerned in the formation of the ^^Z-'-^ '^' ,^ connectixe-tissue portion of the ...^^^ — __- ^ - -:iJ_-'^Bi»- skin. This fate of the " cutis- . ^' '^ r -.^ ^c-i ^ plate" was long age denied by '^ ■""' Balfour, wIk) held that both, layers Developing voluntary muscle; the fibres .ire still uiistn.-iled. X 525. 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 w hich, in turn, become the spindle-cells from which the muscle-fibres are de\eloped. 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 between 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 art early separated by the ingrowth of intersegmental septa of connective tissue which Fig. 490. Developing muscle-fibres in which striation is just appearing, y 375. later support the intersegmental blood-vessels and nerves 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., 1890. * Johns Hopkins Hospital 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 vertebrae 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 of 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 c5f some of the intermuscular septa, these forming transverse tendinous bands traversmg the muscle in a horizontal direction. Such tendinous inscriptions {inscriptiones tendinece) , 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 differentiation 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 m 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 sejj;^mental nerve, or at least those fibres of it w hich 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 e.\j)lanation being thus afforded for the extended course of the long thoracic, long subscaj)ular, and phrenic nerves. The muscles supplied by these nerves, as well as the pectoralis major and minor muscles, are all derived from cervical myomeres, tht-ir adult j)osition 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 converted into tendon or aponeurosis. The intermuscular septa between the muscles of the limbs seem to have arisen in this way, and occasionally relatively large ajjoneurotic 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 xarious 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 connectixe tissue, the perimysium, in which blood-vessels and nerves 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 tendo7is, 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 muscle-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 fasciee 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 fiexor 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 from 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, Central portion Lateral port Tendinous - septa of insertion Tendon of insertion Diagrams showing semi-pinnate {A) and pinnate {B) arrangement of muscle-fibres, which pass from tendon o* origin above to that of insertion below. C, compound pinnate arrangement, as in central division of deltoid muscle. {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;, ov p inflate muscle (e. g. , mterossei 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 tetidon 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 nniscle having thus a compound pinnate arrangement (Fig. 491, O. As a rule, the tendons occur in connection with the extremities 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 i^e.g., digastric, Fig. 497) or to the persistence of some of the dividing lines which separate the \arious embryonic segments of which a muscle may be composed {^e.g., rectus abdominis, Fig. 523) ; or it may 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 {,c.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 tlieir 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, apo7icuroses. It is convenient to recognize two principal layers of fasciae, the superficial and the deep. The snperjicial fascia immediately underlies the skin of the entire body, and is sometimes considered a portion of it and termed the paniiiciilns adiposns, 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 exten- 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 fascist are intimately united. The deep fascia, on the other liand, immediately covers and invests the muscles, and in the intervals between them becomes continuous with the periosteal connec- tive tissue enclosing the bones. Those lamellae 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 arais 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 tendo7i-s heaths^ 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 enclose^, 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- Fig. 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 vin- Phalanx - cula tendiiuim, or, from their general similarity to the mesentery, VieSOtendonS. Diagram showing; relations of ten- T ^j-UiT_ J. don to tendon-sheath as in cross-section In some cases a tendon-sheath may serve to a cer- of fi„ger. tain extent as a pulley, affording a smooth surface over 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 {trochlea 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 fasciae 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 subcutaneous bursce 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 deyelopmental 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. Fio. 4Q,- regions of the bodv and to a certain extent into the liead re.ijion, there beinn, liow- ever. in this last reijion 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 mixetl cranial nerves, arising from cells situated in a ])ortion 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, ])rimarily confined to the cranial region, is supplied by lateral motor nerves, and from its rela- tion to the branchial arches may be termed the branchiomeric musculature ; the other, supplied by anterior motor nerves, is arranged ])rimarily in a series of segmental (metameric) ])lates, and may be termed the metameric mus- culaturc. These two systems constitute the first divisions in the morphological classifica- tion of the musculature. The further subdivision of the l)ranchio- meric muscles is most conveniently made with reference to the \^arious cranial ner\es 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 di\ided into the axial and the appendicular musculature. For the latter group, which includes all the muscles of the limbs, a derivation from the mesodermic so- mites seems ]:)robable, outgrowths from certain somites extending into the limb-buds when these develop ; but it has not yet been possi- ble to demonstrate that this is the case, the limb muscles really making their appearance in an unsegmented mass of mesoblast in the limlvbud which appears to have no connection with the mesoblastic somites, these structures apparently not being continued into the limb- bud, but seeming to stoj) short at its base. In- deed, it is quite possible that the limb muscles should not be included vmder the metameric musculature ; but until it is demonstrated that their mode of development is not a secondary condensation of the embryological history, it seems preferable to retain them as members of that group. The later development of the cranial mes- oblastic somites is somewhat different from that of the others, and it is consequently convenient to group the a.xial muscles derived from them by themselves. And since the somites form in the embryo two clearly defined groups, it seems well to place the derived muscles in two groups which may be termed respectively the orbital and the hypoglossal groups. The remaining somites, which may be grouped together as the trunk somites, in their later development undergo numerous modifications, some of which may be regarded as fundamental and primarily afifecting all of the series, and thus affording a basis for a further subdivision. The most fundamental of these modifications is a division of each somite into a dorsal and a ventral portion, corresponding respectively to the primary divisions of the spinal nerves, and permitting the recognition of a v; V Diagram showiriK grouping of head and trunk myotomes. Ill, I\', \'I, orbital grouj) (supjjlied by cranial ner\es indicated by Roman numerals) rep- resenting persisting first three cephalic myotomes; XII, hypoglossal group, representing persisting last three cephalic myotomes, intervening ones having disappeared; i, i, i, i, i, first myotome of cer\-ical. thoracic, lumbar, sacral, and coccygeal groups of trunk myotomes. Each myotome is di- vided into dorsal and ventral .segments. GENERAL CONSIDERATION OF THE VOLUNTARY MUSCLES. 473 Fig. 494. Dorsal division of spinal ner\'e Dorsal group dorsal and a ventral group of trunk muscles. The portions of the ventral divisions on either side of the mid-ventral line separate to form a subordinate group of mus- cles which may be termed the rec- tus group (Fig. 494), the more lateral portions giving rise to a group which, from the prevailing oblique course of its fibres, may be termed the obliquus gi'oup ; and, finally, from the more dor- sal portions of the ventral muscu- lature there are developed in cer- tain regions of the body muscles which lie ventral to the bodies or processes of the vertebrae, and may be termed the hyposkeletal muscles, in contrast to the re- maining musculature which ex- tends between the skeletal ele- ments or lies dorsal to them, and hence is termed the episkeletal mus- culature. To sum up the classification proposed it may be represented in the following manner Hyposkeletal group Obliquus group Rectus group Diagrammatic cross-section of body, showing primary groups of trunk muscles. I. Branchiomeric Muscles. II. Metameric Muscles. A. Axial Muscles. 1. Orbital muscles. 2. Hypoglossal muscles. 3. Trunk muscles. a. Dorsal, b. Ventral. a. Rectus set. b. Obliquus set. c. Hyposkeletal set. B. Appendicular Muscles. Nerve-Supply. — The segmental regularity of the mesodermic somites is but slightly retained in the adult, numerous modifications, such as fusion, tangential and longitudinal splitting, migration, and even obliteration taking place in them to pro- duce the various muscles of the adult. The various modifications have not in all cases been traced, but a study of the nerve-supply of a muscle gives in many, if not all, cases an important clue to its origin. This depends upon the fact that the muscles may be regarded as the end-organs of the motor nerves, and that the seg- mental relation established in the embryo between a nerve and the muscle-tissue derived from a given mesodermic somite is not disturbed in later development, no matter what changes of relation the muscle-tissue may undergo. Thus, when a muscle, such as the rectus abdominis, is found to be supplied by a number of spinal nerves, it is because it has been formed by the fusion of portions of a corresponding number of mesodermic somites ; and when a muscle, such as the latissimus dorsi, lying mainly in the lumbar region, is found to be supplied by a cervical nerve, it is because it has wandered from its original point of formation in the cervical region. Variations in the nerve-supply are occasionally seen, especially in the limb mus- cles; but it seems probable that such variations are only apparent, the nerv^e-fibres supplying the muscle being in all cases strictly equivalent, arising from the same region of the spinal cord, even although they may pursue in different individuals somewhat different paths in order to reach their destination. Thus, a muscle which normally is supplied by fibres from the median nerve may sometimes be found to be 474 HUMAN ANATOMY. supplied by the ulnar nerve, the nerve- fibres using the ulnar nerve as a pathway by which to reach their destination, instead of the median ncr\e. It is important, therefore, both from the morphological and clinical stand-points, that not only should the nerve along which the fibres pass to reach their tlestination be known, but also the nerve-roots by which they issue from the central nervous system. THE BRANCHIOMERIC MUSCLES. The branchiomeric muscles are those skeletal muscles which are derived from the mesoderm associated with the branchial arches, and are supplied by those cranial nerves whose motor fibres constitute what are termed lateral motor roots. These nerves are the trigeminus, facialis, and glossopharyngeo-vago-accessorius groups, and the classification of the muscles may well be according to their innervation by these three nerve-groups. I. THE TRIGEMINAL MUSCLES. The trigeminal muscles stand in relation primarily to the first embryonic or jaw- arch, and in the adult to the structures developed in association with this, — i.e., to the mandible and the malleus. The mandibular muscles are represented by the muscles of mastication and two muscles, the mylo-hyoid and the anterior belly of the digastric, which extend between the man(Hble and the hyoid bone, and may be termed the submental muscles. Connected with the malleus is a single muscle, the tensor tympani, and an additional trigeminal muscle is found in association with the soft palate, the tensor palati. (a) THE MUSCLES OF MASTICATION. 1. Masseter. 3. Pterygoideus E.xternus. 2. Temporalis. 4. Pterygoideus Internus. I. Masseter (Fig. 495). The masseter is a strong quadrilateral muscle composed of two portions, sep- arated at their origin and posteriorly by a quantity of loose areolar tissue, but united towards their insertion into the mandible. Attachments. — The superficial portion arises by a strong aponeurosis from the anierior two-thirds of the lower border of the zygoma, while the deeper part arises directly from the posterior third of the lower border and the whole of the inner surface of the zygoma. The fibres of the superficial portion pass downward and slightlv backward to be inserted into the outer surface of the angle of the mandible, while those of the deeper portion pass more directh* downward and are inserted into the outer surface of the ascencHng ramus as high as the bases of the articular and coronoid processes, encroaching to a certain extent upon th^ insertion of the temporal muscle. Nerve-Supply. — By the masseteric branch of the anterior portion of the man- dibular division of the trigeminus. Action. — To raise the mandible and, by its superficial portion, to draw it for- ward to a slight extent. Owing to the fibres of the muscle being directed almost perpendicularly to the lever upon which it acts, the masseter works at much less mechanical disadvantage than is usual, and its action is therefore exceedingly powerful. Relations. — A considerable portion of the masseter is subcutaneous. Poste- riorly, however, the parotid gland rests upon its outer surface, and it is crossed by the parotid duct, the transverse facial artery, and branches of the facial nerve. Anteriorly its deep surface is separated from the buccinator muscle by a well-devel- oped mass of fat, the buccal fat-pad (page 489). The Parotideo- Masseteric Fascia. — Covering the anterior surface of the masseter is a thin layer of fascia, the masseteric fascia, attached above to the zygoma THE TRIGEMINAL MUSCLES. 475 and fading out anteriorly beneath the facial muscles. Posteriorly it becomes thicker and divides into two layers to enclose the parotid gland (^parotid fascia), the super- ficial layer becoming continuous behind with the layer of the deep cervical fascia which encloses the sterno-mastoid muscle, while the deeper layer is connected inter- nally with the styloid process and joins the deep cervical fascia below. A thickening of this deeper layer forms a flat band, the stylo-7nandibular ligavient, which passes downward and outward from the styloid process to the angle of the jaw. 2. Temporalis (Fig. 495). The te7nporal fascia forms a strong aponeurotic membrane attached above to the superior temporal line and the portion of bone between this and the inferior line, being along this attachment continuous with the periosteum. Below it divides into two layers which are separated by a quantity of adipose tissue, through which the Fig. 495. Temporal fascia (cut) Temporal — ^-^ muscle, partially , ,^ exposed I ' ■ Buccinator Masseter,_\ deep portion Masseter, superficial portion. Orbicularis oris Lateral aspect of skull with temporal, masseter, buccinator, and oral muscles in place. middle temporal artery may run, and is attached to the zygoma, its superficial layer inserting into the upper border of the arch and its deeper layer into the inner surface. Attachments. — The temporal muscle arises from the upper half of the deep surface of the temporal fascia and from the whole extent of the floor of the temporal fossa. Its fibres converge to an exceedingly strong tendon, which i7iserts into the coronoid process of the mandible, occupying both its borders, the whole of its inner surface, and a varying amount of its outer surface. Nerve-Supply. — By the anterior and posterior deep temporal branches from the anterior portion of the mandibular division of the trigeminus. Action. — To raise the mandible. The more posterior fibres serve to retract the jaw, acting thus as an antagonist of the external pterygoid. 476 HUMAN ANATOMY. Relations. — Superficial to the temporal fascia arc branches of the superficial temporal \essels and the auriculo-temporal nerve. Beneath, the muscle is in relation to the internal maxillary artery and the external pterygoid muscle. 3. Pterygoideus Externus (Fig. 496). Attachments. — The external pterygoid arises by two heads. The upper head takes its origin from the under surface of the great wing of the sphenoid, inter- nal to the infratemporal crest (pterygoid ridge), while the lower head arises from the outer surface of the lateral pterygoid plate. The two heads are at first separated by a narrow triangular interval through which the internal maxillary artery passes, but, passing backward and outward, they soon unite to be inserted into the anterior border of the interarticular fibro-cartilage of the mandibular articulation and into the neck of the condyloid process of the Fig. 496. Irmporal bone (cut) ■ iIKiyle of mandible I'llJi-i head) External Lower head / pterygoid mandible. Nerve-Supply. — By the exter- nal ptcrygoitl branch of the anterior portion of the mandibular division of the trigeminus. Action. — When both muscles act together, they draw the jaw and the interarticular fibro-cartilage for- ward, a moxement which always accompanies and assists in the de- pression of the jaw. When but one muscle acts, the ramus to which it is attached is drawn forward, while the other pivots in its articular surface, the result being an apparent lateral movement of the jaw towards the pivotal side. Relations. — The outer surface of the external pterygoid is in rela- tion to the coronoid process of the mandible and the temporal muscle, its lower head is frequently crossed by the internal maxillary artery and the buccal nerve, and anteriorly it is separated from the masseter by the buccal fat-pad. The deep surface rests upon the upper part of the internal pterygoid muscle, and is in relation to the internal maxillary artery and the inferior dental and lingual branches of the mandibular division of the trigeminus. Internal pterygoid .\i\ Kiiiyoid, stump External and internal pterygoid muscles, seen from within. 4. Pterygoideus Internus (Fig. 496). Attachments. — The internal pterygoid arises from the walls and floor of the pterygoid fossa, the majority of its fibres being attached to the inner surface of the external pterygoid plate and to the tuberosity of the palate bone. A smaller bundle of fibres, forming what may be termed a second head, separated from the main por- tion of the muscle by the lower head of the external pterygoid, frequently arises from the tuberosity of the maxilla and the adjacent portion of the palate bone. From these origins the fibres are directed downward and somewhat outward and backward to be inserted into the inner surface of the angle and ramus of the mandi- ble below the mylo-hyoid groove. Nerve-Supply. — By the internal pterygoid branch from the trunk of the mandibular division of the trigeminus. Action. — Its chief action is to raise the jaw, having in this respect almost as powerful action as the masseter. Owing to the direction of its fibres, it will also assist the external pterygoid in protruding the jaw and in producing its lateral movements. Relations. — The outer surface of the muscle is in relation with the ramus of the mandible, the internal maxillary artery, and the inferior dental and lingual nerves THE TRIGEMINAL MUSCLES. 477 passing between the muscle and the bone. Above its larger head is covered by the external pterygoid. Its inner surface is in contact above with the tensor palati, the superior constrictor of the pharynx, and the ascending palatine artery, while towards its insertion it is in relation with the stylo-hyoid and posterior belly of the digastric and with the submaxillary gland. Variations of the Muscles of Mastication. — The muscles of mastication are all derivatives of a single muscular mass represented by the adductor niandibulce of fishes, and indications of their common origin are not infrequently to be seen in partial unions of the various muscles. Thus, fibres from the posterior portion of the deeper head of the masseter may join the tem- poral, fibres from both the temporal and masseter sometimes pass to the anterior border of the fibro-cartilage of the mandibular articulation, and connections have also been observed between the temporal and the external pterygoid. Additional independent muscles apparently belonging to this group sometimes occur in the pterygoideus proprius, which extends from the infratemporal crest of the sphenoid to the posterior edge of the external pterygoid plate, and in the pterygo-spinosus, which has for its attachments the spine of the sphenoid and the posterior border of the external pter}rgoid plate. The significance of these muscles passing between points which are immovable is somewhat obscure. The close relationship which the pterygo-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. {b) THE SUBMENTAL 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 arises {xova practically the entire length of the mylo-hyoid ridge of the mandible, from which the fibres pass inward and slightly backward to be insej'ted 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 diaphi'agma 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 submaxillary 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 with 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 nerve. 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 belly, which alone belongs to the trigeminal group of muscles, arises from the digastric fossa of the mandible, and is directed downward, backward, and slightly outward to become con- 478 HUMAN ANATOMY. tinuous with the intermediate tendon. Tliis is bound down to the greater horn and body of the hyoid bone by a pulley-Hke 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 o[ the temporal bone, and passes downward and forward to become connected with the intermediate trndoii. Nerve-Supply. — The anterior belly is su])|)lied by the mylo-hyoid nerve from the inferior dental branch of the mandibular di\ ision 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, V\G. 497. Mandible Gvnio-hyoid (niylo-hyoid removed) -Digastric, anlcrior belly Mylo-hyoid- Hyoid bone — Thyro-hyoid membraiK — Stylo-glossus Internal pterygoid Thyro-hyoid Thyroid cartilagi Stylo-pharyngeus Crico-thyrcii'l- Fascial loop binding "oiis to hyoid bone Digastric, posterior belly Thyroid gland Submental muscles from below ; trachea has been displaced downward and backward. according as one or other of the bones is fixed by the antagonizing muscles. By raising the hyoid when the mandible is fixed, it assists the mylo-hyoid in pressing the tongue against the palate during the first portion of the act of deglutition, and in the second portion of that act the posterior belly will assist the stylo-hyoid in drawing the hyoid upward and backward and so help in elevating the larynx. Relations. — The anterior belly rests upon the mylo-hyoid muscle. The pos- terior belly is covered by the sterno-mastoid and splenius muscles, and crosses both the external and internal carotid arteries, the internal jugular vein, and the pneumo- gastric and spinal accessory nerves. Variations. — A close relationship exists between the mylo-hyoid and the anterior belly of the difjastric, and there is usually more or less exchansi:e of fibres between the two muscles, sometimes amounting to a complete fusion. A duplicity of the anterior belly is a rather fre- THE FACIAL MUSCLES. 479 quent variation, and the anterior bellies of opposite sides may be united by the more or less complete conversion of the fascia which typically passes between them into muscular tissue. An independent muscle extending between the body of the hyoid and the symphysis of the mandible, and termed the mento-hyoid, occasionally is found running alongside of the medial border of the anterior belly, and is to be regarded as a separated portion of that muscle. As regards the posterior belly, it may take its origin from any part of the mastoid groove or even from the outer portion of the superior nuchal line, and occasionally it fuses completely with the stylo-hyoid. In certain cases in which there is a failure of the anterior belly to differ- entiate from the mylo-hyoid, the posterior belly is inserted into the angle of the mandible instead of into the hyoid bone, — a condition recalling the arrangement typical in the majority of the mammalia, in which the posterior belly of the digastric is represented by a depressor tnandibiilcB . {_c) THE TRIGEMINAL PALATAL MUSCLE. I. Tensor Palati (Fig. 509). Attachments. — The tensor palati (tensor veil palatini) takes its origin from the scaphoid fossa and spine of the sphenoid and from the outer surface of the car- tilaoinous portion of the Eustachian tube. It descends along the outer surface of the internal pterygoid plate, and, becoming tendinous, bends at right angles around the hamulus and is continued inward to be inserted into the posterior border of the palate bone and into the aponeurosis of the soft palate. Nerve-Supply. — By fibres from the mandibular division of the trigeminus, which traverse the otic ganglion. Action. — It tends to draw the soft palate to one side. The two muscles acting together will stretch the soft palate. {d) THE TRIGEMINAL TYMPANIC MUSCLE. I. Tensor Tympani (Fig. 1252). Attachments. — The tensor tympani is a small bipenniform muscle which lies in a bony canal situated above the Eustachian tube. Its fibres take their origin from the cartilaginous portion of the Eustachian tube, the adjacent portions of the great wing of the sphenoid, and also to a certain extent from the walls of the bony canal. The tympanic end of the Eustachian' tube is separated from the opening of the canal for the tensor by a bony ridge, the processus cochleariformis, over which the tendon of the tensor bends almost at right angles and passes outward across the tympanic cavity to be inserted into the manubrium mallei near its attachment to the head of the bone. Nerve-Supply. — By fibres from the mandibular division of the trigeminus, which traverse the otic ganglion. Action. — The muscle draws the handle of the malleus inward and so tenses the membrana tympani. II. THE FACIAL MUSCLES. The muscles supplied by the facial nerve are readily divisible into two groups. Primarily this musculature is associated with the second branchial or hyoid arch, represented in the adult by the lesser cornu of the hyoid bone, the stylo-hyoid liga- ment, styloid process, and stapes, and a small group of muscles — the stylo-hyoid, the posterior belly of the digastric, and the stapedius — are still found in relation to these structures. From the surface of the mass from which these muscles differentiate there is separated at an early stage a layer which gradually increases in extent and eventually covers all the neck and head in a cowl, as it were, its progress from the hyoid arch being followed by a branch of the facial nerve, which eventually, with the growth of the muscle, increases to such an extent as to appear to be the main stem of the nerve. From the muscular sheet numerous superficial muscles of the head and neck develop, and the entire group so formed may be termed, from one of its principal members, the platysma group, the group retaining the primary relationships forming the hyoidean group. 48o HUMAN ANATOMY. (a) THK HVUIDEAN MUSCLES. I. Stylo-hyoideus. 2. Digastricus (Posterior Belly). 3. Stapedius. I. Stylo-Hyoideus (Figs. 497, 502). Attachments. — The stylo-hyoid forms a slender spindle-shaped muscle which arises from the upper jxjrtion of the styloid process and passes obliquely downward and forward to be inserted into the base of the greater cornu of the hyoid bone, usually dividing before its insertion into two slips, between which the intermediate tendon of the digastric passes. Nerve-Supply. — By a branch from the digastric branch of the facial nerve. Action. — To raise and draw backward the hyoid bone. Relations. — Above the stylo-hyoid descends along the inner border of the posterior bellv of the digastric, passing in front of that muscle below. Internal to it is the stylo-pharyngeus, and below the hyo-glossus and the glosso-pharyngeal and hypoglossal ner\es, passing forward between it and the stylo-pharyngeus. 2. DiGASTKicus (Posterior Belly). See page 478. 3. Stapedius (Fig. 1254). Attachments. — The stapedius arises from the walls of the cavity contained within the pyramidal eminence, and its tendon, entering the tympanic cavity through the aperture at the apex of the eminence, is inserted into the neck of the stapes. Nerve-Supply. — By a small liranch arising from the facial nerve during its course through the lower part of the facial ( Fallopian) canal. Action. — By its contraction it draws the head of the stapes towards the pos- terior wall of the tympanic ca\^ity, depressing the posterior j)art of the foot-plate of the bone while it raises the anterior part, thus tensing the membrane which closes the fenestra ovalis. Variations of the Hyoidean Muscles. — A close relationship exists between the stylo-hyoid and the posterior belly of the dis^astric, the one or the other occasionally failing to separate from the common mass from which they are derived. A bimdle of muscle-fibres sometimes passes from the tip of the styloid process to the angle of the mandible, forming what may be termed the styto-»ia>i(tibu/aris, and recalling by its insertion the condition presented in certain cases by, the posterior belly of the digastric (page 479 K A duplication of the stylo-hyoid has also been observed, the second slip, which has been termed Xh^ styto-Iiyoidens profundus, varying considerably in its insertion, sometimes accompa- nying the stylo-hyoid i:)roper and sometimes inserting into the lesser cornu of the hyoid, and in some cases replacing the stylo-hyoid ligament. The division of the stylo-hyoid near its insertion for the passage of the intermediate tendon of the digastric does not always occur, the insertion being by a single head which may pass either to the outer or the inner side of the tendon. {b^ THE PLATYSMA MUSCLES. [a) Superficial Layer. I. Platysma. i. :2. Occipito-frontalis. 2. 3. Auricularis posterior. 4. Auricularis superior. 3. 5. Auricularis anterior. 4. 6. Orbicularis palpebrarum. 5. 7. Zygomaticus major. 6. 8. Levator labii superioris alaeque 7. nasi. 9. Depressor labii inferioris. 10. Levator menti. {b) Deep Layer. Orbicularis oris. Nasalis (compressor nasi et depressor alae nasi). Levator labii superioris. Levator anguli oris. Risorius. Depressor anguli oris. Buccinator. The comparative and embryological study of the platysma muscles have shown 'their origin from the musculature of the second or hyoid arch and their extension THE FACIAL MUSCLES. 481 thence over the head and neck. At first they are confined entirely to the neck region, but even in the lower mammals the extension upon the head has begun, and in the higher members of this group two portions can be distinguished in the muscle-sheet. The more superficial of these is situated in the lateral and posterior portions of the neck, and extends thence upon the sides of the face and over the vertex of the skull to the orbital and nasal regions of the face. The deeper one lies more anteriorly in the neck, and extends upward over the jaw to the region around the mouth. In the higher forms a differentiation of both layers to form a number of more or less separate muscles takes place and reaches its highest development in man, whose mobility of facial expression is due to the existence of a considerable number of platysma muscles. These muscles have arisen from the common sheets by the partial conversion of these into connective tissue, by the secondary attachment of portions of the sheets to the skeleton, by various modifications of the primary direc- tion of the fibres, and by the obliteration of certain portions of the sheet found in the Fig. 498. Depressor anguli oris Mandible Raphe of mylo-hyoid Platysma-fa Depressor labii inferioris Levator menti Mylo-hyoid H\oid bone Thyroid cartilage Sterno-mastoid Sterno-thyroid Inner end of clavicle Superficial muscles of neck. lower animals, the cervical portion of the deep layer, for instance, being normally lacking in man, the layer being represented only by the muscles of the lips. The platysma musculature is characterized for the most part by the pale color of its fibres, by their aggregation to form thin bands or sheets usually more or less inter- mingled with connective-tissue strands, so that their margins are, as a rule, ill-defined, and by their attachment in frequent cases to the integument. These peculiarities, together with a considerable amount of variation which occurs in the differentiation of the various muscles, have brought about not a little difference in the number of muscles recognized in the group by various authorities, some recognizing as distinct muscles what others regard as merely more or less aberrant or unusually developed slips. {a) THE MUSCLES OF THE SUPERFICIAL LAYER. I. Platysma (Figs. 498, 499). Attachments. — The platysma takes its oris;in from the skin and subcutaneous tissue over the pectoralis major and deltoid muscles on a line extending from the car- tilage of the second rib to the tip of the acromion process. Its fibres are directed 31 482 HUMAN ANATOMY. upward and inward and are inserted into the body of the mandible from the sym- physis to the insertion of the masseter, the more posterior fibres extending; upward upon the face towards the angle of the mouth and becoming lost partly in the fascia of the cheeks and partly among the muscles of the lips. Nerve-Supply. — By the inframandibular branch of the facial nerve. Action. — The contraction of the platysma results in drawing the lower lip downward and outward and at the same time raising the skin of the neck from the underlying parts. It is one of the most important muscles employed in the expression of horror and intense surprise. It does not seem probable that the muscle has much effect in producing depression of the mandible, an action which it might be expected to possess on account of its upper attachment. Relations. — The platysma rests upon the deep fascia of the neck and covers all the structures at the front and sides of that region. Upon its deep surface lie the external jugular vein, the superficial lymph-nodes of the neck, and the superficial branches of the cervical plexus. It covers also the sterno-mastoid muscle and the depressors of the hyoid bone, and, above, the digastric and mylo-hyoid muscles, together with the submaxillary gland and the lower portion of the parotid. Variations. — There is usually more or less decussation of the two muscles across the median line, especially in their upper parts, where, indeed, a certain amount of decussation may be considered a normal condition. The muscle is subject to considerable amounts of variation in its development, sometimes forming a very thin, pale layer largely interspersed with connective tissue, and at other times it is composed of strong, deeply colored bundles with much less inter- mixture of connective tissue. Its extension upon the face may also vary considerably, some- times being traceable as high up as the zygoma and extending backward to behind the ear. (Jn the other hand, it may be very considerably reduced in size, especially below, a complete absence of the lower half of the muscle having been observed. 2. Occipito-Frontalis (Fig. 499). Attachments. — The occipito-frontalis (m. epicranius) is a muscular and aponeu- rotic sheet which covers the entire vertex of the skull from the occipital region to the root of the nose. It consists of two muscular portions, one of which, the occipitalis, arises from the superior nuchal line and inserts after a short course into the posterior border of the epicranial aponeurosis, while the other, iha fro7itaiis , taking its origin from the anterior border of the galea, is i?iserted into the skin in the neighborhood of the eyebrows, over the glabella, and into the superciliary arches, a portion of it being frequently prolonged downward upon the nasal bone, forming what has been termed Xhe^ pyramidalis nasi (m. procerus), which is frequently described as a distinct muscle. The epicranial apo7ieurosis (galea aponeurotica) (Fig. 499) is a dense aponeu- rotic sheet which covers the entire vertex of the cranium and is prolonged laterally over the temporal fascia as a thin layer which extends almost to the zygoma. On its superficial surface it is intimately associated with the integument, being united to its deeper surface by a thin but close and resistant layer of fascia which represents the superficial fascia of other regions of the body and in which are embedded the vessels and nerves of the scalp. The under surface of the galea is, however, smooth, and is connected with the periosteum by a lax layer of connective tissue, so that it is capable of considerable movement to and fro upon the periosteum, the skin being carried with it in such movements. A section through the scalp at the vertex would show from without inward (i) the skin, (2) the dense superficial fascia with its vessels and nerves, (3) the epicranial aponeurosis, (4) loose connective tissue, and (5J periosteum (Fig. 504). Nerve-Supply. — The occipitalis is supplied by branches from the posterior auricular branch of the facial, the frontalis by branches from the rariii temporales of the same nerve. Action. — The occipitalis acting alone will draw backward the galea aponeurotica, while the frontalis draws it forward. If, however, the galea be fixed by the occipitales, the action of the frontales is to raise the eyebrows and throw the skin of the forehead into transverse wrinkles, both of these actions being greatly increased by the simul- taneous contraction of both the occipitales and the frontales. It is consequently the THE FACIAL MUSCLES. 483 muscle employed in the expression of interrogation and surprise and also, in con- junction with the platysma, in that of horror. The transversus niichcs is a thin muscular band, frequently present, arising from the occipital protuberance and extending laterally to terminate in various attachments ; sometimes, for instance, uniting with the posterior border of the sterno-cleido-mastoid or with the auricu- laris posterior. It may take its origin either superficial to or beneath the attachment of the trapezius to the superior nuchal line, and in the former case is to be regarded as a portion of the platysma group of muscles, while in the latter it is more probably a relic of the primary con- nection between the trapezius and the sterno-cleido-mastoid and belongs to that group of muscles (page 501). 3. AuRicuLARis Posterior (Fig. 499). Attachments. — The posterior auricular {retraheiis aiirevt) is composed of a few bundles of fibres which arise from the outer extremity of the superior nuchal line and the base of the mastoid process and pass horizontally forward to be inserted into the posterior surface of the concha. It is frequently imperfectly separated from the occipitalis. Nerve-Supply. — By the posterior auricular branch of the facial nerve. Action. — To draw the auricle backw^ard. Fig. 499, Auricularis superior Occipitalis — Auricularis anterior Auricularis posterior Zygomaticus major Zygomaticus minor Levator anguli oris Levator labii superioris Buccinator Risorius Frontalis Corrugator supercilii Orbicularis palpebrarum Orbital part of same muscle — Pyramidalis nasi Lev. labii sup. alaeque nasi Compressor narium Dilatores naris Depressor alae nasi Orbicularis oris Depressor anguli oris /jb—— Depressor labii inferioris Levator meiiti Platysma Superficial dissection of head, showing 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 (atit-ahens auretn) 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. 4«4 HUMAN ANATOMY. Nerve-Supply. — By fibres from the rami temporales of the facial ner\'e. Action. — To draw the auricle upward and forward. 6. Okbicil.vris Pai-Pkbraktm ( Figs. 499, 500). The orbicularis palpebrarum (in. orbicularis ociili ) is an elliinical sheet whose fibres have their origin in the neighborhood of the inner ani^le of the eye and curve thence, some upward and outwartl 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 customary to regard the muscle as consisting of two main portions, \\\(i pars palpe- bralis and the pars orbitalis. The internal palpebral //^awr;// (li^araentuni 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 gi\es off from its posterior surface a bundle which is reflected in\\ard o\er the lachrvmal sac and Fig. 500. Internal palpebral ligament Tensor tarsi Orbicularis palpebrarum ' Upper tarsal plate ■. «i«Bta. \ Lower tarsal — ~- \ ]»late ^Orbicularis palpebrarum Orbicularis palpebrarum has been dissected from its deeper surface and reflected inward with ejelids, sliowing lachr> nial portion or tensor tarsi. passes behind this to be attached to the crest of the lachrymal bone. This ligament, which isalstj known as the tendo oculi, may 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 amoimt 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. Pars 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 the pars eiliaris or vniscle of Riolan. The fibres which arise from the posterior lachrymal crest are usually regarded as forming either a distinct muscle, which has been termed the tensor tarsi or Horner s tnusele, 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 parti)- to be i?iserted 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 perij>hery tend to scatter themselves among the adjacent platysma muscles and to make numerous 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- tinct muscle, the nialaris. The main muscle arises from the internal palpebral ligament, the frontal proces:> 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 supereilii (Tig. 499 ). Nerve-Supply. — By the rami temporales and zygomatici of the facial nerve. THE FACIAL MUSCLES. 485 Action. — The principal action of the orbicularis palpebrarum is to approximate the uppar 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 insej'ted 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 with 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 quadratus labii stiperioris, of which the levator labii superioris alseque nasi forms the caput atigidare, the levator labii superi- oris proprius the caput infraorbitate, 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 ner\'e. 486 HUMAN ANATOMY. Action. — To draw upward the skin of the chin, thereby causing protrusion of the lower lip, as in poutinij. When its action is combined with contraction of the depressors of the angles of the mouth, it gives an expression of haughtiness or con- tempt, and has thence been termed the m. superbus. When slightly contracted, it gives an expression of firmness or decision. Belonging to the superficial layer of the platysma musculature are a number of additional more or less rudimentary 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). {b) THE MUSCLES OF THE DEEP LAYER. I. Orbicul.vris Oris (Figs. 499, 501, 503). Attachments. — The orbicularis oris is a rather strong elliptical muscle whose fibres occupy tlie thickness of both the upper and lower lips between the skin and the mucous membrane of the mouth. F"or the most part the fibres com {losing the muscle are forward prolongations of the buccinator, but mingled with these there are fibres from all the muscles which are inserted in the vicinity of the mouth, such as the zygomaticus, levator anguli oris, levator labii superioris, depressor anguli oris, depressor labii inferioris, and risorius. It possesses, however, some slight attachment to skeletal structures by three groups of fibres which have frequendy been regarded as distinct muscles. These groups are : (i) the vicisivi labii superioris, a series of bundles of fibres which arise from the incisive fossae of the maxilke and pass downward and outward to mingle with the other fibres of the orbicularis at the angles of the mouth ; (2) the iiicisivi labii inferioris, which arise from the aheolar 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, will tend to pro- Pyramidalis nasi trudc the HpS. 2. N.ASALis (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 alee 7iasi), are inserted into the alar cartilage of the nose, while the more lateral ones, the pars trans- versa (compressor nariuni), often re- ceiving slips from the adjacent levator labii superioris alaeque nasi and the levator anguli oris, extend forward over the ala of the nose to terminate upon 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 nerve. Action. — The more median fibres draw the alar cartilage downward and in- ward, while the more lateral ones slightly depress the tip of the nose and at the same time compress the nostril. Levator labii sup. alaque nasi, nasal portion cut away Depressor alae nasi _ Orbicularis oris Compressor iiarium Dilatores naris Depressor septi 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 alee nasi or myrHforniis, while the latter 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 lip (m. levator labii superioris pro- prius) arises above from the infraorbital margin of the maxilla and extends 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 alaeque 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 inserted 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 angle 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 orbicularis 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 transversus 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 been 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 .tjroup of muscles is covered by a distinct layer of fascia which forms the anterior part of the fascia buccopharynyca and is a dense, resistant sheet of connective tissue intimately Fig. 502. Tcini)Oral Tensor palati Levator palati — Styloid process — Haiiiular process Digastric, posterior belly Superior constrictor Stylo-glossus Pterygo-mandibular ligament Stylo-phyaryn^jeus Stylo-hyoiil Mandible (cut) Hyo-glossus Greater hyoid cornu Middle constrictor Thyro-hyoid Inferior constrictor Corrugator supercilii Orbic. palp., palpebral part I'\ramidalisnasi Orbic. palp., orbital part Lev. laliii sup. al. nasi (lut) i. Le\ator laliii siiperioris (cut) ^ J r — -^ Compressor nan urn a Levator anguli oris Z\^'omaticus Buccinator Orbicularis oris Depressor labii inferiorls Levator menti I'latysma 4 Oral, pharyngeal, and styloitl groups of muscles; 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 alveolar portion of the ma.xilla and to the internal pterygoid plate of the sphenoid, and thence is continued backward over the superior con- i" '"(^ 503- strictor 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 \ertically 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 ptcrygo-mandibiilar liga- ment, 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 orighi is horseshoe-shaped, extending above along the alveolar border and tuberosity of the maxilla and thence upon the hamulus Levator anguli oris Buccinator // ^^' Depressor anguli oris Diagram showing course of component fibres forming orbicularis oris muscle. 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. From this extensive 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 hue al 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 pericra7iimn — 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. Hair- follicles Fibrous septa Outer compact bone Diploe. Inner compact bone Pacchionnii buclie ■Superficial fascia Aponeurosis Subaponeurotic tissue Pericranium — Bone Dura mater Superior longitudinal sinus Portion of frontal section of head hardened in formalin, showing layers of scalp, skull, and meninges. X 214. 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. " Cephalhaematomata" 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 between 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 haematomata 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 difificulty 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 apoyicurosis ; 4, \\\q superficial 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 erysipelatous 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 prevents both their retraction and contraction ; (6) collections of blood after contusions may, 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 ; (7) 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 pharynx, the frontal sinuses, or the ethmoid or nasal bones. The air infiltrates either the subaponeurotic or subcutaneous cellular tissue. Pneiunatocele 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 Region. — 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- maxillary region and thence into the pharynx 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 haematoma 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 150S). 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 cancrvmi oris) once established in the loose cellular tissue and fat of the cheeks, run a rapid and destructi\e course, and may be followed by great dis- tigurement 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 b*^ opened through the mucous membrane. Fig. 505. Upper cut edge of masseter Temporal External pterj-goid Internal pter\-goiii;tus ha\e been a])plied. Not infrecinently a l)nndie of fibres is to be found arising from the basilar i)ortion of the occipital bone or (.-viii from llie inferior surface of tlie petrous portion of the temporal or the spine of the sphenoid, and passiu!^ liownuard to be inst-rted aloni; u itii the piiaryns^o-palaliinis. A buntile which passes from tlie cartila<;inous jjortion of the J'-ustachian lube to be inserted with the palato-pharyngeus has been termed the salpingo-pharyngeus. Fig. 510. Condyles Internal carotid artery Internal jugular vein Central attachment of phar>'nx Mastoid — -. process Internal pterygoi Styloid process — Dijiaslric, — posterior belly Stylo 1- pharyngeus \ Stylo-glossus — t Stylo-hyoid Lateral expan- „ y sioii of Stylo-hyoid »,-^ ' ligament ^V^ Tip of great corn hyoid bone Thyro-hyoid ligament Superior cornu of thyroid cartilage Middle constrictor Inferior constrictor iigitudinal muscle of oesophagus Muscles of pharynx from behind ; portion of inferior constrictor has been removed. 7. Constrictor Pharyngis Medrts (Fig. 510). Attachments. — The middle constrictor of the pharynx is a fan-shaped sheet which arises from the stylo-hyoid ligament 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 orio-in may have considerable independence. Thus the fibres from the greater cormi of the hyoid have been recognized as a muscle, the cerato-pharyngeus, distinct from the remainder, to which the term chondro-pharyngeus 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 be 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 plexus, 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-phary^igeus and crico-pharyngeus. {b) 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, ^x& inserted \nX.o 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 tlie 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 co\ers, KiG. 511. above, the upper part of the posterior belly of the digastric, the splenius capitis, the levator scapula; 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 external and internal carotids, the facial and internal jugular \eins, the cer\ical jjlexus, and the lateral lobe of the thyroid gland. Variations.— Considerable variation exists in the amount of fusion of the two heads, their complete distinctness bein^^y?(r?a/ -.--^-^' v^lf ^ ' tal, lower stemo-niastoid, a stcrno-occipital, and a cleido- \ " ^^^ fjart turned occipital portion, while the deep one is formed by a deep stcrno-)nastcid and a cleido-mastoid portion, the names applied indicating the attachments of the 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. Quadricipilal type of sterno-mastoid, showing tlie components of the muscle. {After Mau brae.) .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 placed 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 cnaillaris sometimes applied to the muscle. It arises above from the superior nuchal line and the external occipital pro- tuberance, and thence along the ligamentum nuchie 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 inserted, 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 lower half they again diminish, so that there is formed by the two muscles of opposite sides, in this region, THE VAGO-ACCESSORY MUSCLES. 5or 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. 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 T7,„ „^ mid-dorsal line and at the same time %^ mikf—'^l rotate it so as to raise the point of the r WM. shoulder. Variations. — Like the sterno-mastoid, the trapezius is a compound muscle consisting of three distinct portions. That portion of the muscle which inserts into the tuberosity of the Sterno-mastoid Aponeurosis of trapezius Trapezius .2i_Acromion Scapular spine Fig. 513. Infraspinatus Rhomboideus major Teres major Latissimus dorsi Superficial dissection of back, showing trapezius and adjacent muscles. ■Lleido occipitalis Splenius ■Cleido occipitalis cervicalis Cla\icle ■Acromion Dorso-scapularis superior ■Tuberosity of spine 1 endinous slip to infraspmous fascia Dorso seapularis inferior .Latissimus dorsi Components of human trapezius muscle. (^Streissler.) 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-occipitalis 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 extends 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 vertebrae, 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. A. thp: axial muscles. As has been pointed out. the liistory of the anterior two groups of myotonies, supphed by cranial nerves, 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. Levator palpebrse superioris. Rectus superior. Rectus internus. 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. Tendinous loop for sup. oblique Superior oblique ciistal part Internal rectu Superior oblique proximal jiart ator palpebrae sup. per tarsal plate Palpebral fissure I. Levator Palpebr^ Superioris (Fig. 516). Attachments. — The levator palpebrae 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 in- serted by 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 orbito- palpchral muscle. This is triangular in shape, with the truncated ape.x united to the levator and with the base attached to the e.xternal 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 upw^ard and backward. Relations. — Immediately above the levator palpebrae 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. Optic ners' Superior rectus Inferior oblique External rectus Stump of levator palpebrae superioris Ocular muscles seen from above after removal of roof of orbit ; elevator of upper eyelid has been cut and reflected forward. THE AXIAL MUSCLES. 503 2. Rectus Superior (Fig. 514). Attachments. — The superior rectus arises from the upper portion of a fibrous ring termed the annulus of Zi7in (annulus 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 nerv^e. Action. — To rotate the eyeball so that the pupil is directed inward. Fig. Superior rectus 515- Sphenoidal fissure External rectus Optic nerve (cut) Spheno-maxillary fissure. Inferior oblique Levator palpebrse superioris Superior oblique / Trochlea, tendon of superior oblique in place Internal rectus Inferior rectus Right orbit seen from before, showing- stumps of ocular muscles attached to common tendinous 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 external 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. Ohliqits Superior (Figs. 514, 516). Attachments. — The superior obli(iue muscle of the eyeball arises a little in front i>f 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 l)one. Thence it is reflected outward, downward, and backward, and, jjassing beneath the superior rectus, is inserted into the sclera beneath the outer margin of that muscle and at about the ecjuator 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 palpebr.ne superioris Superior oblique Superior rectus External rectus (cut) Internal rectus Optic nerve Stump of external rectus Trcn lilea , Insertion of levator palpebrEP superioris into upper tarsal plate Inferior oblique Inferior rectus Lateral view of ocular muscles after removal of outer wall of orbit; elevator of upper lid has been pulled upward and inward. 7. Obliquus Inferior (Fig. 516). Attachments. — The inferior oblicjue muscle arises near the margin of the orbit from a small dei)ression on the orbital surface of the maxilla. 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 cov^er of the e.xternal 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, nerves, and muscles this areolar tissue condenses to form their sheaths, and a special condensation, the capsule of Tenoji (fascia bulbi), 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 \\\^ space of Tetion (spatium 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 anteriorlv 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 fasciae musculares. These fasciae are somewhat thiclcer in their anterior portions than more posteriorly, and give off pro- longations to neighboring parts. From the fascia of the rectus superior a prolonga- tion passes to join the tendon of the levator palpebrae 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 off 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. 517. Levator palpebrae superioris Fat Superior rectus Capsule of Tenon \ Superior oblique (cut) \ Fat \ Optic nerve Space of Tenon Inferior rectus Inferioi oblique - Septum orbitale v.'>\ ''J, 7 tipper fornix of conjunctiva \ ,, i\\ vi4 Upper tarsal plats Lower tarsal plate 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 HLMAN ANATOMY. Fig. 518. ;v«- It has been demonstrated also that the oblique movements of the eyeball are by no means due to the action of the superior and inferior oblique muscles actinp^ 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 e.xternal recti cooperate with the superior oblique. A j)urely 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- (juiring 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. Diagram showing action ol ocular muscles. S,5'i. Q,Q\, sagitlal 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 the levator palpebr^e snperioris has been noted, and a slip from this muscle, termed the tensor trochlece, sometimes passes to the trochlea. 11. THE HYPOGLOSSAL MUSCLES. Genio-glossus. Hyo-glossus. 3. Stylo-glossus. 4. Lingualis. It is well known that the hypoglossal nerve 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. Hyo-Glossus (Fig. 1339). The hyo-glossus is described with the tongue (page 1578). 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 chondro-glossus, and the fibres arisincj 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-glossus and the latter the cerato-glossus. A bundle of fibres, forming: what has been termed the triticeo-s^lossiis, sometimes arises from the cartila.e:o triticea, situated in the lateral hyo-thyroid li.s:ament, 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-glossiis, 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 lingualis 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 phylogenetic 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 conveniently be designated the spiyio-hiimeral 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 axial 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, derived 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 vertebrae and are inserted into the spinous processes, and may therefore be termed the transversospinal 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 by 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 tnagnus Lumbar vertebra Subperitoneal tissue Fascia Peritoneum /^Transversalis fascia riu- deep fascia of the back invests all the muscles of the dorsal group, separating; tlicni from the spiiiu-luimeral j^roup. Above, the fascia is not especially stroni^, and in the cervical antl upper thoracic regions forms what is termed the fascia niichii;, which lies beneath the trapezius and rhomboid muscles. In the lower thoracic and liuubar regions, httwever, the fascia becomes considerably thickened, esjjecially that ])ortion which in\ests the sacro-spinalis {vertebral aponnirosis), form- ing a strong rhomboidal sheet extentling from about the level of the sixth thoracic vertebra to the tip of the sacrum, its anterior borders gi\ ing attachment to various muscles, while the posterior ones are attached to the posterior portions of the iliac crests, where it becomes contin- KiG. 519. uous with the fascia lata covering the gluteal muscles. This dense layer is termed the fascia lunibo-dorsalis ( Fig. 559), and is generally regarded as consisting of two lateral {)or- 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 vertebrae, above 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 \\'\(t faseia trajisversalis. Lumbar spine Skin -Transversal is muscle Internal oblique External oblique Triangle of Petit X /^^'Quadratus lumborum Latissimus dorsi AT Ant. layer of lumbo-dorsal fascia Superficial fascia Posterior layer of lumbo-dorsal fascia Siacro-spinalis Diagram showing formation and relations of lumbo-dorsal fascia to muscles of body-wall. (a) THE TRANSVERSO-CO.STAL TRACT. 1. Sacro-spinalis. 2. Ilio-costalis. 3. Longissimus. 4. Splenius. I. S.\cro-Spinalis (Fig. 520). Attachments. — The sacro-spinalis, sometimes termed the erector spines, 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-Costalis (Fig. 520). Attachments. — The ilio-costalis, also termed the sacro-lnmbalis, 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 groove 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 superior IT" uwrnm^^ — Rectus capitis posticus minor r .^ Jsgagg- Rectus capitis posticus major Obliquus inferior Semispinalis capitis (complexus and biventer) Spinalis colli Cervicalis ascendens --^a--. Transversalis cervicis ffffP^rT^i Accessorius (ilio-costali=; doisi) Sacro-spinalis (erector spinae) Ilio-costalis (ilio-costalis lumboruin) Dissection of muscles of back, showing transverso-costal and transverso-spinal tracts. 5IO HUMAN ANATOMY. crest are niainlv inserted into the lower six or seven ril)s, and form what is termed the ilio-costalis lumiK)riim. With the remainder of the ihac fil^rcs bundles arising from the lower live, six, or se\en ribs dissociate themselves to form the ili(»-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 cervicis 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 \crtebne. Nerve-Supply. — P'rom the posterior divisions of the spinal nerves from the lower cervical U) the first lumbar. Action. — The various portions of the ilio-costalis tend to bend the spinal column backward in the lower cervical, thoracic, and lumbar regions, and also to draw it somewhat to one side. They may likewise ha\ e 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 vertebrc'e. It is continued upward immediately medial to the ilio-costalis to be inserted into the mastoid process of tlie 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 vertebrae to form what is termed the lon^issinuis dorsi. The fibres of this portion of the muscle are inserted along two lines, the medial of which passes along the accessory processes of the lumbar vertebrce 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 transversalis cervicis, which continues the line of the longissimus to an insertion into the posterior tubercles of the transverse processes of the second to the sixth cervical vertebrae ; and, finally, the longissimus capitis or trachelo-mastoid is formed by bundles arising from the transverse processes of the three upjier 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, — P>om 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. Splenius (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 vertebrae and from the lower half of the ligamentum nuchee. It passes upward and slighdy 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 cervical vertebrae, forming the splenius cervicis. The upper portion, which is termed the splenius 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 nerves. 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 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. (d) THE TRANS VERSO-SPINAL TRACT. 1. Spinalis. 6. Intertransversales. 2. Semispinalis. 7. Rectus capitis posticus major. 3. Multitidus. 8. Rectus capitis posticus minor. 4. Rotatores. 9. Obliquus capitis superior. 5. Interspinales. 10. 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 vertebrae 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 inserted into those of the second, third, and fourth vertebrae. The spinalis capitis consists of bundles arisiyig 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 cervical to the last thoracic. Action. — To extend the spinal column. 2. Semispinalis (Fig. 520). AttaQhments. — 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 five 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 i^isei^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. Mui/riFiDUS (Fi}^s. 520, 521). Attachments. — The multifHlus {miiltifidus spimr) constitutes the middle layer of the muscles occupyint; the groove between the transverse and spinous processes Fin. 521. Iiitertraiisversales. ' postcrioies Levatores costarum -^ Lfvatores costarum Interspinales Intertransversalcs laterales Multifidus Rolatores Mullifidus Deep muscles of hack. of the vertebrae, and is covered, in the thoracic and cer\ical regions, by the semi- spinalis. It takes its origin 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 inserted 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 rotajte 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 {rotatores 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 been 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 insufificiently 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 inferior ■nuchal Hne. 33 514 HUMAN ANATOMY. Nerve-Supply. — By a branch from tlic ])(wtcrit)r division of the suboccipital nerve. Action. — To ilraw the- head backward and to rotate it towards the same side. 8. RiiCTUs Capitis Posticus Minor (Fig. 522). Attachments. — The lesser straight muscle ( m. rectus capitis posterior minor) arises from thv posterior tubercle of the atlas and jjasses upward, broadening as it goes, to be I'liscrtcti into the inner portion of the inferior nuchal line. Nerve-Supply. — Hy a branch from the posterior division of the suboccipital nerve. Action. — To chaw tlie head backward. Fig. 522. Rectus capitis posticus. minor 't Rectus capitis posticus. major Obliquus superior Suboccipital IriauKlf Obliquus inferior Supraspinous ligament Posterior tubercle of atlas Transverse process of atlas Interspinales \iiW ~ UJBB-iJ^Multifidus 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 nerve. 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 axis 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 TheSacro-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 axial 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 perfectiy a longitudinal direction and constituting the redus group ; a more lateral group, in which the fibres possess a distincdy oblique or transverse direction, and may consequently be termed the obliquus group ; and, finally, a hyposkeletal group, 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 rnuscles are concerned, a considerable amount of overlapping of certain regions, portions of myotomes which stricdy 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 consequendy impossible to refer them to their proper topographic positiori without doing violence to the individuality of the muscles which they help to form ; but when they remain practically disdnct 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 theback 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 Colics') and partly, after fusing with the superficial layer, which loses its fat, with the dartos of the scrotum. Mb HLMAN ANATOMY. (a) THK RECTUS MUSCLES. I. Rectus abdominis. 2. Pyraniidalis. I. Rectus Abdominis (Fig. 523). Attachments. —The rectus abdominis forms a flat but strong- muscle which tiaversfs tlic entire length of the ventral abdominal wall immediately lateral to the linea alba. It arises from the anterior surface of the xijihoid jjrocess of the sternum and from the cartilages of the fifth, si.xth, and seventh ribs, and is iyiserted by a strong tendon into the crest and symphysis of the jjubis. Fig. 523. Pectoralis major_J Tendon of rectus Rectus, cut and turned up Cut edpe of anterior, sheath of rectus Posterior sliealh of rectus External oblique Semilunar fold Transversalis fascia Deep epigastric artery. Rectus, stump Saphenous opening Sheath of rectus, turned over Tendinous intersection Rectus Crest of ilium Anterior superior iliac spine Pyramidalis External abdominal ring Cribriform fascia closing saphenous openitig Spermatic cord Muscles of anterior abdominal wall. 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 te7idme(£ 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 six occasionally occurring, while, on the other hand, they may be reduced to two. 2. Pyramidalis (Fig. 523), Attachments. — The pyramidalis is a somewhat variable muscle which arises below from the upper surface of the body of the pubis and from the symphysis and is inserted 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. Quadratus 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 obhque 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 flex the thorax 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 ^n^ 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 nei.uhl)orhood of the anterior superior iliac spine directly forward, and those from Poui)art's lii^ament forward and downward, all joining: in a flat aponeu- rosis which unites with the anterior abdominal ajKineurosis at the linea semilunaris. In its lowermost portion the aponeurosis unites with that oi the transversalis to form what is termed the conjohied tendon, and by this it is attached to the crest of the pubis. Fic. 524. Pectoralis major Serratus niaRtius Latissimus dorsi External oblique Petil's triangl Fascia lata Gluteus inaxinius- Origin of pectoralis major I'rom sheath of rectus Line of subcostal arch Linea transversa Linea semilunaris ^ I'inbilicus ea alba ' f<^' _^ Anterior superior iliac spine Su>iiensory ligament of penis I'Mupart's ligament rnialie cord Dissection of lateral body-wall, showing external oblique and adjoining muscles. Nerve-Supply. — F"rom the anterior divisions of the eighth to the twelfth thoracic nerves and from the ilio-hypogastric and ilio-inguinal nerves. Action. — The internal oblique acts very similarly to the external in compressing the abdominal contents, in drawing the lower ribs dow-nward, 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, 167 1). 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. Pectoralis major Serratus tnagnus Latissimus dorsi Edge of cut external oblique Internal oblique Posterior aponeurosis of internal oblique Iliac crest Fascia lata Cut edge of fascia lata Gluteus tnaximus Edge of cut aponeurosis of external oblique Linea alba Anterior aponeurosis of internal oblique Anterior superior iliac spine Conjoined tendon Suspensory ligament Cremaster fibres Dissection of lateral body-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. — T?o 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 tlie ihuni, and the outer one-third of Poupart's h.uainent. Its fibres pass horizontally inward to join the ventral abdominal aponeu- rosis alonj^j the linea semilv.naris ; the lower ones, however, liendiui.' 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. — PVom the anterior divisions of the seventh to the twelfth thoracic nerves antl from the ilio-hypotjastric and ilio-inyuinal nerves. Action. — To compress the contents of the abdomen. I'k;. 526. Serratiis maRiius Latissimus dorsi Edge of cut external oblique Edge of cut internal obli()ae Lumbo-dorsal fascia Fascia lata Cut edge of fascia lata Gluteus maximus Tensor fascite lata --- Pectoral is majot Edge of aponeurosis of external oblique ^1 — ^Edge of aponeurosis of internal oblique Aponeurosis of transversalis Rectus, covered by sheath Conjoined tendon Creniaster fibres Dissection of lateral body-wall, showing transversalis muscle. 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 abdominal 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. 521 thickened somewhat to form the deep crural 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 famus and body of the pubis. A litde 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 infundibuliform fascia, the inner margin of the funnel marking the posidon of the internal abdominal ring. 5. QUADRATUS LUMBORUM (Fig. 527). Attachments.— The quadratus lumborum is a flat quadrilateral muscle which lies towards the back part of the ab- dominal wall, extending between the 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 othei only with difficulty. The anterior layer, which arises from the trans- verse processes of the lower four lum- bar vertebrae 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 plexus. 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. 519) , 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 Fig. 527. XII rib Quadratus lumborum muscle of right side, seen from behind. by the lumbar arteries, and is covered towards its inner margin by the psoas major. 6. Intertransversales Laterales (Fig. 521). Attachments. — The lateral intertransversales are a series 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 abdominal aponeurosis. 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 reetus, except below, where they He a little 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 divides into two layers (Fiij. 529, . / ) which pass one in front and the other behind the rectus, thus forming a sheath for it ( vagina inusculi recti). The line of the division is indicated on the surface of the abdomen by a slight groove, and constitutes w^hat is termed the /ifwa scmi- //tnar/s. 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 ojjposite side to form a strong fibrous band which extends from the front of the xiphoid process of the sternum above to the Fig. 528. ■ symi)hysis pubis be- low, and is termed the //?u'a 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 expansion which occasionally contains muscle-fibres and is termed the ad- miniculuin lincac albae. T\\c 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 Ihie or fold of Douglas (linca semicircularis) (Fig. 523). Uncovered/ fibres of cxtt-r- \ iial oblique .Anterior^ sheath of rec- tus muscle Anterior superior iliac spine liitercoluiniiar fibres External abdoni nal ring Spermatic cord Line» transversa Linea alba . rred ex- ; nal oblique i^ — Linea semilunaris -Suspensory lij^ament of penis Superficial dissection of abdomen, showiiiK ventral aponeurosis. N'arious suji^fjestions have been made in explanation of this sudden change in the thickness of the p(jsteri(jr layer of tlie sheath of the rectus. It has been supposed that it was connected with the passage of the inferior epigastric artery into the substance of the muscle (Henle), a somewhat inadequate cause even if the point of passage of the arterv 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 u ith which the urinary bladder was in ccMitact in fcetal life (Ciegenbaur), and also by the view that the strain exerted on this portion of the sheath is less than that placed upon the upper jwrt, since the latter is acted on by fibres of the oblique and transverse muscles which have bony attachments drawn upward during inspiration, while the lower part is in relaUon 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 tiie development of the processus vaginalis peritonaei, the ixnich of peritoneum which in the embr>-o 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 obliciue 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 lower 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- gular sheet whose free concave lateral border forms the medial boundary of \h^ femo- ral rmg (annulus femoralis) 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 triangular 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 Transversalis muscle Fig. 529. A Transversalis fascia Peri- Division of aponeurosis of internal oblique toneum / Posterior sheath , — Rectus — , External oblique Internal oblique Skin / Aponeurosis of internal oblique Aponeurosis of external oblique Linea alba / Anterior sheath of rectus Superficial fascia Transversalis muscle Internal oblique Transversalis fascia / Peritoneum Linea alba Rectus Superficial fascia Skin Aponeurosis of external oblique Anterior sheath of rectus Diagrams showing constitution of sheath of rectus muscle. A, in 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 ot 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 ahcioniinal wall is traversed on either side by the spermatic cord f)r by the lij^Minentum teres of the uterus, and it is customary to regard the space occnjMed 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 Y^ in. ) in length and is situated immediatelv above Pouj)art's ligament, which it crosses obliciuely from above down- ward, medially, and forward. Its upper or inner end is al)out 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 ligament. It is marked by a more or less distinct depression on the posterior surface of the abdominal wall surrounding the spern.atic cord or round ligament, termed the internal abdominal ring (annulus in^uinalis Fig. 530. Anterior superior iliac spine- — Poupart's ligament Falciform process — Iliac portion of fascia lata — Saphenous openings- — Femoral arterv'-' Femoral vein Internal saphenous vein Aponeurosis^f external oblique Intercolumnar fibres External abdominal ring External pillar Internal pillar riinibernat's ligament,' inner boundary of femoral ring Pubic portion of fascia lata Spermatic cord Scrotum Dissection of right inguinal region, showing external abdominal ring and saphenous opening. 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 infundibnli- fortn fascia. The lower or medial end of the canal corresponds to the external abdominal ring Tannulus inguinalis subcutaneus) TFigs. 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 oblicjue. The fibres of the aponeu- rosis which bound this ring are somewhat thickened, forming what are termed the pillars Ccrura ) of the ring, the uppermost of which, the interna/ pil/ar Ccrus superior ), consists of fibres jiassing to the symphysis pubis ; the lower one. the external pillar (cms 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 intercolumnar fibres (fibrae intcrcrurales ) which extend laterally almost as far out as the anterior superior spine of the ilium. From the margins of the external ring an attenuated prolongation of the aponeurosis of the external oblique is continued downward o\er the spermatic cord as a thin membrane known as the intercolumnar 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 obhque, 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 conjoi?ied tendoyi, 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. Iiiterfoveolar or Hesselbach's ligament Weak area, Coriioined tendon Muscular fibres Lower end of Poupart's ligarrn Urachus Bladder Poupart's ligament Transversalis muscle Spermatic vessels External iliac arterf External iliac vein Deep epigastric artery (cut) Vas deferens Femoral ring Gimbernat's ligament Dissection of posterior surface of anterior abdominal wall, showing relations of conjoined tendon and its expansions to internal abdominal ring. 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 WaU. — Throughout its entire extent, with the exception of a small area in the median Hne 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 urach^is, 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 zimbilicus, may be seen on each side, passing from the side of the bladder -to the umbilicus and representing the obliterated hypogastric arteries of the foetus ; 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 abdominal 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 t\i^ plica umbilicalis lateralis, while the other is t\\Q plica epigastrica. These tAvo folds, together with the urachus, mark off the lower portion of the abdominal wall 526 HUMAN ANATOMY. into three areas or foveie (Fi^. 532). The median of these foveae hes between the urachiis and the lateral umbilical fold and forms the snpravcsica/ fossa, having for its floor the rectus muscle. Between the lateral umbilical and the epigastric folds is the inmr inguina/ fossa, having for its floor the conjoined tendon, and being therefore the region in which direct inguinal hernias arise ; and lateral to the epi- fic. 532. Peritoneal surface Plica epigastric; Hesselbach's triangle Vas deferens. External iliac arterj' External iliac vein Plica hypogastrica. I ) liter edge of rectus muscle Supravesical fossa Outer inguinal fossa Miner inguinal fossa Bladder, somewhat distended Median umbilical ligament Posterior surface of anterior abdominal wall of formalin subject. gastric fold is the outer iyii>;ui7ial 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 Hesselbach. It is almost identical with the middle inguinal fossa, and defines a little more precisely the seat of the direct hernias. (r) THE HVPOSKELETAL MU.SCLES. 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 abdotninal cavity is bounded above by the diaphragm ; below by the floor of the pelvis ; laterally by the diaphragm, the lower ribs, the abdominal muscles, and the lateral expansions of the ilia ; posteriorly by the diaphragm, the tenth, eleventh, and twelfth ribs, the lumbar muscles and vertebrae, the posterior portions of the ilia, and the ischial, sacral, coccygeal, and pubic bones ; and inferiorly by the levatores 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, aflect the relations of the contained viscera, and vary the compression to which'they are subject. The tonicity of the muscular walls brings about a normal intra-abdominal pressure which serves 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. It then, by increasing the outward pressure of the viscera 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 161 5 as are also the regions into which, for convenience, the abdomen proper may be divided by cer- tain arbitrary hues (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 flexure of colon, and part of right kidney. 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. 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. Right Lumbar. Ascending colon, part of right kidney, and sometimes part of ileum. 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 Lumbar. Descending colon, part of jejunum, and sometimes part of left kidney. Right Iliac Caecum 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. Left Iliac 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 nonnal 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 fiabbiness of abdominal muscles and accumulation of fat from want of exercise, and to compression of the upper segment by corsets ; it is increased by the stretching of repeated pregnancies. In infancy and childhood the abdornen 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 iIk- whole anterior abdominal wall becomes concave (scaphoid), especially the upper portion bounded bv the ensilonn cartilaj^e and the subcostal an^de,— the scrobiculus cordis ( paije 171 )'.— which, with the patient supine, may appear to rest directly upon the vertebral column, with walls more nearly vertical than horizontal. Coni^cnitaJ deformities of the abdominal wall usually consist in a failure of the ventral JMates 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 oblic}ue, — i.e., by a line just external to a vertical line dropped from the lowest part of the ninth rib, — are of importance in relation to the etl^ect 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 nerves is well shown by the sudden inspiratorv effort caused by a dash of cold water on the lower thoracic or abdominal region, six of these nerves 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 s?iper- 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 directly 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 Colles'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 by 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 have been described. PRACTICAL CONSIDERATIONS : THE ABDOMEN. 529 Wounds involving the 7nuscular layers of the abdominal wall may gape widely, but the differing directions of the fibres of the external oblique, internal oblique, and transversalis tend to limit this just as they lessen the after-risk of ventral hernia and favor certain physiological acts, as the emptying of the bladder, the bowels, or the uterus. This difference of direction is taken advantage of in gaining access to the abdominal cavity in some operations (page 535). Infection in the lateral intermuscular spaces usually spreads rapidly on account of the abundance of loose cellular tissue. The cellulitis or resulting abscess (or collection of blood or air) will be limited by the semilunar line in front, by the costo- chondral arch above, by Poupart's ligament and the crest of the ilium below, and by the edge of the erector spinae behind ; in other words, by the attachments of the muscles between which they spread (Treves). Beneath the abdominal wall, practically making a portion of it, lies a layer of loose connective tissue — the subperitoneal or subserous alveolar tissue — which connects the peritoneum with the parietes. ' ' Extraperitoneal connective tissue' ' has been sug- gested (Eccles) as a better name for it. Infection of this tissue, whether from without, as in the case of wounds, or by extension from some of the viscera lying wholly or partly behind the peritoneum, as in perirenal abscess or certain forms of appendiceal abscess, is likely to spread widely. Abscesses, especially if chronic, often gravi- tate into the iliac fossa and are arrested at Poupart's ligament by the junction of the transversalis and iliac fasciae, constituting a form of iliac abscess. If they are incised here, it will usually be necessary to go through only the abdominal muscles and aponeuroses, including the transversalis fascia, as the looseness and abundance of the subserous tissue will have permitted the abscess to dissect off and push upward the peritoneum. If the patient is supine, pus in the iliac fossae — i.e., in the shallow lower zone of the abdomen — may gravitate into the deep lateral recesses of the middle zone (page 161 5), and it often takes this direction in cases in which the source of infection is an appendix situated behind the caecum. It should be noted that a true iliac abscess is beneath the iliac fascia, and is therefore more apt to be guided by that fascia to the lowest point of the ilio-psoas space and to pass with the ilio-psoas muscle into the thigh, pointing at the outer side of the fem.oral vessels. The laxity of the subserous tissue favors certain retroperitoneal operations — e.g., uretero-lithotomy — by permitting the stripping forward of the peritoneum itself. The relatively great resistant power of the side of the peritoneum in contact with this tissue is subsequently described (page 1754). The fat contained in this layer — greatest in the lumbar region {perifiephj^ic fat) and in front of the bladder in the space of Retzius (the triangular interval defined by the symphysis pubis, the bladder, and the peritoneum), and abundant in the inguinal and iliac regions — may serve as a guide in approaching the peritoneum by incision, or may mislead if mistaken for the omental fat. The latter error has resulted, as, for example, in operation for ovarian cyst, in regarding the peritoneum as the cyst-wall, and in detaching it from the parietes over a wide area. This fat occasionally works its way through intervals between the fibres of the overlying fascia or muscles, especially along the linea alba, and constitutes the siibserotis lipomata, which, if large enough, are sometimes thought to be irreducible ventral herniae. The laxity of the subse- rous areolar layer between the bladder and the posterior surface of the symphysis pubis permits the peritoneum to be carried up on the summit of a distended bladder as it rises into the abdomen and thus facilitates extraperitoneal access to the an- terior vesical wall (page 1912). Its looseness over the iliacus muscle is a factor in the formation of the sac of inguinal hernia (page 1767). Wounds of the abdom- inal wall dividing this subserous' layer, but leaving the peritoneum untouched, should practically be classified among non-penetrating wounds, although in a sense the abdominal cavity has been opened. The symptoms and dangers of infec- tion will be as above enumerated. Wounds involving the peritoneum are called penetrating wounds, the dangers of which have been considered in the section on the peritoneum. In the closing of abdominal wounds the irregularities that may result from the differing directions of the muscular fibres involved — causing greater retraction at one 34 ^^o HIMAN ANATOMY. point llKin at another- sh<.uUl l>c rcme.nbered. This may make accurate suturing in hivcrs ciitticult but such suturing, together with careful approxunation of the edges of the peril.. neal laver. is necessary to lessen the risk of ventnil hernia. The respirators- movements prevent the attamment of absolute rest during the healing of abdonunal wounds, as they do after fractures of nbs ; but in both cases approximate rest, as secured by strapping with adhesive plaster or by abdominal binders, gives excellent average results. THE LOIN. The />os/ (movable on change of position) due to ascites, or the localized tympany due u< volvulus or' to the escape of gas from a ruptured appendix into a surrounding abscess ; or bv aiistu/taticm, as the absence of the usual intestinal sounds when a general peri- tonitis has arrested peristalsis ; or by inflation of the stomach, as on distinguishing between a growth of that viscus and a retroperitoneal tumor, or of the colon {^inde supra), which will then lie below and perhaps behind an enlarged gall-bladder .and in front and |)r(>bal)lv to the inner side of an enlarged kidney. These and other procedures are too technical to be described here in detail, but are mentioneil that they may be associated with the anatomical relations on which they dei)cnd. . , ., , , It should be noted that Treves and Keith state that the lieo-Cctcal valve corre- sponds to the spino-umbilical line, that the region of the \alve in a normal person is usually tender to pressure, and that the root of the appendix is placed more than one inch lower and perhaps more internally. This statement if contirmed will have a most important bearing on the value of certain symptoms thought to indicate the existence of appendicitis (page 1683), THE THORACIC MUSCLES. {a) THE RECTUS MUSCLES. The rectus abdominis, being supplied by the lower intercostal nerves, is evi- dently a derivative of the thoracic myotomes. That portion of the rectus group of muscles which should be derived from the upper thoracic myotomes is normally unrepresented, although the occasional extension of the rectus abdominis to the upper costal cartilages or even to the clavicle is probably an indication of it. {b) THE OBLIQUUS MUSCLES. 1. Intercostales externi. 4. Levatores costarum. 2. Intercostales interni. 5. Serratus posticus superior. 3. Triangularis sterni. 6. Serratus posticus inferior. Here, again, a considerable portion of the obliqui and transversalis abdominis is derived from thoracic myotomes. In addition, however, a number of muscles belonging to the group occur in connection with the ribs. I. I.NTKRCOSTAI.ES EXTKRXI (Fig. 537). Attachments. — The external intercostal muscles are eleven in number, stretching across all the intercostal spaces from the lower border of one rib to the upper border of the next. The fibres, which are largely interspersed with strands of connecti\'e tissue, are directed downward and forward, and form in each intercostal space a sheet which extends in the upper spaces from the tubercle of the rib to the junction of the rib with its costal cartilage and in the lower spaces is continued upon the cartilages. The interval between the medial borders of the upper muscles and the border of the sternum is occupied by a sheet of connective tissue known as the external intercostal fascia or anterior intercostal aponeurosis. Nerve-Supply.— By the anterior divisions (intercostal nerves) of the thoracic nerves. Action. — To draw the ribs upward. THE THORACIC MUSCLES. 539 2. Intercostales Interni (Fig. 537). Attachments. — The internal intercostals lie immediately" beneath the external and, like these, extend across each of the intercostal spaces. The fibres have a direction almost at right angles to those of the external intercostals, being directed obliquely downward and inward from the lower border of one rib and its costal car- tilage to the upper border of the next. The muscle-sheets so formed extend from the medial extremity of each intercostal space as far back as the angles of the ribs, becoming there continuous with an i?iternal intercostal fascia or posterior intercostal Fig. 537. I rib Clavicle External intercostal fasc la -'-- — Internal intercostal mus- cles, anterior part covered by external fascia Internal intercostal muscles., exposed after removal of external L pper external intercostal muscles Internal intercostal fascia Lower external intercostal muscles Dissection of thoracic wall of left side, showing intercostal muscles and fasciae. aponeurosis which continues backward to the tubercles of the ribs. The medial fibres of the muscles of the lower two intercostal spaces become continuous with the upper portion of the internal oblique muscle of the abdomen. Nerve-Supply.— The anterior divisions (intercostal nerves) of the thoracic nerves. Action. — To draw the ribs upward. The Subcostal Muscles.— Posteriorly the fibres of the various internal intercostals do not confine themselves to a single intercostal space, but extend downward to the'ne.xt space below, spreading out in the muscle-sheet of that space. These fibres, which var}- greatly m the ex- tent of their development, form what are termed the subcostal muscles. 540 HIM AN ANATOMY ;v Tkiancu'i.aris Sterni ( Fil,^ 538). Attachments. — The inani,nilans stc-rni ( m. transvcrsus thoracis) forms a thin sheet silu.iteii upon the posterior surface of the nieiHal i)ortion of the anterior thoracic wall. It ar/srs at one ed.ue by a series of slips from the costal cartilages of the secontl or third to the sixth or seventh rib ; the upjjer fibres are directed obHquely downwaril and mediallv and the lower ones transxersely to be inserted by a thin, Hat tendon to the sides of the lower portion of the sternum and to the xiphoid process. The lower fibres of the muscle are practically continuous with those of the transversus abdominis. Nerve-Supply. — By the anterior divisipns (intercostal nerves^ of the second or third to the sixtli or seventh thoracic nerve. Fig. 538- Internal mammary artery Dissection of anterior thoracic wall from behind, showmg 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.vtorks Costarum (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 laterallv to be inserted into the posterior surface of the next succeeding rib {levatores costarum breves) between the tubercle and the angle, some of the fibres of the lower mus- cles passing over a rib to be ijiserted 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. ^e,. Serratus Posticus Superior (Fig. 539). Attachments. — The superior posterior serratus is a quadrangular, fiat muscle which arises by a flat tendon from the lower part of the ligamentum nuchae and from the spinous processes of the seventh cervical and upper two or three thoracic ver- FiG. 539. r Coniple\Ub Spleiiius capitis et Levator any^uli scapuUe Serratus posticus sup Trapezius — -^ -^=-- (cut) / Vertebral- apoiieurosis — Trachelo-mastoid Internal pterygoid Complexus Biventer cervicis fcalenus medius VII cer\'ical spinous process Complexus Scalenus posticus -Accessorius I. Ilio-costalis < Semispinalis dorsi . Longissimus dorsi Dorsal, cervical, and 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 54^ HUMAN ANATOMY. directed upward and laterally and are inserted into the outer surfaces of the lower four ril)s. Nerve-Supply. l'Vt)in llu- anlrrior divisions of the ninth to the twelfth thoracic ncr\ ts. Action. — To (.haw the ribs to which it is attached downward and outward. The muscle contracts durinif inspiration and assists in this act by counteractinii: tht- tendency which the costal part of the diaphragm has to expend a portion of its con- traction in drawin.i,^ the lower ribs upward and inward. Variations.— X'ariations in the t-xtent of their origin are not uncommon in both the posterior serrati. Strt-tcliiiiK between them there is an aponeurosis, termed llie vertebral aponeurosis, which represents the dejjeneralecl 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. (f) THE HYPOSKELETAL MUSCLES. 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 lamelke which surround the various structures of the neck region. Pos- EiG. 540. Sterno-hyoid Thyrohyoid Omohyoid Arytenoideus Inferior constrictor Carotid sheath - Prevertebral layer Platysma Sternomastoid I.ongus colli Scalenus anticus Scalenus medius Scalenus posticus Trachelomastoid Levator anguli scapuke Splenius colli Multifidus spinie Semispinalis cervicis Trapezius Splenius capitis Thyroid cartilage \'ocal cord Arytenoid cartilage Pharynx Right carotid artery Right internal jugular vein .Vertebral artery V cervical vertebra Spinal cord Ligamentum nuchae Complexus Section across neck at lower border of fiflh cervical vertebra. teriorly the f.tscia is attached to the ligamentum nuchae and, traced laterally, it is found to duide 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 divides 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 siiperfieial 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 greater 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 clavicle, and, more medially, in the interval between the lower portions of the two sterno-cleido- mastoid muscles, it splits into two lamellae, enclosing what is termed the spatium suprasternale 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 fatty 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 thora.x 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 prevertebral 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-thyroid membrane near the median Ime and immediately below the hyoid bone. Nerve-Supply.— From the first, second, and third cervical nerves, through the ansa hypoglossi. Action. — To draw the hyoid bone downward. 54^ HUMAN ANATOMY. Variations.-Tl.e sUrno-liyoid may arise entirely from the clavicle or it may extend its origin to the c- rtilaee of the first ril./ It is often divided transversely bv a tendmous hand which may oaur e herllH^s K.wer part ..., a line with tin- intermediate tendon of the omo-hyoid or, more riJely, in its u,n>er part on a level with the insertion of the sternu-thyro.d. 2. Omo-Hyoideus (Fig. 541). Attachments.— The omo-hyoid is a long, flat muscle consisting of two bellies united hv an intermediate tendon. The inferior belly arises from the lateral portion of the superior border and the superior transverse ligament of the scapula, and is directed forward, mediallv. and slightly upward to terminate in the intermediate tendon This lies behind' the clavicular i)ortion of the sterno-cleido-mastoid, and is enclosed bv the middle laver <.f the deep cervical fascia a specially thickened portion of which binds it down to the posterior surface of the cla\icle and to the first rib The ^uf^erior bellv 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. P'lc. 541. Styloid process Stylo-gtossus — Stylo-pharyngeu Stylo-hyoi DiRaslric, posterior belly. Rectus cai)itis anticus major. Spleiir Sleriio-cleido-mastoid Levator angiili scapulae Buccinator Orbicularis oris Depressor anguli Depressor labii iiiferio':3 — Hyo-glossus — Digastric, anterior belly Mylo-hyoid ■■ Hyoid bone — Inferior pharyngeal constrictor —.-Thvro-hvoid Omo-hyoid, anterior belly Scalenus anticus Omo-hyoid, posterior bell Muscles of rhe neck; larynx has been drawn foiward. 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 plexus and sometimes with the third portion of the subclavian artery, the transv^ersalis 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 lower 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 irifre- quently fuses more or less completely with the sterno-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 inserted 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 larynx downward. Relations. — Superficially the sterno-thyroid is covered by the sterno-hyoid. Deeply it is in relation with the inferior constrictor of the pharynx, 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-Supply. — 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 fixed, 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. inusculi 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 thyroid cartilage to the lobe, isthmus, or pyramid of the thyroid gland. It is termed the levator glandulce thyroidece, 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 low^er 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. (*) THK OHLlgl LS MUSCLES. Scalenus amicus. 3- Scalenus posticvis. Scalenus inedins. 4- Rectus cajjitis lateralis. S. liUertransversales anteriores. I. .ScAi.KM s Anticus (Fig, 542). Attachments.— The anterior scalene (in. scalenus anterior) arises by tour tendinous slips from the anterior tubercles of the transverse processes of the third to the sixth cervical vertebr;e. The four slips unite to form a rather Hat muscle which extends downuartl and forward t<. be insnird into the scalene tubercle on the upper surface of the first rib. 1m(;. 54^- Stenio-mastoid, stump Rectus capitis anticus major Levator angnli scapulae Subscapulari" Serratus magnus, middle portion Scalenus amicus Scalenus me«lius Scalenus posticus I rib Serratus niagnus, upper portion Dissection of riKbt side of neck, showing scalene and 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 fi.xed, it will then raise the first rib, assistinij in inspiration. Relations. — The anterior scalenus lies in front of the roots of the brachial plexus, and near its insertion it passes o\'er the second portion of the subclavian artery and under the subclavian vein. The phrenic nerve rests upon its anterior surface during its course down the neck. 2. SCALENITS MeDIUS (FigS. 54I, 542). Attachments. — The middle scalene is situated behind the scalenus anterior. It arises by six 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 inserted 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 cenacal 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 scalenus 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 sexenth cervical vertebrae 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. bounded l>v the lateral border of KiG. 543- DiRastric, posterior belly Slylo-hyoid (cut ) Slemo-ruasliiid One of these trianijles. the posterior, is Doui - , , the upper part of the trapezius behind and by the lateral border of the sterno- cleido-mast..id in fn.nt. and has for its base the upper border of the claviclr between the insertion of these two muscles. The anterior triangle x% reversed with respect to the posterior one. havin.ii its ape.x downward and its base above. Its ateral 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 Inn 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 muscular ox 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 omohyoid 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. Trapezius /<:. I )i.icastrio . anterior belly SUEMAXIILARV TRIANGLE SUPERIOR CAROTID TRIANGLE — Oino-liyoici, anterior belly inferior carotid (muscular) triangle Onio-hyoid, posterior belly SUBCLAVIAN TRIANGLE Triangles of neck. {(■) THE HYPOSKELETAL MUSCLES. I. Longus colli. 2. Rectus capitis anticus major, 3. Rectus capitis anticus minor. I. Longus Colli (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 vertebra-, the slip to the atlas being inserted into its anterior tubercle. From the lower part of the medial portion slips are given of! which con- stitute the inferior 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. Anterior tubercle of atlas Longus colli, superior oblique , portion ' Rectus capitis anticus major- Lotigus colli, median portion Longus colli, inferior oblique portion Scalenus medius Scalenus anticus I rib Clavicle_ l^VII cervical vertebra I thoracic vertebra Deep dissection of neck, showing 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 cervical vertebrae, 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 (in. rectus capitis anterior) is a short, Hat inusck- which tin'scs from the anterior surface of the lateral mass of the atlas antl is ciirected ohiitiuely ujnvard and medially to he inserted into the basilar portion of the occipital bone, immediately behind the insertion of the longus capitis. Nerve-Supply. — Hy the first cervical (suboccipital) nerve. Action. — To rte.\ 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 transxerse 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 jx)orly 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 exceptionally 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 pre\'ented 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 se\enth cervical spinous process to the ligamentum nuchae ; 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 (;5) a process — prevertebral 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 oesophagus 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 m 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 (f), 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 (d) 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 Space 33 Thyroid body CEsophagu Carotid artery. Internal jugular vein Vertebral vessels Space I ^ Extern, jugular vein /,*^' Spinal nerves, cut j„''' obliquely Spinal cord Trapezius muscle. Vertebral spine. Space 3b Fascia covering posterior triangle Fascia passing beneath trapezius amentum nuctise Section across neck at level of seventh cervical vertebra. This relation of the omo-hyoid is of value in enabling that muscle, when the hyoid is fixed, 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. Hyoid bone below : or. in othrr words, these two muscular forces are acting on the interposed pericardium in (.i)i)osite directions, and so render it tense and resisting:. And the special object, no doul>t, of this piece of anatomy is that (.hum^ a full inspnation, when the lunj!js are ilistended with air and the rii^ht side of the heart K'ort^a-d with blood from a suspension of respiration, the heart should not be encroached upon by the surroumliny lungs." . The pre\ertebral layer ( <", Fig. 546) lymg between the oesophagus and spme 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- panied them into the axilla. Another way oi elucidating the j)ractical effect of the somewhat complex dis- tribution of the cervical fascia is to regard the tJiree 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 s|)ace 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 KiG. 546. space does not exist in fact at the / summit of the neck where the two I k. layers are one, but at the base its ^"^ ill.- • 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 the superficial layer attached to the anterior and posterior borders of the sternum, — Grijber's ' ' suprasternal intra-aponeurotic space," " Burns's space." It contains fat and lym- 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 = 3a + 3<^, Fig. 545): between the pretracheal and prevertebral layers. This in- cludes all the principal structures of the neck. As it communicates di- rectly with the thorax and axilla, supjHHation may travel in those di- rections. It is divided into minor spaces (T,a and T,d) by a layer of fascia coming from the under surface of the sterno- mastoid muscle and by the bucco-pharyngeal fascia, a thin laver that comes of? from the prevertebral fascia where it leaves ""the carotid sheath, and which lines the constrictors of the pharynx, lea\ing 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. Retrovisceral (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 we may conclude that superficial to the outer layer (a. Fig. 545) there might Space 2 Bunis"s spnii Space 4 , I.rft innomin.ntc \ Aortic . Diagram showing relations of cervical fascia in longitudinal .section. fascia 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 "" J j^u^ l*^'" *^"'^' (Space I, Fig. 545), and, in the absence of tension, are unat- tended by throbbmg pam or marked constitutional symptoms. PRACTICAL CONSIDERATIONS : THE NECK. 553 The space between ^ and b (3^, 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 dyspnoea 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 probably 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 /..||f \ 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 " 7' /' /'-""^^^^^-Hyoid bone of the third division of the fifth nerve through the fora- ,' / Outeriayer 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 ^^^^^^XolTiMx^^o^^i^S- 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. Tmnors of the neck may originate in any of the diverse structures of that region. It may be mentioned here that their situation above or beneath 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. 354 HUMAN ANATOMY. Lipoma is frequent ; filironia and enchondroma are occasionally seen in tin region of the liiranientinn nuchie : primary carcinoma is rare. Congenital cysts— " hydroceles" — of the neck are found beneath the deep fascia, usually 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 tin formation of diverticula from the laryngeal mucous membrane. In any event, thev ramify in the various intermuscular spaces, and their complete removal is therefore verv difhcult. Hranchial cysts and dermoids are not infrequent. They should be studied in connection with the eml)ryology of the region. Congenital tumor of the sterno-mastoid is a condition resulting irom either rup- ture of muscular fibres or bruising of the muscle against the under surface of the symphysis during tlelivery. It may be a cause of torticollis. Torticollis— " wrv-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 comple.xus. 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 e.xternal, 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 exclusively 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 ii) 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 jiosteriorly 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 anterif)r triangle, although they are both under cover of the anterior edge of the sterno-mastoid. The anterior triangle 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 withm these various triangles will be described in connection with the vessels, nerves, etc. The dividmg 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 jugular vein 'k Trapezius- Acromio-clavicular joint Acromion process Submaxillary gland Digastric, anterior belly Hyoid bone Thyroid cartilage Cricoid cartilage Lesser supraclavicular fossa Suprasternal notch (jugular fossa) Greater , tuberosity ^' of humerus' Omo-hyoid, posterior belly Supraclavicular fossa Infraclavicular 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 536 HUMAN ANATOMY. posterior belly rim tlie brachial jikxus, which can often he 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 bet%vcen 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 sulmiental 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 {pomuni Adami ), the crico-thyroid space, the cricoid cartilage, and sometimes the upper rings of the trachea mav 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, w^hich perhaps typifies the other extreme of unchangeability. DiAPHRAGMA (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 derivative of the cervical myotomes. It represents the upper portion of a structure which is termed in embryology the septum transversum (page 1701 ), 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 cervical myotomes named. The diaphragm is a muscular sheet composed of fibres radiating from the lower border of the thorax and from the upper lumbar vertebrae towards a central tendi- nous area, termed the centrum kndincwn. According to their origin, the muscle- fibres may 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 sternum 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 origi7i 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 origin (i) from two tendinous arches, the interjial and external arcuate ligaments, which pass over the upper portions of the psoas (arcus 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 crura, from the anterior and lateral surfaces of the upper three or four lumbar vertebrae. 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 Lower end of sternum Inferior vena caf a Right portion of. central tendon Right crus — L* Right greater splanchnic nerve XII rih Middle portion or central tendon _ CEsophagus Left portion ot central tendon Aorta Thoracic duct Inferior vena cava Bifurcation of aorta, turned forward XII rib External arcuate ligament Quadratus lumborum , I 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 (^median arcuate ligament) 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 hiatits cesophageus, through which pass the oesophagus and the vagus nerves and oesophageal branches from the gastric artery and veins. The centrjim tendine2(7n, 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 vemz cavcB {foramen qiiadratum') , 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 docs not, however, form a simple curve, but is divided by a median depression, which traverses it from before backward, into two secondary lateral domes which are unecjually developed, that of the right side extending ujnvard as far as the level of the junction of the fourth costal cartilage and rib, while that of the left reaches onlv to the fifth costo-cartilaginous junction. Nerve-Supply. — From the third, fourth, and sometimes the fifth cervical nerves, bv the phrenic nerves. Action. — To increase the vertical diameter of the thorax, a contraction of the muscK-tibrrs lUpressing the summit of the dome. Relations, The upper surface of the diaphragm forms the floor of the thoracic cavity 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 brandies of the ccjeliac artery. Variations. — Occasionally the diaphraem is incomplete in its posterior portion, a condition which permits the formation of conijenital dia|)hragniatic hernias. lunbryologically 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 the 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 crura and pass to the lower jiortion of the (esopiiagus, mingled with dense connective-tissue fibres, and others which pass from one crus or the other into the mesentery of the upper part of the jejunimi. Probably the suspensory uuiscle of the duodettum, ox inuscle of Treitz, which passes from the left crus to the 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 PPXVIC 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. 55:). iac fascia External iliac vessels Ilio-pectineal line Acetabulum I-evator ani Obturator interiiu Alcock's caiial_ ;_'j;^ ■ Pelvic fascia Obturatf)r fascia Anal fascia Ischio-rectal fossa Seminal vesicle External sphincter Internal sphincter Rectum Diagrammatic frontal section through pelvis, showing relations of fascial layers to pelvic wall and floor. \ Fascia endopelvina \ Pelvic fascia Recto-vesical layer the point mentioned, however, the ventral musculature again appears in the trunk in the pelvic, the perineal, and occasionally the coccvgeal 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 (linca 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 pelvic 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 litde above its lower border, as a lateral pubo-prostatic {pubo-vesical) ligament. Along this tendi- nous arch the pelvic fascia gives off a layer which passes inward to the pelvic viscera, and is termed the fascia endopelvina. In its anterior portion this forms an investment 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 media?! pubo-prostatic {pubo-vesical ) ligameiit. The continuation of the pelvic fascia passes downward over the surface of the pelvic 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 obturator fascia. Along its upper border, nearly corresponding with the arcus tendineus of the pelvic fascia, but lying above 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 levator 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 two layers to form a canal, the canal of Alcock, along which the pudic vessels and nerve pass towards the perineum. In the above description the term pelvic fascia is applied to the layer of fascia which lines the entire true pelvic cavity, — that is to say, the funnel-shaped cavity included between the pel- vic brim and floor. This conception, employed by 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 hue to the white line, the continuation down- ward over the pelvic diaphragm being termed the recto-vesical fascia, irom 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 m. levatoris ani). These two bands are, however, 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 diaphragm, separating the pelvic from the perineal region. The more anterior and larger of these muscles is the levator ani, the coccy- 5bo HUMAN ANATOMY. geus lyinjj alonjj its posterior niari;in. Above the upper marp;in of the latter, and formin^^ the posterior wall of the i)elvis, 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. Lkvator Am (Fig. 551). Attachments. — The levator ani arisis 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 upper 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 coccyx 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 directlv 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 Fio. 551. X Pyriformis Coccygeus Ischial spine ' Obturator ■ iiitenius While hne^ \ Levator ani^ Tip of coccyx Ischial spine * — Rectum (cut) Olnuralor inter- uus covered by pelvic fascia -Urethra (cut) 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 liranches of the pudic nerve. Action. — To bend the coccyx forward and to raise the pelvic floor and viscera. Variations.— Tlie levator ani is always a well-developed muscle, althousjh 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 ilium 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 se])arated 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 lexator 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 ni. 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. 551, 603). Attachments. — The coccygeus, which forms the posterior and lesser portion of the diaphragma pelvis, hes 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-coccygeus, and is represented in the lower mammals by a muscle attached to the caudal vertebras 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 the sacrum and inserting into the coccyx. 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 third, and fourth sacral foramina. It Fig. 552. Greater sacro- sciatic foramen Dorsum of ilium Greater sacro- sciatic foramen Pyriformis Obturator ixiternus Capsule of hip-joint Obturator internus Greater sacro-sciatic ligament of the sacrum, between the flrst, second passes laterally through the great sciatic fora- men, receiving a bundle 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 biirsa m. py^^formis, inter- venes between the tendon of the muscle and the summit of the great trochanter. 36 Deep dissection, showing insertion of pyriform, internal and external obturator muscles. 5(^2 HLMAN ANATOMY. Variations.— Tlu- pyriforniis is occasionally absent, aiui it may be more or less fused with the gluteus minimus or medius. Freciuently it is divided into two or more portions by being perforated bv the sciatic nerve. ... . , • „ l-"rom the comparative standpoint the pvnformis is to be regarded, m part at all events, as a portion of tlie nuisculature extendin.ii l)et\veen the axial skeleton and the pelvic girdle or limb, and is representeil in the lower vertebrates by the taiiJo-Jiinora/is. {b\ Till': i"i:kiNi:AL mtscles. 4. Hulbo-cavernosus. Sphincter ani c.xtcrnus. Transversiis perincei superficialis Ischio-cavernosiis. 5. Transversiis perin^ei profundus. 6. Compressor urethra:. In the early stages of development, while tlie urogenital ducts and the digest- ive tract open into a common terminal cavity, the cloaca, muscle-hbres derived from the second, third, and fourth sacral myotomes arrange themsehes in a flat layer around the external aperture of the ca\ity, forming what is termed the sphiuctcr cloaae. Later, with the di\ision 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 witli the changes which I'racliiis. Supravesical space Syinphjsis pubis Suspensory ligament of TrianKular lij^ament, sup Deep perineal inlerspac TriaiiRular ligam't, inf. la t'relhra Penis, cpri)us cavernosum _^/ — Prostate Cow per's gland Perineal centre fascia perineal interspace 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\i 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 anteriorly with the superficial fascia of the lower portion of the anterior abdominal wall, is, like this, composed of two layers. The more sui)erficial 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 /^^r/V? of Colles, 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 layer, to unite with the superficial fascia of the gluteal region. This posterior portion of the superficial perineal fascia may conveniently be termed the circimianal 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 fascia. This space is the superficial perifieal 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 triangidar 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 superior 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-ui'ethral 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 coccyx 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 tendo7i 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 extending to the integument. The outer two of these layers traverse the substance of the external 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 have been regarded as distinct muscles. One of these lies imme- diately beneath the skin surrounding the anus, and has consequently been termed the spM7icter 5^4 HIMAN AXA'nniY. suh,u(aun,s. The sp/ihutrr snf>nfuia/is is tliat iM.rlu.n ot tlie muscle uliich lies above and to [he uter ;Ule of tin- sphin.te/ snhc.taneus. while mure deeply st.ll. and tornimg a nuK-hke mss c.t fibres cL.selv encirclinK the rectal wall is the sphwctcr pyojundus It is t.on> he Sincter si.brutaneuA that the retractor scroti, when prese.U. .s derived, and fibres from the sphincter superficialis are fre«iuently prolonged in front of the anus t<. various insertions as for instan.e to the tuber ischii. the lower layer ot the tri-oimni iiro-enitale or even the sheath of e corpora cavernosa. This lavering of the external si.hiiuler is pr..bal)ly a relic of the separa- ti..n of the si)hincter doacx into tw.. layers, the subcutaneous and superhcial sphincters re|)re- sentinj,' a portion of the superficial layer, while the deeper one is responsible tt)r the si)hincter priifiindiis. 2. Tkaxsvp:rsus I'i.rinki Sitkri-iciat.is (Fig. 554). Attachments.— The superficial transverse jicrineal nuiscle is an exceedingly variable sheet of imiscle-tibres situated in the" posterior portion of the superficial perineal interspace. In its typical form it may be described as a band of fibres which Fio. 554- Bulbo-caveriioMis ^ Ischio-cavernosus Trans. periiKi-L superncialis Obturator intertills White line Levator am Coccygeu-- Triangular liga- mciil. inf. layer Tendinous jierineal centre Tuberosity of ischium .\nus Obturator fascia ,; Sphincter c.xternus Levator ani Z Gluteus niaximus (cut) — Greater sacro-sciatic li^ment Tip of coccyx Muscles of male perineum and pelvic ffoor. seen from below. arises from the medial stirface of the ischial tuberosity and passes directly medially to be inserted into the central tendon of the perineum. Nerve-Supply. — From the perineal branches of the piidic nerve. Action.— To assist in fi.xing the central tendon of the i)erineum 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 ani and from the external sphincter ani and makes connections with the bulbo-cavernosi. 3. IscHio-C.wF.ftxosrs (Fig. 554). Attachments.— The ischio-cavernosus, also named the erector penis {erector clitoridis), represents the lateral portion of the sphincter cloacae. The two muscles occupy the lateral parts of the superficial perineal interspace, each arisi?ig from the base of the tuberosity of the ischium, enclosing the base of the crus 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 chtoris). 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 uri7ice, the two muscles of opposite sides are united in a median fibrous raphe which extends forward 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 muscle of Hoiiston, or compressor vencB dors alls penis. In the female, in which the muscle has been termed the sphincter vagincs (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 nerve. 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) 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 tuberosities in common with those of the transversi superficiales and pass forward and medially to unite with the bulbo-cavernosi forming what have been termed the ischio-bulbosi. 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 nerve. 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 inferior 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 into the walls of the vagina as it traverses 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-pubicus 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. Tlic limbs make ihcir appearance as two pairs of flat buds (Fig. 69), the upper {)air beini,'^ situated in tlie lower cervical and the lower pair in the lower lunil)qr and upper sacral rej^ions. Into the buds jirocesses extend from the myotomes of the regions concenied and apparently K'^'<-' rise to the more proximal muscles of the liml). but that they are the source of all the limb musculature is as yet undetermined. The i,aeater mass of this musculature develops from a blastema which occujMes 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 lumlxir 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 \entral or pre-axial group and a dorsal or post-axial group, and in harmonv with this arrangeinent the nerve-fibres which pass to the muscles arrange themselves in \entral 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, except in the more proximal portion of the limb, the pre-axial musculature is on the posterior and the i>ost-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 exit 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 mav 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 off, so that it is onlv the more cen- tral (or upper) nerves of the series that reach that portion of the iDud 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 APPENDICULAPv MUSCLES. 567 Dorsal muscles Intel muscular septum Mesoblastic imb core X Post-axial muscles Latero- ventral muscles Body-cavity Pre-axial muscles 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 supplied 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-axial musculature of the brachial region no trace is to be found of the segments supplied by the eighth cervical 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 peh'ic 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- and post-axial groups of limb-muscles. {Kollmann.') 568 HUMAN ANATOMY. THE MUSCLES OF THE UPPER LIMB. TUF MUSCLKS KXTKNDINCi HKTWKEN THH AXIAL SKELETON^ AND THE PECTORAL CilRDLE. (a) TlIK I'KK-AXIAL MUSCLES. Pectoralis major. 2. T,. Subclavius. Pectoralis minor. The Pectoral Fascia. — The superficial jjectoral fascia is continuous above with the suptrtK-ial ci-rvical and below with the superficial abdominal fa.sciai, and covers the entire anterior wall of the thorax. It usually contains a considerabh' amount of fat and has emliedded in it the mammary t,dand. 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 Fu;. 556. Exterii.-il anterior thoracic nerve Cephalic vein ^anch of acroinio-thoracic arter>' Deltoid Distal stump f)f__£ pectoralis major Cut edge of deep- pectoral fasci;i Pectoralis major, cut edge of clavicular portion Pectoralis mnior enclosed \\\ clavi-pectoral fascia Pectoralis major, cut edge of sterno-costal portion Dissection of thoracic wall after removal of greater part of pectoralis major, showing clavi-pectoral fascia enclosing pectoralis minor and continuous with axillary fascia. 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 coverint^ 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 w-hich 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 border 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-claviciilar fascia ox costo-coracoid membraiie. 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 ^ liga?nent (Fig. 560), which passes obHquely downward and laterally from the clavicle to the coracoid process. The coraco-clavicular fascia occasionally contains muscle-fibres (the in. coraco-davicularis) , and is usually perfo- rated by the cephalic vein on its way to join the axillary, 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 ) the pars cla- vicularis, which arises from the inner half of the anterior border of the clavicle ; (2) the pars sterno-costalis, which arises from the anterior surface of the sternum and the upper six costal cartilages ; and (3) t)\& portio abdominalis, which arises from Fig. 557. Deltoid- Pectoralis major, ^f clavicular portion Clavicle Sternum Pectoralis major, sterno- costal portion Serratus magnus Latissimus dorsr Pectoralis major abdominal portion Dissection of thoracic wall, showing pectoralis major. the upper part of the anterior layer of the sheath of the rectus abdommis. 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 passmg 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 sontinuous 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 ner^•es by fibres from the lower four cervical and the first thoracic nerves. 370 HUMAN ANATOMY. Action.— When the arm is abducted to a position at riji^ht anodes to the body, the peclorahs 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 pronouncetl and the Hexor action less so, and a slight amount of internal rotation apj)ears. When the arm is raised above the level of the shoulder and fixed, the muscle will assist in drawing the trunk u|nvard, as in climbing, and it will also assist in raising the rii)s in forced insi)iration. Variations.— Ill tht- lower mammals tin- pectoralis major is represented 1)\ a number of distinctly separate portions, a ci)nclitit)n 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-ct)stal and abdominal i)orti()ns may be i^reatly reduced or even absent. The ;/;. s/e-rmi/is is present in somethin.i!; 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 nuiscle has been variously regarded as a portion of the platysma, a downward pro- lonjjation of the sterno-cleido-mastoid, an upward prolonj^ation of the rectus abdominis, and as a displaced portion of the pectoralis major. The fact that in the majority of cases it is sup- plietl by branches from the antt-rior 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 |>ortion of the rectus trunk muscles. The ihondro-cpilrochlcaris 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 metlial epicondyle of the humerus. 2. Pector.vlis 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 ner\'es from the se\enth 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 plexus. 3. SiTBCLAVius (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 sixth 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 nidimentary. 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 stcruo-choudro-scapularis, the scapulo-claviciilaris, and the sterno-clavicularis (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 man as a band arising from the points named, or from either one of them, or from the first rib, and mserting into the coracoid process of the scapula. In those mammals which possess a rudimentan- 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 pamiiculiis car?iosus, 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 axillary 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 supplied by branches from the anterior thoracic nerves. {b) 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 wall 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 96°, the further elevation through aniother 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 scapulae. 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 tipward 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.— Tin- nri^Mii mav txtt.iul to tin- transvt-rse processes of all the cervical ver- tebne, and may be CiHilinuecl upon the mastoid process above and iijion the uiiper ribs below. Slips may occur coniiectiiiK the levator with various neiKlil>oriu.s; uuisiles, the most iuterestinjj: of these connections beiny: that with the serratus maKUUs, since comparative anatomy shows that the levator was primarilv coutiinious with that nnisde. A .separated portion ot'the outer part of tiie nuiscle is occasionally inserted into the outer end of the clavicle, forminij what is termed the levator i/aiicuhr. 3. Rhomboideus Minor ( Fii,^ 559). Attachments. — The rhomhoideus minor is a band-like muscle which arises from the lower part of the ligamentum nuch?e and from the spinous process of the Fig. 558. Serralus posticus superior Levator anguli scapulae Superior angle of scapula Supraspinatus Coracoid process Tendon of supraspinatus Acromion process Lesser tuberosity of \[ humerus Subscapularis Scalenus posticus Scalenus medius Scak-iius anticus First rib Teres major Serratus mag- nus, upper, middle, and lower por- tions Latissimus dorsi, cut edge ►External oblique 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 so that the lateral angle is moved dow^nward. 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 559. 573 Semispinalis capitis (complexus) I Splenius capitis et colli Sterno-cleido-mastoxdeKS Aponeurosis of trapezius y Trapezius Supraspinatus Infraspinatus — 7— Deltoid Infraspinatus -Rhomboideus majoi Teres major Rhomboideus ma.]oT'''^ ^^ Vertebral aponeurosis '^iji Serratus magnus Serratus posticus inferior Latissimus dors: Aponeurosis of latissimus dorsi (vertebral aponeurosis} Gluteus medius- Giuteus maximus- !• i\ *• I'- 5l Superficial muscles of the back. 57a HUMAN ANATOMY. mt-nts. It is directed downward and laterally and is inserted into the lower two- thirds of the vertebral liorder of the scapula. Nerve-Supply. — Hy the tlorsal scapular nerve from the fifth cer\ ical nerve. Action. — To draw the scapula upwartl and medially, at the same time rotating it so that tile lateral anylc is mo\ed tlownward. Variations of the Rhomboidei. — The rhonihoidei are sometimes entirely wantinij, and the orii^ins of both muscles may be extended beyond tlie usual limits. The occipito-siaf^ularis. is a muscle occasionally i)resent which is intimately associated in its derivation witli 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. Latissi.mus 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 trajjezius, 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 (^bursa 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 ner\es. 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 fi.xed, 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 mit^rated extensively from the region of its first formation, the lower cervical region, and this migration can be witnessed in the ontogeny of the muscle. Consequently variations may be expected and do occur in the extent of the origin of the muscle, who.se descent and backward migration to the vertebral column may be interrupted at various stages. A great arc.ountof 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 triaus;le of Petit, occurs between the borders of the two nniscles and above the crest of the ilium. The floor of the triangle is formed by the internal oblicjuus 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-epitroihtearis. 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 i)ortion 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 extends across from tlie lower border of the pectoralis major to that of the latissimus dorsi and teres major, forming the floor of the a.xilla. 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 considerably 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 cer\ical 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 {bursa m. coraco-brachialis). 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. 4 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 coi^aco-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 cer^■ical nerves. Action. — To abduct the arm. The supraspinous 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. ,76 HUMAN ANATOMY. 2. 1ni-rasi'inatus (Figs. 561, 572). Attachments. — Tin- intnisi)inatus occupies the infraspinous fossa of the scapula and ttr/sts from the entire extent of the fossa, with tlie exception of a portion towards the axillarv border of the bone. It also arises from the infraspinous fascia which covers it. The tibres pass laterally and converi^^e to a strong tendon, which is frequently separated from the capsule of the shoulder-jt)int by a small bursa (bursa DeUoid<^ Long head of biceps Short head of biceps Insertion of pectorahs major Deltoid Fig. 560. Axillary vein Axillary artery j Brachial plexus | | Clavicle Bicep Subclavius — Costo-coracoid ligament —I'ettoralis minor N..- Serratus magiius m. infraspinati) and is inserted into the middle facet of the greater tuberosity 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 ivfraspinatiis minor. On the other hand, the separation which usually exists between the infraspinatus and the teres minor may be entirely wantin.ij. The in frasp27ions 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 Mixor TFig. 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. Dissectioii of thoracic wall and anterior surface of arm. 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. Supraspinatus Spine of scapula Sectional surface of acromion - — Supraspinatus Infraspinatus Subscapularis Teres major ■ Greater tuberosity -Teres minor -Quadrilateral space -Tendon of latissimus dorsi -T Triangular space \, Long (middle) head of __•. triceps ~ Outer head of triceps Latissimus - dorsi Triceps Posterior scapular muscles and part of triceps ; outer part of acromion has been removed. 4. Teres Major (Figs. 561, 572). AttachmentSo^ — The teres major arises from the dorsal surface of the scapula, -along the lower third of its axillary border, and passes laterally to be iiiserted 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 backw^ard 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. A'boA-e 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 triaii.i,ai]ar interval, the base of which is the humerus, lies between the two muscles. This interval is crossed by the longhead of the triceps, which o\erlies the dorsal surface of the teres major, and is thus divided into a more medial triaui^ular space, occupied b\' the dorsal scapular artery, and a more lateral quad- rangular space, through which the posterior circumflex vessels and the circumflex ner\e 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 iyiserted 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 embn,o 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, wliich arises from the axillary border of the scapula and is inserted into the crest oi the lesser tubercle of the humerus and sometimes into the capsule of the shoulder- joint. The subscapular 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 by 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 greatly 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. Fig Trapezius- — -Sterno-cleido-mastoid f Spine of scapula — / ^ ,, Acromion- Dpltoid, spinal portioi Deltoid, acromial portion -Clavicle Pectoralis major Deltoid, clavicular portion Deltoid muscle viewed from side Accessory bundles of fibres are occasionally found arising from the fascia infraspinata or from some point along the axillary border of the scapula, find either insert with the deltoid {m. basio-deltoideus) or join with the upper part of the muscle, being continued onward as tendinous fibres which pass to the acromion process and lateral extremity of the clavicle (ni. costo-deltoideus) . 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 lavicle and scapula have been sufficiently described (page 551). Fracture of the Clavicle. — The action of the muscles which move 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 downward 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 pectorahs major and l)y all the muscles passing from the trunk to the humerus antl scapula. It is rotated on a vertical axis 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-cla\icular (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 slighdy 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 thora.v 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 of much surgical importance. The superficial fascia of the The processes which pass from it to the skin ), bv their in\'ol\ement and contraction in Dissection of fracture of middle of clavicle thorax 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 muscle. 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 above the upper border of the pectoralis minor is known as the costo-coracoid membrane. It, together with the subcla\ius 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 again) 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-thoracic artery Pectoralis minor \ r- u i- \ Cephalic vem Deltoid Pectoralis major distal stump Cut edge of- superficial pec- toral fascia Axillary artery and vein Cut edge of superficial layer of- clavi-pectoral fascia \ Teres major covered by axillary fascia ^ Pectoralis major, clavicular origin Costo-coracoid membrane Deep layer of clavi-pectoral fascia Thoracic branch of acromio- thoracic artery Pectoralis minor, cut edge Dissection of thoracic wall; pectoralis minor has been partly removed, exposing deep layer of clavi-pectoral fascia. 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 subscapulans muscles. Its apex is at the angle made by the fine 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 582 HUMAN ANATOMY that it is continuous above with the neck and inferiorly with the axilla. The latter space is shut in below Iw the continuation of the axillary fascia from the lower bor- der of the |)ectoralis 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, followmg 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. Fic. 566. Clavicle Acromion process Acromion CoratoidJt^^ process Gieiioii^ — ^ ^ cavity f'- Head o humerus Shoulder of subject in which subcoracoitl lux- ation has been produced, showing characteristic deforniiiv. Showina: relation ot hones in preceding subcoracoid luxation. The fascia over the scapular muscles — supraspinous and infraspinous fascia — has already been described in reference to caries, necrosis, and abscess (pages 255. 279). Dislocatio7i of the Shoulder- Joint.— The circumstances that favor or resist dislo- cation of the shoulder-joint have been enumerated (pages 278, 279), but the ana- tomical symptoms of that lesion may now be considered with especial reference to the muscles invoK'ed. Shoulder dislocation is either subglenoid or subcoracoid in the vast majority of cases, the former being almost in\ariably the primary form, for reasons previously given (page 278). A luxation, subglenoid primarily, 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 subclavicular, 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 Acromion- 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 merely be mentioned here. The backward (subspinous) luxation is resisted so strongly by the subscapu- laris, and especially by the 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 apphed to the outer side of the arm will touch both the acromion and the external condyle at the same time (Hamilton) ; and (6) 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) Fig. 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 (d) oedema from similar involvement of the axillary vessels. In all luxations, 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 Biceps Superficial dissection of preceding subcoracoid luxation, showing muscles after removal of skin and fascife. 5«4 HUMAN ANATOMY. weight of the trunk in the supine and recumbent position ; (d) pressure on the acromion and davicle ; (r) the use of a foldetl sheet phiced 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 (^ ) 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 heatl, outward — recjuires 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 e.xact mechanism, but it is safe to say that in its various stages it acts approximately as follows. I. The elbow is flexed, relaxing 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 KlG. 568. .Axillary \essels -Displaced head of Imnierus -Axillary vessels Pectoral is major (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 axis of the body, 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 scai)ular 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 perhaj)s 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 thrf)ugh the rent by which it originally emerged. These details can be worked out satisfactorilv in experimental luxations on the cadaver, and have apparentlv been demonstrated as to the main points by Farabcjeuf, Helferich, and otliers. 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 o[ 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. Biirsce. — 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 subcoracoid luxation, showing displacement of head of humerus and muscles involved. 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 (d) 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. 1 . Biceps 2. Brachialis anticus. POST-AXIAL. 1. Triceps. 2. Anconeus. Superficial fascia^ Deep fascia Musculo- cutaneous nerve Brachialis anticus Brachial vessels Median nerve Basilic vein 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- /- u r • ^^'^' t>- . ' . Cephalic vein Biceps dially It becomes contmu- 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 condyles, 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 ii.termuscular septum Internal intermuscular septum Triceps, outer head Triceps, middle head Tendon of triceps Section across right arm in lower third. 586 HUMAN ANATOMY. bursa aooniia/is o\er the acromion process of the scapula, a bursa olccrani o\er the olecranon process of the ulna, and a bursa may occur over each condyle o\ the humerus. {a) THK PRE-AXIAL MUSCLES. I. Biceps (Figs. 560, 570). Attachments. — The biceps ( m. biceps brachli), as its name indicates, takes origin 1)\- two heads. The long head arises trt)m the upper border of the glenoid cavity of the scapula by a slender round tendon, which tra\erses the cavity of the shouider-joint invested by the synovium ^nd then bends downward into the bicipital groove (intertubercular sulcus ) of the humerus, accompanied by a prolongation of the joint capsule ( vauiina 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 ( laccitus tibrosus), which passes downward and medially to become lost in the fascia of the f(jrearm. Nerve-Supply. — By the musculo-cutaneous nerve from the fifth and sixth cer\ical nerves. Action. — To flex the forearm on the brachium, and when the forearm is in pro- natifni 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 anticus, and the _si.ipinator. Upon its inner side lie the coraco-brachialis above 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 Ions: head is occasionally want- intj, but more frequently additional heads occur. Of these the most frequent, occurring in some- thinjj^ over 10 per cent, of cases, is a head which arises from the medial surface of the humerus, between the insertions of tlie 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. Brachi.\i.i.s 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 from 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 septum and are covered by the brachio-radialis are supplied by a branch from the musculo-spiral nerve. The nerve-fibres come in both cases from the fifth and sixth cervical ner\es. Action.— To flex the forearm. Variations. — The nerve-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-anconens is a small, usually quadrangular 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. Pectoralis minor fShort head Biceps-! Tendon of in- sertion of pec- toralis major Inner head of triceps ■--Coraco- brachialis rendon of latissimus Int. intermuscular septum Brachialis anticus Fig. 571. Brachialis anticus \ Internal Bicipital tuberosity of radius Insertion of biceps Brachialis antic Tendon of insertion of biceps Brachio-radialis Supinator Bicipital fascia condyle Head of — ^^ radius \ "^W Muscles of anterior surface of arm. Brachialis anticus and supinator, seen from m front. derivative of the pre-axial muscle-sheet and is supplied by the ulnar nerve, whose main stem, as it passes down between the olecranon and the inner condyle, is covered by the muscle^ When absent, the muscle is represented by a strong fibrous band. 5«8 HUMAN ANATOMY. if>) THE POST-AXIAL MUSCLES. I. Triceps ( Fij^^s. 570, 572). Attachments. The triceps ( m. triceps brachii) is a stronj^ muscle which occu- pies the entire chjrsal surface of the arm. It arises by three heads. The scapular or Fig. 572. Supraspinatus Spine of Infraspinatus Infraspinatus, cut edge Teres minor (cut) Inferior angle of scapula Acromion process Head of humerus covered by capsular ligament Tendon of insertion of teres minor Axillary border of scapula Pectoralis major Triceps, long heaa Teres major Serratus niagnus Triieps Latissimus dorsi long head takes its oriy;in by a tendon from the infra- U^lenoid 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 g'roovc for the musculo-spiral ner\'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 iiiserted 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 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 occasionally possesses an additional head arising either from the coracoid process of the scapula or from the capsule of the shoulder-joint. 1 i .. v|.~ .liiii j..j.^lri io! M ajjular mus- cles ; portions of infraspinatus and teres minor cut away. 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 inserted 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 basihc 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 effect 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 nerve 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 ; (<:) adduction of the humeral head, leaving a slight depression beneath the tip of the acromion ; (^) obvious tension along the inner edge of the biceps muscle when the forearm is extended ; (d") diminution in the vertical circumference of the shoulder ; and (y) 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 supraspinatus, 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 caused by 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 not 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, 1884. 590 HUMAN ANATOMY. Fig. J-yacturcs of the luinu-rus are much inlliienced by muscular action, although the controlling 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 actit)n 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 antl 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- The upper end of the lower fragment is draw^n 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 fix 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 (I^'ig- 573)- Epiphyseal disjunction 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 ; (c) the crepitus is muffled ; (! radius Flexor longus pullicis Pronator quadratus Tendon of flexor carpi radialis Abductor pollicis, cut Opponens pollicis ^^\Jl Abductor minimi digiti Anterior Adductor pollicis, transverse portion K annular ligament ^Opiionens minimi digiti Flexor brevis — minimi digiti rr=— Luinbri- 7 cales . - — ,^_ Tendotis • oi flexor >.\ililiniis igitorum I I / Dissection of muscles of forearm and hand, anterior surface; superficial muscles have been removed. ulnar ; the fibres come from'! the se\ cnth and cijj^hth cer- vical and the tirst thoracic! ner\es. Action. — The primary] action of the flexor pro- fundus is to flex the ter- minal phalanjj^^es of the second, third, fourth, anc fifth fingers, but, continu- ing its action, it also flexes the remaining phalanges of those digits and fmally the hand. Relations. — In the arm the muscle is co\ered by the flexor sublimis digi- torum and the flexor carjji ulnaris, and has resting uj)on its anterior surface the ulnar \'essels and the median and ulnar ner\es. 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 lon^^^us pollicis. A slip which lias been termed the accessorius ad flcxorem profiindiiDi digitorimi not in- frequently occurs, arising; from the coronoid process of the ulna and joining; with one of the tendons of the ]irofundiis. The sijjnificance of the \ aria- tions of the profundus u ill be considered in connection with those of the flexor longus pol- licis. 2. Flexor Longus Pol- licis (Fig. 578). Attachments. — The long flexor of the thumb (m. flexor pollicis lonuus) lies to the lateral side of the flexor profundus digi- torum and a?'tses 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 volar surface of the thumb to be inserted into the base of its ter- minal phalanx. Nerve-Supply. — By the anterior interosseous nerve from the eighth cervical and first thoracic nerves. 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 subHmis 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 pollicis and the flexor brevis pollicis, 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&flexor carpi radialis brevis. 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 majority 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 flexor 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 flexor mass. In the lower terrestrial vertebrata the superficial and deeper layers, corresponding practi- cally to the sublimis and profundus (plus the flexor longus pollicis), are distinct, their fusion in the monotremes being a secondary 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 Layer. I. Pronator quadratus. I. Pronator Quadratus (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 inserted 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 cervical and the first thoracic nerves. Action. — To pronate the forearm. 598 HUMAN ANATOMY. Variations. — The pronator quadratus usually occupies about the lower fourtli of the fore- ann, but it may l)e considerably reduced or, on the contrary, may extend as hij^h as the middle of the forearm or even hij^her. It rejjresents the lower portit)n of a muscle-sheet which extends in some of the lower mammals almost the entire lenj::th of the forearm, the upper portion of this sheet being represented, as already pointed out, by the coronoid head of the pronator teres. {b) THE POST- AX I. \L .MUSCLES. The post-a.\ial muscles of the forearm may be regarded as consistinj,^ of two layers, the more superficial of which arises from the e?cternal condyle of the humerus, while the deeper one is attached to the bones of the forearm. As was the case with the pre-a.\ial muscles, constituents of both layers have e.xtended into the hand to act as e.xtensors of the digits. (aa) The Siperfici.\l Lavek. 1. Brachio-radialis. 4. E.xtensor communis digitorum. 2. Extensor carpi radialis longior. 5. Extensor minimi digiti. 3. E.xtensor carpi radialis brevior. 6. Extensor carpi ulnaris. I. Br.vchio-R.vdialis (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 nerves. Action. — To Hex the forearm. If the arm be in a position of complete prona- tion, it will ])roduce 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 nerve. 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 extensor brevis pollicis. Variations. — The brachio-radialis is sometimes wantinsj. 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 Carpi Radialis Longior (Figs. 576, 579). Attachments. — The longer of the radial carpal extensors (m. extensor carpi radialis longus ) 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 e.xtensor tendon common to it and the neighboring super- ficial muscles. About the middle of the forearm it is continued into a tendon which passes beneath the posterior annular ligament in 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 division of the musculo-spiral nerve from the sixth and seventh 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 Carpi Radialis Brevior (Fig. 579). Attachments. — The shorter radial carpal extensor (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 exten- 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. extensoris 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 extent 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 tmiddle 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. _A Brachio-radialis .External condyle Anconeus ^Extensor carpi radialis longior _^Extensor carpi radialis brevior Flexor carpi ulnaris Extensor carpi iilnari<; l#li'f|H j ^//g ,^//- Extensor minimi digiti Extensor indicis tendon Tendons or extensor communis , digitorum / Dissection of posterior surface of forearm and hand, showing superficial extensor muscles. 6oo HUMAN ANATOMY. Fig. 580. Olecranon pn Anconeus - - —i'.xtensor carpi /^ radialis lonKior I Kleriial condyle Flexor carpi uliiaris Supinator Posterior interosseous nerve _: — Extensor ossis metacarpi pollicis Extensor brevis pollicis Extensor longus pollicis Extensor carpi radi- alis brevior tendon Extensor carpi radi- alis longior tendon ^Extensor brevis \ pollicis tendon Interossei •\,---^ dorsales Dissection of posterior surface of forearm and hand, showing deep muscles. three obliquely transverse ten- dinous bands (juncturac ten* dinum), the one between the] inde.\and median digits being, however, frequently wanting. As each tendon passes upoi the dorsum of the first phalanj of its digit it spreads out into membranous e.xpansion, whicl: receives the insertions of th< interosseous and lumbrica muscles and then divides int( 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 extensor consist in the absence of one ur other of tiie tendons, usually that to the fifth digit and more rareh' that to the second, or else in tlie occurrence of additional tendons, due to the division of one or more of those tyi)ically occurrinji, cer- tain of the ditjits 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. Extensor Minimi Dig- it: (Fig. 579). Attachments, — The ex- tensor of the little finger ( m. extensor digiti quinti proprius) 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 Brachialis anticus 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 sixth, seventh, and eighth nerves. Fig. 581. Action, — To extend the ht- •, tie 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. Variations. — A fibrous band is often given off from the tendon of the 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 ^n. ulnaris qidnti digiti. Olecranon process External condyle Anconeu; Supinator Radius Dissection of arm, showing deep muscles in vicinity of elbow. (bb) The Deep Layer. 1. Supinator. 3. Extensor brevis pollicis. 2. Extensor ossis metacarpi pollicis. 4. Extensor longus pollicis. 5. Extensor 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 ANATOMY. 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 extensor layer and the rest of it from the deep layer. tor KiG. 582. Brachio-radialis Flexor sublimis digitorum 2. Extensor Ossis Metacarpi Polmcis (Fig. 580). Attachments. — The e.xtensor of the metacarpal bone of the thumb (m. abduc- pollicis lonnus) arises from the middle third of the j^osterior surfaces of the uhia, the interosseous membrane, and the radius. It passes down- ward and laterally, and its ten- don passes through the first comi)artment 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. Variations. — It may be par- tially or wholly fused with the ex- 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. 3. Extensor Brevis Polli- cis (Fig. 580). Attachments. — The short extensor of the thumb (m. exten- sor pollicis brevis), also termed the extensor primi internodii pollicis, lies along the medial border of the extensor ossis metacarpi pollicis. 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. Extensor ossis metacarpi pollicis Extensor brevis pollicis Extensor carpi radialis longior Extensor longus pollicis Ext. carpi radialis brevior Radial artery First dorsal interosseus Radialis indicis artery Superficial dissection of hand, viewed from radial side, showing extensor tendons of thumb. PRACTICAL CONSIDERATIONS : THE FOREARM. 603 Relations. — The relations of the muscle are essentially the same as those of the extensor ossis metacarpi pollicis. 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 seciaidi 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 slightly 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 extend the index-finger. Variations. — The extensor 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 ex- tensor indicis, and passes to the third or fourth finger, forming what has been termed the extensor digiti medii {vel 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 wdth that of the biceps itself. Partly for this reason injuries and diseases affecting the bicipital region are sometimes associated wdth a certain weakness 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 the deep fascia of the forearm, is of importance 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 Hl'MAN ANATOMY. Palniaris lonyus Flexor carpi radialis Pronator radii teres Radial artery Radial nerve \ Flexor longus poUicis Median nerve IJlnar arter>- Flexor subliniis Ulnar nerve oiis at the wrist with the anterior and posterior annular Hi;anients. The septa which run in from it to be attached to the sides of the uhia and radius divide the forearm, with the aid of the interosseous membrane, into two musculo-aponeurotic spaces, an antero-external 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 w()unds se\ ering 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 Tillau.x, 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 layer, — the palmaris, flexor carpi ulnaris, pronator radii teres, etc., — and containing the internal cutaneous and musculo-cutaneous nerves, the perforating branches of the ratlial 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 flexor sublimis, with the brachio-radialis and short supinator externally. This contains Fic. 5S3. the radial nerve, artery. and veins. 3. That be- tween the flexor sublimis and the flexor profundus and flexor longus pollicis. This contains the median nerve 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 nerve. 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. 583). Fractures of the neck of the radius (between the head and the tuberosity) are very rare, as it is co\ered and protected from direct violence by 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 fiexion of the upper frag- ment by the biceps and supinator brevis. 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 by 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, communis Post, inteross. vessels and nerve / \ Interosseous membrane \ \ Extensor carpi ulnaris Extensor ossis metacarpi pollicis Extensor longus pollicis Section across middle of right forearm. PRACTICAL CONSIDERATIONS: THE FOREARM. 605 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 Fig. 584. radii teres 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 expend 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. width, relaxes (in conjunction with the flexion of the elbow) the muscles invoh-ed 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 Dissection of fracture of radius between the two pronator muscles. Dissection of fracture of ole- cranon process of left ulna ; joint opened from behind. Ext. carpi radialis long-. Ext. carpi radialis brev. Lower fragment Brachio-radialis Ext. longus pollicis Radial arterj ^ ^ — ^ Flexor 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. 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- 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 tlie upper end of the palmar splint. The preservatit)n 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. 5.S7. Thenar eminence covered with lateral portion of palmar lascia Hypothcnar eminence Palmar fascia, central portion Palmar fascia, lateral portion —Digital nerves Superficial transverse ligament 1 Digital -arteries ( ^i \ I J \ J 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 pahnar 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 ligarnent beneath the webs of the fingers. The anterior annular ligatnent (ligaraentum 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 flexor carpi radialis passes, and a large ulnar one which gives passage to the other structures mentioned. The tendons are enclosed within synovial sacs which extend 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 poUicis 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 downw^ard 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. («) 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. Flexor brevis poUicis. 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 inserted 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 pollicis brevis) is the most supertkial muscle of the thenar eminence. It crn'scs from the anterior annular ligament and from the scai)hoid bone or the trapezium and i)asses distally to be vi- st'ticd along with the Hexor 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 i)ollicis. Nerve-Supply. — By the median nerve from the sixth and seventh cervical ner\ es. Action. — To flex and abduct the thumb. Variations. — The portion uf tlie muscle arisinij from the carpus is sometimes separate from that takins;; orijjjin Iroiii the transverse carpal ligament. Slips are occasionally sent to the abduc- tor from the extensores carpi radiales, the extensor ossis nietacarpi pollicis, the opponens pol- licis, and the Hexor brevis i)ollicis. 3. Opponexs 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 iiiscrhJ into the whole length of the radial border o\ the first metacarpal. Nerve-Supply. — By the median nerve from the sixth and seventh cervical nerves. Action. — To flex and adduct the thumb, oj)posing it to the other fingers. 4. Flexor Brevis Pollicis (P'igs. 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 PZnglish 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 bre\ is, being described as an additional (first) palmar interosseus (page 612) ; [b] the small slip just noted is the inner or ulnar head of the flexor brevis ; {c) the small slip and all the fibres described as forming the adductor. obli{}uus (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 (|uinti) occupies the ulnar border of the hand. It arises from the anterior annular ligament and from the pisiform bone and is hiserted into the ulnar side of the base of the first phalanx of the little finger. Nerve-Supply. — By the deep division of the ulnar ner\e from the eighth cer- vical and first thoracic nerves. Action. — To abduct the fifth finger. 6. Opponens Minimi Digiti (Fig. 578). Attachments. — This muscle (m. opponens digiti 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 Digiti (Figs. 577, 578). Attachments. — The short flexor of the little linger (m. flexor brevis digiti quinti) lies along the lateral (radial;) border of the abductor minimi digiti. It arises Fig. .s88. Radius- Anterior interosseous artery -Ulna c Cut edge of V anterior annular ligament''"^ ' Opponens pollicis Abductor pollicis Flexor brevis pollicis First palmar interosseus Flexor longus pollicis tendon .y' -^ ■-< Pronator quadratus Flexor carpi ulnaris tendon Cut edge of anterior annular ligament Pisiform bone Adductor pollicis, oblique portion Third palmar interosseus Fourth palmar interosseus '' li Fourth dorsal interosseus 1 V I 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 litde finger. Variations.— The flexor brevis and opponens minimi digiti are often united by muscle- bundles and may even be completely fused. 39 6io HUMAN ANATOMY. {bb) The Muscles ok 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 ( \y.\^(i 597 ). ilifterentiatej into the palmar portions of the tendons of the He.xor profundus digitorum, and ii the mammalia the muscles retain their primary origin and arise from those tender forming the lumbrical muscles. I. LUMBRICALES (Fig. 578). Attachments. — The lumbricals are four slender, band-like muscles, situatec in the jialm of the hand. Counting from the radial side of the hand, X.\\g first am stcotui lumbricals arise from the radial side of the fle.xor profundus tendons to the index and middle fingers respectively, while the third one arises from the adjacen^ sides of the tendons to the middle and ring fingers, and the fourth from those of th« tendons to the ring and little 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 lumbricals are supplied by the medial nerve from the sixth and seventh cervical nerves ; the third and fourth by the deej division of the ulnar nerve from the eighth cervical and first thoracic nerves. Action. — To fiex the first phalanges of the second, third, fourth, and fiftl fingers. At the same time, by their traction upon the extensor tendons, they will tend to keep the second and third phalanges extended. Variations. — Variations in the arrangement of the lumbricals, and especially of the thir4 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. (r to the wrist ; movements of the fingers are not very painful, (r) 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 connective 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 f)ften 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 ot 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. On the 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 — Tendon of flex, longus poll. Adductor poll., obi. portion AbduLtor poll Fkxor. bie\ i>ipoll. Dissection of metacarpo-phalangeal dislocation of thumb. PRACTICAL CONSIDERATIONS: WRIST AND HAND. 617 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 involve 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 exceptionally extend rapidly up the arm. Infection of the palmar surface of a finger (panaritium, paronychia, whitlow, felon ) is of two chief varieties : (a) siibadaneous , 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 ex- tend to the dorsum or to\\'ards the palm ; and {b) thecal, with more severe pain, greater fim- 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 ; {b') 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 ^^essels already mentioned. The interphalangeal joints are often affected because it is opposite them that («) the tendon-sheaths are thinnest and Fig. 594. (<5) 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 extension 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 interphalangeal 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 n y Dissection showing position of bones in dislocation of thumb. 6i8 HUMAN ANATOMY. attributed {a) to the ijrippini; of the neck of the metacarpal hone between the flexor brevis poUicis and the obhque portion of the adductor pollicis (these often being considered as the two heads of the flexor brevis poUicis) ; id) to a similar entanglement of the head and neck in the slit in the capsule ; (stero-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 expansion 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 dejiression 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, 330). 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 groove 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 hollo\^• 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 abo\'e 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 « to a point a little above the middle of the ulnar border of the palm, which 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 ; {d') 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 mo\'ements being towards the mid-line of the hand ; b and c are transverse, and are produced chiefly by flexion {b) oi 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 curved 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 synovial 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 Htde 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 trans\'erse 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 litde 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-phalanijeal joint obliquely. The lower crease corresponds to the inter- phalangeal joint. ^ The pai)illary ridges of the skin covering the termmal phalanges assume varied curves and torm'patterns,— immutable and characteristic in the indi- vidual.—impressions of which have been used of late years for purposes of identifica^i tion of criminals. On the dorsum of the hand the hollow at the base of the thumb (the so-callec "snuff-box" ) is bounded externally ( radially) by the tendon of the extensor of lh< Fi(j. 597- Surface markings "f ri;^ht palm. metacarpal bone of the thumb and the short extensor, and internally by the tendon or the long extensor (Fig. 582). The radial artery, a large vein, — cephalic vein of the thumb (Treves), — and the inner division of the radial ner\e 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. (a) THE PRE-AXIAL MUSCLES. 1. Psoas magnus. 6. Adductor brevis. 2. Iliacus. 7. Adductor magnus. 3. Pectineus. 8. Quadratus femoris. 4. Gracilis. 9. Obturator externus. 5. Adductor longus. 10. 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 vertebrae 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 inserted 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 fiex the body and pelvis upon the femur. Acting from above, it fiexes 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 fioor 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 over 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 HIMAN ANATOMY. The psoas iiiaj^nus appears Id be fomied Iiy the union of a liyposkeletal trunk nuiscle with a femoral nuiscle, the remauiin.u: portions of which are represented by tlie iliacus and pectineus. It is interestiui; to note in tliis connection tiiat in tlu)se mammalia in which the ciuadratus lum- bonmi is well developed the psoas ma.y;iuis is correspondins,dy weak, and vice versa. The psoas parvus or Fig. 598. External amiatc liiraniitit- Xll rib ^^. —Internal arcuate ligament vtitior ( l*"ig. 59.S ) is a long, Hat muscle w iiich lies upon the ventral surface of the psoas ma<;nus, represent- w\% 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 vertebra- 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 converge downward to form a common tendon with the psoas major, which is J7iserted 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 flex the thigh and rotate it slightly i3ftHBg*4><-'"^vTien the thigh is fixed, to flex 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 external cutaneous ancl the anterior crural ner\es ; 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 w ith 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 tn. i/io-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 tlie 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-osoas. Abo\e it is attached to the internal arcuate ligament oi siii)erior spnie of ilium Glmoiis niediiiS' Tensor fascite latx Lesser trochanter -Pvriformis — S\ inph) sis pubis K )hturator (.-.xtcrnus — Adductor loiifjus, cut — Pectitieus, cut and turned down \ Iductor magnus Deep dissection of posterior body-wall and 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 iUo- 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 vesseliV 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 vasorum) 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 femoraie, is the upper end of a space, occu- FlG. 599. Anterior superior iliac spine- Iliac fascia attached to Poupart's ligament Aponeurosis of external oblique Iliacus muscle Anterior crural nerve — Femoral artery '- Femoral vein External abdominal ring r~- ... .^ '^^ - Obturatornerve Gimbernat s lisrament^^ ^^ , . .-> , -^^^^^^^^^^^Hna^^^^H .Artery Femoral ring '''^ ^^''^ Vein Iliac fascia continued as^ posterior wall of femo- ral sheath Pudic branch of obturator' Obturator membrane 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 femoraie, 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 arises 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. 40 626 HUMAN ANATOMY. Nerve-Supply. — From the anterior crural nerve by the second and third lumbar nerves. Action. — To adduct and fle.x the tliigh and rotate it sHghtly outward. Fic 600. 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 a?'isis 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 in- 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 di\ision of the obturator ner\e from the second, third, and fourth lumbar nerves. Action. — To adduct the leg and fle.x the thigh. It will also assist in rotating the leg inward, especially if the thigh be flexed. 5. Adductor Loxgus (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. — "IThe ad- ductor brevis arises from the body and 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. Tendon of extensor quadriceps Tendo patell.-f Muscles of right thigh, antero-median aspect. THE MUSCLES OF THE LOWER LIMB. 627 Greater sacro-sciatic ligamenl Pyriformis, cut Obturator iuternus Tuber ischii Origin of semimem- branosus, semi- tendiuosus, and biceps f^J '" Gluteus minimus Greater trochanter Quadratus femoris, insertion Obturator externus Adductor brevis Adductor magnus ■ — Gluteus maxinius, insertion i J— Dorsum of ilium Perforating arteries ^'astus externus Fourth perforating artery Biceps, short head Biceps, long head, cut Popliteal surface of femur Internal condyle Externa! condyle Deep dissection of posterior surface of right thigh. 628 HUMAN ANATOMY. Nerve-Supply. — Bv the anterior ramus of the ol)turator nerve from the third and fourth Uimbar ner\ es. Action. — To adduct, Hex, and outwardly rotate die thigh. 7. Adductor M.\gxus (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 inserted into nearly the whole length of the inner lip of the linea aspera by a series of tendinous arches which give passage to the j)erforating branches of the profunda femoris 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. — Hy 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 e.xtensor 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 \essels are Fig. 602. Sacrum — Greater sacro-sciatic foramen Greater sacro-sciatic ligament Lesser sacro-sciatic ligament Lesser sacro-scialic foramen Gemellus superior Obturator intern us Gemellus inferior Crest of ilium Tuber ischiis Quadratus femoris Gluteus minimus Pyriformis Greater trochanter Tendon of obturator externus k/li Deep dissection of right buttock, showing muscles attached 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 vastus internus. By this membrane the space occupied by the vessels and nerve is con- verted into a closed passage-w-ay termed Hunter s eanal (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 frorn 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 nerx^e. 8. QuADRATUS 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 extends 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 maximus, 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 Anterior surface of ilium Obturator foramen Symphisis pubis Femur .Greater sacro-sciatic foramen Anterior sacral foramina Piriformis Sacral canal Greater sacro-sciatic foramen Spine of ischium occygeus Coccyx T esser sacro-sciatic foramen Ore Iter sacro-sciatic ligament Obturator internus Tuber ischii Dissection of right postero-lateral wall of pelvis from within, showing pyriformis and obturator internus muscles. circumflex 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, mHses 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 le 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 ni. ol>turatoris intcrni) intervening between the tendon and the bone, passes outward througli the foramen to be inserted 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 ner\-es. Action. — To rotate the thigh outward. II. Ge.melli (Fig. 602). Attachments. — The gemelli are two slender muscles which lie one on either side of the tentlon of the obturator internus. The gemellus superior arises 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 o^emelli, usually the superior, is occasionally wanting. This is \ery i)rohahly due to fusion with adjacent muscles, the gemellus superior with the pyriformis and the inferior with the quadratus femoris. {b) THE POST-AXIAL MU.SCLES. 1. Gluteus ma.ximus. 3. Gluteus medius. 2. Tensor fasciae latee. 4. Gluteus minimus. I. Gluteus Maximus (Figs. 604, 607). Attachments. — The gluteus maximus 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 inserted 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 bursae (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 in. glutaei maximi). Variations. — The lower border of the gluteus maximus is occasionally separated from the •-est of the muscle, forming what may be termed the coccys^eo-femoralis, and it occasionally receives a slip from tlie ischial tuberosity, which has been named the ischio-femoralis. THE MUSCLES OF THE LOWER LIMB. 631 2. Tensor Fasciae Lat^ (Figs. 600, 604). Attachments. — The tensor fasciae latse, also termed the tensor vagincB femo ris, is a flat muscle which arises from the crest of the pj^, g^^ ilium, immediately behind the anterior superior spine, and passes downward and slightly backward to be inserted into the upper portion of the iUo-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 of 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. Biceps, long Biceps, short heacLr Gluteus medius Anterior supe- rior spine of ilium Sartorius Tensor fasciae latae, cut at insertion into fascia Rectus femoris Vastus externus -^ Tendon of quadriceps \. extensor Ilio-tibial band, cut Muscles of right thigh, lateral aspect. A bursa (bursa trochanterica m. glutaei medii anterior) is interposed between the 632 HUMAN ANATOMY. Fio. 605. Crest of ilium Gluteus niaxiinus' X. "iluteus niedius covered by fascia lata 1 terior superior spine of ilium I'ensor fascia' latae ^I'ascia lata, cut edges '^ Symphysis pubis Fascia lata llio-tibial band Tendon of biceps- Patella Lateral surface of right thigh invested by fascia lata. THE FEMORAL MUSCLES. 633 tendon of the muscle ^nd 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 (bursa 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 Sartorius Internal saphenous nerve Femoral vessels Internal saphenous vein Adductor longus Linea aspera, external lip Vastus externus Deep fascia Subcutaneous tissue Skin External intermuscular septum Adductor magnus Semimem- branosus Biceps, long head Greater sciatic nerve Semitendinosus Section across right thigh through Hunter's canal, seen from below. Strong layer 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. Crest of ilium Sacral and lijianieiUous origin of glu- teus maxinius Gluteus^ niaximus iluteus maxi- inus, insertion dially along Poupart's ligament to the body of the pubis ; thence it passes backward and downward along thti inferior rami of tlie 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 it is thin, but over the great tro- chanter of the femur it J becomes greatly thick- j ened, and this thickening] is continued downward upon the lateral surface of i 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 latae and part of the glu- teus maximus, 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 sulcus. In its lower posterior part, where it forms the roof of the popliteal space, the fascia is also somewhat thickened. Anteriorly, just below the inner end of Poupart's ligament, a prolongation of the fascia passes deeply to join with the ilio-pec- tineal portion of the iliac fascia, and so assists in the formation of the sheath for the femoral vessels. Over an oval area, situated immediately external to where this prolongation, which is termed the pubic tus externus Semitendinosus. Semimembranosus Sartorius Gracilis, tendon Gastrocnemius Superficial dissection of posterior surface of right buttock and thigh, showuig muscles undisturbed. portlo7i (Fig. 530) of the fascia lata, is given off, the fascia lata is quite thin and is perforated by the internal saphenous vein, superficial blood-vessels, and lymphatics ; THE FEMORAL MUSCLES. 635 whence it is termed the cribriform fascia (fascia cribrosa), the area which it covers being \.\iQ. fossa ovalis. The cribriform fascia is readily ruptured, the fossa ovalis then Fig. 608. Tuberosity of ischium Quadratus femoris -Pyriformis -Gemellus superior Obturator internus — Gemellus inferior Greater trochanter Adductor magnus • -Gluteus maximus, reflected Semitendinosus Semimembranosus, Gastrocnemius, inner head^ — Biceps, long head Biceps, short head Vastus externus Biceps Popliteal surface of femur Tendon of biceps, Gastrocnemius, outer head Muscles of posterior surface of right buttock and thigh, gluteus maximus and medius having been reflected. appearing as a perforation in the fascia lata, termed the saphenous opening (Fig. 523). The fossa ovalis hes immediately over {i.e., in front of) the lower end of the femoral canal, and is consequently of importance in connection with femoral herniae 636 HUMAN ANATOMY. (paijc 1773 ), which. (.lescciuUng in tlie canal, press against the thin fascia cribrosa and may cause it to bulge forward. The |)art of the fascia lata lying to the outer side of the fossa ovalis, or the saphenous opening, is known as the iliac portion (Fig. 530), which at the lateral margin of the fossa ovalis, where the fascia cribrosa joins the fascia lata, is somewhat thickened to form a curved l)and termed ihc /a/ci/or»i process (maruo falciformis). The latter is prolonged downward, as the cor?iu iufcrius, to join the pubic portion of the fascia lata, and upward, as the cornii supcriiis, also termed \\\q femoral liga- ment or Hey' s ligament, which is somewhat stronger and continued medially to join the inner end of I^oupart's and Gimbernat's ligaments. Septa of connective tissue are continued from the deep surface of the fascia lata to the femur separating the various muscles of the thigh. Two are especially strong ; one, the internal intermiisailar septum (septum intermuscularis medialis), passing to the inner lip of the linea aspera, between the vastus internus and adductor magnus muscles, and the other, the external intermuscular septum ( sci»tum intermuscularis lateralis), to the e.xtcrnal lip between the short head of the bice])S and the vastus e.xternus. To a certain extent these septa furnish surfaces of origin for some of the adjacent muscles. (rt) THE pre:-axial muscles. I. Biceps femoris. 2. Semitendinosus. 3. Semimembranosus. These muscles are popularly known as the hamstring vtuscles. I. Biceps Femoris (Figs. 608, 609). Attachments. — The biceps femoris takes its origin by two distinct heads. The long head arises from lower and inner facet upon the tuberosity of the ischium in common with the semitendinosus, while the short head arises from the whole length of the outer lip of the linea aspera and from the adjacent septum intermus- culare. The fibres C)f both heads are directed downward, and at about the knee unite in a common tendon which passes behind the outer condyle of the femur and is inserted into the head of, the fibula, bifurcating to embrace the long external lateral ligament of the knee-j6fnt. Tendinous bands usually extend also from the tendon to the outer tuberosity of the tibia. Nerve- Supply. — Both heads are supplied by the greater sciatic nerve. The fibres for the short head, however, pass, by way of the external popliteal division of the nerve, from the fifth lumbar and the first and second sacral nerves, while those for the long head pass by the internal popliteal division, coming from the first, second, and third sacral nerves. Action. — To extend the thigh and flex the leg. When the leg is flexed the biceps will rotate it outward, and the long head acting from below assists in extend- ing the trunk upon the hip-joints. Relations. — The common tendon of origin of the biceps and semitendinosus is sometimes separated from the tendon of the semimembranosus by a bursa (bursa m. bicipitis superior ). More rarely a bursa is to be found between the tendon of insertion of the biceps and the lateral head of the gastrocnemius, and almost con- stantly a bursa (bursa m. bicipitis inferior) separates the tendon of insertion from the fibular collateral ligament of the knee-joint. Variations. — The most important variations of the biceps are an occasional absence of the short head and an extension of the insertion to the crural fascia. Both these anomalies are explained by the composition of the muscle, the two heads not only representing: two ori.c;inalIy distinct muscles, but, as is indicated by the ner\e-supplv, the long: head 's a portion of the pre- axial musculature of the thigh, while the short head belon_a:s to the post-axial group. The com- parative anatomy of the muscle shows that the short head is a modified representative of a muscle belonging to the gluteal set, which extended from the caudal vertebrae to the fascia of the cms and has only secondarily become united with the pre-axial muscle, sharing -in its insertion. THE FEMORAL MUSCLES Fig. 609. 637 Sacrum Greater sacrosciat ligament Tuberosity of ischium. — ^-5 Biceps, origin -T^ Semitendinosus, origin Adductor magnus -^.^^r; Crest of ilium Gluteus medius Pyriformis, cut '*!E« ' Obturator internus 4 — Greater trochanter -J — Quadratus femoris Tendon of vastus externus .^ — Gluteus maximus, insertion Vastus externus Biceps, short head i§ Biceps, long head, cut Adductor magnu: Sartorius Tendon of semimembranosus — Ht Popliteus Aponeurotic expansion from tendon of semimembranosus to posterior liga- ment of knee-joint Fibula Deeper dissection of posterior surface of right buttock and thigh, exposing semimembranosus and short head of biceps muscles. 638 HUMAN ANATOMY. 2. Semitendinosus (Fig. 608). Attachments. — The semitendinosus arises from the tuberosity of the ischium! in common with the long head of the biceps. Its fibres extend downward to a long, slender tendon, which passes behind the inner condyle of the femur and then curves' forward along with the tentlon of the gracilis to be inserted, below that tendon and, uiuler cover of the exj)anded tendon of insertion of the sartorius. into the inner surface of the tibia near the tuberosity. Nerve-Supply. — By the internal popliteal division of the greater sciatic nervej from the fifth lumbar and first and second sacral nerves. Action. — To extend the thigh and flex and rotate inward the leg. Acting fror below it will extend the trunk upon the hip-joints. Relations. — A large bursa (bursa anserina) intervenes between the tendons! of the gracilis and semitendinosus and the tibia. 3. Semimembranosus (Fig. 609). Attachments. — The semimembranosus arises by a broad, flat tendon, whicl extends from upper and outer facet upon the tuberosity of the ischium downwarc along the outer border of the muscle to about the middle of the thigh. The muscle- fibres pass downward and inward from this tendon to a tendon of insertion, whicl occupies the medial border of the muscle and passes behind the inner condyle of th< femur and curves forwardto the inner surface of the internal condyle of the tibia,] into which it is inserted. An extension of the tendon of insertion usually passes downward and outward to the jjortion of the deep fascia of the leg which covers th< popliteus muscle ; another band extends upward and outward towards the outer con- dyle of the femur, blending with and materially strengthening the posterior part ol the capsular ligament of the knee-joint. Nerve-Supply. — Rv the internal popliteal division of the greater sciatic nerv( from the fourth and fifth lumbar and first sacral nerves. Action. — To flex the leg and assist somewhat in rotating it inward. Acting from below it will extend the trunk upon the hip-joints. Relations. — The semimembranosus is situated in front of the long head of th< biceps and the semitendinosus and behind the adductor niagnus. The greater sciatic nerve lies along its lateral border (Fig. 606). The tendon of insertion is separated from the inner head of the gastrocnemius by a bursa (bursa m. semimem- branosi medialis), which often communicates with the synovial ca\ity of the knee- joint ; the bursa ra. semimerabranosi lateralis intervenes between the tendon and the inner condyle of the tibia. (b) THE POST-AXIAL MUSCLES. 1. .Sartorius. 4. Crureus. 2. Rectus femoris. 5. Vastus internus. 3. Vastus externus. 6. Subcrureus. I. S.\RTORius (Fig. 610). Attachments. — The sartorius is a long band-like muscle which arises from the anterior superior spine of the ilium and the adjacent part of the notch below it. It descends obliquely downward and inward across the front of the thigh, in the groove between the rectus femoris and the vastus internus, on the one hand, and the adductor muscles, on the other, and then passes directly downward behind the inner condyle of the femur. It finally bends forward to be inserted into the inner surface of the tibia near the tuberosity, covering the insertions of the gracilis and semitendinosus. Nerve-Supply. — By the anterior crural nerve from the second and third lumbar nerves. Action.— To flex the thigh and leg and to rotate the thigh outward ; when the leg is flexed, the muscle will assist in rotating the thigh inward. THE FEMORAL MUSCLES. 639 Relations. — As it passes obliquely across the upper part of the thigh, the sar- r .1 _ 1, 1 1 , r ^ triangular depression which is known as The inner boundary of this triangle is formed Fig. 610. Pectineus torius forms the lateral boundary of Scarpa's triangle (trigonum femorale). by the adductor longus, its base by Poupart's ligament, its floor by the ilio-psoas and pectineus and often to a slight extent by the adductor brevis, and its roof by the fascia lata and the cribriform fascia. The space so bounded is traversed from above down- ward, from the middle of its base to its apex, by the femoral vessels and the anterior crural and crural branch of the genito-crural nerve, and con- tains a number of lymphatic nodes. At its apex it is continuous with the adductor or Hunter's canal. A mucous bursa (bursa ra. sar- torii propria) intervenes between the tendon of the sartorius and those of the gracilis and semimembranosus, and occasionally communicates with the bursa anserina (page 638). The remainder of the post-axial musculature of the thigh is almost en- tirely represented by four large mus- cles, more or less separable above, but united below in a common tendon, which is inserted into the upper bor- der of the patella, and through this and the ligamentum patellae acts upon the tuberosity of the tibia. These muscles have been grouped together as the exteiisor quadriceps femoris, and include the rectus femoris, the vastus externus, the crureus, and the vastus internus. 2. Rectus Femoris (Fig. 610). Attachments. — The rectus fem- oris has a double origin, the one, or straight head, arising from the an- terior inferior spine of the ilium, and the other, or reflected head, from the surface of the ilium a short distance above the acetabulum. The two heads give rise to a single tendon which descends for some distance along the front of the muscle and, in conjunction with a median septum, gives origin to the muscle-fibres. These present a bipinnate arrange- ment, and pass over below into the common tendon to be eventually in- serted by the ligamentum patellae into the tubercle of the tibia. Nerve-Supply. — By the anterior crural nerve from the third and fourth lumbar nerves. Ilio-tibial band -Teiido patellae P Muscles of right thigh, anterior aspect. 640 IILMAN ANATOMY. Action, — To Hex the thigh and extend the leg. Acting from below it will flex the trunk on the hip-joints. Relations. — The rectus femoris rests upon the capsule of the hip-joint above and the crureus below. A bursa frequently intervenes between the surface of the ilium and the head which is inserted above the acetabulum. 3. V.VSTUS EXTERNUS (Fig. 610). Attachments. — The vastus cxternus ( 111. vastus lateralis ) arises from the ante- rior intertrochanteric line, the lateral surface of the greater trochanter, and the outer lip of the linea aspera. The fibres curve downward and inward to unite with the crureus and to be inserted into the common tendon. Nerve-Supply. — By the anterior crural ner\e from the third and fourth lumbar nerves. Action. — To extend the leg. 4. Crureus (Fig. 606). Attachments. — The crureus (in. vastus intermedius) lies below the rectus femoris and between the vastus externus and vastus internus. It arises from the anterior surface of the femur and passes downward into a flat tendon which is inserted into the common tendon a short distance above the patella. Nerve-Supply. — By the anterior crural nerve from the third and fourth lumbar ner\es. Action. — To extend the leg. 5. \'astus Ixterxus (Fig. 600). Attachments. — The vastus internus ( m. vastus medialis) is usually so blended with the crureus as to be hardly separable from it. It arises from the spiral line and from the inner lip of the linea aspera of the femur, the fibres curving downward and outward to be partly united with the crureus and partly ijiserted into the common tendon. Nerve-Supply. — By the anterior crural ner\e from the third and fourth lumbar nerves. Action. — To extend the leg. Owing to the oblique direction of the femur downward and inward the action of the quadriceps femoris would be to draw the patella outward as well as upward, thus tending towards an outward dislocation of that bone. This is obviated, however, by the vastus internus, the bulk of whose fibres arise from the lower part of the femur and are directed more or less trans- versely outward to the inner border of the common tendon. Relations. — The medial border of the vastus internus forms the outer wall of Hunter's canal (Fig. 606). the fascia which forms the roof of the canal extending across between this muscle and the adductor magnus. 6. Subcrureus. Attachments. — The subcrureus (m. articularis genu) is frequently so insepara- bly blended with the cnireus that it may well be regarded as the deepest layer of the latter rather than as a distinct muscle. It arises from the lower part of the anterior surface of the femur and passes downward to be iyiserted into the upper border of the capsule of the knee-joint. Nerve-Supply. — Bv the anterior crural nerve from the third and fourth lumbar nerves. Action. — To tense the capsule of the knee-joint. PRACTICAL CONSIDERATIONS: THE BUTTOCKS. 641 PRACTICAL CONSIDERATIONS: MUSCLES AND FASCI/E OF THE BUTTOCKS, HIP, THIGH, AND KNEE. I. The Buttocks. — The skin over this region is thick and is closely connected with the superficial fascia, which is abundant, loose, and contains much fat. The skin is richly supplied with nerves from the small sciatic, the external and the perforating cutaneous, the ilio-hypogastric, and the external branches of the posterior division of the lumbar and sacral nerves. It is poorly supplied with blood as compared with other cutaneous areas, and hence usually has a relatively low surface temperature. It is coarse, with numerous sebaceous follicles, and is the site of frequent minor forms of irritation, — chafes, bruises, etc., — and is for these reasons a common seat of superficial Fig. 611. Gluteus maximus turned forward Dislocated head of femur bturator internus ' Greater sciatic nerve Quadratus femoris Dissection of posterior luxation of left femur towards dorsum of ilium. furuncles, which, on account of its intimate union with the underlying fascia and its plentiful nerve-supply, are apt to be very painful. The presence of a large quantity of poorly organized fat in the superficial fascia and the frequency of local irritation render the region a favorite seat of lipomata. The laxity of the superficial fascia permits effusions of pus or of blood to attain exceptionally large dimensions, and this is encouraged by gravity in the usually dependent position of the part. The deep fascia attached to the back of the sacrum and coccyx and to the crest of the ilium covers in the gluteus medius and holds it, with the gluteus minimus, in an osseo-fascial space, as the ilio-psoasis held anteriorly by the iliac fascia (page 624). The posterior space, however, is completely closed superiorly and is open only inferiorly, towards the thigh, and antero-internally, towards the sciatic foramina. Abscesses or extravasations of blood in this space may originate in, or may find their 41 64: HUMAN ANATOMY. way into the pelvic cavity ; or, guided by graxity, they may travel long distances down the thigh before pointing. They are apt to be associated with much pain because of the compression of the gluteal and other branches of the sacral plexus between the bone anteriorly and the musculo-aponeurotic wall of the space posteriorly. The gluteus maximus is embraced by a sheath formed by the splitting of this fascia into two layers, the sujjerticial one of which is thinner and less dense than the deep layer. Abscess or hemorrhagic extravasation within the substance of that muscle is, therefore, likely to gi\e more external evidence of its presence and to be less painful than if in or beneath the gluteus medius. The gluteus maximus itself may be ruptured by violent exertion in extending the pehis aiid trunk on the thigh, the latter being fixed, as in raising a heavy weight on the back and shoulders while passing from a stooping to an erect position, or in carrying a similar burden upstairs, the pelvis and femur having then the same relative position at each upward step that they have when the thigh is vertical and the trunk and pelvis are flexed. In the erect position the muscle is relaxed. When it is paralyzed the patient can walk easily on a level, but has trouble in going upstairs or in exchanging a sitting for a standing posture. Wounds of the buttock without fracture of the bones may enter the pelvic caxity through the sacro-sciatic foramina, and Treves has recorded a case of stab wound of the ^'it3. 612. buttock in which the patient died from peri- tonitis, the wound having in\olved the bladder and caused in- traperitoneal extrava- sation of urine. A subgluteal tri- angle has been de- scribed (Guiteras), the boundaries of which are externally the fem- oral and trochanteric insertion of the glu- teus maximus, inter- nally the long head of thebiceps, the tuber ischii, and part of the sacro-sciatic ligament, superiorly the pyri- formis. The floor of the triangle is made by the external rota- tors and the adductor magnus. It is the re- gion of aneurism of J Dislocated head of femur Femoral artery Femoral vein Pectineus Pubic hone Gracilis Adductor longus / Dissection of pubic luxation of hip-joint. or occasional hemorrhage from the sciatic arterv, of emergence of the sciatic nerve, and of one form of sciatic hernia, below the pyriformis. The ' ' triangle' ' is an arti- ficial one, and is mentioned merely as an aid t(") localization of the above structures. The subgluteal bursae are of considerable importance. One is found interposed between the trochanter and each of the gluteal muscles (page 630). Inflammation and enlargement of these bursee will be followed by adduction and flexion of the thigh, because active extension of the thigh, in which the glutei aid, and rotation in- ward, putting them on the stretch, are painful. Flattening of the buttock and oblit- eration of the gluteo-femoral crease may follow atrophy of the muscles from disease (page 381). Caries of the trochanter has resulted from suppuration in these bursse. The bursse over the tuberosities of the ischium frequently enlarge and may cause two solid symmetrical swellings— " weavers' bottom"— which require removal. 2. The Hip and Thigh. — The skin over the hip is less dense than over the buttock, and is still thinner below Poupart's ligament and in the region of Scarpa's PRACTICAL CONSIDERATIONS: THE HIP AND THIGH. 643 triangle. Over all the lower portion of the thigh it is loosely connected by abundant connective tissue with the fascia lata, its attachment being closest along the line of the external intermuscular septum, between the vastus externus and the hamstring muscles. It is coarse externally and thinner over the abductor surfaces. It is easily stripped up by effusions or retracted during operations. The superficial^ fascia in the subinguinal region is in two layers, in the more superficial of which is the subcutaneous fat. The deeper layer is the denser, and on it lie the lymphatic nodes occupying the saphenous opening. It offers, however, in this region, but litde resistance to the progress of pus towards the surface, as it is perforated— hence "cribriform fascia" — by the lymph- vessels passing from the super- ficial to the deep set of inguinal nodes, by the superficial epigastric and external pudic vessels, and by the internal saphenous vein to empty into the femoral. Lipomata are not infrequent in this fascia, especially on the front, but sometimes on the back of the thigh, and on account of its laxity and of the absence of firm attachments of their capsules, are apt to travel downward by gravity. Fig. 613. Femoral artery Femoral vein. PectineuR, upper portion Obturator nerve Internal saphenous vein \ Pectineus, lower portion Adductor longus and brevis, lower portion Ligamentum teres Pectineus, lower portion Dissection of thj-roid luxation of femur, showing muscles ruptured. The deep fascia or fascia lata (page 633), attached above to the lower edge of the great sacro-sciatic ligament, the tuberosity and ramus of the ischium, the crest of the ilium, Poupart's ligament, and the body and ramus of the pubes, and below to the lateral margins of the patella and to the tibia, and continuous posteriorly with the deep fascia of the leg, forms an almost unbroken sheath around the thigh. Its con- tinuity is interrupted only by the saphenous opening (page 635). It is of sufficient strength and density everywhere to influence the course of abscesses and to modify the surface appearance or feel of deep growths. A lipoma beneath the fascia lata may apparently have the density of a malignant growth. A psoas abscess (page 143), after it has followed the muscle under and below Poupart's ligament, usuaUy perfo- rates the sheath and the fascia lata and" points external to the vessels at the upper part of the thigh ; but after escaping from the sheath it may be unable to penetrate the fascia, and may be guided by it to the lower third of the thigh, the knee, or even as low as the leg or ankle. The fascia has been torn or wounded, and, as it embraces the subjacent muscles so ■closely, the latter have bulged through the opening, appearing on the surface of the thigh as rounded elevations varying in size and tension with the position of the limb. 644 HUMAN ANATOMY. Rupture of the fascia has, in recorded instances, been associated with rupture of the ilio-psoas, the rectus, and the biceps fenioris. The outer and inner intermuscular septa (page 636) are of less surgical importance than the corresponding structures in the arm, and have but little effect in limiting or determining the course of a cellulitis or an abscess. On the outer side of the thigh, running from the forepart of the crest of the ilium al)ove to the outer tuberosity of the tibia and the head of the fibula below, is the thickening of the fascia lata known as the ilio-tibial band, the dense, glistening fibres of which bridge over the supratrochanteric space between the summit of the trochan- ter and the iliac crest. Normally at this point the band otTers distinct resistance to pressure with the fingers. In fracture of the neck of the femur, with shortening, it must be relaxed and less resistant (Allis), and this sign is of especial value in obscure cases of impacted fracture of the neck in which crepitus, preternatural mobility, and other of the conventional symptoms of fracture are lacking (pages 364, 367, 390). The relations of the muscles about the hip to dislocation (Figs. 395, 396, pages 377' 37S) and to hip disease (page 3S1) ha\e been described. Suppuration affecting the iliacus or the ilio-psoas has also been dealt with ( page 381 ). Strains of the ilio-psoas muscle are not infrequent, and may, especially in chil- dren, give rise to a mistaken diagnosis of hip-joint disease. In sprains, however, the movements of the joint that do not afTect the ilio-psoas will be painless and most of the other anatomical symptoms ( page 380) will be absent. The extensive bursa between the capsule of the hip-joint and the ilio-psoas muscle {ilio-psoas bursal may enlarge and become \isible at the front of the thigh below the middle of Poupart's ligament. The thigh will be found flexed from reflex irritation of the ilio-psoas and to lessen pressure on the bursa (page 381). As the" latter not infrequently communicates with the hip-joint, infectious disease of one may extend to the other. The adductors are also often strained or overworked, particularly during horse- back exercise, and are sometimes sprained or stretched close to their pelvic origins. The latter injury may result in a sclerosis of one of the adductor tendons, possibly going on to true ossification, and producing a condition seen oftenest in cavalrymen, and known as " rider's bone." Fractures of the femur situated below the neck (page 363) and above the con- dyles (page 366) are much influenced by muscular action, as might be expected from the number and strength of the muscles concerned. Three of these fractures may be considered in this relation : 1. Fracture just below the trochanters (subtrochanteric fracture). This is one of the most difilicult of femoral fractures to manage because of the flexion, abduc- tion, and outward rotation of the upper fragment, caused by the action of the ilio- psoas, the gluteus minimus and medius, the obturators, quadratus, pyriformis, and gemelli. The lower fragment is drawn upward by the rectus, gracilis, tensor fasciae latae, and sartorius, upward and inward by the adductors, upward and a little backward by the hamstrings. In the treatment, elevation and abduction of the thigh — i.e., of the lower fragment — are often resorted to for obvious reasons. 2. Fracture of the middle of the shaft is very frequent (page 365). It is usually moderately oblique from behind downward and forward. The upper frag- ment is almost always in advance of the lower fragment because {a) the fracturing force is more apt to be applied from in front and to the lower rather than the upper part of the thigh ; (b^ the weight of the limb in the supine position would favor a posterior position of the lower fragment ; {c) the ilio-psoas tends to advance the upper fragment, and the adductor magnus and gastrocnemius draw the lower frag- ment somewhat backward (Fig. 614). There is often a forward angulation or bow- ing in the direction of the normal curve of the femoral shaft (page 365), thought to be due to the action of the adductors which subtend the arc of the curve. The shortening is produced, as usual, by the muscles running from the pelvis to the thigh and leg. 3. Fracture just above the condyles (supracondylar fracture). This is usually the result of severe injury or of direct violence. It is commonly oblique from be- hind forward and downward. The fracture takes place at about the point of junction PRACTICAL CONSIDERATIONS: THE KNEE. 645 of the compact tissue of the shaft with the cancellated tissue of the expanded lower extremity. It is from one to two inches higher than the epiphyseal line. The same backward rotation of the lower fragment occurs as in disjunction of the epiphysis (page 365), and in both cases from the action of the gastrocnemius. In the fracture, however, the sharp lower end of the upper fragment is far more apt to project ante- riorly than is the diaphysis in cases of epiphyseal disjunction. It is not infrequently entangled in fibres of the rectus and may lacerate the suprapatellar synovial pouch. The difference probably results from the character of the fracturing force, which in the epiphyseal accident is, in the majority of cases, hyperextension of the leg on the thigh. The action of the ilio-psoas tends to advance the lower end of the upper fragment, but must be feeble. The pectineus slightly and the adductors quite strongly draw it inward. The shortening is produced by the hamstrings, rectus, sartorius, etc. The most difficult element of the deformity to do away with is the posterior rotation of the lower fragment, which may also result in serious pressure upon or injury to the popliteal vessels and nerves. In setting such a fracture it may be neces- sary to relax the chief muscles concerned by flexing the thigh to a right angle with Fig. 614. Fig. 615. Vastus- extern us Lower frajjment Adductor muscles Lower fragment f Popliteal artery — Gastrocnemius outer head Tibia Gastrocnemius, inner head Dissection of fracture of upper third of right femur, showing forward and inward displacement. Dissection of fracture ot lower third of left femur, show- ing displacement of popliteal artery by lower fragment. the pelvis to relax the ilio-psoas, drawing the knee inward a little to relax the ad- ductors, and flexing the leg on the thigh to relax the gastrocnemius, and then to make extension by means of the forearm placed in the ham. Not uncommonly the displacement recurs so obstinately that it becomes necessary to treat the case with the leg fully flexed on the thigh, and even to divide the tendo Achillis. 3. The Knee. — The skin over the front of the knee is dense, coarse, and loose, qualities that diminish the gravity of the frequent injuries to the integument itself and also serve to protect the underlying joint, ' ' especially in stabs with bluntish instruments" (Treves) and, in fact, in many forms of accident in which the free movement of the skin over the subjacent structures serv^es to make the application of force to the latter much less direct. In full flexion the skin, in spite of its laxity, is drawn tensely over the patella, and a fall may result in an extensive wound. The relation of the cutaneous nerves and vessels over the knee to those supply- ing the articulation should be studied in connection with the common application of counterirritants or of blisters to the region. 646 HUMAN ANATOMY. The quadriceps tendon is separated from the femur by a lar^^e bursa, which, in from 70 to 80 per cent, of cases, communicates with the knee-joint and may be in- vohed in its diseases. When se|)arate from the joint and distended by effusion, it mav be mistaken for synovitis of the knee, but the patella will not be floated up and the concavities at either side of that bone and those at the sides of the lij4aniciitum patelUe will not be effaced. The prepatellar bursa, scparatin.u^ the ])atella from the skin, is frecjuently enlarged in persons who spend much time kneeling, — " housemaid's knee." The bursa between the ligamentum patelke and the tubercle of the tibia may be enlarged or inflamed, and is then apt to be painful on account of its compression between two non-distensible structures, the bone and the ligament. The little pad of fat (page 400) between the tubercle and the ligament, which protrudes at the sides of the latrer when the quadriceps extensor is in action (page 405), should not be mis- taken for enlargement of this bursa. Posteriorly — over the ham — the skin is thinner antl less mo\able. The deep fascia — here the popliteal fascia — is dense and exerts marked obstruction to the exten- sion of abscess, growth, or aneurism towards Fig. 616. the surface, in this way causing severe pain from the pressure upon the ner\'es that run through the space. As the latter is open ii ^^^, \\ above and below, abscesses may extend in ' -^"^^ * -Vastus ititenuis either direction. Pus or infection may be guided to the subfascial region in the ham from the pelvis or the buttock by the great sciatic nerve, or from the thigh by the femoral vessels, or >Fractured surfaces from the leg by the short saphenous vein, oi patella ^^ ^^, ^.j^^ deeper vessels and the lymphatics. The relations of the fascia and muscles ,^ ^ of the thigh to the patella and the knee- ■' ^l>om'"'!KltelL^?o-.T«u" Joi^t and to their injuries and diseases have j jar li.Lrament of iiiiee- been suf^cicutly described (Figs. 424-430, '"'"' pages 409-418). The hamstring tendons are not infre- quently dixided, as, for reasons already Disseoon of fracture of patella. g^ven, ankylosis of the knec-joint is usu- ally in the position of flexion (page 412). They are made very tense when the pelvis is strongly flexed on the thigh, the knee remaining extended. They may be ruptured if excessive force is applied under these circumstances. The biceps tendon is easily felt on the outer side of the ham, with the peroneal nerve, also readily palpable, lying against its inner and posterior border. At the inner side of the ham the semitendinosus tendon is nearer the mid-line, nearer the surface, more easily outlined, thinner, and more cord-like than the semimembranosus tendon, which is the most deeply situated of the three hamstrings. The line for dividing these tendons is preferably a little above the level of the knee-joint and about opposite the most salient parts of the femoral condyles. In the popliteal region there are several bursce : (a) the largest is between the inner head of the gastrocnemius and the semimembranosus and the inner condyle of the femur, extending downward to the inner tibial tuberosity and even as low as the upper margin of the popliteus ; it communicates with the joint in 50 per cent, or more of cases CFoucher, Gruber) ; (d) a smaller bursa is found between the serni- membranosus and the internal tuberosity of the tibia, communicating usually with the above-described bursa. Externally there are : (r) a bursa between the lateral ligament and the tendon of the popliteus \ (d) a bursa — a diverticulum of the syno- vial membrane of the knee (Nancrede)— between the same tendon and the external tibial tuberosity ; (' similar to that of the flexor Fig. 620. Inleriial condyle of femur Tendon of semimembranosus Poi>Iiteus Abductor and fJexor brevis hallucis Gastrocnemius Plantaris, cut Head of fibula Peroneus longus Soleus, cut Tibialis posticus Flexor longus hallucis Tendon of peroneus longus Peroneus brevis TiViia and posterior inferior tibio- 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 Flexor brevis minimi digiti Interosseus Lumbricales V_:^- — V-^*^^ ^^^ Tendons of flexor brevis digitorum Deeper dissection of right leg, showing flexors passing into foot. sublimis digitorum and flexor longus pollicis of the forearm. In other words, these muscle represent a layer of muscle-tissue which primarily arose from the bones of the leg and was in- serted 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 Fig. 621. Internal condyle Internal lateral ligament Tibia External condyle Tendon of popliteus "t-Head of fibula Oblique line Tibialis posticus Flexor longus digitorum, drawn aside artery exor longus hallucis, drawn aside Internal lateral ligament Tibialis anticus tJ | '/ / J Abductor hallucis, titiimp k^u&J Insertion of tibialis posticus Insertion of tibialis anticus Tendon of flexor longus hallucis 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 AxNATOMY. {cc) 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 flexor 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 lumba 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. an< 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 interxenes 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. Vastus intemus Inner condyle Insertion ■ : semimeipbranosu? Vastus extemus Popliteal surface of femur External condyle Cut edge of capsular ligament tLong; external lateral litrament Short external lateral ligament Popliteus. 1 f^\ ■ Interosseous membrane ■Fibula Variations. — A portion of the muscle is sometimes inserted into the internal annular ligament. A muscle, which has been called the peroneo-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 the leg;. It is usually ru- dimentant". but may form a well- marked triangrilar sheet. Flexor Accessorius (Fig. 628). Deep dissection of leg, showing popliteus muscle. Attachments. — The ac- cessory flexor 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 of the long flexor. The flexor accessorius. althou.s:h apparentlv located entirely in the foot, is, nevertheless, a crural muscle, since the tendon of the flexor lon8:us disjitorum,' 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 primarilv 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 slip from the posterior ligament of the knee-joint. It passes inward and downward to be inserted into the posterior surface of the tibia above the oblique 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. {b) 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 inserted 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. Relations. — l^y its deep surface and medially the muscle is in relation with the extensor longus hallucis, medially with the tibialis anticus, the anterior tibial ves- sel i^nd, nerve, and deeply with the deep .{O^roneal nerve above and the ankle']ofrf? below. Laterally it is in contact with the peroneus longus above, with the j^croneus.tertius be- low, and with the musculo-cutaneous nerve, which passes downward be- tween it and the peroneus longus (Fig. 617). Tuberale of tibia Intermuscular septum attached to fibula Peroneus brevis. Fibula Peroneus brevis tendon Outer malleolus Extensor brevis digitorum Peroneus tertius tendon Base of fifth metatarsus Portion of deep fascia of leg alf muscles ibialis anticus Extensor longus digitorum Extensor longus hallucis Peroneus tertius '^. ^ Inner malleolus ■ Anterior annu- lar ligament, vertical por- tion Anterior an- nular ligament, horizontal por- tion Extensor brevis digitorum :3 Superficial dissection of anterior surface of right leg, showing muscles undisturbed. Variations. — Considerable variation occurs in the arran.t^ement of the terminal tendons, one of the most usual departures from the typical condition beinjj 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 a?-ists 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 mser/ed 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, \\ hose connec- tions with the metatarsals are interesting in this regard. 4. Extensor 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 Outer tuberos ity of tibia Head of fibula Calf muscle Intermuscular septum Extensor longu digitorum Extensor loiigub hallucis Tubercle of tibia ^Calf muscles Tibialis anticus Crest of tibia 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. 0\'er the metatarso-phalangeal joint it spreads out into a mem- Fig. 624. branous expansion which 1 , , „ ^| receives a tendon of the j "f extensor brevis digitorum | / and is then continued dis- tally to be iyiserted 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 cov- 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 tibialis 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 ma}- 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 hallucis, 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 ^Hthe first phalanx of the hallux. I Peroneus tertius Anterior annular ligament cut edge Outer malleolus Peroneus brevis tendon Base of fifth metatarsus Abductor minimi digiti Muscles of anterior surface of right leg; extensor longus digitorum has been drawn aside to expose extensor longus hallucis. 5. Peroneus Longus (Figs. 625, 629). Attachments.— The peroneus longus arises from the upper part of the latera^ ^surface of the fibula and from the intermuscular septa and crural fascia. Its fib.c= 42 6=;8 HUMAN ANATOMY. extend obliquely downward to a tendon which passes behind the outer malleolus and then runs forward in a groove on the Fig. 625. calcaneum, 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 mserted 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 nerve 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 ner\e 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. 6. Peroneus Brevis (Fig. 624). Attachments. — The peroneus brevis lies beneath the peroneus lon- gus and arises from the lower portion Extensor of the lateral surface of the fibula torum.cut and from the intermuscular septa. Its fibres join a tendon which passes behind the external malleolus and then dis- Head of fibula Tubercle of tibia I-^xtcnsor longus digitorum, cut Tibialis amicus Calf muscles Peroneus longus Intermuscular septum attached to fibula Tendons of ex- ^") tensor longus 'j digitorum, cut Abductor minimi digiti Flexor brevis minimi digiti Superficial dissection of right leg, antero-lateral aspect, showing peroneal muscles. ner\'e from the fourth and fifth lumbar and first sacral nerves. 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 THE MUSCLES OF THE FOOT. 659 Fig. 626. Os calcis, inner tubercle Calcaneo-metatarsal ligament 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 directly 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 qiiintus. Kpero7ieus quartus, 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 ligatnent (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 Plantar fascia central portioi Plantar fascia, inner lateral portion Plantar fascia, slip for great toe Flexor longus hallucis tendon Superficial, transverse met- atarsal ligament Plantar fascia, outer lateral portion Plantar fascia, digital slips Superficial dissection of sole of right foot (subject lying on belly), showing 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) TnH Miscles ok the First Layer. 1. Flexor brevis digitoruin. 3. Abductor hallucis. 2. Flexor brevis hallucis. 4. Abductor minimi digiti. I. Flexor Brevis Digitorum i Fig. 627;. Attachments. — The short flexor of the toes i m. tle.xor 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 ciuadrangular muscle, the fibres of which are collected 1 Fig. Os calcis Abductor hallucis Flexor brevis liallucis Flexor longus hallucis tendon o\er the metatarsal bones into four tendons which pass to the second, third, fourth, and fifth toes. 0\er the first i)halanx of the toe each tendon divides into two ter- minal slips, between which the corresponding tendon of the flexor longus digitorum passes and which are m- soted into the second pha- lanx. Nerve-Supply. — By the internal plantar ner\e from the fourth and fifth lumbar and first sacral nerves. Action. — To flex the second, third, fourth, and Fle.xor brevis fifth toeS. niiiiinii aigili \ Abductor luiiiimi digiti l-'le.xor longus digitorum ten- dons Flexor brevis digitorum ten- dons Flexor tendons in sheath Flex. brev. digi- torum tendon Flexor longus digitorum tendon 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 w liich 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 lay^er of the aponeurosis. 2. Flexor Brevis Hallucis TFig. 628). Attachments. — The short flexor of the great toe Tm. 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 inserted into the inner surface of the base of the first phalanx of the great toe. Nerve-Supply. — By the internal plantar nerve from the fourth lumbar nerve. Action. — To flex the great toe. THE MUSCLES OF THE FOOT. 66 1 Variations. — The flexor brevis hallucis is frequently intimately fused with the abductor hallucis. 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 distinct 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 consisting of two bellies, the second of which is inserted into the lateral side of the base of the first phalanx of the great 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, origni Flexor longus hallucis tendon Tibialis posticus tendoi Flexor longus digitorum tend lU — ■^ Abductor hallucis, part of origni Abductor halluci'-, ■ ui 4v First plantar interosseiis Flexor brevis hallucis Lumbricales Flexor longus hallucis tendon Flexor brevis digitorum Flexor longus digitorum M Os calcis, outer tubercle \bductor minimi digiti, origin F ong plantar ligament -peroneus longus tendon Abductor minimi digiti, occasional insertion (Abductor ossis metatarsi quinti) Flexor accessorius Tubercle of fifth metatarsus Flexor brevis minitni digiti, part of its origin Flexor longus digitorum 1 lexor brevis minimi digiti U^v"^' y^ I^Abductor minimi digiti, >\\j\ ^ ' it' insertion ___^^Flexor longus digitorum ~~'W tendons Flexor brevis digitorum tendons, cut Long and accessory flexors of right sole, exposed by removal 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 calcaneum and from the plantar aponeurosis and being inserted, along with the fiexor 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 extends distally and laterally to be inserted partly into the tuberosity of the fifth metatarsal bone and {)artly into the lateral side of the base of the first phalanx of the little toe. Nerve-Supply. — By the external plantar nerve from the first and second sacral nerves. Action. — To abduct and flex 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 abductur ossis metatarsi 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 Muscles 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 flexor 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 extensor 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 })lantar from the fourth and fifth lumbar and first sacral nerves. Action. — To flex 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 l)urs:e 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. {cc) 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 obliqunm), or adduetor obliqims, 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 \\\q. transve7'se portio7i (caput transversura), or adductor transvet'sns. This extends almost transx'ersely, 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 accessor}' 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 foetus the two portions of the adductor are not separated by a wide interval as in the adult, but lie in contact with each other. I 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 tendon Flexor accessorius, inner head Tibialis posticus tendon Abductor hallucis, cut Flexor brevis hallucis First plantar interosseus Adductor hallucis, oblique portion Tendon of flexor longus digitorum Tendon of flexor brevis digitorum Flexor longus hallucis tendon Os calcis, outer tubercle Abductor minimi digiti Flexor accessorius, outer head Peroneus longus tendon ■Long plantar ligament Abductor ossis metatarsi quinti (part of abductor minimi digiti) Tendon of peroneus longus in sheath Flexor brevis minimi digiti ■Abductor minimi digiti Adductor hallucis, transverse portion Deep dissection of sole of right foot, showing short 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 minimi 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 t]\& 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 flexor brevis 664 HUMAN ANATOMY. hallucis, from the inner cuneiform bones and the adjacent H^amentous 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 iuscrtcci into the outer surface of the base of the first j)halanx 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. Flexoi -^-=i accessorivis Tibialis posticus tendon Long plantar ligament Peroneous brevis tendon Superfuial fibres of long plantar lig, hirrek- of fifth Insertion of percneus longus Insertion of tibialis anticus Adductor obliquus hallucis Variations. — As above stated, tlie first plantar inter- osseus is usually described as a second head of the flexor brevis hallucis. It is some- titiies more or less insepara- fjle from the ol)li(]ue portion of the adductor hallucis. 2. Interossei Dorsales (Figs. 623, 630). Attachments. — The dorsal interossei are also four in number. They a7'ise from the adjacent sides of each pair of met- atarsals and pass distally in the interspaces between these bones. The fibres of each muscle con\erge to a narrow tendon which is inserted into the mem- branous expansions of the extensor tendons o\'er 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 litde toe (m. flexor digiti quinti brevis), which really represents a fifth plantar interosseus, arises from the base of the fifth Tendonsof flex- or brevis hallucis and first plantar interosseus re- flected, with ab- ductor and ad- ductor tendons, showing the two sesamoid bones \ Deep dissection of sole of right foot, showing interosseous muscles. 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 nerve from the second sacral nerve. 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 opponejis quinti digiti. (b) THE POST-AXIAL MUSCLES. I. Extensor Brevis Digitorum (Fig. 624). Attachments. — The short extensor of the toes ( m. extensor digitorum brevis) an'ses 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 tendon to 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 FASCLE 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 o\'er the spine and antero-internal surface of the tibia, to glide away when force is applied partly 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 the head and inner and anterior borders of the tibia, 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 connecti\'e 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 invoh'ing 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. Fu ence on either the skin or fascial surface, and although described as a guide to the anterior tibial artery {g.2\), 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 tibula and runs transversely beneath the soleus and gastrocnemius, is weaker above, where it is covered and reinforced by the latter muscles, and stronger below, where it loses their sup- port. It is continued downward and separates the tendo Achillis 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 i case with the fascia lata, may for a time determine i 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 comj)arati\ely trifling exertion. 2. The Ankle and Foot. — The skin around the ankle and upon the dorsum of the foot is thin and lax. 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 1 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 andj abundant on the dorsum and around the tendo Achillis, in which latter region it contains some fat. Its laxity over the dorsum, while it somewhat protects the instep] from the effects of direct violence, adds greatly to the ease with which swelling orj oedema may occur in cellulitis or, on account of the dependent position of the par 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 ofl 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 pollicis and of the extensor com- Dissection of fracture of left tibia, showing effect 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 flexor longus pol- licis, the flexor longus digitorum, and the tibialis posticus run beneath the internal annular ligament, the last named being the deepest and in the closest proximity 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). 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 ; {b') the shallowness of the groove in which it runs ; (<:) the relative weakness of the single slip of the external annular ligament that covers the tendon; (^) 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 approximately 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 strongest. 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 between 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, adces 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 infra). Club- Foot. — The mechanics of the normal foot have already been sufficiently 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 equino-varus, when congenital, is believed to result from retention of the foetal position,—/.,?., from defective development. The inward rotation of the flexed and crossed limbs in titero, 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 flexion 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 paralvsis of those muscles that oppose the adduction and extension of the foot, — i.e., chiefly of e,6S HIM AN ANATOMY. the extensor longus dij^itoruni and the peronci. Tlic muscles that draw up the heel, the ijastrocnemius and soleus, — the muscles that elevate the inner border of the foot and adiUict it, — the tibalis anticus and posticus and the flexor longus dii,ntoruni, are not resisted ; t)r, if the case is congenital, are assisted by the position of the foot, which is therefore found with {a) the heel elevated ; {d) the inner edjj;e of the sole drawn upward ; (r) its axis turned inward ; (^d) the sole shortened, partly throuii^h 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 ha\ e 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 j)halanges, w hich may be at right angles to the line of the inner side of the leg. Pure ta/ipi-s ranis, in which the elevation of the heel is absent, is very rare. The other varieties of club-foot are seldom congenital. 2. Talipes la/(^its. — 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. T,. Talipes Eqiiiniis. — The heel is drawn up by the gastrocnemius and soleus ; the patient walks on the balls of the toes ; the os calcis and the astragalus are changed in position as in equino-varus. The astragalo-scaphoid and calcaneo- cuboid joints are much flexed, so that the scaphoid may e\cn be in contact with the OS calcis. 4. Talipes Calcaneus. — The extensor longus digitorum and the exten.sor 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 imtil its articular sur- face points in that direction. The patient walks on the heel. Flat-foot results from weakness or relaxation of plantar muscles, fasciae, 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, f)wing 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 bursa? 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 may 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 develop 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 undulv 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 bursae are found over the external malleolus, — " tailors bursa," — over the cuboid in equino-varus, and at other points exposed to pressure in the different forms of club-foot. Gluteus medius Greater trochanter Gluteus maximus Gluteo-femoral crease 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 superior spine, and is more or less Fig. 632. effaced posteriorly where the crest is co\ered by the flat tendon of the erec- tor spinse. The posterior superior Crest of iiium 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. Its 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 latae (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 ot the Extensor brevis digitorum Lateral surface of right leg. showing modelling on living subject. 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 Hexion 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) Antcrio?- 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 fasciee of the thigh and abdomen ; therefore that position is the one most favorable to reduction of cither 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 draw^n 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 re.spectively. 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 ver>' 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 betw^een the sartorius and the tensor fascic-e 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. 6i Poupart's • ligament -Scarpa's triangle eating the position of the ilio-tibial band of fascia between the insertions of the tensor fasciae latae and gluteus maximus and the external tibial tuberosity. 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 indistinctly. The corresponding internal septum— between the vastus internus and the adductors and pecti- neus — produces no surface marking. (^b) Posterior crural i'egion. The ham- strings, descending from beneath the lower edge of the gluteus maximus, cannot at iirst 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 by 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 outline 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 ha\'e 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 mternally 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- Patella' Tubercle of tibia- Subcutaneous- surface of tibia Muscles of calf Antero-median surface of right leg, showing modelling on living subject. 672 HUMAN ANATOMY. sionj they can he made to stand out with the tendon of tlie extensor proprius hallucis between them ; to the outer side of the extensor longus dij^itoruni ten(h)n a sHght iiToovc indicates the interval between that muscle and the peroneus tertius. The latter — as a muscle peculiar to man and probably dexeloping as a result of his assump- tion of the erect posture — is not invariably present. Above, between the extensor loni^us di_y;itorum and the soleus, the peroneus longus makes a longitudinal elevation shading off Ixlow — where the fleshy fibres become tendinous — into the flatter pero- neus brexis. 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 ha\e 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 anticus ; 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 le\el 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 corresi:)onding 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 tw^o 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 conca\ity 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 ha\e but little practical \'alue. As the foot, taken as a whole, acts as a le\er, 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 de\eloped 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 thp 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 lymphatic 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 i7itima, 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 tnedia, which typically is composed of intermingled lamellae of involuntary muscle and elastica and fine fibrillse of fibrous tissue. Outside the media follows the tunica 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 rei)lacing the definitely outlined plates. The presence of a relatively small oval nucleus is readily demonstrated by suitable stains. The involuntary muscle \aries in amount, from the imperfect single layer of muscle-cells found in the arterioles, to the robust muscular coat of many lamelke in the larger arteries. It is relatively best de\eloped 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 fibrilla that extend between the other components of the \ascular wall. Fig. 634. .<4. endothelium of aiteriole after silver-staining ; X 200. B endothelial cells more highly magnified. X 500. The elastic tissue is very conspicuous in all arteries save the smallest, and in many \eins. It prt-sents all variations in amount and arrangement from loose net- works of delicate filires 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 viem- 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 zasorum, as they are called, are usually branches from some neighboring artery, their fa\orite 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 \ascular wall is collected bv small \eins that accom- pany the nutrient arteries, or. as in the case of the veins, empty directly into the venous trunk in \\hose 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, \ki^ perivasczdar lymph- sheaths, 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 ior the muscular tissue and, therefore, are directed to the media, although 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-fibrilte penetrate the media and end among the muscle- fibres in the manner usual in such tissue (page 1015). Special sensory nerve- endings 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 j, after the usual methods of preservation and staining, the intima presents a plicated contour as it follows the foldings of the intomal elastic mefnbraiie that appears as a conspicuous corrugated light band marking the outer boundary 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. Intima ^^^^^^( Endothelium ^^:^^^- Internal elastic membrane -i*^ '^^^^^^^^^^^^t^pi^'^^i^'^^^S^^-^^-'^^S^^'^"^^ Involuntary muscle Elastic tissue Adventitia External elastic membrane Elastica Vasa vasorum 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 dyes, 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 \'asorum 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 tibre-cells that Fig. 6^6. Intima External elastic membrane Advent itia Transverse section of artery of medium size, stained to show elastic tissue. / 100. 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 ^^'^- ^^7- 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 x£Sf,^,\rff^ Small arteries in which muscular coat is reduced to single layer of cells, y 150. STRUCTURE OF BLOOD-VESSELS. 677 -^ Iiitima Media 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 intima consists of the lining endothelium, the cells of which are relatively broad and short, a thin layer of fibrous connective tissue and net-works of fine elastic fibres. A distinct interrfal elastic membrane is seldom pres- ent, at most a condensation of Fig. 638. elastic fibrillae 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 mus- 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 -<^iC^ leaflets ends in narrow prolonga- jl^-^ 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 from 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 \^eins, 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. ir^s ^J^- "^ '. Adventitia Areolar tissue 1 Transverse section of abdominal aorta. X 90. 678 HUMAN ANATOMY. Ititima Longitudinal bundles of striated muscle Media containing striated muscle Adventitia Lack of nuiscle within the media is often compensated by an unusual develop- ment of sudi tissue in the adventitia; in some large veins, as in the hepatic portion of the inferior cava, su- fiG. 639. 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 ])assing into veins of medium size, at first the muscle-cells are short and scattered and only j)artly encircle the tube. Far- Fig. 640. 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 efificient nutrition is mani- festly one insuring the passage of the blood-stream at a re- Transverse section of vein of medium size. Y 250. duced rate of speed in inti- mate relations with the tissue-elements. These requirements are met in the capil- laries whose collectively increased calibre and thin walls favor slowing of the blood- Transverse section of pulmonary artery near its root, showing striated muscle. X 150. Intima 'A: Media Adventitia Transverse section of vein of medium size. STRUCTURE OF BLOOD-VESSELS. 679 Fig. 641. f Portion of fem- oral vein, opened to show bicuspid valve. Stream and the passage of the plasma and oxygen into the surroundino- tissues. The walls of the capillaries consist of only the lining plates, the entire vessel beino- 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 sufiice 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 {adveiititia capillaris) that suggest an external 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 ner\'es 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 Fig, 642. • Capillary Arteriole Capillaries arising from arteriole and ending in small vein in omentum. X 200. the greater the functional activity of an organ, the closer is its capillary net-work. Organs actively engaged in excretion, as the kidneys, or the ehmination of substances 68o HUMAN ANATOMY. from the blood, as the Kings or hver, 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 i^ulmonary alveoli are of remarkable closeness and are often narrower than the capillaries surrounding thcni. 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 sulxlivision 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-trabeculae, little or no connective tissue intervening. F. T. Lewis ^ has shown that the Wolfifian 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 sangidnis in which are suspended vast numbers of small free corpuscular elements, the blood-ccUs. 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 afifinity for oxygen which, taken up from the air during respiration and combined as oxyhemoglobin, 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 erytli- 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 sodivim carbonate. Immediatelv 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, jelly-like mass, the blood-clot or crassatnejituvi, 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 fibrinogen 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 coloring 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. 68i 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 Teichyiann' s or hemin crystals and re- present one of the products derived from the reduction of hemoglobin. Being yielded by Fig. 643. 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 heniatoidin crystals 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 examination, the entire cells are never sharply defined and, according to focal adjustmenf, appear either as light rings enclosing dark centres or vice versa. Viewed in profile, the thicker convex 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 Fig. 644. to piles or rouleaus of coin (Fig. 646). Agitation dis- ^-T--— ^ perses the corpuscles, which, however, may resume their ^"v* *^~~ former grouping when again undisturbed. The columns \ A ^ "''^y Joi^ o"^ another until a net-work of rouleaus is fe ^ formed. If the stratum of blood be thin, the red cells / * I usually later separate, but they may retain their columnar grouping. Crystals of oxyhemoglobin from human blood. X 160. / iV V _ ' ^ £ The long-accepted biconcave discoidal form of the mam- \^ ^ w ^/ malian er>'throcytes 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, Henjin crystals from human similar to a sphere more or less deeply indented, thus reviving blood. X 250. ^j^g 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. >xi., 1902. ' Journal of Medical Research, vol. x., 1904. ^ * A critical review concerning tne form and structure of the red cells is given by Weiden- reich in Ergebnisse d. Anat. u. Entwick., Bd. xiii., 1904. 682 HUMAN ANATOMY. Dresbach' has recorded the presence of elliptical red cells in the blood of an apparently healthy mulatto. The oval corpuscles, which measured .010 mm. by ,004 mm., were approxi- mately constant in size, slijjhtly 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 erjthro- cvtes and leucocytes and the amount of Fig. 645. .0 ^oao ^^ \ Oqq 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 .0x378 mm. OOG > r^^ Red cells from hum.^n blood ; near centre of field. leucocyte seen ^, S65. it/j )V_^ T~^ V«y t T^^ ^ J (tt^Vit ^'''•)' some corpuscles meas- ■^'"^^ f^ — >— ^ urins: as little as .0045 inm. 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 sex and is constant for all races, although ac- cording to Gram, the size of the cor- puscles is somewhat greater in the inhabitants of northern countries. The number of red cells normally contained in one cubic millimeter of blood is approximately 5,000,000 in the male and something less (4,500,- 000) in the female. The number of 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 (.oo69]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, that 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, 1904, and March 24, 1905. Human blood corpuscles ; two leucocytes are seen among the red cells, most of which are grouped in rouleaus. X 625. THE BLOOD. 683 monkey's blood, human lachrymal or nasal secretion, being eliminated, a positive reaction with the serum-test is strong evidence of the presence of human blood. The nonnucleated condition of the mature erythrocytes is the distinguishing characteristic of mammalian blood as contrasted with the colored corpuscles of other vertebrates, 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 secondary deviation from the fundamental type represented by the oval nucleated erythrocyte of the other vertebrates, the nucleated embryonic red cell losing its nucleus as maturity is acquired. In general, the oval nucleated red cells are larger 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 .080 mm., and are approximately 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 external 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 amphiuma. X 750. 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 by 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 conveniently 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 by 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. Ipon treatment with water, aiiueous dilutions of acetic acid, ether, and other reagents, the erythrocytes are promptly decolorized by the e.xtraction 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 antl appears as a mass somewhat resembling a nucleus. When the reaction is feeble, ius with very weak solutions, the hemoglobin is less suddenly precipitated, and api>ears 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 preser\ing the form of the red corpuscles. Fixation by heat, so commonly used in the prepara- tion of blood s|iecimens for clinical examinations, produces alterations and often marked changes in the red cells, and, therefore, is unsuit.ible 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. Uj^on 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 enii)hasized 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 the lymph-\ascular system, from which they are poured into the blood. When examined in fresh and unstained ^^ ^ .jimi ■ preparations, the colorless cells or leuco- t|HP * L t ■^^P^'' 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 Jrrjacrnlarl v t;nhprinl or oval When nlaced normal human blood; a, small lymphocytes; irregUiari\ Spucricai Or 0\ ai. VV ncn piaceu h, iar;je lymphocyte or mononuclear leucocyte; on a warmed slide and maintamed at the c, transitional leucocyte; rf, polymorphonuclear c ^i i_ j r ^i 11 leucocytes; <>, eosinophiie ;/, red cells. X 900. temperature of the body, many 01 these cells soon exhibit amoeboid motion, 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 (exoplasm) and a central granular area {cndoplas^n) 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 body of the cell. Although the size of the colorless corpuscles varies with the type of the cell, as presently 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. E\-en 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 resume of their characteristics, based on the descriptions of EhrHch and of Da Costa, 1 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 chromatin ; 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 position 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 .010 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 examination, 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 granules. Although other types of colorless cells, as myelocytes and mast cells, are of clinical interest, they do not occur in 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 within the cytoplasm of closely packed fine granules that possess a strong affinity for 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 many other hematologists consider the lymphocytes and the leucocytes as entirely distinct elements, believing the former to be derived from lymphoid tissues and the leucocytes exclusively from bone-marrow. Accordingly, the large lymphocytes and the large mononuclear leucocytes are of different nature, although, as universally admitted, their assumed differentiation is at best uncertain. The presence of all forms of white cells in the circulation of the embryo long before the appearance of bone- marrow (Ebner) seems conclusive evidence that the origin of the leucoc}i:es is not limited to the marrow tissue. The Blood Plaques. — In addition to the erythrocytes and leucocytes, 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 beinj.:: colorless and devoid of hemoglobin and in staining readily in verv 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 amoeboid 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 t^\ 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. /^ Granules. — In addition to the corpus- v,,./ cles and the placjues, extremely minute gran- ^ ules occur in varying numbers in normal % human blood. The nature of these particles differs. Some are undoubtedly finely divided fat; others, described by H. F. Miiller under ® the name, hcmoconia., are of uncertain compo- sition, but not fatty; while a certain propor- Human blood, showine: red cells and .. . 111 1 • if 1 i- • • blood plaques. X 625. tiou 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 embrvo so far examined, it is fjrobable 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 embryo and, after the appearance of the large converging trunks, the viteUine veins and. arteries, joins the intra-embryonic trunks that coincidently 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 endothehal plates from which pointed sprouts grow into the surrounding tissue (Fig. 651 j. 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 Fig. 650. larger blood-vessels become rein- .___^ , - of both the red and white cells, including the various forms of the colorless corpuscles. The conclusion of Beard, 2 that the first IvmphoCVteS to appear within the Nucleated etnbryonal eryihro- 1 ^1 • '1 • ' 1 , . , cvtes; two dividing 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. Isxiii., 1909, 'Anatom. Anzeiger, Bd. xviii., 1900. THE HEART. 689 Megakarj ocyte body, has been challenged by Hammar and by Maximovv/ 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 multipUcation 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 formation 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 unsettled. 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, shortly 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 wathin 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 (Kolliker, Kuborn) to the endothehum of the vessels, while Ebner regards those within the bone- marrow as probably derived from fixed connective-tissue cells of the reticvilum. Nei- ther form of these giant marrow-cells is normally found within the post-natal circulation. Nucleated S red cells Leucocytes Osteoclast Osteoblasts 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- dium, 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. 1 Archiv f. mikros. Anatom., Bd. Ixxxiv., 1909. 44 690 HUMAN ANATOMY. It may be regarded as possessiiii^ two surfaces, whicli are not, however, distinctly separated, but pass intt) each other with roundetl edges, especially upt)n 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 pleurae also inter\ ening to a considerable extent; this is the anlcro-siipcrior surface (facies sternocostalis), and for convenience it may be more briefly termed the anterior surface. The other, the postero-itiferior or posterior surface (facies diapiirasiiuatica), rests directly upon the upper surface of the diaphragm. At about one-third of the distance from the base to the a])ex a deep circular groove, more distinct upon the posterior surface, surrounds the heart, separating an P^iG. 654. Superior vena cava Systemic aorta (aorta) Riglit auricular appendage Right auricle Auriculo-ventricular groo\ e Line of reflection ot I)ericardium Ductus arteriosus Pulmonary aorta (pulmonary artery) Coiius arteriosus Right ventricle Left ventricle Anterior inter\'entricu- lar groove Anterior aspect of heart hardened in situ ; probe lies in transverse sinus of pericardium. Upper thin-walled auricular portion of the organ from a lower thick-walled ventricular one ; this groove is termed the aiiriculo-ventricular groove (sulcus coronarius), 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 postet'ior i7iterve?itricu/ar grooves (sulci lonsi- 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, ihepulmotiary 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 aortae. 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 auricles., and com- municate with the corresponding ventricles by aiiricido-ventric^dar orifices guarded by special auricido-ventricular valves. From the lateral part of the anterior sur- face of each auricle a process, the a2u icular appendix, arises. These appendices are Fig. 655. Left common carotid artery Left subclavian artery Innominate artery Left pulmonary artery Vestigial fold Sup. left pulm. vein Left auricular appendix Inf. left pulm. vein Coronary sinus Left ventricle Azygos vein Superior vena cava Right pulmonary artery right pulmonary veins Inferior vena cava Right ventricle Apex Posterior aspect of heart hardened in situ ; showing lines of reflection of pericardium. slightly flattened prolongations of the auricles, and bend forward aroi^nd the bases of the aortae, 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 inferior, 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 niMAX ANATOMY. Position. — The luart may vary considerably in position without bcint; regarded as abnormal, but what may be considered its typical j)osition 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. (3}^ in.) from the median line, this position being- median to and slightly below the junction of the fifth cf)stal cartilage with its rib. The hvil of the base may be a])pr<)ximately indicateil by a line drawn from a ]M)int slightly abo\e the upjier border of the third costal cartilage of the left side, al)out4. S cm. (1-^4 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. ( 1 14^ 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 frf>m in front. Considerable imi)ortance at- taches to the location ot the auriculo- ventricular and aortic orifices with reference to the anterior thoracic wall. The right aiirieiilo-ventriadar ori- Jiee 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 aurieulo-vejitricidar 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 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, / ../ ~"^'" Positicn of heart and valves in relation to anterior thoracic wall. A, aortic valve ; P, valve of pulmonary aona ; T, tri- cuspid valve ; M, mitral valve. 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-\ entricular 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.xth, 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 ahera- 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 co\'ered by the anterior borders of the lungs and pleurae, which separate it from contact with the anterior thoracic w^all. 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 \-ertical 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 absolute did- 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 indi\-idual variation in the size of the heart, and marked discrepancies exist in the obser\'ations that ha\'e 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. (4^-6 in.), a greatest breadth of from 9-11 cm. (3)^-414^ in.) and a thickness of from 5-8 cm. (2-3 J4 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. (9^4^ 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 se\'entieth 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, littie 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 \'entricular portion the greater part of the anterior surface is formed by the right \'entricle, 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 dextrum") is a relatively thin- walled chamber having in cross-section a roughly triangular form, the \'arious sur- 694 HUMAN AxN ATOMY. faces, however, passin^j into one another ahnost insensibly without forminc;^ distinct angles. Viewed externally, the roof of the chamber is directed upward, backward, and somewhat to the rij^ht, 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 coronary sinus. The antero-lateral wall is j)rolonged 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 T 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 ventricle, and is perforated by an oval ai)erture, the right auriculo-ve?i- tricular orifice, which places the ca\'ity of the auricle in communication with that of the right ventricle. Fig. 657. Vena azygos Superior ^^ \ vena cava Right pulmo- nary artery Sup. pulm. vein Inf. pulni. vein Fossa ovdlis, surrouncled by annulus Inferior vena cava Systemic aorta I'ulmonary aorta or artery Right auricular appendage Right ventricle, conus arteriosus Right auriculo- ventricular valve fice of coronary sinus, guarded by Thebesian valve Eustachian valve Depression receiving Thebesian veins Interior of right auricle exposed after removal of part of heart wall. 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 delicat' shining membrane covered by flattened cells and termed the endocardium. Thr general smoothness of the surface is, however, interrupted here and there by minutt- depressions (foramina venarum minimarum ) into some of which open the orifices ot 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 trabeculee, the musculi pectinati, which are everywhere lined upon their free surfaces by endocardium and give to the appendix a somew^hat spongy texture. In the roof of the auricle is seen the circular orifice of the superior vena cava, unguarded by vah'es 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 superior one, measuring from 27-36 mm. in diameter. The lower and lateral margins of this orifice are guarded bv a crescentic fold, the Eiistachian valve (valvula venae cavae inferioris), which tends to direct the blood entering by the \ein upward and medially, and is the remains of a structure of considerable importance during foetal life (page THE CHAMBERS OF THE HEART. 695 Pulmonary aorta Right auricular "age 708). Between the superior and inferior vense 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 07-ifice 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 annulus ovalis (limbus fossae ovalis). The fossa ovalis indicates the position of what was in fcetal 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 systemic 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 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 frequently, 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 examined. 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 obliquely ox&x this surface towards the coronary sinus is a small vein, known as the oblique veiji 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 appendix the spongy structure due to the existence of anastomosing imisculi pectinati also occurs, and occasional depressions of the surface mark the openings of ve7i£e Thebesii, which are, however, much less abundant than in the right auricle. The openings of the piil- 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 frequendy to be observed, and immediately anterior to it there is usually a small crescentic fold, the semilunar fold, whose concavity is Inferior vena cava Coronary sinus Heart of foetus just before birth ; wall of right auricle lias been cut away, showing foramen ovale. 696 HUMAN ANATOMY. directed forward, and w hich represents the free edge of the posterior segment or fold of the auricular septum (page 70S). In the Hoor is situated the large circular auriculo-icnlriculay orifice by which the ca\ity of the auricle communicates with that of the left ventricle. The Ventricles. — "i'he two \entricles present many features in common and may be descritn-d together, such ditierences as exist 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 ape.x downward. The edges of the left ventricle are. however, somewhat more rounded than those of the right, so that its form apj^roaches more nearly that of a cone ; and, furthermore, it is somewhat Fic-. 659 Systemic aorta Left pulmonary artery Superior left pulmonary vein Left auricular append i.\ Part of posterior leaflet of mitral vaht Anterior (aortic) leaflet of mitral valve Left ventricle - Superior vena cava Azygos vein Right pulmonary artery Superior right pulmonary vein Inferior right pulmonary vein Left auricle, opened Inferior vena cava Coronary sinus, cuf Interior of left auricle 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 antero-lateral, posterior, and median, but in using these terms the heart is to be regarded as placed so that its long axis is ver- tical ; in situ the antero-lateral surfaces look largely upward and the posterior sur- faces downward. The median wall is a partition, the interventricular septum (septum ventriculorum), common to the two ventricles, and completelv separates their cavities. Throughout the greater part of its extent this septum is muscular, but towards its upper border it becomes fibrous {pars niembrayiacea^ 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 infundibulnm. 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. Fig. 660. Svstemic aorta Superior vena cava Inferior vena cava Eustachian valve Pectinate muscles Thebesian valve guarding opening of coronary sinus Posterior leaflet o tricuspid valve Pulmonary aorta (pulmonary artery) Left coronary artery ^^^^i Leaflet of aortic valve Anterior(aortic) eaflet of mitral valve Membranous part of interventricu- ar septum Medial leaflet of tricuspid valve Inter\-entricu]ar septum Septal papillary muscles' 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 co\'ered 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 extremity to the wall of the ventricle, but are free from it throughout the intervening 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, chordce tendinece, 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 cohimn(Z carnece is applied, while those of the third group are known 698 HUMAN ANATOMY. as tlic musculi papillans. Quite frequently in the right ventricle and more rarely in the left, a muscular hand 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 hand. Here and there between the column;e carne^e of both ventricles minute orirtces of the Thebesian vessels occur. Around the orifices situated at the I)ases of the ventricles the muscular sub- stance of the heart's walls passes o\er into dense fibrous tissue, of which the portion Fio. 661. Pulmonary aorta (pulmonary arter>' Leaflets of imltnonary semilunar valv Corpus Arantii on posterior leaflet Anterior leaflet of aortic valve, cut Septal chordae of tricusoid valve Interveiitriiular septum Muscle of left ventricle Moderator ban Anterior papillary naiscle Superior vena cava S\steniic aorta Ri^lit coronary artery Right auricular appendage Pectinate muscles Anterior leaflet of tricuspid valve Margin of tricuspid valve Chorda; tendineae Columna carnea Anterior wall of heart hardened in situ and sectioned parallel to posterior surface, viewed from behind ; only 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 proximal portions of the aortse be removed, the fibrous tissue will be seen to form four rings { annuli tibrosi), 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 direcdy 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 auric ido-ve7itricular 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 i^fila 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 mitral 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 infimdibular 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 valves, 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 tendinese 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 nausculi 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 \'alve 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 valves, 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 valve. When distinct accessory segments occur, they also receive the insertion of some of the chordae tendineae. 700 niMAX ANATOMY. The Semilunar Valves. — Allhuugh really belonging to the piihnonarv and systemic aorta-, it is comcnicnt to consider these valves along with the heart, since they prevent the regurgitation of the blood contained in the aorta- into the \entricles at the c»)nipletion of their contraction. The segments guarding these valves are three in number in each aorta and an attached to the fibrous ring of the aortic orifices. Each segment is a crescentit pouch-like structure, whose cavity is directed away from the heart, so that any ten- dency for the blood to return from the aortie into the ventricles will result in the fill- ing of the pouches so that the three are brought into apposition and eli'ectually close the orifice. Their efiliciency 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 Aran- tius, which tills 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 \al\es of the systemic aorta ( valvulao semilunares aortae) are somewhat stronger than those of the jnilmonary aorta (valvulae scmilu- Fio. 662. Post, leaflet ot pulm. valve Left coronary artery, behind left posterior leaflet Anterior cusp of left auriculo-ventricular valve Posterior cusp Fibrous ring surrounding mitral valve oronary artery, behind anterior leaflet Right posterior leaflet ot aortic valve Anterior cusp of right auriculo-ventricular \alve -ff — - Fibrous ring surrounding ■'' tricuspid valve \'alves of heart viewed from above, after 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 in s/tu.so that one is situated anteriorly and the other two right and left posteriorly. In the ]xilmonary aorta one valve segment will be posterior and the others right and left anteriorly. If, however, the heart be held so that its \entricular septum lies in the sagittal plane, then the valve segments differ by 60° from the relative position given abo\e, 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 e.xpected from the manner of development of the valves ('page 710"). 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 detinite 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 f)rifices 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 valve Portion of left ventricle, showing position ( + ) of auriculo-ventricular muscle bundle in membran- ous part of interventricular septum. (Retzer.) 2. Ansiform fasciculi, \^'hich take their origin from the auriculo-\entricular 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 aiiriculo-ventriciilar fasci- cuhcs. 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 (ErlangerJ. 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 vah-es. 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 M'hich 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 Left auriculo- ventricular orifice ^i^Q^ Diag-ram of course of superficial muscle layers originating m right and left auriculo-ventricular rings and in posterior half of tendon of conus arteriosus. {MacCallum.') 702 HUMAN ANATOMY. P'lG Tendon of conus arteriosus Right aiiriculo- venlricular orifice Diagram of course of superficial muscle layers originating in anterior half of tendon of conus arteriosus. (MacCallum.) \entriclcs, and when tlitv 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- ing beneath the fibres from the right ring, encircle the right ven- tricle and finally terminate in the pajiillary 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 difficult 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 found that both the cones are formed by the curving of a con- tinuous sheet of fibres in an S-shaped manner. This deep 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 surrountling its basal portion. Structure. — The heart muscle, the myocardium, is both covered and lined with serous membrane, the epicaj'dium, as the visceral layer 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 co\'ers its free surface and rests upon a stratum of tibro-elastic connective tissue. The elastic fibrillce are very line and numerous and, immediately beneath the endothelium, form a dense net-work. When not separated from the muscle b\' subserous fat, as it con- spicuously is in the in- Fig. 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- ary vessels, as well as the ner\e trunks and the microscopic ganglia connected with the car- diac plexuses, lie be- neath the epicardium or within its deepest laver. The endocardium follows all the irregular- ities of the interior of the heart, lining every 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 Endo- thelium Heart muscle Blood-vessel Section of endocardium. VESSELS OF THE HEART. 703 Fig. Muscular tissue Fibro- elastic tissue of valve- leaflef 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 tlie 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 chordae tendinese is continuous with the middle layer, while meagre peripheral bundles of muscle may be present beneath the endocardium. Al- though thinner than the auriculo- ventricular, the pulmonary and aortic 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 ox, the imperfectly differentiated fibres, known as fibres of Purkinje, are represented in the human heart-muscle by subendocardial fibres. 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 systemic 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, ^hat 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 Chorda; tendiiieas Papillary muscle Longitudinal section of leaflet of tricuspid vah e 20 704 HUMAN ANATOMY. supplied by the lij^htonc, or vice versa, and sudden occlusion of eidier 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 arterv is continued, form a continuous net-work, a passage-way for the blood of one artery into the territory normally suppHed by the other may be formed by their enlargement, opportvmity for which may be affortled in cases in which thi' occlusion of an artery has l)een \ery gradual in its de\elopment. There is, however, another way by whicli the tissue t)t tlie heart may receive nutrition in cases of gradual ucclusion of the coronary arteries, namely, tlirou.^li the Tliebesian orifices in the walls of the auricles aiul ventricles. These openins^s conununicate by means of capillaries witli tile coronary vessels, and it has l)een sliown e\i)erinKntally tliat the heart can he effectively nourisiied by bk)'od |)assing from the chambers of the heart through tlie 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, ami 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 ]:)ulmohary 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 bihircation of the trachea. The Nerves of the Heart. — The nerves of the heart are derived from tlic cardiac ple.xuses and, passing downward along the aort^e, are distributed partly to the auricles and pardy accompany the coronary arteries along the auriculo-ventricular groo\e, where they form the eoronary ple.xns, 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 plexus branches pass into the substance of the heart to terminate upon the muscle- fibres. Some nerve-librcs 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 those which have been deter- mined experimentally for those of the lower mammals, bi tlie latter it has fieen shown that the cardiac ple.xuses contain both afferent and efferent nerve-fibres. The cardiac plexuses are formed by branches from the pneumogastric and sympathetic nerves, 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 the.se fibres art- consequently termed \\\^ accelerator ox an s^mentor fibres. Both the inhibitory and augnientor fibres are efferent, — i.e., they carry impulses from the nerve-centres out to the heart ; in addi- tion, the existence of afferent fibres has been determined among the pneumogastric 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 intestinal 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- minate upon cardiac ganglion-cells which transmit the impulse to the muscle-fibres is a point whicli 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 invohmtary muscular tissue, it would seem probable that the pneumogastric efferent fibres terminate primarily 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 vitelline and allantoic (later umbilical) veins from the extra embryonic vas- cular net- works — converge to- wards a common sac, the sinus venosus, which joins the caudal end of the cylindrical primitive heart. The slightly tapering cephalic extremity of the latter becomes the trmiais arteriosus, from which two trunks, the ventral aortcs, are prolonged forward beneath the primitive pharynx, giving off 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 position 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 primitive auricle, that indicates the position of a contracted passage, the aicricular canal (Fig. 672, C), as the common auriculo-ventricular opening is termed. Coincidently 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 layer Gut-tube Splanch- nopleura Heart-tube Transveise section of very young; rabbit em- bryo, showing two heart- tubes widely separated by unclosed digestive tube. X 150. 7o6 HIM AN ANATOMY. n'cii/ar appoidaa^es, rapidly increase, until they form tlic iiKist conspicuous part of the youny: heart (Fij;. 673, C), embracing the upper part of the truncus arteriosus an< overlying; the ventricle. .Sleanw hile the ventricular segment has assumed the most dependent and ventralj position, for a time ajipearing as a transversely expanding sac (Fig. 672, B) that ii form recalls a greatlv ililatecl stomach, the truncus arteriosus joining the " pylorus,"! and the contracted auricular canal suggesting the oesophagus. Soon, however, the higher right entl of the ventricular segment sinks to the level and gains the ventrall plane of the left end. the ventricle in consequence losing in width but gaining in! height. A shallow longitudinal crescentic furrow, the later interventricular i^rooveX now appears on the surface of the ventricle and suggests the subdivision of this seg-j ment into right and left Fig. 669. chambers, at the sam< — ^,,^^ time indicating the posi-^ ^\ tion of the growing inter- / ^ nal partition that leads toj this separation. Sections of the younj heart ( Fig. 670 ) sho\ the \ enous and ventricularl segments as widely com- municating portions of thel sigmoid tube, the walls ofj which are compo-sed of the] myocardial and endothe-j lial layers. In somewhat' older embryos (Pig. 671), the communication between these di\isions of the heart- tube exhibits a slight con- traction, marking the posi- tion of the later auricular canal, which becomes a nar- row transverse cleft that connects the primitive ven- tricle with the auricular chamber. The myocar- dial layer of the heart- wall, particularly in the ventricle, 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 di\ision is efifected by the formation of a \ertical partition consisting of an upper auricular, a middle valvular, and a lower \entricular part, supplemented by the aortic septum that appears in the truncus arteriosus and subdivides the latter into the pulmonary and systemic aortae. The subdivision of the auricle, which anticipates that of the ventricle, begins in the fourth week with the downward extension of a crescentic fold, the aiirictdar sep- tum, or sepiian primiim, that gradually grows from the postero-superior wall of the auricle towards the auricular canal and fuses with the partition that, as the septiivi inter?)iediicvi, 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 Posterior cardinal vein Right umbilical vein Right vitelline vein Left vitel- line vein 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 can*l (•■•■-4 * j- TT "^J^SSSS??^™^ _£"% 11 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 valvular septum. This opening enlarges and remains as the /oramefi ovale that persists until birth as a direct passage for the blood from the right into the left auricle during the continuance of the foetal 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 ve7itricular 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 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 mto 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 venosiis, 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 with 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 re^aiiens (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 septzim spurium (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 vense 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, Primitive auricle Myocardial layer Primitive ventricle Transverse section of early rabbit em- bryo passing through 5-oung heart, showing venous segment behind and arterial in front. X 75- 7o8 HUMAN ANATOMY. Vis. 671. Aorta Auricles on the contrary, persists and differentiates into the larger Eustachian valve, that guards the lower margin of the inferior vena cava-tmd directs its blood-stream towards the foramen (nale, 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 ()\ale within the interauricular partition. From the roof and anterior wall of the right auricle an additional and relatixely 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 the lunate borders are not in contact. Since the di\ision of the heart into a right and left side is inseparably con- nected with the de\elopment of the lungs and the consequent necessity for a distinct pulmonary circulation, provis- ion for the return of the blood from the lungs to the heart is made by the early formation of the p2ilmonary veins. 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 next by the two secondary 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 fa-tal appropriation. The differentiation of a right and left anriculo-venty-icular valve proceeds from the subdi\ision 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 valves elongate and project into the ventricles 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 chordae tendineae, results from the secondary union of the immature flaps with the trabecuUe of the spongy myocardium of the young heart. The loose muscular walls undergo partial consolidation, so that ;^^ — .Auricular '•■'i-:t} canal pi^^-M— Etidocar- dium -Myocar- dium Truncus arteriosus 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 F;g. 672. A B C Reconstructions of developing hearts; A, from human embryo of about 14. days (2.15 mm. long) ; B, of 21 days (4.2 mm.); C", of 23 days (4.3 mm.); /a, truncus arteriosus: pv, primitive ventricle; sv, sinus venosus; aa,a'a', right and left auricular appendages ; avc, auriculo-ventricular canal. X 20. (^Dr awn from His models.) Fig. 673. A B Reconstructions of developing hearts; A,{rom human embryo of 25 days (5 mm. greatest length); .5, endo- thelial heart from same ; C, of 35 days (13.7 mm.); ra, /a, right and left auricles represented by large auricular appendages; ;y, fo, right and left ventricles; /a, truncus arteriosus; behind, a ca\ity or cleft, known as the transverse sinus of the pericardium (Fig. 654 ), which is continuous at either extremity with the general pericardial cavity, and is roofed in by the parietal lajer, while its walls and floor are formed by the visceral layer. Ill the roof of tlie sinus Iransversus a slight fold is to be found towards the left, which passes backward to the line of attachnient of the roof to the left auricle and thence (>I)li(|ueIy downward in tlie visceral layer CDxering the posterior surface of the auricle lowartls the coro- nary sinus. This duplicaUire, known as the vestigial fold of the pericartliuni i liKamentum v. caviie sinistnic 1, contains in Us upi^er part a fibrous cord and in its lower part the oblique vein of the left auricle ; these two structures, the vein and fibrous cord, together with the coronary sinus, representing the remains of an original left superior vena cava. It may be noted that the line of attachment of the parietal layer between the left pul- monary veins and the inferior vena cava extends high up t)n the posterior surface of the auricle-^ and there is thus formed in this region a poucli-like diverticulum of the pericardium who^' mouth looks downward. This is what has been termed the oblique sinus of the pericardium. Its parietal wall rests upon the cesophagus posteriorly, and in case of extensi\e effusion into the pericardial ca\ ity, compression of the cesophagus sufficient to interfere with the act of swallow- ing may result. The Ligaments of the Pericardium. — The parietal layer of the pericardium is united to the surrounding structures by areolar tissue which may condense to definite bands termed pericardial ligaments. Thus the tissue between the pericardium and the sternum may condense to form a superior and an inferior pcricardio-stenml liga- ment, the former passing to the posterior surface of the manubrium sterni and the latter to the lower part of the gladiolus. Similarly, bundles of fibres are attached to the ape.x of the pericardial cone and to the great \essels of the heart, taking their origin from the prevertebral layer of the cer\-ical fascia which is prolonged downward into the thorax ; these are \.h(t pericardio-vertebral /ioaments. And, finally, a band has been described as extending from the posterior surface of the pericardium to the; upper surface of the diaphragm on either side of the vena cava inferior ; these form what are termed the pericardiophrenic ligaments. The Vessels. — The a?ierics which supply the posterior surface of the parietal layer of the pericardium arise from the thoracic aorta, and those of the anterior sur- face are given off by the internal mammary artery. The vei7is of the parietal layer pursue courses parallel with those of the arteries, and open into the vena azygos behind and the superior phrenic or superior \ena cava anteriorly. The lymphatics pass to the nodes lying in the bifurcation of the trachea. The vas- cular supplv of the \isceral layer is the same as that of the muscular tissue of the heart. The nerves distributed to the pericardium include fibres from the phrenic nerve, especially the left one, and also probably from the cardiac plexus. PRACTICAL CONSIDERATIONS : THE PERICARDIUM. The visceral layer of the pericardium is closely attached to and practically insep- arable from the heart muscle. It is continuous with the jjarietal layer at the base of the heart where the two layers ensheathe the great \essels, covering in especially the first inch and a half of the aorta and pulmonary artery and lea\ing, between those vessels in front and the auricles behind, an open space — the trans\erse sinus — which may be the seat of an effusion walled off by adhesions from the general peri- cardial cavity. The least resistant important structure in immediate relation to this sinus is the superior vena cava, — also intrapericardial at its lowermost portion, — and such effusion might therefore cause fulness of the \eins of the neck or even cyanosis without the evidence of a general pericardial dropsy large enough to give the usual concomitant physical sx^ns (vide infra). In artificial distention of the pericardium the sac tends to assume the shape of two irregular spheres, the upper or smaller one containing the great vessels just mentioned, the lower embracing the heart, the ascending cava, and the pulmonary veins. At the apex of the heart, where the peri- cardium is reflected from the diaphragm, unimportant sinuses, analogous to the costo-phrenic sinus of the pleura, may exist. PRACTICAL CONSIDERATIONS: PERICARDIUM. 717 The parietal layer of the pericardium is in relation with an external fibrous layer which extends beyond the serous investment of the roots of the great vessels, blends with their outer coats, and is directly continuous with the deep cervical fascia, thus connecting the pericardium with two respiratory agents, the diaphragm below and the cervical muscles (omo-hyoid) above. When these act conjointly, as in a full inspiration, they render the pericardium tense and resisting, and minimize the pressure upon the heart by the inflated lungs (page 551). Pericarditis — probably more often overlooked than any other serious disease (Osier) — may arise from wound from without, as in ordinary penetrating wounds of the chest, or from within, as from the passage of a foreign body from the oesoph- agus into the pericardium (page 1614); or it may follow extension of disease from contiguous organs, as in pleuro-pneumonia. The anatomical relations of the peri- cardium explain these occurrences. The more usual causes, as rheumatism, septi- caemia, gout, and nephritis, have no anatomical bearing. Pericarditis is attended by certain symptoms — well detailed by Sibson — ^which should be studied in connection with the anatomy of the heart and pericardium. I. Pain — (jx) spontaneous and direcdy over the heart, the pleurae often being involved, both these serous membranes — like the peritoneum — becoming painful when inflamed, although normally insensitive ; ((5) elicited by pressure (tenderness), the skin over the precordium sometimes participating on account of the connection between the upper intercostal nerves and the ganglia and nerves of the cardiac plexus ; (<:) over the epigastric region and increased by pressure, because, although normally the pericardium below is in direct relation with the thoracic parietes over only a small area behind the xiphoid cartilage, distention of the pericardial sac, as in effusion from pericarditis, carries it downward so that it may be well below the tip of the xiphoid ; (^ ) between the scapulae or deep in the chest, increased by swallowing or by eructations, and worse when the patient is supine, due to the relation between the oesophagus and pericardium just below the aortic arch ; ((?) in the side, usually pleuritic (from extension), and more common on the left side on account of the greater extent to which the inflamed pericardium occupies the left side of the chest than the right side, to the marked backward displacement of the lower lobe of the left lung by the distended pericardial sac, and possibly (Sibson) to the pressure of the latter on the left bronchus increasing in the left lung the tendency to intercur- rent pneumonia. 2. Feeble or irregular heart actio7i, due to («) direct extension of the inflammation from the visceral layer of the pericardium to the heart muscle (myocarditis) ; {b) impUcation of the cardiac nerves ; (c) pressure by the pericardial effusion on the venae cavae and pulmonary veins, impeding the blood-supply to both auricles ; direct pressure upon the auricles interfering with the ventricular supply ; and pressure upon the whole organ both directly from the effusion and indirectly from the compressed and displaced lungs and the other contiguous structures, embarrass- ing its action, especially in diastole. 3. Dyspyioea, due to the pulmonary congestion produced by the previous causes ; sometimes the result of a pleurisy or pleuro- pneumonia by extension ; or perhaps, as Hilton has suggested, partly from fixation or irregular action of the diaphragm through irritation of the pericardiac filament of the phrenic (ramus pericardiacus), usually given off on the right side. 4. Dys- phagia (page 1 6 14) from compression of the oesophagus between the pericardium and the vertebral column, usually relieved when the patient is put in an approximately vertical position. 5. Aphonia, from involvement of the left recurrent laryngeal nerve by contiguity, or of both nerves through their cardiac branches. 6. Fulness of ^ the cervical veins and flushi^ig or cyanosis of the face, due to pressure upon the thin walls of the right auricle and of the superior vena cava. Compression of the left auricle is better resisted on account of the greater thickness of its walls ; when it occurs, it tends to produce pulmonary congestion or apoplexy. TV^ physical signs oi pericarditis are, of course, influenced by the attachment, surroundings, and physical qualities of the pericardium. I. As it is in two layers normally movable upon each other, the roughening caused by inflammation produces 2. friction- sou7id which, when typical, is (a) heard best over the middle and the lower half of the sternum, and over the adjoining left costal cartilages or their interspaces, because there a greater extent of the pericardium is 7i8 HL.MAX ANATOMY. closer to the ear, with fewer intervening structures than elsewhere ; (^) preceded or accompanied by pain (ride supra); {c) usually increased by pressure with the stetho- scope, which brinies the two routjhened pericardial layers into closer apposition ; (- artery. Relations. — Throughout the greater portion of its length the pulmonary aorta is invested 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 appendix, and posteriorly it is in relation with the base of the systemic aorta and the proximal portion of the right coronary artery. More distally 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 f 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 king. 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 cjiindrical 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 convex surface. This cord is the remains of a communication between the pulmonary and systemic aortae 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 rnonths 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 of 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 occurs, 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-like manner to the left side of the vertebral column, 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 coccyx, 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 abdoyninal 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 portion (aorta ascendens) 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 (arcus 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 from 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 pneuniogastric nerves, arranji^ed in that order from right to left, the pneumogastric crossing it on a level with the origin of the left subckuian artery. Remains of tlivmiis II. costal cartilaire \ Fig. 680. Sternum LuiiK^ — ■ Left phrenic nerve Ascending portion Bronchial lymph-node Pleural sac — Transverse portion Left pneumogastric nerve Left recurrent laryngeal nerve Descending portion CEsophagus Thoracic duct .Pericardial sac J^;S^^ Lung Right phrenic nerve — Superior vena cava - Bronchial lymph-node - Bifurcation of trachea — Right pneumogastric nerve Vena az>gos 1\'. thoracic vertebra Part of cross-section 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 ca\a, the trachea, the oesoph- agus, and the body of the fourth thoracic \ertebra, 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 \er- tebra; to the right of it are the (Esophagus and the thoracic duct and also the body of the fourth thoracic vertebra, anci to the left are the left pleura and lung. Branches. — Just above its ^^ origin the aortic arch gives of! (i) the r/g-/if and /e/f coi'onary arteries, and from the upper or conve.x surface of the trans\erse portion there arise in succession, from right to left, (2) the innom- inate or brac]rio-ccphalii\ ( 3 ) the left common carotid, and ( 4 ) the left subclavian artery. Variations.— Owing to the com- plexity of the changes by which the priniar}' arrangement of tfie branchial arch vessels is transformed into the aduU arrangement ( F"igs. 681, 6S21, and owing also to the possibihty of some of the normal changes remaining uncompleted, the variations which oc- cur in connection with the arch of the aorta are rather numerous. Tliey may be conveniently 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 subclavian artery, indications of it persisting as a more or less rudimentarj- I'as aberrans 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 showing primary arrangement of longitudinal stems and series of si.x aortic bows ; 7>1, truncus arteriosus ; VA, DA, ventral and dorsal aort£E ; A, unpaired dorsai aorta ; I- VI^ aortic bows, of which ^'is rudimentary. Diagram showing normal derivations in man of primary vessels by modification of pre- ceding plan; W.aoria; ^^4, aortic arch; /, innominate artery ; CC. common carotids; EC. IC, exter- nal and interna! carotids ; S, sub- clavian artery ; /", pulmonary art- ery; DA, 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 which the aortic arch appears to be split lengthwise into two portions, one of which, the left arch, passes in front of the trachea and oesophagus and gives origin to the left common carotid and the left subclavian arteries, while the other passes Fig. 683. Fig. 684. RAA Right common carotid Developmental variations of Group I, giving rise to anomaly shown in next figure. RAA, LAA, right and left aortic arches ; J?S, Z,S, subclavian arteries; ^, aorta; P, pulmonary artery. Left common carotid Left subclavian Ductus arteriosus ulmonarj' artery Double aortic arch through which trachea and oesophagus pass. [Hommel) . behind the structures named and gives origin to a right common carotid and a right subclavian (Fig. 6S4). 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. Fig. 686. Trachea Right common carotid .CEsophagus Left common carotid Left vertebral Developmental variations 01 Group II, giving rise to anomaly shown in next figure. A, aorta; P, pulmonary artery ; RS. LS. right and left subclavian arteries; Rl^, right vertebral artery. 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 cesophagus. Variations of this condition, depending upon the location and extent 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. Fig. 6S7. cases the vertebral may arise as 111 tlit- normal arrangement from the subclavian, or it may, as it were, exchange [lositions witii the subclavian, arising from the tlescenciing aorta, while the sub- clavian arises, in common witii the right conunon carotid, from an innominate stem ; or the vertebral may arise with the right conunon carotid from the innominate stem, the subclavian alone coming from the tlescending aorta (Fig. 686). Group III. — A third group of anomalies depends upon the complete jiersistence of the right aortic arch, a.ssociated with the disappearance of the di.stal portion of the left one (Fig. 687). In such cases the result is a complete reversal of the aortic arch and its branches, unaccompanied, howe\er, by 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 imite 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 sixth 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 arterj- 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 ( esophagus. \'aria- 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 in 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 \essels may arise from a common stem, the two common 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, \essels which normalh- do not conie into relation with the arch may take origin from it, this being most frequently the case with the \ertebral arteries and Developmental variations less frequently with the internal mammaries ; and, finally, an <'f Group IV. ^, aorta; P, additonal branch to the thvroid gland, the art. thyroidea ima, S'^'an^ ^left '' Lbdavt^' occasionally takes origin from the arch. arteries. Developmental variations of Group III. A, aorta; P, pulmonary artery; RAA, right aortic arch; Z)^, duc- tus arteriosus ; ^.S', LS, right and left subclavian arteries. Fig. 688. Practical Considerations. — The Aortic Arch and Thoracic Aorta. — Surface Relations. — The ascendinj^ aorta beo^ins beneath the sternum just to the ricrht of the inner end of the third left costal cartilao^e. It ascends obliquely and towards the upper border of the second rjo^ht 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 higher than the junction of the first and second pieces of the sternum {angulus Ljidovici). 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 frequently 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. Venozis con- gestion, causing (a) lividity of the face from pressure on the descending cava, the left innominate, and the internal jugular veins ; (^) dizziness aiid headacJie from the same cause ; (<:) swelling and oedema of the right arm from pressure on the sub- clavian vein ; (- vein Inferior left pulmonary vein Termination of left coronary vein Circumflex branch of left coronary artery Left ventricle Superior vena cava Superior right pulmonary vein Right pulmonary artery Inferior right pulmonary vein 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, viewed from below and behind. The right coronary artery (a. coronaria dextra) passes outward from its origin in the right portion ol the auriculf)-ventricular groove, in which it lies, until it reaches the posterior inter\'entricular groove, down which it ( ramus descendens posterior) is continued towards the apex of the heart (Fig. 689). In its course it gives oflf 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 viar_Q;inal artery, descends along the right border of the heart f 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. — Tlie 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 proximal 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 except the two terminal ones, yet in about 10 per cent, of cases there arises from it a vessel which is termed the arteria thyr'oidea 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 extensive reduction of the size of one or other of the inferior thyroid arteries, and, indeed, these arteries may be entirely supplanted by it. It is somewhat variable in its origin, for, instead of arising from the 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 drawn 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. Vasczclar, (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, oedema 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 ; oedema 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, dyspnoea 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 diflerentiate 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 HLMAX 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 api)ear in the wound, and should be tied or drawn out of the way. The sterno-hyt)id and sterno-thyroid muscles are divided close to the sternum. The deep cervical fascia is divided in the line t)f 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 vein may protrude into the wound. Oste(){)lastic resection of the manubrium (Hardenheuer^, 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 tf> the iimer 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 tht 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 ; (^) the upjier aortic intercostals ; W) the inferior phrenic branch of the abdominal aorta (within the diaphragm); (^) the deep epigastric (within the rectus sheath) ; (^) the vertebrals 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 ; (f) the musculo-phrenic branch of the internal mammary ; {^d ) the superior epigastric branch of the internal manmiary ; {e') the vessels in the right half of the circle of Willis ; and (/) the branches of the right external carotid, all receiving their blood-supply 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 ofthe 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, w^here they present a dilatation frequentlv continued into the internal carotid and usually becoming more marked with advancing 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-clavicular articulation. This thoracic portion of the left common carotid is usually about 3 cm. (i^ 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 nerve. 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. E^ch is enclosed within a fibrous sheath formed by the deep cervical fascia (page 550), the sheath also containing the internal jugular vein and the pneumo- gastric nerve, the vein lying 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 ^e 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 y Inferior thyroid arterj- Transverse cervical artery Scalenus anticus Thyroid axis Right common carotid artery Right subclavian artery Internal mammary artery Left common carotid art Innominate artery Innominate veins Superior vena cava Left bronchus Right pulmonary vein Right pulmonary artery Branch of right bronchus Right pulmonary vein Rightauricular appendage Mesial surface of lung Right coronary artery - Subclavian artery -^ Pericardium, upper limit — Ligaraentum arteriosura — ~ Aorta, systemic Left pulmonary artery p- Pulmonary aorta (artery) Pulmonary veins Right ventricle (conus arteriosus) Mesial surface of lung Left coronary artery Diaphragm Dissection showing aortic arch and its branches ; lungs have been pulled aside. inferior thyroid artery pass behind it. Medially are the trachea and the oesophagus, 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. — Aneicrisvi 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 ; {b) because there the vessel is more super- -32 HUMAN ANATOMY. fic\i\\, i.e., least supported l>v oveilyini^ muscle ; ami (^c) because of the increastd resistance to the blood-current at that point. It is seen oftener in the right carotid than in the left. J'nssior-syiiiptonis : pain in the side of the neck, face, and head in the distribution of the superficial cervical plexus of nerves ; duskiness or mottling of the skin from jjressure on the sympathetic ; dyspnaa and cough from lateral deflection of the larynx and trachea ; difcctivc vision, vertigo, or stupor from press- ure on the internal jugular ; hoarseness or aphonia from implication of the recvnri lU larvngeal nerve : dysphagia from direct pressure on the CLSoi)hagus, or — possibly, together with irregular heart action, vomiting, or asthmatic respiration — from press ure on the |)neumogastric. Pii^itat compression may be used in a case of stab wound or in the treatment of aneurism (a) bv 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 sixth cer\ical 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 (b) by grasping the anterior edge of the sterno-mastoid and the artery together between the thumb and fingers, or (c) by 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 flex the head and turn it a litde towards the affected side so as fully to relax the sterno-mastoid. Ligatioti. — 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 ; {b) hemorrhage from wound of the neck, or from j)haryngeal wound or ulceration ; or (i") for the prevention of bleeiling during son^.e ojoerations. Whenever ligation of the external carotid satisfactorily meets the intlications, it is better to tie that vessel {q.v.), as the cerebral circulation is not therel^y 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 vein 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 covered only bv the skin, the platysma, the fasciie, 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 \ein held aside or tied, and the sheath opened over the carotid compartment, — i.e., well to the inner side, — so as to avoid injury to the larger internal jugular vein, which some- times— as in cases of embarrassed respiration — bulges oxgv 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 vagus. 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 clavicle is often ad\is- 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, (<5) the inferior thy- roid, (<:) the profunda cervicis (from the superior intercostal and thus from the sub- clavian), (flf ) the internal carotid and the vessels of the opposite segment of the circle of Willis, and (^) the vertebral, by anastomosing respectively with (a) the external carotid branches, (3) the superior thyroid, (<:) the princeps cervicis (from the occipital), and (af ) and (^) the vessels of the circle of Willis on the affected side. THE EXTERNAL CAROTID ARTERY. The external carotid artery (a carotis externa) (Figs. 692, 693) arises from the common carotid at about the level of the upper border of the thyroid cartilage — a level which corresponds to the body of the fourth cervical vertebra. Thence it is directed upward and slightly backward towards the angle of the jaw, where it enters the substance of the parotid gland and continues upward in that structure to just below the root of the zygoma. Here it gives rise to a large branch, the internal maxillary, and is then continued upward over the root of the zygoma upon the side of the skull, this terminal portion of it being termed the superficial temporal artery. Relations. — In the first portion of its course the external carotid lies in the superior carotid triangle (page 548), and is there crossed by the hypoglossal nerve and the facial vein. Higher up it passes beneath the posterior belly of the digastric and the stylo-hyoid muscles and also beneath the temporo-maxillary vein, and enters the substance of the parotid gland. Posteriorly it is separated from the internal carotid artery by the stylo-glossus and stylo-pharyngeus muscles and the glosso- pharyngeal nerve ; the internal carotid artery lies laterally to it at its origin ; internally it is in relation with the inferior and middle constrictors of the pharynx and the superior laryngeal nerve. Branches. — From the anterior surface of the external carotid arise, from below upward, (i) the superior thyroid, (2) the lingual, (3) ih.Q facial, and (4) the internal maxillary arteries. From its posterior surface, in the same order of succession, arise (5) the ascending pharyngeal, (6) the sterno-rnastoid, (7) the occipital, (8) the posterior auricular arteries. Finally, (9) the superficial temporal artery is to be regarded as a branch which is the continuation upward of the main stem. Variations. — Occasionally the external carotid artery is absent, its branches arising from the common carotid, which is continued directly into the internal carotid. The number of its branches may be reduced by certain of them, the lingual and facial, for instance, arising by a common stem, or they may be increased by the occurrence of various accessory branches pass- ing to regions supplied by the regular ones Practical Considerations. — The external carotid is rarely the subject of anezirism, except as a result of trauma. The tumor is situated below the angle of the jaw. Pressure on the hypoglossal and glosso-pharyngeal nerves and on the internal jugular vein causes various symptoms which are not usually definitely diag- nostic. In one case there was unilateral atrophy of the tongue (Heath) probably from involvement of the hypoglossal. If the aneurism is situated near the origin of the vessel, it may be indistinguishable from aneurism of the common carotid at its usual location, just below the bifurcation. The vessel is not infrequently tied for wound of the neck, for aneurism of one of its branches, and occasionally as a pre- liminary to certain operations, as excision of the superior maxilla or removal of a malignant tonsillar or parotid tumor. In cases of stab or cut-throat wound it is better, when possible, to find and tie both ends of the bleeding vessel, as the free anastomosis between the branches of the two external carotids renders a recurrence of hemorrhage probable after ligation of the main trunk. Ligation. — That part of the line for the common carotid extending from the level of the angle of the lower jaw to that of the middle of the thyroid cartilage is the 734 HUMAN ANATOMY. line for the skin incision. The artery is usually tied below the digastric muscle — i.e., in the superior carotid trianijle (page 548) — and between the origins of the suj)e- rior thyroid and the lingual arteries — because that is the longest interval without branches. After the skin, superficial fascia, platysma, and deep fascia have been divided, the anterior edge of the sterno-mastoid cleared and drawn outward at the lower portion of the wound, and the facial, lingual, or superior thyroid veins— if the\- present — drawn aside or tied and cut, the posterior belly of the digastric muscle above should be identified. Just beneath it the hypoglossal nerve crosses the artery, and a little lower — about the middle of the incision — the tip of the greater cornu of the hyoid bone may be felt. At this level — above the origin of the superior thyroid and below that of the lingual — the artery lies just to the inner side of the internal carotid (but somewhat superficial to it) and of the internal jugular vein, and has the superior laryngeal nerve in close relation behind it. The internal carotid has been tied at this level by mistake for the external carotid. To avoid this it should be remembered that the external carotid (a) is more anterior ; {b) is more superficial ; (r) is usually smaller, especially in the young ; [d) gives o^ branches ; (c) is close to the tip of the hyoid bone ; \f) is in contact with the hvpoglossal ner\e ; and ( g) that compression of the isolated vessel arrests the temjjoral and facial pulses. The needle is passed from without inward to avoid the internal jugular. The ligature has been applied just below the parotid gland — i.e., above the digastric muscle. The incision (on the same line) should extend from the lobe of the ear to the hyoid bone, the sterno-mastoid should be drawn outward, the poste- rior belly of the digastric and the stylo-hyoid muscle downward, and the parotic! upward and inward. The collateral circulation is carried on from the cardiac side through (a) the branches of the opposite external carotid ; {b) the inferior thyroid on the affected side ; (r) the branches of the oj^hthalmic of the same side ; and {d ) the profunda cervicis, anastomosing respecti\ely with {a) the branches of the ligated external carotid ; (b) the superior thyroid ; (r) the facial (from the same vessel — the.external carotid) ; and (a') the princeps cervicis. I. The Superior 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 inversely according to the amount of blood reaching the gland from other sources. It anas- tomoses abundantly with its fellow of the opposite side and with the inferior thyroid branch of the subclavian. Branches. — From its horizontal portion are given off — (a) An infrahyoid branch ( ramus hyoideiis ), which passes along the lower border of thi hyoid bone, supplyiiiij the muscles inserting into that bone. (^) A sterno-mastoid branch (ramus sternocleidomastoideus), always small and occasionally wanting, which passes downward and backward across the sheath enclosing the common carotid to enter the substance of the sterno-cleido-mastoid muscle. (f ) A superior laryngeal branch (a laryngea superior), which passes forward and downward beneath the thyro-hyoid muscle and, piercing the thyro-hyoid membrane along with the superior laryngeal 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 passes horizontally forward over the crico-thyroid membrane and anastomoses with its fellow of the opposite side, giving off branches which perforate the membrane and are distributed to the muscles and mucous membrane of the lower part of the laryn.x. 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 the 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 of temporal Anterior branch of temporal Middle temporal artery - Branches of posterior auricular artery Transverse facial artery Superficial temporal artery Great occipital nerve Trapezius Supra-orbital artery (shown thro' cut in the rausclesJ Frontal artery Nasal artery — Angular artery Facial vein Internal carotid srterj' Branch of ascending cervical External carotid artery Levator anguli scapulse Common carotid artery Scalenus medius Transverse cervical Posterior scapular Lateral nasal artery Termination of infra-orbital artery Septal artery Superior coronary Inferior coronary Buccinator Inferior labial artery Masseteric branch Facial artery Submental artery Muscular branch Submaxillary branch Lingual artery Superior thyroid artery Thyro-hyoid muscle Sterno-mastoid branch Omo-hyoid muscle Stemo-hyoid muscle Sterno-thyroid muscle Subclavian artery Suprascapular artery Subclavian vein Superficial dissection, showing arteries of neck, face and scalp. 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 lingual artery (a. 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 sometim-es given off from a trunk 736 HUMAN ANATOMY. common to it ami one or other of these arteries, especially the facial. In the first part of its course it passes forward and sli.yhtly upward and inward towards the tij) of the lesser cornu of the hyoiii 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 ilirectly forward beneath the mucous membrane covering the under surface of file 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. prol'inida linmiac); it gives branches to the adjacent muscular substance and mucous membrane of the tongue, and near its termination anastomoses with it> fellow of the opposite side. Branches.— ((/) The suprahyoid branch (ramus hyoideus), jjiven off from the first portion pa.sses hori/ontaily forward over tin.- iiyoid bDiie. sendinjj branches to the muscles wiiich ai( inserted into liiat Ijone from below . (d) The dorsal lingual branch (rami dorsales linguae), from the second portion, arises under cover of the posterior border of tiie iiyo-^lossus and, passins^ upward medial to the stylo- glossus, breaks up into branches w hich 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 correspondinji one from the artery of the opposite side, immediately in front of the fora- men Ciecum, and is continued forward in the median line, immediately beneath tiie miicoiis membrane of the tlorsum of the ton.ijue, as far as the tip. (c) The sublingual branch (a. sulilinKualis) is given off near the anterior border of the hyo- glossus muscle and runs forward in the same plane as the ranine arterj-, 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 subma.xillary ( 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- sively with their fellows of the opposite side. The anastomoses of the two aa. dor- sales linguse take place, however, only through exceedingly fine 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 i 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, j 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 maxillan,- or by the submental branch of the facial. The i sulilingual branches are not infreciuently lacking, being replaced by branches of the submental, I and, in addition to its ncjrmal branches, the main arterj- may give rise to a superior laryngeal and an accessory superior thyroid Ijranch. I Practical Considerations. — The lingual artery is tied most frequently as a I 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 bv cutting ofli blood-supply, as in cases of cancer of the tongue or of macroglossia. Ligatioyi. — The artery is for convenience divided into three portions, the _/?;.?/ 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 artery 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 little 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 berieath 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 salivarv 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 alaeque 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 artery (a. angularis). Branches.— The branches of ihe 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 artery which pisses 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 tlie superior constrictor of the pharynx. It terminates by sending branches to the soft palate, the tonsil, and the Eustachian tube. (3) 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. {d) 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 HL'MAN ANATOMY. through tlie sul)ma.\illary ^'l.iiul. It passes forward upon tlie mylu-hyoid muscle, close to its origin, until it reaches tlie nisertion ot the anterior belly of the digastric, when it passes upward upon the ramus of the mandible to supply the depressor labii mlerioris and to anastomose with the mental branches of the inferior dental artery and with the interior labial branches of the facial. It sends l)ranches to the muscles in its vicinity and also to the integument, and branches perforate the mylo-hyoitl muscle to anastomose with liie sublingual branches of the lingual. From the facial portion, (f) The masseteric branches arise from the posterior surface of the artery— and are tiirected 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. laliialis inferior) passes forward along the outer surface of the horizont.d 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. [^) The inferior coronary artery passes forward in the substance of the lower lip between the miicous membrane and orbicularis oris, supplying the latter, and terminates by anastomosing with its fellow of tin- opiiosite side. (/t) 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. st-pti iiarium. (/) The lateral nasal takes its origin just as the artery reaches the naso-labial angle ; it passes forward o\ er the ala of the nose, supplying its muscles and integument. {j) The angular artery (a. angularis) is the terminal portion of the facial artery 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 lachn>'mal sac, and the orbicularis palpebrarum, anastomosing with the nasal branch of the ophthalmic artery and with the infra-orbital branch of the internal ma.xillary. 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 lini^aiae 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 maxillary 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 e.xtend 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 artery. The ascending palatine branch frecjuently 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 Ijranches, as the coronary, but whenever 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 1608), 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 involved ; but as the blood may also be furnished by the ascending pharyngeal, ligation of the external 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 submaxillary 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 {q.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. Deep temporal branches Small meningeal branch — t Middle meningeal' Tympanic bianch Superficial temporal Stylo-mastoid Meningeal branch Posterior auricular Trachelo-mastoideus Occipital artery Sterno-mastoid branch — Trapezius ■ — Splenius Levator anguli scapulae Internal carotid artery External carotid arterj Superior thyroid artery Scalenus medius Common carotid artery Scalenus anticus' Longus colli Superficial cervical Posterior scapular Scalenus medi Tendinous origin of scalenus medius Branches of internal maxillary artery to superior maxilla Posterior superior dental Internal maxillary artery Inferior dental artery Buccal branch Internal pterygoid muscle Buccinator Ranine artery Tonsilar artery j\scending palatine Facial artery, cut Sublingual artery Dorsalis linguae Hyoglossus muscle, cut Suprahyoid branch Lingual artery Larj ngeal branch Sterno-mastoid branch Ascending cervical artery ^iiiill I HI cerHcalartery _ Inferior thyroid artery Thyroid axis Vertebral artery ■Subclavian artery Internal mammary artery Sterno-mastoid brancri buprascapular artery Deeper dissection, siiowing carotid and subclavian arteries. 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 external 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 reg-ard the internal maxillary artery as consisting of three portions. Its first, or mandibular portion, is that which lies inter- 740 HUMAN ANATOMY. nal to tlie neck of the mandible ; the second, or ptcrygoul portion, is that which traverses the zygomatic fossa, and is in relation with the pterygoid muscles ; and the third, or spheno-tnaxil- law portion, extends from where it passes between the two heads of the external pterygoid nnis- cle t« ) Its entrance into the spheno-palaline foramen. Uf the sixteen named branches arising from the internal maxillary artery, live arise from the lirst portion, live from the second, and six from the third. From the first or mandibular portion arise (, i ) the deep auricular, (2) the tympanic, (3) the middle meningeal, (4) the small meningeal, and (5) the inferior dental ariitne^. {^a) The deep auricular (ii. aiiriciilaris profunda) is a small branch which passes behind the temporo-mantlibiilar articulation, to which it semis branches, and perforates the anterior wall of the external auditory meatus to supply the skin lining that passage and the outer surface of the tympanic membrane. (It) The tympanic (a. lympanica anterior), also a small branch, passes upward, gi\mg off branches to the temporo-mandibular articulation, and enters the Glaserian fissure. 1 hence it traverses the iter clK)rcke 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 iirlery. (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 short distance upon the great wing of the sphenoid, di\ ides into an anterior and a posterior terminal branch, which ramify over the surface of the dura and supi^ly nearly the whole of its lateral and superior surfaces, making abundant anasto- moses with the vessel of the opposite side. The anterior branch, the larger of the two terminal branches, passes obliquely forward over the greater w ing of the sphenoid, crosses the anterior inferior angle of the parietal, and then ascends along the anterior border of that bone almost to the su])erior longitudinal sinus, sending off numerous branches. The posterior branch passes backward anti upward over the squamous portion of the temporal bone, and then over the pos terior part of the parietal bone, gi\ ing 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) a petrosal branch (a. peirosus superficialis) which enters the hiatus Fallopii and anastomoses with the terminal por- tion of the st\lo-mastt)id arteries ; to \bb) Gasserian branches, minute twigs which pass to the Gas.serian ganglion and the fifth nerve ; \.o [cc) a tympanic branch (a. tympanica superior) which descends through the i>etro-stiuamous suture to the mucous membrane of the middle ear and the mastoid cells ; and, fmaily, to {dd ) an orbital branch, a small vessel that passes into the orbit through the outermost pi>rtion of the sphenoidal fissure and anastomoses with the lachrymal branch of the ophthalmic. {d ) The small meningeal ( r. meningeus accessorius) is an incon.stant 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 artery and descends along with the inferior dental ner\ e 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 mylofiyoideus), accompanying the mylo-hyoid ner\e to the muscle of that name. Entering the mandibular foramen, it traverses the man- dibular canal, giving off branches to the roots of the lower teeth as it passes them, and finally emerges at the mental foramen as(rr) 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 bianch which distributes twigs to the incisor teeth. From the second, or pterygoid portion, arise branches distributed chiefly to the adjacent muscles ; they are ( i ) the masseteric, (2) the deep temporal, (3 and 4) the internal and exter- nal pterygoid, and (5) the buccal ^rX&ry. {/) The masseteric branch fa masseterica^ passes with the corresponding nerve through the sigmoid notch of the mandible to enter the deep surface of the masseter. (g I The deep temporal branches are two in number, the anterior and the posterior. The posterior branch fa. temporalis profunda posterior) arises close to or in common with the mas- seteric, while the anterior oue fa. temporalis profunda anterior) is given oft" near the termination of the pterygoid portion of the artery. They both pass upward between the temporal muscle and the bone, supplying the muscle and anastomosing with the middle temporal branch of the temporal artery. (// and 7 ) The internal and external pterygoid branches f rami pterygoidei ) 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 hifraorbital, {3) the descending palatine, (4) the Vidian, (5) the 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. 69-5. Anterior temporal Posterior temporal Middle temporal Transverse facial Great meningeal Superficial temporal Small meningeal 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 Sterno-mastoid artery. Coronoid process of mandible with insertion of tem- poral muscle — Buccinator Superior coro- nary artery Inferior coro- nary artery Inferior labial artery Mental branch of facial emerging from mental for- amen Submental artery Genio-hyoid muscle Lingual artery Hyoglossus mus- cle, cut Mylo-hyoid mus- 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. infraorbitaiis) frequently arises in common with the alveolar. It passes forward and upward through the spheno-maxillary fossa and the spheno-maxillary foramen to traverse the infraorbital groove and canal along with the infraorbital nerve. In this part of its course it gives off {aa) orbital branches, distributed to the adipose tissue of the orbit and to the neighboring muscles of the eye, and {bb) anterior dental branches (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. (w) The descending palatine artery (a. palatina descendens) accompanies the anterior pala- tine nerve from the spheno-palatine ganglion through the posterior palatine canal, and, on its 742 IILMAX ANATOMY. emerj::ence from the posterior palatine foramen, divides into an anterior and a posterior branch. The former passes forward beneath the mucous membrane of the hard pahite, which it supphes, and at tlie 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 j)tcryRoidei ) is a small branch which passes backward along the Vidian ner\e through the \i(lian canal, and sends branches to the roof of the pharyn.x and to the Eustachian tube. (o) The pterygo-palatine artery (a. pal.iiina major) is also a somewhat slender branch. It passes backward through the pterygo-palatine foramen along with the pharyngeal nerve from the spheno-palatine ganglion, and supplies the roof of the pharjnx, the Eustachian tube, and the mucous membrane lining tiie sphenoidal cells. {/) The spheno-palatine artery (a. sphenopalatina ) is the terminal branch of the internal maxillary. It pas.ses into the nasal cavity through tiie spheno-palatine foramen along with the spheno-palatine nerve from the spheno-palatine ganglion. Shortly after traversing the foramen it divides into an internal and an external branch. The internal branch, sometimes termed the naso-palaline, passes transversely across the roof of the nasal cavity to reach the septum, upon which it passes downward and forward, giving oli' 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 nerve. The external branch ramifies downward and forward over the lateral wall of tlie 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 artery 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.xillary 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 e.xternal carotid, and with branches of the internal carotid. The most abundant anastomoses with the artery of the opposite side are made throuiifh the branches of the middle mening;eal; the alveolar branch anastomoses with the dental branches of the infraorbital of the same side and with ihe 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 w hich 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 early stages of development the main portion of the internal maxillary- 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 (j/); it makes its exit from the middle ear by the Glaserian fissure and divides into two stems, one of which f Rs') passes through the foramen spinosum (fsp) and is distributed to the supraorbital region, while the other divides into two branches which, from their distribution, are termed the infraorbital i Ri ) and the mandibular (inferior dental) [Rm). A branch {Ras) arises later from the external carotid which anastomoses with the lower stem w here 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 maxillary, which fre- quently arises in the adult from the middle meningeal instead of directly from the internal max- illa r\-. Bv these changes, as may be seen from the accompanying diagrams, the adult internal maxillar\' is formed, the supraorbital branch becoming the middle meningeal ( Mm ) and the mandibular branch the inferior dental, while the infraorbital branch (i*?;) becomes the main stem of the artery from w hich the remaining branches gradually develop. I 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 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 external 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. Fig. 694. Ast Diagrams illustrating development of internal max- illary artery ; A, early stage ; B, later stage; C, common carotid; Ce, Ci, external and internal carotid. For ex- planation of other letters, see text. ( Tandler.) 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. (c) 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 nerve. 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 parodd 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 -, , HUMAN ANATOMY. the integument upon tlie aponeurosis of the occipito-frontaHs. Tlie artery pierces the deeper structures, accompanied by the great occipital nerve, a short chstance lateral to and a little below the external occipital protuberance. Branches.— hi ackiitioii lo its urminal branches, the occipital artery gives off : (ii) A superior sterno-mastoid branch wliicli suppHes the upper part of the sterno-cleido- (f)') Posterior meningeal branches, one or more slender vessels which pass upward along the internal jugular vein and, entering Die skull by the jugular foramen, are supplied to the dura mater of tlu- posterior fossa. [i') An auricular branch (ramus aiiricularis) which jiasses upward over the mastoid process to supply the pinna of tlie ear. ((/') A mastoid branch (ramus mastoideus) wliich enters the skull by tlie mastoid foramen and supplies tlu- mucous nKml)raiie lining the mastoid cells, the diploe, and the dura mater. (e) An arteria princeps cervicis (ramus dcscendens) which arises from the artery, just as it passes out from lit-iieaili tlu- spleiiiiis and descends the neck, sujiplyiiig the adjacent muscles and anastomosing with the siiiierticial cervical brancli of the transversalis colli and with the pro- funda cervicis from the superior intercostal. ( /■) Muscular branches (rami musculares) which are given off all along the course of the artery to the iieigliboriug muscles. Anastomoses. — The occipital artery makes comparatively large and abundant anastomoses in the scalp with the stylomastoid 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 pharjn- geal arter>- or to the stylo-mastoid. Practical Considerations. — The occij)ital artery is rarely formally ligated. The cervical portion may be reached through an incision along the anterior border of the sterno-mastoid, beginning midway between the ramus of the mandible and the lobe of the ear and e.xtending 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 aitery, 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 ner\'e where it turns to cross the neck. The artery may be ligated close behind the nerve, 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 artery 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. 8. 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 suppHes, 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 of! from it. During its course through the canal it gives off 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 maxillary. Arrived at the hiatus Fallopii, the arter}- 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 artery. 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 off 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 vertex 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. {b) Articular branches to the temporo-mandibular articulation. {c) 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 the external auditory meatus. {e) The transverse facial artery (a, transversa faciei) arises just below the main stem of the artery, crosses the zygoma, 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, supplying 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 zygomatic 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, superficial fascia, and some fibres of the attrahens aurem muscle are divided for 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 which it arises on a level with the upper border of the thyroid P'iG. 695. Branch of left middle meningeal .irter; Branch of left middle mcninijea' Basilar artery Posterior inferior cerebellar arterj- Left vertebral artery Right vertebral arter) Aiteria princeps cervicis Axis Left complexus Middle cerebral artery Anterior cerebral artery Anterior clinoid process Middle fossa of skull Int. carotid, cav. portion Sup. maxilla, malar process Int. carotid, petrous portioi Internal maxillary artery Eustachian tube Transverse process of atlas Sup. constictor of pharynx Int. carotid, cervical portioa Ascending pharyngeal Stylo-jjlossus Stylopharyngeus External carotid artery — Stylo-hyoid muscle, cut Lingual artery PjjfjJ'^^ Superior thyroid artery /TiT "^'^Thyro-hyoid muscle SV^BMV ~~~Thyroid cartilage Inferior constrictor of pharynx Deep cervical arterj , • Vertebral artery Transverse process of I. thoracic vertebra I. rib _ Superior intercostal artery ,- Branch to II. intercostal space I. aortic intercostal II. aortic intercostal Subclavian artery ^Innominate artery Internal mammary arten^ Deep dissection, showing internal carotid, vertebral and superior intercostal arteries. cartilage. In \.\\(tjirst or cervical 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 nerve, which lies at first behmd it, but crosses its external 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 forward and inward to enter the cranial cavity at the foramen lacerum medium. It then enters upon the third or intracranial portio?i of its course, ascending at first towards the posterior clinoid process, but soon bending forward 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 cervical 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) 2. tympanic branch. In its intracranial portion, in addition to small branches to the walls of the cavernous sinus and the related cranial nerves, to the Gasserian ganglion, and to the pituitary body, lh.&[edir:\se (^2^ a7iterior ?ne7tingeal branches, (3) the. ophthalmic, i^^) posterior commu- nicating, (5) anterior choroid arteries. And, finally, its terminal branches, (6) the fniddle and ( 7 ) the anterior cerebral arteries. Variations. — In its cervical 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 give rise to branches which normally spring from the external carotid, as, for example, the ascending pharyngeal and the lingual, and accessory 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 1608). Aneurism oi the internal carotid is not common. When it mvoXv&s 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 cervical 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 cervical fascia, and by the stylo-hyoid, stylo-glossus, stylo-pharyngeus, 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 offer 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 symptom. The effects 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 may be reached close to its origin and tied through the same incision as that used in ligating the external carotid (page 733). The sterno- mastoid muscle is drawn outward, the digastric muscle and hypoglossal ner\'e (which are usually seen) upward, and the external carotid artery inward. The two vessels should be carefully distinguished. The needle should be passed from with- r4« HUMAN ANATOMY. out inward, avi)iclin.i,^ tlu- internal jugular vein, the pncuniogastric and synipathet nerves, and the ascending pharyngeal and external carotid arteries. The collateral circulation is carried on through the \ertebrals and the \essels the circle of Willis and is freely re-established. I. The Tympanic Artery. — The tympanic artery (ramus cantticotympanj cus ) is a small vessel which arises from the petrosal portion of the internal carotir It passes through a foramen in the wall of the carotid canal to su|i|)ly the mucoi membrane of the middle ear, anastomosing with the tympanic branches of the styU mastoid and internal maxillary arteries. Fig. 696. Frontal artfr>' Internal branch of supraorbital Superior oblique muscle Superior palpebral branch Inferior palpebral branch Frontal arterj' Nasal artery Anterior ethmoidal branch Supraorbital artery Posterior ethmoidal branch Superior obliijue Superior rectus ' Uptic nerve Ophthalmic arter; Internal carotid artery Posterior clinoid process. Internal carotid, cavernous p«'rtion — lacial artery Nasal artery Levator palpebrx superioris j Superior rectus Lachrymal artery Lachrymal gland Temporal branch • Arteria centralis retinae Loni^ posterior ciliary arteries Short posterior ciliary arteries Middle fossa of skull Branches of right ophthalmic artery, seen from above after rtmoval 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 with the branches of the anterior ramus of the middle meningeal artery. 3. The Ophthalmic Artery. — The ophthalmic artery (a. ophthalraica) (Figs. 696, 697) arises from the internal carotid immediately after it has issued from the roof of the cavernous sinus. It passes forward 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. — (a) 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 ascendmg 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 extend deeply into the substance of the retina, although none reach the layer of visual cells. The}' pass over directly into the corresponding \eins 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 \ariable in their number and origin. Two sets are distinguishable, and are named from their relative position the posterior and anterior ciliary arteries. {aa) T\iQ 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, the 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 h?ig 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 circidus 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, except 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 margm of the cornea, where they divide and anastomose to form a narrow net-work surroundmg that portion of the eyeball and also give branches to the conjunctiva. An anterior ciliary \essel is frequently contributed b\- the lachrymal artery. [c] The lachrymal artery (a lacrimalis) arises from the ophthalmic as it passes upward over the external surface of the optic nerve and passes forward and outward, in company with the lachrymal nerve, along the upper border of the external rectus muscle. It traverses the substance of the lachrj'mal 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 menin- 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. (fif ) 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 in- 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, arises 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. supraorbitals) 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 palpebrae 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 \-ertex of the skull, supplying the integument and periosteum and anastomosing with the superficial temporal artery. In its cou'se 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 HLMAN ANATOMY. smallL-r and less constant of the two, passes through tlie posterior ethmoidal foramen and is distributed to tlie mucous membrane lining; the posterior ethmoidal cells and the upper postt rior jxirt of the nasal septum, where it anastomoses with the spheno-palaline branch of tin internal maxillary. It sometimes arises from the suprat)rl)ital artery. The anterior ethmoidal la. ethm- (a. dorsalis nasi) is the tnie 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 maxillary, 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 through the anastomosis of the malar branch of the lachrymal with the trans^'erse facial artery. It makes a very important anasto- THE POSTERIOR COMMUNICATING ARTERY. 751 Supraorbital 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 anastomosis 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 ill 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, however, 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. 698). Occasionally this branch becomes exceptionally large and forms the main stem of the lachrymal 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 artery. Degenera- portion From middle meningeal Variations of ophthalmic artery ; lachrymal coming chiefly from middle meningeal. {Meyer.) 4. The Posterior Communicating Artery. — The posterior communicating artery (a. comraunicans posterior) (Fig. 702) arises from the posterior surface of the Fig. 699. Branch of ascending frontal artery Parietal artery Fissure of Rolando Precentral sulcus Ascending frontal artery Branches of anterior cere- bral artery from mesial surface Calcarine branches of posteri or cerebral- Anterior inferior cerebellar artery Branches of anterior cerebral artery External orbital artery Inferior frontal artery Middle cerebral artery Temporal branches of middle cerebral artery ^ Paneto-temporal arteries Basilar artery Pons Left vertebral artery Middle cerebellar peduncle Right vertebral artery Laieral 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 crus cerebri, and terminates posteriorly by 752 HUMAN ANATO.Nn'. opcnini,^ tlircctly into the posterior cerebral artery. In its course it gives off twigs to the tuber cinereum. the corpora all)icantia, and the crus cerebri. =i. The Anterior Choroid Artery.— The anterior choroid artery (a. choroi- dca) (Fig. 702) arises from thi' posterior surface of the internal carotid, slightly distal to the posterior conununicating artery. It is directed outward and backwartl at tirst, and then, curving upward between the brain-stem and the temporal lobe, it gives branches to the hiiipocaminis major. It is then continued upward and for- ward as the artery of the choroid plexus of the lateral ventricle, and anastomoses at the foramen of Monro with the artery of the choroid ple.xus of the third \entricle. which comes from the superior cerebellar branch of the basilar artery. 6. The Middle Cerebral Artery. — The middle cerebral artery (a. cerebri media) (Figs. 699, 702) is one of the terminal branches of the internal carotid. It passes at first outward to the lower end of the Sylvian fissure, and is then directed backward and ujjward, Iving at first deei)ly in the fissure close to the surface of the Fig. 700. Miilrllc internal frontal artery Posterior internal frontal artery Fomix. Anterior in- ternal frontal artery Middle commissure Internal orliital arter>' Anterior cerebral artery Anterior commun- icating artery Internal carotid artery External orbital artery Middle cerebral artery From temjKirai branch of mifltile cerebral Posterior communicating artery Anter C.-iliarine tissure Temjioral brandies of posterior cerebral erebral artery Mesial sui^ace of cerebral hemisphere. shnwitiR cortical hianches of anterior and posterior cerebral arteries. island of Reil, but graduallv becoming more superficial until at the posterior e.x- tremity of the horizontal limb of the fissure it reaches the surface and divides into branches which ramify over the lateral surface of the cerebral hemisphere. Branches.— In its course outward to enter the Sylvian fissure it ^ives off a number of --"r" 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 atiiero-lateraf g'lnfflionic 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 Vraudate nucleus, supplying the anterior part of the structures traversed ; (b) the external striate arteries, which after traversing the putamen and the internal capsule terminate in eitlier the caudate nucleus or the optic thalamus. One of the former {/enticulo-sfnafe) vessels, which passes around the outer border of the lenticular nucleus before traver-^ing its substance, is lareer than the others and. since it frequently ruptures, is known as the arfeiy of cerebral hemorrhage. While in the Sylvian fissure the middle cerebral artery- gives off numerous branches to the cortex of the island of Reil and continues into the cortical branches, which are distributed to the lateral surface of the hemisphere and are usually foUi m THE SUBCLAVIAN ARTERY. 753 number, {a) The inferior frontal is distributed to the inferior frontal convolutions, {d) the ascending frontal passes to the lower portion of the ascending frontal convolution' (c) the parietal supplies 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 forward 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 with its fellow of the opposite side by a short transverse vessel termed 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 olfactorj- bulb ; {d) 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 artery anastomosing posteriorly with branches of the posterior cerebral. Anastomoses of the Carotid System. — Although the majority 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 cervical 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 cervicis, a branch of the occipital artery ; (4) abundant communications exist between the terminal branches of the inferior thyroid from the subclavian 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 two aortic arches (Fig. 678),' the two subclavian arteries arise symmetrically from these arches as lateral segmental branches corresponding to the seventh cervical segment. With the disappearance of the lower portion of the right arch, however, an apparent lack of symmetry in their origin supervenes, the vessel 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- -48 754 HUMAN ANATOMY. nietrv is retained ; but, since a portion of the oriji^inal rij^dit aortic arch is inchided ir the adult ri.i,dit subclavian, this vessel is a little more than equivalent to its fello\ of the opposite side. Furthermore, since the innominate stem ascends directl] upward from its orii,nn, a to])o,urai)hical asymmetry of the two vessels results. The orii^in of the rij^/it sKln/avian is opj)osite the v\\y\\i sterno-clavicular articular tion, and from that jioint the artery ascends upward and outward in a gentle curv^ over the dome of the ])leura to the inner border of the .scalenus anticus. The origii) of the left siiMavian is from the termination of the transverse portion of the aorti^ arch, arid is consequendy much deeper in the thora.x (P^ig. 690). From its origii it ascends at first almost vertically and then curves outward and slighdy forward xi reach the inner border of the scalenus anticus. From this point onward the course the two arteries is the same. Passing behind the anterior scalene muscle, each arter continues its course outward across the root of the neck, curving downward to thiij outer border of the first rib, at which i)oint it becomes known as the a.xillary arteryj Fig. 701. -^ ■•^. A Descending branches of cervical plexus Transverse cervical vessels Omohyoid muscle ~ Brachial plexu.- Suprascapular vessel Subclavian artery Subclavian vein Clavicle Clavicular portion of sterno-mastoid External jugular vein Anterior scalene muscle Phrenic nerve Internal jugular vein Sternal portion of sterno-mastoid Common carotid artery ■Sterno-hyoid muscle First rib Dissection of neck, showinj disarticulate! relations of blood-vessels and nerves ; clavicle from sternum and drawn down. In consequence of the difference in origin, the right subclavian artery is usually approximately 7.5 cm. (3in. ) in length, or about one inch shorter than the left. In its course acro.ss 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 <^rn. (i-i)^ in.) above that bone. Most frequently it reaches a point about 1.5 cm. {S/^, 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 fj-ont by the internal jugular and vertebral veins and by the right pneumogastric, phrenic, and superior sympa- thetic cardiac nerves. Behmd, it is in relation with the transverse process of the seventh cervical vertebra, 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 cavity and ascends almost vertically through the superior mediastinum, Behijid, and somewhat medial to it, are the oesophagus, the thoracic duct, and the longus colli muscle, and at its emergence from the thorax the lower cervical sympa- thetic ganglion. Medial, or internal to it, are the trachea and the left recurrent laryn- geal nerve, 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 veins, as well as by the phrenic nerve and the thoracic duct, the latter arching over 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, in front is covered 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 below it is in contact with the pleura. The third portion of the subclavian artery Hes in the supraclavicular fossa, and is covered only by the skin, the platysma, and that part of the deep cervical fascia which contains the external jugular vein and the supraclavicular branches of the cervical plexus, and encloses a quantity of fatty tissue, in which the suprascapular artery passes outward. Belmid, it is in contact with the scalenus medius and the brachial plexus, 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 vessel 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 jnammary, (3) the superior intercostal, and (4) the thyroid axis ; from the second portion no branches are ofiven off ; from the third portion (5) the transverse cervical.^^'^-^^^.^^'V^'^^'' Variations. — The variations in the origin of the subclavian artery have already been consiB^ ' ^'. ((?) 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. Anterior cerebral artery Olfactory tract, cut Anterior cerebral artery Internal carotid artery Pituitary body Anterior choroid artery Posterior communi- cating artery Corpora mammillaria Posterior cerebral artery Superior cerebellar artery A pontine artery — Auditory artery — Trigeminal nerve Vertebral artery Right lobe of cerebellum Anterior communicating artery Internal carotid artery Middle cerebral artery Antero-Iateral gang- lionic arteries Posterior com. arteries ^' ^ Posterior cerebral artery ■t— — Sup. cerebellar artery Anterior inferior cerebel- lar artery — Anterior spinal artery Medulla oblongata ■Posterior inferior cere- bellar artery ■Vertebral artery 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. {k) The internal auditory arteries (aa. auditivae internae), one on each side, are additional!}- given off, and accompany the auditory nerve through the internal auditory meatus to supply the internal ear. (z) 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. (y ) 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 760 HUMAN ANATOMY. nerves, and, curving upward in the tentorial fissure almost parallel with the trochlear nerves, are clislrilniled to liie upper surface of the cerebellum and anastomose with the inferior cen- bellar arteries. (i) The posterior cerebral arteries (aa. ccri;l>ri posteriores ) (I-is;. 702) are the terniinil branches of the basilar I'unu its origin at the anterior border of tlie pons each artery pass« s 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 tlu n passes upon the inferior surface of the cerebral hemisphere, where it breaks \ip into cortical branches which rannfy 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 liranches (Fig. 700) include ihtmiihi ior tonporal, which supplies the anterior parts of the uncinate and occipitt)-temporal convolutions; \\\^ posterior temporal, distributed to the posterior part of the uncinate and the occi|iito-temporal convolutions and the adjoining gyrus lingualis ; the calca- title, the continuation of the iK)sterior cerebral along the calcarine fissure, which passes to the cuneus and the gyrus lingualis, and winds to the outer surface ; and \\\e parieto-oeeipitat, which follows the parieto-occipital fissure to the cuneus and the cjuadrate lobe. Immediately at their origin the posterior cerebrals give rise to a number of small central branches { postero-tnesiat and postero-lateral gaiigliotiic) which dip down into the substance of the posterior j^erforated space to supply the optic thalamus and the adjacent parts of the brain-stem, and somewhat more laterally each gives ofT a posterior choroidal branch, which passes forward in tlie transverse fissure to the choroid ple.xus of the third ventricle. Near where it passes in front of the oculo-motor nerve, each posterior cerebral receives the posterior communicating arter>' which passes back to it from the internal carotid, and more laterally it gives of? some small branches which are distributed to the corpora quadrigemina and the posterior part of the optic thalamus. Variations. — The vertebral arter>- 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 arterj- or the common carotid. It may traverse a foramen in the transverse process of the seventh cervical vertebra, or the lowest vertebrarterial foramen through wiiich it passes mav be the fifth, fourth, third, or even the second. Very rarely the two vertebrals fail to unite to form a single median basilar, that artery being thus represented by two longitudinal trunks united bv transverse anastomoses. Occasionally the basilar divides into two longitudinal stems which reunite farther ft)rward, and its formation by the fusion of two parallel vessels is fretiuently indicated by the presence in its interior of a more or less perfect median sagittal partition. Tlie \ertebral may give origin to an inferior thyroid artery or to the deep cervical, and oc- casionally, in its upper part, to abranch which anastomoses with the occipital. One of the pos- tericjr 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 proximal portion of one or other of the posterior cerebral arteries is reduced to a mefe thread, the blood reaching the terminal ix)rti()ns of the vessel from the internal carotid, through the posterior communicating arter>'. The Circle of W^illis. — The circle or, as it is more properly called, the polygon of Willis (circulus arteriosus) is a continuous anastomosis at the base of the brain (Fiy-. 702) between l)ranches of the internal carotids and subclavians (verte- brals). it surrounds the posterior perforated space and the floor 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 proximal 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 \'essels 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. Arieurism — 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 co7npression of the vertebral 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—/..?. , for from two to two ana a half inches above the clavicle — will usually arrest such bleeding and pulstaion, no matter whether the vertebral or either of the carotids is involved. 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 supra), 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). Ligatio7i 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 clavicle, 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 vessels, 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 di\'ision of that muscle exposes the vertebral artery in a much safer region than below and at a less depth (Dawbarn). The collateral circulati07i is very freely re-established through the vessels of the circle of WiUis. 762 HUMAN ANATOMY. Fig. 703. Cephalic vein Humeril branch asses upward in the groove be- tween the trachea and cesojihagus in company with the recurrent laryngeal nerve. It passes beneath the lower border of the inferior ct)nstrictor of tiie pharynx and enters the laryn.x, to whose mucous membrane and muscles it is distributed. It anastomoses with the superior laryngeal branch of the superior thyroid. Finallv, it gives ofT small branches to the pharj'iix, oesophagus, 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 betw een the subchuian and carotid systems and play an important part in the establish- ment of the collateral circulation after ligation of the common carotid arterj\ 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 thvroid maybe 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 sixth cervical ver- tebra or about the level of the omo-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 Aessel 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. (d) The superficial cervical artery (a. cer\'icalis superficialis) (Fig. 705) passes almost directly laterally from the thyroid axis, 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 c-m. 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 anguli scapulae^ the rhomboidei, and the THE AXILLARY ARTERY. 767 splenir. 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 and 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 plexus, and, passing beneath the posterior belly of the omo-hyoid, reaches the lower portion of the levator anguli scapulse, 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 scapulas muscles. (fl),The ascending terminal branch (ramus ascendens) passes upward to supply the splenius muscles, and forms anastomoses with the superficial cervical. (b) 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 axillary are of considerable importance in the establishment of the collateral circulation from the arm after ligation of the third portion of the subclavian. Addidonal 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 frequently 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 cen'ical, 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 IRMAN ANATOMY. the two condyles of the liumeriis. When, however, the arm han^s vertically, the \essel is slii;htly curved, the convexity of the cur\e looking upward and outward. Relations. — For con\enience in description it is customary to regard the axil- iarv arter\- as consistinj^ of three portions, the first of which is abo\c the upper border of the pectoralis minor, the second hehintl that muscle and the third I)elow its lower border. The first portion of the artery is covered anteriorly by the clavicular portion of the pectoralis major, by the costo-coracoid membrane which separates it from the cephalic vein and the branches of the acroniio-thoracic artery, and by the subcla\ ius muscle. The artery is enclosed along with its accompanying vein and the cords of Fig. 705. Superficial cervical Posterior Pectoralis major, cut and evertol^ Dclloi,!^ scapular^ Trapezius I>c1toi,l, Biceps, long head Brachial plexus Transverse cervical Subclavian artery Scalenus anticus rn'.rnpnlar _ Inferior tluroid _ Thyroid axis Subclaviub nius. Acromial thoracic _ Superior thoracic Alar thoracic Anterior circumflex Axillary artery, third |x>rtion Biceps, short head Coraco-hrachialis Suljscapu* Uris Long thoracic Serratus mairnus Subclavian ami axiilary arteries i>ectoralis minor still in place. the brachial ple.xus in a downward prolongation of the cervical fascia known as the axillary sheath, and rests behind upon the upper serration of the serratus magnus and upon the first intercostal space. The internal anterior thoracic and the posterior thoracic nerves cross it obliquelv behind, the latter ner\e intervening between it and the serratus magnus. Abo\e, 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 por^-ion 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 anterior surface of the subscapularis muscle. External to it is the outer cord of the brachial plexus, 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 and the 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 ( i ) the superior thoracic and (2) the acromial thoracic ; from the second part (3) the long thoracic and (4) the alar thoracic ; and from the third part (5) the subscapular. (6) the anterior circumflex, and (7) th.e 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 a.xillary in common with the subscapular. Practical Considerations. — The axillary artery may require to be ligated on account of wounds, of rupture, of high aneurism of the brachial, or, rarely, in distal ligation for subclavian aneurism. Woiinds 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 and 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 (twenty-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, elevation, and circumduction (which 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. Aneurism 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 portion of the vessel, or that least supported by surrounding structures and most subjected to changes in tension and position and to certain injuries, as those which occur during luxation of the shoulder or during efforts 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. 49 770 HUMAN ANATO.MV. The synipioms are (a) s'arl/ini: sliowin.u iinmediately below the clavicle (in Mohrenheiin's fossa) and jHishinj^ that l)one ui)\vard if the hrst portion is inxolved, or pushing the pectoral muscles forward if the aneurism is lower, or apjiearinjr as a pulsatin.t; tumor in the axilla if the third portion is involved ; {b)a'dc)na of the arm and hand from pressure on the axillary vein ; (r) pain down the arm, in the shoulderi 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 i)ressure on the brachial jilexus and its branches. Di^^ital compression of the axillary artery is only effectively possible in the lowei part of the third portion, where, with the fingers beneath the anterior axillary fold, Fig. 706. . Cut fibres of pecloralis major Clavicle Subdavius Axillary artery // / / Brachial plexus Subclavian vein Pectoral Is major, cut Pectoralis minor IVctoralis major, ^turned back! First intercostal space Second rib Dissection showing relations of axillary artery in first part of its course. the vessel, if the effort is made with due care and gentleness, may be flattened agains^ the humerus just within the edge of the coraco-brachialis and biceps. IJQ;ation of \\\^ first portioti may be effected in two ways : i. With the arr abducted to a right angle, an incision three inches long, slightly convex downwardJ_ and with 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 clavicular 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 seco7id portion 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 circulatioyi 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 thii'd portion above the origin of the subscapular the anastomoses take place between (a) the intercostals, long thoracic, posterior scapular, and suprascapular, and {b) the acromial thoracic, on the cardiac side of the ligature ; and (a) the subscapular, and {b) 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 pectoralis major and the pectoralis minor. It anastomoses with the intercostal arteries and the superior and long thoracics. 772 HUMAN ANATOMY. (d) The clavicular branch, uliicli is the smallest of tiie three, passes upward to supply the subolavius nuiscie, aud auastunuises with the suprascapular artery. (< ) The acromio-humeral branch passes upward and DUtward across tile costo-coracoid nieiubrane aiui over the ci>racoid process of the scapula, and then di\ ides into an acromia/ and a A//w<-/(;/ branch. The former (ramus acromialis) passes upward towards the acromial process to supply the deltt)id nuisde, while the latter (ramus deltoideiis) turns downward in the .i;;roove between the deltoid anil the clavicular porti(»n of tlie pectoralis major, accompanyin.i^ the cephalic vein. It sends branches to the two adjacent muscles and to the inte.ijument, and anastomoses with the anterior circumflex artery. 3. The Long Thoracic Artery. — The long thoracic (a. thoracica lateralis) (Fig. 704) i.s a soinewliat 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 dow nward and for^vard upon the serratus magnus, sending branches to that muscle, the pectoralis minor, and the muscles of the third, fourth, and fifth intercostal Fig. 707. . Transverse cervical artery " Superficial cen ical bnnch " Posterior scapular branch ■ Trapezius, cut Supra- scapular arter>' Khom- boitleus majt"*! Acromion Deltoid, everted Triceps Post, circumflex art. Infraspinatus riceps, scapular head Teres minor Spine of scapula Dorsal scapular artery Subscapularis Teres major Latissinius dorsi Arteries cf posterior aspect of shoulder. spaces. It also sends branches to the mammary gland (rami nianiraarii externi), whence it has been termed the extei'nal mammary arter}'. 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 iiicon- stant small branch which passes to the fascia and lymphatic glands of the axillary space. Its place may be taken bv 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 ner\^e, 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 also gives off — It THE BRACHIAL ARTERY. 773 (a) Thoracic branches (rami thoracodorsales) , which supply the serratus ma'-nius and the muscles of some of the intercostal spaces, and not far from its origin it gives off — (d) 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 arterj- 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 artery varies somewhat in its origin. Occasionally it sprinp-s 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 arter>-, may also arise from this common trunk. The subscapular has been observed to give rise to an aberrant arter>^ 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 circumflex (a. circum- flexa humeri anterior) (Fig. 704) is the smallest of the three branches of the third portion of the axillary, and arises either directly from the artery or from a common trunk with the posterior circumflex ; 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 oE 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- cumflexa 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) is 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. — Anteriorly the brachial artery is covered throughout the greater part of its course by only the deep and superficial fascise and the integument. About the middle of its length it is crossed obliquely, from without inward, by the median nerve, and at the bend of the elbow it passes beneath the aponeurotic slip, the so-called bicipital fascia (lacertus fibrosus) from the tendon of the biceps, and is separated by it from the median basilic vein. Posteriorly 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 ner\-e 774 HUMAN ANATOMY. ami the coraco-brachialis muscle, and, lower down, the biceps and its tendon. Jntcrnally 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 vena- coniites accompany the artery, lying respectively upon its inner and outer sides, and cross branches |)ass between the two. It is also accompanied by two lymphatic \essels which ha\e in their course three or four lyni])hatic nodes, usually of small size. Branches. — The brachial artery gives of? vtusailar branches to the biceps, coraco-brachialis, brachialis anticus, triceps, and pronator radii teres, and a small Fig. 708. 4 Cephalic vein Humeral branch of acromial thoracic artery Pectoralis maj Axillary vein Muscular vein Outer head of median nerve Inner head of median Axillary artery Musculo-cutaneous nerve Brachial artery Superior profunda artery Median nerve Latissimusdorsl tendon Teres major Inferior profunda artery Internal intermuscular septum Anastomotic artery Biceps tendon Ant. cutaneous br. of musculo cutaneous nrv Bicipital fasci.i Inner condyle Olecranon Brachial artery in relation to ner\-es of arm. mdrinit artery for the humerus (a. nutriciao 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 siiper tor profunda, (2) the mferior profunda, and (3) the anastomotica magna. Variations.— The \ariations which the brachial arter\' presents are both numerous and imiiortant, in that they affect materially the origin of the' two terminal branches, the radial and ulnar. ^u^'^^^'^u" ^^''^'^'^ \\\^r^ is a well -developed supracondvloid process on the humerus (page 26S), the brachial arter>- accompanies the median ner\-e behind it, and only passes upon the an- terior surface of the arm after it has passed it. In such cases there generally arises from the upper part of the brachial, or e\en from the axillary, a vessel which descends upon the anterior surface of the 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. bi^achialis superficialis, 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, stump Biceps and coraco-brachialis, stump Axillary artery Anterior circumflex artery Tendon of long head of biceps Insertion of pectoralis major Deltoid Coraco-brachialis ■ Humerus ■ 'Ix ^ Brachial is anticus- l'\' )ii..Lwj [dorsl Teres major and latissimus Superior profunda artery -Brachial artery -Triceps Inferior profunda artery ) /Ft ' 3 Brachialis anticus Tendon of biceps Anastomotic artery Inner condyle Olecranon / / ^_^ ■'ILj^*— i ^^^ Origin of superficial flexors — -"*' .^f-— ' — -. - interior ulnar recurrent artery ■ Posterior ulnar recurrent artery Ulnar 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 bemg contmuous below ^^•lth the common interosseous ; or, finally, it may unite with the lower part ot the brachial artery proper, the portion of the latter between the ongin and anastomosis ot the superficial brachial disap- pearing, so that what is termed a brachial artery is formed, which passes behind instead ot in front of the median nerve. — (, HUMAN ANATOMY. Comparative anatomy and t-inbryoloj;}- both indicate that the occurrence of a well-devel- oped superticial brachial, continuous below with tlie radial, is the primar)- condition, and that the origin of the ratlial as a terminal branch of the brachial proper is a secondary condition, due to an anastomosis between the K)wer part of the original superficial stem and the brachial and to the subsequent diminution or partial obliteration of the former above this anastomosis (Fig. 748 E ). .... Another branch, nomially present but usually insignificant, which may reach an e.xtraor- ilinarv development, is the a. plicir ciibiti supcrjicialis. It arises from the lower portion of tlu brachial and, i)assing inwarti and downward beneath the tendon of the biceps, is distributed tn the tiexor cari)i radialis and the palmaris longus. When abnormally developed, it forms what has been termed the accessory ulnar artcr}\ and passes down the forearm, immediately beneath the deep fascia and between the two muscles ju.st 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 atldition, the brachial may give rise, in its upper ]iart, to the sub.scapular and the posterior circumflex, normally branches of the axillary^ ; in its lower part, \vt the radial recurrent; and, ;it its bifurcation, to the interosseous artery or to the median, which is usually a branch of tli' interosseous. Practical Considerations. — Si)ontaneous aneurism of the brachial artery is rare, and is usually associated with marked arterio-sclerosis or with cardiac diseas< Wounds and traumatic aneurism are common, though lessened in frequency by thi 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 v\as 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 j^oint and sei)arated from it only by the lacertus fibrosus. The line of the artery is from the junction of the anterior and middle thirds tif the axilla to the middle of the bend of the elbow when the arm is abducted and the forearm extended 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 may be 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 abo\ e the beginning of the internal suj^racondyloid ridge, it may most easily be subjected to compression. In the lower third the pressure must be directed backward, as the humerus— separated from it by the brachialis anticus muscle — then lies behind it. Ligation of the vessel at its upper 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 advantage 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 avoided by compression of the axillary 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 flexed, 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). 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 venae 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 difificult when the artery is concealed by the median nerve 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 third — above the bend of the elbow — the inner edo-e of the biceps tendon should be distinctly recognized, and the position of the superficial veins, 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 divided 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 {vide 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 the vessel and deri\'ed from the pectoralis major or from one of the humeral muscles. The collateral circulation 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. (<:) A median collateral branch (a. coUateralis 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. (a') An articular branch, which is given off from the lower portion of the arterj', just before it pierces the external intermuscular septum, and is distributed to the elbow-joint. (i?) Cutaneous branches, which accompany the external cytaneous branches of the mus- culo-spiral nerve. Variations. — The superior profunda occasionally arises from the axillary 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 collateral 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 posterior ulnar recurrent. It gives branches to the triceps and to the brachialis anticus. 778 HIMAN ANATOMY. T,. The Anastomotica Magna. — The anastomotica majfiia (a. collatcralis ulnaris inferior) ( I'ig. 709) arises from the inner surface of the brachial artery, about 4 cm. (i-Vs in. ) above its termination. It passes inward over the brachiahs anticus and beneath the median ner\'e, and, pierciii.u^ tlie internal intermuscular septum, winds around the inner bortler of the humerus and passes transversely across its posterior surface, just al)ove the olecranal fossa. It anastomoses with the posterior ulnar recur- rent and with both the su])erior and inferior profunda arteries, and also, by means of a branch ijiven oflf 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 maj^na, abundant opportunity beinu: thus afforded for a collateral circulation to the forearm after ligation of the brachial. Thus, the suj^erior profunda anastomoses in front of the external condyle of the humerus with the radial recurrent, and its medial collateral branch anastomoses in the neighborhood of the olecranon ])rocess 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 arter\^ (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 \'ertical direction. Arri\ed 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 superticialis), whose convexity looks distally, and terminates opposite the second intermetacarpal space by anastomosing with the superficial \olar branch of the radial. For convenience in description, the ulnar artery may be regarded as consisting of three parts : ( i ) an antibracliial 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 suj)erficial palmar arch is on a level with the thumb when the digit is abducted to a position at right angles to the axis 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 only by 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 ner\'e, 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, immediately to the radial side of the pisiform bone, and is co\'ered by an expansion 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 I THE ULNAR ARTERY. 779 Superficial branch of sup. profunda Musculo- spiral nerve Radial recurrent artery Brachio-radialis Brachialis anticus 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 b?'anches supplying the muscles of the forearm, and, in addition, to ( I ) the ante7-ior ulnar recurrent, (2) the pos- Fig. 710. terior ulnar 7^ecurrent, (3) the common interos- i seous, (4) a 7iutrient * branch, (5) the poster- ior ulnar carpal, and (6) the anterior ulnar carpal. From the carpal 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 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 earher 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 distally in a plane superfi- cial to the original vessel, accompanying the median nerve through the interval between the flexor sublimis digitorum and the flexor profundus digitorum. This median artery, near the wrist anastomoses with the original one, and the latter tiien begins to diminish in size and separates from the median above the point of its anastomosis, forming the anterior interosseous _arten,^ 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 known as the a. comes nervi mediani. 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 Pronator radii teres Radial nerve Radial artery Flexor longus pollicis Anterior carpal arterj Superficial volar artery 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 Common interosseous artery Ulnar nerve Median nerve Ulnar artery Flexor profundus digitorum Flexor sublimis digitorum Palmaris longus tendon Anterior carpal artery Posterior carpal artery Flexor carpi ulnaris Pisiform bone Radial and ulnar arteries : superficial dissection. rJSo HUMAN ANATOMY. a persistent median or interosseous artery, — a condition of u liicli iiuiicatitMis are to be seen in the partici|)atit>n of the interosseous or median artery in the formation of tiie superficial palm r arch (pajje 7.S51. An interestinjr condition in whicli indicatii)ns are clearly retained of all tli stajit-s whicli tlie forearm arteries i)ass throu<;li in tiieir evolution is shown in F'n^. 711. An artery which is the sujierticial hrachial, ami whicii arose from the axillary, descends the arm parallel to the brachial proper and terminates by bectHiiiiii;: the radial. A distinct ulnar has developed anil the anterior interosseous has acquired its tyjiical arranijement, but there is a well-developed median artery which sends a strong branch across to the radial and termi- nates by anastimiosinj; u ilh the superficial palmar l)ranch of the ulnar to form the superficial |)almar arch. Another variation may occur in the form of a " his^h origin" of the ulnar artery, a condi- tion which results from the anastomosis of the superficial brachial artery (page 774) with tin ulnar. In such cases the ulnar frec|uently passes down the forearm in a nnich more superficial position than usual, i)assing o\er, instead of undii, the muscles arising from the internal condyle. Such a superficial course may also be followed when the artery has a normal origin, and occasionally it passes to the ulnar border of the forearm bt ■ tween the palmaris longus and the fle.xor sublimit- digitorum. *^*^ '* ^ Practical Considerations. — The ul- nar artery may be li^ateil for wound or for aneurism — of wliich 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 ii^ cision on the line indicated (v/dc supra through the skin and the thin deep fascia should expose 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 flexor 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 th* interspace thus identified, which runs obliqiu ly inward towards the ulna, the artery will be found lying on the flexor profundus digitorum, with the ulnar ner\e to its inner side. It is often overlapped by the inner deep edge of the flexor sublimis, so that that muscl must be lifted up and drawn outward befor' the vessel can be fully exposed. In sepa rating the muscles care must be taken not t' 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 proftmdus. 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 about 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 divided (Treves). The ulnar ner\e lies in close proximity to the vessel on the ulnar side. .^- Variation of arteii showing retention of developmental conditions THE ULNAR ARTERY. 781 The vense 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. 712) 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 off 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 flexor 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 which 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 axillar>', 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, bet^veen the adjacent edges of the flexor profundus digitorum and the flexor 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 nervi 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 nerve, 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) K nutrient branch is usually given off to the radius and occasionally also to the ulna. 782 HUMAN ANATOMY. (cf) 'I'hu anterior terminal branch jjusses either over or beneath tlie pronator qiiadratus, and terminates usually by anastomosing with branches of the anterior radial antl ulnar carpal and with the palmar recurrent arteries. Occasionally it anastomoses directly w ith the super- ficial palmar arch. (i^t/ ) The posterior terminal branch is larger than the anterior. It i)erforates the inter- osseous membrane, anastomoses with the j^osterior interrosseous artery, and terminates in branches which anastomose w ith the posterior radial and ulnar carpals to form the dor.sal carpal net-work. Variations. — The anterior interosseous arterj- may arise from the radial, and it may form anastomoses below with the radial or with both the radial antl ulnar. The relations which it sometimes possesses willi the superficial palmar arch will be considered later. The median artery is occasionally of considerable size and frecjuently arises from the common interosseous. Its relations to the superficial palmar arch will also be considered later (page 7S5). d. The Posterior Interosseous Artery. — The posterior interosseous (a. inter- ossea (lorsalis; (Fig. 715) passes backward between the radius and ulna, above the concave tipj^er margin of the interrosseous membrane. It thus reaches the posterior portion of the forearm and turns abruptly dow nward 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 j)osteri<)r surface of the forearm it gives of^ 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 carptis. 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 bcme, and winds inward beneath the tendon of the fle.xor carpi ulnaris to the back of the carpus, where it anastomoses with the posterior radial carpal anrl 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 flexor 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 of? from the ulnar artery, just after it has entered the palm. The superior branch arises just after the ulnar artery has passed fhe 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 digit! , and terminates by 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 nerve Supinator brevis Radial recurrent artery tU K^^> • Inferior profunda artery IjS~ Origin of superficial flexors \& «~" Inner condyle Wz-'A V /^ j/';;f>|| — 'Brachialis anticus ^ 1 , / , \ jM'S Anterior ulnar recurrent artery Posterior ulnar recurrent artery Ulnar artery Radial artery Posterior interosseous artery Pronator radii teres Extensor carpi radialis longior IBOS' Brachio-radialis ¥f I'l Flexor longus pollicis Anterior radial carpal artery Radial artery Princeps pollias Branch to superficial palmar arch Median nerve Brachial 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 / f \ *TO7/i ^ Ulnar artery fe=^i'~i - ■ yilut ■ '^^^P palmar arch ^ySTlV^i^^': '■•— Palmar interosseous arteries Digital arteries Radialis indicis Deep arteries of right forearm and hand ; flexor surface. 784 HUMAN ANATOMY. 9. The Digital Arteries. — The di^ntal branches ( aa. diyitalcs volarcs coiii- niunes) arise from the portion of the uhiar artery which passes transversely across the pahn of the hand antl is termed the superficial palmar arch (arcus volaris siipcrficialis). They are four in number; the first of the four, starting from the ulnar border of the hand, passes oblicjuely 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 pollicis Opponeiis pollicis Flexor brevis pollicis Flexor loiigus pollicis tendon Princeps pollicis Kadialis iiidicis — Ulnar nerve I'liiar artery Pisiform bone Anterior annular ligament Deep branch of ulnar artery Digital branches of median ner\'e Abductor minimi digiti Flexor brevis minimi digiti Digital arteries 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 lingers, 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 hranches of the radial anastomose w ith the digitals just before the division of the latter into their collateral branches, and if the interosseae 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 supplv for the radial side of the index- finger and the thumb is from the deep palmar arch, yet oc'casionallv 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. 785 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 forearrn 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 independently to a certain number of digital branches. To the first of these classes belong the cases in which the median or anterior interosseous artery anastomoses directly with the arch formed by the superficial volar and the ulnar, and also tliose 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 arterj' alone, no direct communication takino- 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 vessels to the Variations of palmar arteries replacing superficial arch. ( faschtschinski), thumb and radial side of the index (Fig. 714, A), ox it may be limited to the latter vessels, all four normal digitals being derived from the ulnar. With the absence of the arch there may be associated an extra development of the median artery, 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, with 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 {B ) . 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, curving around the external lateral ligament of the wrist. It then extends downward over the pos- terior surface of the trapezium until it reaches the interval between the first and second metacarpal bones, and here it again changes its direction and passes forward into the palmar surface of tKe hand, across which it is continued inward over 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 portio7i it is preaxial in position, in the second or carpal portion it is postaxial, and in the third or palmar portion 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 between 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 co\'ered only by the deep and superticial fasciae 50 786 HUMAN ANATOMY. antl Uic skin. IN^sterioily it rests succcssi\cly, from above downward, upon tlie tendon of the biceps, the sujjinator brevis, the pronator radii teres, the radial jjortion of the flexor subliniis ili_i,Mtoruni, the flexor longus polhcis, the outer border of the pronator quadratus, and the anterior surface of the lower end of the radius. Inter-j 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 middU thiril of its course it is in contact with the radial nerve. Two vena^ comites accomj pany the artery, lying to its inner antl outer sides. In its carpal portion the ratlial artery rests at first upon the external latera ligament of the wrist and then upon the posterior surface of the trapezium. It passt beneath, successively, the tendons of the extensor ossis metacarpi pollicis, the extenj sor brevis pollicis, and the extensor longus pollicis, being covered in the interva between the last two and to the ulnar side of the extensor longus pollicis only by th€ skin and fasciie, in which are some branches of the radial nerve and tributaries of the radial vein. In its palmar portion, as it passes forward through the proximal portion of the finst intermetacarpal space, the artery lies between the two heads of the first dorsa interosseous muscle. It then bends inward beneath the oblique head of the adductoi pollicis, and, either penetrating that muscle or passing between it and the transverse head of the same muscle, is continued ulnarward beneath the tendons of the lon£ fle.xors, resting upon the bases of the metacarpal bones and upon the interosseous muscles. Branches. — From its antibrachial portion the radial artery gives of! numer- ous inuscular branches to the muscles on the radial side of the forearm, and, it addition, gives origin to (i) the radial recurrent, (2) the a^iterior radial carpal, and| (3) the superficial volar. F"rom its carpal portion it gives rise to (4) \\\it posterior radial carpal, (5) the dorsalis pollicis, and (6) the dorsalis indicis. From its palmar portion its branches are (7) the princeps pollicis, (8) the palmar interosseous (of which there are three), and (9) the reciirrent carpals. Variations.— The hi<(li origin of the radial has already been considered in discussing the variations of tlie brachial artery (page 774). It is the last of the foreiirm arteries to be devel^ oped in tlie comparative series, and its relations with the arterial supply to the hand is due to secondary anastomoses which it makes with vessels originally present, whereby it has come tc give origin to many branches formed before its appearance. Tims the dorsalis indicis and the dorsalis pollicis are primarily digital branches from the dorsal interosseous artery of the first intermetacarpal space, and this artery arose from the posterior carpal arch and has become ai portion of the radial by the anastomosis of that arter>' with the arch. Similarly the portion of the radial which j^asses 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- tinnity with the arch and given it the branches which originally arose from that vessel. The secondary anastomoses of the original radial with i)re-existing vessels have, however, become well established, and variations of the radial, other than its high origin, are rather uncommon. It lias been observed to terminate in an anastomosis w ith an enlarged posterior carpal arch, or in the lower part of the forearm by anastomosis with the anterior interosseous arterv'. Its absence below the point where the radial recurrent is given bflf has also been ob- served, 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 artery. 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 quality of that phenomenon. Practical Considerations. — The radial arter>', like the ulnar, is the subject of idiopathic aneurism only with great rarity, 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 7ipper 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 lozver third the incision should be made 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 anatomique), bounded externally by the tendon of the extensor longus poUicis, internally by the tendons of the extensor brevis poUicis and the extensor ossis metacarpi poUicis, 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 supra). I. The Radial Recurrent Artery. — The radial recurrent (a. recurrens radialis) (Fig. 712) arises from the outer surface of the radial, shordy 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. 788 Hl'MAN ANATOMY. 2. The Anterior Radial Carpal Artery.— carpea volaris) (Fig. 712) is usually a small branch Fio. 715 Triceps, cut Olecranon process Anconeus — Interosseous recurrent artery Extensor carpi ulnaris, cut Superior profunda arter>' - liiachio-radialis -Extensor carpi raiiialis loneior "I-'xternal condyle Head of radius Supinator brevis Posterior interosse- ous artery — Posterior interosse- ous nerve — Extensor carj'' radialis bre%ior Extensor ossis metacarpi pollicis The anterior radial carpal (ramus 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 nunil)er of small branches which anastomose with 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 superficial volar ( ramus volaris supcrfici- alis) (F'ig. 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 over, through, or beneath the adductor pollicis, supplying that and the other muscles of the thenar eminence, and terminates usually by anastomosing with the superficial palmar branch of the ulnar to form the superficial palmar arch. Variations. — The superficial volar is somewhat 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 arter>' (page 784). 4. The Posterior Ra- dial Carpal Artery. — The posterior radial carpal (ramus carpeus dorsalis) (Fig. 715) is a small branch which is gi\en od from the radial just as that vessel passes beneath the tendon of the e.xtensor ossis metacarpi pollicis. It passes horizontally inward beneath Extensor longus pollicis Extensor indicis Posterior ulnar carpal artery Dorsal interosseous arteries Extensor brevis pollicis Anterior interosse- ous artery Posterior radial carpal artery Radial artery Dorsalis pollicis artery Dorsalis indicis arterj' Arteries of extensor surface of forearm and hand. THE RADIAL ARTERY. 789 the tendons of the extensor carpi radiahs 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 3. posterior carpal a) ch or net-work. Branches. — From the posterior carpal arch or net-work a longitudinal stem passes distally m 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 mterval between the bases of the proximal phalanges, it divides into two branches, which run forward upon the mner 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 linger. It termuiates 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 poUicis (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 radialis longior Lower extremity of radius Radial artery Fig. 716. Extensor longus pollicis \ \ Dorsalis indicis Extensor ossis metacarpi pollicis Extensor brevis pollicis Dissection showing relation ot radial artery to extensor tendons in 'snuff box." 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.— The 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 direcdy 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 obliqmim of the adductor, the vessel frequently divides into two branches, one of which is continued distally alon^ the radial bt)rder of the index-finger, forming what has been ternietl 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 tenth )n of the flexor longus poUicis into two branches, which pass distally along the i)almar surface of the thumb, one along the inner and the other along the outer border, anastomosing with the branches of the dorsalis poUicis. Variations.— The a. princeps pollicis is in reality the palmar interosseous artery of the first internietacan^al sjiace, ami. wlitn tleveloiied as described, corresponds in the arranjjement of its branches with the dorsalis indicis. together with the dorsalis pollicis. Frequently, however, the branch to the radial border of tiie index-finsjer 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'tiie superficial palmar arch (page 784). 8. The Palmar Interosseous Arteries. — The palmar interosseous arteries (aa. metacarpeae volarcs ) are three in numi)er, and arise from the deep palmar arch as Fig. 717 Radial artery Anterior carpal branch Superficial volar Posterior carpal branch Metacarpa Dorsales poll Radial arter>- Princeps pollicis Radialis indicis Dorsalis indicis' Branch from radialis in- dicis for superficial arch Ulnar artery Anterior carpal branch osterior carpal branch Posterior carpal branch Posterior carpal arch Deep branch of ulnar A perforating branch of deep palmar arch Superficial palmar arch Dorsal interosseous arteries Palmar interosseous arteries Digital arteries 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 considerably in size, according as the digital branches from the superficial palmar arch are well or poorly developed (page 784). 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 proximally 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 various 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-works. 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. — A^iteriorly 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 'upward 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 vena 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 oesophagus, 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 viscera or to the parietes. The visceral branches are (i) the bronchial, (2) the oesophageal, and (3) the mediastinal. The parietal branches are (4) the aortic i7iter costal arteries, and (5) the diaphragmatic branches. 792 HUMAN ANATOMY. Variations — Tlu- i^assaj^c of tlie llioracic aorta doun the rij;,^ht side of the vertebral column in the upper iiart of if^ course ami the urii,nn from it of the ri^lit subclavian artery have already been discusst-d in connection with the variations of the aortic arch (page 724). It was there pointed out tiiat hotli tiuse al>normalities depend upon the more or less perlect persistence of the lower portit)n of the ri^lu primitive aortic arch. Not mfreciueiUly a modihcation of this condi-| tion is to be seen in tiie existence of a small branch arisuiK from the upper |>art of the thoracid aorta and passing obliciuely u|nvard and to the rifjht behind the a-sophai^is. 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 rijiht primitive aortic arch. It is re.u:arded by some authors as a normal branch of the thoracic aorta, but it is somewhat inconstant in its occurrence. Occasionally it anastomoser with the first or second intercostal branches of tlie superior intercostal artery ( i)age 765). 1. The Bronchial Arteries. — The bronchial arteries (aa. hronchialcs) (Fig.j 718) are somewhat variable in number; while three are usually described, the) may be reduced to two or increased to four. They arise from the upper portior of the thoracic aorta and pass to the right and left bronchi, and are continued alonj 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 of? minute branches toj 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 thel aorta and are continued along this to the lung. They give off srfiall branches to thej 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. oesophageae)] (Fig. 718) of the thoracic aorta are also variable in number, forming a series of four or sometimes five or six small vessels which arise in succession from above downward froin 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 whichl receives branches from the bronchial arteries, from the inferior thyroid above and the gastric artery below. 3. The Mediastinal Arteries. — The mediastinal arteries (rami pericardiaci' are a number of small vessels which arise from the anterior surface of the thoracic aorta and are distributed to the mediastinal lymph-nodes and the posterior surface ol the pericardium. 4. The Aortic Intercostal Arteries. — The aortic intercostals (aa. inter* costales) ( Fig. 718) supplying the tissues of the lower intercostal spaces, are usuall] 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-J inal wall. The arteries arise in pairs from the posterior surface of the thoracic aort 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,| owing 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 artery passes obliquely outward and upward across the space towards the angle of the rib next above, 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, runs 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 w^all in the subcostal groo\'e 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 gi\en of? by the internal mammary or the musculo-phrenic 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 deej) 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 tweU'th 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 vertebrae, the right aortic intercostals are crossed by the thoracic duct and by the vena azygos, and the upper ones are also crossed by the oesophagus. 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 nerves, 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 nerves 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 vertebra 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 axillary artery. 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 axillary 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 vertebral groove, it divides into a spina/ and a muscular branch. The former (ramus spinalis) passes through the interv'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 branch (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 between 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 axillary- line and perforates the external intercostal muscle in company with the lateral cutaneous branch of the corresponding intercostal nerve. It is distributed with the nerve 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 axillary arter\'. (rf) The collateral branch arises as the intercostal approaches the angle of its rib. It passes obliquely outward and downward to the upper border of the rib next below, along which it runs to terminate by anastomosing with the lower of the tw^o anterior intercostal branches given off by the internal mammary 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 usually arise from the superior intercostal branch of the subclavian, but occasionally the arten,' of the second space, and more rarely that of the first, may arise from the thoracic aorta. Or, conversely, the arteries of the third and fourth intercostal spaces, as well as those of the first and secorid, may arise from the superior intercostal, the aortic intercostals being correspondingly reduced m number. 794 HUMAN ANATOMY. Occasionally the second intercostal is formed by a branch from the first aortic intercostal which rnns upward to the second space over the neck of the third rib, and a similar condition may be met witli in the lower arteries, two or more intercostal s|xices being supplied from a common stem. iMually, the ri.i;:lit and left arteries ()f one or all of the pairs may arise from a common stem, sprinijin'j; from the posterior median line of the aorta. Practical considerations of the thoracic aorta are discussed with those of the aortic 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 lower border of the twelfth thoracic vertebra, and passes downward upon the bodies of the four upper lumbar vertebrae- 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 artery. It seems advisable, however, to adhere to the classic definitions of the artery, and to regard the middle sacral, for purposes of description, 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 veins. Anteriorly, in its uppermost part, it is invested by the sympathetic solar plexus, from which branches pass downward along the vessel, forming the aortic plexus. A litde 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, above, the left lobe of the liver, 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 diaphragm, which separates it from the inferior vena 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) artery and vein, and still more laterally the left ureter. Branches. — The branches of the abdominal aorta, like those of the thoracic, may be divided into two sets, visceral and parietal. The visceral branches are (i) the coeliac qxis, (2) the superior mesenteric, and (3) the inferior viescnteric 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 phreiiic, (5) the suprarenal, (6) the ?'enal, and (7) the spermatic or ovarian arteries. The parietal branches are (8) the lumbar arteries, of which there are four pairs, (9) the middle sacral, and (10) the co7nmon iliac arteries. 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 infej-ior phre7iics, (2) the coeliac axis, (3) the suprarenals, (4) the superior mesenteric, (5) the first pair of lumbar arteries, (6) the renals, ij) the spertnatics or ovarians, (8) the seco?id pair of himbars, (9) the inferior mesenteric, ( 10 and 1 1 ) the third 2ind fourth pairs of lumbars, (12) the middle sacral, and (13) the comtnon 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 \ena cava. Variations 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 vertebra. Bifurcation at a higher level than usual is less frequent, but it lias been observed as high as opposite the inter- vertebral disc between the third and fourth vertebrae, and, in very rare cases, the artery has been -*ound to divide as high as the second lumbar vertebra. THE ABDOMINAL AORTA 795 Fig. 718. Vertebral artery Common carotid artery Superior intercostal artery Subclavian artery Innominate artery I. aortic intercostal artery Right bronchus II. and III aortic mtercostal arteries Right and '.eft coronary arteries Leaflets of aortic semilunar valve IV.-VIl. aortic intercostal arteries Vena azygos Thoracic duct Subcostal artery Part of right crus of diaphragm I. lumbar artery Quadratus lumborum Superior mesenteric artery Suprarenal artery Renal artery Inferior mesenteric artery ' Psoas magnus / \ ^ \ muscle — ■/■ — r — V~ 1\. \ Iliac branch of ilio-lumbar artery Trachea Left common carotid artery Scalenus amicus muscle Vertebral artery Sectional surface of I. rib Superior intercostal artery I. and II. aortic intercostal , ,, , , arteries Left bronchus Aorta Upper left bronchial artery CEsophagus Lower left bronchial artery III., IV. and V. aortic intercostals A pericardial branch f CEsophageal branches VI.-X. aortic intercostal arteries An oesophageal branch Inferior phrenic arteries y-Subcostal artery Coeliac axis I. lumbar artery Lumbar fascia — middle layer Suprarenal artery Renal artery IL lumbar artery Spermatic arteries III. lumbar artery Origin of quadratus lumborum IV. lumbar arter>' ^•. Middle sacral artery Left common iliac artery X Internal iliac artery Ilio-lumbar artery- Posterior trunk of int. iliac Anterior trunk of int. iliac External iliac artery Aorta and its branches : ten intercostal arteries are present, first supplying second space ; on right side internal intercostal muscles are in position, on left they have been removed. 7g6 HUMAN ANATOMY. Fig. 719. AltlnHi^h the abcloiiiinal aortic stem is very constant in its relations, consicicral)Ie variation occurs ni the oriijin of its branches. Most of these will be considered in connection with the description of the brandies concerned, but it may be noted here tiiat very frequently a niunber of small branches, terminating in tlie neij^hboring organs or connective tissue and lympii-noiles, arise from the abdominal aorta, in addition to the branches which h.ive already been named. These small branches are rather inconstant, and may arise from either the anterior surface of the aorta, in which case thev are unpaired ves.sels, or in i)airs from its sides. Their existence .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 su|i|>osed 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 ( 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 cceliac axis and the sup- erior and inferior mesenteric arteries, the jiosition oc- cupied by these vessels in the adult being due to a downward migration which they undergo, the culiac a.xis representing the ventral visceral branch of the fourth thoracic tir possibly a higher segment, the sup- erior mesenteric that of the seventh thoracic, and the inferior mesenteric that of the twelfth thoracic. Tin- paired visceral branches are developed mainly in con nection with the embryonic kidney, and on the replace- ment of this by the adult organ the majority of them disappear, the suprarenal, renal, and spermatic arteries and certain inconstant branches which are lost in the neighboring connective tissue representing them in the adult. Of the parietal paired set, the i^bur pairs of lumbar arteries correspond to the four upper lumbar segments, while the conmion 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 arter\ and its branches. DiaRram showing fundamental arrange- ment of branches of andominal aorta. A, main body-trunk ( aorta ) ; /i. somatic branch to body- walls: C paired visceral branches; Z>, unpaired visceral branch ; £. peritoneum. Practical Considerations. — The abdominal aorta is the subject of aneiirism 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 axis 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 ; (^) it rather suddenly contracts about one and a half inches below this level (after having given off 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 cceliac axis, the suprarenals. superior mesenteric, etc.); and {d) the walls at this point are said to be intrinsically weak, often giving way (Woolsey ) during injec- tions of the cadaver. The aneurism may occupy any aspect of the vessel, but is more coinmonly on the anterior wall, whicji receives less support. As it enlarges it will cause some or all of the follow ing symptoms : I. Tumor in the epigastric or hypochondriac region (usually the left because there is less resistance from surrounding organs and because the artery inclines in that direction), having the characteristic bruit and expansile pulsation, commonly capable of being outlined by palpation or grasped (distinguishing it from a " throb- bing aorta"), and unchanged as to pulsation and impulse when the patient is put in the knee-elbow position (ehminating growths of the left lobe of the liver, the pylorus, or the pancreas, in which the tumor falls forvvard — i.e, dow^nward — and the impulse lessens or disappears) (Osier). 2. Dyspnoea, from interference with the descent of the diaphragm. 3. Dysphagia from pressure on the oesophageal opening. 4. Dys THE VISCERAL BRANCHES. 797 pepsia and vomiting directly from pressure upon the stomach, and indirectly from involvement of the solar plexus. 5. Jaundice from compression of the common duct and duodenum. 6. Polyuria followed by alhinihiuria and hcEviaturia or anuria from pressure on the renal nerves. 7. CEdenia of the legs and feet from pressure on the ascending cava. If the tumor enlarges posteriorly there is apt to be also : 8. Pain in the buttocks, thighs, and loins from pressure on the lumbar nerves, and in the back from pressure on the solar plexus and splanchnics, or from erosion of the vertebra ; and rarely there may be : 9. Weakness ox paralysis of the lower extremities from involvement of the cord. As a rule, the pain, distress, and disability are not so great in abdominal as in thoracic aneurism, because of the greater mobility of the abdominal contents, which can be much more easily displaced than those of the middle or posterior mediastinum and with consequences not so directly threatening life. Abdominal aneurisms rupture into the retroperitoneal space, the peritoneal cavity, the intestines (most often the duodenum), or — after ulcerating through the diaphragm — -into the pleura. Compression of the abdominal aorta may be effected by special tourniquets, the intestines being first well emptied and then got out of the way, as far as possible, by rolling the patient on the right side before applying the pad, between which and the skin a soft sponge should be interposed. The pad is placed a little to the left of the umbilicus, or, better — as the aorta may be median in position — directly over the pulsation of the vessel. Macewen has effectively controlled the abdominal aorta by throwing the weight of the body on the aorta through the closed right hand placed a little to the left of the middle line, the knuckle of the index-finger just touching the upper border of the umbilicus. With the left hand the arrest of the blood-cur- rent is ascertained by feeling the femoral at the brim of the pelvis. Only enough weight to arrest the femoral pulse is required. If the patient vomits or coughs, the pressure must be increased, lest the hand be lifted from the aorta by the abdominal muscles. Of course these methods would be applicable only to aneurisms situated near the bifurcation. Compression has cured at least one such case. They have, how- ever, been applied in iliac and common femoral aneurism and to control hemorrhage during inter-ilio-abdominal or hip-joint amputation. Ligatio7i of the abdominal aorta has been done in about a dozen cases with uniformly fatal results. The ligature has been applied between the bifurcation and the origin of the inferior mesenteric artery — one and a half to two inches higher. A median incision with its centre at the umbilicus is made, the peritoneal cavity opened, and the intestines displaced. The layer of peritoneum over the artery is carefully divided — or scratched through — and the vessel isolated, avoiding the sympathetic fibres connecting the aortic plexus (lying above the origin of the inferior mesenteric) with the hypogastric plexus (lying between the common iliacs) (Astley Cooper, Jacobson). The dense areolar tissue surrounding the vessel is penetrated and the aneurism needle is passed through it from right to left to avoid injury to the vena cava. The extraperitoneal operation closely resembles that for ligation of the common iliac (page 808). THE VISCERAL BRANCHES. I. The Cceliac Axis. — The coeliac axis (a. coeliaca) (Figs. 720, 721) arises from the anterior surface of the abdominal aorta, a short distance below the aortic opening of the diaphragm, and is a short, stout trunk from 1-1.5 cm. in length, which projects forward above the upper border of the pancreas. It terminates by dividing simultaneously into (i) \h^ gastric, (2) hepatic, and (3) splenic artey-ies. Variations.— The cceliac axis may be wanting, the three branches to which normally it gives origin arising independently from the aorta. Occasionally it gives rise to but two terminal branches, usually the hepatic and splenic, although more rarely they may be the gastric and splenic ; or, while dividing into three terminal branches, these may be the gastric, hepatic, and a common stem from the two inferior phrenics ; the gastric, splenic, and the right suprarenal ; or the gastric, splenic, and the right gastro-epiploic. It may also give rise to additional branches, such as one or both of the inferior phrenics, a gastro-duodenal, the superior mesenteric, the colica media, or the pancreatica magna, this last being normally a branch of the splenic artery. 79S HUMAN ANATOMY. (a) The Gastric Artery.— The gastric artery (a uastrica sinistra ) ( Fig. 720) is the smallest of the three branches given off from the cceliac axis. In the first portion of its course it passes to the left and slightly upward, across the left crus of the diaphragm, lying behind the posterior layer of the lesser sac of peritoneum. It reaches the lesser cunature of the stomach near the opening of the oesophagus into that viscus where the upper part of the posterior wall of the lesser sac of peritoneum passes^ over upon the stomach to become continuous with the ])()Sterior layer of the lesserj Fig 720. Right lobe of liver Call bladder Common bile duct Inferior vei.a cava Castro-duudenal artery Ripht kidney Pyloric V'ranLh of heijalic artery Duodenum Pancreas Ascendint; colon Crest of ilium Right gastj-o-epiploic artery Abdominal aorta ^^ Spleen _-^ Cceliac axis ,.- Gastric artery Cut edge of diaphragm j Splenic branches of splenic artery — Splenic artery _ Superior mesenteric artery Left gastro- epiploic arteryl Stomach - Transverse coloD Branches of middle colic artery Cceliac axis and its branches. (gastro-hepatic) omentum. It then curves forward, downward, and to the right along the lesser curxature of the stomach, lying between the two layers of the lesser omentum, frequently dividing into two parallel stems in this portion of its course, and terminates near the pyloric end of the stomach by anastomosing with the pyloric branch of the hepatic artery. Branches. — Just at the point where the gastric artery reaches the stomach it gives off — iaa) (Esophageal branches (rami oesophagei) which pass upward to supply the lower portion of the oesophagus, anastomosing with the oesophageal branches of the thoracic aorta and with branches of the inferior phrenic arteries. Throughout the entire length of its course along the lesser curvature of the stomach the gastric artery gives rise to — THE VISCERAL BRANCHES. 799 [bb) Gastric branches which pass downward over both surfaces of the stomach, anasto- mosing with the short gastric branches from the splenic artery and with the gastric branches which pass upward from the gastro-epiploic arch which passes along the greater curvature of the stomach. Some of the branches which^ arise from the more proximal portion of the artery and ramify over the cardiac portion of the stomach are frequently described as the cardiac branches. {cc') A small hepatic branch passes upward between the two layers of the lesser omentum towards the left end of the transverse fissure of the liver, where it anastomoses with the left branch of the hepatic artery. Variations. — The gastric artery occasionally arises directly from the abdominal aorta, in which case it may give rise to one or both of the inferior phrenic arteries. Its hepatic branch is not infrequently enlarged, and then constitutes the main stem of the left branch of the hepatic artery, which thus seems to arise from the gastric {U) The Hepatic Artery. — In the first portion of its course the hepatic artery (a. hepatica) (Figs, 720, 721) passes from left to right and sHghtly forward, over the right crus of the diaphragm, lying beneath the posterior wall of the lesser sac of perito-' neum. Where this passes over into the posterior layer of the lesser (gastro-hepatic) omentum towards the right, the artery bends upward and ascends, in the free edge of the lesser omentum, towards the transverse fissure of the liver, where it divides into two terminal branches. Relations. — In the first portion of its course the hepatic artery rests below upon the upper border of the head of the pancreas and is in contact above with the lower surface of the Spigelian lobe of the liver, upon which it frequently makes a distinct impression. It lies at first upon a plane posterior to the portal vein, but later it crosses the left surface of the vein and comes to lie in front of it. In its course upward in the free edge of the lesser omentum the artery lies anteriorly to the portal vein and upon the left side of the common bile-duct. Branches. — As the hepatic artery passes between the two layers of the lesser omentum it gives origin to two branches, the pyloric and the gastro-duodenal. {aa) The pyloric branch (a gastrica dextra) is the smaller of the two. It descends to the pyloric end of the stomach and then^ bending to the left, runs along the lesser curvature of the stomach, between the two layers of the lesser omentum, and terminates by anastomosing with the gastric arterj^ It gives branches to either side of the pyloric extremity of the stomach and, like the gastric artery, is frequently represented by two parallel vessels. {bb) The gastro-duodenal (a. gastroduodenalis), the larger branch, descends behind the first portion of the duodenum and terminates at its lower border by dividing into two branches, the superior pancreatico-duodenal and the right gastro-epiploic, {aaa) The superior paticreatico-duodenal branch (a pancreaticoduodenalis superior) descends to the head of the pancreas, upon the surface of which it anastomoses with branches of the inferior pancreatico-duodenal branch of the superior mesenteric artery. It sends branches into the substance of the gland and to the walls of the duodenum. {bbb) The right gastro-epiploic artery (a. gastroepiploica dextra) passes to the left along the greater curvature of the stomach, between the folds of the greater omentum, and inosculates with the left gastro-epiploic branch of the splenic artery. It sends branches upward upon both surfaces of the stomach, which anastomose with branches from the gastric artery and from the pyloric branch of the hepatic, and other branches pass downward into the greater omentum (epiploon). {cc) The terminal branches are two in number and pass the one to the right and the other to the left lobe of the liver The right branch ( ramus dexter) passes towards the right extremity of the transverse fissure of the liver, its course lying either in front of the hepatic and cystic ducts or between these two structures. At the extremity of the fissure it divides into a number of branches which enter the substance of the right lobe of the liver. As it passes across the hepatic duct it gives off a cystic branch (a cystica) which runs downward and forward along the cystic duct to the gall-bladder, whose walls it supplies, also giving some small branches to the liver. The left branch (ramus sinister) is directed towards the left end of the transverse fissure, and, after giving off one or two branches which enter the substance of the Spigelian lobe, terminates by dividing into a number of branches which enter the left lobe of the liver. Variations.— Variations of the hepatic artery are exceedingly frequent. The arter>^ itself may arise directly from the aorta instead of from the cceliac axis. or. by the enlargement of its anastomoses and the diminution of the normal main stem, it may appear to be a branch of the 8oo HUMAN ANATOMY. gastric or more frec|uently of the siiptrior mesenteric artery. It has also been described as arisinji from the rijiht renal artery. Further, by the enlarj^jement of anastomoses, associated with a persistence of the normal main stem, accessory hejiatic arteries from the gastric or superior mesenteric, or both, may be present, and aji accessory stem may arise from the aorta. Cireat variation occurs in the point at whicii the artery divides into its two terminal branches. This division may occur as low d(jwn as the origin of the gastro-duodenal branch, so that in its course up the free edge ui the lesser omentum the artery may be represented by two parallel stems which i)ass resjiectively to the right and left lobes of the liver. Indeed, not only may there be a jirecocious division into the two terminal branches, but each of these may again divide, alnn)st at their origin, into two or more stems, no that a number of parallel vessels, one of which usually represents the cy.stic branch, ascend to the liver. Occasionally the cystic, branch or an accessory cystic branch arises from the gastro-duodenal, and this latter vessel may arise from the cceliac a.xis while the liver and gall-bladder are supplied by a stem which arises from the superior mesenteric ( Ikewer). (c) The Splenic Artery. — The splenic artery (a. lienalis) (Figs. 720, 721) is the largest branch of tlie cceliac a.xis. It passes in a more or less tortuous course j over the left crus of the diaphragm and along the upper border of the pancreas, lying behind the posterior wall of the lesser sac of the peritoneum. It crosses the anterior Fui. 721. Under surface of left lobe nf liver CEsophaijeal lir.inche Phrenic arteries y Abdominal aorta ^^ Coeliac Axi< Cystic branch of heiwtic Common bile fiiict End of renal vein in vena cava Hetxitic artery- Portal vein Gastro-duodenal artery r>uodenum Splenic vein Superior mesenteric vein Right ^astro-epiploic artery Sui^erior (>ancreatico. duodenal artery Inferior [«ncrcatico- duodenal artery Ascending colon Middle colic Sii[>eTior mesenteric artery .Splenic artery Trans\ erse colon, turned up 1 eft kidney Sjileen Left gastro-epiploic artery l;r:inch to threat omentum I'.'tncreatica magna Pancreas Descending colon Duodenum Right coli Coeliac axis and its branches : stomach has been removed and transverse colon turned up. surface of the left suprarenal capsule and the upper part of the left kidney, and, passing between the two layers of the lieno-renal ligament, reaches the hilum of the spleen, where it breaks up into a number of branches which pass to the substance of that organ. Branches. — ( aa) Pancreatic branches (rami pancreatici ) are given off from the splenic arterj' throughout the entire e.xtent of its course along the upper border of the pancreas and supply that organ. One branch, much larger than the others (a pancreatica magna), arises at about the junction of the middle and left thirds of the arter>' and. entering the substance of the gland obliquely, passes from left to right along with the pancreatic duct. (/>f>) Short gastric branches (aa gastricae hreves). variable in number are given oflf either from the terminal portion of the artery or from some of its terminal branches. They pass between the layers of the gastro-splenic omentum to the left end of the greater curvature of the stomach, and. passing upon the surfaces of that organ, supply it, and anastomose with the cardiac branches of the gastric artery and with the branches of the left gastro-epiploic. THE VISCERAL BRANCHES 80 1 {cc) The left gastro-epiploic artery (a, gastroepiploica sinistra) arises close to the termination of the splenic and passes between the layers of the gastro-splenic omentum to the greater curvature of the stomach, along which it runs between the layers of the greater omentum, and terminates by inosculating with the right gastro-epiploic branch of the hepatic artery. Throughout its course it gives off numerous branches which pass, on the one hand, upward upon both surfaces of the stomach to anastomose with branches of the gastric artery, and, on the other hand, downward into the greater omentum. Variations.— The splenic is remarkably constant in its course and branches. It may arise directly from the aorta, and it has been observed to give off the gastric artery, a large branch to the left lobe of the liver, and the middle colic artery. 2. The Superior Mesenteric Artery. —The superior mesenteric artery (a. mesenterica superior) (Figs. 721, 722) arises from the anterior surface of the abdominal aorta, about 1.5 cm. below the coeliac axis. It lies at first behind the pancreas, but, passing downward and forward, it emerges between that organ and the upper border of the third portion of the duodenum and enters the mesentery. Fig. 722. Transverse colon — Pancreas Superior mesenteric aitery Middle colic artery Duodenuni Right colic artery Ascending colon Ileo-colic artery Anterior superior spine of ilium Branches to small intestine Csecum Posterior surface of stomach Left colic artery Duodenum Crest of ilium Branches to small intestine Anterior superior spine of ilium Part of jejunum Parts of ileum Superior mesenteric artery and its branches ; transverse colon and stomach have been drawn upward. It passes downward between the two layers of the mesentery, gradually curving towards the right, and terminates near the junction of the ileum with the caecum by anastomosing with its own ileo-colic branch. Branches.— The superior mesenteric artery supplies the whole length of the small intestine, with the exception of the upper part of the duodenum, and also a considerable portion of the large intestine, including the cscum and appendix, the ascendmg colon, and about half the 8o2 HUMAN ANATOMY. transverse colon. The lower portions of tlie duotleiuim and ileum and the larvae intestine arej supplied by branches given off from the concave surface of the artery, while the rest of the sma intestine receives its su|)ply from a somewhat variable number of branches which arise frontl tile convex surface. () The intestinal branches (rami iniestiuales), also called T'asa iuiestiiti huids, are fror ten to si.xteen in number, and arise from the conve.x surface of the artery, those branches whicl: arise from the upper portion of the parent stem being, in general, larger than the lower ones.' The first two or three branches, as they pass towards the intestine between the two layers of the mesentery, divide into an ascending and a descending branch, and these branches inosculate) to form a series of primary arches, which run, in a general way, parallel with the intestine. Lower down, in addition to these primary arches, secondary ones are formed by the inosculationj of branches given off proximally to those which form the primary arches ; still later, tertiary arches make their appearance, and finally the arrangement becomes so complicated as to resemble a net-work rather than a definite series of arches. From the convex surfaces of the primary] arches a large number of parallel straight branches pass to the intestine and are distributed to its walls. They rarely branch in tiieir course through the mesentery, and are usually distributed! to one side of the intestine and then to the other alternately. The rich anastomosis whichj occurs between the varit)us intestinal branches, and which varies greatly in its complexity, serves] to equalize the supply of blood to the entire length of the intestine and to permit of abundant! and rapidly collateral circulation to any portion of the tract from which tlie direct supply may] be cut off' by pressure exerted during peristalsis. (r) The ileo-colic artery (a. ileocolica) arises about half-way down the concave surface of] the superior mesenteric either independently or in common with the right colic branch. It] passes downward and outward, beneath the peritoneum, towards the ileo-ciecal junction, giving] off branches which inosculate with the right colic above, with the terminal portion of the supe- rior mesenteric below, and, in the interval, with one another to form a series of arches fromj which branches are supplied to the terminal portion of the ileum, to the cscum and the vermi- form appendix (a. appendicularis) and to the lower third of the ascending colon. {d ) The right colic artery (a. coiica dextra) arises from the concave surface of the superior] mesenteric either a short distance above or in common with the ileo-colic. It runs towards the! right, behind the peritoneum, passing over the right psoas muscle, the ureter, and the spermaticj (or ovarian) vessels, and as it approaches the ascending colon it divides into an ascending andl a descending branch. These inosculate respectively with the middle colic and the ileo-colic toj form arches, from which branches pass to the upper two-thirds of the ascending and to a portionj of the transverse colon. {e) The middle colic artery (a. coiica media) arises from the concave surface of the superior mesenteric a little below the origin of the inferior pancreatico-duodenal branch. It passes for«> ward and downward between tiie two layers of the transverse mesocolon, and divides into a right and left branch which inosculate respectively with the right colic and with the left colic branch of the infericjr mesenteric to form arches, from which branches pass to the transverse colon. Variations. — Considerable variation occurs in the number and position of the branches of the superior mesenteric artery and also in the complexity of the anastomoses which occur between these. In addition to those usually present, branches may be sent to any of the neigh- boring organs, such as the liver, stomach, and spleen, and the artery may give rise to the hepatic, as already pointed out, or to the gastro- duodenal, or even the gastric or renal artery. It has been observed to supply the place of the inferior mesenteric artery when that vessel was lacking, giving off left colic, sigmoid, and superior hemorrhoidal branches. Froni the embr\ological .stand-point the superior mesenteric represents the intestinal branch of the omphalo-mesenteric artery, which, during the early months of foetal life, passes outward through the umbilicus to be distributed upon the surface of the yolk-sac. Usually this artery disappears, except in so far as it is concerned in the formation of the superior mesenteric artery; but it has been observed to persist, appearing as a branch of the superior mesenteric which is continued forward in a strand of connective tissue from the ileum to the umbilicus, where it anastomoses with the epigastric artery and sends a branch upward along with the round ligament of the liver. 3. The Inferior Mesenteric Artery. — The inferior mesenteric artery (a. mesenterica inferior) (Fig. 723) arises from the anterior surface of the abdominal aorta from 3-4 cm. above the bifurcation of that vessel into the two common iliacs. THE VISCERAL BRANCHES. 803 It passes downward and to the left, beneath the peritoneum and resting upon the left psoas muscle, and, after having crossed the left common iliac, it terminates upon the upper portion of the rectum, this terminal portion being called the superior hem- orrhoidal artery. Branches.— («) The left colic artery (a, colica sinistra) arises shortly below the origin of the artery and passes upward and to the left. It divides into an ascending and a descending branch, the former of which passes between the two layers of the transverse mesocolon to inos- culate with the middle colic branch of the superior mesenteric, while the descending branch, entering the sigmoid mesocolon, anastomoses with the sigmoid arteries. From the arches thus formed branches pass to the left portion of the transverse colon and to the whole of the descend- ing colon. [b) The sigmoid branches (aa. sigmoideae ), two or three in number, are given off as the inferior mesenteric crosses the left common iliac. They run downward and to the left over the Gastric artery Fig. 723. Transverse colon, turned upward Cceliac axis' Hepatic artery Superior mesenteric artery. Renal veins Inferior vena cava Middle colic Right colic Abdominal aorta Ileo-colic artery^ Colic branch. Common iliac arterie: Common iliac veins Appendicular artery Vermiform appendix Middle hemorrhoidal branches of mternal iliac Termination of ileum, cut Part of transverse mesocolon Splenic artery ■Pai creatica magna ■Inferior pancre- atic o- duodenal artery • Left kidney Inferior mesenteric artery -Left colic Descending colon Sigmoid arterj' Sigmoid flexure Superior hemorrhoidal artery (on posterior surface of rectum) Anterior surface of rectum Superior and inferior mesenteric arteries; small intestine has been removed. left psoas muscle and, passing between the two layers of the sigmoid mesocolon, give off as- cending and descending branches which anastomose with one another and with the left colic and superior hemorrhoidal arteries, forming with them arches from which branches pass to the sigmoid colon. {c) The superior hemorrhoidal artery (a. haemorrhoidalis superior) is the terminal portion of the inferior mesenteric. It descends into the pelvis lying between the folds of the mesentery of the pelvic portion of the colon, and at the junction of the colon and rectum divides into two branches which continue down the sides of the rectum, supplying that viscus and making anas- tomoses with the middle hemorrhoidal from the internal iliac and with the inferior hemorrhoidal from the internal pudic. 004 HUMAN ANATOMY. Variations.— The inferior iiKstiUcTic artery may l>e wanting, its place heinj; supplied by branches from the sujK-rior mesenteric. It occasionally jj:ives rise to the micklle colic artery or to an accessor) renal vessel. 4. The Inferior Phrenic Arteries. — The inferior phrenic arteries (aa. phrenicao infcriorcs) (Fi.y^. 71S) most frequently arise from the abdominal aorta, cither sin_y;ly or by a common trunk, immediately beneath the aortic openinj^ of the dia- phragm and above the cocliac axis. They are directed upward and laterally over the crura of the diaphraj^m, to which they sui)ply branches, antl in this portion of their course they also give oH superior suprarenal branches ( rami suprarcnales superiores) to the suprarenal bodies. 0\er the region where the crura pass into the diaphragm proper, each inferior phrenic divides into an internal and an e.xternal branch. The former is the smaller of the two, and passes inward towards the oeso- phageal t)pening of the diaphragm, where it anastomoses with its fellow of the oppo- site side to form an arterial ring from which branches descend upon the oesophagus, su|)plving the lower portion of that structure and anastomosing with the o^so])hageal branches of the gastric artery. The e.xternal branches are directed laterally upon the imder surface of the tlia phragm, supplying it. They pass as far forward as the costal and sternal origins ot the diaphragm, anastomosing with the musculo-phrenic, superior epigastric, and superior phrenic branches of the internal mammary arteries, while other branches raniifv o\ er the lateral portions of the diaphragm, anastomosing with the lower inter- costals and perforating the central tendon to anastomose with the pericardial arteries and with the diaphragmatic branches of the thoracic aorta. Variations.— The inferior phrenic arteries are very variable in their origin. One fre- quently takes its ori.y;in from the cieliac axis or from one of its branches, or both may arise from the axis. Tiiey have also been observed to arise from the superior mesenteric or the renal, or from the abdominal aorta below the superior mesenteric. They also varj- considerably in \ olume. 5. The Suprarenal Arteries. — The suprarenal arteries, sometimes termed the middle suprarcnals ( aa suprarcnales mediae) (Fig. 718) to distinguish them from the suprarenal branches of the inferior ])hrenic and renal arteries, are a pair of small but constant branches which arise from the sides of the abdominal aorta, almost oppo- site the origin of the suijerior mesenteric artery. They pass outward and slightly upward over the crura of the diaphragm to the suprarenal bodies, where they anasto- mose with the other sui:)rarenal branches. 6. The Renal Arteries. — The renal arteries (aa, renales) (Figs. 718, 1591) are two large stems which arise from the sides of the abdominal aorta a little below the origin of the superior mesenteric. Usually the two arteries are opposite each other, but frequently that of the right side arises a little lower down than that of the left side. They are directed outward and slightly downward towards the kidneys, each artery, before reaching the hilum, dividing into from three to f^^•e branches, which enter the substance of the kidney indejiendently at the hilum. Relations. — In their course towards the kidneys the renal arteries restuj)on the lower portions of the crura of the diaphragm and more laterally upon the upper part of the psoas muscles. The right artery is somewhat longer than the left, owing to the position of the abdominal aorta a little to the left of the median line, and it passes behind the inferior \-ena cava. Both vessels are almost concealed beneath the corresponding renal veins, and at the hilum of the kidney the majority of the terminal branches pass in front of the upper portion of the ureter, only one or two passing behind it. Branches. — Near its termination each artery o:ives off branches which pass t< > the adipose tissue surroundin.sjthe kidney, and a ureteral branch which supplies the upper part of the ureter, anastomosing with the ureteral branch of the spermatic (or ovarian) arter>-. More proximally It gives origin to an inferior suprarenal branch (a suprarenalis inferior) which passes upward to the lower part of the suprarenal bod>- and anastomoses with the other branches which go to that structure. Variations. — Not infrequently the division of the renal arteries into their terminal branches takes place early, sometimes immediately at their origin, several stems arising directlv from the aorta and passing outw ard to the kidney.' Accessor}- renal branches may arise from tlie abdomi- THE VISCERAL BRANCHES. 805 nal aorta or from the middle sacral, the common iliac, the internal iliac, or the inferior mesen- teric, and occasionally the renal artery proper may be lacking and its place taken by a vessel from one or other of these origins. These accessory arteries frequently enter the substance of the kidney elsewhere than at the hilum. The two renal arteries may arise b}- a common trunk from the anterior surface of the aorta, and they occasionally give off branches which are either accessory to or replace vessels normally arising elsewhere. Thus they have been observed to give rise to the inferior phrenics, the right branch of the hepatic, the spermaticS; branches to the pancreas and colon, and one or more of the lumbar arteries. 7a. The Spermatic Arteries. — The spermatic arteries (aa. spermaticae intrnae) (Figs. 718, 1591) are two slender vessels which arise from the anterior surface of the aorta a little below the renals. They are directed downward, and slightly outward and forward, towards the lower part of the anterior abdominal wall, and as they approach this each vessel curves mward towards the median line" to reach the internal abdominal ring. Here it comes into relation with the vas deferens and becomes enclosed with it in the spermatic cord. Embedded in this structure, it traverses the inguinal canal and passes into the scrotum, terminating just above the testis by di\'iding into branches which pass to that organ and to the epididymis. Relations. — In its course through the abdomen the left spermatic artery lies behind the peritoneum and rests upon the psoas muscle. About the middle of this portion of its course it crosses obliquely in front of the ureter, and lower down has resting upon it the sigmoid colon. The right artery at first lies in the root of the mesentery ; it descends obliquely upon the anterior surface of the inferior vena cava and then, crossing the ureter obliquely, comes to lie behind the terminal portion of the ileum and frequently behind the vermiform appendix. In the pelvic and inguinal portions of their course the relations of both arteries are the same. The vessels rest upon the psoas muscle to the outer side of the ex- ternal iliac artery, and cross the lower part of that vessel and the accompanying vein to reach the internal abdominal ring. In their course down the spermatic cord the arteries lie behind the anterior group of the spermatic veins and in front of the vas deferens. Branches.^In addition to the terminal {a) testicular and (d) epididymal branches, each spermatic artery gives off — (c) An ureteral branch which is distributed to the middle portion of that duct, anastomosing with the ureteral branch of the renal artery above and with branches from the inferior vesical artery below. {d) Cremasteric branches are given off in the course through the spermatic cord and sup- ply the cremaster muscle, anastomosing with the cremasteric branch of the deep epigastric artery. Variations. — The spermatic arteries occasionally arise by a common tnmk, or, on the other hand, they may arise at different levels. They have been observed to arise from the renals, especially the left one, from the suprarenals, or from the superior mesenteric arter}^ yd. The Ovarian Arteries. — The ovarian arteries (aa. ovaricae) (Fig. 726) correspond in the female to the spermatic arteries of the male, and have a similar origin and similar relations in the abdominal portion of their course. Arrived at the pelvis, however, they cross the common iliac arteries and veins and, traversing the suspensory ligament of the ovary, pass inward between the folds of the broad ligament of the uterus, terminating beneath the ovary by inosculating with the uterine artery. Branches. — Like the spermatic arteries, the ovarian give off (a) ureteral branches. In ad- dition, they give rise to (<5) tubal branches, which pass to the distal portions of the Fallopian tubes; (c) ligamentous branches, which accompany and supply the round ligament of the uterus ; and {d ) ovarian branches, which enter the hilum of the ovar>- and are distributed to its substance. 8. The Lumbar Arteries. — The lumbar arteries (aa. lumbales) (Fig. 718) are arranged in four pairs, and take origin from the sides of the abdominal aorta,_ opposite the four upper lumbar vertebrae. They are directed outward upon the bodies of the vertebra, the lumbar portion of the sympathetic cord descending in front of them, and 8o6 HUMAN ANATOMY. those of the rijjht side also pass beneath the inferior vena cava, while the two upper ones of the same side pass beneath the receptaculum chyli. They then pass beneath the psoas muscle and the branches of the lumbar plexus, the two upper ones also passin.ij beneath the crura of the diaj^hrai^m ; and then, farther out, they pass beneath the qiiadratus Unnl)orum, except in the case of the last pair, which lies ujjon the ante- rior surface of that muscle. At the outer border of the quadratus they pass between the transversalis and the internal oblitiue muscles of the abdomen, and are continued onward in the abdominal wall, eventually piercing the internal oblique and reaching the rectus muscle. Branches.— Tlie lumbar arteries are to be re.s^arded as continuations of the series of inter- costal vessels, and, like the thoracic members of the series, eacii j,nves oft a dorsal branch [ ramus dorsalis). This arises when the vessel lies behind the psoas muscle and is directed jiosteriorly, soon dividinj^ into (a) a spinal branch (ramus spinalis), which enters the spinal canal through the intervertebral foramen and anastomoses with the anterior and posterior spinal arteries • and (d) a muscular branch, which is distributed to the muscles and skin of the back, hi addition, each lumbar artery gives of? numerous branches to the muscles with which it comes into relation. Variations. — One or more of the lumbar arteries may be wanting and t\\ o or more of them may arise by a common stem 9. The Middle Sacral Artery. — The middle sacral artery (a. sacralis media) (Fig. 718), which is to be regarded as the continuation of the abdominal aorta, is a small vessel arising from the posterior surface of the a:orta immediately above its bifurcaUon into the two common iliacs. It passes downward in the median line over the last two lumbar, the sacral and the coccygeal vertebrae, and terminates opposite the tip of the coccyx by sending branches to the coccygeal body or Luschka's gland (glomus coccygcum). Branches. — It sometimes gives rise to a fifth pair of lumbar arteries (aa. lumbales imae), and low er duu n it sends off small lateral branches which send branches inward to the spinal canal through the anterior sacral foramina and anastomose with the lateral sacral branches of the internal iliac artery. These lateral branches appear to represent a continuation of the inter- costal and lumbar series of arteries, the branches which enter the anterior sacral foramina cor- responding to the dorsal branches of those vessels. Variations. — The middle sacral occasionally arises from one or other of the common iliac arteries, and it may give origin to an accessory renal artery. • Practical Considerations. — Some of the h'miches of the abdomiyial aorta, including the splenic, hepatic, renal, superior and inferior mesenteric, and the ovarian, have been the subject of aneurism. These aneurisms do not usually attain any great bulk, seldom exceeding the size of a hen's ^^^. They are apt to be round or oval in shape. Occasionally — espe- cially in the aneurisms of the renal artery — they may almost fill the abdominal cavitv. Except when connected with the hepatic, the renal, or the coeliac axis, they are movable, changing their position in the various movements of the body. They may possess also the characteristics of pulsation and bruit. When the coeliac artery is affected the disease cannot be distinguished from aneurism of the parent trunk. In cases of implication of the hepatic artery, the pressure-effects of the tumor give rise to pain in the right side and to jaundice from obstruction of the hepatic, cystic, and common bile-ducts (Agnew). The renal artery has been found to be aneurismal in a small number of instances, the majority being of traumatic origin. The chief symptoms have been: {a) tumor, varving in size, situated in the region of the kidney, immovable with respiration or with change of posture, and almost always without impulse or bruit, on account prob- ably of the usual disproportion, in renal aneurisms, between the large aneurismal cavity and the size of the Acssel involved ; {b^ hceinatiiria often but not in\'ariably present ; (<:) pain elicited by pressure, or felt in the loin or extending to the genitalia, and sometimes accompanied by retraction of the testis. THE COMMON ILIAC ARTERIES. 807 These abdominal aneurisms are not uncommonly unsuspected until they have reached a late stage, and may even rupture and cause death from hemorrhage with- out having caused more than trifling inconvenience. In a number of cases the pain — especially apt to be felt in the back — has been the only symptom complained of. If a pulsating tumor, or one with a bruit, can be felt, it would be proper to approach the region by an intraperitoneal or — in the case of the renals — possibly an extra- peritoneal incision, and ligate the artery on the cardiac and distal sides of the sac. THE COMMON ILIAC ARTERIES. The common iliac arteries (aa. iliacae communes) (Figs. 724, 726) are usually regarded as the terminal branches of the abdominal aorta, although in reality the middle sacral artery forms the morphological continuation of that vessel, the common iliacs being lateral segmental branches comparable to a pair of lumbar or intercostal arteries. They arise opposite the body of the fourth lumbar vertebra and pass obliquely outward, downward, and forward to about the level of the sacro-iliac articu- lation, where they terminate by dividing into the internal and external iliac arteries. The two common iliacs diverge from each other at an angle of from 6o°-65° in the male and somewhat more (68°-75°) in the female. On account of the position of the abdominal aorta being slightly to the left of the median line, the right artery is slightly longer than the left, and is inclined to the median line at a slightly greater angle. Relations. — The common iliac arteries are covered by peritoneum, which sepa- rates them on the right from the terminal portion of the ileum and on the left from the sigmoid colon. Anteriorly, each artery is crossed by the ureter, and in the female by the ovarian artery and vein, and by the branches of the sympathetic cord which pass downward to the hypogastric plexus. The left common iliac is, in addition, crossed by the superior hemorrhoidal branch of the inferior mesenteric artery. Behind, the vessel of the left side rests upon the bodies of the fourth and fifth lumbar vertebrae, that of the right side being separated from them by the right common iliac vein and by the upper end of the corresponding vein of the left side. Lower both vessels rest upon the psoas muscle. Laterally, they are also in relation with the psoas and with the spermatic artery in the male and, in the case of the vessel of the right side, with the upper part of the right common iliac vein. Medially, are the common iliac veins and the hypogastric plexus. Branches. — The common iliac arteries terminate by dividing into the external and internal iliac arteries. In addition, they give rise only to small vessels which pass to the subjacent psoas muscles and to the neighboring peritoneum and lymph- nodes and the ureters. Variations. — A certain amount of variation occurs in the length of the common iliac arte- ries, depending largely upon the level at which the bifurcation of the abdominal aorta occurs. One or other vessel may give rise to the middle sacral artery or to an accessory renal arter}'. Practical Considerations. — The common iliac artery is very rarely the sub- ject of aneurism. Direct compression of the artery may be made by either of the plans described as applicable to the abdominal aorta, and should be applied about one inch below and a half inch to the right or left of the umbilicus. \Vhile it is easier to get rid of the intestines, as the vessel is placed more laterally, it is not always easy to avoid compression of the aorta itself. Ligation of the common iliac may be required for aneurism lower down, espe- cially of the upper part of the external iliac, or for wound, or as a preliminary to or part of the procedure in the removal of pelvic growths. It may be effected by either : (i) The transperitoneal method, or (2) the extra- peritoneal method, i. A median incision from umbilicus to symphysis, opening the peritoneal cavity, the intestines being kept in the upper segment of the abdomen by pads or by placing the patient in the Trendelenburg position, will give easy access to the vessel. On each side it lies directly beneath the peritoneum, but there are anatomical differences to which Makins has called attention. On the right side the vessel is uncovered by any structure of importance, and may be reached by dividing the peritoneum directly over it vertically. On this side the vena cava 8oS IRMAX ANATOMY. and both coniint>n iliac \dns are in close relation with the artery, the latter two passing beneath it. On the left side, the inferior mesenteric vessels as they enter the sigmoid mesocolon and jiass downward to the rectum cover practically the whole of the artery, and to reach the common iliac comfortably and safely the peritoneum would need to be divided close to the left of the median line of th« ' sacrum and be disjjlaced outward. The vein usually lies on the inner side o^ and somewhat behind the artery. This manu.>uvre has the disachantage of ex- posing the vein freelv, but this would probably give far less trouble than would th< numerous mesenteric \essels when swollen by reason of the loss of their ]:)eritonealJ support. 2. By the extraperitoneal method the vessel is approached through various! incisions ; the best ( Cramjiton ) (especially if it is desirable to apply the ligature at the highest possible point) begins at the tip of the last rib and extends downward tol the ilium and forward to the anterior superior spinous process. The abdominal] muscles and trans\ersalis fascia are divided at the lower extremity of the wound, the peritoneum separated with the finger from the iliac fascia in a direction corresponding to the line of the crista ilii, the abdominal muscles se\ered on the same line, and th( separation of the jieritoneum continued until it is pushed off the psoas and the iliacl vessels, which lie on the inner aspect of that muscle. The ureter is raised with the] peritoneum and remains attached to it. The artery may be similarly approached through an incision i)laced just above] Poupart's ligament and very like that used for the exposure of the external iliac. Thej needle is passed from the vein — /.<"., from left to right — in ligating the right common! iliac, and from right to left if the vessel of the left side is the subject of operation. The collateral circulation is carried on from above the ligature by (a) the inter- nal mammary; {U) the superior hemorrhoidal; (r) the lumbar; {d^ the middU sacral ; and {c) the pudic and obturator of the opposite side, anastomosing respect- ively with {a) the deep epigastric ; {h^ the middle hemorrhoidal (internal iliac) ; (r)] the deep circumflex iliac ; and ( <") the pudic and obturator of the other side {i.e.^ the side of the ligature) from below. THE INTERNAL ILIAC ARTERY. The internal iliac artery (a. hypogastrica) (Fig. 724) arises from the common] iliac and passes almost directly downward in front of the sacro-iliac articulation intoj the pelvis. Opposite the upper border of the great sacro-sciatic foramen it divides] into two main stems, the anterior and posterior divisions, from which branches or distribution are given <^ff-^^ Relations. — I?t.j>ittinwm-'the internal iliac artery is covered by peritoneum an( is crossed obliquely by the ureter. More anteriorly the \essel of the right side is in] relation with some coils of the ileum, while that of the left side is in relation to th< up])er part of the rectum. Posteriorly each artery rests upon the upper part of the! external iliac vein, which separates it from the inner border of the psoas muscle, and isj accompanied throughout its course by the internal iliac vein. Branches. — From the main stem of the arterv, before its division, there arises (i) the ilio-lumbar ?cc\.^ry , and from its posterior division (2) the lateral sacralsA usually two in number, and (3) ihe gluteal. From the anterior division there are] given off a hypogastric axis, which divides into (4) the superior vesical, (5) inferiot vesical, and (6) prostatic or vai^inal branches, and (7) the vesiculo-deferential orj uterine artery, and, in addition, (8) the obturator and (9) middle hemorrhoidal arteries, the main stem terminating by dividing into (10) the internal pudic and] (11) sciafic arteries. Variations. — The internal iliac arteries represent the proximal part of the fcjetal umbilical] or hyposjastric arteries which return the blood from the foetus to the placenta. During intra-j uterine life these vessels are large and appear to be the continuation of the common iliacs, pass-J ing forward beneath the peritoneum to the lateral walls of the bladder and thence upward uponi the anterior abdominal wall to the umbilicus, and thence in the substance of the umbilical cordl to the placenta. After birth the arteries diminish in size, and those portions of them which pass] across the lateral walls of the urinary bladder and up the abdominal wall become converted into solid fibrous cords which persist throughout life and are known as the obliterated hypogastric THE INTERNAL ILIAC ARTERY. 809 arteries. The portions of the arteries which remain patent form the main stems of the internal iliacs, the hypogastric a.xes and the superior vesical arteries ; what are spoken of as the main stems of the anterior divisions of the internal iliacs are really the common trunks by which the sciatic and internal pudic arteries arise from the hypogastric. In the arrangement of the branches of the foetal hypogastric arteries four types may be recognized, and corresponding to each of these is an arrangement of the adult internal iliac branches. Leaving out of consideration for the present the smaller branches, the first type is that in which two large trunks arise from the hypogastric, the posterior one being the gluteal and the anterior a trunk which divides into the pudic and sciatic. The adult Fig. 724. Middle sacral artery Right common iliac artery Ilio-lumbar artery Internal iliac artery Posterior trunk of internal iliac Superior gluteal artery Single trunk dividing into two lateral sacral arteries Pyriformis muscle Anterior trunk of internal iliac Superior hemorrhoidal from inferiormescnteric Rectum Obturator artery Anterior superior spine of il" Deep circumflex iliac artery External iliac arterx External iliac vein Obturator vein. Artery of vas deferens Symphysis pubis- Bladder Right dorsal artery of penis Superior vesical artery ^^ Middle vesical artery I nferior vesical artery Sciatic artery Internal pudic artery Right and left middle hem- orrhoidal arteries Spine of ischium Seminal vesicles Left ureter Anus Internal pudic artery, in ischio- rectal fossa Left dorsal artery of peni: Left corpus cavernosum Corpus Membranous Bulbo-cavemosus muscle spongiosum urethra Dissection of pelvis of male, showing right internal iliac artery 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 hj-pogastric 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 from 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 variatiDiis of the smaller branches, which are (iiiile minierous, will be considered in connection with their description. It may be pointed out, however, that, since the superior vesical arterv is the persistent portion of the original hyiio^astric artery and prmianly the direct ctmtiiiuation ot the hvpojjastric axis, some of the visceral branches which normally arise from the axis may take their orii,nn from the superior vesical. Furthermore, vessels which emhryolt>Kically arise from one or other of the sreat 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 Hi^atcd for hemorrhage, for gluteal and sciatic aneurism, and in the treatment of inoperable pelvic growths. It may be approached intrapcri- toneally by the same incision and the same general jjrocedure as employed in ligation of' the common iliac {^q.v. ). The vein lies behind and to the inner side, and Fig. 725. tp — n Diagram illustrating four types of arrangement of branches from hypogastric (internal iliac) artery : ct, «, iV, common, external and internal iliac artery ; jV, ilio-lumbar; /j, lateral sacral; ^.gluteal; j, sciatic ; />, internal pudic; ha, 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 witliin outward. The relation of the ureter, which crosses the vessel obliquely from without inward and downward, and of the hypogastric ple.xus 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 circjilation is carried on chiefly through (a) the inferior mesen- teric ; {b) the circumflex iliac ; (f) the middle sacral ; {d) the deep femoral ; (h) An aictabular brauch (ramus acct.ibuli ), which jjasses through the cotyloid notch anJ supplies the fatty tissue occuj^yinj; the bottom of the acetabulum. {f) The internal branch runs around the inner border of the obturator ff)ramen, beneat the external obturator muscle, and terminates by anastomosing with the external branch. Variations. — The obturator artery varies greatly in its origin, and these variations may divided into two groups, according as the origin is from the internal or the external iliac systei of arteries. While the origin of the vessel from tiie anterior division of the internal iliac is th| most frecjuent, yet, when compared with all the variations taken together, it occurs in som« what less than 50 per cent, of cases. Of other origins from the system of the internal iliac ther mav be mentioned those from the main stem of the iliac before its division, from its |)osteric clivision, and from the gluteal artery. Furthermore, its origin may occur from either the sciatjl or the internal putlic artery, although such cases are rare. J More freciuent and t>f greater importance from the practical stand-point is the origir 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 frt)m the deep epigastric artery-, being in the remaining cases from the external iliac distal to the deep epigas- tric or from the upper jiart of the common femoral arterj'. Undoubtedly the primary relations of the ()bturatt)r 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. Possibilitit- for such a process are furnished by the normal anastomosis between the pubic branches of tli' 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 puliic anastomosis. The origin of the obturator from the deep ei:)igastric artery ( Fig. 72S) becomes of importance from the fact that, in order to reach its jioint of exit from the pelvis, the obturator canal, the vessel must come into intimate relations w ith 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 tlownward and inward along the free borcler of Ciim- 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 ma\ pass directly across the ring. As regards the relative frequency of each of these courses it i mteresting to note that, according tf) observations made by Jastschinski, the course along th< 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 frecjuent in females than in males ; while the course along the free edge of Gimbernat's ligament occurs in only 17.5 per cent, of ca.ses, and is more common in males than in females. The differences in the two sexes are associated with the differences in the form of the pelvis and of the obturator foramen. Practical Considerations. — Tlie 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 maximus, 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, nearer to the fold of the buttock, it may 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 maximus are sepa- rated, the muscle is relaxed by full extension of the thigh, and the upper bony margin 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 sufificient 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 maximus. 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 gemeUi, the internal obturator, and the quad- ratus femoris, and, after giving off 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 the 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 external 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 fem'Srisv--^ 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 mternal 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 mav give origin to the lateral sacral, the mferior 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 artery with the femoral, and the subsequent diminution of the sciatic being secondary arrangements (page 824). 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 exit from the pelvis, passing between Sl6 HUMAN ANATOMY . 1-IG. 727- Superior eluteal artery Superficial branch of superior ijluteal Gluteus inaxiiiius Stialic after;- Cotcygeal .inrr Internal pu.lii arter Bi' eps. stiitiii Transverse liranch ■ •< internal circuinfle\ Pcrforatinj; l>ran«.hcs of tieep femoral artery Semitendinosiis SemiTneiiil>ran< sns Popliteal artery Muscular branches __r- Superior internal articular artery Gluteus niedius, cut L'ppcr ramus of deep branch of su|>erior gluteal artery Gluteus minimus Muscular branch of sup. gluteal Lower ramus ol deep branch Fyriformis [of sup. g^lu ^ iiluteus medius C.reater sciatic nerve Tendon of obturator intcrnus .\rticular branch from ascending , branch < f internal circumflex i .\rticular branch of sciatic artery ' Anastomotic branch Comes nervi ischiadici Gluteus maximus I roni external circumflex Superior perforating artery From external circumflex \'astus externus Middle perforating artery Inferior perforating artery Biceps— short head Biceps — long head Muscular branch of femoral artery Popliteal vein Superior external articular artery lixternal sural artery Inferior external articular artery Gastrocnemius Arteries ol gluteal regioti and posterior surface of righl thigh. • 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 chtoris). 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 am, 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 transverse 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 off important branches. (r) The artery to the bulb (a. bulbi urethrae or a. bulbi 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. (a? ) The urethral artery (a. urethralis) arises usually some distance anteriorly to the arter^^ 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 cavernosum (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 cavernosum 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- ernosum. 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 doisal ner\-e of 52 8i8 HUMAN ANATOMY. tlie iK-nis (or clitoris), ami still morf laterally the deep external pudic l)ranch of the common femoral artery. On reaching the },dans, it forms an anastomotic circle around the base of that structure, unitinijwith its fellow of the opposite side. Throughout its course it gives 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, inste.id of passing out of the pelvis by the great sacro-sciatic foramen, may be directed forward upon the Hoor of the i)elvis and i)ass out beneath tlie pul)ic symphysis to become the dorsal artery of the penis. .More fretjuently this course is taken by an acussoiy iiitci/ia/ piidicwWxch arises from the jHidic in cases where this vessel appears to arise from the liypogastric 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 tlie ischial tu])erosity and pass oblicjuely forward and medially across the ischio-rectal ff)ssa, anil in some cases it passes at first directly across towards the anus and then bends forward to reach the bulb. The dorsal arterv of the j)enis or clitoris occasionally unites with its fellow of the opposite side to form a single metlian artery, or the two arteries of o])i)osile 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 external iliac, and with its fellow of the opposite side, and it is through these connections that the collateral circulation 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 external iliac are through the sciatic with branches of the profunda femoris, through the ilio-lumbar and gluteal with the external and internal circumflex 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 j, 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. — Anteriorh\ the artery is covered by peritoneum and is enclosed, together with the vein, in a moderately dense sheath derived 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 ileum 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 nerve and by the deep epigastric vein. Some lymph-nodes are also found resting upon its anterior surface. Posteriorly, it rests upon the iliac fascia, which separates it from the psoas muscle ; viedialiy, it is crossed near its lower end by the \'as 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. Latcralh', it is in relation to the genito-crural nerve. Branches. — In addition to some small twigs to the psoas muscle and to the neighboring lymphatic glands, the external iliac gives origin to (i) the deep epigastric and r 2 ) the deep circumflex 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 necessary to reach in a direct THE EXTERNAL ILIAC ARTERY. 819 line from the common iliac to beneath Pqupart'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 814), 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 the 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 above 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. Ligatio7i 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 j 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 circumflex 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 circulation is carried on from above the ligature by {a) the lumbar; {b) the obturator; {c) the sciatic; {d) the gluteal; {e) the internal pudic; and (/) the internal mammary and lower intercostals anastomosing respectively with (a) the deep circumflex itac; {b) the internal circumflex; (c) the perforating (profunda); {d) the external circumflex; (^ ) the external pudic (femoral); and (/) the deep epigastric from below. 820 HUMAN ANATOMY. I. The Deep Epigastric Artery. — The deep epigastric artery (a. cpi^astrica inferior) (Fig. 72S) arises from the anterior surface of the 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 abilominal ring, being crossed in this situation by the vas deferens in the male and the rouiul ligament oi the uterus in the female. It then curves upward and medially along the metlial border of the internal abdominal ring and ascends along the outer bonier of Hesselbach's triangle (page 526), of which it forms the lateral boundary. Throughout this jjortion 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, where it terminates by anastomosing with the superior epigastric branch of the internal mammary artery. Branches. — 'l"liroii.u:liout its course the deep eiiig:astric artery gives oflF a number of branches. (a) 'Ilie cremasteric branch (a. sperm.-itica externa in tlie male, a. Ii){amenti terelis in the female) is given off a sliort distance beyond the origin of the deep epigastric and accompanies Fig. 728. Anterior su|icrior spine of ilium Deep circumflex iliac .irtery Deep epigastric artery Rectus abdominis, turned downward with part of alv dominal wall External iliac arterj Kxtemal ili^c vein I'pper part of left liro.iil lilfament ivissini; over ex- ternal iliac artery as tlie in- AiDdibulo-[telvic ligament Common iliac artery Common iliac \ i i Edge of ovary Round ligament of uterus^ r.il nag i.jiiubernat's ligament ( tbturator nerve Tuhic branch of obturator ( 'bliterated hyijo- gastric artery t'rachus \esical branch of obturator Cut edge of broad ligament Obturator vein Portion ot left half pelvis of female subject viewed from above and right side, showing obturator artery 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 suj^er- ficial perineal arters-. id) 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 artery and the pubic branch of the obturator that the latter vessel comes to arise so frequendy 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 arter>- and supply the muscles of the abdominal walls. They anastomose with branches of the lower intercostal and lumbar arteries. {d ) 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 external iliac higher up than usual, — as high, indeed, as a point 6 cm. (2^ in.) above Poupart's ligament. In such cases it passes downward and forward upon the anterior surface of the external iliac to reach the abdominal wall. It may also arise below its usual position, — that is to say, from the common 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 814), 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 ihum, 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 vaginae 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). [d] 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 off 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 circumflex 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 afforded 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 circumflex 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 flexed upon the pelvis and rotated out^vard. 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 circunillex iliac Rectus femoris, stump Iliacus AscendinR branch of external circumflex Deep femoral arter>' External circumflex artery Transverse brxnch of external circumflex Descending branch of external circumflex Rectus femoris, cut Superficial epigastric ! emoral artery >oep external pudic •Superficial ex- ternal pudic Femoral vein -^Pcctineus -Adductor longus Aponeurotic roof of Hunter s canal Adductor niagnus Vastus exteriius Anastoniofica magna — superficial branch Inner hamstring muscles Vastus ititernus ^^^.^^•From anastomotica magna Tendon of sartorius Anastomotica magna Arteries ot front of thigh ; superficial dissection. THE FEMORAL ARTERY. 823 Relations. — In its uppermost part, for a distance of about 3 cm. fi}^ in.), the femoral artery, together with the accompanying vein, is enclosed within a sheath formed by a prolongation of the transversalis and iliac fasciae below Poupart's liga- ment. This femoral 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 t\\Q 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), while in its .lower half it is contained within a space known as Hiinter' s canal, 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 above with the femoral vein and below with the adductor longus; laterally, 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 circumflex iliac, (3) the superficial external pudic, (4) the deep external pudic, (5) th.e prof u?ida femot is, and (6) rmiscular branches. In Hunter's canal it gives off additional muscular branches and, just before perforating the adductor muscle, (7) the anastomotica mag7ia. 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 this vessel arises. The portion of the artery above the bifurcation is then termed the common femoral, while its continuation through Scarpa's triangle and Hunter's canal is known as the superficial femoral. Variations.^A comparative study of the arteries of the thigh reveals the fact that the exist- ence of a well-developed femoral arten,- 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, extending throughout the whole length of its flexor surface and becoming continuous below with the popliteal artery, the femoral artery 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 nerve. _ 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, correlatiyely 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. tierii isi/iiadiii which loses, as a rule, its continuily with tin- poiihteal. That artery now appears! tube the eontiiuiatioii ol tlu- saphenous (femoral), since there occurs a (ie}:;enerati()n of the] saplienous helow the point wliere tlie anastoniosinj; l)ranch is <^'\\\n ofY. Ihese ciiauKes are shown thajjranunatically in I■"i^^ 74S, (page S49) from wiiicli it will he seen that the femoral artery! below the orij,'in of the profunda is the upper i)art of the original a. saphena, the continuation of] that vessel down the crus being represented only by the superficial branch of the a/ias/omolica\ The principal variations which are shown by the femoral artery are associated with these changes which it has passed through in its development, and rejjresent a cessation of the devel-j opment at one stage or other of its progress. Thus, as already pointed out (page .S15), th« comts ucrvi ischiadici may remain the principal vessel of the thigh, the femoral terminating ic the profunda femoris. Or the development may proceed to the formation of the a. saphenaJ which may arise either immediately above the profunda femoris, in such case the superficiw fenn)ral 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 fullv develojjed, is continued onward wilii the long sajihenous nerve between the adductor nwignus and the vastus medialis, and below the knee-joint perforates the crural fascia and is continued suiH-rticially tlown the inner side of the crus, accompanying the long saphenous nerv( and vein to the internal malleolus, where it makes connections with the posterior tibial arterj and may .sometimes persist as a branch of that ves.sel. In addition to these anomalies, the femoral artery frequently gives off branches which nor-J mally arise from other vessels. Thus it may give rise to the deep epigastric or the deep cir-^ cumlle.x iliac, normally branches of the e.xternal iliac, or to the external or internal circumflex^ normally branches of the profunda femoris. It has also been ol)served to give origin to the ilio- lumbar artery. Practical Considerations. — The femoral artery is more often woiincled thar the brachial on account of the position of its u])per half — in Scarpa's triangle — or the anterior siniace of the limb, and of its relatixely more intimate rehitujn to thel bone at its lower end. In the latter region it has been opened l)y spicules of necrotici bone. Next to the popliteal, it is more frequently the subject of aneurism than anyj other external arterial trunk. On account of the close relation of the lymphatic! 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 vessel than with any other. Compression of the femoral artery has yielded \ery satisfactory results in the treatment of popliteal aneurism. The pressure is best applied in a direction backwardl and outward just below the inferior edge of Pou{)art's ligament where the vessel can be flattened against the brim of the pelvis — the upper margin of the acetabuhmi — just outside the ilio-pectineal eminence, only a \ery thin portion of the ilio-j)soas muscle interv^ening. A litde lower, a more fleshy i)ortion 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 brevis muscles, and more force will be required to obliterate its lumen. At the apex 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. Kxtreme flexion of the thigh upon the trunk will occlude the femoral, a'nd has been used successfully in the cure of popliteal aneurism and for the temporary arrest of hemorrhage. Liiration of the \cssel may be done : i. Between Poupart's ligainent and the origin of the profunda— the common femoral (vide supra). 2. At the apex of Scarpa's triangle. 3. In Hunter's canal. I. The common femoral is rarely ligated except 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 proximity to so large a trunk, (b) The presence of a number of smaller branches— the deep epigastric and deep circumflex iliac coming off immediately abo\'e Poupart's ligament, the superficial epigastric, circumflex iliac, and external pudic, the deep external pudic. and occasionally one of the circumflex arteries ('especially the internal), THE FEMORAL ARTERY. 825 \nterior crural ner\e Crural branch of — g-enito-crural nerve — Femoral arterj' Femoral vein arising from the femoral. This circumstance Hkewise interferes with the firmness and 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 mamtain a sufficient vascular current. The incision should be begun on the abdomen a little abo\'e Poupart's ligament, midway between the anterior superior spine and the symphysis pubis, and extend 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 (^) the internal pudic (from the internal iliac); {b') the gluteal and sciatic (from the same vessel); (r) the deep cir- cumflex iliac, from the Fig. 730. external iliac ; (^d) the ob- turator, and ( obliquely l^ehind the femoral artery and vein, and on arrix ing at the upper border of tlu adductor longus, passes behind that vessel and is continued downward between it . and the adductor magnus, rapidly diminishing in .size. Finally it ])erforates 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, haxing in front of it only the fasciiE 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. — Tlie profunda femoris gives oriijin to the followiiiiij branches : ( i ) the external circiimfex, (2) \h(t iiiiertia/ eircionjiex, (3) the three /•r/'/b/v?//,'/;' arteries. The terminal por- tion of the profunda, alter it lias pierced the adductor magnus, is sometinus spokt-n of as tin- fourth perforatiii!^ artery. {a) The external circumflex artery (a. circumflcxa femoris lateralis) is the largest of the branches of the iirt)funda and arises from it a short distance l)eyond its origin. It is directed horizontally outward across .Scarpa's triangle, resting upon the ilio-psoas nniscle and passing between the superficial and deep branches of the anterior crural nerve. It then passes beneath the .sartorius and rectus nuiscles and terminates by dividing into an ascending, a transverse, and a descending branch. The ascending branch passes upward and outward to heneatii the tensor vaginaj 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 directl\- outward to below the greater trochanter, passing between the rectus and the crureus nuiscles 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 descendinis: branch runs downward beneath the rectus muscle, along with the nerxe, to the vastus lateralis, and usually extends to the neighborlicjod 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 gives 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 ol)turator externus and, finally, upon the anterior surface- of the quadratus femoris, where it divides into its terminal branches. (aa) The ascending branch (ramus ascendcns) passes upward towards the digital fossa of the femur, sending i)ranches 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 tin lower border of the (]uadratus femoris to terminate in the upper portion of the hamstring mus- cles. This branch anastomoses with the sciatic, external cirrumflex. and first perforating ve.s- sels to form the cnicial 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. (r) 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 circumflex iliac Iliacus muscle Femoral artery Tendon of rectus Tensor vaginse femoris Ascending branch of external circumflex Profunda femoris External circumflex Transverse branches of external circumflex Descending branch of external circumflex Vastus externus First perforating artery Adductor brevis Second perforating artery Vastus internus Third perforating artery Adductor longus Fourth perforating artery Deep branch of anastomotica magna ,. - Superficial epigastric artery Psoas muscle Pectineus Spermatic cord - Obturator arterj- wi Mk " Adductor longus ^§^ Adductor brevis - Corpus spongiosum of penis ~ Obturator externus Internal circumflex arterj' Articular branch of internal circumflex ^Adductor magnus Gracilis "^Adductor magnus Femoral arterj* Semimembranosus Superficial branch of anastomotica magna Deep femoral artery and its branches. magnus, and then divides into an ascending and a descending brancn, the latter of which anasto- moses with the ascending branch of the second perforating, while the former assists m the tor- mation of the crucial anastomosis. 830 HUMAN ANATOMY. (db) The second or middle perforating artery (a. perforans secunda ) arises a little below the first and, alter pieniiiK tli<-- adductor bre\ is and tlie adductor magnus, divides into an ascendinj and a descending branch which anastomose respectively with the descending branch of the fir and tile ascending brancii of the third iierforating. A nutrient artery to the femur is usuallj given otT from this vessel, although frequently it comes from the third i)erforating. (ff) The third or inferior perforating artery ^a perforans tenia) arises usually on a lev< with the lower border of the adductor brevis. It pierces the adductt)r niagnus and terminate like the other perforating arteries, by dividing into an ascending and a descending branch. ThI ascending branch anastomoses with the descenchng branch of the second perft)rating, while thd descending one anastomoses with branches from the terminal portion of the profunda. Th4 nutrient artery to the femur is frequently given off by this branch. Variations. — The variations of the profunda and its branches are somewhat numerous, an^ to a very considerable e.xtent are largely associated with one another. In other words, ther may be inore or less dissociation of the various vessels of the profunda complex, one or oth< of them having an independent origin from the femoral, and, indeed, this process may occur such an extent that a profunda femoris as a definite vessel can hardly be said to exist. The point of origin of the profunda from the femoral is stated to be usually about 4 en distant from I'oujjart's ligament, but the figure must be taken as a general a\erage from whici there may be w ide departures. Thus, in 430 limbs (Juain foimd that the distance from Foupart'j ligament of tlie origin of the profunda was between 2.5 and 5.1 cm. in 68 per cent., and this numlx-r it was between 2.5 and 3 S cm. in 42.6 per cent. It was distant less than 2.5 cm. 24.6 per cent, of the limbs and more than 5.1 cm. in only 7.4 per cent. Quain's figures are 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 cm. below Poupart's ligament 183 cases. 3.8-5. 1 cm. 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. 116 cm. below Poupart's ligament i case. Essentially similar results have been obtained by Srb and other observers, and it seer evident from the statistics that the origin of the profunda is more apt to be above than below th(j point taken as the average. One or other of the circumflex arteries may arise independently from the femoral, this conJ 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 ve.ssel may be either above or below that of the profunda. W'hen 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 hv somev\hat 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 perforating 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 arising 9.7 cm. below Poupart's ligament and giving off only the inferior perforating. The internal circumflex may be ver>- miich reduced in size or even absent, its territory being supplied by branches from the obturator arterv'. Occasionally, although rarely, one or other of the perforating branches arises directly from the femoral, and a similar origin has also been observed for the descending branch of the external circumflex. 6. The Muscular Branches. — The muscular branches Trami musculares) of the femoral artery are rather numerous and are distributed to all the muscles upon the front of the thiy;h. They are variable in number and position and do not call for any special description. Fig. 734. Superficial ^ ^—^ circumflex iliac — V\j ^ }^- Superficial epigastric External circumflex Middle perforatiiiK Inferior perforating (profunaa femoris) Diagram showing almost complete dissociation of profunda femoris. {Ruge). r Internal circumflex Superior perforating THE POPLITEAL ARTERY. 831 7. The Anastomotica Magna. — The anastomotica magna (a. genu suprema) (Fig. 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, {d) The deep branch (ramus musculo-articularis) enters the substance of the vastus internus and passes downward to take part in the formation of the circumpatellar plexus, also sending branches to the capsule of the knee-joint. Variations.— The anastomotica magna 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 849) ; 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 ihac 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 vessel 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 by 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 outward, but it soon becomes almost vertical, corresponding practically with the long axis of the popliteal space. Relations. — Ajiteriorly^ the popliteal artery is in relation to the posterior sur- face of the lower part of the femur, from which it is separated, however, 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 covered 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 nerve, 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 above 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 nerve, and the inner head of the gastrocnemius, and externally with the internal popliteal nerve, 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) muscular, (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. reater sciatic nerv Practical Considerations. — Tlie popliteal artery is rarely wounded because of its protected pi^sition on the posterior aspect of the limb antl in the hollow of the- ham. Its upper portion is overlapped by the outer l)order of the semimembranosus muscle, anil its lower portion by the inner head of the gastrocnemius ; the inter- mediate portion, co\ered only by skin, fascia, and areolo-latty tissue, is very 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. ;is 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 i)roximity — in the case of the popliteal — of the iiranches on which the chief anastomotic supply dejjcnds ; and because of the unyielding character of the walls of the space in which the effused blood is confined. . huio/sm of the j)opliteal artery 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 movement bends the artery at such an acute angle that the flow of blood through it is arrested and the pressure above this l"io. 735. 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, (d) The lack of muscular sup- port which the artery — sur- rounded by loose cellular tissue — receives also favors the development of aneur- ism, (c) The artery is said to be unusually liable to ath- eromatous degeneration. {d) It divides a short dis- tance below into two \'essels, thus increasing the blood-pressure above the bifurcation. (- of the flexor surface of the le^ and the direct continuation of the popliteal, developnientally the posterior til)ial is a secondary vessel, the oriji^inal main vessel bein^ the peroneal. Tiie history of the posterior tiliial seems to have been somewliat as follows. Tlie sapiienous artery, whose origin has been mentioned in connection with the variations of the femoral arter>' (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 arterv 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 S49), 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 obser\ed, as a branch of the tibial, passing upward upon the leg in company \\ ith the long saphenous ner\-e. Other variations of the posterior tibial wliich have been observed, however, cannot appar- ently be exjilained as resulting from modifications of the normal course of development, but are rather to h)e regarded as progressive variations due to the enlargement of v\ hat 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 artery. 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. Except 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 infrequently the region at which an env bolus carried down from the popliteal is arrested, and such a clot may 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 abo\e — '■ gangrene almost certainly follows. Compression of the posterior tibial is scarcely possible above 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. Ligatioyi of the posterior tibial mav be done at any part of its course, but in its upper third is an operation of some difificulty. THE POSTERIOR TIBIAL ARTERY. 837 Gastrocnemius, outer head Venae comites Flexor longus digitorum Post, tibial artery Post, tibial nerve Cut edge of soleus muscle Tendon of plantaris I. The artery is best approached from the inner side of the leg. The leg being flexed, the limb 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 "^' ^•^^' 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 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 \'essel 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 \-ein and nerve, the superficial fascia and the deep fascia (with its fibres running trans\-ersely) 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. Tendon of Rex. long, digitorum Tendon of tibialis posticus Post, tibial artery Post, tibial nerve Tendo Achillis Flex. long, hallucis Vence comites Dissection of inner side of right ankle, showing relation of tendons, vessels and nerves as they pass between calcanium and internal malleolus. 838 HUMAiN ANATOMY. clMcled in the line of the skin vvcjund, the inner margin of the soleus displaced outward, and the vessel, with its venit- coniites, 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 t(j the inner side, and the nerve external. 3. To ligate the \essel 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 nerve and flexor longus j)ollicis tendon on the outside. The sheaths of these tendons should not be opened. The collateral circulation is carried on from above the ligature by («r) the anterior and posterior peroneal arteries and their muscular and connnunicating branches; {b^ the external malleolar branch of the anterior tibial; {c) the internal malleolar (anterior tibial); (af) the dorsalis pedis. Anastomosing respectively with (a) the muscular branches and the communicating branch of the posterior tibial ; (3) the external plantar branch of the posterior tibial ; {/) the internal malle- olar (posterior tibial) ; and (a') the internal and external plantars: 1. The Nutrient Artery. — The nutrient artery to the tibia (a. nutritia tibiae) may arise from the posterior tibial, either alx)ve or below the origin of the peroneal artery, or sometimes it arises from that \essel. It pierces the tibialis posticus and enters the nutrient foramen on the posterior surface of the tibia, sending off, before it does so, some small muscular branches. 2. The Peroneal Artery. — The peroneal artery (a. peronaea) (Fig. 736) is by far the largest of the collateral branches of the posterior tibial. It arises about 2.5 cm. below the lower border of the popliteus muscle and is at first directed outward and downward towards the fibula, and then passes vertically downward along the inner surface of that bone to a point about 2.5 cm. above the ankle-joint, where it termi- nates by dividing into the anterior and posterior peroneal arteries. Relations. — In the upper part of its course it is covered posteriorly by the soleus, lying between that muscle and the tibialis posticus. Lower down it passes beneath the flexor longvis hallucis or else tra\erses the substance of that muscle, and just before its termination it emerges from beneath the muscle and becomes super- ficial. It is accompanied by two venee comites. Branches. — In addition to numerous muscular branches to the neighboring muscles and cutaneous branches to the integument of the outer border of the cms, the peroneal artery gives off the following vessels : (fl) The nutrient artery to the fibula (a. mitritine fil)ulae ) enters the nutrient foramen of that bone. {b^ The communicating branch ( ramus comrminicans) passes inward o\irr the lower end of the tibia and beneath the tendo Achillis, a short distance above the terminal bifurcation of the peroneal. It inosculates with the communicating branch of the posterior tibial. (r) The anterior peroneal artery (ramus perforans) is one of the terminal branches of the peroneal. It passes directly forward and, jierfcjrating the interosseous membrane, bends down- ward over the ankle-joint to the dorsum of the foot. It sends branches to the ankle-joint and to the inferior tibio-fibular articulation, as well as to the peroneus tertius muscle, beneath which it passes, and terminates by anastomosing with the tarsal and metatarsal branches of the dorsalis pedis and with the e.xtemal plantar artery upon the side of the foot. [d) The posterior peroneal artery is the other terminal branch of the peroneal, of which it is the direct continuation. It gives origin to the external calcaneal branch which ramifies over the outer surface of the os calcis and terminates by anastomosing w ith the internal cal- caneal branch of the posterior tibial artery and with the tarsal and metatarsal branches of the dorsalis pedis. Variations. — The peroneal artery is exceedingly subject to variation. It is rarely abf.ent, but not infrequently it terminates over the outer malleolus, its lower portion being given ofT from a branch which passes across from the posterior tibial and represents the enlarged anastomosis THE POSTERIOR TIBIAL ARTERY. 839 of the posterior tibial and peroneal communicating branches. Conversely, when the lower por- tion of the posterior tibial is wanting, it may be replaced by the peroneal, which then gives rise to the plantar arteries. Occasionally the peroneal is larger than usual, and may give origin to the anterior tibial artery, and it may give off the nutrient artery for the tibia. The anterior peroneal artery is sometimes absent, but more frequently it is larger than usual and inosculates with the anterior tibial. Occasionally the lower portion of this latter ves- sel is wanting, and the anterior peroneal may then take its place, being continued downward upon the dorsum of the foot as the dorsalis pedis and giving off the branches which normally arise from that vessel. 3. The Communicating Artery. — The communicating artery (r. communicans) (Fig. 736) extends transversely outward across the posterior surface of the tibia, beneath the tendon of the flexor longus hallucis and the ^^'^- 739- tendo Achillis, and an- astomoses with the communicating branch of the peroneal. 4. The Internal Malleolar Artery. — The internal malleolar artery (a. malleolaris posterior medialis) (Fig. 740) passes directly in- ward, beneath the ten- dons of the fiexor longus digitorum and tibialis posticus, to ramify over the internal surface of the inner malleolus, anastomos- ing with the internal malleolar branch of the anterior tibial artery. 5. The Internal Calcaneal Artery. — The internal calcaneal artery (ramus calcaaei medialis) (Fig. 736) arises from the lower part of the posterior tibial, just before it divides into the two plantar vessels. It is frequently represented by several branches which descend along the inner side of the Internal calcanean of posterior tibial Internal annular ligament, cut edge Inner malleolus Abductor hallucis Internal plantar Flexor longus hallucis tendon Princeps hallucis. From external calcanean Internal calcaneal oi external plantar Plantar fascia, cut Flexor brevis digitorum Abductor minimi digit! External plantar artery Interosseous arteries dividing into digital branches Arteries of plantar surface of light foot, superficial dissection. tuberosity of the os calcis, supplying the neighboring parts of the integument and anastomosing with branches of the internal malleolar and posterior peroneal arteries. 6. The Internal Plantar Artery.— The internal plantar artery (a. plantaris medialis) (Fig. 740) is the smaller of the two terminal branches of the posterior tibial. It arises in the groove between the internal malleolus and the os calcis and is directed at first downward and forward, under cover of the abductor hallucis, and then forward along the inner border of the foot, between the abductor hallucis and the flexor brevis digitorum, terminating opposite the head of the first metatarsal bone by anastomosing with one or other of the two branches distributed to the plantar surface of the great toe. Branches.— In its course it gives off muscular branches to the abductor hallucis and the flexor brevis digitorum, cutaneous branches to the integument over the inner border of the foot, and articular branches to the neighboring tarsal joints. In addition, it usually gives off near its % 840 HUMAN ANATOMY. ori}j;in a larger brancli, llic amis(o>no/ic braticli, w liicli passes beneath tlie al)ductor lialliicis U) gain the upper border of tliat muscle, along which it courses forward, giving ofT numerous branches to the abductor and the adjacent integument and anastomosing with the tarsal and metatarsal branches of tlie dorsalis pedis. .More distally it gives off from its outer surface a varying number of ^\ii\v\t^x suprrficial digilal branches, which pass obliquely forward and out- ward across the .sole of the foot to anastomose with one or more of the plantar interosseous branches from the plantar arch. Variations. — Occasionally the superficial digital branches of the internal plantar arise from a common stem which anastomoses with a branch from the e.xternal jilantar to form a superfi- cial plantar arch beneath the superficial fascia. This is the ecjuivalent of the superficial palmar arch of the hand. 7. The External Plantar Artery. — The e.xternal plantar artery (a. plantaris lateralis) (Fig. 740) is the larger of the terminal branches of the posterior tibial. It passes forward antl outward across the sole of the foot, at first between the fle.\f)r bre\ is digitoruni and the fle.xor accessorius, and then in the interval between the fle.xor brevis dit»^itoruni and the abductor minimi dii^iti. Opposite the base of the fifth meta- tarsal bone it turns somewhat aliruptly inward and again crosses the sole of the foot. forming the plantar arch {arcus plantaris), which terminates at the pro.ximal end of the first intermetatarsal space by uniting with the communicating branch from the dorsalis pedis. Relations. — In the first part of its course the e.xternal ])lantar lies beneath the abductor hallucis and the fle.xor brevis digitorum, but as it approaches the fifth meta- tarsal it becomes more superficial, being covered only by the skin and the superficial and plantar fasciae. It rests upon the flexor accessorius and the fle.xor brevis minimi digiti, and is accompanied by the e.xternal i:)lantar nerve. The plantar arch, on the contrary, occupies a much deeper position. It passes beneath the tendons of the fle.xor longus digitorum*, the lumbricales, and the oblique portion of the adductor hallucis, resting upon the pro.ximal ends of the second, third, and fourth metatarsals and upon the interosseous muscles which occur between thosi bones. Branches. — The external plantar arter\' gives rise to {a) numerous muscular branches which supply the various muscles of the plantar surface of the foot, and in its first part to {b) Cutaneous branches which supj^ly the skin over the sole and outer border of the foot, some of them forming anastomoses with branches of the tarsal and metatarsal branches of tht dorsalis pedis. In addition, there are given ofT from the first portion of the arterj- — (r) Calcaneal branches, one or more in number, which arise near the commencement of the external plantar and ramify over the inner surface of the os calcis, anastomosing with the internal calcaneal branches of the posterior tibial. From the plantar arch a number of vessels are given of?. (rf) The articulating branches are given off from the posterior or concave surface of the arch and supply the tarsal articulations. ((f) The posterior perforating branches, four in number, arise either from the plantar arch or from the plantar digital branches of the fourth intermetatarsal space. They ascend in th( intermetarsal spaces between the heads of the dorsal interosseous muscles and terminate by inos- culating with the first, second, and third dorsal interosseous arteries. The branch which pa.sses through the first intermetatarsal space is much larger than the rest and inosculates with the dor- salis pedis artepi- ; it is sometimes regarded as the terminal branch of that vessel. (f) The plantar interosseous arteries faa. metatarsae plantares) are five in number, and are usually numbered in succession frrim the outer side of the foot inward,— that is to say, in the opposite direction to the intermetatarsal spaces in which they lie. The first arises just where the external plantar artery is bending inward to form the plantar arch and passes forward along the inner border of the abductor minimi digiti, later crossing over the flexor brevis minimi digiti to reach the outer surface of the little toe, along which it runs. The second, third, and fourth plantar interosseous arteries arise in succession from the plantar arch as it crosses the fourth, third, and second intermetatarsal spaces, and pass forward, resting upon the interosseous muscles and covered by the tendons of the flexor longus digitorum and the lumbricales, and more distally by the transverse adductor of the great toe. Just before reaching the line of the metatarso-phalangeal articulations each artery gives off an anterior per- foratins!; branch, which passes dorsally to communicate with the corresponding dorsal interos- seous arter>-, and then divides into two plantar digital branches, which pass onward upon the adjacent sides of neighboring digits. \ THE POSTERIOR TIBIAL ARTERY. 841 The y?/?/^ 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 ofif 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 PiQ - .q the dorsalis pedis ar- Tendo Acwiiis tery, under the name of the a. princeps halliicis. 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. Posterior tibi: Internal malleolar Internal lateral ligament Internal plantar Flexor longus hallucis tendon Adductor obliquus, cut Princeps hallucis (V. interosseous) dividing into digital branches Internal calcanean Abductor hallucis Internal calcanean of e.\t. External [plantar plantar - Flexor brevis digitorum Flexor accessorius Superficial fascia Abductor minimi digiti II. and III. plantar interossei and flexor brevis minimi digiti I.-IV. interosseous arteries dividing into digital branches 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, owing 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 established through the anastomoses which its branches form with those of the peroneal and tho'se of the anterior tibial. The anasto- moses with the peroneal are between the communicating branches of the two arteries, between the anterior peroneal and the external plantar, and between the posterior peroneal and the internal calcaneal. With the anterior tibial artery there is communication through the malleolar branches of the two arteries, through the anastomotic branch of the external 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 interossese. « Arteries of plantar surface of riglit foot ; deeper dissection. 842 HUMAN ANATOMY. THE ANTERIOR TIBIAL ARTERY. The anterior tibial artery (a. tibialis anterior) ( Kigs. 742, 743) is the other terminal branch of the pojiliteal. It begins at the lower border of the popliteus muscle, and is at first directed forw ard, 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, where it becomes the dorsalis pedis artery. Its course may be represented by a line drawn from the head of the fibula to a point half-way between the two malleoli. Relations. — In itsctjurse down the leg the anterior tibial artery yki'^X.'^ posttrior/y 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 se{)arates that muscle from the ex- tensor longus digitorum and the extensor proprius hallucis. Lower, however, 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 ner\e lies to the outer side of the artery in its upper and lower thirds ; ia the middle third of the leg it is usually in front of the vessel. Variations. — Tlie anterior tibial artery, as it occurs in man, appears to be the result of a union of two originally distinct vessels, both of which arise from the primitive peroneal artery and pass to the front of the leg. The up- FiG. 741. Peroneus brevis Exi. longus hallucis Ext. longus digilorum Tibialis anticus muscle Tibia Ant. tibial nenc Ant. tibial artery Companion vein permost of these forms the greater portion of the artery, while the lower one, which is represented by the anterior peroneal artery, forms only the lower part of the anterior tibial and its continuation upon the dorsum of the foot, the donsalis pedis. In case of failure 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 bting the continuation of the an- 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 which gives off the ]-)osterior and anterior recurrent branches as well as branches to the popliteus musclei the front of of the leg, in such ca.ses, being sometimes supplied by an in- dependent perforating branch from the pf)sterior 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 o^a fragment in fracture of that bone. It is \ Dissection of middle third of right leg, showing relations of anterior tibial vessels and nerves; e.xtensor muscles have been drawn aside. THE ANTERIOR TIBIAL ARTERY 843 Fig. 74.2. 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 the middle of the anteri- 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 Superior external articular External condyle Inferior external articular Tendon of biceps Anterior tibial recurrent- Peroneus longu: Extensor longus digitorum Extensor proprius hall Peroneus brevis Peroneus longus tendon Anterior peroneal artery External malleolar artery, External calcanean or posterior peroneal artery External malleolus Tarsal artery Extensor brevis digitorum Peroneus brevis tendon Metatarsal artery Posterior perforating ^orsal interosseous arteries Branch of superior internal articular Tendo patellae nternal articular artery Tibialis anticus Interosseous membrane Anterior tibial artery Tibialis anticus Internal malleolar artery Inner malleolus 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 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. tendon of tensor brevis digitorum pedis perforating arteri.^s Tendons of extensor longTis digitorum Arteries of front of leg and dorsum of foot. 844 HUMAN ANATOMY. 2. At tlic middle of the limb 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 extensor proprius pollicis and the tibialis anticus. 3. At the lower third an incision on the same line will expose the \essel lying usually in the innermost of the two mterstices 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 nerve external. The collateral cifailation is carried on from above the ligature by («) the pero- neals ; and {b) 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 th.e many small anastomotic vessels piercing the interosseous membrane and derived from the two tibials. Branches. — In addition to numerous viuscular 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 (.xtcrnal inferior articular branch of the poj^liteal. 2. The posterior recurrent tibial artery (a. rccurrens 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 supj)lies, and terminates by anastomosing with the external and internal . inferior articular branches of the popliteal. 3. The anterior recurrent tibial artery (a. recurrens 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 gi\es 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 (jf 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 anas«^'.nioses with branches from tlie 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 oy 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 Tendon of tibialis anticus Branch of musculo- cutaneous nerve Musculo- cutaneous nerve THE DORSAL ARTERY OF THE FOOT. The dorsal artery of the foot (a. dorsalis pedis) (Fig. 743) is the continuation of the anterior tibial beyond the ankle-joint. It extends to the proximal 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 extensor brevis digitorum which passes to the great toe. It rests successively upon the anterior ligament of ^'*^- 743- 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- ternally it is separated from the innermost ten- don of the extensor lon- gus digitorum and from the extensor 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 exten- sor hallucis proprius. Branches. — In addition to numerous cii- taneous brayiches to the skin of the dorsum of the foot and miisc7clar branches to the extensor brevis digitorum, the dorsalis pedis gives rise to the following vessels. I. The internal tarsal branches (aa. ■ tarseae mediales ) are one Ant. tibial arter\ Ant tibial nerve Tendon of extensor longus hallucis — Dorsalis pedis arterj — Peroneus brevis — Peroneus longus Dissection showing relations of vessels and nerves in vicinity of left ankle ; portion of anterior annular ligament still in place. 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 longus and extensoi 846 HUMAN ANATOMY. brcvis di.y^itorum. It thus forms an arch upon the dorsal surface of the foot corres- ponding in ])osition with the plantar arch below. It anastomoses laterally with the e.xternal tarsal and with the external plantar, and opposite each of the intermetatarsal spaces which it passes — the second, third and fourth — gives of? a dorsal interosse- ous artery (a. metatarsea dorsalis). E;\ch of these passes forward alon^ its intermetatarsal space, and, immediately beyond its ori_ii;^in, gives off a posterior pcrforatius: branch which communicates directly with the corresi)onding posterior perforating branch of tlie plantar arch. At the distal end of its intermetatarsal space each artery gives off an anterior pcrforatinfr branch -~- which unites with the similar branch of the corresponding plantar interosseous, and then divides into two dorsal diQ;ital branches ( aa. (linitalcs dorsalcs) 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 usually termed the a. dorsalis hallucis. Its course is exactly similar to that of each of the other dorsal interosseous arteries, e.xcept that, in addition to the anterior dorsal perforating and terminal dorsal digital branches, it gi^•es ofi", not far from its origin, a third digital branch which })asses forward along the outer surface of the great toe. The posterior communicating artery which should arise from this \essel is represented by the large branch by which the dorsalis pedis communicates with the plantar arch. Variations. — The orijiin of the dorsalis pedis from the peroneal by means of the anterior I peroneal branch has already been noted in connection with tlie variations of the anterior tibial | artery. Another orii^in which has been observed is from tlie external jilantar artL-ry, which sends upward through the astragalo-calcaneal canal a large branch u hich is continued distally upon the dorsum of tlie foot and gives off the tarsal and metatarsal branches. This \essel is represented in tlie adult by a small branch w hich arises from the external tarsal artery and pur- sues the course indicated to anastomose with the external plantar ; it appears to be much more highly developed in the embryo than in the adult ( Leboucq). Other variations in the dorsalis jjedis and its branches depend upon a correlation which exists between the development of the dorsal and plantar system of vessels. If, for example, 1. the plantar interosseie are well develojied, they will, through the anterior perforating branches, ' furnish the main blood-supply for the dorsal digital branches, and the dorsal interosseous ves- I- sels, as well as the metatarsal, may be much reduced. Or the plantar arch, through the pes- ;' 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 n'fet-work of small vessels over the dorsal surface of the tarsus. DE\'ELOPMENT OF THE ARTERIES. In the preceding pages some of the more important facts regarding the development of the arteries have been mentioned in connection with the anomalies in v\hose 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 undivided, the blood leaves it by a single vessel w hich passes forward along the mid-ventral line of the pharynx and divides to form two ventral longitudinal stems, from each of w^hich six lateral branchial vessels arise, the fifth vessel of each stem, counting from before backward, being quite rudimentary 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 trunk, 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 DEVELOPMENT OF THE ARTERIES. 847 Fig. 744. Diagrams illustrating primary arrangement (A) and second- ar>' modifications (B) in branchial arch vessels. TA, truncus arteriosus; /-F7, aortic bows; yA. DA, ventral and dorsal aortse ; A, aorta; AA, aortic arch; /, innominate artery; CC, CE, CI, common, external and internal carotids ; S, subclavian ; P, pulmonary artery ; da. ductus arteriosus. the ventral longitudinal stem divides in the frontal plane into two portions, one of which is con- nected with the sixth 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 fcetus 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 arrangement of branches from aorta (A) \ B, lateral branches to body-wall ; C, paired visceral, D, unpaired visceral branch ; E. peritoneum. 848 HUMAN ANATOMY. P'lc;. 746 tlien lose their original connections with the aorta, so that they seem in the futus to arise from the iliac vessels, and these latter, although primarily somatic in tiieir distribution, give off a number of visceral branches. Of the unpaired \ isceral liranches representatives are to be found in the thoracic region in t]ie u-sophageal and mediastinal vessels and m the abdomen ni the cttliac 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 lowest 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, however, several other longitudinal vessels e.xist, such, for instance, as the vertebrals, 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 dow nwardly directed branches of the lateral segmental \es- 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 le.ss ex- tent , the vertebrals are formed from branches of the lateral cervical 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, ^). 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 nerv'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 princii:)al artery of the forearm ( Fig. 747, B). A further stage is marked by the development of the ulnar artery 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 artery-, which, after traversing 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 arter>- 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 (/?) ; 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 normallv 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. 748, A). The ex- ternal iliac at this stage is a relatively slender vessel which extends 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 si.\ weeks, showing origin of internal nianiniary'(i>«) and epigastric arteries (jf", superficial, rf?, deep) ; a, aorta ; f, vertebral ; ci, common iliac, continunig as large hypogastric (A) ; e.xtcmal iliac, giving oflf deep epigastric and femoral, is still small. ,■ 5. (Mall.) 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. (n n Diagrams illustrating development of arteries of upper limb ; b, brachial ; /.interosseous ; d. digital ; ?«, median; «, ulnar; sb, superficial brachial ; r, radial. Fig. 74S. -saph ■pop -pt mm d d d illustrating development of arteries of lower limb ; s. sciatic ; d digital ; /, feinoral ; , saphenous ; pop, popliteal ; per, peroneal ; pt, at, posterior and anterior tibial. cle and anastomoses with the sciatic artery just above the upper end of the popliteal space ( C). whereupon the portion of the sciatic artery immediately above tne anastomosis degenerates and .54 850 HUMAN ANATOMY. the vessel becoincs reduced to the skndcr a. conies iiervi iscliiadici of the adult. Its lower por- tions, which become tlie popliteal and peroneal arteries, now seem lo be tlie continuation of the femoral (i.e., the saphenous ). From the lower jiart 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 tin saphenous then disappearing except in so far as it is represented by one of tlie branches of the anastomotica magna. The anterior tibial is a late formation resulting from tiie 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 ]>eroneal degenerating after the anastomosis, except in so iar as it persists as the anterior ixroiieal artery ( /)). 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 differences, both of structure (pap:e 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 withstantling an extension to at least 50 per cent, more than their original length without losing their elasticity — a property which explains the more direct course taken by the veins-as compared with the arteries in mobile portions of the body (c.j^., 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, for 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 \eins, however, is the occurrence in them of semilunar valves, arranged usually in pairs, with their caAities directed towards the heart. These \alves resemble in their general form the semilunar valves of the systemic and ])ulmonary aort^e, 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 towards the capillaries. V^alves 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 vense cavae, the pulmonary and the ])ortal \cins. In general they are more numerous in the veins of the limbs than in those of the trunk and in the deep than in the superficial \essels. Their number in any vessel in which they normally occur is subject to con- siderable Aariation 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 tondition, derived from one in which the valves were much more numerous and were situated at regular inter\als along the vessels. In favor of this view it has been found ( Bardeleben) that in certain veins the valves in the adult are separated by 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 individual in which the vein occurs. Thus, in a man measuring 160 mm. in height, the valves of the right long saphenous vein were separated by intervals 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 81 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 maxillary, 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, ophthalmic, periosteal, pulmonary, bronchial, portal, renal, uterine, ovarian, and innominate ( brachio-cephalic ) veins, and the superior and inferior venae 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 subclavian. 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 cavse 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 m 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 mefih- 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 contamed within «5- IRMAN ANATOMY. thf 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 trabecuke of fibrous tissue. These are especially well developetl 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 antl de\eloi)ed 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 t)f 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 in\ade them, pushing before them the attenuated floors of the lakes. Classification of the Veins. — Theoretically a description of the veins should start with the pciipheral \ essels and proceed towards the great trunks, following the course of the blood. Such a method would prove, howexer, 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 af?erents topographically, according to the areas which they drain. From the embryological stand-point, there are primarily four great systems of \-eins : ( i ) the cardinal svstein, represented by the \ena ca\a superior and its tributa- ries : (2) the inferior cava! system; (3) \\\e po7'taI SYstc7?i ; and (4) i\\Q p7(h)wnarv 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 (venae pulmonales) (Figs. 749, 750) are four in number, two ]:)assing 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 independendy into the left auricle, forming what is then termed the middle pulni07iary vein. Each of. the four pulmonary veins has a length of about 15 mm., and for about Dne-third of its course is partially invested by the visceral layer of the pericardium (page 715). _ The right superior vein is usually slightiy 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 He anterior to and below the pulmonary arteries, and are separated by them from the bronchi; the Fig. 749. Right innominate vein Left innominate Left common carotid artery Innominate artery / ___„^. — " 1-eft subclavian artery Stump of sup vena cava' Right appendage Aorta, systemic Left coronary artery Right coronary vessels Right ventricle Injected heart and great vessels, viewed from before ; parts of superior vena cava and aorta have been removed to show right pulmonary artery. 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 betiveen 854 HUMAN ANATUMV. the bronchial and pulmonar)- veins in the region of the smaller bronchi are abundant, and, in addition, the main stems of the pulmonary veins receive at the hilum of the luni^ one or more branches from the larijer bronchial veins. They also receive com- numications from the \enous plexus which surrounds the thoracic aorta in the pos- terior mediastinum, and occasionally also a vein from the pericardium. There is thus a certain comminglinj; of venous blood with the arterialized blood which forms the principal contents of the pulmonary veins. Variations. — At one staj^je 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 which corresponds to the le»t 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 oj^en independently into that structure. An inhibition of this process occasionally obtains, so that but a single vein, repre- senting the original terminal taink, opens into the auricle from one lung or from both. On the other hand, the taking up of the pulmonary vein into the wall of the auricle may proceed further tlian usual, or, to state it perliaps more correctly, the union of the various stenis emerging from the hilum of the lung may be partly delayed until they have reached the original terminal trunk, .so that when this is taken up into the auricle an additional vein will open independentiv 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 veins 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 infej'ior or posterior cardinal veins of each side unite (Fig. 776) to form trunks known as the ducts of Cuvier, 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 \ena cava. The portion of the left superior cardinal between the connecting vessel 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 between 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 : (i) that of the cardiac veins ; (2) that of the superior \ena cava, which includes the jugular and subclavian groups of veins, the original superior cardinals being represented by the internal jugular \eins ; 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 coronarius) (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 coronarii ). At its left end it receives the great coronar)^ 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 K 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 Vieussens. 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 sornewhat 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 apex, where it anastomoses with the veins of the posterior surface, and ascends the anterior Fig. 750. Superior vena cava 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 right pulmonary vein Right pulmonary artery Inferior right pulmonary vein Inferior vena cava Coronary sinus Right coronary vein Right coronary artery Posterior descending branch of right coronary artery Middle cardiac vein 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 vcntriculi sinistri) 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 ctnonarv 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. 750 ) occupies the posterior interxentricular groove, accompanying the right coronary artery. It arises in the vicinity of the apex of the heart and ascends, receiving collateral branches from the posterior surfaces of both \entricles, to oj)en into the coronary sinus near its termination. This, next 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 pana ) (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 ui)per part of the posterior surface of the right \ entricle then opening directly into the auricle. One of the largest and most constant of the.se tributaries ascends along the right I)order 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 \ein of the left auricle (v. obliqua atrii sinistri), also known as Marsliair 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. Aboxe, it is continuous with a fibrous cord contained within the vestigial fold of the pericardium (jiage 716), the cord and \'ein together representing the lower part of an original left superior \ena cava. The degree of development of the vein xaries greatly, and occasionally the fibrous cord retains its original lumen, so that a more or less developed left superior vena ca\'a 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 directly into the right auricle and are situated upon the anterior surface of the right \ entricle, whence they have been termed the anterior cardiac veins (vv. cordis anteriores). They are all comparatixely short vessels and usualh 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 tliis group of \eins. 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 directly 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 vein 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 dehvers to the heart the blood returning from the head, neck, upper hmbs, 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. Anterior jugular Transverse cervical vein Clavicle, cut Suprascapular v Right inferior thyroid Internal mammary vei Right "n ate vein' Superior vena cava' Left internal jugular vein Scalenus anticus muscle External jugular vein Right auricular append: Right coronary or small cardiac vein Right lung, mesial surface Left subclavian vein Clavicle Left inferior thyroid vein Lrib Left innominate vein Superior intercostal vein ■L left posterior intercostal f_ [vein ■^Internal mammary vein Aorta Line of pericardial reflection R. and L. pulmonary arteries A division of left bronchus Pulmonary' arterj' Left pulmonary vein Bronchus Left auricular appendi.v Left lung, mesial surface Diaphragm, thoracic surface Dissection showing innominate veins and superior vena cuva 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 varving from a few to 40 mm. , on an average, perhaps to about one-third its length. The upper extrapericardial portion is in relation anteriorly 858 HUMAN ANATOMY. with the thymus gland or the fatty tissue which rephices it, and is overhipped 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 surface (if the right lung and with the right phrenic nerve ; and to the left it lies alongside the ascending portion of the aortic arch. In its lower intrapericardial j)()rtion it has to the left the systemic aorta: anteriorly, the right auricle; posteriorly, the right pulmonary artery, the right superior pul- monary vein, and the right bronchus, while upon the right it is free. The vena cava superior contains no valves. Tributaries. — In addition to the right and left innominate veins, by the union of which it is formed, the vena cava superior receixes the vena azygos major and small veins from the mediastinum and pericardium. Variations. — Cases have been recorded in which the vena cava superior received the right internal mammary or the ri.ijht superior intercostal vein which normally open into the right innominate vein. It may also receive the vena thyreoidea ima, a vein only occasionally present and draining the territory supplied by tiie art. thyreoidea ima. .\ 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 observed in connection with the innominate veins, and its probable significance will be considered in connection with the variations of those vessels. Practical Considerations. — The superior \ena 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 x^xns (vv. anonymae) (Fig. 751) are two in number, a right and a left. They are situated in the upper portion of the thoracic cavitv, 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 subclavian 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 body, 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. (y^-iy> in.) and an almost vertical course, opening directly downward into the vena cava 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 nerve, 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. (2-3V2 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 extends 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 nerve. It is separated from the mantibrium 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 foaee 026 ) 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 direcdy 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 the neck, and the left superior vena cava then normally undergoes degeneration, traces of it only persisting as the oblinue vein of the left auricle and the coronary smus. ^ Occasionally this normal progress of events fails to occur, the result beino- the comolete absence or imperfect development of the left innominate vein together with a persistence of the leit 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- erate. Various gradations between the embryonic and adult conditions may occur, and the annexed 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. hem.i-azygos, — a condition which will be more especially considered in con- nection with the anomalies of the azygos veins ( page 893 ) . Fig Left internal ju L. subclavian L. innominate L. sup. vena cava L. pulmonary artery Coronary sinus -|i Right int. jugular -R. subclavian -R. innominate R. sup. vena cava R. azygos pulmonary artery R. pulmonary veins 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. Inf. vena cava Posterior 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 weins of its side. The left innominate vein receives in addition (5) the superior phrenic, (6) the thymic, (7) the pericardial, (8) the anterior 7nediastinal, 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. cemcalis 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 communicating with branches of the pos- terior auricular and temporal veins. It passes downward with the occipital artery, pierces the 86o HUMAN ANATOMY. trapezius muscle near its origin Irom tlic suptrior nuchal 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 external jugular Ixlow the posterior auricular. The mastoid emissary vein (page 876) usually opens into one of its branches. 2. The Vertebral Vein. — The \ertebral vein (v. veitcbialis ) accompanies the artery of the same name tlnougli all but the cranial portion of its course, and is usually a single trunk, although frequently it is double or occasionally even plexiform throughout more or less of its course. It arises in the suboccipital triangle from a plexus of small veins with which the occipital and deep cervical veins also communi- cate, and passes downward through the foramina in the trans\erse processes of the six (occasionally seven or five or even only four) upjxT cervical vertebra-. At its exit from the foramen of the sixth vertebra it is continued oblicjuely forward and down- ward behind the inferior thyroid artery and the internal jugular vein, and, j^assing 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 arter}', 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, hi 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 ujiper cervical vertebra-, and accompanies the ascending cervical artery down the neck. \'trs frequenth' it also receives, shortly before its termination, the deep cervical vein. 3. The Internal Mammary Vein. — The internal mammary vein (v. mamma- ria interna) is formed by the union of the venae comites 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 imite, the single vein so formed lying to the inner side of the artcrv and opening above into the innominate vein of the same side. Numerous valves occur in the course of the vein. Tributaries. — Tlie tributaries of the internal mammary veins correspond in general with the branches of the internal mammary artery, with the exception of the superit)r j^hrenic, medi- astinal, pericardial, and thymic branches, which usually open independently into the left innom- inate vein. Its sternal branches form plexuses upon both surfaces oi 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 returning the blood from the pectoral muscles, those of the first ancl 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 manunar\- 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 Cvv. thyreoideae inferiores) ha\c their origin in a venous plexus f plexus thyrcoideus impar ) 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 thvroid \eins. From the plexus two or sometimes three veins descend the neck, following paths quite distinct from those of the inferior thyroid arteries, and open below into the innominate veins, their orifices being guarded by valves. When three veins are present, the odd one occupies a median position and is known I THE SUPERIOR CAVAL SYSTExM. 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 impar receives communications from the superior thyroid veins and also has opening into it the inferior laryngeal veins (vv. laryngeae inferiores) which descend from the lar>-nx. The inferior thyroid veins receive directly branches from the trachea (vv. tracheales) and from the oesophagus (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 A-ein. Usually the veins of both sides are double. They open above into the left innominate \-ein, fre- quently uniting with the thymic, pericardial, and mediastinal \-eins 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) vary considerably in number. They are all small, and empty in part into the left innomi- nate vein and in part into the azygos and internal mammary veins. 8. The Anterior Mediastinal Veins. — The anterior mediastinal veins (v\\ 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 t^^^o 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 insul^cient, 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. b62 HUMAN ANATOMY. Relations. — In the upper part of its course the internal juguhu' rests upon the rectus capitis hiterahs antl the transverse processes of the upper cer\ical \ertebrae. To its inner side and somewhat in front of it is the niternal carotid artery, the "losso- pharyngeal, pneumogastric, spinal accessory, and hypoglossal ner\es separating the two vessels above. The external branch of the spinal accessory crosses it ol)liciuely either in front or behind, and somewhat lower it is crossed anteriorly by the stylo- hvoid 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 pharyn.x, with which it is not, however, directly in contact. Throughout the neck it lies beneath the sterno-cleido-niastoid muscle, imme- diately to the outer side of the common carotid artery, being enclosed in a common SiipCTficial tpmpor.il vHn \ Fig. 753. posterior auricular External auditory meat.. Mastoid vein Occipital vein Internal maxillary vein Temporo-niaxillary vein Posterior trunk of teinporo- maxillary vein \nterior trunk of temi maxillary vein External jugular vein Lingual vein Internal carotid artery 1 ntemal j ugular vein Posterior external jugular vein Superior thyroid vein Cnumion carotid artery Tfans^erse cenical vein iporal muscle, cut Internal maxillary vein Pterygoid venous f-lexus Internal plerjgoid muscle Posterior scapular vein — Common facial vein Ext. carotid arter\ Coninumication bet. lin- gual and anterior jugulai Middle thyroid vein Left innominate veia Subclavian vein Innominate arterv ^ ^^ y / ' \\ Right innominate vein I. rib Internal mammary vein Superior vena cava Inferior thyroid veins Dissection showing deep veins of neck and head. sheath with it, as is also the pneumogastric nerve, which lies behind and between the two \essels. 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 immediatelv 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. — \'ariations of the internal jugular 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 CAVAL SYSTEM. 863 The left internal jugular has been observed much reduced in size, there being a compen- satory enlargement of the correspondmg 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 — vi^ith 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 injurino- 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 carodd 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 by 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 phary7ip:eal, (2) the /«««/, (3) the lingual, (4) the superior thyroid, and (5) the middle thvroid veins. I. The Pharyngeal Veins. — The pharyngeal veins (vv. pharyngeae) are small vessels, varying in number, which open, either independently or after having united to a single stem, either direcdy into the internal jugular or indirectly by way of the 864 HLMAX ANATOMY. lingual or superior thyroid vein, They take their origin from a venous plexus ( picxus pharynj{cus) 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 l)lexus 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 recei\es the \eins ( vv. canalis ptervnoidci ) which accompany the \'idian artery through its canal, and communicates with the pterygoid, oesoj)hagcal, and \ertebral 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. P'rom 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 tlie 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 jimction 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 conmiunicate 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 w hich in- ter\enes between this communication and the internal jugular is termed the common facial vein ( v. facialis comnumis ). Both the facial and the angular \'eins are usually described as being destitute of valves ; these structures do occur, however, but they are always insufficient and form no bar to the passage of blood in an inverse direc- tion— i.t\. from the facial and angular backward into the ophthalmic veins. Relations. — The angular vein rests upon the nasal process of the maxillary \ein 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 be greatly reduced in size. Below, it frequently unites with the lin.s^ial vein to form a lin^o-facial trunk, which may also be joined by the superior thyroid. Instead of opening into the internal jugular, it occasionally passes across the stemo-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 commonlv 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 inwai'd to the brain-case and to the interior of the facial region, while the remaining portion flows dozvnward 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 \olume of blood, making wounds of the vein dangerous. THE SUPERIOR CAVAL SYSTEM. 865 The facial vein is said to be less flaccid than" most superficial veins, and there- fore to remain more patent after section ; it possesses either imperfecdy 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 exceptionally dangerous, as the infection may spread by way of the ophthalmic vein orthe 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) the /ron^a/ and (d) 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, (nral \' Middle tem|" r 1= Occipital vein Internal maxillary vein Temporo- maxillary vein Posterior auricular vein i cation between facial and external jugular vtin External jugular vein Tributary of trans verse cervical vein Posterior extern.il jugular vein Trapezius r/ Frontal veins Supraorbital vein Branch of cftninnini- cation with i.phthal- Angular vein ' — Lateral nasal vein Deep facial vein Submental vein ('ommon facial vein Superficial veins of head and neck ; external jugular lies beneath platysina muscle, which has been partly removed. {k) The submental vein (v. submentalis) accompanies the artery of the same name. It rests upon the superficial surface of the mylo-hyoid muscle and jjasses backward and outward in the submaxillary triangle, beneath the platysma, to open into the cervical portion of the facial. It communicates witli the sublingual vein by several branches which perforate the mylo-hyoid muscle, and, in addition to cutaneous and muscular branches, also receives tributaries from tn^ 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. lingualis) is a short trunk which either opens directly into the internal jugular or unites with the facial vein to form a linguo-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 ranine, 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 submaxillary 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 the extent to which the lingual vein is de- veloped, both its constituent tributaries as well as the dorsales linguae sometimes opening inde- pendently into the internal jugular. It may open into either the external 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 pharj^ngeal 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, {c) 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 ha\^e already been given (page 851). 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 niccting-puint, which is termed the lorcular Hcrophili (con- tlucns siiiuum ), each hiteral sinus passes outward over the squamous portion of the occipital bone alonjj 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 ojjens 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, i)assing 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 frequently termed the sigmoid simis. 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- Skin Superior longitudinal sinus Falx cerebri Cerebral hemisphere Posterior horn of lateral ventricle Tentorium Left lateral sinus — Superior worm Fibro-aponeurotic layers of scalp Parietal layer of dura Bone t-^ — Inferior longitudi- nal sinus, cut obliquely Posterior horn of lateral ventricle Tentorium Right lateral sinus Cerebellum Inferior worm Occipital sinus 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 cross-section (Fig. 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 varies 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. i 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 temporb-sphenoidal regions of the cerebral hemispheres ■,{d) 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 ; (rated sjjace. The basilar vein drains all the central i^art 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 cerebellum. 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 tho.se of the posterior perforated space drain the optic thalami. Practical Considerations. — The free communication of the thin-walled valveless cerebral veins with 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 inastoid vein ; (<5) 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) a.t 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 anaemia 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 ; (d) the division of the sinus at the Torcular Herophili into two trunks diverging at right angles ; (r) the course of the blood-current in the lateral sinus — first horizontal, with a convexity outward ; then — in tlie 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 folia*. 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 ioferiores), somewhat larger than the superior, pass in part forward and outward to open into the 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 vein. 1. The Superior Ophthalmic Vein. — The superior ophthalmic vein (v. oph- thalraica 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. 7iaso-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 {b) 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 {d ) muscular veins (vv. musculares) which return the blood from the levator palpebrse 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 venae vorticosae exist, and they open sometimes into the muscular veins instead of directly 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 venae vorticosae, 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 retinae 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 a.s a definite stem. The vein, when if: 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. St opens posteriorly either directly into the cavernous sinus or else unites with the superior ophthalmic vein. 88o HUMAN ANATOMY. Anastomoses of the Ophthalmic Veins.— The oplithalinic 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 oi valves, through their branches oi origin ; ( 2 ) with the veins of the nasal cavity through the eth- moitlal branches ; and ( ;, ) with the pterygoid plexus by means of a branch of the inferior ojihthal- mic which jxisses tlownward through the spheno-maxillary fissure. Practical Considerations. — The communication between the superior ophthalmic vein — the largest channel in the adult between the vessels of tlie venous system of the head and face antl the sinuses of the dura mater — and the facial vein, while adding to the danger of intracranial complications as a result of infectious (hsease situated upon the face'' (page S73), affords relief to intraocular tension in cases ol pressure upon the cavernous sinus, as from an inflammatory exudate or an intra- orbital or intracranial growth. Such relief delays the apjjcarancc 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 conjunctixae are congested. E.\o[)h- 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. TiiK External Jugular Vein. The e.xternal jugular vein (v. jugularis externa) CFig. 759), notwithstanding its usual connection with the subclavian, is closely related both in its develojMiient and topographical relations with the internal jugular, and may be most con\eniently con- sidered here. It is formed in the neighborhood of the angle of the mandible by the union of the temporo-maxillary and jwsterior auricular veins, and courses downward immediately below the platysma, crossing the sterno-cleido-mastoid mu.scle 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 gixes off a large branch which passes forward and downward to communicate with the facial \ein. At its entrance into the subclavian it is provided with a pair of vab.es, and usually a second pair occurs at about the middle of the neck. A third pair is occasionally present in the interval 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 sometimes the fascia is especially thickened immediately below and to the inner side of the vein. This attachment 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- stituting 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. 88 1 In connection with the abundant variation shown in the size of the external jugular it is interesting to note that in the majority of mammals it is the most important vein of the neck, surpassing the internal jugular in size. It is, however, of later development 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 variation in size is largely dependent upon the extent to which the original direct connection of the facial with it is retained. Fig. 759. Temporal fascia Superficial temporal vein. Middle temporal- vein Occipital vein. Internal maxillary vein Temporo- maxillary vein Posterior auricular vein Stemo-cleido- mastoid Communication between facial and external jugular vein External jugular vein Tributary of trans-- verse cervical vein Posterior external jugular vein Trapezius ^' Frontal veins Supraorbital vein Branch of communi- cation with ophthal- mic vein Angular vein Lateral nasal vein Deep &cial vein Submental vein ommon facial vem Anterior jugular vein Platysma \ Superficial veins of head and neck ; external jugular lies beneath platysma muscle, which has been partly removed. 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 sterno-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 tcmporo- maxillary, (2) \\\q posterior auricular, (3) \\\Kt posterior external jugular, (4) the suprascapular, and (5) the anterior jugular vein. It may also receive the occipital vein (page 859). I. The Tempore- Maxillary Vein. — The temporo-maxillary vein (v, facialis posterior) (Fig. 753; is foniKcl 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 temi^oral artery and is formed just above the zygoma l)y the union (jf the superficial and middle temporal veins. The super- ficial temporal vein (v. temporalis superlicialis j (Fig. 759) is formed by the unicjn 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 with the posterior auricular and occii)ital 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 j/iexus pierce the temporal fascia near the external angle of the eye and communicate with branches of the facial and lachrymal nerves, while other branches jxiss deeply into the substance of the temporal muscle and anastomose with the deej) temporal veins. The middle temporal, from its origin in the plexus, passes backward parallel with the upper border of the zygoma, perforates the temporal fascia, and joins with the superficial temporal \ein. Tributaries. — The temporal vein receives the following tributaries, {a) The anterior auricular veins (vv. auriculares anteriores) 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 gland, communicating with the anterior parotid branches of the facial, {c) The articular veins ( vv. articiilares manililiulae), several in number, arise in a rich plexus which surrounds tlie syno\ial membrane of the temporo-mandibular articulation. This ple.xus receives tympanic branches (vv tympanicae), which accompany the tympanic artery through the Glaserian fissure, and communicates anteriorly with the pterygoid plexus. (ein Rit:ht subclavian vein Right innominate vein Right inferior thyniid vein Right internal mammary vein Superior vena cava Right bronchial vein — Right superior intercostal vein Hepatic veins Inferior vena cava Phrenic vein Suprarenal vein Renal vein Vena azygos Right spermatic vein Quadratus luniborum Branch of communi- cation to vena azygos Ascending lumbar vein Right common iliac vein Ilio-lumbar vein Thoracic duct Left vertebral vein Left inferior thyroid vein Left innominate vein Left internal mammary vein Left superior intercostal vein Left tiri.ui.hial vein Vena hemiazygos acccssoria rhoracic duct Vena hemiazygos Kijjht crus of diaphragm Phrenic vein Suprarenal vein Renal vein Receptaculum chyli "Lumbar fascia Left spermatic vein Ascending lumbar vein Left common iliac veia Ilio-lumbar vein Internal iliac vein External iliac vein fW- Portion of posterior body-wall, showing azygos veins, superior and inferior vena cava, and their tributaries. THE AZYGOS SYSTEM. . 895 the hemiazygos. Occasionally, instead of opening into the superior vena cava, the azygos terminates in the right subclavian, the right innominate vein, or even opens directly into the right auricle. A further anomaly is sometimes presented by the azygos, in its upper part, being situated at the bottom of a deep groove upon the surface of the right lung, which thus comes to have an accessory lobe known as the azygos lobe or lobule. Practical Considerations. — The azygos veins are the connecting links be- tween the cardinal and the inferior caval systems. In cases of obstruction of the inferior cava they are able to carry on the collateral circulation very effectively, through their communication with the common iliac, renal, lumbar, and ilio-lumbar veins. Growths in the posterior mediastinum, enlarged bronchial glands, or aortic aneurisms may so compress these veins as to cause oedema of the chest wall by interference with the intercostal veins which empty into them. The Hemiazygos Vein. The hemiazygos vein (v. hemiazygos) (Fig. 765), also called the azygos minor inferior, is the counterpart, on the left side of the body, of the lower part of the azygos. It arises just below the diaphragm as the continuation upward of the left ascending lumbar vein (page 901), also receiving usually a communicating branch from the left renal vein. It passes upward into the thorax between the medial and intermediate portions of the left crus of the diaphragm, and then ascends upon the left side of the bodies of the lower thoracic vertebrae, passing in front of the lower left intercostal arteries and having the thoracic aorta to its right. At about the level of the eighth or ninth vertebra it bends towards the right and, passing behind the aorta and the oesophagus, opens into the azygos vein. In its course it receives the lower five or four left intercostal veins, which con- stitute its principal tributaries, and in some cases it also receives the accessory hemi- azygos vein. It also receives some branches from the oesophagus and from the posterior mediastinum. The Accessory Hemiazygos Vein. The accessory hemiazygos vein (v. hemiazygos accessoria) (Fig. 765), also called the azygos minor superior, is a descending stem which lies upon the left side of the bodies of the upper thoracic vertebrae and receives the upper left intercostal veins. It begins above at about the second intercostal space by the union of a small vein, which connects it with the left innominate, with the left superior intercostal. When it has reached the level of the seventh or eighth thoracic vertebra it bends to the right and, passing beneath the aorta and the oesophagus, opens into the azygos vein. Quite frequently it opens below into the hemiazygos just as that vein bends towards the right, and even when it has an independent connection with the azygos it may be connected with the hemiazygos by an anastomotic branch. It receives the upper seven or eight left intercostal veins and in addition the left posterior bronchial vein. Variations. — The hemiazygos and accessory hemiazygos veins together represent the left cardinal vein of the embryo which primarily opened into the left Cuvierian duct. With the dis- appearance of the lower part of the left jugular vein the relations of the left cardinal change, the vein making a connection across the middle line with the right cardinal (the azygos). Indi- cations of the original condition are occasionally seen in a fibrous cord which connects the left superior intercostal vein, which is strictly a portion of the accessory hemiazygos, with the oblique vein of the left auricle (page 856). As already pointed out in speaking of variations of the azygos, cases have been observed in which the hemiazygos and accessory hemiazygos occur upon the right side of the body, being formed from the right cardinal, while the left cardinal gives rise to the azygos. And more rarely the two veins have been observed fused to form a single trunk lying upon the anterior surface of the thoracic vertebrae and receiving all the intercostal arteries. A considerable amount of variation exists in the number of intercostal veins received by the hemiazygos and the accessory hemiazygos respectively. Usually they divide between them the intercostals, since they either unite or cross the median line to the azygos over successive vertebrae. The hemiazygos has been observed to cross the vertebral column anywhere from the sixth to the eleventh vertebra, and the accessory may descend as far as the tenth or may cross at the third. In cases where it makes its crossing high up a number of intercostal spaces may inter- 896 HUMAN ANATOMY. \ file between it and the heiuia/ygos, and the veins of tliese then open directly into the a/ygos passing, each independently, across tiie vertebral column beneatli the aorta' and cesophagns. Absence of the accesst)ry hemiazygos has been observed, the upper six or eight inter- costal veins uniting to form a common ascending trunk which o|)ens into the left innominate. In all probability, however, this common ascending stem is jiroperly to be regarded as the accessory hemiazygos, whose normal connection with the innominate has increased in size while its connection with the azygos or hemiazygos has either degenerated or failed to form. The Interco.stal Veins. The intercostal \eins ( vv. intercostalcs ) ( Fi.y;. 765), sometimes desig-nated as posterior intercostal as tlistingiiished from the anterior intercostal tributaries of the internal mammary vein, accompany the intereostal arteries and are twelve in mmiber on each side, one occurring in each intercostal space and one, sometimes termed the subcostal vein, rumiing along the lower border of each twelfth rib. They lie along the upper border of the spaces to which they belong, in a groove on the lower border of the rib, and are above the corresponding arteries. The upper nine or ten veins open anteriorly into the internal mammary or musculo-phrenic veins, but the lower three or two, which are somewhat larger than the rest, have no anterior communica- tion and recei\c tributaries from the abdominal muscles and the diaphragm. In the middle portion of their course the upi)er six or seven \eins give off branches, the costo-axillary veins, which ascend towards the axilla and open into either the long thoracic or tiic thoraco-epigastric vein and so into the axillary, and, as it approaches the vertebral column behind, each vein receives a dorsal branch (ramus dorsalis) which accompanies the spinal branch of the intercostal artery and returns the blood from the skin and muscles of the back and also from the spinal column and its contents, this latter drainage being by means of a spinal branch (ramus spinalis) which connects with the intervertebral veins (page 898). Their posterior termination varies considerably in different individuals, especiallv as regards the upper members of the series. It may be supposed that primarily all the intercostal veins of the right side opened into the azygos vein and all of those of the left side into the hemiazygos or accessory hemiazygos, and this condition holds in the adult with all but the upper two or three veins. On the right side the vein of the first space — that of the second space sometimes uniting with it — frequently accompanies the superior intercostal artery as a right superior intercostal vein, and opens above into either the right innominate or one of its branches, usually the vertebral ; on the left side the vein of the first space opens into the left innominate vein, being sometimes termed the accessory left superior intercostal vein, while the veins of the second, third, and sometimes the fourtli sfxices unite to a common trunk which crosses the arch of the aorta and opens into the left innominate vein, forming the left superior intercostal vein. It is to be noted that this last is connected with the accessory hemiazygos vein and really represents, in part at least, its upper portion, — a fact which is all the more evident from its frequent connection by means of a fibrous cord with the oblique vein of the left auricle ; and, furthermore, it may also be pointed out that the veins of the second, third, and sometimes the fourth spaces of the right side usually unite to a common trunk which opens into the azygos \ein. The principal tributaries and connections of the intercostal veins have already been mentioned, but there remain to be described the interesting arrangement shown by the valves in those veins which connect anteriorly with the internal mammary or musculo-phrenic veins. So far as this arrangement is concerned, each vein may be regarded as consisting of three portions : (i) an anterior portion, in which the con- cavities of the valves look towards the internal mammary or musculo-phrenic veins ; (2) a posterior portion, in which the valves look towards the azygos or hemiazygos veins ; and (3) an intermediate portion, which is destitute of valves. As a result of this arrangement the blood of the anterior portion of each vein must pass to the internal mammary veins (page 860), that of the posterior portion to the azygos or hemiazygos, while in the intermediate portion it may pass in either direction. But it is with this intermediate portion that the costo-axillary veins are connected, so that in the upper six or seven veins, in addition to passing partly anteriorly and partly posteriorly, some of the blood takes an ascending direction and empties into the axillary vein. THE AZYGOS SYSTEM. 897 In the two or three lower veins there is no such double flow, the valves all looking towards the azygos veins. Valves occur at the opening of practically all the intercostals into the azygos veins, the last intercostal forming an exception to this rule, and, furthermore, the valves of the lower veins are apt to be insufficient. The Spinal Veins. The spinal veins, which return the blood from the vertebral column and the adjacent muscles and also from the membranes enclosing the spinal cord, present in a high degree the plexiform arrangement which is characteristic of the veins as com- pared with the arteries. They form a series of longitudinal plexuses which extend practically the entire length of the spinal column, communicating extensively with one another, and may be divided primarily into those which lie external to the spinal canal and those which lie within the canal. The external spinal plexuses (plexus venosi vertebrales extern!) are two in number, anterior and posterior. The anterior external plexus (plexus venosus vertebralis anterior) rests upon the anterior surfaces of the bodies of the vertebrae, and presents considerable differences in the amount of its complexity in different portions of the spinal column. In the thoracic and lumbar regions it forms a net- work with large meshes, in the sacral region it is represented by transverse anasto- moses between the lateral and middle sacral veins, and in the cervical region it reaches its greatest degree of complexity, forming a close net- work, especially dense above and resting partly upon the bodies of the vertebrae and partly upon the longus colli muscles. At each intervertebral foramen the plexus communicates with the veins issuing from the internal spinal plexuses and also with the posterior external plexus, and in addition sends branches to the vertebral veins in the cervical region and to the rami spinales of the intercostal and lumbar veins in the corresponding regions. The posterior external plexuses (plexus venosi vertebrales posteriores) lie partly [upon the posterior surfaces of the laminae of the vertebrae and the ligamenta subflava land partly between the deeper dorsal muscles. As in the case of the anterior plexus, [they are more complicated in the cer\'ical than in the thoracic and lumbar regions. {In the latter their meshes are somewhat elongated longitudinally, and they communi- jcate with the internal plexuses at the intervertebral foramina and also by branches ■which traverse the ligamenta subflava, and they have further communications with the anterior external plexus and with the spinal rami of the intercostal and lumbar ?:eins. In the cervical region, in correspondence with the greater differentiation of Ihe dorsal musculature, the plexuses become divided into several layers, and in the region between the occiput and the axis vertebra their deep layers form an especially Idense net-work, the suboccipital plexus^ with which the occipital, vertebral, deep :ervical, and posterior external jugular veins communicate. Throughout its course Fthe cervical portion of the plexus communicates with the internal and anterior ex- [ternal plexuses and also with the vertebral vein. The internal spinal plexuses (plexus venosi vertebrales interni) are situated in [the dura mater lining the spinal canal and are much closer than the external plexuses. [The veins which form them have a general longitudinal direction and anastomose [abundantly, but nevertheless four subordinate longitudinal lines of vessels can be [recognized, two of which are upon the anterior wall of the spinal canal and two upon [the posterior wall. The anterior internal plexuses lie one on each side of the median line on the [posterior surfaces of the bodies of the vertebrae and the intervertebral disks, from the iforamen magnum to the sacral region. They are composed of rather large veins, petween which are frequent anastomoses, and transverse connecting vessels run across the body of each vertebra between the two plexuses, passing beneath the posterior Icommon vertebral ligament. Into these transverse connections open the basivertebral vei7is (vv. basiverteb rales) which return the blood from the bodies of the vertebrae, jtraversing these to a certain extent to communicate with the anterior external plexus. ""he anterior internal plexuses also communicate opposite each vertebra with the pos- fterior internal plexuses, rings of anastomosing veins thus surrounding the spinal canal [opposite each vertebra and constituting what are termed the retia venosa vertebrarum. 57 898 HUMAN ANATOMY. The posterior internal p/ixiiscs are situated one on either side of the median Hne on the anterior surfaces of the laminae and on the Hgamenta subflava, through which they send branches to communicate with the posterior external i)lexus. They are connected by transverse jjlexuses which complete the retia venosa vertebrarum. and are composed of smaller vessels than the anterior j)lexuses, and the net-work which the}' form is more oi>en. Laterallv, at each intervertebral foramen the internal j^lexuses send branches out from the spinal canal alon^^ the nerve-trunks, and by means of these intervertebral veins (vv. intcrvcrtcbrales), which have the form of plexuses at their origin and receive communicating branches from the external vertebral plexuses and from the veins of the spinal cord, the internal plexuses pour their blood into the vertebral, intercostal, lum- bar, and lateral sacral veins, the connection with the intercostals being through their rami spinales. Above, the internal plexuses form an especially rich rete or plexus around the foramen magnum and communicate with the occipital, marginal, and basilar sinuses. Practical Considerations. — The posterior external spinal plexuses, by means of their communication through the intervertebral foramina and the ligamenta sub- flava with the internal plexuses, may convey infection from without — septic wounds of the back, severe bed-sores, osteitis of the \ertebral laminae — to the interior of the spinal canal. External pachymeningitis has thus originated. In operations upon the spine, these veins bleed so freely that it is often well after se\ering them upon one side to control them by packing and proceed to the exposure of the spine on the opposite side, repeating the packing there. The internal plexuses, interposed between the theca of the cord and the interior walls of the vertebral column, may, as a result of trauma, furnish blood enough to cause compression of the cord. The symptoms are usually relati\ely slow in developing — as compared with those due to injury to the cord itself or to its vessels — and are referable mainly to the lower spinal segments, the blood gra\itating to that portion of the canal. Hemorrhage may occur within the membranes (haematorrhacis), when the blood will likewise tend to gravitate toward the lower end of the cord, and, unless in large amount, may cause no definitely localizing symptoms. Bleeding from the ven^ medulli spinales may take place into the substance of the cord (haemato- myelia), and is most likely to occur in the segments from the fourth cervical to the first dorsal (Thorburn), because of the degree of motion of that portion of the spine, the union toward its base of a fixed and a movable segment, and the frequency with which forces causing excessive flexion or over-extension are applied to the head. If the lesion causes compression only, the paralysis, anaesthesia, etc. , will be only temporary. If it is associated with disorganization of the cord, they will be permanent. The Veins of the Spin.\l Cord. The veins of the spinal cord (vv. medulli spinales ) occur as six longitudinal stems situated upon the surface of the cord and connected by a fine net-work very much as are the arteries. One of these stems traverses the entire length of the cord along the line of the anterior median fissure, and has on either side of it another stem which lies immediately posterior to the line of exit of the anterior nerve-roots. These three stems together form the anterior medulli-spinal veins (\\. spinales externae anteriores). The posterior veins (\y. spinales externae posteriores; have a similar arrangement, one lying along the line of the posterior longitudinal fissure and one posterior to each of the lines of entrance of the posterior nerve-roots. All these stems, together with the plexus which connects them, lie in the pia mater and receive branches (vv. spinales internae) from the substance of the cord. From them branches pass out along the nerve-roots to join the intervertebral veins, and at the upper extremity of the cord they join the veins of the medulla oblongata. THE INFERIOR CAVAL SYSTEM. The inferior ca\al system includes all the veins from the body-wall below the level of the diaphragm ; those from the abdominal and pelvic cavities, with the exception of those from the stomach, intestines (except the lower part of the rectum), THE INFERIOR CAVAL SYSTEM. 899 pancreas, and spleen ; and those from the lower limb. It receives its name from its principal vessel, the inferior vena cava, which conveys its blood to the right auricle. The Inferior Vena Cava. The inferior or ascending vena cava (vena cava inferior) (Figs. 765, 766) is formed by the union of the two common iliac veins either on the right side of the intervertebral disk separating the fourth and fifth lumbar vertebrae or on the right side of the fifth lumbar vertebra. From this point it ascends directly upward to the level of the first Fig. 766. Right suprarenal body Vena cava Right renal vein Right kidney. Right ureter Right spermatic- vein Right spermatic artery Psoas magnus Ureter External iliac artery Vas deferens Spermatic cord Hepatic veins Coeliac axis Superior mesenteric artery Left suprarenal body Left renal vein f^Leit kidney Left renal artery Inferior mesen- teric artery Left ureter Quadratus lumborum Left spermatic artery Common iliac artery Common iliac vein Psoas magnus Left ureter, pelvic portion Rectum (cut) Vas deferens Bladder Inferior vena cava and iliac veins. lumbar vertebra and there begins to bend slightly to the right to reach the fissure of the liver which separates the Spigelian and right lobes. Passing upward in this fissure, it reaches the diaphragm and perforates the left lobe of the centrum tendineum of that structure, so entering the cavity of the thorax, then bends slightly forward and to the left, and opens into the lower and back part of the right auricle of the heart. It is the largest vein of the body, measuring at its entrance into the auricle about 33 mm. in diameter. It increases in size from below upward with the accession of its various tributaries, somewhat sudden increases succeeding the entrance into it of its largest tributaries, the renal and hepatic veins. It contains no valves, unless the Eustachian valve guarding its entrance into the auricle be regarded as belonging to it. 900 HUMAN ANATOMY. Relations. — For convenience in description the vena cava inferior may be regarded as consisting of an abdominal and a thoracic portion. The former, which constitutes by far the greater part of its length, has the following relations. Poste- riorly it rests u\Mm the right side of the lumbar vertebne, upon the origins of the psoas major antl minor muscles, and above upon the right crus of the diaphragm ; it crosses in its course the right lumbar and right renal arteries. Medially it is in close relation with the abdominal aorta throughout the greater portion of its course, but separates from it slightly above, the right crus of the diaphragm intervening. Laterally it is in contact with the psoas major muscle below, and at about the middle of its course it is in close relation with the inner border of the right kidney. Ante- riorly it is covered at its origin by the right common iliac artery and in the lower part of its course by peritoneum. At the level of the third lumbar vertebra it lies beneath the third jjortion of the duodenum, and immediately abo\e that beneath the head of the pancreas and the main stem of the portal vein, wliich crosses it obliquely. Finally, it lies in the \ena caval fissure of the liver, having to the right the right lobe and to the left the SjMgelian lobe, and being sometimes completely surrounded by liver-tissue, owing to a thin portion of it bridging over the fissure. Througliout this part of its course it is firmly united to the walls of the fissure by fibrous bands. In its thoracic portion, which is quite short, measuring not more than 3 cm. in length, it is in relation at first with the right lung and pleura, and in the upper part is enclosed for about 1.2 cm. in the pericardium. Variations. — The dt-veloimient of the inferior vena cava (page 927) shows it to be formed by the union of three primarily distinct structures. Its upper part, between the entrance of the hepatic veins and the riKht auricle, is the upper part of the embryonic ductus venosus, then fol- lows a considerable portion derived from the right subcardinal vein, and, finally, its lower part is formed from the right cardinal vein. Of these embryonic veins the ductus venosus is unpaired, the (jther two are the right members of paired veins, u hose fellows undergo almost complete degeneration. Anomalies of the vena cava, which are not unconunon, are for the most part e.xplicable as a persistence or modification of the embryonic conditums. Thus, that portion of the vessel w hich is formed from the right subcardinal and right cardinal may fail to develop, in which case what is termed a persistence of the cardinals occurs. I'p to a point above the level of the renal veins the vena cava is represented by two parallel trunks lying one on either side of the aorta, the one receiving the right common iliac vein and the other the left. These represent the abdominal IJortions of the cardinal veins ( >r, in the majority of cases, more probably the subcardinals, and unite above with the unpaired ductus venosus, which carries their blood to the heart. In other w ords, such cases are, a.s, a rule, to be regarded as a similar development of both subcardinal veins. Occasionally, howe\er, the development of the right subcardinal to form the vena cava may proceed as usual, but it fails to make a connection with the ductus venosus, one of its con- nections with the right cardinal enlarging so that this vein receives the caval blood, carries it through the aortic opening of the diaphragm, and. as the azygos vein, empties it into the superior vena cava. The hepatic veins open as usual into the ductus venosus, w hich passes to the right auricle in the normal manner, and the vena ca\a inferior is thus represented by two distinct veins, the upper part of the ductus venosus. which in such cases is termed the common hepatic vein ( v. hepatica commimis ), and the subcardinal and cardinal portion. Another variation may be produced by a reversal of the roles of the two subcardinals in forming the vena cava, the left being the one which develops, while the right degenerates. .Such a condition is found in all cases of situs inversus visceruni, but it has also been obserxed in cases in which there w as otherwise a normal arrangement of the organs. In such cases the vena cava in the lower part of its course lies to the left of the aorta instead of to the right, and at the level of the renal arteries it crosses to the right side in front of the aorta, its further course being normal. I?ut just as the lower part of the inferior vena cava, when normally formed from the right subcardinal, may fail to unite with the ductus venosus but retam its primary connection w ith the azygos, so. too, when formed from the left subcardinal. it may retain its connection with the hemiazygos and drain through that vessel into the azygos and so into the superior vena cava. These various cases include the principal \ariations which occur in connection with the vena cava inferior. It may be pointed out that normally connections e.xist between the azygos vein and the vena ca\a below the diaphragm ; by means of the ascending lumbar veins, and also by the thoraco-epigastric veins, connection is established between tributaries of the inferior cava and the e.xternal iliac veins and the a.xillar}- vein. By means of these normally subordinate channels opportunity is afforded for the maintenance of the circulation in case of obliteration of the vena cava. Practical Considerations. — The inferior cava may be ruptured in se\ere abdominal injuries, as m the case of a weight falling upon, or a wagon passing over, the belly. The site of rupture is most often in the portion lying in the hepatic 1 THE INFERIOR CAVAL SYSTEM. 901 Assure. Its relation to the right psoas major muscle has resulted, in cases of psoas abscess, in ulceration and opening of the vein, with fatal hemorrhage. Its relation to the inner border of the right kidney has resulted in its compression by a movable kidney, or by a cancerous growth of the kidney, causing caval thrombosis, a condition which has also been noted in connection with chronic nephritis and with infarction of the renal parenchyma. Its relation to the liver results, in some cases of hepatic enlargement, in compression of the vena cava with oedema of the lower limbs, and other symptoms of obstruction. Its close proximity to the lower end of the bile-duct necessitates caution in cutting operations for the removal of impacted stones from the duct (choledochotomy) (page 1732). Enlarge- ment or growth involving the head of the pancreas may compress the cava sufficiently to cause obstructive symptoms, and the nearness of the vein constitutes one of the very serious obstacles to removal of pancreatic tumors. In ureterotomy or other operation on the right ureter, the close relationship of the vena cava at the point of crossing should be remembered. Thrombosis of the cava, from whatever cause, though it may extend the entire length of the vessel, is apt to be limited to a portion of the vessel, as that between the renal veins and the auricle, or that extending from the iliac veins to the renal veins. The collateral circulation after occlusion may be carried on through the saphenous, superficial abdominal, spermatic, pudic, and deep epigastric veins, and the obturator, inferior mesenteric, external mammary, and azygos veins. Tributaries. — In addition to the common iliac veins by whose union it is formed, the vena cava inferior receives a number of tributaries from the abdominal walls and organs. These may be arranged into two groups according as they drain the parzefes of the abdomen (radices parietales) or its viscera (radices viscerales). Of the former there are : (i) the inferior phrenic and (2) the lumbar veins, and of the latter (3) the hepatic, (4) the renal, (5) the suprarenal, and (6) the spermatic or ovarian veins. 1. The Inferior Phrenic Vein. — The inferior phrenic (v. phrenica inferior) is a paired vein which corresponds to the similarly named artery. It is formed by the union of a number of tributaries which ramify upon the under surface of the diaphragm, and opens into the vena cava just before it passes through the diaphragm. It receives tributaries from the upper portion of the suprarenal capsule, and the left vein, by the enlargement of an anastomosis of its suprarenal tributaries with the suprarenal vein, may open through the latter into the left renal vein. The right vein occasionally opens into the right hepatic vein. 2. The Lumbar Veins. — The lumbar veins (vv. lumbales) are usually four in number on each side, and accompany the corresponding arteries, lying above them. They resemble closely in their relations and tributaries the intercostal veins, of which they are serial homologues. Each vein arises in the muscles of the abdominal wall and passes backward and inward towards the vertebral column, passing beneath the psoas muscle. Shortly before reaching the vena cava it receives a ramus dorsalis. This has its origin in the dorsal integument and muscles, communicating with the posterior external spinal plexus, and receives a ramus spinalis which communicates with one of the lumbar intervertebral veins and so with the internal spinal plexuses. The veins then continue their course towards the vena cava, those of the left side passing beneath the abdominal aorta, and they open into the posterior surface of the vena cava. As it passes upon the lateral surface of its corresponding lumbar vertebra, each of the three lower veins is connected with the one above by an ascending stem, which also places the lowest vein in communication with the ilio-lumbar or the common iliac vein, while from the uppermost vein it is continued on upward to join with the azygos or hemiazygos as the case may be. This ascending stem is the ascending lumbar vein (v. lumbalis ascendens), and is of especial interest as forming an important collateral channel between the inferior and superior venae cavae. Each lumbar vein possesses one or two valves in its course, and sometimes also valves at its entrance into the vena cava. The concavities of these valves are directed towards the vena cava, but the valves are nearly always insufficient and 902 HUMAN ANATOMY. consequently will not pre\ent a How of blood from the vena cava outward to die ascending; lumbar \eins in cases of occlusion of the upper part of the ve.ia cava. 3. The Hepatic Veins. — The hepatic veins (vv. hepaticae) (Fig. 765) return the blood which has been carried to the liver both by the hepatic artery and by the j)ortal \ein. They are two or three in number, and are formed by the union of the intralobular veins of the liver (page 920). They emerge from the substance of the liver at the upper part of the groove in which the vena cava lies, and, passing obliquely upward, enter that vessel at an angle shortly before it passes through the diaphragm. One of the hepatic veins drains the substance of the right lobe of the liver, the other, when there are but two, the remaining lobes. Quite frequently this second or left \ein is replaced by two vessels, one of which drains the left lobe alone, while the other drains the Spigelian and quadrate lobes. Usually, in addition to these principal veins, a varying number of small hepatic veins occur, which make their e.xit from the liver-substance on the walls of the groove for the vena cava and open directly into that vessel without joining the principal hepatic veins. The hepatic veins possess no valves in the adult, and are characterized by the thickness of their walls, which are provided with both circular and longitudinal muscles. Variations. — Occasionally the right vein, more rarely the left, perforates the diai^hragni and ()|)ens eitlier into the thoracic portion of the inferior vena cava or else directly into the right auricle. The two (or three) veins sometimes unite to a single trunk l^efore joining the vena cava, and this trunk has been observed to penetrate the diaphragm and open directly into the right auricle without communicating with the vena cava. 4. The Renal Veins. — The renal veins (vv. renales) (^Fig. 766) are two in number, one returning the blood from each kidney. Each vein is formed at the hilum, or some little distance from it, by the union of from three to five branches which come from the kidney substance, and is directed medially and slightly upward, lying in front of the corresponding artery. On account of the position of the vena cava to the right of the median line, the left \ein is somewhat longer than the right, and passes in front of the abdominal aorta, just below the origin of the superior mesenteric artery, to reach its point of entrance into the xena cava, this point being usually a little higher than that of the right vein. Tributaries. — hi addition to the vessels by whose union it is formed, each renal vein receives (a) an inferior suprarenal vein from the lower part of the suprarenal capsule, accompanying the corresponding artery; (A) adipose veins, which pass transversely across both surfaces of the kidney, taking their origin in its adipose capsule; (c) a ureteric vein, frequently more or less ple.xiform in structure, which returns the blood from the upper part of the ureter, anastomosing below with the ureteric tributaries of the spermatic vein. In addition, the left renal vein receives the left spermatic (ovarian) and the left middle suprarenal veins, both of which will be considered with their fellows of the opposite side. The adipose veins ramifying in the kidney fat penetrate the renal fascia and so come into connection with the tributaries of the lumbar veins, and they also send branches to the spermatic or ovarian veins. A more important communication is, however, made through a vein which arises from the lower surface of each renal and empties on the right side into the first lumbar vein, while on the left side it bifurcates, sending one branch downward to the first lumbar and the other upward to open into the hemiazygos. .Since valves occur but rarely in the renal vein, and its tributaries are likewise either without valves or with insufficient ones, the circulation of the kidney may be maintained by means of these communications of the renal veins, even in cases of obliteration of the vena cava inferior in its ui)j»er portion. Variations. — The renal veins are occasionallv replaced by from two to seven vessels which open independently into the vena cava,— a condition which probably depends upon the failure of the vessels from the different portions of the kidnevs to unite to a common stem. Accessory veins, which communicate with the vena cava below the level of the renals or even with the com- mon iliac, sometimes occur, but more rarelv than the similar arteries. The left renal vein has been observed in several cases to pass alrnost verticallv downward parallel to the vertebral column, opening into the vena cava at the level of the fourth lumbar vertebra THE INFERIOR CAVAL SYSTEM. 903 5. The Middle Suprarenal Veins. — The middle suprarenal veins (vv. suprarenales) are the principal veins of the suprarenal bodies, from which, however, the superior suprarenals, emptying into the phrenics, and the inferior, opening into the renals, also arise. Each vein occupies a groove on the anterior surface of the suprarenal body, and descends obliquely inward to open on the right sjde into the inferior vena cava above the right renal, and on the left side into the left renal. 6a. The Spermatic Veins.— The spermatic veins (vv. spermaticae) begin at the internal abdominal ring, whence they pass upward and inward along with the spermatic arteries and are the continuation upward of the venous plexuses which surround the spermatic cords. Each of these plexuses has its origin in the testicular veins (vv. testiculares) which return the blood from the tunica albuginea testis and from the seminiferous tubules, these latter branches passing towards the hilum of the organ in the trabecular They make their exit from the testis at about the middle of its superior border, and are joined very shortly by the veins of the epididymis. They are then continued up the spermatic cord in the form of from ten to twenty flexuous stems, which anastomose abundantly to form what is termed the pampiniform plexus (plexus pampiniformis), surrounding the spermatic artery. As the cord enters the inguinal canal the plexus is reduced to some three or four stems, which, at the internal abdominal ring, become the spermatic veins. These are two or three stems which anastomose abundantly with one another and consequently present a plexiform arrangement. They surround the abdominal portion of the spermatic artery and, shortly before reaching their termination, unite to a single stem, which on the right side opens at an acute angle into the vena cava inferior below the right renal vein, while on the left side it opens almost at a right angle into the lower border of the left renal vein. The spermatic veins proper possess no valves, except that there is usually a pair at the entrance of the right vein into the vena cava. In the stems of the pampiniform plexus, however, valves are usually to be found, but they are very frequently insufificient. Tributaries. — The spermatic veins receive a ureteric branch from the lower part of the ureter and also peritoneal branches and renal branches from the adipose capsule of that organ. In the scrotum the pampiniform plexus makes connections with the branches of the external pudic veins, and at their entrance into the external abdominal ring the two plexuses of opposite sides are connected by transverse anastomoses which pass in front of the symphysis pubis. A deeper transverse anastomosis also occurs between the two spermatics as they emerge from the internal abdominal rings, and they communicate by means of their peritoneal branches with the branches of the right and left colic veins. Variations. — Occasionally the left vein as well as the right opens directly into the vena cava, and in cases in which that vessel is situated upon the left side it is the left vein which opens directly into it, the right one opening into the right renal vein. They communicate sometimes on one side or the other with a lumbar vein or with the middle suprarenal, and the left vein has been observed to open into the hemiazygos. The spermatic veins are very apt to become varicose, and it is well known that this con- dition is more apt to occur in the left vein than in the right. Various reasons have been assigned for this difference in the two veins, the chief of these being ( i ) that the left vein opens at prac- tically a right angle into the renal, while the right opens at an acute angle into the vena cava ; (2) the left vein is destitute of valves at its opening into the renal, while the right one usually possesses a pair at its orifice ; and (3) that the left vein in its course up the abdominal wall lies beneath . the sigmoid colon, while the right has only coils of the small intestine with their more fluid contents in front of it. 6d. The Ovarian Veins. — The ovarian veins (vv. ovaricae) correspond to the spermatic veins of the male. They take their origin from the veins which issue at the hilum of the ovary and are also connected by wide anastomoses with the veins of the fundus of the uterus. They form a close plexus, the pam- piniform plexus (plexus pampiniformis), which accompanies the ovarian artery between the two layers of the broad ligament parallel with the Fallopian tube, receiving branches from the latter structure and from the round ligament of the 904 HUMAN ANATOMY. uterus. Leaving the broatl lii^amcnt with the o\arian artery, they ascend along that vessel, the number oi trunks becoming reduced to two and eventually to one, and they open above in the same manner as the spermatic veins, the right one into the inferior vena ca\a and the left one into the left renal vein. They possess no valves. Their variations are essentially similar to those presented by the spermatic veins. Practical Considerations. — yVw Tributaries of the Inferior Cava. — In a case of occlusion of the inferior cava by thrombus extending from the renal vein to the right auricle, the phrenic and renal \eins opened into the lumbar and azygos veins, the blood of the abdomen thus gaining the superior ca\a (Allen). The intralobular branches of the hepatic veins may be the source of profuse hemorrhage in cases of wound or rupture of the liver, because {a) they are thin- walled ; (<^) they are not encircled by cellular tissue, but are closely attached to the liver substance and thus cannot collapse or retract, a condition which also predisposes to the entrance of air into the divided veins ; ( f ) they arc vaheless, and the main trunks open direct into the vena cava, any obstruction of which would therefore result in the escape of great quantities of blood ; (d) the flow in the main trunks — from the vein to the cava — is influenced by the mo\emcnts of the diaphragm, the descent of this muscle tending to constrict the ojiening through which the veins pass, and thus to obstruct the current and favor bleeding. Hemorrhage from the liver after a wound or during an operation is \ery difficult to arrest by ligature on account of the thinness of the walls of the intralobular veins and the friability of the liver tissue itself. It is usually controlled by gauze-pressure or by the galvano-cautery. The branches of the portal vein may also bleed freely, but are surrounded by a quantity of lax cellular tissue, as they run in the ' ' portal canals' ' with the branches of the biliary ducts and of the hepatic artery, and can thus retract or collapse when torn or di\ided. More- over, the blood-pressure within the portal vein is low, favoring the spontaneous arrest of hemorrhage. In obstruction of the common duct, preventing the escape of bile into the intestine, the radicles of the hepatic veins take up the bile-stained exudate that results from the increased intra-hepatic tension. Its entrance into the general circulation through the vena ca\a gives rise to jaundice. The relative shortness of the right lenal vein occasionally adds to the difficulties of a right-sided nephrectomy, the pedicle — the vein, artery, ureter, etc. — being shorter and less easily controlled by ligature. As the Acins are subject to variation as well as the arteries — though less frequently — supernumerary or misplaced vessels should be carefully looked for. They may be found emerging from the kidney at either pole, or from the hilum behind the pelvis. Fatal results have followed the failure, during a nephrectomy, to find and secure such aberrant vessels. At times the left renal vein passes behind the aorta, to which occurrence may be attributed the greater frequency of hypenemia of the left kidney (Allen). The renal veins may be obstructed by pressure from retroperitoneal growths, or — in the supine position — from movable abdominal tumors or the gravid uterus, or from traction caused by displacements of the kidney itself, or as a result of congestion in the cardio-pulmonary system, as in pneumonia or valvular heart disease. By whatever cause produced, the congestion, if sufficiently long-continued, may give rise to a form of chronic interstitial nephritis. The communication {vide supra) between the renal veins and the first lumbar vein and — on the left side — the hemiazygos vein, accounts for the undoubted good effect often produced in renal congestions by counter- irritation, blisters, cupping, or leeching in the loin. The spermatic veins are of chief practical interest in their relation to varicocele. The anatomical reasons for the frequency of this condition, and for its occurrence by preference on the left side, are given on page 1961. The veins of the pampiniform plexus proper are usually distinct from those which accompany the vas deferens and its artery. In excision of the former set for varicocele, the vas deferens is always pushed to the rear and held out of harm's way. It carries with it its artery and veins, and the anastomotic communications of the former with the spermatic artery — almost always cut or tied with its venous plexus — and with the scrotal arteries suffice to maintain the nutrition of the testis, while the THE INFERIOR CAVAL SYSTEM. 905 veins of this smaller and posterior group enlarge to carry on the return circulation. Elevation is of especial value in testicular inflammation, as the dependent position of the spermatic veins and their lack of adequate support greatly intensify the engorge- ment and venous obstruction of inflammatory processes. The Common Iliac Veins. The common iliac veins (vv. iliacae communes) (Fig. 765) are two in number, and are formed opposite the sacro-iliac articulations by the union of the internal and external iliac veins. They pass upward, con\'erging as they go, and unite at about the level of the intervertebral disk between the fourth and fifth lumbar vertebrae to form the vena cava inferior. Since their point of union lies somewhat to the right of the median line, the right vein is shorter than the left and its course is more directly upward. Neither vein possesses valves. Relations, — The union of the two veins takes place beneath the right common iliac artery, and the right vein, at its origin, lies behind that vessel, although, since its course is more vertical than that of the artery, it gradually comes to lie somewhat lateral to it above. The left vein near its termination is crossed from without inward by the right common iliac artery, and throughout its course lies medially to the left common iliac artery and on a plane somewhat posterior to it. Variations. — Occasionally the external and internal iliac veins do not unite to form a common stem, but open directly into the inferior vena cava. This may occur on one or both sides. Tributaries. — In addition to the external and internal iliacs, by whose union they are formed, the common iliacs receive but a single tributary, the middle sacral vein (v. sacralis media), and this opens into the left vein. It accompanies the middle sacral artery, and in the lower part of its course it is frequently double, one vessel lying on each side of the artery. Opposite each sacral vertebra it receives a transverse connecting branch from the lateral sacral veins and so forms with these what is termed the anterior sacral plexus. At its origin it communicates with the hemorrhoidal veins. The Internal Iliac Vein. The internal iliac vein (v. hypogastrica) (Fig. 767) of each side is a short but rather large vessel, which accompanies the internal iliac artery, lying to its medial side and in a plane somewhat posterior to it. It extends from the neighborhood of the great sacro-sciatic foramen to the level of the sacro-iliac synchondrosis, where it unites with the external iliac to form the common iliac vein. Tributaries, — Its tributaries correspond in general with the branches of the internal iliac artery, but those which arise in the pelvic viscera present the peculiarity that they take their origin from more or less extensive plexuses which communicate with one another. The stems which pass from these plexuses to the internal iliac also anastomose to a considerable extent, the result being that it is not possible in all cases to recognize definite veins corresponding to the visceral arteries. The following are the tributaries that are, as a rule, to be recognized : ( i ) the gluteal, (2) the lateral sacral, (3) the ilio-hcmbar, (4) the sciatic, (5) the internal pudic, (6) the obturator, (7) the middle hemorrhoidal, (8) the uteri7ie, and (9) the vesical veins. I. The Gluteal Vein. — The gluteal vein (v.'gliitaea superior) accompanies the artery of the same name. Throughout its extrapelvic course its tributaries accom- pany the branches of the artery as valved venae comites, and at the upper part of the greater sacro-sciatic foramen the veins accompanying the two main branches of the artery unite to form a double trunk, united by numerous anastomoses. This trunk, which is occasionally single, passes through the greater sacro-sciatic foramen above the pyriformis muscle and, after a short intrapelvic course, opens into the internal iliac vein. Where they pass through the greater sacro-sciatic foramen both artery and vein are surrounded by a dense connective tissue which renders their separation difficult and brings it about that the lumen of the vein remains patent when emptied of blood. qo6 Hl'MAN ANATOMY. 2. The Lateral Sacral Veins. — The lateral sacral veins (vv. sacrales lateralcs) are usually double, and pass upward with their arteries upon the anterior surface of the sacrum just medial to the anterior sacral foramina, and open above either directly into the internal iliacs or into the gluteal veins. As they pass each sacral foramen they receive tributaries from the internal sjiinal plexuses, and opposite each sacral \ertelira are connecteti bv transverse branches with the middle sacral \eins, these anastomoses fiMiniii^ the auUrior sacra/ p/cxiis. -^. The Ilio-Lumbar Vein. — The ilio-lumbar \ein (v. ili(tluml)alis) follows the course of the corresponding artery and its branches and is richly supjilied with Fig. 767. . Wna c.iAM inferior Cenito-crural nerve Interr^l iliac vein Anterior superior spine of ilium Obturator nen'C External iliac artery and v=in Superior ifluteal vein Right and left common iliac arteries Left coninion iliac vein internal iliac vein -Lateral sacral vein Dorsal, vein of penis Sup. and deep layers of triangular ligament Ischio-caveniosus muscle, cut edge' Cowper's gland Bulbo.caveraosus muscle, cut edge Superior hemorrhoidal vein Lateral sacral vein — Internal pudic vein \esical veins converg- ^ iHK 'n a single tributary of internal iliac vein , 1 riliutaries of internal iliac from vesical plexus Idle htmorrhoidal vein ■L — \esico prostatic plexus Prostate Superficial anal sphincter. «ith \ennus plexus tributary to nferior hemorrhoidal veins Transverse perineal muscle Bulb of corpus spongiosum Veins of pelvis, viewed from left side. valves. Its lumbar tributary receives some of the lower intervertebral veins and occasionally the last lumbar, and anastomoses with the lower portion of the ascending lumbar vein. The iliac tributary, which begins over the crest of the ilium and in the substance of the iliacus muscle, makes anastomoses with tributaries of the deep circumflex iliac vein and thus establishes an important collateral venous path between the external and internal iliacs. The main stem of the vein is a single trunk which opens into the internal iliac or occasionallv into the common iliac. 4. The Sciatic Vein. — The sciatic vein Cv. qlutaca inferior) of either side of the body has essentially the same course as the corresponding artery. Its extrapelvic THE INFERIOR CAVAL SYSTEM. 907 tributaries are venae comites of the branches of the artery, and its usually single main stem passes through the greater sacro-sciatic foramen below the pyriformis to empty into the internal iliac. Anastomoses of comparatively large calibre occur between the extrapelvic portions of the sciatic vein and the internal circumflex and first perforating tribu- taries of the deep femoral vein, thus establishing a collateral venous path between the tributaries of the internal and external iliacs. 5. The Internal Pudic Vein. — The internal pudic vein (v. pudenda interna) is associated throughout the greater part of its course with the artery of the same name. It differs, however, somewhat in its origin, since it is not the direct continuation of the dorsal vein of the penis (or clitoris), although it communicates with that vessel by a small branch immediately below the symphysis pubis, but is rather the continuation of the veins of the corpus cavernosum which accompany the artery to that structure. It is throughout the most of its length double, anastomoses between the two stems surrounding the internal pudic artery. It has its origin between the two layers of the triangular ligament of the perineum and passes backward into the ischio-rectal fossa, lying with the artery at the side of that cavity in a canal {Alcock' s canal) formed by a splitting of the lower edge of the obturator fascia. It leaves the ischio-rectal fossa by the lesser sacro-sciatic foramen and, curving around the spine of the ischium, enters the pelvis through the lower part of the greater sacro-sciatic foramen and empties into the internal iliac. In addition to the communication with the dorsal vein of the penis (or clitoris) already mentioned, the internal pudic vein makes near its origin a connection with the pudendal plexus and, as it curves over the spine of the ischium, with the sciatic vein. It possesses several valves arranged in a rather characteristic manner. Through- out its course through the perineum it is valveless, but both its terminal portion and its communication with the pudendal plexus possess valves whose concavities look in the one case towards the internal iliac and in the other towards the plexus. Blood contained in the perineal portion of the vein may flow, therefore, either towards the internal iliac directly or to the pudendal plexus (Fenwick), and the communication with the latter cannot well be regarded as the origin of the vein, as is sometimes done. Tributaries. — In addition to ia) the vein of the corpus cavernosum (v. profunda penis vel clitoridis) already mentioned, the internal pudic vein receives numerous tributaries which cor- respond with the branches of the arter>'. Among these may be mentioned : {b) the veins of the bulb (vv. buibi urethrae), which are quite numerous and issue from the bulb of the urethra or from the bulbus vestibuli in the female, these latter vessels being quite large ; (r) the superficial peri- neal veins (vv. scrotales posteriores), which return the blood from the integument and superficial muscles of the perineum and from the posterior surface of the scrotum and the posterior portion of the labia majora, anastomosing in these structures with the tributaries of the external pudic veins; {d) the inferior hemorrhoidal veins (vv. haemorrhoidales inferiores), which traverse the ischio-rectal space from the neighborhood of the anus, where they make communications with the hemorrhoidal plexus of the rectum. 6. The Obturator Vein. — The obturator vein (v. obturatoria) accompanies the obturator artery and shares in the variations which that vessel presents (page 814). It takes its origin in the adductor muscles of the thigh, its tributaries uniting to form an internal and an external branch, which curve around the margins of the obturator foramen. ^ The vein formed by the union of these two branches passes through the opening in the upper part of the obturator membrane and passes across the lateral pelvic wall, lying immediately below the artery. It opens, as a rule, into the internal iliac vein. Its communications are somewhat extensive and important. Its external tribu- tary branch receives branches from the scrotum or labia majora and through these communicates with the external pudic veins. At its passage through the opening in the obturator membrane it receives branches from the obturator plexus, which cover both surfaces of the membrane and drain the obturator muscles, and also a branch which passes downward and inward upon the inner surface of the os pubis, frequendy communicating above with the pubic tributary of the deep epigastric vein. 9o8 HUMAN ANATOMY. Additional communications are made with the \esico-prostatic ( vesico-vaginal) plexus and the internal pudic vein, and also with the internal circumflex branch of the deep femoral antl with the sciatic. 7. The Middle Hemorrhoidal Vein. — The middle hemorrhoidal vein (v. haeraorrhoidalis media) has its origin in the hemorrhoidal plexus of the rectum, and after recei\ ins.; tril)utaries from the seminal vesicles, the prostate j^land, and the urinary bladder in the male and from the vagina in the female, opens into the internal iliac or one of its tributaries. It is a comi)arati\cly larg'e vein, and of importance in that it forms through its connection with the hemorrhoidal jilexus a coiumunication between the jxirtal and inferior caval systems of \eins. The hemorrhoidal plexus ( plexus haeiiiorrhoidalis') which surrounds the rectum is composed of two venous net-works, one of which, the internal hemonhoidal plcxns. lies in the submucosa of the rectum, while the other, \h^ external hemorrhoidal plexus, rests upon its outer surface. The internal plexus is characterized in the adult, in that portion of it which lies just above the anal opening, by the occurrence of round or elongated bunches ( gloiiiera haeniorrhoidalia) ffirmed by a number of small veins coiled together into a mass resembling somewhat a Mal])ighian glomerulus. Upon the veins which form the glomera, or upon those extending between adjacent gloniera, ampullar dilatations occur which have been regarded both as the cause and as the result of the glomera formation. Be that as it may, the internal hemorrhoidal plexus presents in the adult, slightly above the anus, a distinct band characterized by the occurrence of glomera and dilatations, and forming what is termed the annulus haemorrhoidalis. The internal plexus opens partly at the anal orifice into the branches of the inferior hemorrhoidal veins and partly, by branches which traverse the muscular coats of the rectum, into the external plexus. This has three sets of efferent veins : (i) the inferior hemorrhoidals, which open into the internal pudic ; (2) the middU' hemorrhoidals, which pass to the internal iliac or one of its branches ; and (3) the superior hemorrhoidal, which leads to the inferior mesenteric and so to the portal vein. The external plexus also communicates with the vesico-prostatic plexus in the male and the \aginal plexus in the female. 8. The Uterine Vein. — The uterine vein (v. uterina) arises opposite the external os uteri from the plexus utero-vaginalis. It is at first a double vein, its two trunks accompanying the uterine artery, and where that vessel crosses the ureter one of the trunks passes with the artery in front of the duct and the other behind it. The t\yo trunks then usually unite to a single vein, which passes into the internal iliac, frequently recei\ing the \esical veins or the obturator. The utero-vaginal plexus is formed by the veins which return the blood from the uterus and vagina. The veins in the substance of the uterus are exceedingly thin-walled, appearing as clefts in sections, and form a more or less distinct layer (stratum vasculare) in the muscular wall of the organ. From this vessels pass to both the anterior and posterior surfaces of the organ and follow a course which is outward and more or less downward towards the lateral borders, where, between the two layers of the broad ligament, they form a rich plexus, the uterine plexus, the vessels of which conxerge towards the origin of the uterine vein, opposite the external OS uteri. The vaginal veins form a rich plexus in the walls of tlie vagina, the emissaries from which are directed laterallv and more or less upward, forming along the lateral walls of the organ a rich vaginal plexus whose stems also converge to the uterine vein at the level of the external os uteri. These two plexuses, the uterine and vaginal, are continuous at the level of the external os uteri and form together the extensive plexus utero-vaginalis. At the fundus of the uterus this plexus makes abundant connections with the pampiniform plexus of the ovarian veins and with the funicular veins which accompany the ligamentum teres. Lower down, throughout its uterine portion, it receives affluents from the plexus of veins which occurs between the layers of the broad ligament, and the lower part of its vaginal portion makes connections anteriorly with the vesico-vaginal jilexus and posteriorly with the external hemorrhoidal plexus. 9. The Vesical Veins. — The vesical veins {\y. vesicales) \ary somewhat in number, but together represent a vessel of considerable size. They arise at the sides of the bladder from a well-marked plexus which occupies in the male the groove THE INFERIOR CAVAL SYSTEM. 909 between the prostate gland and the bladder and is termed the vesico-prostatic plexus. In the female the plexus lies at the sides and base of the bladder, and from its relations posteriorly is known as the vesico-vaginal plexus. From their origin the vesical veins pass upward, outward, and backward to open into the internal iliac. The vesico-prostatic or vesico-vaginal plexus (plexus vesicalis), occupying the position indicated above, is formed principally by the veins which drain the urinary bladder and, in the male, the prostate gland. Posteriorly, in the male, the plexus communicates with the external hemorrhoidal plexus, and in the female with the vaginal plexus, and anteriorly, in both sexes, it communicates extensively with the pudendal plexus. In addition to the drainage which it possesses through the vesical veins, it also drains by way of the obturator veins, branches from it joining those vessels just after they have passed through the obturator foramina. The pudendal plexus (plexus pudendalis), also known as ^^ plexus of Santo - rini, occupies the space between the lower part of the pelvic surface of the symphysis pubis and the anterior surface of the neck of the bladder, becoming continuous posteriorly at the sides with the vesico-prostatic (vesico-vaginal) plexus. Its chief tributary is the deep dorsal vein of the penis (clitoris) (v. dorsalis penis vel clitoridis), which is a single large vein (sometimes partly double in the female) which passes along the dorsal mid-line of the penis or clitoris, beneath the deep fascia (Fig. 767), in the groove between the two corpora cavernosa, and has on either side of it one of the two dorsal arteries. It receives branches from the corpora ca\^ernosa and has its origin in two veins which curve from below upward around the base of the glans penis (clitoridis). At the root of the penis (clitoris) it leaves the dorsal surface and perforates the triangular ligament of the perineum, usually just below the border of the subpubic ligament, so entering the pelvis. It then bifurcates, each of the branches passing into the pudendal plexus. Before entering the pelvis it gives off on either side a small branch which unites with the internal pudic vein, thus representing the course of the artery. In addition to the dorsal vein of the penis (clitoris), the pudendal plexus also receives branches from the internal pudic vein and from the anterior surfaces of the bladder and, in the male, the prostate. It communicates posteriorly and at the sides with the vesico-prostatic (vesico-vaginal) plexus, and through it finds its chief efferents in the \'esical veins, although it is also drained by the obturator veins, with each of which it communicates by one or two branches. The External Iliac Vein. The external iliac vein (v. iliaca externa) (Figs. 766, 767) begins at Poupart's ligament, where the femoral vein becomes continuous with it, and passes upward, backward, and inward to the level of the sacro-iliac articulation, where it unites with the internal iliac to form the common iliac. Its course is along the line of junction of the false and the true pelvis, and it lies upon the inner border of the psoas muscle and internal, or in its upper part internal and posterior, to the external iliac artery. Near its termination it is crossed b}^ the internal iliac artery, on the left side almost at a right angle, on the right more obliquely. Valves are present in about 35 veins out of 100, but in a third of such cases they are insufiicient. Tributaries. — The tributaries of the external iliac vein are : (i) the deep epi- gastric and (2) the deep circumflex iliac \'eins. I. The Deep Epigastric Vein. — The deep epigastric vein (v. epigastrica inferior) has its origin above the umbilicus in the substance of the rectus abdominis muscle, where it anastomoses with the superior epigastric vein. It accompanies the deep epigastric artery as two venae comites which unite below to form a single trunk opening into the external iliac a short distance above Poupart's ligament. Below the level of the umbilicus the vein is provided with valves whose concav- ities are directed downward, but above the umbilicus it is said to be destitute of valves. It receives tributaries from the rectus muscle and, as it passes beneath the 9IO Hl'MAN ANATOMY. internal abdominal rin^-, from the spermatic cord or round lij^i^ament of the uterus. The connections which it makes with otlier veins are numerous and imi)ortant. Its connections with the superior epigastric vein have alreadv been noted ; by this communication is established between the superior and inferior venie cavce. In addition, by means of branches which traverse the sheath of the rectus muscle, it communicates with the subcutaneous and subperitoneal veins of the abdominal wall and with the parumbilical veins, forming through these latter a connection with the portal system of veins. Finally, by means of a pubic branch, which is frequently a tributary of the external iliac rather than of the deep epigastric, it communicates with the obturator vein, and by the enlargement of this communication the obturator vein, just as is the case with the artery, may become a tributary of the deep epigastric. 2. The Deep Circumflex Iliac Vein. — The deep circumflex iliac vein (v. circuniflcxa ilium pntfunda ) has the same course as the corresponding artery, which it surrounds in a plexiform manner. It possesses valves and communicates with the iliolumbar veins. Near its termination it becomes a single trunk and opens into the external iliac a little above the deep epigastric ; occasionally it opens into the latter vessel. THK VEINS OF THE LOWER LIMB. The external iliac vein is the channel by which the blood returning from the lower limb is conveyed to the inferior vena cava and is the direct upward continuation of the femoral vein. Instead, however, of proceeding to a description of this latter vessel and so down the leg, it will be more convenient to begin the account of the veins of the lower limb with those of the foot and proceed upward to the femoral. As in the upper limb, two practically distinct sets of veins can be recognized in the leg ; one set is more or less deeply seated and accompanies the arteries, while the other is superficial and, in the adult, has a course quite independent of the arterial distribution. The deep veins will first be considered. thp: deep veins. The Deep Veins of the Foot. The deep veins of the sole of the foot have their origin in a net-work with more or less distinctly elongated meshes, which occurs upon the plantar surfaces of the digits. These are the plantar digital veins (vv. digitales plantares), and in the webs of the toes the vessels of each digit unite with those of the neighboring ones to form a series of plantar interosseous veins (vv. metatarscae plantares) occupying the metatarsal interspaces and forming vencC comites for the plantar interosseous (metacarpal) arteries. Just as the digital veins unite to form the interosseous, they send dorsal branches (vv. intercapitulares ), which unite with the dorsal interosseous veins, and. in addition, make connections with the superficial plantar veins, and might, indeed, be classed with these quite as appropriately as with the deep set. The plantar interosseous veins pass backward, receixing branches from the neighboring muscles, and open into a venous plantar arch (arcus venosus plantaris). formed by the vena comites of the arterial plantar arch. These are continued pos- teriorly into the external plantar veins, which pass obliquely across the foot along with the corresponding artery and vmite beliind the inner malleolus with the internal plantar veins to form the companion veins of the posterior tibial artery. Both plantar veins give off branches which perforate the plantar aponeurosis and communi- cate with the superficial plantar veins, and connecting vessels also pass across the sole of the foot between the two veins. Upon the dorsum of the foot there exist the dorsal digital veins (\\. diyitales dorsales ), which, like the corresponding plantar veins, may be equally classified with superficial or deep veins, since they make connections with both sets. In the webs of the toes the vessels of adjoining digits unite to form the four dorsal interosseous veins (vv. metatarseae dorsales), which occupy the metatarsal interspaces and com- municate with the corresponding plantar veins by the intercapitular and perforating THE VEINS OF THE LOWER LIMB. 9" veins. They form the vense comites of the dorsal interosseous (metatarsal) arteries and open into the companion veins of the metatarsal artery. These, together with the veins accompanying the tarsal arteries, open into the vense comites of the art. dorsalis pedis, and these in turn are continuous with the venae comites of the anterior tibial artery. The Deep Veins of the Leg. The deep veins of the leg are the vense comites of the posterior and anterior tibial arteries and their branches. The posterior tibial vein (v. tibialis posterior) is formed behind the internal malleolus by the union of the internal and external plantar veins, and consists of two, or in many cases three, veins accompanying the posterior tibial artery. It terminates at the lower border of the popliteus muscle by uniting with the anterior tibial veins to form the popliteal, and possesses in its course from eight to twenty valves. A short distance below the popliteus muscle it receives the peroneal veins (w- peroneae) which accompany the peroneal artery. They are usually of larger calibre than the posterior tibial veins, receiving a larger share of the vessels which come from the posterior crural muscles, and they anastomose with the posterior tibials by frequent transverse branches, and also with the anterior tibials. They possess from eight to ten valves. The anterior tibial veins (vv. tibiales anteriores) are the upward continuation of the venae comites of the art. dorsalis pedis. They accompany the anterior tibial artery, and are united across the artery by numerous transverse anastomoses. They pass with the artery to the posterior surface of the crus above the interosseous mem- brane and unite with the posterior tibials to form the popliteal vein. They make communications with both the peroneal and posterior tibial veins by branches which perforate the interosseous membrane, and are furnished, on the average, with about eleven valves. The Popliteal Vein. The popliteal vein (v. poplitea) (Fig. 768) is a single trunk formed by the union of the anterior and posterior tibial veins at the lower border of the popliteus muscle, and it extends from that point to the opening in the adductor magnus which transmits the femoral artery. It is throughout closely bound down by dense connective tissue to the popliteal artery, and lies between that vessel and the internal popliteal nerve. Its course, however, is not quite parallel to that of the artery, but in its lower part it is slightly internal to the artery and in its upper part somewhat external to it. The popliteal vein possesses from one to four valves and is directly continuous above with the femoral vein. In addition to the popliteal vein, the popliteal artery has two other smaller veins accompanying it. The external one (v. comitans lateralis) has its origin from the veins issuing from the outer head of the gastrocnemius and the soleus, and passes upward along the outer surface of the artery to open into the popliteal vein at about the middle of its course. The inner vena comitans (v- comitans medialis) is formed by the veins issuing from the inner head of the gastrocnemius and ascends along the inner side of the artery, making connections with the inferior and superior internal articular veins, to open into the popliteal vein just below the opening in the adductor magnus. Tributaries.— The majority of the tributaries of the popliteal vein correspond to the branches of the popliteal artery, — that is to say, they are articular and muscular. In addition it receives the short saphenous vein at about the middle of its course. Variations.— The popliteal vein may be considerably shorter tlian usual owing to the fail- ure of the tibial veins to unite at the customary level. Not infrequently the vein is double throughout a portion of its course, more rarely throughout its entire length, and it occasionally lies beneath {i.e., anterior to) the artery. It normally communicates by means of its tributaries with branches of the deep femoral vein, and occasionally this communication becomes so large that the popliteal seems to bifurcate above, one branch becoming continuous with the femoral and the other with the deep femoral. More interesting from the historical stand-point are the rare cases in which the vein '912 HUMAN ANATOMY. ascends the back of the thigh along with the sciatic nerve, either uniting above with one of the branches of the deep femoral or continuing into the pelvis with the ner\'e to become a Vu -68. Tibial nerve Semitendiiiosus muscle^ Popliteal artery Seinimeinbranosus muscle Azygos articular vein Communication with internal saphenous vein Popliteal vein External saphenous vein Sural veins Gastrocnemius muscle, iinier head Popliteus muscle Posterior tibial artery Communication between anterior and posterior tibial veins Posterior tibial veins Communication with deep femoral vein Biceps muscle Superior external articular veins Plantaris muscle Gastrocnemius, outer head Anterior tibial vein Anterior tibial artery Soleus, cut surface Gastrocnemius, cut surface Deep fascia, cut edge Veins of rio;ht popliteal space. tributary- of the interna! iliac vein. This last arrangement recalls an anomaly occasionally pre- sented by the sciatic artery ( page S15 ), and is probably due to the same embrj-ological conditions. THE VEINS OF THE LOWER LIMB. 913 The Femoral Vein. The femoral vein (v. femoralis) (Fig. 769) accompanies the femoral artery from the opening in the adductor muscle through Hunter's canal and Scarpa's triangle to its beginning at the lower border of Poupart's ligament. It is a single Fig. 769. Anterior superior spine of ilium Superficial circumflex iliac vein Sartorius, cut Femoral artery Rectus femoris, cut Femoral vein External circumflex vein Deep femoral vein Vastus externus Rectus femoris, cut Anastomotica magna vein Quadriceps extensor tendon Patella, displaced outwardly Superficial epigastric vein Poupart's ligament External pudic vein Pectineus muscle Dorsal vein of penis Internal saphenous vein Superior perforating vein Deep femoral vein Middle perforating vein Inferior perforating vein Muscular vein Femoral artery Tendon of adductor magnus Internal saphenous vein Popliteal vein Right femoral vein and its tributaries. 58 914 HUMAN ANATOMY. trunk and is the direct continuation of the popliteal vein below, and it terminates by beconiin*; continuous with the external iliac \'ein above. In its lower part it lies slightly external to the artery, but throughout the greater part of its course it rests upon the jiosterior surface of the artery and is enclosed in a common sheath with it. Above it inclines somewhat inwardly and comes to lie upon the inner surface of the artery, between it antl the femoral canal. It possesses from one to five pairs of valves, the most constant pair, present in 8i per cent, of cases, being situated in the upper 5 cm. of the vein and consequently controlling the flow from all the veins of the lower limb. Tributaries. — The tributaries of the femoral vein correspond with the branches of the femoral artery, although some of them communicate with the vein only indirectly, opening primarily into the long saphenous vein, which is itself a tributary of the femoral. Thus, the long saphenous usually receives the external pudic, superficial circumflex iliac, and superficial epigastric veins, and these will be described later with the saphenous veins. Of the remaining tributaries, (i) \\\^ deep fcDWi'al, (2) the vena: eomites, and (3) the anastotuotiea magna , the first two deserve special mention. 1. The Deep Femoral Vein.- — The deep femoral vein (v. profimda fcmoris) accomjxuiies tlie deep femoral artery, and, like it, receives as tributaries perforating veins (vv. pcrforantcs) which take their origin upon the posterior surface of the adductor muscles and anastomose with one another, with tributaries of the popliteal below and with the sciatic above. The lowest perforating vein, which represents the actual beginning of the deep femoral, has communicating with it one of the terminal branches of the short saphenous vein. The deep femoral vein also receives the internal and external circumflex veins (vv. circumflexa fcmoris medialis et lateralis ) which accompany the corresponding arteries as their veUcC comites, the internal circumflex anastomosing with the sciatic and obturator veins and so providing for a possible collateral circulation between the internal and external iliac veins. The deep femoral opens into the femoral usually about 4-5 cm. below Poupart's ligament, but not infrequently at a somewhat higher le\'el, and the circumflex veins may open directly into the femoral instead of into the deeper vein. 2. The Venae Comites. — The venae comites of the femoral artery are two or three small stems which run parallel with the artery and vein through Hunter's canal. One lies to the inner side of the artery (v. comitans medialis) and the other to the outer side (v. comitans lateralis), and when a third is present it accompanies the long saphenous ner\'e. They communicate with, or in some cases recei\e, the veins issuing from the adjacent muscles and open into the femoral vein, usually a little below the point where it receives the deep femoral vein. Variations. — The portion of the femoral vein above the entrance of the deep femoral is sometimes termed the common femoral vein and the rest of it the superficial femoral, the common femoral being formed by the union of the superficial and deep veins. Occasionally the vein lies anterior to the arter>' throughout a considerable portion of its course, and it may be double to a greater or less extent, the two veins in such cases either lying posterior to the arter>' or one on either side of it. It occasionally passes up the leg behind the adductor magnus, passing through the muscle where it is normally perforated by one of the perforating veins, this arrangement being apparently due to the enlargement of a connection with the deep femoral and of the anastomosis between the perforating veins. In such cases the femoral artery is accompanied by one or two small stems, perhaps representing the vente comites, and in those cases in which the popliteal vein passes up the back of the thigh (page 911 ) the femoral is also greatly reduced in size. THE SUPERFICIAL VEINS. The Superfici.\l Veins of the Foot. It has already been pointed out (page 910) that the dorsal and plantar digital veins may be grouped either with the superficial or deep veins of the foot, since they communicate extensively with both sets. The superficial connections of the plantar digitals are with an arcus venosus plantaris cutaneus which runs across the foot at the bases of the toes and, bending upward over the edges of the foot, communicates with the dorsal veins. Posteriorly to this arch is a subcutaneous net- work (rete venosum THE VEINS OF THE LOWER LIMB. 915 Fig. 770. Biceps Popliteal vein Short saphenous vein plantare cutaneum) which is especially close in the fatty pad beneath the heel, but more open towards the bases of the toes. This net-work makes numerous connections with the deep plantar veins, and to a great extent is drained by superficial emissaries which pass upward over the borders of the foot and open into the superficial dorsal veins. These emissaries are larger on the inner than on the outer side of the foot, and they all have a somewhat backward as well as an upward direction, those from the most posterior portions of the plexus passing directly backward and upward over the tuberosity of the heel. Anteriorly the more central portions of the net-work drain into the superficial plantar arch and communicate through this with the dorsal veins. The dorsal digital veins form by their union in pairs the common digital veins (vv- digitales communes pedis), which correspond in position to the dorsal interosseous veins, except that they are subcutaneous. Posteriorly these veins anastomose to from a more or less regular dorsal subcu- taneous arch (arcus venosus dorsalis pedis), which extends across the dorsal portions of the metatarsal bones, being convex distally and increasing in size from the outer to the inner border of the foot. Proximally to this arch there is an irregular net- work of veins (rete venosum dorsale pedis) which makes numerous connections with the deep veins and passes proximally into the net-work of the anterior surface of the crus. Towards the borders of the foot, and forming the lateral and medial boundaries of the net-work, a more or less distinct longitudinal marginal vein can be seen on each side (w. marginales lateralis et medialis), and it is into these that the superficial emissaries from the plantar net-work open from below. The internal marginal vein is somewhat larger than the external and joins the dorsal arch to form the long saphenous vein, while the external is the principal origin of the short saphenous. The Short Saphenous Vein. The short or external saphenous vein (v. saphena parva) (Fig. 770) is the superficial vein of the back of the crus. It begins behind the external malleolus at the upward continuation of the ex- ternal marginal vein of the foot. It lies at first upon the outer border of the tendo Achillis, but later takes a more median position and ascends the pos- terior surface of the leg almost in the median line. At about the middle of the leg it perforates the crural fascia and continues its upward course in the groove between the two heads of the gastrocnemius, and, entering the pop- liteal space, terminates by dividing into two branches, one of which opens into the posterior surface of the popliteal vein about on a level with the origins of the gastrocnemius, while the other passes farther upward to communicate with the beginning of the deep femoral vein. Superficial veins on dorsum of right foot and posterior surface of leg. 9i6 lir.MAN ANATOMY. The short saphenous vein possesses from nine to ten \al\es in its course up the leg. In its lower part it accompanies the external or short saphenous nerve, which lies beneath {i.e., anterior to) it, and above it accompanies a branch of the small sciatic nerve. Tributaries. — The short saphenous vein drains the outer border of the foot and the whole tif the posterior superficial portion of the crus. Near its orig^in it receives the posterior emissaries from the superficial plantar net-work, and throut^hout its course up the crus it recei\es numen^us branches from the superficial net-work of the posterior surface of that i)ortion of the leg, and through this net-work makes communications with the long saphenous vein. The terminal branch which com- municates with the deep femoral vein receives a stem known as the v fenioropoplitca, which runs downward upon the back of the thigh, superficially, receiving branches from the posterior superficial net-work of the thigh and communicating above with the sciatic and gluteal veins. Variations. — Tht- short saphenous vein occasionally o]iens into the Ions: saphenous by the enlargement of one of the anastomoses between the two veins, only a small vessel re|)resenting its communication with tiie pt)pliteai. It has been observed to continue up the thigh without or with but a small communication with the popliteal and deep femoral veins, and, entering the pelvis with the great sciatic nerve, to open into the internal iliac vein \n such cases its femoral portion probably represents the original femoral portion of the sciatic vein, and has the same significance as the prolongation of the popliteal up the thigh, of \\ hich mention has already been made (page 911). The Long S.\phenous Vein. The long or internal saphenous vein (v. saphena manna) (Fig. 771) has its origin in the junction of the inner end of the dorsal arch of the foot with the iimer marginal vein. It passes upward in front of the inner malleolus and then in the groove between the medial border of the tibia and the inner border of the gastrocne- mius muscle. As it approaches the knee-joint it bends slightly backward to pass behind the internal condyle of the femur, and then continues up the thigh in an almost direct course to the fossa ovalis, where it pierces the cribriform fascia and opens into the femoral vein. It is subcutaneous throughout its entire course and possesses from twelve to eighteen vaKes, some of which, especially in old individuals, are apt to be insufficient. Throughout its course up the crus it accompanies the long saphenous nerve, and in the thigh it lies at first along the line of the outer (anterior) edge of the sartorius, but later crosses that muscle obliquely so as to lie internal to it above. Tributaries, — At its origin the long saphenous vein receives some of the more posterior internal emissaries of the plantar net-work, and in its course up the crus it receives the blood from all those portions of the superficial crural net-work which do not communicate with the short saphenous. In the thigh it is the collecting stem for all the superficial veins, those from the posterior surface frequently uniting to form an accessory saphenous vein (\. saphena accessoria), while those from the anterior surface may form an external superficial femoral vein (Fig. 771). Throughout its entire course it makes numerous connections with the deep veins, with the anterior tibial by some five or six branches (vv. sapheno-tibiales a7iterJores^, with the posterior tibial bv usuallv three {vv. sapheno-tibiales posteriores~), and with the femoral or one of its tributaries by usually a single one. Various communications with the small saphenous also occur. In addition to these various connections, the long saphenous receives, just before its entrance into the femoral, a number of vessels which accompany some of the superficial branches of the femoral artery. They are by no means constant tributaries of the saphenous, but frequently pass through the cribriform fascia to open directly into the femoral \'ein. I. The External Pudic Veins. — The external pudic veins (w. pudendae externae) are, like the corresponding arteries, two in number, one superficial and one deep. They have their origin in the external genitals, receiving numerous veins from the anterior surface of the scrotum (vv. scrotales anteriores) or the anterior portions of the labia majora (vv. labiales anteriores). They also receive a THE VEINS OF THE LOWER LIMB. 917 Anterior superior spine of ilium Superficial epigastric vein Femoral vein External superficial femoral vein single or paired vein which runs along the dorsal surface of the penis or clitoris immediately beneath the integment (v. dorsalis penis (clitoridis) subcutanea), and at the symphysis pubis bends later- ally to join the external pudics. I* Fig. 771 2. The Superficial Cir- cumflex Iliac Vein. — The superficial circumflex iliac vein (v. circumflexa ilium superficialis) accompanies the artery of the same name, receiving subcuta- neous branches from the lower lateral portions of the abdomen and from the anterior hip region. It frequently unites with the superficial epigastric vein before opening into the saphenous. 3. The Superficial Epi- gastric Vein, — The superficial epigastric vein (v. epigastrica superficialis) takes its origin from the subcutaneous veins of the lower part of the anterior abdom- inal wall as high as a little abo\'e the umbilicus. It is joined at a varying level by the thoraco- epigastric vein (Fig. 775), which opens above into the axillary vein, and is occasionally pro- longed downward to open independently into the long saphenous. Variations. — The long saphe- nous vein may perforate the fascia lata some distance below the fossa ovalis. It is not infrequently replaced in the crural portion of its course by a net-work of veins in which no special main stem can be recognized, and in the thigh it is occasionally double. Practical Considerations. — The Iliac Veins and THE Veins of the Lower Extremity. The common iliac veins illustrate the rule (Owen) that below the diaphragm the veins of the trunk are on a plane posterior to the arteries (except the renal) and incline generally to the venous — the right — side. Thus the left common iliac is always on the inner (right) side of the corresponding artery and ulti- mately crosses the right artery, on a posterior plane. The right vein begins slightly to the inner side of the right artery, Avhich it crosses — on a posterior plane — to reach the right side of the fifth lumbar vertebra. These relations are important in operations on the common iliac arteries (page 808). Dorsal venous arch Superficial veins of Inner malleolus right lower limb; internal aspect. 9i8 HUMAN ANATOMY. The internal iliac veins may become involved in infections of any of the numerous plexuses from uhicli their tributaries arise. Thus, puerperal metritis may not only lead to pelvic cellulitis (pas^e 2014), but may set up a thrombo-phlebitis in the intra-uterine veins which, sjMeading to the internal and common iliac veins, will obstruct the \enous current from the whole lower extremity, brinyinj:;^ about a \vide-sj)read ttdema, with aching and tenderness ( ])hlegmasia alba dolens, milk leg). Similar conditions sometimes follow septic infection of the prostatic vesical and hemorrhoidal plexuses. The practical relations of these venous channels have been described in connection with the prostate, bladder, and rectum. The branches of the internal iliac vein aid indirectly in supporting the pcKic viscera. They are apt to be varicose in the aged, especially in females. They supply the blood in cases of j)elvic ha-matocele. The external iliac vein is frequently involved in femoral phlebitis, the continuitv of direction and calibre between it and the femoral being practically unbroken. The femoral vein is not infrequently the subject of thrombo-phlebitis, descend- ing, as a result of some form of pelvic infection {vide supra), or ascending, following septic infection of the soft parts or bones of the lower extremity ; or occasionally directly caused by contusion of the vessel just below the groin, or by its bruising during forced flexion of the thigh. Femoral phlebitis is not uncommonly a sequel of enteric fever and of other exhausting diseases, and is a familiar post-operative complication of operations for the remo\ al of the appendix, the uterus, the tubes and ovaries, and other abdomino-pelvic procedures, e\'en when apparently unattended by infection. The predisposing causes are thought to be the relative immobility of the patient and the consequent sluggishness of the circulation, especially in the lower extremities, the dependent position of the limb in bed, and the altered constitution of the blood (in the case of fever) ; the exciting cause is probably a very slight degree of infection. Pain and oedema follow, but such cases almost always do well. On account of its nearness to the artery, both vessels are often wounded at the same time, with the resulting formation — if the communication between them is direct — of an aneurismal vari.x ; or if it is indirect — an aneurismal sac intervening — of a varicose aneurism. Wounds requiring ligation and sudden occlusion of the vein from any cause are dangerous from the risk of development of moist gangrene. Lateral suture of wounds in this vein has been successfully employed in a number of instances. The femoral vein is not infrequently involved in ulcerative malignant or phagedenic processes implicating the skin of the groin and upper thigh, or the inguinal lymphatic nodes. After ligation, the collateral circulation is established between the veins of the buttocks and the internal circumflex veins, and between the veins of the pelvis and the external piiHic veins. The practical relations of the femoral vein to femoral hernia have been described (page 1773). The popliteal vein, together with the artery (which is closer to the bone, and therefore more easily compressed or torn), has been lacerated in supracondyloid fracture of the femur. It has been so compressed by a popliteal aneurism as to cause thrombosis and enormous distention of the veins and of the leg. Owing to the unyielding character of the boundaries of the ham, it may also be sufiftciently com- pressed by inflammatory exudates, by abscess, or by enlarged bursee, to cause swelling and oedema of the foot and leg. The vein is so exceptionally thick-walled that in spite of its more superficial position it is never ruptured alone, but only when the force is sulilicient to tear the artery also. The involvement of both may be favored by the fact that the two vessels are so closely united that it is difficult to separate them, and this also fa\ors the occasional production of aneurismal varix or varicose aneurism after stab-wounds. This close connection makes the denudation of the artery difficult in the operation for its ligation. The veins of the leg are, with the possible exception of the veins of the pampiniform and hemorrhoidal plexuses, more often the subject of varicosity than any other veins of the body. This is due to (i) the high blood-pressure in these veins, resulting from (a) the erect posture of the human species and the consequent THE PORTAL SYSTEM. 919 vertical position of these veins ; {b) the length of the column of blood they carry, extending, in the case of the long saphenous vein, from its beginning at the ankle to the upper orifice of the inferior vena cava ; (c-) in many cases to compression above, as from abdominal or pelvic growths, or the gravid uterus, or from garters. (2) In the superficial veins the frequency of varicosity is also due to the lack of adequate external support to their thin and distensible walls, the saphenous veins, for example, lying outside of the deep fascia in loose connective tissue. (3) To the increased resistance that must be overcome at the points where the deep and superficial vessels communicate, and where in many cases the varicosity seems to begin. At such points the upward current of blood has to overcome — and the walls of the veins to support — not only the downward pressure of the vertical column of blood in the vessels above it, but also the resistance of the blood-stream driven out of the deep vein by the contracting muscles between which it lies, and entering the superficial vein at a right angle. The valve next below this point of entrance prevents the relief that might be obtained from temporary distention of a long lower section of the vein and limits these forces to a circumscribed area, which yields and becomes varicose. The venous plexus between the two layers of the muscles of the calf is often the seat of varices of great size. The six chief veins which pass from the soleus muscle alone to enter into the posterior tibial and peroneal trunks have a united diameter of not less than one inch (Treves). The fact that each of the saphenous veins is accompanied by a sensory nerve accounts for the aches and pains associated with varicosity. THE PORTAL SYSTEM. The portal system is composed of all the veins which have their origin in the walls of the digestive tract below the diaphragm (with the exception of those of the lower part of the rectum) and includes also the veins which return the blood from the pancreas, spleen, and gall-bladder. It presents a marked peculiarity in that the system begins and ends in capillaries, the blood which it contains having entered its constituent veins from the capillaries of the intestine, stomach, and the other organs mentioned above, and passing thence to the liver, where it traverses another set of capillaries, by which it reaches the hepatic veins and so the heart. Coming as it does principally from the intestine, the portal blood is more or less laden with nutritive material, which has been digested and absorbed through the intestinal walls, but is not yet in a condition, so far as some of its constituents are concerned, suitable for assimilation by the tissues. To undergo the changes necessary for its conversion into assimilable material it is carried by the portal vein to the liver, and as it passes through the capillaries of that organ it undergoes the necessary modifications. In other words, the portal vein stands in a somewhat similar relation to the liver that the pulmonary vein does to the lungs. Its purpose is not to convey material to the organ for its nutrition, that being accomplished by the hepatic arteries for the liver just as it is accomplished by the bronchial arteries for the lungs, but to carry to the liver crude material upon which the organ may act, elaborating it and returning it, as required, to the circulation in a purified and assimilable condition. The inclusion of the veins of the spleen, gall-bladder, and pancreas, or even of those of the rectum, in the portal system is to be explained on the ground of topo- graphic relationship rather than on the basis indicated above. The main stem of the portal system will first be described and then its tributaries in succession. The Portal Vein. The portal vein (v. portae) (Figs. 772, 774) is formed behind the head of the pancreas by the union of the superior mesenteric and splenic veins, the latter receiving the inferior mesenteric vein shortly before its union with the superior mesenteric. The two veins unite almost at a right angle, and from their point of union the portal vein passes obliquely upward and to the right, along the free edge of the lesser omentum, towards the transverse fissure of the liver. There it divides into two trunks, of which the right is the larger and shorter and quickly bifurcates into an anterior and a posterior branch. It is distributed to the whole of the right 9^0 HUMAN ANATOMY. lobe of the liver and to the greater part of the Si)i^clian and quadrate lobes, the remainder of these lobes and the left lobe receiviny^ branches from the left trunk. The trunks of the vein or their branches enter the substance of the liver and di\ide in a more or less distinctly dichotomous manner to form interlobtdar veins, which, as their name indicates, occupy a position between the lobules of the organ, antl give off capillaries which traverse the lobule and emi)ty into the intralobular veins, the origins of the hej)atic veins. The jKirtal vein measures about 8 cm. (3^ in. ) in kngth and has a diameter of from 1.5 to 2 cm. Its walls, especially in its uj^per portion, contain a considerable quantitv of muscle-tissue and it is destitute of valves. Relations. — At its origin the portal vein lies behind the head of the pancreas and to the left of the vena cava inferior. As it ascends it comes to lie at first behind Fig. 772. Round lieanient of liver Common bile-tlimt Pyloric Superior mesenteric Right gastro-epiploic vei Tributaries of middle coli S])i^elian lobe of li\er Inferior vena cava Right crus of diaphragm Hepatic artery Spleen Inferior mesenteric vein Left gastro-epiploic vein Pancreas Portal vein and its tributaries: liver has been pulled upward. the first portion of the duodenum and then between the two layers of the lesser omentum. In this latter portion of its course it is associated with the hepatic artery and the common bile-duct, both of which lie anterior to it, the artery to the left and the duct to the right. It enters the transverse fissure towards its right extremity, hence the shortness of the right trunk compared with the left, and its trunks have in front of them the branches of the hepatic artery, the hepatic ducts lying anterior to these. Tributaries. — The tributaries of the portal vein are : (i) the snpe?'ior mesen- teric, (2) the splenic, (3) the inferioi- mesenteric, (4) the j^astric, (5) the py/oric, and (6) the cystic veins. In addition to these principal tributaries, the portal vein, or its branches within the liver, also receives a number of small veins which have their origin in the falciform ligament of the liver and in the lesser omentum, and, further- more, it receives at the transverse fissure (7) soma pa nun bi/ical vei7is which ascend the anterior abdominal wall along with the round ligament. THE PORTAL SYSTEM. 921 I. The Superior Mesenteric Vein, — The superior mesenteric vein (v. mesen- terica superior) (Fig. 773) accompanies the artery of the same name, lying upon its right side. It has its beginning somewhere in the neighborhood of the terminal portion of the ileum and ascends in the line of attachment of the mesentery. Above, it passes over the third portion of the duodenum and then between that portion of the intestine and the lower border of the pancreas, uniting behind the head of the pancreas with the splenic vein to form the portal vein. It possesses no valves. Tributaries. — The tributaries of the superior mesenteric vein correspond with the branches of the corresponding artery, except that it receives in addition the pancreatico-duodenal and right gastro-epiploic veins which accompany the similarly named branches of the hepatic artery. {a) The veins of the small intestine (vv. intestinales) have their origin in the walls of the small intestine from the last portion of the duodenum to within a short distance of the ileo-caecal valve. Their arrangement is essentially similar to that of the arteries of the small intestine, the numerous small branches which emerge from the intestine being united by transverse anasto- moses, as a rule more numerous than those of the arteries, and forming one or more series of venous arcades lying between the two layers of the mesentery. From these arcades branches arise which pass towards the superior mesenteric vein, gradually uniting to form about twenty stems which open independently into the superior mesenteric. The branches of origin of the intestinal veins, just after they emerge from the intestine are provided with valves in the child, but they usually degenerate more or less completely before adult life. [d) The ileo-colic vein (v. ileocolica) arises at the junction of the ileum and caecum by the union of a caecal and an ileal branch, the latter of which anastomoses with the origin of the superior mesenteric. The csecal branch receives an appendicular vein from the appendix vermi- formis, and the main stem passes upward between the two layers of the mesentery' to open into the superior mesenteric just before it passes over the duodenum. {c) The right colic veins (vv. colicae dextrae) originate in the walls of the ascending colon and are two or three in number. They anastomose by transverse branches with the ileo-colic and middle colic veins and pass almost horizontally medially to open into the superior mesenteric. {d) The middle colic vein (v. colica media) emerges from the transverse colon by a number of small branches which anastomose to the right and left with the right and left colic veins, and unite to a single stem which opens into the superior mesenteric just before it passes beneath the pancreas. (e) The right gastro-epiploic vein (v. gastroepiploica dextra) runs from left to right along the greater curvature of the stomach, communicating directly with the left gastro-epiploic at about the middle of the curvature. It receives tributaries from the lower portions of the anterior and posterior surfaces of the stomach and from the greater omentum, and opens into the superior mesenteric shortly before its union with the splenic. It occasionally receives a pancreatico-duodenal vein, and may unite with the middle colic vein to form a gastro-colic vein instead of opening directly into the superior mesenteric. (y") The pancreatico-duodenal veins (vv. pancreaticoduodenales), like the arteries, may be two in number, one of which opens directly into the superior mesenteric and the other into the right gastro-epiploic. Frequently, however, they are broken up into a number of separate vessels arising independently from each of the two viscera concerned, the duodenum (vv. duodenales) and the head of the pancreas (vv. pancreaticae). 2. The Splenic Vein, — The splenic vein (v. lienalis) (Fig. 774) is formed by the union of five or six branches which emerge from the hilum of the spleen. It passes almost horizontally to the right below the splenic artery, resting at first upon the upper border of the pancreas, but later coming to lie behind that organ. Behind the head of the pancreas it unites with the superior mesenteric to form the portal vein. Tributaries. — These correspond with the branches of the artery, and in addition it receives near its termination the inferior mesenteric vein, which for purposes of description will, however, be regarded as independent. (a) The short gastric veins (vv. gastricae breves) arise from the fundus of the stomach and pass between the layers of the gastro-splenic omentum to open partly into the splenic vein and partly into its branches of origin as they emerge from the hilum. {d) The left gastro-epiploic vein (v. gastroepiploica sinistra) passes from right to left along the greater curvature of the stomach, communicating directly with the right gastro-epiploic about half-way along the curvature. It receives branches from the lower portions of both surfaces of the stomach and from the greater omentum, and opens into the splenic vein near its formation. (r) The pancreatic veins (va'. pancreaticae), which maybe five or more in number, open into the splenic vein at various points in its passage behind the pancreas. 922 UIMAN ANATOMY. 1,. The Inferior Mesenteric Vein. — The inferior mesenteric vein (v. mesen- terica^ inferior) ( Fig. 774 J is formed by the junction of the superior hemorrhoidal and siijmoiil veins t)pposite the siiL^inoid flexure of the colon, and passes upward in comjiany with the corresponding artery. It is continued on, however, beyond the point where the artery arises from the abdominal aorta, lying behind the peritoneum slightly medial to the ascending colon, and, finally, it passes beneath the pancreas Fig. Ascending; colon Middle colic vein Right colic vein Superior mesenteric vein Ileo-colic vein Transverse colon Descending colon Left colic vein Pancreas Inferior mesenteric vein Superior mesenteric artery Duodenum, transverse iiart Jejunum Veins of the small intestine Coils of ileum Superior inesenteric vein and its tributaries; transverse colon has been pulled upward. to open usually into the splenic vein not far from its union with the superior mesenteric. Occasionally it opens into the latter vein (Fig. 774) or else equally into both, thus taking a direct part in the formation of the portal vein. Tributaries.^Its tributaries correspond to the branches of the artery. {a) The superior hemorrhoidal vein (v. haemorrhoidalis superior) has its origin from the upper part of the hemorrhoidal plexus by several branches, and, passing upward, unites with the sigmoid veins to form the inferior mesenteric. Through the hemorrhoidal i^lexus it communi- cates with the middle and inferior hemorrhoidal veins, thus placing the porta! and inferior cava! systems in communication. {b) The sigmoid veins (vv. sigmoideae) are variable in number and pass from the sigmoid flexure and the lower portion of the descending colon to the inferior mesenteric, the lowest one uniting with the superior hemorrhoidal to form that vein. THE PORTAL SYSTEM. 923 {c) The left colic vein (v. colica sinistra) has its origin in the walls of the descending colon, anastomosing above with the middle coHc and below with the sigmoid veins. It passes medially to open into the upper part of the inferior mesenteric. 4. The Gastric Vein. — The gastric vein (v. coronaria ventriculi) (Fig. 772) accompanies the gastric artery along the lesser curvature of the stomach. It has its origin at the pyloric end of the stomach, where it anastomoses with the pyloric vein, and passes at first from right to left along the lesser curvature, receiving tributaries from the upper part of both surfaces of the stomach. At the opening of the oesophagus into the stomach it makes connections with the oesophageal veins, and then bends upon itself and passes from left to right behind the posterior wall of the lesser sac of the peritoneum, and terminates either in the portal vein or in the splenic shortly before its union with the superior mesenteric. The peculiar reflected course of the gastric vein is readily understood if it be remembered that the adult position of the stomach is a secondary one. When first formed the long axis of the stomach is practically vertical, the pyloric end being directed downward, and a vein starting at the pylorus will have a direct ascending course to the portal vein. When the stomach as- sumes its adult position the course of the vein with reference to the viscus does not alter, and consequently it passes from pylorus to cardia, and must then bend back upon itself to reach the portal vein. 5. The Pyloric Vein. — The pyloric vein (v. pylorica) (Fig. 772) accompanies the pyloric branch of the hepatic artery. It takes its origin at the pyloric end of the stomach, where it anastomoses with the gastric vein, and passes downward to open into the portal. 6. The Cystic Vein. — The cystic vein (v. cystica) (Fig. 772) returns the blood from the walls of the gall-bladder and opens usually into the right trunk of the portal vein. It is frequently represented by two separate stems. 7. The Parumbilical Veins. — The parumbilical veins (vv. parumbilicales) are a number of small veins which have their origin in the anterior abdominal wall in the neighborhood of the umbilicus and pass upward in the fold of peritoneum which contains the round ligament of the liver. They anastomose below with both the superficial and deep epigastric veins and also with small vessels which pass down- ward alongside of the urachus to empty into the vesical plexus. Above, the majority of them enter the quadrate and left lobes of the liver, but one of them, the vena supraumbilicalis, enters the substance of the round ligament at a varying level and opens into the more or less extensive lumen of that structure, which represents the umbilical vein of foetal life. This lumen appears to persist in the majority of cases, although greatly reduced in size from that of the umbilical vein, and may extend throughout almost the entire length of the round ligament, although perhaps, more usually, it is limited to its upper part, and opens into the right trunk of the portal vein. When the lumen is entirely obliterated it is possible that the supraumbilical vein, which has also been termed the accessory portal vein, may open directly into the portal vein. Collateral Circulation of the Portal Vein. — Considering the fact that the portal vein terminates in capillaries in the substance of the liver, it is evident that certain pathological conditions, such as cirrhotic changes, which may occur in that organ, will more or less completely interfere with the return of the blood to the heart from the intestine, spleen, and pancreas, by producing an obliteration of the capillaries. The possibilities of a collateral circulation are therefore important, and a number of routes occur by which, under stress, the blood of the portal venous system may pass around the liver and reach the heart through one of the other systems. The functional capabilities of these various routes are furthered by the fact that none of the tributaries of the portal vein possess valves except in their finer branches, and the blood can therefore flow in them in a reverse direction if necessary. The principal collateral routes are as follows : 1. Through the gastric vein the blood may pass to the oesophageal veins and thence to the azygos and hemiazygos veins. When this route is functional the oesophageal veins become enlarged and frequently varicose, forming contorted elevations upon the surface of the oesophagus. 2. Through the superior hemorrhoidal veins connections are made by way of the hemor- rhoidal plexus with the hemorrhoidal branches of the internal iliac. These connections seem, however, to be less frequently functional than either the cardiac or parumbilical routes. 924 Hl'MAX ANATOMY. 3. Through the innbilical and siipraiaiihi/iiai veins to llie superficial or deep epigastrics and so to the external iliac veins. It is interesting to note that in cases where this route is lunctiona'. the enlargement of the superficial epigastric veuis is usually accompanied by a de\eK)pment ot varicosities upon them, while this is not the case with the tieep ei)igastrics. An e.\i>lanation of this dilTerence has been found in the fact that the deep veins, before opening into the external iliac, bend slightly backward, so that their orifices are directed in the same way as the flow of blood in the larger stem, whereas the superficial epigastrics open from above into the long saphenoiis veins, their orifices being opposed, therefore, to the How of blood in the saphenous, —a condition which naturally predisposes towards stasis of the bkuxl in the epigastrics and, it may be remarked, also of that in the saphenous. These are the principal routes, but it must be noted that anastomoses also exist between the portal system and the phrenic veins ])y means of the small veins which descend towards the Fig. 774. l.ivcr. undfr surface Si'igelian lobe of liver diaphragn Round ligament Vena cava inferior Portal vein Pyloric vein Cystic -duct Coeliac axis Gall-bladder Gastro-duodenal vein Common bile-duct Renal vein Sui)erior mesenteric \ein Superior mesenteric artery Ascending colon- Gastric vein xliich typically lasses farther to lit- rixht to open nt.. the portal Kidney Splenic artery I-eft gastro- epiploic vein Splenic vein Renal vein ling colon esenteric vein ic vein spermatic vein Inferior mesenteric artery Superior hemorrhoidal vein Termination of ileum Cut edge of Cavity 01 pelvis mesentery Inferior mesenteric and splenic veins and tributaries of portal vein ; stomach and transverse colon have been removed and liver pulled upward. liver in the falciform ligament, and communications with the inferior caval svstem also occur by means of retroperitoneal anastomoses between the peritoneal and mesenteric veins, both of which are quite small. These communications are known as the veitis of Retzius. Finally, it may be mentioned that anomalous and therefore inconstant communications of the portal branches with those of other systems have been observed. Thus the gastric, the short gastrics, or the pyloric vein may anastomose with the phrenics; the splenic or the left gastro-epiploic with the renals ; the right or left colic with the branches from the fatty capsule of the corresponding kidney ; and the duodenal branches may open into the inferior'vena cava. THE PORTAL SYSTEM. 925 Practical Considerations. — The portal system may be obstructed by (a) tumors or swellings involving the liver itself, as carcinoma, hydatids, or abscess ; [d) enlargement of the gall-bladder from new growth or from concretions ; (c) tumors of contiguous structures, as disease of lymph-nodes in the portal fissure or between the layers of the lesser omentum, or carcinoma of the head of the pancreas ; (d) disease of the liver tissue, especially cirrhosis (chronic interstitial hepatitis) in which the interlobular veins are compressed by the contraction of the connective Fig. 775. External jugular vein External jug;ular vein Cephalic vein Axillary artery Axiliarj \ein III., IV., and V anterior perforating veins and tributary of musculo • phrenic vein- Tributaries of superior epigastric vein Tributary of deep epigastric veia- Thoraco- epigastric vein Superficial circumflex iliac veini Saphenous opening Femoral vein Internal saphenous vein Circumflex \ei: Substapular \em \., VI.. and VII. intercostal vein Tributary of musculo-phrenic vein Thoraco-epigastric vein Tributary of deep epigastric vein Superficial epigastric vein Femoral vein Deep dorsal vein of penis Superficial dorsal vein of penis —Internal saphenous vein Superficial veins of anterior body-wall ; pectorahs and external intercostal muscles (of fifth to seventh intercostal spaces) on left side have been removed. tissue in the spaces between the lobules ; (e) valvular disease of the heart leading to backward pressure through the cava and hepatic and intralobular veins which finally reaches the terminal capillaries of the portal vein and then the interlobular veins and the entire portal system, resulting in some cases in the so-called nutmeg liver (cyanotic atrophy). The consequences of portal obstruction are various, but may, as a rule, easily be understood by referring each symptom to its anatomical basis in 926 HUMAN ANATOMY. obstruction of one or the other of the venous tributaries. The chief results are : (i) Enhirgement of the hver itself, at first congestive, later from hyperplasia. Diminution in the quantity of bile or alteration in its character may cause constipa- tion and indigestion ; or escape of its coloring matter and its absorption by the hepatic veins may give rise to jaundice. (2) From congestion of the gastric and intestinal mucosa (through the superior and inferior mesenteric, splenic, and gastric tributaries) there may develop indigestion, flatulence, eructations, and vomiting, often bloody ; serous e.xudation into the bowel — intestinal indigestion, and diarrhoea, some- times with black stools from decomposed blood — or into the general peritoneal cavity — ascites ; enlargement and tenderness of the spleen ; hemorrhoids (from the communication between the middle and inferior, hemorrhoidal veins— systemic — and the sujjerior hemorrhoidal \ein — portal) ; varicosities in the lower extremities, possibly from the same communication between the caval and portal systems, but oftener from the direct interference by an enlarged liver with the current in the inferior cava. Septic inflammation of the liver may reach that organ through any of the portal tributaries. It is not uncommonly the result of infection originating during a dysen- teric attack. Cancer may also reach the liver by venous channels, usually by the gastric or hemorrhoidal tributaries. As the number of e.xtraperitoneal anastomoses between the branches of the parietal vessels (lower intercostal, phrenic, lumbar, ilio-lumbar, epigastric and circum- flex iliac) and branches of vessels that supply viscera without a complete peritoneal covering (liver, kidneys, suprarenals, duodenum, pancreas, ascending and descending colon) are of great importance in case of obstruction to the visceral arterial supply, so the corresponding venous anastomoses are of equal or greater imi:)ortance in obstruction of the portal vein or of the inferior cava. The occasional connection between a parumbilical vein and the external iliacs — through the epigastrics — may also relieve portal obstruction. The above anastomoses explain the effect of leeches or wet cups or counter-irritation of the surface in congestions or inflammations of the partly extraperitoneal viscera. (Woolsey.) Fig. DEVELOPMENT OF THE VEINS. The embr>'onic venous system may be regarded as consisting of three sets of vessels. One of these becomes the pulmonary 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 whichl extend the entire length of the body, one on either side of the median line, receiving throughout] their course lateral somatic and visceral branches! in more or less perfect segmental succession. I 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 primitive jugular, while! that behind it is known as \\\& 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 Cinder. The anterior cardinals take their origin! from veins which ramify over the surface of thej brain and receive at first both the ophthalmic andJ 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-j cranial portions becoming the cavernous andj inferior petrosal sinuses. The facial veins, how- ever, sever their connection with the cerebral] veins and unite with other superficial veins tc form the external jugular — a vessel which ir some mammalia reaches a high degree of devel-^ opment. almost or entirely replacing the internal jugular, which represents the main steni| of the cardinal. In man the original condition, in which the external jugular is of subordinate — Anterior cardinal 'enous sinus of heart Duct of Cuvier Vitelline vein Umbilical vein Posterior cardinal Diagram showing primary symmetrical arrangement of venous svstem. 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 jugular opens independently into the right auricle through the corresponding duct of Cuvier (Fig. 777, yj) , but later a communicating branch extending obliquely across from the left to the right vein is developed (Fig. 777, B), and thereafter the Anterior cardinal (internal jugular) Cuvierian duct Primary inf. Posterior cardinal Internal jugular External jugular Subclavian ■Left innominate Oblique vein of left auricle Coronary sinus Inferior vena cava Diagrams illustrating development of superior vena cava; v4, primary symmeirical arrangement ; .S, 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 Internal jugular (ant. cardinal) Duct of Cuvier Posterior cardinal- Inf. vena cava Azygos Coronary sinus Hemiazygos Inferior vena cava 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 body a venous stem which has a course parallel to that of the cardinals, with which it unites below ( Fig. 778, ^). This is the subcardinal 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. those of the renal veins. The portion of the right suljcardinal which lies anterior to the cross- branch tiien 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 conu- into line with one another and with the terminal portion of the ductus venosus to form the inferior vena cava. The lower portions of botii subcardmals now degenerate, and the ujiper portion of the left vein, diminishing in size, becomes the left suprarenal vein. A cross-branch forms between the two posterior cardinals at the level of the common iliac veins, and the lower part of the left cardinal then disappears (Fig. 778, 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 Vems. — 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 interco.stal veins and terminating above in the ductus Cuvieri. They now constitute the azygos veins, and, on the degeneration of the lower part of the left Fig. 779. DC dv DC anterior cardinal, the left azygos develops connection with the right by one or two transverse branches and then separates from the coronary sinus, the adult condi- tion of the hemiazygos vein being thus acquired. The Portal Vein. — Passing aUjng the umbilical cord to the body of the embryo are two vitelline or o))ipha/o-viesefiteric veins, which have 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 pasi 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 ; above, 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-w ork a well-marked venous stem is formed, e.xtending from the f)oint 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 venosus (Figs. 779, B 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 {!)). In 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 (77), 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 venosus and thence lay the inferior vena cava to tne heart and partlv through the hepatic net-work by way of the communication between the left umbilical and vitelline veins. At birth the placental supply of blood is of course cut of?, the ductus \ tt-" Diagrams illustrating transformations of vitelline and umbilical veins during development of liver-veins. DC, ducts of Cuvier; h, heart; rii. In. rigfit and left umbilical veins; rv, /z/, ri^iit and left vitelline veins; rfz/, ductus venosus ; pv. portal vein. (Hochsteiter.) k 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 also 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 first 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 veins open independently into the auricle. THE FCETAL CIRCULATION. The primary or vitelline circulation of the mammalian embryo, formed by the ramifications of the viteUine 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 example 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 foetus with the placenta — the organ whereby respiration and nutrition are secured to the foetus 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 foetal 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 umbilical 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 afiorded by the development of a short vessel, the ductus venosus, or ductus Arantii, that extends from the portal vein to the inferior vena cava and thus establishes a by-pass for the greater part of the oxygenated 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 cui'rent 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 '59 930 HUMAN ANATOMY. the j)ulnionary artery and towards the lungs. Being uninflated these organs can ajipntpriate only a small i)art of the entire v(jlume of blood brought by the pulmonary artery, hence the necessity of a second by-pass, the ductus arteriosus, or ductus Bolal/i, that extends from the beginning of the ktt pulmonary artery to the adjacent aorta and represents the still pervious distal portion of the last aortic arch on the left side (page 847). By means Fig. 780. of the ductus arteriosus, the venous blood returned from the head and ui)per 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 vessels — 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 fcttal 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 venous returning from the lower half of the body. It is further exident that the blood distributed to the head and upper extremities is less contaminated than that ])assing 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 foetal 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). Diagram of foetal circulation shortly before birth : courseof blood is indicated byarrows. P, placenta; UA, L'\'. umbilical arteries and vein; U, umbilicus; L)\', ductus venosus ; IVC, inferior vena cava ; P\\ portal vein; HV, hepatic veins; RV, LV, right and left ventricle; PA, pulmonary artery; DA, ductus arteri- osus ; SVC. sujjerior vena cava ; AA, abdominal aorta ; HA, hypogastric arteries (internal iliac); EIA, ex- ternal iliac arteries ; I, intestine; 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 lymphs usually colorless, and containing numerous corpuscles known as lymphocytes. Since the latter usually come under observation 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 they take their origin embryologically and into which they finally pour their contents in 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 t^e 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 7iodes 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 Avhich 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 connective 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. 78 I. alve Perivascular lymph-space Lymph-space Lymph-vessel Deeply stained jjround substance Portion of central tendon of rabbit's diaphragm, treated with siiver nitrate; lymphatic vessels are shown as light irregular tracts; lymph-spaces are seen within stained ground substance. X 120. spaces occupied by the aqueous and \itreous 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. -; m the ear have been regarded as lymph-spaces, as is indicated by their names. 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 have 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- portant 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 Lymph- Perivascular lymph-spaces surrounding retinal blood-vessels. X 230. THE LYMPHATIC SYSTEM. 933 Lymphatic capillary net-works within connective-tissue layer of skin ; smaller vessels belong to superficial net-work, larger to deeper. {Teichmann.*) 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. 783), 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 F^g. 783. 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 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 sjudoriparous gland. * Das Saugadersystem. Leipzig, 1861. < Lymph-cells Transverse section of small lymph-vessel. X 210. 934 HUMAN ANATOMY Fig The mucous membranes have essentially the same arrangement, the net-work with- in tlic small intestine, for instance, beinu: arranged in two more or less distinct layers, one i)f 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 connecti\e-tissue in\estmcnt, 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 massi\e organs, such as the li\'er 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 different 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 subcla\ian \cins, 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 stipcTficial set of lymphatic vessels (vasa lymphatica superlicialia), 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, howexer, 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 vessels 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 by experiment and by the observation 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 area drained by right lymphatic duct; lym- phatics of remaining territory received bv 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 right, 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 pelvic 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 openino- 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. 785). 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 calibre 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 ; (<^) the ?nedia, 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 involuntary 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 flatt^ed nodules (Fig. 796) of varying size, some- times singly but more Fig. 786. frequently in chains or groups ( plexus lym- phatici) of from three to six or even ten to fifteen. These are the lymphatic nodes (lym- phoglandulae). As it approaches a node, a lymph - vessel divides into a number of stems, the vasa affere?itia, 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 vasa 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 lymphocytes. Moreover, since these possess a phagocytic function, in cases of infection of any part of the body the nodes along the lymph-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 Medullary cords Efferent lymphatics emerginer from hilum Lymph-sinus Capsule Cortical follicle Afferent lymphatics Lymph-sinus Diagram illustrating architecture of Ij'mph-node. 936 HUiMAN ANATOMY. foci for its distribution to other parts of the system. The nodes therefore, serving as traps for the infective material, possess a hig^h decree of imjiortance from the snri^Mcal 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 \arious regions of the body, especially in the prevertebral regions of the abdomen, structures which resemble lymi)h-n(>des 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 the 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 have been termed the hemolymph nodes, but their exact nature and function have not yet been dehnitely ascertained. By some they are regarded as sjiccial 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 e.xist. Whether or not direct communication exists between the cortical blood-vessels and the medullary lymphatics within these hemolymph nodes is also a question concerning which differences of opinion exist. Structure of Lymphoid Tissue. — Wherever found, whether as diffuse masses, simple nodules, or as the larger and more complex lymph-nodes, lymj^hoid or adenoid I tissue is composed of two chief con- FiG. 787. stituents, the supporting reticulum and the lymphoid cells contained within the meshes of the framework. The retiaihim 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 by the innumerable oxer- lying 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 trabecuke of which, particularly at the j)oints of junction, flattened con- nective tissue cells are closely applied as a more or less complete in\'est- 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 comparativelv large nuclei, which exhibit a strong affinity for nuclear (basic) stains. The simple lymph-nodules, of varying 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 wnth 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 Simple lymph-nodule from large intestine. X 120. THE LYMPHATIC SYSTEM. 937 Although the limits of the lymph-nodules are condensation of the surrounding- connective Fig. 7SS. the birthplaces of new lymphocytes, commonly imperfectly defined by a tissue, a distinct capsule is usually wanting. Definite lymph-channels are found neither upon the surface nor within the simple nodules ; the latter are provided, however, with a generous net-work of capillary blood-vessels (Fig. 792). Intermediate in their complexity of arrangement, between the simple nodules on the one hand and the typical lymph- nodes on the other, stand such structures 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. 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 trabeculae are less regularly disposed and more freely united, thereby breaking up the deeper parts, or medidld, of the node into uncertain cylindrical compartments. The spaces thus imperfecdy defined by the trabecule are Portion ot lymph-nodule, showing of germ-centre. X 350. details - Germ-centre L>mph <;inus Fat Fjg. 789. Lymph-sinus ( ii)bule CIj I rabecula Corti(.al follicles Ly mph s 1^""'" \ a-sa ciieieniia Meauiiary corOS Section of small lymph-node through hilum. X 25. mcompletely filled by masses of compact lymphoid tissue, the general form and arrangement of which correspond to the compartments in which they lie. The masses contamed within the peripheral spaces are spherical or pyriform and constitute 93S HUMAN ANATOMY. Capsulf iiph-siniis - Cortical fullicle . 3i- ■-5] the cortical nodules ; tliose within the communicating central compartments form a net-work of irregular cylinders, the viediillary cords, which are continuous with one another and with the deeper Fat_ll!2j-?*'^^v. ^"^''- '9o- part of the cortical nodules (Fig. 7.S9). The intervals between the tracts of lymphoid tissue and the trabecular frame-work constitute a system of freely intercom- municating channels, the ly)?ip/i - shiuscs, through which j)asses 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 traversing the periph- eral sinuses, the lymph j)asses into the irregular channels of the medulla and towards the point at which the efferent lymjih- vessels leave the nodule. The position of this exit is usually indicated by a more Lymph-sinus - mrr. •55' Lymph -sin us Medullary cord \.*^ Portion of penplier> of hmph-node sliowmg relation between trahecula sinus, and lymphoul tissue. > 50. or less pronounced indentation, known as the hlliwi, 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 trabeciflae 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 linec by an imperfect layer of flattened plate-like cells, that represent the endothelium of the adjoinint lymphatic vessels and also co\'er the more robust trabeculae 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 provided , , ^ , r , v, • ., 1 ' \.i 1 11 1 Portion of medulla ot Ivniph-node, showing details of lympn-sinub With valves, the lymph-channels and medullary cords. X 250. Lymph-sinus THE LYMPHATIC SYSTEM. 939 Cross-section of small lymph-node, injected to show rich vascular supply. X 10. 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 capillary net- works for the supply of the denser lym- phoid tissue. Both meduUated 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 meduUated fibres is uncertain. According to Tonkof!, fibrillae are traceable into the lymphatic tissue of the medulla. Development. — The origin of the first lymph-cells, 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 extends 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 difTerent results and indicated that Sabin' s method of study did not sufifice 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. Jour, of Anatomy, vol. i., 1902. ^ Amer. jour, of Anatomy, vol. v., 1905. 940 HIM AN ANATOMY. Fig veins. The various channels hnally uniti' to form a continuous system which acquires new opening's with the xenons system near the termination of the subclavian \eins, the condition found in the adult hein^- thus established. More recentlv Huntiui^ion and McClure,' working with cat embryos, have also found the earliest traces of the lymjihatic system in a series of spaces which aj^pear in the tissue surroundini^ the intima of the anterior cardinal \eins, 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 \ein later undergoes retrogression, the ventro-medial j^ortion persisting as the internal jugular. As tlu- 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 subclavian vein, and thus forms the primary Ivmphatic trunk of the bodv (Fig. 793). Later, spaces develop along the course of the anterior cardinal \eins 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, develoj) more rapidly than those accompanying the same ])ortion 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 princi])al lymphatic trunks unite with the thoracic duct, yet they may also form temporary or even permanent communications with other veins 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 veins, and that, while this mode of origin of the lymphatics applies to those following the primitive systemic veins, yet the more peripheral portions of the system are de\eloped 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 invasion, however, failing to affect certain of the tissues, such as cartilage and the central nervous 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 lynnphoid elevieyit, 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 ii mm. (14 days); X 9. Lymphatic vessels are heavily shaded ; veins are light. Iti.J., Ex.J.. internal and external jugular veins; Pi.U., primitive ulnar; Ex.M., external mammary; Az., azygos; yCI., inferior vena cava ; G., gastric; S.Af.. superior mesenteric; V., vitelline; Sc, subcar- dinal ; J?. A., renal anastomosis of subcardinals ; Pr.Fi., primitive fibular; c.d., coiniecting branch ; ^tIm. 7"., anterior tibial; c, caudal ; 3y 4t 5< 6, position of corresponding cervical nerves. (/•". T. Lewis.*) THE THORACIC DUCT. 941 cords and germ-centres respectively, and the si7ius-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. Developing lymphatics in rabbit embryo of 21 mm. (17 days); X 6. Lymphatic vessels are heavily shaded ; veins are light; for significance of lettering see preceding figure; in addition, Ce., cephalic; Br., bra- chial; R., radial; Ss., subscapular; ^'c/., sciatic ; /")m one to three in number and are situated immediately in front of the tra.c^us, beneath the parotid fascia. Their affcrcJits come from the anterior surface of the pinna and of the external auditory meatus, from the intey:ument of the temi)oral region, and from the outer portions of the eyelids. Their cffercnts pass to the superior deep cervical nodes. The parotid nodes ( lympho^landnlac parotidcae) are situated in the substance of the parotid gland (Figs. 796, 801 j. They are (juite numerous and vary greatly in size. They F"iG. 796. receive afferent s 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 deej) cer\ical nodes. The submaxillary nodes ( lymphoylaiidiilae sul»ma.\'illarcs ) 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). Oni node which rests upon the facial artery just before it passes o\er 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 affcrenfs, vessels from the submental and facial nodes and also directly 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 eyelids, 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 thos^^ 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 Anterior auricular node Occipital node Superior deep cervical nodes Superficial ccrvicaj nodes '-'1.. r' Superficial lymphatic vessels and nodes of head and neck ; semidiagramniatic. THE LYMPHATICS OF THE HEAD. 947 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 submaxillary nodes and partly to a node of the ^^'^- 797- 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 Thyroid body Sterno- mastoid muscle Submaxillary and submental lymph-nodes, new-born child. {Stahr.*) 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 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 affere^its 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 *Archivf. Anat. u. Physiol., 1898. t Beitrage zur klin. Chirurgie, Bd. 39. Facia! vein Submaxillary nodes Maxillary node Zygomaticus major Buccinator node Mandibular node Facial artery Facial lymph-nodes. ( TrendelA) 948 HUMAN ANATOMY. Fig. Internal carotid artery Retropharyngeal lymph-nodes, {\fosl.*) surfaces of the hyo-tjlossus imiscle and in the interval Ix'tween the two genio-hyo- '•^lossi. From the suri;ical standpoint they are of comparatively little importance, and have been termed "intercalated nodes," to distinynish them from the true terminal nodes of the lingual lymphatics (page 954), in which enlargement occurs in cases of cancerous or 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 pharyn.x. 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 pharyn.x, about on a le\el 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. Affcrcnts come to them from the upper part of the pharynx and from the mucous membrane of the nose, and their effcrtnih pass to the upper deep cervical nodes (Fig. 799). The Lvmph.\tic Vessels. The Scalp. — The Ivmpliatics of the scalp form a rich net-work, which is espe- ciallv dense in the neighborhood of the vertex, 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 |)osterior 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, \.\\q pcrkcllidar 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 epicerebral 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 tiie vessels and the other between the adventitia and the brain substance, and, accompanying the blood-vessels into the pia, *Archiv f. kiln. Chinirgie, 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 interfasciale), 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- FiG. Soo. 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 venae 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 pnetarsal 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 anijle of the orbit, and the former pass downward, obliquely across the cheek, in company with the facial \ ein, to terminate in the subma.xillary nodes, possibly making connections with some of the facial nodes on their way (Eii^. 798). The outer ones pass partly to the anterior auricular and partly to the upper parotid nodes. In the conjimctiva 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 [)ericellular 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 \ein to the facial nodes, while those from its lower portion pass with the efferents from the nasal mucous membrane to the retro- pharyngeal and sujierior deep cervical nodes. The Ear. — No true lymphatics have yet been observed in the tissues of the interjial 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. pcrilyviphatic space. It com- municates with the subdural space of the cranium by the aqueductus cochlcct 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 w^ell as in that of the tympanic membrane. In addi- tion a feebly developed net- work has been described as occurring beneath the ej)ithelium 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 ef!erents 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 extent of the organ, and from it stems pass in three principal *Anatom. Anzeiger, Bd. xv., 1899. Supracla' Lymphatics of posterior surface of auricle of new-born child. (Stahr.*) I 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) 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. 802. 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 1 y m- phatic net-work lies beneath the mucous membrane of the Parotid nodes Lymphatics of nose and cheek. {Ktittner*) nasal cavities, and from it vessels pass in two directions. Those of the anterior and lower portions of the fossse 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 deeper ones communicate with the facial nodes. * Beitrage f. klin. Chirurgie, Bd. xxv., 1899. 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 lower 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, w hose 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 upper Up (Fig. 803) have a course similar to that of the corresponding sul)nuicous stems, with which they may unite, and they terminate principally in the submaxillary nodes, although communication may alst) be made with one of the lower ])arotid nodes. The subcutaneous vessels of the lower lij) are from two to four in number, and pass principally to the submental nodes, from which efferents pass to the sub- FiG. 803. maxillary and superior deep cervical nodes. A noteworthy peculiarity of these lower lip vessels, which is in marked con- trast with what obtains in the submucous stems, is that those of the right and left halves 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 lower gums 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 have 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. — The 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. Subcutaneous lymiihatics of lips and superior deep cervical nodes, new-born child. (Dorendor/.*) THE LYMPHATICS OF THE HEAD. 953 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 external 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 group 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 Fig. S04. Lateral basal lymphatics in 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 to7tgue (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 caecum. 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 papillae, the foHate 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 cervical 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 interval which separates the two genio-hyo-glossal muscles. One or two of them then continue in their downward course and pass, in some cases Apical net-work of lymphatics Lymphatics of dorsum and margins of tongue {Kiittner*) * Beitrage f . klin. Chirurgie, Bd. xxi., 1895. 954 HUMAN ANATOMY. to the right and in some to the left, between the genio-hyo-glossus and the genio- hyoid muscles, jierforate 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 difitcrent groups of nodes stand in relation to the lymphatics of the tongue. ( i ) The submental nodes receive a stem from the tip ; (2) the subma.xillary nodes receive stems from the marginal and cen- tral regions ; (3) the superior deep cervical notles receive stems from the marginal, central, and basal regions ; and (4) the inferior deep cervical nodes receive a stem from the apical region. Basal vessel Fig. 805. Superior deep cervical node 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 afTerents it receives from the tongue. The lymphatics of the floor of the mouth have essentially 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 cervical nodes, while from its entire surface stems pass t(^ the submaxillary and superior deep cervical nodes. The Palate, Pharynx, and Tonsils. — The lymphatics of the hard palate form a fine net-work in the superficial portions of the mucous membrane and are continuous laterally with those of the upper gum. They empty into several 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 pharynx to terminate in those superior deep cervical nodes which are situated on the internal jugular vein above the lex-el 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 lying 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 pharynx and terminate in the lateral retropharvngeal 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 cervical group. Lymphatics of tongue. {Pott ie> .* 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 (postaujricular), 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 nodes — 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 consequence of eczema affecting the skin back of the ear. The close relation of the node to the great occipital nerve, on which it usually lies, gives rise to marked tenderness on pressure, the nerve being compressed between the node and the bone. The source of infection of these nodes may be intracranial — e.g., suppurative meningitis of the cerebellar fossa (Macewen). The posterior atiriciilar or mastoid ?iode, 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 fossae, the naso-pharynx, 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 forward towards the cheek, or inward towards the pharynx, 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 submaxillary 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 pharyn- 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 variety (page 747). Sorne 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-hyoidj by the fact that tlic former is abo\e, tlic latter below, the hyoid bone. Enlargement of a subniaxi/ian' 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 jxirotid — is, however, much less closely and firmly enveloped by its capsule, is more superficial, and is not in near relation to such imjiortant structures. On the other hand, the wide area which drains into the sub- maxillary nodes — the middle of the forehead and of the face, the inner portions of the lids, the mouth, pharynx, anterior portion of the tongue, gums and teeth of the lower jaw — renders them especially liable to pyogenic or tuberculous or syi)hilitic infection, or to secondary involvement in carcinoma of any of these regions — espe- cially of the tongue or lower lip. In examining for enlargement of these nodes, the chin should be lowered so as to relax the depressors of the lower jaw and the deep cervical fascia and permit of more accurate palpation pf 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 laxity 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 masscter muscle should be remembered. The efferent vessels from all these nodes — suboccipital, mastoid, parotid, and submaxillary — enter into the superficial cervical nodes, the eflferent vessels from which, in their turn, enter the deep cervical nodes (page 957). Extracranial lesions of an irritative 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 plexuses 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 cervical fascia, their enlargement may not be early noticed. These variations 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 LYMPHATICS 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- tically a continuous chain of nodes, extending 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 inferior deep cervieal 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 (lymphoylandulae cervicales superticiales) may conveniently be divided into two subgroups, both of which are composed of rather small and somewhat inconstant nodes. The external J7igular 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 usually two or three in number, one or two 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 Fig. 806. Digastric muscle fVi Superior deep vj' cervical node The second subgroup is that of the anterior cervical nodes, which are both variable 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 recurrential 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 (lymphoglandulae 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 le\-el at which the vein is crossed by the omo-hyoid muscle. They lie Anterior cervical node Recurrential node Anterior cervical and recurrential nodes and lymphatics of larynx. {Most.*) either directly upon the vein or slightly posterior to it. Fig. 807. Sterno-mastoid muscle, cut Superior deep cervical node ra^ MfMM- Omo-hvoid a^lff muscle H^^'yf \Vw-,yf jugular vein ^j^^ i Inferior deep cervical node Deep cervical lymph-nodes. the more posterior nodes are the efferent stems for beneath the sterno-cleido- mastoid muscle, and are all united by numerous connecting stems so that they form a veritable 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 the posterior auricular and *Anatom. Anzeiger, Bd. xv., 1899. 958 Hr.MAN ANATOMY. occipital nodes, whik- in the more anterior nodes efferents from the retropharyn- geal, parotid, submaxillary, submental, and superficial cervical nodes terminate. Beloni^iny to the second class and terminating^ in the more posterior nodes are (i) a vessel which descends directly 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 descendinj^ from the tongue ; (2) stems from the nasal mucous membrane, the palate, and the upper portions of the pharynx ; (3) stems from the cer\ical portion of the ctsophagus ; (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 cffcrcnts 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 lielow. The inferior deep cervical nodes dyniphoiilandulac cervicales profundac inferiores), also termed the supyadavicular 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 cervical nodes. In addition to the affercnts 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 froni 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 efferents from the brachial grou])s of the axillary nodes ; and (6) vessels which j)ass to the lower nodes of the left, rarely the right, side from the liver, ascending in the suspensory ligament of that organ, piercing the diaj)hragm, and following the course of the internal mammary vessels upward through the thorax. Their efferents unite with some of those from the superior deep cervical nodes to form a single stem, the jugular trunk (truncus jugularis ), 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, frequently open directly into the subcla\'ian \ein. The Lvmphatic 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 cervical chain. The Larynx and Trachea. — The lymphatic net-work of the larynx is \ery well developed over the greater portion of the mucous membrane and is es{)ecially rich in the regions of the false vocal cords and the ventricles. Over the true vocal cords, however, it is verv feebly developed, and the entire net-work may therefore be regarded as consisting of two portions, one of which is situated above the level 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 w'hich arise from the upper net-work are from three to six in number 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 cervical 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 posteriorly 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 between 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 (Esophagus. — 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. 'Wv^ 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 : (a) 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 cervical triangle ; i^b) 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 externally 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 directly communicate with the superficial group. The deep cervical nodes are accordingly found to be inflamed or enlarged consecutively to a great variety of conditions, — £-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 occasionally the original lesion is on the opposite side. 96o HUMAN ANATOMY. Swellings of this deep chain of glands — esjiecially 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 upj)er group lies behind the posterior belly of the digastric in the angle between the internal jugular and facial \eins. Leaf has suggested that it be called the " jugulo-digastric" node. In some affections of the tonsil 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 inserti(Mi 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 ner\e 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-pharvngeal nerve where it curves around the lower border of the stylo- pharvngeus. 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 pharynx, 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 retropharj'ngeal connective tissue being lax to permit of the free movement of the pharynx 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 pharynx (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 cer\'ical 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 \ery base of the neck, in the sub- claxian triangle, or on the omo-hyoid muscle, are not uncommonlv 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 cer\ical group. In cases of chronic inflammation and enlargement 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 I 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 {b) 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 (lymphoglandulae cubitales superficiales) are arranged in two principal groups. One of these rests upon the brachial fascia imme- diately over the internal condyle of the humerus, and may be termed the epitrochlear 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 efferents 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-pectoral 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 afferents are the deep lymphatics of the forearm and their efferents 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 affcrcnts 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, jjassing to another group. Their effercnts pass partly to the intermediate subgrouj) of the axillary plexus, pardy 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. Bmchial plexus Subclavian artery Intermediate nodes Subclavicular nodes Mammary gland Brachial nodes Subscapular nodes Anterior pectoral nodes Inferior pectoral nodes Axillary lymph-nodes, new-born child. (Oelsner.*) border of the pectoralis major muscle and anterior to the long thoracic artery. They receive affcrcnts from the integument of the anterior surface of the thorax, from the pectoral muscles, and from the mammary gland. Their effc7'ents pass partly to the intermediate and partly to the subclavicular subgroup of the axillary nodes. 3. The inferior pectoral subgroup is composed of two or three small nodes, 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 effercnts pass to the nodes of the intermediate subgroup. 4. The subscapular subgroup (lymphoglandulae 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 *Archivf. klin. Chirurgie, Bd. Ixiv., 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 siibgrotcp 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 afferents from all the terminal subgroups of the axillary plexus, and its efferents pass to the nodes of the subclavicular subgroup. 6. The subclavicular subgroiip 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 subclavius), 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 the external jugular, or else to unite with the jugular trunk on the right side or to 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 by 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. 809. 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 Deito-pectorai hand, for the most part over the intermetacarpal spaces, although abun- dant anasto- moses occur between the r> " vessels of ^^-' neighboring spaces so that EpUrochlear 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 index 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 which 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. (leased 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 curve around the inner border of the hand to join the stems coming from the little tiiiger ; 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 ujnvard alt)ng 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 grouj^s, 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 aflferents from the sub- FiG. 810. .^ ^ Lymphatics of hand : Fig. Sio, palmar. Fig. 8ii, dorsal surface. Superficial digital net-works (a) empty at bases of fingers into larger stems {/>. c), which are tributary to trunks on forearm (rf) ; superficial palmar vessels commu- nicate (Fig. 810, d) with deeper lymphatics. (Sappey.*) 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. 809), the stems of the dorsal grouj) 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 above 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 et iconographie des vaisseaux 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 venae 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 efferents of the epitrochlear nodes, or, these failing, the inner stems of the forearm. They terminate in the brachial nodes of the axillary 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 axilla, 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 mammary nodes THE LYMPHATICS OF THE THORAX. Thk Lymph-Nodes. Certain of the nodes which have been described as belonging to the axillary plexus, namely, those forming the anterior and inferior pectoral subgroups, might well be considered as belonging to the thoracic set, since their afferents drain thi anterior and lateral walls of the thorax. On account of their situation, however, as well as their intimate connection by efferents 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 fiymphoukinduiae sternales; form two chains which extend u])warcls upon the inner surface of the anterior thoracic wall, along the course of the internal mammary blood-vessels ( Fig. 812). They \ary in number from four to ten, ^^^- ^'^- and are situated 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 co\'ered, 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 afTerents for the higher ones; the terminal efferents usually unite to form a single stem which joins the efferents of the anterior mediastinal and bronchial nodes to form the broncho-mediastinal trunk Tpage 968 ). The intercostal nodes (lymphoulandulae 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 usually situated, w^hen present, at the point where the intercostal arteries give off their lateral perforating branches. The afferents of the intercostal nodes drain the posterior portions of the inter- costal spaces. The effere^its of the lower members of the series unite to form a stem which passes downward and terminates in the receptaculum chyli, while those from Lower intermanimary node Lymph-nodes of anterior thoracic wall, viewed from beliiiid. (Based upon figure of Poirier and Cuneo.*) * Poirier et Charpy : Traite d'anatomie 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 (lymphoglandulae 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 nodes, 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 afferents 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 trunk (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 affere7its 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- P „., portant of the thoracic ' ^' nodes, and for the con- venience of description they may be regarded as forming three subgroups (Fig. 813). One of these is formed by the Z'rrtc/Z.?^/ IY^N;^ J^ ^ K\M-^ Tracheal nodes 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 nodes proper, from ten to twelve in number and situated in the angle formed by the two bronchi. They are for the most part large, those beneath the right bronchus being usually larger and more numerous than CEsophagus Recurrent larj'ngeal nerve Left vagus nerv Left bronchus Pulmonary nodes Bronchial node Tracheal and bronchial lymph-nodes, viewed from behind. {Halle.^^ * Clinique m^dicale, Tome iv. 968 HUMAN ANATOMY. those below the left one. The third subi,nt)ui) is formed by the pulmonary nodes, usually of small size and situated in the hilus of the lunj^s, between the larger divisions of the bronchi. The affcnnts 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 effcrcnts 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 antl anterior mediastinal nodes unite to form a single broncho-mediastinal trunk ( truncus broiichomcdiastinalis), which ])asses upward to\\ard tlie 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 sul)cla\ian trunk to open into the arch of the thoracic duct, into which it may also open directly. The Lvmphatic \'essels. 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 little 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 walls 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 ])nrtions of the mammarv 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 exceedinglv fine subareolar net-work, which is a special development of the general subcutaneous net-work of the anterior thoracic wall. From 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 paramamniillary nodes, 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, (i) 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 axillar}- 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 node Fig. 814. Brachial node Subscapular node Anterior pectoral node Vessel passing to anterior pectoral node Inferior pectoral node Subclavian node Vessel passing to subclavian node Intermediate node Subareolar plexus over mammary gland Lymphatics of mammary gland and axillary nodes. {Poirier and Cuneo*) 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 establishment of a collateral path leading to the inguinal nodes. Furthermore, it is to be remembered that, although the anterior pectoral nodes are the termination 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 (Sappey). 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' anatomic humaine, Tome ii., 1902. 970 HUMAN ANATOMY. The vessels from the external intercostals are somewhat larger than those from the internal 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 exceedingly line 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 l\-mph 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 anteriorlv, 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-Avork makes connections with the Ivmphatic vessels of the pleunt. 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 lymphatics 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 visceral layer of the pericardium. The endocardial net-work communicates with the superficial one by branches which traverse 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 o\-er the whole surface of the heart, the vessels 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 inter\'entricular 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 interxentricular 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 Acntricle, unites with the anterior vessels. The conjoined trunk so formed passes upward along the pos- terior surface of the pulmonars' 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-ventricular 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 pulmonary aorta, and also terminates in one of the bronchial nodes. The Lungs. — The lymphatics 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 hilus 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 pulmonary 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 cer\acal 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- titiimi. Anterior Mediastinum. — The nodes in close relation to the internal mammary artery are of practical importance on account of their relations (a) to the diaphragm ; (<5) to the anterior extremities of the intercostal spaces ; (^) to the inner segment of the mammary gland. They may therefore be involved in cases of subpleural (supradiaphragmatic) abscess, of tuberculous or syphilitic or typhoidal caries of the ribs or sternum, or of carcinoma of the breast (page 2035). Middle Mediastijucm. — The nodes just below the bifurcation of the trachea (bronchial, peribronchial), in close relation to the trachea, the bronchi, and the roots of the lungs, are frequently involved in tuberculous infection of the lungs. The pulmonary lymphatics, both perivascular and peribronchial, communicate on the one hand indirectly with the lymph-spaces in the walls of the alveoli beneath the epithelial cells, and on the other with these nodes. Solid particles — and this includes the bacillus tuberculosis and other organisms — are thus enabled to pass from within the alveoli into the lymphatic spaces, and from these they are forced on by the respiratory movements of the lungs to the bronchial nodes, to which all the lymphatics converge. These nodes often contain, especially in coal miners, or in the inhabitants of large cities, a large amount of black pigment, consisting of minute particles of dust, smoke (carbon), etc., that have been inhaled (Taylor). Caseation and ulceration of these nodes have involved the trachea (page 1840), the bronchi (especially the right one, with which the larger number are in close relation), and the oesophagus (page 1614), directly in front of which some of them lie. Their enlargement has also produced various pressure symptoms, — dyspnoea, dys- phagia, stridulous respiration, etc. , — which their relations easily explain. Posterior Mediastirium. — A group of nodes — oesophago-pericardiac (Leaf) — lying between the posterior surface of the pericardium and the oesophagus, are in close relation to the trunk of the pneumogastric nerve and its oesophageal branches. Their infection — through their direct connection with the not infrequently infected nodes in the neck and thorax lying between the trachea and oesophagus — may produce symptoms of vagus irritation. It has been thought (Guiteras) that these nodes and 972 HUMAN ANATOMY. the bronchial nodes are especially enlarged in influenza and that some of the anomalous pulmonary symi)toms of that disease — simulating congestion, ])neumonia, etc., are thus accounted for. Markttl enlargement of the bronchial nodes may be indicated by an area of percussion tiulness below tlK' Kvel of the fourth dorsal vertebra (Veo). In cancer of the oesophagus either the mediastinal nodes or those at the root of the neck mav be involved, as both sets receive lymphatics from that tube. Medias- tinal growth (sarcoma) or abscess may originate in these nodes. Either condition — but especially the neoplasm — will occasion marked symptoms of pressure on the trachea, bronchi, cesoj^hagus, and superior cava and innominate veins, — e.g., dyspncea, dvsphagia, cedema of the face, neck, and upi)er limbs, dilatation of the superficial veins of the abdomen and thorax. THE LYMPHATICS OF THE ABDOMEN. The Lymph-Nodes. The principal nodes of the abdominal region are those associated with the \ iscera and those situated upon the posterior wall in the vicinity of the aorta. A few small and inconstant nodes also occur upon the anterior wall, and of these the most important arc the epigastric, the circumflex iliac, and the umbilical nodes. The epigastric nodes ( lymphoylandulac epinastricae) are three or four in number ancl are interposed in the course of the lymphatic stems which accomj)any Fig. Si 5. i I'mbilical node Deep epigastric artery -^ Iliac node Umbilical node Lymphatic vessels accompanying deep epigastric artery Iliac node Epigastric and umbilical lymph-nodes, seen from behind. (Cuneo and Marcille.*) the deep epigastric vessels (Fig. 815) ; they occur toward the lower part of the vessels and their efferents pass to the lower iliac nodes. The circumflex iliac nodes are from two to four in number when present, but are not unfrequently wanting. They are situated along the course of the deep circumflex iliac vessels ; they receive afferents from the lower lateral portions of the abdominal wall, and send efferents to the lower iliac nodes. The umbilical nodes are situated in the subserous areolar tissue in the neighborhood of the umbilicus. Thev are three in number, one being situated a little below and to one side of the umbilicus, and the other two above the umbilicus Bull, et Mem. Soci^t^ anatom., 1901. THE LYMPHATICS OF THE ABDOMEN. 973 in the median line (Fig. 815). They occur in the net-work which covers the posterior surface of the sheath of the rectus muscles, and are apparently of inconstant occurrence. The remaining abdominal nodes may be regarded as arranged in two principal divisions, one of which includes the groups associated with the various viscera, while the other is formed by the groups occurring in the posterior wall. This latter division may be separated into the coeliac and lumbar nodes. The cceliac nodes vary in number from sixteen to twenty, and are situated in front of the abdominal aorta, around the origins of the coeliac axis and the superior mesenteric artery. They are extensively connected with one another so as to form a distinct coeliac plexus (plexus coeliacus). They receive afferents from the lower portions of the oesophagus, from the diaphragm, and from the gastric, hepatic, pan- creatico-splenic, and mesenteric nodes ; the efferents of the lower nodes pass to the higher members of the group and the efferents of these either open independently Fig. 816. Right suprarenal body Right kidnej Right lateral lumbar nodes Median lumbar node Right ureter Iliac node Left suprarenal body Left kidney Left lateral lumbar nodes Lymphatic vessels from testis Lumbar nodes, new-born child. (Cuneo.*) into the receptaculum chyli, or, more usually, unite to form a common trunk, the truncus intestinalis, which joins the left lumbar trunk to form one of the origins of the thoracic duct (page 943). The lumbar nodes (lymphoglandulae lumbales) are twenty to thirty in number, and form three irregular longitudinal rows along the course of the abdominal aorta (Fig. 816), extending from the level of the second lumbar vertebra to the bifurcation of the aorta, and forming with the aid of connecting vessels a well-marked plexus, the plexus lumbalis. The median row is composed of some five or six large nodes situated upon the anterior surface of the aorta, and of four or five retro-aortic nodes which rest upon the bodies of the third and fourth lumbar vertebrae, immediately below the lower extremity of the receptaculum chyli. Of the lateral rows that of the left side is formed by a number of nodes arranged in an almost vertical series upon the successive heads of the psoas muscle. The right lateral nodes occupy a * Bull, at Mhm. Soci^te anatom., 1901. 974 HUMAN ANATOMY. corresponding position with relation to the right psoas, lying posterior to the vena cava inferior, but a varying number of nodes which may be referred to this group also occur upon the anterior surface of that vessel. Since all the nodes are united by communicating vessels, they form a plexus and will receive aflerents from and give efferents to one another. In addition, the median row receives affcrents from the descending colon and the mesocolic nodes, while the lateral rows receive them from the muscles of the posterior abdominal walls, from the iliac nodes, from the testes in the male and the ovaries, Fallopian tubes, and uterus in the female, and from the kidneys and su])rarenal capsules. The efferents of the upper nodes of the median row pass upward to terminate in the lower coeliac nodes, while those of the lateral rows either pass to the nodes of the median row, or unite together to form on either side a common trunk, the truncus lumbalis, which unites with its fellow to form the receptaculum chyli (page 943 J, or else they perforate the crus of the diaphragm and oj)en independently into the thoracic duct. The visceral abdominal nodes are arranged in groups or chains which follow in general the jjrincipal \isctral branches of the aorta, those following the branches of the coeliac axis and the superior mesenteric artery communicating by their efferents Fig. 817. Superior gastric nodes Inferior gastric nodes Lympliatic nodes and vessels of stomacli. (Polya and Navratil.*) mainly with the coeliac nodes, while those accompanying the inferior mesenteric branches communicate with the median lumbar nodes. Corresponding with the branches of the coeliac axis are the gastric, hepatic, and pancreatico-splenic nodes. The gastric nodes consist of two chains (lympho- glandulae gastricae superiores et infcriores ) situated respectively along the lesser and greater curvatures of the stomach. The superior nodes, three to fifteen in number, are situated along the course of the gastric artery, principally along the lesser curvature of the stomach between the two layers of the gastro-hepatic omentum (Fig. 817), although a few also occur along the course of the artery before it reaches the stomach and others upon the left side of the cardiac orifice of the viscus. The inferior nodes are situated in the vicinity of the pyloric end of the stomach, partly along the right half of the greater curvature, accompanying the right gastro-epiploic vessels, and partly on the posterior surface of the pylorus along the course of the gastro-duodenal vessels. The gastric nodes receive afferents from the stomach and in the case of the retro-pyloric nodes also from the first portion of the duodenum, and their effer-ents pass to the coeliac nodes, those of the superior group following the course of the gastric vessels, while those from the inferior group accompany the gastro-duodenal and hepatic arteries. Deutsche Zeitschrift f. Chirurgie, Bd. Ixix. THE LYMPHATICS OF THE ABDOMEN. 975 The hepatic nodes (lymphoglandulae hepaticae) are more or less clearly arranged in two series. One series accompanies the main stem of the hepatic artery along the upper border of the head of the pancreas and throughout the vertical portion of its course in the free margin of the gastro-hepatic omentum, and the other accompanies the superior pancreatico-duodenal branch and ascends along the bile-duct to the portal fissure. The afferents of the nodes come from the liver, the head of the pancreas, and the first and second portions of the duodenum, and their efferents pass to the coeliac nodes. The pancreatico-splenic nodes (lymphoglandulae pancreaticolienales) accom- pany the splenic artery throughout the greater portion of its course, and are consequently situated along and partly behind the upper border of the pancreas (Fig. 8 1 8). They vary in number from four to ten, and their afferents come from the organs supplied by the splenic artery, — namely, the stomach, pancreas, and spleen, — while their efferents pass to the coeliac nodes. The mesenteric nodes (lymphoglandulae mesentericae) are from one hundred to two hundred in number, and are arranged along the superior mesenteric artery and its branches to the small intestine. They form three more or less distinct series, especially towards the upper portion of the mesentery. One series, in which the Fig. 8i8. Hepatic node Retropyloric node Mesocolic nodes Pancreatico-splenic nodes Transverse mesocolon Transverse colon Pancreatico-splenic, retropyloric, and mesocolic nodes, new-born child ; liver dravi^n upward, stomach and duodenum laterally. {Cuiteo and Delamare.*) nodes are more numerous and smaller than the others, lies close to the intestine, among the terminal branches of the artery ; a second consists of larger scattered nodes situated along the primary branches of the artery ; while the third series includes the closely aggregated nodes which surround its main stem. Towards the lower portion of the ileum the distinction of the first and second series becomes less and less apparent, and at the junction of the ileum and caecum the nodes form a single group, situated a short distance from the intestine between the two layers of the mesentery. These nodes are sometimes termed the ileo-caecal nodes, and associated with them by means of its efferents is a variable group of small nodes, the appendicular nodes, situated partly in the base of the mesenteriole of the appendix and partly in the immediate vicinity of the junction of the ileum and caecum (Fig. 820). The various series of nodes are connected with one another by vessels, which in this region are known as lacteals, and the nodes of the first series receive their afferents from the walls of the small intestine, and, in the case of the ileo-caecal nodes, from the caecum and vermiform appendix. The efferents of the nodes of the third series pass to those nodes of the coeliac group which are situated around the origin of the superior mesenteric artery. * Jour, de I'anat. et de la phj'siol., Tome xxxvi., 1900. 976 HUMAN ANATOMY. The nodes which arc associated with the abdominal portions of the large intestine are known as the mesocolic nodes ( lymphoiilandulae mcsocolicac ) and they consist of from twenty to fifty small nodes which are situated close to the intestine (Fig. 8i8). Their affcrents are received from the entire length of the large intestine, with the exception of the crecum and appendix and the rectum, and the cfferc7its of the nodes associated with the ascending colon and the right half of the trans\'erse colon pass to the lower coeliac nodes, while those of the nodes associated with the left half of the trans\erse colon and with the descending and sigmoid colons ])ass to the median row of lumbar nodes. In addition to the nodes which are properly included in the mesocolic group there are a number of small nodes situated upon the lateral walls of the upper part of the rectum, along the lines of the superior hemorrhoidal vessels (Fig. 821). These ano-rectal nodes are from two to eight in number on each side, and are situated beneath the fibrous investment of the rectum, resting directly upon the outer surface of the muscular coat. They receive their afferents from the neighboring portions of the wall of the rectum and, in the female, from the posterior surface of the \agina, and their cfferents pass to the mesocolic nodes situated in the lower part of the mesentery of the sigmoid colon. The Lvmphatic Vessels. The Abdominal Walls. — The anterior abdominal wall, as regards its lymphatic vessels, may be divided into a supra- and an infra-umbilical region. The lymphatics of the former area belong in reality to the thoracic cutaneous set, passing upward to join the thoracic stems which terminate in the anterior pectoral nodes of the axillary plexus. The vessels of the infra-umbilical region, on the contrary, descend to terminate in the inguinal nodes. Along the line of junction of the two regions anastomoses occur and the vessels of the right half of the abdominal wall also communicate with those of the left half. The subcutaneous Aessels of the posterior abdominal and lumbar regions anastomose with the corresponding vessels of the posterior thoracic region above, and below with those of the gluteal region. They form an extensive net-work, from which stems pass downward and forward, parallel with the crest of the ilium, to terminate in the inguinal nodes. The lymphatic net-work of the deeper structures of the abdominal walls is drained by a number of stems which follow in general the courses of the blood- vessels. - Thus, the stems which lead away from the upper portion of the abdominal wall pass upward along the course of the sui)erior epigastric vessels to terminate in the lower sternal nodes ; another set follows the course of the deep epigastric vessels to terminate in the lower iliac nodes, after tra\ersing the epigastric nodes ; another accompanies the deep circumflex iliac vessels, draining the lower portions of the lateral walls of the abdomen, traversing the circumflex iliac nodes, and also terminating in the iliac nodes ; while other sets accompany the lumbar \essels and terminate in the lateral rows of lumbar nodes. Abundant communications exist between the vessels of adjacent drainage areas and from the region of the umbilicus the lymph flow may follow any one of the paths mentioned above. Attention may be called to the occasional presence of nodes in the course of the vessels arising in the umbilical region (page 972). The Stomach. — The lymphatics of the stomach have their origin in two net-works, one of which is situated in the mucosa and the other in the muscular coat. The net-work of the mucosa occurs uninterruptedly throughout the entire extent of the gastric surface and is continuous Avith the corresponding net-works of both the oesophagus and duodenum. From its deeper surface branches pass to a more open net-work situated upon the outer surface of the submucosa, and from this stems traverse the muscular coat obliquely to terminate in a subserous net-work which also receives branches from the net-work of the muscular coat. Connections between the muscular and mucous net-works occur, but they are so indirect that an extensive cancerous infection of the mucosa may reach the outer layers of the stomach only at limited areas at some distance from one another. The subserous net-work with which both primary net-works communicate gives origin to a number of stems which pass to the gastric nodes, and the course which they follow is such that the entire surface of the stomach may be regarded as presenting THE LYMPHATICS OF THE ABDOMEN. 977 three more or less distinct lymphatic areas (Fig. 817). Not that the areas are perfectly separated from one another ; on the contrary, the subserous net-work is continuous over the entire surface. But the collecting stems from each area follow a definite route toward different node groups. The largest of these areas occupies roughly the whole of the upper border of the stomach from the fundus to the pylorus, and extends downward on either surface to about two-thirds of the distance to the greater curvature. Its collecting stems all pass to the superior cardiac nodes. The second area occupies about the pyloric two-thirds of the greater curvature, and its efferents pass to the inferior gastric nodes, while the third and smallest area occupies the lower part of the fundus and the cardiac one-third of the greater curvature, and sends its efferents to the splenic nodes. It may be remarked that these areas correspond in a general way with the areas drained by the principal veins arising in the stomach walls. Thus, the large upper area corresponds in general with the drainage area of the gastric vein, the lower pyloric area to that of the right gastro-epiploic vein, and the lower cardiac area to that of the left gastro-epiploic. It may further be noted that while the subserous net-work communicates with the superficial net-work of the oesophagus, it seems to be completely cut off from connec- tion with the corresponding duodenal net-work, an arrangement which is in striking contrast to the continuity which exists between the gastric and ^'*^- ^^9- duodenal mucosa net-works and explains the rare extension of a carcinomatous infection of the pylorus to the duodenum by the subserous route. The Small Intestine. — Throughout the entire length of the intestine, both small and large, the lymphatic net - works are arranged in two sets, one of which is situated in the mucosa and the other in the muscular coat. The two net-works are more or less independent, though communicat- ing branches occur, and both open into a subserous net-work from which collecting stems arise. The stems which pass from the duodenum are divisible into two groups according as they arise from the anterior or posterior surface. Those coming from the anterior surface pass to the chain of nodes situated along the course of the inferior pancreatico-duodenal artery, and so to the coeliac nodes, which surround the origin of the superior mesenteric artery, while the posterior stems pass to the hepatic nodes situated along the course of the superior pancreatico- duodenal vessels and so to the coeliac nodes which surround the coeliac axis. Some of the stems which take their origin from the first part of the duodenum pass to those nodes of the inferior gastric group which are situated upon the posterior surface of the pyloric region of the stomach, and, since these nodes also receive afferents from the pylorus, they aflord opportunity for the transference of a superficial infection from the pylorus to the duodenum, a direct route for infection in this direction being wanting (see above). The collecting stems of the jejunum and ileum pass to the first series of mesenteric nodes, situated along the line of attachment of the mesentery to the intestine, and, after traversing these, are continued onward to the second and third series of nodes, whose efferents pass to the coeliac nodes surrounding the origin of the superior mesenteric artery. The vessels issuing from the jejuno-ileum are usually spoken of as the lacteals, on account of their contents, especially at times when absorption of food constituents is proceeding rapidly in the intestine, having a milky appearance, owing to the presence of numerous fat globules in the lymphocytes. 62 Mesenteric lymphatic nodes and vessels ; peritoneal covering of mesentery has been removed. 978 HUMAN ANATOMY. The Large Intestine. — The two sets of lymphatic net-works characteristic of mucous membranes occur in the walls of the large intestine, and they communicate with one another and hnally open into a subserous net-work from which collecting stems take origin. In the vermiform appendix (Fig. 820) these collecting stems are from three to five in number and pass upward in the mesenteriole to terminate in the appendicular nodes or, in the absence of these, directly in the ileo-cacal nodes. The subserous net-work of the base of the appendix communicates freely with that of the ciecum, whose collecting stems have essentially the same course as those of the appendix, passing primarily to the appendicular nodes situated in the neighborhood of the ileo-Citcal junction and thence to the ileo-csecal nodes. The ultimate nodes of the appendicular and cjecal systems are situated in the root of the mesentery along the course of the superior mesenteric vessels ; they belong to the group of mesenteric nodes and receive their aflerents in part from the ileo-caecal nodes. Communications have been described as existing between the appendicular lymphatics and those of the broad ligament of the uterus as well as the iliac nodes. The more recent observations have failed, however, to confirm the existence of any direct connection with these structures, and patholog- FiG. S20. ical conditions of the broad ligament and iliac nodes asso- ciated with acute appendicitis may perhaps be due to a dissemination of the infection through the subperitoneal net- work by way of the so-called appendiculo-ovarian ligament. nodes ,\ ^lESSi .iJS^^KBB'*^ ^ «iA The collecting stems from the subserous net- work of the ascending colon pass primarily to some in- constant mesocolic nodes, situated along the line of attachment of the colon to the abdominal wall, and thence are continued along the lines followed by the right colic vessels to the superior mesenteric nodes. The stems from the tra?is- verse colon have a more varied course in accordance with the arrangement of the blood-vessels. They pass primarily to a series of mesocolic nodes situated between the layers of the transverse mesocolon close to the intestine ; these are of larger size and more numerous than the nodes associated with either the ascending or descending colon and are especially well developed toward either angle of the colon. Their efi'erents pass principally to some four or live nodes situated along the course of the middle colic vessels and thence to the third group of mesenteric nodes, but those from the vicinity of the splenic flexure follow the course of the branches of the left colic vessels and so pass to the nodes of the median lumbar group situated in the neighborhood of the inferior mesenteric artery. The lymphatics of the transverse colon communicate somewhat extensively with those of the great omentum, as the result of the attachment of the latter to the colon, and they are thus placed in connection with the inferior gastric and splenic nodes. The collecting stems from the descending colon and sigmoid flexure pass primarily to mesocolic nodes situated close to the attached surface of the intestine, and thence follow the courses of the left colic and sigmoid vessels to the median 'jumbar nodes situated in the vicinity of the origin of the inferior mesenteric artery. * Deutsche Zeitschrift f. Chirurgie, Bd. Ixix. \'ermiform appendix Ileo-csecal and appendicular lymphatic nodes and vessels. (Polya and Aav> atil .*) I THE LYMPHATICS OF THE ABDOMEN. 979 Fig. 821. The mesocolic nodes associated with the descending colon are less numerous and smaller than those of the sigmoid flexure and resemble in appearance and arrangement those of the ascending colon. The lymphatics of the rechaji (Fig. 821), although belonging in large part to the pelvic region, may, for the sake of completeness of the account of the intestinal lymphatics, be considered here in their entirety. Of the two primary net-works that of the muscular coat is injected only with difificulty, but it communicates with the mucosa net-work and its collecting stems follow the same course as those of the deeper net-work. In the mucosa net-work two zones may be distinguished, one of which includes the greater portion of the net-work and extends down to the lower ends of the columns of Morgagni, while the other includes that portion of the mucosa intervening between that level and the anal integument. The upper zone may be termed the net-work of the rectal mucosa, while the lower one may be designated as the net-work of the anal mucosa, since the region in which it occurs forms the transition between the mu- cosa and the anal integument. The collecting stems from the net-work of the rectal mucosa traverse the muscular coat and enter into relation with the ano-rectal nodes ( page 976 ). After traversing these they are continued onward along the course of the superior hemor- rhoidal vessels and open into the lower mesocolic nodes, from which efferents pass to the median lumbar nodes situated in the neighborhood of the origin of the inferior mesenteric artery. The net- work of the anal mucosa sends numerous branches upward to communicate with the lower part of the rectal mucosa net- work. These branches trav- erse for the most part the columns of Morgagni in which they are so numerous as to earn for themselves the appellation of glomi lymphatici^ while, on the other hand, the mucosa of the depressions between the columns is comparatively poor in lymphatics. Some collecting stems from the anal mucosa perforate the muscular coat and pass to the ano-rectal nodes, and thence along with the stems from the rectal mucosa to the lower mesocolic nodes, while others follow the course of the middle hemorrhoidal vessels and terminate in nodes belonging to the hypogastric group (page 984) situated at the point where the internal iliac artery divides into its leash of branches, or else at the level of the great sacro-sciatic notch, a little below the point where the obturator vein joins the internal iliac. The lymphatics of the anal i7itegu7?tent will be considered together with those of the perineal region (page 987). The Pancreas. — The lymphatics of the pancreas take their origin from a perilobular net-work from which collecting stems pass to the neighboring nodes, following the course of the blood-vessels which supply the gland. The great majority of them pass to the chain of splenic nodes which extends along the upper border of the pancreas, but those of the head of the gland pass in part to nodes of the hepatic Net-work in anal mucous membrane Lymphatics of rectum. {Gerota.*) Net-work in anal integument *Archivf. Anat. u. Physiol., 1895. 9So IIIMAN ANATOMY group, follow ill!:; the course of the superior pancreatico-duodenal vessels, while others again accompany the inferior pancreatico-duodenal vessels to terminate in nodes belonging to the mesenteric group. The Liver. — The lymphatics of the liver are arranged ia perilobular net-works from which stems pass in two principal directions ; those which come from the deeper l)ortions of the net-work follow the course of either the portal or hepatic venous branches, while those arising from the net-works surrounding the more superficial lol>ules pass to the surface of the liver, upon which they anastomose extensi\ely to form a subsennis net-work from which efferent stems arise. The deep eft'erents which accompany the branches of the portal vein take their course in the substance of the capsule of Glisson, two or three stems accompanying each of the larger branches of the vein and anastomosing with one another to form a plexus around the vessel and the accompanying branches of the hepatic artery and bile-duct. As the branches of the vein are followed to their union to form larger trunks, the accompanying lymphatics unite to a considerable extent, so that from fifteen to twenty stems emerge at the trans\ erse fissure and terminate in the hepatic Lymphatics of postero-itiferior surface of liver, a, a. trunks arising from vicinity of right border of liver and ^oing to one of the nodes surrounding inferior cava iC) as it enters thorax; *. trunk arising from inferior sur- tace of right lobe and emptying at hilum into nodes resting on neck of gall-bladder; c, trunks arising near gall- bladder and going to lower hifum-nodes : rf, trunks running on attached surface of gall-bladder; e.e,e, trunks that take origin from superficial net-works and disap))ear in liver to follow branches of portal vein to hilum- nodes; /,/,/. caval nodes receiving vessels from Spigelian lobe {g)\ It. /;, i)tincipal trunks of left lobe; ?', i. i, trunks that arise from superficial net-works and dip into liver to join vessels in capsule of Glisson ; j. trunks from superior surface of liver which follow round ligament to hilum-nodes; k. trunks from superior surface that end in nodes in posterior part of longitudinal fissure (/) ; m, trunks coiniecling these nodes with those in hilum; n (14), nodes connected with terminal part of (esophagus; o. o, o (is), hilum nodes which receive all trunks accompanying vena porta and large part of those from interior surface; />,/>, vessels from quadrate lobe (q). (Sappey.*) nodes situated in the fissure. The stems which accompany the branches of the hepatic vein also form more or less distinct plexuses, and, when they emerge from the liver substance, are from five to six in number. They continue upward along the inferior vena cava, pass with it through the diaphragm, and terminate in the nodes situated on the convex surface of the diaphragm around the orifice for the vena cava. The superficial vessels have more diversified courses, and it will be convenient to consider them as belonging to tw^o groups according as they arise from the superior or inferior surface of the liver. And first those arising from the net-work of the superior surface mav be described. Those which arise toward the posterior portion of the surface of both the right and left lobes pass mainly toward the vena cava inferior and ascend with it through the diaphragm to terminate in the nodes situated * Description et Iconoi^raphie des \'aisseaux iymphatiques, 1874. THE LYMPHATICS OF THE ABDOMEN. 981 around the opening for the vena cava. From the more lateral portions of each lobe, however, the collecting stems take a different course, those from the right lobe uniting to form a single stem which passes backward between the layers of the rio-ht lateral (triangular) ligament, and then passes medially o\'er the surface of the right crus of the diaphragm to terminate in the nodes surrounding the coeliac axis. Those from the lateral portions of the left lobe pass backward between the layers of , the left lateral (triangular) ligament and terminate in the nodes of the superior gastric group which are situated in the neighborhood of the cardiac orifice of the stomach. The collecting stems of the anterior portion of the superior surface are relatively small and are more conspicuous on the right lobe than on the left. They pass forward and downward to curve around the anterior border of the liver, and join with the stems arising from the quadrate lobe and gall-bladder to pass with these to the hepatic nodes situated in the transverse fissure. , Finally, much more important than these, is a group of vessels which arise from a rich subserous net-work situated alono- the line of attachment of the suspensory (falciform) ligament. Some of these vessels take a backward course toward the vena cava and accompany the other vessels of the superior surface which terminate in the caval diaphragmatic nodes, and others pass forward until they meet the upper portion of the round ligament, which they follow to reach the nodes situated in the transverse fissure. The remaining stems of the group, from three to ten in number, pass forward and upward, between the layers of the suspensory ligament, toward the under surface of the diaphragm, traverse that structure near its anterior attachment, and come into connection with a number of small nodes situated behind the xiphoid process of the sternum. From these they are continued upward along the course of the internal mammary vessels to terminate in the lower nodes of the inferior deep cervical group, usually upon the left side, rarely upon the right. This path is of importance as furnishing a direct route by which the metastasis of the left supraclavicular nodes, frequently induced by abdominal carcinomata, may be produced. It must, furthermore, be noted that both these vessels and others which arise from the superior surface of the liver com- municate somewhat extensively with the net-work occurring on the under surface of the diaphragm, and since this net-work communicates abundantly with that of the thoracic surface of the diaphragm, and this again with the vessels of the pleurae, opportunity is afforded for the development of pleuritis, especially upon the right side, as a result of a subdiaphragmatic infection. Turning now to the stems arising from the superficial net-work of the inferior surface of the liver, it will be found that they pass principally to the hepatic nodes situated in the transverse fissure, at least these nodes form the termination for the vessels passing from the left and quadrate lobes, the left half of the Spigelian and the anterior and middle portions of the right lobe. Those, however, which take their origin toward the posterior part of the right lobe and from the right half of the Spigelian pass to the vena cava and, ascending along it, terminate in the dia- phragmatic nodes surrounding its opening into the thorax. The lymphatics of the gall-bladder and common bile-duct have their origin in two net-works, one of which is situated in the mucosa and the other in the muscular coat. Efferents from both net-works pass to the surface to form a superficial net-work, from which collecting stems pass, in the case of the gall-bladder to the nodes situated in the transverse fissure, and in the case of the duct for the most part to a chain of nodes belonging to the hepatic group, which occurs along the line of the duct in the edge of the gastro-hepatic omentum ; those from the lower portion of the duct, however, associate themselves with stems from the duodenum and head of the pancreas which open into the uppermost nodes situated along the course of the superior pancreatico-duodenal vessels. Stated in brief, the destinations of the hepatic lymphatics are principally the hepatic nodes situated in the transverse fissure and the diaphragmatic nodes which surround the opening of the inferior vena cava. A vessel from the right lobe also passes to the coeliac nodes, some from the left lobe to the superior gastric nodes, and an important group passes up in the suspensory ligament to communicate with some of the anterior diaphragmatic nodes and terminate in the lower inferior deep 982 HUMAN ANATOMY. cervical nodes. Finally, it is to be remembered that numerous communications exist between the superficial hepatic lymphatics and those which form the net-work on the abdominal surface of the diaphragm. The Spleen. — The lymphatics of the spleen are arranged in a superficial and a deep set, numerous communications occurring between the two. The vessels of the superficial set are subserous in position and converge toward the hilus to terminate in the adjacent pancreatico-spknic nodes, to w^hich the deep lymphatics, \vhich accompany the blood-\cssels of the spleen, also pass. The Kidneys and Ureters. — The lymphatics of the kidney form three net- works, one of which is situated in the cortical tissue of the kidney, the second, whose meshes are very fine, is situated immediately beneath the fibrous capsule, while the third occurs beneath the peritoneum in the superficial portions of the adipose capsule. The efferents of the cortical net-work follow^ the branches of the renal vessels through the medullary substance and emerge at the hilus in the form of from four to seven \essels, which pass Pig. 823. /^"^ --^ toward the median line of the posterior abdominal wall along the course of the renal \'eins, and termi- nate in the upper nodes of the lateral lumbar groups ( P ig. 823). Those which come from the right kid- ney terminate partly in nodes which lie in front of the inferior vena cava, and partly in two or three large nodes which are situated behind that vessel upon the right crus of the diaphragm. The el^erents from these nodes pierce the crus and terminate directly in the thoracic duct. The uppermost nodes to which the vessels of the left kidney pass are situated upon the left crus of the diaphragm and their efferents also pierce the crus to open into the thoracic duct ; the efferents from the remaining nodes concerned unite with those of the other lateral lumbar nodes to form the lumbar trunks which open into the receptaculum chyli. The net-work which lies beneath the fibrous capsule communicates with both the cortical and subserous net-works, and its drainage is probably mainly through these : a few stems, however, pass toward the hilus, beneath the capsule, and unite with the terminal efferents from the cortical net-work, there being no direct connection betw^een the net-work and the lumbar nodes. The case is different with the subserous net-work, its efferents passing to the upper lateral lumbar nodes quite independently of the cortical efferents. As already noted, it has abundant communication with the net-work beneath the fibrous capsule, and through this with the cortical net-work, so that infections of the kidney tissue are readily communicated to the adipose capsule. The lymphatic net-works of the ureters appear to be limited to the muscular coat and the surface of the ducts (Sakata). The efferents which arise from the upper portions of the net-works, that is to say from the portions above the level at Ovary Lymphatics of kidneys and of ovary, new-born child. (Stahr.*) *Archivf. Anat. u. Physiol., 1900. THE LYMPHATICS OF THE PELVIS. 983 Fig which the ureter is crossed by the spermatic (ovarian) artery, pass upward to unite with the renal efferents or occasionally to terminate directly in the upper lateral lumbar nodes (Fig. 824). The majority of the efferents arise from those portions of the ducts intervening between the crossing of the spermatic (ovarian) arteries and the level at which the ureters cross the common iliac vessels to enter the pelvis, and these vessels pass either to the lower lateral lumbar nodes, or else, in the case of the lower ones, to the upper iliac nodes. Finally, the efferents from the pelvic portions of the ureters either unite with the vessels passing from the bladder, or else communicate directly with certain of the hypogastric nodes. In and beneath the fibrous capsule of the suprarenal bodies a lymphatic net-work occurs, whose efferents on the one hand join the renal lymphatics, and on the other pass into the substance of the organs to communicate with a net- work situated in the glomerular portion of the cortex. From this latter net-work stems pass centrally in the partitions between the cell columns of the cortex to unite with a rich plexus which traverses all portions of the medullary substance. The main stems of this plexus follow the course of the suprarenal blood-vessels and emerge at the hilus of the organ as four or five stems, which pass to the upper lateral lumbar nodes. Some of the stems are also said to pierce the crura of the diaphragm and terminate in the lower nodes of the posterior mediastinal group. Lymphatics of ureters. (Based on several figures by Sakata.*) THE LYMPHATICS OF THE PELVIS. The Lymph-Nodes. The pelvic lymphatic nodes are arranged along the courses of the principal vessels, and may conveniendy be divided into three groups, the iliac, the hypogastric, and the sacral nodes. In addition some small inconstant nodes occur in association with the bladder and these will be described in connection with the vessels arising from that organ (page 985). The epigastric and circumflex iliac nodes, already described in connection with the abdominal region (page 972), are really outliers of the iliac group. The iliac nodes (Fig. 825) are from fifteen to twenty in number and form a plexus (plexus iliacus externus) along the course of the common and external iliac vessels, the uppermost nodes lying at the level of the bifurcation of the aorta and the lowermost around the point of exit of the external iliac vessels beneath Poupart's ligament. Three more or less distinct linear series of nodes can be recognized in the plexus, one of which, along the course of the common iliac artery, is situated close to the outer surface of the artery and along the medial border of the psoas muscle. The second lies behind the artery, resting upon the anterior surface of the vein, while the third unites with its fellow of the opposite side to form a group of three or four nodes resting upon the left common iliac vein and the promontory of the sacrum in the angle formed by the bifurcation of the aorta. Of the series along the line of the external iliac vessels one lies to the outer side of the artery along the medial Archiv f. Anatom. u. Physiol., 1903. 9H HUMAN ANATOMY. border of the psoas, the second in the angle between tlie \ein and the artei\-, and the third along the lower border of the vein, l)etwcen it and the obturator nerve. The \arious nodes of the iliac set coninuinicate with one another so that the iff ( nuts of one node are ajfitrnts for the higher ones. In addition they recei\e ajfennts from the inguinal nodes as well as from the epigastric and circunifle.\ iliac nodes as already stated, and the group situated over the promontory of the sacrum also receives afiferents from both the hypogastric and sacral nodes. Furthermore, aft'erents pass to the iliac nodes from the pehic portions of the ureters, from the bladder and prostate gland, from the lower portion of the uterus and the upper portion of the vagina, from the glans penis and clitoris, from the adductor muscles of the thigh through vessels accomixmying the obturator artery, and, in the case of the lateral series of nodes, from the ])soas muscle and the adjacent sul)serous tissue. The cjffcrcnts pass to the lower lateral lumbar nodes. The internal iliac or hypogastric nodes ( hmphojilandulac hvpogastricao are from nine to twelve in number on each side, and are situated on the lateral walls of the pelvic cavity, along the course of the internal iliac vessel and its branches Fig. S25. Lower lumbar node Iliac nodes Iliac node of promontory group Superficial inguinal nodes Iliac nodes. (Cun'eo and Marcille.*) (Fig. 825). They are connected together to form a plexus (plexus hypoKastricusj, and receive afferents from most of the regions to which the branches of the internal iliac artery are distributed. Thus branches come to them from all the peKic organs, from the deeper portions of the perineum, including the penial j)ortion of the urethra, from the deep portions of the posterior and internal femoral and the gluteal regions. Their efferents pass mainly to the iliac nodes situated on the promontory of the sacrum, those which arise from the obturator node, situated upon the obturator artery as it passes through the obturator foramen, passing, however, to nodes belonging to the inner series of the group accompanying the external iliac \essels. The sacral nodes are situated on the ventral surface of the sacrum, partly along the course of the middle sacral vessels, and partly internal to the second and third anterior sacral foramina, along the course of the lateral sacral arteries (Fig. 829). All the nodes are small and they are united together by lymphatic vessels to form a sacral plexus Tplexus sacralis medius). They receive affcrnits from the neighboring muscles and from the sacrum, and their efferents pass to the iliac nodes situated upon the promontory of the sacrum. The Lymphatic Vessels. Under this heading will be considered the vessels of the \arious pelvic organs, with the exception of those of the rectum, which have already been described (page 979). In addition there will be included the vessels of the external genitalia. Bull, et Mem. Society anatom., 1901. THE LYMPHATICS OF THE PELVIS. 985 Obliterated hypogastric artery Anterior vesical node Lateral \esical node and, on account of their intimate relation with these, the superficial lymphatics of the perineal and circumanal regions. The Bladder. — It was for a long time a matter for discussion whether or not the mucosa of the bladder was provided with a lymphatic net-work, but the general consensus of recent observers is that it is not. Only the muscular coat possesses a net-work, and from this stems pass to the surface of the viscus to form a superficial net-work beneath the peritoneal or fascial investment. This net-work is continuous at the neck of the bladder with those of the urethra and prostate gland, and, at its base, with the net-works of the ureters and seminal vesicles, and, in the female, of the vagina. The efferent stems which take origin from it may be divided into two groups according as they arise upon the anterior or posterior surface. Those passing from the lower part of the anterior surface are directed laterally and those from the upper part pursue a flexuous course downward and laterally to terminate in the nodes of the iliac group situated along the external iliac vessels (Fig. 826). In their course they usually traverse some small nodes situated in close proximity to the bladder and divisible according to their Fig. S26. position into two groups. One of these is situated upon the anterior surface of the bladder, and consists of two or three nodes, the anterior vesical nodes, two of which are usually situated near the apex of the vis- cus in the course of the superior vesical artery, while the third occurs lower down in the retro- pubic tissue. The other group consists of from two to four nodes, the lateral vesical nodes, situated on either side of the bladder along the course of the obliterated hypogastric arteries. Both groups are some- what inconstant, but occur in a large percentage of cases. The vessels from the upper part of the posterior surface of the bladder pass downward and laterally, often traversing some of the lateral vesical nodes, and terminate in the external iliac nodes which receive the stems from the anterior surface. Others pass to the hypogastric nodes, while others again, arising from the base of the bladder, pass at first directly backward past the lateral surfaces of the rectum and then ascend on the sacrum to terminate in the iliac nodes situated upon the promontory. The Prostate Gland. — The lymphatics of the prostate have their origin in net-works surrounding the various acini of the gland. From these net-works stems pass to the surface, where they form a second net-work, and from this the efferent stems pass symmetrically on either side of the median line to somewhat diverse terminations. One or two of the efferents on either side ascend in a tortuous course upon the posterior surface of the bladder, and then bend laterally over the obliterated hypogastric arteries to terminate in one of the middle series of the iliac nodes which accompany the external iliac vessels. Another stem passes backward along the prostatic vessels to terminate in one of the hypogastric nodes ; others pass at first backward on either side of the rectum, and then ascend upon the anterior surface of the sacrum to terminate in the lateral sacral nodes or in the iliac nodes situated on the promontory of the sacrum ; and from the anterior surface of the gland a stem Subhypogastri Anterior vesical node Lymph-nodes of bladder. (Eased on figures of Gerota.*) *Archivf. Anatom. u. Physiol., 1897. 986 HUMAN ANATOMY. Fig. passes downward on cither side of the menil^ranous portion of the urethra, and, aeconipanying the urethral lymphatics along: the course of the internal pudic vessels, terminates in one of the hypogastric nodes situated upon these vessels. The Urethra. — The mucous membrane of the male urethra is furnished throughout its entire extent with a lymphatic net-work, which is especially rich in the region of the glans and tliminishes in complexity in the membranous and prc^static portions of the duct. In the last region it communicates with the net-work in the muscular coat of the neck of the bladder. The efferents from the membranous portion of the duct associate themselves with some of the prostatic efferents and pass to a hypogastric node situated on the course of the internal pudic vessels, and those from the penial portion accompany the vessels vvhich arise from the glans and will be described in the account of the lymphatics of the penis. The net-work of the female urethra corresponds with those of the membranous and prostatic portions of the male duct. The External Reproductive Organs in the Male. — The lymphatics of the scrotum form an exceedingly rich net-work, especially well developed in the vicinity of the raphe and thence extending laterally over the entire surface. From six to eight stems arise from ^^7- this net-work, and the uppermost accompany and eventually anasto- mose with the superhcial efferents from the penis and terminate in the in- ner inguinal nodes. The remaining stems pass upward and outward to terminate in the inner superficial subinguinal nodes. The lymphatics of the penis are di\isible into a superficial and a deep set which correspond respectively to the super- ficial and deep blood- vessels of the organ. The superficial set forms a net-work in the integu- ment of the penis which radiates in all directions from the frenulum, some stems passing forward and upward into the prepuce and some especially strong stems passing dorsally in the furrow behind the corona of the glans. As they approach the dorsal mid-line these latter give off one or two longitudinally directed efferents, or else they unite to form a single stem which runs along the dorsal mid-line. Other stems arising from the more proximal portions of the net-work curve upward from below over the lateral surfaces of the penis, and either unite with the dorsal stems or form independent lateral stems parallel with the dorsal ones. Numerous anastomoses occur between all the longitudinal stems throughout their courses, and, as they approach the symphysis, they bend laterally, some indeed dividing to send branches to either side, and, after the upper stems from the scrotum have united with them, they terminate in the inner inguinal nodes. The deep set forms a net-work especially well developed in the glans, in which a superficial and a deep layer may be distinguished. Both these layers communicate at the meatus with the urethral net-work, and from the deeper layer a special plexus Superficial lymphatic vessels of penis and scrotum and inguinal nodes. (Bruhns.*) Archiv f. Anat. u. Physiol., 1900. THE LYMPHATICS OF THE PELVIS. 987 is developed on either side of the frenulum i^Panizza' s plexus'), from which stems ascend in the groove back of the corona glandis. Into these stems the superficial layer of the net-work opens, and they also receive communications from the super- ficial vessels of the penis. From them one or two stems arise which pass proximally in company with the dorsal vein of the penis toward the suspensory ligament. Here they usually divide to form a more or less distinct plexus, lying immediately over the symphysis pubis and provided with some small lymphatic nodes, and from it two or three stems pass off laterally on either side. These pass across the surface of the pectineus muscle and beneath the spermatic cord, and some then pass either to the inner inguinal or deep subinguinal glands, while others extend along Poupart's ligament to the external abdominal ring and, traversing the inguinal canal, terminate in one of the lower iliac nodes. It is to be noted that owing to the anastomoses and bifurcations of both the superficial and deep longitudinal stems it is possible that a unilateral infection may cause enlargment of the nodes of both sides. The External Reproductive Organs in the Female. — The lymphatics of the external female genitalia have essentially the same distribution as those of the corresponding organs in the male. In both the labia majora and minora rich subcutaneous net-works occur, from which numerous stems arise and pass to the inner- most inguinal and occasionally the inner superficial subinguinal nodes. The stems from the upper parts of the labia ascend at first directly upward toward the mons veneris and then bend suddenly outward to reach their terminal nodes ; those from the lower parts pass either directly upward and outward or else at first directly upward parallel to the outer edges of the labia and then bend suddenly outward. Some of the stems coming from one or other of the labia may pass to the nodes of the opposite side, and, furthermore, communications exist through the anterior and posterior commissures between the net- works of the opposite labia, so that a unilateral infection may produce enlargement of the inguinal nodes on both sides. The lymphatics of the clitoris present essentially the same arrangement as the deep lymphatics of the penis. They form a rich net-work in the glans and from this longitudinal stems arise and pass toward the symphysis pubis, in front of which they form a plexus which usually contains some small nodes. From the plexus stems arise which pass laterally, and terminate either in one of the deep subinguinal nodes or else in the lower iliac nodes, which they reach by traversing the inguinal canal. The Perineum and Circumanal Regions. — The deeper lymphatics of these regions have been considered in connection with the organs to which they belong and there remain for consideration only the subcutaneous vessels. These in the perineal region form an abundant net-work from which stems pass forward, for the most part in the furrow between the perineum and the inner surface of the thigh, and, associating themselves with the stems from the scrotum or labia majora, terminate in the inner inguinal or superficial subinguinal nodes. The subcutaneous lymphatics which surround the anal opening also form a rich net- work, which communicates extensively with that of the anal mucosa (page 979). From it some two or three stems pass forward along the inner side of the thigh to terminate with the perineal and scrotal (labial) stems in the inner inguinal nodes. The Internal Reproductive Organs in the Male. — The testis possesses an abundant supply of lymphatics, which may be divided into a deep and a superficial set. The former takes its origin in a rich net- work which surrounds the seminal ducts, and the stems which compose it pass toward the hilum in the septa, and, issuing, associate themselves with the stems arising from the superficial net-work. This is double, one layer of it lying beneath the tunica albuginea and the other between that investment and the visceral layer of the tunica vaginalis. Both layers are abundantly connected by vessels which traverse the tunica albuginea, and the deeper layer also receives numer- ous comniunicating stems from the deep lymphatics and from the lymphatics of the epididymis. Collecting stems from both layers converge toward the hilum, where they become associated with the stems from the deep net-work, from six to eight or rarely more trunks which ascend along the spermatic cord to the internal abdominal ring. They then follow the course of the spermatic veins upward, and terminate in from two to four of the lateral lumbar nodes (Fig. 816). The nodes to which the vessels from 988 lllMAX ANATOMY the left testis pass lie immediately l)eneath the level of the renal veins, while those in which the stems from the rii^ht testis terminate are lower, beiny situated about midwav between the level of the renal vein and the junction of the common iliac veins. The Ivmphatics ot the vas deferens are ])robably arranged in two net-works, one belonging to the mucosa and the other to the muscular coat, although so far only the latter net-work has been demonstrated. At the testicular end of the duct the net-work communicates with that of the epididymis, and the stems which arise from it accomixmy those of the testis to the lateral lumbar nodes. At the vesical end the net-work communicates with that of the seminal vesicles and its efferents pass to one of the hypogastric nodes. The lymphatics of the seminal vesicles are much more readily demonstrable than those of the vasa deferentia. They arise from two net-works, one of which is situated in the mucosa and the other in the muscularis. Stems from the latter form a third net-work over the surfaces of the vesicles and from this efferents, two or three in number, ])ass to some of the liypogastric nodes. The Internal Reproductive Organs in the Female. — Tlie lymphatics of the ovary are very abundant throughout the substance of the organ, a fine net-work Fig. S2S. Lateral lumbar node Lymphatic vessels from fundus- of uterus Iliac node Lymphatic vessels from body and cervix of uterus Ureter Lymphatic vessels from ovary and upper part of uterus Ovary Fallopian tube Bladder Lymphatics of internal reproductive organs of female. (Poirier.*) surrounding each of the Graafian follicles. The stems which arise from these net- works converge toward the hilus, where they form a rich plexus and from this from six to eight efferents arise and follow the ovarian blood-vessels to terminate in the lateral lumbar nodes (Fig. 828). Owing to thinness of the walls it is difficult to distinguish a definitely layered arrangement of the lymphatic net-work of the Fallopian tubes. It is, however, rich, and communicates with that of the fundus of the uterus. It gives rise to two or three efferents which accompany the ovarian efferents to the lateral lumbar nodes. *Progres Medical, 1890. THE LYMPHATICS OF THE PELVIS. I Iliac node of promontory group In the uterus (Figs. 828, 829) the conditions are much more favorable for determining the existence of separate net-works in the mucosa and muscularis than in the Fallopian tubes, but, nevertheless, much difference of opinion exists as to the occurrence of a mucosa net-work. That of the muscularis can be injected without difficulty, but no conclusive injections have yet been made of the mucosa, and while some authors (Bruhns, Sappey, Poirier) are incUned to admit the existence of a net- work in it, others (Leopold) deny it. However that may be, a well-developed net-work occurs in the muscular coat, in the deeper portions of which it becomes especially rich, and. furthermore, it is more abundant in the cervix than in the body or fundus. From it stems pass to the surface of the organ to form a subserous net-work, from which a number of efferents arise. These may be divided into three principal groups according to their termina- tions. ( I ) The efierents from the fundus, usually two in number, pass outward on either side in the upper portion of the broad ligament, and, associating themselves with the efferents from the ovary, terminate in the lateral lumbar nodes. (2) Small stems pass from the fundus along the round ligament of the uterus to terminate in the inguinal nodes. (3) The P^^ g^g efierents from the body and cervix pass laterally to terminate in the median iliac nodes situated in the angle between the external and internal iliac arteries. In the course of these last vessels, at the point where they cross the ureter, a small idero-vaginal node is occasionally placed. Other efferents have been described as passing from the cervix to a hypo- gastric node situated at the origin of the uterine or vaginal artery, and two or three stems have been found arising from the posterior surface of the cervix and passing back- ward on either side of the rectum to the anterior surface of the sacrum, up which they pass to terminate in the iliac nodes situated upon the sacral promontory CFig. 829). In the vagina there is no question as to the existence of definite net-works in both the mucosa and muscularis. That of the mucosa (Fig. 830) is exceptionally fine and communicates abundantly with the coarser net-work of the muscularis, as well as with the net-work of the \-aginal portion of the cer^'ix above and with that of the labia minora below. From the muscularis net-work stems pass to the surface of the organ to form a third net-work, from which the main efferent stems arise, and these may be arranged in three groups according to their destinations: (i) those which arise from the tipper portion of the vagina join the stems which pass from the cervix of the uterus (Fig. 830) and terminate with these in the median iliac nodes situated in the angle formed by the external and internal iliac arteries ; (2) those arising from the middle portion accompany the vaginal vessels, pasbing obliquely upward, outward, and backward, to terminate in one or two hypogastric nodes situated at the origin of the uterine arteries ; and (3) those from the loiver portion associate themselves with those from the labia minora and terminate with these Lymphatics of uterus. {Cun'eo and ATarcille.*) *Bu]I. et Mem Societe anatom., iqo2. 990 HUMAN ANATOMY. in the inner injTuinal nodes. Certain of tiie stems from tlie middle ix)rtion also pass to the same middle iliac nodes which receive the effcrents from the upper i)ortion, and stems have been observed Fig. S30. Eflerents from cervix uteri Efferents ^ from iiife- _____^/ rior group ~7 \ Lymphatic net-work of vaginal mucous membrane. {Poirier.*) (Bruhiis) passing from the posterior surface of the vagi- na to the lateral lumbar nodes and e\en to the iliac nodes situated on the promontory of the sacrum, while others have been traced to the anorectal nodes (page 976). Finally, it may be noted that the superficial net-work of the anterior surface of the vagina communicates with that of the posterior surface of the bladder. Practical Considera- tions.— The Lyinph- Abodes of the Abdomen and Pelvis. — The snperjieial lymphatics of the wall of the abdomen convey infection, if the pri- mary focus is abo\"e the level of the umbilicus, to the axil- lary nodes ; if it is below that level, to the inguinal nodes. Hence, in cases of furuncle or carbuncle, or of chancre, or of epithelioma, the site of the lesion would determine the region in which adenopathy should be sought. The cicliae group of nodes may be involved in diseases of the greater portion of the digestive tract, or of the stomach, spleen, or part of the liver ; or their enlarge- ment may follow that of the lumbar or of the mesenteric nodes. The nodes in and about the portal fissure, or between the layers of the gastro-hepatic omentum may so enlarge in cases of carcinoma of the stomach or of the li\er as to compress the portal vein (causing ascites) or the common bile duct (causing jaundice). The lymphatic relations of the stomach, liver, spleen, and pancreas have been sufficiently considered from the practical stand-point in connection with these viscera. The mesenteric nodes are frequently and gra\ely involved in various intestinal diseases. They are often infected and enlarged during typhoid fever. They are especially implicated in jx^ritoneal or intestinal tuberculosis. The lymphoid nodules in the neighborhood of Peyer's patches are surrounded by lymphatic plexuses and are a common site of tuberculous ulceration. The bacilli tuberculosis are carried direcdy thence to the mesenteric glands (tabes mesenterica), and sometimes by way of the lymphatic vessels and thoracic duct, may reach the general circulation in large numbers (generalized tuberculosis, acute miliary tuberculosis). In some cases of tuberculous peritonitis associated with mesenteric gland disease, the mesentery undergoes marked and extreme contraction, so that the altered coils of intestine are held closely to the spine, and their lumen may be greatly narrowed (peritonitis deformans) (Tavlor). Mesenteric cysts (serous or chylous cysts) are usually of lymphatic origin, and may be due to lymphatic obstruction or to a degeneration and dilatation of the mes- enteric nodes analogous to the varicosity of inguinal nodes in filarial disease. The clinical signs of such cysts are : i, a prominent, fluctuating, usually spherical swell- ing near the umbilicus ; 2, marked mobility of the tumor— especially in a transverse direction and around the central axis ; 3, the presence of a zone of resonance around the cyst and a belt of resonance across it (Moynihan). The symptoms may be * Progres medical, 1890. THE LYMPHATICS OF THE LOWER EXTREMITY. 991 either (a) chronic, of the nature of colicky pain due to interference with the intes- tine and to gastro-intestinal disturbance, the presence of a tumor distinguishing the case from one of simple gastro-enteritis ; or (^d) those of acute intestinal obstruction (RoUeston). The himbar nodes may be enlarged from septic or malignant disease of the lower extremities, the testes, the fundus of the uterus, the ovary, the kidneys and adr'enals, the sigmoid or rectum. The wide area thus drained by them exposes them frequently to transmitted infection or disease. Their condition in the presence of carcinoma affecting any of these regions or viscera has an important practical bearing upon the question of operative interference, as, practically without excep- tion, if they are involved only palliation can be hoped for. With an empty intes- tinal tract and a thoroughly relaxed abdomen, even moderate enlargement of these nodes may, in thin persons, be detected by palpation. In persons with very mus- cular or very fat abdominal walls, they cannot be felt until they have formed a con- siderable mass. Their great enlargement — especially in carcinoma — often results in swelling and oedema of the lower extremities on account of the obstruction to the current in the inferior cava produced by the pressure of the dense indurated glands which may quite encircle both that vessel and the aorta and may even interfere with the circulation in the latter. The lumbar nodes often enlarge consecutively to enlargement of Xh^ pelvic nodes (obturator, gluteal, sciatic, internal pudic, external and internal iliacs), some of which are also palpable — in thin persons — when the subject of carcinomatous infiltration. The external iliac nodes, for example, lying along the anterior and inner aspect of the external iliac vessels, may, when cancerous, be recognizable in this way, and may be found by their tenderness — though less distinctly felt — in some septic cases. As they receive the lymphatic vessels from the nodes of the groin, and the vessels accompanying the deep circumflex iliac arteries, their enlargement may follow that of the inguinal nodes, or may result from septic or syphilitic or cancerous foci in the supra-inguinal portion of the abdominal wall. In cancer of the testis the iliac and lumbar nodes are in the closest relation to the ascending current of lymph, the inguinal nodes, as a rule, being involved later, after the skin of the scrotum has become infiltrated or ulcerated. In advanced cases, of carcinoma of the rectum or uterus, the obturator, epigastric and external iliac groups become considerably affected. CEdema of the legs often results because («) the enlarged nodes press directly upon the external iliac vessels ; and {b') the lymphatics pass both over and under these vessels to communicate with the obturator node and thus compress the vein in a ring-like carcinomatous mass (Leaf). The pain felt in these cases is due to the pressure of the affected glands upon the nerve-trunks arising from the lumbo- sacral plexus. Similar pains may be felt when any of the pelvic glands are involved as there is a similarly close relation between the obturator node and the obturator nerve ; the gluteal, sciatic, and internal pudic nodes and the first and second sacral and great sciatic nerves ; and the external iliac nodes and the anterior crural nerve. The obturator group of nodes lying between the external iliac vein and the obturator nerve assume surgical importance because sometimes the lowest node of this group is found projecting through the crural canal. The relation of this node to Gimbernat's ligament shows that when enlarged it would appear as a swelling occu- pying a position similar to that of a femoral hernia (Leaf). Cases are on record (White) in which an inflammation of this node has simulated a strangulated femoral hernia. THE LYMPHATICS OF THE LOWER EXTREMITY. The Lymphatic Nodes. The Inguinal Nodes. — The principal group of nodes of the lower extremity is situated in the inguinal region over Scarpa's triangle, where they form a consider- able mass, placed for the most part between the layers of the fascia lata, and consist of from twelve to twenty nodes united by connecting branches to form a plexus, the plexus inguinalis. Though in reality forming a single group, they have been divided for purposes of description into a number of subordinate groups which must be recognized to have merely a conventional value. The first of these divisions is a 992 HUMAN ANATOMY. Fig. 81^1. separation of the nodes which he respectively above and below a horizontal line drawn throui>h the point at which the loni; saphenous win pierces the cribriform fascia, and to those lying above this line the term inguinal nodes ( lymphoiiUindulae hiiiuinalcs) is applied, while those below it are termed the subinguinal nodes (lymphojulandulac siil>iniininales). This latter subgroup is again divided into a stipcr- Jicial ( hmpiioiilaiKlulac subiiiiiuinales supcrticiales) and a deep (lyin|)ho<;lan(liilae sub- iiiiiiiiiialcs profimdae ) set, according as they are situated on or beneath the fascia lata. I-inallv, l)v means of a vertical line passing through the orifice in the cribriform fascia through which the long saphenous vein passes, the inguinal and superficial subinguinal groui)S are each subdivided into an inner and an outer set, a small central group of nodes, surrounding the saphenous orifice, being also sometimes recognizable. It niav, however, again be emphasized that these subdivisions are purely conventional and cannot always be clearly distinguished, nor do they represent, except in a very general way, the terminations of tlefinite drainage areas. Indeed, the numerous connections which exist between the nodes of the various subgroups cause their distinction to be of comparatively little importance from the surgical stand-point. The inguinal nodes are arranged in a more or less distinct chain over the base of Scarpa's triangle, immediately below Poupart's ligament. They receive as ajferents the superficial lym])hatics of the abdominal walls and the gluteal region, the superficial vessels of the scrotum and penis in the male and of the labia majora and minora in the female, as well as those from the perineum and the circumanal region. Their efferents perforate the cribriform fascia, enter the abdomen by the femoral ring, and terminate in the lower iliac nodes. The superficial subinguinal nodes recei\e some afferents from the gluteal regions and also some from the perineum and circumanal regions, but the principal set is formed by the superficial vessels of the leg. Their efferents have essentially the same course as those of the inguinal nodes, piercing the cribriform fascia to accompany the femoral vessels to the abdomen, where they terminate in the lower iliac nodes. In their course through the femoral sheath some of them lie on the anterior surface of the vessels, but the majority lie on their inner side in the crural canal and some of them terminate in the deep subinguinal nodes. The deep subinguinal nodes vary in number from one to three. They are placed along the course of the femoral vein, one occurring immediately beneath the point of junction of the long saphenous vein with the femoral, a second a little higher up in the crural canal, and the third, termed by French authors the node of Cloquet and by the Germans the node of Rosenmiiller, is situated at the entrance into the crural canal from the abdomen. Their principal afferents are the deep lymphatics of the thigh which accompany the femoral vessels and their branches, but in addition they recei\e stems from the superficial subinguinal nodes and the deep vessels of the penis and clitoris. Their efferents pass, like those of the superficial nodes, to the lower iliac nodes. The popliteal nodes riymphoslandHlae popliteae) are some four or more in number and are embedded in the adipose tissue of the popliteal space (Fig. 832). One or two occur in the neighborhood of the short saphenous vein immediately after it has entered the popliteal space, while the rest are situated more deeply upon the popliteal vessels. The more superficial nodes receive as afferents the superficial lymphatics of the leg which accompany the short saphenous vein, while the deeper Superficial inguinal 1\ mph-iiodes; horizontal line subdivides nodes into upper and lower groups; vertical line into median and lateral groups. THE LYMPHATICS OF THE LOWER EXTREMITY. 993 Popliteal lymph-nodes. {Poirier and Ciineo.*) ones receive the vessels which accompany the branches of the popHteal \'essels and also those accompanying the anterior and posterior tibial vessels. Their efferents for the most part accompany the femoral vessels to terminate in Fig. 832. the deep subinguinal nodes. The anterior tibial node (lymphoglandula tibialis anterior) is a small and probably inconstant node situated in the upper part of the course of the lymphatic vessels which accompany the anterior tibial artery. Its effer- ents pass upward along with the anterior tibial and popliteal blood-vessels to terrninate in the deeper popliteal nodes. The Lymphatic Vessels. The lymphatic vessels of the lower extremity may be divided into two groups, one of which consists of the subcutaneous net- work and its efferent stems and the other of those vessels which accompany the principal blood- vessels. The superficial lymphat- ics take their origin from a net-work distributed throughout all portions of the subcutaneous tissue of the extremity, but increasing in richness and complexity toward the distal part of the limb, until in the foot, and especially in the plantar region, it forms a very close and abundant net-work. This plantar net-work extends not only throughout the entire plantar region, but curves dorsally upon both the outer and inner borders of the foot, and also over the posterior surface of the heel, and from these lateral and posterior portions of the net-work as well as from the subcutaneous net-work of the digits numerous collecting stems arise. These anastomose abundantly, and those from the digits, the whole of the inner border of the foot and the distal half of its outer border form an open plexus upon the dorsum of the foot. The stems, several in number, which arise from this plexus pass upward along the inner surface of the leg (Fig. 833), following in general the course of the long saphenous vein and receiving as they go communications from the superficial net-works of the regions they traverse. In the neighborhood of the knee stems arising from the net-work over the anterior tibial region become associated with them, and above the knee branches which drain the net-work of the outer, inner, and posterior surfaces of the thigh also curve upward and inward or forward, as the case may be, to accompany them. The numerous stems so formed are all situated superficially to the fascia lata, and terminate above in the superficial subinguinal nodes, the more anterior stems passing to the outer and the more posterior to the inner members of the group. The stems which arise from the calcaneal portion of the plantar net-work and from that portion of it which curves upward over the posterior half of the outer border of the foot, pass upward upon the posterior surface of the crus in company with the short saphenous vein. They receive communications from the superficial net-work of the calf and, as they approach the bend of the knee, they perforate the crural fascia and terminate in the more superficial popliteal nodes. Finally, from the net-work over the gluteal region a number of collecting stems arise, the majority of which curve forward and converge to terminate in the outer inguinal nodes, some from the more posterior portions of the net-work, however. * Poirier et Charpy : Traits d'anatomie humaine, Tome ii., 1902- 63 994 HUMAN ANATOMY. Fig. 833. passing forward along with the stems from the circumanal region to the inner inguinal or siipirticial sul)inguinal nodes. The deep lymphatics of the lower extremity take their origin mainly in the muscles and form stems which accompany the blood-vessels. From the net-work of the plantar muscles one or two stems take origin w hich follow the course of the plantar arch, ascending to the dorsum of the foot between the first and second metatarsal bones. They then follow the course of the dorsal pedal vessels, recei\'ing the stems which accompany their branches, and then accompany the anterior tibial vessels up the leg. After traversing the anterior tibial nodes they pass with the vessels through the foramen m the interosseous membrane, and, continuing their upward course through the popliteal space, terminate in the deeper popliteal nodes. Other branches arising in the plantar musculature follow the plantar vessels backward, and, ascending behind the internal malleolus, accompany the posterior tibial vessels. Toward the upper part of the crus they receive the stems which accompany the peroneal vessels and their branches, and terminate, like the anterior stems, in the deeper popliteal nodes. From these nodes four large stems issue, and, passing through the hiatus tendineus of the adductor magnus, continue their course up the thigh in company with the femoral vessels. They receive the stems which accompany the various branches of the femoral \essels and terminate above in the deep subinguinal nodes. In addition to these deep femoral lymphatics others occur in the thigh in company with the obturator and sciatic vessels, and the muscles of the gluteal region are drained by stems which accompany the gluteal vessels. All these stems terminate in nodes belonging to the hypogastric group, those accompanying the sciatic ves- sels traversing some small and inconstant nodes situated beneath the pyriformis muscle, while some ten or twelve similar nodes occur along the course of the gluteal stems. Practical Considerations. — The Nodes of the Loivcr Extremity. — The majority of the lymphatics of the sole of the foot unite with those of the inner side of the dorsum and run with the long saphenous vein to enter the inguinal nodes. A smaller number run up the fibular side of the leg. but most of these cross o^'er the leg or at the ham to join the inner lymphatic vessels. A still smaller number run with the short saphenous vein and empty into the popliteal nodes. The far more frequent occurrence of glandular swellings and abscess in the groin than in the ham is thus easily understood. The popliteal nodes {intercondyla7% lying on either side of the popliteal arterv between the t\\o heads of the gastrocnemius, and SKpracondylar, lying deeper and against the back of the femur) are extremely difficult to feel unless they are enlarged, and even then the only one which can be detected is that which lies over the internal popliteal nerve. This node, probably from the constant movement of the knee-joint, is very apt to suppurate as a result of superficial sores about the heel. The intercondylar nodes cannot be felt ; in the first place, because of their deep position, and secondly, because when pressed they become still further forced down between the condyles. The supracondylar nodes lie altogether too deep to be felt by the fingers TLeaf). A small node beneath the fascia close to the point of entry of the short saphenous receives some of the lymphatics that accompany that vein. Superficial lymphatic vessels of lower limb ; semiciiagramniatic. (Based on figures of Sappey.) THE LYMPHATICS OF THE LOWER EXTREMITY. 995 Popliteal abscess will follow pyogenic infection of the popliteal nodes. The pressure effects due to the density and rigidity of the popliteal fascia and the conse- quent necessity for early and free incision and drainage have already been described (pages 646). Enlargement of the popliteal nodes has been mistaken for enlarged bursae — tlaough the nodes are deeper and nearer the median line — for popliteal aneur- ism, and for neoplasms. The iiigidnal nodes are numerous and, on account of their frequent involvement in diseases of the lower extremity and of the genitals, are important. The arrange- ment into a superficial and deep set, and the division of the former into two groups, the horizontal, parallel with and close to Poupart's ligament, and the z'^-r/'zVa/, parallel with and close to the long saphenous vein, is of convenience. The deep set is found to the inner side of the femoral vein and may be said to include one group which is embedded in the fatty layer at the saphenous opening and bears the same relation to the fascia lata that the central group of axillary glands bears to the axillary fascia (Leaf) (page 581). The inguinal nodes receive lymph through the superficial lym- phatics as follows : Lower limb — vertical set of superficial nodes ; lower half of abdomen — middle nodes of horizontal set ; outer surface of buttock — external nodes of horizontal set ; inner surface of buttock — internal nodes of horizontal set, (a few of these vessels go to the vertical nodes ; external genitals — horizontal nodes, a few going to the vertical set ; perineum-vertical set. The deep lymphatics of the lower limb enter the deep set of nodes (Treves). The deep lymphatics of the penis and those that are found with the obturator, gluteal, and sciatic \-essels enter the pelvic nodes. The inguinal nodes comm.unicate with the external and common iliac nodes, the pelvic lymphatics Avith the internal iliac nodes, and both the iliac groups with the lumbar nodes. The deep node lying in the crural canal and upon the septum crurale is variously described as one of the obturator (pelvic) group (Leaf) and as one of the deep set of inguinal nodes (Treves). It should be remembered that when it is inflamed it may not only simulate strangulated hernia, but, on account of the density of the structures by which it is surrounded and their participation in the mo\'ements of the thigh, may give rise to pain suggesting coxalgia. The relations of branches of the anterior crural nerve to the inguinal nodes may, in cases of inflammation or enlargement, give rise to pain or spasm in the region supplied by that nerve. Filariasis (elephantiasis arabum) of the femoral lymphatics, which are obstructed by the worms, gives rise to very great swelling of the lower extremity (Cochin leg, Barbadoes leg). In addition to what has been stated above the practical application of a knowl- edge of the lymphatics of the lower extremity embraces the following considerations : {a) The lymphatic vessels may be inflamed without involvement of the veins, when the course of some of the main vessels can be distinctly traced under the skin. When chronically inflamed, and obstruction exists at the nearest lymphatic gland, the vessels may become thickened, dilated, and tortuous. The lymphatic vessels of the sheath of the penis are, perhaps, more frequently involved in diseased action than those of any other portion of the skin surface. Inflamed lymphatic vessels often co-exist with a chancre. In cases of neglected chancre, associated with an indurated condition of the lymphatic nodes of the groin, they may even form buUa-like swell- ings which sometimes rupture and permit the lymph to escape externally. Rarely dilatation of the lymphatic vessels occurs without apparent cause. (b) The lymphatic vessels may, from causes imperfectly understood, become filled with chylous fluid. In one (Petters), remarkable dilatation of the lymphatics existed in the right groin and in the abdomen, in a patient the subject of valvular heart disease. The glands were converted into cyst-like cavities filled with a yellow fluid. Rosary-like dilatations, similar to those seen at the elbow, occur infrequently below the groin. The inguinal lymphatic glands are the common seat of diseased action dependent upon the transmission of the virus of syphilis, or of any other irritant whose point of entrance is through the external genitals. In the nonsyphilitic infections they frequently suppurate or excite suppurative cellulitis in the parts about them. Acute inflammatory engorgement of one of them has been known to induce fatal peritonitis by direct continuity through the lymphatic vessels of the abdominal wall (Allen). INDEX. Abdomen, examination of, anatomical rela- tions, 536 fascia, superficial of, 515 landmarks and topography of, 531 lymphatics of, 972 lymph-nodes of, 974 muscles of, 515 pract. consid., 526 ventral aponeurosis of, 521 Abdominal cavity, 161 5 aorta, 794 regions, 161 5 hernia, 1759 incisions, anatomy of, 535 ring, external, 524 internal, 524 walls, lymphatics of, 976 posterior surface of, 525 Acervulus, 112 5 Acetabulum, 336 Acoustic area, 1097 striffi, 1258 Acromio-clavicular articulation, 262 pract. consid., 264 Acromion process, 250 Adamantoblasts, 1561 Adipose tissue, 79 chemical composition of, 83 After-birth, 55 Agger nasi, 193 Agminated glands (Peyer's patches), 1641 Air-cells, ethmoidal, 1424 pract. consid., 1429 Air-sacs of lung, 1850 Air-spaces, accessory, 1421 pract. consid., 1426 Ala cinerea, 1097 Albinism, 1461 Alcock's canal, 817 Alimentary canal, 1538 tract, development of, 1694 Alisphenoids, 186 AUantois, 32 arteries of, 33 human, 35 stalk of, 33 veins of, 33 Alveoli of lung, 1850 Ameloblasts, 1561 Amitosis, 14 Amnion, 30 false, 31 folds of, 30 human, 35 cavity of, 35 fluid of, 41 liquor of, 31 suture of, 31 Amniota, 30 Amphiarthrosis, 107 Anal canal, 1673 Analogue, 4 Anamnia, 30 Anaphases of mitosis, 13 Anastomoses, of ophthalmic veins, 880 Angulus Ludovici, 168 Ankle, landmarks of, 672 muscles and fasciae of, pract. consid., 666 Ankle-joint, 438 movements of, 440 pract. consid., 450 Annuli fibrosi, of heart, 698 Annulus ovalis, 695 tympanicus, 1493 of Vieussens, 695 Anorchism, 1950 Anthropology of skull, 228 Anthropotomy, i Antihelix, 1484 Antitragus, 1484 Antrum, 227 of Highmore, 1422 pract. consid., 1428 pylori, 1 61 8 of superior maxilla, 201 Anus, 1673 formation of, 1695 muscles and fasciae of, 1675 pract. consid., 1689 Aorta, abdominal, 794 branches of, pract. consid., Sob plan of branches, 796 pract. consid., 796 dorsal, 721 ptdmonary, 722 segmental arteries of, 847 systemic, 723 thoracic, 791 prac. consid., 726 valves of, 700 ventral, 721 , Aortic arch, 723 pract. consid., 726 variations of, 724 bodies, 1812 bows, 847 septum, 707 Aponeurosis, 468 abdominal, ventral, 521 epicranial, 482 (fascia) plantar, 659 palmar, 606 Appendages,vesicular,of broad ligament, 2002 Appendices epiploicae, 1660 Appendix epididymidis, 1949 testis, 1949 vermiform, 1664 blood-vessels of, 1667 development and growth of, 1668 mesentery of, 1665 orifice of, 1662 peritoneal relations of, 1665 pract. consid., 1681 Aquaeductus cochlea, 1514 vestibuli, 1512 Aqueduct of Fallopius, 1496 Sylvian, 1108 Aqueous humor, 1476 chamber, anterior of, 1476 997 THIS VOLUME CONTAINS PAGES 1 TO 996. 998 INDEX. Aqueous humor, chamber, posterior of, 147 pract. consid., 1476 Arachnoid, of brain, 1203 of spinal cord, 1022 Arantius, nodules of, 700 Archenteron, 25 Arches, visceral, 59 fifth or third branchial, 61 first or mandibular, 60 fourth or second branchial, 61 second or hyoid, 60 third or first branchial, 61 Arcuate nerve-fibres, 107 1 Area acustica, 1097 embryonic, 23 parolfactory, 1 1 53 pellucida, 25 Areola, 2028 Arm, lymphatics, deep, of, 965 sujDerficial, of, 963 muscles and fascia of, pract. consid., 589 Arnold's ganglion, 1246 Arrectores pilorum, 1394 Arterial system, general plan of, 720 Artery or arteries, 719 aberrant, of brachial, 775 allantoic, 33 alveolar, 741 of internal maxillary, 741 anastomoses around the elbow, 778 anastomotica magna, of brachial, 778 of femoral, 831 angular, 738 of facial, 738 aorta, systemic, 723 articular, of popliteal, 833 auditory, internal, 759 auricular, anterior, of temporal, 745 deep, 740 of internal maxillary, 740 of occipital, 744 posterior, 744 axillary, 767 pract. consid., 769 azygos, of vaginal, 812 basilar, 758 brachial, 773 pract. consid., 776 brachialis superficialis, 775 bronchial, 792 buccal, 741 of internal maxillary, 741 to bulb (bulbi urethrae),'8i7 calcaneal, external, 838 internal, 839 of external plantar, 840 calcarine, 760 carotid, common, 730 pract. consid., 731 external, 733 pract. consid., 733 internal, 746 pract. consid., 747 system, anastomoses of, 753 carpal, of anterior radial, 788 of anterior ulnar, 782 arch, posterior, 789 of posterior radial, 788 of posterior ulnar, 782 reta, anterior, 791 centralis retinae, 749 cerebellar, inferior, anterior, 759 posterior, 759 Artery or arteries, cerebellar, superior, 759 cerebral, anterior, 753 middle, 752 posterior, 760 cervical, ascending, of inferior thyroid 766 of transverse cervical, 767 deep, 764 superficial, 766 transverse, 767 choroid, anterior, 752 ciliary, 749 anterior, 749 -posterior, 749 circle of Willis, 760 circumflex, anterior, 773 external, of deep femoral, 828 internal, of deep femoral, 828 posterior, 773 circumpatellar anastomosis, 834 coccygeal, of sciatic, 815 coeliac axis, 797 colic, left, 803 right, 802 comes nervi ischiadici, 815 communicating, anterior, 753 of peroneal, 838 posterior, 751 of posterior tibial, 839 coronary, inferior, 738 of facial, 738 left, 728 right, 728 superior, 738 of facial, 738 of corpus cavernosum, 817 cremasteric, of deep epigastric, 820 of spermatic, 805 crico-thyroid, 734 of superior thyroid, 734 cystic, of hepatic, 799 dental, anterior, of internal maxillary 741 inferior, 740 development of, 846 of lower limb, 848 of upper limb, 848 digital, collateral, of ulnar, 784 of ulnar, 784 dorsal, of foot, S45 of penis (clitoris), 817 dorsalis hallucis, 846 indicis, 789 pedis, 845 pollicis, 789 epigastric, deep, 820 superficial, 826 superior, 763 ethmoidal, 749 anterior, 750 posterior, 749 facial, 737 anastomoses of, 738 glandular branches of, 737 pract. consid., 738 transverse, 745 femoral, 821 anastomoses of, 831 deep, 828 development of, 823 pract. consid., 824 fibular, superior, of anterior tibial, 844 frontal, of ascending middle cerebral, 753 1 THIS VOLUME CONTAINS PAGES 1 TO 996. INDEX. 999 Artery or arteries, frontal, of inferior middle cerebral, 753 internal, anterior, 753 middle, 753 posterior, 753 of ophthalmic, 750 Gasserian, of middle meningeal, 740 gastric, 798 short, of splenic, 800 ■ gastro-duodenal, 799 gastro-epiploic, left, 801 right, 799 glandular, of facial, 737 gluteal, 811 pract. consid., 814 hemorrhoidal, inferior, 817 middle, 813 superior, 803 hepatic, 799 hyaloidea, 1474 hypogastric axis, 808 obliterated, 808 ileo-colic, 802 iliac, circumflex, deep, 821 superficial, 826 common, 807 pract. consid., 807 external, 818 anastomoses of, 821 pract. consid., 819 of ilio-lumbar, 810 internal, 808 anastomoses of, 818 pract. consid., 810 ilio-lumbar, 810 infrahyoid, of superior thyroid, 734 infraorbital, 741 of internal maxillary, 741 innominate, 729 pract. consid., 729 intercostal, of anterior internal mam- mary, 763 aortic, 792 of internal mammary, 765 superior, 764 internal mammary, pract. consid., 764 interosseous, anterior, 781 common, 781 dorsal, 846 posterior, 782 intestinal, of superior mesenteric, 802 labial, inferior, 738 of facial, 738 of internal maxillary, 741 lachrymal, 749 laryngeal, inferior, 766 superior, of superior thyroid, 734 lateral cutaneous, of aortic intercostals, 793 lenticulo-striate, of middle cerebral, 752 lingual, 73 5 anastomoses of, 736 dorsal, 736 pract. consid., 736 lumbar, 805 of ilio-lumbar, 810 malleolar, external, 844 internal, of anterior tibial, 844 of posterior tibial, 839 mammary, of aortic intercostals, 793 internal, 763 lateral internal, 764 masseteric, 740 Artery or arteries, masseteric, of facial, 738 of internal maxillary, 740 mastoid, of occipital, 744 maxillary, internal, 739 anastomoses of, 742 development of, 742 median, 781 mediastinal, of internal mammary, 763 of thoracic aorta, 792 meningeal, anterior, 748 of ascending pharyngeal, 743 middle, 740 of internal maxillary, 740 posterior, of occipital, 744 of vertebral, 758 small, 740 mesenteric, inferior, 802 superior, 801 metacarpal, dorsal, 789 metatarsal, of foot, 845 middle, colic, 802 musculo-phrenic, 763 nasal, lateral, 738 of facial, 738 of ophthalmic, 750 naso-palatine, of internal maxillary, 742 nutrient, of brachial, 774 of peroneal, 838 of posterior tibial, 838 of ulnar, 781 obturator, 813 from deep epigastric, 814 occipital, 743 pract. consid., 744 oesophageal, of gastric, 798 of thoracic aorta, 792 omphalomesenteric, 32 ophthalmic, 748 anastomoses of, 750 orbital, of middle meningeal, 740 of temporal, 745 ovarian, 805 of uterine, 813 palatine, ascending, 737 ' of facial, 737 descending, 741 of internal maxillary, 741 palmar arch, deep, 785 superficial, 784 deep, 782 interosseous, 790 palpebral, of internal maxillary, 741 of ophthalmic, 750 pancreatic, of splenic, 800 pancreatico-duodenal, inferior, 802 superior, 799 parietal, of middle cerebral, 753 parieto-occipital, 760 temporal, 753 parotid, of temporal, 745- perforating, of anterior internal mam- mary, 763 of deep femoral, 828 posterior, of external plantar, 840 of radial, 791 perineal, superficial, 817 transverse, 817 peroneal, anterior, 838 posterior, 838 of posterior tibial, 838 petrosal, of middle meningeal, 740 pharyngeal, ascending, 743 of ascending pharyngeal, 743 THIS VOLUME CONTAINS PAGES 1 TO 996. lOOO INDEX. Artery or arteries, phrenic, inferior, 804 superior, 763 plantar arch, 840 digital, 840 external, 840 internal, 839 interosseous, 840 popliteal, 831 pract. consid., 832 posterior choroidal, 760 princeps cervicis, 744 hallucis, 841 pollicis, 78c) profunda, inferior, 777 sup)erior, 777 prostatic, 81 2 pterygoid, 740 of internal maxillary, 740 pterygo-palatine, 742 of internal maxillary, 742 pubic, of deep epigastric, 820 of obturator, 813 pudic, external, deep, 828 superficial, 826 internal, 815 accessory, 818 pulmonary, 722 valves of, 700 pyloric, of hepatic, 799 radial, 785 development of, 786 pract. consid., 786 recurrent, 787 radialis indicis, 790 superticialis, 775 ranine, 736 recurrent, of palm, 791 ^ of posterior interosseous, 782 renal, 804 sacral, lateral, 810 middle, 806 scapular, dorsal, 773 posterior, 767 sciatic,- 81 5 septal, of nose, 738 sigmoid, 803 spermatic, 805 spheno-palatine, 742 of internal maxillary, 742 spinal, anterior, of vertebral, 759 posterior, of vertebral, 758 splenic, 800 sterno-mastoid, of external carotid, 743 of occipital, 744 of superior thyroid, 734 striate, external, of middle cerebral, 752 internal, of middle cerebral, 752 structure of, 675 stylo-mastoid, 745 subclavian, 753 pract. consid., 756 subcostal, 792 sublingual, 736 submental, 737 of facial, 737 subscapular, 772 suprahyoid, 736 supraorbital, 749 suprarenal, 804 inferior, 804 suprascapular, 767 tarsal, external, 845 internal, 845 Artery or arteries, temporal, anterior, of vertebral, 760 deep, 740 of internal maxillary, 740 middle, 745 posterior, of vertebral, 760 superficial, 745 pract. consid., 745 thoracic, acromial, 771 alar, 772 long, 772 suj)erior, 771 thyroid axis, 765 pract. consid., 766 inferior, 766 superior, 734 pract. consid., 735 tibial, anterior, 842 anastomoses of, 844 pract. consid., 842 posterior, 834 anastomoses of, 841 development of, 836 pract. consid., 836 recurrent, anterior, 844 posterior, 844 tonsillar, 737 of facial, 737 tubal, of ovarian, 805 of uterine, 813 tympanic, of internal carotid, 748 of internal maxillary, 740 of middle meningeal, 740 ulnar, 778 accessory, 776 development of, 779 pract. consid., 780 recurrent, anterior, 781 posterior, 781 umbilical, 54 ureteral, of ovarian, 805 of renal, 804 of spermatic, 805 of uterine, 813 urethral, 817 uterine, 812 vaginal, 812 vertebral, 758 pract. consid., 761 vesical, inferior, 811 middle, 81 1 of obturator, 813 superior, 811 vesiculo-deferential, 812 Vidian, 742 vitelline 32 volar, superficial, 788 Arthrodia, 113 Articulation or articulations, acromio-clavic ular, pract. consid., 264 carpo-metacarpal, 325 movements of, 326 costo-vertebral, 160 of ethmoid, 194 of foot, 440 of frontal bone, 197 of inferior turbinate bone, 208 of lachrymal bone, 207 of malar bone, 210 metacarpo-phalangeal, 327 movements of, 328 of nasal bone, 209 of occipital bone, atlas, and axis, 135 THIS VOLUME CONTAINS PAGES 1 TO 996. INDEX. lOCl Articulation or articulations, of palate bone, 205 of parietal bone, 199 sacro-iliac, 338 scapulo-clavicular, 262 of sphenoid bone, 190 sterno-clavicular, 261 pract. consid., 263 of superior maxilla, 202 of temporal bone, 184 temporo-mandibular, 214 development of, 215 movements of, 215 thoracic anterior, 158 of thorax, 157 of thumb, 326 tibio-fibular, inferior, 396 superior, 396 of vertebral column, 132 of vomer, 206 Arytenoid cartilages, 181 6 Asterion, 228 Astragalus, 423 development of, 425 Astrocytes, 1003 Atlas, 120 development of, 131 variations of, 120 Atria of lung, 1850 Auditory canal, external, 1487 blood-vessels of, 1489 nerves of, 1490 pract. consid., 1491 internal, 1514 ossicles, 1496 path, 1258 Auerbach, plexus of, 1643 Auricle or auricles, 1484 antihelix of, 1484 antitragus of, 1484 blood-vessels of, i486 cartilage of, 1485 concha of, 1484 of heart, 693 helix of, 1484 ligaments of, i486 lobule of, 1484 muscles of, i486 nerves of, 1487 pract. consid., 1490 structure of, 1485 tragus of, 1484 Auricular canal, 705 Auriculo-ventricular bundle of heart, 701 Axilla, 574 muscles and fascia of, pract. consid., 579 Axis, 121 Axis-cylinder, looi Axones, of neurones, 997 Azygos system of veins, 893 Bartholin, glands of, 2026 Basion, 228 Bell, external respiratory nerve of, 1295 Bertin, bones of, 191 columns of, 1876 Bicuspid teeth, 1545 Bile-capillaries, 171 5 Bile-duct, common, 1720 opening of, 1720 pract. consid,, 1731 interlobular, 171 7 lymphatics of, 981 Biliary apparatus, 17 18 Bladder, lymphatics of, 985 urinary, 1901 capacity of, 1903 development of, 1938 in female, 1908 fixation of, 1905 infantile, 1908 interior of, 1904 nerves of, 19 10 peritoneal relations of, 1904 pract. consid., 19 10 relations of, 1906 structure of, 1908 trigone of, 1904 vessels of, 19 10 Blastoderm, 22 bilaminar, 23 trilaminar, 23 Blastodermic layers, 22 derivatives of, 24 vesicle, stage of, 56 Blastomeres, 21 Blastopore, 25 Blastula, 25. Blood, 680 Blood-cells, colored, 681 colorless, 684 development of, 687 Blood-crystals, 681 lakes of dural sinuses, 852 plaques, 685 Blood-vascular system, 673 Blood-vessels of auricle, i486 of bone, 93 of brain, 1206 capillary, 678 of cartilage, 81 development of, 686 of duodenum, 1649 of Eustachian tube, 1504 of external auditory canal, 1489 of eyelids, 1445 of glands, 1535 of hair-follicles, 1394 of kidney, 1884 of liver, 1709 lobular, of liver, 1 7 1 3 of lung, 1853 of membranous labyrinth, 1522 of nasal fossa, 1425 of non-striated muscle, 456 of nose, 1407 of pericardium, 716 of pleura, i860 of rectum, 1679 of retina, 1467 of skin, 1387 of small intestine, 1642 of spinal cord, 1047 of stomach, 1627 of striated muscle, 464. structure of, 673 of sweat glands, 1400 vasa vasorum, 674 Body-cavity, differentiation of, 1700 Body-form, general development of, 56 Body-stalk, 37 Bone or bones, 84 age of, 106 astragalus, 423 of Bertin, 191 blood-vessels of, 93 THIS VOLUME CONTAINS PAGES 1 TO 995. I002 INDEX. Bone or bones, calcaneum, 419 canaliculi of, 86 cancellated, 85 carpus, 309 cells of, 89 chemical composition of, 84 clavicle. 257 compact, 86 development of, 100 cranium, 172 cuboid, 422 cuneiform, 310 external, 428 internal, 426 middle, 427 development of, 94 endochondral, 94 intramembranous, 98 diaphysis of, 104 elasticity of, 105 ethmoid, 191 femur, 352 fibula, 390 frontal, 194 general considerations of, 104 growth of, loi Haversian canals of, 88 system of, 86 humerus, 265 hyoid, 216 ilium, 332 inferior turbinate, 208 innominate, 332 intramembranous, loi ischium, 336 lachrymal, 207 lacunas of, 86 lamellae of, circumferential, 86 Haversian, 86 interstitial, 86 lymphatics of, 93 malar, 209 maxilla, inferior, 211 sujierior, 199 mechanics of, 105 metacarpal, 314 metatarsal, 428 nasal, 209 nerves of, 94 number of, 107 occipital, 172 OS magnum, 312 palate, 204 parietal, 197 parts of, 106 patella, 398 periosteum of, 89 phalanges of foot, 432 of hand, 317 physical properties of, 85 pisiform, 3 1 1 pubes, 334 radius, 287 relation of to figure, 107 ribs, 149 scaphoid, 309 of foot, 425 scapula, 248 semilunar, 310 sesamoid, 104 sex of, 106 shapes of, 104 Sharpey's fibres of, 87 Bone or bones, of shoulder-girdle, 248 skull, 172 sphenoid, 186 S])henoidal, turbinate, 191 sternum, 155 Structure of, 85 subperiosteal, 98 tarsal, 419 temporal, 176 of thorax, 149 tibia, 382 trapezium, 311 trapezoid, 311 ulna; 281 unciform, 31 2 variations of, 107 Volkmann's canals of, 8g vomer, 205 Bone-marrow, 90 cells of, 92 giant cells of, 92 nucleated red cells of, 92 erythroblasts, 92 normoblasts, 92 primary, 95 red, 90 yellow, 93 Bovman, glands of, 141 5 membrane of, 1451 Brachium, inferior, 1107 internal structure of, mo superior, 1107 Brain, 1055 blood-vessels of, 1206 general development of, 1058 lymphatics of, 948 measurements of, 1195 membranes of, 1197 pract. consid., 1207 weight of, 1 196 Brain-sand (acervulus), 1125 Brain-stem, 1056 Brain-vesicles, primary, 1059 secondary, 1061 Branchial arches, derivatives of, 847 Bregma, 228 Bronchial tree, 1847 variations of, 1849 Bronchus or bronchi, 1838 homologies of, 1848 pract. consid., 1840 Bruch, membrane of, 1456 Brunner, glands of, 1639 Buccal fat-pad, 489 Bulb, 1063 of internal jugular vein, 861 olfactory, 11 51 urethral, 1968 Bulbo-tecto-thalamic strands, 11 16 Bulbus vestibuli, 2025 Bulla, of ethmoid, 194 Burns, space of, 543 Bursa or bursas, in acromial, 586 around ankle, 648 bicipito-radial, 586 iliopectineal, 623 of biceps femoris, 636 of gluteal region, 630 of knee-joint, 406 of m. obturat. int., 630 of m. pyriformis, 561 olecranal, 586 THIS VOLUME CONTAINS PAGES 1 TO 996. INDEX. loo-^ Bursa or bursse, subdeltoid, 578 subscapular, 578 Buttocks, landmarks of, 669 muscles and fascia of, pract. consid., 641 Caecum, 1660 blood-vessels of, 1667 interior of, 1661 peritoneal relations of, 1665 position of, 1662 pract. consid., 1680 structure of, 1663 Calamus scriptorius, 1096 Calcaneum, 419 Camper's fascia, 515 Canal or canals, Alcock's, 817 alimentary, 1538 anal, 1673 auditory, external, 1487 auricular of heart, 705 carotid, 184 central, of spinal cord, 1030 of Cloquet (Stilling), 1474 crural, 625 ethmoidal (foramina), 192 facial, 184 femoral, 625 Haversian, of bone, 88 • Hunter's, 628 hyaloid, 1474 incisive, 1413 inguinal, 523 naso-lachrymal, 1479 neural, 26 neurenteric, 25 of Nuck, 2006 palatine, anterior, 201 posterior, 204 of Petit, 1476 pterygo-palatine, 205 reuniens, 151 5 of Scarpa, 201 of Schlemm, 1452 semicircular membranous, 1 5 1 5 osseous, 1 512 structure of, 151 6 of Stenson, 201 of StilUng, 1474 Vidian, 189 Volkmann's, of bone, 89 Canaliculi, of bone, 86 lachrymal, 1478 Canine teeth, 1 544 Canthi of eye, 1442 Capitellum of humerus, 268 Capsule, external, 1172 of Glisson, 1708 internal, 11 73 Suprarenal (body), 1801 of Tenon, 504 Caput medusa, 534 Cardiac muscle, 462 Cardinal system of veins, 854 Carina tracheae, 1837 urethralis, 2016 Carotid body (gland), 1809 chromaffine cells of, 18 10 sheath, 543 Carpo-metacarpal articulations, 325 Carpus, 309 pract. consid., 319 Cartilage or cartilages, 80 Cartilage or cartilages, articular, 81 arytenoid, 181 6 of auricle, 1485 blood-vessels of, 81 capsule of, 80 chemical composition of, 83 costal, 153 cricoid, 1813 cuneiform of Wrisberg, 181 7 development of, 82 elastic, 81 fibrous, 82 hyaline, 80 lacunas of, 80 lateral, of nose, 1405 matrix of, 80 of nasal septum, 1405 of nose, 1404 perichondrium of, 81 of Santorini, 181 7 thyroid, 1814 triangular, of nasal septum, 224 vomerine, 1406 Cartilage-cells, 80 Carunculce hymenales, 2016 salivares, 1581 Caruncle, lachrymal, 1443 Cauda equina of spinal cord, 1025 Cavity, abdominal, 161 5 nasal, 223 pneumatic accessory, 226 segmentation, 22 synovial, of foot, 447 tympanic, 1492 of tympanum, 183 Cell or cells, animal, 6 of bone, 89 of connective tissues, 73 decidual, 47 gustatory, 1435 mastoid, 1504 of Rauber, 23 spermatogenetic, 1943 tactile, of Merkel, 1016 Cell-division, 10 direct, 14 indirect, 11 reduction division, 18 Cell-mass, inner, 23 intermediate, 29 Cementoblasts, 1563 Cementum, 1552 formation of, 1563 Centrosome, 9 Cephalic flexure, 1061 Cerebellar peduncle, fibre-tracts of, 1093 inferior, 1067 inferior, fibre-tracts of, 1093 middle, fibre-tracts of, 1094 superior, fibre-tracts of, 1094 Cerebellum, 1082 architecture of, 1088 cortex of, 1090 histogenesis of, 1105 development of, 11 03 flocculus of, 1085 hemispheres of, 1082 lobus cacuminis of, 1085 centralis of, 1084 clivi of, 1085 culminis of, 1084 lingulae of, 1084 noduli of, 1085 THIS VOLUME CONTAINS PAGES 1 TO 995. I004 INDEX. Cerebellum, lobus pyramidis of, 1086 tuberis of, 1087 uvulae of, 1086 medullary substance of, 1093 nuclei, internal of, 1088 nucleus, dentate of, 1088 emboli formis (embolus) of, 1089 fastigii of, 1089 globosus of, 1089 Purkinje cells of, 1090 tonsil (amygdala) of, 1086 worm of, 1082 Cerebral commissures, development of, 1194 convolutions (gyri), 1135 fissures (sulci), 1 135 hemispheres, 1133 architecture of, 11 55 longitudinal fissure of, 1133 lobes, 1 1 J " localization, 1210 peduncles, 1 107 Cerebro-spinal fluid, 1023 Cerumen, 1489 Cervical flexure, 1062 Cheeks, 1538 lymphatics of, 951 pract. consid., 1594 Choanae, 141 3 (bony), 224 primitive, 1429 Chorda dorsalis, 27 Chordae tendineae, of heart, 697 Choriocapillaris, 1456 Chorion, 32 allantoic, a epithelium of, 49 frondosum, 38 human, 41 laeve, 38 primitive, 31 syncytium of, 49 villi of, 49 Choroid, 1455 development of, 1482 plexus of fourth ventricle, 11 00 of third ventricle, 1131 pract. consid., 1459 structure of, 1456 Chromaffine cells of carotid body, 1810 Chromatin, 9 Cilia, 70 Ciliary body, 1457 ganglion, 1236 muscle, 1458 processes, 1457 ring. 1457 Circulation, foetal, 929 general plan of, 719 Cistema magna, 1203 Claustrum, 1 172 Clava, 1066 Clavicle, 257 development of, 258 fracture of, 259 landmarks of, 260 pract. consid., 258 sexual differences, 258 surface anatomy of, 258 Clinoid process, anterior, 189 processes, middle, 186 posterior, 186 Clitoris, 2024 glans of, 2024 Clitoris, nerves of, 2025 prepuce of, 2024 vessels of, 2025 Cloaca, 1696 Cloquet, canal of, 1474 lymph-nodes of, 992 Coccygeal body, 1810 Coccyx, 127 development of, 131 Cochlea, membranous, 151 7 nerves of, i 521 organ of Corti of, 1519 Reissner's membrane of, 151 7 structure of, 1 5 1 8 osseous, 1 513 Coeliac plexus, lymphatic, 973 Coelom, 28 pericardial, 1700 pleural, 1700 Cohnheim's fields of striated muscle-fibre, 461 Collagen, 83 Colles, fascia of, 562 ligament of, 523 CoUiculi inferiores, 1107 superiores, 1 107 Colliculus, inferior, internal structure of, 1 1 10 superior, internal structure of, mo Colon, 1668 ascending, 1668 blood-vessels of, 1672 descending, 1669 flexure, hepatic of, 1668 splenic of, 1668 lymphatics of, 1672 nerves of, 1672 peritoneal relations of, 1670 pract. consid., 1685 relations of, 1668 transverse, 1668 Colostrum, 2031 corpuscles, 2031 Columnae carneae, of heart, 697 Column, spinal, 114 Columns, anterior, of spinal cord, 1027 lateral, of spinal cord, 1027 of Morgagni, 1674 posterior, of spinal cord, 1027 Commissura habenulae, 11 24 hippocampi, 11 58 hypothalamica, 11 28 Commissure, anterior, 1185 of Meynert, 1115 middle, 11 19 posterior, 1125 Concha, 1484 Condylarthrosis, 113 Conjunctiva, 1441 bulbar, 1445 palpebral, 1445 pract. consid., 1447 Connective substances, chemical composi tion of, 83 tissues, 73 cells of, 73 fixed, 74 typical, 74 wandering, 74 chemical composition of, 83 granule-cells of, 74 ground-substance of, 75 intercellular constituents of, 74 pigment-cells of, 74 THIS VOLUME CONTAINS PAGES 1 TO 996. INDEX. loos Construction, general plan of, i Conus medullaris, of spinal cord, 1021 Convolutions (gyri) cerebral, 113 5 Cooper, ligaments of, 2029 Cord, spermatic, i960 Corium, 1383 Cornea, 1450 pract. consid., 1453 structure of, 1451 Comiculae laryngis, 181 7 Comua sphenoidalia, 191 Corona radiata, 1186 Coronoid process, of ulna, 281 Corpora cavernosa of penis, 1966 mammillaria (albicantia), 11 28 quadrigemina, 1106 Corpus albicans, 1991 Arantii, 700 callosum, 11 55 ciliare, 1457 dentatum, 1088 librosum, 1991 Highmori, 1942 luteum, 1990 spongiosum, of penis, 1967 striatum, 11 69 connections of, 1 1 7 2 development of, 1193 structure of, 1 1 7 1 subthalamicum, 1128 trapezoides, 1079 Corpuscles, corneal, 1452 genital, X017 of Grandry, 10 16 of Hassall, 1799 of Herbst, 10 19 of Meissner, i o 1 7 of Ruffini, 1017 Vater- Pacinian, 10 18 Cortex of cerebellum, 1090 cerebral, histogenesis of, 1192 local variations in, 11 80 nerve-cells of, 1 1 7 6 nerve-fibres of, 11 79 structure of, 1175 Corti, ganglion of, 1257 membrane, 1521 organ of, 1 5 1 9 Costal cartilage, 153 Cotyledons of placenta, 50 Cowper, glands of, 1984 Cranial capacity, 230 nerves, 12 19 abducent (6th), 1249 auditory (8th), 1256 development of, 1376 facial (7th), 1250 glosso-pharyngeal (9th), 1260 hypoglossal (12th), 1275 oculomotor (3rd), 1225 olfactory (ist), 1220 optic (2nd), 1223 pract. consid., 1220 spinal-accessory (nth), 1274 trigeminal (5th), 1230 trochlear (4th), 1228 vagus (loth), 1265 Cranio-cerebral topography, 12 14 Cranium, 172 architecture of, 220 exterior of, 218 fossa, anterior, 220 middle of, 220 Cranium, fossa, posterior of, 220 fractures of, 238 interior of, 220 muscles and fasciae, pract. consid., 489 pract. consid., 235 vault of, 220 Cretinism, 1794 Cricoid cartilage, 1813 Crista galli, of ethmoid, 191 Crura of penis, 1967 Crusta, 1 1 15 Cuboid bone, 422 Cumulus oophorus, 1989 Cuneate nucleus, 1069 tubercle, 1067 Cuneiform bone, 310 external, 428 internal, 426 middle, 427 Cuticle, 1385 Cyvier, ducts of, 854 Cystic duct, 1720 pract. consid., 1731 Cytoplasm, structure of, 7 Dacryon, 228 Darwin, tubercle of, 1484 Decidua, 44 capsularis, 46 cells of, 47 placentalis, 48 reflexa, 45 serotina, 48 vera, 46 Decussation of pyramids, 1064 sensory, 1070 Deiters, cells of, 1521 nucleus, 1076 Demours, membrane of, 1452 Dendrites, of neurones, 997 Dental formula, 1542 papilla, 1558 Dentine, 1550 formation of, 1559 Dentition, first and second, 1564 Derma, 1383 Descemet's membrane, 1452 Deutoplasm, 15 Development of alimentary tract, 1694 of atlas, 131 of auditory nerves, 1525 of axis, 131 of bone, 94 of carpus, 313 of cartilage, 82 of cerebellum, 11 03 of clavicle, 258 of coccyx, 131 of cranial nerves, 1376 of ear, 1523 early, 15 of elastic tissue, 77 of ethmoid bone, 194 of external ear, 1526 of external genital organs, 2043 of eye, 1480 of face, 62 of Fallopian tube, 1999 of femur, 359 of fibrous tissue, 76 of fibula, 393 of frontal bone, 197 of ganglia, 1012 THIS VOLUME CONTAINS PAGES 1 TO 995. ICX56 INDEX. Development, general, of brain, 105^ of general body-form, 56 of glands, 1537 of hairs, 1401 of heart, 705 of humerus, 269 of hyoid bone, 216 of inferior turbinate bone, 208 of innominate bone, 337 of internal ear, 1523 of kidney, 1937 of liver, 1723 of lungs, 1 861 of lymphatic vessels, 939 of lym])h-nodes, 940 of malar bone, 210 of mamniary glands, 2032 of maxilla, inferior, 213 of maxilla, superior, 202 of medulla oblongata, iioi of mesencephalon, 1 1 1 7 of middle ear, 1525 of muscle, non-striated, 457 of muscle, striated, 465 of nails, 1403 of nasal bone, 209 of nerves, 1375 of nervous tissues, 1009 of nose, 1429 of occipital bone, 175 of oral cavity, 62 glands, I 589 of ovary, 1993 of palate bone, 205 of pancreas, 1737 of parietal bone, 199 of patella, 400 of pelvis, 344 of peripheral nerves, loii of peritoneum, 1702 of pharynx, 1603 of pituitary body, 1808 of pons Varolii, 11 03 of prostate gland, 1979 of radius, 293 of reproductive organs, 2037 of respiratory tract, 1861 of ribs, I 53 of sacrum, 129 of scapula, 253 of skin, 1400 of sphenoid bone, 190 of spinal cord, 1049 of spleen, 1787 of sternum, 157 of suprarenal bodies, 1804 of sweat glands, 1 404 of sympathetic system, 1013 of teeth, 1556 of temporal bone, 184 of thymus body, 1800 of thyroid body, 1793 of tibia, 387 of ulna, 285 of urethra, 1938 of urinary bladder, 1938 organs, 1934 of uterus, 2010 of vagina, 2019 of veins, 926 of vertebrae, 128 of vomer, 206 Diaphragm, 556 lymphatics of, 970 of jx'lvis, I 67 6 Diaphragma sclkc, 1200 Diaphysis, of bone, 104 Diarthrosis, 107 Diencephalon, 11 18 Diverticulum of Meckel. 44 Dorsum 'sella?, 186 Douglas, fold of, 522 pouch of, I 743 Duct or ducts, cochlear, 151 7 of Bartholin, 1585 bile,- 1720 of Cuvicr, 854 cystic, 1720 ejaculatory, 1955 Gartner's, 2001 hepatic, 17 18 lactiferous, 2028 lymphatic, right, 945 Miillerian, 2031 nasal (naso-lachrymal) 1479 pancreatic, 1736 paraurethral, 1924 parotid, 1583 of Rathke, 2040 renal, 1894 of Rivinus, 1585 of Santorini, 1736 spermatic, 1953 of Stenson, 1583 sublingual, 1585 submaxillary, 1584 thoracic, 941 thyro-glossal, 1793 vitelline, 32 of Wharton, 1584 of Wirsung, 1736 Wolffian, 1935 Ductus arteriosus (Botalli), 723 endolymphaticus, 1514 venosus (Aarantii), 929 Duodenal glands, 1639 Duodeno-hepatic ligament, 1644 Duodeno-jejtmal flexure, 1645 fossae, 1647 Duodenum, 1644 interior of, 164S Dupuytren's contraction, 616 Dura mater of brain, 1198 of spinal cord, 1022 Ear, 1483 development of, 1523 external, 1484 pract. consid., 1490 internal, 15 10 membranous labyrinth of, 1514 osseous labyrinth of, 1511 perilymph of, 1514 lymphatics of, 950 middlj, 1492 antrum of, i 508 Eustachian tube, 1501 mastoid cells, 1504 pract. consid., 1504 suprameatal triangle, 1510 suprameatic spine, 1508 tympanum or, 1492 Ear-point, 1484 Ectoblast, 23 THIS VOLUME CONTAINS PAGES 1 TO 995. INDEX. 1007 Egg-nucleus, 16 Elastic tissue, 76 development of, 77 Elastin, 83 Elbow-joint, 301 landmarks of, 308 movements of, 303 pract. consid., 305 Embryo, stage of, 56 Eminentia hypoglossi, 1098 teres, 1097 Enamel, 1548 formation of, 1561 Enamel-cells, 1561 Enamel-cuticle, 1550 Enamel-organ, 1560 Enarthrosis, 113 Encephalon, 1055 End-bulbs of Krause, 1016 End-knobs of free sensory nerve-endings, 1015 Endocardium, 702 Endolymph of inembranous labyrinth, 15 14 Endometrium, 2007 Endomysium, 458 Endoneurium, 1006 Endothelium, 71 Enophthalmos, 1439 Ensiform cartilage of sternum, 156 Entoblast, 23 Entoskeleton, 84 Ependymal cells, 1004 Epicardium, 702 Epidermis, 1385 Epididymis, 1947 appendix of, 1949 canal of, 1948 digital fossa of, 1947 globus major of, 1947 minor of, 1947 nerves of, 1948 structure of, 1947 vasa abberrantia of, 1950 vessels of, 1948 Epiglottis, 181 6 ligaments of, 181 7 movements of, 181 7 Epimysium, 458 Epineurium, 1006 Epiphysis, 1124 ossification of, 98' Epispadias, 1928 Epithalamus, 1123 Epithelium of chorion, 49 columnar, 69 glandular, 70 modified, 70 pigmented, 70 specialized, 70 squamous, 68 stratified, 68 transitional, 69 Epitrichium, 1401 Eponychium, 1403 Epoophoron, 2000 Erythroblasts, 92 Erythrocytes, 681 development of, 687 Ethmoid bone, 191 articulations of; 194 bulla of, 194 cells of, 192 development of, 194 Ethmoid turbinate bone, middle of, 193 superior of, 193 uncinate process of, 193 Eustachian tube, 1501 blood-vessels of, 1504 cartilaginous portion, 1502 mucous membrane of, 1503 muscles of, 1503 osseous portion, 1502 pract. consid., 1507 valve, 694 Exocoelom, 32 Exophthalmos, 1439 Exoskeleton, 84 Extremity, lower, 332 landmarks of, 669 lymphatics of, 991 upper, landmarks of, 618 lymphatics of, 961 Eye, 1436 development of, 1480 lymphatics of, 949 plica semilunaris of, 1443 pupil of, 1459 Eyeball, 1448 aqueous humor of, 1476 chamber anterior of, 1476 posterior of, 1476 choroid of, 1455 ciliary body of, 1457 processes of, 1457 cornea of, 1450 fovea centralis of, 1466 iris of, 1459 lens, crystalline of, 1471 macula lutea of, 1466 movements of, 505 optic nerve of, 1469 ora serrata of, 1467 pract. consid., 1449 retina of,- 1462 sclera of, 1449 vascular tunic of, 1454 vitreous body of, 1473 Eye-lashes, 1442 Eyelids, 1441 blood-vessels of, 1445 development of, 1483 lymphatics of, 1445 nerves of, 1446 pract. consid., 1446 structure of, 1443 Face, 222 architecture of, 228 development of, 62 landmarks of, 246 muscles and fasciae, pract. consid., 492 pract. consid., 242 Falciform ligament, 1745 Fallopian tube, 1996 changes in, 1999 course of, 1997 development of, 1999 fimbrise of, 1997 infundibulum of, 1997 isthmus of, 1997 lymphatics of, 988 nerves of, 1999 pract. consid., 1999 relations of, 1997 structure of, 1997 vessels of, 1998 THIS VOLUME CONTAINS PAGES 1 TO 995. ioo8 INDEX. Fallopius, aqueduct of, i8i FaLx cerebelli, 1200 cerebri, 1199 Fascia or fasciae, 470 of abdomen, 515 anal, 1678 of ankle, pract. consid., 666 antibrachial, 592 of anus, 1675 of arm, pract. consid., 589 of axilla and shoulder, pract. consid., 579 axillary, 574 of back, 508 bicipital (semilunar), 586 brachial, 585 bucco-pharyngeal, 488 of buttocks, pract. consid., 641 of Camper, 515 cervical, 542 of Colles, 562 of cranium, pract. consid., 489 cremasteric, i960 cribriform, 635 crural, 647 dentata, 1 166 of face, pract. consid., 492 of foot, pract. consid., 666 of hand, 606 of hip and thigh, pract. consid., 642 iliac, 624 infundibuliform, 524 intercolumnar (external spermatic), 524 of knee, pract. consid., 645 lata, 633 of leg, pract. consid., 665 obturator, 559 of orbit, 504 palmar, 606 palpebral, 1438 parotido-masseteric, 474 pectoral, 568 pelvic, 558 perineal, superficial, 562 plantar, 659 prevertebral, 543 rectal, 1678 recto- vesical, 1678 of rectum, 1675 of scalp, pract. consid., 489 of Scarpa, 5 1 5 temporal, 475 transversalis, 520 Fasciculus, auriculo-ventricular of heart, 701 posterior longitudinal, 11 16 retrofiexus, 11 24 solitarius, 1074 Fat, orbital, 1437 Fat-cells, 79 Fauces, isthmus of, 1 569 pillars of, 1 569 Femoral canal, 625 ring, 625 Femtir, 352 development of, 359 landmarks of, 366 pract. consid., 361 surface anatomy, 360 variations, sexual and individual, 359 Fertilization, 18 Fibres, intercolumnar, 524 Fibrin, canalized, of chorion, 49 Fibro-cartilage, 82 Fibrous tissue, 74 Fibrous tissue, development of, 76 Fibula, 390 development of, 393 pract. consid., 393 Fillet, decussation of, 1070 median, 1115 Fiml)ria, 1 1 59 hippocampi, 1165 Fissure, calcarine, 1146 calloso-marginal, 1139 central, of cerebrum, 1137 collateral, 1 139 ethmoidal, 141 1 ofOlaser, 178 palpebral, 1441 parieto-occipital, 1138 portal, of liver, 1708 pterygo-maxillary, 204 of Rolando, 1 1 3 7 sphenoidal, 188 Speno-maxillary, 222 (sulci) cerebral, 1135 of Sylvius, 1 136 Fistula, cervical, 61 Flexure, cephalic, 58 cervical, of embryo, 59 dorsal, of embryo, 59 sacral, of embryo, 59 Flocculus, 1085 Foetus, membranes of, 30 stage of, 63 eighth month, 66 week, 64 fifth month, 66 week, 63 fourth month, 65 ninth month, 66 seventh month, 66 week, 64 sixth month, 66 week, 63 third month, 65 Follicles, Graafian, 1988 Fontana, spaces of, 1452 Fontanelles, 231 Foot, articulations of, 440 as whole, 447 bones of, 419 landmarks of, 437 pract. consid., 436 joints of, landmarks of, 453 landmarks of, 672 muscles of, 659 and fasciae of, pract. consid., 660 surface anatomy, 449 synovial cavities of, 447 Foramen or foramina, caecum, 1574 ethmoidal, anterior, 192 posterior, 192 jugular, 220 of Luschka, 11 00 of Magendie, 1100 mastoid, 180 of Monro, 1 131 optic, 189 ovale, 188 of heart, 695 pterygo-spinosum, 190 rotundum, 187 sacro-sciatic, great, 341 lesser, 341 sphenoidal, 187 spheno-palatine, 204 THIS VOLUME CONTArNS PAGES 1 TO 996. INDEX. 1009 Foramen or foramina, spinosum, 188 stylo-mastoid, 182 thyroid (obturator), 337 of vena cava, of diaphragm, 557 of VesaHus, 188 of Winslow, 1746 Forceps anterior, of corpus callosum, 1157 posterior, of corpus callosum, 11 58 Forearm, 281 as whole, 299 intrinsic movements of, 299 motion of on humerus, 303 pract. consid., 603 Fore-brain, 1059 Formatio reticularis, 1076 reticularis alba, 1076 grisea, 1074 Fornix, 11 58 pillars of, anterior, 1159 posterior, 11 59 Fossa or fossae, duodeno-jejunal, 1647 glenoid, 178 hyaloidea, 1473 ileo-csecal, 1666 infraspinous, 250 inguinal, inner, 526 lateral, 1743 median, 1742 outer, 526 interpeduncular, 1107 intersigmoid, 1671 ischio-rectal, 1678 jugular, 182 nasal, 1409 navicular of urethra, 1924 ovalis, 695 ovarian, 1986 pararectal, 1744 paravesical, 1744 pericascal, 1666 pineal, 1106 pituitary, 186 retro-colic, 1667 of Rosenmiiller, 1598 spheno-maxillary, 227 subscapular, 249 supraspinous, 250 supratonsillar, 1600 supravesical, 526 Sylvii, 1 137 temporal, 218 zygomatic, 227 Fourchette, 2022 Fourth ventricle, 1096 choroid plexus of, iioo floor of, 1096 roof of, 1099 Fovea centralis, 1466 vagi, 1098 Frenulum of Giacomini, 11 66 Frenum of prepuce, 1966 of tongue, 1573 Frontal bone, 194 articulations of, 197 development of, 197 lobe, 1 139 sinus, 1423, 226 (bony) Fundamental embryological processes, 26 Funiculus cuneatus, 1066 gracilis, 1066 of Rolando, 1067 Furrows, visceral, 59 external, 61 Furrows, inner, 61 inner, second, 62 inner, third, 62 Galen, vein of, 856 Gall-bladder, 17 19 cystic duct of, 1720 fossa of, 1708 lymphatics of, 981 nerves of, 1720 pract. consid., 1729 vessels of, 17 19 Ganglion or ganglia, 1007 Arnold's, 1246 basal, 1 1 69 cervical inferior (sympathetic), 1362 middle (sympathetic), 1362 superior (sympathetic), 1359 ciliary, 1236 coccygeal (impar), sympathetic, 1367 development of, 1012 of Froriep, 1380 Gasserian, 1232 geniculate, 1252 habenulae, 11 23 impar, 1367 interpeduncular, 1 1 24 jugular, of glosso-pharyngeal, 1263 of vagus, 1267 lenticular, 1236 Meckel's, 1240 mesenteric, inferior, 1373 superior, 1372 nodosum of vagus, 1268 ophthalmic, 1236 otic, 1246 petrous, of glosso-pharyngeal, 1264 semilunar, sympathetic, 1369 spheno-palatine, 1240 spinal, 1279 spiral, 1257 spirale of cochlea, 1522 splanchnic, great, sympathetic, 1365 submaxillary, 1247 sympathetic, 1009 of sympathetic system, 1356 vestibular, 1259 Ganglion-crest, 1012 Gartner's duct, 2001 Gasserian ganglion, 1232 Gastric glands, 1623 Gastro-pulmonary system, 1527 Gastrula, 25 Gelatin, 83 Geniculate bodies, lateral, 1107 median, 1107 (internal) internal structure of, 11 10 ganglion, 1252 Genital cord, 2038 folds, 2043 organs, external, development of, 2043 female, 2021 pract. consid., 2027 ridge, 2038 tubercle, 2043 Genu of corpus callosum, 11 55 Germinal spot, 16 Gestation, ectopic, 1999 Giacomini, frenulum of, 11 66 Gianuzzi, crescents of, 1534 Gimbemat, ligament of, 523 Ginglymus, 113 Giraldes, organ of, 1950 Glabella, 228 THIS VOLUME CONTAINS PAGES 1 TO 996. lOIO INDEX. Gladiolus of sternum, 155 Gland or glands, 1531 alveolar (saccular) compound, 1535 (saccular) simple, 1535 anal, 1674 areolar, 2028 of Bartholin, 2026 of Blandin, 1577 blood-vessels of, 1535 of Bowman, 141 5 of Brunner, 1639 cardiac of stomach, 1624 carotid, 1809 ceruminous, 1489 ciliary, 1400 circumanal, 1400 coccygeal, 1810 of Cowper, 1984 cutaneous, 1397 gastric, 1623 • of Henle, 1445 of intestines, 1637 of Krause, 1445 lachrymal, 1477 ducts of, 1477 of Lieberkuhn, 1637 of Luschka, 1810 lymphatics of, 1536 mammary, 2027 Meibomian (tarsal), 1444 of Moll, 1444 of Montgomery, 2028 mucous, 1534 nerves of, 1536 of Xuhn, 1577 ' parotid, 1 582 prostate, 1975 pyloric, 1624 salivary, 1582 sebaceous, 1397 serous, 1534 sexual, development of, 2038 sublingual, 1585 submaxillary, i 583 sweat, 1398 duct of, 1399 structure of, 1399 of tongue, 1575 tubo-alveolar, 1532 tubular, compound, 1532 simple, 1532 of Tyson, 1966 unicellular, 1531 of Zeiss, 1444 Glans of clitoris, 2024 penis, 1968 Glaser, fissure of, 178 Glisson's capsule of liver, 1708 Globus pallidus, 1170 Goblet-cells, 70 Golgi-Mazzoni corpuscles, 10 19 Gonion, 228 Graafian follicles, 1988 Grandrv, corpuscles of, 1016 Growth, 6 of bone, loi Gudden, inferior commissure of, mo Gums, 1567 pract. consid., 1590 Gustatory cells, 1435 Gyrus or gyri, callosal (fornicatus), 11 50 (convolutions) cerebral, 113 5 dentate. 11 66 Gyrus or gyri, development of, 1 190 hippocampal, 1 1 51 Hair-cells (auditory) inner, 1520 outer, 1520 Hair- follicle, 1392 blood-vessels of, 1394 nerves of, 1394 Hairs, 1389 arrangement of, 139 1 develojiment of, 1401 growth of, 1402 structure of, 1391 whorls of, 1 39 1 Hair-shaft, 1391 Hamular process of inner pterygoid plate, 1 89 Hamulus of bony cochlea. 15 14 Hand, 309 deep fascia of, 606 landmarks of, 320 lymphatics 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, 695 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 colunwiae 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 lymphatics, 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 intermedium, 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 THIS VOLUME CONTAINS PAGES 1 TO 996. INDEX. lOII Heidenhain, demilunes of, 1534 Helicotrema, 15 14 Helix, 1484 Hemispheres, association fibres of, 1182 of cerebellum, 1082 cerebral, 1133 commissural fibres of, 11 84 lobes of, 1 139 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, 176S labial, 1769 lumbar, 1777 obturator, 1777 perineal, 1778 sciatic, 1778 scrotal, 1769 . ■ umbilical, 1775 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, 106 1 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, 10 10 of neurones, loii Homologue, 4 Horner, muscle of, 484 Hows hip, lacuna of, 97 Humerus, 265 development of, 269 pract. consid., 270 sexual differences, 269 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, 1806 Hypospadias, 1927 Hypothalamus, 1127 Hypothenar eminence, 607 Ileo-csecal fosss, 1666 valve, 1 661 Ilio-femoral ligament, 369 liio-pectineal line, 334 Ilio-tibial band, 634 Ilium, 332 Implantation, 35 Impregnation, 18 Incisor teeth, 1543 Incus, 1497 Inferior cava! system of veins, 898 Infundibulum, 1129 of nasal cavitj^ 194 of nose, 141 1 Inguinal canal, 523 lymphatic plexus, 991 Inion, 228 Innominate bone, 332 structvire 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 epiploicas, 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 taenia coli of, 1660 lymph-nodules of, 1640 small 1633 blood-vessels of, 1642 glands of Lieberkuhn of, 1637 lymphatics of, 1643 nerves of, 1643 Peyer's patches of, 1640 pract. consid., 1652 structure of, 1634 valvulae conniventes of, 1636 villi of, 1635 solitary nodules of, 1640 Involuntary muscle, 10 15 Iris, 1459 - pract. consid., 1461 structure of, 1460 Irritability, 6 Ischio-rectal fossa, 1678 Ischium, 336 Islands of 'Langerhans, 1735 of Reil, 1 1 49 Isthmus of fauces, 1569 rhombencephali, 1061 Jacobson's nerve, 1264 organ, 141 7 development of, 1432 Jejuno-ileum, 1649 blood-vessels of, 1652 lymphatics of, 1652 mesentery of, 1650 130 THIS VOLUME CONTAINS PAGES 1 TO 906. IOI2 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-sternal, 160 motions in, 166 costo-transverse, 160 costo-vertebral, motions in, 165 crico-arytenoid, 181 6 crico-thyroid, 1815 of ear ossicles, 1498 elbow, 301 fixed, 107 general considerations, 107 half, 108 of hip, 367 interchondral, 160 intersternal, 159 of knee, 400 limitation of motion, 112 metatarso-phalangeal, 447 modes of fixation, 112 of pelvis, 337 of pelvis, pract. consid, 350 radio-ulnar, 297 inferior, pract. consid., 308 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, in Jugular ganglion, of glosso-pharyngeal, 1263 of vagus, 1267 plexus, lymphatics, 956 Karyokinesis, n Karyosomes, 9 Kidney or kidneys, 1869 architecture of, 1875 blood-vessels of, 1884 capsule of, 1869 cortex of, 1876 development of, 1937 ducts of, 1894 fixation of, 1871 glomeruli of, 1876 hilum of, 1869 labyrinth of, 1876 lobule of. 1875 loop of Henle of, i88r lymphatics of, 1885 Malpighian body of, 1879 medulla of, 1876 medullary rays of, 1876 movable, 1888 nerves of, 1886 papillse of, 1875 papillary ducts of, 1882 pelvis of, 1894 Kidney or kidneys, position of, 1870 pract. consid., 1887 pyramids of, 1876 relations of, 1873 sinus of, 1874 structure of, 1877 supporting tissue of, 1883 surfaces of, 1869 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 bursas of, 406 capsule of, 400 landmarks of, 416 movements of, 408 pract. consid., 409 semilunar cartilage of, 402 synovial membrane of, 405 Krause, end-bulbs of, 1016 glands of, 1445 Kupffer, cells of, 1 7 1 7 Labia major, 2021 minora, 2022 nerves of, 2024 vessels of, 2023 Labyrinth, membranous, 1514 blood-vessels of, 1522 canalis reuniens of, 1515 cochlea of, 1517 ductus endolymphaticus of, 15T1; endolj'mph of, 1514 maculae acusticae of, 1516 saccule of, 151 5 semicircular canals cf, 151 5 utricle of, 1514 osseous, 1511 cochlea of, 1513 semicircular canals of, 151 2 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 papillae, 1478 puncta, 1478 sac, 1478 Lactation, 2029 Lacteals, 1643 Lacunae, 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, 19 18 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, 1813 age changes of, 1828 arytenoid cartilages of, 181 6 corniculce laryngis, 181 7 cricoid cartilage of, 18 13 cuneiform cartilages of, 181 7 development of, 1862 elastic sheath of, 181 7 epiglottis, 1 81 6 form of, 1 8 1 8 lymphatics of, 958 mucous membrane of, 1823 muscles of, 1824 nerves of, 1827 ossification of, 1818 position and relations of, 1828 pract. consid., 1828 region, glottic of, 1820 infraglottic of, 1823 supraglottic of, 181 8 sexual differences of, 1828 thyroid cartilage of, 1814 ventricle (sinus) of, 1822 vessels of, 1826 vocal cords, false of, 1820 true of, 1820 ligaments of, 181 8 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, 1471 development of, 148 1 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, 133 coraco-acromial, 256 coraco-clavicular, 262 conoid part, 262 trapezoid part, 262 coronary, of liver, 1721 costo-clavicular or rhomboid, 262 cotyloid, 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 Gimbernat, 523 of Hesselbach, 525 ilio-femoral, 369 ilio-lumbar, 339 interarticular of ribs, 160 interclavicular, 262 interosseous, of foot, 441 interspinous, 134 intertransverse, 135 ischio-femoral, 370 of laminae and processes of vertebrae, 133 lieno-renal, 1747 of liver, 1721 metacarpal, superficial transverse, 607 nuchae, 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. I014 INDEX. Ligament or ligaments, spino-glenoid, 257 stylo-mandibular, 475 subflava, 133 suprascapular or transverse, 256 supraspinous, 133 suspensory, of lens, 1475 of orbit, 1438 of ovary, 1986 thyro-arytenoid, inferior, 18 18 superior, 1817 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 1 50 Linea alba, 522 semilunaris, of abdomen, 532 transversa, of abdomen, 532 Linin, 9 Lips, 1538 lymphatics of, 951 inusL'les of, 1540 nerves of, 1542 pract. consid., 1590 vessels of, 1 542 Liquor amnii, 31 pericardii, 714 Littr6, glands of, 1925 Liver, 1705 bile-capillaries of, 17 15 biliary apparatus, 17 18 blood-vessels of, 1709 borders of, 1707 caudate lobe of, 1709 cells of Kupffer, 1 7 1 7 common bile-duct, 1720 cystic duct of, 1720 development and growth of, 1723 fissure of ductus venosus of, 1707 fossa for o^all-l)Iadder of, 1708 gall-bladder of, 17 19 Glisson's capsule of, 1708 hepatic artery of, 1 7 1 1 ducts of, 1 7 18 veins of, 17 10 impression, oesophageal of, 1708 renal of, 1709 intralobular connective tissue of, 171 7 bile-ducts of, 1717 veins of, 17 10 ligaments of, 1721 coronary, 1 7 2 1 falciform, 1721 round, 1721 triangular, 1721 lobes of, 1706 lobular blood-vessels of, 17 13 lobules of, 1 7 1 2 lymphatics of, 171 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 iissure of, 1708 notch of, 1707 weight of, 1706 Liver-cells, 1714 Lobe or lobes, cerebral, 1135 frontal, 1 139 of hemispheres, 1139 limbic, 1 1 50 occipital, 1 145 olfactory, 11 51 parietal, 1 143 temporal, 1 147 Lobule of auricle, 1484 Loia, pract. consid., 530 Lordosis, 144 Lumbar plexus, lymphatic, 973 Lumbo-sacral cord, 133 1 Lung or lungs, 1843 air-sacs of, 1850 afveoli of, 1850 atria of, 1850 blood-vessels of, 1853 borders of, 1843 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, i86? to thoracic walls, 1855 roots of, 1838 dimensions of, 1840 nerves of, 1839 relations of, 1840 structure of, 1851 surfaces of, 1843 vessels of, 1839 Lunula, of nail, 1395 Luschka, foramina of, iioo gland of, 181 o Lutein cells, 1990 Luys, nucleus of, 11 28 Lymphatic or lymphatics, of abdomen, 972 of abdominal walls, 976 of arm, deep, 965 superficial, 963 of bile-duct, 981 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, 958 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 995. 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, 980 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, 986 internal, female, 988 internal, male, 987 of retina, 1468 of scalp, 948 of seminal vesicles, 988 of skin, 1388 of small intestine, 1643 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 tipper extremity, 961 of ureter, 982 of urethra, 986 of uterus, 989 of vagina, 989 of vas deferens, 988 vessels, development of, 939 Lymph-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 Hngual, 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 Rosenmuller, 992 sternal, 966 structure of, 937 submaxillary, 946 submental, 946 subscapular, 962 superficial 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 Maculse acusticae, 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 995. ioi6 INDEX. Mammary glands, nerves of, 2032 pract. consid., 2033 structure of, 2029 variations of, 2033 vessels of, 2031 Mandible, 21 1 Manubrium of sternum, 155 Marrow of bone, qo 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, 14 12 middle, of nose, 141 1 superior, of nose, 141 1 Meckel, diverticulum of, 44 Mediastinum, anterior, 1833 middle, 1833 posterior, 1833 pract. consid., 1833 superior, 1833 Medulla oblongata, 1063 central gray matter of, 1073 development of, iioi internal structure of, 1068 Medullary folds, 26 groove, 26 sheath, looi velum, inferior, 1099 superior, 1099 Medullated fibres, 1003 Megakaryocytes, 689 Meiijomian (tarsal) glands, 1444 Meissner, corpuscles of, 1017 plexus of, 1643 Membrane or membranes, Bowman's, of Bruch, 1456 cloacal, 1939 costo-coracoid, 568 crico-thyroid, 181 5 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 s^movial, of joint, no tectoria, 1521 thyro-hyoid, 181 5 of tympanum, 1494 vitelline, 15 vitrea, 1456 Meninges of brain, pract. consid., 1208 lymphatics of, 948 Menstruation, 2012 Mcrkel, 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 jcjuno-ileum, 1650 of large intestine, 1670 ])crmancnt, 1752 posterior, part ist, 1746 part 2nd, I 751 part 3rd, 1753 primitive, 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 Mesovarium, 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, 428 Metathalamus, 1 1 26 Meynert, commissure of, 1115 Mid-brain, 1061 Milk, 2030 Milk-ridge, 2032 Mitosis, II 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 996. INDEX. 1017 Mouth, vestibule of, 1538 Mucoid, 83 Mucous membranes, 1528 structure of, 1528 MuUerian duct, 2038 Muscle or muscles, abdominal, 515 abductor hallucis, 661 minimi digiti, 608 minimi, of foot, 662 poUicis, 608 adductor brevis, 626 hallucis, 662 longus, 626 magnus, 628 poUicis, 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., 589 arytenoid, 1826 of auricle, i486 auricularis anterior, 483 posterior, 483 superior, 483 axial, 502 of axilla and shoulder, pract. consid., 579 azygos uvulae, 496 biceps, 586 femoris, 636 brachial, 585 post-axial, 588 pre-axial, 586 brachialis anticus, 586 brachio-radialis, 598 branchiomeric, 474 buccinator, 488 bulbo-cavemosus, 565 of buttocks, pract. consid., 641 cardiac, 462 cervical, 542 chondro-glossus, 1578 ciliary, 1458 coccygeus, 561, 1676 compound pinnate, 469 compressor urethrae, 565 constrictor inferior of pharynx, 1606 middle of pharynx, 1605 pharyngis inferior, 499 medius, 498 superior, 497 superior of pharynx, 1 604 coraco-brachialis, 575 of cranium, pract. consid., 489 cremaster, 519 crico-arytenoid lateral, 1825 posterior, 1825 crico-thyroid, 1824 crural, 647 post-axial, 655 pre-axial, 648 crureus, 640 dartos, 1963 deltoideus, 578 depressor anguli oris, 487 labii inferioris, 485 diaphragma, 556 digastricus, 477 dilator pupillae, 1460 Muscle or muscles, dorsal, of trunk, 507 of Eustachian tube, 1 503 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 poUicis, 603 minimi digiti, 600 ossis metacarpi poUicis, 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 poUicis, 608 carpi radialis, 593 radialis brevis, 597 ulnaris, 594 longus digitorum, 651 hallucis, 651 poUicis, 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, 1578 genio-hyoid, 1578 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, 480 variations of, 480 iliacus, 624 ilio-costalis, 508 infraspinatus, 576 intercostales externi, 538 interni, 539 interossei dorsales of foot, 664 of hand, 613 plantares, 663 volares, 612 interspinales, 513 intertransversales, 513 anteriores, 547 laterales, 521 intratympanic, 1499 involuntary, arrectores pilorum, 1394 nerve-endings of, 1015 ischio-cavernosus, 564 of knee, pract. consid., 645 of larynx, 1824 latissimus dorsi, 574 THIS VOLUME CONTAINS PAGES 1 TO 996. ioi8 INDEX. Mixscle or muscles, of leg, pract. consid., 665 levator anguli oris, 487 scapula?, 571 ani, 560, 1675 labii superioris, 487 labii superioris ala?que nasi, 485 nienti (superbus), 485 palati, 496, 1 57 1 palpebrae superioris, 502 levatores costarum, 540 lingualis, 1579 of lips, 1540 longissimus, 510 longus colli, 548 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 pollicis, 608 orbicularis oris, 4S6 palpebrarum, 484 orbital, 502 of palate and pharynx, 495 palato-glossus, 497, 1579 palato-pharyngeus, 497, 1571 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 platysma, 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 cr 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 rhomboideus 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 semimembranosus, 438 semi pinnate, 469 semispinalis, 511 semitendinosus, 638 serratus magnus, 571 posticus inferior, 541 posticus superior, 541 of soft palate, 1570 soleus, 649 sphincter ani, external, 1676 externus, 563 internal, 1677 pupillffi, 1460 vesical, external, 1925 internal, 1925 spinalis, 511 splenius, 510 stapedius, 480, 1499 sternalis, 570 sterno-cleido-mastoideus, 499 sterno-hyoideus, 543 stemo-thyroideus, 545 striated, attachments of, 468 blood-vessels of, 464 bursa; of, 471 classification of, 471 development of, 465 form of, 469 general considerations of, 468 lymphatics of, 464 ner\'es of, 464 nerve-supply, general, 473 structure, general of, 458 variations, 461 (voluntary), 457 stylo-glossus, 1579 stylo-hyoideus, 480 stylo-pharyngeus, 495, 1606 subclavius, 570 subcostal, 539 subcrureus, 640 submental, 477 subscapularis, 578 supinator, 601 supraspinatus, 575 THIS VOLUME CONTAINS PAGES 1 TO 996. INDEX. 1019 Muscle or muscles, temporalis, 475 tensor fasciae latse, 631 palati, 479, 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, 1014 zygomaticus major, 485 minor, 485 Muscle-fibre, structure of, 459 Muscular system, 454 tissue, general, 454 Myelin, looi Myelocytes, of bone-marrow, 92 Myeloplaxes, of bone-marrow, 92 Myometrium, 2008 Myotome, 30 Myxcedema, 1794 Naboth, ovules of, 2008 Nail, structure of, 1395 Nail-bed, 1396 Nail-plate, 1395 Nails, 1394 development of, 1403 Nares, anterior, 1404 posterior, 14 13 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, 141 3 lymphatics of, 1426 nerves of, 1426 ' ' roof of, 1412 fossag, 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, 1281 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, 1254 digital of median, 130 1 dorsal of clitoris, 13 51 of penis, 13 51 of epididymis, 1948 of external auditory canal, 1490 external cutaneous, of lumbar plexus, 1324 of eyelids, 1446 facial, 1250, 12 51 development of, 1378 genu of, 1 2 5 1 pract. consid., 1255 of Fallopian tube, 1999 frontal, 1234 THIS VOLUME CONTAINS PAGES 1 TO 986. I020 INDEX. Nerve or nerves, ganglionic, of nasal, 1234 genito-crural, 1322 of glands, i 536 glosso-pharyngeal, 1260 development of, 1379 gluteal, inferior, 1333 sui)erior, 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, 13 14 intercosto-humeral, 131 7 intermedins of Wrisberg, of facial, 1250 internal cutaneous, 1303 cutaneous lesser, 1303 interosseous anterior of median, 1300 of kidney, 1886 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 larynx, 1827 lingual, of glosso-pharyngeal, 1264 of hypoglossal, 1277 of mandibular, 1244 of lips, 1542 of liver, 171 1 lumbar, posterior divisions of, 1282 of lungs, 1855 of mammary glands, 2032 mandibular, (maxillary inferior), 1242 masseteric, of mandibular, 1242 maxillary (superior), 1237 median, 1298 branches of, 1300 pract. consid., 1301 jieningeal, 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 na'sal, 1234, 1235 anterior, 1235 external, 1235 fossa, 1426 internal (septal), 1235 lateral, of maxillary, 1240 septum, 1410 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 (jcsophagus, 1 61 3 olfactory, 1220 development of, 1376 pract. consid., 1222 ophthalmic, 1233 optic, 1223 development of, 1482 pract. consid., 1470 orbital, of spheno-palatine ganglion, 1 241 of ovary, 1993 of palate, i 573 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 i pericardial of vagus, 1272 of pericardium, 716 perineal, 1350 peripheral, development of, loii peroneal, communicating, of external 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 pleurae, 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 anterior crural, 1329 short (external), 1342 scapular, posterior, 1295 sciatic, great, 1335 small, 1348 of scrotum, 1964 of skin, 1389 of small intestine, 1643 somatic, 12 18 of spermatic ducts, 1959 spheno-palatine, of maxillary, 1237 THIS VOLUME CONTAINS PAGES 1 TO 996. INDEX. I021 Nerve or nerves, spinal, 1278 spinal-accessory, 1274 pract. consid., 1275 splanchnic, (sympathetic), 1364 of spleen, 1787 stapedial, of facial, 1253 of stomach, 1628 of striated muscle, 464 stylo-hyoid, of facial, 1254 of sublingual gland, 1585 of submaxillary gland, 1585 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 1 5 lower, 1 3 1 5 posterior divisions of, 1282 posterior (long), 1295 pract. consid., 1296 pract. consid., 13 18 second, 13 17 third, 13 1 7 twelfth (subcostal) 1^17 upper, 1315 of thyroid body, 1793 of thymus body, 1800 thyro-hyoid, of hypoglossal, 1277 tibial, anterior, 1336 communicating, 1342 posterior, 1342 recurrent, 1335 of tongue, 1580 tonsillar of glosso-pharyngeal, 1264 of trachea, 1836 trigeminal, 1230 development of, 1378 divisions of, 1232 pract. consid., 1248 trochlear, 1228 development of, 1377 tympanic, of glosso-pharyngeal, 1264 to tympanic plexus, of facial, 1252 ulnar, 1303 branches of, 1305 pract. consid., 1306 of ureter, 1898 of urethra, 1927 of urinary bladder, 1910 of uterus, 2010 of vagina, 2018 vagus, 1265 and spinal accessory, development of, 1380 ganglia of, 1267 pract. consid., 1272 vestibular, of auditory, 1256 Nerve or nerves, visceral, 12 18 Nerve-cells, 998 bipolar, 999 multipolar, 1000 unipolar, 999 Nerve-endings, motor, 1014 of cardiac muscle, 1015 of involuntary m.uscle, 1015 of voluntary muscle, 10 14 sensory, 10 15 encapsulated, 10 16 free, 1015 genital corpuscles, 10 17 Golgi-Mazzoni corpuscles, 10 19 Kra use's end-bulbs, 10 16 Meissner's corpuscles, 1017 Merkel's tactile cells, 1016 neuromuscular endings, 10 19 neurotendinous endings, 1020 Ruffini's corpuscles, 10 17 Vater-Pacinian corpuscles, 10 18 Nerve-fibres, 1000 arcuate, 107 i axis-cylinder of, looi cerebello-olivary, 1072 cerebello-thalamic, 11 14 cortico-bulbar, 1 1 1 5 cortico-pontine, 1115 cortico-spinal, 1 1 1 5 medullary sheath of, 1001 medullated, 1003 neurilemma of, looi nonmedullated, 1003 rubro-thalamic, 1 1 1 4 of sympathetic system, 1356 Nerve-terminations, 1014 Nerve-trunks, 1006 endoneurium of, 1006 epineurium of, 1006 funiculi of, 1006 perineurium of, 1006 Nervous sj'stem, 996 central, 102 1 peripheral, 12 18 sympathetic, 1353 development of, 10 13 tissues, 997 development of, 1009 Neurilemma, looi Neuroblasts, 10 10 Neuro-epithelium, 70 Neuroglia, 1003 ependymal layer of, 1004 glia-fibres of, 1004 of gray matter, of spinal cord, 1035 histogenesis of, 10 10 spider cells of, 1004 Neurokeratin, looi Neuromuscular endings, 1019 Neurone or neurones, 996 axones of, 997 dendrites of, 997 histogenesis of, ion Neurotendinous endings, 1020 Nictitating membrane, 1443 Nipple, 2028 Nodose, ganglion 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, 141 1 inferior meatus of, 141 2 infundibulum of, 141 1 lateral cartilages of, 1405 lymphatics of, 1407 middle meatus of, 1411 nerves of, 1407 olfactory region of, 14 13 pract. consid., 1407 respiratory region of, 1 4 1 5 superior meatus of, 141 1 vestibvile of, 1409 NTostrils, 1404 Notochord, 27 Nuck, canal of, 2006 Nuclein, 9 Nucleolus, 9 Nucleus or nuclei, abducent, 1249 acoustic, 1257 ambiguus, 1074 amygdaloid, 11 72 arcuate, 1076 caudate, 1 169 cuneate, 1069 facial, 1 2 51 dentate, of cerebellum, 1088 emboliformis (embolus) of cerebellum, 1089 facial, 1 2 51 fastigii, of cerebellum, 1089 globosus, of cerebellum, 1089 gracile, 1069 internal, of cerebellum, 1088 of lateral fillet, 1258 lenticular, 1 169 mammillaris, 1129 olivary, 107 1 olivary, superior, 1257 red, 1 1 14 structure of, 8 trapezoideus, 1257 vago-glosso-pharyngeal, 1073 vestibular, of reception, 1259 Nuhn, glands of, 1577 Nutrition, accessory organs of, 1781 Nymphae, 2022 Obelion, 228 Obex, 1096 Occipital bone, 172 lobe, 1 145 protuberance, external, 174 internal, 175 Odontoblasts, 1558 CEsophagus, i6og course and relations of, 1609 lymphatics of, 971 nerves of, 1613 pract. consid., 161 3 structure of, 1611 vessels of, 161 2 Olecranon, of ulna, 281 Olfactory bulb, 11 51 cells, 1 4 14 hairs, 141 5 lobe, 1 1 51 membrane, 1414 pits, 62 region of nose, 14 13 striae, 1 1 53 tract, 1 1 52 trigone, 1 1 53 Olivary eminence, 1066 nuclei, 1071 accessory, 1072 nucleus, inferior, 1072 Omental sac, 1703 Omentum, duodeno-hepatic, 1746 gastro-colic, 1747 gastro-hcpatic (lesucr), 1745 gastro-splenic, 1747 greater, 1747 greater, structure of, 1749 Oocyte, primary, 17 secondary, i 7 Ooplasm, 15 Opercula insula;, 1137 Ophryon, 228 Opisthion, 228 Optic commissure, 1223 entrance or papilla, 1462 recess, i 132 thalami, 11 18 tracts, 1223 Ora serrata, 1467 Oral cavity, development of, 62 glands, development of, 1589 Orbit, 222 axes of, 222 fasciae of, 504 lymphatics of, 949 pract. consid., 1438 Organ or organs, accessory, of nutrition, 1781 of Corti, 1 519 genital, external female, 2021 Jacobson's, 1417 reproductive female, 1985 male, 1941 of respiration, 1813 of sense, 1381 of taste, 1433 urinary, 1869 Oro-pharynx, 1598 Orthognathism, 229 Os intermetatarseum, 432 magnum, 312 Osseous tissue, 84 Ossicles auditory, 1496 articulations of, 1498 incus, 1497 malleus, 1497 movements of, 1 500 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 pellucida of, 1989 Ovary or ovaries, 1085 cortex of, 1987 THIS VOLUME CONTAINS PAGES 1 TO 996. INDEX. 102; Ovary or ovaries, descent of, 2043 development of, 1993 fixation of, 1986 Graaitian follicles of, 1988 hilum of, 1985 ligament of, 1987 medulla of, 1988 nerves of, 1993 position of, 1986 pract. consid., 1995 surfaces of, 1985 suspensory ligament of, 1986 structure of, 1987 vessels of, 1992 Oviduct, 1996 Pacchionian bodies, 1205 depressions, 198 Palate, 1567 bone, 204 articulations of, 205 development of, 205 hard, 1567 lymphatics of, 954 nerves of, 1573 pract. consid., 1592 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 cell-areas of, 1735 islands of Langerhans of, 1735 lymphatics of, 979 nerves of, 1737 pract. consid., 1738 relations to peritoneum of, 1736 structure of, 1734 vessels of, 1736 Panniculus adiposus, 1384 Papilla or papillae, circum vallate, 1575 dental, 1558 of duodenum, 1720 filiform, 1575 fungiform, 1575 lachrymal, 1478 optic, 1462 renal, 1875 Paradidymis, 1950 Parametrium, 2005 Parathyroid bodies, 1795 structure of, 1795 Parietal bone, 197 articulations of, 199 impressions, 199 lobe, 1 1 43 Paroophoron, 2002 Parotid duct, 1583 gland, 1582 nerves of, 1583 relations of, 1582 structure of, 1586 vessels of, 1583 Parovarium, 2000 Patella, 398 development of, 400 movements of, 409 Patella, pract. consid., 416 Pediincle, cerebellar, inferior, 1067 cerebral, 1107 Pelvic girdle, 332 Pelvis, 332 development of, 344 diameters of, 342 diaphragm of, 559 index of, 343 joints of, 337 pract. consid., 350 of kidney, 1894 landmarks of, 349 ligaments of, 337 lymphatics of, 983 position of, 342 pract. consid., 345 sexual differences, 343 surface anatomy of, 345 white lines of, 559 as a whole, 341 Penis, 1965 corpora cavernosa of, 1966 corpus spongiosum of, 1967 crura of, 1967 glans of, 1968 nerves of, 197 1 pract. consid., 1972 prepuce of, 1966 structure of, 1968 vessels of, 1970 Pericsecal fossae, 1666 Pericardium, 714 blood-vessels of, 716 ligaments of, 716 lymphatics of, 716 nerves of, 716 pract. consid., 716 Perichondrium, 81 Pericranium, 489 Perilymph of internal ear, 15 14 Perimetrium, 2009 Perimysium, 458 Perineal body, 2046 Perineum, female, 2046 lymphatics of, 987 male, 191 5 landmarks of, 19 18 triangular ligament of, 563 Perineurium, 1006 Periosteum, 89 alveolar, 1553 Peritoneum, 1740 cavity, lesser of, 1749 development of, 1702 of large intestine, 1670 parietal, anterior, 1742 folds of, 1742 fossae of, 1742 pract. consid., 1754 Perivascular lymph-spaces, 93 1 Pes anserinus, 1252 hippocampi, 1165 Petit, triangle of, 574 Petro-mastoid portion of temporal bone, 179 Petrous ganglion, of glosso-pharyngeal, 1264 subdivision, of petro-mastoid bone, 181 Peyer's patches, 1641 Phalanges of foot, 432 of hand, 317 THIS VOLUME CONTAINS PAGES 1 TO 996. I024 INDEX. Phalanges of hand, development of, 318 pecuharities, 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-, 1 598 nerves of, 1606 oro-, 1598 pract. consid., 1606 primitive, 1694 relations of, 1601 sinus pyriformis of, 1598 vessels of, 1606 Philtrum of lips, 1 540 Pia mater, of brain, 1202 of spinal cord, 1022 Pigment-cells of connective tissue, 74 Pillars of fauces, 1569 Pineal body, 1 124 Pinna, 1484 Pisiform bone, 311 Pituitary body, anterior lobe of, 1806 development of, 1808 (hypophysis) , 1 1 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, ^^ 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, 1643 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 supraiicromial of, 1289 supraclavicular of, 1288 suprasternal of, 1288 pract. consid., 1292 coccygeal, 1352 coeliac, 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 paroti-d, 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, 1103 internal structure of, 1078 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 996. 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, 183 uncinate of ethmoid, 193 Processus cochleariformis, 182 vaginalis, 2041 Proctodaeum, 1695 Prognathism, 229 Pronephros, 1934 Pronucleus, female, 16 male, 20 Prophases of mitosis, 12 Prosencephalon, 1059 Prostate gland, 1975 development of, 1979 lymphatics of, 985 nerves of, 1978 pract. consid., 1979 relations of, 1976 structure of, 1977 vessels of, 1978 Proteins, 8 Protoplasm, 7 Protovertebrae, 29 Psalterium, 11 58 Pseudostomata, 72 Pterion, 228 Pterygoid plate, inner, 189 outer, 189 processes of sphenoid bone, 189 Pubes, 334 Pulmonary system of veins, 852 Pulp of teeth, 1554 Pulvinar, 11 19 Puncta, lachrymal, 1478 Pupil, 1459 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, 1 680 lymphatics of, 1680 muscles and fascias of, 1675 nerves of, 1680 peritoneal relations of, 1679 Rectum, pract. consid., 1689 structure of, 1674 valves of, 1674 Reduction division, 18 Reil, island of, 11 49 limiting sulcus of, 1139 Reissner's fibre, 1030 membrane, of cochlea, 1517 Remak, fibres of, 1003 Renal duct, 1894 Reproduction, 6 Reproductive organs, development of, 2037 external, female, lymphatics of, 987 male, lymphatics of, 986 female, 1985 internal, female, lymphatics of, male, lymphatics of, 987 male, 1941 Respiration, organs of, 1813 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, 1 1 5 1 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, 1137 funiculus of, 1067 Rosenmiiller, fossa of, 1598 lymph-nodes of, 992 organ of, 2000 Rostrum, of corpus callosum, 11 56 of sphenoid bone, 187 Ruffini, corpuscles of, 10 17 Ruysch, membrane of, 1456 Sac, conjunctival, 1443 lachrymal, 1478 vitelline, 32 Saccule, 151 5 structure of, 151 6 Sacral lyinphatic plexus, 984 Sacro-iliac articulation, 338 THIS VOLUME CONTAINS PAGES 1 TO 996. I026 INDEX. Sacro-sciatic ligaments, 339 Sacrum, 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 Scala tympani, 1514 vestibuli, 1514 ScAlp, lymphatics of, 948 muscles and fasciae, pract. consid., 489 Scaphoid, 309 bone of foot, 425 development of, 426 Scapula, 248 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 Schlemm, canal of, 1452 Schwann, sheath of, looi Sclera, 1449 development of, 1482 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 Semilunar bone, 310 cartilages of knee-joint, 402 valves, 700 Seminal vesicles, 1956 lymphatics of, 988 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 intermusciilar, 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 spurium, 707 transversum, 1701 Serosa, 31 Sertoli, cells of, 1943 Sesamoid bones, 104 of foot, 432 of hand, 318 Sharpey's libres of bone, 87 Shoulder, muscles and fascia of, pract consid., 579 Shoulder-girdle, 248 surface anatomy of, 263 Shoulder-joint, 274 bursae of, 277 dislocation of, 582 landmarks of, 280 ligaments of, 274 movements of, 277 pract. consid., 278 Shrapnell's membrane, 1494 Sigmoid cavity, 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, 872 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 praecervicalis, 61 pyriformis of pharynx, 1598 renal, 1874 reunions, 707 sigmoid, 868 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 THIS VOLUME CONTAINS PAGES 1 TO 996. INDEX. 1027 Skin, end-bulbs of Krause, 1389 end-organs of Rtiifini, 1389 genital corpuscles, 1389 Golgi-mazzoni corpuscles, 1389 lymphatics of, 1388 Meissner's corpuscles, 1389 nerves of, 1389 pigmentation of, 1387 stratum corneum of, 1387 germinativum of, 1385 granulosum of, 1386 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, 228 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, i960 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 Spermatozoon, 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, 102 1 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, gray of, 1028 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., 105 1 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 pyramidal (direct). 1046 of Burdach, 1039 direct cerebellar, 1044 of Goll, 1039 of Gower, 1044 lateral (crossed pyramidal) f . 1043 of Lissauer, 1042 white matter of, 1036 ganglia, 1279 nerves, 1278 constitution of, 1278 divisions, primary, anterior, of, i2 8.'i posterior, of, 1279 number of, 1279 size of, 1279 typical, 1284 131 THIS VOLUME CONTAINS PAGES 1 TO 996. I028 INDEX. Spinal nerves, ventral (motor) roots o£, 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, 1787 lymphatics of, 982 movable, 1788 nerves of, i 787 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, 1787 Splenium, of corpus callosum, 11 56 Spongioblasts 10 10 Spongioplasm, 8 Sprains, of spine, 144 Squamous portion of temporal bone, 177 Stapes, 1498 Stenson, canals of, 201 duct, 1583 Stephaniori, 229 Stemo-clavicular articulation, 261 ■ pract. consid., 263 Sternum, 155 development of, 157 pract. consid., 168 sexual differences of 156 variations of, 156 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, 1619 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 Stomodaeum, 1694 Strabismus, 1440 Stratum zonale, of thalamus, 11 23 Stria medullaris, 11 19 Stria?, acoustic, 109G Structure, ele:nents of, 5 Styloid process of ulna, 285 Sublingual ducts, 1585 gland, 1585 nerves of, 1585 structure of, 1587 vessels of, 1585 space, 1581 Submaxillary duct, 1584 ganglion, 1247 gland, 1583 nerves of, i 585 structure of, i 587 vessels of, 1585 Subpatellar fat, 405 Subperiosteal bone, 98 Sub-peritoneal tissue, 1742 Substantia nigra, 1109 Sulci, development of, 1190 fissures, cerebral, 1135 Sulcus hypothalamicus, 11 19 Suprarenal bodies, 1801 accessory, 1805 development of, 1804 growth of, 1804 nerves of, 1803 pract. consid., 1806 relations of, 1801 structure of, 1802 vessels of, 1803 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, 1 109 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 jjenis, 1374 ccEliac, 1370 gastric, 1370 hemorrhoidal, 1374 hepatic, 1370 hypogastric, 1374 mesenteric, inferior, 1373 superior, 1372 ovarian, 1372 pelvic, 1374 phrenic, 13 71 prostatic, 1374 THIS VOLUME CONTAINS PAGES 1 TO 986. INDEX. 1029 Sympathetic system, plexus, renal, 1371 solar, 1368 sperm.atic, 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, 108 Syncytium of chorion, 49 Syndesmosis, 108 System, gastro-pulmonary, 1527 muscular, 454 nervous, 996 uro-genital, 1869 Taenia chorioidea, 11 64 coli, 1660 fornicis, 1163 semicircularis, 1162 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, 1543 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, 1554 pulp-cavity of, 1542 temporary, relations of, 1556 variations of, 1566 Tegmen tympani, 1496 Tegmentum, 11 12 Tela chorioidea, 1097 subcutanea, 1384 Telencephalon, 113 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, 1 147 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, 11 22 Thalamus, 11 18 connections of, 1121 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, 1 1 3 1 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, 1798 vessels of, 1799 weight of, 1797 Thyroid bodies, accessory, 1 793 Thyroid body, 1789 development of, 1793 nerves of, 1793 pract. consid., 1794 shape and relations of, 1789 structure of, 1791 vessels of, 1792 cartilage, 181 4 THIS VOLUME CONTAINS PAGES 1 TO 996. I030 INDEX. Thyroid cartilage, development of, 1S15 growth of, 1815 gland, lymphatics of, 959 Tibia. 382 development of, 387 landmarks of, 390 pract. consid., 3S7 structure of, 387 variations of, 383 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 caecum of, 1574 frenum of, 1573 glands of, 1575 growth and changes of, 1580 lymphatics of, 952 muscles of, 1577 nerves of, 1 580 papillce, circumvallate of, 1575 filiform of, 1575 fungiform of, 1575 pract. consid., 1594 vessels of, 1580 Tonsil or tonsils (amygdala), of cerebellum, 1086 faucial, 1600 faucial, relations of, 1602 lingual, 1575 lymphatics of, 954 pharyngeal, 1601 pract. consid., 1608 tubal, 1503 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 1 14 habenulo-peduncular, 11 24 mammillo-thalamic, 1121 of mesial fillet, 1076 olfactory, 11 52 thalamocipetal, lower, 1122 Tragus, 1484 Trapezium, 311 Trapezoid bone, 311 Treitz, muscle of, 558 Triangle of Hesselbach, 526 rectal, 1916 uro-genital, 191 6 Triangles of neck, 547 Trigone of bladder, urinary, 1904 Trigonum acustici, 1097 habenulae, 1 1 23 hypoglossi, 1097 lemnisci, 1108 urogenitale, 563 vagi, 1097 Trochanter, greater, of femur, 352 lesser, of feinur, 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, 208 middle, of ethmoid, 193 superior, of ethmoid, 193 Tvmpanic portion of temporal bone, 179 Tympanum, 1492 attic of, 1500 cavity of, 183 contents of, 1496 membrane of, 1494 pract. consid., 1505 mucous membrane of, 1 500 oval window of, 1495 pract. consid., 1504 prom.onotory of, 1495 pyramid of, 1496 round window of, 1495 secondary membrane of, 1495 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., i8g8 THIS VOLUME CONTAINS PAGES 1 TO 996. 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, 1877 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, 1516 Uveal tract, 1454 Uvula, 1569 Vagina, 2016 development of, 2019 fornix, anterior of, 2016 posterior of, 2016 lymphatics of, 989 nerves of, 2018 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 avuiculo-ventricular, of heart. 699 Eustachian, 694 of Hasner, 1479 ileo-cagcal, 1661 mitral, 699 of Morgagni, 1674 pulmonary, 700 of pulmonarj^ artery, 700 rectal (Houston's), 1674 semilunar, 700 Thebesian, 695 tricuspid, 699 Valvulae conniventes, 1636 Vasa aberrantia of epididj^mis, 1950 Vas deferens, 1954 ampulla of, 1955 lymphatics of, 988 Vasa vasortim, 674 Vater, ampulla of, 1721 Vater-Pacinian corpuscles, 10 18 Vein or veins, allantoic, Ti;^ circulation, 929 angular, of facial, 864 auditory, internal, 869 aiiricular, anterior, 882 posterior, 883 axillary, 887 pract. consid., 888 azygos, 893 arch, 893 development of, 928 major, 893 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, 856 great, 855 middle, 856 posterior, 856 small, 856 valves of, 856 cardinal, 926 posterior, 854 superior, 854 system of, 854 centralis retinse, 879 cephalic, 890 accessory, 890 median, 891 cerebellar, inferior, 879 superior, 878 median, 878 cerebral, 877 great, 877 inferior, 877 posterior, 869 internal, 877 middle, 877 pract. consid., 878 superior, 877 cervical, ascending, of vertebral, 860 THIS VOLUME CONTAINS PAGES 1 TO 99S. I032 INDEX. Vein oi veins, cervical, deep, 859 middle, 884 chordae Willissi, 870 choroid, 877 ciliary, anterior, 879 posterior, 879 circulation, foetal, 929 circumflex, iliac, deep, 910 superficial, 917 of leg. 914 classification of, 852 clitoris, 909 colic, middle, 921 right, 921 condyloid, anterior. 874 confluence of the sinuses, 868 coronary, of facial, 865 inferior, of facial, 865 left. 855 right, 856 of corpus callosum, anterior, 878 posterior, 877 cavernosum. 907 striatum, 877 cofto-axillary. 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, 883 development of, 926 diploic, 874 anterior, 875 occipital. 875 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, 876 of Vesalius, 876 mastoid. 876 occipital, 876 parietal, 876 pract. consid., 876 epigastric, deep. 909 superficial. 917 superior, of internal mammary, 860 ethmoidal, 879 facial, 864 common, 864 deep, 865 pract. consid., 864 transverse, 882 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 accessory, 895 hemorrhoidal, inferior, 907 middle, 908 plexus, 908 superior, 922 hepatic, 902 pract. consid., 904 hepatiea communis, 900 ileo-colic, 921 iliac, 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, 858 development of, 859 pract. consid., 859 intercapitular of hand, 889 intercostal, 896 anterior, of internal mammary 860 superior, 896 accessory left, 896 intervertebral, 898 jugular, anterior, 884 external, 880 posterior, 884 pract. consid., 881 internal, 861 bulbs of, 861 prac. consid., 863 labial, inferior, of facial, 865 superior, 865 lacVmae of dural sinuses, 852 laryngeal, inferior, 861 superior, of superior thyroid, 867 of leg, deep, 911 pract. consid., 918 of limbs, 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, 855 of Marshall, 856 masseteric, of facial. 866 mastoid emissary, 869 maxillary, internal, 882 internal, anterior, of facial, 865 median, 890 deep, 886 mediastinal, anterior, 861 medulli-spinal. 898 meningeal, middle. 883 mesenteric, inferior, 922 superior. 921 metacarpal, dorsal, 889 nasal, lateral, of facial, 865 oblique, of heart. 695 of left auricle. 856 obturator, 907 1 THIS VOLUME CONTAINS PAGES 1 TO 996. INDEX. 1033 Vein or veins, occipital, 859 ophthalmic, anastomoses of, 880 inferior, 879 pract. consid., 880 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, 882 parumbilical, 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, 897 pterygoid, 882 sacral, 905 of Santorini, 909 venosus mammillae, 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, 852 anastomoses of, 853 pyloric, 923 radial, 886 superficial, 891 accessory, 891 renal, 902 pract. consid., 904 of Retzius, 924 sacral, anterior, plexus, 905 lateral, 906 middle, 905 saphenous, accessory, 916 long, 916 short, 915 sciatic, 906 of septum lucidum, 877 sigmoid, 922 sinus, basilar, 874 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 of, 851 intercavernous, 872 lateral, 867 pract. consid., 869 longitudinal, inferior, 871 superior, 870 pract. consid., 870 marginal, 872 occipital, 872 petrosal, inferior, 874 superior, 874 spheno-parietal, 874 straight, 872 small, of Galen, 877 intestine, 921 spermatic, 903 pract. consid., 904 spheno-palatine, 882 spinal, 897 cord, 898 pract. consid., 898 splenic, 921 sterno-mastoid, of superior thyroid 867 structure of, 677 subclavian, 884 pract. consid., 885 subcostal, 896 sublingual, 867 submental, of facial, 866 superficial of hand, 889 superior caval system, 857 supraorbital, of facial, 865 suprarenal, middle, 903 inferior, 902 suprascapular, 884 Sylvian, deep, 878 temporal, deep, 883 middle, 882 superficial, 882 temporo-maxillary, 882 testicular, 903 Thebesian, 694 thoracic, acromial, 890 long, 887 thoraco-epigastric, 888 thjrmic, 861 ' thyroid, inferior, 860 pract. consid., 861 middle, 867 plexus, 860 superior, 867 tibial, anterior, 911 posterior, 911 torcular Herophili, 868 tympanic, of temporal, 882 ulnar, 886 superficial, 890 umbilical, 54 of upper extremity, 886 pract. consid., 891 ureteric, of renal, 902 of spermatic, 903 uterine, 908 plexus, 908 utero-vaginal plexus, 908 vaginal, 908 plexus, 908 valves of, 850, 851 vena cava inferior, 899 development of, 937 THIS VOLUME CONTAINS PAGES 1 TO 996. I034 Vein or veins, vena cava superior, 857 development of, 927 pract. consid., 858 cephalica poUicis, 88y salvatella, 889 supraunibilicalis, 923 thyreoidea ima, 861 venae comites, 851 vorticosae, 879 vertebral, 860 vesical, 908 vesico-prostatic plexus, 909 vesico-vaginal plexus, 909 vitelline circulation, 929 Velum interpositum, 11 62 Ventricle or ventricles, lifth, 11 60 fourth, 1096 of heart, 696 lateral, 11 60 anterior horn of, 11 60 body of, 1 161 choroid plexus of, 1 1 62 inferior (descending) horn of, 1 164 posterior horn of, 11 68 (sinus) of larynx, 1822 third, 1 131 Vermiform appendix, 1664 Vemix caseosa, 66 Vertebra or vertebra?, 114 articular surfaces of, 116 body of, 115 cervical, 116 development of, 128 dimensions of, 122 gradual regional changes of, 122 laminae of, 115 lumbar, 117 mammillary processes of, 118 peculiar, 119 pedicles of, 115 presacral, 128 prominens, 121 spinal foramen of, 115 spinous process of, 115 structure of, 128 thoracic, 115 transverse processes of, 115 variations of, 131 Verumontanum, 1922 Vesalius, foramen of, 188 Vesicle, germinal, 15 umbilical, 42 Vesicles, seminal, 1956 Vessels of clitoris, 2025 of epididymis, 1948 of Fallopian tube, 1998 of gall-bladder, 17 19 of labia, 2023 of larynx, 1826 of lips, 1542 of mammary glands, 2031 of oesophagus, 161 2 of ovary, 1992 of palate, 1572 of pancreas, 1736 of parotid gland, 1583 of penis, 1970 of pharynx, 1606 of prostate gland, 1978 of roots of lungs, 1839 of scrotum, 1964 INDEX. Vessels of seminal vesicles, 1958 of spermatic ducts, 1958 of spleen, 1786 of sublingual gland, 1585 of submaxillary gland, 1585 of suprarenal bodies, 1803 of testis, 1948 of thymus body, 1799 of thyroid body, 1792 of tongue, 1580 of trachea, 1836 of ureter, 1897 of urethra, 1926 of urinary bladder, 19 10 of uterus, 2009 of vagina, 2018 Vestibule of mouth, 1538 of nose, 1409 of osseous labyrinth, 1511 of vagina, 2022 Vicq d'Azyr, bundle of, 1121 Vidian canal, 189 Villi of chorion, 49 of intestine, 1635 lacteals of, 1636 Vincula tendinum, 471 Vital manifestations, 6 Vitelline arteries, 32 duct, 32 membrane, 15 sac, 32 Vitello-intestinal duct, 37 Vitellus, 15 Vitreous body, 1473 pract. consid., 1474 Vocal cords, false, 1820 true, 1820 Volkmann's canals, of bone, 89 Volvulus, 1687 Vomer, 205 Vulva, 2021 Wharton, duct of, 1584 jelly of, 54 White lines of pelvis, 559 of anal canal, 1673 Winslow, foramen of, 1746 Wirsung, duct of, 1736 Wisdom-tooth, 1546 Wolffian body, 1935 duct, 1935 Womb, 2003 Worm of cerebellum, 1082 Wrist, anterior annular ligament, 607 movements of, 326 pract. consid., 613 surface anatomy of, 328 Wrist- joint, landmarks of, 330 pract. consid., 329 Xiphoid process of sternum, 156 Yolk-stalk, 37 Zeiss, glands of, 1444 Zinn, annulus of, 503 zonula of, 1475 Zona pellucida, 15 radiata, 15 Zonula of Zinn, 1475 Zuckerkandl, bodies of, 181 2 Zygomatic process of temporal bone, 178 THIS VOLUME CONTAINS PAGES 1 TO 906. 7 <. 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